Method for monitoring an exhaust-gas catalytic converter of an internal combustion engine
Patent Information
- Application Number
- EP2023821563
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-12-16
- Filing Date
- 2023-12-06
- Publication Date
- 2025-10-22
Smart Images
Figure 1.1
Abstract
Description
[0001]Rolls-Royce Solutions GmbH DESCRIPTION Method for monitoring an exhaust gas catalytic converter of an internal combustion engine The invention relates to a method for monitoring an exhaust gas catalytic converter of an internal combustion engine. Furthermore, the invention relates to an internal combustion engine having an exhaust gas catalytic converter, a reactant metering device, and a control device that is configured to carry out a method for monitoring the exhaust gas catalytic converter of the internal combustion engine. It is known that internal combustion engines having an exhaust gas catalytic converter and in particular a reactant metering device use an NH3 sensor to monitor the exhaust gas catalytic converter and in particular to detect NH3 slip, particularly in applications where, for example, an NH3 catalyst cannot be used due to the use of sulfur-containing fuels.The NH3 sensor is arranged fluidically downstream of the exhaust gas catalytic converter and configured to measure an NH3 concentration in the exhaust gas. This makes it possible to detect NH3 slip in accordance with legal requirements. A disadvantage of this is that such an NH3 sensor must be regularly serviced. A further disadvantage is that such an NH3 sensor is cross-sensitive to nitrogen oxides. The invention is therefore based on the object of creating a method for monitoring an exhaust gas catalytic converter of an internal combustion engine and an internal combustion engine with a control device for carrying out such a method, wherein the aforementioned disadvantages are at least partially remedied, preferably avoided. The object is achieved by providing the present technical teaching, in particular the teaching of the independent claims and the embodiments disclosed in the dependent claims and the description.The object is achieved by providing a method for monitoring an exhaust gas catalytic converter of an internal combustion engine having a reactant dosing device, wherein the reactant dosing device is arranged in particular upstream of the exhaust gas catalytic converter. The internal combustion engine is operated at a first load point with a first dosing rate of the reactant dosing device. During operation at the first dosing rate, a first actual NH3 value and a first actual catalyst efficiency are determined. Furthermore, a first observation value is calculated based on the first actual NH3 value, the first actual catalyst efficiency, a first target NH3 value, and a first target catalyst efficiency. The internal combustion engine is then operated at the first load point with a second dosing rate of the reactant dosing device.During operation at the second dosing rate, a second actual NH3 value and a second actual catalyst efficiency are determined. Furthermore, a second observation value is calculated based on the second actual NH3 value, the second actual catalyst efficiency, a second target NH3 value, and a second target catalyst efficiency. The first observation value and the second observation value are then compared, and the catalytic converter is evaluated based on the comparison. Advantageously, this allows the functionality of the catalytic converter to be determined in a simple manner. Advantageously, this makes it possible, in particular, to determine an NH3 post-catalytic converter concentration, i.e., a concentration of NH3 in the exhaust gas that exists after passing through the catalytic converter, without using an NH3 sensor.Furthermore, it is possible to monitor compliance with legal and internal requirements regarding the NH3 post-catalyst concentration and thus NH3 emissions, in particular without using an NH3 sensor. Furthermore, it is advantageously possible to adapt the control of the reactant dosing device, i.e. in particular the NH3 dosing, to the exhaust gas catalyst, in particular to aging of the exhaust gas catalyst. In particular, a reactant, preferably a reducing agent, is introduced into the exhaust gas by means of the reactant dosing device. In particular, ammonia or an ammonia-releasing reagent, in particular a urea-water solution, is used as the reducing agent. In particular, an increase in the dosing rate of the reactant dosing device leads to an increase in the actual NH3 value. Furthermore, a reduction in the dosing rate of the reactant dosing device leads to a reduction in the actual NH3 value.If there is no NH3 slip at the exhaust catalyst, increasing the dosing rate of the reactant dosing device leads to an increase in the actual catalyst efficiency. Furthermore, if there is no NH3 slip at the exhaust catalyst, reducing the dosing rate of the reactant dosing device leads to a reduction in the actual catalyst efficiency. This advantageously shows that the NH3 post-catalyst concentration is almost constant. In this case, the exhaust catalyst can advantageously be assessed as functional at the first load point at the first dosing rate and the second dosing rate. If the exhaust catalyst is operating at an NH3 slip limit, changing the dosing rate of the reactant dosing device leads to almost no or only a slight, particularly within predetermined limits, change in the actual catalyst efficiency.This advantageously makes it possible to recognize that the NH3 post-catalyst concentration has changed at least slightly. If there is NH3 slip at the exhaust catalyst, increasing the metering rate of the reactant metering device leads to a reduction in the actual catalyst efficiency. Furthermore, if there is NH3 slip at the exhaust catalyst, reducing the metering rate of the reactant metering device leads to an increase in the actual catalyst efficiency. This advantageously makes it possible to recognize that the NH3 post-catalyst concentration increases or decreases with an increase or decrease in the metering rate. As a result, the exhaust catalyst can advantageously be assessed as non-functional at the first load point at the first