Sixth Semester Mechanical Engineering ME 6602 — Automobile Engineering

1. Mention any four engine components along with materials  Cylinder block: Cast iron or aluminum with steel sleeves  Cylinder head: Aluminum alloy  Crank case: Alloy steels  Oil sump: Pressed steel sheet 2. Define lift force. Aerodynamic lift force is the vertical component of the resultant force caused by the pressure distribution on the body. 3. Name the resistance in vehicle motion. i) Air resistance ii) Gradient resistance iii) miscellaneous resistance

4. What are the advantages of diesel engines in cars? 1. Diesel engines offer significantly higher efficiency than current gasoline spark-ignition engines 2. Although the modern diesel engine is very clean 3. Fuel cost is low compared to petrol.

5. What are three types of vehicle axle? i)Front axle. ii)Rear axle. iii)Stub axle 6. Give the requirements of air fuel ratio in SI engine The SI engine automobiles run with the help of a mixture of gasoline and air. The amount of mixture depends on (i) engine displacement (ii) Minimum revolution per minute (iii) volumetric efficiency. 7. State the purpose of turbocharger  To reduce weight per horse power of the engine as required in an aero engines

 To reduce the space occupied by the engine as required in marine engines  To improve volumetric efficiency of the engine at high altitudes, as in aero engines and high speeds as in racing cars

8. What is the function of a catalytic converter in SI engine The catalytic converter converts the pollutants like HC, CO and NO2 into harmless gases. It oxides HC and CO into water and CO2. 9. State the important units of electronic fuel injection system. a.) Fuel delivery system b) Air induction system c) Electronic control unit d) Sensor system and air flow system. 10. What is exhaust gas recirculation? The process of recirculating about 10% of the inert gas back into the intake manifold to reduce the combustion temperature when peak combustion temperature exceeds 19500C. It is done to avoid the formation of excessive nitrogen oxides (NO2) formation. 11. Why epicyclic gears are used in overdrive units? In the transmissions, the high gear positions produces a 1:1 ratio between the clutch gear and transmission output shaft. There is neither gear reduction nor gear increase through the transmission.

12.What are the functions of clutch? i)To engage or disengage the rest of the transmission as required. ii)To transmit the engine power to rear wheels without shock. iii)To enable the gear to get engaged when the vehicle is in motion.

13.State the various functions of propeller shaft. It transmits rotary motion of the gearbox output shaft to the differential and then through the axle shafts to the wheels. It transmits motion at an angle which is varying frequently. It allows some changes in length between gearbox and rear axle. 14. What are the features of a good quality clutch? It should be capable of transmitting maximum torque of the engine. The clutch should be able to engage gradually and positively without the occurrence of sudden jerks.

The design of the clutch is such that it should ensure the dissipation of heat sufficiently which is generated during operation.

15. What are the different types of gear boxes used in an automobile? Manual Transmissioni) Sliding mesh gearbox ii) Constant mesh gearbox, iii) Synchromesh gearbox Automatic gear box, i) Hydromatic gearbox, ii) Torque converter gearbox 16. Define “anti – roll bar”. 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. 17 What are the types of stub axle? i) Elliot type stub axle ii) Reversed Elliot stub axle iii) Lamoine stub axle iii) Reversed lamoine stub axle 18.State the purpose of master cylinder.  The required hydraulic pressure is built up to operate the system.  It maintains a constant volume of fluid in the system.  To bleed or force air out of the brake line and wheel cylinder, a pump is used. 19. What are the brake compensation? When brakes fade two things happen. First, the pads can heat up to the point friction reduced. This can be caused by the resins or other ingredients breaking down. Second, the temperatures can cause the brake fluid to boil. 20. What are the different types of damper used in shock absorber? 1. Pneumatic damper 2. Hydraulic damper 3. Mechanical spring type damper.

21. What is LPG? Liquefied Petroleum gas is made of a mixture of propane and other similar types of hydrocarbon gases.

22. What is fuel cell? A fuel cell produces electricity directly from the reaction between hydrogen and oxygen from the air.

23. What is the composition of natural gas? Natural gas is a mixture of light hydrocarbons including methane, ethane, propane and pentanes. Other compounds found in natural gas include CO2 helium, hydrogen sulphide and nitrogen. The composition of natural gas never constant, however the primary component of natural gas is methane, which has a simple hydrocarbon structure composed of one carbon atom and four hydrogen atoms (CH4). 24. Define Hybrid vehicle. The vehicle which is using more than one source of energy to run is called hybrid vehicle. Hybrid means something that is mixed together from to things.

