Abstract: A fluid-friction clutch for a cooling fan of an internal combustion engine, the clutch being fitted on the water-pump shaft which drives the impeller of a water pump for the internal combustion engine and being controlled by an expansion-type thermostat element which is located in a longitudinal bore through the water-pump shaft. Cooling water of the internal combustion engine is applied directly to the expansion-type thermostat element, this water being continuously conveyed through the longitudinal bore in the water-pump shaft by utilizing the pressure-difference created in the cooling water by the impeller of the water pump. In order to cool both the working chamber of the fluid-friction clutch and the clutch-bearing, a cooling line is arranged inside the working chamber and connected to the cooling-water circulation inside the longitudinal bore through the water-pump shaft.

Abstract: A rotating fluid shear friction coupling with at least one shear friction gap formed by a wall rotating along with the input side and by a wall rotating along with the output side, and with two spaces in communication with the working gap, one on the inlet side and one on the outlet side; the radially outermost passage of the inlet side space into the working gap has radially a larger spacing from the center of rotation than the radially outermost passage from the outlet side space whereby the two spaces are separated from one another by a wall provided with controllable passages; the working gap is also provided with means, for example, in the form of a helical feed groove for the continuous automatic feed of the working medium through the working gap in the direction toward the space on the outlet side; the space on the outlet side has thereby a space portion which is delimited radially outwardly by walls that preferably rotate with one another as a unit, and is disposed radially outwardly of the radius of