| 摘要 |
An electronic control unit (21) limits the pressure of urea water to be supplied to an addition valve (17) to a limit value through drive control of a pump (16) when the temperature of the addition valve (17) has a value as high as a reference value or more. Consequently, the pressure of the urea water to be supplied to the addition valve decreases from a prescribed value to the limit value, accordingly the boiling point of the urea water present in the addition valve (17) decreases, and thereby the urea water changes from a liquid state to a gas state. Under the state in which the urea water present in the addition valve (17) has turned to a gas, a metal material that forms the addition valve (17) does not corrode even if the urea water reaches a high temperature. In consequence, a phenomenon in which the urea water in the addition valve (17) reaches a high temperature in a liquid state and thereby the metal material that forms the addition valve (17) corrodes can be prevented. |
