Urea spray scr control system

A urea spray selective catalytic reduction control system comprising a selective catalytic reduction catalyst provided in a discharge pipe of an engine and a dosing valve for injecting urea water at an upstream side of the selective catalytic reduction catalyst, wherein the urea spray selective catalytic reduction control system controls injection of the urea water from the dosing valve, and

• the urea spray selective catalytic reduction control system includes a plurality of NOx model maps corresponding to an atmospheric pressure condition, an outdoor air temperature, and an engine water temperature, and determines the amount of NOx from each NOx model map on a basis of detection values of an atmospheric pressure detector, an outdoor air temperature detector, and an engine water temperature detector, and controls the amount of injection of the urea water from the dosing valve on a basis of the amount of NOx thus determined.