Modelling of steady-state mechanical power losses in planetary gear trains of automatic transmissions

Abstract

In this study, steady-state mechanical power loss model of an automatic transmission gear train consisting of multiple stages of planetary gear sets is developed. Load dependent (mechanical) power losses at the internal (ring-planet) and external (sun-planet) gear meshes and planet bearing interfaces are included through elastohydrodynamic lubrication (EHL) based power loss formulations. At the end, efficiency of an 8-speed automatic transmission is studied under representative operating conditions to quantify the contribution of various loss mechanisms to the total loss under variable speed, load and temperature conditions. Impact of gear surface roughness amplitudes on the resultant power losses is also described.