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H SMUKH GOSW MI COLLEGE OF ENGINEERING
[Study Material] | [Mr. Kartik Suthar]
[AUTOMOBILE SYSTEM] [DEPARTMENT OF AUTOMOBILE]
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Q. Explain various vehicle layout and also state advantage and
disadvantage for front engine front wheel drive and rear engine
rear wheel drive.
In automotive design, the automobile layout describes where on the vehicle
the engine and drive wheels are found. Many different combinations of engine location
and driven wheels are found in practice, and the location of each is dependent on the
application for which the vehicle will be used. Factors influencing the design choice
include cost, complexity, reliability, packaging (location and size of the passenger
compartment and boot),weight distribution, and the vehicle's intendedhandling
characteristics.
Front-wheel-drive layouts
Front-wheel-drive layouts are those in which the front wheels of the vehicle are driven.
The most popular layout used in cars today is the front-engine, front-wheel drive, with
the engine in front of the front axle, driving the front wheels.
As the steered wheels are also the driven wheels, FF (front-engine, front-wheel-drive
layout) cars are generally considered superior to FR (front-engine, rear-wheel-drive
layout) cars in conditions such as snow, mud, or wet tarmac. The weight of the engine
over the driven wheels also improves grip in such conditions. However, powerful cars
rarely use the FF layout because weight transference under acceleration reduces the
weight on the front wheels and reduces their traction, limiting the torque which can be
utilized. Electronic traction control can avoid wheel spin but largely negates the benefit of
extra torque/power.
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Advantages
Interior space: Since the powertrain is a single unit contained in the engine
compartment of the vehicle, there is no need to devote interior space for
a driveshaft tunnel or rear differential, increasing the volume available for
passengers and cargo.
Weight: Fewer components usually means lower weight.
Improved fuel efficiency due to less weight
Improved drivetrain efficiency: the direct connection between engine and
transaxle reduce the mass and mechanical inertia of the drivetrain compared to a
rear-wheel-drive vehicle with a similar engine and transmission, allowing
greater fuel economy.
Placing the mass of the drivetrain over the driven wheels moves the centre of
gravity farther forward than a comparable rear-wheel-drive layout,
improving traction and directional stability on wet, snowy, or icy surfaces.
Disadvantages
Front-engine front-wheel-drive layouts are "nose heavy" with more weight
distribution forward, which makes them prone to understeer, especially in high
horsepower applications.
Torque steer is the tendency for some front-wheel-drive cars to pull to the left or
right under hard acceleration. It is a result of the offset between the point about
which the wheel steers (it is aligned with the points where the wheel is connected
to the steering mechanisms) and the centroid of its contact patch. In some towing
situations, front-wheel-drive cars can be at a traction disadvantage since there
will be less weight on the driving wheels. Because of this, the weight that the
vehicle is rated to safely tow is likely to be less than that of a rear-wheel-drive or
four-wheel-drive vehicle of the same size and power.
Traction can be reduced while attempting to climb a slope in slippery conditions
such as snow- or ice-covered roadways.
Due to geometry and packaging constraints, the CV joints (constant-velocity
joints) attached to the wheel hub have a tendency to wear out much earlier than
the universal joints typically used in their rear-wheel-drive counterpart.
Turning circle — FF layouts almost always use a Transverse engine ("east-west")
installation, which limits the amount by which the front wheels can turn, thus
increasing the turning circle of a front-wheel-drive car compared to a rear-wheel-
drive one with the same wheelbase.
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Rear-wheel-drive layouts
Advantages
Even weight distribution — The layout of a rear-wheel-drive car is much closer to
an even fore-and-aft weight distribution than a front-wheel-drive car, as more of
the engine can lie between the front and rear wheels (in the case of a midengine layout, the entire engine), and the transmission is moved much farther
back.
Weight transfer during acceleration — During heavy acceleration, weight is placed
on the rear, or driving wheels, which improves traction.
Better braking — the more even weight distribution helps prevent lockup from the
rear wheels becoming unloaded under heavy braking.
Towing — Rear-wheel drive puts the wheels which are pulling the load closer to
the point where a trailer articulates, helping steering, especially for large loads.
Disadvantages
On snow, ice and sand, rear-wheel drive loses its traction advantage to front- or all-
wheel-drive vehicles, which have greater weight on the driven wheels. This issue is
particularly noticeable on pickup trucks, as the weight of the engine and cab will
significantly shift the weight from the rear to the front wheels.
Some rear engine cars (e.g., Porsche 911) can suffer from reduced steering ability
under heavy acceleration, because the engine is outside the wheelbase and at the
opposite end of the car from the wheels doing the steering although the engine
weight over the rear wheels provides outstanding traction and grip during
acceleration.
A rear-wheel drive vehicle with four-wheel drive, compared to a front-wheel drive
vehicle with four-wheel drive, will have a less efficient interior packaging since the
transmission is often under the front passenger compartment between the two seats,
whereas the latter can package all the components under the hood.
Increased weight — The components of a rear-wheel-drive vehicle's power train areless complex, but they are larger. The driveshaft adds weight. There is extra sheet
metal to form the transmission tunnel. There is a rear axle or rear half-shafts, which
are typically longer than those in a front-wheel-drive car. A rear-wheel-drive car will
weigh slightly more than a comparable front-wheel-drive car (but less than four-
wheel drive).
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Four-wheel-drive layouts
Most 4WD layouts are front-engine and are derivatives of earlier front-engine, two-
wheel-drive designs. They fall into two major categories:
Front-engine, rear-wheel drive derived 4WD systems, standard in most sport utility
vehicles and in passenger cars, (usually referred to “front engine, rear-wheel
drive/four-wheel drive”).
Transverse and longitudinal engine 4WD systems derived almost exclusively
from front-engine, front-drive layouts, fitted to luxury, sporting and heavy duty
segments, for example the transverse-engine Mitsubishi 3000GT VR-4 and Toyota
RAV4 and the longitudinal-engine Audi Quattro and most of the Subaru line.
Rear-engine, rear-wheel-drive layout
Most of the traits of the RR configuration are shared with the mid-engine, or MR.
Placing the engine near the driven rear wheels allows for a physically smaller, lighter,
less complex, and more efficient drivetrain, since there is no need for a driveshaft,
and the differential can be integrated with the transmission, commonly referred to as
a transaxle.
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Rear-engine, front-wheel-drive layout
A rear-engine, front-wheel-drive layout is one in which the engine is behind the rear
wheels, but drives the front wheels via a driveshaft, like a conventional front-engine,
rear-wheel-drive vehicle traveling in reverse.
Q.Briefly explain the shock absorber in suspension system.
Let's start our discussion of shock absorbers with one of very important point: despite
what many people think, conventional shock absorbers do not support vehicle weight.
Instead, the primary purpose of the shock absorber is to control spring and
suspension movement. This is accomplished by turning the kinetic energy of
suspension movement into thermal energy, or heat energy, to be dissipated through
the hydraulic fluid.
Shock absorbers are basically oil pumps. A piston is attached to the end of the piston
rod and works against hydraulic fluid in the pressure tube. As the suspension travels
up and down, the hydraulic fluid is forced through tiny holes, called orifices, inside
the piston. However, these orifices let only a small amount of fluid through the
piston. This slows down the piston, which in turn slows down spring and suspension
movement.
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The amount of resistance a shock absorber develops depends on the speed of the
suspension and the number and size of the orifices in the piston. All modern shock
absorbers are velocity sensitive hydraulic damping devices - meaning the faster the
suspension moves, the more resistance the shock absorber provides. Because of this
feature, shock absorbers adjust to road conditions. As a result, shock absorbers reduce
the rate of: Bounce,Roll or sway,Brake dive and Acceleration squat.
Shock absorbers work on the principle of fluid displacement on both the compression and
extension cycle. A typical car or light truck will have more resistance during its extension
cycle then its compression cycle. The compression cycle controls the motion of a vehicle's
unsprung weight, while extension controls the heavier sprung weight.
Compression cycle
During the compression stroke or downward movement, some fluid flows through the
piston from chamber B to chamber A and some through the compression valve into the
reserve tube. To control the flow, there are three valving stages each in the piston and in
the compression valve. At the piston, oil flows through the oil ports, and at slow piston
speeds, the first stage bleeds come into play and restrict the amount of oil flow. This
allows a controlled flow of fluid from chamber B to chamber A.
At faster piston speeds, the increase in fluid pressure below the piston in chamber B
causes the discs to open up away from the valve seat.
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At high speeds, the limit of the second stage discs phases into the third stage orifice
restrictions. Compression control, then, is the force that results from a higher pressure
present in chamber B, which acts on the bottom of the piston and the piston rod area.
