WO2001055565A2 - METHOD AND DEVICE FOR DETECTING A NOx CONCENTRATION OF AN EXHAUST GAS STREAM PERTAINING TO A COMBUSTION ENGINE - Google Patents
METHOD AND DEVICE FOR DETECTING A NOx CONCENTRATION OF AN EXHAUST GAS STREAM PERTAINING TO A COMBUSTION ENGINE Download PDFInfo
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- WO2001055565A2 WO2001055565A2 PCT/EP2001/000540 EP0100540W WO0155565A2 WO 2001055565 A2 WO2001055565 A2 WO 2001055565A2 EP 0100540 W EP0100540 W EP 0100540W WO 0155565 A2 WO0155565 A2 WO 0155565A2
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- 238000000034 method Methods 0.000 title claims abstract description 32
- 238000002485 combustion reaction Methods 0.000 title claims abstract description 28
- 239000003054 catalyst Substances 0.000 claims abstract description 6
- 230000003197 catalytic effect Effects 0.000 claims description 21
- 230000008929 regeneration Effects 0.000 claims description 15
- 238000011069 regeneration method Methods 0.000 claims description 15
- 239000003638 chemical reducing agent Substances 0.000 claims description 5
- 238000010521 absorption reaction Methods 0.000 claims description 3
- 238000006477 desulfuration reaction Methods 0.000 claims description 3
- 230000023556 desulfurization Effects 0.000 claims description 3
- 238000001514 detection method Methods 0.000 claims description 3
- 239000000446 fuel Substances 0.000 claims description 3
- 238000002405 diagnostic procedure Methods 0.000 claims description 2
- 230000001052 transient effect Effects 0.000 claims 1
- 238000010200 validation analysis Methods 0.000 claims 1
- 239000007789 gas Substances 0.000 description 14
- 238000005259 measurement Methods 0.000 description 4
- 238000012937 correction Methods 0.000 description 3
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 3
- 238000012935 Averaging Methods 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- XKMRRTOUMJRJIA-UHFFFAOYSA-N ammonia nh3 Chemical compound N.N XKMRRTOUMJRJIA-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000009499 grossing Methods 0.000 description 1
- 238000012067 mathematical method Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000001172 regenerating effect Effects 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
Classifications
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- 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
- F02D41/24—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means
- F02D41/2406—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means using essentially read only memories
- F02D41/2425—Particular ways of programming the data
- F02D41/2429—Methods of calibrating or learning
- F02D41/2441—Methods of calibrating or learning characterised by the learning conditions
-
- 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
- F02D41/24—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means
- F02D41/2406—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means using essentially read only memories
- F02D41/2425—Particular ways of programming the data
- F02D41/2429—Methods of calibrating or learning
- F02D41/2451—Methods of calibrating or learning characterised by what is learned or calibrated
- F02D41/2474—Characteristics of sensors
Definitions
- the invention relates to a method and a device for determining a NO ⁇ concentration of an exhaust gas flow of an internal combustion engine by means of a NO x- sensitive measuring device, in particular an NO x probe, arranged downstream of a NO x storage catalytic converter in an exhaust gas line of the internal combustion engine.
- NO ⁇ storage catalytic converters In the exhaust duct of the internal combustion engine, which are operated alternately in NO x storage phases and regeneration phases. For maximum reduction of a NO x emission, it is advantageous to control the NO ⁇ storage catalytic converter or the internal combustion engine as a function of a NO ⁇ concentration present behind the NOx storage catalytic converter. This requires an exact detection of a current NO ⁇ concentration, for which NOx sensors are used.
- Each NO x sensor has an individual error measure, which leads to deviations of a displayed measured value from an actual actual value of the NO ⁇ concentration.
- These individual inaccuracies in the characteristic of the sensor NO ⁇ - lead to errors in the control of the internal combustion engine so that, for example, an NO x -Beladungsgrad of the NOx trap is detected inaccurately, can be switched whereby a regenerating too late. This leads to increased NO x emissions.
- the invention has for its object to improve the accuracy of the determination of the NO ⁇ content of an exhaust gas.
- the method according to the invention provides, in an operating phase of the internal combustion engine in which it is known that the NO ⁇ concentration at the position of the NOx-sensitive measuring device passes through a value close to zero Search for a minimum of a signal curve of the measuring device and to take the found minimum as the zero point for a calibration of the measuring device.
- the search for the minimum is carried out directly or shortly after NO regeneration or desulfurization of the NOx storage catalytic converter. Following NO ⁇ or sulfur regeneration, even with a severely damaged catalytic converter, it can be assumed that the NO. Absorption will be almost 100% accurate. In this phase, a NOx concentration of 0 to 5 ppm behind the catalytic converter can be expected at least for a limited period of time, so that a minimal signal of the NO ⁇ measuring device obtained in this phase with a negligible error as zero point for an offset correction of the NO ⁇ sensor can be taken over.
- signal values of the measuring device are detected at predetermined time intervals or according to predetermined exhaust gas or reducing agent throughputs in order to search for the minimum.
- Each measured signal value is compared with a last saved minimum. If the signal value is less than the last found minimum, it is saved as a new minimum.
- the search for the minimum is ended after a predetermined duration or a predetermined exhaust gas or reducing agent throughput has elapsed.
- the described method ensures that a minimum found in this way corresponds to an absolute minimum in the signal curve of the measuring device and not, for example, a local minimum, which can be caused, for example, by an irregularity in the sensor characteristic.
