automobile transmission system solved papers.pdf

Automobile Transmission System Solved paper-I

By Prof. Syed J.M.

Lecturer in Auto.Engg. Govt. Polytechnic, Nagpur

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1. a) Attempt any SIX of the following:

i) State different types of vehicle layout.

Ans: Many different combinations of engine location and driven wheels are found in practice, and the location of each is dependent on the application the vehicle will be used for.

i) Two-wheel drive Two-wheel drive is a type of automobile layout in which two of the four car wheels are used to propel the vehicle forward. A two-wheel drive vehicle can be- 1) Front-wheel-drive layouts(FWD), 2) Rear-wheel-drive layouts(RWD), 3) Mid-engine, rear wheel drive

ii) Fourwheel drive In four wheel drive configuration all the four wheels are responsible for driving the automobile forward. An all-wheel drive system is one in which all wheels are drive wheels; the four wheels are full-time drive wheels. It may be- 1) Front engine, all-wheel drive, 2) Rear engine, all-wheel drive, 3) Mid-engine, all-wheel drive.

ii) State necessity and function of a frame.

Ans: A frame is the main structure of the chassis of a motor vehicle. It provides strength needed

for supporting vehicular components and payload placed upon it. It is the main mounting for all

the components including the body. So it is also called as underbody.

Functions of frame: 1. To carry load of the passengers or goods carried in the body. 2. To support the load of the body, engine, gear box etc. 3. To withstand the forces caused due to the sudden braking or acceleration 4. To withstand the stresses caused due to the bad road condition. 5. To withstand centrifugal force while cornering.

iii) State application of frame -channel section and box section one each.

Ans: By far the most common, the Channel section or C-rail has been used on nearly every type of vehicle at one time or another like buses and trucks. It is made by taking a flat piece of steel and rolling both sides over to form a c-shaped beam running the length of the vehicle. Originally, boxed frames used on cars were made by welding two matching c-rails together to form a rectangular tube. Modern techniques, however, use a process similar to making c-rails in that a piece of steel is bent into four sides and then welded where both ends meet. Hat or "U" frames may be either right-side-up or inverted with the open area facing down. Not commonly used due to weakness and a propensity to rust, however they can be found on some cars and Studebakers.

iv) State the necessity of clutch in an automobile.

Ans: Clutch is used to engage or disengage the engine to the transmission or gear box. An automobile clutch transmits torque from the engine to the transmission, and the driver uses a release mechanism to control the flow of the torque between them. The clutch is located between the back of the engine and the front of the transmission.

v) State the function of transfer case.

Ans: A transfer case is a part of a four-wheel-drive system found in four-wheel-drive and all-wheel-drive vehicles. The transfer case is connected to the transmission and also to the front and rear axles by means of drive shafts. It is also referred to as a "transfer gear case", "transfer gearbox, transfer box" or "jockey box". The transfer case receives power from the transmission and sends it to both the front and rear axles. This can be done with a set of gears, but the majority of transfer cases manufactured today is chain driven.

vi) State functions of propeller shaft and list its components.

Ans: The propeller shaft is a solid or hollow tube which transmits power from the gear box to the rear axle. The drive shaft, or propeller shaft, connects the transmission output shaft to the differential pinion shaft. The propeller shaft consists of- 1) Uuniversal joints, 2) Ssleeve and sliding shaft, 3) The flanges, and 4) The main bearing.

vii) State the necessity of differential in four wheeler vehicle.

Ans: On live axles, one wheel must turn at a different speed than the other as the vehicle goes around a corner. Additional gearing is required to allow for the difference in the speed of the wheels. The gearing assembly designed to do this job is called a differential.

viii) State the functions of rear axle used in automobile.

Ans: This is the arrangements for supporting the road-wheels on live axles and providing the driving traction use an axle-hub mounted on to the axle-casing and supported by ball or roller-bearing. The axle shaft transmits the drive from the differential sun wheel to the rear hub.

b) Attempt any TWO of the following: i) Draw a neat sketch of front engine rear wheel drive layout. State any two advantages and disadvantages of it.

Ans:

Advantages: Improves weight distribution compared with layouts that have more weight on one axel. Good traction when accelerating and braking. Safer in a front crash, less systems in the front mean less risk on intrusion. When going up a steep slope, the weight transfer to the back improves traction. Steer and drive are done by different axels, so the wear is more equal between the wheels in each axel. Disadvantages: Reduces back seats leg room space, a tunnel is needed for the propeller shaft. Reduces boot space. Heavier and more expensive. If stuck in mud or snow it is harder to drive away than in a front wheel drive car.

ii) Why multiplate clutch is used in two wheelers instead of single plate clutch?

Ans: 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 two wheeler which has less space and compact design It is also used in some electronically controlled drive systems. The clutch plates are alternatively fitted with engine shaft and the shaft of gear box. The plates are firmly held by the force of coil springs and they assembled in a drum.

iii) Explain construction and working of single plate coil spring type clutch with neat sketch.

Ans: A single plate clutch is commonly used in cars and light vehicles. It has only one clutch plate which is mounted on the splines of the clutch shaft. The clutch has following components :Flywheel, Clutch Disk, Pressure Plate, Throw out bearingor Release Bearing, Pilot bearing-centers and supports the transmission input shaft. A flywheel is mounted on the crankshaft of the engine. A pressure plate is connected to the flywheel through the bolts and clutch springs. It is free to slide on the clutch shaft with the movement of clutch pedal. When clutch is in engaged position, the clutch plate remains gripped between flywheel and pressure plate. Friction linings are provided on both the sides of clutch plate.

Fig. Single plate (disc) clutch.

Operation of clutch When the engine is running and the flywheel is rotating, the pressure plate also rotates as the pressure plate is attached to the flywheel. The friction disc is located between the two. When the driver has pushed down the clutch pedal the clutch is released. This action forces the pressure plate to move away from the friction disc. There are now air gaps between the flywheel and the friction disc, and between the friction disc and the pressure plate. No power can be transmitted through the clutch. When the driver releases the clutch pedal, power can flow through the clutch. Springs in the clutch force the pressure plate against the friction disc. This action clamps the friction disk tightly between the flywheel and the pressure

2. Attempt any FOUR of the following:

a) Differentiate between single plate clutch and multiplate clutch.

Ans: A single plate clutch is commonly used in cars and light vehicles. It has only one clutch plate which is mounted on the splines of the clutch shaft. When clutch is in engaged position, the clutch plate remains gripped between flywheel and pressure plate. 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. It is also used in some electronically controlled all-wheel

drive systems. The clutch plates are alternatively fitted with engine shaft and the shaft of gear box. The plates are firmly held by the force of coil springs and they assembled in a drum.

b) Compare between dry clutch and wet clutch on the basis of construction, torque transmission, heat discipation and application.

Ans:

Dry clutch Wet clutch A dry clutch, as the name implies, is not bathed in fluid. A dry clutch can transmit large torque and less drive train loss due to the non slippery surfaces of a clutch. There is no oil circulated, which result into clutch knocking, heat dissipation by air. The dry clutch is commonly used in cars and light vehicles.

A wet clutch is immersed in a cooling lubricating fluid. Stacking multiple clutch discs can compensate and so eliminate slippage under power when fully engaged. It gives smoother performance and longer life; tend to lose heat to the liquid. , It is used in sports bike, racing cars and heavy vehicles.

c) Explain construction and working of variator drive with neat sketch.

Ans: At present variable speed drive (variator) application of automatic stepless transmission or CVT for a great number of cars is taking place.This consists of a V shaped drive belt and two pulleys, each of two cones, whose effective diameter can be changed so that the V belt runs nearer the spindle or nearer the rim, depending on the separation of the cones. These are synchronized so that the belt always remains at the same optimal tension. The variable-diameter pulley is made of two 20-degree cones facing each other. A belt rides in the groove between the two cones. CVTs (continuously variable transmission).may use hydraulic pressure, centrifugal force or spring tension to create the force necessary to adjust the pulley halves.

Fig.Variator Drive.

When the two cones of the pulley are far apart (when the diameter increases), the belt rides lower in the groove, and the radius of the belt loop going around the pulley gets smaller. When the cones are close together (when the diameter decreases), the belt rides higher in the groove, and the radius of the belt loop going around the pulley gets larger. One of the pulleys, known as the drive pulley (or driving pulley), is connected to the crankshaft of the engine. The second pulley is called the driven pulley because the first pulley is turning it. As an output pulley, the driven pulley transfers energy to the driveshaft. The distance between the centers of the pulleys to where the belt makes contact in the groove is known as the pitch radius.

d) Explain clutch operating mechanism with simple sketch in friction clutch.

