Method, computing unit and computer program for determining the amount of NOx and NH3 in an exhaust gas downstream of an internal combustion engine and an NH3 storage unit

Abstract

The invention relates to a method (200) for determining (290) the amount of NH3 contained in an exhaust gas (10) downstream of an internal combustion engine (1) using an NH3 and NOx sensitive NX sensor (17, 18, 19), comprising receiving (210) a sensor signal from the NX sensor and determining the amount of NH3 based on the sensor signal and depending (220, 240, 260) on the fulfillment of at least one condition (331, 332, 333), wherein the at least one condition (331, 332, 333) is the presence of an exhaust gas temperature exceeding a minimum exhaust gas temperature, in particular for the first time, as a first condition, and / or the presence of an exhaust gas temperature exceeding a maximum exhaust gas temperature as a second condition, and / or the presence of heat input into an exhaust gas system (120) upstream of the NX-Sensors (17, 18, 19), which exceeds a minimum heat input, as the first condition,and / or the presence of a heat input into an exhaust system (120) upstream of the NX sensor (17, 18, 19) that exceeds a maximum heat input, as the second condition. In embodiments of the invention, further conditions can also be checked, wherein, in particular, the presence of a sensor signal level that exceeds a minimum level can be used as a third condition, and / or the presence of a sensor signal gradient that exceeds a positive threshold can be used as a fourth condition. Furthermore, a computing unit (20) and a computer program for carrying out such a method (200) are proposed.

Description

[0001] The present invention relates to a method for determining the amount of NOx and NH3 in an exhaust gas downstream of an internal combustion engine and an NH3 storage device, as well as a computing unit and a computer program for carrying it out. Background of the invention

[0002] As emissions standards become increasingly stringent (e.g., existing EU6, anticipated EU7, and corresponding regulations in other jurisdictions), exhaust aftertreatment of internal combustion engines and, increasingly, on-board monitoring (OBM) of their performance are mandatory. Exhaust aftertreatment converts pollutants contained in the exhaust gas of the internal combustion engine (e.g., carbon monoxide CO, hydrocarbons CH, nitrogen oxides NOx, ammonia NH3, etc.) into less harmful substances. This is generally achieved using catalysts and, if necessary, auxiliary substances (e.g., urea, secondary air injection, etc.). Monitoring can be carried out using suitable sensors (e.g., a lambda sensor downstream of a catalyst, an NOx sensor, etc.).

[0003] Sensors typically used in exhaust systems for NOx exhibit cross-sensitivity to NH3, so that such a sensor signal can be interpreted as being based on both an NH3 content of the exhaust gas and a NOx content of the exhaust gas.

[0004] NH3 can be stored very effectively by NH3 storage media, such as condensate in the exhaust system. If the storage capacity of the medium is lost, e.g., through evaporation of the water, the NH3 is released again.

[0005] One way to discriminate between NH3 and NOx during the discharge phase of the NH3 storage system is to analyze the typically significantly different dynamics of the concentrations of both components in combustion engine exhaust gases: Downstream of the NH3 storage system, the NH3 concentration exhibits considerably lower gradients than is typically the case for NOx. A method for discriminating between NH3 and NOx emissions without an NH3 storage system is described, for example, in DE 10 2022 209 970.2. Disclosure of the invention

[0006] According to the invention, a method for determining the amount of NOx and NH3 in an exhaust gas downstream of an internal combustion engine and an NH3 storage device, as well as a computing unit, a machine-readable storage medium, and a computer program for carrying out this method, with the features of the independent claims, are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0007] Within the scope of this invention, a quantity of NOx or NH3 is understood to mean a NOx or NH3 concentration and / or a quantity of NOx or NH3 substance and / or a NOx or NH3 mass flow and / or a NOx or NH3 mass flow.

