The FDU houses the torque splitting differential and provides the directional translation from longitudinal to transverse. It also provides the ratio adjustment between gearbox output and wheel speed.
The fixed ball joint is fitted to the outboard area of a sideshaft enabling the shaft to articulate with the wheel suspension movement. This joint was developed according to the principle that the balls should always assume a position corresponding to the bisected articulation angle between the axes of the driving and driven shafts. The joint takes on the function of two bevel gears but has the important advantage of enabling continuous change of articulation angle. The centre points of the tracks are offset from the centre-point of the joint. At all times these crossing ball tracks maintain the balls in position at the half-angle (the bisecting plane). The torque is normally transferred by six balls. To improve the track control of the balls a cage is positioned between the outer and inner races. The cage holds the balls on the outer joint housing, preventing them from dropping out. This design was originally patented by Alfred Hans Rzeppa in 1929, with the offset control feature further developed by Bernard Stuber in 1933. In 1959, the Mini was the first car to use a ball-type constant velocity joint, whilst the Rzeppa style joint was fitted to the DKW Junior F11.
In principle four-wheel drive is a combination of front-wheel and rear-wheel drive systems. With four-wheel drive vehicles, power produced by the engine is transferred to all four of its wheels at the same time. There are different ways that this can operate:
This system is also known as Full Time Four Wheel Drive. The Transfer Case or Power Transfer unit provides a fixed torque distribution to the front and rear axles via a centre differential.
The vehicle normally operates in two-wheel drive. When four-wheel drive is engaged, both front and rear wheels are mechanically locked together (no differentiation between the front and the rear axles can occur).
One Axle (or transaxle) primarily drives the vehicle. A Transfer Case or Power Transfer Unit directs torque to the secondary axle via a passive or active Torque Management Device with fully variable torque distribution.
A selectable driveline disconnect system for four wheel drive applications. The inner differential case containing the pinion gears is interconnected to the outer differential case by a cam ring (dog tooth clutch). An actuator (pneumatic type or shift motor type) pushes the cam ring into the inner differential case. The opposing dog tooth profiles engage and directly lock the inner differential case to the outer differential case. The specific interface geometry between the drive cam and differential case assures a dog tooth clutch engagement under all loads. In the disengaged position (2WD), the inner differential case rotates freely inside the outer differential case. In the engaged position (4WD), the inner differential case is locked to the outer differential case.
Power produced by the engine, typically mounted transversely in the front of the vehicle, is transferred through the gearbox and sideshafts to the front wheels. Front wheel drive allows compact packaging for engine transmission and driveline resulting in more space in the passenger compartment.
This is used in hydrogen vehicles, where the fuel cell creates electricity from hydrogen to provide power to the electric motor.