Research On Dynamic Modeling And Fault Feature Extraction Of Cracked Gear Systems

Gear transmission is an important power transmission type in mechanical equipment.Its accuracy and smoothness often determine the overall dynamic performance of the equipment.Due to the cyclic loading,it is easy to induce fatigue crack in the tooth root of gears.As the crack grows,it will affect the stability of the transmission system,and may even cause catastrophe.Therefore,in this paper,the spur gear system is taken as the research object.Considering real gear foundation structure,the crack propagation paths in the meshing process are simulated,and the time-varying meshing stiffness under different crack growth states is calculated.Based on the meshing stiffness of cracked gear pairs,the finite-element dynamic model is established and the influences of different crack states and different gear foundation types on dynamic response are analyzed.Meanwhile,a multi-body dynamic and experimental methods are also adopted to discuss the influence of cracks states on the vibration response.Based on the simulated and experimental signals,the statistical indictors of time domain and frequency domain are used to the fault feature extraction of cracked gear systems.The research contents of this paper are listed as follows:(1)Considering complex foundation structure of gear pairs,the two-dimensional gear cracks are simulated,and the crack propagation paths are verified by the experimental method.Meanwhile,the loaded tooth contact analysis method is proposed to calculate the time-varying meshing stiffness of cracked gear pairs under different foundation types and different crack lengths.Based on the parameter analysis,it is proved that the influence of the web thickness on the mesh stiffness is more obvious than that of the rim thickness.Meanwhile,the influence of the crack fault on the mesh stiffness in single-tooth contact zone is more obvious than that in double-tooth contact zone.(2)Considering different gear foundation structures,three-dimensional spatial cracks are simulated by the extended finite element method.The crack propagation paths under different load conditions are simulated.Some crack propagation results are verified by that obtained from some literatures.Furthermore,the loaded tooth contact analysis method is used to calculate the time-varying meshing stiffness under different three-dimensional crack states.The results show that the spatial non-penetrating crack usually extends along the tooth width at the early stage and then along the tooth thickness direction.The influence of the penetrating crack on mesh stiffness is more obvious than that of the non-penetrating crack.(3)Considering the flexible deformation of the gear shafts,the linear support of the bearing and the time-varying mesh stiffness of cracked gear pairs,the geared rotor dynamic model is established.The dynamic responses under different crack states,torques and foundation types are analyzed,and the simulated sign al are verified by that from the experiment.It is proved that the increase of torques will aggravate the time domain impact phenomenon caused by crack fault.As the crack grows,the impact amplitude in time domain gradually increases and the amplitudes of sideband frequencies gradually increase in frequency domain.(4)Considering the flexible deformation of the shafts,the linear support of the bearing and the flexible gear,a multi-body dynamic model of the cracked gear system is establised in ADAMS software and the influences of different foundation types and different crack states on dynamic response are analyzed.The results prove that the multi-body dynamic model can consider the misalignment caused by the shaft’s deformation.To sum up,the multi-body dynamic model can analyze the influence of foundation types and crack states on dynamic response accurately.(5)In order to study the fault characteristics of cracked gear systems,a single-degree-of-freedom model is used to analyze the modulation mechanism of vibration signal.Then,based on the simulated signals obtained from the finite element dynamic model,multi-body dynamic model and experimental signal,the original and residual signals of the fault gear systems are used to analyze the fault feature under different crack states and torques.The results prove that the increase of torques can enhance the fault characteristics of the cracked gear system.The NA4*indictor of the residual signal is used to evaluate the crack fault degrees and the SLF indictor can represent the crack propagation process.