Group
28
Ignition
systems
D
esign and function
-
Speed and
crankshaft
position
information
Inductive speed/p
osition pick-up
Function
and
location
The
purpose
o
f the
speed/position
pick
-
up
(1) is
to
s
upply the
control
unit
(3)
with
information on engine speed
and
crankshah position. The pick
-u
p
is
mounted
close
to the flywheel
(2)
(o
r
carrier
plate
on
automatic models), the
periphery of which
is
provided with a series
of drilled
holes
.
The
location of
the pick
-up
such
that
it is in
flu
enced
by
this
con
figuration
of holes
.
Construction
A
.
Th
e
pick
-
up
(
1
) cons
i
sts
of a permanent magnet
(
4
).
a
pole
tip
(5)
which
co
ncentrates the
magne
t
ic
f
i
eld
a
t
the end
of
the
device and a
coil
(
6
).
The magnet
creates a
magnetic field whi
ch
varies in
strength depending on whether a
hole
or 'too
th
'
is passing the tip
.
Operation
An
alternating voltage
is induced in
the
pick-up coil
when
one of
the pro
jec
tions
or
'
teeth
'
on
the
fl
ywhee
l
passes the
tip. This variable
signal is
transmitted by
a lead
to the
control unit.
In
effect,
therefore. th
e pick-up supplies
t
he
control
unit with a
unique al
t
ernating vol
t
age
-
an elec
t
rical
'
picture
'
of
the
flywhee
l
from which
the
unit
can
determine
both
the
engine speed and crankshah
position.
Signal
B
.
The
frequency
of the
signal
the period
between
two
successive
voltage peaks)
i
s
a measure of
the
engine
spee
d
.
To p
r
ovide a reference signal for the
crankshah
position
,
one or more
'
t
eeth'
(o
ne
or
two
in
the case
of
4-
cy
linder
engines
and three
on
6-cylinder un
i
ts)
on
the flywheel
/
carrier
plate
are
made
longer
than
th
e othe
r
s.
The
con
tr
ol
unit
detects the
c
rankshaft position by
sensing
the interruption
i
n
signal
(
8
)
which occurs as a long tooth
passes the pick-up. This reference
signal is
used to determine the top dead centre (TOC) position.
"
