EP1756560A1 - Sensor element for determining a physical property of a test gas - Google Patents

Sensor element for determining a physical property of a test gas

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Publication number
EP1756560A1
EP1756560A1 EP05743048A EP05743048A EP1756560A1 EP 1756560 A1 EP1756560 A1 EP 1756560A1 EP 05743048 A EP05743048 A EP 05743048A EP 05743048 A EP05743048 A EP 05743048A EP 1756560 A1 EP1756560 A1 EP 1756560A1
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EP
European Patent Office
Prior art keywords
gas
sensor element
electrode
reference electrode
volume
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.)
Withdrawn
Application number
EP05743048A
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German (de)
French (fr)
Inventor
Jens Schneider
Detlef Heimann
Thomas Wahl
Thomas Egner
Gerhard Schneider
Hans-Joerg Renz
Harald Neumann
Andreas Schaak
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Robert Bosch GmbH
Original Assignee
Robert Bosch GmbH
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Filing date
Publication date
Application filed by Robert Bosch GmbH filed Critical Robert Bosch GmbH
Publication of EP1756560A1 publication Critical patent/EP1756560A1/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Withdrawn legal-status Critical Current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
    • G01N27/403—Cells and electrode assemblies
    • G01N27/406—Cells and probes with solid electrolytes
    • G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
    • G01N27/4071—Cells and probes with solid electrolytes for investigating or analysing gases using sensor elements of laminated structure

Definitions

  • the invention is based on a sensor element for determining a physical property of a measurement gas, in particular the pressure or the concentration of a gas component in a gas mixture, in particular in the exhaust gas of an internal combustion engine, according to the preamble of claim 1.
  • a known electrochemical sensor for determining the oxygen content in gas mixtures which has a heating device for generating the operating temperature of the sensor element (DE 198 15 700 AI) is the volume provided with pores, via which the reference electrode is connected to a reference gas channel carrying the reference gas , formed as a layer plane between the reference channel and the reference electrode and serves the improved heat coupling between the reference electrode and the resistance heating element of the heating device with uniform heat distribution.
  • the porous layer relieves increased mechanical stresses that occur at the edge of the reference gas channel to the adjacent solid electrolyte and that increase
  • the outer sensor areas, in which electrodes are arranged, are particularly affected by the exhaust gas from internal combustion engines. Due to the presence of foreign substances in the exhaust gas, such as acidic exhaust gas components, e.g. phosphorus or sulfur Compounds, neutral particles and oil ashes with Ca, P, Zn, Mn, Fe-containing compounds as well as lead and silicon compounds, there can be deposits on or direct chemical interactions with the electrodes, which change the electrode activity, the so-called Result in electrode poisoning or electrode passivation.
  • the sensor element according to the invention with the features of claim 1 has the advantage that, through the selection of the bulk material through which the reference electrode is acted upon by the reference gas, with regard to its physical and chemical properties, in particular with regard to its affinity for binding those usually present in the reference gas Foreign substances, the latter bound in the porous volume or undergo a chemical reaction in the porous volume and thus cannot interact with the electrode surface of the reference electrode. Since the reference electrode is generally arranged in a reference channel which is formed in the interior of the solid electrolyte, there are no high demands on the mechanical strength of the bulk material.
  • the porous volume is designed as a porous protective layer which covers the free surfaces of the reference electrode arranged on the solid electrolyte.
  • the protective layer is applied in the form of a paste in a specific work step and then baked in a cofiring process.
  • the porous volume completely fills at least one channel section of a reference gas channel upstream of the reference electrode, in which the reference electrode is arranged.
  • the bulk material is introduced into the reference channel in the form of a paste and then burned in by cofiring so that the channel cross section is completely filled.
  • the porosity and layer thickness are optimized so that a free gas exchange between the reference electrode and the reference gas channel is guaranteed without impairing the sensor function.
  • the porosity of the filling volume is 20-60% and the layer thickness of the porous protective layer is 5-50 microns.
  • FIG. 1 shows a cross section of a sensor element for determining the oxygen concentration in the exhaust gas of an internal combustion engine
  • FIG. 3 shows the same representation as in FIG. 1 with a modification of the sensor element
  • the sensor element shown in FIGS. 1 and 2 in two different sectional views for a jump probe working according to the Nernst principle (potentiometric) for measuring the oxygen concentration in the exhaust gas of an internal combustion engine or an internal combustion engine as an exemplary embodiment of a general sensor element for determining a physical property of a measuring gas has a solid electrolyte body 11, which consists of a plurality of oxygen-ion-conducting solid electrolyte layers 111-114, which are partly as ceramic films, such as the solid electrolyte layers 111, 112 and 114, and partly as printed layer, such as the solid electrolyte layer 113, is composed.
