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

Abstract

The invention relates to a method for operating a drive unit for a motor vehicle, which comprises an exhaust gas-generating drive unit, an exhaust gas aftertreatment device (1) for treating the exhaust gas, and a lambda sensor (3) arranged upstream of the exhaust gas aftertreatment device (1). It is provided that a combustion air ratio for exhaust gas present downstream of the lambda sensor (3) is determined from a measured value of the lambda sensor (3) by means of a signal filter having at least one linear time-invariant transfer element, using a filter coefficient determined as a function of temperature. The invention further relates to a drive unit 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, an exhaust gas aftertreatment device for treating the exhaust gas, and a lambda sensor arranged upstream of the exhaust gas aftertreatment device. The invention further relates to a drive unit for a motor vehicle and a computer program product.

[0002] For example, the prior art document EP 1 388 659 B1 describes a control unit for regulating the air-fuel ratio of an internal combustion engine, comprising: a first exhaust gas sensor for detecting the oxygen concentration of the exhaust gas; a first decimation filter connected to the first exhaust gas sensor to eliminate chemical noise contained in an output signal of the first exhaust gas sensor; and a control unit connected to the first decimation filter, wherein the control unit is configured to determine a manipulated variable for adjusting the air-fuel ratio such that an output value from the first decimation filter converges to a setpoint.

[0003] The first decimation filter further comprises: a first oversampler for oversampling the output signal of the first exhaust gas sensor in a shorter cycle than the cycle used to determine the manipulated variable; a first low-pass filter for smoothing the oversampled value; and a first down-sample button for re-sampling the smoothed value in the cycle used to determine the manipulated variable, in order to output the re-sampled value. The re-sampled value represents the output signal of the first exhaust gas sensor from which the chemical noise has been removed.

[0004] Further state of the art is known from publications US 6,006,153 and US 2010 / 0077728 A1.

[0005] The object of the invention is to propose a method for operating a drive unit for a motor vehicle which has advantages over known methods, in particular enabling a reliable determination of the combustion air ratio, preferably for modeling the exhaust aftertreatment device using an exhaust aftertreatment model.

[0006] 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 a combustion air ratio for exhaust gas present downstream of the lambda sensor is determined from a measured value of the lambda sensor by means of a signal filter having at least one linear time-invariant transfer element, using a filter coefficient determined as a function of temperature.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] The exhaust aftertreatment system is preferably designed as a vehicle catalyst, in particular as a three-way catalyst, oxidation catalyst, NOₓ storage catalyst, or SCR catalyst. The vehicle catalyst may be integrated into a particulate filter, in particular 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 or the vehicle catalyst, as well as on the temperature of the exhaust aftertreatment system.

[0012] 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 dynamics, 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.

[0013] 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. Specifically, the conversion efficiency decreases the greater the temperature difference between the exhaust aftertreatment system or the vehicle's catalytic converter and its operating temperature—that is, the greater the absolute difference between the temperatures. The temperature of the exhaust aftertreatment system or the vehicle's catalytic converter refers, for example, to the temperature of a ceramic honeycomb structure coated with the catalytic material.

[0014] The combustion air-fuel ratio, determined by a lambda sensor, is one of the parameters used to operate the drive unit. The lambda sensor is located upstream of the exhaust aftertreatment system; the exhaust gas flowing past or over the lambda sensor then flows through the exhaust aftertreatment system. The lambda sensor determines the combustion air-fuel ratio upstream of the exhaust aftertreatment system. However, to determine the exhaust gas composition with high accuracy, particularly when using the exhaust aftertreatment model, it is necessary to determine the combustion air-fuel ratio not only at the lambda sensor but also downstream of it, specifically within the exhaust aftertreatment system itself, or preferably directly downstream of it.

[0015] This has not been feasible to date, or at best only with considerable effort. However, the applicant has surprisingly discovered that the air-fuel ratio downstream of the lambda sensor can be determined with sufficiently high accuracy using the signal filter. The signal filter comprises at least one linear time-invariant transfer element. Naturally, the signal filter can also include several such transfer elements. Wherever this description refers to the transfer element or at least one transfer element, the explanations are always equivalent. Explanations concerning the transfer element are therefore applicable to the at least one transfer element, and explanations concerning the at least one transfer element are applicable to the transfer element.In the case of multiple transfer elements, the explanations relating to the transfer element or at least one transfer element are applicable to each of the multiple transfer elements.

