Control Method And Simulation Analysis Of Electric Power Steering System On Car

With the development of electronization for automobile, Electric Power Steering System (hence forth EPS), the future of power steering technology, gradually replaces the traditional Hydraulic Power-assisted Steering System. EPS has the advantages of smaller volume, lighter weight, simpler structure, easier installation and maintenance, lower consumption, better environmental protection and so on. Additionally, with assist directly from motor, it owes to adjusting steering assisting force according to vehicle speed, which enables it fit for many kinds of vehicle such as car, truck etc. A lot of external famous automobile companies have adopted this kind of steering system and it is necessary for automobile industry of our country to master this high-tech as soon as possible because of foreign technology monopoly. Therefore, it is of great importance to study and develop this kind of steering system.This dissertation aims to study the dynamic analysis, control strategy and modeling of EPS, to make a theoretical basis for the design and development of EPS.At first, in view of referring to a large amount of revelant scientific literature, the characteristics, structure and principle of EPS system were elaborated in this thesis, and a detailed description of key parts such as torque sensor, motor and ECU, etc, were offered. Thus this thesis provides foundations for the development and parts selection of system.Secondly, a detailed study of EPS system from perspective of assist characteristic and that of control strategies was carried out, and a decision-making strategy of motor's target current on the basis of fuzzy control was worked out. It produced the assist characteristic curves at different velocity and torque input of steering wheel, which show that the assist control strategy based on fuzzy control can meet the actual requirements of EPS system. At the same time, the damping control strategy and return control strategy for enhancing comfortability and stability of driving were discussed.Morever, after the simplified two degrees model of vehicle was established; a dynamic model of EPS system was also established. One current controller based on PID was designed, thus on the basis of these researches, a dynamic simulation software baesd on MATLAB/Simulink was also independently developed. The results of simulation figures show that the current controller had good performance at both response speed and follow-up characteristics, as well as the assist control strategy and the current control strategy could meet the requirements of EPS system.At last, an experimental device of EPS based on PC including hardware and software was developed. It described and analyzed a detailed hardware diagram. According to the functional demands of EPS system, the software components and the working flowcharts were then presented in modular. Besides, the experimental device had been assembled and debugged, as well as some valuable data received, which would be useful for further development of EPS in the following.