  • yttrium-stabilized or partially stabilized zirconium oxide Z ⁇ O 2
  • the integrated shape of the planar, ceramic solid electrolyte body 11 is produced by laminating together the ceramic films printed with functional layers and then sintering the laminated structure.
  • the protective layer 13 is porous, so that the outer electrode 12 is exposed through the protective layer 13 to the exhaust gas surrounding the sensor element.
  • a reference electrode 14 is applied to the surface of the first solid electrolyte layer 111 facing away from the outer electrode 12.
  • the reference electrode 14 is arranged in a reference gas channel 15 which is introduced into the second solid electrolyte layer 112 and is covered by the first solid electrolyte layer 111 upwards and by the third solid electrolyte layer 113 downwards.
  • an electrical resistance heater 16 is provided between the third solid electrolyte layer 113 and the fourth solid electrolyte layer 114, which has a heating surface 17, preferably laid in a meandering shape, and two conductor tracks for the power supply, not shown here, leading to the heating surface 17.
  • the heating surface 17 and the supply tracks are in an electrical composed of two insulating layers
  • Insulation 18 embedded which is laterally surrounded by a sealing frame 19.
  • a sealing frame 19 it is possible to omit the sealing frame 19 and to lead the insulation 18 to the side surfaces of the solid electrolyte body 11.
  • the reference gas duct 15 is acted upon by a reference gas, atmospheric air preferably being used as the reference gas, which air is taken from the engine compartment of a vehicle equipped with the internal combustion engine.
  • a reference gas atmospheric air preferably being used as the reference gas
  • the reference electrode 14 is not directly exposed to the reference gas or the reference air, but rather through a porous volume, the bulk material of which with regard to its physical and chemical properties is selected so that the foreign substances contained in the reference gas are bound in volume and or are subjected to a chemical reaction.
  • Sources of such contamination of the reference air are insulating and sealing materials as well as cleaning agents and lubricants, which are usually found in the engine compartment of the Vehicle.
  • the porosity of the volume is optimized so that a free gas exchange between the reference electrode 14 and the reference gas channel 15 can take place. Due to the volume material selected with regard to its affinity for binding the foreign substances contained in the reference gas, when the reference gas diffuses through the volume, these foreign substances are bound in volume or exposed to a chemical conversion process in volume, so that the foreign substances do not interact with the electrode surface of the reference electrode 14 and there can not cause an accelerated aging of the reference electrode 14.
  • the volume is advantageously composed as follows:
  • the porous volume is designed as a porous protective layer 20 which completely covers the free electrode surface of the reference electrode 14.
  • the layer thickness is, for example, 5-100 ⁇ m.
  • the protective layer 20 is applied as a paste to the reference electrode 14 during the manufacturing process of the sensor element and then baked in a cofiring process.
  • the porous volume completely fills a channel section of the reference gas channel 15, the channel section of the reference electrode 14, as seen from the mouth of the reference gas channel 15, being upstream.
  • the volume here forms a porous protective barrier 21, through which the reference electrode 14 is acted upon by the reference gas or the reference air.
  • the porosity of the volume filled into the reference gas channel 15 is measured at 20-60%.
  • the invention is not limited to the sensor element described for a jump probe operating according to the Nernst principle.
  • the invention can also be used with the same advantage in the case of sensor elements equipped with a reference electrode 14 for pressure measurement in a gas, in particular in the exhaust gas of an internal combustion engine.

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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)
  • Measuring Oxygen Concentration In Cells (AREA)

Abstract

The invention relates to a sensor element for determining a physical property of a test gas, especially the pressure or the concentration of a gas constituent in a gas mixture, especially in the exhaust gas of an internal combustion engine, said sensor element comprising an electrode (12) which is exposed to the test gas, and a reference electrode (14) which is exposed to a reference gas, especially the surrounding atmosphere, through a porous volume (20). The two electrodes (12, 14) are separated by a solid electrolyte (111). In order to avoid the reference electrode (14) from ageing prematurely as a result of deposits of foreign substances contained in the reference gas or chemical interactions caused by the foreign substances, the volume material is selected in terms of the physical and chemical properties thereof in such a way that the foreign substances are absorbed therein (21) and/or subjected to a chemical reaction.

