Study On The Speed Sensor-less Control Strategy Of Electro-Hydraulic Power Steering System

Electro-Hydraulic Power Steering(EHPS)system can promote the driving comfort and safety by changing the steering power according to steering conditions and consume less energy than the system whose power is uncontrollable,so the study of Electro-Hydraulic Power Steering system has become the focus in the study domain of vehicle steering.Motors are used as the power to drive hydraulic pumps to provide hydraulic power in EHPS system,the size of the power is controlled by the electronic control unit who can calculate the required power according to vehicle running status and operation of the driver,at last,the realization of the power adjustment can be done by motor speed.So the steering portability at low speeds and good road feeling performance at high speeds can be balanced.This article mainly focuses on the motor control,where a speed sensor-less vector control has been designed to realize the assist characteristics of EHPS system.The speed control scheme of induction motors based on speed sensor-less vector control has been designed based on the study of the structure,principle and assist characteristics of EHPS system.And the simulation analysis of the rapidity,handiness and road feeling of the steering system has been done based on the linear assistance characteristics curve.Firstly,the structures and principles of EHPS system have been analyzed,and the types of the motor and steering valve have been chosen,besides,the linear assistance characteristics curves at different speeds have been obtained by Matlab software;Then the mathematical models of induction motors,vector control and rotor speed identification based on full-order flux observer have been built.On this basis,the co-simulation models of AMEsim and Simulink have been established,in which the AMEsim models of mechanical hydraulic system and the Simulink models of EHPS control system based on speed sensorless were combined through an interface;At last,the simulation results showed that the sensor-less vector control of induction motors based on full-order flux observer could make the rotor speed follow the reference values rapidly and stably,the speed estimation errors were very small.When the estimated speed was used as the speed close-loop signal,the output power of EHPS system could meet the requirements of steering portability and road feel very well.So the designed control strategy of EHPS system can get rid of speed sensors on the premise of ensuring good steering characteristics,simplifying the motor structure,improving the stability of the whole system,saving the cost and reducing the energy consumption.