Traction control in a four-wheel drive vehicle

Traction control in a four-wheel drive vehicle involves wheel braking and reduction of engine torque. A target slip for each wheel is determined at 31 in dependence on a reference slip, vehicle speed, actual yaw rate, and yaw rate deviation. When traction control is needed, as determined in judging section 32 by a comparison of the actual and target slip for each wheel, a signal is outputted to calculating means 33 which produces a braking force, according to the difference between the target slip and the actual slip, for each wheel and to calculating means 35 which produces a signal to the engine control apparatus 15 to reduce engine torque. The reference slip is that acheived by a wheel when in a straight running condition or in a neutral steer condition when executing a turn.