Method and calculation unit for determining the filling level of exhaust gas components in a catalyst

Abstract

To provide a method capable of reducing emission of harmful substances as a whole and simultaneously controlling a combustion process more efficiently.SOLUTION: The present invention relates to a method for determining a filling level of at least one exhaust gas component, which is generated in a combustion process and can be stored in a catalyzer. In the method: a change of the filling level of the at least one exhaust gas component in the catalyzer during the combustion process is decided (230); during a time period in which the combustion process is not operated, a change of the filling level caused by diffusion of the at least one exhaust gas component in the catalyzer is decided (260); and on the basis of the decided change during the combustion process and the change caused by the diffusion, the filling level of the at least one exhaust gas component in the catalyzer is determined (270). The invention furthermore relates to a computing unit and a computer program, which are for carrying out such a method (200).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for determining the filling level of exhaust gas components in a catalytic converter, as well as to a calculation unit and a computer program for carrying this out. [Background technology]

[0002] Modern vehicles are often equipped with catalytic converters to after-treat the exhaust gases of the internal combustion engine. In many cases, these catalytic converters are monitored and / or controlled.

[0003] Incomplete combustion of the fuel / air mixture in a gasoline engine results in the emission of numerous combustion products in addition to nitrogen (N2), carbon dioxide (CO2), and water (H2O), among which hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO X ) are regulated by law. With the current state of the art, current exhaust gas limit values for motor vehicles can only be met by catalytic exhaust gas aftertreatment. For example, three-way catalysts are used to convert the above-mentioned harmful components.

[0004] HC, CO and NO X Simultaneously, high conversion rates for 1 / 2 are only achieved in the case of three-way catalysts in a narrow lambda region centered around the stoichiometric operating point (lambda=1), the so-called "catalyst window" or "conversion window."

[0005] To activate the three-way catalyst in the conversion window, modern engine control systems typically use lambda control based on signals from lambda probes located before and after the three-way catalyst. To control the lambda air-fuel ratio, which is a measure of the fuel / air ratio composition of the internal combustion engine, the oxygen content of the exhaust gas before the three-way catalyst is measured by an input lambda probe located there. Depending on this measurement value, the control unit corrects the fuel amount or injection time, which are set by a feedforward control function, for example, in the form of a base value.

[0006] Within the scope of the feedforward control, a base value for the fuel quantity to be injected is set, for example, as a function of the engine speed or load. For even more precise control, the oxygen concentration of the exhaust gas downstream of the three-way catalytic converter can additionally be detected by a separate lambda probe. The signal of this output lambda probe can be used for a constant value control that is superimposed on the lambda control before the three-way catalytic converter, which is based on the signal of the input lambda probe. The lambda probe arranged after the three-way catalytic converter is usually a jump lambda probe, which has a very steep characteristic curve around lambda=1 and can therefore display lambda=1 very precisely.

[0007] In addition to the constant value control, which generally controls only small deviations from lambda=1 and is designed to be relatively slow, another functionality in the form of a lambda feedforward control after large deviations from lambda=1 can be provided in order to quickly reach the conversion window again, which is important, for example, after a phase with a coasting stop, in which the three-way catalyst is loaded with oxygen. The loading with oxygen is NO X It has a negative effect on conversion.

[0008] Due to the oxygen storage capacity of three-way catalysts, after a rich or lean lambda has occurred before the three-way catalyst, lambda = 1 can still be true for a few more seconds after the three-way catalyst. This property of the three-way catalyst to temporarily store oxygen is utilized to compensate for short-term deviations from lambda = 1 before the three-way catalyst. If a lambda not equal to 1 occurs before the three-way catalyst for a long period of time, the same lambda will also be true after the three-way catalyst as soon as the oxygen filling level exceeds the oxygen storage capacity under lambda > 1 (excess oxygen) or when there is no more oxygen stored in the three-way catalyst under lambda < 1.

[0009] At this point, the jump lambda probe after the three-way catalyst also indicates a deviation from the conversion window. However, until this point, the signal from the lambda probe after the three-way catalyst does not indicate an impending deviation, and therefore, fixed-value control based on this signal often reacts too slowly, to the point that fuel distribution is unable to react in time before the deviation occurs. This results in high emissions. Therefore, such control concepts have the disadvantage that deviations from the conversion window, based on the voltage of the jump lambda probe after the three-way catalyst, are only recognized late.

[0010] Patent document 1 discloses a model-based control concept in which lambda sensors are arranged before and after the catalytic converter in the direction of exhaust gas flow, and a catalytic converter model is used to model the catalytic converter filling level of one or more exhaust gas components, in particular oxygen. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] German Patent Application Publication No. 102016222418A1 Summary of the Invention

[0012] According to the invention, a method for determining the filling level in a catalytic converter of at least one exhaust gas component produced in a combustion process and capable of accumulating in the catalytic converter, as well as a computing unit and a computer program for carrying out the method, are proposed, which have the features of the respective independent claims. Preferred embodiments are the subject of the dependent claims and the following description.

