| abstract |
[PROBLEMS] To prevent freezing of a reducing agent such as urea water, and thereby to prevent breakage of components of a reducing agent supply system. A DPF 12 and an SCR catalyst 13 are disposed in an exhaust pipe 11, and a urea water addition valve 15 for adding and supplying urea water into the exhaust pipe 11 is provided between the DPF 12 and the SCR catalyst 13. Is provided. As a configuration of the urea water supply system, urea water of a predetermined concentration is stored in the urea water tank 21, and a urea water pump 22 is provided in the tank 21. The urea water pump 22 is configured to be able to rotate forward and reverse. A urea water supply pipe 23 is connected to the urea water pump 22. After stopping the engine, the ECU 30 drives the urea water pump 22 in a urea water sucking back state (reverse rotation driving state) different from the normal urea water discharging state (forward rotation driving state). As a result, the urea water remaining in the urea water addition valve 15 and the urea water supply pipe 23 is recovered in the urea water tank 21. [Selection] Figure 1 |