| 摘要 |
PROBLEM TO BE SOLVED: To provide an exhaust emission control system for an internal combustion engine that includes two types or more of catalysts having a function for reducing and eliminating NOx in exhaust gas and that can improve NOx elimination performance totally while suppressing deterioration of fuel consumption penalties.SOLUTION: An exhaust emission control system includes: an LNT catalyst for occluding NOx in the oxidative atmosphere and reducing and eliminating the occluded NOx in the reduction atmosphere; an SCR catalyst for reducing and eliminating NOx by reacting NHand NOx with each other; and an FI-ECU for performing a DeNOx operation mode for reducing and eliminating the NOx occluded in the LNT catalyst in response to the satisfaction of a predetermined condition so as to cause the LNT catalyst to have the reduction atmosphere. When an estimated value Scr_tmp of a temperature of the SCR catalyst is higher than a switching temperature SCR_LNT_MODE_TMP determined within a temperature range enabling reduction and elimination of NOx by using the SCR catalyst, the FI-ECU prohibits the execution of the DeNOx operation mode (reduction processing of the LNT catalyst).SELECTED DRAWING: Figure 10 |
