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

Abstract

The invention relates to a method for operating a drive unit for a motor vehicle, which has an exhaust gas generating drive unit, an exhaust gas aftertreatment device (1) for aftertreatment of the exhaust gas and a lambda probe (3) arranged upstream of the exhaust gas aftertreatment device (1).The invention provides that combustion air conditions for exhaust gas present at several locations downstream of the lambda sensor (3) are determined from a measured value of the lambda sensor (3) by means of signal filters (15, 16, 17), each having a linear time-invariant transfer element (18, 19, 20). The signal filters (15, 16, 17) are arranged in parallel to each other, so that each receives a quantity determined from the measured value as an input, or in series to each other, so that one of the signal filters (15, 16, 17) receives the quantity determined from the measured value as an input and at least one subsequent signal filter (15, 16, 17) receives an output value from a preceding signal filter (15, 16, 17) as an input. The invention further relates to a drive unit for a motor vehicle and a computer program product.

Description

[0001] The invention relates to a method for operating a drive unit for a motor vehicle, which comprises an exhaust gas-generating drive unit, an exhaust gas aftertreatment device for treating the exhaust gas, and a lambda sensor arranged upstream of the exhaust gas aftertreatment device. The invention further relates to a drive unit for a motor vehicle and a computer program product.

[0002] For example, German patent application DE 41 12 477 C2 is known from the prior art. This describes 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, comprising the following steps: measuring the mass airflow drawn in by the engine; calculating the oxygen flow drawn in by the engine; determining the deviation of the lambda value upstream of the catalyst from lambda value one, which is positive in the case of a lean mixture and negative in the case of a rich mixture; and calculating the partial oxygen flow from the engine into the catalyst, which is an oxygen supply flow in the case of positive deviation values ​​and an oxygen withdrawal flow in the case of negative values, each with reference to the effect at the catalyst.

[0003] Furthermore, the following steps are provided: specifying the oxygen storage volume of the catalyst as the amount of oxygen that the catalyst can assume with a continuous oxygen supply flow, starting from the oxygen-free state up to an overflow threshold, at which the gas flowing out of its outlet has an oxygen concentration above a predetermined threshold; and calculating the temporal behavior of the lambda value at the outlet of the catalyst by setting it to one as long as the oxygen storage is in a filling state below the overflow threshold or an emptying state above a depletion threshold, where the depletion threshold corresponds to a predetermined low oxygen concentration at the outlet of the catalyst; conversely, setting it at least temporarily to the lambda value at the inlet of the catalyst when the overflow threshold is exceeded or the depletion threshold is undershot.

[0004] The object of the invention is to propose a method for operating a drive unit for a motor vehicle which has advantages over known methods, in particular enabling a reliable determination of the combustion air conditions, preferably for modeling the exhaust aftertreatment device using an exhaust aftertreatment model.

[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 combustion air conditions for exhaust gas present at several locations downstream of the lambda sensor are determined from a measured value of the lambda sensor by means of signal filters, each having a linear time-invariant transfer element, wherein the signal filters are arranged in parallel to each other, so that a quantity determined from the measured value is supplied to each of them as an input, or are arranged in series to each other, so that the quantity determined from the measured value is supplied to one of the signal filters as an input and an output quantity of a preceding signal filter is supplied to at least one subsequent signal filter as an input.

[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 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.

[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 dynamics, between the engine and the exhaust aftertreatment system. As the exhaust gas passes through the aftertreatment system, some of the substances contained within it are transformed, thus changing its composition. The substances present in the exhaust gas downstream of the aftertreatment system, which constitute the exhaust gas, are also referred to as tailpipe emissions, since this is the composition of the exhaust gas released into the environment through the engine's tailpipe.

[0012] The amount of pollutants contained in tailpipe emissions depends on the raw emissions, but also on the conversion rate or conversion efficiency of the exhaust aftertreatment system or the vehicle's catalytic converter. The conversion rate, and thus the conversion efficiency of the vehicle's catalytic converter, 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's catalytic converter, as well as on the temperature of the exhaust aftertreatment system.

[0013] The conversion rate is therefore temperature-dependent. In particular, the conversion rate is lower the further the temperature of the exhaust aftertreatment system deviates from its operating temperature; that is, the greater the absolute difference between the temperatures. The temperature of the exhaust aftertreatment system refers, for example, to the temperature of the support substrate, especially the ceramic honeycomb structure, which is coated with the catalytic layer.

