Dynamic Modelling and Fault Diagnosis of a High Contact Ratio Gear

High contact ratio (HCR) gears are needed in different cases for having lower generated stresses and smoother operation as compared to the standard low contact ratio (LCR) gears. For the purpose of gear fault diagnosis and to avoid possible failure consequences due to tooth cracks, it is important to study the possibility of fault detection with crack propagation. A reduction in the gear mesh stiffness due to the existence of a crack can be used to detect and assess tooth damage. Time-varying gear mesh stiffness has an impact on the system’s dynamic response, and then the gear diagnosis indicators applied to the response signal will be affected. The current paper studies the influence of increasing the tooth addendum for having a HCR on the gear diagnosis indicators, namely the RMS, kurtosis, peak value and crest factor. Twenty different crack cases are modelled by using both the LCR and HCR designs. For every crack case, the mesh stiffness is evaluated and input to a gear dynamic model that is built for obtaining the system dynamic response. The results of the applied gear diagnosis indicators show that in the HCR design case, the indicators change with the crack size will have a lower increase than in the LCR one. Therefore, the LCR design case can be detected earlier than the HCR case.