Patent ID: 8276437

Claim:
A clogging determining device for a reducing agent injection valve in an exhaust gas purification system having: a pump for pressure-feeding reducing agent for reducing NO in exhaust gas discharged from an internal combustion engine; a reducing agent injection valve for supplying reducing agent pressure-fed from the pump into an exhaust gas passage; a supply passage disposed between the pump and the reducing agent injection valve; and pressure detecting means for detecting the pressure in the supply passage, the clogging determining device comprising: opened-valve pressure reduction amount calculating means for calculating an opened-valve pressure reduction amount representing a pressure reduction amount in the supply passage which is reduced in a predetermined time from any time point of a time of the stop of pressure feed, a time when a predetermined time elapses after the stop of the pressure feed, and a time when the pressure in the supply passage reaches a predetermined value, when the pressure-feeding operation of the pump is stopped under the state that the reducing agent injection valve is set to an injection mode; closed-valve pressure reduction amount calculating means for calculating a closed-valve pressure reduction amount representing the pressure reduction amount in the supply passage which is reduced in a predetermined time from any time point of a time of the stop of pressure feed, a time when a predetermined time elapses after the stop of the pressure feed, and a time when the pressure in the supply passage reaches a predetermined valve, when the pressure-feeding operation of the pump is stopped under the state that the reducing agent injection valve is set to a full-close mode; and clogging determining means for comparing the opened-valve pressure reduction amount with the closed-valve pressure reduction amount to determine clogging of the reducing agent injection valve.