The final drive transfers the torque from the power-train to the shafts of the drive axle. In the case of the straight mounted engine, a diagonally cut cone and crown wheel combination (see figure 2) is always necessary. Transverse engines transfer their torque through diagonally cut spur wheels (see figure 2 on the right) to the drive wheels. The torque increases at the same ratio as the RPMs sink.
Motor car -> 2,5 - 4 : 1, truck -> higher, except with external planetary gears
The smaller bevel wheel or spur gear is linked to the gearbox, the larger, through a differential gear, with the driving wheels. The transmission ratio is, in motor cars 2,5- to to just under 4:1 and in trucks can be, particularly construction site vehicles, distinctly higher. The highest torque is generally reached on the axle drive shafts to the wheels. Tractors, trucks and busses with external planetary gears are the exception. In this case, also the transmission ratio between bevel gear and crown wheel is lower.
Diagonally cut or hypoid gear with axle offset
The same as in the gearbox, the gear wheels have diagonally cut teeth to achieve a quieter running and higher resilience. In the case of the hypoid drive, the axle of the bevel wheel is placed lower than that of the crown wheel. The outcome of this is a certain distance between the two center axles. The gear wheels are lubricated when the larger crown wheel dips into an oil bath thus distributing the oil in miniscule droplets. This type of lubrication is thus known as 'dip lubricating'.
Simpler pressure circulation possible in spite of dip lubrication
Only very seldom is this type of lubrication replaced by pressure circulation lubrication. Only then, If the highly accelerated oil is caught in a suitably formed pocket and e.g., is led back through a nearby oil cooler.
Tolerances according to the stamped in values
The crown wheel and bevel gear must always be replaced as a pair and their tooth backlash must be adjusted according to the stamped in values using a measuring gauge. This backlash was determined especially for this particular pairing in a quiet running test by the manufacturer. 09/09