Extension cycle
As the piston and rod move upward toward the top of the pressure tube, the volume of
chamber A is reduced and thus is at a higher pressure than chamber B. Because of this
higher pressure, fluid flows down through the piston's 3-stage extension valve into
chamber B.
However, the piston rod volume has been withdrawn from chamber B greatly increasing
its volume. Thus the volume of fluid from chamber A is insufficient to fill chamber B. The
pressure in the reserve tube is now greater than that in chamber B, forcing the
compression intake valve to unseat. Fluid then flows from the reserve tube into chamber
B, keeping the pressure tube full.
Extension control is a force present as a result of the higher pressure in chamber A,
acting on the topside of the piston area
Advantages:
Improves handling by reducing roll, sway and dive
Reduces aeration offering a greater range of control over a wider variety of road
conditions as compared to non-gas units
Reduced fade - shocks can lose damping capability as they heat up during use. Gas
charged shocks could cut this loss of performance, called fade
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Q. What is the function of a clutch? Write down principle of
clutch.Explain single plate clutch.
Clutch and it's functions:
Clutch is a device used in the transmission system of a motor vehicle to engageand disengage the engine to the transmission. Thus the clutch is located between
the engine and the transmission. Typically a clutch consits of clutch fork, thrust
bearing, diaphragm, cover, pressure plate, clutch plate, and a flywheel as shown
below in the figure.
Functions of a clutch are as follows,
When the clutch is engaged, the power flows from the engine to the rear wheels through
the transmission system and the vehicle moves.
When the clutch is disengaged, the power is not transmitted to the rear wheels and the
vehicles stops while the engine is still running.
The clutch is disengaged when starting the engine, when shifting the gears, when stopping
the vehicle and when idling the engine.
The clutch is kept engaged when the vehicle is moving.
The clutch also permits the gradual taking up of the load. When properly operated, it
prevents jerky motion of the vehicle.
Principle of Operation of Clutch:
The clutch works on the principle of friction. When two friction surfaces are
brought in contacts with each other and pressed they are united due to the
friction between them. If one is revolved, the other will also revolve. The friction
between the two surfaces depends upon the area of the surfaces, pressure applied
upon them and coefficient of friction of the surface materials. The two surfaces
can be separated and brought into contact when required.
One surface is considered as driving member and the other as driven member,
the driving member is kept rotating. When the driven member is brought in
contact with the driving member, it also starts rotating. When the driven member,
it also starts rotating. When the driven member is separated from the driving
member it does not revolve.
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Single Plate Clutch :- A single plate friction clutch consisting of a clutch disk
between the flywheel and a pressure plate. Both the pressure plate and the
flywheel rotates with the engine crankshaft or the driving shaft. And both sides of
clutch disc are faced with friction material(usually of ferrodo).The clutch disc is
mounted on the hub which is free to move axially along the splines of the driven
shaft but not turnable towards the transmission input shaft.
The pressure plate pushes the clutch plate towards the flywheel by a set of strong
springs which are arranged radially inside the body. The three levers(also known
as release levers or fingers) are carried on pivots suspended from the case of the
body. These are arranged in such a manner so that the pressure plate moves
away from the flywheel by the inward movement of a thrust bearing. The bearing
is mounted upon a forked shaft and moves forward when the clutch pedal is
pressed.
By pressing the clutch pedal down, the thrust bearing moves towards the flywheelby means of linkage force, and press the longer end of the lever inwards. Due to
this, the lever turns on their suspended pivot and forces the pressure plate to
move away from the flywheel this action compresses the clutch springs which in
turn moves the pressure plate away from the clutch plate and remove the
pressure from the clutch plate. This enables the clutch plate to move back from
the flywheel and thus, the driven shaft becomes stationary.By moving the foot
back from the clutch pedal, the thrust bearing moves back and allows the spring
to extend which pushes the clutch plate backwards the flywheel.This engages the
flywheel and the clutch plate which starts the motion of the driven shaft.
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Q. Explain various types of resistance and power required for
propulsion.
Power for Propulsion
The motion of a vehicle moving on a road is resisted by aerodynamic forces,
known as wind or air resistance, and road resistance which is generally termed as
rolling resistance. In addition to these two types of resistances, the vehicle has to
overcome grade resistance when it moves up on a gradient, because the weight of
the vehicle is to be lifted through a vertical distance. Hence, the power required to
propel a vehicle is proportional to the total resistance to its motion and the speed.
The calculation of engine power takes into account the losses in transmission.
Hence required engine power,
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Air Resistance
This is the resistance offered by air to the movement of a vehicle. The air
resistance has an influence on the performance, ride and stability of the
vehicle and depends upon the size and shape of the body of the vehicle, its
speed and the wind velocity. The last term should be taken into account whenindicated, otherwise it can be neglected. Hence in general, air resistance,
Rolling Resistance
The magnitude of rolling resistance depends mainly on
(a) the nature of road surface,
(b) the types of tire viz. pneumatic or solid rubber type,
(c) the weight of the vehicle, and
(d) the speed of the vehicle.
The rolling resistance is expressed as
Where W = total weight of the vehicle, N
and K = constant of rolling resistance and depends on the nature of road
surface and types of tires = 0.0059 for good roads = 0.18 for loose sand roads
= 0.015, a representative value. A more widely accepted expression for the
rolling resistance is given by
Where V = speed of the vehicle, km/hr.
Mean values of a and 6 are 0.015 and 0.00016 respectively.
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Grade Resistance
The component of the weight of the vehicle parallel to the gradient or the
slope on which it moves is termed as ‘grade resistance’. Thus it depends upon
the steepness of the grade. If the gradient is expressed as 1 in 5, it means
that for every 5 meters the vehicle moves, it is lifted up by 1 meter. Hence,
grade resistance is expressed as
Q.Explain construction, working and arrangement of sliding mesh
gearbox with the help of neat sketch.
Transmission Manual Gear Box
Gear box
Introduction:-
The mechanism that transmits engine four to the rear wheel (in case of rear wheel
drive vehicle) or to the front wheel. (In front wheel drive vehicle) or to all the four
wheel (in four wheel drive vehicles) is known as a transmission system.
It comprises of the following man units.
Function of gear box:-
The gear box and its associated units perform the following function on.
A gear box assists in variation of torque (or tractates effort) produced by the
engine in accordance with the driving conditions.
A large torque is required at the start of the vehicle and a low torque at higher
speeds.
It helps in smooth running of the vehicle at different speed since variation a
torque induces.
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Types of transmission:
Several kinds of transmission are employed on auto vehicles. These can be 4 classified as
follows:
1) Manual transmission.
1) Sliding mesh gearbox.2) Constant mesh gearbox.
3) Synchromesh gearbox.
4) Synchromesh gear box with over drive.
2) Semi- Automatic transmission.
1) Electric controlled with a avid drive.
2) Electric controlled with over drive.
3) Fluid – torque drive.
3) Automatic drive.
1) Hydromantic drive.
2) Torque converter drive.
Sliding mesh gear box:
Sliding mesh gear box shown in figure.
Sliding mesh gear box
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1st Gear:
When driver wand’s to move the vehicle he engage the 1st dog to the with the
help of gear shifting levees as the dog slides on engage to the 1st gear it starts
rotate with 1st gear and tends to rotate the main shaft like 1st gear operates.
2nd Gear:
As driver move fast again he slides the second dog and makes engage with
second gear on main shaft (medium gear). As the dog engager to the second
gear it rotates with second gear and tents to rotate the main shaft with high
speed and low torque.
3rd Gear(Top gear):
To move the vehicle fast a gain the driver shift the second dog and make
engages to the third or top gear. As the dog engages to the 3rdgear the dog
rotates with gear and lends to rotate the main shaft with faster.
Constant mesh gear box:
Constant mesh gear box is the modified gear box of sliding mesh gear box.
In this type of gear box all the gears of main shaft are errantly engaged with lag
shaft gears.
Do to that the possibility of bricking teeth gets reduced as well as the noise of
gear box get ridicule.
Construction of gear box:
The various sizes of helical gears are mounted on main shaft with bearing; they
are free to rotate on main shaft.
The dogs are provided on main shaft in between two gears such that they can
slide the two spines the remaining construction is safe.
Same as sliding mesh gear box.
Working:
Constant mesh gear box shown in figure.
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Neutral gear:
When engine start and the clutch get rotate. If rotates clutch gear and lay shaft
gear, all the gears on main shaft also get rotate because the no one dog is
engage to the gear.
Reverse gear: As the driver wand’s to move the vehicle back he shifts the first dog towards
digger gear which is engages to the idler gear. As the dog engages its start
rotate with the gear in reverse or opposite direction and tends to rotate the main
shaft in reverse direction.
