Method for operating a drive unit for a motor vehicle, 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 (12) designed as a vehicle catalyst for aftertreating the exhaust gas with temperature-dependent conversion capacity for pollutants contained in the exhaust gas. It is provided that a section of the exhaust gas aftertreatment unit (12) is determined in which the exhaust gas aftertreatment unit (12) has a temperature that corresponds at least to an operating temperature of the exhaust gas aftertreatment unit (12), an exhaust gas flow rate threshold is determined from this section, and the drive unit (2) is operated such that the exhaust gas flow rate of the exhaust gas generated by the drive unit (2) does not exceed the exhaust gas flow rate threshold.The invention further relates to a drive device (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 includes an exhaust gas-generating drive unit and an exhaust gas aftertreatment device designed as a vehicle catalyst for aftertreating the exhaust gas with temperature-dependent conversion capacity for pollutants contained in the exhaust gas. The invention further relates to a drive unit for a motor vehicle and a computer program product.

[0002] For example, German patent application DE 10 2021 102 240 A1 is known from the prior art. This relates to a method for operating an internal combustion engine comprising a combustion engine and an exhaust system with an exhaust aftertreatment device, wherein the exhaust aftertreatment device includes a nitrogen oxide converter and a nitrogen oxide storage device. It is provided that when the temperature of the nitrogen oxide converter is below its start-up temperature, the combustion engine is operated in a lean condition, and when the temperature of the nitrogen oxide converter is at least equal to the start-up temperature, the combustion engine is operated at least temporarily in a stoichiometric condition and the nitrogen oxide storage device is regenerated.

[0003] Furthermore, US 10,738,674 B2 discloses a device for heating a catalytic exhaust aftertreatment system.

[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 ensuring low tailpipe emissions of the drive unit.

[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 a component of the exhaust aftertreatment system is determined in which the exhaust aftertreatment system has a temperature that corresponds at least to an operating temperature of the exhaust aftertreatment system, an exhaust flow threshold is determined from the component, and the drive unit is operated such that the exhaust flow rate of the exhaust gas generated by the drive unit corresponds at most to the exhaust flow threshold.

[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 drive system serves to propel the motor vehicle, thus providing a drive torque directed towards propelling the motor vehicle. The drive unit comprises the drive system to provide this drive torque. The drive unit is preferably an internal combustion engine, in particular a gasoline or diesel engine. During operation, the drive unit is supplied with fuel and fresh gas at least intermittently, the fresh gas containing fresh air at least intermittently. Additionally, the fresh gas may contain exhaust gas if exhaust gas recirculation is implemented, whereby 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.

[0008] 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.

[0009] The exhaust aftertreatment system is in the form of a vehicle catalyst, in particular a three-way catalyst, oxidation catalyst, NO x - Storage catalyst or as an SCR catalyst. The vehicle catalyst is particularly preferably integrated into a particulate filter, especially a gasoline particulate filter or a diesel particulate filter. For this purpose, the particulate filter is, for example, provided with a catalytic coating. The conversion rate, and thus the conversion performance of the exhaust aftertreatment system, with which the pollutants are converted into harmless products, depends in particular on the composition of the exhaust gas supplied to the exhaust aftertreatment system and the temperature of the exhaust aftertreatment system.

[0010] The components of the exhaust gas produced by the engine are also referred to as raw emissions. Raw emissions describe the composition of the exhaust gas upstream of the exhaust aftertreatment system, or in terms of flow characteristics, between the engine and the exhaust aftertreatment system. As the exhaust gas passes through the aftertreatment system, some of the substances contained within it are transformed, thus changing its composition. The substances present in the exhaust gas downstream of the aftertreatment system, which constitute the exhaust gas, are also referred to as tailpipe emissions, since this is the composition of the exhaust gas released into the environment through the engine's tailpipe.

[0011] As mentioned, the amount of pollutants contained in the tailpipe emissions depends on the raw emissions, but also on the conversion efficiency of the exhaust aftertreatment system. This efficiency is temperature-dependent. Specifically, the conversion efficiency decreases the further the temperature of the exhaust aftertreatment system deviates from its operating temperature; in other words, the greater the absolute difference between the temperatures. The temperature of the exhaust aftertreatment system refers specifically to the temperature of a ceramic honeycomb structure coated with the catalytic material.

