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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.
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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.
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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.
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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
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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.
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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..
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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.
3. Attempt any FOUR of the following:
a) Draw a neat sketch of torque converter.
Ans:
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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.
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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.
4. Attempt any FOUR of the following:
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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.
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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
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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
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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.
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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.
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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:
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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.
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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.
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Automobile Transmission System Solved paper-II
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) 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.
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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.
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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.
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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:
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) 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
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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.
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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.
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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,
Fig Centrifugal clutch.
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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.
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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.
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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.
Fig. Synchromesh gearbox.
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.
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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.
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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.
5. Attempt any FOUR of the following:
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.
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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.
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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.
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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.
6. Attempt any FOUR of the following:
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.
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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.
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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
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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.
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Automobile Transmission System Solved paper-III
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) 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.
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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,
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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..
2. Attempt any FOUR of the following:
a) Compare between a dry clutch and wet clutch on the basis of
construction, torque transmission, heat dissipation 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.
b) Explain construction and working of clutch plate with neat
sketch.
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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
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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
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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) Draw a neat labelled sketch of sliding mesh gear box in
reverse gear engaged position. Ans:
3. Attempt any FOUR of the following:
a) Explain with neat sketch construction and working of torque
converter.
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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.
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Fig. Synchromesh gearbox.
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.
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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
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traction forces transmitted to the car frame by using other
suspension components such as leaf springs or trailing arms.
4. Attempt any FOUR of the following:
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.
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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