WO2001022073A1 - Exhaust-gas sensor for igniting an exothermal reaction - Google Patents

Exhaust-gas sensor for igniting an exothermal reaction Download PDF

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Publication number
WO2001022073A1
WO2001022073A1 PCT/DE2000/002912 DE0002912W WO0122073A1 WO 2001022073 A1 WO2001022073 A1 WO 2001022073A1 DE 0002912 W DE0002912 W DE 0002912W WO 0122073 A1 WO0122073 A1 WO 0122073A1
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WO
WIPO (PCT)
Prior art keywords
exhaust gas
heating
gas sensor
temperature
sensor according
Prior art date
Application number
PCT/DE2000/002912
Other languages
German (de)
French (fr)
Inventor
Helmut Weyl
Konrad Henkelmann
Wilhelm Sorg
Original Assignee
Robert Bosch Gmbh
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 Robert Bosch Gmbh filed Critical Robert Bosch Gmbh
Priority to EP00969204A priority Critical patent/EP1216413A1/en
Priority to JP2001525195A priority patent/JP2003510493A/en
Publication of WO2001022073A1 publication Critical patent/WO2001022073A1/en

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Classifications

    • 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
    • F02D41/1493—Details
    • F02D41/1494—Control of sensor heater
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/024—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to increase temperature of the exhaust gas treating apparatus
    • F02D41/025—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to increase temperature of the exhaust gas treating apparatus by changing the composition of the exhaust gas, e.g. for exothermic reaction on exhaust gas treating apparatus
    • 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
    • G01N27/4067—Means for heating or controlling the temperature of the solid electrolyte
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the invention relates to an exhaust gas sensor with a housing for mounting in an exhaust gas line of an internal combustion engine, a heating device and a sensor element held in the housing, which can be heated to a first temperature suitable for measuring the exhaust gas.
  • an exhaust gas sensor is known for example from DE 41 26 378 AI.
  • Such sensors are used for regulating the air-fuel mixture with which the internal combustion engine is supplied, in order to achieve the lowest possible pollutant contents in the exhaust gases in cooperation with a downstream catalytic converter.
  • the invention shows a way how the energy contained in unburned exhaust gas components of the internal combustion engine can be used with little effort and in a short time after the start of the internal combustion engine for rapid warming up of a catalytic converter without constructive changes in the exhaust gas line of the internal combustion engine being required for this.
  • an exhaust gas sensor of the type defined at the beginning of the description which has a heating power supply which, in a first operating phase, has a high output for quickly heating a component of the exhaust gas sensor exposed to the exhaust gas to one for igniting a thermal afterburning of the unburned components sufficient second temperature and in a subsequent second phase of operation provides a lower power to keep the sensor learning ts at the first temperature.
  • the heating device can be divided into two heating circuits, the first of which is designed to maintain the first temperature and the second for rapid heating to the second temperature.
  • the first heating circuit is intended to be operated continuously as long as the internal combustion engine is running, whereas the second is only to be operated in the starting phase before the catalytic converter has reached its working temperature, that is to say the first temperature.
  • the component to be heated can be a section of the sensor element made of ceramic material.
  • a sensor element conventionally comprises a first heating device in order to heat a solid electrolyte enclosed between two measuring electrodes to a temperature at which a measurable ion current, which is dependent on the oxygen content of the exhaust gas, flows between the electrodes.
  • this heating device can comprise a single heating circuit, which is designed for a greater heating power, which allows it to
  • the housing of the exhaust gas sensor has a shielding body for protecting the ceramic sensor element against direct flow against the exhaust gas and the solids therein, and the shielding body contains the component which can be heated to the second temperature.
  • the heated shielding body not only prevents a direct impact of colder exhaust gases on the hot sensor element during the starting phase of the internal combustion engine, but also preheats the portion of the exhaust gas that reaches the sensor element, so that temperature shocks are avoided otherwise can lead to cracking and thus to the destruction of the sensor element.
  • a simple way of limiting the power output by the heating power supply to a lower value than in the first during the second operating phase is to deliver a pulsed heating current by the heating power supply.
  • the heating power supply monitors the internal resistance of the sensor element in accordance with a preferred variant and changes from the first to the second operating phase when the internal resistance falls below a limit value. Since the ionic conductivity of the sensor element increases with increasing temperature, a strong reduction in the internal resistance of the sensor element corresponds to a significant increase in the temperature, and if this temperature has a value exceeds, which is above that which would be expected at the heating power used for the sensor element in the absence of the afterburning reaction, this is an indication that the afterburning has started.
  • the internal resistance of the heating device which increases with increasing temperature, is used by the heating power supply monitoring the internal resistance and changing from the first to the second operating phase when the residual resistance exceeds a limit value which indicates the onset of the afterburning reaction ,
  • the comparison with the limit value can be carried out cyclically and thus limited to individual discrete acquisition times.
  • the heating power supply should expediently switch to the second operating phase after a predetermined maximum duration, regardless of the value of the monitored internal resistance.
  • Figure 1 shows an axial section of part of an exhaust gas sensor according to the invention, mounted in a wall of an exhaust pipe;
  • Figure 2 shows a heater of an exhaust gas sensor and a heating power supply
  • Figure 3 shows a variant of the heating device of a sensor.
  • Figure 1 shows the head section 10 of an exhaust gas sensor in axial section. It comprises a metallic housing 12 with an external thread 13 which is tightly screwed into a wall 14 of an exhaust pipe.
  • a cylindrical longitudinal bore 15 contains a ceramic molded body 20, with a continuous bore 24 of rectangular cross section, in which a planar sensor element 26 is held and sealed by a sealing packing 33, which is received in a connection 30 on the connecting body 30 of the molded body 20.
  • contact fields 43 for tapping a measurement signal from the sensor element or for feeding a heating current for a heating device arranged at the exhaust-side end 27 and embedded in the interior of the sensor element 26.
  • the exhaust-side end 27 of the sensor element 26 protrudes from the housing 12 and is surrounded by a double-walled protective tube 40 with a plurality of gas inlet and outlet openings 41.
