Method for estimating NOx and NH3 concentration fraction downstream of SCR catalytic converter of internal combustion engine

Abstract

The invention relates to a method for estimating a NOx and NH3 concentration fraction downstream of at least one SCR catalytic converter (22) of an internal combustion engine (10) arranged in an exhaust system (11).

Description

Background Art

[0001] DE 10 2014 201 304 A1 relates to a method for operating a catalytic converter system, which is configured to reduce nitrogen oxides in exhaust gas from an internal combustion engine, the catalytic converter system comprising at least one SCR catalytic converter (150), which is operated with a reactant stored in the SCR catalytic converter (150), so that a specific reactant filling level is present in the SCR catalytic converter (150), wherein the reactant is metered (Zudosierung) based on a model (604, 606) by means of an NH3 filling level controller (602), and modeling errors are compensated by means of an NH3 filling level observer (605). Summary of the invention

[0002] In a first aspect, the present invention relates to a method for estimating NOx and NH3 concentration portions downstream of at least one SCR10 catalytic converter arranged in an exhaust system of an internal combustion engine, wherein a first NOx concentration sensor value upstream of the SCR catalytic converter and downstream of the internal combustion engine is determined with the aid of a first NOx sensor, wherein a second NOx concentration sensor value downstream of the SCR catalytic converter is determined with the aid of a second NOx sensor, wherein the first and second NOx sensors have a cross-sensitivity to ammonia, wherein a division into a modeled NOx concentration portion and a modeled NH3 concentration portion is performed based on the first and second NOx concentration sensor values ​​with the aid of a model, in particular at the position of the second NOx sensor, wherein the model determines an NH3 effectiveness value for each modeled NH3 concentration portion. Wherein, if there is a valid modeled NH3 concentration share, the NH3 ratio filter value determined in the previous measurement is updated according to the effective modeled NH3 concentration share, and the allocation of the absolute NH3 concentration share is performed according to the effective modeled NH3 concentration share and the current second NOx concentration sensor value, wherein if there is no valid modeled NH3 concentration share, the allocation of the absolute NH3 concentration share is performed according to the current second NOx concentration value and the NH3 ratio filter value determined in the previous measurement.

[0003] The advantage of the method is that the NOx and NH3 emissions are statistically distributed based on historically collected data for the current SCR system, without having to rely on the current distribution. For technical reasons, these current functions are currently unable to continuously and accurately divide the emissions into NOx and NH3 concentration proportions. Measurement results show that the possible distribution between the NOx and NH3 concentration proportions for the emissions can be inferred from the historical behavior of the SCR system. The new method therefore focuses on continuously determining the filter values ​​for the division for the SCR system and thus dividing the emissions recorded in the blind phase with the help of historical values. For this purpose, the NH3 ratio filter value is permanently determined and the division of the emissions proportions is thus carried out.

[0004] Furthermore, the NH3 ratio filter value is only updated if the determined emissions are sufficiently plausible. For this purpose, for example, a check is performed for each determined NH3 concentration component: whether the determined value is plausible. This can be performed, for example, by the size of the emissions deviation.

[0005] In a special embodiment, the updating of the NH3 ratio value is performed in a filtered manner as a function of the currently valid modeled NH3 concentration component, the currently determined second NOx concentration sensor value and the NH3 ratio filter value determined in the previous measurement, in particular the filtering is performed using an exponentially weighted smoothed average value. This has the particular advantage that an accurate NH3 ratio value is thereby obtained.

[0006] In an alternative embodiment, a valid modeled NH3 concentration component is present if the NH3 effectiveness value exceeds a predefinable effectiveness threshold value, and no valid modeled NH3 concentration component is present if the NH3 effectiveness value is below the predefinable effectiveness threshold value. It can also be advantageous to only perform an update if the emissions are sufficiently determined. This can be performed, for example, by the size of the emissions deviation.

[0007] In an advantageous embodiment, the weighting for updating the NH3 ratio filter value is performed as a function of the second NOx concentration sensor value. It can also be advantageous to link the weighting for updating the NH3 ratio value to the emissions determined by the second NOx sensor. Since these sensors are subject to certain measurement tolerances, measurement results with higher emissions can be assigned more weight than measurement results with emissions that are just detectable.

[0008] In a further refinement, a weighting is performed for updating the NH 3 ratio filter value as a function of the NH 3 effectiveness value.

[0009] Furthermore, it may be advantageous to link the weight used to update the NH3 ratio value to the emissions determined via the second NOx sensor. Since sensors are subject to certain measurement tolerances, measurements with higher emissions may be assigned more weight than measurements with emissions that are just detectable.

