Method for operating a drive unit for a motor vehicle, corresponding drive unit for a motor vehicle and computer program product

Abstract

The invention relates to a method for operating a drive unit (1) for a motor vehicle, which has an exhaust gas generating drive unit (2) and an exhaust gas aftertreatment device (3), wherein a first measured value is measured upstream of the exhaust gas aftertreatment device (3) by means of a first lambda probe (5) and a second measured value is measured 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.The invention provides that the intake air-fuel ratio is determined from a lambda value derived from the second measured value and a filter value determined from the lambda value using a filter. The invention further relates to a drive unit (1) for a motor vehicle and a computer program product.

Description

[0001] The invention relates to a method for operating a drive unit for a motor vehicle, which has an exhaust gas-generating drive unit and an exhaust gas aftertreatment device, wherein a first measured value is measured upstream of the exhaust gas aftertreatment device by means of a first lambda probe and a second measured value is measured downstream of the first lambda probe, and wherein an 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, wherein the inlet combustion air ratio is determined from a lambda value determined from the second measured value and a filter value determined from the lambda value by means of a filter.The invention further relates to a drive device for a motor vehicle and a computer program product.

[0002] For example, the prior art includes German patent application DE 10 2023 201 660 B3. This describes a method according to the preamble of claim 1, wherein the inlet combustion air ratio is determined from the second measured value independently of the first measured value.

[0003] Furthermore, the publication DE 10 2013 203 019 A1 discloses a method for monitoring an exhaust gas sensor coupled in an engine exhaust, which includes: indicating the reduction in exhaust gas sensor function based on a time delay and a line length of each sample of a quantity of exhaust gas sensor reactions collected during an instructed change in the air-fuel ratio.

[0004] German patent application DE 10 2009 000 298 A1 describes a method for adjusting a lambda sensor signal provided by a lambda sensor located in the exhaust manifold of an internal combustion engine, wherein the lambda sensor signal is adjusted during overrun fuel cut-off of the internal combustion engine. It is provided that a throttle valve located in the intake manifold of the internal combustion engine is opened during overrun fuel cut-off, and that the lambda sensor signal is adjusted only after the throttle valve has opened during overrun fuel cut-off.

[0005] Furthermore, the publication DE 103 23 248 A1 discloses a method for operating an internal combustion engine, in particular a gasoline engine, in particular a motor vehicle, with at least one catalyst arranged in an exhaust system, wherein the internal combustion engine is optionally operated in a stoichiometric mode with an air-fuel ratio Lambda essentially equal to 1, in a lean operating mode with an air-fuel ratio Lambda greater than 1, in an unfired overrun mode or in a substoichiometric mode with an air-fuel ratio Lambda less than 1.

[0006] Finally, the prior art includes the publication DE 10 2021 132 412 B3 and the subsequently published publication DE 10 2025 103 948 A1.

[0007] It is intended that, after a transition from lean operating mode or overrun mode to substoichiometric operation, the value of lambda is selected for a predetermined time or a time defined by the signal of an oxygen-sensitive measuring device in such a way as to deviate from a value specified for substoichiometric operation, such that a function of a maximum temperature of the catalyst after the transition, depending on the lambda value, the predetermined time period or the time period defined by the signal of an oxygen-sensitive measuring device, and a resulting sum of thermal and chemical energy input into the catalyst, exhibits a minimum.

[0008] The object of the invention is to propose a method for operating a drive unit for a motor vehicle which has advantages over the prior art, in particular reliably monitoring pollutant emissions from the drive unit in order to ensure compliance with limit values.

[0009] According to the invention, this is achieved by a method for operating a drive unit for a motor vehicle with the features of claim 1. It is provided that an input signal is supplied to the filter and, upon the occurrence of a specific operating event, an output value determined from an output signal of the filter is adjusted towards a preset value.

[0010] Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims. It should be noted that the exemplary embodiments described in the description are not limiting; rather, any variations of the features disclosed in the description, the claims, and the figures are possible.

[0011] The method is designed for operating the drive system. It is preferably implemented by means of a control unit for the drive system. The drive system or its control unit is preferably an integral part of the motor vehicle, but can of course also be separate from it, particularly until the drive system or the control unit is mounted on or in the motor vehicle. The drive system serves to propel the motor vehicle, i.e., to provide a drive torque directed towards propelling the motor vehicle. To provide the drive torque, the drive system includes the drive unit. The drive unit is preferably an internal combustion engine, in particular a gasoline engine or a diesel engine.

