The Modeling And Simulation Analysis Of Four-wheel Steering Vehicle

In recent decades, our country's economy has developed rapidly, during this period, the development of automobile industry has entered a fast track, has become one of the pillar industry in China. However, as more and more cars entered innumberable families, frequent accidents happen, automobile safety are more and more concerned,the vehicle manipulation stability which is closely related to auto safety thus become the focus of attention. The stand or fall of automotive steering system has a direct impact on the vehicle manipulation stability,how to design an efficient steering system is one of the important links in car design, but also one of the research topics of automobile safety.Because of many disadvantages such as big turning radius and poor mobility when low-speed steering, and bad manipulation stability when high-speed steering, the traditional front wheel steering system more and more can not meet the people's requirements to the performance of cars. As the thorough research on car dynamics, people are beginning to realize that four-wheel steering system can effectively improve the mobility of car when low-speed steering and the manipulation stability when high-speed steering, therefore, four-wheel steering system now has become chassis control technology research hotspot again after silence for many years.According to momentum theorem and moment of momentum theorem of Newton vector mechanics system, and Newton's second law, this paper deduce two degrees four-wheel steering dynamics model, and with ADAMS/CAR establish four-wheel steering vehicle multibody dynamics model which includes car tires, suspension system, steering system, braking system, engine system, body systems and so on.Taking two degrees four-wheel steering dynamics model for example, this paper has studied three classic control methods of four-wheel steering, through the simulation analysis, the results show that the three control methods in a certain extent improve the manipulation stability of car when low-speed and high-speed steering, but all of them have their shortcomings, namely cannot achieve two control objectives at the same time that body side slip angle maintain zero and steady gain of yaw-rate keep in ideal value goal nearby. In order to solve this problem, this paper proposes a new kind of four-wheel steering control method, the fractional order PID control method, and proceed manipulation stability simulation experiment with four-wheel steering car which is under this control method, the simulation results prove that under this control method the four-wheel steering system can make body side slip angle maintain zero and steady gain of yaw-rate keep in ideal value goal nearby, that means the four-wheel steering car which is under this control method not only improves auto manipulation stability of the car, but also make the car drivers used to driving front wheel steering car can be well to four-wheel steering car driving.Because the two degrees four-wheel steering dynamics model is based on numerous hypothesis conditions derived, which is different from actual car in a great extent, so its simulation results has certain limitations, and not accurate enough. In order to provide more accurate and more reference valuable simulation results for practical automotive, this paper also carry out control research on four-wheel steering vehicle multibody dynamics model, on the basis of fractional order PID, and bring in fuzzy control theories, then design fuzzy fractional order PID controller, the simulation results proved that the four-wheel steering vehicle multibody dynamics model which is controled by this controller, can make cars to get good manipulation stability.