Unit iii by suman

AUTOMOTIVE ENGINEERINGUNIT-III

Suman Deka, F-Batch, Roll no-108

REAR WHEEL DRIVE LAYOUT

REAR AXLE A group of subassemblies or a separate unit of a

motor-vehicle chassis (such as an automobile and tractor) that transmits torque from the propeller shaft or directly from the gear box to the propelling mechanism (wheels).

In most motor vehicles the rear axle has a housing, tubes for the axle shafts, a final drive (including the differential with reduction gears), and the axle shafts. The final drive and axle shafts are part of the motor-vehicle transmission.

Wheel brakes are mounted on the rear axle, as are the hubs for the wheels. The rear axle is joined to the frame or body of the motor vehicle by a suspension.

FIG: REAR AXLE OF A FORD F-550 CUMMINS PICK-UP VAN

LAYOUT OF REAR AXLE

LAYOUT OF CONVENTIONAL REAR AXLE

FUNCTIONS OF A REAR AXLE:

(1) Changing the direction of driveshaft rotation by 90 degrees to rotate the axle shafts.

(2) Providing a final speed reduction between the drive shaft and the axle shafts through the final – drive gears or differential gears.

(3) Providing differential action , so that one wheel can turn at a different speed as compared to the pother wheel, when required, Providing axle shafts or half-shafts to drive the rear wheels.

(4) Acting as a thrust and torque reaction member during acceleration and breaking.

FINAL DRIVE

A final drive is that part of a power transmission system between the drive shaft and the differential. Its function is to change the direction  of  the power transmitted by  the  drive shaft  through  90 degrees to the driving  axles.  At  the  same time  it  provides  a  fixed reduction between the speed of the drive shaft and the axle driving the wheels, i.e. the car moves at different speeds while the engine runs at most efficient stage.

FINAL DRIVE COMPONENTS

1. Drive Axle2. Final Drive3. Suspension Cross Member4. Trailing arm5. Outer CV Joint6. Driveshaft7. Suspension Strut

FIG: BMW 540i Final Drive

SINGLE REDUCTION AXLE:

A single axle construction in which one sets of reduction gears are used for reduction of gear ratio.

A reduction axle decreases the drive shaft speed to a less and manageable speed.

If you have a 4:1 gear box then the wheels moves 1/4 as fast but has 4 times the torque! But the car will be capable of carrying 4 times the load.

SINGLE REDUCTION

DOUBLE REDUCTION AXLE:

(1) A double reduction axle construction in which two sets of reduction gears are used for reduction of gear ratio to produce higher torque.

(2) If we have a double reduction axle system with two independent gearswith gear ratio 5:1 and 4:1, then the final gear reduction will be 20:1.

(3) For the same condition torque will be increased 20 times as well as the load carrying capacity.

(4) Double axle reduction is used for heavy vehicle used to carry very high loads.

DOUBLE REDUCTION GEAR

FIG: REDUCTION OF GEAR BY WORM GEARS (SINGLE REDUCTION AXLE)

INSIDE VIEW OF FINAL DRIVE UNIT(DIFFERENTIAL)

REAR AXLE

BEVEL GEAR

PINION

CROWN WHEEL

Propeller Shaft or Drive

shaft

• It carries the power from the Transmission or the Gearbox to the Differential.

• It is a long tube like structure made up of hard steel.

• It is provided with universal Joints at one end and the other has splines to fit it inside the yoke.

• If there are multiple shafts in the vehicle, it can be mounted in the cross member of the frame and also can be inserted into the center bearing and mounted in the member.

Drive Shaft Mechanism

Transmits engine torque to the differential, or from the differential to the drive wheels.

Differential or Rear Final Drive

• It is a very important device which converts mechanical energy to Motion.

• It provides less motion to the inner wheel and greater motion to the outer wheel while the vehicle is being turned.

• Drive pinion and Driven gear and Planetary gear assy. are the important parts installed inside the housing.

• It holds the wheel hubs and break drums and the cylinders and also carry half axel shafts which help in moving the vehicle.

A special gearbox designed so that the torque fed into it is split and delivered to two outputs that can turn at different speeds.

Differential Mechanism

DIFFERENTIAL

A Differential is a part of an automobile which provides relative movement of two rear wheels when the car is taking a turn.

It consists of: (1) Differential (2) Rear axle (3) Wheels (4) Bearings

The Differential is a provided in such a way that the propeller shafts connects the rear axles.

INSIDE OF A DIFFERENTIAL

FUNCTIONS OF A DIFFERENTIAL

Differential gearing allows power to be split to two shafts (let's just say wheels), traveling at different speeds, with equal TORQUE going to each wheel. The differential gear carrier rotates at the AVERAGE speed of the two wheels.

It causes your driveshaft to deliver power to your axels. It contains gears that transfer the engine rotation 90 degrees.

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 (or lack thereof) 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 (rotational force) 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.

DIFFERENTIAL LOCK

FIG: LOCKING DIFFERENTIAL

REAR AXLE

REAR AXLE

In between the differential and drive wheels there is the rear axleto transmit power from the differential to drive wheels. Rear axle is made up of two half-shafts connecting each wheels, and the differential joints the two half-shafts. In rear wheel drive vehicle the rear axle is the drive axle.

A housing completely encloses the rear axle to protect it from dust, sand and injury.

TYPES OF REAR AXLE

FIG: LIVE AXLE FIG: DEAD AXLE

REAR AXLE HOUSING

The rear axles are enclosed in a protective casing known as REAR AXLE HOUSING.

It prevents the axle as well as the differential from dirt, sand and injury. It also work as a container for the lubricants.

Fig: Mercedes Benz Rear Axle Housing (Banjo Type)

TYPES OF REAR AXLE:

(1) Banjo Type (2) Split Type

A Banjo type rear axle is one in which the housing comprises of only one body, i.e. the whole housing is just in one piece. A Split type rear axle is one in which the housing comprises of more than one parts joined by various means which can be dissembled when needed.

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