Method for testing the functionality of an exhaust aftertreatment device and motor vehicle

Abstract

The invention relates to a method for testing the functionality of an exhaust gas aftertreatment device (4) arranged in an exhaust system (2) through which exhaust gas from an internal combustion engine (1) can flow, through which the exhaust gas can flow, and designed to aftertreat the exhaust gas. In this method, a first variable is determined which characterizes a heat input into the exhaust gas aftertreatment device (4). A second variable is determined which characterizes an average power of the internal combustion engine (1), the average power of which describes a work performed by the internal combustion engine (1) within a time period divided by the time period. By means of a nitrogen oxide sensor (6), a measured variable which characterizes a quantity of nitrogen oxides contained in the exhaust gas is measured at a measuring point (MS) arranged downstream of the exhaust gas aftertreatment device (4).A third quantity is determined by using the measured quantity as the third quantity or by determining the third quantity from the measured quantity.

Description

The invention relates to a method for checking the functionality of an exhaust gas aftertreatment device, in particular of a motor vehicle. The invention further relates to a motor vehicle.EP 3 642 460 B1 discloses an exhaust gas aftertreatment system for an internal combustion engine. EP 2 791 493 B1 discloses a method for monitoring the dynamics of gas sensors of an internal combustion engine. DE 11 2013 007 779 B4 discloses a catalyst composition as known. Furthermore, JP 5 807 116 B2 discloses a motor vehicle having an internal combustion engine. The prior art also includes AT 520 896 B1, and DE 10 2021 117 611 A1.It is the object of the present invention to provide a method and a motor vehicle, so that an exhaust gas aftertreatment device for aftertreating exhaust gas of an internal combustion engine can be tested particularly advantageously with regard to a functionality of the exhaust gas aftertreatment device.This object is achieved according to the invention by a method having the features of patent claim 1 and by a motor vehicle having the features of patent claim 9. Advantageous embodiments of the invention are the subject of the dependent claims.A first aspect of the invention relates to a method for checking the functionality of an exhaust gas aftertreatment device which is arranged in an exhaust system through which exhaust gas of an internal combustion engine, in particular of a motor vehicle, can flow and through which the exhaust gas of the internal combustion engine can flow and which is designed in particular for targeted aftertreatment of the exhaust gas. The feature that the exhaust gas aftertreatment device is designed for, in particular targeted, aftertreatment of the exhaust gas is to be understood in particular to mean that at least one substance contained in the exhaust gas, which is in particular a chemical composition or a chemical molecule, can be removed at least partially from the exhaust gas by means of the exhaust gas aftertreatment device, for example by the exhaust gas aftertreatment device being catalytically active for a chemical reaction and thus being able to catalytically support and / or bring about the chemical reaction in which the substance as a first substance or first reactant reacts with at least one second substance designed as a second reactant to form at least one third substance as a product, which is different from the first substance and from the second substance. The first substance is, for example, nitrogen oxides contained in the exhaust gas, which are also referred to as NOx. The second substance is, for example, ammonia. The third substance is or comprises, for example, nitrogen and water. The ammonia can be provided or is provided, for example, by an in particular liquid reducing agent. The reducing agent, which is in particular liquid, is, for example, an aqueous urea solution. For example, a metering device is provided, by means of which the reducing agent can be introduced, in particular injected, into the exhaust gas flowing through the exhaust system at at least or exactly one introduction point, wherein the introduction point is arranged upstream of the exhaust gas aftertreatment device in the flow direction of the exhaust gas flowing through the exhaust system and the exhaust gas aftertreatment device. In particular, the aforementioned chemical reaction, for which the exhaust gas aftertreatment device is catalytically active, is a selective catalytic reaction, for example. Checking the functionality of the exhaust gas aftertreatment device is to be understood in particular to mean that, during or by checking the functionality of the exhaust gas aftertreatment device, a capability, in particular a capability or a capability, of the exhaust gas aftertreatment device is to be checked or checked, the exhaust gas aftertreatment device being able to posttreat the exhaust gas and in the process in particular to be able to remove the first substance from the exhaust gas. In particular, checking the functionality of the exhaust gas aftertreatment device is to be understood as meaning that the functionality of the exhaust gas aftertreatment device is evaluated with respect to the aftertreatment of the exhaust gas, that is to say in particular the capability of the exhaust gas aftertreatment device to be able to remove at least the first substance from the exhaust gas, with the result that, by or during checking the functionality of the exhaust gas aftertreatment device, an evaluation of the exhaust gas aftertreatment device, also referred to as evaluation, is carried out with respect to the capability thereof, in particular the capability of removing the first substance from the exhaust gas. Thus, for example, the performance of the exhaust gas aftertreatment device is to be understood as meaning a performance of the exhaust gas aftertreatment device for the stated chemical catalytic effect and / or support.In order to be able to test, in particular evaluate, the functionality, in particular the performance, of the exhaust gas aftertreatment device in a robust and meaningful manner, it is provided in the method according to the invention that a first variable is determined by means of an electronic computing device, by means of which the method is carried out, which characterizes, i.e. describes or specifies, a heat input into the exhaust gas aftertreatment device.For example, the electronic computing device is a component of the aforementioned motor vehicle. The motor vehicle thus has, in