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

Abstract

A method for operating a drive unit (1) for a motor vehicle is disclosed, which has an exhaust gas generating drive unit (2), an exhaust gas aftertreatment device (3) for aftertreatment of the exhaust gas and a lambda probe (6) arranged downstream of the exhaust gas aftertreatment device (3), 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, and the inlet combustion air ratio is determined from a measured value of the lambda probe (6).The provision is that the determination of the inlet combustion air ratio is carried out taking into account a temporal gradient determined on the basis of the measured value when the measured value lies in a first measurement range, and without influence of the temporal gradient of the measured value when the measured value lies in a second measurement range different from the first measurement range.

Description

[0001] 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 aftertreatment device for treating the exhaust gas, and a lambda sensor arranged downstream of the exhaust aftertreatment device. The exhaust concentration of at least one exhaust gas component downstream of the exhaust aftertreatment device is determined by means of an exhaust aftertreatment model. The model receives as input variables an inlet concentration determined for an inlet point and an inlet air-fuel ratio determined for the inlet point. The inlet air-fuel ratio is determined from a measured value of the lambda sensor. The invention further relates to a drive unit for a motor vehicle and a computer program.

[0002] For example, the prior art document DE 10 2023 201 660 B3 describes 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 for aftertreating the exhaust gas, wherein a first measured value is taken upstream of the exhaust gas aftertreatment device by means of a first lambda probe and a second measured value is taken 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.The plan is to determine the intake air-to-combustion air ratio from the second measurement independently of the first measurement.

[0003] Furthermore, document US 2013 / 0245919 A1 describes a method in which the amount of fuel injected is adjusted based on the oxidation state of a catalyst. The oxidation state is based on the reaction rates of a multitude of exhaust gas species along a catalyst longitudinal axis and a set of axially averaged mass balance and energy balance equations for a fluid phase and a washcoat of the catalyst.

[0004] 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.

[0005] 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 the determination of the intake air-fuel ratio is carried out when the measured value lies within a first measurement range, in particular according to a first relationship, taking into account a temporal gradient determined on the basis of the measured value, and when the measured value lies within a second measurement range different from the first measurement range, in particular according to a second relationship different from the first relationship, without influence of the temporal gradient of the measured value.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] As mentioned, 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 of the exhaust aftertreatment system or the vehicle's catalytic converter deviates from its operating temperature; in other words, 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.

[0013] To determine the pollutant emissions of the propulsion system, i.e., the quantity of at least one exhaust component released into the external environment, the exhaust aftertreatment model is used. This model simulates the conversion of the at least one exhaust component by the aftertreatment system. For this purpose, the inlet concentration of the at least one exhaust component present at the inlet point is fed into the exhaust aftertreatment model as a first input variable.

[0014] 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.

[0015] 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.

[0016] 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 could be possible to set the inlet air-fuel ratio equal to a combustion air ratio determined from the measurement of another lambda sensor upstream of the exhaust aftertreatment system. This measurement 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.

[0017] However, the reading from such an additional lambda sensor is typically subject to a comparatively large measurement error, especially if the additional 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 reading from the additional lambda sensor using a trim control based on a reading from the primary lambda sensor. The additional lambda sensor can also be referred to as the first lambda sensor, and the primary lambda sensor as the second lambda sensor. The first lambda sensor is located upstream of the exhaust aftertreatment system, whereas the second lambda sensor is located downstream of the exhaust aftertreatment system.

[0018] The first lambda sensor measures an initial reading, and the second lambda sensor measures a second reading. This second reading describes the air-fuel ratio, or the amount of residual oxygen, downstream of the first lambda sensor, more precisely, downstream of the exhaust aftertreatment system. For example, it is possible to adjust the second reading to a target value as part of a trim control system and then determine an offset applied to the first reading, particularly for lambda control based on the first reading.

[0019] However, it has been found that while the initial measurement after trim control is sufficiently accurate for lambda control, it is not necessarily accurate enough for the exhaust aftertreatment model. Furthermore, the wideband lambda sensor does not have ideal dynamic characteristics. This becomes apparent, for example, after engine braking, when, following a sudden change in the fuel-air mixture composition, the lambda sensor lags behind this change for a certain period. This leads to an error in the exhaust aftertreatment model.

