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, which drive device has an exhaust-gas-generating drive unit (2) and an exhaust-gas aftertreatment device (3) for aftertreating the exhaust gas, wherein by means of a first lambda probe (5) upstream of the exhaust-gas aftertreatment device (3) a first measurement value is measured and by means of a second lambda probe (6) downstream of the first lambda probe (6) a second measurement value is measured, and wherein an exit concentration of at least one exhaust gas component downstream of the exhaust-gas aftertreatment device (3) is determined by means of an exhaust-gas aftertreatment model, the exhaust-gas aftertreatment model being supplied with an entry concentration determined for an entry point (14) and an entry combustion air ratio determined for the entry point (14) as input variables. According to the invention, the entry combustion air ratio from the second measurement value is determined independently of the first measurement 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, US 2013 / 0245919 A1 is known from the prior art. This discloses a method in which a fuel injection quantity is adjusted based on the oxidation state of a catalyst. The oxidation state is based on the reaction rates of a plurality of exhaust gas species across a catalyst's longitudinal axis and a set of axially averaged mass balance and energy balance equations for a fluid phase and a catalyst washcoat.

[0005] It is an object of the invention to propose a method for operating a drive device for a motor vehicle, which has advantages over the prior art, in particular reliably monitors pollutant emissions from the drive device in order to ensure compliance with limit values.

[0006] This is achieved according to the invention with a method for operating a drive device for a motor vehicle having the features of claim 1. It is provided that the inlet combustion air ratio is determined from the second measured value independently of the first measured value.

[0007] 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.

[0008] The drive device serves to drive the motor vehicle, i.e. to provide a drive torque directed towards driving the motor vehicle. The drive device is preferably a component of the motor vehicle, but can of course also be separate from it. To provide the drive torque, the drive device comprises the drive unit, which is preferably designed as an internal combustion engine. 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 fresh gas supplied to the drive unit form a fuel-fresh gas mixture with a specific composition, which is reacted in the drive unit.

[0009] During operation of the drive unit, exhaust gas is produced due to the chemical reaction between fuel and fresh gas, which is discharged towards the outside environment of the drive system or motor vehicle. Since the exhaust gas produced by the drive unit contains pollutants, the exhaust gas is first fed to the exhaust gas aftertreatment system before being released into the outside environment. In the exhaust gas aftertreatment system, the pollutants are at least partially converted into less hazardous products. Only after passing through the exhaust gas aftertreatment system is the exhaust gas discharged into the outside environment. The exhaust gas aftertreatment system exists, for example, as a vehicle catalytic converter, in particular as a three-way catalytic converter, oxidation catalytic converter, NOx storage catalytic converter or SCR catalytic converter.However, it can also be designed as a particle filter, in particular as a gasoline particle filter or as a diesel particle filter, preferably with an integrated vehicle catalyst, for example with a catalytic coating.

[0010] To determine the pollutant emissions of the drive system, i.e., the amount of at least one exhaust gas component released into the ambient environment, the exhaust gas aftertreatment model is used. The exhaust gas aftertreatment model models the conversion of the at least one exhaust gas component using the exhaust gas aftertreatment system. For this purpose, the inlet concentration of the at least one exhaust gas component present at the inlet point is fed to the exhaust gas aftertreatment model as a first input variable.

[0011] The inlet point refers, in particular, to the point at which the exhaust gas enters the exhaust aftertreatment system. Alternatively, the inlet point refers to the point at which the exhaust gas enters a specific section of the exhaust aftertreatment system, in particular one of several sections. Based on the inlet concentration, the exhaust aftertreatment model calculates an outlet concentration present at an outlet point. Analogous to the inlet point, the outlet point refers to the point at which the exhaust gas exits the exhaust aftertreatment system or the section of the exhaust aftertreatment system.

