Idler Gears
Idler
gears are those type of intermediate gears that are inserted between two
other types of gears. Typically an Idler Gear performs three functions.
Firstly Idler Gear facilitates to change the direction of rotation of output
shaft. Secondly Idler gear typically help in reducing the size of the
input/output gears while continuing to maintain the spacing of the shafts.
Thirdly,
Idler
gears can also make changes in the spacing between the output and
input axles. Interestingly, Idler gears do not have any impact on the gear
ratio between the output and input gears. The gear ratio is calculated as if
there was no Idler Gear. Services of Idler Gears are also utilized for
transmitting rotation among distant shafts in cases where it would not be
wise to just, make the distant gears bigger in order to bring them together.
Functioning of the Idler Gear
The important function performed by the idler Gear can be understood from
the working of a typical gear, considering what happens when there is no
Idler Gear.
As is clear from the next image, the direction of rotation of output axle
is in opposite direction to that of the input axle. Now see what happens if
in between the two, an idler gear is added. The output axle stats rotating
in the same direction as that of the input axle. Now another interesting
tale concerning Idler Gears, if a second idler gear is added the input and
output axle would again start rotating in opposite directions.
Application of the Idler Gears
An idler gear working in the manual transmission system plays a vital role.
Internally a manual transmission system looks like this.
Let us take a close look at the Idler Gear now:
The reverse gear on the manual transmission system typically uses an Idler
gear. It helps in the following way. In the above diagram the blue coloured
reverse gear turns in a direction that is opposite to all other blue
coloured gears. So, it is not possible to throw the transmission into
reverse position as long as the car is moving ahead. The dog teeth would
never engage, now the Idler Gear helps the reverse gear to slide into a mesh
with the other gears for reversing the direction of rotation.
Let us the application of Idler Gear in the application related to
Automotive differential.
Idler Gears in Automotive Differential
The image shown above is of an Automotive differential, typically using a
bevel-gear epicyclic train. It is the pinion which, drives the
ring gear (crown wheel). The Crown Gear is
able to rotate freely, and carries the Idler Gears. Though only one Idler
Gear is required here, but extra Gears can give a better symmetry. In the
epicyclic chain, the ring gear is able to correspond to the planet carrier,
while the Idler Gears correspond to the planet gears. The function of the
Idler Gears is to drive the side gears on the half-axles. This corresponds
to the sun and ring gears, and in effect are the output gears. As the two
half-axles start revolving at a similar speed, there is no revolving of
Idler Gears. But as soon as the half-axles start moving at different speeds,
the idlers also start revolving. The differential puts same amount of torque
to the side gears (idlers drive them at equal distances), but allows them to
rotate at varying speeds.
