| 摘要 |
PROBLEM TO BE SOLVED: To lessen reduction in output of an engine when rich operation is performed. SOLUTION: Rich operation of first and second cylinders and that of third and fourth cylinders are performed at timings different from each other, so that the timing of the rich operation of the first and second cylinders do not coincide with that of the third and fourth cylinders. For example, when lean operation of a first cylinder group consisting of the first and second cylinders and that of a second cylinder group consisting of the third and fourth cylinders are performed, after the first group undergoes the rich operation in a predetermined short period of time so as to be returned to the lean operating state again, the second group undergoes the rich operation so as to be returned to the lean operating state again. Thereafter, the procedures described above are repeated in a certain cycle. COPYRIGHT: (C)2003,JPO
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