[0012] During operation, the drive unit is supplied with fuel and fresh gas at least intermittently, with the fresh gas containing fresh air at least intermittently. Additionally, the fresh gas may contain exhaust gas if exhaust gas recirculation is implemented, in which the exhaust gas generated by the drive unit is at least partially returned to the drive unit as a component of the fresh gas. The fuel and fresh gas supplied to the drive unit form a fuel-fresh gas mixture with a specific composition, which is then reacted within the drive unit.

[0013] During operation of the engine, exhaust gas is produced due to the chemical reaction of fuel and fresh air. This exhaust gas is discharged towards the outside environment of the engine or vehicle. Since the exhaust gas generated by the engine contains pollutants, it is first routed to an exhaust aftertreatment system before being released into the environment. In the exhaust aftertreatment system, the pollutants are at least partially converted into less harmful products. Only after passing through the exhaust aftertreatment system is the exhaust gas discharged into the environment, primarily through an exhaust pipe on the engine.

[0014] The exhaust aftertreatment system is, for example, a vehicle catalyst, in particular a three-way catalyst, oxidation catalyst, NO x- Storage catalyst or SCR catalyst. The vehicle catalyst may be integrated into a particulate filter, particularly a gasoline particulate filter or a diesel particulate filter. For this purpose, the particulate filter is, for example, provided with a catalytic coating. The conversion rate, and thus the conversion capacity of the vehicle catalyst, with which the pollutants are converted into less harmful products, depends in particular on the composition of the exhaust gas supplied to the exhaust aftertreatment system and the temperature of the exhaust aftertreatment system.

[0015] The components of the exhaust gas produced by the engine are also referred to as raw emissions. Raw emissions describe the composition of the exhaust gas upstream of the exhaust aftertreatment system, or in terms of flow characteristics, between the engine and the exhaust aftertreatment system. As the exhaust gas passes through the aftertreatment system, some of the substances contained within it are transformed, thus changing its composition. The substances present in the exhaust gas downstream of the aftertreatment system, which constitute the exhaust gas, are also referred to as tailpipe emissions, since this is the composition of the exhaust gas released into the environment through the engine's tailpipe.

[0016] As mentioned earlier, the amount of pollutants contained in the tailpipe emissions depends on the raw emissions, but also on the conversion efficiency of the exhaust aftertreatment system or the vehicle's catalytic converter. This efficiency is temperature-dependent. In particular, the conversion efficiency is lower the further the temperature of the exhaust aftertreatment system deviates from its operating temperature; that is, the greater the absolute difference between the temperatures. The temperature of the exhaust aftertreatment system refers, for example, to the temperature of a ceramic honeycomb structure coated with the catalytic material.

[0017] To determine the pollutant emissions of the propulsion system, i.e., the quantity of at least one exhaust component released into the environment, the exhaust aftertreatment model is used. This model simulates the conversion of at least one exhaust component by the aftertreatment system. For this purpose, the inlet concentration of at least one exhaust component present at an inlet point is fed into the model as a first input. Nitrogen oxide, i.e., nitrogen monoxide and / or nitrogen dioxide, is used as an example of an exhaust component. However, any component of the exhaust gas can be used as the exhaust component. Furthermore, any number of outlet concentrations of any number of exhaust components can be determined using the exhaust aftertreatment model; thus, multiple exhaust components can also be used.

[0018] The term "inlet point" refers specifically to the point where the exhaust gas enters the exhaust aftertreatment system. Alternatively, it can also refer to the point where the exhaust gas enters a specific section of the exhaust aftertreatment system, particularly one of several sections. Based on the inlet concentration, the exhaust aftertreatment model calculates an outlet concentration present at an outlet point. Analogously, the outlet point refers to the point where the exhaust gas exits the exhaust aftertreatment system or section thereof.

[0019] The inlet concentration can, in principle, be determined in any way. For example, it can be determined as a function of an operating point of the drive unit, where the operating point is characterized, for example, by the drive torque currently provided by the drive unit and / or an instantaneous rotational speed of the drive unit. If the inlet point is the point at which the exhaust gas enters the exhaust aftertreatment system, then the inlet concentration present at the inlet point is, for example, equal to a raw emission from the drive unit, i.e., equal to the quantity of at least one exhaust gas component produced or emitted by the drive unit. If the inlet point is located downstream of this point, the inlet concentration present at the inlet point is preferably determined using the exhaust 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 aftertreatment system preceding the section.

