Dynamic modeling and response of a spur planetary gear system with journal bearings under gravity effects

This paper focuses on the modeling method and the gravity-induced dynamic response of a spur planetary gear system with journal bearings. The lumped-parameter model of a planetary gear system with journal bearings is established. Both contact on drive-side and back-side of the tooth are considered simultaneously. Linear and nonlinear bearing force models are introduced into the system model separately to take the planet bearing oil-film forces into account. A demonstration is given to show the adopted nonlinear oil-film force model is still valid for the lubrication of support for planet gears. Equilibrium positions of the planet gear are depicted under different input rotational speeds and input torques. Under gravity effect, system responses at different rotational speeds are calculated by employing Newmark integration; tooth wedging at ring-planet meshes is examined with different backlashes. The system responses are presented as vibration spectra, planet bearing forces, orbits of members, tooth forces, and the percentage of tooth wedging in one carrier cycle. The results show that the gravity effect dominates the response at low rotational speeds. The linear bearing force model is not valid in some cases. The fluctuation of the bearing force and the enlargement of the planet orbits are induced by gravity effect. Tooth wedging is the combined effect of gravity, centrifugal force, and planet bearing clearance.