Patent ID: 8327618

Claim:
A catalyst deterioration determination device for determining deterioration of an exhaust gas purging catalyst arranged in an exhaust passage of an internal combustion engine, the determination device comprising: An Electronic Control Unit with a programmable logic that is configured to: forcibly changes change an air-fuel ratio of an air-fuel mixture, calculate 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 perform deterioration determination on the catalyst based on the calculated oxygen occlusion amount, with the engine including 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 stoichiometric air-fuel ratio, set 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, and variably set the prohibition period to be longer as a total increased amount of fuel during the increasing correction increases.