Ans: The clutch linkage transmits and multiplies the driver's leg force to the fork of the clutch pressure plate. Whether the linkage is mechanical or hydraulic, the linkage should have some sort of adjustment for clutch play (a certain amount of slack in the clutch linkage).A mechanical clutch linkage usually consists of the clutch pedal, a series of linkage rods and arms, or a cable.

Mechanical clutch linkage A clutch linkage mechanism uses levers and rods to transfer motion from the clutch pedal to the clutch fork. One configuration is shown in figure . When the pedal is pressed, a pushrod shoves on the bell crank and the bell crank reverses the forward movement of the clutch pedal. The other end of the bell crank is connected to the release rod. The release rod transfers bell crank movement to the clutch fork. It also provides a method of adjustment for the clutch.

e) Explain working of centrifugal clutch with neat sketch.

Ans: This clutch system employs centrifugal force to automatically engage the clutch when the engine rpm rises above a threshold and to automatically disengage the clutch when the engine rpm falls low enough. The most common types have friction pads or shoes attached to the driven shaft, rotating inside a clutch bell attached to the output shaft. On the center shaft there are an assorted number of extension springs, which connect to a clutch shoe. When the center shaft spins fast enough, the springs extend causing the clutch shoes to engage the friction face. As the load increases, the speed drops, disengaging the clutch, letting the speed rise again and reengaging the clutch..

Fig Centrifugal clutch.

f) Differentiate between sliding mesh and constant mesh gear box.

Ans: Following points are important for the comparison of sliding mesh and constant mesh gear box.

Sliding mesh gearbox Constant mesh gear box All gears used are spur gears. The gears are mounted on the main shaft and can be slide. Gear wheels on the main shaft engage with lay shaft gears by sliding. These are noisy.

Helical and herringbone gear can be used. The gears on the main shaft are bushed and free to rotate. Dog clutches engage with gears on the main shaft to obtain desired speed. These are quieter.


a) Draw a neat sketch of torque converter.

Ans:

b) Draw a neat sketch of sliding mesh gear box engaged in first gear and show power flow for the same.

Ans:

c) Differentiate between Hotchkiss drive and torque tube drive.

Ans: Comparison of Hotchkiss drive and torque tube drive:

Hotchkiss drive Torque tube drive . The Hotchkiss drive is a system of power transmission which is not enclosed. It uses universal joints at both ends of the drive shaft, also a sliding joint. It allows the use of cross-type universals. Hotchkiss drive has the traction forces transmitted to the frame by using other suspension components such as leaf springs or trailing arms. Used in pick-up trucks and sport utility vehicles.

In this design a solid drive shaft is enclosed in a hollow torque tube. A "torque ball" is used at one end of the torque tube. A ball and socket type of joint is used. The "torque tube" transmits this force by directly coupling the axle differential to the transmission; a pan hard rod is often used for this purpose. It is used for rear-wheel drive layout sport cars.

d) Why constant mesh gear box require double de-clutching?

Ans: In constant mesh gear box, for smooth engagement of dog clutches it is necessary that the speed of main shaft and sliding dog clutch must be equal. To obtain lower gear, the speeds of the clutch shaft, lay shaft and main shaft must be increased. This is done by double declutching. The clutch is disengaged and the gear is brought to neutral. Then the clutch is engaged and accelerator pedal pressed to increase the speed of the main shaft gears. Again the clutch is disengaged and the gear moved to the required lower gear and the clutch is again engaged. As the clutch is disengaged twice, it is called double declutching.

e) How the lubrication of gear box is done?

Ans: The moving parts in the gearbox are lubricated by partially filling the box with the correct grade oil through a level plug hole located on the side of the casing, until the oil starts to drain back out of the hole. The plug is then screwed on to prevent spilling out of oil during operation of the gearbox. The oil level submerges the lay shaft or secondary-shaft cluster gears, so that the oil is dragged around with the gearwheel teeth when the gears revolve. This helps the oil to spread and flow between the individual gearwheels, output main shaft and primary shaft, dog-clutch assemblies, and support bearings. The selector mechanisms are lubricated by oil splashing up from the gar teeth. A drain-hole and a screw plug are usually provided at the lowest point in the oil-bath casing, to drain used oil. Overfilling the gearbox creates a pumping action, which builds-up pressure within the box and eventually forces oil past the input shaft and output shaft oil seals. For smooth flow of oil between the shafts and the gears revolving relative to them, two or three holes are drilled radially in each gearwheel. Heavy-duty commercial vehicles use a forced-feed lubrication system in which a gear pump pressurizes oil along an axial hole in both the primary and main shafts.

f) Explain the working of synchromesh gear box with neat sketch.

Ans:In modern cars, synchromesh devices are used in gear boxes to synchronize the rotation of gears that are about to be meshed. This gear box is provided with synchromesh devices by which two gears to be engaged are first brought into frictional contact which they are engaged smoothly. When the gear lever is moved, the synchronizer cone meets with a similar cone on the pinion. Due to the friction, the rotating pinion is made to rotate at the same speed as the synchromesh unit. To give a positive drive further movement of the gear lever enables the coupling to override several spring loaded balls and the coupling engages with the dog on the ride of the pinion. Since both pinion and synchromesh unit are moving at the same speed, this engagement is done without noise or damage to the dogs.

Fig. Synchromesh gearbox.


a) Draw a neat sketch of differential and label it.

Ans:

A, drive shaft; B, axle drive shaft; C, differential gears; D, differential housing attached to bevel gears; E, bevel-gear transmission.

Fig. Bevel gear differential.

b) Explain with neat sketch split and banjo type rear axle casing. Ans: The casing used now days is either a banjo or carrier-type. In the past a split (trumpet) casing was occasionally used. The type of axle casing used decides the method for the removal of the final drive. Split type: In this type the axle casing is made in two halves and then bolted together for assembly. This type has a major disadvantage that in case of any fault, whole of axle has to be removed as a unit and then disassembled. This type is absolute now. In the split type axle arrangement a central housing contains the final drive and it is fitted with a tube on each side to carry the half axles and bearings in all types the inner ends of the half shafts are connected to the gears of the differential. Banjo type: In the banjo or Separate Carrier axle, the axle is a single unit and the final drive assembly is carried in a separate casing which is bolted to the axle housing. The banjo construction is often used for the axle cases of the smaller and higher vehicles. This type of axle of one-piece type, shaped like a banjo. The two half shafts are pull from sides. Therefore in case of any need for repairs, the half shafts can be taken out directly from the sides and the differential assembly removed by opening bolts only. On some banjo axles a domed plate is bolted to the rear face of the casing. Removal of this plate provides excess to the final drive gears.

Fig. Two types rear axle casing.

c) Write the functions of constant velocity Rezappa and Tripod joint. Ans: They are mainly used in front wheel drive and all-wheel drive cars. Rear wheel drive cars with independent rear suspension typically use CV joints at the ends of the rear axle half shafts, and increasingly use them on the prop shafts. There are two basic types: Rzeppa joints and tripod CV joints. Rzeppa CV joints, are used as the outer joints on most front-wheel drive cars and mini vans. Tripod CV joint is designed to plunge in and out, and is used as the inner CV joint on most domestic front-wheel drive vehicles. There are also some Japanese and European front-wheel drive cars that use a tripod joint as the outer joint.

d) State any two advantages and any two drawbacks of torque converter.

Ans: The advantages of a torque converter :

1) Torque converters allow a car to start and stop without user intervention.

2) Because torque converters are very heavy, they tend to act as a sort of inertial flywheel.

Drawbacks of torque converter:

1) The torque converter can slip almost indefinitely. 2) Torque converters hold several quarts of transmission fluid.

e) Explain steel disc wheel with neat sketch.

Ans: This is a wheel which processes the steel-made rim and the disc into one by welding, and it is used mainly for passenger vehicle especially original equipment tires. Disc wheels are light

compared to alloy steel wheels and are resistant to corrosion to some extent. It will give a light increase in fuel economy due to decrease in weight.

Fig. Wheel construction.

f) Explain specification of tyres with one example.