  • the sensor element 26 is made up of a plurality of sintered ceramic layers which form porous measuring electrodes, an interposed solid electrolyte, covering and insulating layers. A conductor is embedded between two insulating layers and forms a resistance heating device.
  • FIG. 2 shows such a sensor 26 in section along the plane of the heating device 2.
  • the heating device 2 conventionally comprises a heating meander 3, which is arranged near the exhaust-side end 27 for heating the solid electrolyte, and conductor tracks 4, which connect the heating meander 3 with contact pads 43 Connect at the contact end of the sensor element.
  • a heating current supply 5 is connected to these contact fields, a measuring instrument 6 is shown schematically in one of the lines between the heating current supply 5 and the sensor element 26.
  • a drawn diagram illustrates the mode of operation of the heating power supply 5.
  • the current consumption of the heating device 2 is measured with the aid of the measuring device 6, and the power supply 5 compares at regular intervals of approx. - 8th -
  • the measured value with a predetermined limit value.
  • the heating current initially decreases because the resistance of the heating device increases with increasing self-heating.
  • the limit value " is set in such a way that it allows the difference between these two stages of heating to be recorded.
  • this limit value must be selected depending on the specific operating conditions of the sensor; a typical temperature at which the afterburning starts can be Depending on the concentration of the unburned constituents in the exhaust gas and the residual oxygen content, deviations upwards and downwards are possible ..
  • the heating power is selected so that ignition is typically achieved within 3 to 4 s after the start of heating ,
  • the heating power supply 5 changes from its first operating phase, in which it supplies an increased, in the example continuous output voltage, to a second operating phase, in which it delivers a pulsed one
  • Output voltage supplies can be applied.
  • the pulse duty factor of the heating power supply 5 in the second operating phase is determined such that a functional temperature, referred to here as the first temperature, required for the measuring operation of the sensor element is continuously maintained.
  • the heating power supply 5 changes to the second operating phase, regardless of the measured value supplied by the measuring instrument 6, in order to damage the sensor and its environment as a result of overheating to avoid.
  • FIG. 3 shows a heating device 2 'of a sensor element 26 according to a variant of the invention.
  • the heating device comprises two separate heating meanders 3 'and 3' ', each of which is connected via its own supply lines 4', 4 '' to contact fields at the contact-side end of the sensor element.
  • the heating meander 3 ′′ is arranged below (not shown) measuring electrodes of the sensor element 26 in order to heat them up to their functional temperature.
  • the two heating meanders 3 ', 3'' are each connected to separate outputs of a heating power supply (not shown), the current consumption of one of them, preferably the heating meander 3', is measured with a measuring instrument as in the case of FIG.
  • the measuring instrument is shown separately symbolically, but can expediently be integrated into the heating power supply.
  • the heating power supply has two like that in FIG Operating phases on, a first that starts and continues with the start of the internal combustion engine until it can be concluded from the measured value of the detected current that the onset of the post-combustion reaction, or until a maximum duration of the first operating phase has been exceeded, and a subsequent second operating phase , In this second operating phase, the heating current supply interrupts the current to the heating meander 3 'and only maintains that to the heating meander 3''.
  • the exhaust side end 27 of the sensor element 26 is thus heated ' by means of heating meander 3' very quickly, preferably within a few seconds, to the temperature required to ignite the afterburning.
  • the heating current supply can also supply a fixed output current instead of a fixed output voltage, with a voltage measuring instrument then being used as the measuring instrument for measuring the heating power. Any other type of temperature measurement is also suitable.
  • the measuring instrument could also be arranged in the circuit of the measuring electrodes in order to detect an ion current flowing between them in a temperature-dependent manner.
  • This variant is particularly useful when a heating element is used both for quickly heating the sensor element to the post-combustion temperature and for maintaining a working temperature, as in the case of FIG. 2.
  • provision is made to attach a heating element for quickly igniting the afterburning to a shielding body, which further protects the ceramic sensor element 26 against direct flow by cold exhaust gas in a starting phase of the internal combustion engine, for example on the double-walled protective tube 40 from FIG 1.
  • Such a variant has the advantage that it reaches a large exhaust gas volume and heats it in a short time, and that at the same time it preheats part of the exhaust gas stream that reaches the sensor element 26, so that temperature shocks, which lead to cracking on the sensor element and thus its destruction can be effectively avoided.
  • the evaluation of the current in the measuring circuit of the ceramic exhaust gas sensor would also be considered, since the sensor element is also exposed to the exhaust gas stream, which may be more heated by post-combustion, and thus supplies a measuring current dependent on its temperature.
  • the heating power supply can already transition to its second operating state or be switched off.

Abstract

The invention relates to an exhaust-gas sensor which comprises a housing for the assembly in an exhaust-gas pipe in an internal combustion engine. The inventive sensor also comprises a heating device (2) and a sensor element (26) that is held in the housing and can be heated to a first temperature for measuring the exhaust-gas. A heating current supply (5) provides high power in a first operating phase for quickly heating a component of the exhaust-gas sensor (26) to a second temperature which is sufficient for igniting afterburning of the exhaust-gas, whereby said component is exposed to the exhaust-gas. The heating current supply (5) provides lower power in a following, second operating phase for maintaining the sensor element (26) at the first temperature.

Description

Abgassensor zum Zünden einer exothermen ReaktionExhaust gas sensor to ignite an exothermic reaction
Die Erfindung betrifft einen Abgassensor mit einem Gehäuse zur Montage in einer Abgasleitung einer Brennkraftmaschine, einer Heizeinrichtung und einem in dem Gehäuse gehalterten Sensorelement, das auf eine erste, zum Messen des Abgases geeignete Temperatur beheizbar ist. Ein solcher Abgassensor ist zum Beispiel aus DE 41 26 378 AI bekannt.The invention relates to an exhaust gas sensor with a housing for mounting in an exhaust gas line of an internal combustion engine, a heating device and a sensor element held in the housing, which can be heated to a first temperature suitable for measuring the exhaust gas. Such an exhaust gas sensor is known for example from DE 41 26 378 AI.
