Downloaded From : www.EasyEngineering.net
ww
w.E a
syE
ngi
nee
rin
g.n
et
**Note: Other Websites/Blogs Owners Please do not Copy (or) Republish this Materials without Legal Permission of the Publishers.
**Disclimers : EasyEngineering not the original publisher of this Book/Material on net. This e-book/Material has been collected from other sources of net. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
ww w.E
asy En gin ee
rin g.n et
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
ANNA UNIVERSITY ME6602
SYLLABUS·
Reg. 2013
AUTOMOBILE ENGINEERING
UNIT I VEHICLE STRUCTURE AND ENGINES
Types of automobiles, vehicle construction and different layouts, chassis, frame and body, Vehicle aerodynamics (various resistances and moments involved), IC engines -components functions and materials, variable valve timing (VVT).
ww
UNIT II ENGIN'= AUXILIARY SYSTEMS Electronically controlled gasoline injection system for SI engines, Electronically
w.E
controlled diesel injection system (Unit injector system, Rotary distributor type and common rail direct injection system), Electronic ignition system (Transistorized coil
asy
ignition system, capacitive discharge ignition system), Turbo chargers (WGT, VGT), Engine emission control by three way catalytic converter system, Emission norms (Euro and BS).
En
gin eer
UNIT III TRANSMISSION SYSTEMS Clutch-types and construction, gear boxes- manual and automatic, gear shift mechanisms, Over drive, transfer box, fluid flywheel, torque converter, propeller
ing
shaft, slip joints, universal joints, Differential and rear axle, Hotchkiss Drive and Torque Tube Drive.
UNIT IV STEERING, BRAKES AND SUSPENSION SYSTEMS
.ne
t
Steering geometry and types of steering gear box-Power Steering, Types of Front Axle, Types of Suspension Systems, Pneumatic and Hydraulic Braking Systems, Antilock Braking System (ABS), electronic brake force distribution (EBD) and Traction Control. UNIT V ALTERNATIVE ENERGY SOURCES Use of Natural Gas, Liquefied Petroleum Gas, Bio-diesel, Bio-ethanol, Gasohol and Hydrogen in Automobiles- Engine modifications required -Performance, Combustion and EmiSSionCharacteristics of SI and CI engines with these alternate fuels - Electric and Hvbrid Vehicles, Fuel Cell.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
t
I
CONTENTS
ww w.E a
syE
ngi
UNIT 1 Vehicle Structure and Engines UNIT 2
nee r
Engine Auxiliary Systems
UNIT 3 Transmission Systems
ing
UNIT 4 Steering, Brakes and Suspension Systems UNIT 5 Alternative Energy Sources
.ne
t
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Contents
Introduction
1.1
1.1.1. Brief History of Automobiles
1.2
1.1.2. Requirements of an Automobile
1.5
General classification of vehicles
1.5
1.2.1. Single unit vehicles
1.5
1.2.2. Articulated vehicles
1.6
1.2.3. Heavy tractor vehicles
1.6
1.3.
Types of automobiles
1.6
1.4.
Vehicle construction
1.10
1.5.
Different layouts of a car
1.12
1.1.
1.2.
ww w.E a 1.5.1.
syE
ngi
Layout for the light passenger vehicle (car)
1.12
nee r
112
1.5.1.1. Front engine 1.5.1.2. Rear engine
1.5.1.3. Central or mid-engine
1.6.
1.7.
1.5.2.
Front engine front wheel drive
1.5.3.
Front engine rear wheel drive
1.5.4.
Rear engine rear wheel drive
1.5.5.
Four-wheel drive
1.12
ing
1.13
.ne
1.14 1.16
t
1.17 1.18 1.19
Chassis 1.6.1.
Basic construction of chassis
1.19
1.6.2.
Main components of chassis
1.20
1.6.3.
Classification of chassis
1.20
1.6.4.
Characteristics of a good chassis
1.22
1.6.5.
Layout of chassis
1.22
1.6.6.
Components and drive systems in chassis
1.23
Frame
1.27
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
•
Automobile
Functions or importance of frame
1.27
1.7.2.
Requirements of a good frame
1.28
1.7.3.
Frame construction
1.28
1.7.4.
Types of frame
1.30
1.7.5.
Load on chassis frame (various resistances and moments involved)
1.34
1.7.6.
Materials for frame
1.35
1.7.7.
Sub frames
1.35
1.7.8.
Frame defects
1.37
1.7.9.
Frame repair and alignment
1.37
1.7.10.
Checking frame alignment
1.38
ww
1.8.
1.9.
Engineering
1.7.1.
w.E
Body
1.39
1.8.1.
Importance of vehicle body design
1.40
1.8.2.
Requirements of vehicle body
1.40
1.8.3.
Types of vehicle body
1.41
1.8.4.
Body construction and its components
1.43
1.8.5.
Materials for body construction
1.51
asy E
Vehicle aerodynamics
ngi
nee rin
1.9.1.
Resistances to vehicle motion
1.9.2.
Aerodynamics of automobile body
1.52 1.52
g.n et
1.54
1.10.
Internal combustion engine (IC engine)
1.11.
Engine construction
1.12.
Components of IC Engine
1.58
1.12.1.
Cylinder block
1.58
1.12.2.
Cylinder head
1.58
1.12.:
Crankcase
1.59
1.12.4.
Oil Sump or Oil Pan
1.59
1.12.5.
Cylinder liners
1.59
1.12.6.
Piston
1.60
1.12.7.
Connecting rod
1.64
1.56
1.56
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1.12.8.
Piston rings
fBI 1.65
1.12.9.
Crank shaft
1.66
I Contents 1.12.10. Flywheel
1.66
1.12.11. Cam Shaft
1.67
1.12.12. Spark Plug
1.68
1.12.13. Valves
1.68
1.12.14. Valve mechanisms
1.69
1.13.
Classification ofIC engines
1.71
1.14.
Working principle ofIC engines
1.73
ww w.E a 1.14.1.
Working of four stroke cycle (petrol) SI engine
1.73
1.14.2.
Working of four stroke cycle (diesel) CI engine
1.75
1.14.3.
Working of two stroke cycle SI engine (petrol engine)
1.76
1.14.4.
Working of two stroke cycle CI engine (diesel engine)
1.78
1.14.5.
Comparison of SI engine and CI engine
1.79
1.14.6.
Comparison of two-stroke and four-stroke engines
syE
ngi
1.80
1.15.
Classification based on number of cylinders
1.82
1.16.
Classification based on arrangement of cylinders
1.84
1.17.
Classification based on length of cylinders
1.91
1.18
Classification based on arrangement of valves
1.19.
Classification based on methods of cooling
1.20.
Wankel engine
1.21.
Valve timing diagram for a four-stroke cycle SI engine
1.22.
Valve timing diagram for a four stroke CI engine
1.100
1.23.
Variable valve timing (VVT)
1.101
nee r
ing
.ne
1.92 1.95
t
1.95 1.98
1.23.1.
Types of variable valve timing
1.103
1.23.2.
Advantages of variable valve timing
1.104
1.23.3.
Applications of variable valve timing
1.105
1.24.
Two mark questions and answers
1.105
1.25.
Solved questions
1.126
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
2.1.
Carburetors
2.1
L.1.i.
2.1
Functions of carburetor
2.2.
Factors affecting fuel vaporization
2.2
2.3.
Types of carburetor
2.2
2.3.1.
Simple carburetor
2.3
2.3.1.1.
Defects in a simple carburetor
2.4
2.3.2.
Solex carburetor
2.13
ww
w.E
2.4.
2.5.
2.6.
2.7.
2.3.3.
S.U carburetor
2.19
2.3.4.
Zenith carburetor
2.21
2.3.5.
Carter carburetor
2.22
asy E
Electronically controlled gasoline injection system for SI engine
2.25
2.4.1.
Limitations of carburetor or necessity of petrol fuel injection
2.25
2.4.2.
Types of gasoline injection system
2.4.3.
Working of electronically controlled gasoline injection system 2.27
ngi
nee rin
Electronic diesel injection system 2.5.1.
Components of electronic diesel injection system
2.5.2.
Unit injector system
2.5.3.
Rotary distributor system
2.5.4.
Common rail direct injection system (CRDI)
2.25
2.30
g.n et
2.31
2.33
2.35
2.36
Ignition system
2.38
2.6.1.
Battery ignition system or coil system
2.38
2.6.2.
Magneto ignition system
2.40
2.6.3.
Electronic ignition system
2.43
2.6.4.
Transistorised ignition system
2.46
2.6.5.
Capacitive discharge ignition system
2.47
2.6.6.
Distributorless ignition system
2.48
Supercharging
2.49
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I
ED I
Contents
2.7.1. 2.8.
2.56
Engine emission and its control 2.9.1.
Automobile engine pollutants
2.57
2.9.2.
Diesel engine emission
2.59
2.9.3.
SI engine emission
2.59
2.9.4.
Pollution control
2.60
2.9.5.
Evaporative emission control for SI engine
2.62
2.9.6.
Evaporative emission control system for CI engine
2.64
2.9.7.
Exhaust gas recirculation (EGR) system
2.64
2.9.8.
Crankcase emission control system
2.66
2.9.9.
Engine emission control by catalytic converter
asy E
2.69
ngi
2.10.1.
Setting emission norms
2.69
2.10.2.
EURONorms
2.70
2.10.3.
BS NonIl~
Two mark questions and answers
2.12.
Solved questions
3.3.
nee
2.72
rin
2.77
g.n e
2.90
t 3.1
Introduction 3.1.1.
3.2.
2.66
Emission norms (Euro and BS)
2.11.
3.1.
2.5£1
Methods of turbocharging
ww w.E 2.10.
2.52
Turbo chargers 2.8.1.
2.9.
2.49
Types of supercharging methods
Functions or purposes of transmission systems
3.2 3.2
Clutch 3.2.1
Principles of operation of friction clutch
3.3
3.2.2.
Functions of clutch
3.3
3.2.3.
Characteristics or requirements of a clutch
3.3
Types of clutches
3.4
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
•
Automobile
Engineering
3.3.1.
Single plate clutch
3.5
3.3.2.
Multi-plate clutch
3.9
3.3.3.
Cone clutch
3.10
3.3.4.
Centrifugal clutch
3.11
3.3.5.
Semi-centrifugal clutch
3.12
3.3.6.
Diaphragm clutch
3.13
3.3.7.
Positive clutch (or) dog and spline clutch
3.15
3.3.8.
Hydraulic clutch
3.16
3.3.9.
Electro-magnetic clutch
3.17
3.3.10.
Vacuum clutch
3.18
ww w.E a 3.4.
Trouble shooting of clutch
3.19
3.5.
Gearbox
3.22
3.6.
3.5.1.
Necessity of transmission
3.22
3.5.2.
Purposes of transmission
3.23
3.5.3.
Resistances to motion
3.23
3.5.4.
Tractive effort
3.24
syE
Types of gearbox
ngi
3.6.1.
Sliding mesh gearbox
3.6.2.
Constant mesh gearbox
3.6.3.
Synchromesh gearbox
3.6.4.
Epicyclic gearbox
3.6.5.
Automatic gearbox
nee r
3.25
ing
3.25
.ne
3.29 3.32
t
3.34 3.36
3.7.
Hydromatic transmission
3.37
3.8.
Shift or selector mechanism
3.42
3.9.
Trouble shooting of gearbox
3.43
3.10.
Overdrives
3.47
3.10.1.
Operation
3.49
3.10.2.
Construction
3.49
3.10.3.
Free-wheel assembly
3.50
3.10.4.
Pawl action
3.51
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IDI
I Contents 3.10.5.
Electrical controls
3.52
3.10.6.
Trouble shooting chart for overdrive
3.54
3.11.
Transfer box
3.55
3.12.
Fluid flywheel
3.57
3.13.
Torque converter gearbox
3.58
3.13.1.
Difference between fluid coupling and torque convertor
3.61
3.14.
Propeller shaft
3.62
3.14.1.
Functions of propeller shaft
3.62
3.14.2.
Propeller shaft construction
3.64
ww w.E 3.l5.
Slip joints
3.65
3.16.
Universal joints
3.66
3.16.1.
Types of universal joints
3.66
3.16.2.
Maintenance of propeller shafts and universal joints
3.69
3.16.3.
Trouble shooting for propeller shaft
3.70
3.17.
Differential
asy E
ngi
3.71
3.17.1.
Need for the differential gear unit
3.71
3.17.2.
Major components of differential
3.72
3.17.3.
Construction
3.17.4.
Basic principle of operation
3.17.5.
Types of differential
nee
3.17.5.1. Conventional differential
rin
3.72
g.n e
3.17.5.2. Limited slip differential or self-locking differential or
3.74
t
3.74
3.74
differential lockout 3.17.5.3. Non-slip differential
3.78
3.17.5.4. Double reduction type differential
3.78
3.17.6. 3.18.
3.73
Trouble shooting for differential
3.79 3.81
Rear axle 3.18.1.
Construction of rear axles
3.82
3.18.2.
Rear axle casing
3.82
3.18.3.
Types of loads acting on rear axles
3.85
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
3.19.
Engineering
3.18.4.
Types of rear axles
3.85
3.18.5.
Comparison of different types of rear axles
3.8R
3.18.6.
Rear axle drives
3.88
3.18.6.1. Hotchkiss drive
J.88
3.18.6.2. Torque tube drive
3.89
3.18.6.3. Comparison between Hotchkiss drive and torque tube drive
3.90
3.18.7.
3.91
Trouble shooting for rear axle
Two mark questions and answers
3.92
Solved questions
3.108
ww w.E a 3.20.
4.1.
Steering system
syE
ngi
4.1
nee r
4.1.1.
Requirements and functions of the steering system
4.2
4.1.2.
Layout of steering system
4.3
4.1.3.
Principle of operation of steering system
4.1.4.
Fundamentals of steering mechanism or condition for true rolling motion
4.1.5.
Ackerman - Jeantaud steering linkage
4.1.6.
Davis steering gear
4.1.7.
Steering linkage for vehicle with
ing
4.7
.ne
t
4.7 4.9 4.11
independent front suspension
4.12
4.1.8.
Steering geometry
4.12
4.1.9.
Wheel alignment
4.19
4.1.10.
Steering gears
4.20
4.1.11.
Types of steering gear box
4.21
4.1.12.
Steering ratio
4.27
4.1.13.
Turning radius and slip angle
4.28
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Contents
4.2.
4.1.15.
Centre point steering
4.30
4.1.16.
Cornering force
4.32
4.1.17.
Reversible and irreversible steering
4.33
4.1.18.
Power steering
1.33
4.1.19.
Trouble shooting for steering system
4.37 4.4~
Front axle 4.2.1.
Functions of front axle
4.44
4.2.2.
Construction and components of front axle
4.44
4.2.3.
Types of front axles
4.46 4.47
Stub axle
4.3.1.
4.4.
4.29
Understeering and oversteering
ww w.E
4.3.
Ell I
4.1.14.
4.47
Types of stub axles
asy E
4.48
Suspension system
4.4.1.
Components .ofsuspension system
4.49
4.4.2.
Functions or objectives of suspension system
4.49
4.4.3.
Requirements of suspension system
4.50
4.4.4.
Principles of suspension system
4.50
4.4.5.
Sprung weight and unsprung weight
4.4.6.
Basic suspension movements
4.4.7.
Types of suspension springs
4.4.8.
Leaf spring suspension
4.4.9.
Helper springs
4.58
4.4.10.
Coil spring
4.59
4.4.11.
Torsion bar
4.60
4.4.12.
Rubber springs
4.61
4.4.13.
Air springs
4.63
4.4.14.
~ydro elastic suspension
4.66
4.4.15.
Shock absorber
4.68
Types of suspension system
4.71
4.4.16. 4.4.17.
iI
ngi
nee
rin
4.50
g.n e
4.52 4.54
t
4.55
i
Independent front suspension
4.71
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
4.5.
Automobile
Engineering
4.4.18.
Rigid axle front suspension
4.78
4.4.19.
Independent rear suspension
4.79
4.4.20.
Interconnected suspension system
4.82
4.4.21.
Anti-roll bar (stabilizer)
4.84
4.4.22.
Trouble shooting in springs and suspension
4.86
Braking system
4.90
4.5.1.
Requirements of braking system
4.90
4.5.2.
Stopping distance, time and braking efficiency
4.91
4.5.3.
Theory of braking or principle of braking
4.92
4.5.4.
Friction resistance and coefficient of friction
4.93
ww
w.E
4.5.5.
Types of brakes
4.94
4.5.6.
Drum brake
4.95
4.5.6.1. Types of drum brakes
4.97
4.5.7.
asy
Disc brakes
En
4.98
gin eer
4.5.7.1. Components of disc brake
4.98
4.5.7.2. Types of disc brake
4.99
4.5.8.
Comparison between drum brake and disc brake
4.103
4.5.9.
Hydraulic brakes
4.104
ing
4.5.9.1. Master cylinder 4.5.9.2. Wheel cylinder
4.5.9.3. Advantages and disadvantages of hydraulic brakes
.ne
4.105 4.108
t
4.109
4.5.9.4. Brake fluid of hydraulic brake system
4.110
4.5.9.5. Bleeding of hydraulic brakes
4.111
4.5.10.
4.112
Mechanical brakes
4.5.10.1. Fixed expander brake
4.113
4.5.10.2. Leading and trailing shoes
4.114
4.5.10.3. Floating-cam brake
4.114
4.5.10.4. Floating anchor brake
4.115
4.5.10.5. Brakes with two leading shoes
4.116
4.5.10.6. Brakes with two trailing shoes
4.116
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Contents 4.5.11.
Air assisted hydraulic braking system
4.117
4.5.12.
Pneumatic braking system
4.117
4.5.12.1. Comparison between pneumatic and hydraulic brakmg systems 4.119 4.5.13.
Transmission or propeller shaft parking brake
4.120
4.5.14.
Servo brake systems
4.121
4.5.15.
Power-assisted braking system
4.122
4.5.15.1. Vacuum assisted hydraulic brake
4.123
4.5.16.
Brake valve
4.124
4.5.17.
Brake adjustments
4.125
ww w.E
4.5.17.1. Micram adjuster
4.125
4.5.17.2. Taper screw adjuster
4.126
4.5.17.3. Girling mechanical brake adjuster
4.127
asy E
4.5.18.
Brake compensation
4.128
4.5.19.
Retarder
4.128
4.5.19.1. Hydraulic retarder 4.5.19.2. Electric retarder 4.5.20.
ngi
4.128
nee
4.129 4.129
Antilock braking systems (ABS)
4.5.20.1. Need of ABS in automobile 4.5.20.2. Components of ABS 4.5.20.3. Working principle of ABS
rin
4.130
g.n e
4.131 4.134
t
4.136
4.5.20.4. Types of anti-lock brakes 4.5.20.5. Advantages and disadvantages of ABS
4.136
4.5.21.
Electronic brake force distribution (EBD)
4.137
4.5.22.
Traction control
4.139
4.55.22.1. Function of a traction control
4.139
4.55.22.2. Components ofTCS systems
4.140
4.5.23.
4.141
Trouble shooting in brakes
4.6.
Two mark questions and answers
4.148
4.58.
Solved questions
4.174
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
5.1.
Introduction to alternative energy sources
5.1
5.2.
Alternative fuels
5.2
5.3.
Properties of alternate fuels
5.4
5.4.
Use of natural gas in automobiles
5.8
5.4.1.
5.9
History of natural gas
ww w.E 5.4.2.
Properties/characteristics
5.4.3.
Various forms of natural gas
5.11
5.4.4.
Natural gas production
5.13
5.4.5.
Natural gas vehicles (NGVs)
5.14
5.4.6.
Natural gas consumption pattern in different countries
5.17
5.4.7.
Compressed natural gas (CNG) and
asy E
of natural gas
ngi
Liquefied natural gas (LNG) 5.4.8. 5.5.
5.6.
5.7.
nee
5.10
5.17
Advantages and Disadvantages of LNG
5.18
rin
Use of liquefied petroleum gas (LPG) in automobiles
5.19
5.5.1.
Properties / characteristics of LPG
5.20
5.5.2.
LPG equipment
5.5.3.
LPG fuel/engine
5.5.4.
Current state of LPG engine/vehicle technology
5.5.5.
LPG vehicles
5.25
5.5.6.
Advantages and disadvantages of LPG
5.27
Use ofbio-diesel
interaction
g.n e
5.23
t
5.24 5.24
in automobiles
5.29
5.6.1.
Properties ofbiodiesel
5.30
5.6.2.
Biodiesel production
5.30
5.6.3.
Advantages and disadvantages of biodiesel
5.31
Use of bio-ethanol in automobiles
5.33
5.7.1.
Sources ofbio-ethanol
(Alcohol)
5.7.2.
Bio-Ethanol (Alcohol) production
5.34 5.35
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Contents
5.8.
5.10.
5.11.
5.37
Performance of ethanol-based engine
5.7.4.
Engine cold start during winter
5.39
5.7.5.
Fuel economy
5.39
5.7.6.
Ethanol fuel mixtures
5AO
5.7.7.
Properties/Characteristics of Ethanol / Alcohol
5.40
5.7.8.
Advantages and disadvantages of Ethanol / Alcohol
5.40
Use of gasohol in automobiles
5.42
5.8.1.
Potential of gasohol in India
5.43
5.8.2.
Gasohol fueled vehicles
5.45
5.8.3.
Advantages and disadvantages of gasohol
5.45
ww w.E
5.9.
rEI I
5.7.3.
Use of hydrogen fuels in automobiles
·5.46
5.9.1.
Sources of hydrogen
5.46
5.9.2.
Advantages and disadvantages of using hydrogen as fuel
5.47
5.9.3.
Hydrogen as a fuel
5.48
5.9.4.
Hydrogen properties
5.9.5.
Production of hydrogen
5.9.6.
Hydrogen from natural gas
5.9.7.
Thermochemical processes
5.9.8.
Other methods of producing hydrogen
5.9.9.
Methods of using hydrogen in CI engines
5.9.10.
Challenges for hydrogen fuel
5.9.11.
Hydrogen fueled vehicles
asy E
ngi
5.48
nee
5.49
rin
5.51 5.52
g.n e
5.53 5.55
t
5.56 5.57
Engine modifications required for alternate fuels
5.57
5.10.1.
Need for engine modification
5.57
5.10.2.
Engine modification for bio-ethanol
5.58
5.10.3
Engine modification biodiesel
5.61
Performance of SI and CI engines with alternate fuels 5.11.1.
5.62
Performance of a 4-stroke SI engine "sing CNG as an alternative fuel
5.62
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
-
Automobile
5.11.2. 5.11.3. 5.11.4.
Engineering
Performance of spark ignition engine fuelled with methane, methanol, hydrogen, propane and ethanol gasoline fuels
5.64
Performance of compression ignition (CI) engine fuelled with biodiesel as an alternate fuel
5.67
Performance of soyabean oil as an alternate fuel for CI engine at variable compression ratio
5.68
5.12.
.Combustion ofSI and CI engines with alternate fuels
5.69
5.13.
Emission characteristics ofSI and CI engines with alternate fuels
5.70
5.14.
Electric vehicles
5.71
5.14.1.
History of electric vehicles
5.72
5.14.2.
Working of electric vehicles
5.72
5.14.3.
Electric vehicles
5.73
5.14.4.
Maintenance considerations
5.74
5.14.5.
Benefits of electric vehicles
5.75
5.14.6.
Limitations of electric vehicles
ww w.E a 5.15.
5.16.
syE
Hybrid vehicles
ngi
5.75 5.76
nee r
5.15.1.
Working of hybrid vehicles
5.15.2.
Parallel HEV design
5.15.3.
Series HEV design
5.15.4.
Hybrid electric vehicle components
5.15.5.
Hybrid electric vehicle benefits
5.15.6.
Hybrid electric vehicles
5.76
ing
5.77
.ne
5.78 5.79
t
5.86 5.87 5.89
Use of fuel cells in automobiles 5.16.1.
History of fuel cell
5.89
5.16.2.
Comparison of a fuel cell car and battery car
5.90
5.16.3.
Comparison of gasoline cars and fuel cell car
5.90
5.16.4.
Working principle of a fuel cell
5.90
5.16.5.
Parts of a fuel cell
5.91
5.16.6.
Types of fuel cells
5.94
5.16.6.1. Hydrogen-oxygen cell
5.94
5.16.6.~. Polymer electrolyte membrane (PEM) fuel cells
5.95
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Contents
ami 5.96
5.16.6.3. Direct methanol fuel cells 5.16:.6.4.Alkaline fuel cells
5.97
5.16.6.5. Phosphoric acid fuel cells (PAFCs)
5.98
5.16.6.6. Molten carbonate fuel cells
5.99
5.16.6.7. Solid oxide fuel cells
5.100
5.16.7.8. Regenerative fuel cells
5.101
5.16.7.
Conversion efficiency of fuel cells
5.101
5.16.8.
Advantages and disadvantages of fuel cells
5.101
5.16.9.
Applications of fuel cells
5.102
ww
5.16.10. Fuel cell vehicles
5.103
w.E asy En gin ee
5.17.
Twonuukqu~wnsand~en
5.105
5.18.
Solvedquestwns
5.125
**********************************************************************
rin g.
net
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I ww w.E
asy E
ngi
UNIT -1
nee
Types of automobiles, vehicle construction
J and
different layouts, chassis, frame and body, Ve'hicle
rin
aerodynamics (various resistances and moments involved),
Ie
g.n e
engines - components functions and
materials, variable valve timing (VVT).
t
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
-
I Vehicle StrUcture and Engines
ww w.E 1.1. INTRODUCTION
GJ VEHICLE STRUCTURE AND ENGINES
asy E
ngi
The term automobile or automotive stands for a vehicle which can be moved by itself. Therefore, an automobile is a self-propelled vehicle. It is used for the transportation of
nee
passengers and goods from one place to another on the ground. A vehicle producing
POWt>i
within itself for its- propulsion is known as self-propelled vehicles. Example. s.oooters,
rin
mopeds, cars, lorry, bus, jeep, tractors, ship, airplanes, helicopters, rockets etc.
g.n e
Automobile vehicles differ from aeronautical vehicle .such as ships, airplanes, helicopters, rockets etc., which fly in air and from.marine vehicles such as motor boat which sail in water
t
Modern automobiles are produced by using complex components of machineries and therefore, it requires a caretul attention for making it to perform the task in a safe, eeonomical and efficient way. It is made up of a frame supported by the body and power producing units and power transmitting units. These units are further-supported by tyres ano Wheelswhich are connected by springs and axles. In general, the power is produced by internal combustion engines. This power inturn is transmitted to rear wheels through various transmission ~ystems such as clutch, propeller shaft, gear box, differential units etc. The various units are held together in a proper position and arranged on the frame. The automobile is propelled through the friction between tyre and ground. The super structure or
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
-
Automobile EnginHl1ng
'I
body of the automobile provides protection and comfort to the passenger. The 'essential features of the typical automobile (i.e. truck) are shown in Figure 1.1. Cab
ww w.E
Differential
asy E
Figure 1.1Essential features of an automobile
1.1.1.Brief History of Automobiles
ngi
Germany is the birth place of automobile. It was invented there. It went through its initial phases and it was developed to a high level of technical maturity. The list of German
nee
rin
automobile pioneers is a long one starting with Nicholas Cugnot, August, Otto, Carl Benz, Gottlieb, Daimler, Wilhelm Maybach and Rudolf Diesel and going all the way up to Ferdinand Porsche and Felix Wankel.
g.n e
The leading manufactures or motor vehicles in the world are as follows. 1. U.S.A.: General Motors, Ford-Ford cars, Chrysler, Dodge
t
2. U.K.: Rolls-Royce Limited, Aston Martin, Bentley, Daimler 3. Japan: Toyota, Nissan, Honda, Suzuki, Mazda, Isuzu, Mitsubishi 4. Germany: BMW, Volkswagen, Audi, Skoda, Mercedes-Benz, Porsche, Daimler AG, Opel, Porsche 5. Italy: FIAT 6. Sweden: Volvo 7. France: Renault
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
8. India: TATA motors, Mahindra & Mahindra, Hindustan Motors, Premier Automobiles Limited, Force Motors, Jaguar, Land Rover (Note. Jaguar, and Land Rover are acquired by TATA Motors in 2008) 9. South Korea: Hyundai, KIA Motors, SsangYong Motor The invention of automobiles is not the product of a single man, single country or a single generation in any country. It is the evolution and development of many men at various generations in different countries. The real history of automobile was started during 15th century (i.e. during Leonardo Da Vinci's period). But up to 18th century, it was not seriously considered for the development in
ww
practice.
Captain Nicholas Cugnot, a French engineer is considered to be the father of
w.E asy En gin ee
"Automobiles". He built the first road vehicle in 1769whlch was propelled by its own-power. Actually, this vehicle was a 3 wheeler with a steam engine having four seats. It attained a speed of2.5miles per hour only for a period of 15minutes. During 1770s, he ~uilt another selfpropelled vehicle which could run at 8mph carrving.e to 5 Jo1IS..()f weight. Richard Trevithick of England first built a practical full sized stearn automobile in 1801. Julis Griffith of England built the first comfortable stearn vehicle in 1821.
rin g.
Onesiphore Pacquaur of France took out a patent on the differential for road vehicle in 1827.
net
Etienne Lenoir of France (Paris) constructed an internal combustion engine which was run by gas during 1860. Two years later, he fitted one of his engines in a vehicle. He drove it for about 6miles.
Nikolaus A.Otto and Engen Langen of Germany invented four stroke engine in 1876 which was run by gas. It was further improved by Gottlieb Daimler of Germany (in 1885) who substituted oil for gas. The present day automobile is the development of this vehicle. Karl Benz of Germany built a tricycle with an l.C, engine in 1885-86 which was working an Otto cycle. The speed of this engine was 10mph and produced 8HP. In 1886, Daimler produced a four-wheeled vehicle with high-speed gas engine (800rpm to 1OOOrpm)which was considered as the greatest achievement in the history of automobile.
In 1890, Charles Duryea, J. Frank Duryea, Elwood Haynes, Henry Ford and Ransom E. Olds, and Alexander Winton manufactured a.gasoline automobile in America.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1IIII~__ ~__ ~
~~
~~__ ~__ -=
A_m_o_m_O_b_'_le_E_n~g~l_n_e_en_n~g~~ Penhard and Levassor of France developed a first gasoline automobile which incorporated many essential features of the present day automobile in 1895. This car contained a vertical engine, modern type of chassis, sliding gear transmission operated by right hand, clutch, brake and a foot operated accelerator. Before 1900, a considerable work was carried in Germany, France, England and America on the development of gasoline automobile. Until 1910, the automobile was in the experimental work. During 1900-1906, the production and sales of automobile became a real business. The world's largest manufacturing industry was built in America. In America alone, there were 121 car manufacturers in which some of the familiar names are Chrysler, Nash. Hudson. Packard, Autocar, Oldsmobile, White, Ford, Cadillac, Buick overland, Maxwell, Franklin etc.
ww w.E
Ford started an automobile industry with an initial run of 20000 vehicles in 1908 and it was the period when the mass production was begun at the lowest possible price.
asy E
Year 1920 was the period of gradual change and refinement in the automobile design. The spark ignition gasoline engine was made with compact, light, high speed, less vibration,
ngi
air or water cooled and noiseless in nature. The engines were located in front of chassis. The
nee
sliding gear transmission and poppet valve were used in almost every engine. History of automobile in India:
rin
In 1898, an American company imported three "Oldsmobiles" cars into Bombay
g.n e
(Mumbai). One of which was sold to Jamshedji Tata, an industrialist. It was the first motor car in India.
t
In 1903, an American company began to operate a public taxi service with a tleet of SO
cars.
In order to create and manufacture indigenous product, two automobile factories were set up in India. They were the Permier Automobiles Ltd., Bombay in 1943 and Hindustan Motors Ltd., Calcutta in 1944. Now-a-days, there are many automobile industries for manufacturing automobile vehicles. Maharastra and Tamil Nadu are the major states which are producing most of the automobile and auxiliary manufacturing units.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Sttvcture and Engines 1.1.2.Requirements of an Automobile Vehicle
The following requirements must be fulfilled for an automobile. 1. It should develop power by itself. 2. The rate of power development must be easily controlled. 3. There should be an arrangement to transmit developed power to wheels. 4. An arrangement must exist to continue and discontinue power flow to wheels. 5. It should be possible to control or vary the torque. 6. The driving thrust should successfully be carried in the vehicle.
ww
7. It must have a directional control. 8. An arrangement must exist to stop the vehicle while it is running.
w.E asy En gin ee
All above requirements are fulfilled by the following arrangements. 1. The power is developed by the engme.
2. The rate of power development is controlled bv an accelerometer. 3. The power developed by the engine is transmitted to wheels by transmission system.
4. The gear box is provided for varying or changing the torque.
rin g.
5. The driving thrust is carried to the chassis frame through the suspension system. 6. Directional control is maintained through the steering. 7. The moving vehicle is stopped by means of brakes. 1.2. GENERAL CLASSIFICATIONOF VEHICLES
net
There are various types of automobiles vehicles used in the world. In general, these automobiles can be classified into three main groups. 1. Single unit vehicles or load carriers 2. Articulated vehicles 3. Heavy tractor vehicles. 1.2.1.Single Unit Vehicles These are conventional four-wheel types. The great majority of vehicles are of two axle design. In these vehicles, the front axle is a steering or.non-driving axle. With the passage of time; many changes have taken place in axles and driving arrangements. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
-
Automobile Engineering
1.2.2.Articulated Vehicles A lower powered three-wheeler with a single steering wheel in front and a conventional .
rear driving axle are an example of articulated vehicles. It has a greater handling ability in awkward places. It can be turned about its own tail due to three-wheel construction. The coupling mechanism between semi-trailer and tractor in most of these vehicles is arranged for automatic connection and coupling up. If it is necessary, it is reversed into a position. But for uncoupling operation, a lever is provided within the driver's cabin to reverse the whole process. A pair of retractable wheels in front is also provided. Along with the coupling or uncoupling operation, they can be automatically raised or lowered.
ww w.E
1.2.3. Heavy Tractor Vehicles Heavy tractor or independent tractor vehicles are used to move heavy loads. They . commonly operate in pair either in tendon or as 'puller' or 'pusher'. While descending appreciable gradients, the stability is provided by the 'puller' or 'pusher' arrangement.
asy E
1.3. TYPES OF AUTOMOBILES
ngi
nee
Automobiles can be classified with respect to different purposes. A general classification of the automobiles is shown schematically in Figure 1.2. (i) With respect to the purpose:
rin
g.n e
(a) Passenger vehicles. Examples: Car, bus,jeep, scooter, mopeds and motor cycle. (b) Goods carriers. Examples: Trucks and Lorries. (ii) Weight of the vehicle: (a) Heavy weight vehicle such as buses, trucks and trailers.
t
(b) Light weight vehicles such as.cars.jeeps etc. (c) Medium weight vehicles such as minibus and station wagon. (iii) With respect to the fuel used: (a) Petrol vehicles Examples: Scooters, cars, motors cycles etc. (b) Diesel vehicles Examples: Buses, trucks etc. (c) Gas vehicles Examples: Coal gas, LPG, CNG vehicles. (d) Electric vehicle Examples: Heavy cranes, battery truck, cars and forklifts. (e) Solar vehicle. Downloaded From : www.EasyEngineering.net
..
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
ww
Double deck
w.E asy En gin ee
Air conditioned
rin g.
net
Figure 1.2 Classification of automobiles (iv) With respect to body style: According to body style following are major styles. a) Closed cars such as, sedan cars, saloon cars, SUV~ coupe etc. b) Open cars such as sport cars and convertible cars. c) Special style vehicles such as estate car, station wagon etc.
Downloaded From : www.EasyEngineering.net
..
Downloaded From : www.EasyEngineering.net
,
Automobile
Enpineering
(v) With respect to capacity: (a) Heavy transport vehicle or heavy motor vehicles. Example: Bus, Lorries, Trucks, Tractors. (b) Light transport vehicle or light motor vehicles. Example: Car, Scooter, Mopeds, Motor cycles, Jeeps.
(vi) With respect to the number of wheels: (a) Two wheelers. Examples: Scooters, Mopeds. (b) Four wheelers. Examples: Car, Jeep, Buses.Trucks, (c) Three wheelers. Examples: Auto, Tempos
ww w.E
(d) Six wheelers. Example: Heavy trucks.'
(vii) With respect to the drive of the vehicle: (a) Single wheel drive vehicles
asy E
(b) Two wheel drive vehicles
(c) Four wheel drive vehicles (d) Six wheel drive vehicles.
ngi
(viii) With respect to the side of driver seat:
nee
(a) Left hand drive. Example: Most of the American, European and UAE vehicles.
rin
(b) Right hand drive. Example: Most of the Indian vehicles. (ix) With respect to the side of power drive:
(a) Front wheel drive. Example: Most of the light weight cars. (b) Rear wheel drive. Example: Trucks and Buses.
g.n e
t
(c) Four wheel drive. Example: Jeep, military trucks and off-road vehicles. (x) With respect to transmission: (a) Conventional type: In this type, ordinary gear box is fitted. Example: Most of Indian vehicles. (b) Semi-automatic type: A combination of manual plus some automatic gear box is fitted. Example: Most of British vehicles. (c) Fully automatic type: In this type, vehicles are equipped with full automatic transmission system by using epicyclic gears and torque convertors. Example: American and European vehicles.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Vehicle Structure
".
and Engines
(xi) With respect to their construction: (a) Single unit vehicles (b) Articulated vehicles (c) Heavy tractor vehicles. (xii) With respect to motion: (a) Reciprocating Piston engines (b) Rotary - Wankel engine (c) Gas turbine.
ww w.E
(xiii) With respect to the suspension:
(a) Conventional type. Leaf spring (b) Independent. Coil, torsion bar, pneumatic.
asy E
(xiv) With respect to engine capacity:
The capacity of the engine is expressed in swept volume of the cylinder which is normally expressed in cubic centimeter (CC). Examples of engine capacity of some of the vehicles are given in Table 1.1.
ngi
nee
Table 1.1 Engine capacity of some automobile
rin
Vehicle
Engine capacity (CC)
TVSXL
50
Bajaj Discover 100, TVS Sport, Hero Splendor
100
Bajaj Pulsar 150 DTSi,
t
150
Hero Xtreme, Maruti Suzuki Alto, Chevrolet Spark
g.n e
800
(xv) With respect to combination of number of wheels and axles: The digital figures like 4x2, 4x4, 6x4 etc. are commonly used in the classification of vehicles. By increasing the number of axles, the load per axle can be reduced which protects the tyres from overloading and the road surface from damage.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
I..
Engineering
1.4. VEHICLE CONSTRUCTION
Before invention of automobile, the most common type of vehicle used in our country was a bullock cart. Now-a-days, People are also using bullock cart in rural areas. It is better to understand the construction of bullock cart before discussing automobiles. Figure 1.3 shows a bullock cart.
ww
w.E
asy
En
gin eer
Figure 1.3 Construction of a bullock cart A bullock cart consists of the following main parts. (i) Frame (ii) Wheels and axle (iii) Yoke (iv) Body or superstructure and platform.
ing
These parts can be divided into the following two main portions.
.ne
t
(i) Machine portion (ii) Carriage portion Machine portion consists of a frame in which wheels are attached through the axle. f yoke is fixed at the front of the frame through which the cart is pulled by bullocks. The carriage portion consists of platform and body which is mounted over frames. The platform consists of two long beam connected by cross members. The load or goods to be carried by this portion and the total load are borne by the frame. The basic construction of automobile is similar to a cart. An automobile also consists of a machine portion and carriage portion similar to a cart. The difference between a cart and an Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
II1'II
Vehicle Structure and Engines
automobile is that cart is a simple vehicle whereas automobile is a self-propelled vehicle. A vehicle consists of engine to drive the vehicle. In addition, an automobile also consists of power transmission systems such as clutch, gear box, propeller shaft, universal joints, differential etc. Automobile is also provided with steering for directional control, acceleration for speed control and brakes for stopping purposes. The speed of the cart is slow as compared to automobiles. Due to this fact, the automobile is subjected to more shocks which in tum put more strains on the frame. Therefore, the automobile is needed robust frame and shock absorbers to bear all stresses and strains. The axle is not directly fitted with the frame in the automobile. It is suspended with the frame through strong springs. In order to arrest shocks and save the passengers from jerks
ww
and jolts due to rough road condition, shock absorbers are provided.
w.E asy En gin ee
Figure 1.4 shows the layout of a car. It consists of an engine which is located at the front of vehicles followed by transmission systems. The radiator is located in front of the engine. Various other parts of the vehicle shown in Figure 1.4 are generator, starter, steering, clutch, rear axle, differential, universai joint, wheel, tyres, body, lamp etc. Gear shift
Engine crank case
Steering w'ih,,:ee~I
Universal joints
_
rin g.
net
Flywheel
Figure 1.4 Layout of a car The power developed by the engine is transmitted to the rear wheel through clutch, gearbox, propeller shaft, universal joint and differential. Lamps are provided in the automobile so that they could be safely driven during night hours. A hom is provided for making warning sound to other road users. The body or superstructure is built up to fulfill the requirements or trends of the passenger.
A
brake is provided to the vehicle to stop or slow down the speed whenever
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I"
Automobile Engineering
required. A fuel tank is provided to store the required amount of fuel. A radiator is provided for cooling the engine and related parts of the vehicle. 1.5. DIFFERENTLAYOUTS OF A CAR 1.5.1. Layout for the Light Passenger Vehicle (Car) Due to various developments in technology and changes in lifestyle, a motor vehicle has changed to meet upcoming requirements. Recent days, many types of layouts are used with their own specific advantages and disadvantages. These changes occur in the location of the engine and the driving arrangement in terms of number of wheels driven and location of wheels. The engine can be positioned laterally or longitudinally to drive either front wheels or
ww w.E a
rear wheels or all four wheels. 1.5.1.1.Front Engine
syE
Many reasons are involved for placing the engine at the front of a car as shown in Figure 1.5. The large mass of an engine placing at the front of the car gives the occupants protection
ngi
in the event of a head-on collision. The engine cooling is simple as it can get benefit of ail
nee r
movement against the motion of vehicle. Also, the cornering ability of a vehicle is generally better if the weight is concentrated at the front side because the weight of the engine is placed over steered wheels.
ing
.ne
t
Figure 1.5 Front engine 1.5.1.2.Rear engine By placing the engine at the rear of the vehicle, it can be made as a unit to incorporate the clutch, gearbox and final drive assembly. So, it is necessary to use some form of independent rear suspension systems.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
Most rear-engine layouts have been restricted to comparatively small cars because the weight of the engine at the rear has poor effect in handling of the car. So, it makes 'tailheavy'. The engine mass on a rear-engine car acts behind the rear axle line. It creates a pendulum effect during cornering. So, it makes difficult for most drivers due to high speeds. TATA Nano, Volkswagen Beetle and Porsche sports cars are the example of a rear engine location. Rear located engines can also take up a large amount of space which would on a frontengine car used for carrying luggage. Most of the space vacated by moving the engine from the front can be used for luggage. At the same time, this space is usually less than available space in rear side. Vertical engines are used in rear-engine cars. A 'flat' engine or a conventional engine mounted on its side will provide the additional space for luggage above the engine.
ww
w.E asy En gin ee
The main advantage of a rear-engine layout is the increased load on the rear driving wheels which will provide better grip on the road. Figure 1.6 shows the typical layout of a rear-engme car.
Figure 1.6 Rear engine
rin g.
net
1.5.1.3. Central or Mid-Engine
Generally, the central or mid-engine location is applied in sports cars. In a rear-engined car, the engine overhangs the rear axle line but in a mid-engined car, the engine is forward of the rear axle line. This location provides excellent weight distribution to achieve both good handling and maximum traction from driving wheels. This advantage attracts and makes useful for sports and special cars but it becomes disadvantages when it is applied to traditional passenger cars. The main disadvantage is that the mid-engine location takes up space which will normally be occupied by passengers in conventional layout cars. Most cars using a mid-
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
engine position are always sports cars fitted with only two seats, one for the driver and the other for passenger. The mid-engined
layout shown in Figure 1.7 combines the engine and transmission
components in one unit. Mid-engined cars are normally rear-wheel driven.
ww w.E
Figure 1.7 Mid-engine
asy E
1.5.2. Front Engine Front Wheel Drive
ngi
The majority of light vehicles have the engine at the front of the vehicle with the driving power being transmitted to front wheels. In the arrangement shown in Figure 1.8, the engine
nee
and transmission units are placed transversely at the front of the vehicle. So, they are at right angles to the main axis of the vehicle. FinalDrive
Frontwheel
Clutch
rin
g.n e
Rearwheel
t
...
III
o
-CII
s: ....o c
~
LL
Drive shaft
Universal Joint
Figure 1.8 Front enginefront wheel drive Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
.....
No propeller shaft is used in the front engine front wheel drive and differentials are included in the same assembly. This layout provides an optimum body-luggage space and a flat front line resulting a transverse longitudinal engine position. A good road adhesion is provided by the large proportion of vehicle's weight acting on driven wheels. Advantages:
1. Because the engine and transmission system are placed over the front wheels the road holding is improved especially in wet and slippery conditions. 2. Good steering stability is achieved because the driving force at the wheels is in the direction that the vehicle is being steered. There is also a tendency for front-wheel drive vehicles to understeer which can improve drivability when cornering.
ww w.E
3. Passenger and cargo space~ are good because there is no need for a transmission shaft to the rear axle.
4. Good road adhesion is obtained due to a large part of the vehicle weights are carried on driving wheels under normal conditions,
asy E
5. Under steady conditions, this drive is preferred by many drivers.
ngi
6. Lower flat floor line is provided due to dispensing with the propeller shaft resulting less centre of gravity.
nee
7. The engine clutch, gear box and final drive are combined similar to a rear engine car.
rin
It provides a more comfortable drive due to final drive spring.
Disadvantages:
1. Complicated drive shafts are needed for constant velocity Joints.
g.n e
t
2. Acceleration is affected because the load transfer to rear of the vehicle lightens the load on the drive axle at the front. 3. The turning circle radius is limited by the angle through which a constant-velocity joint can function. 4. Due to the combination of steered and driven wheels with short shafts, special universal joints and more complicated assembly are required. 5. To prevent the rear wheels from skidding under heavy brake, the required weight at the rear usually necessitates a special arrangement. 6. The tractive effort is reduced which is mostly required on steep gradients and during acceleration.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
11.5.3. Front
Automobile
Engineering
Engine Rear Wheel Drive
In this layout, a front mounted engine-clutch-gear box unit drives a beam type rear axle suspended on leaf springs through a propeller shaft with two universal joints. With the help of coil springs, the front wheels are independently sprung.
ww w.E
Figure 1.9 Front engine rear wheel drive
asy E
This layout is one of the oldest layouts which remain unchanged for many years. Some of the advantages provided by this system are as follows. Advantages:
ngi
nee
I. It is reasonably balanced weight distribution between front and rear wheels providing good handling characteristics.
rin
2. For easy front wheel steering movement, the engine occupies the reduced width between arches.
g.n e
3. Behind the rear seats, a large luggage space is available by providing the increased carrying capacity as well as space for easy body movement.
t
4. Accessibility to various components such as engine, gear box and rear axle are better compared to other layouts. 5. The control linkages such as accelerator, choke, clutch and gear box are short and simple. 6. For the full benefits of the natural air stream created by vehicles, the movement is taken by the forward facing radiator in reduced power losses from a large fan. Disadvantages: 1. A single or split propeller shaft with universal joints and supporting bearings between front mounted gearbox and rear axle may generate vibration, drumming, howl and other noises under certain operating conditions.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
2.
The floor tunnel is necessary to provide a clearance for the operation of a propellershaft system and it may interfere with passenger leg-room.
3.
In case of a rigid casing for the axle and final drive, more weight is not supported by the suspension system so that the quality of the suspension ride may be reduced.
4.
Additional universal joints and drive shafts are required for independent rear suspension.
5. A rear-wheel-drive vehicle when stuck in mud, tends to plough further into the ground when attempts are made to drive away.
1.5.4. Rear Engine Rear Wheel Drive
ww
This arrangement
eliminates the necessity for a propeller
w.E asy En ( gin ee
shaft when the engine
mounted adjacent to driven wheels. The engine-clutch-gearbox-final unit in this layout. In order to reduce the 'overhang'
IS
drive forms a single
distance between wheel centres and
the front side of the engine, the final drive is generally placed between clutch and gear box. Gearbox
Rear wheel
CI'Jtch
(
...
III U
-.... ... Q)
.=.
0
e
0
LL
(
rin g.
)
net
Universal _; Joint
Figure 1.10 Rear engine rear wheel drive Advantages: 1.
Short driveline because the engine, gearbox and final drive can be built into a single unit.
2.
A majority of weight at the rear of the vehicle gives improved traction during hill climbing and acceleration.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
_
Automobile
Engineering
3.
It has a simple drive shaft layout compared to a front wheel drive.
4.
Effective rear wheel braking is possible with this layout.
5.
Due to the absence of the propeller shaft, the obstructed floor space is reduced.
6.
The exhaust gases, fumes, engine heat and noises are carried away from passengers.
7.
The drive arrangement results a compact layout and short car.
8.
The front of the vehicle can be designed for good visibility and smooth air flow.
Disadvantages: 1.
The rearward concentration of weight causes the vehicle to be more affected by side
ww w.E
winds at high speeds. It makes the vehicle unstable resulting over-steering and turning very sharply into a curve.
2.
It is difficult to accommodate the liquid cooling of the engine.
3.
It is difficult to accommodate the fuel tank in a safe zone ofthe vehicle.
4.
Space for luggage is reduced.
5.
Steering is difficult in slippery conditions.
6.
It has a restricted luggage compartment due to narrow front which houses the fuel tank also.
7.
Natural air cooling is not possible because it requires a powerful fan.
8.
Long linkages are required for the engine, clutch and gear box controls.
asy E
ngi
nee
1.5.5. Four-Wheel Drive
rin
g.n e
t
To increase the effective use of the vehicle required to travel on rough unconstructed roads and trucks, a special arrangement known asfour-wheel drive is provided. Due to all four wheels getting driven, the whole weight of the vehicle is available for traction. The system is provided in jeeps which are known as 4x4 wheel drive or all-wheel drive vehicles. These vehicles are also called off-road vehicles as it is constructed mainly for the purpose of unformed or off-road driving conditions. Example: Mahindra Scorpio, Maruti Suzuki Gypsy, Tata Safari, Toyota Fortuner, Mitsubishi Pajero, MahindraBolero etc. Advantages: 1. The increased traction is obtainable from four driven wheels which is especially useful on soft or slippery ground. 2. If the front wheel drops into a ditch, they tend to climb out with a rear wheel drive. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
liP-
Vehicle Structure and Engines
3. Wear oftyres and other driveline components are more evenly shared. Differential Front Axle
Engine Clutch Gear Box Transfer Box
ww w.E
Universal Joint
asy E
~ Differential
ngi
Figure 1.11 Four-wheel drive
Disadvantages: 1. It increases weight and bulk. 2. It increases cost. 3. It increases fuel consumption.
nee
rin
g.n e
4. It increases maintenance due to complexity of transmission system.
5. It is possibly difficult to accommodate an anti-locking brake system.
t
1.6. CHASSIS ,
To construct any automobile, chassis is the basic requirement:Chassis is a French term
and it was initially used to denote the frame or main structure of a vehicle. It is extensively used in complex vehicles except the body. A vehicle without body is called chassis. 1.6.1. Basic Construction of Chassis Chassis is the back bone of the vehicle. The components of the vehicle such as power plants, transmission system, axles, wheels and tyres, suspension, controlling systems such as
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lma
Automobile
Engineering
braking, steering etc., and also electrical system parts are mounted on the chassis frame. It is the main mounting of all components including the body. So, it is also called carrying unit. 1.6.2. Main Components
of Chassis
1.
Frame
2.
Front suspension
3.
Steering mechanism
4.
Engine, clutch and gear box
5.
Radiator
6.
Propeller shaft
7.
Wheels
8.
Rear and front springs and shock absorber
9.
Differential unit
10.
Universal joint
11.
Brakes and braking systems
12.
Storage battery
13.
Fuel tank
14.
Electrical systems
15.
Silencer
16.
Shock absorbers, fuel tank, petrol and hydraulics pipe cables and some means of mounting these components.
ww w.E
1.6.3. Classification
asy E
ngi
nee
rin
g.n e
t
of Chassis
The chassis can be classified into different types on the following basis. 1.According to the fitting of engine: (a) Full-forward (b) Semi-forward (c) Bus chassis (d) Engine at back (e) Engine at centre.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
_
In full-forward chassis, the engine is fitted outside the driver cabin or seat. Example: Cars and Mahindra jeeps. In semi-forward
chassis, a half portion of the engine is exactly in the driver's cabin
whereas the remaining half is at the front side but it is outside the driver's cabin. Example: Tata SE series of vehicles.
ww
(a) Conventional drive
(b) Froru engine drive
w.E asy En gin ee (c) Rear engine drive
(d) Centre engine drive
Figure 1.12 Classification of chassis according to thefitting of engine
rin g.
In bus chassis, the total engine is fitted in the driver cabin. It provides the increased floor area in the vehicle. The driver seat is just above the front wheel. Example: Busses and trucks.
net
In most of the vehicles, the engine is fitted at the front portion of chassis. The drive is only given to front wheels. Example: Matador vehicles. In some vehicles, the engine is fitted at the back portion of the chassis. Example: Volkswagen cars, Leyland bus of England. In some vehicles, the engine may be fitted at the centre of the chassis. Example: Royal tiger world master buses of Delhi transport.
2. According to the number of wheels fitted in the vehicles and the number of driving wheels: (a) 4 x 2 drive chassis - It has four wheels out of which 2 are driving wheels (b) 4 x 4 drive chassis - It has four wheels and all of them are driving wheels (c) 6 x 2 drive chassis - It has six wheels out of which 2 are driving wheels (d) 6 x 4 drive chassis - It has six wheels out of which 4 are driving wheels.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IrIm
Automobile
1.6.4. Characteristics
Engineering
of a Good Chassis
For a good chassis design and its good performances,
it must have the following
characteristics. 1.
Fast pickup
2.
Strength
3.
Safety
4.
Durability
5.
Dependability
ww 6.
Ease of control
7.
Quietness
8.
Speed
w.E asy En gin ee
9.
Power accessibility
10.
Economy of operation
11.
Low centre of gravity
12.
Stability
13.
Load clearance
14.
Braking ability
15.
Good springing
16.
Simplicity of lubrication.
1.6.5. Layout of Chassis
rin g.
net
Figure 1.13 shows the front and top views layout of the typical chassis. In this layout, the engine location is at the front end of the vehicle. The engine is connected to the gearbox through clutch. The drive of the engine can be connected or disconnected from the gearbox by using clutch assembly. The clutch pedal provided at the vicinity of the driver facilitates to engage or disengage the clutch with gearbox whenever required. From gearbox, power is transmitted to the differential through a propeller shaft and universal joints and finally to the wheels via rear axles. The radiator is placed at the front side of the engine.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Dump iron
Rear spring
Front . spring
Front view (Elevation)
ww w.E
asy E
ngi
nee
Side
members
Universal joint
Top view (Plan) Figure 1.13 Layout of chassis
rin
Petrol
tank
g.n e
t
1.6.6. Components and Drive Systems in Chassis 1. Frame:
Frame is the foundation for carrying the engine and body of the vehicle. It also carries steering, power train etc. by means of springs, axles, rubber pads etc. The frames are made of box, tubular, channel or U-shaped section, welded or riveted together. In order to make them rigid to withstand shocks, blow twists and vibration mats, cross-bracing or cross members are used When the engine, wheels, power trains, brackets and steering systems are fitted on the frame, the assembly is known as chassis. Frame bends upward in a shape
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
_
Automobile Engineering
at the fear to provide space for rear springs. It is tapered at the front to provide space for turning front wheels when steered. 2. Suspe_nsionsystems: "--~
Suspension systems are used in vehicles. ~ to insulate the wheel and axles from the frame ~
in order to avoid the transmission of road effects to passengers while travelling on uneven road
~
to provide a comfortable ride to passengers and
~
to avoid additional stresses in the motor car frame.
ww
3. Steering system: The function of the steering system is to enable the driver to accurately control the direction taken by the vehicle under all operating conditions. The system must be light and
w.E
easy to operate, free from shock and vibration as direct as possible. The steering system also helps to convert the rotary motion of the driver's steering wheel into the angular turning of the front wheels as well as to multiply the driver's effort with the leverage or mechanical advantage of turning wheels.
asy
4. Braking system:
En
gin eer
The most vital factor in running and controlling the modem vehicle is the braking system. In order to bring the moving motor vehicle to rest or slow down in a shortest possible
ing
time, the energy of motion possessed by the vehicle must be converted into some other form
.ne
of energy. Brake is a friction device for converting the power of momentum or kinetic energy of the moving vehicle into heat. 5. Internal combustion engines:
t
'In internal combustion engines, the combustion takes place within the engine unlike steam engines which work using steam which has externally been. raised in a boiler. In all Internal Combustion (IC) engines, the air is supplied along with a measured quantity of fuel. This fuel bums within the engine and it produces a high pressure and high temperature gas. 6.._ Clute":
It is a friction type uncoupling device. It consists of a single steel disc faced with suitable friction material. It is clamped between two surfaces directly driven by the engine. For disengagirlg the clutch, the two surfaces are ,Positively separated by pressing the clutch pedal. The main function of the clutch is to take up the drive smoothly from the engine and to release
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
_u .. .;.
Vehicle Structure and Engines
or disengage whenever desired. The disengagement of clutch is reouired while changing the gear or bringing the vehicle to rest. 7. Gearbox: It consists of various types of gears which are constantly in mesh. The gear change-takes place by sliding the dogs. The main function of the gear-box is to provide the necessary variation to the torque applied by the engine to the road wheel according to the operating conditions. The necessary variations are provided due to the presence of different gear ratio among various meshing gears. 8. Propeller shaft:
ww w.E
The function is to transmit the power from the rear end of the gear-box to the final reduction gear in the axle. The vertical movement of the rear axle relative to the frame is also accommodated. It is an ordinary Hook~'s joint. The small and limited angular displacement in the rubber joints is advantageous in damping out torsional vibrations. 9. Universaljoint:
asy E
Due to the flexibility of road springs, the rear axle is constantly moving up and down.
ngi
The propeller shaft fitted to the rear axle must also be free to move up and down. To permit the turning of the propeller shaft, this movement takes place and universal joints are fitted at
nee
each of its ends. Therefore, the relative movement between engine and driving wheel is maintained by the universaljoint, 10. Differential:
rin
g.n e
The differential gear carries the power from propeller shaft to rear wheel axles. It helps
t
two rear wheels to turn at different speeds when rounding a curve. The outer wheel must overrun than the inner wheels when taking a turn. The differential gear also ensures that the final output torque is equally distributed between two wheels without any consideration of their relative speeds. 11. Springs: Springs are fitted between frame and wheel to prevent the upward movement of the frame along with up and down movement of the wheel. A spring is a reservoir of energy which is stored in steel springs by bending them or by twining them. When the spring resumes to its normal state, this energy is released.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
12. Front axle: It is used for steering front wheels carried on stub axles swiveling upon kingpin's axle extremities. Steering arms and track rod link, two stub axles are together used for swiveling them by a steering wheel about kingpins. The steering wheel linked to one cf the stub axle by a shaft, a gear box and suitable linkage are operated by the driver's hand wheel. An axle in which one-piece beam is used to support the vehicle through springs (axle and spring arrangement) was previously used. Now, an arrangement known as independent front suspension replaces the axle and spring arrangement. Under the control of springs, wheels are free to rise and fall independently in the vertical direction to each other.
ww
13. Rear axle:
Rear axle or driving axle is a tube such as shaft enclosing driving shafts with suitable
w.E
bearings for rotating the wheels. It is used for fixing the rear wheels. It is enlarged at the centre for enclosing the final drive gears used for providing main speed reduction between -engine and driving wheels. The change of direction from the line of propeuer shah to the
asy
transverse line of the axle shafts is also provided by the rear axle.
En
When going round a curve, the inner wheel has to travel for a smaller distance in
gin eer
comparison to the outer wheel. But both the rear wheel would rotate at the same speed if they are connected by a shaft. This rotation of both wheels would result the slipping of one or both of them on the road surface causing excessive tyre wear as well as severe twisting loads on the shaft. Moreover, two wheels of exact diameter can only tum at the same speed without slip on
ing
.ne
the straight road. Each wheel is provided with its own separate half-shaft connected by a differential gear and meeting at the centre of the axle. Therefore, when going round a curve, the wheels are free to rotate at different speeds although they are provided with equal drive by the differential gear.
t
For preventing the transmission of shock from uneven road surfaces to the vehicle, springs are used to support the vehicle on the axle. In order to allow the vertical movements of wheels relative to the frame as well as to allow the parts of the shaft to operate at different angle final drive gears and the differential gear are used. These are mounted in a casting attached to the frame with independent sprung wheels attached by means of shafts through devices called universaljoints. 14. Battery:
In reality, the battery is the heart of the electrical system of a motor vehicle. It supplies current to the cranking motor and ignition system. The function of the battery is to store electrical energy which can be used whenever required. Battery may be called nerve- centre of Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Vehicle Structure and Engines
.
-J
the whole installation because it supplies electrical energy for operating all electrical devices and other units except the charging device. It also supplies the electricity for operating the various electrical devices when the vehicle is not operating or running slowly and generator speed is insufficient to meet the full load requirements. 15. Wheels: The wheels are fitted below the chassis to support the load of the vehicle and passengers. They are fitted with hollow rubber tyres filled with air in rubber tubes under sufficien, pressure necessary for carrying the load. The shocks caused by road irregularities are absorbed by them. By fitting springs between wheels and vehicle to allow the vertical movement of the wheels in relation to vehicle, a greater part of unevenness of road surfaces is taken care of.
ww w.E a
1.7. FRAME
The frame is the main part of a chassis. It is the backbone of the vehicle. All other parts
of the chassis are mounted on the frame. It is a rigid structure which forms a skeleton to hold all major parts together.
syE
ngi
At the front end of the frame, the engine is mounted. The engine in tum is connected to clutch and transmission unit to form a complete power assembly. The frame is supported by wheel end tyre assembly. Some parts of the steering system are connected to the frame and
nee r
remaining to the body. The fuel tank is fastened to the rear end of the frame.
ing
1.7.1. Functions or Importance of Frame
1. To form the base for mounting engine and transmission systems.
.ne
t
2. To withstand the engine and transmission thrust and torque stresses as well as accelerating and braking torque. 3. To carry the load of passengers and goods in the body. 4. To accommodate a suspension system. 5. To carry the other parts of the vehicle. 6. To resist the effect of centrifugal forces when cornering a curve. 7. To withstand bending and twisting stresses due to the fluctuating or rear and front axles. 8. To support the load of the body, engine, gear box, battery, fuel tank etc.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
It must be strong, light and designed to withstand the shock blows, twists, vibrations and other strains to which it is subjected to road conditions. It should also resist the distorting force such as (a) weight of the components and passengers causing a sagging effect due to bending action. (b) horizontal forces provided by road irregularities. (c) upward twisting forces caused by road shocks.
ww
1.7.3. Frame Construction
w.E
In order to provide good resistance to bending and torsional effect, the frame sections are made of proper forms. A typical passenger car frame is shown in Figure 1.14. There are three common types of frame sections such as channel, tubular and box sections. They are 'made from cold rolled open earth steel or heat-treated alloy steel.
asy E
ngi
Channel section provides good resistance to bending but it is poor in resistance to torsion while tubular section provides good resistance to torsion and poor in resistance to bending.
nee rin
The box sections provide comparatively better resistant to bending and torsion. These sections are shown in Figure 1.15. Side member
X-member
1J C
Q)
.._
a:I
Q)
a:
g.n et
Front cross member
Figure 1.14A typical carframe
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
Channel section
Tubular section
Box section
I-section
Figure 1.15 Frame sections The frame is narrow at the front end because of short turning radius of front wheels. It is
ww
widening out at the rear end to provide a bigger space for body. The rear and front ends of the frame are curved upward to accommodate the movement of the axle due to springing and they are also kept the chassis height as low. It also avoids the
w.E
impact effect due to rear axle bouncing.
asy
En Cross member
gin eer
'C
c:
W
'-
«S
ing
/'"
Side member
(I)
a:
.ne
t
Figure 1.16 Conventional frame Figure 1.16 shows the simplified diagram of the frame. It consists of two longitudinal or side members of channel section. The side members are braced by many number of eros; members of channel or tubular section. In a conventional design, the cross members are at right angles to side members shown in Figure 1.16. Several modern chassis frames have cross members which has the cross section in the form of 'X' between side members shown in Figure 1.17. The brackets are provided to connect springs and support running boards. If necessary,
..
more brackets are provided to support the engine, gear box etc. The engine, clutch and
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
_
Automobile
Engineering
1-
geaf.&oxate bolted together to form one rigid assembly. It is usually mounted at the front end of the frame by means of rubber pads to withstand engine vibrations. Body mounting brackets
Cross member
ww
w.E
1.7.4. Types of Frame
asy E
Figure 1.17X-type/rame
ngi
nee rin
There are three types of chassis frame construction as follows. 1. Conventional frame construction 2. Semi-integral frame construction 3. Integral or Frameless construction 1. Conventional frame construction:
g.n et
This type of frame is also called non-load carrying frame. The loads on the vehicle are transferred to the suspension by this type of frame. The frame supports various parts of the vehicle such as engine, power transmission elements and car body. The total frame is mounted on the wheel axle by means of springs. The body of the vehicle is made of flexible materials such as wood and mounted on the frame by using rubber mountings between body and frame. This arrangement makes the body completely isolated from frame deflection. It is mostly used in heavy vehicles such as trucks. For commercial vehicles with relatively low volume production, it has advantages of
strong-chassis of less weight which is sufficient to carry considerable pay loads and localized accident damage. It is easy to repair in comparison to the integral chassis. Further, both long
---
wheel base version and short wheel base version of the same vehicle can be produced. The Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
cross-sections of the frame are usually channel, tubular or box type. Figure 1.18 shows a dismantled view of conventional chassis frame and body construction.
ww w.E
asy E
ngi
Figure 1.18 Dismantled view of chassisframe and body construction 2. Semi-integral frame construction:
nee
rin
In this type of frame, the rubber body mountings are replaced by relatively stiff mountings. This arrangement also transfers a part of the frame load to the body structure. This
g.n e
type of frame is mainly used in European cars and American cars. But, this construction is heavy in nature as compared to the conventional type. 3. Integral frame construction or Frameless construction:
t
This type of construction is also called chassis-less, unitary or monocoque construction. Now a-days, it is used in passenger cars. This construction provides a stiff light construction which is particularly suitable for mass-produced vehicles. In this type of construction, there is no separate frame. All assembly units are attached to the body. In this design, heavy side members of the frame are eliminated and cross members are combined with the floor of the body. The body of the vehicle gives a mounting for engine, transmission, suspension and other mechanical units and components. This type of construction is led to much reduction of weight. Figure 1.19 shows the frameless chassis construction of a passenger car with the loading distribution arrangements whereas Figure 1.20 shows the dismantled view of frameless chassis construction for passenger car.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
ww
w.E
Figure 1.19 Frameless chassis construction for car
asy
En
gin eer
ing
.ne
t
Figure 1.20 Dismantled view of'frameless construction for car The structure includes a floor structure having side members, cross members, floor and other components. They are welded together form a single assembly. The surfaces have ribbed portions.to increase the strength and rigidity. For carrying the engine and front suspension, a sub-frame is also attached to the front of the body shell. The floor and side panel surfaces have pressed grooves to increase stiffness. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
iiDi
Vehicle Structure and Engines Box section roof rails & headers
Radiator yoke
ww
w.E
Box section rails
asy
Heavy structural sill
Figure 1.21Assembly view of frameless construction
En
In this type of construction, the stresses are evenly distributed throughout the structure. A strong structure with good torsional rigidity and resistance in bending are provided by this
gin eer
construction. The structure is also free from shakes on rough roads which cause an increased life of door locks, hinges and many other small parts along with a reduced body rattle.
ing
.ne
t
Figure 1.22 Frameless chassis construction for bus Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I'"
Automobile Engineering
Very low carbon (0.1%) steel with good ductility is required for manufacturing panels by pressing. The structural members are required to be stiffened by forming thin steel sheets into intricate sections by spot welding due to low strength of this material. Entire body is immersed in a rust protective solution to increase corrosion resistance and rusting resistance. In order to avoid the objectionable drumming sound from panel due to vibration, a sound damping material should be packed on inside of the panel. Figure 1.21 and Figure 1.22 show assembled view offrameless chassis construction for car and bus respectively. 1.7.5. Load on Chassis Frame (Various Resistances and Moments involved)
ww
A chassis frame is subjected to the following loads.
1. Loads of short duration:
w.E
When the vehicle is crossing a broken patch of road, it is acted upon by heavy and suddenly applied loads of short duration. This load results the longitudinal torsion.
asy
2. Combinedloadsof momentaryduration:
En
These loads occur while negotiating curve, applying brakes and striking a pot hole.
3. Inertia loads:
gin eer
These loads are applied on the vehicle due to brake applied for a short period. This load tends to bend side members in the vertical plane.
4. Impact loads:
ing
.ne
These loads are applied during collision of vehicles with another object. It results the general collapse.
5. Load due to roadcamber:
t
It is the load due to road camber, side wind and cornering force while taking a tum. It results the lateral bending of side members.
6. Load due to wheelimpact: Load due to wheel impact with road obstacles may cause a particular wheel to remain obstructed while the other wheel tends to move forward. It will tend to distort the frame to parallelogram shape.
7. Static loads: Loads due to chassis parts such as engine, steering, gearbox, fuel tank, body etc. are constantly acting on the frame. They are called static loads. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
.N
I Vehicle Structure and Engines 8. Overloads:
The load of the vehicle exceeds beyond the specified design load known as overloads. 1.7.6. Materials for Frame The various steels used for conventional pressed frame are as follows. 1. Aluminium alloy (ALPAX) 2. Mild steel sheet 3. Carbon steel sheet
ww w.E
4. Nickel alloy steel sheet. .
The composition of sheet nickel alloy steel is given as follows. Carbon
0.25 to 0.35%
Magnanese
0.35 to 0.75%
Silicon
0.30% (Maximum)
Nickel
3%
Phosphorus
0.05% (max)
Sulphur
0.5% (max.).
asy E
ngi
nee
1.7.7. Sub Frames
rin
g.n e
In normal vehicles, various components are bolted on the main frame. But sometimes,
t
the component on vehicle is installed on sub frames which are bolted on the main frame. The sub frame provides a greater strength and furthermore, it is supported at three points on the main frame.
Sub frames are structural modules which are designed to carry specific automotive components such as engine or axle and suspension. The purpose of a sub frame in an automobile is to distribute high local loads over a wider area of the body structure (most relevant in thin-walled monocoque body designs) and to isolate vibration and harshness from rest of the body. The sub frames are bolted or welded to the vehicle body. Bolted sub frames are sometimes equipped with rubber bushings or springs to damp noise and vibrations. An additional benefit is that sub frames can bel separately assembled and integrated into the vehicle on an automated assembly line when required.
Downloaded From : www.EasyEngineering.net
5.
Downloaded From : www.EasyEngineering.net
I Vehicle Structure and Engines
". alignment may be determined by "X" or diagonal method of checking from given points on
each side rail. The most convenient way to make this check particularly is when the body is on the chassis, all points are marked on the floor from which measurements
should be taken.
Dropping a plumb-bob from each point indicated, the floor is directly marked underneath the point. Then the vehicle is moved away from layout on the floor as per the procedure as follows. 1. The frame width is checked at front end and rear end using corresponding marks on the floor. If the width corresponds to specifications, the centre line is drawn for the full length of the vehicle, half-way between marks indicating front and rear widths. If
ww w.E
the frame width is not correct, centre line cannot be laid out from checking points at
the end of frame. It can be drawn through intersections of any two pairs of equal diagonals.
2.
With the centre line properly laid out, the distance is measured between points over
asy E
the entire length of chassis. If the frame is in a proper alignment, the measurement should not vary.
3.
.:
ngi
The point is located at which the frame is sprung. Then, diagonals marked as A-B, B-
nee
C and C-D are measured. If the diagonals in each pair are within the limit, then the part of the frame included between points of measurements
may be kept as satis-
rin
factory alignment. These diagonals should intersect at the centre line. If the measured values do Dot satisfy above-mentioned
limits, it indicates the further correction to be
made between those points.
o
c
B
o
c
B
g.n e A
t
A
F.Wure 1.24 Checking/rame alignment 1.8. BODY The basic form of the modem automobile bcdy is older horse
d-ver carriage. They have
a single seat type body construction which provides less safety to the passenger from weather. Larger and more stylish bodies were developed and manufactured
with passage of time to
provide increased space, safety or protection to the passengers. /
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile EnglOeering Body is the super-structure for all vehicles. It may either be constructed separately and
bolted to the chassis or manufactured integral with the chassis (i.e. Frameless construction). The chassis and the body make the complete vehicle. A body consists of windows and doors, engine cover, roof, luggage cover etc. The electrical system in the body is connected to the chassis electrical units so that the battery and the generator/alternator can furnish the required electrical energy to the system. 1.8.1. Importance of Vehicle Body Design 1. Weight of the body is 40% of total weight of the car and 60 to 70% of total weight of buses. Therefore, the reduction in body weight is important.
ww w.E
~
2. If the weight of the body is reduced, it will also improve the fuel economy (i.e. mileage). 3. The body of the vehicle determines its aerodynamic characteristics. Better aerodynamic structure leads to fuel economy at high speed and stability in cross
asy E
winds. The positive pressure at the front of the vehicle should be minimized and it should be deflected smoothly to prevent the creation of eddies.
ngi
nee
4. The body is also important for aesthetic and ergonomics consideration. It should give pleasant appeal and style for the customer. 1.8.2. Requirements of Vehicle Body
The vehicle body should fulfill the following requirements.
rin
g.n e
t
1. It must be strong enough to withstand all types of forces acting on the vehicle. The .. forces are including the weight of the car, inertia, luggage, braking and cornering forces. 2. Stresses induced in the body should be distributed evenly to all portions. 3. Weight of the body should be as minimum as possible. 4. It should be able to cope with impact loads of reasonable magnitude. 5. It should have reasonable fatigue life. 6. It must provide adequate space for both passengers and the luggage. 7. It should have minimum number of components. 8. It must have sufficient torsional stiffness i.e., ability to resist the twisting stresses produced by irregular road surface. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
9. It should have good access to the engine and suspension elements. 10. It must ensure a quite ride, easy entry and exit. 11. It should create minimum vibration during running. 12. The shape of the body should be minimum drag.
13. It is easy to manufacture as well as cheap in cost. 14. It should be designed in such a way that passengers and luggage are protected from bad weather. 15. It should give appeal finish in shape and colour.
ww w.E
1.8.3. Types of Vehicle Body
For different types of auto-vehicles, passenger space and overall dimensions vary. Various types of bodies for different vehicles can be listed as below. 1. Car
2. Straight truck 3. Truck - half body type
asy E
4. Truck-platform type 5. Tractor 6. Tractor with articulated trailer 7. Tanker 8. Dumper truck 9. Delivery van 10. Station wagon
ngi
nee
rin
g.n e
t
11. Pick-up 12. Jeep
13. Buses 14. Mini-buses 15. Three wheeler (i.e., Auto rickshaw) The car bodies have great resistance to wind. For high-speed vehicles, a special attention is given to streamline the body. The streamlining is the process for shaping the body to reduce air resistance. It is mainly used for racing cars.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Truck IIall body
Truck Punjab body or straight truck
Tractor
Truck platform type
ww w.E
asy E
Pick-up
Tructor wUlt articulated trailer
Dumper truck
ngi
C;~
nee
Delivery rllll
rin Tanker
g.n e
t
Dumper truck.
Car
Jeep
Figure 1.25 Different types of bodiesfor different vehicles Straight truck vehicle bodies are constructed into two parts. One is driver cabin and other one is goods carriage. Goods carriage is a closed type with particular standard height. These
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and
vehicles are used to carry goods which are affected by weather conditions. Example. Vegetables, sugar, rice, sea foods etc. Truck half body is having driver cabin as usual but the goods carriage has open at the top. It is used to carry various goods which are not affected by weather. Truck platform type has also a separate driver cabin. Its goods carriage is a platform type. It usually carries goods such as iron billets, barrels, concrete slabs etc. Tractor consists of small length body in addition to driven cabin. Usually, an articulated trailer is attached to the rear end of the trailer. This trailer has various cabins. Figure 1.25 shows different types of bodies normally designed for different vehicles. It may be an open
ww w.E
type or a closed type depending on the purpose of use. It is used to carry passenger cars, mopeds, motor cycles etc. Most of these vehicles have six wheels. Tanker is the vehicle which consists of a tank to carry fluids of various natures. The tank may be welded or bolted to the chassis frame behind the driver cabin. The tank has an opening
asy E
at the top to pour fluid and a drain cock at the bottom to drain the fluid. Dumper truck has heavy goods carrying panel with open top in the rear side. The rear side
ngi
can be tilted up and down by hydraulic cylinders. It is used to carry brick, stones, marbles etc. 1.8.4. Body Construction
and its Components
nee
rin
The main purpose of designing the car body is for containing and protection of the engine
g.n e
and accessories as well as the passenger. To fulfill above requirements, the vehicle body has various components which are grouped under the following three groups. (a) Structure: All load carrying elements are defined as structure.
t
(b) Finish: This group includes all unstressed units such as bonnet, boot, lid, bumper etc. (c) Equipment: This group includes various parts such as rim, seats, doors, window etc. The various components of car body are: body, sheets, pillar-less frame, front and rear doors, front panel, roof panel, floor panel with engine beams, wheel arches, bonnet, wind screen pillar, wind screen, front and rear window, front and rear bumper, cowl assembly, front and rear seats, luggage space as a continuation of passenger compartment, folding roof with windup windows, sliding roof and folded flat windscreen, hood etc. All steel sections of bodies are stamped out by dies separately and welded to other sections for forming the steel bodies. The body of the car is made up of many sheet metal panels. Each panel is so designed to give enough strength and rigidity to the assembled unit.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
locations of the body, the reinforcing members are incorporated at proper interspaces, Front Roof Wind window screenpillar-\----:T--t--~_ Wind
ww w.E
arches
asy E
Doorpiller
Door panels
Figure 1.26 Components of car body
ngi
The main skeleton of the car body has two types of panels: 1. Outer panel. 2. Inner panel. The outside panels provide the shape of the car body whereas the inner panels reinforce the
nee
shell of the body. The various curved shapes are given to outer panels to provide the strength to panels. The inner panels provide mounting locations for various trim panels and connecting
rin
assemblies. These two panels are welded together to pillars and rails so as to form the skeleton of the car body.
g.n e
Initially, the floor of the cal"body is assembled and then pillars, rails and panels are
t
welded in order to form the complete car body. The floor is made up of 3 pressed steel panels such as front, centre and rear sections as shown in Figure 1.27. 'Each unit is so designed that it gives a low profile and the
Cal"
accommodates more
passengers. In order to give additional strength, rigidity and prevent excessive vibration, metal
.
strips have been welded at different places of the floor panel. Then the rear wheel houses inner panels and rocker panels are welded to the floor. The wheel house panel is welded to the floor to provide sufficient clearance for the up and down movement of wheels while running on the road. The box shaped rocker panels which are fixed to sides of the floor, as shown in Figure 1.28, provide additional strength to the floor panel.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Rear section Front section
Centre section
ww
Figure 1.27 Floor assemhly of car
w.E asy En gin ee Floor
Rocker pannel
Figure 1.28Rocker panels attached tofloor
rin g.
The cowl assembly or the front portion of the car is made up of many smaller panel stampings of steel sheet metal shown in Figure 1.29. Usually, the cowl assembly is welded to
net
the rocker panel and floor panel. The wind-shield opening frame accommodates the front glass which is curved in shape in many cars. The top outer cowl panel is sometimes vented to allow the fresh air to enter into the car. The dashboard panel accommodates different warning and indicating devices required to operate the car. The instrument panel is usually welded to the cowl but in some design, it is also bolted to the cowl. The pillars on sides of the cowl are used for fastening the front door hinges and cowl side panels. The fire wall of the cowl assembly is the sheet metal panel which separates the front passenger space from the engine space. This wall is insulated in such a way that the engine heat and noise are prevented from entering into the passenger space.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
ww w.E
asy E
Cowl body mounts
Engineering
Cowl side panels
ngi
Figure 1.29 Cowl assembly
nee
Figure 1.30 Construction
Roof rail supports
rin
g.n e
t
0/ centre pillars and roo/rails Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
The centre pillar supports the rear doors and hinges and sticker plates of front doors. It also supports the roof rails and centre pillars as shown in Figure 1.30. The roof rails and centre pilJars are usually of box section. It gives maximum strength to the body. Drip mountings are added to side rails of the roof panel as shown in Figure 1.31. The drip mountings are U shaped channel. It is used to catch and direct the water of the roofto the back of the car during raining: 'rhe, roof panel is welded to the top side rails. The rear window and front windshield frames are attached to the roof.panel by spot welding. U-shaped drip moulding
ww
w.E asy En gin ee Figure 1.31 Drip mountings
Rear window panel
rin g.
net
Drain trough
Figure 1.32 Quarter panels The rear quarter panels are welded to the rear wheel house panel, the floor panel and the rear of the rocker panel as shown in Figure 1.32. The trunk lid provides cover for the trunk compartment. It is attached to the body with the help of hinges as shown in Figure 1.33. In order to prevent the water and dust to enter into the compartment, a rubber weather strip is provided. Locking arrangement is also provided for the rear compartment. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
ww w.E
asy E
ngi
Engineering
Figure 1.33 Trunk lid
nee
Engine compartment is formed by assembling different sheet metal panels. This
rin
assembly covers the frent wheels and therefore, it prevents the dirt, mud, snow etc. being thrown off by front tyres on engine and body of the car. The radiator support is provided to
g.n e
support the radiator by means of bolts. A stone shield is bolted to the radiator support and the fenders. It prevents the striking of small flying stones on to the radiator grills and radiator and
t
thus, it avoids their damage. The two tenders which cover the front wheels are connected by the radiator support. The arrangement of engine hood is shown in Figure 1.34. It is constructed in the same manner as the trunk lid. It has inner and outer panels. The inner panel acts as the reinforcement to the engine hood. It provides mounting locations for the hood lock and hinges. The outer panel gives the shape to the body. The hood is attached to the car body by means of hinges. One of the most important components inside the car body is a seat. The seats of the car are of various types such as folding back, bucket or rigid. The seats of the present day cars are generally of the bucket type. The seats are mounted Uli laiiS wiucl; :::~L: them adjustable. The
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
back can also be tilted at the convenient position and they are also provided with head rest for safety in case of accident.
ww w.E
asy E
ngi
nee
rin
g.n e
t
Present day cars use four doors, two in front and two in rear. The front doors are hinged on front pillars whereas rear doors are hinged on centre pillars. Each door is provided with a check arm consisting of an articulated plate secured on pillar and sliding into a slot in door. The rubber weather strips are bonded with a special compound around doors. Each the door consists of door handle, window, window glass regulator crank, arm rest, drop glass panel as shown in Figure 1.36. In modern cars, five doors are provided. Fifth door is used as a trunk Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lid. The special glass used in automobiles prevents the passenger seriously injured in case of any accident. It is specially designed in such a way that it does not form sharp edges when broken. Four way adjustable headrest
ww w.E
asy E
Adjustable seat wings
ngi
Figure 1.35Self adjusting seat Anti-draft
nee
rin
g.n e
t
Figure 1.36Front door of Fiat 1100 select car
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
Bumpers are provided at the front and rear end of the car. These are used to protect the front end and rear end of the car from damage in case of light collisions. They are manufactured by heavy gauge steel sheet. It is of £. channel section with the open side turned inwards. It is bolted or riveted to ends of the longitudinal members of the car frame or front body rails. Bumpers of modern cars are manufactured using fibre reinforced composite sheets. 1.8.6. Materials for Body Construction The materials usedfor construction of various parts of the body are steel, wood, plastics, toughened glass and aluminium. In earlier days, wooden bodies were used for construction. But now-a-days, steel is mainly used for body construction because of low cost and easy to manufacture.
ww
w.E asy En gin ee
WQoden bodies require a separate steel chassis frame to carry the load. The body structure was ~eavy. Further, wooden bodies are flexed considerably and hence, they have short life: Initial cost is also high. Therefore, these bodies become obsolescence now-a-days. Sheet metal is widely used for body construction. It has high stiffness which results negligible non-flexing and hence, it has longer life. Its initial cost is also less. Aluminium has also been used by some manufactures because of its good formability, light in weight and more resistance to corrosion qualities. But, its main disadvantage is lesser stiffness and rigidity.
rin g.
Present day, plastic bodies are popular. Thermoplastics are quite often used for many components such as boot covers, grills etc., whereas thermosetting plastics are mainly used for
net
body shells. ~temost widely used thermosetting plastic is glass fibre reinforced resin. This material can be moulded to any shape easily. The resulting structure is of light weight. The latest type of plastics used for body construction is carbon fibre reinforced plastics. It is stronger than steel and also weightless. But the cost is very high. Wind screen/and window panels are made by toughened glass. As already mentioned in the previous section, it has a special property when broken. It does not form sharp edges or pieces. All broken pieces are in the form of rounded granules which do not cause injury. There are two different types of safety glasses, namely, laminated safety glass and tempered safety glass. Laminated safety glass consists of two layers of glass bonded together with the help of another inner layer of vinyl transparent plas~ic under heat and pressure. When this glass is shattered by impact, the centre layer of plastic holds the broken pieces of glass together and thus it is not allowing them to fly. These glasses are generally used for windscreen of the vehicle. The tempered safety glass is made from a single piece of case-hardened or heatDownloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
treated glass. Initially, it is cut to the required shape and then heat treated until it becomes soft. Then it is blasted with cold air to the outer surface to create tension between inner soft and outer hard surface. Thus, it becomes five times harder than ordinary glass. These glasses are used for side or rear windows.
1.9. VEHICLE AERODYNAMICS 1.9.1. Resistances to Vehicle Motion The fundamentals of vehicle design involve the basic principles of Newton's second law of motion. According to Newton's second law the acceleration of an object is proportional to the net force exerted on it. Hence, an object accelerates when the net force acting on it is not zero. In a vehicle, several forces act on it and the net or resultant force governs the motion
ww
w.E asy En gin ee
according to the Newton's second law. The propulsion unit of the vehicle delivers the force necessary to move the vehicle forward. This force of the propulsion unit helps the vehicle to overcome the resisting forces due to gravity, air and tire resistance. The acceleration of the vehicle depends on. );;>
the power delivered by the propulsion unit
);;>
the road conditions
);;> );;>
"the aerodynamics of the vehicle
the composite mass of the vehicle.
rin g.
Broadly the resistances can be categorized into the following categories. (i) Air resistance or Aerodynamic drag (ii) Gradient resistance (iii) Rolling resistance
net
(iv) Inertia force. All the above produce a restraining force working against the tractive force. The tractive force must be greater than or equal to the resistive forces in order to maintain a sustainable motion. 1.Air resistance / Aerodynamic drag: A vehicle traveling at a particular speed in air encounters a force resistmg its motion. This force is known as aerodynamic drag. Simply speaking, it is the resistance offered by air to the vehicle motion. It depends upon the following factors. (I) Size of the vehicle Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
..
,
I Vehicle Structure and Engines (2) Shape of the vehicle (3) Speed of the vehicle (4) Wind velocity.
2. Gradient resistance: It is the component of the vehicle's weight which is parallel to the plane of the road. When a vehicle goes up or down a slope, its weight produces a component of force that is always directed downwards. If the vehicle travels uphill, a component of its weight works in a direction opposite to its motion. If some energy is not supplied to overcome this backward force, then the vehicle would slow down, stall and roll backwards. If the vehicle is trading " a slope of 8, then the weight of the vehicle. W has two components. one uphill at. perpendicular to the road surface (with a value W x Cos 8) and the other along the road
ww
w.E asy En gin ee
surface (with a value W x Sin 8). The component along the road surface is the one that tries to restrict the motion. The gradient resistance is given by. FG = W x Sin 8
J. Rolling resistance:
The rolling resistance of tyres on hard surfaces is due to hysteresis it. the tyre material. When a vehicle rolls, it rolls with its tyres in contact with the road surface. The relative motion of two hard surfaces produces a friction. Further, neither the road, nor the tyre is perfectly rigid. Hence, both flex under the load slightly. As there is a gradual deformation at
rin g.
the contact between the road and the tyre, greatest at the bottom most point and least at the
net
entry and exit points, the slip of the tyre with respect to the road produces another type of loss of energy which results in a resistance. Rolling resistance is the sum of the following components. ). Tyre Rolling resistance: Resistance from tyre deformation ). Road rolling resistance: Resistance from tyre penetration and surface compression. ). Resistance due to tyre slip angle: Resistance from tyre slippage and air circulation around wheel. ). Resistance due to bearing friction and residual braking.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I·M
Automobile Engineering
4.lnertiaforce: In addition to the driving resistance occurring in steady state motion, inertia forces also occur during acceleration and braking. The total mass of the vehicle and the inertia mass of those rotating parts of the drive accelerated or braked are the factors influencing the resistance to acceleration. The rotational component is a function of the gear ratio. The moment of inertia of the rotating drive elements of engine, clutch, gearbox, drive shaft, etc., including all the road wheels are reduced to the driving axle.
1.9.2.Aerodynamics of Automobile Body
ww
Aero means air, dynamics means motion. Aerodynamics is the behaviour of air in motion
relative to the vehicle body. The body design pertaining to shape and size of the vehicle must
w.E asy En gin ee
have acceptable aerodynamic characteristics.
The following are various aerodynamic forces acting on the vehicle. (i) Dragforce (Fj: Force of air drag is acting in the direction of vehicle motion with the wind acting along the longitudinal direction axis. This force is also called air resistance. It offers the resistance to motion of the vehicle. The various factors such as profile drag (57% of total vehicle), induced drag (8%), skin friction (10%), interference drag (15%) and cooling and ventilation system drag (10%) affect the total drag. The total aerodynamic drag can be calculated by using the equation.
2A Ii. ~ =C .r pV -2
rin g.
where
net
C,= drag coefficient p = den~~ of air V = Velocity of air
A
= Proj~
area of the vehicle viewed from front.
The main causes of aerodynamic drag are: );>
shape drag
);>
skin friction drli
The shape drag is due to the shape of the vehicle. The forward motion of the vehicle pushes the air in front of it. However, the air cannot instantaneously move out of the way and
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Vehicle Structure and Engines
11m i
its pressure is thus increased. This results in high air pressure in the front of the vehicle. The air behind the vehicle cannot instantaneously fill the space left by the forward motion of the vehicle. This creates a zone of low air pressure. Hence, the motion of the vehicle creates two zones of pressure. The high pressure zone in the front of the vehicle opposes its movement by pushing. On the other hand, the low pressure zone developed at the rear of the vehicle opposes its motion by pulling it backwards. The profile of the body should be carefully selected to avoid the drag force. The air close to the skin of the vehicle moves almost at the speed of the vehicle while the air away from the vehicle remains still. The difference in speed between two air molecules. produces friction. Skin friction drag can be reduced by using very smooth and well-polished body. Avoiding excessive projections such as door handles, mirrors, aerials helps in reducing drag.
ww
w.E MzC) asy En gin ee Yawing moment
Rolling moment
rin g.
Figure 1.37Forces ami moments acting on the vehicle body (ii) Lift force (FJ:
net
Aerodynamic lift force is the vertical component of the resultant force caused by the pressure distribution on the body. Lift force can be calculated by using the equation F_ =C_pV -
2A 2
where Cz = lift coefficient p = density of air. The aerodynamic lift will tend to reduce the pressure between tyres and ground which causes the loss of steering on the front axle and loss of traction on the rear axle. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'Automobile
Engineering
(iii) Cross windforce (Fy): Cross wind force is acting in the lateral direction on the side of the vehicle. It is formed by the asymmetric flow of air around the vehicle body. These forces are acting at the centre of pressure instead of centre of gravity and hence, they cause various moments as follows. a.
Pitching moment (My) is caused by the drag force F, or lift force F, about Y axis. This moment makes the rear wheels lift off from the ground and further it reduces the available traction.
b.
Yawing moment (MJ is caused by the cross wind force Fy about Z axis.
c.
Rolling moment (My) is caused by the cross wind force Fy about Z.
ww
Figure 1.37 shows the forces and moment acting on the vehicle body.
w.E
1.10. INTERNAL COMBUSTION ENGINE (IC ENGINE)
asy
An engine is a prime mover. It is a heart of the automobile. It is one of the important and
En
biggest units in automobiles. If it fails to work, the vehicle is dead. Internal Combustion engine (K' engine) is a heat engine which converts the chemical energy of fuel into
gin eer
mechanical energy. The chemical energy of a fuel is first converted into thermal energy by !
means of combustion or oxidation with air inside the engine. This thermal energy is again converted into useful work through mechanical mechanism of the engine. Most of the IC '
ing
engines are reciprocating engines having pistons that reciprocate back and forth inside a cylinder internally within the engine. 1.11. ENGINE CONSTRUCTION
.ne
t
Figure 1.38 shows the construction details of an IC engine (Four stroke petrol engine). The main components of a four stroke cycle engine are cylinder, piston, connecting rod, piston rings, cam shaft, crank shaft, crank case, inlet and outlet valves, spark plug, cylinder head, push rod, gudgeon or piston pin, rocker arm, cam follower, valve spring, big end bearing, inlet port, exhaust port etc. The piston reciprocates inside the cylinder. Piston rings are inserted in the circumferential grooves of the piston. The cylinder and cylinder head are bolted together.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lliiJI
Vehicle Structure and Engines Rocket
Inlet port
ww w.E a
syE
ngi
nee r
ing
Figure 1.38 Constructional details of IC engine
.ne
The reciprocating motion of the piston is converted into rotary motion of the crankshaft by means of a connecting rod and crank. The small end of the connecting rod is connected to
t
the piston by a gudgeon pin or piston pin. The big end of the connecting rod is connected to the crank pin. Crank pin is a bearing surface and it is rigidly fixed to the crankshaft. The crankshaft is mounted on the main bearing. The main bearings are housed in the crankcase. Camshaft is driven by the crankshaft through timing gears. The camshaft actuates the inlet and outlet valves. The valve springs are provided to bring back the valves to the closed position. The oil sump containing lubricating oil is ~rovided at the bottom of the crankcase. Lubricating oil is circulated to various parts of the engine from the oil sump. A spark plug is provided in petrol engines to ignite the air-fuel mixture in the engine cylinder. An injector is provided in diesel engines to inject the fuel into hot compressed air during power stroke.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engine-ering
1.12. COMPONENTS OF IC ENGINE The following are the list of major components found in most of the reciprocating
I.e.
engines. 1.12.1. Cylinder Block It is the main body of an engine which contains cylinders. The piston reciprocates inside the cylinder to develop power. The cylinders are accurately finished to accommodate pistons. The cylinder block also houses crank, crankshaft, piston and other engine parts. During combustion, high pressure and temperature will be developed inside the cylinder. Therefore, it
ww w.E a
should be made of material which can resist high temperature and pressure. It is made of grey cast iron or aluminium with steel sleeves. In water-cooled engines, the cylinder block is provided with water jackets for the circulation of cooling water as shown in Figure 1.39. Cylinder head
Cylinder
syE
Hole for spark plug
ngi
nee r
ing
Water Jackets
Figure 1.39 Engine cylinder
.ne
t
1.12.2. Cylinder Head The cylinder head is bolted at the top of the cylinder block. It houses the inlet and exhaust valves through which the charge is taken inside of the cylinder and burnt gases are exhausted to the atmosphere from the cylinder. It also contains a spark plug hole or injector hole and cooling water jacket. The materials used for cylinder heads are cast iron, aluminum alloy etc.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
"ji-
Vehicle Structure and Engines
1.12.3. Crankcase
It may be cast integral with the cylinder block. Sometimes, it is separately cast and bolted to the cylinder block. It supports crankshaft and camshaft with the help of bearings. Sometimes, the bottom of crankcase may be used as oil sump. It is made of cast iron, -aluminum alloys or alloy steels. 1.12.4. Oil Sump or Oil Pan Oil sump is fitted at the bottom of crankcase by using a gasket. It contains lubricating oil. A drain plug is provided to the oil-sump to drain out the oil. It is made of pressed steel sheet.
ww w.E a
1.12.5. , Cylinder Liners
Inside the cylinder, the piston constantly moving up and down which will cause wear in cylinders. When the cylinder diameter is increased beyond certain limit, the entire cylinder block should be discarded and it is costly. To avoid cylinder wear, a separate liner which is in the form of sleeve is inserted into the cylinder bore. Here, the wear will take place in the liner only which can be replaced easily when worn out. There are two types of liners.
syE
ngi
1. Wet liner:
nee r
The liners are surrounded by cooling water shown in Figure 1.40. It provides wearresisting surface for the piston to reciprocate. It also acts as a seal for the water jacket.
ing
2. Dry liner:
.ne
Dry liners have metal-to-metal contact with the cylinder block. They are not directly in
t
touch with cooling water. Liner material should withstand abrasive wear and corrosive wear. Chromiumplated mild steel tubes are used as liners. Cylinder Block
Cooling water
Cylinder Block
Dry liner
Figure 1.40 Cylinder liners
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile Engineering
1.12.6. Piston It is a cylindrical shaped mass which reciprocates inside the cylinder. The piston serves
the following purposes. ,_. It acts as a movable gas tight seal to keep gases inside the cylinder. ,_. It transmits the force of explosion in the cylinder to the crankshaft through connecting
rod.
Lands
ww
/7-::,.,.-Piston pin boss
w.E
asy E
Figure 1.41Piston
ngi
The top Of the piston is called crown and sides are called skirt. It has grooves to hold piston rings and oil ring. It is opened at the bottom end and closed at the top. Sometimes, Tslots are provided in the skirt to allow expansion.
nee rin
Piston is made of cast iron, Aluminium alloy, chrome-Nickel alloy, nickel-iron alloy and cast steel. They are manufactured by casting orforging method. Various types of automotive pistons: (i) Trunk piston:
g.n et
Trunk pistons are long relative to their diameter. They act both as piston and as a cylindrical crosshead. As the connecting rod is angled for a part of its rotation, there is also a side force that reacts along the side, of the piston against the cylinder wall. A longer piston helps to support it. Trunk pistons have been a common design of piston since early days of the reciprocating internal combustion engine. They were used for both petrol and diesel engines although high speed engines have now adopted the lighter weight slipper piston.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
",-
Vehicle Structure and Engines
A characteristic of most trunk pistons particularly for diesel engines is that they have a groove for an oil ring below the gudgeon pin not just the rings between gudgeon pin and crown.
lands
ww
Piston Boss
w.E
asy
En
gin eer
Figure 1.42 Trunk piston
(ii) Crosshead piston:
Large slow-speed diesel engines may require additional support for the side forces on the
ing
piston. These engines typically use crosshead pistons. The main piston has a large piston rod extending downwards from the piston to a second smaller-diameter piston. The main piston is
.ne a t
responsible for gas sealing and it carries the piston rings. The smaller piston is purely
mechanical guide. It runs within a small cylinder as a trunk guide and also carries the gudgeon pin. Because of the additional weight of these pistons, they are not used for high-speed engines. Cross head
Piston rod
:::::::~.:::::~-·-..:::O""----I
Figure 1.43 Crosshead piston Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
(iii) Slipper piston:
A slipper piston, also called as partial skirt piston, is a piston for a petrol engine which has been reduced in size and weight as much as possible. In extreme cases, they are reduced to the piston crown, support for the piston rings and just enough of the piston skirt remaining to leave two lands so as to stop the piston rocking in the bore. The sides of the piston skirt around the gudgeon pin are reduced away from the cylinder wall. The purpose is mostly to reduce the reciprocating mass, thus making it easier to balance the engine and so, it permits high speeds. A secondary benefit may be some reduction in friction with the cylinder wall.
ww w.E a
syE
ngi
nee r
Figure 1.44 Slipper piston (iv) Deflector piston:
ing
.ne
Deflector pistons are used in two-stroke engines with crankcase compression where the
t
gas flow within the cylinder must be carefully directed in order to provide efficient scavenging. With cross scavenging, the transfer (inlet to the cylinder) and exhaust ports are directly on facing sides of the cylinder wall. To prevent the incoming mixture passing straight across from one port to the other, the piston has raised a rib on its crown. It is intended to deflect the incoming mixture upwards and around the combustion chamber. Much effort and many different designs of piston crown are taken in developing improved scavenging. The crowns developed are from a simple rib to a large asymmetric bulge usually with a steep face on the inlet side and a gentle curve on the exhaust as shown in Figure 1.45.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
ww w.E a
syE
ngi
nee r
Figure 1.45 Deflector piston Various types of piston failure: (i) Piston wear:
ing
.ne
Problems are related to the piston and rings will usually fall into one of two categories, excessive wear or piston seizure. Excessive wear can often be detected visually even before
t
any measurements are taken. From normal operation, the wear pattern on the thrust face of a piston will cover 20-40% of the face. If it covers 50% or more with visible vertical scratches, there has been contamination between piston and cylinder wall causing excessive wear.
(ii) Piston erosion: The erosion at the top edge of the piston is also due to wear. As the rings wear, oil consumption increases thereby more combustion deposits results and a carbon ridge forms at the top of the cylinder. In the area near the exhaust valve, the carbon becomes hard and abrasive from e .haust temperatures. When the piston repeatedly hits those hard deposits, the material is gradually eaten away.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
Damage from contamination entering an engine can occur over an extended period of time with very slight leakage or it can be quite rapid if a significant amount of dirt is entering. (iii) Piston crack: If a user ignores the first signs of wear (oil consumption and blue exhaust smoke) and continues to run the engine, the wear will progress to the point that the piston begins to "slap" because of excessive running clearance. The piston slap puts increased stress on the piston skirts and they can begin to crack. With continued operation, the cracks will progress across the thrust face and towards the oil ring groove. (iv) Piston seizure:
ww
Piston seizure is also a common type of failure but it can be little more difficult to analyze. There are a number of possible causes but the appearance does not vary much from
w.E
one to another. Possible causes include overheating from insufficient cooling air, lack of lubrication, insufficient running clearance, oil additives and contamination or foreign material in the engine. 1.12.7. Connecting
asy
Rod
En
gin eer
Shank
Small end
ing
.ne - B
t
y
~
{f--l---~-tJ I
.~.
I
Big end
Figure 1.46 Connecting rod
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
It is used to connect the piston and crankshaft with the help of bearings. It is usually steel forging of circular, rectangular, I, T or H cross-sections. Its small end is connected with the piston by the piston pin and its big end is connected to the crank by the crank pin. It has a passage for the transfer for lubricating oil from the big end bearing to small end bearing. The connecting rod must withstand heavy thrust. Hence, it must have great strength and rigidity. They are generally made of plain carbon steel, Aluminium alloy and nickel alloy steels. 1.12.8. Piston Rings They are used to maintain air tight sealing between piston and cylinder to prevent gas leakages. Piston rings are fitted in grooves which are provided for them at the top portion of the piston skirt. Two types of piston rings are used in a piston.
ww w.E a
syE
Ring cap
ngi
nee r
ing
Ends
Compression ring
.ne
t
Oil ring Figure 1.47 Piston rings Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
a) Compression rings: These rings provide an effective seal for high pressure gases inside the cylinder. Each piston is provided with at least two compression rings. b) Oil rings: These rings wipe off the excess oil from cylinder walls. It also returns excess oil to the oil sump through slots provided in rings. The materials used for piston rings are cast iron, alloy cast iron containing silicon and manganese, alloy steels etc. Piston rings are generally coated with chromium or cadmium. 1.12.9. Crank Shaft
ww
It is used to convert the reciprocating motion of the piston into rotary motion. Big end of the connecting rod is connected to crank shaft. It can be a single crank type for single cylinder engines and a multiple crank type for multi cylinder engine. The crankshaft is held in position by main bearings. There are minimum two bearings provided to support the crankshaft.
w.E
asy E
Figure 1.48 shows the cranks shaft of a four-cylinder in-line engine. The counter weights are provided to keep the system in a perfect balance. Crankshaft gear, vibration damper and fan belt pulley are connected to the front end of the crankshaft. Flywheel is mounted at the rear end of the crankshaft. The material of the crankshaft should be strong enough to resist heavy impact force of the piston. They are made from a hot billet steel, carbon steel, nickel-
ngi
chromium and other heat treated alloy steels. Main journals
nee rin
g.n et
Bearing for flywheel
Crank pins
Figure 1.48 Crank shaft 1.12.10. Flywheel
The flywheel is heavy and perfectly balanced wheel usually connected to the rear end of the crankshaft. Flywheel serves as an energy reservoir. It stores energy during power stroke Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
qta
Vehicle Structure and Engines
and releases energy during other strokes. Thus, it gives a constant output torque. It is usually made of cast iron or cast steel. 1.12.11. Cam Shaft It is used to convert rotary motion of the camshaft into linear motion of the follower or lifter. Thus, it operates the inlet and exhaust valves through rocker arms. It has as many cams .as the number of valves in an engine. An additional cam is also' provided to drive the fuel pump. The camshaft rotates inside the plain bearings. It is driven by crankshaft through chain or gear train. It is rotated at half of the speed of crankshaft. Camshaft is usually made of chilled cast iron and billet steel; however forged steel, gray cast iron or nickel steel may be used depending upon the application.
ww
w.E
Cam
Bearing
/asy
En
gin eer
Figure 1.49 (a) Cam shaft
ing
Bearing shells
Chain sprocket
.ne
t
Eccentric tor mechanically operated fuel pump
Figure 1.49 (b) Cam shaft asse".~ly Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I'"
Automobile Engineering
1.12.12. Spark Plug
The function of the spark plug is to ignite the air-fuel mixture after completing the compression stroke in the petrol engine. It is usually mounted in the cylinder head. It is only used in petrol engines. Reasons for the spark plug failure: The following are four reasons due to which the spark plug may fail to function properly. a) Sooted spark plug: Insulator nose, electrodes and air space are covered in velvety black soot due to faulty carburation. b) Spark plug insulator damage: Scorching is due to sparks jumping across the insulator
ww
which may be caused because of a spark plug adaptor worn out, the rubber gasket tom, brittled or hardened.
w.E
c) Worn spark plugs: Center and ground electrode show a visible material loss due to aggressive fuel or oil additives, thermal overload and exceeding replacement interval.
asy E
d) Incorrect tightening torque causes traces of hydrocarbons on spark plug body, broken ground electrodes. 1.12.13. Valves
ngi
nee rin
Valves are used for closing and opening the passage of a cylinder. There are two valves in an engine cylinder such as inlet and exhaust valves.
g.n et
Fresh air-fuel mixture or air alone enters into the cylinder through the inlet valve. Exhaust gases are forced out through the exhaust valves. Valves are operated by cam and rocker arm mechanisms. There are three types of valves such as sleeve valve, rotary valve and poppet valve. A poppet valve (also called mushroom valve) valves are most commonly used. Figure 1.50 shows a poppet valve. Normally, the valve contains head or poppet (angular face ground 30° to 45°), face, stem and spring retainer lock groove. The head of the inlet valve is bigger than the head of the exhaust valve. Inlet valve is made of plain nickel, nickel-chrome or chrome-molybdenum. The exhaust valve is subjected to more heat. Hence, it should be made of high heat resistance material such as silicon-chrome steel, high speed steel, cobalt-chrome steel and tungsten steel.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Vehicle Structure and Engines
UM Head
_j
'c----""'"-----.
Valve angle
ww w.E
$pring retainer lock groove
asy E
ngi
nee
Figure 1.50Partsof poppet valve 1.12.14.Valve Mechanisms
rin
g.n e
The valves are actuated by cams mounted on a cam shaft. The different types of valve operating mechanisms are as follows. (i)
side valve mechanism
t
(ii) overhead valve mechanism (iii) overhead inlet and side exhaust valve mechanisms.
(i)Side valvemechanism: This mechanism is shown in Figure 1.51. The cam mounted on the camshaft operates the valve tappet during its rotation. The valve tappet is pushed up. The valve tappet pushes the valve from its sheet against the spring force. Thus, the valve is opened. When the cam is not in action, the valve returns to its seat by the valve spring and spring retainer.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
(ii) Overhead valve mechanism:
Figure 1.52 shows overhead valve mechanism.. Here, the valves are located in the cylinder head. When the cam rotates, the valve lifter pushes the push rod upwards. The push rod moves the rocker arm. Since the rocker arm is pivoted at its centre, it pushes the valve off its seat against the spring force. Thus, the valve is opened. When the cam is not in action, the valve returns to its seat by the valve spring and spring retainer. Adjustable screw
ww
Rocker
Engine block
w.E
Valve steam guide
asy E
ngi
Piston rod
nee rin Engine block
g.n et
Valve lifter or tappet
Figure 1.51 Side valve mechanism valve
Figure 1.52 Overhead mechanism
(iii) Overhead inlet and side~ exhaust valve mechanism: , .,' .:.
,
In this system, inlet valve is located in the cylinder head whereas the exhaust valve is located in the cylinder block. The inlet valve is actuated by overhead valve mechanism. The exhaust valve is actuated by a side valve mechanism.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
1.13. CLASSIFICATION OF IC ENGINES
Ie engines are classified on the basis of following parameters. (i) Type of ignition: a. Spark Ignition (SI) engines b. Compression Ignition (CI) engines. (ii) Cycle of operation (Thermodynamics, cycle): a. Otto cycle engine b. Diesel cycle engine c. Dual cycle engine
ww w.E
(iii)Engine cycle per stroke: a. Four stroke cycle b. Two stroke cycle (iv) Types offuel used: a. Petrol engine b. Diesel engine c. Gas engine (v) Method of cooling: a. Air-cooled engines
b. Water-cooled engines. (vi) Number of cylinders: a. Single cylinder engine
asy E
ngi
nee
rin
g.n e
t
b. Two cylinder engine c. Three cylinder engine d. Four cylinder engine e. Six cylinder engine f. Eight cylinder engine g. Twelve cylinder engine h. Sixteen cylinder engine.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
(vii) Valve location:
a. Square engine b. L-head engine c. I-head engine d. F-head engine e. T-head engine. (viii)ArrangemJIl1of cylinders: a. Vertical engine b. Horizontal engine
ww
c. Radial engine
w.E
d. V-engine engine
e. Opposed cylinder engine. (ix) Speed of the engine:
a. Low speed engine
asy
b. Medium speed engine c. High speed engine
(x) Types of lubrication system: a. Wet sump lubrication system b. Dry sump lubrication system (xi) Metlwd of governing: a. Quantity governing
En
gin eer
ing
.ne
t
b. Quality governing c.Hit and Miss governing (xii) Field of application: a. Automobile, truck, bus b. Locomotive engine c. Stationary engine d. Marine engine e. Aircraft engine.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Vehicle Structure and Engines 1.14. WORKING PRINCIPLE OF IC ENGINES 1.14.1. Working of Four Stroke Cycle (petrol) SI Engine
As name implies, four stroke cycle engine operation consists of the following four strokes. 1. Suction stroke 2. Compression stroke 3. Power or expansion stroke 4. Exhaust stroke.
ww w.E
1. Suction stroke:
At the beginning of the stroke, the piston is at the top dead centre (TOC) and it is ready to move downward. As the piston moves downwards. the vacuum is created inside the cylinder. Due to this vacuum, the air fuel mixture from the carburetor is sucked into the cylinder through inlet valves till the piston reaches bottom dead centre (BOC). During suction stroke. the exhaust valve remains in a closed condition and inlet valve remains open. At the end of'the suction stroke, the inlet valve will be closed as shown in Figure 1.53(a). 2. Compression stroke:
asy E
ngi
nee
During the compression stroke, both the inlet and exhaust valves are in closed condition and the piston moves upward from BOC to compress the air fuel mixture. This process will continue till the piston reaches TOC as shown in Figure 1.53(b). The compression ratio of engine varies from 6 to 8. The pressure at the end of compression is about 600 to 1200kNlm2•
rin
g.n e
The temperature at the end of the compression is 250 to 300°C. At the end of this stroke, the mixture is ignited by a spark plug. It instantaneously leads to increase both pressure and temperature of the mixture.
t
3. Power or expanslon stroke: Both pressure and temperature ranges of the ignited mixture are 1800 to 2000°C and 3000 to 4000KNlm2 respectively. During the expansion stroke, both valves are in closed condition. The rise in pressure of the mixture exerts an impulse on the piston and pushes it downward. Therefore, the piston moves from TOC to BOC. This stroke is known as power stroke which is shown in Figure 1.53(c). 4. Exhaust stroke: During exhaust stroke, the piston moves from BOC-to TOC, the exhaust valve is opened and inlet valve is closed. The burnt gases are released through the exhaust valve when the
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
ImJI
Automobile
Engineering
piston moves upward. As the piston reaches TOe, the inlet valves will again open and the fresh air fuel mixture enters into the cylinder for the next cycle of operation. Similarly, only one power stroke is produced in each and every four stroke of the piston or two revolution of the crankshaft. Hence, it is termed esfour-stroke engine. Delivery valve
Delivery valve
Inlet valve
ww w.E a
Inlet valve
tot Connecting rod
syE
(a) Suction stroke
~
0
~
(c) Power stroke
ngi
nee r
(b) Compression stroke
tot
ing
.ne
t
(d) Exhaust stroke
Figure 1.53 Working offour stroke Sf engine
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
1.14.2. Working of Four Stroke Cycle (Diesel) CI Engine
The working of four-stroke cr engine is similar to SI engine except. Here, the fuel injector is placed instead of a spark plug and only air is sucked into the cylinder during suction stroke. The operations are described as follows. Delivery valve
Delivery valve
Fuel injector
ww w.E (a) Suction stroke
l
0
l
(e) Power stroke
Inlet valve Inlet valve
tot Connecting rod
asy E
ngi
nee
(b) Compression stroke
rin
tot
g.n e
t
(d) Exhaust stroke
Figure 1.54 Working of four stroke CI engine
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lrml
Automobile Engineering
1. Suction stroke:
During suction stroke, the piston moves from TOC to BOC. The inlet valve is in open condition whereas the exhaust valve is closed. When the piston moves from top to bottom, the fresh air is admitted inside the cylinder through inlet valve as shown in Figure 1.54(a). 2. Compression stroke: During compression stroke, both the inlet and exhaust valves are closed. The piston moves from BOC to TOC to compress the air. In case of CI engines, the compression ratio varies from ]2 -to 18. The pressure at the end of compression is from 3500 kNlm2 to 4000kNlm2. The temperature of the compressed air reaches from 600°C to 700°C. 3. Power stroke:
ww
In this stroke also, both inlet and exhaust valves are in a closed position. The fuel injector opens just before the beginning of the third stroke, it injects the fuel in atomized form. The ignition of fuel automatically takes place at high pressure and temperature. Both pressure and temperature will further increase due to combustion, it pushes the piston towards down. Thus, it produces power stroke.
w.E
4. Exhaust stroke:
asy E
ngi
During this stroke, the inlet valve is closed and the exhaust valve is opened. The piston moves from BOC to TOC. It blows out the burnt gases from the cylinder. Thus, one cycle of operation is completed and repeated again and again in the same manner.
nee rin
1.14.3.Working of Two Stroke Cycle SI Engine (Petrol Engine)
The working principle of two stroke SI engine is described as follows. 1..First stroke (suction and compression):
g.n et
The first stroke consists of the suction and compression processes: During the first stroke, the piston moves upward from BOC to TOC. When the piston is at BOC, the partially compressed air fuel mixture from crank case enters into the cylinder through a transfer port as shown Figure 1.55(a). Then, the piston moves upward and compresses the air contained in it till the piston reaches TOe. At the end of the compression stroke, the spark plug produces the spark, it will ignite the compressed high pressure fuel air mixture. When the piston is at TOC, the inlet port opens and the air fuel mixture from the carburettor enters into the crankcase as . shown in Figure 1.55(b). Thus, one stroke of the piston is completed.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
mal
Vehicle Structure and Engines
2. Second stroke (expansion or power and ex/must stroke):
When air fuel mixture is ignited, both pressure and temperature of the products of combustion will suddenly increase. Therefore, the piston receives power impulse from the expanded gas and it pushes the piston downward and it also produces the power stroke. This process is described in Figure 1.55(c). During expansion stroke, some of the heat energy produced is converted into mechanical work. Spark plug
ww w.E Deflector
Piston
asy E
(a) Suction stroke
(c) Power stroke
Connecting rod
ngi
nee
(b) Compression stroke
rin
g.n e
t
(d) Exhaust stroke
Fiuure 1.55 Working of two stroke SI engine
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
During downward stroke of piston, already entered air fuel mixture in the crankcase is partially compressed by the underside of the piston. This pre-compression process is called ·crankcase compression. At the end of power stroke, the exhaust port opens and burnt gases are sent out of the engine through this port as shown in Figure 1.55(d). At the same time, all burnt gases are not exhausted. Some portions will remain in the cylinder. When the piston moves to BDC, the fresh air fuel mixture from crankcase enters into the cylinder to sweep out the burnt gases. The process of sweeping out·the exhaust gases with help of fresh air fuel mixture is known as scavenging. The scavenging helps to remove the burnt gases from the cylinder.
ww w.E a
1.14.4.Working of Two Stroke Cycle CI Engine (Diesel Engine) The working of two stroke CI engine slightly differs from SI engine. Instead of sparkplug, the fuel injector is placed at the top of the cylinder. 1. First stroke:
syE
In the first stroke, the piston moves from BDC to TDC. When the piston is at BDC, partially compressed air from the crank case enters into the cylinder through the transfer port as shown in Figure 1.56(a). Then, the piston moves upward and further compresses the air into high pressure and temperature till the piston reaches TDC. At the end of the compression stroke, the fuel injector injects the fuel in atomized form and automaticatly ignited by the compressed air. During the upward movement of the piston, a slight vacuum will be produced at the crankcase to suck the air from atmosphere.
ngi
nee r
2. Second stroke:
ing
.ne
t
When the fuel and air are ignited, it suddenly increases the pressure and temperature 0':the gas. Therefore, the gases will expand and push the piston downward and producing the power stroke as shown in Figure 1.56(c). During expansion, some of the heat energy produced is converted into mechanical work. During downward stroke of the piston, it first uncovers the exhaust port·and the burnt gases are sent out of the engine as shown in Figure 1.56(d). At the same time, all burnt gases are not exhausted. Therefore, the scavenging takes place in the cylinder. At the time of downward movement of the piston, already entered air in the crankcase is partially compressed by the underside of the piston. This process is called crankcase compression.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
••
Vehicle Structure and Engines Fuel injector
Deflector
Connecting rod
ww w.E
Crankcase
(b) Compression stroke
(a) Suction stroke
asy E
ngi
nee
rin
g.n e
t
(d) Exhaust stroke
(c) Power stroke
Figure 1.56 Working of two stroke CI engine
1.14.5.Comparison of 51 Engine and CI Engine S.No. 1.
