Automobile Differential

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Chapter 1

Introduction

1.1 Automobile Differential

A differential is a mechanical device capable of transmitting torque and make rotation

through three shafts, one as input and other two are as output for different speed as vehicle

makes turn. The differential allows each of the driving wheels to rotate at different speeds, while

supplying equal torque to each of them. The differential is found on all modern cars and trucks,

and also in many all-wheel-drive vehicles. These all-wheel-drive vehicles need a differential

between each set of drive wheels, and they need one between the front and the back wheels as

well, because the front wheels travel a different distance through a turn than the rear wheels.

Figure 1.1 automobile differential

1.2 Purpose

A vehicle's wheels rotate at different speeds, mainly when turning corners. The

differential is designed to drive a pair of wheels with equal torque while allowing them to rotate

at different speeds. In vehicles without a differential, such as racing motor both driving wheels

are forced to rotate at the same speed, usually on a common axle driven by a simple chain-drive

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mechanism. When cornering, the inner wheel needs to travel a shorter distance than the outer

wheel, so with no differential, the result is the inner wheel spinning and/or the outer wheel

Dragging, and this results in difficult and unpredictable handling, damage to tires and roads, and

strain on the entire drivetrain. The problem was solved in 1827 by Pequer of France who

invented the differential. This mechanism rotates the wheels at different speeds, while

maintaining a drive to both wheels.

1.3 History

There are many claims to the invention of the differential gear but it is possible that it was

known, at least in some places, in ancient times. Some historical milestones of the differential

include:

100 BC–70 BC: The Antikythera mechanism has been dated to this period. It was

discovered in 1902 on a shipwreck by sponge divers, and modern research suggests that it

used a differential gear to determine the angle between the ecliptic positions of the sun

and moon, and thus the phase of the moon.

30 BC–20 BC: Differential gear systems possibly used in China

227–239 AD: Despite doubts from fellow ministers at court, Ma Jun from the Kingdom

of Wei in China invents the first historically verifiable south-pointing chariot, which

provided cardinal direction as a non-magnetic, mechanized compass. Some such chariots

may have used differential gears.

658, 666 AD: two Chinese Buddhist monks and engineers create south-pointing chariots

for Emperor Tenjiof Japan.

1027, 1107 AD: Documented Chinese reproductions of the south-pointing chariot by Yan

Su and then Wu Deren, which described in detail the mechanical functions and gear

ratios of the device much more so than earlier Chinese records.

1720: Joseph Williamson uses a differential gear in a clock.

1810: Rudolph Ackermann of Germany invents a four-wheel steering system for

carriages, which some later writers mistakenly report as a differential.

1827: modern automotive differential patented by watchmaker Onésiphore

Pequer (1792–1852) of the Conservatoire des Arts et Métiers in France for use on a steam

cart.

1832: Richard Roberts of England patents 'gear of compensation', a differential for road

locomotives.

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1874: Aveling and Porter of Rochester, Kent list a crane locomotive in their catalogue

fitted with their patent differential gear on the rear axle.

1876: James Starley of Coventry invents chain-drive differential for use on bicycles;

invention later used on automobiles by Karl Benz.

1897: first use of differential on an Australian steam car by David Shearer.

1958: Vernon Gleasman patents the Torsen dual-drive differential, a type of limited slip

differential that relies solely on the action of gearing instead of a combination of clutches

and gears.

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Chapter 2

Differential Mechanism

2.1 Various Parts of the differential

Pinion Drive Gear: It transfers power from the driveshaft to the ring gear mainly having

helical gear on it.

Figure 2.1.1 Pinion gear and crown wheel with helical gear

Crown wheel/ring gear: Ring gear transfers power from pinion gear to the differential

case assembly. Ring gear reduces the gear ratio that helps in increasing the torque value.

