Patent ID: 7950224

Claim:
A method for controlling an exhaust gas purification system, the system having a diesel particulate filter device for purifying particulate matter in an exhaust gas and a selective catalytic reduction type catalytic device for purifying NOx in the exhaust gas, these devices being disposed, in that order, from the upstream side in an exhaust passage of an internal combustion engine, the system furthermore having an aqueous solution supply device that supplies an aqueous ammonia solution to the selective catalytic reduction type catalytic device, being disposed at the downstream side of the diesel particulate filter device and additionally at the upstream side of the selective catalytic reduction type catalytic device, the system furthermore having aqueous solution supply amount adjusting means that adjusts the supply amount of the aqueous ammonia solution, wherein, the method comprising the steps of: measuring in advance NOx emission amounts during ordinary operation and NOx emission amounts during forced regeneration of the diesel particulate filter device, and on the basis of the measured results, preparing a NOx emission map for ordinary operation and a NOx emission map for forced regeneration of the diesel particulate filter device; during ordinary operation, calculating a NOx emission amount from the NOx emission map for ordinary operation, calculating a supply amount of aqueous ammonia solution necessary for reducing the calculated NOx emission amount, and supplying the aqueous ammonia solution to bring the supplied amount to the calculated supply amount; and during forced regeneration of the diesel particulate filter device, calculating a NOx emission amount from the NOx emission map for forced regeneration, calculating a supply amount of aqueous ammonia solution corresponding to the calculated NOx emission amount, and supplying the aqueous ammonia solution to bring the supplied amount to the calculated supply amount.