its completely produced state, the internal combustion engine and thus the exhaust system and the exhaust gas aftertreatment device, wherein the motor vehicle can be driven by means of the internal combustion engine. The motor vehicle is also referred to simply as a vehicle and is preferably a motor vehicle, in particular a passenger car. For example, the motor vehicle is driven by means of the internal combustion engine during the method. The internal combustion engine is operable in a fired mode. In the fired operation of the internal combustion engine, combustion processes take place in the internal combustion engine, in particular in combustion chambers of the internal combustion engine. During the combustion process, a respective mixture, also referred to as a fuel-air mixture, is burned, in particular ignited and burned, resulting in the exhaust gas. For example, the internal combustion engine is operated in the fired mode in the method.The internal combustion engine is preferably a spark-ignited internal combustion engine, that is to say in particular a spark ignition engine.In the method, a second variable is determined by means of the electronic computing device, which second variable characterizes an average power of the internal combustion engine, also referred to as average engine power. The average power of the internal combustion engine describes a work performed by the internal combustion engine within an, in particular predefinable or predefined, time period divided by the time period. In other words, the average power of the internal combustion engine describes an energy required by the internal combustion engine to perform the work within the time period divided by the time period. The time period thus extends continuously without interruption from a first point in time to a second point in time. The time interval is also referred to as a time window, window or observation window. For example, the method begins at the first point in time. At the first time, the fired operation of the internal combustion engine starts. In other words, it is provided that at the first point in time the initially deactivated internal combustion engine is activated, i.e. started and thereby transferred to its fired operation, so that the fired operation of the internal combustion engine begins at the first point in time.In particular, it is conceivable that a trip of the motor vehicle, also referred to as a driving cycle, begins at the first point in time, so that, for example, the time span is at least a part of the driving cycle mentioned. It is conceivable that the fired operation of the internal combustion engine ends at the second point in time. For example, the internal combustion engine is thus deactivated at the second point in time, so that the fired operation of the internal combustion engine is ended at the second point in time. For example, the travel of the motor vehicle is ended at the second point in time, in particular in such a way that, for example, the motor vehicle is parked and deactivated at the second point in time. For example, the initially deactivated internal combustion engine is started at the first point in time as a result of an operation, in particular actuation, of an operating element of the motor vehicle effected by a person, so that, for example, at the first point in time, the fired operation of the initially deactivated internal combustion engine is started as a result of the operation of the operating element. In particular, it is conceivable that the internal combustion engine is deactivated before the first point in time. For example, at the second point in time, the fired operation of the internal combustion engine is deactivated as a result of renewed operation, in particular actuation, of the operating element effected by the person or by another person, so that, for example, at the second point in time, the fired operation of the internal combustion engine is ended as a result of renewed operation, in particular actuation, of the operating element. It is conceivable that between the first time and the second time an operation of the operating element and / or a deactivation of the internal combustion engine effected by operating the operating element, i.e. the fired operation of the internal combustion engine, is omitted. Thus, it is preferably provided that between the first time and the second time, an activation of the internal combustion engine effected by operating the operating element, i.e. the fired operation, is omitted.The heat input is or characterizes a heating or a temperature of the exhaust gas aftertreatment device. In other words, the heat input is characteristic of a heating or a temperature of the exhaust gas aftertreatment device. In other words, the heat input is a measure for a heating and / or for a temperature of the exhaust gas aftertreatment device. In particular, it is provided that the first variable characterizes the heat input as a heat input into the exhaust gas aftertreatment device occurring within the time span. In other words, for example, the heat input into the exhaust gas aftertreatment device characterized by the first variable is a heat input into the exhaust gas aftertreatment device occurring within the time period, that is to say over the time period.The average power of the internal combustion engine is, characterized or describes a dynamics of the internal combustion engine, in particular within the time period, and therefore over the time period. The larger the first variable or a first value of the first variable, the larger the heat input into the exhaust gas aftertreatment device, which in particular takes place within the time period. The greater the second variable or a second value of the second variable, the greater is the average power of the internal combustion engine and the greater is a dynamic of the internal combustion engine within the time period, that is to say considered over the time period.In the method, a measured variable is measured and thus recorded by means of a nitrogen oxide sensor, which is referred to as a NOx sensor, at a measurement point arranged downstream of the exhaust gas aftertreatment device in the flow direction of the exhaust gas flowing through the exhaust system, which characterizes a quantity of nitrogen oxides (NOx) contained in the exhaust gas.A third variable is ascertained by means of the electronic computing device by using the measured variable as the third variable or by ascertaining, in particular calculating, the third variable from the measured variable. For example, the nitrogen oxide sensor provides an, in particular electrical, signal which characterizes the quantity