Automatic Transmission, How it works ?

Some technologies are easier to understand
with the help of 3D animation.

But, what about the 6-Speed
automatic transmission from Allison.

To visualize and understand this beautiful
planetary gear set mechanism,

a 2D animation will be ideal.

You can consider this 2D drawing as
a cross section of the 3D model.

A planetary gear set has
2 inputs and 1 output.

If you properly understand
working of a planetary gear set,

you can easily understand automatic
transmissions from the 2D animation.

The essence of the planetary gear set is that

just by giving different speeds
to the ring and sun gears,

you will be able to get different
speeds at the output.

The beauty of automatic transmissions lies

in how these different input
speeds are transmitted.

Let's see it in the 2D animation.

This 3D planetary set
is represented in 2D as shown.

In an automatic transmission,

the input and the output are
not directly connected.

They are connected through
an intermediate shaft as shown.

Now, a small suggestion before you proceed.

You will be able to explain
all seven gears by yourself

by pausing the video for a moment
and understanding the mechanism.

Please try that at every single gear.

You will be amazed by
the brilliance of this mechanism.

If you press clutch C1,

the input will be connected to the sun gear.

If you press clutch C5, the output
ring gear will be stationary.

This will result in the first gear.

Now let's add one more gear set.

Here comes the tricky part.

The carrier of this set is connected
to the ring gear of the first set.

This simply means that

the output of the second set is
connected to the input of the first set.

Think for a moment about what happens
when you apply C1 and C4.

Since C4 is applied, the ring gear of
the second set will be stationary.

This makes the carrier turn.

This carrier is connected to
the ring gear of the first set.

So, the ring gear of
the first set will also turn.

This, in turn, will increase
the output speed

or we will get the second gear.

To obtain a fourth gear or direct drive,
a rotating clutch module is also used.

We know that for a direct drive,

both the sun and the ring gear
should rotate at the input speed.

If we press C2 and C1 together,
this is what happens.

In the very same mechanism,

if you apply C2 and C4 you will
get very high speed at the output.

Think for a moment and
try to understand this.

It is clear that the carrier of the second
set will turn at the input speed.

However, here the ring gear is stationary.

This makes the sun gear turn at almost
three times the speed of the input.

Eventually,

a very high output speed is obtained.

One more gear set is used to obtain
the remaining gear ratios.

However, the sun gear of this set
is not connected to the shaft.

Instead, it is connected to
the rotating clutch module.

So, this sun gear will always turn
at the input speed.

And here again,

the output of the set is connected
to the input of the adjacent set.

For the remaining gear ratios,
C3 is always applied.

This means that the brown carrier
or ring gear of the second set

will turn at one-third of the input speed
for the remaining cases.

For the third gear, apply C1 as well.

For the fifth gear,
apply C2 along with C3.

The reverse is an interesting mechanism.

Here, C5 is applied along with C3.

So here, the carrier of
the second set is stationary.

This means that the planet gears of
this set will not be able to revolve

and that they will simply spin.

This spin is in the same
direction as the input.

This planetary spin will make

the corresponding sun gear spin
in the opposite direction.

As a result, the output sun gear will
also turn in the opposite direction

and we will get the the reverse gear.

We hope that you enjoyed the brilliance
of the Allison transmission mechanism.

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