Derartige Sensoren werden eingesetzt für die Regelung des Luftkraftstoffgemisches, mit dem die Brennkraftmaschine versorgt wird, um in Zusammen- wirken mit einem nachgeschalteten Katalysator möglichst niedrige Schadstoffgehalte der Abgase zu erzielen.Such sensors are used for regulating the air-fuel mixture with which the internal combustion engine is supplied, in order to achieve the lowest possible pollutant contents in the exhaust gases in cooperation with a downstream catalytic converter.
Um künftige Abgasgrenzwerte sicher einzuhalten, ist eine stetige Weiterentwicklung der Techniken zur Abgasnachbehandlung erforderlich. Ein wesentlicher Anteil des Rest-Schadstoffausstoßes von Brennkraftmaschinen mit Katalysator entfällt auch in deren Startphase, in der der Katalysator die zu einem ef- fizienten Betrieb erforderliche Temperatur noch nicht erreicht hat . Es besteht daher großes Interesse an Mitteln, mit denen ein solcher Katalysator nach dem Starten der Brennkraftmaschine so schnell wie möglich auf seine Arbeitstemperatur erhitzt werden kann. Der wohl wirtschaftlichste Weg hierzu ist die Nutzung von exothermen Reaktionen, das heißt die Nachverbrennung unverbrannter Abgasbe- standteile wie CO und diversen Kohlenwasserstoffen im Abgasstrang zwischen dem Auslaß der Brenn- kraftmaschine und dem Einlaß des Katalysators. Kon- struktive Änderungen des Abgasstrangs zu diesem Zweck sind kostenaufwendig und zumeist bei bereits in Betrieb genommenen Brennkraftmaschinen nicht nachträglich durchsetzbar und allein nicht zielführend.In order to reliably comply with future exhaust gas limit values, continuous further development of exhaust aftertreatment techniques is necessary. A significant proportion of the residual pollutant emissions of internal combustion engines with catalytic converters is also eliminated in their start-up phase, in which the catalytic converter has not yet reached the temperature required for efficient operation. There is therefore great interest in means by which such a catalytic converter can start so quickly after starting the internal combustion engine can be heated to its working temperature as possible. The most economical way to do this is to use exothermic reactions, that is, the afterburning of unburned exhaust gas components such as CO and various hydrocarbons in the exhaust line between the outlet of the internal combustion engine and the inlet of the catalytic converter. Structural changes to the exhaust system for this purpose are costly and, in most cases, cannot be carried out retrospectively in internal combustion engines that have already been put into operation and alone are not effective.
Vorteile der ErfindungAdvantages of the invention
Die Erfindung weist einen Weg, wie die in unverbrannten Abgasbestandteilen der Brennkraftmaschine enthaltene Energie mit geringem Aufwand und in kurzer Zeit nach dem Start der Brennkraftmaschine zur raschen Aufwärmung eines Katalysators nutzbar gemacht werden kann, ohne daß hierfür konstruktive Veränderungen im Abgasstrang der Brennkraftmaschine erforderlich sind. Es wird zu diesem Zweck lediglich ein Abgassensor der zu Beginn der Beschreibung definierten Art benötigt, der eine Heizstromversorgung besitzt, die in einer ersten Betriebspha.se eine hohe Leistung zum schnellen Erhitzen eines dem Abgas ausgesetzten Bauteils des Abgassensors auf eine zum Zünden einer thermischen Nachverbrennung der unverbrannten Bestandteile ausreichende zweite Temperatur und in einer darauffolgenden zweiten Betriebsphase eine niedrigere Leistung zum Halten des Sensorelerne ts auf der ersten Temperatur bereitstellt. Um bei einer herkömmlichen Brennkraftmaschine mit Katalysator eine deutliche Verringerung des Schadstoffausstoßes in der Startphase zu erzielen, genügt es, deren herkömmlichen Abgassensor durch einen nach der vorliegenden Er- findung zu ersetzen.The invention shows a way how the energy contained in unburned exhaust gas components of the internal combustion engine can be used with little effort and in a short time after the start of the internal combustion engine for rapid warming up of a catalytic converter without constructive changes in the exhaust gas line of the internal combustion engine being required for this. All that is required for this purpose is an exhaust gas sensor of the type defined at the beginning of the description, which has a heating power supply which, in a first operating phase, has a high output for quickly heating a component of the exhaust gas sensor exposed to the exhaust gas to one for igniting a thermal afterburning of the unburned components sufficient second temperature and in a subsequent second phase of operation provides a lower power to keep the sensor learning ts at the first temperature. To at a conventional In order to achieve a significant reduction in pollutant emissions in the starting phase of an internal combustion engine with a catalyst, it is sufficient to replace its conventional exhaust gas sensor with one according to the present invention.
Die Heizeinrichtung kann in zwei Heizkreise unterteilt sein, von denen der erste zum Aufrechterhalten der ersten Temperatur und der zweite zum schnellen Aufheizen auf die zweite Temperatur angelegt ist. Der erste Heizkreis ist vorgesehen, um ständig betrieben zu werden, solange die Brennkraftmaschine läuft, wohingegen der zweite nur in der Startphase betrieben werden soll, bevor der Ka- talysator seine Arbeitstemperatur, das heißt die erste Temperatur, erreicht hat.The heating device can be divided into two heating circuits, the first of which is designed to maintain the first temperature and the second for rapid heating to the second temperature. The first heating circuit is intended to be operated continuously as long as the internal combustion engine is running, whereas the second is only to be operated in the starting phase before the catalytic converter has reached its working temperature, that is to say the first temperature.
