Method and computing unit for determining the filling level of exhaust gas components in a catalytic converter

Abstract

The invention relates to a method and a computing unit for determining a filling level of an exhaust gas component in a catalytic converter. The invention relates to a method for determining a filling level of at least one exhaust gas component, which is generated in a combustion process, storable in a catalytic converter (130), wherein a change of the filling level of the at least one exhaust gas component in the catalytic converter (130) is determined (230) during a combustion process; wherein a diffusion-induced change of the filling level of the at least one exhaust gas component in the catalytic converter (130) is determined (260) during a period of time in which the combustion process is not running; and wherein the filling level of the at least one exhaust gas component in the catalytic converter (130) is determined (270) based on the determined change during the combustion process and based on the diffusion-induced change. Furthermore, the invention relates to a computing unit (140) for carrying out such a method (200) and to a computer program.

Description

Technical Field

[0001] The present invention relates to a method for determining the filling level of exhaust gas components in a catalyst, and to a computing unit and computer program for performing the method. Background Technology

[0002] Modern motor vehicles are often equipped with catalytic converters for after-treatment of exhaust gases from internal combustion engines. In many cases, these catalytic converters are monitored and / or regulated.

[0003] When the fuel / air mixture undergoes incomplete combustion in a gasoline engine, in addition to nitrogen (N2), carbon dioxide (CO2), and water (H2O), a variety of combustion products are emitted, including hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). x Legally, this is restricted. With current technology, compliance with applicable emission limits for motor vehicles can only be achieved through catalytic converters. These harmful components can be converted using, for example, a three-way catalytic converter.

[0004] In a three-way catalytic converter, HCl, CO, and NO are achieved only within a narrow λ range (λ=1) around the stoichiometric operating point (the so-called "catalytic window" or "conversion window"). x At the same time, it has a high conversion rate.

[0005] To operate the three-way catalytic converter within the transition window, current engine control systems typically employ λ regulation, based on signals from λ detectors positioned before and after the catalytic converter. To adjust the charge coefficient λ (a measure of the fuel / air ratio of the internal combustion engine), the oxygen content of the exhaust gas before the catalytic converter is measured using a λ detector located on the input side. Based on this measurement, the regulation corrects the fuel quantity or injection duration, which is pre-given, for example, in the form of a base value of a pre-control function.

[0006] Within the pre-controlled range, a baseline value for the amount of fuel to be injected is predetermined based on, for example, the engine speed and load. For even more precise regulation, additional λ detectors can be used to detect the oxygen concentration in the exhaust gas downstream of the three-way catalytic converter. The signal from the output-side λ detector can be used for guided regulation, which is superimposed on the λ regulation based on the input-side λ detector signal before the three-way catalytic converter. As the λ detector positioned after the three-way catalytic converter, a step-λ detector is typically used, which has a very steep characteristic curve at λ=1 and therefore can very accurately indicate λ=1.

[0007] In addition to the usual guide adjustment that only corrects and relatively slowly corrects small deviations from λ=1, to quickly reach the switching window, another function can be set in the form of λ pre-control with a large deviation from λ=1. This is important, for example, after a coasting disconnect phase, in which oxygen is loaded into the three-way catalytic converter. Loading oxygen hinders NO. x Conversion.

[0008] Due to the oxygen storage capacity of the three-way catalytic converter, after a concentrated or lean oxygen level (λ) has been set before the catalytic converter, there may be a period of several seconds after the catalytic converter where λ=1. The temporary oxygen storage characteristic of the three-way catalytic converter is fully utilized to compensate for the short-term deviation from λ=1 before the catalytic converter. If a λ other than 1 exists before the catalytic converter for a longer period, the same λ will appear after the catalytic converter if the oxygen filling level exceeds the oxygen storage capacity when λ>1 (oxygen excess), or if oxygen is no longer stored in the catalytic converter when λ<1.

[0009] At this point in time, the step-laminar detector following the three-way catalytic converter indicates the exit from the transition window. However, until this point, the signal from the lambda detector following the three-way catalytic converter does not indicate the impending gap, and the steering based on this signal often reacts too late, so that fuel metering can no longer react in time before the gap. As a result, increased emissions occur. This steering scheme therefore has the disadvantage that the steering scheme, which relies on the voltage of the step-laminar detector following the three-way catalytic converter, only identifies the exit from the transition window very late.

