Gear Train Mean:
The gear wheel transmitted motion between one shaft to another shaft, So the multiple set of gear transmit motion from single main gear to various revolving parts is known as gear train. It require small area during the power transmission and to obtain large speed reduction. The gear train maybe for spur gear, helical gear and spiral gear. That gear train mainly used for multiple speed reduction in between long distance. Simple, Compound and epicyclic are types of gear train used in modern industry.
The velocity ratio and train value of gear train:
Velocity ratio or speed ratio
The speed ratio of the gear train is defined as the ratio between speed of the driver to speed of the driven. (or) the ratio between number of teeth on driven gear to number of teeth on driver.
Velocity or speed ratio = speed of driver/ speed of driven shaft
(or)
= number of teeth on driven gear / number of teeth on driver
Train value:
The train value is reciprocal Of the speed ratio.
Train Value = 1/ Velocity Ratio
Various types of gear train :
The various types of gear train used in modern industries.
- Simple gear trains
- compound gear trains
- reverted gear trains
- Epicyclic gear trains (or) planetary gear trains
Simple gear train:
The gear trains is having only one gear on each shaft is known as simple gear train.When the two gear are mating together, they rotating in opposite direction to each other. N1 and N2 to take care in number of teeth consider for gear 1 & Gear 2. Therefore gear 1 is driver and gear 2 is driven when the motion of the gear drivers in opposite direction. If want to change the desired direction of the gear drive and the centre distance will be more in gear by using Idle or intermediate gear placed in between two set of gear.
N1 and N2 = speed of gear 1 and gear 2
T1 & T2 = number of teeth on gear 1 and gear 2
So,
The velocity ratio and train value in simple gear train with idler gear:
Assume, the motion transmit between gear 1 to Gear 3 through idler Gear 2.So We get
- N1, N2, N3 = Speed of gears 1 (driver) , Gear 2 (idler), Gear 3 (Driven) Respectively
- T1, T2, T3 = Number of Teeth of gears 1 (driver) , Gear 2 (idler), Gear 3 (Driven) Respectively
The Respective Speed Ratio is,
Compound gear train:
The compound gear train is defined as one or more gear mounted in same shaft. So same number of revolution provided in gear during motion transmitted.The speed of both gear are same because of mounted in same shaft as shown in figure.
Now, Meshing gear (1&2)
Meshing Gear (3 & 4)
Meshing Gear (5 & 6)
Where, 
Now Multiply above Equation,
Finally We Get,
So, 
Advantages of compound gear trains:
- Large speed ratio can be obtained with smaller gear.
- The motion can be transmitted in round bend and corner.
- The different types of gear can be used in order to suit given condition.
Reverted gear train:
The first and last gear are mounted on same axis of rotation in shaft is known as reverted gear trains . when one gear are loosely placed. Reverted gear train as shown in figure, when gear 1 and 2 are rotate in opposite direction. Gear 2 and 3 are mounted in same shaft The gear 3 rotate in same direction as that of gear 2. Now the gear 3 drive to gear 4 and it same direction that of gear 1.Now the motion of gear 1 (First) and gear 4 (Last) are same is called reverted gear trains.It used for power is to be transmitted within the less space.
Speed Ratio,
So,
Application of reverted gear train
- Automobile gearbox
- Back gear for lathe
- Speed reducer in industrial application
- Clock mechanism (to connect hour hand to minute hand)
Epicyclic gear trains:
The epicyclic gear trains as shown in figure. Where the gear B rolls around outside of stationery gear A as arm C revolves. Which is used to transmit high velocity ratio. It is also called as Planetary gear or Sun and Planet gear trains, because of the gear B goes around and around the gear A (just for planet gear move around the sun gear). Which motion of planets around the sun gear is called planetary motion, therefore the gear B motion around Gear A is known as planetary motion.
Application of epicyclic gear train
- Automobile differential gear
- Lathe back gear
- Pulley blocks
- Hoist and wrist watch
Types of epicyclic gear train
- Simple epicyclic gear trains
- Compound epicyclic gear trains
Simple epicyclic gear trains
There is only one Gear on each shaft in any epicyclic gear train, which is called simple epicyclic gear trains. This is shown in above figure.
Compound Epicyclic gear trains
The gear have more than one Gear on the shaft in any epicyclic Gear trains, there is called compound epicyclic gear train. Example For, Sun and Planet gear is a compound epicyclic gear train.
Sun gear: the gear placed on centre position is called sun gear.
Planet gear: there are placed on whose axes move are called planet gear.
D= Sun Gear
B-C = Planet Gear
A = Annulus Gear
