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Modelling of damping in lubricated line contacts – Applications to spur gear dynamic simulations

The various damping mechanisms in elasto-hydrodynamic lubrication contacts are investigated with the objective of deriving damping models representative of the lubricant contributions which can readily be used in gear dynamic simulations. Several simplified models are proposed which make it possible to simulate the damping caused by tooth friction and lubricant squeezing by the teeth with and without momentary contact losses and impacts. A one-degree-of-freedom gear dynamic model is set up which combines these lubricant damping sources along with structural damping. A number of comparisons with benchmark experimental evidence are presented for a range of operating conditions and gear geometries which prove that the proposed approach is sound in the case of spur gears. It is shown that the damping associated with lubricant squeezing contributes for the most part when contact losses and shocks between the teeth occur at critical speeds. For permanent contact conditions, however, structural damping appears as the major contributor to the overall system damping.