Page 143 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Nippon Denso Co. 125

1) measuring the airhiel ratio upstream and downstream of a catalytic converter by means of
two sensors with different responsiveness. The responsiveness of the downstream sensor is
lower than the responsiveness of the upstream sensor by a range from 20% exclusive to
100% inclusive
2) forming the locus ratio /A of the locus lengths I, of the output wave forms of the two
sensors

where V(0 is the output voltage of a sensor, /o is the time at which a period of this wave
form begins and tN is the time at which a period of this wave form ends
3) detecting the degradation of the catalytic converter when the locus ratio is out of a
predetermined range.
The ratio of opening area of the air holes of the downstream sensor to the opening area of the
air holes of the upstream sensor is an additional parameter for detecting the degradation of the
catalytic converter.

The method of JP8246854 (1996) also uses a locus ratio of the output signals of the upstream
and downstream sensor to assess the efficiency of the catalytic converter. The locus ratio is
based on the frequencies of the two signals.

The method of JP7103039 (1995) comprises the following steps:
1) feedback-controlling the engine airhel ratio based on the output signal of the upstream
oxygen sensor, to continuously fluctuate the air/fuel ratio of the exhaust gas introduced in
the catalytic converter at a specific amplitude and period
2) correcting either the amplitude or the period of the aidfuel ratio fluctuation of the exhaust
gas introduced in the catalytic converter by increasing its value
3) detecting the aidfuel ratio of the exhaust gases by means of the downstream sensor. When
the output signal of the downstream sensor does not fluctuate despite the increase of either
the amplitude or the period of the aidfuel ratio fluctuation of the exhaust gas introduced in
the catalytic converter, then the increase range of either the amplitude or period of the
fluctuation is hrther increased till the downstream output signal starts fluctuating
4) assessing the efficiency of the catalytic converter fiom the necessary increase of either the
amplitude or period of the aidfuel ratio fluctuation of the exhaust gas introduced in the
catalytic converter till the downstream output signal starts fluctuating.

The method of US5528898 (1996) comprises the following steps: