Fiat Bravo Service Manual page 182

Bravo-Brava ^
16v
Engine
Fuel system
mm
10.
ENGINE IDLE SPEED ACTUATOR
(step motor) (WEBER B02)
1. Bearing
2. Lead screw
3. Coils
4. Magnets
5. Screw
6. Anti-rotation
grooves
7. Plunger
The actuator is fitted to the butterfly valve case and consists
of:
- An electric step motor with two windings in the stator
and a rotor that contains a certain number of permanent
magnet pairs.
- A worm and screw reduction unit that converts rotato­
ry motion into linear motion.
In order to idle, i.e. with throttle (4) fully closed, the en­
gine needs a certain amount of air (Qo) and fuel to over­
come internal friction and maintain rpm levels.
To the quantity of air Qo that leaks through the closed but­
terfly valve (4) during idling, an additional quantity of air
Q must be added to allow the engine to maintain rpm lev­
els constant, particularly during warm up and when elec­
trical users or external loads are activated (air conditioner,
automatic transmission, etc).
To achieve this result, the system uses a step motor (1)
fastened to butterfly valve case (5) controlled by ECU (6)
which moves a rod fitted with a plunger (3) during opera­
tion. This alters the cross-section of by-pass duct (2) and
thus the amount of air (Qo + Q) taken in by the engine.
In order to govern this type of action, the ECU uses an­
gular engine speed and coolant temperature input from
the relevant sensors.
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