In this paper a yaw stability control algorithm along with an emergency roll control strategy have been developed. The yaw stability controller and emergency roll controller were both developed using linear two degree-of-freedom vehicle models. The yaw stability controller is based on Lyapunov stability criteria and uses vehicle lateral acceleration and yaw rate measurements to calculate the corrective yaw moment required to stabilize the vehicle yaw motion. The corrective yaw moment is then applied by means of a differential braking strategy in which one wheel is selected to be braked with appropriate brake torque applied. The emergency roll control strategy is based on a rollover coefficient related to vehicle static stability factor. The emergency roll control strategy utilizes vehicle lateral acceleration measurements to calculate the roll coefficient. If the roll coefficient exceeds some predetermined threshold value the emergency roll control strategy will deploy. The emergency roll strategy consists of actuators located near the vehicle suspension that apply an upward force to the vehicle body to counter the roll direction.
This paper also incorporates the yaw stability control algorithm and the emergency roll control strategy in vehicle simulation software to test their performance. The vehicle simulation software includes non-linear, multiple degree of freedom models for several vehicle components, including tires, suspension, steering, and aerodynamics. Simulations have been run on a simulated vehicle performing severe emergency manoeuvres on various driving surfaces for potential tripped and untripped rollover incidents. The performance of a vehicle equipped with both the yaw stability controller and emergency roll controller was compared to a vehicle equipped with just the yaw stability controller and also compared to an uncontrolled vehicle. Vehicle lateral acceleration, lateral velocity, yaw rate, and roll angle were observed for the three cases. It was found that during a potential untripped rollover situation the yaw stability controller can significantly improve the vehicle yaw stability which leads to improved vehicle roll stability. It was also found that the addition of the emergency roll control further improves the vehicle roll stability. The results also showed that during a potential tripped rollover in which a vehicle strikes an object while moving laterally the likelihood of rollover is decreased for a vehicle equipped with yaw stability control, while the addition of the emergency roll control does not do much to help prevent tripped rollovers.