1. Field of the Invention
This invention relates generally to a vehicle rollover avoidance system and, more particularly, to a vehicle rollover avoidance system that employs a roll control factor and a yaw rate stability control factor to control semi-active suspension dampers to mitigate the risk of vehicle rollover.
2. Discussion of the Related Art
It is known in the art to mitigate a potential vehicle rollover using differential braking control, rear-wheel steering control, front-wheel steering control, or any combination thereof. A vehicle rollover avoidance system may receive vehicle dynamics information from various sensors, such as yaw rate sensors, lateral acceleration sensors and roll rate sensors, to determine the proper amount of action to be taken to detect a potential vehicle rollover. A balance typically needs to be provided between estimating the vehicle roll motion and the vehicle yaw motion to provide the optimal vehicle response. Thus, it is usually necessary to detect certain vehicle conditions to provide the roll detection. To precisely identify vehicle roll stability conditions, it may be advantageous to know the vehicle's roll rate and roll angle because they are the most important states in vehicle roll dynamics.
Under normal driving conditions, drivers can direct the vehicle to the desired heading through the control of the steering wheel. When the vehicle is turning, there are actually three motions taking place with the vehicle. Particularly, a turning motion, or yaw, is occurring, as the vehicle body is turning around an imaginary access vertical to the ground through the so-called yaw-center of the vehicle. Also, there is subtle vehicle sliding laterally, sometimes in the direction of the turn and sometimes away from the turn, depending mainly on the vehicle speed. Further, a tilting motion or roll motion occurs as the vehicle's body is turning around an imaginary axis parallel to the ground through the so-called roll-axis of the vehicle.
Under normal vehicle maneuvering conditions, the tire/road contact surfaces can generate sufficient forces to sustain the desired vehicle motions, and drivers are accustomed with these motions as they occur. However, when the vehicle maneuver starts approaching limit-handling conditions, the tire/road contact surfaces can no longer sustain the desired yaw motion and side-slip motion, and the vehicle body will exhibit an increased roll motion. As a result, a discrepancy will build up between the vehicle's yaw rate and its desired yaw rate, and between the vehicle's side-slip velocity and its desired side-slip velocity. Further, if the roll motion becomes too large, the vehicle may roll over.