Reducing agent supply apparatus, method for controlling the same, and exhaust gas purification apparatus

A method for controlling a reducing agent supply apparatus, the reducing agent supply apparatus comprising:

• a storage tank for storing liquid reducing agent;
• a pump for pumping the reducing agent;
• a reducing agent injection valve for injecting the reducing agent pumped by the pump in an exhaust pipe of an internal combustion engine;
• and a reducing agent passage connecting the pump to the reducing agent injection valve,
• wherein, on part of the reducing agent passage, a siphon function portion is provided for, even when, at the start of the internal combustion engine, the reducing agent injection valve is in injection failure due to solidification of the reducing agent in the reducing agent injection valve, causing some of the reducing agent to reach the reducing agent injection valve after the start of the pump to cause the solidified reducing agent to melt,
• wherein, when the internal combustion engine stops, a purge process of collecting the reducing agent in the reducing agent passage into the storage tank is performed,
• wherein the method comprising the steps of:
• at the start of the internal combustion engine, determining whether or not, after the start of pumping the reducing agent, injection of the reducing agent has been performed according to an injection instruction to the reducing agent injection valve;
• and
• if the injection of the reducing agent has not been performed, temporarily decreasing pressure in the reducing agent passage and then increasing the pressure again, and
• wherein the steps are repeated until the injection of the reducing agent is performed.