This computational work investigates planetary gear load sharing of three-mount suspension wind turbine
gearboxes. A three-dimensional multibody dynamic model is established, addressing gravity, bending
moments, fluctuating mesh stiffness, nonlinear tooth contact, and bearing clearance. A flexible main shaft,
planetary carrier, housing, and gear shafts are modeled using reduced degrees-of-freedom through modal
condensation. This drivetrain model is validated against the experimental data of the Gearbox Reliability
Collaborative for gearbox internal loads.
Planet load sharing is a combined effect of gravity, bending moment, bearing clearance, and input torque.
Influences of each of these parameters and their combined effects on the resulting planet load sharing are
investigated. Bending moments and gravity induce fundamental excitations in the rotating carrier frame,
which can increase gearbox internal loads and disturb load sharing. Clearance in carrier bearings reduces the
bearing stiffness, and thus the bending moment from the rotor can be transmitted into gear meshes. With
bearing clearance, the bending moment can cause tooth micropitting and can induce planet bearing fatigue,
leading to reduced gearbox life. At low input torque, planet bearings are susceptible to skidding. At rated
torque and beyond, planet bearings are at risk of fatigue.

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