Method for reducing deposits in metering devices

Abstract

The invention relates to a method for reducing deposits in a metering device for metering a liquid medium in an SCR system of an internal combustion engine. For this purpose, it is checked whether there is a stable operation of the internal combustion engine. In the case of identifying a stable operation of the internal combustion engine, the metering quantity of at least one metering valve is changed.

Description

Field of the Invention

[0001] The invention relates to a method for reducing deposits in a metering device for metering a liquid medium in an SCR system of an internal combustion engine. Background Art

[0002] In the field of motor vehicle technology, SCR catalytic converter systems for reducing nitrogen oxides by metering an aqueous urea solution (HWL) are known.

[0003] The aqueous solution of urea forms a crystal layer when the water evaporates. This especially causes caking and blockages in the region of the metering site, where the aqueous urea solution is metered into the exhaust system by means of at least one metering valve. During normal operation of the internal combustion engine at appropriate or high loads, the aqueous urea solution is injected at about 0.25 to 1 Hz and thus dissolves or sprays off crystals that may have formed on the metering site.

[0004] There are special operating conditions of the engine operation in which there are very long stable operating phases. Especially in the so-called off-highway sector (in addition to construction machinery and transport machinery, different types of motorized special machinery also belong to this off-highway sector), it often occurs that the internal combustion engine operates in stable operation for a longer period of time. When the flow, temperature and metering quantity in the exhaust system remain constant for a longer time, the risk of deposit formation is particularly high.

[0005] Functions are known from the prior art that are supposed to reduce the formation of such deposits. Here, for example, spraying of the reducing agent is carried out, which is introduced into the exhaust system through the metering valve only for cleaning purposes to dissolve or spray off the crystals that have already formed. However, this function is disadvantageous for the exhaust system because the unwanted reducing agent enters the exhaust section and is not converted as required in the corresponding operating conditions of the internal combustion engine, whereby unwanted gases leave the exhaust system. Therefore, it is desirable that the SCR catalytic converter system operates in as many operating conditions as possible such that, on the one hand, it can always be metered into the exhaust system as required for the purpose of exhaust gas conversion and, on the other hand, deposits on the metering site are reduced. Summary of the Invention

[0006] The present invention relates to a method for reducing deposits in a metering device for metering a liquid medium in an SCR system of an internal combustion engine. According to the invention, it is checked whether there is a stable operation of the internal combustion engine. If such a stable operation of the internal combustion engine is recognized, then the metering quantity of at least one metering valve is changed relative to a standard value. This means that in stable operation, the total metering quantity generally also has a constant value, which is also referred to as the standard value. That is to say, the metering quantity generally has the standard value in stable operation. According to the invention, in stable operation, a uniform constant metering quantity is not dispensed, but a variable metering quantity is dispensed. The variable metering quantity is determined so as to ensure proper exhaust gas cleaning without restricting harmful components and without forming deposits.

[0007] In a particularly advantageous first design, it is provided that in the case of two metering valves, the metering quantity of the first metering valve is increased by a specific value, and the metering quantity on the second metering valve is decreased by the same value. The total metering quantity remains the same overall, and thus ensures the proper operation of the catalytic converter system. By increasing or decreasing the metering quantity, a changed and thus non-constant metering quantity is obtained on the respective metering valve, which prevents the formation of deposits or eliminates existing deposits.

[0008] In a further design, it is provided that the metering quantity is increased by a specific value from manipulation to manipulation and then decreased by the same value in a subsequent manipulation. This means that the metering quantity is adjusted with respect to time. The metering quantity can, for example, be superimposed with a sinusoidal signal.

[0009] In a further advantageous design, it is provided that the manipulation of the internal combustion engine is changed accordingly, so that the demand for the reducing agent changes. Here, operating parameters are changed, which have no significant influence on the torque and / or speed of the internal combustion engine in their combination. This means that an operating state is selected in which higher nitrogen oxides occur in the untreated exhaust gas, and the nitrogen oxides are reduced again by an adapted and thus increased metering of the aqueous urea solution. By this treatment method, to a certain extent, the stable operation is left, and the metering quantity is no longer constant.

[0010] On the other hand, the present invention relates to new program code together with processing instructions, which creates a computer program executable on a control device, in particular source code with compilation and / or linking instructions, wherein when the program code is converted according to the processing instructions, i.e., in particular compiled and / or linked into an executable computer program, the program code generates a computer program for implementing all steps of one of the described methods. The program code can in particular be provided as source code, which can, for example, be downloaded from a server on the Internet. Description of the Drawings

[0011] Further advantages and design features of the present invention are derived from the description and the drawings. Among them:

[0012] Figure 1 Schematically shows a metering device for an SCR catalytic converter system;

[0013] Figure 2 Illustrates an embodiment of a method according to the present invention by means of a flow chart. Detailed Description

[0014] In Figure 1 a device is shown.

