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 unit (4) for aftertreating the exhaust gas, wherein a first measured value is taken by means of a first lambda sensor (6) upstream of the exhaust gas aftertreatment unit (4) and a second measured value is taken by means of a second lambda sensor (7) downstream of the exhaust gas aftertreatment unit (4). It is provided that a combustion air ratio is determined from the second measured value, taking into account a correction value determined as a function of the first measured value. 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 aftertreatment device for treating the exhaust gas, wherein a first measured value is taken by means of a first lambda sensor upstream of the exhaust aftertreatment device and a second measured value is taken by means of a second lambda sensor downstream of the exhaust aftertreatment device, wherein a combustion air ratio is determined from the second measured value, taking into account a correction value determined as a function of the first measured value. The invention further relates to a drive unit for a motor vehicle and a computer program product.

[0002] For example, the prior art includes the publication DE 10 2018 216 980 A1.This describes a method for controlling the filling of an exhaust gas component storage tank of a catalyst in the exhaust gas of an internal combustion engine, in which a first catalyst model is supplied with signals from a first exhaust gas probe extending upstream of the catalyst into the exhaust gas stream and detecting a concentration of the exhaust gas component, in addition to other signals, and an actual fill level of the exhaust gas component storage tank is determined, whereby a lambda setpoint is generated, a predetermined target fill level is converted into a base lambda setpoint, a deviation of the actual fill level from the predetermined target fill level is determined and processed by a fill level control into a lambda setpoint correction value, a sum of the base lambda setpoint and the lambda setpoint correction is calculated and the sum is used to generate a correction value with which a fuel metering to at least one combustion chamber of the internal combustion engine is influenced.

[0003] Furthermore, the publication DE 10 2015 117 530 B 4 describes a system for the aftertreatment of an exhaust gas flow, which includes: a first NO x -Sensor configured to provide an initial NO x -concentration value; and a computer-based processor device; wherein the first NO x The sensor is configured to also monitor a first lambda value in the exhaust gas flow. It is intended that the first NO x -Sensor upstream of a lean NO x -trap device is arranged; wherein the system has a second NO x -Sensor downstream of the lean NO x -Trap device and upstream of an SCRF device, wherein the second NO x -Sensor is configured to provide a second lambda value and a second NO value x -Concentration value in the exhaust gas flow downstream of the lean NOₓ x-to monitor trap device; wherein the computer-based processor device is configured to calibrate the monitored first lambda value with respect to the presence of H2; and wherein the computer-based processor device is further configured to monitor the first NO x -to calibrate the concentration value, which includes, if the calibrated lambda value indicates lean operation, by readings of the first NO x -Sensors NO x is approximated, and, if the calibrated lambda value indicates a rich operating condition, by the dimensions of the first NO x -Sensors NH3 is approximated.

[0004] Furthermore, a method for simulating the temporal behavior of the lambda value at the outlet of an exhaust gas catalyst in a motor vehicle with an internal combustion engine is known from the publication DE 41 12 477 C2.

[0005] The publication DE 10 2013 216 595 A1 relates to a method for correcting a voltage-lambda characteristic curve of a second lambda sensor arranged in an exhaust channel of an internal combustion engine in the exhaust stream behind a catalyst, wherein an output signal of a first lambda sensor arranged before the catalyst is detected and corrected.The system provides that the internal combustion engine is operated at an operating point where the lambda values ​​of the exhaust gas before and after the catalytic converter are the same, that the temperature of the second lambda sensor is set to a target temperature, that the first lambda value determined by the first lambda sensor is compared with the second lambda value determined by the second lambda sensor, that a temperature to be corrected for the second lambda sensor is determined from the comparison of the first and second lambda values, and that the voltage-lambda characteristic curve of the second lambda sensor is corrected by taking into account the temperature deviation between the target temperature and the temperature to be corrected.

[0006] The prior art documents DE 42 12 022 A1 and DE 10 2023 201 660 B3 are also known.

