The permanent four-wheel drive system 4MOTION has a long tradition at Volkswagen. This four-wheel drive principle distributes the engine's power permanently and according to demand to all four wheels. The 4MOTION system provides high active safety, reliable traction on virtually all surfaces and optimum directional stability at all times, even in cross-winds. The fact that its extra safety reserves are available permanently gives it a clear edge over driver-operated four-wheel drive systems.
The technology behind 4MOTION four-wheel drive is based on an electrohydraulic multi-plate clutch (Haldex). It features an electronic control system that responds instantly to changes in wheel traction by adjusting the locking effect of the Haldex clutch. When required, the Haldex clutch distributes up to 50 percent of the drive torque to the rear axle.
The multi-plate clutch is integrated between the propshaft and rear axle differential. Inside a housing is the component responsible for the torque distribution, a wet multi-plate clutch pack in an oil bath.
The clutch is operated by hydraulic pressure on the clutch pack, squeezing the clutch plates together. Modulating this pressure varies the locking effect between the front and rear axles. The more pressure is exerted on the multi-plate clutch, the more drive torque can be transferred to the rear axle.
Two annular piston pumps supply the necessary pressure to press together the multi-plate clutch pack. They are driven by the difference in the rotating speeds of the input and output shafts by means of a cam disc. The pressure can be steplessly varied by an electronically/hydraulically controlled valve. To do so, the control unit processes information from various sources including wheel speed, ABS braking functions and engine management.