Method for estimating the NOx and NH3 concentration fraction downstream of at least one SCR catalyst arranged in an exhaust stream of an internal combustion engine

Abstract

Method for estimating the NOx and NH3 concentration fraction downstream of at least one SCR catalyst (22) arranged in an exhaust stream (11) of an internal combustion engine (10).

Description

State of the art

[0001] DE 10 2014 201 304 A1 concerns a method for operating a catalyst system designed to reduce nitrogen oxide emissions from the exhaust gases of an internal combustion engine, which includes at least one SCR catalyst (150) operated with a reagent that can be stored in the SCR catalyst (150) so that a certain reagent level is present in the SCR catalyst (150), wherein the dose of reagent is based on models (604, 606) using an NH3 level controller (602), modeling errors are compensated using an NH3 level monitor (605). Disclosure of the invention

[0002] In a first aspect, the invention relates to a method for estimating the NOx and NH3 concentration fraction downstream of at least one SCR catalyst arranged in an exhaust stream of an internal combustion engine, wherein a first NOx concentration sensor value is determined upstream of the SCR catalyst and downstream of the internal combustion engine by means of a first NOx sensor, where a second NOx concentration sensor value is determined downstream of the SCR catalyst using a second NOx sensor, where the first and second NOx sensors exhibit cross-sensitivity to ammonia, where, depending on the first and second NOx concentration sensor values, a model is used to divide the concentration into a modeled NOx concentration fraction and a modeled NH3 concentration fraction, particularly at the location of the second NOx sensor. where the model determines an NH3 validity value for each modeled NH3 concentration fraction, where, if a valid modeled NH3 concentration fraction is present, an NH3 ratio filter value determined in a previous measurement is updated depending on the valid modeled NH3 concentration fraction, and an assignment of an absolute NH3 concentration fraction is carried out depending on the valid modeled NH3 concentration fraction and the current second NOx concentration sensor value. where, if no valid modeled NH3 concentration fraction is available, an assignment of the absolute NH3 concentration fraction is carried out depending on the current second NOx concentration value and the NH3 ratio filter value determined in a previous measurement.

[0003] The advantage of this method lies in the statistical allocation of NOx and NH3 emissions based on historically collected data for the existing SCR system, without relying on a current allocation. For technical reasons, current functions are not yet capable of continuously and precisely distributing emissions into NOx and NH3 concentration fractions.

[0004] Measurements have shown that the historical behavior of the SCR system allows for inferences about the likely distribution between NOx and NH3 concentrations in the emissions. The new approach therefore aims to continuously determine a filter value for the SCR system's emissions distribution, thereby allocating the recorded emissions during blind phases using these historical values.

[0005] For this purpose, an NH3 ratio filter value is continuously determined and used to divide the emission shares.

[0006] Furthermore, the NH3 ratio filter value is only updated if the measured emissions can be sufficiently relied upon. For this purpose, for example, the reliability of each measured NH3 concentration fraction is checked. This can be done, for instance, by examining the magnitude of the emission spike.

[0007] In a special embodiment, the update of the NH3 ratio value is filtered depending on the currently valid modeled NH3 concentration fraction, the currently determined second NOx concentration sensor value and the NH3 ratio filter value determined in a previous measurement; in particular, the filtering is carried out using an exponentially weighted moving average.

[0008] This has the particular advantage that a precise NH3 ratio is obtained.

[0009] In an alternative configuration, if the NH3 validity value exceeds a predefinable validity threshold, a validly modeled NH3 concentration fraction is present, and if the NH3 validity value falls below a predefinable validity threshold, no validly modeled NH3 concentration fraction is present.

[0010] It remains advantageous to perform an update only when sufficient emissions are determined. This can be done, for example, by monitoring the magnitude of the emission spike.

[0011] In an advantageous embodiment, a weighting is performed for updating the NH3 ratio filter value depending on the second NOx concentration sensor value.

[0012] Furthermore, it can be advantageous to link the weighting for updating the NH3 ratio value to the emissions determined by the second NOx sensor. Since the sensors are subject to certain measurement tolerances, measurements with higher emissions can be assigned more weight than measurements with just detectable emissions.

[0013] In a further embodiment, a weighting is performed for the update of the NH3 ratio filter value depending on the NH3 validity value.

[0014] Furthermore, it can be advantageous to link the weighting for updating the NH3 ratio value to the emissions determined by the second NOx sensor. Since the sensors are subject to certain measurement tolerances, measurements with higher emissions can be assigned more weight than measurements with just detectable emissions.

[0015] In a special embodiment, depending on the second NOx concentration sensor value, the beginning and end of emission phases are detected when the second NOx concentration sensor value NOx2 exceeds and falls below a first predefinable threshold value.

