| The high-speed on-off valve controlled by PWM signal can achieve "stepless" regulation of flow,but when the high-speed on-off valve itself malfunctions,the corresponding system cannot work properly;When one of the parallel digital valves malfunctions,the other valves can operate normally,but can only perform "staged" flow regulation.This paper gives a new solution combining the advantages of high-speed on-off valve and parallel digital valve: the parallel array digital valve system not only meets the requirements of reliability,but also takes into account the "stepless" regulation of control flow.This paper first discusses the working principle of high-speed on-off valve under low frequency PWM signal and high frequency PWM signal,and establishes the average flow mathematical model of high-speed on-off valve under low frequency PWM signal control.The parallel array digital valve system is constructed,and three flow control modes of the digital valve system are analyzed respectively.Then the structure and working principle of the normally closed and normally open electromagnetic on-off valves are discussed.Taking the normally closed valve as an example,the mechanical-electrical-magnetic-hydraulic mathematical model is derived,and the mathematical model of the opening and closing delay time is derived on this basis.According to the structural dimensions and electromagnetic parameters of the two electromagnetic on-off valves,the electromagnetic on-off valve simulation model is built using the electromagnetic library and HCD library of AMESim,and the current changes and valve core displacement changes at the opening and closing stages of the normally closed valve and the normally open valve under different pressure differences are analyzed.The optimization method of opening and closing characteristics is adopted in the simulation.The results show that the method can effectively shorten the time of opening and closing stages.Then the valve group control strategy of the parallel array digital valve system is studied for the flow,and it is realized in AMESim by using the signal library and state machine.The static and dynamic characteristics of the digital valve system under the control strategy of valve group are discussed respectively.The simulation results show that the number of flow unit groups constituting the digital valve system and the volume formed by the pipeline connecting the valves will affect the flow control accuracy.The speed characteristics of the hydraulic cylinder system controlled by digital valve are analyzed,and the mathematical model of speed fluctuation is deduced by using the state space method.The corresponding relationship between the speed fluctuation amplitude and the discrete flow frequency is solved by writing an iterative algorithm in MATLAB.Finally,an experimental system of electromagnetic on-off valve opening and closing characteristics is built to verify the optimization method of opening and closing characteristics,and the opening and closing characteristics of the normally closed valve and the normally open valve before and after optimization are compared and discussed under different pressure differences.The results show that after optimization,the time of the opening and closing stages is shortened,especially the time of the normally closed valve closing stage and the time of the normally open valve opening stage. |
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