Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw

232 Chapter Eleven
MAGNETIC
FIELD
INCREASES
PICKUP
COIL
POLE
PIECE
SIGNAL 0
AIR GAP VOLTAGE
DECREASES
+
POSITIVE
SIGNAL
VOLTAGE
PULSE SHAPER
AND PULSE
AMPLIFIER
IGNITION
SWITCH
ELECTRONIC
CONTROL UNIT
POWER
TRANSISTOR
-
BATTERY + -
RELUCTOR
(ARMATURE)
BALLAST
RESISTOR
+ -
IGNITION
COIL
DISTRIBUTOR
CAP
SPARK
PLUG
PICKUP
COIL
STRONG
MAGNETIC
FIELD
NARROW
AIR GAP
+
0
ZERO SIGNAL
VOLTAGE
Figure 11-6. Schematic of a typical magnetic pulse
generator ignition system.
-
IGNITION
MAGNETIC
FIELD
REVERSES
+
AIR GAP
WIDENS
0
-
NEGATIVE
SIGNAL
VOLTAGE
Figure 11-5. The pickup coil generates an AC voltage
signal as the reluctor moves closer and then away
from the magnetic field.
or signal voltage. Hall Effect is the ability to generate
a small voltage signal in semiconductor material
by passing current through it in one
direction and applying a magnetic field to it at a
right angle to its surface. If the input current is
held steady and magnetic field fluctuates, the
output voltage changes in proportion to field
strength.
Most Hall Effect switches in distributors have a
Hall element or device, a permanent magnet, and a
ring of metal blades similar to a trigger wheel.
Some blades are designed to hang down. These are
typically found in Bosch and Chrysler systems,
Figure 11-9, while others may be on a separate ring
on the distributor shaft, typically found in GM and
Figure 11-7. A magnetic pulse generator installed in
the distributor housing. (Courtesy of Ford Motor Company)
Ford distributors. When the shutter blade enters the
gap between the magnet and the Hall element, it
creates a magnetic shunt that changes the field
strength through the Hall element, thereby creating
an analog voltage signal. The Hall element contains
a logic gate that converts the analog signal into a
digital voltage signal. This digital signal triggers
the switching transistor. The transistor transmits a
digital square waveform at varying frequency to
the powertrain control module (PCM).
The Hall Effect switch requires an extra connection
for input voltage; however, its output voltage
does not depend on the speed of the rotating
trigger wheel. Therefore, its main advantage over