An epicyclic arrangement in which planet gears mesh with a central sun gear and an internal ring gear while riding on a rotating carrier. Holding one member and driving another gives different ratios; with the ring fixed, sun in and carrier out, the ratio is one plus ring teeth over sun teeth, so a 20-tooth sun in an 80-tooth ring gives 5:1. Load splits across several planets, giving high torque in a small volume, provided the planets share load evenly.
Planetary gear set on the wind turbine has one planet doing all the work, the carrier must be twisted.
Uneven wear from planet to planet points to carrier pin bore errors; a floating sun gear helps the planets share load.
Also heard as
- epicyclic gearing
- planetary
- planetary stage
Related terms
Internal gear
A gear with teeth cut on the inside of a ring, meshing with a pinion running inside it.
Gear ratio
The number of teeth on the driven gear divided by those on the driver, setting speed reduction and torque gain.
Micropitting
Very fine surface fatigue pits, too small to see one by one, that give tooth flanks a dull gray look.