| 摘要 |
An individual exhaust passage is provided independently for each cylinder group in an internal combustion engine having a plurality of cylinder groups each having a plurality of cylinders. A first catalyst is provided in each of the individual exhaust passages. Downstream of those first catalysts, the individual exhaust passages merge to form a common exhaust passage in which a second catalyst is provided. When control of the internal combustion engine is switched from cylinder group-specific control to stoichiometric control, an air-fuel ratio control portion makes the air-fuel ratio of a cylinder group in which the air-fuel ratio was made rich by cylinder group-specific control lean for a predetermined period of time, and makes the air-fuel ratio of a cylinder group in which the air-fuel ratio was made lean by the cylinder group-specific control rich for a predetermined period of time.
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