Bei dem zu erhitzenden Bauteil kann es sich einer ersten Ausgestaltung der Erfindung zufolge um einen Abschnitt des Sensorelements aus Keramikmaterial handeln. Ein solches Sensorelement umfaßt herkömmlicherweise erste Heizeinrichtung, um einen zwischen zwei Meßelektroden eingeschlossenen festen Elektrolyten auf eine Temperatur zu erhitzen, bei der zwischen den Elektroden ein meßbarer, vom Sau- erstoffgehalt des Abgases abhängiger Ionenstrom fließt. Einer Variante dieser Ausgestaltung zufolge kann diese Heizeinrichtung einen einzelnen Heizkreis umfassen, der für eine größere Heizleistung ausgelegt ist, die es erlaubt, die zumAccording to a first embodiment of the invention, the component to be heated can be a section of the sensor element made of ceramic material. Such a sensor element conventionally comprises a first heating device in order to heat a solid electrolyte enclosed between two measuring electrodes to a temperature at which a measurable ion current, which is dependent on the oxygen content of the exhaust gas, flows between the electrodes. According to a variant of this embodiment, this heating device can comprise a single heating circuit, which is designed for a greater heating power, which allows it to
Zünden der Nachverbrennung erforderliche zweite Temperatur in kurzer Zeit, vorzugsweise in nicht mehr als 5 Sekunden, zu erreichen. Einer zweiten Ausgestaltung der Erfindung zufolge weist das Gehäuse des Abgassensors einen Abschirmkörper zum Schutz des keramischen Sensorelements vor einem direkten Anströmen durch das Abgas und die darin befindlichen Feststoffe auf, und der Abschirmkδrper beinhaltet das auf die zweite Temperatur erhitzbare Bauteil . Ein Vorteil dieser Ausgestaltung ist, daß der beheizte Abschirmkörper nicht nur einen direkten Aufprall von kälteren Abgasen auf das heiße Sensorelement während der Startphase der Brennkraftmaschine verhindert, sondern zusätzlichen denjenigen Anteil des Abgases, der das Sensorelement erreicht, vorheizt, so daß Temperaturschocks vermieden werden, die andernfalls zu Rißbildung und damit zur Zerstörung des Sensorelements führen können.Ignition of the afterburning required second temperature to be reached in a short time, preferably in no more than 5 seconds. According to a second embodiment of the invention, the housing of the exhaust gas sensor has a shielding body for protecting the ceramic sensor element against direct flow against the exhaust gas and the solids therein, and the shielding body contains the component which can be heated to the second temperature. An advantage of this embodiment is that the heated shielding body not only prevents a direct impact of colder exhaust gases on the hot sensor element during the starting phase of the internal combustion engine, but also preheats the portion of the exhaust gas that reaches the sensor element, so that temperature shocks are avoided otherwise can lead to cracking and thus to the destruction of the sensor element.
Eine einfache Möglichkeit, die von der Heizstromversorgung abgegebene Leistung während der zweiten Betriebsphase auf einen niedrigeren Wert als in der ersten zu begrenzen, ist die Abgabe eines gepulsten Heizstroms durch die Heizstromversorgung.A simple way of limiting the power output by the heating power supply to a lower value than in the first during the second operating phase is to deliver a pulsed heating current by the heating power supply.
Um das Einsetzen der Nachverbrennungsreaktion zu- verlässig zu erkennen, überwacht die Heizstromversorgung gemäß einer bevorzugten Variante den Innenwiderstand des Sensorelements und wechselt von der ersten in die zweite Betriebsphase, wenn der Innenwiderstand einen Grenzwert unterschreitet . Da die Ionenleitfähigkeit des Sensorelements mit steigender Temperatur zunimmt, entspricht eine starke Verringerung des Innenwiderstands des Sensorelements einer deutlichen Steigerung der Temperatur, und wenn diese Temperatur einen Wert überschreitet, der oberhalb von demjenigen liegt, der bei der eingesetzten Heizleistung für das Sensorelement in Abwesenheit der Nachverbrennungsreaktion zu erwarten wäre, so ist dies ein Hinweis darauf, daß die Nachverbrennung in Gang gekommen ist .In order to reliably detect the onset of the afterburning reaction, the heating power supply monitors the internal resistance of the sensor element in accordance with a preferred variant and changes from the first to the second operating phase when the internal resistance falls below a limit value. Since the ionic conductivity of the sensor element increases with increasing temperature, a strong reduction in the internal resistance of the sensor element corresponds to a significant increase in the temperature, and if this temperature has a value exceeds, which is above that which would be expected at the heating power used for the sensor element in the absence of the afterburning reaction, this is an indication that the afterburning has started.
Gemäß einer zweiten bevorzugten Variante wird der mit steigender Temperatur anwachsende Innenwider- stand der Heizeinrichtung ausgenutzt, indem die Heizstromversorgung den Innenwiderstand überwacht und von der ersten in die zweite Betriebsphase wechselt, wenn der Irmenwiderstand einen Grenzwert überschreitet, der auf das Einsetzen der Nachver- brennungsreaktion hinweist.According to a second preferred variant, the internal resistance of the heating device, which increases with increasing temperature, is used by the heating power supply monitoring the internal resistance and changing from the first to the second operating phase when the residual resistance exceeds a limit value which indicates the onset of the afterburning reaction ,
Um ein zu frühes Wechseln in die zweite Betriebsphase zu vermeiden, bevor die Nachverbrennung sicher in Gang gekommen ist, kann der Vergleich mit dem Grenzwert zyklisch und somit auf einzelne diskrete Erfassungszeitpunkte begrenzt durchgeführt werden.In order to avoid an early change to the second operating phase before the afterburning has started, the comparison with the limit value can be carried out cyclically and thus limited to individual discrete acquisition times.
Um unter anomalen Bedingungen eine Überhitzung zu vermeiden, die zu Schäden am Abgassensor, der Brennkraftmaschine oder dem Katalysator führen könnte, sollte die Heizstromversorgung zweckmäßigerweise nach einer vorgegebenen Maximaldauer unabhängig vom Wert des überwachten Innenwiderstands in die zweite Betriebsphase wechseln.In order to avoid overheating under abnormal conditions, which could lead to damage to the exhaust gas sensor, the internal combustion engine or the catalytic converter, the heating power supply should expediently switch to the second operating phase after a predetermined maximum duration, regardless of the value of the monitored internal resistance.
