DIFFERENTIAL UNIT

INTRODUCTION – rear axles Crossbar that support the vehicle on which one or more wheels turn. Two types of rear axles 1. live axle (drive axle) – supports weight of vehicle and drive the wheels that connected to halfshaft. 2. dead axle (non drive axle) – supports weight of the vehicle but does not drive the wheels. Drive axles that wheels can pivot for steering called steerable drive axle – used in 4 wheel drive.

INTRODUCTION – rear axles

Functions of rear drive axles Rear axles performs several function, 1. changing drive shaft rotation by 90⁰ to rotate the axle shaft. 2. provide final speed reduction between drive shaft and axles shaft through final drive gears. 3. provide differential action so one wheel can turn faster than other. 4. provide axle shaft to drive the wheels. 5. act as thrust and torque reaction member during acceleration and braking.

Functions of rear drive axles

Rear axles housing and casing Differential and final drive gears in rear-drive vehicle are housed in rear axle housing, or carrier and also contains two drive axle shafts. Two types of axle housings found on modem automobiles 1. removable carrier (Banjo) 2. integral carrier (Split) Removable carrier axle housing is open on front side. Differential is mounted in a carrier assembly and can be removed as a unit from the axle housing.

Rear axles housing and casing - removable

Rear axles housing and casing Integral housing is found on late model cars and light trucks. Consist of cast iron carrier as the center of axle housing, steel axle tubes that pressed into both sides of the carrier to form the complete axle housing units. Integral housing have a removable rear cover that allows access to differential assembly. Differential components must be removed and serviced separately. For many operations, a case spread must be used to remove the components.

Rear axles housing and casing - integral

Final drive gears Set of gears that transmit torque from transmission to the differential. Made up from driving gear (pinion) and driven gear (ring gear) and usually use hypoid gear type. Ring gear is connect to differential housing and 3 or 4 times larger than pinion gear. When pinion turns it will reduces speed of axle shaft while increasing the torque that applied. Pinion gear attached with rear end of drive shaft and mesh with ring gear at below centerline of ring gear.

Differentials

Differentials Gear assembly that permits the shafts to turn in different speed while continuing transmit torque. Differential applications 1. rear drive axle – front engine rear wheel drive vehicles. 2. transaxles – front engine front wheel drive and rear engine rear wheel drive vehicles. 3. front drive axles and rear drive axles – four wheel drive vehicles. 4. transfer case of some four wheel drive vehicles.

Differentials components

Differentials gearing Final gear reduction in drive train occurs in differential assembly. Amount of torque a gear set delivers depends on the gear ratio between the drive pinion gear and the driven ring gear (axle ratio). Final drive gear ratio determines how many times a drive pinion tooth will make contact with a particular ring gear tooth during one revolution.

Differentials action

Limited Slip Differential LSD or anti-spin is another type of traction aiding device that uses a mechanical system that activates under centrifugal force to positively lock the left and right spider gears together when one wheel spins a certain amount faster than the other. This type behaves as an open differential unless one wheel begins to spin and exceeds that threshold. LSD will remain open unless enough torque is applied to cause one wheel to lose traction and spin, at which point it will engage.

Limited Slip Differential Figure (a) shows two-wheel-drive vehicle equipped with an open differential. (one side not enough torque) Figure (b) shows two-wheel drive vehicle equipped with a limited-slip differential. (both equally torque & speed)

Limited Slip Differential Use preload force from spring and torque that generated by side gears as the two axles rotate at different rates to apply the clutches and limit the amount of difference in the speed of two axles. There are basically two designs that are commonly used: 1. clutch pack type 2. brake cone type Noted that some vehicles use a viscous clutch in their limited-slip drive axles

Limited Slip Differential – clutch pack Used set of clutch pack & spring force to apply the clutch and transfer the torque equally.

Limited Slip Differential – cone clutch Uses two cone shaped friction components to lock the side gears to the differential case. Exterior surface of the cones is coated with friction material that grabs the inside surface of the case. Friction surface on the cones has a coarse spiral thread to provide a passage for lubricant

Axle Shaft Purpose of an axle shaft is to transfer driving torque from the differential assembly to the vehicle's driving wheels. There are two types of rear axles: 1. Dead axle - does not drive a vehicle, only supports the vehicle load and provides a mounting place for the wheels. 2. Live axle – drives the vehicle. Drive axles transfer torque from the differential to each driving wheel. Rear axles can also help carry the weight of the vehicle or even act as part of the suspension.

Axle Shaft Three types of driving axles are commonly used: i. semifloating, ii. three-quarter floating iii. full-floating.

Diagnosis & Troubleshooting One reasons are serviced is to correct a noise problem. Knowing when and under what conditions the noise is noticeable is a big help in identifying which bearing or component is the likely cause. Typical noise and its sources include: 1. Grinding or growling noise while turning – usual cause is a defective axle bearing. 2. Whine noise during cruise – drive pinion bearings are the likely causes of this type of noise