Nonlinear Contact Analysis of Gear Teeth for Malfunction Diagnostics

Gearboxes sustain a variety of faults such as broken-shafts, eroded, broken, or missing teeth, and even broken-cases. Casing mounted accelerometers can detect fault patterns but the signals are complicated and difficult to interpret. This study considers the tooth loading of ideal gears and gears with defects. A large industrial gearbox used in a 12m electric mining shovel is modeled. The nonlinear contact mechanics is analyzed to predict the bearing supporting force variation vs. the gear tooth loading after a 3-D CAD model of the gearbox is transferred into multi-body dynamics software. The contact mechanics model of the meshing teeth is built by careful calculation and selection of the contact simulation parameters such as the stiffness, force exponent, and damping and friction coefficients. To simulate the real working environment of the gearbox, simulated bearing support forces are mixed with white noise. The signal is subsequently processed by the Db5 wavelet of the MATLAB Wavelet toolbox. Wavelet analysis results show that bearing supporting force fluctuation cycle is almost the same with that of the meshing forces of the fault gearing pairs, which could be used to predict the tooth malfunction of the gearbox.