| 摘要 |
PROBLEM TO BE SOLVED: To shorten time required for the regeneration of an NOx absorbent and to improve fuel consumption by keeping oxygen concentration relatively high while maintaining an air-fuel ratio to a rich air-fuel ratio. SOLUTION: This exhaust emission control device for an internal combustion engine is provided with an upstream catalyst 3 provided with a function of trapping and holding oxygen in exhaust gas when the air-fuel ratio of inflow exhaust gas is a lean air-fuel ratio, and changed in the holdable quantity of oxygen according to oxygen concentration in the atmosphere; a downstream catalyst 4 provided with a function of trapping and holding NOx in the exhaust gas when the air-fuel ratio of the inflow exhaust gas is a lean air-fuel ratio, and reducing the held NOx by reducing agent components in the exhaust gas when the air-fuel ratio of the inflow exhaust gas is a rich air-fuel ratio; and a control means for controlling the exhaust gas flowing into the upstream catalyst 3, into the state of the air-fuel ratio being the rich air-fuel ratio and the oxygen concentration being higher than specified oxygen concentration when the downstream catalyst 4 is to reduce the held NOx.
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