Crown wheel and pinion gear are meshes with hypoid gear orientation. A hypoid gear is a

style of spiral bevel gear whose main variance is that the mating gears' axes do not

intersect. The hypoid gear is offset from the gear center, allowing unique configurations

and a large diameter shaft. The teeth on a hypoid gear are helical, and the pitch surface is

best described as a hyperboloid.

Spider/planet gear: spider gears are connected at the end of the cross-pin that transfer

power from ring gear to side 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).This two kinds of rotations are shown in figure.

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Figure 2.1.2 the basic components of a standard differential

Cross-pin: It link the spider gear with the crown wheel so spider gear can make rotation

through crown wheel.

Figure 2.1.3 possible rotations of spider gear

Side/sun gear: It transfer power from spider gear to rear axles and help both wheels to

turn independently when turning.

Differential case assembly: It holds the ring gear and other components that drive the

rear axle.

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2.2 Functional Description

The following description of a differential applies to a "traditional” rear-wheel-drive car or

truck with an "open" differential, Torque is supplied from the engine, via the transmission, to a

driveshaft, which runs to the final drive unit and 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 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, which are

a cluster of four opposed bevel gears in perpendicular plane, so each bevel gear meshes with two

neighbours, and rotates counter to the third, that it faces and does not mesh with. The two sun

wheel gears are aligned on the same axis as the crown wheel gear, and 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’s rotation. Most automotive

applications contain two opposing planet gears. As the differential carrier rotates, the changing

axis orientation of the planet gears imparts the motion of the ring gear to the motion of the sun

gears by pushing on them rather than turning against them, but because the planet gears are not

restricted from turning against each other, within that motion, the sun gears can counter-rotate

relative to the ring gear and to each other under the same force. Direction of rotation of the

planet gear is depends on the vehicle’s turning direction.

2.3 Differential Operation

Now let’s see how the differential manages to rotate the side gears at different speeds as

demanded by different driving scenarios. Consider three different cases

1. Vehicle moves in straight direction

2. Vehicle takes right turn

3. Vehicle takes left turn

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2.3.1 Vehicle moves in straight direction

In this case, both right and left wheel have to travel same distance so same speed is require.

Input torque is applied to the ring gear (blue), which turns the entire carrier (blue), providing

torque to both side gears (red and yellow), which in turn may drive the left and right wheels.

Figure 2.3.1 Vehicle moves in straight direction

If the resistance at both wheels is equal, the spider gear (green) does not spin, and both wheels

turn at the same rate. 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.

2.3.2 Vehicle takes right turn

Now consider the case when the vehicle is taking a right turn. In this case a certain amount of

tension would build up when cornering as the outside wheel tries to rotate quicker that the inside

wheel due to the bigger arc of travel. 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. Here during right turn left wheel have to travel more than the left wheel so the speed or

require to left wheel is more. When properly meshed, the side gear has to have the same

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Figure 2.3.2 Travelling distance of wheels during right turn

Peripheral velocity as the spider gear. 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

Figure 2.3.3 Direction of rotation of spider gear during right turn

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.2.3.3. 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.

2.3.3 Vehicle takes left turn

Now consider the case when the vehicle is taking a left turn. Here the right wheel have to

travel more distance than left wheel that require more rotational speed of the wheel. In this case

the speed of spider gear is in opposite direction as compare to previous case shown in figure

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2.3.4. So the speed of the right sun gear will more because of sum of spinning and rotational

velocity of spider gear and contrast to the left side gear. This means the right side gear will have

higher speed compared to the left side gear.

Figure 2.3.4 Travelling distance of wheels and direction of rotation of spider gear during

left turn

2.4 Use of more Spider gears

In order to carry a greater load, one more spider gear is usually added. 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.

Figure 2.4 Double spider gear arrangement

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2.5 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.

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. In

which the power is transmitted to differential by main shaft and that power further transmitted to

rear axles that are mounted at 90 degree with the main shaft.

