| As one of the efficient motions and power transmission mechanisms in mechanical equipment,the gear transmission system has extensive and important applications in daily and industrial production.Studying the dynamic characteristics of the gear transmission system in different states will provide theoretical support for system failure prevention and diagnosis.The previous research on the dynamics of the gear transmission system mainly involved the calculation of the stiffness of the gear transmission and the conversion and transmission between the combined gears.The nonlinear characteristics of the bearings are usually simplified or even ignored.With the advancement and improvement of modern support theory,the influence of the nonlinear characteristics of the support bearing on the rotor system has received more and more attention.It is of great theoretical value and engineering significance to study the dynamic characteristics of transmission gears and supporting bearings from the perspective of the system.This work was supported by a grant from the National Natural Science Foundation of China(No.51705302).Taking the two-stage helical gear transmission system as the research object,on the basis of considering the time-varying meshing stiffness of the gear and the non-linear support characteristics of the bearing,the gear-rotor-bearing bending-torsion coupling dynamic model is established from the perspective of the system.The influence of gear failure and bearing failure on the dynamic characteristics of the gear transmission system,and the reliability of the model was verified based on the two-stage helical gearbox test bench.The main work of the thesis includes the following aspects:(1)The time-varying dynamic characteristics of gear meshing are studied.The time-varying meshing stiffness of the helical gear pair is solved using the potential energy method and the harmonic fitting method.The difference between the meshing force of helical gear and spur gear is analyzed.The calculation method of the time-varying meshing force of helical gear is determined,and the meshing dynamic model of helical gear pair under normal condition is established.(2)The nonlinear load characteristics of angular contact ball bearings are studied.The relationship between the internal parts of the bearing is analyzed from two aspects of kinematics and quasi-dynamics.The calculation method of the nonlinear bearing force of the bearing is determined,and the influence of the bearing pedestal(or the housing)on the dynamic response of the bearing is considered,a dynamic model of bearing support under normal conditions was established.(3)From the perspective of the system,a two-stage helical gear-rotor-bearing bending-torsion coupling dynamic model is established under normal conditions.And taking the gear tooth root crack and bearing inner and outer ring damage failures as typical failures,the changes of the gear meshing dynamic model and the bearing support dynamic model under the fault state are analyzed,and the dynamic model of the gear transmission system under the fault state is established.(4)The Runge-Kutta method is used to solve the acceleration response of the system model under normal and fault conditions,and the characteristics of the response signal in the time domain and frequency domain are analyzed.The dynamic response characteristics of the gear transmission system are summarized,and the influence of different fault states on the system dynamic response is summarized.The verification experiment of the dynamic model was carried out on the two-stage helical gear-rotor test rig.The comparison between the experimental signal and the simulation signal verified the effectiveness of the system dynamic model established in this paper. |
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