[0008] The invention addresses, in particular, the problem that (condensed) water can be present within a typical exhaust system of an internal combustion engine when the exhaust system temperature is sufficiently low. Water is capable of very effectively absorbing significant amounts of NH3 (e.g., in the form of dissolved NH3 or dissolved ammonium hydroxide, which forms from NH3 in combination with water; for the sake of simplicity, the term NH3 is used here to encompass all forms of free and / or water-soluble NH3). For example, 1 L of water at a temperature of 20°C can absorb up to 500 g of NH3. Therefore, (condensed) water in the exhaust system is considered an NH3 reservoir.The invention can also be used to address thermal NH3 desorption from SCR, ASC, or similar catalysts that can absorb NH3 similarly to water through sorption, but release it again at elevated temperatures or excessively high fill levels if the NH3 is not converted (e.g., by O2 during overrun within the appropriate temperature range). The invention therefore employs a method of determining separate NOx and NH3 quantities in an exhaust gas downstream of an internal combustion engine and an NH3 storage system, based on a sensor signal from an NX sensor that is sensitive to both NOx and NH3. To differentiate between NOx and NH3 contributions to the sensor signal, the fulfillment and / or non-fulfillment of one or more conditions is checked, and the quantities of NH3 and NOx in the exhaust gas are determined depending on this fulfillment or non-fulfillment.

[0009] The conditions whose fulfillment or non-fulfillment is analyzed to differentiate between NH3 and NOx emissions can, in various configurations, comprise one or more from the group consisting of a first condition, a second condition, a third condition, and a fourth condition. In the following, a condition will be referred to as "true" if it is fulfilled and as "false" if it is not. When a condition is referred to as "withdrawal" in the following, this refers to a situation in which the condition in question was initially fulfilled but subsequently ceased to be fulfilled.

[0010] By verifying that the condition(s) are met and / or that they interact with each other, it can be ensured that NOx emissions are not mistakenly identified as NH3 emissions (or vice versa).

[0011] The first condition is met when an exhaust gas temperature in the catalyst exceeds a minimum temperature, particularly for the first time, and / or when there is a heat input into an exhaust system upstream of the NX sensor above a minimum heat input. Specifically, the minimum temperature can be chosen such that, upon exceeding it, the release of NH3 from a corresponding storage medium (e.g., water or a dedicated NH3 storage system within the exhaust system) is enabled. For example, a minimum temperature of approximately 60°C can be assumed for NH3 release from water, as this is associated with significant water evaporation. Similarly, significant water evaporation or NH3 release from a dedicated NH3 storage medium can also be assumed in the case of a minimum heat input. In the case of NH3 absorbed in storage catalysts, a minimum temperature of approximately...It can be assumed that at 300°C, a release of NH3 from the storage tank will begin.

[0012] The second condition is triggered when the exhaust gas temperature in the catalyst exceeds a maximum temperature. The reversal of this second condition can be implemented with hysteresis to account for system cooling and restarts. Alternatively or additionally, the second condition can be triggered if heat input into an exhaust system upstream of the NX sensor is detected above a maximum heat input. In this case as well, the reversal of this second condition can be implemented with hysteresis. The maximum temperature can be chosen such that exceeding it indicates that a corresponding NH3 storage tank is completely empty (e.g., for water above its boiling point; with a safety margin, for example, 120°C or 150°C; for NH3 from storage catalysts, a maximum temperature of, for example, 500°C can be used).

[0013] The third condition becomes true when a sensor signal level is present that exceeds a minimum level for the first time, whereby the cancellation of this condition may be subject to hysteresis (e.g. a cancellation minimum level that is below the minimum level for the condition to be fulfilled).

[0014] The fourth condition becomes true when a sensor signal gradient exceeds a positive threshold. This condition is reversed when a sensor signal gradient ceases to fall below a negative threshold.

[0015] Thus, before the minimum temperature or minimum heat input is exceeded (first condition incorrect), the sensor signal can be interpreted as NOx, since NH3 is completely absorbed and retained in corresponding NH3 storage tanks.

[0016] If the maximum temperature or the maximum heat input is exceeded (first condition true, second condition true), it can be assumed that all NH3 from the respective NH3 storage tanks has already been released. Therefore, sensor signals received at higher exhaust gas temperatures can be attributed directly to emissions from the internal combustion engine that were not temporarily stored in the NH3 storage tank. In such cases, a distinction can be made between NH3-related influences on the sensor signal and NOx-related influences according to the method described in DE 10 2022 209 970.2.