SI or Petrol engine
CI or Diesel engine
During suction stroke, the air fuel During suction stroke, the air is only mixture is drawn from carburettor. drawn from the atmosphere.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
tag
Automobile Engineering
2.
Carburettor is used to mix the air Fuel injector or atomizer is required and fuel in required proportion. to inject the fuel into cylinder in atomized form.
3.
Spark plug is required to ignite the Fuel is ignited automatically by high fuel air mixture. pressure and temperature air.
4.
The compression ratio varies from The compression ratio varies from 12 6 to 8. to 18.
5.
It is operated by Otto cycle or It IS operated by Diesel cycle or constant volume cycle. constant pressure cycle.
ww 6.
The starting is easy due to lower The starting is little difficult due to compression ratio. higher compression ratio.
7.
Running cost is high because of Running cost is less because of lower high cost of fuel. cost of fuel.
8.
For the same power, less space is For the same power, more space is required. required.
9.
Initial cost is low.
10.
Maintenance cost is less because Maintenance cost is more because of of few parts. more number of parts.
w.E
asy
En
gin eer Initial cost is high.
ing
11.
Thermal efficiency is low.
12.
These are used for high speed These are applications. operations.
.ne
Thermal efficiency is considerably used for low speed
t
1.14.6.Comparison of Two-Stroke and Four-Stroke Engines Two stroke cycle engine
Four stroke cycle engine
Advantages
Disadvantages
S.No. 1.
A cycle is completed in 2 strokes A cycle is completed in 4 strokes or or one revolution of the two revolution of the crank shaft. crankshaft.
2.
It develops twice the number of
It develops half the number of power Downloaded From : www.EasyEngineering.net
l
Downloaded From : www.EasyEngineering.net
0:'.
Vehicle Structure and Engines
power strokes than the four stroke
stroke than two stroke engine:
engines.
3.
For the same power developed, the two stroke engine is much lighter, less bulky and it occupies less floor area.
4.
Turning moment is more uniform and hence,
lighter
flywheel
is
required.
ww w.E 5.
It
contains
operated
ports
by
therefore,
the
which piston
no
For the same power developed, the four stroke engine is bulky, heavier and it occupies more floor area.
Turning moment is not uniform and hence, heavier flywheel is required.
are itself
separate
asy E
It contains valves which are operated by separate mechanisms.
mechanisms are required.
6.
Initial cost is low due to less complexity in mechanism.
ngi
7.
Mechanical efficiency is more.
8.
It is easy to start.
9.
It can be run in either direction
and complicated mechanisms.
nee
Mechanical efficiency is low.
It requires separate starting motor.
which is useful in marine engines.
s.
Initial cost is high because of heavier
rin
g.n e
It can be run in only one direction.
Two stroke cycle engine
Four stroke cycle engine
Disadvantages
Advantages
1.
Thermal efficiency is low.
Thermal efficiency is high.
2.
Volumetric efficiency is low.
Volumetric efficiency is more.
3.
Greater
Lesser cooling
No.
cooling and lubrication
and lubrication
are required.
required.
4.
Overall efficiency is less.
Overall efficiency is mo. ~.
5.
Greater rate of wear and tear.
Lesser rate of wear and tear.
6.
It is used in light vehicles only (e.g.)
scooters,
motor
cycles,
-_
t
are
Used in heavy vehicles such as cars,
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Ilmi
Automobile
mopeds etc. 7.
buses, trucks etc.
Sudden release of exhaust gases makes the exhaust noisier.
8.
Specific
fuel
consumption
IS
fresh charge with exhaust gases. Less compression ratio.
ww w.E
Release
of exhaust
uniform
and
gas
hence
is more noiseless
operation.
more because of escaping of the
9.
Engineering
Specific
fuel consumption
IS
less
because of separate exhaust stroke. More compression ratio.
1.15. CLASSIFICATION BASED ON NUMBER OF CYLINDERS (i) Single
cylinder engine.
It has only one cylinder. A single cylinder engines are generally used in light motor
asy E
vehicles such as mopeds, motor cycles and scooters. Maximum size of the cylinder is restricted to 250-300CC. Although a single cylinder engine seems to be the most popular choice due to few parts to manufacture
ngi
and maintain, the disadvantages
are more than
advantages. Since, it requires heavy construction for more power due to higher unbalanced
nee
forces. Also the weight increases at a greater rate in comparison to the power providing a lower power to weight ratio. A single cyl inder engine may be two stroke or four stroke cycle
rin
engine. Some of the vehicles which consist of single cylinder engine with their CC are given below.
cc
Vehicle Rajdoot
=>
175
Vespa
=>
150
TVSXL
=>
50
Bajaj M80
=>
80
TVS Max 100R
=>
100
Bajaj pulsar
=>
150 and 180
Yamaha RX 100
=>
100
g.n e
t
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
lID I
Vehicle Structure and Engines
Reasons
0/ using single cylinder two stroke petrol engines on two wheelers:
The following are the reasons for using single cylinder two stroke petrol engines on two wheelers. (i)
Two stroke cycle engines are compact in size than the four stroke cycle engines for the same power capacity.
(ii)
Since two wheelers such as mopeds, scooters, bikes etc. are light duty vehicles used for carrying one or two passengers only, the power developed by single cylinder is sufficient to carry the load.
(iii) Since the single cylinder two stroke petrol engines are lighter engines, the vehicle
ww
using these engines are also lighter in weight. Therefore, for the same tractive force, a two wheeler gives higher acceleration.
(iv)
w.E asy En gin ee
A petrol engine runs at a lower compression ratio than a diesel engine. Therefore,
the weight to power ratio of a petrol engine is less than a diesel engine. (v)
Single cylinder two stroke engines are air-cooled engines and they do not require water, radiator and circulating pump. Therefore, weight to power ratio of such engine is less.
(ii) Mutt! cylinder engines:
Multi cylinder engine has two, three, four, six, eight twelve or sixteen cylinders which are arranged in many different ways. As compared to single cylinder engine, the unbalanced
rin g.
forces due to reciprocating parts are much lesser as the number of cylinders increases. Also more power can be developed with less weight to power ratio.
Reasons/or using multi cylinder diesel engines in commercial vehicles:
The following are the reasons for using multi cylinder diesel engines
net
111
commercial
vehicles such as trucks and busses. (i)
A multi cylinder engine develops marc power required to propel the commercial vehicles as it carries greater load.
(ii) Diesel engines normally run at higher compression ratio of 18.1. At this high compression ratio, the thermal efficiency of a multi cylinder engines is higher than an Otto cycle petrol engine. Therefore, a diesel engine gives better fuel economy. (iii) The swept volume of the multi cylinder engine is high and also surface volume ratio is increased. It results a greater power output and also better cooling which is
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIDII
Automobile Engineering
esseritial for the protection of engine parts such as cylinder head, cylinder liner, piston etc. The lubricating oil is also prevented from partial oxidation. (iv) Vibrations in multi cylinder engine are less due to balancing of the crank. 1.16. CLASSIFICATION BASED ON ARRANGEMENT OF CYLINDERS The cylinders can be arranged in several ways such as vertical, horizontal, inline, V-type, flat or pancake, radial. Single cylinder engines can be arranged in either vertical or horizontal direction as shown in Figure 1.57.
ww w.E a /'
"..
.,. ..
--- ........... "" ...
....
I I I I I I • ,
\, ",
syE , , , I
I
"
.............. _-_ ....,.... '
/
I I I
(a) Vertical engine
ngi
(b) Horizontal engine
nee r
ing
Figure 1.57Single cylinder engines Merits of horizontal engines:
.ne
I. The inertia forces of the reciprocating parts i.e. primary and secondary forces :
..
t
combine together to give an impulse to the chassis frame of the vehicle as the stroke of the engine piston is horizontal. If the cylinder head is towards the front end of the vehicle, then a driving impulse is obtained from the engine. This impulse force slides the engine forward on a smooth floor when the running engine is placed on the floor. Therefore, a vehicle fitted with horizontal engine tends to push forward the moped or the scooter by its impulsive force. 2. Fuel economy is also more. Demerits of horizontal engines: I. The crankcase cannot be used for storing lubrication oil for splash lubrication.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
liD
Vehicle Structure and Engines
2. There will be excessive wear at the lower side of the piston and cylinder liner where the cylinder liner gives support to the engine because the weight of the piston is carried by the cylinder liner. 3. Consumption of lubricating oil is more due to the lubricating oil which dribbles from bearings not returning to the crankcase but it is thrown out by the centrifugal forces. Cylinders Cylinders
ww
w.E ~" ~\
Crankshaft
Bearing
asy En gin ee
(a) Inline vertical engine
(b) V-type engine
rin g.
net
(c) Opposed cylinder engine
Figure 1.58 Two cylinder engines Two cylinder engines have two cylinders which can be arranged in three ways such as inline vertical, opposed cylinder and V-type. In inline engine, the cylinders are arranged in side-by-side, one row and parallel to each other.shown in Figure 1.58 (a). The cylinders are zenerally placed in a vertical direction. The range of size of the twin cylinder engine varies Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile
Engineering
from 500 to 1000CC for heavy vehicles and three wheelers. It varies from 600 to 800CC for small cars. In V-type engines (Figure 1.58 (b)), the cylinders are arranged in two rows. The two rows are set at an angle of 60° or 90° to each other. This arrangement is more compact and economical than inline type. In opposed cylinder arrangement, the two cylinders are arranged horizontally opposite to each other. The piston and connecting rod movements are identical. The crankshaft and cam shafts are positioned between two cylinders shown in Figure 1.58 (c). In three cylinder engines, cylinders are arranged vertically in-line with the crankpins
ww w.E
arranged at 120° intervals around the shaft. They produce power impulse every 120° of crank rotation indicating that the torque produced is comparatively smooth. Three cylinder engines are only confined to two strokes. The crankcase serves as intake and pre-compression chamber. The crankcase is divided into three compartments. Each sealed off section of the crank case is provided to one of the cylinders. Figure 1.59 shows a three cylinder inline four stroke cycle engine.
asy E
ngi
nee
rin
~ ~ Bearing
g.n e
t
Figure 1.59 Three cylinder inllne four stroke engine Four cylinder engines have become increasingly popular in recent years. A basic reason is the trend towards small, lightweight and fuel-efficient cars. 1800 crankshaft arrangement is always used. The balance of the four cylinder engines is not as good as the balance of the opposed two-cylinder engines. But the torque is much more uniform. In these engines, two pairs of four cylinders are moving in the opposite direction. The pairs move up and down together with each cylinder being on a different stroke. In case of four cylinder four stroke engines, four power strokes in two revolutions of the crankshaft with firing interval of 180°
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
are produced. In a four cylinder engine, the cylinders may be arranged inline, opposed, square four or flat 4 and V-four manner.
ww w.E
Figure 1.60 Four cylinder inline engine
In inlinefour cylinder engines, piston 1 and piston 4 are always moving in pair opposite
asy E
to the direction of piston pair 2 and 3 shown in Figure 1.60. In this arrangement, firing interval is regular. Since, this engine is similar to two, two-cylinder engines arranged end to end, the overall balance is very good due to the two rocking coup~es by neutralizing each other, the engine is not completely balanced and a secondary vibration is produced. It can be reduced by
ngi
nee
using light weight pistons and connecting rods.
rin
Piston
4
Cylinders
g.n e
t
3
§1~Bearing Connecting rod
Figure 1.61 Opposedfour cylinder engine In an opposed four cylinder engin~, the cylinders are arranged horizontally in pairs on each side of a flat four crankshaft. Here, the engine balance is superior to inline engine. In this engine, one power stroke is occurred in every 1800 of crankshaft rotation. The torque is also Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile Engineering
smooth. Figure 1.61 shows this type of arrangement. This arrangement is also called flat four or pancake engine. This arrangement is found in air cooled Volkswagen and water cooled Jewett's Javelin. \
V-four engines have cylinders arranged in two rows of two cylinders each. The two rows are set at an angle (preferably 60°) to each other. The crankshaft and cam shafts are positioned between two cylinders as shown in Figure 1.62. It is similar to two cylinder V engines having a common crank shaft. This arrangement is more compact and economical than inline type. The engine has a firing order of 1, 3, 4 and 2 with firing interval of 180°. This engine is balanced by using a balance shaft that runs in a direction opposite to the crankshaft.
ww w.E
asy E
Figure 1.62 V-4 engine
ngt i
+5
nee
6
rin
g.n e
t
Figure 1.63 Six cylinder inline engine Some five cylinder automotive engines are being built. Mercedes produces a fivecylinder diesel engine. Volkswagen has a five cylinder inline spark-ignition engine for a frontdrive car. Six-cylinder engines give a better dynamic balance and a more uniform tor.quethan fourcylinder engines: Most of the high powered as well as modern cars of the moderate powers are employing six cylinder engines. Though expensive and complication involve in these engines,
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
they are much smoother; more flexible and quieter running. It requires only a light flywheel due to the lower ratio of maximum to mean torque. Six cylinder engines are generally inline engines built with 120° crank shafts. The arrangement of crank shaft is as shown in Figure 1.63. This arrangement is such that the crank throws of cylinders 1 and 6, 2 and 5, and 3 and 4 are in the same revolution of the crankshaft. The possible firing order for good distributions of fuel is 1-5-3-6-2-4 and 1-4-2-6-3-5. Six cylinder V-engines are very important engines which are built to have a bank of three cylinders set at an angle or at V to each other. Same crank pin is used to attach connecting rods from opposing cylinders in two banks. The arrangement of cylinders in V-6 engine is shown in Figure 1.64.
ww w.E
Opposed six-cylinder engines are also av_,ailable.The arrangement of cylinders is in the similar manner of a four cylinder opposed engine. Three cylinders are placed in each side of two rows but they are opposite to each other.
asy E
ngi
nee
Figure 1.64 V-6 engine
rin
g.n e
t
The eight-cylinder engines have many advantages over six cylinder engines. They provide more uniform torque and better acceleration while the balance is not very good. Eight cylinder inline engines provide a long engine with long and expensive crank and camshaft. The interval of explosions of this engine is 90°. The crank throws for different pairs of cylinders are in the same radial plane such as cylinders 1 and 8, cylinders 2 and 7, 3 and 6, and 4 and 5. The firing order is 1-6-2-5-8-3-7-4 or 1-8-2-6-4-5-3-7. The disadvantages of this engine are long and expensive crankshaft and its liability to torsional oscillation of the crankshaft. Eight cylinder V-engines employing two banks of four cylinders each at right angle have replaced the inline eight-cylinder models in most of the higher power automobiles. The angle between cylinder rows in V-8 engine is usually kept as 90°. These engines can operate smoothly and silently. V-8 engines are almost universally in use. The Rolls Royce and Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
Daimler car manufacturers are producing different V-8 model engines. Three big manufactures of car i.e., Ford, Chrysler and General Motors are employing V-8 engine as standard engines.
ww w.E
Figure 1.65 V-8 engine
Advantages of V-engines over inline engines: The main advantages ofV-8 engines are summarized as follows.
asy E
1. It is the shortest of all the eight-cylinder engines other than radial engines. It is also a lighter and more rigid engine. The shorter engine provides more space for passenger on small wheel base.
ngi
nee
2. It provides relatively a simple valve gear, arranged both for the side valve or overhead valve type engine, enabling a single crankshaft to be located above the
rin
crank shaft for 90° angle arrangement of two cylinder banks.
g.n e
3. It permits the use of intake manifolds that assure relatively even distribution of airfuel mixture to all cylinders since all cylinders are relatively close together.
t
4. Good engine balance can be obtained by suitable choice of crankshaft angles. A good balance would be resulted if two outer cranks at 90° to the parallel inner pairs in the same plane are provided. 5. It is not affected by similar torsional vibrations similar to an in-line type. 6. Since, the carburetor and other parts are rested between two rows of cylinders, it permits lowering the engine load line and thus it lowers the car profile. 7. Instead of an eight-throw as inline type, only a four throw crankshaft is used. In this case, same crank pin is used for operating two connecting rods from opposite cylinders. This arrangement provides even firing intervals between cylinders. Twelve cylinder engines were originally designed for aeroplanes. But certain cars such as Rolls Royse, Daimler and Lincoln Zephyer also use these engines. These engines consist of Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
two sets of six cylinder inline engines with each forming a bank V-inclined at 60° or 75°. They have common crankshaft and camshaft with six sets of forked and plain connecting rods. The Italian Ferrari is the only car which is being manufactured with a twelve-cylinder engine. Sixteen-cylinder engines having two sets of straight light cylinders inclined at an angle of V have been used in Cadillac cars. These engines have been perfectly balanced with top gear performance. The cylinders arranged in two banks of eight cylinders each are inclined at 135°. Radial engines are mostly used in aircrafts, These engines are air-cooled and they have cylinders arranged in a star form about the crankshaft axis. The cylinders are radiating from a common centre similar to spokes of the wheel. A common crankpin is employed for all connecting rods. To get uniform firing intervals, the cylinders are odd in number such as 5, 7,
ww
9 etc. These engines are compact with low weight per horsepower and accessibility, simplicity of the single throw crank shaft and single cam ring for operating the valves. But, they are not
w.E asy En gin ee
used in motor vehicles due to more frontal area and more complicated exhaust pipe system.
Figure 1.66Radial engine
rin g.
net
1.17. CLASSIFICATION BASED ON l.ENGTH OF CYLINDERS
(i) Square engine: Engine which has same bore and stroke is called square engine. Usually, engines have a bore/stroke ratio of 0.95 to 1.04 referred as square engines. (ii) Oversquare engine: A piston engine is oversquare or short stroke if its cylinders have a greater bore than stroke. Since a shorter stroke means less friction and less stress on the crankshaft. An oversquare engine is generally more reliable, wears less and it can be run at higher speed. In Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
oversquare engines, power does not suffer but low-speed torque does to some degree since torque is relative to crank throw. An oversquare engine cannot have as high compression ratio as which is similar to an engine with a lower bore/stroke ratio and using the same octane fuel. It causes the oversquare engine to have poor fuel economy and poor exhaust emissions. Engines can be modified by being "de-stroked", shortening the stroke to increase maximum rpms and top-end horsepower at the expense of low-end torque. Oversquare engines are lighter and shorter than similar undersquare engines along the direction of piston travel but they are wider in directions perpendicular to piston travel. As the length is not a large problem, these engine types are highly favored by many manufacturers because of their power and compact size.
ww w.E
(ii) Undersquare engine:
A piston engine is undersquare or long stroke if cylinders have a smaller bore than stroke. Since a longer stroke usually means greater friction, more stress on the crankshaft and a smaller bore means smaller valves which restrict gaseous exchange. An undersquare engine usually has a lower redline than an oversquare engine but it may generate more low-end
asy E
ngi
torque. In addition, a long stroke or undersquare engine can have a higher compression ratio with the same octane fuel compared to a similar displacement engine with higher bore/stroke
nee
ratio. It also equals better fuel economy and better emissions. An undersquare engine does not overheat as easily as similar oversquare engine. Engines can be modified with a "stroker"
rin
crankshaft which increases engine stroke from stock thereby increasing torque. Undersquare
g.n e
engines typically are shorter in length, heavier and taller than equivalent oversquare which is one of the reasons why this type of engine is not generally used.
1.18. CLASSIFICATION BASED ON ARRANGEMENT OF VALVES
t
(i) L-Ilead engine: Spark plug
Figure 1.67 L-head engine
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Vehicle Structure and Engines
i ••
In this arrangement, all valves are arranged in one line (except in case of V-8 engine) with the intake and exhaust valves are arranged side by side. The combustion chamber and the cylinder are arranged in the form of inverted 'L'. All valves can be operated by a single crankshaft. Figure 1.67 shows this arrangement.
Advantages: I. One cam shaft is only required. 2. Height is reduced. 3. As valves are arranged in one line, the- removal of the cylinder is quite easy for servicing.
ww
4. It is more dependable.
Disadvantages:
w.E asy En gin ee
1. More space for combustion chamber is required. 2. Knocking tendency is more than T-head engine. 3. Location of spark plug is difficult.
4. High compression ratio is not possible.
(ii) I-head engine:
In these engines, the cylinder head carries the valve. It is also called overhead valve engine. In case of inline engines, valves are arranged in a single row and valves may be
rin g.
~arranged in a single row or double row in each bank in case of V-engines. All valves are actuated by a single crankshaft. Cylinder head
net
Cylinder block
Figure 1.68 I-head engine Advantages: 1.
A single camshaft actuates all valves.
2.
Clearance volume is less. Hence, the compression ratio can be increased
considerably. ., Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
3.
The spark plug can be located at the centre.
4.
Smooth operation can be obtained.
Engineering
Disadvantages: 1.
More valve mechanism parts are involved.
2.
The cylinder head requires more cooling.
3.
It is more complicated design.
4.
The size of the inlet and exhaust valves is limited.
(iii) T-head engine: It has the inlet valve on one side and the exhaust valve on the other side of the cylinder. Thus, two cam shafts are required to operate them. The combustion chamber and the cylinder
ww w.E
form a letter' T . Generally, small engines are made with T-head arrangement. Spark plug
asy E
ngi
nee
Figure 1.69 T-head engine Disadvantages: 1.
Unequal temperature occurs in the cylinder.
2.
More power is wasted in operating two camshafts.
3.
Cost and weight are more.
rin
g.n e
t
(iv) F-head engine:
Figure 1.70 F-head engine
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
In this arrangement, inlet valves are located in the cylinder head and exhaust valves by sides of cylinders. These engines being combination of L-head and l-head engineers are known as F-head engines. Both inlet and exhaust sets are driven from the same camshaft.
Advantages: 1.
More turbulence is possible.
2.
More speed is possible.
Disadvantages: 1.
More space is required for the combustion chamber.
2.
Location of spark plug is difficult.
3.
Design of combustion chamber is difficult
ww
w.E asy En gin ee
1.19. CLASSIFICATION BASED ON METHODS OF COOLING
(i) Air-cooled engines:
In these engines, cylinders are usually mounted separately. They have metal fins which provide a large surface area. It permits the engine heat to be carried away from cylinders. Aircooled engines have shrouds which direct the airflow around cylinders for cooling. Aircooling is generally provided in one cylinder or two cylinder engines such as mopeds, motor
rin g.
cycles and scooters. Some of the earlier car models were air-cooled.
(ii) Water cooled engines:
net
Most of the present day engines are water-cooled. These engines use a liquid i.e. water to take heat from engines. These engines have water jackets around cylinders and combustion chambers. The water is passed through all parts of the engine and it takes away the heat from it and passed through the radiator for cooling. In the radiator, water is cooled by passing air around the fined tube. 1.20. WANKEL ENGINE
This engine was introduced by Felix Wankel in 1954. The engine works on ordinary Otto cycle. It is a rotary combustion engine. The piston in this engine undergoes rotary motion. This engine has been developed by Dr. Walter Froede of Germany for installation in NSU motor vehicles. This engine was installed in two seater NSU spider sports car for the first time. Several automobile manufacturers in various countries have obtained licenses and started the manufacture of Wankel rotary engine.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering,
Construction details: The engine rotor has three lobes. The rotor rotates in an eccentric pattern. The lobes are in contact with the oval housing to form a tight seal. This seal is equivalent to the seal formed by piston rings against the cylinder wall in a reciprocating engine. The rotor is mounted on the crankshaft through external and internal gears. The rotor lobes A, Band C are placed tightly against the side of oval housing shown in Figure 1.71 (a). Th"erotor also has over-shaped recesses which are shown as dashed lines. The oval chamber not only revolves about its own centre but also it is a circular path around the output shaft. This engine has inlet and exhaust parts. The housing is surrounded by water jackets for cooling. When the engine runs, the four cycles of operation will also take place around the rotor simultaneously. The working of engine and its action during one complete rotation of the rotor are shown in Figure 1.71.
ww
Working:
w.E asy En gin ee
1. Intake process:
In Figure 1.71 (a), lobe A has passed the intake port and the air fuel mixture is starting to enter (1). As the rotor moves as the space between lobes A and C will increase (2) as shown in Figure 1.71(b). This motion produces vacuum which causes the air fuel mixture to enter. The air fuel mixture continues to enter as the space between lobes A and C are continued to increase in (3) of Figure 1.71(c). The lobe C starts to move past the intake port as shown in
rin g.
Figure 1.71 (d). Further movement of rotor carries lobe C past the intake port. So, the air fuel mixture is sealed between lobes A and (C) at (4).
2. Compression process:
net
In Figure 1.71 (a), the air fuel mixture has been trapped between lobes and A and B at (5). Further rotation of the rotor decreases the space between lobes A and B at (6). By that time, the rotor reaches the position shown in Figure 1.71 (c) and the space (7) is minimum. This position is same as TOC position of the piston on the compression stroke in the reciprocating engine. Now, the spark plug fires and ignites the compressed mixture.
3. Power or expansion process: Pressure exerted on the side of the rotor when the combustion takes place and it forces the rotor to move around. This process is similar to a power stroke of the reciprocating engine. The high pressure of the burnt mixture in (8) forces the rotor around to position (9) again. Expansion continues to rotate the rotor until the leading lobe passes through the exhaust port.
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines IS
=> Ignition Start
EVO
=> Exhaust Valve Open
EVC
=> Exhaust Valve Close
TDC
=> Top Dead Center
BOC
=> Bottom Dead Center.
Theoretical valve timing diagram: The exact moment at which each of the valves opens and closes with reference to the position of piston and crank can be shown graphically in a diagram. This diagram is known as
ww w.E
"valve timing diagram".
In theoretical valve timing diagram, inlet and exhaust valves open and close at both dead centers. Similarly, all processes are sharply completed at TDC or BOC. Figure 1.72 shows theoretical valve timing diagram for four stroke SI engines.
asy En gi TOC
nee r
ing .ne
t
I soc
EVO
Figure 1.72 Theoretical valve timing diagramjOf'1jour stroke Sf engines Actual valve timing diagram: Figure 1.73 shows actual valve timing diagram for four stroke SI engine. The inlet valve
opens 10-30° before TOC. The air-fuel mixture is sucked into the cylinder till the inlet valve closes. The inlet valve closes 30-40°' or 'even 60° after BOC. The charge is compressed till the spark occurs. The spark is produced 20-40° before TDC. It gi\leS sufficient time for the fuel to Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
111m
Automobile Engineering
burn. Both pressure and temperature inc~ease.The burnt gases are expanded till the exhaust valve opens. The exhaust valve opens 30-60° before BOC. The exhaust gases are forced out from the cylinder till the e:>dtaustvalve closes. The exhaust valve closes 8-20° after TOC. Before closing, the inlet valve again opens 10-30° before TOC. If the piston is positioned between fourth stroke (exhaust) and the first stroke (intake) at TOC, both valves open. The period between NO and EVC is known as valve overlap period. The angle of valve overlap is the sum of the angle of opening the intake valve before TOC and closing of the exhaust valve after TOC. In Figure 1.73, the angle of overlap is specified as 10°.
ww w
TOC
.Ea
syE ngi
m )(
'2 iii o· ::I
nee
rin
g.n et
1.22. VALVE TIMING DIAGRAM FOR A FOUR STROKE CI ENGINE
Figure 1.74 shows the actual valve-timing diagram for four-stroke diesel (CI) engine. The inlet valve opens (IVO) 10° to 25° before TOC. Fresh air is sucked into the engine cylinder till the inlet valve closes. The inlet valve closes (IVC) 25° to 50° after BOC. The air is compressed till the fuel is injected. The fuel injection starts (FIS) 5° to 10° before TOC in the compression stroke. The air-fuel mixture burns. Both temperature and pressure increase. The burning gases are expanded till the exhaust valve opens. The exhaust valve opens (EVO) 30° to 50° before BOC. The exhaust gases are forced out of the cylinder till the exhaust valve closes.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'.,11
I Vehicle Structure and Engines
The exhaust valves close (EVC) 10° to 15° after TDC. Before closing the exhaust valve, the inlet valve again opens 10° to 25° before TDC. The period when both the inlet and exhaust valves are opened is known as valve overlap period. The angle between these two events is known as angle of valve overlap. In Figure 1.74, the angle of overlap is specified as 5°. Toe
ww w.E
~
1l :s
1/1 o· ::::s
asy En gi
nee r
Figure 1.74 Actual valve timing diagram for four stroke CI engines 1.23. VARIABLE VALVE TIMING (VVT)
ing .ne
t
Fixed valve timing has been a standard feature of all engines until relatively recent times. The valves opened and closed at a fixed period in relation to crankshaft rotation at all engine speeds and loads. When the inlet and exhaust valve timing is fixed, the timing is not suitable for all engine operating speeds and loads. So, there is increase in use of mechanisms to provide variable valve timing (VVT). The variable valve timing systems alter the valve timing to suit engine speed and load conditions. Although systems are purely mechanical-based systems, most modern systems make use of the electronic engine management system to regulate the mechanical actuation of changes to the valve timing. A petrol engine has to operate at varying engine speeds from idle, typically 750 rpm through to high speeds up to 7000 rpm and above. So, the engine will have valve timing more suitable for one particular engine speed which is generally at around 50% to 60% of the engine's maximum speed. Therefore, the variable valve timing results the increased combustion efficiency at the selected engine speed. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering TOC IVO
ww w.E rvc
EVC
asy En gi
EVO
BDC
nee r
Figure 1.75 Variable valve timing for four cylinder engine
ing .ne
Variable valve timing optimises the overlap period during engine operation. It allows different overlap periods to be used at different engine speeds. Practically, VVT systems are used to enable good power or torque to be achieved over the whole engine speed range but the added benefit of valve overlap is to facilitate the mixing of some exhaust gas with the fresh charge of air. Therefore, the combustion temperature and NOx emission are reduced.
t
(i) Slow engine speeds:
At slow engine speeds, if the inlet valve timing is altered so that it is retarded or opened late, all of the exhaust gas will be expelled through the exhaust valve and the cylinder will fiI with fresh uncontaminated mixture. So, a fresh mixture will provide a good bum of the gas during next power stroke. Therefore, the engine is stable when it is at idle. (ii) High engine speeds:
At high speed, if the inlet valve timing is advanced, the fresh mixture can be drawn into the cylinder by the depression caused by the flow of exhaust gas through the exhaust valve. The flow of exhaust gas will improve the gas flow. through the cylinder at higher engine speeds. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
msl
Vehicle Structure and Engines
(iii) Valve opening period:
The valve opening period is dictated by the profile of the cam lobe which is constant with conventional valve operating gear. When the engine is at low to medium speeds, the valve opening period allows sufficient fresh mixture into the cylinder to provide good engine performance. At higher engine speeds, the volumetric efficiency of an engine will increase if the opening period of the valve is increased. It is possible to increase the valve opening period by increasing the valve lift. Increasing the valve lift at high engine speeds provides an increase in the volume of fresh mixture drawn into the cylinder. So, it results an increase in engine power.
ww w.E
1.23.1. Types of Variable Valve Timing There are three types of variable valve timing such as cam changing VVT, cam phasing VVT and combined cam changing and cam phasing VVT. 1. Cam changing VVT:
asy En gi
This type ofVVT uses various cam profiles to lift valves based on load and speed. It also uses two rocker arms for normal working in its two intake valves and third rocker arm is placed between other two arms. If the engine runs more than 5000 to 6000 rpm, the Electronic , Control Unit (ECU) activates an oil pressure controlled pin to lock these three rocker arms
nee r
simultaneously. The center rocker arm follows the random profile and transfers the same movement to intake valves in keep opening it for longer period.
ing .ne
Similarly, when the engine speed reduces below the threshold speed, the spring connected to it will deactivate the pin to reduce the oil pressur~ because rocker arms are not locked. It is due to less control of valves by outer lobes. It is carried out in three stages. Stage 1. Low speed
t
Both intake and exhaust valves are configured for slow speed. Stage 2. Medium speed In this stage, intake valves are configured for high speed and exhaust valves are configured for slow speed. So, medium speed is obtained. Stage 3. High speed In this stage, both intake and exhaust valves are configured for high speed. Therpfnrp high speed is obtained.
~.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lam
Automobile Engineering
Advantage: It is very much powerful at top end. Disadvantages: 1. Stage 2 or stage 3 is non-continuous and not much improvement to torque. 2. It is also complex in nature. 2. Cam phasing VVT: It is the simplest, cheapest and most commonly used mechanism in recent days. It is obtained by just shifting the phase angle of camshafts. At high speed, the inlet camshaft
ww w.E
rotates 30° advance to enable previous intake. It can be achieved by engine management system based on the need and type of actuation. Generally. the actuation is done by hydraulic valve gears.
asy En gi
This arrangement does not alter the duration of valve opening but it allows valve to open early or late based on the requirement. If the valves are opened early, they also close early. Advantages:
I. It is cheap and simple.
nee r
2. It improves the torque throughout the running process. Disadvantage:
ing .ne
It provides lack of variable lift.and variable opening duration. It results the less top end power.
3. Combined cam changing and cam phasing VVT:
t
It offers the benefit of both cam changing and cam phasing VVT in terms of top end power and flexibility throughout running. The only drawback is more complex in design. Toyota and Porsche have this design. 1.23.2. Advantages of Variable Valve Timing 1. It allows to recirculate internal exhaust gas. 2. Increased torque can be obtained. 3. It ensures better fuel economy. 4. It reduces nitrogen oxide. 5. Hydrocarbon emissions can be controlled.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Vehicle Structure and Engines 1.23.3. Applications
of Variable Valve Timing
Different manufacturers use different types ofVVT as listed below.
S.No. 1.
Configuration
Type of automobile
It offers continuous variable valve
BMW
Type of valve Valvetronic
timing and valve lift on intake cam only. It can be relied for amount of valve lift to throttle the engine.
2.
3.
4.
It allows to vary the timing of
VANOS
ww w.E VTEC
VarioCam
BMW
valves by moving the position of camshafts
relative to the driving
gear. It uses two camshaft profiles and
asy En gi
selects
electronically
Honda
between
profiles.
-
It varies intake timing by adjusting
Porsche
the tension of a cam chain.
5.
AVCS/AVLS
AVeS
nee r
- It allows to change the
timing
(phase)
pressure.
with
hydraulic
Subaru Mitsubishi MIVEC
ing .ne
AVLS - It varies duration, timing
and lift by switching between two different sets of cam lobes.
t
1.24. TWO MARK QUESTIONS AND ANSWERS
1. Explain tile various applications 0/ automobiles.
{Anna Univ. Dec'OBI
Automobiles are used for the transportation of passengers and goods from one place to the other on the ground.
2. How are automobiles classified? Automobiles
{Anna Univ. May'I21
can be classified with respect to different purposes which are as
follows.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
AUWIIJ1oJ'Jile Engineering
(i) With respect to the purpose:
(a) Passenger vehicles. Examples: Car, Bus, Jeep, Scooter, Mopeds, Motor cycle. (b) Goods carriers. Examples: Trucks, Lorrys. (ii) With respect to thefuel used: (a)
Petrol vehicles
(b)
Diesel vehicles
(c)
Gas vehicles
(d)
Electric vehicle
(e)
Solar vehicle.
ww w.E
(iii) With respect to capacity:
(a) Heavy Transport vehicle or Heavy Motor vehicles. Example: Bus, Lorries, Trucks, Tractors.
asy En gi
(b) Light transport vehicle or light motor vehicles. Example: Car, Scooter, Mopeds, Motor cycles, Jeeps. (iv) With respect to the number of wheeIs:
nee r
(a) Two wheelers. Examples: Scooters, Motor cycles, Mopeds.
ing .ne
(b) Four wheelers. Examples: Car, Jeep, Buses, Trucks. (c) Three wheelers. Examples: Auto, Tempos (d) Six wheelers. Example: Heavy trucks. (v) With respect to the drive of the vehicle:
(a)
t
Single wheel drive vehicles
(b) Two wheel drive vehicles (c)
Four wheel drive vehicles
(d) Six wheel drive vehicles.
J. How are automohiles classified based on capacity? Give examples. [Anna Univ. May'] (i)
Heavy transport vehicle or heavy motor vehicles. Example. Bus, Lorri Trucks, Tractors.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Rl
I Vehicle Structure lind Engines
(ii) Light transport vehicle or light motor vehicles. Example. Car, Scooter,
Mopeds, Motor cycles, Jeeps. 4. What is meant by self-propelled vehicle? A vehicle producing power within itself for its propulsion is known as selfpropelled vehicle.
5. Give examples to self-propelled vehicles. Examples to self-propelled vehicles are scooters, mopeds, cars, lorry, bus, jeep, tractors, ship, aeroplanes, helicopters, rockets etc.
ww w.E
6. What is known as unitary or monocoque construction ill all atuomobile? {Anna Univ. Dec'l3] Unitary or monocoque construction combines the bodywork and its underlying structure into a single load-bearing unit.
asy En gi
7. State the major types of automobiles according to the fuel used. (a) Petrol vehicles
(b) Diesel vehicles
nee r
(c) Gas vehicles
(d) Electric vehicle
ing .ne
(e) Solar vehicle. 8. Brieflyaplain
offroad" vehlcle willi example. [Anna Univ. May'08 & May'll]
lI
t
An off-road vehicle may be any type of a vehicle which is capable of driving on and off paved or gravel surface. It is generally characterized by having large tires with deep, open treads and a flexible suspension or even caterpillar tracks. Other vehicles which do not travel public streets or highways are generally known as off-highway vehicles which are tractors, forklifts, cranes, backhoes, bulldozers and Golf carts. 9. Classify automobiles with respect to the number of wheels. (a) Two wheelers. Examples: Scooters, motor cycles and mopeds. (b) Four wheelers. Examples: Car,jeep, buses and trucks. (c) Three wheelers. Examples: Auto and tempos (d) Six wheelers. Example: Heavy trucks.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIImI
Automoblfe Engineering
10. Classify automobiles witl, respect to the drive of the vehicle. (a) Left hand drive (b) Right hand drive. 11. How automobiles are streamlined based on type of transmission used? (a) Conventional automobiles (b) Semi-automatic automobiles (c) Automatic automobiles. 12. Mention any four requirements of an automobile.
ww w.E 1.
It should develop power by itself.
2.
The rate of power development must be easily controlled.
3.
There should be an arrangement to transmit the power developed to the
wheels.
4.
asy En gi
An arrangement must exist to continue and discontinue power flow to the wheels.
13. How are tile requirements of an automobile fulfilled?
nee r
1.
The rate of power development is controlled by an accelerometer.
2.
The power developed by the engine is transmitted to wheels by a transmission system.
ing .ne
3.
The gear box is provided for varying or changing the torque.
4.
The driving thrust is carried to the chassis frame through the suspension system.
5.
Directional control is maintained through the steering.
6.
The moving vehicle is stopped by means of brakes.
t
14. Wluu is the difference between normal control and forward control in commercial vehicles?
{Anna Univ. Dec'14/
In normal control commercial vehicles, engine is located at the front of the driver's cab to give more cab space, less noise, heat and ease entry and exit Forward control is a body style of truck or van that has a vertical front or "flat face" with the cab sitting above the front axle. In other words, it can be stated that engine is located either at the side or below the driver's cab.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Vehicle Structure and Engines
mpi
15. How does EMS operate?
{Anna Univ. Dec'14J
Emergency Medical Services (EMS) provide out-of-hospital acute medical care and transport to definitive care for those in need. 16. What is the needfor a gearbox in an automobile?
{Anna Univ. Dec'UJ
The main function of the gear-box is to provide the necessary variation to the torque applied by the engine to the road wheel according to the operating conditions. 17. Describe briefly the machine portion in bullock cart. Machine portion consists of a frame in which wheels are attached through the axle. A yoke is fixed at the front end of the frame through which the bullocks pull the cart.
ww w.E
18. Mention the various parts of
II
car.
asy En gi
Various parts of a car are generator, starter, steering, clutch, rear axle, differential, universal joint, wheel, tyres, body, lamp etc.
. 19. What is meant by the term "chassis"?
It is the main structure of a vehicle which is used to the complex vehicle except the body. A vehicle without body is called chassis.
nee r
20. What is chassis? How its design is related to vehicle aerodynamics?
ing .ne
{Anna Univ. Dec'Uj.
A vehicle without body is called chassis. Chassis design is related to vehicle aerodynamics due to various loads such as loads of short duration, combined loads of
t
moment any duration, inertia loads, impact loads, load due to road camber, load due to wheel impact, static loads and overloads. 21. List any four compartments of a chassis. 1. Frame 2. Steering mechanism 3. Engine, clutch and gear box. 4. Radiator 5. Wheels 6. Rear and front springs and shock absorber
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
111m
Automobile Engineering
7. Differential unit 8. Propeller shaft and Universal joint.
22. Classify chassis based on number of wheels. (a) 4 x 2 drive chassis - It has four wheels out of which 2 are driving wheels. (b) 4 x 4 drive chassis - It has four wheels and all of them are driving wheels. (c) 6 x 2 drive chassis - It has six wheels out of which 2 are driving wheels. (d) 6 x 4 drive chassis - It has six wheels out of which 4 are driving wheels. 23. How chassis system is classified based onflttlng engine?
ww w
1. Full-forward
2. Semi-forward
.Ea
3. Bus chassis
4. Engine at back
5. Engine at centre.
syE ngi
24. List any six characteristics of a good chassis. 1. Durability 2. Dependability 3. Ease of control 4. Quietness
nee
5. Speed 6. Power accessibility.
rin
g.n et
25. List out the various materials used in the construction of chassis frames. [Anna Univ. May'07j The various steels used in conventional pressed frame are mild steel sheet, carbon steel sheet and nickel alloy steel sheet. 26. Enumerate the merits and demerits offront engine rear drive chassis layout. [Anna Univ. May'07j The drive of the engine can be connected or disconnected from the gearbox by the driver with the help of a clutch pedal.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
27. How does frame act?
The frame is the main part of the chassis. It is the backbone of the vehicle. All other parts of the chassis are mounted on the frame. It is the rigid structure which forms a skeleton to hold all major parts together. 28. Whyframe is narrow at the front? Frame is narrow at the front to provide a better steering lock so that turning radius should be small or minimum. 29. What are the functions of'frames in automobile?
{Anna Univ. May'l1J
1. To form the base for mounting engine and transmission systems.
ww w.E
2. To withstand the engine and transmission thrust and torque stresses as well as accelerating and braking torque.
3. To accommodate the suspension system.
asy En gi
4. To carry the other parts of the vehicle and its passengers. 5. To resist the effect of centrifugal forces when cornering a curve.
6. To withstand bending and twisting stresses due to the fluctuating or rear and front axle. 30. Give any two requirements of goodframe.
nee r
(a) Horizontal forces provided by road irregularities.
ing .ne
(b) Upward twisting forces caused by road shocks to provide a torsional effect. 31. Name and sketch the various types of sectionsfor automobile frames.
Channel section
Box section
Tubular section
t
I-section
Figure 1.76 Types offrame sections 32. What are the shapes offrame section? 1. Channel section 2. Box section 3. Tubular section, and Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lam
Automobile
Engineering
4. I - section. 33. Which section of'frame offers maximum resistance to Torsion and bending? Frame with X-member provides a better resistance to twisting or torsion effect whereas to resist bending moment, a frame should have double section frame. 34. List out the various loads acting on the chassis frame. 1. Loads of short duration 2. Combined loads of moment any duration 3. Inertia loads 4. Impact loads
ww w.E
5. Loads due to road camber
6. Loads due to wheel impact
7. Static loads 8. Overloads.
asy En gi
35. What types of components are mounted on the chassisframe? l. Engine and radiator
nee r
2. Transmission system 3. Suspension system 4. Road wheels 5. Steering system 6. Brakes.
36. State the composition of sheet nickel alloy. Carbon
0.25 to 0.35%
Magnanese
0.35 to 0.75%
Silicon
0.30% (Maximum)
Nickel
3%
Phosphorus
0.05% (max)
Sulphur
0.5% (max.)
ing .ne
t
37. Classifyframes. 1. Conventional frame construction
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
2. Semi-integrai frame construction 3. Integral or Frameless construction. 38. Describe briefly semi-integral frame construction. In this type of frame, the rubber body mountings are replaced by relatively stiff mountings. This arrangement transfers a part of the frame load to the body structure. This type of frame is mainly used in European cars and American cars. At the same time, the construction is heavy in nature as compared to the conventional type. 39. What do you understand byframeless frame? Frameless frames are frames in which floor is strengthen by cross members and
ww w.E
these member is welded together. Sometimes, sub members are also used as per the requirement.
{Anna Univ. Dec'12j
40. State the advantages of'frameless construction.
asy En gi
1. The construction provides a stiff light construction particularly suitable for massproduced vehicles.
2. No separate frame is used.
3. All assembly units are attached to the body.
nee r
4. It reduces weight and consequent saving in fuel consumption. 5. It lowers manufacturing cost
ing .ne
6. During collision the body crumbles, it absorbs the shock due to impact and thus providing safety to the passengers.
7. Compared to framed construction lower body position may be obtained, thus it results the increased stability of the automobile.
t
41. Write short note on sub frames. In normal vehicles, various components are bolted on the main frame. Sometimes, components on vehicle are mounted on sub frames which are bolted on the main frame. The sub frame provides a greater strength besides it is supported at three points on the main frame. The advantage of sub frame is the component bolted on the sub frame which is isolated from the main frame on which various types of forces act such as tv-isting force, bending force etc. It reduces the vibration. It also helps to simplify the 0\ erhead or repair and increases the production of vehicle in assembly line.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
42. What are the adl'!lntages ofsub-frames? 1. The mass of the sub frame alone helps to damp vibration. 2. The provision of sub frame simplifies the production on the assembly line and facilities the subsequent repair. 43. What are the defects that can appear in a chassis body?
[Anna Unlv. Dec'09]
(a) Dislocated parts (b) Cracks (c) Broken welds (d) Buckling.
ww w.E
44. What is the role of body in automobiles? Body is the super-structure for all vehicles. It may either be constructed separately and bolted to the chassis or manufactured integral with the chassis (i.e. Frameless construction). The chassis and body make the complete vehicle.
asy En gi
45. List the importance of vehicle body design.
1. Weight of the body is about 40% of total weight of the car and 60 to 70010 of total weight of buses. Therefore, the reduction in body weight is important.
nee r
2. If the weight of the body is reduced.jt improves the fuel economy (i.e. mileage).
ing .ne
3. The body of the vehicle determines its aerodynamic characteristics. Better aerodynamic structure leads to fuel economy at high speed and stability in cross wind.
t
4. The body is also important for aesthetic and ergonomics consideration. It should give pleasant appeal and style for the customer. 46. Mention any four requirements of the vehicle body. 1. It must be strong enough to withstand all types of forces acting on the vehicle. The forces are including the weight of car, inertia, luggage, braking and cornering forces. I
2. Stresses induced in the body should be distributed evenly to all portions. 3. Weight of the body should be as minimum as possible. 4. It should be able to cope with impact loads of reasonable magnitude. 47. Classify vehicle body. 1. Car
2. Straight trUCK Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehlcl. StructUTe and Engines 3. Truck half body
4. Truck-platform type
5. Tractor
6. Tractor with articulated trailer
7. Tanker
8. Dumper truck
9. Delivery van
10. Station wagon
II. Pick-up
12. Jeep
13. Buses
14. Mini-buses
15. Three wheeler (i.e. Auto Rickshaw). 48. How are main components
ww w.E
0/ body grouped?
(a) Structure: All load carrying elements are defined as structure. (b) Finish: This group includes all unstressed units such as bonnet, boot, lid, bumper etc.
(c) Equipment: This group includes various parts such as rim, seats, doors, window etc.
asy En gi
49. What are the materials used/or cylinder block and oil pan? {Anna Univ. May'll] For cylindrical block.
(1) Grey cast iron (2) Aluminium. For oil pan. (I) Hybrid nylon
nee r
ing .ne
(2) Aluminium modular
t
(3) Rubber edged metal. 50. State the functions of centre pillar in automobiles.
The centre pillar supports the rear doors and hinges. It also supports the sticker plates of the front doors. 51. Where are bumpers provided? Wlty? Bumpers are provided at the front and rear end of the car. They are used to protect the front end and rear end of the car from damage in case of light collisions. 52. Give the materials usedfor manufacturing of autol1Wbilebody. The materials used for construction of various parts of the body are steel, wood, plastics, toughened glass and aluminium. In earlier days, wooden bodies were used Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIII'lI
Automobile Engineering
for construction. But now-a-days, steel is mainly used for body construction because of low cost and easy to manufacture. 53. What is. double over head camshaft engine?
[Anna Univ. May'12}
Double Over Head Camshaft (DOHC) engine has two camshafts located within the cylinder head. One is operating the intake valves and the other one is operating exhaust valves. This design reduces the valve train inertia more than a single overhead camshaft engine since the rocker arms are reduced in size or eliminated. 54. Name the resistances to vehicle motion.
[Anna Univ. May'15}
1. Loads of short duration
ww w.E
2. Combined loads of moment any duration 3. Inertia loads
4. Impact loads
asy En gi
5. Load due to road camber
6. Load due to wheel impact 7. Static loads 8. Overloads.
55. Wluu is meant by dragforce and lift force?
nee r
ing .ne
Force of air drag is acting in the direction of vehicle motion with the wind acting along the longitudinal direction axis. This force is also called air resistance. Aerodynamic lift force is the vertical component of the resultant force caused by
t
the pressure distribution on the body. 56. Define cross windforce.
Cross wind force is acting in the lateral direction on the side of the vehicle. It is formed by the asymmetric flow of air around the vehicle body. 57. What are the three moments acting in cross windforce? 1. Pitching moment (M;,.) 2. Yawing moment (MJ 3. Rolling moment (My)
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
~/e
am
Structureand Engines
58. Define 'bouncing' and 'pitching', The vertical movement of the complete body is called bouncing. In other words, the complete body of the vehicle moves up and down called bounce or bouncing. Rocking chair action or rotating action about a transverse axis through the vehicle parallel to ground is known as pitching.
59. Whatis meant by IC engine? Internal Combustion engine (IC engine) is a heat engine which converts the chemical energy of a fuel into mechanical energy. The chemical energy of a fuel is first converted into thermal energy by means of products of combustion or oxidation
ww w.E
with air inside the engine. This thermal energy is converted into useful work through the mechanical mechanism of the engine.
[Anna Univ.Nov'lOJ
60. Whatis theprincipleof ignitionin CI engine?
asy En gi
The pressurised air is combusted by injecting atomised fuel in CI engines. Due to
high pressure and temperature at the end of compression, the fuel gets ignited automatically when it is injected in an automised form.
61. Discuss the relative advantages and disadvantagesof internal combustion and externalcombustionengines. [Anna Univ.May'l1J Advantages of internal combustion engines:
nee r
1. It provides lower weight to power output ratio. 2. It is simple in design. 3. It needs less initial cost.
ing .ne
t
4. It produces high efficiency. Advantage of external combustion engines. Cheaper fuels can be used. Disadvantages of internal combustion engines:
1. As much as rich fuel hydrocarbon based fuel should be used. 2. They need of some governing mechanisms to stabilize the output power throughout cycle. Disadvantages of external combustion engines: 1. It is large in size. 2. Transportation of heat in place to place needs special devices. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIIDI
Automobile Engineering
62. Mention any four engine components along with materials. [Anna Univ. May'08 & May'I5] 1. Cylinder block: It is made of grey cast iron or aluminium with steel sleeves. 2. Cylinder head: The materials used for cylinder heads are cast iron, aluminum alloy etc. 3. Crank case: It is made of cast iron, aluminum alloys or alloy steels. 4.
Oil sump: It is made of pressed steel sheet.
5. Cylinder liners: Chromium plated mild steel tubes are used for manufacturing liners.
ww w.E
6. Piston: Piston is made of cast iron, Aluminium alloy, chrome-Nickel alloy, nickel-iron alloy and cast steel.
63. State the purpose of providing piston in IC engines.
asy En gi
I. Piston acts as a movable gas tight seal to keep the gases inside the cylinder.
2. Piston transmits the force of explosion in the cylinder to the crankshaft through connecting rod.
nee r
64. Why should a material for cylinder block or head have higher thermal conductivity? What happens if this factor is overdone? [Anna Univ. Dec'I2]
ing .ne
As the engine cylinder block has to withstand high temperature and vibration when the engine is in running conditions, it should have good thermal conductivity to give out the heat produced during the combustion process in minimum time. Engine seizer will happen due to overheating if this factor is overdone. 65. What are the purposes of using cylinder liners?
t
Inside the cylinder, the piston constantly is moving up and down which will cause wear of cylinder. When the cylinder diameter is increased beyond certain limit, the entire cylinder block should be discarded which is costly. To avoid early cylinder wear, a separate liner which is in the form of sleeve is inserted into the cylinder bore, Then, the wear will take place in the liner only which can be replaced easily when worn out. 66. Name the prominent material for the manufacture of valves ami valve seat inserts. [Alina trc« Dec'07] Inlet valve is made of plain nickel, nickef~chromeor chrome-molybdenum. The exhaust valve is subjected to more heat. Hence, it should be made of high heat Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
resistance material such as silicon-chrome steel, high speed steel, cobalt-chrome steel and tungsten steel. 67. What are the types of piston rings? );>
Compression rings
);>
Oil rings. {Anna Univ. Apr'08j
68. What are the functions of piston rings?
The functions are to maintain air tight sealing between piston and cylinder to prevent gas leakages, to wipe off the excess oil from the cylinder walls and also to return the excess oil to the oil sump through slots provided on the rings.
ww w.E
69. State any four reasons due to which, the spark plug may fail tofunction properly. {Anna Univ. Dec'13j
The following are the four reasons due to which the spark plug may fair to
function properly.
asy En gi
a) Sooted spark plug: Insulator nose, electrodes and air space are covered in velvety black soot due to faulty carburation.
b) Spark plug insulator damage: Scorching due to sparks jumping across the insulator which may be caused because of spark plug adaptor worn out, the rubber gasket torn, embrittled or hardened.
nee r
ing .ne
c) Worn spark plugs: Center and ground electrode show visible material loss due to aggressive fuel or oil additives, thermal overload and exceeding replacement interval.
t
d) Incorrect tightening torque causes traces of hydrocarbons on spark plug body and broken ground electrodes. 70. What is the use of connecting rod? It is used to connect the piston and crankshaft with the help of bearings. 71. What is the purpose ofthejlywheel in an Ie engine? Where is it located? {Anna Univ. Nov'10j Flywheel serves as an energy reservoir. It stores energy during power stroke and
o
it releases energy during other strokes to give a constant output torque. It is located on the crankshaft.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Engineering 72. How are diesel engines identified at the moment of seeing any IC engines? Absence of spark plug 73. What is the function of push rod and rocker arm?
{Anna Univ. Nov'07j
The push rod and rocker arm actuates valves according to the engine stroke by cams. 74. Classify IC engines according to cycle of operation. a. Four stroke cycle b. Two stroke cycle. 75. What is known as valve overlap?
ww w.E
,{Anna Univ. Dec'13}
Valve overlap is the period during the valve timing where both intake and exhaust valves open. The valve overlap is the sum of the angle of opening the intake valve before TOC and closing of the exhaust valve after TOC. If the piston is positioned between 4th stroke (exhaust) and lSIstroke (intake) at TDC, both valves open.
asy En gi
76. Compare two-stroke andfour-stroke engine. Two stroke cycle engine S.No. Advantages 1.
Cycle is completed in two stroke or
nee r
Four stroke cycle engine Disadvantages
ing .ne
One cycle is completed in four stroke
one revolution of the crankshaft.
or two revolution of the crank shaft.
2.
It develops twice the number of power strokes than four stroke engines.
It develops half the number of power stroke than two stroke engine.
3.
Thermal efficiency is low.
Thermal efficiency is high.
4.
Volumetric efficiency is low.
5.
Greater cooling and lubrication are Lesser cooling and lubrication are required. required.
6.
Overall efficiency is less.
"-
t
Volumetric efficiency is more.
Overall efficiency is more.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
77.Mention anyfour applicationsof twostrokeengine andfour strokeengine. [Anna Univ.Dec'llj 1. Automobiles such as trucks, bus, scooters etc. 2. Marine applications 3. Aircraft applications 4. Power plants, such diesel power plants 5. Hybrid power generation, such as combined solar-diesel power plant, wind-diesel power plant etc.
78. CompareSI and CI engines.
ww w.E S.No.
CI or Dieselengine
SI or Petrolengi~e
1.
During suction stroke, air fuel During suction stroke, air is only drawn from the atmosphere. mixture is drawn from carburetor.
2.
Carburetor is used to mix the air and
Fuel injector or atomizer is required to
fuel in required proportion.
inject the fuel into cylinder in atomized
asy En gi
form.
Spark plug is required to ignite the
3.
fuel air mixture.
nee r
Fuel is ignited automatically by high pressure & temperature air.
ing .ne
Compression ratio varies from 12 to 18.
4.
Compression ratio varies from 6 to 8.
5.
It IS operated by Otto cycle or It is operated by Diesel cycle or constant pressure cycle. constant volume cycle.
6.
The starting is easy due to lower
The starting is little difficult due to
compression ratio.
highei compression ratio.
t
79. Classify IC engines according to cycle of lubrication system and field of application. Types of lubrication system: a. Wet sump lubrication system b. Dry sump lubrication system. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Ima
Automobile Engineering
Field of application: a. Automobiles, truck, bus and locomotive engine b. Stationary engine c. Marine engine d. Aircraft engine. 80. What is a square engine?
[Anna Univ. Dec'07}
Engine which has same bore and stroke is called square engine. Usually, engines that have a bore/stroke ratio of 0.95 to 1.04 are referred as square engines. 81. Write down the firing order of 4 and 6 cylinder engine.
ww w.E
[Anna Univ. May'11}
1. For 4 cylinders engine, the firing order is 1 - 3 - 4 - 2 or 1 - 4 - 3 - 2.
2. For six cylinders engine, the firing order is 1 - 5 - 3 - 6 - 2 - 4
or
1 - 4-
2 - 6 - 3 - 5.
asy En gi
82. Write any two merits and demerits of horizontal engines? [Anna Univ. Dec'13} Merits of horizontal engines:
1. The inertia forces of the reciprocating parts combined together to give an
nee r
impulse to the chassis frame of the vehicle as the stroke of the engine piston is horizontal. If the cylinder head is towards the front end of the vehicle, then a driving impulse is obtained from the engine. This impulse force slides the
ing .ne
engine forward on a smooth floor when the running engine is placed on the floor. Therefore, a vehicle fitted with horizontal engine tends to push forward the moped or the scooter by its impulsive force. 2. Fuel economy is also more.
t
Demerits of horizontal engines: 1. The crankcase cannot be used for storing lubrication oil for splash lubrication. 2. There will be excessive wear at the lower side of the piston and cylinder liner where the cylinder liner gives support to the engine because the weight of the piston is carried by the cylinder liner. 3. Consumption of lubricating oil is more due the lubricating oil which dribbles from the bearings returning to the crankcase but it is thrown out by the centrifugal forces.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Vehicle Structure and Engines
83. List down the classification of LC engines based on the number of strokes and method of charging. {Anna Univ. Dec'OS] (i) Engine cycle per stroke:
a. Four stroke cycle b. Two stroke cycle (ii) Types offuel used or methods of charging:
a. Petrol engine b. Diesel engine c. Gas engine.
ww w.E
{Anna Univ. May'14]
84. What are the advantages of diesel engines in cars?
I. The running cost of diesel engine is low because of the lower cost of diesel and higher fuel economy i.e. mileage.
asy En gi
2. The thermal efficiency is up to about 40%. 3. Overheating trouble is less due to high thermal efficiency. 4. Diesel engines are more easily turbo-charged.
85. Define the term valve timing diagram.
nee r
The exact moment at which each of the valves opens and closes with reference to
ing .ne
the position of piston and crank can graphically be shown in a diagram. This diagram is known as "valve timing diagram".
86. Differentiate between ideal and actual valve timing diagrams of a petrol engine.
t
[Anna Univ. Oct' 01}
Theoretical valve timing diagram: In theoretical valve timing diagram, both inlet and exhaust valves open and close at both dead centres. Similarly, all processes are sharply completed from TDC orBDC. Actual valve timing diagram: The inlet valve opens to-30° before TDC. The air-fuel mixture is sucked into the cylinder till the inlet valve closes. The inlet valve closes 30-40° or even 60° after BDC. The charge is compressed till the spark occurs.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
A
Engineering
The spark is produced 20-40° before TOC. It gives sufficient time for the fuel to burn. Both pressure and temperature increase. The burnt gases expand till the exhaust valve opens. The exhaust valve opens 30-60° before BOC. The exhaust gases are forced out from the cylinder till the exhaust valve closes. The exhaust valve closes 8-20° after TDC. Before it closes, again the inlet valve opens 10-30° before TOC. 87. Draw the valve timing diagram/or a CI engine.
ww w.E
[Anna Univ. Dec'lOJ
TOC
asy En gi
i :s
nee r
'"o· :s
ing .ne
t
BOC
Figure 1. 77Actual valve timing diagram IVO
=> Inlet Valve Open
IVC
=> Inlet Valve Close
EVO
=> Exhaust Valve Open
EVC
=> Exhaust Valve Close
TDC
=> Top Dead Center
BOC
=> Bottom Dead Center
IVO
=> Inlet Valve Open
IYC
=> Inlet Valve Close
EVO
=> Exhaust Valve Open
EVC
=> Exhaust Valve Close
IS
=> Ignition Start
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
88. What are the types of VVT?
1. 2. 3.
Cam changing VVT Cam phasing VVT Combined cam changing and cam phasing VVT.
89. How is medium speed obtained in cam changing VVT? Intake valves are configured for high speed and exhaust valves are configured for slow speed. So, medium speed is obtained. 90. List down the advantages and disadvantages of cam changing VVT. Advantage:
ww w.E
It is very much powerful at top end.
Disadvantages:
1. Stage 2 or stage 3 is non-continuous and not much improvement to torque.
asy En gi
2. It is also complex in nature.
91. Mention the various advantages and disadvantages of cam phasing in VVT. Advantages:
nee r
1. It is cheap and simple.
2. It improves the torque throughout the running process. Disadvantage:
ing .ne
It provides lack of variable lift and variable opening duration. It results the less top end power. 92. What is combined cam changing and cam phasing VVT?
t
It offers the benefit of both cam changing and cam phasing VVT in terms of top end power and flexibility throughout running. The only drawback is more complex in design. Toyota and Porsche have this design. 93. List down the advantages of VVT. 1. It allows to recirculate internal exhaust gas. 2. Increased torque can be obtained. 3. It ensures better fuel economy. 4. It reduces nitrogen oxide.
S. Hydrocarbon emissions can be controlled. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering 94. Tabulate any two applications of VVT.
Type of valve Valvetronic
Configuration
Type of automobile
It offers continuous variable valve
BMW
timing and valve lift on intake cam only. It can be relied for amount of valve lift to throttle the engine. VANOS
ww w.E VTEC
It allows to vary the timing of valves by moving the position of camshafts relative to the driving gear.
BMW
It uses two camshaft profiles and electronically selects between
Honda
asy En gi profiles.
1.25. SOLVED QUESTIONS
1. Describe the brief history of the automobile. Refer chapter 1.1.1 in page 1.2.
nee r
ing .ne
2. What are the aspects considered in the design and construction of a body? Refer chapter I.S.4 in page 1.43. 3. Classify automobiles.
[Anna Univ. Dec'l4j
Refer chapter 1.3 in page 1.6.
t
4. Explain vehicle construction of a bullock cart with its neat sketch. Refer chapter 1.4 in page 1.10. 5. Draw the layout of an automobile and indicate its various components. [Anna Univ.Dec '05, May' 10, May' 12 & Dec' 12] Refer chapter 1.5 in page 1.12. 6. List the various requirements of a good chassis and frame. Refer chapter 1.6.4 in page 1.22.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Vehicle Structure and Engines
-"
.....
7. Draw the layout of conventional chassis with a neat diagram and explain about the various parts on it. [Anna Univ.May' 11] Refer chapter 1.6.5 in page 1.22. 8. Explain the construction of various frames used in automobiles with neat sketch. [Anna Univ.May'07, Dec '09 & May '11]
Or Discuss the frame type chassis construction with neat sketch. [Anna Univ. May'15] Refer chapter 1.7.3 in page 1.28. 9. List out the functions of frame in an automobile and explain anyone type of semi
ww w.E integral frame.
[Anna Univ.Dec '07]
Refer chapter 1.7.1 in page 1.27 and refer page 1.31.
10. Explain briefly semi integral and integral type vehicle body construction.
asy En gi
[Anna Univ. Dec' 14]
Refer page 1.31.
[Anna Univ. Dec' 12]
11. Write a note on sub-frames.
Refer chapter 1.7.7 in page 1.35.
nee r
12. Write short notes on the following with respect to vehicle motion.
ing .ne
(i) Aerodynamic drag Refer page 1.52. (ii) Gradient resistance
t
Refer page 1.53.
[Anna Univ. May'll,Dec'J3&
(iii) Rolling resistance.
Dec'U]]
Refer page 1.53. 13. Explain briefly the construction of an S.1. engine.
[Anna Univ. May '06]
Refer chapter 1.11 in page 1.56.
14. Explain the various components of engine with a neat sketch. [Anna Univ. May '06, Dec '08 & Dec' 14]
Or List the engine parts, materials, methods of manufacture and their func .ons. [Anna Univ. May'14 & Dec '14] Refer chapter 1.12 in page 1.58. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
M'
Automobile :Englneerlng
15. Describe in detail on various types of automotive pistons. [Anna Univ. Dec'12] Refer chapter 1.12.6 in page 1.60. 16. Discuss in detail various types of piston failure.
[Anna Univ. Dec'12]
Refer page 1.63. 17. What are the types of valve used to control air fuel mixture in the engine cylinder to force the exhaust gaseous out at correct time? [Anna Univ. May'12] Refer chapter 1.12.13 in page 1.68. 18. Classify IC engines.
ww w.E
Refer chapter 1.13 in page 1.71.
19. Give reasons.
(i) For using single cylinder two stroke petrol engines on two wheelers
asy En gi
Refer chapter 1.14.3 in page 1.76.
(ii) For using multi cylinder diesel engines in commercial vehicles. Refer chapter 1.15 in page 1.82.
[Anna Univ. May'14]
nee r
20. Explain engine classification based on valve arrangement with a neat diagram. Qefer chapter 1.18 in page 1.92.
---------_._----
END of Unit
ing .ne
[Anna Univ. May'11]
t
1'------------
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I ww w.E
UNIT - 2
I
asy En gi
Electronically controlled gasoline mjection system
nee r
for 81 engines, Electronically controlled diesel
ing .ne
injection system (Unit injector system, Rotary distributor type and common rail direct injection
system), Electronic ignition system (Transistorized coil ignition system, capacitive discharge ignition
system), Turbo chargers (WGT, VGT), Engine
t
emission control by three way catalytic converter system, Emission norms (Euro and 88).
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary
UM
Systems
ww w.E
2.1. CARBURETORS
ENGINE AUXILIARY SYSTEMS
asy En gi
Carburetor is a device used for atomizing and vapourizing the fuel and mixing it with the air in varying proportions to suit for changing the operating conditions of engines. The
nee r
process of breaking up and mixing the fuel with the air is called carburetion. The term vapourization and atomization should be understood clearly. Vaporization is a
ing .ne
change of state of the fuel from liquid to vapour whereas atomization is a mechanical breaking-up of the liquid into small particles so that every minute particle of the fuel is surrounded by the air.
t
The carburetor is supposed to supply the fuel air mixture in correct proportion under different conditions of temperature, speed and load on engine. Relatively rich mixture of air fuel ratio of 12:1 is required by the engine while accelerating or running at high speeds. A leaner mixture of air-fuel ratio of 16:1 is sufficient while running on levelled roads. For idling, a richer mixture of about 14:I is needed. Similarly, an extremely rich mixture having a ratio of 9: 1 is required during cold starting. 2.1.1. Functions of Carburetor 1. It prepares a mixture of petrol and air in correct proportions. 2. It maintains a small reserve of petrol in the float chamber at constant head. 3. It atomizes and vapourizes the fuel.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
4. It supplies a fine spray of petrol. 5. It produces a homogeneous mixture. 6. It measures and supplies the proper quantity and proportions of air and fuel under all conditions of engine operations such as temperature, speed and load. 2.2. FACTORS AFFECTING FUEL VAPORIZATION (i) Concentration of the substance evaporating in the air:
If the air contains a high concentration of the substance evaporating, the given substance will evaporate more slowly.
ww w.E
(ii) Concentration of other substances in the air:
If the air is saturated with other substances. it can have a lower capacity for the substance evaporating. (iii) Flow rate of air:
asy En gi
It is a part related to the concentration point. If fresh air is moving over the substance at all time, the concentration of the substance in air is less likely to go up with time thereby encouraging faster evaporation. (iv) Inter-molecular forces:
nee r
The stronger is the force keeping the molecules together in the liquid state, the more energy one must get to escape. (v) Pressure:
ing .ne
Evaporation happens faster if there is less exertion on the surface keeping the
t
molecules from launching themselves. (vi) Surface area:
A substance which has a larger surface area will evaporate faster as there are more surface molecules per unit of volume which are potentially able to escape. 2.3. TYPES OF CARBURETOR The carburetors can be classified according to the following considerations. I. According to the direction offlow. a. Uplift carburetors or updraft carburetor
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Engine Auxiliary
Systems
b. Down draft carburetor c. Horizontal carburetor. 2. According to the arrangement of thefloat chamber a. Eccentric carburetor b. Concentric carburetor. 3. According to the number of units a. Single carburetor b. Double carburetor. 4. According to the metering system
ww
a. Air bled jet carburetor
w.E
b. Metering pin type carburetor.
S. According to the type of venturi
asy E
a. Plain venturi carburetor
b. Double venturi carburetor c. Vane venturi carburetor
ngi
d. Nozzle bar venturi carburetor e. Triple venturi carburetor.
6. According to the type of power system a. Manually operated carburetor b. Vacuum controlled carburetor.
nee rin
g.n et
2.3.1. Simple Carburetor The main components of a simple carburetor are float chamber, float, nozzle, venturi, throttle valve, inlet valve and metering jet. In the float chamber, a constant level of petrol is maintained by the float and a needle valve. The float chamber is ventilated to atmosphere. It is used to maintain the atmospheric pressure inside the chamber, The float which is normally a metallic hollow cylinder rises and closes the inlet valve as the fuel level in the float chamber increases.to a certain level.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IU-
Automobile Engineering
The mixing chamber contains venturi, nozzle and throttle valve. The venturi tube is fitted with the inlet manifold. This tube has a narrow opening called venturi. A nozzle is provided just below the centre of this venturi. The nozzle keeps the same level of petrol as the level in the float chamber. The mixing chamber has two butterfly valves. One is to allow air into the mixing chamber known as choke valve. The other one b to allow air-fuel mixture to the engine known as throttle valve. Air venturi Vent Needle valve
ww w.E
asy En gi tt
Petrol
Float chamber
I
Air-fuel mixture
nee r
Figure 2.1 Simple carburetor Working:
ing .ne
t
During suction stroke, vacuum is created inside the cylinder. It causes the pressure difference between cylinder and outside the carburetor. Due to this, the atmospheric air enters the carburetor. The air flows through venturi. The venturi increases the velocity of air and reduces the pressure. It produces the partial vacuum at the tip of the nozzle. Because of this vacuum, the fuel comes out from the nozzle in the form of fine spray. These fine fuel particles mix with the incoming air to form air-fuel mixture. Thus, it gives a homogeneous mixture of air-fuel to the engine. 2.3.1.1.Defects in a Simple Carburetor A simple carburetor is found useful only to a particular load and speed condition. But in actual practice, the engine has to run at different speeds and load conditions.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Engine Auxiliary Systems
There are two basic reasons for defects in a simple carburetor. (i) If the carburetor is set or worked at high speed and at full throttle, it will not work properly at lower speed and part throttle. It is due to insufficient suction created at the venturi for drawing fuel from the main nozzle. Similarly, if the carburetor is set to work at low speeds and part throttle, it will not work properly at high speed and full throttle. (ii) With the change of pressure heads, coefficients of discharge for air and fuel vary in different quantities. At certain value of head, the coefficient of discharge for air becomes constant while in case of fuel it increases gradually. Therefore, at high head i.e., high engine speed, the air fuel ratio becomes rich and rich. Hence, if the
ww
carburetor is set at one particular speed, it will give rich mixture at higher speeds
w.E
and lean mixture at lower speeds.
Therefore, a number of defects are found in case of a simple carburetor. The remedies for
asy E
removing these defects are also explained here. 1. Starting diffICulty:
ngi
For starting the engine from rest, it requires rich mixture. But, the simple carburetor will supply lean mixture during starting. It will create starting difficulty for the engine. In order to
nee rin
enrich fuel mixture at very low speeds, devices such as ticklers, choke, adjustable area jet and a separate air passage are used. (a) Ticklers:
g.n et
Ticklers are the devices used for flooding of the carburetor while starting an engine. More fuel will be supplied by depressing the tickler which would depress the float. .----...,.-
Fuel from pump
chamber
Figure 2.2 Ticklers
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IfJM
Automobile
Engineering
(b) Choke: A choke is a simple butterfly valve (i.e. same as throttle valve) fitted at the top of the air horn shown in Figure 2.3. It may be operated by hand or by automatic. During starting, in order to provide a rich mixture, the chock is kept closed so that very small quantity of air passes through it. The suction applied to the nozzle is quite sufficient to deliver a large percentage of fuel. Airflow
~
ww w.E
asy En gi '----=-float
Fuelfrom chamber
Throttlevalve
nee r
Figure 2.3 Choke
Air
ing .ne Air
t
Figure 2.4 Eccentric mounting of choke
Figure 2.5 Strangler in choke
In order to open the chock immediately after starting of the engine, any of the following two methods are employed.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary Systems
tIM
(i) Chock is fitted eccentrically shown in Figure 2.4. When the engine starts, the air force on the two side of the choke spindle are unequal. It produces turning moment to open the choke. (ii) A strangler valve is fitted on the choke shown in Figure 2.5. When the engine is
started, the stranger is opened against the spring pressure by the air pressure which forces to allow the entry of air in the carburetor. (c) Adjustable areajet: In this arrangement, a long tapered needle is screwed into the jet. During starting, the screw is loosened so that the area of the jet is increased to provide increased fuel shown in
ww
Figure 2.6.
Adjusting
w.E
asy E
ngi
nee rin
Figure 2.6 Adjustable areajet (d) Separate air passage: Air flow
tl~
Venturi
g.n et
Separate air passage Main
nozzle '__--~uel from float chamber
L ~_
Air
r-----~rew
Throttle valve
Figure 2.7 Separate air passage Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IN:-
Automobile
Engineering
A separate air passage is provided just below the throttle valve shown in Figure 2.7. During starting, a throttle valve is kept closed and the auxiliary passage allows the flow of air and the fuel goes through it because the whole of suction is now applied to it resulting in rich mixture. 2. Idling diffiCUlty: During idling and slow speed running, a rich mixture is needed by the engine. Although it is less rich a mixture (about 10:1) when compared to required for starting, the quantity required is more. It is done by providing a separate idle jet and an air bleed hole. With this arrangement, the metered quantity of air fuel mixture is drawn into idle passage where they form an emulsion. This mixture is then supplied through the idle port which is located on the
ww w.E
engine side of the throttle shown in Figure 2.8.
nozzle
Airflow
~~ ~
asy En gi
nee r Idlejet
ing .ne
Throttle
t
Figure 2.8 Idling circuit The idle adjustment screw is provided for controlling the volume of the mixture and hence, the idle speed is obtained. A transfer port is provided for smooth changing of idle circuit to the main nozzle circuit when the engine is accelerated from idling to main running condition. When the throttle opens slightly, the transfer port is also opened to the manifold which causes additional quantity of mixture to enter the engine. When the throttle is opened, further the idle circuit will be stopped supplying the mixture.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
-
I Engine Auxiliary Systems 3. Acceleration difficulty:
When sudden acceleration is desired, the throttle valve will be opened suddenly. It results a maximum amount of air flow with lagging of the fuel which produces lean mixture. It causes a defect of "Engine stumble or hesitation". To remove this defect, a separate pump shown in Figure 2.9 is connected through linkage to the accelerator pedal. It is used to provide the increased fuel momentarily. The fuel is forced out of the acceleration jet when the acceleration pump is pressed to open the outlet valve. When the pedal releases, the piston would move up to suck the fuel from the float chamber.
ww
Linkage connected to acceleratorpedal
w.E
asy E
'___-'--_~Fuel
Piston
Accsleratlnq pump
from float chamber
...,~
ngi
_______I,__ --_-__ --_--_-__.J..._~ __ --
-------------------
Throttle valve
nee rin
Air fuel mixture to engine
Figure 2.9 Accelerating circuit
g.n et
4. Load and speed variation difficulty or compensation system in carburetor:
As already stated, a simple carburetor would provide rich mixture at high speed and lean mixture at low speed. For maintaining the desired mixture proportions at various speeds, automation devices known as compensating devices are provided in modern carburetors. The process of providing additional air or fuel required to maintain the correct air fuel mixture is called compensation in carburetor. Automatic compensation systems are provided in latest carburetors to maintain the correct air fuel mixture at high speed. They are as follows. (i) Auxiliary or extra air valve compensation (ii) Restricted air bleed compensation
(iii) Compensating jet compensation (iv) Multiple jet compensation. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1(i); Auxiliary or extra air valve compensation:
Automobile Engineering
According to the opening of throttle valve, an extra air valve as shown in Figure 2.10 is also opened to keep the air-fuel ratio at a constant level reasonably. (ii) Restricted air bleed compensation:
Fuel from pump
Roat
ww w.E
asy En gi
nee r
Figure 2.10 Extra air valve compensation
ing .ne Fuel from pump
Float chamber
t
Throttle valve
To induction manifold
Figure 2.11 Restricted air bleed compensation
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary Systems
•••
There is a jet with many holes fitted in the carburetor in this system. The air coming from the restricted air bleed opening mixes with the fuel in the jet tube and the mixture comes out through the nozzle. At starting and low speeds. the pressure drop in the venturi is small due to the effect of viscosity and surface tension of the air fuel mixture being less than the fuel alone. More quantity of fuel flows into the venturi giving a rich mixture. But at high speeds, the pressure drop in venturi is high and hence, a lean mixture is given when the throttle is opened more. Thus, the restricted air bleed compensation provides rich mixture at starting at low speed and lean mixture at high speed. (iii) Compensatingjet compensation 0/ unrestricted air ble!d compensation: Here, there are two jets namely main jet from the float chamber and compensating jet
ww
through a vertical tube C which is opened to atmospheric air. At opening of the throttle, both jets supply the fuel to the required quantity in the venturi. For higher load and speed
w.E
conditions, the throttle valve opened to supply more fuel supply from the main jet increases
asy ttt E
and from compensating jet, it decreases and makes the mixture lean at high speed. To induction manifold
ngi
nee rin
FIQlit
ttt
g.n et
Air
Figure 2.12 Compensating jet (iv) Multiple jet compensation: As the name implies, there are three to five jets with a cap E opening different jet passages in tum as the throttle valve is opened. When the throttle valve is not operated, the fuel supply is only from the nozzle. When the throttle opening is small, the suction is applied to the cap which opens the nozzle 1. When the throttle valve is further opened, the cap will lift up. The nozzle 2 opens to supply the fuel. The nozzle 3 is-so adjusted that it gives less amount
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering
of fuel than nozzle 2. Thus, the compensation is obtained. Similarly, on further opening of the throttle valve, nozzle 4 and 5 come into action. 5. Attitude influence: With the increase of attitude, the atmospheric pressure and air density decrease. It results proportionately less air and more fuel in the mixture. This factor has much influence in hills area. Slow
running
---"r---:---n-- Bypas
ww w.E 5 Jet
E
t
asy En gi 4
3
2
._----------_. -----------------------_.
nee r
-------------
1
Float chamber
Figure 2.13 Multiple jet compensation
ing .ne
For controlling this effect as in case of Zenith carburetor, the top of the float chamber is
t
connected to the air horn by means of two extra pipes shown in Figure 2.13. A valve is provided in the pipe AB. It is kept closed for ordinary low attitudes and hence, the fuel in the float chamber is under atmospheric pressure because of pipe CD. With the increase of attitude, the valve is opened gradually to apply suction to the float chamber. It results the decreased fuel supply and decreased pressure. Therefore, a weak mixture is obtained at high attitudes. 6. Influence of weather: A simple carburetor can provide the correct air fuel mixture at a particular speed as well as for a particular weather. When a simple carburetor is set to work properly for particular summer weather, it would give a weak mixture in winter. Since the air density increases to a large extend as compared with increase in fuel density, the viscosity of fuel is also affected by
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary
*,.
Systems
variation in temperature. In the same manner, a carburetor set for winter would give too rich mixture in summer. Climatic control devices are provided in most of the modern carburetors. The mixture strength is controlled by these devices by varying the fuel jet area or the air intake.
ww w.E t t t asy E Venturi
Float chamber
Air
Figure 2.14 Attitude control
7. Icing difficulty:
ngi
nee r
When the fuel is atomized and evaporated in the carburetor for mixing it with air, the cooling of the surrounding area takes place. Due to this effect of cooling, there is a danger of
ing
ice formation and chocking of venturi tube in cold areas. To avoid this de1 ct,
.ne
(i) idle parts of the carburetor and throttle value are heated by means of exhaust gases from the engine.
t
(ii)the hot water is supplied by the engine cooling system for heating the carburetor. This water passes through the water passages provided in the carburetor body. 2.3.2. Solex Carburetor It is a down draught type of carburetor shown in Figure 2.15. It is used in Fiat, Ambassador and Willys Jeep. It is manufactured in India by MIs Carburetor Limited, Chennai. It has a special provision for a progressive starter. The various circuits for this carburetor are explained below. (1) Float circuit (2) Starting circuit
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I..
Automobile Engineering
(3) Idle and low speed circuit (4) Norrral running circuit (5) Acceleration circuit.
ww
w.E
asy E
"C ID ID
...
li 'iii
:i. c
~
ngi
~
8.
nee rin
s... ~ ::: -e
e
....~
g.n et ~
II')
.....
r.i
~ :::
.~ ~
~
a) Float circuit: The float circuit consists of a float chamber, float and a needle valve arrangement. The float is pivoted to the float chamber in a lever. The lever is attached with the needle valve. The Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary
f,.
Systems
needle valve seats on the valve seat through which the fuel comes into the float chamber. When the needle valve is opened, the fuel enters the chamber. When the fuel reaches the predetermined height, the needle valve close the passage as the float moves up. If the fuel level drops, the float will move down and the inlet is opened as the needle valve also moves down. +--
ww
w.E
Petrol inlet
----------
asy E
Aoat chamber
ngi
Figure 2.16 Float circuit
b) Starting circuit:
nee rin
Figure 2.17 shows the construction of a starting circuit. There is a starter valve in the form of a float disc with holes of different sizes. The starter valve is operated by a starter
g.n et
lever. The starter lever is connected to a lever in the dash board. At the time of starting, the starter lever is operated by the driver from dash board and the position of starter valve is adjusted in such a way that bigger holes are connecting holes. These holes connect the petrol jet and starting passage. Now, more fuel comes from a petrol jet. This petrol mixes with the air coming from the air jet and flows to the engine through starting passage. This air fuel mixture is rich enough for starting. At this time, the throttle valve is in closed position. After the engine has started, the starter lever is brought to the second position. Now, the smaller holes in the starter valve connect the passage. Therefore, less amount of petrol comes and it mixes wAh the starting air supply. In this position, the throttle valve is also partly opened so that the petrol is also coming from the main jet. This reduced mixture supply is sufficient to keep the engine running. When the engine reaches the normal running temperature, the starter is brought to 'off position.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IfmI
Automobile
Engineering
Air jet
ww
w.E
Starting port
asy E
Figure 2.17 Starting circuit
(c) Idling or low speed circuit:
ngi Air
nee rin Pilot air jet
g.n et
Idle port Idling screw
Figure 2.18 Idling circuit
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
,'.
I Engine Auxiliary Systems
ww
w.E
asy
En
Figure 2.19 Slow speed circuit
gin eer
At idling, the throttle valve is almost closed. The engine suction is applied at the pilot jet. Thisjet gets petrol from main jet circuit. The air is drawn from the pilot air jet and mixed with the petrol coming from pilot petrol jet. This mixture enters the cylinder through an idle port.
ing
During slow running period, the throttle valve is made to open slightly. The suction is also
.ne
created at slow speed openings. These slow speed openings are provided just above the throttle valve. Once, the air and fuel start to flow through the slow speed opening, the mixture supply through the idle port is stopped. (d) Normal running circuit:
t
During normal running, the throttle valve is partly opened. Now, the engine suction is applied at the main jet. The fuel is supplied through emulsion tube. There are holes in the emulsion tube at different heights. If the suction is less, the fuel comes out up to the first hole. When the suction increases, the fuel supply will come out from the first hole up to the last hole in the tube. The air enters directly through venturi and it mixes with the fuel and then it flows to the cylinder. The air-fuel mixture is governed by the throttle valve.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile Engineering
Air bleed tube
,, '_,
'----~-- Petrol from
L------r--
ww
--
float chamber
w.E
e) Acceleration circuit:
Figure 2.20 Normal running circuit
asy E
For immediate pick up of speed, the circuit will accelerate. During acceleration and
ngi
sudden throttle opening, the engine requires some extra fuel supply. The extra fuel is supplied through a separate fuel passage by the accelerator pump. Figure 2.21 shows an acceleration circuit.
nee rin
Diaphragm
g.n et
Figure 2.21 Accelerating circuit Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
f,.
I EngineAuxiliary Systems
Acceleration circuit consists of a pump chamber connected to float chamber. There is an accelerator pump in this circuit. It is a diaphragm type pump. The diaphragm is actuated by a lever. The diaphragm is held in position by a compression spring. When the lever is pressed, the diaphragm moves against the spring tension and forces the fuel through the acceleration jet. The fuel is sprayed into venturi through a curved injector tube. When the pedal is released, the diaphragm will move back and suck the fuel from float chamber through a pump inlet valve. Thus, the pump is ready for the next charge. 2.3.3. S.U. Carburetor This carburetor is an example of constant vacuum type of a carburetor. In this carburetor,
ww w.E a
the orifice area is varied to meet the varying demand of carburetor and the pressure difference is kept constant. Therefore, it is also called variable venturi carburetor. This carburetor contains only one fuel jet in which a tapered needle slides up and down.
syE
The needle is fitted to the piston which is contained in housing and moves up and down due to the difference between engine suction and atmospheric pressure. The movement of piston in
ngi
tum varies with the size of the jet through the needle movement. The up and down movements of the tapering needle cause the annular area for fuel flow to increase or decrease. Figure 2.22 shows this arrangement.
nee r
A damper plunger is placed in the hollow piston rod. Oil of suitable viscosity is filled in
ing
piston rod. The damper plunger has one-way valve in it. It regulates the rate of lift of the
.ne
piston. At the same time, it allows the piston to fall freely when throttle valve is closed. When the throttle valve is opened suddenly for acceleration, the lifting speed of the piston is retarded
t
by the damper plunger. Therefore, there is no necessity of acceleration pump in this carburetor. Similarly, there is no separate idling or slow running circuit. Since, the position of piston is adjusted automatically by engine suction as already explained. A jet adjusting nut is provided to adjust the mixture strength. When the nut is tightened, • the jet will move up thereby reducing the annular area for fuel flow. Similarly, loosening of nut lowers the jet and thus it increases the fuel flow. The underside of suction disc is opened to atmospheric pressure through the hole in the flange. The upper side of the disc is opened to the engine suction through a hole from the underside of the piston. When the engine suction is increased, the pressure difference between fupper and lower sides of the disc will increase. It causes the disc to move up. Thus, the taper needle is withdrawn from the jet due to which more fuel flows out.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
Hollow piston rod Damper plunger
ww w.E a Airtuel mixture
Air in
syE
ngi
Fuelfrom float chamoer
nee r
ing
.ne
t
Jet operating lever
Figure 2.22 S. U Carburetor When the engine is stationary, the pressure difference is same on both sides of the disc which results the piston to move down to its lowest position and close the jet through the needle. For starting purpose, the needle is kept constant to its lowest position and the jet itself is moved down from the rest by means of a jet operating lever. This lever is operated by a knob controlled by a cable attached at dash-board. When the knob is pulled, the jet moves down and the fuel flows from it to form the fuel air mixture for starting. When the knob is pushed down, Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary Systems
f••
the jet returns to its original position. S.U. carburetors are used in Ambassador and Standard Motor Cars. 2.3.4. Zenith Carburetor Zenith carburetor is quite popular with England cars and is available in different form and models. Few such models are given below. (i)
Zenith VE type carburetor
(ii) Zenith Stromberg carburetor (iii) Zenith 30 VIG II carburetor'
ww w.E a
(iv) Zenith NV type carburetor (v) Zenith DBE type carburetor (vi) Zenith WIA type carburetor etc.
syE
Instead of employing two side by side jets in other types, a compound jet consists of an inner main jet and a concentric outer jet is used in this carburetor. It is most popular due to its easy starting, slow running, better economy as well as simple to adjust and requiring no
ngi
adjustment once set. A standard model of a Zenith carburetor is shown in Figure 2.23. It is an
nee r
old type of Zenith carburetor but in modem Zenith carburetors, economy devices as well as accelerating pumps are also provided.
ing
It consists of three jets namely, main jet, compensating jet and idling jet. An outer cover
.ne
is provided for the main jet. The annular space between main jet and outer cover forms the delivery tube for compensating jet.
t
A choke is used for starting. For idling and slow speed running, a throttle valve is closed and the air enters through holes A and B which mixes with the fuel in idling passage and then the mixture passes to the idling jet. A knob is provided for idle adjustment which controls the opening of B. It affects the air intake in B and thus, the quality of mixture is controlled. When the throttle is opened slightly, some air will flow through venturi. The fuel mixture would be supplied by both main jet and slow running jet. When the throttle is opened further, the depression at the slow running jet will be destroyed. The whole of the suction is being applied at the main and compensating jets. A
irrect air fuel ratio at different speed is maintained by a compensating jet. In this carburetor, a provision is also made for collecting any sediment or dirt entering with the petrol.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I..
Automobile Engineering
Idle adjusting knob
ww w.E a Air
syE
ngi
Compensating
jet
Fuel
nee r
Figure 2.23 Zenith carburetor 2.3.5. Carter Carburetor
ing
.ne
Carter carburetor is a downdraft carburetor. It is an American make carburetor and used
t
in Jeep. Figure 2.24 shows a diagrammatic view of this carburetor. It consists of the following circuits. (i) Float circuit (ii) Starting circuit (iii) Idle and low speed circuit (iv) Part throttle circuit (v) Full throttle circuit (vi) Acceleration pump circuit.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Engine Auxiliary
Systems
Construction: The petrol enters the float chamber. The air enters the carb..sretor from the top and the choke valve in the passage remains open during normal running. This carburetor consists of three venturies. The smallest venturi i.e. primary venturi lies above the fuel leve' in the float chamber. Other, two venturi's are below the fuel level and one is below other. At very low speeds, suction in the primary venturi is adequate to draw petrol. The nozzle enters the primary venturi at an angle delivering the fuel upward against the air stream in an atomized form. The mixture from the primary venturi enters through the secondary venturi where it is surrounded by a blanket of air stream and it finally leads to mam venturi. In main venturi, again the fresh air supply insulates the stream from the second venturi. The mixture reaches
ww
the engine iIllatomized form.
w.E
Multiple venturies result the better formation of the mixture at very low speed causing steady and smooth operation at very low and also at very high speeds. Operation: (i) Float circuit:
asy E
ngi
The float chamber contains float. The inlet needle valve operated by a float controls the supply of fuel from the fuel filter into float chamber. (ii) Starting circuit:
nee rin
The choke valve of usual type is used for starting purposes. During starting, the choke
g.n et
valve is in closed position; the whole of the engine suction is applied to the main nozzle which delivers the fuel. As the air flow is quite small, the mixture supplied is very rich. (iii) Idle and low speed running:
For idling, a rich mixture of small quantity is required. During idling, a throttle valve is almost closed. The whole of the engine suction is applied to the idle port. Consequently, the petrol is drawn through the idle feed jet and air through first bypass and a rich mixture is supplied. In low speed operations, the throttle valve is opened. The main nozzle also starts supplying the fuel at this speed port through idle passage. (iv) Part throttle circuit: The throttle valve is opened further for increasing the speed. The fuel is delivered by the
main nozzle only.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
..
ww
s
a a
~
J0
~
'f
tIS
w.E .c 0
~ ::
=
1 g
l1!
u::
asy
0
~
~
En
f"'I
~
gin eer
i·
'E"~ _I::
..
Q,lGl
N
~
:: .~ ~
~.9 :.(
ing
.ne
t
(v) Full throttle circuit: I
Now, the throttle valve is fully opened. Maximum amount of air is passed through th~ venturi. The higher rate of fuel flow is required. It is achieved by means of the metering rod. Metering rod has two or more steps of diameter. The area of opening between metering rod jet and metering rod governs the amount of petrol drawn into the engine. The metering rod is connected to the accelerator pedal through linkage. When the accelerator pedal is pressed, the
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
throttle is held wide open and simultaneously,
the metering rod is lifted up. Hence, the
smallest section of the rod is injet and the maximum quantity of petrol flows out
(vi) Accelerating pump circuit: The accelerating pump is used to overcome flat spot during acceleration. The construction of pump is similar to Figure 2.21 of "acceleration difficulty" in a previous topic. When the throttle is suddenly opened by pressing accelerator pedal, a pump will be actuated and a small quantity of petrol is spurted into the choke by an acceleration jet. Leaving the accelerator pedal causes the pump piston to move up thereby sucking of fuel from the float chamber for the next operation.
ww
2.4. ELECTRONICALLY CONTROLLED GASOLINE INJECTION SYSTEM FOR 51 ENGINE
w.E
2.4.1. Limitations of Carburetor or Necessity of Petrol Fuel Injection
asy
Modem carburetors have certain limitations as given below. (i)
En
In multi cylinder 'engines, it becomes very difficult for a single carburetor to supply
gin eer
uniform quality and quantity. Since, the induction passages are of unequal lengths. (ii)
Venturi throat of the carburetor causes a restriction in the passage of air flow to the engine. If the throat is made larger for this reason, the problem of suitable mixture
ing
supply becomes acute at low speed and air velocity decreases which causes less efficient atomization.
.ne
(iii) The carburetor has many wearing parts. After wear, it operates less efficiently.
t
(iv) There is a loss of volumetric efficiency due to restricted flow of mixture in various parts such as choke tubes, jets, throttle valves, inlet pipe bends etc.
All of above limitations of carburetor may be avoided by introducing the fuel through injection rather than carburetion. The main difference between petrol and diesel injection is that the diesel is injected at the end of compression stroke only due to high pressure ratio in diesel engines whereas it may be injected at any time of suction stroke itself in petrol injection. There is no critical timing for petrol injection. 2.4.2. Types of Gasoline Injection System In a petrol injection system, the fuel is injected into the intake manifold through fuel injection valves. There are two basic gasoline injection arrangements. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
(i)
MUlti-point injection system
(ii) Monopoint injection system.
(i) Multi-pointfuel injection (MPFl) system It is also called port injection system. In this system, there is an injection valve for each engine cylinder shown in.Figure 2.25 (a). Each injection valve is placed in the intake port near the intake valve shown in Figure 2.25 (b). The main advantage of this system is that it allows more time for mixing of air and petrol. Air
ww
Equal fuel to each cylinder through injection valves
w.E
asy (a)
En Fuel
gin eer
Port Injector
ing
Figure 2.25 Multipoint or port injection system (ii) Monopoint or single-point fuel injection system:
(b)
.ne
t
Manifold Injector
Figure 2.26 Monopoint injection system Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
This system is also called throttle body injection. In this system, an injection valve is positioned slightly above each throat of the throttle body shown in Figure 2.26. The injection valve sprays fuel into the air just before it passes through the throttle valve and enters the intake manifold. This method simplifies the construction of the engine block. Also, it does not obstruct hot spots near the valves affecting cooling water jacket size at the place. Moreover, it requires only one circuit in the computer to control injection which simplifies the construction of electronic control unit. Thus, it reduces the cost of the system. 2.4.3. Working of Electronically Controlled Gasoline Injection System In electronically controlled gasoline injection system for SI engines, fuel supply and timings are controlled by electronic means. Electronic fuel injection has developed with the development of solid-state electronic devices such as diodes and transistors. Recent days, these systems are commonly used as they function quickly and respond automatically to the
ww
w.E
change in manifold air pressure, engine speed, crankshaft: angle and many other secondary factors. This system is developed by Robert Bosch Corporation. Figure 2.27 shows an electronic gasoline injection system of Bosch L-type. It consists of the following four units: (i)
asy
Fuel delivery system
(ii) Air induction system
En
(iii) Sensors and air flow control system (iv) Electronic control unit.
(i) Fuel delivery system:
gin eer
ing
.ne
The reason for using gasoline fuel injection is to control the air-fuel ratio of the engine
t
more precisely. This system consists of an electrically driven fuel pump which draws fuel from the fuel tank through filter and forces it into the pressure line. At the end of the pressure line, a fuel pressure regulator is placed. The fuel pressure regulator is connected to the intake manifold. The pressure difference between fuel pressure and manifold pressure is kept constant by this regulator so that the quantity of fuel injected is dependent only on the injection open time. In this Bosch L-type system, fuel metering is controlled by engine speed and measuring the intake air flow.
(ii) Air induction system: The incoming air fromatmospbereflows
initially through air filter and then through air
flow sensor. This air flow sensor measures the amount of air flow in the manifold and generates a voltage signal which is dependent on the amount of air flow. The air flow meter
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
consists of a rectangular
plate which turns in a rectangular
shaped channel to a defined
angular position dependent on the pressure from flowing air. It returns to original position during normal condition by using a spiral coil spring.
Ql
Fuel pressure regulator
~
Inlet
c: .... ::J
(i)
....
'ijj ::J
U.
ww w.E a
syE
Engine speed signa~"'_"":::':':"'-r....l
ngi
nee r
Figure 2.27 Electronic gasoline injection system (iii) Sensors and airflow control system:
ing
Typical sensors used in electronic gasoline injection system are as follows. (i)
.ne
Air flow sensor: A sensor senses Electronic Control Unit (ECU) how much air is being drawn into the intake manifold for adjusting the quantity of fuel.
t
(ii) Intake air temperature sensor: This sensor measures the temperature of the intake air for fine tuning the mixture strength. (iii) Exhaust gas oxygen (EGO) sensor.; A sensor located in the exhaust system which provides ECU about the amount of oxygen in exhaust gases. From this, ECU can determine if the air/fuel ratio is correct. (iv) Manifold absolute pressure (MAP) sensor: It senses the vacuum pressure in the engines inlet manifold and it gives an indication of the load to the engine. (v) Speed/crankshaft sensor: It provides the information to ECU about engine rotating speed and the position of the crankshaft.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Engine Auxiliary Systems
(vi) Engine temperature sensor: This sensor senses the temperature of the coolant in the engine. Coolant temperature is used determine if more fuel is needed when the engine is cold or warming up. (vii) Crankshaft position sensor: ECU needs to know how fast the engine's spinning ard where the crankshaft is in its rotation. ECU fires the spark and injectors at the right time. (viii)Knock sensor: The knock sensor is a microphone type sensor that detects the sounds of knocking (detonation) so that ignition timing can be retarded. A cold start valve is fitted just behind the injection valve to inject additional fuel for cold
ww w.E a
start. This valve has exceptionally good atomization characteristics. The operation of cold start valve is controlled by a thermo time switch sensor to ensure cold start up to - 33°C. The extra fuel is needed by ordinary starting and warm up period is also supplied by this valve. After cold start, the additional air required with richer air-fuel mixture is supplied by an
syE
auxiliary air valve during idling condition which by-passes the throttle valve. It is the additional idling speed. The opening of the air valve varies as a function of engine temperature.
ngi
nee r
A throttle valve switch is attached to the throttle valve. It is equipped with a set of contacts which generates a sequence of voltage signals during opening of the throttle valve.
ing
This signal results the injection of additional fuel required for acceleration through an electronic control unit.
(iv) Electronic Control Unit (ECU):
.ne
t
It is the heart of a fuel injection system. It contains a computer which takes information from sensors and controls the amount of fuel injected by operating the injectors for just the right amount of time. The unit contains a number of printed circuit boards on which a series of transistors, diodes and other electronic components are mounted. It makes vital data analysis circuits respond to various input signals. The data measured in the form of signals by various sensors such as manifold air pressure, engine speed, crank angle, oxygen in exhaust etc. are transmitted to the electronic control unit. This unit computes the air-fuel ratio required for the best performance of the engine during each engine cycle and it sends signal to the iniection-velve -and-other p1ll'tSfOf the system. The amount of fuel injected is varied by varying the injector opening time only. ECU cannot be adjusted or serviced.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Advantages: 1. A very high quality fuel distribution is obtained. Therefore, higher compression ratios can be adopted without any danger of detonation occurring. 2.' It increases the volumetric efficiency and hence, it also increases power and torque. 3. The manifold in an injection system carries only air. So, there is no problem of air and fuel separation and the design of manifold becomes simple. 4. It reduces the specific fuel consumption due to better distribution of mixture to each cylinder. S. It is free from blowbacks and icing.
ww w.E a
6. Exhaust emissions are less due to precise air-fuel ratio according to engine requirements .:
7. Better starting and acceleration are ensured than a carburetor system. Disadvantag~s:
syE
1. Initial cost is very high because of precise and complicated components of the
ngi
electronic circuit. It is the major disadvantage.
nee r
2. More complicated mechanism because of electronic system injection nozzle and fuel injection pump.
ing
3. Increased service problem occurs. 4. More noise is generated.
.ne
S. Weight and space requirement are more than a conventional carburetor.
2.5. ELECTRONIC DIESEL INJECTION SYSTEM
t
In conventional diesel injection system, a precise controlling of various parameters related to the injection process such as timing, rate of fuel injection, end of injection, quantity of fuel injected etc. is difficult if the engine is operated at high speed. It may result the reduced efficiency and higher emission levels. Conventional systems only senses a few parameters and meter the fuel quantity or adjust the injection timing. Therefore, electronically controlled diesel injection systems have been developed. This system facilitates the precise , control of the following parameters. (a) Quantity of fuel injection (b) Injection timing Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Engine Auxiliary
Systems
(c) Rate of injection during various stages of injection (d) Injection pressure (e) Speed of nozzle opening (f) Pilot injection timing and its quantity.
Electronically controlled diesel injection system may use the following parameters which can significantly affect the performance of the engine as input. (i)
Intake air mass flow rate
(ii)
Intake air temperature and pressure
ww w.E a (iii)
Engine temperature
(iv)
Lubricating oil temperature
(v)
Engine speed
(vi)
Crankshaft position
syE
(vii) Turbocharger boost pressure
(viii) Accelerator pedal position (ix)
Exhaust gas oxygen level.
ngi
nee r
2.5.1. Components of Electronic Diesel Injection System
ing
The components of electronically controlled diesel injection systems are divided into the following three main groups. )0
array of physical inputs is converted into electrical signal outputs. )0
.ne
Electronic sensors for registering operating conditions and changes. A wide
t
Actuators or solenoids which convert the control unit's electrical output signal into mechanical control movement.
)0
ECU (Electronic Control Unit) with microprocessors which process information from various sensors in accordance with programmed software and outputs required electrical signals into actuators and solenoids.
Various sensors used in electronically controlled diesel injection systems are as follows. )0
Injection pump speed sensor: It monitors pump rotational speed.
)0
Fuel rack position sensor: It monitors pump fuel rack position.
)0
Charge air pressure sensor: It measures pressure side of the turbocharger. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
~
Fuel pressure sensor: It measures fuel pressure.
» »
Engine position sensor Temperature sensors: These sensors measure various operating temperatures such as
•
Intake temperature
•
Charge air temperature
• •
Coolant temperature Fuel temperature
ww• w.E a
Exhaust temperature (Pyrometer)
•
» »
Ambient temperature
Vehicle speed sensor: It .monitors vehicle speed.
syE
Brake pedal sensor: It operates with cruise control, exhaust brake, idle control.
);. Clutch pedal sensor: It operates with cruise control, exhaust brake, idle control.
»
pedal.
»
ngi
Accelerator pedal sensor: It monitors the amount of force given to the accelerator
nee r
Injector needle movement sensor: It monitors the actual injection time and feeds the information to the ECU.
ing
.ne
Electro-magnetic actuators are usually located on the fuel pump to transfer electrical
t
signals into mechanical action. Various actuators used in electronically controlled diesel injection systems are as follows.
» » » » » »
Injectors
}Ii>
Electronic shutoff valve
»
Rail-pressure control valve.
Boost-pressure actuator Fuel rack actuator Intake-duct switch off actuator Throttle-valve actuator Exhaust-gas recirculation actuator
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I EngineAuxiliary Systems
, ..
The injection of fuel or the quantity of injected fuel has a decisive influence on engine starting, idling, power and emissions. The ECU is programmed with relevant data to where the fuel rack position has an equivalent signal for the amount of fuel being injected. The driver requests the torque or engine speed requirements via accelerator pedal potentiometer thereby sending a signal to the ECU. Depending on the data collected from various sensors ECU calculates the quantity of fuel required, thus altering the fuel rack to the required position. The road speed function can be used to evaluate vehicle speed. Further functions can include exhaust brake operation which, when activated, will result in the fuel pump rack position being set to zero delivery or idle. The engine ECU can also interface with various other vehicle systems e.g. traction control and carry out self-monitoring duties and self-
ww w.E a
diagnostic functions to keep the system working at an optimal level. There are dlfferent types of electronically controlled diesel injection systems. They are
as follows. (i)
Unit injector system
syE
(ii) Rotary distributor system
ngi
(iii) Common rail direct injection system. 2.5.2. Unit Injector System
nee r
ing
This system is also called individual pump injection system. The Unit Injector System (UIS) combines the injection nozzle and the high-pressure pump in a single assembly. One
.ne
such unit injector is fitted in the head of each engine cylinder as shown in Figure 2.28. The
t
high pressure is built up by the activation of the pump plunger of the unit injector by the engine camshaft via a tappet or rocker arm.
The basic operation can be described as a sequence of four separate phases such asfilling phase, spill phase, injection phase and pressure reduction phase. A low pressure fuel delivery pump supplies filtered diesel fuel into the cylinder head fuel ducts, and into each injector fuel port of constant stroke pump plunger injector. (i) Fill phase: The constant stroke pump element (plunger of th:epump) on the way up draws fuel from the supply duct into the chamber and the fuel line is open as long as electric solenoid valve remains de-energized.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I'··
Automobile
Engineering
(ii) SpiUphase: The plunger of the pump is on the way down, and as long as solenoid valve remains deenergized the fuel line is open and fuel flows in through into the return duct.
.1'1"
.1'1" Injection nozzles Pump with an ii .dividual cylinder for each nozzle
ww
w.E
asy E
ngi
Figure 2.28 Unit injector system
(iii)Injection phase:
nee rin
The plunger of the pump is still on the way down, the solenoid is now energized and fuel line is now closed. The fuel cannot pass back into return duct and it is compressed by the
g.n et
plunger until t~e pressure exceeds specific "opening" pressure. Then the injector nozzle needle lifts.and it allows fuel to be injected into the combustion chamber. (iv) Pressure reduction phase:
The plunger is still on its way down. The engine ECU de-energizes the solenoid when the required quantity of fuel is delivered. Due to this, the fuel valve opens and fuel can flow back into return duct causing pressure drop which in turn causes the injector nozzle needle to.shut. Hence, no more fuel is injected. Advantages: )00-
High performance for clean and powerful engines
)00-
High engine power balanced against low consumption and low engine emissions
~
High degree of efficiency due to compact design
)00-
Low noise level due to direct assembly in the engine block
)00-
Injection pressures up to 2,200 bar for the ideal combination of air-fuel mixture. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary Systems )>
(.
.
flM
The injection nozzle operates with a rapid-switching solenoid valve which is triggered electronically. It can produce a pilot injection which reduces engine noise.
Disadvantages: }>
Separate unit is required for each cylinder with actuation
}>
Unit injector system is quite compact since at all operating loads and speeds, each pump in this unit should very precisely match its companions and extremely close tolerances are required during manufacturing. Therefore, it involves high costs.
2.5.3. Rotary Distributor System
ww w.E
Figure 2.29' shows a schematic diagram of the rotary distributor system. In distributor
systems, the fuel is metered at a central point. Nozzle
asy E
ngi
nee
Distributor block ---+I
rin
g.n e
t
Cams
Primary pump
Figure 2.29 Distributor system A pump which pressurizes the fuel also meters the fuel and times the injection. The fuel pump supplies the required amount of fuel after metering it to a rotating distributor at the 'correct time for supply to each cylinder. The fuel is distributed to cylinders in a correct firing
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
order operated by poppet valves which are opened to admit the fuel to nozzles. Distributor pumps use control sleeves for metering the injected quantity. Thus, they can be easily made to work with an electronically controlled solenoid actuator.
Advantages: )i;>
Simple construction
)i;>
Low initial cost
)i;>
Easy maintenance
)i;>
Balanced cylinder fueling
ww
Disadvantages: )i;>
Overall reduced durability
)i;>
Practically suitable for small bore engines.
w.E
asy
2.5.4. Common Rail Direct Injection System (CRDI)
En
Generally, diesel engines have the specific advantage of good fuel efficiency and low
gin eer
CO2 emissions. Therefore, various new technologies have been developed in order to reduce harmful emissions. One of such technologies is called Common Rail Direct Injection (CRDI) system of direct fuel injection. In this system, commencement of combustion takes place
ing
directly into the main combustion chamber located in a cavity on the top of the piston crown. This system injects diesel five times more accurately than the normal injection system by high
.ne
response injectors with electronic control. It results the greater reduction of particulate matter
t
and NOx thereby improving the fuel efficiency and increasing its torque. So, they lead to reduce engine noise and vibration. Variouscomponents ofCRDI System are: )i;>
High Pressure Fuel Pump
)i;>
Common Fuel Rail
)i;>
Injectors
)i;>
Engine Control Unit
A common rail system consists of pressure accumulator called common rail (or in simple words, a fuel distribution pipe) which is mounted along the engine block. The rail is fed by a high pressure multi-cylinder fuel pump. .The injectors are activated by solenoid valves. Both the solenoid valves and fuel pump are electronically controlled.
Downloaded From : www.EasyEngineering.net
-----------
---
---
-------------------------------------
Downloaded From : www.EasyEngineering.net
.M
I Engine Auxiliary Systems
Fuel from fuel tank
~~~--_.---~~h~p~~ pump and filter
ww w.E a
Multlcyllnder fuel pump
Figure 2.30 Common rail direct injection system
In the common rail injection system, the injection pressure does not depend on engine
syE
speed and load. So, the control of injection parameters is easy. Usually, a pilot injection is introduced in order to reduce engine noise and NOx emissions. The injectors use a needle-and
ngi
seat- type valve to control the fuel flow. The fuel pressure is fed to both top and bottom of the needle valve. The pressure on the bottom will push the needle off its seat by bleeding some of-
nee r
the pressure off the top. Thus, the fuel will flow through nozzle holes.
A.dvantages:
ing
(i)
It delivers 25010 more power and torque than the normal direct injection engine.
(ii)
Initial cost is low.
(iii)
Superior pick up is possible.
(iv)
It maintains lower levels of noise and vibration.
(v)
Higher mileage is obtained.
(vi)
Emissions are low.
(vii)
Fuel consumption is less.
(viii)
Improved performance is obtained.
.ne
t
Disadvantages: (i) (ii) (iii)
Many parts involve the complicated design. Production cost is high. High degree of engine maintenance is required.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
12.6. IGNITION SYSTEM
Automobile Engineering
This system is a part of the electrical system which carries the electric current to the spark plug where the spark necessary to ignite the fuel-air mixture in the combustion chamber is produced. This system supplies high-voltage of current (as much as 20000 Volts) to produce spark at the spark plug. The spark is provided at the exact time in various cylinders according to the firing order of the engine. There are different types of ignition systems used in petrol engines. They are as follows. 1. Coil ignition system or battery ignition system
ww
2. Magneto ignition system
w.E
3. Electronic ignition system and
4. Transistorised ignition system.
asy
En
2.6.1. Battery Ignition System or Coil Ignition System
It is employed in petrol engines. Figure 2.31 shows the wiring diagram of a simple coil
gin eer
ignition system of a four cylinder engine. This system is used in automobiles. Construction:
ing
It consists of a battery, ignition coil, condenser, contact breaker, distributor and spark plugs as shown in Figure 2.32. Generally, 6 or 12 volts battery is used. The ignition coil
.ne
consists of two windings primary and secondary. The primary winding consists of thick wire
t
with less number of turns. The primary winding is formed of 200-300 turns of thick wire of #20-gage to produce a resistance of about 1.5 ohms. The secondary winding located inside the primary winding consists of 21,000 turns of thin enameled wire of #38-40 gages with sufficiently insulated to withstand high voltage. It is wound closer to the core with one end connected to the secondary terminal and the other end is wound either to the metal case or the primary coil. The secondary winding consists of more number of turns of thin wire. The condenser is connected across the contact breaker. It prevents excess arcing and pitting of contact breaker points. The contact breaker is housed in the distributor itself. It makes and breaks the primary ignition circuit. The distributor distributes the high voltage to the respective spark plugs having regular intervals in the sequence of firing order of the engine. (The sequence in which the firing or power occurs in a multi cylinder engine is known esfiringorder. The firing order Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I
Il!ngln. Auxiliary Sy~tems _ of I 4-cylinder in-line engine is 1-3-4-2 or 1-4-3-2. The firing order of a 6-cylinder in-line
~tigh1"I. 1~S·3-6-2-4). The spark plug is fitted on the combustion chamber of the engine. It produces spark to ignite the fuel-air mixture. The rotor of the distributor and contact breaker cam are driven by the engine. There are two circuits in this system. One is the primary circuit. It goo.ists of battery, primary coil of the ignition coil, condenser and contact breaker. The other circuit i8 the secondary circuit. It consists of secondary coil, distributor and spark plugs. .-------~To
ww w.E
distributor
Primarywinding
asy E
Secondarywinding
ngi
Figure 2.31
Working:
nee
The ignition switch is switched on and the engine is cranked. The cranking of the engine opens and closes the contact breaker points through a cam.
rin
Spark plugs
g.n e
t
istributor
Condenser
Figure 2.32 Battery ignition system
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
leg
Automobile Engineering
Wizenthe contact breaker points are closed: 1. The current flows from the battery to the contact breaker points through the switch and primary winding and then it returns to a battery through the earth. 2. This current builds up a magnetic field in the primary winding of the ignition coil. 3. When the primary current is at the highest peak, the contact breaker points will be opened by the cam. When the contact breaker points are opened: 1. The magnetic field sets up in the primary winding which is suddenly collapsed.
ww
2. A high voltage (15000 volts) is generated in the secondary winding of the ignition coil.
w.E
3. This high voltage is directed to the rotor of the distributor.
asy
4. The rotor directs this high voltage to the individual spark plugs in the sequence of the firing order of the engine.
En
5. This high voltage tries to 'cross the spark plug gap (0.45 to 0.6mm) and the spark is produced. This spark ignites the fuel-air mixture. Advantages: (i)
gin eer
ing
It provides better sparks at low speeds of the engine during starting and idling due
to availability of maximum current throughout the engine speed range.
.ne
(ii)
The initial cost is low as compared with magneto ignition system.
(iii)
The maintenance cost is negligible except battery.
(iv)
Spark efficiency remains unaffected by various positions of the timing control
t
mechanism. Disadvantages: (i)
Frequent battery down occurs when the engine is not in use continuously. It causes a starting trouble.
(ii)
The weight is greater than magneto ignition system.
(iii)
Wiring mechanism is more complicated.
