Fluid coupling

a hydrodynamic or 'hydrokinetic' device used to transmit rotating mechanical power

A fluid coupling or hydraulic coupling or fluid flywheel is a device used to transmit rotating mechanical power.[1] It has been used in automobile transmissions as an alternative to a mechanical clutch. It is simpler than a torque converter, but it does not provide any torque multiplication, so it must be used together with a gearbox.

Daimler car fluid flywheel of the 1930s

References

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  1. Fluid coupling encyclopedia2.thefreedictionary.com