ELECTRONIC CONTROL SYSTEM
- Oxygen Sensor (02 Sensor
)
2
. TITANIA
ELEMENT TYP
E
This oxygen sensor consists of a semiconductor
element made of titanium dioxide
(Ti02, which
is, like Zr02, a kind of ceramic)
. This sensor uses
a thick film type titania element formed on the
front end of a laminated substrate to detect the
oxygen concentration in the exhaust gas
.
Protective
cover
OHP 2
7
OPERATION
The properties of titania are such that its
resistance changes in accordance with the
oxygen concentration of the exhaust gas
. This
resistance changes abruptly at the boundary
between a lean and a rich theoretical air-fuel
ratio, as shown in the following graph
. The
resistance of titania also changes greatly in
response to changes in temperature
. A heater is
therefore built into the laminated substrate to
keep the temperature of the element constant
.
x
T
Theoretical
8i air-fuel rati
o
~
U
V
No air
into
exhaust gass
Much air
int
o
exhaustgas
s
Richer a Air-fuel
c*
Leaner
(no air) ratio
(
much air)
OHP 27
This sensor is connected to the Engine ECU, as
shown in the following circuit diagram
. A 1V
potential is supplied at all times to the OX ±i
terminal by the Engine ECU
. The Engine ECU has
a built-in comparator* which compares the
voltage drop at the OX terminal (due to the
change in resistance of the titania) to a
reference voltage (0
.45 V)
. If the result shows
that the OX voltage is greater than 0
.45 V (that
is, if the oxygen sensor resistance is low), the
Engine ECU judges that the air-fuel ratio is rich
.
If the OX voltage is lower than 0
.45 V (oxygen
sensor resistance high), it judges that the air-
fuel ratio is lean
.
*See page 37 for details on the comparator
.
ELECTRICAL CIRCUITRY
Engine EC
U
Check
connector
OX~
+
OX
OHP 2
7
1
V
0
.45
V
32
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