Research On Vehicle AFS And ESP And Their Coordinated Control/Integrated Control

The safety and handling stability of the vehicle is particularly important for the vehicle.Experts and scholars at home and abroad continuously studied and improved the Active Front Steering system(AFS)and Electronic Stability Program(ESP).The joint control of AFS and ESP has become the development direction of vehicle control technology in the future.Combing with the research status at home and abroad,this thesis analyzes the control principle of AFS and ESP,and realizes the coordination/integration control of AFS and ESP.The specific work content is as follows:(1)The longitudinal,lateral,yaw motion of the vehicle and the rotation motion of the four wheels around its central axis are considered to establish seven degrees of freedom model of vehicle.Considering that the tire is affected by non-linear factors,the Dugoff tire model is selected to analyze stress condition of tires.Based on the linear two degrees of freedom reference model,the condition of lateral force of tire reach the limit of lateral adhesion is considered and then the ideal yaw rate and side slip angle are determined.(2)Based on the above models,the yaw velocity are regarded as the control target to design the AFS by PID control,integral separation PID control,fuzzy control,fuzzy PID control,linear quadratic optimal control and sliding mode control principle.(3)Considering that it is difficult to directly measure the vehicle side slip angle and the road adhesion coefficient is affected by the road surface change,the side slip angle of vehicle is estimated by linear expansion observation principle and the tire-road adhesion coefficient is estimated base on the fuzzy identification principle.Based on the above models,the yaw velocity and the side slip angle are regarded as the control objectives to design ESP according to PID control,fuzzy control,fuzzy PID control and sliding mode control principle.Then the ESP is designed through the adaptive of the tire side stiffness.It calculate the braking force of the wheels by the load distribution between the shafts,and the wheels were applied with the braking force by formulating the single wheel braking wheel selection strategy,which jointly constituted ESP.(4)Taking vehicle maneuverability,stability and track retention performance as the observation indexes.It determines which AFS and ESP have the best control effect by the simulation on sinusoidal condition and the double line change condition.Then the coordination control strategy of AFS and ESP are formulated by analyzing the working conditions of AFS and ESP.Finally,the integrated controller of AFS and ESP is designed based on lyapunov's direct method,the function of AFS is replaced by sliding mode control,which constitutes the integrated control of AFS and ESP.By comparing the without control,AFS individual control,ESP individual control,AFS and ESP coordination control and integrated control effect on the lateral wind condition,sinusoidal hysteresis condition and double lane change conditions under high speed low adhesion road.Finally,it get following conclusions: the AFS and ESP individual control effect is good;AFS and ESP coordination control effect is better which can satisfy the maneuverability and stability of vehicle and track performance requirements,achieve the goal of control of the vehicle;AFS and ESP integration control effect is good,which can provide reference for the development of the integrated chassis control system.