EP0268598B1 - Spark plug with surface discharge section - Google Patents

Spark plug with surface discharge section Download PDF

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Publication number
EP0268598B1
EP0268598B1 EP87902423A EP87902423A EP0268598B1 EP 0268598 B1 EP0268598 B1 EP 0268598B1 EP 87902423 A EP87902423 A EP 87902423A EP 87902423 A EP87902423 A EP 87902423A EP 0268598 B1 EP0268598 B1 EP 0268598B1
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EP
European Patent Office
Prior art keywords
spark plug
insulating body
combustion chamber
plug according
dielectric coating
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Expired
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EP87902423A
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German (de)
French (fr)
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EP0268598A1 (en
Inventor
Walter Benedikt
Werner Herden
Jürgen SCHMATZ
Siegbert Schwab
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Robert Bosch GmbH
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Robert Bosch GmbH
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Publication of EP0268598A1 publication Critical patent/EP0268598A1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
    • H01T13/00—Sparking plugs
    • H01T13/20—Sparking plugs characterised by features of the electrodes or insulation
    • H01T13/32—Sparking plugs characterised by features of the electrodes or insulation characterised by features of the earthed electrode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
    • H01T13/00—Sparking plugs
    • H01T13/52—Sparking plugs characterised by a discharge along a surface

Definitions

  • the invention relates to a spark plug with a sliding spark gap for internal combustion engines according to the preamble of claim 1.
  • Such spark plugs with sliding spark gaps which form on the combustion chamber-side surface of the insulating body between the center and ground electrodes, are distinguished by an ignition voltage that is substantially lower than that of a spark plug with air spark gap. It has been shown that the higher the dielectric constant of the insulating body material, the lower the ignition voltage.
  • such an insulating body made of high-dielectric material leads to a relatively high capacity in a spark plug, which causes a breakdown discharge at the sliding spark gap.
  • the surfaces of the electrodes and especially the slideway of the spark gap are severely eroded, which in turn significantly impairs the proper functioning of the spark plug and its service life.
  • EP-A-0.236.376 forms a state of the art according to Article 54 (3) EPC. Overall, however, the total capacity of the spark plug cannot be kept small enough, so that the energy still causes significant erosion in the insulating body surface in breakdown phases that sometimes occur.
  • the spark plug according to the invention with the characterizing features of claim 1 has the advantage that the coaxial layer structure of the insulating body or candle block results in a coaxial capacitor with a layered dielectric, the total capacity of which is due to the smaller capacitance of the low-dielectric layer, i.e. the layer with the much smaller one Dielectric constant is determined. Without increasing the candle capacity, ceramics with a relative dielectric constant of up to 10,000 can therefore be used in the high-dielectric layer if only the low-dielectric layer has a relatively small dielectric constant of approximately 10 to 50.
  • the spark plug according to the invention if an advantageously high-dielectric slideway is provided, has only a small plug capacity and, as a result, shows only slight erosions on the slideway. Due to the high dielectric constant of the insulating body surface on which the slideway is formed, the ignition voltage requirement of the spark plug is low, so that a considerable part of the energy made available by the ignition system is transferred to the fuel mixture. This creates good ignition conditions even for lean fuel mixtures. Due to the low ignition voltage requirement, all advantages of a low-voltage ignition, such as a smaller ignition coil, good interference suppression, and low expenditure on high-voltage insulation result.
  • Fig. 1 to 6 each have a spark plug half in side view and half cut longitudinally according to six different embodiments.
  • the spark plugs for internal combustion engines shown in the drawing all have an insulating body 10, which is enclosed on a longitudinal section by a metallic plug housing 11.
  • the plug housing 11 carries an external thread 13 on an end section 12 with a reduced diameter by means of which the spark plug is inserted into a cylinder head of the internal combustion engine, not shown, is screwed in.
  • a hexagon key 14 is used for screwing in.
  • the end section 12 carries an annular ground electrode 15 on its end face projecting into the combustion chamber of the internal combustion engine.
  • the rotationally symmetrical insulating body 10 which has a central axial through bore 16, projects out of the candle housing 11 on both sides thereof.
  • a metallic connecting bolt 17 is arranged within the through bore 16 and carries a connecting piece 18 for the electrical connection of the spark plug to the ignition system at its end section remote from the combustion chamber.
  • the connecting bolt 17 and the center electrode 19 are conductively connected to one another by a glass melt flow mass 20.
  • the insulating body 10 has, at least in the end section on the combustion chamber side, two coaxial material layers with completely different dielectric constants which lie completely or partially against one another in the radial direction.
  • the relative dielectric constant of the materials used is between 10 and 10,000, preferably between 50 and 5000.
  • the materials used in the two material layers are paired in such a way that the difference between their dielectric constants is as large as possible.
  • the insulating body 10 consists essentially of a completely continuous base body 21 made of aluminum oxide ceramic with a relatively low dielectric constant (less than 15), and a sleeve 22 made of high-dielectric material pushed open from the end of the base body 21 on the combustion chamber side. e.g. B. barium titanium oxide (Ba2 Ti03), with a relative dielectric constant of approx. 5000.
  • the base body 21 is reduced in diameter via an end section on the combustion chamber side.
  • the sleeve 22 extends from the front end of the base body 21 over almost the entire overlap area of the candle housing 11, while in FIG.
  • the sleeve 22 covers the base body 21 only in the combustion chamber end of the insulating body 10 and approximately in the middle of the end section 12 of the candle housing 11 ends.
  • the annular end face of the sleeve 22 remote from the combustion chamber is covered by a radially projecting shoulder of the base body 21.
  • a high-voltage-resistant annular insulating disk 23 made of silicone or epoxy resin is inserted.
  • the end faces of the base body 21 and the sleeve 22 on the combustion chamber side are covered by an end face 24, which is made of the same material as the central electrode 19 and is conductively connected to it.
  • the sleeve 22 can be omitted and the high-dielectric layer directly on the insulating body 10 made of aluminum oxide ceramic, for. B. be applied by plasma spraying.
  • the high-dielectric layer or layers on the insulating body 10 exclusively in the slideway area between the end face 24 of the center electrode 19 and the ground electrode 15.
  • the base body 21 and the sleeve 22 do not run coaxially to one another as far as the front end of the insulating body 10 on the combustion chamber side, but only overlap in the axial direction, the base body 21 being at a distance from the end of the insulating body 10 on the combustion chamber side ends within the encompassing area of the candle housing 11, while the sleeve 22 extends to the free end.
  • the central electrode 19 is widened down to the sleeve 22, so that the sleeve 22 directly surrounds the base body 21 on a longitudinal section and directly surrounds the central electrode 19 on a further longitudinal section adjoining the combustion chamber.
  • the insulating body 10 in turn has a base body 25 made of aluminum oxide ceramic, which contains the through-bore 16 and ends within the metallic plug housing 11. At a distance from the end of the base body 25 on the combustion chamber side, the diameter of the through hole is enlarged.
  • a hollow pin 26 made of highly dielectric material is inserted into this cylinder ring, which remains between the center electrode 19 and the base body 25, so that it surrounds the end region of the center electrode 19 on the one hand and is enclosed by the base body 25 over a longitudinal section.
  • the central electrode 19 and the connecting pin 17 are not connected to one another via a glass melt flow mass, but are separated from one another by a highly insulating separating layer 27, which is pierced by a contact pin 28 for the electrically conductive connection of connecting pin 17 and central electrode 19.
  • Electrode in the end area on the combustion chamber is similar to that of the spark plug in FIG. 3.
  • the diameter of the center electrode 19 in turn increases in the end section on the combustion chamber side.
  • the hollow pin 26 is here funnel-shaped and in turn surrounds the center electrode 19 up to its end on the combustion chamber side. Its outer circumference is aligned with the outer circumference of the base body 25.

