The Research On Anti-roll Control Of Sport Utility Vehicle Based On Differential Braking

Differential braking technology is a kind of vehicle anti-rollover control technology differing from active steer technology and active suspension technology. Its hardware is based on the ESP system, and its software is integrated in the tradition planar stability control system. Because of the ESP hardware, the differential braking technology has the advantage in the cost of system. The active steer equipment and active suspension are not needed so that the differential braking technology becomes the hot research topic and the common adopted technical proposal for auto companies.Firstly, vehicle models for states estimation and control are constructed including vehicle planar model, suspension model and tire model. The suspension model is developed and a new suspension model for the tire lift off is proposed in this paper.Secondly, the research about vehicle side-slip angle estimation on line is developed for the risk of tripped rollover due to the drift out of vehicle. A variable structure extended kalman filter is proposed in this paper. This new method involves advantage of model-based method and integration method, and it can improve the robustness of algorithm against sensor noise and model error. The test results of Carsim-Matlab/Simulink simulation and real vehicle tests show the method can obtain good estimation for vehicle side-slip angle. The research about vehicle roll angle and roll rate estimation on line are also developed for the risk of un-tripped rollover due to the heavy roll motion of vehicle. An estimation method based on the unscented kalman filter is proposed according to the suspension model. This method chooses the suitable suspension model according to the recognition of vehicle tire lift off state. The results of Carsim-Matlab/Simulink simulation tests show that the method can obtain accurate estimated roll angle and roll rate. Especially when the tire lifts off, the method can achieve better result compared with the traditional unscented kalman filter method.Finally, based on the estimated vehicle side-slip angle, roll angle and roll rate, A model predictive control method for anti-rollover control based on the hierarchical structure is proposed. This anti-rollover controller include yaw rate following control, vehicle sideslip control and roll motion control. In the upper controller, through the analysis of the constraint, the method integrating the rollover control constraint directly is not adopted. An independent roll motion control logic is proposed based on the predicted lateral load transfer ratio. Meanwhile, the nominal value of yaw rate is limited by the roll motion so as to decrease the risk of rollover through yaw rate following control. The target of longitudinal tire force from the model predictive controller is realized by the slip ratio controller and brake pressure controller. The results of Carsim-Matlab/Simulink simulation tests show the control method can improve the stability and safety of vehicle for both the un-tripped and the tripped rollover. This paper also analyses the ability of the differential braking method for anti-rollover control and proposed the warning concept of Time to Stability(TTS) which consider the intervention of braking. The controllable area for rollover based on the TTS is proposed in the paper.