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Abstract

The present invention has its object to judge the establishment of conditions influencing on the evaluation of performance of a NOx catalyst, whereby when being established, the evaluation of performance of the NOx catalyst is stopped to thereby prevent the performance of the NOx catalyst from being erroneously judged. The aforementioned object is realized by an engine exhaust purifying apparatus comprising a NOx trap which is provided in an exhaust passage of an engine to trap NOx in exhaust gases by adsorption or absorption when the air/fuel ratio of a mixture gas is lean, and to release or reduce NOx when the air/fuel ratio is rich, and NOx trapping quantity judging means for evaluating the exhaust purifying performance including the NOx trapping quantity of the NOx trap, wherein the operating state of the NOx trap is measured directly or indirectly, and when the measured operating state is judged to be beyond a predetermined range, the purifying performance evaluation of the NOx trap is inhibited or stopped. Further, the aforementioned object is realized by an engine exhaust purifying apparatus comprising a NOx trap which is provided in the engine exhaust passage to trap such as adsorption or absorption NOx of exhaust gases when the air/fuel ratio of exhaust gases is lean, and to release or reduce NOx when the air/fuel ratio is rich, and NOx trapping quantity judging means for evaluating the exhaust purifying performance including the NOx trapping quantity of the NOx trap, characterized in that the operating state of the NOx trap is measured directly or indirectly, and when the measured operating state is judged to be beyond the predetermined range, the purifying performance evaluation of the NOx trap is inhibited or stopped. According to the present invention, since the release of oxygen stored and the timing of the release of NOx trapped are detected separately by the output of the air/fuel ratio sensor at the downstream of the NO trap for trapping NOx, it is possible to provide an engine exhaust purifying apparatus capable of detecting the NOx trap quantity and the oxygen storage capacity separately with good accuracy. Under the circumstances that the aforesaid detection accuracy cannot be secured, it is possible to prevent an erroneous detection by inhibiting or stopping the detecting operation.

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First Claim