of nitrogen oxides measured by means of the nitrogen oxide sensor. For example, the electronic computing device can receive the signal, as a result of which the electronic computing device determines the measurement variable. The electronic computing device can use the measured variable as the third variable, or the electronic computing device can determine, in particular calculate, the third variable from the measured variable.By means of the electronic computing device, the first variable is compared with a first threshold value, in particular a predefinable or predefined first threshold value. In other words, a first comparison is carried out by means of the electronic computing device, in which the first variable is compared with the first threshold value. By means of the electronic computing device, the second variable is compared with a second threshold value, in particular a predefinable or predefined second threshold value. In other words, a second comparison is carried out by means of the electronic computing device, in which the second variable is compared with the second threshold value.Then and preferably only when the first variable exceeds the first threshold value and, in particular simultaneously, the second variable exceeds the second threshold value, the functionality of the exhaust gas aftertreatment device is checked by means of the electronic computing device by comparing the third variable with a third threshold value. Thus, testing the operability of the exhaust after-treatment device is or comprises comparing the third quantity with the third threshold value. In other words, if it is determined by the first comparison and the second comparison that the first variable exceeds the first threshold value, in particular simultaneously, the second variable exceeds the second threshold value, the functionality of the exhaust gas aftertreatment device is checked by means of the electronic computing device by carrying out a third comparison by means of the electronic computing device, in which the third variable is compared with the third threshold value, which is predetermined or predeterminable, for example. Thus, the functionality of the exhaust system is checked by means of the electronic computing device, and in particular only when the first variable exceeds the first threshold value and, in particular simultaneously, exceeds the second variable and the second threshold value, depending on the third comparison.It is very preferably provided that in the method the motor vehicle and / or the internal combustion engine is operated as a function of the comparison of the third variable with the third value, i.e. as a function of the third comparison.The method makes it possible to evaluate the performance of the exhaust gas aftertreatment device in a meaningful and robust manner with regard to its function or capability of removing the first substance, in particular the nitrogen oxides, from the exhaust gas, since the performance of the exhaust gas aftertreatment device is then and preferably only checked in particular by the third comparison or as a function of the third comparison if both a first criterion and, in particular simultaneously, a second criterion are fulfilled. The first criterion is fulfilled if the first variable is greater than the first threshold value. The second criterion is fulfilled if the second variable is greater than the first threshold value. If the two criteria are met, in particular simultaneously, it can be assumed on the one hand that the exhaust gas aftertreatment device is sufficiently warm, therefore has a sufficiently high temperature and therefore should in principle be able or should in principle be able to posttreat the exhaust gas as desired, that is to say with a sufficient performance, that is to say if the exhaust gas aftertreatment device is not excessively aged or damaged. If the second criterion is fulfilled, it can be assumed that the internal combustion engine was operated sufficiently dynamically during the time period, that is to say that the dynamics of the internal combustion engine were sufficiently high over the time period and the exhaust gas aftertreatment device has thus been warmed up sufficiently quickly in order to be able to posttreat the exhaust gas, in particular if the exhaust gas aftertreatment device is not excessively aged or damaged. If both criteria are fulfilled, it is possible to draw conclusions as to whether or not the exhaust gas aftertreatment device is still sufficiently powerful with regard to the aftertreatment of the exhaust gas, and consequently whether or not the exhaust gas aftertreatment device is still having its desired functionality with regard to the aftertreatment of the exhaust gas, depending on the third comparison.If, for example, the third variable exceeds the third threshold value, in particular while both criteria are met, it can be deduced in a particularly meaningful manner, that is to say with sufficiently high certainty, that the exhaust gas aftertreatment device is no longer sufficiently powerful for aftertreating the exhaust gas, and therefore the exhaust gas can no longer be aftertreated as desired. If, however, it is determined, for example, on the basis of the third comparison that the third variable is less than or equal to the third threshold value, in particular while the two criteria are fulfilled, it can be concluded with certainty, robust and with a high level of relevance that the exhaust gas aftertreatment device is still sufficiently powerful with regard to the aftertreatment of the exhaust gas, and therefore still has its desired functionality for aftertreatment of the exhaust gas.The operation of the motor vehicle dependent on the third comparison, and therefore on the comparison of the third variable with the third threshold value, comprises, for example, that, depending on the comparison of the third variable with the third threshold value, in particular depending on the third comparison, at least one interior of the motor vehicle, also referred to as a passenger compartment, passenger compartment or cabin, outputs an indication signal that is optically and / or haptically and / or acoustically perceptible by a person present in the interior, in particular by means of an electronic or electrical reproduction device of the motor vehicle. Alternatively or additionally, the operation of the motor vehicle dependent on the comparison of the third variable with the third threshold value, i.e. on the third comparison, can comprise the internal combustion engine, in particular the fired operation, being automatically ended and / or the motor vehicle being automatically shut down.The