Frictional Effects on the Diagnostics of Helical Gear Tooth Defects

Tooth Defect is a common failure mode that frequently occurs in gears. To develop successful diagnostic techniques, this study examines the capability of helical gear dynamic responses with the inclusion of different time-varying friction models, i.e. friction-free, Coulomb and elasto-hydrodynamic lubrication (EHL) models. The gear system is a 10-DOF (degree-of-freedom) vibration system, which incorporates the effects of gear pair, supporting bearings, driving motor and loading system. Moreover, it couples the transverse and torsional motions resulting from time-varying friction forces, time varying mesh stiffness excitations and different tooth breakage severities. To explore the vibration response, spectral peaks at characteristic mesh frequency and its harmonics along with their sidebands are considered in the light of the impulsive sources from tooth damages and different frictional excitation models. It has found that the sidebands exhibit significant difference between different friction models and mesh components for tooth defects. It is concluded that the frictional effect should be taken into account if it is to be an accurate method for the detection and diagnostic different tooth surface defects.