| 摘要 |
A control unit calculates an amount of produced ammonia from an amount of a dosed urea aqueous solution according to an engine operation state, and calculates a NOx purification ratio in the case of dosing the amount of the dosed urea aqueous solution according to the operation state to exhaust gas on an exhaust upstream side of an SCR catalyst. Moreover, the control unit estimates an amount of adsorbed ammonia to the SCR catalyst based on the produced ammonia amount and the NOx purification ratio. Then, the control unit subtracts the amount of the urea aqueous solution corresponding to the amount of the adsorbed ammonia from the amount of the dosed urea aqueous solution according to the operation state to correct the amount of the dosed urea aqueous solution, and controls the dosing of the urea aqueous solution based on the corrected amount of the dosed urea aqueous solution. |
