Functional description

The air-distribution-flap motor is activated via the LIN bus by the control unit for the heater/air conditioning system and supplied with voltage and earth. In the idle state, the control unit for the heater/air conditioning system switches the supply voltage off.

The air-distribution-flap motor is fitted with an integrated circuit. This circuit controls the coil of the air-distribution-flap motor. The circuit has bus- and diagnosis capabilities. After activation of the air-distribution-flap motor, position feedback is provided via the integrated switching circuit (actual position) to the control unit for the heater/air conditioning system.

After the vehicle has stopped and after a specified waiting period (stored in the memory chip of control unit for the heater/air conditioning system), the air-distribution-flap motor is moved to a certain parking position. The air-distribution-flap motor is reinitialized to this parking position after starting up.

• Deactivation in the event of blocking

  The integrated circuit detects blocking of the air-distribution-flap motor in that there is increased current consumption within the adjustment range. The integrated switching circuit reports the fault via the LIN bus to the control unit for the heater/air conditioning system. The control unit for the heater/air conditioning system no longer activates the defective air-distribution-flap motor. If blocking occurs outside of the adjusting range, an end stop is correctly detected.

• Reference run

The air-distribution-flap motor is unable to detect the current position (actual position). The air-distribution-flap motor always moves relative to an end position of the air-distribution flap (reference point). One of the end positions of the air-distribution flap (closed or fully opened) serves as the reference point.

The air-distribution flap is moved to an end position after replacement of the control unit for the heater/air conditioning system and after an interruption in the voltage supply.

The end position is selected in such a way that the subsequent nominal position can be reached by the shortest path. The reference run can also be triggered by the BMW diagnostic system.

Two cams of different widths are provided on the cam disc to allow the cam disc to be unambiguously positioned. When the microswitch for the air distribution moves over a cam, this leads to a change in state of the microswitch.

The control unit for the heater/air conditioning system monitors and evaluates the status of the microswitch (contact open or closed). This status information is the acknowledgement for the position of the air-distribution-flap motor or cam disk.

This mechanism achieves reliable and rapid positioning of the cam disk.

Courtesy of BMW OF NORTH AMERICA, INC.