- a very preferred embodiment of the method according to the invention therefore provides for the minimum found to be subjected to a plausibility check. For this, one or more criteria must be met before a minimum is accepted as the zero point for the calibration. According to a preferred embodiment, for example, it is required that the minimum found must fall below an upper threshold value. Furthermore, falling below the upper threshold value may be required for a certain minimum period. As another Criterion can be specified that the minimum found is located at a sufficiently large distance from a start and an end point of the minimum search. In this way, it is checked whether the "valley floor" in which the minimum lies is really in the time window of the minimum search.
- An extremely advantageous embodiment of the method also provides that the minimum search is terminated and / or a found minimum is not adopted as the zero point for the calibration of the measuring device if predetermined boundary conditions for operating parameters are not met during the minimum search.
- An important boundary condition relates, for example, to a temperature of the NO ⁇ storage catalytic converter, which should be in a range which ensures satisfactory NO x absorption.
- Another boundary condition requires lean operation of the internal combustion engine and / or the presence of a lean exhaust gas in the area of the NO ⁇ storage catalytic converter and / or in the area of the measuring device. In addition, this can be requested over a predetermined minimum period.
- the internal combustion engine is not in a fuel cut-off phase and / or not in an idle state and / or not in a highly unsteady operating mode during the minimum search.
- a satisfactory NO ⁇ storage behavior of a NO ⁇ storage catalytic converter can be required, which is determined, for example, by a diagnostic method.
- An upper and / or lower limit can also be specified for a NO x raw mass flow emitted by the internal combustion engine.
- the device according to the invention provides means with which the method steps described above can be carried out.
- These means preferably comprise a control unit, in which the procedure for controlling the method steps for determining a NOx concentration is stored in digital form, wherein the control unit can be integrated in an engine control unit.
- Figure 1 is a schematic representation of an exhaust duct
- Figure 2 is a representation of a sensor characteristic of an NO ⁇ sensor
- Figure 3 shows a sensor signal as a function of time during the
- the arrangement of an internal combustion engine 10 shown schematically in FIG. 1 has an exhaust tract 12 with an optional pre-catalytic converter 14 arranged therein and a NO x storage catalytic converter 16.
- a NO x sensor 18 is also arranged in the exhaust duct 12 downstream of the NO ⁇ storage catalytic converter 16.
- the NO x sensor 18 transmits a measurement signal to an engine control unit 20 in which a control unit 22 is integrated.
- the internal combustion engine 10 by, for example, influence on a Popespeisendes air-fuel mixture increases.
- FIG. 2 shows a characteristic curve K of a NO x sensor 18.
- the output signal OUT of the sensor 18, which can be a voltage, for example, is shown here as a function of a NO x concentration in the exhaust gas.
- the characteristic curve K which runs linearly in the area of application of the NO x sensor 18 is characterized by the slope S, that is to say its sensitivity, and by the so-called offset OS, which corresponds to an output signal in the absence of NO x in the exhaust gas.
- the zero point of the characteristic curve is known as a special case, it can at least be used for an offset correction.
- the output signal OUT of the NO ⁇ sensor In order to detect the zero point signal of the NO ⁇ sensor 18, in a situation in which the NO ⁇ concentration at the position of the sensor 18 is known or can be assumed to be approximately zero, the output signal OUT of the NO ⁇ sensor must be obtained 18 can be measured. The signal measured in this way can then be defined as the zero point of the sensor 18.
- An operating situation in which a NO ⁇ concentration behind the NO x storage catalytic converter 16 can be assumed to be close to zero with a sufficiently high probability is given shortly after regeneration, in particular NO x regeneration, of the NO x storage catalytic converter 16 ,
- FIG. 3 shows an idealized time profile of a signal curve SK of a NO x sensor 18 arranged downstream of a NO x storage catalytic converter 16 during the change from a rich operating mode (regeneration phase R) to a lean operating mode M of the internal combustion engine 10.
- the sensor signal OUT remains at a relatively high level. This is due on the one hand to an incomplete reduction of desorbed nitrogen oxides NO x and on the other hand to the formation of ammonia NH3 during regeneration R, to which the NO x sensor 18 also responds.
- the signal OUT initially remains at this relatively high level depending on a dead volume of the exhaust gas duct and on a space velocity of the exhaust gas.
- an inherent inertia of the NO ⁇ sensor 18 leads to a delay in the response of the signal curve SK, even if lean exhaust gas is already present behind the NO ⁇ storage catalytic converter 16.
- the signal curve SK runs through a minimum min shortly after the switchover to the lean mode M, in order then to rise again very slowly as a result of increasing loading of the NO x storage catalytic converter 16.
- signal curves SK which correspond to a less ideal course than the one shown, are also accessible to the evaluation.
- the described method thus also enables a low signal-to-noise ratio, that is, a high one Background noise, and in the event of irregularities in the characteristic curve K, as is observed in particular in the case of aged NO x sensors 18, reliable detection of the minimum min.
- the minimum search is ended after a predetermined period of time after switching to the lean mode M at the time t £. Instead of a period of time, an exhaust gas or reducing agent mass which has been passed through or a number of measuring points can also be specified.
- the minimum for calibration is only released if further boundary conditions are met.
- This relates, for example, to a temperature of the NO x storage catalytic converter 16, which should be in a range that guarantees reliable storage of NO x .
- a threshold value SW is shown in FIG. It can also be required that the threshold SW must be undershot for a predetermined minimum duration.
- the minimum min is immediately released as the zero point of the NO x sensor 18 and an offset correction of the sensor 18 is carried out.
- the found minimum min remains valid until a new minimum is determined in a subsequent minimum search.
- a minimum search can be carried out after each NOx regeneration - provided the boundary conditions described are met.