[0020] Therefore, the intake air-fuel ratio is to be determined from the reading of the lambda sensor located downstream of the exhaust aftertreatment system, i.e., the aforementioned second lambda sensor. Specifically, the intake air-fuel ratio is to be 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.

[0021] In other words, the first measurement is completely disregarded when determining the inlet air-fuel ratio; only the second measurement is considered. This allows the inlet air-fuel ratio to be determined with such high accuracy that the exhaust aftertreatment model can be successfully implemented, and the outlet concentration accurately reflects the actual concentration of at least one exhaust component present at the outlet point.

[0022] However, the applicant surprisingly discovered that there is an operating range of the drive system in which this approach also leads to errors. This is primarily due to the fact that the exhaust aftertreatment system has an oxygen storage unit, which influences the residual oxygen content or the lambda value of the exhaust gas downstream of the exhaust aftertreatment system. A change in the oxygen storage unit's fill level can be detected based on the lambda sensor reading. In particular, the applicant found that different measurement ranges of the lambda sensor reading must be distinguished when determining the intake air-fuel ratio from the lambda sensor reading.

[0023] If the measured value lies within the first measurement range, the intake air-fuel ratio is preferably determined according to the first relationship, taking the time gradient into account. If, however, the measured value lies within the second measurement range, the second relationship is used to determine the intake air-fuel ratio; in any case, the time gradient has no influence. The two measurement ranges are distinct from each other; in particular, they do not overlap. The second measurement range lies outside the first measurement range, and vice versa.

[0024] When using the first relationship to determine the intake air-to-fuel ratio, the temporal gradient of the measured value is taken into account. However, when using the second relationship, the temporal gradient has no influence; in particular, it is not considered. The measurement ranges are specifically chosen such that the temporal gradient of the measured value is only considered when determining the intake air-to-fuel ratio if the oxygen reservoir is partially filled, i.e., only partially filled, and specifically if it is at least partially and at most only partially filled. If, on the other hand, the oxygen reservoir is completely empty or completely full, the temporal gradient of the measured value should have no influence on the intake air-to-fuel ratio.

[0025] For the first measurement range, the intake air-fuel ratio does not directly correspond to the combustion air-fuel ratio determined from the measured value; instead, a correction is applied. This correction involves determining the time gradient or time derivative of the combustion air-fuel ratio. Based on this, the intake air-fuel ratio is then determined, so that it is expressed as a function of at least the time gradient of the combustion air-fuel ratio. This allows the intake air-fuel ratio to be determined with high accuracy in a relatively simple manner.

[0026] If a switching lambda sensor or a binary lambda sensor is used, the measured value describes an electrical voltage and is therefore given in volts. For example, it is assumed that the oxygen storage tank of the exhaust aftertreatment system is completely full if the measured value is less than a first voltage. The first voltage is preferably at most 150 mV, at most 100 mV, or at most 75 mV. Conversely, it is assumed that the oxygen storage tank is completely full if the measured value is greater than a second voltage. The second voltage is preferably at least 750 mV, at least 800 mV, or at least 850 mV.

[0027] In other words, the first measurement range extends from the first voltage to the second voltage, for example, from 75 mV to 850 mV, from 100 mV to 800 mV, or from 150 mV to 750 mV. This means that if the measured value lies between these two ranges, the time gradient of the measured value is taken into account when determining the intake air-fuel ratio. However, if the measured value is lower than the first voltage or higher than the second voltage, the intake air-fuel ratio is determined without the influence of the time gradient. The gradient could be, for example, the time gradient of the lambda sensor's own measurement or a time gradient of a parameter derived from the measured value. This approach ensures high accuracy of the intake air-fuel ratio and, consequently, of the exhaust aftertreatment model.

[0028] A further development of the invention provides that a switching lambda sensor is used as the lambda probe. The other lambda probe can be in the form of a wideband lambda probe. While the wideband lambda probe has a comparatively broad measuring range, this is not the case for the switching lambda probe. The switching lambda probe is, for example, in the form of a single Nernst cell and can also be referred to as a voltage switching probe. The wideband lambda probe, 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 probe typically has a higher accuracy than the wideband lambda probe.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.

