METHOD AND PROCESSING UNIT FOR ADAPTING MODELED REACTION KINETICS OF A CATALYTIC CONVERTER

Abstract

A method for adapting modeled reaction kinetics of a reaction taking place in a catalytic converter, with model-based fill level feedback control. The method includes specifying a setpoint value for at least one fill level of at least one exhaust-gas component that can be stored in the catalytic converter; calculating at least one fill level of the catalytic converter using a signal of an exhaust-gas sensor upstream of the catalytic converter and using a catalytic converter model with at least one storage capacity and reaction kinetics of the at least one reaction taking place in the catalytic converter; setting an air-fuel mixture such that the calculated fill level approximates the specified setpoint value; ascertaining a difference between a signal of the exhaust-gas sensor upstream of the catalytic converter and a signal of an exhaust-gas sensor downstream of the catalytic converter; and deactivating the fill-level-dependent setting of the air-fuel mixture.

Claims

1. A method (200) for adapting modeled reaction kinetics (260) of at least one reaction taking place in a catalytic converter (130), with model-based fill level feedback control (210), the method comprising: specification of a setpoint value for at least one fill level, in the catalytic converter, of at least one exhaust-gas component that can be stored in the catalytic converter; calculation, via a processing unit (140), of at least one fill level of the catalytic converter using a signal of an exhaust-gas sensor (145) upstream of the catalytic converter (130) and using a catalytic converter model with at least one storage capacity and reaction kinetics of the at least one reaction taking place in the catalytic converter (130); fill-level-dependent setting of a composition of an air-fuel mixture such that the calculated fill level approximates to the specified setpoint value; ascertainment (220) of a difference between a detected signal of the exhaust-gas sensor (145) upstream of the catalytic converter (130) and a detected signal of an exhaust-gas sensor (147) downstream of the catalytic converter (130); and deactivation (240) of the fill-level-dependent setting of the composition of the air-fuel mixture, renewed ascertainment (250) of the difference between the signals of the exhaust-gas sensors (145, 147) upstream and downstream of the catalytic converter (130) in the case of deactivated fill-level-dependent setting of the composition of the air-fuel mixture, and correction (260) of the reaction kinetics of the at least one reaction taking place in the catalytic converter (130) in accordance with a discrepancy between the differences between the detected signals of the exhaust-gas sensors upstream and downstream of the catalytic converter in the case of activated and deactivated fill-level-dependent setting of the composition of the air-fuel mixture.

2. The method (200) according to claim 1, wherein the fill-level-dependent setting of the composition of the air-fuel mixture is deactivated (240) when the difference between the signals of the exhaust-gas sensors (145, 147) upstream and downstream of the catalytic converter (130) deviates (230) by more than a specified difference threshold value from an offset value.

3. The method (200) according to claim 1, wherein the at least one fill level describes a quantity, presently stored in the catalytic converter (130), of at least one exhaust-gas component of an internal combustion engine (120) selected from the group consisting of oxygen, nitrogen oxide, carbon monoxide and hydrocarbons.

4. The method (200) according to claim 1, wherein the catalytic converter (130) is part of an exhaust-gas aftertreatment system of a motor vehicle.

5. The method (200) according to claim 1, furthermore comprising, before the deactivation (240) of the fill-level-dependent setting of the composition of the air-fuel mixture: comparison of an expected discharge of oxygen from the catalytic converter proceeding from the commencement of a purging operation of the catalytic converter until a setpoint value of the fill level of the catalytic converter is attained with a discharge of oxygen proceeding from the commencement of the purging until a reaction of the exhaust-gas sensor (147) downstream of the catalytic converter (130) occurs, and correction of the storage capacity of the catalytic converter model if a deviation between the two comparison variables exceeds a specified threshold value.

6. The method (200) according to claim 1, wherein the correction (260) of the reaction kinetics comprises a correction of time constants of the at least one reaction for at least two different temperatures of the catalytic converter (130).

7. The method (200) according to claim 1, wherein the correction (260) of the reaction kinetics is performed such that there is subsequently no discrepancy between the differences in the signals of the exhaust-gas sensors (145, 147) upstream and downstream of the catalytic converter (130) in the case of activated and deactivated fill-level-dependent setting of the composition of the air-fuel mixture.