[0020] As an additional input variable, the inlet air-fuel ratio is fed into the exhaust aftertreatment model. This ratio is determined analogously to the inlet concentration for the inlet point. For example, it is intended that the inlet air-fuel ratio be set equal to a combustion air-fuel ratio, which is determined from the measured value of the first lambda sensor upstream of the exhaust aftertreatment system. This measured value thus describes the combustion air-fuel ratio present in the exhaust gas upstream of the exhaust aftertreatment system, or rather, the amount of residual oxygen present in the exhaust gas at that point.

[0021] However, the reading from the first lambda sensor can sometimes be subject to a comparatively large measurement error, especially if the first lambda sensor is a wideband sensor. Even an error of less than one percent leads to an intolerable loss of accuracy in the exhaust aftertreatment model. For this reason, it may be necessary to correct the first reading from the first lambda sensor using a trim control based on the second reading from the second lambda sensor. This second reading is taken using the second lambda sensor and describes the air-fuel ratio, or the amount of residual oxygen, downstream of the first lambda sensor, specifically downstream of the exhaust aftertreatment system.For example, it is intended to regulate the second measured value to a target value and to determine an offset from this, which is then applied to the first measured value, particularly for performing lambda control based on the first measured value. Specifically, it is intended to determine a combustion air ratio from the measured value corrected in the manner described and to use this as the intake combustion air ratio.

[0022] Alternatively, the intake air-fuel ratio can be determined from the second reading of the second lambda sensor, which is preferably located downstream of the exhaust aftertreatment system. Preferably, the intake air-fuel ratio is determined from the second reading of the second lambda sensor independently of the first reading of the first lambda sensor. This means that the intake air-fuel ratio depends only on the second reading measured downstream of the first lambda sensor, more precisely downstream of the exhaust aftertreatment system, and not on the first reading.

[0023] In other words, with this approach, the first measurement is not directly considered when determining the inlet air-fuel ratio; only the second measurement is taken into account. This allows the inlet air-fuel ratio to be determined with such high accuracy that the exhaust aftertreatment model can also be successfully implemented, and the outlet concentration accurately reflects the actual concentration of the exhaust component present at the outlet point.

[0024] In summary, the intake air-fuel ratio supplied to the exhaust aftertreatment model can be determined from the measured value of the first lambda sensor and / or the measured value of the second lambda sensor. For example, the aforementioned trim control is applied here, so that the measured value of the first lambda sensor, or the first measured value in a form corrected based on the measured value of the second lambda sensor, is incorporated into the intake air-fuel ratio. However, the applicant has surprisingly found that a particularly high accuracy of the intake air-fuel ratio is achieved if it takes into account both the lambda value determined from the second measured value and the filter value determined from the lambda value using the filter.This means that the intake air-to-fuel ratio is given as a function of the lambda value and the filter value; for example, the intake air-to-fuel ratio is given as a function of the lambda value and the filter value.

[0025] The lambda value preferably refers to an air-fuel ratio determined from the second measured value, and in particular, exclusively from the second measured value. The lambda value is thus the air-fuel ratio exhibited by the exhaust gas when flowing towards and / or across the second lambda sensor. The second measured value is, for example, in the form of an electrical voltage, which, in the case of a switching lambda sensor, can also be referred to as the Nernst voltage. The lambda value is determined from this voltage. The filter value is derived from the lambda value by applying the lambda value to the filter; that is, the lambda value, or a quantity derived from the lambda value, serves as the filter's input. The filter provides the filter value as its output.Ultimately, this means that the intake air-to-combustion air ratio is determined from an unfiltered value and a filtered value, with the filtered value being obtained by filtering the unfiltered value. This achieves the advantages already mentioned.

[0026] A further development of the invention provides that a broadband lambda sensor is used as the first lambda sensor and / or a jump-type lambda sensor as the second lambda sensor. While the broadband lambda sensor has a comparatively wide measuring range, this is not the case for the jump-type lambda sensor. The jump-type lambda sensor is, for example, in the form of a single Nernst cell and can also be referred to as a voltage-switching sensor. The broadband lambda sensor, on the other hand, consists of a Nernst cell and a pump cell.

