Comprehensive tribodynamic analysis of lubricated gear contacts for direct identification of gear whine noise in electric drive units

This study focuses on gear whine noise of electric drive units (EDUs) with helical gear transmission. A combined analytical and experimental approach is adopted to better understand dynamic transmission error (DTE) as the root cause of emitted gear whine noise. A fully analytical gear model based on potential energy method is developed to calculate time-varying meshing stiffness (TVMS). A lubricated contact model based on identification of regimes of lubrication is applied to precisely account for contact stiffness and damping variations. It is observed that local variations in lubricated contact generate undulations in DTE and dynamic load signatures. The frequency of the undulations, as observed from the comparison between the measured acceleration and sound pressure signals and the predicted DTEs, is determined by the resonance between the meshing frequency (including its multiples) and the harmonic frequencies of the gear pair. Greater amplitudes of undulations in lubricated contact stiffness are observed, followed by excessive vibrations in DTE, when multiples of meshing frequency coincide with gear pair harmonics and super-harmonics simultaneously. The superimposition effect exacerbates the vibrations indicating possibility of higher gear whine noise. Lower gearbox and meshing orders propagate as airborne noise, whilst higher frequency multiples are more noticeable as structural vibrations. Such comprehensive analysis linking the emitted gear whine noise and vibrations to the changes in the regime of lubrication in gear contacts is novel contribution of this research and has not hitherto been reported for helical gear whine noise and EDU NVH analyses.