Method for operating drive system of motor vehicle and corresponding drive system

Abstract

The invention relates to a method for operating a power plant (1) of a motor vehicle, comprising a power unit (2) for generating exhaust gas and an exhaust gas aftertreatment device (3) for performing exhaust gas aftertreatment, a first measured value being measured upstream of the exhaust gas aftertreatment device (3) by means of a first lambda sensor (5), and a second measured value being measured upstream of the exhaust gas aftertreatment device (3) by means of a second lambda sensor (6). A second measured value is measured downstream of the first lambda sensor (6) by means of a second lambda sensor (6), and an exhaust concentration of the at least one exhaust component downstream of the exhaust aftertreatment device (3) is determined by means of an exhaust aftertreatment model. The intake concentration determined for the intake point (14) and the intake air-fuel ratio determined for the intake point (14) are input as input parameters for the exhaust aftertreatment model. According to the invention, the intake air-fuel ratio is determined from the second measured value independently of the first measured value. The invention also relates to a power plant (1) for a motor vehicle.

Description

Technical Field

[0001] The invention relates to a method for operating a power unit of a motor vehicle, the power unit comprising a power unit for generating exhaust gas and an exhaust gas aftertreatment device for after-treating the exhaust gas. The invention also relates to a power unit for a motor vehicle. Background Art

[0002] The prior art, for example, discloses US 2013 / 0245919 A1. This document discloses a method for regulating the fuel injection quantity based on the oxidation state of the catalyst. The oxidation state is based on the reaction rates of various exhaust gas species along the longitudinal axis of the catalyst and a set of mass and energy balance equations for axial homogenization of the fluid phase and the catalyst coating. Summary of the Invention

[0003] The object of the present invention is to provide a method for operating a power unit of a motor vehicle, which method has advantages over the prior art in particular in that pollutant emissions from the power unit are reliably monitored in order to ensure adherence to limit values.

[0004] This object is achieved according to the invention by a method for operating a power unit of a motor vehicle having the features of claim 1. Provision is made here for the inlet air-fuel ratio to be determined independently of the first measured value from the second measured value.

[0005] Advantageous embodiments with suitable developments of the invention are given in the dependent claims. It should be noted that the exemplary embodiments described in the description are not restrictive; rather, any modifications of the features disclosed in the description, claims and drawings are possible.

[0006] The power unit is used to drive a motor vehicle and, in this regard, to provide a drive torque for driving the motor vehicle. The power unit is preferably a component of the motor vehicle, but can of course also be arranged separately therefrom. To provide the drive torque, the power unit has a power unit, which is preferably designed as an internal combustion engine. During operation of the power unit, fuel and fresh gas are at least temporarily supplied to the power unit, wherein the fresh gas at least temporarily contains fresh air. In addition, if exhaust gas recirculation is implemented, in which the exhaust gas generated by the power unit is at least partially returned to the power unit, i.e., as a component of the fresh gas, the fresh gas contains exhaust gas. The fuel and fresh gas supplied to the power unit form a fuel-fresh gas mixture with a specific composition, which reacts in the power unit.

[0007] During the operation of the power unit, exhaust gas is generated due to the chemical reaction between the fuel and the fresh gas, and this exhaust gas is discharged in the direction of the external environment of the power unit or the motor vehicle. Because the exhaust gas generated by the power unit contains harmful substances, the exhaust gas is first input into an exhaust gas aftertreatment device before being discharged into the external environment. In the exhaust gas aftertreatment device, the harmful substances are at least partially converted into more harmless products. Only after passing through the exhaust gas aftertreatment device is the exhaust gas discharged to the external environment. The exhaust gas aftertreatment device is designed, for example, as a vehicle catalytic converter, in particular a three-way catalytic converter, an oxidation catalytic converter, a NOx storage catalytic converter or an SCR catalytic converter. However, the exhaust gas aftertreatment device can also be designed as a particle filter, in particular a gasoline particle filter or a diesel particle filter, preferably with an integrated vehicle catalytic converter, for example with a catalytic coating.

[0008] An exhaust gas aftertreatment model is used to determine the pollutant emissions of a power plant, i.e., the amount of at least one exhaust gas component discharged into the external environment. The exhaust gas aftertreatment model models the conversion of at least one exhaust gas component by means of an exhaust gas aftertreatment device. For this purpose, the exhaust gas aftertreatment model is fed with the inlet concentration of the at least one exhaust gas component present at the inlet point as a first input parameter.

