Page 52 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

34 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

where the existing oxygen content can be measured, for example, in grams of oxygen per gram
of intake mixture. The sloichiomelric oxygen content is what is theoretically
necessary for complete combustion of the fuel. In a precisely correct intake mixture, h is equal
to one. The stoichiometric engine aidfuel ratio for petrol engines is equal to 14.7. When h is
less than one in the intake mixture (rich air/fiel mixture), carbon monoxide (CO) and
hydrocarbons (HC) appear in the exhaust gases downstream of the converter. When h is more
than one (lean aidfuel mixture) nitrogen oxide (NO,) appears.

In the patent literature different types of oxygen sensors are used for monitoring purposes like
EGO (Exhaust Gas Oxygen) sensors or UEGO (Universal Exhaust Gas Oxygen) sensors or
HEGO (Heated Exhaust Gas Oxygen) sensors.

Air Flow
---+
+

Fig. 12 (from [9], p. 22)

Before examining in detail the diagnosing methods that use h or oxygen sensors, it is
worthwhile to explain the operation principles of these sensors as described in [l].