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Analytical Chemistry (AREA)
- Exhaust Gas After Treatment (AREA)
Abstract
Description
Verfahren und Vorrichtung zur Bestimmung einer NOx-Konzentration eines Abgasstromes einer VerbrennungskraftmaschineMethod and device for determining a NO x concentration of an exhaust gas flow of an internal combustion engine
Die Erfindung betrifft ein Verfahren sowie eine Vorrichtung zur Bestimmung einer NOχ- Konzentration eines Abgasstromes einer Verbrennungskraftmaschine mittels einer stromab eines NOx-Speicherkatalysators in einem Abgasstrang der Verbrennungskraftmaschine angeordneten NOx-empfindlichen Meßeinrichtung, insbesondere einer NOx-Sonde.The invention relates to a method and a device for determining a NOχ concentration of an exhaust gas flow of an internal combustion engine by means of a NO x- sensitive measuring device, in particular an NO x probe, arranged downstream of a NO x storage catalytic converter in an exhaust gas line of the internal combustion engine.
Zur Durchführung einer Nachbehandlung von Abgasen von mindestens zeitweise magerlaufenden Verbrennungskraftmaschinen ist es bekannt, NOχ- Speicherkatalysatoren im Abgaskanal der Verbrennungskraftmaschine anzuordnen, die alternierend in NOx-Einlagerungsphasen und Regenerationsphasen betrieben werden. Für eine maximale Reduzierung einer NOx-Emission ist es vorteilhaft, den NOχ- Speicherkatalysator beziehungsweise die Verbrennungskraftmaschine in Abhängigkeit von einer hinter dem NOx-Speicherkatalysator vorliegenden NOχ-Konzentration zu steuern. Dies setzt eine exakte Erfassung einer aktuellen NOχ-Konzentration voraus, wofür NOx-Sensoren eingesetzt werden.To carry out an aftertreatment of exhaust gases from at least occasionally lean-burn internal combustion engines, it is known to arrange NOχ storage catalytic converters in the exhaust duct of the internal combustion engine, which are operated alternately in NO x storage phases and regeneration phases. For maximum reduction of a NO x emission, it is advantageous to control the NOχ storage catalytic converter or the internal combustion engine as a function of a NO χ concentration present behind the NOx storage catalytic converter. This requires an exact detection of a current NOχ concentration, for which NOx sensors are used.
Jeder NOx-Sensor weist ein individuelles Fehlermaß auf, das zu Abweichungen eines angezeigten Meßwertes von einem tatsächlich vorliegenden IST-Wert der NOχ- Konzentration führt. Diese individuellen Ungenauigkeiten in der Kennlinie des NOχ- Sensors führen zu Fehlern in der Steuerung der Verbrennungskraftmaschine, so daß beispielsweise ein NOx-Beladungsgrad des NOx-Speichers ungenau erkannt wird, wodurch eine Regeneration zu spät eingeschaltet werden kann. Dies führt zu erhöhten NOx-Emissionen.Each NO x sensor has an individual error measure, which leads to deviations of a displayed measured value from an actual actual value of the NOχ concentration. These individual inaccuracies in the characteristic of the sensor NOχ- lead to errors in the control of the internal combustion engine so that, for example, an NO x -Beladungsgrad of the NOx trap is detected inaccurately, can be switched whereby a regenerating too late. This leads to increased NO x emissions.
Der Erfindung liegt die Aufgabe zugrunde, die Genauigkeit der Bestimmung des NOχ- Gehaltes eines Abgases zu verbessern.The invention has for its object to improve the accuracy of the determination of the NOχ content of an exhaust gas.
Diese Aufgabe wird durch die Merkmale der unabhängigen Ansprüche 1 und 18 gelöst. Das erfindungsgemäße Verfahren sieht vor, in einer Betriebsphase der Verbrennungskraftmaschine, in der bekannt ist, daß die NOχ-Konzentration an der Position der NOx-empfindlichen Meßeinrichtung einen Wert nahe Null durchläuft, eine Suche nach einem Minimum einer Signalkurve der Meßeinrichtung durchzuführen und das gefundene Minimum als Nullpunkt für eine Kalibrierung der Meßeinrichtung zu übernehmen.This object is solved by the features of independent claims 1 and 18. The method according to the invention provides, in an operating phase of the internal combustion engine in which it is known that the NO χ concentration at the position of the NOx-sensitive measuring device passes through a value close to zero Search for a minimum of a signal curve of the measuring device and to take the found minimum as the zero point for a calibration of the measuring device.
Nach einer sehr bevorzugten Ausgestaltung der Erfindung wird die Suche nach dem Minimum direkt oder kurz nach einer NO -Regeneration oder einer Entschwefelung des NOx-Speicherkatalysators durchgeführt. Im Anschluß einer NOχ- oder Schwefelregeneration kann selbst bei einem stark geschädigten Katalysator mit hinreichender Genauigkeit von einer annähernd 100%igen NOχ-Absorption ausgegangen werden. In dieser Phase ist zumindest für eine begrenzte Dauer mit einer NOx-Konzentration von 0 bis 5 ppm hinter dem Katalysator zu rechnen, so daß ein in dieser Phase erhaltenes minimales Signal der NOχ-Meßeinrichtung mit einem vernachlässigbaren Fehler als Nullpunkt für eine Offset-Korrektur des NOχ-Sensors übernommen werden kann.According to a very preferred embodiment of the invention, the search for the minimum is carried out directly or shortly after NO regeneration or desulfurization of the NOx storage catalytic converter. Following NOχ or sulfur regeneration, even with a severely damaged catalytic converter, it can be assumed that the NO. Absorption will be almost 100% accurate. In this phase, a NOx concentration of 0 to 5 ppm behind the catalytic converter can be expected at least for a limited period of time, so that a minimal signal of the NO χ measuring device obtained in this phase with a negligible error as zero point for an offset correction of the NOχ sensor can be taken over.