[0014] The combustion air-fuel ratio, determined by the lambda sensor, is one of the factors used to operate the drive unit. The lambda sensor is located upstream of the exhaust aftertreatment system; the exhaust gas flowing past or over the lambda sensor then flows through the aftertreatment system. The lambda sensor determines the combustion air-fuel ratio upstream of the exhaust aftertreatment system.

[0015] In order to determine the composition of the exhaust gas downstream of the lambda probe, in particular downstream of the exhaust aftertreatment device, with high accuracy, preferably using the exhaust aftertreatment model, it is necessary to determine the air-fuel ratio not only at the lambda probe, but also downstream of the lambda probe, in particular in the exhaust aftertreatment device or downstream of the exhaust aftertreatment device, preferably directly downstream of the exhaust aftertreatment device.

[0016] This has not been feasible to date, or at best only with considerable effort. However, the applicant has surprisingly discovered that the air-fuel ratio downstream of the lambda sensor can be determined with sufficiently high accuracy using signal filters. Each signal filter has at least one linear, time-invariant transfer element. Naturally, the signal filters can also have several such transfer elements. The signal filter, or transfer element, is characterized by one or more filter coefficients. If several transfer elements are present, they can use the same filter coefficient or different filter coefficients.

[0017] Whenever this description refers to the transfer element or at least one transfer element, the explanations are always equivalent. Explanations concerning the transfer element apply to at least one transfer element, and explanations concerning at least one transfer element apply to the transfer element. In the case of multiple transfer elements, the explanations concerning the transfer element or at least one transfer element apply to each of the multiple transfer elements.

[0018] Particularly when using the exhaust aftertreatment model, it is insufficient to determine the air-fuel ratio at only one location. Therefore, according to the invention, it is provided that such an air-fuel ratio is determined for several locations downstream of the lambda sensor, so that ultimately multiple air-fuel ratios are available, particularly as input variables for the exhaust aftertreatment model. A separate signal filter is provided for each of the air-fuel ratios, so that ultimately the number of signal filters corresponds to the number of air-fuel ratios to be determined. In other words, a separate signal filter is provided for each of the air-fuel ratios, and each signal filter is used to determine one of the air-fuel ratios.

[0019] The locations for which the combustion air-fuel ratio is determined are preferably spatially spaced apart from one another; in particular, they are equidistant from each other, meaning they have identical distances between them. In other words, the locations follow one another at constant intervals in the direction of exhaust gas flow. Preferably, the locations are situated within the exhaust gas aftertreatment system; in particular, they correspond to the exhaust gas inlet points into individual sections of the exhaust gas aftertreatment system, which are calculated using the exhaust gas aftertreatment model.

[0020] The signal filters can be interconnected in different ways. In one variant of the method, parallel signal filters are used. In this case, each of the parallel signal filters is fed its input, namely the quantity derived from the measured value. This quantity can be derived from the measured value in any way; it can also be determined so that the quantity directly corresponds to the measured value, i.e., is equated with it. For example, the measured value from the lambda sensor is available as an electrical voltage. In this case, the electrical voltage can be used as the quantity.

[0021] Alternatively, the voltage can be converted into an air-fuel ratio, i.e., a lambda value. This air-fuel ratio is then fed to each of the signal filters. Ultimately, the parallel arrangement of the signal filters means that each receives the same input signal. The filter coefficients of the signal filters are selected such that the air-fuel ratios for the multiple positions are determined; in particular, the filter coefficients are chosen to be different from each other. This approach allows for a precise determination of the air-fuel ratios.

[0022] In a second variant, the signal filters are alternatively arranged in series, i.e., connected together. In this case, the value determined from the measured value is fed as an input to the first signal filter. For each subsequent signal filter, the input is derived from the output of the preceding signal filter. Thus, if the combustion air ratios are determined using, for example, three signal filters, the value determined from the measured value is fed as an input to the first signal filter, which then provides an output.

[0023] The output of the first signal filter is fed as input to a second signal filter, which in turn produces an output for the second filter. The output of the second filter is then fed as input to a third filter, and the output of the third filter is used as input for a fourth filter, which itself provides an output. The combustion air ratios for the various positions are determined from the outputs of the signal filters; for example, the combustion air ratios correspond to the outputs, or they are calculated from them using a mathematical relationship, a characteristic curve, or a table.