[0013] The present invention applies a method for determining the filling level of exhaust gas components in the catalytic converter, in particular oxygen in a three-way catalytic converter, by taking into account not only the combustion-induced changes in the components in the catalytic converter but also diffusion processes occurring outside of combustion. In particular, the present invention applies to this purpose modeling of the diffusion of gaseous oxygen into the catalytic converter when the internal combustion engine is stopped and the uptake and accumulation of oxygen in the catalytic converter.

[0014] As a result, the current filling level at any given time can be determined more accurately. Taking into account the diffusion processes that lead to changes in the oxygen filling level in the catalytic converter allows for an even more improved model-based control of the catalytic converter, which in particular allows deviations from the catalytic converter window to be recognized early and prevented as far as possible, or allows the catalytic converter to be returned to the catalytic converter window after a deviation with as few emissions as possible. For example, when combustion is restarted, the catalytic converter filling level is modeled more accurately from the start. This allows harmful emissions to be prevented more reliably and reduced overall, while at the same time the combustion process can be controlled more efficiently.

[0015] In a preferred embodiment, at least one state variable of the catalyst, in particular the temperature and / or the temperature distribution, is determined and the change in the catalyst filling level due to diffusion is determined as a function of the at least one state variable, which is preferred because temperature and other influencing parameters have a decisive influence on the diffusion process.

[0016] Preferably, the concentration of at least one exhaust gas component is determined upstream and / or downstream of the catalytic converter, and the diffusion direction and / or diffusion rate of the at least one exhaust gas component is calculated with reference to the concentration gradient determined therefrom and taken into account in the calculation of the change in catalytic converter filling level due to diffusion, whereby the diffusion direction and diffusion rate can be determined more accurately, which has a positive effect on the filling level model.

[0017] Preferably, the filling level of at least one exhaust gas component after the restart of combustion is controlled based on the determined filling level, i.e., the determined value is adapted as an actual value to the setpoint by the control of the combustion. This includes, in particular, controlling the combustion process so that the filling level is increased when the setpoint is below and decreased when the setpoint is above. 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 controlling the subsequent operation of the combustion process, thereby reducing emissions overall.

[0018] Preferably, the at least one exhaust gas component comprises oxygen and / or hydrocarbons and / or carbon monoxide and / or nitrogen oxides, which are of particular importance for the control of the exhaust gas catalytic converter. In particular, the diffusion of oxygen into the catalytic converter plays a crucial role in reducing overall emissions.

[0019] In particular, combustion processes are preferably carried out in internal combustion engines of vehicles, which require special adaptation since such applications contribute significantly to the emission of corresponding pollutants into the environment and are subject to special legal restrictions.

[0020] A computing unit according to the invention, for example a control unit of a motor vehicle, is set up, in particular programmatically, to carry out the method according to the invention.

[0021] The implementation of the method according to the invention in the form of a computer program or computer program product having program code for performing all the method steps is also preferred, since this results in particularly low costs, especially when the executing control device is also utilized for further functions and therefore already exists. Suitable data carriers for providing the computer program are, in particular, magnetic, optical, and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, etc. Downloading the program via a computer network (Internet, intranet, etc.) is also possible.

[0022] Other advantages and embodiments of the invention will become apparent from the specification and accompanying drawings.

[0023] The invention is illustrated diagrammatically by way of example in the drawings and will be explained below with reference to the drawings. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a schematic diagram showing an arrangement including an internal combustion engine set up for carrying out a preferred embodiment of the method according to the invention; [Figure 2] 1 illustrates, in greatly simplified flow chart form, a preferred embodiment of the method according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0025] FIG. 1 shows in a schematic drawing an arrangement, generally designated 100, which may be located, for example, in a vehicle, set up for carrying out a preferred embodiment of the method according to the invention.

[0026] The structure 100 includes an internal combustion engine 120, such as a diesel or gasoline engine, a fuel preparation device 110, an exhaust gas catalyst 130, which may be configured, for example, as a three-way catalyst, a calculation unit 140, such as an engine control unit (ECU), and sensors 145, 147, which may be provided, for example, in the form of lambda sensors, thermocouples, pressure sensors, and / or measuring instruments for concentration, temperature, pressure, or other physical or chemical quantities that can describe or influence the state of the exhaust gas system.

