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AssigneeHitachi, Ltd.
InventorsEisaku Fukuchi, Akihito Numata, Kenichi Kotabe, Heikichi Kamoshida, Kenji Mizushima
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In an apparatus for diagnosing an exhaust gas purifying device, a catalyst deterioration level detector 104 detects the deterioration level of a catalyst from a relationship between a catalyst-upstream air-fuel-ratio detector 101 and a catalyst-downstream air-fuel-ratio detector 102. A catalyst-deterioration-level correction section 111 corrects the catalyst deterioration level detected by the catalyst deterioration level detector 104 based on a falling response ratio representing the ratio between a falling response index of the catalyst-upstream air-fuel-ratio detector 101 and a falling response index of the catalyst-downstream air-fuel-ratio detector 102 or based on a rising response ratio representing the ratio between a rising response index of the catalyst-upstream air-fuel-ratio detector 101 and a rising response index of the catalyst-downstream air-fuel-ratio detector 102. A catalyst deterioration judgment section 112 determines that the catalyst is deteriorated from information provided by the catalyst-deterioration-level correction section 111. This allows any deteriorated catalyst to be precisely detected even if an air-fuel ratio sensor downstream of the catalyst is degraded in terms of rising response.
An apparatus for diagnosing an exhaust gas purifying device used in an internal combustion engine which provides an air-fuel ratio control unit that detects the air-fuel ratio of an exhaust gas of the internal combustion engine and regulates a fuel injection amount so as to maintain the air-fuel ratio of the exhaust gas at a predetermined value, the apparatus comprising:
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