Patent ID: 7318510

Claim:
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 ).