DE10326932A1 - Process to monitor the condition of a nitric oxide sensor in an automotive exhaust system by comparison of a cold value with a known threshold value - Google Patents

Process to monitor the condition of a nitric oxide sensor in an automotive exhaust system by comparison of a cold value with a known threshold value Download PDF

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DE10326932A1
DE10326932A1 DE10326932A DE10326932A DE10326932A1 DE 10326932 A1 DE10326932 A1 DE 10326932A1 DE 10326932 A DE10326932 A DE 10326932A DE 10326932 A DE10326932 A DE 10326932A DE 10326932 A1 DE10326932 A1 DE 10326932A1
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nitrogen oxide
sensor
phase
oxide sensor
value
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Bodo Odendall
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Audi AG
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Audi AG
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
    • F01N3/0842—Nitrogen oxides
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N11/00—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/146—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an NOx content or concentration
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/22—Safety or indicating devices for abnormal conditions
    • F02D41/222—Safety or indicating devices for abnormal conditions relating to the failure of sensors or parameter detection devices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
    • F01N2560/02—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor
    • F01N2560/026—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting NOx
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0814—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
    • F02D41/0275—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a NOx trap or adsorbent
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Exhaust Gas After Treatment (AREA)

Abstract

In a process to monitor the condition of a nitric oxide sensor in an automotive catalyst, a nitric oxide diagnostic value is logged over a given time (A) at the beginning of the lean burn phase. This value is compared with a diagnostic threshold value so chosen, that the sensor is identified as defective on reaching or exceeding the threshold. An automotive exhaust system has a nitrogen oxide catalytic converter with a nitrogen oxide sensor. In a process to monitor sensor accuracy, the motor is operated in a first predetermined lean-burn phase, during which period the nitric oxides are stored in the catalyst. In a subsequent rich-burn phase the nitric oxides are progressively released in response to sensor indication of the nitric oxide charge level. The initial diagnostic time lapse (A) is up to 10 seconds. The threshold value is chosen in accordance with a given catalyst temperature and exhaust gas flow.

Description

Die Erfindung betrifft ein Verfahren zur Überprüfung eines Stickoxid-Sensors einer einen Stickoxid-Speicherkatalysator aufweisenden Brennkraftmaschine, insbesondere einer Brennkraftmaschine für Kraftfahrzeuge nach dem Oberbegriff des Anspruchs 1.The The invention relates to a method for checking a nitrogen oxide sensor a combustion engine having a nitrogen oxide storage catalyst, in particular an internal combustion engine for motor vehicles according to the preamble of claim 1.

