Compared to simple planetary gears, compound planetary gears have the advantages of larger reduction ratio, higher torque-to-weight ratio, and more flexible configurations.

Train), and multi-stage structures (the system contains two or more planet sets). Compound planetary gears involve one or more of the following three types of structures: meshed-planet (there are at least two more planets in mesh with each other in each planet train), stepped-planet (there exists a shaft connection between two planets in each planet Simple planetary gears have one sun, one ring, one carrier, and one planet set. Planetary gears (or epicyclic gears) are typically classified as simple or compound planetary gears. Epicyclic gearing systems also incorporate the use of an outer ring gear or annulus, which meshes with the planet gears. Typically, the planet gears are mounted on a movable arm or carrier, which itself may rotate relative to the sun gear. 7 Gear ratio of reversed epicyclic gearingĮpicyclic gearing or planetary gearing is a gear system consisting of one or more outer, or planet, gears or pinions, revolving about a central sun gear or sun wheel.5 Torque ratios of standard epicyclic gearing.4 Accelerations of standard epicyclic gearing.3 Gear ratio of standard epicyclic gearing.In this case, the ring gear is usually fixed and the sun gear is driven.

The combination of epicycle gear trains with a planet engaging both a sun gear and a ring gear is called a planetary gear train. In this case, the curve traced by a point on the pitch circle of the planet is a hypocycloid. In this simplified case, the sun gear is fixed and the planetary gear(s) roll around the sun gear.Īn epicyclic gear train can be assembled so the planet gear rolls on the inside of the pitch circle of a fixed, outer gear ring, or ring gear, sometimes called an annular gear. A point on the pitch circle of the planet gear traces an epicycloid curve.

The planet and sun gears mesh so that their pitch circles roll without slip. A carrier connects the centers of the two gears and rotates to carry one gear, called the planet gear or planet pinion, around the other, called the sun gear or sun wheel. The red marks show the relative displacement of the sun gear and carrier, when the carrier is rotated 45° clockwise and the ring gear is held fixed.Īn epicyclic gear train (also known as a planetary gearset) consists of two gears mounted so that the center of one gear revolves around the center of the other. This planetary gear train consists of a sun gear (yellow), planet gears (blue) supported by the carrier (green) and a ring gear (pink).

Torque bow gears of war