[0027] The pump cell is adjusted so that a combustion air-fuel ratio of λ = 1 is measured using the Nernst cell. The current and / or voltage of the electrical current used to operate the pump cell then represents a measure of the actual combustion air-fuel ratio present in the exhaust gas. The use of a wideband lambda sensor as the first lambda sensor and a narrowband lambda sensor as the second lambda sensor enables, in particular, precise lambda control.

[0028] A further development of the invention provides that the second measured value is converted into an air-fuel ratio using a probe characteristic curve, from which the intake air-fuel ratio is determined. The second measured value is thus first converted into the air-fuel ratio using the probe characteristic curve. The probe characteristic curve is calibrated to the second lambda sensor and describes its behavior. In particular, the probe characteristic curve contains values ​​for the air-fuel ratio, 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.

[0029] The intake air-fuel ratio is then determined from the combustion air-fuel ratio, specifically by using the combustion air-fuel ratio as the lambda value underlying the intake air-fuel ratio. Using the probe characteristic curve to convert the second measured value into the combustion air-fuel ratio is, on the one hand, computationally efficient and, on the other hand, sufficiently accurate to operate the exhaust aftertreatment model based on the combustion air-fuel ratio.

[0030] A further development of the invention provides that the intake air-to-fuel ratio is determined from a sum containing the lambda value and the filter value, wherein the filter value is determined using the filter from a time derivative of the lambda value. This means that the lambda value and the filter value derived from the lambda value are summed to obtain the sum. The intake air-to-fuel ratio is then determined from this sum. Preferably, the intake air-to-fuel ratio corresponds to the sum of the lambda value and the filter value. The lambda value is not directly supplied to the filter; instead, the time derivative of the lambda value is used as the filter's input. This approach serves to achieve the advantages already explained.

[0031] A further development of the invention provides for the use of a low-pass filter. The low-pass filter filters out signal components with higher frequencies and allows signal components with lower frequencies to pass through. Ultimately, the filter value is therefore the low-pass filtered time derivative of the lambda value. This approach also serves to reliably achieve the advantages already mentioned.

[0032] A further development of the invention provides that the intake air-fuel ratio is determined using a high-pass filter of the lambda value. The lambda value is fed to the high-pass filter as an input signal, and upon the occurrence of a specific operating event, an output value determined from an output signal of the high-pass filter is adjusted towards a target value. The determination of the intake air-fuel ratio from the lambda value and the filter value is performed directly using the high-pass filter to which the lambda value is fed. It has been explained above that the intake air-fuel ratio is the sum of the lambda value and the low-pass filtered time derivative of the lambda value. Applying the high-pass filter to the lambda value is equivalent to this procedure, resulting in the aforementioned sum.Preferably, the high-pass filter is a first-order filter; however, a higher-order filter can also be used.

[0033] The high-pass filter has an input signal and an output signal. The input signal is fed into the high-pass filter, which generates and provides the output signal from the input signal by filtering it. The input signal is determined from an input quantity, and the filter's output signal is determined from the output signal. Due to the use of the high-pass filter to determine the intake air-fuel ratio, there may be a delayed response of the intake air-fuel ratio to a change in the second measurement. Deviations can occur, in particular, when switching between a lean and a rich fuel-air mixture, or vice versa.

[0034] This occurs particularly after overrun operation of the drive unit, during which the drive unit is driven by an externally supplied torque, meaning it provides no or only a negative drive torque itself. No fuel is supplied to the drive unit during overrun operation. When switching from overrun operation to powered operation of the drive unit, during which the drive unit receives not only fresh gas but also fuel, the second measured value changes rapidly, but this change is not reflected in the combustion ratio at the intake air temperature with sufficient speed.

[0035] For this reason, it is intended that, upon the occurrence of a specific operational event, the output value, which is determined from the output signal of the high-pass filter, is adjusted towards the target value. In other words, it is preferably intended that the input signal is determined from the lambda value and fed to the high-pass filter. In particular, the input signal corresponds to the lambda value. The high-pass filter determines the output signal from the input signal by filtering, and the output value is then determined from this output signal. For example, the output value corresponds to the output signal of the high-pass filter.

