| 摘要 |
<p>PURPOSE: To prevent the diagnosis in a deactivated condition in which the conversion ratio is low by providing a deterioration diagnosis part of a catalytic device with a diagnosis inhibition judging part by which diagnosis is inhibited until the catalyst is activated. CONSTITUTION: An output signals S3, S4 of an upstream oxygen sensor of a catalytic device 2 and a downstream oxygen sensor thereof are input into a deterioration diagnosis part 11 respectively, and they are supplied to data sampling parts 14A, 14B through bypass filters 12A, 12B and low-pass filters 13A, 13B respectively. An outputs of the data sampling parts 14A, 14B are supplied to a correlation coefficient calculating part 16 for calculating the mutual correlation coefficients of the output signals of an air-fuel ratio sensors before and after the catalyst. By the calculation the deterioration index indicating the degree of deterioration of the catalytic device 2 is obtained by a deterioration index calculating part 17, and the final deterioration index is obtained by a final deterioration index calculating part 18 on the basis of both the deterioration index thus obtained and a correction value obtained by a correction value calculating part 30. Thereafter, until it is judged that the catalyst has been activated, the processing of a comparison part 20 and a judging part 21 is inhibited by a diagnosis inhibition judging part 19.</p> |