[0024] With the signal filters arranged in parallel, the combustion air ratios depend directly and exclusively on the lambda sensor reading. For the signal filters arranged in series, the combustion air ratios are determined at least partially using the output variables, such that at least one of the combustion air ratios depends directly on another. The combustion air ratio that depends directly on one of the combustion air ratios is only indirectly dependent on the measured value or the value derived from it. In any case, the described procedure achieves a high accuracy of the combustion air ratios, thus ensuring reliable operation of the drive system, and in particular, reliable implementation of the exhaust aftertreatment model.

[0025] A further development of the invention provides 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 which comprises several exhaust aftertreatment sub-models for modeling different sections of the exhaust aftertreatment device, wherein the exhaust aftertreatment sub-models are supplied with inlet concentrations determined for several inlet points as well as inlet combustion air ratios determined for the inlet points, wherein the combustion air ratios are used as inlet combustion air ratios.

[0026] To determine the pollutant emissions of the propulsion system, i.e., the amount of at least one exhaust component released into the environment, the exhaust aftertreatment model is used. This model simulates the conversion of the at least one exhaust component by the aftertreatment system. The aftertreatment model contains several sub-models that represent different sections of the aftertreatment system.

[0027] 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, or—preferably—at least four 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.

[0028] Each exhaust aftertreatment sub-model has one of the inlet concentrations and one of the inlet combustion air ratios as input variables. The inlet concentration and the inlet combustion air ratio for each section are determined for a specific inlet point of that section. Using the respective exhaust aftertreatment sub-model, a specific outlet concentration for an outlet point of the respective section is determined from the respective inlet concentration and the respective inlet combustion air ratio. Preferably, the outlet concentration of a flow-technically preceding section is used as the inlet concentration of a flow-technically immediately following section.

[0029] The exhaust aftertreatment model is based on a step-by-step calculation of the outlet concentration of at least one exhaust gas component across the exhaust aftertreatment system. The combustion air ratios determined using the signal filters are used as the inlet combustion air ratios. Each of the exhaust aftertreatment sub-models is thus fed one of the inlet combustion air ratios as an input. In other words, each of the inlet combustion air ratios is fed to one of the exhaust aftertreatment sub-models as an input. The measured value from the lambda sensor, or the value derived from it, can also be fed to one of the exhaust aftertreatment sub-models as an input.

[0030] The inlet points describe the conditions present in the exhaust gas at the inlet side of the respective section. An inlet point is understood to be, in particular, the point at which the exhaust gas enters the exhaust aftertreatment system or the respective section of the exhaust aftertreatment system. More precisely, the inlet point refers to the point at which the exhaust gas enters one of the several sections of the exhaust aftertreatment system. Based on the inlet concentration, the respective exhaust aftertreatment sub-model calculates an outlet concentration of at least one exhaust gas component present at an outlet point of the respective section. Analogously to the inlet point, the outlet point refers to the point at which the exhaust gas exits the exhaust aftertreatment system or the section thereof.

[0031] The inlet concentration for the most upstream section of the exhaust aftertreatment system 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 determined using the exhaust aftertreatment model or one of the exhaust aftertreatment sub-models. In particular, in this case, the inlet concentration for one of the sections corresponds to the outlet concentration for a section of the exhaust aftertreatment system that is fluidically upstream of the section in question.

[0032] As an additional input variable, the inlet air-fuel ratio is fed into the exhaust aftertreatment model or the exhaust aftertreatment sub-model for the most upstream section of the exhaust aftertreatment system. This ratio is determined analogously to the inlet concentration for the inlet point. For example, the inlet air-fuel ratio could be set to the same value as the combustion air-fuel ratio determined from the lambda sensor reading upstream of the exhaust aftertreatment system. This reading describes the combustion air-fuel ratio present in the exhaust gas upstream of the exhaust aftertreatment system, or rather, the amount of residual oxygen present in the exhaust gas at that point.The intake air conditions for the downstream sections are also determined from the lambda sensor reading, using the respective signal filter. A separate signal filter is provided for each section. This method achieves particularly high accuracy.

[0033] A further development of the invention provides that different filter coefficients are used for the signal filters arranged in parallel, and / or that the same filter coefficients are used for the signal filters arranged in series. For the first variant of the method with the parallel signal filters, the filter coefficients are selected such that they describe the change in the composition of the exhaust gas, in particular due to the exhaust aftertreatment system, from the lambda sensor to the respective points located downstream of the lambda sensor.

