Transmission

TRANSMISSIONThe mechanism that transmits the power developed by the engine of automobile to the engine to the driving wheels is called the TRANSMISSION SYSTEM (or POWER TRAIN)

Layout of automobile Transmission systemIt is consists of Clutch The gear box Propeller shaft Differential Rear axle Wheel Tyres

Requirements of transmission system1. To provide for disconnecting the engine from the driving wheels2. When the engine is running, to enable the connection to the driving wheels to be made smoothly and without shock.3. To enable the leverage between the engine and driving wheels to be varied.4. Enable the driving wheels to rotate at different speeds.5. Provide for relative movement between the engine and driving wheels.

ClutchA clutch is a mechanism which enables the rotary motion of one shaft to be transmitted at will to second shaft . Clutch is located between engine and gear box. When the clutch is engaged, the power flows from the engine to the rear wheels through the transmission system and the vehicle moves . when the clutch is disengaged ,the power is not transmitted to the rear wheels and the vehicle stops, while the engine is still running. Clutch is disengaged when a)Starting the engine,b) Shifting the gears,c) Idling the engine Cutch is engaged only when the vehicle is to move and is kept engaged when the vehicle ismoving.Principle:It operates on the principle of friction. When two surfaces are brought in contact and are held against each other due to friction between them, they can be used to transmit power. If one is rotated, then other also rotates. One surface is connected to engine and other to the transmission system of automobile. Thus, clutch is nothing but a combination of two friction surfaces.Main parts of a clutch:It consists of (a) A driving member, (b) A driven member, and (c) An operating member.

Driving member has a flywheel which is mounted on the engine crankshaft. A disc is bolted to flywheel which is known as pressure plate or driving disc. The driven member is a disc called clutch plate. This plate can slide freely to and fro on the clutch shaft. The operating member consists of a pedal or lever which can be pressed to disengaged the driving and driven plate.

Types of clutch(a)Friction Clutch: (i) single plate clutch, (ii) multi-plate clutch, or (iii) cone clutch. Multi-plate clutch can be either wet or dry. A wet clutch is operated in an oil batch whereas a dry clutch does not use oil. (b) Centrifugal clutch. (c) Semi-centrifugal clutch. (d) Hydraulic clutch. (e) Positive clutch. (f) Vacuum clutch. (g) Electromagnetic clutch.

1. Torque transmission---The clutch must be able to transmit maximum torque of the engine2. Gradual engagement----The clutch should engage gradually to avoid sudden jerks3. Heat dissipation---The clutch should be able to dissipate large quantity of heat which is generated during the clutch operation due to friction4. Dynamic balancing---The clutch should be dynamically balanced. This is particularly required in case of high speed engine clutches.5. Vibration damping ---The clutch should have suitable mechanism to damp vibrations and to eliminate noise produced during power transmitted.6. Size---The clutch should be as small as possible so that it occupies minimum space 7. Inertia -- clutch rotating parts should have minimum inertia 8. Clutch free pedal play to reduce effective clamping load on carbon thrust bearing9. Ease of operation as clutch transmits higher torque , its disengagement should not tiresome the driver10. Lightness

Disadvantages of single plate clutchSince only one friction plate it is not effective in transferring the power.Advantages of multiplate 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.

Advantages of diaphragm clutch1) It is more compact than other design.2) It is easier to balance rotationally and is less subjected to unwanted effects due to centrifugal force at high rotational speeds 3) It gives uniformly distributed pressure on pressure plate.4) It needs no release levers.5)minium effort is sufficient to disengage the clutch.6)it provides minium number of moving components and hence minimum internal friction.

Universal joint;A universal joint is used where two shafts connected at an angle to transmit torque. The universal joint permits the torque transmission at angle ,and also while this angle is changing constantly while the vehicle is moving on the road.

Propeller shaft(drive line shaft or drive shaft);The propeller shaft is connected between the gear box and the differential with universal joint at each end.it transmits rotary motion of the gear box output shaft to the differential.