method makes it possible to make a valid statement about the functionality of the exhaust gas aftertreatment device, that is to say about the capability of the exhaust gas aftertreatment device to be able to posttreat the exhaust gas. The method ensures that the functionality of the exhaust gas aftertreatment device is checked when, and in particular only when, the exhaust gas aftertreatment device, also referred to as exhaust system, is sufficiently, in particular completely, warmed through and is thus in principle ready for the aftertreatment of the exhaust gas and when the internal combustion engine has been operated in sufficiently synchronized fashion. The background of the invention is in particular that if the exhaust gas aftertreatment device does not have a sufficiently high temperature and is therefore still too cold, it is not possible to make a valid statement about the performance or functionality of the exhaust gas aftertreatment device, that is to say that the performance of the exhaust gas aftertreatment device cannot be evaluated validly with regard to the aftertreatment of the exhaust gas. The same applies if the exhaust gas aftertreatment device is sufficiently warm, i.e. has a sufficiently high temperature in order to be able to treat the exhaust gas in a fundamentally advantageous manner, but this temperature of the exhaust gas aftertreatment device results from an only insufficiently dynamic operation of the internal combustion engine.If, for example, the internal combustion engine is activated in particular at the first point in time and then not operated dynamically, but rather is allowed to run continuously at idle, in particular during the period of time mentioned, it is possible in principle that, if the period of time is sufficiently long, the exhaust gas aftertreatment device comes to a sufficiently high temperature, which is sufficiently high for the exhaust gas aftertreatment device to be able to subsequently treat the exhaust gas in a fundamentally advantageous manner, but then a dynamic of the internal combustion engine taking place during the period of time is only inadequate, that is to say not sufficient for it to be possible to evaluate the performance of the exhaust gas aftertreatment device valid. A valid evaluation of the performance of the exhaust gas aftertreatment device with regard to the aftertreatment of the exhaust gas is possible and only if both the heat input into the exhaust gas aftertreatment device occurring within the time period is sufficiently high and a dynamic of an operation of the internal combustion engine occurring, in particular activated, during the time period is sufficiently high. Against this background, the method enables a reliable, robust and valid evaluation of the performance of the exhaust gas aftertreatment device, since the functionality of the exhaust gas aftertreatment device is checked in dependence on the third comparison only when both the first variable exceeds the first threshold value and, in particular simultaneously, the second variable exceeds the second threshold value.In order to be able to test the functionality of the exhaust gas aftertreatment device in a particularly robust manner, it is provided in the invention that a temporal profile of the third variable is determined by means of the electronic computing device, wherein the temporal profile of the third variable describes a temporal change of the third variable which takes place during the time period. By means of the electronic computing device, a first partial variable, which is or comprises an absolute first mass of the nitrogen oxides measured by the nitrogen oxide sensor within a first part of the time span, is determined by integrating over time a first profile part of the time profile corresponding to the first part of the time span over the first part of the time span. The first part of the time period and thus the first extension part thus extend continuously and thus without interruption from the first point in time to a third point in time lying between the first point in time and the second point in time.A second partial variable, which is or comprises an absolute second mass of the nitrogen oxides measured by the nitrogen oxide sensor within a second part of the time period directly adjoining the first part of the time period, is determined by integrating over the second part of the time period a second part of the time period corresponding to the second part of the time period and directly adjoining the first part of the time period. Thus, the second part of the time period and thus the second extension part extend continuously and thus without interruption from the third point in time to the second point in time.Furthermore, it is provided that the functionality of the exhaust gas aftertreatment device is checked as a function of the part variables. In particular, it is provided that the vehicle is operated as a function of the sub-variables. In particular, the operation of the motor vehicle, which is also referred to simply as a vehicle, as a function of the component variables can comprise the aforementioned indication signal being output in the interior space and / or the internal combustion engine being operated as a function of the component variables and / or the motor vehicle being shut down as a function of the component variables. Since the first sub-variable and the second sub-variable are determined, the temporal profile is divided into the aforementioned profile parts. The first mass of the nitrogen oxides is a mass which flows through or has flowed through the exhaust gas aftertreatment device, while the exhaust gas aftertreatment device is still cold, for example, and is therefore below its operating or starting temperature. The second mass is, for example, a mass that flows through or has flowed through the exhaust gas aftertreatment device, while the exhaust gas aftertreatment device has a temperature that is greater than or equal to the operating or starting temperature. The first mass is or describes cold emissions, while the second mass is or describes warm emissions, for example. The time profile is divided on the basis of the temperature of the exhaust gas aftertreatment device. Thus, the third point in time is a point in time at which the exhaust gas aftertreatment device, which becomes warmer over the time period and thus, for example, viewed from the first point in time to the second point in time, first reaches or exceeds the operating or starting temperature viewed from the first point in time to the second point in time. From the first point in time to the third point in time, the temporal profile characterizes or characterizes