Method for operating a drive device for a motor vehicle and corresponding drive device

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] Method for operating a drive device for a motor vehicle and corresponding drive device

[0002] DESCRIPTION:

[0003] The invention relates to a method for operating a drive device for a motor vehicle, which has an exhaust-generating drive unit and an exhaust aftertreatment device for aftertreating the exhaust gas. The invention further relates to a drive device for a motor vehicle.

[0004] For example, DE 10 2004 017 274 A1 is known from the prior art. This describes a method for diagnosing emissions in a multi-row emission system, the method comprising the steps of: obtaining a plurality of emission measurement values, each of the measurement values ​​corresponding to a row of the multi-row emission system; converting each measurement value into a scaled value as a percentage of a threshold value; summing the scaled values ​​to obtain a total emission value for the multi-row emission system; and triggering an alert when the total emission value exceeds the threshold value.

[0005] The object of the invention is to propose a method for operating a drive system for a motor vehicle that offers advantages over known methods, in particular enabling a reliable assessment of the influence of age on the conversion performance of the exhaust gas aftertreatment system. This is achieved according to the invention with a method for operating a drive system for a motor vehicle having the features of claim 1.It is provided that during normal operation of the drive device for the exhaust gas aftertreatment device, a first value of an aging variable describing its condition is determined and for at least one exhaust gas component of the exhaust gas, a second starting material quantity fraction is determined from a first starting material quantity fraction of the exhaust gas component present downstream of the exhaust gas aftertreatment device, which second starting material quantity fraction would or will occur if the exhaust gas aftertreatment device were replaced by another exhaust gas aftertreatment device of the same construction and having a second value of the aging variable different from the first value.

[0006] Advantageous embodiments with useful further developments of the invention are specified in the dependent claims. It should be noted that the exemplary embodiments explained in the description are not limiting; rather, any variations of the features disclosed in the description, the claims, and the figures are feasible.

[0007] The drive device serves to drive the motor vehicle, i.e. to provide a drive torque directed towards driving the motor vehicle. To provide the drive torque, the drive device has the drive unit. During operation of the drive device, fuel and fresh gas are supplied to the drive unit at least temporarily, wherein the fresh gas at least temporarily contains fresh air. In addition, the fresh gas can comprise exhaust gas, provided that exhaust gas recirculation is implemented, in which the exhaust gas generated by the drive unit is at least partially recirculated into the drive unit, namely as a component of the fresh gas. The fuel and the fresh gas supplied to the drive unit form a fuel-fresh gas mixture with a specific composition, which is reacted in the drive unit.During operation of the drive unit, the chemical reaction between fuel and fresh gas produces exhaust gas, which is discharged to the environment outside the drive system or the motor vehicle. Since the exhaust gas generated by the drive unit contains pollutants, the exhaust gas is first fed to the exhaust aftertreatment system before being released into the environment. In the exhaust aftertreatment system, the pollutants are at least partially converted into less hazardous products. Only after passing through the exhaust aftertreatment system is the exhaust gas discharged to the environment outside.

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

[0009] The conversion rate and thus the conversion performance of the exhaust gas aftertreatment system, with which pollutants are converted into less hazardous products, depend in particular on the composition of the exhaust gas fed to the exhaust gas aftertreatment system and / or on the storage load of the exhaust gas aftertreatment system, which in turn is related to the composition of the exhaust gas. Storage load refers to the loading of the exhaust gas aftertreatment system with another exhaust gas component, i.e. the quantity of the additional exhaust gas component temporarily stored in the exhaust gas aftertreatment system. The condition of the exhaust gas aftertreatment system also influences the conversion rate. This condition refers in particular to an aging state that steadily worsens over the service life of the exhaust gas aftertreatment system.

[0010] The condition of the exhaust gas aftertreatment system can be determined, for example, by first determining the storage capacity, in particular the oxygen storage capacity or the ammonia storage capacity, of the exhaust gas aftertreatment system. The condition can be derived from this. A defect in the exhaust gas aftertreatment system is preferably detected as soon as the storage capacity falls below a capacity threshold.

[0011] The quantity of exhaust component released into the ambient environment by the drive system depends on numerous factors. For example, it is determined by the drive unit and its individual components, but also by the exhaust gas aftertreatment system. If it is determined that the quantity of exhaust component downstream of the exhaust gas aftertreatment system is too large, for example because the first starting mass fraction of the exhaust component exceeds a threshold value, this can have numerous causes. Therefore, a simple method is being sought to determine, with minimal computational effort, the component that is causing the first starting mass fraction to exceed the threshold value. The exhaust component is essentially any constituent of the exhaust gas.