2.6.2. Magneto Ignition System In this system, the battery is replaced with a magneto. Figure 2.33 shows the wiring diagram of a magneto ignition system. It consists of a switch, magneto, contact breaker, Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
condenser, distributor and spark plugs. This system is used in two wheelers such as motor cycles, scooters etc. Spark plugs Rotating ~nat assemblY
ww w.E
asy E
ngi
Condenser
Figure 2.33 Magneto ignition system
Construction:
nee
rin
The magneto ignition system consists of a rotating magnet assembly driven by an engine
g.n e
and a fixed armature. The armature consists of primary and secondary windings. The primary circuit consists of a primary winding, condenser and contact breaker. The secondary circuit consists of a secondary windings, distributor and spark plugs. When the contact breaker points are closed:
t
1. The current flows in the primary circuit. 2. It produces a magnetic field in the primary winding. 3. When the primary current is at the highest peak, the contact breaker points will be opened by the cam. When the contact breaker points are opened: 1. There is a break in the primary circuit. 2. The magnetic field in the primary winding is suddenly collapsed. 3. A high voltage (15000 volts) is generated in the secondary win~ng.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
If,.
Automobll. Engii!_'f1n, _]
4. This high voltage is distributed to the respective spark plugs through the rotor oftht distributor. 5. The high voltage tries to cross the spark plug gap and a spark is produced in the gap. This spark ignites the fuel-air mixture in the engine cylinder.
Advantages: (i)
It has no maintenance problem similar to a coil ignition (i.e. for battery). So, it is more reliable.
(ii)
When the speed increases, it provides better intensity pf spark and thue, It provides better combustion as compared to battery coil ignition system.
ww w.E a (iii)
Less space is required as compared to battery ignition system.
(iv)
It is light in weight and compact in size.
Disadvantages: (i) (ii)
Initial cost is very high as compared with coil ignition system. Minimum 75rpm is necessary to start the engine.
(iii)
For higher power engines, some other devices are necessary to start ignition.
syE
ngi
Comparison of the magneto and coil ignition system: 1. Simplicity:
nee r
A coil ignition system requires a greater attention against possible defects b'CfW$O tho
ing
wiring is quite complicated. On the other hand, the wiring of a magneto ignition IYlttm hi comparatively simple and it forms a compact unit. 2. Cost:
.ne
Due to less precision work, the manufacturing cost in coil ignition system is leSi magneto ignition.
t
than In
3. Starting and low speed operation: At the time of starting and low speeds, the strength of the spark in magneto ignition hi low while a good spark is given by the coil ignition. 4. Strength of spark at high speeds: With the increase in speed, the strength of spark given by the magneto ignition system increases but it decreases in th~ case of coil system as shown in Figure 2.34. Therefore, it Iii unsuitable for high speed racing cars and airplanes.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary Systems
fiil
1
system Coil ignition
system
Speed (R.P.M.)
ww w.E
Figure 2.34
5. Dependence on battery and charging dynamo: The operation of the coil ignition system is greatly influenced by the condition of the
asy E
battery and charging dynamo. If a car stands for a few weeks and its battery gets discharged, it becomes difficult to start the engine even by hand cranking. But, there is no such difficulty experienced in magneto ignition system which is more reliable. 2.6.3. Electronic Ignition System
ngi
nee
rin
There are some drawbacks in above discussed magneto ignition system. Firstly, the contact breaker points will wear out or burn when it is operated with heavy current. Secondly,
g.n e
the contact breaker is only a mechanical device which cannot operate precisely at high speed due to the dwell period which is not sufficient for building up the magnetic. field to its full
t
value at that particular speed. The conventional contact breaker can give satisfactory performance only about 400 "Parksper second which limits the engine speed. At low speeds, relatively high current is drawn from the battery due to the contacts remaining closed for longer time. Thus, the system becomes inefficient at low speeds. The disadvantages of the convention COil~RCt breaker assisted ignition system can be completely eliminated by the use of electronic controlled ignition system using contactless triggers to give timing system. The basic difference between contact point' and electronic ignition systems is in the primary circuit. In the contact breaker system, the primary circuit is opened and closed by the electronic control unit shown in Figure 2.35. The secondary circuits are practically similar to previous systems.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Ignition switch
To spark plugs
Distributor (8) Contact point Ignition system Ignition switch
ww w.E a
syE
ArmatlJr.
(b) Electronic Ignition system
ngi
Figure 2.35 Difference between contact point and electronic Ignition ',Ntllm
nee r
In the secondary circuit, the distributor, ignition coil and wiring are altered to handl~ tho higher voltage that the electronic ignition system produces. The high voltage (about
ing
47,OOOvolts)has the advantage that the spark plugs with wider gaps can be used. It
rOll't,. ,.
longer spark which can ignite lean air-fuel mixture. As a result, engines can run on 10M mixture for better fuel economy. Construction:
.ne
t
A schematic diagram of an electronic ignition system is shown in Figure 2.36. It conlijliits of a battery, ignition switch, electronic control unit, magnetic pick-up, reluctor or
armature,
ignition coil, distributor and spark plugs. The construction of battery, ignition switch. ignition coil, distributor and spark plug is similar to previous methods. In this system, a magnetic pickup is used instead of contact breaks points in a conventional system. Also a cam iii replaced by a reluctor or armature. The magnetic pick-up is shown in Figure 2.37. It consists of a sensor coil through which the magnetic flux is generated by a permanent magnet. A star shaped rotor called reluctor or armature is mounted on the distributor shaft which modulates the flux density in the coil and induced voltage in the coil due to the consequent changes in the flux. This voltage serves as a
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Engine Auxiliary Systems
. . ..
•
trigger signal for the high voltage generator circuit. Since there is one spark plug per cylinder, the number of teeth of armature is equal to the number of engine cylinders.
Electronic control unit
. Ignition switch
ww w.E
asy E
Reluctor or armature
ngi
Figure 2.36 Electronic ignition system Reluctoror
nee
Sensor coil
Permanent magnet
rin
To electronic control unit
g.n e
t
Figure 2.37 Magnetic pickup control unit Working: When the ignition switch is closed (i.e. switch is 'ON' .), the reluctor rotates which makes the teeth of the reluctor cone closer to the permanent magnet. It reduces the air gap between reluctor tooth and sensor coil. Thus, the reluctor provides a path for the magnetic lines from the magnet. The magnetic field is passed on to the pick up every time when the reluctor teeth pass the pickup coil in which an electric pulse is generated. This small current then triggers the electronic control unit which stops the flow of battery current to the ignition coil. The magnetic field in the primary winding collapses and the high voltage is generated: in the secondary winding. It led to spark in a spark plug via distributor. Meanwhile, the reluctor Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering -,teeth pass past the pickup coil. Therefore, the pulse unit is ended. It causes the electronic
control unit to close the primary circuit. Advantages: 1. The parts such as reluctor, magnetic pickup and electronic control module are not subjected to wear as in case of a mechanical contact breaker. 2. Periodic adjustment of engine timing is not necessary. 3. It gives very accurate control oftiming. 2.6.4. Transistorised Ignition System
ww w.E a
A transistor interrupts a relatively high current carrying circuit, i.e, it controls high current in the collector circuit with less current in the base circuit. Therefore, a transistor is used to assist the work of a contact breaker. Hence, this system is known as Transistor-
assisted ignition system or transistorized ignition system. Construction:
syE
It consists of battery, ignition switch, transistor, collector, emitter, ballast resistor, contact
ngi
breaker, ignition coil. distributor and spark plugs. The emitter of the transistor is connected to the ignition coil through a ballast resistor. A collector is connected to the battery.
nee r
Working: The cam in th~ distributor is rotated by the engine. It opens and closes the contact breaker
ing
points.
Wh(l" ,h(l contact breaker points are closed: 1. J\ small CU11'ent flows in the base circuit of the transistor.
.ne
t
2, A large current flows in the emitter or collector circuit of the transistor and the primary winding of the Ignition coil due to the normal transistor action. 3. A magnetic field is aet tlp in the primary winding of the coil.
JYh~n'he ca,,'act breaker poln~ "re opent
1. The current flow in the base circuit is stopped. 2. The primary current and the magnetic field in the coil collapse suddenly due to immediate reverting of the transistor to the non-conductive state. 3. It produces a high voltage in the secondary circuit.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
r ~ngine
Auxiliary
Systems
.
Uti I
.
4. This high voltage is directed to the respective spark pjug~through tho rotor of the distributor. 5. This high voltage produces a spark when it is tried to jump the spark plug gap. It ignites air-fuel mixture in the cylinder. Ignition coil
~
I€mifipA
w1w w.E sw~cI1
..::::.:.Sattery
asy E Capacitor
ngi
4dv(m'(#fI(J~;
J~
n inpre~~s the life of contact breaker points.
2. It gives higher ignition voltage.
3. It gives longer duration of spark.
nee
rin
g.n e
~: It hll~VllJ1l~~~J.m~t~ control pfHrnillg·
t
~: n n~~9~less maintenance. 1J~(#f/y(#n'41Jf!S;
I: Mpr~ mpcj1~ni~alpoints are needed similar to a conventional system. ~: It has a tendency to side tracking.
'.1,1.
Capacitive Discharge Ignition System
t)apacitive discharge ignition (CD!) is most widely used today on automotive and marine engines. A CD! module has capacitor storage of its own as shown in Ftgure 2.39 and it sends a short high voltage (about 250+ volts) pulse through the coil. The coil now acts similar to a Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering
1
transformer and it multiplies this voltage even higher. Mod~rn COl coils step up the voltage ':b~i1t"lho:1. So, a typical 250V COl module output is stepped up to over 25,000V output from the coil. Diode Excitor
i
Diode
COII+
@
Capacitor
s
'9nition Stop Switch-
N
ww
w.E
asy
Figure 2.39 Capacitive discharge ignition system
En
The huge advantage of COl is the higher coil output and hotter spark. The spark duration
gin eer
is much shorter (about 10-12 microseconds) and accurate. It is better at high RPM but it can be a problem for both starting period and lean mixture or high compression situations. COl systems can use low resistance coils. 2.6.6. Distributoriess Ignition System
ing
.ne
An ignition system does not use a distributor to route high voltage to spark plugs called
t
Distrtbiaorless Ignition System (DIS). This system is also called as Direct Ignition System (DIS).The high voltage plug wire runs directly from the ignition coil to the spark plug. The spark timing is controlled by an Ignition Control Unit (ICU) and Engine Control Unit (ECU). Some DIS systems have one coil for every two spark plugs (a shared system) while others has a separate coil for each spark plug. EI~minatingthe distributor makes the system more reliable and it eliminates maintenance. This system uses either a magnetic crankshaft sensor, camshaft position sensor or both to determine crankshaft position and engine speed. This signal is sent to the ignition control module or engine control module which then energizes the appropriate coil.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Engine Auxiliary
Systems
Ignition module Engine control module
1/1
C)
"5
0-
-t: (\1 c.
Magnetic trigger
Magnetic pick-up
ww w.E
(/)
®
Figure 2.40 Distributorless ignition system
The advantages DIS are as follows. 1. No timing adjustments are required.
asy E
2. No distributor cap and rotor are required.
3. There are no moving parts to wear out. 4. Less maintenance is required.
ngi
nee
5. It does not need a distributor which accumulates moisture and cause starting problems.
rin
6. It does not require a distributor to drive thus providing less engine drag. 2.7. SUPERCHARGING
g.n e
t
An engine may not produce the same power output when it is operated at different locations and altitudes. It is due to variation in ambient!conditions. Supercharging and turbo charging are used to overcome this problem.
Supercharging is the process of supplying the air fuel mixture to the engine just above the atmosphere pressure. A supercharger increases the pressure of the air fuel mixture from the carburetor before it enters the engine. Supercharger is a pressure boosting device which supplies air in a diesel engine or air-fuel mixture in a petrol engine at high pressure. 2.7.1. Types of Supercharging Methods Superchargers are broadly classified into the following types according to the method of gas transfer.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
1. Positive displacement type: Positive displacement bloMts afid compressors deliver at constant level of press¥e increase at all engine .peeds (RPM). Major types of positive-displacement pumps include roots blower, twin-screw, sliding vane and scroll-type superchargers. 2. Dynamic compressors type: Dynamic compressors do not deliver pressure at low speed and above a threshold speed, the pressure increases with engine speed. Dynamic compressors rely on accelerating the aif f6 high speed and then exchanging its velocity for the increase in pressure by diffusing or slowing it down. Major types of dynamic compressor are centrifugal and multi-stage axial-
ww
flow. The following are the most commonly used superchargers.
w.E
a) Centrifugal type supercharging: Centrifugal supercharging compresses the air inside the case of the supercharger using an impeller. Then, it discharges the air out of a scroll to the motor. This design is similar to
asy
turbo-charging except for centrifugal superchargers which do not use the exhaust to build pressure. They use a belt driven by the crank pulley to spin the impeller. The ability to change
En
gin eer
the impeller sizes and spin the impeller at different speeds creates a more inexpensive way to have flexibility.
Casing Impeller
Delivery pipe
ing
.ne
t
Figure 2.41 Centrifugal type supercharging
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary Systems
'ijl
b) Roots type supercharging:
The roots type supercharger is the first style supercharger and it can be dated back to the 18808when the Roots brothers designed it as an air conveyor for mine shafts. Roots blowers act similar to air pumps (not compressors) and in general, roots blowers have a two or three lobe rotor design depending on the size of the case. Roots blowers will give the positive pressure to the motor from just a crack of the throttle and it will give the pressure at full throttle irrespective of the rpm of the motor. Roots blowers are also extremely reliable and they require very little maintenance which is why Ford, GM, Mercedes, Jaguar and Austin Martin have all featured Roots blowers as original equipment on select high performance vehicles.
ww w.E
asy E
ngi
nee
Figure 2.42 Roots type supercharging c) Screw type supercharging:
rin
g.n e
Screw type superchargers are derived from roots type concept but with vast
t
improvements for street use. Although from the outside, screw type superchargers may look more similar to roots type superchargers, on the inside, it pas a twin-screw design that compresses air unlike roots type superchargers which pump the ,air into the motor. Screw type superchargers have an axial-flow design that compresses the air as it moves between screws to create the posi~ive pressure without creating the heat which roots type superchargers can create. The screw type supercharger has the ability to produce a dramatic increased power from idle and throughout the rest of the power curve make them a great choice for heavy vehicles, towing or commercial use. Modifications required on engines supercharging:
The following modifications make the engine more suitable for supercharging: (i)
Increase the valve overlap period to permit complete scavenging of the clearance volume. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
If.,. (ii)
Automobile
Engineer/ng~
Increase the clearance volume by decreasing the compression ratio.
(iii) The injection system of I ditsel englne must be modified to supply the increased amount of fuel. It is achleved by jjffi'Virlinggreater area in nozzle than normally aspirated engines. (iv)
In case of a turbocharged engine, the exhaust valve should open a bit earlier in order to supply more energy to the turbocharger.
(v)
For normally aspired engine, the exhaust manifold is water-cooled. But, the exhaust manifold of turbocharged engine is insulated to reduce the heat loss.
ww
Air out
w.E
Helical screw rotor
asy
En
Gears
gin eer
ing
Air in
Figure 2.43 Screw type supercharging
.ne
t
2.8. TURBO CHARGERS Generally, a centrifugal or axial flow or displacement type supercharger which is driven by the engine crankshaft is used in Ie engines. Some superchargers are driven by a gas turbine which is driven by using engine exhaust gases. This type of supercharger is called turbocharger. This arrangement facilitates the utilization, of exhaust gas energy and hence avoiding the utilization of engine Plowerto run supercharger.
Purpose of turbocharger: I. To reduce the weight per horse power ofthe engine as required in aero engines. 2. To reduce the space occupied by the engine as required in marine engines.
Downloaded From : www.EasyEngineering.net
14.
Downloaded From : www.EasyEngineering.net
.1
I Engine Auxiliary Systems
3. To have better turbulence and it ensures more complete combustion giving greater power and low specific fuel consumption. 4. To improve volumetric efficiency of the engine at high altitudes, as in aero engines, and at high speeds as in racing cars. 5. To maintain the power of a reciprocating
Ie engines even at high altitudes where less
oxygen is available for combustion.
Principle of working of a turbocharger: Figure 2.44 shows a turbocharger driven by engine exhaust gas. A turbocharger is driven by a gas turbine. Exhaust gas from the engine flows along the exhaust manifold and through
ww w.E
nozzle box assembly and it enters into the blades of the gas turbine where the mechanical work is done by the gas turbine. Exhaust to gas turbine
Compressed air
asy E
ngi
Engine
Atmospheric air
nee
rin
Exhaust to atmosphere
g.n e
t
FiglU'e 2.44 Exhaust gas driven turbocharger The wheel of the gas turbine and the impeller of the supercharger are mounted on one common shaft. Thus, the supercharger compresses the atmospheric air in case of diesel engines or air fuel mixture in case of petrol engines and it enters the engine cylinder. By using a turbocharger, the engine fuel economy is improved by the use of the kinetic energy of exhaust gases. The turbocharger o~tput can be controlled for its optimum performance by introducing by-pass passage and disc valve on both inlet and outlet passages shown in Figure 2.45.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
..... .....Airin
~-----.l"'"
Bypass ...J.....Gassesfrom engine
'-
ww
Figure 2.45 Control of turbocharger output
w.E
2.8.1. Methods of Turbocharging Turbocharging is carried out in six methods such as
asy
1. Constant pressure turbocharging
2. Pulse turbocharging
En
3. Pulse converter turbocharging 4. Two-stage turbocharging
5. Miller turbocharging 6. Hyperbar turbocharging.
gin eer
ing
1. Constant pressure turbocharging:
.ne
The discharge or exhaust of all cylinders is connected to a common manifold which are
t
maintained at higher pressure than atmospheric pressure. Usually, the exhaust gas expands in exhaust valves without doing work at constant pressure process connected to a common manifold. Then it enters the turbine. So, the internal energy in the form of blow energy is converted into useful work in the turbine. If higher is the pressure ratio in the turbine maintained, the greater will be the recovery of blow-down energy. 2. Pulse turbocharging: A part of blow-down energy is converted into exhaust pulses immediately when the exhaust valves open. These pulses enter into the turbine where more energy is recovered. Dissimilar to constant pressure turbocharging, the exhaust of all cylinders does not hinder with each other due to the use of separate exhaust pipe for each cylinder.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Engine Auxiliary
Systems
3. Pulse converter turbocharging: /
This method of turbocharging combines the advantages of both pulse turbocharging and constant pressure turbocharging. It is achieved by connecting the various branches of manifolds together. Then it is connected with a specially designed venturi junction called pulse converter. It is done before the turbine. 4. Two-stage turbocharger: If two turbochargers of variou~ sizes are connected in series, it is known as two-stage turbocharger. Among these two turbochargers, a high pressure turbocharger is operated on pulse mode and a low pressure stage,on constant pressure mode. This type of turbocharging is mainly used in diesel engines which require high degree of supercharging. ~
ww w.E
Alillerturbochar,ging:
Miller system increases the expansion ratio relative to compression ratio in such a way to early closure of inlet valve when the boost pressure is increased. This mehtod is not popular due to frequent exhaust valve failures. 6. Hyper turbocharglng:
asy E
ngi
Power output
nee
,...------1 Dieselenginet----.,
By-pass control t-----I
Combustion chamber
rin
g.n e
t
Figure 2.46 Hyper turbocharging This type of turbocharging consists of diesel engine, turbine, by-pass control and auxiliary combustion chamber. In a diesel engine, low compression is obtained and high presusre ratio Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1*11•
Automobile Engineering
is maintained in turbine. The auillary combustion chamber is placed between drect exhaust valve and turbine. First, the turbocharger is started using an electrical starter. It is running by passing air. Then-it-is-injected into the auxiliary combustion chamber when the engine is idle condition. The amount of by passed and fuel injection are controlled according to the operating conditions. After reaching sufficient pressure and temperature, the diesel engine is started. Advantages: (i) It provides high power-to-weight ratio. (ii) High brake mean effective pressure can be obtained.
ww w.E
(iii) Thermal loading is moderate. (iv) Surge pre-operation is possible by using a by pass control. (v) Good torque and accerlaertion can be achieved. Disadvantages:
asy E
(i)
Fuel consumption increase throughout the operation due to low compression ratio.
(ii)
System is more complex.
LimiUltUlnsof turbocharging:
ngi
nee
0)
Special exhaust manifolds are required for the turbocharging system.
(ii)
In order to inject more fuel per unit time, fuel injection needs modification.
rin
g.n e
(iii) In contrast to a naturally aspired engine which can digest solid particles in the inlet air without undue stress, a turbocharged engine can pass only the minutest material particles without damage. (j\{)
t
It is difficult to obtain good efficiency over a wide range of operations since the efficiency of the turbine blades is sensitive to gas velocity.
(v)
Turbochargers are costly and add complexity. Adding a turbo can often cause a cascade of other engine modifications to cope with the increased power such as exhaust manifold, intercooler, gauges, plumbing, lubrication and pistons.
2.9. ENGINE EMISSION AND ITS CONTROL
Emission control is a term frequently used in day-to-day life among automobile and other manufacturing industries throughout the world. The awareness among the public about climate change and greenhouse effect due to environmental pollution, over the last century has
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Engine Auxiliary
Systems
made the government and industrial corporate throughout the world, highly conscious about the control of emissions from their products. Presently, automobile engine emissions are one of the main elements which playa major role in environmental pollution. Day-by-day the number of vehicles increases which leads to increase the emission of pollutants from vehicles. I.C. engines convert heat energy into mechanical energy by burning fuel in its combustion chamber called cylinder. Mostly, petrol and diesel oil are used as fuels for I.C. engines. These fuels contain hydrogen and carbon in various combinations. During combustion, oxygen combines with hydrogen and carbon to form water (H20), carbon monoxide (CO) and carbon dioxide (C02). The fuel of the nitrogen in air combines with oxygen forming nitrogen oxide (N02). Remaining fuel goes unburnt by resulting smoke and
ww w.E
ash. Mainly incomplete combustion offuels in automobile emits polluted engine exhaust. Exhaust gas constituents consist of partly burnt petrol, carbon monoxide, nitrogen oxides
asy E
and if sulphur in petrol and sulphur oxides pollute the air. The oxides of nitrogen together with hydrocarbons react in the presence of sunlight and they form petrochemical smog. As a result, smog is created, the atmosphere becomes dirty and breathing becomes difficult. Its bad
ngi
effect includes crop damage, eye irritation, objectionable odour, decrease of visibility, cracking in rubber etc.
nee
rin
Smog is a kind of fog mixed with other substances. The smog covers the cities like a blanket for days together during winter. The heat generated in large cities tends to circulate air
g.n e
within a dome-like shape. Smog with smoke is the most visible evidence of air pollution.
t
Some of the atmospheric pollutants are not visible until mixed with moisture. Unburnt petrol, carbon monoxide, leaded compounds from leaded petrol and other gases which pollute the air may not be seen. All these pollutants are deadly harmful for men, animals and food crops. Men inhale nearly 15 kg of air per day. If these pollutants are added to the air, it gives harmful effects to men such as asthma, eczema, emphysema, cardiovascular troubles, lung and stomach cancer. 2.9.1. Automobile
Engine Pollutants
Pollutants are produced by the incomplete combustion of the air-fuel mixture in the combustion chamber of the automobile engines. The following pollutants are emitted from the exhaust of the automobile engine. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
1) Carbon monoxide (CO): CO is mostly produced under rich air fuel mixture due to the lack of sufficient oxygen for the combustion of the fuel. CO has more affinity than oxygen for hemoglobin in our blood. It reduces the ability of hemoglobin to carry O2 to body tissues. Hence, it will affect the nervous system and vision if the percentage of CO is more. Finally, it affects heart. 1) Carbon Dioxide (COl):
During complete combustion, the hydrocarbons in the fuel are converted into carbon dioxide which is 13.7% of exhaust gas. The amount of carbon dioxide in the exhaust gas is directly proportional to the fuel consumption.
ww w.E
3) Oxides of nitrogen (NOx): NOx is produced from secondary reactions which occur in all combustion processes where air containing nitrogen is burned. In high temperatures, nitrogen reacts with oxygen and
asy E
produces nitric oxide (NO) and nitrogen dioxide (N02)' They affect living organisms. They affect the blood purification system. It may be mixed with moisture. It may also produce dilute nitric acid in the heart and affect the heart. 4) Hydrocarbons:
ngi
nee
Hydrocarbon (HC) emissions are also the result of inadequate amount of oxygen being present to support the complete combustion of the air fuel mixture. Hydrocarbon produces
rin
smog. It affects the vision of human being. Smog is the mixture of fog and smoke. 5) Water:
g.n e
The chemical reaction which occurs between hydro carbons based on fuel and air from
t
the atmosphere causeS water to be produced as one of the products. Water constitutes 13.1% of exhaust gas from an IC engine. 6) Photo chemical smog: Some hydrocarbons and oxides of nitrogen in exhaust react with at_mosphericair in the presence of sunlight and produce photochemical smog. It damages the plant's life. It reduces the visibility. It produces eye irritation and affects the respiratory system of human beings. 7)Smoke: Smoke is produced because of insufficient mixing of fuel and air. It contains CO and CO2• When cold starting, blue white smoke is produced when more carbon particles are mixed with exhaust. Smog is produced by smoke. It causes irritation of eyes, coughing, headache and vomiting. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary Systems
Ii.
8) Lead: Lead is poisonous. It is a toxic air pollutant. It is produced from the combustion of gasoline. It affects liver and kidneys. It causes mental effects to children. 9) Particulate:
Particulates are minute separate particles found in the air. They may be solid or liquid particles. The dust soot and fly ash are included in it. It causes respiratory diseases such as bronchitis and lung cancer and allergic diseases. 10) Sulphur oxide: Sulphur oxide is produced if the fuel has sulphur. It may damage the plants. It causes
ww w.E
irritation to eye and throat and it gives respiratory troubles to children. It corrodes materials. 2.9.2. Diesel Engine Emission A well-maintained diesel engine emits a negligible amount of carbon monoxide and
asy E
hydrocarbons, though considerable amount of nitrogen oxides are emitted. Diesel smoke is another pollutant in case of diesel engines. The diesel smokes are of two types. They are
ngi
(I) white smoke and (2) black smoke. The white smoke normally arises due to: (i)
very low operating temperature
nee
(ii) very long delay between start of fuel injection and beginning of combustion.
rin
White smoke appears during starting and warming up. The black smoke appears after the
g.n e
engine has fully warmed up and accelerating or pulling under load. The black smoke is a suspending of soot particles in exhaust gases. It results from incomplete combustion of fuel.
t
Blue smoke occurs due to excessive lubricating oil consumption. Its emission indicates a very poor condition of the engine such as worn-out piston rings or valve guide etc. The blue smoke is not considered as a serious pollution. 2.9.3. 51Engine Emission There are three main sources of air pollution due to petrol engine. I.
Evaporative emission
2.
Crankcase blow-by, and
3.
Exhaust emission.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1. Evaporative
emission:
Evaporative emission takes place from the fuel supply system. The main reason of hydrocarbon evaporation is high temperature. Fuel volatility, locations of tank, layer of fuel line and mode of operation also affect the evaporation. About 30% of the total hydrocarbon emission is occurring from the fuel tank, fuel line and carburetor.
2. Crankcase blow-by: Crank case blow-by means the leakage past the piston and piston rings trom the cylinder to the crank case. In blow-by gases, there are 85% or raw hydrocarbons (HC) and rest 15% of the current gases. It is about 20% of the total hydrocarbon emission from the engine and it may be 30% of rings worn out. The blow-by gases are controlled by the crankcase ventilation system.
ww w.E
3. Exhaust emission:
The exhaust emission contains HC, CO and N02. HC occurs in exhaust gas due to incomplete combustion. The emission of HC is closely related to many designing and operating factors such as induction system, combustion chamber design, air fuel ratio, speed, load and mode of operation. Lean mixture gives lower HC emission.
asy E
ngi
nee
CO occurs due to insufficient amount of air in the air fuel mixture or insufficient time for complete combustion.
rin
The combination of nitric oxide (NO) and nitrogen dioxide (N02) (called
axtde« oj
g.n e
nitrogen NOx) occurs only in the engine exhaust. High temperatures and avaiiabiUty of oxygen are the two main reasons for the formation of N02. The spark advance and air-fuel ratio are the two important factors which affect the formation ofN02•
t
2.9.4. Pollution Control The pollution may be controlled by the following two ways. I. The formation of pollutants is prevented as far as possible. 2. The pollutants are destroyed after they are formed.
Control of hydrocarbon: Formation of hydrocarbon may be reduced by the following methods. 1. Reducing the compression ratio. 2. Changing the design of combustion chamber.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
fj,_
I Engine Auxiliary Systems 3. Changing the design of piston. 4. By supplying lean mixture. S. By maintaining of piston and piston ring. Destroying the hydrocarbon may be done by the following methods. I. By supplying air to the inlet manifold. 2. By using after burner. 3. By using catalytic converter. Control of
co:
ww
Methods of reducing CO are as follows.
t. By using closed loop control.
w.E
2. By supplying lean mixture.
asy E
3. By providing suitable overlap of valves. Methods of destroying CO are given below.
ngi
1. By using reactor in the exhaust manifold. 2. By using after burner. 3. By using catalyst converter.
nee rin
Control of oxides of nitrogen:
Methods of reducing oxides of nitrogen are listed below.
1. By supplying the exhaust again to the inlet manifold.
g.n et
2. By spraying water in the inlet manifold to add moisture to the mixture.
3. By using catalyst converter in the exhaust, the oxides of nitrogen can be destroyed. Control of smoke and smog: Methods of reducing smoke and smog are given below. 1. Running the engine with a limited load. 2. Maintaining the engine well. 3. By adding barium salt in the fuel. 4. By using a catalyst muffier.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
If,.
Automobile Engineering
Odour control: Me.hods to control odour are as follows. 1. By using catalyst muffler. 2.
By changing the injection system in diesel engine.
2.9.5. Evaporative Emission Control for SI engine Petrol vapour from fuel tank escapes into atmosphere by evaporation. This vapour comes out through a filter cap vent or tank vent tube. When the engine is not running, petrol will evaporate in the carburetor float chamber. In the uncontrolled vehicles, fuel vapours from the
ww
fuel tank and carburettor were vented into the atmosphere that constituted about 20% of all hydrocarbon emissions from a gasoline passenger car.
w.E
Vapour liquid separater
Vent valve
asy E
Carburetor
ngi
Intake manifold
Purge control valve
Carbon Canister
nee rin
: : : Fuel tank ::
g.n et
Figure 2.47 Evaporative Emission Controlfor Sf engine A simple and moueru
< .
ative emission control system is shown in Figure 2.47. The
evaporative emission control system consists of a device to store fuel vapour produced in the fuel system due to evaporation. A vapour-liquid separator is provided at the top of a fuel tank. Vapour goes to the top of the separator where the liquid petrol is separated and it is returned to the tank. A vent valve is provided for venteing the fuel vapour to the canister. A canister containing activated charcoal is used to store the fuel vapour. The canister adsorbs the vapour and stores it. "Adsorption" refers to the process of trapping of the petrol vapour by the activated charcoal
particles
packed inside the canister.
Due to the adsorption
process,
hydrocarbons are left in the canister and the, air.leaves-to the atmosphere. When engine is running, the vacuum created in the intake manifold is used to draw fuel vapour from the canister into the engine. Purging air is sucked through the canister which leads the fuel vapour from canister to the engine. Purging is the process by which the petrol vapour is removed from the charcoal particles inside the canister. An electronically controlled Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary
f'D
Systems
purge valve is used. During engine acceleration additional mixture enrichment can be tolerated and under these operating conditions the stored fuel vapours are usually purged into the intake manifold. This system is a fully closed system. A sealed fuel tank filler cap is used and a stable fuel tank pressure is maintained by the purging process of the canister. Figure 2.48 shows a float type vent valve. When the pressure increases, the float goes up and closes the air vent and the vent is connected to the canister through orifice. Carburetor float bowl has two vents. One is connected to the air cleaner and it helps to compensate a clogged air cleaner. The other vents connect to the charcoal canister. Various arrangements may control this vent.
ww
w.E
Orifice To canister
asy E
ngi
Figure 2.48
nee rin
A special filter cap is provided on the fuel tank which maintains some pressure in the
g.n et
tank which forces fuel vapour from tank to canister. Flow of vapour from the fuel tank may be controlled by a mechanically operated vent valve or an electrically operated solenoid valve. The throttle linkage operates the mechanical valve. It allows the vapour from float chamber to canister during idling.
When the throttle is opened, the vent valve is closed. So, the electrical vent valve is open with the ignition switch 'off. When the ignition switch is 'on' the vent valve is closed by the energization of solenoid. When the engine is operated, the fresh vapour enters through the canister and picks up the petrol vapour from carbon in the canister. This action of clearing the trapped petrol vapour from the canister is called purging. This air then flows into the intake manifold and it becomes a part of air-fuel mixture entering the engine cylinders to be burnt. Some evaporative control systems have the purge valve in the purge line. It connects to the throttle body and it discharges vapour just above the throttle valve into the intake air.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile Engineering
2.9.6. Evaporative Emission Control System for CI Engine The fuel injection system of CI engine has no float bowl. Therefore, the evaporative cc-nrol system is used only fuel vapour from the fuel tank. Figure 2.49 illustrates the system. In this, the canister has two connections. One is the connection to fuel tank and the other one is the purge line to the throttle body. Instead of a vacuum operated purge valve, an electric purge control solenoid may be used. It is mounted on the canister or in the purge line. Other processes are similar to the one discussed in SI engine. Air
ww w.E
Purge line
asy E
, .••. Vapour •• Restrictor . - - - - - - - - -
Canister
::::
ngi
Diesel :::
Figure 2.49 Evaporative emission control system/or CI engine 2.9.7. Exhaust Gas Recirculation (EGR) System
nee
rin
Excessive nitrogen oxides (N02) form when the peak combustion temperature exceeds
g.n e
1950°C. To lower the combustion temperature, many engines have EGR system. The heat capacity of the exhaust gas is higher than the air as it contains significant amount oftri-atomic
t
gases CO2 and water vapours. Therefore, addition of exhaust gas to fresh intake charge has a higher effect in lowering the combustion temperatures compared to simple leaning of the charge. It recirculates 5 to 10% of the exhaust gas back into the intake manifold. At higher EGR rates, frequency of partial and complete misfire cycles increases resulting in unacceptably higher
He emissions
and loss in fuel economy and power. EGR systems are
made to operate mostly in the part-load range. These are deactivated at engine idle, because large amount of residual gas is already present in the cylinder. The cooler exhaust gas absorbs heat from combustion process. It reduces the peak combustion temperature and lowers the formation of N02• EGR system provides a passage between exhaust manifold and inlet manifold. An EGR control valve is used to regulate flow of EGR depending upon engine operating conditions. The intake manifold pressure or exhaust back pressure may be used to control EGR r~te as these parameters vary with engine load. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
! Engine Auxiliary
,ta
Systems
Figure 2.50 shows a simplified diagram of a conventional EGR valve. It consists of a springloaded vacuum diaphragm linked to a tapered valve. A vacuum chamber is provided at the top of the valve. Air
j
ww
-t' w.E~ asy
Exhaust gas
7'
'77/7/
I
L..----::-----------:l
. 7777777777777777777777777~... ~
Intake manifold
Figure 2.50 Exhaust Gas Recirculation (EGR) System
En
This valve controls the passage of exhaust gas. The chamber is connected by a tube to a vacuum port in the throttle body. When there is no vacuum at this port, the spring pushes the
gin eer
diaphragm down and keeps the passage closed. Therefore, happens during idle when N02 formation is at a minimum.
DO
exhaust gas recirculates. It
ing
When the throttle is opened from the idle position, vacuum applied will gradually open
.ne
the tapered valve. It causes the exhaust gas to flow into the mtake manifold. At wide-open
t
throttle, the intake manifold vacuum is low and EGR valve is closed by the spring. Thus, EGR valve systems do not affect full power operation. The exhaust gas is recirculated only in this system when the engine operating conditions are supposed to form N02• Many engines have thermal vacuum switch. It prevents EGR until engine temperature reaches 38°C. This switch is mounted in the engine water jacket where it connected with coolant temperature. The switch closes when the engine is cold. It prevents--EGRjust after a cold engine starts, After the engine warms up, the switch is opened. In the modern engines, EGR rate is controlled by the engine electronic control unit. A pressure sensor in the exhaust or intake provides signal to the electronic control module of the engine, which in its tum regulates the operation of the EGR valve.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile
Engineering
2.9.8. Crankc;:ase Emission Control System A small amount of charge in the cylinder leaks past piston rings into crankcase of the reciprocating engines.'Near top dead centre (TDC) when the rings change their position in the grooves at the end of compression stroke, combustion has already begun and the cylinder pressures are high. A significant part of charge stored in the piston- ring-cylinder gap leaks into the crankcase. These gases are known as 'crankcase blow-by' and their flow rate increases as the engine is worn out and the piston-cylinder clearances and ring gaps increase. In the homogeneous charge engines, the crankcase blow by gas is high in HC concentration. Only a small fraction of the gas stored in the ring crevices and hence blow-by gases may consist of partially burnt mixture. This source contributes about 20% of total hydrocarbons
ww w.E
emitted by an uncontrolled car. The crankcase blow-by gases in the uncontrolled engines were ventilated to atmosphere
under the effect of pressure difference occurring naturally between the crankcase and atmosphere. For control of crankcase emissions, the blow-by gases are recycled back to the
asy E
engine assisted by a positive pressure drop between the crankcase and intake manifold.
ngi
When engine is running and intake charge is throttled the intake manifold is at a lower pressure than the crankcase. The blow-by gases mix with the intake charge to be burned inside
nee
the engine cylinder to CO2 and H20. A tube connects crankcase or cylinder head cover to the intake manifold below throttle valve, which leads the blow-by gases back to the engine. Due
rin
to suction effect of intake manifold as the pressure in the crankcase falls, ventilation air from
g.n e
the air cleaner is drawn into the crankcase that continuously purges it. A one-way valve is used to control the flow of blow-by gases. This valve restricts flow of blow-by gases during
t
idling and very light loads which otherwise would cause excessive leaning of the charge by ventilation air. Under normal engine operation, PCV valve is fully open providing free flow of the gases while under high intake manifold vacuum the flow is restricted. 2.9.9. Engine Emission Control by Catalytic Converter The term catalytic converter covers the stainless steel box mounted in the exhaust system. The catalyst is inside the cover which is a ceramic or metallic base with an active coating incorporating alumina, ceria and other oxides and combinations of precious metals such as platinum, palladium and rhodium. The base can be protected from vibration and shock by a resilient ceramic or metallic 'mat'. The catalytic converter converts the pollutants such as HC, CO and N02 into harmless gases. It is placed between exhaust manifold and silencer. All
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary Systems
fl.
exhaust gas must flow through it. The catalyst causes a chemical change without being a part of the chemical reaction. The inside of the catalytic converter is a honeycomb set of passageways or small ceramic beads coated with catalysts. A chemical reaction takes place to make the pollutants less harmful. There are many passages for the exhaust gases to flow and allow for the maximum amount of surface area for the hot gases to pass. There are two main types of structures used in catalytic converters such as honeycomb and ceramic beads. Most cars today use a honeycomb structure. Catalytic converters can either be a two-way or three-way type.
a) Two-way or oxidation catalytic converter:
ww w.E a
Early converters, called "two-way" (or oxidation) catalytic converter converts harmful carbon monoxide (CO) and hydrocarbons (HC) produced by relatively inefficient, low compression engines to harmless carbon dioxide (C02) and water vapor with the assistance of a precious-metallic catalyst. But these converters have little effect on nitrogen oxides (NOx)
syE
and particulate matter. Two-way converters are most effective when used with engines that have a lean air/fuel mix because this condition provides ample oxygen to burn pollutants.
b) 3-way catalytic converter:
ngi
nee r
Most cars today are equipped with a 3-way catalytic converter. The term 3-way refers to the three emissions which help to reduce: carbon monoxide (CO), hydrocarbons (HC) or volatile organic compounds (VOCs) and NOx molecules. 3-way converters use two different
ing
types of catalysts such as a reduction catalyst and an oxidization catalyst. Both types consist
.ne
of a base structure coated with a catalyst such as platinum, rhodium and palladium. The
t
scheme is to create a structure which exposes the maximum surface area of the catalyst to the exhaust flow while minimizing the amount of catalyst required.
3-way converters lise two catalyst processes. They are reduction and oxidation processes. A sophisticated engine control system converts three harmful gasses such as HC, CO and oxides of nitrogen (NOx)' It is not an easy task because the catalyst requires to clean up. NOx is most effective with a rich air/fuel mix whereas HC and CO reduction are most effective with a lean air/fuel bias. To operate properly, first, a three-way converter must convert NOx and then HC and CO contents are converted into lean bias.
(i) Reduction catalyst: The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help in reducing NOx emissions. When an NO or N02 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I,id:-
Automobile
Engineering
oxygen in the form of O2• The nitrogen atoms bond with other nitrogen atoms which are also stuck to the catalyst, forming N2• 2NO => N%+ 0%
or
(ii) .Oxidation catalyst: The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas.
ww
2CO + o, => 2CO:z
w.E
Vehicles with catalyst converter must use unleaded petrol. Lead in petrol rests the catalyst and makes it ineffective. For the catalytic converter to most effective, the air fuel
asy
mixture must have stoichiometric ratio of 14.7: 1. To achieve the described air fuel ratio at all operating conditions, a feedback system is used. It determines the correct air fuel ratio of the intake charge by measuring the amount of oxygen remaining in exhaust gases.
En
gin eer
The diesel engine catalytic converter is a pure oxidation catalytic converter. It oxidizes HC and CO into water and COt. It cannot reduce N02• e~(IlJ
\\o~ ~O.,.
lI.~y.c. 'S''b-~'i>
f(;:#l ~\~
ing
C0(\1
L.J
.ne
t
Figure 2.51 Catalytic converter
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I EngineAuxiliary Systems
Rml
2.10. EMISSIONNORMS (EURO AND as) Emission norms for automobiles are the standards set by the authority of different countries focusing on controlling the amount of pollutants released into the environment from automobiles. Each stage of emission standards specifically describes the amount of pollutants from vehicles such as carbon monoxide (CO), nitrogen oxides (NOx), sulphur dioxide, carbon dioxide (C02), hydrocarbons (HC) and particulates which can be emitted from an automobile into the environment. These regulatory standards differ from natton to nation. But the aim is common to control the environmental pollution. Parameters determining emission from vehicles:
ww w.E a
While each one of the following four factors have direct environmental implications, the vehicle and fuel systems have to be addressed as a whole and jointly optimized in order to achieve significant reduction in emission. ~
Vehicular technology
~
Fuel quality
~
Inspection& maintenance of in-use vehicles
~
Road and traffic management.
syE
2.10.1. Setting Emission Norms
ngi
nee r
ing
The focus here is on simulation of actual driving versus assumed driving pattern in a cycle based on long observation and trials on road. In simulation, the vehicle is "exercised" on
.ne
a "tread mill" called chassis dynamometer replicating the assumed driving-pattern of the
t
country. This is called the driving cycle of the country. The emissions are measured over the cycle and the results computed to give mass emissions.
For the emission standards to deliver real emission reductions it is crucial that the test cycles under which the emissions have to comply as much as possible reflect normal driving situations. In the United States, emissions standards are managed by the Environmental Protection Agency (EPA). The state of California has special dispensation to circulate more stringent vehicle emissions standards, and other states may choose to follow either the national or California standards. In European countries the regulatory standards are called the Euro Norms and designated by the letters EU suffixed by numerals I, II, III and IV in the increasing order of stringency.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
I..
The norms for vehicles vary from country to country reflecting the differences in traffic density and regulation, road infrastructure, fuel quality, maintenance standards. India uses Euro standards with only one modification which is lower maximum speed of 90 km/h in the last part of the cycle instead of 120 km/h as mandated in the EU norms. This cycle is called modified European cycle. The other components of the driving cycle such as idling period, acceleration and dece~eration rate and periods, cruising period are exactly the same.as Euro practice. The norms derived from this cycle are called Bharat Stage standards which is designated by the symbol BS suffixed by numerals in the increasing order of stringency. The Indian emission standards are set by The Automotive Research Association of India (ARAl).
ww w.E
2.10.2. EURO Norms
Euro norms refer to the permissible emission levels for both petrol and diesel vehicles,
asy En gi
which have been implemented in Europe. In European Union member countries, some automobile manufacturing countries in Asia and Africa and several non-manufacturing countries imports vehicles which have adopted European emission standard as their standards. European standards are set on the classification of vehicles based on their weight and engine capacity. There are different standards for 2 wheelers and 4 wheelers. European standards are called Euro levels starting from EURO-/' As the proportion of two wheelers are small in
nee r
capacity and they are equipped with 4 stroke engine in European countries. The emission
ing .ne
regulations for 2 wheelers are not much strict. European countries have progressed from EURO-I to EURO- V. By January 2014, they launched EURO- VI standard.
t
European Union (EU) adopted catalyst-forcing standards for new gasoline-fu~lIed cars in early 1990s called Euro-I standards and Euro-II was released in 1996 with several advantages. Euro-III was released in 2000 and Euro-IV was followed in 2005. Similar requirements were adopted for diesel cars and light and heavy commercial vehicles. Euro-V standards for cars will further restrict emissions from both petrol and diesel cars, of carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOx) and particulate matters (PM) which are considered harmful to human health. The tighter standards were applied from September 2009 for new models of cars and in January 2011 for all new cars. For each vehicle type, different standards apply. Compliance is determined by running the engine at a standardised test cycle. Non-compliant vehicles cannot be sold in the European Union, but new standards do not apply to vehicles already on the roads. Within the European
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I EngineAuxiliary Systems
RI_
Union, road transport is responsible for about 20% of all CO2 emissions, with passenger cars contributing about 12%. Allowable emissions limits of Euro standards for gasoline and diesel passenger cars are given in the following tables. Euro emission limits for gasoline cars (values in g/Km): NMHC
THC
PM
HC+NOx
NOx
Tier
Date
CO
Euro 1
July 1992
2.72 (3.16)
-
-
-
0.97 (1.13) 0.5
ww
Euro 2
January 1996
2.2
-
-
-
Euro 3
January 2000
0.20
-
0.15
Euro4
January 2005
1.0
0.10
-
0.08
Euro 5
w.E
2.3
September 2009
1.0
0.10
0.068
0.06
Euro 6
September 2014
1.0
En
0.068
0.06
THC
NMHC
asy
0.10
-
0.005
gin e er -
0.005
Euro emission limits for diesel cars (values in g/km): Tier
Date
Euro 1
July 1992
CO 2.72
-
NOx
-
HC+NOx
ing
0.97 (1.13)
PM
I
0.14
Euro2
January 1996
1.0
-
-
-
Euro 3
January 2000
0.64
-
-
0.50
0.56
.ne
Eur04
January 2005
0.50
0.30
0.025
September 2009
0.5
-
0.25
Euro 5
-
0.18
0.230
0.005
Euro 6
September 2014
0.5
-
-
0.08
0.170
0.005
(3.16)
0.7
(0.18) 0.08
0.05
t
Euro-V standards include several parameters in order to minimize engine emission harmfulness. They are as follows. (i)
Optimising diesel engines
(ii) Making particulate filters compulsory
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
(iii) Tax incentives to reduce emissions (iv) International cooperation. Beyond Euro- V, the three institutions have agreed on introducing longer-term limits, under a Euro-VI stage which has been adopted at the same time as Euro-Vbut it will enter into force after five years. Euro- VI will set significantly lower emission limits for NOx emissions from diesel cars. 2.10.3. BS Norms Bharat Stage (BS) emission standards are emission standards instituted by the
ww
Government of India to regulate the output of air pollutants from internal combustion engine equipment, including motor vehicles. The standards and the timeline for implementation are set by the Central Pollution Control Board under the Ministry of Environment & Forests.
w.E
The first Indian emission regulations were)dle emission limits which was started in 1989. Then it is replaced by mass emission limits for both petrol (in 1991) and diesel vehicles
asy
En
(in1992). On April 29, 1999 the Supreme Court of India ruled that all vehicles in India have to meet Euro I or India 2000 norms by June 1, 1999 and Euro II will be mandatory in the National Capital Region (NCR) by April 2000. Car makers were not prepared for this
gin eer
transition and in a subsequent judgment the implementation date for Euro II was not enforced. In 2002, the Indian government accepted the report submitted by the Mashelkar committee. \ The committee proposed a road map for the roll out ofEuro based emission norms for India. It
ing
.ne
also recommended a phased implementation of future norms with the regulations being implemented in major cities first and extended to the rest of the country after a few years.
t
Based on the recommendations of the committee, the National Auto Fuel policy was announced officially in 2003. The roadmap for implementation of the Bharat Stage norms was laid out till 2010. The policy also created guidelines for auto fuels, reduction of pollution from older vehicles and R&D for air quality data creation and health administration. In 2000, India started adopting European emission and fuel regulations for four wheeled light-duty and for heavy vehicles. Indian emission regulations are also used for two- and three-wheeled vehicles. Progressively stringent norms have been rolled out since then. All new vehicles manufactured after the implementation of the norms have to be compliant with the regulations. Since October 2010, BS III norms have been enforced across the country. In 13 major cities, Bharat stage IV emission norms are in place since April 2010. India is using European emission norms with a time lag of five years with BS-IV norms currently applicable in 50 cities where the required grade of fuel is available while the rest of Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary Systems
"jl
the country follows BS-III standards. But many vehicles are BS-I and BS-II compliant and more polluting. Overview of the Emission Norms in India: );>
1991 - Idle CO Limits for Gasoline Vehicles and Free Acceleration Smoke for Diesel Vehicles, Mass Emission Norms for Gasoline Vehicles.
);>
1992 - Mass Emission Norms for Diesel Vehicles.
);>
1996 - Revision of Mass Emission Norms for Gasoline and Diesel Vehicles, mandatory fitment of Catalytic Converter for Cars in Metros on Unleaded Gasoline.
ww w.E a
)0>
1998 - Cold Start Norms Introduced.
)0>
2000 - India 2000 (Eq. to Euro I) Norms, Modified IDC (Indian Driving Cycle), Bharat Stage II Norms for Delhi.
)0>
syE
2001 - Bharat Stage II (Eq. to Euro II) Norms for All Metros, Emission Norms for CNG & LPG Vehicles.
ngi
)0>
2003 - Bharat Stage II (Eq. to Euro II) Norms for 11 major cities.
)0>
2005 - From I April Bharat Stage III (Eq. to Euro III) Norms for 11 major cities.
)0>
2010 - Bharat Stage III Emission Norms for 4-wheelers for entire country whereas
nee r
ing
Bharat Stage - IV (Eq. to Euro IV) for 11 major cities. Effectiveness of graduation to Bharat norms:
.ne
t
The country has simply adapted the European cycle to the Bharat cycle by just reducing the maximum speed in the last phase. This modification alone will not give sufficient justification to simulate the randomness of frequent acceleration and deceleration and long periods of idling, which are prone to excessive discharge of exhaust emissions. The Indian Driving Cycle (IDC) developed by the ARAJ after long-term effort is a more realistic approach. The two-wh~eler industry recognized the merit of this and the IDC has become the preferred cycle used to establish emission norms for these vehicles. India must urgently use innovative methods to arrive at mass emissions under actual service conditions. After rationalizing these methods we may arrive at appropriate norms in a way equivalent to the Euro norms.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
I(
AutomoliillFEngiReering
The ultimate aim is that mass emissions to atmosphere must not exceed the values recommended by international standards. For export purposes however we have to comply with Euro or any other norms acceptable in the foreign market. We have to balance th= market forces and the societal objective of keeping our air cleaner. BS emission standards for light duty vehicles (values in g/Km): Emissions standards for light duty gasoline and diesel vehicles with (Gross Vehicle Weight (GVW) ~ 3,500 kg) are summarized in Table 2.1 and Table 2.2 respectively. Ranges of emission limits refer to different classes of light commercial vehicles. The lowest limit in each range applies to passenger cars (GVW ~ 2,500 kg; up to 6 seats).
ww
Table 2.1: BS emission standards for gasoline vehicles (values in g/Km)
Year
1991
1996
w.E Reference
-
-
1998
CO
asy E
-
3.00 - 4.36
-
4.34 - 6.20
-
ngi
1.50 - 2.18
-
-
0.97 - 1.70
2005
Eur02
2.2 - 5.0
Eur04
-
-
2.72 - 6.90
2010
NO\;
8.68 - 12.4
Euro 1
Euro 3
2.0-2.9
14.3-27.1
2000
2010
HC+NOx
HC
2.3
0.20
4.17 5.22
0.25 0.29
1.0
0.1
1.81
0.13
2.27
0.16
-
nee rin 0.5 - 0.7
0.15
-
0.18 0.21 0.08
-
0.10
PM
I
-
I
-.-
-
g.n et -
-
0.11
Table 2.2: BS emission standards for diesel vehicles (values in glKm) Year
Reference
1992
-
17.3 - 32.6
1996
-
5.0 - 9.0
-
-
CO
2000
Euro 1
2.72 - 6.90
2005
Euro 2
1.0 - 1.5
HC
HC+NOx
NOx
PM
2.7 - 3.7
-
-
-
2.0 - 4.0
-
-
0.97 - 1.70
-
0.14 - 0.25
0.7 - 1.2
0.08 - 0.17
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary 2010
2010
Systems
Euro 3
0.64 0.80 0.95
Eur04
0.50 0.63 0.74
-
-
0.56 0.72 0.86
0.50 0.65 0.78
0.05 0.07 0.10
0.30 0.39
0.25 0.33 0.39
0.025 0.04 0.06
0.46
The test cycle has been the for low power vehicles (with maximum speed limited to 90 kmlh). Before 2000, emissions were measured over an Indian test cycle. Engines for use in light-duty vehicles can be also emission tested using an engine dynamometer. The respective
ww w.E
emission standards are listed in Table 2.3. Table 2.3: Alternative BS emission standards for light-duty diesel engines (values in g/Km) Year
Reference
1992
-
1996
-
2000
Euro I
2005
Euro II
asy E
NOx
HC
CO
PM
14.0
3.5
18.0
-
11.20
2.40
14.4
-
1.1
8.0
0.36
7.0
0.15
4.5
4.0
ngi
nee
1.1
BS emission standards for heavy duty vehicles (values in g/Km)
rin
g.n e
Emission standards for new heavy-duty diesel engines applicable to vehicles of GVW > 3,500 kg are listed in Table 2.4.
Table 2.4: BS emission standards for diesel heavy duty vehicles (values in g/Km)
NOx
PM
-
-
2.40
14.4
-
4.5
1.1
8.0
0.36
Euro II
4.0
1.1
7.0
0.15
Euro 1lI
2.1
0.66
5.0
0.10
HC
Year
Reference
CO
1992
-
17.3 - 32.6
2.7 - 3.7
1996
-
11.20
2000
Euro I
2005 2010
t
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
~8·0
01·0
O~·O
~O·O
.ne
t
-
-
ing
-
OO·Z Ov·~
-
-
-
O~·O 00·1
III sa vo·o toz -osooz II sa
S3P!q3 A 13S3!([133qM.-£ pUB -z ~Z· 1 OO·Z
nee r
-
-
~Z·I ~Z·Z OO·V
~·1 OO·Z os·v
ZI - 8
III sa II sa Isa
vO·OIOZ vo·~OOZ OOOZ 9661
~C9 O£-ZI
1661
S3P!q3 A IO.l:).3d133qM.-£
0·1
-
~·1
-
OO·Z
-
09·£
-
-
ZI-8
-
0·1
-
xON+:JH
WJ
-
ngi
syE
ww w.E a III sa
II sa Isa
vO·OIOZ
rosooz
OOOZ 9661
1661
O£ - ZI
S31J!q3A IO.ll3d 133qM.-Z "':0'
,,:ims
O:J
:JH
"Iva
31q1U lJU!M.0nOj3ql U! P"lS!I 3JU S3{O!q3A(OJl3d (33qM.-Z pun -£ JOj SpJUpUUlSUO!SS!wg:
(IUJI/:i U! s"nlvtt) s"FJ!'1"tt IO.ll"d 1""'1tK-Zpun -f .10/ SpJVPUVIS UO!SS!IU"SU
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary Systems 2.11. TWO MARK QUESTIONS AND ANSWERS 1. What are the factors that affect fuel vaporization?
{Anna Univ. Dec'Uj
(i) Concentration of the substance evaporating in the air (ii) Concentration of other substances in the air (iii) Flow rate of air (iv) Inter-molecular forces (v) Surface area (vi) Pressure and Temperature of the substance 2. What is carburetor?
ww
Carburetor is a device used for atomi~ing and vaporizing the fuel and mixing it
with the air in varying proportions to suit the changing operating conditions of vehicle engines.
w.E
3. What is meant by carburetion?
asy
The process of breaking up and mixing the fuel with the air is called carburetion.
En
4. Lis/out the major drawbacks of using carburettor in multi cylinder engines.
(i)
gin eer
{Anna Univ. DecJ09j
In multi cylinder engines, it becomes very difficult for a sinzle carburettor to supply uniform quality and quantity. Since the induction passages are of unequal lengths.
ing
.ne
(ii) Venturi throat of the carburettor causes a restriction in the passage of air flow to the engine. If the throat is made larger, the problem of suitable mixture supply
t
becomes acute at low speed and air velocity decreases which causes less efficient atomization.
(iii) There is a loss of volumetric efficiency due to restricted flow of mixture in various parts such as choke tubes, jets, throttle valves, inlet pipe bends etc. 5. Define the terms vapourization and atomization. Vaporization is a change of state of the fuel from a liquid to a vapour. Atomization is a mechanical breaking-up of the liquid into small particles so that every minute particle of the fuel is surrounded by the air. 6. What are the functions of carburetor?
{Anna Un;v. Nov'05!
1. It maintains a small reserve of petrol in the float chamber at constant head. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1"1:1
Automobile
Engineering
2. It atomizes and vaporizes the fuel. 3. It prepares a mixture of petrol and air in correct proportions. 4. It supplies a fine spray of petrol. 5. It produces a homogeneous mixture. 6. It measures and supplies the proper quantity and proportions of air and fuel under all conditions of engine operations such as temperature, speed and load. 7. Classify carburetor. 1. According to the direction of flow. a. Uplift carburetor
ww w.E
b. Down draft carburetor
c. Horizontal carburetor
2. According to the arrangement of the float chamber a.
asy E
Eccentric carburetor
b. Concentric carburetor
ngi
3. According to the number of units a.
Single carburetor
nee
b. Double carburetor
4. According to the metering system a.
Air bled jet carburetor
b.
Metering pin type carburetor
5. According to the type of venturi
rin
g.n e
t
a. Plain venturi carburetor b. Double venturi carburetor c. Vane venturi carburetor d. Nozzle bar venturi carburetor e. Triple venturi carburetor 6. According to the type of power system. a. Manually operated carburetor b. Vacuum controlled carburetor.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I
.hl
Engine Auxiliary Systems
8. What is the function offloat chamber in a simple carburetor? In the float chamber, a constant level of petrol is maintained by the float and a needle valve. The float chamber is ventilated to atmosphere. It is used to maintain the atmospheric pressure inside the chamber. 9. What does the mixing chamber do? The mixing chamber has two butterfly valves. One chamber is to allow air into the mixing chamber and it is known as choke valve. The other one is to allow air-fuel mixture to the engine and known as throttle valve. [Anna Ulliv. Apr'08j
10. What is a variablejet carburetor?
ww
Adjusting screw
~_-Venturi
w.E
asy
En
gin eer
Fuel nozzle
ing
Figure 2.52 A long tapered needle is screwed into the jet. During starting, the screw is loosened
.ne
so that the area of the jet is increased to provide the increased fuel. It is also called adjustablejet. 11. State the two basic reasons for defects in a carburetor.
t
(i) If the carburetor is set of working at high speed and at full throttle, it will not work properly at lower speed and part throttle. It is due to insufficient suction created at the venturi for drawing fuel from the main nozzle. Similarly, if the carburetor is set to work at low speed and part throttle, it will not work properly at high speed and full throttle. (ii) With the change of pressure heads, coefficients of discharge for air and fuel vary in different quantities. At the certain value of head, the coefficient of discharge for air becomes constant while in case of fuel it increases gradually. Therefore, at high head i.e., high engine speed, the air fuel ratio goes on becoming rich and
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1-
Automobile Engineering
rich. Hence, if the carburetor is set. at one particular speed, it will give rich mixture at high speed and lean mixture at lower speed.
12. List the various defects occurred in a simple carburetor. 1. Starting difficulty 2. Idling difficulty 3. Acceleration difficulty 4. Load and speed variation difficulty or compensation system in carburetor 5. Attitude influence 6. Influence of weather
ww w.E a 7. Icing difficulty.
13. What is meant by compensation?
(Anna Univ. Dec'14/
The process of providing additional air or fuel when it requires to maintain the correct air fuel mixture is called compensation in carburetor.
syE
U. Mention the different circuits involved in solex carburetor.
1. Float circuit 2. Starting circuit
3. Idle and low speed circuit
ngi
4. Normal running circuit 5. Acceleration circuit.
nee r
ing
.ne
t
15. What is a variable-venture carburetor? Both the variable venture carburetor and SU carburetor are one and the same or not. Say true orfalse.
In this carburetor, the orifice area is varied to meet the varying demand of carburetor and the pressure difference is kept constant. Therefore, it is called variable venturi carburetor. Yes, both are same. 16. What are the circuits involved in carter carburetor? a) Float circuit b) Starting circuit c) Idle and low speed circuit d) Part throttle circuit
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I engine Auxiliary
'J:.
Systems
e) Full throttle circuit f) Acceleration pump circuit. 17. What are the limitations of carburetor? (i)
In multi cylinder engines, it becomes difficult for a single carburetor to supply uniform quality and quantity since the induction passages are of unequal lengths.
(ii) Venturi throat of the carburetor causes a restriction in the passage of air flow to the engine. If the throat is made larger, the problem of suitable mixture supply becomes acute at low speeds and air velocity decreases which causes less efficient atomization.
ww w.E
(iii) The carburetor has many wearing parts. After wear, it operates less efficiency. (iv) There is a loss of volumetric efficiency due to restricted flow of mixture in various parts such as choke tubes, jets, throttle valves, inlet pipe bends etc.
asy E
18. State the important units of electronic fuel injection system. (i)
Fuel delivery system
(ii) Air induction system
ngi
(iii) Sensors and air flow control system (iv) Electronic control unit.
nee
rin
[Anna Univ. May'll & May'15}
19. State the purpose of turbocharger.
g.n e
1. To reduce the weight per horse power of the engine as required in aero engines. 2. To reduce the space occupied by the engine as required in marine engines.
t
3. To have better turbulence and it ensures more complete combustion giving greater power and low specific fuel consumption. 4. To improve volumetric efficiency of the engine at high altitudes as in aero engines and at high speed as in racing cars. 5. To maintain the power of a reciprocating Ie engines even at high altitude where less oxygen is available for combustion. 20. Enlist the limitations of turbocharging. (i)
[Anna Univ. May'14}
Special exhaust manifolds are required for the turbocharging system.
(ii) In order to inject more fuel per unit time, the fuel injection needs modification.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering (iii) In contrast to a naturally aspired engine which can digest solid particles in the inlet air without undue stress, a turbocharged engine can pass only the minutest material particles without damage. (iv) It is difficult to obtain good efficiency over a wide range of operations since the efficiency of the turbine blades is very sensitive to gas velocity. (v) Turbochargers
are costly and add complexity. Adding a turbo can often cause a
cascade of other engine modifications to cope with the increased power such as exhaust manifold, intercooler, gauges, plumbing, lubrication and pistons.
21. What are the advantages and disadvantages of ECU?
[Alma Univ. Apr'OS]
ww
Advantages: 1. A very high quality fuel distribution is obtained. Therefore, higher compression ratios can be adopted without any danger of detonation occurring.
w.E
asy E
2. Volumetric efficiency, power and torque are increased. Disadvantages:
ngi
1. Initials cost is very high. It is the greatest disadvantage.
nee rin
2. It has more complicated mechanism because of electronic system injection nozzle and fuel injection pump. 22. What do you understand by monopoint and multipoint injection system?
g.n et
[Anna Univ. Apr'OS, Nov'OS & Apr'lO] In multipoint system, there is an injection valve for each engine cylinder. The main advantage of this system is that it allows more time for the mixing of air and petrol. In monopoint system, an injection valve is positioned slightly above each throat of the throttle body. The injection valve sprays fuel into the air just before it passes through the throttle valve and it enters the intake manifold. 23. Write the main requirements of an injector nozzle.
[Anna Univ. May'14]
The main requirements of an injector nozzle are as follows: (i)
To inject fuel at a sufficiently high pressure so that the fuel enters the cylinder with a hi-gilvelocity. It -¬ Feates liner droplet size of fuel. The momentum of smaller droplets is less. Hence, the penetration is also less.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary Systems
fj:i'
(ii) Penetration should not be high so as to impinge on cylinder walls which
may results poor starting. (iii) Fuel supply and cut-off should be rapid. There should be no dribbling. [Anna Univ. May'12j
24. What are the various types of fuel injection nozzle? (i) Single hole nozzle (ii) Multi hcle nozzle
(iii) Long stem nozzle (iv) Pintle nozzle (v) Delay nozzle
ww w.E
(vi) Pintaux nozzle. [Anna Univ. May'15j
25. What is gasoline injection system?
If the fuel is injected directly into the combustion chamber instead of the intake
asy E
port. the injection system is said to be gasoline injection system. [Anna Univ. May'08j
26. What are the requirements of a spark plug? (i)
ngi
The spark plug must have an insulated passageway for this high voltage to travel down to the electrode where it can jump the gap, it can conduct into the engine block and grounded.
nee
rin
(ii) The plug also has to withstand the extreme heat and pressure inside the cylinder.
g.n e
It must be designed to deposit from fuel additives which do not build up on the plug.
t
27. State any four reasons due to which the spark plug may fail tofunction properly. [Anna Univ. Dec'13j The following are the four reasons due to which the spark plug may fail to.function properly: a) Sooted spark plug: Insulator nose, electrodes and air space are covered in velvety, black soot due to faulty carburation. b) Spark plug insulator damage: Scorching is due to sparks jumping.across the insulator which may be caused because of spark plug adaptor was worn out, the rubber gasket was torn out, embrittled or hardened.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
".1:"
Automobile Engineering
c) Worn spark plugs: Center and ground electrode show visible material loss due to aggressive fuel or oil additives, thermal overload and exceeding replacement interval. d) Incorrect tightening torque: It causes traces of hydrocarbons on spark plug body, broken ground electrodes.
28. Give tile requirements of airfuel ratio in SI engine.
[Anna Univ. Apr'Ll]
SI engine automobiles run with the help of a mixture of gasoline and air. The amount of mixture depends on (i) engine displacement (ii) maximum revolution per minute and (iii) volumetric efficiency.
ww
29. What are the classifications of an ignition system? I.
2.
3. 4.
[Anna Univ. May'12}
w.E
Coil ignition system or battery ignition system. Magneto ignition system.
asy
Electronic ignition system, and
Transistorised ignition system.
En
30. Name the component of Battery Coil ignition system used in vehicles. (i) Distributor (ii) Contact breaker (iii) Primary winding
gin eer
[Anna Univ. Dec'08j
ing
(iv) Secondary winding.
31. State the advantages and disadvantages of battery ignition system.
.ne
t
Advantages: );;>
It provides better sparks at low speed of the engine during starting and idling due to availability of maximum current throughout the engine speed range.
);;>
The initial cost is low compared with magneto ignition system.
);;>
The maintenance cost is negligible except battery.
);;>
Spark efficiency remains unaffected by various positions of the timing control mechanism.
Disadvantages: );;>
The weight is greater than magneto ignition system.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
[E/J9me Auxiliary
fJ:b'
Systems
~
Frequent battery down occurs when the engine is not in use continuously. It causes the starting trouble.
~
Wiring mechanism is more complicated.
32. Describe the function of secondary circuit in electronic ignition system. In the secondary circuit, the distributor, ignition coil and wiring are altered to handle the higher voltage that the electronic ignition system produces. The high voltage . (about 47,000 volts) has the advantage that the spark plugs with wider gaps can be used. It results a longer spark which can ignite leaner air-fuel mixtures. As a result, engines can run on leaner mixtures for better fuel economy.
ww w.E
33. State the advantages of transistorised ignition system. I. It increases the life of contact breaker points.
2. It gives higher ignition voltage.
asy E
3. It gives longer duration of spark.
4. It has very accurate control of timing.
ngi
5. It needs only less maintenance. 34. What is supercharging?
nee
{Anna Univ. May'09J
Supercharging is the process of supplying the air fuel mixture to the engine above
rin
. the atmosphere pressure. A supercharger increases the pressure of the air fuel mixture from the carburetor before it enters the engine.
g.n e
35. Which is most common type of supercharger for automotive engines? Why are the automotive petrol engines rarely supercharged?
t
{Anna Unlv:Dec'12J
There are several kinds of supercharges such as centrifugal, roots, vane, rotary, twin screw and axial flow fan. The most common type of supercharger is a root supercharger. Due to its poor fuel economy, supercharging of a petrol engine is not very popular and it is used only when a large amount of power is needed or to restore the loss of density at high altitude. Supercharging of petrol engine increases the intake temperature of the engine which reduces the ignition delay and it increases the flame speed. Both these effects result a greater tendency to knock or pre-ignite. For this reason, the 16.
supercharged petrol engines employ lower compression ratios.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lmill
Automobile Engineering
36. What is meant by turbocharging in automotive engines?
J
[Anna Univ. Dec'09/
The process of forcing induction of an internal combustion engine to increase the density of air entering the engine to produce more power using a gas compressor is called turbocharging. [Anna Univ. Dec'08)
37. What is the use of turbo charger?
I. To reduce the weight per horse power of the engine as required in aero engines. 2. To reduce the space occupied by the engine as required in marine engines. 3. To have better turbulence and it ensures more complete combustion giving greater power and low specific fuel consumption.
ww
4. To improve volumetric efficiency of the engine at high altitudes as
In
aero
w.E
engines and at high speeds as in racing cars.
5. To maintain the power of a reciprocating Ie engines even at high altitudes where less oxygen is available for combustion.
asy E
[Anna Univ. Dec'14)
38. How does a turbo charger work?
ngi
It spins an air compressor by pushing extra air (and oxygen) into cylinders and it allows them to burn more fuel in each second with the help of exhaust gas to drive a
nee rin
turbine. The turbocharger on a car is similar to the principle to a piston engine. 39. State how turbo charging is different from supercharging.
[Anna Univ. May' 1O}
g.n et
Supercharging is the process of supplying the air fuel mixture to the engine above the atmosphere pressure. A supercharger increases the pressure of the air fuel mixture from the carburetor before it enters the engine whereas turbocharging is the process of forcing induction of an engine to increase the density of air entering the engine to produce more power using a gas compressor. 40. What do you understand by the term DTS-I?
[Anna Univ. Dec'14)
DTS-I refers a digital twin spark ignition. This technology introduces usage of two spark plugs having 90° angle which ensures the complete fuel combustion as well as better fuel economy. 41. What is meant by air pollution? What (Irethe pollutants emitted by an automobile? [Anna Univ. May'06} Exhaust gas constituents consist of partly burnt petrol, carbon monoxide, nitrogen oxides and if sulphur in petrol and sulphur oxides, pollute the air. The oxides of nitrogen together with hydrocarbons react in the presence of sunlight and form Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I
N:f-
Engine Auxiliary Systems
petrochemical smog. As a result, smog is created, the atmosphere becomes dirty and breathing becomes difficult. Its bad effect includes crop damage, eye irritation, objectionable odour, decrease of visibility, cracking in rubber etc. Air pollutants are as follows: 1. Carbon monoxide 2. Oxides of nitrogen 3. Hydrocarbons 4. Photochemical smog 5. Smoke
ww w.E 6. Lead
7. Particulate
8. Sulphur oxide.
asy E
42. Write short notes on oxides of nitrogen, smoke and particulates. 1) Oxides of nitrogen:
ngi
In high temperatures, nitrogen reacts with oxygen and it produces nitric oxide and
nee
nitrogen dioxide. They affect living organisms. They affect blood purification system. It may be mixed with moisture and produce dilute nitric acid in the heart and affects the heart. 2) Smoke:
rin
g.n e
Smoke is produced because of insufficient mixing of fuel and air. it contains CO
t
and CO2• When cold starting, blue white smoke is produced when more carbon particles are mixed with exhaust. Smog is produced by smoke. It causes irritation of eyes, coughing, headache and vomiting. 3) Particulate: Particulates are minute separate particles found in the air. They may be solid or liquid particles. The dust soot and fly ash are included in it. It causes the respiratory diseases such as bronchitis and lung cancer and allergic diseases. 43. What are the sources of air pollution by petrol engine? 1. Exhaust emissions through tail pipe. 2. Evaporative losses through carburetor, and 3. Crankcase blow by. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
-
Automobile Engineering
44. What are the parameters to be controlled in engine exhaust? 1. The formation of pollutants is prevented as far as possible. 2. The pollutants are destroyed after they are formed.
45. What are the various methods usedfor the measurement of emission parameters? [Anna Univ. May'Ll] I.
Promulgated in the Federal register.
2.
Source category approved alternative methods.
3.
Historical conditional method.
4.
Draft method of direct measurement of gas velocity and volumetric flow rate.
5.
Particulate screening method.
ww
w.E
46. WhatisEGR?
EGR refers to exhaust gas recirculation. Excessive nitrogen oxides (N02) form
asy
when the peak combustion
temperature
exceeds 1950°C. To lower the combustion
En
temperature, many engines have EGR system. The heat capacity of the exhaust gas is higher than the air as it contains significant amount of tri-atomic gases CO2 and water
gin eer
vapours. Therefore, addition of exhaust gas to fresh intake charge has a higher effect in lowering the combustion temperatures
compared to simple leaning of the charge. It
recirculates 5 to 10% of the exhaust gas back into the intake manifold.
47. What is the necessity of treating the exhaust gas?
ing
.ne
Treating the exhaust gas means the process of cleaning or reducing the percentage
t
of pollutants in them. It takes place after the exhaust gas leaves the engine cylinders and before it exists the tailpipe and enters the atmosphere. It reduces the amount of HC, CO and N02 in the exhaust gas. The exhaust gas is treated in two ways. One is by injecting fresh air into the exhaust system. The other one is by sending the exhaust gas through catalytic converter.
48. What does catalytic converter do·r The catalytic converter converts the pollutants such as HC, CO and N02
into
harmless gases. It oxidizes HC and CO into water and CO2•
49. What is a catalytic converter? The catalyst is inside the cover which has a ceramic or metallic base with an active . coating incorporating alumina, ceria and other oxides and combinations of the precious metals platinum, palladium and rhodium. The basecan be protected from vibration and Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary Systems
'J:PI
shock by a resilient ceramic or metallic 'mat'. The catalytic converter converts the pollutants such as HC, CO and N02 into harmless gases. It is placed between exhaust manifold and silencer. All exhaust gas must flow through it. The catalyst causes a chemical change without being a part of the chemical reaction. 50. How does oxidation catalyst differ from reduction catalyst? Oxidation catalyst adds oxygen with pollution and hydrogen catalyst reduces oxygen but the same time, the hydrogen will be increased. 51. Why unleaded petrol must he used if catalytic converter is used in a car?
ww w.E
[Anna Univ. May'05J
Unleaded petrol must be used if catalytic converter is used in a car because lead in petrol reacts with the catalyst and makes it ineffective. 52. What are the types of oxygen catalytic converter?
asy E
a) Two-way or oxidation catalytic converter b) 3-way catalytic converter.
ngi
53. At what air-fuel ratio does the three way catalytic converter operate at maximum efficiency? How is this ratio achieved precisely?
nee
{Anna Univ. Dec'12J
The three way catalytic converter operates at maximum efficiency when the
rin
catalytic converter receives exhaust from an engine running slightly above the
g.n e
stoichiometric point. This point is between 14.6 and 14.8 parts air to 1 part fuel by weight for gasoline. This ratio achieved precisely using a computerized closed-loop feedback fuel injection system using one or more oxygen sensors. 2.12. SOLVED QUESTIONS
1. What are the functions of carburetor?
t
[Anna Univ.Apr'06]
Refer chapter 2.1.1 in page 2.1. 2. Sketch and explain the construction and operation of a simple carburetor. [Anna Univ.Apr '06]
Refer chapter 2.3.1 in page 2.3. 3. Briefly explain the defects in a simple carburetor. Refer chapter 2.3.1.1 in page 2.4.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
4.
Explain the construction and working of Solex carburetor. [Anna Univ. Nov '07 & May '08] Refer chapter 2.3.2 in page 2.13.
5.
Explain the principle of operation of a carburetor used in two wheelers with a sketch. [Anna Univ.Nov'05] Refer chapter 2.3.3 in page 2.19.
6.
Explain the working of a zenith carburetor with a neat sketch. Refer chapter 2.3.4 in page 2.21.
7.
Explain the working of a modern carburetor with a sketch.
ww
[Anna Univ. Apr '10 & Dec '14]
w.E
Refer chapter 2.3.5 in page 2.22.
8.
What are the limitations of carburetor?
asy
Refer chapter 2.4.1 in page 2.25. 9.
En
Explain the operation of a MPFI system and compare it with TBI system.
gin eer
[Anna Univ. Nov'07, Dec '08, Dec '09, Apr' 10 & May' 11] Refer page 2.26.
10. Explain working principle of electronic fuel injection system.
ing
[Anna Univ. Apr '05, Nov '07, Dec '08, Dec '12, Dec'J3 & May '14] Refer chapter 2.4.3 in page 2.27.
.ne
II. Briefly explain the electronic diesel injection system with necessary controls. [Anna Univ. Dec'
t
13 & May' 15]
Refer chapter 2.5 in page 2.30. 12. What is Unit injector system? Explain its types with suitable diagram. [Anna Univ. May' 12] Refer chapter 2.5.2 in page 2.33. 13. Explain the following with suitable sketches:
(i) Rotary distributor type
[Anna Univ. Dec '14 & May '15]
Refer chapter 2.5.3 in page 2.35. (ii) Common rail direct injection system.
[Anna Univ. May' 14, Dec' 14& May' 15]
Refer chapter 2.5.4 in page 2.36. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Engine Auxiliary
DI'
Systems
14. List the various electronic ignition systems in use. Describe anyone
I
of them clearly
stating its advantages over the conventional ignition system. [Anna Univ. Dec' 12] Refer chapter 2.6 in page 2.38. 15.- Draw the layout of a battery ignition system and mention the function of each [Anna Univ.Nov '05 & Apr '06] component. Refer chapter 2.6.1 in page 2.38. 16. Compare the salient features of contact breaker ignition with electronic ignition. [Anna Univ. Nov '07] Refer page 2.38.
ww w.E
17. Explain the working of any two ignition system used in automobiles. Refer chapter 2.6.1 & 2.62 in page 2.38 & 2.40 respectively.
18. With a neat sketch, explain the working of a magneto coil ignition system. [Anna Univ. Apr'10]
asy E
Refer chapter 2.6.2 in page 2.40.
ngi
[Anna Univ. May '08]
19. Explain COl ignition system with a suitable diagram.
nee
Refer chapter 2.6.5 in page 2.47.
rin
20. What is distributor less ignition system? Explain with neat diagram. [Anna Univ. May '12] Refer chapter 2.6.6 in page 2.48. 21. Explain briefly the main types of supercharging methods. Refer chapter 2.7.1 in page 2.49.
g.n e
[Anna Univ. Dec' 12]
t
22. Brief the modifications to be done in an engine to make it suitable for supercharging. [Anna Univ. May'14] Refer page 2.51. 23. Explain a turbocharger with a neat sketch.
[Anna Univ. May '08 & Dec' 13]
Refer chapter 2.8 in page 2.52.
24. Explain briefly about SI engine emission. Refer chapter 2.9.3 in page 2.59.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
ImJI
Automobile Engineering
25. Write short notes on air pollution and its pollutants. Refer chapter 2.9.4 in page 2.60. 26. Describe briefly evaporative emission control system for CI engine. Refer chapter 2.9.5 in page 2.62. [Anna Univ. Dec' 13]
27. Explain engine emission control system. Refer chapter 2.9.5 in page 2.62. 28. What is EGR? and explain the system with suitable sketch.
[Anna Univ. May '05]
Refer chapter 2.9.7 in page 2.64.
ww w.E a
29. Discuss the construction and working principle of3-way Catalytic controller. [Anna Univ. May '07, May '08, Dec '08, May '09, May '10, May'II, Dec'JJ, May'l3, Dec'J4 & May '15]
Refer chapter 2.9.9 in page 2.66.
syE
30. What do you know about emission norms? Discuss.·
[Anna Univ. May '09]
ngi
Refer chapter 2.10 in page 2.69.
--------------------------
nee r
END of Unit 2 ---------------------------
ing
.ne
t
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
ww w.E
asy E
ngi
I
3
UNIT -
Clutch-types and construction, gear boxes- manual and automatic, gear shift mechanisms, Over drive, transfer propeller
box, fluid shaft,
nee
flywheel, torque
slip
joints,
converter,
rin
universal
joints,
Differential and rear axle, Hotchkiss Drive and Torque Tube Drive.
g.n e
t
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
..
Systems
ww w.E
3.1. INTRODUCTION
TRANSMISSION SYSTEMS
asy E
ngi
Transmission system is the system by means of which power developed by the engine is transmitted to road wheels to propel the vehicle. In automobiles, the power is developed by the engine which is used to turn wheels. Therefore, the engine is to be connected to the
nee
transmission systems for transmitting power to wheels. Also, there should be a system by
rin
means of which engine could be engaged and disengaged with the transmission system
g.n e
smoothly and without shock so that the vehicle mechanism is not damaged and passengers do not feel inconvenience. A clutch is employed in automobiles for this purpose. )
(
Ii It..t-
l
)
(
Rear axle
II
1
Clutch
Propeller shaft
/
~"~
t
{H
Engine
Gear box
I
Q)
xC1l
C
e
u,
Differential J
r
II
1111 (
)
(
)
Figure 3.1 General arrangement of power transmission
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
The engines employed in automobiles are of very high speed. Hence, a speed reduction is necessary to reduce the speed to moderate level as well as to get the required high torque while moving from rest. For this purpose, a gearbox is employed in automobiles. Figure 3.1 shows the general arrangement of power transmission system of an automobile. The various parts of the system are elaborately discussed in further topics of this unit. The motion of the crankshaft is transmitted to the gearbox through the clutch. The gearbox consists of a set of gears to change the speed according to the requirement. The motion is then transmitted to the propeller shaft from gearbox through a universal joint. The purpose of universal joint is to connect two shafts at an angle for power transmission. The power is transmitted to the differential unit through another universal joint. Finally, the power is transmitted from
ww
differential to wheels through the rear end. The differential unit is used to provide the relative motion between two run wheels while the vehicle is taking a turn.
w.E
3.~.1. Functions or Purposes of Transmission
asy
Systems
1. It enables the running engine to be connected or disconnected from the driving wheel smoothly and without shock.
En
2. It enables the leverage between engine and driving wheel.
gin eer
3. It enables the reduction of engine speeds.
4. It enables the turn of the drive round through 90°.
ing
5. It enables the driving wheel to be driven at different speeds.
6. It serves as a safety device by slipping when the torque transmitted through it
.ne
exceeds a safe value, thus preventing the breakage of parts in the transmission train. 3.2. CLUTCH
t
Clutch is a mechanism used to connect or disconnect the engine from the rest of transmission elements. It is located between engine and gearbox. During normal running and stationary position, it is always in engaged condition. The clutch is disengaged when the driver processes the clutch pedal. The clutch is disengaged for starting, changing gears, stopping and idling. When the clutch is engaged, the engine will be connected to the transmission and power flows from engine to rear wheels through a transmission system. When 'the clutch is disengaged by pressing the clutch pedal, the engine will be disengaged from the transmission. Thus, the power does not flow to rear wheels while the engine is still running. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
U·
Transmission Systems
3.2.1. Principles of Operation of Friction Clutch
The clutch works on the principle of friction. In Figure 3.2, the driving shaft A with flange C is rotating at 'N' rpm and shaft B with the flange 0 is keyed to the driven shaft which is in stationary position when the clutch is not engaged. Now, external force is applied to the flange 0 so that it comes in contact with flange C, As soon as the contact is made, they are united due to friction between them and the flange 0 starts rotating with flange C. The rotational speed of flange D depends on the friction between surfaces C and D which in turn proportional to the external force applied.
ww w.E
asy E
(a) Disengaged position
(b) Engaged position
Figure 3.2 Principle of'friction clutch
ngi
If ::le force is gradually increased, the speed force transmitted will a.so be increased gradually. The torque transmitted by the friction clutch depends on pressure applied on flange,
nee
coefficient of friction of the surface materials and radius of the flange. By increasing anyone of them, the force transmitted can be increased. 3.2.2. Functions of Clutch
rin
g.n e
t
(a) To permit the engagement or disengagement of a gear when the vehicle is stationary and the engine is running. (b) To transmit the engine power to rear wheels smoothly without shocks to the transmission system when the vehicle is in motion. (c) To permit the engaging of the gears when the vehicle is in motion without damaging ~ear wheels. 3.2.3. Characteristics or Requirements of a Clutch A clutch must have the following requirements. (a) Transmission of torque: It should be capable of transmitting maximum torque of the engine. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
(b) Gradual engagement: The clutch should be able to engage gradually and positively without the occurrence of suddenjerks. (c) Dissipation of heat: The design of the clutch is such that it should ensure the dissipation of heat sufficiently which is generated during operation. (d) Dynamic balancing: The clutch should be dynamically balanced to the vibration in transmission system. It is very important requirement in modern cars which is operated at high speed.
ww w.E
(e) Size of the clutch:
The size of the clutch should be as smaller as possible so that it will occupy minimum space.
(f) Free pedal clutch play:
asy E
In order to reduce effective clamping load on the car thrust bearing as well as wear on it, a
ngi
provision should be made for clutch free pedal play.
nee
(g) Vibration damping:
A suitable mechanism should be incorporated within the clutch for damping of vibration and elimination of noise produced during the transmission. (h) Non-exertive operation of disengagement:
rin
g.n e
The clutch must have non-tiresome operation of disengagement for the driver for higher power transmission.
t
3.3. TYPES OF CLUTCHES ~
The clutches are classified as follows. 1. Friction clutch (i) Single plate clutch (ii) Multi-plate clutch ~
Wet clutch
~
Dry clutch
Downloaded From : www.EasyEngineering.net
-
Downloaded From : www.EasyEngineering.net
.
Automobile En.r:Jin'~Ar:;nn
single plate clutch. consists of a flywhee I, c Iutch pate, I fri releas,,- ,.,"'_ ncnon or pressure plate, clutch cover '''>'-'~'~~'''''><>.t'-'1:Qh shaft. The various parts of the clutch are explained below. '
(i) Fly wheel:
The flywheel is the mounting surf:ace for the clutch. The flywheel rotates
as the engine crankshaft rotates. The friction or pressure plate bolts to the flywheel face. The clutch disc is clamped and held against the flywheel by the spring action of the pressure plate. The face of the flywheel is precision machined to a smooth surface. The face of the flywheel that touches the clutch disc is made of iron. Even if the flywheel were aluminum, the face is iron because it wears well and dissipates heat better. A pilot bearing or busn bearing supports the spigot end
ww w
of the clutch shaft which is also housed in the flywheel. It is also the second driving member.
(ii) Pilot Bearing:
.Ea syE
The pilot bearing or bushing is pressed into the end of the crankshaft to suppurt the end of the transmission input shaft. The pilot bearing is a solid bronze bushing, but it also may be a roller or ball bearing. The end of the transmission input shaft has a small journal machined on its end. This journal slides inside the pilot bearing. The pilot bearing prevents the transmission shaft and clutch disc from wobbling up and down when the clutch is released. It
ngi n
also assists the input shaft center the disc on the flywheel.
(iii) Clutch plate or disc plate
eer
ing .
It is one of the important driving members of a single plate clutch. Figure 3.4 shows the constructional details of the clutch plate. A clutch disc is the plate between flywheel and
net
friction or pressure plate. It has a series of facings inverted on both sides to enlarge the friction. These clutch facings are made of asbestos material. They are highly wear and heat resistive.
The clutch plate consists of a central hub machined with internal splines to limit the axial travel along the splined gearbox during shaft. A cushion drive clutch plate is pr~vide.dwith id d . ti . t the torsional vibrations or modern motor vehicles. It helps to provi e a ampmg ac Ion agams variations ofthe driving torque between engine and transmission. . h b to the driven plate The damping action is achieved by coupling the splmed center U ith torsi(1ll..sprlngs.
'de6W1 with the help of a flexible mounting. The clutch pia.te is also provi
y'
. so The purpose of torsion springs is to cushion _,;f,l'uffJb eaiageme: /.
as to
danger of the clutch disc getting wrapped or broken.
,,/
\ /'
nate tb-:
/'
Downloaded From : www.EasyEngineering.net
./
Downloaded From : www.EasyEngineering.net
Transmission Systems
ww w.E
asy E
ngi
nee
Figure 3.4 Clutch'plate (iv) Pressure plate:
rin
g.n e
t
The pressure plate is made of special cast iron. It is the heaviest part of the clutch assembly. The main function of the pressure plate is to establish even contact with the driven plate facing through which the pressure springs can exert a sufficient force to transmit the full torque of the engine. The pressure plate presses the clutch plate on to the flywheel from its machined surface. Between pressure plate and clutch cover assembly, pressure springs are fitted. The pressure will be withdrawn from the flywheel whenever release levers are depressed by the toggle or release levers are pivoted accordingly. (v) Clutch cover assembly: Clutch cover assembly is bolted to the flywheel. It consists of pressure plate, release lever mechanism clutch cover and pressure springs. Figure 3.5 shows the view of the clutch cover Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
assembly. In general, the clutch plate revolves with the flywheel. But when the clutch is disengaged, the flywheel as well as the pressure plates will be forced to rotate independently from driven plate and driving shaft. The release mechanism is used to release the clutch. The pressure plate is backed by a number of coil springs and housed with them in a pressed-steel cover bolted to the flywheel. The springs push the pressure plate against the cover. (vi) Release mechanism: The clutch levers are pivoted on pins in the clutch cover. Their outer ends are located and positioned on pressure plate legs and inner ends are projecting towards the clutch shaft. A careful and accurate adjustment of the release mechanism is one of the most important factors
ww w.E
of governing the performance of a clutch assembly.
Starter
ringgear--
Clutch plate (Driven member)
Pressure springs
..-.........~"
asy E
ngi
nee
rin
g.n e
Figure 3.5 Clutch plate assembly
t
(vii) Withdrawalforce and rearing: The withdrawal force carrying the bearings is pivoted on a ball-mounted fulcrum in the clutch outer casing. The bearing is generally facing the inner end ofthe toggle lever. The other end of the force is connected to the clutch pedal by means of rods and levers. (viii) Primary or clutch shaft: The clutch plate is assembled on a splined shaft that carries the rotary motion to the transmission. This shaft is called the clutch shaft, or transmission input shaft. It is also known as driving shaft of a gearbox. One end of the clutch shaft is attached to the crankshaft or flywheel and the other end is,connected to the gearbox or forms a part of the gear box. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
ft·
Transmission Systems
Working: Due to friction between flywheel, clutch plate and pressure plate surfaces, the clutch plate revolves with the flywheel. As the clutch plate revolves, the clutch shaft will also revolve. The clutch shaft is connected to the gearbox. Normally, the clutch plate is always kept in between flywheel and pressure plate by the number of pressure springs. When the clutch pedal is pressed, the pressure plate moves out against the pressure springs and the gap between pressure plate and flywheel increases. Now, the clutch plate is free to rotate. Thus, power is not transmitted. This position is called clutch release or declutching. As soon as the pedal is released, the pressure spring forces the pressure plate towards the flywheel. The clutch plate is gripped between flywheel and pressure plate. It is called clutch
ww w.E
engaging. At this position, the power is transmitted to the gearbox. Advantages:
1. It makes easy to change gears than a cone type.
asy E
2. It is reliable than a cone clutch. Disadvantages:
1. It requires more force to release.
ngi
2. Space required to accommodate the clutch is more as compared to multi-plate clutch. 3.3.2. Multi-Plate Clutch
nee
rin
g.n e
Multi-plate clutches are used in heavy vehicles with racing cars and motorcycles for
t
transmitting high torque. As compared to single plate clutch, these are smooth and easy to operate due to their assembly of friction surface's contact. It may be used where the space is very limited. As the number of clutch plates is increased, the friction surfaces will be also increased. The increase in friction surface obviously increases the capacity of the clutch to transmit more torque for the same size. The multi-plate clutch of small size transmits approximately the same torque as a single plate clutch of twice the diameter. These clutches may be wet or dry type. When the clutch of this type is operated in a bath of oil, it is called wet clutch. But, this oil immersed wet clutches are generally used in conjunction with a part of the automatic transmission. The multi-plate clutch consists of
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
number of clutch plates. Its construction is similar to a single plate clutch except that the number of clutch plates. The total number of clutch plates is divided into two sets in which one from each set is alternatively arranged as shown in Figure 3.6. One set of plate slides in grooves on the flywheel and other one slides on splines on the pressure plate hub. These plates are firmly pressed by a strong coil spring and assembled in a drum. Multiplate clutch works in the same way as the single plate clutch by operating the clutch pedal. Clutch pedal
ww w.E
Spigot end
asy E
"Bearing
ngi
nee
Figure 3.6 Multi-plate clutc/t Advantages:
rin
I. Increased torque transmission capacity could be obtained.
g.n e
t
2. The diameter is reduced as it has more friction surface which reduces the size of the clutch assembly. 3. It is highly reliable. 4. It is suitable for heavy vehicles.
3.3.3. Cone Clutch Since the contact surfaces of this type of clutch are in the form of cone, it is called cone clutch. It consists of two cones having leather facings. These cones are known as male and female cones. One cone is fixed with the driving shaft i.e., flywheel whereas the male member is splined on the driven,shaft i.e., gear box shaft. Figure 3.7 shows the construction details.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
Systems
between plates is increased as the speed of rotation of the clutch increases in proportion to the pressure requirements. It is accomplished by means of weights linked to the pressure plate as shown in Figure 3.9. As the weight is linked to the pressure plate, the outward radial pull of centrifugal force is translated into pressure on the plate. This pressure increases as the weight increases. Pressure plate
Clutch shaft
ww w.E
asy E
ngi
Figure 3.9 Semi-centrifugal clutch
nee
As the speed increases, the rotating weights will tend to move the pressure plate towards the flywheel. The ends of release levers are also moved back against the throw-out bearing
rin
along with this movement of the pressure plate. This construction permits the use of relatively
g.n e
light clutch pressure springs which exert low pressure at idling speed and facilitate depressing the clutch pedal for gear shifting. 3.3.6. Diaphragm Clutch
t
The construction of this type of clutch is similar to a single plate clutch except that ttl diaphragm springs called Belleville springs are used instead of the ordinary coil spring. This type of clutch is more advantages because it requires no release levers and the spring itself acts as a series of levers. The pressure of the spring is always varying. It increases till the spring reaches to its flat position and decreases with the passing of this position. If this clutch is used, the driver does not require to exert such heavy pedal pressure to hold the clutch out of
engagerrrenras-in -the ease-of coil-spring.type clutch.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
Front pivot ring Cover Oiaphram spring
Throwout bearing
ww
w.E
(a) Engaged position
asy E
(b) Disengaged position
Figure 3.10 Diaphragm clutch
ngi
Figure 3.10 shows the construction detaus of the diaphragm clutch. It consists of a diaphragm spring which is supported on a fulcrum retaining ring i.e. pivot ring so that any
nee rin
section through the spring can be regarded as a simple lever.
In the engaged position, the spring pivots on the rear pivot rings as it is held in a clutch cover so that its outer rim contacts the pressure plate. In this position, the pressure plate is in
g.n et
contact with its outer rim. Therefore, sufficient pressure is exerted by the spring making a firm contact between pressure plate and clutch plate as well as the flywheel in its natural conical position.
To disengage the clutch, the pedal is depressed to cause the linkage to move throw-out bearing towards the flywheel. As the bearing contacts the inner position of the conical spring, it moves forward which causes the rim to move backward since the spring pivots on the front pivot ring. It removes the pressure on the pressure plate and releases the clutch disc from contact with both driving members. Advantages: 1. It requires lower operating effort due to reduced friction in the clutch mechanism. 2. There is a constant and uniform load on the driven plate throughout the life of a clutch.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
U.
Transmission Systems
3. - At high speeds, the clamping load on the diaphragm springs is not affected as in the case of coil spring which starts bowing or distorting transversely. 4. The dangerous vibrations in the vehicles are altogether eliminated because it provides accurate balance at all times. 5. Due to its compact design, a clutch housing required is quite short. 6. Due to firm foundation and absence of vibrations, it eliminates squeaks and rafting. 3.3.7. Positive Clutch (or) Dog and Spline Clutch The positive clutch consists of two components, namely a driving member and a driven member. It is quite simple in construction and operation. Itis generally used to lock two shafts
ww
w.E asy En gin ee
together or for locking a gear to shaft. It consists of a sliding sleeve fitted with the driving member having two sets of internal splines. The smaller diameter splines are used to slide on a splined driving shaft whereas the bigger diameter splines match with the external dog clutch teeth on the driving shaft.
Dog clutch teeth
~ Shaft A Driven member
Figure 3.11 Dog and spline clutch
rin g.
net
Figure 3.11 shows this arrangement, when the sleeve is made to slide on the splined shaft, the larger internal splines match with the dog clutch teeth of the driven shaft. Thus, the sleeve turns the splined shaft with the driven shaft. It is called engaged position. These clutches are usually operated in conjunction with some type of synchronizing mechanism because they can only be operated when both sets of teeth match perfectly. To disengage the clutch, the sleeve is moved back on the splined shaft to have no contact with the driving shaft.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imy
Automobile Engineering
3.3.8. Hydraulic Clutch
A hydraulically operated clutch is used under the following circumstances, (i) When the clutch is located so that it would be difficult to run rods or cable from the foot pedal to the clutch.
.'
(ii) In heavy-duty mechanically operated clutches with high clutch spring pressure, the force required by the driver to release the clutch becomes excessive. Clutch pedal
Oil reservoir
ww w.E Master cylinder
asy E Slave cylinder
Clutch
ngi
Clutch release fork
nee
rin
Figure 3.12 Hydraulic operated clutch
g.n e
Figure 3.12 shows the line diagram of hydraulic clutch. It consists of a master cylinder
t
and a slave cylinder and an oil reservoir. When the clutch pedal is pressed, the fluid under pressure from the master cylinder reaches the slave cylinder. The slave cylinder is mounted on the clutch itself. The fluid actuates the slave cylinder push rod which further operates the clutch release fork to disengage the clutch. The hydraulic system is designed to multiply the driver's efforts so that a light force applied to the foot pedal produces a much greater force on the clutch fork. A small piston in the master cylinder travels a relatively long distance with only a low input force. It moves the larger piston in the slave cylinder for short distance in transmitting a greater force. Another advantage is that no mechanical linkage is required. Only hydraulic lines are required. These lines can be performed to any angle by flexible turning. Since, it has no mechanical linkage
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
Systems
.,.
between cylinders it does not involve frictional wears especially when it is subjected to heavy forces. Therefore, it is mainly used in heavy duty operations. 3.3.9. Electro-Magn~tic Clutch An electro-magnetic clutch consists of an engine flywheel provided with electric winding. A driven plate lined with friction materials is provided. It is free to move on splines of the gearbox shaft. A pressure plate is applied for engaging or disengaging the clutch. Figure 3.13 shows the simplified diagram of this type of clutch. The operation of this clutch takes place when the electric current is passed through the electric winding placed on the flywheel. When {hewinding gets energized, the pressure plate moves towards the flywheel due to increase in armature attraction. It results the engagement of a clutch. The clutch is disengaged when the current supplied to the winding is cut off. There is no longer contact between pressure plate and intermediate plate. Since, the current from vehicles dynamo
ww
w.E asy En gin ee
increases with increase in speed, the clutch engaging force will also increase with the engine speed to provide a progressive clutch engagement.
rin g. shaft
net
Clutch plate
Figure 3.13 Electromagnetic clute" This type of clutch is best suited where the remote operation is desired. Since no linkages are required to control its engagement. The main disadvantage of this type of clutch is that the heat produced due to armature current is high. Its initial cost is also high.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
[EII:M
Automobile
Engineering
3.3.10. Vacuum Clutch The vacuum clutch is operated in the same way as the hydraulic clutch. The only difference is that it is operated by vacuum pressure whereas the hydraulic clutch is operated by oil pressure. In vacuum clutches, the partial vacuum existing in the engine manifold is used for operating it. Figure 3.14 shows the line diagram of a vacuum clutch. It consists of a vacuum cylinder, solenoid valve, reservoir and non-return valve. One end of the reservoir is connected to the inlet manifold through a non-return valve whereas the other end is connected to the vacuum cylinder through a solenoid switch. The solenoid valve is operated by the battery and the
ww w.E
circuit incorporates a switch which is placed in the gear lever. The switch is operated when the driver holds the lever to change gears. A piston in the vacuum cylinder is connected to the clutch through linkages. When the throttle is opened in the engine inlet manifold, the pressure in the manifold increases due to which the non-return valve closes. It isolates the reservoir from the manifold. Thus, a vacuum exists in the reservoir all time.
To inlet manifold
asy E
ngi
Switch in the gear lever
nee
Solenoid
rin
g.n e
Vaccum cylinder
t
Reservoir Vent
Figure 3.14 Vacuum operated clutch During normal running conditions, the switch in the gear lever remains open and the solenoid valve remains in its bottom. The atmospheric pressure acts on both sides of the piston of vacuum cylinders. Since, the vacuum cylinder is opened to the atmosphere through vent. When the driven member holds the lever to change the gear, the switch is closed. It causes the solenoid to pull the valve up. Now, one side of the vacuum cylinder is connected to the reservoir. Due to the vacuum pressure, the piston moves in the left hand side to actuate the Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I TransmissionSystems
Uk·
clutch When the driver is not operating gear lever, the switch will be opened and the clutch remains engaged due to spring force. 3.4. TROUBLE SHOOTING OF CLUTCH
1. Clutch slips while engaged
----------------------------------------------------------------------------------------------------------Remedies
Causes
----------------------------------------------------------------------------------------------------------I. Incorrect pedal-linkage adjustment.
Readjustment has to be made.
2. Broken or weak pressure springs.
Replacement of corresponding springs
ww
should be carried out.
w.E asy En gin ee
3. Binding in clutch-release linkage.
Adjustment and lubrication should be done.
4. Broken engine mount.
Replacement should be carried out.
5. Worn friction-disk facings.
Replace facings or disk
6. Grease or oil on disk facings.
Replace facings or disk
7. Incorrectly adjusted release levers.
Readjust
8. Warped clutch disk.
Replace.
rin g.
----------------------------------------------------------------------------------------------------------
...
net
2. Clutch chatters or grabs when engaged ----------------------------------------------------------------------------------------------------------Remedies Causes ----------------------------------------------------------------------------------------------------------Free, adjust, and lubricate. I. Binding in clutch-release linkage. 2. Broken engine mount.
Replace.
3. Oil or grease on disk facings.
Replace facings or disk glazed or loose facings.
4. Binding of friction-disk hub.
Clean and lubricate.
5. Splines on clutch shaft.
Replace defective parts.
6. Broken disk facings or pressure plate.
Replace broken parts.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
17. Warpped clutch disk.
Automobile
Engineering
Replace.
----------------------------------------------------------------------------------------------------------3. Clutch spins or drags when disengaged ----------------------------------------------------------------------------------------------------------Causes Remedies ---------------------------------------------
,.
.a
_
1. Incorrect pedal-linkage adjustment.
Readjust.
2. Warpped friction disk or pressure.
Replace defective part plate.
3. Loose friction-disk facing.
Readjust.
4. Improper release-lever adjustment.
ww
Clean and lubricate.
5. Friction-disk hub binding on clutch shaft.
Replace.
6. Broken engine mount.
Replace.
w.E asy En gin ee
----------------------------------------------------------------------------------------------------------4. Clutch noises with clutch engaged
---------------------------------------------------------------~------------------------------------------Causes
Remedies ---------------------------------------------------------------------------------------------------------I. Friction-disk hub looses on clutch shaft. Replace worn out parts.
rin g.
2. Friction-disk dampener springs broken or weak.
Replace disk.
3. Misalignment of engine and transmission.
Realign.
net
----------------------------------------------------------------------------------------------------------5. Clutch noises with clutch disengaged Causes
Remedies
-----------------------------------------------------------------------------------------------------------
1. Clutch thrown out bearing worn, binding, or out of lubricant.
Lubricate or replace.
2. Release levers not properly
Readjust or replace.
assembly adjusted. 3. Pilot bearing in crankshaft worn or out of lubricant.
Lubricate or replace.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
engine speed, more will be powerful contact between driving and driven members to obtain the engagement. Figure 3.8 shows the construction of centrifugal clutch. The simplest form of centrifugal clutch consists of two members, one is fitted on the driving shaft and other one is attached to driven shaft. The driven member is just a drum whichI encloses the driving member. The driving member consists of a spider, shoes having friction lining at outer end and springs. The shoes are attached to the spider by means of springs as shown in Figure 3.8. The springs exert a radially inward force which is assumed constant. Cover plate
ww w.E
Shoes
asy E
ngi
nee
Figure 3.8 Centrifugal clutch
rin
g.n e
The driving member rotates with the engine shaft. As the engine speed increases, the
t
shoes inside the driving member drum will fly outward due to centrifugal force and come into contact with the inner surface of the driving member. The increase in centrifugal force due to higher engine speed binds the driving member with the driven member thereby results the rotation of both member and shafts at the same speed. The magnitude of the centrifugal force depends on the speed at which the shoe is revolving. When the engine speed decreases, the centrifugal force will decrease which results the disengagement of clutch. The force with which the shoe presses against the driven member is the difference between centrifugal force and spring force. The centrifugal clutch is extensively used in light two wheelers such as mopeds or two wheelers without gears and lawn movers. 3.3.5. Semi-Centrifugal Clutch These clutches are similar to the centrifugal clutches with only difference of relatively light clutch pressure springs exerting low pressure at idling speed. In this clutch, the pressure ..,;
."
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Transmission Systems When the clutch is in engaged position, the male cone is fully inside the female cone in such a manner that the friction surfaces are in perfect contact. It is done by the pressure springs which keep the male cone pressed all time. Now, the torque is transmitted from the engine via the flywheel and the male cone to the gearbox. Flywheel
ww w.E
asy E
ngi
Figure 3.7 Cone clutch
nee
When the clutch pedal is pressed, the male cone slides against the spring force and the clutch is disengaged. Hence, no power is transmitted.
Advantage:
rin
g.n e
Normal force acting on the contact surface is larger than the axial force which reduces the effort required to operate the clutch.
Disadvantages:
t
I. If the angle of cone is smaller than 200, the male cone tends to bind or joint in tJ female cone. It requires heavy force to disengage the clutch. 2. A small amount of wear on cone surface results a considerable axial movement of the male cone for which it will be difficult to allow. 3.3.4. Centrifugal Clutch This clutch is controlled by the engine speed through an accelerator. When the engine speed falls down, the clutch will automatically disengage. When the speed rises above the predetermined value the clutch is engaged. Greater is the centrifugal force due to higher
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
RI_
I Transmission Systems Replace pressure- plate.
4. Retracting spring (diaphragm-spring assembly clutch) worn.
----------------------------------------------------------------------------------------------------------6. Clutch-pedal pulsations
----------------------------------------------------------------------------------------------------------Remedies
Causes
----------------------------------------------------------------------------------------------------------I. Engine and transmission not aligned.
Realign.
2. Flywheel is not seated on flywheel.
Seat properly, straighten, replace crankshaft flange or flywheel bent.
ww w.E
3. Clutch housing distorted.
Realign or replace.
4. Release levers not evenly adjusted.
Readjust or replace assembly.
5. Warped pressure plate or friction disk.
Realign or replace.
6. Pressure-plate assembly misaligned.
Realign.
7. Broken diaphragm.
asy E
ngi
Replace.
-----------------------------------------------------------------------------------------------------------
nee
7. Friction-disk-facing wear
rin
----------------------------------------------------------------------------------------------------------Remedies
Causes
g.n e
----------------------------------------------------------------------------------------------------------Keep foot off clutch except, when
I. Driver "rides" clutch.
necessary. 2. Excessive and incorrect use.
Reduce use of clutch.
3. Cracks in flywheel.
Replace pressure-plate face.
4. Weak or broken pressure springs.
Replace.
5. Warped pressure plate or friction disk.
Replace defective parts.
6. Improper pedal-linkage adjustment.
Readjust.
7. Clutch-release linkage binding.
Free, readjust, and lubricate.
t
-----------------------------------------------------------------------------------------------------------
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'ft.
Automobile Engineering
8. Clutch pedal stiff
----------------------------------------------------------------------------------------------------------Remedies
Causes
----------------------------------------------------------------------------------------------------------1. Clutch linkage lacks lubricant.
Lubricate.
2. Clutch-pedal shaft binds.
Make it free in flocr mat.
3. Misaligned linkage parts.
Realign.
4. Overcenter spring out of adjustment.
Readjust.
ww w.E a
Replace.
5. Bent clutch pedal.
----------------------------------------------------------------------------------------------------------3.5. GEARBOX
syE
Gearbox is a speed and torque changing device. It changes speed and torque between engine and driving wheels. The mechanism through which the driving torque of the engine is transmitted to the driving wheel is the gearbox. Torque is not directly transferred but it can be done in the form of power using a suitable device. It is done between engine of the automobile
ngi
nee r
and driving wheels. During this, the gear ratio varies between engine and rear wheels. More power is required to keep an automobile in motion when compared to power
ing
required for keeping it rolling after starting. It means, ~lteautomobile requires more power at
.ne
the starting while the engine may be developing less power. A transmission system does to turn the engine crankshaft to four, eight or twelve time approximately for each wheel revolution. A reverse gear is also set for backing the car.
t
3.5.1. Necessity of Transmission When a vehicle is running, various resistances oppose it. In order to keep vehicles moving at a uniform speed, a driving force or tractive effort is equal to the sum of all opposing forces. If the tractive effort increases the total opposing resistance, the excess tractive effort will accelerate the vehicle. If the tractive effort is less than the total resistance, the excess of the resistances will lower the speed of the vehicle. When a vehicle starts to move from rest, it needs more force or high torque and also for hill climbing, accelerating or carrying heavy loads due to various opposing resistances. It can
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission Systems
_
be achieved by running the engine at high speed and wheels at low speeds. After starting the vehicle, it is moving due to momentum gained by the weight ofvehic!e. The same force or torque does not need to keep the vehicle in moving. So, the speed of the road wheels has to be progressively increased when the vehicle gains speed gradually. The gearbox is mainly provided for high torque at the time of starting, hill climbing, acceleration and pulling a load. It can be achieved by a set of gears which are enclosed in a gearbox and gear changing mechanism. 3.5.2. Purposes of Transmission
ww w.E
1. It helps the engine to disconnect from driving wheels. 2. It helps the running engine to be connected to the driving wheel smoothly and without shock. 3. It provides the leverage between engine and driving wheels to be varied.
asy E
4. It helps to reduce the engine speed in the ratio of 4 : I in case of passenger cars and in a greater ratio in case of heavy vehicles such as trucks and lorries.
ngi
5. It helps the driving wheels to be driven at different speeds.
nee
6. It gives the relative movement between engine and driving wheels due to flexing of the road springs. 3.5.3. Resistances to Motion
A moving vehicle has to overcome the following resistances. 1.Air resistance:
rin
g.n e
t
It is the resistance offered by air to the vehicle motion. It depends on the following factors. (l) Size of vehicle (2) Shape of vehicle (3) Speed of vehicle, and (4) Wind velocity. 2. Gradient resistances: It is the component of the vehicle's weight which is parallel to the plane of the road. This component remains constant but independent of the vehicle's speed.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
I ..
Engineering
3. Miscellaneous resistance: Other resistances such as rolling resistances depend on the following parameters. (1) Road characteristics (2) Tyre characteristics (3) Weight of the vehicle (4) Vehicle speed. 3.5.4. Tractive Effort
ww
The torque available on the wheel produces a driving force which is parallel to the road known as tractive effort.
w.E
The graph shows the detail of total resistance for the particular road with different gradients. The curves A, B, C. D are total resistance curves for different gradients. The curves
asy E
1,2,3 represent the tractive effort in first, second and third gears respectively.
t
o
ngi
nee rin
o
g.n et
M N P R Vehicle speed __..
Figure 3.15 Tractive effort Both curves are plotted with the same scales in Figure 3.15. When the vehicle is running in 3rd gear on a gradient, it will give the total resistance curve. So, OP is the stabilizing speed. If the speed at any instant is more than OP, say OR, then the excess resistance called
tractive effort will be decelerated to OP. Similarly, if the speed at any instant is less than OP, say ON, then the excess tractive effort will be accelerated to speed OP.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
,f. I
Systems
In the same 3rd gear, the next higher gradient curve B is considered. In this case, the stabilizing speed has slightly decreased. The curve C does not cross the curve of 3rd gear. So, the vehicle is not able to run at this gradient in 3rd gear. Therefore, we are lin a position to shift on to 2nd gear. Now, the stabilizing speed OM is obtained. Similarly, the vehicle is not able to run in the 2nd gear for gradient D. Thus, the vehicle has to be shifted in the 151 gear.
The vehicle requires more acceleration at the time of starting to gain the required speed quickly. The maximum tractive effort is available in the first gear. Therefore, the vehicle is running in the first gear at the beginning. Then, it is shifted to 2nd gear and so on. Similarly, when the vehicle is running across a steeper gradient, then it is always shifted to the first gear
ww
by accelerating at very slow speed.
w.E
3.6. TYPES OF GEARBOX
asy
There are many types of gearboxes. Generally, it can be classified as follows. 1. Manual transmission
(a) Sliding mesh gearbox
(b) Constant mesh gearbox (c) Synchromesh gearbox 2. Epicyclic gearbox 3. Automatic transmission (a) Hydramatic gearbox (b) Torque converter gearbox.
En
gin eer
ing
.ne
t
3.6.1. Sliding Mesh Gearbox Among the manual gear transmissions, this sliding mesh type is simple in construction. It consists of the following parts. 1. Output shaft 2. Low and reverse sliding gear 3. Second sliding gear 4. Clutch 5. Input shaft Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
I ..
Engineering
6. Clutch gear 7. Counter shaft drive gear 8. Counter shaft 9. Low speed gear 10. Second gear 11. Reverse gear 12. Reverse idler gear 13. Gear shift fork.
ww
It is the simplest type of gearbox. In this gearbox, spur gears are used. Figure 3.16 shows
the construction of a sliding mesh type transmission having three forward and one reverse
w.E
speeds. There are three gears (1, 6 and 5) attached on the main shaft and four gears (2, 3,4 and 7) on the lay shaft.
asy E
The two gears on the main shaft (6 and 5) can be slided by a shafting yoke and mesh with the gears (3 and 4) on lay shaft. Therefore, it is called sliding mesh gearbox. A separate idler gear (8) is mounted on the idler shaft.
ngi n
3
2
1
R
eer --
Gear shift fork
ing .ne t
Figure 3,16 Sliding mesh gearbox (i) Gears in neutral: When the engine is running and the clutch is engaged, the counter shaft is driven by the cultch gear. The cultch gear rotates in opposite direction to the counter shaft. The low speed and high speed gears that are fitted on the transmission main shaft or gearbox shaft do not
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission Systems
...
m I
rotate because they are not engaged with any driving gears. Therefore, there 1s no motion transmitted from clutch to output shaft. Hence, the vehicle is stationary. (ii) First or low speed gear: When the gear shift fork moves towards direction (1) by operating the gear shift lever, the sliding gear (5) on the output shaft will be shifted forward to mesh with low speed gear (4) on the countershaft. It results the rotations of input shaft being transmitted in the order (1) ::::(2):::} (4):::} (5) to tum the output shaft, as shown in Figure 3.17. This gear combination is the one that produces the lowest speed from the input shaft and low transmission.
ww
w.E
asy
En
gin eer
Figure 3.17 First or low speed gear (iii) Second gear:
ing
When the gear shift fork is moved toward direction 2, the second sliding gear (6) will be shifted backward to mesh with the second speed gear (3) but gear (5) and gear (4) are
.ne
unmeshed. The rotation of input shaft is transmitted in the order (1) :::}(2) :::}(3) :::}(6) to tum the output shaft, as shown in Figure 3.18. It is the transmission in the second speed.
t
Figure 3.18 Second gear
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
(iv) Third or top gear: When the gear shift fork is moved toward direction 3, the clutch (6) will be meshed directly with the clutch gear (1) and gear (3) is unmeshed, as shown in Figure 3.19. Due to this, both the input and output shafts are coupled and rotated together. It is the transmission in the third or top speed.
ww
w.E
(v) Reverse gear:
asy E
Figure 3.19 Third or top gear
ngi
When the gear shift fork is moved toward direction R, the sliding gear'(S) will be shifted
nee rin
backward to mesh with the reverse idler gear (8), as shown in Figure 3.20. Then the rotation of input shaft is transmitted in the order (1) => (2) => (7) => (8) => (5) to turn the output shaft in reverse direction. It is the transmission in reverse speed. Even though there is no measure to
g.n et
allow easy meshing of gears, "double clutching" technique must be acquired for shifting gears properly. The gears also have some disadvantages such as noisy and defects. So, this type is not practically in current use.
