Sun Microsystems MCS 2000 SL - Page 71

LAMBDA
Lambda
is a number
which
indicates in
a
simple
way
how much
air
is
present
in the
fuel mixture being
burnt. When
"Lambda"
equals one
(1,00)
this
means
that there is
just
enough air
fbr complete
combustion
of
the fuel
and
no
excess
oxygen.
Any
reading
over
1.00
indicates
excess
air
(1ean
mixture) and a
reading
less the
1,00
indicates
not
enough
air
(rich
mixture).
Lambda
is
directly
related to airlfuel
ratio
with
the ideal
AFR
(14,7
: 1) being
Lambda't
,00
Lambda
=
ACTUAL
AFR
IDEAL
AFR
Figure 37,
Lambda Sensor
A Lambda sensor
is
a ceramic
device
placed
in
the
exhaust
system on
the
engine
side of
the
catalytic
converter.
It
consists
of a body
of ceramic
material,
the
surface
of
which
has
porous
platinum
e'lectrodes.
One
electrode
is
open
to
atmosphere
and
the other
is in the exhaust
stream.
When the
oxygen
content
on both
sides of
the electrodes
is
different,
a voltage
is
created.
Therefore,
the
function
of
the
Lambda
sensolis
to detect
the amount of oxygen
in the
exhaust
gas
and
to
feed
the
resultant voltage
generated
to the Electronic
Control Unit.
The
ECU will evaluate the signal
received
from the Lambda
sensor and
will
increase
or decrease
the
quantity
of
fuel suppliedin
order
to
maintain
the
correct air/fue1
ratio
or Lambda
1,00. A signal
from a
lambda
sensor
is
shown
in
figure 7
on
page
24.
The Lamda sensor
wil'l not operate below
250 degrees centigrade,
before
that temperature, the system
will
operate
under
"Open
Loop"
(No
Control).
In order
to
speed up
the operation of
the Lambda sensor,
some are
pre-heated.
These
are
identified by
three or
four wires coming
f rom the
Lambda
sensor
instead
of one.
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