[0012] In the case of the exhaust gas aftertreatment system, the first value of the aging variable is determined during the intended operation of the drive system. The aging variable describes the condition of the exhaust gas aftertreatment system, in particular its age. For example, the aging variable or the first value is determined from a calendar age of the exhaust gas aftertreatment system, in particular the difference between the current date and the date of manufacture or commissioning of the exhaust gas aftertreatment system, and / or an operating period of the exhaust gas aftertreatment system. Operating period is understood here as a cumulative period over which exhaust gas flowed through the exhaust gas aftertreatment system.

[0013] The second output mass fraction is determined from the first starting material fraction of the exhaust gas component present downstream of the exhaust gas aftertreatment device, namely using the aging variable or the first value of the aging variable. The second output mass fraction is understood to be the output mass fraction that would be present downstream of the exhaust gas aftertreatment device after replacing the exhaust gas aftertreatment device with the other exhaust gas aftertreatment device or after an actual replacement. The first or second output mass fraction describes the proportion of the mass of the exhaust gas component to the mass of the exhaust gas. The output mass fraction is given as a molar fraction and therefore quantitatively describes the composition of the exhaust gas.

[0014] The other exhaust aftertreatment device is identical in construction to the exhaust aftertreatment device, but has a different aging value. In particular, the second aging value assigned to the other exhaust aftertreatment device is selected such that it corresponds to an exhaust aftertreatment device that is newer than the exhaust aftertreatment device. For better differentiation, the exhaust aftertreatment device is also referred to as the first exhaust aftertreatment device in this description, and the other exhaust aftertreatment device is also referred to as the second exhaust aftertreatment device. The second starting material fraction is determined during the intended operation of the drive device. This means that it is performed during normal driving of the motor vehicle.Preferably, the determination is carried out repeatedly or periodically, for example, at regular or irregular intervals. It can also be carried out continuously, i.e., continuously, if technically feasible and possible. The second starting material mass fraction is therefore not determined just once, but multiple times, especially during each operation of the drive system. This ensures reliable monitoring of the drive unit.

[0015] Preferably, the need to replace the exhaust gas aftertreatment device is determined based on the first and second feedstock mass fractions. Preferably, if the first feedstock mass fraction exceeds the aforementioned threshold value, the second feedstock mass fraction is compared with the threshold value. If it is also greater than the threshold value, the threshold value is not exceeded, or at least not solely, by the exhaust gas aftertreatment device. If, on the other hand, the second feedstock mass fraction is lower than the threshold value, a sufficiently low feedstock mass fraction of the exhaust gas component can likely be achieved simply by replacing the exhaust gas aftertreatment device, without replacing or at least checking other components of the drive system.Accordingly, the procedure described can be used to determine extremely efficiently whether the exhaust aftertreatment system needs to be replaced.

[0016] It may be provided not to compare the first starting material quantity fraction or the second starting material quantity fraction with the threshold value directly, but rather to carry out this comparison only indirectly. In this case, it is preferably provided to derive a quantity from the respective starting material quantity fraction, i.e. from the first starting material quantity fraction and / or the second starting material quantity fraction, and to compare this quantity with the threshold value. For example, a throughput of the exhaust gas component is determined from the respective starting material quantity fraction and a mass throughput of the exhaust gas, in particular the exhaust gas mass flow. The throughput is preferably integrated over time to result in a quantity of the exhaust gas component. From this quantity, a distance-related quantity can be determined using the distance covered by the motor vehicle over time, for example in the unit g / km.The distance-related quantity is then compared with the threshold value and the procedure described above is followed.

[0017] A further development of the invention provides that the first value of the aging variable is determined from a storage capacity of the exhaust gas aftertreatment device for another 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. The use of the storage capacity to determine the state of the exhaust gas aftertreatment device has already been mentioned. The first value of the aging variable is available as 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 gas aftertreatment device.