Es ist ferner bevorzugt, daß für die Suche nach dem Minimum Signalwerte der Meßeinrichtung in vorgegebenen Zeitabständen oder nach vorgegebenen Abgas- oder Reduktionsmitteldurchsätzen erfaßt werden. Dabei wird jeder gemessene Signalwert mit einem zuletzt gespeicherten Minimum verglichen. Ist der Signalwert kleiner als das zuletzt gefundene Minimum, so wird er als ein neues Minimum gespeichert. Die Suche nach dem Minimum wird nach Ablauf einer vorgegebenen Dauer oder eines vorgegebenen Abgas- oder Reduktionsmitteldurchsatzes beendet. Das geschilderte Verfahren stellt sicher, daß ein so gefundenes Minimum einem absoluten Minimum im Signalverlauf der Meßeinrichtung entspricht und nicht etwa einem lokalen Minimum, das beispielsweise durch eine Unregelmäßigkeit in der Sensorkennlinie hervorgerufen werden kann.It is further preferred that signal values of the measuring device are detected at predetermined time intervals or according to predetermined exhaust gas or reducing agent throughputs in order to search for the minimum. Each measured signal value is compared with a last saved minimum. If the signal value is less than the last found minimum, it is saved as a new minimum. The search for the minimum is ended after a predetermined duration or a predetermined exhaust gas or reducing agent throughput has elapsed. The described method ensures that a minimum found in this way corresponds to an absolute minimum in the signal curve of the measuring device and not, for example, a local minimum, which can be caused, for example, by an irregularity in the sensor characteristic.
Da eine mögliche Fehlkalibrierung der NOx-empfindlichen Meßeinrichtung dramatische Folgen auf die Steuerung von Speicherkatalysator und Verbrennungskraftmaschine haben kann, sind strenge Anforderungen an die Sicherheit eines gefundenen Minimums zu stellen. Daher sieht eine sehr bevorzugte Ausführung des erfindungsgemäßen Verfahrens vor, das gefundene Minimum einer Plausibilitätskontrolle zu unterziehen. Hierfür sind ein oder mehrere Kriterien zu erfüllen, ehe ein Minimum als Nullpunkt für die Kalibrierung übernommen wird. Gemäß einer bevorzugten Ausgestaltung wird beispielsweise gefordert, daß das gefundene Minimum einen oberen Schwellenwert unterschreiten muß. Ferner kann das Unterschreiten des oberen Schwellenwertes für eine gewisse Mindestdauer gefordert sein. Als weiteres Kriterium kann vorgegeben sein, daß das gefundene Minimum sich in einem hinreichend großen Abstand zu einem Anfangs- und einem Endpunkt der Minimumsuche befindet. Auf diese Weise wird überprüft, ob die "Talsohle", in welcher das Minimum liegt, wirklich in dem Zeitfenster der Minimumsuche liegt.Since a possible incorrect calibration of the NO x sensitive measuring device can have dramatic consequences on the management of storage catalyst and engine, strict requirements must be placed a minimum found on safety. A very preferred embodiment of the method according to the invention therefore provides for the minimum found to be subjected to a plausibility check. For this, one or more criteria must be met before a minimum is accepted as the zero point for the calibration. According to a preferred embodiment, for example, it is required that the minimum found must fall below an upper threshold value. Furthermore, falling below the upper threshold value may be required for a certain minimum period. As another Criterion can be specified that the minimum found is located at a sufficiently large distance from a start and an end point of the minimum search. In this way, it is checked whether the "valley floor" in which the minimum lies is really in the time window of the minimum search.
Es kann ferner vorteilhaft sein, den Signalverlauf vor seiner Auswertung zu glätten, indem beispielsweise benachbarte Meßpunkte gemittelt werden. Weitere mathematische Verfahren zur Kurvenglättung ("Smoothing") sind bekannt und sollen hier nicht näher erläutert werden.It can also be advantageous to smooth the signal curve before it is evaluated, for example by averaging adjacent measurement points. Further mathematical methods for smoothing curves are known and will not be explained in more detail here.
Eine äußerst vorteilhafte Ausgestaltung des Verfahrens sieht ferner vor, daß die Minimumsuche abgebrochen und/oder ein gefundenes Minimum nicht als Nullpunkt für die Kalibrierung der Meßeinrichtung übernommen wird, wenn während der Minimumsuche vorgegebene Randbedingungen für Betriebsparameter nicht erfüllt sind. Eine wichtige Randbedingung betrifft etwa eine Temperatur des NOχ- Speicherkatalysators, die in einem Bereich liegen sollte, der eine zufriedenstellende NOx-Absorption gewährleistet. Eine andere Randbedingung fordert einen Magerbetrieb der Verbrennungskraftmaschine und/oder das Vorliegen eines mageren Abgases im Bereich des NOχ-Speicherkatalysators und/oder im Bereich der Meßeinrichtung. Zusätzlich kann dies über eine vorgegebene Mindestdauer gefordert werden. Ferner kann vorausgesetzt werden, daß sich die Verbrennungskraftmaschine nicht in einer Schubabschaltungsphase und/oder nicht in einem Leerlauf und/oder nicht in einem stark instationären Betriebsmodus während der Minimumsuche befindet. Außerdem kann ein zufriedenstellendes NOχ-Speicherverhalten eines NOχ-Speicherkatalysators gefordert werden, welches beispielsweise durch ein Diagnoseverfahren ermittelt wird. Auch kann für einen von der Verbrennungskraftmaschine emittierten NOx- Rohmassenstrom eine obere und/oder untere Grenze vorgegeben werden.An extremely advantageous embodiment of the method also provides that the minimum search is terminated and / or a found minimum is not adopted as the zero point for the calibration of the measuring device if predetermined boundary conditions for operating parameters are not met during the minimum search. An important boundary condition relates, for example, to a temperature of the NOχ storage catalytic converter, which should be in a range which ensures satisfactory NO x absorption. Another boundary condition requires lean operation of the internal combustion engine and / or the presence of a lean exhaust gas in the area of the NO χ storage catalytic converter and / or in the area of the measuring device. In addition, this can be requested over a predetermined minimum period. Furthermore, it can be assumed that the internal combustion engine is not in a fuel cut-off phase and / or not in an idle state and / or not in a highly unsteady operating mode during the minimum search. In addition, a satisfactory NOχ storage behavior of a NO χ storage catalytic converter can be required, which is determined, for example, by a diagnostic method. An upper and / or lower limit can also be specified for a NO x raw mass flow emitted by the internal combustion engine.
