Page 255 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey
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Catalytic Converter Functionality Diagnosis by Means of Temperature Measurements 23 7
For instance, when a throttle controlling the admission of a combustible mixture to the engine
is opened, the temperature of exhaust gas entering the converter can rise dramatically but,
because of thermal lags, the temperature of exhaust gas leaving the converter rises more
slowly. This can result in an indication of incorrect operation of a converter which is actually
operating efficiently.
Similar problems can occur during other modes of operation of the engine giving rise to
spurious or transient temperature differences which are detected as indicating inefficient
operation of the converter.
An additional problem for detecting correctly the efficiency of an exhaust gas catalytic
converter is a possible deterioration of a temperature sensor. The output of such a deteriorated
sensor must be corrected during the diagnosis procedure in order to avoid erroneous results.
Air Flow
--*
T
Characteristic
field
Load," "%Speed
Fig. 100 (from [I] p. 174)
As already discussed in the Introduction of this monograph, it is common nowadays to use
catalytic converters in exhaust systems that are heated during start-up of the engine in order to
