Idle Speed/Throttle Actuator - Electronic: Description and Operation
DESCRIPTIONA dual-winding Idle speed positioner is fitted; together with the Digital Motor Electronics (DME) control unit it regulates the engine's idle speed (84O ±4O rpm on vehicles with manual gearbox 88O ±4O rpm on vehicles with Tiptronic transmission).
The Idle speed positioner performs the following tasks:
- Cylinder filling control (constant idle speed when engine warm)
- Cold-idling speed (idle speed boost to overcome internal engine friction)
- Cruising speed boost (underpressure limiting on the overrun)
- Starting speed increase (additional air during the starting process)
The following incoming information is processed by the DME control unit:
- Position of throttle valve (idle speed identification)
- Engine temperature (NTC II)
- Engine speed (speed sensor)
OPERATION
The Idle speed positioner receives a cyclical electrical signal from the DME control unit, acting alternately on both windings during an actuation period. This process generates opposite torques at the armature. Under the influence of the armature's inertia, the positioner is adjusted to a particular angle which corresponds to the duty ratio of the signal received.
When the incoming signals are altered, e.g. as a result of a change in speed, the signal's duty ratio to the positioner also changes. The programmed reference speed is compared with the actual speed in the control unit. The air throughput is then altered via the positioner until the reference and target speeds match.
1 - Electrical connection
2 - Housing
3 - Permanent magnet
4 - Armature
5 - Bypass air duct
6 - Rotary slide