| Power steering system is one of key subsystems in vehicles which affects the driving safety of vehicles. It can reduce steering force and improve the drive dynamics. With the development of science and technology and the increase of the environmental protection consciousness of people, to produce more portable, safer, more energy saving power steering system is the urgent task for auto industry. The study on improvements of its structure and dynamic performance has been the research subject in vehicle engineering technology field for many years. Since 1980s, due to the defect of conventional hydraulic power steering system in maintain appropriate road feeling in high speed driving, researchers in developed countries have begun to develop electro-hydraulic power steering system(EHPS) whose pump is driven by electric motor. With the deepening of the research, some application have been used in cars.The research of EHPS starts later in China and the deepness and extent inferior to developed contries.Many key technologies of EHPS can’t be broken through and the application example didn’t appear. Starting from the difficulty of how to characterize road feel in vehicle handling, this paper studies deeply in steering wheel torque, motor pump target speed, system stability and optimized design method of EHPS.First, a comprehensive steering road feel concept, which takes steering wheel torque and angle into account, is proposed, and a method of calculating the desired steering wheel torque is brought forward in this paper. Combined with an example, the desired steering wheel torque in various driving conditions is calculated and the results are compared with the experiment ones from other references. The result of comparison shows that the method is reasonable and feasible.Second, based on the road feeling strength theory,a new way to calculate the motor pump target speed is proposed. In order to illustrates its validity, a calculational examples is doned and results are compared with an experimental ones. It shows that the method is feasible, and provides reference for the design of EHPS.Thirdly, in order to meet the needs of the best comprehensive road feeling strength, a study is made on motor pump body and its control methods. The dynamic performance requirements of the control system and basic physical parameters of the motor pump are given out. According to the working characteristic of motor pump, a Fuzzy-PID control system is recommend,and its stability analysised.Fourthly, A new optimized design method for EHPS,which is based on optimization of road feeling which is feedback by steering wheel, is proposed in this paper. And it also proves that the ideal damping ratio value of daynamic system be 0.5.Fifthly, based on the Matlab program, a EHPS and vehicle handling dynamics simulation model build, the simulation example based on best road feeling is carry out, its results are compared with the experiment and the theoretical computation ones. The comparison shows that the simulation system is reliabile,and provides simulation platform for the EHPS’s design.Finally, the EHPS test bench is designed and a bench test is carried out.The experiment results show that the test bench software and hardware is reliable and the EHPS design theory and method proposed by this paper is feasibility. |
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