Method for estimating NOx and NH3 concentration ratio downstream of SCR catalytic converter

Abstract

The invention relates to a method for estimating a ratio of NOx and NH3 concentrations downstream of at least one SCR catalytic converter (22) of an internal combustion engine (10) arranged in an exhaust gas 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 gases from an internal combustion engine, the catalytic converter system comprising at least one SCR catalytic converter (150), which is operated with a reactant that can be stored in the SCR catalytic converter (150), so that a specific reactant level is present in the SCR catalytic converter (150), wherein the reactant is added based on a model (604, 606) by means of an NH3 level regulator (602), and modeling errors are compensated by means of an NH3 level observer (605). Summary of the invention

[0002] In a first aspect, the invention relates to a method for estimating the ratio of NOx and NH3 concentrations downstream of at least one SCR catalytic converter arranged in the exhaust gas system of an internal combustion engine,

[0003] wherein a first NOx concentration sensor value is determined upstream of the SCR catalytic converter and downstream of the internal combustion engine by means of a first NOx sensor,

[0004] wherein a second NOx concentration sensor value downstream of the SCR catalytic converter (22) is determined by means of a second NOx sensor,

[0005] wherein the first and second NOx sensors have cross-sensitivity to ammonia,

[0006] wherein a division into a modeled NOx concentration ratio and a modeled NH3 concentration ratio is performed based on the first and second NOx concentration sensor values ​​with the aid of a model, in particular at the location of the second NOx sensor,

[0007] wherein when the second NOx concentration sensor value exceeds a first predeterminable threshold value, the emission phase is identified based on the second NOx concentration sensor value,

[0008] wherein the model determines and stores the modeled NH3 concentration ratio and NOx concentration ratio at discrete time points,

[0009] wherein a ratio between the determined modeled NH3 concentration ratio and the second NOx concentration sensor value is determined,

[0010] A first counter is incremented when the ratio exceeds a predeterminable NH3 threshold value and is decremented when the ratio falls below a predeterminable NOx threshold value, wherein a NOx concentration ratio and an NH3 concentration ratio are assigned to a second NOx concentration sensor signal determined in the emission phase based on the first counter.

[0011] The method has the particular advantage that, if a sufficiently reliable database is available, a statistical distribution of the NOx concentration ratio and the NH3 concentration ratio can be made. In this case, the method improves the reliable distribution of the NOx and NH3 cross-sensitivities of the NOx sensors arranged downstream of the SCR catalytic converter. In this case, the distribution of the NOx concentration ratio and the NH3 concentration ratio can be carried out over the entire driving cycle, as required by emission regulations such as the EU7 OBM. In this case, the method starts with a statistical evaluation of the NOx concentration ratio and the NH3 concentration ratio with the start of the identified emission phase, wherein the distribution of the NOx concentration ratio and the NH3 concentration ratio is only carried out when a sufficiently reliable distribution result is available.

[0012] In a special embodiment, the second counter is incremented as long as the model reports back a valid measurement, wherein the end of the emission phase is recognized and the second counter is stopped when the second NOx concentration sensor value falls below a first predefinable threshold value.

[0013] In another embodiment, when the second counter exceeds a predeterminable validity threshold, there is a valid discharge phase. In addition, when the second counter is below a predeterminable validity threshold, there is no valid discharge phase, so that the substitute value is then used for allocation.

[0014] This method provides the particular advantage that, based on the second counter, it can be set from when there are sufficient valid measurements to allocate the NOx concentration ratio and the NH3 concentration ratio. In the absence of a sufficiently valid emission phase, substitute values ​​can be used for the allocation of the NOx concentration ratio and the NH3 concentration ratio.

[0015] In an advantageous embodiment, a proportional allocation of the NOx concentration ratio and the NH3 concentration ratio is carried out when the first counter is between a predeterminable upper maximum NH3 threshold value and a predeterminable lower minimum NOx threshold value.

[0016] In a special embodiment, only an NH3 concentration ratio is assigned to the emission phase when the first counter is greater than or equal to a predeterminable NH3 upper maximum threshold value. In the case where the second counter reaches or exceeds the NH3 upper maximum threshold value, there is a sufficiently strong indication that the emissions detected in the emission phase are present as NH3 emissions.