Description

Sensorelement zur Bestimmung einer physikalischen Eigenschaft eines MessgasesSensor element for determining a physical property of a measuring gas
Stand der TechnikState of the art
Die Erfindung geht aus von einem Sensorelement zur Bestimmung einer physikalischen Eigenschaft eines Messgases, insbesondere des Drucks oder der Konzentration einer Gaskomponente in einem Gasgemisch, insbesondere im Abgas einer Brennkraftmaschine, nach dem Oberbegriff des Anspruchs 1.The invention is based on a sensor element for determining a physical property of a measurement gas, in particular the pressure or the concentration of a gas component in a gas mixture, in particular in the exhaust gas of an internal combustion engine, according to the preamble of claim 1.
Bei einem bekannten elektrochemischen Sensor zur Bestimmung des Sauerstoffgehalts in Gasgemischen, der eine Heizeinrichtung zur Erzeugung der Betriebstemperatur des Sensorelements aufweist, (DE 198 15 700 AI) ist das mit Poren versehene Volumen, über das die Referenzelektrode mit einem das Referenzgas führenden Referenzgaskanal in Verbindung steht, als Schichtebene zwischen dem Referenzkanal und der Referenzelektrode ausgebildet und dient der verbesserten Wärmekopplung zwischen Referenzelektrode und Widerstandheizelement der Heizeinrichtung bei gleichmäßiger Wärmeverteilung. Außerdem werden durch die poröse Schicht erhöhte mechanische Spannungen abgebaut, die an der Kante des Referenzgaskanals zum benachbarten Festelektrolyten hin auftreten und die zuIn a known electrochemical sensor for determining the oxygen content in gas mixtures, which has a heating device for generating the operating temperature of the sensor element (DE 198 15 700 AI) is the volume provided with pores, via which the reference electrode is connected to a reference gas channel carrying the reference gas , formed as a layer plane between the reference channel and the reference electrode and serves the improved heat coupling between the reference electrode and the resistance heating element of the heating device with uniform heat distribution. In addition, the porous layer relieves increased mechanical stresses that occur at the edge of the reference gas channel to the adjacent solid electrolyte and that increase
Spannungsrissen im Festelektrolytkörper fuhren können. Ferner wird durch den großflächigen Kontakt der Referenzelektrode mit der benachbarten porösen Schicht eine bessere Haftung erzielt, weil die Referenzelektrode dadurch beim Laminieren des aus Folien zusammengesetzten Festelektrolytkörpers zwischen benachbarten Folien eingepresst gehalten wird.Stress cracks in the solid electrolyte body can lead. Furthermore, better contact is achieved through the large-area contact of the reference electrode with the adjacent porous layer, because the reference electrode is thereby pressed between adjacent foils when the solid electrolyte body composed of foils is laminated.
Bei Sensorelementen dieser Art wird die Funktionalität aufgrund von Alterungsprozessen langfristig beeinträchtigt. Besonders betroffen sind dabei die dem Abgas von Brennkraftmaschinen ausgesetzten äußeren Sensorbereiche, in denen Elektroden angeordnet sind. Durch die Gegenwart von Fremdstoffen im Abgas, wie saure Abgasbestandteile, z.B. Phosphor- oder Schwefel- Verbindungen, neutrale Partikel und Ölaschen mit Ca-, P-, Zn-, Mn-, Fe-haltigen Verbindungen sowie Blei und Siliziumverbindungen, kann es zu Ablagerungen auf oder zu direkten chemischen Wechselwirkungen mit den Elektroden kommen, die eine veränderte Elektrodenaktivität, die sog. Elektrodenvergiftung oder Elektrodenpassivierung, zur Folge haben.With sensor elements of this type, the functionality is impaired in the long term due to aging processes. The outer sensor areas, in which electrodes are arranged, are particularly affected by the exhaust gas from internal combustion engines. Due to the presence of foreign substances in the exhaust gas, such as acidic exhaust gas components, e.g. phosphorus or sulfur Compounds, neutral particles and oil ashes with Ca, P, Zn, Mn, Fe-containing compounds as well as lead and silicon compounds, there can be deposits on or direct chemical interactions with the electrodes, which change the electrode activity, the so-called Result in electrode poisoning or electrode passivation.