Clutches can also be classified as dry clutch and wet clutch.Description Wet clutch Dry clutch

Heat dissipation Good Bad

Life Longer life Short

Torque transmission Lower Higher

Clamping force More Less

Coefficient of friction Less due to oil presence More

GEAR BOX:

Necessity of gear box in an automobile transmission.The gearbox is necessary in the transmission system to maintain engine speed at the most economical value under all conditions of vehicle movement. An ideal gear box would provide an infinite range of gear ratios, so that the engine speed should be kept at or near that the maximum power is developed whatever the speed of the vehicle.

Function of a gear box

An automobile is able to provide varying speed and torque through its gear box. Various functions of a gear box are listed below:(a) To provide high torque at the time of starting, vehicle acceleration, climbing up a hill. (b) To provide more than forward speeds by providing more than one gear ratios. In modern cars, five forward gears and reverse gear is provided. For given engine speed, higher speed can be obtained by running in higher (4th and 5th) gears. (c) Gear box provides a reverse gear for driving the vehicle in reverse direction.

(d)transmission can be disconnected from engine by neutral position of gear box.

Types of gear boxes(a) Selective type gear boxes:(i) Sliding mesh gear box (ii) Constant mesh gear box (iii) Synchromesh gear box

(b) Progressive type gear box (c) Epicyclic type gear box.

Sliding mesh gearbox: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. 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.Mechanism: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 slided 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 boxA simplified diagram of constant mesh box has been shown in Figure. 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 rigiddily 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.Synchromesh gearbox;This type of gearbox is similar to the constant mesh type gearbox. Instead of using dog clutches here synchronizers are used. The modern cars use helical gears and synchromesh devices in gearboxes, that synchronize the rotation of gears that are about to be meshed.

In this gear box ,the meshing of gears are smooth ,as it works like a friction clutch ,and then engages the dog clutch perfectly .the operation of a synchronous gear unit is as shown in fig . it consists of external cone on the gear wheel and a corresponding internal cone on the synchromesh unit .this synchromesh unit is the equivalent of the dog clutch.When the gear shift lever is operated ,first the cones engages smoothly by which the speeds of both the shafts are synchronized and then the gears engage positively ,thereby giving a very smooth gear change .all this happens in operation of the gear shifts lever itself .similarly other gears are operated.Progressive type gear box Usually this gear boxes are used in motors cyles.in this gear boxes the gears pass through the intervening speeds while shifting from one speed to another .there is a neutral position between two positions .these gear boxes are a combination of sliding and constant mesh gear boxes. The various gear speeds are obtained by sliding the dog clutch or gear to the required position.Epicyclic or planetary type gear boxThe epicylic or planetary type transmission uses no sliding dogs or gears to engage but different gear speeds are obtained by merely tightening brake bands on the gear drums, which simplify gear changing .a planetary gear set consists of ring gear or annular wheel, sun gear and planet gears with carrier .in order to obtain different speeds any one of these units can be held from rotation by means of brake bands.

Gear trainsA combination of two or more gears, which meshis in such a way that power is transmitted from driving shaft to driven shaft, is known as gear train.Types of gear trains;There are three types of gear trains:(a) Simple gear train, (b) Compound gear train, and (c) Epicyclic gear train.

Simple Gear Train;If the axes of all the gears remain fixed relative to each other, the gear train is known as simple gear train.Type of gear box

Sliding mesh Gear noise due to the type of gear. The difficulty of obtaining a smooth, quit and quick change of gear without the great skill and judgment. Prevents two gears engaging simultaneously If this occurs the gearbox will lock up and shaft rotation will be impossible.

Constant mesh As the gear remain always in mesh, it is no longer necessary to use straight spur gear. Instead helical gear is used which are quieter running. Wear of dog teeth on engaging and disengaging is reduced because here all the teeth of the dog clutches are involved compared to only two or three teeth in the case of sliding gears. If any damage happens dog clutches are broken not the gears. the teeths on helical gear are very thin thus leading to wear but not as much in sliding mesh. Double decluthing is required.

