Gearbox Diagnostics Development Using Dynamic Modeling

We present experience using a detailed dynamic model of gear meshing to simulate vibration response and evaluate gear diagnostic algorithms. Many model forms have been used for this and other purposes such as vibration analysis. We formulate a dynamic model that takes a bottom-up approach to modeling the tooth loads generated during meshing. The advantages of this approach over others include: 1) It accurately captures nuances of mesh dynamics due to non-ideal tooth geometry (spacing error, profile error, cracks, pitting). Accuracy in this regard is crucial when using vibration data to diagnose faults, for instance to distinguish the effect of critical faults such as tooth root cracks from less critical faults such as tooth profile error introduced during manufacturing. 2) The model is extensible to operating conditions (speed, torque, temperature) beyond those used to tune and validate the model. This is important due to the cost and time required to gather comprehensive operational and test bench data. The model is used to explore the performance of common diagnostic features when cracks and tooth spacing errors are introduced into ideal gear pairs, for a range of operating conditions. Finding the right features and conditions is important for accurate and early determination of the size of a gear crack that may impact the safety of flight. It will also enable appropriate maintenance actions to be taken to prevent unnecessary damage and unnecessary removals of a gearbox.