[0009] An entry point is to be understood, in particular, as the point at which the exhaust gas enters the exhaust aftertreatment device. Alternatively, the entry point refers to the point at which the exhaust gas enters a specific section of the exhaust aftertreatment device, in particular, one of a plurality of sections. The exhaust aftertreatment model calculates the exhaust concentration at the exit point based on the entry concentration. Similarly to the entry point, the exit point refers to the point at which the exhaust gas exits the exhaust aftertreatment device or a section of the exhaust aftertreatment device.

[0010] The inlet concentration can, in principle, be determined in any manner and method, for example, as a function of the operating point of the power unit, wherein the operating point is characterized, for example, by the current drive torque provided by the power unit and / or the current speed of the power unit. If the inlet location is the location at which the exhaust gas enters the exhaust gas aftertreatment device, the inlet concentration present at this inlet location is equal to the raw exhaust gas volume of the power unit, i.e., the amount of at least one exhaust gas component generated or emitted by the power unit. If the inlet location is downstream of this location, the inlet concentration present at this inlet location is preferably determined using an exhaust gas aftertreatment model. In this case, for example, the inlet concentration for one of the sections corresponds to the exhaust gas concentration for the section of the exhaust gas aftertreatment device preceding this section.

[0011] The exhaust gas aftertreatment model inputs an additional input variable, the inlet air-fuel ratio, which is determined in a manner similar to the inlet concentration for the inlet point. For example, provision can be made for the inlet air-fuel ratio to be set equal to an air-fuel ratio determined from a first measured value measured upstream of the exhaust gas aftertreatment device using a first lambda probe. In this context, the first measured value describes the air-fuel ratio present in the exhaust gas upstream of the exhaust gas aftertreatment device, or the amount of residual oxygen present there.

[0012] However, particularly when a broadband lambda sensor is used as the first lambda sensor, the first measured value often has a relatively large measurement error. Even a measurement error of less than one percent can lead to an intolerable loss of accuracy in the exhaust gas aftertreatment model. For this reason, it can be provided that the first measured value is corrected by means of a fine-tuning control based on a second measured value. The second measured value is measured using a second lambda sensor and describes the air-fuel ratio or residual oxygen downstream of the first lambda sensor, particularly downstream of an exhaust gas aftertreatment device. For example, it is provided that the second measured value is adjusted to a target value and an offset is determined therefrom, to which the first measured value is applied, particularly for performing a lambda control based on the first measured value.

[0013] However, the applicant's research has demonstrated that, while the first measured value has sufficient accuracy for lambda control after fine-tuning, it is not mandatory for use in the exhaust aftertreatment model. Furthermore, broadband lambda sensors do not have ideal dynamic characteristics. This becomes apparent, for example, after a power unit's boost operation: after a sudden change in the composition of the fuel-fresh gas mixture, the sensor responds to this change with a certain delay within a certain period of time. This leads to errors in the exhaust aftertreatment model.

[0014] For this reason, it is now provided that the intake air-fuel ratio is determined from the second measured value independently of the first measured value. This means that the intake air-fuel ratio is based solely on the second measured value measured downstream of the first lambda sensor, but not on the first measured value. In other words, the first measured value is completely disregarded in the determination of the intake air-fuel ratio, and only the second measured value is considered—of the two measured values. This allows the intake air-fuel ratio to be determined with such high accuracy that the exhaust aftertreatment model can still be executed with good results, so that the exhaust concentration describes the actual concentration of at least one exhaust component in the exhaust gas at the outlet location with high accuracy.

[0015] A refinement of the present invention provides for the use of a broadband lambda sensor as the first lambda sensor and / or a step lambda sensor as the second lambda sensor. A broadband lambda sensor has a relatively wide measuring range, which is not the case for a step lambda sensor. A step lambda sensor exists, for example, in the form of a single Nernst cell and can also be referred to as a voltage step sensor. A broadband lambda sensor, on the other hand, comprises a Nernst cell and a pump cell. The pump cell is regulated in such a way that an air-fuel ratio lambda = 1 is measured with the aid of the Nernst cell. In this case, the current intensity and / or the voltage of the current used to operate the pump cell is a measure for the air-fuel ratio actually present in the exhaust gas. The use of a broadband lambda sensor as the first lambda sensor and a step lambda sensor as the second lambda sensor makes it possible, in particular, to carry out the lambda regulation with precision.