Over drive:
An over drive is infect a super top gear which provide a speed ration over the top
gear.
It reduces engine wear and vibration and also saved fuel.
Automatic gear box:
The parts use in automatic gear box is as follows.
1) Epicyclical gear box. (Planetary gear box)
2) Torque converter.
3) Clutch packs and brake bands.
4) Freewheel or overrunning clutch.
5) Hydraulic valve controls.
6) Shifting control.
Epicyclical gear box:
Epicyclical gear box shown in figure.
Epicyclical gear box
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An epicyclical gear box consists of two or more epicyclical gear sets.
This gear box is having sun gear planet gear and internal gear is also could
annular gear the sun gear is mounted on driving shaft and the annular gear on
driven shaft.
To captain the necessary gear combinations needed for gear reduction, direct
drive, reverse, neutral and over drive the planetary set are use in automatic gear
box.
The planetary gear set is always in mesh and consists of pinion gear mounted on
planetary carrier by shaft.
Torque converter:
The torque converter is also a kind of fluid flywheel (drive) but change in the
torque by providing variable gear ration so that additional part that is stator is
used its gear ration is maximum when starting from rest and decreases as the
vehicle gars speed.
Construction:
It uses
1) Stator.
2) A driving pump impeller.
3) Turbine.
Working:
Torque convertor shown in figure.
Torque converter
The fluid fitted in the torque converter is oil circulates under part to the other.
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The housing from one oil float B charged by the stationary blade B such way that
the oil return that pump impeller after passing through the turbine as the vehicle
picks up the speed the blade being to turn along with the other member so the
torque multiples thus the power from engine crank shaft transfer to the turbine.
Q.What is the function of transfer case in vehicle? Explain the
construction and operation of transfer case with neat sketch.
Inside of a 231 New Process Gear transfer case. Part-time/Manual, shift on the fly
A transfer case is a part of the drivetrain of four-wheel-drive, all-wheel-drive, and other
multiple powered axle vehicles. The transfer case transfers power from
thetransmission to the front and rear axles by means of drive shafts. It also synchronizes
the difference between the rotation of the front and rear wheels, and may contain one or
more sets of low range gears for off-road use.
Functions
The transfer case receives power from the transmission and sends it to both
the front and rear axles. This can be done with gears, hydraulics, or chain
drive. 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.
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Transfer cases that are designed to allow for normal road use synchronize the
difference between the rotation of the front and rear wheels,[1] in much the
same way the differential acts on a given axle. This is necessary because the
front and rear tires never turn at the same speed. Different rates of tirerotation are generally due to different tire diameters (since front and rear tires
inevitably wear at different rates) and different gear ratios in the front and
rear differentials since manufacturers will often have a slightly lower ratio in
the front vs. the rear to help with control (such as a 3.55:1 in the rear
differential and a 3.54:1 in the front differential). If the transfer case did not
make up the difference between the two different rates of rotation, binding
would occur and the transfer case could become damaged. This is also why a
transfer case that is not designed for on-road use must never be driven on dry
pavement.
Transfer cases designed for off-road use can mechanically lock the front and
rear axles when needed[2] (e.g. when one of the axles is on a slippery
surfaces or stuck in mud, whereas the other has better traction). This is the
equivalent to the differential lock.
The transfer case may contain one or more sets of low range gears for off-
road use. Low range gears are engaged with a shifter or electronic switch. On
many transfer cases, this shifter is the same as the one that selects 2WD or
4WD operation. Low range gears allow the vehicle to drive at much slower
speeds while still operating within the usable power band / RPM range of the
engine. This also increases the torque available at the axles. Low-range gears
are used during slow-speed or extreme off-road maneuvers, such
as rockcrawling, navigating dangerous roads, or when pulling a heavy load.
This feature is often absent on all-wheel-drive cars. Some very large vehicles,
such as heavy equipment or military trucks, have more than one low-range
gear.
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Q. What is the importance of differential in vehicle? Explain its
construction and working.
Most 4-wheel drive vehicles have both a front and rear differential. Thedifferential works
with your transmission to deliver power from the engine to the axle that turns your
wheels. The differential also makes turning your car possible.
Why the Differential gear is used?
Wheels receive power from the engine via a drive shaft. The wheels that receive
power and make the vehicle move forward are called the drive wheels. The main
function of the differential gear is to allow the drive wheels to turn at different
rpms while both receiving power from the engine.
Power from the engine is flowed to the wheels via a drive shaft
Consider these wheels, which are negotiating a turn. It is clear that the left wheel
has to travel a greater distance compared to the right wheel.
While taking a right turn the left wheel has to travel more distance; this means more speed to left wheel
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This means that the left wheel has to rotate at a higher speed compared to the right
wheel. If these wheels were connected using a solid shaft, the wheels would have to slip
to accomplish the turn. This is exactly where a differential comes in handy. The ingenious
mechanism in a differential allows the left and right wheels to turn at different rpms,
while transferring power to both wheels.
Parts of a Differential
We will now learn how the differential achieves this in a step-by-step manner using the
simplest configuration. Power from the engine is transferred to the ring gear through a
pinion gear. The ring gear is connected to a spider gear.
Motion from the pinion gear is transferred to the spider gear
The spider gear lies at the heart of the differential, and special mention should be made
about its rotation. The spider gear is free to make 2 kinds of rotations: one along with
the ring gear (rotation) and the second on its own axis (spin).
Spider gear is free to make 2 kinds of rotations
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The spider gear is meshed with 2 side gears. You can see that both the spider and side
gears are bevel gears. Power flow from the drive shaft to the drive wheels follows the
following pattern. From the drive shaft power is transferred to the pinion gear first, and
since the pinion and ring gear are meshed, power flows to the ring gear. As the spider
gear is connected with the ring gear, power flows to it. Finally from the spider gear,
power gets transferred to both the side gears.
The basic components of a standard differential
Differential Operation
Now let’s see how the differential manages to rotate the side gears (drive wheels) atdifferent speeds as demanded by different driving scenarios.
The vehicle moves straight
In this case, the spider gear rotates along with the ring gear but does not rotate on its
own axis. So the spider gear will push and make both the side gears turn, and both will
turn at the same speed. In short, when the vehicle moves straight, the spider-side gear
assembly will move as a single solid unit.
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While the vehicle moves straight, the spider gear does not spin; it pushes and rotates the side gears
The vehicle takes a right turn
Now consider the case when the vehicle is taking a right turn. The spider gear plays a
pivotal role in this case. Along with the rotation of the ring gear it rotates on its own axis.
So, the spider gear is has a combined rotation. The effect of the combined rotation on
the side gear is interesting.
To get peripheral velocity at left and right side of spider gear we have to consider both rotation and spin of it
When properly meshed, the side gear has to have the same peripheral velocity as the
spider gear. Technically speaking, both gears should have the same pitch line velocity.
When the spider gear is spinning as well as rotating, peripheral velocity on the left side of
spider gear is the sum of the spinning and rotational velocities. But on the right side, it is
the difference of the two, since the spin velocity is in the opposite direction on this side.
This fact is clearly depicted in Fig. This means the left side gear will have higher speed
compared to the right side gear. This is the way the differential manages to turn left and
right wheels at different speeds.
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The vehicle takes a left turn
While taking a left turn, the right wheel should rotate at a higher speed. By comparing
with the previous case, it is clear that, if the spider gear spins in the opposite direction,
the right side gear will have a higher speed.
While taking left turn the spider gear spins in opposite direction
Use of more Spider gears
In order to carry a greater load, one more spider gear is usually added. Note that the
spider gears should spin in opposite directions to have the proper gear motion. A four-
spider-gear arrangement is also used for vehicles with heavy loads. In such cases, the
spider gears are connected to ends of a cross bar, and the spider gears are free to spin
independently.
Double spider gear arrangement is usually used to carry more loads
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Other functions of the Differential
Apart from allowing the wheels to rotate at different rpm differential has 2 more
functions. First is speed reduction at the pinion-ring gear assembly. This is achieved by
using a ring gear which is having almost 4 to 5 times number of teeth as that of the
pinion gear. Such huge gear ratio will bring down the speed of the ring gear in the same
ratio. Since the power flow at the pinion and ring gear are the same, such a speed
reduction will result in a high torque multiplication.
You can also note one specialty of the ring gear, they are hypoid gears. The hypoid gears
have more contact area compared to the other gear pairs and will make sure that the
gear operation is smooth.
The other function of the differential is to turn the power flow direction by 90 degree.
Drawback of a Standard Differential
The differential we have gone through so far is known as open or standard differential . It
is capable of turning the wheels at different rpm, but it has got one major drawback.