Brennkraftmaschinen, die zusätzlich zu einer homogenen Betriebsweise auch im Magerbetrieb betrieben werden können, sind allgemein bekannt. Der Magerbetrieb bei derartigen Brennkraftmaschinen bringt jedoch den Nachteil einer erheblich größeren Stickoxidmenge im Abgas mit sich, so dass die Stickoxide (NOX) im mageren Abgas mit einem herkömmlichen Drei-Wege-Katalysator nicht mehr vollständig reduziert werden können. Um die Stickoxid-Emissionen im Rahmen vorgeschriebener Grenzen, z. B. des Euro-IV-Grenzwertes zu halten, werden in Verbindung mit derartigen Brennkraftmaschinen zusätzlich Stickoxid-Speicherkatalysatoren eingesetzt. Diese Stickoxid-Speicherkatalysatoren werden so betrieben, dass darin die von der Brennkraftmaschine im Magerbetrieb erzeugten großen Mengen an Stickoxiden eingespeichert werden. Mit zunehmender gespeicherter Stickoxidmenge wird ein Sättigungszustand im Stickoxid-Speicherkatalysator erreicht, so dass der Stickoxid-Speicherkatalysator entladen werden muss. Dazu wird für eine sogenannte Entladephase kurzfristig mittels der Motorsteuerung bzw. dem Motorsteuergerät auf einen unterstöchiometrischen, fetten Motorbetrieb umgeschalten, bei dem die Brennkraftmaschine mit einem fetten, einen Luftmangel aufweisenden Gemisch betrieben wird. Durch diesen fetten Betrieb wird die für die Reduktion der gespeicherten Stickoxidmenge erforderliche Menge an Reduktionsmittel in den Stickoxid-Speicherkatalysator eingeleitet. Die Einspeicherung der sich im mageren Abgas befindlichen Stickoxide durch den Stickoxid-Speicherkatalysator wird in der Regel durch einen Stickoxid-Sensor überwacht, der örtlich gesehen nach dem Stickoxid-Speicherkatalysator im Abgassystem angeordnet ist. Ein derartiger Stickoxid-Sensor ist grundsätzlich mit einer Messungenauigkeit behaftet. Darin liegt jedoch das Problem, dass es oftmals nicht möglich ist, zwischen einem geringen Stickoxid-Schlupf durch den Stickoxid-Speicherkatalysator hindurch und einer Messungenauigkeit bzw. einem Defekt des Stickoxid-Sensors zu unterscheiden. So kann beispielsweise eine Messungenauigkeit bzw. ein Defekt des Stickoxid-Sensors, die bzw. der sich z. B. durch einen Offset des Messsignals ausdrückt, irrtümlicher Weise den Schluss auf einen bereits erheblich gealterten Stickoxid-Speicherkatalysator bzw. sogar einen defekten Stickoxid-Speicherkatalysator zulassen.Internal combustion engines, the additional operated in a homogeneous mode of operation even in lean operation can be are well known. The lean operation brings in such internal combustion engines but the disadvantage of a significantly larger amount of nitrogen oxide in the exhaust gas with it, so that the nitrogen oxides (NOX) in the lean exhaust gas with a usual Three-way catalytic converter not completely reduced anymore can be. To the nitrogen oxide emissions within prescribed limits, eg. B. the Euro IV limit, Be in conjunction with such internal combustion engine additionally nitrogen oxide storage catalysts used. These nitrogen oxide storage catalysts are operated in such a way that that in it generated by the internal combustion engine in lean operation huge Amounts of nitrogen oxides are stored. With increasing stored Nitrogen oxide becomes a saturation state achieved in the nitrogen oxide storage catalyst, so that the nitrogen oxide storage catalyst must be unloaded. This is for a so-called discharge phase short term by means of the engine control or the engine control unit to a sub-stoichiometric, fat Switched engine operation, in which the internal combustion engine with a fat, a deficient mixture is operated. By this fat operation is the for the amount required to reduce the stored amount of nitrogen oxide introduced to reducing agent in the nitrogen oxide storage catalyst. The storage of the nitrogen oxides located in the lean exhaust gas The nitrogen oxide storage catalyst is usually by a Nitrogen oxide sensor monitors, the local seen after the nitrogen oxide storage catalyst is arranged in the exhaust system. Such a nitrogen oxide sensor is basically with a measurement inaccuracy. Therein, however, lies the problem that Often not possible is, between a small nitrogen oxide slip through the nitrogen oxide storage catalyst through and a measurement inaccuracy or a defect of the nitrogen oxide sensor to distinguish. For example, a measurement inaccuracy or a defect of the nitrogen oxide sensor, the or z. B. by expresses an offset of the measurement signal, erroneously the conclusion of a already significantly aged nitrogen oxide storage catalyst or even allow a defective nitrogen oxide storage catalyst.

Um diese Probleme zu vermeiden, ist es aus der gattungsbildenden DE 100 49 685 A1 bereits bekannt, die Funktionsfähigkeit eines Stickoxid-Sensors im Rahmen einer sogenannten On-Board-Diagnose (OBD) zu überprüfen. Konkret wird hierzu ein den Lambda-Wert des Abgases charakterisierendes Breitband-Lambdasignal oder ein Lambda-Sprungsignal ermittelt. Diese ermittelten Werte des Lambda-Signals werden mit bei vorgegebenen Betriebsparametern plausiblen Lambda-Werten des Abgases verglichen, wobei in Abhängigkeit von dem Vergleichsergebnis ein Stickoxid-Sensor-Diagnosesignal gebildet wird.To avoid these problems, it is from the generic DE 100 49 685 A1 already known to check the functionality of a nitric oxide sensor as part of a so-called on-board diagnosis (OBD). Specifically, for this purpose, a broadband lambda signal characterizing the lambda value of the exhaust gas or a lambda jump signal is determined. These determined values of the lambda signal are compared with lambda values of the exhaust gas which are plausible at given operating parameters, a nitrogen oxide sensor diagnostic signal being formed as a function of the comparison result.

