| 摘要 |
PROBLEM TO BE SOLVED: To effectively enforce a subsequent HC processing, suppressing exhaust amount of Nox without damaging output performance at the time of high load by controlling an air-fuel ratio so that oxygen storage amount of three way catalyst may be a preliminarily fixed target value in a prescribed high load operation area before the starting of HC adsorption of an HC adsorption material. SOLUTION: Whether a catalyst temperature Tc by a temperature sensor 12 detecting a catalyst temperature of HC adsorption catalyst 10 reaches a desorption temperature Tc1 or not is judged. At the time of Tc<Tc1, oxygen storage amount OS of three way catalyst 9 is estimated and calculated and next, a load state of an engine is decided by fuel injection amount or intake air amount. When an area is decided to be a high load operating area beyond a prescribed load area, equivalence ratio correction value is calculated based on target value and estimated arithmetic value of oxygen storage amount and next, this equivalence ratio correction value is reduced from a theoretical air fuel ratio and a target equivalence ratio is set. By repeating this control, oxygen storage amount of three way catalyst 9 is maintained to the target value and the air fuel ratio is controlled to a thin side at only this limit, at the time of high load. |