Ans: There's a lot of useful information molded into the sidewall of a tyre. It shows the name of the tyre, its size, whether it is tubeless or tube type, the tyre grade, speed rating, the maximum load, maximum inflation, an important safety warning, and more. A popular size for passenger cars is, for example:

205/45R16 83 V

Where: '205' represents the approximate width of the tyre in millimeters '45' represents the sidewall height as a percentage of the width of the tyre - 45% of 205mm in this instance. 'R' represents the construction type - in this, as in almost all modern tyres, denotes a RADIAL construction. '16' represents the diameter of the wheel measured in inches. '83' represents the load index. 'V' represents the speed rating.

5. Attempt any TWO of the following:

a) Explain construction and working of three quarter floating type rear axle with neat sketch.

Ans: Three-quarter floating axle

Fig.Three quarter floating axle.

A three-quarter floating axle is the same as semi-floating, with one difference. The bearing supporting the outer end of the axle shaft is moved from inside the axle housing to the outside. This method of mounting the axles places most of the weight of the vehicle on the ends of the axle housing rather than the ends of the axle shafts. The wheel is solidly keyed to a taper on the end of the axle shaft, so side-thrust is still taken by the axle shaft as the vehicle turns or skids

b) Draw a neat sketch of full floating rear axle and explain how it differs from semi floating and three quarter floating rear axle from construction point of view.

Ans:

Fig. Full-floating axle. Full floating axle The full-floating design is typically used in most light trucks, medium duty trucks and heavy-duty trucks, as well as most agricultural applications, such as large tractors and combines. The drive wheel is carried on the outer end of the axle housing by a pair of tapered roller bearings. The bearings are located outside the axle housing. In this way, the axle housings take the full weight of the vehicle and absorb all stresses or end thrust caused by turning, skidding, and pulling. Only the axle shaft transmits torque from the differential.

c) Explain construction and operation of hollow tube propeller shaft with neat sketch.

Ans: The propeller shaft consists of universal joints, sleeve and sliding shaft. It transfers engine torque to the rear axle through one or more universal joints.The flanges connect the propeller shaft to the gearbox. The main bearing support and guide the propeller shaft. Universal or U-joints allow the drive shaft to flex when the drive angle changes. The splines on the ends at the propeller shaft fit perfectly into the splines in the sleeve. This allows a length variation between the driving and the driven unit to vary slightly without damaging the output and input bearings.

Fig. Drive shaft with universal joints at each end.

6. Attempt any TWO of the following:

a) Explain any two types of frames with neat sketch. State any two advantages of each.

Ans: There are following types of frames: 1. Conventional frame, 2. Integral frame, and 3. Semi-integral frame.

1. Conventional frame Conventional frames are basically two side rails joined together by cross members.The cross members are either welded or riveted to the rails with the strongest one supporting the engine and suspension. The body is then bolted onto the frame using rubber body mounts as spaces between the frame and body to isolate the vehicle from road vibrations. There are several types of conventional frames. The ladder frame is the simplest and earliest version of the automobile frame. It is constructed with two main side-rails connected to each other by cross members.

Advantage

a) It is the strongest, therefore is used for heavy truck construction, and b) This design offers good beam resistance because of its continuous rails from front to rear.

Fig. Ladder Frame.

1. Integral frame or Unibody In this type of construction, there is no frame and all the assembly units are attached to the body. It is also called unitized frame-body construction. In this case, the body shell and underbody are welded into single unit. All the functions of the frame carried out by the body itself. By far the most common design in use today, sometimes referred to as a sort of frame,this frame is used now a day in most of the cars. Advantage

a) Due to elimination of long frame it is cheaper, and b) Due to less weight most economical..

Fig. Integral frame.

b) Explain tyre construction with neat sketch.

Ans: The fundamental materials of modern tires are synthetic rubber, natural rubber, fabric and wire, along with other compound chemicals. Carcass (Casing) is the main body of the tire consisting of wire beads and body plies. The carcass does not including the tread or sidewall rubber. A tire carcass is composed of several parts. Typical components used in tire assembly are:

Body ply Plies are layers of relatively inextensible cords embedded in the rubber to hold its shape by preventing the rubber from stretching in response to the internal pressure. The orientations of the plies play a large role in the performance of the tire and are one of the main ways that tires are categorized. The earliest textile used was cotton; later materials include rayon, nylon, polyester, and Kevlar. Passenger tires typically have one or two body plies. Body plies give the tire structure strength. Truck tires, off-road tires, and aircraft tires have progressively more plies. Sidewall The sidewall is that part of the tire that bridges between the tread and bead. The sidewall is largely rubber but reinforced with fabric or steel cords that provide for strength and flexibility. The sidewall transmits the torque applied by the drive axle to the tread to create traction. The sidewall, in conjunction with the air inflation, also supports the load of the vehicle. Sidewalls are molded with manufacturer-specific detail; government mandated warning labels, and other consumer information, and sometimes decorative ornamentation, like whitewalls. Belt package Belts are one or more rubber-coated plies of steel, polyester, nylon, Kevlar or other material running circumferentially around the tire under the tread. The steel cords are oriented radially in radial tire construction, and at opposing angles in bias tire construction. They are designed to reinforce body plies to hold the tread flat on the road. Belts give the tire strength and dent resistance while allowing it to remain flexible. Passenger tires are usually made with two or three belts. Inner Liner A layer of specially compounded rubber forming the inside of a tubeless tire, designed to inhibit loss of air pressure. The inner liner assures that the tire will hold high-pressure air inside, without the air gradually diffusing through the rubber structure.

Fig, Tyre cross section.

Apex and Chafer The apex is a triangular extruded profile that mates against the bead. The apex provides a cushion between the rigid bead and the flexible inner liner and body ply assembly. Alternatively called "filler" (as in the diagram above). The chafer protects the cord as it appears on the rim wheel the chafer is the lining between the tyre and the rim.

Beads The bead is that part of the tire that contacts the rim on the wheel. The bead is typically reinforced with steel wire and compounded of high strength, low flexibility rubber. Bead wire is coated with special alloys of bronze or brass. Coatings protect the steel from corrosion. Copper in the alloy and sulfur in the rubber cross-link to produce copper sulfide, which improves bonding of the bead to the rubber. Beads are inflexible and inelastic, and provide the mechanical strength to fit the tire to the wheel.

c) Differentiate between tube tyre and tubeless tyre on the basis of weight, fuel efficiency, life and road holding.

Ans: Comparison between tube tyre and tubeless tyre:

Tube tyre Tubeless tyres .A tube tyre consists of a tube of air that is placed inside the tyre and weighs more. It has less fuel efficiency and safety. They have shorter life than tubeless. It has more components, generates heat while on the move and causes vibrations.

A tubeless tyre weighs less and reduces un-sprung weight of the vehicle. Safety and more fuel efficiency. They last longer than tubes. Its resistance when driving is much lower and has less friction, making it more economical.

Automobile Transmission System Solved paper-II

By Prof. Syed J.M.


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i) What is meant by Vehicle Layout ? Give one example.

Ans: An automobile layout is the orientation of the wheels, engine, and drive components in relation to each other. Many different combinations of engine location and driven wheels are found in practice, and the location of each is dependent on the application the vehicle will be used for. For example- Front-wheel-drive layouts (FWD), Rear-wheel-drive layouts (RWD).

ii) Define -An Automobile. State its major parts. Ans: An automobile is a wheeled motor vehicle for transporting passengers, which also carries its own engine or motor. Most definitions of the term specify that automobiles are designed to run primarily on roads, and to be constructed principally for the transport of people rather than goods. The automobiles are generally considered to be consisting of two major assemblies, chassis and body. The chassis consists of :the frame, the engine, the transmission system, the steering system and the brakes.

iii) What is the working principle of automotive clutches ? Ans: Automotive clutches: operate 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. They may be (i) single plate clutch, (ii) multi-plate clutch, or (iii) cone clutch.

iv) List the types of gear boxes. Ans: Gearbox (transmission) has different types.

1) Sliding-mesh, 2) Constant-mesh, 3) Synchro-mesh, 4) Automatic gearbox

Ssome of them are old-fashion and had been replaced, and some are in use in modern cars.

v) What is transfer case.