Figure 3.20 Reverse gear
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Transmission Systems
\
Figure 3.21 shows the construction ofa constant mesh type gearbox having three forward and one reverse speeds. In this type of gearbox, all gears are in constantly in mesh and dog clutches are used for engaging and disengaging the gears. The dog clutches (D) and D2) are mounted on the main shaft. One (D2) is connected between clutch gear and reverse gear whereas the other (D)) is placed between low speed gear and reverse gear. The splines are provided on the main shaft for the linear movement of dogs. Dog clutch can slide on the shaft and rotate along with it. All gears are rigidly fixed on the counter shaft. All main shaft and lay shaft gears, and idler gears are engaged by dog clutch to obtain opposite and slow speed. Only reverse gears are spur gear type and all others are helical gears.
ww
Second gear Slidingdpg clutch
w.E
Clutch gear",
asy
En
gin eer
ing
Figure 3.21 Constant mesh gearbox
.ne
t
Figure 3.22 First gear of constant mesh gearbox Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
(i)First gear: The dog clutch (0,) is shifted to left side for engaging on (7), as shown in Figure 3.22. Now, the power is transmitted through the gear (1) => (2) => (4) => (7) to the dog clutch 0,. Then, it is transmitted to the main shaft through splines. Hence, the first gear speed is obtained. (ii) Second gear:
In this, the dog clutch (0,) is disengaged and the dog clutch (02) is shifted to right to lock with the gear (8) as shown in Figure 3.23. Therefore, the power is transmitted from clutch shaft through (1) => (2) => (3) => (8) to dog clutch (02) and then to the main shaft. So, the
ww
main shaft rotates with the second gear speed.
w.E
asy E
ngi
nee rin
Figure 3.23 Second gear of constant mesh gearhox
g.n et
Figure 3.24 Third gear of constant mesh gearhox
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
",.
Transmission Systems
(iii) Third or top gear:
The dog clutch (D2) is moved left to engage with the gear (l) on clutch shaft as shown in Figure 3.24. Now, the engine speed is directly supplied to the main shaft. It is called top gear speed. (iv) Reverse gear: First, the dog clutch O2 is disengaged. Then the dog clutch 01 is shifted to right to engage with the gear (6). Therefore, the power is transmitted from clutch shaft through (I) ~ (2) ~ (5) ~ (Idler gear) ~ (6) to dog clutch (02) and then to the main shaft. The idler gear causes the main shaft to rotate in the opposite direction.
ww
w.E
asy
En
gin eer
ing
Figure 3.25 Reverse gear of constant mesh gearhox
.ne
As compared with the sliding mesh type, the constant mesh type gearbox meshes more
t
readily with the gears having less danger of damaging during meshing because the gear diameters are smaller with few numbers of teeth. So, this type has more defects when compared to a synchromesh type. The necessity of double clutching is needed so that it is not used to any large extent. Advantages of the constant mesh gearbox over the sliding mesh type: 1. Helical or double helical gear teeth can be used for the gears instead of spur gears except reverse gears. So, a quicker gearing can be achieved. 2. Synchronizing devices can be used for smooth engagement of gears. 3. Only damage occurs on dog clutch teeth and not to teeth of gear wheels. 4. Once the dog clutches are engaged, there is no motion between their teeth but the power is transmitted through the sliding action of the teeth of one wheel on those of Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I...
Automobile
Engineering
the other when the gear teeth are engaged. To transmit the motion properly, the teeth are suitably shaped. 3.6.3. Synchromesh
Gearbox
To simplify the operations of changing gears without the occurrence of clashes and their consequent damage, a synchromesh gearbox is used in different types of motor vehicles. The synchronizer helps to synchronize the speeds of two gears to be engaged without necessity of faster running gear to slow down. Nowadays, both helical gears and synchromesh units are used in car gearboxes. It is used for easy and noiseless gear changing operation. The arrangement is similar to a constant
ww
mesh gearbox. But, it has synchromesh unit instead of dog clutches. Synchromesh device first
w.E
engages two gears into frictional contact. Once their speed attains equal or synchronized, they are engaged smoothly.
asy E
Generally, synchromesh units are connected with top two gears only. The reverse and first gears are not connected with synchromesh units. They are engaged when the vehicle is stationary.
ngi
nee rin
The main features of this type of gearbox are as follows.
1. The main shaft or output gears are freely rotated on bushes of the output shaft. They are internally placed by splined thrust washers. Generally, single or double helical gears are used in constant mesh with the long shaft gears.
g.n et
2. When their speed is equalized or synchronized by their cones, the output gears will be locked to their shaft by the dog clutch.
Figure 3.26 shows the synchromesh unit. The synchromesh unit helps to synchronize the speed of two gears to be engaged without necessity of faster running gear to slow down. Quick shift is possible and noise is reduced by eliminating any clashing of gears. The clutch brake of unit is engaged with the faster running gear of these two gears. The speed of the faster running gear has to be quickly slowed down to the slow turning gears before putting into operation. It is done for intermediate and high-speed gears. In an Ambassador car, this system is incorporated on second, third and fourth gears. A synchronizing unit has a set of sleeves. These sleeves slide endwise. The inner sleeve is splined on the main shaft. It contains gunmetal faced female cones on both ends. These cones are mounted over male cones integrated with each main gear having secondary toothed wheel. The inner sleeve is fitted over the outer sleeve which contains internal teeth to engage _ Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
Systems
_
I
with the teeth of secondary wheel. The outer sleeve is locked at different positions through balls. Springs are held on the inner sleeve. The shifting fork links into the groove at the outer sleeve to slide it endwise for achieving various gear speeds.
ww
w.E
asy E
Figure 3.26 Synchromesh unit
ngi
The synchronizing unit slides on the splines of the main shaft to engage the cones and then the outer sleeve slides over the inner sleeve or hub to engage the gears through a dog clutch. \Vhen the synchronizing unit is moved to either left or right, the female cone in the inner sleeve is mounted over the male cone. This female cone is an integrated with the gear
nee rin
which is moving free over the main shaft. The friction of the cones helps to revolve the main
g.n et
shaft with the main gear. Also, it speeds up or slows down as required until the speed of the main shaft and gear is same. The clutch is easier to the gear with the main shaft through the synchronizing unit when the speed is synchronized. 'The synchronization of speed obtained with a partial movement of the gear shift lever. Further movement of the gear lever causes the outer toothed sleeve to slide relative to cones. It tends to engage with the secondary wheel in the form of a dog clutch. It results the driving member of main shaft rotate with the main gear. Advantages: 1. Gear changing is very much simplified. 2. Less wear in gears. 3. It allows the usage of helical gears that run quietly. Disadvantages: 1. The design is very much complex.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
12. Initial cost is high.
Automobile Engineering
~
3. Quick change of gears occurs due to noise of crashing. 3.6.4. Epicyclic Gearbox
In ordinary gearing, the axes of various gears are fixed. These gears are simply rotated I about their axes. In the case of epicyclic gearing, at least one of the gears not only rotates about its own axis but also rotates about some other axes. The two arrangements of the epicyclic gear trains are shown in Figure 3.27. In Figure 3.27 (a) arrangements, a spur pinion called sun wheel is an integral part of shaft
ww
which is made to rotate freely about its own axis XsX. The pinion shaft is mounted on bearings in the frame. Also, 11crankshaft or carrier arm is also made to rotate freely about the
w.E
same axis x-x. This arm is connected with a spur pinion called planet wheel by crankpin. The planet wheel is freely to revolve about its own axis y-Y. When the carrier arm is rotated on its bearings, the planet wheel will also rotate bodily about the axis XsX.
asy E
The planet wheel is meshed with the spur pinion and also meshed with an internally toothed ring called annulus. The annulus is one part of the frame as a fixed unit. The annulus
ngi
is circular and concentric with the axis X-X. It is an epicyclic train of gearing. It provides a
nee rin
definite and fixed speed or gear ratio between the shaft attached to the sun wheel and the shaft _ of the carrier arm.
(a)
g.n et
(b)
Figure 3.27 Epicyclic gear box In Figure 3.27 (b), the sun wheel (1) is a part of integral shaft which is freely to rotate about its axis in the frame. This sun wheel is meshed with the teeth A of the compound planet Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
Systems
I
~.,.-
wheel. Now, the compound wheel freely revolves on the pin of the carrier arm. The carrier arm called shaft is mounted in the frame. It is free to revolve about the sun wheel. The portion B of the compound planet wheel is meshed with the sun wheel (1). When the carrier arm shaft is turned, the shaft attached to the sun wheel (1) will also be driven in the same direction as the carrier arm rotates. But its speed is low. The epicyclic or sun and planet type gearbox have no sliding dogs or gears to engage. But different gear speeds can be obtained by tightening brake bands on the gear drum. Hence, gear changing is simplified. Figure 3.:28shows an epicyclic gearbox. The compound gear 1, 3, 5 is located to a pin
ww
fixed on a wheel A. The compound gear is freely rotated on the pin. Gears 1, 3 and 5 are meshed with three different gears 2, 4 and 6 respectively. They are connected in turn to drums
w.E
7, 8 and 9. The drums 7 and 8 have brakes in their outer circumference and a number of clutch plates are provided on drum 9. A hub is attached to the flywheel spigot shaft N in which a
asy
number of clutch plates are fitted.
En
For obtaining top speed, the member lOis pressed against clutch plates. It will engage the clutch by connecting the shaft N to the output shaft P directly. Thus, the top speed gear is obtained.
gin eer ing rl;~'"01-~~~ :"; .ne 3 5
-
I!
InputShJ~ Ii -,
Iii,
!-:::J
-
;lutCh plates
Ii
~
N
l'-
~
Output shaft(P) )'
~I~---------~--------------~
~~
~
t
10
~O 1»1 diiti'ii
7
~
8
9
Figure 3.28 Epicyclic gearhox For obtaining low speed, the clutch is disengaged and brake is applied on drum 8. It is done withthe-help.ofa gear change lever. This action locks the gear 4 by decreasing the speed of gear 2. Hence, the output shaft is reduced.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering
Fo~obtaining reverse speed, the clutch is disengaged and brake is applied on drum 10. It locks the gear 6 by reversing the direction of rotation of 2 with respect to the input shaft. Thus, the speed of 2 is also reduced. Advantages of epicyclic gearbox: 1. The planetary gears are in constant mesh. Hence, dog clutches or sliding gears are not used. 2. External contracting hand brackets or multi-plate clutches of relatively small dimensions are used for changing the gears. 3. It is a more compact unit because the planetary gear operates within a ring gear with
ww
its external surface of cylindrical form.
w.E
4. It is distributed over several gear wheels instead of having the load on only one pair of gears.
asy E
5. A greater area of gear tooth contact can be obtained due to distribution of loads. 6. In comparison to the three or four speed gearbox, gears and gear housings of this
ngi
gearbox can be made smaller in overall dimensions. 3.6.5. Automatic Gearbox
nee rin
Various speeds are obtained automatically in gearboxes are known as automatic gearbox.
g.n et
Generally, the driver selects the car condition such as neutral, forward or reverse. The selection, timing and engagement of gear for the required gear speed are selected automatically when the accelerator is pressed or depressed. Automatic gearbox does not require gear change lever and clutch pedal. Since, both clutch and transmission are a combined unit which works automatically. The automatic gearbox is operated in two ways namely 1. Hydramatic transmission, and 2. Torque converter transmission. In the case of hydramatic transmission gearbox, the planetary gear sets are connected in such a way that power may be transmitted through them. A centrifugal governor in the transmission chooses the: proper g~ar according to the speed and throttle position. The gear shifting from one gear to another gear is done through hydraulically operated pistons by actuating springs. These springs control the brake bands on the planetary gear sets and clutches within the planetary unit. The various shifts are achieved by the throttle and Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
UfM
Systems
centrifugal governor. Torque converter transmission system employs fluid coupling, torque converter and epicyclic gear arrangement. If all different devices are combined into one unit, they will do their duties jointly without any interruptions. Now-a-days, automatic transmissions are popular with various names prescribed by the manufacturers. They may differ in construction slightly. Somebody employ only fluid coupling with the planetary transmission. But others may include a torque converter with fluid coupling and planetary transmission as per their requirements.
3.7. HYDRAMATIC TRANSMISSION In this case, the transmission is done by fully automatic system. It has a combined four
ww
speed forward and reverse automatic geared transmissions with a flywheel. Three sets of
w.E
constant mesh helical planetary gears are connected in series to provide in the geared transmission. The two sets of planetary gears are used to obtain the four forward speeds in a
asy E
hydramatic gear system. The impact of the automatic shifts is cus~ioned and also the fluid flywheel reduces the torque reactions of the engine. Motor veh icles attached with hydramatic drive are not connected with clutch pedals. But the accelerator and brake are used for the purpose of control.
ngi
nee rin
Hydraulically operated pistons actuated by springs controls brake bands on the planetary gear set. Clutches within the planetary unit are used for doing the change from one gear to another. The gears are shifted to higher speeds with throttle opening because throttle position
g.n et
and the centrifugal governor govern the various speed shifts. By this, maximum power and acceleration are obtained. A lever and sector segment are located on the steering column to -
adjust any of the four positions such as neutral, drive, low and reverse. This arrangement helps driver to control the vehicle movement position. The transmission is shifted automatically in the driver position in any of the four forward speeds. Only, the first and the second gear positions are used to drive. The low position is for hill climbing or heavy or muddy terrain. The fluid flywheel is a part of the gear train providing drive from the internal gear in the front unit by a shaft linkage. A torus cover is bolted to the engine flywheel and it encloses the fluid flywheel. A drum enclosing a brake band for locking the drum and the sun gear is attached to sun gear if the front unit is used for gear reduction. The gear is held stationary in internal gear driving. Then the planet cage is made to connect the driven member of the front unit shown in Figure 3.29. A hollow intermediate shaft having front section is connected with the driving member called driving torus.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I ..
Automobile
Engineering
Sun gear
ww w.E
Figure 3.29 Hydramatic gearbox
asy En gi
The rear section splined to the clutch hub of the rear unit is attached to a splined planet cage. The power from the internal gear of the front unit is transmitted forward through the intermediate shaft to the driving torus. It is done by the planet cage. By this, the power is transferred to the driven member or driven torus. A main shaft which is turning inside the intermediate shaft is attached to a splined driven torus. It is for transmitting power rearward to
nee r
the sun gear of the rear unit. If the rear unit is in reduction, the internal gear is fastened to a
ing .ne
drum and brake band assembly in position. The planet cage splined to the output shaft is the driven member when the internal gear is held stationary. It is achieved by sun gear receiving power from the main shaft, called driving member.
t
The two units are provided with hydraulically operated multiple disc clutches to lock various gears together if they are in direct drive. The planet cage is locked by the clutch. At the same time, the sun gear is in the front set. The clutch connects with the internal gear in the rear unit while applying the rear section of the intermediate shaft. (i) First gear: Both units are located in the first gear in such a way to produce maximum gear ratio. They are held stationary when the brake bands are applied hydraulically and also with spring operated devices known as 'servos'. Then, the power is transmitted from the flywheel to the torus cover, then to the internal gear and to the planet cage with the sun gear when the front unit is locked. Thus, the engine is running.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
Systems
_
The planet cage usually moves around the stationary sun gear with reduced speed. The power is transmitted by the cage to the driving torus through the front section of the intermediate shaft. Then the power from the driven torus is transmitted to the sun gear of the rear unit. The sun gear drives the plant cage when the planet pinions move around the stationary internal gear. (ii) Second gear:
The front unit is placed in a direct drive by releasing the front band and also the front clutch is applied to obtain the second speed. The power is first transmitted to the torus cover and then to the locked front unit from the flywheel. Then the front section of the intermediate shaft transmits the power directly to the fluid flywheel. Then, it is transmitted back to sun gear of the rear unit through the main shaft or driving shaft to the driven torus. The rear unit
ww
transmits the power to the output shaft. (iii) Third gear:
w.E
asy E
The controls are operated to release the clutch and also for applying the band in the front unit to provide this speed. To transmit this speed to the direct drive, the clutch is moved back. Then the band is released and the clutch is applied in the rear unit. Now, the gear ratio is
ngi
1.45:1. It is similar to front unit. The planet cage is driven by the internal gear. Now, the
nee rin
power is transmitted from the flywheel to the torus cover. The intermediate shaft is transmitting the power forward to the fluid flywheel but reversed to the locked clutch of the rear unit. The rear unit is already driven by the planet cage. Therefore, the intermediate shaft
g.n et
and the fluid flywheel transmit power to the rear unit through the main shaft to the rear sun gear. 40 % of power flows through the fluid coupling and 60 % flows through the intermediate shaft directly to the rear unit. Both the slippage and loss of power are considerably reduced due to this arrangement. (iv) Fourth gear: The direct drive is obtained by controlling the transmission by locking the clutch and releasing the band in the front unit. Now, the power is transmitted from the flywheel through the torus cover to the locked front unit. The power is transmitted in two paths. One is along the intermediate shaft which is transmitted from forward to the fluid flywheel. The other one is to the clutch hub of the rear unit similar to the third gear. By dividing 40 % power through the fluid drive main shaft, rear sun gear and 60 % directly through the intermediate shaft, the slippage is reduced.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Ism
Automobile
Engineering
ww
w.E
asy E
ngi
nee rin
g.n et
(v) Reverse gear: A third set of planetary gears is added to obtain the reverse gear in addition to gears used in the rear unit shown in Figure 3.30. A reverse unit has a sun gear which is fastened to the internal gear of the rear unit, a planet cage which is splined to the output shaft and an internal gear. Both external and internal teeth are provided in the internal gear. When the pawl called anchorpin engages its external teeth, it is held as stationary in the reverse gear. The pawl and the external teeth are provided in a parking brake while the internal gear is held by a hydraulic cone clutch in modern designs. The controls shift the front unit into Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIDI I
Transmission Systems
reduction to release the rear band and clutch. It is also held the gear stationary by engaging the anchor pinion. The power flows similar to the first gear which means from the flywheel to the torus cover, to the front internal gear; to the planet cage, to the intermediate shaft and to the fluid flywheel. The power is transmitted by the main shaft to the rear sun gear. Due to locked reverse internal gear, the reverse planet cage cannot turn freely. Therefore, the rear planet cage will act as an idler to force the rear unit internal gear in such a way to turn in reverse direction with the rear unit. The reverse planet cage turns the output shaft in reverse direction due to the rear unit internal gear driving the reverse sun gear turning in a reverse direction. Reversal is obtained by a compound reverse gear set which is already combined with the reduction produced in the
ww
front unit.
(vi) Neutral gear:
w.E
The front band and clutch and also rear clutch are released by controls provided on a selector lever. Due to this action, the engine flywheel is completely disengaged from the output shaft. It causes no power transmission. The controls release the rear band and also set
asy E
the blocked piston in the cone reverse units when the engine is running. Advantages of automatic transmission:
1. It is a simplified driving control.
ngi
nee rin
2. It gives less physical and manual fatigue to the driver.
3. There is no clutch pedal and gear lever and hence, it makes the simplification of driver's compartment.
g.n et
4. It provides smoother running under all conditions due to hydraulic coupling and automatic gear change. 5. No shocks or jerky driving are produced while running. 6. Improved acceleration and hill climbing are obtained. 7. Fuel consumption is reduced. 8. It has less wear and tear due to planetary gearing. 9. Noise free gear shifting is possible. 10, It has longer life.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile
Engineering
3.8. SHIFT OR SELECTOR MECHANISM For gear changing and selecting a particular gear train to operation, the selector mechanism is implemented to obtain the same easier. In this case, the gears are shifted by a gear shift lever. In manually operated selective transmission systems, the gear shift lever is mounted either on steering column or on the floor board. (a) Floor mounted shift mechanism: In this type, the selector mechanism is provided at the top of the gearbox as shown in Figure 3.31. The gear lever is ball mounted in the gearbox cover. It provides movement in any direction. The lower end of the gear lever is fitted into a slot in the selector sleeve. Forks are
ww
mounted on sleeves on three separate selector rods. They are supported in the gearbox casing. Each selector sleeve can slide on its rod just to avoid unwanted engagement of gears. Slots are provided on selector rods. The sleeves are made with spring loaded balls. These balls
w.E
oppose the movement of the forks until some force is applied to the gear lever to overcome
asy E
their resistance. Grooves are made on the gear bosses where the selection forks are fitted. Transverse motion of gear lever selects the fork to engage for obtaining the longitudinal movement. Then the fork is sliding to engage the selector gear.
ngi
nee rin
g.n et
Gear
Figure 3.31 Floor board type shift mechanism (b) Steering column mounted gear shift mechanism: In this type, one gear lever rod is placed on the steering column shown in Figure 3.32. A tongue is fitted on the gear lever rod to engage forks by the axial movement of rod. Then the angular movement of the gear shift lever slides in the gearbox and there by engaging the selected gear. Gear lever is moved-axially upward and then moved radially forward or backward for obtaining the first or second gear. The gear lever is moved downwards from the neutral Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I
EmIl
Transmission Systems
I
position and then moved radially forward or backward to obtain the third and fourth gear speed, To obtain reverse gear, the knob is moved outwards, the lever then pushed downwards in the neutral position to the extreme position. After this, the lever is moved backwards, thus engaging the reverse gear. 3
z'"
Link to top & Reverse gears fork
Link to 1st & gears fork
.--.@
N
,®- _-_-0 ,/
R'
® :'
.'N
1
,
02
ww
Rod
w.E
Steering column
asy E
Figure 3.32 Steering column mounted gear shift mechanism
ngi
3.9. TROUBLE SHOOTING OF GEARBOX
nee rin
1. Hard shifting into gear ----------------------------------------------------------------------------- --------------------------------Remedies Causes
g.n et
--------------------------------------------------------------------------------------------------------------Adjust.
1. Gearshift linkage out of adjustment. 2. Gearshift linkage needs lubrication.
Lubricate.
3. Clutch not disengaged.
Adjust.
4. Excessive clutch pedal free play.
Adjust.
5. Shifter work bent.
Replace or straighten.
6. Sliding gears or synchronizer tight on
Replace defective parts.
shaft splines. 7. Gear teeth battered.
Replace defective gears.
8. Synchronizing unit damaged or springs
Replace unit or defective parts and install spring properly.
improperly installed. 9. Shifter tube binding in steering column.
Correct the tube alignment.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile
Engineering
Lubricate and replace bushing.
10. End of transmission input shaft binding in crankshaft pilot bushing.
--------------------------------------------------------------------------------------------------------------2. Transmission sticks in gear
--------------------------------------------------------------------------------------------------------------Remedies Causes --------------------------------------------------------------------------------------------------------------Adjust of adjustment. 1. Gearshift linkage out of adjustment and disconnected.
ww w.E
2. Gearshift linkage needs lubrication
Lubricate.
3. Clutch not disengaged.
Adjust.
4. Detent balls stuck.
Free: lubricate.
asy En gi
5. Synchronizing unit struck.
Free: replace-damaged unit.
6. Incorrect or insufficient lubricant
Replace with correct lubricant.
in transmission.
7. Internal shifter components damaged parts.
nee r
and correct amount. Remove transmission to inspect
ing .ne
and service shifter.
--------------------------------------------------------------------------------------------------------------3. Transmission slips out of gear
t
--------------------------------------------------------------------------------------------------------------Causes
Remedies
--------------------------------------------------------------------------------------------------------------1. Gear shift linkage out of adjustment.
Adjust.
2. On floor shift, shift boot stiff or shift
Replace boot: adjust console to
lever binding.
relieve binding.
3. Weak lockout springs.
Replace.
4. Bearings or gears worn.
Replace
5. End play of shaft or
Replace worn or loose parts.
gears excessive. 6. Synchronizer worn or defective.
Repair; replace. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
Systems >
•
7. Transmission loose on clutch housing or misaligned.
Tighten mountings bolts; Correct alignment.
8. Clutch housing misalignment.
Correct alignment.
9. Pilot bushing in crankshaft loose
Replace.
or broken. Replace.
10. Input shaft retainer loose or broken.
ww
Replace. 11. Broken engine mount. --------------------------------------------------------------------------------------------------------------4. No power through transmission
w.E
--------------------------------------------------------------------------------------------------------------Remedies Causes
asy
--------------------------------------------------------------------------------------------------------------. Adjust. 1. Clutch slipping. 2. Gear teeth stripped.
En
3. Shifter fork or other linkage part broken.
gin eer
Replace gears. Replace. Replace.
4. Gear or shaft broken.
ing
Replace. 5. Drive key or spline sheared off --------------------------------------------------------------------------------------------------------------5. Transmission noisy in neutral
.ne
--------------------------------------------------------------------------------------------------------------~ Remedies Causes
t
--------------------------------------------------------------------------------------------------------------Replace gears. 1. Gear worn or tooth broken or chipped. 2. Bearings worn or dry.
Replace: lubricate.
3. Input shaft bearing defective.
Replace.
4. Pilot bushing worn or loose in crankshaft.
Replace.
5. Transmission misaligned with engine.
Realign.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1m.
Automobile Engineering Replace worn or damaged
6. Counters haft worn or bent, or thrust plate or washers.
damaged parts.
-------------------------------------------------------------------------------------------------------------
... -
6. Gears clash during shifting
--------------------------------------------------------------------------------------------------------------Causes
Remedies
--------------------------------------------------------------------------------------------------------------1. Synchronizer defective.
Repair or replace.
2. Clutch not disengaging pedal free play
Adjust.
incorrect.
ww w.E
3. Hydraulic system defective.
Check cylinder, add fluid, etc.
4. Idle speed excessive.
Readjust.
asy En gi
5. Pilot bushing binding.
Replace.
6. Gearshift linkage out of adjustment.
Adjust.
7. Lubricant incorrect.
Replace with correct lubricant.
--------------------------------------------------------------------------------------------------------------
nee r
7. Oil leakages ------------------------------------------------------------------------------------------------------------_ Causes Remedies
ing .ne
.. -
-----------------------------------------------------------------------------------------------------
._--------
1. Foaming due to incorrect lubricant.
Replace with correct lubricant.
2. Oil level to high.
Use proper amount of oil.
3. Gaskets broken or missing.
Replace.
4. Oil seals damaged or missing.
Replace.
5. Oil slingers damaged, improperly
Replace correctly.
t
installed or missing. 6. Drain plug loose.
Tighten.
7. Transmission retainer bolts loose.
Tighten.
8. Transmission or extension case cracked.
Replace.
<)_
T, ..... J.....""-
Sneedometer gear retainer loose.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
IIlII I
Systems
10. Side cover loose.
Tighten.
11. Extension housing seal worn or drive line yoke worn.
Replace.
8. Transmission noisy in reverse Causes
Remedies
1. Reverse idler gear or bushing worn
Replace.
or damaged.
ww
2. Reverse gear on main shaft worn
Replace.
w.E
or damaged.
3. Counter gear worn or damaged.
Replace.
4. Shift mechanism damaged.
Repair, replace defective parts and
asy E
ngi
readjust.
nee rin
9. Transmission noisy in gear Causes 1. Clutch friction disk defective.
Remedies Replace.
g.n et
2. Incorrect or insufficient lubricant.
Replace with proper enough lubricant.
3. Rear main bearing worn or dry.
Replace or lubricate.
4. Gear loose on main shaft.
Replace worn parts.
5. Synchronizer worn or damaged.
Replace worn or damaged parts.
3.10. OVERDRIVES In transmissions, the high gear position produces a I:1 ratio between clutch gear and transmission output shaft. There is neither gear reduction nor gear increase through the Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
transmission. It is the direct drive. At intermediate and higher car speeds, it is sometimes desirable to have the transmission output shaft turned faster than the clutch gear and engine crankshaft. Therefore, some transmission systems are designed with gears to provide an over drive ratio. A transmission is in overdrive when the transmission output shaft is turning faster than the transmission input shaft or clutch gear. Some years ago, many cars were equipped with a separate overdrive unit which was attached to the rear end of the transmission. Today, the overdrive is built into the transmission. Many four-speed and five-speed transmissions have overdrive. The top gear position causes the transmission main shaft to overdrive (tum faster) than the clutch gear.
ww
Overdrive is a device which is used to step up the gear ratio in the car. It is mounted in
between transmission and propeller shaft. It provides a high cruising speed with a comparatively low engine speed (up to about 20-25% less) on long journeys. Due to this, less wear of the engine parts, vibration and noise are produced. Though the friction losses at lower
w.E
asy E
speeds are less, there will be a possibility in saving fuel with the overdrive. Overdrive is generally fixed at the top gear only. Overdrives are fixed on gears other than the top gear for increasing the torque ratios available in some sport cars. For examples, by
ngi
connecting overdrive at the top, third and second gear, seven forward speeds or torque ratios can be obtained. Usually, overdrives are operated either manually or automatically at a predetermined speed.
nee rin
g.n et
A method of obtaining a fourth forward speed especially in modern passenger cars is through "overdrive" only. It provides a speed ratio "over or high" with the direct or highspeed ratio. Only 70% of the propeller-shaft speed is permissible to operate the engine by this overdrive when the car is operating at higher speed range. The overdrives reduce engine wear, vibration and save gasoline even the car is operated in high gear. Overdrives are used as supplement to conventional transmissions. Slightly higher rear-axle gear ratio is used with an overdrive.
Advantages 0/ overdrive: 1. It allows a lower engine speed to maintain the car at highway speed. 2. It does not require as much as power to keep it moving. Therefore, the engine can turn more slowly, produce less power and still maintain car speed. 3. This system saves fuel. 4. Wear on the engine and accessories are reduced. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
m. I
Systems
5. A typical overdrive transmission can maintain a car speed of 88 kmlhr while allowing the engine to tum at the equivalent of only 70 kmlhr. 3.10.1. Operation The shift to overdrive can be obtained when the car is running above a predetermined cut-in speed from 32 to 51 kmlhr by lifting the foot momentarily from the accelerator. The action of the overdrive is controlled by a centrifugally operated switch. As the car slows down below another predetermined speed (slightly lower than the cut-in speed), it is returned to third speed automatically in most designs. Greater power and acceleration are needed through
ww
the overdrive gear ratio when a car runs on the road. So, the car gear is shifted back gear when an overdrive is depressed by the accelerator to the full-throttle position.
10
direct
w.E
3.10.2. Construction
asy E
A design of overdrive used in late-model American passenger cars is shown in Figure 3.33. This arrangement has a planetary gear set, a solenoid and pawl arrangement to lock the
ngi
sun gear, a rail and fork assembly which is linked to a dash-control knob. It is used for disconnecting the overdrive when it is not in use. On that time, a freewheel assembly or
nee rin
overrunning clutch drives the main shaft below the cut-in speed. Ring gear Planetary gear
Ring gear
g.n et Sun gear plate
cam
Figure 3.33 Planetary gear set arrangement 0/ overdrive mechanism
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
fa
Automobile Engineering
The planetary gears are used to increase the speed. It is done by arranging the ring gear driven with the planet-pinion cage. At the same time, the sun gear is locked. Due to this, the speed of the main shaft increases with decrease in power available to driving wheels. The minimum speed of the engine varies with different models called cut-in speed. If the engine runs below this speed, the drive is made direct by unlocking the sun gear through the solenoid. This solenoid withdraws the pawl held to the gear plate. The operation of solenoid is controlled by an electrical circuit. When the engine speed is above the cut-in speed, the electrical controls having the solenoid move the pawl to engage with the gear plate. Thus, the sun gear is locked. The power
ww
is transmitted from the transmission main shaft to the planet-pinion cage, to the ring gear and to the overdrive main shaft. When the pinions rotate around the stationary sun gear, the ring
w.E
gear is driven at increased speed. Generally, the gear ratio is about 0.7 : 1. The ring gear is splined to the outer case of the freewheel assembly. It is a part of the overdrive main shaft.
asy E
If the pawl is not engaged in the gear plate, the sun gear is unlocked. Due to this, the planetary gears will not transmit power. When the unit is in direct drive, the power will flow from the transmission main shaft to the freewheel assembly and to the overdrive main shaft.
ngi
nee rin
3.10.3. Freewheel Assembly or Overrunning clutch
Freewheel assembly or overrunning clutch, sprang clutch or one-way clutch are essential
g.n et
parts of every overdrive. This mechanism transmits the rotational motion only in one direction but not in reverse direction. It is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft.
The unit runs free whenever the power is transmitted through the planetary gears. Otherwise, whenever the engine slows down, the transmission main shaft is started to drive the output shaft. The construction and principles of operation of a typical freewheel unit are shown in Figure 3.34. It consists of cam, rollers and outer race. One part of the free wheel unit consists of a hub having internal splines. These internal splines connect the transmission shaft to freewheel unit. The outside surface of the hub is splined with cam and it has four cam profiles to hold twelve rollers in a cage between them and outer race. The outer race is splined for connecting with the overdrive output shaft.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
mill
Systems Steel rollers outer casing
/
Spring
Hub or splined shaft
~~~Y.r;t-
ww
w.E
asy
En
Figure 3.34 Freewheeling assembly
gin eer
When the transmission output shaft rotates faster than the overdrive main shaft as shown in Figure 3.34, the rollers are shifted into narrow parts between cam and outer race to perform the locking action. By this, the transmission output shaft rotations are transmitted through cam
ing
to rollers and to outer race and then to drive the propeller shaft. It is the r -thod to drive the output shaft in direct drive.
.ne
When the outer race turns faster than cam, the outer race becomes the driving member.
t
Now, rollers are dropped into valley parts of the cam to unlock the connection between transmission
output
shaft and overdrive
main
iaft. Thus, the free wheel is moved
independent of the hub. So, the entire assembly acts as a roller bearing. The torque is not transferred from the outer race to cam.
3.10.4. Pawl Action Before engaging the pawl with the gear plate to lock the sun gear in overdrive, several conditions must be satisfied. First, the control knob at the dash must be in overdrive position to move the rail and fork assembly into the position. Then the vehicle must be moved at a speed above the cut-in speed and then the driver must momentarily release the accelerator pedal.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I~
I
Automobile Engineering
When the vehicle speed is above the cut-in speed, the solenoid is energized by electrical controls. By this, the pawl is pushed towards the position of engagement with the gear plate. The movement of the pawl is locked by the blocker ring as shown in Figure 3.35(a). When the driver releases the accelerator pedal, the freewheeling unit is slipped and also the engine is slowed down. It drives the output shaft to drive the ring gear at a speed greater than the speed of the planet cage. When the speed of the engine-driven planet cage comes to 0.7 of ring gear, the speed of the engine is decreased. Thus, the sun gear is moved backward. In Figure 3.35(b), the blocker ring is moved by its frictional drive from the sun gear-driven control plate hub. It also rotates slightly backward and releases the pawl by snapping into the first notch of the gear-control plate. It is carried out when the control plate rotates backward less than 113 of a turn. For ensuring smooth running action of the shift from direct drive to overdrive, a perfect synchronizing mechanism is used.
ww w.E
Sun gear control plate
asy En gi
Frictional engagement
nee r
(a) Pawl released
ing .ne
(b)Pawl engaged
Figure 3.35
t
The CC11 speed of 5 or 6 kmlhr below the cut-in speed is maintained, once the overdrive is engaged. So, the electrical controls shown in Figure 3.36 are put into action to withdraw the pawl. The free-wheel direct drive is released when the throttle closes. 3.10.5. Electrical Controls of Overdrive The overdrive electric control serves the following purposes. 1. It energizes the solenoid as the car reaches cut-in speed. 2. It disconnects the ignition circuit momentarily. 3. It opens the solenoid circuit when the kick down switch is closed if the driver wants to come out of overdrive,
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
u)l1
Systems
~----~--------------------------~~ Solenoid terminal Relay assembly Relay contact pOif1t,:
Armature
Governor
ww
Battery
w.E
asy E
Kickdown switch
Accelerator pedal
ngi
nee rin
Figure 3.36 Overdrive electrical control
A typical overdrive electrical circuit is shown in Figure 3.36. The governor has weights that will fly out as the speed increases and closed a set of contact points when it is at and above the cut-in speed (32-52 kmlhr). This action is performed by the circuit from the battery
g.n et
through the ignition switch, to the ignition coil and battery terminal of the relay assembly. Then the current flows through the windings of the relay electromagnet to THSW terminal of the relay. This THSW terminal is connected to the terminal of the kick down switch which forms the circuit if the switch is in any position except completely depressed. The circuit is continued to the rail switch to the governor contacts. This circuit is called governor-control circuit. The energizing of the relay winding provides the armature to close the relay contact points which forms another circuit. It is from the battery through the ignition switch to the ignition and battery terminal of the relay. Therefore, the contact points are crossed the solenoid terminal of the relay which is already connected to the terminal of the solenoid.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IfDII
Automobile Engineering
Solenoid: This unit has two winnings which form a strong electromagnet when energized by battery current from the relay. A plunger is attracted by both windings. The pawl is forced towards engagement. First, the winding called pull-in coil draws the large current. Then it is cut out by the movement of the plunger. It is done by opening a set of contact points by its motion. Thus, the small winding called hold- in coil current is left to complete the movement of the pawl. Therefore, it is held in engaged position during overdrive operation. Two springs are compressed by the movement of the plunger. The inner one engages the pawl when the accelerator is released.
Similarly, the outer one withdraws the pawl when it is
returned to direct drive. A pair of ignition ground-contact points is controlled by the plunger.
ww w.E
These points are closed when the plunger holds the-pawl in the engaged position and opened when the pawl releases.
Kickdown or Throttle Switch:
asy En gi
This switch is used to return the direct drive when it is above the cut-in speed by pressing the accelerator pedal down past the full-throttle position. The governor-control
circuit between
contacts of the kickdown switch is opened by this movement as shown in Figure 3.36. At that time, the relay windings are de-energized. Thus, the relay-contact points are opened. Due to
nee r
opening of contact points, the current supplied to the hold-in coil is cut off. So, the outer spring of the solenoid acts
to
withdraw the pawl.
ing .ne
The fully depressed throttle switch forms the circuit across terminals when it is forced to bottom position. It provides to ground the ignition system through the ignition ground contacts of the solenoid. Still, the pawl is engaged. Therefore, the engine looses its power and
t
the output shaft begins to drive the engine. Hence, the pawl is released from its pinched position. The outer spring withdraws the solenoid by opening the ignition ground contacts to restore the ignition circuit. It is carried out rapidly not more than three or four ignition misses during the entire process. For returning to overdrive, the accelerator pedal must be released by the driver. So, the car speed is still above the cut-in speed.
3.10.6. Troubleshooting Chart for Overdrive --------------------------------------------------------------------------------Symptoms
Causes
---------------------~------------------------------------------------------------------------------------------1. Overdrive does not freewheel.
(1) Broken roller, roller cage stuck or drive cams worn. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Systems
(2) (a) Dash in.
(b) Missing or blown fuse. (c) Open circuit in governor or relay circuit. (d) Binding in the dash-control cable or misalignment of shift trail, (e) Defective or stuck kick down switch. (f) Defective governor or solenoid.
ww
(g) Wrong connections in the wiring.
w.E
(h) Blocker ring not in proper position.
----------------------------------------------------------------------------------------------------------------
asy E
2. Overdrive does not engage.
(a) Grounded circuit between governor and relay.
ngi
(b) Improper installation of the solenoid.
nee rin
(c) Defective governor, relay, solenoid or throttle switch.
(d) Improper wire connections at terminals.
g.n et
---------------------------------------------------------------------------------------------------------------3. Overdrive does not release.
(a) Kickdown (throttle) switch defective or not properly adjusted.
(b) Open circuit between solenoid and ignition distributor.
---------------~----------------------7_---------------------~.~-----------------------------------------------3.11. TRANSFER BOX Transfer box is a part of a four-wheel-drive system used in four-wheel-drive or all-wheeldrive vehicles. It is also called as "transfer gear case", "transfer gearbox", "transfer box",
o
'jockey box" or "T-case".
Ttie function of transfer box is to distribute the torque generated in
engine to all four wheels of the vehicle. The transfer box is connected to the engine, front
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile
I
Engineering
axles and rear axles through drive shafts. This shifting mechanism is placed in the transfer case. The transfer gear box is controlled by the driver. The control is located in the vehicle compartment. It is either in the form of a transfer lever or a button.
ww w.E
"
asy En gi Gearbox
nee r
Figure 3.37 Positionof transfercase or transfer box Figure 3.37 shows the position of transfer case or transfer box in the vehicle. The front
ing .ne
axle drive is disengaged and the transfer box is put for longer shift lever in forward position when the vehicle is running on hard surface and unleveled roads. During this stage, the shorter shift lever will control the gear ratio such as low and high. Only low gear will be engaged
t
when the longer shift lever is for front drive. The noise will be produced at higher speeds due to inherent resonance behaviour of spur gear train used in the transfer box.
Functions01transferbox: (a) It receives power from the transmission and sends to both front and rear axles. (b) The on-road transfer case coordinates the difference between rotation of the front and rear wheels. (c) It locks the front and rear axles mechanically when required. (d) It provides low and high range of speeds.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Transmission Systems
'M
Types: 1. Gear-driven type transfer box 2. Chain-driven type transfer box 3. Housing type transfer box 4. Transfer case shift type.
3.12. FLUID FLYWHEEL It is also known asjluid clutch ot fluid coupling which couples the driving member with driven member through a media of fluid. It consists of two members in which one is driving
ww
member and the other one is driven member as shown in Figure 3.38. Among them, the driving member is connected with the engine flywheel and the driven member is connected
w.E
with the transmission shaft. These two members are not made to contact with each other. The driven member is free to slide on splines provided on the transmission shaft. The two rotors are filled with fluid of required viscosity. Radial ribs are provided to form a number of
asy E
passages to avoid the formation of eddies. They also guide the fluid to flow in the desired direction.
ngi /
nee rin Driving member
g.n et
Figure 3.38 Fluid flywheel When the engine is started, the driving member called impeller starts to move inside the housing containing oil. Pockets of moving driving member are completely filled with oil. Due to this, the centrifugal force forces the oil outward radially. The pockets are designed in such a
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering 1way that the splashed oil will strike the pockets or vanes of the driven member. Hence. it is
forced to move in the same direction. When the engine speed increases. the oil which is coming out from the pocket of the driving member strikes the pockets of the driven member with greater force. Thus, it tends the driven member to rotate at the same speed. Advantages: I. It gives smoother power take up than the centrifugal type when the engine accelerated.
IS
2. The fluid in the coupling behaves as a cushioning agent between engine and gearbox in order to absorb shocks during braking or coasting down on incline.
ww
3. No need ofseparate pedal or lever to operate.
w.E
4. The driving member acts as a flywheel on the crankshaft. Thus. it is smoothened out the torque variation.
asy E
5. There is no wear on moving parts.
6. No need of adjustment is required.
ngi
7. No maintenance is necessary. except maintaining required oil level. 3. It is simple in design.
nee rin
9. There is no jerk on transmission when the gear engages. It damps all shocks and strains. 10. No skill is required for operating.
g.n et
II. Car can be stopped in gear and moved off just by pressing accelerator pedal itself. Dlsadvantages: I. There is a drag on the gear box-shaft even the slip is 100%.
2. It has the gear changing difficult with the ordinary crash type gearbox. So. the fluid flywheel is generally used with epicyclic gearbox which avoids this difficulty. 3.13. TORQUE CONVERTER GEARBOX The constructional features of a torque converter are similar to a fluid flywheel. The only difference is that it has an additional stationary member called "stator or reaction member". All members have blades or vanes of specific shape. But the operation is not similar. In the case of fluid flywheel, the same torque is transmitted
as given by the engine shaft. But, the
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
.1
Systems
torque converter increases the torque in the ratio of about 2: 1 to 3: 1. So, the torque converter does the same purpose similar to a gearbox that too in a better way. Only finite number of steps in torque variation can be obtained in gearbox. But, the output torque variation is continuously obtained. Hence, the efficiency of a torque converter is high only within narrow limits of speed. A single stage torque converter is shown in Figure 3.39. It consists of three main parts. 1. Impeller or driving member: This driving member is connected to the engine. 2. Turbine or driven member: This driven member is connected to the road wheels through the transmission gears and the drive line, and
ww
3. Stator: It is connected to the frame through a free wheel.
w.E
Input shuft
asy E
ngi
nee rin
Figure 3.39 Torque converter
g.n et
Apart from this, a transmission oil pump keeps the converter with full of oil under pressure. This oil pressure is necessary to keep the converter rotating. Due to rotation, the oil is pushed in the outward direction by the centrifugal force. It tends to form air pockets near the centre of the converter. The phenomenon of forming air pockets due to low pressure is called cavitation. It can be avoided by keeping the converter pressure between 200 to 1200kPa. The impeller is started to rotate when the engine starts. First, the oil from the impeller is pushed into the turbine due to high centrifugal force at the impeller. At that time, the turbine is held stationary. Due to this, the oil gets high kinetic energy from the engine through the impeller which hits the outer edge of the turbine. The flow of the high-energy oil creates Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I.
Automobile Engineering
enough force that tends to rotate the turbine. This force increases with increase in engine speed. When it is great enough, the turbine starts rotating. Thus, the vehicle moves. The turbine blade angle changes the direction of the oil flow to come out of the turbine at the centre. Now, its direction is entirely backward. If there is no stator, it will enter the impeller directly and push the impeller in the opposite direction. Thus, it will cause a loss of power. The fluid from the turbine is just made to strike a stationary member to avoid this dragging action on the impeller. It means, a stator changes its direction suitably to leave the oil from the stator striking the impeller in the same direction of impeller turning as shown in Figure 3.40. The stator is also called reactor because it takes reaction while working. Then the oil is thrown back by the impeller into the turbine at the outer edge continuously. The repeated pushing of turbine blades makes the torque on the turbine to increase which is called
ww
phenomenon of torque multiplication. Deflecting the fluid in the favourable direction on the stator and subsequent torque multiplication occur if the turbine speed (i.e. vehicle speed) is
w.E
less than the impeller speed (i.e. engine speed). Hence, the maximum torque multiplication iii
asy E
possible when the turbine is stationary and impeller is running fast with the engine speed called stall. The maximum torque multiplication at stall is about 2.1 to 2.6.
ngi
When the vehicle starts to move, the turbine speed will start to increase. But the torque multiplication will gradually reduce due to decrease of the difference in both impeller and
nee rin
turbine speeds. When the turbine speed becomes equal to the impeller speed, the torque multiplication will become unity. This speed is equal to direct gear. Stator (Free wheeling)
Stator (Stationary) Turbine
+
Impeller
g.n et
Impeller
Figure 3.40
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
inl'rPQ<:p<:
nearly 85% to 90% of the impe
point will reach. Due to this, the oil leaves the turbine in the forward direction which hits the back of the stator blade. The stator blades make the flow of fluid from the turbine to impeller. .... T-hestator is located on a freewheel clutch called cne way clutch to avoid the fluid flow in the impeller. The fluid flow initiates to rotate the turbine or impeller in the opposite direction.
ww
Input shaft
w.E
asy E
ngi
nee rin
Figure 3.41 Centrifugal clutch with torque converter
The centrifugal clutch used along with the conventional three-member torque converter is shown in Figure 3.41. The centrifugal clutch consists of a number of sliding friction shoes or
g.n et
friction pads which are arranged around the circumference of the damper assembly. The damper assembly consists of damper springs and a free wheel. The friction shoes slide outward due to centrifugal force with increase in turbine speed till it contacts with the cover. The power from the converter cover flows directly through the damper assembly to the turbine shaft. The centrifugal clutch is designed in such a way that there is some slip at high loads. A spilt occurs between direct mechanical drive and hydraulic drive through the torque converter when the vehicle is under load. 3.13.1. Difference between Fluid Coupling and Torque Convertor S.No. 1.
Fluici coupling
Torque converter
It is used to transmit rotary motion
It is also used to transmit rotary motion
from a shaft to another parallel from a shaft to another with increased
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
-
.I, ...
...".....-...,..__ . ~
J
coplanar shaft.
torque.
2.
Casing rotates with shafts.
Casing is stationary.
3.
Output speed is less than the input Output speed is more than the input speed. speed.
4.
There are no stationary guide Stationary guide vanes are provided in vanes in the flow path. the flow path.
S.
There is no torque multiplication It provides' torque multiplication between between shafts. shafts during acceleration.
ww w.E
3.14. PROPELLER SHAFT
asy En gi
The propeller shaft is connected between transmission shaft (i.e. gearbox output shaft) and pinion shaft (i.e. input shaft) of the differential at the wheel axle. The propeller shaft is also called driveline shaft or drive shaft. The propeller shaft takes power from engine and it transmits to clutch, transmission gearbox unit and driving wheels of the vehicle through the final drive and differential unit. 3.14.1. Functions of Propeller Shaft
nee r
ing .ne
The engine is mounted at the front end and rear wheels of the vehicle are driven in mOJit of automotive vehicles. This arrangement requires a longer propeller shaft. It can be avoided by using more number of propeller shafts to make up the length in commercial vehicles. A typical propeller shaft assembly is shown in Figure 3.42. Universaljoint Universaljoint Hollow shaft
t
Figure 3.42 Propetler shaft Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
Systems
..
The engine is located at the front end and the front wheels of the vehicle are driven in some vehicles. The engine is kept at the front and the rear wheels are driven in some other vehicles. In this arrangement, a short propeller shaft is used to drive rear wheels. The engine and the transmission units are connected to the vehicle frame with some flexible mountings. The rear axle housing with differential and wheels are connected to the vehicle frame by suspension springs. Both the transmission output shaft and the input shaft to the rear axle housing are in different planes as shown in Figure 3.43. It restricts the propeller shaft to keep inclined. Whenever the rear wheels absorb irregularities in the road, the rear axle housing will move up and down by compressing and expanding the suspension spring. Then the angle between transmission output shaft and propeller shaft is changed shown in Figure' 3.43. Also, the
ww
length occupied by the propeller shaft will change. The length occupied by the propeller shaft
w.E
is defined as the distance between transmission shaft and pinion shaft of the differential. The variation in the length of the propeller shaft is due to the rotation of propeller shaft and the
asy
rear axle housing. The rear axle rotation housing is in the form of arcs with different points as
En
their centers of rotation. But, the rear axle housing moves in a shorter arc when compared to the propeller shaft. It is due to the centre of the rear axle housing arc which is the point of
gin eer
attachment of the rear spring or control arm to the vehicle frame. It causes a reduction in length occupied by the propeller shaft making the angle between transmission and propeller shaft increased. To transmission
ing
.ne
t
Figure 3.43 The functions of the propeller shaft are as follows. 1. It transmits rotary motion of the gearbox output shaft to the differential and then through the axle shafts to wheels. 2. It transmits motion at an angle which frequently varies. 3. It allows some changes in length between gearbox and rear axle.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
A_u_to_m__Ob_'_1$Engm88ring
~11IIiI==.='~
3.14.2. Propeller Shaft Construction The variation of the angle and length are considered in design and construction of the propeller shaft during vehicle movement. The propeller shaft is made of two shafts and two types of flexible joints such as one splined sleeve called slip joint and two universal joints. The shafts are thin walled steel tubes. The diameter varies from 50 mm to 70 mm and the thickness varies from 1.5 mm to 7.5 mm according to the type of applications. The reason for using a tubular section is that it is lighter in weight but stronger when compared to a solid shaft of the same size. Also, it is inexpensive. The shafts are made of welded or seamless tubing. Universal joints are fitted at the ends
ww w.E
of the propeller shaft. Two separate types of drives known as universal joints are connected with the propeller shaft. If any variation in the inclination of the propeller shaft occurs, the universal joints will rake care of. So, a propeller shaft consists of three parts. Universal joints are connected at both ends to provide the variation in position of rear axles and the slip joint is
asy En gi
used to provide for its length variation as shown in Figure 3.43. The overall length of the vehicle is not too long. So, the propeller shaft of single length is enough in most of cars. But, the distance between transmission shaft and pinion shaft of the differential is more in the case of trucks, buses and long chassis cars. In these cases, one or
nee r
more intermediate propeller shafts are connected to the gearbox main shaft and other end is connected to the main propeller shaft. The intermediate propeller shaft is always supported in
ing .ne
a bearing unit. The bearing unit consists of a bracket, rubber pad and ball bearing. Generally, there are two types of propeller shafts. 1. Solid or open type 2. Hollow or enclosed type.
t
1. Open type: The open type of propeller shaft is used in heavy commercial vehicles, different types of cars and light vehicles. It has a tubular in cross-section but it is not enclosed. Two universal joints connected one at each end. One of the universaljoints is connected to the gearbox main shaft or output shaft and other one is connected to the driving axle pinion shaft. The propeller shaft is comparatively longer. So, it is made up of two portions. It is connected to the chassis cross member with the help of a bearing. The front universal joint is splined and connected to the propeller shaft to provide a telescopic action for any fore. and aft movement of the-rear axle relative to the gearbox.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
-,,' Enclosed type: It prevents the twisting of the axle on its springs during power transmission. In this type, the propeller shaft is of a solid cross-section. In this case, the propeller shaft is supported by roller bearingllinside torque tubes rigidly at both front and rear axles. A torque tube is a rigid extension of the axle housing. The diameter of this propeller shaft is small when compared to open type. In some models, only one universal joint is used. It is fitted to the gearbox casing by a ball joint or large spherical bearing to resist the torque reaction. The torque and twisting metlon of rear axle casing are resisted by tube when the brake is applied. The rear end of the
lihaft is connected to the bevel pinion shaft by a splined sleeve. The splined sleeve is used along with rivets In both shafts to prevent longitudinal movement.
ww w.E
3,15. SLIP JOINTS
The propeller shaft is inclined towards down from the transmission main shaft to the rear
asy
axle as stated earlier. The propeller shaft will also be shortened and lengthened again when the axle rises as the rear springs are compressed and at the time the axle returns to its original
En
position. A slip joint is used between propeller shaft and universal joint connecting the
gin
propeller shaft to compensate for this change of length and it helps to transmit power from engine to rear axle at the same time. In cars having a torque-tube drive, a slip joint is not
eer
necessary. The joint consists of a male splined end of the main shaft to slide in corresponding
ing .ne t
grooves with the female member of the joint as shown in Figure 3.44. The female part is integral with the universal-joint hub. The splines enable the slip joint to transmit power for compensating any change of length in the propeller shaft when sliding. Universal joint yoke
External splines on transmission output shaft
Figure 3.44 Slip joint
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
3.16. UNIVERSAL JOINTS Universal joints are mainly used to make a flexible connection between two rigid shafts at an angle. It permits the transmission of constantly varying power. It is used to connect the propeller shaft with the gear box shaft to transmit rotary motion. In case of an automobile, a gearbox is rigidly mounted. Due to the action of the road springs, the position of the rear axle is constantly varied and the allowance is provided if the gearbox is mounted to the rear axle by a propeller shaft. Hence, universal joints are used for connecting two shafts inclined to one another at angle and also for transmitting the rotary motion from engine to road wheels throughout the variations in position of the rear axle with respect to gearbox and chassis.
ww
The transmission of power under varying condition is impossible without using of a flexible device or universal joint. This flexible device is also used in vehicles having coupling
w.E asy En gin ee
shaft between clutch and gearbox, between main gearbox and auxiliary gearbox and also on driving shafts of the driven front axle. A universal joint consists of two yokes. These yokes are connected to each end of the shaft. The two yokes are joined by a central or connecting cross piece. The connecting cross piece will tum bearings of the yoke with the change in angularity between shafts. They do not transmit motion uniformly if the shafts are operating at an angle. Hence, the driven shaft increases to maximum and then it decreases to minimum. The rise and fall of driven shaft are twice in each revolution due to rotation of pivot pins in different planes.
rin g.
net
Figure 3.45 Universaljoints 3.16.1. Types of Universal Joints Universaljoints are classified as follows. (a) Variable velocity joints, (b) Constant Velocity (CV) joints.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Transmission
UM
Systems
(a) Variable velocityjoints: In this case, both the driven and driving shafts do not turn at the same speed even though each part of a revolution is at the same rpm. The driven and driving shafts should be placed in a straight line to turn at the same speed through each part of a revolution. But in actual practice, it will not be feasible in any automobiles. The drive shaft is always inclined. If there is an angle between driven and driving shafts, the driven shaft will tum lower than driving shaft through half a revolution and it is faster than driving shaft through the othehalf revolution. Hence, the average speed of the driven shaft is equal to the driving shaft. The speed variation in the driven shaft increases with increase in flex angle of the universal joint.
ww w.E
The yokes on the shafts connected with the universal joints should not be in different planes if two variable velocity universal joints are used in one drive line. It provides the balancing to the speed variations. Variable velocityjoints are of the following types.
asy
(a) Cross or spider type (b) Ring type
(c) Ball and trunion type. (i) Cross or spider type:
En
gin
eer
In universal joints, the two yokes in which one is connected to the driving shaft and the
ing .ne t
other one is connected to the driven shaft at right angle to each other by a cross or spider. Needle type bearings are mounted between yokes and cross ends. These types of joints are generally used in driving shafts. (ii) Ring type:
This type of joint uses a flexible ring. The shafts are having two or three armed spiders. The arms are bolted to opposite faces of flexible ring. The arms of one spider are arranged midway between the arms of the other shown in Figure 3.46. The flexible ring is made of one or more rings of rubber to provide enough strength. A number of thin steel discs are used instead of fabric rings. This joint itself provides a considerable amount of axial movement of the shaft. It smoothens the torque fluctuations and it needs no lubrication. The main drawback is that the ring does not withstand for longer period.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
ww w.E
Engineering
Fabr1cdl
Figure 3.46 Ring type universal joint
(iii) Ball and trunion type:
asy E
A combination of both universal and slip joint in one assembly is used in this type. A pin
or cross shaft is connected crosswise in 'T' fashion in the end of universal joint shaft. Each
ngi
end of the cross shaft has a ball mounted on needle bearings. The complete assembly freely slides in grooves machined in the outer body of the joint. A heavy spring resists excessive longitudinal movement of the shaft. The power is transmitted through the trunion, balls and
nee
rin
cross shaft. The bending moment occurs in one direction by rolling action of balls. It is also in the other direction by moving balls lengthwise in trunion grooves. The open end of the shaft is covered by leather or rubber boot covers. (b) Constant velocityjoints:
g.n e
t
In this type of joint, the driven shaft is turned at the same speed as the driving shaft turns through each part of revolution at any degree of flex. These joints are mainly used in front drive axles for transmitting power through a large angle required. Cadillac cars use ball and socket type constant velocity joints in their propeller shafts. These types of joints are of the following main types. (i) Rzeppa, (ii) Bendix Weiss, (iii) Tracta. (i) Rzeppa:
It consists of spherical inner and outer ball races having grooves cut parallel to shafts. Steel balls are placed in grooves on the spherical recess shown in Figure 3.47. The torque Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1- Transmission Systems
l
...
transmission is done from one race to another ball. The circular pattern of balls cause. shafts to turn at the same velocity.
(ii) Bendix Weiss: The principle of driving through balls held in a circle around a sphere is used in this type of joint. Four numbers of driving balls are held into machined races in close fitting yokes. A fifth or centre ball is placed between two yokes as an inner race. The driving balls are arranged themselves in a circle in the same manner to Rzeppa joint. The aligning action of the balls gives a constant velocity joint. Outer spherical socket
ww w.E
asy E
ngi
nee
Figure 3.47 Constant velocityjoint (iii) Tracta:
rin
g.n e
This joint differs from the above two joints. Four yokes are used in this joint in which
t
two yokes are fastened to shafts and the other two are floating at the centre of the joint. The mating parts of the yokes are made into segments of a circle. Both circular segments and floating action of the two yokes provide a constant velocity joint. 3.16.2.Maintenance of Propeller Shafts and Universal Joints
Inspection procedures: Serviceability of propeller shafts, slip joints and universal joints can be determined by inspection while they are installed on vehicles. In general, these parts are inspected similar to normal vehicles. If a rear propeller shaft is to be inspected, chocks are placed in front and rear of front wheels. Then. wheels are raised to the propeller shaft being examined so the wheels are free to tum.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1-
..
.
Automobile Engineering
The propeller shaft IS carefully looked for big dents, Breaks or cracks are inspected at the welded seams at each end. Excess dirt or tar is cleaned off which may stuck to the shaft causing it to be unbalanced. A proper mounting is checked to make sure that the propeller shaft has been installed with the slip joint end nearest the transmission. Also, the yokes are made sure on each end of the propeller shaft are aligned.
The slip joint oil seal and the universal joints are examined. The slip joint oil seal cover is checked for its position and location. The universaljoint mounting bolts must be tight and it must have no stripped threads. Each universal joint bearing is checked for breaks or cracks. Cracks usually occur in the bearing at the inside of yokes. At this time, missing and cracked bearing grease seals are inspected which are also atthe inside of yokes. Broken or missing bearing are seriously checked for retaining snap rings.
ww w.E a
Universal joints and slip joints should be properly lubricated before the inspection starts for looseness. The joints are lubricated for good functioning of vehicles. All grease fittings should be replaced when they are severely damaged.
syE ng i
After lubricating, the propeller shaft is checked for the shake and any noted looseness. With the hand brake is applied and wheels are off the ground, the propeller shaft back is attempted to rotate. No looseness is allowed at the universal joint bearings but a very small
nee
amount of slack is normal at slip joint splines. The transmission in neutral is placed and the
rin
propeller shaft is turned by hand and listened for squeaking, grinding or grating sounds. These noises indicate improperly lubricated or defective bearings. 3.16.3. Trouble Shooting
tor Propeller
Shaft
g.n
Propeller shaft vibration
et
---------------------------------_ .._-----------------------------------------------------------_._ .._----_ Causes
Remedies
-----------------------------------------------------------------------------------------------------~--.-I. Inspect propeller shaft for foreign material or damage. 2. Inspectpropeller shaft for loose screws.
Clean foreign material from propeller shaft, or replace if damaged. If any screws are loose, tighten.
3. Check universal joints for play or looseness. Repair or replace universaljoint. Ifrust is visible around universaljoint, disassemble and inspect.
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
Transmission
Systems
4. Remove universal joint, disassemble
Replace universal joint if damaged.
and inspect.
-_._------------------------------------------------------------------------------------------------------3.17. DIFFERENTIAL 3.17.1. Need for the Differential Gear Unit
Both right and left wheels are always rotated at the same speed when the vehicle is running on flat roads. But when the vehicle travels on curved road during turning the inner wheels need to run slower than the outer wheel as it is required to travel less distance. So, the wheels are designed in such a way that they rotate at different speeds.
ww
The path of the inside wheel (A) and the path of the outside wheel (B) of a vehicle when
w.E asy En gin ee
it turns along ~ curve are shown in Figure 3.48 for comparison. The outside wheel (B) draws an arc with the radius of distance OB and the inside wheel (A) draws an arc with radius of distance ~A. Therefore, the distance travelled by the outside wheel is more than the inside wheel.
rin g.
net
RPM of inside wheel < RPM of outside wheel
Figure 3.48 The outside wheel is forced to move faster and rotates more than the inside wheel. The wheel (A) on the rough surface naturally must run at higher rpm than other wheel (B) on the flat surface. Both wheels run at an identical rpm on ordinary roads due to contact between road surface and two wheels. The difference in rpm between right and left wheels occurs due to the difference in amount of tire inflation and wear. Mostly, both wheels are forced to run at
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIIlJI
Automobile Engineering of them slips. So, tyres will wear faster. Therefore, the driving
the same rpm even anyone
performance of vehicles will be slightly affected. Thus, a differential device is incorporated to allow the differences in rpm when it is transmitting equal torque.
3.17.2. Major Components of Differential The following main components are used in the differential assembly. l. Drive pinion or Bevel pinion 2.
Ring gear or Crown wheel
3.
Differential case
ww w.E 4.
Differential side gear or Sun gears
5. Differential pinions (or) Planet gears
6. Axle shafts or Half shafts 7.
asy E
Pinion shaft or Cross pin (or) spider.
3.17.3. Construction
ngi
nee
rin
g.n e
Differential side gear or sun gear
t
Differential pinion or planet gear
Figure 3.49 Rear wheel drive differential Figure 3.49 shows the basic parts of the type of differential used in rear-wheel-drive cars. On the inner ends of each axle a smaller bevel gear called differential side gear is mounted. Two bevel gears are put together to mesh both driving and driven shafts at an angle of 90°. The differential case is mounted with two wheel axles and differential
side gears. The
differential case has bearings which rotate two axle shafts. Then, the two pinion gears and their supporting shaft, called pinion shafts, are fitted into the differential case. Then, the
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
Transmission
mw
Systems
pinion shaft is meshed with the two differential side gears connected to inner ends of the axle shafts. The ring gear is bolted to a flange on the differential case. The' ring gear rotates the differential case. Finally, the drive pinion is mounted. The drive pinion is assembled with the differential housing called differential case or carrier. The driver shaft is connected with the drive pinion by a universal joint and it is meshed with the ring gear. So, the drive pinion is rotated when the driver shaft turns. Thus, the ring gear is rotated. 3.17.4. Basic Principle of Operation
Input torque is applied to the ring gear through drive pinion, which turns the entire
ww
differential ca~e. The differential case is connected to both the differential side gears only
w.E asy En gin ee
through the differential pinions. Torque is transmitted to the differential side gears through the differential pinions. The differential pinions revolve around the axis of the differential case, driving the differential side gears. While the car is running on a-straight road, the resistance at both wheels is equal and the ring gear, differential case, differential pinion gears and two differential side gears will turn as a unit. Itresults the side gears rotating at the same speed as the ring gear makes both drive wheels to rotate at the same speed. The differential pinions revolve without spinning about its own axis, and both wheels turn at the same rate.
rin g.
If the left differential side gear encounters resistance (when the vehicle runs on curved path), the differential pinions spin as well as revolve which allows the left differential side
net
gear to slow down, with an equal speeding up of the right differential side gear. It causes the outer wheel to turn faster than the inner wheel. Thus, for example, if the vehicle is making a turn to the right, the main ring gear may make 10 full rotations. During that time, the left wheel will make more rotations because it has further to travel, and the right wheel will make fewer rotations as it has less distance to travel. The differential side gears will rotate in opposite directions relative to the ring gear by, say, 2 full turns each, resulting in the left wheel making 12 rotations, and the right wheel making 8 rotations. The rotation of the ring gear is always the average of the rotations of the differential side gears.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
3.17.5.Typesof Differential Normally, the differential is of any on-eof the following type. 1. Conventional differential 2. Limited slip differential 3. Non slip differential 4. Double reduction differential. 3.17.5.1.ConventionalDifferential
ww
Axle Shaft . Differential Case
w.E asy En gin ee
Differential Side Gear
rin g.
Figure 3.50 Pictorial view of differential The conventional differential is shown in Figure 3.50.
7 shows
net the pictorial
representation of the differential. The principle of operation is same as described earlier. 3.17.5.2.Limited Slip Differential or Self-Locking Differential or Differential Lockout The standard differential works well in most situations. However, on very slippery surfaces such as icy or muddy roads, a lack of driving force, called traction force, can cause rear wheels to slip because the standard differential will drive the wheel with the least traction. If one drive wheel is on dry pavement and the other is on ice or mud, the ring gear and differential case will drive the pinion gears. But, the pinion gears will not drive both side Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
Systems
.,.
I
gears. When the pinion gears are driven by the differential case, they will walk around the side gear related to the wheel on dry pavement. It results the pinion gears driving the slipping wheel and the vehicle will not move. The standard differential sends almost all engine power to the slipping wheel. This problem can be avoided by using differential locks. Differential locks overcome traction problems by sending the same power to both wheels while allowing the vehicle to make normal turns.
ww
w.E asy En gin ee Figure 3.51 Limited slip differential
The limited slip differential (LSD) restricts the differential rpm between two wheels, two
rin g.
thrust washers and a clutch plate which are incorporated in the differential case shown in Figure 3.51.
net
When the resistance of left side differential gear is larger than the wheel, the right side differential gear will rotate. It makes the teeth of the right side differential clutch member climbing the teeth of the left side differential clutch member. So, it makes two ciutch members to move away from each other. Hence, the side gears are pushed against the thrust washers. Due to this, the rpm of the rear axle shafts comes closer to the differential case due to the friction between side gears and thrust washers. So, it is called the limited slip effect. Types of limited-slip differential: The two most common types of limited-slip differential are as follows. I. Clutch-plate differential 2. Cone clutch differential.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
~l"~
I~f~ ..
A_u_to_m__o_b_il_e_E_n~g_in_e_e_n_n~g~__
~1-
1. Clutch-plate differential:
The clutch-plate differential uses several friction discs which are similar to small manual clutch discs. The main difference between this limited-slip differential and a standard differential is the clutch packs placed between side gears and differential case. The clutch friction discs are made of steel covered with a friction material. The clutch plates are made of steel. The discs and plates are alternately splined to the side gear and dogged (meaning tabs fit into grooves) to the differential case. Grooves in discs or plates are for better grabbing power. Drive Pinion
ww w.E
asy E
Axle Shaft
ngi
nee
Thrust Member
rin
Figure 3.52 Clutch-plate differential
g.n e
t
The pinion gears, side gears and other parts are similar to a standard differential. The differential case of the limited-slip differential is made in two parts to allow for clutch pack removal. The discs and plates are applied by the preload springs and by the mechanical pressure of the pinion gears on the side gears. Since, the pinion and side gears are bevel gears, their teeth try to come out of engagement when the differential is transmitting engine torque. It creates a pushing action on the side gears and forces them outward against the differential case. The outward pressure of the side gears presses the friction discs and steel plates together between side gears and case. Whenever the discs and plates are pressed together, the splined and dogged connections ensure the side gear:and differential case are locked together.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
Systems
,,,.
When the vehicle is moving straight ahead, the clutch-plate differential operates similar to a standard differential. The rear wheels and the differential case tum at the same speed. The clutch packs are applied but they are not needed. When the vehicle is making a tum, a high torque caused by the outer wheel rotating faster than the case and it causes the clutch pack to slip. It allows the differential to operate similar to a standard differential when making turns. The discs and plates slide against each other discs turn with side gears, plates turning with case allowing different rotating speeds between case and side gears. Therefore, rear wheels rotate at different speeds. 2. Cone clutch differential:
ww
It is next version of the limited-slip differential. In place of clutch packs, the friction
lined cones are used. The cone differential uses a cone-shaped clutch which engages a
w.E asy En gin ee
matching cone-shaped receptacle. The operation is similar to the clutch-plate differential. Preload spring and side gear pressures force the cone into a dished depression in the differential case. Friction tries to lock the cone. Therefore, the side gear sends power to the wheel with the most traction. Both clutch-plate and cone differentials require a special limited-slip gear oil. Using ordinary gear oil in limited-slip differentials, it will cause the discs and plates or cones to slip and vibrate during turns. Cone Clutch
rin g.
net
Differential pinion or planet gear
Figure 3.53 Cone differential
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
3.17.5.3. Non Slip Differential The differential is a torque controlled differential. Preloading the system is possible. So, the differentialis operated by resultant moments.Preload can be adjusted. Advantages: (i) Maximum traction can be achieved for all grip levels (adjustable). (ii) Fuel consumption is reduced.
(iii) Tyre wear is reduced. (iv) A comfort driving is obtained.
ww
(v) Constant speed drive is ensured.
(vi) Understeer in corners is reduced.
w.E asy En gin ee
3.17.5.4. Double Reduction Type Differential
In final drives, there is a single fixed gear reduction. It is the only gear reduction in most automobiles and light- and some medium duty trucks between drive shaft and wheels. Doublereduction final drives are used for heavy-duty trucks. In this arrangement, it is not necessary to have a large ring gear to get the necessary gear reduction.
The first gear reduction is obtained through a pinion and ring gear as the single fixed gear
rin g.
reduction final drive. The secondary pinion is mounted on the primary ring gear shaft. The second gear reduction is the result of the secondary pinion which is rigidly attached to the
net
primary ring gear and driving a large helical gear which is attached to the differential case. Differential Gear (Second Reduction Stage)
Bevel Pinion and Bevel Drive Gears (First Reduction Stage)
Figure 3.54 Double-reduction differential
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
Systems
design vehicles such as 5-ton Double-reduction final drives may be truck. Many commercially designed vehicles of this size use a single- reduction or doublereduction. 3.17.6. Trouble shooting for Differential
1. Differential noisy ---------------------------------------------------------------------------------------------------------_. Remedies Causes -----------------------------------------------------------------------------------------------------------
ww
1. Check to see if front wheel drive is engaged.
w.E
Disengage front wheel drive when traveling on hard, flat surfaces.
2. Check lubrication level in axle housing differential.
If low, fill to proper oil level.
3. Check for loose inner wheel adapter nuts
(a) If inner wheel adapter nuts are
or loose lug nuts.
asy
En
loose, tighten.
gin eer
4. Check for loose or damaged wheel bearings. Raise wheel off ground. Use prey bar to check for excessive play.
(b) If lug nuts are loose, tighten. (a) Adjust wheel bearings ifloose.
ing .ne t
(b) If damaged, replace wheel bearings.
(a) Iftyres will not rotate, check
5. Check differential operation. Remove differential propeller shaft(s). Raise wheels
brake shoe condition and
manually tum wheels, observe differential
operation.
operation.
(b) Remove brake drums. If brake system components are defective, repair or replace as necessary. (c) If tyres still will not rotate, replace differential.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering
(d) Iftyre rotation drags at some points during full rotation, remove and inspect axle shafts. (e) If axle shafts are defective, replace.
------------------------------------------------------~-----~---------------------------------------------2. Differential clunks during turns or initial takeoff
----------------------------------------------------------------------------------------------------------Causes
ww w.E
Remedies
-------------------------------------------------------------------------------_._------------------------1. Check for loose or damaged wheel bearings. Raise wheel off ground. Use bar to
(a) Adjust wheel bearings if loose. (b) If damaged, replace wheel bearings.
check for excessive play.
asy E
2. Check torque rod for damage.
3. Check differential propeller shaft(s) and universal joint(s) condition.
4. Check front axle shafts and universal joints for defects.
Repair or replace torque rods.
ngi
Repair or replace defective components.
nee
(a) Repair or replace defective
rin
components.
g.n e
(b) If problem still exists, replace differential.
t
----------------------------------------------------------------------------------------------------------3. Differential vibrates
----------------------------------------------------------------------------------------------------------Causes
Remedies
----------------------------------------------------------------------------------------------------------1. Check tyres and rims condition.
Repair or replace defective components.
2. Check front axle shafts and universal joints for defects.
(a) Repair or replace defective components. (b) If problem still exists, replace differential.
------------------------------------------------------------------------------------------------------Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
,':1.
Systems
4. Differential leaks oil
Remedies
Causes 1. Check axle seals condition.
Replace seals if defective.
2. Inspect drum for presence of gear oil.
If gear oil is present in or around drums, replace axle seals,
3. Check housing for loose hardware.
Tighten all loose hardware. '
ww w.E
3.18. REAR AXLE
The power is transmitted through rear axles to driving wheels. On modern passenger cars almost ail rear axles are live axles. It includes revolving shafts for driving wheels. In ordinary
asy
cars, the live axle will be at the front and the rear axle will be dead which simply remains stationary.
En
All live axle shafts are splitted into two parts in modern cars. Each part is driven by one
gin
of the differential gears through a spline connection, Both shaft and gears are completely
eer
enclosed by a housing protected from water, dust and injury to inner bearings a~d to provide a container for the lubricant. The rear axles are basically of two types such as 1. dead axles and 2. live axles.
ing .ne t
Dead axles do not rotate with wheels. It ·is also called stationary axles. Horse driven vehicle has a dead axle. The rear weight of the vehicle is only supported. A chain drive is used in these axles. In a front wheel drive car, the rear axles are the dead axles which are held stationary and wheels only rotating on them. Live axles are connected to the wheel for rotating together. The differential is supported by the inner end of the axle. Half shafts or driving axles are the other types of axles. It revolves inside the casing. Bevels are splined for receiving one end of the each of the half shaft. Ball or roller bearings are used to support the other end of half shaft. According to the arrangement of the bearings, the half shaft or the driving axle supports the following. (a) Total weight of the rear wheel causes bending and also the shearing action.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IfIfJI
AutOmobile Engineering
(b) Bending load and also an end thrust or pull caused by side thrust on the wheels when cornering. (c) Driving torque. Functions of rear axle: 1. To transmit power from differential to the wheels. 2. To carry weight of automobile. 3.18.1. Construction of Rear Axles On light commercial vehicles, a conventional spiral bevel of hypoid-type rear axle
ww w.E
construction is used. As the load-carrying capacity of the vehicle increases, the axle ratio also has to be increased to give the required torque at rear wheels. When this ratio reaches approximately 8:1, the single bevel gear axle is given way to a worm and worm wheel arrangement or uses a double reduction arrangement to give the desired ratio within increased
asy
strength. Medium carbon alloy steel containing nickel and chromium and molybdenum are
En
used to manufacture axles to withstand various stresses.
gin
Pinion shaft
eer
Crown wheel
ing .ne t
W'leel
Figure 3.55 Rear axle 3.18.2. Rear Axle Casing There are the following three types of rear axle casing. 1. Split type axle casing Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
":pl
I Transmission Systems 2. Banjo type axle casing 3. Carrier type axle casing. (i) Split type axle casing
In these types of units, the casings are made into two halves with central rings as shown in Figure 3.56. Then, it is bolted together during assembling. The central ring has a neck to support one of the bevel-pinion shaft bearings. The left hand side of the ring is made opened whereas the right hand side is closed by the web which forms a cup to fit the other pinion shaft bearing. Two extensions are bolted on both sides of the central ring. The outer ends of the extension carry the wheel bearing, spring seats and brake anchorage brackets. The
ww w.E
differential unit is carried in bearings which are housed at one side in the recess of the central ring and at the other side in the cup supported in the right hand side extension.
asy
En
gin
eer
Figure 3.56 Split type axle casing (ii) Banjo type axle casing
ing .ne t
The tubular axle section of this casing is made up of steel pressings which are welded together and suitably strengthened to withstand the bending load. The centre of this casing with the axle tube on one side resembles a banjo. The final drive assembly is mounted in detachable malleable iron housing and it is secured by a ring of bolts to the axle casing as shown in Figure 3.57. The axle shafts slide into this assembly from the road wheel end of the casing. On some banjo axles, a domed plate is bolted to the rear face of the casing. The removal of this plate provides recess to the final drive gears where the axle shaft is secured to the differential; it enables the axle shaft to be unlocked from the sun gear.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
ww
Engineering
Figure 3.57 Banjo type axle casing
w.E asy En gin ee
A lubricant level plug is screwed into the domed cover or the final drive housing at a height about one third up the crown wheel which is normally just below axle tubes. It allows lubricating hub bearings by splashing due to rotation of the crown wheel. The final drive becomes hot during operation. Hence, some form of air vent is provided to release the pressure in the axle casing. (iii) Carrier type axle casing
This type of casing is more rigid than a banjo type and it is often employed to support a hypoid gear. The final drive assembly is installed in a rigid malleable cast iron carrier into
rin g.
which axle tubes are pressed and welded. For additional rigidity, reinforcing ribs are extended from the pinion nose to the main carrier casing. A domed plate is fitted at the rear of the casing to provide access to the final drive gear.
net
Figure 3.58 Carrier type axle casing Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
Systems
3.18.3. Types of Loads Acting on Rear Axles The weight of the body and load due to occupants is transmitted through springs to the axle casting. The casting is supported by wheels. Various forces and torques experienced by the rear axle are as follows. 1. Weight of the body:
The rear axle may be considered as a beam supported at ends and loaded at two points. The rear weight of the body is transmitted to the rear axle through two suspension springs. The reaction forces come from road wheels. This weight causes both shear force and bending moment in the axle shaft.
ww w.E
2. Driving thrust:
The driving torque produced in the engine causes the thrust to be produced in the road wheels which has to be transmitted from the axle casing to the chassis frame and the body of the vehicle. It is carried out by some form of member connecting the axle casing and the chassis frame in the longitudinal direction. Such members are called thrust members or radius rods. 3. Torque reaction:
asy
En
gin
If the road wheels are prevented from rotating with the propeller shaft, the bevel pinion
eer
will tend to roll round the crown wheel. This tendency is also present when the vehicles are running. Then only the bevel pinion always tends to climb round the crown wheel. Hence,
ing .ne t
there is a force on the axle casing which supports to rotate the bevel pinion called torque
reaction. Similarly, the braking torque on the axle casing is opposite to the direction of torque reaction. This tendency on the part of the axle casing has to be opposed because the propeller shaft would be subjected to heavy bending loads. It can be effectively done by means of a member in which one end is attached to the axle casing and the other end is attached to the frame to remain the direction of the vehicle axis. 4. Side thrust:
Often the rear axle experiences side thrust or pull due to any side load on the wheel e.g. the cornering force. 3.18.4. Types of Rear Axles There are three types of live axles. 1. Semi-floating,
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1":(·
Automobile Engineering
2. Three-quarter floating, and 3. Full-floating. Almost all modern passenger car axles are semi-floating type. (i) Semi-Floating axle In semi-floating axle, inner end is only supported by the differential side gear. The differential case carrying the inner bearing between these differential side gears and axle housing supports the axle. Since, the inner end of the axle shaft supports the weight of the car and the outer end carries end thrusts it is called semi-floating. The inner end of the axle shaft is splined to the differential side gear shown in Figure 3.59.
ww
The outer end is directly flanged to the wheels using bolts. The wheel, drum and bearing
retainer plate should be removed to withdraw the hie shaft. It results the axle shaft to support the weight of the car .and also transmits the rotation to wheels. The bearings mounted on the axle by retainer axle bearings are mostly pre-lubricated.
w.E asy En gin ee Figure 3.59 Semi floating axle
rin g.
net
In a semi floating axle, the various forces acting on the half shaft are as follows. 1. Side thrusts when a vehicle negotiates a corner. 2. Shear force and bending movement due to weight of the vehicle. 3. Twisting caused due to driving and braking torques. (ii) Three-Quarter floating axle
A three-quarter floating axle is shown in Figure 3.60. The single bearing supports the wheel hub located at the center of the wheel hub. It runs on the axle housing. The axle shaft is rigidly keyed with the hub. So, it provides the driving connection and it maintains the alignment of the wheel. The construction of the inner end axle shaft is similar to a semi-
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
,'IJ
Systems
floating axle. Still three-quarter floating axle has only one bearing at the outer end and it will carry some bending stresses. So, it is not a full-floating type.
ww w.E
asy
Figure 3.60 Three-Quarter floating axle
En
The three-quarter floating axle sustains the following loads.
gin
1. Bending load due to side thrust, when the vehicle is cornering, and 2. Twisting caused due to driving and the braking thrusts. (iii)Full-Floating axle
eer
ing .ne t
Axle shaft
Figure 3.61 Full floating axle The wheel hub is directly supported by two bearings running upon the axle housing as shown in Figure 3.61. The axle shaft is connected with the wheel hub flange by couplings through which the rotary motion of the axle shaft is transmitted to the hub and wheel. The axle Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I~
Automobile Engineering shaft is removed from the housing without disturbing the wheel. It is done by simply
removing the hubcap and coupling. Hence, the axle is relieved of all strains by the weight of the vehicle or end thrusts. So, it is called full-floating. The wheel comes off and the vehicle drops. The full-floating axle is used in most of the trucks. Either taper-roller or ball bearings can be used in all applications. 3.18.5. Comparison of Different Types of Rear Axles Description
S.No.
ww I.
2.
3.
4. 5.
Full-j1oating rear axle High
Cost
Three-quarter floating rear axle Medium
w.E asy En gin ee
Vertical load taken
Side load
Driving torque to the wheels
Application
Nil
Low
Yes, by a single bearing placed over the axle casing
Semi-j1oating rear axle
Yes, taken by half shaft bearings
Nil
Present
Present
Yes
Yes
Yes
In heavy
vehicles
3.18.6. Rear Axle Drives
More in cars
rin g.
In medium vehicles
net
The whole of the rear axle unit moves forward and the vehicle is also pushed when the road wheels begin to rotate. The provisions are made to impart the thrust of the axle to the chassis. Both power and torque are transmitted to wheels by the engine. This torque does not rotate the wheels to the desired direction but it also rotates the differential housing in the opposite direction. So, this reaction is known as torque reaction or rear end torque. The arrangement to withstand both thrust and torque reaction is given below. i) Hotchkiss drive ii) Torque tube drive. 3.18.6.1.Hotchkiss Drive Hotchkiss drive consists of a propeller shaft, two longitudinal leaf springs. The propeller shaft has a slip joint. The front end of the leaf springs is hinged to the frame and the rear end Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
,':P.
Transmission Systems
is connected with the frame by swinging shackles as shown in Figure 3.62. The slip joint provides the increased length of propeller shaft if the rear springs get deflected. The rear-end torque is borne by springs. It gets deflected while driving fast and also while braking. The deflection helps to improve flexibility and damp shocks. Then, the driving force is transferred from the axle casing to the front end of the spring and then to the frame. Hence, both rear-end torque and driving thrust are opposed by springs. Shackle
ww
w.E asy En gin ee Figure 3.62 Hotchkiss drive
3.18.6.2. Torque Tube Drive
Gear shan or transmission output shaft
Frame
rin g.
net
Gear shaft or
Universal joint Cross section of differential housing
Figure 3.63 Torque tube drive Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I~
Automobile Engineering
A hollow tube encloses the propeller shaft in this type. The tube is rigidly connected to the differential housing at one end. The other end of the tube is connected to the gearbox casing by a flexible ball and socket arrangement as shown in Figure 3.63. The driving thrust and rear end torque are carried by a hollow tube. The tube is used in bearing to support the propeller shaft. Only one universal joint is enough at the gearbox. There is no sliding joint needed in the propeller shaft. Helical or torsion bar springs are used when the rear end torque and driving thrust are carried out by a torque tube. If laminated springs are used, shackles will also be placed at both ends. The driving thrust is transferred to the front end of the frame through gearbox, In Hotchkiss drive, the driving thrust is transferred to the rear end of frame through cup and
ww
gearbox shaft.
w.E asy En gin ee
3.18.6.3.Comparison Between Hotchkiss Drive and Torque Tube Drive S.No.
Description
Hotchkiss drive
Torque tube drive
1.
N umber of universal joint
It has two numbers.
It has only one number.
2.
Slip joint in propeller shaft
It is needed.
It is not needed.
Posture of Propeller
It is open.
I
3.
4.
Effect on propeller shaft
It can bend and the length changes. One end is fixed and
5.
Spring support
the other end is in shackle position.
6.
Geometry of spring
It deflects.
It is enclosed within the
rin g. torque tube
It cannot bend and there
net
is no change in length.
Both ends are in shackle position.
It does not deflect.
Torque and brake 7.
Load on spring
reactions, driving and
Only side thrust acts.
side thrusts act. 8.
.Effect on final drive shaft
The position alters
There is no shift in position.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Transmission
.".
Systems
3.18.7. Trouble Shooting For Rear Axle 1. Axle noisy on acceleration
----------------------------------------------------------------------------------------------------------Remedies
Causes
----------------------------------------------------------------------------------------------------------1. Heavy heat contact on ring gear.
Correct it.
2. Improper adjustment of pinion and ring gear.
Readjust.
3. Rough pinion bearings.
Replace.
ww
Adjust.
4. Loose pinion bearings.
w.E
----------------------------------------------------------------------------------------------------------2. Axle noisy on coast
asy
----------------------------------------------------------------------------------------------------------Causes
En
Remedies
-----------------------------------------------------------------------------------------------------------
gin eer
1. Excessive backlash in ring gear and pinion.
Adjust.
2. End play in the pinion shaft.
Readjust.
3. Heavy toe contact on ring gear.
ing .ne t
Readjust. Replace.
4. Rough bearings.
----------------------------------------------------------------------------------------------------------3. Axle noisy on both coast and acceleration
----------------------------------------------------------------------------------------------------------Remedies
Causes
------------------------------------------------------------------------------~---------------------------1. Worn differential gears.
Replace.
2. Worn pinion and ring gears.
Replace.
3. Defective bearings.
Replace.
4. Excessive backlash between ring gear and pinion.
Adjust.
5. Pinion set too deep in ring gear.
Adjust.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'am
Automobile
6. Pinion and ring gear too tight.
Engineering
Adjust.
4. Backlash Causes
Remedies
1. Axle shaft splines worn.
Replace axle shaft.
2. Axle shaft nut loose.
Tighten as necessary.
3. Worn universal joints.
Replace.
4. Worn differential bearings.
Replace.
ww
w.E asy En gin ee
S. Worn differential side gear thrust washers.
Replace.
3.19. TWO MARK QUESTIONS AND ANSWERS
1. State the functions of transmission on systems.
1. It enables the running engine to be connected or disconnected from the driving wheel smoothly and without shock.
rin g.
2. It enables the leverage between engine and driving wheel. 3. It enables the reduction of engine speeds.
4. It enables the turn of the drive round through 90°.
S. It enables the driving wheel to be driven at different speeds.
net
6. It is based on the effect of torque reaction during thrust and braking effort effectively. 2. What is a clutch? Clutch is a mechanism used to connect or disconnect the engine from the rest of transmission elements. 3. Mention the function of a clutch. 1.
[Anna Univ. Apr'OS & Nov'OS]
To permit engagement or disengagement of a gear when the vehicle is stationary and the engine is running.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Transmission Systems
PIi"
u, To 'transmit the engine power to rear wheels smoothly without shocks to the transmission system while the vehicle is in motion. lll.
To permit the engaging of gears when the vehicle is in motion without damaging gear wheels. {Anna Univ:Apr'OS, Nov'OS & May'15J
4. Name the types of clutches.
1. Friction clutch (i). Single plate clutch (ii), Multiple clutch
.:. .:.
Wet
ww w.E Dry
2. Cone clutch
.:. .:.
Internal
asy
External
3. Centrifugal clutch.
4. Semi centrifugal clutch.
S. Coil pressure spring clutch.
En
gin
6. Conical spring clutch or diaphragm clutch .• :. Tapered .:. Crown spring
eer
-
7. Positive clutch - dog and spline clutch 8. Hydraulic clutch 9. Vacuum clutch
ing .ne t
10. Electromagnetic clutch 11. Overrunning clutch 5. What are the features of a good quality clutch? (i)
[Anna Univ. May'I2l
It should be capable of transmitting maximum torque of the engine.
(ii) The clutch should be able to engage gradually and positively without the occurrence of sudden jerks. (iii) The design of the clutch is such that it should ensure the dissipation of heat sufficiently which is generated during operation.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
(iv) The clutch should be dynamically balanced to the vibration in transmission system. It is very important requirement in modern cars which is operated at high speeds. (v) A suitable mechanism should be incorporated within the clutch for damping of vibration and elimination of noise produced during the transmission. 6. Mention anyfour important requirements of a clutch. (a) Transmission of torque: It should be capable of transmitting maximum torque of the engine.
(b) Gradual engagement:
ww
The clutch should be able to engage gradually and positively without the occurrence of sudden jerks.
(c)
w.E asy En gin ee
Vibration damping:
A suitable mechanism should be incorporated within the clutch for damping of vibration and elimination of noise produced during the transmission. (d) Size of the clutch:
The size of the clutch should be as smaller as possible so that it will occupy minimum space. 7. List the various part of a single plate clutch. (i) Fly wheel
(ii) Clutch plate or disc plate (iii) Pressure plate (iv) Clutch cover assembly
rin g.
net
(v) Release mechanism (vi) Withdrawal force and rearing (vii) Primary or clutch shaft. 8. What are the advantages of a single plate clutch?
[Anna Univ. May'llj
1. It makes easy to change gears than cone type. 2. It is reliable than cone clutch.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
U·
Transmission Systems
9. Why multi-plate clutches are used in automobiles? As compared to single plate clutch, they are smooth and easy to operate due to their assembly of friction surfaces contact. 10. Give the two types of multi-plate clutches. Wet and dry type 11. Distinguish between single and multi-plate clutch.
[Anna Univ. May'09]
1. Multi-plate increases torque transmission capacity. 2. The diameter is reduced as it has more friction surface which reduces the size of the clutch assembly.
ww w.E
3. It is highly reliable.
4. It is suitable for heavy vehicles.
12. How cone clutches are engaged and disengaged?
asy
When the clutch is in engaged position, the male cone is fully inside the female
cone in such a manner that the friction-surfaces are in perfect contact. It is done by the pressure springs which keep the male cone pressed all time. Now, the torque is
En
gin
transmitted from the engine via the flywheel and the male cone to the gearbox. When the clutch pedal is pressed, the male cone slides against the spring force and the clutch is disengaged. 13. What is known as one way clutch?
eer
ing .ne t
[Anna Univ. May'14]
The one way clutch or unidirectional clutch will transmit a drive when rotated in one direction and will 'freewheel' when turned in the opposite direction. 14. What is the special springs used in diaphragm clutch? Belleville springs 15. What are the advantages of a diaphragm clutch? 1. It requires lower operating effort due to reduced friction in the clutch mechanism. 2. There is a constant and uniform load on the driven plate throughout the life of a clutch. 3. At high speeds, the clamping load on the diaphragm springs is not affected although the coil spring starts bowing or distorting transversely. 4. The dangerous vibrations in vehicles are altogether eliminated because it provides accurate balance at all time.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
16. How is dog and spline clutch disengaged? The sleeve is moved back on the splined shaft to have no contact with the driving shaft. 17. What is the necessity of hydraulic operated clutch in automobiles? I.
When the clutch is located so that it would be difficult to run from the foot pedal to the clutch.
11.
In heavy-duty mechanically operated clutches with high clutch spring pressure, the force required by the driver to release the clutch becomes excessive.
18. Describe briefly the actuation of hydraulic operated clutch.
ww
It consists of a master cylinder and a slave cylinder and an oil reservoir. When
the clutch pedal is pressed, the fluid under pressure from the master cylinder reaches the slave cylinder. The slave cylinder is mounted on the clutch itself. The fluid actuates slave cylinder push rod which further operates the clutch release fork to disengage the clutch.
w.E
asy
En
19. How does electro-magnetic clutch work?
gin eer
An electro-magnetic clutch consists of an engine flywheel provided with electric winding. A driven plate lined with friction materials is provided. It is free to move on splines of the gearbox shaft. A pressure plate is applied for engaging or disengaging
ing .ne t
the clutch. The operation of this clutch takes place when the electric current is passed through the electric winding placed on the flywheel. When the winding gets energized, the pressure plate is attached by it. It results the engagement of clutch.
The clutch is disengaged when the current supplied to the winding is cut off. It results the increase in armature attraction towards the flywheel. There is no longer compact between pressure plate and intermediate plate. Since, the current from the vehicles dynamo increases with increase in speed, the clutch engaging force will also increase with the engine speed to provide a progressive clutch engagement. 20. How the vacuum operated clutch works during normal working condition? The switch in the gear lever remains open and the solenoid valve remains in its bottom. The atmospheric pressure acts on both the side of the piston of the vacuum cylinders. Since, the vacuum cylinder is opened the atmosphere through vent.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
ww
w.E a
syE
ngi
nee
rin
g.n
et
**Note: Other Websites/Blogs Owners Please do not Copy (or) Republish this Materials without Legal Permission of the Publishers.
**Disclimers : EasyEngineering not the original publisher of this Book/Material on net. This e-book/Material has been collected from other sources of net. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
Systems
[Anna Univ. Apr'06j
21. What do you mean byfluid flywheei?
The member which couples the driving member with driven member through a media of fluid is known asfluidflywheel. [Anna Univ. Dec'14J
22. What is the/unction 0/ aflywheel?
It couples the driving member with driven member through a media of fluid. 23. What are the merits and demerits of using fluid flywheel?
{Anna Univ. Dec'14J
Merits: 1. It gives a smoother power take up than the centrifugal type when the engine is accelerated.
ww
2. The fluid in the coupling behaves as a cushioning agent between engine and gearbox in order to absorb shocks during braking or coasting down on.
w.E
incline.
asy
3. No need of separate pedal or lever is required to operate. 4. The drivi,ng member acts as a flywheel on the crankshaft. Thus, it
En
IS
smoothened out the torque variation. Demerits:
gin eer
1. There is a drag on the gear box-shaft even the slip is 100%. 2. It has the gear changing difficult with the ordinary crash type gearbox. So,
ing .ne t
the fluid flywheel is generally used with epicyclic gearbox which avoids this clifficulty. 24. What is 4WD and A WD?
{Anna Univ. Dec'14j
4WD refers a four-wheel drive car and AWD refer an all-wheel drive car. 25. What is the necessity of transmlssion?
{Anna Univ. May'llJ
More power is required to keep an automobile in. motion when compared to power required for keeping it rolling after starting. It means, the automobile requires more power at the starting while the engine may be developing less power. A transmission system does to tum the engine crankshaft to four, .eight or twelve time approximately for each wheel revolution. A reverse gear is also set for backing the car.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
26. State any four important purposes of transmission system. 1.
It helps the engine to be disconnected from the driving wheels.
2.
It helps the running engine to be connected to the driving wheel smoothly and without shock.
3.
It provides the leverage between engine and driving wheels to be varied.
4.
It helps to reduce the engine speed in the ratio of 4 : 1 in case of passenger cars and in a greater ratio in case of lorries.
27. What is known as selective transmission?
[Anna Univ. Dec'13j
ww w.E
Selective transmission is a transmission In which the available forward and reverse gears may be engaged in any order without passing progressively through the different changes of gear.
28. List out the various resistance to motion.
asy
1. Air resistance
2. Gradient resistances
En
3. Miscellaneous resistance. 29. Define tractive effort.
gin
eer
The torque available on the wheel produces a driving force which is parallel to the road known as tractive effort. 30. Classify gearbox. 1. Manual transmission (a) Sliding mesh gearbox
ing .ne t
[Anna Univ. Dec'08 & May'I2j
(b) Constant mesh gearbox (c) Synchromesh gearbox
.
2. Epicyclic gearbox 3. Automatic gearbox (a) Hydramatic gearbox (b) Torque converter gearbox.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
•• p-
Transmission Systems
31. How vehicle is kept stationary while using sliding mesh gearbox? When the engine is running and the clutch is engaged, the counter shaft is driven by the cultch gear. The cultch gear rotates in opposite direction to the clutch shaft. The low speed and high speed gears are fitted on the transmission main shaft or gearbox shaft which does not rotate. At the same time, they are not engaged with any driving gears. Therefore, there is no motion transmitted from clutch to propeller shaft. Hence, the vehicle is stationary. 32. What is meant by 'double declutching' in constant mesh gear box? [Anna Univ. Dec'09J
ww w.E asy
It is the process of depressing the clutch, moving into neural position, releasing
the clutch, matching the engine speed, depressing the clutch and engaging .he next gear.
33. Why is double clutching technique used? Even though there is no measure to allow easy meshing of gears, "double clutching" technique must be acquired for shifting gears properly.
En gi
34. What are the advantages 0/ constant mesh gearbox over the sliding mesh type?
nee
1. Helical or double helical gear teeth can be used for gears instead of spur gears except reverse gears. So, quicker gearing can be achieved.
rin
2. Synchronizing devices can be used for smooth engagement of gears.
g.n et
3. Only damage occurs on dog clutch teeth and not to the teeth of the gear wheels.
4. Once the dog clutches are engaged, there is no motion between their teeth but the power is transmitted through the sliding action of the teeth of one wheel on diose of the other when the gear teeth are engaged. To transmit the motion properly, the teeth are suitably shaped. 35. What is a synchronizer? Why synchromesh device is usually not employed/or the {Anna Univ. Dec'12J reverse gear? A synchronizer is part of a synchromesh manual transmission which allows the smooth engagement of gears. Synchronizers equalize th~ speed of the. shaft and gear before they are engaged. The action of the synchronizer eliminates gear clashing and allows for smooth changing of gears.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
Reverse gear is not normally synchronized because the gear rotation is required for synchronizer action and reverse is normally selected when the car is not moving. 36. Why synchroniser is required in the automotive transmission system? [Anna Univ. Dec'13] Synchronizer is used for smooth engagement of gears while the changing the gears during vehicle running condition. The synchronizer helps to synchronize the speeds of the two gears to be engaged without necessary of faster running gear to slowdown. 37. What is thefunction of synchromesh unitin a gear box? [Anna Univ. Apr'05]
ww
To simplify the operations of changing gears without the occurrence of clas~es and their consequent damage, a synchromesh gearbox is used in different types of motor vehicles.
w.E asy En gin ee
38. What is thejunction of a synchronizer in a gearbox?
[Anna Univ. Apr'06]
The synchronizer helps to synchronize the speed of two gears to be engaged without necessity of faster running gear to slow down. 39. Mention the main features of synchromesh gearbox.
1. The main shaft or output gears are freely rotated on bushes of the output shaft.
rin g.
They are internally placed by splined thrust washers. Generally, single or double helical gears are used in constant mesh with the long shaft gears.
net
2. When their speed is equalized or synchronized by their cones, the output gears will be locked to their shaft by the dog clutch. 40. What are the advantages of epicyclic gearbox?
1. The planetary gears are in constant mesh. Hence, dog clutches or sliding gears are not used. 2. External contracting hand brackets or multiplate clutches of relatively small dimensions are used for changing the gears. 3. It is a more compact unit because the planetary gear operates within a ring gear with its external surface ofcylindrical form. 4. It is distributed over several gear wheels instead of having the load on only one pair of gears.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Transmission
"('11
Systems
41. Why epicyclic gears are used in overdrive units? [Anna Univ. Dec'07] & May'll] In transmissions, the high gear position'produces a 1:1 ratio between clutch gear and transmission output shaft. There is neither gear reduction nor gear increase through the transmission. It is the direct drive. At intermediate and higher car speeds, it is sometimes desirable to have the transmission output shaft turned faster than the clutch gear and engine crankshaft. Therefore, some transmission systems are designed with gears to provide an over drive ratio. 42. Write down the methods of operating automatic gearbox. 1. Hydramatic transmission, and
ww w.E asy
2. Torque converter transmission.
43. What is hydramatic transmission? In this case, the transmission is done by fully automatic system. It has a
combined four speed forward and reverse automatic geared transmissions with a flywheel. Three sets of constant mesh helical planetary gears are connected in series
En gi
to p~byide in the geared transmission. The two sets of planetary gears are used to obtciin the four forward speeds in a hydramatic gear system. The impact of the
nee
automatic shifts is cushioned and also the fluid flywheel reduces the torque reactions of the engine. Motor vehicles attached with hydramatic drive are not connected with
rin
clutch pedals. But the accelerator and brake ar.eused for the purpose of control.
g.n et
44. How the vehicle is running in neutral gear using hydramatic transmission?
The front band and clutch and also rear clutch are released by controls provided on a selector lever. Due to this action, the engine flywheel is completely disengaged from the output shaft. It causes no power transmission. 45. How torque converter gearbox differs from fluid flywheel? The only difference is that it has an additional stationary member called "stator or reaction member". [Anna Univ. Dec'08j
46. What is the use of Torque converter?
The torque converter increases the torque in the ratio of about 2: 1 to 3: 1. 47. What are the main parts of single stage torque converter? 1. Impeller or the driving member: This driving member is connected to the engine.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
2. Turbine or the driven member: This driven member is connected tothe road wheels through the transmission gears and the drive iine, and 3. Stator: It is connected to the frame through a free wheel. 48. What is afree wheel? What is the importance offree wheel in the transmission of an automobile? {Anna Univ. Dec'I2j A freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft. It allows the drive shaft of a motor vehicle to continue turning when its speed is greater than the engine shaft.
ww
49. What are the advantages of automatic transmission systems?
w.E asy En gin ee
1. It is a simplified driving control.
2. It gives less physical and manual fatigue to the driver.
3. There is no clutch pedal and gear lever and hence, it makes the simplification of driver's compartment. 4. It provides smoother running under all conditions due to hydraulic coul?lingand automatic gear change. 50. What do you know about over drive?
{Anna Univ. May'09j
rin g.
Overdrive is a device which is useu to step up the gear ratio in the car. It is mounted in between transmission and propeller shaft. 51. Why overdrive is used in some vehicles?
net
{Anna Univ. Dec'14j
Overdrive is used in cars for cruising on the highway or for increasing overall top speed. 52. What are the advantages of overdrives?
{Anna Univ. Nov'05 & May'IOj
a. It allows a lower engine speed to maintain the car at highway speed. b. It does not require as much power to keep it moving. Therefore, the engine can turn more slowly, produce less power and still maintain car speed. c. This system saves fuel. d. Wear on the engine and accessories are reduced. 53. Mention the functions of an overdrive.
{Anna Univ. May'IOj
1. It energizes the solenoid as the car reaches cut in speed. 2. It disconnects the ignition circuit momentarily. Downloaded From : www.EasyEngineering.net
.3
Downloaded From : www.EasyEngineering.net
Transmission
Systems
3. It opens the solenoid circuit when the kick down switch is closed if the driver wants to come out of overdrive. 54. What is propeller shaft? Where it is located? The propeller shaft is connected between transmission shaft called gearbox output shaft and pinion shaft called input shaft of the differential at the wheel axle. The propeller shaft is also called driveline shaft or drive shaft. 55. State the various/unctions of propeller shaft.
{Anna Univ. May'08j
1. It.\~~I)~mitsrotary motion of the gearbox output shaft to the differential and
then through the axle shafts to the wheels.
ww w.E asy
2. It transmits motion at an angle which is varying frequently. 3. It allows some changes in length between gearbox and rear axle.
56. What is thefunction of universal joint in a propeller shaft?{Anna Univ. Apr'05j It is used to connect propeller shaft and gear box shaft and to provide between
propeller shaft and gear box during transmission of rotary motion.
En gi
57. Name the two type~ of propeller shafts. I. Solid or open type
2. Hollow or enclosed type.
nee
rin
58. What is the use of slip joint in transmission system? {Anna Univ. Dec'09, May'll & -M,ay'15j
g.n et
A slip joint is used between a propeller shaft and universal joint connecting the propeller shaft to compensate the change in length and it helps to transmit power from the engine to the rear axle at the same time. 59. Classify universal joints. (a) Variable velocity joints, (b) Constant velocity (C.V.) joints. 60. What are the types of variable velocityjoints? (a) Cross or spider type, (b) Ring type, (c) Ball and trunion type.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IUI,"
Automobile Engineering
61. What are the basic/unctions of the differential unit? (1) Straight ahead travel (2) Turning (3) One wheel on a Muddy surface. 62. What are the/unctions of rear axle? 1. To transmit power from differential to wheels. 2. To carry weight of automobile. 63. What are the different types of loads acting on rear axle? 1. Side thrust
ww w.E . ';,\\H..
\'-'n "L
'··'-YY\
2. Torque reaction
3. Driving thrust
4. Weight of the body
asy
64. Name the types of Rear axle housings. a) Split Type
b) Banjo Type
c) Carrier Type
En
gin
eer
65. What are banjo type and split type axle housings?
Banjo type: single piece housing in final drive.
ing .ne t
Split type: two pieces housing in final drive for easy maintenance. 66. What is 'Half Shafts'?
Half shaft is the type of drive axle which extends from the differential to the hub of an independently suspended suspension system. 67. Name the types of rear axles used in various Indian vehicles. [Anna Univ. Nov'05] 1. Semi floating axle-fiat and jeep. 2. Three-quarter floating axle-ambassador. 3. Full floating axle-trucks, buses and other heavy vehicles. 68. What do you mean byfull floating housing? In a full floating housing, there is'no load on the axle shaft. The whole load of vehicle is on the axle housing.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Transmission Systems 69. What do you mean by three quarter floating housing?
In three-quarter
floating rear axle, bearings are on the outer side of axle casing
between casing and wheel. In this case, a major part of vehicle weight is taken by axle casing and not by an axle. It is the main-advantage of three-quarter floating type over half floating type. Thus, axle breakdown is less in this case.
70. What do you mean by semi floating IIousing? In a semi floating rear axle, the axle is at the centre of the axle casing and the bearings are inside' the axle casing. The weight of vehicle is transmitted first to suspension spring, then to axle casing, next to axle and finally to ground.
ww w.E asy
71. What are the variousforces acting on the three-quarter floating axle? The three-quarter floating axle sustains the following loads:
1. Bending load due to side thrust when the vehicle is cornering, and
2.
Twisting caused due to driving and the braking thrusts.
72. Distinguish between full-floating rear axle and three-quarter floating rear axle. Description
S.No. 1.
2.
Cost Vertical load
En gi
Fult-floating rear axle
Nil
nee
Nil
Present
Yes
Yes
In heavy vehicles
More in cars
High
Side load Driving torque
4.
Medium
rin
Yes, by a single bearing
to the wheels Application
5.
g.n et
placed over the axle casing
taken
3.
Three-quarter floating rear axle ,
73. Distinguish between/ull-j1.oating rear axle and semi-j1oating rear axle. S.No.
Description
Full-j1.oatingrear axle
Semi-j1oating-rear axle Low
1.
Cost
High
2.
Vertical load taken
Nil
3.
Side load
Nil
Present
4.
Application
In heavy vehicles
In medium vehicles
Yes, taken by naif shaft bearings
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
fiiI~lil
Automobile Engineering
5.
Driving torque to the wheels
Yes
Yes
74. What are the variousforces acting on the semijloating axle? In a semi floating axle, the various forces acting on the half shaft are as follows. I. Side thrusts when a vehicle negotiates a corner. 2. Shear force and bending movement due to weight of the vehicle. 3. Twisting caused due to driving and braking torques. 75. What is meant by multi-axle vehicle?
ww w.E
~ .Il.,
A multi-axle vehicle is a vehicle which has more than two conventional axles. Extra axles are usually added to weight restriction or to accommodate different vehicle designs such as articulation or rarely to implement trailer buses.
asy
76. What are the reasons/or multiple axles? I. Extra axles may be provided on shorter buses and coaches to accommodate
En
extra equipment loads such as passenger lifts or comforts such as toilets televisions, climate controls.
gin
eer
2. Adding axles to chassis designs is done for specific reasons such as weight or
-
legalities as having extra axles means extra costs for the operator in terms of
ing .ne t
tyre replacement and to an extent and higher fuel consumption.
3. In some buses, the rearmost axle is connected to the steering with the rear most set steering in the opposite direction to the front axle. This steering arrangement makes it possible for the longer triple axle buses to negotiate corners with greater ease than other case. 77. What are the types
0/ rear axle drive?
1. Hotchkiss drive 2. Torque tube drive. 78. What is torque tube? A torque tube is a housing in which propeller shaft e~closes. It is attached to the drive axle housing. Its one portion is connected with gear box and other portion is with the differential box.
Downloaded From : www.EasyEngineering.net
j
Downloaded From : www.EasyEngineering.net
Transmission
dliD
Systems
79. Distinguish between Hotchkiss drive anti torque tube drive. S.No.
Description
1.
Number
of
Hotchkiss drive
universal
Torque tube drive
It has two numbers.
It has only one number.
It is needed.
It is not needed.
It is open.
It is enclosed within the
joint
2.
Slip joint in propeller shaft
3.
Posture of Propeller
torque tube. 4.
Effect on propeller shaft
ww w.E asy
It can bend and the
It cannot bend and no
length changes .
change in length
80. What do you understand by Hotchkiss drive?
{Anna Univ. May'lOJ
The Hotchkiss drive is a system of power transmission.
form of power transmission Hotchkiss
for front-engine
drive is a shaft-drive
in rear-wheel
system. All shaft-drive
En gi
It was the dominant drive layout cars.
systems consist of a
driveshaft extending from the transmission in front to the differential in the rear. It uses universal joints at both ends of the driveshaft which is not enclosed.
nee
81. Why two universal joints are requiredfor a Hotchkiss drive system? A universal joint is used where two shafts are connected at an angle to transmit
rin
torque. One universal joint is used to connect the transmission
main shaft and
g.n et
propeller shaft and other universal joint is used to connect the other end of the propelle. shaft and the differential pinion shaft. Thus, the connections between three shafts are flexible and at an angle with each other. The universal joint permits the torque transmission
not only at an angle but also while this angle is changing
constantly.
82. What is the advantage of the Hotchkiss drive?
{Anna Univ. May'llJ
I. Spline in Hotchkiss drive eliminates thrust transmitted back up the drive shaft from wheels 2. The drive allows simple rear-axle positioning using parallel leaf spring ..
83. Mention few important causes of axle failures.
{Anna Univ. May'14j
Following are some important causes of axle failure:
(i)
Overloading of vehicle.
(ii)
Entry of dust or abrasive particles in the axle. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIIliZI
Automobile Engineering
(iii) The lubrication is not maintained at the required level. (iv) The replaced parts are not of the correct type. (v) Usage of incorrect grade lubrication. 3.20. SOLVED QUESTIONS 1. What are the purposes of transmission systems? Refer chapter 3.1.1 in page 3.2. 2. What is meant by clutch? List out the requirements. [Anna Univ. N(lv'OS & Nov '07]
ww
Refer chapter 3.2 in page 3.2.
3. What are the features of a good quality clutch? Explain the working of multi plate
w.E asy En gin ee
dutch with a neat sketch.
[Anna Univ. May' J0]
Refer chapter 3.2.3 in page 3.3.
4. Classify clutches.
Refer chapter 3.3 in page 3.4.
5. Explain the function of clutch. Draw anyone type of clutch and explain in detail. [Anna Univ. Dec '08]
rin g.
Refer chapter 3.2.2 in page 3.3 and chapter 3.3.1 in page 3.5.
6. Discuss about working principle of single plate clutch.
net
[Anna Univ. Apr 'OS,Apr '06 & May'JS] Refer chapter 3.3.1 in page 3.5.
7. Explain the working of friction clutches. What are the assumptions made in pressure calculation?
[Anna Univ. Dec' 14]
Refer chapter 3.3.2 in page 3.9. 8. How semi- automatic clutch works? Explain. Refer chapter 3.3.5 in page 3.12. 9. Explain the working ofa diaphragm clutch with a neat sketch. Refer chapter 3.3.6 in page 3.13.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Transmission Systems 10. Write short notes on positive clutch and hydraulic clutch. Refer chapter 3.3.7 in page 3.15 and chapter 3.3.8 in page 3.16. II. Compare hydraulic, mechanical, electrical and vacuum methods of operating clutches. Describe a hydraulically operated clutch in detail with the help of simple diagrams. [Anna Univ. Dec '12] Refer chapters 3.3.1 to 3.3.10 in pages 3.5 to 3.18 for comparison of hydraulic, mechanical, electrical and vacuum methods of operating clutches. Refer chapter 3.3.8 in page 3.16 for the description of hydraulically operated clutch.
ww w.E asy
12. Briefly explain the trouble shooting of clutch. Refer chapter 3.4 in page 3.19.
13. Explain various types of resistance to motion. Refer chapter 3.5.3 in page 3.23.
14. What is tractive effort?
En gi
Refer chapter 3.5.4 in page 3.24.
[Anna Univ. Dec '14]
nee
15. Explain types of gear boxes in detail with neat sketches. [Anna Univ. May'14] Refer chapter 3.6 in page 3.25.
16. Explain the sliding mesh gearbox with a suitable sketch.
rin
g.n et
[Anna Univ. Apr '05, Apr '06 & May '09] Refer chapter 3.6.1 in page 3.26.
17. Discuss the construction and operation of a constant mesh gear box. [Anna Univ. Nov05 & May' J 11 Refer chapter 3.6.2 in page 3.29. 18. With a neat sketch, explain the working principle of synchromesh gear box. [Anna Univ. Dec '09, May' J 0 & May' J 2] Refer chapter 3.6.3 in page 3.32. 19. Explain the working of Wilson epicyclic gear box.
[Anna Univ. Dec '07]
Refer chapter 3.6.4 in page 3.34.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering
20. Explain in detail the automatic transmission system.
[Anna Univ. Dec' 14]
Refer chapter 3.6.5 in page 3.36. 21. Describe the working of a hydramatic gearbox with a neat sketch. Refer chapter 3.7 in page 3.37. 22. Describe in detail various types of gear selector mechanisms used in automobiles. Discuss also the advantages and disadvantages of each and state what the modem trend is.
[Anna Univ. Dec '12 & May '15] Refer chapter 3.8 in page 3.42.
ww w.E asy
23. Explain the various trouble shootings that can be occurred in gearbox. Refer chapter 3.9 in page 3.43.
24. Describe the construction and working of an over drive with a neat sketch and list out its advantages.
[Anna Univ. Dec' 13]
En gi
Refer chapter 3.10 in page 3.47.
.
25. Explain the working principle and application of a freewheel drive in transmission system.
nee
Refer chapter 3.10.3 in in page 3.52.
[Anna Univ. May'10]
rin
26. Explain the working of a pawl action with its neat sketches. Refer chapter 3.10.4 in page 3.51.
27. Write short notes on electric controls with its neat sketches. Refer chapter 3.10.5 in page 3.52.
g.n et
28. Explain the trouble shooting of overdrive. Refer chapter 3.10.6 in page 3.54. 29. Explain the working principle of fluid flywheel with the help ofa sketch. [Anna Univ. Nov '05 & Nov '08] Refer chapter 3.12 in page 3.57. 30. What is meant by a fluid coupling and torque converter?
[Anna Univ. Apr '06]
Refer chapter 3.12 in page 3.57 for fluid coupling and chapter 3.13 in page 3.59 for torque converter.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
mil
Systems 31. What is torque converter? Explain its working principle with suitable diagram.
Transmission
[Anna Univ. May '12, Dec '12 & May '15] Refer chapter 3.13 in page 3.58. 32. What is the difference between a fluid coupling and torque converter? [Anna Univ. Apr '05] Refer chapter 3.13.1 in page 3.61. 33. Explain briefly the construction of the propeller shaft with neat sketch. [Anna Univ. Dec '08, May' 10, May' 11 & Dec' 14]
ww
Refer chapter 3.14 in page 3.62. ,I
34. Give the short notes on slip joint with a neat sketch.
w.E
[Anna Univ. Dec '08, May' 10 & May' 11]
Refer chapter 3.15 in page 3.65.
asy
35. Describe in detail various universal joints usedin automobiles. [Anna Univ. Dec '08, May' 10, May' 11 & Dec' 12]
En
Refer chapter 3.1" in page 3.66. 36. What are the needs for differential unit?
gin eer
Refer chapter 3.17 in page 3.71. 37. Explain the
\':\1
.ous basic functions of the differential unit.
