Method and processing unit for ascertaining a catalytic converter state

Abstract

A method (200) for ascertaining a catalytic converter state is proposed, 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 a manner dependent on measured values detected by means of one or more sensors (145, 147), wherein a frequency and/or a degree of the adaptation of the catalytic converter model is detected (260). The catalytic converter state is ascertained (270) as non-critical if the frequency and/or the degree of the adaptation do not exceed a predeterminable threshold value or is ascertained (270) as critical if the frequency and/or the degree of the adaptation exceed the predeterminable threshold value.

Claims

1. A method (200) for ascertaining a catalytic converter state, the method comprising: monitoring, via one or more sensors (145, 147) and a computer, an exhaust-gas catalytic converter (130) based on a catalytic converter model, wherein the catalytic converter model is adapted (250) in a manner dependent on measured values detected by means of the one or more sensors (145, 147), detecting (260), via the computer, a frequency, a degree, or a frequency and degree of the adaptation of the catalytic converter model, determining (270), via the computer, the catalytic converter state as non-critical when the frequency and/or the degree of the adaptation do not exceed a predetermined threshold value, determining (270), via the computer, the catalytic converter state as critical when the frequency and/or the degree of the adaptation exceed the predeterminable threshold value, and outputting (280), via an output device, an indication indicative of the catalytic converter state being critical, wherein, from the detected adaptations of the catalytic converter model, an adaptation requirement function is ascertained, the adaptation requirement function is differentiated, the absolute value of the derivative is integrated, and the integral of the derivative absolute value of the adaptation requirement function is used as the frequency and/or the degree of the adaptation of the catalytic converter model.

2. The method (200) according to claim 1, wherein the detected measured values are lambda values upstream and/or downstream of the catalytic converter.

3. The method (200) according to claim 1, wherein the frequency and/or the degree of the adaptation of the catalytic converter model are based on a predetermined exhaust-gas flow rate.

4. The method (200) according to claim 1, wherein the adaptation requirement function is a function of a difference between at least one of the detected measured values and at least one model value determined by means of the catalytic converter model.

5. The method (200) according to claim 1, wherein the catalytic converter (130) has a storage capacity for at least one exhaust-gas component and the catalytic converter model is used at least for performing closed-loop control of a fill level of the catalytic converter (130) with respect to said at least one exhaust-gas component.

6. The method (200) according to claim 1, wherein the catalytic converter state comprises a conversion capability of the catalytic converter (130).

7. The method (200) according to claim 1, wherein the exhaust-gas catalytic converter (130) is arranged in an exhaust-gas aftertreatment system of a vehicle (100).

8. A processing unit (140) comprising at least one computer configured to monitor an exhaust-gas catalytic converter (130) based on a catalytic converter model, wherein the catalytic converter model is adapted (250) in a manner dependent on measured values detected by means of one or more sensors (145, 147), detect (260) a frequency, a degree, or a frequency and degree of the adaptation of the catalytic converter model, determine (270) the catalytic converter state as non-critical when the frequency and/or the degree of the adaptation do not exceed a predetermined threshold value, determine (270) the catalytic converter state as critical when the frequency and/or the degree of the adaptation exceed the predeterminable threshold value, and outputting (280), with an output device, an indication indicative of the catalytic converter state being critical, wherein, from the detected adaptations of the catalytic converter model, an adaptation requirement function is ascertained, the adaptation requirement function is differentiated, the absolute value of the derivative is integrated, and the integral of the derivative absolute value of the adaptation requirement function is used as the frequency and/or the degree of the adaptation of the catalytic converter model.

9. A non-transitory, computer-readable medium containing instructions that when executed by a computer cause the computer to monitor an exhaust-gas catalytic converter (130) based on a catalytic converter model, wherein the catalytic converter model is adapted (250) in a manner dependent on measured values detected by means of one or more sensors (145, 147), detect (260) a frequency, a degree, or a frequency and degree of the adaptation of the catalytic converter model, determine (270) the catalytic converter state as non-critical when the frequency and/or the degree of the adaptation do not exceed a predetermined threshold value, determine (270) the catalytic converter state as critical when the frequency and/or the degree of the adaptation exceed the predeterminable threshold value, and outputting (280), with an output device, an indication indicative of the catalytic converter state being critical, wherein, from the detected adaptations of the catalytic converter model, an adaptation requirement function is ascertained, the adaptation requirement function is differentiated, the absolute value of the derivative is integrated, and the integral of the derivative absolute value of the adaptation requirement function is used as the frequency and/or the degree of the adaptation of the catalytic converter model.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and configurations of the invention will emerge from the description and the appended drawing.