the cold emissions, and from the third point in time, in particular to the second point in time, the temporal profile characterizes or characterizes the warm emissions. By this distinction between the cold emissions and the warm emissions or by dividing the time profile into the first profile part and the second profile part, a high degree of robustness can be realized, since the performance of the exhaust gas aftertreatment device can be evaluated in a robust and valid manner.In order to be able to check the functionality of the exhaust system particularly advantageously and validly, it is provided in one embodiment of the invention that the first variable is or comprises an exhaust gas mass flow integral, wherein the exhaust gas mass flow integral describes a mass flow of the exhaust gas that is temporal and in this case integrated in particular over the time period.It has proven particularly advantageous if the mass flow of the exhaust gas is integrated over the time span to determine the exhaust gas mass flow integral. The exhaust gas mass flow integral is or thus describes, for example, a mass of the exhaust gas that has flowed through the exhaust gas aftertreatment device within the time interval, in particular absolute mass of the exhaust gas, also referred to as exhaust gas mass. As a result, the performance of the exhaust gas aftertreatment device can be tested, i.e. evaluated, in a particularly advantageous manner.In order to be able to test and in particular evaluate the functionality of the exhaust gas aftertreatment device in a particularly advantageous manner, it is provided in a further embodiment of the invention that the second variable is or comprises a heat flow integral, wherein the heat flow integral describes a heat flow into the exhaust gas aftertreatment device which is integrated over time and in the process over the time period.It has proven particularly advantageous if the heat flow is integrated over the time period in order to determine the heat flow integral. Thus, for example, the heat flow integral is or describes a heat or quantity of heat that has flowed, that is to say introduced or introduced, in particular absolute, into the exhaust gas aftertreatment device within the time period. As a result, it is possible to make a statement particularly advantageously about whether the exhaust gas aftertreatment device is sufficiently warm in order to be able to check its performance or functionality.In order to be able to test the performance of the exhaust gas aftertreatment device in a particularly advantageous manner, it is provided in a further embodiment of the invention that, in order to determine the heat flow integral, the exhaust gas mass flow integral is multiplied by a temperature of the exhaust gas aftertreatment device and / or of the exhaust gas.In order to realize a particularly advantageous check of the functionality of the exhaust gas aftertreatment device, it has proven to be particularly advantageous if the temperature is a temperature occurring within the time period.For example, the temperature is measured by means of a temperature sensor.It has been found to be particularly advantageous if the third variable is or comprises an absolute mass of the nitrogen oxides measured by the nitrogen oxide sensor within the time span. As a result, the performance or functionality of the exhaust gas aftertreatment device can be tested particularly advantageously.For example, a quotient is formed from the subvariables, in particular by dividing the second subvariable by the first subvariable. In this case, it is preferably provided that the functionality of the exhaust gas aftertreatment device is checked as a function of the quotient, as a result of which the functionality can be evaluated in a particularly valid manner. For example, the motor vehicle is operated as a function of the quotient, in particular as described above.In particular, the method according to the invention makes it possible to be able to evaluate the performance of the exhaust gas aftertreatment device for aftertreatment of the exhaust gas on the basis of at least almost any journey and / or any operation of the internal combustion engine in which the two criteria are met. In particular, it is possible to use any journey or operation of the internal combustion engine in which the criteria are fulfilled in order to evaluate the performance of the exhaust gas aftertreatment device. Journeys or operations in which the criteria are not simultaneously fulfilled can be discarded and are ignored, for example, with regard to evaluating the performance of the exhaust gas aftertreatment device. The method makes it possible in particular to also use very short operating times of the internal combustion engine and / or very short journeys of the motor vehicle in order to be able to check the functionality of the exhaust gas aftertreatment device valid, specifically when both criteria are fulfilled, in particular simultaneously, within these short operating times and / or journeys. As a result, the exhaust gas aftertreatment device can be advantageously tested.A second aspect of the invention relates to a motor vehicle which is also referred to simply as a vehicle and is preferably designed as a motor vehicle, in particular as a passenger vehicle, and which is designed to carry out a method according to the first aspect of the invention. Advantages and advantageous configurations of the first aspect of the invention are to be regarded as advantages and advantageous configurations of the second aspect of the invention and vice versa.For example, the quotient is compared with an in particular predefinable or predefined fourth threshold value by means of the electronic computing device. In other words, for example, a fourth comparison is carried out by means of the electronic computing device, in which the quotient, that is to say a result which is calculated by dividing the second subvariable by the first subvariable, is compared with the fourth threshold value. As a result, the functionality of the exhaust gas aftertreatment device is checked as a function of the quotient, that is to say as a function of the result or of the fourth comparison. If, for example, it is determined by the fourth comparison that the quotient, i.e. the result exceeds the fourth threshold value, in particular while the third variable simultaneously exceeds the third threshold value, then it can be deduced valid, i.e. meaningful and robust, that the exhaust gas aftertreatment device is no longer capable of post-treating the exhaust gas as desired. However, if it is determined, for example, by the fourth comparison that the quotient or