Cooling System: Description and Operation

Electric Fan, Infinite Fan Control

The vehicles feature infinite fan control enabling adjustment according to requirements. This new feature permits infinite control of the fan speed as a function of the coolant temperature and the refrigerant pressure in the air conditioning system, instead of two-stage control. The air throughput required is calculated by the Motronic control unit which transmits the information to the gateway control module via the CAN. The Gateway controller then sends the signal to the front control module. The front control module activates the radiator fan control module using a pulse-width modulated (PWM) activation signal which activates the left and right radiator fans via the power output. This has the advantage of requiring less current and therefore creates less of a load on the vehicle electrical system.

With stepped control, when a temperature threshold was exceeded the next fan speed had to cover the entire allocated temperature range. With infinite control, the fan speed can be continuously adjusted to the actual requirement. This means that the fan speeds can often be reduced, thereby decreasing noise and vibrations.