Torque Converter

[mort]

Originally Posted by Cobb

No one has mentioned it, but I was lead to believe by physics that the tc offers a 2 to 1 gear reduction and increase in twisting force/reduction in rpms for when the going gets tough?

Torque converter design tries to reach an acceptable compromise of efficiency and torque multiplication. 2 :1 is about average for stall conditions of modern automotive converters - see wikipedia At stall the efficiency goes to 0 as the output is at 0 rpm, but between stall and cruise the efficiency can be as high as 98% But for 3 element convertors like used in modern cars the maximum torque multiplication occurs at stall. Multiple element designs can have high power efficiency through most of the operating range - leading to very high torque multiplication at high rpm slip.
-mort

[Christ]

No reduction in RPM though, the function of a torque converter is much like slipping a manual clutch, as I mentioned earlier. It basically allows a range of engine speeds for a given vehicle speed, increasing the range of power available at a given vehicle speed.

In other words, in a manual transmission with the clutch fully engaged, you have a range of power from no throttle to WOT [generally speaking] for a given vehicle speed, because the engine is locked in relation based on the selected gear.

For a torque converter, while the engine may be locked to the transmission by a gear, the torque converter allows the engine to 'slip' to a higher RPM, transmitting more torque to the selected gear which, in turn, leads to higher output at the wheels. This is one of the reasons that, despite the power losses for automatic transmissions, they tend to have the capability to accelerate faster.

[P-hack]

engine/impeller spools up, speed ratio goes down, wheels get more torque (at the cost of efficiency) via the converter, and more hp from the engine.

vehicle speeds up, speed ratio moves towards 1, efficiency improves, torque multiplication declines, converter locks up.