Reducing Agent Metering System with Evacuation of the Reducing Agent Line after Completion of Metering

Abstract

The invention relates to a reducing agent metering system for injection of a reducing agent into the exhaust gas flow of an internal combustion engine for selective catalytic reduction, the metering system being connected/connectable to a reducing agent tank from which the reducing agent is taken and delivered by means of a delivery pump via a delivery line ( 1 ) and is introduced into the exhaust gas flow of the internal combustion engine via at least one nozzle, a Venturi tube ( 2 ) being integrated into the delivery line ( 1 ) and having a branch ( 3 ) which discharges into the nozzle, at the outlet ( 4 ) of the Venturi tube ( 2 ) there being an openable shutoff element so that with the shutoff element opened the reducing agent which is located in the nozzle and the branch ( 3 ) is intaken as a suction medium into the Venturi tube ( 2 ) and is carried away via the outlet ( 4 ).

1 . A reducing agent metering system for injection of a reducing agent into the exhaust gas flow of an internal combustion engine for selective catalytic reduction, the metering system being connected/connectable to a reducing agent tank from which the reducing agent is taken and delivered by means of a delivery pump via a delivery line ( 1 ) and is introduced into the exhaust gas flow of the internal combustion engine via at least one nozzle, characterized in that a Venturi tube ( 2 ) is integrated into the delivery line ( 1 ) and has a branch ( 3 ) which discharges into the nozzle, at the outlet ( 4 ) of the Venturi tube ( 2 ) there being an openable shutoff element so that with the shutoff element opened the reducing agent which is located in the nozzle and the branch ( 3 ) is intaken as a suction medium into the Venturi tube ( 2 ) and is carried away via the outlet ( 4 ). 
     
     
         2 . The metering system as claimed in  claim 1 , wherein the branch ( 3 ) is located in the region of a narrowing ( 5 ) of the Venturi tube ( 2 ). 
     
     
         3 . The metering system as claimed in  claim 1 , wherein the branch ( 3 ) is spaced apart from the Venturi tube ( 2 ) or is located directly in front of a cross sectional widening ( 6 ) of the Venturi tube ( 2 ). 
     
     
         4 . The metering system as claimed in  claim 2 , wherein the branch ( 3 ) is located in the region of a propellant nozzle of the delivery line ( 1 ), which nozzle discharges into the Venturi tube ( 2 ). 
     
     
         5 . The metering system as claimed in  claim 2 , wherein downstream of the branch ( 3 ) there is a cross sectional narrowing ( 7 ) followed by a diffusor ( 8 ). 
     
     
         6 . The metering system as claimed in  claim 2 , wherein the branch ( 3 ) is located vertically on the Venturi tube ( 2 ) or wherein the branch ( 3 ) and the Venturi tube ( 2 ) include an acute angle (α). 
     
     
         7 . The metering system as claimed in  claim 2 , wherein the inside diameter of the Venturi tube ( 2 ) in the region of the branch ( 3 ) and/or the inside diameter of the branch ( 3 ) on the Venturi tube ( 2 ) is less than or equal to 5 mm, especially less than or equal to 4 mm, especially less than or equal to 3 mm, especially less than or equal to 2 mm, especially less than or equal to 1 mm, especially less than or equal to 0.8 mm. 
     
     
         8 . The metering system as claimed in  claim 2 , wherein there is a compressed air supply and the reducing agent is atomized inside or outside of the nozzle by means of compressed air, especially wherein the compressed air supply has a switching valve and/or a pressure control valve. 
     
     
         9 . The metering system as claimed in  claim 2 , wherein the metering pump is a membrane pump or a piston pump or a centrifugal pump or an orbital pump or a geared pump. 
     
     
         10 . A method for operating a reducing agent metering system for injection of a reducing agent into the exhaust gas flow of an internal combustion engine for selective catalytic reduction, the metering system being connected/connectable to a reducing agent tank from which the reducing agent is taken and delivered by means of a delivery pump via a delivery line ( 1 ) and is introduced into the exhaust gas flow of the internal combustion engine via at least one nozzle, characterized in that a Venturi tube ( 2 ) is integrated into the delivery line ( 1 ) and has a branch ( 3 ) which discharges into the nozzle, at the outlet ( 4 ) of the Venturi tube ( 2 ) there being an openable shutoff element which is closed during metering operation and is opened when metering is completed so that with the shutoff element opened the reducing agent which is located in the nozzle and the branch ( 3 ) is intaken as a suction medium into the Venturi tube ( 2 ) and is carried away via the outlet ( 4 ). 
     
     
         11 . The metering system as claimed in  claim 2 , wherein the branch ( 3 ) is spaced apart from the Venturi tube ( 2 ) or is located directly in front of a cross sectional widening ( 6 ) of the Venturi tube ( 2 ). 
     
     
         12 . The metering system as claimed in  claim 3 , wherein the branch ( 3 ) is located in the region of a propellant nozzle of the delivery line ( 1 ), which nozzle discharges into the Venturi tube ( 2 ). 
     
     
         13 . The metering system as claimed in  claim 3 , wherein downstream of the branch ( 3 ) there is a cross sectional narrowing ( 7 ) followed by a diffusor ( 8 ). 
     
     
         14 . The metering system as claimed in  claim 3 , wherein the branch ( 3 ) is located vertically on the Venturi tube ( 2 ) or wherein the branch ( 3 ) and the Venturi tube ( 2 ) include an acute angle (α). 
     
     
         15 . The metering system as claimed in  claim 3 , wherein the inside diameter of the Venturi tube ( 2 ) in the region of the branch ( 3 ) and/or the inside diameter of the branch ( 3 ) on the Venturi tube ( 2 ) is less than or equal to 5 mm, especially less than or equal to 4 mm, especially less than or equal to 3 mm, especially less than or equal to 2 mm, especially less than or equal to 1 mm, especially less than or equal to 0.8 mm. 
     
     
         16 . The metering system as claimed in  claim 3 , wherein there is a compressed air supply and the reducing agent is atomized inside or outside of the nozzle by means of compressed air, especially wherein the compressed air supply has a switching valve and/or a pressure control valve. 
     
     
         17 . The metering system as claimed in  claim 3 , wherein the metering pump is a membrane pump or a piston pump or a centrifugal pump or an orbital pump or a geared pump. 
     
     
         18 . The metering system as claimed in  claim 1 , wherein the branch ( 3 ) is located in the region of a propellant nozzle of the delivery line ( 1 ), which nozzle discharges into the Venturi tube ( 2 ). 
     
     
         19 . The metering system as claimed in  claim 2 , wherein downstream of the branch ( 3 ) there is a cross sectional narrowing ( 7 ) followed by a diffusor ( 8 ). 
     
     
         20 . The metering system as claimed in  claim 6 , wherein the inside diameter of the Venturi tube ( 2 ) in the region of the branch ( 3 ) and/or the inside diameter of the branch ( 3 ) on the Venturi tube ( 2 ) is less than or equal to 5 mm, especially less than or equal to 4 mm, especially less than or equal to 3 mm, especially less than or equal to 2 mm, especially less than or equal to 1 mm, especially less than or equal to 0.8 mm.