Transient mixed thermo-elastohydrodynamic lubrication in multi-speed transmissions

Abstract

Noise, vibration and harshness (NVH) refinement as well as thermo‐mechanical efficiency are the key design attributes of modern compact multi‐speed transmissions. Therefore, unlike simple gear pair models, a full transmission model is required for a simultaneous study. The prominent NVH concern is transmission rattle, dominated by the intermittent unintended meshing of several lightly loaded unselected loose gear pairs arising from the system compactness. These gear pairs are subject to hydrodynamic impacts. The thermo‐mechanical efficiency is dominated by the engaged gears, with simultaneous meshing of teeth pairs subject to thermo‐elastohydrodynamic regime of lubrication, with often quite thin films, promoting asperity interactions. Therefore, a full transmission model is presented, comprising system dynamics, lubricated contacts, asperity interactions and thermal balance. Generic multi‐physics models of this type are a prerequisite for in‐depth analysis of transmission efficiency and operational refinement. Hitherto, such an approach has not been reported in literature.