Research On Control Strategy And Key Problems Of Electronic Stability Control System

Electronic Stability Control is one of the most important product of vehicle activesafety.It consists of anti-lock brake system(ABS),traction control system(TCS)and active yaw control(AYC).ESC can improve vehicle handling stability and inhibit excessive braking,excessive driving,oversteer and understeer by adjusting wheel brake pressure and engine torque.ESC is not only an important active-safety product but also a basic platform technique for serieres of advanced vehicle chassis control systems like advanced driver assistant system,unmanned vehicle and so on.Thus the study of key problems in ESC is very meaningful.Based on existing research on ESC,this research focuses on several key problems in ESC,such as estimation of the key variables used in AYC,engine torque control method in AYC,AYC upper control algorithm based on model prediction control and accurate wheel pressure estimation and control method using typical hydraulic control unit in ESC.A design method of nominal state variables in AYC is proposed.This method has advantages in fast identifying unstable states and reduce false intervention of AYC.An engine torque pre-control algorithm is proposed,in which vehicle velocity is controlled by adjusting engine torque,in this way,the stability of the vehicle is improved.This method is used as an important supplement of active brake control,it can improve the control quality of AYC in both transient and steady status.An AYC upper control method based on model prediction control method is proposed in this research.The yaw moment control problem is transferred into a constrained linear time variant model prediction control problem and solved using quadratic programming method.The effect of different controller parameters is studied.This controller derives better yawrate following result than traditional optimal controller and requires more reasonable active brake control input.An estimation method of key variables in ESC is developed,which includes estimation method of tire-road friction coefficient and estimation method of vehicle sideslip angle.The friction coefficient estimation method used a dual-nonlinear index to correct the using friction coefficient and get the real friction coefficient.The estimation method of vehicle sideslip angle combines an active modified unscented Kalman filter observer and a sensor based observer to get the accurate estimation of vehicle sideslip angle.Both methods are verified and get satisfied results.An algorithm for accurate controlling the wheel brake pressure is designed.The hydraulic characteristics of each part of the ESC hydraulic control unit is studied.The control parameters of each actuation unit is derivated stepwisely.This method can be used in ESC electronic control unit and provide reliable brake system control for hierarchical controller design of ESC.