Method for operating a propulsion system for a motored vehicle as well as an according propulsion system

Abstract

The invention relates to a method for operating a drive device (1) for a motor vehicle, said drive device having an exhaust gas-producing drive assembly and an exhaust gas aftertreatment device (2) for the aftertreatment of the exhaust gas. According to the invention, during a normal operation of the drive device (1), a first value of an aging variable which describes the state of the exhaust gas aftertreatment device is determined for the exhaust gas aftertreatment device (2), and for at least one exhaust gas component of the exhaust from a first output material proportion of the exhaust gas component, said proportion lying downstream of the exhaust gas aftertreatment device (2), a second output material proportion is ascertained which would occur if the exhaust gas aftertreatment device (2) were replaced by another structurally identical exhaust gas aftertreatment device with a second aging variable value which differs from the first value. The invention also relates to a drive device (1) for a motor vehicle.

Description

[0001] The invention relates to a method for operating a drive unit for a motor vehicle, which includes an exhaust gas-generating drive unit and an exhaust gas aftertreatment device for treating the exhaust gas. The invention further relates to a drive unit for a motor vehicle.

[0002] For example, the prior art includes German patent application DE 10 2004 017 274 A1. This describes a method for diagnosing emissions in a multi-row emission system, the method comprising the following steps: obtaining a large number of emission measurements, each measurement corresponding to a row of the multi-row emission system; converting each measurement into a scaled value as a percentage of a threshold; adding the scaled values ​​to obtain a total emission value for the multi-row emission system; and triggering an alert if the total emission value exceeds the threshold. Further methods for diagnosing emissions are known from the following publications: DE 199 63 927 A1, US 2016 / 312675 A1, EP 3 196 433 B1, DE 10 2014 202491 A1 or DE 10 2011 055166 A1.

[0003] The object of the invention is to propose a method for operating a drive unit for a motor vehicle which has advantages over known methods, in particular enabling a reliable assessment of the influence of age on the conversion performance of the exhaust aftertreatment device.

[0004] According to the invention, this is achieved by a method for operating a drive unit for a motor vehicle with the features of claim 1. It is provided that, during intended operation of the drive unit for the exhaust aftertreatment system, a first value of an aging parameter describing its state is determined, and for at least one exhaust gas component, a second initial component is determined from a first initial component present downstream of the exhaust aftertreatment system. This second initial component would occur, or will occur, if the exhaust aftertreatment system were replaced with a structurally identical exhaust aftertreatment system that has a second value of the aging parameter different from the first.

[0005] Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims. It should be noted that the exemplary embodiments described in the description are not limiting; rather, any variations of the features disclosed in the description, the claims, and the figures are possible.

[0006] The drive system serves to propel the motor vehicle, thus providing the drive torque directed towards propelling the vehicle. To provide this drive torque, the drive system comprises the drive unit. During operation, the drive unit is supplied with fuel and fresh gas, at least intermittently, whereby the fresh gas contains fresh air, at least intermittently. Additionally, the fresh gas may contain exhaust gas if exhaust gas recirculation is implemented, in which the exhaust gas generated by the drive unit is at least partially returned to the drive unit as a component of the fresh gas. The fuel and fresh gas supplied to the drive unit form a fuel-fresh gas mixture with a specific composition, which is then reacted within the drive unit.

[0007] During operation of the engine, exhaust gas is produced due to the chemical reaction between fuel and fresh air. This exhaust gas is discharged towards the outside environment of the engine or vehicle. Since the exhaust gas generated by the engine contains pollutants, it is first routed to an exhaust aftertreatment system before being released into the environment. In the exhaust aftertreatment system, the pollutants are at least partially converted into less harmful products. Only after passing through the exhaust aftertreatment system is the exhaust gas released into the environment.

[0008] The exhaust aftertreatment system is, for example, a vehicle catalyst, in particular a three-way catalyst, oxidation catalyst, NOₓ storage catalyst, or SCR catalyst. However, it can also be designed as a particulate filter, in particular a gasoline particulate filter or a diesel particulate filter, preferably with an integrated vehicle catalyst, for example, with a catalytic coating. The exhaust aftertreatment system has a certain storage capacity for a further exhaust component. The further exhaust component is understood to be an exhaust component that can correspond to, but preferably differs from, the at least one other exhaust component. For example, the further exhaust component is oxygen, particularly if the drive unit is a gasoline engine. If, on the other hand, the drive unit is a diesel engine, the further exhaust component is preferably ammonia.In the latter case, the aforementioned SCR catalyst is particularly preferred as an exhaust aftertreatment device.

