Method for operating a reagent metering valve and apparatus for carrying out the method

Abstract

A method is proposed for operating a metering valve which is realized as a solenoid valve which is actuated by an electromagnet that interacts with an armature which is connected fixedly to a valve needle and, furthermore, is loaded with a pulse-width modulated metering signal which defines the metering of a reagent which is to be introduced into the exhaust-gas region of an internal combustion engine or of a preliminary stage of a reagent, as is an apparatus for carrying out the method. The opening duration of the metering valve is limited to a minimum opening duration, for which the metering valve is opened completely and which is fixed in such a way that a spray mist is always produced during the metering. The procedure according to this invention prevents the reagent from crystallizing and, as a result, firstly ensures exact metering of the reagent and secondly counteracts clogging of the metering valve, in particular if a urea/water solution is provided as preliminary stage of the reagent.

1 - 11 . (canceled) 
     
     
         12 . A method of operating a metering valve, especially a solenoid valve, wherein the metering valve is actuated by an electromagnet that interacts with an armature, wherein the armature is connected fixedly to a valve needle, and wherein the electromagnet is loaded with a pulse-width modulated metering signal that defines: a) a metering of a reagent into an exhaust-gas area of an internal combustion engine; and b) a metering of a preliminary stage of the reagent, the method comprising:
 limiting an opening duration of the metering valve to a minimum opening duration, wherein the metering valve is opened completely and fixed to produce a spray mist.   
     
     
         13 . A method according to  claim 12 , further comprising determining the minimum opening duration based on an operating pressure of the reagent. 
     
     
         14 . A method according to  claim 12 , further comprising determining the minimum opening duration based on an operating voltage of the electromagnet. 
     
     
         15 . A method according to  claim 12 , further comprising determining the minimum opening duration based on at least one of:
 a measure for an exhaust gas temperature;   a measure for an exhaust gas mass flow;   a measure for an exhaust gas pressure; and   a measure for an operating temperature of the metering valve and/or the reagent.   
     
     
         16 . A method according to  claim 12 , further comprising determining a beginning of the opening duration at a specified time by an inductance-modification of the electromagnet. 
     
     
         17 . A method according to  claim 16 , further comprising determining the inductance-modification by evaluating a current that flows through the electromagnet. 
     
     
         18 . A device, especially at least one customized control unit, to implement a method of operating a metering valve, especially a solenoid valve, wherein the metering valve is actuated by an electromagnet that interacts with an armature, wherein the armature is connected fixedly to a valve needle, and wherein the electromagnet is loaded with a pulse-width modulated metering signal that defines: a) a metering of a reagent into an exhaust-gas area of an internal combustion engine; and b) a metering of a preliminary stage of the reagent, the method comprising: limiting an opening duration of the metering valve to a minimum opening duration, wherein the metering valve is opened completely and fixed to produce a spray mist. 
     
     
         19 . The device of  claim 18 , wherein the metering valve is a fuel injection valve. 
     
     
         20 . The device of  claim 18 , wherein a urea/water solution is provided as the preliminary stage of the reagent. 
     
     
         21 . A computer program to implement steps, if executed on a computer, of a method of operating a metering valve, especially a solenoid valve, wherein the metering valve is actuated by an electromagnet that interacts with an armature, wherein the armature is connected fixedly to a valve needle, and wherein the electromagnet is loaded with a pulse-width modulated metering signal that defines: a) a metering of a reagent into an exhaust-gas area of an internal combustion engine; and b) a metering of a preliminary stage of the reagent, the method comprising: limiting an opening duration of the metering valve to a minimum opening duration, wherein the metering valve is opened completely and fixed to produce a spray mist. 
     
     
         22 . A computer program product with a program code that is saved on a machine readable medium to implement steps, if executed on a computer or on a control unit, of a method of operating a metering valve, especially a solenoid valve, wherein the metering valve is actuated by an electromagnet that interacts with an armature, wherein the armature is connected fixedly to a valve needle, and wherein the electromagnet is loaded with a pulse-width modulated metering signal that defines: a) a metering of a reagent into an exhaust-gas area of an internal combustion engine; and b) a metering of a preliminary stage of the reagent, the method comprising: limiting an opening duration of the metering valve to a minimum opening duration, wherein the metering valve is opened completely and fixed to produce a spray mist.