| 摘要 |
An air-fuel ratio control system for an internal combustion engine having a first and second groups of cylinders and first and second catalytic converters arranged respectively in first and second exhaust systems extending from the respective cylinder groups, includes first and second upstream oxygen sensors upstream of the catalytic converters, and a single downstream oxygen sensor downstream of the catalytic converters. The air-fuel ratios of air-fuel mixtures supplied into the first and second cylinder groups are controlled by the use of first and second air-fuel ratio control amounts based on outputs from the respective first and second upstream oxygen sensors and the downstream oxygen sensor, when the engine is in a predetermined operating condition. The air-fuel ratio of an air-fuel mixture supplied into one of the first and second cylinder groups is controlled by the use of a third air-fuel ratio control amount based solely on an output from the downstream oxygen sensor, and the air-fuel ratio of an air-fuel mixture supplied into the other cylinder group by the use of a predetermined value, when the engine is in an operating condition other than the predetermined operating condition, whereby deterioration of the first or second catalytic converter is detected based on the downstream oxygen sensor output. |
