Study on Steering Character of Four-wheel Steering Vehicle
|School||Wuhan University of Technology|
|Keywords||Four Wheel Steering Nolinear Tire Model Control Stability OptimalControl Fuzzy Control|
With the development of modern society and technology, people attach importance to road safety. In order to guarantee safety, auto control stability should also be valued. Four-wheel steering technology is a kind of technology which can change the direction both front and rear wheel, rear wheel can turn independently. At low speed, front and rear wheel turn out-of-phase, which can reduce automobile turning radius, improve the mobility and flexibility of car; At high speed, t front and rear wheel turn in-phase, which can improve the car comprehensively tracking ability, improve the car driving stability.First, this paper briefly introduced the background and significance,summarizes the car four-wheel steering system in recent years both at home and abroad present research situation and development trend, this paper expounds the main research work. Second, set a linear2-d four-wheel steering model, establish the tire cornering characteristics of nonlinear model, in matlab/simulink flat, we established the nonlinear second freedom four-wheel steering vehicle model. Third, this paper introduces the characteristics of the four-wheel steering vehicles, evaluation index of four-wheel steering control stability are analyzed, including four-wheel steering vehicle on the front step input Angle of transient and steady response, and the four-wheel steering vehicle and front wheel steering vehicle are compared, the result shows that four-wheel steering control stability is better than the front wheel steering. Four-wheel steering vehicles of linear and nonlinear motion have comparative and analysis, the results showed that the linear and nonlinear were consistent. In the fourth chapter, the control of front and rear wheel corner ratio, the angular velocity feedback control,the joint control between a proportional control and the angular velocity feedback control were compared and analyzed separately, the result shows that the joint control of proportional control and the angular velocity feedback control is better than the former two control method. And then the different structural parameters influence on the vehicle steering stability is analyzed.The angular ratio feedforward control and a feedback control in the turn of the car put the angular velocity and lateral acceleration down excessively, in order to improve it and lighten the burden of driving, add additional yawing moment, introduce the linear quadratic optimal control and establish four-wheel steering linear2-d model with additional yawing moment, design a joint optimal controller and establish the simulink model, and the simulation results solve the problem that the steady yaw velocity and lateral acceleration drop off excessively. Considering the tire characteristics of nonlinear factors, introduce the fuzzy control, and design controllers on the basis of angular velocity feedback, and compare with other control methods, verify that the four-wheel steering fuzzy control can be applied to nonlinear four-wheel steering vehicles and also can solve the problem that steady yaw velocity and lateral acceleration drop off excessively, improve the vehicle steering stability. Finally, design Angle and yawing moment nonlinear fuzzy control system and establish the simulink model, and the simulation results are more actual.