[0007] 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 the provision of a combustion air ratio based on the second measured value with high accuracy.

[0008] 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 outlet concentration of at least one exhaust gas component downstream of the exhaust aftertreatment device is determined by means of an exhaust 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 at least temporarily using the combustion air ratio determined from the second measured value and the correction value, wherein the inlet combustion air ratio is determined by interpolation from the first measured value and the second measured value.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] The exhaust aftertreatment system is preferably designed as a vehicle catalyst, in particular as a three-way catalyst, oxidation catalyst, NO x- Storage catalyst or SCR catalyst. The vehicle catalyst has, for example, a catalytic coating applied to a support substrate. The catalytic coating can also be referred to as a washcoat. The support substrate is preferably a ceramic substrate, for example made of cordierite. The support substrate is preferably designed as a honeycomb structure with a plurality of thin-walled channels. The vehicle catalyst can 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 the catalytic coating.

[0014] The operation of the drive unit is determined based on the first and second measured values. The first measured value is taken using the first lambda sensor upstream of the exhaust aftertreatment system. This first measurement describes the air-fuel ratio present in the exhaust gas upstream of the aftertreatment system, or rather, the amount of residual oxygen present there. The second measured value is taken using the second lambda sensor downstream of the exhaust aftertreatment system and therefore describes the air-fuel ratio, or rather, the amount of residual oxygen downstream of the aftertreatment system.

[0015] Depending on the design and / or condition of the lambda sensors, the measured values ​​may be subject to error. This is particularly true if one of the lambda sensors is a wideband sensor. While these are characterized by a large measuring range, they typically have an offset error. This means that the measured value using the wideband lambda sensor deviates in a specific direction from the value that actually describes the air-fuel ratio in the exhaust gas by a certain difference or offset value. To improve the accuracy of the second measured value, it should therefore be corrected using the correction value, or the air-fuel ratio should be determined from the second measured value taking the correction value into account. This means that the air-fuel ratio is given as a function of the second measured value and the correction value.

[0016] In principle, it is possible to first apply the correction value to the second measured value, in particular by adding or subtracting the correction value from the second measured value, and then to determine the air-fuel ratio from the corrected second measured value. However, it is also possible to first determine the air-fuel ratio from the second measured value and then correct the air-fuel ratio determined in this way with the correction value. Insofar as this description refers to correcting the second measured value and determining the air-fuel ratio from the corrected second measured value, both variants are preferably understood to be included.

[0017] In summary, the second reading from the second lambda sensor, located downstream of the exhaust aftertreatment system, is to be adjusted based on the first reading, which is measured using the first lambda sensor located upstream of the exhaust aftertreatment system. Consequently, the downstream lambda sensor is calibrated using the upstream lambda sensor. This results in a high accuracy of the air-fuel ratio, enabling reliable operation of the engine based on this ratio. For example, the air-fuel ratio can be used to determine the concentration of at least one exhaust gas component and to operate the engine based on this concentration. Additionally or alternatively, the air-fuel ratio is used to adjust the composition of the fuel-air mixture.

[0018] A further development of the invention provides that a switching lambda sensor is used as the first lambda sensor and / or a wideband lambda sensor or a lambda module of a nitrogen oxide sensor is used as the second lambda sensor. The switching lambda sensor is in particular in the form of a Nernst cell, preferably a single Nernst cell, and can also be referred to as a voltage switching sensor. It is characterized by high accuracy, especially around a combustion air-fuel ratio of λ = 1.

[0019] The second lambda sensor is the wideband lambda sensor or the lambda module of the nitrogen oxide sensor. Compared to the narrowband lambda sensor, the wideband lambda sensor has a broader measuring range. It typically consists of a Nernst cell and a pump cell. The pump cell is adjusted so that the Nernst cell measures an air-fuel ratio of λ = 1. The current and / or voltage used to operate the pump cell then represents a measure of the actual air-fuel ratio present in the exhaust gas. Alternatively, the nitrogen oxide sensor or its lambda module serves as the second lambda sensor. The nitrogen oxide sensor is used to determine the proportion of nitrogen oxides present in the exhaust gas downstream of the exhaust aftertreatment system.

