EP1105720A1 - Method and device for calibrating a probe system comprised of an exhaust probe and of a control circuit for a motor vehicle - Google Patents

Method and device for calibrating a probe system comprised of an exhaust probe and of a control circuit for a motor vehicle

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Publication number
EP1105720A1
EP1105720A1 EP99952345A EP99952345A EP1105720A1 EP 1105720 A1 EP1105720 A1 EP 1105720A1 EP 99952345 A EP99952345 A EP 99952345A EP 99952345 A EP99952345 A EP 99952345A EP 1105720 A1 EP1105720 A1 EP 1105720A1
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EP
European Patent Office
Prior art keywords
control circuit
test
values
probe
microcontroller
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP99952345A
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German (de)
French (fr)
Inventor
Markus Amtmann
Stephan Bolz
Jürgen RÖSSLER
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Continental Automotive GmbH
Original Assignee
Siemens AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Publication of EP1105720A1 publication Critical patent/EP1105720A1/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/416—Systems
    • G01N27/417—Systems using cells, i.e. more than one cell and probes with solid electrolytes
    • G01N27/4175—Calibrating or checking the analyser

Definitions

  • Method and device for calibrating a probe system consisting of an exhaust gas probe and a control circuit for a motor vehicle
  • the invention relates to a method and a device for calibrating a probe system, consisting of an exhaust gas probe and a control circuit for a motor vehicle.
  • NO x sensor It is known to use thick-film sensors to measure the concentration of pollutants in the exhaust gas of an internal combustion engine. Such a sensor is described using the example of a NO x sensor in N. Kato et al., "Performance of Thick Film NO x sensor on Diesel and Gasoline Engines", Society of Automotive Engineers, publication 970858, 1997.
  • This NO x sensor has two measuring cells and three oxygen pumping cells and realizes the following measuring concept: In a first measuring cell, to which the gas to be measured is supplied via a diffusion barrier, a first oxygen concentration is set by means of a first oxygen-ion pumping current, whereby no decomposition of NO x takes place.
  • the oxygen content is further reduced by means of a second oxygen-ion pumping current and NO x is decomposed at a measuring electrode.
  • the oxygen generated in this way is recorded as a measure of the NO x concentration.
  • the entire NO x sensor is heated to an elevated temperature, e.g. B. 700 ° C brought.
  • the invention is based on the technical problem of developing a method which makes it possible to individually calibrate exhaust gas probes together with the associated control circuit at the end of the production process and in the course of their service life, and to compensate for component tolerances in the control circuit.
  • the problem is solved by a method having the features of patent claim 1 and by a device according to patent claim 8.
  • Advantageous further developments of the invention are laid down in the subclaims. If a microcontroller is used in connection with an analog circuit to regulate the pump currents, it is possible to save application-specific data of the probe system.
  • the measured values recorded under specified test conditions are stored in a programmable read-only memory, for example an EPROM, which is preferably integrated in the microcontroller, as correction or test values.
  • the test values then serve as a reference for an independent recalibration of the probe system during the lifetime.
  • the correction values are used to compensate for further component tolerances, such as offset voltages from operational amplifiers.
  • FIG. 1 shows a schematic sectional illustration of a NO x sensor
  • FIG. 2 shows a block diagram of a circuit arrangement for regulating a pump current
  • Figure 3 is a schematic representation of an arrangement for
  • Thick film NO x sensors consist of a multilayer, sintered ceramic substrate. In the manufacturing process, several electrodes are applied to the individual ceramic carriers. These electrodes form the pump and measuring cells required to implement a NO x sensor. The electrical properties of the electrodes and the ceramic substrate change during the sintering process and over time.
  • a NO x sensor 1 (FIG. 1) consisting of a solid electrolyte 2, in this case zirconium dioxide, takes over one first diffusion barrier 3 on the exhaust gas to be measured.
  • the exhaust gas diffuses through the diffusion barrier 3 into a first measuring cell 4.
  • the oxygen content in this measuring cell is measured by means of a first Nernst voltage VNO between a first pump electrode 5 and a reference electrode 6 exposed to ambient air.
  • the reference electrode 6 is arranged in an air channel 7, into which ambient air passes through an opening 8. Both electrodes 5, 6 are conventional platinum electrodes.
  • the measured value of the first Nernst voltage VNO is used to set a first control voltage VpO.
  • the control voltage VpO drives a first oxygen ion pump current IpO through the solid electrolyte 2 of the NO x sensor 1 between the first pump electrode 5 and an outer electrode 9 - the pump electrode 5 and the outer electrode 9 form a first pump cell.
  • the control voltage VpO is set by a controller so that there is a predetermined oxygen concentration in the first measuring cell 4.
  • the first measuring cell 4 is connected to a second measuring cell 10 via a second diffusion barrier 11. Through this diffusion barrier 11, the gas present in the measuring cell 4 diffuses into the second measuring cell 10.
  • the second oxygen concentration in the second measuring cell 10 is via a second Nernst voltage VN1 between a second pump electrode 12, which is also a platinum electrode, and the reference electrode 6 measured and used by a controller to specify a second control voltage Vpl, which drives a second oxygen ion pump current Ipl.
  • the second oxygen ion pump current Ipl from the second measuring cell 10 flows from the second pump electrode 12 through the solid electrolyte 2 to the outer electrode 9 (second pump cell). With his help a predetermined oxygen concentration is set in the second measuring cell 10.
  • a third oxygen concentration is measured via a third Nernst voltage VN2 between the measuring electrode 13 and the reference electrode 6 and used by a controller to specify a third control voltage Vp2.
