EXHAUST EMISSION CONTROL DEVICE AND EXHAUST EMISSION CONTROL METHOD FOR DIESEL ENGINE

摘要

PROBLEM TO BE SOLVED: To provide a device capable of positively controlling exhaust emission in such a manner that a catalyst temperature is maintained within an active range.

SOLUTION: This exhaust emission control device comprises: an NOx trap catalyst 9 which has a characteristic indicating an inversion rate of a predetermined value or higher in a predetermined active range and disabling an inversion rate equal to or higher than a predetermined value to be obtained when the catalyst is heated to a temperature higher than the active range; a temperature detection means 61 for detecting the temperature of the catalyst 9; an operating state determination means 30 for determining whether the operating state is such a state that the exhaust temperature at the inlet of the catalyst is lowered gradually or not; a high temperature determination means 30 for determining whether or not the detected catalyst temperature is high so that it exceeds the active range; and a temperature reduction means 30 for lowering the catalyst temperature to the active range according to results of the determinations when the operating state is such a state that the exhaust temperature at the catalyst inlet is lowered gradually and the catalyst temperature is high so that it exceeds the active range.

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