Weiter ist auch aus der DE 100 62 289 A1 ein Verfahren zur Diagnose eines Stickoxid-Sensors im Abgastrakt einer Brennkraftmaschine bekannt, bei der der Stickoxid-Sensor den Anstieg von NH3 zu Beginn der fetten Betriebsphase misst. Geht dieser gemessene Wert nicht steil nach oben, dann wird der Stickoxid-Sensor als fehlerhaft erkannt. Alternativ zu dieser Verfahrensweise wird hier ferner noch vorgeschlagen, auf die maximal erreichte Signalgröße des Stickoxid-Sensors bezogen auf die NH3-Menge im gesamten Fettbetrieb abzustellen. Insgesamt wird daher bei diesen Verfahrensweisen jeweils auf die Querempfindlichkeit des Stickoxid-Sensors gegenüber NH3 abgestellt. Eine ähnliche Verfahrensführung ist auch aus der WO 00/00728 bekannt.Next is also from the DE 100 62 289 A1 a method for the diagnosis of a nitrogen oxide sensor in the exhaust system of an internal combustion engine, in which the nitrogen oxide sensor measures the increase of NH 3 at the beginning of the rich operating phase. If this measured value does not rise steeply, then the nitrogen oxide sensor is detected as defective. As an alternative to this procedure, it is further proposed here to switch to the maximum signal size of the nitrogen oxide sensor, based on the amount of NH 3 in the entire rich operation. Overall, therefore, with these procedures, the cross-sensitivity of the nitrogen oxide sensor to NH 3 is taken into account. A similar procedure is also known from WO 00/00728.

Aufgabe der Erfindung ist es, ein alternatives Verfahren zur Überprüfung eines Stickoxid-Sensors einer einen Stickoxid-Speicherkatalysator aufweisenden Brennkraftmaschine, insbesondere einer Brennkraftmaschine für Kraftfahrzeuge, zur Verfügung zu stellen, mit dem auf einfache Weise sowie mit hoher Funktionssicherheit eine Überprüfung des Stickoxid-Sensors durchführbar ist.task The invention is an alternative method for checking a Nitrogen sensor of a nitrogen oxide storage catalytic converter having Internal combustion engine, in particular an internal combustion engine for motor vehicles, to disposal to provide, with the simple and with high reliability a review of the Nitrogen sensor feasible is.

Diese Aufgabe wird gelöst mit den Merkmalen des Patentanspruchs 1.These Task is solved with the features of claim 1.

Gemäß Anspruch 1 wird mittels dem Stickoxid-Sensor lediglich unmittelbar zu Beginn der Magerbetriebsphase als Einspeicherphase während eines vorgebbaren Diagnosezeitraums, der wesentlich kürzer als die gesamte Einspeicherphase ist, wenigstens ein Stickoxid-Diagnosewert erfasst, der mit einem vorgebbaren Stickoxid-Sensorschwellwert verglichen wird, der so festgelegt ist, dass der Stickoxid-Sensor nach Erreichen oder Überschreiten des Stickoxid-Sensorschwellwertes als fehlerhaft erkannt wird.According to claim 1 is by means of the nitrogen oxide sensor only immediately at the beginning the lean operating phase as a storage phase during a predefinable diagnostic period, the much shorter as the entire injection phase, at least one nitric oxide diagnostic value detected, compared with a predetermined nitrogen oxide sensor threshold which is set so that the nitric oxide sensor after reaching or crossing of the nitrogen oxide sensor threshold is detected as faulty.