[0036] The initial value is used to determine the intake air-fuel ratio; for example, the intake air-fuel ratio is set equal to the initial value. If the operating event occurs, the initial value is adjusted differently from the output signal of the high-pass filter, specifically in the direction of the target value. Ultimately, in this case, the initial value does not correspond to the output signal but is modified in the direction of the target value; for example, it equals the target value. This approach allows even rapid changes in the second measured value, and thus the lambda value, to be reliably taken into account, resulting in a particularly high accuracy of the exhaust aftertreatment model.

[0037] A further development of the invention provides that the occurrence of an operating event is detected when a change in the input signal occurs in a defined direction, in particular only when changing in the defined direction, and / or when the input signal from a certain direction reaches a threshold value, and / or when a change in an operating parameter of the drive unit occurs. The occurrence of the operating event can be detected in different ways, and consequently, the output value can be adjusted.

[0038] In a first variant, the system is designed to detect the occurrence of an operational event and adjust the output value if the input signal changes in the defined direction. Specifically, the system only detects the occurrence of an operational event when the input signal changes in the defined direction, not when the input signal changes in the opposite direction. The defined direction refers specifically to a decrease in the input signal or the lambda value. Therefore, if the lambda value decreases, the output value is adjusted; however, no adjustment is made if the lambda value increases.

[0039] In a second variant, the system detects an operational event and consequently adjusts the output value if the input signal, particularly the lambda value, reaches the threshold from a specific direction. Therefore, it is necessary that, firstly, the input signal or lambda value reaches the threshold, and secondly, that this occurs from the specified direction. For example, the output value is only adjusted if the input signal or lambda value reaches the threshold from a direction of higher values, whereas it remains unchanged if the input signal reaches the threshold from a direction of lower values. A combustion air ratio greater than one, specifically at least 1.5, at least 1.75, or at least 2, is used as the threshold.

[0040] In a third variant, the system is designed to detect the occurrence of an operational event and adjust the output value if the operating parameter of the drive unit changes. The operating parameter preferably refers to the composition of the fuel-air mixture. Specifically, the output value is adjusted if the composition changes from a lean to a rich mixture, whereas it is not adjusted if the composition changes from a rich to a lean mixture.

[0041] Of course, it is possible to consider only one of the aforementioned conditions. However, it is also possible to detect the occurrence of the operational event if only one of several conditions is met, particularly if all conditions are met. Alternatively, it may be possible to require that several or even all of the aforementioned conditions be met for the operational event to be detected. The described procedure, in turn, achieves a particularly high degree of accuracy in determining the intake air-to-combustion air ratio.

[0042] A further development of the invention provides that the output value is adjusted only if the input signal changes in the defined direction by a specific amount. Thus, a minor change in the input signal is insufficient; the change must exceed a threshold. This ensures that even slight fluctuations or disturbances in the second measurement signal do not trigger the output value adjustment.

[0043] A further development of the invention provides that the output value is adjusted towards the target value by one of the following methods: setting the output value to the target value, adjusting a time constant of the high-pass filter, and writing the target value to a memory cell of the high-pass filter. According to the first variant, the high-pass filter continues to operate normally, but the output signal it provides is temporarily not used. Instead, the output value is not determined from the output signal, but rather set to the target value.

[0044] Alternatively, the filter's time constant is adjusted so that the input signal is reflected in the output signal as quickly as possible. Specifically, the time constant is set to a specific filter step size, ensuring that the output signal matches or corresponds to the input signal in the next filter step. For example, the filter's time constant is set to the smallest possible value, ideally the lowest possible value.

[0045] Another alternative is to write the target value into the filter's memory cell. The filter operates digitally and therefore has a memory cell in which a value necessary for the filter's operation is stored, in particular a value dependent on the lambda value and / or a value on which the determined intake air-fuel ratio depends. This value is overwritten with the target value. The memory cell is specifically designed so that writing the target value into it immediately aligns the filter's output signal with, or even matches, the target value. The described procedure enables particularly effective determination of the intake air-fuel ratio.

[0046] A further development of the invention provides that the lambda value is used as the setpoint. It is therefore intended to use the lambda value directly as the setpoint and to adjust the filter's output value, and thus the filter value, accordingly. This achieves the advantages already explained.