the result is less than or equal to the fourth threshold value, in particular while the third variable is less than or equal to the third threshold value, then it can be deduced in a valid and robust manner that the exhaust gas aftertreatment device still has sufficient functionality, and therefore sufficiently high performance, for aftertreatment of the exhaust gas. In other words, the exhaust gas aftertreatment device is no longer functional in the first case, wherein the exhaust gas aftertreatment device is still functional in the second case.Further details of the invention will become apparent from the following description of a preferred exemplary embodiment with the accompanying drawing. The following shows: FIG. 1 shows a schematic illustration of an exhaust system through which exhaust gas of an internal combustion engine of a motor vehicle can flow; and FIG. 2 shows a diagram for illustrating a method for checking the functionality of an exhaust gas aftertreatment device arranged in the exhaust system and designed for aftertreatment of the exhaust gas.In the figures, identical or functionally identical elements are provided with identical reference symbols.FIG. 1 shows a schematic illustration of an exhaust system 2 of the motor vehicle through which exhaust gas from an internal combustion engine 1 of a motor vehicle can flow. This means that the motor vehicle, which is also referred to simply as a vehicle and is preferably designed as a motor vehicle, in particular as a passenger car, and the interior of which, which is also referred to as a passenger compartment, passenger compartment or cabin, is formed by a structure of the motor vehicle, which structure is designed, for example, as a self-supporting body, has the internal combustion engine 1 and the exhaust system 2 and can be driven by means of the internal combustion engine 1. Persons such as, for example, the driver or the driver of the motor vehicle can be present in the interior of the motor vehicle, in particular during a respective journey of the motor vehicle. A flow of the exhaust gas of the internal combustion engine 1 through the exhaust system 2 is illustrated by an arrow 3.An exhaust gas aftertreatment device 4 is arranged in the exhaust system 2, through which the exhaust gas can flow. The exhaust gas aftertreatment device 4 is designed to posttreat the exhaust gas in a targeted manner. Aftertreating the exhaust gas is to be understood, for example, as meaning that at least one substance contained in the exhaust gas can be at least partially removed from the exhaust gas by means of the exhaust gas aftertreatment device, in particular as meaning that the substance reacts as reactant in a chemical reaction, in particular with at least or exactly one second reactant, to form at least one product different from the substance, wherein the exhaust gas aftertreatment device is catalytically active, for example, for the chemical reaction, that is to say that the exhaust gas aftertreatment device can, for example, catalytically effect and / or support the chemical reaction.With reference to FIGS. 1 and 2, a method for checking a functionality of the exhaust gas aftertreatment device 4 is explained below. The functionality of the exhaust gas aftertreatment device 4 is a capability or capability of the exhaust gas aftertreatment device 4 to remove nitrogen oxides contained in the exhaust gas from the exhaust gas, thus for example to catalytically support and / or to effect a selective catalytic reduction as the chemical reaction mentioned. Thus, the checking of the functionality is or comprises, for example, an evaluation of the stated performance of the exhaust gas aftertreatment device 4.In the method, a first variable is determined by means of an electronic computing device 5, in particular of the motor vehicle, which is shown particularly schematically in FIG. 1 and characterizes a heat input into the exhaust gas aftertreatment device 4. In the method, a second variable is ascertained by means of the electronic computing device 5, which second variable characterizes an average power of the internal combustion engine 1, the average power of which variable describes a work performed by the internal combustion engine, that is to say performed work divided by the time period, within a time period. In particular, the first variable characterizes the mentioned heat input as a heat input into the exhaust gas aftertreatment device 4 occurring within the time period, i.e. over the time period.In the method, a measured variable is measured by means of a nitrogen oxide sensor 6 at a measurement point MS arranged downstream of the exhaust gas aftertreatment device 4 in the flow direction of the exhaust gas flowing through the exhaust system 2, which characterizes a quantity of the nitrogen oxides contained in the exhaust gas. A third variable is ascertained by means of the electronic computing device 5 by using the measured variable as the third variable or by ascertaining, in particular calculating, the third variable from the measured variable. By means of the electronic computing device, the first variable is compared with a first threshold value, which can be predetermined or is predetermined, for example. For example, the first threshold value is stored in an electrical or electronic data memory of the electronic computing device 5. By means of the electronic computing device 5, the second variable is compared with a second threshold value, which can be predetermined or is predetermined, for example. For example, the second threshold value is stored in the data memory of the electronic computing device 5.By means of the electronic computing device 5, the third variable is compared with a third threshold value, which can be predetermined or is predetermined, for example. For example, the third threshold value may be stored in the data memory. Then and in particular only when the first variable exceeds the first threshold value and, in particular simultaneously, the second variable exceeds the second threshold value, the functionality of the exhaust gas aftertreatment device 4 is checked by means of the electronic computing device as a function of the comparison of the third variable with the third threshold value. Thus, the comparison of the third variable with the third threshold value and also the checking of the functionality take place when and preferably only when the first variable exceeds the first threshold value and, in particular simultaneously, the second variable exceeds the second threshold value. This makes it possible to ensure that the functionality of the exhaust gas aftertreatment device 4 is tested then and preferably only