[0020] The nitrogen oxide sensor incorporates an integrated lambda module, which determines the oxygen content in the exhaust gas and thus the air-fuel ratio. The lambda module is similar in design to a wideband lambda sensor and includes a Nernst cell and a pump cell. Additionally, the nitrogen oxide sensor features further electrochemical cells that enable selective measurement of the nitrogen oxide content. For this purpose, the exhaust gas is conditioned in several stages, with the pump cell at least partially removing the oxygen before a detection cell actually measures the nitrogen oxide concentration.

[0021] During operation of the detection cell, a specific current and / or voltage is established. These values ​​represent a measure of the nitrogen oxide concentration in the exhaust gas. By utilizing the lambda module of the nitrogen oxide sensor, a separate lambda sensor downstream of the exhaust aftertreatment system can be omitted. The narrowband lambda sensor typically exhibits higher accuracy than the wideband lambda sensor. Accordingly, extremely high accuracy can be achieved by using the first lambda sensor to calibrate the second.

[0022] A further development of the invention provides that the correction value is determined by comparing the second measured value with a reference value derived from the first measured value. The reference value is understood to be a value that describes the air-fuel ratio downstream of the exhaust aftertreatment system, in particular at the second lambda sensor. This is done using a corresponding calculation method. After determining the reference value, it is compared with the second measured value, and the correction value is determined based on this comparison. For example, a difference between the second measured value and the reference value is calculated, and the correction value is determined from this difference; for example, the correction value is set equal to the difference. This enables a particularly effective correction of the second measured value.

[0023] A further development of the invention provides that the reference value is determined using at least one signal filter having a linear time-invariant transfer element. The applicant has surprisingly found that the air-fuel ratio downstream of the first lambda sensor, in particular downstream of the exhaust aftertreatment system, can be determined with sufficiently high accuracy using the signal filter. It may be possible to use only a single signal filter to determine the reference value. Preferably, however, several signal filters are used.

[0024] The signal filter(s) each have at least one linear, time-invariant transfer element. Naturally, the signal filter(s) can also have several such transfer elements. The signal filter or transfer element is characterized by one or more filter coefficients. If multiple transfer elements are present, they can use the same filter coefficient or different filter coefficients.

[0025] Whenever this description refers to the signal filter or at least one signal filter, the explanations are always equivalent. Explanations regarding the signal filter apply to at least one signal filter, and vice versa. In the case of multiple signal filters, explanations regarding the signal filter or at least one signal filter apply to each of the multiple signal filters.

[0026] The signal filter receives an input value, namely a value derived from the measured value. This value can be determined from the first measured value in any way; it can even be configured so that the value directly corresponds to the first measured value, i.e., is equated with it. For example, the first measured value from the first lambda sensor is available as an electrical voltage. In this case, the electrical voltage can be used as the input value. Alternatively, the electrical voltage can be converted into an air-fuel ratio, i.e., a lambda value. The air-fuel ratio is then fed into the signal filter as an input value. This approach enables the determination of the reference value with high accuracy.

[0027] The signal filter may have only one or more transfer elements. In the case of multiple transfer elements, these are preferably connected in series. For example, the transfer element is a first-order PT1 element, so the signal filter is a first-order signal filter. The first-order PT1 element is a linear time-invariant transfer element with proportional transfer characteristics and a first-order delay. The transfer function of the first-order 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 preferably determined as a function of at least the temperature. Such a procedure allows for a highly accurate determination of the reference value.

[0028] In the case of multiple transfer elements, these are preferably all of the same type, and in particular, the multiple transfer elements are first-order (PT1) elements. In this case, the signal filter preferably comprises exclusively first-order (PT1) elements. The transfer elements are preferably connected in series. 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 reference value.

