Apparatus for judging catalyst of catalytic converter in internal

Abstract

An apparatus for judging of a catalyst of a catalytic converter provided in an exhaust system of an internal combustion engine so as to purify an exhaust gas generated from the internal combustion engine. The apparatus is arranged to be responsive to the output signal of a gas concentration sensor provided downstream of the converter to detect a concentration of a specified component of the exhaust gas. Included in the apparatus is a judgment unit responsive to the output signal therefrom so as to judge the catalyst of the catalytic converter on the basis of the output signal therefrom. The judgment unit compares a predetermined judgment threshold with an amplitude of the output signal therefrom to detect, on the basis of the comparison result, whether the catalyst of the converter is in a deteriorated state. The judgment unit relatively corrects the predetermined judgment threshold with respect to the output signal on the basis of the difference between the output signal therefrom under the condition that an air-fuel ratio is in a predetermined rich state and the output signal therefrom under the condition that the air-fuel ratio is in a predetermined lean state. This arrangement allows accurate detection of the deterioration of the catalyst irrespective of the deterioration of the gas concentration sensor itself.