| 摘要 |
<P>PROBLEM TO BE SOLVED: To properly diagnose deterioration of an exhaust gas purification catalyst, even when a catalyst downstream-side exhaust gas sensor is deteriorated, in a deterioration diagnosis device for the exhaust gas purification catalyst. <P>SOLUTION: The number of times in which an output value of a downstream-side exhaust gas sensor 64 exceeds a downstream-side rich/lean determination level in a prescribed period of time is calculated as an inversion frequency Nr of the downstream-side exhaust gas sensor while controlling an internal combustion engine 2 so that an output value of an upstream-side exhaust gas sensor 62 for the catalyst is modulated by a continuous wave to rich/lean. A frequency ratio Nr/Nf is calculated on the basis of the inversion frequency Nr and an inversion frequency Nf of the upstream-side exhaust gas sensor in the prescribed period of time. A catalyst deterioration determination unit 76 is provided, for determining that the exhaust gas purification catalyst is deteriorated when the frequency ratio Nr/Nf is larger than a preset deterioration determination prescribed value. A modulation degree operation unit 78 is provided, for operating a modulation degree of the output value of the upstream-side exhaust gas sensor toward an expansion direction when a sensor deterioration determination unit 74 determines the deterioration of the downstream-side exhaust gas sensor. <P>COPYRIGHT: (C)2012,JPO&INPIT |
