Variable structure model following control of four-wheel-steering vehicle

A new strategy to optimise the design parameters of four-wheel-steering system (4WS) and to control 4WS is presented in this paper. The optimal control laws of 4WS on a series of combined roads, which are defined as standard roads where the vehicle is tested, are studied, based on the closed-loop control model of the driver-vehicle-road. The actual vehicle model with roll, yaw and lateral motions is considered as an uncertain system, where the cornering stiffness of the front and rear wheels and outer disturbance are defined as uncertain parameters varying over a limited range. A new controller of model-following variable structure is constructed and used for controlling the steering of front and rear wheels of the actual vehicle, so that the steering characteristics of uncertain vehicle model and nonlinear vehicle model can follow the steering characteristics of the reference model (nominal model).