[0017] After the minimum temperature or minimum heat input is exceeded for the first time, but without exceeding the maximum temperature (first condition true, second condition false), a release of NH3 from the water (or other NH3 storage) can be expected. However, this release may be superimposed by NOx emissions from the combustion engine. In this context, the third and fourth conditions for distinguishing between NOx and NH3 come into play, differentiating the slower dynamics of NH3 release, as previously explained, from the faster dynamics of NOx emissions.

[0018] If the signal level exceeds the minimum level without a prior detection of a signal gradient above the positive threshold (third condition true, fourth condition false), this signal is interpreted as NH3 from the memory. However, if a signal gradient above the positive threshold is detected (third and fourth conditions true), the signal is interpreted as a mixed signal. In particular, the signal level at the onset of the fourth condition is interpreted as being caused by NH3. Any signal level exceeding this is interpreted as NOx. In other words, under this interpretation, the NH3 content of the exhaust gas is "frozen"—that is, assumed to be constant—at the onset of the fourth condition, while the sensor signal exceeding the corresponding signal level is interpreted as being caused by NOx. This accounts for the different emission dynamics of the species involved.

[0019] However, if a signal gradient above the positive threshold is detected without the signal level having previously reached the corresponding minimum level (third condition false and fourth condition true), the sensor signal is interpreted as NOx and the detection of the third condition is temporarily switched off to prevent a brief exceedance of the minimum level by NOx emissions from the internal combustion engine from leading to the assumption that the NH3 storage has started releasing NH3.

[0020] Determining the amount of NH3 and / or, as described above, the amount of NOx, in at least one embodiment, involves applying a respective arithmetic operation to the sensor signal. In particular, the arithmetic operation may include integrating the sensor signal and / or multiplying the sensor signal by a calibration parameter, and / or filtering the sensor signal. Specifically, a calculation method used for NOx may differ from a calculation method used for NH3.

[0021] A computing unit according to the invention, e.g. a control unit of a motor vehicle, is, in particular in terms of programming, equipped to carry out a method according to the invention.

[0022] Implementing a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, as this incurs particularly low costs, especially if an executing control unit is already available for other tasks. Finally, a machine-readable storage medium is provided with a computer program stored on it as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical, and electrical storage media, such as hard drives, flash memory, EEPROMs, DVDs, etc. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or wireless (e.g., via a WLAN network, a 3G, 4G, 5G, or 6G connection, etc.).

[0023] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0024] The invention is schematically illustrated in the drawing using an exemplary embodiment and is described below with reference to the drawing. Brief description of the drawings Fig. Figure 1 schematically shows an arrangement with an exhaust system as it can be used within the scope of the invention. Fig. Figure 2 schematically shows an embodiment of a method according to the invention in the form of a simplified flowchart. Fig. Figure 3 shows signal profiles as they can be observed in embodiments of the invention, in the form of diagrams of a respective signal level over time. embodiment(s) of the invention

[0025] In Fig. 1 is an arrangement 100, as it can be used within the scope of the invention, shown schematically and designated overall as 100.

[0026] The arrangement 100 comprises an internal combustion engine 1 and an exhaust system 120 with several catalysts 11, 12, 13 arranged downstream of the internal combustion engine 1. In the illustrated example, several sensors 17, 18, 19 are provided, in particular sensors designed to determine the composition of the exhaust gas in the exhaust system. The sensors 17, 18, 19 are each connected to a processing unit 20, for example, a control unit of a motor vehicle comprising the arrangement 100.

[0027] In the example shown, the computing unit 20 is furthermore connected to the internal combustion engine 1 and to external devices 14, 15, 16, for example secondary air supply lines, exhaust gas burners, reducing agent dosing units, electrical heating elements or similar, each of which is assigned to one of the catalysts 11, 12, 13, via a data-conducting connection. In particular, electrical heating elements can also be arranged directly in the catalyst or within a housing of the catalyst.

[0028] Exhaust gas 10 generated by the internal combustion engine 1 is successively fed to the catalysts 11, 12, 13 for purification and / or detoxification. Each catalyst 11, 12, 13 can be designed for a specific detoxification process or for multiple simultaneous detoxification processes. For example, a first catalyst 11, which may be located near the internal combustion engine 1, can be configured as a three-way catalyst (TWC), while a second 12 and third 13 catalyst may comprise other catalysts and / or purification components such as NOx storage catalysts, SCR catalysts, particulate filters, or similar devices. The second and third catalysts 12, 13 may also comprise one or more additional TWCs. Furthermore, the first catalyst 11 may also comprise one or more other purification components and need not necessarily be configured as a TWC.