[0015] Figure 1 Shows the metering device 9 of the SCR catalytic converter system, which is used to meter the aqueous urea solution (HWL) into the exhaust system 10 of the only schematically shown internal combustion engine 11 of a motor vehicle. The SCR catalytic converter system is used in a manner known per se to reduce nitrogen oxides in the exhaust gas of the internal combustion engine 11 by means of selective catalytic reduction technology (SCR). For the reduction, the reducing agent HWL is injected into the exhaust system 10 upstream of the SCR catalytic converter 12 through the metering valve 13.

[0016] The HWL 22 is stored in the HWL tank 14. A suction line 15 is provided for removing the HWL 22, and the urine HWL 22 is transported out of the HWL tank 14 by the transport pump 16. The HWL 22 is precisely and as required injected into the exhaust system 10. For this purpose, the pressure of the HWL 22 in the pressure line 17 is decisive, and this pressure is therefore adjusted to a preset target pressure. To detect the pressure in the pressure line 17, a pressure sensor 18 can be provided, which transmits the detected pressure signal to the control device 19, so that the transport pump 16 can adjust the preset target pressure through the signal output of the control device 19. The control device 19 is also connected to the engine control device 100 (which is connected to the internal combustion engine 11 through the first signal line 102 for controlling the internal combustion engine) through another signal line 104, in order to transmit data on the operating state of the SCR catalytic converter system to the engine control device 100 and / or in order to transmit data on the operating state of the internal combustion engine 11 to the control device 19.

[0017] In an embodiment, a plurality of metering valves can also be installed in the exhaust facility, and the additional metering valve 13a is preferably arranged in front of the additional catalytic converter 12a.

[0018] The manipulation of the metering valve 13 is likewise achieved by controlling the signal output of the control device 19. The metering rate for controlling the metering quantity corresponding to each time unit is achieved by the metering valve 13 in such a way that the valve is opened on the one hand with a specific frequency and on the other hand the corresponding opening duration of the valve is also controlled. The typical frequency ranges from 0.25 Hz to 1 Hz. The typical opening duration ranges from 5 ms to 950 ms.

[0019] Furthermore, the HWL quality sensor 20 immersed in the HWL 22 can be arranged in the HWL tank 14, and the urea content of the HWL 22 is measured by means of the HWL quality sensor. The measurement can be achieved in a known manner, for example, by measuring the running time of a sound signal. However, within the scope of the present invention, the measurement technique used here is not important. The signal detected or generated by the quality sensor 20 is conveyed via the signal path 21 to the control device 19 for further processing.

[0020] The method described subsequently is preferably implemented Figure 1 in the control device 19 shown. However, since the location where the method is implemented is not important, the method can also be implemented in a separate control device, in particular in an engine control device 100 for controlling the internal combustion engine 11.

[0021] It is provided according to the invention that during a longer-term constant power output of the engine, in particular during a longer-term constant speed and / or constant torque, the metering quantity in the exhaust gas facility is changed. That is to say, a variable metering quantity is obtained at a stable speed and / or torque.

[0022] In a particularly advantageous first design, it is provided that in the case of two metering valves, the metering quantity of the first metering valve is increased by a specific value, and the metering quantity of the second metering valve is decreased by the same value. The total metering quantity remains the same overall, and thus the proper operation of the catalytic converter system is ensured. By increasing or decreasing the metering quantity, a changed and thus non-constant metering quantity is obtained on the corresponding metering valve, which prevents the formation of deposits or eliminates existing deposits.

[0023] In a further design, it is provided that the metering quantity is increased by a specific value from manipulation to manipulation and is then decreased by the same value in a subsequent manipulation. This means that the metering quantity is adjusted with respect to time. The metering quantity can, for example, be superimposed with a sinusoidal signal.

[0024] In a further advantageous design, the control of the internal combustion engine is correspondingly changed such that the demand for the reducing agent is changed. Here, the operating parameters are changed, which have no influence on the torque and / or the rotational speed of the internal combustion engine. This means that an operating state is selected in which higher nitrogen oxides occur in the untreated exhaust gas and the nitrogen oxides are reduced again by an adapted and thus increased dosage of the aqueous urea solution. By this treatment method, the stable operation is to a certain extent left and the dosage quantity is no longer constant.