[0029] The filter coefficient of the signal filter(s) is preferably determined as a function of one of the following parameters: temperature, exhaust gas flow rate, and oxygen storage capacity of the exhaust aftertreatment system. Preferably, at least the temperature is used to determine the filter coefficient, while the exhaust gas flow rate and / or oxygen storage capacity are only optional. This means that the filter coefficient is a function of temperature. In particular, 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 substrate. The temperature is determined, for example, using a temperature model for the exhaust aftertreatment system or an exhaust aftertreatment model.Alternatively, the temperature can also be measured.

[0030] Additionally, the filter coefficient is preferably determined as a function of the exhaust gas flow rate and / or the oxygen storage capacity. 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.

[0031] A further development of the invention provides for the use of a dead-time element in the signal filter. The dead-time element receives an input signal and makes it available again as an output signal after a time delay. Thus, any change in the input signal causes a delayed change in the output signal. The dead-time element is characterized by a time constant, which can also be referred to as propagation time, transmission time, or dead time. The dead-time element is implemented, for example, using a FIFO (First In First Out) memory. The memory has a specific number of memory locations arranged sequentially. The input signal is pushed into the memory, i.e., a first memory location is filled with it.

[0032] The values ​​stored in the memory locations are shifted incrementally, so that the input value travels through the memory until it reaches the last memory location. An output value of the dead-time element is then set to the last memory location, or the value contained in the last memory location is used as the output value. For example, the dead-time element can be connected downstream of the transfer element, so that the transfer element, or several transfer elements, and the dead-time element are connected in series. The advantages already explained are achieved with this approach.

[0033] A further development of the invention provides that the correction value is determined by calculating the average of the difference between the second measured value and the reference value, or by calculating the difference between the average of the second measured value and the average of the reference value. Ultimately, the correction value thus corresponds to a function of the second measured value and the reference value. It can be provided that the difference between the second measured value and the reference value is first calculated and then averaged. The correction value corresponds to the average value obtained from the averaging. Alternatively, it is provided that the average value is determined for both the second measured value and the reference value. In this case, the correction value is set equal to the difference between the average values. The average values ​​in each case are understood to be time-averaged values.This approach allows for a particularly precise correction of the second measurement.

[0034] A further development of the invention provides that the correction value is determined, in particular only and / or exclusively, if at least one of the following conditions is met: the first lambda sensor is operational, the second lambda sensor is operational, the heat input into the exhaust aftertreatment device is less than a heat input threshold, the operating point of the drive unit is within an operating point range, the temporal change of the operating point is within a change range, and the temperature of the first exhaust aftertreatment device is within a temperature range.

[0035] Determining the correction value includes, in particular, calculating the mean or means. The correction value, mean, or means are determined only and / or exclusively if one or more, preferably all, of the aforementioned conditions are met. This means that each or all of the conditions must be met; it is not sufficient for one or more of the conditions to be met.

[0036] For example, it is a prerequisite that the first and / or second lambda sensors are operational, i.e., providing meaningful readings. The operational readiness of the lambda sensors depends on their temperature, so it is assumed that the respective lambda sensor is operational if its temperature is within its operating temperature range. Additionally or alternatively, the heat input into the exhaust aftertreatment system is determined. Heat input refers specifically to the heat transfer from the exhaust gas into the exhaust aftertreatment system, for example, into the carrier substrate. If the heat input, ultimately a heat flow from the exhaust gas into the exhaust aftertreatment system, is less than the corresponding threshold value, then the condition is met.

[0037] The operating point of the drive unit can also be considered. The operating point is characterized in particular by the rotational speed and / or torque of the drive unit, and ultimately, by the power supplied by the drive unit. If the operating point, for example, the rotational speed, torque, and / or power, lies within the defined operating point range, the condition is met. The change over time of the operating point can also be used as a decision criterion. The change over time of the operating point refers, for example, to the change over time of the rotational speed, torque, and / or power. If it lies within the defined range of change, the condition is considered met. Additionally or alternatively, the temperature of the exhaust aftertreatment system is used.The relevant condition is considered fulfilled if the temperature is within the specified temperature range. Using one or more of the aforementioned conditions ensures that the correction value is obtained with a high degree of accuracy.