Ans: A transfer case is a part of a four-wheel-drive system found in four-wheel-drive and all-wheel-drive vehicles. The transfer case is connected to the transmission and also to the front and rear axles by means of drive shafts. It is also referred to as a "transfer gear case", "transfer gearbox, transfer box" or "jockey box". vi) State the components of differential unit. Ans: Differential unit consists of a spiral bevel pinion gear meshes with the large spiral bevel ring gear, known as the crown wheel. The crown wheel and pinion may mesh in hypoid orientation. The crown wheel gear is attached to the differential carrier or cage, which contains the 'sun' and 'planet' wheels or gears. The two sun wheel gears drive the axle half shafts connected to the vehicle's driven wheels. The other two planet gears are aligned on a perpendicular axis which changes orientation with the ring gear.

vii) Write functions of following- 1) Universal joint , 2) Slip joint Ans: Functions of universal joint and slip joint A universal joint is a flexible coupling between two shafts that permits one shaft to drive another at an angle to it. The universal joint is flexible in a sense that it will permit power to be transmitted while the angle of the other shaft is continually varied. A slip joint is a mechanical construction allowing extension and compression in a linear structure. Slip joints can be designed to allow continuous relative motion of two components or it can allow an adjustment from one temporarily fixed position to another.

viii) State the materials used for chassis frame. Ans: Chassis frames are basically manufactured from steel. Aluminum is another raw material that has increasingly become popular for manufacturing these auto frames.

b) Attempt any TWO of the following: i) Draw four sections of chassis frame and write their significance. Ans:

(A) (B) (C) (D) (E)

(A) C-section, (B)Circular closed tube, (C) Box section, (D) Top-hat-section, (E) I-section.

Fig. Chassis Frame Sections.

The types of cross-sections most commonly used for making frame are: (a) Channel section- Good resistance to bending, (b) Tubular section- Good resistance to torsion, and (c) Box section- Good resistance to both bending and torsion. (d) Hat or "U" frame section Hat or "U" frames may be either right-side-up or inverted with the open area facing down.

ii) State the loads acting on chassis frame. Ans: Various loads acting on the frame are: 1. Short duration Load - While crossing a broken patch. 2. Momentary duration Load - While taking a curve. 3. Impact Loads - Due to the collision of the vehicle. 4. Inertia Load - While applying brakes. 5. Static Loads - Loads due to chassis parts.

iii) Sketch and describe hydraulically operated clutch mechanism. Ans: Hydraulically-operated Linkage

Fig. Clutch linkage mechanism- Hydraulic.

A more convenient way to transmit force and movement is by hydraulic linkage in which the fluid is forced through a flexible plastic pipeline, spun between the foot-pedal and the clutch bell-housing. A master-cylinder, mounted on the bulkhead and a push-rod joining the clutch-pedal to the sliding piston, provides the control of the clutch action. A slave cylinder unit containing the piston is installed on an extension formed on the bell-housing flange. The slave piston relays the slightest movement to the fork-lever through the slave pushrod. Depressing the clutch pedal creates pressure in the clutch master cylinder, actuating the slave cylinder which, in turn, moves the release arm and disengages the clutch. When the pedal is released, engagement of the clutch occurs due to which the fluid returns to the master-cylinder and its reservoir. Hydraulic types of clutch operating systems are normally found in heavy construction equipment where extreme pressure is required to operate the clutch.

2. Attempt any FOUR of the following: a) Differentiate between Torque convertor and Fluid coupling.

Ans: : Comparison between Torque convertor and Fluid coupling:

Torque Convertor Fluid Coupling . Torque Convertor has three elements, an impeller a turbine and a stator. It has the additional ability to multiply torque "convert" the power. It is the actual shifting device, and it can work under load. The blades of the turbine and impeller are curved. .

A fluid coupling has 2 members, an impeller and turbine. Fluid Coupling is basically a one-to-one "coupling". A fluid coupling acts more like a clutch than anything. The impeller and turbine have large number of radial vanes.

b) Differentiate between Dry and Wet clutch. Ans:



c) Describe construction and working of fluid coupling. Ans: A fluid coupling has been used in automobile transmissions as an alternative to a mechanical clutch. Fluid couplings work on the hydrodynamic principle. It consists of a pump-generally known as impeller and a turbine generally known as rotor, both enclosed suitably in a casing. The impeller and the rotor are bowl-shaped and have large number of radial vanes. They face each other with an air gap. Oil is filled in the fluid coupling from the filling plug provided on its body. The impeller or pump typically is connected to the flywheel of the engine and thus is turned by the engine's crankshaft. The turbine is connected to the input shaft of the transmission.The power is transmitted by virtue of the fluid filled in the coupling. The impeller when rotated imparts velocity and energy to the fluid, which is converted into mechanical energy in the rotor thus rotating it. The fluid follows a closed circuit of flow from impeller to rotor through the air gap at the outer periphery and from rotor to impeller again through the air gap at the inner periphery. As a fluid

coupling operates kinetically, low viscosity fluids are preferred. Multi-grade motor oils or automatic transmission fluids are used.

Fig. Fluid coupling.

d) Draw a neat labelled diagram of Diaphragm type single plate clutch in disengaged position. Ans:

Fig.Diaphragm clutches.

e) Describe the lubrication of gear box. Ans: Lubrication of gear box The moving parts in the gearbox are lubricated by partially filling the box with the correct grade oil through a level plug hole located on the side of the casing, until the oil starts to drain back out of the hole. The plug is then screwed on to prevent spilling out of oil during operation of the gearbox. The oil level submerges the lay shaft or secondary-shaft cluster gears, so that the oil is dragged around with the gearwheel teeth when the gears revolve. This helps the oil to spread and flow between the individual gearwheels, output main shaft and primary shaft, dog-clutch assemblies, and support bearings. The selector mechanisms are lubricated by oil splashing up from the gar teeth. A drain-hole and a screw plug are usually provided at the lowest point in the oil-bath casing, to drain used oil.

Overfilling the gearbox creates a pumping action, which builds-up pressure within the box and eventually forces oil past the input shaft and output shaft oil seals. For smooth flow of oil between the shafts and the gears revolving relative to them, two or three holes are drilled radially in each gearwheel. Heavy-duty commercial vehicles use a forced-feed lubrication system in which a gear pump pressurizes oil along an axial hole in both the primary and main shafts.

f) Explain the clutch operating mechanism with single sketch in friction clutch. Ans: The clutch linkage transmits and multiplies the driver's leg force to the fork of the clutch pressure plate. A mechanical clutch linkage usually consists of the clutch pedal, a series of linkage rods and arms, or a cable. One configuration is shown in figure. The clutch cable mechanism uses a steel cable inside a flexible housing to transfer pedal movement to the clutch fork. As shown in figure, the cable is usually fastened to the upper end of the clutch pedal, with the other end of the cable connecting to the clutch fork. The cable housing is mounted in a stationary position. This allows the cable to slide inside the housing whenever the clutch pedal is moved. One end of the clutch cable housing has a threaded sleeve for clutch adjustment.

Fig. Clutch operating systems (cable type of linkage).

3. Attempt any TWO of the following: a) Draw a schematic diagram of constant mesh gear box in neutral position and label it. Describe its construction and working.

Ans: Constant mesh gear box In this design, the mainshaft pinions revolves freely on bushes or needle-roller bearings and are all in constant engagement with the corresponding lay shaft wheels. The gear operation is obtained by locking the respective gear to the main shaft by means of a dog clutch. With this arrangement the quieter-running helical gears can be employed, and during gear changing the noise and wear are reduced by the simultaneous engagement of all the dogs instead of only a pair of gear teeth as on the sliding-mesh gearbox. The layout of the box is shown in the figure.

Fig. Constant mesh gearbox.

In this type of gear box, all the gears of main shaft are inconstant mesh with the corresponding gears on the lay shaft. Two dog clutches are provided to the main shaft one between the clutch gear and second gear and the other between the first and reverse gears. The dog clutches are provided which are free to slide on the main shaft. When the left dog clutch is slide to the left by means of selector mechanism, its teeth are engaged with those on the gear and then the top gear enclosed. However when slide to right makes contact with the second gear and second gear is obtained.

b) Write in detail classification of clutches. Describe working of centrifugal clutch with schematic diagram.