[0029] It is understood that appropriately adapted catalysts can be used for the exhaust systems of a diesel engine, in particular oxidation catalysts, lean NOx traps (LNT), SCR catalysts, particulate filters and the like.

[0030] For the sake of readability, the invention is explained in more detail here using an example with a gasoline engine as the internal combustion engine 1.

[0031] In the embodiment of the invention presented here, at least one of the catalysts 11, 12, 13 is configured as a TWC catalyst. In such a case, the sensors 17, 18, 19 are each configured as NX sensors, which output a signal whose intensity (e.g., the magnitude of a signal voltage) depends on the concentration of non-elemental nitrogen compounds in the exhaust gas being analyzed. Typically, such sensors are not selective for nitrogen oxides but exhibit cross-sensitivity to other nitrogen compounds, particularly ammonia. During operation of the internal combustion engine 1, ammonia (NH3) is formed by the reaction of nitrogen oxides (NOx) from the internal combustion engine 1 in a TWC (e.g., catalyst 11) at sufficient temperature and insufficient air. This ammonia is then stored, for example, in condensate and / or in dedicated storage tanks in the catalysts further downstream (e.g., in the exhaust gas recirculation system).Catalysts 12, 13) are stored in the exhaust system 120 and released (again) when the water evaporates. As already mentioned at the beginning, the term "NH3" in the terminology used here also refers to all species derived from ammonia, such as ammonium hydrate or other dissociated and / or sorbed species in a storage system.

[0032] In Fig. Figure 2 is an embodiment of a method according to the invention, schematically represented in the form of a simplified flowchart and designated overall by 200.

[0033] If reference is made to device components in the description of method 200, these relate in particular to, but are not limited to, the following: Fig. 1. Components discussed. For the sake of simplicity and to avoid repetition, the procedure 200 is described with respect to the NX sensor 19 downstream of the TWC catalyst 13; however, it can also be carried out for one of the other TWC catalysts 11, 12 (using the NX sensor 17, 18) or for several of the TWC catalysts 11, 12, 13. In particular, when using the last NX sensor 19, all ammonia contained in (condensed) water, which is expelled when the exhaust system 120 is heated, can be detected.

[0034] In Fig. 3 are signal waveforms as they appear within the framework of the in Fig. The effects of the process 200 described in Figure 2 can be observed in the form of diagrams showing the respective signal level over time. A first diagram 310 illustrates the application of an advantageous embodiment of a method according to the invention, for example, method 200. Fig. 2. The abscissa of diagram 310 represents time t, while the ordinate represents the signal level of a sensor 17, 18, 19, proportionally divided according to exhaust gas component (here denoted as the quantity l of the corresponding exhaust gas component). The sensor signal is thus divided into a first signal component 311, which is attributable to NH3, and a second signal component 312, which is attributable to NOx.

[0035] For comparison purposes, a second diagram 320 is also shown, which represents signals from a sensor arrangement not typically provided in the arrangement 100 at an outlet of the exhaust system 120, which has specific sensitivity for NH3 and NOx, for example, an FTIR measuring device (infrared spectrometer). The abscissa of diagram 320 is a time axis in which time t is synchronized with the time axis of diagram 310 such that gas transit times between the sensor 17, 18, 19, which provides diagram 310, and the sensor arrangement that provides diagram 320 are disregarded. The signals of the comparison diagram 320 are significantly less sharp compared to the sensor signals of diagram 310, which can be attributed in particular to the longer gas transit times to the outlet of the exhaust system 120 and the associated partial mixing.

[0036] Finally, in Fig. Figure 3 shows a third diagram 330, which illustrates control signals as they can be used in embodiments of the invention. The abscissa corresponds to the same time axis t that is also used in the two diagrams 310 and 320, while a logical value (e.g., 0 or 1, or False or True) is plotted on the ordinate of the third diagram 330.

[0037] In the first step of procedure 200, a signal from an NX sensor, for example a signal from sensor 19, is received. This occurs in diagrams 310, 320, and 330 from time t=t0. In step 210, the received signal can also be appropriately filtered and / or smoothed.