[0012] The inlet concentration can in principle be determined in any desired manner; for example, it is determined as a function of an operating point of the drive unit, wherein the operating point is characterized, for example, by the drive torque currently provided by the drive unit and / or a current speed of the drive unit. If the inlet point is the point at which the exhaust gas enters the exhaust gas aftertreatment device, the inlet concentration present at the inlet point is equal to a raw emission of the drive unit, i.e. equal to the quantity of at least one exhaust gas component generated or emitted by the drive unit. If the inlet point is downstream of this point, the inlet concentration present at the inlet point is preferably determined using the exhaust gas aftertreatment model.For example, in this case the inlet concentration for one of the sections corresponds to the outlet concentration for a section of the exhaust gas aftertreatment device preceding the section.

[0013] The inlet combustion air ratio, which is determined analogously to the inlet concentration for the inlet point, is fed to the exhaust gas aftertreatment model as an additional input variable. For example, it could be provided that the inlet combustion air ratio is set equal to a combustion air ratio determined from the first measured value measured using the first lambda probe upstream of the exhaust gas aftertreatment device. The first measured value describes the combustion air ratio present in the exhaust gas upstream of the exhaust gas aftertreatment device, or a quantity of residual oxygen present there in the exhaust gas.

[0014] However, the first measured value is usually subject to a comparatively large measurement error, particularly if a broadband lambda sensor is used as the first lambda sensor. Even a measurement error of less than one percent leads to an intolerable loss of accuracy in the exhaust gas aftertreatment model. For this reason, it can be provided to correct the first measured value using a trim control based on the second measured value. The second measured value is measured using the second lambda sensor and describes the combustion air ratio or the amount of residual oxygen downstream of the first lambda sensor, in particular downstream of the exhaust gas aftertreatment device. For example, it is provided to regulate the second measured value to a target value and from this to determine an offset which is applied to the first measured value, in particular for carrying out lambda control based on the first measured value.

[0015] However, the applicant's investigations have shown that the first measured value after implementing the trim control is sufficiently accurate for lambda control, but not necessarily for the exhaust aftertreatment model. In addition, the broadband lambda sensor does not have ideal dynamic properties. This becomes noticeable, for example, after the engine is coasting, when, following a sudden change in the composition of the fuel-fresh gas mixture, the sensor lags behind this change for a certain period of time. This leads to errors in the exhaust aftertreatment model.

[0016] For this reason, it is now provided that the inlet combustion air ratio is determined from the second measured value independently of the first measured value. This means that the inlet combustion air ratio depends only on the second measured value measured downstream of the first lambda probe, and not on the first measured value. In other words, the first measured value is not taken into account at all when determining the inlet combustion air ratio; instead, only the second measured value of the two measured values ​​is taken into account. This allows the inlet combustion air ratio to be determined with such high accuracy that the exhaust gas aftertreatment model can also be implemented with good results, so that the outlet concentration describes the concentration of the at least one exhaust gas component actually present in the exhaust gas at the outlet point with high accuracy.

[0017] A further development of the invention provides for a broadband lambda sensor to be used as the first lambda sensor and / or a step-wave lambda sensor to be used as the second lambda sensor. While the broadband lambda sensor has a comparatively wide measuring range, this is not the case for the step-wave lambda sensor. The step-wave lambda sensor is, for example, in the form of a single Nernst cell and can also be referred to as a voltage step sensor. The broadband lambda sensor, on the other hand, consists of a Nernst cell and a pump cell. The pump cell is adjusted such that a combustion air ratio of A = 1 is measured using the Nernst cell. The current and / or the voltage of the electrical current used to operate the pump cell then represents a measure of the combustion air ratio actually present in the exhaust gas.The use of the broadband lambda sensor as the first lambda sensor and the jump lambda sensor as the second lambda sensor enables, in particular, precise implementation of the lambda control.

[0018] A further development of the invention provides that the second measured value is converted into a combustion air ratio using a probe characteristic curve, from which the inlet combustion air ratio is determined. The second measured value is therefore first converted into the combustion air ratio, namely using the probe characteristic curve. The probe characteristic curve is matched to the second lambda probe and describes its behavior. In particular, values ​​for the combustion air ratio are stored in the probe characteristic curve, which are available for different measured values. The probe characteristic curve can be stored in any desired way, for example using a mathematical relationship, a characteristic map and / or a table. The inlet combustion air ratio is then determined from the combustion air ratio.The use of the probe characteristic curve to convert the second measured value into the combustion air ratio can be implemented with little computational effort and is sufficiently accurate to operate the exhaust gas aftertreatment model based on the combustion air ratio.

