Exhaust purification apparatus and method for internal combustion engines

摘要

An exhaust purification apparatus for reducing nitrogen oxides in the exhaust gas emitted from an exhaust passage of an internal combustion engine. The catalyst is located in the exhaust passage. The catalyst occludes nitrogen oxides when the air fuel ratio of air-fuel mixture supplied to the combustion chamber is lean and reduces and emits the stored nitrogen oxides when the air-fuel ratio is rich. An ECU controls the air-fuel ratio of the air-fuel mixture to be rich when the nitrogen oxides stored in the catalyst is reduced and emitted. The ECU judges whether the engine operation is stable. The ECU permits use of the rich spike control only when the engine operation is stable.