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(11) | EP 2 792 863 A8 |
| (12) | CORRECTED EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 153(4) EPC |
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| (54) | EXHAUST PURIFICATION DEVICE OF INTERNAL COMBUSTION ENGINE |
| (57) A three way catalyst (20) and an NOx storage catalyst (22) are arranged in an engine exhaust passage. In an engine low
load operating region, a combustion is performed under a lean air-fuel ratio, and
when NOx should be released from the NOx storage catalyst (22), the air-fuel ratio in a combustion chamber (5) is made rich.
In an engine medium load operating region, the base air-fuel ratio is made lower as
compared with the engine low load operating region, and the air-fuel ratio in the
combustion chamber (5) is made rich at a shorter period as compared with the engine
low load operating region. When the operating state of the engine is switched from
the engine low load operating region to the engine medium load operating region, the
air-fuel ratio in the combustion chamber (5) is temporarily made rich, and the degree
of richness of the air-fuel ratio at this time is stepwise lowered.
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