metering rate and the second metering rate. In particular, the method is carried out at a steady-state first load point.In one embodiment, upon detection of NH3 slip, the first dosing rate and the second dosing rate are each reduced by a predetermined reduction value, thereby obtaining a first new dosing rate and a second new dosing rate. The method is then carried out again using the first new dosing rate and the second new dosing rate at the first load point. This iterative procedure is repeated until an NH3 slip limit is reached or no more NH3 slip is detected. Subsequently, the first new dosing rate or the second new dosing rate is preferably stored as a maximum dosing rate of the exhaust gas catalyst at the first load point. In particular, the predetermined reduction value is at least 0.5% to at most 1%. In particular, the predetermined reduction value is preferably at least 0.6%, preferably at least 0.7%, preferably at least 0.8%, preferably at least 0.9%.Alternatively or additionally, the predetermined reduction value is preferably at most 0.9%, preferably at most 0.8%, preferably at most 0.7%, preferably at most 0.6%. In particular, a time interval between two consecutive executions of the method is at least 50 seconds to at most 200 seconds, preferably 100 seconds. In particular, between two consecutive executions of the method, the observation values are shifted such that the first observation value is zero and a distance between the first observation value and the second observation value remains constant. In the context of the present technical teaching, an actual NH3 value is denoted by the formula symbol ^^. Ist In particular, the first actual NH3 value is and the second actual NH3 value is denoted by . Furthermore, a target NH3 value is denoted by the symbol ^^ Soll In particular, the first target NH3 value is indicated by ^^S 1 O ll and the second target NH3 value with ^^ S 2 O ll In the context of the present technical teaching, an actual catalyst efficiency is denoted by the symbol ^^ Ist In particular, the first actual catalyst efficiency is denoted by ^^ 1 I st and the second actual catalyst efficiency with ^^ I 2 s t Furthermore, a target catalyst efficiency is indicated with the symbol ^^ Soll In particular, the first target catalyst efficiency is denoted by ^^ 1 S oll and the second target catalyst efficiency with ^^ S 2 O llIn the context of the present technical teaching, an observation value is denoted by the symbol B. In particular, the first observation value is denoted by B1 and the second observation value by B2. In particular, the observation value is a function of the actual NH3 value, the target NH3 value, the actual catalyst efficiency and the target catalyst efficiency, in particular ^^( ^^ Ist , ^^ Soll , ^^ Ist , ^^ Soll ). In one embodiment, ^^1= ^^( ^^ I 1 s t , ^^ S 1 O ll , ^^ 1 I st , ^^ 1 S oll ) for the first observation value and ^^2= ^^( ^^ I 2 s t , ^^ S 2 O ll , ^^ I 2 s t , ^^ S 2 O ll) for the second observation value. In an alternative embodiment, the observation values are shifted such that the first observation value is zero and a distance between the first observation value and the second observation value remains constant. In particular, ^^1= ^^ 1 S oll ) for the first observation value and ^^2= ^^ 1 S oll) for the second observation value. In particular, the target NH3 value, in particular the first target NH3 value and the second target NH3 value, and the target catalyst efficiency, in particular the first target catalyst efficiency and the second target catalyst efficiency, are provided. Preferably, the target NH3 value, in particular the first target NH3 value and the second target NH3 value, and the target catalyst efficiency, in particular the first target catalyst efficiency and the second target catalyst efficiency, are stored in a control device of the internal combustion engine - in particular depending on the load point and / or depending on the exhaust gas temperature - in a characteristic map that is particularly test bench-data-based. In one embodiment, the first target NH3 value and the second target NH3 value are identical. Alternatively or additionally, the first target catalyst efficiency and the second target catalyst efficiency are identical.In particular, the observation value B is calculated using the formula ^^. ( ^^ Ist , ^^ Soll , ^^ Ist , ^^ Soll ) = ( ^^ Ist − ^^ Soll ) − ( ^^ Ist − ^^ Soll ) is calculated. According to a further development of the invention, it is provided that the actual NH3 value, in particular the first actual NH3 value and the second actual NH3 value, is determined by means of a first NOx sensor arranged fluidically upstream of the exhaust gas catalyst and a control of the NO x sensor and the reactant metering device arranged on the exhaust gas catalyst. In particular, the first NO x -Sensor a NO x -Pre-catalyst concentration, especially in ppm, is determined. Furthermore, the first NO xsensor and the NH3 dosing device, an NH3 pre-catalyst concentration, particularly in ppm, is determined. In particular, based on the NOx pre-catalyst concentration, a NO x -target concentration and a predetermined conversion factor, the NH3 pre-catalyst concentration is determined. In particular, during operation at the first load point with the first dosing rate, a first NOx pre-catalyst concentration and a first NH3 pre-catalyst concentration are determined. In addition, during operation at the first load point with the second dosing rate, a second NOx pre-catalyst concentration and a second NH3 pre-catalyst concentration are determined. Preferably, the actual NH3 value is determined as the quotient of the NH3 pre-catalyst concentration and the NO x-Pre-catalyst- concentration is calculated, whereby the first actual NH3 value is the quotient of the first NH3 pre-catalyst concentration and the first NOx pre-catalyst concentration and the second actual NH3 value is the quotient of the second NH3 pre-catalyst concentration and the second NO x -Pre-catalyst concentration. According to a further development of the invention, it is provided that the actual catalyst efficiency, in particular the first actual catalyst efficiency and the second actual catalyst efficiency, by means