Syncromesh Clutching is required only once thus quicker operation and less wear. Synchronizer is used which provides more smoother and quieter gear shifts

Epicycle gear box All gear are in constant mesh and to engage any desire gear one simply has to apply the particular brake or the clutch. Provides more compact unit. No need of dog clutches and sliding gear. Hand brackets or small multiple clutches are used for changing gears. load is distributed among many gears. For this, the drive from the engine need not to be disconnected as in case of ordinary gearbox.Thus gear changing operation becomes very easy with an epicyclic gearbox Grearter stability due to even distribution of mass. Design is complex

Compound Gear Train;There are more than gears on the shaft (generally intermediate shaft) in a compound gear train. Two gears are moved on intermediate shaft, therefore, boththe gear s have same speed.Driven gear is also known as follower.Epicyclic Gear Train;If the axe of the shafts, on which gears are attached, move relative to a fixed axis, then the gear train is known as epicyclic gear train.

Manual Transmission;Figure 1Two-speed manual transmission gearbox.Manual transmission is also referred to as stick shift transmission because you need to use the transmission stick every time you change the gears. To perform the gear shift, the transmission system must first be disengaged from the engine. After the target gear is selected, the transmission and engine are engaged with each other again to perform the power transmission. The gear selector fork can be moved forward and backward to move the collar to engage it to the target gears (blue). The gears (blue) are driven by the engine, while the collar (purple) connects to the wheels. To engage the collar to the gear, the power from the engine must be temporarily removed so the gear will lose the driving force. Therefore, the gear and the collar can be engaged without causing grinding due to different spin speeds. However, the collar and gear still have different spinning speeds due to the gear ratio change when shifting. For the modern car, a mechanism called a synchronizer is added to the collar to synchronize the spinning speed between collar and gears to make the gears mesh smoothly. The synchronizer is made of frictional materials. When the collar tries to mesh with the gear, the synchronizer will touch the gear first and use friction force to drive the gear to spin at the same speed as the collar. This will ensure that the collar is meshed into the gear very smoothly without grinding (Figure 3). For some cars without synchronizers, a driving skill called double clutching must be performed during gear shifting to avoid gear grinding.Figure 2; clutch

Figure 3;the synchronizer drives the gear to spin at the same speed as the collar to avoid grinding when meshing.

For a standard 5-speed manual transmission system, three dif-ferent gear selector forks are used. This H shift pattern enables the driver to select fivc different gear ratios and a reverse gear. The clutch, used to temporarily disconnect power from the en-gine.When the thrust pad is pushed, it lifts the pressure pad so the driven pad (clutch plate) is disengaged from the flywheel. The flywheel, which is connected to the gears of the transmission system, will stop spinning. On the other hand, when the thrust pad is released, the spring pushes the driven pad back to engage the flywheel and drives it spinning. Figure 4;the Side-View of a Standard 5-Speed Manual Transmission System.

Figure 5;The Top-View of The Standard 5-Speed Manual Transmission SystemAutomatic Transmission:

Fig a Planetary Gear Set.Automatic Transmissions can be basically divided into two types: those used inFront-engine, front-wheel drive (FF) vehicles and those used in front-engine, rear-wheeldrive (FR) vehicles.

The gear set is the same as those in a manual transmission box; however, a vacuum cylinder or a hydraulic cylinder is used to per-form automatic gear shifting. The clutch selects the gear range only but isnt used when driving. The first range (or low range) contains the 1st and 2nd gears, while the second range (or high range) contains 3rd and 4th gears. To move the car, the clutch and brake must be depressed and a gear range must be selected (low, high, or reverse.) After the gear range is selected, the clutch can be released. To move the car, the brake is released and the gas is stepped on. The gear is changed automatically (between 1 and 2 or between 3 and 4) during driving.The automatic system for current automobiles uses a planetary gear set instead of the traditional manual transmission gear set. The planetary gear set contains four parts: sun gear, planet gears, planet carrier, and ring gear (Figure a.) Based on this planetary set design, sun gear, planet carrier, and ring gear spin centrifugally. By locking one of them, the planetary set can generate three different gear ratios, including one reverse gear, without engaging and disengaging the gear set.

