| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To accurately detect the degradation of a downstream catalyst disposed downstream in a plurality of catalysts disposed along an exhaust passage while proper emission characteristics are maintained. <P>SOLUTION: An upstream catalyst 28 and the downstream catalyst 30 are disposed in series along the exhaust passage 14. An inter-catalyst oxygen sensor 34 is disposed between the upstream catalyst 28 and the downstream catalyst 30. An oxygen sensor 36 after the catalyst is disposed downstream the downstream catalyst 30. If the output of the inter-catalytic oxygen sensor 34 is inverted from rich to lean, an air-fuel ratio before the catalyst occurring on the upstream side from the upstream catalyst is inverted from lean to rich. Further, if the output of the inter-catalyst oxygen sensor 34 is inverted from lean to rich, in order to invert the air-fuel ratio before the catalyst from rich to lean, an active air-fuel ratio control is performed. The fault of the downstream catalyst 30 is judged based on the output of the sensor generated from the oxygen sensor 36 after the catalyst during the performance of the active air-fuel ratio control. <P>COPYRIGHT: (C)2004,JPO</p> |
