DE102019220346A1 - Procedure for clearing a blockage in a metering valve - Google Patents

Abstract

The invention relates to a method for removing a blockage in a metering valve which is connected to a reducing agent line of an SCR catalytic converter system. When the metering valve is in the closed position, the reducing agent line is filled with a reducing agent solution and an overpressure is built up in the reducing agent line (52).

Description

The present invention relates to a method for clearing a blockage in a metering valve. The present invention also relates to a computer program that executes each step of the method, as well as a machine-readable storage medium that stores the computer program. Finally, the invention relates to an electronic control device which is set up to carry out the method.

State of the art

In order to reduce the proportion of nitrogen oxides in the exhaust gas of an internal combustion engine, in particular a diesel engine, it is known to arrange one or more SCR (selective catalytic reduction) catalysts in its exhaust line. This reduces the nitrogen oxides contained in the exhaust gas in the presence of ammonia as a reducing agent to nitrogen. In order to provide the ammonia, a reducing agent solution is metered into the exhaust system upstream of the SCR catalytic converter. As a rule, an aqueous urea solution (urea-water solution; HWL) is used for this, which contains urea as an ammonia-releasing reagent. A 32.5% UWL is commercially available ^{under the name AdBlue ®.}

An SCR catalytic converter system includes, in addition to one or more SCR catalytic converters, among other things, a reducing agent tank for storing the HWL, a conveying device and hydraulic lines. The reducing agent solution is metered in by means of one or more metering valves, which are usually designed as needle valves. In particular, when high exhaust gas temperatures promote evaporation of the aqueous portion of the UWL in the metering valve, the urea can crystallize out of the UWL in the area of the metering valve needle after partial or complete sucking back of the UWL into a reducing agent tank. This can lead to the mobility of the metering valve needle being partially blocked and thus hindered, or even completely blocked. This condition is also known as a sticky dispensing valve needle. If the metering valve needle is partially or completely blocked, the reducing agent solution cannot be metered in. The SCR catalytic converter system is therefore not functional.

Disclosure of the invention

The method for eliminating a partial or complete blockage of a metering valve which is connected to a reducing agent line of an SCR catalytic converter system provides that the reducing agent line is filled with a reducing agent solution when the metering valve is in the closed position. An overpressure is built up in the reducing agent line. The overpressure is built up in particular up to a prescribable pressure threshold value. The pressurized reducing agent solution can dissolve urea crystals in the metering valve and thus restore the mobility of the metering valve needle. In particular, the metering valve is a needle valve. The blockage is then a blockage of a metering valve needle of the metering valve and the closed position of the metering valve is a closed position of the metering valve needle.

The procedure can only be carried out when the metering valve is in the closed position. Otherwise, the reducing agent solution would immediately exit through the metering valve into the exhaust line in which the metering valve is arranged. A closed position of the metering valve when there is a blockage of the metering valve usually occurs when the blockage has taken place in a closed position of the metering valve. When the SCR catalytic converter system is started, the position of the metering valve can in particular be taken from a memory entry that was generated when the SCR catalytic converter system was previously switched off. Usually, when the SCR catalytic converter system is switched off, the metering valve is temporarily opened to suck back reducing agent solution from the reducing agent line or to equalize pressure. If the metering valve is designed as a needle valve, the back suction process can be recognized by means of an algorithm. The subsequent closing then takes place through a mechanical reset. When the SCR catalytic converter system is switched off, the position of the metering valve is no longer changed.

After the overpressure has built up, a predefinable period of time is preferably waited for and the metering valve is then activated. In particular, the period is specified in such a way that it can be expected that urea crystals will dissolve in the pressurized reducing agent solution within this period. The control can be used to check the function of the metering valve to find out whether it is still blocked.

If the control of the metering valve does not lead to the metering valve opening, then it is preferred that the waiting is repeated for a predeterminable period of time. Afterwards, a renewed activation can be used to check whether the blockage of the metering valve has been lifted this time.

If a predefinable number of repetitions has been carried out without triggering the metering valve to open the Dosing valve leads, then an error entry is preferably generated, which can be stored in an electronic control unit. The error entry documents that the blockage of the metering valve could not be removed and the SCR catalytic converter system is therefore not functional. The reducing agent solution can then be sucked back from the reducing agent line.

The method for clearing a blockage of the metering valve can be carried out simultaneously or sequentially with other measures in order to clear the blockage. Such a measure can be, for example, heating up the metering valve by energizing the metering valve, the aim of which is to bring about thermal decomposition of urea crystals in the metering valve.

The computer program is set up to carry out each step of the method, in particular when it runs on a computing device or on an electronic control device. It enables the implementation of different embodiments of the method on an electronic control unit without having to make structural changes to it. For this purpose, it is stored on the machine-readable storage medium.

By uploading the computer program to a conventional electronic control device, an electronic control device is obtained which is set up to remove a blockage in a metering valve by means of the method.

Figure list

• 1 zeigt schematisch ein SCR-Katalysatorsystem, in dem eine Blockade einer Dosierventilnadel eines Dosierventils mittels Ausführungsbeispielen des erfindungsgemäßen Verfahrens behoben werden kann.
• 2 zeigt ein Ablaufdiagramm eines Verfahrens gemäß einem Ausführungsbeispiel der Erfindung.

