DEVICE FOR DETERMINING IMBALANCE IN AIR-FUEL RATIO BETWEEN CYLINDERS FOR INTERNAL COMBUSTION ENGINE

摘要

A device for determining the imbalance in air-fuel ratio between cylinders (a determination device) finds, on the basis of the output value from an air-fuel ratio sensor (67), an air-fuel ratio fluctuation index amount the absolute value of which becomes larger as the fluctuation of the air-fuel ratio of exhaust gas passing a position at which the air-fuel ratio sensor is disposed becomes larger, and further finds an imbalance determination parameter which becomes larger as the absolute value of the air-fuel ratio fluctuation index amount becomes larger. The determination device finds the mean value of air-fuel ratios of the exhaust gas in a period during which the imbalance determination parameter is found, and finds an imbalance determination threshold value which becomes smaller as the mean value of air-fuel ratios becomes closer to the theoretical air-fuel ratio. When the imbalance determination parameter is larger than the imbalance determination threshold value, the determination device determines that a state of imbalance in air-fuel ratio between cylinders occurs.