| 摘要 |
<p>PROBLEM TO BE SOLVED: To accurately judge deterioration of a catalyst based on the outputs of an O2 sensor on the downstream side of the catalyst regardless of the air-fuel ratio fluctuation range of a catalyst-containing gas in an internal combustion engine which performs feedback control of the air-fuel ratio based on outputs of an A/F sensor provided on the upstream side of the catalyst. SOLUTION: When an O2 sensor output locus length LVOS or an O2 sensor-to- A/F sensor output locus length ratio LVOS/LVAF is plotted on a y-axis and an A/F sensor output locus length LVAF is plotted on an x-axis, a threshold for discriminating between a normal catalyst and deteriorated ones can be set within a specific range of the LVAF. When the locus length LVAF is within such a predetermined range, a determination process based on the locus length LVOS or the locus length ratio LVOS/LVAF is performed. Also, a deterioration criterion is varied depending on the locus length LVAF.</p> |