then, and therefore that the performance of the exhaust gas aftertreatment device 4 is evaluated only when the exhaust gas aftertreatment device 4 is sufficiently warm and thus has a temperature which is greater than or equal to a light-off or operating temperature of the exhaust gas aftertreatment device 4, and when the internal combustion engine 1 has simultaneously been operated sufficiently dynamically during the time period, that is to say within the time period, such that the sufficiently high temperature of the exhaust gas aftertreatment device 4 results from sufficiently dynamic operation of the internal combustion engine 1. If the comparisons show that although the temperature of the exhaust gas aftertreatment device 4 is greater than or equal to the operating and / or starting temperature, this results only from inadequate dynamic operation of the internal combustion engine 1, the functionality of the exhaust gas aftertreatment device 4 is not tested, since the functionality of the exhaust gas aftertreatment device 4 cannot then be tested validly. If the comparisons show that, although the internal combustion engine 1 has been or is operated sufficiently dynamically during the time interval, the temperature of the exhaust gas aftertreatment device 4 is lower than the operating and / or starting temperature, the functionality of the exhaust gas aftertreatment device 4 is likewise not tested, since it could not be tested valid. Then and only when the first variable exceeds the first threshold value and the second variable exceeds the second threshold value, criteria are fulfilled which permit a valid check or evaluation of the performance or functionality of the exhaust gas aftertreatment device 4, so that, for example, then and only when the first variable exceeds the first threshold value and at the same time the second variable exceeds the second threshold value, the performance of the exhaust gas aftertreatment device 4 is checked as a function of the comparison of the third variable with the third threshold value. FIG. 2 shows a diagram, on whose abscissa 7 the time is plotted. The third variable is plotted on the ordinate 8 of the diagram or values of the third variable are plotted. In particular, the time relative to the image plane of FIG. 2 is plotted on the abscissa 7 as viewed from left to right.For example, the third variable is plotted on the ordinate 8 with reference to the image plane of FIG. 2 rising from bottom to top. Entered in the diagram are first time curves 9 of the third variable, second time curves 10 of the third variable and third time curves 11 of the third variable. Curves 9 illustrate a first state of exhaust aftertreatment device 4, which is new in the first state, such that the first state is a new state. Curves 10 characterize a second state of exhaust gas aftertreatment device 4, exhaust gas aftertreatment device 4 being aged in the second state. Both in the first state and in the second state, the exhaust gas aftertreatment device 4 has sufficient functionality, that is to say sufficient capacity for aftertreating the exhaust gas and thus removing the nitrogen oxides from the exhaust gas. The time curves 11 illustrate a third state of the exhaust gas aftertreatment device 4, which is no longer functional in the third state and therefore no longer has sufficient capacity to post treat the exhaust gas and thus remove the nitrogen oxides from the exhaust gas. It can be seen that the mentioned time span extends from a first time t 1, in particular continuously, to a second time t 2 following the first time t 1 in time. A third time lying between the times T 1 and T 2 is denoted by t 3. A first part of the time period extends continuously from the time t 1 to the time t 3 and is denoted by T 1. A second part T 2 of the time period extends continuously from the time t 3 to the time t 2. Accordingly, the respective course 9, 10, 11 has a respective first course part and a respective second course part. It can be seen that the second part T 2 directly adjoins the first part T 1, and the respective second extension part adjoins the respective first extension part in each case. The respective first extension part extends continuously from the time t 1 to the time t 3, and the respective second extension part extends continuously from the time t 3 to the time t 2.The respective first profile part characterizes, describes or illustrates a change in an absolute first mass of the nitrogen oxides measured by the nitrogen oxide sensor 6 within the first part T 1 of the time span, wherein, as can be seen from FIG. 2, the first mass naturally increases, that is to say becomes greater, as the time span progresses. The respective second profile part characterizes, describes or illustrates a change in an absolute second mass of the nitrogen oxides measured by the nitrogen oxide sensor 6 within the second part T 2 of the time span, wherein the second mass naturally increases as the time span progresses. By integrating the respective first profile part over time over the first part T 1 of the time period, the respective absolute first mass of the nitrogen oxides measured by the nitrogen oxide sensor within the first part T 1 of the time period can be determined, in particular calculated, from the respective first profile part. By temporal integration, i.e. temporal integration of the respective second profile part over the second part T 2 of the time period, the respective absolute second mass of the nitrogen oxides measured within the second part T 2 of the time period by the nitrogen oxide sensor 6 can be determined, in particular calculated, from the respective second profile part. The respective absolute first mass is a respective first sub-variable or is characterized by a respective first sub-variable. The respective absolute second mass is a respective second sub-variable or is characterized by a respective second sub-variable. For example, the respective second mass or the respective second sub-variable is divided by the associated respective first mass or by the respective associated first sub-variable by means of the electronic computing device 5, whereby a respective result is determined. If, for example, the third variable exceeds the third threshold value and if, for example, the respective result simultaneously exceeds a respective fourth threshold value, which is, for example, predefinable or predefined and is, for example, stored in the data memory, it is possible to conclude that the exhaust gas aftertreatment device 4 is in the third state and is therefore no longer sufficiently powerful to be able to posttreat the exhaust gas. However, if, for example, the third variable is less than or equal to the third threshold value and if, in particular, the respective result is less than or equal to the fourth threshold value at the same time, it can be concluded in a robust and valid manner that the exhaust gas aftertreatment device 4 is in the first state or in the second state and therefore still has sufficiently good performance or functionality for aftertreating the exhaust gas, and consequently for being able to remove the nitrogen oxides from the exhaust gas. The method thus enables a valid, robust and meaningful checking of the functionality of the exhaust gas aftertreatment device 4.List of reference characters1 Internal combustion engine 2 Exhaust system 3 Arrow 4 Exhaust gas aftertreatment device 5 Electronic computing device 6 Nitrogen oxide sensor 7 Abscissa 8 Ordinate 9 Temporal profile 10 Temporal profile 11 Temporal profile MS Measurement point t 1 Point in time t 2 Point in time t 3 Point in time T 1 First part T 2 Second part