[0017] In an advantageous embodiment, only a NOx concentration proportion is assigned to the emission phase when the first counter is less than or equal to a predeterminable NOx lower minimum threshold value. In the case where the second counter reaches or falls below the NOx lower minimum threshold value, there is a sufficiently strong indication that the emissions detected in the emission phase are present as NOx emissions.

[0018] In a further embodiment, the third counter is incremented with the detection of the emission phase, wherein the third counter is stopped with the end of the emission phase, wherein the NOx concentration ratio is only assigned when the third counter falls below a predefinable time threshold value.

[0019] In a further aspect, the invention relates to an apparatus, in particular a control apparatus, and to a computer program, which are arranged, in particular programmed, to perform one of the methods. In a further aspect, the invention relates to a machine-readable storage medium, on which a computer program is stored. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention is explained in more detail below based on the embodiments shown in the drawings.

[0021] Figure 1 A schematic diagram shows an SCR system having an SCR catalytic converter of an internal combustion engine,

[0022] Figure 2 a) shows an exemplary measurement of a second NOx sensor plotted during time t,

[0023] b) shows the NH3 concentration ratio r determined by the model M during time t NH3,M An exemplary determination of

[0024] c) shows an exemplary determination of a first counter with a predefinable upper maximum threshold value for NH3 and a predefinable lower minimum threshold value for NOx,

[0025] d) shows a predeterminable validity threshold S Val An exemplary determination of the second counter,

[0026] Figure 3 A schematic flow chart shows an exemplary design 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

[0027] The internal combustion engine 10 has an SCR system 20 in its exhaust system 11, which is Figure 1. The SCR system has a reducing agent metering unit 21, by means of which a urea aqueous solution (AdBlue) can be fed into the exhaust system 11. At the high temperature of the exhaust gas, ammonia is released from the urea aqueous solution. The 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. The first NOx sensor 31 and the 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 the 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 the 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.

[0028] In an alternative embodiment, an NH3 sensor 33 can also be installed downstream of the SCR catalytic converter 22. The NH3 sensor can determine the NH3 concentration ratio r NH3 All NOx sensors 31, 32 forward their signals to the electronic control device 100. Since the NOx sensors 31, 32 are 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 arranged upstream of the reducing agent metering unit 21, so that the first NOx sensor 31 reliably measures only the amount of nitrogen oxides in the exhaust gas. The reducing agent metering unit 21 also reports the amount of ammonia metered into the exhaust system 11 to the control device 100.

[0029] The control device 100 also stores a model M, which can determine the NOx concentration ratio r according to the first NOx concentration sensor value NOx1 and the second NOx concentration sensor value NOx2. NOx,M and NH3 concentration ratio r NH3,M Alternatively, the exhaust gas temperature from the temperature sensor 12 may be used as an input variable.

[0030] However, the described model M does not provide a continuous NOx concentration ratio and NH 3 concentration ratio and is based on the first and second NOx sensor signals upstream and downstream of the SCR catalytic converter 22 .

[0031] Figure 2 An exemplary measurement of the proposed method is shown in FIG. The time axis t is used as abscissa for all diagrams a)–d).

[0032] In the upper diagram a), an exemplary measurement of the second NOx sensor 32 is shown in parts per million (ppm) during the time t. Furthermore, a first predeterminable threshold value S NOx2 , an emission phase is identified when the second NOx concentration sensor value NOx2 exceeds the threshold value, and an emission phase is identified when the second NOx concentration sensor value NOx2 again falls below the first predeterminable threshold value S NOx2 The emission phase ends when the emission phase ends. The detection of the end of the emission phase can also preferably be performed in a filtered manner, so that the second NOx concentration sensor value NOx2 must be below a first predeterminable threshold value S NOx2 A minimum period of time.

[0033] Graph b) shows the modeled NH3 concentration ratio r determined by the model M during time t in parts per million (ppm) NH3,M .

[0034] In diagram c), the maximum threshold NH3 for the NH3 with a predeterminable NH3 is shown. max and the predeterminable minimum NOx threshold NOx min A first counter Z1 (having a quantity n) is provided.

[0035] It can be seen that the first counter Z1 only displays a change when the model M is able to determine a valid measurement value. In particular, the first counter Z1 changes according to the NH3 concentration ratio r determined by the model M. NH3,M Count.