[0034] This implies that the filter coefficients of the signal filters must be consistently different from one another. For the second variant, which uses parallel signal filters, identical filter coefficients are preferred. This is particularly the case if the points downstream of the lambda sensor are identically spaced. Otherwise, different filter coefficients can also be used here. In any case, the described procedure achieves high accuracy.

[0035] A further development of the invention provides that the signal filters each have only one transmission element, or that each signal filter has, in addition to its respective transmission element, a further transmission element connected in series with the transmission element. In the former case, each signal filter has only a single transmission element, so that the number of transmission elements corresponds to the number of signal filters and vice versa. Alternatively, it can be provided that the signal filters each have the further transmission element, namely in addition to the transmission element already present. The transmission element and the further transmission element are arranged in series, i.e., connected together in series.

[0036] In principle, any number of additional transmission elements can be present; the signal filters can therefore each have two or more additional transmission elements, and thus a total of at least three transmission elements. In the case of a serial arrangement of the transmission elements, an input signal is fed to the first transmission element at one input, whereupon the first transmission element provides an output signal at one output. This output signal is used as the input signal for a second transmission element. This process can be repeated for any number of transmission elements. The input signal for the first transmission element is an input signal from the signal filter. An output signal from the last transmission element, for example, the second one, is used as the output signal of the signal filter.

[0037] Preferably, the transfer elements are all of the same type, and preferably, the multiple transfer elements are configured as first-order (PT1) elements. In this case, the signal filters each consist exclusively of first-order (PT1) elements. The signal filter is thus an nth-order signal filter, in particular a second-order signal filter. This also serves to achieve particularly high accuracy in determining the air-fuel ratio and thus also the exhaust concentration of at least one exhaust gas component. In the case of series connection of the signal filters, higher-order signal filters are effectively obtained. For example, a fourth-order signal filter results from a series connection of two second-order signal filters. Accordingly, the output signal of a first of these signal filters is filtered by an nth-order signal filter, and the output signal of a second of these signal filters is filtered by a 2nth-order signal filter.

[0038] A further development of the invention provides that the filter coefficients are 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 coefficients, while the exhaust gas flow rate and / or the oxygen storage capacity are only optional. This means that the filter coefficients are given as a function of the temperature. In particular, the filter coefficients are proportional to the temperature. The term "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 support substrate. The temperature is determined, for example, using a temperature model for the exhaust aftertreatment system or by means of the exhaust aftertreatment model.Alternatively, the temperature can also be measured.

[0039] Additionally, the filter coefficients are preferably determined as a function of the exhaust gas flow rate and / or the oxygen storage capacity. Preferably, the filter coefficients are inversely proportional to the exhaust gas flow rate and / or optionally 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 coefficients. 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.

[0040] A further development of the invention provides that a first-order lag element (PT1 element) is used as the transfer element and / or as a further transfer element. The first-order lag element is a linear time-invariant transfer element with proportional transfer characteristics and a first-order delay. The transfer function of the first-order lag element is G s = K / 1 + T ⋅ s ,

[0041] 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 enables a highly accurate determination of the combustion air-fuel ratio.

[0042] A further development of the invention provides that a dead-time element is used in each of the signal filters. The dead-time element receives an input signal and makes it available again as an output signal after a time delay. Any change in the input signal thus 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, transit time, or dead time. The dead-time element is implemented, for example, using a FIFO (First In First Out) memory. The memory has a certain number of memory locations arranged sequentially. The input signal is pushed into the memory, i.e., a first memory location is filled with it. The values ​​contained in the memory locations are shifted incrementally, so that the value of the input signal moves through the memory until it reaches the last memory location.The output of the dead-time element is set equal to the last memory location, or the value contained in the last memory location is used as the output.

[0043] Accordingly, a relatively large amount of memory is required to implement the dead-time element. However, it requires less processing power than the transfer element or any subsequent transfer element. The advantages already mentioned are also achieved using the dead-time element. For example, the dead-time element is intended to be connected downstream of the transfer element, so that the transfer element and the dead-time element are connected in series. Several transfer elements can also be connected in series with the dead-time element, in particular one for each of the signal filters. The advantages already explained are achieved with this approach.

