CAC Gasoline Engine Maintenance And Servicing Manual
91
6 zirconiumλ sensor is designed to detect the oxygen in exhaust emission
In endothermal engine, the combustion is produced by the reaction of hydrogen and oxygen and then
emits heat. Fuel is composed of hydrocarbons. It includes carbon atom and hydrogen atom which are
combined together by different modes (paraffin, olefine, aromatics).
The main products of the air and fuel combusting are carbon dioxide (CO
2
), vapor (H
2
O), carbon
monoxide (CO) and a small percent of unburned hydrocarbon (HC) and nitrogen oxide (NO
X
). The last two are
measured by ppm.
For the pollution problem, only carbon monoxide exists largely in the form of bulk.
Nitrogen oxides is composed of the oxidized mixture. The main ingredients are as following:
dinitrogen oxide, nitrogen monoside (NO), nitrogen dioxide
NO
X
is the traditional symbol for these oxide. NO covers over 95% of them.
In order to minimize pollution (CO、HC and NO
X
),
“λsensor” is installed into the system to detect the
oxygen content in exhaust emission.
The signal coming from the sensor is sent to ECU for adjusting the mixing ratio of air and fuel, ensuring
the catalytic converter work under the optimal condition.
The sensor is located in the first section of exhaust pipe, in front of the catalytic converter.
It is enclosed by ceramic zirconia body (1) with thin platinum plate at one end. The latter one is inserted
in a protecting boot and installed in a metallic body (3). The protective casing works for the further protection
and has the sensor in the exhaust manifold.
The outside of the ceramic body(b) is exposed to the exhaust emission and the inside (a) is exposed to
ambient atmosphere. The working principle of sensor is as following: When the temperature is over 300℃,the
ceramic material will be the conductor of ferric oxide. Under this condition, if the percentage content of the
oxygen in the two sides of sensor (a, b) are not the same, the voltage difference will occur in the two sides. The
difference of measured oxygen content in two ambient (at the side of air and at the side of exhaust) tells ECU
that the remainin oxygen content in the exhaust is not propriate for ensuring the combustion with no harmful
exhaust products produced
The ceramic material under 300℃ is non-linear, therefore the sensor doesn’t send the useful signal. ECU
has a special function, i.e. stop adjusting the mixture during engine warming (open loop operation).
the sensor is equipped with a heating unit (4) to reach the operation temperature as soon as possible.
When the current flows over the heating unit, it shortens the time for ceramic becoming the conductor of iron
and may have the sensor installed in the relatively rear area of exhaust pipe.
λsensor inspection:
Fig. 150 oxygen sensor
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