| The automobile electric power steering system is one of new technologies of development of the automobile steering system, which has been obtained universal recognition in automotive industries in various countries. Electric power steering system is the power steering system which directly depending on electromotor to supply assistant torque, which can reduce steering efforts of the drivers and guarantee the automobile steering handily and agilely in low velocity, running steadily and reliably in high velocity. EPS has the advantages of saving fuel, and being in favor of environmental protection, etc. Currently, study of EPS system is just junior stage in China, and there is no product of EPS expecting technology absorbing the advanced overseas.Based on the lateral dynamic theory of vehicles, self-aligning torque and load performance are studied at first. A rack and pinion steering gear system and an electric power assist system are mathematically modeled, and it is analyzed that the influence of the load elastic coefficient on the knuckle tie rod displacement and torque sensor measure value of EPS.Secondly, simulation model of EPS system is founded. Sympathetic peak is studied, for torque sensor is used in the turning system, and cascade compensate is presented to restrain the peak and do several simulations in bode diagram. Fuzzy PID motor current controller is designed to make sure the good tracking character of its output current. Meantime, this paper has been analyzed quantification the steering road feel intensity. Adjust assist gain according to the vehicle speed can enhance driver's road feel. Manipulate stability analysis of EPS system is presented, and the simple conclusion is achieved that the maximum assist gain cannot exceed the main reducer's gear radio in order to keep stabilization.At last, the hardware circuit diagrams of the Electron Control Unit are introduced in the EPS system and the realization method of software is also mentioned.
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