Air flow control unit

The airflow control unit has a positioning mechanism(19) for automatic opening and closing of a shutter-type element. The positioning mechanism consists of a first toothed quadrant(24) interacting with an adjusting wheel(22) mounted on a rotational pivot, and a second toothed quadrant(25) meshing with the first. The second toothed segment interacts with the first via a leg spring(26) in such a way that the spring slackens towards each side of the engagement apex point.