Der Erfindung liegt die Erkenntnis zugrunde, dass der Stickoxid-Speicherkatalysator unmittelbar zu Beginn der Magerphase als Einspeicherphase einen sehr geringen und von dem Alterungszustand des Stickoxid-Speicherkatalysators nahezu vollständig unabhängigen Stickoxid-Schlupf aufweist. D. h., erfindungsgemäß wird hier zur Überprüfung des Stickoxid-Sensors ausgenutzt, dass ein neuer Stickoxid-Speicherkatalysator ebenso wie z. B. ein bereits sehr stark gealterter Stickoxid-Speicherkatalysator jeweils unmittelbar zu Beginn der Magerbetriebsphase der Brennkraftmaschine und damit der Stickoxid-Einspeicherung ein ähnliches bis nahezu identisches Verhalten zeigen. Dadurch wird ein sehr einfaches und sehr funktionssicheres Verfahren zur Überprüfung eines Stickoxid-Sensors zur Verfügung gestellt.The invention is based on the finding that the nitrogen oxide storage catalyst is direct has at the beginning of the lean phase as Einspeicherphase a very low and almost completely independent of the aging state of the nitrogen oxide storage catalytic nitrogen oxide slip. D. h., According to the invention is exploited here for checking the nitrogen oxide sensor that a new nitrogen oxide storage catalyst as well as z. B. an already very strong aged nitrogen oxide storage catalyst each directly at the beginning of the lean operation phase of the engine and thus the nitrogen oxide storage show a similar to almost identical behavior. This provides a very simple and very reliable method for checking a nitrogen oxide sensor.

Gemäß einer besonders bevorzugten konkreten Verfahrensführung nach Anspruch 2 ist vorgesehen, dass der Diagnosezeitraum vom Einspeicherphasenbeginn als Magerbetriebsphasenbeginn ausgehend weniger als 10 Sekunden, bevorzugt weniger als 7,5 Sekunden und höchst bevorzugt weniger als 5 Sekunden beträgt. Diese Werte sind insbesondere im Bezug auf Magerphasenzyklen zu sehen, die im Falle eines bereits sehr stark gealterten Stickoxid-Speicherkatalysators in etwa bei einer Minute liegen. Zudem kann dabei der Stickoxid-Schwellwert nach Anspruch 3 in Abhängigkeit von einer bestimmten Katalysatortemperatur und/oder eines Abgasmassenstroms festgelegt werden. Beispielsweise kann als Bezugsgröße eine Abgasmasse von 60 kg pro Stunde und eine Katalysatortemperatur von 300°C zugrundegelegt werden.According to one Particularly preferred concrete process control according to claim 2 is provided, that the diagnosis period from the storage phase start as a lean operation phase start starting less than 10 seconds, preferably less than 7.5 seconds and most preferably less than 5 seconds. These values are especially in the Terms of lean-phase cycles seen in the case of one already very strong aged nitrogen oxide storage catalyst at about a minute lie. In addition, while the nitrogen oxide threshold after Claim 3 in dependence from a certain catalyst temperature and / or an exhaust gas mass flow be determined. For example, as a reference a Exhaust mass of 60 kg per hour and a catalyst temperature of 300 ° C based become.

Besonders vorteilhafte Betriebsergebnisse ergeben sich auch mit einer Verfahrensführung gemäß Anspruch 4, die vorsieht, dass mehrere Stickoxid-Sensor-Schwellwerte zur Ausbildung von Schwellwert-Vergleichsbereichen festgelegt sind. So kann beispielsweise in Verbindung mit lediglich zwei Schwellwert-Vergleichsbereichen ein innerhalb eines ersten, unteren Schwellwert-Vergleichsbereiches liegender Stickoxid-Diagnosewert die Notwendigkeit der Offset-Korrektur des Stickoxid-Sensors anzeigen, während sich der daran nach oben hin anschließende zweite, obere Schwellwert-Vergleichsbereich, dessen Werte höher liegen als die des ersten Schwellwert-Vergleichsbereiches, im Falle eines innerhalb dieses Schwellwert-Vergleichsbereiches liegenden Stickoxid-Diagnosewertes den Defekt des Stickoxid-Sensors anzeigt.Especially advantageous operating results also result with a process control according to claim 4, which provides for multiple nitrogen oxide sensor thresholds to form threshold comparison ranges are fixed. So, for example, in conjunction with only two threshold comparison ranges within a first, low threshold comparison range lying nitrogen oxide diagnostic value indicate the need for offset correction of the nitric oxide sensor, while This is followed by the second, upper threshold comparison range, which adjoins it at the top Values higher lie as those of the first threshold comparison range, in the case of within this threshold comparison range lying nitrogen oxide diagnostic value the defect of the nitrogen oxide sensor displays.

Die Erfindung wird nachfolgend anhand einer Zeichnung näher erläutert.The The invention will be explained in more detail with reference to a drawing.

