Importance

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Abstract

A device for determining the abnormal degree of deterioration of a catalyst of a catalytic converter arranged in an internal combustion engine exhaust system is disclosed. The device includes first and second air-fuel ratio sensors located upstream and downstream of the catalyst. The device determines a first purification ability based on readings of the sensors during a warmup stage of the catalyst, and a second purification ability after the warmup is completed. An overall purification ability of the catalyst is determined by combining the purification ability of the catalyst during warmup and the purification ability of the catalyst after warmup, where the weight of the purification ability during warmup is less than the purification ability after warmup in the overall purification ability. If the overall purification ability of the catalyst is less than a certain amount, then the device determines that the catalyst has deteriorated.

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First Claim