Catalyst monitor using arc length ratio of pre- and post-catalyst sensor signals
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United States of America Patent
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May 4, 1999
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N/A
app pub date -
Jan 22, 1997
filing date -
Jan 22, 1997
priority date (Note) -
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Abstract
A method and system for monitoring the efficiency of a catalytic converter include determining a ratio of signal arc lengths from an upstream exhaust gas sensor and a downstream exhaust gas sensor which generate signals indicative of oxygen content in the exhaust upstream and downstream, respectively, relative to the converter. A controller processes the signals to determine the ratio of the arc length of the rear or downstream sensor signal to the arc length of the front or upstream sensor signal over a test period. The arc length is calculated by summing over the test period a series of incremental arc lengths for each incremental time interval in the test period. An incremental signal length may be calculated using the square root of the sum of the square of the change in value of a signal during an incremental time interval and the square of the duration of the incremental time interval. The ratio is indicative of the efficiency of the converter which may be compared with subsequently generated ratios to monitor converter efficiency over time.
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