What is Epicyclic Gearbox? Working Principle of Epicyclic Transmission.


The Epicyclic gearbox could be a gear system having 1 or more planet gears, rotating a couple of central, or sun gear. Typically, the earth gears square measure mounted on a movable arm or carrier, that itself might rotate relative to the sun gear. Epicyclic gearing systems additionally incorporate the utilization of AN outer ring gear or annulus, that meshes with the earth gears. Planetary gears (or circle gears) square measure generally classified as straightforward or compound planetary gears.

straightforward planetary gears have one sun, one ring, one carrier, and one planet set. Compound planetary gears involve one or additional of the subsequent 3 varieties of structures: meshed-planet (there square measure a minimum of 2 additional planets in mesh with one another in every planet train), stepped-planet (there exists a shaft association between 2 planets in every planet train), and multi-stage structures (the system contains 2 or additional planet sets). Compared to straightforward planetary gears, compound planetary gears have the benefits of larger reduction ratio, higher torque-to-weight ratio, and additional versatile configurations.

The axes of all gears square measure sometimes parallel, except for special cases like pencil sharpeners and differentials, they will be placed at AN angle, introducing parts of bevel gear (see below). Further, the sun, planet carrier, and ring axes square measure sometimes coaxial. Bookwheel, from Agostino Ramelli’s LE various et artifice machine, 1588.

Epicyclic gearbox
Epicyclic gearbox

Working Principle

Epicyclic gearing is additionally on the market that consists of a sun, a carrier, and 2 planets that mesh with one another. One planet meshes with the sun gear, whereas the second planet meshes with the ring gear. For this case, once the carrier is mounted, the ring gear rotates within the same direction because the sun gear, therefore providing a reversal in direction compared to plain epicyclic gearing.

In an ordinary gearbox, the axes of the several gears are fixed, the rotation of the gears being simply rotations about their own axes. In epicyclic gearbox, at least 1 gear not only rotates about its own axis but also rotates about some other axis. As shown in Fig. 28.10 the gear B rotates about its axis YY, it also bodily rotates about the axis XX of the gear A. The epicyclic or sun and planet type gearbox uses no sliding dogs or gears to engage, but different gear speeds are obtained by merely tightening brake bends on the gear-drums, which simplify gear changing.

The figure shows an epicyclic gearbox. The compound gear ACE is mounted on a pin fixed to a wheel G.The compound gear is free to rotate on the pin. Gears A, Cand E have meshed with three different gears B, D, and F respectively, which are connected in turn to the drums H. Jand K. The drums H and J have brakes in their outer circumference and drum K is provided with a number of clutch plates. A hud is fitted to the
flywheel spigot shaft N to which a number of clutch plates are attached. When the member M is pressed against the clutch plates, it engages the clutch, thereby connecting the shaft N to the output shaft P, directly. It is top speed gear.

To obtain low-speed gear, disengage the clutch and apply the brake on drum J with the help of the gear change lever. This action locks the gear D, thereby decreasing the speed of gear B and hence that of the output shaft. To obtain reverse gear, disengage the clutch and apply the brake on drum M. This locks the gear F, thereby reversing the direction of rotation of B with respect to the input shaft. The speed of B is also reduced.

A cross-sectional view of Epicyclic gearbox
A cross-sectional view of Epicyclic gearbox


  1. The planetary gears are in constant mesh and hence dog clutches or sliding gears are not used.
  2. It provides a more compact unit operating about a common central axis because the planetary gear operates within a ring gear with its external surface of the cylindrical form.
  3. External contracting hand brackets or multi-plate clutches of relatively small dimensions are used for changing the gears.
  4. Instead of having the load on only one pair of gears, it is distributed over several gear wheels.
Epicyclic gearbox
Epicyclic gearbox

Watch the animation video below for understanding the Epicyclic gearbox:

understanding the Epicyclic gearbox

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