On Control Algorithms Of Vehicle Antilock Braking System Based On Slip Ratio

With the development of automobile industry and the rising speed of vehicle, how to maintain the directional stability and steering capability during the automotive braking process become the focuses of attention. Nowadays, in various technology of improving vehicle braking performance, Antilock Braking System (ABS) is the most effective way and it is widely used. The development of control technology is the mainly key for the development of ABS. On the one hand it needs to expand the ABS control range and to enhance the control functions; On the other hand it needs to use the intelligent control theory to implement high-precision robust control. As the nonlinearity and uncertainties are included in ABS, especially the maximum adhesion coefficient which has a great influence on system performance is an uncertain parameter that changes in a certain range. Therefore it is meaningful to use the parametric uncertain nonlinear control theory in research of ABS.Several ABS control algorithms are proposed based on the robust control and intelligent control. We make further to study on the design of vehicle model and ABS controller including the stability analysis. The main research works and conclusions are as follows:Firstly, according to the public documents published at domestic and abroad, a quarter-car model, wheel tires model and braking system model are established. In order to simplify the whole analyses and design processes, a quarter-car model is adopted to describe the whole braking process. The analysis shows that the quarter-car model can reflect the complicated nonlinear and fast time-varying dynamicity characteristics and so on of ABS. This research work has a certain representation, and it also meets the needs of theoretical study and simulation study which are based on model control system.ABS sliding mode controller is designed for the robust control in the ABS requirements. Simulation results under all kinds of braking conditions show that the designed sliding mode robust controller is effective and robustness; the nonlinear ABS control algorithm is given based on the global sliding mode control. The scheme can eliminates the reaching phase from sliding mode control, ensuring the system robustness during the whole braking process. Simulation results show that this method enables the wheel slip ratio to converge to the best value quickly and keeps the slip ratio oscillation small. Secondly, a new robust adaptive sliding mode ABS controller is designed according to the self-learning ability of neural network and rapidity of the sliding mode control. Utilizing the RBF neural network to realize the control strategy, the adaptive control law is proposed based on the neural network, which can weaken the chattering in the sliding mode control system. Simulation results under all kinds of braking condition show that the scheme can obtain very excellent control performance. The algorithm is robustness for the parameters perturbations and load disturbance.Thirdly, the state of ABS always can not measure completely. In view of this situation, the ABS control algorithm based on the observer is proposed. In the present of input saturation, the robust ABS controller is designed; a robust ABS scheme based on H-infinty theory is presented for considering the inaccuracy in the model establishing process, uncertainties and external disturbance. The simulation results show that this method enables the wheel slip ratio quickly converges to the expected value and has the strong robustness for the loading perturbation and the parameter change.Considering the nonlinear term and uncertainties in the ABS systems, the state estimation problem becomes quite difficult. To solve this problem, the disturbance sliding-mode observer is designed. The feed-forward compensation is introduced in the observer to counteract the affection of the uncertainty terms, so the observers’problem is realized for the uncertain systems. Then, an observer-based sliding mode controller is presented using the estimation state. The simulation results show that the designed sliding mode controller based on observer can significantly improve the directional stability of the vehicle during braking.According to the T-S fuzzy model has a characteristic of approximate nonlinear, T-S fuzzy controller based on observer is designed. A T-S fuzzy modeling is done for the nonlinear ABS control system. The performance of safety is improved by choosing appropriate fuzzy rules and membership functions. Simulation results show that the designed ABS controller has strong stability and robustness in the unmodeled dynamics and uncertainties.Lastly, the summary of the whole dissertation is given and the research directions in future are put forward.