8. A non-transitory, computer-readable medium containing instructions that when executed by a computer cause the computer to adapt modeled reaction kinetics (260) of at least one reaction taking place in a catalytic converter (130), with model-based fill level feedback control (210), by: specifying a setpoint value for at least one fill level, in the catalytic converter, of at least one exhaust-gas component that can be stored in the catalytic converter; calculating at least one fill level of the catalytic converter using a signal of an exhaust-gas sensor (145) upstream of the catalytic converter (130) and using a catalytic converter model with at least one storage capacity and reaction kinetics of the at least one reaction taking place in the catalytic converter (130); fill-level-dependent setting of a composition of an air-fuel mixture such that the calculated fill level approximates to the specified setpoint value; ascertaining (220) a difference between a detected signal of the exhaust-gas sensor (145) upstream of the catalytic converter (130) and a detected signal of an exhaust-gas sensor (147) downstream of the catalytic converter (130); and deactivating (240) the fill-level-dependent setting of the composition of the air-fuel mixture, renewed ascertainment (250) of the difference between the signals of the exhaust-gas sensors (145, 147) upstream and downstream of the catalytic converter (130) in the case of deactivated fill-level-dependent setting of the composition of the air-fuel mixture, and correction (260) of the reaction kinetics of the at least one reaction taking place in the catalytic converter (130) in accordance with a discrepancy between the differences between the detected signals of the exhaust-gas sensors upstream and downstream of the catalytic converter in the case of activated and deactivated fill-level-dependent setting of the composition of the air-fuel mixture.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 shows, in a highly schematic illustration, an arrangement that is configured for carrying out an advantageous embodiment of a method according to the invention.

[0037] FIG. 2 shows an advantageous configuration of a method according to the invention in the form of a simplified flow diagram.

DETAILED DESCRIPTION

[0038] FIG. 1 schematically illustrates, in the form of a block diagram, an arrangement 100 which may be part of a vehicle in which a method according to the invention can be used. The arrangement 100 is preferably configured for carrying out a method 200 according to FIG. 2, and has an internal combustion engine 120, for example a gasoline engine, a catalytic converter 130 and a processing unit 140. Furthermore, the arrangement 100 may have a fuel treatment device 110, for example in the form of injection pump(s), turbocharger(s) etc., or combinations of these.

[0039] Furthermore, such an arrangement has exhaust-gas sensors 145, 147, in particular lambda probes, which are arranged upstream and downstream of the catalytic converter 130 in an exhaust-gas system of the arrangement 100.

[0040] The processing unit 140 controls, inter alia, the operation of the internal combustion engine 120, for example through control of ignition times, valve opening times and composition, quantity and/or pressure of the air-fuel mixture provided by the fuel treatment device 110.

[0041] Exhaust gas generated during the operation of the internal combustion engine 120 is fed to the catalytic converter 130. Upstream of the catalytic converter 130, the air ratio lambda of the exhaust gas is measured by means of a first lambda probe 145, and said first lambda value is transmitted to the processing unit 140. Reactions of exhaust-gas constituents with one another are accelerated, or made possible in the first place, by the catalytic converter 130, for example a three-way catalytic converter, such that hazardous constituents, such as carbon monoxide, nitrogen oxides and incompletely burned hydrocarbons, are converted into relatively non-hazardous products such as water vapor, nitrogen and carbon dioxide. Downstream of the catalytic converter 130, a second lambda value is ascertained by means of a second lambda probe 147 and is transmitted to the processing unit 140.

[0042] The first and the second lambda value may intermittently or permanently deviate from one another because, owing to the reactions in the catalytic converter 130, the compositions of the exhaust gas upstream and downstream of the catalytic converter 130 deviate from one another. Furthermore, the exhaust gas requires a certain time to flow through the catalytic converter 130 (so-called dead time). This dead time is in particular dependent on a present volume flow of the exhaust gas, that is to say on a present operating state of the internal combustion engine 120. For example, a greater exhaust-gas quantity is produced per unit of time during operation of the internal combustion engine 120 under full load than during idling operation. As a result, the respective dead time changes in a manner dependent on the operating state of the internal combustion engine 120, because the volume of the catalytic converter 130 is constant.

[0043] The processing unit 140 is advantageously configured to carry out the method 200 according to a preferred embodiment of the invention as illustrated in FIG. 2. For this purpose, in a normal operation step 210, the catalytic converter 130 is operated with model-based fill level feedback control, in such a way that the internal combustion engine 120 is controlled so as to generate an exhaust gas which has a composition suitable for setting a fill level of the catalytic converter 130 with respect to at least one exhaust-gas component, in particular oxygen, in accordance with a fill level specification. Here, the fill level is in particular calculated on the basis of a fill level model using measurement data from the first lambda sensor 145 described with regard to FIG. 1.

