Study On Lateral Dynamics Characters And Control Of 4WS Vehicle

My research is focused on lateral dynamics and its control for four-wheel-steering (4WS) vehicle. Based on current situation that linear, nonlinear and uncertain factors are not synthetically considered in the research of handleability and stability. Therefore the handleability and stability study including linear, nonlinear and uncertain factors is the topic of this thesis.Firstly, the car lateral dynamics model are constructed which including proportional feed-forward and feedback. Then simulation is performed using Matlab/Simulink with same parameters and work condition for 4WS and FWS vehicle in frequency and time domain respectively. The simulation results show that main technical index including yaw-rate wave amplitude and overshoot are better than that of FWS, although their phase are almost same. which means the 4WS technology can ensure an enhanced stability.Secondly, the theoretical analysis is performed adapting modern nonlinear dynamics and Hopf bifurcation theory for 4WS nonlinear dynamics model. And precondition of Hopf bifurcation was analyzed. The Hopf bifurcation normal form is deduced basing on center manifold theorem and Normal Form theory. Then Periodic Solution stability can be judged on coefficients of Hopf bifurcation center manifold. The theoretical analysis is valuated using simulation for system model.Thirdly, the 4WS uncertain model of two and three DOFs is constructed with environmental disturbance, which is analyzed using the robust H∞control theory. And with recursive solution, H∞optimal controller is designed basing on the resistance index of environmental disturbance, which can improve system robustness. Then with application of mixed H2 /H∞control theory, a H2 /H∞optimal controller is designed with environmental disturbance resistance as index. The simulation shows its excellent performance which is theoretical basis of 4WS controller development.Then taking consideration of whole vehicle multi-body system dynamics, a ADAMS dynamics model is constructed for 4WS vehicle with three axles. Simulation is conducted for model transient response in time domain with front wheel steering angle as step input, results indicates that the handleability and stability with 4WS are better than those with FWS. The research about influence of vehicle parameter on handleability and stability provides theoretical base for optimum design scheme of 4WS vehicle.At last, on basis of the above mentioned research results, design methods of hardware, software, data interface module and mechanical actuators are also discussed. A 4WS controller is designed using 32-bit ARM processor which is an embedded real time operating system. The target of high-speed stability and low-speed maneuverability is achieved for 4WS vehicle. Model experiment and prototype test can prove that the controller can meet requirements of 4WS system.My research on 4WS lateral dynamics and development of 4WS controller can provide a good support for further research of 4WS technology.This paper is supported by the National Natural Science Foundation of China (No.50075060) and Tianjin Science and Technology Development Project(No.033105011).