Claims

Method for checking the functionality of an exhaust gas aftertreatment device (4) which is arranged in an exhaust system (2) through which exhaust gas from an internal combustion engine (1) can flow and through which the exhaust gas can flow and which is designed for aftertreatment of the exhaust gas, in which: - a first variable which characterizes a heat input into the exhaust gas aftertreatment device (4) is determined by means of an electronic computing device (5); - a second variable which characterizes an average power of the internal combustion engine (1) is determined by means of the electronic computing device (5), the average power of said second variable describing a work performed by the internal combustion engine (1) within a time period divided by the time period; - a measured variable which characterizes an amount of nitrogen oxides contained in the exhaust gas is measured by means of a nitrogen oxide sensor (6) at a measurement point (MS) arranged downstream of the exhaust gas aftertreatment device (4); a third variable is determined by means of the electronic computing device (5) by using the measured variable as the third variable or by determining the third variable from the measured variable; the first variable is compared with a first threshold value by means of the electronic computing device (5); the second variable is compared with a second threshold value by means of the electronic computing device (5); and - if the first variable exceeds the first threshold value and the second variable exceeds the second threshold value, the functionality of the exhaust gas aftertreatment device (4) is checked by means of the electronic computing device (5) by comparing the third variable with a third threshold value; characterized in that: - the time period extends continuously, thus without interruption, from a first point in time (t1) to a second point in time (t2), wherein, at the first point in time (t1), the initially deactivated internal combustion engine (1) is started and is thereby transferred into its fired operation, such that the fired operation of the internal combustion engine (1) begins at the first point in time (t1); - a temporal profile (9, 10, 11) of the third variable is determined by means of the electronic computing device (5), the temporal profile of said third variable describing a temporal change of the third variable that takes place during the time period; the temporal profile (9, 10, 11) is divided into a first profile part and a second profile part by: ◯ determining, by means of the electronic computing device (5), a first partial variable which is or comprises an absolute first mass of the nitrogen oxides measured by the nitrogen oxide sensor (5) within a first part (T1) of the time period, by integrating the first profile part of the temporal profile (9, 10, 11) corresponding to the first part (T1) of the time period over time via the first part (T1) of the time period; ◯ a second partial variable, which is or comprises an absolute second mass of the nitrogen oxides measured by the nitrogen oxide sensor (5) within a second part (T2) of the time period directly adjoining the first part (T1) of the time period, is determined by integrating the second part of the time period (9, 10, 11) over the second part (T2) of the time period, which second part corresponds to the second part (T2) of the time period and directly adjoining the first part; the first part (T1) of the time period extends continuously from the first time (t1) to a third time (t3) lying between the first time (t1) and the second time (t2); the second part (T2) of the time period extends continuously from the third time (t3) to the second time (t2); the time profile is divided on the basis of a temperature of the exhaust gas aftertreatment device (4) in such a way that the third time (t3) is a time at which the exhaust gas aftertreatment device (4) warming up over the time period and thus viewed from the first time to the second time reaches or exceeds its operating or starting temperature for the first time viewed from the first time to the second time; and the functionality of the exhaust gas aftertreatment device (4) is tested as a function of the part variables.Method according to Claim 1, characterized in that the first variable is or comprises an exhaust gas mass flow integral which describes a temporally integrated mass flow of the exhaust gas.Method according to Claim 2, characterized in that, in order to determine the exhaust gas mass flow integral, the mass flow of the exhaust gas is integrated over the time period.Method according to one of the preceding claims, characterized in that the second variable is or comprises an integral heat flow which describes a temporally integrated heat flow in the exhaust gas aftertreatment device (4).Method according to Claim 4, characterized in that, in order to determine the heat flow integral, the heat flow is integrated over the time period.Method according to Claim 2 or 3 and according to Claim 4 or 5, characterized in that, in order to determine the heat flow integral, the exhaust gas mass flow integral is multiplied by a temperature of the exhaust gas aftertreatment device (4) and / or of the exhaust gas.Method according to claim 6, characterised in that the temperature is a temperature occurring within the period of time.Method according to one of the preceding claims, characterized in that the third variable is or comprises an absolute mass of the nitrogen oxides measured by the nitrogen oxide sensor (5) within the time interval.Motor vehicle which is designed to carry out a method according to one of the preceding claims.

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