[0010] From DE 10 2016 222 418 A1, a model-based regulation scheme is known, in which λ sensors are arranged before and after the catalyst in the direction of exhaust gas flow, and the catalyst model is used to model the fill level of the catalyst in one or more exhaust gas components, especially oxygen. Summary of the Invention

[0011] According to the present invention, a method, as well as a computing unit and computer program for performing the method, are proposed: the method is used to determine the fill level of at least one exhaust gas component that can be stored in a catalyst, the exhaust gas component being generated during combustion. Advantageous construction schemes are also the subject of this invention.

[0012] According to the invention, a method for determining the fill level of at least one exhaust gas component in a catalyst, said at least one exhaust gas component being stored in the catalyst and generated during combustion, wherein changes in the fill level of said at least one exhaust gas component in the catalyst are determined during the combustion process, wherein the concentration of said at least one exhaust gas component upstream and / or downstream of the catalyst is determined and a concentration gradient is thereby determined, wherein during periods when the combustion process is not running, the diffusion-induced change in the fill level of said at least one exhaust gas component in the catalyst is determined by considering the diffusion direction of said at least one exhaust gas component calculated based on the concentration gradient, wherein the fill level of said at least one exhaust gas component in the catalyst is determined based on the determined change during the combustion process and based on the diffusion-induced change, and wherein, after combustion is resumed, the fill level of said at least one exhaust gas component is adjusted based on the determined fill level. The invention utilizes measures that, when determining the fill level of an exhaust gas component in a catalyst (especially the fill level of oxygen in a three-way catalytic converter), not only consider changes in the component in the catalyst caused by combustion, but also consider diffusion processes occurring outside of combustion. In particular, the present invention utilizes modeling of the diffusion of gaseous oxygen into the catalyst and the storage of oxygen into the catalyst in the case of a vertical internal combustion engine.

[0013] This allows for more accurate determination of instantaneous fill levels. By considering the diffusion processes that lead to changes in oxygen fill levels in the catalyst, model-based adjustments to the catalyst can be implemented to further improve its performance. These adjustments can be used to identify and prevent, as much as possible, departure from the catalyst window, or to allow the catalyst to return to the window with minimal emissions after departure. For example, modeling of the catalyst fill level is more accurate from the outset when combustion is resumed. This allows for more reliable prevention and overall reduction of harmful emissions, while simultaneously enabling more effective control of the combustion process.

[0014] In a favorable construction scheme, at least one state variable of the catalyst, particularly temperature and / or temperature distribution, is determined, and the diffusion-induced change in the catalyst fill level is determined based on at least one state variable. This is advantageous because temperature and other influencing parameters have a decisive impact on the diffusion process.

[0015] Advantageously, the concentration of at least one exhaust gas component upstream and / or downstream of the catalyst is determined, and the diffusion direction and / or diffusion rate of the at least one exhaust gas component is calculated based on the concentration gradient thus determined, and said diffusion direction and / or diffusion rate are taken into account in the calculation of the diffusion-induced changes in the catalyst fill level. In this way, the diffusion direction and diffusion rate can be determined more accurately, which has a positive impact on the fill level model.

[0016] Advantageously, after combustion is resumed, the fill level of at least one exhaust gas component is adjusted based on the measured fill level, i.e., the measured value is used as the actual value to adapt combustion to the rated value. In particular, this includes controlling the combustion process such that if the fill level is below the rated value, the fill level is increased, and if the fill level is above the rated value, the fill level is decreased. In this way, the diffusion of exhaust gas components during the time when the combustion process is not running can be taken into account in the subsequent operation of the controlled combustion process, so as to reduce emissions overall.

[0017] Preferably, at least one exhaust gas component includes oxygen and / or hydrocarbons and / or carbon monoxide and / or nitrogen oxides. These are particularly relevant to the control of the exhaust gas catalyst. In particular, the diffusion of oxygen into the catalyst plays a decisive role in reducing total emissions.

