Development And Test Of Control Algorithm Of Anti-lock Braking System For Commercial Vehicle Based On Rapid Control Prototyping

Today the Anti-lock Braking System (ABS) is one of the standard safety equipment since ABS has developed perfectly in 90s last century. And ABS has been forced to fit through the law in some countries. Domestic research of ABS started from 80s at last century, and has made great achievement, and some manufactures has produced as products and equipped for many series of trucks and buses, but the control effect still has a great gap compared with the foreign. So it is great important to be worked on and develop our own ABS and do not depended on the foreign product. Now the research on the active safety is very popular in many automotive manufactures, academe and high schools, including the anti-lock braking system. Based on the research of braking system for commercial vehicle, this dissertation presents the groundwork of development of ABS, develop and test practical control logic of ABS for commercial vehicle.1. Introduction of Anti-lock Braking System for commercial vehicle and development tools.The friction coefficient between the tire and road is variable while the slip ratio change, and achieve its peak value when the slip ration is in the range of 15%~20%. The function of ABS is restrict the slip ratio in the range, then the dangerous condition while braking can be prevented, and the braking distance can be reduced, and the brake force can reach the top value under some condition.Anti-lock system is composed of wheel speed sensor, brake pressure actuator and electronic control unit (ECU). The operational circuit in ECU receives the filtered sine waves with different amplitude and frequency from the sensor, and then ECU can recognize the moving state of the wheel and send instruction to the actuator to increase, decrease or hold the pressure in brake chambers, to achieve the aim of anti-lock.In order to deal with different road condition and harmonize the movement of all wheels, the ABS has many different control mode and layout mode, such as high selection control, low selection control, individual control and modified individual control in control mode, and six channel system and four channel system in layout mode. In this dissertation individual control, low selection control and modified individual control is adapted for the four channel system.2. Practical control algorithm of ABS for commercial vehicle The control logic of ABS that developed is logic threshold values method which is developed perfectly, and adopted for the unitary ABS product for air brake system and hydraulic brake system. Some methods of estimation of vehicle speed are advanced including maximum of wheel speed, method of slope, method of fixed point estimation, ect. of which the advantage and disadvantage are listed, but all the methods are use while in the dissertation.Based on the control logic of logic threshold values of BOSCH, control algorithm in different road condition are advanced in detail, including on high mue road, low mue road, and mue-slip road. The logic is controlled by different threshold values, of longitudinal acceleration and slip ratio, combined with the two type threshold it can optimize the effect. Control effect depend much on the selection of threshold, then the boundary of P1R3 is taken into account.3. model building for vehicle system and simulation of the control algorithmFollowed by the V model of dSPACE system, model building is the second step of product development. While developing ABS system the vehicle model is necessary, and the model of vehicle body, tire, air brake system are analyzed in detail. Then the vehicle model of 8 degree of freedom is built with Matlab/Simulink, and the control logic is built with Stateflow which is based on the infinite state machine. Compared with the result of simulation between that with and without ABS, the control logic is tested to be right through the simulation.4. Achievement and test of rapid control prototypingAfter the second step, it is the phrase of rapid control prototyping(RCP) model. First the hardware circuit of ABS is designed, however only the function is advanced. Then the logic relationship between the control algorithm and model is replaced by RTI block, and realize the linkage between hardware and software, and the complete the configuration of I/O. Some experiments of RCP for different road conditions are designed under Controldesk environment, which are used for real vehicle test in ground test field. After analyzing the data that captured during the test, the control algorithm developed above is proved to be practical. However, there's still some fault in the logic, which deep in the logic itself and also in the restriction of test condition. Much more work has to be done to improve the control algorithm, but most of important is real ECU test in real vehicle that containing target code, and complete the four and five step of V model, make sure the performance of ABS working steady. Otherwise, faulty diagnosis system must be added in, including faults on speed sensor, solenoid valve, power, software and CPU, etc.