[0044] A further development of the invention provides that a further exhaust aftertreatment device and a further lambda sensor are arranged upstream of the exhaust aftertreatment device, wherein the measured value of the lambda sensor and a measured value of the further lambda sensor are used to perform lambda control. In addition to the exhaust aftertreatment device and the lambda sensor, the further exhaust aftertreatment device and the further lambda sensor are thus present, which are arranged upstream of the exhaust aftertreatment device and preferably upstream of the lambda sensor.

[0045] The secondary exhaust aftertreatment system can be designed analogously to the primary exhaust aftertreatment system, in particular it may be a vehicle catalytic converter. For example, the lambda sensor is fluidically positioned between the primary exhaust aftertreatment system and the secondary exhaust aftertreatment system. From a fluid dynamics perspective, the secondary lambda sensor is located on the side of the secondary exhaust aftertreatment system facing away from the primary lambda sensor, so that the secondary exhaust aftertreatment system is fluidically situated between the primary lambda sensor and the secondary lambda sensor. Therefore, the exhaust gas flows from the engine in the following sequence: secondary lambda sensor, secondary exhaust aftertreatment system, primary lambda sensor, and exhaust aftertreatment system.

[0046] The exhaust aftertreatment system can also be referred to as the first exhaust aftertreatment system, and the subsequent exhaust aftertreatment system as the second exhaust aftertreatment system. Similarly, the lambda sensor can be referred to as the first lambda sensor, and the subsequent lambda sensor as the second lambda sensor. Using the first lambda sensor, a first air-fuel ratio is determined fluid-measured between the second and first exhaust aftertreatment systems, and using the second lambda sensor, a second air-fuel ratio is determined upstream of the second exhaust aftertreatment system.

[0047] The first air-fuel ratio is the air-fuel ratio present in the exhaust gas downstream of the second lambda sensor, and in particular downstream of the second exhaust aftertreatment system. The second air-fuel ratio corresponds to the air-fuel ratio in the exhaust gas upstream of the second exhaust aftertreatment system, or, in terms of flow dynamics, between the engine and the second exhaust aftertreatment system. The first and second air-fuel ratios are preferably used for lambda control and trim control, respectively.In this process, the composition of the fuel-air mixture is adjusted in particular based on the second combustion air ratio, whereas the first combustion air ratio is used to correct the second combustion air ratio or a target value to which the second combustion air ratio is set in the course of lambda control, within the framework of trim control.

[0048] In principle, it may be possible to adjust the composition of the fuel-air mixture solely based on the first combustion air ratio or solely based on the second combustion air ratio, i.e., without considering the other combustion air ratio. In either case, the respective combustion air ratio is adjusted to the corresponding target value. For this purpose, it is specifically intended that the composition of the fuel-air mixture be adjusted so that the respective combustion air ratio changes towards the target value, in particular until it reaches the target value. For example, the respective combustion air ratio is regulated by adjusting the composition of the fuel-air mixture to the target value.

[0049] However, it is particularly preferred to use both the first and second air-fuel ratios to adjust the composition of the fuel-air mixture. In this case, both air-fuel ratios are preferably set to a respective target value. Specifically, it is therefore provided that the first air-fuel ratio is set to a first target value and the second air-fuel ratio to a second target value, namely by appropriately adjusting the composition of the fuel-air mixture.

[0050] A further development of the invention provides that the exhaust aftertreatment device is a first exhaust aftertreatment device and the air-fuel ratio is a first air-fuel ratio, wherein a second exhaust aftertreatment device is located upstream of the lambda sensor, and a second air-fuel ratio for exhaust gas present upstream of the lambda sensor is determined by gradient calculation from the lambda sensor reading. Using the lambda sensor or the measured value, the air-fuel ratio is thus determined not only downstream of the lambda sensor, particularly in the first exhaust aftertreatment device, but also upstream of the lambda sensor, particularly in the second exhaust aftertreatment device. For this purpose, a gradient is calculated from the lambda sensor reading.The gradient is, for example, the time gradient of the measured value of the lambda sensor itself, or a time gradient of a quantity determined from the measured value.

[0051] For example, the air-fuel ratio at the lambda sensor is first determined from the measured value, and then the second air-fuel ratio is calculated using the time gradient of this air-fuel ratio. For example, the second air-fuel ratio is calculated using the relationship λ 1 = k ⋅ dλ 2 / dt + λ 2 The values ​​are determined where λ₁ is the first air-fuel ratio, λ₂ is the second air-fuel ratio, k is a correction factor, and t is time. Preferably, the second air-fuel ratio is used for a further exhaust aftertreatment model, by means of which the further exhaust aftertreatment device is modeled.

