Method and computing unit for determining a catalytic converter status

Abstract

The invention relates to a method (200) for determining a catalytic converter state, wherein an exhaust-gas catalytic converter (130) is monitored on the basis of a catalytic converter model. Here, the catalytic converter model is adapted (250) in accordance with measured values detected by one or more sensors (145, 147), wherein the frequency and / or extent of the adaptation of the catalytic converter model is detected (260). When the frequency and / or extent of the adaptation does not exceed a predeterminable threshold value, the catalytic converter state is determined (270) to be non-critical, or when the frequency and / or extent of the adaptation exceeds a predeterminable threshold value, the catalytic converter state is determined (270) to be critical.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for determining a state of a catalytic converter, and to a computing unit and a computer program for carrying out the method. BACKGROUND

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

[0003] In the case of incomplete combustion of the air-fuel mixture in a gasoline engine, a large number of combustion products are emitted in addition to nitrogen (N2), carbon dioxide (CO2) and water (H2O), among them hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). X According to today's state of the art, only catalytic exhaust gas aftertreatment makes it possible to keep the effective exhaust gas limits for motor vehicles. By means of, for example, a three-way catalytic converter, the mentioned harmful substance components can be converted.

[0004] In the case of a three-way catalytic converter, high conversion rates for HC, CO and NOx X At the same time, high conversion rates can only be achieved in a limited lambda range around the stoichiometric operating point (lambda = 1), the so-called "catalytic converter window" or "conversion window".

[0005] In order to operate the three-way catalytic converter in the conversion window, in today's motor control systems lambda regulation is usually applied, which is based on the signals of lambda probes arranged in front of and behind the three-way catalytic converter. In order to regulate the air coefficient lambda, which is a composed variable for the fuel / air ratio of the internal combustion engine, the oxygen content of the exhaust gas in front of the three-way catalytic converter is measured using a lambda probe arranged there on the inlet side. According to this measured value, the regulation, for example, corrects the fuel quantity or injection duration, which is predefined in the form of a base value by a pre-control function.

[0006] Under the framework of the pre-control, a base value of the fuel quantity to be injected is predefined according to, for example, the rotational speed and the load of the internal combustion engine. For more precise regulation, the oxygen concentration of the exhaust gas downstream of the three-way catalytic converter can additionally be detected using a further lambda probe. The signal of this lambda probe on the outlet side can be used for a pilot regulation, which overlaps with the lambda regulation in front of the three-way catalytic converter based on the signal of the lambda probe on the inlet side. As a lambda probe arranged behind the three-way catalytic converter, a step lambda probe is usually used, which can have a very steep characteristic curve in the case of lambda = 1 and thus can indicate lambda = 1 very precisely.

[0007] Guided regulation generally adjusts only small deviations of λ=1 and is designed to be relatively slow. In addition to guided regulation, further functions can be configured for larger deviations of λ=1, in the form of λ pre-control, to enable a rapid return to the conversion window. This is important, for example, after a phase with coasting operation disconnection, in which the three-way catalytic converter is loaded with oxygen. Loading with oxygen affects NO... X The transformation had negative effects.

[0008] Due to the oxygen storage capacity of the three-way catalytic converter, after setting a rich or lean oxygen level (λ) upstream of the catalytic converter, λ = 1 can still exist downstream of the catalytic converter for a few seconds. This temporary oxygen storage characteristic of the three-way catalytic converter is utilized to compensate for the short-term deviation of λ = 1 upstream of the catalytic converter. If λ is not equal to 1 upstream of the catalytic converter for a longer period, then once the oxygen fill level exceeds the oxygen storage capacity (oxygen excess) when λ > 1, or once oxygen is no longer stored in the catalytic converter when λ < 1, the same λ is set downstream of the catalytic converter.

[0009] Then, at that time point, the step-laminar detector behind the three-way catalytic converter also indicates the departure of the conversion window. However, prior to this time point, the signal from the laminar detector behind the three-way catalytic converter does not indicate the impending rush, and therefore, the guidance regulation based on this signal often reacts so late that the fuel mix can no longer react in time before the rush. As a result, increased emissions occur. Therefore, this regulation scheme has the disadvantage that, by means of the voltage of the step-laminar detector behind the three-way catalytic converter, the regulation scheme identifies the departure of the conversion window relatively late.

