EXHAUST GAS CONTROL APPARATUS FOR INTERNAL COMBUSTION ENGINE

摘要

According to the present invention, a ternary catalyst (20) and an NOx storage catalyst (22) are disposed in an engine exhaust passage. In a pre-established low-load operation area of the engine, combustion is performed with a lean base air-fuel ratio in a combustion chamber (5), and a rich air-fuel ratio is used in the combustion chamber (5) when NOx is to be emitted from the NOx storage catalyst (22). In a pre-established high-load operation area of the engine, feedback control is performed to bring the air-fuel ratio in the combustion chamber (5) to a theoretical air-fuel ratio. In a pre-established medium-load operation area of the engine, combustion is performed in the combustion chamber (5) with a lower base air-fuel ratio than the base air-fuel ratio in the low-load operation area of the engine, and a richer air-fuel ratio is used in the combustion chamber (5) with a shorter cycle than the rich air-fuel ratio cycle for NOx emission in the low-load operation area of the engine.