[0016] A refinement of the present invention provides that the second measured value is converted into an air-fuel ratio with the aid of a sensor characteristic curve, from which the inlet air-fuel ratio is determined. Thus, the second measured value is first converted into an air-fuel ratio using the sensor characteristic curve. The sensor characteristic curve is adapted to the second lambda sensor and describes its behavior. In particular, values ​​for the air-fuel ratio are stored in the sensor characteristic curve, which exist for different measured values. The sensor characteristic curve can be stored in any manner and method, for example using mathematical formulas, combined characteristic curves and / or graphs. The inlet air-fuel ratio is then determined solely from the air-fuel ratio. The "sensor characteristic curve is used to convert the second measured value into an air-fuel ratio" can be implemented, on the one hand, with little computational effort and, on the other hand, with sufficient precision to operate the exhaust gas aftertreatment model based on the air-fuel ratio.

[0017] One refinement of the present invention provides for determining the incoming air-fuel ratio based on a time derivative of the air-fuel ratio. In this context, the incoming air-fuel ratio does not directly correspond to the air-fuel ratio determined by the second measured value, but rather is corrected. This correction consists in determining the time derivative of the air-fuel ratio. Based on this, the incoming air-fuel ratio is then determined, so that it exists as a function of at least the time derivative of the air-fuel ratio. This allows the incoming air-fuel ratio to be determined relatively simply and with high accuracy.

[0018] One refinement of the present invention provides for applying a correction factor to the time derivative used in determining the inlet air-fuel ratio. This correction factor describes the influence of the exhaust aftertreatment device. Because the second measured value is measured downstream of the first lambda sensor and, in particular, downstream of the inlet location, the exhaust aftertreatment device significantly influences the inlet air-fuel ratio determined from the second measured value. In particular, the inlet air-fuel ratio is dependent on the oxygen storage capacity of the exhaust aftertreatment device and / or the exhaust mass flow rate of exhaust gas flowing through the exhaust aftertreatment device. For this reason, the time derivative of the air-fuel ratio is first applied with the correction factor, and then incorporated into the inlet air-fuel ratio. This further improves the accuracy of the exhaust aftertreatment model.

[0019] One refinement of the present invention provides for determining the correction factor based on at least one of the following parameters: the oxygen storage capacity of the exhaust gas aftertreatment device, the exhaust gas mass flow rate, and a location parameter describing the location of the inlet point. This has already been mentioned. The oxygen storage capacity describes the oxygen storage capacity of the exhaust gas aftertreatment device. Here, the oxygen storage capacity represents the maximum amount of oxygen that can be temporarily stored. The exhaust gas mass flow rate, on the other hand, describes the mass flow rate of the exhaust gas currently flowing through the exhaust gas aftertreatment device. The location parameter relates to the arrangement of the inlet point, in particular, its arrangement relative to the exhaust gas aftertreatment device and / or relative to the second lambda sensor.

[0020] The correction factor can be determined from the oxygen storage capacity, the exhaust mass flow rate, or both. Taking both parameters into account has a particularly significant impact on the accuracy of the exhaust aftertreatment model. Additionally or alternatively, position parameters can be used, particularly when modeling multiple sections of the exhaust aftertreatment system.

[0021] One refinement of the present invention provides for determining the incoming air-fuel ratio based on the air-fuel ratio and a time derivative. Overall, the incoming air-fuel ratio therefore exists as a function of the air-fuel ratio, wherein the air-fuel ratio is added to the incoming air-fuel ratio multiple times, once directly and once in the form of a time derivative. Preferably, the incoming air-fuel ratio is determined as the sum of the air-fuel ratio and the time derivative of the air-fuel ratio, preferably with an applied correction factor. This method achieves a particularly high accuracy of the incoming air-fuel ratio and, therefore, a high accuracy of the exhaust gas aftertreatment model.

[0022] For example, the air-fuel ratio can be determined by the following formula:

[0023]

[0024] Where λ1 is the incoming air-fuel ratio, λ2 is the air-fuel ratio, k is the correction factor and t is time.

[0025] A refinement of the present invention provides that the exhaust gas aftertreatment model includes 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 including the inlet concentration and one of a plurality of inlet air-fuel ratios including the inlet air-fuel ratio are input as input parameters to each of the plurality of exhaust gas aftertreatment sub-models, wherein a corresponding inlet concentration and a corresponding inlet air-fuel ratio are determined for one of a plurality of inlet locations including the inlet location, and each of the inlet air-fuel ratios is determined from a second measured value independently of the first measured value.