[0018] The initial storage capacity is, for example, the storage capacity that the exhaust aftertreatment system exhibits upon commissioning. For example, it corresponds to a maximum value of the storage capacity over the service life of the exhaust aftertreatment system. The initial storage capacity is therefore the highest storage capacity that the exhaust aftertreatment system exhibits over its operating life. Typically, when the exhaust aftertreatment system is in brand-new condition, the storage capacity corresponds to the initial capacity. Additionally or alternatively, the second value is set equal to a value that the aging parameter exhibits in the brand-new exhaust aftertreatment system. This makes it possible to determine what effects replacing the exhaust aftertreatment system with the brand-new exhaust aftertreatment system would have.The procedure described enables a rapid diagnosis of the exhaust aftertreatment system.

[0019] A further development of the invention provides that an aging factor is determined from the first value and the second value, and the second output mass fraction is determined from the first output mass fraction using a mathematical relationship that takes the aging factor into account. The aging factor is thus a function of the first value and the second value of the aging variable. For example, the aging factor corresponds to the result of dividing the first value by the second value. After the aging factor has been determined, the mathematical relationship that takes the aging factor into account is used to determine the second output mass fraction from the first output mass fraction. Preferably, an input mass fraction present upstream of the exhaust gas aftertreatment device is also taken into account.The procedure described enables efficient diagnosis of the exhaust aftertreatment system.

[0020] A further development of the invention provides that the mathematical relationship is the connection where x is the aging factor, yi is an input mass fraction present upstream of the exhaust gas aftertreatment device, y2,ait is the first output mass fraction and y2,neu is the second output mass fraction. The relationship can be derived as follows: The output mass fraction for the first exhaust gas aftertreatment device can be and for the second exhaust aftertreatment system with The aging factor x is defined as This results in and finally

[0021] This contains the expression defined above, so that the relationship in y2,new\ Xy2,ait — yi > yi ). This rearranged yields

[0022] A further development of the invention provides that if the first starting material quantity fraction exceeds a threshold value and the second starting material quantity fraction simultaneously falls below the threshold value, an exchange signal is generated which indicates the need to exchange the exhaust gas aftertreatment device.

[0023] This has already been pointed out above. Preferably, the exchange signal is only generated if the first starting material mass fraction simultaneously exceeds the threshold value and the second starting material mass fraction falls below the threshold value. If both the first starting material mass fraction and the second starting material mass fraction exceed the threshold value, the exchange signal is not generated, since replacing the exhaust gas aftertreatment device would likely have no effect.

[0024] The replacement signal is preferably stored in a fault memory of the drive system so that it can be subsequently read out. Additionally or alternatively, the replacement signal is displayed to the driver of the motor vehicle, particularly visually and / or acoustically. The driver is accordingly alerted to the need to replace the exhaust aftertreatment system. The described procedure enables the need to replace the exhaust aftertreatment system to be detected quickly and reliably.

[0025] A further development of the invention provides that an output mass fraction of the exhaust gas component present downstream of the exhaust gas aftertreatment device is determined from the input mass fraction of the exhaust gas component present upstream of the exhaust gas aftertreatment device by means of a reaction equation, wherein at least one calculation variable 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 mass fraction is used as the first output mass fraction.

[0026] Due to increasingly stringent emissions regulations, it is necessary to determine the quantity of pollutants present downstream of the exhaust gas aftertreatment device. For this purpose, a measurement can be taken, for example. However, this is complex, particularly if measurements would have to be taken for a large number of exhaust gas components. Furthermore, measuring is often not feasible. For this reason, it is planned to perform a calculation for at least one exhaust gas component. The exhaust gas component is essentially any component of the exhaust gas, in particular a component whose initial mass fraction is not or cannot be measured downstream of the exhaust gas aftertreatment device.

[0027] The calculation is based on the input mass fraction of the exhaust gas component present upstream of the exhaust gas aftertreatment device. The input mass fraction describes the proportion of the mass of the exhaust gas component to the mass of the exhaust gas. The input mass fraction is given as a mole fraction and therefore quantitatively describes the composition of the exhaust gas. From the input mass fraction, the output mass fraction of the exhaust gas component present downstream of the exhaust gas aftertreatment device is determined. The output mass fraction also quantitatively describes the composition of the exhaust gas, whereby the mass of the exhaust component downstream of the exhaust gas aftertreatment device is set in relation to the mass of the exhaust gas present there. The output mass fraction is therefore also given as a mole fraction.The output mass fraction is determined from the input mass fraction using the reaction equation. The reaction equation describes the change in the mass fraction of the exhaust gas component as the exhaust gas passes through the exhaust aftertreatment system. However, since the conversion rate or conversion efficiency of the exhaust aftertreatment system changes over time, the reaction equation must be adapted to the state of the exhaust aftertreatment system in order to determine the output mass fraction with high accuracy.