Unlike a manual transmission system, automatic transmission doesnt use a clutch to disconnect power from the engine temporarily when shifting gears. Instead, a device called a torque converter is usedto prevent power from being temporarily disconnected from the engine and also to pre-vent the vehicle from stalling when the transmission is in gear. Consider two fans facing each other: when one of them is turned on and starts spinning, the other one will also start spinning at a lower speed (see Figure b). Thats because the first fan moves the air to drive the second fan to spin. This is the same idea as the torque converter of an automatic transmission system, except that it uses fluid instead of air as the transportation media.

Fig b

Torque ConverterA torque converter consists of four parts, a pump (impeller), turbine, stator, and transmission fluid. The pump is connected to the engine and transfers engine power to the transmission fluid. The fluid causes the turbine, which is connected to the input shaft, to spin. The stator is used to redirect fluid returning from the turbine before it hits the pump, again to increase the efficiency. In this design, even when the vehicle is in gear but not moving (the turbine is forced to stop), the pump can still keep spinning without causing the engine to stall.

When the vehicle speed is slow, the turbine is always spinning more slowly than the pump. However, when the vehicle moves at high speed, the turbine can spin at almost the same speed as the pump. Therefore, for mod-ern cars, a lock up will occur between pump and turbine when the vehicle is at high speed in fourth gear, which makes the torque converter work more efficiently.The Structure of a Torque Converter.

TIPTRONIC:Tiptronic transmission is a special type of automatic transmission with a computer controlled automatic shift. The driver can switch the transmission to manual mode, which lets her shift the gear at her wish sequentially up (+) or down (-) without disengaging the clutch. This works just like a manual transmission; however, it still uses a torque converter to transfer power from the engine.

Tiptronic transmission.

Continuously-Variable Transmission (CVT)The continuously-variable transmission is also an automatic transmission system, which changes the diameters of input shaft and output shaft directly, instead of going through several gears to perform gear ratio change. This design can generate an infinite number of possible gear ratios. Unlike the complicated planetary automatic transmission system, a CVT only has three major parts; a drive pulley connected to the input shaft, a driven pulley connected to the output shaft, and a belt. Figure 1shows the structure of the most common pulley based CVT systems. If two cones of the pulley fall apart, the diameter of the pulley becomes small; while they are close, the diameter of the pulley is large. Because the length of the driving belt is fixed, when the diameter of the drive pulley becomes small, the diameter of the driven pulley must become large by closing two cones of the pulley together, and vice versa. Based on this infinite number of gear ratios design, it is said that CVT is the most efficient transmission system in the world.Fig1;Pulley Based CVT.

Semi-automatic TransmissionA semi-automatic transmission is a very advanced system, which still uses a clutch to perform the gear shift instead of a torque converter. Unlike the manual transmission, the computer doesall of the clutch disengaging, gear shifting, and clutch engaging. This not only makes the gear shifting faster than manual transmission, but also prevents the vehicle from stalling when the car is stationary. Like a tiptronic transmission, a semi-automatic transmission can also be switched to manual mode to perform gear shifting at the drivers wish. The two most common semi-auto-matic transmissions are direct shift transmission (aka dual-clutch transmission) and electrohydraulic manual transmission (aka sequential transmission).

Direct shift transmissionFigure shows the structure of the direct shift transmission. Like a conventional manual transmission system, it uses a collar, synchronizer, and gear set to perform gear shift. The clutch set is like that inside the automatic planetary gear transmission system, which controls the gear ratio change. Unlike the conventional manual transmission system, there are two differ-ent gear/collar sets, with each connected to two different input/output shafts. One set contains odd (1st, 3rd, 5th) gears, while the other contains even (2nd, 4th, 6th) gears. It is just like two conven-tional manual transmission gear boxes in one. To automatically shift from 1st gear to 2nd gear, first the computer detects that the spinning speed of the input shaft is too high, and engages the 2nd gears collar to the 2nd gear. The clutch then disengages from 1st gears input shaft, and engages the 2nd gears input shaft. Controlled by computer, the gear shift becomes extremely fast compared with a conven-tional manual transmission. Using direct contact of the clutch instead of fluid coupling also im-proves power transmission efficiency. Another advanced technology used for direct shift trans-mission allows it to perform double clutching by shifting the gear to neutral first, adjusting the spinning speed of the input shaft, and then shifting to the next gear. This makes gear shifting very smooth.