[0016] The signal filter is characterized by one or more filter coefficients. The filter coefficient, in particular, describes the transfer element. If multiple transfer elements are present, they can use the same or different filter coefficients. In any case, the filter coefficient is determined as a function of temperature. This means that the filter coefficient(s) are a function of temperature. Specifically, the filter coefficient is proportional to the temperature. Temperature can refer, for example, to the temperature of the exhaust gas or the temperature of the exhaust aftertreatment system, especially the temperature of the ceramic body. The temperature is determined, for example, using a temperature model for the exhaust aftertreatment system or by means of the exhaust aftertreatment model.Alternatively, the temperature can also be measured. Using the signal filter to determine the air-fuel ratio in the exhaust gas downstream of the lambda sensor makes this possible with particularly low computational effort and yet high accuracy.

[0017] A further development of the invention provides that the filter coefficient is additionally determined as a function of the exhaust gas flow rate and / or the oxygen storage capacity of the exhaust aftertreatment system. Preferably, the filter coefficient is inversely proportional to the exhaust gas flow rate and / or inversely proportional to the oxygen storage capacity. Particularly preferably, the temperature, the exhaust gas flow rate, and the oxygen storage capacity are all incorporated into the filter coefficient. For this purpose, it is possible, for example, to determine a partial coefficient from each of the aforementioned quantities and to combine the partial coefficients by multiplication to obtain the filter coefficient.Thus, a first sub-coefficient is determined as a function of temperature, a second sub-coefficient as a function of exhaust gas flow rate, and a third sub-coefficient as a function of oxygen storage capacity. The filter coefficient is then obtained by multiplying the first sub-coefficient by the second sub-coefficient and the third sub-coefficient. This further improves the accuracy.

[0018] A further development of the invention provides that a first-order lag element (PT1 element) is used as at least one of the transfer elements. The PT1 element is a linear time-invariant transfer element with proportional transfer characteristics and a first-order delay. The transfer function of the PT1 element is given by... G s = K / 1 + T ⋅ s , where K is a transfer constant or gain factor and T is the time constant. Preferably, the gain factor is chosen to be constant and the time constant corresponds to the aforementioned filter coefficient; thus, the time constant is determined as a function of at least the temperature. Such a procedure enables a highly accurate determination of the combustion air ratio.

[0019] A further development of the invention provides that a signal filter with multiple transfer elements, in particular multiple transfer elements connected in series, is used as the signal filter. The signal filter thus has not just one transfer element, but several transfer elements, which are preferably connected in series. This means that an input signal is supplied to a first of the transfer elements at an input, whereupon the first transfer element provides an output signal at an output. This output signal is used as an input signal for a second transfer element. This can be repeated for any number of transfer elements. An input signal of the signal filter is used as the input signal for the first transfer element. An output signal of the last, for example, the second, transfer element is used as the output signal of the signal filter.

[0020] Preferably, the transfer elements are all of the same type, and preferably the multiple transfer elements are configured as first-order PT1 elements. In this case, the signal filter consists exclusively of first-order PT1 elements. The signal filter is thus an nth-order signal filter, in particular a second-order signal filter. This also serves to achieve particularly high accuracy in determining the air-fuel ratio.

[0021] A further development of the invention provides that the outlet concentration of at least one exhaust gas component downstream of the exhaust aftertreatment device is determined using an exhaust aftertreatment model. This model receives as input variables an inlet concentration determined for an inlet point and an inlet air-fuel ratio determined for the inlet point, with the air-fuel ratio being used as the inlet air-fuel ratio for the exhaust aftertreatment device. The exhaust aftertreatment model is used to determine the pollutant emission of the propulsion system, i.e., the quantity of the at least one exhaust gas component discharged into the ambient environment. The exhaust aftertreatment model simulates the conversion of the at least one exhaust gas component by the exhaust aftertreatment device.For this purpose, the exhaust aftertreatment model is fed the inlet concentration of at least one exhaust component present at the inlet point as a first input variable.

[0022] 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.

[0023] 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.

[0024] 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, the inlet air-fuel ratio could be set to the same value as the combustion air-fuel ratio determined from the lambda sensor reading upstream of the exhaust aftertreatment system. This reading describes the combustion air-fuel ratio present in the exhaust gas upstream of the aftertreatment system, or rather, the amount of residual oxygen present in the exhaust gas at that point. The combustion air-fuel ratio determined in this manner provides a precise basis for running the exhaust aftertreatment model.

