| 摘要 |
An exhaust-emission purifying apparatus for an internal combustion engine, includes an NOx purifying catalyst disposed in an exhaust system of the engine to purify NOx in an exhaust emission of the engine, and hold a specific substance (in addition to NOx) in the exhaust emission by adsorption or absorption of the specific substance. A controller is operable to detect an NOx purifying ability of the NOx purifying catalyst which is lowered with an increase in the amount of the specific substance held by the catalyst. The controller compares the detected NOx purifying ability with a predetermined threshold value to determine whether the catalyst has been poisoned with the specific substance. When the controller determines that the catalyst has been poisoned with the specific substance, the controller commands at least the engine to effect a poisoning removing treatment of the catalyst, for releasing the specific substance from the catalyst. The threshold value is varied, for example, based upon the operating condition of the engine.
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