conventional rear wheel drive, a beam axle assembly

The function of the final drive is to; transmit or turn the drive through 90º Gear B is turning on the horizontal axis and it is driving gear A, which is turning on the vertical axis.

The function of the final drive is to; provides a permanent reduction in transmission output The pinion gear is the drive gear and will need to turn several times to rotate the crown wheel once.

Identify the components of a basic final drive assembly.

Gear design Spiral bevel Hypoid spiral bevel Bevel gears

Bevel Gears Bevel gears are primarily used to transfer power between intersecting shafts. The teeth of these gears are formed on a conical surface. Standard bevel gears have teeth that are cut straight. The teeth point toward the apex of the cone on which they are machined.

Types of gears used in final drives. Straight cut bevel gears. These gears are cheap to produce but are very noisy in operation, not suitable for modern motor vehicles

Spiral Bevel Gears Spiral bevel gears have teeth that have been cut at an angle. The larger surface contact area makes for a smoother, quieter running system, much like helical gears. Hypoid bevel gears are a special type of spiral gear that will allow non-intersecting, non-parallel shafts to mesh. Hypoid gears are stronger, operate more quietly, and can be used for higher reduction ratios than spiral bevel gears.

Types of gears used in final drives. Spiral cut bevel gears. These gears are quite in operation due to the gears sliding into mesh. They are able to transmit more torque.

Hypoid gears These gears are a special spiral bevel gear set with the pinion offset from the centre line of the crown wheel.

Hypoid gears Give 2 reasons why hypoid gears are the most common gear set used in final drive units. The prop shaft is lower so the floor can be made flatter. There is a greater area of tooth contact and therefore greater torque transmitting.

Crown wheel and pinion terminology. Clearance. The distance between the top of the tooth and its mating gear. Backlash. The space between the teeth in mesh.

Final drive gear ratios. Calculate the following gear ratios. If the pinion gear has 10 teeth and the crown wheel has 41 teeth, what is the finial drive reduction? 41/10=4.1:1 If the final drive ratio is 4.1:1, fifth gear ratio is 0.95:1 and the engine speed is 2500rpm, calculate the wheel speed in fifth gear. 4.1 x 0.95 = 3.895:1 overall gear ratio 2500/3.895 = 641.85rpm wheel speed

Final drive adjustments. Pinion preload To ensure correct gear alignment with the crown wheel, all end float in the pinion bearings must be removed by preloading the bearings. This is to ensure correct alignment of the crown wheel and pinion gears thus reducing noise and wear

Measuring Pinion Preload The tool shown is known as a torque meter. Preload varies from manufacturer to manufacturer - a rough figure would be 0.9 – 1.3 Nm.

Final drive adjustments. Backlash Backlash is the working clearance between the teeth on each of the gears or the space between the teeth to allow for thermal expansion and correct lubrication of the mating teeth

Measure Backlash If out of spec the side bearing preload will need adjusting. Backlash varies from vehicle to vehicle. Often around 0.13 – 0.18 mm.

Final drive gear types RWD Vs FWD

The differential Final drive

. List the 2 main functions of the differential apply equal torque to each wheel allow the wheels to rotate at different speeds.

Identify the components of the differential assembly.

Planet gears Half shafts Diff case Sun gears Cross pin

describe how the differential operates Driving straight ahead. When driving ahead the complete differential assembly turns as 1 unit and both wheels rotate at the same speed.

describe how the differential operates Driving around a corner. When the vehicle turns a corner, the inner wheel slows down , this causes the planet gears to rotate on the cross pin which allows the outer wheel to turn faster while still delivering equal torque to both wheels.