Patent ID: 8186147

Claim:
A catalyst deterioration-determining device that determines deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine, for purifying exhaust gases, the catalyst having an oxygen storage capability for storing oxygen, comprising: a first oxygen concentration parameter sensor that detects an upstream oxygen concentration parameter indicative of an oxygen concentration in exhaust gases on an upstream side of the catalyst; a second oxygen concentration parameter sensor that detects a downstream oxygen concentration parameter indicative of an oxygen concentration in exhaust gases on a downstream side of the catalyst; control means for controlling exhaust gases flowing into the catalyst by switching the exhaust gases between an oxidation atmosphere and a reduction atmosphere; correction means for correcting the upstream oxygen concentration parameter and the downstream oxygen concentration parameter which are detected after the exhaust gases are switched by said control means, such that the upstream oxygen concentration parameter and the downstream oxygen concentration parameter which are detected after lapse of a predetermined time period coincide with each other; and deterioration determination means for determining deterioration of the catalyst based on results of comparison between the upstream oxygen concentration parameter and the downstream oxygen concentration parameter which are corrected.