Patent ID: 7861514
Filing Date: 2011-01-04
Classification: F01N,Y02T

Abstract:
1. A method for detecting deterioration of a catalyst, comprising steps of: alternately supplying exhaust gas of a lean air/fuel ratio and exhaust gas of a rich air/fuel ratio to the catalyst; varying the air/fuel ratio of the lean air/fuel ratio exhaust gas and the air/fuel ratio of the rich air/fuel ratio exhaust gas thus alternately supplied to the catalyst as a function of the exhaust gas flow amount supplied to the catalyst, wherein the air/fuel ratio of the supplied exhaust gas is brought closer to the stoichiometric air/fuel ratio when the exhaust gas flow amount supplied to the catalyst is great, as compared to when the exhaust gas flow amount supplied to the catalyst is small; and deciding upon the degree of deterioration of the catalyst, based upon at least one of the air/fuel ratio change time period from the initiation of supply of lean air/fuel ratio exhaust gas to the catalyst until the air/fuel ratio of the exhaust gas on the catalyst downstream side changes over to a lean air/fuel ratio, and the air/fuel ratio change time period from the initiation of supply of rich air/fuel ratio exhaust gas to the catalyst until the air/fuel ratio of the exhaust gas on the catalyst downstream side changes over to a rich air/fuel ratio, wherein the lean air/fuel ratio and the rich air/fuel ratio of the exhaust gas which flows into the catalyst are adjusted so that the length of the section of the catalyst over which oxygen is absorbed and emitted by the catalyst is kept substantially constant throughout the entirety of deciding upon the degree of deterioration.