| Planetary gearboxes are widely used in wind power, helicopters, mechanical equipment and other large complex machinery, in which the gear is the most important mechanical transmission component. Tooth surface pitting is one of the most common mechanical drive failure modes. Finally the small pit forms a clear erosion scar and turns into crack and fracture with further development. As a result of inappropriate operating conditions, application of heavy load beyond the designed capacity or end of fatigue life,gear faults frequently occur in practice.These phenomena which are often not found could lead to disastrous consequences. To prevent this situation happening, it is very important to study vibration mechanism and characteristics of gear failures. However, the gear transmission system working condition is very complex. These factors make the research of gear fault vibration mechanism difficult and seriously hamper the development of gear failure prevention technology. Therefore, the study of stiffness calculation and dynamic modeling of a planetary gear with pitting failure has important theoretical and practical engineering value. The main work to be carried out is described as follows:(1) Literature review on planetary gear meshing stiffness calculation and dynamic response. Search the relevant references and then make a summary. As a result, the current research status and the trend of this field can be obtained. It also includes the contents of recent methods of mesh stiffness calculations and dynamic modeling of health gear and tooth surface pitting gears. Based on the review result, advantages and limitations of commonly used methods can be analyzed and compared, which provides the theoretical basis for the following research topic;(2) Based on the previous team research work, the energy method would be used to derive the calculation formula of mesh stiffness. The gear involute geometry characteristics can be used to determine influencing parameters which varies with the change of degree of fault. After computing the numerical mesh stiffness using the derived formula, the stiffness curve can be plotted. Then the effect law of mesh stiffness can be proved by comparing with the mesh stiffness of health gear;(3) Build the dynamic model of planetary gear system. Quality-spring-damper is common and more accurate form. Its structure is come from the real planetary gear in the equipment Drivetrain Dynamics Simulator(DDS). The dynamic model can be established and MATLAB codes would be completed to obtain vibration responses of the planetary gear;(4) Using the same planetary gear as an object, a finite element model of planetary gear transmission system can be build using ANSYS software. Applying the same constrains, defining the actual material properties, a simulation model can be build. Comparing the simulation results, the accuracy of the designed parametric formula can be evaluated;(5) For analyzing the accuracy of the designed parameter model, vibration data would be collected from the DDS with tooth surface pitting failure, and then the corresponding dynamic response can be obtained. Comparing the results of parameter model with the experimental results, the effectiveness of parameter model can be analyzed.This thesis focuses on the calculation of mesh stiffness of the planetary gear and the dynamic modeling of the planetary gear. The mesh stiffness calculation derivation and finite element analysis method would be discussed. The performance of the parametric method to be designed would be compared with the finite element simulation and the analysis based on real test data. It has important theoretical significance to further enrich and develop the theory of gear stiffness and the application will produce good economic and social benefits. |
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