  • Vp2 is applied between the measuring electrode 13 and the outer electrode 9 (third pump cell)
  • the N0 x is decomposed and the oxygen released is pumped through the solid electrolyte 2 to the outer electrode 9 in a third oxygen-ion pumping current Ip2.
  • the ion pump current Ip2 is carried only by oxygen ions which originate from the decomposition of N0 x . It is therefore a measure of the NO x concentration in the measuring cell 10 and thus in the exhaust gas to be measured. Since such NO x sensors have a strong temperature dependence, a heating element 14 ensures that the probe temperature is always kept in a predetermined temperature range in order to maintain the necessary measurement accuracy.
  • a microcontroller 20 in conjunction with an analog circuit 21 is used to regulate the pump currents.
  • the circuit arrangement of an individual pump current control circuit is shown in detail in FIG.
  • the control circuit of the entire NO x sensor has such a circuit arrangement for each pump cell to be controlled.
  • the required digital circuit components can be implemented within a single microcontroller 20.
  • a PWM unit 22 in the microcontroller 20 generates a pulse-width-modulated signal, which with the aid of an analog filter circuit 23 in a DC voltage is converted. Depending on the requirements of the required current strength, this voltage is given either directly or via an impedance converter 24 to a measuring resistor 25, which is connected in series with the pump cell 27 of the NO x sensor 1 to be controlled.
  • the pump cell is in the form of a
  • the voltage potentials before and after the measuring resistor 25 are read alternately via a multiplexer 31. Since the input of the NO x sensor 1 is usually very high-resistance, an impedance converter 32, for example a buffer amplifier, can be connected into the measuring line, which is used to measure the potential value after the measuring resistor 25.
  • an impedance converter 32 for example a buffer amplifier
  • the Nernst voltages required to regulate the pump current are also calculated in the microcontroller 20.
  • both the Nernst potential V Nerns and the reference potential V Ref of the corresponding measuring cell 33 of the NO x sensor 1 are read in by a second A / D converter 34 in the microcontroller 20.
  • the measuring cell 33 corresponds to either the first measuring cell 4 or the second measuring cell 10 from FIG. 1 and is shown schematically as a DC voltage source.
  • two impedance converters 35 and 36 are also provided here, for example in the form of buffer amplifiers.
  • a pump current difference .DELTA.Ip is calculated within the microcontroller 20 from the read potential values.
  • B a PID controller, which controls the PWM unit 22.
  • a programmable read-only memory 39 for example an EPROM, which is preferably integrated in the microcontroller, serves to store the potentials read in on the A / D converters 30 and 34.
  • a probe system 50 consisting of a NO x probe 51 and the associated control circuit 52, is calibrated with the arrangement according to FIG. 3.
  • the NO x probe 51 is composed of the NO x sensor 1, a sensor line 53 and a sensor plug 54.
  • the arrangement of the control circuit 52 in the housing of the sensor connector 54 results in very short connecting lines. In this way, despite the line losses that occur, a sufficiently precise transmission of the signal currents, which are usually only in the nA range, can be ensured.
  • the test parameters for example NO x concentration and gas temperature, are set and monitored in a test chamber 56 by a test control computer 55.
  • the NO x sensor 1 records the corresponding measured values and forwards them to the control circuit 52 via the sensor line 51.
  • the control circuit 52 the measured values present at the A / D converters of the microcontroller 20 are stored either directly or after an internal evaluation, for example by comparison with predetermined target values, in characteristic maps made available for this purpose in the programmable read-only memory 39.
  • the communication with the test control computer 55 necessary for controlling the control circuit 52 takes place via a serial interface 57 integrated in the control circuit and a data line 58.
  • the individual pump current control circuits must be measured under different, characteristic operating conditions after completion of the probe system, i.e. after connecting the NO x probe to the associated control circuit.
  • Offset voltages the probe system is first tested under electrically neutral test conditions. For this purpose, the heating element is switched off and on The duty cycle of the pulse width modulated signal is set to 0% so that no pump current flows.
  • the values now read by the A / D converters correspond exactly to the offset voltages present. These can be stored as correction values in the programmable read-only memory 39 and can be used to coordinate the respective pump currents.
  • This compensation can also be repeated after the control system has been installed in a motor vehicle, for example at the request of the central engine control or in the course of an inspection in a workshop.
  • Each pump current control loop of the probe system is then tested successively under different test conditions.
  • the pump currents determined in this case - ie the measured values applied to the first A / D converter 30 - are stored in the read-only memory 39 and subsequently serve as a reference for regular, independent recalibration of the system over the course of its service life.
  • the Nernst and reference potentials present at the second A / D converter 34 can also be stored in the read-only memory 39.
  • a / D converters can read and store various application-specific data from the probe system. In this way, each probe system can be calibrated individually and fully automatically at the end of the manufacturing process using a test facility. A complex and costly comparison of electronic components, as would be necessary with a purely analog control circuit, can be avoided in this way. Due to the possibility of independent recalibration of the probe system, the circuit design of the control circuit is largely independent of component tolerances.
  • the invention has been described by way of example for a NO x sensor; corresponding methods and devices are also available for others based on the principle of galvanic acid Material concentration cell with solid electrolyte exhaust gas probes, such as linear oxygen probes, suitable.

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Molecular Biology (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)
  • Measuring Oxygen Concentration In Cells (AREA)

Abstract

According to the invention, the control circuit (52) of an exhaust probe comprises a microcontroller (20) in combination with analog protective circuits (21). Under predetermined test conditions in a test chamber (56), recorded measured values are stored in characteristic diagrams in a programmable fixed value memory (39). These values then serve as a reference for a successive subsequent calibration of the probe system.