[0027] In particular, the present invention applies modeling of the diffusion of gaseous oxygen into the catalytic converter 130 and the uptake and storage of oxygen in the catalytic converter 130 when the internal combustion engine 120 is stopped. To this end, it is intended that the latest catalytic converter state variables are detected during the transition from the operating phase of the internal combustion engine to the diffusion phase when the internal combustion engine is stopped. This may be, for example, the oxygen or rich gas component filling level, or the filling level distribution in the catalytic converter, the catalytic converter storage capacity, the average catalytic converter temperature, or the temperature distribution in the catalytic converter. These state variables are used to initialize a catalytic converter diffusion model that reflects the time trend of the actual catalytic converter oxygen filling level during the diffusion phase.

[0028] Conversely, when transitioning from the diffusion phase to the phase in which the internal combustion engine is operating, the state variables of the diffusion model are detected and used to initialize a model of the catalyst that reflects the time trend of the actual catalyst oxygen filling level when the internal combustion engine 120 is operating.

[0029] In this way, an improved correspondence between the modeled and actual catalytic converter state variables can be achieved immediately after the diffusion phase. This in turn allows for better control of the catalytic converter fill level after the internal combustion engine starts, thereby further reducing emissions. Tighter legal requirements can be met with less catalytic converter expenditure.

[0030] An embodiment of a method according to the present invention is shown in greatly simplified flow chart form in FIG. 2 and is generally designated 200 .

[0031] The method begins with an initialization step 210 in which commands are issued, for example, from the controller 140 to each module of the architecture 100 .

[0032] In step 220, the state of the exhaust gases generated by the internal combustion engine 120 is determined. To this end, signals can be evaluated by one or more sensors 145, 147, for example, by a lambda probe 145 arranged upstream of the exhaust gas catalytic converter 130. For example, in step 220, the mass flow rate and oxygen concentration of the exhaust gas are determined. From this determined state of the exhaust gases, the filling level of the exhaust gas catalytic converter 130 is determined in step 230. For example, the filling level relates to the oxygen stored in the catalytic converter 130 relative to the maximum amount of oxygen that can or currently can be stored. For example, a model calculation based on a catalytic converter plant model, which is digitized using the sensor data detected in step 220, can be used for this purpose. Current and / or previous control parameters output or output by the control device 140 to the internal combustion engine 120 or the fuel preparation device 110 can also be incorporated into such a model calculation. Modeling of the oxygen filling level in a catalyst is described, for example, in Lino Guzzella and Christopher H. Onder: Introduction to Modeling and Control of Internal Combustion Engine Systems (ISBN978-3-642-10774-4), Chapter 2.8.3.

[0033] In step 250, the condition of the exhaust gas catalyst 130 is monitored, for example, by one or more sensors 145, 147 determining the temperature or temperature distribution within the catalyst 130, the concentration of one or more exhaust gas components within, upstream of, and / or downstream of the catalyst 130, and / or 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 controlled based on the determined catalytic converter filling level and other parameters, such as the current load demand, the settings for the desired or required exhaust gas composition, the current exhaust gas temperature, etc. For this purpose, the control device 140 can influence the fuel preparation device 110, for example, by adjusting the amount of fuel dispensed or by influencing the position of the throttle valve for the combustion air supply. Influence on the internal combustion engine 120 can also be exerted, for example, by setting the ignition time point.

[0035] The method 200 then returns to the initialization step 210 .

[0036] If, on the other hand, it is determined in step 240 that the internal combustion engine 120 is not running, then in step 260 the diffusion of at least one exhaust gas component, in particular oxygen diffusion, into, out of or within the exhaust gas catalyst is determined, taking into account the catalyst state determined in step 250. For example, the catalyst temperature is taken into account for this purpose, in that the diffusion rate is higher at higher temperatures than at lower temperatures. Furthermore, a temperature threshold value can be set, above or below which no diffusion is determined, for example because the catalyst cannot store exhaust gas components at such a temperature.

[0037] Furthermore, when determining the diffusion of exhaust gas components, it is preferable to take into account the concentrations of exhaust gas components at various locations within or around the catalytic converter 130. This is because diffusion occurs in the direction of the concentration gradient. The direction of diffusion therefore depends on the relative concentrations of exhaust gas components at locations that are fluidly connected to each other. It is advantageous to take into account oxygen sources and oxygen sinks around the catalytic converter. The change in gaseous oxygen concentration in and around the catalytic converter is preferably described in a position-resolved manner, for example, using a diffusion equation (Fick's second law). Similarly, it is also possible to describe the concentration change in multiple catalytic converters installed one behind the other.