[0047] The invention further relates to a drive unit for a motor vehicle, in particular for carrying out the method according to the explanations in this description, wherein the drive unit has an exhaust gas generating drive unit and an exhaust gas aftertreatment device and is designed and configured to measure a first measured value by means of a first lambda probe upstream of the exhaust gas aftertreatment device and a second measured value by means of a second lambda probe downstream of the first lambda probe, wherein an 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.

[0048] The drive unit is also designed and configured to determine the intake air-fuel ratio from a lambda value derived from the second measured value and a filter value determined from the lambda value using a filter. It is provided that an input signal is supplied to the filter, and upon the occurrence of a specific operating event, an output value determined from an output signal of the filter is adjusted towards a target value. The advantages of such a drive unit design and procedure have already been mentioned. Both the drive unit and the method for operating it can be further developed as explained in this description, and reference is made to these explanations in this regard.

[0049] Furthermore, the invention relates to a computer program product comprising commands that cause the drive device to execute the described method as described herein. For the advantages and possible advantageous embodiments, reference is made to the description in its entirety.

[0050] The features and combinations of features described in the description, in particular those described in the following figure description and / or shown in the figures, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention, in particular the scope of the claims. Thus, embodiments that are not explicitly shown or explained in the description and / or the figures, but which emerge from or can be derived from the explained embodiments, particularly within the scope of the claims, are also to be considered as encompassed by the invention.

[0051] The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. The drawing shows: Fig. 1 a schematic representation of a drive system for a motor vehicle with a drive unit and an exhaust aftertreatment system, as well as Fig. 2 a diagram showing the curves for a combustion air ratio over time.

[0052] The Fig. Figure 1 shows a schematic representation of a drive unit 1, which includes an exhaust gas-generating drive unit 2 and an exhaust gas aftertreatment unit 3, here in the form of a vehicle catalyst. Fuel and fresh gas are supplied to the drive unit 2, forming a fuel-fresh gas mixture which react chemically to produce exhaust gas. The exhaust gas is fed to the exhaust gas aftertreatment unit 3 and flows through it in the direction of arrow 4.

[0053] Upstream of the exhaust aftertreatment system 3, a first measurement is taken using a first lambda sensor 5, and downstream of the exhaust aftertreatment system 3, a second measurement is taken using a second lambda sensor 6. These two measurements describe the residual oxygen content of the exhaust gas and the air-fuel ratio at the respective points.

[0054] Using the first measured value, a lambda controller 7 is operated, and using the second measured value, a trim controller 8 is operated. The output values ​​of both controllers 7 and 8 are calculated using a setpoint supplied via an input 9, specifically in a calculation module 10. The composition of the fuel-air mixture is determined from the result of this calculation.

[0055] Furthermore, the composition of the exhaust gas downstream of the exhaust aftertreatment device 3 is determined using an exhaust aftertreatment model. This is done for at least one exhaust gas component, but preferably for several exhaust gas components. The exhaust aftertreatment model comprises several exhaust aftertreatment sub-models; in the embodiment shown here, there are five exhaust aftertreatment sub-models. Each of the exhaust aftertreatment sub-models is used to calculate one of several sections 11 of the exhaust aftertreatment device 3. The sections 11 extend from an inlet 12 to an outlet 13 of the exhaust aftertreatment device 3 and are directly adjacent to one another. The sections 11 thus extend continuously and without interruption from the inlet 12 to the outlet 13.

[0056] For each of the sections 11, an inlet concentration and an inlet combustion engine ratio are determined at a respective inlet point 14. Using the respective exhaust aftertreatment sub-model, an outlet concentration of the former exhaust component is subsequently determined at a respective outlet point 15 of the corresponding section 11. Preferably, the inlet concentration for a more downstream section 11 is used as 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 aftertreatment device 3, and the outlet concentration of the exhaust aftertreatment device 3 is equal to the outlet concentration of the most downstream section 11.

[0057] The exhaust aftertreatment model, or each of its sub-models, determines a conversion rate for the respective exhaust gas component depending on the specific intake air-fuel ratio. This conversion rate is stored, for example, in a map or similar, for various intake air-fuel ratios. For instance, one or more of the following exhaust gas components are used: hydrocarbons, carbon oxides (especially carbon monoxide), hydrogen (especially molecular hydrogen), nitrogen oxides (especially nitrogen monoxide and / or nitrogen dioxide), and oxygen (especially molecular oxygen).

