Patent ID: 6637195
Filing Date: 2003-10-28
Classification: F02D

Abstract:
An engine exhaust purifying apparatus comprising:an air flow sensor arranged to sense an engine intake air amount; a catalyst disposed in an engine exhaust passage; an upstream exhaust sensor disposed in the engine exhaust passage on an upstream side of the catalyst, and arranged to sense an upstream exhaust condition representing an air-fuel ratio of an inflowing exhaust gas mixture flowing into the catalyst; a downstream exhaust sensor disposed on a downstream side of the catalyst and arranged to sense a downstream exhaust condition representing an air-fuel ratio of an outflowing exhaust gas mixture flowing out of the catalyst; and a controller configured; to compute an estimated oxygen storage amount of the catalyst in accordance with the air-fuel ratio of the inflowing exhaust gas mixture and the engine intake air amount; to control an air-fuel ratio of the engine in accordance with the estimated oxygen storage amount so as to bring an actual oxygen storage amount of the catalyst to a desired value; to correct the estimated oxygen storage amount to reduce an error in computing the estimated oxygen storage amount when the downstream exhaust condition sensed by the downstream exhaust sensor becomes equal to a predetermined threshold; and to modify the threshold in accordance with the intake air amount.