Ans: The types of clutches used in vehicles are given below: (a) Friction Clutch: It may be (i) single plate clutch, (ii) multi-plate clutch, or (iii) cone clutch. Multi-plate clutch can be either wet or dry. (b) Centrifugal clutch, (c) Semi-centrifugal clutch, (d) Hydraulic clutch,. (e) Positive clutch. (f) Vacuum clutch, (g) Electromagnetic clutch,


Centrifugal clutch: This clutch system employs centrifugal force to automatically engage the clutch when the engine rpm rises above a threshold and to automatically disengage the clutch when the engine rpm falls low enough. The most common types have friction pads or shoes attached to the driven shaft, rotating inside a clutch bell attached to the output shaft. On the center shaft there are an assorted number of extension springs, which connect to a clutch shoe. When the center shaft spins fast enough, the springs extend causing the clutch shoes to engage the friction face. As the load increases, the speed drops, disengaging the clutch, letting the speed rise again and reengaging the clutch..

c) What is meant by Tyre Inflation ? Describe the effect of inflation pressure on tyre life. What is importance of tyre rotation.

Ans: Tyre inflation and Effect of inflation pressure on the life of tyre: Tires are specified by the vehicle manufacturer with a recommended inflation pressure, which permits safe operation within the specified load rating and vehicle loading. Most tires are stamped with a maximum pressure rating. With low tire pressure, due to the side wall being more pliable, the tire will absorb more of the irregular forces from normal driving, and with this constant bending of the side wall as it absorbs the contours of the road, it heats up the tire wall to possibly dangerous temperatures, as well as degrades the steel wire reinforcement; this often leads to side wall blow-outs. In an extreme case of this phenomenon, the vehicle may drive into a pot-hole, or a hard elevation in the road. Due to the low tire pressure, the side wall at the contact area will temporarily collapse, thereby wedging the tire between the wheel and road, resulting in a tire laceration and blow-out, as well as a damaged wheel. High tire pressures are more inclined to keep its shape during any encounter, and will thus transmit the forces of the road to the suspension, rather than being damaged it. This allows for an increased reaction speed, and feels" the driver perceives of the road. It may be that very high tire pressures have only two downsides: The sacrifice in comfort; and the increased chance of obtaining a puncture when driving over sharp objects, such as on a newly scraped gravel road. Over-inflation may increase the wear on the center contact patch, and under-inflation will cause a concave tread, resulting in less center contact. An increased tire pressure has many benefits, including decreased rolling resistance. It has been found, that an increased tire pressure almost exclusively results in shorter stopping distances, except in some circumstances that may be attributed to the low sample size. If tire pressure is too low, the tire contact patch is changed more than if it were over-inflated. This increases rolling resistance, tire flexing, and friction between the road and tire. Under-inflation can lead to tire overheating, premature tread wear, and tread separation in severe cases. Tyre rotation Tires may exhibit irregular wear patterns once installed on a vehicle and partially worn. Furthermore, front-wheel drive vehicles tend to wear the front tires at a greater rate compared to the rears. Tire rotation is the procedure of moving tires to different car positions, such as front-to-rear, in order to even out the wear, thereby extending the life of the tire. However care must be taken with unidirectional tires (tires that are designed to rotate in one direction only, for a vehicle that is going forward) so that the correct rotational direction - indicated on the side wall with an arrow-like symbol - is maintained after the swap.

4. Attempt any FOUR of the following: a) What is multi-plate clutch ? Give its three applications with specific reasons.

Ans: Multi plate clutch 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. It is also used in two wheelers and some electronically controlled all-wheel drive systems. The clutch plates are alternatively fitted with engine shaft and the shaft of gear box. The 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.

Fig. Multi plate clutch.

b) Draw a power flow diagram for a synchromesh gear box, when third gear is engaged and describe it.

Ans: Synchromesh gear box

The clutch gear is rigidly fixed to the clutch shaft. It remains always connected to the drive gear of the lay shaft (counter shaft). The other gears also rigidly fixed to the counter shaft. The power is transmitted from the engine to the clutch shaft of gear box and will be transmitted to the main shaft through counter shaft. The required speed is obtained by shifting the gears in counter shaft by the selective mechanism coupling. For gear changing in the third gear position, the coupling is slid in to mesh with the third gear.

Ratio = Number of teeth on the output gear = Toutput /Tinput Number of teeth on the input

c) With sketch describe how synchronisation of speed is obtained by synchromesh device ?

Ans: In modern cars, synchromesh devices are used in gear boxes to synchronize the rotation of gears that are about to be meshed. This gear box is provided with synchromesh devices by which two gears to be engaged are first brought into frictional contact which they are engaged smoothly. When the gear lever is moved, the synchronizer conemeets with a similar cone on the pinion. Due to the friction, the rotating pinion is made to rotate at the same speed as the synchromesh unit. To give a positive drive further movement of the gear lever enables the coupling to override several spring loaded balls and the coupling engages with the dog on the ride of the pinion. Since both pinion and synchromesh unit are moving at the same speed, this engagement is done without noise or damage to the dogs.


d) Describe working of Hotchkiss drive with sketch.

Ans: The Hotchkiss drive is made up of a drive shaft connected to the transmission output shaft and the differential pinion gear shaft. U-joints are used in the front and rear. The Hotchkiss drive transfers the torque of the output shaft to the differential. Sometimes this drive comes in two pieces to reduce vibration and make it easier to install with three U-joints. The two-piece types need ball bearings in a dust proof housing as center support for the shafts.

Fig. A Hotchkiss drive.

In the Hotchkiss drive, slip-splines or a plunge-type (ball and trunnion u-joint) eliminate thrust transmitted back up the driveshaft from the axle, allowing simple rear-axle positioning using parallel leaf springs. The Hotchkiss drive uses two universal joints which has the effect of canceling the speed fluctuations and gives a constant speed even when the shaft is no longer straight. The Hotchkiss drive has the traction forces transmitted to the car frame by using other suspension components such as leaf springs or trailing arms.

e) Differentiate between Torque tube drive and Hotchkiss drive.

Ans: Comparison of Hotchkiss drive and torque tube drive:

Hotchkiss drive Torque tube drive . The Hotchkiss drive is a system of power transmission which is not enclosed. It uses universal joints at both ends of the drive shaft, also a sliding joint. It allows the use of cross-type universals. Hotchkiss drive has the traction forces transmitted to the frame by using other suspension components such as leaf springs or trailing arms. Used in pick-up trucks and sport utility vehicles.

In this design a solid drive shaft is enclosed in a hollow torque tube. A "torque ball" is used at one end of the torque tube. A ball and socket type of joint is used. The "torque tube" transmits this force by directly coupling the axle differential to the transmission; a pan hard rod is often used for this purpose. It is used for rear-wheel drive layout sport cars.

f) State necessity of final drive and differential. Also write its location in different types of vehicle layouts.

Ans: A vehicle's wheels rotate at different speeds, mainly when turning corners. This is necessary when the vehicle turns, making the wheel that is travelling around the outside of the turning curve roll farther and faster than the other. On live axles, one wheel must turn at a different speed than the other as the vehicle goes around a corner. Additional gearing is required to allow for the difference in the speed of the wheels. The gearing assembly designed to do this job is called a differential. A final drive is the part of the power train between the propeller shaft and the differential. It is the part of the axle assembly that provides the 90 change in direction of the power flow and increases torque or turning force. The differential assembly is mounted in the axle housing and is bolted to, and driven by, the final drive ring gear. Final drive gears are incorporated in vehicle driving axles for the following reasons:

b) To provide a right-angle drive from either the propeller shaft or the gearbox lay shaft, to the driven wheels.

c) To permit an additional and constant gear reduction in the transmission system. These functions can be performed by bevel or worm and spur gears.

For the front wheel drive vehicle the differential is attached at the front axles whereas in case of rear wheel drive it is fitted to the rear axle. All wheel drive vehicle needs a differential between each sets of drive wheels and one more differential at the center of the front and rear wheels.


a) Sketch cross and yoke type universal joint and describe its working.

Ans:

A U-joint which is also called a Cardan joint, is used on both ends of the drive shafts in rear-wheel and four-wheel drive vehicles. A universal joint is a flexible coupling between two shafts that permits one shaft to drive another at an angle to it. The universal joint is flexible in a sense that it will permit power to be transmitted while the angle of the other shaft is continually varied. Fig. shows a cross and yoke type universal joint. It has two yoke and a cross member. A slip joint is a mechanical construction allowing extension and compression in a linear structure. Slip joints can be designed to allow continuous relative motion of two components or it can allow an adjustment from one temporarily fixed position to another. b) What is constant velocity (C. V) joint ? State its two types. In which vehicle C. V. joints are used ? Why ?

