Patent ID: 8590291

Claim:
A reducing agent collection method for collecting a reducing agent inside reducing agent supply paths into a storage tank when an internal combustion engine is stopped in an exhaust gas purification apparatus that adds the reducing agent to an exhaust gas upstream side of a reducing catalyst disposed inside an exhaust gas passageway of an internal combustion engine and reduces and purifies nitrogen oxides contained in exhaust gas using the reducing catalyst, the reducing agent collection method comprising the steps of: closing the reducing agent injection valve in response to a stopping of the internal combustion engine when the reducing agent injection valve is opened when the internal combustion engine stops; starting operation of a reducing agent collecting means with the reducing agent injection valve closed in response to the stopping of the internal combustion engine, wherein the reducing agent collecting means collects reducing agent inside the reducing agent supply paths into the storage tank; and automatically opening the reducing agent injection valve in response to an expiration of a predetermined time period after the operation of the reducing agent collecting means is started.