[0038] In step 220, it is checked whether a first condition, here the presence of an exhaust gas temperature that lies within a temperature range above a minimum exhaust gas temperature, for example 60°C, and / or whether a second condition, here the presence of an exhaust gas temperature that lies within a temperature range above a maximum exhaust gas temperature, for example 150°C, is met. The limits of these temperature ranges are chosen in the example described here such that any (condensed) water present in the exhaust system 120 begins to evaporate at the minimum exhaust gas temperature, or that NH3 dissolved in the water begins to be driven out of the water at the minimum exhaust gas temperature, and that all water present in the exhaust system 120 is completely evaporated when the maximum exhaust gas temperature is reached. Alternatively or additionally, other orFurther temperature ranges can be defined at which other NH3 storage components, if any, within the exhaust system 120 are emptied (e.g., storage catalysts or similar). Alternatively, instead of temperature, the amount of heat introduced into the exhaust system 120 can also be considered within the framework of the first and second conditions. Regardless of the specific design of the temperature ranges, a hysteresis condition can be implemented within the framework of the first and second conditions, for example, such that after exceeding the maximum temperature (i.e., the complete emptying of the NH3 storage, e.g., through evaporation of the stored water), the minimum temperature must first be undershot (especially for a minimum duration) before the first condition can again be considered fulfilled.This is because, after an NH3 storage facility has been completely emptied, an NH3 storage level must first be built up again before emissions from this storage facility can be assumed.

[0039] Instead of falling below the minimum temperature, falling below a temperature threshold below the minimum temperature can also be used as the hysteresis condition. This allows the thermodynamic behavior of the NH3 storage (water or storage catalyst) to be modeled even better, since significant condensation of water is generally to be expected at temperatures well below the evaporation temperature. Similarly, significant amounts of NH3 are to be expected to be stored in an NH3 storage system at temperatures well below the minimum temperature required for discharge. The hysteresis condition can also be tested across multiple operating cycles (for example, after starting internal combustion engine 1, it can first be checked whether the minimum temperature (or threshold below the minimum temperature) has been reached in the meantime, following a maximum temperature exceedance in a previous operating cycle).the lower temperature threshold) was undercut.

[0040] If the first condition is not met (e.g., t <t1 in Fig. 3) Procedure 200 continues with step 230, in which the received sensor signal is evaluated as being caused by NOx. For example, in step 230, the signal level can be calculated using a first calibration factor to determine the amount of NOx in the exhaust gas (signal component 312 in diagram 310).

[0041] If, however, step 220 determines that the first condition is met and the second condition is not (i.e., that the exhaust gas temperature is within the described temperature range above the minimum temperature and below the maximum temperature; indicated in diagram 330 by means of control signal 331), the procedure continues with step 240, in which it is checked whether a third condition is met. In the example shown here, the third condition is the presence of a sensor signal level that exceeds a minimum level (especially for the first time) (e.g., t2). <t<t5 in Fig. 3).

[0042] If the third condition is not met, procedure 200 continues with step 250, in which the received sensor signal is evaluated as being caused by NOx (for example, according to the procedure described in relation to step 230).

[0043] If, however, step 240 reveals that the third condition is also met (indicated in diagram 330 by means of control signal 332), the procedure continues with step 260.

[0044] In principle, if the third condition in step 240 is met, it can be assumed that an NH3 storage system has begun releasing NH3. As mentioned earlier, the reversal of this third condition can also be subject to hysteresis (e.g., a minimum reversal level that is below the minimum level required for the condition to be met). This can, for example, prevent short-term signal fluctuations from affecting the emission measurement. Furthermore, this approach better reflects reality, in that the dynamics of NH3 release from a storage system also depend on the NH3 concentration in the storage system or on the total amount stored, and that as the storage concentration or amount decreases, the concentration in the exhaust gas decreases gradually rather than abruptly.This can be clearly seen in the following example: if NH3 is present dissolved in condensate in the exhaust system 120, and the water begins to evaporate, the boundary layer relevant for evaporation between the water and the air or exhaust gas stream will typically decrease over time (a water reservoir typically dries out from the edges) and will not dry out the entire area at once. Therefore, the NH3 concentration in the exhaust gas decreases slowly as a water reservoir begins to dry out, until the reservoir is completely dry. This behavior is well represented by a hysteresis-based cancellation of the third condition. To ensure that the emission is indeed NH3, it must be distinguished from any potential NOx emission. This is the purpose of step 260.

