Automobile Differential Unit

AUTOMOBILE DIFFERENTIAL
UNIT
A MECHANICAL GEAR ASSEMBLY UNIT WHICH PROVIDE DIFFERENT
SPEED/TORQUE TO SAME AXLE WHEELS
SIVARAMAN.K M.Tech-AEES ARAI
AUTOMOBILE DIFFERENTIAL UNIT

REQUIREMENT
• Transfers power from driveshaft to the wheels
• Provides final gear reduction
• Splits amount of torque going to each wheel
• Allow the wheels to rotate at different speeds in turns

DIFFERENTIAL AT REAR AXLE

HISTORY(BC)
• 227–239 AD: 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: 2 Chinese Buddhist monks and engineers create south-pointing chariots for
Emperor Tenji of Japan
• 1720: Joseph Williamson uses a differential gear in a clock.
• 1810: Rudolph Ackermann of Germany invents a four-wheel steering system for carriages
• 1827: modern automotive differential patented by watchmaker Onésiphore Pecqueur
(1792–1852) of the Conservatoire des Arts et Métiers in France for use on a steam cart.
(Sources: Britannica Online and[3])
• Antikythera Mechanism
HISTORY(AD)

TYPES
• Open Differential
• Locked Differential
• Active/Electronic Differential
• Limited Slip Differential

DIFFERENTIAL GEAR TRAIN ON A TURNING CAR

OPEN DIFFERENTIAL
• These are commonly used differential to achieve Different Speeds at
wheels of the same axle
• Application includes normal passenger car and bus

OPEN DIFFERENTIAL TYPICAL PARTS
• Pinion Drive Gear: Transfers power from the driveshaft to the ring gear
• Ring Gear: Transfers power to the Differential case assembly
• Side/spider gears: Help both wheels to turn independently when turning
• Differential case assembly: Holds the Ring gear and other components
that drive the rear axle
• Rear drive axles: Steel shafts that transfer torque from the differential
assembly to the drive wheels
• Rear axle bearings: Ball or roller bearings that fit between the axles and
the inside of the axle housing
• Axle housing: Metal body that encloses and supports parts of the rear axle
assembly

OPEN DIFFERENTIAL SCHEMATIC

OPEN DIFFERENTIAL IMAGE

POWER FLOW
• Drive shaft spins the Pinion gear
• Pinion gear turns the larger ring gear to produce
gear reduction
• Ring gear attached to differential case, hence it
rotates with the ring gear
• Differential case spins the sun gears which are
attached to the axles
• Axles transfer the power to the wheels

DIFFERENTIAL GEAR RATIO
STRAIGHT TURNING

VEHICLE TRAVELLING STRAIGHT
• Input torque is applied to the ring gear, which
turns the entire carrier, providing torque to
both side gears, which
in turn may drive the left and right wheels
• If the resistance at both wheels is equal, the
pinion gear does not rotate, and both turn at
the same rate wheels

VEHICLE TAKING A CURVE
• If the left side gear (red) encounters resistance,
the pinion gear(green) rotates about the left
side gear, in turn applying extra rotation to the
right side gear (yellow)

LOCKED DIFFERENTIAL
• These are used to achieve Different Torques at wheels of the same
axle
• Locking means joining the two independent pinion gear
• Application includes race car and off-road vehicles and 4 Wheel Drive

LOCKING DIFFERENTIAL NECESSITY
• To provide increased traction compared to
the normal differential unit
CASE :
When one rear axle wheel is stuck in the
mud,
 Open differential will concentrate in
rotating the stuck wheel
 Locked differential will push the vehicle
with the help of torque available at the
free wheel

ACTIVE/ELECTRONIC DIFFERENTIAL
(Both Open & Locked)
• Dynamically Locking the differential
using a electromagnetic clutch
• When cornering, the inner and outer
wheels rotate at different speeds,
because the inner wheels describe a
smaller turning radius. The electronic
differential uses the steering wheel
command signal and the motor speed
signals to control the power to each
wheel so that all wheels are supplied
with the torque they need

LIMITED SLIP DIFFERENTIAL
• A limited slip differential (LSD), is very similar to the open differential
unit but has additional link that prevents wheel spin and loss of
traction
• The standard differential delivers maximum torque to the wheel with
minimum traction. The limited slip differential delivers maximum
torque to the wheel with maximum traction
• It is mainly used in off road vehicles
• TYPES :
i. Clutch Pack
ii. Cone Clutch
iii. Torsen

LIMITED SLIP DIFFERENTIAL - CLUTCH
• The clutch pack limited slip differential uses a set of friction discs and steel
plates to lock the axles together whenever one drive wheel experiences
uncontrolled slippage. The friction discs are sandwiched between the steel
plates inside the differential case. The friction disc is splined and turns with
the differential side gears. The steel plates turn with the differential case.
• Springs (bellville springs, coil springs, or leaf springs) force the friction disc
and steel plates together. As a result, both rear axles try to turn with the
differential case.
• Spring force and thrust action of the spider gears applies the clutch pack.
Under high torque conditions, the rotation of the differential pinion gears
PUSHES OUT on the axle side gears. The axle side gears then push on the
clutch discs. This action helps lock the disc and keeps both wheels turning.

LIMITED SLIP DIFFERENTIAL - CLUTCH

LIMITED SLIP DIFFERENTIAL – CLUTCH WORKING
• When driving normally, the vehicle can turn a comer without both
wheels rotating at the same speed.
• As the vehicle turns a corner, the inner drive wheel must slow down.
• The unequal speed between the side gears causes the side gear
pinions to walk around the side gears.
• This walking will cause the outer axle shaft to rotate faster than the
differential case, allowing the pinion shaft on the side to slide down a
V-shaped ramp.
• This action releases the outer clutches causing the clutch pack to slip
when the vehicle is turning.

