Pitting and Crack Coexistence in a Model-Based Gear Dynamic System (Part I)

The analysis of the coexistence of pitting and cracking in a model-based dynamic gear system is uncommon. Most studies on the analysis of spur gear faults focus exclusively on a single defect, either pitting or cracking. This paper is focused on extracting and diagnosing the features of a two-stage spur gear's combination of pitting and cracking and determining which of the two has the most effect on the gear vibrations. The governing equations for coupled lateral and torsional vibrations of a two-stage spur gear model are established based on the energy principle. Numerical simulations based on feature extraction and diagnosis of coexistence of pitting and cracking in spur gears are carried out under stochastic perturbations of the initial conditions. Furthermore, Time-Frequency techniques and a Revolution Per Minute-Frequency map are used in various simulation scenarios to identify effective and sensitive signals to reflect high fault features. The results and analysis reveal that the Short-time Fourier transform (STFT) and RPM-Frequency map are appropriate indicators to extract the features and detect and diagnose that the pitting has a stronger influence than the cracking in a gear system with two-stage.