of the first NO x sensor and a second NOx sensor arranged downstream of the exhaust gas catalyst. In particular, the first NO x -Sensors the NO x-Pre-catalyst concentration, in particular in the unit ppm, is determined. Furthermore, a NOx post-catalyst concentration, in particular in the unit ppm, is determined by means of the second NOx sensor. In particular, during operation at the first load point with the first dosing rate, the first NOx pre-catalyst concentration and a first NOx post-catalyst concentration are determined. In addition, during operation at the first load point with the second dosing rate, the second NO x -Pre-catalyst concentration and a second NO x -Post-catalyst concentration is determined. The actual catalyst efficiency is preferably determined from the equation where with ^^ nach the NOx post-catalyst concentration and with ^^ vor is the NOx pre-catalyst concentration. Furthermore, the following equations apply to the first actual catalyst efficiency and the second actual catalyst efficiency.According to a further development of the invention, the second dosing rate of the reactant dosing device is selected to be greater or smaller than the first dosing rate. In one embodiment, the second dosing rate of the reactant dosing device is selected to be at least 5% to a maximum of 20% greater than the first dosing rate of the reactant dosing device. In a further embodiment, the second dosing rate of the reactant dosing device is selected to be at least 5% to a maximum of 20% smaller than the first dosing rate of the reactant dosing device. In one embodiment, the method is repeated iteratively until an NH3 slip limit is reached or no more NH3 slip is detected, and in addition, the second dosing rate is selected to be smaller than the first dosing rate.As soon as the NH3 slip limit is reached or no more NH3 slip is detected, the first new dosing rate is preferably stored as a maximum dosing rate of the exhaust gas catalyst at the first load point. In an alternative embodiment, the method is repeated iteratively until an NH3 slip limit is reached or no more NH3 slip is detected, and in addition, the second dosing rate is selected to be greater than the first dosing rate. As soon as the NH3 slip limit is reached or no more NH3 slip is detected, the second new dosing rate is preferably stored as a maximum dosing rate of the exhaust gas catalyst at the first load point. The first dosing rate is preferably selected to be greater than the second dosing rate. This advantageously enables more sensitive detection of the NH3 slip and thus also more precise evaluation of the exhaust gas catalyst.In particular, the reaction equilibrium in the catalyst shifts from oxidation reactions to selective reduction reactions when NH3 slip occurs at the first dosing rate. This increases NOx conversion, even though the metered NH3 pre-catalyst concentration decreases. In contrast, with NH3 slip, NOx conversion changes only slightly when the metered NH3 pre-catalyst concentration is increased. In particular, the equation ^^2 = ^^ ∙ ^^1 applies to the first dosing rate D1 and the second dosing rate D2, where α has a value of 0.80 to 0.95 or 1.05 to 1.2. This determines the value of the second dosing rate in relation to the value of the first dosing rate. In particular, a difference between the first dosing rate and the second dosing rate is selected as a function of the exhaust gas temperature.Preferably, at an exhaust gas temperature of less than 300°C, the second dosing rate is selected to be at most 20% higher than the first dosing rate. Alternatively or additionally, at an exhaust gas temperature of at least 300°C to at most 400°C, the second dosing rate is selected to be at least 5% to at most 20% higher than the first dosing rate. Alternatively or additionally, at an exhaust gas temperature of more than 400°C, the second dosing rate is selected to be at least 5% higher than the first dosing rate. In a preferred embodiment, at an exhaust gas temperature of less than 300°C, the second dosing rate is selected to be 20% higher than the first dosing rate.Alternatively or additionally, at an exhaust gas temperature of more than 400°C, the second dosing rate is selected to be 5% higher than the first dosing rate. Alternatively or additionally, at an exhaust gas temperature of at least 300°C and at most 400°C, a dosing rate increase from the first dosing rate to the second dosing rate is interpolated, in particular linearly, as a function of the exhaust gas temperature between 20% and 5%. Alternatively, at an exhaust gas temperature of less than 300°C, the second dosing rate is selected to be at most 20% lower than the first dosing rate. Alternatively or additionally, at an exhaust gas temperature of at least 300°C and at most 400°C, the second dosing rate is selected to be at least 5% to at most 20% lower than the first dosing rate. Alternatively or additionally, at an exhaust gas temperature of more than 400°C, the second dosing rate is selected to be at least 5% lower than the first dosing rate.In a preferred embodiment, at an exhaust gas temperature of less than 300°C, the second dosing rate is selected to be 20% lower than the first dosing rate. Alternatively or additionally, at an exhaust gas temperature of more than 400°C, the second dosing rate is selected to be 5% lower than the first dosing rate. Alternatively or additionally, at an exhaust gas temperature of at least 300°C to at most 400°C, a dosing rate reduction from the first dosing rate to the second dosing rate is interpolated, in particular linearly as a function of the exhaust gas temperature, between 20% and 5%. According to a development of the invention, the first observation value and the second observation value are compared by calculating a difference between the first observation value and the second observation value. In this case, NH3 slip of the internal combustion engine, in particular of the exhaust gas catalytic converter, is detected if the absolute value of the difference is greater than a predetermined threshold value.According to a further development of the invention, a weighted first observation value is determined from the first observation value by means of a weighting function, and