[0010] A model-based regulation scheme is known from DE 10 2016 222 418 A1, in which λ sensors are arranged in front of and behind a catalyst along the direction of exhaust gas flow, and a catalyst model is used to calculate the λ value, which is measured behind the catalyst. If the actually measured λ value differs from the calculated λ value, the catalyst model is adapted. Specifically, the fill level of the catalyst at one or more exhaust gas components, particularly oxygen, is modeled here.

[0011] As the catalytic converter ages, it is able to convert exhaust gases worse than when it was new. Therefore, it is generally legally mandated to check exhaust systems via motor control during vehicle operation (on-board diagnostics). Here, catalytic converter diagnostics has the task of identifying and indicating, via a control light (MIL), an unacceptably drastic decline in conversion capacity that results in an unacceptable increase in emissions.

[0012] A feasible approach for active diagnostics of the catalyst involves determining the catalyst's oxygen storage capacity (OSC) and activating a control lamp when the OSC is too low. This is based on the empirical assumption that as the OSC decreases, the catalyst's conversion efficiency also decreases. In this active diagnostic method, the catalyst first removes oxygen, for example, through a rich air-fuel mixture. Subsequently, oxygen is introduced into the catalyst through a lean air-fuel mixture, and the amount of oxygen introduced is integrated over a prolonged period until a λ detector at the back of the catalyst indicates a lean mixture. The integrated amount of oxygen corresponds to the catalyst's OSC. The method is repeated multiple times if necessary to obtain reliable diagnostic results. Summary of the Invention

[0013] Against this backdrop, the present invention provides a method for determining the state of a catalyst, as well as a computing unit and computer program for performing the method. Advantageous designs are derived from the embodiments and the subject matter described below.

[0014] The method according to the present invention aims at an adaptive catalyst model. Here, for example, a catalyst model can be configured to achieve multi-level adaptation, using which the uncertainties of measurement parameters or model parameters and road segment models are compensated for, the measurement parameters or model parameters being included in the road segment model on which the model is based.

[0015] Such multi-level adaptations combine, for example, highly precise adaptations that work continuously with small deviations and rapid corrections that work discontinuously with large deviations.

[0016] Here, the continuous adaptation and discontinuous correction can be based on signal values ​​from different ranges of signals from sensors, particularly in the exhaust gas stream downstream of the catalyst, and thus from the λ detector arranged on the outlet side, but from which two fundamentally different pieces of information are derived. Such a model allows for consideration of the different efficiencies of signal values ​​from different ranges in terms of exhaust gas composition and catalyst fill level.

[0017] Furthermore, multiple signal value ranges can be set, within which continuous adaptations are activated individually, discontinuous corrections are activated individually, or both together.

[0018] In cases of discontinuous correction, such as when the voltage of the λ detector on the outlet side indicates rich or lean exhaust gas emission downstream of the catalyst and thus an excessively low or high actual oxygen fill level, the modeled fill level is corrected based on the actual fill level. This correction is performed discontinuously to allow for evaluation of the response of the λ detector voltage downstream of the catalyst. Because this response is delayed due to dead time and the storage characteristics of the catalyst, an adaptive catalyst model can be specifically configured to perform the correction only once, starting with the λ value of the signal from the λ detector located downstream of the catalyst allowing for the inference of the actual oxygen fill level of the catalyst.

[0019] In the aforementioned case of continuous adaptation, for example, the λ signal from a step λ detector behind the catalyst is compared with a modeled λ signal behind the catalyst. From this comparison, the λ offset between the λ value before and after the catalyst can be derived. This λ offset is used to correct, for example, a target λ value constructed through pre-control.

[0020] In principle, model-based adjustment of the catalytic converter fill level has the advantage of identifying the impending departure of the catalytic converter window earlier than in guided adjustment based on signals from exhaust gas detectors located downstream of the catalytic converter. This allows for a proactive and targeted adjustment of the air-fuel mixture to counteract the departure of the catalytic converter window.

[0021] This invention utilizes the fact that as catalysts age, their oxygen storage and / or conversion capabilities decrease, and therefore adaptive catalyst models must be adapted more drastically or frequently. The increasing adaptation requirements allow for the inference of catalyst aging, and more precisely, not only in cases of decreased storage capacity but also in cases where this is not the case. In particular, in the latter case, other methods of catalyst diagnostics often fail.

[0022] For example, observations of various current catalytic converters, particularly those with high noble metal loadings, indicate that while high oxygen storage capacity is necessary, it is insufficient for the high conversion capacity of the catalytic converter. Thus, catalytic converters that are normal in a diagnostic sense (i.e., possess sufficiently high storage capacity) may still result in unacceptable emissions due to inadequate conversion capacity.

