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Bajrang Engineering Works
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Bajrang Engineering Works

Planetary Gear Unit

Working Applications

Did You Know?
The planetary gear sets can produce different gear ratios, depending on the type of gear used as the input, output, and the one held still.
Planetary Gear Unit are a bit complex. This is because the planetary gear centers revolves around a sun gear at a rate that is known as train frequency. Planetary gear RPM, sun gear RPM, or the train frequency shows tendency to modulate the tooth mesh frequency. Now this behaviour results in a complex set of sidebands in the spectrum. This can be difficult to understand and interpret. A Planetary gear set has basically three main parts. They are the following:

Planetary Gear Unit

Planetary Gear Unit

Any of the three components can act as the input, output or one that is held stationary. The gear ratio depends on the particular gears playing which role. Please see the image below showing the constituents of the Planetary Gear system.

Working of a Planetary Gear Unit
The functioning of a Planetary Gear system can be understood. With the help of the following example.
Planetary Gear Unit
Imagine that a 6:1 gear ratio is required along with the condition that the input is turning in the identical direction as the output. Also there is requirement that the axis of the output gear is the same as that of the input gear. There is a common application, where you need this same-axis capability. It is in the electric screwdriver. This can be very easily solved by the use of a planetary gear system. The working is shown below.

Here, the sun gear (represented by yellow colour) engages all three Planetary Gears (represented by red colour) simultaneously. All the three gears are firmly attached to a plate known as the planet carrier. They are all engaged in the inside of the blue gear (in the ring). So a 6:1 gear ratio is achieved when the output shaft is connected to the blue ring gear, while the planet carrier stays put in a stationary position.

Planetary Gear UnitApplication of Planetary Gear Units
Perhaps the most popular application of the Planetary Gears lies in the Automatic transmission systems. As in the image on the left is the ring gear, followed by the planet carrier along with the two sun gears.

An automatic transmission comprises of two complete planetary gear sets that is folded into a single component. The planetary Gears produces different gear ratios in the automatic transmission system.

Compound Planetary Gearset
The automatic transmission system uses another variation of Planetary Gear Unit which is known by the name of Compound Planetary Gearset. This is similar to a single planetary gear set. But in reality, it behaves like a combination of two planetary gear sets. Here, the ring gear is the output of the transmission, also it consists of two sun gears along with two sets of planets.
Compound Planetary Gearset
The figure above shows the planets as found in a planet carrier. Out of the planet on right and left the right planet does not engage the ring gear rather, it engages the other planet. While the planet on the left is the one to engage the ring gear.





Effectively sums up all that is happening in the world of gears.

·Gear Blank
·Gear Cutting
·Gear Hobbing
·Heat Treatment of Gears