a weighted second observation value is determined from the second observation value. Furthermore, the weighted first observation value and the weighted second observation value are compared, and the exhaust gas catalytic converter is evaluated based on the comparison. Advantageously, the weighting function makes it possible to transform an observation value in such a way that an evaluation of the exhaust gas catalytic converter based on the weighted observation values is possible more easily and reliably than, in particular, based on the non-weighted observation values. In the context of the present technical teaching, a weighted observation value is denoted by the formula symbol B. g In particular, the weighted first observation value is denoted by ^^ ^^ and the ^^1 weighted second observation value is denoted by ^^2. In particular, the weighting function is denoted by the formula symbol ^^(∙). In particular, ^^ ^^ 1 = ^^ ^ ^^ for the weighted first observation value and ^^ ^^ 2 = ^^ for the weighted second observation value. In particular, a polynomial is used as the weighting function, whereby the formula for the weighting function is ^^ ( ^^ ) = ∙ ^^ ^^ applies. Parameters a iand the i-th powers of the observation value B are used. In particular, a general parabola is used, which interpolates the points {(−5; 4), (−4; 3), (−3; 2), (−2; 1.5), (−1; 1), (0; 1)(1; 1), (2; 1.5), (3; 2), (4; 3), (5; 4)}. Alternatively, a polynomial is used, which interpolates the points {(−6; 2), (−2; 2), (−1; 1), (1; 1), (2; 2), (6; 2)}. In particular, a positive gain factor is assigned to an observation value using the weighting function. In particular, the weighting function ^^( ^^) is chosen such that a first distance between a first observation value ^^1 and a second observation value ^^2 is greater than a second distance between the associated weighted first observation value ^^ ^^ 1 and the associated weighted second observation value ^^ ^^2 if the first observation value ^^1 and the second observation value ^^2 are greater than an interval lower limit and smaller than an interval upper limit. In addition, the weighting function ^^( ^^) is chosen such that a first distance between a first observation value ^^1 and a second observation value ^^2 is smaller than a second distance between the associated weighted first observation value ^^ ^^ 1 and the associated weighted second observation value ^^ ^^2 if the first observation value ^^1 and the second observation value ^^2 are less than or equal to an interval lower limit and greater than or equal to an interval upper limit. In particular, the weighted first observation value and the weighted second observation value are compared by calculating a difference between the weighted first observation value and the weighted second observation value. In this case, an NH3 slip of the internal combustion engine, in particular of the exhaust gas catalytic converter, is detected if the absolute value of the difference is greater than the predetermined threshold value. According to a development of the invention, it is provided that during operation at the first load point with the second dosing rate, a second observation value is determined at a plurality of times. The plurality of second observation values are then integrated, whereby an integrated second observation value is obtained.The integrated second observation value is compared with the first observation value, and the exhaust catalyst is evaluated based on the comparison. In particular, an observation value, in particular the second observation value, has signal noise, so that the integration advantageously makes it possible to evaluate the exhaust catalyst independently of the signal noise. In particular, the first observation value and the integrated second observation value are compared by calculating a difference between the first observation value and the integrated second observation value. NH3 slip of the internal combustion engine, in particular of the exhaust catalyst, is detected if the absolute value of the difference is greater than the predetermined threshold.According to a further development of the invention, during operation at the first load point with the second dosing rate, a weighted second observation value is determined at a plurality of points in time. Subsequently, the plurality of weighted second observation values are integrated, obtaining an integrated weighted second observation value. The integrated weighted second observation value is compared with the weighted first observation value, and the exhaust gas catalyst is evaluated based on the comparison. In particular, the weighted first observation value and the integrated weighted second observation value are compared by calculating a difference between the weighted first observation value and the integrated weighted second observation value.In this case, an NH3 slip of the internal combustion engine, in particular of the exhaust gas catalytic converter, is detected if the absolute value of the difference is greater than the predetermined threshold. In the context of the present technical teaching, a time period between setting the second dosing rate and the earliest determination of a first second observation value or a weighted first second observation value is defined as the minimum time ^^. min Furthermore, in the context of the present technical teaching, a time period between setting the second dosing rate and the last determination of an n-th second observation value or a weighted n-th second observation value is referred to as the maximum time ^^ max In one embodiment, the minimum time is ^^ minat most 1 second, preferably at most 2 seconds, preferably at most 5 seconds, preferably at most 10 seconds, preferably at most 15 seconds. Alternatively or additionally, the maximum time is ^^ max at most 30 seconds, preferably at most 25 seconds, preferably at most 20 seconds, preferably at most 15 seconds. Alternatively or additionally, the time interval between the minimum time ^^ min and the maximum time ^^ max maximum 30 seconds, preferably maximum 20 seconds, preferably maximum 10 seconds. In particular, the minimum time ^^ min and the maximum time ^^ max selected depending on the