[0029] A further development of the invention provides that the second measurement range comprises several sub-ranges, each directly adjoining the first measurement range on opposite sides. The sub-ranges thus enclose the first measurement range between them. In particular, a first sub-range borders directly on a first boundary of the first measurement range, and a second sub-range borders directly on a second boundary of the first measurement range. The first boundary preferably limits the first measurement range in the direction of smaller values, and the second boundary in the direction of larger values. The division of the second measurement range into several sub-ranges enables reliable consideration of the described boundaries when determining the intake air-fuel ratio.

[0030] A further development of the invention provides that the determination of the intake air-fuel ratio from the lambda sensor reading is carried out in such a way that the intake air-fuel ratio assumes identical lambda values ​​for readings within the second measurement range. Thus, for readings within the second measurement range, the intake air-fuel ratio should be constant and should not change after the reading leaves the first measurement range. Preferably, different lambda values ​​are used for the different sub-ranges. For example, the intake air-fuel ratio is set to a first lambda value when a reading is present in the first sub-range, and to a second lambda value when a reading is present in the second sub-range, regardless of the actual reading.

[0031] For example, the first lambda value is λ > 1, and the second lambda value is λ < 1. Preferably, the first value is at least 1.01, at least 1.02, or at least 1.03. Additionally or alternatively, the second value is at most 0.99, at most 0.98, or at most 0.97. Due to the use of identical lambda values ​​under the aforementioned conditions, the time gradient of the measured value within the second measurement range is zero and is therefore not considered when determining the intake air-fuel ratio, thus not influencing it. This allows for a particularly simple calculation of the intake air-fuel ratio.

[0032] A further development of the invention provides that the measured value is converted into an air-fuel ratio using a probe characteristic curve, from which the intake air-fuel ratio is determined. The measured value is thus first converted into the air-fuel ratio using the probe characteristic curve. The probe characteristic curve is calibrated to the lambda probe and describes its behavior. In particular, the probe characteristic curve contains values ​​for the air-fuel ratio that are available for different measured values. The probe characteristic curve can be stored in any way, for example, using a mathematical relationship, a characteristic map, and / or a table. Only from the air-fuel ratio is the intake air-fuel ratio then determined.The use of the probe characteristic curve to convert the measured value into the air-fuel ratio is, on the one hand, feasible with low computational effort and, on the other hand, sufficiently accurate to operate the exhaust aftertreatment model based on the air-fuel ratio.

[0033] A further development of the invention provides that the probe characteristic curve is adjusted such that it contains different lambda values ​​for the air-fuel ratio for measured values ​​lying in the first measurement range and identical lambda values ​​for measured values ​​lying in the second measurement range. By adjusting the probe characteristic curve, the previously described procedure is implemented, namely that the air-fuel ratio assumes identical lambda values ​​for measured values ​​lying in the second measurement range. By adjusting the probe characteristic curve, the entire method can be implemented with low computational power; in particular, no case check is required to determine whether the measured value lies in the first or the second measurement range.

[0034] A further development of the invention provides that the intake air-fuel ratio is determined from the intake air-fuel ratio and the time gradient for the measured value lying in the first measurement range, and is set equal to the intake air-fuel ratio for the measured value lying in the second measurement range. Consequently, a case distinction is required. First, it is checked in which measurement range the measured value lies, and then the appropriate relationship for determining the intake air-fuel ratio is selected. According to the first relationship, the intake air-fuel ratio depends on the time gradient; for the second relationship, such a dependency does not exist; rather, the intake air-fuel ratio is independent of the time gradient. Such a procedure can be implemented with minimal effort.

[0035] A further development of the invention provides that the determination of the intake air-to-fuel ratio is always carried out based on the intake air-to-fuel ratio and the time gradient, regardless of the measured value. In this approach, the case distinction is omitted, and a relationship is always used whose input variables are always the intake air-to-fuel ratio and the time gradient. With this approach, it is necessary to ensure that the intake air-to-fuel ratio is set to constant values ​​when the measured value lies outside the first measurement range. Accordingly, the time gradient is always zero under this condition and has no influence on the intake air-to-fuel ratio. Such an approach can be implemented with particularly low computational effort.

