Nonlinear dynamics and stability of wind turbine planetary gear sets under gravity effects

• We investigate planetary gear dynamics considering gravity effects.
• We develop an analysis tool that could minimize planetary gear vibration.
• Gravity is a fundamental vibration source in wind turbine planetary gears.
• Gravity causes tooth wedging and nonlinear bearing-raceway contacts.
• Optimizing carrier-bearing clearance could prevent gear tooth wedging.

This paper investigates the dynamics of wind turbine planetary gear sets under the effect of gravity using a modified harmonic balance method that includes simultaneous excitations. This modified method along with arc-length continuation and Floquet theory is applied to a lumped-parameter planetary gear model including gravity, fluctuating mesh stiffness, bearing clearance, and nonlinear tooth contact to obtain the dynamic response of the system. The calculated dynamic responses compare well with time domain-integrated mathematical models and experimental results. Gravity is a fundamental vibration source in wind turbine planetary gear sets and plays an important role in the system dynamic response compared to excitations from tooth meshing alone. Gravity causes nonlinear effects induced by tooth wedging and bearing-raceway contacts. Tooth wedging, also known as a tight mesh, occurs when a gear tooth comes into contact on the drive-side and back-side simultaneously and it is a source of planet-bearing failures. Clearance in carrier bearings decreases bearing stiffness and significantly reduces the lowest resonant frequencies of the translational modes. Gear tooth wedging can be prevented if the carrier-bearing clearance is less than the tooth backlash.