Method for operating a urea-water solution metering system and motor vehicle using the system

Abstract

A method for operating a device for providing a liquid reactant to an exhaust gas system. The device includes at least one tank and an injection nozzle connected to one another by a line. The line has a pump for feeding the reactant. A controllable return line connected between the pump and the injection nozzle leads from the line to the tank. A controller controls operation of the injection nozzle, the pump and the return line, so that the reactant is only circulated intermittently through the controllable return line. A motor vehicle using the method is also provided.

1 . A method for operating a device for providing a liquid reactant to an exhaust system, the method comprising the following steps:
 supplying the liquid reactant in the device from at least one tank through a line to an injection nozzle leading to the exhaust system;   conveying the liquid reactant through the line with a pump;   returning the liquid reactant from the line to the tank through a controllable return line connected between the pump and the injection nozzle;   controlling operation of the injection nozzle, the pump and the return line with a controller; and   only intermittently circulating the reactant through the controllable return line.   
     
     
         2 . The method according to  claim 1 , which further comprises circulating the reactant for a conveying time period corresponding to at least two times a time required for the device to convey the reactant from the tank through the controllable return line and back into the tank. 
     
     
         3 . The method according to  claim 1 , which further comprises circulating the reactant for a conveying time period corresponding to at most five times a time required for the device to convey the reactant from the tank through the controllable return line and back into the tank. 
     
     
         4 . The method according to  claim 1 , which further comprises initiating the circulation of the reactant by using a device for identifying at least solid matter or gases in the reactant. 
     
     
         5 . The method according to  claim 1 , which further comprises initiating the circulation of the reactant at a start of operation by using a device for identifying a tank state variable. 
     
     
         6 . The method according to  claim 1 , which further comprises circulating the reactant at a conveying rate being greater than when the reactant is conveyed for injection. 
     
     
         7 . The method according to  claim 1 , which further comprises conveying a liquid urea-water solution as the reactant. 
     
     
         8 . A motor vehicle, comprising:
 an internal combustion engine;   an exhaust system defining an exhaust gas flow direction from said internal combustion engine, said exhaust system including an SCR catalytic converter and an injection location for injecting a liquid reactant into said exhaust system upstream of said SCR catalytic converter in said flow direction; and   at least one device including at least:
 a tank for the liquid reactant; 
 a controllable injection nozzle at said injection location; 
 a line interconnecting said tank and said injection nozzle; 
 a pump for conveying the reactant from said tank to said injection nozzle; 
 a return line connected to said line at a location between said pump and said injection nozzle, said return line leading to said tank; 
 a valve for controlling said return line; and 
 a controller for controlling operation of said injection nozzle, said pump and said return line by carrying out the method according to  claim 1 .