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Chapter 3

Types of Differential

3.1 Open Differential

An open differential is the mechanism that receives the power from the transmission usually

through a driveshaft and splits that power in two and sends it to the left and right of the driven

wheels and allows them to rotate at different speeds.

The open differential often referred to as just a differential can also be used to split the power

between the front and rear wheels in an all/four wheel drive vehicles and then two other

differentials can further split the power to the left and right wheels. The ability to rotate both

driven wheels at different speeds is the primary objective of the differential, it separates the both

wheels by allowing them to have their own final shaft instead of one continuous shaft between

the both wheels. If there is a vehicle that is required to only travel in a straight line then a

differential would not be required, the driveshaft could be connected to a single final shaft. The

problem with a single shaft is that it does not allow the vehicle to corner properly. The outer

wheels rotate faster than the inner wheels and the lack of a differential does not facilitate this. A

rear wheel drive differential will be used to explain a common configuration of the open

differential and how it operates. The differential mechanism is housed inside of a round metal

casing with an opening at the front to connect the driveshaft. Inside of this casing is also

lubricated as anywhere else where metal rubs on or against metal. Inside of the case the

driveshaft rotates a disc using teeth on the edge of the driveshaft and the disc similar to gears.

This disc can be on the left or the right side on the inside of the casing and whichever side its on

it is attached to one of the sun wheels.

The shaft to both wheels has a sun wheel inside of the casing. Both sun wheels are connected

to each other by two or more planet gears and the planet gears rotate from an extension off the

main disc. All of these components rotate as the vehicle moves. Even with all of these

components the differential allows the two shafts to each have half of

the torque and horsepower and they rotate equally when moving in a straight line.

When the vehicle is cornering the inner wheel rotates slower and offers more resistance, this

causes the planet wheels to rotate on its own axis and it increases the speed of the outer by the

same percentage that the inner wheel slows down. A rear wheel drive vehicles will have one

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differential will have one differential, a front wheel drive vehicle will also have one differential

but it is usually integrated into the transmission. A part time four wheel drive should have two

differentials and a full time four/all-wheel drive would have three differentials but the center

differential could be integrated into the transmission. There have been improvements to the basic

or open differential which would be the limited slip differential and the locking differential.

3.2 Limited Slip Differential

To overcome the drawback of standard differential, traction aiding devices are use. One

solution is the limited slip differential (LSD).

3.2.1 Construction:

The basic components of a limited slip differential are pinion gear, ring gear, case, spider

gears and side gears. Apart from its basic components a Limited slip differential has got a series

of friction and steel plates packed between the side gear and the casing. Friction discs are having

internal teeth and they are locked with the splines of the side gear. So the friction discs and the

side gear will always move together.

Fig.3.2.1 it is clear from the figure that steel plates are locked with the case and friction disc

with the side gear

Steels plates are having external tabs and are made to fit in the case groove. So they can rotate

with the case.

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Fig.3.2.2 Pre-load spring in an LSD will always give a thrust force

If any of the clutch pack assembly is well pressed, the frictional force within them will make

it move as a single solid unit. Since steel plates are locked with the case and friction discs with

the side gear, in a well pressed clutch pack casing and the clutch pack will move together. Or

motion from the casing is directly passed to the corresponding axle. Space between the side gears

is fitted with a pre-load spring. Pre load spring will always give a thrust force and will press

clutch pack together.

3.2.2 Separating action of Bevel gears

Spider and side gear are bevel gears. It has got one specialty. When torque is transmitted

through a bevel gear system axial forces are also induced apart from the tangential force. The

axial force tries to separate out the gears.

Fig.3.2.3 During power transmission through a bevel gear system axial forces are also

induced

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Now side gear and axle are 2 separate units. The side gear has got a small allowance for axial

movement.

Fig.3.2.4 Side gear and axle are two separate units have small axial movement

So during high torque transmission through spider-side gear arrangement, a high separating

thrust force is also transmitted to the clutch pack. This force presses and locks the clutch pack

assembly against wall of the casing.

