Study On Modeling, Controlling And Testing Of Eps At All Operating Conditions

With the great improvement of people's living standard, automobile is coming into people's lives and works gradually, and becoming an indispensable means of transportation. Safe, energy-saving and environmental protection are today's automotive technology development topics, electric power steering system (EPS) is not only with the advantagy of energy-saving, environmental protection, small size, light weight, simple structure, but also it can improve the steeting function and driving safty, represents the future of automotive power steering technology development. This dissertation aims at studying electric power steering system dynamics analysis, modeling, control methods and test methods under the conditions of park steering, travel steering and low-adhesion road surfaces (all operating conditions), porviding use for the further theoretical and experimental research of EPS. The research contents of this dissertation are listed as follow:(1) Firstly, a review on the development of automotive steering technology, the advantage of EPS, and the research progress of EPS is introduced. Then the contents and innovation points of this dissertation are given.(2) By analyzing the dynamic, kinematics and steering resistance characteristics of automobile steering system, a mathematic model for mechanical steering system and EPS is established by Newton law, and the assist characteristics is analyzed theoretically and simulated. Based on 2 degrees of freedom of the vehicle model, the effects of EPS on vehicle handling performance are discussed.(3) Based on the mathematical model of electric power steering system (EPS),a method for estimating the state of steering wheel is obtained, in which the signals of steering wheel moment sensor and estimated steering angle are used. A fuzzy PD control strategy was applied to assist motor or self-align, and the strategy is simulated;(4) Based on the combination of tire model of park steering and 7 degree-of-freedom vehicle model with Doguff tyre model, the dynamic model for steering system under the park and the travel steering condition is build. According to the sliding mode control theory (SMC), a controller for EPS controlling power assistant and self-align is designed, and the simulation tests are developed.(5) The EPS model based on whole vehicle dynamics is established and the ratio of self alignment torque and nominal alignment torque are utilized to estimate the road friction. Furthermore, a new assistant torque control strategy based on road friction and a time-varying sliding mode return control strategy are introduced for EPS, and the simulation tests are also carried out for control strategy validation. (6) By analyzing the characteristics of steering resistance torque in a whole vehicle dynamics model, a LabVIEW PXI hardware-in-the-loop test platform for EPS is established. The CAN signal angle sensor and electronically controlled hydraulic proportional valve are set as input and output interfaces of test system, the assistant torque control strategy based on road friction and the time-varying sliding mode return control strategy are validated on the platform;(7) Based on enhanced 8-bit-microcontroller and ARM7 microcontroller, the electronic control unit (ECU) of EPS is designed. To validate the effectiveness of control strategy, the feasibility of software and reliability of ECU, a comparison road test is made between the vehicle with self-developed EPS and without EPS. Moreover, the fault diagnosis system of EPS is developed and the corresponding road test is also carried out;(8)At last,we conclude this dissertation, and some useful suggestions are given for future research..