[0019] A further development of the invention provides that the inlet combustion air ratio is determined based on a time derivative of the combustion air ratio. The inlet combustion air ratio does not directly correspond to the combustion air ratio determined from the second measured value; instead, a correction is made. This involves determining the time derivative of the combustion air ratio. On this basis, the inlet combustion air ratio is subsequently determined, so that it is available as a function at least of the time derivative of the combustion air ratio. This allows the inlet combustion air ratio to be determined with high accuracy in a comparatively simple manner.

[0020] A further development of the invention provides that the time derivative, subjected to a correction factor describing an influence of the exhaust gas aftertreatment device, is used to determine the inlet combustion air ratio. Since the second measured value is measured downstream of the first lambda probe and in particular downstream of the inlet point, the exhaust gas aftertreatment device significantly influences the inlet combustion air ratio determined from the second measured value. In particular, the inlet combustion air ratio depends on the oxygen storage capacity of the exhaust gas aftertreatment device and / or the exhaust gas mass flow of the exhaust gas flowing through the exhaust gas aftertreatment device. For this reason, the time derivative of the combustion air ratio is first subjected to the correction factor before it is incorporated into the inlet combustion air ratio.This can further increase the accuracy of the exhaust aftertreatment model.

[0021] A further development of the invention provides that the correction factor is determined as a function of at least one of the following variables: an oxygen storage capacity of the exhaust gas aftertreatment device, an exhaust gas mass flow of the exhaust gas, and a position variable describing a position of the inlet point. This has already been pointed out. The oxygen storage capacity describes the ability of the exhaust gas aftertreatment device to temporarily store oxygen. Here, the oxygen storage capacity represents the maximum amount of oxygen that can be temporarily stored. The exhaust gas mass flow, on the other hand, describes the mass flow of the exhaust gas currently flowing through the exhaust gas aftertreatment device. The position variable relates to the arrangement of the inlet point, in particular relative to the exhaust gas aftertreatment device and / or relative to the second lambda sensor.

[0022] The correction factor can be determined from the oxygen storage capacity, the exhaust gas mass flow, or both the oxygen storage capacity and the exhaust gas mass flow. Considering both parameters has a particularly significant impact on the accuracy of the exhaust aftertreatment model. Additionally or alternatively, the position variable is used, especially if multiple sections of the exhaust aftertreatment system are modeled.

[0023] A further development of the invention provides that the inlet combustion air ratio is determined based on the combustion air ratio and the time derivative. Overall, the inlet combustion air ratio is thus a function of the combustion air ratio, which is incorporated into the inlet combustion air ratio multiple times, namely once directly and once in the form of the time derivative. The inlet combustion air ratio is preferably the sum of the combustion air ratio and the time derivative of the combustion air ratio, preferably with the correction factor applied. This results in a particularly high accuracy of the inlet combustion air ratio and, consequently, a high accuracy of the exhaust gas aftertreatment model.

[0024] For example, the inlet combustion air ratio can be calculated using the relationship where Ai is the inlet combustion air ratio, A2 is the combustion air ratio, k is the correction factor and t is the time.

[0025] A further development of the invention provides that the exhaust gas aftertreatment model comprises a plurality of exhaust gas aftertreatment sub-models for modeling different sections of the exhaust gas aftertreatment device, wherein one of a plurality of inlet concentrations comprising the inlet concentration and one of a plurality of inlet combustion air ratios comprising the inlet combustion air ratio are supplied to each of the exhaust gas aftertreatment sub-models as input variables, wherein the respective inlet concentration and the respective inlet combustion air ratio are determined for one of a plurality of inlet points comprising the inlet point and each of the inlet combustion air ratios is determined from the second measured value independently of the first measured value.

[0026] This means that the exhaust aftertreatment device is not considered as a whole, but rather the exhaust aftertreatment device is divided into several sections. The sections preferably extend from a beginning to an end of the exhaust aftertreatment device and particularly preferably directly adjoin one another. For example, the exhaust aftertreatment device is divided into at least two, at least three, at least four, or—preferably—at least five sections. An exhaust aftertreatment submodel is available for each of these sections, with the exhaust aftertreatment submodels of the multiple sections collectively forming the exhaust aftertreatment model.