Die erfindungsgemäße Vorrichtung sieht Mittel vor, mit welchen die oben beschriebenen Verfahrensschritte ausführbar sind. Bevorzugterweise umfassen diese Mittel eine Steuereinheit, in der die Prozedur zur Steuerung der Verfahrensschritte zur Bestimmung einer NOx-Konzentration in digitaler Form hinterlegt ist, wobei die Steuereinheit in ein Motorsteuergerät integriert sein kann.The device according to the invention provides means with which the method steps described above can be carried out. These means preferably comprise a control unit, in which the procedure for controlling the method steps for determining a NOx concentration is stored in digital form, wherein the control unit can be integrated in an engine control unit.
Weitere bevorzugte Ausgestaltungen der Erfindung ergeben sich aus den übrigen, in den Unteransprüchen genannten Merkmalen. Die Erfindung wird nachfolgend in Ausführungsbeispielen anhand der zugehörigen Zeichnungen näher erläutert. Es zeigen:Further preferred embodiments of the invention result from the other features mentioned in the subclaims. The invention is explained in more detail below in exemplary embodiments with reference to the associated drawings. Show it:
Figur 1 eine schematische Darstellung eines Abgaskanals einerFigure 1 is a schematic representation of an exhaust duct
Verbrennungskraftmaschine;Internal combustion engine;
Figur 2 eine Darstellung einer Sensorkennlinie eines NOχ-Sensors undFigure 2 is a representation of a sensor characteristic of an NO χ sensor and
Figur 3 ein Sensorsignal in Abhängigkeit der Zeit während desFigure 3 shows a sensor signal as a function of time during the
Umschaltens zwischen Regeneration und Magerbetrieb.Switching between regeneration and lean operation.
Die in Figur 1 schematisch dargestellte Anordnung einer Verbrennungskraftmaschine 10 weist einen Abgastrakt 12 mit einem hierin angeordneten optionalen Vorkatalysator 14 und einen NOx-Speicherkatalysator 16 auf. Stromab des NOχ-Speicherkatalysators 16 ist außerdem ein NOx-Sensor 18 in dem Abgaskanal 12 angeordnet. Der NOx- Sensor 18 gibt ein Meßsignal an ein Motorsteuergerät 20 weiter, in welchem eine Steuereinheit 22 integriert ist. In Abhängigkeit einer von dem NOχ-Sensor 18 ermittelten NOx-Konzentration steuert das Motorsteuergerät 20 die Verbrennungskraftmaschine 10, indem es beispielsweise Einfluß auf ein einzuspeisendes Luft-Kraftstoff-Gemisch nimmt.The arrangement of an internal combustion engine 10 shown schematically in FIG. 1 has an exhaust tract 12 with an optional pre-catalytic converter 14 arranged therein and a NO x storage catalytic converter 16. A NO x sensor 18 is also arranged in the exhaust duct 12 downstream of the NO χ storage catalytic converter 16. The NO x sensor 18 transmits a measurement signal to an engine control unit 20 in which a control unit 22 is integrated. In response to a NO detected by the NO χ concentration sensor 18 x controls the engine control unit 20, the internal combustion engine 10 by, for example, influence on a einzuspeisendes air-fuel mixture increases.
