The Mechanism Research And Design Of Electric Power Steering System Of Pure Electric Vehicle

With the development of modern control theory and the microelectronics technology, electric power steering system (EPS) has become a focal point of research in the vehicle engineering field in recent years, more and more universities, research institutions and auto manufacturers pay their attention to it. In this paper, we choose the column type electric power steering system of pure electric vehicle as the main object of study, and use the method such as theoretical analysis, computer system simulation, bench test and real vehicle test to study the column type EPS, the main research contents are as follows:The working principle and the characteristics of the electric power steering system of the pure electric vehicle have been analyzed in detail, followed by the system control strategies and algorithms study. By the way of analyzing of the steering control of vehicles and the requirements and characteristics of the drivers, we have determined the basic characteristics of the assist requirements.In the electric power steering system, we use the control strategies such as the assist control, the return control, the damp control and the compensate control. Meanwhile by analyzing and comparing three kinds of typical characteristic curves, we proposed to design a new ideal characteristic curve that applies to the EPS of pure electric vehicle. The characteristic curve should be straight when the steering angle is small, when the angle is larger than a special value, the quadratic curve that the slope of the tangent slope larger than before should be chosen, and this paper gives us the basic algorithm for the new characteristic curve, the computer simulation, controller design, bench test and the real vehicle experiments will prove its correctness. With the determinate assist model and the generated assist curve, we are enabled to give better consideration to steering portability and road feel.ADAMS dynamic simulation software is adopted in our EPS system research, the pure electric vehicle Multi-body vehicle dynamics ADAMS simulation model is built in the ADAMS/car module, including front / rear suspension, steering system, front and rear wheels and road spectrum, and the steady-state steering vehicle simulation is carried out. At the same time we also finish the control model of the control strategies and controller design based on a new electric power steering system assist characteristic curves in Matlab/Simulink environment. We introduce the entire vehicle model that is built in ADAMS/car module to MATLAB/simulink by the software interface, and then we connect the vehicle model with the simulation model of EPS control system in MATLAB. By combining ADAMS/car and Matlab/Simulink, we make a comprehensive joint simulation analysis. The co-simulation analysis and simulation results show that the way that we connect the entire vehicle dynamics model built in ADAMS with the mathematic model of the control system built in MATLAB by which we studied the electric power steering system study is effective. Furthermore, the simulation results demonstrate the validity and effectiveness of our control strategies and calculation methods.This paper has developed the EPS system hardware and software design based on pure electric vehicle and realized the basic functions of the EPS. We analyzed the selecting and matching principles of key vehicle parts and designed a corresponding control circuit based on our analysis of different characteristics of ECU's input and output signals. As for an assist motor we adopted a permanent-magmet direct current motor that is drived by an H-bridge comsisted of 4 NMOS tubes. This kind of assist motors are controlled by a feedback control system of PWM and assist motor current Fuzzy_PID. The system software is divided into two layers. The upper layer finishes control strategies and algorithms methods while the lower layer finishes the closed-loop control of assist motor current. This paper also provides the flow diagram of main soft module. This provides the experimental basis for further test.We also studied the bench test plan of the electric assist system. Based on our analysis we determinate the signals simulation method of the running states of various vehicles needed in our test. Both the rotating speed of the motor and vehicle speed are directly input to ECU by signals generator. By inputting the turning torque signals and turning signals derived from sensors to ECU and adopting spring imitation, we completed designing EPS test trestle and carried out comparative experiments on it. Our test results indicate that by adding EPS the turning portability is highly improved. And then we conducted related real vehicle tests. We proposed the algorithms method of flexible current transition under low speed and if we implement it in the future we would considerably reduce vibration of the steering wheel caused by great current fluctuation.We studied anti-interference performance and reliability of both software and hardware systems. Moreover we carried out communication test with the upper level controller of the electric vehicle.The results of the theoretical analysis, computer simulation, bench test, real vehicle test show that they coincide very well, which have important theoretical and practical values to the fundamental research, design, development and application of electric power steering system.