[0045] In step 260, it is checked whether a fourth condition is met. In the example shown here, this fourth condition is used to distinguish a signal peak caused by NOx in the exhaust gas from signal components caused by NH3. As explained at the beginning, the NOx emission behavior of a typical exhaust system downstream of an internal combustion engine exhibits significantly higher dynamics than the NH3 emission behavior from an NH3 storage system. The fourth condition takes advantage of this difference in dynamics. A NOx signal peak (e.g., in Fig. Signal component 312 or 322 (in the period between t3 and t4) is typically characterized by very steep edges or signal gradients with a very high magnitude. In other words, the beginning of a NOx peak is characterized by a high positive signal gradient, and the end of the peak by a high negative signal gradient. The criterion for detecting the beginning of an NOx peak can be the exceeding of a positive threshold by the first derivative of the appropriately filtered sensor signal (also referred to as the sensor signal gradient). The criteria for detecting the end of an NOx peak can be the falling below and subsequent exceeding of a negative threshold by the first derivative of the appropriately filtered sensor signal.Therefore, a NOx peak can be identified as lying between such edges, and it can be assumed that all NOx is converted by corresponding catalyst reactions outside this range. The fourth condition can thus be considered true when a sensor signal gradient exceeds a positive threshold. The reversal of this condition is linked to the presence of a sensor signal gradient that ends the fall below a negative threshold. In other words, the fourth condition, once initially fulfilled, remains true until the sensor signal gradient first falls below a negative threshold and then again exceeds it. For example, 150 ppm / s can be used as a positive threshold, while -50 ppm / s can be used as a negative threshold.

[0046] If the fourth condition is not met (i.e., no high dynamic signal is present), the procedure 200 continues with step 280, in which the sensor signal is evaluated as being caused by NH3 (signal component 311 or 321 in Fig. 3) The received sensor signal or the respective signal level can be combined with a second calibration factor to determine the amount of NH3 in the exhaust gas. The second calibration factor can, for example, be the same as the first calibration factor (e.g., if the sensor used is equally sensitive to NH3 as to NOx) or have a different value than the first calibration factor (e.g., if the sensor sensitivity for NH3 is different from that for NOx).

[0047] If, in step 260, it is determined that a NOx peak is currently present (i.e., the fourth condition is met), the sensor signal is interpreted as being (at least partially) caused by NOx and evaluated accordingly in step 270. In step 270, an NH3 quantity measured at a point in time immediately before the onset of a NOx peak can be assumed to remain constant, and the sensor signal can thus be divided as being based on a combination of NH3 and NOx content. A portion of the current signal level that exceeds the signal level received in the preceding period is converted into a corresponding NOx content, while the NH3 content of the exhaust gas is assumed to be constant throughout the entire duration of the NOx peak.

[0048] In other words, as long as a NOx peak is detected, the last value for the NH3 quantity can be "frozen" and the detected NH3 quantity used for further calculations. Any peak beyond this is interpreted as the NOx quantity. If a NOx peak is detected before the start of NH3 release, the detection of NH3 release can be stopped until the end of the NOx peak, and the total quantity can be interpreted as the NOx peak.

[0049] In embodiments of method 200, the NH3 component of the signal from the last step 280 can also be subtracted from the sensor signal in the current step 270 before the detection of a NOx peak (from the previous iteration of method 200) (this is in Fig. 2 indicated by a dashed arrow between steps 280 and 270).

[0050] In Fig. 3 is the period in which a NOx peak was detected (between t=t3 and t=t4) and is marked by a corresponding control signal 333. To reliably distinguish a NOx peak from a steeper gradient in the NH3 quantity at higher loads, additional information, such as exhaust gas mass flow and / or the (voltage) signal of a lambda sensor downstream of the first catalyst 11 in the exhaust system 120, can be used. If the latter does not fall below a lower threshold, it can be assumed that no NOx peak is present. If the sensor used for procedure 200 is activated in a grid step, a signal jump can occur as a result of the activation. To prevent this signal jump from being evaluated as a high positive gradient and thus as the beginning of a NOx peak, the NOx peak detection is deactivated for this calculation step or this iteration of procedure 200.