3.2.3 Working of Limited Slip Differential

Now back to the initial problem. Since one wheel is on a high traction surface, the torque

transmitted to it will be higher. So the thrust force developed due to the bevel gear separation

action also will be high at that side. Thus clutch pack at high traction wheel side will be pressed

Fig.3.2.5 Thrust force induced due to the bevel gear separation action is high for the high

traction wheel

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.

firmly and clutch pack will be locked. So power from the differential casing will flow directly to

high traction axle via clutch pack assembly.

On the other hand clutch pack on the low traction wheel side is not engaged yet, so power

flow will be limited to that side. So the vehicle will be able to overcome the traction difference

problem

However while taking a turn the LSD can act like a normal differential. In this case thrust force

developed due to bevel gear separation action won’t be that high. So the plates in clutch pack

will easily overcome frictional resistance and will be able to slip against each other. Thus the

right and left wheel can have different speed just like an open differential.

3.3 Locking Differential

A locking differential, differential lock, diff lock or locker is a variation on the standard

automotive differential. A locking differential may provide increased traction compared to a

standard, or "open" differential by restricting each of the two wheels on an axle to the same

rotational speed without regard to available traction or differences in resistance seen at each

wheel.

A locking differential is designed to overcome the chief limitation of a standard open

differential by essentially "locking" both wheels on an axle together as if on a common shaft.

This forces both wheels to turn in unison, regardless of the traction available to either wheel

individually.

When the differential is unlocked (open differential), it allows each wheel to rotate at

different speeds (such as when negotiating a turn), thus avoiding tire scuffing. An open (or

unlocked) differential always provides the same torque to each of the two wheels, on that axle.

So although the wheels can rotate at different speeds, they apply the same rotational force, even

if one is entirely stationary, and the other spinning.

By contrast, a locked differential forces both left and right wheels on the same axle to rotate

at the same speed under nearly all circumstances, without regard to tractional differences seen at

either wheel. Therefore, each wheel can apply as much rotational force as the traction under it

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will allow, and the torques on each side-shaft will be unequal. (Unequal torque, equal rotational

speeds).

A locked differential can provide a significant traction advantage over an open differential,

but only when the traction under each wheel differs significantly.

3.3.1 Automatic lockers

Automatic lockers lock and unlock automatically with no direct input from the driver. Some

automatic locking differential designs ensure that engine power is always transmitted to both

wheels, regardless of traction conditions, and will "unlock" only when one wheel is required to

spin faster than the other during cornering. These would be more correctly termed "automatic

unlocking" differentials, because their at-rest position is locked. They will never allow either

wheel to spin slower than the differential carrier or axle as a whole, but will permit a wheel to be

over-driven faster than the carrier speed. The most common example of this type would be the

famous "Detroit Locker," also known as the "Detroit No-Spin," which replaces the entire

differential carrier assembly. Others, sometimes referred to as "lunchbox lockers," employ the

stock differential carrier and replace only the internal spider gears and shafts with interlocking

plates. Both types of automatic lockers will allow for a degree of differential wheel speed while

turning corners in conditions of equal traction, but will otherwise lock both axle shafts together

when traction conditions demand it.

Pros: Automatic action, no driver interaction necessary, no stopping for (dis-) engagement

necessary, continuous driving even in unforeseen road condition changes

Cons: Increased tire wear and noticeable impact on driving behavior. During cornering,

which half-axle is uncoupled is dependent on torque direction applied by the driveline. When

the torque direction is reversed, the speed of the driveline is suddenly forced to change from

the inner to outer axle, accompanied by tire chirping and a large jerk. During cornering, the

automatic locker is characterized by heavy understeer which transitions instantly to power

over steer when traction is exceeded.

