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Vehicle stability control system is a new idea which can enhance the vehicle stability and handling in the emergency situation. This system requires of the yaw rate, side slip angle, and road friction in order to control the traction force and the braking force at the individual wheels. This paper proposes an observer for vehicle stability control system. This observer consisted of the state observer for vehicle motion identification and the road condition estimator for the identification of the road friction coefficient. The state observer uses 2 degree-of-freedom bicycle model with the Dugoff tire and estimates the system variables based on the Kalman filter. The road condition estimator uses the same vehicle model and identifies the tire-road friction based on the recursive least square method. Both estimators make use of each other information.

Vehicle stability control system can enhance the vehicle stability and handling in the emergency situations through the control of traction and braking forces at the individual wheels. Because this system needs to handle the nonlinear and complex vehicle dynamics, the controller is required to have the robustness and the simple structure for practical applications in order to achieve the desired performance. This paper proposes a new controller based on the multiple sliding mode control theory for vehicle stability control system to satisfy these requirements. The proposed controller for the lateral motion makes use of both the sideslip angle and the yaw rate. It brings the vehicle sideslip angle and the yaw rate close to the desired ones so that the vehicle dynamics becomes stable and the vehicle traces the desired course even in limit cornering.