[0038] The invention provides that 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 at least temporarily using the combustion air ratio determined from the second measured value and the correction value.

[0039] The components of the exhaust gas produced by the engine are referred to as raw emissions. Raw emissions describe the composition of the exhaust gas upstream of the exhaust aftertreatment system, or, more precisely, the flow characteristics between the engine and the exhaust aftertreatment system. As the exhaust gas passes through the aftertreatment system, some of the substances it contains are converted, thus altering its composition. The conversion rate, and therefore the conversion capacity of the vehicle's catalytic converter, which transforms the pollutants into less harmful products, depends primarily on the composition of the exhaust gas supplied to the aftertreatment system, as well as the temperature of the aftertreatment system.

[0040] The substances present in the exhaust gas downstream of the exhaust aftertreatment system, which constitute the exhaust gas, are also referred to as tailpipe emissions, since the exhaust gas with this composition is released into the environment through the exhaust pipe of the engine. As already 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.

[0041] In particular, the conversion efficiency decreases the greater the temperature of the exhaust aftertreatment system or the vehicle catalyst deviates from its operating temperature; that is, the greater the absolute difference between the temperatures. The temperature of the exhaust aftertreatment system or the vehicle catalyst refers, for example, to the temperature of a ceramic substrate coated with the catalytic layer.

[0042] 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.

[0043] 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.

[0044] 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 in particular 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, the inlet concentration present at the inlet point is equal to the raw emission of 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.

[0045] 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 stipulated that the inlet air-fuel ratio is equal to the combustion air-fuel ratio determined from the first measurement taken upstream of the exhaust aftertreatment system using the first lambda sensor. This first measurement 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.

[0046] However, the air-fuel ratio changes across the exhaust aftertreatment system, making it impractical to determine the intake air-fuel ratio from the first measurement, or even from the first measurement alone. Therefore, it is intended to use the second measurement, or rather the air-fuel ratio derived from it, in addition to or as an alternative to the first measurement taken by the first lambda sensor, when determining the intake air-fuel ratio. The second measurement, or the air-fuel ratio derived from it, is corrected using the correction value, resulting in high accuracy.

[0047] Preferably, the drive unit is operated depending on the discharge concentration; in particular, an operating parameter of the drive unit is determined from the discharge concentration and set on the drive unit. For example, it is provided that if a threshold value is exceeded by the discharge concentration, the power output of the drive unit is limited so that the drive power provided by it is always less than its rated power.

[0048] The invention provides that the inlet air-fuel ratio is determined by interpolation from the first and second measured values. The second measured value describes the air-fuel ratio downstream of the exhaust aftertreatment system and is therefore no more directly applicable than the first measured value. It is therefore intended to determine the inlet air-fuel ratio by interpolation from the first and second measured values, for example, by linear interpolation. The interpolation is performed in a position-dependent manner, i.e., depending on the position of the inlet point, for example, relative to the first lambda sensor and / or the second lambda sensor, or relative to the exhaust aftertreatment system.This allows the inlet combustion air ratio to be determined with high accuracy, so that the exhaust aftertreatment model can also be carried out with good results and the outlet concentration describes the actual concentration of at least one exhaust gas component present at the outlet point with high accuracy.

[0049] A further development of the invention provides that the first measured value is converted into an air-fuel ratio using a probe characteristic curve, from which the intake air-fuel ratio is calculated by interpolation. The first measured value is thus initially converted into the air-fuel ratio using the probe characteristic curve. The probe characteristic curve is calibrated to the first 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 desired way, for example, using a mathematical relationship, a characteristic map, and / or a table.

[0050] The intake air-fuel ratio is then determined from the combustion air-fuel ratio, namely by interpolation between the combustion air-fuel ratio determined from the first measurement and the second measurement, or a combustion air-fuel ratio determined from the second measurement. Using the probe characteristic curve to convert the first measurement 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.

