Research On Control Strategy Of Active Front Steering System For Automotive

Active front steering system can change the angle characteristic by providing a extraordinaryangle independent of drivers to steering wheel. Thus, it can not only combine steering stability withdriving safety but also change the function of steering system.Based on the two-degree-freedom vehicle model, the dynamic model of the active front steeringsystem (AFS) is built, including the steering wheel model, active steering motor model, two-rowplanetary gear transmission model, tire model, and gear-rack model. In view of the effects of vehiclespeed and steering wheel angle on vehicle stability, three control strategies of variable steering ratio areproposed to keep steering gain constant. The first ideal steering ratio is designed by keeping the yawrate gain fixed. The second ideal steering ratio is designed by keeping the lateral acceleration gain fixed.The third ideal steering ratio is designed based on curve fitting. The angel step steering simulation iscarried out to analyze and compare the different responses of handling stability of active front steeringsystem with different variable steering ratio control strategies at different vehicle speed. The activefront steering system simulation model of varying steering ratio based on adaptive fuzzy PID control isdesigned on the platform of Matlab/Simulink. Meanwhile, the control strategy of varying steering ratiois proposed on the basis of adaptive fuzzy PID control. Based on Linear Quadratic Regulator (LQR)optimal control theory, the yaw rate controller and extraordinary angle feedback controller are designed.The active front steering system collaborative simulation models are built on the platform ofMatlab/Simulink and Carsim to validate the effectiveness of the proposed effectiveness of handlingstability controller under the different side-wind gust. In conclusion, the main research content aboveprovides theoretical basis for the development and design of active front steering system.