[0052] A further development of the invention provides that a jump-type lambda sensor is used. Another lambda sensor can be in the form of a broadband lambda sensor. While the broadband lambda sensor has a comparatively wide measuring range, this is not the case for the jump-type lambda sensor. The jump-type lambda sensor is, for example, in the form of a single Nernst cell and can also be referred to as a voltage-switching sensor. The broadband lambda sensor, on the other hand, consists of a Nernst cell and a pump cell.

[0053] The pump cell is adjusted so that a combustion air-fuel ratio of λ = 1 is measured using the Nernst cell. The current and / or voltage of the electrical current used to operate the pump cell then represents a measure of the actual combustion air-fuel ratio present in the exhaust gas. A narrowband lambda sensor typically exhibits higher accuracy than a wideband lambda sensor. Accordingly, extremely high accuracy can be achieved by using a narrowband lambda sensor to measure the value from which the combustion air-fuel ratio is subsequently determined.

[0054] 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 probe arranged upstream of the exhaust gas aftertreatment device.

[0055] The drive system is designed and configured to determine combustion air conditions for exhaust gas located at several points downstream of the lambda sensor from a measured value of the lambda sensor by means of signal filters, each having a linear time-invariant transfer element, wherein the signal filters are arranged in parallel to each other, so that each is supplied with a quantity determined from the measured value as an input quantity, or are arranged in series to each other, so that one of the signal filters is supplied with the quantity determined from the measured value as an input quantity and at least one subsequent signal filter is supplied with an output quantity of each preceding signal filter as an input quantity.

[0056] The advantages of such a drive system design and such a procedure have already been mentioned. Both the drive system and the method for operating it may be further developed as explained in this description, and reference is made to those explanations.

[0057] 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.

[0058] 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.

[0059] The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. The drawing shows: Figure 1 is a schematic representation of a section of a drive unit, more precisely an exhaust aftertreatment unit of the drive unit, and Figure 2 is a schematic representation of a transmission system, which illustrates by way of example the determination of combustion air ratios from a measured value of a lambda probe, and Figure 3 is several diagrams in which combustion air ratios in different sections of the exhaust aftertreatment unit are plotted over time for different determination methods.

[0060] The Figure 1Figure 1 shows a highly schematic representation of a section of a drive unit that includes an exhaust gas-generating drive system, specifically an exhaust aftertreatment unit 1 of the drive unit. Fuel and fresh gas are supplied to the drive system, forming a fuel-fresh gas mixture that reacts chemically to produce exhaust gas. The exhaust gas is fed to the exhaust aftertreatment unit and flows through it in the direction of arrow 2. Upstream of the exhaust aftertreatment unit 1, a lambda sensor 3 measures the air-fuel ratio. This measurement describes the residual oxygen content of the exhaust gas, or the air-fuel ratio at the lambda sensor 3.

[0061] Based on the measured value from lambda sensor 3, the composition of the exhaust gas downstream of the exhaust aftertreatment device 1 is determined using an exhaust aftertreatment model. This is done for at least one exhaust gas component, but preferably for several exhaust gas components. The exhaust aftertreatment model comprises several exhaust aftertreatment sub-models; in the embodiment shown here, four exhaust aftertreatment sub-models. Using each of the exhaust aftertreatment sub-models, one of several sections 4 of the exhaust aftertreatment device 1 is calculated. The sections 4 extend from an inlet 5 to an outlet 6 of the exhaust aftertreatment device 1 and are directly adjacent to each other. The sections 4 thus extend continuously and without interruption from the inlet 5 to the outlet 6.

[0062] For each of the sections 4, an inlet concentration and an inlet air-fuel ratio are determined, namely at the respective inlet point 7. Using the respective exhaust aftertreatment sub-model, an outlet concentration of the respective exhaust gas component is subsequently determined at a respective outlet point 8 of the corresponding section 4. Preferably, the inlet concentration for a further downstream section 4 is equal to the outlet concentration of the immediately upstream section 4. The inlet concentration of the most upstream section 4 is equal to the inlet concentration of the exhaust aftertreatment device 1, and the outlet concentration of the exhaust aftertreatment device 1 is equal to the outlet concentration of the most downstream section 4.

[0063] 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).

