| Planetary gearbox(PG)has been widely used as central transmission part in various industrial equipments,such as fan,shield machine,helicopter and ship and other large equipment because of its excellent performance.However,because the PG usually works at low-speed,overload and other harsh conditons,backgraound and various fault are great threats to its safe and reliable operations.It is reported,as an early faults,the tooth root crack is so easy to be ignored that it further deteriorates into tooth broken,tooth missing or other serious failures with continued operations.Therefore,it has great theoretical and engineering values to establish a dynamic model for the PG as reliatic as possible so that the PG with cracks can be diagnosized accurately by analyzing its dynamic responses for studying fault diagnosis and reliability theory.In this thesis,research contents and the corresponding results are summarized as follows:(1)An improved tooth root crack model is proposed in this thesis to remove the problems existing in the existing tooth root crack models,in which the crack propagates along both of the crack depth and tooth width,meanwhile,parabolas are chosn as the propagation paths.This improvement can remove the errors caused by oversimplification of setting single direction and straight lines.Futhermore,20 models with different degrees of crack are established by using the software CREO and can be used to simulate states of tooth root cracks,which provides the basis of analyzing the effects on the PG when having varying degrees of tooth cracks.(2)To solve the limitation of a rigid PG model that cannot accurately reflect real cases and properities of PG,two components of the PG,i.e.the first sun gear with tooth crack,and the first carrier connecting the first stage and the second stage,are set as flexible bodies.Refer to the real PG,an improved rigid-flexible coupled model is modeled for a two-stage planetary gearbox by using the software CREO,ADAMS,and ANSYS.The results indicate that the presented model can simulate the operations of the PG,at the same time,keep the balance between the performance and the computation cost.Using this model,vibration responses can be obtained for further signal processing and analysis.(3)To analyzing the PG with various tooth cracks,the spectral features and statistical features are analyzed by using the vibration responses from the dynamic model,and then quantitative analysis results are obtained by analyzing the effects caused by cracks.The comparison with the analytical model,the presented dynamic model is verified to be correct.The comparison between the rigid model and the hybrid model indicates that the hybrid model is more suitable for analyzing the response of the PG with cracks.The last comparison of using commonly used statistical features demonstrates the performance degradation of the PG with the growth of the crack when only setting the same crack depth or the same tooth width on the crack of the sun gear.By the way,the features having fault sensitivity are also selected from these results.It provides a valuable reference for the study of performance degradation and reliability of the PG.(4)At the end of research work,experimental verification is also completed.Some faulty sun gears with different sizes of tooth root cracks are made by using the technology of electrosparking.All these gears are brought into the operation of PG simulator in the lab.The experiments and data acquisition are carried out under the same woke condition as the pervious simulations.The analyses and results demonstrate that the presented model is correct.In addition,these results also provide supports for further experiments on the performance degradation and remaining life prediction.In one word,this thesis presents the improvements on the modeling of tooth root crack and the model for a two-stage PG with various healthy statuses.Using this rigidflexible coupled model,simulations,verifications and analyese are conducted.Relevant results not only provide theoretical basis for studying the methods for fault diagnosis,prognosis and reliability of the PG,but also give practical support for the real operation and early warning of the PG. |
