STEERING OF 4WD VEHICLES WITH INDEPENDENT WHEEL TORQUE CONTROL

This paper investigates the steering performance of a new configuratio n 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 whe el to give a tyre speed differential between the outside and inside ty res. The wheel torque difference between the outside and inside tyres, which controls the tyre velocity difference, is a function of the han dwheel angle and the error between the expected yaw rate and the measu red yaw rate. In order to control steer stability, a stability compens ator for tyre/road adhesion limit is developed and the yaw rate and ya w acceleration are used as control variables. This strategy first eval uates the vehicle stability and then reacts depending on whether the s tability criteria is satisfied. The study shows that IWTC vehicles can be well steered by applying the methods developed in this research.