Electrohydraulic manual transmissionAnother famous semi-automatic trans-mission is an electrohydraulic manual transmission (aka sequential transmission). The gear set is almost the same as the conventional transmission sys-tem, except that the shifting of the se-lector is not an H pattern. Instead, all selector forks are connected to a drum .The drum has several grooves, and each has a ball sliding in it. Each fork hooks up to a ball and can be moved forward and backward when the drum is turning.Based on the pattern of the grooves on the drum, by turning the drum, each fork can move forward and backward in turn, which makes gear selection sequential. Therefore, it is impossible for an electrohydraulic manual transmission to perform a gear shift from 1st to 3rd or 4th to 2nd. The shifting must be sequential, like 1st2nd3rd4th, or 4th3rd2nd1st.

SequentialtransmissionAsequential transmissionis a type oftransmissionused onmotorcyclesand high-performance cars forauto racing, wheregearsare selected in order, and direct access to specific gears is not possible.cars with smts have a manual transmission with no clutch pedal; the clutch is automatically engaged.in a race car, the motion of the shift lever is either "push forward" to up-shift or "pull backward" to downshift. if you are in a gear and you want to go to a higher gear (e.g. from 2nd to 3rd), you push the shift lever forward. to go from 3rd to 4th, you push the lever forward again. to go from 4th to 5th, you press it forward again. it is the same motion every time. to drop back down a gear, say from 5th to 4th, you pull the lever backward. in european mass-produced automobiles, the shift lever , the motion of the shift lever is either "push forward" to up-shift or "pull backward" to downshiftmoves forward and backward to shift into higher and lower gears, respectively. in formula one cars, there are actually two paddles on the sides of the steering wheel, instead of a shift lever. the left paddle up-shifts, while the right paddle downshifts. on a motorcycle, you do the same thing, but instead of moving a lever back and forth with your hand, you move a lever up and down with your foot.

ADVANTAGES OF MANUAL TRANSMISSION OVER AUTOMATIC TRANSMISSION-

1. it is easier to build a strong manual transmission than an automatic one. this because a manual system has one clutch to operate, whereas an automatic system has a number of clutch packs that function in harmony with each other.

2.manual transmissions normally do not require active cooling, because not much power is dissipated as heat through the transmission.

3. manual gearshifts are more fuel efficient as compared to their automatic counterpart. torque convertor used to engage and disengage automatic gears may lose power and reduce acceleration as well as fuel economy.

4.manual transmissions generally require less maintenance than automatic transmissions.an automatic transmission is made up of several components and a breakdown of even a single component can stall the car completely.

Advantages of automatic transmission over manual transmission-

1.the manual transmission locks and unlocks different sets ofgearsto the output shaft to achieve the various gear ratios, while in an automatic transmission; the same set of gears produces all of the different gear ratios. the planetary gearset is the device that makes this possible in an automatic transmission.

2.automatic cars are easier to use, especially for the inexperienced car driver. manual system requires better driving skills, whereas with an automatic, the clever system does it all on its own. this holds a greater advantage for new and inexperienced drivers and also helps during congested traffic situations where it becomes difficult to change gears every second.

3.automatic transmission requires less attention and concentration from the driver because the automatic gears start functioning as soon as the system feels the need of a gear change.

4.automatic cars have better ability to control traction when approaching steep hills or engine braking during descents. manual gears are difficult to operate on steep climbs.

Advantages of using sequential transmission-

1.it provides a direct connection between engine and transmission, allowing 100 percent of the engine's power to be transmitted to the wheels.

2.the smt provides more immediate response and ensures that the engine rpms do not drop when the driver lifts off the accelerator (as happens with an automatic), giving her more precise control over power output.

