Control unit and control method for reductant supply device

Abstract

A reductant supply device having a reductant injection valve with an injection tip that is fixed to an exhaust pipe on the exhaust gas upstream side of a reduction catalyst, the device directly injecting and supplying an urea aqueous solution which is pressure-fed to the reductant injection valve in a state of a liquid fluid, by controlling opening and closing of the reductant injection valve. The device includes a cooling water circulation passage; a flow rate control valve; a temperature sensor for detecting a temperature at the tip of the reductant injection valve; and a controller for controlling the flow rate control valve based on the temperature at the tip such that the temperature at the tip of the reductant injection valve is maintained at a temperature between equal to or higher than a boiling point of the urea aqueous solution and equal to or lower than 130° C.

1 . A reductant supply device which is used in an exhaust gas purification device that injects and supplies, as a reductant, a urea aqueous solution to an exhaust gas upstream side of a reduction catalyst disposed in an exhaust gas passage of an internal combustion engine, and that reduces and purifies nitrogen oxides contained in exhaust gas using the reduction catalyst,
 the reductant supply device having a reductant injection valve with an injection tip that is fixed to an exhaust pipe on the exhaust gas upstream side of the reduction catalyst,   the reductant supply device directly injecting and supplying the urea aqueous solution which is pressure-fed to the reductant injection valve in a state of a liquid fluid, by controlling opening and closing of the reductant injection valve and,   the reductant supply device comprising:   a cooling water circulation passage that circulates at least part of cooling water of the internal combustion engine to cool the reductant injection valve;   a flow rate control valve for adjusting a flow rate of cooling water flowing through the cooling water circulation passage;   a temperature sensor for detecting a temperature at the tip of the reductant injection valve; and   a controller for controlling the flow rate control valve based on the temperature at the tip of the reductant injection valve such that the temperature at the tip of the reductant injection valve is maintained at a temperature between equal to or higher than a boiling point of the urea aqueous solution and equal to or lower than 130° C.   
     
     
         2 . The reductant supply device according to  claim 1 , wherein the controller controls the flow rate control valve such that the temperature at the tip of the reductant injection valve is between equal to or higher than 100° C. and equal to or lower than 120° C. 
     
     
         3 . The reductant supply device according to  claim 1 , wherein the temperature sensor calculates a temperature at the tip of the reductant injection valve based on at least one of a temperature of the exhaust gas, a flow rate of the exhaust gas, a temperature of the urea aqueous solution, a temperature of the cooling water, an outside air temperature, and an injection supply amount from the reductant injection valve. 
     
     
         4 . The reductant supply device according to  claim 1  wherein if the cooling water circulation passage, the flow rate control valve and the controller are respectively referred to as a first cooling water circulation passage, first flow rate control valve and first controller, the reductant supply device further comprising:
 a second cooling water circulation passage that circulates at least part of the cooling water of the internal combustion engine in order to adjust a temperature of the urea aqueous solution in a storage tank that stores the urea aqueous solution; 
 a second flow rate control valve for adjusting a flow rate of the cooling water that flows through the second cooling water circulation passage; and 
 a second controller for controlling the second flow rate control valve based on the temperature of the urea aqueous solution in the storage tank. 
 
     
     
         5 . A control method for a reductant supply device which is used in an exhaust gas purification device that injects and supplies, as a reductant, a urea aqueous solution to an exhaust gas upstream side of a reduction catalyst disposed in an exhaust gas passage of an internal combustion engine, and that reduces and purifies nitrogen oxides contained in exhaust gas using the reduction catalyst,
 the reductant supply device having a reductant injection valve with an injection tip that is fixed to an exhaust pipe on the exhaust gas upstream side of the reduction catalyst,   the reductant supply device directly injecting and supplying the urea aqueous solution which is pressure-fed to the reductant injection valve in a state of a liquid fluid, by controlling opening and closing of the reductant injection valve and,   the control method comprising:   cooling the reductant injection valve by circulating at least part of cooling water of the internal combustion engine;   detecting a temperature at the tip of the reductant injection valve; and   controlling a flow rate of the cooling water such that the temperature at the tip of the reductant injection valve is maintained at a temperature between equal to or higher than a boiling point of the urea aqueous solution and equal to or lower than 130° C. based on the temperature at the tip of the reductant injection valve.