Some other automatic lockers operate as an open differential until wheel slip is encountered

and then they lock up. This style generally uses an internal governor to monitor vehicle speed

and wheel slip. An example of this is the Eaton Automatic Locking Differential (ALD), or Eaton

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Automatic Differential Lock (ADL), developed by the Eaton Corporation and introduced in

1973.

Some other automatic lockers operate as an open differential until high torque is applied and

then they lock up. This style generally uses internal gears systems with very high friction. An

example of this is the ZF "sliding pins and cams" available for use in early Volkswagens

Fig. 3.3 ARB Air locking differential fitted to a Mitsubishi Delica L400 LWB

3.3.2 Disadvantages

Because they do not operate as smoothly as standard differentials, automatic locking

differentials are often responsible for increased tire wear. Some older automatic locking

differentials are known for making a clicking or banging noise when locking and unlocking as

the vehicle negotiates turns. This is annoying to many drivers. Also, automatic locking

differentials will affect the ability of a vehicle to steer, particularly if a locker is located in the

front axle. Aside from tire scuffing while turning any degree on high friction (low slip) surfaces,

locked axles provoke understeer and, if used on the front axle, will increase steering forces

required to turn the vehicle. Furthermore, automatically locking differentials can cause a loss of

control on ice where an open differential would allow one wheel to spin and the other to

hold, while not transferring power. An example of this would be a vehicle parked sideways on a

slippery grade. When both wheels spin, the vehicle will break traction and slide down the grade.

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3.3.3 Alternatives

Limited slip differentials are considered a compromise between a standard differential and a

locking differential because they operate more smoothly, and they do direct some extra torque to

the wheel with the most traction compared to a standard differential, but they are not capable of

100% lockup.

Traction control systems are also used in many modern vehicles either in addition or as a

replacement of locking differentials. One example is that offered by Volkswagen under the name

of electronic differential lock (EDL). This EDL is not in fact a differential lock, but operates at

each wheel. Sensors monitor wheel speeds, and if one is rotating more than 100 RPM more than

the other EDL system momentarily brakes it. This transfers more power to the other wheel, but

still employs the open differential, which is the same as on cars without the EDL option.

Electronic traction control systems may be integrated with anti-lock braking systems, which have

a similar action on braking and use some similar components. Such systems are used for example

on the most recent Nissan Pathfinder, Land Rover Defender, Land Rover Freelander,

the McLaren P1 and the McLaren 650s.

3.3.4 Applications

Race cars often use locking differentials in order to maintain traction during high speed

maneuvers or when accelerating at extreme rates. Additionally, vehicle dynamics are made

more predictable when there is a loss of traction, as the driver knows that neither wheel will

suddenly sap power if it encounters a low-friction surface.

Some utility vehicles such as tow trucks, forklifts, tractors, and heavy equipment use locking

differentials to maintain traction, especially when driving on soft, muddy, or uneven

surfaces. Lockers are common in agricultural equipment and military trucks. On some farm

tractors, there is a pedal that can be stepped on with the operator's heel to lock the differential

as needed.

Differential locking can also be used in the sport of drifting as an alternative to a limited slip

differential.

Four-wheel drive vehicles that drive off-road often use a locking differential to keep from

getting stuck when driving on loose, muddy, or rocky terrain. Locking differentials are

considered essential equipment for serious off-road driving. Many such vehicles have a

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locking differential on the central differential (between the front and rear axles), rear

differential and front differential; or any combination of any of the three. Differential locks

are also used on some "non-utility" four-wheel-drive vehicles (such as the Mitsubishi

Shogun) to compensate for a relative lack of axle articulation (vertical wheel movement).

High amounts of articulation are desirable for off-road driving, to allow the wheels to

maintain ground contact over uneven surfaces, but this can lead to excessive body-roll at

high speeds on the road, as well as vague steering. Such 4x4s often have suspension systems

designed as a compromise between articulation and handling. If articulation is limited, one

wheel on an axle may be lifted off the ground by rough terrain, thus losing all traction to all

wheels (all power goes to the lifted wheel, which spins freely). A rear locking differential is

often supplied to make up for this compromise – if a wheel is lifted off the ground, the

locking differential can be brought into play, driving the wheel that remains on the ground.

