Fiat Bravo Service Manual page 235

Bravo-Brava $ 1
16v
Engine
Fuel system
10.
ENGINE TIMING SENSOR
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2. Magnetic material
3. Gap
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The engine timing signal, together with the
engine rpm and TDC signal, allows the con­
trol unit to recognize the succession of cylin­
ders to implement the injection timing.
This signal is generated by a Hall effect sen­
sor, fitted by the exhaust camshaft drive pul­
ley.
NOTE It is not possible to carry out any ad­
justments to the angular position of
the sensor.
Operating principle
A semi-conductor layer through which the
current flows, immersed in a normal magnetic
field (lines of force perpendicular to the di­
rection of the current) generates a difference
in power, known as Hall effect voltage.
If the intensity of the current remains con­
stant, the voltage generated only depends on
the intensity of the magnetic field. It is there­
fore sufficient if the intensity of the field va­
ries periodically to obtain a modulated elec­
trical signal.
In pratice, to obtain this change, the sensor
has a metal ring passed through it (fixed to
the inner part of the timing pulley) equipped
with a series of openings: as it moves, when
the ring covers the sensor, it blocks the mag­
netic field and the signal remains low, whilst
as it passes the openings, the field closes and
the signal becomes high.
The alternating of the signals therefore de­
pends on the succession of the openings
(see "signal management" chapter).
Copyright by Fiat Auto
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