exhaust gas temperature, whereby preferably the time interval between the minimum time ^^ min and the maximum time ^^ max is constant regardless of the exhaust gas temperature. In particular, the minimum time ^^ min and the maximum time ^^ maxsmaller as the exhaust gas temperature increases. According to a development of the invention, the method is carried out for a plurality of load points, wherein an evaluation of the internal combustion engine and in particular of the exhaust gas catalytic converter - depending on the respective load point - is stored in a load map. Advantageously, the exhaust gas catalytic converter can thus be evaluated for the plurality of load points. Furthermore, a maximum dosing rate of the reactant dosing device can advantageously be determined on the basis of the evaluation for the plurality of load points. In particular, the load map is spanned by an exhaust gas mass and the exhaust gas temperature and has a plurality of map tiles. In particular, a map tile is a contiguous area over a plurality of load points, which are each determined in particular by an exhaust gas mass and an exhaust gas temperature.In one embodiment, in addition to the evaluation of the internal combustion engine and in particular of the exhaust gas catalytic converter, a maximum dosing rate of the reactant dosing device is stored in the load map. This advantageously allows the reactant dosing device to be optimally adjusted for the majority of load points. In particular, the maximum dosing rate is stored for a load field tile in which the load point is located. In addition, the maximum dosing rate is preferably stored in at least one further load field tile that is directly adjacent to the load field tile containing the load point. According to a further development of the invention, it is provided that, in addition to the evaluation, an evaluation operating hour is stored in the load map, wherein the evaluation operating hour indicates the time of the evaluation.Advantageously, the evaluation operating hour makes it easy to decide whether and when it is advisable to repeat the method. In particular, the evaluation operating hour is stored for a load field tile in which the load point is located. In addition, the evaluation operating hour is preferably stored in at least one further load field tile that is directly adjacent to the load field tile containing the load point. In one embodiment, when the internal combustion engine is operating at the first load point, the evaluation operating hour is compared with a current operating hour of the internal combustion engine, and the method for monitoring the exhaust gas catalytic converter is carried out based on the comparison.In particular, the method for monitoring the exhaust gas catalyst is carried out when the difference between the evaluation operating hour and the current operating hour is greater than 24 hours, preferably greater than 100 hours. This object is also achieved by providing an internal combustion engine with an exhaust gas catalyst, a reactant metering device, a first NOx sensor, a second NOx sensor, and a control device. The first NOx sensor is x -Sensor is arranged fluidically upstream of the exhaust catalyst. Furthermore, the reactant metering device is arranged fluidically between the first NOx sensor and the exhaust catalyst. The second NO xThe sensor is arranged fluidically downstream of the exhaust gas catalyst. In addition, the control device is configured to carry out a method according to the invention or a method according to one or more of the previously described embodiments. In connection with the internal combustion engine, the advantages that have already been explained in connection with the method for monitoring the exhaust gas catalyst arise in particular. The control device is preferably connected to the reactant metering device, the first NO x- sensor and the second NOx sensor and configured to control them respectively. Preferably, the target NH3 value, in particular the first target NH3 value and the second target NH3 value, and the target catalyst efficiency, in particular the first target catalyst efficiency and the second target catalyst efficiency, are stored in the control device of the internal combustion engine - in particular dependent on the load point and / or the exhaust gas temperature - in a characteristic map, which is particularly test bench-data-based. In particular, the reactant metering device is configured to introduce a reactant, in particular a reducing agent, preferably ammonia or an ammonia-releasing reagent, in particular a urea-water solution, into the exhaust gas. The invention is explained in more detail below with reference to the drawing. Therein: Fig. 1 shows a schematic representation of an embodiment of an internal combustion engine, Fig.Figure 2 shows a flowchart of a first exemplary embodiment of a method for monitoring an exhaust gas catalyst, and Figure 3 shows a flowchart of a second exemplary embodiment of the method for monitoring the exhaust gas catalyst. Figure 1 shows a schematic representation of an exemplary embodiment of an internal combustion engine 1. The internal combustion engine 1 has an exhaust gas catalyst 3, a reactant metering device 5, and a first NO. x -Sensor 7.1, a second NO x -Sensor 7.2 and a control device 9. The first NO x -Sensor 7.1, the reactant metering device 5, the exhaust gas catalyst 3 and the second NO x -Sensor 7.2 are fluidically connected to each other and to a combustion chamber of the internal combustion engine 1 in such a way that exhaust gas from the combustion chamber first passes through the first NO x -Sensor 7.1, then through the reactant metering device 5, then through the exhaust gas catalyst 3 and then through the second NOx -Sensor 7.2 flows. The reactant metering device 5 is configured to introduce a reactant, in particular a reducing agent, preferably ammonia or an ammonia-releasing reagent, in particular a urea-water solution, into an exhaust gas of the internal combustion engine 1 at a predetermined metering rate 11, in particular a first metering rate 11.1 or a second metering rate 11.2. The first NO x Sensor 7.1 is configured, in particular, to determine a NOx pre-catalyst