Research On Four Wheel Steering Of Vehicle Based On Fuzzy Control Simulation

The four wheel steering (4WS) is the development result of vehicle technology and it can improve the active safety and handling stability. In lower velocity 4WS can efficiently improve the steering maneuverability and in high velocity it can prevent the vehicle to swing and Side Slipping. 4WS is a advanced technology with broad future.The main context of this thesis is about the control method and simulation of the 4WS as following:Firstly, a 2 degree of freedom (DOF) and 3 DOF vehicle dynamic models are derived and with different control strategies to simulate, the simulation result showed that 4WS can effectively to improve the handling and stability.Secondly, the model used in 4WS of the most research is a linear 2 DOF model with the hypothesis that the tire did not reach the limited range, in this thesis a multibody 4WS model is presented using ADAMS which consider the suspension kinematics joints, the nonlinear of the tire, bushing, spring, damper and the load transfer effect, the model showed the detail of the vehicle.Thirdly, it is difficult to build the state equation for a complicated nonlinear vehicle model, and its dynamic equation has nonlinear and time-change characters. Thus, a new intelligent control method is proposed using fuzzy control strategy which is suitable for nonlinear systems. A fuzzy control strategy model of 4ws was built by Matlab/Simulink fuzzy control toolbox, using the fuzzy control strategy to drive the rear wheel.Lastly, the sideslip angle feedback control fuzzy controller and the yaw velocity of vehicle feedback control fuzzy controller are designed. Three kinds of fuzzy control methods--sideslip feedback control, yaw velocity of vehicle control and sideslip and yaw velocity united feedback control are studied in this thesis. The results show that these three kinds of control methods can improve handing and stability of vehicle.