Study On Characteristic Of Active Front Steering System

The Active Front Steering System(AFS) integrates a set of dual planetary gears mechanism on the steering column between the steering wheel and rack-pinion redirector,using for providing the superposition angle to front wheel,thus realizing the variable steering ratio function. Compared with Electric Power Steering System(EPS),it is more easily and more flexible when the vehicles travels with low speed and it enhances the handling stability through attaching a front wheel angle when the vehicles travels with high speed,which is the core to EPS.Firstly,a mathematics model of active front steering system and entire vehicle dynamic model were built.On the basis of these models,the operating principle and operating mode of dual planetary gears mechanism were analysed.The curve of perfect variable drive ratio was designed,the results coincides the curve of perfect variable steering ratio of the actual BMW.Secondly,the control strategy of additional steering angle was proposed to improve vehicle handling stability and portability.The strategy of yaw rate feedback control and the coordination control of AFS and DYC were proposed to improve vehicle handling stability,with the tools of MATLAB/Simulink,the simulation results show that controllers have good performance.After that,the idea of control strategy between active front steering and Electronic Stability Program(ESP) was introduced,the idea of integration control strategy between active front steering and active suspension was also proposed.They both meet active safety concept of vehicles.In addition,the evaluation standard of active front steering was puted forward according to Electric Power Steering System(EPS), including the objective evaluation and subjective evaluation,particularly evaluation of variable steering ratio and flexibility.Finally,several loading methods were compared.As a result,magnetic partical brake was choosed.The test project was proposed on the basis of characteristic of AFS,It includes the current characteristic test,portability test with low speed,handling stability with high speed.In addition,the data acquisition programme and human-machine communication interface were designed with the tool of labVIEW.