[0025] This can be achieved, for example, by changing operating parameters such as the injection time point, the injection process, the exhaust gas recirculation or the throttle valve position without changing the engine power. Here, one or more of these operating parameters can be changed. In addition, the dosage of the aqueous urea solution into the exhaust gas facility can be changed such that the reduction of the nitrogen oxides is not impaired. Here, the storage effect in the catalytic converter is fully utilized.

[0026] Figure 2 A possible embodiment of the method according to the invention is illustrated by means of a flow diagram. In a first step 200, an average value M1 of the measured variable is formed over a certain time period. Subsequently, in step 210, a second average value M2 of the measured variable is formed over the same time period. A subsequent query 220 checks whether the difference between the two average values M2 and M1 is greater than 0 or a threshold value, i.e., whether the average value between the two measurements in steps 200 and 210 has changed significantly. If this is the case, i.e., the average value of the measured values has changed, then the program ends in step 230 because the stable operating state has been left. If query 220 identifies that the average value has not changed, then query 235 checks whether the average value has changed since time T1. If this is the case, i.e., the average value has changed once in the time period T1, then step 240 follows, in which the average value M1 is overwritten with the average value M2, and then step 210 follows immediately, in which the average value M2 is recalculated again. If query 235 identifies that the average value has not changed in the time period T1, then query 250 is carried out. In this query, it is checked whether the second time period T2 has expired. If this is the case, then the program ends 230. If this is not the case, then the dosage quantity is changed in step 260. Subsequently, step 240 is carried out again.

[0027] Measuring variables are continuously monitored in order to identify a stable operating state. Particularly suitable as measuring variables are the position of the accelerator pedal, the engine speed, the engine torque, the air mass flow, the exhaust gas mass flow, the exhaust gas temperature and / or the required metering quantity. One or more of these variables can be examined to identify the presence of stable operation. In order to identify stable operation, the measured variables are averaged over a specific time period. The two averages are compared with each other. If the two averages only differ insignificantly from each other, i.e. the difference between the two averages is approximately 0, then stable operation is identified. This identification takes place in step 220.

[0028] According to the invention, the metering quantity is only changed if the stable operation lasts longer than a specific duration T1. That is to say, only if the stable operation lasts longer than a preset duration T1 are the corresponding measures for changing the metering quantity taken. This is checked in query 235. The duration T1 of stable operation (from which there is an increased risk of deposits) is related to the engine operating point. For example, the risk of deposits is very small at exhaust gas temperatures above 350 °C, so that corresponding measures are usually not required here, or the permitted duration T1 for stable operation can be set to infinity. Conversely, deposits often occur, for example, below 350 °C. For temperatures below this threshold, the permitted duration T1 for which stable operation can last is preset to be relatively small. It is therefore particularly advantageous to preset the duration T1 during which stable operation can exist without increasing the metering quantity according to the operating state. Preferably, the duration T1 is preset according to the temperature value. In particular, the duration T1 is preset according to the exhaust gas temperature or the temperature sensor in the exhaust system.

[0029] According to the invention, it can be provided that the change in the metering quantity is revoked again after a certain time T2, that is to say, after the duration T2, a return is made to normal operation without a change in the metering quantity, and this is ensured by query 250.

[0030] If stable operation is identified for a time longer than the duration T1 and the metering quantity is also changed for a time not longer than the duration T2, then in addition the metering quantity is changed in step 260.

Claims

1. A method for reducing deposits in a metering device for metering a liquid medium in an SCR system of an internal combustion engine, characterized in that, Check whether there is a stable operation of the internal combustion engine, and change the metering quantity of at least one metering valve in the case of identifying the stable operation of the internal combustion engine, wherein in the first metering valve, the metering quantity is increased by a specific value relative to the standard value, and in the second metering valve, the same value is decreased.

2. The method according to claim 1, wherein In the first actuation of the metering valve, the metering quantity is increased by a specific value, and in the subsequent second actuation of the metering valve, the same value is decreased.

3. The method according to any one of the preceding claims, characterized in that, Change at least one operating parameter of the internal combustion engine so as to change the metering quantity.

4. The method according to claim 1 or 2 above, characterized in that, When the change in the average value of the operating characteristic parameters relative to the previous average value of the operating characteristic parameters is less than the threshold value, a stable operation is identified.

5. The method according to claim 1 or 2 above, characterized in that, When the stable operation lasts longer than a preset duration, change the metering quantity.

6. A computer program product comprising a computer program configured to perform all steps of the method according to any one of claims 1 to 5.

7. A machine-readable storage medium having stored thereon a computer program configured to perform all steps of the method according to any one of claims 1 to 5.

8. A control device configured to perform all steps of the method according to any one of claims 1 to 5.

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