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 (14) of an internal combustion engine (1). The catalyst (56) is located in the exhaust passage (14). The catalyst (56) stores nitrogen oxides when the air fuel ratio of air-fuel mixture supplied to the combustion chamber (5) is lean and reduces and emits the stored nitrogen oxides when the air-fuel ratio is rich. An ECU (30) controls the air-fuel ratio of the air-fuel mixture to be rich when the nitrogen oxides stored in the catalyst (56) is reduced and emitted. The ECU (30) judges whether the engine operation is stable. The ECU (30) permits use of the rich spike controll only when the engine operation is stable.