[0009] The conversion rate, and thus the conversion efficiency of the exhaust aftertreatment system, which converts pollutants into less harmful products, depends primarily on the composition of the exhaust gas supplied to the system and / or on the storage load of the system, which in turn is related to the composition of the exhaust gas. Storage load refers to the amount of additional exhaust gas components stored in the system. The condition of the exhaust aftertreatment system also influences the conversion rate. This condition is particularly relevant in the context of aging, which steadily deteriorates over the system's service life.

[0010] The condition of the exhaust aftertreatment system can be determined, for example, by first determining its storage capacity, in particular its oxygen storage capacity or ammonia storage capacity. The system's condition can then be derived from this value. Preferably, a defect in the exhaust aftertreatment system is detected as soon as the storage capacity falls below a certain threshold.

[0011] The amount of exhaust component released into the environment by the engine depends on numerous factors. For example, it is determined by the engine and its individual components, as well as by the exhaust aftertreatment system. If it is found that the amount of exhaust component downstream of the aftertreatment system is too high, for instance because the initial fraction of the exhaust component exceeds a threshold, this can have numerous causes. Therefore, a simple method is sought to identify, with minimal computational effort, the component responsible for the initial fraction exceeding the threshold. The exhaust component is, in principle, any constituent of the exhaust gas.

[0012] In the case of the exhaust aftertreatment system, the first value of the aging parameter is determined during the intended operation of the drive system. The aging parameter describes the condition of the exhaust aftertreatment system, in particular its age. For example, the aging parameter, or the first value, is determined from the calendar age of the exhaust aftertreatment system, specifically the difference between the current date and the manufacturing or commissioning date of the exhaust aftertreatment system, and / or from the operating time of the exhaust aftertreatment system. Operating time here refers to the cumulative duration over which exhaust gas has flowed through the exhaust aftertreatment system.

[0013] The second fraction of the exhaust gas component is determined from the first fraction present downstream of the exhaust aftertreatment system, using the aging parameter or the first value of the aging parameter. The second fraction is defined here as the fraction that would be present downstream of the exhaust aftertreatment system after replacing the existing system with another system, or that is present after an actual replacement. The first and second fractions describe the proportion of the exhaust gas component to the total amount of exhaust gas. The fraction is expressed as a mole fraction and thus quantitatively describes the composition of the exhaust gas.

[0014] The other exhaust aftertreatment system is identical in construction to the first exhaust aftertreatment system, but has a different aging parameter value. Specifically, the second aging parameter value assigned to the other exhaust aftertreatment system is chosen to correspond to an exhaust aftertreatment system that is newer than the first. For clarity, in this description, the first exhaust aftertreatment system will be referred to as the first exhaust aftertreatment system, and the other exhaust aftertreatment system as the second exhaust aftertreatment system.

[0015] The determination of the second feedstock fraction is carried out during the intended operation of the drive system. This means that it is performed during normal driving of the vehicle. Preferably, the determination is carried out multiple times or periodically, for example, at regular or irregular intervals. It can also be carried out continuously, i.e., permanently, where technically feasible and practical. The second feedstock fraction is therefore not determined only once, but repeatedly, in particular several times during each operation of the drive system. This ensures reliable monitoring of the drive unit.

[0016] Preferably, the necessity of replacing the exhaust aftertreatment system is determined based on the first and second emissions fractions. Preferably, if the first emissions fraction exceeds the aforementioned threshold, the second emissions fraction is compared to the threshold. If it is also higher than the threshold, the exceedance of the threshold is not caused, or at least not solely caused, by the exhaust aftertreatment system. Conversely, if the second emissions fraction is lower than the threshold, a sufficiently low emissions fraction can likely be achieved simply by replacing the exhaust aftertreatment system, without replacing or even inspecting other components of the drive system.Accordingly, the described procedure can be used to determine extremely efficiently whether the exhaust aftertreatment system needs to be replaced.