Es zeigen:It demonstrate:

1 eine schematische Auftragung der Stickoxid-Emissionen vor und nach einem neuen Stickoxid-Speicherkatalysator im Vergleich zum Stickoxid-Schlupf, 1 a schematic plot of nitrogen oxide emissions before and after a new nitrogen oxide storage catalyst in comparison to nitrogen oxide slip,

2 eine schematische Auftragung der Stickoxid-Emissionen vor und nach einem Stickoxid-Speicherkatalysator, der einen mittleren Alterungsgrad aufweist, im Vergleich zum Stickoxid-Schlupf, und 2 a schematic plot of the nitrogen oxide emissions before and after a nitrogen oxide storage catalyst having a medium degree of aging, compared to the nitrogen oxide slip, and

3 eine schematische Auftragung der Stickoxid-Emissionen vor und nach einem Stickoxid-Speicherkatalysator, der bereits sehr stark gealtert ist, im Vergleich zum Stickoxid-Schlupf. 3 a schematic plot of the nitrogen oxide emissions before and after a nitrogen oxide storage catalyst, which has already aged a lot, compared to the nitrogen oxide slip.

In den 1 bis 3 sind jeweils die Stickoxid-Emissionen vor und nach dem Stickoxid-Speicherkatalysator für einen neuen Stickoxid-Speicherkatalysator (1), für einen Stickoxid-Speicherkatalysator mit mittlerer Alterungsstufe (2) und für einen bereits sehr stark gealterten Stickoxid-Speicherkatalysator (3) dargestellt, wobei die Kurven 1 jeweils die Stickoxid-Emissionen vor dem Stickoxid-Speicherkatalysator, die Kurven 2 den Stickoxid-Schlupf, d. h. den durch den Stickoxid-Speicherkatalysator hindurchgehenden und nicht eingespeicherten Stickoxidmengenanteil bezeichnen, und die Kurven 3 jeweils die Stickoxid-Emissionen nach dem Stickoxid-Speicherkatalysator bezeichnen.In the 1 to 3 are each the nitrogen oxide emissions before and after the nitrogen oxide storage catalyst for a new nitrogen oxide storage catalyst ( 1 ), for a middle-aged nitrogen oxide storage catalyst ( 2 ) and for an already strongly aged nitrogen oxide storage catalyst ( 3 ), the curves 1 respectively the nitrogen oxide emissions before the nitrogen oxide storage catalytic converter, the curves 2 denote the nitrogen oxide slip, ie the amount of nitrogen oxide passing through the nitrogen oxide storage catalyst and not stored, and the curves 3 each denote the nitrogen oxide emissions after the nitrogen oxide storage catalyst.

Die Zeitabschnitte, in denen die Stickoxid-Emissionen im Bereich von 400 ppm liegen, stellen die Magerbetriebsphasen der Brennkraftmaschine dar, d. h. während dieses Zeitraumes wird der Stickoxid-Speicherkatalysator mit Stickoxiden beladen. Diejenigen Zeitabschnitte, in denen die Stickoxid-Emissionen unter 10 ppm liegen, bezeichnen diejenigen Betriebsphasen der Brennkraftmaschine, in denen diese mit einem fetten Gemisch betrieben wird und bei denen der Stickoxid-Speicherkatalysator entladen wird.The Periods during which nitrogen oxide emissions range from 400 ppm, put the lean operating phases of the internal combustion engine dar. d. H. while This period is the nitrogen oxide storage catalyst with nitrogen oxides loaded. Those periods of time in which the nitrogen oxide emissions under 10 ppm are those operating phases of the internal combustion engine, in which it is operated with a rich mixture and in which the nitrogen oxide storage catalyst is discharged.

Ein Vergleich der 1 bis 3 zeigt deutlich, dass sich bei einem Stickoxid-Speicherkatalysator mit zunehmender Alterung die Einspeicherzeiten, d. h. somit die Zeiträume, in denen der Stickoxid-Speicherkatalysator Stickoxid einspeichern kann, verringern. Dies bedeutet, dass der Stickoxid-Speicherkatalysator mit zunehmender Alterung öfter durch Umschalten auf den Fettbetrieb entladen werden muss.A comparison of 1 to 3 clearly shows that with a nitrogen oxide storage catalyst with increasing aging Einspeicherzeiten, ie thus reduce the periods during which the nitrogen oxide storage catalyst can store nitrogen oxide. This means that the nitrogen oxide storage catalyst must be discharged more often by switching to the rich operation with increasing aging.

