Road Friction Estimation Method Under Complex Operations Used By ESP System

With the rapid development of the vehicle industry, and customers’ demands aboutvehicle safety stronger and stronger, Vehicle Dynamics Control (VDC) has become aheated research in the vehicle control fields for recent years, which mainly includingactive safety technologies like Anti-Brake System (ABS), Traction Control System (TCS)and Active Yaw Control (AYC). The timely and accurate intervention of the controlsystem plays a significant role under some extremely dangerous emergencies like avoidinga crash etc. As to the state values as the road friction used in the control system, alsoaffects the performance basically.Based on the research achievements of the vehicle dynamics and control group invehicle dynamic field, this paper focused on the estimation of the road friction coefficientunder complex operating conditions from off-line simulating to real vehicle ground test todevelop and verify the algorithm. Firstly, the road friction of the individual sub-system of theVDC system under common situations like braking, driving and steering was estimatedrespectively, then synthesizing the friction coefficient of the sub-systems to confirm the oneunder complex situations, realizing the comprehensive estimation.For ABS, the road friction was estimated based on the control method called brake decaypower combining with the fuzzy logic control; and for TCS, the balanced rotation equation ofthe driving wheels were utilized to obtain the utilized road friction, then the reference one wascalculated by introducing a certainty factor which reflects the relationship between the utilizedroad friction and the slip ratio; as to the AYC system, this paper adopted two nonlinear extentswhich decides how much can the lateral acceleration be believed to obtain the compensativevalue, then classified the original value of the friction coefficient into different ones, andfinally complete the estimation also considering the special time points while the steeringwheel was back to zero which may lead a considerable error, this method was based on onepaper published in the journal “Vehicle System Dynamics”, and made plenty of improvementsto make sure the robustness. The algorithm proposed in this paper was validated through ground test on asphalt,snowy and icy road respectively, which demonstrated that the road friction estimation methodbased on the signal fusion under complex operations is timely and accurate, it can satisfy thecontrol demands.