fluid coupling

Fluid coupling:
Nowadays, the fluid coupling is no longer used in the drive of an automatic gearbox. Today, the torque converter is used for this. The torque converter gives a better efficiency. This can be seen in the graph. See Torque Converter page.
The efficiency of a fluid coupling is almost equal to that of a plate coupling. However, the return collapses completely at almost full coupling. The drive would then fail. A torque converter does not have these properties. Due to the internal vanes, the torque is already increased at a low speed.