What is a Torque Converter?

[Ruckuz]

Thanks go out to "Mud Sweat And Gears" for this info.



The Torque Converter
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. Repeat: there is no direct connection between the engine and the transmission.

Instead, the engine turns the transmission by means of a process called hydraulic coupling.

Think of two electric fans in a room. Line them up a few feet apart, one in front of the other, both facing the same direction. Now turn on the rear fan. What happens? If you've turned the fan up high enough, and if the fans are close enough together, the front fan will begin to turn as well. In this same manner does the engine crankshaft influence the transmission shaft, causing it to rotate.

The identical process occurs in a torque converter, except that transmission fluid takes the place of air.

But there's more. Inside the torque converter are several components that help multiply the power. These are the impeller (or pump), the turbine, and the stator (or guide wheel).

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.

Picture two halves of a chambered nautilus, and this will perhaps give you a better image.

As one fan begins to spin, the other will spin as well. Through centrifugal force, the fluid moves to the outside of the blades, where it is redirected by a third fan, called a stator, back to the turbine side. This continual flow of fluid is what causes the power to be multiplied.


The Lockup Torque Converter
Because the only connection between two sides of a torque converter is a fluid connection, there is always a little slippage, running from about 2-8%. To increase efficiency and gas mileage, most modern automatic transmissions also have something called a lockup clutch (aka, torque converter clutch).

It works like this. As the speed of the car nears 40 miles per hour, the highly pressurized transmission fluid is channeled through the transmission shaft and activates a clutch piston. This metal pin locks the turbine to the impeller, in effect bypassing the torque converter. It remains this way until the vehicle slows below 40 mph, at which point the clutch piston disengages and the torque converter kicks in again. Simple, right?

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