Since the beginning of the 1980's, 4WS (four wheel steering) has been regarded as a promising tool to improve vehicle handling and not only have many research and development studies been carried out on the 4WS control system and its effect on the vehicle handling but also it has been installed in some real vehicles. As any 4WS control which has been considered as an effective chassis control for passenger cars depends on tyre lateral forces produced by steer angle, it has some limit especially in a severe maneuvering such as with high lateral and/or longitudinal acceleration(s) due to tyre saturation property of lateral force to side slip angle, even though some adaptation to running environment or some nonlinear control technique is considered in the control. In order to overcome this drawback of 4WS, attention is focused upon a direct yaw moment control (DYC) with yaw mom ent produced by longitudinal forces on right and left wheels in opposite direction each other. One of the main concerns in this paper is what type of control law is suitable for the DYC to improve active safety of vehicle handling compared with the control law fitted to the 4WS.
Abstract