[0026] This means that the exhaust aftertreatment device is not viewed as a whole, but rather divided into a plurality of segments. These segments preferably extend from the initial end to the final end of the exhaust aftertreatment device and are particularly preferably directly adjacent to 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 segments. An exhaust aftertreatment submodel is provided for each of these segments, wherein the exhaust aftertreatment submodels of the plurality of segments collectively form the exhaust aftertreatment model.

[0027] Each of the exhaust gas aftertreatment submodels has one of the inlet concentrations and one of the inlet air-fuel ratios as input parameters. The inlet concentrations mentioned above are components of multiple inlet concentrations, and the inlet air-fuel ratios are components of multiple inlet air-fuel ratios. The inlet concentrations and inlet air-fuel ratios are determined for each segment for the corresponding inlet point of the segment.

[0028] Using the corresponding exhaust gas aftertreatment submodel, the corresponding exhaust gas concentration is determined for the exhaust point of the corresponding segment from the corresponding inlet concentration and the corresponding inlet air-fuel ratio. Preferably, the exhaust gas concentration of the segment located fluidically upstream is used as the inlet concentration for the segment directly downstream of the segment. In this regard, the exhaust gas aftertreatment model is based on a step-by-step calculation of the exhaust gas concentration of at least one exhaust gas component passing through the exhaust gas aftertreatment device. This allows for particularly high accuracy.

[0029] One refinement of the present invention provides for determining one of the incoming air-fuel ratios from the second measured value by filtering. In principle, all incoming air-fuel ratios are determined from the second measured value independently of the first measured value. Preferably, the method already described is used for at least one of the incoming air-fuel ratios, thereby determining the respective incoming air-fuel ratio using the time derivative of the air-fuel ratio.

[0030] However, at least one further incoming air-fuel ratio is determined from the second measured value by filtering. It is particularly preferred that the air-fuel ratio is determined from the second measured value, again using the sensor characteristic curve. This air-fuel ratio is then filtered, and the filtering result is used as the incoming air-fuel ratio. A low-pass filter can be used as the filter.

[0031] Particularly preferably, the inlet air-fuel ratio is determined based on the time derivative if the entry point of the corresponding segment is arranged upstream of the second lambda sensor. Conversely, filtering is used if the entry point of the corresponding segment is downstream of the second lambda sensor. This approach also enables the use of the method if the second lambda sensor is not arranged downstream of the exhaust gas aftertreatment device, but rather within the exhaust gas aftertreatment device.

[0032] The present invention further relates to a power plant for a motor vehicle, in particular for carrying out a method according to an embodiment within the scope of the description, wherein the power plant comprises a power unit for generating exhaust gas and an exhaust gas aftertreatment device for exhaust gas aftertreatment, wherein a first measured value is measured upstream of the exhaust gas aftertreatment device by means of a first lambda sensor, and a second measured value is measured downstream of the first lambda sensor by means of a second lambda sensor, wherein an exhaust gas 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, the exhaust gas aftertreatment model being fed with an inlet concentration determined for the entry point and an inlet air-fuel ratio determined for the entry point as input parameters. The power plant is configured and designed to determine the inlet air-fuel ratio from the second measured value independently of the first measured value.

[0033] The advantages of this embodiment or this type of power plant have already been pointed out. The power plant and the method for operating the power plant can be further developed according to the embodiments within the scope of the description, so that reference is made to these embodiments 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 respectively indicated combination but also in other combinations or alone without departing from the scope of the present invention. Therefore, embodiments are also to be considered as being encompassed by the present invention, which are not shown or described in detail in the description and / or the figures, but which nevertheless result from or can be derived from the described embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be described in detail below based on the embodiments shown in the accompanying drawings, without limiting the present invention.

[0036] Figure 1A schematic diagram of a power plant for a motor vehicle is shown, the power plant having a power unit and an exhaust gas aftertreatment device, and

[0037] Figure 2 A graph is shown in which changes in the air-fuel ratio are plotted against time. DETAILED DESCRIPTION

[0038] Figure 1 The schematic diagram shows a power plant 1 having a power unit 2 for generating exhaust gas and an exhaust gas aftertreatment device 3, in this case in the form of a vehicle catalytic converter. Fuel and fresh gas are supplied to the power unit 2, which form a fuel-fresh gas mixture and chemically react with each other to generate exhaust gas. The exhaust gas is supplied to the exhaust gas aftertreatment device 3 and flows through it in the direction of arrow 4.

