Research On Control Strategy Of Automobile Electric Power Steering System

The automobile industry is one of the most important industries in the country,and it has a significant impact on the country's economy and people's lives.The power steering system is an important part of assisting automobile steering,and it has a safety,portability,and stability when the car turns.Wait for the decisive role.This paper introduces the five types of power steering systems by referring to the development history and technical data of steering systems at home and abroad: mechanical steering system,hydraulic power steering system,electrically hydraulic power steering system,electric power steering systems,and steering by-wire system.Compared with several other steering systems,the Electric Power Steering System(EPS)has good road feel,variable power assistance,simple structure,energy saving,environmental protection,and high safety.It is in line with the current trend of automobile intelligence and Internet,and is an ideal choice for pure electric vehicles in the future.In this paper,a new control strategy was proposed with Column-assist type EPS as the research object.The work is as follows:(1)Explained the principles of EPS: torque sensor,vehicle speed sensor,power assist motor,electromagnetic clutch,reduction mechanism and mechanical steering gear,and select DC motor as power assist motor and the rack-and-pinion steering gear as mechanical steering gear.Analyzed the mechanical characteristics of each component of EPS,and establish a mathematical model for each part by Newton's second law.Determined the state-space equation with motor voltage,steering wheel torque,and road reaction torque as inputs and steering wheel angle and motor angle as outputs.(2)Detailed analysis of the advantages and disadvantages of the three common EPS power-assisting characteristic curves(straight,polyline,and curve),and designed a hybrd assisting characteristic curve based on the basic requirements that the curve needs to meet.The boosting torque was used to provide greater assist torque at low speeds to increase portability of operation,and reduces assist torque at high speeds to improve driving stability.The calculation process of the boosting characteristic curve parameters was given.(3)Analyze the three main control modes of EPS: assist control,return control and damping control.Aiming at the control strategy of EPS system,this paper studied PID control,fuzzy PID control and integral sliding mode control,and proved the stability of integral sliding mode control using Lyapunov's theorem.The power assist controller and the return damping controller were designed.The Kalman filter was used to estimate the steering state required by the controller,and the judgment of return to normal working conditions was analyzed and improved.(4)According to the mathematical model of EPS,used MATLAB / Simulink to build an overall control model for assist control and a simulation model for return damping control,compare and analyze the three control modes,and finally selected integral sliding mode control.Under the integral sliding mode control,the performances of motor angle tracking,torque tracking,assisted control and return-to-control were simulated and analyzed,which verifies the feasibility of the EPS control strategy.