| 摘要 |
<p>PURPOSE:To fully exhibit purification ability of individual one in a plural number of arranged catalyst and accurately detect deterioration of these catalyst. CONSTITUTION:An air-fuel ratio feedback correction coefficient is set based on an air-fuel ratio detected by first and second oxygen sensors 16a, 16b arranged on flowing-in side and flowing-out side of a first catalyst 15a interposed on the top stream among a plural number of catalyst 15a to 15c and deterioration dianosis of the catalyst 15a-15c is performed by comparing the lean/rich switching times for the air-fuel ratio detected by the oxygen sensor 16c arranged on the discharge side of a third catalyst 15c, with that for the air-fuel ratio detected by the first oxygen sensor 16a. Stable air-fuel controllability can be secured, since the air-fuel ratio feedback correction coefficient is set based on the oxygen storage ability of one catalyst. The deterioration diagnosis of the catalyst is also accurately performed.</p> |
