| 摘要 |
PROBLEM TO BE SOLVED: To provide an air-fuel ratio controller precisely detecting degradation of a catalyst in an internal combustion engine. SOLUTION: For a plurality of groups of cylinders of a multi-cylinder internal combustion engine, the learning control of air-fuel ratio is effected during the feedback control of the air-fuel ratio, and the feedback control of air-fuel ratio for each group of cylinders is effected based on the result of learning of either group of cylinders and the output of an oxygen sensor for that group, on condition that the learning results have converged. Thus, by synchronizing the periods of air-fuel ratio values detected by the oxygen sensors for the groups of cylinders, diagnosis on degradation of a catalyst is made using the period of variation in the output of any of the oxygen sensors located upstream of the catalyst. Diagnosis is made with high accuracy by obtaining the results of diagnosis made by the oxygen sensors.
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