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6 SENSORS AND ACTUATORS

Figure 6.19
EGO Mounting and
Structure

FPO

Because the exhaust con- The quantity of oxygen in the exhaust gas is represented by the oxygen
tains fewer oxygen ions partial pressure. Basically, this partial pressure is that proportion of the total
than air, the “air” elec- exhaust gas pressure (nearly at atmospheric pressure) that is due to the
trode becomes negative quantity of oxygen. The exhaust gas oxygen partial pressure for a rich mixture
with respect to the varies over the range of 10 –16 to 10 –32 of atmospheric pressure. The oxygen
–2
“exhaust” electrode. partial pressure for a lean mixture is roughly 10 atmosphere. Consequently,
for a rich mixture there is a relatively low oxygen concentration in the exhaust
and a higher EGO sensor output. Correspondingly, for a lean mixture the
exhaust gas oxygen concentration is relatively high (meaning that the
difference between exhaust gas and atmospheric oxygen concentrations is
lower), resulting in a relatively low EGO sensor output voltage. For a fully
warmed EGO sensor the output voltage is about 1 volt for a rich mixture and
about .1 volt for a lean mixture.

210 UNDERSTANDING AUTOMOTIVE ELECTRONICS