Page 135 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey
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Chapter 1.5
Nippon Denso Co.
The methods proposed by Nippon Denso Co. have been applied, except otherwise mentioned,
for an engine layout similar to that of fig. 40.
In JP2136538 (1990) a deceleration state of the engine is detected during which the fuel
supply to the engine is stopped. When the fie1 supply starts again, a clock measures the time
elapsed for the oxygen content of the exhaust gases downstream of the catalytic converter to
fall below a predetermined threshold. If this elapsed time is shorter than a predetermined one,
the catalytic converter is considered as degraded.
The methods of DE4101616 (1991) and US5154055 (1992) comprise the following steps:
1) measuring the aidfuel ratio of the exhaust gases upstream and downstream of the catalytic
converter by means of the upstream and downstream sensor
2) detecting a first delay time difference T, between the inversion time of an output of the
upstream air/fbel ration sensor and the inversion time of an output of the downstream
air/fuel ratio sensor (fig. 57) when a rotational speed of the engine is within a first
predetermined range and a load of the engine is within a second predetermined range
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