| 摘要 |
<p>PURPOSE:To heighten the measuring-computing accuracy of the degradation judging parameter of a specific catalyst element, that is, the diagnostic accuracy of degradation judgment by obtaining the purification coefficient of the specific catalyst element from the respective residual purification coefficients of residual catalyst elements excluding the specific catalyst element to diagnose the degraded state of the specific catalyst element. CONSTITUTION:In an internal combustion engine 2 provided with an exhaust emission control device 8 with plural catalyst elements disposed at an exhaust passage 6, in regular succession from the upper reaches, a diagnosis device for the exhaust emission control device 8 is provided, and its control means 22 obtains the total purification coefficient Z of the exhaust emission control device 8 from the detection signals of a first and a third O2 sensors 16, 20 and obtains the second purification coefficient Y of the second catalyst element 14 from the detection signals of the second and third O2 sensors 18, 20 so as to obtain the first purification coefficient X of the first catalyst element 12 from the purification coefficients Z, Y. The first purification coefficient X of the first catalyst element 12 is compared with the preset reference value K to judge the degraded state of the first catalyst element 12. In the case of X>=K, the first catalyst element 12 is diagnosed to be degraded, and an alarm lamp is lighted.</p> |