[0023] In addition to oxygen storage capacity, it is also possible to monitor the storage capacity for other exhaust gas components, such as nitrogen oxides (NOx), based on a model.X The invention also has the advantage of being able to be used in the combination of this type of adaptive model.

[0024] This invention enables catalyst diagnostics without the need to adjust operating parameters that are detrimental to emissions technology. Furthermore, as already mentioned, the diagnostic method according to this invention also does not rely on storage capacity to evaluate actual conversion capacity.

[0025] Therefore, the basic concept of the present invention is to evaluate adaptation requirements over a longer time period, such as a few minutes or 5 minutes, which are determined, for example, through continuous adaptation and / or discontinuous correction as already described. Specifically, the adaptation requirements, or fit requirements, are a function of the difference between a measured λ value after the catalyst and a modeled λ value after the catalyst, or generally the difference between at least one measured value and at least one model value determined by means of a catalyst model.

[0026] The λ offset between the λ value before and after the catalyst (e.g., due to an offset error of the λ detector before the catalyst or a leak in the exhaust system) systematically leads to the need to maintain the same adaptation over a longer period of time, meaning that the model must be constantly recalibrated within more or less the same range.

[0027] In contrast, the decline in the catalyst's conversion capacity, which is unrelated to its oxygen storage capacity, leads to a temporally variable adaptation requirement. This is because the modeled state parameters of the catalyst (e.g., oxygen fill levels in different regions of the catalyst or the λ value at the catalyst outlet) are calculated using reaction kinetics that depend on the catalyst's oxygen storage capacity. If the catalyst's conversion capacity is now unrelated to its oxygen storage capacity, then the modeled reaction kinetics are inconsistent with the actual reaction kinetics. Similarly, the modeled state parameters of the catalyst are inconsistent with the actual catalyst state parameters. In particular, the modeled λ value at the catalyst outlet is inconsistent with the λ value measured at the catalyst outlet using the λ detector. Because the modeled kinetics used not only for reactions with lean exhaust components but also for reactions with rich exhaust components are mismatched with the actual kinetics, this does not result in a systematic deviation of the λ value behind the catalyst from λ=1, as in the case of λ offset, but rather in the ejection of both lean and rich exhaust gases. This leads to the following situation: in this case, the adaptive demand along the direction of concentration and along the direction of sparseness is determined alternately, or at least one adaptive demand, which does not change systematically, more drastically, or more frequently.

[0028] Such anomalous adaptation requirements are identified by observing the development of adaptation or correction requirements in the catalyst model.

[0029] It is appropriate to observe only when operating conditions lead to the expectation of reliable adaptation or diagnostic results. Specifically, during periods when the catalyst is operating in a state that cannot be sufficiently accurately mapped by the catalyst model, the observation of changing adaptation requirements is either disregarded or less drastically weighted. Examples of this include operating states with drastic changes in load requirements, high fuel tank ventilation ratios, or high airflow rates from the intake to exhaust valves of the internal combustion engine. It is also possible to specify that adaptation requirements are not observed at all during such periods, or that observation is only activated during periods where adaptation requirements can be considered to be primarily caused by the actual catalyst state. For this purpose, it is also possible to specify analyzing the current operating state of the internal combustion engine to determine whether to activate or weight the observed adaptation requirements. If abnormally high or unusually frequent changes in adaptation requirements are identified during the observation period, this indicates that the model-based state parameters are inconsistent with the actual state parameters, and that the catalyst's conversion capacity is no longer sufficiently high.

[0030] The measurements detected here are advantageously λ values ​​upstream and / or downstream of the catalyst. In many cases, these are already being measured, thus avoiding additional measurement costs, and are directly correlated with the function of the catalyst, thereby facilitating the diagnosis of effectiveness.

[0031] Preferably, the frequency and / or extent of adaptation of the catalyst model are related to a predetermined exhaust gas volume. In other words, when a large exhaust gas volume passes through the catalyst, a shorter time period can be considered within which the corresponding adaptation of the catalyst model is taken into account to determine the catalyst state, while the observation period is extended under low exhaust gas volume flow conditions to ensure that the same diagnostic quality is maintained. Therefore, the diagnostics can be adapted to the current operating point or load condition.

