MOTO GUZZI 2003 V11 series Werkstatt-Handbuch Seite 141

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26 LAMBDA SENSOR
This sensor, also known as oxygen sensor, transfers the
information relating to the amount of oxygen present
inside the exhaust gases to the fuel supply control unit.
The electronic system can thus keep an optimal air-fuel
mixture ratio.
The Lambda sensor is used since to ensure a correct
catalytic muffler operation, this latter shall treat the
exhaust gases coming from a slightly "rich" combustion
(14.5 kg of air per kg of fuel instead of the chemically
correct ratio of 14.7 to 1).
The Lambda sensor emits a voltage signal that, whenever
the sensor itself is reached by the exhaust gases of
stoichiometric composition, will decrease a lot. The
electric voltage released by the sensor is high when the
gas mixture is slightly "rich" and decreases to zero when
the mixture becomes slightly "weaker".
The Lambda "A" probe has a ceramic body; its end is
positioned inside the expansion chamber so as to be
lapped by the gases, while the other end is in direct
contact with the atmosphere. The ceramic surface
(zirconia) is equipped with electrodes made of a very
thin foil of platinum, permeable to gases. The ceramic
surface starts conducting oxygen ions at a temperature
of about 300° C. If the oxygen amount starts differing at
the two sensor ends, an electric voltage is originated
between the two electrodes due to the special
composition of this material. This allows measuring the
difference in oxygen content between the exhaust gases
and the outer environment. When the air-fuel mixture
sent inside the combustion chamber is not correct, engine
gases of burnt material still contain some oxygen. It is
thus possible to adjust injection through the electronic
control unit in order to make the engine always run with
the optimal mixture.
The sensor takes its name from the lambda factor = (A/
F) / 14.5, so
lambda = 1 means mixture in stoichiometric ratio
lambda > 1 means weak mixture
lambda <1 means rich mixture.
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