Engine Idle Speed Actuator (Step Motor) - Fiat Bravo Service Manual

Engine
Fuel system
Q. Air f l o w regulated by actuator (variable)
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Q o - A i r f , o w
36
leaking t h r o u g h throttle (constant)
Bravo- Brava 9
ENGINE IDLE SPEED ACTUATOR
(step motor)
1 .
Bearing
2.
W o r m screw
3.
Coils
4. M a g n e t
A.
Actuator used on premodification cars
B. Actuator used on postmodification cars
The actuator is secured to the throttle body and c o n -
sists of:
- an electric stepp motor w i t h t w o w i n d i n g s in t h e
stator and a rotor w h i c h includes a certain number
of pairs of permanent magnetic poles;
- a w o r m screw type reduction gear w h i c h converts
rotary m o t i o n into rectilinear m o t i o n .
To run at idle speed, i.e w i t h throttle ( 4 ) fully closed,
the engine needs a certain amount of air ( Q o ) a n d
fuel to overcome internal frictionand maintain
speed of rotation. The amount of air ( Q o ) that leaks
thorugh closed throttle ( 4 ) w i t h the engine i d l i n g
must be increased w h i l e the engine is w a r m i n g up or
w h e n external services or loads are activated (e.g.
automatic air conditioner
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 ) a n d
controlled by a drive circuit ( 6 ) located inside t h e
injection-ignition control unit. The motor drives a
push-rod equipped w i t h a plunger ( 3 ) , w h i c h alters
the cross section of by pass duct ( 2 ) and thus t h e
amount of air (Qo + Q) taken up by the engine. T o
control this type of action, the control unit uses a n -
gular engine speed and coolant temperature signals
from the relevant sensors.
+ 12V o -
r.
21
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1998 range
5.
Screw
6.
Anti-turn grooves
7.
Plunger
etc.) by an additional
6
40
20
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A . J j
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Publication n° 506.670/21
16v
its