| 摘要 |
<p>PROBLEM TO BE SOLVED: To surely and accurately diagnose deterioration of a catalyst, corresponding to exhaust gas controlled at a higher purification level. SOLUTION: When acquisition of data for diagnosis is unfinished and a diagnostic allowing condition is formed and a diagnostic interrupt condition is not formed, data of output voltage FVO2 of an FO2 sensor is stored (S1 to S4) for every execution of routines. Exhaust gas attaining delay time TFRCAT required for exhaust gas passing the FO2 sensor on the upstream side of a catalytic converter to reach an RO2 sensor on the downstream side of the catalytic converter is determined (S5), based in intake air quantity Q. The absolute value of the difference of output voltage of the FO2 sensor and the output voltage of the RO2 sensor for the same exhaust gas is determined based on he exhaust gas reaching delay time TFRCAT, and an integrated value SUMDER of tained by interacting the absolute value of the different of the output voltage is updates (S6, S7). The integration is continued (S8) by prescribed diagnostic time. By comparing the integrated valle with a decision threshold and deciding deterioration of the catalyst after the integration is completed, deterioration of the catalyst is diagnosed surely and accurately.</p> |