[0017] It may be possible not to directly compare the first or second feedstock fraction with the threshold value, but rather to perform this comparison indirectly. In this case, it is preferably possible to derive a quantity from each feedstock fraction, i.e., from the first and / or second feedstock fraction, and to compare this quantity with the threshold value. For example, a throughput of the exhaust gas component is determined from the respective feedstock fraction and a mass flow rate of the exhaust gas, in particular the exhaust gas mass flow. Preferably, the throughput is integrated over time, resulting in a quantity of the exhaust gas component. From this quantity, a distance-related quantity can be determined using the distance traveled by the vehicle during that time, for example, in the unit g / km.The quantity per route is then compared with the threshold value, and the procedure described above is followed.

[0018] A further development of the invention provides that the first value of the aging parameter is determined from the storage capacity of the exhaust aftertreatment system for another exhaust component and / or that the second value for the other exhaust aftertreatment system is a value corresponding to that of a brand-new exhaust aftertreatment system. The use of the storage capacity to determine the condition of the exhaust aftertreatment system has already been mentioned. The first value of the aging parameter is a function of this storage capacity. For example, the first value corresponds to a ratio between the currently available storage capacity and an initial storage capacity of the exhaust aftertreatment system.

[0019] The initial storage capacity is, for example, the storage capacity that the exhaust aftertreatment system has at its initial commissioning. It may also represent a maximum storage capacity over the system's lifetime. In this sense, the initial storage capacity is the highest storage capacity the exhaust aftertreatment system will have over its operating period. Typically, when the exhaust aftertreatment system is brand new, its storage capacity is equal to its initial capacity.

[0020] Additionally or alternatively, the second value is set to the value representing the aging parameter of a brand-new exhaust aftertreatment system. This makes it possible to determine the effects of replacing the exhaust aftertreatment system with a brand-new one. The described procedure allows for a rapid diagnosis of the exhaust aftertreatment system.

[0021] A further development of the invention provides that an aging factor is determined from the first and second values, and that the second feedstock fraction is calculated from the first feedstock fraction using a mathematical relationship that takes the aging factor into account. The aging factor is thus a function of the first and second values ​​of the aging quantity. For example, the aging factor corresponds to the result of dividing the first value by the second value. After determining the aging factor, the mathematical relationship that takes the aging factor into account is used to calculate the second feedstock fraction from the first feedstock fraction. Preferably, an input fraction located upstream of the exhaust aftertreatment system is also taken into account.The described procedure, in turn, enables efficient diagnosis of the exhaust aftertreatment system.

[0022] A further development of the invention provides that the mathematical relationship is the connection y 2 , neu = y 1 y 2 , alt y 1 1 x is used where x is the aging factor, y 1 is an input mass fraction present upstream of the exhaust aftertreatment device, y 2,old is the first output mass fraction and y 2,new is the second output mass fraction.

[0023] The relationship can be derived as follows: The feedstock fraction for the first exhaust aftertreatment system can be determined with y 2 , alt = y 1 e − k alt T 0 e E R 1 T 0 − 1 T Θ n ˙ l and for the second exhaust aftertreatment system with y 2 , neu = y 1 e − k neu T 0 e E R 1 T 0 − 1 T Θ n ˙ l The aging factor x is given as x = k alt T 0 k neu T 0 defined. This results in y 2 , alt = y 1 e − k neu T 0 × e E R 1 T 0 − 1 T Θ n ˙ l and finally y 2 , alt = y 1 e − k neu T 0 e E R 1 T 0 − 1 T Θ n ˙ l x

[0024] The expression defined above is found here, so that the relationship in y 2 , alt = y 1 y 2 , neu y 1 x can be rewritten. Rearranged, this results in y 2 , neu = y 1 y 2 , alt y 1 1 x

[0025] According to the invention, if the first feedstock fraction exceeds a threshold value and the second feedstock fraction simultaneously falls below the threshold value, a replacement signal is generated, indicating the need to replace the exhaust aftertreatment system. This has already been mentioned above. Preferably, the replacement signal is only generated if the first feedstock fraction exceeds the threshold value and the second feedstock fraction falls below the threshold value. If both the first and second feedstock fractions exceed the threshold value, the replacement signal is not generated, since replacing the exhaust aftertreatment system would likely have no effect.

[0026] The replacement signal is preferably stored in a fault memory of the drive unit so that it can be read out subsequently. Additionally or alternatively, the replacement signal is displayed to the driver of the vehicle, in particular visually and / or audibly. The driver is thus alerted to the need to replace the exhaust aftertreatment system. The described procedure makes it possible to quickly and reliably identify the need to replace the exhaust aftertreatment system.

