Study On The Control Strategy Of Four Wheel Steering Vehicle

Using four-wheel steering technology, the steering characteristics of vehicle are effectively improved. At low speed, four-wheel steering vehicle show more flexible; at high speed, the steering stability of four-wheel steering vehicle increases largely. Based on different control strategies conrollers for four-wheel steering vehicle model, the four-wheel steering in handling stability is discussed. The main contents of this thesis can be summarized as follows:(1) Based on three degrees of freedom nonlinear four-wheel-steering vehicle dynamic equation, the model of four-wheel-steering vehicle is established taking a full account of the nonlinear of the tires.(2) Through establishing the vehicle dynamic model in ADAMS/View and using the measure fuction,simulate and analysis the steering characteristics of vehicle. The simulation results at low speed show that comparing four-wheel steering technology with front wheel steering technology, turning radius of vehicle decreases and the vehicle drivability is significantly improved.Then,simulate and observe the yaw rate and body side-slip angle of vehicle at high speed, the simulation results show that four-wheel steering technology can effectively improve vehicle handling stability.(3)Thesis studies the fuzzy PID control strategy, and further builds fuzzy PID controller in the MATLAB/Simulink toolbox.Then, ultilizing fuzzy PID controller to control and optimize the side-slip angle and yaw rate of the vehicle,the step steer test and single lane change test are proceeded.The simulation demonstates that the fuzzy PID control strategy largely improves features of the side-slip angle and yaw rate of the vehicle. (4)Finally, this paper introduces the principle of BP neural network and structure, determines the neural network topology structure and learning algorithm. Four-wheel steering vehicle model with fuzzy PID control strategy is used as sampling model, and the rear wheel Angle is served as output training data. Using the trained BP neural network controller to control four-wheel steering vehicle model, the step steer test starts. The simulation demonstates that BP neural network control strategy has a good stability and adaptability.To sum up,based on the research of fuzzy control strategy and BP neural network control strategy, conclusion can be made that:The above two kinds of control strategy can improve the features of side-slip angle and yaw rate,and increase the stability and reliability of the vehicle.This thesis provide application of advanced control technology in the four-wheel steering a theory basis.