Design Of Electric Power Steering System And Vehicle Matching Software

EPS (Electric Power Steering System), which was developed in order to meet steering handiness at low speed and road feeling at high speed, completely abandoned the hydraulic mechanism, is a power steering system which adopts motor to provide assist torque, and it is controlled by ECU (Electric Control Unit), according to the velocity of the vehicle and the torque of the steering wheel. Torque that is exported by motor is translated by steering system gear and can be used to help driver steer. In the EPS system, matching technology is very important for vehicle handling performance. A perfect matching condition can provide good handling performance, reduce accident and protect the passengers.The thesis is focused on the matching technology between the EPS steering system and the vehicle. The following is the main content of the thesis:Chapter one introduces the structure and principle of power steering system, development actuality of the matching technology, the key components, advantages, key technology and the development trend of EPS.Chapter two carries through the study of the evaluation of EPS performance and gives some test examples. The thesis also brings forward steering efforts test, steering returnability test, on-center handling test and the tests about the EPS components to evaluate the performance of EPS and analyses the evaluation index of EPS.In chapter three, the matching design of the assist characteristic is studied. Straight-line type, broken-line type and curve-line type assist characteristic are discussed systematically. The influence of the straight-line type assist coefficient to the steering maneuverability and the road feeling of the steering are simulated respectively. The results show that increasing the straight-line type assist coefficient can improve the steering maneuverability and enhance the transient response of the steering. But the road sense in high speed is reduced. The thesis also discuses the align control, the damp control and the compensate control of EPS. In chapter four, the matching design of EPS key parts such as motor, torque sensor, gear box with the whole vehicle is carried out. It is summarized that the position of the motor is decided by the space in front of the vehicle, load of the front axes and the motor characteristic. The maximal output torque of the motor should be matched with the load of the front axes, the gear box of the EPS and the steering gear angle ratio. The rotation speed of the motor ought to mach with the rotation speed of the steering wheel desired by driver. The influence of the motor moment of inertia to the transient response of the steering is simulated. The result shows that if the moment of inertia is in excess of the normal value, the steering moment and the yaw rate become to be unsteady. That is very dangerous at high speed. So, in order to ensure the stability of the EPS, the motor moment of inertia ought to be as low as possible. The influence of gear box gain to the performance of the whole vehicle is simulated. The result shows that increasing the gear box gain can improve the steering maneuverability. But the road feeling in high speed is reduced and the dynamic characteristic of the whole vehicle is going worse. The influence of the torque sensor torsion stiffness to the performance of the whole vehicle is simulated. The result shows that increasing the torsion stiffness of the torque sensor can enhance the transient response of the steering, and also increase the understeer performance. So it must be considered synthetically to choose the torque sensor.In chapter five, based on GUI of MATLAB, the software of EPS matching has been developed. This software includes the parameter matching and evaluation tests. The user can easily get the results of the parameter calculation and the figures of the evaluation tests by filling in the data needed in the application image. It saves time, and is convenient even for the unsophisticated users.Chapter six is the conclusions and the further work. It is to sum up thesis work, and point out the shortage of the thesis and the future research direction.