3.4 Torsen Differential

Torsen is a trade mark of the JTEKT Corporation. The Torsen differential has many patented

components and, is the most unique and ingenious method of providing differential action while

overcoming the traction difference problem.

3.4.1 The internal components

The internal components of a Torsen are quite different from that of a conventional

differential. An exploded view of the Torsen is given in Fig.3.4.1

Fig.3.4.1 An exploded view of Torsen differential

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At the heart of the system lies a specially shaped gear pair assembly, one gear is a spur gear,

and the other one is a worm gear.

Fig.3.4.2 a worm gear-worm wheel mesh lies at the heart of the Torsen

A Torsen works on the simple principle of worm gear- worm wheel; that is a spinning worm

gear can rotate the wheel, but the rotating wheel cannot spin the worm gear.

Fig.3.4.3 The worm gear- worm wheel principle lies at the heart of the Torsen operation

A pair of such worm wheels are fitted with the case, so the engine power received by the case

is transferred to the worm wheels. Each end of the wheels is fitted with a spur gear. As a result, a

simplified Torsen differential will look as shown in the Fig.3.4.4

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Fig.3.4.4 The complete Torsen differential

3.4.2 The vehicle moves straight

When the vehicle moves straight, the worm wheels will push and turn the worm gears. So

both the drive wheels will rotate at the same speed. Please note here that, in this condition the

worm wheels do not spin on its own axis. In this condition, the whole mechanism moves as a

single solid unit.

Fig.3.4.5 when the vehicle moves straight, worm wheels just push and turn the worm gears

at the same speeds.

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3.4.3 The vehicle takes a right turn

When the vehicle is negotiating a right turn, the left wheel needs to rotate at a higher speed

than the right wheel. This fact is clear from the Fig.3.4.6.

Fig.3.4.6 During a right turn the left wheel has to travel more distance

Fig.3.4.7 The right worm wheel will spin opposite to the right worm wheel; this is due to the

opposite relative motion left worm wheel is experiencing

While taking a left turn the worm wheels will spin in an exact opposite way to that shown in

Fig.4.4.7.

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This speed differential is perfectly supported in a Torsen. The worm wheel is subjected to

relative motion not the absolute motion. The worm wheel is fitted between the case and worm

gear, so the relative motion between the case and worm gear is what makes the worm gear turn.

The worm gear of the faster left axle will make the corresponding worm wheel spin on its

own axis. On the other side, relative to the case the slow right axle is turning in the opposite

direction; thus the right worm wheel will spin in the opposite direction. The meshing spur gears

at the ends of worm wheel will make sure that, the worm wheels are spinning at the same speed.

Thus it guarantees a perfect differential action. Perfect differential action implies equal amount

of speed loss and speed gain to the right and left wheels. With the perfect differential the vehicle

will be able to negotiate a smooth turn.

3.4.4 Overcoming the Traction difference problem

Now let’s try to understand how the Torsen overcomes the drive wheel traction difference

problem. As you might be aware, when your vehicle encounters a situation as shown, the

slippery wheel starts to spin very rapidly and will draw the majority of the engine’s power. As a

result, the vehicle will get stuck.

Fig.3.4.8 A typical traction difference problem a vehicle is experiencing

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But, if a Torsen differential is used in this case, as soon as the slippery wheel starts to spin

excessively, the speed change will be transferred to the corresponding worm wheel. The right

worm wheel transfers the speed change to the left worm wheel, since they are connected through

spur gears. Here comes the tricky part. The left side worm wheel will not be able to turn the

corresponding worm gear, because, as we said, a worm wheel cannot drive a worm gear. As a

result, the whole mechanism gets locked, and the left and right wheels turn together.

