Research On Dynamics And Robust Control Of 4-wheel Steering Vehicle

With the continuous development of automobile technology,the demand for active safty of automobile is higher and higher,the handling stability affects safty of the passengers and drivers directly,automobile is demanded to follow the driver's instruction even quicker objectively,so the 4WS appears.Four Wheel Steering 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 vehicle speed,yaw velocity and lateral acceleration. Therefore,4WS can enhance the handling stability and improve the active safety of vehicles.Based on the theory of vehicle dynamics and control technology,the thesis investigates the following issues:Firstly,the main steering modes of 4WS vehicle are introduced and compared with the 2WS vehicle,its advantage can be got.the 2DOF 4WS and the 3DOF dynamic model is built,and the 2DOF dynamic model is analysed.The transfer function and the state-space formula are derived with the help of feedforward and feedback control style.The steering characteristics of 4WS is analysed.Taken front tire turning angle as step input,the steady state response and the transient response are researched analysed.Secondly,the method of linear Matrix Inequality(LMI)and its theorem are introduced.The 4WS 2DOF model based on external disturbance is built,based on the theory of H_∞robust control,output feedbackH₂/H_∞mixed control,state feedback H₂ /H_∞mixed control,LMI method,zero side-slip-angle control strategy,the different controllers with the feedforward and feedback control style is designed.Refering the parameters of a certain car in our country,the 4WS is simulated,with the help of MATLAB/Simulink,and the results of the simulation is compared with the traditional 2WS vehicle model respectively. Lastly,the three results are compared together,it can be concluded that the output feedback H₂ / H_∞mixed control is the the optimal way.In conclusion,the dynamic characteristics and control method are deeply researched theoretically,Excellent performance is obtained by H₂ and H_∞mixed control,external disturbance is attenuated perfectly and the system robust performance is enhanced.