Patent ID: 6263667
Filing Date: 2001-07-24
Classification: B01D,F01N,F02D,Y02T

Abstract:
An exhaust gas purification device for an engine comprising:a NO.sub.X occluding and reducing catalyst disposed in the exhaust gas passage of an internal combustion engine and absorbing NO.sub.X in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the catalyst is at a lean air-fuel ratio and releasing and reducing the absorbed NO.sub.X when the air-fuel ratio of the exhaust gas flowing into the catalyst is at a stoichiometric or a rich air-fuel ratio;an air-fuel ratio sensor disposed in the exhaust gas passage downstream of the catalyst and detecting the air-fuel ratio of the exhaust gas flowing out from the catalyst;rich spike means for carrying out a rich spike operation for changing the air-fuel ratio of the exhaust gas flowing into the catalyst from a lean air-fuel ratio to a rich air-fuel ratio and, after maintaining the rich air-fuel ratio for a predetermined rich spike period, from the rich air-fuel ratio to a lean air-fuel ratio;evaluating means for evaluating the degree of deterioration of the catalyst based on an actual rich spike time and a reference rich spike time, wherein the actual rich spike time is defined by the time lapsed from the time where the air-fuel ratio of the exhaust gas flowing out from the catalyst becomes stoichiometric to the time where the air-fuel ratio of the exhaust gas flowing out from the catalyst becomes lower than a stoichiometric air-fuel ratio after the rich spike operation starts and the reference rich spike time is defined by the time required for a new NO.sub.X occluding and reducing catalyst to release the absorbed NO.sub.X.