[0012] Particularly after a restart or re-start of the engine, the temperature of the exhaust aftertreatment system is lower than the operating temperature, at least across a portion of it. This is especially true if the exhaust aftertreatment system is heated by the exhaust gas itself and no additional heat is supplied beyond that contained in the exhaust gas. When heated by the exhaust gas, upstream sections of the exhaust aftertreatment system are heated first, so the temperature of downstream sections changes more slowly towards the operating temperature. This results in areas of the exhaust aftertreatment system with varying temperatures.

[0013] Different conversion rates occur in the areas of the exhaust aftertreatment system with different temperatures.

[0014] For example, the exhaust aftertreatment system exhibits a higher conversion efficiency in a first zone where the temperature has already reached operating temperature than in a second zone where the temperature is (still) lower than operating temperature. This means that the exhaust aftertreatment system's ability to treat the exhaust gas, or to convert the pollutants contained in the exhaust gas, is reduced. Accordingly, it is necessary to take measures to prevent unacceptably high pollutant emissions into the environment.

[0015] To this end, it is necessary to first determine the portion of the exhaust aftertreatment system in which the temperature of the exhaust aftertreatment system has already reached its operating temperature. This portion can be expressed, for example, as a proportion of the total length of the exhaust aftertreatment system or a honeycomb structure of the exhaust aftertreatment system in the main exhaust gas flow direction, or as a volume fraction of the total volume of the exhaust aftertreatment system or at least of its honeycomb structure. The portion is typically expressed as a percentage.

[0016] The exhaust gas flow rate threshold is then determined from the system component calculated in this way. This threshold describes the maximum exhaust gas flow rate at which the exhaust aftertreatment system, in its current state (i.e., with the current temperature distribution within the system), achieves the desired conversion efficiency. Until the exhaust gas flow rate threshold is reached by an actual exhaust gas flow rate through the aftertreatment system, it is ensured that the system achieves a conversion efficiency that is at least equal to, or even higher than, the desired conversion efficiency. Exhaust gas flow rate is preferably understood as a mass flow rate or a volume flow rate, i.e., an exhaust gas mass or volume per unit of time. The exhaust gas flow rate is expressed, for example, in kg / h (mass) or m³ / h. 3 / h (volume) is specified.

[0017] After determining the exhaust gas flow threshold, the drive unit is operated in such a way that the actual exhaust gas flow rate of the exhaust gas produced by the drive unit through the exhaust aftertreatment system does not exceed the exhaust gas flow threshold. For this purpose, the rated power of the drive unit is limited, for example, to a maximum rated power at which the exhaust gas flow rate does not exceed the exhaust gas flow threshold.

[0018] For example, the drive unit is designed to determine a target power output from the position of a control element, particularly an accelerator pedal, or to receive it from a driver assistance system that provides a corresponding target value. A setpoint power is then calculated from this target power and set on the drive unit, which is subsequently operated in such a way that the actual power output provided by the drive unit corresponds to the setpoint power. Preferably, the actual power output of the drive unit is regulated to match the setpoint power. To account for the exhaust gas flow threshold, the setpoint power is initially set to the target power, but is then limited towards higher values ​​up to the maximum power output at which the exhaust gas flow corresponds to the exhaust gas flow threshold.The described procedure ensures that the exhaust gas discharged from the drive unit into the external environment, i.e. the tailpipe emissions of the drive unit, always comply with specified values.

[0019] A further development of the invention provides that the component value is determined using a catalyst model to which at least one of the following quantities is supplied as input: the exhaust gas temperature, the exhaust gas flow rate, and the heat of reaction generated by the exhaust gas aftertreatment in the exhaust aftertreatment device. The catalyst model thus serves, at least, to determine the temperature distribution in the exhaust aftertreatment device and, accordingly, also the component value. Additionally, the catalyst model can be used to determine the composition of the exhaust gas downstream of the exhaust aftertreatment device, in particular from the raw emissions, i.e., the composition of the exhaust gas generated by the engine upstream of the exhaust aftertreatment device and the input quantity.

[0020] The exhaust gas temperature is, in particular, the temperature of the exhaust gas upstream of the exhaust aftertreatment system, preferably directly upstream of the exhaust aftertreatment system. As already explained, the exhaust gas flow rate is the quantity of exhaust gas flowing through the exhaust aftertreatment system per unit of time. The heat of reaction, on the other hand, describes the quantity of heat generated within the exhaust aftertreatment system itself per unit of time, namely due to the chemical reactions occurring within it during the conversion of the pollutants. At least one of the aforementioned quantities, but preferably several or all of them, are used as input for the catalyst model, which has at least the system component as its output.Using the described procedure, the equipment component and thus the exhaust gas flow threshold can be determined with high accuracy, reliably preventing the occurrence of undesirably large tailpipe emissions.

