Patent ID: 6751950
Filing Date: 2004-06-22
Classification: F01N,F02D

Abstract:
An emission control apparatus for engine, comprising a fuel injection valve for the supply of fuel to the engine, a first air-fuel ratio detecting means for detecting an air-fuel ratio of exhaust gas, an upstream-side catalytic converter for purifying hazardous components contained in the exhaust gas, a second air-fuel ratio detecting means for detecting an air-fuel ratio of the exhaust gas, and a downstream-side catalytic converter for purifying the hazardous components contained in the exhaust gas, the first air-fuel ratio detecting means, the upstream-side catalytic converter, the second air-fuel ratio detecting means, and the downstream-side catalytic converter being disposed in an exhaust passage of the engine successively from an upstream side of the exhaust passage, characterized by further comprising:a fuel supply stop means for stopping the supply of fuel injected by the fuel injection valve during operation of the engine; a first occluded oxygen quantity estimating means for estimating a total amount of oxygen occluded by the upstream-side catalyst and the downstream-side catalyst; a first air-fuel ratio enriching means for enriching the air-fuel ratio of the exhaust gas when a return is made from the state in which the supply of fuel is stopped by the fuel supply stop means; and a second air-fuel ratio enriching means which, upon lapse of a predetermined period after execution of the enriching operation of the first air-fuel ratio enriching means, sets the air-fuel ratio of the exhaust gas to a rich ratio smaller than the degree of richness set by the first air-fuel ratio enriching means, wherein the air-fuel ratio enriching operation of the second air-fuel ratio enriching means is stopped when the total amount of oxygen occluded in the upstream-side catalyst and the downstream-side catalyst, which is estimated by the first occluded oxygen quantity estimating means, has become smaller than a predetermined value.