Design And Research Of A New Steering System For Autonomous Vehicle

With the continuous improvement of the intelligent level of the automobile,the functional safety of the steering system of the automatic driving automobile is becoming more and more perfect.As an important executive component of the automatic driving automobile,the steering by wire system should not only meet the functional requirements of the automatic driving,but also ensure the safety and redundancy of the steering system.Due to the current regulatory requirements and technical maturity,it is difficult to achieve highly automatic driving above L4 in a short period of time,and the machine cannot completely replace the driver to control the vehicle.Therefore,the steering by wire system for automatic driving vehicles must have the driver takeover function to achieve man-machine driving.Although the steering by wire system has an ideal transmission ratio and driving sense,it often requires overlapping hardware to ensure the safety redundancy of the system.Even so,the steering by wire system equipped with Infiniti Q50 still retains the steering column while embedding an electromagnetic clutch to achieve the mechanical steering function,providing the final safety guarantee for the steering system.Based on the inspiration of this product,this thesis tentatively proposes a new type of steer by wire system for autonomous vehicles.The permanent magnet clutch is embedded in the steering column.The control of the permanent magnet clutch adjusts the transmitted road sense torque to achieve the steering wheel silence and overload protection functions of the steering system,and achieve the safety redundancy function of the steering system while using less hardware.The research contents of the new steering by wire system in this thesis are as follows:(1)The structure design and function analysis of the new steering by wire system are carried out.On this basis,a permanent magnet clutch that can achieve specific functions is designed.The research is conducted from the working principle,mathematical model and simulation analysis of the permanent magnet clutch,and finally the shape and size of the clutch used are determined.(2)The mathematical model of the new steering by wire system is established,including vehicle model,tire model and power steering model;The road feeling characteristics of driver takeover mode are analyzed emphatically.(3)The mathematical model of the new steering by wire system is used to design and research the control strategies of the automatic driving mode,the driver taking over mode and other functions,in which the permanent magnet synchronous motor is controlled by a three closed loop vector control method,and the fuzzy self-tuning PI control method is used to improve the control accuracy of the motor.(4)By using the method of joint simulation and setting typical working conditions through Pre Scan,the functions involved in the new steering by wire system proposed in this thesis are verified.The simulation results show that the model of the steering by wire system is reasonable and the strategy is feasible.