[0021] A further development of the invention provides that, in determining the exhaust gas flow threshold, at least one of the following parameters is taken into account in addition to the equipment component: a conversion power threshold and the exhaust gas temperature. The determination of the exhaust gas flow threshold is also carried out using a model, which is, for example, in the form of a mathematical relationship, a characteristic map, or a table. The exhaust gas flow threshold is used as the output variable of the model. The conversion power threshold and / or the exhaust gas temperature are used as input variables for the model.

[0022] The conversion power threshold corresponds to the minimum conversion power that the exhaust aftertreatment system must provide to achieve the desired tailpipe emissions. The conversion power threshold can therefore also be referred to as the minimum conversion power. The exhaust gas temperature is preferably the temperature of the exhaust gas upstream of the exhaust aftertreatment system, particularly immediately upstream of the system. At least one of these parameters is considered as an input when determining the exhaust gas flow threshold, but preferably several or both. This ensures particularly high accuracy in determining the exhaust gas flow threshold and correspondingly guarantees sufficiently low tailpipe emissions.

[0023] A further development of the invention provides that a value of at least 90%, at least 95%, or at least 98% is used for the conversion power threshold. Such a selection of the conversion power threshold ensures particularly reliable exhaust gas aftertreatment.

[0024] A further development of the invention provides that the exhaust gas flow threshold is determined using several characteristic maps stored for different values ​​of the device component. These characteristic maps are stored in the drive unit, for example, in a control unit of the drive unit, by means of which the described method is implemented. The characteristic maps relate the parameters used to determine the exhaust gas flow threshold to this threshold. For example, each of the characteristic maps describes the exhaust gas flow threshold for the conversion power threshold and / or the exhaust gas temperature.

[0025] It can be provided that the conversion power is plotted against the exhaust gas flow rate and / or the exhaust gas temperature in each of the characteristic maps. The system then determines, based on the respective characteristic map, the exhaust gas flow rate threshold up to which the conversion power is at least equal to the conversion power threshold. The stored characteristic maps describe different values ​​of the system's contribution. Using these characteristic maps, the exhaust gas flow rate threshold can be determined with high accuracy, ensuring that the desired tailpipe emissions are reliably met.

[0026] A further development of the invention provides that the characteristic maps are stored for at least values ​​of 0% and 100% of the system component. At a value of 0%, the temperature across the entire exhaust aftertreatment system is lower than its operating temperature; at a value of 100%, the temperature across the entire exhaust aftertreatment system is at least equal to the operating temperature. The characteristic maps thus encompass all possible values ​​of the system component, so that determining the exhaust gas flow threshold can be easily carried out, for example, by interpolation.

[0027] Preferably, characteristic curves are available for additional values ​​of the setup component; in particular, at least 5, at least 10, or at least 20 characteristic curves for different values ​​of the setup component are stored. The values ​​of the setup component can be evenly spaced from one another. Preferably, however, the distance between the values ​​decreases with increasing values, so that smaller values ​​have a greater distance from each other than larger values. This further improves the accuracy.

[0028] A further development of the invention provides that, based on the device component, a characteristic map is selected from the several stored characteristic maps and the selected characteristic map is used to determine the exhaust gas flow threshold. In particular, the characteristic map is selected that corresponds to or is closest to a value of the device component that is stored. The exhaust gas flow threshold is then determined based on this selected characteristic map. This already ensures a high degree of accuracy.

[0029] A further development of the invention provides that, based on the specific component of the system, a characteristic map is interpolated from the several stored characteristic maps, and the interpolated characteristic map is used to determine the exhaust gas flow threshold. This procedure is particularly useful if no characteristic map is stored for the specific component of the system, but rather characteristic maps are stored for values ​​of the component that differ from the specific component. In this case, for example, characteristic maps are selected that are stored for values ​​that are closest to the specific component on opposite sides of the system. The characteristic map is then interpolated from these, for example by linear interpolation. The exhaust gas flow threshold is then read from the interpolated characteristic map and used to control the drive unit.The described procedure further improves the accuracy of the exhaust gas flow threshold.