Description

Beschreibungdescription
Verfahren und Vorrichtung zum Kalibrieren eines Sondensystems, bestehend aus einer Abgassonde und einer Regelschal- tung für ein KraftfahrzeugMethod and device for calibrating a probe system, consisting of an exhaust gas probe and a control circuit for a motor vehicle
Die Erfindung betrifft ein Verfahren und eine Vorrichtung zum Kalibrieren eines Sondensystems, bestehend aus einer Abgassonde und einer Regelschaltung für ein Kraftfahrzeug.The invention relates to a method and a device for calibrating a probe system, consisting of an exhaust gas probe and a control circuit for a motor vehicle.
Im Zuge eines steigenden ümweltbewußtseins und daraus resultierender, immer strengerer Abgasverordnungen erlangt die Schadstoffverringerung in Abgasen von Brennkraftmaschinen in Kraftfahrzeugen eine immer größere Bedeutung. Für die Einhal- tung der heute gültigen Emissionsgrenzwerte für Schadstoffe, wie Kohlenmonoxid (CO) , Stickoxide (NOx)und Kohlenwasserstoffe (HC) ist einerseits eine gezielte Motorsteuerung und andererseits eine katalytische Nachbehandlung der Abgase notwendig. Für beide Maßnahmen werden Meßwerte von Abgassonden - z.B. Lambdasonden oder NOx-Sonden - benötigt. Mit dem Begriff Sonde sei im folgenden stets eine Einheit aus Sensor, Sensorleitung und Sensorstecker bezeichnet.In the course of increasing environmental awareness and the resulting, ever stricter exhaust gas regulations, the reduction of pollutants in exhaust gases from internal combustion engines in motor vehicles is becoming increasingly important. In order to comply with the current emission limit values for pollutants such as carbon monoxide (CO), nitrogen oxides (NO x ) and hydrocarbons (HC), targeted engine control is required on the one hand and catalytic after-treatment of the exhaust gases on the other. Measured values from exhaust gas probes - for example lambda probes or NO x probes - are required for both measures. In the following, the term probe always refers to a unit consisting of a sensor, sensor line and sensor connector.
Zur Messung der Schadstoff onzentration im Abgas einer Brenn- kraftmaschine ist es bekannt, Dickschicht-Sensoren zu verwenden. Ein solcher Sensor ist am Beispiel eines NOx-Sensors in der Druckschrift N. Kato et al., "Performance of Thick Film NOx-Sensor on Diesel and Gasoline Engines", Society of Automotive Engineers, Veröffentlichung 970858, 1997, beschrieben. Dieser NOx-Sensor weist zwei Meßzellen und drei Sauerstoffpumpzellen auf und verwirklicht folgendes Meßkonzept: In einer ersten Meßzelle, der das zu messende Gas über eine Diffusionsbarriere zugeführt wird, wird mittels eines ersten Sau- erstoff-Ionen-Pumpstroms eine erste Sauerstoffkonzentration eingestellt, wobei keine Zersetzung von NOx stattfindet. In einer zweiten Meßzelle, die über eine Diffusionsbarriere mit der ersten Meßzelle verbunden ist, wird der Sauerstoffgehalt mittels eines zweiten Sauerstoff-Ionen-Pumpstroms weiter abgesenkt und NOx an einer Meßelektrode zersetzt. Der so er- zeugte Sauerstoff wird als Maß für die NOx-Konzentration erfaßt. Der gesamte NOx-Sensor wird dabei mittels eines elektrischen Heizelements auf eine erhöhte Temperatur, z. B. 700°C, gebracht.It is known to use thick-film sensors to measure the concentration of pollutants in the exhaust gas of an internal combustion engine. Such a sensor is described using the example of a NO x sensor in N. Kato et al., "Performance of Thick Film NO x sensor on Diesel and Gasoline Engines", Society of Automotive Engineers, publication 970858, 1997. This NO x sensor has two measuring cells and three oxygen pumping cells and realizes the following measuring concept: In a first measuring cell, to which the gas to be measured is supplied via a diffusion barrier, a first oxygen concentration is set by means of a first oxygen-ion pumping current, whereby no decomposition of NO x takes place. In In a second measuring cell, which is connected to the first measuring cell via a diffusion barrier, the oxygen content is further reduced by means of a second oxygen-ion pumping current and NO x is decomposed at a measuring electrode. The oxygen generated in this way is recorded as a measure of the NO x concentration. The entire NO x sensor is heated to an elevated temperature, e.g. B. 700 ° C brought.
Bei der Herstellung derartiger Sensoren treten technologiebedingt große Fertigungstoleranzen auf. Zudem verändern sich die Sensoreigenschaften, wie z.B. die Impedanz der Pumpzellen, mit der Zeit. Da die Signalströme von Abgassonden mit derartigen Sensoren meist nur im nA-Bereich liegen, beeinflu- ßen auch Bauteiltoleranzen der Regelschaltung die Meßgenauigkeit in erheblichem Maße. Eine für den Serieneinsatz in einem Kraftfahrzeug ausreichende Meßgenauigkeit kann somit einerseits nur mit einer individuellen Kalibrierung des Sonden- Regelschaltung-Systems - im folgenden kurz als Sondensystem bezeichnet - sichergestellt werden, andererseits muß eine Nachkalibrierung während der Lebensdauer der Sonde möglich sein .Due to the technology, large manufacturing tolerances occur in the manufacture of such sensors. In addition, the sensor properties change, e.g. the impedance of the pumping cells, over time. Since the signal currents from exhaust gas probes with such sensors are usually only in the nA range, component tolerances in the control circuit also have a considerable influence on the measurement accuracy. A measuring accuracy sufficient for series use in a motor vehicle can therefore only be ensured on the one hand with an individual calibration of the probe control circuit system - hereinafter referred to briefly as the probe system - on the other hand, recalibration must be possible during the life of the probe.
