外文介绍自动变速器是如何工作的

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Introduction to How Automatic Transmissions Work
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!

Purpose of an Automatic Transmission
Just like that of a manual transmission， the automatic transmissions 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.
Youve probably never tried driving a manual transmission car using only third gear.
If you did， youd 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 very quickly and would be n