Research On The Load Spectrum Compiling Of The Pressure In The Hydraulic System Of An Excavator

High demands of quality and reliability of excavators the machines are put forward due to the poor working environment and heavy task.Fatigue analysis and reliability test of whole machines and their key components based on load spectrum are important tools to improve the quality and reliability of excavators.Accurate load spectrum compiling provides guarantee for reasonability of the analysis and test results.This paper is based on the National Science and Technology Support Project—“Research on the generic technology of energy conservation and emissions reduction of engineering machineries”(Item no.: 2015BAF07B01).Pressure load of the excavator hydraulic system is selected as the objective load.In load testing,three operators are arranged to conduct the test,and differences of the load characteristics between different operators are analyzed.Due to the differences between the characteristics,the percentile extrapolation method(PEM)is proposed into extrapolating,and the method is optimized based on the Multi-criteria Decision-making Technology(MDT).With the extrapolated load,an example of compiling a program loading spectrum is proposed based on the equivalent damage principle of the pump body.The main research contents and analysis conclusions of this paper are as follows:1.A load test scheme of the key components in an excavator is formulated.In the scheme,several aspects such as establishment of the test system,preparation before testing and data monitoring and settling are qualified.Emphasis in the scheme is the arrangement of three operators.When the test is finished,the sample length validation and the stability and ergodic test are conducted to ensure that the testing data meet the requirements;2.The wavelet method is used to reduce the noise of the load and the correlation dimension is proposed to evaluate the effect.The least square method is used to eliminate the trend of the load,and the complete work cycle of an excavator is divided based on the working characteristics.The load characteristic value is applied to replace the whole load to verify the differences of load characteristics,based on the significant difference analysis method,the otherness as well as the impact of human factor is verified,which proves the necessity of the application of PEM;3.With the characteristic that PEM is appropriate for extrapolating the load withotherness,PEM is applied in this paper.For improving the efficiency of percentile extrapolation,mileage extrapolation has to be conducted first.From the basic steps and arithmetic,the parameter estimation extrapolation method,the extreme value extrapolation method and the nonparametric extrapolation method are analyzed deeply.Their key points,merits and demerits as well as application ranges are summarized,and a mileage extrapolation software is programmed.In view of the fact that the pressure load here is medium and small load,the nonparametric extrapolation method is selected to extrapolate the load;4.The fundamental of PEM is introduced.For reducing the subjectivity and blindness in quantile confirming,optimization of PEM is proposed.Based on the extrapolation with the quantiles in advance,key characteristics of the extrapolated spectra are chosen as criterions,comprehensive weights of the criterions are calculated with MDT to form a weight vector,which is used to optimize the load characteristics and decide the optimized quantile.Taking the pressure load after mileage extrapolation as initial load,the percentile extrapolation is conducted and the optimization effect is verified;5.For application,the long-term load spectrum after extrapolation has to be translated into program loading spectra,and the translation has to be conducted according to application requirements.Pressure load in hydraulic system has wide-range applications,this paper takes the pump body as the research object,and the fatigue damage equivalent of a pump body is the principle.With the basis of dimensions reducing of the load spectrum and determination of the material property value,the loading magnitudes and corresponding frequencies are obtained according to experimental conditions and physical limitations,which gives a typical example of program loading spectrum compiling.The compilied loading spectrum will be used in the bench test.