Page 231 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Chapter I. 15

Fuji Heavy Industries Ltd.

The method of JP3281960 (1991) diagnoses the deterioration of a catalytic converter in a
state that an aidfuel ratio is stabilized. This is achieved by setting a delaying of the execution
of the diagnosis when engine operating conditions are judged to be in a predetermined range
for diagnosing the condition of the converter. The assessment of the condition of the converter
is realized by comparing the signals of the upstream and the downstream sensor.

In the detection method of USS337556 (1994) the following steps are considered:
I ) establishing certain engine operating conditions
2) detecting a first air/fuel ratio variation upstream of the catalytic converter by means of the
upstream sensor
3) detecting a second aidfuel ratio variation downstream of the catalytic converter by means of
the downstream sensor
4) setting a first upper and a lower slice level of the upstream aidfuel ratio sensor in
accordance with each engine operating condition. Upper (lower) slice level is a predefined
value being lower (higher) than the maximum (minimum) value of the sensor output signal
for each operating condition and it always cuts the sensor output signal during deterioration
detection
5) producing a first number signal from the number of intersections of the output of the
upstream aidfuel ration sensor with the first slice levels
6) setting a second upper and a lower slice level of the downstream air/f%el ratio sensor in
accordance with each engine operating condition
7) producing a second number signal from the number of intersections (cuts) of the output of
the downstream air/f%el ratio sensor with the second slice levels

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