Planetary Gears Poster.pdf
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Planetary Gears Planetary gear trains are one of the main subdivisions of the simple ep icyclic gear train family. The epicyclic gear train family in general has a central “sun” gear which meshes with and is surrounde d by planet gears. The outermost gear, the ring gear, meshes with each of the planet gears. The planet gears are held to a cage or carrier that fixes the planets in there orbit relative to each other. There are five distinct advantages to using an ep icyclic gear train as opposed to a single load path paralle l gear train: 1) Bec aus e they s har e load b etween sev era l gear me she s, epic ycl ic trai ns t ake up l ess spa ce a nd have a lighter weight. 2) Bec aus e th ey sha re load betw een sev eral meshe s, e picyclic trai ns hav e small er a nd s tiff er components which lead to reduced noise and vibration while increasing efficiency. 3) The inp ut and o utput s haf ts of epicy cli c trai ns a re conc ent ric so n o be ndi ng moments or t orques are created from radial forces that develop from the change of the force’s line of action. 4) The input and output shafts of epicy cli c trai ns a re conc entric so driver an d dr iven eq uipment can be mounted in line, providing additional space savings. 5) The reduce d si ze o f ep icy clic compon ents often off set s the co st of addit ion al part s, espe cia lly when manufacturing many gear trains. In very high horsepower units the compone nts of parallel shaft designs become so bulky that epicyclic trains gain a further economical advantage.² As with all design choices, there are disadvantag es to epicyclic gear trains: 1) Complexity. 2) Assembly o f ge ar trains is limi ted to specifi c te eth pe r ge ar ratios. 3) E ff i ci en c y cal c ul at io ns ar e d if fi cu lt . 4) Dr iver and d riv en equipment must be i n li ne to av oi d ad di tio nal ge ar ing. The three main types of simple epicyclic gears are the planetary, the star, and the solar. These three types differ only in arrangement. Table re-created from "Gear Handbook" By: Darle W. Dudley, McGraw-Hill books, pg. 3-15, 1962 N s =number of sun teeth, N p =number of planet teeth, N r =Number of ring teeth (per gear) 1.2:1-1.7:1 (N s /N r )+1 Carrier Ring Sun Solar…………………………… 2:1-11:1 (N r /N s ) Ring Sun Carrier Star……………………………. 3:1-12:1 (N r /N s )+1 Carrier Sun Ring Planetary……………………… Range of ratios normally used Over-all Gear ratio Output Member Input Member Fixed Member Arrangement of ep icyclic train Poster By Mike Amato Justin Lanier Jake Leachman Michael Maughan
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Planetary GearsPlanetary gear trains are one of the main subdivisions of the simple epicyclic gear train family. The epicyclic gear
train family in general has a central “sun” gear which meshes with and is surrounded by planet gears. The
outermost gear, the ring gear, meshes with each of the planet gears. The planet gears are held to a cage or carrier
that fixes the planets in there orbit relative to each other.
There are five distinct advantages to using an epicyclic gear train as opposed to a single load path parallel gear
train:
1) Because they share load between several gear meshes, epicyclic trains take up less space and
have a lighter weight.2) Because they share load between several meshes, epicyclic trains have smaller and stiffer
components which lead to reduced noise and vibration while increasing efficiency.
3) The input and output shafts of epicyclic trains are concentric so no bending moments or torques
are created from radial forces that develop from the change of the force’s line of action.
4) The input and output shafts of epicyclic trains are concentric so driver and driven equipment can
be mounted in line, providing additional space savings.
5) The reduced size of epicyclic components often offsets the cost of additional parts, especially
when manufacturing many gear trains. In very high horsepower units the components of parallel
shaft designs become so bulky that epicyclic trains gain a further economical advantage.²
As with all design choices, there are disadvantages to epicyclic gear trains:
1) Complexity.
2) Assembly of gear trains is limited to specific teeth per gear ratios.
3) Efficiency calculations are difficult.
4) Driver and driven equipment must be in line to avoid additional gearing.
The three main types of simple epicyclic gears are the planetary, the star, and the solar. These three types differ only in arrangement.
Table re-created from "Gear Handbook" By: Darle W. Dudley, McGraw-Hill books, pg. 3-15, 1962
Ns=number of sun teeth, Np=number of planet teeth, Nr =Number of ring teeth (per gear)
1.2:1-1.7:1(Ns/Nr )+1Carrier RingSunSolar……………………………
2:1-11:1(Nr /Ns)RingSunCarrier Star…………………………….
3:1-12:1(Nr /Ns)+1Carrier SunRingPlanetary………………………
Range of ratios
normally used
Over-all
Gear ratio
Output
Member
Input
Member
Fixed
Member Arrangement of epicyclic train
Poster ByMike Amato
Justin Lanier
Jake Leachman
Michael Maughan
