Research On Optimal Control Of Vehicle

Four Wheel Steering (4WS) is an advanced vehicle control technique which can improve steering characteristics. Compared with traditional front wheel steering vehicles,4WS vehicles can steer the front wheels and the rear wheels individually for cornering,according to the vehicle motion states such as the information of vehicle speed, yaw velocity and lateral acceleration. Therefore, 4WS can enhance the handling stability and improve the active safety for vehicles.Based on the theory of Vehicle Dynamics and control technology, this paper investigates the following issues: firstly, a 2DOF 4WS vehicle model is built up by using the Newton equations, containing lateral and yawing motions. Secondly, based on the 4WS vehicle model with linear tire lateral force characteristics, the Model Reference Adaptive control algorithm is designed to use feed-forward plus feed-back control framework by following the reference model. And the simulation is processed in MATLAB/Simulink to verify the control algorithm.By comparison and analysis of the simulation results, the following conclusions can be drawn: the designed control algorithms can keep the sideslip angle of the vehicle approaching to zero. By following the reference model, the performances of the yaw velocity and lateral acceleration responses are improved. Consequently, the handling stability is enhanced.