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, whichin 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 tothe normal differential unit

CASE :

When one rear axle wheel is stuck in themud,

Open differential will concentrate inrotating the stuck wheel

Locked differential will push the vehiclewith the help of torque available at thefree wheel


ACTIVE/ELECTRONIC DIFFERENTIAL (Both Open & Locked)• Dynamically Locking the differential

using a electromagnetic clutch

• When cornering, the inner and outerwheels rotate at different speeds,because the inner wheels describe asmaller turning radius. The electronicdifferential uses the steering wheelcommand signal and the motor speedsignals to control the power to eachwheel so that all wheels are suppliedwith 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 Packii. Cone Clutchiii. 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 withhigher speeds• Clean the bearing setup if persist change it

• Ring and Pinion, show up as whining orhowling noise that changes when going fromacceleration 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 andpinion gear is too great. Adjust gear and pinionto 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 PengajianTinggi

• http://www.popularmechanics.com/cars/how-to/g1140/how-to-care-for-your-cars-differential/?slide=1

• http://www.tpub.com/basae/127.htm


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_(mechanical_device)

http://www.popularmechanics.com/cars/how-to/g1140/how-to-care-for-your-cars-differential/?slide=1

http://www.tpub.com/basae/127.htm

Automotive

Automobile Differential Unit