3.it uses a solid coupling, as opposed to a fluid coupling (torque converter)

4.the sequential shift lever takes up less space in the race car cockpit.

5.the sequential shift is quicker.

6.the sequential shift is consistent. you do not have to think before gear change.

7.the hand location is consistent; the shift lever is always in the same place for the next shift.

8.the gearbox reduces the risk of blowing up engine due to mis-shift.

Final drive: the final drive is last stage in transferring power from the engine to the road wheels.it brings down, the speed of the propeller shaft to that of the wheels.Working: fig (1) shows a simple final drive system. The propeller shaft has a small pinion at its right end. This pinion is in mesh with crown wheel. This crown rotates the rear axles. The axles are in half portions. The pinion rotates when propeller shaft is rotating. The pinion is a bevel pinion. Therefore it rotates the crown wheel at right angles. The crown wheel in turn rotates the rear axles. The crown wheel is larger than the bevel pinion. Therefore the speed of the crown wheel is lower than the speed of the bevel pinion.

Fig (1): final drive; 1.Propeller shaft; 2.bevel pinion; 3.crown wheel; 4.Back axleDifferential: The function of the differential unit is to allow different speeds to the wheels. For instance a car is moving a bend on the road. Its inner wheel will be rotating at a speed lower than its outer wheel. Fig: differential; 1. Pinion on the propeller shaft; 2.Crown wheel; 3.half shafts; 4.Bevel gears of Differential; 5.bevel pinions of differential.Principle and operation of differential:In fig (a) the inner wheel axle has been stopped by hand. But the differential unit is still rotating. Thus the outer wheel can now rotate at a faster speed. A similar arrangement is made in the differential unit.

Fig (a): Principle of differential; 1.inner wheel; 2.Outer wheel;There are three different types of arrangements for the crown wheel and pinion of the propeller shaft.First bevel arrangement: Fig (i). This is the arrangement made in older models. In this the teeth of the crown wheel are straight. A bevel pinion of the propeller shaft is in mesh with the bevel gear of the crown wheel.Fig (i): Meshing of straight bevel gears; 1.Bevel pinion of straight teeth; 2. Bevel gear of straight teeth;Spiral bevel gear arrangement: Fig (ii).In this the teeth of the crown wheel are in the form of a spiral gear. The pinion of the propeller shaft also has teeth in the same spiral form. Fig(ii):Meshing of spiral bevel gears; 1.Pinion of spiral teeth; 2.Crown wheel of spiral teeth;Hypoid spiral gear arrangement: Fig (iii). This is a form of bevel pinion and crown wheel drive. The axis of the pinion shaft is below the center of the crown wheel.Fig (iii): Hypoid-spiral gears arrangement; 1.Pinion of hypoid-spiral teeth; 2. Crown wheel of hypoid-spiral teeth.

Disadvantages of bevel gear arrangement Sound is developed when both teeth mesh.Meshing is rough.When the parts get worn out, it is not uniform on both the crown wheel and pinion.Advantages of spiral bevel arrangement No sound is developed when these teeth mesh. The meshing is also very smooth. Also, when the parts get worn out, they do so uniformly on both the crown wheel and pinion.

Advantages of hypoid spiral gear arrangementIn this arrangement too the running is noiseless.Another advantage is that a lower propeller shaft can be placed without any difficulty.

Typical Differential configurations1 Open differential 2 Locked differential3 Limited slip differential

Open differential Advantages Simple design Robust and reliable Few moving parts Inexpensive to produce Disadvantage Supplies equal torque to both wheels Results in wheel spin

Applications Used in most production cars ,both in cars and trucksLocked Differential Advantages No moving parts ,extremely durable and strong Maintains constant speed between both wheels when one wheel loses traction Disadvantages Sometimes during a curve maintains constant speed between both wheels. Applications Purely offroad vehicles, Drag racing ,oval racing.

Limited slip differential(LSD) Advantages Manages vehicle traction mechanically Completely passive system ,no user or electrical controller input required. Disadvantages Many moving components, more susceptible to failure. Expensive to produce. Applications High end or performance oriented production vehicles. Road racing.