concentration, in particular in the unit ppm. Furthermore, the first NOx sensor 7.1 and the reactant metering device 5 are configured, in particular, to determine a NH3 pre-catalyst concentration, in particular in the unit ppm. In addition, the second NO x-Sensor 7.2 is configured to determine a NOx post-catalyst concentration, in particular in the unit ppm. The control device 9 is operatively connected to the reactant metering device 5, the first NOx sensor 7.1 and the second NOx sensor 7.2 and is configured to control them respectively. Furthermore, the control device 9 is configured to carry out a method for monitoring the exhaust gas catalytic converter 3. The method is explained in more detail in Figures 2 and 3. Figure 2 shows a flowchart of a first exemplary embodiment of a method for monitoring the exhaust gas catalytic converter 3. Identical and functionally identical elements are provided with the same reference numerals in all figures, so that reference is made to the preceding description in this respect. In a first step S1, a load point, in particular a first load point, of the internal combustion engine 1 is set. The load point is preferably a steady-state load point.In a second step S2, a first dosing rate 11.1 of the reactant dosing device 5 and a second dosing rate 11.2 of the reactant dosing device 5 are determined. Preferably, the second dosing rate 11.2 is selected to be at least 5% to at most 20% greater than the first dosing rate 11.1. Alternatively, the second dosing rate 11.2 is selected to be at least 5% to at most 20% smaller than the first dosing rate 11.1. In a third step S3, the internal combustion engine 1 is operated at the first load point with the first dosing rate 11.1. During this time, a first actual NH3 value 13.1 and a first actual catalyst efficiency 15.1 are determined. In a fourth step S4, a first observation value 21.1 is calculated based on the first actual NH3 value 13.1, the first actual catalyst efficiency 15.1, a first target NH3 value 17.1 and a first target catalyst efficiency 19.1.In particular, the first target NH3 value 17.1 and the first target catalyst efficiency 19.1 are provided. Preferably, the first target NH3 value 17.1 and the first target catalyst efficiency 19.1 are stored in the control device 9 of the internal combustion engine 1—in particular, dependent on the load point and / or the exhaust gas temperature—in a characteristic map, in particular based on test bench data. In a fifth step S5, the internal combustion engine 1 is operated at the first load point with the second dosing rate 11.2. During this time, a second actual NH3 value 13.2 and a second actual catalyst efficiency 15.2 are determined. Preferably, in the third step S3 and in the fifth step S5, the first actual NH3 value 13.1 and the second actual NH3 value 13.2 are determined by means of the first NOx sensor 7.1 arranged fluidically upstream of the exhaust gas catalytic converter 3 and a control of the flow-related sensor 7.1 arranged fluidically between the first NO. x-Sensor 7.1 and the reactant metering device 5 arranged between the exhaust gas catalyst 3. In particular, in the third step S3, a first NOx pre-catalyst concentration and a first NH3 pre-catalyst concentration are determined, wherein the first actual NH3 value 13.1 is the quotient of the first NH3 pre-catalyst concentration and the first NO x-Pre-catalyst concentration. In addition, in the fifth step S5, a second NOx pre-catalyst concentration and a second NH3 pre-catalyst concentration are determined, wherein the second actual NH3 value 13.2 results from the quotient of the second NH3 pre-catalyst concentration and the second NOx pre-catalyst concentration. Preferably, in the third step S3 and in the fifth step S5, the first actual catalyst efficiency 15.1 and the second actual catalyst efficiency 15.2 are determined by means of the first NOx sensor 7.1 and the second NO sensor arranged downstream of the exhaust gas catalyst 3. x -Sensor 7.2. In particular, in the third step S3, the first NOx pre-catalyst concentration and a first NOx post-catalyst concentration are determined, wherein the first actual catalyst efficiency 15.1 is determined by means of the equation is calculated, where ^^ n 1 a chthe first NOx post-catalyst concentration and with ^^ v 1 or the first NOx pre-catalyst concentration is referred to. In addition, in the fifth step S5, the second NOx pre-catalyst concentration and a second NOx post-catalyst concentration are determined, wherein the second actual catalyst efficiency 15.2 is determined using the equation is calculated, where ^^ n 2 a ch the second NO x -Post-catalyst concentration and with ^^ v 2 or the second NO x-Pre-catalyst concentration. In a sixth step S6, a second observation value 21.2 is calculated based on the second actual NH3 value 13.2, the second actual catalyst efficiency 15.2, a second target NH3 value 17.2 and a second target catalyst efficiency 19.2. In particular, the second target NH3 value 17.2 and the second target catalyst efficiency 19.2 are provided. Preferably, the second target NH3 value 17.2 and the second target catalyst efficiency 19.2 are stored in the control device 9 of the internal combustion engine 1 - in particular dependent on the load point and / or dependent on the exhaust gas temperature - in the characteristic map, which is in particular test bench-data-based. In particular, the first target NH3 value 17.1 and the second target NH3 value 17.2 are identical. Alternatively or additionally, the first target catalyst efficiency 19.1 and the second target catalyst efficiency 19.2 are identical.In particular, steps S3 and S4 are combined in a first determination step BS1 for determining the first observation value 21.1. In addition, steps S5 and S6 are combined in a second determination step BS2 for determining the second observation value 21.2. In a seventh step S7, the first observation value 21.1 and the second observation value 21.2 are compared, thereby obtaining a comparison 23. Preferably, the first observation value 21.1 and the second observation value 21.2 are compared by calculating a difference between the first observation value 21.1 and the second observation value 21.2. In an eighth step S8, the