Study On Extrapolation Method Of Fatigue Load Of Gear In Power Split Device

As a core component of hybrid electric vehicle, power split device (PSD)influences the control strategies and dynamic performance of vehicle. Load spectrumis the basis of fatigue damage prediction of component, and it also is an effectivemean to improve the design reliability of PSD. In the process of compiling fatigueload spectrum of gear in PSD, selection of load extrapolation method has greatinfluence on the extrapolation results. In this paper, combining with the nationalnatural science foundation of China:“design theory and method for power split deviceof hybrid electric vehicle in multi-field coupling”, load extrapolation method anddynamics of gear are researched, and nonparametric extrapolation method based onmulti-criteria decision-making is proposed.(1) Four extrapolation methods consisting of parametric method，rain-flow matrixextrapolation，POT extrapolation，duration and percentile extrapolation are presented.Application conditions, advantages and disadvantages of each method are analyzedrespectively，and the extrapolation procedures are described in detail. By comparingthe extrapolation results, it is concluded that the selection of method has greatinfluence on results.(2) The nonparametric extrapolation method is analyzed in detail, andcharacteristics of four kernel functions are studied. Combined with the distributioncharacteristics of data in rainflow matrix, range, interquartile range and the standarddeviation of mean and amplitude as the criteria for selecting kernel function aredetermined. Through applying optimization theory and the Jaynes maximum entropyprinciple to synthesize the subjective weight and objective weight, kernel functionselection method based on multi-criteria decision-making is proposed.(3) Kinematics relations of three terminals in PSD are introduced and data ofmixed working condition are simulated by ADVISOR. The rigid-flexible coupledmodel is established using ANSYS software to produce flexible gear. The influence ofcollision force index and damping to dynamic simulation of gear are studied, and theoptimal parameters are conformed. The different fluctuations of gear meshing force for flexible gear and rigid gear in dynamic simulation are summarized, and meshingforce curves of typical maximum load working conditions are obtained.(4) The finite element contact analysis for gear is done, and the maximumbending stress distribution resulting in fatigue fracture of gear is concluded. The stressspectrum of high load working condition is calculated and the relationship betweenstress amplitude and frequency is obtained according to ISO. The torque of half shaftgear is extrapolated applying nonparametric extrapolation method proposed in thispaper. The two-dimensional design spectrum and one-dimensional fatigue test loadspectrum of whole life torque are compiled.Nonparametric extrapolation method based on multi-criteria decision-makingproposed in this paper considers the distribution characteristic of load. The selectionof kernel functions is more reasonable, and it improves the precision of compiling gearload spectrum.