Apparatus for purifying exhaust gas of engine

摘要

A catalyst (17) of a NOx absorbing-and-reducing type is disposed in an exhaust passage (10) of an engine (1). The catalyst (17) absorbs a NOx component in an exhaust gas under an over-oxygen atmosphere and reductively emits the absorbed NOx component according to reduction of oxygen concentration. A control unit (20) of the engine (1) estimates a momentary amount of the absorbed NOx component, and further estimates an integrated amount of the absorbed NOx component according to the integration of the momentary amounts. Then the control unit (20) lets the catalyst (17) to emit the NOx component when the integrated amount is equal to or greater than a predetermined absorption amount. In addition, the control unit (20) corrects the momentary amount to a smaller value in adverse proportion to the increase in the integrated amount. <IMAGE>