Der Erfindung liegt das technische Problem zugrunde, ein Ver- fahren zu entwickeln, das es ermöglicht, Abgassonden am Ende des Herstellungsprozesses und im Laufe ihrer Lebensdauer zusammen mit der zugehörigen Regelschaltung individuell zu kalibrieren und Bauteiltoleranzen der Regelschaltung zu kompensieren.The invention is based on the technical problem of developing a method which makes it possible to individually calibrate exhaust gas probes together with the associated control circuit at the end of the production process and in the course of their service life, and to compensate for component tolerances in the control circuit.
Das Problem wird erfindungsgemäß durch ein Verfahren mit den Merkmalen des Patentanspruchs 1 und durch eine Vorrichtung nach Patentanspruch 8 gelöst. Vorteilhafte Weiterbildungen der Erfindung sind in den Unteransprüchen niedergelegt. Wird zum Regeln der Pumpströme ein MikroController in Verbindung mit einer analogen Beschaltung verwendet, so bietet sich die Möglichkeit, applikationsspezifische Daten des Sondensy- stems zu speichern. Die unter vorgegebenen Prüfbedingungen aufgenommenen Meßwerte werden in einem vorzugsweise in den Mikrocontroller integrierten, programmierbaren Festwertspeicher, z.B. einem EPROM, als Korrektur- oder Prüfwerte abgelegt. Die Prüfwerte dienen dann als Referenz für eine selbständige Nachkalibrierung des Sondensystems während der Le- benszeit. Die Korrekturwerte dienen zur Kompensation weiterer Bauteiltoleranzen, wie z.B. Offsetspannungen von Operationsverstärkern.According to the invention, the problem is solved by a method having the features of patent claim 1 and by a device according to patent claim 8. Advantageous further developments of the invention are laid down in the subclaims. If a microcontroller is used in connection with an analog circuit to regulate the pump currents, it is possible to save application-specific data of the probe system. The measured values recorded under specified test conditions are stored in a programmable read-only memory, for example an EPROM, which is preferably integrated in the microcontroller, as correction or test values. The test values then serve as a reference for an independent recalibration of the probe system during the lifetime. The correction values are used to compensate for further component tolerances, such as offset voltages from operational amplifiers.
Ein Ausführungsbeispiel der Erfindung wird im folgenden für einen NOx-Sensor anhand der Figuren erläutert. Es zeigen:An embodiment of the invention is explained below for a NO x sensor with reference to the figures. Show it:
Figur 1 eine schematische Schnittdarstellung eines NOx- Sensors,FIG. 1 shows a schematic sectional illustration of a NO x sensor,
Figur 2 ein Blockschaltbild einer Schaltungsanordnung zum Re- geln eines Pumpstroms undFIG. 2 shows a block diagram of a circuit arrangement for regulating a pump current and
Figur 3 eine schematische Darstellung einer Anordnung zurFigure 3 is a schematic representation of an arrangement for
Durchführung des erfindungsgemäßen Verfahrens zur Kalibrierung eines SondensystemsImplementation of the method according to the invention for the calibration of a probe system
Dickfilm-NOx-Sensoren bestehen aus einem mehrlagigen, gesinterten Keramiksubstrat . Beim Herstellungsprozeß werden auf die einzelnen Keramikträger mehrere Elektroden aufgebracht. Diese Elektroden bilden die für die Realisierung eines NOx- Sensors erforderlichen Pump- und Meßzellen. Während des Sin- terprozesses und im Laufe der Zeit verändern sich die elektrischen Eigenschaften der eingebrachten Elektroden und des Keramiksubstrats.Thick film NO x sensors consist of a multilayer, sintered ceramic substrate. In the manufacturing process, several electrodes are applied to the individual ceramic carriers. These electrodes form the pump and measuring cells required to implement a NO x sensor. The electrical properties of the electrodes and the ceramic substrate change during the sintering process and over time.
Ein aus einem Festkörperelektrolyten 2, in diesem Fall Zir- kondioxid, bestehender NOx-Sensor 1 (Figur 1) nimmt über eine erste Diffusionsbarriere 3 das zu messende Abgas auf. Das Abgas diffundiert durch die Diffusionsbarriere 3 in eine erste Meßzelle 4. Der Sauerstoffgehalt in dieser Meßzelle wird mittels einer ersten Nernstspannung VNO zwischen einer ersten Pumpelektrode 5 und einer Umgebungsluft ausgesetzten Referenzelektrode 6 gemessen. Dabei ist die Referenzelektrode 6 in einem Luftkanal 7 angeordnet, in den über eine Öffnung 8 Umgebungsluft gelangt. Beide Elektroden 5, 6 sind herkömmliche Platinelektroden.A NO x sensor 1 (FIG. 1) consisting of a solid electrolyte 2, in this case zirconium dioxide, takes over one first diffusion barrier 3 on the exhaust gas to be measured. The exhaust gas diffuses through the diffusion barrier 3 into a first measuring cell 4. The oxygen content in this measuring cell is measured by means of a first Nernst voltage VNO between a first pump electrode 5 and a reference electrode 6 exposed to ambient air. The reference electrode 6 is arranged in an air channel 7, into which ambient air passes through an opening 8. Both electrodes 5, 6 are conventional platinum electrodes.