[0058] The respective inlet air-fuel ratio is preferably determined independently of the first measured value, and in particular solely from the second measured value. Thus, the inlet air-fuel ratio for each of the sections 11 is determined based on 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. The combustion air ratio thus determined is differentiated over time, and the inlet air-fuel ratio is determined as the sum of the combustion air ratio and the time derivative of the combustion air ratio. In particular, the inlet air-fuel ratio is determined by filtering the second measured value or the lambda value determined from the second measured value.

[0059] The Fig.Figure 2 shows a diagram in which curves 16, 17, and 18 are plotted over time. Curve 16 describes the lambda value determined from the second measured value, curve 17 a first value of the intake air-fuel ratio, which is determined by filtering the lambda value, and curve 18 a second value of the intake air-fuel ratio, which is also determined by filtering the lambda value but is modified depending on the occurrence of an operating event.

[0060] The term "operating event" refers in particular to a change in the direction of the lambda value, which occurs, for example, due to a change in an operating parameter of the drive unit 2, preferably due to a change in the composition of the fuel-air mixture. It can be seen that the first value of the intake air-fuel ratio, according to curve 17, reacts to the change in the lambda value with a significantly longer delay than the second value. Accordingly, it is advantageous to use the second value of the intake air-fuel ratio for operating the exhaust aftertreatment model. This yields particularly accurate results. REFERENCE MARK LIST: 1 Drive unit 2 Drive unit 3 Exhaust aftertreatment system 4 Arrow 5 1. Lambda sensor 6 2. Lambda sensor 7 Lambda controllers 8 trim controls 9 Entrance 10 Calculation module Section 11 12 Admission 13 Outlet 14 Entry point 15 Exit point 16 Course 17 Course 18 Course

Claims

[1] Method for operating a drive unit (1) for a motor vehicle, which has an exhaust gas-generating drive unit (2) and an exhaust gas aftertreatment device (3), 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 (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 as input variables an inlet concentration determined for an inlet point (14) and an inlet air-fuel ratio determined for the inlet point (14) are supplied, wherein the inlet air-fuel ratio is determined from a lambda value determined from the second measured value and a filter value determined from the lambda value by means of a filter,characterized by , that an input signal is supplied to the filter and, when a specific operating event occurs, an output value determined from an output signal of the filter is adjusted towards a target value. [2] Method according to claim 1, characterized by , that the inlet combustion air ratio is determined from a sum which contains the lambda value and the filter value, wherein the filter value is determined using the filter from a time derivative of the lambda value. [3] Method according to any one of the preceding claims, characterized by that a low-pass filter is used as the filter. [4] Method according to any one of the preceding claims, characterized by, that the occurrence of the operating event is detected when a change in the input signal occurs in a defined direction and / or the input signal from a certain direction reaches a threshold value and / or a change in an operating parameter of the drive unit (2) occurs. [5] Method according to any one of the preceding claims, characterized by , that the output value is only adjusted if the input signal changes in the defined direction by a certain amount. [6] Method according to any one of the preceding claims, characterized by , that the adjustment of the output value towards the target value is carried out using one of the following procedures: setting the output value to the target value, adjusting a time constant of the high-pass filter and writing the target value into a memory cell of the high-pass filter. [7] Method according to any one of the preceding claims, characterized by , that the lambda value is used as the default value. [8] Drive unit (1) for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive unit (1) has an exhaust gas generating drive unit (2) and an exhaust gas aftertreatment unit (3) and is designed and configured to measure a first measured value by means of a first lambda sensor (5) upstream of the exhaust gas aftertreatment unit (3) and a second measured value by means of a second lambda sensor (6) downstream of the first lambda sensor (5), and wherein an outlet concentration of at least one exhaust gas component downstream of the exhaust gas aftertreatment unit (3) 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,wherein the drive device (1) is also designed and configured to determine the inlet combustion air ratio from a lambda value determined from the second measured value and a filter value determined from the lambda value by means of a filter, characterized by , that an input signal is supplied to the filter and, when a specific operating event occurs, an output value determined from an output signal of the filter is adjusted towards a target value. [9] Computer program product comprising instructions that cause the drive device according to claim 8 to execute the method according to one or more of claims 1 to 7.

Images