Gearbox Arrangements

From Wind wiki

There are two ways in which the parallel axis gears may be organized inside each gear stage – the parallel shaft and the epicyclic arrangement.

Parallel shaft is a simple arrangement consisting two external gears that mesh with each other. The epicyclic arrangement, on the other hand is an alternative arrangement. It consists of planet gears placed on a planet carrier that meshes with a sun gear inside and with an annulus gear outside. The sun and planet gears are external and the annulus is internal because its teeth are placed inside. Either the annulus or planet carrier is normally fixed; however, there should be an increased gear ratio if the annulus is fixed.

Epicyclic arrangement is advantageous in the sense that it allows sharing of loads between planets to reduce the load of any gear. Because of increased complexity in this arrangement, the gears and the gearbox can be designed smaller and lighter. One can save more materials in the input stages of the gearbox, so the epicyclic arrangement is used in the input stages and the parallel shaft in the output stage. The alternative arrangement also gives greater efficiency because of less sliding that occurs between the annulus and the teeth of the planet.

Another difference between the two arrangements is the way their gear teeth are loaded. In parallel shaft gear stages, the teeth are loaded in one direction. In epicyclic arrangement, they are loaded in both directions. Tooth bending is more possible in epicyclic gearing because the number of teeth on the smallest gear cannot be reduced indefinitely.