Im herkömmlichen Verfahren wird der Meßwert der ersten Nernstspannung VNO dazu verwendet, eine erste Stellspannung VpO einzustellen. Die Stellspannung VpO treibt einen ersten Sauerstoff-Ionen-Pumpstrom IpO durch den Festkörperelektroly- ten 2 des NOx-Sensors 1 zwischen der ersten Pumpelektrode 5 und einer Außenelektrode 9 - die Pumpelektrode 5 und die Außenelektrode 9 bilden eine erste Pumpzelle. Dabei wird die Stellspannung VpO von einem Regler so eingestellt, daß in der ersten Meßzelle 4 eine vorbestimmte Sauerstoffkonzentration vorliegt.In the conventional method, the measured value of the first Nernst voltage VNO is used to set a first control voltage VpO. The control voltage VpO drives a first oxygen ion pump current IpO through the solid electrolyte 2 of the NO x sensor 1 between the first pump electrode 5 and an outer electrode 9 - the pump electrode 5 and the outer electrode 9 form a first pump cell. The control voltage VpO is set by a controller so that there is a predetermined oxygen concentration in the first measuring cell 4.
Die erste Meßzelle 4 ist mit einer zweiten Meßzelle 10 über eine zweite Diffusionsbarriere 11 verbunden. Durch diese Diffusionsbarriere 11 diffundiert das in der Meßzelle 4 vorhan- dene Gas in die zweite Meßzelle 10. Die zweite Sauerstof konzentration in der zweiten Meßzelle 10 wird über eine zweite Nernstspannung VN1 zwischen einer zweiten Pumpelektrode 12, die ebenfalls eine Platinelektrode ist, und der Referenzelektrode 6 gemessen und von einem Regler zur Vorgabe einer zwei- ten Stellspannung Vpl verwendet, die einen zweiten Sauerstoff-Ionen-Pumpstrom Ipl treibt. Der zweite Sauerstoff- Ionen-Pumpstrom Ipl aus der zweiten Meßzelle 10 fließt von' der zweiten Pumpelektrode 12 durch den Festkörperelektrolyten 2 zur Außenelektrode 9 (zweite Pumpzelle). Mit seiner Hilfe wird in der zweiten Meßzelle 10 eine vorbestimmte Sauerstoffkonzentration eingestellt.The first measuring cell 4 is connected to a second measuring cell 10 via a second diffusion barrier 11. Through this diffusion barrier 11, the gas present in the measuring cell 4 diffuses into the second measuring cell 10. The second oxygen concentration in the second measuring cell 10 is via a second Nernst voltage VN1 between a second pump electrode 12, which is also a platinum electrode, and the reference electrode 6 measured and used by a controller to specify a second control voltage Vpl, which drives a second oxygen ion pump current Ipl. The second oxygen ion pump current Ipl from the second measuring cell 10 flows from the second pump electrode 12 through the solid electrolyte 2 to the outer electrode 9 (second pump cell). With his help a predetermined oxygen concentration is set in the second measuring cell 10.
Die von den bisherigen Vorgängen in den Meßzellen 4 und 10 nicht betroffene NOx-Konzentration wird nun an einer Meßelektrode 13, die katalytisch wirksam ausgestaltet ist, bestimmt. Dazu wird eine dritte Sauerstoffkonzentration über eine dritte Nernstspannung VN2 zwischen der Meßelektrode 13 und der Referenzelektrode 6 gemessen und von einem Regler zur Vorgabe einer dritten Stellspannung Vp2 verwendet. Unter Anlegen dieser Stellspannung Vp2 zwischen der Meßelektrode 13 und der Außenelektrode 9 (dritte Pumpzelle) wird das N0x zersetzt und der freigewordene Sauerstoff wird durch den Festkörperelektrolyten 2 in einem dritten Sauerstoff-Ionen-Pumpstrom Ip2 zur Außenelektrode 9 hin gepumpt. Der dritte Sauerstoff-The NO x concentration not affected by the previous processes in the measuring cells 4 and 10 is now determined on a measuring electrode 13 which is designed to be catalytically effective. For this purpose, a third oxygen concentration is measured via a third Nernst voltage VN2 between the measuring electrode 13 and the reference electrode 6 and used by a controller to specify a third control voltage Vp2. When this control voltage Vp2 is applied between the measuring electrode 13 and the outer electrode 9 (third pump cell), the N0 x is decomposed and the oxygen released is pumped through the solid electrolyte 2 to the outer electrode 9 in a third oxygen-ion pumping current Ip2. The third oxygen
Ionen-Pumpstrom Ip2 wird bei ausreichend geringem Restsauerstoffgehalt in der Meßzelle 10 nur von Sauerstoffionen getragen, die aus der Zersetzung von N0x stammen. Er ist somit ein Maß für die NOx-Konzentration in der Meßzelle 10 und somit im zu messenden Abgas. Da derartige NOx-Sensoren eine starke Temperaturabhängigkeit aufweisen, sorgt ein Heizelement 14 dafür, daß die Sondentemperatur zur Einhaltung der notwendigen Meßgenaugkeit stets in einem vorgegebenen Temperaturbereich gehalten wird.If the residual oxygen content in the measuring cell 10 is sufficiently low, the ion pump current Ip2 is carried only by oxygen ions which originate from the decomposition of N0 x . It is therefore a measure of the NO x concentration in the measuring cell 10 and thus in the exhaust gas to be measured. Since such NO x sensors have a strong temperature dependence, a heating element 14 ensures that the probe temperature is always kept in a predetermined temperature range in order to maintain the necessary measurement accuracy.
