| Loader is the typical mechanical equipment in earthworks, which was widely used in building, transportation, mining, national defense engineering and other fields, to shorten construction period, relieve labor intensity, improve project quality and reduce project cost. Because of the poor working condition, the components of loader's power train are subject to a complex alternating load in the course of work, and then the phenomenon of fatigue failure occurred in machine parts is very serious and which is difficult to effectively resolve at the static realm by the way of augmenting structural sizes of parts to increase the safety factor. At present, the fatigue intensity design of loader's parts in foreign developed countries was widely carried out according to the load spectrum, their similar products considering the reliability design are obviously superior to domestic ones. By way of the course curves reflected the change law of random loads for components, load spectrum is signify much to perform the dynamic design of products. The practices in automobile, aviation and other fields are fully proved that the design of limited life of parts is carried out based on the load spectrum, which has great significance to solve the problem of fatigue failure, improve the service life and reliability of parts and enhance the market competitiveness of products. As the premise and foundation of guiding the fatigue design, how to achieve accurate load signal and scientific compose-spectrum come to especially important.As research work supported by the project of National Natural Science Foundation of China, namely, Research on the key technologies of load spectrum in the power train of wheeled mobile machinery shop and the R & D projects of Guangxi Liugong Machinery Ltd., namely, Research on the compile method of load spectrum of CLG856 loader power train and its application, the load signal testing of loader power train and its method of preparation of load spectrum were studied in this paper. First, we introduce the research meaning, content, methods of load spectrum of loader power train, and the research trends of fatigue load spectrum at home and abroad, and the problem we have to overcome. Then, based on the field test and theoretical analysis, a series of pretreatment were carried out such as zero load signal, noise filtering, eliminate the singular points, elicited the conclusions and methods of piecewise treatment to load signals. And then, the information of amplitude and frequency after the rain-flow counting was taken the distribution assumption and tested by probability statistics method. Joint probability density function of both amplitude was found during this method. Finally, we obtained the two-dimensional design spectrum of both amplitude on the basis of statistically conclude to the extremum load of both amplitude, and gave the spectrum load project of fatigue test program.The main works and contents are as follows:(1) In this paper, we introduced the research background, meaning of load spectrum of loader power train and their engineering value. In the following, we summarize the application status and research trends of fatigue load spectrum at home and abroad, and pointed out the problems in current study of loaders load spectrum. Based on above, the research means for this paper was determined.(2)In order to accurately obtain load signals of key pieces of loader, and ensure the test samples which have sufficient representation, the experimental prototype was taken strictly overhaul before trial, and the specific requirements on test environment and operating methods were given, and also the test point selection, test system construction, sub-sample size were given sufficient argumentation. Eventually, the signal of load-time course of key pieces of loader power train were obtained with synchronous multi-parameters testing by the mode of "cable test" combine with "wireless remote". In the experimentation, we offered a complete set of way from parts restructuring design, sensors install, signal testing to test data inspection, which provided reference with the measured the loader's load signals.(3) The size of sampling frequency and filter method were determined basing the basic theories of signal collect and process. The advanced engineering software of Nsoft, Matlab and Vib etc. were synthetically used, the deal with noise filter of data, check and eliminate of excrescent peak value, eliminate of zero line drifts and trend item and so on were actualized, the "pure" load signals and the veracity of datum and results were insured.(4) Through the time-frequency analysis of loader's operating characteristics and actually measure signals, the understandings of load change regulations to time-field characteristics and frequency composing were deepen. And also, we elicited the subsection means of load signals and a conclusion that the calmly treat with load signals can be realized according to the operating segment, which provided the theoretical basis for the preparation of "shovel - continued - shovel" spectrum to loader power train operating segment.(5)By using the rain flow counting to record the information of both amplitude, with both the engineering software Matlab and the 6a quality manage software Minitab, and applied the method of probability statistics, it was completed that the parameters estimation of probability distributing of both amplitude and its hypothesis testing in this paper, and obtained two-dimensional spectrum and one dimension program load spectrum for each test points, and put forward an rationalization suggestion on add load to test-bed.Finally, a summarization was given, and also, we introduced the future direction of R & D focus for loader load spectrum.In this paper, we gave the method of signal testing and preparation about loader's power train, which provided guidance on the future R & D of transmission shaft in power train, and offered some experience reference for key pieces of loader load spectrum. It has higher practical value.
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