Influence of Centrifugal Forces on Oil Flow in Journal Bearing of Planetary Gear

Planetary gears have a wide application in different areas of industry. At present moment, they find application in geared turbofan aircraft engine. For high speed or heavy-loaded gears fluid film bearings used in supports. Main characteristics of fluid film bearing such as stiffness and damping based upon hydrodynamic fluid pressure caused by relative motion of sliding surfaces. In most of applications, fluid inertia forces are negligible in comparison with hydrodynamic forces, but if some applications their influence on bearing characteristics could be sufficient and should be taken into account. Planet wheel journal bearing are an example where influence of fluid inertia forces have an influence on bearing characteristics. For taking into account inertia forces acting on oil film in journal bearing of planet wheel the conventional mathematical model for oil flow in journal bearing based on Reynolds equation requires modification. 1. Inertia forces For any type of planetary gear each planet wheel (2) taking a part in compound motion: rotation with carrier (H) with angular speed ωH and rotation about self axis with angular speed ω2 (Figure 1). One sliding surface of bearing is a part of carrier and another is a part of planet wheel and this causes fluid velocity distribution in bearing gap. Therefore centrifugal and Coriolis forces acting on fluid in bearing gap. These forces can be determined using carrier and planet wheel angular speeds that receiving for selected type of planetary gear and transmission ratio. Centrifugal and Coriolis forces in fluid should be taken into account in fluid flow in bearing mathematical model.