Research On Anti-Rollover Control And Evaluation Method For Sport Utility Vehicle

Recently, Sport Utility Vehicle (SUV) becomes more and more popular for their better power performance and off-road ability. However, vehicle rollover, as a serious safety problem, has been the worse weakness for Sport Utility Vehicle. The injury cased by vehicle rollover accidents is only second to collision accidents. Therefore, vehicle rollover has drawn much more attention of both researchers and automakers. Compared with other countries abroad, the research in this field starts relatively late in our country.SUV have higher center of gravity and less wheelbase, because of which they are easier to lose lateral stability when steering in high speed driving condition, even to rollover. In addition, before rollover, drivers even can not feel that the vehicle is going to rollover until the rollover threshold is reached. Therefore, there's no enough time for drivers to take proper measures, such as breaking, reducing the throttle opening, or steering in time et al, to prevent rollover.Therefore, it is necessary to design a proper active vehicle dynamics control system for rollover prevention to solve the problem. This control system can monitor the driving condition of the vehicle real-time, warn the driver before rollover and at the same time control the vehicle to avoid rollover, to improve the rollover stability in high speed steering condition of the goal SUV.The main research contents and conclusions are as follows in this paper:(1) First, this paper uses a dynamical performance index, based on simplified reference model, as the trigger condition of the warning and control system. The linear simplified reference model has three degree of freedom, including lateral motion, yaw motion, and roll motion. The three degree of freedom model can indicate the rollover motion of the target SUV. This paper choose Lateral-Load Transfer Ratio(LTR)as the dynamics performance index, to indicate the rollover stability of the vehicle. Then, the Anti-Rollover Control(ARC)uses differential braking as the actuator, and lateral acceleration as the feedback control signal. PID algorithm is used as the control algorithm to calculate the needed compensation yaw moment. When the system detects the danger of rollover, the controller will be triggered, differential braking will brake the outer front wheel to produce compensation yaw moment needed for rollover prevention.(2) In this paper, the Worst Case Method(WCE) is used to evaluate the rollover stability of the SUV. The WCE method searches for the worst steering operation condition, based on optimization method, which maximizes the performance cost function; and then, it solves the worst steer condition through numerical method. The initial guess value of steer wheel input is based on the standard Fishhook test. Compared with Fishhook test, the worst case method can generate worse rollover steering case in the same condition, such as road condition, vehicle speed, maximum steering wheel angle. Therefore, the method can be used to evaluate the rollover stability.(3) The typical driving test conditions are chosen to simulate the vehicle performance in this paper: J-turn, Double line change, Fishhook, and the worse case from WCE method. Though these test conditions, the PID control algorithm and the active anti-rollover control system's control effect are verified. Simulation results showed that the differential braking based active anti-rollover control system designed in this paper could steady the rollover motion of SUV and prevent the vehicle rollover effectively.