Deterioration determination apparatus for exhaust emission control device of internal combustion engine

A deterioration determination apparatus for an exhaust emission control device used for an internal combustion engine, the exhaust emission control device for the internal combustion engine comprising a first catalyst, arranged in an exhaust passage of the internal combustion engine and conducting a catalytic action in relation to exhaust gas passed through the exhaust passage, and a second catalyst, arranged in a downstream of the first catalyst in the exhaust passage of the internal combustion engine and conducting a catalytic action in relation to the exhaust gas passed through the exhaust passage, the deterioration determination apparatus comprising:

• a first sensor, arranged between the first catalyst and the second catalyst in the exhaust passage of the internal combustion engine and detecting information about an air-fuel ratio of the exhaust gas passed through the exhaust passage;
• a second sensor, arranged in a downstream of the second catalyst in the exhaust passage of the internal combustion engine and detecting information about an air-fuel ratio of the exhaust gas passed through the exhaust passage;
• control means for feedback controlling an air-fuel ratio of mixture gas supplied to the internal combustion engine, based on the information detected by the second sensor;
• measurement means for measuring an amplitude of the air-fuel ratio of the exhaust gas from the information detected by the first sensor while the control means is conducting feedback control;
• and
• determination means for determining whether the second catalyst deteriorates based on the amplitude of the air-fuel ratio measured by the measurement means.