Abstract:Vehicle stability criterion is the basis of vehicle stability controls and decides the control intervention time and exit time. A phase plane method based criterion combing the sideslip angle method and the yaw rate method is proposed, which can coordinate the control of both vehicle sideslip angle and yaw rate. By means of phase plane method the data bases of the stable region thresholds are obtained, which contributes to establishing look up tables of the thresholds for real time control. Deviation functions of the sideslip angle and the yaw rate are designed to indicate the deviation between vehicle actual states and the reference states. Meanwhile, relative positions of the vehicle states and the stable region boundaries are also described by the deviation functions. When the vehicle states are beyond the stable region, the vehicle stability control should intervene timely to make the vehicle back to stable state.