The Study And Development Of Electric Power-assisted Steering System Based On Fuzzy Control

It's an inevitable trend for automobiles to undergo a process of electronization. After electronic technology has been widely used in engine, transmission, brake and suspension, cars both made at home and abroad adopt Electric Power-assisted Steering system (henceforth EPS), which gradually replaces the traditional Hydraulic Power-assisted Steering system. With assist directly from motor, the EPS system has assist controlled by ECU, which enables EPS system has such advantages as:adjustable in assist magnitude, good in road feel, environmentally–friendly, energy-saving, and convenient in repairing, etc. The EPS system is both a topic hotly talked in current vehicle technology and one of the top techniques.The characteristics, principle and structure 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 system development and selecting of parts.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 produces 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. Moreover, the damping control strategy and return control strategy for enhancing comfortability and stability of driving were discussed.On the basis of these research, a simulation model of EPS system was established, and two different current controllers based on PID and adaptive fuzzy PID were designed. The results of simulation show that the current controllers have good performance at both response speed and following characteristics, and that the assist control strategy and the current control strategy can meet the requirements of EPS system.At last, a set of hardware design scheme of ECU was proposed. The driver board of permanent magnet brushless DC motor in EPS system and its three working modes corresponding to control strategies were introduced. According to the functional demands of EPS system, the software components and the working flowcharts were then presented.Research of this thesis provides important theoretic foundations and design methods for development of EPS system. Such a study will be of significance in practice guiding.