Zum Regeln der Pumpströme wird ein Mikrocontroller 20 in Verbindung mit einer analogen Beschaltung 21 verwendet. Die Schaltungsanordnung eines einzelnen Pumpstromregelkreises ist in Figur 2 detailliert dargestellt. Die Regelschaltung des gesamten NOx-Sensors weist für jede zu steuernde Pumpzelle eine derartige Schaltungsanordnung auf. Dabei können die erforderlichen digitalen Schaltungsanteile innerhalb eines einzigen Mikrocontrollers 20 realisiert werden. Eine PWM-Einheit 22 im Mikrocontroller 20 erzeugt ein pulsweitenmoduliertes Signal, das mit Hilfe einer analogen Filterschaltung 23 in eine Gleichspannung umgewandelt wird. Diese Spannung wird je nach Anforderung an die benötigte Stromstärke entweder direkt oder über einen Impedanzwandler 24 auf einen Meßwiderstand 25 gegeben, der in Serie zur zu steuernden Pumpzelle 27 des NOx- Sensors 1 liegt. Die Pumpzelle ist in Figur 2 in Form einerA microcontroller 20 in conjunction with an analog circuit 21 is used to regulate the pump currents. The circuit arrangement of an individual pump current control circuit is shown in detail in FIG. The control circuit of the entire NO x sensor has such a circuit arrangement for each pump cell to be controlled. The required digital circuit components can be implemented within a single microcontroller 20. A PWM unit 22 in the microcontroller 20 generates a pulse-width-modulated signal, which with the aid of an analog filter circuit 23 in a DC voltage is converted. Depending on the requirements of the required current strength, this voltage is given either directly or via an impedance converter 24 to a measuring resistor 25, which is connected in series with the pump cell 27 of the NO x sensor 1 to be controlled. The pump cell is in the form of a
Ersatzschaltung der zugehörigen Impedanz dargestellt.Equivalent circuit of the associated impedance shown.
Mit Hilfe eines ersten A/D-Wandlers 30 im Mikrocontroller 20 werden über einen Multiplexer 31 abwechselnd die Spannungspo- tentiale vor und nach dem Meßwiderstand 25 eingelesen. Da der Eingang des NOx-Sensors 1 meist sehr hochohmig ist, kann ein Impedanzwandler 32, z.B. ein Bufferverstärker, in die Meßleitung, die zur Messung des Potentialwerts nach dem Meßwiderstand 25 dient, geschaltet werden.With the aid of a first A / D converter 30 in the microcontroller 20, the voltage potentials before and after the measuring resistor 25 are read alternately via a multiplexer 31. Since the input of the NO x sensor 1 is usually very high-resistance, an impedance converter 32, for example a buffer amplifier, can be connected into the measuring line, which is used to measure the potential value after the measuring resistor 25.
Die zum Regeln des Pumpstroms benötigten Nernstspannungen werden ebenfalls im Mikrocontroller 20 berechnet. Dazu wird sowohl das Nernstpotential VNerns als auch das Referenzpotential VRef der entsprechenden Meßzelle 33 des NOx-Sensors 1 von einem zweiten A/D-Wandler 34 im Mikrocontroller 20 eingelesen. Die Meßzelle 33 entspricht dabei entweder der ersten Meßzelle 4 oder der zweiten Meßzelle 10 aus Figur 1 und ist schematisch als Gleichspannungsquelle dargestellt. Aufgrund der hohen Ausgangsimpedanz des NOx-Sensors 1 sind auch hier zwei Impedanzwandler 35 und 36, z.B. in Form von Bufferverstärkern vorgesehen.The Nernst voltages required to regulate the pump current are also calculated in the microcontroller 20. For this purpose, both the Nernst potential V Nerns and the reference potential V Ref of the corresponding measuring cell 33 of the NO x sensor 1 are read in by a second A / D converter 34 in the microcontroller 20. The measuring cell 33 corresponds to either the first measuring cell 4 or the second measuring cell 10 from FIG. 1 and is shown schematically as a DC voltage source. Because of the high output impedance of the NO x sensor 1, two impedance converters 35 and 36 are also provided here, for example in the form of buffer amplifiers.
In einer Auswerteschaltung 37 wird innerhalb des Mikrocon- trollers 20 aus den eingelesenen Potentialwerten eine Pump- Stromdifferenz ΔIp berechnet, die einem Regler 38, z. B. einem PID-Regler, zugeführt wird, der die PWM-Einheit 22 steuert. Ein vorzugsweise in den Mikrocontroller integrierter ' programmierbarer Festwertspeicher 39, z.B. ein EPROM, dient zur Speicherung der an den A/D-Wandlern 30 und 34 eingelese- nen Potentiale. Ein Sondensystem 50, bestehend aus einer NOx-Sonde 51 und der zugehörigen Regelschaltung 52, wird mit der Anordnung nach Figur 3 kalibriert. Die NOx-Sonde 51 setzt sich dabei aus dem NOx-Sensor 1, einer Sensorleitung 53 und einem Sensorstecker 54 zusammen. Durch Anordnung der Regelschaltung 52 im Gehäuse des Sensorsteckers 54 ergeben sich sehr kurze Verbindungsleitungen. Auf diese Weise kann trotz auftretender Leitungsver- luste eine ausreichend genaue Übertragung der meist nur im nA-Bereich liegenden Signalströme sichergestellt werden.In an evaluation circuit 37, a pump current difference .DELTA.Ip is calculated within the microcontroller 20 from the read potential values. B. a PID controller, which controls the PWM unit 22. A programmable read-only memory 39, for example an EPROM, which is preferably integrated in the microcontroller, serves to store the potentials read in on the A / D converters 30 and 34. A probe system 50, consisting of a NO x probe 51 and the associated control circuit 52, is calibrated with the arrangement according to FIG. 3. The NO x probe 51 is composed of the NO x sensor 1, a sensor line 53 and a sensor plug 54. The arrangement of the control circuit 52 in the housing of the sensor connector 54 results in very short connecting lines. In this way, despite the line losses that occur, a sufficiently precise transmission of the signal currents, which are usually only in the nA range, can be ensured.