PART B

1. Discuss the Vehicle construction and layouts for automobiles and discuss the advantages of each. The position of the power train components within the vehicle has implication both for the engineering of the vehicle and the driveline components including the transmission itself. Effects include: _ 1. The space available for the power train and how it is packaged within the vehicle Including the location of ancillary components 2. The weight distribution, since the power train components are relatively heavy 3. The structure to support the power train and react against the driving torques 4. Vehicle handling and ride both from weight distribution and the location of the driven wheel set 5. Safety structure and passenger protection. 6. The choice of vehicle layout is determined principally by the target market sector and brand image that the vehicle is required to project. Possible alternatives include saloons, ranging from large luxury saloons to micro or town cars, sports coupe´s or convertibles, estate cars or off-highway

vehicles. In many cases, the same vehicle platform will be front-, rear and four-

wheel drive vehicles to be developed easily from the same vehicle platform as the engine installation and front structure of the vehicle can remain the same in each. a) Front-Engine Front Wheel Drive:

With a longitudinal engine transmission assembly , again including a differential and the drive being taken to the front wheels. This configuration is used for larger front-wheel-drive vehicles where the size (i.e. length) of the engine gearbox assembly makes installation across the vehicle impossible. It also allows (or all-wheel) drive power train frequently used in off highway vehicles. The greater height of these vehicles allows the engine to be mounted above the front axle line with the front differential alongside It is also possible to derive fourwheel-drive configurations from the two wheel-drive layouts.

b) Front-Engine Rear-Wheel-Drive

The main alternative, however, is the classic front-engine Rear-wheel-drive layout as in Fig. The engine and transmission are still in line but mounted longitudinally with a connecting shaft to a separate rear mounted final drive and differential that are apart of the rear axle. c) Rear-Engine Rear-Wheel-Drive

A common variant amongst two-seater sports vehicles is shown in Fig with the engine and transmission transversely mounted to the rear of the vehicle and driving the rear wheels. If the engine is in front of the rear axle then this is usually referred to as a mid-engine layout.

d) Four Wheel Drive

The final example shown in Fig. is a four-wheel used for several of these variants. The vehicle layout must also be sufficiently flexible to accommodate different engine and transmission options that are offered with many vehicles.

2.

Discuss the frame type of chassis construction with neat sketch

Frame Front, suspension, Steering mechanism, Radiator, Engine, Clutch, Gear box, Propeller shaft, Rear springs, Road wheels, Differential, Brakes and braking system, Storage battery, Silencer, Shock absorbers, Fuel tank, Petrol tank, Hydraulic pipe cables

Functions of Major Components of an Automobile a) Chassis and Frame The chassis is formed by the frame with the frame side members and cross members. The frame is usually made of box, tubular and channel members that are welded or riveted together. In addition to this, it comprises of the springs with the axles and wheels, the steering system and the brakes, the fuel tank, the exhaust system, the radiator, the battery and other accessories. Along with this the frame supports the body. Classification of Chassis a) Full forward It is that in which the engine is fitted outside the driver cabin or seat like in cars and old trucks. In this type of arrangement the driver seat is far enough from the front wheels and is not able to see just in front of the vehicle. b) Semi-forward Half portion of the engine is in the driver cabin and the remaining half is out side the cabin like in bed ford pick up , standard. It provides better visibility to the drivers. c) Bus chassis The whole engine is fitted infront of the driver cabin. It provides increase floor space in the vehicle. The driver seat is just above the front wheel and he can see the front wheel and full front road right from the front wheels. d) Engine in front Most of the vehicles the engine is fitted in front portion of the chassis. The drive is given to the front wheels only like matador vehicle. e) Engine at centre Fitted at the centre of the chassis. This arrangement provides full space of chassis place to use.

3.Explain the various Components of Engine with a neat sketch? The core of the engine is the cylinder, with the piston moving up and down inside the cylinder. The engine described above has one cylinder. That is typical of most lawn mowers, but most cars have more than one cylinder (four, six and eight cylinders are common). In a multi-cylinder engine, the cylinders usually are arranged in one of three ways: inline, V or flat (also known as horizontally opposed or boxer), as shown in the following figures. Different configurations have different advantages and disadvantages in terms of smoothness, manufacturing cost and shape characteristics. These advantages and disadvantages make them more suitable for certain vehicles.

