Research On Integrated Steering System Of EPS And AFS

EPS(Electric Power Steering) can provide a real-time Assisting torque or damping moment for the driver and through controling the power motor, the vehicle steering portability, road sense and return performance can be improved. AFS(Active Front Steering) can change the transmission ratio of steering system in real time. Through controling the displacement motor of AFS : the steering sensitivity and handling and stability can be improved when vehicle is running at low speed and the transmission ratio of steering system is small; the driving stability and safety can be improved when vehicle is running at high speed and the transmission ratio of steering system is large. EPS can only achieve power steering, but can not achieve controling the variable transmission of steering system. AFS can only achieve controling the variable transmission of steering system, but can not achieve power steering. On the other hand, the existing integrated steering system is more integrated with AFS and hydraulic power system, such as the active steering system of BWM. However, hydraulic power system has the disadvantages of hydraulic system. Therefore, the proposed of integrated steering system of EPS and AFS has important significance.Firstly, this paper designed an active steering coupling mechanism and analysed integrated steering system of EPS and AFS on the basis of the above.In this paper, the basic performance of the new active steering coupling mechanism is analyzed in detail, and the basic parameters are optimized and the parameters of motor are matched.Secondly, vehicle models in addition to vehicle steering system are matched and modeled uniformly based on the Carsim software. The dynamics mathematical model of steering wheel steering column, steering column virtual sensor, power motor, displacement motor, planetary gear, steering gear rack, front wheel steering assembly was established respectively based on the MATLAB/Simulink software. The calculation model of return moment is established based on the Matlab/simulink software and the friction torque caused by dry friction was considered in order to improve the reality of model.Then, the control system of integrated steering system of EPS and AFS was studied.The EPS control strategy includes basic assist control, motor compensation control, damping control, back control, EPS correction control and fuzzy PID current control. The AFS control strategy is designed based on the ideal transmission which is based on fixed yaw angular velocity gain and the transmission ratio of steering system was controled precisely by fuzzy adaptive PID control method.Finally, the dynamics Co simulation and analysis of the vehicle equipped with integrated steering system of EPS and AFS based on the Carsim and Matlab/simulink software is carried out. From the results of simulation above, we conclude that: The vehicle equipped with integrated steering system of EPS and AFS has good operation stability and sensitivity in all speed; Integrated steering system of EPS and AFS can reduce driver's intensity significantly and reduce parking difficulty in low speed directly and improve vehicle stability effectively.