Dynamic Modeling And Vibration Characteristic Analysis Of Local Fault Of Wind Power Gear Transmission System

As an efficient and clean energy,wind energy is becoming more and more popular.As the key component of the wind turbine,the gearbox is prone to produce faults,while the working environment of the wind generator is complex,the maintenance is difficult and the cost is relatively high.Therefore,the condition monitoring and early fault diagnosis of gear transmission system are of great significance to maintain the normal operation of the equipment.This paper takes gear transmission system as the research object,analyzes the dynamic characteristics of local fault,and studies the fault mechanism of gear system,which can provide theoretical basis for later fault diagnosis.The main content of this paper is as follows:Firstly,the main excitation of gear dynamic model is studied,and the typical failure modes and causes of gear system are analyzed.As the main internal excitation,time-varying meshing stiffness is compared with different stiffness calculation methods.Considering the time-varying meshing stiffness,sliding friction and meshing damping,a6-DOF gear dynamic model is established.Secondly,considering the actual tooth profile curve,the tooth profile is divided into two parts: the transition curve and the involute curve.The section area and the section inertia moment of each part of the meshing point are given respectively.Based on the stiffness algorithm of healthy gear,the change rule of the stiffness when the tooth crack propagates along the tooth depth is analyzed by using the energy method,and the discussion is made according to whether the crack passes through the tooth centerline.The time-varying meshing stiffness of a single spalling defect is calculated,and the effects of shear stiffness,bending stiffness,axial compression stiffness and Hertz stiffness are studied.Based on the analysis of the evolution law of gear spalling defects,the calculation formulas of multiple spalling defects on the tooth surface are given,and the time-varying meshing stiffness with different fault degrees is calculated.Then,the stiffness of the gears with different crack growth length and spalling width is brought into the model,and the vibration displacement response of the gear system in the vertical direction is solved by Runge Kutta method.The results show that when thefault size is small,the fault feature is not easy to extract and the impact is not obvious;with the increase of the fault size,the impact in the time domain signal increases gradually,and the side band in the frequency spectrum is also growing.The dynamic response of the broken tooth fault is studied,and the accuracy of the theoretical model is verified by the actual signal.Finally,aiming at the phenomenon that the early fault features are not obvious,a method by segmenting the stiffness is proposed.The method of segmenting the stiffness curve of crack and spalling defect is given respectively.Through the short-time Fourier transform of each segment corresponding to the segmented stiffness,and the analysis of the signal in time-frequency domain,the fault can be identified and the fault location can be determined in the time-frequency spectrum.The sensitivity of different statistical indicators to different crack growth degree and spalling degree are calculated in time domain and frequency domain respectively.The results show that the pulse factor is more sensitive to the fault characteristics.