Fan Clutch: Description and Operation

Visctronic Drive Fan (VDF)







The cooling fan electronic clutch is controlled by the PCM. The PCM monitors Engine Oil Temperature (EOT) and Engine Coolant Temperature (ECT) and sends a duty cycle command to the fan clutch to achieve adequate cooling. When a circuit fault is detected the PCM will set a DTC.

Signal Functions

The visctronic drive fan (VDF) is an electrically actuated viscous clutch that consists of three main elements:
- a working chamber
- a reservoir chamber
- an actuator (electromechanical valve and speed sensor)

The actuator valve controls the fluid flow from the reservoir into the working chamber. Once viscous fluid is in the working chamber, "shearing" of the fluid will result in fan rotation. The valve is activated via a pulse width modulated (PWM) output signal from the PCM. By opening and closing the fluid port valve, the PCM can control fan speed. Fan speed is measured through a Hall-Effect sensor and is monitored by the PCM during closed loop operation.

The PCM optimizes fan speed based on engine coolant temperature (ECT), engine oil temperature (EOT), transmission fluid temperature (TFT), intake air temperature (IAT), or air conditioning requirements. When an increased demand for fan speed is requested for vehicle cooling, the PCM will monitor the fan speed through the Hall-Effect sensor. If a fan speed increase is required, the PCM will output the PWM signal to the fluid port, providing the required fan speed increase.

Detection/Management

During KOER Self-Test, the PCM commands 100% duty cycle. A DTC is set if the PCM detects the voltage on the valve control circuit is not within the expected range or if the fan speed is less than a calibrated value.