[0028] For this reason, the calculation variable included in the reaction equation is determined depending on the storage capacity of the exhaust gas aftertreatment system. By incorporating the storage capacity of the exhaust gas aftertreatment system into the reaction equation, the accuracy of the determined starting material fraction is significantly increased. In particular, the reaction equation is adjusted towards higher reaction rates the larger the storage capacity is. Conversely, the smaller the storage capacity is, the lower the reaction equation is adjusted towards lower reaction rates. Consequently, aging of the exhaust gas aftertreatment system is reliably taken into account. The starting material fraction determined in the manner described is used as the first starting material fraction and is subsequently used to determine the second starting material fraction.

[0029] For example, if the feedstock quantity exceeds a threshold value, it is provided to detect a fault in the exhaust gas aftertreatment system. In this case, for example, an error signal can be displayed to the driver of the motor vehicle and / or the drive unit can be controlled in such a way that the feedstock quantity changes towards the threshold value, in particular up to this value. If the feedstock quantity fractions of several exhaust gas components are determined, each exhaust gas component is preferably assigned a separate threshold value, with which the respective feedstock quantity fraction is compared. Again, this procedure can provide for the route-related quantity to be determined from the respective feedstock quantity fraction and to compare this with the threshold value.

[0030] A further development of the invention provides that one of the following variables is used as the at least one calculation variable: rate constant, initial rate constant, adaptation variable, activation energy, and reaction inhibition variable. The rate constant is understood to mean, in particular, the rate constant of the chemical reaction taking place for the exhaust gas component in the exhaust gas aftertreatment device. The rate constant is typically temperature-dependent and is therefore at least a function of temperature and, in this case, also a function of storage capacity.

[0031] The rate constant can be divided into the initial rate constant and the adjustment variable, or can be determined from these variables. The rate constant is preferably obtained by multiplying the initial rate constant by the adjustment variable. The initial rate constant describes the rate constant at a defined temperature, in particular at an initial temperature To. The initial temperature preferably corresponds to a temperature under standard conditions, for example, it is 0 °C or 20 °C. The initial rate constant is accordingly available for a constant temperature and is therefore dependent only on the storage capacity for a given exhaust gas component.

[0032] The adjustment variable describes the influence of temperature on the rate constant, based on the initial rate constant. It is based primarily on the initial temperature and the current temperature. The adjustment variable depends on the temperature and the storage capacity. The activation energy can also be included in the adjustment variable. Activation energy is the energy that must be overcome for the chemical reaction described by the reaction equation to occur. For a given exhaust gas component, the activation energy depends solely on the storage capacity.

[0033] Finally, the reaction inhibition variable describes the influence of a current storage fill level of the exhaust gas aftertreatment system with the additional exhaust gas component on the reaction rate or the rate constant. The reaction inhibition variable is preferably dependent on both the storage fill level and the storage capacity or is a function of both. At least one of the aforementioned variables is taken into account in the reaction equation. For example, several or even all of the variables are used in the reaction equation to determine the initial mass fraction of the exhaust gas component. Preferably, the initial rate constant, the activation energy, and the reaction inhibition variable are used in the reaction equation as calculation variables dependent on the storage capacity. This achieves a particularly high level of accuracy.

[0034] A further development of the invention provides that the rate constant is determined from the initial rate constant and the adjustment variable. This has already been mentioned. The rate constant results, in particular, from multiplying the initial rate constant by the adjustment variable. The adjustment variable can therefore also be referred to as the reaction rate factor. The use of these two variables to determine the rate constant enables high accuracy in determining the starting material fraction.

[0035] A further development of the invention provides that the rate constant is corrected using the reaction inhibition variable. It has already been mentioned that the reservoir fill level can influence the reaction rate. This is taken into account via the reaction inhibition variable, which is determined from the reservoir fill level. Preferably, the calculation variable used in the reaction equation results from multiplying the rate constant by the reaction inhibition variable, or the reaction rate used in the reaction equation is corrected by multiplying it by the reaction inhibition variable. This also results in the aforementioned high accuracy.

