A methodology to predict power losses of planetary gear sets

Abstract

Planetary gear sets possess numerous advantages over their parallel-axis counterparts in terms of their power density, tolerance insensitivity and noise attributes in addition to their kinematic flexibility. One potential disadvantage of planetary gear sets is power losses due to multiple planet branches, resulting from an increased number of gear meshes and bearings. The power losses of a planetary gear set can be grouped in two categories based on their dependence on load. Load-dependent (mechanical) power losses are induced by friction in external and internal gear mesh contact interfaces as well as at planet bearings while load-independent (spin) losses are associated with drag of the carrier assembly and gears, bearing viscous losses and oil-air pocketing at gear mesh interfaces. With the assumption that these components of power losses are independent of each other, this study proposes a methodology that implements a family of models to predict total power loss of planetary gear sets including primary mechanical and spin loss components. Power loss predictions of the proposed methodology are compared to published experiments (1) to assess its accuracy within typical ranges of operating conditions and design variations.