[0016] In an advantageous embodiment, emission phases can be used for the process. For example, emission phases that are too short can be discarded or used as a weighting criterion for updating the NH3 ratio.

[0017] In an advantageous embodiment, a mean temperature for the SCR catalyst is determined for each emission phase, and a weighting for updating the NH3 ratio filter value is carried out depending on the mean SCR temperature for the SCR catalyst of the respective emission phase.

[0018] In an advantageous embodiment, emission phases can be used for the process. For example, emission phases that are too short can be discarded or used as a weighting criterion for updating the NH3 ratio.

[0019] In a further embodiment, depending on n predefinable temperature ranges for the SCR catalyst, an NH3 ratio filter value is updated as a function of the mean SCR temperature of the SCR catalyst.

[0020] The use of temperature ranges for the SCR catalyst in the process is particularly advantageous. The ratio filter value can then be updated with different weightings, depending on the current temperature range of the SCR catalyst. In an advantageous embodiment, a separate NH3 ratio filter value is available for each temperature range, and this value is only updated based on data in which the temperature of the SCR catalyst has been recorded.

[0021] In further aspects, the invention relates to a device, in particular a control unit, and a computer program, which are configured, in particular programmed, to execute one of the methods. In yet another aspect, the invention relates to a machine-readable storage medium on which the computer program is stored. Brief description of the drawings

[0022] The invention will be explained in more detail below with reference to an embodiment illustrated in the figures. The figures show: Fig. 1 in a schematic representation an SCR system with an SCR catalyst of an internal combustion engine, Fig. 2 a schematic flowchart of an exemplary embodiment of the inventive method for estimating the NOx and NH3 concentration downstream of at least one SCR catalyst of an internal combustion engine. Exemplary embodiments of the invention

[0023] An internal combustion engine 10 has an SCR system 20 in its exhaust stream 11, which is located in Fig. Figure 1 shows a system that includes a reducing agent dosing unit 21, which injects a urea-water solution (AdBlue) into the exhaust stream 11. Ammonia is released from this solution at the high temperatures of the exhaust gas. A first SCR catalyst 22 is arranged downstream of the reducing agent dosing unit 21. Further SCR catalysts can be arranged downstream of the first SCR catalyst 22. A first NOx sensor 31 and a temperature sensor 12 are arranged upstream of the reducing agent dosing unit 21 and downstream of an internal combustion engine 10 in the exhaust stream 11. The first NOx sensor 31 measures a first NOx concentration sensor value NOx1, preferably as a NOx concentration or as a NOx mass flow rate. A second NOx sensor 32 is arranged downstream of the first SCR catalyst 22 and measures a second NOx concentration sensor value NOx2, preferably as NOx concentration or as a NOx mass flow.This applies in particular to the NH3 concentration or NH3 mass flow rate.

[0024] In an optional configuration, an NH3 sensor 33 can also be installed downstream of the SCR catalyst 22. The NH3 sensor can measure an NH3 concentration fraction r NH3,S determine.

[0025] All NOx sensors 31 and 32 transmit their signals to an electronic control unit 100. Since the NOx sensors 31 and 32 are also cross-sensitive to ammonia in addition to nitrogen oxides, their signals are sum signals of nitrogen oxides and ammonia. However, the first NOx sensor 31 is located upstream of the reducing agent dosing unit 21, so that it reliably measures only the amount of nitrogen oxide in the exhaust gas. The reducing agent dosing unit 21 also reports the amount of ammonia injected into the exhaust stream 11 to the control unit 100.

[0026] The internal combustion engine 10 can also be designed as a hydrogen combustion engine in an alternative configuration.

[0027] The control unit 100 also contains model M, which breaks down the sum signals of the first NOx sensor 31 and the second NOx sensor 32 into a NOx concentration component and an NH3 concentration component and stores them in the control unit 100.

[0028] In the Fig. Figure 2 shows an exemplary sequence of the procedure for estimating a NOx and an NH3 concentration downstream of at least one SCR catalyst 22 arranged in an exhaust stream 11 of an internal combustion engine 10 using a flow diagram.

[0029] In a first step, the first and second NOx concentration sensor values ​​NOx1;NOx2 are continuously determined by the control unit 100. Using a model M stored on the control unit 100, a modeled NH3 concentration fraction r is calculated at discrete time points as a function of the first and second NOx concentration sensor values ​​NOx1;NOx2. NH3,M,i and a NOx concentration fraction r NOx,M,i determined. The modeled NH3 concentration fraction and the modeled NOx concentration fraction correspond to an NH3 and NOx concentration signal downstream of the SCR catalyst 22, in particular at the location of the second NOx sensor 32.

[0030] Optionally, a temperature signal T is also available. exh,i The temperature sensor 12 determines the temperature and can be used as an input for the Model M.