Ein Vergleich der 1 bis 3 zeigt aber auch, dass, wie dies in den 1 bis 3 lediglich beispielhaft und schematisch mit A bezeichnet worden ist, der Stickoxid-Speicherkatalysator unmittelbar zu Beginn der Einspeicherung, d. h. unmittelbar zu Beginn der Magerbetriebsphase einen sehr geringen und von dem Alterungszustand nahezu vollständig unabhängigen Stickoxid-Schlupf aufweist. Bezugszeichen A bezeichnet hier einen vorgegebenen Diagnosezeitraum von z. B. 5 Sekunden, während dem mittels einem Stickoxid-Sensor wenigstens ein Stickoxid-Diagnosewert erfasst wird, der mit einem ebenfalls vorgegebenen Stickoxid-Sensorschwellwert verglichen wird, wobei der Stickoxid-Sensorschwellwert so festgefegt ist, dass der Stickoxid-Sensor nach Erreichen oder Überschreiten des Stickoxid-Sensorschwellwertes als fehlerhaft erkannt wird. Dieser Stickoxid-Sensorschwellwert ist beispielsweise in einem Motorsteuergerät der Brennkraftmaschine abgelegt. Sollte der während des Diagnosezeitraums von hier beispielhaft 5 Sekunden erfasste Stickoxid-Diagnosewert den Stickoxid-Sensorschwellwert erreichen und/oder Überschreiten, d. h. falls der Stickoxid-Sensor direkt nach einer erfolgreich durchgeführten Stickoxid-Regeneration Stickoxid-Schlupfwerte anzeigt, die über dem definierten Stickoxid-Sensorschwellwert liegen, dann wird erkannt, dass der Stickoxid-Sensor falsche Werte liefert. Beispielsweise kann hierbei auch festgelegt werden, dass bis zu definierten Schwellwerten eine Offset-Korrektur durchgeführt werden kann, während ab einer weiteren Schwelle der Stickoxid-Sensor als defekt zu erkennen ist.A comparison of 1 to 3 But also shows that, as in the 1 to 3 has been designated only by way of example and schematically with A, the nitrogen oxide storage catalyst immediately at the beginning of storage, ie immediately at the beginning of the lean operating phase has a very low and almost completely independent of the aging state nitrogen oxide slip. Reference symbol A here denotes a predetermined diag nose period of z. B. 5 seconds, during which by means of a nitrogen oxide sensor at least one nitrogen oxide diagnostic value is detected, which is compared with a likewise predetermined nitrogen oxide sensor threshold, the nitrogen oxide sensor threshold is so festgefegt that the nitrogen oxide sensor after reaching or exceeding the Nitrogen sensor threshold is detected as faulty. This nitrogen oxide sensor threshold is stored, for example, in an engine control unit of the internal combustion engine. Should the nitrogen oxide diagnostic value acquired during the diagnostic period from here, for example 5 seconds, reach and / or exceed the nitrogen oxide sensor threshold, ie if the nitrogen oxide sensor indicates nitrogen oxide slip values directly after a successfully performed nitrogen oxide regeneration, which exceeds the defined nitrogen oxide sensor threshold value lie, then it is detected that the nitric oxide sensor provides incorrect values. For example, it can also be determined here that an offset correction can be carried out up to defined threshold values, while from a further threshold the nitrogen oxide sensor can be identified as defective.

Claims (4)

