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THIS ESSAY IS ABOUT HOW AUTOMATIC TRANSMISSION WORKS AUTOMATIC TRANSMISSIONS HAVE ALL THE FEATURES OF MANUAL TRANSMISSIONS AND A LOT MORE. HAPPY READING...

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How Automatic Transmissions Work

by Karim Nice

If you have ever driven a car with an automatic transmission, then you know that there are two big differences between an automatic transmission and a manual transmission:

There is no clutch pedal in an automatic transmission car.

There is no gear shift in an automatic transmission car. Once you put the transmission into Drive, everything else is automatic!

Both the automatic transmission (plus its torque converter) and a manual transmission (with its clutch) accomplish exactly the same thing, but they do it in totally different ways. It turns out that the way an automatic transmission does it is absolutely amazing!

Location of the automatic transmission

In this edition of
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Notice that the first gear ratio listed above is a reduction -- the output speed is slower than the input speed. The second is an overdrive -- the output speed is faster than the input speed. The last is a reduction again, but the output direction is reversed. There are several other ratios that can be gotten out of this planetary gear set, but these are the ones that are relevant to our automatic transmission. You can try these out in the animation below:

Animation of the different gear ratios related to automatic transmissions

Click on the buttons on the left in the table above.

So this one set of gears can produce all of these different gear ratios without having to engage or disengage any other gears. With two of these gearsets in a row, we can get the four forward gears and one reverse gear our transmission needs. We 'll put the two sets of gears together in the next section.

Gears

This automatic transmission uses a set of gears, called a compound planetary gearset, that looks like a single planetary gearset but actually behaves like two planetary gearsets combined. It has one ring gear that is always the output of the transmission, but it has two sun gears and two sets of planets.

Let 's look at some of the parts:

How the gears in the transmission are put
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