Figur 2 zeigt modellhaft eine Kennlinie K eines NOx-Sensors 18. Es ist hier das Ausgabesignal OUT des Sensors 18, das beispielsweise eine Spannung sein kann, in Abhängigkeit einer NOx-Konzentration im Abgas dargestellt. Die im Anwendungsbereich des NOx-Sensors 18 linear verlaufende Kennlinie K wird durch die Steigung S, also ihrer Empfindlichkeit, sowie durch den sogenannten Offset OS, der einem ausgegebenen Signal in Abwesenheit von NOx im Abgas entspricht, charakterisiert. Für die Kalibrierung der Kennlinie K des NOχ-Sensors 18 ist, wie für jede Gerade, die Kenntnis zweier Punkte auf der Kennlinie K hinreichend. Ist als ein Spezialfall der Nullpunkt der Kennlinie bekannt, so kann dieser immerhin zu einer Offset-Korrektur herangezogen werden. Um das Nullpunkt-Signal des NOχ-Sensors 18 zu erfassen, muß dieses in einer Situation, in welcher die NOχ-Konzentration an der Position des Sensors 18 als annähernd Null bekannt ist oder angenommen werden kann, das Ausgabesignal OUT des NOχ-Sensors 18 gemessen werden. Das so gemessene Signal kann dann als Nullpunkt des Sensors 18 festgelegt werden. Eine Betriebssituation, in der mit hinreichend großer Wahrscheinlichkeit von einer NOχ- Konzentration hinter dem NOx-Speicherkatalysator 16 als nahe Null ausgegangen werden kann, ist kurz nach einer Regeneration, insbesondere einer NOx-Regeneration, des NOx-Spei-cherkatalysators 16 gegeben.FIG. 2 shows a characteristic curve K of a NO x sensor 18. The output signal OUT of the sensor 18, which can be a voltage, for example, is shown here as a function of a NO x concentration in the exhaust gas. The characteristic curve K which runs linearly in the area of application of the NO x sensor 18 is characterized by the slope S, that is to say its sensitivity, and by the so-called offset OS, which corresponds to an output signal in the absence of NO x in the exhaust gas. For the calibration of the characteristic curve K of the NOχ sensor 18, as for any straight line, the knowledge of two points on the characteristic curve K is sufficient. If the zero point of the characteristic curve is known as a special case, it can at least be used for an offset correction. In order to detect the zero point signal of the NOχ sensor 18, in a situation in which the NO χ concentration at the position of the sensor 18 is known or can be assumed to be approximately zero, the output signal OUT of the NO χ sensor must be obtained 18 can be measured. The signal measured in this way can then be defined as the zero point of the sensor 18. An operating situation in which a NOχ concentration behind the NO x storage catalytic converter 16 can be assumed to be close to zero with a sufficiently high probability is given shortly after regeneration, in particular NO x regeneration, of the NO x storage catalytic converter 16 ,
Figur 3 zeigt einen idealisierten zeitlichen Verlauf einer Signalkurve SK eines stromab eines NOx-Speicherkatalysators 16 angeordneten NOx-Sensors 18 während des Wechsels von einem fetten Betriebsmodus (Regenerationsphase R) in einen mageren Betriebsmodus M der Verbrennungskraftmaschine 10. Während der NOχ-Regeneration R verharrt das Sensorsignal OUT auf einem relativ hohen Niveau. Dies ist zum einen auf eine unvollständige Reduktion von desorbierten Stickoxiden NOx zurückzuführen und andererseits auf eine Entstehung von Ammoniak NH3 während der Regeneration R, auf welches der NOx-Sensor 18 ebenfalls anspricht. Für eine kurze Weile nach Beendigung der Regeneration R und Umschalten der Verbrennungskraftmaschine 10 in einen Magermodus M zu einem Zeitpunkt t^ bleibt das Signal OUT in Abhängigkeit von einem Totvolumen des Abgaskanals sowie von einer Raumgeschwindigkeit des Abgases zunächst noch auf diesem relativ hohen Niveau. Zusätzlich führt eine inhärente Trägheit des NOχ-Sensors 18 zu einer Verzögerung der Antwort der Signalkurve SK, selbst wenn bereits mageres Abgas hinter dem NOχ- Speicherkatalysator 16 vorliegt. Nach einem dann folgenden steilen Abfall durchläuft die Signalkurve SK kurz nach dem Umschalten in den Magermodus M ein Minimum min, um dann wieder sehr langsam infolge einer zunehmenden Beladung des NOx- Speicherkatalysators 16 anzusteigen. Eine zuverlässige Voraussage des Zeitpunktes des Minimums min ist praktisch nicht möglich, weshalb die Vorgabe einer festen Zeitspanne nach Umschaltung aus dem Regenerationsmodus R in den Magermodus M zur Messung des Nullpunktsignals des NOx-Sensors 18 als wenig sinnvoll erscheint. Aus diesem Grund ist entsprechend der vorliegenden Erfindung vorgesehen, den Verlauf der Signalkurve SK über eine längere Betriebsphase nach Beendigung der Regeneration R zu beobachten und das globale Minimum min in dieser Phase zu ermitteln. Dies geschieht vorzugsweise, indem in dem vorgegebenen Zeitfenster Meßsignale erfaßt und sukzessiv miteinander verglichen werden. Unterschreitet ein aktuelles Meßsignal ein vorläufiges Minimum, so wird das aktuelle Signal als neues Minimum gemerkt. Auf diese Weise bleiben sogenannte Ausreißer oder scharfe Spannungsspitzen unberücksichtigt, die zu lokalen Minima führen können. Somit sind auch Signalkurven SK, die einem weniger idealen Verlauf entsprechen als dem dargestellten, der Auswertung zugänglich. Das geschilderte Verfahren ermöglicht also auch, bei einem niedrigen Signal-Rausch-Verhältnis, das heißt bei einem hohem Grundrauschen, und bei Unregelmäßigkeiten in der Kennlinie K, wie es insbesondere bei gealterten NOx-Sensoren 18 beobachtet wird, eine zuverlässige Detektion des Minimums min.FIG. 3 shows an idealized time profile of a signal curve SK of a NO x sensor 18 arranged downstream of a NO x storage catalytic converter 16 during the change from a rich operating mode (regeneration phase R) to a lean operating mode M of the internal combustion engine 10. During the NOχ regeneration R the sensor signal OUT remains at a relatively high level. This is due on the one hand to an incomplete reduction of desorbed nitrogen oxides NO x and on the other hand to the formation of ammonia NH3 during regeneration R, to which the NO x sensor 18 also responds. For a short time after the regeneration R has ended and the internal combustion engine 10 has switched to a lean mode M at a time t 1, the signal OUT initially remains at this relatively high level depending on a dead volume of the exhaust gas duct and on a space velocity of the exhaust gas. In addition, an inherent inertia of the NOχ sensor 18 leads to a delay in the response of the signal curve SK, even if lean exhaust gas is already present behind the NOχ storage catalytic converter 16. After a subsequent steep drop, the signal curve SK runs through a minimum min shortly after the switchover to the lean mode M, in order then to rise again very slowly as a result of increasing loading of the NO x storage catalytic converter 16. A reliable prediction of the time of the minimum min is practically not possible, which is why the specification of a fixed time period after switching from the regeneration mode R to the lean mode M for measuring the zero point signal of the NO x sensor 18 appears to be of little use. For this reason, it is provided according to the present invention to observe the course of the signal curve SK over a longer operating phase after the regeneration R has ended and to determine the global minimum min in this phase. This is preferably done by recording measurement signals in the predetermined time window and comparing them successively with one another. If a current measurement signal falls below a provisional minimum, the current signal is noted as a new minimum. In this way, so-called outliers or sharp voltage peaks are ignored, which can lead to local minima. Thus signal curves SK, which correspond to a less ideal course than the one shown, are also accessible to the evaluation. The described method thus also enables a low signal-to-noise ratio, that is, a high one Background noise, and in the event of irregularities in the characteristic curve K, as is observed in particular in the case of aged NO x sensors 18, reliable detection of the minimum min.