[0031] In the further embodiment, the method is based on the determined NH3 concentration fraction r. NH3,M, especially downstream of the SCR catalyst 22, described.

[0032] In an alternative embodiment, the NH3 concentration fraction can be determined by an NH3 sensor installed downstream of the SCR catalyst 22.

[0033] Furthermore, the model M determines the value r for each modeled NH3 concentration fraction. NH3,M,i an NH3 validity value VW i .

[0034] Preferably, a validly modeled NH3 concentration fraction r is used. NH3,M,i before, when the NH3 validity value VW i a predefinable validity threshold S VW exceeds and there is no validly modeled NH3 concentration fraction r NH3,M,i before, when the NH3 validity value VW i a predefinable validity threshold S VW falls below a certain threshold.

[0035] The process then continues in step 210.

[0036] In step 210, for each modeled NH3 concentration fraction r NH3,M,i with a valid NH3 validity value VW i an NH3 ratio filter value determined in a previous measurement (i - 1) NH3 ratio,i-1 Updated.

[0037] The NH3 ratio NH3 ratio,i-1 The control unit 100 can be initialized with a predefinable value for startup.

[0038] In a special configuration, an initialization value for the NH3 ratio is stored in the EEPROM of control unit 100.

[0039] An update of the NH3 ratio value NH3 ratio,i This is done, for example, as an exponentially weighted moving average between the NH3 ratio filter value determined in a previous measurement. ratio,i-1 and the currently determined modeled NH3 concentration fraction r NH3,M,i .

[0040] Thus, an assignment of the absolute NH3 concentration fraction r is possible.NH3,abs depending on the validly modeled NH3 concentration fraction r NH3,M,i and the current second NOx concentration sensor value NOx2 i carried out.

[0041] In an alternative configuration, different weightings can be used for updating the NH3 ratio. ratio,i This can be carried out. For example, a weighting of the update of the NH3 ratio value depending on the level of currently measured emissions can be determined, e.g., via the second NOx concentration sensor value NOx2,i. This assumes that emission phases E x Measurements with higher emissions allow for a more precise conclusion regarding the distribution of NOx and NH3 concentrations than measurements with lower emissions. This is primarily due to the tolerances of the NOx and NH3 sensors used.

[0042] In another alternative configuration, the weighting for updating the NH3 ratio value can be... ratio,i depending on the level of the determined NH3 validity value VW i be performed.

[0043] Contrary to what VW states, no valid NH3 validity value is obtained. i Determined by model M, the determined modeled NH3 concentration fraction r can be used. NH3,M,i cannot be trusted.

[0044] In this case, an assignment of the absolute NH3 concentration fraction r is made. NH3,abs depending on the current second NOx concentration value NOx2 i and the NH3 ratio filter value determined in a previous measurement i - 1 NH3 ratio,i-1 carried out.

[0045] The procedure can then be continued or terminated in step 210.

[0046] In a particular embodiment, several, in particular n, NH3 ratio filter values ​​can be used. ratio,n, for the process.

[0047] In a specific configuration, n predefinable SCR temperature ranges are defined and, for each determined modeled NH3 concentration fraction r, a corresponding value is assigned. NH3,M,i a mean temperature T exh,i determined for the SCR catalyst 22.

[0048] Depending on the average SCR temperature T exh,i Then only the NH3 ratio filter value will be displayed. ratio,n updated, which is assigned to the predefined temperature range.

[0049] For example, a first SCR temperature range is 200-350°C. A second temperature range is between 351-600°C. Thus, for the first temperature range, a first NH3 ratio filter value is NH3. ratio,1 and for the second temperature range a second NH3 ratio filter value NH3 ratio 2. These are two separate NH3 ratio filters.

[0050] If the average SCR temperature is, for example, 370°C and the modeled NH3 concentration fraction r determined by model M is NH3,M,i Valid, only the corresponding second ratio filter value NH3 would be valid. ratio,2 Updated.

[0051] In the case that the modeled NH3 concentration fraction r NH3,M,i If this is not valid, an assignment of the absolute NH3 concentration fraction r would be invalid. NH3,abs depending on the current second NOx concentration value NOx2 i and the second NH3 ratio filter value determined in a previous measurement i - 1 NH3 ratio,i-1,2 carried out.

[0052] In an alternative embodiment, there can be multiple filters depending on different mileage levels. For example, if the vehicle's current mileage is less than 5000 km, a new NH3 ratio filter is formed every 5000 kilometers.

[0053] In a specific configuration, emission phases E are particularly x or evaluation phases E x for the process. This is done in particular depending on the second NOx concentration sensor value NOx2, whereby a beginning and an end of the emission phases E x is detected when the second NOx concentration sensor value, NOx2, exceeds a first predefinable threshold value S. NOX2 exceeds and falls below the required minimum.