[0044] In a step 220, a first and a second lambda value are measured by means of the lambda probes 145, 147 upstream and downstream of the catalytic converter 130. This may take place both during the course of the normal operation as per step 210 and for the purposes of adaptation and/or diagnosis, for example in order to adapt the catalytic converter model for the normal operation 210, or in order to identify whether the catalytic converter 130 is functioning as intended.

[0045] In a step 230, the two ascertained lambda values of the sensors 145, 147 are compared with one another, and the difference between the two values is compared with an expected or acceptable offset value. If the difference between the first and second lambda values lies in the range of the acceptable offset value, the method 200 returns to the normal operation step 210 and adapts the catalytic converter model on the basis of the measured values if necessary.

[0046] However, if the discrepancy between the difference of the lambda values and offset value exceeds a specifiable difference threshold value, then the method 200 continues with a step 240, in which the fill level feedback control is deactivated. In a subsequent step 250, it is then once again the case that the lambda values upstream and downstream of the catalytic converter 130 are then determined, and the difference between the first and second lambda values is ascertained. The discrepancy between the differences in the case of active and deactivated fill level feedback control is used in a step 260 for the calculation of an adaptation of the reaction kinetics of at least one reaction taking place in the catalytic converter 130, for example of the introduction of oxygen into storage or the release of oxygen from storage. Since these measurements can in each case be performed only at a presently prevailing temperature, it is expediently provided that the reaction kinetics are correspondingly also adapted for other temperatures—taking into consideration a corresponding scaling parameter. For this purpose, based on the calculated adaptation of the reaction kinetics for the present temperature, it is for example possible for all stored sampling points of a corresponding temperature-dependent characteristic curve to be adapted. For example, it may be taken into consideration here that a corresponding time constant varies to a greater degree with increasing temperature, such that a temperature-dependent adaptation may comprise a combined compression or stretching and shifting of the corresponding characteristic curve.

[0047] If, accordingly, it is for example the case that the introduction of oxygen into storage in the catalytic converter 130 takes place more quickly than corresponds to the kinetics stored in the control unit 140, then lean exhaust gas is in fact better reduced, and in fact a richer exhaust-gas lambda than expected will take effect downstream of the catalytic converter 130, because the model-based feedback control 210 of the catalytic converter 130 is based on the stored kinetics. This deviation of the exhaust-gas lambda actually measured downstream of the catalytic converter 130 from the expected (typically stoichiometric) exhaust-gas lambda is a measure for the deviation of the actual kinetics from the stored kinetics. A conversion of the lambda difference into a correction factor for the kinetics may be performed for example by means of a correction characteristic curve. In the example, owing to the rich deviation of the exhaust-gas lambda in the stored kinetics, the time constant for the introduction of oxygen into storage would be reduced. Analogously, an actually more quickly occurring release of oxygen from storage would lead to a better oxidation of rich exhaust gas and to a leaner exhaust-gas lambda. Likewise, it is self-evidently possible for the adaptation of the kinetics to comprise an increase of the corresponding time constants if a correspondingly slower reaction rate is indicated by the difference between the lambda values upstream and downstream of the catalytic converter.

[0048] Since other effects that have nothing to do with the reaction kinetics can also lead to a deviation of the actual exhaust-gas lambda downstream of the catalytic converter from the expected exhaust-gas lambda downstream of the catalytic converter (for example a tolerance of the lambda sensor upstream of the catalytic converter), an adaptation of the reaction kinetics would be counter-productive in such a case. In order to separate the different causes, the difference between the lambda values is detected once in step 220 in the case of active control intervention, and once in step 250 in the case of inactive control intervention, of the model-based feedback control 210 of the catalytic converter 130. Only the discrepancy between the two differences can be caused by reaction kinetics in the catalytic converter model that do not reflect reality.

[0049] After adaptation of the stored reaction kinetics has been performed in the step 260, the method returns to the normal operation step 210 and reactivates the fill level feedback control of the catalytic converter 130.

[0050] It is self-evident that some of the steps discussed with regard to FIG. 2 may also be combined or may possibly take place in a different, for example reversed, sequence. For example, for certain diagnostic functions, it may be necessary to deactivate the fill level feedback control of the catalytic converter. If such a function is implemented, it is self-evidently also possible for the difference between the lambda values in the case of inactive fill level feedback control to firstly be ascertained before the difference in the case of active control intervention for fill level feedback control is ascertained. Furthermore, the detection of measured values and the decision as to whether a threshold value is overshot by a measured value, or by a variable derived therefrom, may for example be combined into a single step.