Ans: A constant velocity joint is a joint does essentially the same thing as a U-joint. CV joints allow a drive shaft to transmit power through a variable angle, at constant rotational speed, without an appreciable increase in friction or play. There are two basic types: Rzeppa joints and tripod CV joints. They are mainly used in front wheel drive and all-wheel drive cars. Rear wheel drive cars with independent rear suspension typically use CV joints at the ends of the rear axle half shafts, and increasingly use them on the prop shafts. CV joints come in a variety of styles. All CV joints are enclosed by a rubber or hard plastic boot. The boot keeps grease in and contaminants out. All front-wheel drive cars have four CV joints: one inner joint and one outer joint on each of the vehicle's two drives hafts or half shafts. The CV joint that attaches one end of each half shaft to the differential portion of the transaxle is called an inboard. Inboard or plunge joints must accommodate the in-and-out movement of the half shafts as the suspension operates. The CV joint at the other end of the half shaft is called an outboard or fixed joint.

c) Describe principle of working of differential with sketch.

Ans: The rotating motion (Torque) is supplied from the engine through the transmission, to propeller shaft, which runs to the final drive unit that contains the differential. A spiral bevel pinion gear takes its drive from the end of the propeller shaft, and is encased within the housing of the final drive unit. This meshes with the large spiral bevel ring gear, known as the crown wheel. The crown wheel gear is attached to the differential carrier or cage, which contains the 'sun' and 'planet' wheels or gears. The carrier is connected to both the side gears only through the planet gear. Torque is transmitted to the side gears through the planet gear. The planet gear revolves around the axis of the carrier, driving the side gears.

A, drive shaft; B, axle drive shaft; C, differential gears; D, differential housing attached to bevel gears; E, bevel-gear transmission.

Fig. Bevel gear differential.

If the resistance at both wheels is equal, the planet gear revolves without spinning about its own axis, and both wheels turn at the same rate. If the left side gear encounters resistance, the planet gear spins as well as revolving, allowing the left side gear to slow down, with an equal speeding up of the right side gear. When the vehicle is traveling in a straight line, there will be no differential movement of the planetary system of gears other than the minute movements necessary to compensate for slight differences in wheel diameter, undulations in the road. If the vehicle is making a turn, the outer wheel will make more rotations because it has further to travel, and the inner wheel will make fewer rotations as it has less distance to travel. This also means the differential side gears travel at two different speeds. When the differential side gears rotate at two different speeds, they cause the pinions to rotate on their shafts. The pinions walk around the slower side gear and force the other side gear to turn faster or speed up. The pinion rotates as it travels between the two side gears.

d) Explain necessity and types of loads acting on rear axle.

Ans: The axle shaft transmits the drive from the differential sun wheel to the rear hub. Various forces and torques experienced by the rear axle are weight of the body, driving thrust, torque reaction and side thrust. There is a force on the axle casing to rotate called torque reaction. The braking torque on the axle casing is opposite in direction to the torque reaction.

Loads acting on the rear axle The rear live axle half shafts have to withstand the following loads:

1. Shearing force due to vehicle weight.

2. End thrust caused by the side forces on account of cornering, side wind etc.

3. Bending moment on account of the offset of the vehicle load and the end thrust.

4. Driving torque.

e) Sketch and describe any two types of rear axle casings.

Ans: The casing used now days is either a banjo or carrier-type. In the past a split (trumpet) casing was occasionally used. The type of axle casing used decides the method for the removal of the final drive.

Fig. Two types rear axle casing. Split type In this type the axle casing is made in two halves and then bolted together for assembly. This type has a major disadvantage that in case of any fault, whole of axle has to be removed as a unit and then disassembled. This type is absolute now. In the split type axle arrangement a central housing contains the final drive and it is fitted with a tube on each side to carry the half axles and bearings in all types the inner ends of the half shafts are connected to the gears of the differential. Banjo type In the banjo or Separate Carrier axle, the axle is a single unit and the final drive assembly is carried in a separate casing which is bolted to the axle housing. The banjo construction is often used for the axle cases of the smaller and higher vehicles. This type of axle of one-piece type, shaped like a banjo. The two half shafts are pull from sides. Therefore in case of any need for repairs, the half shafts can be taken out directly from the sides and the differential assembly removed by opening bolts only. On some banjo axles a domed plate is bolted to the rear face of the casing. Removal of this plate provides excess to the final drive gears.

f) Give one example of tyre nomenclature and write meaning of each term.

Ans: There's a lot of useful information molded into the sidewall of a tyre. It shows the name of the tyre, its size, whether it is tubeless or tube type, the tyre grade, speed rating, the maximum load, maximum inflation, an important safety warning, and more. A popular size for passenger cars is, for example:

205/45R16 83 V Where: '205' represents the approximate width of the tyre in millimeters '45' represents the sidewall height as a percentage of the width of the tyre - 45% of 205mm in this instance. 'R' represents the construction type - in this, as in almost all modern tyres, denotes a RADIAL construction. '16' represents the diameter of the wheel measured in inches. '83' represents the load index. 'V' represents the speed rating.


a) Write functions of wheel. Describe with sketch construction of alloy wheel.

Ans: Wheels and rims are the significant parts of any vehicle. Wheels are circular rings on which automobile tires are fitted. The rim is the periphery of the wheel and the tire is fitted upon the wheel. The rim is actually the ring of wheel and the center of wheel is connected to the rim. The rim and center together make up the entire wheel. Both wheels and rims are integral parts of all automobiles. They play a significant role in the appearance and performance of a vehicle. Automotive wheels are typically made from pressed and welded steel, or a composite of light weight metal alloys, such as aluminum or magnesium. These alloy wheels may be either cast or forged. The mounted tire and wheel assembly is then bolted to the vehicle's hub. A decorative hubcap and trim ring may be placed over the wheel. These wheels based on the use of light metals such as aluminium and magnesium has become popular in the market. Tires are mounted onto wheels that have most often had integral rims on their outer edges to hold the tire.

Fig. Wheel construction.

b) Compare Tubed tyre with Tubeless tyre.

Ans: Comparison between tube tyre and tubeless tyre:

Tube tyre Tubeless tyres .A tube tyre consists of a tube of air that is placed inside the tyre and weighs more. It has less fuel efficiency and safety. They have shorter life than tubeless. It has more components, generates heat while on the move and causes vibrations.

A tubeless tyre weighs less and reduces un-sprung weight of the vehicle. Safety and more fuel efficiency. They last longer than tubes. Its resistance when driving is much lower and has less friction, making it more economical.

c) State types of tyres based on construction and compare them with each other.

An: Types of Tyres Many tires used in industrial and commercial applications are non-pneumatic, and are manufactured from solid rubber and plastic compounds via molding operations. Semi-pneumatic tires have a hollow center, but they are not pressurized, have also been designed for automotive use. There are two basic types of tire construction that mud, all terrain and street tires use as their foundation. They are bias-ply and radial designs. Each type of tire construction has its own unique set of characteristics that are the key to its performance, whether on road or off road and these characteristics can help to define the purpose of the tire. 1) Radial The radial is a type of tire that is constructed with rubber coated, reinforcing belts that are assembled parallel and run from side to side, bead to bead at an angle of 90 degrees to the circumferential centerline of the tire. This makes the tire more flexible which reduces rolling resistance to improve fuel economy. The belts may be cord or steel. The advantages of this construction include longer tread life, better steering control, and lower rolling resistance. Disadvantages of the radial tire include a harder ride at low speeds on rough roads and in the context of off-roading, decreased "self-cleaning" ability and lower grip ability at low speeds.

2) Bias or cross ply The bias ply tire construction utilizing rubber-coated layers known as plies composed of textile cords, usually nylon and sometimes Kevlar. The plies layered diagonal from one bead to the other bead at about a 30 degree angle. One ply is set on a bias in one direction as succeeding plies are set alternately in opposing directions as they cross each other and the ends are wrapped around the bead wires, anchoring them to the rim of the wheel. The design allows the entire tire body to flex easily, providing a smooth ride on rough surfaces. The major disadvantages of a bias tire: increased rolling resistance and less control and traction at higher speeds.

3) Belted bias A belted bias tire starts with two or more bias-plies to which stabilizer belts are bonded directly beneath the tread. This construction provides smoother ride that is similar to the bias tire, while lessening rolling resistance because the belts increase tread stiffness. The plies and belts are at different angles, which improve performance compared to non-belted bias tires. The belts may be cord or steel.

d) Sketch the arrangement of live rear axle and describe how torque transmission takes place ?

Ans

Fig. The semi floating axle.

