Dynamical Analysis And Research On Control Strategy Of Electro-hydraulic Power Steering System

Steering performance is one of the main properties of the car. It affects the vehicle's handling stability and vehicle driving safety. On the other hand, it plays an important role on the driver ride comfort. Electric Hydraulic Power Steering system(EHPS) has good road feeling and High fuel efficiency. Therefore, it is necessary for the dynamic analysis of vehicle steering system and research of control strategy.This paper is based on the talent project of Changzhou City, Jiangsu Province and the enterprise horizontal topic. According to the electric hydraulic power steering system of a passenger car, its dynamic model is built and the experiment platform is built in order to study its control strategy. The main contents are as follows :First, it built the dynamic model of mechanical system and hydraulic system, and combined with vehicle dynamic model based on flow continuity equation and newton's mechanical laws. It solved the transient response by using Runge-Kutta numerical method in order to analyze vehicle system dynamic s response. It analyzed the influence of key parameters, for instance the torsion stiffness, on the steering system and vehicle performance. The results show that: under the step input, some parameters, such as the torsion stiffness, pinion radius, steering gear ratio and piston area, play an important role on rack displacement output response. These parameters have some effect on the automotive performance, for instance, the vehicle yaw rate, sideslip angle and Lateral output transient response.Second, the control theory of electric hydraulic power steering system is discussed in-depth. The basic requirements of power curve and control strategy are researched, together with analyzing the rotary valve features, to design the assist curve. The pump can achieve different flow by adjusting the motor speed in order to change assistance with the change of vehicle speed.Third, the electro-hydraulic power steering system test platform was built, including the design of the mechanical structure and control of the test rig module. Some integrated tests on power motor of the dynamical characteristics w ere processed to deal with the experimental results to analyze the power characteristics to map the related curve.Forth, According to assist curve from the test data and the requirements of the steering characteristic, the fuzzy controller which is based on MATLAB was built, including designing power curve, comparing with the original power curve, it meets basic power requirements to change its output with different co nditions.In the end, the work what were did will provide theoretical guidance and engineering reference for the product development and the vehicle matching design of power steering system.