[0036] In the present case, the first counter Z1 initially remains unchanged until the model M determines the NH3 concentration ratio r NH3,M The first counter Z1 is incremented continuously and takes the maximum threshold NH3 max The value of .

[0037] In an alternative design, the first counter Z1 can also take a value greater than the maximum threshold NH3 max value and is less than the minimum threshold NOx min The value of .

[0038] Diagram d) shows the second counter Z2 (with number n) and the predefinable validity threshold value S Val It can be seen that only when the model M has a NH3 concentration ratio r NH3,M The second counter Z2 is incremented only when there is a valid measurement. Here, the second counter Z2 can be reset to 0 again when the end of the discharge phase is detected.

[0039] In this measurement it can be seen that the second counter Z2 exceeds a predefinable validity threshold value S Val In an advantageous embodiment, the second counter Z2 exceeds the validity threshold SVal , the NOx concentration ratio and the NH3 concentration ratio r are performed on the second NOx concentration sensor signal NOx2 determined in the emission phase. NOx ; r NH3 Verification of the allocation.

[0040] Figure 3 An exemplary sequence of a method for estimating NOx and NH 3 concentrations downstream of at least one SCR catalytic converter 22 of an internal combustion engine 10 arranged in the exhaust system 11 is shown on the basis of a flow chart.

[0041] In a first step 200, the control device 100 continuously determines a first and a second NOx concentration sensor value NOx1; NOx2. If the second NOx concentration sensor value NOx2 exceeds a first predeterminable threshold value S NOx2 , then the emission phase is identified. Here, the first predeterminable threshold value S NOx2 Preferably it may be 5 ppm.

[0042] In a special design, the second NOx concentration sensor value NOx2 can also be filtered during a predeterminable time period to determine the first predeterminable threshold value S. NOx2 The method then continues with step 210.

[0043] In step 210, when the emission phase is identified, the model M stored in the control device 100 is started. Here, the model M determines the modeled NH3 concentration ratio r at discrete time points based on the first and second NOx concentration sensor values ​​NOx1; NOx2 NH3,M and the modeled NOx concentration ratio r NOx,M .

[0044] The modeled NH 3 and NOx concentration ratio corresponds here to the NH 3 and NOx concentration signals downstream of the SCR catalytic converter 22 , in particular at the location of the second NOx sensor 32 .

[0045] Optionally, the temperature signal of the temperature sensor 12 may also be used as an input variable of the M model.

[0046] In another embodiment, based on the determined modeled NH3 concentration ratio r NH3,M In the alternative design, the NH3 concentration ratio, in particular the modeled NH3 concentration ratio r NH3,M , can be determined by the NH 3 sensor 33 installed downstream of the SCR catalytic converter 22 . The method then continues with step 220 .

[0047] In step 220, the determined modeled NH3 concentration ratio r is continuously determined. NH3,Mand the ratio V between the second NOx concentration sensor value NOx2. This will be performed for each discrete measurement value of the model M.

[0048] If the ratio V exceeds a predeterminable NH3 threshold value S NH3 , the first counter Z1 is incremented if the ratio V is below a predeterminable NOx threshold value S NOx , the first counter Z1 is decremented. In addition, the model M reports back a status bit for each measurement value determined to determine whether the measurement is valid. As long as the status bit reports back a valid measurement, the second counter Z2 is incremented. The method then continues with step 230.

[0049] In step 230, when the second NOx concentration sensor value NOx2 is again below the first predeterminable threshold value S NOx2 The end of the emission phase is identified when

[0050] At this point in time, the second counter Z2 is compared to a predeterminable validity threshold value S Val If the second counter Z2 is greater than or equal to a predeterminable validity threshold S Val , the NOx concentration ratio and the NH3 concentration ratio r are calculated based on the first counter Z1 for the second NOx concentration sensor signal NOx2 determined in the emission phase. NOx ; r NH3 allocation.

[0051] If the second counter Z2 falls below a predeterminable validity threshold S Val , then the dispensing is suspended due to the preferred presence of a too short discharge phase.

[0052] Alternatively, if the second counter falls below a predefinable validity threshold S Val When the NOx concentration ratio and NH3 concentration ratio are calculated based on the pre-set replacement values, NOx ; r NH3 Preferably, when the emission phase is too short, it is assumed that only the NOx concentration ratio r NOx .