Cylinder block This is a cast structure with cylindrical holes bored to guide and support the pistons and to harness the working gases. It also provides a jacket to contain a liquid coolant

Cylinder head This casting encloses the combustion end of the cylinder block and houses both the inlet and exhaust poppet-valves and their ports to admit air- fuel mixture and to exhaust the combustion products.

Crankcase This is a cast rigid structure which supports and houses the crankshaft and bearings. It is usually cast as a mono-construction with the cylinder block.

Valves The intake and exhaust valves open at the proper time to let in air and fuel and to let out exhaust. Note that both valves are closed during compression and combustion so that the combustion chamber is sealed.

Spark plug The spark plug supplies the spark that ignites the air/fuel mixture so that combustion can occur. The spark must happen at just the right moment for things to work properly.

Piston A piston is a cylindrical piece of metal that moves up and down inside the cylinder.

Piston rings Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder. The rings serve two purposes:    

They prevent the fuel/air mixture and exhaust in the combustion chamber from leaking into the sump during compression and combustion.  They keep oil in the sump from leaking into the combustion area, where it would be burned and lost.  Most cars that "burn oil" and have to have a quart added every 1,000 miles are burning it because the engine is old and the rings no longer seal things properly. 

Connecting rod The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle can change as the piston moves and the crankshaft rotates.

Crankshaft The crankshaft turns the piston's up and down motion into circular motion just like a crank on a jack-in-the-box does.

4 . Explain the working Principle of MULTIPLATE CLUTCH with a neat sketch? Multi-plate clutch consists of more than one clutch plates contrary to single plate clutch which consists of only one plate. Friction surfaces are made in case of multi-plate clutch. Due to increased number of friction surfaces, a multi-plate clutch can transmit large torque. Therefore, it is used in racing cars and heavy motor vehicles which have high engine power. The clutch plates are alternatively fitted with engine shaft and the shaft of gear box. Here plates are firmly held by the force of coil springs and they assembled in a drum. One plate slides in the grooves on the flywheel and the next plate slides on spines provided on pressure plate. Thus, each alternate plate slides in grooves on the flywheel and the other on splines of pressure plate. If we take two consecutive plates, then one has inner and other has outer splines. When the clutch pedal is pressed, the pressure plate moves back against the force of coil spring, then the clutch plates are disengaged and engine flywheel and gear box are decoupled. However, when clutch pedal is not pressed the clutch remain in engaged position and the power can be transmitted from engine flywheel to the gear box. This type of clutch has been shown in Figure 3.2.

5.Explain the working Principle of SLIDING MESH GEAR BOX with a neat sketch? It is simplest type of gear box out of the available gear boxes. In this type of gear box, gears are changed by sliding one gear on the other. This gear box consists of three shafts; main shaft, clutch shaft and a counter shaft. In a four speed gear box (which includes one reverse gear), the counter shaft has four gears which are rigidly connected to it. Clutch shaft has one gear and main shaft has two gears. The two gears on the main shaft can slide in the horizontal direction along the splines of the main shaft. However, the gears on the counter shaft cannot slide. The clutch gear is rigidly fixed to the clutch shaft. It is always connected to the countershaft drive gear. The two gears on the main shaft can be slided by the shifter yoke by operating the shift lever (not shown in Figures). These two gears are second gear and low/reverse gear respectively. These gears can be meshed with corresponding gears on the countershaft with the help of shifter yoke and shift lever. Shift lever is operated by hand in four wheelers for changing the gears. A reverse idler gear is mounted on another (third) shaft and is always in mesh with reverse gear on countershaft.

Fig 3.3

First Gear When first gear position is selected by the shift lever, first gear (large gear) on the main shaft slides and is connected to first gear on the countershaft. The direction of rotation of main shaft is same as that of clutch shaft. In first gear, small gear of countershaft meshes with larger gear on main shaft, speed reduction in the ratio 3 : 1 (approximate) is obtained. Second Gear When second gear is selected by the shift lever, second gear on countershaft meshes with second gear (small gear on main shaft) on the main shaft. The direction of main shaft is same as that of clutch shaft. Speed reduction of the order of 2 : 1 is obtained in second gear. Third Gear In third gear, the main shaft is slides axially towards the clutch shaft so that main shaft is directly connected to the clutch shaft. In this position, the main shaft rotates at the speed of clutch shaft. Thus, a speed ratio of 1 : 1 is obtained. It can be noted that the clutch gear is directly connected to engine crankshaft and main shaft is connected to the wheels through propeller shaft. Reverse Gear When the shift lever is operated to engage the reverse gear, the larger (reverse) gear of the main shaft meshes with the reverse idler gear. Reverse idler gear is always connected to reverse gear on countershaft. The reverse idler gear between countershaft reverse gear and main shaft larger gear changes the direction of rotation of main shaft. Thus, the direction of main shaft becomes opposite to that of clutch shaft. Therefore, wheels of the automobile start moving in backward direction. (Note : Countershaft is also known as lay shaft.) In modern cars, there are five forward gears and reverse gear. Hence, they provide five speed ratios for forward racing and one for backward movement. CONSTANT MESH GEAR BOX A simplified diagram of constant mesh box has been shown in Figure 3.4. In this gear box, all gears on the main transmission shaft are constantly connected to corresponding gears on countershaft or lay shaft. In addition, two dog clutches are provided on the main shaft. One dog clutch is between the second gear and cutch gear and another is between the first gear and reverse gear. Splines are out on main