[0051] A further development of the invention provides that the interpolation is performed depending on a position assigned to the inlet point relative to the first and second lambda sensors and / or relative to an inlet and an outlet of the exhaust aftertreatment system. The position is assigned to the inlet point; for example, the position corresponds to the position of the inlet point itself. Here, the position is understood to be a spatial position, at least a position along a flow direction of the exhaust gas from the direction of the first lambda sensor towards the second lambda sensor.

[0052] In addition to the position, the interpolation process uses the positions of the first and second lambda sensors, or the inlet and outlet of the exhaust aftertreatment system. For example, the distance between the position and the first lambda sensor or the inlet is determined, and the interpolation is then performed based on this distance, taking into account the distance between the second and first lambda sensors, or the distance between the outlet and the inlet. This allows for a highly accurate determination of the air-fuel ratio at the specified position.

[0053] A further development of the invention provides that the interpolation is performed in the form of a weighted interpolation with weights raised to an exponent. The weights describe the arrangement of the position relative to the lambda sensors or relative to the exhaust aftertreatment system. A relationship on the basis of which the interpolation is performed can be written, for example, as follows: λE=((1−t)p⋅λ1+tp⋅λ2) / ((1−t)p+tp) where λ1 corresponds to a first air-fuel ratio determined from the first measurement, λ2 to a second air-fuel ratio determined from the second measurement, t to a ratio describing the position, and p to the exponent. The ratio t results, for example, from the ratio between the distance of the position to the inlet of the exhaust aftertreatment system and the distance between the outlet and the inlet of the exhaust aftertreatment system. The quantity λ Eis the intake air-to-combustion air ratio.

[0054] The interpolation can be performed linearly, for example, in which case p = 1. However, the exponent can also be other than 1. In particular, it is chosen such that it depends on the conversion power of the exhaust aftertreatment system. For example, the exponent is chosen to remain constant over time, especially p = 0.5 or p = 2. It can also be chosen as a function of a state variable that describes a state of the exhaust aftertreatment system. In particular, a temperature of the exhaust aftertreatment system, preferably a temperature of a honeycomb structure of the exhaust aftertreatment system, is used as such a state variable. This also results in particularly high accuracy.

[0055] 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 is determined as the inlet combustion air ratio for one of several inlet points comprising the inlet point and each of the inlet combustion air ratios is determined by interpolation from the first measured value and the second measured value.

[0056] This means that the exhaust aftertreatment system is not considered as a whole, but rather divided into several sections. These sections preferably extend from a beginning to an end, or from an inlet to an outlet, of the exhaust aftertreatment system and are particularly preferably directly adjacent to one another. For example, the exhaust aftertreatment system is divided into at least two, at least three, at least four, or 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.

[0057] 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.

[0058] 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.

[0059] A further development of the invention provides that the position associated with the inlet point is located downstream of the inlet point, in particular within the respective section. The position is therefore not located directly at the inlet point or at an inlet point of the respective section of the exhaust aftertreatment device. Rather, it is arranged downstream of the inlet point. Particularly preferably, the position is located centrally, or at least approximately centrally, within the respective section when viewed in the direction of exhaust gas flow, i.e., between the inlet point and the outlet point of the respective section, and in particular, centrally between these. The applicant has found that particularly good results are achieved with this approach.

[0060] A further development of the invention provides that, in addition to the exhaust aftertreatment device, a further exhaust aftertreatment device is used for aftertreating the exhaust gas, which is located upstream of the exhaust aftertreatment device, wherein the first lambda sensor is arranged fluidically between the exhaust aftertreatment device and the further exhaust aftertreatment device, and the second lambda sensor is arranged downstream of the exhaust aftertreatment device. Such a configuration of the drive unit has already been mentioned.

