Patent ID: 9328643
Filing Date: 2016-05-03
CPC Classification: F01N,Y02T

Claim Text:
1. A selective catalytic reduction system for an engine, comprising: a dosing valve to inject urea solution into an exhaust pipe on an upstream side of a selective catalytic reduction device for performing a purification reaction; a detector to detect a temperature of exhaust gas in the exhaust pipe; a supply line that supplies the urea solution from a urea tank to the dosing valve and from the dosing valve back to the urea tank, wherein the dosing valve is closed when the detected exhaust gas temperature is lower than a temperature at which the selective catalytic reduction device performs the purification reaction; and a controller configured to, when the detected exhaust gas temperature is lower than the temperature at which the selective catalytic reduction device performs the purification reaction but equal to or higher than a temperature at which the urea solution crystallizes, forcibly empty the dosing valve by opening the dosing valve and sucking the exhaust gas from the exhaust pipe into the open dosing valve and supplying the exhaust gas from the dosing valve to the urea tank to move the urea solution from the dosing valve to the urea tank, so as to prevent crystallization of the urea solution and prevent fixation of crystallized urea solution to an interior of the dosing valve, even if the engine is running.