Fiat 1996 Brava Service Manual page 448

Engine
Fuel system
Bravo- Brava 9 **
1998 range
ENGINE IDLE SPEED ACTUATOR
(step m o t o r )
1. Bearing 5. Screw
2. Worm screw 6. Anti-turn grooves
3. Coils 7. Plunger
4. Magnet
A. Actuator used on premodification cars
B. Actuator used on postmodification cars
The actuator is secured to the throttle body and con­
sists of:
- an electric stepp motor with two windings in the
stator and a rotor which includes a certain number
of pairs of permanent magnetic poles;
- a worm screw type reduction gear which converts
rotary motion into rectilinear motion.
To run at idle speed, i.e with throttle (4) fully closed,
the engine needs a certain amount of air (Qo) and
fuel to overcome internal frictionand maintain its
speed of rotation. The amount of air (Qo) that leaks
thorugh closed throttle (4) with the engine idling
must be increased while the engine is warming up or
when external services or loads are activated (e.g.
automatic air conditioner etc.) by an additional
quantity of air (Q) to allow the engine to maintain a
constant rpm. To achieve this result, the system uses
a step motor (1) secured to throttle body (5) and
controlled by a drive circuit (6) located inside the
injection-ignition control unit. The motor drives a
push-rod equipped with a plunger (3), which alters
the cross section of by pass duct (2) and thus the
amount of air (Qo + Q) taken up by the engine. To
control this type of action, the control unit uses an­
gular engine speed and coolant temperature signals
from the relevant sensors.
+ 12V o -
r,
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Q. Air flow regulated by actuator (variable)
J M l l l l I
Q o
-
A i r f , o w
leaking through throttle (constant)
36
Publication n° 506.670/21