[0039] A first measured value is measured upstream of exhaust gas aftertreatment device 3 by means of a first lambda probe 5, and a second measured value is measured downstream of exhaust gas aftertreatment device 3 by means of a second lambda probe 6. Both measured values ​​indicate the residual oxygen content of the exhaust gas or the air-fuel ratio at the corresponding location.

[0040] The lambda controller 7 is operated using the first measured value, while the fine-tuning controller 8 is operated using the second measured value. The initial parameters of both controllers 7 and 8 are calculated in a calculation module 10 using the target values ​​input via input 9. The composition of the fuel-fresh gas mixture is determined based on the calculation results.

[0041] Furthermore, the composition of the exhaust gas downstream of the exhaust aftertreatment device 3 is determined using the exhaust aftertreatment model. This is done for at least one exhaust gas component, but preferably for a plurality of exhaust gas components. The exhaust aftertreatment model includes a plurality of exhaust gas aftertreatment sub-models, five of which are included in the exemplary embodiment shown here. Each of the exhaust gas aftertreatment sub-models is used to calculate one of the plurality of sections 11 of the exhaust gas aftertreatment device 3. 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 extend continuously and uninterruptedly from the inlet 12 to the outlet 13.

[0042] For each of the segments 11, the inlet concentration and inlet air-fuel ratio at the corresponding inlet location 14 are determined. Subsequently, the exhaust concentration of the corresponding exhaust component at the corresponding exhaust location 15 of the corresponding segment 11 is determined using the corresponding exhaust aftertreatment sub-model. Preferably, the inlet concentration of the further downstream segment 11 is equal to the exhaust concentration of the respective immediately upstream segment 11. The inlet concentration of the most upstream segment 11 is equal to the inlet concentration of the exhaust aftertreatment device 3, and the exhaust concentration of the exhaust aftertreatment device 3 is equal to the exhaust concentration of the most downstream segment 11.

[0043] Each exhaust gas aftertreatment submodel in the exhaust gas aftertreatment model, or exhaust gas aftertreatment submodel, determines a conversion rate for a corresponding exhaust gas component based on a corresponding intake air-fuel ratio. The conversion rates are stored, for example, in a performance map, i.e., for different intake air-fuel ratios. For example, one or more of the following exhaust gas components may be used as exhaust gas components: hydrocarbons; carbon oxides, particularly carbon monoxide; hydrogen, particularly molecular hydrogen; nitrogen oxides, particularly nitrogen monoxide and / or nitrogen dioxide; and oxygen, particularly molecular oxygen.

[0044] The respective intake air-fuel ratio is not determined based on the first measured value, but rather independently of the first measured value, from the second measured value. The intake air-fuel ratio for each of the segments 11 is determined based on the measured value measured downstream of the respective intake point 14. To this end, the air-fuel ratio is first determined from the second measured value using the sensor characteristic curve for the second lambda sensor 6. The air-fuel ratio thus determined is then derivatized over time, and the time derivative is multiplied by a correction factor. The intake air-fuel ratio is the sum of the intake air-fuel ratio and the correction factor multiplied by the time derivative of the air-fuel ratio.

[0045] The correction factor is proportional to the oxygen storage capacity and inversely proportional to the exhaust gas mass flow rate. The position of the respective segment 11 of the exhaust gas aftertreatment device 3 is taken into account in the correction factor. Therefore, the farther the inlet point 14 is from the second lambda sensor 6, the larger the correction factor. For example, the position parameter included in the correction factor is 1 for the inlet 12 and 0 for the outlet 13. The position parameter for the inlet point 14 between the inlet 12 and the outlet 13 is determined using linear interpolation. Thus, for the five segments 11 shown here (whose inlet points 14 are equidistantly spaced from one another), position parameters of 1.0, 0.8, 0.6, 0.4, and 0.2 are obtained. The respective position parameter is multiplied by a time derivative, for example, as a component of the correction factor.

