The Research On Test And Evaluation Method Of Frequency Characteristics Of Electro-hydraulic Proportional Directional Valve

The frequency characteristic is one of the most critical dynamic characteristics of the electro-hydraulic proportional directional valve.Accurate measurement and objective evaluation are important basis for judging the dynamic characteristics of the electro-hydraulic proportional directional valve.Frequency characteristic is usually obtained by frequency-sweep method.This method uses a signal,whose frequency changes with the exponential or linear law over time,to stimulate the tested valve,and the spool displacement is response signal.When the frequency of the excitation signal exceeds the valve bandwidth,the amplitude of the response signal is rapidly attenuated.Inevitably,the noise will jump into the acquisition channel,which seriously affects the accuracy of the frequency characteristic test.In addition,there is no method to quantitatively evaluate the frequency characteristic test result of the electro-hydraulic proportional directional valve.The existing method qualitative making a judgment according to the test curve,and the evaluation is arbitrarily large.To address this concern of the accuracy of acquisition channel noise influence frequency characteristics test,an integrated filtering method that combines ensemble empirical mode decomposition with median filtering and smoothing filtering—EEMD synthesis filtering.This method completely inherits the advantages of EEMD,median filtering and smoothing filtering.Using EEMD to preprocess the response signal of tested valve can eliminate most of the noise in the response signal,increase the signal-to-noise ratio of the characteristic signal,and the residual noise in the response signal basically is impulse noise,which can be eliminated by median filter.On this basis,the FFT of the test signal and the FFT the processing result are obtained thereby their ratio being obtained.Next,the amplitude and angle phase of the ratio are gained.Furthermore,the smoothing filter is used to further process the amplitude and angle phase,which can greatly enhance the accuracy of the frequency characteristic test results.In addition,in order to make a more qualitative evaluation for the test results of frequency characteristics,this paper proposes two evaluation methods of frequency characteristic tests: index weighting method and envelope method,which can preliminarily estimate the test result of the frequency characteristics electro-hydraulic proportional directional valve frequency characteristic.In Matlab/Simulink,the EEMD synthesis filter is applied to the simulation test of frequency characteristics of the electro-hydraulic proportional directional valve.The results show that when the acquisition channel has impulse noise and the signal-to-noise ratio is-9.3 dB,this method can decrease the root mean square error of the frequency characteristic from 4.2to 1.7,and the root mean square error of the phase frequency characteristic from 19.5 to 5.2.Moreover,an electro-hydraulic proportional valve characteristic test bench was designed,and the frequency characteristics of the Rexroth 4WRKE10 electro-hydraulic proportional directional valve were tested thereby obtained the frequency characteristics electro-hydraulic proportional directional valve frequency characteristic through EEMD synthesis filtering.Finally,the test results are appraised by index weighting evaluation and envelope method.The evaluation results show that compared with the test results obtained without data processing method,the accuracy of the amplitude-frequency characteristic test is improved by about 59%,and the accuracy of the phase-frequency characteristic test is improved by about 60%.