Fig.3.4.9 The excessive speed of slipping wheel make the system locked due to the 'basic

principle of worm gear-worm wheel’

This allows a large amount of power to be transferred to the high-traction wheel, and the

vehicle can thereby overcome the traction difference problem. To carry the load 2 more worm

wheel pairs are added.

3.4.5 Pros and Cons of Torsen differential

The other technologies allow the drive wheel to slip for a limited amount of time before it

gets locked, in Torsen the locking action is instantaneous. That means as soon as the vehicle

encounters a traction difference track the wheels will get locked. They are also compact

compared to their counter parts. Some disadvantages of the Torsen differential are that is noisy,

costly and more difficult to assemble.

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Chapter 4

Differential Problems

4.1 Bearings Problems

It makes humming noise and gets louder when speed increases. Stethoscope is use to listen

for a humming sound by the carrier bearings and the pinion bearings.

Fig 4.1 pinion bearing

4.2 Ring and Pinion Problems

Will show up as whining or howling noise that changes when going from acceleration to

deceleration. Lack of service or low fluid can also cause this problem. If backlash (clearance)

between ring gear and pinion gear is too great, a clunking sound can be produced, especially

when an automatic transmission is shifted into gear.

Fig 4.2 Broken gear teeth

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Ring and pinion gear backlash refers to the amount of space between the meshing teeth of the

gears. Backlash is needed to allow for the heat expansion and lubrication. Too little backlash will

cause the gears to jam and too much backlash will cause gear noise (whining, roaring, or

clunking). .

4.3 Differential Fluids

For lubrication fluid, a very heavy oil, must be used in rear axle housings. Special hypoid oils

are used in the differential case. Even another type of fluid, or oil must be used in a positraction

type differential. The oil is circulated by the ring gear, and flung all over all the parts. Special

troughs, or gullies are used to bring the oil back to certain spots, like the ring and pinion area and

the piston bearings. The fluid is kept in with gaskets and oil seals. The bottom of the housing has

a drain plug, and another filler plug is located part way up the housing. The housing must never

be filled above this plug. The housing fluid lubricates some of the outer bearings, but others have

lubrication fittings for the injection of wheel bearing grease. A hand gun, not a pressure grease

gun must be used to grease these bearings. Finally, some bearings are filled with grease at the

factory and are sealed. These never require attention unless they are defective.

4.4 Loss of traction

One undesirable side effect of a conventional differential is that it can limit traction under less

than ideal conditions. The amount of traction required to propel the vehicle at any given moment

depends on the load at that instant means how heavy the vehicle is, how much drag and friction

there is, the gradient of the road, the vehicle's momentum.

The torque applied to each driving wheel is a result of the engine, transmission and drive

axles applying a twisting force against the resistance of the traction at that road wheel. In lower

gears and thus at lower speeds, and unless the load is exceptionally high, the drivetrain

can supply as much torque as necessary, so the limiting factor becomes the traction under each

wheel. It is therefore convenient to define traction as the amount of torque that can be generated

between the tire and the road surface, before the wheel starts to slip. If the torque applied to one

of the drive wheels exceeds the threshold of traction, then that wheel will spin, and thus only

provide torque at each other driven wheel limited by the sliding friction at the slipping wheel.

The reduced net traction may still be enough to propel the vehicle.

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4.5 Disadvantage of open (standard) differential

Fig 4.5 wheel rotates on slippery surface

By considering the case of a standard (or "open") differential in off-roading or snow situations

where one wheel begins to slip and rotates with high speed because both wheels are free to

rotate. In such a case the slipping wheel will receive the majority of the power in the form of

low-torque, high rpm rotation, while the contacting wheel will remain stationary or almost in

dead condition. So the vehicle will not be able to move.