[0025] A further development of the invention provides that the exhaust aftertreatment model comprises several exhaust aftertreatment sub-models for modeling different sections of the exhaust aftertreatment device, wherein each of the exhaust aftertreatment sub-models is supplied as input variables one of several inlet concentrations comprising the inlet concentration and one of several inlet combustion air ratios comprising the inlet combustion air ratio, wherein the respective inlet concentration and the respective inlet combustion air ratio are determined for one of several inlet points comprising the inlet point and each of the inlet combustion air ratios is determined from the measured value of the lambda probe by means of a respective signal filter using the filter coefficient determined as a function of the temperature.

[0026] This means that the exhaust aftertreatment system is not considered as a whole, but rather divided into several sections. These sections preferably extend from one end to the other and are particularly preferably directly adjacent to each other. For example, the exhaust aftertreatment system is divided into at least two, at least three, at least four, or—preferably—at least five sections. A separate exhaust aftertreatment sub-model exists for each of these sections, and the exhaust aftertreatment sub-models of the multiple sections together form the complete exhaust aftertreatment model.

[0027] Each of the exhaust aftertreatment sub-models has one of the inlet concentrations and one of the inlet combustion air ratios as input variables. The inlet concentration mentioned at the beginning is a component of these multiple inlet concentrations, and the inlet combustion air ratio mentioned is a component of these multiple inlet combustion air ratios. The inlet concentration and the inlet combustion air ratio for each section are determined for a specific inlet point within that section.

[0028] Using the respective exhaust aftertreatment sub-model, an outlet concentration for each outlet point of the respective section is determined from the respective inlet concentration and the respective inlet air-fuel ratio. Preferably, the outlet concentration of a flow-technically preceding section is used as the inlet concentration of a flow-technically immediately following section. The exhaust aftertreatment model is thus based on a stepwise calculation of the outlet concentration of at least one exhaust gas component across the exhaust aftertreatment system. This allows for particularly high accuracy.

[0029] The intake air mixture for the several sections is determined from the lambda sensor reading, specifically using the respective signal filter. A separate signal filter is provided for each section, and its filter coefficient is determined as a function of temperature. Preferably, the temperature of the respective section is used. This can be determined, for example, using a temperature model.

[0030] The signal filters of the sections are preferably connected in series. This means that the signal filter of the first section, which is located furthest upstream in terms of flow, receives the measured value from the lambda sensor, or the combustion air ratio determined from it, as its input signal. An output signal from this signal filter is then fed as an input signal to a signal filter of the second section, which follows the first in terms of flow, and so on, until the respective inlet combustion air ratio is available for all sections. In other words, the signal filters of the exhaust aftertreatment sub-models are intended to be used in series, so that at least one of the signal filters uses an output signal from another of the signal filters as its input signal. This achieves high accuracy.

[0031] A further development of the invention provides that a further exhaust aftertreatment device is arranged upstream of the exhaust aftertreatment device, in particular upstream of the lambda sensor, and a further lambda sensor is arranged upstream of the further exhaust aftertreatment device, wherein the measured value of the lambda sensor and a measured value of the further lambda sensor are used to perform lambda control. In addition to the exhaust aftertreatment device and the lambda sensor, the further exhaust aftertreatment device and the further lambda sensor are thus present, which are arranged upstream of the exhaust aftertreatment device and preferably upstream of the lambda sensor.

[0032] The secondary exhaust aftertreatment system can be designed analogously to the primary exhaust aftertreatment system, and in particular, it may be a vehicle catalytic converter. For example, the lambda sensor is fluidically positioned between the primary exhaust aftertreatment system and the secondary exhaust aftertreatment system. From a fluid dynamics perspective, the secondary lambda sensor is located on the side of the secondary exhaust aftertreatment system facing away from the primary lambda sensor, so that the secondary exhaust aftertreatment system is fluidically situated between the primary lambda sensor and the secondary lambda sensor. Exhaust gas from the engine therefore flows in the following sequence: secondary lambda sensor, secondary exhaust aftertreatment system, primary lambda sensor, and secondary exhaust aftertreatment system.

