System for controlling the drehmomentuebertragung in a four wheel drive vehicle

A control system for a full time four wheel drive vehicle having a transfer case including a planetary gear differential and an electromagnetically actuated clutch assembly for biasing torque between the front and rear drive wheels in response to signals from the control system. The control system includes apparatus (116) for detecting wheel slip and a device (118), responsive to the detection of wheel slip for calculating a maximum torque level to be established by the clutch assembly as a function of the total torque delivered to the transfer case and for programming clutch torque application over a predetermined time period and in a manner biasing torque through the differential to eliminate wheel slip. The control system compares actual wheel slip with a desired wheel slip by means of a feedback control loop to produce a slip speed error signal. Switch logic means gives a maximum clutch torque command when the error is above an upper limit and a zero torque command when it is below a lower limit.