The torque converter lockup clutch ist the so called "Drehmomentwandler Überbrückungskupplung".
But my knowledge about those deep technical stuff is limited.
Maybe some other members can explain you how it works exactly.
BUt what I know is that the torque converter takes the place of those clutch,
to seperate the load from the power source.
So it can multiply torque when there is a substantial difference between input and output rotational speed, providing the equivalent of a reduction gear.
This lockup clutch improves cruising power transmission efficiency and reduces heat.
The converter contains 3 rotating devices, such as the turbine, impeller and stator.
Hope this helps you out a little bit.