[0027] A further development of the invention provides that, from the input fraction of the exhaust gas component present upstream of the exhaust gas aftertreatment device, an output fraction of the exhaust gas component present downstream of the exhaust gas aftertreatment device is determined by means of a reaction equation, wherein at least one calculation parameter contained in the reaction equation is determined as a function of the storage capacity of the exhaust gas aftertreatment device for the further exhaust gas component, and wherein the output fraction is used as the first output fraction.

[0028] Due to increasingly stringent emissions regulations, it is necessary to determine the quantity of pollutants present downstream of the exhaust aftertreatment system. This can be done, for example, by taking measurements. However, this is complex, especially if measurements would have to be taken for a large number of exhaust gas components. In many cases, measurement is also not practically feasible. For this reason, it is planned to perform a calculation for at least one exhaust gas component. An exhaust gas component is essentially any constituent of the exhaust gas, particularly a component whose initial mass fraction is not measured, or cannot be measured, downstream of the exhaust aftertreatment system.

[0029] The calculation is based on the input fraction of the exhaust gas component present upstream of the exhaust aftertreatment system. The input fraction describes the proportion of the exhaust gas component's amount of substance to the total amount of substance in the exhaust gas. The input fraction is expressed as a mole fraction and thus quantitatively describes the composition of the exhaust gas. From the input fraction, the output fraction of the exhaust gas component present downstream of the exhaust aftertreatment system is determined. The output fraction also quantitatively describes the composition of the exhaust gas, relating the amount of substance of the exhaust gas component downstream of the aftertreatment system to the total amount of substance in the exhaust gas present there. The output fraction is also expressed as a mole fraction.

[0030] The determination of the feed fraction from the input fraction is carried out using the reaction equation. This equation describes the change in the mole fraction of the exhaust gas component as the exhaust gas passes through the aftertreatment system. However, since the conversion rate or conversion capacity of the aftertreatment system changes over time, the reaction equation must be adjusted to reflect the current state of the system in order to determine the feed fraction with high accuracy.

[0031] For this reason, the calculated parameter included in the reaction equation is determined based on the storage capacity of the exhaust aftertreatment system. Incorporating the storage capacity of the exhaust aftertreatment system into the reaction equation significantly increases the accuracy of the calculated feedstock fraction. Specifically, the reaction equation is adjusted towards higher reaction rates as the storage capacity increases. Conversely, the reaction equation is adjusted towards lower reaction rates as the storage capacity decreases. Consequently, the aging of the exhaust aftertreatment system is reliably accounted for. The feedstock fraction determined in this manner is used as the first feedstock fraction and is then used to determine the second feedstock fraction.

[0032] For example, it is intended that if a threshold value is exceeded by the proportion of the exhaust gas, a fault in the exhaust aftertreatment system can be detected. In this case, for example, a fault signal can be displayed to the driver of the vehicle and / or the engine can be controlled in such a way that the proportion of the exhaust gas changes towards the threshold value, in particular down to this value. If the proportions of the exhaust gas components of several components are determined, preferably a separate threshold value is assigned to each component, against which the respective proportion of the exhaust gas component is compared. Again, this approach can include determining the distance-related quantity from the respective proportion of the exhaust gas component and comparing this with the threshold value.

[0033] A further development of the invention provides that one of the following quantities is used as at least one calculation parameter: rate constant, output rate constant, adjustment parameter, activation energy, and reaction inhibition parameter. The rate constant is understood to be, in particular, the rate constant of the chemical reaction occurring for the exhaust gas component in the exhaust aftertreatment system. The rate constant is typically temperature-dependent and is therefore available at least as a function of temperature and, in this case, additionally as a function of the storage capacity.

[0034] The velocity constant can be divided into the output velocity constant and the adjustment parameter, or determined from these quantities. Preferably, the velocity constant is obtained by multiplying the output velocity constant by the adjustment parameter. The output velocity constant describes the velocity constant at a defined temperature, in particular at an output temperature T0. The output temperature preferably corresponds to a temperature under standard conditions, for example, 0 °C or 20 °C. The output velocity constant is thus defined for a constant temperature and is therefore, for a given exhaust gas component, dependent only on the storage capacity.