Consider a situation where one wheel of the vehicle is on a surface with good traction
and the other wheel on a slippery track.
A standard differential vehicle on different traction surfaces will not be able to move
In this case a standard differential will send the majority of the power to the slippery
wheel, so the vehicle won’t be able to move. To overcome this problem, Limited Slip
Differentials are introduced. We will learn more about them in a separate article.
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Q. Explain the construction and working of Drum brakes with neat
sketch.
A drum brake is a brake that uses friction caused by a set of shoes or pads that press
outward against a rotating cylinder-shaped part called a brake drum.
Components
Drum brake components include the backing plate, brake drum, shoe, wheel cylinder,
and various springs and pins.
Backing plate
The backing plate provides a base for the other components. It attaches to the axlesleeve and provides a non-rotating rigid mounting surface for the wheel cylinder, brake
shoes, and assorted hardware. Since all braking operations exert pressure on the backing
plate, it must be strong and wear-resistant. Levers for emergency or parking brakes, and
automatic brake-shoe adjuster were also added in recent years.
Back plate made in the pressing shop.
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Brake drum
The brake drum is generally made of a special type of cast iron that is heat-conductive
and wear-resistant. It rotates with the wheel and axle. When a driver applies the brakes,
the lining pushes radially against the inner surface of the drum, and the ensuing friction
slows or stops rotation of the wheel and axle, and thus the vehicle. This frictiongenerates substantial heat.
Wheel cylinder
Cut-away section of a wheel cylinder.
One wheel cylinder operates the brake on each wheel. Two pistons operate the shoes,
one at each end of the wheel cylinder. The leading shoe (closest to the front of the
vehicle) is known as the primary shoe. The trailing shoe is known as the secondary shoe.
Hydraulic pressure from the master cylinder acts on the piston cup, pushing the pistons
toward the shoes, forcing them against the drum. When the driver releases the brakes,
the brake shoe springs restore the shoes to their original (disengaged) position. The
parts of the wheel cylinder are shown to the right.
Brake shoe
Brake shoes are typically made of two pieces of steel welded together. The friction
material is either riveted to the lining table or attached with adhesive. The crescent-
shaped piece is called the Web and contains holes and slots in different shapes for return
springs, hold-down hardware, parking brake linkage and self-adjusting components. All
the application force of the wheel cylinder is applied through the web to the lining table
and brake lining. The edge of the lining table generally has three “V"-shaped notches or
tabs on each side called nibs. The nibs rest against the support pads of the backing plate
to which the shoes are installed.
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Each brake assembly has two shoes, a primary and secondary. The primary shoe is
located toward the front of the vehicle and has the lining positioned differently from the
secondary shoe. Quite often, the two shoes are interchangeable, so close inspection for
any variation is important.
Brake shoe assembly
Linings must be resistant to heat and wear and have a high friction coefficient unaffected
by fluctuations in temperature and humidity. Materials that make up the brake shoe
include, friction modifiers (which can include graphite and cashew nut shells), powdered
metal such as lead, zinc, brass, aluminium and other metals that resist heat fade,
binders, curing agents and fillers such as rubber chips to reduce brake noise.
Normal braking
When the brakes are applied, brake fluid is forced under pressure from the master
cylinder into the wheel cylinder, which in turn pushes the brake shoes into contact with
the machined surface on the inside of the drum. This rubbing action reduces the rotation
of the brake drum, which is coupled to the wheel. Hence the speed of the vehicle is
reduced. When the pressure is released, return springs pull the shoes back to their rest
position.
Automatic self-adjustment
As the brake linings wear, the shoes must travel a greater distance to reach the drum.
When the distance reaches a certain point, a self-adjusting mechanism automatically
reacts by adjusting the rest position of the shoes so that they are closer to the drum.
Here, the adjusting lever rocks enough to advance the adjuster gear by one tooth. The
adjuster has threads on it, like a bolt, so that it unscrews a little bit when it turns,
lengthening to fill in the gap. When the brake shoes wear a little more, the adjuster can
advance again, so it always keeps the shoes close to the drum. Typically the adjusters
only operate when the vehicle is going in reverse and the brakes are engaged.
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Emergency brake
The parking brakes (emergency brake) system controls the brakes through a series of
steel cables that are connected to either a hand lever or a foot pedal. The idea is that the
system is fully mechanical and completely bypasses the hydraulic system so that the
vehicle can be brought to a stop even if there is a total brake failure. Here the cable pullson a lever mounted in the brake and is directly connected to the brake shoes. This has
the effect of bypassing the wheel cylinder and controlling the brakes directly.
Q. Distinguish between semifloating and fullfloating rear axles with
the aid of suitable sketches.
There are two types of rear axles found on light-duty 4x4s: semi-floating and full-
floating. Each has its advantages and disadvantages.
A semi-floating axle is very common on the rear of most 4x4s. It consists of an axleshaft
on each side that is splined on the inner end where it mates to the differential and has a
wheel flange where the wheel studs mount at the other end. This assembly typically
mates to the end of the axlehousing using some type of flange arrangement. The
axleshaft also rides on a large roller or ball bearing out at the end of the axlehousing.
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This Dana 35C semi-floater rear axle from a late-model Jeep TJ uses a flanged outer axle
housing (brake backing plate and components removed).
The shaft and flange that holds the wheel studs are all one piece.
The axleshaft in a semi-floating assembly serves two purposes. First, it attaches
to the wheel and is used to support the weight of the vehicle and its cargo.
Second, the axleshaft must transmit the rotational torque from the differential out
to the wheel.
A full-floating axle can be found on the rear of some 4x4s, but it is generally
reserved for vehicles that are designed for severe duty, or are intended to carryheavy loads. This type of axle uses an axleshaft on each side that is simply
splined at both ends or splined on the inner end and has a drive flange on the
outer end. The shaft mates to the differential in the same way as a semi-floater.
However, the outer end of the shaft differs. Here, the splined end of the shaft
slides into a locking hub or an internal splined steel drive plate that bolts to a hub
cap, similar to what is found on a front axle. In some cases, the drive flange may
be part of the shaft itself. In either case, the axleshaft is allowed to float in the
system.
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For a full-floater system, the axleshaft only serves to transmit the rotational
torque from the differential out to the wheel. It does not carry the weight of the
vehicle like a semi-floater does. On a full floater, a spindle is attached to the outer
end of the axlehousing. The hub's cap is attached to this spindle and rides on
tapered roller bearings. It is this assembly that carries the vehicle weight. As
such, a full-floating axle system is considerably stronger than an equivalently
sized semi-floating system.
A full-floater axle is easily recognized externally by the drive flange or locking hub that is
evident in the center hole of the wheel.
For those of you who carry heavy loads, this means your axle load capacity is
greatly increased with a full-floater. Load ratings for similar vehicles with the two
different axles are usually significantly different. If you do hard-core 'wheeling on
big tires, a full-floater means that your axleshafts can also handle much more
loading than a similar semi-floater could because it now must only handle torque
loading.
Further advantages of a full-floater include being able to remove a brokenaxleshaft, yet still have the ability to keep a functional rolling tire on that corner of
the vehicle. This can be done since the wheel actually bolts to the hub that rides
on the spindle attached to the axlehousing. If the axle has manual locking hubs, it
may be possible to unlock the rear hubs for towing a disabled vehicle on the trail
or for flat towing over the road.
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It is now possible to convert some semi-floater rear axles to full-floaters using
aftermarket kits. These kits allow an owner to easily upgrade the axleshaft
strength of his axle. However, such a kit does not upgrade the differential
assembly, so axles with this portion as a weak link would not benefit much from
such a conversion.
This is part of a Toyota full-floater bolt-on conversion kit. A spindle is attached to the
rear housing flange, and a wheel hub is supported using tapered roller bearings, such as
those typically found in the front axle.
When it comes to holding the axleshafts in a semi-floating axle housing, there are
two methods. One uses a C-clip inside the differential assembly, and the other
uses a pressed bearing out at the wheel end of the axleshaft. On a C-clip-style
axle, the axleshaft rides on roller bearings and is held in the axlehousing by a C-
clip in the differential assembly. The clip fits in a small groove machined near the
end of the axleshaft. To remove this clip requires the removal of the differential
inspection cover, and may require partial disassembly of the carrier itself
depending on the specific type of limited slip or locker used in the axle. Once the
clip is removed, the axleshaft can be slid out of the axlehousing.
On an axle using a pressed bearing setup, the axle is held in place by the
pressed-on wheel ball bearing and possibly a pressed collar or retaining clip
adjacent to the bearing. The bearing assembly usually fits into a flanged cup that
bolts to a mating flange on the outer axlehousing. This type of axle uses ball
bearings because the bearings must support both radial and axial loads
(perpendicular and parallel to the axleshaft).
