Patent ID: 8161735

Claim:
A clogging determining device for a reducing agent passage in an exhaust gas purification system having a pump for pressure-feeding reducing agent to reduce NO x in exhaust gas discharged from an internal combustion engine, a reducing agent injection valve for supplying the reducing agent pressure-fed from the pump to an exhaust gas passage, a first reducing agent passage disposed between the pump and the reducing agent injection valve, and a pressure sensor for detecting the pressure in the first reducing agent passage, the clogging determining device comprising: pump driving control means for subjecting the pump to DUTY control so that a value detected by the pressure sensor is kept to a predetermined value; driving DUTY determining means for determining whether a driving DUTY of the pump is less than a predetermined threshold value; pressure reduction amount calculating means for calculating a pressure reduction amount by which the pressure value detected by the pressure sensor is reduced within a predetermined time after the pump is stopped and also the reducing agent injection valve is fully opened when it is determined that the driving DUTY of the pump is less than the threshold value; and clogging determining means for determining on a basis of the pressure reduction amount calculated by the pressure reduction amount calculating means whether clogging occurs in the first reducing agent passage.