Weitere Vorteile und Merkmale der Erfindung ergeben sich aus der nachfolgenden Beschreibung von Ausführungsbeispielen mit Bezug auf die Figuren. -6-Further advantages and features of the invention result from the following description of exemplary embodiments with reference to the figures. -6-
Figurencharacters
Figur 1 zeigt in einem axialen Schnitt einen Teil eines Abgassensors gemäß der Erfindung, montiert in einer Wand einer Abgasleitung; ^ Figure 1 shows an axial section of part of an exhaust gas sensor according to the invention, mounted in a wall of an exhaust pipe; ^
Figur 2 zeigt eine Heizeinrichtung eines Abgassensors und eine Heizstromversorgung; undFigure 2 shows a heater of an exhaust gas sensor and a heating power supply; and
Figur 3 zeigt eine Variante der Heizeinrichtung eines Sensors.Figure 3 shows a variant of the heating device of a sensor.
Figur 1 zeigt den Kopfabschnitt 10 eines Abgassensors im axialen Schnitt. Er umfaßt ein metallisches Gehäuse 12 mit einem Außengewinde 13, das in einer Wand 14 einer Abgasleitung dicht verschraubt is . Ein zylindrische Längsbohrung 15 enthält einen keramischen Formkörper 20, mit einer durchlaufenden Bohrung 24 von rechteckigem Querschnitt, in der ein planares Sensorelement 26 gehalten und durch eine Dichtpackung 33 abgedichtet ist, die in einer an- schlußseitigen Auf eitung 30 des Formkörpers 20 aufgenommen ist . Am anschlußseitigen Ende des Sensorelements 26 befinden sich Kontaktfelder 43 zum Abgreifen eines Meßsignals des Sensorelements beziehungsweise zum Einspeisen eines Heizstroms für eine am abgasseitigen Ende 27 angeordnete, im Inneren des Sensorelements 26 eingebettete Heizeinrichtung . Das abgasseitige Ende 27 des Sensorelements 26 ragt aus dem Gehäuse 12 heraus und ist von einem doppel- wandigen Schutzrohr 40 mit einer Mehrzahl von Gas- ein- und -auslaßδffnungen 41 umgeben.Figure 1 shows the head section 10 of an exhaust gas sensor in axial section. It comprises a metallic housing 12 with an external thread 13 which is tightly screwed into a wall 14 of an exhaust pipe. A cylindrical longitudinal bore 15 contains a ceramic molded body 20, with a continuous bore 24 of rectangular cross section, in which a planar sensor element 26 is held and sealed by a sealing packing 33, which is received in a connection 30 on the connecting body 30 of the molded body 20. At the connection-side end of the sensor element 26 there are contact fields 43 for tapping a measurement signal from the sensor element or for feeding a heating current for a heating device arranged at the exhaust-side end 27 and embedded in the interior of the sensor element 26. The exhaust-side end 27 of the sensor element 26 protrudes from the housing 12 and is surrounded by a double-walled protective tube 40 with a plurality of gas inlet and outlet openings 41.
Das Sensorelement 26 ist aus einer Mehrzahl von gesinterten Kera ikschichten aufgebaut, die poröse Meßelektroden, einen dazwischenliegenden festen Elektrolyten, Abdeck- und Isolierschichten bilden. Zwischen zwei Isolierschichten ist ein Leiter eingebettet, der eine Widerstands-Heizeinrichtύng bildet.The sensor element 26 is made up of a plurality of sintered ceramic layers which form porous measuring electrodes, an interposed solid electrolyte, covering and insulating layers. A conductor is embedded between two insulating layers and forms a resistance heating device.
Figur 2 zeigt einen solchen Sensor 26 im Schnitt entlang der Ebene der Heizeinrichtung 2. Die Heizeinrichtung 2 umfaßt in herkömmlicher Weise einen in der Nähe des abgasseitigen Endes 27 zum Beheizen des festen Elektrolyten angeordneten Heizmäander 3 sowie Leiterbahnen 4, die den Heizmäander 3 mit Kontaktfeidern 43 am kontaktseitigen Ende des Sensorelements verbinden. An diese Kontaktfeider ist eine Heizstromversorgung 5 angeschlossen, ein Meßinstrument 6 ist schematisch in einer der Leitungen zwischen der Heizstromversorgung 5 und dem Sensore- lement 26 dargestellt. Ein eingezeichnetes Diagramm veranschaulicht die Arbeitsweise der Heizstromversorgung 5. Der Zeitpunkt t=0 im Koordinatenursprung des Diagramms entspricht dem Anlassen der Brennkraftmaschine . Ab diesem Zeitpunkt liefert die Heizstromversorgung 5 zunächst kontinuierlich eine VersorgungsSpannung U an die Heizeinrichtung 2. Die Stromaufnahme der Heizeinrichtung 2 wird mit Hilfe des Meßgeräts 6 gemessen, und die Stromversorgung 5 vergleicht in regelmäßigen Zeitabständen von ca. - 8 -FIG. 2 shows such a sensor 26 in section along the plane of the heating device 2. The heating device 2 conventionally comprises a heating meander 3, which is arranged near the exhaust-side end 27 for heating the solid electrolyte, and conductor tracks 4, which connect the heating meander 3 with contact pads 43 Connect at the contact end of the sensor element. A heating current supply 5 is connected to these contact fields, a measuring instrument 6 is shown schematically in one of the lines between the heating current supply 5 and the sensor element 26. A drawn diagram illustrates the mode of operation of the heating power supply 5. The time t = 0 in the coordinate origin of the diagram corresponds to the starting of the internal combustion engine. From this point in time, the heating power supply 5 initially continuously supplies a supply voltage U to the heating device 2. The current consumption of the heating device 2 is measured with the aid of the measuring device 6, and the power supply 5 compares at regular intervals of approx. - 8th -
