Steering of 4WD vehicles with independent wheel torque control

This paper investigates the steering performance of a new configuration of automotive vehicles -- 4WD vehicles with independent wheel torque control (IWTC). The vehicle model has no steer linkages and a turning manoeuvre can be realised by controlling the wheel torque at each wheel to give a tyre speed differential between the outside and inside tyres. The wheel torque difference between the outside and inside tyres, which controls the tyre velocity difference, is a function of the handwheel angle and the error between the expected yaw rate and the measured yaw rate. In order to control steer stability, a stability compensator for tyre/road adhesion limit is developed and the yaw rate and yaw acceleration are used as control variables. This strategy first evaluates the vehicle stability and then reacts depending on whether the stability criteria is satisfied. The study shows that IWTC vehicles can be well steered by applying the methods developed in this research