[0046] Figure 2 A diagram is shown, which depicts the profiles 16, 17, 18, 19, 20, and 21 of the air-fuel ratio over time t. Profile 16 corresponds to the air-fuel ratio calculated from the second measured value, and the other profiles 17 to 21 are derived from this profile 16, i.e., in the manner and method described. Thus, profile 16 shows the exhaust concentration of at least one exhaust gas component of the most downstream segment 11. Profile 17 depicts the inlet concentration of this segment 11 and, correspondingly, the exhaust concentration of the immediately upstream segment 11. Profiles 18 to 21 depict the inlet concentration of segments 11 further upstream. Finally, profile 21 shows that profiles 16 to 21, by way of example, illustrate a sudden change in the composition of the fuel-fresh gas mixture. At time t1, the mixture changes from a rich mixture to a lean mixture; at time t2, the mixture changes from a lean mixture to a rich mixture.

[0047] List of reference numerals:

[0048] 1 Power equipment

[0049] 2 Power Unit

[0050] 3 Exhaust after-treatment device

[0051] 4 arrows

[0052] 5. First lambda sensor

[0053] 6 Second lambda sensor

[0054] 7 λ Regulator

[0055] 8 fine-tuning regulators

[0056] 9 Input

[0057] 10 Computing Module

[0058] 11 sections

[0059] 12 Entrance

[0060] 13 Exit

[0061] 14 Entry site

[0062] 15. Excretion site

[0063] 16 Change curve

[0064] 17 Change curve

[0065] 18 Change curve

[0066] 19 Change curve

[0067] 20 Change curve

[0068] 21 Change curve

Claims

1. A method for operating a power unit (1) of a motor vehicle, the power unit comprising a power unit (2) for generating exhaust gas and an exhaust gas aftertreatment device (3) for performing exhaust gas aftertreatment, wherein: A first measured value is measured upstream of an exhaust gas aftertreatment device (3) by means of a first lambda sensor (5), and a second measured value is measured downstream of the first lambda sensor (6) by means of a second lambda sensor (6), wherein an exhaust 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, an inlet concentration determined for an inlet point (14) and an inlet air-fuel ratio determined for the inlet point (14) are input to the exhaust gas aftertreatment model as input parameters, characterized in that the inlet air-fuel ratio is determined from the second measured value independently of the first measured value.

2. The method according to claim 1, characterized in that A broadband lambda sensor is used as the first lambda sensor (5), and / or a step lambda sensor is used as the second lambda sensor (6).

3. The method according to any one of the preceding claims, characterized in that The second measured value is converted with the aid of the sensor characteristic curve into an air-fuel ratio, from which the intake air-fuel ratio is determined.

4. The method according to any one of the preceding claims, characterized in that The entering air-fuel ratio is determined based on the time derivative of the air-fuel ratio.

5. The method according to any one of the preceding claims, characterized in that The time derivative used in determining the intake air-fuel ratio is subjected to a correction factor which describes the influence of the exhaust aftertreatment device (3).

6. The method according to any one of the preceding claims, characterized in that The correction factor is determined based on at least one of the following parameters: an oxygen storage capacity of the exhaust gas aftertreatment device (3), an exhaust gas mass flow rate of the exhaust gas, and a position parameter describing the position of the inlet point.

7. The method according to any one of the preceding claims, characterized in that The entry air-fuel ratio is determined based on the air-fuel ratio and the time derivative.

8. The method according to any 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 including an inlet concentration and one of a plurality of inlet air-fuel ratios including an inlet air-fuel ratio are input as input parameters to each of the plurality of exhaust gas aftertreatment sub-models, wherein a corresponding inlet concentration and a corresponding inlet air-fuel ratio are determined for one of a plurality of inlet locations (14) including an inlet location (14), and each of the inlet air-fuel ratios is determined from a second measured value independently of a first measured value.

9. The method according to any one of the preceding claims, characterized in that One of the incoming air-fuel ratios is determined from the second measured value by means of filtering.

10. A power unit (1) for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein: The power device (1) has a power unit (2) for generating exhaust gas and an exhaust gas aftertreatment device (3) for performing exhaust gas aftertreatment, wherein a first measured value is measured upstream of the exhaust gas aftertreatment device (3) by means of a first lambda sensor (5), and a second measured value is measured downstream of the first lambda sensor (5) by means of a second lambda sensor (6), wherein an exhaust 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, and the exhaust gas aftertreatment model is input with an inlet concentration determined for an inlet location (14) and an inlet air-fuel ratio determined for the inlet location (14) as input parameters, characterized in that the power device (1) is configured and designed to determine the inlet air-fuel ratio from the second measured value independently of the first measured value.

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