[0027] Each of the exhaust gas aftertreatment submodels has one of the inlet concentrations and one of the inlet combustion air ratios as input variables. The inlet concentration mentioned above is a component of these multiple inlet concentrations, and the inlet combustion air ratio mentioned above is a component of the multiple inlet combustion air ratios. The inlet concentration and the inlet combustion air ratio for each section are determined for a respective inlet point of this section.

[0028] Using the respective exhaust gas aftertreatment submodel, a respective outlet concentration for an outlet point of the respective section is determined from the respective inlet concentration and the respective inlet combustion air ratio. Preferably, the outlet concentration of a fluidically preceding section is used as the inlet concentration of a section fluidically immediately following this section. The exhaust gas aftertreatment model is based on a stepwise calculation of the outlet concentration of at least one exhaust gas component across the exhaust gas aftertreatment device. This allows for a particularly high level of accuracy.

[0029] A further development of the invention provides that one of the inlet combustion air ratios is determined by filtering from the second measured value. In principle, all inlet combustion air ratios are determined from the second measured value and independently of the first measured value. Preferably, the procedure already described is used for at least one of the inlet combustion air ratios, so that the corresponding inlet combustion air ratio is determined using the time derivative of the combustion air ratio.

[0030] However, at least one other of the inlet combustion air ratios is determined by filtering from the second measured value. Particularly preferred is to determine the combustion air ratio from the second measured value, again using the probe characteristic curve. This combustion air ratio is then filtered, and the filtering result is used as the inlet combustion air ratio. A low-pass filter is used as the filter.

[0031] Particularly preferably, the inlet combustion air ratio is determined based on the time derivative if the inlet point of the respective section is located upstream of the second lambda probe. Filtering, however, is used if the inlet point of the respective section is downstream of the second lambda probe. Such an approach enables the use of the described method even if the second lambda probe is located in the exhaust gas aftertreatment device, rather than downstream of the exhaust gas aftertreatment device.

[0032] The invention further relates to a drive device for a motor vehicle, in particular for carrying out the method according to the statements 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, wherein a first measured value is measured by means of a first lambda probe upstream of the exhaust gas aftertreatment device and a second measured value is measured by means of a second lambda probe downstream of the first lambda probe, and wherein the outlet concentration of at least one exhaust gas component downstream of the exhaust gas aftertreatment device is determined by means of an exhaust gas aftertreatment model to which an inlet concentration determined for an inlet point and an inlet combustion air ratio determined for the inlet point are supplied as input variables.The drive device is provided and designed to determine the inlet combustion air ratio from the second measured value independently of the first measured value.

[0033] The advantages of such a design of the drive device 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.

[0034] 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.

[0035] 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:

[0036] Figure 1 is a schematic representation of a drive device for a motor vehicle with a drive unit and an exhaust gas aftertreatment device, and

[0037] Figure 2 is a diagram in which the course of a combustion air ratio is plotted over time.

[0038] Figure 1 shows a schematic representation of a drive system 1 comprising an exhaust-generating drive unit 2 and an exhaust aftertreatment device 3, here in the form of a vehicle catalytic converter. Fuel and fresh gas are supplied to the drive unit 2, forming a fuel-fresh gas mixture and reacting chemically with each other to produce exhaust gas. The exhaust gas is supplied to the exhaust aftertreatment device 3 and flows through it in the direction of arrow 4.

[0039] Upstream of the exhaust gas aftertreatment device 3, a first measured value is measured by a first lambda probe 5, and downstream of the exhaust gas aftertreatment device 3, a second measured value is measured by a second lambda probe 6. The two measured values ​​describe a residual oxygen content of the exhaust gas and a combustion air ratio at the respective location.

[0040] A lambda controller 7 is operated using the first measured value and a trim controller 8 is operated using the second measured value. Output variables of the two controllers 7 and 8 are calculated with a setpoint supplied via an input 9, namely in a calculation module 10. The composition of the fuel-fresh gas mixture is determined from a result of the calculation.