[0036] A further development of the invention provides that the time gradient is applied with a correction factor describing the influence of the exhaust aftertreatment system and used to determine the inlet air-fuel ratio. Since the measured value is taken downstream of the inlet point or downstream of the exhaust aftertreatment system, the exhaust aftertreatment system significantly influences the measured value and thus the inlet air-fuel ratio determined from it. In particular, the inlet air-fuel ratio depends on the oxygen storage capacity of the

[0037] Exhaust aftertreatment system and / or the exhaust gas mass flow rate of the exhaust gas flowing through the exhaust aftertreatment system. For this reason, the time gradient of the air-fuel ratio is first applied to the correction factor before it is incorporated into the inlet air-fuel ratio. This further increases the accuracy of the exhaust aftertreatment model.

[0038] A further development of the invention provides that the correction factor is determined as a function of at least one of the following parameters: the oxygen storage capacity of the exhaust aftertreatment system, the exhaust gas mass flow rate, and a position parameter describing the location of the inlet. The oxygen storage capacity describes the ability of the exhaust aftertreatment system to temporarily store oxygen. Here, the oxygen storage capacity represents the maximum amount of oxygen that can be temporarily stored. The exhaust gas mass flow rate, on the other hand, describes the mass flow rate of the exhaust gas currently flowing through the exhaust aftertreatment system. The position parameter relates to the arrangement of the inlet, in particular relative to the exhaust aftertreatment system and / or relative to the lambda sensor.

[0039] The correction factor can be determined from the oxygen storage capacity, the exhaust gas mass flow rate, or both. Considering both parameters has a particularly significant impact on the accuracy of the exhaust aftertreatment model. Additionally or alternatively, the position parameter is used, especially if multiple sections of the exhaust aftertreatment system are modeled using the exhaust aftertreatment model.

[0040] A further development of the invention provides that the intake air-fuel ratio is determined, at least in the first measurement range, based on the combustion air-fuel ratio and the time gradient. Overall, the intake air-fuel ratio is thus a function of the combustion air-fuel ratio, which is incorporated into the intake air-fuel ratio multiple times: once directly and once in the form of the time gradient. Preferably, the intake air-fuel ratio is obtained as the sum of the combustion air-fuel ratio and the time gradient of the combustion air-fuel ratio, preferably with the correction factor applied. In this way, a particularly high accuracy of the intake air-fuel ratio is achieved, and consequently, a high accuracy of the exhaust aftertreatment model.

[0041] For example, the air-fuel ratio at the lambda sensor is first determined from the measured value, and then the intake air-fuel ratio is calculated using the time gradient of this air-fuel ratio. For example, the intake air-fuel ratio is calculated using the relationship λ E = k ⋅ dλ / dt + λ determined where λ E is the inlet air-to-air ratio, λ is the air-to-air ratio determined from the measured value, k is a correction factor and t is the time.

[0042] 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, in particular from the second measured value independently of the first measured value.

[0043] 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.

[0044] 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.

[0045] Using the respective exhaust aftertreatment sub-model, an outlet concentration for each outlet 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 the at least one exhaust gas component across the exhaust aftertreatment system. This allows for particularly high accuracy.

[0046] A further development of the invention provides that one of the inlet combustion air ratios is determined from the measured value by means of filtering. In principle, all inlet combustion air ratios are determined from the measured value, in particular from the second measured value and independently of the first measured value. Preferably, the procedure already described is used for at least one of the inlet combustion air ratios, so that the corresponding inlet combustion air ratio is determined at least temporarily using the time gradient of the combustion air ratio.

[0047] At least one other inlet combustion air ratio is determined from the measured value by filtering. It is particularly preferred to determine the combustion air ratio from the measured value, again using the probe characteristic curve. This combustion air ratio is then filtered, and the result of the filtering is used as the inlet combustion air ratio. A low-pass filter is particularly suitable for this purpose.