The vehicle with non-independent rear suspension uses either a dead axle or a live axle. The dead axle only supports the weight of the vehicle, but the live axle besides fulfilling this task, contains a gear and shaft mechanism to drive the road wheels. The arrangements for supporting the road-wheels on live axles and providing the driving traction use an axle-hub mounted on to the axle-casing and supported by ball or roller-bearing. The axle shaft transmits the drive from the differential sun wheel to the rear hub.There are several types of rear axle designs: semi floating, three-quarter floating, and full floating. However the semi- and full-floating types are the most common. The semi floating axle is used in passenger vehicles and light trucks. In vehicles equipped with this type of axle, the shaft, as well as the housing, supports the weight of the vehicle. The inner end of the axle is carried by the side gears in the differential housing. This relieves the axle shafts of the weight of the differential and the stresses caused by its operation that are taken by the axle housing. The inner ends of the axle transmit only turning effort, or torque, and are not acted upon by any other force. The outer end is carried by a bearing located between the shaft and the housing It transfers the load from the shaft to the housing. The axle shafts take the stresses caused by turning, skidding, or wobbling of the wheels. The axle shafts are flanged or tapered on the ends. When the tapered axle is used, the brake drum and hub are pressed onto the shafts, using keys to prevent the assemblies from turning on the shafts. In some cases, the outer ends of the shafts may have serrations or splines to correspond with those on the drum and hub assembly.

e) What is meant by Double reduction axle ? State its two applications.

Ans: Concept of double reduction axle The vehicles carrying heavy loads and requiring high torque double reduction drives are used. The reduction required in such vehicles is much larger, i.e. 5:1 to 10:1. If this large reduction is obtained in one stage, the gear ratio being very large either the pinion will be too small having very few teeth, or it will be too weak and inefficient or the crown wheel will be too large, reducing the

ground clearance drastically. Double-reduction final drives are used for heavy-duty trucks and buses.

Fig. Double Reduction Drive Axle.

In the final drives shown in fig., there is a single fixed gear reduction. With 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 reduction final drive. Referring to fig., notice that 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 primary ring gear, driving a large helical gear which is attached to the differential case.

f) Draw a neat sketch of full floating type rear axle and lable the parts.

Ans:

Fig. Full-floating axle.

Automobile Transmission System Solved paper-III

By Prof. Syed J.M.


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(i) Why is the Frame narrow at the front?

Ans: Automotive frame is narrow in the front for providing short turning radius to front wheels. It widens out at the rear side to provide larger space in the body.

(ii) What are the loads acting on the Chassis Frame?

Ans: Various loads acting on the frame are: 1. Short duration Load - While crossing a broken patch. 2. Momentary duration Load - While taking a curve. 3. Impact Loads - Due to the collision of the vehicle. 4. Inertia Load - While applying brakes. 5. Static Loads - Loads due to chassis parts.

(iii) State the functions of the Frame.

Ans: Functions of frame: 1. To carry load of the passengers or goods carried in the body. 2. To support the load of the body, engine, gear box etc. 3. To withstand the forces caused due to the sudden braking or acceleration 4. To withstand the stresses caused due to the bad road condition. 5. To withstand centrifugal force while cornering.

(iv) State the materials for clutch lining.

Ans: The clutch disc is installed between the pressure plate assembly and the flywheel. Various materials have been used for the disc friction facings, including asbestos in the past. Modern clutches typically use a compound organic resin with copper wire facing or a ceramic material. A typical coefficient of friction used on a friction disc surface is 0.35 for organic and 0.25 for ceramic. Ceramic materials are typically used in heavy applications such as trucks carrying large loads or racing, though the harder ceramic materials increase flywheel and pressure plate wear.

(v) State the types of Gear Boxes.

Ans: Gearbox (transmission) has different types. 1) Sliding-mesh, 2) Constant-mesh, 3) Synchro-mesh, 4) Automatic gearbox

Ssome of them are old-fashion and had been replaced, and some are in use in modern cars.

(vi) Why hallow propeller shaft is used for transmission?

Ans: The propeller shaft is a solid or hollow tube which transmits power from the gear box to the rear axle. Drive shafts are usually hollow in order to weigh less, but of a large diameter so that they are strong. The propeller shaft either made of steel/aluminum or composite material.

(vii) What is function of differential gears?

Ans: On live axles, one wheel must turn at a different speed than the other as the vehicle goes around a corner. Additional gearing is required to allow for the difference in the speed of the wheels. The gearing assembly designed to do this job is called a differential.

(viii) What is differential lock?

Ans: A differential lock or diff-lock literally locks out the differential action, thus forcing the torque to be split equally between two wheels or two axles. This forces both wheels to turn in unison, regardless of the traction available to either wheel individually.

b) Attempt any TWO of the following:

(i) Classify vehicle layout with respect to:

1) Location of engine 2) No. of live axles 3) Arrangement of engine 4) Application.

Ans: Many different combinations of engine location and driven wheels are found in practice, and the location of each is dependent on the application the vehicle will be used for.

1) Location of engine:- a) Front engine, front wheel drive, b) Rear engine, rear wheel drive. c) Front engine, rear wheel drive.

2) No. of live axles: - a) Front-wheel-drive layouts (FWD), b) Rear-wheel-drive layouts (RWD), c) Fourwheel drive layout (FWD).

3) Arrangement of engine:-a) A transverse engine FF designs, b) FR longitudinal engine designs,

c) Mid-engine, rear wheel drive.

4) Application:- a) Two-wheel drive, b) Four-wheel drive, c) All-wheel drive. (ii) Draw a neat labelled sketch of clutch used in heavy vehicle.

Fig. Multi plate clutch.

(iii) State two applications of multiplate clutch and centrifugal clutch.

Ans: 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. Centrifugal clutches are often used in mopeds, under bones, lawnmowers, go-karts, chainsaws, and mini bikes..


a) Compare between a dry clutch and wet clutch on the basis of construction, torque transmission, heat dissipation and application. Ans:



b) Explain construction and working of clutch plate with neat sketch.

Ans: The clutch plate or driven member consists of a round metal plate attached to a splined hub. The outer portion of the round plate is covered with a friction material of molded or woven asbestos and is riveted or bonded to the plate. The thickness of the clutch plate and/or facings may be warped to give a softer clutch engagement. Coil springs are often installed in the hub to help provide a cushion against the twisting force of clutch engagement. The splined hub is mated to (and turns) a splined transmission shaft when the clutch is engaged.

Fig. A clutch disc.

c) Explain hydraulic clutch operation mechanism with the help of block diagram.

Ans: Hydraulically-operated Linkage: A more convenient way to transmit force and movement is by hydraulic linkage in which the fluid is forced through a flexible plastic pipeline, spun between the foot-pedal and the clutch bell-housing. A master-cylinder, mounted on the bulkhead and a push-rod joining the clutch-pedal to the sliding piston, provides the control of the clutch action. A slave cylinder unit containing the piston is installed on an extension formed on the bell-housing flange. The slave piston relays the slightest movement to the fork-lever through the slave pushrod.

Fig. Clutch linkage mechanism- Hydraulic. Depressing the clutch pedal creates pressure in the clutch master cylinder, actuating the slave cylinder which, in turn, moves the release arm and disengages the clutch. When the pedal is

released, engagement of the clutch occurs due to which the fluid returns to the master-cylinder and its reservoir. Hydraulic types of clutch operating systems are normally found in heavy construction equipment where extreme pressure is required to operate the clutch.

d) Explain construction and working of fluid coupling with neat sketch.

Ans: A fluid coupling has been used in automobile transmissions as an alternative to a mechanical clutch. Fluid couplings work on the hydrodynamic principle.

Fig. Fluid coupling.

It consists of a pump-generally known as impeller and a turbine generally known as rotor, both enclosed suitably in a casing. The impeller and the rotor are bowl-shaped and have large number of radial vanes. They face each other with an air gap. Oil is filled in the fluid coupling from the filling plug provided on its body. The impeller or pump typically is connected to the flywheel of the engine and thus is turned by the engine's crankshaft. The turbine is connected to the input shaft of the transmission. The power is transmitted by virtue of the fluid filled in the coupling. The impeller when rotated imparts velocity and energy to the fluid, which is converted into mechanical energy in the rotor thus rotating it. The fluid follows a closed circuit of flow from impeller to rotor through the air gap at the outer periphery and from rotor to impeller again through the air gap at the inner periphery. As a fluid coupling operates kinetically, low viscosity fluids are preferred. Multi-grade motor oils or automatic transmission fluids are used.

e) Explain the working of clutch used in two wheeler vehicle.

