Exhaust purification device of an internal combustion engine

An exhaust purification device of an internal combustion engine, comprising:

• a NOX selective reducing catalyst in an engine exhaust passage;
• and
• an aqueous urea tank that stores aqueous urea fed into the NOX selective reducing catalyst to selectively reduce NOX contained in an exhaust gas with ammonia generated from the aqueous urea, the aqueous urea tank including a main tank and a sub tank arranged inside the main tank and smaller than the main tank;
• aqueous urea refill judging means for judging if aqueous urea has been refilled in the aqueous urea tank;
• NOx purification rate judging means for judging if NOx purification rate has fallen below an allowable level;
• a control unit configured to judge that a refilled aqueous urea is abnormal when it is judged that the NOx purification rate has fallen to below the allowable level at the time of engine operation right after the aqueous urea tank has been refilled with aqueous urea;
• a communication hole formed in the bottom end of the sub tank that continuously communicates an inside of the sub tank with an inside of the main tank;
• and
• an aqueous urea feed valve in the exhaust passage, upstream of the NOX selective reducing catalyst, that feeds the aqueous urea to the NOX selective reducing catalyst,
• wherein a top end of the sub tank is open within the main tank and a bottom end of the sub tank is closed by a bottom wall,
• wherein an inner end of an aqueous urea refill pipe attached to the main tank is open towards the inside of the sub tank to feed the refilled urea into the sub tank, and
• wherein an inlet for aqueous urea fed into the aqueous urea feed valve is arranged at a bottom of the sub tank.