Die Minimumsuche wird nach Ablauf einer vorgegebenen Zeitspanne nach Umschaltung in den Magermodus M zum Zeitpunkt t£ beendet. Statt einer Zeitspanne kann ebensogut eine durchgesetzte Abgas- oder Reduktionsmittelmasse oder eine Anzahl von Meßpunkten vorgegeben werden.The minimum search is ended after a predetermined period of time after switching to the lean mode M at the time t £. Instead of a period of time, an exhaust gas or reducing agent mass which has been passed through or a number of measuring points can also be specified.
Wie bereits oben erläutert, ist weiterhin vorgesehen, daß das Minimum zur Kalibrierung nur dann freigegeben wird, wenn weitere Randbedingungen erfüllt sind. Dies betrifft beispielsweise eine Temperatur des NOx-Speicherkatalysator 16, die in einem Bereich liegen sollte, der eine zuverlässige Einspeicherung von NOx garantiert. Als zusätzliche Maßnahme zur Validierung eines gefundenen Minimums min ist es vorteilhaft, das gefundene Minimum min anhand vorgegebener Kriterien zu überprüfen. So ist in Figur 3 beispielhaft ein Schwellenwert SW dargestellt, dessen Unterschreitung Voraussetzung für die Freigabe des gefundenen Minimums min sein kann. Es kann femer gefordert werden, daß die Schwelle SW für eine vorgegebene Mindestdauer unterschritten werden muß.As already explained above, it is further provided that the minimum for calibration is only released if further boundary conditions are met. This relates, for example, to a temperature of the NO x storage catalytic converter 16, which should be in a range that guarantees reliable storage of NO x . As an additional measure for validating a found minimum min, it is advantageous to check the found minimum min on the basis of predetermined criteria. For example, a threshold value SW is shown in FIG. It can also be required that the threshold SW must be undershot for a predetermined minimum duration.
Sind während der gesamten Minimumsuche die vorgegebenen Randbedingungen erfüllt und entspricht das gefundene globale Minimum min den aufgestellten Kriterien, so wird das Minimum min unmittelbar als Nullpunkt des NOx-Sensors 18 freigegeben und eine Offset-Korrektur des Sensors 18 durchgeführt. Das gefundene Minimum min behält solange seine Gültigkeit, bis ein neues Minimum in einer nachfolgenden Minimumsuche ermittelt wird. Eine Minimumsuche kann - unter Einhaltung der beschriebenen Randbedingungen - nach jeder NOx-Regeneration durchgeführt werden. If the specified boundary conditions are met during the entire minimum search and the global minimum min found corresponds to the established criteria, the minimum min is immediately released as the zero point of the NO x sensor 18 and an offset correction of the sensor 18 is carried out. The found minimum min remains valid until a new minimum is determined in a subsequent minimum search. A minimum search can be carried out after each NOx regeneration - provided the boundary conditions described are met.