Ans: Centrifugal clutch: This clutch system employs centrifugal force to automatically engage the clutch when the engine rpm rises above a threshold and to automatically disengage the clutch when the engine rpm falls low enough. The most common types have friction pads or shoes attached to the driven shaft, rotating inside a clutch bell attached to the output shaft. On the center shaft there are an assorted number of extension springs, which connect to a clutch shoe. When the center shaft spins fast

enough, the springs extend causing the clutch shoes to engage the friction face. As the load increases, the speed drops, disengaging the clutch, letting the speed rise again and reengaging the clutch..


f) Draw a neat labelled sketch of sliding mesh gear box in reverse gear engaged position. Ans:


a) Explain with neat sketch construction and working of torque converter.

Ans: There are four components inside the very strong housing of the torque converter- Pump, Turbine, Stator, and Transmission fluid. The housing of the torque converter is bolted to the flywheel of the engine, so it turns at whatever speed the engine is running at. The fins that make up the pump of the torque converter are attached to the housing, so they also turn at the same speed as the engine. As pump spins, fluid is flung to the outside and as fluid is flung to the outside, a vacuum is created that draws more fluid in at the center. The fluid then enters the blades of the turbine, which is connected to the transmission.

Fig Torque converter.

The turbine causes the transmission to spin, which basically moves the vehicle. The blades of the turbine are curved. This means that the fluid, which enters the turbine from the outside, has to change direction before it exits the center of the turbine. It is this directional change that causes the turbine to spin. The fluid exits the turbine at the center, moving in a different direction than when it entered. If the fluid were allowed to hit the pump, it would slow the engine down, wasting power. This is why a torque converter has a stator. The torque converter turbine is where it connects to the transmission.

b) Explain with sketch synchromesh device used in gear box.

Ans: In modern cars, synchromesh devices are used in gear boxes to synchronize the rotation of gears that are about to be meshed. This gear box is provided with synchromesh devices by which two gears to be engaged are first brought into frictional contact which they are engaged smoothly. When the gear lever is moved, the synchronizer conemeets with a similar cone on the pinion. Due to the friction, the rotating pinion is made to rotate at the same speed as the synchromesh unit. To give a positive drive further movement of the gear lever enables the coupling to override several spring loaded balls and the coupling engages with the dog on the ride of the pinion. Since both pinion and synchromesh unit are moving at the same speed, this engagement is done without noise or damage to the dogs.


c) Draw a labelled sketch of gear selector mechanism with gear lever on top of gear box.

Ans:

d) Explain construction and working of transfer case with neat sketch.

Ans: A transfer case is a part of a four-wheel-drive system found in four-wheel-drive and all-wheel-drive vehicles. The transfer case is connected to the transmission and also to the front and rear axles by means of drive shafts. It is also referred to as a "transfer gear case", "transfer gearbox, transfer box" or "jockey box". The transfer case receives power from the transmission and sends it to both the front and rear axles. This can be done with a set of gears, but the majority of transfer cases manufactured today is chain driven.

Fig Transfer case.

On some vehicles, such as four-wheel-drive trucks or vehicles intended for off-road use, this feature is controlled by the driver. The driver can put the transfer case into either "two-wheel-drive" or "four-wheel-drive" mode. This is sometimes accomplished by means of a shifter, similar to that in a manual transmission. On some vehicles this may be electronically operated by a switch instead. Some vehicles, such as all-wheel-drive sports cars, have transfer cases that are not selectable. Such a transfer case is permanently "locked" into all-wheel-drive mode.

4) What is double declutching? Explain.

Ans: In constant mesh gear box, for smooth engagement of dog clutches it is necessary that the speed of main shaft and sliding dog clutch must be equal. To obtain lower gear, the speeds of the clutch shaft, lay shaft and main shaft must be increased. This is done by double declutching. The clutch is disengaged and the gear is brought to neutral. Then the clutch is engaged and accelerator pedal pressed to increase the speed of the main shaft gears. Again the clutch is disengaged and the gear moved to the required lower gear and the clutch is again engaged. As the clutch is disengaged twice, it is called double declutching.

5) Explain Hotchkiss drive used in vehicle.

Ans: The Hotchkiss drive is made up of a drive shaft connected to the transmission output shaft and the differential pinion gear shaft. U-joints are used in the front and rear. The Hotchkiss drive transfers the torque of the output shaft to the differential. Sometimes this drive comes in two pieces to reduce vibration and make it easier to install with three U-joints. The two-piece types need ball bearings in a dust proof housing as center support for the shafts. The Hotchkiss drive requires that the springs be rigid enough to withstand the twisting action (torque) of the rear axle and the driving and braking forces that the springs transmit to the frame.

Fig. Hotchkiss drive.

Rubber is added into this arrangement for noise and vibration reduction. In the Hotchkiss drive, slip-splines or a plunge-type (ball and trunnion u-joint) eliminate thrust transmitted back up the driveshaft from the axle, allowing simple rear-axle positioning using parallel leaf springs. The Hotchkiss drive uses two universal joints which has the effect of canceling the speed fluctuations and gives a constant speed even when the shaft is no longer straight. The Hotchkiss drive has the

traction forces transmitted to the car frame by using other suspension components such as leaf springs or trailing arms.


a) What is the difference between three speed and four speed gearbox? Where are these used?

Ans: The power flow through the three-speed transmission can be charted in the same manner as the four-speed transmission. As a rule, the power flow in high gear is usually straight through the transmission-input shaft to the main shaft, which would be locked together. When in the reduction gears, the power flow is through the input shaft, to the cluster gear unit, and through the reduction gear to the main shaft. The transmission gear ratios allow the engine to be operated most efficiently under a variety of driving and load conditions. A power (lower) gear ratio starts the vehicle moving and speed gear ratios keep the vehicle moving. By comparing gear ratios, driver can see which transmission transmits more power to the drive wheels as the name indicates the three speeds gearbox has three gear ratios where as the four speeds gearbox has four speed gear ratios. This provides more power to the drive wheels, compared to the three-speed transmission's low gear. Three sped gearbox generally used in light vehicles and the four speed gearbox is used in medium vehicles like cars and vans.

b) Describe with neat sketch construction and working of propeller shaft.

Ans: The propeller shaft consists of universal joints, sleeve and sliding shaft. It transfers engine torque to the rear axle through one or more universal joints.The flanges connect the propeller shaft to the gearbox. The main bearing support and guide the propeller shaft. Universal or U-joints allow the drive shaft to flex when the drive angle changes. The shaft must be quite straight and balanced to avoid vibrating. Since it usually turns at engine speeds, a lot of damage can be caused if the shaft is unbalanced, or bent.

Fig. Drive shaft with universal joints at each end. The splines on the ends at the propeller shaft fit perfectly into the splines in the sleeve. This allows a length variation between the driving and the driven unit to vary slightly without damaging the output and input bearings. The drive shaft can be either open or enclosed, depending on the type of drive used. The Hotchkiss drive has an open drive shaft that operates a rear axle assembly mounted on springs. Torque tubes differ from the Hotchkiss design in that a solid drive shaft is enclosed in a hollow torque tube and rotates within a support bearing to prevent whipping.

c) Explain loads acting on rear axle.

Ans: Loads acting on the rear axle The rear live axle half shafts have to withstand the following loads:

1. Shearing force due to vehicle weight.

2. End thrust caused by the side forces on account of cornering, side wind etc.

3. Bending moment on account of the offset of the vehicle load and the end thrust.

4. Driving torque.

d) Explain banjo type rear axle casing. Ans: In the banjo or Separate Carrier axle, the axle is a single unit and the final drive assembly is carried in a separate casing which is bolted to the axle housing. The banjo construction is often used for the axle cases of the smaller and higher vehicles. This type of axle of one-piece type, shaped like a banjo. The two half shafts are pull from sides. Therefore in case of any need for repairs, the half shafts can be taken out directly from the sides and the differential assembly removed by opening bolts only.

Fig.Banjo type rear axle casing.

The tubular axle section of this casing is built up of steel pressings, which is welded together and suitably strengthened to withstand the bending load. On some banjo axles a domed plate is bolted to the rear face of the casing. Removal of this plate provides excess to the final drive gears and in Cases where the axle shaft is secured to the differential, this enables the axle shaft

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