Stepper Motors

Purpose
Stepper motors are installed to adjust the various flaps.

Calibration
The control unit assumes that, after completing the calibration phase, the stepper motors are in a defined position since the stepper motors cannot signal back their position to the control unit. The calibration phase is triggered when the power supply (terminal 15 and terminal 30) of the control unit was interrupted. The calibration phase is then started after ignition "ON".

Defect Detection
When a defect is detected, a differentiation is made between a short to positive and a break.

In the case of a short to positive, the cause may also be due to a interphase short-circuit, i.e. connection to another winding of the motor. The corresponding motor is switched off if the control unit detects a stepper motor defect. It resumes operation when the ignition was switched off for > 3 minutes or a calibration run is triggered and the motor is found to be OK.

The stepper motors have an adjustment time of approximately 12 - 16 seconds. An exception to this is the fresh air motor which has an opening time of approximately 12 seconds and a closing time of approximately 2 seconds.

If the system voltage drops below 10V with the ignition switched on, the activation frequency is halved so that the adjustment time is doubled. If the system voltage drops below 9V, the motor is no longer activated by the control unit. As of this voltage, reliable activation of the stepper motor is no longer possible.