CATALYST DEGRADATION DETERMINATION DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

A catalyst deterioration determination device for determining deterioration of an exhaust gas purging catalyst arranged in an exhaust passage of an internal combustion engine is disclosed. The determination device forcibly changes an air-fuel ratio of an air-fuel mixture, calculates an oxygen occlusion amount of the catalyst based on an oxygen concentration of the exhaust gas at a downstream side of the catalyst that varies after the forcible changing of the air-fuel ratio, and performs deterioration determination on the catalyst based on the calculated oxygen occlusion amount. The engine includes a function for performing increasing correction on a fuel injection amount so that the air-fuel ratio of the air-fuel mixture becomes richer than the stoichometric air-fuel ratio. The determination device includes a prohibition unit which sets a prohibition period when calculating the oxygen occlusion amount after the increasing correction ends to prohibit calculation of the oxygen occlusion amount immediately after the increasing correction ends. The prohibition unit variably sets the prohibition period to be longer as a total increased amount of fuel during the increasing correction increases.