[0048] The intake air-to-combustion air ratio is preferably determined at least temporarily using the temporal gradient in the manner described, provided that the inlet point of the respective section is located upstream of the lambda sensor. Filtering, on the other hand, is used if the inlet point of the respective section is located downstream of the lambda sensor. This approach allows the described method to be used even when the lambda sensor is located not downstream of the exhaust aftertreatment system, but within the exhaust aftertreatment system itself.

[0049] 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, an exhaust gas aftertreatment device for aftertreatment of the exhaust gas and a lambda sensor arranged downstream of the exhaust gas aftertreatment device, and wherein the drive unit is provided and configured to determine an outlet concentration of at least one exhaust gas component downstream of the exhaust gas aftertreatment device 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, and to determine the inlet combustion air ratio from a measured value of the lambda sensor.

[0050] The drive device is also designed and configured to determine the inlet combustion air ratio when the measured value lies within a first measurement range, in particular according to a first relationship, taking into account a temporal gradient determined on the basis of the measured value, and when the measured value lies within a second measurement range different from the first measurement range, in particular according to a second relationship different from the first relationship, without influence of the temporal gradient of the measured value.

[0051] 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 the description, and reference is made to that description in this regard.

[0052] 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.

[0053] 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.

[0054] The invention is explained below with reference to the embodiments shown in the figures, without limiting the invention. The figures show: Figure 1 is a schematic representation of a drive unit for a motor vehicle with a drive unit and an exhaust aftertreatment device, and Figure 2 is a diagram in which an adapted probe characteristic of a lambda probe of the drive unit is shown.

[0055] The Figure 1 Figure 1 shows a schematic representation of a drive unit 1, which has an exhaust gas generating drive unit 2 and an exhaust gas aftertreatment unit 3, here in the form of a vehicle catalyst.

[0056] 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 aftertreatment system 3 and flows through it in the direction of arrow 4.

[0057] 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.

[0058] 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 the two controllers 7 and 8 are calculated with a setpoint supplied via an input 9, namely in a calculation module 10. The composition of the fuel-air mixture is determined from one of the results of this calculation.

[0059] 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, 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.

[0060] For each of the sections 11, an inlet concentration and an inlet air-fuel ratio are determined at a respective inlet point 14. Using the respective exhaust aftertreatment sub-model, an outlet concentration of the respective exhaust gas component is subsequently determined at a respective outlet point 15 of the corresponding section 11. Preferably, the inlet concentration for a further downstream section 11 is 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.

[0061] 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).

[0062] The respective inlet air-fuel ratio is not determined based on the first measurement, but rather from the second measurement, independently of the first. Thus, the inlet air-fuel ratio for each of the sections 11 is determined based on a measurement taken downstream of the respective inlet point 14. For this purpose, an air-fuel ratio is first determined from the second measurement, namely using a probe characteristic curve for the second lambda probe 6. The air-fuel ratio thus determined is differentiated over time, and the time gradient is multiplied by a correction factor. The inlet air-fuel ratio is obtained as the sum of the inlet air-fuel ratio and the result of multiplying the correction factor by the time gradient of the air-fuel ratio.

[0063] The correction factor is proportional to the oxygen storage capacity and inversely proportional to the exhaust gas mass flow rate. The position of each section 11 of the exhaust aftertreatment system 3 is taken into account in the correction factor. Thus, the correction factor is larger the further the inlet point 14 is from the second lambda sensor 6. For example, a position parameter included in the correction factor is one for the inlet 12 and zero for the outlet 13, and is determined by linear interpolation for the inlet points 14 located between the inlet 12 and the outlet 13. For the five sections 11 shown here, whose inlet points 14 are equidistant from each other, this results in position parameters of 1.0, 0.8, 0.6, 0.4, and 0.2. The respective position parameter is multiplied by the time gradient, for example, as a component of the correction factor.