Refer chapter 3.17.1 in page 3.71.
ing .ne t
38. Explain the principle and working of a differential with a neat sketch.
[Anna Untv. Nov '05, Apr '06, Dec '07, May'09, May '11, May '14, Nov '14& May '15] Refer chapter 3.17.4 in page 3.73. 39. Describe the working of a self-locking differential unit. Refer chapter 3.17.5.2 in page 3.74. 40. Discuss the principle of a differential with a neat sketch and state the mechanism for [Anna Univ. May' 10 & Dec' 13]
power lock or non-slip. Refer chapter 3.18.7.3 in page 3.78. 41. Explain the rear axle casing with neat sketches. Refer chapter 3.18.2 in page 3.82.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIIIS
Automobile Engineering 42. What are the different loads acting on a rear axle of a vehicle? Refer chapter 3.18.3 in page 3.85.
43. Explain the different types of rear axles with neat sketch. Refer chapter 3.18.4 in page 3.85. 44. Discuss the following with simple sketch of a torque tube drive. [Anna Univ. May '09 & Dec '14] Refer chapter 3.18.6.2 in page 3.89. 45. Write short notes on the following:
ww w.E asy (i) Hotchkiss drive
[Anna Univ. Dec '07 & Dec '09]
Refer chapter 3.18.6.1 in page 3.88.
(ii) Iransfer box.
[Anna Univ. Dec '09]
Reier chapter 3.11 in page 3.55.
----------------
E ngi -----------------------.-----------nee rin g.n et END of Unit 3 -,----
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I
UNIT - 4
ww
w.E
asy
En
gin eer
Steering geometry and types of steering gear boxPower Steering, Types of Front Axle, Types of
ing
Suspension Systems, Pneumatic and Hydraulic
.ne
Braking Systems, Antilock Braking System (ABS), electronic
brake force
Traction Control.
distribution
(EBD) and
t
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
ww
w.E
4.1. STEERING SYSTEM
STEERING, BRAKES AND SUSPENSION SYSTEMS
asy E
ngi
Automobiles are controlled by a steering system. Steering system provides the directional change for the movement of an automobile and it maintains in a position as per the driver's
nee rin
decision without much strain on him. The steering system allows the driver to guide the vehicle along the road and tum left or right as desired. The wheels are changed from their straight ahead ·position for turning the vehicle to one side. It is obtained by mounting the steering wheel assembly suitably on the axle.
g.n et
The safety of any automobile mainly depends on the performance of the steering and braking systems. Many of the accidents are happened due to the driver's negligence, improper job of inspecting, repairing or maintaining the steering system. These problems can be avoided by knowing thoroughly about steering system. So, the knowledge about this system is very important to operate the vehicle in a safe mode. Steering is done by moving the axes of rotation of front ...heels with respect to the chassis frame. So, the inner wheel turns through a greater angle than outer one. If it is not so, a greater wear will occur. Ea~h wheel rolls OIl: arc with-a steering having a common centre. For ensuring a proper control of the automobile, the driver must be able to (a) tum in different directions so thatit may not go astray. (b) control the speed of the vehicle for moving according to requirements. (c) slow down or stop when required whether slowly or suddenly. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering
By supplying more or less quantity of fuel, the accelerator controls the engine speed. The speed of the vehicle is changed by a gearshift lever for obtaining different gear speed. For stopping the vehicle, brakes are used. The.steering should be arranged in such a way that the wheels roll without slipping or scuffing. So, the steering must be light and stable with a certain degree of self-adjusting ability. 4.1.1. Requirements and Functions of the Steering System Requirements of the steering system: For ensuring proper, smooth operation and performance of the steering system, the steering system of any vehicle should satisfy the following requirements.
ww
'!
1. It multiples the turning efforts applied on the steering wheel by the driver.
w.E
2. The shocks of the road surface absorbed by wheels should not be transmitted to the driver's hands.
asy E
3. When the driver releases the steering wheel after completing the turn, the wheel should achieve a straight ahead position immediately, called self-rightening effect.
ngi
4. It must keep the wheel at all time in rolling motion without rubbing on the road
nee rin
5. This system should associate to control the speed. 6. It must be light and stable.
7. It must easily be operated with less maintenance. Functions of the steering system:
g.n et
A good steering system must perform the following functions satisfactorily. 1. It provides wheels swinging to the left or right. 2. It provides vehicle turning as per the will of the driver. 3. It provides the directional stability. 4. It helps to control wear and tear oftyres. 5. It helps in achieving the self-rightening effect.
6. It converts the rotary movement of the steering wheel into an angular turn of front wheels. 7
It multiples the effort of the driver by leverage to make Wheelseasy to turn.
8. It absorbs a major part of road shocks in such a way from being transmitted to hands of the driver.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering, Srakes and Suspension Systems The above-mentioned functions are done into two portions such as I. by providing steering gears at the end of the steering column, and 2. by providing linkage between steering gear and wheels. 4.1.2. Layout of Steering System or Components of Steering System
Various components of the steering system are shown in Figure 4.1.
ww w.E
Track rod
asy E
ngi
nee
Figure 4.1 Layout of steering system The following are the main components of steering system. 1. Steering wheel
2. Steering column or shaft.
rin
g.n e
t
3. Steering gear
4. Drop arm or pitman arm 5. Bafljoints 6. Drag link
7. Steering arm 8. Stub axle 9. Left spindle and kingpin 10. Left tie rod arm 11. Track rod or tie-rod Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1l1li
Automobile Engineering
12. Right tie rod ann, spindle and kingpin 13. Steering stops.
ww
w.E
asy
En
gin eer
ing
Figure 4.2 Arrangement of steering system components 1. Steering wheel:
.ne
t
It is the control wheel to steer a vehicle by the driver. It contains traffic indicator switch, light switch, wiper switch etc. 2. Steering linkage: The steering wheels are turned by the steering linkage. The steering linkage consists of pitman arm, ball joints, drag link, steering arm, spindle, tie rod and kingpin assembly. Different forms of steering linkages are shown in Figure 4.3. (a) Pitman arm: It is also called drop arm which converts the output torque from the steering gear into force to the drag link. It is connected to the sector shaft of the steering gear by a split joint. Either full serrations or partial splines are used for transmitting the torque from the sector shaft to the pitman arm. The split arm is tightened around the sector shaft bv a clamping bolt. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and
It is done for differentiating the male and female serrations or splines. The end of the pitman arm connected with the drag link has a tapered hole. The ball stud on the drag link is fixed into this hole.
-8t--~I8-- -8':lA-~J8-8)={8-- -8CV78-ww-8~8-- -8'g=78-w. (1)
(2)
(3)
(4)
Ea (5)
(6)
syE
Figure 4.3 Variousforms of steering linkages
(b) Ball joints:
ngi
These joints are connected at both ends of the drag link and tie rod. It performs the
nee r
angular displacement, rotational movement of the drag link and the tie rod produced by the front wheel rotation and suspension articulation. (e) Drag link:
ing
.ne
It is connected between pitman arm and steering arm. It is a single prece forged
component having a ball joint socket formed at the end in some other cases. (d) Steering arm:
t
It is also a forged component which is connected to the steering knuckle. During turning, the drag link force is converted into a turning moment about the left kingpin. The steering arm is connected to the spindle through a keyway, locking taper and nut. The arm is extended either to the front or rear spindles according to package constraints. The end of the steering arm connects with the drag link and a tapered hole receives the ball stud. (e) Left spindle and kingpin: The torque obtained by the steering arm rotates the left spindle, wheel and tyre about the kingpin.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
(f) Left tie rod arm: The left tie rod arm is connected with the spindle in the same way as the steering arm. It converts the available torque to turn the right wheel into force in the tie rod. The tie rod has a tapered hole to receive the tie rod ball stud.
(g) Tie rod: The tie rod is a tubular member. Both the left and right tie rod arms are connected by this tie rod. The force is transmitted between these two components. The tie rod ends have female threads. But the ball joint shafts have mating male threads. The threaded connections are held together firmly by locking clamps after setting the correct length. The length of the tie rod is an adjustable one to the specified amount.
ww
In the direct cross type steering linkage. the pitman arm is directly connected to one tie
w.E
rod which in turn is connected to another tie rod. The other end of the tie rod is connected to steering arms.
asy
(It) Right tie rod arm, spindle and kingpin:
En
It converts the force from tie rod into a moment to turn through the knuckle arm, the right spindle wheel and the tyre about the kingpin. The right spindle and the kingpin assembly are
gin eer
merely similar assembly on the left side. But it has no steering arm connected to it.
(i) Steering stops:
ing
Stops are used to limit the angular deflections of front wheels. It also avoids the rubbing oftyres against the frame produced by wear and tear oftyres. These steering stops are used at
.ne
two different places. First, they are fixed' in the path of motion of the steering arm or drop arm. Then, they are fixed in the path of motion of the steering knuckle.
3. Steering shaft:
t
The steering shaft is fitted inside the hollow steering column. When the steering wheel is turned, the steering shaft will also be rotated. Due to this, the motion is transmitted to the steering box.
4. Steering gear: The pitman arm is splined to the steering gear box rocker arm at one end and the other end is connected to the drag Iink by a ball joint.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
4.1.3. Principle of Operation of Steering System Generally, the steering system has a worm drive in the steering gear box. The driving worm is bolted to steering tube end. A cross shaft is rotated by the driven gear at right angle to the steering tube. During turning of the steering wheel, this motion is transmitted through a steering gear. So. the direction of motion is changed and obtained through the multiple twisting forces with respect to gear ratio. The output shaft is revolved for moving the pitman arm. Then the motion is transmitted to steering knuckles via drag link intermediate steering arm hinged in a frame bracket. The following functions are carried out when a steering wheel takes a right turn. I.
2. 3.
ww w.E
Both steering wheel and steering tube are rotated clockwise by rotating the roller shaft through the steering gear. Due to this action. the bottom end moves forward for pushing the drag link.
asy E
The tie rods are forced to turn left direction by an intermediate steering arm. Thus, it receives a push of the drag link.
ngi
4.
The right steering arm is pulled by the right tie rod to turn the right steering knuckle and wheel to the right.
5.
The left steering arm is pushed by the left tie rod for turning the left steering knuckle and wheel to the right.
nee
rin
g.n e
The same procedure is used but the reversed actions take place while taking a left turn.
t
4.1.4. Fundamentals of Steering Mechanism or Condition for True Rolling Motion
The main function of the steering system of a vehicle is to convert the rotary movement of the steering wheel into angular turn of the wheels. To keep the straight-ahead motion of the vehicle at high speed due to bumps and change the path of the vehicle with the minimum amount of driver's effort, a mechanism known as steering mechanism is used. At the same time, the relative motion of a vehicle wheel to the ground should be pure rolling. During turning or moving the vehicle on a curved path, the wheels should follow a true radius or definite radius with each of the radius originating from the same centre. The circle based on the common centre is known as instantaneous centre. For perfect steering we must always have an instantaneous centre about which all the wheels must rotate to avoid skidding of wheels. For this purpose inner wheel has to turn more than the outer wheel.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
The relationship of the wheels of a vehicle is shown in Figure 4.4. The various radii of front and rear wheels about pivots are PC, PA, PF and PE. Here P is the common centre or point of turning.
Il:.:..ioo-- a ---1-1 A
ww w.E a
syE
I-
ngi
Figure 4.4 Construction of steering mechanism
nee r
Assuming that the outer steered wheel has to turn through angle ¢ and the inner steered turns through angle
e for pure rolling and avoiding any lateral slip. Then the angles can be
ing
calculated from the wheel base and track of the vehicle by using known value of required turning circle. Now From~AEP,
EF=PE-PF
cot e=
PE
-
EA
.ne
... (4.1)
t
... (4.2)
PE=EA cot $
Similarly, from ~CFP, PF
cot8= -
Fe
PF= Fe cot
e
... (4.3)
Substituting (4.2) and (4.3) in (4.1), EF= EA cote -Fe cot
e Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
.,.
Steering, Brakes and Suspension Systems
ButEA=FC EF= EA cote -EA cot e
Dividing throughout by EA.
-EF = cott/JEA
cotO =
Track Wheelbase
= -a = constant b
cot t/J= Constant + cot 0 Steering is obtained by turning the axes of rotation of two front wheels relative to the chassis or body of the vehicle. The axis of the wheel on inside of the curve must be turned through a larger angle than the axis of the wheel on outside of the curve to satisfy the condition of concentric circular arcs as shown in Figure 4.4. Therefore, two front axles should be operated by the steering system by satisfying the above equation for any value of radius of
ww w.E
asy E
curvature followed"bythe vehicle.
ngi
4.1.5. Ackerman - Jeantaud Steering Linkage
nee
The Ackerman - Jeantaud steering linkage is shown in Figure 4.5. This linkage is based on a four bar chain with two longer links (AC and KL) of unequal lengths with two shorter links (AK and CL) of equal lengths.
c
,, ,
K
" ,_
rin
g.n e
_
a
A
t
......... .... -_ .. M
N
P
x
d
x
Figure 4.5 Ackermann steering mechanism When the vehicle is running along a straight path, the longer links will become parallel and each of shorter links will be inclined at an angle a. to the longitudinal axis of the vehicle. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile
Engineering
The short link is turned to increase the angle a for steering the vehicle to the right. Now, the long connecting link LK makes the short link AK to turn in reducing the angle a. AK with angle ~ turns is less than the angle through a small angle than the right front axle.
e of CL. It means, the
left front axle turns
e depends upon the ratio of (AK / AC) and angle a. For known values of (AK / AC) and a, the values of e and ~ are obtained by either ,graphically or arithmetically. The difference between cot ~ and cot e for each pair of e and ~ values will increase slowly at first and then it will increase rapidly when e increases. The value of ~ obtained for a given value of
PM PN cot ~ - cot e = -- -AM cs
ww But
w.E
e, except e = o.
Ackermann mechanism can only give a correct steering for one value of
Similarly, a corresponding value of 8 can be obtained when the vehicle is turning left. For
asy
small values of 8, the angle ~ will be too high for correct steering and it would be too low for
En
large values of 8. The errors occurred in values of ~ are negligible even
e
is large in this
mechanism. But, the error in steering will produce wear on tyres. The distance of the point of
gin eer
intersection of arms AK and CL from the line AC is 0.7 of the wheel base obtained. This distance makes 8 to increase at correct steering. The movements of KL in the direction parallel to the axle beam AC will be same if the slight inclination of the track rod is neglected. Let, this movement is Y. If L'K' is the correct steering position, the wheels are turning to the right and r will be the cross arm radius. Therefore, for correct steering, .
S1l1 (a+
ing
8) =-x+ y r
.
S1l1 (a-~)
x-y
= --
.ne
t
... (4.4) ... (4.5)
r
Adding (4.4) and (4.5),
.
SIl1 (a+8)
Now where
. x+ y x- y +SIl1 (a-~) =--+--= r r .
S1l1 a
x
2x r
(:.sin a=~)
r
a-(d+x)
= - =_-'--_--'-
r
r
a = half the Ackermann angle.
So, the variable 8 and ~ are calculated from above equations for correct steering. Therefore, the movement y parallel to the axle beam will result a greater angular movement. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
Systems
4.1.6. Davis Steering Gear
Davis steering gear is an exact steering mechanism as shown in Figure 4.6. The slotted links AK and BL are connected to left and right front wheels respectively. They are arranged to turn on pivots at A and B respectively. The link KL is in front of the link AB at a distance h from the link AB. The link KL is restricted to move in the direction length and parallel to AB by the sliding constraints at M and N. The link KL is attached to slotted levers AK and BL by a sliding and turning pair at each end. When the mechanism is in the mid position having wheels at orientation WI and W2, the vehicle will move along a straight path. Steering is obtained by moving the link KL to the right or left of its normal position.
ww w.E c
Straight
asy E
D
ngi
nee
Figure 4.6 Davis steering gear mechanism When the steering effected to the left, the wheels newly orients to WI' and W{ Then the axes of the left and right wheels (WI' and W2') make an angle
rin
e and respectively. If the
g.n e
intersection of three axes is at P, then the steering will be correct tor all positions of the steering gear. The two arms AK and BL intersect at a distance H in front of AB. The slide
t
blocks are pivoted on these pins and moved with the turning of bell crank levers when the steering wheel operates. When the vehicle is running straight, the gear is said to be in midposition. The short arms AK and BL are inclined at an angle 90 + a to their stub axles AC and BD respectively. The correct steering depends on the suitable selection of cross-arm angle a
and it is given by tana=where
b 21
b = AB = distance between the pivots of front axles
I = wheel base. The range of(b / l) is 0.4 to 0.5, thus angle a lies on between 11.30 and 14.10.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lID
Automobile Engineering
4.1.7. Steering Linkage for Vehicle with Independent Front Suspension
In case of a conventional rigid axle suspension, the main axle beam ensures the movement of stub axle in the horizontal plane only. Therefore, there is no vertical deflection of the suspension and hence, there is no change in effective track rod length. In the case of independent suspension, the two stub axles can move up or down independent of each other due to which distance of ball-joint ends of the two track rod arms continuously varies. On account of a single track rod as in conventional system, the above-mentioned case cannot be used.
ww w.E
r-
TieRods
asy E
Relay Rod
ngi
Steering Gear
Steering Wheel
nee
rin
g.n e
Figure 4.7 Steering linkage for independent front suspension
t
Figure 4.7 shows the construction details of steering linkage for independent front suspension. Three piece track rod is used, the center portion being called relay rod is used, which is connected at one end to an idler arm supported on body structure and the drop arm of steering gear at the other end through ball joints. The relay rod is restricted to move in a horizontal plane only. The movements in vertical plane are provided by the outer portions. 4.1.8. Steering Geometry
Since the steering linkage consists of different mechanisms such as support arms, tie rod, pitman arm, drag link etc. connected together they form angles in relation to each other. Steering geometry is the angular representation and obtaining relationship between these linkages and front wheels. It is essential to know the name of various angles which is produced in steering geometry. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
e"-
Steering, Brakes and Suspension Systems
The important angles pertaining to steering geometry are as follows. 1. Castor 2. Camber 3. Kingpin inclination 4. Toe-in 5. Toe-out. (i) Camber:
When the front of the vehicle is viewed, the angle between centre line oftyre and vertical
ww w.E
line is called camber. Figure 4.8 shows the camber angle. The camber is also named as wheel rake. When the wheels are tilted inwards at the top, it is negative. It is positive when it tilts outward at the top. The camber is referred in degrees. The front wheels are come to a vertical position when the vehicle loads are with a positive camber. At that time, the camber should not exceed to 2°.
Wheel
asy E
-~---
ngi
Included angle
Wheel Camber
nee
Front axle
Figure 4.8 Camber
rin
g.n e
t
Due to excessive positive camber, the outer tread section of tyres and shoulder will wear faster. To avoid this type of wear, the camber angle should be kept equal at both front wheels. The tyre life will be maximum when the camber angle in running condition is zero with average load. Similarly, if the vehicle with equal camber on both wheels is running on road, it will pull away the car towards the side of the road. To avoid this, high camber is slightly provided to the right wheel than the left one in India. Similarly, high camber is slightly provided on the left wheel in the case of left hand drive vehicles in Western countries. The change in spring height also changes the camber. When the camber is zero, slight irregularities on the road may occur to change the wheel load thereby changing the direction
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile
Engineering
of the camber effect. This phenomenon is called 'wander'. So, the exact amount of camber is specified '.Jytaking the kingpin inclination into account. Reason of camber angle provided in steering system: Camber angle alters the handling qualities of a particular suspension design. Particularly, a negative camber improves grip when cornering because it places the tyre at a better angle to the road, transmitting the forces through the vertical plane of the tyre rather than through a shear force across it.
ww
w.E
asy
En
gin eer
Figure 4.9 Effect of positive camber
Off-road vehicles such as agricultural tractors generally use positive camber. In such vehicles, the positive camber angle helps to achieve a lower steering effort. For maximum
ing
straight-line acceleration, the greatest traction will be attained when the camber angle is zero and the tread is flat on the road. Effects of wheel camber: 1. Bending stresses in the kingpin and stub axle are reduced.
.ne
2. Steering effort is drastically reduced.
t
3. Shock loads are not permitted to transmit to the steering wheel at high speeds. 4. It imparts the directional stability. (ii) Castor:
Tilting the kingpin axis either forward or backward from the vertical line is known as castor. The angle between the vertical line and kingpin centre line in the plane of the wheel when it is viewed from the side is known as castor angle. When the top of the kingpin is inclined in backward direction, the castor angle is positive. The caster angle is negative, when the top of the kingpin is inclined in forward
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
tl,.
Systems
direction. It ranges from 2° to 7° in modern vehicles. Excessive castor causes excessive wobbling on front wheels.
'
ingpin
,
Front wheel
, ~
Vertical
ww w.E
Effects of castor:
iI ,\
Figure 4.10 Castor
asy E
1. The positive castor gives the directional stability and it keeps the wheels to straight ahead after completing its turns. Similarly, the negative castor provides easy steering.
ngi
2. The excessive positive castor tends the vehicle rolling out. Similarly, the excessive negative castor makes the wheel to toe-out.
nee
3. If caster angle on both wheels is same, both wheels will be equally balanced. If it is greater on one side, wheels are pulled towards the wheel having lesser castor angle. 4. Usually, about 30 of castor gives good results.
rin
(iii)J(ingpin inclination:
g.n e
t
The angle between vertical line and centre of the kingpin or steering axle when viewing from the front of the vehicle is called kingpin inclination. It usually varies from 3.50 to 7.5°. Effects of kingpin inclination: 1. Both kingpin inclination and castor give directional stability. 2. Particularly steering effort is reduced when the vehicle is stationary. 3. Tyre wear also is greatly reduced. 4. During turning of the wheel, this inclination raises the vehicle. So, the force is exerted on wheels to straighten up automatically after completing its turn.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile
Engineering
5. The kingpin inclination should be equal on both sides. If it is greater on one side, the vehicle will be pulled to the other side having the greater angle. (iv) Toe-in and Toe-out: Usually, front wheels are slightly turned to the front side. It means, the distance (A) between front ends is slightly less than distance (B) between back ends when it is viewed from top as shown in Figure 4.11. Then the wheels are said to be toe-in. Similarly, the wheels are said to be toe-out when the distance A is greater than B as shown in Figure 4.12. The amount of toe-in does not exceed 3mm.
ww w.E
Front of vehicle J~~~---A
o
----~~
o
Main axle
asy E
ngi B
Figure 4.11 Toe-in
nee
Front of vehicle
A
,)
Main axle
rin
o
g.n e
t
B
Figure 4.12 Toe-out Effects of toe - in: The toe-in is given to ensure the parallel rolling of front wheels, stabilized steering and no 'side slipping and less tyre wear.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
Systems
An improper toe-in produces the following effects. 1. Tyre slip 2. Tyre Wear on outside of the tread 3. Tyre scrub bend 4.
Poor steering stability.
Effect of toe-out: The inner front wheel turns for larger angle than the outer wheel while turning as shown in Figure 4.13. So, the wheels are made to toe-out on turns due to the difference in their turning angles thereby avoiding tyre scrub. By keeping the proper relation between steering
ww n w.E o=: "", I "" ,·,····,.l ""'" a i syE i'" " """" I ngi ............ .. i I "'/:'" n e ()-i--. ----LQ--------------_~Le_!:h., rin g.
knuckle arms, tie-rods and drop arm, the toe-out occurs. Front
Outside wheel
_~~eel
_-(/
Inside wheel
j
I
I'
.••.•.•
"'"
,
,
Figure 4.13
net
In modern cars, the kingpin is replaced by ball joints. It is named as 'steering axis inclination'. It is also defined as the inclination of the ball joint-axis from vertical (Figure 4.14) to steering axis which is an imaginary line drawn through the lower and the upper steering pivot points.
Figure 4.14 Steering axis angle Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
[mil
Automobile Engineering
(v) Combined angle ami scrub radius: Combined angle or included angle is the angle between vertical plane of the wheel centre line and kingpin centre line, called steering axis. Combined angle is the sum of camber plus kingpin inclination called steering axis inclination. In a rear-wheel drive vehicle, the suspension cross member is pushed by the tractive force of the vehicle and the body is made to move forward during drive. The road resistance acts on the wheel at the contact point on the road. The distance between two points is known as scrub radius. When the tyre centre line lies on the intersection of the steering axis, this radius will be zero as shown in Figure 4.15.
ww w.E
Combined angle
~
asy E
ngi
nee
Figure 4.15 Combined angle
It will be negative when the tyre centre line lies inside the steering axis. It is always
rin
referred in mm. This radius is mainly depending on the steering axis inclination, the wheel
g.n e
offset and suspension height. In the case of front wheel drive vehicles, the tractive force acts on front wheels at the contact point on the road. It is reversed in the case of rear-wheel drive. Effect of combined angle:
t
Figure 4.16 shows the effect of combined angle variation on the scrub radius. If the scrub radius is not equal to zero, a torque acted on the wheel turns away from the straight ahead position. Effect of scrub radius: (i)
When the scrub radius is negative, the wheel is caused to toe-in as shown in Figure 4. 16(a).
(ii)
When the scrub radius is positive, the wheel is caused to toe-out shown in Figure 4.16c(c).
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering, Brakes and Suspension Systems
IDa ]
(iii) When the scrub radius becomes zero, the wheel is kept in straight position without any toe-in or toe-out shown in Figure 4.16 (b). This position is known as centre point steering. In case if the centre point steering is implemented, any small change in the combined angle will cause to the point of intersection alternately above and below the ground. Thus, toe-in or toe-out is caused. A large scrub radius will cause a greater torque required to turn the wheel. It means, higher loads on the steering linkage and suspension components act. It results a greater wear of steering linkage and unequal braking on the front wheels. Wheel
,I
Wheel
,I
/
ww w.E ,
Tractive I force •
t resistance Road (a)
asy t E Tractive force
(b)
Road resistance
ngi
Tractive I force •
t
Road resistance
(c)
nee
Figure 4.16 Effect of combined angle variation in rear wheel drive vehicle
rin
The scrub radius is a parameter to provide necessary road feel to the driver. The
g.n e
recommended value of combined angle is from 9° to 10° and the scrub radius can be up to about 12 mm. 4.1.9. Wheel Alignment
t
The wheel alignment is the positioning of front wheels and steering mechanisms. It provides a good directional stability, easy steering, minimum tyre wear and good riding qualities to vehicles. Excessi~e tyre wear, vibration, hard steering, shimmy etc. are produced because of incorrect alignment of wheels. The important factors are involved in wheel alignment as follows. 1. Castor 2. Camber 3. Toe-in
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile Engineering
4. Toe-out 5. Kingpin inclination. Wheel alignment procedure: To ensure the proper wheel alignment, camber, caster, toe-in and ki.ngpin inclination should properly be set. They must be kept within the specified limit according to the car manufacturer specification for easy and safe driving. The full weight of the car should be kept on the ground during adjusting these parameters within the specified limit. The following checking, inspection and adjustment are carried out while doing the wheel alignment. (1)
Wheel bearing adjustment should be checked and correction should be carried out if it is required to keep the parameters within the specified limit.
ww w.E
(2)
The kingpins and their bushingshould be checked and thoroughly inspected for w excessive play.
(3)
Spring should be checked tor breaks or- sags.
(4)
Bending of the steering arms should be checked. Due to incorrect toe-out on turning it results the wearing oftyres.
(5)
Factors such as frame alignment, spring conditions, position of the rear axle. condition of the shock absorbers etc., should be checked.
asy E
ngi
nee
A front wheel alignment depends upon the following factors. 1. Running straight down a road 2. Entering and leaving a tum easily, and 3. Resisting road shocks.
rin
g.n e
t
4.1.10. Steering Gears The rotary motion of the steering wheel is converted into straight-line motion of the linkage by the steering gear. There are two types of steering gears. 1. The pitman-arm type, and 2. The rack-and-pinion type. Both types of gear are used in a manual steering system or a power-steering system. In other words, the steering gear converts the turning motion of the steering wheel into to andfro
Downloaded From : www.EasyEngineering.net
I
25.
Downloaded From : www.EasyEngineering.net
I Steering, Brakes and Suspension Systems
_
motions of the link rod of the steering linkage. Also, it gives the required leverage to provide the ability to the driver to steer the vehicle without fatigue. The steering gear assembly not only steers front wheels but it also reduces the steering wheel turning effort by increasing the output torque. The reduction ratio is known as steering gear ratio. It varies from 18 to 20:1. The steering effect is reduced by a large ratio. At the same time, the steering wheel is turned more when it is moving around a curve. 4.1.11. Types of Steering Gear Box Different types of steering gears are used on different vehicles. According.to the method
ww w.E
of coupling the steering tube with the cross shaft, various types of steering gears are as follows.
1. Cam and roller
2. Recirculating ball
3. Rack and pinion.
4. Cam and tum lever 5. Screw and nut
asy E
6. Cam and peg 7. Worm and roller 8. Worm and sector. 9. Worm and ball bearing (1) Cam anti roller type
ngi
nee
rin
g.n e
t
The cam and roller steering boxes are efficient. The details of the cam and roller steering gear are shown in Figure 4.17. The name itself refers to a cam meshed steering gears having" cam and rollers. The cam is carried by the steering shaft connected with rollers. Then, a rocker lever supports the double roller through ball bearings. The rocker lever is one part of the pitman arm shaft. The drop arm spindle carries V-shaped roller. This spindle is carried by ball bearings in the casing. The roller carried by the pin has the provision for moving the roller into closer mesh with the member. This member contains spiral grooves. The races support the roller carried on the centre position of the pin. The centre portion of the pin is eccentric upto end portions. These portions are already supported by the drop arm spindle. By moving the steering wheel and steering shaft, the cam is rotated. Due to this rotation, the roller is constrained to follow the Downloaded From : www.EasyEngineering.net
,,,.
Downloaded From : www.EasyEngineering.net
Automobile Engineering
helix of the groove. When the cam rotates, the roller is followed by the cam and made the rocker shaft to rotate. Thus, the drop arm is actuated as shown in Figure 4.17. To ensure the constant depth of mesh and evenly distributing the load and wear on mating parts, the contour of the cam is properly designed to match with our aim. Steering shaft
:Y
ww w.E
Figure 4.17 Cam ami roller steering gear
(2) Recirculating Ball Type
asy E
A worm and a nut are placed at. the end of the steering shaft as shown in Figure 4.18. I Steel balls are loaded between two sets of grooves of worm and nut for recirculation. The balls are fed back to the nut connected by a half nut with the transfer tube. The nut has teeth
ngi
on its circumference. These teeth are meshed with a toothed wheel sector. The drop arm connected to this sector steers front wheels through the link rod and steering arms.
nee
rin
g.n e
t
/
End plate adjuster
Figure 4.18 Recirculating ball type steering gear When the driver turns the steering wheel, the two steel ball races will roll in grooves and make the nut to travel along the length of the worm. The motion from the nut is transmitted to ..
a wheel sector. The front wheels are displaced by the drop arm. Then the steel' balls are Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering, Brakes and Suspension
Systems
...
recirculated by the ball guides in worm grooves. These balls reduce the friction and increase the efficiency of the mechanism to 90%. This type of steering gear system is mainly applied in heavy commercial vehicles. (3) Rack and pinion type: ,
Figure 4.19 demonstrates the rack and pinion steering system which consists of rack, pinion, tie rods! ball joints, universal joint, rubber boot and spring pads. The pinion is mounted at the end of the steering shaft. A .universal joint is connected at the bottom end of the steering shaft to mount the steering box centrally. This universal joint also provides more leg space. A rack is engaged
ww w.E
with the pinion. The rack reciprocates sideways to give lateral movement to front wheels. The tie rods are connected to this rack by ball joints enclosed in beiiow type rubber dust boots. The ball joints give rise and fall of wheels. Spring pads connected with the rack reduce the backlash between gears to a minimum.
asy E
Dust boot
Pinion Housing
Rack
ngi
/'
nee
rin
Figure 4.19 Rack and pinion type steering gear
g.n e
The driver's effort is transmitted to the front wheel through the steering wheel to steering
t
shaft and finally to the steering knuckle. This type of steering gear is mainly used in cars having independent front suspension. Both Hindustan ambassador and maruthi-800 mainly use of this mechanism. (4) Cam anti lever type: In this type, the cam is mounted at the lower end of the steering shaft. It is a variable pitch worm. Ball bearings supbort the cam. A twin lever carrying studs meshes in the groove of the cam. This arrangement provides minimum of friction when the contact is made betw.een cam and a small stud. When the cam turns, the studs will also move in an arc.This movement makes the pitman arm shaft and pitman arm to rock. The steering is achieved by the rocking movement of drop arm. The cam is cylindrical in shape as shown in Figure 4.20. It provides non-reversibility at the centre part of the cam.
Downloaded From : www.EasyEngineering.net
..
Downloaded From : www.EasyEngineering.net
,
Automobile EngineeringCasing
J
Pitman arm shaft
ww
Figure 4.20 Cam and lever type steering gear
w.E
(5) Worm and roller gear: Worm and roller gears have two-toothed roller which are fastened to the cross shaft called roller shaft or sector shaft or Pitman shaft. The threads of the worm gear are meshed with roller shaft at the end of a steering tube as shown in Figure 4.21.
asy E
ngi
nee rin
g.n et
Figure 4.21 Worm ami roller lyRe steering t:,ear When the worm shaft is turned b~'the steering tube, the roller will also be moved in arc for rotating the roller shaft thereby turning the pin connected to the shaft. The roller is mounted on ball bearings or on anti-friction bearings. The control of both backlash and end float of the rocker shaft is obtained by an adjusting screw. The bearings are designed to resist both radial and end thrust, Then the steering gear is bolted to the frame. This type of gear system is used on Ford car and American passenger cars.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
".f-
Systems
(6) Screw and nut gear:
These types of steering boxes are commonly used. The details of the screw and nut steering gear are shown in Figure 4.22. A screw and nut gear has a phosphor-bronze of steel nut which is screwed on to a multi-start Acme thread formed on the inner column. The rotation of the nut is prevented by a ball mounted in the rocker arm. A single ball race provided at the top end of the rocker shaft carries the axial thrust of the column. A shaft connects the screw with the steering wheel.
ww w.E Nul
asy E
Nut Drop arm
ngi
Figure 4.22 Screw ami nut gear
nee
The nut sliding in the housing supports the lower end. The nut at the top end adjusts the end float of the inner column. Therefore, as the screw is turned by rotating the steering wheel,
rin
g.n e
the nut provided on the screw will be moved axially up and down. This movement causes to rotate the drop arm through two arm spindles. This spindle is mounted on ball bearings in casing. The drop arm is taken by this spindle at its outer end. The two arms of the spindle are attached to the nut by bronze pads. These pads are placed and made to rotate in cylindrical
t
recesses provided on sides of the nut. Also, these pads have parallel grooves to receive the arms of the spindle. The bronze pads cause the arms of the two armed spindles moving in circular paths. (7) Cam and peg: The steering gear has a tapered peg in the rocker arm engaged with a special cam prov.idedon the inner column as shown in Figure 4.23. The peg is moved along the groove for rotating the rocker shaft by rotating the cam. Shims help to control the end float of the column. An adjusting screw on the side cover is connected to govern the backlash and end float of the rocker shaft. The rocker arm is rotated with high efficiency cam and peg gear rotates by a peg in bearings.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I...
Automobile Engineering
ww
w.E
asy
En
gin eer
Adjusting screw
Figure 4.23 Cam and peg type steering gear (8) Worm and ball bearing:
ing
In a worm and ball bearing, the motion transmission from the steering tube is involved
.ne
the pitman arm consisting of a worm and a ball nut. A worm is connected at the lower end of
t
the steering shaft whereas a ball nut is connected with worm. The worm also has mating spiral grooves. Steel balls are circulated for obtaining frictionless drive between worm and nut similar to recirculating ball type steering gear. Two sets of balls are connected with each set independently. The ball nut is moved downward by rolling action of balls when the steering shaft is turned left. The balls reached the outer surface of the nut enter the return guides. The balls are circulated in the reverse direction due to movement of a ball nut. Pitman shaft sector forged integral with the pitman engages the teeth with the teeth on the ball nut. The teeth of theball bearing nut moving up or down the shaft will be moved on the sector teeth to force the ;()~SS snaft and rotate. (9) ~J.r0T111anil sector: Worm and sector are based on the principle of transmitting the motion from the steering tube to the Pitman arm. This steering gear has a case hardened steel worm and sector. The sector is located on bearings made of malleable iron or light alloy casting. The worm is Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering,
Brakes and Suspension
Syst~ms
~ .. ..,-
attached with the inner column and it forms a part of the rocker shaft. Figure 4.24 describes this arrangement.
ww w.E
Figure 4.24 Worm and sector type steering gear
asy E
The worm gear is manufactured with a larger backlash in the lock positions due to greater wear. The risk of seizure at full lock is reduced to compensate this wear by adjusting the box. The end float and backlash are also reduced. The box is connected to the level of the plug with normal gear oil for lubrication the steering gear. The worm at the end of the steering shaft meshes with a sector mounted on a sector shaft. When the worm rotates, the steering wheel will rotate. Also, the sector will rotate the section shaft. So, the motion is transmitted to the wheel through the linkage.
ngi
nee
rin
4.1.12. Steering Ratio
g.n e
t
As the steering linkage gives a mechanical advantage or leverage, the front wheels will turn through a small angle than cross or sector shaft. The number of degrees through which the steering wheel is turned is divided into number of degrees for which front wheels turn. It is known as overall steering ratio. Steering ratio refers the number of turns on the steering wheel required to produce one turn of the steering-gear cross-shaft. In other words, the ratio of the output force to the input force applied is known as steering ratio. It is done by the pitman arm. This steering ratio ranges from 11: I to 24: I in passenger cars having no power steering. This ratio varies from 15 to 20% higher than steering gear ratio in both manual steering and power steering. A variable reduction ratio on steering gears is obtained by varying the pitch of the worm or cam. It is higher for the straight-ahead range and lower for outer ranges. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
.
Steering gear ratio is defined as the ratio between number of degrees of rotation of the
steering wheel and number of degrees through which the cross shaft is free to rotate at the same time. High steering ratios are called slow steering because the steering wheel has to be turned for many degrees to obtain a small steering effect. Low steering ratios is called fast or quick steering because steering wheel has to be turned to obtain a large steering effect. Vehicles connected with-the power steering have average steering gear ratios of20% less than vehicles with manual steering. Steering ratio is determined by following two factors. I. Steering-linkage ratio, and 2. Gear ratio in the steering gear.
ww w.E
The steering linkage ratio is determined by the relative length of the pitman arm and the steering arm. If the effective lengths of the pitman arm and the steering arm are equal, the linkage has a ratio of 1:1. If the pitman arm is shorter than steering arm, the linkage ratio will
asy E
be less than I: I. For example, the pitman arm is about twice as long as the steering arm. It shows, for every degree the pitman arm swings, the wheels will pivot about 2°. Therefore, the steering-linkage ratio is about 1:2.
ngi
In the case of a rack-and-pinion steering system, the steering ratio is largely determined by the diameter of the pinion gear. This steering ratio ranges from 14:1 to 24: 1 in passenger cars without power steering.
nee
4.1.13. Turning Radius and Slip Angle
rin
g.n e
t
The radius of the circle on which the outside front wheel travels when front wheels are turned to their extreme outer position is called turning radius. This radius ranges from 5 m to 8 m in passenger cars. It is 45 feet for buses or trucks. So, the maximum rotation of steering knuckles is more than 35° from straight ahead position. The turning radius is always proportional to the wheelbase of a car. When vehicle turns about a particular side, the vehicle wheels will move some angle to sustain the.side thrust. The angle moment of wheels to resistance the force is called slip angle. In other words, while making a turn, wheels are not always positioned in the direction of the vehicle movement. Jt is due to the distortion of tyre tread. The angle between wheel inclination and path followed by the wheel is known as slip angle. This angle may vary from 8° to 10°for dry and slippery pavement respectively.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering,
Brakes and Suspension
4.1.14. Understeering
Systems
and Oversteering
The centrifugal force exerts on wheels during a tum. There are two conditions arrived while making a tum as shown in Figure 4.25.
,,
,
,.: , ,"
,;"
ww w.E
" ,,'
." , , ,.
Centre for rotation
Centre for rotation
(b) Oversteer
(a) Understeer
asy E
Figure 4.25 Understeer and oversteer
(i)
When the slip angles at front wheels are greater than rear wheels shown in Figure
ngi
4.25 (a), the radius of the tum increases. At this condition, the vehicle turns less than the rotation given by the steering wheel. Otherwise, the vehicle will try to move away from its normal direction of motion. Therefore, the vehicle is kept on the right
nee
rin
path. So, the vehicle is needed to steer for a little more than the th~oretical steer. It is the condition of understeer.
g.n e
(ii) When the slip angles at front wheels are less than rear wheels as shown in Figure
t
4.25 (b), the radius of the tum decreases. At that time, the vehicle will tum more than the rotation given by the steering wheel. Otherwise, the vehicle will try to move in from its normal direction of motion. Therefore, the vehicle is kept at the right path. So, the vehicle is needed a little less steer than theoretical steer. It is the condition of oversteer. Among these two, understeer is less undesirable and the driver reacts naturally and positively by steering in the desired direction. In the case of oversteer, the driver should always be conscious of loosing the control so that a greater care is required. Due to , this reason, the vehicles are designed in such way to obtain understeer conditions at normal speed. Whenever (he driver wants to obtain higher speed, the situation will first change to neutral steer and then to oversteer. The driver has only less time to carry out corrective action. So, ci. sharp transition from understeer to oversteer is particularly dangerous. This explanation Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
of understeer and oversteer conditions are mainly applicable to vehicle moving in turnings because it is equally valid when the vehicle is moving straight position.
ww w.E a
(a) Understeer
(b) Oversteer Figure 4.2$
The steering characteristics of the car always depend on the tyre grip or slip angle effects
syE
and their magnitudes, All wheels (both the front and rear wheels) of the vehicle are affected b)' thi&angle.
ngi
~.1.15.Centr~PQint St~@ri"Q
nee r
When tile kingpin and the wheel centre line are parallel and arrangement has the following disadvantages. a) The force acting at
90° to the axle, the
ing
.ne
the kingpin fer pulling the wheel should overcome the resistance
wheel during running. These forces acting together on the wheels will force to push outward or splay. The splaying effect is increased due to application of brake. of the
b)
t
Large bending stresses are impcsed on the stub axles and kingpins due to the kingpin causing
the wheel
to
run through
an
are about
the kingpin instead of its own vertical
centre line.
c) Heavy steering owing to the distance between kingpin and centre line of the wheel. The wheel has to be
moved in
an arc about the pin instead of its own vertical centre
line. To overcome these disadvantages, the wheel and kingpin are so arranged that the centre line of the wheel meets the centre line of the kingpin at the road surface as shown in Figure 4.26. This condition is known as
centre point steering.
Downloaded From : www.EasyEngineering.net '-
Downloaded From : www.EasyEngineering.net
Wheel centre line
./
\J
1 I
ww w.E
Vertical
I I
,I King pin I'"centre line
I
Figure 4.26 Cenre point steering
asy E
When front wheels follow this condition,
me bending
stress and splaying put couple will
be reduced. Swivel, heavy steering spray and very high stresses are reduced by tilting the wheels outwards at the top and the kingpin inwards at the top. It is done by bringing the wheel and the kingpin centers closer together,
ngi
nee
The condition of centre point steering can be obtained by
rin
1. Camber: This is achieved by stub axle at an angle which allows the wheel centre line to meet the kingpin centre line.
g.n e
2, Kingpin inclination: The kingpin swivel axis is inclined so that the centre line of the kingpin meets the centre line of the wheel.
t
J. The use of dished wheels: Wheels that are dished towards the middle of the vehicle so that the wheel centre line is more in line with the kingpin centre line. EVIiIn
though the centre point steering appears to be idle, it also has the following
disadvantages. ~
'Spread' effect of the tyre causes the wheel to 'scrub' as the wheel rotated on the road surface and give 'heavy steering' and
~
Increased tyre wear occurs.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lma
Automobile Engineering
4.1.16. Cornering Force When vehicle turns, a centrifugal force is acting on the vehicle which produces the thrust on the vehicle. This force can be counteracted by the side thrust of vehicle wheels for some angle with direction of motion of vehicle, called slip angle. The force produce to this is called
corneringpower orforce. Corneming power
Side force sustai ned Slip angle
ww
w.E
asy
En
gin eer
ing
Figure 4.27 Corneringforce and slip angle
.ne
t
The rate at which cornering force builds up is described by relaxation length. Slip angle describes the deformation of the tire contact patch, and this deflection of the contact patch deforms the tire in a fashion akin to a spring. As with deformation of a spring, deformation of the tire contact patch generates a reaction force in the tire which is called the cornering force. Integrating 'the force generated by every tread element along the contact patch length gives the total cornering force. Although the term, "tread element" is used, the compliance in the tire that-leads tothis effect is actually a combination of sidewall deflection and deflection of the rubber within the contact patch. The exact ratio of sidewall compliance to tread compliance is factor in tire construction and inflation pressure.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
teering, Brakes and Suspension Systems
4.1.17. Reversible And Irreversible Steering (i) Reversible Steering
When the deflection of road wheels is transmitted through the steering wheel to road surface, the system is called reversible steering. If every imperfection of road surface causes the steering to rotate, it causes much strain on the part of the driver to control the vehicle. Therefore, this type of reversibility should be avoided. But some degree of reversibility needed to keep the wheel straight after taking a curve. (ii) Irreversible Steering
If no deflection to the steering the front road wheels are transferred, it is said to be irreversible steering. If the steering wheel is not returned easily, it will produce unwanted stresses on the steering. So, some degree of irreversible is also required.
ww w.E
4.1.18. Power Steering
asy E
The front wheels are turned to the right or left as per the will of the driver through the mechanical advantage of the steering gear and the linkage. When a car is manually steered, the driver has to apply all steering force.
ngi
There are some disadvantages in manual steering.
nee
1. It is bigger and heavier in engines on cars.
rin
2. Low-pressure tyres should be used in case of cars. The larger steering ratio is
g.n e
required to steer these cars. For this, more turns of the steering wheel are required to move to the desired distance.
t
Larger tyres having heavier weight on vehicles make the car more difficult in parking. So, the driver has to apply the greater physical strength for driving vehicles. To overcome this difficulty, a power-assisted steering has been introduced as shown in Figure 4.28. It is done by an external source. Automobiles always do not have full power steering. They have only power-assisted steering called power steering. The car cannot be steered when the engine stalls or the powersteering system fails without mechanical connection between steering wheel and front wheels. The car can manually be steered when the power assist is not available. This power-steering system uses compressed air, electrical devices and hycraulic pressure. Some re air-operated power steering. But, now-a-days, hydraulic oil pressure is used in all cars an most trucks having power-steering systems.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I,.
Automobile
Engineering
The power steering is to improve the driving comfort. Most modem automobiles have wide and low-pressure tyres with increased tyre-to-road surface contact area. There are two types of power-steering systems used in automobiles. ' 1. Integral type, and 2. ainkage type. In an integral type, the power piston is integrated along with the steering gear whereas the power piston is connected between frame of the vehicle and steering linkage in case of linkage type. It is mainly used along with a vehicle built in trucks.
For road feel or vehicle steering response, power steering is used to reduce the steering
ww w.E a
wheel turning effort, to turn sharp corner easily, to negotiate winding roads and to move vehicles in a confined space and also to offer some resistance to make the driver feel and retain.
The road feel helps the driver to sense and predetermine the approach of front wheels in slipping sidewgy point due to turns, winds etc. A greater effort is required by the driver to exert the desired torque at the steering wheel in case of heavy vehicles and loaded commercial vehicles. It is to control the vehicle. Power assisted steering is used in all types of vehicles, i.e.
syE
ngi
nee r
.. eavy cars and commercial vehicles, medium weight cars etc. Working of power steering:
ing
A simple hydraulic power assisted steering is illustrated in Figure 4.28. It consists of a
.ne
fluid reservoir, hydraulic pump, hydraulic ram;'control valve, steering shaft, steering box and steering wheel.
t
Ste!ering column HP fluid Return LP fluid
Hydraulic control valve
Pump Hydraulic ram
Figure 4.28 Power steering
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
IIDI
Systems
The engine driven by hydraulic pumps supply oil under pressure from the oil reservoir to feed lines. A hydraulic control valve provided below the steering measures the input pressure at the steering wheel. Then the pressure is converted into the hydraulic ram. When the steering wheel is stationary, the oil will exert the same pressure on both sides of the piston and retain the piston at rest. When the driver turns the steering wheel, the control valve is moved by the steering arm. At that time, one of the ports closes while the other one opens. A high-pressure (HP) oil enters one side thereby moving the piston. Then this movement of the piston actuates steering linkage to move in the required direction. (a) Neutral (Straight-ahead) position:
ww w.E
Fluid is sent to the control valve from the pump. If the control valve is in the neutral position, the whole fluid will be sent through the control valve into the relief port and back to the pump as shown in Figure 4.29. Due to this, the pressure is produced and the pressure on the cylinder piston becomes equal on both sides. Due to this, the piston will not move in either direction.
asy En - -gine- t e - ring . Pump
Control valve
+
Power cylinder
net
~r-----~--------------~~ r---------------~------~ c
a::
Figure 4.29 Straight ahead position (b) Tuning of vehicles: When the steering main shaft is turned in either direction, the control valve will also be moved thereby closing one of the fluid passages. The other passage is then opened widely by producing a change in fluid' flow volum'e. Thus, the pressure is created. Then, the pressure difference is developed between both sides of the piston which forces the piston in Jhe direction of the lower pressure. Due to this, the fluid in the cylinder is forced back to the pump through the control valve as shown in Figure 4.30.
Downloaded From : www.EasyEngineering.net
,
..
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
This system is used in big cars and heavy commercial vehicles. It is very much suitable
for low speed and the vehicle for parking purposes while reversing.
Steering effort is
decreased by increasing the gear ratio of the steering gear. A large rotary motion of the steering wheel is produced when the vehicle turns. Some .sort of a steering assist device is necessary to keep the steering angle and small steering effort.
-
Pump
Control valve
ww
-
-
w.tE
Power cylinder
asy
t
En
gin eer
Figure 4.30 Turning position .cequirements of power steering with suitable steering force:
ing
Although power steering is a mechanism used for reducing the steering effort, the effort should be varied with driving conditions. Usually, more steering effort is required when the
.ne
vehicle stops or moves at low speed. At middle-range speeds, less steering effort is required
t
when the vehicle speed increases. Less steering effort is required during high-speed driving. Many models have power steering with special devices on the pump and the gear housing to ensure the proper steering effort. The following are some of the arrangement made for this ,
purpose. ((I) Vehicles speed-sensing type: Vehicle speed is detected by a speed sensor and the fluid pressure acting on the piston varies accordingly. The fluid pressure is increased to lighten the force required for steering when the vehicle stops or moves at a low speed. At high speed, the pressure is reduced to lower the amount of assist and thus, the appropriate steering wheel response is provided.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
,·t-
Steering, Brakes and Suspension Systems
(b) Engine rpm sensing type:
Most power steering pumps supply a constant volume of fluid to the gear housing according to the speed (rpm) while the pump is operated. So, the flow volume of the fluid is reduced above a certain speed with less pressure on the piston in case of a RPM sensing type. Counter measures over Breakdown: The driver should still steer the vehicle manually to make the termination of fluid flow from pump to gear housing. There is fluid leakage caused by the loss of the fluid at zero power steering. On that time, the steering effort required will be higher but hindrance to steering will be zero.
ww w.E
4.1.19. Trouble Shooting for Steering System
(i) Manual Steering troubles and their causes
asy E
1. Hard steering
-----------------------------------------------------------------------------------------------------------Remedies Causes
ngi
-----------------------------------------------------------------------------------------------------------Inflate tyres to correct pressure. (a) Low or uneven tyre pressure. (b) Steering gear adjusted too tight.
nee
rin
Disconnect drag link, check and adjust steering gear.
(c) Steering linkage binding.
free up and lubricate. (d) Incorrect or insufficient
g.n e
Locate points of excessive friction,
t
Lubricate with recommended lubricants.
lubrication. (e) Incorrect caster, camber, toe-in or king-pin inclination.
Measure each one. Adjust or repair to obtain correct values.
(f) Steering arms or knuckles or suspension arms bent or broken.
Replace bent or broken units.
(g) Front spring or springs weak
Replace spring.
or sagging. ).
(h) Frame bent or broken.
Check frame alignment and repair or replace. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lID
Automobile Engineering
(i) Steering shaft or tubing bent.
Replace bent units.
U) Spherical ball joints too tight.
Replace.
-----------------------------------------------------------------------------------------------------------2. Excessive play or looseness in tile steering system -----------------------------------------------------------------------------------------------------------Remedies Causes
-----------------------------------------------------------------------------------------------------------(a) Steering linkage loose or worn.
ww w.E
Locate points of excessive play. Tighten connections or replace worn parts. Adjust steering gear or replace worn
(b) Steering gear adjusted too loose or worn.
asy E
parts. Replace.
(c) Kingpins, steering knuckle bushings and bearings or spherical joints worn.
ngi
(d) Front-wheel bearings too loose or worn.
(e) Steering gear housing loose on
nee
Tighten or replace.
Tighten.
frame of cross member.
rin
(f) Steering wheel loose on post.
Tighten.
(g) Steering gear flexible coupling
Tighten or replace.
g.n e
I
t
loose or worn.
----------------------------------------------------------------------------------------------------------_. 3. Steering becomes erratic when tile brakes are applied
----------------------------------------------------------------------------------------------------------Causes
Remedies
-----------------------------------------------------------------------------------------------------------(a) Brake lining worn or soaked or brake fluid.
Replace lining. Locate with oil, grease and remove causes of oil, grease or brake fluid.
(b) Brakes poorly adjusted.
Adjust brakes.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
, Steering, Brakes and Suspension
Systems
(c) Insufficient or uneven caster.
Measure caster and adjust to correct
Replace steering knuckle. (d) Steering knuckle bent -----------------------------------------------------------------------------------------------------------4. Car wanders can only be kept in a straight line with much steering ------------------------------------------------------------------------------------------------------------
Remedies Causes -----------------------------------------------------------------------------------------------------------Replace bent parts. (a) Steering knuckle and/or king pin bent.
ww w.E
(b) Rear-axle housing shifted.
Align rear axle housing. Repair cause of shift.
(c) Stabilizer inoperative.
asy E
(d) Kingpin and bushings or
Repair stabilizer. Repair stabilizer.
spherical joint too tight.
(e) Upper or lower control arm
ngi
Free up or replace parts.
nee
shaft binding. -----------------------------------------------------------------------------------------------------------5. Front wheels shimmy
rin
g.n e
-----------------------------------------------------------------------------------------------------------Causes
Remedies
t
---------------------~-------------------------------------------------------------------------------------(a) Wheels, tyres or brake drums
Balance each complete assembly.
out of balance. (b) Wheels or tyres out of true.
True up or replace.
(c) Shock absorbers inoperative.
Refill, repair or replace.
(d) Toe-in incorrect.
Measure and adjust to specification.
(e) Eccentric or bulged tyres.
Replace tyres.
(f) Loose spring U-bolts.
Tighten U-bolts.
'_
. _
------------------------------------------------------------------------------------------------------------
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
II!7'iII
Automobile
Engineering
6. Front wheel tramp. (Wheels move up and down together and separately) -----------------------------------------------------------------------------------------------------------Causes Remedies (a) Wheel or tyre not concentric.
Replace one both.
7. Car pulls continuously to one side Causes
ww w.E
Remedies
(a) Rear wheels not tracking with
Check rear-wheel front
alignment.
wheels.
(b) Wheel bearings too tight.
Adjust wheel bearings.
asy E
(c) Upper and lower suspension
Tighten to correct torque.
arm mounting bolts loose.
ngi
-------------------------------------------~---------------------------------------------------------------8. Scuffed tyres
nee
Causes
Remedies
rin
g.n e
(a) Wrong toe-in.
Measure.and adjust to specifications.
(b) Uneven camber.
Measure and adjust to equal and correct value.
(c) Incorrect toe-out on turns.
t
Replace steering knuckle arms or steering knuckle if the arms are integral.
(d) Excessive speed on turns.
Slow down on turns.
(e) Suspension arms bent or twisted.
Replace arms.
9. Hard steering when parking Causes (a) Lose pump belt.
Remedies Tighten to specifications. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering, Brakes and Suspension Systems (b) Low oil level.
Fill reservoir. Repair any leaks.
(c) Low oil pressure.
Check for kinks or foreign matter in hoses and remove them. Locate loss of pressure in pump, steering assembly, or valve body. Repair or replace.
{a)-Pump lacks capacity.
Check pump capacity. Repair or replace if necessary.
ww
10. Poor return of gear to center after turning
w.E asy En gin ee Remedies
Causes
Control valve and/or actuator
Free up, clean, or replace as lever
sticking or binding.
required.
11. Momentary increase in effort when turning wheel rapidly Remedies
Causes
Air in system
Bleed system.
rin g.
12. Excessive wheel kick-back or loose steering Remedies
Causes Air in system.
net
Bleed system.
13. Steering wheel surges orjerks when turning Causes Loose pump belt.
Remedies Tighten to specifications.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1l1li
Automobile Engineering
14. Car pulls continuously to one side. Steering effort is very light in direction of pull and heavy in opposite direction Remedies
Causes
Replace.
Worn or damaged valve and/or shaft assembly.
15. Pump is noisy
ww w.E
Remedies
Causes ___ i
(a) Worn pump.
Tighten.
(b) Damaged hose.
Replace.
(c) Leaking seals at side cover, pitman shaft, housing etc.
Replace.
asy E
ngi
(ii) Power Steering troubles and their causes
Troubles I. Steering hard when parking vehicle.
nee Causes
_
rin
g.n e
(a) Pump belt loose. (b) Oil level low.
(c) Oil pressure low.
t
(d) Pump lacks capacity. 2. Steering gear does not return quickly to centre after
(a) Control valve sticky. (b) Actuator lever binding.
negotiating turn. 3. Temporary increase in turning
(a) Air in the system.
effort when steering wheel
(b) Pump belt loose.
turned rapidly.
(c) Oil level low. (d) Oil pressure low. (e) Pump lacks capacity.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
el·
Steering, Brakes and Suspension Systems
4. Steering wheel jerks while negotiating turn.
(a) Pump belt loose. (b) Oil pressure low.
5. Vehicle pulls to one side.
Valveand/or shaft assembly damaged or worn. (a) Pump worn.
6. Noisy pump.
(b) Air in the system. (c) Pump belt loose. (d) Oil level low. (e) Hoses touching other parts of the
ww w.E
vehicle.
7. External oil leaks.
(b) Damaged or worn hose.
asy E
8. Excessive looseness in the steering system.
(a) Hose connection loose. (c) Leaky seals. (a) Air in the system. (b) Steering gear improperly adjusted.
ngi
(c) Worn steering linkage.
nee
(d) Kingpin or ball joints worn. (e) Steering gear parts worn.
rin
(f) Steering gear mounting loose.
g.n e
(g) Front wheel bearings too loose or worn.
t
-----------------------------------------------------------------------------------------------------------4.2. FRONT AXLE
The major unit on front part of the motor vehicle is front axle. It takes the weight of the front portion of the automobile. It gives steering facility and absorbs shocks. The weight of the front part of the vehicle is transmitted to the road surface through front wheels by the front axle of a vehicle. It also houses the mechanism for steering the vehicle to absorb shocks due to road surface variations.
Downloaded From : www.EasyEngineering.net
..
Downloaded From : www.EasyEngineering.net
,
Automobile Engineering
4.2.1. Functions of Front Axle 1. It turns the front wheel easily. 2.
It provides a cushioning effect though a spring.
3.
It takes the weight of front vehicle.
4.
It provides steering action.
S.
The spring transmits cushion effect to the vehicle.
6.
It controls the ride through shock absorber.
7.
It takes the braking system.
8.
It transmits power to the front wheels in case of four wheel drive.
ww 9.
It carries both the hub and wheels
w.E asy En 'Sgin ee
4.2.2. Construction and Components of Front Axle
Axle beam is a major part of the front axle. It is used to transmit the vehicle weight to the front wheel through the spring. A typical front axle shown in Figure 4.31 elaborates the front axle components with steering linkage. Steeringcolumn
\
'-oroparm
Kingpin
rin g.
net
Steeringarm
Figure 4.31 Front axle components with steering linkage The ends of the axle beam are shaped in such way to assemble the stub axle. The ends of tne axle beam are shaped either as a yoke or plain surface with drilled hole to hold a swivel pin connecting the stub axle portion of the assembly. The wheels are connected on stub axles. The inclined steering arms are located to track rod ends. The third steering arm is connected to
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension Systems
_
the drag link. The steering linkage is connected by the drag link to the drop arm of the steering box. The main axle beam is attached to stub axles by kingpins. The front road wheels are connected on these stub axles. The components of the front axle are axle beam, stub axle, swivel pin and track load. 1. Axle beam:
Axle beams are made by drop forging of steel having 0.4% carbon or 1-3% nickel steel. The front axle beam is formed into l-section in the centre portion. The ends are made into either circular or elliptical. l-section construction carries bending loads caused by the load of the vehicle and torque by braking of wheels. The centre portion of the front axle is provided a downward sweep to maintain the chassis height low.
ww w.E
This axle beam is already hinged with stub axles. Springs are mounted on the axle beam at equidistance from its centre known as ~prmg pads or seats. In some other cases, these springs may be boIted with the axle beam. It reduces the swing or sway of the vehicle while turning the vehicle.
Section at AA
asy E
ngi
nee
8
~ Section at B8
Figure 4.32 Axle beam 2. Kingpin or Swivel pin:
rin
g.n e
t
The steering spindle and steering knuckle assemblies are pinned at the ends of axle beam in order to permit wheels to be turned by (he steering gear. This pin is known as kingpin or steering knuckle pin. It is also called swivel pins. The pins are made of good quality case hardened steels used to secure the stub axle to the axle beam. It is exactly located and locked by cotter pins in position. 3. Track rod: The two stub axles arms of the front axle are connected with ends of a track rod through knuckle or ball joints known as track rod ends. The connection is done by screws to ensure adjustments. In the stub axle, left hand and right hand threads are formed at eaeh end. Toe-in is increased by lengthening the rod and it is decreased by shortening the same.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1m:.J
Automobile Engineering
4. Pu/l and push rod or drag link: Pull and push rod also called drag link is connected between steering arm of the front axle and drop arm of the steering assemble. But the cross-section is tubular. Spring loaded ball sockets are provided at each end. One end is connected to the steering arm of the stub axle whereas the other end is connected to the steering drop arm.
4.2.3. Types of Front Axles There are two types of the front axles based on the rotation as follows. 1. Live front axle
ww w.E 2.
Dead front axle.
~~
~~~
asy E
(a) Straight axle
Steering pin attachment
ngi ~~
(b) Double drop axle Kingpin
m<
Stub axle
nee
rin
~9kn"ckl'
I section (c) Fully drop axle
g.n e
t
Figure 4.33 Different types offront axle Generally, the front axle is a dead axle. In heavy vehicles and most of cars, the front axle is a live axle. These types of axle are used in modern cars and heavier vehicles. The front axles are called as dead axles when they do not rotate but live axles transmit power to rear wheels. A live front axle also transmits the driving power to front wheels having different swiveling mechanisms. The dead front axle has enough rigidity and strength to transmit the weight of the vehicle from swings to front wheels.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
Systems
There are two types of the front axles based on the axle beam as follows. I. Straight axle 2. Double drop axle 3. Fully drop axle. Figure 433 illustrates these three types of front axle arrangements.
4.3. STUB AXLE The steering wheels have to turn the front wheel. It is done by hinging the stub axle .vith steering knuckle at the axle beam. The pin which forms the pivot of this hinge is called
ww
kingpin. The front wheels are mounted on stub axles by kingpins. The stub axles ere the forging of 3% nickel steel and alloy steels having chromium and molybdenum. The stub axle
w.E asy En gin ee
turns on the kingpin. Phosphor bronze bushes are mounted into forked ends of the axle to provide a bearing surface for the kingpin. Vertical loads are carried out by a steel washer or between lower fork and underside of the axle beam. The stub axle wheel two ball bearings which can be adjusted by means
of an adjusting
revolves
over
nut. Oil seals are
provided to prevent the leakage of lubricant from the bearings.
4.3.1. Types of Stub Axles
rin g.
Following are four types of stub axles which are shown in Figure 4.34. 1. Elliot 2. Reversed elliot 3. Lamoine 4. Reversed lamoine.
net
1. Elliot stub axle: The Elliot stub axle is connected to the front axle by placing in the yoke end with a kingpin and a cotter is used to join these two together shown in Figure 4.34 (a). The king pin is usually fixed in the stub axle forging and its end turns in the forked end of the axle beam.
2. Reversed Elliot stub axle: In reversed Elliot type stub axle, the arrangement is reversed. The kingpin is fixed in the axle beam. Its ends turn in the forks of the steering knuckle shown in Figure 4.34 (b).
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile Engineering
/
Stub axle (a) washer
Kingpin
./
ww w.E (c)
(b)
StUbru :
:
Kingpin
asy E
(d)
Figure 4.34 Types of stub axles
3. Lamoille stub axle:
ngi
nee
In lamoine type stub axle, a L-shaped spindle is used instead of yoke type hinge as shown in Figure 4.34 (c). 4. Inverted lamoille stub axle:
rin
g.n e
The construction is similar to the lamoine stub axle but the upside of the axle is inverted so that the wheel axle is below the axle beam as shown in Figure 4.34 (d). In modern vehicles, the front axles are straight. The centre of gravity of the vehicles decreases to provide good stability and safety to high-speed vehicles.
t
4.4. SUSPENSION SYSTEM
The chassis of vehicle is connected to the front and rear wheels through the medium of springs, shock absorbers and axles. All parts perform the function of protecting parts from shocks are known as suspension system. The automobile chassis is indirectly connected with axles by springs. It is done to prevent the vehicle body from road shocks due to bounce, pitch, roll or sway. These road shocks provide an uncomfortable ride and also additional stress to the automobile frame and body.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering,
Brakes and Suspension
Systems
.,.
Suspension system has a spring and damper. The energy of road shock produced by the spring oscillates. These oscillations are arrested by the damper known as shock absorber. 4.4.1. Components
of Suspension
System
1. Springs are used to neutralize the shocks from the road surface. 2. Dampers, called shock absorbers, are used to improve a riding comfort by limiting the free oscillation of springs. 3. Stabilizer, called sway bar or anti-roll bar, is to prevent lateral swinging of the car. 4. A linkage system holds above components to control the longitudinal and lateral movements of wheels.
ww
w.E asy En gin ee
4.4.2. Functions or Objectives of Suspension System
1. To eliminate road shocks from transmission to vehicle components. 2. To obtain good road holding while driving, cornering and braking. 3. To keep the proper steering geometry.
4. To obtain a particular height to body structure. 5. To resist the torque and braking reactions.
rin g.
8. To maintain the stability of the vehicle while traveling over rough round or when turning in order to minimize the rolling, pitching or vertical movement tendency.
net
9. To safeguard the occupants against road shocks and provide a riding comfort.
10. To minimize the effects of stresses due to road shocks on the mechanism of the motor vehicle and provide a cushioning effect. 11. To keep the body perfectly in level while travelling over rough uneven ground. I.e. the up and down movements of wheels should be relative to the body. 12. To prevent the structure of the vehicle from shock loading and vibration due to irregularities of the road surface without impairing its stability. 13. To obtain the requisite height to body structure. 14. To support the body on the axles and keep the proper geometrical relationship between the body and wheels.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIID
Automobile
4.4.3. Requirements
of Suspension
Engineering
System
1. There should be minimum deflection. 2.
It should be of minimum weight.
3.
It should have low maintenance and low operating cost.
4.
It should have minimum tyre wear.
5.
It should be of low initial cost.
4.4.4. Principles of Suspension
ww
System
fhe principles of the suspension system are due to springing action of motor vehicles. I.
Supporting the weight of vehicle.
2.
Absorbing satisfactorily larger and smaller road impacts with the help of a single
w.E asy En gin ee
springing device. 3.
The reduction
of rolling or pitching of the body to a minimum
design and
attachment of springs.
4.4.5. Sprung Weight and Unsprung Weight
The body of vehicle is supported by springs. The weight of the body is supported by
rin g.
springs called sprung weight. Wheels, axles and other parts of the automobile which are not supported
by springs,
called the unsprung weight.
Unsprung weight is the weight of
everything between springs and road and a portion of weight of springs itself.
net
If greater is the sprung weight of an automobile, the better will be the riding comfort. This tendency of the body reduces the jolt. Sprung weight is the weight of vehicle minus unsprung weight :. Sprung weight
= Total
weight of vehicle - unsprung weight.
Greater is the unsprung weight on a wheel, the greater will be the energy stored by the unsprung weight due to road bump and greater will be the disturbances. This greater unsprung weight increases tyre deflections but it reduces the vertica! velocity on road bump. Lesser unsprung weight causes higher natural frequencies of the unsprung. A lighter wheel moves on road irregularities without producing much reaction to the cnassis frame, body and occupants. If the weight of wheel increases, its movement is highly noticeable to vehicle occupants. When the unsprung weight on the wheel becomes equal to the Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'B·
i Steering, Brakes and Suspension Systems
sprung weight above the wheel, the sprung weight will move as much as unsprung weight. So, the unsprung weight moves up and down over road irregularities. Therefore, the unsprung weight is kept as low as possible due to the reduced unsprung weight thereby resulting a better ride.
Sprung weight
ww
t
w.E asy En gin ee ~
Unsprung weight
Figure 4.35 Sprung and unsprung weight
Effects of unsprung weight:
The unsprung weight of a wheel controls a trade-off between a wheel's bump and its vibration isolation. Bumps and surface imperfections in the road cause tyre compression which induces the force on the unsprung weight. Then, the unsprung weight responds to this
rin g.
force with movement of its own. The amount of movement for short bumps is inversely
net
proportional to the weight. A lighter wheel which readily moves in response to road bumps will have more constant grip when tracking over an imperfect road. Therefore, lighter wheels are especially sought for high-performance applications. In contrast, a heavier wheel which moves less will not absorb as much vibration. "he irregularities of the road surface will transfer to the cabin through the geometry of the suspension and hence, ride quality and road noise are deteriorated. For longer bumps, the greater unsprung mass causes more energy to be absorbed by wheels and it makes the ride worse. Pneumatic or elastic tyres help by providing some springing action for most of the unsprung mass but the damping which can be included in tyres is limited due to fuel economy and overheating. The shock absorbers damp the wheel bounce if any spring motion must be less stiff than the optimum value. So, the wheels produce some vibrations after each bump before comingto rest.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I.,.
Automobile
Engineering
High unsprung weight also exacerbates the wheel control issues under hard acceleration or braking. If the vehicle does not have adequate wheel location in the vertical plane, the vertical forces exerted by acceleration or hard braking combined with high unsprung mass can lead to severe the wheel hop, compromising traction and steering control. Similar to above case, there is a positive effect of unsprung mass. High frequency road irregularities such as gravels in an asphalt or concrete road surface are isolated from the body more completely because the tyres and springs act as separate filter stages with the unsprung weight tending to uncouple them. Similarly, sound and vibration isolation are improved in production automobiles by the use of rubber bushings between frame and suspension in the
ww w.E
form of flexibility in the frame or body work and flexibility in seats. 4.4.6. Basic Suspension
Movements
A vehicle is always subjected for moving over road irregularities. The road will not be
asy E
. 100% levelled. The road surface has pits and falls. The vehicle will go up and down due to cross over bumps and pits in the road. It also passes through bends, curves and zig-zag path.
ngi
The following basic movements are occurred when the vehicle is in motion. (a) Bouncing (b) Pitching (c) Rolling
nee
(d) Yawing. Yawing
rin
g.n e
t
Figure 4.36 Movements of vehicle
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
t....
[SteWing, Brakes and Suspension Systems
(i) Bouncing
The vertical movement of the complete body is called bouncing. In other words, the complete body of the vehicle moves up and down, it is called bounce or bouncing. It may be either front end or rear end bounce. It occurs when the springs are soft.
~
ww
(ii) Pitching
- - --
w.E
Figure 4.3i Bouncing
asy
Rocking chair action or rotating action about a transverse axis through the vehicle parallel to ground is known as pitching. Due to this. the front suspension will move out of phase thereby resulting a rocking effect.
En
gin eer
Diagonal pitch is defined as the combined radius and pitching action of rolling and pitching. Pitching arises in vehicles having softer springs than harder springs.
~
,'------y
"
'I
..
- - ....
, _-----1
,"
;0-
L
.::
...
ing
'~,
"-
------
::==:__
.ne
0 \~ t \\
::.::
Figure 4.38 Pitcllillg (iii) Rolling
The movement of the wheel about longitudinal axis produced by centrifugal force when cornering is known as rolling. It results the body rolling in the lateral which means side-toside direction. Anti-sway bars, stabilizers, pitch and roll control bars, mechanical leveling devices, hydroelastic systems, etc., are employed in cars to control the suspension movements.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIID
Automobile Engineering
ww
(lv) Yawing
Figure 4.39 Rolling
w.E
Yawing is the movement of the car's longitudinal centerline to the right and left in
relation to the car's center of gravity. On roads where pitching occurs, there will be a chance to occur yawing,
asy E
ngi
nee rin
Figure 4.40 Yawing
g.n et
4.4.7. Types of Suspension Springs Springs are main important parts of any suspension system which are classified as follows. 1. Steel springs a) Leaf springs b) Tapered leaf springs c) Coil springs d) Torsion bar Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering, Brakes and Suspension
Systems
2. Rubber springs a) Compression springs b) Compression-shear springs c) Steel reinforced springs d) Progressive spring e) Face shear spring 3. Air springs a) Bellow type springs
ww
b) Piston type springs
4. Plastic springs.
w.E
4.4.8. Leaf Spring Suspension
asy
Figure 4.41 shows the construction of the laminated lear spring suspension. It has a number of leaves of increasing lengths made of steel plates. The spring eye is mounted to the
En
gin eer
frame by a pin called shackle pin. The centre portion of the spring is attached to the front axle by a V-bolt. One end of the spring is mounted on the frame with a simple pin. The other end is mounted by a shackle with the frame.
ing
.ne
t
Figure 4.41 Lea/spring suspension
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIID
Automobile Engineering
The stiffness or spring rate of the coil spring decides the capacity of the spring which is defined as the force required for unit deflection. It is governed by the following factors. ~
The length of the spring: Shorter spring will have higher stiffness and vice versa.
~
The width of the leaf: Wider spring will have higher stiffness and vice versa.
~
The thickness of the leaf: Thicker leaf will have higher stiffness and vice versa.
~
The number of leaves: Greater the number of leaves higher the stiffness is.
To obtain a smooth ride, a low-rate stiffness spring is required. The low rate spring will deflect a larger amount under a given load. Normal springs have a constant rate, and give a deflection which is proportional to the load applied.
ww
When a laminated leaf spring deflects, the leaves slide over each other and cause interplate friction. Although this has a beneficial damping effect, the hard ride, noise and wear occurs. Hence, it is necessary to reduce this friction as much as possible.
w.E
asy
Older designs of spring had to be sprayed with penetrating oil, but the new designs have the following features to eliminate the need of periodic attention.
En
"» Synthetic rubber buttons are provided at the ends of the leaves
gin eer
~
Inter-leaf plates of low friction materials are incorporated
)io>
Less number of leaves
Types of leaf springs:
Differenttypes of leaf springs based on its design are as follows. 1. Semi elliptical spring 2. Quarter elliptical spring
ing
.ne
t
3. Three quarter elliptical spring 4. Full elliptical spring 5. Transverse spring 6. Platform type spring. The construction details of various types of laminated leaf springs designs are given in Figures 4.42 to 4.45 which are self-explanatory.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering, Brakes and Suspension Systems Frame Side Member
Shackle
Figure 4.42 Semi elliptical spring Frame Side Member
ww w.E
asy E Front Axle
ngi
Figure 4.43 Quarter elliptical spring Eye
nee "
rin
Master leaf
Graduated leaves
~
Centre bolt
g.n e
t
Figure 4.44 Full-elliptical leaf spring Frame Cross Member
Front Axle
Figure 4.45 Transverse spring Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
4.4.9. Helper Springs
Where there are fluctuations in the loads, helper springs are used in trucks and many other vehicles. It is mounted above the mainspring as shown in Figure 4.46. It is arranged in such a way that if the load is less, the main spring is operated. Both the main and helper springs are operated if the load exceeds a certain value. Shackle
Frame
ww
w.E
asy
En
gin eer
Figure 4.46 He/per springs
Helper springs are used along with the main leaf springs on many commercial vehicles. It is more suitable for a wide range of loading. Helper springs are mainly provided on rear
ing
.ne
suspension. When the load on the road wheel increases, ends of the helper spring isjust made to touch the special brackets fitted to the side member thereby operating the helper spring. Characteristics of he/per springs:
t
1. Due to springs having enough rigidity to hold the axis in the proper position, they are required. . 2. Controlling of own oscillation through inter-leaf friction is performed. 3. These springs have durability in heavy-duty applications. 4. Due to inter-leaf friction, it is difficult to absorb minute vibrations from the road surface. So, leaf springs are more suitable for large commercial vehicles which can carry heavy loads.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
Systems
4.4.10. Coil Spring
A coil spring is a steel wire. The required length is coiled throughout. The coil springs are used in both rear and front independent suspensions. The energy stored per unit volume is approximately twice in the coil spring when compared to leaf spring. The coil spring carries both shear and bending stresses but both torque reaction and side thrust cannot be carried out. So, some special arrangements are made to position the axles relative to the frame. Both driving reaction and braking torque reaction are also considered in arranging the coil spring. A helper spring is additionally used, as shown in Figure 4.47, to give progressive stiffness against the increasing load.
ww • • w • .E • asy• En • g •
:
(a) Helical coil spring
-
'~" ~HeIPe,
spnng
~Main ~
ine eri
spring
7~~
(b) Helper coil spring
Figure 4.47 Coil springs are again classified into two types. l. Tension, and
2. Compression springs
ng.
net
Characteristics ofcoil spring: I. The energy absorption rate per unit of weight is greater when compared to leaf springs. 2. Soft springs can be coiled. 3. Due to no inter-leaf friction with leaf springs, no control of oscillation is necessary by the spring itself but shock absorbers are needed. 4. Due to no resistance to lateral forces, linkage mechanisms to support the axle such as suspension arm, lateral control rod, etc. are required.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIID
Automobile Engineering
4.4.11. Torsion Bar
A torsion bar is a steel bar operated by both twisting and shear stress. Two long steel bars form springs. Torsion bar can be used with independent suspensions. It is a simple bar in which one end is fitted to the frame whereas the other end is fitted to the end of a wheel arm. The structure with a bearing supports the projection of the second end of the bar. The other end of the wheel arm is attached with the spindle of the wheel using kingpin. When the wheel strikes a bump, it will start to vibrate up and down thereby producing a torque on the torsion bar called spring. Torsion bar spring is lighter in weight when compared to leaf springs. It also occupies less space. Torsion tubes replace torsion bars in many cases. The main disadvantage of the torsion bar spring is that it does not carry the
ww
braking or driving torque. Therefore. additional linkages are needed. Due to the absence of friction force, the damping is required to absorb road shocks. The simple torsion bar is shown
w.E
in Figure 4.48.
asy
Wheel hub
En
gin eer Bearing
ing
Figure 4.48 Torsion bar
.ne
t
Advantages of torsion springs: 1. This spring needs less space. 2. It is lighter than leaf spring system. 3. This system provides very neat and compact design. 4. In some cases, torsion tubes are used instead of torsion bars. Disadvantage of torsion springs: It does not take the driving or braking torque. Therefore, inconvenient additional link mechanisms are provided for this purpose.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
"ii-
Steering, Brakes and Suspension Systems
4.4.12. Rubber Springs
As rubber can store more energy per unit mass than any other type of spring material, considerable weight can be saved with rubber suspension. Rubber springs, if works on compres-sion or shear, can be used as the main suspension spring, otherwise can be fitted along with metal springs to improve the suspension characteristics. Large rubber 'bump' stops used in many suspension layouts stiffens the suspension spring against maximum deflection: Rubber springs absorb oscillations by the internal friction generation if they are stretched by an external force. The advantages of rubber springs are as follows. I. Springs can be made into any desired shape.
ww
2. Springs do not require to be lubricated.
w.E asy En gin ee
The spring is installed between the frame and the top link of the suspension system. When the spring is connected to a point near the link pivot, deflection of the spring reduces to a minimum, without affecting the total wheel movement. This arrangement of spring provides a rising-rate characteristic, which is 'soft' for small wheel movements but becomes harder as the spring deflects.
The energy released from the rubber spring after deflection is considerably less than that imparted to it. This internal loss of energy is called hysteresis, which is an advantage, because lower-duty dampers may be used. Some rubber suspension systems have a tendency to 'settle down' or 'creep' during the initial stages of service, therefore allowance for this must be provided.
rin g.
net
Different form of rubber springs based on the load carrying capacity and design are shown in Figure 4.49.
(a) Compression spring
(b) Compression shear spring
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lma
Automobile Engineering
(c) Steel reinforced spring
ww w.E
asy E
(d) Progressive spring
ngi
(e) Face shear spring
nee
rin
(/) Torsional shear spring
Figure 4:49 Different forms of rubber springs
g.n e
t
Rubber springs are not suitable ~orsupporting heavy loads. So, rubber springs are mainly used as auxiliary springs or bushings, spacers, cushions, stoppers and other supports for the suspension components. Advantages of rubber springs: 1. Greater energy per unit weight than the steel can be stored. So, the springing system can be made more compact. 2. The rubber has good vibration damping properties. 3. The absence of squeaking is always present in steel springs. Rubber springs do not. 4. The number of required bearings is low. 5. Rubber suspension system is having longer life. 6. Rubber is more reliable as it will not fail suddenly like metal springs.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
~t~I~¥i!t!!-!!!!__]
Steering, Brakes and suspe~n'!:.s~;~on~s~y::s~te~m~s
4.4.13. Air Suspension System
. Air springs are used in air suspension systems. The installation and configuration of air suspension systems varies for different makes and models but the underlying principle remains the same. The metal spring (coil or leaf) is removed, and an air bag, also referred to as an air spring, is inserted or fabricated to fit in the place of the factory spring. When air pressure is supplied to the air bag, the suspension can be adjusted either up or down (lifted or lowered). Air spring is nothing but a flexible bellows, usually made from textile-reinforced rubber, containing compressed air which is used to carry load on vehicles. The air pressure inflates the bellows, and raises the chassis from the axle. Air springs have elasticity or "springiness"
ww
when it is compressed. It is used on many heavy-duty trucks, trailers and buses on the road today.
w.E asy En gin ee
Characteristics of air springs:
1. They are soft if the vehicle is not loaded but the stiffness increases when the load is increased by increasing the air pressure inside the chamber. So, it gives the optimum riding comfort when the vehicle is lightly loaded and fully loaded conditions. 2. The height of the vehicle is kept constant by varying the air pressure whenever the load variation occurs.
rin g.
3. Air springs increase vehicle stability by absorbing road shock.
4. Air spring systems are designed to maximize safe load carrying capacity, stability and overall ride quality. Three basic types of air springs are available as follows. );>
the double-convoluted,
);>
the tapered-sleeve, and
);>
the rolling-sleeve.
net
The double-convoluted design looks like a small tyres kept one over the other. These type of air springs generally has more load capacity, a shorter stroke, and a more progressive spring rate which is best suited for use on most front suspensions where the spring sits considerably inboard of the suspension's load point. This has the effect of multiplying loadcapacity requirements while dividing travel requirements.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIID
Automobile Engineering
Tapered- and rolling-sleeve air springs are smaller in diameter with a longer stroke and a more linear spring rate. They are best suited for most rear end applications because there has more travel requirements and fewer load-capacity requirements. Devices for controlling the air pressure and compressors for compressing air are required in the air spring suspensions. These systems generally employ a small, electric or enginedriven air compressors which sometimes fill an on-board air receiver tank which stores compressed air for use in the future without delay. But the suspension system is more complex. The electronically modulated air suspension is incorporated along with air spring in modern vehicles. Types of air suspension:
ww
The following are different types of air suspension systems based on the design of air springs used.
w.E asy En gin ee
a) Bellow type air suspension b) Piston type air suspension
c) Elongated bellows air suspension. (i) Bellow type air suspension (Spring):
This type of spring consists of rubber bellows. The bellows are made into circular sections having two convolutions for proper functioning as shown in Figure 4.50. So, a bellow type air suspension replaces the coil spring.
rin g.
Frame member
net
Flexible bellows
o Figure 4.50 Bellow type air spring
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering, Brakes and Suspension Systems (ii) Piston type air suspension (Spring):
This spring has a metal air container in the form of an inverted drum. The drum is connected to the frame. A sliding piston is connected to the lower wishbone. A flexible diaphragm provides a seal. The diaphragm is tightly connected at its outer circumference to the lip of the drum and at the centre to the piston as shown in Figure 4.51.
ww
w.E asy En gin ee Figure 4.51 Piston type air spring
(iii)Elotlgated bellows air spring:
rin g.
Frame Member
net
Elongated Bellows
Air--~
Figure 4.52 Elongated bellows air spring
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lID
Automobile Engineering
When this system of suspension is employed to the rear axle of the vehicle, then elongated bellows are used. These bellows are of approximately rectangular in shape but they are with semi-circular ends having generally two convolutions. These elbows are arranged between rear axle and frame of the vehicle. To resist the torques and thrusts, the radius rods are used at the rear axle.
Advantages of air suspension: I. A variable space for wheel deflection is used for optimum utilization. 2. The change in headlamp alignment due to varying loads is completely eliminated. 3. The spring rate varies with loading and unloading thereby reducing dynamic
ww w.E loading.
4.4.14. Hydro Elastic Suspension
asy E
This suspension is intended to improve the vehicle's resistance to pitch and the tendency
of the body to oscillate to and fro directions when the front springs are compressed and the rear springs are simultaneously expanded. The continuous forward and backward pitching
ngi
motion provides a most uncomfortable ride which may become serious when the frequency of vibration of front and rear springs is the same.
nee
The hydro elastic suspension layout on a vehicle uses interconnected rubber displacer
rin
units installed between frame and independent suspension linkage to control the wheel. The interconnection is carried out using two pipes as shown in Figure 4.53. One pipe links the left
g.n e
hand side units together and the other pipe is on the right-hand side. The system is pressurized
t
with an anti-freeze liquid after removing air. Each displacer unit contains a rubber spring, a metal separating member which holds two rubber damper valves, rubber diaphragm attached to the suspension linkage which holds the wheel and a metal body which is secured to the frame of the vehicle. Figure 4.53 illustrates the arrangement of hydro elastic displacer unit.
•
•
Figure 4.53 Action of hydro elastic units
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension Systems
_
Road irregularities normally cause the vehicle to pitch, roll and bounce. A sudden upward movement of the front wheel causes the diaphragm to displace the liquid through the damper. This action in turn forces the liquid along the pipe to the rear unit where it moves the diaphragm and it raises the rear of the car to the level of the front. When the front wheel descends, the liquid will return and the vehicle will come to its normal riding position. During this sequence, the liquid has to pass the damper valve in each unit and the restriction to liquid flow at valves and pipelines damp out the tendency of pitch oscillation.
ww
w.E asy En gin ee ,.1,---
Rubber Element Pot Member Damper Valve
Passages (Holes)
Rubber Flap Valve Spring 'V" ....... .,.._,,4-- Bleed Holes Separating Member
'-.JIj~-¥:I---
Diaphragm
Skirt '-------Stem
rin g.
Figure 4.54 Hydro elastic displacer unit
net
When a vehicle is cornering, the body of the vehicle tilts or rolls outwards due to centrifugal force. This tilting action is apparent when 'soft' conventional springs are used. The hydro elastic system is 'soft' during movement of a single wheel but if the two outside suspension units are loaded during cornering, a stiffening of the hydro elastic system occurs. Under this type of loading, the displacement of the fluid from one unit to the other unit does not occur. Instead of deflecting the rubber springs due to the increased liquid pressure, the springs provide a marked resistance to the tilt of the body. During bouncing of the vehicle, four wheels deflect at the same time. To resist this motion, all hydro elastic displacer units perform in similar way to react to roll.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
4.4.15. Shock Absorber
Shock absorbers will not efficiently absorb road shocks if the suspension springs are highly rigid. They will be continuously vibrated for a longer time if springs are sufficiently flexible. To overcome this difficulty, a system having compromise between flexibility and stiffness should be used. Shock absorbers are used as a part of the suspension system. They provide more resistance to the motion of the spring and road wheel in order to damp out vibrations. Purpose of shock absorber: (i) To control the vibrations on springs.
ww
(ii) To provide comfortable ride.
w.E asy En gin ee
(iii) To act flexible and to be rigid enough.
(iv) To resist the unnecessary motion of the spring.
Types of shock absorbers:
I. Mechanical shock absorber (friction type) 2. Hydraulic shock absorber.
Again the hydraulic shock absorbers are further divided into various types. 1. Van type
2. Piston type
a. Single acting b. Double acting
rin g.
3. Telescopic type.
net
Difference between the function of spring mid shock absorber: S.No.
Springs
Shock absorbers
I.
It is connected between wheels and It is connected between axle and lower vehicle frame. end of the chassis frame.
2.
It acts as a cushion load shock to The shock absorber provides resistance to keep the vehicle body leveled up the motion of springs and road wheels for over uneven surfaces and absorb damping out vibrations. It is done for driving and braking torque loads or several complete oscillations thereby stresses and also to resist the body resulting in discomfort to passengers. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
Systems
tilting and rolling on comers and bends. 3.
In a motor vehicle suspension system, springs are not used. It is an only compromise between flexibility and stiffness. If it is too flexible, it will flex and rebound
A smooth ride without any excessive and repetitive rebounds and road shocks are obtained using a relatively flexible or soft spring and a shock absorber.
repeatedly and excessively providing a rough ride. (i)
ww w.E
Telescopic Shock Absorber:
Construction:
asy
The upper eye of the telescopic shock absorber is attached to the axle and the lower eye is attached to the chassis frame as shown in Figure 4.55. A two way valve VI is connected to a
En
rod. Another one two-way valve V2 is connected to the lower end of the cylinder. The fluid occupies in the space between above and below the valve VI and also the annular space between cylinder and tube. A gland is provided on the head. Fluid scrapped (Jutby the rod is
gin
eer
brought down into the annular space through the inclined passage. Working:
ing .ne t
When the vehicle comes across a bump, the lower eye will move up. So, the fluid follows from lower side of the valve VI to the upper side. Due to less volume of the space above valve VI than the volume of the rod, the pressure is exerted on valve V2• Thus, the damping force is produced by this pressure of the fluid. The fluid will flow from the upper side of the valve VI tv lower side when the lower eye moves down and from lower side of the valve V2 to its upper side. When a car absorbs shocks from the road surface, the suspension springs will compress and expand because the spring has the characteristic of continuing to oscillate for a long time of oscillation to stop. So, a riding comfort will be poor even the damp oscillation is supplied. Shock absorbers provide better road-holding characteristics and improved steering stability to tyres. The stronger is the damping force, the more will be the oscillations of the body. But, the shock from the damping effect becomes greater than the strength of the stronger damping force. The damping force varies with the speed of the piston. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering 1Various types of shock absorbers are used dependent on the change in damping force.
ww w.E
Cylinder
asy
En
gin
eer
Figure 4.55 Telescopic shock absorber Advantages of telescopic shock absorber:
ing .ne t
I. Large amount of energy is dissipated due to large volume of fluid displaced without causing a high temperature rise.
2. There is no wear development in the damper with the absence of connecting arm pivots. 3. The applied force is increased when compared to indirect acting type. Low fluid pressure due to fairly large piston area is occurred with reduced levers. 4. The leakage is very less due to lower pressure and absence of the rotating shaft entering the reservoir. 5. Cost is less than springs. 6. No need of topping up is necessary in most of the telescopic dampers.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
Systems
4.4.16. Types of Suspension System
Generally, the following two basic types of suspension system are given below. (i) Front end suspension (a) Independent front suspension (b) Rigid axle front suspension (ii) Rear end suspension (a) Longitudinal leaf spring rear suspension (b) Transverse leaf spring rear suspension
ww w.E
(c) Coil spring rear end suspension.·
4.4.17. Independent Front Suspension
The independent front suspension was developed in the 1930's to improve vehicle ride control and riding comfort. In this type of suspension, each front wheel is mounted on its own axle and independently supported by a coil or torsion bar or leaf spring. This allows the wheels to respond individually to road conditions. Now-a-days, all vehicles use this suspension system. Coil springs are commonly used in this suspension system. This suspension system completely prevents the wheel wobble. A greater wheel movement is utilized without affecting the steering system. The steering conditions and qualities are
asy
En
gin
improved by a wider spacing of the front springs. Types of independent front suspensions: 1. Longitudinal suspension 2. Transverse suspension
eer
ing .ne t
3. Sliding suspension 4. Mac Pherson Strut and link type suspension 5. Parallelogram type suspension or Wishbone type 6. Trailing link type suspension 7. Vertical guide suspension. 1. Longitudinal independent front suspension: Helical spring is connected between two wishbones (arms in U shape) with the support of frame member as shown in Figure 4.56. The arms are in the shape of U. The upper wishbone is hinged at the inner end on a hydraulic damper. The outer end is hinged at stub axle carrier.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
The lower wishbone has enough length for providing more constant track when wheels lift. So. the braking torque resists the arms of the lower wishbone. Shock Upper wishbone Stub axle carrier
ww
w.E asy En gin ee
axle
wishbone
Rubber stop
Figure 4.56 Longitudinal independent front suspension
2. Transverse independent front suspension:
In this type, two trailing arms are connected one above the other transversely at the front
rin g.
portion of the vehicle. The stub axle assembly is connected with ends of arms. Radius rods are of 45° to the centre line of the vehicle used to support it. Figure 4.57 illustrates transverse independent front suspension system arrangement. Leaf
net
Support
Elevation
Figure 4.57 Transverse independent front suspension
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering,
Brakes and Suspension Systems
3. Sliding type independent front suspension: The stub axle moves up and down and it rotates in frame members. There is no change in track, wheel attitude and wheel base throughout the rise and fall o~ the wheel. The line diagram of the sliding type independent front suspension is shown in Figure 4.58.
ww w.E
Figure 4.58 Sliding type independent front suspension
asy
4. Mac Pherson strut and link type independent front suspension:
En
It is used in an integral body construction due to wider spaced loading points. Instead of
the normal top link, a flexible mounting and a telescopic damper are used. Both rolling action and shocks absorption are readily obtained as shown in Figure 4.59.
gin
eer
Figure 4.59 Strut and link suspension system
ing .ne t
5. Parallelogram independent front suspension or wishbone type: The stub axle carrier connects an upper and lower link. The lower link is larger than the upper but it may not be parallel. It keeps the same the track width when the wheels rise and fall produced by the wheel scrubbing sideways. The various schematic arrangements of parallelogram independent front suspension using coil, torsion and leaf springs are shown in Figure 4.60. The use of coil springs in the front axle suspension of cars is universal. It consists of upper and lower wishbone arms pivoted to the frame member. The spring is placed between lower wishbone and underside of the cross-member. The vehicle weight is transmitted from body and cross-member to the coil spring through which it goes to the lower wishbone Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
11111
Automobile Engineering
member. A shock absorber is placed inside the coil spring and it is attached to the crossmember and lower wishbone member. Stub axle corner
(b)
ww w.E
(a)
asy (c)
En
(d)
Figure 4.60 Parallelogram independent front suspension
gin
The wishbone anTIS are similar to a chicken wishbone or letter V in shape as shown in
eer
Figure 4.61. Due to V-shape, the wishbone not only positions wheels and it transmits the vehicle load to the springs but also they resist acceleration, braking and cornering (side) forces.
Upper Wishbone
ing .ne t
Lower Wishbone
Figure 4.61 Wishbone type independent suspension with coil springs
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Ina
Steering, Brakes and Suspension Systems
t
The upper arms are shorter in length than nes. It helps to keep the wheel track constant thereby avoiding the tyre scrub thus minimiz-ingtyre wear. However, a small change in the camber angle occurs with such an arrangement as shown in Figure 4.62. The wishbone type is the most popular independent suspension system.
'" r it,1 ~
/--
Change in
I \! Camber Angle
,
I II ,I 1,1
\<..
1 ,I II
i >.
I !i !iii" i ' I I :-_.tr---~ T;' Iljii!i:W~~\ ",1 I
ww
j,
1
I' , I!
I: II
w.E
!i
h-~'
'I j'i: If I.· :.
1\'-1 i!
il·
I __ ~ ,cd.
1--~LL_% // -
~
)-
i ' . b-----_,.__ _:~~ I
-<;
i\,'1I) ~.Ii
asy
Figure 4.62 Changes ill camber angle ill wishbone suspension
En
Advantages: I. Better cornering characteristics are obtained.
gin eer
2. The track length remains constant although a slight change in camber takes place. It enhances tyre life.
ing .ne t
Disadvantages: I. The wheels on corners leaning outwards with the body results the undesired steering effects. 2. Variation in tracks length results the adverse tyre wear. 6. Trailing link independent front suspension:
Trailing arm
Figure 4.63 Trailing arm independent suspension The suspension system maintains constant track and wheel attitude with a slight change in wheel base and caster angle. A coil spring is connected with the trailing arm which is
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lID
Automobile
Engineering
already attached to the shaft. But this shaft is carried by the wheel hub. When the wheel moves up and down, it will wind and unwind the spring. The coil spring may be replaced by a torsion bar. Figure 4.63 shows line diagram of this type of suspension system. 7. Vertical guide suspension: In this type, the kingpin is directly connected to the cross member of the frame. It moves up and down thereby compressing and expanding the coil springs as shown in Figure 4.64. Upper spring rod
ww w.E
asy \ En
Cross member
gin
Figure 4.64 Vertical guide suspension 8. Swinging half axle suspension:
eer
ing .ne t
In this type of suspension system, wheels are mounted rigidly on half axles which are pivoted at their ends to the chassis member at the middle of the car as shown in Figure 4.65. The main disadvantage of this system is lip and down movements of the wheel causing the camber angle to vary.
o 0 r---------------~,
-----------~
Figure 4.65 Swinging half axle suspension
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
e·;4
Systems
Advantages of independent front suspension system:
1. Unsprung weight is reduced with improved ride and better road holding while turning and braking. 2. Instead of tilting the frame and body, it is kept horizontal and wheels are vertical when encountered a road bump. 3. The wheels are sprung independently but springing movement of one wheel is not transmitted to the other side. 4. A greater degree of vertical springing movement is provided. 5. In both wheels wobble and steering tramp are reduced.
ww w.E
6. Greater resilience is provided with better springing action than most rigid axle vehicles. 7. The independent front suspension gives more space for engine accommodation. 8. Front springs are arranged for sufficient distance apart to satisfy understeer conditions and they are also preferable to over steer.
asy
En
9. Softer suspension provides the low spring rate which enables large wheel movement,
gin
10. The caster angle is affected on beam axles by spring deflection while braking or
eer
accelerating thereby producing the axle to twist between stub axle and spring seats.
ing .ne t
I 1. The tendency of rotating wheels is reduced by the independent front suspension when it turns about the kingpin due to gyroscopic action. Thus, the wheel wobbling or shimmy is reduced. Disadvantages: 1.
The wheel cambering with body roll reduces the concerning power.
2.
There is a slight chrnge in wheel track, causing tyre scrub during bouncing of one wheel.
3.
A more rigid chassis or sub-frame structure is required.
4.
A more complicated suspension and steering linkage and pivot joints are necessary so that the suspension becomes more expensive and it tends to wear more.
5.
Effects of unbalanced-wheel-assembly are transmitted to the steering-wheel more easily.
6.
Steering-geometry alignment is more critical and it requires more frequent attention.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
ilJD
Automobile
Engineering
4.4.18. ;1igid Axle Front Suspension Rigid axle front suspension is also called as dependent front suspension. This type of suspension uses a solid axle. This type of suspension has been universally drawing the independent
front wheel suspension.
This design consists
used before
of one steel or
aluminium beam extending the width of the vehicle. This beam is held in place by leaf springs. This design also uses kingpins and bushings to attach the wheels outboard of the axle. Because of its load carrying ability, the solid axle is only used on heavy trucks, and off-road vehicles. It is not suitable for use on modern passenger cars for three important reasons.
>-
Transfer of Road Shock: There is transfer of road shock from one wheel to the other due to the way the wheels are connected to the axle. This causes a rough ride and
ww w.E
could result in loss of traction.
,.
Unsprung Weight."Because the solid axle has a lot of unsprung weight, it needs more
spring and shock control to keep the tyres in contact with the road .
asy
.,. Wheel Alignment: The solid axle design makes no provisions for alignment. Figure 4.66 illustrates a typical rigid axle front wheel suspension.
En
It has either two
longitudinal leaf springs or a transverse spring along with shock absorbers.
gin Frame
Springs
eer
ing .ne t
Axle
Figure 4.66 Rigid axlefront wheel suspension employing longitudinalleafspring In this type of suspension, the front wheel hub rotates on anti-friction
bearings and
steering spindles already connected with steering knuckles. The steering spindle and steering knuckle assemblies are pinned at axle ends to permit the wheels turning. This pin is called
kingpin or steering knuckle pin.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lila
Steering, Brakes and Suspension Systems
Where the forked portion is integral with the steering knuckle and fitted over the end of the axle as shown in Figure 4.66, the construction is called a "Reverse Elliot." In an "Elliot" type, the ends of the axle are forked to hold the steering knuckle extension between ends. Front axles are called as "dead" axles which do not rotate. But, in contrast, rear axles are called as "live" axles which transmit power to rear wheels. 4.4.19. Independent
Rear Suspension
Any suspension that can be used on the front end of the'car can be used on the rear end. The versions of the independent' front systems described in the previous section can be found on the rear axles. But, in the rear end of the car, the steering Iinkage is absent. Therefore, rear
ww
independent
suspensions
can be simplified
w.E
versions of front ones, although
the basic
principles remain the same.
As explained in the independent front axle suspension, here also the wheels are mounted
asy
in separate axles and sprung independently.
Figure 4.67 illustrates a method of rear wheel
independent suspension. Universal couplings are used to keep the wheels vertical. Sliding
En
coupling is necessary to keep the wheel track constant to avoid scrubbings oftyres.
gin eer
Differential "
Wheel
unit
ing .ne t
Figure 4.67 Rear wheel independent suspension Types of independent rear suspension: 1. Longitudinal leaf spring rear end suspension 2. Transverse leaf spring rear end suspension 3. Coil spring rear end suspension, Both longitudinal leaf spring and coil spring suspensions are mainly used in vehicles but transverse leaf spring suspensions are rarely used. In addition to above types, there are some more types of such as
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lid
AutomobileEngineerini] 1. Parallel link system 2.
Swinging arm type
3:
Swinging half axles.
In parallel link system. wheels are attached with a backbone-type wishbone shaped.links.
frame using two
In swinging arm type, a spring or a torsion bar is used at the pivot. These axles are used in most of vehicles. It has two axle tubes joined to the final drive housing which allows the wheel to rise or fall. A universal joint is fixed to allow the change in drive axle at the centre of each axle joint.
ww w.E
1. Longitudinal leaf spring rear end suspensions: Laminated leaf spring, as shown in Figure 4.68 (a), is used as a suspension member in this type of system. The front end of the longest leaf is bending into a circle to form the spring
asy
eye. The spring eye is attached to the spring hanger by a bolt. The spring hanger is fixed to the vehicle frame rubber bushings inserted in the spring hanger support the bolt as shown in Figure 4.68 (b).
En
r gineer
ing .ne t
(a)
Hanger Auxiliary Spring
Axle
(b) Figure 4.68 Longitudinal lea! spring rear end suspension Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
,':1.
Systems
The rear end of the spring is also bending to form a spring eye. This spring eye is attached to the car frame through a shackle. The shackle allows the change in the length of the leaf spring as it bends. The centre portion of the spring is attached to the rear axle housing by a pair of 'U' bolts. At the intermediate positions of the spring length, the rebound clips are located. When the leaf spring is pushed either upward or downward by bumps, the distance between two spring eyes changes. The tile shackle permits this change in length. The shackle also includes rubber bushings. They absorb vibrations and prevent it from reaching the car frame and body. 2. Transverse lea/ spring rear end suspension: This system is quite simple in which a single transverse spring is used. Such springs are mounted in inverted positions parallel and above the rear axle. Each end is shackled to the rear axle as shown in Figure 4.69 (a).
ww
w.E
asy
En
gin eer
Differential Case
Rear Axle
ing .ne t
Tubular Cross Member Hinged Link
Transverse Spring Assembly (b)
Figure 4.69 Trans verse lea/spring rear end suspension The transverse rear springs are always used in combination with torque tube drive. Therefore, they do not carry the driving thrust and torque. Figure 4.69 (b) shows the another arrangement of this type of spring in which each rear wheel is independently suspended by one end of the transverse spring while the tubular cross member is attached to the high centre Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lID
Automobile Engineering
portion. In this type, each rear wheel is driven by axle shaft by two universal joints at its ends and differential unit. The differential unit is attached to the frame.
3. Coil spring rear end suspensions: The coil springs, as shown in Figure 4.70, are seated in the pan shaped brackets attached to the rear axle and they are compressed against similar spring seats incorporated into the frame (or) body. There are two control arms (or) links attached between rear axle housing and car frame. They permit upward (or) downward movement of the axle housing regarding the car frame. This type of suspension is always used along with a torque tube drive. Therefore, the coil
ww
springs are not subjected to driving thrust. The excessive roll of side way while rounding a curve is prevented by a shock absorber mounted in rubber bushings. Energy stored in given
w.E
weight of spring coil and torsion bar springs are superior to leaf springs.
asy
En
gin eer
ing .ne t
Figure 4.70 Coil spring rear end suspension Disadvantages of the independent rear suspension: 1. The initial cost is high. 2.
Greater maintenance is required.
3.
Misalignment of steering geometry is obtained.
4.
Wear of the components wear out easily and quickly.
4.4.20. Interconnected Suspension System The interconnected
suspension
system also called Front and Rear Inter-Connected
(FRIC) suspension is a system which links the front and rear suspension of the car using hydraulics and aims to give better stability and drivability for the driver called stable and
consistent aerodynamic platform. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
II:"
Steering, Brakes and Suspension Systems
Ordinarily,
shock absorbers control the wheel movement
by passing hydraulic fluid
through valves between upper and lower reservoirs. The speed at which the fluid flows through these valves limits the speed at which the suspension bounces t':' and down. Using a separate one-way valve, it makes the limit different for "bound" and "renound." FRIC system is understood to link the front and rear suspension hydraulically and it can be adjusted in a similar way as brake balance. The 'FRTC device also connects the left and right suspensions acting similar to an antiroll bar in order to keep a constant ride height and aerodynamic balance. In FRlC, the fluid is displaced not from one chamber to another but via pipes through a
ww
valve block and into the opposite hydraulic unit. However, the upper and lower chambers are interconnected left to right make the system to react differently to inputs from the suspension.
w.E
They are a resistance to roll or heave.
Cross-linked interconnected suspension system: "Cross-linked"
asy
shock absorbers have the lower reservoir of one damper linked to the
En
upper reservoir of another damper. When the car rolls in a corner, the outer hydraulic elements will compress and the inner elements will rise. With the same effect, when the centre
gin eer
element is in pitch, the hydraulic fluid is transferred from one side to the other side to increase the spring effect in preventing the car rolling. The upper chamber on one side and the lower chamber on the other side create high pressure. As these chambers are cross connected to the
ing .ne t
high pressure chamber on their opposite side, it creates the resistance between two systems to displace their fluid. It has the effect of increasing roll stiffness in cars. It prevents body roll and stabilizing the car during turns.
Figure 4.71 Cross-linked interconnected suspension system
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imll
Automobile Engineering
Parallel-linked interconnected suspension system: "Parallel-linked" shock absorbers have upper and lower reservoirs connected to their counterparts. When the car brakes (in heave), the weight shifts forwards and the front suspension compresses and the rear rises. The pressure builds up on one side of the centre element on the front suspension and this pressure in the hydraulic fluid is transferred to the rear centre element. It increases the spring effect at the front and reduces it at the rear and hence the car will not dive nose down under braking. When the car is in heave, both upper chambers create high pressure. It creates the resistance between two systems to displace their tluid. It has the effect of increasing the car's heave stiffness. The car's ride height will remain more consistent for better control of the front wing and diffuser aero. It prevents dive
ww
and squat under braking and acceleration because both sides resist compression instead of accepting it.
w.E
asy c::::>
¢=:J
En
gin eer -- n ing. net I
.... r-
n
Front
Heave
~
Rear
Figure 4.72 Parallel-linked interconnected suspension system 4.4.21. Anti-Roll Bar (Stabilizer)
Stabilizer or a sway bar is used in all independent suspension to decrease the tendency of the vehicle to roll or tip on either side when making a tum known as anti-roll bar. It is in the form of torsion bar made of alloy steel. The torsion bar is attached to springs by two short rods. Anti-roll bar is passed through rubber bti'shesin the frame. By connecting a stabilizer bar between front suspension members, the roll stiffness is improved. It is supported by two bearings (bushes) which are already connected to the frame. . has a series of tubular rods which connect opposite wheels and suspension units on a car to each other. These rods are connected by torsion springs. It reduces the body roll or Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension Systems lateral motion during a vehicle's turning. The bar is a part of vehicle's
oiIiIo .......
I";~,,,
it is designed to increase the vehicle's lateral roll stiffness. Working: When the car moves on the road, one of the sides will move up and decrease the load on spring produced by the nearer rod to move down. On the other hand, the load is increased by moving the near rod up. So, the bar is twisted. Hence, the vehicle is not to rollout and it gives the stability against lateral forces. Lower wishbone
ww w.E asy
Busnes fitted to frame
En gi
nee
Figure 4.73 Anti roll bar
rin
In normally constructed of tubular steel, the U-shaped stabilizer bar is often connected to
g.n et
the frame of the vehicle at two points as well as to the suspension on both sides of the vehicle as shown in Figure 4.73. When the wheels move in the same direction, the bar does not bend but if the wheels move in different directions, even slightly, it twists thereby causing extra stiffness. This design is intended to reduce body lean during cornering which can affect the tyre's grip on the road and-therefore, the stability of the vehicle's cornering ability increases.
The drawback of anti-roll bar is the connection of the stabiIizer bar w.th both sides of the vehicle. Both wheels are essentially connected to each other, So, bumps from one wheel can be transferred to the other wheel by causing side-to-side motion which can be uncomfortable. This motion also affects the handling of the vehicle. Stiffer bar produces more shaking the motion to the vehicle. In more extrefDe situations, the stabilizer can cause wheels on the outside of a turn to lose its contact with the road thereby causing both handling problem and safety issue. )
Sometimes, higher-end vehicles come with active stabilizer systems which are controlled by a computer and it can change the amount of stiffness of the system. They generally allow for a small amount of roll so that cornering feels more natural but the computer can react to Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'ID
Automobile Engineering
different amount of torsion being placed on the bar and adjust accordingly. It is a fairly high-
end feature and it does not come standard on most vehicles but it greatly enhances the feel and performance of the car since the vehicle will react to steering situations as they arise rather than acting as a static system. It only reacts to forces placed on it.
Conditionsfor operating the anti-roll bar: I.
One wheel is lifted relative to other wheel, half the total anti-roll stiffness acts downwards on the wheel and the reaction on the vehicle body tends to resist pody roll.
2.
If both wheels lift by the same amount, the bar is not twisted and there is no transfer of
ww
load to the vehicle body.
3.
If the displacements of the wheels are mutually opposed, the full effect of the anti-roll
w.E
stiffness is produced.
asy
4.4.22. Trouble Shooting in Springs and Suspension
En
1.Front wheel low speed shimmy
gin ----------------------------------------------------------------------------------------------------------------eer ing .ne t
----------------------------------------------------------------------------------------------------------------Causes
Remedies
1. Uneven tyre pressure.
Inflate to correct pressure.
2. Loose ball joints or king-pin.
Replace.
3. Front springs soft.
Replace.
4. Irregular tyre tread.
Match treads.
5. Loose linkage.
Readjust and replace worn parts.
6. Looseness ill steering gear.
Replace worn parts.
----------------------------------------------------------------------------------------------------------------2. Front wheel tramp
----------------------------------------------------------------------------------------------------------------Causes
Remedies
----------------------------------------------------------------------------------------------------------------1. Wheels unbalanced.
Rebalance.
2. Excessive wheel run out.
Replace.
3. Shock absorber defective.
Replace.
----------------------------------------------------------------------------------------------------------------Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
,,:.-
Steering, Sreke•• nd Su.p.ns/on Systems
3. Rough ride
-_..__
...._-_
-----_._---------------------------------------------------------------------------
_
CaUlllI
__
Remedies
_----_._---_ .._--------------------------------------------------------------------
1. Excessive tyre pressure.
Reduce to the correct pressure.
2. Shock absorber defective.
Replace.
3. Excessive friction in suspension.
Lubricate parts.
--------_ ----_
-_ _----------------------------------------------------------------------------4. Sway
Oil
turns
w ww -----_ ..--_ ..-..------------------------------------------------------------------------------.Ea syE .. ngi nee ----_ .... .....-----------------------------:------------------------------------------------------------------rin ................. _---_.-.--_._._----------------------------------------------------------------------------------g.n et
---------~
..__
------------------------------------------------------------------------------------------
ClIuses __ _
Remedies
_
1. Stabiliser bar loose.
Tighten as required.
2. Sagging or weak springs.
Replace.
3. Incorrect caster.
Re-adjust.
--------------------------------------------------------------------------------------------------
~
5. Breakage of spring
_-_
Causes
Remedies
1. Over loading.
Avoid.
2. Loose centre bolt.
Tighten centre bolts.
3. Loose U-bolt.
Tighten U-bolt.
4. Defective shock absorber.
Replace.
S. Tight spring shackle.
Loosen as necessary.
-------------_._------------------------------------------------------------------------------------------------6. Sagging spring
----------------------------------------------------------------------------------------------------------------Causes
Remedies
----_. ---------------------------------------------------------------------":"------------------------------------1. Leaf broken.
Replace.
2. Weak spring.
Replace.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1-..\ 3.
Automobile Engineering
Short coil spring.
Install shim or replace.
4. Defective shock absorber.
Replace.
7. Noises in the suspension system Causes
Remedies
Commonly attributed to any loose.
Examine the parts carefully.
Worn or unlubricated part such as U-bolts, rebound clips, shackles, shock absorber linkages etc.
Locate the cause and correct as required.
ww
w.E
Causes
8. Rough ride
asy
En
1. Rusted or corroded leaves.
2. Seized pins in the shackles. 3. Defective shock absorber. 4. Worn lubricating pads.
Remedies
gin eer
Lubricate the leaves. Set right at once.
Replace. Replace.
9. Suspension tooflexible
ing .ne t
Causes
Remedi~s
1. Unrequired lubrication of spring.
Clean springs thoroughly.
2. Weak springs.
Replace.
3. Broken leaves.
Replace.
4. Defective damper.
Replace.
--------------------------~--------------.-----------------------------------------------------------------------
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
11:,-
Systems
10. Sagging spring ... ------------------------------------------------------------..--------------------------------------------------Causes Remedies ----------------------------------------------------------------------------------------------------------------l. Weak springs. Replace. 2. Broken leaves.
Change new one.
----------------------------------------------------------------------------------------------------------------11. Noise
-----------------------------------------------------------------------------------------------------------------
ww w.E asy Causes
Remedies
----------------------------------------------------------------------------------------------------------------I. Lack of lubrication.
Lubricate correctly.
2. Loose U-bolts.
Tighten it properly.
3., Loose shackle pins.
Tighten it.
4. Defective shock absorbers.
En gi
Replace.
---------------------_ ..._-----------------------------------------------------------------------------------------
nee
12. Vehicle sags to one side
----------------------------------------------------------------------------------------------------------------Causes
Remedies
rin
g.n et
----------------------------------------------------------------------------------------------------------------1. Weak road springs.
Replace.
2. Broken spring leaves.
Replace.
3. Incorrect adjustment of coil
. Adjust properly.
springs or torsion bars.
4. Defective suspension units.
Repair or replace.
S. Defective shock absorbers.
Replace.
----------------------------------------------------------------------------------------------------------------13. Harsh suspension or excessive road shocks transmitted to vehicle
----------------------------------------------------------------------------------------------------------------Causes
Remedies
----------------------------------------------------------------------------------------------------------------1. Spring leaves corroded causing excessive friction.
(i) Clean and lubricate. (ii) Replace. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IEM'.
Automobll. Eniin~!~"n;__ 2. Wear depressions in spring leaves.
Replace springs. o'
3. Wrong fitting of extra-load leaves.
Fit properly.
4. Seized shackle pins.
(i) Free up, clean and lubricate.
J
(ii) Replace damaged parts.
5. Defective shock absorbers.
Replace.
6. Suspension arm pivots seized.
(i) Free up, clean and lubricate. (ii) Replace detective pins and bushes.
7. Torsion bars incorrectly adjusted.
ww
Adjust properly. Replace.
