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5-4
OIL
SENSOR
541
DESCRIPTION
The
oil
sensor mainly functions
to
detect posi-
tion
of
the
surface of
engine
oil
in
the crankcase
of engines
for
general
use
and
to stop
the
en-
gine automatically
when
the
oil level goes
down
below
the
lower
limit
specified.
This
prevents
sei-
zure
of
engine from occurring
due
to insufficient
amount of oil
in
the crankcase.
Since
the
sensor
has
been
designed
to.consume
a part
of
power supplied to the igniter
to
ener-
gize
its
electronics circuit, any other external
power
supply
is
not
necessary
so
that
it
can
be
mounted at the oil
filler
port.
OIL
SENSOR
Fig.
5-
17
Introduction
of
newly
developed
sensing
principle features
super
durability and no change
with
the
passage
of
time
as
it
does
not
use
any
moving part.
Merits
due
to introduction of electrical conductivity detection are
as
follows
;
@
It
has resistance
to
mechanical shocks
and
property
of
no
change
with
the passage
of
time as
@
At
the
same time,
it
is
capable of detecting the
oil
level
stably
as
it
is
not influenced
by
engine
@
No
error occurs due to foam and
flow
of the oil.
@I
Influence against
the
ignition
system
or
the
electronics
units
can
be neglected because an electric
sensing
element
consists
simply
of electrodes having no moving parts.
vibrations.
current
supplied
to
the
sensor can be decreased.
5-4-2
PRINCIPLE
OF
SENSING OIL LEVEL
There
is
a great
difference
between electric resistance
of
air
and
that
of
oil. Since the resistance
of
air
is
far higher than that of oil, more electric current passes through
the
oil
than
through
the
air, although
absolute value of the current
is
very
small.
The
sensor
detects
this
current difference and
make
use
of
it.
The
sensor
judges
the oil quantity,
by
comparing a current flowing across a pair of electrodes (inner
and
outer)
with
the
reference,
in
such
a way
that
if
a
current
flows
between the electrodes
more
than the
reference, sufficient oil
is
in
the
crankcase, on
the
other
hand,
if
a
current flows
less
than
the
reference,
oil
is
not sufficient. Since an electric current
is
flown
to
detect
oil
quantity,
this
is
called the “electrical
conductivity detection” type of sensor.
The
oil
level
to
be detected
is
determined
by
the length
of
elec-
trodes
and
their mounting positions
with
the engine.
5-4-3
HOW
IT
OPERATES
[Power
supply]
The sensor makes use
of
a part of primary power source
for
ignition
of
the engine
(igniter)
to
drive
the
sensor
circuit. Power to
the
sensor
can
usually
be
derived
from
the
“stop button”
by
branching
wires
out.
-
16-