(2) The invention is illustrated schematically in the drawing on the basis of an exemplary embodiment, and will be described below with reference to the drawing.

(3) FIG. 1 shows a schematic illustration of a vehicle in which a method according to the invention can be used.

(4) FIG. 2 shows an advantageous configuration of a method according to the invention in the form of a flow diagram.

DETAILED DESCRIPTION

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

(6) Furthermore, a vehicle of said type 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 vehicle 100.

(7) The processing unit controls inter alia the operation of the internal combustion engine 120, for example through the control of ignition times, valve opening times and composition, flow rate and/or pressure of the fuel-air mixture provided by the fuel preparation device 110.

(8) Exhaust gas that is 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 this 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, such that harmful constituents, such as for example carbon monoxide, nitrogen oxides and incompletely burned hydrocarbons, are converted into relatively non-harmful 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 transmitted to the processing unit 140.

(9) The first and the second lambda value may temporarily or permanently deviate from one another because, as a result of 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, during operation of the internal combustion engine 120, a higher exhaust-gas quantity is produced per unit of time at full load than during idling operation. The respective dead time thus 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.

(10) The processing unit 140 is advantageously configured to carry out the method 200 according to a preferred embodiment of the invention, which is illustrated in FIG. 2. For this purpose, after an initialization step 210, 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 in a first step 220.

(11) In parallel with this, in a step 230, a lambda value of the exhaust gas downstream of the catalytic converter 130 is calculated, in a manner dependent on the present operating state of the internal combustion engine 120 and in particular on the first lambda value, by means of a system model.

(12) In a further step 240, the calculated lambda value is compared by the processing unit 140 with the second lambda value measured by the lambda probe 147.

(13) If the measured value substantially corresponds to the calculated value, the method returns to the steps 220 and 230 and continues the calculation by means of the system model and the measurement of first and second lambda values.

(14) However, if the values do not correspond to one another, which may be characterized in particular by the fact that an absolute value of the difference between calculated and measured values exceeds a predetermined threshold value, the system model is adapted in a step 250. After such an adaptation of the system model, the method 200 returns to the step 230 and, on the basis of the adapted system model, newly calculates the lambda value downstream of the catalytic converter 130. The adaptation 250 of the system model is in this case preferably performed, in terms of the degree thereof, in a manner corresponding to the absolute value of the deviation between modeled and measured lambda values. A deviation which is large in terms of absolute value accordingly gives rise to a large adaptation, and a small deviation gives rise to a correspondingly small adaptation. In particular, the adaptation requirement is a function of the difference between the measured lambda value and the calculated lambda value downstream of the catalytic converter 130.

(15) In a step 260, the degree of the adaptation(s) 250, and the frequency thereof, in particular normalized with respect to the volume flow of the exhaust gas, is detected and evaluated. For this purpose, it is ascertained in particular whether the adaptation requirement (both absolute value and frequency) has changed over time or in relation to the volume flow.

(16) In order to identify exceptionally large or exceptionally frequent changes in the adaptation requirement, the adaptation requirement is for example detected numerically and differentiated (in particular numerically), and the absolute value of the derivative of the adaptation requirement is integrated over the observation period. The derivative and consequently also the integral of the absolute value of the derivative of the adaptation requirement are 0 if the adaptation requirement does not change (that is to say is constant) during the observation period. The more frequently, or the greater the degree to which, the adaptation requirement changes, the higher the values that the integral will assume. An inadmissible drop in the conversion capability of the catalytic converter can thus be assumed to be present in particular if the integral exceeds a predetermined threshold value.

(17) In a step 270, it is therefore correspondingly ascertained whether said change in the adaptation requirement exceeds the predetermined threshold value. If the threshold value has been exceeded, the state of the catalytic converter 130 is, in a step 280, indicated as being critical. In the step 280, for this purpose, it is preferably the case that a warning message is triggered, for example in the form of an actuation of a warning lamp, an outputting of a warning tone, or an outputting of a speech or text message.

(18) By contrast, if it is identified in step 270 that the predetermined threshold value has not been exceeded with regard to the change in the degree or the frequency of the adaptation requirement, the method 200 returns to the initialization step 210 or to the measurement 220 and modeling 230 of the respective first and second lambda values.