Research And Development Of Electro-hydraulic Power Steering System

Electrical-hydraulic power steering system(EHPS) remains the advantage of working smoothly and high power density while realizing variable power steering which are attributed to traditional mechanical hydraulic steering system(HPS). Due to the better steering feel and better fuel economy, it has been used more and more widely. Research on EHPS in China starts late and the study is still in the exploratory stage, therefore it has important significance to develop EHPS and its related technology.In this paper, the method of combining theory and application, combining simulation and experiment is used to research on electro-hydraulic power steering system, an indepth analysis and research on the principle and assist characteristics EHPS has been conducted, then design and develop the EHPS controller and prototype, finally complete its experimental verification.Based on a wealth of bibliographies, this paper analyzed the theory of EHPS, established the mathematical model of each component of EHPS. According to mathematical model, the paper analyzed the steering response of EHPS, obtained the desired power steering characteristic and the stress of road feeling. And designed desired power steering characteristic of EHPS on the basis of them. Then analyzed the relationship between the EHPS motor speed, vehicle speed and power steering characteristic, developed the EHPS power control strategy.In order to verify the property of variable power characteristics of EHPS with power control strategy, a simulation analysis that using AMESim software to build simulation models of EHPS system based on a mathematical model and importing control strategy was carried out. The simulation results show that with the developed EHPS control strategies, the EHPS can achieve variable assist characteristics under different speed and meanwhile the performance of response and follow nature is very well.The EHPS Controller is the core of the electrical part of EHPS,it has a direct impact on the performance of EHPS, there for, the development of EHPS controller is an important link of the EHPS’ development. Based on a combination of EHPS control strategy and the result of the simulation, the hardware and the software of EHPS controller has been designed.Finally, this paper built the EHPS test bench and tested the performance of the EHPS prototype. The result of the bench test show that the EHPS prototype can not only meet the requirements of steering handiness at low speed driving but also assure proper road feel and essential feel of stability at high speed operation, and meanwhile, the result also shows the excellent performance of response and follow nature of the prototype. And then a field test has been conducted, tested the speed following performance and the work reliability of the EHPS motor.