Research On Control Method Of 4WS Vehicle

Along with science's and technology's development, the request of the vehicle performance has been higher and higher, especially ,handling stability has become an important research aspect at present. The performance of the steering system influences vehicle's handing stability, changes the portability as well as driver's working strength and the working efficiency, and 4WS vehicle has better ability of following the mark and the handling stability compared with FWS. Based on the original strategy, this paper investigates the control methods of 4WS based on different control theory.The semiem- pirical tire model is established on the analysis of tire sideslip characteristic.And then the force loded on the vehicle is analyzed and a 3DOF 4WS vehicle model is built up containing lateral, yaw and roll motions.Based on the 4WS vehicle model with nonlinear tire lateral force characteristics, the control algorithm is designed to use"the front wheel corner compensation plus active rear wheel control". The front wheel corner is compensated according to yaw-rate error while rear wheel begin to move according to current motion state. It is different with usual control strategy largely. In this course, reference mode is built which has good veracity. Linear-Quadratic (LQ) optimal control theory, the pole assignment theory, and the stability design theory are studied and used to design 4WS controllers, at the same time, good effect and some skill are obtained. Then the time weighting's erroneous absolute value integral(ITAE) criterion is used to control 4WS. It makes the sideslip close to zero.Taking the vehicle as the uncertainty object, robustness control of 4WS vehicle is researched. According to robust control theory, aμsynthesis controller is designed based on the vehicle model with consideration of disturbance uncertainty and unmodel dynamics. the simulation result indicate thatμsynthesis controller is good at improving handling stability and robustness of the vehicle.Research shows that the strategy of"the front wheel corner compensation plus active rear wheel control"is effective. the front wheel corner compensation makes yaw-rate follow the reference mode while the active rear wheel steering insure the handling stability of the vehicle. ITAE method has the best performance of handling stability,it makes the sideslip close to zero; the stability design and the pole assignment methods have better performance than LQ method for the optimize, but the pole assignment method brings about bad performance when the poles are choosed irrelevantly; At last, theμsynthesis control method improve the handling stability and robustness synchronously.