Durch einen Testkontrollrechner 55 werden die Prüfparameter, z.B. NOx-Konzentration und Gastemperatur, in einer Testkammer 56 eingestellt und überwacht. Der NOx-Sensor 1 nimmt die ent- sprechenden Meßwerte auf und leitet sie über die Sensorleitung 51 an die Regelschaltung 52 weiter. In der Regelschaltung 52 werden die an den A/D-Wandlern des MikroControllers 20 anstehenden Meßwerte entweder unmittelbar oder nach einer internen Auswertung, z.B. durch Vergleich mit vorgeggebenen Sollwerten, in eigens dafür zur Verfügung gestellten Kennfeldern im programmierbaren Festwertspeicher 39, gespeichert. Die zur Steuerung der Regelschaltung 52 notwendige Kommunikation mit dem Testkontrollrechner 55 erfolgt über eine in die Regelschaltung integrierte serielle Schnittstelle 57 und eine Datenleitung 58.The test parameters, for example NO x concentration and gas temperature, are set and monitored in a test chamber 56 by a test control computer 55. The NO x sensor 1 records the corresponding measured values and forwards them to the control circuit 52 via the sensor line 51. In the control circuit 52, the measured values present at the A / D converters of the microcontroller 20 are stored either directly or after an internal evaluation, for example by comparison with predetermined target values, in characteristic maps made available for this purpose in the programmable read-only memory 39. The communication with the test control computer 55 necessary for controlling the control circuit 52 takes place via a serial interface 57 integrated in the control circuit and a data line 58.
Um technologiebedingte Fertigungstoleranzen und Bauteiltoleranzen innerhalb der Regelschaltung kompensieren zu können, müssen nach Fertigstellung des Sondensystems, also nach dem Verbinden der NOx-Sonde mit der zugehörigen Regelschaltung, die einzelnen Pumpstromregelkreise unter verschiedenen, charakteristischen Betriebsbedingungen vermessen werden. Um ". Offsetspannungen kompensieren zu können, wird das Sondensystem zunächst unter elektrisch neutralen Prüfbedingungen ge- testet. Hierzu wird das Heizelement abgeschaltet und ein Tastverhätnis des pulweitenmodulierten Signals von 0% eingestellt, so daß kein Pumpstrom mehr fließt. Die nun von den A/D-Wandlern eingelesenen Werte entsprechen genau den anliegenden Offsetspannungen. Diese können als Korrekturwerte im programmierbaren Festwertspeicher 39 abgelegt und zur Koorek- tur der jeweiligen Pumpströme verwendet werden. Diese Kompensation kann auch nach Einbau des Regelsystems in ein Kraftfahrzeug wiederholt werden, z.B. auf Anforderung der zentralen Motorsteuerung oder im Zuge einer Inspektion in einer Werkstätte. Anschließend wird jeder Pumpstromregelkreis des Sondensystems nacheinander unter verschiedenen Prüfbedingungen getestet. Die dabei ermittelten Pumpströme - d.h. die am ersten A/D-Wandler 30 anliegenden Meßwerte - werden im Festwertspeicher 39 gespeichert und dienen anschließend als Refe- renz für eine regelmäßige, selbständige Nachkalibrierung des Systems im Laufe seiner Lebensdauer. Zusätzlich können auch die am zweiten A/D-Wandler 34 anstehenden Nernst- und Referenzpotentiale im Festwertspeicher 39 gespeichert werden.In order to be able to compensate for technology-related manufacturing tolerances and component tolerances within the control circuit, the individual pump current control circuits must be measured under different, characteristic operating conditions after completion of the probe system, i.e. after connecting the NO x probe to the associated control circuit. In order to be able to compensate ". Offset voltages, the probe system is first tested under electrically neutral test conditions. For this purpose, the heating element is switched off and on The duty cycle of the pulse width modulated signal is set to 0% so that no pump current flows. The values now read by the A / D converters correspond exactly to the offset voltages present. These can be stored as correction values in the programmable read-only memory 39 and can be used to coordinate the respective pump currents. This compensation can also be repeated after the control system has been installed in a motor vehicle, for example at the request of the central engine control or in the course of an inspection in a workshop. Each pump current control loop of the probe system is then tested successively under different test conditions. The pump currents determined in this case - ie the measured values applied to the first A / D converter 30 - are stored in the read-only memory 39 and subsequently serve as a reference for regular, independent recalibration of the system over the course of its service life. In addition, the Nernst and reference potentials present at the second A / D converter 34 can also be stored in the read-only memory 39.
Durch den Einsatz eines MikroControllers mit integriertenBy using a microcontroller with integrated
A/D-Wandlern lassen sich verschiedene applikationsspezifische Daten des Sondensystems einlesen und speichern. Auf diese Weise kann jedes Sondensystem am Ende des Herstellungsprozesses mit Hilfe einer Prüfeinrichtung individuell und voll au- tomatisiert kalibriert werden. Ein aufwendiger und kostenintensiver Abgleich von elektronischen Bauelementen, wie er bei einer rein analogen Regelschaltung notwendig wäre, kann dadurch vermieden werden. Durch die Möglichkeit der selbständigen Nachkalibrierung des Sondensystems wird das Schaltungsde- sign der Regelschaltung weitgehend unabhängig von Bauteiltoleranzen.A / D converters can read and store various application-specific data from the probe system. In this way, each probe system can be calibrated individually and fully automatically at the end of the manufacturing process using a test facility. A complex and costly comparison of electronic components, as would be necessary with a purely analog control circuit, can be avoided in this way. Due to the possibility of independent recalibration of the probe system, the circuit design of the control circuit is largely independent of component tolerances.
