| 摘要 |
Aqueous urea solution in a tank (15) is pumped by rotating a pump (16) in a normal direction, and supplied to a piping (14) and an addition valve (17) to add aqueous urea solution through the addition valve (17) to an exhaust passage (8) while an internal combustion engine (1) is operated. In contrast, when the internal combustion engine (1) is stopped, the pump (16) is rotated in a reverse direction through execution of a recovery process to recover aqueous urea solution in the addition valve (17) and the piping (14) to the tank (15). Aqueous urea solution is drawn by the pump (16), and exhaust gas at high temperature in the exhaust passage (8) is drawn into the addition valve (17) and the piping (14). During the execution of the above described recovery process, when a temperature detected by a temperature sensor (31) becomes a high value greater than or equal to a threshold value, namely when fluid with a temperature to be detected by the temperature sensor (31) is changed from aqueous urea solution to the exhaust gas with a temperature higher than that of aqueous urea solution, the above described recovery process is terminated. |