[0036] A further development of the invention provides that the at least one calculation variable is determined as a function of the storage capacity using a mathematical relationship, a characteristic map, or a table. The mathematical relationship, the characteristic map, or the table has the storage capacity as the input variable and the at least one calculation variable as the output variable. If multiple calculation variables are used in the reaction equation, a separate mathematical relationship, a separate characteristic map, or a table is preferably available for each of the calculation variables used.

[0037] For example, characteristic maps are used for all calculation variables. However, it is also possible for one calculation variable to be determined using a characteristic map and another calculation variable using a mathematical relationship or a table. The mathematical relationship, the characteristic map, or the table are preferably stored in the drive system or a control unit of the drive system at the factory, and are particularly immutable. The described procedure enables the precise determination of the starting mass fraction of the exhaust gas component.

[0038] A further development of the invention provides that one of the following components is used as the 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, in particular, any hydrocarbon, for example, methane. However, particularly preferably, the total hydrocarbon (THC) is used, i.e., several or all of the hydrocarbons present in the exhaust gas.

[0039] The determination of the output mass fraction from the respective input mass fraction is carried out for at least one of the aforementioned exhaust gas components, but preferably for several of the components. It is particularly preferably carried out for all of the aforementioned components. This means that for each of the aforementioned components, the respective output mass fraction is determined from the respective input mass fraction, namely using a respective reaction equation with a respective calculation variable that is determined as a function of the storage capacity of the exhaust gas aftertreatment device. Consequently, the output mass fractions of numerous different exhaust gas components downstream of the exhaust gas aftertreatment device are known.

[0040] A further development of the invention provides that the input mass fraction is determined for a currently prevailing operating point of the drive unit. The input mass fraction corresponds to a raw emission of the exhaust gas component from the drive unit, thus to the mass fraction of the exhaust gas component in the exhaust gas flowing between the drive unit and the exhaust gas aftertreatment device. The input mass fraction is determined for the at least one exhaust gas component for the currently prevailing operating point of the drive unit, wherein the operating point is characterized in particular by a speed of the drive unit and / or a drive torque provided by the drive unit.

[0041] The input mass fraction is preferably determined using a mathematical relationship, a characteristic map, or a table, with the operating point serving as the input variable and the input mass fraction serving as the output variable. This procedure enables the input mass fraction for the at least one exhaust gas component to be determined with high accuracy and, accordingly, the output mass fraction to be determined precisely.

[0042] A further development of the invention provides that the reaction equation is the relationship is used, where yi is the input mole fraction, y2 is the output mole fraction, k is the rate constant, E is the activation energy, R is the general gas constant, To is the temperature at standard conditions, T is the instantaneous temperature, θ is the reaction inhibition quantity, I is a length and h is an area-related molar flow rate.

[0043] The relationship is derived as follows: where y is the dimensionless mole fraction of the exhaust gas component and r is the reaction rate in the unit mol / (sm 3 ). The molar flow rate has the unit mol / (sm 2 ). With r = k(T) y where k is the rate constant in units of mol / (sm 3 ), the relationship dy n— = - (T) y

[0044] By rearranging we get dy fc(T)

[0045] - = - ; — al yn

[0046] If this relationship is integrated, one arrives at

[0047] This is transformed to give

[0048] Finally, the relationship

[0049] In this, the dimensionless reaction inhibition quantity 0 is also taken into account, so that the relationship In this case, the rate constant k can be resolved and the relationship

[0050] A further development of the invention provides that the reaction equation is used for a subsection of the exhaust gas aftertreatment device and the reaction equation is also used for at least one further subsection of the exhaust gas aftertreatment device, wherein the at least one calculation variable contained in the reaction equation is determined as a function of the storage capacity of the exhaust gas aftertreatment device, and wherein the starting material quantity fraction determined for the subsection is used as the input material quantity fraction for the at least one further subsection.

[0051] The reaction equation does not describe the entire exhaust gas aftertreatment system, but only the subsection. Accordingly, it is necessary to perform a calculation for the at least one further subsection as well. The subsection and the at least one further subsection form part of several subsections into which the exhaust gas aftertreatment system is divided, in particular in the direction of a main flow direction of the exhaust gas through the exhaust gas aftertreatment system.

[0052] For each of the subsections, i.e., 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 variable, and the output mass fraction represents the output variable. The input mass fraction of the most upstream subsection is set equal to the input mass fraction upstream of the exhaust gas aftertreatment device. The output mass fraction downstream of the exhaust gas aftertreatment device is set equal to the output mass fraction of the most downstream subsection.

