Method and apparatus for controlling sulfur poisoning recovery of a catalyst

摘要

In the state where an air-fuel ratio AF is equal to or lower than a reference air-fuel ratio AFr (AF≤AFr) ("YES" in step S204), when at least one of the condition that an upstream side exhaust gas temperature Texin of an exhaust gas control catalyst on the downstream (38a) side is higher than a high temperature determination reference temperature Tsin (Texin > Tsin) (step S206) and the condition that a downstream side exhaust gas temperature Texout of the exhaust gas control catalyst on the downstream side (38a) is higher than a high temperature determination reference temperature Tsout (Texout > Tsout) (step S208) is satisfied, a sulfur poisoning recovery computation is performed (step S210). The degree of recovery from sulfur poisoning can be thus obtained with high accuracy. Accordingly, a catalyst bed temperature increasing process and an air-fuel ratio decreasing process can be appropriately performed by the sulfur poisoning recovery control. As a result, heat degradation of the exhaust gas control catalyst on the downstream side (38a) is not promoted and reduction in fuel efficiency is not caused, even when a failure, e.g., degradation and clogging, occurs in the exhaust gas control catalyst on the upstream side (36a).