4.6 Automobile without Differential

Although most automobiles in the developed world use differentials there are a few that do

not. Several different types exist:

Race cars and trucks in certain classes. Drag racing is done in a straight line (and often on

a prepared surface), which obviates the need for a differential. A spool (a cylindrical

device on which film, magnetic tape, thread, or other flexible materials can be wound) is

used to make a solid connection between both drive wheels, which is simpler and less

likely to break under very heavy acceleration. Racing on dirt or mud tracks also allows

the use of spools, because the loose surface gives way while cornering. NASCAR

(National Association for Stock Car Auto Racing) mandates the use of spools in their

cars, which does cause axle wind-up, and degrades handling in turns. Other forms of

racing without differentials includes tractor pulling, mud bogging and

other 4x4 motorsports where differential action is not needed.

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Vehicles with a single driving wheel. Besides motorcycles, which are generally not

classified as automobiles, this group includes most three-wheeled cars. These were quite

common in Europe in the mid-20th Century, but have now become rare there. They are

still common in some areas of the developing world, such as India. Some early four-

wheeled cars also had only one driving wheel to avoid the need for a differential.

However, this arrangement led to many problems. The system was unbalanced, the

driving wheel would easily spin, etc. Because of these problems, few such vehicles were

made.

Vehicles using two freewheels. A freewheel, as used on a pedal bicycle for example,

allows a road wheel to rotate faster than the mechanism that drives it, allowing a cyclist

to stop pedaling while going downhill. Some early automobiles had the engine driving

two freewheels, one for each driving road wheel. When the vehicle turned, the engine

would continue to drive the wheel on the inside of the curve, but the wheel on the outside

was permitted to rotate faster by its freewheel. Thus, while turning, the vehicle had only

one driving wheel. Driving in reverse is also impossible as is engine braking due to

freewheels.

Vehicles with continuously variable transmissions, such as the DAF Daffodil. The

Daffodil, and other similar vehicles which were made until the 1970s by the Dutch

company DAF, had a type of transmission that used an arrangement of belts and pulleys

to provide an infinite number of gear ratios. The engine drove two separate transmissions

which ran the two driving wheels. When the vehicle turned, the two wheels could rotate

at different speeds, making the two transmissions shift to different gear ratios, thus

functionally substituting for a differential. The slower moving wheel received more

driving torque than the faster one, so the system had limited-slip characteristics. The

duplication also provided redundancy. If one belt broke, the vehicle could still be driven.

Vehicles with separate motors for the driving wheels. Electric cars can have a separate

motor for each driving wheel, eliminating the need for a differential, but usually with

some form of gearing at each motor to get the large wheel torques necessary. A multi-

motor electric vehicle such as the Dual Motor Tesla Model S can electronically control

the power distribution between the motors on a millisecond scale, in this case acting as a

Centre differential where open differentials are still employed left-to-right.

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Conclusion

In this study we have seen the importance of differential, its working and different types of it

and how they are different than each other and its usefulness according to the requirement in

automobile. In automobile and other wheeled vehicles, normally the differential allows each of

the driving wheels to rotate at different speeds, while supplying equal torque to each of them.

Apart from the standard differential the other types like LSD, Torsen and locking differential are

used for avoiding traction problem. LSD prevents excessive power from being allocated to one

wheel, and thereby keeping both wheels in powered rotation.

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References

(1) Dr.N.K. Giri, Automobile Technology, pp 1173-1179

(2)Wikipedia-the free encyclopedia, “differential”, July, 2015,

https://en.wikipedia.org/wiki/Differential_ (mechanical device)

(3) howstuffworks, a division of Info Space LLC-1998, http://auto.howstuffworks.com/

(4)Learn Engineering, Imajey consulting engineering pvt. Ltd. -2011,

http://www.learnengineering.org/2014/05/working-of-differential.html (straight/turn concept)

(5) R.K. Rajput, Automobile Engineering, pp 151-154

(6) Kirpal Singh, Automobile Engineering , vol. 1, pp 216-220