1/2 bis l Sekunden den Meßwert mit einem vorgegebenen Grenzwert. Im Laufe des Aufheizens des Sensorelements 26 nimmt die Heizstromstärke zunächst ab, weil der Widerstand der Heizeinrichtung mit zunehmender Eigenerwärmung steigt. Sobald durch das Zünden der unverbrauchten Abgasbestandteile durch das glühende Sensorelement die Nachverbrennung einsetzt, führt diese zu einer zusätzlichen, von außen aufgeprägten Erwärmung der Heizeinrichtung, die zu einer weiteren Verringerung der Heizstromstärke führt. Der Grenzwert" ist so festgelegt, daß er den Unterschied zwischen diesen zwei Etappen der Erwärmung zu erfassen gestattet . Der genaue Wert dieses Grenzwerts ist in Abhängigkeit von den konkreten Ξinsatzbedingungen des Sensors zu wählen; eine typische Temperatur, bei der die Nachverbrennung einsetzt, kann im Bereich von ca. 800°C liegen, je nach Konzentration der unverbrannten Bestandteile im Abgas und dem Restsauerstoffgehalt sind Abweichungen nach oben und unten möglich. Die Heizleistung ist so gewählt, daß ein Zünden typischerweise innerhalb von 3 bis 4 s nach Beginn des Aufheizens erreicht wird.1/2 to 1 seconds the measured value with a predetermined limit value. In the course of heating the sensor element 26, the heating current initially decreases because the resistance of the heating device increases with increasing self-heating. As soon as the afterburning starts due to the ignition of the unused exhaust gas components by the glowing sensor element, this leads to additional heating of the heating device, which is impressed from the outside, which leads to a further reduction in the heating current strength. The limit value " is set in such a way that it allows the difference between these two stages of heating to be recorded. The exact value of this limit value must be selected depending on the specific operating conditions of the sensor; a typical temperature at which the afterburning starts can be Depending on the concentration of the unburned constituents in the exhaust gas and the residual oxygen content, deviations upwards and downwards are possible .. The heating power is selected so that ignition is typically achieved within 3 to 4 s after the start of heating ,
Wenn der Vergleich ergibt, daß der Grenzwert erreicht oder überschritten ist, wechselt die Heiz- stromversorgung 5 aus ihrer ersten Betriebsphase, in der sie eine erhöhte, im Beispiel kontinuierliche AusgangsSpannung liefert, in eine zweite Betriebsphase, in der sie eine gepulsteIf the comparison shows that the limit value has been reached or exceeded, the heating power supply 5 changes from its first operating phase, in which it supplies an increased, in the example continuous output voltage, to a second operating phase, in which it delivers a pulsed one
AusgangsSpannung liefert. Alternativ dazu wäre es auch möglich, in der zweiten Betriebsphase eine kontinuierliche AusgangsSpannung mit einem niedrigeren Wert als in der ersten Phase zu liefern. Das Tastverhältnis der Heizstromversorgung 5 in der zweiten Betriebsphase ist so festgelegt, daß eine hier als erste Temperatur bezeichnete für den Meßbetrieb des Sensorelements erforderliche Funktions-Temperatur kontinuierlich aufrechterhalten wird.Output voltage supplies. Alternatively, it would also be possible to apply a continuous output voltage with a lower value in the second operating phase than in the first phase deliver. The pulse duty factor of the heating power supply 5 in the second operating phase is determined such that a functional temperature, referred to here as the first temperature, required for the measuring operation of the sensor element is continuously maintained.
Wenn nach einer vorgegebenen Maximaldauer der ersten Betriebsphase von zum Beispiel 15 bis 30 Se- künden der Grenzwert nicht überschritten worden ist, wechselt die Heizstromversorgung 5 unabhängig vom vom Meßinstrument 6 gelieferten Meßwert in die zweite Betriebsphase, um Schäden am Sensor und dessen Umgebung infolge von Überhitzung zu vermeiden.If, after a predetermined maximum duration of the first operating phase of, for example, 15 to 30 seconds, the limit value has not been exceeded, the heating power supply 5 changes to the second operating phase, regardless of the measured value supplied by the measuring instrument 6, in order to damage the sensor and its environment as a result of overheating to avoid.
Figur 3 zeigt eine Heizeinrichtung 2' eines Sensorelements 26 gemäß einer Variante der Erfindung. Die Heizeinrichtung umfaßt zwei getrennte Heizmäander 3' und 3'', die jeweils über eigene Zuleitungen 4', 4'' mit Kontaktfeldern am kontaktseitigen Ende des Sensorelements verbunden sind. Der Heizmäander 3'' ist unterhalb von (nicht dargestellten) Meßelektroden des Sensorelements 26 angeordnet, um diese auf ihre Funktionstemperatur zu erhitzen.Figure 3 shows a heating device 2 'of a sensor element 26 according to a variant of the invention. The heating device comprises two separate heating meanders 3 'and 3' ', each of which is connected via its own supply lines 4', 4 '' to contact fields at the contact-side end of the sensor element. The heating meander 3 ″ is arranged below (not shown) measuring electrodes of the sensor element 26 in order to heat them up to their functional temperature.
