Importance

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Abstract

A catalyst deterioration detection device for an internal combustion engine, according to the present invention, includes a three-way catalyst mounted in an exhaust passage of the internal combustion engine and having an O.sub.2 storage capability and an air-fuel ratio sensor, mounted upstream of the three-way catalyst, for linearly detecting an air-fuel ratio. An air-fuel ratio feedback control unit, based on the output of the air-fuel ratio sensor, calculates a feedback correction amount consisting of a proportional term for bringing the air-fuel ratio to stoichiometry and an integral term for bringing an integrated value of an error between the air-fuel ratio and stoichiometry to zero. An O.sub.2 sensor, mounted downstream of the three-way catalyst, detects whether the air-fuel ratio is rich or lean. A catalyst deterioration determining unit determines deterioration of the three-way catalyst on the basis of the length of a response curve that the output of the O.sub.2 sensor describes during the time that air-fuel ratio feedback control is being performed by the air-fuel ratio feedback control unit. A response curve length calculation interrupting unit interrupts the calculation of the response curve length being performed by the catalyst deterioration determining unit for a predetermined length of time when the output of the air-fuel ratio sensor or the amount of change of the output has exceeded a preset value.

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First Claim