[0033] The exhaust aftertreatment system can also be referred to as the first exhaust aftertreatment system, and the subsequent exhaust aftertreatment system as the second exhaust aftertreatment system. Similarly, the lambda sensor can be referred to as the first lambda sensor, and the subsequent lambda sensor as the second lambda sensor. Using the first lambda sensor, a first air-fuel ratio is determined fluid-measured between the second and first exhaust aftertreatment systems, and using the second lambda sensor, a second air-fuel ratio is determined upstream of the second exhaust aftertreatment system.

[0034] The first air-fuel ratio is the air-fuel ratio present in the exhaust gas downstream of the second lambda sensor, specifically downstream of the second exhaust aftertreatment system. The second air-fuel ratio corresponds to the air-fuel ratio in the exhaust gas upstream of the second exhaust aftertreatment system, or, in terms of flow dynamics, between the engine and the second exhaust aftertreatment system.

[0035] The first and second air-fuel ratios are preferably used for lambda control and trim control. In particular, the composition of the fuel-air mixture is adjusted based on the second air-fuel ratio, whereas the first air-fuel ratio is used to correct the second air-fuel ratio or a setpoint to which the second air-fuel ratio is adjusted during lambda control, within the framework of trim control.

[0036] In principle, it may be possible to adjust the composition of the fuel-air mixture solely based on the first combustion air ratio or solely based on the second combustion air ratio, i.e., without considering the other combustion air ratio. In either case, the respective combustion air ratio is adjusted to the corresponding target value. For this purpose, it is specifically intended that the composition of the fuel-air mixture be adjusted so that the respective combustion air ratio changes towards the target value, in particular until it reaches the target value. For example, the respective combustion air ratio is regulated by adjusting the composition of the fuel-air mixture to the target value.

[0037] However, it is particularly preferred to use both the first and second air-fuel ratios to adjust the composition of the fuel-air mixture. In this case, both air-fuel ratios are preferably set to a respective target value. Specifically, it is therefore provided that the first air-fuel ratio is set to a first target value and the second air-fuel ratio to a second target value, namely by appropriately adjusting the composition of the fuel-air mixture.

[0038] A further development of the invention provides that the exhaust aftertreatment device is a first exhaust aftertreatment device and the air-fuel ratio is a first air-fuel ratio, wherein a second exhaust aftertreatment device is located upstream of the lambda sensor, and a second air-fuel ratio for exhaust gas present upstream of the lambda sensor is determined by gradient calculation from the lambda sensor reading. Using the lambda sensor or the measured value, the air-fuel ratio is thus determined not only downstream of the lambda sensor, particularly in the first exhaust aftertreatment device, but also upstream of the lambda sensor, particularly in the second exhaust aftertreatment device. For this purpose, a gradient is calculated from the lambda sensor reading.The gradient is, for example, the time gradient of the measured value of the lambda sensor itself, or a time gradient of a quantity determined from the measured value.

[0039] For example, the air-fuel ratio at the lambda sensor is first determined from the measured value, and then the second air-fuel ratio is calculated using the time gradient of this air-fuel ratio. For example, the second air-fuel ratio is calculated using the relationship λ 1 = k ⋅ dλ 2 / dt + λ 2 The values ​​are determined where λ₁ is the first air-fuel ratio, λ₂ is the second air-fuel ratio, k is a correction factor, and t is time. Preferably, the second air-fuel ratio is used for a further exhaust aftertreatment model, by means of which the further exhaust aftertreatment device is modeled.

[0040] A further development of the invention provides for the use of a switching lambda sensor. Another lambda sensor can be in the form of a wideband lambda sensor. While the wideband lambda sensor has a comparatively broad measuring range, this is not the case for the switching lambda sensor. The switching 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 wideband 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-fuel ratio of λ = 1 is measured by means of 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 actual combustion air-fuel ratio present in the exhaust gas. The switching lambda sensor typically exhibits higher accuracy than the wideband lambda sensor.Accordingly, extremely high accuracy can be achieved by using the jump lambda probe to measure the measured value, from which the air-fuel ratio is subsequently determined.

[0041] The invention further relates to a drive unit for a motor vehicle, in particular for carrying out the method as explained in this description, wherein the drive unit comprises an exhaust gas-generating drive unit, an exhaust gas aftertreatment device for treating the exhaust gas, and a lambda sensor arranged upstream of the exhaust gas aftertreatment device. The drive unit is designed and configured to determine an air-fuel ratio for exhaust gas present downstream of the lambda sensor from a measured value of the lambda sensor by means of a signal filter having at least one linear time-invariant transfer element, using a filter coefficient determined as a function of temperature.

