Mode-decomposing Measurement Method Of Extreme Load And Its Application In Power Coupling Device Of HEV

Damage of automotive systems and components are vastly caused by fatiguefailure. In this process, extreme load is the main factor for fatigue crack generation,extension and the final fatigue fracture. Therefore, extreme load measurement andload spectrum compiling, both of which are the basis and prerequisites of intensityexamination, reliability design and life prediction for mechanical products, are ofgreat importance to mechanical design and optimization. However, due to the multiplepower sources, hybrid vehicles have a variety of working modes, which lead to theload characteristic difference among each of them. Thus, traditional loadmeasurement and establishment methods are not applicable. Based on the workingcharacteristics of different modes and combining with the National Natural FundProject (51375202and51075179), this paper proposes the mode-decomposingmethod for extreme load measurement and compiles the specific load spectrums foreach mode. The main research contents and conclusions are as follows:（1）Based on the detailed analysis of the working principle of hybrid electricvehicles and characteristics of each mode, mode-decomposing method for extremeload measurement is proposed using extreme value theory. Load-time history for eachpower supply is obtained using advisor simulation. Load sample data is screened andpreliminary statistical analysis is also conducted on this data.（2）Aiming at load samples of each mode, the BMM model of extreme valuetheory is selected to fit the extreme value distribution statistics. It can be known fromthe fitting results that three distribution types of the extreme value theory all appearedin the samples. Meanwhile, extreme value distributions for each terminal are alsodifferent, which illustrates the feasibility and necessity of mode-decomposing methodfor extreme load measurement.（3）Load spectrum compiling for each mode of hybrid vehicles. The processand key technology of load spectrum compiling are established in this research. Byanalyzing the load sample characteristics of each mode, statistical counting and loadextrapolation, the load spectrum for the total life of two-dimension amplitude isobtained. Then nonzero mean stress, Miner linear loss theory, etc. are adopted tocompile the entire life load spectrum for each mode.（4）Set planetary gear train as the main research object and based on the load spectrum extrapolation of each mode, two modes which have greater effect on fatiguefailure (combining drive mode and generating mode) are selected. Influences ofdifferent loading cycles for each mode on key components in hybrid vehicles arecompared.Based on the multi-mode working characteristic of hybrid vehicles, themode-decomposing method of extreme load measurement is proposed. The feasibilityand necessity of method are verified from multiple angles. The entire life loadspectrum for each mode is also acquired, which provides sufficient foundations for thedesign and exploitation of key components in hybrid vehicles.