Simulation Research On Automotive Stability Control Strategy

With the development of the automobile industry, more and more requirements of safety capability are set upon the vehicles. When a vehicle is cornering at an excessive speed, the lateral forces on all the four wheels will determine the lateral acceleration and yaw moment, so the tire side forces may easily reach the grip limit; after that the vehicle becomes unstable, especially on a road with a low friction coefficient (lowμ), such as a snow-covered road. Electronic Stability Program (shortened as ESP) can stabilize the vehicle behavior under the limit situation by controlling longitudinal forces on four wheels independently. At present, ESP has become the international research focus in the vehicle active safety field and it is gradually equipped to the moderate and top cars; while in china, the research in this field has just started.This dissertation focuses on how to develop the vehicle stability control system. Based on the abroad achievements in this field, the design and simulation of vehicle stability control logic are discussed. Altogether there are five chapters. In Chapter One, the function and the construction of the vehicle stability control system are introduced; the history of the vehicle stability and its present status are discussed; the contents of the dissertation are also put forward in this part.In Chapter Two, the researches about the automobile stability control principle analysis and system modeling are carried on. According to the detailed analysis about the automobile stability, we know that the yaw rate error may represent the characteristic of the automobile steering. When the vehicle side slip angle is very large, it is difficult for the driver to change yaw moment by steering. Analysis onthe vehicle stability in critical cornering has been carried out by using the phase-plane method, the vehicle side slip angleβand its angular velocityβ. When vehicle is stable,β?βphase-plane is converged to the stable state. This article applied the widespread vehicles dynamics software-CarSim to establish the entire vehicle model. In order to enable the established control strategy to approach the actual situation, this article fully considered the execution characteristic and established the pressure modulator model.In Chapter Three, vehicle stability control strategy is established and the open loop simulation is conducted. This dissertation only focuses on the control of the front two wheels. The basic principles of the ESP control strategies based on the yaw rate and the slip angle are first analyzed in this chapter. Then, the author established a system simulation frame and testified the vehicle stability with several typical situations under the same starting conditions. The research results show that the vehicles with the ESP are easier to control and more stable than the ones without ESP by adjusting the wheel longitudinal force when vehicle is steering and affected by the lateral force. This is significant for the improvement of vehicle safety standard and the reduction of accident hazard. The author also compared the advantages and disadvantages of these two different control strategies under practical effect. At the end of this chapter, the author explored the vehicle slip angle estimation and the actual realization issues based on the wheel slip control system. In the simulation, the correctness of the estimation programme and control strategy are being testified.In Chapter Four, with the reference to the drivers'model probed by the other members within the discussion group, the author simulated the ESP control strategy within the closed loop and testified the operating mode simulations of thesingle lane and double lane. The results show this control strategy can effectively improve the stability of the vehicle under high-speed steering so as to release the drivers'burden under danger circumstance.Chapter Five is the conclusion part. In this final chapter, the author summarized the achievement of thesis and forecasted the research prospect.Through the theory analysis about the vehicle dynamics, it is indicated that ESP system breaks through the limitation of traditional system as ABS or TCS which only use the wheels to control anti-lock or sliding. The ESP system views the whole vehicle as a controlled system and by adjusting the longitudinal force on each wheel, ESP system can realize its objective. By the simulation analysis under both the open loop and closed loop of ESP system, we can get the conclusion that the control strategy of this dissertation is correct. The ESP control system can effectively improve the stability of the vehicle under high-speed steering circumstance so as to assist the drivers'steering operation.