8. Coil springs stiff.
_____________________________________________________________________
w.E
•••
•••••
"'"."W·.
4.5. BRAKING SYSTEM
asy
The mechanism which is used to slow and stop the vehicle is known as braking system. It
En
is an important component of a vehicle. In other words. the total system starting from brake pedal or lever to the brake shoe is known as braking system.
Principle of braking system:
gin eer
In this system, the kinetic energy is converted into heat energy due to friction between two mating surfaces of brake lining and brake drum. Then. the heat is dissipated into the atmosphere.
Need for brakes:
ing .ne t
I.
To stop or slow down the vehicle at the will of an operator.
2.
To control the vehicle descending a hill.
3.
To keep the vehicle in a desired position even at rest.
4.
To park the vehicle and hold it in stationary position without the presence of driver.
4.5.1. Requirements of Braking System I. It should have good anti-fade characteristics. 2. It should be consistent with safety. 3. It should not be skidding while applying brake. 4. It should have a better cooling system. S. It should be strong enough to stop the vehicle within the minimum distance. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
e".
Systems
6. It should have less weight. 7. It should be reliable. 8. It should be easy to adjust having a proper maintenance. 9. It should produce less noise and vibration while applying brake. 10. It should work efticiently irrespective of road condition and quality. 11. The retardation must be uniform throughout its application. 12. The pedal effort must be within the convenient capacity of the driver. 13. It should have long life.
ww w.E asy
4.5.2. Stopping Distance, Time and Braking Efficiency
Stopping distance:
The distance required to stop the vehicle after applying brake is proportional to the square of speed at which brakes are applied. The stopping distance depends upon the following factors.
En gi
1. Grip between the tyre and road surface,
2. Tyre tread condition, 3. Tyre inflation, and 4. Nature of road surface.
The stopping distance is calculated by V2 d=2a where
d = Stopping distance in meters
nee
rin
g.n et
V= Velocity of the vehicle in mls a = Deceleration in mls', Stopping time: It is the time required to stop the vehicle completely after applying brake. The stopping time is computed by V a
t=-
where
t
= Stopping time in seconds Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lu.
Automobile
Engineering
V= Velocity of the vehicle in mls a =Deceleration in mls', Braking efficiency: To measure the efficiency of a braking system, specific methods are adapted. Braking efficiency is defined as the rate at which the braking system brings a vehicle to rest from certain road speed. Table 4.2 Braking efficiency S.No.
Condition of Brake
Braking efficiency (%)
1
Ideal
100
2
Perfect
90
3
Very Good
70
4
Fair
60
5
Bad
ww w.E asy 1
i1
En gi
30
If the braking efficiency is less than 60%, it is indirectly indicating-the danger condition • of the brake. So, the driver needs to do necessary corrective action.
nee
The braking efficiency is calculated by the equation llHr
where
a = zs: x 100 g
= Braking retardation g = acceleration due to gravity.
all,.
rin
g.n et
4.5.3. Theory of Braking Or Principle of Braking While operating the braking system, the kinetic energy of moving vehicle. is converted into heat energy. . The brake is a friction creating device which ,causes the speed reduction of the vehicle at a faster rate than the speed reduction obtained by changing gears and closing dOWBthe accelerator. Then the work done on the brake should be equal to the kinetic energy of moving vehicle to stop the vehicle. This rate cannot be high enough to stop the vehicle instantaneously.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
Systems
So, the kinetic energy is given by
wv2
K.E=--
2g
C.G
-4----,
R - Vertical
Reaction
V - Vehicle Speed W - weight
FR - Frictional Resistance C.G - Centre of Gravity
ww w.E asy
R
R
Figure 4.74 Theory of braking
When the vehicle is stopped, the kinetic energy becomes zero. So, the work done on the
En gi
brake is the product of average frictional resistance (Fu) at the road wheel junction and the distance (d) moved by the vehicle before halting. Work done on brake = K.E F, d= II
where
WV2 2g
nee
rin
d is stopping distance or braking distance.
g.n et
Similarly, the work done on the brake can be calculated at any instant when the vehicle is slowed down from velocity VI to V2 in a distance 'x'. Then brake work done is equal to the loss in kinetic energy of the vehicle which is given by
4.5.4. Friction Resistance and Coefficient of Friction
The frictional resistance (Ft?) expressed between wheel and road surface is proportional to the vertical reaction (R) and it is related by, FR = pR where
p is the coefficient of friction between wheel tyre and road surface. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
_
Automobile
Engineering
The maximum value of coefficient of friction can be unity for ideal case. In real case, it if less than 1. This value depends upon the following factors. 1. road surface condition (dry, wet, slippery, muddy etc.)
2. tyre tread pattern 3. inflation pressure, and 4. material of road surface. 4.5.5. Types of Brakes The automobile brakes are classified on the basis of following.
ww
1. According to the applications: 0) Service or running or foot brake
w.E
(ii) Parking or emergency or hand brake.
asy
2. According to the number of wheels: (i) Two wheel brakes
En
(ii) Four wheel brakes.
3, According to the brake gear: (i) Mechanical brake (a) Hand brake (b) Foot brake.
gin eer
(ii) Power brake: (a) With booster
ing .ne t
(b) Without booster. 4. According to construction: (i) Drum brake
(ii) Disc brake. 5. According to location (i) Transmission brakes (ii) Wheel brakes.
6. According to method of braking contact:
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
(i) Internal expanding brakes
(ii) External expanding brakes. 7. According to the power unit: (i) Cylinder brake
(il) Diaphragm brake. 8. According to power transmission: {i} Direet acting brake (ll) Geared brake,
ww
9. According to method of applying brakefarce: (i) Single acting brake
w.E asy E (ii) Double acting brake.
J (). According to power employed: (i) Yael-HIm brakes
a, Atmospheric suspended
ngi nee
h. Vacuumsuspended
(ii) Air Of pneumatic brakes
(iii) Hydraulic brakes (iv) Hydrostatic brakes
rin
(v) Electric brakes.
g.n
et
It. brake drum is connected to the wheel and also a back plate is mounted on the axle ~asillg, Two brake shoes are connected on the back plate. Friction linings, called brake linings, ar~ provideq 011 br&ke shoes as shown in Figure 4.75. One or two retractor springs are ~pnn!3~~~ to keep brake shoes away from the drum without applying brakes. The brake shoes af@ tightly fixed af one end but the force
F is applied at the other end by a brake actuating
m~ChllJ1ism.It forces the brake shoes towards the revolving drum. Therefore, the brake is
Ilppli~d. An aclj~st~r is linked to compensate the wear of friction lining. The relative braking
torque obtained
at shoes varies with the pedal force according to the type of expander. It is
already connected or floating to lead or trail the shoes.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
,ww
Automobile
w.E
Engineering
Stationary plate
asy
Figure 4.75 Construction of a drum brake
Table 4.3-Main parts of drum brake and itsfunctions
En
Parts of drum brake
gin eer Functions
1. Brake pedal
To operate the brake
2. Links and Levers
To provide mechanical connections.
3. Brake drum
It
moves
with
circumference
road
wheel
of which the
and
ing .ne t with
expanding
the
inner
brake shoes
comes into contact to retard its speed or hold it from moving.
4. Backplate (or) Torque
To support all accessories.
plate 5. Anchor
To support the brake shoes.
6. Cam
It expands the brake shoes.
7. Brake shoes and lining
They are radial
plates
having
linings
of frictional
material fixed at their back. 8. Brake shoe retracting spring
It connects both the brake shoes at their loose ends and helps them in contacting after the brakes are released.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and
9. Adjuster
Systems
To adjust the brake.
4.5.6.1. Types of Drum Brakes There are two types of drum brakes as follows. (i) External contacting brakes .(ii) Internal expanding brakes 1. External contracting brake: The main components of external contracting brakes are brake drum, bandwidth lining, operating lever, push'rod, return spring and adjusting lever.
ww w.E asy
To operating cable or rod
En gi
Push
r:
nee
rin
g.n et
Figure 4.76 Construction of an external contracting brake Working: When the push rod is started to function by the hand through operating, then the lined brake band fixed around the drum will be tightened in order to lock or slow down the rotating drum as shown in Figure 4.76. The return spring brings the band back to the off position when the brake is released. This system is pneumatically operated. The main disadvantages are greater wear and tear. To park the vehicle in position, this type of brake is mainly used.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
2. Internal expanding brake:
These internal expanding brakes have the following parts such as brake drum, stationary plate, two brake shoes, anchor pins and retracting spring. Working: When the cam is turned, the shoes with brake linings will be moved beside the drum as shown in Figure 4.75. The brake linings create friction between rotating drum and expanding shoes. The force of the friction isjust opposite to the direction of drum rotation. Therefore, the vehicle is stopped or slowed down. When the brake releases, the retracting spring is brought shoes back to the off position. It is mainly used in modern vehicles. It is tightly connected to
ww
the steering knuckle in a front wheel brake.
w.E asy E
4.6.7. Disc Brakes
A disc brake is a type of brake that uses calipers to squeeze pairs of pads against a disc in order to create friction that retards the rotation of a shaft, such as a vehicle axle, either to reduce its rotational speed or to hold it stationary. The friction elements are shaped like pads
ngi nee
and are squeezed inwards to clamp a rotating disc or wheel.
Inspection hole
rin
g.n
et
Figure 4.77 Components of disc brake 4.5.7.1. Components of Disc Brake A disc brake assembly consists of a caliper, brake pads, and rotor as shown in Figure 4.77. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
The caliper is the nonrotating unit in the system and it may be mounted to the spindle or splash shield to provide support. The brake caliper assembly includes the caliper housing, the piston(s), the dust boot(s), the brake pads or shoes, and the bleeder screw. The caliper is fitted with one or more pistons that are hydraulically actuated by the fluid pressure developed in the system. When the brake pedal is applied, brake fluid flows into the caliper cylinder. The piston is then forced outward by fluid pressure to apply the brake pads to the rotor. The piston boot keeps road dirt and water off the caliper piston and wall of the cylinder. The boot and seal fit into grooves cut in the caliper cylinder and piston. A bleeder screw allows air to be removed from the hydraulic system.
ww
(ii)Disc brake pads:
w.E asy E
Disc brake pads consist of steel shoes to which the lining is riveted or bonded. Brake pad linings are made of either asbestos (asbestos fiber filled) or semi-metallic (metal particle filled) friction material. Many new vehicles, especially those with front-wheel drive, use semimetallic linings. Semi-metallic linings withstand higher operating temperatures without losing their frictional properties. Anti-rattle clips are frequently used to keep the brake pads from vibrating and rattling. (iii) Brake disc:
ngi nee
rin
It is also called brake rotor. The brake disc uses friction from the brake pads to slow or
g.n
stop the vehicle. Made of cast iron, the rotor may be an integral part of the wheel hub. However, on many front-wheel drive vehicles, the disc and hub are separate units. The brake
et
disc may be a ventilated rib or solid type. The ventilated rib disc is hollow that allows cooling air to circulate inside the disc. 4.5.7.2. Types of Disc Brake Disc brakes can be classified as follows. 1. Fixed caliper (or) swinging caliper type 2. Floating caliper type, and 3. Sliding caliper type. Floating and sliding are the most common types. The fixed caliper may be found on older vehicles.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imm
Automobile Engineering
1. Fixed caliper (lise brake: The caliper is pivoted about a fulcrum pin but one of the friction pads is connected to the. caliper shown in Figure 4.78. The other pad is pressed by the fluid pressure against the disc to apply the brake. So, the caliper automatically makes to adjust its position by swinging about the pin. In this design, the caliper usually is made in two pieces and has two or more pistons in use. The pistons accomplish the centering action of the fixed caliper, as they move in their bores. If the lining should wear unevenly on one side of the caliper. the piston would take up the excess clearance simply by moving further out of the bore. As the brakes are applied, fluid pressure enters the caliper on one side and is routed to the other through an internal passage or
ww
by an external tube connected to the opposite half of the caliper. As pressure is increased, the pistons force the brake pads against the rotor evenly, therefore maintaining an equal amount of pressure on both sides of the rotor.
w.E asy E
Friction pad Piston
ngi nee
rin
g.n
et
Caliper
Figure 4. 78 Fixed caliper disc brake 2. Floating caliper disc brake: The floating caliper type disc brake is designed to move laterally on its mount. This movement allows the caliper to maintain a centered position with respect to the rotor as shown in Figure 4.79. This design also permits the braking force to be applied equally to both sides of the rotor. The floating caliper usually is a one-piece solid construction and uses a single piston to develop the braking force.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and
Hydraulic pressure
Pad
Rotor disc Steering kunckle
ww
Figure 4. 79 Floating caliper disc brake
Operation of a floating caliper is as follows. ~
w.E asy E
Fluid under pressure enters the piston cavity and forces the piston outward. As
this happens the brake pad contacts the rotor. ~ .Additional pressure then forces the caliper assembly to move in the opposite direction of the piston, thereby forcing the brake pad on the opposite side to contact the rotor.
ngi nee
)- As pressure is built up behind the piston, it forces the brake pads to tighten against the rotor. This action develops additional braking force. 3. Sliding caliper disc bra_:
Friction pad
rin
g.n
et
Fluid under pressure
Figure 4.80 Sliding caliper disc brake
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
le",N
Automobile
EngineerIng
The sliding caliper type disc brake, as shown in Figure 4.80, is mounted in a slot in the caliper adapter. It is a variation of the floating caliper, using a single piston and operating on the same principle, whereby the piston applies pressure to one brake pad and the movable caliper applies pressure to the other. This design has two major sections such as the sliding caliper and the caliper adapter (anchor plate). Each has two angular machined surfaces. This is where the sliding contacts come into play. The machined surfaces of the caliper housing slide on the mated surfaces of the caliper adapter when the brakes are applied. 4. Clute" type disc brakes: A pair of pressure plates with many segments made of friction material is wound for 3600 around friction surfaces. Then these plates are axially moved outwards two revolving disc
ww w
surfaces made by inner faces of the drum. This type of brake is fully enclosed by the drum in such a way to act as ribs. The heat is dissipated through these ribs. Out of all these benefits, the clutch type brakes are used in limited applications.
.Ea syE
Advantages and disadvantages of disc brakes: Advantages:
ngi n
1. It provides better stability because of uniform pressure distribution over pads.
2. It allows less bearing load on the application of the brake.
eer
3. The disc pads are not affecteddue to higher temperature.
ing .
4. Fading is less due to exposing of disk for allowing heat radiation.
net
5. The construction is very simple and the brake pads can be easily replaced or serviced readily. 6. There is no self-energizing effect.
7. The brakes get wetted because the disk brakes will recover the braking effect quicker due to the centrifugal force throwing off the water. 8. Repair and maintenance are easy. 9. Friction surfaces are directly exposed to cooling air. 10. It has less weight than drum type. Disadvantages: 1. Surface pressure (braking pressure) is larger due to limited area of braking. So, the
greater friction resistance and heat resistance are needed.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
,.t,g
Systems
2. Due to absence of self-energizing effect, high hydraulic pressure is required to attain sufficient braking effect. 3. The cost is high. 4. External aids are required to prevent damage to disk by sand and dirt. 5. Complete protection to the disc from the road is to be provided. 6. Higher temperature causes evaporation of brake fluid and deterioration of seals. 7. The pads wear off more quickly than the brake shoe linings of the drum type. 8. External servo mechanism is needed.
ww w
9. Hand brakes can easily be fitted in drum brakes but it is not easy in drum brakes. 4.6.8. Comparison between Drum Brake and Disc Brake
.Ea syE
Table 4.4 Comparison between drum brake anti disc brake
S.No. I.
2.
Disc Brake
Description
Drum Brake
Life of friction material
It IS reasonable (about 15,000km)
Visibility of wear from
ngi n
It is reasonable (about 25,000 km)
eer
It is not possible.
outside
It can be seen at a glance.
ing .
It is inferior.
3.
Heat dissipation
It is inferior.
4:
Replacement of friction
It is troublesome and time
material
Consuming.
5.
Weight
It is heavy.
It is lighter (by 25%)
6.
Cooling
It is too slow.
It more efficient due to
\
net
It is easy and rapid.
i
exposure to atmosphere.
7.
Braking effect
it
Generally,
is
It is more consistent.
inconsistent. 8.
Temperature effect
Drum expands and tends to
It is unaffected.
separate out from linings.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'M.Mi) 9.
Automobile Engineering Water
and
dirt
It accumulates.
It is self -cleaning.
collection 10.
Self-energizing action
It exists.
It is absent.
II.
Brake pedal effort
It is higher.
It is proportional
to
retarded. 12.
13.
of hydraulic
Some
system in released state
exists.
pressure on the piston.
Resistance to folding
It is fair.
It is excellent.
It is comparatively less.
It is more.
Behavior
ww 14.
Force needed to apply
pressure
always
There is no hydraulic
brake
w.E asy E
15.
Nature of wear
Non uniform occurs.
Uniform occurs.
16.
Shape of friction lining
It is curved in nature.
It has straight linings.
4.5.9.H~raulic Brakes
ngi nee
Today, most of the cars use hydraulic brake system on all wheels with additional hand brake to stop the rear wheel movement. The liquid pressure supplies hydraulic brakes. The
rin
pedal force is transmitted to the brake shoe by definite quantity of liquid passing through a
g.n
force transmission system. Then the force applied to the pedal is multiplied and transmitted to brake shoes by a suitable transmission system based upon Pascal's principle. It states that the
et
total pressure acting on the transmission system is equal to the sum of pressures acting in all directions without any losses.
Hydraulic braking system consists of two main components which are master cylinder and wheel cylinder. The master cylinder is attached to the wheel cylinder by tubes on each of four wheels. The system has light liquid pressure which acts as a brake fluid. This brake fluid is a mixture of glycerin and alcohol or castor oil, denatured alcohol and some additives.
Construction: A wheel brake has a cylinder brake drum connected on the inner side of the wheel as shown in Figure 4.81. Two brake shoes are connected inside the brake drums. The shoes are fixed with heat and wear resisting brake lining on their surface. The brake pedal is fitted to the master cylinder piston by a piston rod.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering,
Brakes and Suspension
e,m.,
Systems
I
Working: When the brake is applied, the driver depresses the pedal to force the piston into the master cylinder. It will increase the pressure of the fluid in the master cylinder. So, the entry hydraulic system pressure is increased. This pressure is transmitted equally to the wheel cylinder on each of four brakes. Then, it forces the wheel cylinder piston outwards. Due to this, the brake shoes are forced out against the brake drums. Hence, the brake is applied. When the driver releases the brake pedal, the master cylinder piston is returned to its original position by return spring. Thus, the fluid pressure in the entry system decreases to original value. It allows retracting springs on wheel brakes to pull the brake shoes out of contact along with brake drums. Therefore, the wheel cylinder pistons also come back to their original inward position. Thus, the brake is released.
ww w
Shoes
.Ea syE
Brake pedal
ngi n
eer
ing .
net
Figure 4.81 Hydraulic brake system 4.6.9.1.Master Cylinder
The central unit in the hydraulic braking system is master cylinder. It produces the required hydraulic pressure to operate the system. The pressure of the driver's foot on brakes pedal is transmitted to the master cylinder piston through different linkage arrangements. So, the master cylinder is considered as the heart of the hydraulic braking system.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I,'t,zij
Automobile Englne.rlng . ]
Purposes of a master cylinder: 1. The required hydraulic pressure is built up to operate the system. 2. It maintains a constant volume of fluid in the system. 3. To bleed or force air out of the brake line and wheel cylinder, a pump is used. Construction
0/ master cylinder:
Master cylinder is made of cast iron. It has brackets and holes for mounting. The two main types of chambers are as follows. (i)
Fluid reservoir
ww w
(ii) Compression chamber.
.Ea syE
ngi n
eer
--+-
ing .
valve assembly
piston
Figure 4.82 Construction
Fluid to wheel cylinders
0/ a master cylinder
net
The main parts of a master cylinder, as shown in Figure 4.82, are as follows. 1. Brake fluid reservoir 2. Cylinder or compression chamber 3. Piston assembly 4. Check valve or control valve, and 5. Piston return spring. 1.Brake fluid reservoir: It is an integral reservoir with master cylinder for storing additional fluid through a hole at the top of the cylinder. It is done to compensate minute leakages and lining wear produced Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
by fluid movement. A vent cap is provided to allow expansion or contraction
of the fluid
without forming pressure or vacuum. The fluid is contacted a rubber diaphragm to follow the level up and down for removing dust, moisture etc.
2. Cylinder: The main cylinder is a smooth walled structure containing piston, primary and secondary rubber cups, coil spring and a check valve at the mouth of the cylinder. A reservoir is connected with two holes intake port and compensating port.
3. Piston assembly: A piston slides inside the cylinder. Leakage past over the piston is completely eliminated by a primary rubber cup pressing against the inner face of the piston. A secondary rubber cup is connected at the outer piston end-to prevent the fluid from leaving the master cylinder. If the rubber primary cup is connected with a number of small bleeder ports passing through the . I head of the inner piston, the cylinder is operated by a brake pedal through the push rod connected to the brake pedal linkage. The dust boot keeps road dirt and water off the piston
ww w
.Ea syE
and wall of the cylinder.
4. Check valve and piston spring:
ngi n
One end of cylinder is connected with the piston while the other end is connected with . a ,
eer
check valve. The cylinder is held by a coil spring to a rubber seat with the one end pressing against the check valve. A piston primary cup is pressed against the other end.
Working of master cylinder:
ing .
net
When the brake pedal is released, the master cylinder piston will be moved forward to force the liquid under pressure into the system. The relief port is arrested by sealing the system. The liquid pressure is transmitted by moving the wheel to wheel cylinders. The brake shoes are forced out by these pistons against brake drums. When the brake pedal is depressed, the return spring quickly forces the master cylinder piston back against the piston stop. A vacuum is produced in the cylinder in front of the piston. So, the . primary cup is collapsed to allow the liquid to flow from the reservoir through ,
the filler port past the piston. When the pedal is in OFF condition, the liquid will flow from the reservoir to the relief port through the master cylinder, supply lines and wheel cylinder as shown in Figure 4.83. A complete column of liquid is always same between master cylinder niston and wheel cyJinder pistons.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
Piston A
(i) Of/ position of both brakes
ww w.E asy
(ii) Operating both brakes
En gi
(iii) Operating the rear brake only
'"""""..._""O""C;'-""'_.._..;"_~ _
nee
rin
_;;::,,.__.....__....;::,..,_.__---'.....c;.-'--I
~
!'':
",,_..,.-....,.....,........;~~~
," ,
g.n et
Damaged
(iv) Operating the front brake only Figure 4.83 Working of master cylinder 4.6.9.2.Wheel Cylinder The following are the functions of wheel cylinder. 1. It actuates the shoes outward to contact the brake drum.
2. It converts the hydraulic pressure of very low value into a significant value of mechanical force of higher value.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension Systems
Construction of wheel cylinder: The wheel cylinder, as shown in Figure 4.84, which is connected with the cast iron housing are fitted into the individual wheels. An expander unit activates the brake shoes, Two pistons are connected with brake shoes through piston rods. Two-cup washers are connected at the inner side of the piston with a spring connected between them. Rubber boots and dust covers are used to keep the cyl inder free from dust.
A bleeder valve is used for pumping out air and liquid during bleeding. The mechanism is sealed by the rubber
I.:Up
to arrest any leakage of the brake tluid.
Working:
ww w
The brake fluid goes into the master cylinder when the brake effort is applied. The builtup pressure is sent to the space between two pistons in opposite direction to each other. Then, this outward movement is transmitted through links and piston rods by operating brake shoes.
.Ea syE
ngi n
Piston
eer
ing .
net
cover
Figure 4.84 Construction of wheel cylinder 4.6.9.3.Advantages and Disadvantages of Hydraulic Brakes Advantages ofhydraulic brakes: 1, The system is mechanically simple in construction due to absence of brake rods, joints etc.
2. This system provides equal braking effort at all four wheels when compared to a mechanical braking system. 3. All wheel brakes are forced to act together without any consideration in individual Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Ipm
Automobile Engineering
adjustments. 4. It gives an increased braking effort. 5. It gives equal pressure at all four wheels. 6. It is a self-compensating system. 7. The wear rate is low because of self-lubrication of the system. 8. Similar to mechanical brakes, they do not go in straight lines using rod and cables which makes braking linkage simple in design. 9. The brakes provide differential braking action between front and rear brakes using wheels cylinders for the front and also rear wheels of different sizes.
ww
10. They give a high mechanical advantage without use of long levers.
w.E asy E
Disadvantages of J,Yl/rOlllic brakes:
I. Complete braking system should be liable if any fault making pressure loss or the breakage of a pipe to one wheel occurs.
2. The brake shoes should be liable to get ruined when the brake fluid leaks out.
ngi nee
4.5.'.4. Brake FluId of Hydraulic Brake System
Brake fluid is the blood of any hydraulic brake system. This brake fluid is the mixture of
rin
castor oil and alcohol. At that same time, it should not affect rubber parts, it should not freeze and it should have higher boiling points and should not corrode the parts.
g.n
et
Modern brake fluid is specially prepared to perform a variety of functions. Brake fluid should be able to flow freely at extremely high temperatures (SOO°F) and at very low temperatures (- 104°F). Brake fluid should also act as a lubricant to many parts where the contact occurs. It is done to ensure smooth and even operation. In addition, the brake fluid should be non-corrosive and free from rust in brake lines, various assemblies afld eomponents, It should also resist evaporation, Modern brake fluid-should be compatible with rubber to avoid damage to
CliPS
and seal to the system. Sulncient swell is needed to form a good seal.
At the same time, the swell will not be high. Brake tluid has the identification letters of SAE and pOT. These letters refer the nature, blend anu performance characteristic of particular brand of brake fluid.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I
Steering, Brakes and Suspension Systems
Characteristics of hydraulic brake fluid: 1" It should remain fluid at low temperature. 2. It should not corrode or rust metallic parts in the brake system. 3. It should not vapourize at high temperature encountered in actual service. 4. It should act as a lubricant to moving parts inside the system.
S. It should mix satisfactorily with other makes of hydraulic brake fluids. 6. It should retain all its characteristics 'for a maximum long period. 7. It should not soften the rubber parts used in the hydraulic brake system.
ww w.E
8. It should be non~compressible.
4.5.9.6.Bleeding of Hydraulic Brakes When any part of hydraulic line is replaced, air will be trapped into the system. Due to
asy En gi
compressed air, the effort of brake pedal becomes waste in applying brakes. Unless air from the system i~completely removed, the brakes will not function properly. The process of removing air from the brake system is called bleeding. Back Platf)
nee r
ing .ne
t
Figure 4.85 lJIefiJdingof brakes Bleeding is started from the first wheel cylinder from master cylinder. The nearest wheel cylinder is bled at the end but it is not reentered into brake lines. A bleeding tube is fitted at the bleeder valve on wheel cylinder. The other end of bleeding tube is immersed in the glass jar' having brake fluid. The brake pedal is operated till the pressure development will be 3 or 4 times. So, the pedal comes up. Now, the brake pedal is pressed and bleeder valve is
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lam
Automobile
Engineering
unscrewed. When the bleeder valve opens, the fluid will come out and enter into the glass jar. Then, air bubbles will come along with fluid in the jar. Now, the brake pedal will come down to the footboard. So, it is released and pressed down again. This process is repeated again and again till the whole air is drained from the wheel cylinder. The bleeder valve will be screwed on when the pedal is pressed. Fluid is sent from glass jar to the master cylinder not to allow air entering into the system when the fluid in the master cylinder reduces. The main steps involved in bleeding operation are as follows. (a) The reservoir should be full.
ww w.E
(b) One end of the rubber tube should be connected to bleeder valve while the other rube is dipped in a fluid contained in the container.
(c) The bleeder valve should be opened and pedal pumped slowly until the air bubble cease to appear.
asy En gi
(d) The same procedure should be repeated for all wheel cylinders. (e) The reservoir should be topped up.
4.5.10. Mechanical Brakes
nee r Floating
ing .ne
Thinner lining
t
lining Turning moment
Fixed anchor
Figure 4.86 Construction of a mechanical brake Figure 4.86 illustrates the operation of mechanical brake. The pressure is applied by a separate foot pedal or hand pull. It is widely used in parking brakes. Brake is applied through Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Blakes and Suspension
"iD
Systems
cables, cams and linkages etc. The brake shoe is operated by the cam against the revolving brake drum to stop or slow down the motion of the car. Now, the cam is actuated by a mechanical linkage. If the pull is applied, the linkage will be moved by brake shoes for making in contact with the brake drum. The brake lining is connected to brake shoes by rivets. It increases the co-efficient of friction which eliminates the metal contact to prevent wear on metallic shoes. The parking brake is connected to the drive shaft which is operated by a cable within a conduit leading to a hand lever. Multiplication of the leverage at the brake hand cam or lever is obtained through leverage at the brake hand lever.
ww w.E
4.5.10.1. Fixed Expander Brake
The system consists of a cam or toggle fixed on the back plate. In Figure 4.87 (a), the upper ends of the shoes are placed on the cam while the lower ends are hinged with the anchor
asy En gi
pins. When the cam is slightly rotated by means of pedal and levers and linkages, it expands both shoes against the brake drum to slow down or to stop it. Similarly, in toggle operated lever, the toggle is fixed on the back plate and it is free to rotate on the pin. In Figure 4.87 (b), brake shoes are hinged to the toggle by means of two connecting rods provided at each end of the toggle. When the toggle is actuated by means of pedal, it results the expansion of brake
nee r
shoes against the drum to slow down or to stall it. When the pedal is released, then the retracting spring returns the toggle or cam to the off position.
ing .ne Toggle Layer
Brake Lining
Brake Drum
(a) Cam operated
t
(b) Toggle lever operated
Figure 4.87 Fixed expander brakes
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Ipm
Automobile Engineering
4.5.10.2.Leading and Trailing Shoes The shoes which drag along with the drum create more thrust or friction against the brake drum called leading shoes. On the other hand, the shoe which tends to move away from the drum while braking is called trailing shoe. Brake Drum
ww w.E
Friction Unlng
asy En gi
Trailing Shoe
Leading ShOe
Figure 4.88 Leading and trailing shoes
nee r
When the brakes are applied, the force observed on the leading shoe is more than the trailing shoe because the tip of the trailing shoe is thrown off the drum. These unequal forces on two shoes create uneven wears on brake linings. In contrast, if the direction of rotation of the drum is reversed, then the leading shoe acts as a trailing shoe and the trailing shoe acts as a
ing .ne
leading shoe. Therefore, in modem systems, this unevenness of forces has been altered by
t
providing either leading shoes or trailing shoes. 4.5.10.3.Floating Anchor Brake
The system consists of a fixed cam and both shoes are linked together at the floating anchor as shown in Figure 4.89. Both shoes have a common anchor pin fixed on the back plate. When the braking force is applied on the primary shoe (leading shoe), it tends to rotate with the brake drum and it increases braking force on the secondary shoe (traiIing shoe). In this system, both shoes are of self-emerging type to increase the braking torque. This system is highly sensitive with the coefficient of friction variation. Therefore, a proper care should be taken in the selection of fittings to brake linings.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering, Brakes and Suspension Systems Brake
Directionof Rotation
Drum
~
Fixe~Anohor
Friction Lining
Friction Linin;
Primary Shoe
Secondary Shoe
ww w.E
o....--=""";:-7"''--T'-- Force Appliedto
Secondry Shoe -_. Fixed Anchor
asy En gi
Figure 4.89 Floating anchor brakes
4.5.10.4. Floating-Cam Brake
This system consists of a floating cam instead of fixed on the back plate to apply 'equal forces on both shoes and a greater braking torque is produced by a given effort. However, the
nee r
lining wear on the leading shoe is more than the trailing shoe. Therefore, thicker lining is fitted on the leading shoe as shown in Figure 4.90. The anchor remains fixed in the system. FixedCam
ing .ne
TrailingShoe
t
Thinner Lining
Turning Moment!
Fixed Anchor
Figure 4.90 Floating-cam brakes
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lam
Automobile Engineering
4.5.10.5.Brakes with Two Leading Shoes The system consists of two fixed cams which expand to the individual shoe. The ends of shoes are hinged to the anchor pins fixed on the back plate as shown in Figure 4.91. In this system, both shoes act as leading shoes. Therefore, an increased braking torque for the same actuating force is obtained. Both shoes drag along with the brake drum and they create equal amount of friction. Therefore, the lining wear is also equal on the shoes. Fixed Cam Fixed Anchor - Braek Drum
ww w.E
Leading Shoe
Leading Shoe
Brake Lining
Turning Moment
asy En gi
Brake Lining
Turning Moment
Fixed Anchor -_-
nee r Fixed Cam
Figure 4.91 Brakes with two leading shoes 4.5.10.6. Brakes with Two Tn,iling Shoes
ing .ne
t
If the direction of the drum rotation is reversed, then the two-leading-shoe arrangement becomes a two-trailing-shoe brake. This system needs an increased actuating force for the corresponding braking torque. The coefficient of friction of lining effects is less in this arrangement due to less braking torque.Therefore, the lining wear is also less in this system. In most modern systems for providing the powerful braking on front wheels, the leading shoes are used at the front and trailing shoes at rear wheels. This arrangement results the increase in adhesion of front tyres and reduced in adhesion at the rear. 4.5.10.7. Mechanical Brake Linkages It is a mechanism of rods and levers in between the brake pedal or hand lever and actuating levers to multiply the braking effect. The rods and levers are arranged to
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
,.It,
I Steering, Brakes and Suspension Systems
accommodate both upward and downward motions of wheels. The brakes are always applied in pairs because the single brake would skid the vehicle to one side.
4,5.11. Air Assisted Hydraulic Braking System This system of brake is mainly used in Tata vehicles. Compressed air is used to boost up braking. Only 50% of pressure on the pedal is sufficient to obtain the desired effort. Therefore, the efficiency of the braking is better when compared to a simple hydraulic system. This compressed air is used along with hydraulic oil for braking. The main parts of pneumatic braking system are as follows.
ww w.E 1. Compressor
2. Air Governor
3. Booster
4. Air Reservoir
asy En gi
5. Hydraulic Master cylinder
6. Wheel cylinder.
Air compressor receives power from the engine for driving it. First, fresh air is admitted
nee r
to the cylinder and then it is compressed. Then the compressed air is sent to the reservoir. Governor controls the air in the reservoir. When the pressure in the reservoir attains 5.3 kg,
ing .ne
this governor will not allow the air to go to the tank because additional pressure may cause the bursting of tank. An air bottle is also connected with the governor.
t
The main parts of brake booster are air control unit, other piston and cylinder. When the pedal releases, a rod will press the lever. Then, a valve is opened and pressurised air is entered. Next, the piston is moved by the pressure. So, the push rod is moved in the hydraulic master cylinder quickly thereby ensuring effective braking. The piston rod used in this brake system is hollow with two holes for controlling the compressed air. The push rod still holds the brakes but more pressure is required when any failure occurs in producing compressed air. If any leakage in the booster occurs, it should be immediately repaired.
4.5.12. Pneumatic Brakin~ System The air is sucked by the compressor
from atmosphere
through the filter and it is
compressed air as shown in Figure 4.92. During compression, both pressure and temperature increase. Then, the compressed air is passed to the reservoir through an unloaded valve by lifting at a pre-determined reservoir pressure. Due to this, the compressor load is released. The Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Ism
Automobile Engineering
air is allowed to flow to various accessories and diaphragm units at each wheel. It flows through the brake valve from the reservoir. The control of brake valve is effected the intensity of braking according to requirements. Compressor To accessories
Brake chamber
ww w.E
asy En gi
Figure 4.92 Layout of pneumatic braking system
nee r
Heavy vehicles of buses and trucks need a heavy effort at brakes thereby producing
ing .ne
compressed. The main parts are air filter, unloaded valve, air tank, brake valve and brake chamber. The line pressure is regulated by the unloaded valve. This unloaded valve is connected to one side of the air tank.
Table 4.5 Main parts of an air brake ami itsfunctions Parts of air brake
Functions
t
1. Air compressor
It builds up air pressure in reservoir.
2. Unloader valve
It is mounted in the air pressure system between the compressor and reservoir.
3. Air reservoir
It stores compressed air at the specified pressure to apply brake.
4. Brake valve
It is the usually valve operated by the brake pedal.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lSteering, Brakea and Suspension Systems 5. Brake chamber
"'kl
I
It converts the energy of the compressed air into mechanical force and motion required to operate the vehicle brakes.
When the line pressure attains the upper limit, this valve gets opened to allow air to the atmosphere. Brake valve is connected to the driver's pedal which controls the air pressure acting on four brake chambers. When the driver releases the brake pedal, force is exerted on the graduated spring and piston. The exhaust valve seat will also move downward when the piston moves downwards to contact the exhaust valve and seals the exhaust opening in the piston stem. By continuous downward movement of piston, the inlet valve is forced. At that time, air pressure from the air tank forces through the inlet valve and to brake chambers for
ww w.E
applying the brake through delivery ports. When the driver releases the pedal fully, the graduated spring is compressed and strike by the piston shoulder in the body. So, the inlet valve is fully opened and full air tank pressure is
asy En gi
admitted to pass through brake valve into the brake chamber. When the driver releases the pedal, the exhaust valve gets opened to allow full air pressure in brake chambers. So, the brake on the vehicle is fully released. Advantages of pneumatic brakes:
nee r
1. It is more effective when compared to other brakes.
ing .ne
2. The air brake parts are easily located where the chassis design making is simple.
3. The compressed air can be used for tyre inflation wipers, horn and other accessories. 4. It employs only air as the working medium which is easily available. 5. It is easy to store air at high pressure.
6. It provides heavy braking effect used in heavy vehicles and trucks.
t
7. It provides better control. 8. It reduces the stopping distance. 9. It mainly allows less wear and tear of parts. 10. It has flexible hose connection. 4.5.12.1.Comparison between Pneumatic and Hydraulic Braking Systems S.No. l.
Hydraulic brake
Pneumatic brake
Force applied on the brake pedal is In pneumatic brakes, the brake shoes
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lma
Automobile Engineering
i
transmitted to brake shoe through a are operated confined brakefluid. pressure. Advantages
by
means
of air
.
Disadvantages
-
2.
Mechanical linkages, joints etc. are Construction eliminated so as to have simple complicated. construction.
3.
Equal braking effort at all points to Unequal braking effort at all points to all four wheels. all four wheels.
4.
Self-lubricating.
5.
High mechanical advantage i.e. Lower mechanical advantage. less effort required to operate brake.
Non self-lubricating.
ww 6.
. ..
w.E
asy E
Differential braking action can be Differential braking action for permitted by using wheel cylinders different cylinders is not possible. of different sizes for front & rear wheels.
ngi
nee rin
Disadvantages
7.
8.
of each component is
Advantages
Fails the whole system when there These are very powerful as compared is leakage or damage to any part of to the mechanical or hydraulic system. brakes. This system
g.n et
used to apply Its location and working is very easy brakes intermittently and simple. IS
4.5.13. Transmission Or Propeller Shaft Parking Brake Transmission brakes are of external-contracting type, internal-expanding type or disc type. All brakes are operated to lock the transmission of main shaft or the propeller shaft when the mechanical brake is applied. The rear wheels are prevented from turning to avoid the rotation of the propeller main shaft through axle shafts, differential, rear-axle gears and universals. The internal-expanding type is similar to a mechanical type. The drum is connected to the propeller or transmission shaft to replace the wheel.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
"'1'
Systems
In case of an external-contracting
brake type, the drum is connected to the end of the
transmission main shaft using fasteners. The lined brake band is fitted around the drum. Due to this, the cable moves the push rod and operating lever. So, the band tightens sufficiently to lock the drum. The band is released by the return spring when the lever releases. The adjusting lever adjusts the initial tightness of the drum to compensate for band lining wear. This type of brake is used to control planetary gear operation in the case of Hydramatic and Torque Converter transmissions. 4.5.14. Servo Brake Systems
ww
The additional
mechanism
which is connected to reduce the driver's effort during
applying brakes is known as servomechanism.
w.E
When the weight of the vehicle increases, more
braking effort is required to stop the vehicle. After reaching the desired limit, it is difficult to apply the effort required conveniently by an ordinary driver. This limit is almost three tones of
asy E
the weight of the vehicle. The use of the servo action or self-energization performed beyond this limit.
Mechanical servo mechanism:
of brakes is
ngi
nee rin
Initially, mechanical servos were used. After some time, the vacuum operated servos are used. Disc A is always rotating when the vehicle is in motion as shown in Figure 4.93. Another disc B is. pressed against disc A in ordinary single plate clutch. A lever C is connected with the shaft of 13. Then rod D is connected to brake linkage.
D
A
n
g.n et
~--r---~~~
To brakes
Figure 4.93 Mechanical servo When disc A rotates, disc B is pressed on to disc A with a force F and a driving torque will act on B causing to rotate in the same direction. The disc B will rotate slightly under the Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
111m
Automobile Engineering action of this torque by pulling the rod D and applying brakes. The rod D exerts a torque equal due to pull. This torque is opposite to the driving torque between discs. At this condition, the movement is arrested and slip is produced between discs. The above mentioned mechanical servo can be slightly modified for obtaining servo action in both directions.
ww
i.,.'~"
w.E
asy E
To
ngi
........ c:+------. brakes
nee rin
Figure 4.94 Mechanical servo (modified)
The modified mechanical servo transmits force only in tension. When the disc B is
g.n et
rotated in clockwise direction, only chain X will transmit the force. Due to this, the arm of \
'
bell crank lever is pulled up as shown in 4.94. .It results the application of brakes. When the disc B rotates in anticlockwise direction, the chain X will not transmit any force and the arm of the lever will be pulled up by chain Y. Therefore, the brake is applied. 4.5.15. Power-Assisted Braking System Generally, a braking in automobiles magnifies a small force applied to the brake pedal into a proportionately larger force applied to slow or stop the vehicle called power brake. Most all modern vehicles use power assisted brakes. The power brake is a modern braking tool for cars to make braking safer and easier. Power brakes are of two types as follows. (i) Vacuum assisted hydraulic brakes (ii) Pneumatic brakes.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
"fD
Systems
4.5.15.1. Vacuum Assisted Hydraulic Brake
Construction: When the vacuum produced in the manifold of the engine or a separately power driven exhauster is used to assist the braking effort, the system is known a" vacuum assisted hydraulic brakes. Figure 4.95 shows a simplified sketch of this system.
ww w.E a Brake Fluid
ffi~'t---
~To .... brakes
syE
ngi
Vacuum reservoir
---------- -- --.--
Non-return ('}(}~--'-v'alve
n rlnlet ee r
manifold
Master cylinder
Figure 4.95 Vacuum servo brake
ing
.ne
t
The system has a vacuum reservoir placed on the inlet manifold of the engine through a non-return valve. Again, a vacuum reservoir is connected with the servo cylinder on both sides of the piston. The connection is obtained through the control unit on the left side about the right side connection obtained directly. Then the piston is again connected to the piston of the boost cylinder or the brake linkage. Two valves are connected with the control unit. The lower valve is controlled by connection between reservoir and right side of the servo cylinder piston. However, the upper valve controls the connection between atmosphere and left-side of the servo cylinder piston. The other side of the piston of the contro.ltllnit is operated .by the pedal effort through a master cylinder.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
11.:ei
Automobile
Engineering
Working: When the brake pedal is in off condition, the lower valve is opened and the upper valve is closed. So, the air from atmosphere is stopped thereby forming a vacuum from reservoir which acts on both sides ofthe servo cylinder. When the brake pedal is pressed, the brake fluid is forced to push the piston in the control unit. So, the lower valve is closed and the upper valve of the control unit is opened. At that time, the left side of the servo cylinder piston is left to atmospheric pressure. Then, the right side on the cylinder is vacuum. Now, this vacuum moves the servo piston to right. It results the movement of power transmission through the mechanical or hydraulic system to wheel cylinders to apply brakes. Therefore, the driver effort is used to control the position of valves.
ww
There are two types of vacuum servo brakes. Both are having a piston or a diaphragm operating in 1 cylinder with suitable linkage for brake applications. In the former type, both sides of the piston are left to atmosphere when brakes are in the depressed position. In t'ie ' latter type, both sides of the piston are subjected to engine vacuum in brakes in the released position.
w.E
4.5.16. Brake Valve
asy E
ngi
nee rin
A brake pedal is connected to the driver pedal and it controls air pressure action on the individual brake chamber. The brake valve has a hollow piston of spring loaded type with ports and air bleed hole. A double beat valve connects the air reservoir to the hollow piston. The either end of this valve is extended as inlet and exhaust valve. When the driver applies the brake, the force
IS
g.n et
transmitted to this brake valve though
linkage arrangement. [t makes the hollow piston to get lowered down against the designed spring to get compressed. This downward movement of the piston along with the double beat valve makes the inlet valve to open and the exhaust valve to close. This opening of the inlet valve allows the compressed air from the reservoir to enter into the individual chamber. Simultaneously, the compressed air is also allowed to flow through the bleed hole to the underside of the piston in the chamber. It balances the mechanical force applied on the piston by the driver. Once, the pressure in the chamber exceeds beyond the limit, the hollow piston gets lifted up to open the exhaust valve. [t makes the air to escape through the exhaust port till the pressure on either side of the piston gets equalized. At this point, the movement of the double beat valve closes the inlet valve. If the driver wishes tc increase the braking intensity, he has to press the pedal further. The increased force on the hollow piston makes it moves :.hwn, opening the valve further and admitting more air under pressure. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
SJsering, Brakes and Suspension
Systems Applied force through linkage
Exhaust port
Grouting spring
ww
w.E
Exhaust valve
To stop light switch
asy _-+--
--+-_Air
to brake chamber
En
gin eer
Air from reservoir
Figure 4.96 Brake valve 4.5.17. Brake Adjustments
The following are the types of brake adjustment instruments.
1. Micram adjuster, and
ing
.ne
t
2. Taper screw adjuster. 4.5.17.1.Micram A.1juster The mechanism has two scroll members connected one for each brake shoe. Each scroll member is located between brake shoes. Simultaneously, the member is connected to the actuating plunger. This system is very effective and compact. The scroll member is connected with toothed cam and turned by a screwdriver as shown in Figure 4.97. The position of the adjustment is locked by providing the tooth of a cam. This system is mainly used in hydraulic brakes.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lam
Automobile
Engineering
.~ Bracket Adjustment screw
ww w.E
Toothed cam
Brake shoe
asy En gi
Figure 4.97 Micram adjuster
4.5.17.2. Taper Screw Adjuster
nee r
Anchor pin
Brake
lining
ing .ne
Brake shoe
t
Adjusting screw
Figure 4.98 Taper screw adjustment In this screw adjuster system, a screw adjusts the shoes known as star adjusting screw. The upper ends of the shoes are pinned with the projections made on the anchor pin as shown Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
Ilfi'
Systems
in Figure 4.98. The lower ends are fitted by the star adjusting screw. The expander unit is connected just below the anchor pin and shoes are kept by return springs. One more helical spring is connected at the lower side for holding shoes at ends of the adjusting screw. Whenever brakes are adjusted, the adjusting screw will be turned by using a lever or screwdriver through the window connected in the back plate. So, the shoes are expanded outwards. Hence, the clearance between linings and drum is reduced. A screw type adjuster is used in mechanical and hydraulic system of brakes.
4.6.17.3.Girllng Mechanical Brake Adjuster The girting mechanical brake adjuster is in the form of a conical end
ww
SCft)W.
The conical
end is connected between two tappets as shown in Figure 4.99. The tappet has slots at its end. The shoe ends are fixed on this slot. When the screw rotates. the conical enJ will move down.
w.E
Therefore, the tappets move outward, Due to this, the connected shoe ends also moves outward.
asy E
ngi
nee rin
g.n et
Figure 4.99 Girting brake adjuster Advantages of girling brakes: 1. It is easily adjustable without jacking up the vehicle. 2.
It minimizes the driver effort.
3.
It uses a mechanical compensator.
4.
It provides a self-centering effort.
5.
Less traction distance is sufficient for applying the brake.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lam
Automobile Engineering
4.5.18. Brake Compensation When brakes fade, two things are happened. First, the pads are heated up to the point and then the friction generated is reduced. It can be caused by resins or other ingredients breaking down. Second, the temperature can cause the brake fluid to boil. When the fluid boils, it is changed to vapour form. The fluid vapour is compressible. Both conditions will lead a spongy brake pedal. Brake fade compensation IS more than a bunch of algorithms which estimate the temperature in the· brake system by using the applied time, brake pressure, acceleration/deceleration etc. When the computer determines the pads or fluid have exceeded a certain threshold, it will close some valves and turn on an ABS pump during braking. It expands the pressures at wheels and prevents the pedal from going to the floor.
ww
w.E
4.5.19. Retarder
asy E
A retarder is a device used to expand or replace some of the functions of primary friction-based braking systems, usually on heavy vehicles.
ngi
Friction-based braking systems are susceptible to brake fade when they are extensively used for continuous periods which are dangerous if the braking performance drops below the required stopping distance of the vehicle or if a truck or bus is descending a long decline. Because of this reason, such heavy vehicles are frequently fitted with a supplementary system which is not friction-based.
nee rin
g.n et
Retarders are not restricted to road motor vehicles -bUtthey may also be used in railway systems. Retarder serves to slow vehicles or maintains a steady speed on declines and helps to prevent the vehicle running awc::ry by accelerating down the decline. At the same time, they do not bring the vehicles to a standstill when their effectiveness decreases. Mainly, they provide an additional assistance to slow vehicles with the final braking done by a conventional friction braking system. 4.5.19.1.Hydraulic Retarder Hydraulic retarders use the viscous drag forces between dynamic and static vanes in a fluid-filled chamber to achieve retardation. Many hydraulic retarders use standard transmission fluid such as gear oil, a separate oil and water. A simple retarder uses vanes attached to a transmission driveshaft between clutch and road wheels. They can also be separately driven through gears off a driveshaft. The vanes are Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering,
"fl'
Brakes and Suspension Systems
enclosed in a static chamber with small clearance to chamber wall similar to an automatic transmission. When retardation is required, fluid (oil or water) is pumped into the chamber and the viscous drag induced will slow the vehicle. The working fluid will be heated and circulated through a cooling system. The degree of retardation can be varied by adjusting the fill level of the chamber. Hydraulic retarders are extremely quiet, often inaudible over the sound of a running engine and especially quiet in operation compared to engine brakes.
ww w.E a
4.5.18.2. Electric Retarder
The electric retarder uses electromagnetic induction to provide a retardation force. An electric retardation unit can be placed on an axle, transmission or driveline and it consists of a rotor attached to the axle, transmission or driveline and a stator securely attached to the
syE
vehicle chassis. There are no contact surfaces between rotor and stator due to no working fluid.
ngi
When the retardation is required, the electrical windings in the stator takes power from the vehicle battery to produce a magnetic field through which the rotor moves. It induces eddy current in the rotor and produces an opposing magnetic field to the stator. The opposing magnetic field slows the rotor. The rotor incorporates internal vanes to provide its own air
nee r
ing
cooling. Therefore, no load is placed on the vehicle's engine cooling system. The operation of the system is extremely quiet.
.ne
t
A hybrid vehicle uses the electrical retardation to assist the mechanical brakes while recycling the energy. The electric traction motor acts as a generator to charge the battery. The power stored in the battery is used to accelerate the vehicle. 4.5.20. Antilock Braking Systems (ABS) Stopping safely is one of the most important functions a motor vehicle. Failure of the brake system will invariably lead to a property damage, personal injury or even death. Consequently, a great deal of consideration has been given to improve the brake system in trucks and passenger cars over last nine decades. One of the latest improvements is an antilock brake system which prevents a vehicle's brakes from locking up and skidding during hard stops on wet or icy roads.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
11m)
Automobile Engineering
The problem of skidding reveals the overwhelming weakness of all motor vehicle braking systems. They depend strongly on the coefficient of static friction between tyre and road. If the tyre momentarily loses its adhesion to the road while brakes are applied, the friction of brakes will be against drums or rotors which lock the wheel solidly and the tyre begins skidding across the road. In this condition, the braking force of the wheel is depend on the sliding friction between tyre and road which is much less than static friction. Under wet or icy conditions, the sliding friction is reduced even further thereby resulting significantly the longer stopping distance. In addition, when the front wheels are in this condition, they cannot be used to steer the vehicle irrespective of the angle of front wheels and,the vehicle continues to skid whatever be
ww
the direction of its momentum until either the driver releases brakes or the vehicle collides
w.E
with solid. Antilock Braking Systems (ABS) is a form of electronic braking which helps a driver to control the vehicle under heavy braking by preventing wheels from locking up.
asy E
4.5.20.1.Need of ASS in Automobile
ngi
Braking systems take the force applied to the foot pedal by the driver and transfer the force through a mechanical system to brakes on the wheel. The mechanism works by
nee rin
increasing the input force through a servo to the master cylinder which converts the force into pressure applied by brakes. The master cylinder has two pressure chambers. Both are responsible for the braking pressure on two of wheels and to provide an extra level of safety.
g.n et
During failure, the wheels may stop rotating before the car comes to a halt. This process is known as locking up. Locking up refers the braking force on the wheel not being transferred efficiently to stop the vehicle due to tyre sliding upon the road.
It leads to longer stopping distance than the wheel because there is a reduced gnp between car and road which' in turn leads to an increased chance of losing control of the vehicle and , skidding. On vehicles without ABS, the best method to regain the control of the vehicle is to press brakes by taking your foot off the pedal and reapply it. It allows the tyres to regain traction upon the road rather than skid over the surface. ABS works similar to traction control but it is in an effective manner. Electric sensors monitor the speed of the wheel as it rotates and detect if it is about to lock up under braking. When it happens, the brakes are automatically released and then rapidly reapplied. It occurs several times as fast as possible to prevent a skid and to ensure a vehicle steered by the driver to avoid a collision.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
am
[Steering, Brakes and Suspension Systems Rear axle service I Spring brake actuator
Modulator values
o
~
Exciter
a>
:J 0.
E 0 0 0
a> "S
"'0 0
2":-
~
a>
0
:;::
Cl til
co
c:
ww
::E
eC
10
is
0
o
w.E s:
.8
';: IFl
~ ~
a>
asy m
a> c: 'a' c: UJ
a>
Quick release valve
IFl
c:
s:
j! ~
g c
~!I
~ +
iO~
••
U
'6 ~ a>
ztil
E ..!!!
0
'c 0 ~
En
a>
0.
0
ASS Electronic Control Unit (ECU)
"E ..!!!
c:::
\
a>
IFl
"'0
a> a>
Service brake valve
0. IFl
li
gin eer
~
ing
~
<
~ c
I-
Figure 4.100 Components of ABS /
.ne
t
4.5.20.2. Components of ABS Modern antilock braking systems has the following features, I, Wheel speed sensors (pickup and exciter)
2. Electronic Control Unit (ECU) 3. Hydraulic modulator valves 4. Pump motor and accumulator. Figure 4.101 describes the structure and arrangement of these components of modern antilock braking system. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lam
Automobile
Engineering
1. Wheel speed sensors (WSS): Wheel Speed Sensors (WSS) consist of a magnetic pickup and a toothed sensor ring which may be mounted in steering knuckles, wheel hubs, brake backing plates, transmission tail shaft or differential housing. On some applications, the sensor is an integral part of the wheel bearing and hub assembly.
Permanent magnet
Toothed wheel
ww
w.E
Space
asy
Figure 4.101 Wheel speed sensor
En
The wheel speed sensor pickup has a magnetic core surrounded by coil windings. As the
gin eer
wheel turns, teeth on the sensor ring move through the pickup magnetic field. It reverses the polarity of the magnetic field and induces an AC voltage in pickup windings. The number of voltage pulses per second is induced in the pickup change in direct proportion to the wheel
ing
speed. So, when the speed increases, the frequency and amplitude of the wheel speed sensor are going up.
.ne
t
Magnetic pick-up sensor
Toothed sensor ring
Figure 4.102 Typical speed sensor assembly
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
WSS signal is sent to the antilock brake control module where AC signal is converted into a digital signal and then it is processed. The control module counts pulses to monitor the changes in wheel speed. 1.
Electronic Control Unit (ECU): ABS electronic control unit is a microprocessor which functions similar to the engine
control computer. ECU processes all ABS information and signal functions. It receives and interprets voltage pulses generated by the sensor pickup as the exciter teeth pass-by and it uses this information to determine the following parameters. );. impending wheel lock-up, and
ww
)- when/how to activate ABS modulator valves.
w.E
The key inputs for ABS electronic control unit come from the wheel speed sensors and a brake pedal switch. The switch signals are passed to the control unit when brakes are being
asy
applied. It causes the signals to go from a standby mode to an active mode. During braking, ECU uses voltage pulses from each wheel speed sensor to determine
En
wheel speed change. If ECU determines the pulse rate of sensed wheels by indicating
gin eer
imminent lock-up, ABS modulator valves modify brake air pressure as needed.
J. Hydraulic modulator valve:
ABS modulator valves regulate the fluid pressure to brakes during ABS action. If no
ing
commands are received from.ECU, the modulator valve allows fluid to flow freely and it has no effect on the brake pressure. ECU commands the modulator valve to either );0
change the fluid pressure to the brake chamber or
,
hold the ex.iateg pressure.
.ne
t
The hydraulic modulator or actuator unit contains ABS solenoid valves for each brake circuit. The exact number of valves per circuit depends on ABS system. Some have a pair of on-off solenoid valves for each brake circuit while others use a single valve that can operate more than one position. The modulator valve has to control more fluid flow. Therefore, it includes two larger diaphragm valves which are controlled by solenoids. It usually has three ports such as supply port, delivery port and exhaust port. o
The supply port receives air from a quick release or relay valve
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lam
Automobile Engineering );>
The delivery port sends air to the brake chambers
);>
The exhaust port vents air from the brake chamber(s).
When an ECU controlling a separate modulator valve detects impending wheel lockup, it will activate solenoids to close the supply port and open the exhaust port. When sufficient air is vented to prevent wheel lockup, the exhaust valve will close and ECU will either );>
keep the supply port closed to maintain existing pressure or
)l>
open the supply port to allow brake application pressure to increase and repeat the cycle.
ww
4. Pump motor ami accumulator: A high pressure electric pump is used in some ABS systems to generate power assist for
w.E
normal braking as well as the reuse of brake pressure during ABS braking. Some systems, it is used only for the reuse of pressure during ABS braking.
asy
The pump motor is energized through a relay that is switched on and off by ABS
En
electronic control unit. The fluid pressure which is generated by the pump is stored in the accumulator. The accumulator consists of a pressure storage chamber filled with nitrogen gas where the hydraulic modulator is a part of the master cylinder assembly.
gin eer I
I
When the pump fails, there is enough reserve pressure in the accumulator for 10 to 20 power-assisted stops. Next, there is 110 power assist. The brakes still work but with increased effort.
ing
.ne
On ABS systems, a conventional master cylinder and vacuum booster are for power
t
assist and a small accumulator or pair of accumulators may be used as temporary holding reservoirs for brake fluid during hold-release-reapply cycle. 4.5.20.3.Working Principle of ABS Wheel speed sensors are placed on each wheel for controlling the speed. Each speed sensor has a toothed wheel such as a gear which rotates at the same speed as the vehicle wheel or axle. It is a permanent magnet wrapped with a coil of wire called pick-up coil. As each tooth rotates past the permanent magnet, it will cause the ~agnetic field to concentrate and increase slightly. Then, it induces a small pulse of current in the coil of wire. The pulsed output from the wheel speed sensors goes to an ECU which monitors each I
wheel speed relative to the speed of other wheels. As long as the brakes are not being applied and all monitored wheels are rotating roughly at the same speed, the system takes no action. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
,.&,
Systems
However, the brakes are being applied and one or more of the monitored wheels suddenly begin to reduce the speed at high rate than other controllers and then they activate the antilock system. In an automobile, brakes are actuated by hydraulic pressure. In ASS, electrically operated solenoid valves are used to hold, release and reapply the hydraulic pressure to brakes. ASS controller operates solenoid valves built into high pressure side of the master brake cylinder. These valves are normally open and do not interfere with braking. When the controller senses a wheel locking up while braking, it .will first activate a solenoid to close a
ww
valve in the affected wheel brake line to prevent the pressure from increasing further. If the locked wheel continues to lose its speed, the controller activates a second solenoid which bleeds pressure off the affected brake line for effective releasing of the brake irrespective of the driver effort. As soon as the wheel regains traction and its speed increases, the solenoids
w.E
asy E
are de-activated and normal braking resumes.
If conditions are that the wheel starts to skid again, the brake wilt promptly begin to lock up and ASS will take over. This cycle is repeated 12 to 15 times per second until either the
ngi
road condition changes or the driver releases brakes. The driver will be able to detect this
nee rin
rapid cycling as a vibration felt through the brake pedal but it will not have to take any action. ASS will minimize the skid and will allow the driver to maintain a directional control of the vehicle. Figure 4. I03 describes the steps in ASS. 2. Piston pushes brake fluid
3. Brakefluidsqueezes brakepadsonto brakedisc
g.n et
c"C
~8
~ 5l { l3 8. Zl
I/)
80._~ a. ;;; 51 ';;
~a
6. Fluid is beld off into accumulator I reservoir This releases pad pressure L-_'&--I 7. Fluid is pumped back to reapply pressure.
'---+-
5. Control unit activates accumulator and pump
I-::J
detects when the wheel is about to lock - the driver has pushed too hard
Figure 4.103 Steps in antilock braking systems
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
4.5.20.4.Types of Anti·Lock Brakes Anti-lock braking systems use different schemes depending on the type of brakes in use. It is usually referred by the number of channels. It means the number of valves which are individually controlled and number of speed sensors. 1. Four-channel.four-sensor ABS: There is a speed sensor and a separate valve for all four wheels. The controller monitors each wheel individually to make sure whether it is achieving maximum braking force or not. Each wheel speed sensor would give its input into a separate control circuit. 2. Three-channel, three-sensor ABS:
ww
It is commonly found on pickup trucks with four-wheel ABS. It has a speed sensor and
w.E
valve for each of front wheels and one sensor for both rear wheels. The speed sensor for the rear wheels is located in the rear axle.
asy E
This system provides individual control to front wheels. So, they can achieve maximum braking force. However, the rear wheels are monitored together and both have to start to lock up before ABS will activate on rear wheels. The sensor reads the combined or average speed
ngi
of both rear wheels. It is possible for one of rear wheels locking up during a stop and reducing the brake effectiveness. This type of setup saves the cost of an additional sensor and it reduces the complexity of the system by allowing both rear wheels to be controlled simultaneously. 3. Olle:.eh(lltllel,one-sensor ABS:
nee rin
g.n et
This system is commonly found on pickup trucks with rear-wheel ABS. It has one valve to cotwol· both rear wheels and one speed sensor located in,·ttle rear axle. This system is operated similar to the rear end of a three-channel system. The rear wheels are monitored together and both have to start to lock up before ABS kicks in. In this system, it is also possible that one of rear wheels will lock and reduce the brake effectiveness because the rearwheel antilock systems have only a single channel and they are much less complex and less costl,.llfl three and four-channels four-wheel counterparts. 4.5.20.6.Advantages and Disadvantages of ABS Advantages of ABS: "
ABS guarantees stable braking characteristics on aU road surfaces, hence avoids overturning of the vehicle.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension );.>
eDt,
Systems
ABS reduces friction on wheels and road, thus increases efficiency of tires (up to
30%). );.>
Although
ABS will not decrease a vehicle's
stopping distance
compared
to an
identical non-ABS vehicle, it ensures the shortest distance in which a vehicle can be brought to rest. );.>
ABS is particularly effective in wet or icy roads upon which a vehicle is much more likely to skid.
);.>
Steering control is effective, i.e., vehicle can be steered smoothly while braking. Thus minimizes the accidents.
);.>
ww w.E a
A driver without experience can drive ABS vehicle effectively, than an experienced
driver on the non-ABS vehicle.
Disadvantages of ABS: );.>
Initial cost for ABS vehicle is high as require significantly
traditional braking system.
);.>
syE
more parts than a
Maintenance issues arise as the whole braking system is controlled by engine control
unit.
ngi
nee r
);.>
On concrete roads, the ABS vehicle stopping distance might be needed more.
);.>
It is easy to cause a problem in an ABS system by messing around with the brakes. Problems include disorientation
ing
of the ABS system, where a compensating
brake
sensor causes the vehicle to shudder, make loud noise or generally brake worse.
4.5.21. Electronic Brake Force Distribution
(EBD)
.ne
t
EBD (Electronic Brake Force Distribution) is a technology that enables the braking force of a vehicle to be increased or applied automatically depending on road conditions, speed of the vehicle, weight of vehicle, etc. EBD is based on the principle of the weight being supported by wheels of your car not evenly distributed. An EBD system can not only detect how much weight is being supported by each wheel but it varies the amount of braking power sent to each wheel on an instant-byinstant basis. EBD functions as a subsystem of the ABS system to control the effective adhesion utilization by rear wheels. The pressure of rear wheels are approximately
calculated to the
ideal brake force distribution in a partial braking operation. To obtain EBD, the conventional brake design is modified in the direction of rear axle over-braking
and the components of
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
II'I'Im
Auto,!,oblle Engineering,
J
ABS are used. EBD can apply more or less braking pressure to each wheel in order to maximize the stopping power while maintaining the vehicular control. In some systems, BBlt distributes more braking pressure at rear brakes during initial brake application before the effects of weight transfer become noticeable. EBD helps to reduce the strain on the hydraulic brake force valve in the vehicle.
ww w.E a
syE
ngi
nee r
ing
Figure 4.104 Vehicle load withou: and witll EBD
.ne
In a regular braking system, when the brake pedal is applied, the brake fluid flows from
t
master cylinder to wheel cylinders. When the fluid enters inside the wheel cylinder, the pressure of the fluid will force two pistons to push out to result the brake shoes or pads being pushed out. This push or pressure is in direct proportion to the push by pistons which causes shoes or pads to rub against the drum or caliper. This reaction creates friction and decreases turning of wheels. EBD monitors electronically through sensors such as the conditions of the road, feel of pressure on the brake pedal and vehicle weight to determine when to apply pressure to the wheel cylinders. The sensors are designed to monitor the movement of wheels and determine based on weight which wheels need the maximum force applied. Since the front end has the most weight on a vehicle, EBD system recognizes and electronically controls back brakes so when the driver applies the brakes, the back brakes do not lock up causing a skid. EBD is a ·gooa-system for drivers because it can increase the Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering, Brakes and Suspension Systems
mafM. vehicle's ability to stop under any conditions. But, it is only effective if the ECU works along with sensors to make up the system. If one of those sensors fails, a dangerous mesh may happen. 4.5.22. Traction Control In recent few years, some selected automobile manufacturers have introduced the systems with addition of traction and tracking control during both acceleration and braking. Anti-lock braking system (ABS) releases the brakes momentarily when the wheel speed sensors gives a signal to lock wheels during braking but the traction control applies the brakes momentarily to one of drive wheels when the wheel speed sensors indicates a wheel rotating faster than others during acceleration.
ww
w.E
4.5.22.1. Function of a Traction Control
asy
A Traction Control System (TCS) also known as Anti-Slip Regulation (ASR) is typically a secondary function of ABS. The primary function of the traction control system is to
En
maintain the traction and stability of the vehicle regardless of the road surface condition. It is
gin eer
achieved by reducing the drive torque applied to rear wheels or pulsing the rear wheel brakes to eliminate the wheel slip depending on the version of traction control installed. The electronics for traction control operation are incorporated in ABS control module
ing
and share many of same ABS sensors. The module decides the speed of the vehicle through a calculated average of the four wheel speed sensor inputs.
.ne
When the traction-control system determines one wheel spinning more quickly than
t
others, it automatically pumps the brake fluid to the particular wheel to reduce its speed and
lessen wheel slip. If one of the driven wheels tends to spin, traction control is activated. The traction control system reduces the drive torque supplied by the engine. If necessary, brakes are applied to individual wheels in order to regulate the slip of driven wheels as quickly as possible to the optimum level. A critical slip ratio of greater than 5% between wheels will cause the traction control regulation to start. This slip ratio is established when the control module detects a wheel speed difference of2 MPH or higher.
4.5.22.2. Components of
rcs Systems Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering
Main.components are an electronic control unit (ECU), one or more hydraulic modulator assemblies, one or more wheel speed sensors and a wiring harness. Wheel Speed Sensor
~
Battery
~
Actuator Solenoids
__..
Actuator pump motor
__..
Slip Indicator light
~
ABSrrCS TRACOFF Switch
ww w.E a
~
Stop Light Switch
Throttle position sensor
Electronic ControlUnit
--+
~ ~
syE
ngi
~
TRAC OFF light ABS warning light
n~I eer
Injectors
Electronic controlmodule
~
ing
I
Shift solenoid valves
Figure 4.105 Layout of traction control
.ne
1. Wheel sensors:
t
Wheel sensors are the key components of both ABS and TCS systems. In order to determine the vehicle wheel speed, a Wheel Speed Sensor (WSS) is placed on each wheel. As the teeth pass by the pickup core, a sinusoidal pulse train is generated with a frequency proportional to' the speed of the wheel. This generated frequency is directly proportional to wheel revolutions/time and an analog of the wheel ground speed. Scaling arithmetic in ECU microprocessor software is used to convert the input frequency analog to ground speed (mph or kph). They are compared to determine the individual wheel slip.
2. Pumps, valves, accumulators and motors: Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Steering,
mD
Brakes and Suspension Systems
TCS hydraulic control units (HCUs) contain pumps, valves, accumulators and motors which perform ECU commanded functions for the system operation. Most HCUs are relatively insulated from crash damage but few are located in the frontal crush zone such as front wheel speed sensors. 3. TCSECUs: ECU of ABS is shared by traction control system. Most TCS ECUs are relatively insulated from crash damage. During crash damage to a wheel sensor, it will cause a snapshot frame. In most cases, individual wheel braking is enough to control the wheel slip. In some traction-control systems, a special type of traction control reduces engine power
ww
to slipping wheels. On a few of these vehicles, drivers may sense a pulsation of the gas pedal when the system is reducing the engine power similar to a brake pedal pulsates and when the antilock braking system is working.
w.E
asy
4.6.23. Trouble Shooting in Brakes
En
1. Pedal can be moved to strike floorboard without producing brake action
Causes
I. Low level oftluid in master
cylinder reservoir. 2. Leak in hydraulic system.
gin eer Remedies
Fill reservoir with brake fluid.
ing
and bleed system. 3. Normal wear of linings.
.ne
Locate and repair leak and also refill
Adjust brakes. See minor brake adjustment. If brakes cannot be
t
adjusted, the lining must be replaced and the drums must be checked. 4. Brake shoes not properly
Adjust brake shoes.
adjusted. 5. Defective master cylinder.
Rebuild with new parts or replace.
6. Air in system.
Bleed system. Seek cause of air entrance.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Ims
Automobile
Engineering
2. One wheel drags Causes
Remedies
1. Weak or broken brake shoe
Replace spring.
return spring. 2. Brake adjusted too tight.
Re-adjust to proper clearance.
3. Wheel cylinder piston and/or
Replace cup and/or piston.
cup stuck.
ww w.E a
4. Loose or worn wheel or axle
Tighten or replace.
bearing.
S. Clogged or kmked line.
Replace.
6. Brake shoes binding.
Free up shoes.
syE
7. Brake drum out-of-round.
8. Loose backing plate.
Turn down in lathe or replace.
ngi
Tighten or replace.
nee r
J. Car pulls to one side on application of the brakes
ing
Causes
Remedies
1. Grease, oil, or brake fluid soaked
Replace lining. Clean brake drum.
.... "I
.ne
linking.
Seek source of grease, oil or brake fluid.
Loose wheel.bearings.
Tighten or replace.
3. Low tyre pressure,
Inflate tyre to correct pressure,
4. Loose backing plate, spring
Tighten.
t
If-bolts, steering etc.
S. Primary and secondary shoes
Place shoes in correct reversed.
positions.
6. Line on opposite side restricted.
Replace line.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
Systems
"'D
7. Drums out of round.
Tum down in lathe or replace.
8. Poor brake adjustment.
Adjust brake. Include anchor pin adjustment.
9. Unequal camber.
Adjust camber to correct value on both wheels.
1O. Faulty wheel cylinder.
Replace.
----------------------------------------------------------------------------------------------------------------4. Springy or spongy brake pedal
----------------------------------------------------------~------------------------------------------------------
ww w.E
Remedies
Causes
---------------------------------------~------------------------------------------------------------------------1. Air in lines.
Bleed lines. Seek cause of air entrance.
2. Poor shoe adjustment.
Adjust shoe to correct clearance.
3. Brake drum out of round.
Turn down drum or replace.
asy E
------.---------~----~-------------------------------------------------------------------------------------------
ngi
5. Excessive pedal pressure required to lIpply brakes
nee
-----------.--------------------------------------------------------------------------------------------~-------Remedies
Causes
rin
-----------------------------------------------------------------------------------------------------------~----Replace linings. I. Oil-soaked or improper linings. Adjust shoes.
3. Partial lining contact due to
Adjust anchor pin or pins to produce correct toe and heel clearances.
improper anchor pin adjustment.
t
4. Warped brake shoes.
Replace or regrind and shim lining.
S.
Free up. Lubricate where necessary.
Pedal and/or shoes binding.
Free up or replace.
6. Brake line restricted. __________________
g.n e
2. Poor shoe adjustments.
6.
------------------------------------------------------------
6. Brakes chatter or squeak
Oil
application
-------------------------------------------------_ .._------------------------------------------------------------Causes
Remedies
----------------------------------------------------------------------------------------------------------------I. Linings not well cemented or
Reline shoes.
riveted to shoes. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I"'''
Automobile
Engineering
2. Loose backing plate or shoe support.
Tighten.
3. Front suspension loose.
Tighten or repair.
4. Oily linings.
Replace linings.
5. Poor brake adjustment.
Adjust brakes.
6. Dirt embedded in lining.
Clean linings with wire brush or replace them.
7. Brake drum out of round, scored or cracked.
Re-bore or replace drum.
ww
8. Shoes scraping backing plate.
Clean and lubricate contact surfaces.
--------------------~~~------------------------------------------------------------------------------------------
w.E
7. Power brake cylinder does not boost pedal pressure
asy
----------------------------------------------------------------------------------------------------------------Causes
En
Remedies
----------------------------------------------------------------------------------------------------------------1. Vacuum check valve stuck.
2. Vacuum pipe bent, broken, or obstructed. 3. Air inlet blocked.
4. Air valve sticking on power piston.
gin eer
Free up or replace. Replace. Tighten all connections.
ing
Check air cleaner. Clean or replace.
.ne
Disassemble the power piston. Free valve or replace.
t
.---------------------------------------------------------------------------------------------------------------, 8. Power unit does not release properly (hydraulic system is in good condition) ------------------------------------------------------------------------------------.----------.--
Causes
----.
Remedies
----------------------------------------------------------------------------------------------------------------1. Binding push rod.
Free lip or replace.
2. Internal friction in power unit.
Disassemble unit. Lock for weak or broken springs, dry rubber cups and O-ring seals.
-----------------------------------------------------------------------------------------------------------------
Downloaded From : www.EasyEngineering.net
~ I
Downloaded From : www.EasyEngineering.net
9. Brake pedal suddenly requires longer travel to apply brakes, brake warning light goes on Causes
Remedies
Leak in front or rear hydraulic system (double master cylinder
Locate cause of leak and make
design).
necessary repairs. Reset warning light switch.
, 10. One brake drags
ww w.E Causes
Remedies
l. Shoes out of adjustment.
Adjust.
asy E
2. Clogged brake line.
Clear or replace line.
3. Wheel cylinder defective.
Repair or replace.
4. Weak or broken return spring
ngi
Replace.
nee
S. Loose wheel bearing.
Adjust bearing.
11. All brakes drag
rin
g.n e
Causes
Remedies
1. Incorrect linkage adjustment.
Adjust.
2. Trouble in master cylinder.
Repair or replace.
3. Mineral oil in system.
Replace damaged rubber parts, use
t
only recommended brake fluid.
12. Brakes too sensitives Causes
Remedies
1. Shoes out of adjustment.
Adjust. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
,",1iI
Automobile
Engineering
2. Wrong linings.
Install correct linings.
.3. Brake linings greasy.
Replace, check oil seals avoid over lubrication.
4. Drums scored.
Tum or grind drums.
5. Backing plate loose.
Tighten.
6. Power-brake assembly
Overhaul or replace.
malfunctioning. Replace linings and oil seals, avoid over lubrication.
7. Brake linings soaked with oil.
ww w.E
----------------------------------------------------------------------------------------------------------------13. Noisy brakes
asy E
--------------------------------------~.-------------------------------------------------------------------------Causes'
Remedies
-----------------------------------------------------------------.----------------------------------------------1. Linings worn.
ngi
Replace.
4. Drums worn or rough.
nee
5. Loose parts.
Tighten.
2. Shoes warped. 3. Shoes rivets loose.
Replace.
Replace shoe or lining,
rin
Turn or grind drums.
g.n e
t
---------------7------------------------------------------------------------------------------------------------14. Air in system
----------------------------------------------------------------------------------------------------------------Remedies
Causes
----------------------------------------------------------------------------------------------------------------I. Defective master cylinder.
Repair or replace.
2. Loose connections, damaged tube.
Tighten connections, replace tube.
3. Brake fluid lost.
See item 15 below.
-----------------------------------------------------------------------------------------------------------------
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
Systems
15. Loss of brakefluid
----------------------------------------------------------------------_ .._---------------------------------------Remedies
Causes
------------------------------------------------------------------------------------------------------------.---I. Master cylinder leaks.
Repair or replace.
2. Wheel cylinder leaks.
Repair or replace.
3. Loose connections, damaged tube.
Tighten connections and replace tube.
(Note: After repair, add brake fluid and bleed system)
ww w.E
--------------------------------------------------~-------------------------------------------------------------16. Brakes do not self-adjust
----------------------------------------------------------------------------------------------------------------Causes
asy E
Remedies
----------------------------------------------------------------------------------------------------------------Free and clean up.
1. Adjustment screw stuck.
2. Adjustment lever does not engage star wheel
ngi
Repair, free up or replace adjuster.
nee
3. Adjuster incorrectly installed.
Install correctly.
rin
----------------------------------------------------------------------------------------------------------------17. Warning light comes on wile" braking
g.n e
----------------------------------------------------------------------------------------------------------------Remedies
Causes
t
----------------------------------------------------------------------------------------------------------------Check both sections for braking action.
1. One section has failed.
Repair defective section. 2. Pressure differential valve defective.
Replace.
----------------------------------------------------------------------------------------------------------------. 18. Excessive pedal travel
----------------------------------------------------------------------------------------------------------------Causes
Remedies
----------------------------------------------------------------------------------------------------------------1. Excessive dish run-out.
Check, run out if excessive.
2. Air leak or insufficient fluid.
Install new disk check.
---------------------------------------------------------------------------------------------------------------Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
19. Brakes heat up during driving andfall to release Causes
Remedies
1. Power-brake malfunction.
Check and correct power unit.
2. Sticking pedal linkage.
Free up sticking pedal linkage.
3. Operator riding brake pedal.
Instruct owner how to drive disk brakes.
4. Frozen or seized piston.
Disassemble cliper, install new piston, seal boots.
ww w.E
5. Residual press,:!revalve in
Remove valve from cylinder.
master cylinder.
asy E
4.6. TWO MARK QUESTIONS AND ANSWERS
ngi
1. What are the requirements of steering system? I. It multiples the turning efforts applied on the steering wheel by the driver.
nee
2. The shocks of the road surface absorbed by wheels should not be transmitted to the driver's hands.
rin
g.n e
3. When the driver releases the steering wheel after completing the tum, the wheel should achieve a straight ahead position immediately, called self-rightening effect.
t
4. It must keep the wheel at all time in rolling motion without rubbing on the road. 2. How does a steering-wheel take a right turn? I. Both the steering wheel and steering tube are rotated clockwise by rotating the roller shaft through 'he steering gear. 2. Due to this action, the bottom end moves forward for pushing the drag link. 3. The tie rods are forced to left side by an intermediate steering arm. Thus, it receives a push of the drag link. 4. The right steering arm is pulled by the right tie rod to turn the right steering knuckle and wheel to right side. S. The left steering arm is pushed by the left tie rod for turning the left steering knuckle and wheel to right side. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension Systems
3. List out the components of steering system. ] . Steering linkage (a) Pitman arm
(b) Balljoints
(c) Drag link
(d) Steeringjarm
(e) Left spindle and kingpin
(f) Left tie rod arm
(g) Tie rod
(h) Right tie rod arm, spindle and kingpin
(i) Steering stops 2. Steering shaft 3. Steering gear.
ww
4. Define instantaneous centre of a vehicle.
w.E asy En gin ee
During turning or moving the vehicle on a curved path, the wheels should follow a true radius or definite radius with each of the radius originating from its centre. The circles should be based on the common centre known as instantaneous centre to avoid skidding of wheels.
5. How is steering geometry defined?
Steering geometry is the angular representation and obtaining relationship between front wheels. 6. What is Ackermann steering principle?
rin g.
[Anna Univ. May'09J
This linkage is based on a four bar chain with two longer links of unequal lengths
net
with two shorter links of equal lengths. The mechanism is simple. When the vehicle is running along a straight path, the longer links will become parallel and each of the shorter links will be inclined at an angle exto the longitudinal axis of the vehicle.
7. Define camber, castor and toe-in witlt sketches. [Alina Univ. Nov'05, Apr'06 & May'14J Camber: When the front of the vehicle is viewed, the angle between centre line of the tyre and vertical line is called camber. Castor: Tilting the kingpin axis either forward or backward from the vertical line is j
known as castor. Toe-in: The wheels are said to be toe in when the distance A is lesser than B. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
III'm
Automobile Engineering Wheel r----WheeICamber •
'
Kingpin
,
.
I ,
Front axle '3..
ww w.E
Vertical
(a) Camber
(a) Castor
)~.~----
asy E o
i \
Front of vehicle
A
Main axle
ngi
----~~~l
o
nee
B
(c)Toe-in
rin
Figure 4.106 Camber, Castor and Toe-in 8. Define the terms toe-out.
g.n e
{Anna Univ. May'14}
t
The wheels are said to be toe out when the distance A is greater than B Figure 4.106 (c). 9. Write down any two effects of toe-in and toe-out. Effects of toe-in: 1. Tyre slip : 2. Tyre Wear on outside of the tread 3. Tyre scrub bend 4. Poor steering stability. Effect of toe-out: It avoids tyre scrub.
Downloaded From : www.EasyEngineering.net
In
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension Systems
[Anna Univ. Dec'13]
10. Why is camber angle provided in steering system?
Camber angle alters the handling qualities of a particular suspension design. Particularly, a negative camber improves the grip when cornering because it places the tyre at better angle to the road, transmitting the forces through the vertical plane of the tyre rather than through a shear force across it. Off-road vehicles such as agricultural tractors generally use positive camber. In such vehicles, the positive camber angle helps to achieve a lower steering effort. For maximum straight-line acceleration, the greatest traction will be attained when the camber angle is zero and the tread is flat on the road. 11. What is meant by wander?
ww
The change of spring height also changes the camber. When the camber is zero,
slight irregularities on the road may occur to change the wheel load thereby changing
w.E asy En gin ee
the direction of the camber effect. This phenomenon is called 'wander'.
12. Note down the effects of castor.
When the top of the kingpin will be backward, the castor angle is positive. The caster angle is negative when the top of the kingpin will be in forward. 13. What is kingpin inclination?
The angle between vertical line and centre of the kingpin or steering axle when
rin g.
viewing is carried out from the front of the vehicle is called kingpin inclination. 14. Mention tile effects of kingpin inclination.
1. Both kingpin inclination and castor give the directional stability.
net
2. Particularly steering effort is reduced when the vehicle is stationary. 3. Tyre wear also is greatly reduced.
4. During turning of the Wheel,this inclination raises the vehicle. By this, a force is exerted on wheels to straighten up automatically after completing its turn. I
..
....
5. The kingpin inclination should be 'equal on both sides. If it is greater on one side, the vehicle will be pulled to the side having the greater angle. , I
.-
15. What are the effects of combined angle and scrub radius? Effects of combined angle: If the scrub radius is not equal to zero, a torque acted on wheel turns away from straight ahead position.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lam
Automobile Engineering
Effect of scrub radius: (a) When the scrub radius is negative, the wheel is caused to toe-in. (b) When the scrub radius is positive, the wheel is caused to toe-out. (c) A large scrub radius will cause a greater torque required to turn the wheel. So, higher loads on the steering linkage and suspension components act. It results a greater wear of steering linkage and unequal braking on the front wheels.
16. What is meant by centre point steering? When the scrub radius becomes zero, the wheel is kept in a straight position without any toe-in or toe-out This position is known as centre point steering.
ww w.E
17. Name tile types of steering gears. 1. The pitman-arm type, and
2. The rack-and-pinion type.
asy E
18. List out tile different types of steering gear system. 1. Worm and roller 2. Worm and sector 3. Cam and roller 4. Cam and peg 5. Cam and turn lever 6. Screw and nut 7. Recirculating ball 8. Worm and ball bearing
ngi
nee
{Anna Univ. Dec '14)
rin
g.n e
t
9. Rack and pinion.
19. Define overall steering ratio. The number of degrees through which the steering wheel is turned is divided into number of degrees when the front wheels turn. It is known as overall steering ratio.
20. How is steering ratio determined? The steering gear assembly not only steers the front wheels but also it reduces the steering wheel turning effort by increasing the output torque. The reduction ratio is known as steering gear ratio.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
Systems
_
In other words, the ratio of the output force to the input force applied is known as steering ratio. 21. What is meant by the term turning radius? The radius of the circle on which the outside front wheel travels when the front wheels turn to their extreme outer position is called turning radius. 22. Define slip angle. The angle between wheel inclination and path followed by the wheel is known as slip angle.
ww
23. How are oversteer and understeer defined witlt respect to slip angle? When the slip angles of front wheels are greater than rear wheels, it is the condition of understeer;
w.E
asy
When the slip angles of front wheels are less than rear wheels, it is the condition of oversteer.
En
24. Wluu are the disadvantages of manual steering over power steering?
gin eer
1. It is smaller and simpler in engines on cars.
2. High-pressure tyres should be used in case of cars. The smaller steering ratio is required to steer these cars. So, it needs less turns of the steering wheel to move to the desired distance.
ing
25. Specify the methods of power steering. 1. Integral type, and 2. Linkage type.
.ne
t
26. State the functions of thefront axle. 1. It takes the weight of the front of the vehicle. 2. It provides a better steering action. 3. A spring transmits cushion effect to the vehicle. 4. It controls the ride through shock absorber. 5. It takes the braking system. 6. It transmits power to front wheels in case of four wheel drive. 7. It carries both hub and wheels.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lam
Automobile Engineering
. i1
27. What is steering knuckle pin? The centre portion of the front axle is provided a downward sweep to maintain the chassis height low. The steering spindle and steering knuckle assemblies are pinned at ends of axle in order to permit the wheels to be turned by the steering gear. This pin is known as kingpin or steering knuckle pin. [Alina Univ. May'12/
28. Draw tit least any two types 0/ stub axles. Kingpin Front
ww w.E (a)
Stub axle :I:
asy E
Figure 4.107(a) Elliot stub axle
29. List out the types
0//rollt
axle.
I. Live front axle.
2. Dead front axle. 30. Name the types of stub axles.
I.-_---'.+..:._ . .....J Thrust washer
Figure 4.107 (b) Reversed Elliot
ngi
[Anna Univ. Apr'06 & May'15/
nee
1. Elliot
2. Reversed elliot
rin
[Anna Univ. May'l1/
3. Lamoine 4. Reversed lamoine.
g.n e
t
31. Define suspension system. The chassis of vehicle is connected to the front and rear wheels through the medium of springs, shock absorbers and axles. All parts perform the function of protecting the parts from shocks are known as suspension system, 32. Describe the various components of suspension system with its functions briefly. I. Springs neutralize the shocks from the road surface. 2. Dampers are called shock abs ..bers to improve a riding comfort by limiting the free oscillation of springs. 3. Stabilizer is called sway bar or am. 'rJllbar to prevent lateral swaying of the car. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
rrm
Systems
4. A linkage system holds above components to control the longitudinal and lateral movements of wheels. 33. Wluu tire the functions of suspension system? I. To eliminate road shocks from transmission to vehicle components. 2. To maintain stability of the vehicle in pitching or rolling while in motion. 3. To safeguard occupants from road shocks. 4. To obtain good road holding while driving, cornering and braking. 5. To keep proper steering geometry 6. To obtain particular height to body structure.
ww w.E
7. To resist torque and braking reactions. 8. To keep the body of the motor vehicle on even keel while traveling over rough round or when turning in order to minimize rolling, pitching or vertical
asy E
movement tendency.
34. Wtuu are the requirements of suspension system?
ngi
1. It should have minimum deflection.
nee
2. It should be of low initial cost.
3. It should be of minimum weight.
rin
4. It should have low maintenance and low operating cost. 5. It should have minimum tyre wear. 35. How sprung am/unsprung
g.n e
weights are defined? Write down the relation between
sprung and unsprung weights.
t
The body of vehicle is supported by springs. The weight of the body is supported by springs called sprung weight. Unsprung Weight is the weight of everything between springs and road in a portion of weight of springs itself. :. Sprung weight = Total weight of vehicle - unsprung weight. 36. What are the effects of unsprung weight? The unsprung weight of a wheel controls a trade-off between a wheel's bump and its vibration isolation. Bumps and surface imperfections in the road cause tyre compression which induces a force on the unsprung weight. The unsprung weight
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lam
..Automobile Engineering,
J
responds to this force with movement of its own. For short bumps, the arnoun movement is inversely proportional to the weight. A lighter wheel which readily moves in response to road bumps will have more grip and more constant grip when tracking over an imperfect road. Due to this, lighter wheels are sought especially for high-performance applications. In contrast, a heavier wheel which moves less will not absorb as much vibration. The irregularities of the road surface will transfer to the cabin through the geometry of the suspension. Therefore, ride quality and road noise are deteriorated. For longer bumps, wheels follow a greater unsprung mass which causes more energy to be absorbed by the wheels and it makes the ride worse. 37. What are the different types of movements occurred when the vehicle is in motion?
ww w.E a (a) Bouncing
(b) Pitching
(c) Rolling
(d) Yawing.
syE
38. Define 'bouncing' and 'pitching'.
ngi
The vertical movement of a complete body is called bouncing. In other words, the complete body of the vehicle moves up and down, then it is called bounce or bouncing.
nee r
ing
Rocking chair action or rotating action about a transverse axis through the vehicle parallel to ground is known as pitching. 39. Define 'Rolling'.
.ne
t
The movement of the wheel about longitudinal axis produced by centrifugal force when cornering is known as rolling. It results a body rolling in the lateral direction which means side-to-side direction. 40. Define 'Yawing'. Yawing is the movement of the car's longitudinal centerline to the right and left in relation to the car's center of gravity. On roads, where pitching occurs, there will be a chance to occur yawing. 41. What are different types of spring system used in suspension of automobiles? 1. Steel springs a) Leaf springs
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
Systems
b) Tapered leaf springs c) Coil springs d) Torsion bar 2. Rubber springs a) Compression springs b) Compression-shear springs c) Steel reinforced springs d) Progressive spring e) Face shear spring
ww w.E 3. Air springs
a) Bellow type springs b) Piston type springs
asy E
4. Plastic springs
42. Mention the various types of leaf springs used in automobiles. 1. Semi elliptical spring
2. Quarter elliptical spring
ngi
nee
3. Three quarter elliptical spring 4. Transverse spring 5. Full elliptical spring 6. Platform type spring. 43. How are leaf springs lubricated?
rin
g.n e
t
Leaf springs are lubricated by feeding lubricants form a centre grease nipple through grooved oil ways or by spraying oil on the leaves. 44. Define master leaf. The longest leaf is called master leaf 45. Define shackle pin. The spring eye is mounted to the frame by a pin known as shackle pin. 46. Write short notes on helper springs. Where fluctuations are in their loads, helper springs are used in trucks and many other vehicles. It is mounted inside the main spring. If the load is less, the main spring Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Irnm
Automobile Engineering
is operated. Both the main and helper springs are operated when the load exceeds a certain value. Helper springs are mainly provided on rear suspension. When the load increases on the road wheel, the helper spring isjust made to touch ends of the helper spring. 47. Write down the characteristics of helper springs. 1. Due to the springs having enough rigidity to hold the axis in the proper position, they are required. 2. Controlling of own oscillation through inter-leaf friction is performed. 3. These springs have durability in heavy-duty applications.
ww
4. Due to inter-leaf friction, it is very difficult to absorb minute vibrations from the road surface. Hence, leaf springs are more suitable for large commercial
w.E
vehicles which can carry heavy loads regarding high durability.
asy
48. What is the purpose of the coil spring in rear end suspension? The coil spring controls the suspension travel and it provides wide height control.
En
49. Write down the characteristics of coil spring.
gin eer
I. The energy absorption rate per unit of weight is greater when compared to leaf springs. 2. Soft springs can be coiled.
ing
3. Due to no inter-leaf friction with leaf springs, no control of oscillation is
.ne
necessary by the spring itself but shock absorbers are necessary.
t
4. Due to no resistance to lateral forces, linkage mechanisms to support the axle such as suspension arm, lateral control rod, etc. are required. 50. What is meant by torsion bar? A torsion bar is a steel bar which is operated by both twisting and absorbing shear stress only. 51. State the advantages of a torsion bar. I. It is lighter as compared to leaf spring. 2. It occupies less space. 52. State the advantages and disadvantages of a torsion bar.
[Anna Univ. Dec'12j
Advantages: 1. This spring needs less space. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
"lOt'
Steering, Brakes and Suspension Systems
2. It is lighter than leaf spring system. 3. This system provides very neat and compact design. 4.
In some cases, the torsion tubes are used instead of torsion bars.
Disadvantages: I. It does not take the braking or driving trust so that addition linkages have to be provided. 2. The absence of friction force, the damping necessity is used to control the vibrations produced due to road shocks. {Anna Univ. Dec'12J
53. Define cornering force and cornering power.
ww w.E a
All vehicles experience cornering force every time they tum. Cornering force or
side force is lateral (i.e., parallel to the road surface) force prcduced by a vehicle tyre during cornering. Cornering force is generated by tyre slip which is proportional to slip angle at low slip angles. Slip angle describes the deformation of the tyre contact patch and this deflection of the contact patch deforms the tyre in a fashion akin to a
syE
spring.
ngi
Tyre cornering power can be defined by the relationship between tyre lateral
nee r
forces and tyre slip. It depends on factors such as steering input and road conditions as well as vehicle conditions such as vehicle loading, tyre tread wear, tyre damage and tyre inflation pressure. 54. Name tile different types of rubber springs. a) Compression springs b) Compression-shear springs
ing
.ne
t
c) Steel reinforced springs d) Progressive spring e) Face shear spring. 55. How does rubber spring absorb shocks during running of the vehicle? Rubber springs absorb vibrations by the internal friction generation if they are stretched by an external force.
56. State tile advantagesof rubbersprings. I. Greater energy per unit weight than the steel can be stored. So, the springing systems are made more compact. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'U",I
Automobile Engineering
2. The rublYerhas ~80d vibration damping properties. 3. The absence of squeaking is always present in steel springs. 4. The number of required bearings is low for the rubber suspension system having longer life. 5. Rubber is more reliable, So, a rubber suspension cannot suddenly fail similar to metal springs. 57. Define air springs. The springs which have elasticity or "springiness" when it is compressed are known as 'air springs '.
ww
58. Classify air suspension system.
w.E
a. Bellow type air suspension
b. Piston type air suspension
asy E
c. Elongated bellows air spring. 59. Write down the advantages of air suspension system.
ngi
1. A variable space for wheel deflection is used for the optimum use.
nee rin
2. Change in head lamp alignment due to varying loads is completely eliminated. 3. The spring rate varies with loading and unloading thereby reducing dynamic loading. 60. Write down the characteristics of air springs.
g.n et
1. They are softer if the vehicle is not loaded. Simultaneously, the spring constant
increases when the load is increased by increasing the air pressure inside the chamber. So, it gives optimum riding comfort when the vehicle is lightly loaded and fully loaded conditions. 2. The height of the vehicle is kept constant though the load variation by varying the air pressure. 61. Write a short on hydro elastic suspension. The hydro elastic suspension system intends to improve the vehicle's resistance to pitch, the tendency of the body to oscillate in a to and fro direction when the front springs are compressed and rear springs are simultaneously expanded. The continuous forward and backward pitching motion provides a most uncomfortable ride which
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Systems
may become serious when the frequency of vibration of fr~ml and rear springs is same. 62. What are the advantages of independent suspension systemi: 1. Unsprung weight is reduced with improved ride and better road holding while turning and braking. 2. Instead of tilling the frame and body, it is kept horizontal and wheels are vertical when encountered a road bump. 3. The wheels are sprung independently but springing movement of one wheel is not transmitted to the other side.
ww w.E a
4. Both the wheel wobbling and steering tramp are reduced. 5. Greater resilience is provided with better springing action than most rigid axle vehicles.
6. The independent accommodation.
front
suspension
syE
63. Classify suspension system. (i)
gives
Front end suspension
more
space
for
engine
ngi
a. Independent front suspension b. Rigid axle front suspension (ii) Rear end suspension
nee r
a. Longitudinal leaf spring rear suspension b. Transverse leaf spring rear suspension c. Coil spring rear end suspension
ing
.ne
t
64. Classify independent from suspension system. 1. Longitudinal suspension 2. Transverse suspension 3. Sliding suspension 4. Parallelogram type suspension 5. Strut and link type suspension 6. Trailing link type suspension 7. Vertical guide suspension.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
,
65. What are the advantages offront wheel independent suspension? 1.
Since the independent suspension has less unsprung mass, road-wheels follow the contour of the road irregularities up to higher speeds than for the heavy rigid-axle-beam suspension.
2.
An anti-roll bar if it is used along with the independent suspension provides the necessary resisting stiffness to oppose body roll during cornering. Therefore, softer springs can be employed for normal vertical loads.
3.
The engine and chassis structure can be lowered so also the centre of the car in order to move the engine forward to provide more room for passengers.
ww 4.
Independent suspension usually lowers the roll centre. So, the body rolls before the wheels break away from the road providing a warning to the driver.
w.E
66. What are the advantages of Mac Pherson strut type oJ suspension?
asy
1. It provides an increased road safety.
En
2. It improves ride comfort and light and self-stabilizing steering. 67. What are the advantages of Wishbone type.suspension?
gin eer
I. Better cornering characteristics are obtained.
2. The track length remains constant although a slight change in camber takes place which is better for tyre life.
ing
.ne
68. What are the disadvantages of Wishbone type suspension?
I. The wheels on comers lean outwards with the body resulting in undesired steering effects. 2. Variation in tracks length resulting in adverse tyre wear.
t
69. Classify independent rear suspension system. I. Longitudinal leaf spring rear end suspension 2. Transverse leaf spring rear end suspension 3. Coil spring rear end suspension. 70. What is the disadvantage of having rigid axle suspension?
[Anna Univ. May'14}
I. Running comfort is poor due to unsprung weight. 2. Vibrations and oscillations occur rather easily since movements of left and right wheels mutually influence one another.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
,.,N.
Systems
71. What are the purposes of shock absorbers? (i)
To control the vibrations on springs.
(ii) To provide comfortable ride. (iii) To act flexible and to be rigid enough. (iv) To resist the unnecessary motion of the spring. 72. What are the main/unctions of the shock absorber? 1. To control the quick bouncing of the wheel. 2. To control the slow bouncing of the body in the suspension spring.
ww w.E a
3. To keep all the four wheels on the road during a tum at high speed.
73. Classify shock absorbers. 1. Mechanical shock absorber (Friction type)
2. Hydraulic shock absorber
syE
Again the Hydraulic shock absorbers are further divided into: (i)
Van type
(ii) Piston type
a. Single acting b. Double acting (iii) Telescopic type.
ngi
nee r
74. Mention the advantages of telescopic shock absorber.
ing
.ne
t
1.
Large amount of energy is dissipated due to large volume of fluid displaced without causing a high temperature rise.
2.
There is no wear development in the damper with the absence of connecting arm pivots.
3.
The applied force is increased when compared to indirect acting type. Low fluid pressure due to fairly large piston area is occurred with reduced levers.
4.
The leakage is less due to low pressure and absence of the rotating shaft entering the reservoir.
75. Give a brief note
011
damper.
[Anna Univ. May'08j
Shock absorbers or dampers will not absorb road shocks efficiently if the suspension springs are highly rigid. They will be continuously vibrated for a longer
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'I'Mi
Automobile Engineering
time if springs,are sufficiently flexible. To overcome this difficulty, a system having compromise between flexibility and stiffness should be used. Shock absorbers are used as a part of the suspension system. They provide more resistance to the motion of the spring and road wheel in order to damp out vibrations. 76. What are the different types of damper used in shock absorber? {Anna Univ. May'12) (i) Pneumatic damper (ii) Hydraulic damper
ww
(iii) Mechanical spring type damper.
w.E
77. Write down any two differences between springs and shock absorbers with respect to itsfunctions. S. No. 1.
2.
asy E Springs
Shock absorbers
It is connected between wheels and vehicle frame.
It is connected between axle and
ngi
lower end of the chassis frame.
nee rin
It acts as a cushion load shock, The shock absorber provides to keep the vehicle body levelled resistance to the motion of the up over uneven surfaces and absorb
driving
and
springs and road wheels for
g.n et
braking damping out vibrations. It is
torque loads or stresses and also done
for
several
complete
to resist the body tilting and
oscillations thereb~ resulting in
rolling on corners and bends.
discomfort to the passengers.
78. Define "anti-roll bar".
{Anna Univ. May'll)
Stabilizer or a sway bar is used in all independent suspension to decrease the tendency of the vehicle to roll or tip on either side when making a turn known as anti-roll bar. 79. What is aframe stabilizer? Aframe stabilizer is a device designed to resist any tendency of vehicles to dip on either sides and resist centrifugal force which is the cause of slipping on curve.
Downloaded From : www.EasyEngineering.net
--------
--
- -
Downloaded From : www.EasyEngineering.net
"'dI
: Steering, Brakes and Suspension Systems
80. Define braking system.
_I
The mechanism which is used to slow and stop the vehicle is known as bra, system. In other words, the total system starting from brake pedal or lever to brake shoe is known as braking system. 81. What does stopping distance mean? The distance required to stop a vehicle is known as stopping distance. The distance required to stop a vehicle is proportional to the square of speed at which brakes are applied. 82. What are the factors affecting the stopping distance?
ww w.E
The stopping distance depends on the: I. grip between the tyre and road surface.
2. tyre tread condition.
asy E
3. tyre inflation.
4. nature of road surface. 83. Define stopping time.
ngi
nee
It is the duration of brake applied to a complete stop. 84. Define braking efficiency.
rin
It is defined as the rate at which the braking system brings a vehicle to 'rest . from a certain road speed known as braking efficiency. 85. State the need for brakes. 1. To stop or slow down the vehicle at the will of the operator-
g.n e
t
2. To control the vehicle descending a hill 3. To keep the vehicle in a desired position even in rest. 86. What is theprinciple of braking system? In this system, the kinetic energy is converted into heat energy due to friction between two mating surfaces of brake lining and brake ,~rum. Then, the heat dissipated into the atmosphere. 87. What are the requirements of braking system? "T.
I. It should have good anti-fade characteristics. 2. It should be consistent with safety.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
le'MiI
Automobile Engineering
3. It should not be skidding while applying brake. 4. It should have a better cooling system. S. It should be strong enough to stop the vehicle with in a minimum distance. 6. It should have less weight. 7. It should be reliable. 8. It should be easy to adjust for a proper maintenance. [Anna Univ. Dec'13J
88. What causes vapour lock in a braking system?
The condition that causes vapour locking in a brake system is overheating of the fluid due to frequent brake application. Although brake fluids are designed to
ww w.E
work at extreme temperatures above 2S0°C but still as the age of brake fluids goes on increasing, it starts loosing its properties and hence, under high pressure and temperatures vapours are developed by applying brakes.
asy E
[Anna Univ. Nov'08J
89. List tile different types 0/ brakes available. 1. According to the applications
ngi
(i) Service or running or foot brake
nee
(ii) Parking or emergency or hand brake 2. According to the number of wheels (i) Two wheel brakes
(ii) Four wheel brakes. 3. According to the brake gear (i) Mechanical brake
rin
g.n e
t
1. Hand brake 2. Foot brake (ii) Power brake 1.
Booster
2.
Non-booster
4. According to construction (i) Drum brake (ii) Disc brake.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
t"i'
Steering, Brakes and Suspension Systems
[Anna Univ. Dec'14]
90. Compare disc and drum brakes. Description
Drum brake
Disc brake
1.
Life of friction material.
reasonable is It (about 15,000 km).
It is reasonable (about 25,000 km).
2.
Visibility of wear from It is not possible.
S.No.
outside.
It is inferior.
It is inferior.
3.
Heat dissipation.
4.
Replacement of friction It is troublesome and time consuming. material.
5.
Weight.
ww w.E
It can be seen at a glance.
It is easy and rapid.
It is lighter (by 25%)
It is heavy.
91. What are different mechanisms of brake actuation?
asy E
(a) Mechanical brakes (b) Hydraulic brakes (c) Electric brakes
(d) Vacuum brakes (e) Air brakes.
ngi
nee
92. What are the factor affecting the coefficient offriction?
rin
g.n e
The value of Jl can be unity but it is practically less than unity. It depends on the following factor. 1. Condition of road - dry, wet, muddy, snowy etc.
t
2. Type oftyre trade 3. Tyre inflation- correct, over, under. 93. What isfading of brakes? Fading of brakes means that the friction is decreased between brake drum and brake lining due to regular use of brake. 94. What is brakes compensation?
{Anna Univ. May'12J
When brakes fade two things happen. First, the pads are heated up to the point and the friction generated is reduced. It can be caused by resins or other ingredients breakinz down. Second. the temoeratures can cause the brake fluid to boil. When the
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
,ell4:J
Automobile Engineering
fluid boils, it will change to oil vapour. Oil vapour is compressible. Both conditions may cause a spongy brake pedal. Brake fade compensation the temperature
is more than a bunch of algorithms which estimate
in the brake system by using the applied time, brake pressures,
acceleration/deceleration
etc. When the computer determines the pads or fluid have
exceeded a certain threshold, it will close some valves and turn on ABS pump when the drive hits the pedal. It expands the pressures at wheels and prevents the pedal from going to the floor.
95. List tire various types of drum brake.
ww w.E a
I. External contracting brakes
2. Internal expanding brakes.
96. State tirepurposes of a master cylinder. I" The required hydraulic pressure is built up to operate the system.
syE
2. It maintains a constant volume of fluid in the system.
ngi
3. To bleed or force air out of the brake line and wheel cylinder, a pump i~ used.
97. List out the various parts of a master cylinder. I.
Brake fluid reservoir
2.
Cylinder or compression chamber
3.
Piston assembly
4.
Check valve or control valve
s.
Piston return spring.
nee r
ing
.ne
98. What are tire characteristics of hydraulic brakefluid?
t
I. It should remain fluid at low temperature. 2. It should not corrode or rust metallic parts in the brake system. 3. It should not vapourize at high temperature encountered in actual service. 4. It should act as a lubricant to the moving parts inside the system. S. It should mix satisfactorily with other makes of hydraulic brake fluids. 6. It should retain all its characteristics for a maximum long period. 7. It should not soften the,rubber'parts'used
in the hydraulic brake system.
8. It should be non-compressible.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
Systems
99. Mention anyfour advantages of hydraulic brakes. 1. The system is mechanically very simple in construction due to the absence of brake roads, joints etc. 2. This system gives equal braking effort at all four wheels when compared to mechanical braking system. 3. All wheel brakes are forced to act together without any consideration
In
individual adjustments. 4. It gives an increased braking effort. S. It gives equal pressures at all points.
ww
6. It is a self-compensating
system.
w.E asy En gin ee
100. Note down the advantages of air brakes. I.
It is more powerful when compared to other brakes.
2.
The air brake parts are easily located where the chassis design making is simple.
3.
The compressed air can be used for tyre inflation wipers, hom and other accessories.
101. What are the special types of spot type disc brake? I. Fixed caliper (or) Swinging caliper type 2. Floating caliper, and 3. Sliding caliper type.
rin g.
102. Distinguish between disc brake with drum brake. S.No.
6.
Description
Drum brake
Disc brake
l.
Heat dissipation
Better
Inferior
2.
Braking effect
Consistent
Inconsistent
3.
Nature of wear
Uniform
Non uniform
4.
Weight
Lighter
Bulky
5.
Water and dirt collection
Self-cleaning
Accumulates
Shape of friction lining
Straight shape
Curved shape
net
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IIIiii
Automobile Engineering
103. What are the advantages of grdling brakes? 1. They can easily be adjusted without jacking up the vehicle. 2. The driver effort can be minimized. 3. It uses a mechanical compensator. 4. It provides a self-centering effort. 104. What is meant by bleeding of brakes? 1. The process of removing air bubbles present in the braking system is called bleeding.
ww w.E
2. When any part of hydraulic line is replaced, air will be trapped into the system. Due to compressed air, the effort of brake pedal goes waste in applying brakes. Unless air from the system is completely removed, the brakes will not function properly.
asy E
105. What is the minor and major adjustment of brakes? 1. Minor adjustment refers the adjustment of brake shoes to compensate lining
ngi
wear without removing the wheel.
nee
2. Major adjustment is installation of new shoes or relining the old shoes. 106. Define servo brakes.
rin
Mechanism which assists the driver's effort for applying brakes is called servo
g.n e
mechanism. Servo means self-energization. Servo Brakes generally used when the vehicle load is above 3 tonnes. 107. What is the purpose of brake shoe adjustor?
t
The purpose of adjustor is to compensate the wear of brake leather due to regular use of vehicle. 108. What are the advantages disc brake systems? I. Better stability because of uniform pressure distribution over pads. 2. Less bearing load on the application of the brake. 3. Higher temperature does not affect disc pads. 4. Simple design of brake adjuster. 109. What are the disadvantages disc brake systems? I. It is costlier than drum brakes. Downloaded From : www.EasyEngineering.net
..
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension
,
Systems
2. Complete protection to the disc from the road is to be provided.
3. Higher temperature causes evaporation of brake fluid and deterioration of seals. 4. The pads wear off more quickly than the brake shoe linings of the drum type. 110. What is tire locking of witeel during braking? When the braking force is more than force of adhesion, then the wheel is stopped and started slipping on the road. The stopping of wheel by braking is called locking.
ww w.E
111. Whichfactors generally effect braking? I. Radius of brake drum and diameter of wheel.
2. Area of brake lining and amount of pressure applied.
asy E
3. Coefficient of friction.
112. Writefew advantages of hydraulic system of braking.
ngi
1. There is less friction in hydraulic system of braking because there are fewer joints as compared to mechanical brakes. 2. System is self-lubricating.
nee
3. In hydraulic system equal pressure is in every circuit. 4. System is more flexible than mechanical system.
113. What are the disadvantages hydraulic brake systems?
rin
g.n e
t
I. Complete braking system is liable to be affected if any fault causing pressure loss or breakage of a pipe to one wheel occurs.
2. The brake shoes are liable to get ruined if the brake fluid leaks out. 114. What is a leading shoe? A leading shoe is the tip dragged along the drum even when there is no brake force. Due to this reason, leading shoe fades more than trailing shoe. 115. What are the merits of air brakes? I. It is more effective and heavy effort at brakes. 2. It employs only air as the working medium which is easily available. 3. It is easy to store air at high pressure.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
It• .,
Automobile Engineering
4. It provides heavy braking effect and used in heavy vehicles and trucks. 116. What is the function of brake valve? Function of the brake valve is to control the intensity of the braking system in air brakes. It is operated by either a foot treadle or push rods linkage. 117. Define power brake. A brake on an automobile which magnifies a small force applied to the brake pedal into a proportionately larger force applied to slow or stop the vehicle is called power brake. 118. Mention some of the power-assisted braking system.
ww w.E a
1. Vacuum assisted hydraulic brakes
2. Compressed air brakes or pneumatic brake.
119. What are the troubles shooting in brake system?
syE
1. Loss of efficiency in braking:
(a) Brake lining does not work properly if oil is entered into brake drum.
ngi
(b) Due to defective master cylinder, it needs overhauling.
nee r
(c) If air enters into braking system, the braking does not work properly. (d) Brake lining is fade due to regular use or worn out friction lining.
2. Brakes overheating:
ing
.ne
Overheating of brakes occur while we drive a vehicle ascending down the hill or due to faulty binding material used for brakes binding. 120. What is the need of anti/ock braking system?
t
{Anna Un;v. May'09}
The problem of skidding reveals the overwhelming weakness of all motor vehicle braking systems. They depend strongly on the coefficient of static friction between tyre and road. If the tyre momentarily loses its adhesion to the road while brakes are applied, the friction of brakes will be against drums or rotors which lock the wheel solidly and the tyre begins skidding across the road. In addition, when the front wheels are in this condition, they cannot be used to steer the vehicle irrespective of the angle of front wheels and the vehicle continues to skid whatever be the direction of its momentum until either the driver releases brakes or the vehicle collides with solid. Antilock Braking Systems (ABS) is a form
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
of electronic braking which helps a driver to control the vehicle under heavy braking by preventing wheels from locking up.
121. List down the components of ABS system. 1. Wheel speed sensors (pickup and exciter)
2. Electronic Control Unit (ECU) 3. Hydraulic modulator valves 4. Pump motor and accumulator. 122. State the function electronic conlTol unit in ABS.
ww
ABS electronic control unit is a microprocessor that functions such as an
engine control computer. ECU processes all ABS information and signal functions.
w.E asy En gin ee
It receives and interprets voltage pulses generated by the sensor pickup as the exciter teeth pass by and it uses this information.
123. What is thefunction of hydraulic modulator valve?
ABS modulator valves regulate the fluid pressure to the brakes during ABS action. When not receiving commands from ECU, the modulator valve allows fluid to flow freely and it has no effect on the brake pressure. 124. What are the types of anti-lock brakes? 1. Four-channel, four-sensor ABS
2. Three-channel, three-sensor ABS 3. One-channel, one-sensor ABS.
rin g.
125. State the advantage..~of ABS.
net
Although ABS will not decrease a vehicle's stopping distance compared to an identical vehicle without ABS, the shortest distance in which a vehicle can be brought to rest is achieved. It is particularly effective in doing this on surfaces which are wet or icy upon which a vehicle is much more likely to skid. The main benefit of ABS is the control that a driver has over the vehicle's steering. In an emergency, the driver of a vehicle equipped with ABS will have a better chance of steering around the obstacle is due to the reduced risk of skidding.' 126. What is meant by traction control?
{Anna Univ. May'15j
The control system which maintains the traction and stability of the vehicle regardless of the road surface condition is known as traction control. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
.E'
Automobile Engineering
4.7. SOLVED QUESTIONS 1. What are the requirements and functions of steering system? Refer chapter 4.1.1 in page 4.2. 2.
Explain the steering principle, its need, functions in detail with proper sketches and [Anna Univ. May' 14]
mention the parts of steering system,
Refer chapters 4.1, 4.1.1 & 4.1.2 in pages 4.1, 4.2 & 4.3 respectively. 3.
Draw the layout of steering system and explain in detail. Refer chapter 4.1.2 in page 4.3.
ww
4.
[An~a Univ. Nov '05]
List down the various components of a steering system.
w.E asy En gin ee
Refer chapter 4.1.2 in page 4.3.
5.
Derive that cot
tP = constant + cos 8.
Refer chapter 4.1.4 in page 4.7. 6.
Explain Davis steering gear mechanism. Refer chapter 4.1.6 in page 4.11.
7.
What is meant by steering geometry and explain anyone type of steering gear box.
rin g.
[Anna
Univ. May '08 & Dec '08]
Refer chapter 4.1.8 in page 4.12 for steering geometry and chapter 4.1.11 in page 4.21 for type of steering gear box. 8.
What are the different types of steering gears used in an automobile?
net
[Anna Univ. Apr '06] Refer chapter 4.11 in page 4.21. 9.
Explain the working of cam and lever type steering gear with a neat sketch. Refer page 4.23.
10. Sketch a recirculating ball type steering gear and explain its working principle. [Anna Univ. Nov '07 & May' 12] Refer page 4.22. 11. Explain the rack and pinion steering system of an automobile.
[Anna Univ. Apr '05]
Refer page 4.23.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Srakes and Suspension
t'tlOj
Systems
12. Describe the phenomena of under steering and over steering. Refer chapter 4.1.14 in page 4.29.
13. Sketch and explain a typical power steering gear box and compare it with ordinary steering system. [Anna Univ. May '09 & May' 11] Refer chapter 4.18 in page 4.33. 14. Write short note on (i) Steering gear mechanisms Refer chapter 4.1.4 in page 4.7.
ww w.E
(ii) Steering geometry Refer chapter 4.1.8 in page 4.13.
(iii) Power steering.
asy E
[Anna Univ. Dec' 13]
Refer chapter 4.1.18 in page 4.33.
ngi
15. Mention the various trouble shooting for steering system.
nee
Refer chapter 4.1.19 in page 4.37. 16. Write short notes on wheel alignment.
Refer chapter 4.1.9 in page 4.19.
rin
g.n e
17. Explain the four parameters of wheel alignment with neat sketches. [Anna Refer chapter 4.1.19in page 4.19.
Univ. Dec'14J
t
[Anna Univ. May '08 & Dec '08]
18. Illustrate the types of front axle. Refer chapter 4.2.3 in page 4.46. 19. What are the objectives of suspension system? Refer chapter 4.4.2 in page 4.49.