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Here you can see the axleshaft and end plate of a typical full-floater that uses an
attached drive flange. Other full-floater axles may have the shaft and drive flange as
separate pieces.
There are advantages and disadvantages to disassembling each type of axle. The
C-clip variety requires access to the differential area, but the press bearing variety
requires brake line work and brake bleeding. Another difference is that when an
axleshaft on a C-clip assembly breaks, there is nothing left holding the axleshaft
in the housing so the tire and wheel assembly will readily separate from the
vehicle. On a pressed bearing-type axle, the wheel and tire will usually remain
intact, with the bearing pressed to the axleshaft holding the assembly together.
Here is a stock semi-floater Toyota truck rear axle. It uses a bearing cup that holds a
ball bearing held to the shaft by a press-fit collar and a retaining clip. It bolts to the axle
housing flange using the four studs pressed into the bearing cup.
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Q.Compare disc and drum type brake for automobile.
Modern braking systems are wonders of technology, using sensors, computers and
precisely engineered parts to safely stop your ride, but this wasn’t always the case. While
some cars use a drum brake system that has remained largely unchanged for nearly 100
years, most cars use a modern, disc brake system. In this article we’ll cover the
differences between drum and disc brakes and the advantages of using either type.
Centric Premium Brake Drums
When it comes to brakes, drums are the dinosaur of the group. They’ve been around for
eons and due to their simplicity and low manufacturing cost, they’re still in use. And
while they’re outperformed by disc brakes, they can still get the job done.
What are drum brakes?
Drums are made from cast iron and are named for their “drum-like” shape
All brake components are contained within the confines of the drum.
You could get a car with drums on all 4 wheels until the early 1970’s. Now, you’ll
usually see drums on the rear axles of economy cars and trucks.
How do they work?
Drum brakes work by forcing 2 arched “shoes” housed within the drum, to expand
outward into the inner wall of the spinning drum, using hydraulic and centrifugal
force.
This generates friction, slowing the drum and your car.
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What are the benefits of drum brakes?
The enclosed, all-in-one design of brake drums simplifies maintenance, with most
components being held in place by spring tension. To replace a set of shoes, you
simply pry the springs in a drum brake system loose with a brake tool and the
entire braking assembly comes apart. Swap in a new set of shoes, reconnect the
brackets & springs, put the drum back on and you’re done.
There’s no need for compressors, or opening fluid lines to retract pistons with
these setups. As a matter of fact, replacing brake shoes on some vehicles can be
accomplished in under 2 minutes, once the drum is removed.
Replacement brake shoes tend to be very affordable.
As cars became faster, drum brakes simply couldn’t keep up. Due to their design, drum
brakes quickly overheat and lose their stopping power. As a response to this, disc brakes
began appearing as a better-performing alternative to drum brakes on American cars in
the early 60’s.
EBC Ultimax Slotted Rotors
What are disc brakes?
A disc brake system is comprised of a large metal rotor, 2 flat brake pads and a
hydraulic clamp called a “caliper”.
Brake rotors are typically made from iron but can also be made from exotic
materials like carbon composites and ceramics for racing purposes.
Vanes are usually cast into rotors to increase cooling effectiveness.
Disc brake calipers use up to 8 pistons, providing massive clamping force.
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How do they work?
Pressing the brake pedal in a car with disc brakes, forces brake fluid to fill the
caliper.
A metal piston inside the caliper is then forced against the back of each brakepad.
This presses the pad’s friction material against the spinning rotor, quickly slowing
the brake rotor and your car.
What are the benefits of disc brakes?
Increased stopping power over drum brakes.
Better heat dissipation than drum brakes. Disc brake systems can be inspected without removing your wheels.
Unlike drum brakes, disc brake system are completely, self-adjusting.
Brake pedal feel and modulation are improved.
Disc brakes are more common, so you have a wide selection of performance disc
brake pads to choose from.
Q.Briefly explains the desirable tyre properties for vehicle.
Desirable Tyre Properties The tyres for automotive use have many tough functions to
perform, for which they must possess some desirable properties. It is seen that some of
these properties are conflicting with others, so that the final tyre design must incorporate
an optimum combination of all these.
The desirable properties are:(i). Load carrying : The tyre should be able to carry the weight of the vehicle and its
occupants without distortion. The tyre material should resist bending, tensile,
compressive and tensional stresses some of which come up during steering and braking.
(ii). Cushioning : It should absorb the shock loads caused due to road irregularities and
damp the vibrations fast.
(iii). Uniform Wear : The tyre should not develop skidding even on wet roads. Uniform
wear reduces tyre skid and vibrations due to road irregularities.
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(IV). none skidding : - The tread pattern design must be such that the tyre not skids
much on wet roads. The rubber must have a high coefficient of friction.
(V). Power consumption : The tyre must have a lower rolling resistance and therefore
must consume least of the engine power.
(VI). Noise : Tyre noise should be minimum. This depends upon the tread pattern and
type of road
(VII). Balance : - The tyre should be statically and dynamically balanced or else this may
give rise to wheel wobble.
(VIII). Durability: - A tyre must have durability, a good abrasion resistance, safety and
low cost.
Q. What is perfect steering? Derive expression for the basic
condition for the perfect Steering mechanism.
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The steering gear mechanism is used to change the direction of two or more of the wheel
axle’s with reference to the chassis, so as to move the automobile in the desired path.
The steering is done by front wheels and back wheels remain straight and do not turn.
The condition for correct steering is that all the four wheels must rotate about the same
instantaneous centre which lies on the axis of the back wheels.
Let the axis of the inner wheels makes a larger angle θ than the angle φ subtended by
the axis of outer wheel.
Let, a = wheel track
b = wheel base
c = distance between the pivots A and B of the front axle
From triangle IBP
From triangle IAP
This is the fundamental equation for correct steering.
Q. What is an independent suspension? Explain the MacPherson
strut type of independentSuspension In detail.
Independent suspension is a broad term for any automobile suspensionsystem that
allows each wheel on the same axle to move vertically (i.e. reacting to a bump in the
road) independently of each other. This is contrasted with a beam axle or deDion
axle system in which the wheels are linked – movement on one side affects the wheel on
the other side. Note that "independent" refers to the motion or path of movement of the
wheels/suspension. It is common for the left and right sides of the suspension to be
connected with anti-roll bars or other such mechanisms. The anti-roll bar ties the left and
right suspension spring rates together but does not tie their motion together.
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Advantages
This system provides many advantages over other suspension systems. For example, in
solid axle suspension systems, when one wheel hits a bump, it affects both wheels. This
will compromise traction, smoothness of the ride, and could also cause a dangerous
wheel shimmy when moving at high speeds. According to "Car Suspension Bible" with
independent suspension systems, the bump only affects the contacted wheel. This offers
many advantages such as greater ride comfort, better traction, and safer, more stable
vehicles on and off the road.
How Does a MacPherson Strut Suspension Work?
Components of a MacPherson strut suspension system.
MacPherson strut suspension systems typically utilize either a steering knuckle or a hub
carrier that has two mounting points that attach it to the body of the vehicle. The lower
mounting point attaches to a track control arm or lower control arm, and it is this
connection that dictates both the longitudinal and lateral orientation of the wheel
assembly.
In turn, the upper mounting point of the knuckle or hub is attached in some way to anassembly that contains a coil spring and a shock absorber. It is this combination of
housing, spring, and dampener that is referred to as a strut or, more properly, as a
Macpherson Strut. It typically extends upward into the unibody shell and bolts to a
location that is referred to as a strut tower.
The other main defining factor in a MacPherson strut suspension is the way that the axis
of the strut itself also serves as the upper steering pivot (the lower pivot is the mounting
point between the knuckle and control or track arm.) This upper pivot point is attached to
a tie rod end that, in turn, is attached to the steering gear.
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Advantages and Disadvantages of MacPherson Strut Suspensions
The main advantages of MacPherson struts are related to the relative simplicity of
these systems. Since the upper control arm is entirely elimited, MacPherson strut
suspensions require less components, which means that they are less expensiveto produce than other types of suspension systems. This simplicity also means
that they take up less space, which is a huge benefit for smaller vehicles. Since
less space is taken up to either side of the engine compartment, there is more
room for the engine and other components.
The simplicity of MacPherson strut suspensions means that the entire assembly, hub,
rotor, and brake caliper included, can be removed as a single unit.