Die Erfindung wurde beispielhaft für einen NOx-Sensor beschrieben, entsprechende Verfahren und Vorrichtungen sind auch für andere nach dem Prinzip der galvanischen Sauer- stoffkonzentrationszelle mit Festelektrolyt arbeitende Abgassonden, z.B. lineare Sauerstoffsonden, geeignet. The invention has been described by way of example for a NO x sensor; corresponding methods and devices are also available for others based on the principle of galvanic acid Material concentration cell with solid electrolyte exhaust gas probes, such as linear oxygen probes, suitable.

Claims

Patentansprüche claims
1. Verfahren zum Kalibrieren eines Sondensystems, bestehend aus einer nach dem Prinzip der galvanischen Sauerstoffkonzen- trationszelle mit Festelektrolyt arbeitenden Abgassonde (51) und einer Regelschaltung (52), wobei zum Regeln der Pumpströme ein Mikrocontroller (20) in Verbindung mit einer analogen Beschaltung (21) verwendet wird, bei dem1. Method for calibrating a probe system, consisting of an exhaust gas probe (51) operating on the principle of the galvanic oxygen concentration cell with solid electrolyte and a control circuit (52), a microcontroller (20) in connection with an analog circuit () for controlling the pump currents. 21) is used in which
- unter vorgegebenen Prüfbedingungen Meßwerte von der Abgas- sonde (51) aufgenommen werden,- Measured values are recorded by the exhaust gas probe (51) under specified test conditions,
- die Meßwerte in den Mikrocontroller (20) eingelesen werden und- The measured values are read into the microcontroller (20) and
- die eingelesenen Meßwerte in einem programmierbaren Festwertspeicher (39) in der Regelschaltung (52) als Korrektur- oder Prüfwerte gespeichert werden.- The measured values read are stored in a programmable read-only memory (39) in the control circuit (52) as correction or test values.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die eingelesenen Meßwerte im Microcontroller (20) ausgewertet werden und die ausgewerteten Meßwerte im programmierbaren Festwertspeicher (39) in der Regelschaltung (52) als Korrektur- oder Prüfwerte gespeichert werden.2. The method according to claim 1, characterized in that the read-in measured values are evaluated in the microcontroller (20) and the evaluated measured values are stored in the programmable read-only memory (39) in the control circuit (52) as correction or test values.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die Korrektur- und Prüfwerte in Kennfeldern im program- mierbaren Festwertspeicher (39) gespeichert werden.3. The method according to claim 1 or 2, characterized in that the correction and test values are stored in maps in the programmable read-only memory (39).
4. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß der programmierbare Festwertspeicher (39) in den Mikrocontroller (20) integriert ist.4. The method according to any one of claims 1 to 3, characterized in that the programmable read-only memory (39) is integrated in the microcontroller (20).
5. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die unter elektrisch neutralen Bedingungen aufgenommenen Meßwerte der Abgassonde (1) im programmierbaren Festwertspeicher (39) als Korrekturwerte gespeichert werden. 5. The method according to any one of the preceding claims, characterized in that the measured values of the exhaust gas probe (1) recorded under electrically neutral conditions are stored in the programmable read-only memory (39) as correction values.
6. Verfahren nach Anspruch 4, dadurch gekennzeichnet, daß ^die Korrekturwerte zur Korrektur der Pumpströme verwendet werden.6. The method according to claim 4, characterized in that ^ the correction values are used to correct the pump currents.
7. Verfahren nach einem der Ansprüche 1 bis 3, dadurch ge- kennzeichnet, daß die Prüfwerte als Referenz für eine spätere Nachkalibrierung des Sensorsystems verwendet werden.7. The method according to any one of claims 1 to 3, characterized in that the test values are used as a reference for a later recalibration of the sensor system.
8. Vorrichtung zum Kalibrieren eines Sensorsyste s (50), bestehend aus einer Abgassonde (51) und einer Regelschaltung (52) für ein Kraftfahrzeug, insbesondere nach einem Verfahren gemäß einem der Ansprüche 1 bis 6, die aufweist8. Device for calibrating a sensor system (50), consisting of an exhaust gas probe (51) and a control circuit (52) for a motor vehicle, in particular according to a method according to one of claims 1 to 6, which comprises
- eine Testkammer (56) , die ein Prüfgas mit veränderlichen Prüfparametern enthält,a test chamber (56) which contains a test gas with variable test parameters,
- einen Testkontrollrechner (55) , durch den die Prüfparameter in der Testkammer (56) eingestellt und überwacht werden, und- A test control computer (55), through which the test parameters in the test chamber (56) are set and monitored, and
- eine Datenleitung (58) über die die Regelschaltung (52) und der Testkontrollrechner (55) miteinander kommunizieren.- A data line (58) via which the control circuit (52) and the test control computer (55) communicate with one another.
9. Vorrichtung nach Anspruch 5, dadurch gekennzeichnet, daß die Regelschaltung (52) eine serielle Schnittstelle (57) aufweist, über die die Datenleitung (58) an die Regelschaltung (52) angeschlossen ist. 9. The device according to claim 5, characterized in that the control circuit (52) has a serial interface (57) via which the data line (58) is connected to the control circuit (52).
EP99952345A 1998-08-10 1999-08-10 Method and device for calibrating a probe system comprised of an exhaust probe and of a control circuit for a motor vehicle Withdrawn EP1105720A1 (en)

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DE19836127A DE19836127A1 (en) 1998-08-10 1998-08-10 Calibration of solid-electrolyte exhaust gas oxygen sensor and associated circuitry comprises use of test cell and test supervision computer, to compensate tolerances and drift before and during useful life
DE19836127 1998-08-10
PCT/DE1999/002490 WO2000010002A1 (en) 1998-08-10 1999-08-10 Method and device for calibrating a probe system comprised of an exhaust probe and of a control circuit for a motor vehicle

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