Planetary gear vibration

Planetary gears are widely used in applications because they are compact, lightweight, and have high power density. For example, planetary gears are used in automotive, wind turbine, and helicopter transmissions. My research in planetary gears includes:

• Dynamic planet load sharing and the effects that manufacturing and assembly errors have on load sharing.

• Features of planetary gear measured vibration.

• Structured vibration modes of planetary gears including gyroscopic effects.

Planetary gear load sharing

The benefits of planetary gears are realized only when the planets share the applied load. The figure below shows an example of the individual loads on each planet of a four-planet planetary gear based on a helicopter application. The planets

Structured vibration modes of planetary gears with gyroscopic effects

Planetary gears are a gyroscopic system when the carrier rotates. The carrier rotation induces gyroscopic terms in the form of Coriolis and centripetal accelerations in all of the components.

Planetary gears have three types of vibration modes that have very structured properties.

Planet modes are modes that have no motion of the ring, carrier, and sun. In these modes only the planets vibrate. There are three of these modes when there are four or more planets.

Rotational modes are modes that have only rotation of the ring, carrier, and sun. These components have no translational vibration. In these modes all the planets have identical radial and tangential vibration.

Translational modes are modes that have only translation, and no rotation, of the ring, carrier, and sun. In these modes the planet vibrations are out-of-phase with one another, and their phase difference is exactly equal to the planet positioning angle. The ring, carrier, and sun will orbit about their nominal positions in either the direction of carrier rotation or the direction opposite of carrier rotation. These are called forward and backward orbit modes.