Device and method for metering a reductant for eliminating nitrogen oxides from exhaust gases

Abstract

A method and a device are proposed for metering a reducing agent, in which means are provided for supplying the reducing agent into a catalytic converter system via a line, for the removal of nitrogen oxides from the exhaust gases, particularly of a Diesel engine, at the end of the line a metering means, especially a metering valve, being situated, and means being provided for regulating the pressure of the reducing agent in the line; the means for regulating the pressure ( 11, 12, 13; 11, 52, 70; 11, 13, 100 ) and/or the metering means ( 7; 120 ) being able to interact with a pressure recording element ( 12; 70; 100 ) which records pressure changes on the output side of the metering means facing away from the line, so that the pressure changes influence the pressure regulation and the metering.

What is claimed is:  
     
         1 . A device for metering a reducing agent, particularly urea or a urea/water solution, having means for supplying the reducing agent into a catalytic converter system via a line for removing nitrogen oxides from the exhaust gases, especially of a Diesel engine, a metering means, particularly a metering valve, being situated at the end of the line, having means for regulating the pressure of the reducing agent in the line, 
 wherein the means for regulating the pressure ( 11 ,  12 ,  13 ;  11 ,  52 ,  70 ;  11 ,  13 ,  100 ) and/or the metering means ( 7 ;  120 ) are able to interact with a pressure recording element ( 12 ;  70 ;  100 ) which records pressure changes at the output side of the metering means facing away from the line, so that the pressure changes have an influence on the pressure regulation and the metering.    
     
     
         2 . The device as recited in  claim 1 , 
 wherein the difference or the quotient of the value of the pressure in the line and the pressure on the output side of the metering means facing away from the line is kept constant.    
     
     
         3 . The device as recited in one of the preceding claims, 
 wherein the means for regulating the pressure include a relief valve ( 11 ).    
     
     
         4 . The device as recited in  claim 3 , 
 wherein the relief valve has a pneumatic connection ( 13 ); the pressure recording element has an additional line ( 12 ) connected to the relief valve;    and the line is connected to the pneumatic connection.    
     
     
         5 . The device as recited in one of the preceding claims, 
 wherein the pressure recording element has a pressure sensor ( 70 ).    
     
     
         6 . The device as recited in  claim 5 , 
 wherein the pressure sensor is connected to a regulator, especially to a regulator ( 52 ) integrated into a control unit ( 40 ) which is able to control the means for regulating the pressure and/or the metering means as a function of the pressure changes.    
     
     
         7 . The device as recited in one of the preceding claims, 
 wherein the metered reducing agent supply goes into a mixing chamber ( 8 ) to form an aerosol, so that the aerosol is able to be introduced into the catalytic converter system ( 30 ) via an aerosol line ( 25 ).    
     
     
         8 . The device as recited in  claim 7 , 
 wherein means ( 20 ,  21 ,  22 ,  23 ,  24 ,  63 ) are provided for metering an air supply into the mixing chamber ( 8 ).    
     
     
         9 . The device as recited in one of claims  1  through  6 , 
 wherein the metering means are mounted on an exhaust gas pipe that leads to the catalytic converter system, the output side of the metering means facing away from the line penetrating into the exhaust gas pipe.  
 
     
     
         10 . A method for metering a reducing agent, particularly urea or a urea/water solution, the reducing agent being supplied in a metered manner to a catalytic converter system, while the pressure of the reducing agent is regulated, for the removal of nitrogen oxides from the exhaust gases, especially of a Diesel engine, with the aid of a metering means, particularly a metering valve, wherein the pressure changes are recorded at the side of the metering means facing the catalytic converter system and have an influence on the pressure regulation and/or the control of the metering means.