[0035] The adjustment parameter describes the influence of temperature on the rate constant, starting from the initial rate constant. It is based, in particular, on the initial temperature and the current temperature. The adjustment parameter depends on the temperature and the storage capacity. Additionally, the activation energy can be incorporated into the adjustment parameter. Activation energy is the energy that must be overcome for the chemical reaction described by the reaction equation to proceed. For a given exhaust gas component, the activation energy depends solely on the storage capacity.

[0036] Finally, the reaction inhibition parameter describes the influence of the instantaneous fill level of the exhaust aftertreatment system containing the additional exhaust gas component on the reaction rate or the rate constant. The reaction inhibition parameter is preferably dependent on both the fill level and the storage capacity, or is expressed as a function of these. At least one of these parameters is considered in the reaction equation. For example, several or even all of these parameters are used in the reaction equation to determine the initial molar fraction of the exhaust gas component. Preferably, the initial rate constant, the activation energy, and the reaction inhibition parameter are used as calculated parameters in the reaction equation that depend on the storage capacity. This achieves particularly high accuracy.

[0037] A further development of the invention provides that the rate constant is determined from the initial rate constant and the adjustment parameter. This has already been mentioned. The rate constant is obtained, in particular, by multiplying the initial rate constant by the adjustment parameter. The adjustment parameter can also be referred to as the reaction rate factor. The use of these two parameters to determine the rate constant enables high accuracy in determining the molar fraction of the reactant.

[0038] A further development of the invention provides that the rate constant is corrected using the reaction inhibition factor. It has already been mentioned that the storage level can influence the reaction rate. This is taken into account via the reaction inhibition factor, which is determined from the storage level. Preferably, the calculated value used in the reaction equation is obtained by multiplying the rate constant by the reaction inhibition factor, or the reaction rate used in the reaction equation is corrected by multiplying it by the reaction inhibition factor. This also results in the aforementioned high accuracy.

[0039] A further development of the invention provides that the at least one calculated variable is determined as a function of the storage capacity by means of a mathematical relationship, a characteristic map, or a table. The mathematical relationship, characteristic map, or table takes the storage capacity as its input and the at least one calculated variable as its output. If several calculated variables are used in the reaction equation, a separate mathematical relationship, characteristic map, or table is preferably provided for each of the calculated variables used.

[0040] For example, characteristic maps are used for all calculation parameters. However, it is also possible to determine one of the calculation parameters using a characteristic map and another using a mathematical relationship or a table. The mathematical relationship, the characteristic map, or the table is preferably stored at the factory in the drive unit or a control unit of the drive unit, and in particular, it is permanently stored. The described procedure enables the precise determination of the initial mass fraction of the exhaust gas component.

[0041] A further development of the invention provides that one of the following components is used as at least one exhaust gas component: hydrocarbon, in particular total hydrocarbon, carbon oxide, in particular carbon monoxide and / or carbon dioxide, hydrogen, methane, ammonia, oxygen, and nitrogen oxide, in particular nitrogen monoxide and / or nitrogen dioxide. The term hydrocarbon is understood to mean any hydrocarbon, for example, methane. However, total hydrocarbon (THC) is particularly preferred, i.e., several or all of the hydrocarbons present in the exhaust gas.

[0042] The determination of the feed fraction from the respective input fraction is carried out for at least one of the aforementioned exhaust gas components, but preferably for several of the components. It is particularly preferred that this is done for all of the aforementioned components. This means that for each of the aforementioned components, the respective feed fraction is determined from the respective input fraction, namely using a respective reaction equation with a respective calculation parameter that is determined as a function of the storage capacity of the exhaust aftertreatment system. Consequently, the feed fractions of numerous different exhaust gas components downstream of the exhaust aftertreatment system are known.

[0043] A further development of the invention provides that the input mass fraction is determined for a currently existing operating point of the drive unit. The input mass fraction corresponds to a raw emission of the exhaust gas component from the drive unit, i.e., the mass fraction of the exhaust gas component in the exhaust gas flow between the drive unit and the exhaust aftertreatment device. The input mass fraction is determined for at least one exhaust gas component for the currently existing operating point of the drive unit, wherein the operating point is characterized in particular by a rotational speed of the drive unit and / or a drive torque provided by the drive unit.