Aber auch im Referenzgas, insbesondere wenn als Referenzgas die Umgebungsluft im Motorraum eines Fahrzeugs herangezogen wird, sind - wenn auch in kleinerem Maße - Verunreinigungen enthalten, die zu einer beschleunigten Alterung der Referenzelektrode führen. Quellen für solche Verunreinigungen in dem Referenzgas bzw. in der Referenzluft sind Isolier- und Dichtmaterialien sowie Reinigungs- und Schmiermittel, die im Motorraum des Fahrzeugs eingesetzt werden.But even in the reference gas, especially if the ambient air in the engine compartment of a vehicle is used as the reference gas, impurities are present, albeit to a lesser extent, which lead to accelerated aging of the reference electrode. Sources of such contamination in the reference gas or in the reference air are insulating and sealing materials, as well as cleaning agents and lubricants, which are used in the engine compartment of the vehicle.
Vorteile der ErfindungAdvantages of the invention
Das erfindungsgemäße Sensorelement mit den Merkmalen des Anspruchs 1 hat den Vorteil, dass durch die Auswahl des Volumenmaterials, durch das hindurch die Referenzelektrode mit dem Referenzgas beaufschlagt wird, bezüglich seiner physikalischen und chemischen Eigenschaften, insbesondere bezüglich seiner Affinität zur Bindung der in den Referenzgas üblicherweise vorhandenen Fremdstoffe, letztere im porösen Volumen gebunden oder im porösen Volumen eine chemische Reaktion eingehen und so nicht in Wechselwirkung mit der Elektrodenfläche der Referenzelektrode treten können. Da im allgemeinen die Referenzelektrode in einem Referenzkanal angeordnet ist, der im Innern des Festelektrolyten ausgebildet ist, besteht keine hohe Anforderungen an die mechanische Festigkeit des Volumenmaterials.The sensor element according to the invention with the features of claim 1 has the advantage that, through the selection of the bulk material through which the reference electrode is acted upon by the reference gas, with regard to its physical and chemical properties, in particular with regard to its affinity for binding those usually present in the reference gas Foreign substances, the latter bound in the porous volume or undergo a chemical reaction in the porous volume and thus cannot interact with the electrode surface of the reference electrode. Since the reference electrode is generally arranged in a reference channel which is formed in the interior of the solid electrolyte, there are no high demands on the mechanical strength of the bulk material.
Durch die in den weiteren Ansprüchen aufgeführten Maßnahmen sind vorteilhafte Weiterbildungen und Verbesserungen des im Anspruch 1 angegebenen Sensorelements möglich.Advantageous further developments and improvements of the sensor element specified in claim 1 are possible through the measures listed in the further claims.
Gemäß einer vorteilhaften Ausfuhrungsform der Erfindung ist das poröse Volumen als poröse Schutzschicht ausgeführt, die die freien Flächen der auf dem Festelektrolyten angeordneten Referenzelektrode bedeckt. Dabei wird die Schutzschicht in einem gezielten Arbeitsgang in Form einer Paste aufgebracht und anschließend in einem Cofiring-Prozess eingebrannt. Gemäß einer vorteilhaften Ausführungsform der Erfindung füllt das poröse Volumen zumindest einen der Referenzelektrode vorgelagerten Kanalabschnitt eines Referenzgaskanals, in dem die Referenzelektrode angeordnet ist, vollständig aus. Auch hier wird das Volumenmaterial in Form einer Paste in den Referenzkanal eingebracht und dann durch Cofiring eingebrannt, so dass der Kanalquerschnitt vollständig ausgefüllt ist. In beiden Fällen wird die Porosität und Schichtdicke so optimiert, dass ein freier Gasaustausch zwischen Referenzelektrode und Referenzgaskanal gewährleistet ist, ohne die Sensorfunktion zu beeinträchtigen. Beispielhaft beträgt die Porosität des Füllvolumens 20 - 60% und die Schichtdicke der porösen Schutzschicht 5 - 50 microns.According to an advantageous embodiment of the invention, the porous volume is designed as a porous protective layer which covers the free surfaces of the reference electrode arranged on the solid electrolyte. The protective layer is applied in the form of a paste in a specific work step and then baked in a cofiring process. According to an advantageous embodiment of the invention, the porous volume completely fills at least one channel section of a reference gas channel upstream of the reference electrode, in which the reference electrode is arranged. Here, too, the bulk material is introduced into the reference channel in the form of a paste and then burned in by cofiring so that the channel cross section is completely filled. In both cases, the porosity and layer thickness are optimized so that a free gas exchange between the reference electrode and the reference gas channel is guaranteed without impairing the sensor function. For example, the porosity of the filling volume is 20-60% and the layer thickness of the porous protective layer is 5-50 microns.