[0010] In a specific embodiment, the start and end of the emission phase are identified based on the second NOx concentration sensor value NOx2 when it exceeds and falls below a predeterminable first threshold value. In an advantageous embodiment, multiple emission phases can be used for the method. For example, emission phases that are too short can be discarded or can also be used as a weighting criterion for updating the NH3 ratio value.

[0011] In an advantageous embodiment, an average temperature of the SCR catalytic converter is determined for each emission phase, and a weighting for updating the NH3 ratio filter value is performed as a function of the average SCR temperature of the SCR catalytic converter for the respective emission phase. In an advantageous embodiment, a plurality of emission phases can be used for the method. For example, emission phases that are too short can be discarded or can also be used as a weighting criterion for updating the NH3 ratio value.

[0012] In a further embodiment, the NH3 ratio filter value is updated in each case as a function of the average SCR temperature of the SCR catalytic converter, depending on n predeterminable temperature ranges of the SCR catalytic converter. For example, it is particularly advantageous to use a plurality of temperature ranges of the SCR catalytic converter for the method. Thus, for example, the ratio filter value can be updated in a differently weighted manner depending on which temperature range the SCR catalytic converter is currently in. In an advantageous embodiment, there is an individual NH3 ratio filter value for each temperature range, which is also updated only as a function of the data for the temperature of the SCR catalytic converter in which it is already present.

[0013] In a further aspect, the invention relates to an apparatus, in particular a control device and a computer program, which are arranged, in particular programmed, to perform one of the methods. In yet another aspect, the invention relates to a machine-readable storage medium having a computer program stored thereon. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention is explained in more detail below using the embodiments shown in the accompanying drawings. In which:

[0015] Figure 1 A schematic diagram shows an SCR system having an SCR catalytic converter of an internal combustion engine;

[0016] Figure 2 A schematic flow chart shows an exemplary embodiment of a method according to the invention for estimating NOx and NH3 concentrations downstream of at least one SCR catalytic converter of an internal combustion engine. DETAILED DESCRIPTION

[0017] like Figure 1 As shown, the internal combustion engine 10 has an SCR system 20 in its exhaust system 11. The SCR system has a reducing agent metering unit 21, through which a urea aqueous solution (AdBlue) can be injected into the exhaust system 11. At high temperatures of the exhaust gas, ammonia is released. A first SCR catalytic converter 22 is arranged downstream of the reducing agent metering unit 21. Another SCR catalytic converter can be arranged downstream of the first SCR catalytic converter 22. A first NOx sensor 31 and a temperature sensor 12 are arranged upstream of the reducing agent metering unit 21 and downstream of the internal combustion engine 10 in the exhaust system 11. The first NOx sensor 31 measures a first NOx concentration sensor value NOx1 here, preferably as a NOx concentration or as a NOx mass flow. The second NOx sensor 32 is arranged downstream of the first SCR catalytic converter 22 and measures a second NOx concentration sensor value NOx2 here, preferably as a NOx concentration or as a NOx mass flow. This is also particularly applicable to NH3 concentration or NH3 mass flow.

[0018] In an alternative design, the NH3 sensor 33 can also be installed downstream of the SCR catalytic converter 22. The NH3 sensor can determine the NH3 concentration proportion r NH3，S All NOx sensors 31, 32 transmit their signals to the electronic control device 100. Since, in addition to nitrogen oxides, the NOx sensors 31, 32 also react cross-sensitively to ammonia, their signals are sum signals of nitrogen oxides and ammonia. However, the first NOx sensor 31 is arranged upstream of the reducing agent metering unit 21, so that it reliably measures only the amount of nitrogen oxides in the exhaust gas. The reducing agent metering unit 21 also transmits the amount of ammonia metered into the exhaust system 11 to the control device 100.

[0019] In an alternative embodiment, the internal combustion engine 10 can also be designed as a hydrogen burner.

[0020] A model M is also stored in the control device 100 , which decomposes the sum signal of the first NOx sensor 31 and the second NOx sensor 32 into NOx concentration components and NH 3 concentration components, respectively, and stores them in the control device 100 .

[0021] exist Figure 2 An exemplary sequence of a method for estimating NOx and NH3 concentrations downstream of at least one SCR catalytic converter 22 arranged in the exhaust system 11 of an internal combustion engine 10 is shown in FIG.

