Procedure to diagnose an exhaust gas treatment device and device to implement the procedure

Abstract

A procedure for the pressure diagnosis in a reagent substance metering system, which introduces a reagent substance into an exhaust gas area of an internal combustion engine upstream in front of at least one exhaust treatment device as well as a device to implement the procedure is proposed. The reagent substance pressure occurring between a metering valve and a security valve disposed downstream after the metering valve is measured during different operating conditions of the metering valve and/or the security valve and is compared with at least one threshold value. An error signal is provided when the threshold is exceeded. The procedural approach according to the invention allows for a leakage diagnosis of the reagent substance metering system. Furthermore, the procedural approach according to the invention allows for a diagnosis of metering valve and/or the security valve and/or the check valve. The procedural approach according to the invention contributes overall to the elevation of the security, especially if the reagent substance is combustible.

1 . A method of diagnosing a pressure in a reagent substance metering system, which introduces a reagent substance into an exhaust gas area of an internal combustion engine upstream of at least one exhaust gas treatment device, the metering system including a continuous metering valve, a switchable security valve, and a check valve disposed in a direction of flow of the reagent substance that is brought to a specified source pressure, the method comprising: 
 measuring a reagent substance pressure between the metering valve and the security valve;    comparing the reagent substance pressure with at least one threshold value; and providing an error signal if the reagent substance pressure is greater than the threshold value.    
   
   
       2 . A method according to  claim 1 , further comprising determining if the reagent substance pressure is greater than an opening pressure of the check valve and less than the source pressure when the metering valve and the security valve are closed.  
   
   
       3 . A method according to  claim 1 , further comprising determining if the reagent substance pressure corresponds at least approximately to the source pressure when the metering valve is open and the security valve is closed.  
   
   
       4 . A method according to  claim 3 , further comprising determining if the reagent substance pressure continues at least approximately to correspond to the source pressure after a subsequent closing of the metering valve.  
   
   
       5 . A method according to  claim 4 , further comprising determining, after a subsequent closing of the metering valve, if the reagent substance pressure continues at least approximately to correspond to an opening pressure of the check valve.  
   
   
       6 . A method according to  claim 1 , further comprising determining, after a subsequent closing of the metering valve, if the reagent substance pressure continues at least approximately to correspond to the opening pressure of the check valve.  
   
   
       7 . A device that diagnoses a pressure in a reagent metering system, the device comprising a control unit for the implementation of a method of diagnosing a pressure in a reagent substance metering system, which introduced a reagent substance into an exhaust gas area of an internal combustion engine upstream of at least one exhaust gas treatment device, the metering system including a continuous metering valve, a switchable security valve, and a check valve disposed in a direction of flow of the reagent substance that is brought to a specified source pressure, the method comprising: measuring, a reagent substance pressure between the metering valve and the security valve; comparing the reagent substance pressure with at least one threshold value; and 
 providing an error signal if the reagent substance pressure is greater than the threshold value.    
   
   
       8 . A device according to  claim 7 , wherein the control unit contains a diagnostic control, a threshold set point as well as a comparator to compare the reagent substance pressure with at least a threshold value.  
   
   
       9 . A device according to  claim 7 , wherein the entire reagent substance metering system includes only one pressure sensor disposed between the metering valve and the security valve.  
   
   
       10 . A computer program, operable on a computing system, which executes all steps of a method of diagnosing a pressure in a reagent substance metering system, which introduces a reagent substance into an exhaust gas area of an internal combustion engine upstream of at least one exhaust gas treatment device, the metering system including a continuous metering valve, a switchable security valve, and a check valve disposed in a direction of flow of the reagent substance that is brought to a specified source pressure, the method comprising: measuring a reagent substance pressure between the metering valve and the security valve; comparing the reagent substance pressure with at least one threshold value; and providing an error signal if the reagent substance pressure is greater than the threshold value.  
   
   
       11 . A computer program product with a stored program code, executable on a computing system or in a control unit, on a machine readable carrier for the implementation of diagnosing a pressure in a reagent substance metering system, which introduces a reagent substance into an exhaust gas area of an internal combustion engine upstream of at least one exhaust gas treatment device, the metering system including a continuous metering valve, a switchable security valve, and a check valve disposed in a direction of flow of the reagent substance that is brought to a specified source pressure, the method comprising: measuring a reagent substance pressure between the metering valve and the security valve; comparing the reagent substance pressure with at least one threshold value; and providing an error signal if the reagent substance pressure is greater than the threshold value.