Research On Traction/Brake Control System For Light Off-road Vehicle

When driving on weak adhesive road, the driven-wheels are tending to over slip, which is disadvantaged to the performance of startup, acceleration, climbing and safety. The wheels also tend to lockup on panic braking, which result in longer stop distance, worse handling stability and more seriously worn tires. The traction & brake control system controls the slip/skid state of wheels, so as to make use of the road adhesion effectively and improve performances of traction, braking and stability of a vehicle. Works in this thesis are based on the research of projects "Research on Traction Control System for Off-road Vehicle" and "Research on Anti-slip/Anti-skid Control System for CA6440 Light Bus". In the thesis, research on traction & brake control system for a light off-road vehicle and its utilized rapid development method are performed, which include control algorithm design, vehicle dynamics modeling, off-line simulation platform, HiL (hardware-in-the-loop) test platform and onboard test platform. By the usage of off-line simulation, HiL test and road test, verifying and debugging to the software and hardware of traction & brake control system are accomplished in the stage of control algorithm prototype. The results of the thesis provide an important reference to the development of 4WD traction & brake control system.1. Traction & Brake Control Algorithm Based on Thresholds Self-adjustingAccording to the needs of the project, study on traction & brake control algorithm, aimed in utilizing, for a light off-road vehicle is performed:①Main scheme of control for 4WD Traction & Brake control strategy is brought out.②Velocity estimating strategy for 4WD Traction & Brake is put forward.③Threshold adjusting strategy on the basis of vehicle velocity and wheel speed is put forward.④Traction control algorithm based on threshold self-adjusting, including throttle control algorithm and brake control algorithm on driven-wheel, was designed.⑤Brake control algorithm based on threshold self-adjusting, including anti-lock brake control algorithm and brake force distribution control algorithm, was designed.The researches on the algorithms provide an academic foundation for the development of 4WD traction & brake control system.2. Vehicle Dynamics ModelingAccording to the needs of strategy research, the main scheme for 4WD vehicle dynamics simulation software, based on which the function and project of the dynamics models are decided, is confirmed firstly. Equations for the models, including driver model, vehicle body model, engine model, powertrain model, wheel dynamics model, tire model, braking system model, road input module and other assistant modules, are provided. Using these models, conditions such as 4WD startup and acceleration, 2WD acceleration with gear shifting, brake with different brake pedal input on different road with necessary driver feedback control can be simulated.In this part, program foundations for vehicle dynamics software are made. 3. Off-line Simulation Platform and the SimulationThe vehicle dynamics software is designed on the basis of its main scheme and vehicle dynamics models. Vehicle dynamics simulation modules, which can fulfill the demands of research on startup and acceleration for 4WD and 2WD and study on brake, are programmed by Matlab/Simulink. And these modules, together with the control algorithm prototype, the graphic user interface and 3D virtual environment, are integrated into four-wheel drive traction & brake control off-line simulation platform.Simulations for designed traction & brake control system are executed using this platform. The results show that:①The platform satisfy the research demands.②Over-slip of driven wheels are avoided efficiently using traction control, and the capabilities of startup, acceleration and climbing of the vehicle are improved obviously. The throttle control and brake control response properly with good adaptability on jump-u road. The control of throttle and brake is distributed properly with the increase of vehicle speed from better traction to better stability.③Using brake control, wheels lockup is avoided efficiently with shorter stop distance. The pressure grade is adjusted automatically with good adaptability on jump-u road. On split-μroad, the performance of brake and stability are both acceptable.④During simulation, neither the wheel speed fluctuation caused by D-class road nor by impact road input would result in improper response of control system.The study of off-line simulation provides a foundation for HiL test platform establishment, HiL test and road test.4. HiL Test Platform and HiL TestA HiL test platform, which can be used in traction & brake control system study and development, is built according to the needs of research for a light off-road vehicle:①Vehicle handles including accelerator, steering wheel and brake pedal are use to input real-time driver reaction during the test. An electro-throttle is adopted, and an accelerator feel simulator is designed. Furthermore, the brake system is re-arranged and HCUs are embedded in it. A throttle position sensor and four pressure sensors are adopted to monitor the work of the actuators. Then, the construction of the hardware system is completed.②Signal processing system, including data acquisition cards and data progress signal processing integrated box, is adopted to acquire sensors' signal, drive actuators and generate the simulated wheel speed.③Software system is built using Matlab to simulate vehicle motions, setup the acquisition cards and inspect the actuators. The hardware such as controller and actuators can be embedded to the platform in order to simulate vehicle actual work environment with high accurateness indoors. And the periodic of development of traction & brake control system is greatly shortened.HiL tests, including 4WD startup and acceleration, 2WD acceleration with gear shifting and panic brake based on algorithm prototype, are performed. The results show that: By traction control, the over slip of driven wheels are avoided efficiently, and the throttle and brake control are cooperated properly. The capabilities of startup and acceleration are improved obviously, and the control system responses properly in time on jump-μroad. Using brake control, wheels lockup is avoided efficiently. The pressure grade is adjusted automatically on jump-μroad. On split-μroad, the performance of brake and stability are both quite acceptable.The results of HiL test give a better proof of the validity and adaptability to the algorithm, and prepared for the final road test.5. Onboard Rapid Development Platform and Road TestOnboard rapid development platforms for light off-road vehicle is integrated, based on HiL platform, by arranging the sensors, actuators and data processing system on it.Traction control road tests, including startup and acceleration on ice road and splitμroad straightly, and cornering on ice road, are preformed based on control algorithm prototype. The results show that vehicle motions from the sensors are identified properly, and then, after analysis by the algorithm, the engine and brake actuators response properly, and prevent the driven wheels from over-slipping, so as to improve the capabilities of startup, acceleration and stability.