| Good handling stability not only improves the driver’s experience,but also improves the safety performance of the car and protects the safety of life and property.This paper aims to improve the steering stability of the vehicle,and proposes a feedforward controller that takes the four-wheel steering characteristic with the front and rear wheel angles as variable transmission ratios and the vehicle state as control constraints to solve the wheel angles.In addition,considering the uncertainty of the road surface,a secondary performance-guaranteed controller with additional yaw moment is proposed to improve the convergence speed of the feedforward controller on low-adhesion roads.Firstly,the feedforward controller takes the minimum absolute value of the vehicle’s front and rear wheel slip angles as the system performance index,and obtains the feedforward controller constraints according to the variable transmission ratio characteristics,the ideal center of mass slip angle and the yaw rate following the ideal state.,Use linear programming to solve the controller.The simulation verifies that under different working conditions,the feedforward controller can reasonably allocate wheel angles,make full use of road attachment conditions,and enhance the steering stability of the vehicle.Secondly,considering the uncertain factors of the vehicle in driving,such as the influence of vehicle speed and road adhesion coefficient on vehicle handling and stability.Based on the two-free-of-freedom model of the vehicle,a control strategy is proposed that takes the desired yaw rate and the side slip angle of the center of mass as the tracking objects of the control system,and adds the yaw moment as the control input.The optimal guaranteed performance feedback controller based on robust control theory is designed.The yaw moment formed by the difference in driving force is used to distribute the four-wheel drive force so that the yaw rate and the side slip angle of the center of mass of the vehicle can track the ideal model well when turning.Finally,the controller is applied to co-simulation to study the vehicle stability under step input and sinusoidal input conditions to verify the accuracy of the simulation model and the stability and speed of the controller. |