[0018] Advantageously, the combustion process is performed inside the internal combustion engine, especially in vehicles. These applications contribute significantly to the emission of corresponding harmful substances into the surrounding environment and are subject to particular legal restrictions, creating a special need for adaptation.

[0019] The computing unit (e.g., a control device for a motor vehicle) according to the invention is specifically configured using programming techniques to execute the method according to the invention.

[0020] An embodiment of the method according to the invention in the form of a computer program or computer program product is also advantageous, having program code for performing all method steps, because this results in particularly low cost, especially when the control device used for implementation is also used for other tasks and is therefore already present. Suitable data carriers for providing the computer program are, in particular, magnetic, optical, and electrical memories, such as, for example, hard disks, flash memory, EEPROM, DVDs, and more. Downloading the program via a computer network (Internet, intranet, etc.) is also possible. Attached Figure Description

[0021] Other advantages and construction methods of the present invention will become apparent from this description and the accompanying drawings.

[0022] The invention is illustrated schematically with reference to the embodiments in the accompanying drawings, and is described below with reference to the drawings.

[0023] Figure 1 A schematic diagram illustrates an apparatus having an internal combustion engine, the apparatus being configured with an advantageous structure for performing the method according to the invention.

[0024] Figure 2 An advantageous construction scheme of the method according to the invention is shown in the form of a highly simplified flowchart. Detailed Implementation

[0025] exist Figure 1 The device is shown in the diagram and is generally marked with 100. The device is configured in an advantageous way for performing the method according to the invention, and the device can be arranged, for example, in a vehicle.

[0026] The device 100 includes: an internal combustion engine 120, such as a diesel engine or a gasoline engine; a fuel treatment device 110; an exhaust gas catalytic converter 130, which may be configured as a three-way catalytic converter, for example; a computing unit 140, such as an engine control unit (ECU); and sensors 145, 147, which are provided, for example, in the form of a laser sensor, a thermocouple, a pressure sensor, and / or a measuring device for concentration, temperature, pressure, or other physical or chemical variables that may describe or affect the state of the exhaust system.

[0027] In particular, the present invention utilizes modeling of the diffusion of gaseous oxygen into the catalyst 130 and the storage of oxygen into the catalyst 130 in the case of a vertical internal combustion engine 120. For this purpose, it can be configured to detect the current state variables of the catalyst during the transition from the operating phase to the diffusion phase in the vertical internal combustion engine. These include, for example, the fill level in the catalyst, such as the oxygen fill level or the fill level or distribution of the oil and gas components, the storage capacity of the catalyst, and the average temperature of the catalyst or the temperature distribution within the catalyst. Using these state variables, a diffusion model of the catalyst is initialized, which depicts the temporal evolution of the oxygen fill level of the actual catalyst during the diffusion phase.

[0028] During the transition from the diffusion stage to the stage with an operating internal combustion engine, the state variables of the diffusion model are detected in reverse, and the catalyst model is initialized with the aid of the state variables. The catalyst model depicts the time evolution of the oxygen fill level of the actual catalyst under the condition of an operating internal combustion engine 120.

[0029] This approach allows for better consistency between the modeled and actual state variables of the catalyst, directly after the diffusion stage. Furthermore, it enables better calibration of the catalyst's fill level after the internal combustion engine starts. Emissions can thus be reduced. For the catalyst, stringent legal requirements can be met at a lower cost.

[0030] exist Figure 2 The construction scheme of the method according to the invention is shown in a very simplified flowchart, and the construction scheme of the method according to the invention is generally indicated by 200.

[0031] The method begins with an initialization step 210, in which, for example, instructions for controlling device 140 are output to components of device 100.

