andy chuksThe automatic gear 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.
The key to the modern automatic transmission is the torque converter. It takes the place of a clutch in a manual transmission.
A direct descendant of an earlier component called a fluid coupling, the torque converter offers the advantage of multiplying the turning power provided by the engine. It is connected to the motor by means of a metal rod known as the transmission shaft (sometimes called the input shaft), which fits next to but does not touch the engine crankshaft.
A torque converter is like a giant doughnut. The impeller and the turbine (the two fans in the analogy above) face one another inside the round metal casing. The impeller is on the engine side, the turbine on the tranny side. Both of these components have blades that catch the transmission fluid and cause them to spin.
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