Verfahren zur Überprüfung eines Stickoxid-Sensors einer einen Stickoxid-Speicherkatalysator aufweisenden Brennkraftmaschine, insbesondere einer Brennkraftmaschine für Kraftfahrzeuge, bei dem die Brennkraftmaschine in einer ersten Betriebsphase als Magerbetriebsphase für einen vorgebbaren Magerbetriebs-Zeitraum mit einem mageren Gemisch betrieben wird, wobei während dieser Magerbetriebsphase Stickoxide in den Stickoxid-Speicherkatalysator eingespeichert werden, und bei dem die Brennkraftmaschine in einer weiteren Betriebsphase als Fettphase oder Entladephase für einen vorgebbaren Fettbetriebs-Zeitraum mit einem fetten Gemisch betrieben wird, wobei während dieser Fettbetriebsphase die in den Stickoxid-Speicherkatalysator eingespeicherten Stickoxide aus dem Stickoxid-Speicherkatalysator ausgespeichert werden, und wobei das Umschalten in die Fettbetriebsphase als Entladephase in Abhängigkeit von einem mittels dem Stickoxid-Sensor erfassten Stickoxidwert als Stickoxid-Schlupf nach dem Stickoxid-Speicherkatalysator erfolgt, dadurch gekennzeichnet, dass unmittelbar zu Beginn der Magerbetriebsphase als Einspeicherphase mittels dem Stickoxid-Sensor während eines vorgebbaren Diagnosezeitraums (A) wenigstens ein Stickoxid-Diagnosewert erfasst wird, der mit einem vorgebbaren Stickoxid-Sensorschwellwert verglichen wird, der so festgelegt ist, dass der Stickoxid-Sensor nach Erreichen oder Überschreiten des Stickoxid-Sensorschweilwertes als fehlerhaft erkannt wird.Method for checking a nitrogen oxide sensor of a combustion engine having a nitrogen oxide storage catalytic converter, in particular an internal combustion engine for motor vehicles, in which the internal combustion engine is operated as a lean operating phase for a predeterminable lean operating period with a lean mixture in a first operating phase, during which lean operating phase nitrogen oxides in the nitrogen oxide storage catalytic converter are stored, and in which the internal combustion engine is operated in a further phase of operation as a rich phase or discharge phase for a predetermined Fettbetriebs period with a rich mixture, wherein stored in the nitrogen oxide storage catalyst nitrogen oxides from the nitrogen oxide storage catalyst during this rich operating phase be stored, and wherein the switching to the rich operating phase as the discharge phase as a function of a detected by means of the nitrogen oxide sensor nitrogen oxide value as nitrogen oxide slip after d em nitric oxide storage catalyst is carried out, characterized in that immediately at the beginning of the lean operating phase as Einspeicherphase by means of the nitrogen oxide sensor during a predetermined diagnostic period (A) at least one nitric oxide diagnostic value is detected, which is compared with a predetermined nitrogen oxide sensor threshold value set so is that the nitrogen oxide sensor is detected as defective after reaching or exceeding the nitrogen oxide Sensorschweilwertes. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass der Diagnosezeitraum (A) vom Einspeicherphasenbeginn ausgehend weniger als 10 Sekunden, bevorzugt weniger als 7,5 Sekunden höchst bevorzugt weniger als 5 Sekunden beträgt.Method according to claim 1, characterized in that that the diagnosis period (A) starting from Einspeicherphasenbeginn less than 10 seconds, preferably less than 7.5 seconds most preferred less than 5 seconds. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass der Stickoxid-Schwellwert in Abhängigkeit von einer bestimmten Katalysatortemperatur und/oder eines Abgasmassenstroms festgelegt wird.Method according to claim 1 or 2, characterized that the nitrogen oxide threshold depends on a particular Catalyst temperature and / or an exhaust gas mass flow set becomes. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass mehrere Stickoxid-Sensorschwellwerte zur Ausbildung von Schwellwert-Vergleichsbereichen festgelegt sind dergestalt, dass ein innerhalb eines ersten Schwellwert-Vergleichsbereiches liegender Stickoxid-Diagnosewert die Notwendigkeit der Offsetkorrektur des Stickoxid-Sensors anzeigt, und dass ein Schwellwert-Vergleichsbereich vorgesehen ist, dessen Werte höher liegen als die des ersten Schwellwert-Vergleichsbereiches, wobei ein innerhalb dieses Schwellwert-Vergleichsbereiches liegender Stickoxid-Diagnosewert den Defekt des Stickoxid-Sensors anzeigt.Method according to one of claims 1 to 3, characterized that multiple nitrogen oxide sensor thresholds to form threshold comparison ranges are defined in this way, that one within a first Threshold comparison range lying nitrogen oxide diagnostic value the Indicates the need for the offset correction of the nitrogen oxide sensor, and that a threshold comparison range is provided, its values higher lie than those of the first threshold comparison range, wherein a within this threshold comparison range lying nitrogen oxide diagnostic value indicates the defect of the nitrogen oxide sensor.
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