[0032] In step 220, the state of the exhaust gas produced by the internal combustion engine 120 is determined. For this purpose, signals detected by one or more sensors 145, 147 (e.g., a lambda detector 145) arranged upstream of the exhaust gas catalyst 130 can be evaluated. For example, in step 220, the mass flow rate and oxygen concentration of the exhaust gas are measured. From the measured state of the exhaust gas, the fill level of the exhaust gas catalyst 130 is determined in step 230. For example, the fill level relates to the amount of oxygen stored in the catalyst 130, and is related to the maximum or currently highest amount of oxygen that can be stored. For this purpose, for example, a model calculation based on a catalyst plant model can be considered, which is parameterized, for example, using the sensor data detected in step 220. Current and / or earlier control parameters output or previously output by the control device 140 to the internal combustion engine 120 or the fuel treatment device 110 can also be incorporated into such model calculations. Modeling of oxygen fill levels in catalysts is described, for example, in Lino Guzzella and Christopher H. Onder’s “Introduction to Modeling and Control of Internal Combustion Engine Systems” (ISBN 978-3-642-10774-0), Section 2.8.3.

[0033] In step 250, the state of the exhaust gas catalyst 130 is monitored. For example, this is done by using one or more sensors 145 and 147 to measure the temperature or temperature distribution within the catalyst 130, to measure the concentration of one or more exhaust gas components within, upstream of and / or downstream of the catalyst 130, and / or to measure the pressure upstream of, within and / or downstream of the catalyst 130.

[0034] In step 240, it is determined whether the internal combustion engine is currently running. If so, in step 280, the operation of the internal combustion engine 120 is adjusted based on the determined catalytic converter fill level and, if necessary, other parameters such as current load requirements, pre-defined desired or required exhaust gas components, current exhaust gas temperature, etc. For this purpose, the fuel treatment equipment 110 can be affected from the control device 140 side. For example, the amount of metered fuel can be set, or the position of the throttle valve for combustion air supply can be affected. The influence on the internal combustion engine 120 can also be performed directly, for example, by pre-setting the ignition timing.

[0035] Then, method 200 returns to initialization step 210.

[0036] If it is determined in step 240 that the internal combustion engine 120 has stopped operating, then in step 260, taking into account the catalytic converter state determined in step 250, the diffusion of at least one exhaust gas component (especially oxygen) into or from the exhaust gas catalytic converter or within the exhaust gas catalytic converter is determined. For example, the temperature of the catalytic converter is considered for this purpose, such that the diffusion rate at high temperatures is greater than the diffusion rate at low temperatures. Furthermore, a temperature threshold can be set below or above which no diffusion is determined, because, for example, the catalytic converter cannot store exhaust gas components at such temperatures.

[0037] When determining the diffusion of exhaust gas components, it is also advantageous to consider the concentration of the exhaust gas components within or at different locations within the environment of the catalyst 130, since diffusion proceeds along the direction of the concentration gradient. Therefore, the diffusion direction depends on the relative concentration of the exhaust gas components at locations where they are fluidly connected. Here, oxygen sources and sinks in the environment surrounding the catalyst are suitably considered. Preferably, the changes in the concentration of gaseous oxygen within and around the catalyst are described in a spatially resolved manner, for example, using a diffusion equation (Second Fick's Law). Similarly, it is possible to describe the concentration changes in multiple sequentially arranged catalysts.

[0038] If unoccupied storage sites exist and the catalyst temperature is sufficiently high, gaseous oxygen introduced into the catalyst can be stored within it. The temperature-dependent kinetics of storage are preferably modeled using the Arrhenius method. The number of unoccupied storage sites is determined by calculating the total available storage sites, the storage sites already occupied by oxygen, and the storage sites occupied by other exhaust gas components. Oxygen storage is also preferably described in a spatially resolved manner, for example, by modeling multiple axial plates (Scheiben). Alternatively, although less accurate, the variation in oxygen fill level during the diffusion phase can also be described data-driven, for example, by a family of characteristic curves relating to the duration of the diffusion phase and the temperature of (multiple) catalysts.

[0039] In step 270, the measured diffusion is offset using the catalyst fill level finally determined in step 230 or given in advance in initialization step 210, and the updated fill level of the catalyst is thus determined.

[0040] The method 200 then returns to step 240, or returns to the initialization step 210.