[0064] The Figure 2Figure 1 shows a schematic representation of a transmission system, which illustrates different variants for determining the inlet combustion air ratios for Section 4. An inlet 9 is shown, at which a value determined from the measured value of the lambda sensor 3 is provided as an input variable. The input variable is fed to different filter units 10, 11, 12, and 13. Several combustion air ratios result from each of the filter units 10, 11, 12, and 13, which are fed as output variables to the exhaust aftertreatment model 14. Of course, preferably only one of the filter units 10, 11, 12, and 13 and only one exhaust aftertreatment model 14 are used at any given time. The other elements are omitted.

[0065] In the illustrated embodiment, each of the filter devices 10, 11, 12, and 13 has three signal filters 15, 16, and 17. Each of the signal filters 15, 16, and 17 provides an output variable which is fed to the exhaust aftertreatment model 14. In total, the exhaust aftertreatment model 14 receives the variable determined from the measured value, which is provided at input 9, as well as the output variables resulting from the signal filters 15, 16, and 17. The combustion air-fuel ratio measured by the lambda sensor 3 is fed to a first exhaust aftertreatment sub-model, and the combustion air-fuel ratios determined using the signal filters 15, 16, and 17 are fed to the subsequent exhaust aftertreatment sub-models.

[0066] In the case of filter device 10, the signal filters 15, 16, and 17 are arranged in parallel and each has a transfer element 18, 19, and 20, respectively. The transfer elements 18, 19, and 20 are designed as first-order lag elements (PT1 elements). A filter coefficient is supplied to each of the transfer elements 18, 19, and 20, with the filter coefficient for transfer element 18 being provided at an input 21, for transfer element 19 at an input 22, and for transfer element 20 at an input 23. The filter coefficients for the transfer elements 18, 19, and 20 are preferably different from one another.

[0067] For filter assembly 11, signal filters 15, 16, and 17 are connected in series. Each signal filter 15, 16, and 18 in turn has one of the transfer elements 18, 19, and 20, which are again implemented as first-order lag elements (PT1 elements). Filter coefficients, supplied at input 24, are fed to signal filters 15, 16, and 17, or rather to transfer elements 18, 19, and 20. The filter coefficients for signal filters 15, 16, and 17 are therefore identical.

[0068] For the filter arrangement 12, the signal filters 15, 16, and 17 are again arranged in series. In addition to the respective transfer element 18, 19, and 20, each of the signal filters 15, 16, and 17 has a further transfer element 25, 26, and 27, respectively. Filter coefficients are provided to the signal filters 15, 16, and 17, or rather to their transfer elements 18, 19, 20, and 24, 26, and 27, via an input 28. The filter coefficients are preferably identical.

[0069] In filter assembly 13, the signal filters 15, 16, and 17, in addition to the transfer elements 18, 19, and 20, have dead-time elements 29, 30, and 31. Filter coefficients are provided to the signal filters 15, 16, and 17 of filter assembly 13, or rather to their transfer elements 18, 19, and 20, via input 28. A propagation delay or dead time is provided for the dead-time elements 29, 30, and 31 via input 32. Preferably, the same dead time is used for all dead-time elements 29, 30, and 31.

[0070] The Figure 3The diagrams show the combustion air ratios for the several sections 4 over time. Each diagram contains curves 33, 34, 35, and 36. Curve 33 represents the lambda sensor reading, or the combustion air ratio determined from it, which is used as the inlet combustion air ratio for the first section 4. Curve 34 describes the inlet combustion air ratio for the second section 4, curve 35 for the third section 4, and curve 36 for the fourth section 4. The top diagram shows curves 33, 34, 35, and 36 for the first filter unit 10, the second diagram for the second filter unit 11, the third diagram for the third filter unit 12, and the bottom diagram for the fourth filter unit 13. It is understood that only one of the filter units 10, 11, 12, and 13 is used at any given time.The joint presentation serves only for illustrative purposes.

