| 摘要 |
<P>PROBLEM TO BE SOLVED: To accurately determine whether catalyst is deteriorated or not irrespective of a flow rate of exhaust gas. <P>SOLUTION: Whether the exhaust gas purifying catalyst 5 arranged in the gas exhaust passage 3 of an engine 1 is deteriorated or not, is determined by detecting reduction of O<SB>2</SB>storage function of the catalyst. When detecting the deterioration, exhaust gas having a rich air-fuel ratio and exhaust gas having a lean air-fuel ratio are alternately supplied to the catalyst to obtain an amount of oxygen occlusion of the catalyst based on timing at which the air-fuel ratio of the exhaust gas passing through the catalyst after switching the air-fuel ratios is changed by following the air-fuel ratio of flowing-in exhaust gas and detect reduction of the O<SB>2</SB>storage function. At this time, the air-fuel ratio of the exhaust gas having the rich air-fuel ratio and the exhaust gas having the lean air-fuel ratio is set to approach a theoretical air-fuel ratio, the larger the flow rate of exhaust is, to prevent inferred error of amount of oxygen occlusion occurring when flow rate of exhaust gas is large, and to determine the deterioration of the catalyst accurately irrespective of the flow rate of exhaust gas. <P>COPYRIGHT: (C)2007,JPO&INPIT |