shaft so that all the gears are feed on it. Dog clutches can also slide on main shaft and rotate with it. However, all the gears on countershaft are giddily fixed to it. Different gear ratios (speed ratios) are obtained as follows :

For Three Forward and One Reverse Gear Top or 3rd speed gear is obtained when the left dog clutch is slided to left to mesh with clutch gear by using the gear shift lever. In this case, main shaft rotates at the same speed as that of clutch gear or engine crankshaft speed which is the maximum speed. Speed ratio obtained is 1 : 1. Second gear is obtained when dog cutch (left side) meshes with second gear. In this condition clutch gear rotates the drive gear on countershaft and countershaft drives the second gear on the main shaft. All other gears on main shaft are free, so they do not move. In the same manner, first gear is obtained when right hand side dog clutch meshes with first gear. Reverse gear is obtained when right side dog clutch meshes with reverse gear on main shaft. Advantage of Constant Mesh Gear Box Since all the gears are in constant mesh, wear and tear of gears and any possible damage of gears do not occur in engaging and disengaging gears. Also, any sound are not generated in engaged/disengaged.

6. Explain the working principle of AUTOMOBILE DIFFERENTIAL GEAR TRAIN with a neat sketch?

It consists of sun gears, planet pinion, a cage, a crown wheel and a bevel pinion. A sun gear is attached to inner end of each rear axle (half shaft). A cage is attached on left axle. A crown gear is attached to the cage and the cage rotates with the crown gear. The crown gear is rotated by the bevel pinion. Crown gear and cage remain free on the left rear axle. Two planet pinions are on a shaft which is supported by the cage. The planet pinions mesh with the sun gears. The rear wheels are attached to outer ends of two rear axles. When the cage rotates, sun gears rotate. Thus, the wheels also rotate. In case one inner wheel runs slower than other when the vehicle takes a turn, the planet gears spin on their shaft, transmit more rotary motion to outer wheel. When vehicle runs in straight line, the crown gear, cage, planet pinions and sun gears turn together as a unit. Thus there is no relative motion.

Differential Gear Train on a Turning Car The car is turning about a circle with nominal radius rn. (For this discussion, we assume that the axis of the wheel axle for the driven (rear) wheels passes through the turn circle center. This is typically true only for a fairly large radius of turn.)

The outer wheel traverses an arc with radius ro and the inner wheel traverses an arc with radius ri. As illustrated, the lengths of the arcs traversed are so, sn, and si. The outer arc so is obviously larger than the inner arc si for a given traversed angle theta. Some way of ensuring that the outer wheel is able to turn slightly faster than the inner wheel must be ensured in order to prevent binding and slippage of the tires on the road. For non-driven wheels which simply rotate freely independently of other machinery, this is not a problem. Driven wheels connected to the engine via the driveshaft, however, must both be turned by gearing and this gear train must allow for differential movement of the left wheel with respect to the right wheel. This is a difficult problem since for every turning circle the differential rotation of the left and right wheels is different. Fortunately, the

automobile differential solves this problem with only one transmission and one drive shaft for both driven wheels. Since s=r(THETA), the length of the arc traversed for a given theta is proportional to the radius. Since ro is greater than rn by the same amount that ri is less than rn, the right wheel center must travel further than the car center by the same amount that the left wheel center must travel less further than the car center. As its name implies, a differential allows the left and right drive wheels to turn differentially with respect to each other. As can be seen by turning the drive wheels of a car on a mechanic's lift, turning one drive wheel results in the opposite wheel turning at the same rate in the opposite direction. TYPES OF DIFFERENTIAL Conventional Type Conventional type differential described in Section 5.6 delivers same torque to each rear wheel. If any of the wheels slips due to any reason the wheel does not rotate and vehicle does not move. Non-slip or Self Locking Type Non-slip or self locking type differential overcomes this drawback. It construction is similar to that of conventional type differential. But, two sets of clutch plates are provided additionally. Also, the ends of planet shafts are left loose in notches provided on the differential cage.

