Page 242 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

224 Methods for Monitoring and Diagnosing the EWciency of Catalytic Converters

k, : engine air/fuel ratio ricMean adjustment parameter
4) judging engine air/fiel ratio rich/lean adjusting parameters, to determine whether the aidfuel
ratio is stoihiometric, rich or lean
5) determining that the converter is deteriorated when the actual oxygen content of the exhaust
gases downstream of the catalytic converter does not exist within a range of the virtual
oxygen content set in accordance with a state of the engine aidfuel ratio (step 3)

The method of DE19654693 (1997) comprises the following steps:
1) checking if the engine cooling temperature is higher than a predetermined threshold
2) checking if the temperature of the exhaust gas is higher than a predetermined threshold, and
if both conditions of step 1 and 2 are fulfilled then
3) feedback-controlling the engine aidfuel ratio based on the output signal of the upstream
oxygen sensor
4) measuring the oxygen content of the exhaust gas upstream and downstream of the catalytic
converter by means of the two oxygen sensors
5) calculating a first ratio of the measured output signals of the two sensors during a rich
engine aidfuel condition
6) calculating a second ratio of the measured output signals of the two sensors during a lean
engine aidfuel condition
7) calculating a first sum of first ratios during a predetermined time period
8) calculating a second sum of second ratios during the predetermined time period
9) comparing the first sum of ratios with a first predetermined reference value
10) comparing the second sum of ratios with a second predetermined reference value
1 1) determining the condition of the catalytic converter by means of the results of steps 9 to 10

0 Osaka Gas Co. Ltd

In the method of JP5010181 (1993), a catalytic converter is installed in the exhaust system of
a methane engine. A first oxygen sensor for methane activation is installed upstream of the
converter and a second oxygen sensor for methane activation or methane low activation is
installed downstream of the converter. During a degraded state of the converter, for each pair
of output signals of the two sensors, an output value of the output signal of the upstream
sensor is stored as a deterioration reference value. This reference value is compared to the
output signal of the upstream sensor during testing, and the converter is considered as
deteriorated when the output signal value is higher than the reference one.

In the method of JP5018231 (1993), a rhodium catalytic converter is installed in the exhaust
system of a methane engine. A first oxygen sensor is installed upstream of the converter and a
second oxygen sensor is installed downstream of the converter. The deterioration of the