A Study On Slip-ratio Control Based ABS In Brake-by-wire Systems

The recently growing need for modern vehicles requires the automotive industry to develop cars with better safety, higher fuel efficiency and little pollution.The BBW systems provide better control of pedal stiffness,vehicle stability, and brake force distribution than a conventional hydraulic or electro-hydraulic system, which makes it the most promissing brake system in the future.In terms of enhancing active safety, augmenting energy economy and avoiding traffic accidents,it is acknowledged that anti-lock braking systems (ABS)have devoted significant contributions.Lately, ABS has been generally used as the standard device for all new cars.However, the control strategy of the logic threshold control method implemented in commercial vehicles is not optimal from theoretical point of view.As a matter of fact, the optimal Anti-lock Braking System combining with vehicle dynamics control, which can keep the braking process optimal and stable, is an ideal ABS control strategy. Furthermore,the conventional hydraulic brake system has also constrainted vehicles from better braking performance.In order for ABS to overcome its inherent deficiencies and to obtain higher braking efficiency, a study on slip-ratio control based ABS of Brake-by-wire (BBW) system had been investigated after reviewing relevant research literatures,focusing on its key technology as well as its realization algorithms.The research scope of this paper is illustrated as follows:Firstly, the advantages of the BBW systems over conventional hydraulic or electrohydraulic systems were described here, followed by the detailed discussion of the working principle and structure of BBW systems.In an attempt to model the BBW brake system, vehicle dynamics and main components were analysed as well.Secondly, the movement state of vehicles when braking was theoretically explored.As a result, the ideal control process for optimal ABS was concluded.Then, with the magnificent combination of nonparametric estimation method-local polynomial fitting and tire/road model under the least square principle, an optimal slip-raio estimator was developed.Estimation results prove the effectiveness and agreeable accuracy of the designed identification method.In addition,a sliding mode controller(SMC),which is robust for uncertainty and disturbance in nonlinear system, was designed for ABS in BBW systems.Its advantages overcome the defects of the Proportional, integral and defferential (PID) controller and achieve the continuous control as well.One common measure was then taken to restrain the inherent chattering problem of SMC.Thereafter, simulation models of the designed ABS control strategy for a BBW system were established under the MATLAB/SIMULINK environment.The simulation tests were devided into several categories to thoroughly compare the performance of the algorithm with other strateties and to conclude its advantages from the simulation results.Finally,hardware-in-loop experiments,based on TMS320F2812 Digital Signal Processor (DSP),were carried out to further analyse the practical feasibility of the developed algorithm.The Q format of the fixed-point number and object-oriented programing methods were utilized, which facilitates the program to be easily understood and modified.According to the test conditions selected in simulation test, the experimental results showed the effctiveness and feasibility of the proposed method as well.