| 摘要 |
PROBLEM TO BE SOLVED: To solve such a problem that an auxiliary control constant for controlling a feedback correction coefficient is lowered to a lower limit value when a sub oxygen sensor on a downstream side of a catalyst of an exhaust system outputs a signal showing that an air-fuel ratio is rich, the feedback correction coefficient is excessively corrected and an inside of the catalyst becomes a lean atmosphere, and thereby sometimes nitrogen oxide is unexpectedly exhausted in a large amount. SOLUTION: A main oxygen sensor is provided on a catalyst upstream side of the exhaust system, and the sub oxygen sensor is provided on the catalyst downstream side. The feedback correction coefficient is increased or decreased based on a signal from the main oxygen sensor, and the air-fuel ratio of an air-fuel mixture is feedback-controlled. The auxiliary control constant used for increasing or decreasing the feedback correction coefficient is controlled based on an output signal from the sub oxygen sensor. The air-fuel ratio is detected to be rich based on the output signal from the sub oxygen sensor. The fuel is increased for correction when the air-fuel ratio is rich and inside of the catalyst is in the lean atmosphere. COPYRIGHT: (C)2004,JPO
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