Investigation On Fault Mechanism Of A NGW-Type Planetary Gearbox With Multi-Source Damages

The loading capacity and transmission precision of planetary gearbox directly affect the service performance of the speed-changed device.During the service period,the multi-source damages will decrease both the loading capacity and the transmission accuracy of the planetary gearbox.In order to detect the degradation mechanism of transmission performance of the planetary gearbox,it is necessary to investigate the influence of multi-source damages on the vibration characteristics of the planetary transmission system.In view of this,this paper took a NGW-type planetary gearbox as the research object,to investigate failure mechanism of planetary gear transmission including multi-source damages of tooth crack and surface wear.By establishing analytical models of mesh stiffness and transmission error,the effects of multi-source damages on the internal excitations of the system were explored.And then,the effects of multi-source damages were incorporated into the dynamic model of the planetary transmission system to analyze the vibration characteristics of the system.The full content is summarized as follows:(1)From the perspective of system energy,analytical models of the mesh stiffness of the internal and external mesh pair without damage were established.The mesh stiffness model of the internal mesh pair accounts for the effect of foundation deformation.Based on these models,analytical models of the mesh stiffness considering local and distributed damages of tooth crack and surface wear were established.The effects of gear damages on the loading capacity of the gear pair were revealed.And the variation of the mesh stiffness among the damage evolution period was predicted.The relevant findings provide a theoretical basis for determining the internal stiffness excitation of the planetary gear system.(2)Integrating the comprehensive influence of gear manufacturing error and assembling error,tooth elastic deformation and gear damages,analytical calculation models of the gear transmission error were established.The manufacturing error and assembling error determined by the gear precision and the shaft-hole tolerances were deduced by using the probabilistic method.The tooth elastic deformation caused by the external load and the tooth integrated error was calculated.And then,integrating the load-distributed model and Hertz contact model,the depth of surface wear,which carried out based on Archard’s wear formula,was incorporated into the established transmission error model.The relevant findings provide a theoretical basis for determining the internal displacement excitation of the planetary gear system.(3)On the basis of pre-determining the mesh stiffness exciatitions and transmission error exciatitions,a translational-torsional-coupled dynamic model of the NGW-type planetary gearbox including the multi-source damages of tooth crack and surface wear was established.Based on this model,the vibration characteristics of the planetary gear system under the condition of health,single damage and multi-source damages were analyzed successively,and the corresponding vibration characteristics were extracted.The research results show that the transmission system presented two corresponding damage characteristics under the condition of multi-source damages of tooth crack and surface wear,and the damage characteristics in the multi-source damages state are more significant than the damage characteristics in double single damages.(4)A power transmission test bench was set up and experimental research was carried out.The experimental results were basically consistent with the theoretical analysis results,which verified the correctness of the modelling and the parameters calculating for the planetary gear system.In summary,this paper revealed the effects of the multi-source damages of tooth crack and surface wear on the internal excitations of the planetary transmission system,and explored the vibration characteristics of the planetary transmission system under multi-source damages condition,which is expected to provide a theoretical foundation for condition monitoring and damage diagnosis of planetary gearbox.