Liquid friction clutch

A drive for cooling fans in motor vehicles, the drive comprising:

• a primary cooler (4) located in a primary cooling circuit (3),
• a primary temperature sensor (23),
• at least two secondary coolers (7, 8) located in respective secondary cooling circuits (5, 6),
• a fluid friction clutch including driving and driven clutch members (9, 10), and
• a reservoir (17) for a viscous fluid, the reservoir (17) being limited by a separating member (18) and being connectable to a working chamber (19) by at least one first opening (20) in the separating member (18), the working chamber (19) extending into a region between the clutch members (9, 10) in which torque is transmitted from the driving clutch member (9) to the driven clutch member (10) by the viscous fluid, and wherein filling of the working chamber (19) with the viscous fluid is controlled by a first control element (21) opening and closing the first opening (20) in the separating member (18) depending on the temperature of cooling air passing through the primary cooler (4) sensed by the primary temperature sensor (23),
• characterized in that each of the at least two secondary cooling circuits (5, 6) includes a secondary temperature sensor (40, 41), the secondary temperature sensors (40, 41) being operatively connected to a control unit (38, 39) arranged to control a second control element (31), wherein the separating member (18) comprises at least one second opening (30), the second control element (31) being arranged in the working chamber (19), the control unit (39) moving the second control element (31) to press against the separating member against the bias of a spring member to close the at least one second opening (30) in accordance with a sensed temperature detected by one or more of the secondary temperature sensors (40, 41) and moving the second control element away from the separating member to open the at least one second opening in accordance with the sensed temperature rising above a predetermined value to control the filling of the working chamber (19) with the viscous fluid, and wherein control of the second control element (31) is independent of control of the first control element (21).