[0044] The determination of the input mass fraction is preferably carried out using a mathematical relationship, a characteristic map, or a table, with the operating point being used as the input variable and the input mass fraction as the output variable. This approach enables the determination of the input mass fraction for at least one exhaust gas component with high accuracy and, correspondingly, a precise determination of the output mass fraction.

[0045] A further development of the invention provides that the reaction equation is the relationship y 2 = y 1 e − k T 0 e E R 1 T 0 − 1 T Θ n ˙ l is used where y 1 is the input mole fraction, y 2 is the output mole fraction, k is the rate constant, E is the activation energy, R is the universal gas constant, T 0 is the temperature at standard conditions, T is the instantaneous temperature, Θ is the reaction inhibition quantity, l is a length and ṅ is an area-related mass flow rate.

[0046] The relationship is derived as follows: n ˙ dy dl = − r , where y is the dimensionless mole fraction of the exhaust gas component and r is the reaction rate in units of mol / (sm³). The mass flow rate has the unit mol / (sm²). r = k T y where k is the rate constant in the unit mol / (sm 3< ), the following relationship results: n ˙ dy dl = − k T y

[0047] By changing the setting, you get dy y = − k T n ˙ dl

[0048] Integrating this relationship leads to... ln y 2 − ln y 1 = − k T n ˙ l

[0049] This, when rearranged, gives ln y 2 y 1 = − k T n ˙ l

[0050] Finally, the relationship develops y 2 = y 1 e − k T n ˙ l

[0051] In this, the dimensionless reaction inhibition quantity Θ is also taken into account, so that one can derive the following relationship y 2 = y 1 e − k T θ n ˙ l This is obtained. The velocity constant k can then be solved for in this equation, resulting in the following relationship: y 2 = y 1 e − k T 0 e E R 1 T 0 − 1 T θ n ˙ l

[0052] A further development of the invention provides that the reaction equation is used for a subsection of the exhaust aftertreatment device and that the reaction equation is also used for at least one further subsection of the exhaust aftertreatment device, wherein the at least one calculation parameter contained in the reaction equation is determined as a function of the storage capacity of the exhaust aftertreatment device, and wherein the feedstock fraction determined for the subsection is used as the input fraction for the at least one further subsection.

[0053] The reaction equation does not describe the entire exhaust aftertreatment system, but only the relevant section. Therefore, it is necessary to perform a calculation for at least one further section as well. This section and the at least one further section form part of several sections into which the exhaust aftertreatment system is divided, particularly in the direction of a main exhaust gas flow through the system.

[0054] For each of the subsections, and in particular for the subsection and the at least one further subsection, the input mass fraction and the output mass fraction are available. The input mass fraction represents the input quantity, and the output mass fraction represents the output quantity. The input mass fraction of the most upstream subsection is set equal to the input mass fraction present upstream of the exhaust aftertreatment system. The output mass fraction present downstream of the exhaust aftertreatment system is set equal to the output mass fraction of the most downstream subsection.

[0055] With the exception of the most upstream of the subsections, the input fraction for each subsection is set equal to the output fraction of the subsection immediately upstream of that subsection. The procedure for each subsection is then carried out analogously to that for the subsection itself. However, if the temperature is required, the temperature present in the respective subsection is used. This ensures a high degree of accuracy for the described method.

[0056] The relationship given above for determining the second starting material fraction is also valid in this case. Specifically, the following applies: y 2 = y 1 e − r n ˙ l

[0057] For a new exhaust aftertreatment system with, purely by way of example, five subsections, this results in the following: y 2 , neu = y 1 e − r neu n ˙ L 5 e − r neu n ˙ L 5 e − r neu n ˙ L 5 e − r neu n ˙ L 5 e − r neu n ˙ L 5 = e − r neu n ˙ L where r is the reaction rate and L is the total length of the exhaust aftertreatment system. For an aged exhaust aftertreatment system, it is assumed that r alt = xr neu This applies. y 2 , alt = y 1 e − x r neu n ˙ L 5 e − x r neu n ˙ L 5 e − x r neu n ˙ L 5 e − x r neu n ˙ L 5 e − x r neu n ˙ L 5 be set up. This can be used to y 2 , alt = y 1 e − r neu n ˙ L x to be rewritten.

