On-board diagnostic catalyst monitoring system

A method for determining the effectiveness of a catalyst having both first, relatively high oxidizable material provided to remove emissions from the exhaust of an internal combustion engine and a second, relatively low oxidizable material provided to remove emissions from such exhaust, such method comprising:

• generating a first signal indicative of an exhaust gas air fuel ratio relative to stoichiometry upstream of the converter, such first signal having first transitions when the first signal varies between a lean air-fuel ratio signal level and a rich air-fuel ratio signal level and having second transitions when the first signal varies between a rich air-fuel ratio signal level and a lean air-fuel ratio signal level;
• generating a second signal indicative of an exhaust gas air fuel ratio relative to stoichiometry downstream of the converter, such second signal having a first transition when the second signal varies between a lean air-fuel ratio signal level and a rich air-fuel ratio signal level and second transition when the second signal varies between a rich air-fuel ratio signal level and a lean air-fuel ratio signal level;
• determining said first time when the first signal has a first transitions from a lean to rich air fuel ratio relative stoichiometry;
• determining said second time when the second signal has a first transition from a lean to rich air fuel ratio relative stoichiometry;
• determining a catalyst operating efficiency based on the difference between the first and second times, such determining being independent of a time delay between the second transition of the first signal and the second transition of the second signal.

A method for determining the effectiveness of a catalyst having both first, relatively high oxidizable material provided to remove emissions from the exhaust of an internal combustion engine and a second, relatively low oxidizable material provided to remove emissions from such exhaust, such method comprising:

• measuring an upstream time history of a signal produced by an exhaust gas oxygen sensor upstream of the converter and a time history of an exhaust gas oxygen sensor disposed downstream of the converter, such time histories having first transitions when such time history varies between a lean air-fuel ratio signal level and a rich air-fuel ratio signal level and second transitions when such time history varies between a rich air-fuel ratio signal level and a lean air-fuel ratio signal level;
• determining a time delay between the upstream time history and the downstream time history during the first transitions;
• comparing the determined time delay with a reference time delay to determine the efficiency of the converter;
• determining the effectiveness of the converter from such comparison independent of the second transitions.

A system for determining the effectiveness of a catalyst having both first, relatively high oxidizable material provided to remove emissions from the exhaust of an internal combustion engine and a second, relatively low oxidizable material provided to remove emissions from such exhaust, such system comprising:

• a first sensor for generating a first signal indicative of an exhaust gas air fuel ratio relative to stoichiometry upstream of the converter, such first signal having first transitions when the first signal varies between a lean air-fuel ratio signal level and a rich air-fuel ratio signal level and having second transitions when the first signal varies between a rich air-fuel ratio signal level and a lean air-fuel ratio signal level;
• a second sensor for generating a second signal indicative of an exhaust gas air fuel ratio relative to stoichiometry downstream of the converter, such second signal having a first transition when the second signal varies between a lean air-fuel ratio signal level and a rich air-fuel ratio signal level and second transition when the second signal varies between a rich air-fuel ratio signal level and a lean air-fuel ratio signal level;
• a processors for determining a first time when the first signal has a first transitions from a lean to rich air fuel ratio relative stoichiometry, for determining a second time when the second signal has a first transitions from a lean to rich air fuel ratio relative stoichiometry and for determining a catalyst operating efficiency based on the difference between the first and second times, such determining being independent of a time delay between the second transition of the first signal and the second transition of the second signal.