[0038] The gaseous oxygen taken into the catalytic converter can be stored in the catalytic converter if there is unoccupied storage space and the catalytic converter temperature is high enough. The temperature-dependent dynamics of this storage are preferably modeled using the Arrhenius equation. The number of unoccupied storage spaces is determined by calculating the total available storage space, the storage space already occupied by oxygen, and the storage space occupied by other exhaust gas components. The oxygen storage is also preferably described in a position-resolved manner, for example, by modeling multiple axial disks. Alternatively, the change in the oxygen filling level during the diffusion phase can be described in a database, albeit less precisely, for example, by a characteristic map that depends on the duration of the diffusion phase and the catalytic converter temperature.

[0039] In step 270, the determined diffusion is offset with the catalyst fill level most recently determined in step 230 or set in initialization step 210, thus determining an updated catalyst fill level.

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

[0041] The linearity of method 200 as depicted herein is primarily for ease of understanding. In various embodiments, many of steps 210-280 can be performed simultaneously or in a different order without impairing method 200 as a whole. For example, exhaust gas concentration measurements can be performed substantially continuously and are independent of whether a fill level calculation has already been completed. Temperature can also be detected substantially continuously. In contrast, determining the diffusion of exhaust gas components is particularly meaningful when new exhaust gas is not currently being generated, i.e., when the internal combustion engine 120 is not running. Conversely, when the internal combustion engine 120 is running, the flow rate of the exhaust gas generated thereby through the catalytic converter 130 is typically high enough that the diffusion of exhaust gas components has, at most, a negligible effect on the transport processes occurring in the catalytic converter.

[0042] Thus, while the internal combustion engine 120 is running, the filling level of the catalytic converter 130 is primarily determined by the balance between the exhaust gas components carried into the catalytic converter 130 by the internal combustion engine and those carried out from the catalytic converter 130 toward the atmosphere. In contrast, when the internal combustion engine is not running, depending on the current state of the catalytic converter 130 and its surroundings, a reverse flow direction may possibly occur for at least some of the exhaust gas components, so that, for example, oxygen may be carried into the catalytic converter from the direction of the tailpipe. This situation can be taken into account by the above-described method 200, thereby providing an overall more accurate filling level of the catalytic converter 130 with respect to the exhaust gas components accumulated therein, and accordingly, enabling more precise and emission-optimized control of the internal combustion engine. Determining the catalytic converter filling level can, in particular, provide as accurate an actual value as possible for filling level control, especially when combustion is restarted, thus serving to properly control the combustion process from the start.

[0043] In this way, significant emissions optimization potential is within reach, especially for vehicles equipped with start-stop systems and hybrid electric vehicles.

[0044] Corresponding advantages can be realized for applications other than engine travel, and the more frequently the corresponding combustion process is started and stopped, the more pronounced these advantages become. [Explanation of symbols]

[0045] 120 Internal combustion engine 130 Catalyst 140 computing units

Claims

1. A method for determining a filling level in a catalyst (130) of at least one exhaust gas component produced in a combustion process and capable of accumulating in the catalyst (130), comprising determining (230) a change in the filling level of the at least one exhaust gas component in the catalyst (130) during the combustion process; A concentration of the at least one exhaust gas component is determined (220) upstream and downstream of the catalyst, and a concentration gradient of the at least one exhaust gas component is determined based on the concentration of the at least one exhaust gas component upstream and downstream of the catalyst (130); During periods when the combustion process is not operating, a diffusion direction and / or a diffusion rate of the at least one exhaust gas component is calculated based on the concentration gradient, and a change in the filling level due to the diffusion of the at least one exhaust gas component in the catalytic converter (130) is determined (260) based on the diffusion direction and / or the diffusion rate. The method of determining (270) the filling level of the at least one exhaust gas component in the catalyst (130) based on the determined change in the filling level during the combustion process and the change in the filling level due to the diffusion.

2. At least one state variable of the catalyst (130) is determined (250), and the change in the filling level due to the diffusion is determined (260) in dependence on the at least one state variable; Any of the at least one state quantity is the temperature or temperature distribution of the catalyst (130). The method (200) of claim 1.

3. A method as described in claim 1 or 2, wherein the filling level of at least one exhaust gas component after the combustion process is restarted is controlled based on the filling level determined based on changes in the filling level during the combustion process and changes in the filling level due to diffusion.

4. 4. The method of claim 3, wherein the combustion process is controlled (280) such that the filling level is increased when below a target value and decreased when above the target value.

5. A method according to any one of claims 1 to 4, wherein the at least one exhaust gas component comprises oxygen and / or hydrocarbons and / or carbon monoxide and / or nitrogen oxides.

6. A method according to any one of claims 1 to 5, wherein the combustion process is carried out inside an internal combustion engine (120) of a vehicle.

7. A computing unit (140) set up to perform the method of any one of claims 1 to 6.

8. A computer program that causes a computing unit to execute the method according to any one of claims 1 to 6.

9. A machine-readable storage medium having stored thereon the computer program according to claim 8.

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