Zeichnungdrawing
Die Erfindung ist anhand von in der Zeichnung dargestellten Ausfuhrungsbeispielen im folgenden näher beschrieben. Es zeigen in schematisierter Darstellung:The invention is described below with reference to exemplary embodiments shown in the drawing. In a schematic representation:
Fig. 1 einen Querschnitt eines Sensorelements zur Bestimmung der Sauerstoffkonzentration im Abgas einer Brennkraftmaschine,1 shows a cross section of a sensor element for determining the oxygen concentration in the exhaust gas of an internal combustion engine,
Fig. 2 ausschnittweise einen Schnitt längs der Linie II - II in Fig. 1,2 a section along the line II - II in Fig. 1,
Fig. 3 eine gleiche Darstellung wie in Fig. 1 mit einer Modifikation des Sensorelements,3 shows the same representation as in FIG. 1 with a modification of the sensor element,
Fig. 4 ausschnittweise einen Schnitt längs der Linie IV - IV in Fig. 3.4 shows a section along the line IV-IV in FIG. 3.
Beschreibung der AusfuhrungsbeispieleDescription of the exemplary embodiments
Das in Fig. 1 und 2 in zwei verschiedenen Schnittdarstellungen gezeigte Sensorelement für eine nach dem Nernstprinzip (potentiometrisch) arbeitende Sprungsonde zur Messung der Sauerstoffkonzentration im Abgas einer Brennkraftmaschine oder eines Verbrennungsmotors als Ausfuhrungsbeispiel für ein allgemeines Sensorelement zur Bestimmung einer physikalischen Eigenschaft eines Messgases weist einen Festelektrolytkörper 11 auf, der aus mehreren, sauerstoffionenleitenden Festelektrolytschichten 111 - 114, die zum Teil als keramische Folien, wie die Festelektrolytschichten 111, 112 und 114, und zum Teil als gedruckte Schicht, wie die Festelektrolytschicht 113, ausgeführt sind, zusammengesetzt ist. Als Festelektrolytmaterial wird beispielsweise yttriumstabilisiertes oder -teilstabilisiertes Zirkoniumoxid (ZιO2) verwendet. Die integrierte Form des planaren, keramischen Festelektrolytkörpers 11 wird durch Zusammenlaminieren der mit Funktionsschichten bedruckten keramischen Folien und anschließendem Sintern der laminierten Struktur hergestellt.The sensor element shown in FIGS. 1 and 2 in two different sectional views for a jump probe working according to the Nernst principle (potentiometric) for measuring the oxygen concentration in the exhaust gas of an internal combustion engine or an internal combustion engine as an exemplary embodiment of a general sensor element for determining a physical property of a measuring gas has a solid electrolyte body 11, which consists of a plurality of oxygen-ion-conducting solid electrolyte layers 111-114, which are partly as ceramic films, such as the solid electrolyte layers 111, 112 and 114, and partly as printed layer, such as the solid electrolyte layer 113, is composed. For example, yttrium-stabilized or partially stabilized zirconium oxide (ZιO 2 ) is used as the solid electrolyte material. The integrated shape of the planar, ceramic solid electrolyte body 11 is produced by laminating together the ceramic films printed with functional layers and then sintering the laminated structure.
Auf der ersten Festelektrolytschicht 111 ist auf einer Außenfläche des Festelektrolytkörpers 11 eine äußere Elektrode 12 aufgebracht, die von einer Schutzschicht 13 überzogen ist. Die Schutzschicht 13 ist porös ausgebildet, so dass die äußere Elektrode 12 durch die Schutzschicht 13 hindurch dem das Sensorelement umgebenden Abgas ausgesetzt ist. Auf der von der äußeren Elektrode 12 abgekehrten Oberfläche der ersten Festelektrolytschicht 111 ist eine Referenzelektrode 14 aufgebracht. Die Referenzelektrode 14 ist in einem Referenzgaskanal 15 angeordnet, der in die zweite Festelektrolytschicht 112 eingebracht ist und von der ersten Festelektrolytschicht 111 nach oben und von der dritten Festelektrolytschicht 113 nach unten abgedeckt ist.An outer electrode 12, which is covered by a protective layer 13, is applied to the first solid electrolyte layer 111 on an outer surface of the solid electrolyte body 11. The protective layer 13 is porous, so that the outer electrode 12 is exposed through the protective layer 13 to the exhaust gas surrounding the sensor element. A reference electrode 14 is applied to the surface of the first solid electrolyte layer 111 facing away from the outer electrode 12. The reference electrode 14 is arranged in a reference gas channel 15 which is introduced into the second solid electrolyte layer 112 and is covered by the first solid electrolyte layer 111 upwards and by the third solid electrolyte layer 113 downwards.