[0053] With the exception of the most upstream section, for each of the sections, the respective input mass fraction is set equal to the output mass fraction of the section immediately upstream of the respective section. For each of the sections, the procedure is analogous to that for the subsection. However, if the temperature is required, the temperature present in the respective subsection is used. This ensures a high level of accuracy for the described method. The relationship given above for determining the second output mass fraction is also valid in this case.

[0054] -(4z y2= yi e kn J

[0055] For a new exhaust gas aftertreatment system with five sections, purely as an example, this results in where r is the reaction rate and L is the total length of the exhaust aftertreatment device. For an aged exhaust aftertreatment device, it is assumed that

[0056] 1 old ~~ * new applies. This allows the relationship This can be be rewritten.

[0057] From the given relationships follow and

[0058] This again results in

[0059] The invention further relates to a drive device for a motor vehicle, in particular for carrying out the method according to the explanations in the context of this description, wherein the drive device has a drive unit generating exhaust gas and an exhaust gas aftertreatment device for aftertreating the exhaust gas.The drive device is provided and designed to determine a first value of an aging variable describing the state of the exhaust gas aftertreatment device during normal operation of the drive device and to determine a second starting material quantity fraction of the exhaust gas component for at least one exhaust gas component of the exhaust gas from a first starting material quantity fraction of the exhaust gas component present downstream of the exhaust gas aftertreatment device, which second starting material quantity fraction would or will occur if the exhaust gas aftertreatment device were replaced by another exhaust gas aftertreatment device of the same construction and having a second value of the aging variable different from the first value.

[0060] The advantages of such a drive device design or such a procedure have already been pointed out. Both the drive device and the method for its operation can be further developed according to the explanations in this description, so reference is made to these in this regard.

[0061] The features and feature combinations described in the description, in particular the features and feature combinations described in the following description of the figures and / or shown in the figures, can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments are also considered to be encompassed by the invention that are not explicitly shown or explained in the description and / or the figures, but which follow from or can be derived from the explained embodiments.

[0062] The invention will be explained in more detail below with reference to the exemplary embodiments shown in the drawings, without limiting the invention. In the drawings:

[0063] Figure 1 is a schematic representation of a region of a drive device, namely an exhaust gas aftertreatment device of the drive device, and

[0064] Figure 2 is a schematic detailed representation of a section of the exhaust gas aftertreatment system.

[0065] Figure 1 shows a schematic representation of a region of a drive device 1 for a motor vehicle, namely an exhaust gas aftertreatment device 2. The exhaust gas aftertreatment device 2 is in the form of a vehicle catalytic converter. It has an inlet port 3 and an outlet port 4. Exhaust gas from a drive unit of the drive device 1 is supplied to the exhaust gas aftertreatment device 2 via the inlet port 3. The exhaust gas flows through the exhaust gas aftertreatment device 2, starting from the inlet port 3, toward the outlet port S4 and exits the exhaust gas aftertreatment device 2 through the outlet port 4 toward the outside environment.

[0066] The exhaust gas aftertreatment device 2 is divided into several subsections 5, each containing catalytically active material. Upstream of the subsections 5, an exhaust gas component has an input mass fraction yi. Downstream of the exhaust gas aftertreatment device, the exhaust gas component has an output mass fraction yo. For each of the subsections 5, there is also an input mass fraction yi and an output mass fraction y2, with the exhaust gas component being supplied to the subsection with the input mass fraction yi and being removed with the output mass fraction y2.

[0067] For the sub-section 5 closest to the inlet connection 3, the input mass fraction yi corresponds to the input mass fraction yi present upstream of the exhaust gas aftertreatment device 2. For the sub-sections 5 following in the flow direction of the exhaust gas, the input mass fraction yi is set equal to the output mass fraction y2 of the immediately preceding sub-section 5. The output mass fraction yo downstream of the exhaust gas aftertreatment device 2 is set equal to the output mass fraction y2 of the sub-section 5 closest to the outlet connection 4.