[0061] Viewed in the direction of exhaust gas flow, the following components follow the engine: the further exhaust aftertreatment system, the first lambda sensor, the exhaust aftertreatment system, and the second lambda sensor. Preferably, a further lambda sensor, in particular a wideband lambda sensor, is located upstream of the further exhaust aftertreatment system. The further exhaust aftertreatment system can be designed analogously to the exhaust aftertreatment system, for example, as a vehicle catalytic converter or the like. The use of the further exhaust aftertreatment system enables a particularly effective conversion of the pollutants contained in the exhaust gas.

[0062] 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 for aftertreatment of the exhaust gas 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 exhaust gas aftertreatment device.

[0063] The drive unit is also designed and configured to determine a combustion air-fuel ratio from the second measured value, taking into account a correction value determined based on the first measured 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 may be further developed as described, and reference is made to these details.

[0064] 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.

[0065] 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.

[0066] The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. The only embodiment shown is... Fig. 1 A schematic representation of a drive system for a motor vehicle with a drive unit and an exhaust aftertreatment system.

[0067] The Fig. Figure 1 shows a schematic representation of a drive unit 1, which includes an exhaust gas-generating drive unit 2, in particular an internal combustion engine, as well as exhaust gas aftertreatment devices 3 and 4, each 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 reacts chemically with each other, producing exhaust gas. The exhaust gas is discharged from the drive unit 2 and fed to the exhaust gas aftertreatment devices 3 and 4, so that it first flows through the exhaust gas aftertreatment device 3 and then through the exhaust gas aftertreatment device 4 before being released into the outside environment.

[0068] A lambda sensor 5 is arranged between the drive unit 2 and the exhaust aftertreatment system 3. Furthermore, a first lambda sensor 6 is located between the exhaust aftertreatment systems 3 and 4, and a second lambda sensor 7 is located downstream of the exhaust aftertreatment system 4. The second lambda sensor 7 is, in particular, a component of a nitrogen oxide sensor 8, specifically as a lambda module of this nitrogen oxide sensor 8. The measured values ​​of the lambda sensors 5, 6, and 7 each describe a residual oxygen content of the exhaust gas or a combustion air ratio at the respective location.

[0069] Using a measured value from lambda sensor 5, a lambda controller 9 is operated, and using the measured value from the first lambda sensor 6, a trim controller 10 is operated. The output values ​​of the two controllers 9 and 10 are calculated with a setpoint supplied via an input 11, namely in a calculation module 12. The composition of the fuel-air mixture is determined from the result of the calculation.

[0070] Furthermore, the composition of the exhaust gas downstream of the exhaust gas aftertreatment devices 3 and 4 is determined using two exhaust gas aftertreatment models, for example, using a first exhaust gas aftertreatment model for the exhaust gas aftertreatment device 3 and a second exhaust gas aftertreatment model for the exhaust gas aftertreatment device 4. The exhaust gas aftertreatment models determine the composition of the exhaust gas for at least one exhaust gas component, preferably for several exhaust gas components.

[0071] The exhaust aftertreatment models each comprise several exhaust aftertreatment sub-models, for example, at least four, five, or six exhaust aftertreatment sub-models. Each exhaust aftertreatment sub-model is used to calculate one of several sections 13 of the respective exhaust aftertreatment device 3 or 4. The sections 13 each extend from an inlet 14 to the outlet 15 of the respective exhaust aftertreatment device 3 or 4. They extend continuously and without interruption from the respective inlet 14 to the respective outlet 15.

[0072] For each of the sections 13, an inlet concentration and an inlet combustion ratio are determined at a respective inlet point 16. Using the respective exhaust aftertreatment sub-model, an outlet concentration of the respective exhaust gas component is subsequently determined at a respective outlet point 17 of the corresponding section 13. Preferably, the inlet concentration for a further downstream section 13 is equal to the outlet concentration of the immediately upstream section 13. The inlet concentration of the most upstream section 13 is equal to the inlet concentration of the respective exhaust aftertreatment device 3 or 4, and the outlet concentration of the respective exhaust aftertreatment device 3 or 4 is equal to the outlet concentration of the most downstream section 13.

[0073] 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).