Zur Beheizung des Elektrodenbereichs ist zwischen der dritten Festelektrolytschicht 113 und der vierten Festelektrolytschicht 114 ein elektrischer Widerstandsheizer 16 vorgesehen, der eine vorzugsweise in Mäanderform verlegte Heizfläche 17 und zwei zu der Heizfläche 17 führende, hier nicht dargestellte Leiterbahnen für die Stromzuführung aufweist. Die Heizfläche 17 und die Zuleitungsbahnen sind in einer aus zwei Isolierschichten zusammengesetzten elektrischenTo heat the electrode area, an electrical resistance heater 16 is provided between the third solid electrolyte layer 113 and the fourth solid electrolyte layer 114, which has a heating surface 17, preferably laid in a meandering shape, and two conductor tracks for the power supply, not shown here, leading to the heating surface 17. The heating surface 17 and the supply tracks are in an electrical composed of two insulating layers
Isolierung 18 eingebettet, die seitlich von einem Dichtrahmen 19 umgeben ist. Selbstverständlich ist es möglich, den Dichtrahmen 19 wegfallen zu lassen und die Isolierung 18 bis an die Seitenflächen des Festelektrolytkörpers 11 zu führen.Insulation 18 embedded, which is laterally surrounded by a sealing frame 19. Of course, it is possible to omit the sealing frame 19 and to lead the insulation 18 to the side surfaces of the solid electrolyte body 11.
Der Referenzgaskanal 15 ist mit einem Referenzgas beaufschlagt, wobei als Referenzgas vorzugsweise atmosphärische Luft eingesetzt wird, die im Motorraum eines mit dem Verbrennungsmotor ausgestatteten Fahrzeugs entnommen wird. Um die Referenzelektrode 14 vor Verunreinigungen durch Fremd- oder Schadstoffe zu schützen, die in der Referenzluft enthalten sind, ist die Referenzelektrode 14 nicht direkt dem Referenzgas bzw. der Referenzluft ausgesetzt, sondern durch ein poröses Volumen hindurch, dessen Volumenmaterial bezüglich seiner physikalischen und chemischen Eigenschaften so gewählt ist, dass die im Referenzgas enthaltenen Fremdstoffe im Volumen gebunden und oder einer chemischen Reaktion unterzogen werden. Quellen für eine solche Verunreinigung der Referenzluft sind Isolier- und Dichtmaterialen sowie Reinigungs- und Schmiermittel, die üblicherweise im Motorraum des Fahrzeugs eingesetzt werden. Die Porosität des Volumens ist optimiert, damit ein freier Gasaustausch zwischen Referenzelektrode 14 und Referenzgaskanal 15 stattfinden kann. Durch das bezüglich seiner Affinität zur Bindung der im Referenzgas enthaltenen Fremdstoffe ausgewählte Volumenmaterial werden beim Hindurchdiffundieren des Referenzgases durch das Volumen diese Fremdstoffe im Volumen gebunden bzw. im Volumen einem chemischen Umwandlungsprozess ausgesetzt, so dass die Fremdstoffe nicht in Wechselwirkung mit der Elektrodenfläche der Referenzelektrode 14 treten und dort eine beschleunigte Alterung der Referenzelektrode 14 nicht bewirken können.The reference gas duct 15 is acted upon by a reference gas, atmospheric air preferably being used as the reference gas, which air is taken from the engine compartment of a vehicle equipped with the internal combustion engine. In order to protect the reference electrode 14 from contamination by foreign substances or pollutants that are contained in the reference air, the reference electrode 14 is not directly exposed to the reference gas or the reference air, but rather through a porous volume, the bulk material of which with regard to its physical and chemical properties is selected so that the foreign substances contained in the reference gas are bound in volume and or are subjected to a chemical reaction. Sources of such contamination of the reference air are insulating and sealing materials as well as cleaning agents and lubricants, which are usually found in the engine compartment of the Vehicle. The porosity of the volume is optimized so that a free gas exchange between the reference electrode 14 and the reference gas channel 15 can take place. Due to the volume material selected with regard to its affinity for binding the foreign substances contained in the reference gas, when the reference gas diffuses through the volume, these foreign substances are bound in volume or exposed to a chemical conversion process in volume, so that the foreign substances do not interact with the electrode surface of the reference electrode 14 and there can not cause an accelerated aging of the reference electrode 14.