exhaust gas catalytic converter 3 is evaluated based on the comparison 23.In this case, the difference is preferably compared with a predetermined threshold value 25, wherein an NH3 slip of the internal combustion engine 1, in particular of the exhaust gas catalytic converter 3, is detected if the absolute value of the difference is greater than a predetermined threshold value 25. Preferably, the second determination step BS2 is carried out multiple times, wherein a second observation value 21.2 is determined at a plurality of times. Subsequently, in an optional ninth step S9, the plurality of second observation values 21.2 are integrated, whereby an integrated second observation value 27 is obtained. In the seventh step S7, the integrated second observation value 27 is then compared with the first observation value 21.1, wherein the exhaust gas catalytic converter 3 is evaluated based on the comparison 23. In particular, the first observation value 21.1 and the integrated second observation value 27 are compared by determining a difference from the first observation value 21.1 and the integrated second observation value 27. In this case, an NH3 slip of the internal combustion engine 1, in particular of the exhaust gas catalytic converter 3, is detected if the absolute value of the difference is greater than the predetermined threshold value 25. If an NH3 slip is detected in the eighth step S8, the method is optionally started again with the second step S2. In this case, the first dosing rate 11.1 and the second dosing rate 11.2 are each reduced by a predetermined reduction value. Subsequently, steps S3 to S8, in particular steps S3 to S9, are carried out again. Preferably, this iterative procedure is repeated until an NH3 slip limit is reached in the eighth step S8 or no more NH3 slip is detected.In particular, the time interval between two consecutive executions of steps S2 to S8, in particular steps S2 to S9, is at least 50 seconds to a maximum of 200 seconds, preferably 100 seconds. In an optional tenth step S10, the evaluation of the internal combustion engine 1 and in particular of the exhaust gas catalytic converter 3 is stored in a load map. Preferably, steps S1 to S10 are performed for a plurality of load points, wherein the evaluation of the internal combustion engine 1 and in particular of the exhaust gas catalytic converter 3 is stored in the load map. Preferably, in addition to the evaluation, an evaluation operating hour is stored in the load map, wherein the evaluation operating hour indicates the time of the evaluation. Figure 3 shows a flowchart of a second exemplary embodiment of the method for monitoring the exhaust gas catalytic converter 3.Analogous to Figure 2, in the first step S1, a load point, in particular a first load point, of the internal combustion engine 1 is set. Furthermore, also analogous to Figure 2, in the second step S2, the first dosing rate 11.1 and the second dosing rate 11.2 are determined. Thereafter, the first determination step BS1 and the second determination step BS2 according to Figure 2 are carried out, whereby the first observation value 21.1 and the second observation value 21.2 are obtained. In an eleventh step S11, the first observation value 21.1 is weighted using a weighting function 29, whereby a weighted first observation value 31.1 is determined. In a twelfth step S12, the second observation value 21.2 is weighted using the weighting function 29, whereby a weighted second observation value 31.2 is determined. In the seventh step S7, the weighted first observation value 31.1 and the weighted second observation value 31.2, whereby the comparison 23 is obtained. Preferably, the weighted first observation value 31.1 and the weighted second observation value 31.2 are compared by calculating a difference between the weighted first observation value 31.1 and the weighted second observation value 31.2. The eighth step S8 and the optional tenth step S10 are analogous to Figure 2. Preferably, the second determination step BS2, analogous to Figure 2, is carried out multiple times, wherein a second observation value 21.2 is determined at a plurality of points in time. Furthermore, each of the second observation values 21.2 is weighted in the twelfth step S12, whereby a plurality of weighted second observation values 31.2 are obtained. Subsequently, in an optional thirteenth step S13, the plurality of weighted second observation values 31.2 are integrated, whereby an integrated weighted second observation value 33 is obtained.In the seventh step S7, the integrated weighted second observation value 33 is then compared with the weighted first observation value 31.1, wherein the exhaust gas catalytic converter 3 is evaluated based on the comparison 23. In particular, the weighted first observation value 31.1 and the integrated weighted second observation value 33 are compared by calculating a difference between the weighted first observation value 31.1 and the integrated weighted second observation value 33. In this case, an NH3 slip of the internal combustion engine 1, in particular of the exhaust gas catalytic converter 3, is detected if the absolute value of the difference is greater than the predetermined threshold value 25. If an NH3 slip is detected in the eighth step S8, the method is optionally started again with the second step S2. In this case, the first dosing rate 11.1 and the second dosing rate 11.2 are each reduced by a predetermined reduction value.Subsequently, steps S3 to S12, in particular steps S3 to S13, are carried out again. This iterative procedure is preferably repeated until an NH3 slip limit is reached in the eighth step S8 or no more NH3 slip is detected. In particular, a time interval between two consecutive executions of steps S2 to S12, in particular steps S2 to S13, is at least 50 seconds to at most 200 seconds, preferably 100 seconds. Preferably, steps S1 to S12, in particular steps S1 to S13, are carried out for a plurality of load points, wherein the evaluation of the internal combustion engine 1 and in particular of the exhaust gas catalytic converter 3 is stored in the load map. Preferably, in addition to the evaluation, the evaluation operating hour is stored in the load map.
