Study On Corner Braking System Of Anti-lock Braking System For Commercial Vehicle

The centrifugal force leads to the load transfer between the inner and outside tires of the cornering, when the vehicle is braking on the cornering. The load of inner tires decreases and the load of outside tires increases. The transfer occurs more heavily, and the cornering stiffness is less, and the slip angle of tire is bigger. Because the changes of the slip angle of tire and the vertical force of tire, the target slip ratio for every wheel should be varied. This article aims to improve the brake performance of the vehicle on the cornering by fuzzy control of the optimized slip ratio.The article is comprised of five chapters:The first chapter is the introduction. It introduces the general structure and theory of the Anti-lock Brake System, and expounds the relation between the cornering braking system and the ABS, then summarizes the overseas and domestic study statue of the task. The main study content is put forward at last.The second chapter is the modeling of the vehicle dynamics. The vehicle model of the 8 degrees freedom is established including the longitudinal, lateral, yaw, roll degree freedom and four wheel vertical degrees freedom. The brake and the tire is modeled in the end. This work is the foundation of simulation.The third chapter is the estimation of the reference speed and cornering detection and control. The control arithmetic bases on slip ratio control. The precision of the slip ratio directly influences the final control effect. If the estimation of the reference speed is too small, the wheel will be control on the unstable area, otherwise, if the estimation of the reference is too big, then the actual slip ratio is below the target slip ratio , and the braking efficiency is low. This article introduces the wheel speed distinguished beyond the method of the average wheel speed, which can improve the precision of the estimation of the reference speed. When the vehicle is under the condition of drive on the cornering, the average value of the four wheels'speed is close to the actual speed of the vehicle. When the vehicle is under the condition of braking, the choice of the wheel which is the most close to the vehicle speed is reasonable. If the vehicle is braking, most of the wheel speed would be abandoned for the fluctuation of the wheel speed. This article analyses the theory of the estimation of the reference speed, sets up the particular flow chart, and makes the block of the estimation of the reference speed using software MATLAB. Cornering identification is the precondition of the cornering braking control. This test introduces the method of software and hardware for cornering identification. The wheel speed is used to identify the cornering because of the foundation of ABS. the method of difference of the inner and outside wheel speed and, method of turning factor and the method of difference of the inner and outside slip ratio have been analyzed and compared and then a better way to diagnose the cornering is obtained. This means can recognize mu split and cornering in the same time. In the last of the chapter, the means of optimized target slip ratio has been brought forward.The conventional means of fixed target slip ratio will result that the slip ratio of the front. left wheel is too small and that of the front. right wheel is too big which will lead to the low brake efficiency and vehicle instability. Because the front axe influences the brake efficiency mostly, this method is used in the front axe and the rear axe takes the method of the fixed slip ratio.The forth chapter tells the control arithmetic and the design of the fuzzy controller. The control for ABS is comprised of the method of limited value and that of slip ratio. This paper adopts the method of slip ratio control because of the complexity and precision of the cornering braking. The controller has two inputs and one output. The slip ratio and the differential coefficient of the slip ratio are the input signal and the variation value of the brake pressure is the output. The input value is divided into five parts, and the output five parts. The controller can be designed using the MATLAB.The fifth chapter is the simulation and analyze of the arithmetic of the cornering braking control. The simulation model is obtained by the control arithmetic of the third chapter and the controller of the forth chapter. The curves of the wheel speed and vehicle speed, the slip ratio, the braking moment, the vertical force of the tyre and the lateral acceleration of vehicle body are compared between fuzzy control and the traditional limited value control in open loop and close loop. The stabilization and performance of braking are taken into account. Through the comparison, it is clear that the braking performance of the fuzzy control is similar with that of the limited value control and the braking stabilization of the fuzzy control is better than that of limited value in the low mu road surface in the other hand, the braking performance of the fuzzy control is better than that of the limited value control and the braking stabilization of the fuzzy control is similar with that of limited value in the high mu road surface. in a word the fuzzy control is better than the limited control.The sixth chapter is the full conclusion of the article and the research prospect. The next study emphasis is that the cornering braking control assorts with the ESP and improving the performance of the cornering braking.