[0042] The advantages of such a drive system design and such a procedure have already been mentioned. Both the drive system and the method for operating it may be further developed as explained in this description, and reference is made to those explanations.

[0043] 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.

[0044] 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, are not only usable 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.

[0045] The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. The drawing shows: Figure 1 shows a schematic representation of an area of ​​a drive device, more precisely an exhaust aftertreatment device, and Figure 2 shows several diagrams in which combustion air ratios in different sections of the exhaust aftertreatment device as well as partial filter coefficients and a filter coefficient of a signal filter used to determine the combustion air ratio are plotted over time.

[0046] The Figure 1Figure 1 shows a highly schematic representation of a section of a drive unit that includes an exhaust gas-generating drive system, specifically an exhaust aftertreatment unit 1 of the drive unit. Fuel and fresh gas are supplied to the drive system, forming a fuel-fresh gas mixture that reacts chemically to produce exhaust gas. The exhaust gas is fed to the exhaust aftertreatment unit 1 and flows through it in the direction of arrow 2. Upstream of the exhaust aftertreatment unit 1, a lambda sensor 3 measures the air-fuel ratio. This measurement describes the residual oxygen content of the exhaust gas, or the air-fuel ratio at the lambda sensor 3.

[0047] Based on the measured value from lambda sensor 3, the composition of the exhaust gas downstream of the exhaust aftertreatment device 1 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, five exhaust aftertreatment sub-models. Each of the exhaust aftertreatment sub-models is used to calculate one of several sections 4 of the exhaust aftertreatment device 1. The sections 4 extend from an inlet 5 to an outlet 6 of the exhaust aftertreatment device 1 and are directly adjacent to each other. The sections 4 thus extend continuously and without interruption from the inlet 5 to the outlet 6.

[0048] For each of the sections 4, an inlet concentration and an inlet air-fuel ratio are determined at a respective inlet point 7. Using the respective exhaust aftertreatment sub-model, an outlet concentration of the respective exhaust gas component is subsequently determined at a respective outlet point 8 of the corresponding section 4. Preferably, the inlet concentration for a further downstream section 4 is equal to the outlet concentration of the immediately upstream section 4. The inlet concentration of the most upstream section 4 is equal to the inlet concentration of the exhaust aftertreatment device 1, and the outlet concentration of the exhaust aftertreatment device 1 is equal to the outlet concentration of the most downstream section 4.

[0049] 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).

[0050] The respective intake air-fuel ratio is calculated from the measured value of lambda sensor 3. Thus, the intake air-fuel ratio for each of the sections 4 is determined based on the measured value taken upstream of the exhaust aftertreatment system 1. For this purpose, a signal filter is used for each of the sections 4, which has at least one linear time-invariant transfer element. A filter coefficient of the signal filter or the transfer element is determined as a function of temperature. Preferably, the filter coefficient is additionally dependent on the exhaust gas flow rate through the exhaust aftertreatment system 1 and / or the oxygen storage capacity of the exhaust aftertreatment system 1. The latter is preferably determined as a function of the aging state of the exhaust aftertreatment system 1.

[0051] Each of the signal filters preferably has several transfer elements, in particular several PT1 elements connected in series. The signal filters and their transfer elements are also connected in series for sections 4. Thus, for a first of the sections 4, the signal filter is a second-order signal filter, for a second of the sections 4, a fourth-order signal filter, for a third of the sections 4, a sixth-order signal filter, and so on.

[0052] The Figure 2The diagram shows several diagrams plotting combustion air ratios for the various sections 4, several partial filter coefficients, and one filter coefficient over time. The first diagram at the top displays curves 9, 10, 11, 12, 13, and 14. Curve 9 represents the measured value from lambda sensor 3 and the combustion air ratio derived from it, which is used as the inlet combustion air ratio for the first section 4. Curve 10 describes the inlet combustion air ratio for the second section 4, curve 11 for the third section 4, curve 12 for the fourth section 4, curve 13 for the fifth section 4, and curve 14 at the outlet 6 of the exhaust aftertreatment system 1.

