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

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 HowStuffWorks, we'll work our way through an automatic transmission. We'll start with the key to the whole system: planetary gearsets. Then we'll see how the transmission is put together, learn how the controls work and discuss some of the intricacies involved in controlling a transmission.

Epicyclic gearing or planetary gearing as used in ...

Gear shift stick of my Mazda Protege SE 1999.

Automatic transmission cut

Some Basics

Just like that of a manual transmission, the automatic transmission's primary job is to allow the engine to operate in its narrow range of speeds while providing a wide range of output speeds.

Without a transmission, cars would be limited to one gear ratio, and that ratio would have to be selected to allow the car to travel at the desired top speed. If you wanted a top speed of 80 mph, then the gear ratio would be similar to third gear in most manual transmission cars.

You've probably never tried driving a manual transmission car using only third gear. If you did, you'd quickly find out that you had almost no acceleration when starting out, and at high speeds, the engine would be screaming along near the red-line. A car like this would wear out...