Group
28
Ignition systems
Design
and function - Speed and crankshaft position
information
Speed and crankshaft
position information
A
8
N
Hall generator
Function
and
location
The Hall
generator (1) supplies
the
control uni
t
with information
on engine speed
and
crankshaft
position. The de-
vice
is
mounted inside
the
distributor
cap.
Construction
:
The generator
is
based on
th
e
principle
of
the
Halt
effect, whereby the flow of current in a semiconductor is
deflected
if the
componen
t
is exposed to a magnetic field. This causes a potential difference (i
.
e. an excess of e
l
ec
tr
o
n
s on one
side of the
semiconduc
tor
and a deficiency on
the
producing a voltage
known
as
the Hall
vol
t
age.
Following
amplification, this voltage is employed by the
cont
r
ol
unit as a
signal
to
con
trol the timing
.
The Hall
generator (1) is
a U-shaped
element
w
i
th an opening for the trigger
ro
tor
(2).
The number
of
rotor
vanes is
the
same as
the
number of cylinders in
the
engine.
The generator
consists of a
Hall
-Ie
element (3)
co
mprising a Hall
effect detector
and a transistor amplifier
.
A magnet
(4)
with
a
three
-
pole
connector
(5) is
located
on
the opposite
side of
the
rotor
t
o
the
Hall
·
IC element
.
The
connec
tor
term
inals
are connected respectively
to
a
12
V supply
(+),
a 5
V reference signal
from the
control
unit
(01
and ground
(-)-
Signal
A
.
In th
is
position,
the
magnetic field
is
blocked by
the tr
igger
rotor
vane and
the Hall effect
is
absent. No
voltage is
induced
in
the Halt-IC element
and
the
ground connection
rema
ins
open.
As a
result, a
5
V signal
present atter-
minal
(01.
B
.
In this
position,
the
rotor exposes
the Hal
l·
IC e
le
ment to the
influence of
the magnetic f
ie
ld and the
resultant
Hall
voltage
fed to the transistor
amplifier.
The 5
V signal
at terminal
(0)
is then
connected
to ground across
the
terminal
and
the
voltage at (0)
falls to
0 V.
Thus, the
signal
from the Hall
generator
varies between 0 and
5 V
in the form of a square-wave
signal,
the control
unit deriving
its
engine speed
information
from measurement
of
the duration of the alternating half waves.
crankshaft
position signal
is
obtained by adjusting the basic
se
tt
ing of
the distributor
to
coincide
with the
posi
t
ive
flank
of
th
e
Hall generator signal
(i.e.
the half-wave generated when
the
rotor blocks
the magnetic
field) a few
cranksha
ft
degrees before TDC.
20
