| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a catalyst degradation diagnostic apparatus capable of accurately diagnosing a catalyst for degradation. <P>SOLUTION: This catalyst degradation diagnostic apparatus comprises an air-fuel ratio detection means on the upstream side of the catalyst, an oxygen concentration detection means on the downstream side of the catalyst, an oxygen amount calculation means calculating an oxygen amount released from the catalyst into an exhaust passage and an oxygen amount stored in the catalyst based on the detected air-fuel ratio and an oxygen concentration, a frequency defect determination means determining that the output frequency of the oxygen concentration detection means is abnormal when a difference between the calculated oxygen amount and the maximum oxygen amount calculated to date is equal to or higher than a first prescribed value and continuously setting on a frequency defect flag, and a catalyst degradation diagnostic means calculating the oxygen storage capacity of the catalyst by using the oxygen amount and, based on whether the frequency defect flag is on or not and the oxygen storage capacity, diagnosing the catalyst for degradation. <P>COPYRIGHT: (C)2006,JPO&NCIPI</p> |