[0032] Preferably, an alarm signal is given when a critical catalytic converter condition is determined. This allows, for example, legitimate preset conditions to be met, and enables timely replacement and / or maintenance of defective or malfunctioning catalytic converters to prevent emissions of harmful substances that could harm the environment and / or health. Such an alarm signal can be given, in particular, in the form of an alarm light, an alarm sound, and / or as a corresponding fault signal stored in the fault memory of the vehicle's onboard computer.

[0033] The computing unit according to the invention, such as the controller of a motor vehicle, is specifically configured, in terms of programming technology, to execute the method according to the invention.

[0034] It is also advantageous to execute the method according to the invention in the form of a computer program or a computer program product with program code for performing all method steps, as this results in particularly low costs, especially if the controller used for implementation is also used for other tasks 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 memory, EEPROM, DVDs, and others. The program can also be downloaded via computer networks (Internet, intranet, etc.).

[0035] The present invention is described herein and hereinafter using a three-way catalytic converter as an example, but in spirit it can also be applied to other types of catalytic converters. Attached Figure Description

[0036] Other advantages and design solutions of the present invention can be derived from the specification and drawings.

[0037] The present invention is schematically illustrated in the accompanying drawings by means of embodiments and is described below with reference to the drawings. Wherein:

[0038] Figure 1 A schematic view of a vehicle in which the method according to the invention can be applied;

[0039] Figure 2 An advantageous design scheme according to the method of the invention is shown in the form of a flowchart. Detailed Implementation

[0040] exist Figure 1 The diagram schematically illustrates a vehicle 100 in block form, in which the method according to the invention can be applied. The vehicle 100 is preferably configured to perform the method according to... Figure 2 The method 200 includes, for example, an internal combustion engine 120 (a gasoline engine), a catalytic converter 130, and a computing unit 140. Furthermore, the vehicle 100 may also include a fuel processing device 110, for example, in the form of an injection pump, a turbocharger, or a combination thereof.

[0041] In addition, the vehicle also has (exhaust gas) sensors 145, 147, and in particular a λ detector, which are arranged upstream and downstream of the catalytic converter 130 in the exhaust system of the vehicle 100.

[0042] The computing unit first controls the operation of the internal combustion engine 120, for example by controlling the ignition timing, valve opening time, and the composition, quantity, and / or pressure of the fuel-air mixture provided by the fuel processing equipment 110.

[0043] Exhaust gas generated during the operation of the internal combustion engine 120 is supplied to the catalytic converter 130. Upstream of the catalytic converter 130, the air coefficient λ of the exhaust gas is measured by means of a first λ detector 145, and this first λ value is transmitted to the computing unit 140. The catalytic converter accelerates, or enables, the reactions between the components of the exhaust gas to occur, such that harmful components, such as carbon monoxide, nitrogen oxides, and incompletely burned hydrocarbons, are converted into relatively harmless products such as water vapor, nitrogen, and carbon dioxide. Downstream of the catalytic converter 130, a second λ value is determined by a second λ detector 147 and transmitted to the computing unit 140.

[0044] The first and second λ values ​​can differ from each other temporarily or permanently because the composition of the exhaust gases upstream and downstream of the catalyst 130 differs due to the reactions within the catalyst 130. Furthermore, the exhaust gases require a certain amount of time to flow through the catalyst 130 (the so-called dead time). This dead time depends particularly on the current volumetric flow rate of the exhaust gases, i.e., on the current operating state of the internal combustion engine 120. For example, the internal combustion engine 120 produces a higher volume of exhaust gases per unit time when operating at full load than when idling. Because the volume of the catalyst 130 is constant, the corresponding dead time varies according to the operating state of the internal combustion engine 120.

[0045] The computing unit 140 is advantageously configured to perform, according to a preferred embodiment of the invention, in... Figure 2 Method 200 is shown in the figure. For this purpose, after initialization step 210, first and second λ values ​​are measured in first step 220 by λ detectors 145, 147 upstream and downstream of the catalyst 130.

[0046] In parallel with this, in step 230, the λ value of the exhaust gas downstream of the catalyst 130 is calculated based on the current operating state of the internal combustion engine 120 and, in particular, the first λ value, by means of a road segment model.

[0047] In another step 240, the calculation unit 140 compares the calculated λ value with a second λ value measured by the λ detector 147.

[0048] If the measured value is substantially consistent with the calculated value, the method returns to steps 220 and 230 and continues to rely on the calculation of the road segment model and the measurement of the first and second λ values.

