A nonlinear analysis of closed loop driver/vehicle performance with four-wheel steering control

This dissertation describes the nonlinear analysis of closed loop driver/automobile system performance during both ordinary and collision avoidance maneuvers. The vehicle is considered to be equipped with either a conventional front wheel steering system (FWS) or one of several types of four wheel steering systems (4WS).; A refined nonlinear 5 degree-of-freedom (DOF) "bicycle model" and a nonlinear 8DOF, four wheel vehicle model were developed. A comprehensive nonlinear tire model and a multi-loop driver model (developed by previous investigators), were integrated with the vehicle model in this study, In addition, a new 4WS control system, which was designed using an adaptive control theory (Time Delay Control), has been proposed. Compared with existing 4WS systems, this new 4WS system requires less knowledge of difficult-to-measure vehicle parameters, and provides more robust control in the case of unpredictable external disturbances.; The simulation results indicate that the following potential benefits may be obtained from the 4WS systems: (a) fast yaw rate and lateral acceleration responses; (b) stabilization of the vehicle during collision avoidance maneuvers; (c) reduction of the driver's workload during both ordinary and collision avoidance maneuvers; and (e) less sensitivity of the vehicle to unpredictable disturbances.