Planetary gearboxes are widely used in several applications. Generally, due to their small size and to the high reduction ratios that can be achieved, they are employed for transmissions with high power density. There are several fields of applications of this type of transmissions, including but not limited to automotive, aerospace, and power generation. In order to improve the design and to perform monitoring activities, and in the definition of maintenance schedules for the machine, the availability of physical models able to accurately describe the behavior of the gearbox, both in healthy conditions and in the presence of damages, would represent a great support. Analytical studies of the behavior of planetary gearboxes are present in the literature as well as numeric approaches. This paper presents an approach to characterize the behavior of the transmission, based on a hybrid FE-analytical formulation. The method used also allows to simulate several operating states by changing the boundary conditions in the system. More in detail, the solver separately computes analytically the contact points from the rest of the model and therefore allows to maintain a coarser mesh even in the contact region. In this way, the computational effort can be reduced without affecting the accuracy of the results. This approach has been used to investigate and understand the vibro-dynamical behavior of a planetary gearbox in several operating and healthy conditions. The results obtained have been validated with the measurements on a real gearbox. The frequency spectrum of the gearbox has been determined up to 14000Hz. On the other side, the same approach has been used to characterize the effects of typical gears failure, like pitting, on the frequency spectrum. The capability to introduce the effect of damages in the model of a planetary gearbox represents the first indispensable step of a Structural Health Monitoring strategy. State-of-art and challenges are analyzed and discussed in the paper.
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