| 摘要 |
<P>PROBLEM TO BE SOLVED: To execute a catalyst degradation diagnosis of a bypass catalyst converter 18 without switching a flow passage selector valve 4. <P>SOLUTION: Upstream side main passages 2 are connected to cylinders 1 to form one downstream side main passage 7 through the medium of an intermediate main passage 3. A main catalyst 8 is interposed on the way of the downstream side main passage 7. An upstream side bypass passages 11 are branched off from each of the upstream side main passages 2 as a bypass flow passage and eventually made to be one downstream side bypass passage 16, which contains a bypass catalyst 18 therein. An exhaust reflux passage 20 is branched off from the bypass catalyst 18 downstream region. A flow passage selector valve 4 is closed only in a cold time to switch an exhaust flow. If exhaust reflux is executed even if the flow passage selector valve 4 is opened, exhaust gas is circulated through the bypass catalyst 18. The catalytic deterioration diagnosis can be performed from detection signals of air-fuel ratio sensors 21, 22 on the upstream side and downstream side. <P>COPYRIGHT: (C)2007,JPO&INPIT |