[0053] In a special design, if the first counter Z1 is greater than or equal to a predeterminable maximum NH3 threshold value NH3 max , then only the NH3 concentration proportion r is assigned to the second NOx concentration sensor signal NOx2 determined in the emission phase NH3 Even if the second counter Z2 falls below a predeterminable validity threshold S Val , or you can maintain that allocation.

[0054] In another embodiment, if the first counter Z1 is less than or equal to a predeterminable NOx lower minimum threshold value NOxmin , then the second NOx concentration sensor signal NOx2 determined in the emission phase is only assigned the NOx concentration ratio r NOx Even if the second counter Z2 falls below a predeterminable validity threshold S Val , or the allocation can be maintained.

[0055] In a special design, the third counter Z3 is incremented as the discharge phase is detected and ends at the end of the discharge phase.

[0056] If the third counter Z3 falls below a predeterminable time threshold S time,min , then the second NOx concentration sensor signal NOx2 determined in the emission phase is only assigned the NOx concentration ratio r NOx .

[0057] The method can then be ended or started again from the beginning in step 200 .

Claims

1. A method for estimating the ratio of NOx and NH3 concentrations downstream of at least one SCR catalytic converter (22) arranged in an 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), wherein the first and second NOx sensors (31, 32) have cross-sensitivity to ammonia (NH3), According to the first and second NOx concentration sensor values ​​(NOx1; NOx2), a modeled NOx concentration ratio (r) is determined by means of a model (M), in particular at the location of the second NOx sensor (32). NOx,M ) and the modeled NH3 concentration ratio (r NH3,M ), When the second NOx concentration sensor value (NOx2) exceeds a first predeterminable threshold value (S NOx2 ), identifying the emission phase according to the second NOx concentration sensor value (NOx2), The model (M) determines and stores the modeled NH3 concentration ratio and NOx concentration ratio (r NH3,M ; r NOx,M ), The modeled NH3 concentration ratio (r NH3,M ) and the second NOx concentration sensor value (NOx2), When the ratio (V) exceeds a predeterminable NH3 threshold value (S NH3 ), and when the ratio (V) falls below a predeterminable NOx threshold value (S NOx ), the first counter (Z1) is decremented, wherein the NOx concentration ratio and the NH3 concentration ratio (r) are calculated for the second NOx concentration sensor signal (NOx2) determined in the emission phase according to the first counter (Z1); NOx ; r NH3 ) allocation.

2. The method according to claim 1, characterized in that As long as the model (M) reports back a valid measurement, a second counter (Z2) is incremented, When the second NOx concentration sensor value (NOx2) is lower than the first predeterminable threshold value (S NOx2 ), the end of the discharge phase is detected and the second counter (Z2) is stopped.

3. The method according to claim 2, characterized in that When the second counter (Z2) exceeds a predeterminable validity threshold (S Val ), there is a valid discharge phase, and when the second counter (Z2) is below the predeterminable validity threshold (S Val ), there is no valid emission phase, and the allocation is performed using alternative values.

4. The method according to claim 1, characterized in that: When the first counter (Z1) is at a predeterminable NH3 upper maximum threshold value (NH3 max ) and a predeterminable minimum NOx threshold (NOx min ) between the NOx concentration ratio and the NH3 concentration ratio (r NOx ; r NH3 ) in proportion.

5. The method according to claim 1, characterized in that When the first counter (Z1) is greater than or equal to a predeterminable NH3 upper maximum threshold value (NH3 max ), only the NH3 concentration ratio is allocated to the emission stage.

6. The method according to claim 1, characterized in that When the first counter (Z1) is less than or equal to a predeterminable NOx lower minimum threshold value (NOx min ), only the NOx concentration ratio is allocated to the emission stage.

7. The method according to claim 1, characterized in that With the detection of the emission phase, a third counter (Z3) is incremented, wherein the third counter (Z3) is stopped with the end of the emission phase, wherein the third counter (Z3) is stopped when the third counter (Z3) falls below a predeterminable time threshold value (S time,min ), only the NOx concentration ratio (r NOx ).

8. The method according to claim 1, characterized in that The NOx concentration ratio and the NH3 concentration ratio are converted into NOx mass flow rate and NH3 mass flow rate.

9. A computer program arranged to perform the method according to any one of claims 1 to 8.

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

11. A device, 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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