Claims
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP01909650A EP1255917B1 (en) | 2000-01-26 | 2001-01-18 | METHOD AND DEVICE FOR DETECTING A NOx CONCENTRATION OF AN EXHAUST GAS STREAM PERTAINING TO A COMBUSTION ENGINE |
| DE50108081T DE50108081D1 (en) | 2000-01-26 | 2001-01-18 | METHOD AND DEVICE FOR DETERMINING NOXX CONCENTRATION OF AN EXHAUST GAS FLOW OF AN INTERNAL COMBUSTION ENGINE |
| AU2001237318A AU2001237318A1 (en) | 2000-01-26 | 2001-01-18 | Method and device for detecting a nox concentration of an exhaust gas stream pertaining to combustion engine |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE10003228.1 | 2000-01-26 | ||
| DE2000103228 DE10003228A1 (en) | 2000-01-26 | 2000-01-26 | Method and device for determining a NOx concentration of an exhaust gas flow of an internal combustion engine |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| WO2001055565A2 true WO2001055565A2 (en) | 2001-08-02 |
| WO2001055565A3 WO2001055565A3 (en) | 2002-01-10 |
Family
ID=7628738
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/EP2001/000540 WO2001055565A2 (en) | 2000-01-26 | 2001-01-18 | METHOD AND DEVICE FOR DETECTING A NOx CONCENTRATION OF AN EXHAUST GAS STREAM PERTAINING TO A COMBUSTION ENGINE |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP1255917B1 (en) |
| AU (1) | AU2001237318A1 (en) |
| DE (2) | DE10003228A1 (en) |
| WO (1) | WO2001055565A2 (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1365234A3 (en) * | 2002-01-24 | 2004-06-23 | Volkswagen AG | Method for correcting the NOx signal of a NOx sensor |
| EP1434049A1 (en) * | 2002-12-29 | 2004-06-30 | Volkswagen AG | Method of and device for monitoring the NOx signal of an NOx sensor |
| FR2853934A1 (en) * | 2003-04-16 | 2004-10-22 | Volkswagen Ag | Procedure for determining offset signal value from NOx detector in IC engine exhaust system, uses signal values taken during stoichiometric operating mode |
| FR2948979A1 (en) * | 2009-08-07 | 2011-02-11 | Peugeot Citroen Automobiles Sa | Nitrogen oxide sensor diagnosing and controlling method for e.g. diesel engine of motor vehicle, involves calibrating zero value of nitrogen oxide sensor during phase in which engine functions along rich combustion mode |
| CN114166990A (en) * | 2021-12-03 | 2022-03-11 | 国网湖南省电力有限公司 | Detection method for uniformity of denitrification and ammonia injection based on time-domain characteristic analysis of NOx concentration |
| WO2023165777A1 (en) * | 2022-03-03 | 2023-09-07 | Vitesco Technologies GmbH | Method for calibrating an exhaust gas sensor of an internal combustion engine for a vehicle, and internal combustion engine for a vehicle |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10223385B4 (en) * | 2002-05-25 | 2017-01-05 | Volkswagen Ag | Method and device for controlling a sensor |
| DE10249610B4 (en) * | 2002-10-18 | 2010-10-07 | Volkswagen Ag | Method and device for controlling a NOx storage catalytic converter |
| DE10310954A1 (en) * | 2003-03-13 | 2004-09-23 | Robert Bosch Gmbh | Diagnostic procedure for a NOx sensor |
| DE10339062A1 (en) * | 2003-04-16 | 2004-11-11 | Volkswagen Ag | Method for determining an offset value of a sensor signal and device for carrying out the method |
| DE10326932A1 (en) * | 2003-06-16 | 2005-01-27 | Audi Ag | 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 |
| DE102004022814B4 (en) * | 2004-05-08 | 2010-06-10 | Audi Ag | Method for operating a lean-running internal combustion engine of a vehicle, in particular of a motor vehicle |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1074833A1 (en) * | 1997-03-21 | 2001-02-07 | Ngk Spark Plug Co., Ltd | Method and apparatus for measuring NOx gas concentration |
| DE69815256T2 (en) * | 1997-10-14 | 2004-05-06 | NGK Spark Plug Co., Ltd., Nagoya | Method and device for determining the operating state of a NOx occlusion catalyst |
| JP3684854B2 (en) * | 1998-07-02 | 2005-08-17 | 日産自動車株式会社 | Catalyst deterioration diagnosis device for internal combustion engine |
-
2000
- 2000-01-26 DE DE2000103228 patent/DE10003228A1/en not_active Withdrawn
-
2001
- 2001-01-18 DE DE50108081T patent/DE50108081D1/en not_active Expired - Lifetime
- 2001-01-18 WO PCT/EP2001/000540 patent/WO2001055565A2/en active IP Right Grant
- 2001-01-18 EP EP01909650A patent/EP1255917B1/en not_active Expired - Lifetime
- 2001-01-18 AU AU2001237318A patent/AU2001237318A1/en not_active Abandoned
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1365234A3 (en) * | 2002-01-24 | 2004-06-23 | Volkswagen AG | Method for correcting the NOx signal of a NOx sensor |
| EP1434049A1 (en) * | 2002-12-29 | 2004-06-30 | Volkswagen AG | Method of and device for monitoring the NOx signal of an NOx sensor |
| FR2853934A1 (en) * | 2003-04-16 | 2004-10-22 | Volkswagen Ag | Procedure for determining offset signal value from NOx detector in IC engine exhaust system, uses signal values taken during stoichiometric operating mode |
| FR2948979A1 (en) * | 2009-08-07 | 2011-02-11 | Peugeot Citroen Automobiles Sa | Nitrogen oxide sensor diagnosing and controlling method for e.g. diesel engine of motor vehicle, involves calibrating zero value of nitrogen oxide sensor during phase in which engine functions along rich combustion mode |
| CN114166990A (en) * | 2021-12-03 | 2022-03-11 | 国网湖南省电力有限公司 | Detection method for uniformity of denitrification and ammonia injection based on time-domain characteristic analysis of NOx concentration |
| CN114166990B (en) * | 2021-12-03 | 2023-11-14 | 国网湖南省电力有限公司 | Based on NO x Denitrification ammonia injection uniformity detection method for concentration time domain feature analysis |
| WO2023165777A1 (en) * | 2022-03-03 | 2023-09-07 | Vitesco Technologies GmbH | Method for calibrating an exhaust gas sensor of an internal combustion engine for a vehicle, and internal combustion engine for a vehicle |
Also Published As
| Publication number | Publication date |
|---|---|
| WO2001055565A3 (en) | 2002-01-10 |
| DE50108081D1 (en) | 2005-12-22 |
| DE10003228A1 (en) | 2001-09-06 |
| AU2001237318A1 (en) | 2001-08-07 |
| EP1255917B1 (en) | 2005-11-16 |
| EP1255917A2 (en) | 2002-11-13 |
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