[0041] Furthermore, the composition of the exhaust gas downstream of the exhaust gas aftertreatment device 3 is determined using an exhaust gas aftertreatment model. This is done for at least one exhaust gas component, but preferably for several exhaust gas components. The exhaust gas aftertreatment model comprises several exhaust gas aftertreatment submodels, five exhaust gas aftertreatment submodels in the exemplary embodiment shown here. Using each of the exhaust gas aftertreatment submodels, one of several sections 11 of the exhaust gas aftertreatment device 3 is calculated. The sections 11 extend from an inlet 12 to an outlet 13 of the exhaust gas aftertreatment device 3 and are directly adjacent to one another. The sections 11 therefore extend continuously and uninterruptedly from the inlet 12 to the outlet 13.

[0042] For each of the sections 11, an inlet concentration and an inlet combustion air ratio are determined, namely at a respective inlet point 14. Using the respective exhaust gas aftertreatment submodel, an outlet concentration of the respective exhaust gas component is subsequently determined at a respective outlet point 15 of the corresponding section 11. Preferably, the inlet concentration for a further downstream section 11 is equal to the outlet concentration of the immediately upstream section 11. The inlet concentration of the most upstream section 11 is equal to the inlet concentration of the exhaust gas aftertreatment device 3, and the outlet concentration of the exhaust gas aftertreatment device 3 is equal to the outlet concentration of the most downstream section 11.

[0043] The exhaust gas aftertreatment model or each of the exhaust gas aftertreatment submodels determines a conversion rate for the respective exhaust gas component as a function of the respective inlet combustion air ratio. The conversion rate is stored, for example, in a characteristic map or the like, specifically for various inlet combustion air ratios. For example, one or more of the following exhaust gas components is used as the exhaust gas component: hydrocarbon, carbon oxide, in particular carbon monoxide, hydrogen, in particular molecular hydrogen, nitrogen oxide, in particular nitrogen monoxide and / or nitrogen dioxide, and oxygen, in particular molecular oxygen.

[0044] The respective inlet combustion air ratio is not determined from the first measured value, but from the second measured value, independently of the first measured value. Therefore, the inlet combustion air ratio for each of the sections 11 is determined from a measured value taken downstream of the respective inlet point 14. For this purpose, a combustion air ratio is first determined from the second measured value, namely using a probe characteristic curve for the second lambda probe 6. The combustion air ratio thus determined is derived over time, and the time derivative is multiplied by a correction factor. The inlet combustion air ratio results from the sum of the inlet combustion air ratio and the result of multiplying the correction factor by the time derivative of the combustion air ratio.

[0045] The correction factor is proportional to the oxygen storage capacity and inversely proportional to the exhaust gas mass flow. The position of the respective section 11 of the exhaust gas aftertreatment device 3 is taken into account in the correction factor. Thus, the further the inlet point 14 is from the second lambda probe 6, the greater the correction factor. For example, a position variable included in the correction factor is one for the inlet 12 and zero for the outlet 13 and is determined for the inlet points 14 located between the inlet 12 and the outlet 13 by means of linear interpolation. For the five sections 11 shown here, whose inlet points 14 are equidistant from one another, the position variables are 1.0, 0.8, 0.6, 0.4 and 0.2. The respective position variable is multiplied by the time derivative, for example as a component of the correction factor.Figure 2 shows a diagram in which curves 16, 17, 18, 19, 20, and 21 describe combustion air ratios over time t. Curve 16 corresponds to a combustion air ratio calculated from the second measured value; the other curves 17 to 21 are derived from this curve 16, namely in the manner described. Curve 16 thus shows the outlet concentration of at least one exhaust gas component of the furthest downstream section 11. Curve 17 describes the inlet concentration for this section 11 and, accordingly, the outlet concentration of the immediately upstream section 11.

[0046] Curves 18 to 21 describe the inlet concentrations for the further upstream sections 11. At the latest, curve 21 makes it clear that curves 16 to 21 are shown as examples of a sudden change in the composition of the fuel-fresh gas mixture. At a time t1, the mixture switches from a rich to a lean mixture, and at a time t2, the mixture switches from a lean to a rich mixture.

