The Visco® clutch has the task of making the frictional connection
to the fan wheel depending on the temperature and influencing
its speed. If no cooling air is required, the Visco® clutch switches
off and continues to run at a lower speed. The Visco clutch
is triggered by a bi-metal element which is exposed to environmental
temperature. A bore hole is released by a pressure pin
and silicone oil flows from the store into the working chamber.
There, the drive torque is transferred to the fan wheel, the continuously
variable speed of which is set automatically on the basis
of the operating conditions by means of wear-free viscous friction.
In the case of the electrically driven Visco® clutch, control
takes place directly via sensors. A regulator processes the values
and a pulsed control current carries these to the integrated electromagnet.
The defined guided magnetic field regulates the valve
which controls the internal oil flow via an armature. An additional
sensor for fan speed completes the regulator circuit. This increases
the dynamics of fan switch-on and -off. Cooling to match
requirements improves the level of coolant temperature, engine
noise as well as fuel consumption.