[0054] Validity can be maintained across the respective emission phase E x can be determined. In particular, the emissions in phase E can be determined. x determined NH3 validity values ​​VW i,Ex cumulatively against the predefinable first threshold S NOx2 to be compared. If the cumulative validity value exceeds the predefinable first threshold S NOx2 is the emission phase E xvalid and the cumulative validity value falls below the predefinable first threshold S NOx2 is the emission phase E x Not valid.

[0055] In an advantageous embodiment, an update of the NH3 ratio filter value NH3 can be performed. ratio,i depending on the emission phase E x by means of one or a combination of the cumulative quantities of the NH3 validity value, the temperature of the SCR catalyst 22, the second NOx concentration sensor value NOx2 and the modeled NH3 concentration fraction. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2014 201 304 A1

[0001]

Claims

[1] Method for estimating a NOx and a NH3 concentration fraction downstream of at least one SCR catalyst (22) of an internal combustion engine (10) arranged in an exhaust system (11), wherein a first NOx concentration sensor value (NOx1) is determined upstream of the SCR catalyst (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) is determined downstream of the SCR catalyst (22) by means of a second NOx sensor (32), wherein the first and second NOx sensors (31, 32) have a cross-sensitivity to ammonia (NH3), wherein, depending on the first and second NOx concentration sensor values ​​(NOx1;NOx2), a model (M) is used to divide the NOx concentration into a modeled NOx concentration fraction (r NOx,M,i ) and a modeled NH3 concentration fraction (r NH3,M,i), in particular at the location of the second NOx sensor (32), where the model (M) for each modeled NH3 concentration fraction (r NH3,M,i ) an NH3 validity value (VW i ) determined, where if a valid modeled NH3 concentration fraction (r NH3,M,i ) is present depending on the valid modeled NH3 concentration fraction (r NH3,M,i ) an NH3 ratio filter value determined in a previous measurement (i - 1) (NH3 ratio,i-1 ) is updated and an assignment of an absolute NH3 concentration fraction (r NH3,abs) depending on the valid modeled NH3 concentration fraction (r NH3,M,i ) and the current second NOx concentration sensor value (NOx2 i ) is carried out, where if no valid modeled NH3 concentration fraction (r NH3,M,i ), an assignment of the absolute NH3 concentration fraction (r NH3,abs) depending on the current second NOx concentration value (NOx2 i ) and the NH3 ratio filter value determined in a previous measurement (i - 1) (NH3 ratio,i-1 ) is carried out. [2] Method according to claim 1, characterized by that the update of the NH3 ratio value (NH3 ratio,i ) filtered depending on the currently valid modeled NH3 concentration fraction (r NH3,M,i ), the current determined second NOx concentration sensor value (NOx2 i ) and the NH3 ratio filter value determined in a previous measurement (i - 1) (NH3 ratio,i-1 ), in particular the filtering is carried out using an exponentially weighted moving average. [3] Method according to claim 1, characterized by that if the NH3 validity value (VW i ) a predeterminable validity threshold (S VW ) exceeds a valid modelled NH3 concentration fraction (r NH3,M,i) and if the NH3 validity value (VW i ) a predeterminable validity threshold (S VW ) no valid modelled NH3 concentration fraction (r NH3,M,i ) is present. [4] Method according to claim 1, characterized by that a weighting for updating the NH3 ratio filter value (NH3 ratio,i ) depending on the second NOx concentration sensor value (NOx2 i ) is carried out. [5] Method according to claim 3, characterized by that a weighting for updating the NH3 ratio filter value (NH3 ratio,i ) depending on the NH3 validity value (VW i ) is carried out. [6] Method according to claim 1, characterized by that depending on the second NOx concentration sensor value (NOx2 i ) a beginning and an end of emission phases (E x ) is detected when the second NOx concentration sensor value (NOx2) exceeds a first predeterminable threshold value (SNOx2 ) exceeds and falls below. [7] Method according to claim 6, characterized by that a mean temperature (T SCR,m ) for the SCR catalyst (22) for each emission phase (E x ) and a weighting for updating the NH3 ratio filter value (NH3 ratio,i ) depending on the average SCR temperature (T SCR,m ) for the SCR catalyst (22) of the respective emission phase (E x ) is carried out. [8] Method according to claim 1, characterized by that depending on n predeterminable temperature ranges for the SCR catalyst (22) an NH3 ratio filter value (NH3 ratio,i,n ) depending on the average SCR temperature (T SCR,m ) of the SCR catalyst (22) is updated. [9] Computer program which is designed to carry out a method according to one of claims 1 to 8. [10] An electronic storage medium comprising a computer program according to claim 9. [11] Device, in particular control device (100), which is designed to carry out a method according to one of claims 1 to 8.

Images