Study On Coupled Friction Excitation And Fault Excitations Modelling And Dynamic Characteristics Of Helical Gears

Gear transmission system and its underlying components have an irreplaceable position in the equipment manufacturing industry of our country. With the development of science and technology, the higher performance transmission are eagerly needed, such as high-speed, heavy-duty, high reliability, low noise, small size and so on. Helical gear transmission with many outstanding advantages, such as good meshing performance, larger overlap coefficient, steady transmission, low vibration and noise and high load capacity, has been widely applied in the fields of aerospace, metallurgy, wind turbine, ship, mine machinery, petrificstion, hoisting and transportation et. al. However, its complicated structure and internal excitations are usually bound to cause gear incipient failure, which is one of the key factors limiting the development of helical gear transmission with long service life and high reliability. Tooth surface friction accelerated the emergence of gear early failures, and gear early failures occur exacerbated tooth surfaces friction, further lead to gear damage. It has high theoretical meaning and important practical engineering values for the study of modelling method of coupled friction excitation and fault excitations, build dynamics model of helical gears with friction and fault, and unroll the relationship between the internal nonlinear dynamic excitations and external vibration features.This thesis aims at solving the problems about modelling method and dynamic characteristics of coupled friction excitation and fault excitations of helical gears. Based on the time-varying contact line length, it starts with investigating the coupling mechanism of friction excitation and fault excitations, and a series research about internal dynamic excitation and vibration response of helical gears are carried out. The main research contents include:① For the problem that it lacks of refined formulation for the calculation of friction excitation of helical gears with various contact ratio, a refined general formulation for the calculation of time-varying contact line, frictional force and torque is proposed with time-varying normal force and time-varying friction coefficient based on the idea of “segmentation method”. A test method of tooth surface friction force in helical gears is proposed based on the deformation of axle and the applied load. This formulation enables the analytical calculation of friction excitation for helical gears with various contact ratio. Key gear parameters such as modification coefficient, helix angle and face width are analyzed to illustrate their effects on the time-varying contact line, frictional force and torque, which could supply some guidance for choosing gear parameters in the design of helical gears to reduce the frictional excitations.② For there is no good solution for the model and calculation of the internal excitation in helical gears with spalling defect to reveal the change of the dynamic characteristics, the calculation methods of friction excitations and contact stiffness are proposed based on the time-varying length of contact line in helical gears. An analytical helical gear pair model is developed by incorporating the time-varying sliding friction and mesh stiffness based on the changes of friction force and contact stiffness. The effects of the dynamic characteristics on helical gears are found with coupling surface spalling excitation and friction excitation. The developed analytical model provides a new method for the study of excitation characteristics in helical gears with tooth spalling defect.③ While for the problem that it lacks of effective method to establish the three-dimensional dynamics model of helical gears with sliding friction and tooth breakage defect, and to reveal the changes in the dynamic characteristics, the calculation method of meshing stiffness of helical gears with tooth breakage defect is proposed. An coupling three-dimensional analytical helical gear pair model is developed by incorporating the time-varying sliding friction force and dynamic mesh force with considering the mass eccentric induced by tooth breakage defect. The influence of the form and size of tooth breakage on the dynamic characteristics of helical gears are illustrated. The developed analytical model provides a new method for the study of excitation characteristics in helical gears with tooth breakage.④ For there is currently no satisfactory solution for the modeling and calculation of the internal excitation in helical gears with mesh misalignment and sliding friction that would reveal the changes in the dynamic characteristics, the calculation methods of friction excitations and error excitations induced by mesh misalignment are proposed. An analytical helical gear pair model is developed by incorporating the time-varying sliding friction and mesh stiffness based on the changes of friction force and dynamic mesh force induced by mesh misalignment. The rules governing the variation of the dynamic response are obtained using simulations of helical gear pair examples with different mesh misalignment. The developed analytical model provides a new method for the study of excitation characteristics in helical gears with mesh misalignment.⑤ Experiments on tooth spalling, tooth breakage and mesh misalignment of helical gears have been carried out with the gear fault simulation test bench. Comparisons between the experimental results and theoretical results validate the theoretical vibration response features of the helical gears with tooth spalling, tooth breakage and mesh misalignment.