Die zwei Heizmäander 3 ',3'' sind jeweils an eigene Ausgänge einer (nicht dargestellten) Heizstromversorgung angeschlossen, die Stromaufnahme von einem von ihnen, vorzugsweise des Heizmäanders 3', wird wie im Falle von Figur 2 mit einem Meßinstrument gemessen. Das Meßinstrument ist symbolisch separat dargestellt, kann aber zweckmäßigerweise in die HeizStromversorgung integriert sein. Die Heizstromversorgung weist wie die aus Figur 2 zwei Betriebsphasen auf, eine erste, die mit dem Starten der Brennkraftmaschine beginnt und andauert, bis aus dem gemessenen Wert der erfaßten Stromstärke auf das Einsetzen der Nachverbrennungsreaktion gefolgert werden kann, oder bis eine maximale Dauer der ersten Betriebsphase überschritten ist, und eine daran anschließende zweite Betriebsphase. In dieser zweiten Betriebsphase unterbricht die Heizstromversorgung den Strom zum Heizmäander 3 ' und erhält nur den zum Heizmäander 3'' aufrecht. Bei dieser Variante des Abgassensors wird' mittels Heizmäander 3' somit das abgasseitige Ende 27 des Sensorelements 26 sehr schnell, vorzugsweise innerhalb weniger Sekunden, auf die zum Zünden der Nachverbrennung erforderliche Temperatur erhitzt.The two heating meanders 3 ', 3''are each connected to separate outputs of a heating power supply (not shown), the current consumption of one of them, preferably the heating meander 3', is measured with a measuring instrument as in the case of FIG. The measuring instrument is shown separately symbolically, but can expediently be integrated into the heating power supply. The heating power supply has two like that in FIG Operating phases on, a first that starts and continues with the start of the internal combustion engine until it can be concluded from the measured value of the detected current that the onset of the post-combustion reaction, or until a maximum duration of the first operating phase has been exceeded, and a subsequent second operating phase , In this second operating phase, the heating current supply interrupts the current to the heating meander 3 'and only maintains that to the heating meander 3''. In this variant of the exhaust gas sensor, the exhaust side end 27 of the sensor element 26 is thus heated ' by means of heating meander 3' very quickly, preferably within a few seconds, to the temperature required to ignite the afterburning.
Selbstverständlich kann die Heizstromversorgung anstelle einer festen Ausgangsspannung auch einen festen Ausgangsstrom liefern, wobei dann als Meßin- strument zum Erfassen der Heizleistung ein Span- nungsmeßinstrument eingesetzt wird. Jede andere Art der Erfassung der Temperatur ist auch geeignet.Of course, the heating current supply can also supply a fixed output current instead of a fixed output voltage, with a voltage measuring instrument then being used as the measuring instrument for measuring the heating power. Any other type of temperature measurement is also suitable.
Einer weiteren Alternative zufolge könnte das MeS- instrument auch im Stromkreis der Meßelektroden angeordnet sein, um einen zwischen diesen temperaturabhängig fließenden Ionenstrom zu erfassen. Diese Variante bietet sich insbesondere dann an, wenn ein Heizelement sowohl zum schnellen Erhitzen des Sensorelements auf die Nachverbrennungstemperatur wie auch zum Aufrechterhalten einer Arbeitstemperatur verwendet wird, wie im Falle der Figur 2. Einer weiteren alternativen Ausgestaltung zufolge ist vorgesehen, ein Heizelement zum schnellen Zünden der Nachverbrennung an einem Abschirmkδrper anzubringen, der ferner das keramische Sen- sorelement 26 vor direktem Anströmen durch kaltes Abgas in einer Startphase der Brennkraftmaschine schützt, so etwa an dem doppelwandigen Schutzrohr 40 aus Figur 1. Eine solche Variante hat den Vorteil, daß sie ein großes Abgasvplumen erreicht und in kurzer Zeit erhitzt, und daß sie gleichzeitig einen Teil des Abgasstroms, der das Sensorelement 26 erreicht, vorheizt, so daß Temperaturschocks , die zur Rißbildung am Sensorelement und damit zu dessen Zerstörung führen können, wirksam vermieden werden. Auch hier ist eine Erfassung des Einsetzens der Nachverbrennung anhand der Temperatur des beheizten Schutzrohrs über den Innenwiderstand von dessen integriertem Heizelement möglich. Auch die Auswertung des Stroms im Meßkreis des keramischen Abgassensors käme in Betracht, da das Sensorelement ebenfalls dem gegebenenfalls durch Nachverbrennung stärker erhitzten Abgasstrom ausgesetzt ist und somit einen von dessen Temperatur abhängigen Meßstrom liefert. Zu dem Zeitpunkt, an dem der Katalysator seine für die katalytische Nachverbrennung erforderliche Temperatur erreicht hat, kann die Heizstromversorgung bereits in ihren zweiten Betriebszustand übergehen beziehungsweise abgeschaltet werden. According to a further alternative, the measuring instrument could also be arranged in the circuit of the measuring electrodes in order to detect an ion current flowing between them in a temperature-dependent manner. This variant is particularly useful when a heating element is used both for quickly heating the sensor element to the post-combustion temperature and for maintaining a working temperature, as in the case of FIG. 2. According to a further alternative embodiment, provision is made to attach a heating element for quickly igniting the afterburning to a shielding body, which further protects the ceramic sensor element 26 against direct flow by cold exhaust gas in a starting phase of the internal combustion engine, for example on the double-walled protective tube 40 from FIG 1. Such a variant has the advantage that it reaches a large exhaust gas volume and heats it in a short time, and that at the same time it preheats part of the exhaust gas stream that reaches the sensor element 26, so that temperature shocks, which lead to cracking on the sensor element and thus its destruction can be effectively avoided. Here too, it is possible to determine the onset of the afterburning on the basis of the temperature of the heated protective tube via the internal resistance of its integrated heating element. The evaluation of the current in the measuring circuit of the ceramic exhaust gas sensor would also be considered, since the sensor element is also exposed to the exhaust gas stream, which may be more heated by post-combustion, and thus supplies a measuring current dependent on its temperature. At the point in time at which the catalytic converter has reached its temperature required for catalytic afterburning, the heating power supply can already transition to its second operating state or be switched off.