[0047] LIST OF REFERENCE SYMBOLS:

[0048] 1 drive device

[0049] 2 drive unit

[0050] 3 Exhaust aftertreatment system

[0051] 4 Arrow

[0052] 5 1. Lambda sensor

[0053] 6 2. Lambda sensor

[0054] 7 lambda controllers

[0055] 8 trim controls

[0056] 9 Entrance

[0057] 10 Calculation module

[0058] Section 11

[0059] 12 Entrance

[0060] 13 Outlet

[0061] 14 Entry point

[0062] 15 Exit point

[0063] 16 History

[0064] 17 History

[0065] 18 History

[0066] 19 History

[0067] 20 History

[0068] 21 History

Claims

PATENT CLAIMS:

1. A method for operating a drive device (1) for a motor vehicle, which drive device has an exhaust gas-generating drive unit (2) and an exhaust gas aftertreatment device (3) for aftertreating the exhaust gas, wherein a first measured value is measured by means of a first lambda probe (5) upstream of the exhaust gas aftertreatment device (3) and a second measured value is measured by means of a second lambda probe (6) downstream of the first lambda probe (6), and wherein an outlet concentration of at least one exhaust gas component downstream of the exhaust gas aftertreatment device (3) is determined by means of an exhaust gas aftertreatment model to which an inlet concentration determined for an inlet point (14) and an inlet combustion air ratio determined for the inlet point (14) are supplied as input variables, characterized in that the inlet combustion air ratio is determined from the second measured value independently of the first measured value.

2. Method according to claim 1, characterized in that a broadband lambda probe is used as the first lambda probe (5) and / or a jump lambda probe is used as the second lambda probe (6).

3. Method according to one of the preceding claims, characterized in that the second measured value is converted by means of a probe characteristic curve into a combustion air ratio from which the inlet combustion air ratio is determined.

4. Method according to one of the preceding claims, characterized in that the inlet combustion air ratio is determined based on a time derivative of the combustion air ratio.

5. Method according to one of the preceding claims, characterized in that the time derivative is subjected to a factor describing an influence of the exhaust gas aftertreatment device (3). Correction factor used in determining the inlet combustion air ratio.

6. Method according to one of the preceding claims, characterized in that the correction factor is determined as a function of at least one of the following variables: an oxygen storage capacity of the exhaust gas aftertreatment device (3), an exhaust gas mass flow of the exhaust gas and a position variable describing a position of the entry point.

7. Method according to one of the preceding claims, characterized in that the inlet combustion air ratio is determined based on the combustion air ratio and the time derivative.

8. Method according to one of the preceding claims, characterized in that the exhaust gas aftertreatment model comprises a plurality of exhaust gas aftertreatment sub-models for modeling different sections (11) of the exhaust gas aftertreatment device (3), wherein one of a plurality of inlet concentrations comprising the inlet concentration and one of a plurality of inlet combustion air ratios comprising the inlet combustion air ratio are supplied to each of the exhaust gas aftertreatment sub-models as input variables, wherein the respective inlet concentration and the respective inlet combustion air ratio are determined for one of a plurality of inlet points (14) comprising the inlet point (14), and each of the inlet combustion air ratios is determined from the second measured value independently of the first measured value.

9. Method according to one of the preceding claims, characterized in that one of the inlet combustion air ratios is determined by filtering from the second measured value.

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) is connected to an exhaust gas generating Drive unit (2) and an exhaust gas aftertreatment device (3) for aftertreating the exhaust gas, wherein a first measured value is measured by means of a first lambda probe (5) upstream of the exhaust gas aftertreatment device (3) and a second measured value is measured by means of a second lambda probe (6) downstream of the first lambda probe (5), and wherein an outlet concentration of at least one exhaust gas component downstream of the exhaust gas aftertreatment device (3) is determined by means of an exhaust gas aftertreatment model to which an inlet concentration determined for an inlet point (14) and an inlet combustion air ratio determined for the inlet point (14) are supplied as input variables, characterized in that the drive device (1) is provided and designed to determine the inlet combustion air ratio from the second measured value independently of the first measured value.

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