Of course, the overall simplicity of MacPherson strut suspensions also leads to a
handful of disadvantages. Although it makes it easier to set the suspension
geometry when performing repairs (i.e. if nothing is bent, and you bolt everything
in place, then the caster and camber will both be correct), that same simplicity
means that the camber angle necessarily changes when the vertical position of
the wheel changes. The net effect is that MacPherson strut suspensions aretypically seen as possessing inferior handling characteristics to other suspension
systems (i.e. double wishbone, etc.)
The other main issue with MacPherson struts is related to the way that the mount
to the body of vehicles. Since the top of the strut is typically mounted high up in a
strut tower, and its axis extends straight down to the wheel, vibrations from the
wheel are transmitted directly into the body of the vehicle. That can result in
excessive road noise and vibration, which is mitigated somewhat by bushings and
other components and mechanisms.
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Macpherson Strut Failure
Since the strut in a MacPherson strut system is an integral part of both the
steering and suspension systems, a failure can be catastrophic. If a failure occurs
at the tie rod end mounting point, or at the control arm mounting point, the tire
may pivot at an angle and cause the driver to lose control. In some cases, the
vehicle may even roll. Failures like these are typically the result of manufacturing
defects or impact damage rather than worn out or poorly maintained parts.
Most Macpherson strut failures are related to the dampener wearing out, which
happens at regular intervals. In most cases, this type of failure can be repaired by
removing the strut assembly, releasing the spring tension with a special
compressor tool, and replacing the shock absorber cartridge. This is often a
simple bolt-on procedure, but some strut assemblies must be carefully aligned
afterwards to ensure proper camber and caster settings.
Q. Write down the difference between chassis, frame and body.
Classify various chassis And explain one of them.
Chassis Chassis is a French term which is now denotes the whole vehicle except body in
case of heavy vehicles. In case of light vehicles of mono construction, it denotes
the whole vehicle except additional fittings in the body. “Chassis consists of
engine, power train, brakes, steering system and wheels mounted on a frame”.
Frame
The frame is the main part of the chassis on which remaining parts of chassis are
mounted. The frame should be extremely rigid and strong so that it can withstandshocks, twists, stresses and vibrations to which it is subjected while vehicle is
moving on road. It is also called underbody. The frame is supported on the wheels
and tyre assemblies. The 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.
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Automotive chassis is a skeletal frame on which various mechanical parts like
engine, tires, axle assemblies, brakes, steering etc. are bolted. The chassis isconsidered to be the most significant component of an automobile. It is the mostcrucial element that gives strength and stability to the vehicle under different
conditions. Automobile frames provide strength and flexibility to the automobile.The backbone of any automobile, it is the supporting frame to which the body ofan engine, axle assemblies are affixed. Tie bars, that are essential parts of
automotive frames, are fasteners that bind different auto parts together.
Automotive chassis is considered to be one of the significant structures of anautomobile. It is usually made of a steel frame, which holds the body and motorof an automotive vehicle. More precisely, automotive chassis or automobilechassis is a skeletal frame on which various mechanical parts like engine, tires,
axle assemblies, brakes, steering etc are bolted. At the time of manufacturing, thebody of a vehicle is flexibly molded according to the structure of chassis.Automobile chassis is usually made of light sheet metal or composite plastics. Itprovides strength needed for supporting vehicular components and payload placed
upon it. Automotive chassis or automobile chassis helps keep an automobile rigid,stiff and unbending. Auto chassis ensures low levels of noise, vibrations and
harshness throughout the automobile.
The different types of automobile chassis include:
Ladder Chassis:
Ladder chassis is considered to be one of the oldest forms of automotive chassis
or automobile chassis that is still used by most of the SUVs till today. As its nameconnotes, ladder chassis resembles a shape of a ladder having two longitudinalrails inter linked by several lateral and cross braces.
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Backbone Chassis:
Backbone chassis has a rectangular tube like backbone, usually made up of glassfibre that is used for joining front and rear axle together. This type of automotivechassis or automobile chassis is strong and powerful enough to provide support
smaller sports car. Backbone chassis is easy to make and cost effective.
Monocoque Chassis:
Monocoque Chassis is a one-piece structure that prescribes the overall shape of avehicle. This type of automotive chassis is manufactured by welding floor pan andother pieces together. Since monocoque chassis is cost effective and suitable forrobotised production, most of the vehicles today make use of steel platedmonocoque chassis.
Motorcycle Chassis:
An important type of automotive chassis, motorcycle chassis comprise of
different auto parts and components like auto frame, wheels, two wheeler brakesand suspension. Its basically the frame for motorbikes that holds thesecomponents together. A motorbike chassis can be manufactured from differentmaterials. But the commonly used materials are steel, aluminum, or magnesium.
Car Chassis:
The main structure of a car is known as chassis. Car chassis functions as a
support for the different car parts. Automotive parts like engine, suspension& steering mechanism braking system, auto wheels, axle assemblies andtransmission are mounted on the car chassis.
Integral Chassis
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Tata Nano Chassis
Bus Chassis
Bus chassis is the design and quality of bus chassis depends on the capacity of bus. Itcan be tailor made according to the needs and can be availed with features like
transverse mounted engine, air suspension as well as anti-roll bars. A well manufacturedbus chassis offers various benefits like high torque from low revs, superior brakeperformance and more. Bus chassis designed for urban routes differs from the one
manufactured for suburban routes.
Truck Chassis
Truck chassis, the backbone of any truck is designed to provide a comfortable and
dependable ride. New invention in automotive sector has influenced the automobilechassis manufacturers to adopt latest trends and come up with new designs. In thepresent world, a truck chassis comes with enhanced geometry, power steering, discbrakes and other truck parts.
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Q.Classify steering systems. Explain with a neat sketch any one of
the Steering system.
One of the important human interface systems in the autmobile is the steering gear. The
steering gear is a device for converting the rotary motion of the steering wheel into
straight line motion of the linkage. The steering gears are enclosed in a box, called the
steering gear box. The steering wheel is connected directly to the steering linkage it
would require a great effort to move the front wheels. Therefore to assist the driver, a
reduction system is used.
The different types of steering gears are as follows:
Worm and sector steering gear
Worm and roller steering gear.
Cam and double lever steering gear
Worm and ball bearing nut steering gear.
Cam and roller steering gear.
Cam and peg steering gear.
Recirculation ball nut steering gear.
Rack and pinion steering gear.
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1) Rack & Pinion type
Advantages:
simple construction
economical and uncomplicated to manufacture
easy to operate due to good degree of efficiency
contact between steering rack and pinion is free of play and even internal
damping is maintained
tie rods can be joined directly to the steering rack
minimal steering elasticity compliance
compact
the idler arm (including bearing) and the intermediate rod are no longer needed
easy to limit steering rack travel and therefore the steering angle
Disadvantages:
greater sensitivity to impacts
greater stress in the case of tie rod angular forces
disturbance of the steering wheel is easier to feel (particularly in front-wheel
drives).
tie rod length sometimes too short where it is connected at the ends of the rack
(sidetake-off design).
size of the steering angle dependent on steering rack travel
this sometimes requires short steering arms resulting in higher forces in the entire
steering system.
decrease in steering ratio over the steer angle associated with heavy steering
during parking if the vehicle.
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2) Recirculating Ball type
Advantages:
Can be used on rigid axles
Ability to transfer high forces.
A large wheel input angle possible – the steering gear shaft has a rotation range
up to ±45°, which can be further increased by the steering ratio.
It is therefore possible to use long steering arms.
This results in only low load to the pit-man and intermediate arms in the event of
tie rod diagonal forces occurring.
It is also possible to design tie rods of any length desired, and to have steering
kinematics that allow an increase in the overall steering ratio iS with increasing
steering angles. The operating forces necessary to park the vehicle are reduced in
such cases.
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Disadvantages:
Higher cost
It is heavier than Rack & Pinion steering system
Steering feedback is not responsive
Dead point - at a certain point the steering feedback will be zero.
Q.Explain the following terms with neat sketch:
Caster,Camber,Slipangle,Toein & Toeout
What is Camber?
Camber is the angle of the wheel relative to the vertical of the vehicle, and depending on
the tilt, is either considered positive camber or negative camber. When the top of thetires tilt away from the center of the vehicle you have positive camber, and when the top
of the tires are tilted inward you have negative camber. One isn’t better than the other,
but varying camber angles have different effects on your vehicle.
Positive Camber- - When your wheels are tilted outward, the vehicle has
improved stability.
Negative Camber- High performance vehicles that require better cornering tend
to use negative camber, because it gives the driver more control in this regard.
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What is Caster?
Caster is the angle that identifies the forward or backward slope of a line that is drawn
through the upper and lower steering pivot points. It does not affect tire wear, but caster
does have an influence on the directional control of the steering. Caster angle settings
allow manufacturers to balance steering effort, high speed stability, and front end
cornering effectiveness.