[0022] In a first step 200, first and second NOx concentration sensor values ​​NOx1; NOx2 are continuously determined by the control device 100. Using a model M stored on the control device 100, a modeled NH3 concentration fraction r is determined at discrete time points based on the first and second NOx concentration sensor values ​​NOx1; NOx2. NH3，M，i and NOx concentration fraction r NOx，M，i The modeled NH3 concentration component and the modeled NOx concentration component correspond to the NH3 and NOx concentration signals downstream of the SCR catalytic converter 22 , in particular at the location of the second NOx sensor 32 . Optionally, the temperature signal T of the temperature sensor 12 exh，i is also determined and can be used as an input variable for the model M. In another exemplary embodiment, based on the determined NH 3 concentration portion r, in particular downstream of the SCR catalytic converter 22 NH3，M In an alternative embodiment, the NH 3 concentration component can be determined by an NH 3 sensor installed downstream of the SCR catalytic converter 22 .

[0023] In addition, the model M has a modeled NH3 concentration fraction r for each NH3，M，i Determine the NH3 effectiveness value VW i .

[0024] Preferably, if the NH3 effectiveness value VW i Exceeding a predeterminable validity threshold S VW , then there is an effective modeled NH3 concentration fraction r NH3，M，i , and if the NH3 effectiveness value VW i falls below a predeterminable validity threshold S VW , then there is no effective modeled NH3 concentration fraction r NH3，M，i .

[0025] The method then continues at step 210 .

[0026] In step 210, the effective NH3 effectiveness value VW is used. i For each modeled NH3 concentration fraction r NH3，M，i Update the NH3 ratio filter value NH3 determined in the previous measurement (i-1) ratio，i-1 NH3 ratio value NH3 ratio，i-1Initialization with predeterminable values ​​may be performed at the beginning in control unit 100. In a special embodiment, in particular an initialization value is stored for the NH3 ratio value in an EEPROM of control unit 100.

[0027] NH3 ratio value NH3 ratio，i The update of the NH3 ratio filter value NH3 is determined, for example, in a previous measurement. ratio，i-1 The modeled NH3 concentration fraction r NH3，M，i The exponentially weighted smoothed average between . Therefore, according to the effective modeled NH3 concentration fraction r NH3，M，i and the current second NOx concentration sensor value NOx2 i To implement the absolute NH3 concentration fraction r NH3，abs allocation.

[0028] In alternative designs, different weightings may be implemented to update the NH3 ratio value NH3 ratio，i For example, the weighting for updating the NH3 ratio value can be determined based on the size of the currently determined emissions, for example via the second NOx concentration sensor value NOx2,i. It is assumed here that emission phases E with higher emissions are compared to measurement results with lower emissions. x A more precise conclusion can be drawn about the division of the NOx and NH3 concentration components. This is mainly due to the tolerances of the NOx and NH3 sensors used.

[0029] In another alternative design, the NH3 effectiveness value VW can be determined according to the i The size of NH3 is used to update the NH3 ratio value NH3 ratio，i weighted.

[0030] On the other hand, if the model M does not determine a valid NH3 availability value VW i , then the determined modeled NH3 concentration fraction r NH3，M，i Not credible.

[0031] In this case, according to the current second NOx concentration value NOx2 i and the NH3 ratio filter value NH3 determined in the previous measurement i-1 ratio，i-1 To implement the absolute NH3 concentration fraction r NH3，abs allocation.

[0032] The method can then continue in step 210 or end.

[0033] In a particular embodiment, a plurality, in particular n, of NH3 ratio filter values ​​NH3 ratio，nIn a specific embodiment, n predeterminable SCR temperature ranges are set, and for each determined modeled NH 3 concentration proportion r NH3，M，i Determine the average temperature T of the SCR catalytic converter 22 exh，i According to the average SCR temperature T exh，i , then only the NH3 ratio filter value NH3 assigned to the predefinable temperature range is updated ratio，n For example, the first SCR temperature range is a temperature of 200-350° C. The second temperature range is between 351-600° C. Therefore, a first NH3 ratio filter value NH3 is derived for the first temperature range. ratio，1 And a second NH3 ratio filter value NH3 is derived for a second temperature range ratio，2 These are two independent NH3 ratio filters.

[0034] If the average SCR temperature is, for example, 370° C. and the modeled NH 3 concentration fraction r determined by the model M is NH3，M，i If it is valid, only the corresponding second ratio filter value NH3 is updated ratio，2 In the modeled NH3 concentration fraction r NH3，M，i If it is invalid, then according to the current second NOx concentration value Nox2i and the second NH3 ratio filter value NH3 determined in the previous measurement i-1 ratio，i-1，2 To implement the absolute NH3 concentration fraction r NH3，abs allocation.

[0035] In an alternative embodiment, there may be multiple filters for different mileages. For example, if the current mileage of the vehicle is less than 5000 kilometers, then for each of the next 5000 kilometers, for example, a new NH3 ratio filter (NH3- ).

