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Service. Self Study Programme 206 Four Wheel Drive with Haldex Coupling Design and Function Volkswagen and Audi have been building per manent four wheel drive systems for almost 15 years. In Volkswagen s system, a viscous cou The viscous coupling previously used by Volks pling distributes input torque to the rear axle; in wagen was able to detect slip alone, but not the Audi s system this job is performed by a Torsen cause of it. differential. The development of the Haldex coupling is a The slip recognising system is activated by a dif giant step forward in modern four wheel drive ference in speeds between the front and rear technology. The Haldex coupling is controllable. axles. Once activated, it distributes input torque A processor also makes allowance for additional to both axles. information during the control process. Slip is no longer the only decisive factor in the distribution of drive forces; the car s dynamic state is also a factor. The processor accesses the ABS wheel speed sensors and the engine control unit acce lerator pedal signal via the CAN bus. This data provides the processor with all the information it needs on road speed, cornering, overrun or traction mode, and can respond opti mally to any driving situation. Advantages of the Haldex coupling Permanent four wheel drive with electroni cally controlled multi plate clutch Front drive characteristic Quick response No strain on clutch when parking and man oeuvring vehicle Compatible with different tyres e.g. emer gency wheel No restrictions on towing with the axle raised off the ground Fully combinable with traction control systems such as ABS, EDL, TCS, EBD and ESP SSP 206/001 NEW Important Note The Self Study Programme Please always refer to the relevant Service Literature is not a Workshop Manual. for all inspection, adjustment and repair instructions. Table of contents Four wheel drive .4 Haldex coup