Planetary Gear Unit
|
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:
- Sun Gear
- Planet Gears along with planet gears' carrier
- Ring Gear
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.
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.
Application
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.
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.