[0074] The respective intake air-fuel ratio is determined based on the measured values ​​of the first lambda sensor 6 and the second lambda sensor 7. For this purpose, the measured values ​​of lambda sensors 6 and 7 are first converted into combustion air ratios, for example, using a sensor characteristic curve for the respective lambda sensor 6 or 7. The intake air-fuel ratio is then determined from the combustion air ratios by interpolation, for example, by linear interpolation. In particular, intake air-fuel ratios are determined for several positions within the respective exhaust aftertreatment system 3 or 4. Lambda sensors 6 and 7 are connected to a control unit 18, which performs the corresponding calculations. REFERENCE MARK LIST: 1 Drive unit 2 Drive unit 3 Exhaust aftertreatment system 4 Exhaust aftertreatment system 5 Lambda sensor 6 1. Lambda sensor 7 2. Lambda sensor 8 Nitrogen oxide sensor 9 Lambda controllers 10 trim controls 11 Entrance 12 Calculation module Section 13 14 Admission 15 Outlet 16 Entry point 17 Exit point 18 Control unit

Claims

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 (4) for aftertreating the exhaust gas, wherein a first measured value is measured upstream of the exhaust gas aftertreatment device (4) by means of a first lambda sensor (6) and a second measured value is measured downstream of the exhaust gas aftertreatment device (4) by means of a second lambda sensor (7), wherein a combustion air ratio is determined from the second measured value taking into account a correction value determined as a function of the first measured value, characterized in that an outlet concentration of at least one exhaust gas component downstream of the exhaust gas aftertreatment device (4) is determined by means of an exhaust gas aftertreatment model,the input variables are an inlet concentration determined for an inlet point (16) and an inlet combustion air ratio determined for the inlet point (16), wherein the inlet combustion air ratio is determined at least temporarily using the combustion air ratio determined from the second measured value and the correction value, wherein the inlet combustion air ratio is determined by interpolation from the first measured value and the second measured value. Method according to claim 1, characterized in that a switching lambda sensor (6) and / or a wideband lambda sensor or a lambda module of a nitrogen oxide sensor (8) is used as the first lambda sensor (6). Method according to one of the preceding claims, characterized in that the correction value is determined by comparing the second measured value with a reference value determined from the first measured value. Method according to claim 3, characterized in that the reference value is determined using at least one signal filter having a linear time-invariant transfer element. Method according to claim 3 or 4, characterized in that the correction value is determined by forming an average of a difference between the second measured value and the reference value or by calculating a difference between an average of the second measured value and an average of the reference value. Method according to one of the preceding claims, characterized in that the correction value is determined if at least one of the following conditions is met: the first lambda probe (6) is operational, the second lambda probe (7) is operational, the heat input into the exhaust aftertreatment device (4) is less than a heat input threshold value, an operating point of the drive unit (2) lies within an operating point range, a temporal change of the operating point lies within a change range, and a temperature of the exhaust aftertreatment device (4) lies within a temperature range. 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 (4) for aftertreating the exhaust gas and is provided and configured to measure a first measured value by means of a first lambda sensor (6) upstream of the exhaust gas aftertreatment unit (4) and a second measured value by means of a second lambda sensor (7) downstream of the exhaust gas aftertreatment unit (4), wherein the drive unit (1) is also provided and configured to determine an air-fuel ratio from the second measured value, taking into account a correction value determined as a function of the first measured value, characterized in thatthat an outlet concentration of at least one exhaust gas component downstream of the exhaust aftertreatment device (4) is determined by means of an exhaust aftertreatment model, to which an inlet concentration determined for an inlet point (16) and an inlet combustion air ratio determined for the inlet point (16) are supplied as input variables, wherein the inlet combustion air ratio is determined at least temporarily using the combustion air ratio determined from the second measured value and the correction value, wherein the inlet combustion air ratio is determined by interpolation from the first measured value and the second measured value. Computer program product comprising commands that cause the drive device (1) according to claim 7 to execute the method according to one or more of claims 1 to 6.

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