[0064] The Figure 2Figure 1 shows a diagram depicting a modified sensor characteristic curve 16. The combustion air ratio is plotted against a measured value from the second lambda sensor 6, expressed as a voltage. It is evident that the sensor characteristic curve 16 is variable within a range of the measured value from the second lambda sensor 6, i.e., between the voltages U1 and U2. This range between the measured values ​​U1 and U2 represents a first measurement range. Outside the first measurement range lies a second measurement range, which here consists of two sub-ranges: a first sub-range for U < U1 and a second sub-range for U > U2.

[0065] In the second measurement range, i.e., in both the first and second sub-ranges, the probe characteristic curve exhibits a constant profile, independent of the actual measured value U. The lambda value exhibited by the probe characteristic curve 16 in the second measurement range depends on the respective sub-range. Specifically, it is stipulated that for U ≤ U₁, the relationship λ = λ₁ holds, and for U ≥ U₂, the relationship λ = λ₂ holds. In the first measurement range, i.e., for U₁ < U < U₂, λ = f(U) applies; thus, the lambda value is a function of the measured value. This approach enables a particularly simple determination of the intake air-fuel ratio. REFERENCE MARK LIST:

[0066] 1 Drive unit 2 Drive unit 3 Exhaust aftertreatment unit 4 Arrow 51. Lambda probe 62. Lambda probe 7 Lambda controller 8 Trim controller 9 Input 10 Calculation module 11 Section 12 Inlet 13 Outlet 14 Inlet point 15 Outlet point 16 Probe characteristic curve

Claims

1. Method for operating a drive unit (1) for a motor vehicle, which has an exhaust gas generating drive unit (2), an exhaust gas aftertreatment device (3) for aftertreatment of the exhaust gas and a lambda sensor (6) arranged downstream of the exhaust gas aftertreatment device (3), 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, and the inlet combustion air ratio is determined from a measured value of the lambda sensor (6), characterized by the fact thatThe determination of the inlet combustion air ratio is carried out when the measured value lies in a first measurement range, taking into account a temporal gradient determined from the measured value, and when the measured value lies in a second measurement range different from the first measurement range, without influence of the temporal gradient of the measured value.

2. Method according to claim 1, characterized by the fact that A switching lambda sensor is used as the lambda probe (6).

3. Method according to any one of the preceding claims, characterized by the fact that the second measurement range has several sub-ranges that directly adjoin the first measurement range on opposite sides.

4. Method according to any one of the preceding claims, characterized by the fact thatThe determination of the inlet air-fuel ratio from the measured value of the lambda probe (6) is carried out in such a way that the air-fuel ratio assumes identical lambda values ​​for measured values ​​lying in the second measuring range.

5. Method according to any one of the preceding claims, characterized by the fact that the measured value is converted into a combustion air ratio using a probe characteristic curve (16), from which the inlet combustion air ratio is determined.

6. Method according to any one of the preceding claims, characterized by the fact that the probe characteristic curve (16) is adjusted such that it contains different lambda values ​​for the air-fuel ratio for measured values ​​in the first measurement range and identical lambda values ​​for measured values ​​in the second measurement range.

7. Method according to any of the preceding claims, characterized by the fact thatThe inlet air ratio is determined from the combustion air ratio and the time gradient for the measured value lying in the first measurement range, and is set equal to the combustion air ratio for the measured value lying in the second measurement range.

8. Method according to any one of the preceding claims, characterized by the fact that The determination of the inlet combustion air ratio is always carried out based on the combustion air ratio and the time gradient, regardless of the measured value.

9. 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) comprises an exhaust gas generating drive unit (2), an exhaust gas aftertreatment unit (3) for aftertreatment of the exhaust gas and a lambda sensor (6) arranged downstream of the exhaust gas aftertreatment unit (3), and wherein the drive unit (1) is provided and configured to determine an outlet concentration of at least one exhaust gas component downstream of the exhaust gas aftertreatment unit (3) 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, and the inlet combustion air ratio is determined from a measured value of the lambda sensor (6), characterized by the fact thatThe drive system (1) is also designed and configured to determine the inlet combustion air ratio when the measured value lies in a first measurement range, taking into account a temporal gradient determined on the basis of the measured value, and when the measured value lies in a second measurement range different from the first measurement range, without the influence of the temporal gradient of the measured value.

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

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