Positive Caster- - If the line slopes towards the rear of the vehicle, then you
have positive caster. The down side to positive caster is if the vehicle does not
have power steering. In this case steering effort will be increased. Positive caster
is primarily beneficial to the vehicle as it increases the lean of the tire when the
vehicle is cornering, while returning it to an upright position when driving straight
ahead.
Negative Caster- - If the line slopes towards the front of the vehicle then the
caster is negative. Negative caster will allow you to steer less around turns, but
may cause you to drift if you are driving straight forward.
Positive and negative caster mainly apply to race cars, and unless your vehicle is lifted or
customized in some way that calls for an adjustment, street cars usually run on factory
determined settings.
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What is Toe?
Toe is a measurement that determines how much the front and/or rear wheels are turned
in or out from a straight-ahead position. The amount of toe, whether it’s toe-in or toe-
out, is expressed as the difference between the track widths as they are measured at theleading and trailing edges of the tires. Toe is expressed in degrees or fractions of an inch,
and while your wheels should be pointed directly ahead as you are traveling straight
forward, there are some benefits to toeing depending on the type of vehicle that you
drive.
The purpose of toe is to ensure that all four wheels roll parallel to one another. However,
race cars use toe-out to promote enhanced turning ability. Street cars, or basic
passenger cars, use toe-in because there is no need to corner quickly. Toe-in also
provides increased stability because it discourages turning. If your vehicle has the proper
amount of toe you should experience ideal straight line stability, corner entry, and very
little tire wear.
In vehicle dynamics, slip angle or sideslip angle is the angle between a rolling wheel's
actual direction of travel and the direction towards which it is pointing (i.e., the angle of
the vector sum of wheel forward velocity and lateral velocity ). For a free-rolling
wheel this slip angle results in a force parallel to the axle and the component of the force
perpendicular to the wheel's direction of travel is the cornering force. This cornering force
increases approximately linearly for the first few degrees of slip angle, then increases
non-linearly to a maximum before beginning to decrease.
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Q. Name the different types of suspension spring .Explain Leafspring.
Springs
Springs are your suspension system's first line of defense. As you drive over any surface,
you will inevitably encounter bumps and dips. These variations in the surface of a street
(or backcountry trail) send vertical energy through your wheels. Humps send your tires
skyward, and holes draw them down. The spring's job is to absorb this energy and bring
your wheels back to a state of equilibrium, which is when they are all at their standard
height.There are 3 basic type of springs used on modern automobiles: coil springs, leaf springs
and torsion bars.
Coil Springs:
Like an industrial-grade Slinky, a coil spring is basically a heavy-duty strip of metal that
has been wound around to form a spiral or helix. Coil springs are ideal for absorbing up-
down energy, but their design does not deal well with side-to-side motion. As such, coils
springs are typically found on all 4 wheels of most cars, and on the front suspensions of
some trucks and SUVs. Eibach Pro Kit Springs are an excellent example of coil springs.
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Leaf Springs:
Picture Robin Hood's trusty bow mounted to the underbelly of an automobile–that's
basically what a leaf spring looks like. More specifically, a leaf spring is a stack of steel
strips, called leaves. All the leaves are curved, and their arc flexes up and down when it
goes over uneven paths. Leaf springs have a proven track record that spans all the way
back to the medieval times, when they were used to support the axles of horse-drawn
carriages and olden-time paddy wagons. Today, leaf springs are primarily used on rear-
wheel drive automobiles, 4-wheel drive rigs, heavy-duty trucks, vans and SUVs. They do
not deliver the same ride quality as coil springs, but leaf springs are more robust and
handle weight better. A shining example of leaf springs: Skyjacker Softride Lifting Leaf
Springs.
Torsion Bars:
Instead of flexing or compressing, a torsion bar absorbs energy by twisting. One end of
the torsion bar is fixed firmly to a vehicle's frame, and the other side links to the
vehicle's control arm. When the auto runs across a rough patch of road, the up-down
energy flows into the torsion bar, which then twists. Because only the one side is
mounted firm, the torsion bar will only rotate so far before it spins back in the opposite
direction. Torsion bars are primarily used on front-end suspensions, and are found on all
types of automobiles. Rancho Torsion Barsrepresent a solid set of replacement bars for
vehicles with this suspension type.
Dampeners:
As Newton's 3rd Law of Motion states, for every action there is an equal and opposite
reaction. When a suspension spring takes in upward energy, it has to release it as a
downward force. However, that downward momentum then causes the spring to bounce
back upward. This back and forth resonance, or jounce to engineers, would go on for
miles if not for another key suspension component: dampeners (aka shock absorbers).
A spring would not improve your ride unless teamed up with a shock. It's the shock's job
to make the energy from your springs soft and as bounce-free as possible. Imagine
dropping a basketball off the roof of your house. If it falls onto concrete, it will bounce
back up and dribble down the driveway. On the other hand, if it falls onto a pile of pillows
or leaves, then it will just stop and wait for you.
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A leaf spring is a simple form of spring commonly used for
the suspension inwheeled vehicles. Originally called a laminated or carriage spring, and
sometimes referred to as a semi-elliptical spring or cart spring, it is one of the oldest
forms of springing, dating back to medieval times.
A leaf spring takes the form of a slender arc-shaped length of spring
steel ofrectangular cross-section. In the most common configuration, the center of the
arc provides location for the axle, while tie holes are provided at either end for attaching
to the vehicle body. For very heavy vehicles, a leaf spring can be made from several
leaves stacked on top of each other in several layers, often with progressively shorter
leaves. Leaf springs can serve locating and to some extent damping as well as springing
functions. While the interleaf friction provides a damping action, it is not well controlled
and results in stiction in the motion of the suspension. For this reason some
manufacturers have used mono-leaf springs.
A leaf spring can either be attached directly to the frame at both ends or attached
directly at one end, usually the front, with the other end attached through a shackle, a
short swinging arm. The shackle takes up the tendency of the leaf spring to elongate
when compressed and thus makes for softer springiness. Some springs terminated in a
concave end, called a spoon end (seldom used now), to carry a swiveling member.
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Elliptic
Semi-elliptic
Three quarter-elliptic
Quarter-elliptic
Transverse
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Q. Classify tyres and compare between radial ply and bias ply tyres.
Construction types
A cross-section of a tire showing ply orientations
Bias
Bias tire (or cross ply) construction utilizes body ply cords that extend diagonally from
bead to bead, usually at angles in the range of 30 to 40 degrees, with successive plies
laid at opposing angles forming a crisscross pattern to which the tread is applied. The
design allows the entire tire body to flex easily, providing the main advantage of this
construction, a smooth ride on rough surfaces. This cushioning characteristic also causes
the major disadvantages of a bias tire: increased rolling resistance and less control
and traction at higher speeds. This outdated technology is still made in limited quantities
to supply collector vehicles. It is possible to fit older American cars with modern tires, if
historical authenticity is not paramount.
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. Thedesign was introduced by Armstrong, while Goodyear made it popular with the "Polyglas"
trademark tire featuring a polyester carcass with belts of fiberglass. The "belted" tire
starts two main plies of polyester, rayon, or nylon annealed as in conventional tires, and
then placed on top are circumferential belts at different angles that improve performance
compared to non-belted bias tires. The belts may be fiberglass or steel. This technology
was a temporary, not invented here stop-gap, introduced by U.S. manufacturers to
forestall the radial tire.
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Radial
Radial tire construction utilizes body ply cords extending from the beads and across the
tread so that the cords are laid at approximately right angles to the centerline of the
tread, and parallel to each other, as well as stabilizer belts directly beneath the tread.
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. Following the
1968 Consumer Reports announcement of their superiority, radials began an inexorable
climb in new car market share, reaching 100% in the 1980's.
Semi-pneumatic
Semi-pneumatic tires have a hollow center, but they are not pressurized. They are light-
weight, low-cost, puncture proof, and provide cushioning. These tires often come as a
complete assembly with the wheel and even integral ball bearings. They are used
on lawn mowers, wheelchairs, and wheelbarrows. They can also be rugged, typically used
in industrial applications, and are designed to not pull off their rim under use.
Tires that are hollow but are not pressurized have also been designed for automotive
use, such as the Tweel (a portmanteau of tire and wheel), which is an experimental tire
design being developed at Michelin. The outer casing is rubber as in ordinary radial tires,but the interior has special compressible polyurethane springs to contribute to a
comfortable ride. Besides the impossibility of going flat, the tires are intended to combine
the comfort offered by higher-profile tires (with tall sidewalls) with the resistance to
cornering forces offered by low profile tires. They have not yet been delivered for broad
market use.
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Q. Explain with neat sketch working and construction of master
cylinder for Hydraulic braking system.