[0051] At the end of an iteration of procedure 200, all determined quantities of NOx and NH3 are summed with quantities determined from previous iterations to determine a total mass of emitted NOx and / or a total mass of NH3. This is in Fig. 2 is symbolized by steps 290 (integration of the determined NH3 quantities over time or over a quantity of exhaust gas emitted during this time) and 295 (integration of the determined NOx quantities over time or over a quantity of exhaust gas emitted during this time).

[0052] If all available NH3 storage (water and / or storage catalysts) are detected as empty (e.g., if the signal level falls below a predefined threshold, and / or the exhaust gas temperature rises above the maximum exhaust gas temperature), the system can switch to emission differentiation without intermediate storage. In the example shown here, this state can be considered reached at time t=t5 (second condition no longer met; control signal 332 shows a value of logic 0 or false). If the absence of water (or other complete emptying of the NH3 storage) was detected in the previous cycle and the temperature has not fallen below a predefined threshold (especially the minimum exhaust gas temperature) in the meantime, a water-free (or NH3-free) system is assumed. Alternatively or additionally, procedure 200 can remain active (or be deactivated).nevertheless be activated), in order to detect NH3 emissions that occur at a later time (e.g. through appropriate re-dosing of urea and / or NH3 formation in one of the catalysts 11, 12, 13). QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] DE 10 2022 209 970.2 [0005, 0016]

Claims

[1] Method (200) for determining (290) the quantity of NH3 contained in an exhaust gas (10) downstream of an internal combustion engine (1) using an NH3 and NOx sensitive NX sensor (17, 18, 19), comprising receiving (210) a sensor signal from the NX sensor and determining the quantity of NH3 based on the sensor signal and depending (220, 240, 260) on the fulfillment of at least one condition (331, 332, 333), wherein the at least one condition (331, 332, 333) is the presence of an exhaust gas temperature exceeding a minimum exhaust gas temperature, in particular for the first time, as a first condition, and / or the presence of an exhaust gas temperature exceeding a maximum exhaust gas temperature as a second condition, and / or the presence of heat input into an exhaust gas system (120) upstream of the NX-Sensors (17, 18, 19), which exceeds a minimum heat input, as the first condition,and / or the presence of a heat input into an exhaust system (120) upstream of the NX sensor (17, 18, 19) that exceeds a maximum heat input, as the second condition. [2] Method (200) according to claim 1, comprising checking (220, 240, 260) whether the at least one condition is met, and determining the amount of NH3 when the first condition is met and the second condition is not met. [3] Method (200) according to claim 2, comprising determining (295) an amount of NOx contained in the exhaust gas based on the sensor signal when the first condition is not met or the second condition is met. [4] Method (200) according to any of the preceding claims, wherein determining the NH3 quantity (290) and / or, if according to claim 3, the NOx quantity (295) comprises applying a respective arithmetic operation (230, 250, 270, 280, 290, 295) to the sensor signal. [5] Method (200) according to claim 4, wherein the computational operation comprises an integration (290, 295) of the sensor signal and / or a multiplication (230, 250, 270, 280) of the sensor signal with a calibration parameter, and / or a filtering of the sensor signal. [6] Method (200) according to one of the preceding claims, wherein the at least one condition (331, 332, 333) further comprises the presence of a sensor signal level exceeding a minimum level as a third condition, and / or the presence of a sensor signal gradient exceeding a positive threshold as a fourth condition, wherein the fourth condition is considered to be fulfilled after its initial fulfillment until the sensor signal gradient first falls below a negative threshold and then exceeds it again, and wherein the sensor signal is interpreted as being caused by NH3 when the third condition is fulfilled and the fourth condition is not fulfilled, and / or wherein the sensor signal is interpreted as being caused at least partially by NOx when the fourth condition is fulfilled. [7] Computing unit (20) configured to perform all process steps of a process (200) according to any of the preceding claims. [8] Computer program that causes a computing unit to perform all the process steps of a method according to any one of claims 1 to 6 when executed on the computing unit. [9] Machine-readable storage medium with a computer program stored thereon according to claim 8.

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