Claims

Patentansprüche claims
1. Abgassensor mit einem Gehäuse (12) zur Montage in einer Abgasleitung einer Brennkraftmaschine, mit einer Heizeinrichtung (2,2') und einem in dem Gehäuse (12) gehalterten, auf eine erste Temperatur zum Messen des Abgases beheizbaren Sensorelement (26) gekennzeichnet durch eine HeizStromversorgung (5) , die in einer ersten Betriebsphase eine hohe Leistung zum schnellen Erhitzen eines dem Abgas ausgesetzten Bauteils (26,40) des Abgassensors auf eine zum Zünden einer thermischen Nachverbrennung von unverbrannten Bestandteilen des Abgases ausreichende zweite Temperatur und in einer darauffolgenden zweiten Betriebsphase eine niedrigere Leistung zum Halten des Sensorelements (26) auf der ersten Temperatur bereitstellt.1. Exhaust gas sensor with a housing (12) for mounting in an exhaust pipe of an internal combustion engine, with a heating device (2,2 ') and in the housing (12), to a first temperature for measuring the exhaust gas, heated sensor element (26) by means of a heating power supply (5) which, in a first operating phase, provides a high output for rapidly heating a component (26, 40) of the exhaust gas sensor exposed to the exhaust gas to a second temperature sufficient to ignite thermal afterburning of unburned components of the exhaust gas and in a subsequent second Operating phase provides a lower power to keep the sensor element (26) at the first temperature.
2. Abgassensor nach Anspruch 1, dadurch gekennzeichnet, daß die Heizeinrichtung (2') zwei Heizkreise (3' ,3'') umfaßt, von denen der erste (3'') zum Aufrechterhalten der ersten Temperatur ausgelegt ist, und der zweite (3') zum schnellen Aufheizen auf die zweite Temperatur ausgelegt ist.2. Exhaust gas sensor according to claim 1, characterized in that the heating device (2 ') comprises two heating circuits (3', 3 ''), of which the first (3 '') is designed to maintain the first temperature, and the second ( 3 ') is designed for rapid heating to the second temperature.
3. Abgassensor nach Anspruch 1 oder 2, dadurch ge- kennzeichnet, daß das Bauteil ein Abschnitt des keramischen Sensorelements (26) ist. 3. Exhaust gas sensor according to claim 1 or 2, characterized in that the component is a section of the ceramic sensor element (26).
4. Abgassensor nach Anspruch 3, dadurch gekennzeichnet, daß das keramische Sensorelement (26) die Heizeinrichtung (2,2') umfaßt.4. Exhaust gas sensor according to claim 3, characterized in that the ceramic sensor element (26) comprises the heating device (2,2 ').
5. Abgassensor nach Anspruch 2, dadurch gekennzeichnet, daß das Gehäuse einen Abschirmkδrper (40) zum Schutz des keramischen Sensorelements (26) vor einem direkten Anströmen durch das Abgas aufweist, und daß in dem Abschirmkδrper ( (40) das auf die zweite Temperatur erhitzbare Bauteil integriert ist.5. Exhaust gas sensor according to claim 2, characterized in that the housing has a Abschirmkδrper (40) for protecting the ceramic sensor element (26) against a direct inflow by the exhaust gas, and that in the Abschirmkδrper ( (40) that can be heated to the second temperature Component is integrated.
6. Abgassensor nach Anspruch 5, dadurch gekennzeichnet, daß das erste Heizelement am Sensorele- ment und das zweite Heizelement am Abschirmkδrper zum Zünden der Nachverbrennung angeordnet ist.6. Exhaust gas sensor according to claim 5, characterized in that the first heating element is arranged on the sensor element and the second heating element on the shielding body for igniting the afterburning.
7. Abgassensor nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Heizstrom- Versorgung (5) in der zweiten Betriebsphase einen gepulsten Heizstrom abgibt .7. Exhaust gas sensor according to one of the preceding claims, characterized in that the heating current supply (5) emits a pulsed heating current in the second operating phase.
8. Abgassensor nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Heizstrom- Versorgung (5) den Innenwiderstand des Sensorelements überwacht und von der ersten in die zweite Betriebsphase wechselt, wenn der Innenwiderstand einen Grenzwert unterschreitet.8. Exhaust gas sensor according to one of the preceding claims, characterized in that the heating current supply (5) monitors the internal resistance of the sensor element and changes from the first to the second operating phase when the internal resistance falls below a limit.
9. Abgassensor nach einem der Ansprüche 1 bis 7, dadurch gekennzeichnet, daß die HeizStromversorgung den Innenwiderstand der Heizeinrichtung (2,2') überwacht und von der ersten in die zweite Be- triebsphase wechselt, wenn der Innenwiderstand einen Grenzwert überschreitet .9. Exhaust gas sensor according to one of claims 1 to 7, characterized in that the heating power supply monitors the internal resistance of the heating device (2,2 ') and from the first to the second loading drive phase changes when the internal resistance exceeds a limit.
10. Abgassensor nach Anspruch 8 oder 9, dadurch ge- kennzeichnet, daß die Heizstromversorgung (5) den10. Exhaust gas sensor according to claim 8 or 9, characterized in that the heating power supply (5)
Vergleich zyklisch während der ersten Betriebsphase ausführt .Executes comparison cyclically during the first operating phase.
11. Abgassensor nach einem der Ansprüche 8 bis 10, dadurch gekennzeichnet, daß die Heizstromversorgung11. Exhaust gas sensor according to one of claims 8 to 10, characterized in that the heating current supply
(5) nach einer vorgegebenen Maximaldauer unabhängig vom überwachten Innenwiderstand in die zweite Betriebsphase wechselt .(5) changes to the second operating phase after a specified maximum duration regardless of the monitored internal resistance.
12. Abgassensor nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Heizeinrichtung (2,2') ausgelegt ist, um die erste Temperatur mit einer Aufheizzeit von maximal 5 Sekunden zu erreichen. 12. Exhaust gas sensor according to one of the preceding claims, characterized in that the heating device (2,2 ') is designed to reach the first temperature with a heating-up time of at most 5 seconds.
PCT/DE2000/002912 1999-09-17 2000-08-25 Exhaust-gas sensor for igniting an exothermal reaction WO2001022073A1 (en)

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EP00969204A EP1216413A1 (en) 1999-09-17 2000-08-25 Exhaust-gas sensor for igniting an exothermal reaction
JP2001525195A JP2003510493A (en) 1999-09-17 2000-08-25 Exhaust gas sensor for ignition of external thermal reactions

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DE19944555A DE19944555A1 (en) 1999-09-17 1999-09-17 Exhaust gas sensor to ignite an exothermic reaction

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