Page 235 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Other Methods 217

Pierburg GmbH & Co. KG

In the method of CB2177513 (1987) the following procedure is considered:
1) detecting the oxygen content of the exhaust gases upstream and downstream of the catalytic
converter by means of two oxygen sensors
2) increasing the amplitude of the engine airhe1 ratio oscillation around the stoichiometric
value, by applying a periodic signal whose frequency is much lower than that of the output
signal of the upstream sensor when this is hnctioning in normal operation. The periodic
signal can be an externally generated one or an electronically filtered signal of the upstream
sensor or the output signal of the downstream sensor
3) checking the amplitude of the output signal of the downstream sensor
4) judging that the catalytic converter is deteriorated when the detected amplitude of the signal
of the downstream sensor becomes higher than a predetermined threshold.

Bayerische Motoren Werke AG

In the method of DE3830515 (1990) the following steps are considered:
1) establishing stable operating conditions of the engine
2) detecting the oxygen content of the exhaust gases upstream and downstream of the catalytic
converter by means of two oxygen sensors
3) calculating averaged values in time for each of the two output signals
4) calculating the difference of the averaged oxygen contents detected from the two sensors
5) calculating the ratio I< of this difference to the averaged oxygen content vo2 detected
upstream of the catalytic converter

6) comparing this ratio It to a predetermined value to draw conclusions about the condition of
the catalytic converter