[0030] The invention further relates to a drive unit for a motor vehicle, in particular for carrying out the method according to the descriptions in this document, wherein the drive unit has an exhaust gas generating drive unit and an exhaust gas aftertreatment device designed as a vehicle catalyst for aftertreatment of the exhaust gas with temperature-dependent conversion capacity for pollutants contained in the exhaust gas.The drive unit is designed and configured to determine a component of the exhaust aftertreatment system in which the exhaust aftertreatment system has a temperature that corresponds at least to an operating temperature of the exhaust aftertreatment system, to determine an exhaust flow threshold value from the component, and to operate the drive unit in such a way that the exhaust flow rate of the exhaust gas generated by the drive unit does not exceed the exhaust flow threshold value.

[0031] The advantages of such a design of the drive system and such a procedure have already been mentioned. Both the drive system for the motor vehicle and the method for operating it can be further developed as described in this document, and reference is made to these details.

[0032] Furthermore, the invention relates to a computer program product comprising commands that cause the drive device to execute the described process steps according to the details of this description. For the advantages and possible advantageous embodiments, reference is made to the description in its entirety.

[0033] 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. 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, are also to be considered as encompassed by the invention.

[0034] The invention is explained in more detail below with reference to the exemplary embodiments illustrated in the drawing, without limiting the invention. The drawing shows: Fig. 1 a schematic representation of a drive unit for a motor vehicle, as well as Fig. 2 a characteristic map in which a conversion power of an exhaust aftertreatment device is plotted against an exhaust gas temperature and an exhaust gas mass.

[0035] The Fig. Figure 1 shows a schematic representation of a drive unit 1, which has a drive unit 2, in this case an internal combustion engine, and an exhaust system 3. In the illustrated embodiment, the drive unit 2 has several cylinders 4, each with a combustion chamber. Each of the cylinders 4 has at least one intake valve 5 and at least one exhaust valve 6. Fresh gas from a fresh gas tract 7 can be supplied to the respective cylinder 4 via each of the intake valves 5, whereas exhaust gas can be discharged from the corresponding cylinder 4 through each of the exhaust valves 6, namely in the direction of the exhaust system 3.

[0036] Fresh gas is supplied to the inlet valves 5 by means of a compressor 8, which is part of an exhaust gas turbocharger 9. In addition to the compressor 8, the exhaust gas turbocharger 9 has a turbine 10, which is fluidically connected to the outlet valves 6 via an exhaust line 11, which is part of the exhaust system 3. Downstream of the turbine 10 is an exhaust aftertreatment system 12, which here is designed as a vehicle catalyst, specifically a three-way catalyst. Downstream of the exhaust aftertreatment system 12, the exhaust system 3 opens into the external environment of the drive unit 1, for example via a tailpipe. It should be noted that the exhaust gas turbocharger 9 is purely optional. It can therefore be omitted.

[0037] Upstream of the exhaust aftertreatment system 12, a first lambda sensor 13 is located to determine the residual oxygen content and, correspondingly, the air-fuel ratio of the exhaust gas. Downstream of the exhaust aftertreatment system 12, a second lambda sensor 14 determines the residual oxygen content and, correspondingly, the air-fuel ratio of the exhaust gas. These two air-fuel ratios are used to adjust the composition of a fuel-air mixture, which reacts chemically in the drive unit 2, producing the exhaust gas. In the exhaust aftertreatment system 12, pollutants contained in the exhaust gas are converted into less harmful products.

[0038] The conversion capacity of the exhaust aftertreatment system 12, which converts the pollutants, is temperature-dependent. This temperature dependence applies not only to the exhaust gas temperature itself, but also to the catalyst temperature of the exhaust aftertreatment system 12. To ensure that the conversion capacity of the exhaust aftertreatment system 12 is always sufficiently high to achieve the desired tailpipe emissions, the portion of the system 12 in which a temperature at least corresponds to the operating temperature of the exhaust aftertreatment system 12 is present must first be determined.From this component of the equipment, an exhaust gas flow rate threshold is then determined and the drive unit 2 is operated in such a way that the exhaust gas flow rate, i.e. the exhaust gas flow rate of the exhaust gas generated by the drive unit 2, corresponds at most to the exhaust gas flow rate threshold.