[0041] The linearity shown here in method 200 is entirely for comprehensibility. In different construction schemes, multiple steps in steps 210 to 280 can be performed simultaneously or in a different order without generally interfering with method 200. For example, exhaust gas concentration measurements can be performed substantially continuously and are independent of whether the fill level calculation has been completed. Temperature can also be monitored substantially continuously. Determining the diffusion of exhaust gas components is particularly meaningful if no fresh exhaust gas is being generated, i.e., the internal combustion engine is not running. If the internal combustion engine 120 is running, the flow velocity of the exhaust gas generated through the catalyst 130 is generally high enough that the diffusion of exhaust gas components may at most have a negligible effect on the transport process taking place in the catalyst.

[0042] The fill level of the catalytic converter 130 is thus dominated by a calculation during the operation of the internal combustion engine 120, which is a calculation of the exhaust gas components input into the catalytic converter 130 by the internal combustion engine and the exhaust gas components dispersed from the catalytic converter 130 toward the atmosphere. If the internal combustion engine stops operating, the reverse flow direction can be determined, at least for a portion of the exhaust gas components, depending on the current state of the catalytic converter 130 and its environment, such that, for example, oxygen can be input into the catalytic converter from the direction of the tailpipe. This situation is considered using the described method 200, so that a more accurate fill level of the catalytic converter 130 can be provided relative to the exhaust gas components stored therein, and correspondingly, the control of the internal combustion engine can be performed more precisely and in an emissions-optimized manner. The determination of the catalytic converter fill level can be used, particularly for fill level adjustment, to use the most accurate actual value possible when combustion is resumed, and thus to properly control the combustion process from the beginning.

[0043] Especially for vehicles equipped with start-stop systems, or for hybrid vehicles, there is significant potential for emissions optimization.

[0044] For applications beyond super-motorized mobility, the corresponding advantages can also be achieved, and the more frequently the corresponding combustion process is put into and stopped, the stronger these advantages become.

Claims

1. A method for determining the fill level of at least one exhaust gas component in a catalyst (130), said at least one exhaust gas component being capable of being stored in said catalyst (130), said at least one exhaust gas component being generated during combustion. in, During the combustion process, the change in the fill level of the at least one exhaust gas component in the catalyst (130) is determined (230). Wherein, the concentration of at least one exhaust gas component (220) upstream and / or downstream of the catalyst is determined, and the concentration gradient is thereby measured. During the period when the combustion process is not in operation, the change in the diffusion of the at least one exhaust gas component in the catalyst (130) caused by the diffusion of the at least one exhaust gas component is determined (260) by taking into account the diffusion direction of the at least one exhaust gas component calculated based on the concentration gradient. Among them, based on the changes determined during the combustion process and based on the changes caused by diffusion, the filling level of the at least one exhaust gas component in the catalyst (130) is determined (270), and Wherein, after combustion is restored, the fill level of the at least one exhaust gas component is adjusted based on the measured fill level.

2. The method (200) according to claim 1, wherein, Determine (250) at least one state variable of the catalyst (130), and determine (260) the diffusion-induced change in the fill level based on the at least one state variable.

3. The method (200) according to claim 2, wherein, The at least one state variable is temperature and / or temperature distribution.

4. The method according to claim 1, wherein, The diffusion rate of the at least one exhaust gas component is calculated based on the concentration gradient, and the diffusion direction and / or diffusion rate of the at least one exhaust gas component are taken into account in determining the diffusion-induced change of the filling level (260).

5. The method according to claim 1, wherein, The combustion process is controlled (280) such that if the fill level is below the rated value, the fill level is increased, and if the fill level is above the rated value, the fill level is decreased.

6. The method (200) according to any one of claims 1-5, wherein, The at least one component of the exhaust gas includes oxygen and / or hydrocarbons and / or carbon monoxide and / or nitrogen oxides.

7. The method (200) according to any one of claims 1-5, wherein, The combustion process is performed inside the internal combustion engine (120).

8. The method (200) according to claim 7, wherein, The internal combustion engine (120) is located in the vehicle.

9. A computer program product having a computer program, wherein when the computer program is executed on a computing unit (140), the computer program causes the computing unit (140) to perform all method steps of the method according to any one of claims 1 to 8.

10. A machine-readable storage medium having a computer program stored thereon, which, when executed on a computing unit (140), causes the computing unit (140) to perform all the method steps of the method according to any one of claims 1 to 8.

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