[0053] In a second diagram, curve 15 shows a partial filter coefficient determined over time based on temperature; in a third diagram, curve 16 shows a partial filter coefficient determined over time based on exhaust gas flow rate; in a fourth diagram, curve 17 shows a partial filter coefficient determined over time based on the oxygen storage capacity of the exhaust aftertreatment system 1; and in a fifth diagram, curve 18 shows the filter coefficient over time. The filter coefficient of curve 18 is obtained by multiplying the partial filter coefficients according to curves 15, 16, and 17. Using the described procedure, the air-fuel ratio in each of sections 4, and thus the concentration of at least one exhaust gas component, can be determined with high accuracy. REFERENCE MARK LIST:

[0054] 1 Exhaust aftertreatment system 2 Arrow 3 Lambda probe 4 Section 5 Inlet 6 Outlet 7 Inlet point 8 Outlet point 9 Pathway 10 Pathway 11 Pathway 12 Pathway 13 Pathway 14 Pathway 15 Pathway 16 Pathway 17 Pathway 18 Pathway

Claims

1. Method for operating a drive unit for a motor vehicle, which has an exhaust gas generating drive unit, an exhaust gas aftertreatment device (1) for aftertreatment of the exhaust gas and a lambda probe (3) arranged upstream of the exhaust gas aftertreatment device (1), characterized by the fact that A combustion air ratio for exhaust gas present downstream of the lambda probe (3) is determined from a measured value of the lambda probe (3) by means of a signal filter having at least one linear time-invariant transfer element using a filter coefficient determined as a function of temperature.

2. Method according to claim 1, characterized by the fact that the filter coefficient is additionally determined depending on the exhaust gas flow rate and / or the oxygen storage capacity of the exhaust gas aftertreatment device (1).

3. Method according to any one of the preceding claims, characterized by the fact thatwhen at least one transfer element is a PT1 element.

4. Method according to any one of the preceding claims, characterized by the fact that A signal filter with multiple transfer elements is used as a signal filter.

5. Method according to any one of the preceding claims, characterized by the fact that an outlet concentration of at least one exhaust gas component of the exhaust gas downstream of the exhaust gas aftertreatment device (1) is determined by means of an exhaust gas aftertreatment model to which an inlet concentration determined for an inlet point (7) and an inlet combustion air ratio determined for the inlet point (7) are supplied as input variables, wherein the combustion air ratio is used as the inlet combustion air ratio for the exhaust gas aftertreatment device (1).

6. Method according to any one of the preceding claims, characterized by the fact thatThe exhaust aftertreatment model comprises several exhaust aftertreatment sub-models for modeling different sections (4) of the exhaust aftertreatment device (1), wherein each of the exhaust aftertreatment sub-models is supplied as input variables one of several inlet concentrations comprising the inlet concentration and one of several inlet combustion air ratios comprising the inlet combustion air ratio, wherein the respective inlet concentration and the respective inlet combustion air ratio are determined for one of several inlet points (7) comprising the inlet point (7) and each of the inlet combustion air ratios is determined from the measured value of the lambda probe (3) by means of a respective signal filter using a filter coefficient determined as a function of the temperature.

7. Method according to any of the preceding claims, characterized by the fact thatUpstream of the exhaust aftertreatment device (1) a further exhaust aftertreatment device and upstream of the further exhaust aftertreatment device a further lambda probe is arranged, wherein the measured value of the lambda probe and a measured value of the further lambda probe are used to carry out lambda control.

8. Method according to any one of the preceding claims, characterized by the fact that the exhaust aftertreatment device (1) is a first exhaust aftertreatment device and the air-fuel ratio is a first air-fuel ratio, wherein a second exhaust aftertreatment device is located upstream of the lambda probe (3) and a second air-fuel ratio for exhaust gas located upstream of the lambda probe (3) is determined by gradient formation from the measured value of the lambda probe.

9. Drive unit for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive unit has an exhaust gas generating drive unit, an exhaust gas aftertreatment device (1) for aftertreatment of the exhaust gas and a lambda probe (3) arranged upstream of the exhaust gas aftertreatment device (1), characterized by the fact that The drive device is designed and configured to determine a combustion air ratio for exhaust gas downstream of the lambda probe (3) from a measured value of the lambda probe (3) by means of a signal filter having at least one linear time-invariant transfer element using a filter coefficient that is dependent on a temperature.

10. Computer program product comprising commands that cause the drive device according to claim 9 to execute the method according to one or more of claims 1 to 8.

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