Gear Trains
In a gearbox,
gears and gear trains are used to provide speed and torque conversions from a
rotating power source to another device. It is widely used
in industrial, civilian and military applications, for example in helicopters,
wind turbines, bucket wheel excavators, tracked loaders, and milling machines.
In industrial applications, gearboxes may work under constant operation
condition or varying operation condition.
Types of Gear trains
According to the arrangement of gear wheels, gear trains can be
classified into four categories: simple gear train, compound gear train,
reverted gear train and planetary gear train (epicyclic gear train).
1. Simple gear train
The simple
gear train has one gear mounted on each shaft. The gear which is mounted on the main shaft is driver gear and the gear to which power is supplied is called driven gear. The gears which are used to connect the driver and the driven gears are called idlers. The direction of rotation of driven gear depends on the numbers of idlers or the idle gears. If there are even numbers of idlers in between the driver and the driven gear then the rotation of the driven gear will be opposite to the driver gear. And if there the odd number of idlers are present then the driven gear will have the same direction of rotation as the driver gear.
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| Simple Gear Train |
2. Compound gear train
If there is
more than one gear mounted on a shaft, the gear train is called the compound
gear train.
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| Compound Gear Train |
3. Reverted Gear Train
If the axes of
the driving gear shaft and the driven gear shaft are coaxial, the gear train is
known as reverted gear train.
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| Reverted Gear Train |
4. Planetary gear train
If one gear
rotates on its own axis and also revolves around the axis of another gear, this
gear train is termed as planetary gear train.
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| Planetary Gear Train |
A basic
planetary gear set contains one sun gear, one internal gear (ring gear), one
carrier and several planet gears that mesh with the sun gear and the ring gear
simultaneously. The first three gear trains are collectively called fixed-axis gear
trains since all gears only rotate on their own axis and all their axes are
fixed.
Comparing with
fixed axis gearboxes, planetary gearboxes can afford higher torque load due to
the load sharing among multiple gear pairs and generate larger transmission
ratio with equal or smaller volume.