[0068] Figure 2 shows a schematic detailed representation of one of the sections 5. This has a certain length I in the main flow direction of the exhaust gas and is flowed through by a certain exhaust gas mass flow, which is here defined as the flow cross-sectional area-specific molar mass flow with the unit mol / (ms 2). It is shown that the molar fraction of the exhaust gas component decreases from the input molar fraction yi towards the output molar fraction y2 and exhibits a specific gradient that can be specified as dy / dl. When summed or integrated over the length I of section 5, the output molar fraction y2 results from the input molar fraction yi. Using the described procedure, an extremely high degree of accuracy can be achieved in determining the output molar fraction y2.

[0069] During normal operation of the drive system 1, a first value of an aging variable is determined for the exhaust gas aftertreatment system 2, which describes the condition of the wastewater treatment system 2. The aforementioned output mass fraction yo is then used as the first output mass fraction yo.ait or y2,ait and is used to determine a second output mass fraction yo.neu or y2,neu. This is done taking into account the first value of the aging variable and preferably also the input mass fraction yi. The division of the exhaust gas aftertreatment system 2 into the multiple subsections 5 has no influence on this. The described procedure can be used effectively to determine whether the exhaust gas aftertreatment system 2 needs to be replaced.

[0070] LIST OF REFERENCE SYMBOLS:

[0071] 1 drive device

[0072] 2 Exhaust aftertreatment system 3 Inlet connection

[0073] 4 Outlet connection

[0074] 5 Subsection

Claims

PATENT CLAIMS: 1 . Method for operating a drive device (1) for a motor vehicle, which has a drive unit generating exhaust gas and an exhaust gas aftertreatment device (2) for aftertreating the exhaust gas, characterized in that during normal operation of the drive device (1) for the exhaust gas aftertreatment device (2) a first value of an aging variable describing its state is determined and for at least one exhaust gas component of the exhaust gas from a first starting material quantity fraction of the exhaust gas component present downstream of the exhaust gas aftertreatment device (2) a second starting material quantity fraction is determined, which would occur if the exhaust gas aftertreatment device (2) were replaced by another exhaust gas aftertreatment device of the same construction and having a second value of the aging variable different from the first value.

2. Method according to claim 1, characterized in that the first value of the aging 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, characterized in that an ageing factor is determined from the first value and the second value and the second starting material quantity fraction is determined from the first starting material quantity fraction by means of a mathematical relationship taking the ageing factor into account.

4. Method according to one of the preceding claims, characterized in that the mathematical relationship is the relationship is used, where x is the ageing factor, yi is an input mass fraction present upstream of the exhaust gas aftertreatment device, y2,ait is the first output mass fraction and y2,neu is the second output mass fraction.

5. Method according to one of the preceding claims, characterized in that when a threshold value is exceeded by the first starting material quantity proportion and the threshold value is simultaneously undershot by the second starting material quantity proportion, an exchange signal is generated which indicates the need to exchange the exhaust gas aftertreatment device (2).

6. Method according to one of the preceding claims, characterized in that an output mass fraction of the exhaust gas component present downstream of the exhaust gas aftertreatment device (2) is determined from the input mass fraction of the exhaust gas component present upstream of the exhaust gas aftertreatment device (2) by means of a reaction equation, wherein at least one calculation 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 mass fraction is used as the first output mass fraction.

7. Method according to one of the preceding claims, characterized in that one of the following variables is used as the at least one calculation variable: rate constant, initial rate constant, adjustment variable, activation energy and reaction inhibition variable.

8. Method according to one of the preceding claims, characterized 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.

9. Method according to one of the preceding claims, characterized in that the reaction equation is the relationship is used, where yi is the input mole fraction, y2 is the output mole fraction, k is the rate constant, E is the activation energy, R is the general gas constant, To is the temperature at standard conditions, T is the instantaneous temperature, 0 is the reaction inhibition quantity, I is a length and an area-related molar flow rate.

10. Drive device (1) for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive device (1) has a drive unit generating exhaust gas and an exhaust gas aftertreatment device (2) for aftertreating the exhaust gas, characterized in that the drive device (1) is provided and designed to determine a first value of an aging variable describing the state of the exhaust gas aftertreatment device (2) during normal operation of the drive device (1) and to determine a second starting material quantity for at least one exhaust gas component of the exhaust gas from a first starting material quantity fraction of the exhaust gas component present downstream of the exhaust gas aftertreatment device (2),which would occur if the exhaust gas aftertreatment device (2) were replaced by another exhaust gas aftertreatment device (2) of the same construction and having a second value of the aging variable different from the first value.

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