Patent ID: 7900440

Claim:
An exhaust emission control device for an internal combustion engine, comprising: a NOx catalyst that is disposed in an exhaust system of the engine, for trapping NOx in exhaust gases emitted from the engine; and regeneration operation-executing means for executing a regeneration operation for reducing SOx deposited on said NOx catalyst and causing said NOx catalyst to release the reduced SOx, said regeneration operation-executing means having: first regeneration operation-executing means for setting a control parameter for controlling operation of the engine to a first predetermined value that is capable of controlling exhaust gases to a predetermined reducing condition, and at the same time, controlling a temperature of said NOx catalyst within a predetermined target temperature range including a predetermined target temperature, second regeneration operation-executing means for setting the control parameter to a second predetermined value that is capable of controlling exhaust gases to a predetermined reducing condition, and at the same time, controlling the temperature of said NOx catalyst to a temperature higher than the target temperature range, and third regeneration operation-executing means for setting the control parameter to a third predetermined value that is capable of controlling exhaust gases to a predetermined reducing condition, and controlling the temperature of said NOx catalyst to a temperature lower than the target temperature range, the exhaust emission control device further comprising: catalyst temperature-detecting means for detecting the temperature of said NOx catalyst; and regeneration operation-selecting means for selecting, as said regeneration operation-executing means, said first regeneration operation-executing means when the detected temperature of said NOx catalyst is within the target temperature range, said second regeneration operation-executing means when the detected temperature of said NOx catalyst is lower than the target temperature range, and said third regeneration operation-executing means when the detected temperature of said NOx catalyst is higher than the target temperature range.