[0036] In a specific design, multiple emission stages E are determined for this method in particular. x or Evaluation Phase E x This is done in particular as a function of the second NOx concentration sensor value NOx2, wherein the second NOx concentration sensor value NOx2 is detected when it exceeds and falls below a predefinable first threshold value S Nox2 When the emission phase E is identified x Here, the corresponding discharge phase E x In particular, the emission phase E x The NH3 effectiveness value determined in Cumulatively relative to a predefinable first threshold value S NOx2 If the accumulated validity value exceeds a predeterminable first threshold value SNOx2 , then the emission stage E x Valid, and if the accumulated validity value is below a predeterminable first threshold value S Nox2 , then the emission stage E x invalid.

[0037] In an advantageous embodiment, the NH3 ratio filter value NH3 ratio，i The update can be based on the emission stage E x The calculation is performed using the accumulated variable of the NH 3 effectiveness value, the temperature of the SCR catalytic converter 22 , the second NOx concentration sensor value NOx2 , and the modeled NH 3 concentration share, or a combination thereof.

Claims

1. A method for estimating NOx and NH3 concentration components downstream of at least one SCR catalytic converter (22) arranged in the exhaust system (11) of an internal combustion engine (10), wherein a first NOx concentration sensor value (NOx1) is determined upstream of the SCR catalytic converter (22) and downstream of the internal combustion engine (10) by means of a first NOx sensor (31), wherein a second NOx concentration sensor value (NOx2) downstream of the SCR catalytic converter (22) is determined by means of a second NOx sensor (32), The first and second NOx sensors (31, 32) have a cross sensitivity to ammonia (NH3), wherein a division into modeled NOx concentration components (r NOx，M，i ) and the modeled NH3 concentration fraction (r NH3，M，i ), in particular at the location of the second NOx sensor (32), wherein the model (M) for each modeled NH3 concentration fraction (r NH3，M，i ) to determine the NH3 effectiveness value (VW i ), If there is an effective modeled NH3 concentration fraction (r NH3，M，i ), then according to the effective modeled NH3 concentration fraction (r NH3，M，i ) and updates the NH3 ratio filter value (NH3) determined in the previous measurement (i-1) ratio，i-1 ), and according to the effective modeled NH3 concentration fraction (r NH3，M，i ) and the current second NOx concentration sensor value (NOx2 i ) to implement the absolute NH3 concentration fraction (r NH3,abs ), where if there is no valid modeled NH3 concentration share (r NH3，M，i ), then according to the current second NOx concentration value (Nox2 i ) and the NH3 ratio filter value (NH3 ratio，i-1 ) and execute the absolute NH3 concentration share (r NH3，abs ) allocation.

2. The method according to claim 1, characterized in that According to the currently valid modeled NH3 concentration fraction (r NH3，M，i ), the second NOx concentration sensor value currently determined (NOx2 i ) and the NH3 ratio filter value (NH3 ratio，i-1 ) performs the NH3 ratio value (NH3 ratio，i ), wherein the filtering is performed in particular using an exponentially weighted smoothed average.

3. The method according to claim 1, characterized in that If the NH3 effectiveness value (VW i ) exceeds a predeterminable validity threshold (S VW ), then there is an effective modeled NH3 concentration fraction (r NH3,M,i ), and if the NH3 effectiveness value (VW i ) is below a predeterminable validity threshold (S VW ), there is no effective modeled NH3 concentration fraction (r NH3，M，i ).

4. The method according to claim 1, characterized in that: According to the second NOx concentration sensor value (NOx2 i ) is executed to update the NH3 ratio filter value (NH3 ratio，i ) weighted.

5. The method according to claim 3, characterized in that: According to the NH3 effectiveness value (VW i ) is executed to update the NH3 ratio filter value (NH3 ratio，i ) weighted.

6. The method according to claim 1, characterized in that When the second NOx concentration sensor value (NOx2) exceeds and falls below a predeterminable first threshold value (S NOx2 ), according to the second NOx concentration sensor value (NOx2 i ) to identify the emission stage (E x )’s beginning and end.

7. The method according to claim 6, characterized in that For each emission stage (E x ) determines the average temperature (T SCR,m ), and according to the corresponding emission stage (E x ) of the SCR catalytic converter (22) SCR，m ) is executed to update the NH3 ratio filter value (NH3 ratio,i ) weighted.

8. The method according to claim 1, characterized in that According to n predeterminable temperature ranges of the SCR catalytic converter (22), according to the average SCR temperature (T SCR,m ) to update the NH3 ratio filter value (NH3 ratio，i，n ). 9 . A computer program configured to execute the method according to claim 1 .

10. An electronic storage medium having a computer program according to claim 9.

11. An apparatus, in particular a control device (100), which is configured to carry out the method according to any one of claims 1 to 8.

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