[0071] Using the described filter arrangement 10, 11, 12, and 13, the combustion air conditions can be accurately determined at several points downstream of the lambda sensor 3. The use of the signal filters 15, 16, and 17 requires minimal computational effort. This also applies to the transfer elements 18, 19, and 20 as well as 24, 26, and 27, i.e., to the dead-time elements 29, 30, and 31. Based on the determined combustion air conditions, the operation of the exhaust aftertreatment model, and consequently the determination of the concentration of at least one exhaust gas component downstream of the exhaust aftertreatment device 1, is also possible with high accuracy. REFERENCE MARK LIST:

[0072] 1 Exhaust aftertreatment unit 2 Arrow 3 Lambda probe 4 Section 5 Inlet 6 Outlet 7 Inlet point 8 Outlet point 9 Inlet 10 Filter unit 11 Filter unit 12 Filter unit 13 Filter unit 14 Exhaust aftertreatment model 15 Signal filter 16 Signal filter 17 Signal filter 18 Transmission element 19 Transmission element 20 Transmission element 21 Inlet 22 Inlet 23 Inlet 24 Inlet 25 Transmission element 26 Transmission element 27 Transmission element 28 Inlet 29 Dead time element 30 Dead time element 31 Dead time element 32 Inlet 33 Pathway 34 Pathway 35 Pathway 36 Pathway

Claims

1. Method for operating a drive unit for a motor vehicle, which has an exhaust gas generating drive unit, an exhaust gas aftertreatment device (1) for aftertreatment of the exhaust gas and a lambda probe (3) arranged upstream of the exhaust gas aftertreatment device (1), characterized by the fact thatCombustion air conditions for exhaust gas present at several locations downstream of the lambda sensor (3) are determined from a measured value of the lambda sensor (3) by means of signal filters (15, 16, 17) each having a linear time-invariant transfer element (18, 19, 20), wherein the signal filters (15, 16, 17) are arranged in parallel to each other, so that a quantity determined from the measured value is supplied to each of them as an input, or in series to each other, so that the quantity determined from the measured value is supplied to one of the signal filters (15, 16, 17) as an input and at least one subsequent signal filter (15, 16, 17) is supplied with an output of each preceding signal filter (15, 16, 17) as an input.

2. Method according to claim 1, characterized by the fact thatan outlet concentration of at least one exhaust gas component downstream of the exhaust aftertreatment device (1) is determined by means of an exhaust aftertreatment model (14) which comprises several exhaust aftertreatment sub-models for modeling different sections of the exhaust aftertreatment device (1), wherein the exhaust aftertreatment sub-models are supplied with inlet concentrations determined for several inlet points (7) as input variables and inlet combustion air ratios determined for the inlet points (7), wherein the combustion air ratios are used as inlet combustion air ratios.

3. Method according to any one of the preceding claims, characterized by the fact that different filter coefficients are used for the parallel signal filters (15, 16, 17), and / or the same filter coefficients are used for the serial signal filters (15, 16, 17).

4. Method according to any one of the preceding claims, characterized by the fact that the signal filters (15, 16, 17) each have only one transmission element (18, 19, 20), or that each of the signal filters (15, 16, 17) has, in addition to the respective transmission element (18, 19, 20), another transmission element (25, 26, 27) which is connected in series with the transmission element (18, 19, 20).

5. Method according to any one of the preceding claims, characterized by the fact that the filter coefficients are determined depending on one of the following quantities: temperature, exhaust gas flow rate and oxygen storage capacity of the exhaust aftertreatment system (1).

6. Method according to any one of the preceding claims, characterized by the fact that a PT1 element is used as a transfer element (18, 19, 20) and / or as a further transfer element (25, 26, 27).

7. Method according to any of the preceding claims, characterized by the fact thatIn each of the signal filters (15, 16, 17) a dead time element (9, 20, 30, 31) is used.

8. Method according to any one of the preceding claims, characterized by the fact that Upstream of the exhaust aftertreatment device (1) a further exhaust aftertreatment device and upstream of the further exhaust aftertreatment device a further lambda probe is arranged, wherein the measured value of the lambda probe (3) and a measured value of the further lambda probe are used to perform lambda control.

9. Drive unit for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive unit has an exhaust gas generating drive unit, an exhaust gas aftertreatment device (1) for aftertreatment of the exhaust gas and a lambda probe (3) arranged upstream of the exhaust gas aftertreatment device (1), characterized by the fact thatThe drive system is designed and configured to determine combustion air conditions for exhaust gas present at several locations downstream of the lambda sensor (3) from a measured value of the lambda sensor (3) by means of signal filters (15, 16, 17) each having a linear time-invariant transfer element (18, 19, 20), wherein the signal filters (15, 16, 17) are arranged in parallel to each other, so that each is supplied with a quantity determined from the measured value as an input, or in series to each other, so that one of the signal filters (15, 16, 17) receives the quantity determined from the measured value as an input and at least one subsequent signal filter receives an output quantity of each preceding signal filter (15, 16, 17) as an input.

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

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