Study And Development Of The Automotive Column-type Electric Power Steering System

Electric power steering system(EPS)is a new developing direction of power steering system in automotive. The principle of EPS is the assistant motor works according to the measured torque and vehicle signals. So that power steering can be realized. Besides EPS has the light steering torque like Hydraulic Power Steering (HPS) system, it has many other characteristics such as steering placidly, low energy consuming, environment protecting and so on. Therefore it is a certain tendency that EPS being instead of HPS. But, at present, the R&D of the domestic EPS is behindhand, and all the EPS used in vehicles has no independent knowledge property right. Therefore it is very important in academic and practical significance in R&D of EPS. The main content of this thesis is as follows: 1)The structures of EPS are analyzed. The main components of EPS are introduced in detail. Then the distributed torque in EPS is analyzed and the control system model is set up. 2)Three control modes are discussed and the control strategy of EPS is studied in detail. Three principal modules in the control strategy are discussed—the predicted module which predicts motor rotational speed and steering rotational speed, the power-assistant module and the return control module. 3)The assistant torque curves of the motor are designed by using the B-spline, so that any kind of custom-built assistant torque curves can be designed according to different kinds of automobiles. 4)The hardware frame of EPS is studied. The developed controller based on 8-bit MCU MC68HC908MR8 is introduced and many related circuit units are designed, including the control circuit, the driver control circuit and so on. The software structure is discussed, then the steering control program flowchart is given. The results of the experiment show that the developed EPS control can satisfy most driving situations and has nice production foreground. Finally, a summary of works involved in the thesis is given and some problems for the future are discussed, which forms the objectives for future research and works.