The Haldex-clutch enables for all wheel driven vehicles an electronical control. This is not always the case with the (only mechanically operating) Torsen differential. So the torque can be unequally distributed on the front and rear axle. In addition, the all-wheel drive is decouplable case of ABS and other functions.
Differences in rotational speed between front and rear axles set a wobble plate pump in motion visible in the picture. These guaranteed by the red marked pistons a pressure build-up within the shortest possible time. This affects to a multi-plate clutch after a detour via a control valve, and thus connects the front and rear axle completely or only to a certain percentage. It is controlled electronically and can be changed at short term.
The electric oil pump, still smaller at the first Haldex versions and responsible only for the pre-pressure, but in case of Haldex 4 and 5 (top picture 3) solely responsible for the pressure generation. It replaces the pressure accumulator and the swash plate pump. With the latter Haldex could become active only after the occurrence of slippage. This is now already previously possible, for example, when starting to distribute the torque more to the rear axle.
The connection between front and rear axle is not permanent, the manufacturer justifies this with a lower consumption. Nevertheless, all components for the additional rear-wheel drive constantly running with. Though, in the curve the all-wheel drive can be activated in a flash and thus additional cornering force can be generated. 1.4 kg shall be more lightweight Haldex 5, relativized by the fact that the additional effort for the all-wheel drive is a total of well over 100 kg. 05/15