Topic:
Fluid Coupling:
The fluid coupling is no longer used in the drive of an automatic transmission. Nowadays, the torque converter is used instead. The torque converter provides better efficiency, which is visible in the graph. See the Torque Converter page.
The efficiency of a fluid coupling is nearly equal to that of the plate clutch. However, when almost fully coupled, its efficiency drops significantly, which would cause the drive to fail. A torque converter does not have these characteristics. Due to the internal vanes, the torque is already increased at low speed.
