Page 195 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

NGK Spark Plug Co. 177

HI is compared with a predetermined mean converted rate of HC, CO and NO, to determine a
mean converted rate of the catalytic converter for HC, CO and NO, in the exhaust gases.
R2 is compared with a predetermined mean converted rate of NO, to determine a mean
converted rate of the catalytic converter for NO, in the exhaust gases.
I& is compared with a predetermined mean converted rate of HC and CO to determine a mean
converted rate of the catalytic converter for HC and CO in the exhaust gases.

The method of US5357750 (1994) allows a determination to be made of the conversion rate of
particular component gases, NO,, CO and HC, of the exhaust gas converted by the catalytic
converter and includes the steps of
1) producing a nearly linear diagram graphically relating the output of an air/f%el ratio detector
located downstream of the catalytic converter with a predetermined mean converted rate of
HC, CO and NO,
2) determining whether exhaust gas input to the catalytic converter is rich or lean in airhel
ratio, based on the output of an oxygen sensor located upstream of the catalytic converter
3) measuring the output amplitude of an airhe1 ratio detector located downstream of the
catalytic converter
4) using the diagram obtained in step 1, matching the amplitude obtained in step 3 with the
diagram obtained in step 1 and finding a corresponding converted rate from the diagram
based on the matching
5) determining that the converted rate obtained in step 4 is the converted rate of the NO,
component gas of the exhaust gas when the oxygen sensor located upstream of the catalytic
converter determines that the exhaust gas is lean
6) determining that the converted rate obtained in step 4 is the converted rate of either the HC
or CO component gases of the exhaust gas when the oxygen sensor located upstream of the
catalytic converter determines that the exhaust gas is rich.

Other methods proposed by NGK Spark Plug: .IPS196588 (1993).