[0058] The relationships given imply y 2 , neu y 1 = e − r n ˙ L and y 2 , alt = y 1 e − r neu n ˙ L x = y 1 y 2 , neu y 1 x

[0059] This again results in y 2 , neu = y 1 y 2 , alt y 1 1 x

[0060] The invention further relates to a drive unit for a motor vehicle, in particular for carrying out the method according to the descriptions in this document, wherein the drive unit has an exhaust gas generating drive unit and an exhaust gas aftertreatment device for aftertreatment of the exhaust gas.The drive unit is designed and configured to determine, during intended operation of the drive unit for the exhaust aftertreatment system, a first value of an aging parameter describing its state, and to determine, for at least one exhaust gas component, a second initial component from a first initial component present downstream of the exhaust aftertreatment system. This second initial component would occur, or will occur, if the exhaust aftertreatment system were replaced with an identical exhaust aftertreatment system exhibiting a second value of the aging parameter that differs from the first value.

[0061] The advantages of such a drive system design and such a procedure have already been mentioned. Both the drive system and the method for operating it can be further developed as described in this document, and reference is made to these details.

[0062] The features and combinations of features described in the description, in particular those described in the following figure description and / or shown in the figures, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention. Thus, embodiments that are not explicitly shown or explained in the description and / or the figures, but which emerge from or can be derived from the explained embodiments, are also to be considered as encompassed by the invention.

[0063] The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. The drawing shows: Figure 1 is a schematic representation of a section of a drive unit, namely an exhaust aftertreatment unit of the drive unit, and Figure 2 is a schematic detailed representation of a section of the exhaust aftertreatment unit.

[0064] The Figure 1 Figure 1 shows a schematic representation of a section of a drive unit 1 for a motor vehicle, namely an exhaust aftertreatment system 2. The exhaust aftertreatment system 2 is in the form of a vehicle catalytic converter. It has an inlet port 3 and an outlet port 4. Exhaust gas from the drive unit 1 is fed into the exhaust aftertreatment system 2 via the inlet port 3. The exhaust gas flows through the exhaust aftertreatment system 2 from the inlet port 3 towards the outlet port 4 and exits the exhaust aftertreatment system 2 through the outlet port 4 towards the outside environment.

[0065] The exhaust gas aftertreatment system 2 is divided into several subsections 5, in which catalytically active material is present. Upstream of the subsections 5, an exhaust gas component has an input fraction yI. Downstream of the exhaust gas aftertreatment system, the exhaust gas component has an output fraction yO. For each of the subsections 5, there is also an input fraction y1 and an output fraction y2, wherein the exhaust gas component with the input fraction y1 is supplied to the subsection and with the output fraction y2 is removed.

[0066] For the section 5 closest to the inlet port 3, the input mass fraction y1 corresponds to the input mass fraction yI located upstream of the exhaust aftertreatment device 2. For the subsequent sections 5 in the direction of exhaust gas flow, the input mass fraction y1 is set equal to the output mass fraction y2 of the immediately preceding section 5. The output mass fraction yO downstream of the exhaust aftertreatment device 2 is set equal to the output mass fraction y2 of the section 5 closest to the outlet port 4.

[0067] The Figure 2Figure 5 shows a schematic detail of one of the subsections. This subsection has a specific length l in the main flow direction of the exhaust gas and is traversed by a specific exhaust gas mass flow rate, which is given here as the cross-sectional area-specific molar mass flow rate with the unit mol / (ms²). It is shown that the mole fraction of the exhaust gas component decreases from the initial mole fraction y₁ towards the final mole fraction y₂, exhibiting a specific gradient that can be expressed as dy / dl. Summing or integrating over the length l of subsection 5 thus yields the final mole fraction y₂ from the initial mole fraction y₁. The described procedure allows for extremely high accuracy in determining the final mole fraction y₂.

[0068] During the intended operation of the drive unit 1, a first value of an aging parameter is determined for the exhaust gas aftertreatment unit 2, which describes the condition of the wastewater treatment unit 2. The aforementioned feedstock fraction yO is then used as the first feedstock fraction yO,old or y2,old and is used to determine a second feedstock fraction yO,new or y2,new. This is done taking into account the first value of the aging parameter and preferably also the feedstock fraction yI. The division of the exhaust gas aftertreatment unit 2 into the several subsections 5 has no influence on this. The described procedure can be effectively used to determine whether the exhaust gas aftertreatment unit 2 needs to be replaced. REFERENCE MARK LIST:

