Engine exhaust gas cleaning system

摘要

An object of the present invention is to provide an engine exhaust gas cleaning system which can accurately judge whether or not there is the remaining capacity in an NOx trapping amount of an NOx trapping agent, can optimize the timing of NOx purge control, and can diagnose the deterioration of the NOx trapping agent. The present invention is characterized by an engine exhaust gas cleaning system comprising an operating control parameter changing means for changing operating control parameters of the engine in order to change an amount of NOx trapped to the NOx trapping agent; a concentration detecting means for detecting a concentration of a specified component in the exhaust gas at a position downstream of the NOx trapping agent; an air-fuel ratio changing means for temporarily changing the air-fuel ratio of the exhaust gas to a stoichiometric air-fuel ratio or a rich air-fuel ratio with a preset period; and an NOx trapping amount change detecting means for detecting change in the amount of NOx trapped to the NOx trapping agent based on change in a detected result of the concentration detecting means when the air-fuel ratio is changed after changing the operating control parameter.