Metering apparatus and method for operating it

This is a continuation-in-part application of pending international patent application PCT/EP2007/001307 filed Feb. 15, 2007 and claiming the priority of German patent application 10 2006 007 658.3 filed Feb. 18, 1996.

The present invention relates to a metering apparatus for the metered dispensing of a first medium into an exhaust gas system of an internal combustion engine, having a conditioning apparatus which can be fed the first medium and a second medium, and having a dispensing apparatus which is connected to the conditioning apparatus and via which the first medium and/or the second medium can be introduced into the exhaust gas system, cleaning of the conditioning apparatus and/or the dispensing apparatus from constituent parts of the first medium being made possible by the second medium. Furthermore, the invention relates to a method for operating a metering apparatus.

DE 102 23 766 A1 discloses a method, in which a urea solution for exhaust gas aftertreatment is introduced as required via an injection nozzle into an exhaust gas flow of a motor vehicle diesel engine. In order to clean the injection nozzle, a cleaning fluid is passed through the injection nozzle immediately after urea metering.

DE 101 50 518 C1 discloses a method for treating the exhaust gas of an internal combustion engine, wherein a liquid reducing agent from a supply container is fed via a reducing agent line and a metering valve to a mixing chamber and is mixed there with a gas flow. The mixture is introduced into an exhaust gas line via a mixture line. In order to prevent damage to the apparatus as a result of the reducing agent freezing, the flow of the reducing agent is interrupted after the internal combustion engine is switched off, and only gas is fed to the mixing chamber. The mixing chamber, the mixture line, the metering valve and the reducing agent line are filled with gas via suitable valve switching and are therefore protected against damage if the reducing agent freezes.

DE 102 54 981 A1 discloses an apparatus for exhaust gas aftertreatment, in which apparatus a reducing agent is stored in a supply container. The reducing agent can be fed to an exhaust gas line via a reducing agent line. A switchable valve element, via which compressed air can be introduced into the reducing agent line, is arranged in the reducing agent line. Here, the switchable valve element makes it possible for compressed air to flow through the reducing agent line, optionally in the direction of the exhaust gas line or in the direction of the supply container. It is possible as a result to remove the reducing agent by blowing it out of the reducing agent line.

It is an object of the present invention to provide a metering apparatus of the type mentioned in the introduction, wherein however simple and effective cleaning is made possible. It is a further object of the present invention to provide a method for operating a metering apparatus of this type in such a way that a satisfactory cleaning action can be achieved.

In a metering apparatus for the metered introduction of a first medium into an exhaust gas system of an internal combustion engine, which includes a conditioning apparatus in which also a second medium is introduced via a dispensing apparatus which is connected to the conditioning apparatus and via which the first medium and the second medium are introduced into the exhaust gas system, a supply unit for supplying a third medium, which is different from the second medium in its physical properties and/or its chemical composition, is connected to the conditioning apparatus for cleaning of the conditioning apparatus and the dispensing apparatus from constituent parts of the first medium by the third medium or a mixture of the second and the third medium.

Herein, the first medium preferably serves as working medium, by way of which a desired physical and/or chemical effect can be achieved in the exhaust gas flow, for example temperature control of the exhaust gas flow, a direct chemical reaction with components of the exhaust gas or a catalytic action for exhaust gas aftertreatment. The second medium and the third medium are two different media for effectively cleaning the conditioning apparatus and/or the dispensing apparatus at least from constituent parts of the first medium. Here, the apparatus can be cleaned with the aid of the second medium, the third medium or any desired combination of the first, second and/or third medium. Furthermore, a mixture formation comprising the first medium and one of the other media can be provided in the conditioning device. The metering apparatus according to the invention makes it possible, in particular, to use in each case a particular medium or a mixture for cleaning the conditioning apparatus and/or the dispensing apparatus by which the best possible cleaning effect can be achieved under the given operating conditions.

In one particular embodiment, a gas, in particular air, is provided as second medium and a solvent, in which at least constituent parts of the first medium can be dissolved, is provided as third medium. Two media are therefore provided for cleaning the conditioning apparatus and/or the dispensing apparatus, the cleaning action of which is based in each case on different working mechanisms. The feed of a gas makes it possible, in particular, to remove the first medium in a simple way by blowing it out of the apparatus.

Any possible residues of the first medium which cannot be removed by blowing out, for example deposits or crystallizations, can be dissolved and rinsed out by a feed of the solvent. The first medium can also be provided as solvent.

In a further refinement of the invention, a metering element is arranged in a line of the conditioning apparatus, and the feed of the third medium is provided upstream of the metering element. A flow variable of the medium or mixture which flows through the line can be influenced with the aid of the metering element, for example a throughput or a flow speed. The metering element can be configured, in particular, as a valve, diaphragm valve, nozzle, diffuser or venturi nozzle. Metering elements are particularly susceptible to contamination by the first medium. A flow as required of the third medium through the metering element makes it possible to effectively remove contamination, in particular in the form of deposits and crystallizations.

In a further refinement of the invention, a sensor apparatus for a measured variable is arranged in a line of the conditioning apparatus, and a feed of the third medium is activated if the measured variable deviates from a reference value or a threshold value is reached. Variables which allow deductions to be made about a degree of contamination of the metering apparatus, for example a throughput or a pressure difference, are preferably provided as measured variables. Corresponding values for the measured variable at identical operating conditions and with an undisrupted throughflow preferably serve as reference values. The reference values are preferably defined as a function of the operating point of the internal combustion engine or the metering apparatus. It is possible in this way to feed the third medium as required if an operating state of the internal combustion engine or the metering apparatus deviates from a reference state.

The method according to the invention for operating a metering apparatus having a conditioning apparatus and a dispensing apparatus is distinguished by the fact that the conditioning apparatus is fed a third medium from time to time. Different media or mixtures are therefore available for cleaning the conditioning apparatus and/or the dispensing apparatus from constituent parts of the first medium.

In one refinement of the invention, the third medium is fed into the system upstream of a metering element which is arranged in a line of the conditioning apparatus. It is possible in this way to clean the metering element if required with the aid of the third medium.

In a further refinement of the invention, a measured variable is monitored in a line of the conditioning apparatus and/or the dispensing apparatus and the feed of the third medium is performed in the event of a change with respect to a reference value by a predefinable amount or if a predefined threshold value is reached. Disruptions which are caused, in particular, by contamination can be determined by monitoring a measured variable and comparing it with a reference value, so that the third medium can be used as required.

In a further refinement of the invention, the second medium and the third medium are introduced alternately within a predefinable time period. This refinement of the method is suitable, in particular, for preventative cleaning of the conditioning apparatus and/or the dispensing apparatus, before contamination is formed in a significant amount. Preventative cleaning of this type can take place, for example, under low load conditions or after the internal combustion engine is switched off. An optimum cleaning effect can be achieved by the alternate introduction of the second medium and the third medium.

In a further refinement of the invention, a feed of the first medium is reduced during the feed of the second medium and/or the third medium. In particular, the feed of the first medium is suppressed completely here. Contamination by the first medium can be removed particularly effectively in the case of a reduced feed of the first medium.

The invention will become more readily apparent from the following description of an exemplary embodiment thereof on the basis of the accompanying drawing.