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The Haldex clutch.

Thinking on its feet

The Haldex clutch is an electronically controlled multi-plate clutch. The driving forces are distributed across the axles variably and adaptively according to different driving conditions. The general principle of the Haldex clutch is that it always allocates the driving forces to the axle with the better traction. In this way, 4MOTION is able to respond ideally and in a flash to any driving situation. Despite that capability, the accustomed feel of a front-wheel drive vehicle is retained. The possibility of torsional stresses on the drive train during parking and manoeuvring is eliminated. The Haldex clutch can also be combined without restriction with all driving dynamics control systems (ABS, EDL, ASR, EBD and ESP).

The power transmission between the front and rear axles is handled by the multi-plate clutch. Electronically actuated pumps regulate the pressure on the plates of the clutch. As the exerted pressure rises, the plate sets are pressed against each other. In this way the power transmission between the sets of plates, and thus the distribution of power between the axles, can be regulated very precisely.

The function of the electronic control is to balance the slip and the resultant differences in rotation speed between the axles, and also to compensate for other variables such as the driving dynamics conditions and the driving torque. The control by the electronic control unit takes account of other driving dynamics information such as road speed, cornering and overrun or acceleration modes.