Research On Control Strategy Of Electric Power Steering System

Electric Power Steering (EPS) system is a new developing technology of power steering system in automotive. The principle of EPS is that the assistant motor works according to the measured torque and vehicle signals so that power steering can be modified and the performance of steering can be perfect. Besides EPS has the light steering torque like Hydraulic Power Steering (HPS) system, it has many other advantages such as steering placidly, low energy consuming, environment protecting and so on. Therefore it is an absolute tendency that HPS is taken place by EPS. Control strategy is one of the most essential technologies of EPS, and it is significant in both academy and practice to take much research and development in this area.The thesis introduces the development of steering technology and the features of EPS including function, types and advantages, and summarizes the research status about the EPS control logic. The research content is confirmed based on the particular defects of the EPS control logic. Moreover, the method to evaluate the road feeling and handing stability is summarized based on the available materials. After kinematical analyses of the automotive steering system the torque and angel dynamic models are built and kinematical character of the automobile steer can be learned through the simulation, and then an EPS simulation model is finally built with the kinematical analysis.According to the need of the vehicle and the driver on steering control, the basic assist characteristic is confirmed. The assist control, the compensation control, the damp control and the return control are all adopted in the EPS model. In the research of the assist control, three kinds of assist control models are compared, and the basic assist control strategy is selected. The assist characteristic curve is designed by fuzzy control theory.Several control strategies that can be adopted in EPS are listed and compared. The algorithm of basic assist characteristic in this thesis is confirmed. The simulation model of control strategy is built respectively based on fuzzy control theory and PID control theory via the Matlab/Simulink software, and then the model is simulated in order to find out the factors and influences of outputs based on different inputs. The simulation infers that the control strategy of EPS built in the thesis can greatly inflect and meet the need of assist characteristic.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.