20. Explain the elements, types and stages ofa suspension system. [Anna Univ. Dec'J3] Refer chapter 4.4.4 in page 4.50. 21. Give short note on leaf spring suspension system.
[Anna Univ. May '08]
Refer chapter 4.4.8 in page 4.55.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'-4
'.-
Automobile Engineering
22. Explain the various suspension systems available and discuss anyone type. [Anna Univ. Dec '08]
Refer chapter 4.4.7 in page 4.54. 23. Describe the construction of helper springs. Compare its advantages over coil springs. Refer chapter 4.4.9 in page 4.58. 24. With an aid of neat sketch, explain the working principle of pneumatic suspension system.
[Anna Univ. May '15]
Refer chapter 4.4.13 in page 4.63.
ww
25. With a neat diagram explain the construction and operation of a shock absorber.
w.E asy En gin ee
~Anna Univ. Apr '06]
Refer chapter 4.4.15 in page 4.68.
26. Explain the operation of a telescopic type shock absorber with a sketch. [Anna Univ. Nov '05 & May '09]
Refer page 4.69.
27. Explain independent suspension system with neat sketches.
[Anna Univ. May'14]
Refer chapter 4.4.17 in page 4.71.
rin g.
28. List out the advantages offront independent suspension system.
[Anna Univ. Apr '05 & Nov '07]
Refer page 4.77.
net
29. What is an interconnected suspension system? Discuss the mam constructional features of any such system and also its working.
[Anna Univ. Dec' 12]
Refer charter 4.4.20 in page 4.82. 30. What is antiroll bar? Explain. Refer chapter 4.4.21 in page 4.84. 31. Obtain the trouble shooting for springs and suspension system. Refer chapter 4.24.22in page 4.86. 32. Write a short note on stopping distance, time and braking efficiency. Refer chapter 4.5.2 in page 4.91.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Steering, Brakes and Suspension Systems
'Wi
33. Explain about the theory of braking system. Refer chapter 4.5.3 in page 4.92. 34. Classify brakes. Refer chapter 4.5.5 in page 4.94. 35. Explain the working of disc brake system.
[Anna Univ. Apr '05]
Refer chapter 4.5.7 in page 4.98. 36. What are the significances of brake fluid? Refer chapter 4.5.9.4 in page 4.110.
ww
37. With the aid of a diagram explain the function of the main parts of the master cylinder. [Anna Univ. May '12]
w.E asy En gin ee
Refer chapter 4.5.9.1 in page 4.105.
38. Explain the process bleeding of hydraulic brakes. Refer chapter 4.5.9.5 in page 4.111.
39. Describe the construction and working of mechanical brakes with its sketch. Refer chapter 4.5.10 in page 4.112.
rin g.
40. Explain the operation of hydraulic braking system with neat sketch.
[Anna Univ. Nov'05, Apr '06 & May '08]
Refer chapter 4.5.9 in page 4.104.
net
41. With neat sketch explain the working principle of pneumatic braking system.
[Anna Univ. May' 11]
Refer chapter 4.5.12 in page 4.117. 42. Compare and contrast pneumatic and hydraulic braking systems. [Anna Univ. Dec' 13]
Refer chapter 4.5.12.1 in page 4.119. 43. Explain the construction and working of vacuum servo braking system. [Anna Univ. Nov'07]
Refer chapter 4.5.14 in page 4.121. 44. Discuss the need of ABS in automobiles. Refer chapter 4.5.20.1 in page 4.130. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
lam 45. Explain briefly the each component of ABS. Refer chapter 4.5.20.2 in page 4.131.
46. What is the working principle of antilock braking system? Explain with neat sketch. [Anna Univ. Dec '08, Dec' 12 & May' 15] Refer chapters 4.5.20.3 in pages 4.134. 47. Discuss the various types of ABS with its features. Refer chapters 4.5.20.4 in pages 4.136. 48. Explain
ww
how wheel skidding
is caused and describe
techniques employed to prevent skidding.
the principles of various [Anna Univ. Dec' 12]
w.E asy En gin e-------------------eri ng. net
Refer page 4.129 for causes of wheel skidding.
Refer chapters 4.5.20 & 4.5.22 in pages 4.129 & 4.139 for various techniques employed to prevent skidding which includes ABS & Traction control systems.
49. Mention various trouble shooting for brakes. Refer chapter 4.5.23 in page 4.143.
____________________
END of Unit 4 --------------------------
----------------_.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
UNIT -
5
I
ww w.E
asy
En
gin
eer
Use of Natural Gas, Liquefied Petroleum Gas, Bio-
ing .ne t
diesel, Bio-ethanol, Gasohol and Hydrogen in Automobiles - Engine modifications required Performance,
Combustion
and
Emission
Characteristics of SI and CI engines with these
alternate fuels - Electric and Hybrid Vehicles, Fuel Cell.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources
ww w.E
l:1li I
ALTERNATIVE' ENERGY SOURCES
asy
5.1. INTRODUCTION TO ALTERNATIVE ENERGY SOURCES
En
Alternative fuels are important because of their potential ability to improve both environment and reduce India dependence on imported petroleum. The fuels identified include
gin
eer
two alcohols: ethanol and methanol. Three fuels are gases at normal temperature and pressures, liquefied petroleum gas (LPG), natural gas and hydrogen. In addition, electricity is also used as one of alternating fuels.
ing .ne t
The currently used fuels are hydrocarbons such as petrol, diesel, coal etc. These fuels are for another 75 years. In order to escape from the forth-coming danger, there is a need of searching alternate fuels to meet our minimum energy needs. Fuels such as hydrogen, fuel cells, natural gas hydrates, gasohol and bio-diesel can be utilized in future for another 800 years. Reasons for wing Alternate Fuels in Ie Engines:
.
During 21sl century, crude oil and petroleum products will become scarce and costly to find and produce. At the same time, there will likely be an increase in number of automobiles and other Ie engines. Although fuel economy of engines is greatly improved from the past and it will probably continue to be improved, numbers alone dictate that there will be a great demand for fuel in coming decades. Gasoline will become scarce and costly. This is the main reason for looking for alternate fuel technology.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I..
Automobile
Engineering
1
Another reason of motivating the development of alternate fuels for IC engine is the concern over emission problems of gasoline engines. Alternate fuels can be combineJ with other air-polluting systems. The large number of automobiles is a major contributor to the air pollution in the world. A third reason for alternate fuel development in India and the other industrialized countries is the fact that a large percentage of crude oil must be imported from other countries which control the large number of oil fields. It creates the nation dependency on the foreign currency and makes the foreign trade deficit. 5"2. ALTERNATIVE FUELS
ww w.E
Before proceeding with a detailed description of the composition and physical characteristics of fuels, a brief overview of each fuel is covered below for better understanding about alternate fuels.
asy
In many parts of the world, natural gas is found dissolved in aquifers under normal hydrostatic pressure which is primarily in the form of methane (CH4). The amount of gas dissolved increases substantially with depth. At depth up to 4000 m, 0.5 to 1.5 cubic meter of
En
gin
gas is dissolved per meter of water in aquifers. The level increases from 7 to 20 at the depth of 7000 to 8000 m. It is expected to occur nearly in all-sedimentary basins. When used as a
eer
transportation fuel, natural gas must be at least 88% of methane with the balance being higher
ing .ne t
weight hydrocarbons. Natural gas has lower energy density than conventional fuels but it achieves a comparable range in most vehicles with large fuel storage devices. However, these devices add weight and reduce cargo or passenger capacity. Some transportation and energy experts consider natural gas to be a renewable resource because of its abundant availability; Compressed Natural Gas (CNG) is the dominant form of the fuel used. Liquefied Natural Gas (LNG) is less common. Liquefied petroleum gas (LPG) consists mainly of propane, propylene, butane and butylene in various mixtures. It is produced as a by-product of natural gas processing and petroleum refining. Propane or LPG is used in all major end-use sectors as a heating fuel, engine fuel, cooking fuel and chemical feedstock. The components of LPG are gases at normal temperature and pressure. With moderate pressure (100 to 300 psi), they condense to liquids and make them easy to store and transport. LPG has many of the storage and transportation advantages of liquids along with fuel advantages of gases. Biodiesel is a clean burning alternative fuel produced from domestic, renewable resources such as soybean oil or recycled grease. It can be used in compression-ignition Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative
011 I
Energy Sources
(diesel) engines with few or no modifications. Biodiesel is simple to use, biodegradable, nontoxic and essentially free of sulphur and aromatics. Although biodiesel contains no petroleum, it can be blended in any proportion with petroleum diesel. B20 (20% biodiesell80 % petroleum diesel) is the most common blend and it has significant environmental benefits with a minimum increase in cost of fleet operations and other consumers. Ethanol is a renewable, domestically produced resource derived primarily from corn (although ethanol can be produced from any resource containing starch, sugar or cellulosic material). The fuel can be blended with gasoline, diesel or used as pure fuel. Ethanol has a low energy density than gasoline or diesel but it can achieve a comparable range with large size of fuel tank. The common form of fuel is E85 in which an 85% blend with 15% gasoline (petrol)
ww
is also called Gasohol. In E95, 95% ethanol and 5% diesel blend can be used as a diesel replacement. Ethanol is also used as an additive to gasoline (approximately 10%) and it is
w.E
being tested as an additive to diesel.
asy
Hydrogen is the most abundant element in the Universe but it is rarely found in its uncombined form on earth. When combusted (oxidized), it creates only water vapour and heat as by-products. The exhaust is free from carbon dioxide. While no transportation distribution
En
gin eer
system currently exists for hydrogen transportation use, the ability to create the fuel from a variety of resources including natural gas and its clean-burning properties makes it to a desirable alternative fuel and worthy of consideration.
ing .ne t
Hydrogen has a very low density in its liquefied form. Its density is one tenth of gasoline. It possesses no ignition problem owing to wide 'range of A:F ratio possible.
Though some automakers are testing hydrogen-burning cars, they are not currently feasible or economical. The greatest potential use for hydrogen as a transportation fuel is in fuel cells. A vehicle produces power from electricity when hydrogen and oxygen are combined. A fuel cell is two to three times more efficient than an internal combustion engine. As Juie Verne predicted "Water would be one day as a fuel furnishing in-exhaustible sourer>of energy". It is coming true in the form of Hydrogen. Hydrogen is user friendly and eco-friendly fuel. These fuels can serve us in future. Capability of utilizing these fuels can have a life of another 800 years.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1l1li
Automobile
Engineering
5.3. PROPERTIES OF ALTERNATE FUELS Although a large number of fuel properties influence engine performance, subsets of these properties are reviewed to highlight differences among the petroleum-based and alternative fuels in this section. 1. Energy density:
Conventional gasoline (petrol), oxygenated and reformulated gasoline and diesel which are liquids have higher energy densities. Ethanol and methanol also are liquids at atmospheric pressure and ambient temperature. So, they are stored and handled similar to gasoline though they have less energy density. Methanol has about half the energy .content of gasoline on a volume basis while ethanol has about two-thirds of energy density.
ww
LPG while a gas at normal temperature and pressure is stored in a liquid form under the pressure in the range from 100psi to 300 psi. While butane has higher energydensityper m3
w.E asy En gin ee
than propane, both propane and butane nave lower energy content per m3 than diesel or petrol. Natural gas is stored in the vehicle fuel tanks under pressure as a compressed gas. Even under fairly high pressure, both mass density and energy density of a gas are considerably less than liquid. The energy density disadvantage of CNG is partially resolved with LNG because LNG is simply natural gas which has been liquefied. LNG tanks might be pressurized around 30 psi and hold the liquid at a temperature of -260° F. Sometimes, two to four times more LNG than CNG which can be stored onboard.
rin g.
Hydrogen is less dense than natural gas. For example, hydrogen contains only about onefourth the energy per unit volume of natural gas at the same pressure.
net
Electricity for an electric vehicle is commonly stored in a battery. Today's electric vehicles use lead acid batteries which contain the specific energy of 30.6 watt-hours per kilogram. It is about 1I400th of the energy density of gasoline. As a result, a large number of storage batteries are needed to achieve an acceptable performance. The number of batteries increases the vehicle weight and takes additional space. 2. Volatility: Volatility indicates a fuel's ability to vapourize under different temperature and pressure. It is the property that most affects startup the engine performance and it is of particular interest for SI engines while high volatility is desirable in cold weather. It can cause loss of power or vapour lock in warmer weather. High volatility can also' lead to increased evaporative emissions. Thus, volatility is controlled for both engine performance and emissions. Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
a::a:a
I Alternative Energy Sources
Volatility is not an issue with hydrogen, CNG or LPG. As gases, they do not need to vapourize before burning, making cold-start enrichment or further blending for cold-start reasons unnecessary. The alcohols are less volatile than gasoline when used. in clean form or 85% alcohol blends. The vapour pressure for ethanol is 16 kPa and 32 kPa for methanol. Also, it varies for gasoline between 55 kPa and 103 kPa. Ethanol and methanol are insufficiently volatile for cold-engine starts in spark ignition engines even at moderate temperature. Because of low volatility, the most important performance issues for alcohol fuels are cold start problem and misfiring during warm-up.
ww
3. Octane number: Octane number is a measure a fuel's tendency to knock in a SI engine. Knocking occurs when the gasoline-air vapour mixture prematurely self-ignites as the mixture is compressed during the upward movement of the piston. The self-ignition occurs before the cylinder reaches the top of its stroke thereby causing the cylinder to push against the crank shaft. It
w.E
asy
creates a knock which not only works against the motive power of the engine but also puts a strain on mechanical parts. Generally, the higher is the octane number, the higher will be the
En
gin eer
compression ratio which can be tolerated without knocking. Engines with higher compression ratio have more power and higher efficiencies. The octane number does not cover the full range of factors influencing knock in engines,
ing .ne t
particularly for gaseous fuels such as CNG an,dhydrogen. While all of alternative fuels have better octane ratings than gasoline, natural gas and hydrogen exhibit the strongest antiknock characteristics. More quantities of other constituents in natural gas -such as propane increase the tendency of this fuel to knock while the inert elements such as carbon dioxide and nitrogen decrease the tendency. Natural gas can be used in engines with compression ratio as high as 15:1. Hydrogen has a road octane number greater than natural gas. However, it increases the compression ratio in hydrogen-fueled engines which can be limited because of a tendency to ignite prematurely prior to spark ignition. While not as good as natural gas or hydrogen, LPG has excellent antiknock characteristics. It has a road octane number of 104 allowing dedicated propane vehicles to take the advantage of engines with slightly higher compression ratio than gasoline. Both clean ethanol and methanol have road octane number of 100 which is closer to LPG's octane number. Compression ratio for alcohol fuels might be raised to 13:1.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
I ..
Engineering
I
4. Cetane number: The combustion and ignition characteristics of CI engine fuels are expressed in th_eform of cetane number. Fuels with high cetane numbers have low auto-ignition temperature and short ignition delay times. Since a high octane number means a low cetane number, none of alternative fuels have cetane values high enough to be used alone in unmodified CI engines, However, engine designers are developing modified CI engines for heavy-duty use which include an ignition device and it changes to accommodate the lack of cetane value in these fuels. 5. Heat of vapourization:
ww w.E
Heat of vapourization affects both engine power and efficiency. It is the amount of heat
absorbed by fuel as it evaporates from a liquid state which occurs when the fuel is mixed with air prior to combustion. High heat of vaporization leads to improved cooling ability. The higher cooling during the intake stroke of a SI engine results a denser air/fuel mixture. A denser mixture has two effects. They are (l) allowing for greater power and (2) permitting a greater compression ratio which improves both power and efficiency. However, although a high heat of vapourization improves power and efficiency, it also adds to cold start problems
asy
En
gin
when there is less heat in the air or in the engine to vapourize the fuel prior to spark ignition.
eer
The alcohol fuels have higher heat of vapourization than gasoline or diesel. For methanol, a typical power increase about 10 % from increased air/fuel mixture density has
ing .ne t
been observed in unmodified automotive engines using methanol instead of gasoline. 6. Flame speed:
The speed at which a flame front propagates through a fuel/air mixture can affect engine performance and emissions. High flame speed allows the complete combustion and potentially lean fuel mixtures. While liquid fuels have similar flame speed. methanol is thought to have a higher flame speed than gasoline. However, natural gas has a slow flame speed than other fuels which impairs the spark-engine efficiency unless the spark timing is advanced to compensate. Hydrogen has the highest flame speed of alternative fuels which reduces burning time and heat losses from the cylinder. It improves the thermal efficiency over fuels with lower flame speed. 7. Flame temperature and luminosity: The alcohol fuels distinguish themselves in this area. For alcohol fuels, the flame temperature is lower than gasoline and luminosity is
S0
low that less thermal energy is lost
through conduction or radiation. Low flame temperature also helps to reduce the formation of Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Alternative
Energy Sources
nitrogen oxide. However, low luminosity is a safety issue because the flame is essentially invisible. Hydrogen also is virtually invisible when burning. 8. Auto-ignition temperature: Auto-ignition temperature is a temperature at which the fuel will self-ignite. Self-ignition is a concern in the environment where the fuel might escape and come into contact with hot engine parts. As a safety feature, high auto-ignition temperatures are desirable. Hydrogen has the highest auto-ignition temperature about 1,065°F followed by natural gas, propane, methanol and ethanol. Gasoline and diesel have the lowest auto-ignition temperatures at 495°F and 600°F respectively. Based on this measure, all alternative fuels have an advantage over gasoline. While both natural gas and hydrogen have high auto-ignition temperature, they require different amount of energy to ignite mixtures of fuel and air. Since the natural gas fuel/air mixtures are difficult to ignite, natural-gas-fueled engines must use high-energy spark plugs. Hydrogen fuel/air mixtures need less energy to ignite. For stoichiometric fuel/air ratio,
ww
w.E
hydrogen requires one-tenth of the energy to ignite than hydrocarbon fuels. 9. Flashpoint:
asy
En
The flashpoint is the lowest temperature at which combustible mixtures of fuel vapour
gin eer
and air form above the fuel. In the presence of a spark, such mixtures will ignite. A high flashpoint is desirable from a safety standpoint but none of alternative fuels has an advantage in this area. All fuels but diesel has flashpoint at ambient or lower than the ambient
ing .ne t
temperature. However, the alcohol fuels have higher flashpoint than gasoline. 10. Flammability:
Flammability limits the range of fuel/air mixtures that ignite. From a safety perspective, a wide range is less desirable than a narrow range. Among hydrocarbon fuels, meth~nol has the widest flammability limits (7.3% to 36%) followed by ethanol. In partially filled or empty storage tanks, alcohol fuels are to produce more combustible mixture above fuel than other alternative hydrocarbon fuels. Gasoline tank vapors are too rich in fuel to ignite and the addition of gasoline to the alcohol fuels reduces the flammability limits ofM-85 and E-85 compared to M-IOOand E-95, respectively. Relative to gasoline, the safety concerns associated with the wide flammability limits of alcohols are offset by safety advantages of alcohol fuels relatively high lowerflammability limit, higher flashpoint temperature, higher auto-ignition temperature and lower vapor pressure than gasoline. For example, the high lower-flammability limit of methanol keeps it from igniting in air at concentration below about 6% while gasoline will ignite at concentration as low as 1.4%. Hydrogen has the widest flammability limit of all alternative Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile
Engineering
fuels ranging from 4.1% to 74%. When coupled with small amount of energy neede~ to ignite fuel-air mixtures, the wide flammability limit present is a safety concern for hydrogen relative to other fuels. 5.4. USE OF NATURAL GAS IN AUTOMOBILES
Natural gas is a fossil fuel such as petroleum and coal. Natural gas is called fossil fuel because most scientists believe that it was formed from remains of ancient sea plants and animals. When the plants and tiny sea animals died, they sank at the bottom of oceans where they were buried by sediment and sand is turned into sedimentary rock. The layers of plants and animal matter and sedimentary rock continued to build until the pressure and heat from the earth turned remains into petroleum and natural gas.
ww w.E
Natural gas is trapped in more underground rocks such as sponge traps water in pockets.
Natural gas is really a mixture of gases. The main ingredient is methane (CH4). People use natural gas mostly for heating. Natural gas should not be confused with gasoline which is made from petroleum.
asy
En
Natural gas represents more than one fifth of total energy consumption in the world. It has been the fastest growing fossil fuel since 1970's. Due to economical and ecological advantages that it presents as well as its safety qualities (e.g. reduced flammable range),
gin
eer
natural gas is an increasingly attractive source of energy in many countries. At present, natural
ing .ne t
gas is the second energy source after oil. According to Energy Information Administration, natural gas is accounted for 23% of world energy production in 1999. It has excellent perspectives for future demand.
Natural gas presents a competitive advantage over other energy sources. It is seen as economically more efficient because only 10% of the natural gas produced is wasted before it gets to final consumption. In addition, technological advances are constantly improving their efficiencies in extraction, transportation and storage techniques as well as in equipment which uses natural gas. Although resources of natural gas are finite and natural gas is a non-renewable source of energy, these resources are plentiful all over the world. Natural gas reserves are continuously increasing as new exploration and extraction techniques which allow wider and deeper drilling. Natural gas is considered as an environment friendly clean fuel, offering important environmental benefits when compared to other fossil fuels. The superior environmental
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
Alternative
Energy Sources
qualities over coal or oil are that emissions of sulphur dioxide are negligible or the level of nitrous oxide and carbon dioxide emissions are less. It helps to reduce the problems of acid rain, ozone layer or greenhouse gases. Natural gas is used for heating, cooling and several other industry uses while it is increasingly becoming the favoured fuel for power generation. Many automakers around the world are developing vehicles to run on natural gas. Cars, vans, buses and small trucks generally use natural gas which has been compressed called compressed natural gas or eNG and stored at high-pressure cylinders. 5.4.1. History of Natural Gas
ww
The ancient people of Greece, Persia and India discovered natural gas many centuries
ago. The people were mystified by burning springs created when natural gas seeped from cracks in the ground and it was ignited by lightening. They sometimes built temples around
w.E
these eternal flames and worshipped the fire.
asy
The discovery of natural gas dates from ancient times in Middle East. Thousands of years ago, natural gas seeps ignited when lightning and created "burning springs". In Persia, Greece
En
or India, people built temples around these "eternal flames" for their religious practice.
gin eer
However, they did not recognize the energy value of natural gas. It was done in China around .900 BC. About 2,500 years ago, the Chinese recognized that natural gas could be put to work. The Chinese drilled the first known natural gas well in 211 BC. The Chinese piped the gas
ing .ne t
from shallow wells and burnt it under large pans to evaporate sea water to make salt.
In Europe, natural gas was unknown until it was discovered in Great Britain in 1659 although it was not commercialised until about 1790. In 1821 in United States, residents observed gas bubbles rising to the
SUi
face from a creek. William Hart, considered as
America's "father of natural gas", dug the first natural gas well in North America.
Throughout 19th century, natural gas was used almost exclusively as a source of light and its use remained localized because of lack of transport structures. Also making the transport facility was difficult to transport large quantities of natural gas through long distances. There was an important change in 1890 with the invention of leak proof pipeline coupling. However, existing techniques did not allow for gas going further than 160 km and it was mostly flared of left in the earth. Transportation of natural gas to long distance became practical in 1920s as a result of technological advances in pipelines. It was only after World War II that the use of natural gas grew rapidly because of the development of pipeline network and storage system.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IiIliII
Automobile Engineerin!(] In early days of oil exploration, natural gas was often an unwelcome by-product as natural gas reservoirs were tapped in drilling process and workers were forced to stop drilling to let the gas vent freely into air. Now, particularly after the oil shortages of seventies, natural gas has become an important source of energy in the world. The gas industry has been highly regulated for many years mainly as it was regarded as" natural monopoly. In last 30 years, there has been a move away from price regulation and towards liberalization of natural gas markets. These movements have resulted a greater competition in the market and a dynamic and innovative natural gas industry. In addition, natural gas can be better explored, extracted and transported to consumers. Innovations also help to improve the natural gas applications and create new ones. Natural gas is increasingly
ww w.E
used for power generation.
5.4.2. Properties I Characteristics
of Natural Gas
asy
Natural gas is colourless, odourless, tasteless, shapeless and lighter than air. It is gaseous at any temperature over -161° C. When it is at its natural state, it is not possible to see or
En
smell natural gas. For safety reasons, Mercaptan (i.e. a chemical odorant that smells a little such as rotten eggs) is added to natural gas so that it can be smelled ifthere is a gas leak.
gin
Natural gas is a mixture of light hydrocarbons including methane, ethane, propane,
eer
butanes and pentanes. Other compounds found in natural gas including CO2, helium,
ing .ne t
hydrogen sulphide and nitrogen. However, the composition of natural gas is never constant and the primary component of natural gas is methane:(typically, at least 90%) which has a simple hydrocarbon structure composed of one carbon atom and four hydrogen atoms (CH4). Methane is highly flammable and it easily and completely burns while it emits little air pollution. Natural gas is neither c?rrosive nor toxic. Its ignition temperature is high and it has a narrow flammability rar:ge, making it an inherently safe fossil fuel compared to other fueJ sources. In addition, because of its specific gravity of 0.60 which is lower than air (1.00), natural gas rises if escaping. Thus, it dissipates from the site of any leak. When natural gas is cooled to a temperature of approximately -260°F at atmospheric pressure, it condenses to a liquid called Liquefied Natural Gas (LNG). One volume of this liquid takes up about 1/600th of the volume of natural gas. LNG weighs less than one-half of water which is actually about 45%. LNG is odourless, colourless, non-corrosive and nontoxic. While vapourizing, it burns only in concentration of 5% to 15% when mixed with air. Neither LNG nor its vapour can explode in an unconfined environment. Since LNG takes less volume and weight, natural gas is liquefied for ease of storing and transporting.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative
dill I
Energy Sources
Natural gas is considered as a clean fuel because of its environment friendly properties. A commercialised natural gas is practically sulphur free and thus, it produces virtually no sulphur dioxide (S02)' Natural gas emits lower level of nitrogen oxides (NOx) emissions than oil or coal and emissions of carbon dioxide (C02) are less than other fossil fuels. 5.4.3. Various Forms of Natural Gas 1. Methane: Natural gas is primarily methane (CH4). It makes natural gas as a friendly fuel for the environment. Methane as a hydrocarbon is considered non-reactive. It means, hydrocarbon emissions of natural gas do not react with sunlight to create smog. When natural gas is used as an engine fuel, the Society of Automotive Engineers (SAE) has established a standard minimum methane content of95%.
ww w.E
Advantages of methane asfuels in automobiles:
asy
(i)
It has very low emissions of ozone-forming hydrocarbons, toxics and carbon monoxide.
(ii)
It can be made from a variety of feed stocks including renewable.
En
gin
(iii) It is excellent fuel especially for fleet vehicles. Disadvantages of methane asfuels in automobiles: (i)
Vehicle cost is higher.
(ii) Vehicle range is lower. (iii) It has less convenient refueling. 2. Ethanol:
eer
ing .ne t
Ethanol called "grain alcohol" is the primary automotive fuel in Brazil and ethanol/gasoline blend is known as "gasohol" which has been used in the United States for many years. Pure ethanol fuel offers the excellent performance and low hydrocarbon and toxic emissions. It can be produced domestically from corn or other crops as well as from cellulose materials such as wood or paper wastes which potentially minimizes the accumulation of greenhouse gases since these "renewable" feedstock draw carbon dioxide in atmosphere as they grow. With current technology and price structures, ethanol is more expensive than gasoline. New technologies offer the hope of significantly reduced cost. Advantages of ethanol asfuels in automobiles: (i)
It is excellent automotive fuel.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Iata
Automobile
(ii)
Engineering
I
It has very low emissions of ozone-forming hydrocarbons and toxics.
(iii) It can be made from renewable sources. (iv) It can be domestically produced. Disadvantages of ethanol asfuels in automobiles: (i)
Fuel cost is high.
(ii) Vehicle range is somewhat lower. 3. Methanol: Methanol called "wood alcohol" is a high-performance liquid fuel which emits low level toxic and ozone-forming compounds. It can be produced at price comparable to gasoline from natural gas and it can also be produced from coal and wood. All major auto manufacturers
ww w.E
have produced cars which run on "M85" which has a blend of 85% methanol and 15% gasoline. Cars that bum pure methanol (MI00) offer much greater air quality and efficiency.
asy
Many auto manufacturers have developed the advanced MI00 prototypes. Methanol has been the fuel of choice for racecars because of its superior performance and fire safety characteristics.
En
gin
Advantages of methanol asfuels in automobiles: (i) It is excellent automotive fuel.
eer
(iii It has very low emissions of ozone-forming hydrocarbons and toxics.
ing .ne t
(iii) It can be made from a variety of feedstock including renewable. Disadvantage of methanol asfuels in automobiles: (i) Vehicle range is less. 4. Propane:
Propane or liquefied petroleum gas (LPG) is a by-product of petroleum refining and natural gas production. It bums completely than gasoline but it is limited in supply. Propanefueled vehicles are already common in many parts of the world. Advantages of propane asfuels in automobiles: (i)
It is cheaper than gasoline today.
(ii) It is widely available clean fuel today. (iii) Emissions are less in ozone forming hydrocarbons and toxics. (iv) It is excellent fuel especially for fleet vehicles.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
".
I Alternative Energy S('urces Disadvantages of propane asfuels in automobiles: (i)
Cost will rise with demand.
(ii) It has limited supply.
(iii) No energy security or trade balance benefits occur. 5. Reformulated and oxygenated gasoline: The petroleum industry is beginning to market gasoline formulations which emit less hydrocarbons, nitrogen oxides, carbon monoxide and toxics than conventional gasoline. These new gasoline's can be introduced without a major modification to existing vehicles or the fuel distribution system. The clean air act requires some gasoline modifications to reduce carbon
ww
monoxide emissions beginning in 1992 and use of reformulated gasoline in certain polluted cities beginning in 1995.
w.E
Advantages of reformulated gasoline asfuels in automobiles: (i)
asy
It can be used in all cars without changing vehicles or fuel distribution system.
(ii) It produces lower emissions of ozone forming hydrocarbons and nitrogen oxides.
En
Disadvantages of reformulated gasoline asfuels in automobiles: (i)
Fuel cost is high.
gin eer
(ii) Few energy security or trade balance benefits and toxics occur. 5.4.4. Natural Gas Production
ing .ne t
Natural gas can be hard to find since it is trapped in porous rocks deep underground. Scientists use many methods to find natural gas deposits. They may look at surface rocks to find clues about underground formations. They may set off small explosions or drop heavy weights on the surface to record the sound waves as they bounce back from rock layers underground. Natural gas can be found in pockets by itself or petroleum deposits. Natural gas wells average 1500 m deep. After natural gas comes out from the ground, it is sent to a plant where it is cleaned to remove impurities and separated into its various parts. Gas streams produced from reservoirs contain natural gas and other materials. It should be processed to separate the gas' from petroleum liquid and to remove contaminants. First, the gas is separated from free liquid such as crude oil, hydrocarbon condensate, water and entrained solids. The separated gas is further processed to meet the specified requirements. ... The combination of processes in a typical gas plant is shown in Figure' 5.1. A dehydration plant controls water content. A gas processing plant removes certain hydrocarbon components Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IWIi
Automobile Engineering
I
to hydrocarbon dew-point specifications and a gas sweetening plant removes hydrogen sulfide and other sulphur compounds (when present). Sui hur Residue gas
Production well gas
ww
Gas I--_~I Sweetening
Separation
Dehydration & liquid recovery
NGL
Condensate Stebilization I-----..:....:..:..:..:...:..:..:..::..:.:..:...::.__-----+l
w.E
Figure 5.1 Production of natural gas
asy
5.4.5. Natural Gas Vehicles (NGVs)
En
Light-duty vehicles designed to run on natural gas include cars, minivans and vans
gin eer
mainly for fleets. Natural gas engines are also being designed and used for buses and other heavy-duty vehicles. A natural gas vehicle contains a high-strength fuel tank, fuel lock filter/shutoff valve, regulator, air-fuel mixer and a .microprocessor for air/fuel ratio control. A
ing .ne t
dual-fueled system retains the gasoline fuel system components and a mechanism is installed to change between systems. The extra weight of carrying two fuel systems detracts from the efficiency of dual-hard fueled systems. (i) Fuel storage:
A eNG vehicle stores gaseous fuel at a pressure of 165 bar to 250 bar. Even at a pressure of 250 bar, a unit volume of eNG has less than one-fourth of the energy content of gasoline which means a much greater storage requirement for the vehicle. A cylinder for the storage of pressurized gas certified by any recognized authority is required on all eNG vehicles. A typical cylinder is certified to withstand 700 bar and it is about 10 inches in diameter and 4 feet long. While eNG tanks are filled to the certification pressure of the refueling system (165 bar; 200 bar; or 250 bar), the equilibrium pressure tends to be IOta 20% lesser. Thus, it reduces the driving range further. The original gasoline tank is retained in most converted dual-fueled eNG vehicles.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative
Energy Sources
".
CNG tanks are larger and fuel-plus-tank weight is higher than liquid fuel/tank alternatives. However, research efforts are directed at developing lighter tanks. Cheaper and lighter natural gas cylinders for school buses, light and heavy-duty trucks have been developed. One new cylinder has a cold-drawn aluminum liner which is thinner and lighter than the steel or extruded aluminum typically used. The end of the liner is covered with a lowcost fiberglass which protects the cylinder. Most of the prior discussion on CNG applies to Liquefied Natural Gas (LNG). However, the energy density and associated vehicle tank tradeoffs are different from CNG. LNG tanks might be pressurized around 2 bar and hold the liquid at a temperature of -260° F. Between
ww w.E asy
two and three times, the natural gas can be stored as liquid onboard than compressed state. (ii) Engine systems:
Engine modifications allow more efficient use of natural gas which increases the compression ratio, different spark plug type, placement of hard seat inserts under exhaust valves and modification of the intake manifold to eliminate "heating" features for gasoline use
En gi
during warm up. Most conversions today are done on newer vehicles containing fuel-injection gasoline engines which are constructed with many of modifications.
nee
Natural gas has higher octane value than gasoline with generally good performance characteristics. As a gas, it has few cold-start problems. Its octane value allows for the use of
rin
higher engine compression ratio than gasoline. Higher compression ratio allows high power and fuel efficiency. The efficiency and power gains achievable from higher compression ratio
g.n et
help to offset the power loss relative to gasoline caused by the low energy density of natural gas. Differences in density of natural gas and air keep these two gases from forming a homogeneous mixture when first combined. Fluctuations in the air/fuel mixture can result an engine misfire. Time and turbulence are needed inside the engine to create the uniform mixture. The characteristics of natural gas indicate that an engine is designed to improve efficiency and lower carbon monoxide emissions would be a high-compression and lean-bum engine. Other characteristics make the optimization challenging. For example, lean-bum engines can encourage the formation of NOx because excess oxygen is present and high flame temperature of natural gas increases the peak combustion temperature. Non-methane hydrocarbon emissions are low relative to gasoline since natural gas is predominantly methane. However, total hydrocarbon emissions from natural gas engines can be high because
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Iljl.
Automobile Engineering
I
methane is slow to react than other hydrocarbons. Also, the slow flame speed of natural gas in lean-fuel mixtures may prevent the complete combustion during power stroke. Several ~?untries have Natural Gas Vehicles (NGVs). The top ten countries in terms of NGV population are given in Table 5.1. Table 5.1 NGVs in the world* As on
Country
NG vehicles Refueling stations
1
Iran
3,000,000
1,960
December 2012
2
Pakistan
2,900,000
3,330
December 2012
3
Argentina
2,140,000
1,902
October 2012
1,739,676
1,701
December 2012
1,577,000
2,784
December 2012
1,250,000
724
December 2012
746,470
959
June 2012
S.No.
ww 4
5
w.E Brazil China
6
India
7
Italy
8
Ukraine
asy
En
390,000
gin eer
May 2012
324
\
9
Colombia
380,000
10
Thailand
358,000
690
December 2012
470
December 2012
ing .ne t
*Source: NGV Global. http://www.iangv.org!current-ngv-stats/
World NGV commercialisation activities- have taken place for different reasons in different countries since their initial introduction is in Italy in the mid ofl930's. Each country'. has a different set of market conditions, economics, gas availability/supply, technology development which cause NGV commercialisation to progress at different rates. In India, narural gas vehicles can be commercially viable only in cities where natural gas pipelines exist or would be laid in future. Cost of establishing fresh gas grids are quite high and it may not be feasible to dispense CNG for automotive purposes in most cities in near future. The review of NGVs programmes in different countries reveals that NGVs have been commercially successful proposition in countries which have adequate indigenous resources of natural gas, a well-developed gas grid and a long established usage of gas as domestic / commercial fuel.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
".
I Alternative Energy Sources 5.4.6. Natural Gas Consumption Pattern In Different Countries
Natural gas and its proportionate of use in an economy are indirectly related to the development of NGVs. Natural gas consumption by sector in above mentioned countries is shown in Table 5.2. Table 5.2 NG consumption by sector Country
Argentina
Power! Industrial %
Commercial! Residential! Others %
64
36
ww w.E asy Italy
58.6
41.3
Pakistan
76.1
23.9
USA
55.9
44.1
India
97
3
Venezuela
40
60
Egypt
85.2
14.8
China
89
South Korea
En gi
52.4
nee
11
rin
47.6
g.n et
5.4.7. Compressed Natural Gas (CNG) and Liquefied Natural Gas (LNG)
The interest in natural gas as an alternative fuel stems mainly from its clean burning qualities, its domestic resource base and its commercial availability to end users. Because of the gaseous nature of this fuel, it must be stored onboard vehicle either in compressed gaseous state (CNG) or in liquefied state (LNG). Natural gas is liquefied at reduced temperature and contained in this state in insulated pressurized tanks. It is easily transported through pipelines and cost is same or slightly less than gasoline. In Australia, CNG is compressed to around 20MPa for onboard storage. Compressed natural gas (CNG) vehicles emit low level toxics and ozone-forming hydrocarbons. But CNG fuel must be stored under pressure in heavy tanks and the cost of .commodating these tanks must be considered. There are significant tradeoffs for CNG vehicles among emissions, vehicle power, efficiency and range.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering
Several vehicles are available today such as Honda Civic CGX, Toyota Camry and Ford Crown Victoria which are operated on compressed natural gas. Some run on natural gas only and others can run on natural gas and gasoline, called bi-fuel vehicles. Liquefied natural gas (LNG) is natural gas in its liquid form. When natural gas is cooled to -259°F (-161°C), it becomes a clean, colorless and odorless liquid. LNG is generally refrigerated to -ISO°C for liquefaction and it requires vacuum-insulated cryogenic tanks to maintain it in liquid form for storage. LNG is neither corrosive nor toxic. Natural gas is primarily methane with low concentration of other hydrocarbons, water, carbon dioxide. nitrogen, oxygen and some sulphur compounds. During the process known as liquefaction, natural gas is cooled below its boiling point and most of these compounds are removed. The remaining natural gas is primarily methane with only less amount of other hydrocarbons. Liquefying natural gas results the purest form of methane when heated back to a gas.
ww w.E asy
For heavy-duty applications requiring long-range capability and large volumes of onboard fuel storage, LNG provides all benefits of clean burning natural gas in liquid form. LNG vehicles are essentially natural gas vehicles which store methane as liquid. LNG vehicles include a heat exchanger installed between fuel tank and engine to warm the liquid
En gi
and convert the fuel back to a gaseous state.
5.4.8. Advantages and Disadvantages of LNG Advantages of liquefied natural gas:
nee
rin
g.n et
LNG has very low particle emissions because of its low carbon to hydrogen ratio. 2
There are negligible evaporative emissions which require no relevant control.
3
Due to its low carbon-to-hydrogen ratio, it produces less carbon dioxide per volume of fuel than diesel.
4
It has low cold-start emissions due to its gaseous state.
5
It has extended flammability limits which allow stable combustion at lean mixtures.
6
It has a lower adiabatic flame temperature than diesel which leads to lower NOx emissions.
7
It has much higher ignition temperature than diesel, making it more difficult to autoignite and thus, it is safe.
S
It contains non-toxic components. The liquefaction process removes impurities.
9
LNG is pure methane which is a non-toxic gas.
10 It is lighter than air and thus, it is safer than spilled diesel. Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources
..
I
11 Engines fueled with LNG in heavy-duty vehicles offer more quiet operation than equivalent diesel engines making them more attractive for the use in urban areas. 12 It has nearly zero sulphur levels and thus, it is negligible sulphate emissions. 13 NG pricing is stable and predictable which removes uncertainty to business caused by fuel price fluctuations. 16. NG use does not give rise to issue with groundwater contamination such as those experienced through diesel/petrol spillage or leakage from underwater storage. Disadvantages of liquefied natural gas: There is a considerable extra infrastructure involved in gas liquefaction.
ww w.E asy
2
It requires dedicated catalysts with high loading of active catalytic components to maximize methane oxidation.
3
Its driving range is limited because its energy content per volume is relatively low.
4
It requires special refueling stations and handling of a cryogenic liquid and making it suitable only for fleet operations.
5
The energy required to liquefy NG leads to increased greenhouse gas emissions in comparison to eNG.
En gi
nee
6
Exhaust emissions of methane are relatively high compared with low sulphur diesel.
7
Refueling is considered to be the 'least-safe' moment of its use.
S
It can give rise to backfire in the inlet manifold if the ignition system fails in use.
rin
5.5. USE OF LIQUEFIED PETROLEUM GAS (LPG) IN AUTOMOBILES
g.n et
Most people pronounce Liquefied Petroleum Gas (LPG) as "propane" because LPG is mostly made up of propane. Actually, LPG is made of a mixture of propane and other similar types of hydrocarbon gases. Different batches of LPG have slightly different amount of (.
various kinde;of hydrocarbon molecules. These hydrocarbons are gases at room temperature but turn to liquid when they are compressed. LPG is stored in special tanks which keep it under pressure. Therefore, it stays as liquid. The pressure of these tanks is usually about 14bar. LPG is the name given to the mixture of petroleum gases released during the extraction of crude oil and natural gas during refining the crude oil. It consists of a mixture of hydrocarbons including major components of propane and butane and minor components are normal-butane, iso-butane, pentane, ethane, propene and butene together with small quantities Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imil
Automobile Engineering
of additives including sulphur to give it an odour for safety reasons. Propane (C3HS)and butane (C4HIO) are the main components but different mixing ratios are used in different countries which reflect the local market prices, production facilities and climatic conditions. LPG is a gas which can be stored in a liquid state under low pressure due to its low vapour tension. The percentage of passenger cars running worldwide on LPG is currently I% which includes some 2.5 millions in Europe. Countries with the most developed LPG markets are Italy, Poland, Netherlands, Czech Republic and France in Europe, South Korea Japan, Australia, and USA and involve passenger cars, taxis, LDVs and HDVs. The varying LPG composition between countries not only dictates the Octane number but it also affects exhaust
ww w.E asy
emissions, mainly CO. A higher butane number leads to lower NOx levels while a higher propane number reduces CO levels. There are various types of vehicle running on LPG: converted (retrofitted) gasoline engines for passenger cars and light duty vehicles (LDVs) operating as dual-fuel systems as well as dedicated LPG engines. Some are converted diesel engines operating in the compression-ignition mode with diesel pilot injection. Most of LPG heavy duty vehicles
En gi
(HDVs) engines are converted into diesel engines operating in the spark-ignition mode with
nee
modified cylinder head and combustion chamber. The last two types are intended for medium and heavy-duty applications and employ dedicated and retrofitted engines.
rin
LPG fueled engines can pollute less than gasoline and diesel engines. LPG usually costs
g.n et
less than gasoline for the same amount of energy. In some countries, LPG is used as a vehicle fuel than in California. In Netherlands, over 10% of the motor fuel used is LPG. 5.5.1. Properties I Characteristics of LPG 1. Physical Properties: The important typical properties and characteristics of LPG currently marketed are as follows: Property (Units / Conditions)
Value
Relative molar mass
44.1
Carbon content (mass %)
82
Hydrogen content (mass %)
18
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative
Ifl.l
Energy Sources
0
Oxygen content (mass %)
0.S4 - 0.S7'
Specific Gravity of Liquid at IS0C Sp. Volume of Gas at lSoC, 760 mm Hg. (lit/g of gas)
0.44
Relative density (@ISoC/ 1 bar)
0.5
Boiling temperature (OC/1 bar)
-42
Auto-ignition temperature eC)
480
Octane number (RON)
112
ww
99.S
Octane number (MON)
w.E asy E
Methane number
3S
Stoichiometric air/fuel ratio (mass)
IS.7
Flammability limits
0.42 to 2.0
Theoretical Maximum Flame Temperature in air (0C)
2000
Theoretical Max. Flame Temperature in Oxygen (0C)
28S0
Vapour pressure @ 38°C (kPa)
1300
Freezing temperature (0C)
ngi nee
"
-
.
rin
Flash point temperature (0C)
-187
g.n
-104
890
Minimum Ignition Temperature (0C) Sp. heat (kJ/kg-K) @ 1 bar.& ISOC
liquid phase
2.48
gas phase
1.67
Lower heating/calorific value (MJ/kg)
46
Gross Calorific Value of LPG (keal/kg)
11,400
Viscosity (MPa-s at IS°C)
liquid phase
11.10-5
gas phase
80.10-7
Sulphur concentration (ppm, mass)
Specific CO2 formation (g/MJ)
64.7
et
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1The following characteristics are very important.
Automobile Engineering
2. Vapourpressure: The pressure inside a closed container in which LPG is stored will be equal to the vapour pressure of the liquid and gaseous LPG in the container and it corresponds to its temperature. Vapour pressure is a characteristic of a liquid which depends upon its temperature. If the temperature of liquid LPG inside a container remains constant, the pressure inside the container when full and when nearly empty will be practically the same. 3. Boiling point: The boiling point of LPG ranges from - 42°C to - 5°C.
ww w.E asy
4. Density / specific gravity:
LPG in gaseous state is around twice as heavy as air. Any leakage of LPG tends to settle
down at the floor level. Ground level ventilation to djsperse leaking gas prevents the accumulation and it is therefore more important. Liquid LPG is almost half as heavy as water and when it expands generates 246 volumes of gaseous LPG. 5. Toxicity:
En gi
LPG contains no toxic components such as carbon monoxide and it is therefore nonpoisonous. If leakage of a large amount of LPG occurs in a closed space, difficulty in
nee
breathing and asphyxiation due to lack of oxygen can be caused. LPG is slightly anesthetic
rin
when high concentrations are breathed in sufficient quantities over a period of time and the result would be an upset stomach and headache which are warning symptoms. 6. Limits of inflammability:
g.n et
Fuel gases will burn only when mixed with air in certain proportions. The minimum and maximum concentrations of a fuel gas in gas/air mixture between lower and upper limits of inflammability. The limits of inflammability of LPG are narrower than other fuel gases and making LPG relatively safe in use. 7. Odour: LPG is naturally odourless. LPG is distinctively odourised to give the warning in case of leakage. Its smell is detectable in air at concentration down to 1/5 of the lower explosive limit. In other words, it can be smelt long before it becomes dangerous enough to catch fire. 8. Calorific value: The amount of heat available from a given quantity of fuel is determined by the calorific value of the fuel. The calorific value of LPG is very high and it is uniform. Downloaded From : www.EasyEngineering.net
I
---
-_
.. _--
----
Downloaded From : www.EasyEngineering.net
I Alternative
Energy Sources
9. Other important properties: ~
LPG reaches lower limit of flammability quicker as compared to other gases.
~
"Auto - refrigeration" occurs when liquefied LPG evaporates into gaseous LPG.
~
Pressure of air in lines / vessels / cylinders will cause built up of high pressure.
~
Liquefied LPG can cause "Cold Bums".
~
Explosion can occur in case of ignition of accumulated LPG - air mixtures.
~
LPG can be ignited by static electric charges, tiny sparks, etc.
~
Pressure inside a cylinder drops marginally with use.
ww w.E asy
5.5.2. LPG Equipment
1.LPGfuei tank:
LPG tanks are constructed of heavy gauge steel in compliance with the boiler and pressure vessel code of the American Society of Mechanical Engineers (ASME) to withstand a pressure of 70 bar. Normal working pressure within the tank varies depending on the ambient temperature and the quantity of fuel in the tank. A common operating pressure is in the range of9-12 bar. Propane tanks limit the liquid level to 80% of the total tank volume by using an auto-stop fill valve. Tanks are equipped with a pressure relief valve which can
En gi
nee
release propane vapours to the atmosphere to prevent the tank rupture under abnormally highpressure condition. Each tank also includes a manual shut-off valve. The propane fuel tank is
rin
g.n et
installed along with a fueling port, fuel lines and pressure safety valves. A filter removes particles and contaminants which may present in the propane.
2. Vapourizer:
LPG system draws fuel from the bottom of the tank and it sends the liquid propane to the vapourizer. The vapourizer converts the liquid to gas. The primary heat source for this vapourization is engine coolant flowing through specially designed water jackets cast into the vapourizer body. Many vapourizers include an internal pressure regulator to control the pressure of the fuel sent to the engine. 3. Fuel metering: Early propane systems used a mixer operated as a conventional venturi device in a manner quite similar to a gasoline carburetor. Vapourized propane is drawn through a fixed orifice in response to engine air flow. As intake air enters the engine, a venturi effect is created through the mixer. This slight pressure drop is acted on a spring-loaded diaphragm in
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imil
Automobile
Engineering
proportion with air flow. The result is a simple fairly accurate flow meter which controls the volume of fuel to the engine as a function of air flow. Changes in altitude, ambient weather conditions and even temperature cause significant variations in the fuel mixture which cannot be compensated for using a mixer. Electronically controlled closed-loop fuel injection provides a much more precise method of metering the fuel. Based on sensor inputs, the electronic control module (ECM) determines the engine operating conditions and then, it modifies the injector pulse width to maintain a stochiometric mixture. 5.5.3. LPG Fuel I Engine Interaction
ww w.E asy
Due to limited LPG refuelling infrastructure, the automotive manufacturers who were
keen to promote the 'world car' concept had no other option but to opt for bi-fuel LPG sparkignition engines which are capable of running everywhere with gasoline, LPG or both. It was the trend in the passenger car and light-duty vehicle market. On the other hand, for the medium and heavy-duty LPG markets, the options are to convert diesel engines into bi-fuel diesel/LPG versions with diesel acting as auto-ignition improver or to convert them into spark-ignition engines by burning LPG in either stoichiometric or lean burn mode. Direct-injection gasoline engines represent the best hope for improving the fuel efficiency of spark-ignition engines to achieve the efficiency of indirect-
En gi
nee
rin
injection diesel engines but it is not in direct-injection diesels which is at least 10-15% higher probably beyond the reach. 5.5.4. Current State of LPG Engine I Vehicle Technology
g.n et
Over years, a number of (i.e. first mechanical and then electronically-controlled) fuel preparation LPG bi-fuel systems were developed with increasing degree of sophistication ranging from carburettors to single and multi-point injections. The microprocessor-controlled LPG injection systems operate with a pressure difference in contrast to carburettor-based systems and these systems are self-adjusting with a closed-loop. They are known as third generation LPG equipment. It can be operated continuous, simultaneous and sequential fuel injection pattern. The most advanced multi-point fuel injection systems use an accurate gas metering unit (orifice meter) combined with two-stage pressure regulators to supply the same amount of fuel to each cvlinder through injectors positioned close to inlet valves. They are microprocessorcontrolled through information received from the engine speed, manifold absolute pressure Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
Alternative Energy Sources
and lambda sensors as well as from temperature readings of the air, water and necessitates a dedicated engine management system in order to allow the operation of gas preparation system in both bi-fuel and single-fuel gasoline engine conversions. Over years, liquid LPG injection systems have been developed which offer better accuracy in fuel metering as well as improved reliability but their main advantage for bi-fuel engine conversions is their compatibility with gasoline injection in terms of a common control strategy. However, there is still a need for separate electronic control units although certain functions are per,formed by only one microprocessor. ;
In heavy-dutyapplications, diesel engine conversions are very much popular, less in bi.t'
.
ww w.E asy
fuel (diesel/LPG) compression ignition versions and increasingly more in single-fuel (LPG) spark-ignition ones. In bi-fuel diesel conversions, a second LPG fuel injection system is added to the engine and the correct mixture of diesel/LPG is burnt following auto-ignition of a small quantity of diesel fuel. The amount of diesel fuel replaced by LPG is about 25-40%. So, it simply represents a convenient approach for countries with less stringent emission standards than Europe.
En gi
The more radical approach is the conversion of the diesel engine to run with LPG in a spark-ignition mode which requires major modifications to the cylinder head and piston to
nee
accommodate LPG's higher octane rating, ignition and combustion characteristics as well as
rin
different fuel metering requirements. These engines tend to be turbocharged and it can operate with either homogeneous or lean LPG/air mixtures depending on the desired engine power
g.n et
output. However, a variable geometry turbocharging is needed in this case to limit the inlet boost pressure through control of the turbine inlet flow rate which adds to the total cost of the system. Therefore, the existing trend is for HDV LPG dedicated engines to dominate the market. 5.5.5. LPG Vehicles
The total number of vehicles in the world operating on LPG was around 5.6 million in year 1999. The major countries using LPG as an automotive fuel are Italy, Netherlands, Poland, USA, Canada, Mexico, Australia, New Zealand, Algeria, Turkey, Iran, South Korea, and Japan. Among these countries, the largest number of LPG vehicles over 1.2 million are in Italy. China is one of the recent entrants in this area with around 50,000 vehicles in the year 1999.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
_
Automobile
Engineering
In India, LPG is the main domestic fuel in urban areas. The indigenous availability of LPG is expected to fall much short of the household demand alone. LPG to be competitive as an auto fuel in India would need Government support by way of substantially lower taxation. 1. Passenger cars: Most of gaseous fueled passenger car engines are petrol engines retrofitted with eNG / LPG kits. Earlier, cars were fitted with simple carburetor system for inducting gaseous fuel such as eNG or LPG and they were designated asfirst generation kit. Subsequently, in order to make the engine operated on stoichiometric air fuel ratio, this design was modified and kit was classified as second generation kit. ~or meeting the stringent emission norms, further improvements were made in kits by incorporating multi-point fuel injection system and the kit was designated as third generation kit. In'70s and early ,80s, gaseous fuel cars had
ww
w.E asy E
substantially low exhaust emission level than gasoline cars. However, the introduction of advanced design petrol cars in recent years with substantially lower emission levels is created new comparison levels between petrol and gaseou,sfuels. With respect to emissions, the advanced technology gasoline vehicles with three-way catalysts are so clean that the fuel itself (that is, whether liquid or gas) plays a relatively minor
ngi nee
role especially for regulated emissions. Under these circumstances, converting an advanced petrol vehicle to gaseous fuel could even increase rather than decrease emissions. 2. Two/three wheelers:
rin
g.n
Earlier two and three wheelers operating in India were mostly powered by 2 stroke petrol engines. The inherent design of 2 stroke engine is responsible for higher hydrocarbon
et
emissions. Further, the combustion of lubricant along with the fuel is responsible for particulate emissions from such vehicles. However, their NOx emissions are low. 3. Buses: At present, there is no gas engine having the same kind of power output, fuel economy and reliability similar to a modern diesel engine. Therefore, gas engines for bus applications are mostly based on converted. diesel engines. The conversion to gaseous fuel engines (eNG or LPG) for heavy duty application involves changeover to SI operation. The engine manufacturers use either stoichiometric or lean burn combustion. In diesel buses, the conversion techniques presently being used in India are not proven technologies. For conversion, the existing diesel engine is modified to run on eNG by replacing piston, cylinder head, cooling system, intake manifold, incorporation 'of ignition system and converting into SI engine. It is not a reliable system and there are complaints of
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources
..
engine overheating, spark plug fouling, engine head leaking, etc. CNG engines in India are not original gas engines but it is converted from diesel engines using the diesel engine block. A diesel engine converted to a eNG engine has different speed-torque characteristics which lead to the problem of failure in clutch plate, overheating, loss in power etc. More experience and continuous improvements will lead to improved level of technology in this area. 4. Outcome of conversion of old vehicles to LPG vehicle: ~
In the case of old model petrol passenger cars, a change-over to gaseous fuels in most cases results the reduction in CO emissions. However, NOx in some cases may go up. Particulates are low in both cases.
~
ww
In the case of old generation diesel cars and three-wheelers, conversion!
retrofitment/replacement of the engine to four-stroke engine on petrol or gaseous fuel give benefits in terms of reduced particulate matter emissions.
w.E asy E
~ In the case of diesel buses, a change over to eNG results the benefits in terms of particulate matter emissions with a disadvantage on CO and other emissions. )iI>
In the case of old generation two stroke petrol three-wheelers, a change-over to four-
ngi nee
stroke engine provides particulate emission benefits, both with petrol and gaseous fuels but there may be a penalty on CO and NOx emissions. ~
rin
Road performance of alternative fuel vehicles depends on the use of standard kits of right quality. While adulteration in liquid fuels affects emission performance,
g.n
use/fitment of sub-standard conversion kits adversely affects the emission performance in alternative fuel vehicles. 5.5.6. Advantages and Disadvantages of LPG
et
Advantages of LPG: 1. It has very low sulphur level giving a rise to insignificant sulphate emissions. 2. It has low cold start emissions due to its gaseous state at ambient pressure and temperature. 3. It has relatively high octane number with propane having the best antiknock properties relative to other components. 4. It has lower peak pressure during combustion which generally reduces noise and improves durability. Noise levels can be less.than 50% of equivalent diesel engines. 5. It can be stored as liquid under very low pressures (~5bar) and ambient temperature. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Im:-
Automobile
6. Its refuelling process in LPG tanks gasoline.
IS
Engineering
I
relatively fast (-3minutes) i.e. similar to
7. LPG fuel systems are sealed and evaporative losses are negligible. 8. It is easily transportable and offers 'stand-alone' storage capability with simple and self-contained LPG dispensing facility with minimum support infrastructure. 9. LPG vehicles do not require special catalysts. 10. It contains negligible toxic components. 11. With proper design and positioning of the port fuel injector, volumetric efficiency and power losses are too low. Turbo-charging may not be necessary.
ww w.E asy
12. Its high Octane.number provides room for increasing the compression ratio and fuel, efficiency of dedicated engines.
l3. LPG has lower particulate emissions and low noise level relative to diesels thereby making it more attractive in urban areas. 14. Its low emissions have low greenhouse gas effect and low NOx precursors.
En gi
15. It has higher calorific value than gasoline on a mass basis.
Disadvantages of LPG:
nee
I. Although LPG has a relatively high energy content per mass, its energy content per
rin
unit volume is low because LPG tanks take more space and weigh more than gasoline tanks.
2. It is heavier than air which requires appropriate handling.
g.n et
3. Its vapour flammability limits in air (2-10% by volume) are wider than gasoline which makes LPG ignitable more easily. 4. It has a high expansion coefficient which necessitates only partial filling of the tank not more than 80% of its capacity. 5. The filling system of the LPG tanks is not uniform across the country. So, it demands different adaptors to connect service pump and vehicle. 6. It can give rise to backfiring in the inlet manifold unless a multi-point fuel injection system is used. 7. LPG in liquid form can cause cold bums to the skin in case of inappropriate use.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative
Energy Sources
5.S. USE OF BIO-DIESEL IN AUTOMOBILES Biodiesel is a fuel derived from vegetable oil or animal fats. It can be used as an additive to or entirely replace conventional petroleum diesel fuel. The majority of biodiesel is made from soybean or canola oils but it is also made from waste stream sources such as used cooking oils or animal fats. In most cases, biodiesel is mixed with conventional diesel because of high cost of biodiesel, engine compatibility issues and cold weather operating concerns are considered. Common blends are B20 or 20% biodiesel and B2 or 2% biodiesel. The environmental benefits of using biodiesel scales with the percentage of biodiesel contains in
ww
the blend. •
BIOQ: 100% biodiesel offers the most overall environmental benefits. Use of BI00 may require engine or fuel system component modification and it can cause operating
w.E asy E
problems especially in cold weather. •
B20: 20% biodiesel offers about one fifth of the environmental benefits ofBI00 but it can be more broadly applied to existing engines with little or no modification.
•
B2: 2% biodiesel offers little environmental or petroleum dependence benefit and it could be potentially used an environmental marketing tool.
ngi nee
rin
Using biodiesel in a conventional diesel engine substantially reduces emissions of unburnt hydrocarbons, carbon monoxide, sulfates, polycyclic aromatic hydrocarbons, nitrated polycyclic aromatic hydrocarbons and particulate matter. These reductions increase when the amount of biodiesel blended into diesel fuel increases; The best emission reductions are seen with BI00.
g.n
et
The use of biodiesel decreases the solid carbon fraction of particulate matter (since the oxygen in biodiesel enables more complete combustion to CO2) and it reduces the sulphate fraction (biodiesel contains less than 15 ppm sulphur) while the soluble or hydrocarbon, fraction stays the same or increases. Therefore, biodiesel works well with emission control technologies such as diesel oxidation catalysts. Emissions of nitrogen oxides increase with the concentration of biodiesel in the fuel and the increase is roughly 2% for B20. Some biodiesel produces more nitrogen oxides than others and some additives have shown a promise reduction in the increase of nitrogen oxides. More R&D is needed to resolve this issue.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'am
Automobile Engineering
5.6.1. Properties of Biodiesel
Biodiesel's Physical Characteristics Specific gravity
0.87 to 0.89
Kinematic viscosity @ 40°C
3.7 to 5.8
Cetane number
46 to 70
Higher heating value (Btu/lb)
16,928 to 17,996
Lower heating value (Btu/lb)
15,700 to 16,735
ww w.E asy Sulphur, wt%
0.0 to 0.0024
Flash Point (closed cup) °C
130.0
Cloud point °C
-lltol6
Pour point °C
-15 to 13
Iodine number
5.6.2. Biodiesel Production
En gi
60 to 135
nee
rin
Biodiesel fuel can be made from new or used vegetable oils and animal fats which are
g.n et
nontoxic, biodegradable and renewable resources. Fats and oils are chemically reacted with an alcohol (methanol is the usual choice) to produce chemical compounds known as fatty acid
methyl esters. Biodiesel is the name given to these esters when they are intended for use as fuel. Glycerol (used in pharmaceuticals and cosmetics among other markets) is produced as a co-product. There are three basic routes to ester production from oils and fats. );>
Base catalyzed transesterification
of the oil with alcohol.
);>
Direct acid catalyzed esterification of the oil with methanol.
);>
Conversion of the oil to fatty acids and then to Alkyl esters with acid catalysis.
The majority of the alkyl esters produced today is done with the base catalyzed reactor because it is the most economic for several reasons. );>
Low temperature (150°F) and pressure (20 psi) processing.
);>
High conversion (98%) with minimal side reactions and reaction time.
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
Alternative Energy!>ources )i>
Direct conversion to methyl ester with no intermediate steps.
)i>
Exotic materials of construction are not necessary.
Biodiesel is produced from vegetable oils by converting the triglyceride oils to methyl (or ethyl) esters with a process known as transesterification. In transesterification process, alcohol reacts with the oil to release three "ester chains" from the glycerin backbone of each triglyceride. The reaction requires heat and a strong base catalyst (e.g. sodium or potassium hydroxide which has already been mixed with the methanol) to achieve complete conversion of the vegetable oil into the separated esters and glycerin. The methanol is charged in excess to assist in quick conversion and recovered for reuse.
ww w.E a
The glycerin can be further purified for sale to the pharmaceutical and cosmetic industries. The mono-alkyl esters become biodiesel with one-eighth the viscosity of the original vegetable oil. Each ester chain, usually 18 carbons in length for soy esters retains two oxygen atoms forming the "ester" and giving the product its unique combustion qualities as an
syE ngi
oxygenated vegetable based fuel. Biodiesel is nearly 10% oxygen by weight. The general process of producing biodiesel is shown in Figure 5.2. Recycled Greases
Vegetable oils
Methanol + KOH ----)~l
nee
Crude biodiesel
Glycerin
Sulphuric acid + metanol
rin
g.n et
Biodiesel
Figure 5.2 Production of Biodiesel 5.6.3. Advantages and Disadvantages of Biodiesel Advantages of Biodiesel ~
Special pumps or high pressure equipment for fueling is not needed because little fossil energy is required to move biodiesel. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I.. );>
Automobile
Engineering
I
It can be used in conventional diesel engines. So, special vehicles or engines to run biodiesel do not need to be purchased.
);>
Clean biodiesel (l00% biodiesel) reduces carbon dioxide emissions by more than 75% over petroleum diesel. Using a blend of 20% biodiesel reduces carbon dioxide emissions by 15%. It reduces the global warming.
);>
Use of biodiesel in a conventional diesel engine will result a substantial reduction of unburnt hydrocarbons, carbon monoxide and particulate matter. Biodiesel reduces emissions of carbon monoxide (CO) by approximately 50 % and carbon dioxide by 78.8 % on a net lifecycle basis.
ww w.E a );>
Since biodiesel is made entirely from vegetable oil, it does not contain any sulphur, aromatic hydrocarbons, metals or crude oil residues.
);>
The lack of toxic and carcinogenic aromatics (benzene, toluene and xylene) in biodiesel reduces impact on human health and the environment.
);>
syE ngi
The high cetane rating of biodiesel (ranging from 46 to 70) is another measure of the additive's ability to improve the combustion efficiency.
i>
nee
As an oxygenated vegetable hydrocarbon, biodiesel itself burns cleanly but it also improves the efficiency of combustion by blending with petroleum fuel.
);>
rin
Since biodiesel can be used in conventional diesel engines, the renewable fuel can
g.n et
directly replace petroleum products by reducing the country's dependence on imported oil. \
);>
Biodiesel offers safety benefits over petroleum diesel because it is much less combustible with a flash point greater than 150°C when compared to 77°C for petroleum diesel. It is safe to handle, store and transport.
Disadvantages of Biodiesel: );>
The flash point of biodiesel (> ISO "C) is significantly higher than diesel (64°C) or gasoline (-45°C). The gel point of biodiesel varies depending on the proportion of different types of esters contained. In practice, it often requires the heating of storage tanks especially in cooler climates.
);>
Pure biodiesel (B I ooj can be used in any petroleum diesel engine, though it is more commonly used in lower concentrations. Some areas have mandated ultra-low sulphur petro-diesel which reduces the natural viscosity and lubricity of the fuel due to the removal of sulphur and certain other materials. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
..
,
Alternative Energy Sourc
s
5.7. USE OF BIO-ETHA
OL IN AUTOMOBILES
Ethanol fuel is ethyl alcohol (or simply alcohol) which is found as the similar type of alcohol in alcoholic beverages. It is most often used as a motor fuel mainly as a bio-fuel additive for gasoline. Bio-ethanol is one of form of renewable energy. It can be produced from agricultural feed-stocks. It can be made from very common crops such as sugar cane, potato, manioc and corn. Cellulosic ethanol offers more advantages because cellulose fibers, a major and universal component in plant cells walls can be used to produce ethanol. According to the International Energy Agency, cellulosic ethanol will allow ethanol fuels to play an important role in future.
ww w.E
The current manufacturing cost of ethanol and biodiesel in India is about Rs. 38/litre, which is much lesser than petrol and diesel price. It puts bio-fuels in a favourable position for meeting India's energy needs especially as the cost of petroleum is expected to continue its upward trend. In addition to provide energy security and a decreased dependence on oil
asy En gi
imports, bio-fuels offer several significant benefits such as reduced emission of pollutants and greenhouse gases and increased employment in the agricultural sector. Ethanol currently produced in India by the fermentation of sugarcane molasses is an excellent bio-fuel and it can be blended with petrol. Domestic ethanol production in 2015 will be closer to 2.1 billion liters compared to 2 billion liters in CY 2014, due to an incremental
nee r
rise in sugarcane production. With a normal production rate of 2.1 billion liters a year, India is
ing .ne
the world's fourth largest producer of ethanol after Brazil, the United States and China. The government of Indi (Gal) approved India's National Biofuel Policy on December 24, 2009. The policy encourages use of renewable fuel as an alternative to petroleum and proposes to
t
supplement India's fuel supply with a 20 percent biofuel (bioethanol and biodiesel) mandate by end of 12th Five-Year Plan (2017). In a bid to renew its focus and implement tire Ethanol Blending Program (EBP), on November 22, 2012, the Cabinet Committee of Economic Affairs (CCEA) recommended a five-percent ethanol blending mandate. The GOI's current target of five-percent blending.of ethanol in gasoline has been partially successful in years of surplus sugar production and unfilled when sugar production declines. Presently, the contracted ethanol supply for calendar year 2014 is sufficient to meet 2.7-percent blending target. The new Indian administration. is considering an increase in Gal's ethanol blending mandate from the current level of five percent to 10 percent in CY 2015. Government-owned petroleum companies are expected to procure 550 million liters of ethanol in CY 2014, 37
indicating that ethanol would make up about 2.1 percent ofTndia's fuel market.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering
I
Ethanol has a research octane number of 120, much higher than petrol which is between 87 and 98. Thus, ethanol blending increases the octane number without having to add a carcinogenic substance such as benzene or a health-risk posing chemical such as methyl tertiary butyl ether (MTBE). The energy content of ethanol is only 26.9 Ml/kg compared to 44.0 Ml/kg for petrol. The fuel economy (km/litre) of a petrol-powered engine would be 38.9% higher than an ethanol-powered engine. In actuality, this difference is 30 % since ethanol engines can run more efficiently because of higher octane rating. For a 10 % ethanol blend, the fuel economy advantage of a petrol engine is only 3 %. The flammability limit of ethanol (19 % in air) is higher than petrol (7.6 %) and likewise the auto-ignition temperature of ethanol is higher than petrol (366 versus 300°C). Thus, ethanol is safer than petrol due to
ww w
the low risk of catching fire. Ethanol's higher latent heat of vapourization and greater propensity to absorb moisture may lead to engine starting and corrosion problems but none of these problems have manifested in millions of hours of running automobile engines in Brazil.
.Ea
syE ngi
5.7.1. Sources of Bio-ethanol (Alcohol)
As already stated, ethanol is a renewable energy source because the energy is generated by using a resource of sunlight which is available abundantly without depletion.
nee
Bio-ethanol is generally produced by the conversion of carbon based feedstock. Agricultural feed stocks are considered as renewable sources due to energy obtained from the
rin
sun using photosynthesis. Ethanol can be produced from a variety of feed stocks such as sugar
g.n et
cane, bagasse, miscanthus, sugar beet, sorghum, grain, switchgrass, barley, hemp, kenaf, potatoes, sweet potatoes, cassava, sunflower, fruit, molasses, corn, stover, grain, wheat, straw, cotton, other biomass, as well as many types of cellulose waste and harvestings.
Ethanol can be produced from petroleum product. It is made by the catalytic hydration of ethylene with sulfuric acid as the catalyst. It can also be produced from ethylene or acetylene from calcium carbide, coal, oil gas and other sources. The petroleum derived ethanol called synthetic ethanol is chemically identical to bio-ethanol but it can be differentiated only by radiocarbon dating. An alternative process to produce bio-ethanol is also under the research done by Algenol from algae. Ethanol is produced by fermentation process of grow algae with the use of sunlight.
!
Currently, the production of ethanol from corn uses only a small part of the .com plant. The corn kernels are taken from the corn plant but only the starches have 50% of the dry kernel mass. This kernel mass is converte<\ into ethanol. Another two types of ethanol Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources
.W
production process are under development. In the first type, enzymes are used and the plant cellulose is converted into ethanol by yeast fermentation. In the second type, the pyrolysis is converted the whole plant to either a liquid bio-oil or a syngas. For these two types also, grasses, wood or agricultural waste material such as straw can be used. 6.7.2. ~io-Ethanol (Alcohol) Production Ethanol is a product of fermentation. Fermentation is a sequence of reactions which release energy from organic molecules in the absence of oxygen. In fermentation process, energy is obtained when sugar is changed to ethanol and carbon dioxide. Changing com to
ww w.E a
.
ethanol by fermentation takes place in many steps. Starch in com must be broken into simple sugars before the fermentation process can occur. In earlier times, it was done by chewing the corn. It allowed the salivary enzymes to naturally break down the starch. Today, it is achieved by cooking corn and adding enzymes alpha amylase and gluco amylase. These enzymes function as catalysts to speed up the chemical reaction.
syE ngi
Once a simple sugar is obtained, yeast will be added. Yeast is a single-celled fungus that feeds on the sugar and causes the fermentation. As the fungus feeds on the sugar, it produces alcohol (ethanol) and carbon dioxide. In fermentation, the ethanol retains much of the energy that was originally in sugar which explains why ethanol is an excellent fuel. Ethanol is
nee
rin
produced from com by using one of two standard processes such as wet milling process or dry milling process. Dry milling plants cost less to build and produce higher yields of ethanol (2.7 gallons per bushel of corn) but the value of the co-products is less.
1. Dry Milling Process:
g.n et
Most of the ethanol plants in the country utilize a dry milling process. The major steps of dry milling are outlined below and it is illustrated in Figure 5.3. (a) Milling: After the corn (or other grain or biomass) is cleaned, first it passes through hammer mills which grind it into a fine powder. (b) Liquefaction: The meal is then mixed with water and an enzyme (alpha amylase) and it passes through cookers where the starch is liquefied. A pH of 7 is maintained by adding sulphuric acid or sodium hydroxide. Heat is applied to enable the liquefaction process. Cookers with a high temperature stage (120°-150° C) and a lower temperature holding period (95° C) are used. The high temperatures reduce bacteria levels in the mash. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
ww w.E a
syE ngi
Distilledgrains & Solubles
Syrub
nee
rin
Figure 5.3 Production of ethanol by dry milling process (c) Sa«/Iarijication:
g.n et
The mash from cookers is cooled and the enzyme gluco amylase is added to convert starch molecules to fermentable sugars (dextrose). (d) Fermentation:
YettSt is added to the mash to ferment sugars to ethanol and carbon dioxide. Using a continuous process, the fermenting mash flows through several fermenters until the mash is fully fermented and leaves the tank. In a batch fermentation process, the mash stays in one fermenter for 48 hours. (e) Dimllation: The fermented mash called "beer" contains 10 % alcohol as well as all non-fermentable solids from the corn and yeast cells. The mash is then pumped to continuous flow and multicolumn' distillation system where the alcohol is removed from solids and water. The alcohol leaves the top of the final column with the range of 96 % strength and the residue mash called
stillage is transferred from the base of the column to the co-product processing area. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Alternative Energy Sources (f)
Dehydration:
The alcohol then passes through a dehydration system where the remaining water is removed. Most plants use a molecular sieve to capture the last bit of water in the ethanol. The alcohol at this stage is called anhydrous ethanol (pure ethanol, without water). (g) Denaturing: Ethanol is used as fuel and it is then denatured with a small amount (2-5%) of some product such as gasoline to make it unfit for human consumption. 2. Wet Milling Process: The wet-milling operation is more elaborate because the grain must be separated into its
ww w.E
components. The major steps of wet milling process are outlined below and it is illustrated in Figure 5.4. After milling, the corn is heated in a solution of water and sulphur dioxide for 24 to 48 hours to loosen germs and hull fiber. The germ is then removed from the kernel and corn
asy En gi
oil is extracted from the germ. The remaining germ meal is added to hulls and fiber to form corn gluten feed. A high-protein portion of the kernel called gluten is separated and it becomes corn gluten meal which is used for animal feed. In wet milling, only the starch is fermented unlike dry milling when the entire mash is fermented.
nee r
Once the alcohol fuel is made, it will have to be stored. The same precaution is used which is used for gasoline storage. Alcohol is hygroscopic (absorbs moisture). So, the small vents are made in the storage tank. 6.7.3. Performance of Ethanol·Based Engine
ing .ne
t
Ethanol is most commonly used to power automobiles even if it is used to power other vehicles such as farm tractors, boats and airplanes. Ethanol (E 100) consumption in an engine is approximately 51% higher than gasoline since the energy per unit volume of ethanol is 34% lower than gasoline. The higher compression ratio in an ethanol engine provides increased power output and better fuel economy than lower compression ratio. Usually, ethanol engines give slightly better power and torque output than gasoline-powered engines. An engine powered by alcohol if converted correctly will have performance equivalent if not greater than the same power plant burning gasoline because of alcohol having a higher "octane" rating and it can stand much greater compression ratio. Even without changing the compression ratio, an alcohol-powered engine with fairly low compression still holds its own against its gasoline-burning counterpart. Also, if the timing is advanced safely short of the
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering
"knock" limit, the torque range is broadened considerably thereby allowing the vehicle to pull under load exceptionally well.
Steep Water
ww w.E
asy En gi
nee r
ing .ne
t
FUEL Livestock & Poultry feeds
Figure 5.4 Production of ethanol by wet milling process
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
,'p-
I Alternative Energy Sources 5.7.4. Engine Cold Start during Winter
High ethanol blends have a problem to achieve enough vapour pressure for the fuel to evaporate and spark the ignition during cold weather. When the vapour pressure is below 45kPa starting a cold engine becomes difficult. To avoid this problem at temperatures below II°C and to reduce ethanol higher emissions during cold weather, both US and European markets, E85 is used as the maximum blend in flexible fuel vehicles and they are optimized to run at such a blend. Sometimes, E70 is also used with the maximum blend in some of US states. 5.7.5. Fuel Economy
ww w.E
Theoretically, all fuel-driven vehicles have a fuel economy which is directly proportional to the fuel's energy content. The fuel economy of an engine is directly proportional to how rich is the air/fuel mixture and it is dependent on how large the main jet is the carburetor.
asy En gi
Alcohol requires a richer air/fuel mix than gasoline (9-to-1 as opposed to 15-to-l) but this difference is not reflected proportionately with respect to economy and it is partially due to alcohol having a higher "octane" rating. So, it can be utilized more efficiently. An increase in engine compression ratio will improve alcohol mileage considerably. In practice, many other
nee r
variables will play and affect the performance of a particular fuel in an engine.
ing .ne
140 ~
t
::::J VI VI
~ a.,.... .... 0l0l
.~ ::
~0e:.0 120
Q) ::::J
Ol
c:
u..
10 Ol
'L::
:2:
::::J
~a.,
0:,
----. --
Ethanol Gasoline
,, ,
20 ...... .__
Percent excess fuel lean
Percent excess fuel rich
-~)o~
Figure 5.5 Ethanol Vs Gasoline on engine performance Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1Automobile Engineering I ~~--~~------------------------~--~. 5.7.6. Ethanol Fuel Mixtures To avoid engine stall due to slugs of water in the fuel lines interrupting fuel flow, the fuel used in automobiles should be a single phase. The fraction of water that an ethanol-gasoline fuel can contain without phase separation increases with the percentage of ethanol. For example, E30 can have up to 2% water. About 71% ethanol is more in fuel and the remainder can be a proportion of water or gasoline and phase separation will not occur. But the fuel mileage decreases with increased water content. 5.7.7. Properties/Characteristics (a) Ethanol/Alcohol
of Ethanol/ Alcohol
is on the average about 16 points higher on the research octane
ww w.E
scale than premium gasoline. So, alcohols have higher octane rating than the gasoline.
(b) Alcohols contain only 63% of the energy but gasoline has more because of the presence of oxygen in the alcohol's structure. Hence, heating value is less.
asy En gi
(c) Alcohols are highly volatile than gasoline.
(d) Alcohols have a higher flash point than gasoline and hence, it is much safer automotive fuel. (e) Latent heat of vapourization of alcohols is more than gasoline. Hence, the engine should be operated at a much lower temperature.
nee r
(f) When gasoline is burned in an engine, it produces carbon monoxide and other
ing .ne
poisonous fumes as it contains lead, sulfur and other noxious materials. Alcohol, on the other hand, burns completely.
t
(g) Alcohol requires a richer air/fuel mix than gasoline (9: 1 as opposed to 15:1) due to the fact that alcohol has a higher "octane" rating and it can be utilized more efficiently.
5.7.8. Advantages and Disadvantages of Ethanol/ Alcohol Advantages of using ethanol or alcohol as afuel: I. It can be obtained from a number of sources both natural and manufactured. 2. It is high octane fuel with anti-knock index numbers (octane number) of over 100. High octane numbers result at least in part from the high flame speed of alcohol. Engines using high-octane fuel can run more efficiently by using higher compression ratio. 3. Generally, it produces less overall emissions when compared to gasoline.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative
Energy Sources
I
..
4. When burned, it forms more moles of exhaust which gives higher pressure and more power in the expansion stroke. 5. It has high evaporative cooling which results a cooler intake process and compression stroke. It raises the volumetric efficiency of the engine and reduces the required work input in the compression stroke. 6. It has low sulfur content in the fuel. 7. Ethanol reduces the country's dependence on imported oil in lowering the trade deficit and ensuring a dependable source of fuel should foreign suppliers be interrupted.
ww w.E
8. Farmers see an increased demand for grain which helps to stabilize the prices. 9. The quality of the environment improves. Carbon monoxide emissions are reduced (more than 25 %) and lead and other carcinogens (cancer causing agents) are removed from gasoline.
asy En gi
10. Car owners benefit from mcreased octane in gasoline which reduces engine "knock", Ethanol-blended fuels also absorb moisture and clean the fuel system. 11. Ethanol blends such as E-IO unleaded can be used in virtually all gas engines without any engine or mechanical revisions.
nee r
12. Ethanol guards against gas line freeze by absorbing moisture which may get in the
ing .ne
tank during cold weather.
13. Ethanol is low in reactivity and high in oxygen content in making It an effective tool
t
in reducing ozone pollution.
14. Ethanol is a safe replacement for toxic octane enhancers in gasoline such as benzene, toluene and xylene. 15. Ethanol reduces greenhorse gas emissions because it is produced from renewable agricultural feed stocks.
Disadvantages of using ethanol or alcohol as afuel: 1. Low energy content of the fuel which means almost twice as much alcohol as gasoline must be burned to give the same energy input to the engine. Hence more storage capacity of fuel tank is required. 2. Even with the lower energy content of alcohol, engine power for a given displacement would be the same because of low air-fuel ratio needed by alcohol. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IDElI
Automobile
Engineering
3. Engines run on ethanol may give starting problems when the air is cool. 4. Alcohol contains oxygen and thus,.it requires less air for stoichiometric combustion. More fuel can be burned with the same amount of air. 5. More aldehydes are present in exhaust. If as much alcohol fuel was consumed as gasoline, aldehyde emissions would be a serious exhaust pollution problem. 6. Alcohol is much more corrosive than gasoline on copper, brass, aluminum, rubber, and many plastics. It puts some restrictions on the design and manufacturing of engines to be used with this fuel. It should also be considered when alcohol fuels are used in engine systems. Methanol is corrosive on metals. It can be remedied by using nickel in engine alloys.
ww w.E
7. Poor cold weather starting characteristics due to low vapour pressure and evaporation. Often a small amount of gasoline is added to alcohol fuel which greatly improves cold-weather starting.
asy En . gin eer
8. Poor ignition characteristics in general.
9. Alcohols have almost invisible flames which are considered as dangerous when handling fuel. Again, a small amount of gasoline removes this danger. 10. Danger of storage tank flammability due to low vapour pressure. Air can leak into storage tanks and create a combustible mixture.
ing .ne
11. Low flame temperatures generate less NOx but the resulting low exhaust temperature take longer to heat the catalytic converter to an efficient operating temperature.
t
12. Many people find the strong odor of alcohol very offensive. Headaches and dizziness have been experienced when refueling an automobile. 13. Vapour lock in fuel delivery systems may happen frequently. 14. The downstream processing for ethanol recovery is costly as it requires a lot of energy. 5.8. USE OF GASOHOL IN AUTOMOBILES
Gasohol is a mixture of 10% ethanol (ethyl alcohol) and 90% unleaded gasoline. Although automobiles could be designed to operate on alcohol alone for the foreseeable future, the most economic use of ethanol is as an octane booster in gasoline. So, gasohol is a much cleaner fuel than gasoline itself. Gasohol can be used without modifying the,carburetor
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I /~/temative Energy
mil I
Sources
or fuel injector, ignition timing or fuel lines of an automobile. This fuel has higher octane value and anti-knock properties than gasoline and burns slowly and completely results the reduced emissions of some pollutants but it also vapourizes more readily and potentially aggravating ozone pollution in warm weather. Ethanol is an alternative energy source. It is an alcohol made by fermenting corn or other similar biomass material as explained earlier. There are three primary ways that ethanol can be used as a transportation fuel. I. As a blend of 10 % ethanol with 90 % unleaded gasoline called "E':::') 0 Unleaded"; 2. As a component of reformulated gasoline, both directly and as ethyl tertiary butyl
ww w.E ether (ETBE) or
3. As a primary fuel with 85 parts of ethanol blended with 15 parts of unleaded gasoline called "E-85."
asy En gi
Gasohol, a gasoline extender is made from a mixture of gasoline (90%) and ethanol (10%) often obtained by fermenting agricultural crops or crop wastes) or gasoline (97%) and methanol or wood alcohol (3%). Ethanol-based gasohol is expensive and energy intensive to produce and it can damage rubber seals and diaphragms and certain finishes if the ethanol is present in higher concentrations. Methanol-based gasohol is also expensive to produce and it
nee r
is toxic and corrosive and its emissions produce cancer-causing formaldehyde. 5.8.1. Potential of Gasohol in India
ing .ne
India is the second largest producer of sugarcane in the world with a production level of
t
280 Million tonnes per annum. Brazil is the number one producer and it produces 320 Million tonnes of sugarcane in a year. India stands in the fourth place in the world in Ethanol production with a production about 2.1 billion litres per annum. Brazil which produces 16.1 billion litres per year stands I"t the top. The installed capacity in India is 2.7 Billion litres per annum in 278 distilleries. Therefore, only 50% of our capacity in ethanol production is utilized. Another significant feature relates to the use of Sugarcane produced in India. Only 60% of sugarcane produced is processed for producing white sugar in 416 sugar mills located in different regions of India. 30% of sugarcane is used for making Gur and Khandasari sweeteners widely used in rural areas of India. The remaining 10% are used as seed. Ethanol or Ethyl Alcohol production in India is mainly from Molasses waste products from sugar mills. On a worldwide basis, out of the total annual production of 33.3, Billion litres of Ethanol 68% is used as an automotive fuel, 21% is utilized for industrial purposes and Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'mil
Automobile
Engineering'
the remaining 11% is used for beverages. In India, the entire production of Ethanol is used for industrial purposes and producing beverages. The utilizing Ethanol as a fuel in the transportation sector is yet to be decided.
The interest shown in the use of Ethanol as an automotive fuel in India has been rather sporadic in nature and it was largely related to crisis management situations. Very early reported work was carried out in Indian Institute of Science (HSc), Bangalore in 1950s soon after the Second World War. Substantial interest was shown in this area during the end of 70's and the beginning of 80's on account of steep rise in crude prices. Almost all National Level Technical Institutions and Technical Universities embarked on Research and Development work pertaining to the use of Ethanol in gasoline and diesel engines used in Agricultural and Transportation sectors.
ww w.E
The research conducted in Anna University, Chennai on fleet tests using two models of SI Engine driven cars available during 1979-1984. These vehicles were converted to run either on 100% Ethanol (denatured Alcohol) or with a mixture of 90% gasoline and 10% ethanol (gasohol). CI engines (Diesels) were run on dual fuel mode using a carburettor. It was possible to operate passenger buses on dual fuel mode with 45% diesel replacement under
asy En gi
dual fuel operation. The investigations enabled the collection of valuable data on optimal modifications necessary for converting an existing SI engines for neat ethanol operation. Long
nee r
duration trials yielded a valuable data on material compatibility and lubricating oil requirements for ethanol operation.
ing .ne
Emission measurements showed a considerable reduction in conventional pollutants such as CO, HC, and NOx during ethanol operation. However, there was an increase in Aldehyde emission levels. The interest in such investigations dwindled as there was neither clear-cut
t
Government policy nor a direction for the use of Ethanol as a fuel in the transportation sector. In this view, Automotive and Sugar Industries did not support such developmental works. Nevertheless the data obtained and the experience gained has been well documented and it can be used for future investigations. The use of a gasohol (mixture of gasoline and ethanol) such as E85 in different proportions in automobiles is likely to become very popular in future. There is a trend to develop Flexible Fuel Vehicles (FFVs) which can be operated on different ratio of Ethanol and Gasoline. It is desirable to discuss about the features of FFVs and look at the possibility of developing such vehicles in India. Another possible source of alcohol production in the country is the surplus food grain which is rotting in the godowns (warehouses) of Food Corporation of India. The rotten grain Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources
I
~
can be converted to sugars and fermented to alcohol by the semi-utilized production capacity of the distillery industry. Pollution control cost of grain-based alcohol is relatively much low as compared to molasses based-alcohol. Ethanol (alcohol) is an established bio-fuel for transport and industry sectors in several countries notably in Brazil and USA. India with its favourable agro-climatic conditions for sugarcane and sweet sorghum production has tremendous potential to develop this source of bio-energy which can save its foreign exchange spent largely for the import of petroleum. 5.8.2. Gasohol Fueled vehicles
ww w.E
In 1990s, variable fuel vehicles are introduced and operated. These vehicles are capable
of operating on unleaded fuel with ethanol mixtures up to 85 % without having to make any engine adjustments. These vehicles were introduced in 1992 arid they have been used extensively in federal and state fleets and some city governments. They became commercially available shortly thereafter.
asy En gi
E-85 v~hicles have been designed for versatility. The key component in a variable fuel vehicle is a sensor that determines percentage of ethanol in the fuel. With the help of a
nee r
computer, the vehicle automatically adjusts for best performance and emissions. Chrysler began offering E-85 minivans in the 1998 model year and Ford continues to offer the Taurus
ing .ne
and added Windstar and Ranger to E-85 flexible fuel vehicles in 1999 model year. Ford, GMC, Chevrolet and Daimler-Chrysler are now offering E-85 variable fuel vehicles. 5.8.3. Advantages and Disadvantages of Gasohol Advantages of using gasohol as afuel:
t
1. Gasohol can burn more completely and thus increasing the potential combustion energy which will produce the most power. 2. Its high octane numbers result in running the engine more efficiently by using higher compression ratio. 3. Generally, it produces less overall emissions wherr compared to gasoline and hence reduces greenhouse gas emissions. 4. It has high evaporative cooling which results a cooler intake process and compression stroke. It raises the volumetric efficiency of the engine and reduces the required work input in ttre compfession stroke. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I..
Automobile Engineering
5. It has low sulfur content in the fuel. 6. Gasohol reduces the country's dependence on imported oil. 7. It can improve the agricultural economies by providing farmers with a stable income for particular crops such as maize and sugar beets. 8. Burning gasohol is cleaner and less harmful to the environment than burning straight gasoline. 9. Car owners benefit from increased octane in gasoline which reduces engine "knock". Ethanol-blended fuels also absorb moisture and clean the fuel system.
ww w.E
10. It can be used in virtually all gas engines without any engine or mechanical revisions.
Disadvantagesof usinggasoholas afuel: I. Gasohol increases the emissions of aldehydes which are reactive and it will probably bring smog problems.
asy En gi
2. Despite the new emissions are less reactive and will not contribute significantly to photochemical smog, it will also increases evaporative emissions.
nee r
3. It may increase the emission of nitrogen oxides (NOx) as well. The degree to which emissions increase are depending on the vehicle and emission control technology used.
ing .ne
4. Even with the lower energy content of alcohol, engine power for a given displacement would be the same because of low air-fuel ratio needed by alcohol.
t
5. Gasohol is more corrosive than gasoline on engine components such as carburettor. Hence special metals are required in design. 5.9. USE OF HYDROGEN FUELS IN AUTOMOBILES 5.9.1. Sources of Hydrogen
Hydrogen is the lightest element which may someday replace heavier compounds as a source of energy for transportation and many other applicatior:s. Although low-cost technology to allow this odorless, colorless, diffuse gas to be collected, hydrogen's potential to be a clean energy source has some hope about a future "hydrogen economy" which would not rely on fossil fuels.
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
Dill I
I Alternative Energy Sources
Finding sources of hydrogen fuel is harder than the people think. Although hydrogen is the most abundant material in the Universe, very little of it exists in free form in the atmosphere. It must be extracted from other compounds. As a fuel, the hydrogen is used in the form of gas. Since hydrogen does not exist on Earth as a gas, it must be separated from other compounds. It is considered as a s~condary source of energy because another form of energy is needed to produce the hydrogen fuel. The primary sources of energy to produce-hydrogen are natural gas, water, coal or oil. These sources go through different types of processes that allow hydrogen fuel to be made. Natural gas and methanol provide much of the raw material for hydrogen today. Another major source is water (H20). The hydrogen and oxygen in water can be dissociated with an electric current in a process called electrolysis.
ww
w.E
5.9.2. Advantages and Disadvantages of using Hydrogen as Fuel
asy E
Advantages of using hydrogen asfuel:
1. Hydrogen combustion produces only water as a by-product. Hydrogen generates energy without releasing greenhouse gasses or pollutant particles.
ngi
nee rin
2. The only pollution-free source of hydrogen is water which is also the most abundantly available. A simple process called electrolysis can liberate hydrogen from water. 3. Hydrogen has higher energy density than petroleum-based fuels. It means, it supplies more energy per volume than gasoline, diesel or kerosene.
g.n et
4. Hydrogen has the potential to run a fuel-cell engine with greater efficiency over an internal combustion engine. Disadvantages of using hydrogen asfuel:
I. Heavy, bulky fuel storage, both in vehicle and at the service station. Hydrogen can be stored either as a cryogenic liquid or as a compressed gas. If stored as a liquid, it would have to be kept under pressure at very low temperature. It would require a thermally super-insulated fuel tank. Storing in a gas phase would require a heavy pressure vessel with limited capacity. 2. It is difficult to refuel. 3. It produces poor engine volumetric efficiency. Any time, a gaseous fuel is used in an engine the fuel will displace some of the inlet air and it will result poor volumetric efficiency. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
I
Automobile Engineering
4. -Fuel cost would be high at present-day technology and availability. 5. NOx emissions are high because of high flame temperature. 6. It may detonate.
5.9.3. Hydrogen as a Fuel Hydrogen has the highest energy content per unit weight of any known fuel 120.7 kJ/g. It burns cleanly. When hydrogen is burnt with oxygen, only byproducts are heat and water. When burnt with air which is 79% nitrogen (on a volumetric basis), some oxides of nitrogen
ww
are formed.
Hydrogen in its liquid form has been used as a fuel in space vehicles for years. Hydrogen
w.E
has high combustion energy per kg relative to other fuels which means hydrogen is more efficient on a weight basis than fuels currently used in air or ground transportation.
asy E
This
weight factor makes hydrogen an attractive fuel. Hydrogen
is both flammable
and buoyant. It is flammable
ngi
over a wider range of
concentrations than either gasoline or natural gas but due to its buoyancy, it dissipates more rapidly than either of these fuels in a spill. Hydrogen gas like other gases used today should be used in areas which can be ventilated.
nee rin
Hydrogen can be used safely when .guidelines for its proper handling and storage are observed. Individuals
who work with hydrogen systems are trained
g.n et in hydrogen's
safe
handling and used by observing precautions such as preventing hydrogen leaks, taking proper action if leaks occur, eliminating
the opportunity for leaked hydrogen to accumulate and
eliminating sources of ignition,
Hydrogen fuel is unique. It is clean. Its primary combustion by-product is clean water vapour. Hydrogen is versatile- It can be used in applications requiring electricity or gas and it can link the fossil-based energy supply today with the renewable energy tomorrow. As the cost of hydrogen comes down and its availability increases, interest in its use as
fl
fuel will intensify. Therefore, public awareness of hydrogen safety is essential.
5.9.4. Hydrogen Properties Hydrogen is a colourless,
odourless, tasteless and non-poisonous
gas under normal
conditions on Earth. It typically exists as a diatomic molecule i.e. each molecule has two atoms of hydrogen. So, pure hydrogen is commonly expressed as "H2". Hydrogen is the most Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources
UP-
abundant element in the universe accounting for 90% of the universe by weight. However, it is not commonly found in its pure form since it readily combines with other elements. It is also the lightest element having a density of 0.08988 grams per liter at standard pressure. Hydrogen has several important chemical properties that affect its use as a fuel. •
It readily combines with oxygen to form water which is absolutely necessary for the life on this planet.
•
It has high energy content per weight (nearly 3 times as much 'as gasoline) but the energy density per volume is quite low at standard temperature and pressure. Volumetric energy density can be increased by storing the hydrogen under increased
ww
pressure or storing it at extremely low temperature as liquid. Hydrogen can also be
adsorbed into metal hydrides.
•
w.E
Hydrogen is highly flammable. It only takes a small amount of energy to ignite it and make it bum. It also has a wide flammability range, it means, it can burn when it makes up to 74% of the air by volume.
asy E
ngi
•
Hydrogen bums with a pale-blue almost-invisible flame in making hydrogen fires difficult to see.
•
The combustion of hydrogen does not produce carbon dioxide (C02), particulate or sulphur emissions. It can produce nitrous oxide (NOx) emissions under some conditions.
•
nee rin
g.n et
Hydrogen can be produced from renewable resources such as by reforming ethanol and by the electrolysis of water.
5.9.5. Production of Hydrogen Hydrogen is the simplest and most abundant element in the universe which holds great promise as a fuel. Two methods are generally used to produce hydrogen gas such as ' electrolysis and synthesis gas production. Electrolysis uses electrical energy to separate hydrogen and oxygen atoms in water molecules. The electrical energy can come from any electricity source including renewable fuels and solar energy. Some scientists envision a future in which large arrays of solar panels will provide this electric current. So, electrolysis is unlikely to become the predominant method for producing large quantities' of hydrogen. Non-electric ways ofproducing hydrogen such as biomass gasification may require less primary energy and will potentially cost less. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I...
Automobile
I
Engineering
The predominant method of producing synthesis gas (a combination of carbon monoxide and hydrogen) is steam reforming of natural gas. In a steam reformer, methane or another hydrocarbon is passed over a catalyst along with steam. The process takes place under high temperature and pressure using a special receptacle. The reaction converts the methane and water to CO and hydrogen. Another mechanism for producing energy using hydrogen gas is the fuel cell. A fuel cell uses hydrogen to produce an electric current. A fuel cell has a battery. It has electrodes, electrolyte and positive and negative terminals. But it produces electric current continuously rather than recharging and storing the chemical energy.
ww
About 95% of the hydrogen, reforming natural gas is used today. Remaining is highpurity hydrogen from water electrolysis by using electricity mainly generated by burning
w.E
fossil fuels. Some of the specific technologies are used to produce hydrogen include.
asy E
•
Steam reforming converts methane (and other hydrocarbons in natural gas) into hydrogen and carbon monoxide by reaction with steam over a nickel catalyst.
•
Electrolysis uses electrical current to split water into hydrogen at the cathode (+) and oxygen at the anode (-).
•
ngi
nee rin
Steam electrolysis (a variation on conventional electrolysis) uses heat instead of electricity to provide some of the energy needed to split water in making the process more energy efficient.
•
g.n et
Thermochemical water splitting uses chemicals and heat in multiple steps to split water into its component parts.
•
Photo-electrochemical systems use semi-conducting photovoltaics to split water using only sunlight.
materials
such
as
•
Photo-biological systems use microorganisms to split water using sunlight.
•
Biological systems use microbes to break down a variety of biomass feed stocks into hydrogen.
•
Thermal water splitting uses a very high temperature approximately IOOO°C to split water.
•
Gasification uses heat to break down biomass or coal into a gas from which pure hydrogen can be generated.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources
-
Once hydrogen is produced, it must be transported to its point of use. Its low volumetric energy density makes it challenging to transport and deliver. Today, hydrogen is stored and transported as a compressed gas or cryogenic liquid. 5.9.6. Hydrogen from Natural Gas
1. Natural gas steam reforming: The production of hydrogen from natural gas is an integral part of the strategy to introduce hydrogen into the transportation and utility energy sectors by reducing the cost of conventional and developing innovative hydrogen production processes that rely on cheap fossil feedstock, Today, nearly all hydrogen productions are based on fossil raw materials. Worldwide, 48% of hydrogen is produced from natural gas, 30% from oil (mostly consumed
ww
w.E
in refineries), 18% from coal and the remaining 4% via water electrolysis. Modification of the conventional steam methane reforminw(SMR) process to incorporate
asy
an adsorbent in the reformer to remove CO2 from the product stream may offer a number of
En
advantages over conventional processes.
gin eer
Upsetting the reaction equilibrium in this way drives the reaction to produce additional hydrogen at low temperature than conventional SMR reactors. Although it is still in the research stage, the cost of hydrogen from this modified process is expected to be 25%-30% low primarily because of reduced capital and operating cost, In addition, the adsorption of
ing
CO2 in the reforming stage results a high-purity CO2 stream from the adsorbent regeneration step. It has interesting implications in a carbon-constramed world. 2. Ion Transport Membranes:
.ne
t
Although steam reforming of natural gas to produce hydrogen is a mature technology, it is operating at or near its theoretical limits and it is still much too expensive for producing hydrogen for future automobiles and other applications. Advanced Ion Transport Membranes (ITM) may simplify the process of producing hydrogen from natural gas and separating it by combining these processes·into a single step to low cost and increase efficiencies. ITM systems combine the separation of air to produce oxygen and the subsequent use of that oxygen in a process called partial oxidation to generate synthesis gas. The process takes place in a single step. The technology uses non-porous ceramic membranes fabricated from multi-component metallic oxides which conduct both electrons and oxygen ions at temperature greater than 700°C. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I..
Automobile Engineering Steam and Natural gas Air ITM Ceramic membrane
Oxygen passes through membrane
ww
w.E
Nitrogen-rich depleted air
Synthesis gas
asy E
Figure 5. 6 Preparation of hydrogen from natural gas
ngi
During operation, oxygen from a hot air stream is reduced by catalysts at one surface of the membrane to create oxygen ions. The oxygen ions flow through the membrane under a chemical gradient to the opposite membrane surface where they partially oxidize a pre-
nee rin
reformed hot mixture of steam and natural gas to form synthesis gas, a mixture of carbon monoxide and hydrogen. The ratio of hydrogen to carbon monoxide is partly dependent on the amount of steam used.
g.n et
The synthesis gas then proceeds to a water-gas shift reactor':where additional steam is added to convert the steam and carbon monoxide into more hydrogen and carbon dioxide. This mixture of hydrogen, carbon dioxide and trace amounts of carbon monoxide are then separated to produce a hydrogen product stream and a concentrated carbon dioxide stream which can be captured and eventually sequestered. The current technology used to separate hydrogen from synthesis gas is by Pressure Swing Adsorption (PSA). However, advanced membrane technologies which are under development have the potential to reduce the cost of this process step. 5.9.7. Thermochemical Processes Thermochemical hydrogen production technologies use heat and chemical reactions to convert hydrocarbon feed stocks to hydrogen. Steam methane reforming, partial oxidation of methane and biomass gasification and pyrolysis can be used to produce hydrogen. Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Altematlve Energy Sources 1. Steam
methane reforming:
In this process, high-temperature steam' is used to extract hydrogen from natural gas. It is the most common method of producing hydrogen and 95 % of the hydrogen in use today is produced by this process.
2. Partial oxidation/ceramic membrane reactor: Scientists are developing a ceramic membrane reactor for simultaneous separation of oxygen from air and partial oxidation of methane. If successful, this process could result the improved production of hydrogen and synthesis gas when compared to conventional reformers.
ww w.E a
3. Other thermal processes:
They include gasifying or burning biomass (i.e., biological material such as plants or agricultural waste) to produce hydrogen.
syE
5.9.8. Other Methods of Producing Hydrogen
1. Biomass gasification and pyrolysis:
ngi
The thermal processing techniques for plant material (biomass) and fossil fuels are
nee r
similar to a number of downstream unit operations being essentially same for both feed stocks. Using agricultural residues ana wastes or biomass specifically grown for energy uses,
ing
hydrogen can be produced via pyrolysis-or gasification process. Biomass pyrolysis produces a
.ne
liquid product (bio-oil) such as petroleum which contains a wide spectrum of components that can be separated into valuable chemicals and fuels.
t
Dissimilar to petroleum, bio-oil contains a significant number of highly reactive oxygenated components derived mainly from constitutive carbohydrates and lignin. These components can be transformed into products including hydrogen. Co-product strategies are designed to produce high value chemicals such as phenolic resins in conjunction with hydrogen.
2. Electrolytic processes: Electrolytic hydrogen production processes the use of electrical energy to split water into hydrogen and oxygen.
Electrolysis: In electrolysis, electricity is used to separate water (H20) into hydrogen (H2) and oxygen (02),
The electricity can come from fossil fuels such as coal or from
renewable sources such as nuclear, solar or hydroelectric power. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IUD
Automobile
Engineering
I
3. Water electrolysis: Until 1950s, water electrolyzers were in widespread use for hydrogen (or oxygen) production. Currently, electrolysis provides only a small percentage of the world's hydrogen, most of which is supplied to applications requiring small volumes of high purity hydrogen (or oxygen such as for breathing atmospheres for submarines). There is significant renewed interest in the use of electrolyzers to produce hydrogen as a fuel for automotive applications with a number of refueling stations installed around the world. In addition, research continues in the integration of intermittent renewable resources (PV and wind) with electrolyzers for producing hydrogen to be used as a fuel or energy storage.
ww
4. Reversiblefuel cells / electrolyzers: Operating the Proton Exchange Membrane (PEM) fuel cell "in reverse" as an electrolyzer
w.E
is possible but optimum operating conditions are for the power production mode and for the hydrogen production mode, they are significantly different. Design issues for the reversible
asy E
fuel cell system include thermal management, humidification and catalyst type and loading. 5. Photolytic processes:
ngi
Photolytic hydrogen production technologies use the energy from sunlight to split water into hydrogen and oxygen. Emerging direct water-splitting technologies include photobiological and photo-electrochemical systems.
nee rin
Photolytic methods: Photolysis is a chemical change caused by light. Two photolytic processes are being explored.
g.n et
(a) Photo-biological methods where microbes produce hydrogen when exposed to light, and
(b) Photo-electrolysis where special metals are exposed to light and submersed in water which generates enough electricity to generate hydrogen by splitting the water.
a. Photo-biological method: Certain photosynthetic microbes produce hydrogen in their metabolic activities using light energy. By employing catalysts and engineered systems, hydrogen production efficiency could reach 24%. Photo-biological technology holds a great promise because oxygen is produced along with the hydrogen. The technology must overcome the limitation of oxygen sensitivity of the hydrogen-evolving enzyme systems. Researchers are addressing this issue by screening for naturally occurring organisms which are more tolerant of oxygen and by creating new genetic forms of the organisms that can sustain hydrogen production in the Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'i.
I Alternative Energy Sources
presence of oxygen. A new system is also being developed which uses a metabolic switch (sulphur deprivation) to cycle algal cells between photosynthetic growth phase and hydrogen production phase. Unlike cyano-bacteria or algae, photosynthetic bacteria do not oxidize the water. They do, however, evolve hydrogen from biomass (previously generated from sunlight, water and carbon dioxide). These bacteria use several different enzymatic mechanisms with near-term commercial potential for biological hydrogen production from biomass. b. Photo-electrolysis method: Multifunction cell technology developed by PV industry is being used for photoelectrochemical (PEC) light harvesting systems that generate sufficient voltage to split water
ww
and they are stable in a water/electrolyte environment. Theoretical efficiency for tandem
w.E
junction systems is 42%, practical systems could achieve 18%-24% efficiency, low-cost multi-junction amorphous silicon (a-Si) systems could achieve 7%-12% efficiency. It is one of
asy E
the advantages of a direct conversion hydrogen generation system. It is not only eliminating most of the costs of the electrolyzer but it also has the possibility of increasing the overall efficiency of the process. Research results the development of PEC water splitting systems which have shown a solar-to-hydrogen efficiency of 12.4% lower heating value (LHV) using
ngi
nee rin
concentrated light. Low-cost Si tandem designs with appropriate stability and performance are also being developed. An outdoor test of Si cells resulted a solar-to-hydrogen efficiency of 7.8% LHV under natural sunlight. 5.9.9. Methods of using Hydrogen in CI Engines
g.n et
The following are the two methods by which hydrogen can be used in CI engines: Method 1:
Hydrogen is introduced with air and using spray of diesel to ignite the mixture i.e. by the
dualfuelmode, The limiting conditions are when the diesel quantity is too small to produce effective ignition i.e, failure of ignition and when the hydrogen-air mixture is so rich that the combustion becomes unacceptably violent. In between these limits, a wide range of diesel to hydrogen proportions can be tolerated. Method 2: In this method, hydrogen is directly injected into the cylinder at the end of compression and the gas spray is made to impinge on a hot glow plug in the combustion chamber i.e. by surface ignition since the self-ignition temperature of hydrogen is very high. It is also possible
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1-
Automobile Engineering
to feed a very lean hydrogen-air mixture during intake into an engine and then it injects the bulk of hydrogen towards the end of compression stroke. 5.9.10. Challenges for Hydrogen Fuel
Technology validation addresses the following key challenges to pave the way for commercialization of fuel cell and hydrogen infrastructure technologies. 1. Fuel cell cost and durability:
Statistical data for fuel cell vehicles which are operated under controlled and real-world conditions are very limited and often proprietary. Vehicle drivability, operation and
ww w.E a
survivability in extreme climates and emissions have not yet been proven. The development and testing of complete integrated fuel cell power systems are required to benchmark and validate for optimal component development. 2. Hydrogen storage:
syE
Statistical cost, durability, fast-fill, discharge performance and structural integrity data of
hydrogen storage systems will be needed to proceed with technology commercialization. Current technology does not provide a reasonable cost and volume for transportation or stationary applications. An understanding of composite tank operating cycle life and failure due to accident or neglect are lacking. Cycle life of hydride storage systems need to be evaluated in real-world circumstances.
ngi
3. Hydrogen production and delivery:
nee r
ing
.ne
The high cost of hydrogen production, low availability of the hydrogen production
t
systems, the challenge of providing safe production and delivery systems is early penetration barriers. There are few data on the cost, efficiencies and availabilities of integrated coal-tohydrogen/power plants with sequestration options. Data on high-temperature production of hydrogen from nuclear power are limited. Similarly, there is little operational, durability and efficiency information for renewable hydrogen production systems. Hydrogen delivery options need to be determined and assessed as a part of system demonstrations for every potential production technology. A validation of integrated systems is required to optimize component development. 4. Public acceptance: The hydrogen economy will be a revolutionary change from the world today. Education of general public, training personnel in handling and maintenance of hydrogen system
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative
i:iiMJ
Energy Sources
components, adoption of codes and standards, development of certified procedures and training manuals for fuel cells and safety will foster hydrogen's acceptance as a fuel. 5.9.11. Hydrogen Fueled Vehicles There have only been a small number of prototype hydrogen vehicles made. Most of them have been experimental vehicles made by car manufacturers. Nearly, all of these prototype cars were equipped with internal combustion engines which are similar to gasoline. Figure 5.7 shows a hydrogen powered bus.
ww w.E a
syE
ngi
nee r
Figure 5.7 Hydrogen powered bus
ing
5.10. ENGINE MODIFICATIONS REQUIRED FOR ALTERNATE FUELS 5.10.1. Need for Engine Modification
.ne
t
Impending possible energy crisis in future, rising costs and toxic emissions associated with conventional petroleum fuels have originated people to search out and investigate the possibility of utilization of alternate clean arid non-polluting gaseous fuels for internal combustion engines. Due to increasing number of cars and decreasing of oil resources, the use of alternative fuels will be inevitable in future. The alternative fuels used in gasoline and diesel engines are becoming the interest today to use in conventional engines. The adequacy of fuel supply, process efficiency, ease of transport, safety of storage and modifications are required in the distribution/refueling network in the vehicle and fuel compatibility with vehicle engine. Two categories of fuels are explored such as alcoholic fuels and gaseous fuels. Alcohols , could be produced from renewable resources and they produce less exhaust pollutants. Gaseous fuels offer cleaner combustion due to improved fuel-air mixture preparation than Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I~
Automobile Engineering
conventional liquid fuels. Specifically, the fuels are biodiesel used in a compression ignition engine and bio-ethanol used in a spark ignition engine. In addition, CNG (compressed natural gas) is a gaseous form of natural gas by providing some substantial benefits compared to gasoline and diesel fuels. They offer the advantages such as less fuel costs, high octane and clean exhaust emissions. The use of alternative fuels may be achieved either by modifying conventional fuels slightly in blending non-edible oils or by converting an existing engine to operate on either original fuel or alternative fuel "dual fueling" or a specially designed engine for the new fuel will offer better performance.
ww
The fuel usage of CNG is carried out in three ways such as dual fuel, bi-fuel and dedicated/mono Fuel.
w.E
1. Dual fuel engine:
asy E
If both diesel and natural gas are introduced into engine cylinders during compression, it is called dual fuel engine. It is the direct development of a conventional engine. 2. Bi..Juel engine:
ngi
The engine was developed from conventional petrol engines where the fuel system has
nee rin
been modified to operate either petrol or gas. When natural gas refueling is not available, normal running on petrol is possible. 3. Dedicated/single fuel:
"
g.n et
It is a specially designed engine to operate only natural gas under optimum level. 6,10.2. Engine Modification for Bio-Ethanol (Alcohol) and Gasohol
'The addition of an ethanol E 10 blend to petrol wiII increase the octane number of the petrol fuel hy two points. Therefore, bio-ethanol is termed as an "octane enhancer". An .-ethanclE 10 blend of fuel will normally have an oxygen content of 3.5%. The oxygen present
in.ethanol affects the air to fuel ratio. The air / fuel ratio of ethanol is 12.7:1 which is slightly less than the 14,.6: 1 air / Wei ratio used for conventional fuels. 1. Fuel filters: It is necessary to change vehicle's fuel filter more often as ethanol blends can loosen solid deposits in fuel tanks and fuel lines.
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative
'iii.
Energy Sources
2. Cold starting:
Ethanol blends have high latent heat of evaporation than pure petrol thereby having poor cold start ability in winter. Hence, some vehicles have small petrol tank fitted containing pure petrol for starting the vehicle in cold weather. 3. Mechanical modifications required/or bioethanol as afuel in SI engine: Generally, the modifications might be carried out in the following elements of engine irrespective of type of engines such as changes to cylinder walls, cylinder heads, valves and valve seats, pistons, piston rings, intake manifolds and carburetors, nickel plating of steel fuel lines, fuel tanks to prevent ethanol E20 corrosion and high fuel flow rate injectors to
ww w.E
compensate oxygenate qualities of ethanol. When gasoline containing more than 25% ethanol is used in SI engines, some modification must be made to the engine. Before mechanical modifications are undertaken on an engine, a choice must be made to the ease of reversibility of the engine change and the availability of alcohol fuel for all anticipated vehicle lise, cost of the engine modifications, and
asy E
expertise required in making the engine modification. (a) Reversible modifications:
ngi
nee
These modifications can be done with the relative ease to permit operation on convention fuels. These modifications include as follows: 1. Changing the spark timing. 2. Changing the vacuum advance. 3. Modifying the carburetion for increased fuel flow.
rin
g.n e
4. Heating the air-fuel mixture to ensure the vapourization of the alcohol, and 5. Using various methods to enhance the cold starting ability of the engine.
t
(i) Spark timing: The spark timing of an engine must be advanced to run on ethanol. It is done to provide ethanol with enough time to complete combustion since ethanol burns slower than gasoline. (ii) Vacuum advance:
The vacuum advance affects the fuel economy of the engine operating on ethanol. So, the vacuum advance is set to give an additional 10°of advance over idle ignition time.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IDD
Automobile Engineering
(iii) Carburettor modification: Generally, engines require more volume of fuel when operated on ethanol as compared to operation on gasoline. The correct stoichiometric air-fuel mixture for ethanol is 9:1 while the correct mixture for gasoline is 14.7: 1. It is due to the difference in energy content per volume because ethanol has low energy content per volume than gasoline. The fuel-flow increase is achieved by modifying the carburetor. The general procedure for the fuel flow increase is to enlarge the carburettor fuel jet diameter 1.5 times. It can be done by drilling out the original to replace the jet. (iv) Preheating air-fuel mixture:
ww
The air-ethanol fuel mixture requires 2.5 times more heat for vapourization th~ gasoline.
