fluid flywheel

[Agnes]

a kind of fluid coupling in which the flywheel is the driving rotor

[Ernestdyday]

A fluid coupling or hydraulic coupling is a hydrodynamic or hydrokinetic device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch. It also has widespread application in marine and industrial machine drives, where variable speed operation and controlled start-up without shock loading of the power transmission system is essential.
Hydrokinetic drives, such as this, should be distinguished from hydrostatic drives, such as hydraulic pump and motor combinations.