Double Reduction Type Double reduction type differential provides further speed reduction by additional gear. This type of differential is used in heavy duty automobiles which require larger gear reduction between engine and wheels.

7. Explain the working principle of Hybrid vehicle in automobile

engineering? A hybrid vehicle uses multiple propulsion systems to provide motive power. The most common type of hybrid vehicle is the gasoline-electric hybrid vehicles, which use gasoline (petrol) and electric batteries for the energy used to power internal-combustion engines (ICEs) and electric motors. These motors are usually relatively small and would be considered "underpowered" by themselves, but they can provide a normal driving experience when used in combination during acceleration and other maneuvers that require greater power. The Toyota Prius first went on sale in Japan in 1997 and it is sold worldwide since 2000. By 2010 the Prius is sold in more than 70 countries and regions, with Japan and the United States as its largest markets. In May 2008, global cumulative Prius sales reached the 1 million units, and by September 2010, the Prius reached worldwide cumulative sales of 2 million units, and 3 million units by June 2013. The Honda Insight is a two-seater hatchback hybrid automobile manufactured by Honda. It was the first mass-produced hybrid automobile sold in the United States, introduced in 1999, and produced until 2006. Honda introduced the second-generation Insight in Japan in February 2009, and the new Insight went on sale in the U.S. on April 22, 2009. Honda also offers the Honda Civic Hybrid since 2002. As of October 2013, there are over 50 models of hybrid electric cars available in several world markets, and about 7 million hybrid electric vehicles have been sold worldwide, led by Toyota Motor Company (TMC) with more than 5.5 million Lexus and Toyota hybrids sold by August 2013, followed by Honda Motor Co., Ltd. with cumulative global sales of more than 1 million hybrids by September 2012, and Ford Motor Corporation with more than 277 thousand

hybrids sold in the United States by September 2013. The world's best selling hybrid is the Toyota Prius, with 3 million units sold by June 2013. Global sales are led by the United States with over 3 million units sold by October 2013, followed by Japan with over 2.6 million hybrids by September 2013, and Europe with more than 650,000 units by August 2013. Until 2010 most plug-in hybrids on the road in the US were conversions of conventional hybrid electric vehicles, and the most prominent PHEVs were conversions of 2004 or later Toyota Prius, which have had plug-in charging and

more batteries added and their electric-only range extended. Chinese battery manufacturer and automaker BYD Auto released the F3DM to the Chinese fleet market in December 2008 and began sales to the general public in Shenzhen in March 2010. General Motors began deliveries of the Chevrolet Volt in the U.S. in December 2010. Deliveries to retail customers of the Fisker Karma began in the U.S. in November 2011. During 2012, the Toyota Prius Plug-in Hybrid, Ford CMax Energi, and Volvo V60 Plug-in Hybrid were released. The Honda Accord Plug-in Hybrid, Mitsubishi Outlander P-HEV, Ford Fusion Energi and McLaren P1 (limited edition) were released in 2013. As of October 2013, the Volt/Ampera family of plug-in hybrids, with combined sales of over 60,000 units, is the top selling plug-in hybrid in the world, and the second best selling plug-in electric car after the Nissan Leaf. The Elantra LPI Hybrid, launched in the South Korean domestic market in July 2009, is a hybrid vehicle powered by an internal combustion engine built to run on liquefied petroleum gas (LPG) as a fuel. The Elantra PLI is a mild hybridand the first hybrid to adopt advanced lithium polymer (Li–Poly) batteries.

Parallel hybrid

Parallel hybrid systems, which are most commonly produced at present, have both an internal combustion engine (ICE) and an electric motor coupled. If they are joined at an axis in parallel, the speeds at this axis must be identical and the supplied torques add together. Most electric bicycles are of this type. When only one of the two sources is being used, the other must either also rotate in an idling manner, be connected by a one-way clutch, or freewheel. With cars, the two sources may be applied to the same shaft- for example with the electric motor lying between the engine and transmission. The speeds are thus equal and the torques add up, with the electric motor adding or subtracting torque to the system as necessary. The Honda Insight uses this system. An alternative parallel hybrid layout is the 'through the road' type. Here a conventional drivetrain powers one axle, with an electric motor or motors driving the other. The batteries can be recharged through regenerative braking, or by loading the electrically driven wheels during cruise. Power is thus transferred from the engine to the batteries through the road surface. This layout also has the advantage of providing four-wheel-drive in some conditions. An example of this principle is a bicycle fitted with a front hub motor, which assists the cyclist's pedal power at the rear wheel. Parallel hybrids can be further categorized depending upon how balanced the different portions are at providing motive power. In some cases, the combustion engine is dominant (the electric motor turns on only when a boost is needed) and vice versa. Others can run with just the electric system operating. But