LIMITED SLIP DIFFERENTIAL - CONE
• A cone clutch limited slip differential uses the friction produced by
cone-shaped axle gears to provide improved traction. These cones fit
behind and are splined to the axle shafts. With the axles splined to
the cones. the axles tend to rotate with the differential case. Coil
springs are situated between the side gears to wedge the clutches
into the differential case.
• Under rapid acceleration or when one wheel loses traction. the
differential pinion gears, as they drive the cones, push outward on the
cone gears. This action increases friction between the cones and case,
driving the wheels with even greater torque.

LIMITED SLIP DIFFERENTIAL - CONE

LIMITED SLIP DIFFERENTIAL – CONE WORKING
• When a vehicle goes around a corner, the inner drive wheel must slow
down.
• The unequal speed between the side gears will cause the side gear pinions
to walk around the side gears.
• This walking action causes the outer axle shaft to rotate faster than the
differential case. Because the cones have spiral grooves cut into their clutch
surfaces, the inner cone will draw itself into the case and lock tight and the
outer cone clutch will back itself out of the case.
• This action allows the outer drive axle to free wheel.
• The end result is the majority of the engine torque is sent to the inner
drive wheel.

LIMITED SLIP DIFFERENTIAL - TORSEN
• Torsen differentials can be used in one or more positions on a motor
vehicle:
• Center - used to apportion appropriate torque distribution between front
and rear axles on an all-wheel drive vehicle.
• Rear - used to apportion appropriate torque distribution between left and
right sides in rear axles. This may be on either a rear-wheel drive or four-
wheel drive vehicle.
• Front - used to apportion appropriate torque distribution between left and
right sides in front axles. This may be on either a front-wheel drive or four-
wheel drive vehicle.
• A four-wheel-drive vehicle, for example, may use either one, two, or three
Torsen differentials.

LIMITED SLIP DIFFERENTIAL - TORSEN

LIMITED SLIP DIFFERENTIAL – TORSEN WORKING
• The Torsen differential works just like a conventional differential but can
lock up if a torque imbalance occurs, the maximum ratio of torque
imbalance being defined by the Torque Bias Ratio (TBR).
• When a Torsen has a 3:1 TBR, that means that one side of the differential
can handle up to 75% while the other side would have to only handle 25%
of applied torque.
• During acceleration under asymmetric traction conditions, so long as the
higher traction side can handle the higher percentage of applied torque, no
relative wheel spin will occur.
• When the traction difference exceeds the TBR, the slower output side of
the differential receives the tractive torque of the faster wheel multiplied
by the TBR; any extra torque remaining from applied torque contributes to
the angular acceleration of the faster output side of the differential.

LIMITED SLIP DIFFERENTIAL – TORSEN TYPES
There are currently three types of Torsen differentials,
• The original Torsen T-1 (Type A) uses crossed axis helical gears to increase
internal friction. The Type I can be designed for higher torque bias ratios
than the Type II, but typically has higher backlash and the potential for
Noise, Vibration, and Harshness (NVH) issues, and requires a precise
setup/installation.
• The later Torsen T-2 (Type B) uses a parallel gear arrangement to achieve a
similar effect. There is also a specialist application of the T-2, known as the
T-2R (RaceMaster).
• The latest Torsen T-3 (Type C) is a planetary type differential, in that the
nominal torque split is not 50:50. The Type C is available as single or twin
version; the Torsen twin C differential has front and center differential in
the same unit.

DIFFERENTIAL MAINTENANCE
Differential lubrication
• Change this oil every 30,000 to 50,000 miles (or as specified in user
manual)
• Use recommended oil for differential since different type requires
different oil density and properties
• After draining the used oil, clean the differential completely and then
fill the new lubricating oil
• Ensure the seal in the unit is good to avoid leakage and dust
accumulation

DIFFERENTIAL UNIT DISASSEMBLY
• Procedures for removal, disassembly, and reassembly vary depending
on the type of differential, make, and model. Always refer to the
manufacturer's service manual. However, there are several
procedures that relate to almost any type of differential.
To remove a separate carrier differential, perform the following:
• Remove the drive shaft
• Place a drain pan under the differential. Remove the drain plug and
drain the lubricant
• Unbolt the nuts around the outside of the carrier
• Force the differential carrier away from the housing

REMOVING REAR AXLE
• Remove the center pin, use a magnet
and remove the c-clips
• Holding the axle on to the sun gears,
and remove the axle

REMOVING REAR AXLE
• Remove the bolts holding the axle
flange to the drum/disc backing plate
and pull the axle

DIFFERENTIAL PROBLEMS
• Bearings, humming sound gets louder with
higher speeds
• Clean the bearing setup if persist change it
• Ring and Pinion, show up as whining or
howling noise that changes when going from
acceleration to deceleration
• Lack of service or low fluid can cause this
problem. Fill proper lubricant oil to avoid it
• If backlash (clearance) between ring gear and
pinion gear is too great. Adjust gear and pinion
to avoid the noise
BEARING
RACK & PINION

REFERENCES
• https://www.expeditionexchange.com/tractech/
• http://www.efunda.com/designstandards/gears/gears_auto_diff.cfm
• https://en.wikipedia.org/wiki/Locking_differential
• https://en.wikipedia.org/wiki/Electronic_differential
• https://en.wikipedia.org/wiki/Differential_%28mechanical_device%29
• LSD by Mohamed Hairi Bin Abdul Shukur, et, al. of Kementerian Pengajian
Tinggi
• http://www.popularmechanics.com/cars/how-to/g1140/how-to-care-for-
your-cars-differential/?slide=1
• http://www.tpub.com/basae/127.htm

Automobile Differential Unit

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