[0069] 1. Drive unit 2. Exhaust aftertreatment unit 3. Inlet connection 4. Outlet connection 5. Section

Claims

1. Method for operating a drive device (1) for a motor vehicle, which has an exhaust gas-producing drive unit and an exhaust gas aftertreatment device (2) for aftertreatment of the exhaust gas, wherein for the exhaust gas aftertreatment device (2), during operation according to an intended use of the drive device (1), a first value of an ageing variable describing its condition is determined, characterised in that, for at least one exhaust gas component of the exhaust gas, based on a first output material quantity ratio of the exhaust gas component present downstream of the exhaust gas aftertreatment device (2), a second output material quantity ratio is determined, which would occur in the event of a replacement of the exhaust gas aftertreatment device (2) by another exhaust gas aftertreatment device of identical construction and having a second value of the ageing variable that is different from the first value, wherein a replacement signal indicating the need to replace the exhaust gas aftertreatment device (2) is generated if the first output material quantity ratio exceeds a threshold value and the second output material quantity ratio simultaneously falls below the threshold value.

2. Method according to claim 1, characterised in that the first value of the ageing variable is determined from a storage capacity of the exhaust gas aftertreatment device (2) for a further exhaust gas component and / or a value corresponding to a brand-new exhaust gas aftertreatment device is used as the second value for the other exhaust gas aftertreatment device.

3. Method according to one of the preceding claims, characterised in that an ageing factor is determined from the first value and the second value and the second output material quantity ratio is determined from the first output material quantity ratio by means of a mathematical relationship that takes the ageing factor into account.

4. Method according to claim 3, characterised in that the relationship y 2 , neu = y 1 y 2 , alt y 1 1 x is used as the mathematical relationship, wherein x is the ageing factor, y1 is an input material quantity ratio present upstream of the exhaust gas aftertreatment device, y2,old is the first output material quantity ratio and y2,new is the second output material quantity ratio.

5. Method according to claim 4, characterised in that an output material quantity ratio of the exhaust gas present downstream of the exhaust gas aftertreatment device (2) is determined based on the input material quantity ratio of the exhaust gas component present upstream of the exhaust gas aftertreatment device (2) by means of a reaction equation, wherein at least one computation variable contained in the reaction equation is determined as a function of the storage capacity of the exhaust gas aftertreatment device (2) for the further exhaust gas component, and wherein the output material quantity ratio is used as the first output material quantity ratio.

6. Method according to claim 5, characterised in that one of the following variables is used as the at least one computation variable: speed constant, initial speed constant, adaption variable, activation energy and reaction inhibition variable.

7. Method according to one of the preceding claims, characterised in that one of the following components is used as the at least one exhaust gas component: hydrocarbon, carbon oxide, hydrogen, methane, ammonia, oxygen, nitrogen oxide.

8. Method according to claim 5 or 6, characterised in that the relationship y 2 = y 1 e − k T 0 e E R 1 T 0 − 1 T Θ n ˙ l is used as the reaction equation, wherein y1 is the input material quantity ratio, y2 is the output material quantity ratio, k is the speed constant, E is the activation energy, R is the universal gas constant, T0 is the temperature under standard conditions, T is the instantaneous temperature, Θ is the reaction inhibition variable, l is a length and ṅ is an arearelated material throughput.

9. Drive device (1) for a motor vehicle for carrying out the method according to one or more of the preceding claims, wherein the drive device (1) has an exhaust gasgenerating drive unit and an exhaust gas aftertreatment device (2) for aftertreatment of the exhaust gas, wherein the drive device (1) is provided and configured to determine for the exhaust gas aftertreatment device (2), during operation according to an intended use of the drive device (1), a first value of an ageing variable describing its condition, characterised in that the drive device (1) is further provided and configured to determine, for at least one exhaust gas component of the exhaust gas, based on a first output material quantity ratio of the exhaust gas component present downstream of the exhaust gas aftertreatment device (2), a second output material quantity ratio, which would occur in the event of a replacement of the exhaust gas aftertreatment device (2) by another exhaust gas aftertreatment device of identical construction and having a second value of the ageing variable that is different from the first value, wherein a replacement signal indicating the need to replace the exhaust gas aftertreatment device (2) is generated if the first output material quantity ratio exceeds a threshold value and the second output material quantity ratio simultaneously falls below the threshold value.

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