because current parallel hybrids are unable to provide all-electric (ICE=OFF) propulsion, they are often categorized as mild hybrids (see below). Because parallel hybrids can use a smaller battery pack as they rely more on regenerative braking and the internal combustion engine can also act as a generator for supplemental recharging, they are more efficient on highway driving compared to urban stop-and-go conditions or city driving. Honda's Insight, Civic, and Accord hybrids are examples of production parallel hybrids. General Motors Parallel Hybrid Truck (PHT) and BAS Hybrids such as the Saturn VUE and Aura Greenline and Chevrolet Malibu hybrids are also considered as utilizing a parallel architecture.

Series hybrid

Series hybrids have also been referred to as extended-range electric vehicles (EREV) or range-extended electric vehicles (REEV) where they are designed to be run mostly by the battery, but have a petrol or diesel generator to recharge the battery when going on a long drive. However, range extension can be accomplished with either series or parallel hybrid layouts. Alternatively, it can be viewed as an electric transmission, with the battery storing reserve power until it is needed. In a series-hybrid system, the combustion engine drives an electric generator instead of directly driving the wheels. The generator provides power for the driving electric motors. In short, a series-hybrid is simple, the vehicle is driven only by electric motor traction with a generator set providing the electric power. Unlike piston internal combustion engines, electric motors are highly efficient with exceptionally high power-to-weight ratios providing adequate torque when running

over a wide speed range. Internal combustion engines run at their most efficient when turning at a constant speed. An engine turning a generator can be designed to run at maximum efficiency constant speed, or a series of constant speeds. Combining the two gives maximum efficiency and performance. Conventional mechanical transmissions add weight, bulk and sap power from the engine with automatic shifting being complex. Unlike combustion engines, with electric motors matched to the vehicle a multiple-speed transmission is not essential and often only a simple constant-ratio gearbox is required. This arrangement is common in diesel-electric locomotives and ships. Ferdinand Porsche used this arrangement in the early 20th century in racing cars, effectively inventing the series-hybrid arrangement. Porsche named the system, System Mixt. A wheel hub motor arrangement, with a motor in each of the two front wheels was used, setting speed records. This arrangement was sometimes referred to as an electric transmission, as the electric generator and electric traction motor replaced a mechanical transmission. The vehicle could not move unless the internal combustion engine was running. The arrangement was difficult for production cars as synchronization was not possible of the electric driving motors and the generator set power, resulting in higher fuel consumption. This is no longer an issue with modern computer engine management systems optimizing when the generator runs to match the power needed. Since Ferdinand Porsche's series-hybrid car, electric motors have become substantially smaller, lighter and efficient over the years. These advances have given the advantage to the electric transmission in normal road vehicle operating conditions, over a conventional internal combustion engine and mechanical automatic transmission. One of the advantages is the smoother progressive ride with no stepped gear ratio changes.

Power-split or series-parallel hybrid

Power-split hybrid or series-parallel hybrid are parallel hybrids. They incorporate power-split devices allowing for power paths from the engine to the wheels that can be either mechanical or electrical. The main principle behind this system is the decoupling of the power supplied by the engine (or other primary source) from the power demanded by the driver. A combustion engine's torque output is minimal at lower RPMs and, in a conventional vehicle, a larger engine is necessary for acceptable acceleration from standstill. The larger engine, however, has more power than needed for steady speed cruising. An electric motor, on the other hand, exhibits maximum torque at standstill and is well-suited to complement the engine's torque deficiency at low RPMs. In a power-split hybrid, a smaller, less flexible, and highly efficient engine can be used. The conventional Otto cycle (higher power density, more low-rpm torque, and lower fuel efficiency) is often also modified to a Miller cycle or Atkinson cycle (lower power density, less low-rpm torque, higher fuel efficiency). The smaller engine, using a more efficient cycle and often operating in the favorable region of the brake specific fuel consumption map, contributes significantly to the higher overall efficiency of the vehicle.