[0039] The Fig.Figure 2 shows a characteristic map in which the conversion capacity x of the exhaust aftertreatment system 12 is plotted against an exhaust gas mass flow rate ̇ṁ and a temperature T, where the exhaust gas mass flow rate is given in kg / h and the temperature in °C. The characteristic map is based on a system operating time of 20%, thus indicating the conversion capacity of the exhaust aftertreatment system 12 for this 20% operating time, during which the system operates at a temperature at least equal to its operating temperature. Conversely, this means that for a further 80% operating time, the exhaust aftertreatment system operates at a temperature lower than its operating temperature.

[0040] It is clearly evident that the conversion efficiency decreases with decreasing temperature and increasing exhaust gas mass. For the given component share of the exhaust aftertreatment system 12, here 20%, the exhaust gas mass is determined for the given exhaust gas temperature at which the conversion efficiency corresponds to a conversion efficiency threshold of at least 0.9, at least 0.95, or at least 0.98. This exhaust gas mass is then used as the exhaust gas flow rate threshold, and the drive unit 2 is operated in such a way that the actual exhaust gas flow rate is less than or at most equal to the exhaust gas flow rate threshold. This ensures that the desired tailpipe emissions are achieved. REFERENCE MARK LIST: 1 Drive unit 2 Drive unit 3 Exhaust system 4 cylinders 5 Inlet valve 6 exhaust valve 7 Fresh gas tract 8 compressors 9 exhaust gas turbochargers 10 Turbine 11 Exhaust pipe 12 Exhaust aftertreatment system 13 1. Lambda sensor 14 2. Lambda sensor QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2021 102 240 A1

[0002] US 10,738,674 B2

[0003]

Claims

[1] Method for operating a drive device (1) for a motor vehicle, which has an exhaust gas generating drive unit (2) and an exhaust gas aftertreatment device (12) designed as a vehicle catalyst for aftertreating the exhaust gas with temperature-dependent conversion performance for pollutants contained in the exhaust gas, characterized by that a device portion of the exhaust gas aftertreatment device (12) is determined, in which the exhaust gas aftertreatment device (12) has a temperature which corresponds at least to an operating temperature of the exhaust gas aftertreatment device (12), an exhaust gas throughput threshold value is determined from the device portion and the drive unit (2) is operated in such a way that an exhaust gas throughput of the exhaust gas generated by the drive unit (2) corresponds at most to the exhaust gas throughput threshold value. [2] Method according to claim 1, characterized bythat the device proportion is determined on the basis of a catalyst model to which at least one of the following variables is supplied as an input variable: a temperature of the exhaust gas, an exhaust gas throughput and a reaction heat arising due to the aftertreatment of the exhaust gas in the exhaust gas aftertreatment device (12). [3] Method according to one of the preceding claims, characterized by that in determining the exhaust gas flow rate threshold, in addition to the device share, at least one of the following variables is taken into account: a conversion power threshold and the temperature of the exhaust gas. [4] Method according to one of the preceding claims, characterized by that the conversion performance threshold is set to a value of at least 90%, at least 95%, or at least 98%. [5] Method according to one of the preceding claims, characterized bythat the exhaust gas flow threshold is determined using several maps stored for different values ​​of the device share. [6] Method according to one of the preceding claims, characterized by that the characteristic maps are stored at least for values ​​of 0% and 100% of the facility share. [7] Method according to one of the preceding claims, characterized by that a map is selected from the several stored maps based on the device share and the selected map is used to determine the exhaust gas flow threshold value. [8] Method according to one of the preceding claims, characterized by that a map is interpolated from the several stored maps based on the device share and the interpolated map is used to determine the exhaust gas flow threshold value. [9] Drive device (1) for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive device (1) has an exhaust gas generating drive unit (2) and an exhaust gas aftertreatment device (12) designed as a vehicle catalyst for aftertreating the exhaust gas with temperature-dependent conversion performance for pollutants contained in the exhaust gas, characterized byin that the drive device (1) is provided and designed to determine a device portion of the exhaust gas aftertreatment device (12) in which the exhaust gas aftertreatment device (12) has a temperature which corresponds at least to an operating temperature of the exhaust gas aftertreatment device (12), to determine an exhaust gas throughput threshold value from the device portion and to operate the drive unit (2) in such a way that an exhaust gas throughput of the exhaust gas generated by the drive unit (2) corresponds at most to the exhaust gas throughput threshold value. [10] Computer program product comprising instructions which cause the drive device (1) according to claim 9 to carry out the method steps according to one of claims 1 to 8.

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