[0049] However, if the values ​​are inconsistent with each other, particularly if the difference between the calculated and measured values ​​exceeds a predetermined threshold, then the stretcher model is adapted or fitted in step 250. After such adaptation of the stretcher model, method 200 returns to step 230, and the λ value downstream of the catalyst 130 is recalculated using the adapted stretcher model. Here, the adaptation 250 of the stretcher model is preferably performed to a degree based on the deviation between the modeled and measured λ values. Thus, a high deviation in value results in a drastic adaptation, and a low deviation results in a correspondingly small adaptation. In particular, the adaptation requirement is a function of the difference between the measured λ value and the calculated λ value downstream of the catalyst 130.

[0050] In step 260, the degree and frequency of the adaptation 250 are detected and analyzed, particularly normalized to the volumetric flow rate of the exhaust gas. Specifically, it is determined whether the adaptation requirement (not only in value but also in frequency) has changed over time or in terms of volumetric flow rate.

[0051] To identify abnormally high or frequent changes in adaptation demand, for example, the adaptation demand is detected quantitatively, differentiated (especially numerically), and integrated over the observation period with respect to the derivative of the adaptation demand. Then, when the adaptation demand remains unchanged (i.e., constant) during the observation period, the derivative of the adaptation demand and therefore the integral of the derivative's value are 0. The more frequently or drastically the adaptation demand changes, the higher the value of the integral. Therefore, when the integral exceeds a predetermined threshold, it can be particularly considered that an unacceptable decrease in the catalyst's conversion capacity has occurred.

[0052] Therefore, in step 270, it is determined accordingly whether the change in the adaptation requirement exceeds a predetermined threshold. If the threshold is exceeded, the state of the catalyst 130 is indicated as critical in step 280. For this purpose, an alarm signal is preferably triggered in step 280, for example, by operating an alarm light, emitting an alarm sound, or providing voice or text information.

[0053] Conversely, if it is determined in step 270 that the degree or frequency of change in the adaptation requirement has not exceeded a predetermined threshold, then method 200 returns to initialization step 210 or the measurement 220 and modeling 230 of the corresponding first and second λ values.

Claims

1. A method (200) for determining the state of a catalyst, wherein an exhaust gas catalyst (130) is monitored based on a catalyst model. A first λ detector (145) is arranged upstream of the catalyst (130) to obtain a first λ value, and a second λ detector (147) is arranged downstream of the catalyst (130) to obtain a second λ value. In parallel, the λ value of the exhaust gas downstream of the catalyst (130) is calculated using a road segment model based on the current operating state of the internal combustion engine (120) and the first λ value. The calculated λ value is compared with a second λ value measured by a second λ detector (147), and if the values ​​are inconsistent, the road segment model is adapted. The detection (260) involves the frequency and / or degree of fit of the catalyst model, wherein the detected fit of the catalyst model determines a fit requirement function, the fit requirement function is differentiated, the value of the derivative is integrated, and the integral of the derivative of the fit requirement function is used as the frequency and / or degree of fit of the catalyst model, wherein the fit requirement function is a function of the difference between the measured second λ value and the calculated λ value. And when the frequency and / or extent of adaptation does not exceed a predetermined threshold, the catalyst state is determined (270) to be non-critical, and When the frequency and / or extent of adaptation exceeds a predetermined threshold, the catalyst state is determined (270) to be critical.

2. The method (200) according to claim 1, wherein the frequency and / or extent of adaptation of the catalyst model is related to a predetermined exhaust gas volume.

3. The method (200) according to claim 1 or 2, wherein when a critical catalyst condition is determined (270), an alarm signal (280) is given.

4. The method (200) according to claim 1 or 2, wherein the catalyst (130) has storage capacity for at least one exhaust gas component, and the catalyst model is at least used to: adjust the fill level of the catalyst (130) with respect to the at least one exhaust gas component.

5. The method (200) according to claim 4, wherein the catalyst (130) has the capacity for storing oxygen.

6. The method (200) according to claim 1 or 2, wherein the catalyst state includes the conversion capacity of the catalyst (130).

7. The method (200) according to claim 1 or 2, wherein the exhaust gas catalyst (130) is arranged in the exhaust gas aftertreatment system of the vehicle (100).

8. A computing unit (140) configured to perform all the method steps of the method (200) according to any one of claims 1 to 7.

9. A computer program product configured to perform all the method steps of the method (200) according to any one of claims 1 to 7.

10. A machine-readable storage medium having a computer program stored thereon, which, when executed, causes a computing unit (140) according to claim 8 to perform all the method steps of the method (200) according to any one of claims 1 to 7.

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