SUV Rollover Control Using Pulsed Active Rear Steering Strategy

For the last two decades, motor vehicle rollover crashes have been a serious safety problem. With the increase in popularity of Sports Utility Vehicles(SUVs) since 1990 s, in 2002, statistics released by the National Highway Traffic Safety Administration(NHTSA) showed that nearly 11,000 were killed in rollover accidents with 25% of these riding in a SUV. This number increased to 33% in 2008. Due to SUVs possessing a higher center of gravity and suspension characteristics, and consequently a lower static stability factor, the vehicle is more likely to rollover. This is especially true for maneuvers such as driving fast during sharp turns, obstacle avoidance, and rapid multiple lane changes, where rollovers occur as a direct result of the tires shifting the load. Different solutions have been studied to help address this problem. Active techniques on vehicle rollover control generally fall into four categories: a) Active or semi-active suspension control, b) Differential Braking Control(DBS), c) Active Steering Control(ASC) and d) Integrated Control. This thesis proposed a novel active steering technique named Pulsed Active Rear Steering System(PARS) for enhancing vehicular stability to reduce the likelihood of rollover for motor vehicles, particularly for Sport Utility Vehicles(SUVs). The main research works of the thesis are as follows:Active steering control is an efficient approach used to improve the vehicle's yaw and roll dynamics. This study takes the SUV as the example, a 3DOF model is established by adding the roll motion to the single track model. The 3DOF vehicle model directly and accurately describes basic vehicle characteristics in yaw motion, lateral motion and roll motion. A rollover coefficient “R” is chosen to estimate the risk of a rollover and used as the controller's variable for PARS system.In the Pulsed Active Steering(PAS), the front and/or rear wheel steering angles are excited by a pulsation, which is added or subtracted from the steering input. Under the concept of pulsed active steering, one control strategy called Pulsed Active Rear Steering(PARS) was investigated and discussed in detail. To design this system, the pulse signal parameters(frequency and amplitude) were evaluated to determine their optimum values. A full vehicle model was built in Car Sim and co-simulated with Matlab/Simulink as the control module. Simulations of J-turn maneuver, double lane change maneuver and slalom maneuver are performed to verify the PARS system. Moreover, we designed and prototyped the proposed system for an SUV, and conducted road tests with different typical maneuvers.At last, Results from simulations and experiments confirmed that the proposed PARS system is promising for SUV rollover prevention. The control module shows efficient response on its function. And the PARS system does not have any disturbance under normal driving conditions, it only activates when the vehicle loses stability and rollover.