Claims
CLAIMS 1. Method for monitoring an exhaust gas catalyst (3) of an internal combustion engine (1) with a reactant metering device (5), wherein ^ the internal combustion engine (1) is operated at a first load point with a first metering rate (11.1) of the reactant metering device (5), wherein ^ during operation with the first metering rate (11.1) a first actual NH3 value (13.1) and a first actual catalyst efficiency (15.1) are determined, wherein ^ a first observation value (21.1) is calculated based on the first actual NH3 value (13.1), the first actual catalyst efficiency (15.1), a first target NH3 value (17.1) and a first target catalyst efficiency (19.1), wherein ^ the internal combustion engine (1) is operated at the first load point with a second metering rate (11.2) of the reactant metering device (5), wherein ^ during operation with the second metering rate (11.2) a second actual NH3 value (13.2) and a second actual catalyst efficiency (15.2), wherein ^ a second observation value (21.2) is calculated on the basis of the second actual NH3 value (13.2), the second actual catalyst efficiency (15.2), a second target NH3 value (17.2) and a second target catalyst efficiency (19.2), wherein ^ the first observation value (21.1) and the second observation value (21.2) are compared, wherein ^ the exhaust gas catalyst (3) is evaluated on the basis of the comparison (23).
2. Method according to claim 1, wherein ^ an actual NH3 value (13), in particular the first actual NH3 value (13.1) and the second actual NH3 value (13.2), is determined by means of a first NO arranged fluidically upstream of the exhaust gas catalyst (3). x -Sensor (7.1) and a control of the fluidically connected between the first NO x-Sensor (7.1) and the exhaust gas catalyst (3) arranged reactant metering device (5), and / or ^ an actual catalyst efficiency (15), in particular the first actual catalyst efficiency (15.1) and the second actual catalyst efficiency (15.2), by means of the first NO x-sensor (17.1) and a second NOx sensor (17.2) arranged downstream of the exhaust gas catalytic converter (3) in terms of flow.
3. Method according to one of the preceding claims, wherein the second metering rate (11.2) of the reactant metering device (5) is selected to be greater or smaller than the first metering rate (11.1) - in particular by at least 5% to at most 20%.
4. Method according to one of the preceding claims, wherein ^ the first observation value (21.1) and the second observation value (21.2) are compared by calculating a difference between the first observation value (21.1) and the second observation value (21.2), wherein ^ an NH3 slip of the internal combustion engine (1) is detected if the absolute value of the difference is greater than a predetermined threshold value (25).
5. Method according to one of the preceding claims, wherein ^ a weighted first observation value (31.1) and a weighted second observation value (31.2) is determined from the second observation value (21.2), wherein ^ the weighted first observation value (31.1) and the weighted second observation value (31.2) are compared, wherein ^ the exhaust gas catalyst (3) is evaluated based on the comparison (23).
6. Method according to one of the preceding claims, wherein ^ at the first load point with the second dosing rate (11.2) at a plurality of points in time in each case a second observation value (21.2) is determined, wherein ^ the plurality of second observation values (21.2) are integrated, wherein an integrated second observation value (27) is obtained, wherein ^ the integrated second observation value (27) is compared with the first observation value (21.1), wherein ^ the exhaust gas catalyst (3) is evaluated based on the comparison (23).
7. Method according to claim 5, wherein. ^ at the first load point with the second dosing rate (11.2) at a plurality of points in time, a weighted second observation value (31.2) is determined, wherein ^ the plurality of weighted second observation values (31.2) are integrated, obtaining an integrated weighted second observation value (33), wherein ^ the integrated weighted second observation value (33) is compared with the weighted first observation value (31.1), wherein ^ the exhaust gas catalyst (3) is evaluated based on the comparison (23).
8. Method according to one of the preceding claims, wherein ^ the method is carried out for a plurality of load points, wherein ^ an evaluation of the internal combustion engine (1) is stored in a load map.
9. Method according to claim 8, wherein in addition to the evaluation, an evaluation operating hour is stored in the load map, wherein the evaluation operating hour indicates the time of the evaluation. 10.Internal combustion engine (1) with an exhaust gas catalyst (3), a reactant metering device (5), a first NOx sensor (7.1), a second NOx sensor (7.2) and a control device (9), wherein ^ the first NOx sensor (7.1) is arranged fluidically upstream of the exhaust gas catalyst (3), wherein ^ the reactant metering device (5) is fluidically arranged between the first NO. x -Sensor (7.1) and the exhaust gas catalyst (3), wherein ^ the second NOx sensor (7.2) is arranged fluidically downstream of the exhaust gas catalyst (3), and wherein ^ the control device (9) is set up to carry out a method according to one of the preceding claims.