Therefore, some additional heat may be desirable for the air fuel mixture before it enters the cylinder.
w.E
(v) Cold start modification:
asy E
One of main problems in using ethanol engine is low temperature. This problem arises due to the requirement of more heat for vapourization of ethanol than gasoline. The cold-start problem with ethanol can be overcome in several different ways. It can be overcome by the use of additives. (b) Irreversible modifications:
ngi
nee rin
Modifications are hard to remove. They also are usually more expensive, require more
g.n et
expertise and can be very hazardous when the engine fails. The possible modifications are: 1. Cam shaft change,
2. Increasing the engine compression ratio and 3. Using turbochargers or superchargers. (i) Camshaft change:
The cam shaft is changed in such a way to provide more RPM torque, easier starting and better fuel economy. (ii) Increasing in compression ratio:
The compression ratio is increased to increase the octane rating of ethanol to produce more power. The increased compression ratio is from 7: 2: I to 11:1. (iii) Using turbochargers or superchargers: The turbochargers and superchargers are used in order to increase the fuel admit pressure during suction stroke of the engine. Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative
Energy Sources
4. Mechanical modificationsrequiredfor bioethanolas afuel ill CI Engine: The efficiency of ethanol used CI engines will not be beneficial than SI engines. The following modifications may be carried out for the possible production of efficiency given below. 1. Converting diesel engine to a high compression spark ignition engine. 2. Modifying the diesel to tolerate straight ethanol injection. 3. Changing carburetor for the use of ethanol, and 4. Using dual injection of ethanol and diesel fuel.
ww w.E
5.10.3 Engine Modification for Biodiesel Almost all modern diesel engines will run on biodiesel by providing significant efficiency positively. The biodiesel is of high enough quality. In general, biodiesel engines need less engine modification than bioethanol. (i) Rubber seals:
asy E
ngi
Older vehicles rubber seals used in fuel lines may require the replacement by non-rubber products because the biodiesel reacts with rubber. If a low blend is used (5% biodiesel), then the concentration ofbiodiesel is not high enough to cause this problem. (ii) Coldstarting:
nee
rin
g.n e
Cold starting can be a problem sometimes when using high blends. It is due to biodiesel thickening more during cold weather than fossil diesel. The proper arrangements should be incorporated either by having a fuel heating system or using biodegradable additives which reduce the viscosity. This effect will not be a problem with lower blends.
t
(iii) Oil changing:
Engines running on biodiesel tend to require more frequent oil changes. It will be the case for blends above 20%. (lv)Engine timing: For higher blends, the engine performance will be improved with a slight change to engine timing of 2° or 3° for 100% blend. The use of advanced injection timing and increased injection pressure has been known to reduce NOx emissions. (v) Engine modiflcations: Before installing an engine of greater capacity than one originally supplied, a statement of requirements should be obtained. The following factors will be considered: Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
[am
I
1. Weight of the vehicle 2. Power and torque output in relation to braking 3. Strength of the vehicle 4. Effect on steering and suspension components
S. The effect on vehicle handling. 5.11. PERFORMANCE OF SI AND CI ENGINES WITH ALTERNATE FUELS Ihe performance of alternate fuels can be tested by using various blended fuels of conventional petrol and diesel. For example, the performance of Compressed Natural Gas
ww
(CNG), blended ethanol and methanol gasoline fuels used in SI engines and the performance
w.E
ofbiodiesel and soya bean oil as alternate fuels in CI engine are reported.
asy E
5.11.1. Performance of a 4·Stroke SI Engine Using CNG The experiments are carried out at full load conditions of an engine with variable speed
ngi
operation to compute the performance parameters. The particulars of various components pertaining to the test facility are single cylinder petrol engine, eddy current dynamometer, exhaust gas analyzer, fuel temperature control device, CNG mass flow meter, petrol mass
nee rin
flow meters, fuel consumption device, data acquisition system, CNG conversion kit and CNG storage cylinder.
g.n et
The test engine is converted from a petrol engine to CNG mode and modified with a suitable bi-fuelling system. The performance test is carried out for both fuels (CNG and petrol) at engine speed ranging from 1500-5500 rpm. All tests are carried out at full load conditions.
The volumetric efficiency of CNG fuelled engine is less than petrol engine as CNG engine occupies more volume of inlet air as shown in Figure 5.8. The engine torque and brake power of CNG fuelled engine are considerably lower than a petrol engine. It is due to lower volumetric efficiency of CNG fuelled engine as shown in Figure 5.9 and Figure 5.10. The brake mean effective pressure (BMEP) is inversely proportional to engine air/fuel ratio for CNG fuelled engine and petrol fuelled engine with respect to engine speed as shown in Figure 5.11. Figure 5.12 shows that brake specific fuel consumption (BSFC) is less for CNG engine than petrol engine for the given engine speed range of 1500 to 5500 rpm.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative
mal
Energy Sources
~
YO
.S
85
0
>--. u ::: 80
..... - ....... -- __
_,
.~
u E 75
-CNG
II)
·c 70 o
-
- - Petrol
E 65 :::l 0 60
;>-
1500
2500
4500
3500
ww w.E a
Engine Speed in Rpm
Figure 5.8 Variation of volumetric efficiency versus engine speed 'J..)
9
... c I
Z .5 ()
:::l
r::r ....
r3
syE
8.5 8 7.5 7 6.5 6
ngi
1500
2500
3500
-CNG - - Petrol
nee r
4500
5500
Engine Speedin Rpm
ing
Figure 5.9 Variation of Torque versus engine speed 7
-- ....
6 ~
.ne
t
5
..:.c::
.5 4
....
()
3
0-
2
::: 0
-eNG - - Petrol
1500
2500
3500
4500
5500
Engine Speed in Rpm Figure 5.10 Variation of power versus engine speed Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Imil
Automobile Engineering
- ",
l~
17 16
~
, ,-
,.....
t.:J
~, -'
co 15 .5 0.. 14
, -eNG
13 12
~
co
I
- - Petrol
II
1500
2500
4500
3500
5500
EngineSpeedin Rpm
ww w.E, , _ -as _yE
Figure 5.11 Variation of BMEP versus engine speed
3M
....
..= ~ ~ .._
oIl
34 30 26 22
'-
.S 18 U t.t... Vl
14
co 10 1500
2500
.... ,
_,
~
~
~
-eNG
ngi
- - Petrol
nee r
4500
3500
Engine Speed in Rpm
5500
ing
Figure 5.12 Variation of BSFC versus engine speed
.ne
t
5.11.2.Performance of 51 Engine Fuelled with Methane, Methanol, Hydrogen, Propane and Ethanol Gasoline Fuels
The power, torque, brake mean effective pressure, brake specific fuel consumption, methane, methanol, hydrogen, propane and ethanol gasoline fuels at various engine speed are tested. The power and torque developed by the engine depend on an engine's in-cylinder mixture conditions. Therefore, the, volumetric efficiency plays a major role among other engine parameters. The liquid fuels produce a cooling effect on intake charge as they have the latent heat of vapourization during vapourizing. Therefore, the density of intake mixture is increased by enhancing the engine volumetric efficiency but it is not for gaseous fuels. Alternatively, gaseous fuels have the effect on decreasing volumetric efficiency due to large volume of fuel in inlet mixture. Therefore, the decrease in volumetric efficiency happens when the engine is Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
fuelled by gaseous fuels as shown in Figure 5.13. For example, the engine has the minimum volumetric efficiency when fuelled with hydrogen and methane. The other fuels are liquid at ambient temperature. So, these fuels cool faster due to the largest latent heat of vapourization.
-Gasoline -- -Methane ----- Methanol --Hydrogen
ww w.E
-Propane -0- -Ethanol Engine Speed in Rpm
asy E
Figure 5.13 Volumetric efficiency
0/ different fuels
with engine speed
The engine produces less power when operating on methane and hydrogen as shown in Figure 5.14 which is due to low volumetric efficiency of methane and hydrogen fueled engine. The engine power is more for gasoline than other/fuels because the engine is designed for
ngi
nee
gasoline. iVV
c,
80
rin
g.n e
c:::
-G~oline
:.... > " 0
60
"... o::l
40
---Methane -----Methanol -llydrogen --Propane -0- -Ethanol
....
0..
.;;,,:
~
20 1500
2500
3500
4500
t
5500
Engine Speed in Rpm
Figure 5.14 Variation of brake power versus engine speedfor dlfferent fuels For naturally aspirated spark ignition engines, the maximum pressure values are in the range 850 kPa to 1050 kPa at the engine speed for maximum torque. At the maximum power, BMEP values are 10% to 15% lower as shown in Figure 5.15. The reduction in BMEP with the methane fuel is throughout the speed range due to longer ignition delay and lower flame speed of methane. As the combustion starts earlier with respect to TDe, there is a greater Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering
I
amount of negative work done on the piston before TDC compared to gasoline. The remaining BMEP is lost due to the displacement of air by gaseous fuels.
...
10
0UJ
8
---Methane
:::;'E
7
-----Methanol
6
-Hydrogen -Propane
.E 9 c: co
-Gasoline
5
-0
4
ww w.E 1500
2500
4500
3500
-Ethanol
5500
EngineSpeed in Rpm
Figure 5.15 Variation oj BMEP versus engine speedJor differentJuels
asy E
The brake specific fuel consumption (BSFC) of methanol is the highest, as shown in
Figure 5.16, followed by ethanol due to the lower heating values of methanol and ethanol and followed by lesser values of their stoichiometric air/fuel ratio. Simultaneously, .BSFC of
ngi
methane is less than gasoline because methane has higher heating value than gasoline.
nee
Therefore, the specified amount of heat can be released with less amount of fuel. Due to the highest heating value and highest stoichiometric air/fuel ratio of hydrogen, the engine develops less BSFC with hydrogen. 700
.... ,..600 ~ 500
.--.
-
.~400 ~300~==~~~~~~~~_~ t/) "00 CO 100
o
__
. --a.... .
__
__
rin
.-Q
'-e-"'
__ ~_
+---------------1----...------,-----.--------,
1500
2500
3500
4500
g.n e
-Gasoline
- --Methane ----- Methanol -Hydrogen -Propane
t
-O-Ethanol
5500
Engine Speed in Rpm Figure 5.16 Variation oj BSFC versus engine speedJor different fuels
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
,j'. J
I Alternative Energy Sources
5.11.3. Performance of Compression Ignition (CI) Engine Fuelled with Biodlesel
The performance test of bio-hydro carbon fuels is carried on the engine similar to conventional engines. An electrical dynamometer is loaded when the engine reaches the operating temperature. After attaining the equilibrium state, the speed, fuel consumption and manometer head are noted. For example, the same test is conducted for various blends of 825 (25%biodiesel) and B50 (50% biodiesel). The emission values are also recorded.
•. 0
c"
w
35
~ 30
0:: 25
-Diesel
ww
- - -B .25 ····-850
20
15
.Ea
I()-1-----.-
----,------..,------,
.2
syE ngi nee 3
4
s
Brake power (kW)
Figure 5.17 Variation of BTE versus brake power At full load conditions, 850 provides higher brake thermal efficiency (BTE) than B25
rin g.
and pure diesel fuel as shown in Figure 5.17. At the same time, the brake thermal efficiency of the biodiesel blend 825 is lower than pure diesel-at full load conditions because the brake
net
thermal efficiency depends on the combustion quality of the fuel. Therefore, 850 gives better blend to operate Ie engines to produce good results. ,_ 0.7 .J::.
~
0,(>
.u.
en 0.5
.;.t!.
-Diesel - - - B 25
,:: 0.4
u
- - - =_"=_-:..:'1- .......
~ 0.3
-----850
0.2
0.1 2
4
3
5
Brake power (kW)
Figure 5.18 Variation of BSFC versus brake power
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
AutomobileEngin~ring
The specific fuel consumption (SFC) mainly depends on the mass flow rate of hydrogen. The mass flow rate of hydrogen is low for biodiesel whereas for diesel and it is slightly high. Therefore, it leads to increase in specific fuel consumption. At low load condition, the specific fuel consumption of fuel blend B25 is lower than diesel as shown in Figure 5.18. At full load condition, the specific fuel consumption of the fuel blend B25 and B50 is higher than diesel fuel. At the same time, the specific fuel consumption decreases with increase in injection pressure. 5.11.4. Performance of Soyabean Oil as an Alternate Fuel for CI Engine
ww w.E a
The engine is tested. for 100% diesel and 50-50% soya blended diesel. At higher
compression ratio, the temperature and pressure of air at the beginning of injection are higher. 100% diesel oil has the lowest BSFC than blended diesel due to the difference in specific gravities and heating values. Therefore, the engine responds to load by increasing the fuel flow for the lower energy value fuels. Hence, BSFC of soyabean oil is increased considerably than 100% diesel as shown in Figure 5.19.
syE
0.9
ngi
,,
.E 0.8
,,
~ 0.7
..:.::
,, ,
'20 0.6
..:.::
,,
.s u w...
0.5 0.4 ~ 0.3 0.2
"
...
.. ..__
nee r
ing
-----
-Soya
---Diesel
0.1
o
0.5
1.5
2
2.5
3
oil
3.;
.ne
t
Brake power (kW)
Figure 5.19 Variation 0/ BSFC versus brake power The brake thermal efficiency (BTE) decreases as the proportion of soyabean oil increases in the soyabean oil -diesel oil blends as shown in Figure 5.20. The wall temperature of the combustion chamber increases with the compression ratio increase thereby reducing its volumetric efficiency. The decrease in volumetric efficiency and the effect of ignition delay are the main reasons for the deterioration of fuel combustion resulting the increase in fuel consumption and reducing BTE.
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
Alternative
Energy Sources
30 25
..=
c"
.S
!:::
i!l
, ,, ,,
20 15
,"
10
,," ,,
-Soya oil ---Diesel
S 0 0
0.5
1.5
1.5
3
3.5
Brake power (kW)
ww
Figure 5.20 Variation of BTE versus brake power
w.E asy En gin ee
5.12. COMBUSTION "OF 51 AND CI ENGINES WITH ALTERNATE FUELS
The start of combustion before Top Dead Centre (TOC) when running on pure diesel fuel is delayed for dual-fuel operation. Since the fuel metering system continues to inject fuel throughout the delay period in dual-fuel systems large quantities of premixed fuel would be involved when ignition finally occurs. Only a small quantity of pilot fuel reacts with O2 before auto-ignition of the mixture.
The high frequency pressure fluctuations occur during knocking by decaying its
rin g.
amplitude with time. These pressure fluctuations produce the sharp metallic noise called knock. The degree of knock depends on the ratio of the alternative fuel (natural gas) to the pilot fuel. This ratio is selected on the basis of load and speed of the engine.
net
Usually, the ignition occurs at different points in both SI and CI engines when the alternate fuel is used after the delay period unlike pilot fuel engine. Both ignition and combustion processes take place in two stages. The first combustion will take place for pilot or main fuel during auto-ignition followed by a finite time interval and then the second combustion will start. This finite time is sufficient for the heat transfer to end gas to take place which enhances the end gas pressure, temperature and reaction rate. These processes are powered by the combustion chamber design and the level of turbulence in the cylinder. The increase in speed increases the ignition delay when running on pure diesel fuel. The pressure rise is due to ignition of pilot fuel which influences the heat release during combustion. This pressure rise can be viewed by the oscilloscope screen which is less than maximum peak as shown in Figure 5.21 and Figure 5.22.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1-
Automobile
Engineering
I
--Diesel ---B25% ••~•• B50%
-200 -150 -100
-50
o
50
100
150 200
ww w.E a
Crank angle (deg.)
Figure 5.21 Variation of Pressure versus crank angle 14U
syE
-Diesel
ngi
40 Crank angle (deg.)
---B25%
nee r 80
•••••• B50%
ing
Figure 5.22 Variation of heat release versus crank angle
.ne
t
5.13. EMISSION CHARACTERISTICS OF SI AND CI ENGINES WITH ALTERNATE FUELS The emissions of both SI and CI engines are carbon monoxide, un-burnt hydrocarbons, nitric oxide and nitrogen dioxide in exhaust gas. The variation of exhaust gas temperature is with load for various blends and diesel. The exhaust gas temperature increases with increase in brake power for all blends. (a) Carbon Monoxide Emission It is the amount of carbon monoxide (CO) content in exhaust gases emitting from burning of different fuel types. CO concentration in exhaust mostly depends on air/fuel ratio.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative
Energy Sources
_
A rich mixture causes more CO in exhaust gases. The closer is to stoichiometric point, less will be the amount of CO. Carbon to hydrogen ratio of fuel is another parameter in which formation of CO is affected. In lean mixtures, there is another additional source of CO caused by the flame interaction with walls, oil films and deposits. Hydrogen produces no CO because there are no carbon atoms in hydrogen molecules but there is a lubricant oil film on cylinder walls that interact with the flame and it produces a little amount of CO even with hydrogen fuelled engine. (b) Un-burnt hydrocarbon emission It is the measurement of un-burnt hydrocarbon (HC) in exhaust gases. The temperature caused by combustion is very high inside the cylinder. As the piston expends, some amount of
ww w.E
oil is evaporated by heat. Simultaneously, the evaporated oil and incompletely burned oil contribute to HC emission. (c) Nitric oxide (NOx) emission
asy E
NOx formation take place at high temperature and increase of NOx is caused by higher combustion temperature of hydrogen and methane. There are two main reasons for this
ngi
increase in temperature. First, gaseous fuels do not have the cooling effect which will cause a higher :nitial temperature for in-cylinder charge. Next, more spark advance is required for
nee
methane due to the low flame speed of methane which rises a peak of combustion temperature and pressure. (d) Nitrogen Dioxide Emissions
rin
g.n e
The emission ofN02 gradually increases with increase in brake load on all fuel types. (e) Carbon Dioxide Emissions
t
The CO2 emission for all blended fuels is less as compared to diesel at all loads. The rising trend of CO2 emission with load is due to high fuel entry as the load increases. Biofuels contain lower carbon content as compared to diesel and hence, the CO2 emission is comparatively low. 5.14. ELECTRIC VEHICLES
Battery-powered vehicles give off virtually no pollution and offer one of the best options for reducing motor vehicle emissions in polluted cities. The driving range of today's electric cars is limited by the amount of power and the battery can provide. Current batteries take hours to recharge and the cost of electric vehicles is high. Recent developments in electric vehicle technology show much promise for future. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
lma
Automobile Engineering
I
5.14.1. History of Electric Vehicles
Electric vehicles (EVs) have been around for a very long time. In early 1900s, there were more electric vehicles than gasoline-powered cars. The vehicle pictured in Figure 5.23 is a Rauch and Lang Electric Sedan which was built around 1922. Gasoline was very expensive during those days. It also was hard to start a gasoline engine because it had to turn and turn and turn a crank in front of the car to get it to start. They did not have a key to start the car such as now. Gasoline vehicles were also noisy and put out a lot of smoke. The cars either had no mufflers or mufflers did not do a good job. So, electric vehicles were a big hit. At one time, there were 50,000 electric vehicles on roads and streets of
ww w.E a
the United States. But electric vehicles soon faded away such as the horse-driven carriage. Ways of cheaply making gasoline were discovered. A new invention called an electric starter was made. It started the car with a key instead of a crank. A gasoline car could go much farther than an electric one. So, gasoline-powered vehicles soon became the main method of transporting people.
syE
ngi
nee r
ing
Figure 5.23 Rauch and Lang Electric Sedan
.ne
t
Automobile companies are making cars cleaner and cleaner. Ten cars built today to produce the same amount of pollution that it would get from just one car built 15 years ago. Oil companies are creating cleaner fuels such as a new gasoline called reformulated gasoline. But electric vehicles are back on the road. 5.14.2. Working of Electric Vehicles
Electric vehicles (EVs) do not burn gasoline in an engine. They use electricity stored on the car in batteries. Sometimes, 12 or 24 batteries or more are needed to power the car such as a remote-controlled and model electric car. EVs have an electric motor which turns wheels and a battery to run.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative
iHM
Energy Sources
Electricity, the same energy that lights lamps and runs TV is stored in batteries on an EV. In an EV, batteries and other energy storage devices are used to store the electricity that powers the electric motor in the vehicle. Figure 5.24 shows the typical arrangement of batteries and electric motor in an electric car. The batteries can be lead acid batteries or Ni-cad (nickel-cadmium). EV batteries must be replenished by plugging in the vehicle to a power source.
ww w.E
asy E
Batteries store electricity
Figure 5.24 Electric vehicles
ngi
Better batteries which hold more energy and last longer are being developed. In 2001, by
nee
'the time today's fifth graders are ready to drive, electric vehicles are able to go 150 to 200 miles before recharging.
rin
Some EVs have on-board chargers whereas others plug into a charger located outside the
g.n e
vehicle but both must use electricity which comes from the power grid to replenish the battery. Although electricity production may contribute to air pollution, an EV is a zero emission vehicle and its motor produces no exhaust 01 emissions.
t
5.14.3. Electric Vehicles
Electric Vehicles (EVs) come in a variety of shapes and sizes. They can be light-duty delivery vehicles or heavy-duty trams and buses because the range of an EV (approximately 80 miles) is limited by weight, design and type of battery used. EVs are particularly well suited to short-distance and high-use applications. One of the first modem EVs was the General Motors Impact. GM changed its name and started selling GM "EV1" in 1997. This sleek looking car even sets a World Record of more than 180 miles per hour. EV I is very aerodynamic. It means that air slides around the body of
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
''''liM I the car very easily. Less air resistance or drag is required less energy to power the car at Automobile
Engineering
freeway speeds. EV I is as aerodynamic as somejet fighter aircraft. Some EVs such as Toyota RAV-4 EV are made by major auto companies. Other electric vehicles built today are made by small car companies or by people who build them in their own garages as a hobby. Some people build cars from kits and make them look such as gasoline roadsters or such as sports cars. Other people convert regular cars into electric vehicles. They pull out the motor and gas tank and put an electric motor and batteries into the car. Beginning in 1999, nearly all of the major auto companies such as Ford, General Motors, Toyota, Chrysler and Honda offered at least one model electric car. The numbers has dropped in 2002 with many auto companies working on hybrid vehicles which are the combination of small internal combustion engine and an electric motor.
ww
w.E
There are other types of electric vehicles. Many cities use electric-powered buses, trolleys, subways or light-rail. Even most trains are electric. Other places will use electric buses with batteries because they do not want wires over roads.
asy E
ngi
Other people are using electric-powered bicycles. The motor is mounted above the rear wheel and under the seat. The bag which is hanging from the middle holds the battery. The
nee rin
bike can go 20 miles per hour and it can travel 20 miles before needing a recharge. For people who have disabilities, an electric-powered bike might allow them to be free to act as outdoors. 5.14.4. Maintenance ccnstderattons
g.n et
Service requirements for EVs are few than gasoline-powered vehicles. EVs d~ not require tune-ups, oil changes, timing belts, water pumps, radiators, fuel injectors or tailpipes. They require battery maintenance, Electric batteries have a limited number of charging cycles (the number of times a battery can be charged and discharged). and it will typically need to be replaced within 3-6 years. Different types of batteries (such as lead-acid, nickel-metal hydride and lithium-ion) are available depending on the manufacturer and vehicle. Auto suppliers will assist fleets with maintenance training for EVs. Some colleges also offer the training for EV (and other alternative fuel vehicle) mechanics.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative
'ftW
Energy Sources
5.14.5. Benefits of Electric Vehicles EVs are zero emission vehicles. It means, they produce no tailpipe or evaporative emissions that contribute to air pollution and global warming (although electricity production is not pollution-free). The cost of electricity per kilowatt-hour usually compares favorably to gasoline but it varies depending on location. More than 95% of the electricity used to charge EVs originates from domestic resources. So, driving an EV reduces the nation's dependence on imported oil. As mentioned previously, EV s require less service because they do not need oil and they have no timing belts, water pumps, radiators, fuel injectors or tailpipes. Advantages of electric
ww
vehicles are summarised below: 1. There is no pollution due to emission. i.e., zero emission.
w.E asy En gin ee
2.
It ensures smooth operation. i.e., vibration and noise is less.
3.
Cost of operation is less.
4.
Less maintenance is required.
5.
It is easy to start the vehicle.
6.
It takes up less space on the road. So, they help to reduce traffic congestion.
5.14.6. Limitations
Most EVstoday
of Electric Vehicles
rin g.
can only go about 100 miles before you need to plug and recharge their
net
batteries. They are not such as the energizer that keeps on going. But, 50 to 100 miles is plenty for most people who only drive for a short distance to and from work, to and school or to do some shopping such as Ford.
from
Some EVs with special batteries can go for a longer distance. The car that is made by a company in Massachusetts called Solectria. It is called "Sunrise." In 1995, a Solectria Sunrise set a world record for going 238 miles on one charge. Electric vehicles are more expensive to buy than gasoline cars but when more and more EVs are made the price of EVs should drop to the same cost as gasoline cars. Summary of limitations of electric vehicles is given below: 1. It has less initial torque.
-
2.
It is more expensive.
3.
Frequent recharging of battery is needed and also battery charging needs more time.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'4'1-
Automobile
Engineering
4. The performance is poor. 5. Less variety of vehicles is available in the market.
5.15. HYBRID VEHICLES
The word hybrid means, something is mixed together from two things. Usually, it refers to plants 0" animals that are breed from different dissimilar parents. Hybrid electric vehicles (HEVs) typically combine the internal combustion engine of a conventional vehicle with the battery and electric motor of an electric vehicle. The combination offers low emissions, power, range and convenient fueling of conventional (gasoline and diesel) vehicles and they never need to be plugged in. The inherent flexibility ofHEVs makes them well suited for fleet and personal transportation.
ww w.E a
5.15.1. Working Principle of Hybrid Vehicles
syE
Hybrid electric vehicles (HEVs) are powered by two energy sources such as an energy conversion unit (combustion engine or fuel cell) and an energy storage device (batteries or ultra-capacitors) as shown in Figure 5.25. The energy conversion unit may be powered by
ngi
gasoline, methanol, compressed natural gas, hydrogen or other alternative fuels. Hybrid
nee r
electric vehicles have the potential to be two to three times more fuel-efficient than conventional vehicles.
ing
Inverter
.ne
t
Battery pack
Figure 5.25 Hybrid vehicles HEVs can have a parallel design, a series design or a combination of these two. In a parallel design, the energy conversion unit and electric propulsion system are connected directly to vehicle's wheels. The primary engine is used for highway driving. The electric motor provides the added power during hill climbing, acceleration and other periods of high
Downloaded From : www.EasyEngineering.net
I·
Downloaded From : www.EasyEngineering.net
Alternative Energy Sources
demand. In a series design, the primary engine is connected to a generator which produces the electricity. The electricity charges the batteries which drive an electric motor which powers wheels. HEYs can also be built to use the series configuration at low speed and the parallel configuration for highway driving and acceleration. In contrast to electric vehicles, batteries in HEYs do not need to be plugged into recharge. Instead, they are recharged using a regenerative braking or by using an on-board generator. 5.15.2. Parallel HEV Design
ww w.E
A hybrid electric vehicle (HEY) with a parallel configuration has a direct mechanical connection between hybrid power unit and wheels as in a conventional vehicle but it also has an electric motor which drives wheels as shown in Figure 5.26. For example, a parallel vehicle could use power produced by an internal combustion engine for highway driving while using both engine and electric motor power for accelerating.
~
Battery
Driver Power
- ---~
Engine
asy En gi Electric Power
nee r Inverter
ing .ne
0000
Motor/Generator
t
Drive Wheels Reduction gear
Figure 5.26 Parallel HEV design Some benefits of a parallel configuration are as follows: 1. A smaller engine provides more efficient operation and therefore, better fuel economy is without sacrificing acceleration power. The vehicle has more power because both engine and motor supply power simultaneously. 2. Most parallel vehicles do not need a separate generator because the motor regenerates batteries. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
3. Power does not need to be redirected through batteries and it can therefore be more efficient. 5.15.3. Series HEV Design A hybrid electric vehicle (HEV) with a series configuration uses the heat engine or fuel cell with a generator to produce electricity for the battery pack and electric motor as shown in Figure 5.27. Series HEVs have no mechanical connection between hybrid power unit and wheels. All motive power is transferred from chemical energy to mechanical energy and from mechanical energy to electrical energy and then back to mechanical energy to drive wheels.
ww w.E a ~ ----~
Engine
Battery
Driver Power Electric Power
syE 0000 ngi
Inverter
Motor
nee
rin
g.n et
Drive Wheels
Reduction gear
Figure 5.27 Series HEV design There are some benefits of a series configuration as follows: 1. The engine never idles which reduces vehicle emissions.
2. The engine can be continuously operated in its most efficient region. 3. The engine drives a generator to run at optimum performance. 4. The design allows for a variety of options when mounting engine and vehicle components. 5. Some series hybrids do not need a transmission. The disadvantage is that series HEVs require larger and therefore, heavier battery packs than parallel vehicles. In addition, the engine works hard to maintain the battery charge Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
because the system is not operating in parallel. There is also inefficiency of converting the chemical energy to mechanical to electrical energy and back to mechanical energy. 5.15.4. Hybrid Electric Vehicle Components
A hybrid electric vehicle (HEY) is an optimized mix of various components. A typical hybrid configuration is shown in Figure 5.28. The following components are primarily used in hybrid vehicles: I. Electric traction motors/controllers.
ww w.E a
2. Electric energy storage systems such as batteries and ultra-capacitors. 3. Hybrid power units such as spark ignition engines, compression ignition direct injection (diesel) engines, gas turbines and fuel cells.
4. Fuel systems for hybrid power units. 5. Transmissions.
syE ngi
To help in reducing emissions and improve vehicle efficiencies, the following systems and components are being improved through research and development: 1. Emission control systems.
2. Energy management and systems control. 3. Thermal management of components.
nee
4. Lightweight and aerodynamic body/chassis.
rin
5. Low rolling resistance (including body design and tires). 6. Reduction of accessory loads.
g.n et
Figure 5.28 Configuration of hybrid vehicle Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IUD
Automobile Engineering
1. Hybrid electric vehicle motors/controllers: Motors are energy suppliers of HEY drive systems. In HEY, an electric traction motor converts the electrical energy from the energy storage unit to mechanical energy which drives wheels of the vehicle. Unlike a traditional vehicle, where the engine must "ramp up" before the full torque can be provided and an electric motor provides full torque at low speed. This characteristic gives the vehicle excellent "off the line" acceleration. 2. Hybrid electric vehicle batteries: Battery is an essential component of HEYs. Although a few production of HEYs with advanced batteries has been introduced in the market, no current battery technology has demonstrated an economically acceptable combination of power, energy efficiency and life cycle for high-volume production vehicles. The various types of batteries used in hybrid vehicles are explained below.
ww w.E
(i) Lead-Acid batteries:
asy En gi
Lead-acid batteries can be designed to be high power, inexpensive, safe and reliable. A recycling infrastructure is in place for them. But low specific energy, poor cold temperature performance and short calendar and cycle life are still impediments to their use. Advanced high-power lead-acid batteries are being developed for HEY applications. (ii) Nickel-cadmium batteries:
nee r
ing .ne
Although nickel-cadmium batteries used in many electronic consumer products have high specific energy and better life cycle than lead-acid batteries, they do not deliver sufficient power and they are not being considered for HEY applications. (iii) Nickel-metal hydride batteries:
t
Nickel-metal hydride batteries used routinely in computer and medical equipment offer the reasonable specific energy and specific power capabilities. Nickel-metal hydride batteries have a much longer life cycle than lead acid batteries and they are safe and abuse-tolerant. These batteries have been used successfully in producing electric vehicles and recently in lowvolume production HEYs. The main challenges with nickel-metal hydride batteries are their high cost, high self-discharge and heat generation at high temperatures, need to control losses of hydrogen and low cell efficiency. (iv) Lithium ion batteries:
The lithium ion batteries are rapidly penetrating into laptop and cell-phone markets because of their high specific energy. They also have high specific power, high-energy efficiency, good high-temperature performance and low self-discharge. Components of Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
om
I· Alternative Energy Sources 1 lithium-ion batteries could also be recycled. These characteristics make lithium ion batteries suitable for HEV applications. However, to make them commercially viable for HEVs, further development is needed similar to EV-design versions including improvement in calendar and cycle life, higher degree of cell and battery safety, abuse tolerance and acceptable cost. (v) Lithium polymer batteries: Lithium polymer batteries with high specific energy initially developed for EV applications also have the potential to provide high specific power for HEV applications. The other key characteristics of the lithium polymer are safety, good cycle and calendar life. The battery could be commercially viable if the cost is lowered and increased specific power -batteries are developed.
ww w.E
3. Hybrid electric vehicle power units: (i) Spark ignition engines:
A Spark Ignition (SI) engine runs on an Otto cycle. Most gasoline engines run on a modified Otto cycle. This cycle uses a stoichiometric air-fuel mixture which is combined prior to enter the combustion chamber. Once in the combustion chamber, the mixture is compressed and then ignited using a spark plug (spark ignition). SI engine is controlled by limiting the
asy En gi
amount'of air allowed into the engine. It is accompushed through the use of a throttling valve placed on the air intake (carburetor or throttle body). (ii) Compression ignition engines:
nee r
ing .ne
Progress continues to advance the compression-ignition direct-injection (CIDl) engine which has the highest thermal efficiency of any internal combustion engine. Challenges to improvements include a lower specific power than gasoline engine, significant particulate matter, nitrogen oxides in exhaust, noise, vibration and smell of the engine.
t
The recent advancements in high-speed automotive diesel engmes which address some of these shortcomings have made them nearly ideal candidates for HEV applications. These advancements include h~h-pressure direct fuel injection, low oxides of nitrogen catalysts and sophisticated electronic controls. With a thermal efficiency upward of 40% and wellunderstood maintenance, reliability, manufacturing and operating characteristics, the highspeed CIDI engine shows a great promise as a near-term hybrid power unit. (iii) Gas turbine engines: The gas turbine engine runs on a Bryton cycle using a continuous combustion process. In this cycle, a compressor (usually radial flow for automotive applications) raises the pressure and temperature of the inlet air. The air is then moved into the burner where the fuel is Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
I fl,ltomobile Engineerlnf/l
injected and combusted to raise the temperature of air. Power is produced when the heated high-pressure mixture is expanded through a turbine and cooled through a condenser. When a turbine engine is directly coupled to a generator, it is often called turbo generator or turbo alternator. The power output of a turbine is controlled through the amount of fuel injected into the burner. Many turbines have adjustable vanes and gearing to decrease the fuel consumption during partial load conditions and to improve acceleration. (iv) Fuel cells: Fuel cells generate electricity through an electrochemical reaction that combines
ww w.E a
hydrogen with oxygen in ambient air. Pure hydrogen or any fossil fuel that has been "reformed," can be used to produce hydrogen gas. Methanol is a common fuel choice. For the most part, the fuel cell's only emission is water vapour giving it potential as the cleanest hybrid power unit alternative. Efficient, quiet and reliable fuel cells are predicted to .demonstrate energy conversion efficiencies up to 50% relatively high in comparison to 20%25% efficiency of standard SI gasoline engines.
syE ngi
The choice of fuel for a fuel-cell-powered HEV has important implications for required infrastructure, system accessories, efficiency, cost and design. Although its viability has been well-proven in the space program, very high capital costs, large size, long start-up times and immature technologies make it a longer-term enabling technology for an HEV. 4. Fuel systems for hybrid electric vehicle:
nee
rin
g.n et
The two primary fuels used in automobiles today are gasoline and diesel. The infrastructure is in place to produce, refine, truck or tank diesel and gasoline. Many of today's HEVs and available in near future will use either gasoline or diesel to fuel the hybrid power units. However, to ensure the security of our oil supply and to address increasing environmental concerns associated with gasoline and diesel, alternative fuels are very I
attractive. The opportunity for fuels such as biodiesel, natural gas (eNG & LNG), ethanol, hydrogen and propane to be used as alternative fuels for vehicles is great. Many alternative fuel vehicles are already being used effectively around the world. These fuels have the potential to be used in HEVs as well. 5. Emission control system for hybrid electric vehicle: Automotive emissions contribute significantly to urban air quality problems. HEVs can reduce this contribution significantly through increased fuel economy, use of alternative fuels, and improved power unit and after treatment technology.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative
@:5.
Energy Sources
A well-tuned spark ignition engine produces relatively low emissions. Significant emissions occur when the vehicle is started and warmed up. During this time, the engine must be choked to run properly. It creates excess unbumt fuel in exhaust which leads to hydrocarbon and carbon monoxide emissions. During normal driving, emissions are relatively low because the air-to-fuel mixture is precisely controlled thereby allowing the catalytic converter to effectively reduce emissions. The diesel engine emissions are primarily nitrogen oxides (NOx) and particulate matter (PM). NOx is produced because the engine is operated with a lean air-to-fuel mixture. The high compression ratio of a diesel engine (required because of compression ignition) creates much higher pressure and temperature in the combustion cylinder. This lean mixture and high temperature cause the higher level of NO x production. At high engine loads, where more fuel is injected, some of the fuel bums incompletely leading to the black smoke characteristic of a
ww w.E
diesel engine.
asy En gi
The fuel cell produces water as emissions when operating on pure hydrogen. Other types of fuel cells have reformers that convert methane to hydrogen and then use the hydrogen. The reformer produces some emissions in the conversion process but overall emission levels are low.
6. Energy management for hybrid electric vehicle:
nee r
A Hybrid Electric Vehicle (HEV) has two or more sources of on-board power. The
ing .ne
integration of these power-producing components with the electrical energy storage components allows for many different types of HEV designs. A power control strategy is needed to control the flow of power and to maintain adequate reserves of energy in storage devices. Although this is an added complexity not found in conventional vehicles, it allows
t
the components to work together in an optimal manner to achieve multiple design objectives such as high fuel economy and low emissions. The biggest distinction between different hybrid designs is whether they are parallel or series or a combination of these two. In a parallel design, an Auxiliary Power Unit (APU) can mechanically drive wheels. In a series design, APU generates electricity and it does not directly drive wheels. A third type combines the best aspects of both and it is called combined or a series/parallel design. A combined design allows APU to directly drive wheels but also it has the ability to charge the energy storage device through a generator. The combined hybrid is a subset of the parallel design since it can directly drive wheels from APU. The way the hardware components are connected (parallel, series or a combination of the two) will be
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
,,:!.
I
Automobile
Engineering]
referred as the "hardware configuration" and the management of power flow among components will be referred as "control strategy" or more generally "energy management." A secondary distinction between hybrids is charge sustaining versus charge-depleting hardware configurations and control strategies. Charge-depleting vehicles allow their batteries to become depleted and cannot recharge them at the same rate they are being discharged. The common "range-extender" is a charge-depleting vehicle unless APU is larger than the average power load of the vehicle over a given cycle. A charge-sustaining hybrid has an APU that is adequately sized to meet the average power load and if operated under the expected conditions, it will be able to keep adequate electrical energy storage reserves indefinitely.
ww w.E
7. Control strategiesfor HEVs: The flexibility in HEV design comes from the ability of the control strategy to manage how much power is flowing to or from each component. The components can be integrated with a control strategy to achieve the optimal design for a given set of design constraints. There are many (often conflicting) objectives desirable for HEVs. The primary ones are to
asy En gi
•
maximize the fuel economy
•
minimize emissions
•
minimize propulsion system cost to keep the vehicles affordable to the consumer market
•
do all of above while maintaining or improving on acceptable performance (acceleration, range, handling, noise, etc.).
nee r
ing .ne
To achieve these objectives, the hardware configuration and power control strategy are
t
designed together. The hardware configuration dictates to some extent what control strategies make sense but there is still a wide spectrum of control strategies for each hardware configuration. Before a control strategy is. implemented, an HEV consists simply of hardware components hooked up electrically and mechanically. The control strategy brings the components together as a system and it provides the intelligence which makes the components work together. The implementation requires other connections to control individual components. (i) Mechanical control: It includes mechanically controlled clutches, throttles controlled by the accelerator pedal and dials on dashboard and other controls activated mechanically by the driver.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
(ii) Electrical control:
With the increased use of on-board computers in today's conventional vehicles, electrical controls will most likely be the dominant means of implementing control strategies. It will be done through software programs running on microchips that then activate relays and other electromechanical systems to perform the desired functions. These computing systems will most likely have multiple data input measured on the current state of the vehicle such as component temperatures, battery voltage, current and state of charge as well as the standard desired response requested by the driver such as braking and acceleration. 8. Hybrid electric vehicle thermal management:
ww w.E
As conventional gasoline engines require a cooling system, HEVs need a proper thermal management of the power and energy storage units for optimum performance and durability. The type of thermal management system required will depend on the type of power and energy storage units selected. In many cases, waste heat from these components can be used
asy En gi
for cabin air and other heating needs. 1. Batteries
2. Power units 3. Exhaust systems 4. Fuel system
5. Waste heat utilization. (i) Batteries:
nee r
ing .ne
The performance and life-cycle costs of electric vehicles (EV) and hybrid electric
t
vehicles (HEV) depend on the performance and life of their battery packs. Each battery operates over a particular operating range to achieve optimum life and performance. Temperature variations from module to module in a battery pack could result an un-balanced pack and thus, it reduces the performance. It is important to regulate a battery pack operating temperature because it affects performance (power and capacity), charge acceptance (during regenerative braking) and vehicle operating and maintenance expenses. Battery thermal management is critical for high-power battery packs used in EVsand HEVs are to maintain their battery packs within the desired temperature range. (ii) Power units:
Fuel cells offer high efficiency and fuel-flexible power systems with low to zero emissions for future HEV designs irrespective of the reformer. There are variety of thermal issues to be addressed in the development and application of fuel cells for hybrid'vehicles. For Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering
example, solid oxide fuel cells potentially offer very high efficiencies and low cost than PEM or phosphoric acid cells but they run hotter. Isolation of this heat from the rest of the vehicle is important not only for improved efficiency but also passenger safety. Reducing the warm-up time of fuel cells via thermal management is important to achieve quick power and minimal emissions. More standard power units such as small diesel or spark-ignition engines also need proper cooling. (iii) Exhaust systems:
60% to 80% of emissions in an auto's typical driving cycle come from "cold start" emissions and pollutants that are emitted before the catalytic converter is hot enough to begin catalyzing combustion products.
ww w.E
(iv) Fuel system:
As emissions standards tighten and exhaust control technologies improve the issue of evaporative emissions becomes increasingly important. Thermal management of fuel tanks is one approach to reduce these emissions. (v) Waste heat utilization:
asy En gi
Heat recovered from any of above sources can be used in a variety of ways. For winter
nee r
driving, heat recovery from HEV sources such as power unit exhaust, propulsion motors, batteries and power inverter can significantly improve the cabin warm-up. Because of their
ing .ne
small power units, hybrid vehicles generally cannot supply enough heat to the cabin via tne conventional coolant-to-air heat exchanger. Waste heat can also be converted into electricity via thermoelectric devices.
t
5.15.5. Hybrid Electric Vehicle Benefits 1. Low emissions and high efficiency:
Hybrid Electric Vehicle (HEV) emissions vary depending on the vehicle and its configuration. But in general, HEVs have lower emissions than conventional vehicles because an electric motor is used with an internal combustion engine which offsets how often the engine is used and therefore, it reduces fuel use and emissions. An HEV can easily control the engine's operating point which enables the vehicle to be more efficient and pollute less. Finally, an HEV engine can power electric components which are more efficient than mechanical counterparts normally used.
Downloaded From : www.EasyEngineering.net
1
Downloaded From : www.EasyEngineering.net
I Altemativ~EnergySources 2. Highfuel economy ana lOW costs: HEVs can go 10-18 miles per litre of gasoline. It allows drivers to fuel less often and it gets more miles on a tank of fuel than they would drive a conventional vehicle. In addition to the cost saving associated with vehicle operation, HEVs are very cost competitive with similar conventional vehicles. 3. Outstanding performance: Auto manufacturers are making HEVs with performance, safety and cost comparable to a conventional vehicle because these three elements are most important to consumers. Ry combining gasoline with electric power, hybrids will have the same or greater range than
ww w.E
traditional combustion engines. HEV is able to operate approximately two times more efficiently than conventional vehicles. 4. Energy security:
asy En gi
Because HEVs ace efficient and have high fuel economy, less fuel is used than
conventional vehicles. In addition, HEVs have the potential of running on alternative fuels which can be renewable and produced in our country. Therefore, HEVs can reduce Nation's dependence on fossil fuels and help to decrease foreign oil imports thereby increasing energy security.
nee r
5.15.6. Hybrid Electric Vehicles
ing .ne
Hybrid Electric Vehicles (HEVs) are not just for niche market applications. Hybrids are available in various shapes and sizes. They are currently being used in a variety of
t
applications. Their range, ease of use, ease of fueling and various vehicle configuration options make them prime vehicles for anyone to use. 1. Consumer applications: Many consumers are looking for a vehicle which is fuel efficient, reliable, cost effective and safe. Today's HEVs are made just as safe, comfortable and reliable as conventional vehicles but it can get approximately double the fuel economy. Toyota and Honda are successfully selling their current light-duty HEV models and they are planning to phase-in other options such as hybridized Camry and Accord in nextseveral years. Other auto manufacturers are also gearing up to sell HEVs including sport utility vehicle hybrids. One car is the Honda Insight which can get up to 18 miles per litre on the freeway. The car uses a small 1.0-liter and 3-cylinder engine with an ultra-thin electric motor. Its primary Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_
Automobile Engineering
power comes from the gasoline engine but it uses the electric motor when it is accelerating or climbing hills. The electric motor does not need an external power supply for recharging. Its batteries are recharged by regenerative braking. It means, energy from forward momentum is captured during braking. This energy is then used to recharge batteries. Honda is also making its Civic sedan available as a hybrid which gets 13.5 miles per litre (mpl) on the highway compared to a gasoline-only model and it gets 10 mp/ on the highway. Another hybrid on the road is a Toyota Prius. This four-person car gets 13 mp/. It uses advanced technology to combine a small gas engine with an electric motor. At very slow speed, the car runs on its electric motor. Driving around the city, high speed and freeway speed, it shifts both gasoline motor and electric motor while also recharging the battery.
ww w.E
Other automobile companies will be releasing other types of hybrid vehicles soon. In 2003 model year, Ford began selling a hybrid-electrici Escape Sport Utility Vehicle. This vehicle will use an electric motor around town and a gasoline engine while on the freeway. The vehicle's gas engine will shut off when it is stopped such as in a traffic jam. The regular gasoline-powered Escape gets 6 mp/ in the city and 7.5 mp/ on the highway. The Hybrid Escape will get 10.5 mp/ but that better mileage may cost more than the gasoline model's.
asy En gi
Incentives from government agencies may help to decrease extra cost. Other auto companies are also working on hybrid SUVs. Daimler Chrysler is working on a hybrid Dodge Durango
nee r
which will achieve a combined average of 5 mpg. The regular gasoline model gets only 4.1 mpl.
ing .ne
General Motors and Toyota are working together to develop a small hybrid SUV. Honda is planning a hybrid version of its CR- V. 2. Bus applications:
t
There are several different hybrid buses available which can easily be used as a shuttle bus, transit bus, school bus or trolley bus. 3. Heavy duty truck applications: Advanced heavy hybrid vehicles will likely be commercialized in several vehicle classes later in this decade and they will significantly improve fuel efficiency while simultaneously reducing vehicle emissions. Heavy-duty trucks can easily be hybridized and they can make a significantly positive impact on fuel economy and emissions.
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources
":PM
5.16. USE OF FUEL CELLS IN AUTOMOBILES
A fuel cell produces electricity directly fromthe reaction between hydrogen (derived from a hydrogen-containing fuel or produced from the electrolysis of water) and oxygen from air. Like an internal combustion engine in a conventional car, it turns fuel into power by causing it to release energy. In an internal combustion engine, the fuel bums in tiny explosions that push the pistons up and down. When the fuel burns, it is being oxidized. In other words, the fuel combines oxygen and it produces energy in the form of heat and mechanical motion. In a fuel cell, the fuel is also oxidized but the resulting energy takes in the form of electricity. When powered by pure hydrogen, by-products of the reaction are heat and
ww
water.
A fuel cell power system has many components but its heart is the fuel cell stack which is
w.E
made of many thin flat cells layered together. (Although the term fuel cell is often used to describe the entire stack strictly speaking, it refers only the individual cells.) Each cell
asy E
produces electricity and output of all cells is combined to power the vehicle. ~ Fuel cells have the potential to revolutionize the way we power our nation, offering
ngi
cleaner, more-efficient alternatives to the combustion of gasoline and other ,. fossil fuels.
nee rin
The amount of power produced by a fuel cell depends on several factors including fuel cell type, cell size, the temperature at which it operates and the pressure at which the gases are supplied to the cell.
g.n et
A single fuel cell produces enough electricity for only small applications. Therefore, to provide the power needed for most applications, individual fuel cells are combined in series into a fuel cell stack. A typical fuel cell stack may consist of hundreds of fuel cells. 5.16.1. History of Fuel Cell
Fuel cell technology is over 150 years old. The first fuel cell was demonstrated by Sir William Grove in 1839. Grove used porous platinum electrodes and sulphuric acid as the electrolyte bath. William White Jaques later substituted phosphoric acid in the electrolyte bath and he was the person who coined the term "fuel cell." A significant fuel cell research was done in Germany during 1920's which laid the groundwork for subsequent development of carbonate cycle and solid oxide fuel cells. In 1960s, NASA began using alkaline fuel cells to provide onboard electrical power for spacecraft.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I..
Automobile
5.16.2. Comparison
Engineering
of a Fuel Cell Car and Battery Car
Fuel cell and battery-powered vehicles are both propelled by electric motors. Therefore, both vehicle types can be designed with similar performance characteristics, The primary difference in these vehicle types is the source of electricity. Battery-electric vehicles are powered by electricity stored in a battery. Since the battery merely stores energy instead of generating it, it must be recharged regularly. On the other hand, fuel cells produce electricity from hydrogen or some other fuel. Such as gasoline-powered vehicles, fuel cell vehicles are refueled rather than recharged. Refueling usually takes much less time than recharging. Fuel cell vehicles can typically go further before
ww w.E
refueling due to storage limitations of current battery designs. However, both technologies need to improve their driving ranges in order to compete with gasoline and diesel-powered vehicles. 5.16.3. Comparison
asy En gi
of Fuel Cell Car and Gasoline Cars
Fuel Cell Vehicles (FCVs) are different from conventional gasoline and diesel-powered vehicles in several ways. First, FCVs are propelled by an electric motor instead of an internal combustion engine. This electric motor is powered with electricity provided by fuel cells. Fuel cell vehicles are more energy-efficient and emit fewer greenhouse gases and pollutants than
nee r
ing .ne
vehicles powered with conventional fuel. In addition to these benefits, fuel cell vehicles are quiet and they can provide more power for electrical accessories such as onboard navigation and control systems.
t
Gasoline vehicles currently have an advantage in terms of driving range. Most gasoline vehicles can travel 300 to 400 miles before refueling while most current FCVs can only travel about 250 miles. However, scientists are developing technologies which will allow FCYs to travel further between refills. 5.16.4. Working Principle of a Fuel Cell
A fuel cell is an electrochemical device in which the chemical energy of a conventional fuel is directly converted into low voltage DC electrical energy. One of the main advantages of such device is that Carnot limitation on efficiency does not apply because tile conversion can be carried out isothermally. A fuel cell is frequently described as a primary battery in which the fuel and oxidizer are stored in the battery and fed to it as needed.
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources
UIII
Figure 5.29 shows a schematic diagram of a fuel cell. The fuel gas diffuses through the anode and it is oxidized. Therefore, it releases electrons to the external circuit. The oxidized fuel diffuses through the cathode and it is reduced by electrons coming from anode by the way of external circuit.
Electrons
ww w.E Fuelin-
asy En gi
Figure 5.29 Schematicof afuel cell
The fuel cell is a device which keeps the fuel molecules from mixing with the oxidizer
nee r
molecules in permitting the transfer of electron by a metallic path that may contain a lead of available fuels. Hydrogen has so far given the most promising results, although cells consuming coal, oil or natural gas would be economically much more useful for large scale applications. Some of the possible reactions are given below. Hydrogen/oxygen 1.23 V Nitrogen
1.56 V
Carbon (Coal) Methane
1.02 V
1.05 V
2Hz + Oz => 2 HzO N214 + 0
ing .ne
t
=> 2 H20 + N2
C +Oi => COz CH4 + 202 => CO2 + 2 H20
5.16.5. Parts of a Fuel Cell
Polymer Electrolyte Membrane (PEM) fuel cells are the current focus of research for fuel cell vehicle applications. PEM fuel cells are made from several layers of different materials as shown in the Figure 5.29. The three key layers in a PEM fuel cell include the following: ..•
Membrane electrode assembly Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
•
Catalyst
•
Hardware.
Other layers of materials are designed to draw fuel and air into the cell and to conduct electrical current through the cell. 1. Membrane electrode assembly: Electrodes such as anode and cathode, catalyst and polymer electrolyte membrane together form the membrane electrode assembly (MEA) of a PEM fuel cell. a) Anode:
ww w.E
Anode is negative side of the fuel cell which has several jobs. It conducts the electrons which are bred from hydrogen molecules in order to use in an external circuit. Channels etched into the anode disperse the hydrogen gas equally over the surface of catalyst. b) Cathode:
asy En gi
Cathode is positive side of the fuel cell also containing channels which distribute oxygen
to the surface of catalyst. It conducts electrons back from the external circuit to the catalyst where they can recombine with the hydrogen ions and oxygen to form water. c) Polymer electrolyte membrane:
nee r
Polymer Electrolyte Membrane (PEM) is a specially treated material which looks similar to ordinary kitchen plastic wrap which conducts only positively charged ions and blocks
ing .ne
electrons. rEM is the key to the fuel cell technology. It will permit only the necessary ions to pass between anode and cathode. Other substances passing through the electrolyte will disrupt the chemical reaction. 2. Catalyst:
t
All electrochemical reactions in the fuel cell consist of two separate reactions such as an oxidation half-reaction at the anode and a reduction in half-reaction at the cathode. Normally, two half-reactions will occur very slowly at low operating temperature of a PEM fuel cell. So, each of the electrode is coated at one side with a catalyst layer which speeds up the reaction of oxygen and hydrogen. It is usually made of platinum powder very thin coated onto carbon paper or cloth. The catalyst is rough and porous to expose the maximum surface area of the platinum to the hydrogen or oxygen. The platinum-coated side of the catalyst faces PEM. Platinum-group metals are critical to catalytic reactions in the fuel cell but they are very expensive.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources
U·
3. Chemistry of afuel cell: Anode side: H2:::::) 2Ir + 2eCathode side: O2 + 4Ir + 4e- :::::) 2H20 Net reaction:
2H2 + 02 :::::)2H20 The pressurized hydrogen gas (H2) enters the fuel cell at anode side. This gas is forced through the catalyst by the pressure. When a H2 molecule comes in contact with the platinum
ww w.E
on the catalyst, it splits into two H+ ions and two electrons (e"). The electrons are conducted through the anode where they make their way through the external circuit and return to the cathode side of fuel cell.
asy En gi
Meanwhile, on the cathode side of the fuel cell, oxygen gas (02) is forced through the catalyst where it forms two oxygen atoms. Each of these atoms has a strong negative charge. This negative charge attracts two W ions through the membrane where they combine with an oxygen atom and two of electrons from the external circuit to form a water molecule (H20).
nee r
This reaction in a single fuel cell produces only about 0.7 V. To obtain this voltage up to a reasonable level, many separate fuel cells must be combined to form a fuel-cell stack. 4. Hardware:
ing .ne
The backing layers, flow fields and current collectors are designed to maximize the current from a membrane/electrode assembly. The backing layers are one next to anode and
t
the other next to cathode is usually made of a porous carbon paper or carbon cloth about thickness of 4 to 12 sheets of paper. The backing layers have to be made of a material which can conduct electrons that leave anode and enter cathode. The porous nature of the backing material ensures the effective diffusion of each reactant gas to the catalyst on the membrane/electrode assembly. The gas spreads out as it diffuses so that it will be in contact with the entire surface area of the catalyzed membrane when it penetrates backing. The backing layers also help in managing water in the fuel cell. Too little or too much water can cause the cell to stop operating. Water can build up in flow channels of plates or can clog the pores in the carbon cloth preventing reactive gases from reaching electrodes. Each plate also acts as a current collector. Electrons produced by the oxidation of hydrogen must Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
,..
.
Automobile
Engineering
I
1. be conducted through the anode and next, through the backing layer along the length of the stack and through the plate before they can exit the cell. 2. travel through an external circuit, and 3. re-enter the cell at cathode plate. With the addition of flow fields and current collectors, PEM fuel cell completes only a load-containing external circuit such as an electric motor which requires electric current. 5.16.6. Types of Fuel Cells
Fuel cells are classified on the basis of electrolyte used. It determines the type of chemical reactions that take place in the cell, kind of catalysts required, temperature range in which the cell operates, fuel required and other factors. These characteristics in tum affect the applications for which these cells are most suitable. There are several types of fuel cells
ww w.E
currently under development, each with its own advantages, limitations and potential applications.
asy En gi
1. Hydrogen-oxygen fuel cell
2. Polymer Electrolyte Membrane (PEM) fuel cell 3. Direct methanol fuel cell
4. Alkaline fuel cell
5. Phosphoric acid fuel cell 6. Molten carbonate fuel cell
7. Solid oxide fuel cell 8. Regenerative fuel cell. 5.16.6.1. Hydrogen-Oxygen
nee r
ing .ne
t
Cell
The hydrogen-oxygen device shown in Figure 5.30 is a typical type of fuel cell. It has three chambers separated by two porous electrodes, anode and cathode. The middle chamber between electrodes is filled with a strong solution of potassium hydroxide. The surfaces of electrodes are chemically treated to repel the electrolyte so that there is minimum leakage of potassium hydroxide into outer chambers. The gases diffuse through electrodes undergoing reactions as shown below: Anode:
2H2+4(OHf
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative
Energy Sources
O2 + 2 H20 + 4 e-:::) 4 (OHf 4 KOH :::) 4 K++ 4 (OHf
Cathode:
Cell reaction: The water formed is drawn off from the side. The electrolyte provides the (OH)- ions needed for the reaction and it remains unchanged at the end since these ions are regenerated. The electrons liberated at the anode find their way to move to the cathode through the external circuit. This transfer is equivalent to the flow of a current from cathode to anode. Such cells when properly designed and operated have an open circuit voltage of about 1.1 V. The electrolyte fuel efficiencies are as high as 60% - 70%.
ww
w.E
Oxygen
asy E
ngi
nee rin
Figure 5.30 Hydrogen-oxygen fuel cell There are two types of hydrogen fuel cells such as (i) Low temperature cell, and (ii) High pressure cell.
g.n et
Low temperature cell is operated at 90°C and less pressurized up to 4 atmospheric pressure. In the case of high pressure cell, pressure and temperature are 45 atmospheric pressure and 300°C respectively. Gases should be free from carbon dioxide. Otherwise, the gas will react with potassium hydroxide and produce potassium carbonate. This type of fuel cell is mainly suited for low voltage and high current applications. 5.16.6.2. Polymer Electrolyte Membrane (PEM) Fuel Cells
Polymer Electrolyte Membrane (PEM) fuel cells also called proton exchange membrane
fuel cells deliver high power density and offer the advantages of low weight and volume when compared to other fuel cells. PEM fuel cells use a solid polymer as an electrolyte and porous carbon electrodes containing a platinum catalyst. They need only hydrogen, oxygen from air
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile
Engineering
and water to operate. It does not require corrosive fluids similar to some other fuel cells. They are typically fueled with pure hydrogen supplied from storage tanks or onboard reformers. Electric current
ww w.E
asy En gi
Anode Electrolyte Cathode
Figure 5.31 Polymerelectrolytemembranefuel cell The chemical reaction and its description are already discussed in the earlier topic '5.16.5. Parts of a Fuel cell'. Kindly refer.
nee r
ing .ne
Polymer electrolyte membrane fuel cells operate at relatively low temperature around 80°C. Low temperature operation allows them to start quickly (less warm-up time) and it results less wear on system components thereby resulting better durability. However, it requires a noble-metal catalyst (platinum) which is used to separate hydrogen electrons and
t
protons. It is added with the system cost.
The platinum catalyst is also extremely sensitive to CO poisoning making it necessary to employ an additional reactor to reduce CO in the fuel gas if hydrogen is derived from an alcohol or hydrocarbon fuel. It is also added with the cost. PEM fuel cells are primarily used for the transport applications and some stationary applications. 5.16.6.3.Direct Methanol Fuel Cells Most fuel cells are powered by hydrogen which can be fed to a fuel cell system directly or it can be generated within the fuel cell system by reforming hydrogen-rich fuels such as methanol, ethanol and hydrocarbon fuels. Direct Methanol Fuel Cells (DMFCs) are powered by pure methanol which is mixed with steam and fed directly to the fuel cell anode.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative
diiil
Energy Sources
Direct methanol fuel cells do not have many of the fuel storage problems since methanol has higher energy density than hydrogen in gasoline or diesel fuel. Methanol is also easy to transport and supply to the public using current infrastructure since it is liquid such as gasoline. Direct methanol fuel cell technology is relatively new when compared to fuel cells powered by pure hydrogen. DMFC research and development are roughly 3-4 years behind than other fuel cell types. 5.16.6.4. Alkaline Fuel Cells
Alkaline Fuel Cells (AFCs) were one of the first fuel cell technologies developed and
ww
they were the first type widely used in US. A space program is to produce electrical energy
w.E
and water onboard spacecraft. These fuel cells use a solution of potassium hydroxide in water as the electrolyte using a variety of non-precious metals as a catalyst at anode and cathode.
asy
High-temperature AFCs operate at temperature between 100°C and 250°C. However, newer AFC designs operate at low temperature of roughly 23°C to 70°C.
En
Electriccurrent
Hydrogen in eH2_
gin eer Oxygen in
-----02
e ee H+ e11+ ~
... ...
-
ing
.ne
t
Water and Anode Electrolyte Cathode Figure 5.32 Alkalinefuel cell AFC's high performance is due to the rate at which the chemical reactions take place in the cell. They have also demonstrated the efficiency of 60% in space applications. The disadvantage of this fuel cell type is that it is easily poisoned by carbon dioxide 1.
(C02), Even small amount of CO2 in the air can affect this cell's operation. So, it should purify
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IDIll
Automobile Engineering
I
both hydrogen and oxygen used in the cell. This purification process is costly. The susceptibility to poisoning-also affects the cell's lifetime further adding to cost. 5.16.6.5. Phosphoric
Acid Fuel Cells (PAFCs)
Phosphoric Acid Fuel Cells (PAFCs) use liquid phosphoric acid as an electrolyte. The acid is contained in a Teflon-bonded silicon carbide matrix and porous carbon electrodes containing a platinum catalyst. The chemical reactions take place in- the cell shown in Figure 5.33. Electric current
ww
w.E
asy E
-
ngi
nee ----r
Air in Fuel in Anode Cathode Phospheric acid (Electrolyte)
Figure 5.33 Phosphoric acidfuel cell
ing .ne t
Usually, PAFC is considered as the "first generation" of modern fuel cells. It is one of the most grown-up cell types and currently used over 200 units. This type of fuel cell is typically used for stationary power generation but some PAFCs have been used to power large vehicles such as city buses. PAFCs are more tolerant of impurities in fossil fuels which have been reformed into hydrogen than PEM cells because they are easily "poisoned" by carbon monoxide. PAFCs are also less powerful than other fuel cells for the same weight and volume. As a result, these fuel cells are typically large and heavy. PAFCs are also expensive. Similar to PEM fuel cells, . PAFCs require an expensive platinum catalyst which raises the cost of fuel cell.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources 5.16.6.6.Molten Carbonate Fuel Cells -
Molten Carbonate Fuel Cells (MCFCs) are currently being developed for natural gas and coal-based power plants for electrical utility, industrial and military applications. MCFCs are high-temperature fuel cells which use an electrolyte composed of a molten carbonate salt mixture suspended in a porous chemically inert ceramic lithium aluminum oxide (LiAI02) matrix. Since they operate at extremely high temperature of 650°C and above, non-precious l
metals can be used as catalysts at the anode and cathode which reduces its cost. Electric current Hydrogen ih
ww w.E a H2-
Water and Heat out
s - - yEn gin t - -eer ing .ne t ~
Carbon dioxide in
Metal carbonate Anode (Electrolyte) Cathode
Figure 5.34 Molten carbonatefuel cell
Dissimilar to alkaline, phosphoric acid and polymer electrolyte membrane fuel cells, MCFCs do not require an external reformer to convert more energy-dense fuel to hydrogen. Due to high temperature, these MCFCs are operated to convert into hydrogen within the fuel cell itself by a process called internal reforming which also reduces the cost. Molten carbonate fuel cells are not prone to carbon monoxide or carbon dioxide "poisoning". They can even use carbon dioxides as fuel making them more attractive for fueling with gases made from coal because they are more resistant to impurities than other fuel cell types. The primary disadvantage of current MCFC technology is durability. High temperatures are preferred to operate these cells to avoid component breakdown and the corrosive electrolyte is used to reduce the corrosion because the corrosion affects the cell life. Scientists are currently exploring corrosion-resistant materials for components as well as fuel cell designs which increase the cell life without decreasing its performance. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IImI
Automobile Engineering
I
5.16.6.7.Solid Oxide Fuel Cells Solid Oxide Fuel Cells (SOFCs) use hard and non-porous ceramic compound as the
electrolyte. Since the electrolyte is a solid, cells do not have to be constructed in the plate similar to the configuration
of typical other fuel cell types. The efficiency of SOFCs is
expected around 50-60% in converting fuel to electricity. These cells can be used where the system wants to capture and utilize the system's waste heat (co-generation).
The overall fuel
efficiency is around 80-85%. SOFCs operate at high temperature around 1,000°C. High temperature operation removes the need for precious metal catalyst thereby reducing its cost. It also allows SOFCs to reform fuels internally which enables the use of a variety of fuels and it reduces the cost associated
ww
with adding a reformer to the system.
w.E
Electric current
asy E
Fuel----r..L,.-_::,.--L.,--_. in e
A ir in
...,_---
ngi
nee rin Unused gases out
---
water
....
Anode Electrolyte Cathode
g.n et
Figure 5.35 Solid oxidefuel cell SOFCs are also the most sulphur-resistant fuel cell type. They ean tolerate several orders of magnitude more sulphur than other cell types. In addition, they are not poisoned by carbon monoxide (CO) which can even be used as fuel. It allows SOFCs to use gases made from coal. High-temperature
operation is the main disadvantage of this cell. It results a slow start-up
and it requires significant thermal shielding to retain heat and protect personnel which may be acceptable
for utility applications
but it is not for transportation
and small portable
applications.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Altemative Energy Sources 5.16.6.8.Regenerative Fuel Cells Regenerative fuel cells produce electricity from hydrogen and oxygen. They generate heat and water as by-products similar to other fuel cells. However, the regenerative fuel cell systems can also use the electricity from solar power or some other sources to divide the excess water into oxygen and hydrogen fuel. This process is called electrolysis. It is a comparatively young fuel cell technology being developed by NASA. 5.16.7. Conversion Efficiency of Fuel Cells The electrical energy produced by fuel cells depends mainly on free energy of overall chemical reaction. Most of the fuel cells have maximum efficiency of 70% but fuel cell such as hydrogen and oxygen is with 50-60%. Again, the efficiency of fuel cell is low with air
ww w.E a
instead of pure oxygen as the source. 5.16.8. Advantages and Disatlvantages of Fuel Cells Advantages offuel cells:
syE
ngi
I. Fuel cells eliminate pollution caused by burning fossil fuels; the only by-product is water.
nee r
2. Fuel cells do not need conventional fuels such as oil or gas and can therefore eliminate economic dependence on politically unstable countries.
ing
3. Since hydrogen can be produced anywhere where there, is water and electricity, production of potential fuel can be distributed.
.ne
t
4. Fuel cells can achieve high efficiencies in energy conversion terms, especially where the waste heat from the cell is utilised in cogeneration situation. 5. Installation of smaller stationary fuel cells leads to a more stabilized and decentralized power grid. 6. Fuel cells convert chemical energy directly into electricity without the combustion process. As a result, a fuel cell is not governed by thermodynamic laws, such as the Carnot efficiency associated with heat engines, currently used for power generation. 7. A high power density allows fuel cells to be relatively compact source of electric power, beneficial in application with space constraints. In a fuel cell system, the fuel cell itself is nearly dwarfed by other components of the system such as the fuel reformer and power inverter
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Ims
Automobile Engineering
8. Fuel cells, due to their nature of operation, are extremely quiet in operation. This allows fuel cells to be used in residential or built-up areas where the noise pollution is undesirable. 9. The maintenance of fuel cells is simple since there are few moving parts system.
In
the
10. The absence of combustion and moving parts means that fuel cell technologies are expected to 'provide much improved reliability over traditional combustion engines. 11. Use a variety of fuels, renewable energy and clean fossil fuels. 12. Fuel cells can be responsive to changing electrical loads.
ww
13. Fuel cells provide high quality DC power. 14. Fuel cells have no "memory effect" when they are getting refueled.
w.E
15. Operating times are much longer than with batteries, since doubling the operating time needs only doubling the amount of fuel and not the doubling of the capacity of the unit itself.
asy E
Disadvantages offuel cells:
ngi
1. Initial cost is high. Fuel cells are currently very expensive to produce, since most units are hand-made. 2. Service life is low.
3. Operation requires repleisable fuel supply. 4. Some fuel cells use expensive materials.
nee rin
g.n et
5. Fuelling fuel cells is still a major problem since the production, transportation, distribution and storage of hydrogen i.~cult.
6. Reforming hydrocarbons via reformer to produce hydrogen is technically challenging and not clearly environmentally friendly. 7. The technology is not yet fully developed and few products are available. 8. The refueling and the starting time of fuel cell vehicles are longer and the driving range is shorter than in a "normal" car. , 5.16.9. Applications of Fuel Cells I. They can also be used for stationary applications such as providing electricity to power homes and business. 2. They are used in central power stations. Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources
I:11iD
3. Fuel cells have the potential to replace the internal combustion engine in vehicles. They can be used in transportation applications such as powering automobiles, buses, cycles and other vehicles. 4. Many portable devices can be powered by fuel cells such as laptop computers and cell phones. 5. They are used in spacecraft power stations. 6. Low temperature fuel cells (PEM, DMFC) have low heat transmission which makes them ideal for military applications. 5.16.10. Fuel Cell Vehicles
ww w.E a
Fuel cells can be used to provide propulsion or auxiliary power for many transportation
applications. Aside from spacecraft which typically use alkaline fuel cells for onboard power, Polymer Electrolyte Membrane (PEM) fuel cells are the primary type used in transportation.
syE
Few fuel-cell-powered transportation products are currently in use today, even fewer are
available commercially. A handful of fuel-cell-based passenger cars have been leased to
ngi
government and Universities but they are not available for sale to the public. About 200 auxiliary power units have been used in US and Russian spacecraft. 1. Highway vehicles:
nee r
ing
Since highway vehicles account for a large share of petroleum use, carbon dioxide (a primary greenhouse gas) emissions and air pollution, advances in fuel cell power systems for vehicles could substantially improve our energy security and air quality. While- fuel-cell-
.ne
t
powered cars are not available commercially, almost every major auto manufacturer has a fuel-cell vehicle program with various targets for demonstration in near future. Figure 5.36 describes the typical arrangement of various components in a fuel cell powered passenger car. Figure 5.37 illustrates the layout of components in a fuel cell powered vehicle. Other highway-based applications include large passenger buses and long-haul trucks. Fuel cell Auxiliary Power Units (APUs) for commercial trucks could also reduce energy use and emissions since these vehicles must often run while idle to provide electricity for refrigeration, heaters and air conditioners and sleeper compartment accessories.
2. Other surface transportation: Other potential surface transportation applications include rail locomotives, mining locomotives, scooters and personal mobility vehicles for the disabled.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Inm
Automobile Engineering
ww w.E
Power electronics
Cathode
Electro engine
asy En gi
Figure 5.36 Arrangements of Components in Fuel cell car
nee r
ing .ne
Figure 5.37 Layout of components in Fuel cell vehicle
t
3. Aerospace: Fuel cells are often used in aerospace applications. They have been used to provide auxiliary power in spacecraft since 1960s all 18 Apollo missions and over 100 Space Shuttle missions. Other similar applications include powering near-Earth orbit (NEO) satellites. 4. Marine vehicles: Ships and submarines are other possible applications for fuel cells by providing both propulsion and auxiliary power. Recreational and personal watercraft may also be powered by fuel cells.
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
,fi,a
I Alternative Energy Sources 5.17. TWO MARK QUESTIONS AND ANSWERS
1. What are the different alternative fuels suitable for automobiles? [Anna Univ. May'llj 1. Ethanol
2. Methanol 3. Gasohol
4. Bio-diesel 5. Liquefied petroleum gas (LPG) 6. Natural gas
ww w.E a 7. Hydrogen
8. Fuel cells.
2. List down the properties of alternatefuels. 1. Energy density
2. Volatility
3. Octane number
syE
4. Cetane number 5. Heat of vapourization
ngi
6. Flame speed 7. Flame temperature and luminosity 8. Auto-ignition temperature
nee r
ing
9. Flashpoint
.ne
t
10. Flammability. [Anna Univ. May'14J
3. Define energy intensity.
The evolution of the ratio of energy use to economic output is called energy intensity. The ratio is usually depicted as E / GDP where E stands for energy and GDP stands for gross domestic product i.e. economic output. 4. Define volatility. Volatility indicates a fuel's ability to vapourize under different temperature and pressure.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering 5.
What is meant hy octane number?
Octane numbers measure a fuel's tendency to knock in a spark ignition engine. 6. Define flame speed.. The speed at which a flame front propagates through a fuel/air mixture can affect the engine performance and emissions. 7. Define auto-ignition temperature of fuels. Auto-ignition temperature is a temperature at which the fuel will self-ignite. Selfignition is a concern in environment where the fuel might escape and come into contact with hot engine parts.
ww
8. Define flash point.
w.E
The flashpoint is the lowest temperature at which combustible mixtures of fuel vapour and air form above the fuel.
asy E
9. What is the composition of natural gas?
{Anna Univ.Nov'05]
Natural gas is at least 88% methane with the balance being higher weight hydrocarbons.
ngi
10. List out the various forms of natural gas.
nee rin
Various forms of natural gas are methane, ethane, methanol, ethanol, reformulated and oxygenated gasoline. Ll, State the advantages of methane asfuels ill automobiles. (a) (b)
g.n et
low emissions of ozone-forming hydrocarbons, toxics and carbon made from a variety of feed stocks including renewables.
(c) It is excellent fuel especially for fleet vehicles. 12. Write down the advantages and disadvantages of propane gas. Advantages of propane asfuels in automobiles: (i)
It is cheaper than gasoline today.
(ii) It is widely available clean fuel today.
(iii) It produces lower emissions of ozone - forming hydrocarbons and toxics. (iv) It is elcellent fuel especially for fleet vehicles.
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative
'tl'iA
Energy Sources
Disadvantages of propane asjuels in automobiles: (i)
Cost will rise with demand.
(ii) It has limited supply. (iii) There is no energy security or trade balance benefits occur. 13. What is meant by reformulated and oxygenated gasoline? The petroleum industry is beginning to market gasoline formulations that emit less hydrocarbons, nitrogen oxides, carbon monoxide and toxics than conventional gasoline. These new gasoline is called reformulated and oxygenated gasoline. 14. State the advantages of liquefied natural gas.
ww
I. Due to its low carbon-to-hydrogen ratio, it produces less carbon dioxide per GJ
w.E
of fuel than diesel.
2. It has low cold-start emissions due to its gaseous state.
asy
3. It has extended flammability limits, allowing stable combustion at lean mixtures.
En
4. It has a lower adiabatic flame temperature than diesel which leads to reduce NOx emissions.
gin eer
5. It has much higher ignition temperature than diesel making it more difficult to auto-ignite and it is thus safe.
ing
6. It contains non-toxic components. The liquefaction process removes impurities. 7. LNG is pure methane which is a non-toxic gas.
: ,.. ~
8. It is much lighter than air and thus it is safer than spill~crdiesel.
.ne
t
9. Methane is not a volatile organic compound (VOC). 15. Mention any four disadvantages of liquefied natural gas. 1. Its' driving range is limited because its energy content per volume IS relatively low. 2. It requires special refueling stations and handling of a cryogenic-liquid making it suitable only for fleet operations. . }; The energy required to liquefy NG leads to increas~~ouse
gas
emissions when compared to CNG.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1_ 4.
Automobile Engineering Exhaust emissions of methane, a greenhouse gas are relatively high compared with low sulphur diesel.
16. Write down the fuel characteristics of natural gas. NG has different
fuel characteristics
from fuels normally
used in internal
combustion engines. It has lower heating value of 52.9M1lkg. According to Perry's Chemical Engineering Handbook, the higher heating value of LNG at -164°C is 23.9
MIlL. It corresponds to a lower heating value of 21.7 MIlL which is less than automotive diesel (38.6 MIlL). 17. What is the composition of LPG?
{Anna Univ.Nov'05j
ww w.E a
LPG is the mixture of petroleum gases released during the extraction of crude oil
and natural
gas or during refining the crude oil. It consists
of a mixture of
hydrocarbons including major components of propane and butane, minor components
such as normal-butane,
iso-butane, pentane, ethane, propene and butene together with
syE
small quantities of additives including sulphur to give it an odour for safety reasons.
Propane (C3HS) and butane (C4HIO) are the main components ratio is used in different countries.
18. List down the properties of LPG.
ngi
Properly (units/conditions) Relative molar mass
nee r
but different mixing
Value
ing
Carbon content (mass %)
44.1 82
Hydrogen content (mass %)
18
Oxygen content (mass %)
0
Specific Gravity of Liquid at 15°C
.ne
t
0.54 - 0.57 \
Sp. Volume of Gas at 15°C, 760 mm Hg.(Iitig of gas)
0.4"
Relative density (@15°CI I bar)
0.5
Boiling temperature eCI I bar)
-42
Autoignition temperature (0C)
480
Octane number (RON)
112
Octane number (MON)
99.5
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative
IIZ'DI J
Energy Sources
Methane number
35
Stoichiometric air/fuel ratio (mass)
15.7
Vapour pressure @ 38°C (kPa)
1300
freezing temperature eC)
-187
~-.----
flash poine ternperature (0C)
-104
Sp. heat (kJ/kg-K) @ 1 bar & 15°C
ww w.E
liquid phase
2.48
gas phase
1.67
Latent heat of vapourisation @ I bar (kJ/kg)
426
Lower heating/calorific value (MJ/kg)
46
Gross Calorific Value of LPG (kcal/kg)
11,400
asy E
Viscosity (MPa-s at 15°C) for liquid phase
11.10-5
For gas phase
80.10-7
ngi
19. Write down the components of LPG equipment.
nee
1. LPG fuel tank 2.
Vapourizer
3.
Fuel meter.
20. What are types of LPG vehicles available in the market?
rin
g.n e
1. Passenger cars 2.
Two/three wheelers
3.
Buses.
21. Compare LPG and CNG cars working principles. S.No.
,
1.
[Anna Univ. May'09j
LPG
CNG
Liquefied petroleum gas (LPG)
It is a mixture of light hydrocarbons
consists
including methane, ethane, propane,
propylene,
mainly
of
propane,
butane and butylene
t
butanes and pentanes.
in various mixtures. Propane or LPG I is used in all
Light-duty vehicles designed to run Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile Engineering
2.
I
major end-use sectors as a on 'natural gas include cars, heating fuel, engine fuel, l111l11VanS and vans - mainly for cooking fuel and chemical fleets. feedstock.
22. What is LPG? What are the advantages ami disadvantages of using it in automobiles?
[Anna Uni., May'l1 & May'12J
Liquefied Petroleum Gas (LPG) is made of a mixture of propane and other similar types of hydrocarbon gases. Advantages of LPG:
ww 1.
It has very low sulphur levels giving a rise to insignificant sulphate emissions.
2.
It has low cold start emissions due to its gaseous state at ambient pressure and temperature.
3.
It has relatively high octane number with propane having the best antiknock
w.E
asy
properties relative to other components. 4.
En
It has lower peak pressure during combustion whicn generally reduces noise and improves durability. Noise levels can be less than 50% of equivalent diesel engines.
5.
gin eer
It can be stored as liquid under low pressure (~5bar) and ambient temperature.
Disadvantages of LPG: 1.
ing
Although LPG has a relatively high energy content per mass, its energy content per unit volume is low.
.ne
t
2.
It is heavier than air which requires appropriate handling.
3.
It's vapour flammability limit in air (2-10% by volume) is wider than gasoline which makes LPG ignitable more easily.
4.
It has a high expansion coefficient which necessitates only partial filling of the
tank to not more than 80% of its capacity. 23. What are the advantages of using compressed natural gas over diesel? [Anna Univ. May'l1J 1.
Due to its low carbon-to-hydrogen ratio, it produces less carbon dioxide per GJ of fuel than diesel.
2.
It has low cold-start emissions due to its gaseous state.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
! Alternative
am
Energy Sources
3.
I
It has extended flammability limits allowing stable combustion at lean mixtures.
4.
It has a low adiabatic flame temperaturylmn diesel thereby leading to low NOx emissions.
5.
It has much higher ignition temperature than diesel in making it more difficult
to auto-ignite. Thus, it is safe. 6.
It contains non-toxic components. The liquefaction process removes ilmpurities.
7.
LNG is pure methane which is a non-toxic gas.
ww w.E S.
It is much lighter than air and thus, it is safer than spilled diesel.
9.
Methane is not a volatile organic compound (VOC).
-c.,
24. How is biodiesel prepared? The majority of biodiesel is made from soybean or canola oils but it is also made from waste stream sources such as used cooking oils or animal fats.
asy E
25. Why blodiesel is mixed with conventional diesel?
ngi
Biodiesel is mixed with conventional diesel because of high cost of biodiesel,
nee
engine compatibility issues and cold weather operating concerns. 26. List down the available common biodiesel blends. 1.
B20, or 20% biodiesel, and
ii. B2, or 2% biodiesel.
rin
27. What does BI00 refer?
g.n e
t
BI00 is the 100% biodiesel which offers the most overall environmental benefits. The use of B I00 may require engine or fuel system component modification and it can cause operating problems especially in cold weather. 28. Give any four advantages of biodiesel.
[Anna Univ. Nov'08 & May'15j
1. It is a substitute or extender for traditional petroleum diesel and special pumps or high pressure equipment for fueling is not needed because little"fossil energy is required to move biodiesel. 2. Scientists believe carbon dioxide is one of the main greenhouse gases contributing to global warming. Neat biodiesel (100% biodiesel) reduces carbon dioxide emissions by more than 75% over petroleum diesel.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
_
Automobile Engineering
I
3. Use of biodiesel in a conventional diesel engine wilt result a substantial reduction of unbumt hydrocarbons, carbon monoxide and particulate matter. Biodiesel reduces emissions of carbon monoxide (CO) by approximately 50 % and carbon dioxide by 78.8 % on a net lifecycle basis because the carbon in biodiesel emissions is recycled from carbon present in atmosphere rather than being new carbon from petroleum that was sequestered in the earth's crust. 4. Since biodiesel is made entirely from vegetable oil, it does not contain any sulphur, aromatic hydrocarbons, metals or crude oil residues. 29. What are the basic routes of producing esterfrom oils andfats?
ww
1. Base catalyzed transesterification of the oil with alcohol.
2. Direct acid catalyzed esterification of the oil with methanol.
w.E
3. Conversion of the oil to fatt): acids, and then to Alkyl esters with acid catalysis.
asy E
30. State the reasons alkyl esters produced with the base catalyzed reactors. 1. Low temperature (150U F) and pressure (20 psi) processmg.
ngi
2. High conversion (98%) with minimal side reactions and reaction time. 3. Direct conversion to methyl ester with no intermediate steps.
nee rin
4. Exotic materials of construction are not necessary.
[Anna Univ. May'll]
31.. Define "transesterification process".
g.n et
Biodiesel is produced from vegetable oils by converting the triglyceride oils to methyl (or ethyl) esters with a process known as transesterification. 12. What is Bio-ethanolt
Bio-ethanol is one of form of renewable energy. It can be produced from agricultural feed stocks. It can be made from very common crops such as sugar cane, potato, manioc and corn. 33. Write short notes on ethanol based engines. Ethanol is most commonly used to power automobiles even if it is used to power other vehicles such as farm tractors, boats and airplanes. Ethanol (E 100) consumption in an engine is approximately 51% higher than gasoline since the energy per unit volume of ethanol is 34% less than gasoline. The higher compression ratio in an ethanol-only engine provides the increased power output and better fuel economy than lower compression ratio. Usually, ethanol-only engines give slightly better power and torque output than gasoline-powered engines. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Alternative Energy Sources
34. Why is ethanol fuel mixtures used in automobiles?
Ethanol has a research octane number of 120 which is higher than petrol, between 87 and 98. Thus, ethanol blending increases the octane number without adding a carcinogenic substance such as benzene or a health-risk posing chemical such as methyl tertiary butyl ether (MTBE). The energy content of ethanol is only 26.9 MJ/kg compared to 44.0 MJ/kg of petrol. The fuel economy (kmllitre) of a petrol-powered engine would be 38.9 % higher than an ethanol-powered engine. In actuality, this difference is 30 % since ethanol engines can run more efficiently (at a higher compression ratio) because of high octane rating. For a 10 % ethanol blend, the fuel economy advantage of a petrol engine is only 3 %. The flammability limit of ethanol (19 % in air) is higher than petrol (7.6 %), and likewise the auto-ignition temperature of ethanol is higher than petrol (366 versus 300°C). Thus, ethanol is safer
ww w.E
than petrol due to the low like hood of catching fire.
asy E
35. What is meant gasohol?
Gasohol is a mixture of 10% of ethanol (commonly known as grain alcohol or
ngi
beverage alcohol) and 90% of unleaded gasoline.
nee
36. List down the different way.\'ethanol can be used as a transportation fuel:
rin
(a) As a blend of 10 % ethanol with 90 % unleaded gasoline called "E-IO Unleaded".
g.n e
(b) As a component of reformulated gasoline, both directly and as ethyl tertiary butyl ether (ETBE), or
t
(c) As a primary fuel with 85 parts of ethanol blended with 15 parts of unleaded gasoline called "E-85." 37. How can befermentation process defined? Fermentation is a sequence of reactions which release energy from organic molecules in the absence of oxygen. 38. What are the major steps of dry milling ethanol process? (a) Milling (b) Liquefaction (c) Saccharification (d) Fermentation 42
(e) Distillation Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1""'
Automobile Engineering (f) Dehydration
(g) Denaturing. 39. List down the properties of gasohol. a) Octane rating b) Heat value c) Volatility d) Latent heat of vapourization
ww
e) Exhaust emissions
f)
Alcohol/water mix
w.E
g) Engine economy.
asy E
40. What are the advantages and limitations of alcohols as engine fuel? Advantages:
{Anna Univ. Apr'05 & Dec'14J
ngi
1. Low emissions of ozone-forming hydrocarbons and toxics.
nee rin
2.
It can be made from renewable sources.
3.
It can be domestically produced.
Limitations: I. Fuel cost is high. 2. Vehicle range is less. 41. Write down any six advantages of ethanol
g.n et
I. Car owners benefit from increased octane in gasoline which reducer. engine "knock" or "pinging." Ethanol-blended fuels also absorb moisture and clean the fuel system. 2. Ethanol blends such as E-IO unleaded can be used in all gas engines without engine or mechanical revisions. 3. Ethanol guards against gas line freeze by absorbing moisture which may get in the tank during cold weather. 4. Ethanol is low in reactivity and high in oxygen content making it an effective tool in reducing ozone pollution. Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
"j,U
I Alternative Energy Sources
5. Ethanol is a safe replacement for toxic octane enhancers in gasoline such as benzene, toluene and xylene. 6. Ethanol reduces greenhouse gas emissions because it is produced from renewable agricultural feed stocks. 42. Compare the properties of alcohols and gasoline as engine fuels. [Anna Univ. Dec'12] (a) Alcohol is 16 points higher on the research octane scale than premium gasoline. It means, alcohols have higher octane rating than gasoline.
ww w.E
(b) Alcohols contain only 63% of the energy that gasoline has mainly because of the presence of oxygen in alcohol's structure. Hence, heating value is less.
(c) Alcohols are highly volatile than gasoline. (d) Alcohols have higher flash point than gasoline and hence, it is a much safer the automotive fuel.
asy E
(e) Latent heat of vapourization of alcohols is more than gasoline. When a substance undergoes a change in form (from a liquid to a vapour), it must absorb a certain
ngi
amount of additional heat from its surroundings to take place. Since alcohol must absorb roughly 2 Y2 times the amount of heat what gasoline does and the heat naturally is taken from the engine block, the engine should operate at much lower temperature.
nee
rin
g.n e
(f) Alcohol requires a richer air/fuel mix than gasoline (9:1 as opposed to 15:1) due to alcohol having higher "octane" rating and it can be utilized more efficiently. 43. Define the process of electrolysis.
t
Electrolysis is a process in which the hydrogen and oxygen in water can be dissociated by electric current. 44. Why is hydrogen called as secondary energy source?
[Anna Univ. May'14]
As a fuel, hydrogen is used in the form of gas. Since hydrogen does not exist on earth as a gas, it must be separated from other compounds. It is considered as a secondary source of energy because another form of energy is needed to produce the i hydrogen fuel. The primary sources of energy to produce hydrogen are natural gas, water, coal or oil. These sources go through different types of processes that allow hydrogen fuel to be made.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1mB
Automobile Engineering
45. What are the methods for using hydrogen as afuel?
{Anna Univ. May'lOj
1. Hydrogen in its liquid form has been used as a fuel in space .vehicles for years. Hydrogen
has high combustion
energy per pound relative to any other fuel
meaning that hydrogen is more efficient on weight basis than fuels currently used in air or ground transportation. 2. Hydrogen is both flammable and buoyant. It is flammable over a wider range of concentrations
than either gasoline or natural gas but due to its buoyancy, it
dissipates more rapidly than either of these fuels in a spill. Hydrogen gas such as other gases used today should be used in areas that can be ventilated.
ww w.E a
3. Hydrogen can and has been used safely when guidelines for its proper handling and storage are observed.
4. It can be used in applications requiring electricity or gas and it can link the fossil-
syE
based energy supply of today with the renewable energy tomorrow.
46. Mention any two methods of producing hydrogen gas.
ngi
I. Steam reforming of natural gas. 2.
nee r
Electrolysis of water.
47. List out tile various technologies used in producing hydrogen gas.
ing
I. Steam reforming converts methane (other hydrocarbons
in natural gas) into
.ne
hydrogen and carbon monoxide by reaction with steam over a nickel catalyst, 2.
(+) and oxygen at the anode (-). 3.
t
Electrolysis uses electrical current to split water into hydrogen at the cathode
Steam electrolysis (a variation on conventional electrolysis) uses heat instead of electricity to provioe some of the energy needed to split water making the process more energy efficient.
4.
Thermochemical
water splitting uses chemicals and heat in multiple steps to
split water into component parts. 5.
Photoelectrochemical
systems
use
semi-conducting
materials
(such
as
photovoltaics) to split water using only sunlight. 6.
Photobiological systems use microorganisms to split water using sunlight.
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I
Dig
Alternative Energy Sources
7.
Biological systems use microbes to break down a variety of biomass feed stocks into hydrogen.
48. Mention any four properties of hydrogen gas. 1. Colorless, odorless, tasteless and nonpoisonous gas under normal conditions. 2. It readily combines with oxygen to form water which is absolutely necessary for life on this planet. 3. It has high energy content per weight (nearly 3 times as much as gasoline) but the energy density per volume is quite low at standard temperature and
ww w.E pressure.
4. Hydrogen is highly flammable. It also has a wide flammability range and it can burn when it makes up to 74% of the air by volume.
asy E
S. Hydrogen burns with a pale-blue, almost-invisible flame in making hydrogen fires difficult.
ngi
49. Describe briefly natural gas steam reforming.
The production of hydrogen from natural gas is an integral part of the strategy to introduce hydrogen into the transportation and utility energy sectors by reducing the cost of conventional and developing innovative hydrogen production processes which
nee
rely on cheap fossil feed stocks.
50. Write short notes on biomass gasification ami pyrolysis.
rin
g.n e
t
The thermal processing techniques for plant material (biomass) and fossil fuels are similar with a number of the downstream unit operations being essentially same for both feed stocks. Using agricultural residues and wastes or biomass specifically grown for energy uses, hydrogen can be produced via pyrolysis or gasification. Biomass pyrolysis produces a liquid product (bio-oil). such as petroleum contains a wide spectrum of components which can be separated into valuable chemicals and fuels. 51. How are electrolytic processes carried out? Electrolytic hydrogen production processes use electrical energy to split water into hydrogen and oxygen. In electrolysis, electricity is used to separate water (H20) into hydrogen (H2) and oxygen (02). The electricity can come from fossil fuels such as coal or from renewable sources such as nuclear, solar or hydroelectric power.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I.:'
I
Automobile Engineering
52. State any four disadvantages of using hydrogen asfuel.
{Anna Univ. Dec'13}
a) Heavy bulky fuel storage both in vehicle and at the service station. Hydrogen can be stored either as cryogenic liquid or compressed gas. If stored as a liquid, it would have to be kept under pressure at low temperature. It would require a thermally super-insulated fuel tank. Storing in a gas phase would require a heavy pressure vessel with limited capacity. b) It is difficult to refuel. c) Poor engine volumetric efficiency. Any time a gaseous fuel is used in an engine, the fuel will displace some of the inlet air and poor volumetric efficiency will result.
ww w.E a
d) Fuel cost would be high at present-day technology and availability.
e) NOx emissions are high because of high flame temperature.
syE
53. What are the advantages and disadvantages 0/ electricity asfuels in automobiles? Advantages:
ngi
(i)
Potential for zero vehicle emissions is possible.
(ii)
Power plant emissions control is easy.
nee r
(iii) It can recharge at night when power demand is low.
ing
Disadvantages: (i)
Current technology is limited.
(ii) It has higher vehicle cost, lower range and performance. (iii) It has less convenient refueling. 54. Enumerate the limitations of electnc vehicle.
.ne
t
{Anna Univ. Nov'07 & May'll}
I. Initial torque is less. 2. It is more expensive. 3. Frequent recharging of battery is needed also battery charging needs more time. 4. The performance is poor. 5. A variety of vehicles is less available in the market. 55. What isfuel cell?
{Anna Univ. May'08, May'12 & May'14}
A fuel cell produces electricity directly from the reaction between hydrogen (derived from a hydrogen-containing fuel or produced from-the electrolysis of water) and oxygen from air. Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative Energy sources
"'pi
[Anna Univ. May'08)
56. Briefly explain fuel cell.
Like an internal combustion engine in a conventional car, it turns fuel into power by causing it to release energy. In an internal co: bustion engine, the fuel burns in tiny explosions that push the piston up and down. When the fuel burns, it is being oxidized. In other words, the fuel combines with oxygen and it produces energy in the form of heat and mechanical motion. In a fuel cell, the fuel is also oxidized. but the resulting energy takes in the form of electricity. When powered by pure hydrogen, the only by-products of the reaction are heat and water.
ww w.E
57. What is meant by reversiblefuel cell? Some fuel cells can be run in reverse under certain conditions which produces hydrogen via electrolysis. It is called reversible fuel cell.
asy E
58. Explain the application offuel cell. 1. Highway vehicles
2. Other surface transportation 3. Aerospace 4. Marine vehicles.
[Anna Univ. Nov'08)
ngi
nee
59. How can we define photolytic process?
rin
g.n e
Photolytic hydrogen production technologies use the energy from sunlight to split water into hydrogen and oxygen. Emerging direct water-splitting technologies include photobiological and photoelectrochemical systems.
60. Define the following processes: Photo~iological and Photo electrolysis I
t
(a) Photobiological process: Certain photosynthetic microbes produce hydrogen in their metabolic activities using light energy. By employing catalysts and engineered systems, hydrogen production efficiency could reach 24%. Photobiological technology holds great promise because oxygen is produced along with the hydrogen, the technology must overcome the limitation of oxygen sensitivity of hydrogen-evolving enzyme systems. (bJPhotoelectrolysis: Multifunction cell technology developed by PV industry is used for photoelectrochemical (PEC) light harvesting systems which generate sufficient voltage to split water and they are stable in a water/electrolyte environment. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
1
"",.t,j
Automobile Engineering
I
61. Mention the various methods of storing hydrogen. (i) High-pressure storage tanks (ii) Liquid hydrogen (iii) Metal hydrides (iv) Carbon nanotubes. 62. List out the various benefits of a parallel configuration 1.
0/ EVs.
A smaller engine provides more efficient operation and therefore, it produces
ww w.E a
better fuel economy without sacrificing acceleration power. The vehicle has more power because both engine and motor supply power simultaneously.
2.
Most parallel vehicles do not need a separate generator because the motor regenerates the batteries.
3.
Power does not need to be redirected through batteries. Therefore, it can be more efficient.
syE
63. Define a hybrid vehicle.
ngi
[Anna Univ. May'08 & May'H}
nee r
The vehicle which is using more than one source of energy to run is called hybrid vehicle. Hybrid means that it is mixed together from two things. Usually, it refers to
ing
plants or animals that are breed from different dissimilar parents. 64. Mention the classification
0/ Hybrid vehicles?
1. Toyota Prius hybrid electric vehicle
.ne
[Anna Univ. May'lO]
2. Ford Escape hybrid electric vehicle
t
3. Fuel cell powered hybrid electric vehicle 4. Heavy duty truck applications. 65. State the benefits 0/ a series configuration. 1. The engine never idles which reduces vehicle emissions. 2. The engine can continuously operate in its most efficient region. 3. The engine drives a generator to run at optimum performance. 4. The design allows for a variety of options when mounting the engine and vehicle components. 5. Some series hybrids do not need a transmission.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources
Utl'
66. What are the components of a hybrid vehicle?
{Anna Univ. May '10 & Dec'}3}
1. Electric traction motors/controllers. 2. Electric energy storage systems such as batteries and ultra-capacitors. 3. Hybrid power units such as spark ignition engines, compression ignition direct injection (diesel) engines, gas turbines and fuel cells. 4. Fuel systems for hybrid power units. 5. Transmissions. 67. What are the different types batteries used in hybrid vehicles?
ww
1. Lead-Acid batteries
w.E asy En gin ee
2. Nickel-Cadmium batteries
3. Nickel-Metal hydride batteries 4. Lithium ion batteries
5. Lithium polymer batteries
6. Hybrid electric vehicle spark ignition engines. 68. Describe briefly hybrid electric vehicle gas turbine.
The gas turbine engine runs on a Brayton cycle using a continuous combustion process. In this cycle, a compressor (usually radial flow for automotive applications) raises the pressure and temperature of inlet air. The air is then moved into the burner
rin g.
net
where the fuel is injected and combusted to raise the temperature of air. Power is produced when heated. A high-pressure mixture is expanded and cooled through a turbine. When a turbine engine is directly coupled to a generator, it is often called
turbo generator or turbo alternator.
The power output of a turbine is controlled through the amount of fuel injected into burner. Many turbines have adjustable vanes and gearing to decrease the fuel consumption during partial load conditions and improve acceleration. 69. What is a turbo alternator? If a turbine engine is directly coupled to a generator, it is called turbo generator
or turbo alternator. 70. Mention the dismhtantage.v (if lIybril/ electric vehicle ga.\'turbine engines. I. Turbine engines have high manufacturing cost because of the complicated design and expensive manufacturing. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
2.
Automobile Engineering A turbine engine changes speed slowly. A gas turbine is slow to respond (reiative to a reciprocating engine) to change in throttle request.
3. A gas turbine is less suitable for low-power applications. At partial throttle conditions, the efficiency of gas turbine decreases. 4. A turbine requires intercoolers, regenerators and reheaters to reach efficiencies comparable to current gasoline engines. It adds significant cost and complexity to a turbine engine. 71. What are the objectives of hybrid electric vehicles?
ww
(i) To maximize the fuel economy (ii) To minimize emissions
w.E asy En gin ee
(iii) To minimize propulsion system cost to keep the vehicles affordable to the consumer market (iv) To do all of above while maintaining or improving on acceptable performance.
72. List the various control strategies in hybrid system. (i) Mechanical control (ii) Electrical control.
73. State tile applications of IIybrid vehicles. 1. Consumer applications. 2. Bus applications. 3. Heavy duty truck applications.
rin g.
net
74. What is meant by afuel cell and "ow it works? {Anna Univ. Apr'06 & May'09j A fuel cell produces electricity directly from the reaction between hydrogen (derived from a hydrogen-containing fuel or produced from the electrolysis of water) and oxygen from air. 75. Write down tile comparison between a fuel cell powered car to one powered by a battery. Fuel cell and battery-powered vehicles are both propelled by electric motors. Therefore, both vehicle types can be designed with similar performance characteristics. The primary difference in these vehicles is the source of electricity. Battery-electric vehicles are powered by electricity stored in a battery. Since the battery merely stores energy instead of generating it, it must be recharged regularly. Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources
OlD
Fuel cells generate electricity from hydrogen or some other fuel. Such as gasoline-powered vehicles, fuel cell vehicles are refueled rather than recharged. Refueling usually takes much less time than recharging. Fuel cell vehicles can typically go further before refueling due to the storage limitations of current battery designs. However, both technologies need to improve their driving range in order to compete with gasoline and diesel-powered vehicles.
76.Mention the variousparts offuel ceiL I. Membrane electrode assembly
ww
2. Catalyst 3. Chemistry of a Fuel Cell
w.E asy En gin ee
4. Hardware.
77. List downthe major sectionsof afuel cell vehicles. (i)
Fuel processing section
(ii) Fuel cell power pack
(iii) Power conditioning section
(iv) Switchgear and supply section (v) Control subsystem section (vi) Heating section.
78. Mention anyfour typesof'fuel cells.
rin g.
net
{Anna Univ.Nov'05]
I)
Hydrogen-oxygen fuel cell
2)
Polymer electrolyte membrane (PEM) fuel cell
3)
Direct methanol fuel cell
4)
Alkaline fuel cell
5)
Phosphoric acid fuel cell
6)
Molten carbonate fuel cell
7)
Solid oxide fuel cell
8)
Regenerative fuel cell.
79. Whatare thefactors to be consideredin benefitsoffuel cellst 1. Fuel cells are cleaner and more efficient than traditional combustion-based engines and power plants. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
2.
Using pure hydrogen to power fuel cell vehicles offers the distinct advantage of zero emissions but only on the vehicle not at the hydrogen production source.
3.
Fuel cell vehicles are expected to achieve overall energy conversion throughout efficiencies around twice oftoday's typical gasoline internal combustion engines.
4. Hydrogen is the most abundant element in the universe and it can be found on Earth in virtually unlimited quantities. Using hydrogen or other domestically produced alternative fuels to power fuel cell vehicles will help to reduce our nation's dependence on imported oil.
ww
80. What is the difference between variousfuel cells?
{Anna Univ. Dec'12]
The main difference between various fuel cells is the type of electrolyte used.
w.E asy En gin ee
Fuel cells are classified on the basis of electrolyte used by the difference in startup time ranging from I second for Proton exchange membrane fuel cells (PEMFC) to 10 min for Solid oxide fuel cells (SOFes).
81. What are the advantages offuel cells?
1. Fuel cells eliminate pollution caused by burning fossil fuels; the only byproduct is water. 2. Fuel cells do not need conventional fuels such as oil or gas and can therefore eliminate economic dependence on politically unstable countries.
rin g.
3. Since hydrogen can be produced anywhere where there is water and electricity, production of potential fuel can be distributed.
net
4. Fuel cells can achieve high efficiencies in energy conversion terms, especially where the waste heat from the cell is utilised in cogeneration situation.
S. Installation of smaller stationary fuel cells leads to a more stabilized and decentralized power grid. 82. What are the disadvantages offuel cells? 1. Initial cost is high. Fuel cells are currently very expensive to produce, since most units are hand-made. 2. Service life is low. 3. Operation requires repleisable fuel supply. 4. Some fuel cells use expensive materials. 5. Fuelling fuel cells is still a major problem since the production, transportation, distribution and storage of hydrogen is difficult. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources 83. List the various applications of'fuel cells. I. They can also be used for stationary applications such as providing electricity to power homes and business. 2. They are used in central power stations. 3. Fuel cells have the potential to replace the internal combustion engine
In
vehicles. They can be used in transportation applications such as powering automobiles, buses, cycles and other vehicles. 4. Many portable devices.can be powered by fuel cells such as laptop computers and cell phones.
ww w.E
5. They are used in spacecraft power stations.
asy
5.18. SOLVED QUESTIONS
I. Explain the reasons for looking for alternate fuels for IC engines. Refer page 5.1.
En
[Anna Univ. Dec' 12]
gin
eer
2. What are the alternative energy sources for automobiles? Refer chapter 5.2 in page 5.2.
3. Explain the various properties of alternative fuels. Refer chapter 5.3 in page 5.4.
[Anna Univ. Dec '14]
ing .ne t
4. Explain the production of natural gas with a neat sketch in detail. Refer chapter 5.4.4 in page 5.13. 5. What are the ~nefits of natural gas? Refer chapter 5.4.8 in page 5.18. 6. Write short notes on constraints in CNG.
[Anna Univ. Nov '07]
Refer chapter 5.4.7 in page 5.17. 7. Describe the salient features of using LPG as an alternate fuel. [Anna Univ. Apr '06] Refer chapter 5.5.1 in page 5.20.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
IdfliJ
Automobile Engineering
8. Draw and explain the operation of liquefied petroleum gas system. [Anna Univ. Nov '08 & May '09, May ']0 & May ']5]
Refer chapter 5.5.5 in page 5.25. 9. What is LPG? What are the advantages and disadvantages of using it in automobiles? [Anna Univ. Dec ']4]
Refer chapter 5.5 in page 5.19 for the definition of LPG and chapter 5.5.6 in page 5.27 for advantages and disadvantages of LPG. 10. Explain briefly about the history, current uses, process of utilization and advantages of biomass as a fuel. [Anna Univ. May'] 4 & Dec'] 4]
ww
w.E asy En gin ee
Refer chapter 5.6 in page 5.29.
11. How bio diesel is produced? Explain and its usage in automobile. [Anna Univ. May '08]
Refer chapter 5.6.2 in page 5.30.
12. Enumerate the advantages and disadvantages of using alcohol as a fuel.
Refer chapter 5.7.8 in page 5.40.
[Anna Univ. May'14]
rin g.
]3. Explain how Bio-ethanol is prepared and used in automobiles. Refer chapter 5.7.2 in page 5.35.
14. Explain the bio-ethanol consumption in India and reason for the same. Refer chapter 5.7 in page 5.33.
net
15. What are the advantages and disadvantages of using 1. Alcohol and Refer chapter 5.7.8 in page 5.40. 2. Hydrogen in Ie engines.
[Anna Univ. May'] 2]
Refer chapter 5.9.2 in page 5.97. 16. Discuss "hydrogen is a part of life or not". Or Explain why hydrogen is considered as the most favourable fuel for future. [Anna Univ. Apr '06]
Refer chapter 5.9 in page 5.76. Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Alternative Energy Sources [Anna Univ. Nov '051
17. Discuss the properties of hydrogen. Refer chapter 5.9.4 in page 5.48. 18. Explain electrolysis process in hydrogen production. Refer chapter 5.9.5 in page 5.49.
19. List out the various thermo chemical processes. Explain any two in detail. Refer chapter 5.9.7 in page 5.52. 20. Explain the two methods by which hydrogen can be used in CI engine. [Anna Univ. Nov '07, May:08 ..May' 11 & Dec' 12]
ww
w.E asy En gin ee
Refer chapter 5.9.9 in page 5.55.
21. Explain the engine modification required to use alternate fuels in automobiles. [Anna Univ. Dec' 14] Refer chapter 5.10 in page 5.57.
22. Explain the modification required in 'Sf and CI engines to employ alternate fuels to produce on par performance, combustion and emission characteristics of conventional engines. [Anna Univ. Dec' 13] Refer chapter 5.10.2 in page 5.58.
rin g.
23. Describe the steps involved in analysing the engine performance while using alternate fuels. Refer chanter 5.11 in page 5.62.
net
24. Explain in detail about the electrical vehicle system with a block diagram. [Anna Univ. Nov '08 & May '09, Dec'J3 & May '15] Refer chapter 5.14.3 in page 5.73. 25. What are the advantages and limitations of Electric vehicle?
[Anna Univ. Apr '05]
Refer chapter 5.14.5 & 5.14.6 in page 5.75. 26. What is meant by hybrid vehicle? Give its merits.
[Anna Univ. Nov '08]
Refer chapter 5.15 in page 5.76. 27. With a layout diagram, explain the working features of hybrid vehicles.
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
'Ilt.,:1
Automobile
Engfneerlng
28. Write short notes on hybrid electric vehicle components. Refer chapter 5.15.4 in page 5.79. [Anna Univ. Dec'] 4]
29. Explain the different types of hybrid vehicles with neat sketch. Refer chapter 5.15.1 in page 5.76. 30. Why fuel cells are not preferred for automobiles now?
[Anna Univ. Dec' 14]
Refer chapter 5.16 in page 5.89. 31. Compare a fuel-powered car to one powered by a battery.
ww w.E
Refer chapter 5.16.2 in page 5.90.
i
32. Explain fuel cell with a neat sketch. Give their disadvantages and advantages.
asy E
[Anna Univ. Nov '05, Nov'OB, May'Ll & May ']5]
Refer chapter 5.16.4 in page 5.90 for the description of fuel cell and chapter 5.16.8 in page 5.101 for advantages and disadvantages of fuel cell.
ngi
33. Describe the various parts of fuel cell.
Refer chapter 5.16.5 in page 5.91. 34. What are the various kinds of fuel cells?
Refer chapter 5.16.6 in page 5.94.
nee
rin
35. Explain with a neat sketch PEM based fuel and its working. Refer chapter 5.16.6.2 in page 5.95.
g.n e
[Anna Univ. Dec']2]
36. Explain the working of direct methanol fuel cell with its neat sketch.
t
Refer chapter 5.16.6.3 in page 5.96. 37. How do alkaline fuel cells work? Explain with its sketch. Refer chapter 5.16.6.4 in page 5.97. 38. Explain the working of phosphoric acid fuel cells with a neat sketch. Refer chapter 5.16.6.5 in page 5.98.
39. Describe the working of molten carbonate fuel cell with a neat sketch. Refer chapter 5.16.6.6 in page 5.99.
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
I Altemative Energy Sources
am
40. Explain solid polymer fuel cell with a neat sketch.
[Anna Univ. Dec'J4J
Refer chapter 5.16.6.7 in page 5.100. 41. Enumerate the advantages and disadvantages of fuel cells.
[Anna Univ.Nov'07]
Refer chapter 5.16.8 in page 5.101. 42. Explain briefly the applications of fuel cells. Refer chapter 5.16.9 in page 5.102.
ww
-----
ENlJfvl1Jnit 5
···l-"·~
w.E asy En gin ee
•.ol'''''___
rin g.
net
Downloaded From : www.EasyEngineering.net
I
Downloaded From : www.EasyEngineering.net
ww
w.E a Solvedsy Anna En University Question gPapers' ine eri ng
.ne
t
Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Solved Anna University
Question Papers
B.E/B.TECH. DEGREE EXAMINATION - MAY/JUNE 2016 Sixth semester Mechanical Engineering ME 6602 - AUTOMOBILE ENGINEERING (Regulation 2013) Time: Three hours
Maximum: 100marks Answer ALL questions
ww w.E
Part A - (10 x 2
= 20 Marks)
1. What are the types of cross sectional franes used in automobile? ~
Channel section
~
Box section
~
Tubular section
~
I - section.
asy E
ngi
2. What are the forces acting on the running vehicles? ~
Dragforce
~
Lift force
~
Cross wind force.
nee
3. Define "Continuous Injection" of petrol engine.
rin
g.n e
t
The injection system which provides a continuous spray of fuel from each injector at a point before the intake valve is known as continuous injection system. 4. State the diesel vehicle emission norms of Euro BS IV in g/km: Bharat Stage (BS) IV which is equivalent to Euro- VI significantly states lower emission limits for NOx emissions from diesel cars. The following table shows the diesel vehicle emission norms ofEuro BS IV in g/km.
~
.-
Reference
I
CO
HC+NOx
NOx
PM
BS-VI
I
0.63
0.39
0.33
0.04
.
Whatarethefuncdonsofgearbox? The functions of gear box are as follows: 1. It helps the engine to disconnect from driving wheels. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
_
Automobile
Engineering
' ... ' " 2. It helps the running engine to be connected to the driving wheel smoothly and without
I
shock. 3. It provides the leverage between engine and driving wheels to be varied. 4. It helps to reduce the engine speed in the ratio of 4 : l-in case of passenger cars and in a greater ratio in case of heavy vehicles such as trucks and lorries. 5. It helps the driving wheels to be driven at different speeds. 6. It gives the relative movement between engine and driving wheels due to flexing of the road springs.
ww
6. What are the functions
0/ differential
ass.:mbly?
w.E asy En gin ee
The functions of differential assembly are as follows:
1. Differential assembly allows the drive wheels to tum at different rpms while both receiving power from the engine.
2. It applies pressure to the side gears in such a way to begin one of the tires to slip. 7. What is the/unction of the tension spring in the clutch plate?
The functions of the tension spring in the clutch plate are as follows:
rin g.
I. To maintain the stability of the vehicle while traveling over rough round or when turning in order to minimize the rolling, pitching or vertical movement tendency.
net
2. To minimize the effects of stresses due to road shocks on the mechanism of the motor vehicle and provide a cushioning effect. 8. Name the classifications
0/ brake system.
1. According to the applications: (i) Service or running or foot brake (ii) Parking or emergency or hand brake. 2. According to the number ofwheels: (i) Two wheel brakes (ii) Four wheel brakes. 3. According to the brake gear:
(i) Mechanical brake (a) Hand brake Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Solved Anna University
Question Papers
(b) Foot brake. (ii) Power brake: (a) With booster (b) Without booster. 4. According to construction: (i) Drum brake (ii) Disc brake.
ww
9. Writeshort notes on " L.P.G.".
w.E asy En gin ee
Most people pronounce Liquefied Petroleum .Gas (LPG) as "propane" because LPG is mostly made up of propane. Actually, LPG is made of a mixture of propane and other similar types of hydrocarbon gases. LPG is stored in special tanks which keep it under pressure. Therefore, it stays as liquid. LPG is the name given to the mixture of petroleum gases released during the extraction of crude oil and natural gas during refining the crude oil. It consists of a mixture of hydrocarbons including major components of propane and butane and minor components are normal-butane, iso-butane, pentane, ethane, propene and butane together with small quantities of additives including sulphur to give it an odour for safety reasons.
10. Why alcoholis an alternatefuel for S.l engine?
rin g.
Alcohols have the potential to reduce NOx, CO, HC and particulates when they are used in SI engine.
=
Part B - (5 x 16 80 Marks)
net
11. (a) (i) Writeshort notes on thefollowing engineparts: (a) Piston (b) Cylinder head (c) Piston ring (d) Gudgeon pin (e) Flywheel (f) Exhaust valve (g) Lubricationpump. (8) (a) Piston
Refer chapter 1.12.6 in page 1.60.
(b) Cylinder head
Refer chapter 1.12.2 in page 1.58.
(c) Piston ring
Refer chapter 1.12.8 in page 1.65.
(d) Gudgeon pin
Refer chapter 1.12.7 in page 1.64.
(e) Flywheel
Refer chapter 1.12.10 in page 1.66.
(t) Exhaust valve
Refer chapter 1.12.13 in page 1.68. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Automobile (I) Lubrication pump:
The lubricating oil pump is used to pressurise the oil and circulate it .to different engine parts. It is generally driven by a spiral or warm gear on the cam shaft. The different types of oil pumps in use are 1. Gear pump 2. Eccentric rotor pump 3. Eccentric vane pump and
ww w
4. Plunger pump. (8)
(ii) Draw the layouts of automobile chassis and explain its significance.
.Ea syE
Refer chapter 1.6.4 and 1.6.5 in page 1.22. Or
(b) (i) Write short notes on the following;
ngi n
(a) Valve mecahnism and (b) Cranshaft
eer
Valve mecahnism -
Refer chapter 1.12.14 in page 1.69.
Crankshaft
Refer chapter 1.12.9 in page 1.66.
(ii) What are the functions of carburettor?
ing .
net
Refer chapter 2.1.1 in page 2.1.
12. (a) (i) What are the advantages of Transistorized Coil Ignition (TCI) system?
(4)
Refer chapter 2.6.4 in page 2.46. (ii) Sketch and explain the Capacitive Discharge Ignition System.
(12)
Refer chapter 2.6.5 in page 2.47. Or (b) Describe the working of distributor type offuel pllmp with a sketch.
(16)
Refer chapter 2.5.3 in page 2.35. 13. (a) (i) What are the types.of rear axle casing?
(4)
Refer chapter 2.6.5 in page 2.47. Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
Solved Anna University
Question Papers
(ii) What are the types of rear axle drive? And explain with a neat sketch?
(12)
Refer chapter 3.18.2 in page 3.82. Or
(b) (i) What are the requirements of the cltuch?
(8)
Refer chapter 3.2.3 in page 3.3. (ii) Sketch and explain the working method of torque tube type
ww
0/ propeUer shaft. (8)
Refer chapter 3.18.6.2 in page 3.89.
w.E asy En gin ee
(8)
U. (a) (i) List the types of suspension spring used in automobile.
Refer chapter 4.4.7 in page 4.54. (ii) Describe the working method
0/ Antilock
Braking System.
(8)
Refer chapter 4.5.20 in page 4.129. Or
(b)
m Draw the schematic diagram of pneumatic
braking system and explain it.
Refer chapter 4.5.12 in page 4.117.
rin g.
15. (a) (i) What are the merits and demerits of LPG as a motor fuel? Refer chapter 5.5.6 in page 5.27. (ii) List the advantages of LNG.
(8)
net
(8)
(8)
Refer chapter 5.4.8 in page 5.18. Or
(b) (i) What are the the merits and demeritso/Hydrogen/uel?
(8)
Refer chapter 5.9.2 in page 5.47. (ii) Explain the merits of Ethanol fuel:
(8)
Refer chapter 5.7.8 in page 5.40.
*********************************************************************** Downloaded From : www.EasyEngineering.net
Downloaded From : www.EasyEngineering.net
ww
w.E a
syE
ngi
nee
rin
g.n
et
**Note: Other Websites/Blogs Owners Please do not Copy (or) Republish this Materials without Legal Permission of the Publishers.
**Disclimers : EasyEngineering not the original publisher of this Book/Material on net. This e-book/Material has been collected from other sources of net. Downloaded From : www.EasyEngineering.net
