| 摘要 |
PROBLEM TO BE SOLVED: To accelerate the effective use of a urea aqueous solution in an engine exhaust emission control device for selectively reducing and purifying NOx using ammonia produced from the urea aqueous solution.SOLUTION: The produced amount of ammonia produced from the added amount of the urea aqueous solution according to an engine operating state is computed (S4), and an NOx purification rate when adding the added amount of the urea aqueous solution corresponding to the engine operating state to the exhaust upstream of an SCR catalyst is computed (S5 and 6). Presumed operation of the adsorbed amount of ammonia adsorbed to the SCR catalyst is carried out based on the produced amount of ammonia and the NOx purification rate (S7). Subtraction correction of the amount of the urea aqueous solution equivalent to the adsorbed amount of ammonia is made from the added amount of the urea aqueous solution corresponding to the engine operating state (S10 and 11), and addition control of the urea aqueous solution is performed based on the added amount of the urea aqueous solution after correction (S3). |