The Master Cylinder
Here is where you'll find the master cylinder:
Master cylinder location
In the figure below, the plastic tank you see is the brake-fluid reservoir, the master
cylinder's brake-fluid source. The electrical connection is a sensor that triggers a warning
light when the brake fluid gets low.
The master cylinder, reservoir and sensor
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As you'll see here, there are two pistons and two springs inside the cylinder.
Diagram of master cylinder
The Master Cylinder in Action
When you press the brake pedal, it pushes on the primary piston through a
linkage. Pressure builds in the cylinder and lines as the brake pedal is depressed
further. The pressure between the primary and secondary piston forces the
secondary piston to compress the fluid in its circuit. If the brakes are operating
properly, the pressure will be the same in both circuits.
The valve does the job of three separate devices:
The metering valve
The pressure differential switch
The proportioning valve
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Combination valve sections
Metering Valve
The metering valve section of the combination valve is required on cars that have disc
brakes on the front wheels and drum brakes on the rear wheels. If you have read How
Disc Brakes Works and How Drum Brakes Work, you know that the disc brake pad is
normally in contact with the disc, while the drum brake shoes are normally pulled away
from the drum. Because of this, the disc brakes are in a position to engage before the
drum brakes when you push the brake pedal down.
The metering valve compensates for this, making the drum brakes engage just before
the disc brakes. The metering valve does not allow any pressure to the disc brakes until
a threshold pressure has been reached. The threshold pressure is low compared to the
maximum pressure in the braking system, so the drum brakes just barely engage before
the disc brakes kick in.
Having the rear brakes engage before the front brakes provides a lot more stability
during braking. Applying the rear brakes first helps keep the car in a straight line, much
like the rudder helps a plane fly in straight line.
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Pressure Differential Switch
The pressure differential valve is the device that alerts you if you have a leak in one of
your brake circuits. The valve contains a specially shaped piston in the middle of a
cylinder. Each side of the piston is exposed to the pressure in one of the two brake
circuits. As long as the pressure in both circuits is the same, the piston will stay centered
in its cylinder. But if one side develops a leak, the pressure will drop in that circuit,
forcing the piston off-center. This closes a switch, which turns on a light in the
instrument panel of the car. The wires for this switch are visible in the picture above.
Proportioning Valve
The proportioning valve reduces the pressure to the rear brakes. Regardless of what type
of brakes a car has, the rear brakes require less force than the front brakes.
The amount of brake force that can be applied to a wheel without locking it depends on
the amount of weight on the wheel. More weight means more brake force can be applied.
If you have ever slammed on your brakes, you know that an abrupt stop makes your car
lean forward. The front gets lower and the back gets higher. This is because a lot of
weight is transferred to the front of the car when you stop. Also, most cars have more
weight over the front wheels to start with because that is where the engine is located.
If equal braking force were applied at all four wheels during a stop, the rear wheels
would lock up before the front wheels. The proportioning valve only lets a certain portion
of the pressure through to the rear wheels so that the front wheels apply more braking
force. If the proportioning valve were set to 70 percent and the brake pressure were
1,000 pounds per square inch (psi) for the front brakes, the rear brakes would get 700
psi.
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Q. Discuss Vacuum brake with suitable diagram
How the automatic vacuum brake works
Vacuum brake cylinder in running position: the vacuum is the same above and below the piston
Air at atmospheric pressure from the train pipe is admitted below the piston, which is forced up
In its simplest form, the automatic vacuum brake consists of a continuous pipe—the train
pipe—running throughout the length of the train. In normal running a partial vacuum is
maintained in the train pipe, and the brakes are released. When air is admitted to the
train pipe, the air pressure acts against pistons in cylinders in each vehicle. A vacuum is
sustained on the other face of the pistons, so that a net force is applied. A mechanical
linkage transmits this force to brake shoes which act on the treads of the wheels.
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The fittings to achieve this are:
a train pipe: a steel pipe running the length of each vehicle, with flexible vacuum
hoses at each end of the vehicles, and coupled between adjacent vehicles; at the
end of the train, the final hose is seated on an air-tight plug;
an ejector on the locomotive, to create vacuum in the train pipe;
controls for the driver to bring the ejector into action, and to admit air to the train
pipe; these may be separate controls or a combined brake valve;
a brake cylinder on each vehicle containing a piston, connected by rigging to the
brake shoes on the vehicle; and
a vacuum (pressure) gauge on the locomotive to indicate to the driver the degree
of vacuum in the train pipe.
The brake cylinder is contained in a larger housing—this gives a reserve of vacuum as
the piston operates. The cylinder rocks slightly in operation to maintain alignment with
the brake rigging cranks, so it is supported in turning bearings, and the vacuum pipe
connection to it is flexible. The piston in the brake cylinder has a flexible piston ring that
allows air to pass from the upper part of the cylinder to the lower part if necessary.
When the vehicles have been at rest, so that the brake is not charged, the brake pistons
will have dropped to their lower position in the absence of a pressure differential (as air
will have leaked slowly into the upper part of the cylinder, destroying the vacuum).
When a locomotive is coupled to the vehicles, the driver moves the brake control to the
"release" position and air is exhausted from the train pipe, creating a partial vacuum. Air
in the upper part of the brake cylinders is also exhausted from the train pipe, through
a non-return valve.
If the driver now moves his control to the "brake" position, air is admitted to the train
pipe. According to the driver's manipulation of the control, some or the entire vacuum
will be destroyed in the process. The ball valve closes and there is a higher air pressure
under the brake pistons than above it, and the pressure differential forces the piston
upwards, applying the brakes. The driver can control the amount of braking effort by
admitting more or less air to the train pipe.
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Q. Write a short note on Power steering
Power Rack-and-pinion
When the rack-and-pinion is in a power-steering system, the rack has a slightly different
design.
Part of the rack contains a cylinder with a piston in the middle. The piston is connected to
the rack. There are two fluid ports, one on either side of the piston. Supplying higher-
pressure fluid to one side of the piston forces the piston to move, which in turn movesthe rack, providing the power assist.
Q. Explain types of Drive.
A drive system is an arrangement, which transmits the driving thrust from the
road wheels to the vehicle body and also incorporates a means to resist the
movement of the main components due to torque reaction.
In the early days only leaf springs were used for the rear suspension of a vehicle,
and hence these springs were often utilized to provide the drive thrust and torque
reaction functions of the drive system. Since 1950, three notable drive systems
are in use on motor cars and these basic systems have undergone several
modifications to meet modern requirements.
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The drive systems include,
Hotchkiss open-type
Four-link (semi-Hotchkiss)
Torque tube
De-Dion
Hotchkiss Open-type Drive
This type of drive is commonly used on passenger cars and heavy commercial vehicles.
This arrangement uses two rear leaf springs, which are longitudinally mounted, and are
connected to the frame by a ‘fixed’ pivot at the front, and swinging shackles at the rear.
A universal joint is mounted at each end of the exposed or ‘open’ type propeller shaft,
with provision for accommodating change in shaft length due to the deflection of the
springs. This drive, therefore, incorporates an open propeller shaft with
two universal joints and a slip joint.
Hotchkiss open-type drive (light commercial vehicle)
To resist torque reaction the axle is clamped to the springs using ‘U’ bolts. Under heavy
driving conditions the springs deflect up at the front and down at the rear and vice versa
during braking. This movement helps to damp driving shocks and improves transmission
flexibility. A universal joint is installed at rear to accommodate continuous up and down
motion of the axle. Driving thrust is transferred from casing to the spring by the friction
between the two surfaces, and then transmitted through the front section of the springs
to the vehicle frame. If the ‘U’ bolts become loose, the spring centre bolt (axle location
bolt) has to take the full driving thrust, so that early failure of the bolt takes place due to
the high shearing force.
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Torque-tube Drive
This drive system is generally used in passenger cars and light commercial vehicles.
Whereas the Hotchkiss drive uses stiff springs to resist torque reaction and driving
thrust, the torque tube drive permits the use of either ‘softer’ springs or another form ofspring, like helical to perform their only intended duty so that a ‘softer’ ride is possible.
Figure illustrates a layout using laminated springs, which are connected to the frame by a
swinging shackle at each end. A tubular member called torque-tube, encloses the
propeller shaft and is bolted rigidly to the axle casing. The torque-tube is positioned at
the front by a ball and socket joint, which is located at the rear of the gearbox or cross-
member of the frame. Bracing rods are introduced between the axle casing and the
torque tube to strengthen the arrangement. A small-diameter propeller shaft is installed
inside the torque tube and splined to the final-drive pinion. Auniversal joint is installed in the centre of the ball joint to allow for angular deflections of
the drive.