Research On Traction Control Method Based On PWM Driven Wheel Brake Control For Light Offroad Vehicle

Traction Control System(TCS), which gets the optimal longitudinal traction by controlling the vehicle driving slip ratio, is a novel class of active safety control system developed from the last mid-eighties. It is based on the principle of retaining the driving slip ratio round the optimization, so that the automobile will achieve the maximized road adhesion coefficient and certain lateral stability.The traditional traction braking intervention is only on-off controlled by solenoid valve and always gets an over control modulation. In this article, PWM is brought in TCS based on the advanced experiences. By this way, the pressure of braking cylinder can be fine-tuned and the slip ratio of driving wheel will be maintained near the optimization, so that the motor vehicles are in the best performance.According to the national key program"Research on TCS of the Light Off-Road Vehicle", we take the vehicles hydraulic brake system as the object and propose the traction control method based on PMW .The following researches have been finished: 1. Establishment of systems model based on union simulation platform.A simulation model of traction control system is established based on MATLAB/Simulink and AMESim union simulation platform according to the principle of vehicle system. The research was also done on simulation modeling of the system by using MATLAB/Simulink and AMESim, which are superior at data processing and hydraulic system modeling simulation respectively. The model was designed as a modularization. The eight degrees of freedom modules of the entire vehicle and the hydraulic brake system module are established, which make them available to simulate the response of driver, the hydraulic system dynamic response characteristic on the operating mode and the state motion of the entire vehicle, also control parameter, change the operating mode and control mode, display the state of vehicle under the traction control and variable change curve of control system.2. The theoretical analysis to the system hydraulic pressure characteristic.The response characteristic of high speed switch valve, which is the key element of brake pressure modulator, affects the hydraulic system response directly. In this article, a Two-position two-port high speed switch valve is adopted, it is used a way of to introduce briefly its characteristic and control mode, emphasizes to analyze its characteristic response and mentions the academic evidence and method which are to identify the control carrier frequency of PWM and the spatial ratio operating region. We have also analyzed the traction control system hydraulic project based on PWM, taken theoretical analysis and chosen for other key elements, done the research on the response characteristic, and initially discussed the way of establishing a braking system response characteristic experience model with the brake pressure modulator. 3. Establishing the hydraulic system dynamic responded test platform and experimentizing.A hydraulic dynamic responded test platform of traction control system based on PWM is established, which emerges a PWM control signal and carries on the test to the system response characteristic. We obtained a system response characteristic curve under the condition of an un-working hydraulic pump while a working high speed switch valve and a system increase-decrease pressure responded curve with a working hydraulic pump. The research was done on the system response under different carrier frequencies and duty cycle control. The experiment carrier frequency and different duty cycle operating region were identified. Finally, the AMESim model accuracy was confirmed though the experiment.4. The identification of the controlling strategy in traction control system based on PWMUnder the consideration of the common summarizing formerly traction control algorithm, the PID control algorithm of high simpleness, reliability and widespread application, and computer control, the PID control algorithm is adopted to control the PWM duty cycle and further more to control the braking wheel cylinder pressure and keep the vehicle slip rate round the optimization. In this way, the traction control can be realized.5. Off-line simulation research based on union simulation platformThe off-line simulation has been carried on based on MATLAB/Simulink and AMESim union simulation platform, and the control performance of traction brake control based on PWM is conformed. We have tried the off-line simulation with and without traction brake control on typical operating mode , the result showed that the PWM based on PID made it available to effectively control the duty cycle, tune the braking cylinder, keep the wheel speed round the purpose,control the driving wheel excessive slip and enhance he vehicle driving performance.