| As a clean and renewable energy,wind energy has been paid more and more attention.Gearbox is an important part of the wind turbine.Due to the bad working environment,the fault occurs frequently,the maintenance is difficult and the cost is high.Therefore,the early fault diagnosis of the gear transmission system is of great significance to maintain the normal operation of the equipment.The fault caused by gear box pitting is one of the typical forms of wind power generator failure,so the research on gear pitting fault can lay a theoretical foundation for early fault diagnosis of gear system.In this paper,gear transmission system is taken as the research object,the mechanism of gear fatigue pitting fault is studied,and the vibration characteristics of gear transmission system under pitting fault are analyzed,which provides a theoretical basis for later fault diagnosis.The main contents of this paper are as follows:Firstly,the mechanism of gear fatigue pitting is studied.The formation process of fatigue pitting caused by two-dimensional fatigue crack propagation under lubricating oil was analyzed.The pressure distribution under line contact elastohydrodynamic lubrication is calculated by simplifying gear mesh model,the influence of contact pressure on fatigue crack is analyzed,and the crack propagation mechanism is studied.Simulation the fatigue crack propagation results in the formation of fatigue pitting by using the extended finite element method,and the pitting appearance is analyzed.Compared with the actual experiment,the pitting shape is basically the same,which proves the effectiveness of the method.Then,a partial spherical pitting model is proposed.Based on the potential energy method,the gear time-varying mesh stiffness formulas of single pitting and multi pitting faults are derived.The evolution model of single pitting and the multi pitting distribution model of different fault degrees based on random distribution are proposed.The effects of different fault degrees on gear time-varying mesh stiffness and Hertz contact stiffness are analyzed.The influence of the proposed pitting model on bending stiffness,axial compression stiffness,shear stiffness and overall mesh stiffness is compared with rectangular and oblique cylindrical pitting models.The gear time-varying mesh stiffness with different pitting degrees obtained by the proposed method and the finite element method are compared,and the results show that the difference is small,which verifies the effectiveness of the proposed method.Finally,considering the nonlinear factors such as gear time-varying mesh stiffness,friction,backlash and transmission error,a 6-DOF dynamic model of gear transmission system is established by using lumped parameter method.The different pitting degrees of gear time-varying mesh stiffness is brought into the dynamic model,and the Runge Kutta method is used to solve the dynamic equation.The vertical displacement response of gear transmission system is obtained,and the pitting fault signal is analyzed in time domain and frequency domain.By comparing the simulation signal with the experimental signal,the validity of the dynamic model of pitting gear transmission system is verified.The results show that the pulse factor is sensitive to the fault and can be used as the evaluation index of pitting fault. |
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