Lightly loaded vibro-impacts of lubricated gear contacts: Model and experiments

Low-frequency external excitations in drivetrains are known to cause vibro-impact motions characterized by tooth separations and sequences of impacts along the drive and coast-side backlash boundaries. Such vibro-impact motions are called gear rattling under completely unloaded conditions and gear hammering under lightly loaded conditions, both causing adverse noise and durability concerns. Recent experimental and theoretical studies under dry contact condition revealed that gears transmitting event light loads can exhibit sequences of periodic and non-periodic vibro-impact motions. This study aims at complementing those earlier studies both theoretically and experimentally by including lubrication effects. On the experimental side, tightly controlled vibro-impact measurements under dry and lubricated conditions are presented. A discrete dynamic model of the same set-up is proposed with two different gear mesh interface formulations: a piecewise-linear (PL) formulation to represent dry contact conditions and a hydrodynamic (HD) lubrication formulation intended to capture lubricant effects. Results indicate that the measured sound pressure levels and predict impact severity levels are reduced by lubrication. While the lubrication does not change angular displacements at all, its influence on impact accelerations and velocities is significant, describing the mechanisms of how lubricant reduces rattle noise. The PL and HD versions of the model are shown to correlate well with the corresponding dry and lubricated gear rattle experiments, suggesting that they can be effective in quantifying lubricant effects on gear vibro-impacts.