Für den Einsatz des Sensorelements im Abgas eines Verbrennungsmotors ist das Volumen vorteilhaft wie folgt zusammengesetzt:For the use of the sensor element in the exhaust gas of an internal combustion engine, the volume is advantageously composed as follows:
30 - 70 % Yttriumoxid (Y203)/Zirkoniumoxid (Zr02) 30 - 70 % Aluminiumoxid (A1203) 0 - 20 % Lithiumoxid (Li203) 0 - 20 % Calciumoxid (CaO) 0 - 20 % Magnesiumoxid (MgO) 0 - 20 % Titanoxid (Ti02) 0 - 20 % Ceroxid (Ce02)30 - 70% yttrium oxide (Y 2 0 3 ) / zirconium oxide (Zr0 2 ) 30 - 70% aluminum oxide (A1 2 0 3 ) 0 - 20% lithium oxide (Li 2 0 3 ) 0 - 20% calcium oxide (CaO) 0 - 20 % Magnesium oxide (MgO) 0 - 20% titanium oxide (Ti0 2 ) 0 - 20% cerium oxide (Ce0 2 )
In dem Ausführungsbeispiel der Fig. 1 und 2 ist das poröse Volumen als poröse Schutzschicht 20 ausgebildet, die die freie Elektrodenfläche der Referenzelektrode 14 vollständig bedeckt. Die Schichtdicke beträgt beispielhaft 5 - 100 μm. Die Schutzschicht 20 wird beim Fertigungspro- zess des Sensorelements als Paste auf die Referenzelektrode 14 aufgebracht und anschließend in einem Cofiring-Prozess eingebrannt.In the exemplary embodiment in FIGS. 1 and 2, the porous volume is designed as a porous protective layer 20 which completely covers the free electrode surface of the reference electrode 14. The layer thickness is, for example, 5-100 μm. The protective layer 20 is applied as a paste to the reference electrode 14 during the manufacturing process of the sensor element and then baked in a cofiring process.
Im Ausführungsbeispiel der Fig. 3 und 4 füllt das poröse Volumen einen Kanalabschnitt des Referenzgaskanals 15 vollständig aus, wobei der Kanalabschnitt der Referenzelektrode 14, von der Mündung des Referenzgaskanals 15 aus gesehen, vorgelagert ist. Das Volumen bildet hier eine poröse Schutzbarriere 21, durch die hindurch die Referenzelektrode 14 von dem Referenzgas bzw. der Referenzluft beaufschlagt wird. Selbstverständlich ist es möglich, nicht nur einen Kanalabschnitt, sondern den gesamten Referenzgaskanal 15 mit Volumenmaterial völlig auszufüllen. In beiden Fällen wird die Porosität des in den Referenzgaskanal 15 eingefüllten Volumens zu 20 - 60% bemessen. Die Erfindung ist nicht auf das beschriebene Sensorelement für eine nach dem Nernstprinzip arbeitende Sprungsonde beschränkt. Der erfindungsgemäße Schutz der Referenzelektrode 14 vor schädlichen Verunreinigungen im Referenzgas kann ebenso bei Sensorelementen für planare Breitbandsonden, wie sie in der DE 199 41 051 AI beschrieben sind, oder für als sog. Fingersonden ausgebildete λ=l- oder Sprungsonden, wie sie in der DE 43 12 506 AI beschrieben sind, herbeigeführt werden. Auch bei mit einer Referenzelektrode 14 ausgestatteten Sensorelementen zur Druckmessung in einem Gas, insbesondere im Abgas einer Brennkraftmaschine, kann die Erfindung mit gleichem Vorteil eingesetzt werden. In the exemplary embodiment in FIGS. 3 and 4, the porous volume completely fills a channel section of the reference gas channel 15, the channel section of the reference electrode 14, as seen from the mouth of the reference gas channel 15, being upstream. The volume here forms a porous protective barrier 21, through which the reference electrode 14 is acted upon by the reference gas or the reference air. Of course, it is possible to fill not only one channel section, but the entire reference gas channel 15 with bulk material. In both cases, the porosity of the volume filled into the reference gas channel 15 is measured at 20-60%. The invention is not limited to the sensor element described for a jump probe operating according to the Nernst principle. The inventive protection of the reference electrode 14 against harmful impurities in the reference gas can also be used for sensor elements for planar broadband probes, as described in DE 199 41 051 AI, or for so-called finger probes λ = 1 or step probes, as described in DE 43 12 506 AI are described, can be brought about. The invention can also be used with the same advantage in the case of sensor elements equipped with a reference electrode 14 for pressure measurement in a gas, in particular in the exhaust gas of an internal combustion engine.