Embodiments of the invention are shown in the drawings and are explained in more detail in the following description.

• 1 shows schematically an SCR catalytic converter system in which a blockage of a metering valve needle of a metering valve can be eliminated by means of exemplary embodiments of the method according to the invention.
• 2 shows a flow chart of a method according to an embodiment of the invention.

Embodiments of the invention

An internal combustion engine 10 of a motor vehicle that is in 1 is shown has an exhaust line 11 on. To nitrogen oxides in the exhaust gas of the internal combustion engine 10 to reduce is an SCR catalytic converter system 20th intended. This has an SCR catalytic converter 21 on, the one in the exhaust system 11 is arranged. In a reducing agent tank 22nd a UWL is stored as a reducing agent solution. By means of a suction line 23 can the reducing agent solution from a pump 24 sucked in and into a reducing agent line 25th are transported, which acts as a pressure line. This reducing agent line 25th opens into a metering valve 26th that is a dispensing valve needle 27 having. The dosing valve 26th is upstream of the SCR catalyst 21 in the exhaust system 11 arranged. A pressure sensor 28 is on the reducing agent line 25th arranged to measure an overpressure prevailing in this. It sends its measured values to an electronic control unit 30th . This also controls the pump 24 and the metering valve 26th .

In one exemplary embodiment of the method according to the invention, it is started after a start 40 of the process a control 41 of the dosing valve 26th to increase the mobility of the dispensing valve needle 27 to check. When an exam 42 shows that from the electrical current flow of the metering valve 26th an unimpaired mobility of the metering valve needle 27 can be closed, then a release takes place 43 of the SCR catalyst system 20th for its regular operation and the procedure will end 44. When the exam 42 however, it shows that the mobility of the metering valve needle 27 is partially or completely blocked, it is necessary to take measures to remove the blockage.

First, the position of the metering valve needle 27 a memory entry in the electronic control unit 30th taken 50. This memory entry was made when the SCR catalytic converter system was switched off beforehand 20th generated. An examination is then carried out 51 whether the metering valve needle 27 is closed according to this memory entry. If this is not the case, the method is ended 44. The blockage of the metering valve needle is released 27 is then not possible by means of the measures of the method according to this exemplary embodiment of the invention. However, other measures such as heating the metering valve needle can be used 27 by electrical control of the dosing valve 26th taken to ensure the functionality of the metering valve 26th and thus of the entire SCR catalytic converter system 20th restore.

When the exam 51 however, that results in the metering valve needle 27 is closed, so is by means of the pump 24 the reducing agent line 25th with reducing agent solution from the reducing agent tank 22nd filled and an overpressure built up until the pressure sensor 28 indicates that the overpressure has risen to a predetermined pressure threshold value 52. Then there is a wait 53 for a given period of time. When this predetermined period of time has passed, it is done in the same way as in step 41 a driving 54 of the dosing valve 26th to check whether the blockage of the dispensing valve needle 27 was repealed. If a subsequent exam 55 results in an unhindered opening of the metering valve needle 27 is now possible, the release takes place 43 of the SCR catalyst system 20th and the process is ended 44.

Is an opening of the dosing valve needle 27 not yet possible without impairment, so the steps 53 to 55 repeated. Before each repetition, however, there is an examination 56 whether a specified maximum number of repetitions has already been carried out. If this is the case, no further repetition is necessary. Instead, a generation takes place 57 an error entry in the electronic control unit 30th . This is followed by sucking back 58 the reducing agent solution from the metering valve 26th and the reducing agent line 25th into the reducing agent tank 22nd carried out. The method is then ended 44 without the SCR catalytic converter system having been released.

Claims (8)

Method for clearing a blockage of a metering valve (26) which is connected to a reducing agent line (25) of an SCR catalyst system (20), characterized in that when the metering valve (26) is in the closed position, the reducing agent line (25) is filled with a reducing agent solution and an overpressure is built up in the reducing agent line (52). Procedure according to Claim 1 , characterized in that the position of the metering valve (26) when the SCR catalytic converter system (20) is started is taken from a memory entry (50) which was generated when the SCR catalytic converter system (20) was previously switched off. Procedure according to Claim 1 or 2 , characterized in that after the overpressure (52) has built up, a predefinable period of time is waited for (53) and the metering valve (26) is then activated (54). Procedure according to Claim 3 , characterized in that the waiting (53) is repeated for the predeterminable period of time if the control of the metering valve (26) does not lead to the metering valve (26) opening. Procedure according to Claim 4 , characterized in that an error entry is generated (57) if a predeterminable number of repetitions has been carried out without activation of the metering valve (26) leading to the metering valve (26) opening. Computer program which is set up, each step of the method according to one of the Claims 1 to 5 perform. Machine-readable storage medium on which a computer program is based Claim 6 is stored. Electronic control device (30) which is set up to use a method according to one of the Claims 1 to 5 to remove a blockage in a metering valve (26).

Images