Claims

Patentansprüche claims
1. Sensorelement zur Bestimmung einer physikalischen Eigenschaft eines Messgases, insbesondere des Drucks oder der Konzentration einer Gaskomponente in einem Messgas, insbesondere im Abgas einer Brennkraftmaschine, mit einer dem Messgas ausgesetzten Elektrode (12) und mit einer durch ein poröses Volumen hindurch einem Referenzgas, insbesondere Umgebungsluft, ausgesetzten Referenzelektrode (14), die durch einen Festelektrolyten vonein- ander getrennt sind, dadurch gekennzeichnet, dass das Volumenmaterial bezüglich seiner physikalischen und chemischen Eigenschaften so ausgewählt ist, dass im Referenzgas enthaltene Fremdstoffe im Volumen gebunden und/oder zu einer chemischen Reaktion veranlasst werden.1. Sensor element for determining a physical property of a measurement gas, in particular the pressure or the concentration of a gas component in a measurement gas, in particular in the exhaust gas of an internal combustion engine, with an electrode (12) exposed to the measurement gas and with a reference gas, in particular through a porous volume Ambient air, exposed reference electrode (14), which are separated from each other by a solid electrolyte, characterized in that the bulk material is selected with regard to its physical and chemical properties so that foreign substances contained in the reference gas are bound in volume and / or cause a chemical reaction become.
2. Sensorelement nach Anspruch 1, dadurch gekennzeichnet, dass die Referenzelektrode (14) in einem im Festelektrolyten ausgebildeten Referenzgaskanal (15) angeordnet ist, der mit dem Referenzgas beaufschlagt ist.2. Sensor element according to claim 1, characterized in that the reference electrode (14) is arranged in a reference gas channel (15) formed in the solid electrolyte which is acted upon by the reference gas.
3. Sensorelement nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass die Referenz- elektrode (14) auf den Festelektrolyten aufgetragen ist und das poröse Volumen als poröse3. Sensor element according to claim 1 or 2, characterized in that the reference electrode (14) is applied to the solid electrolyte and the porous volume as porous
Schutzschicht die freie Elektrodenfläche der Referenzelektrode (14) vollständig bedeckt.Protective layer completely covers the free electrode surface of the reference electrode (14).
4. Sensorelement nach Anspruch 3, dadurch gekennzeichnet, dass die Schichtdicke 5 - 100 μm beträgt.4. Sensor element according to claim 3, characterized in that the layer thickness is 5 - 100 microns.
5. Sensorelement nach Anspruch 2, dadurch gekennzeichnet, dass das poröse Volumen zumindest einen der Referenzelektrode (14) vorgelagerten Kanalabschnitt des Referenzgaskanals (15) vollständig ausfüllt. 5. Sensor element according to claim 2, characterized in that the porous volume completely fills at least one of the reference electrode (14) upstream channel section of the reference gas channel (15).
6. Sensorelement nach einem der Ansprüche 1 - 5, dadurch gekennzeichnet, dass die Porosität des Volumens 20 - 60% beträgt.6. Sensor element according to one of claims 1-5, characterized in that the porosity of the volume is 20-60%.
7. Sensorelement nach einem der Ansprüche 1 - 6, dadurch gekennzeichnet, dass das Volu- menmaterial aus folgenden Komponenten mit den genannten Anteilen zusammengesetzt ist:7. Sensor element according to one of claims 1-6, characterized in that the bulk material is composed of the following components with the stated proportions:
Y203/Zr02 30 - 70%Y 2 0 3 / Zr0 2 30 - 70%
A1203 30 - 70%A1 2 0 3 30 - 70%
Li203 0 - 20%Li 2 0 3 0 - 20%
CaO 0 - 20%CaO 0 - 20%
MgO 0 - 20%MgO 0-20%
Ti02 0 - 20%Ti0 2 0 - 20%
Ce02 0 - 20% Ce0 2 0 - 20%
EP05743048A 2004-06-05 2005-04-27 Sensor element for determining a physical property of a test gas Withdrawn EP1756560A1 (en)

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