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  • Spark Plugs (AREA)
  • Ignition Installations For Internal Combustion Engines (AREA)

Abstract

A spark plug with a surface discharge section for internal combustion engines is provided with a spark plug barrel (11) with an annular earthed electrode (15), an insulating body (10) surrounded by the barrel (11) on a longitudinal section and a central electrode (19) housed in a through-hole (16) in the insulating body (10), and exposed on the combustion chamber side. The surface discharge section is formed between the central electrode (19) and the earthed electrode (15) along a discharge path on the surface of the insulating body (10). In order to obtain a low plug capacity with a highly dielectric discharge path, the insulating body (10) is provided at least in the end section of the combustion chamber side with at least two coaxial material layers (21, 22) which are totally or partially adjacent to one another in the radial direction and having highly different dielectric constance.

Description

Die Erfindung geht aus von einer Zündkerze mit Gleitfunkenstrecke für Brennkraftmaschinen nach der Gattung des Anspruchs 1.The invention relates to a spark plug with a sliding spark gap for internal combustion engines according to the preamble of claim 1.

Solche Zündkerzen mit Gleitfunkenstrecke, die sich an der brennraumseitigen Oberfläche des lsolierkörpers zwischen der Mittel- und Masseelektrode ausbildet, zeichnen sich durch eine gegenüber einer Zündkerze mit Luftfunkenstrecke wesentlich niedrigere Zündspannung aus. Es hat sich dabei gezeigt, dass die Zündspannung umso niedriger ist, je grösser die Dielektrizitätskonstante des Isolierkörperwerkstoffes ist. Ein solcher lsolierkörper aus hochdielektrischem Material führt jedoch in einer Zündkerze zu einer relativ hohen Kapazität, die an der Gleitfunkenstrecke eine Durchbruchentladung bewirkt. Infolge des bei der Durchbruchentladung entstehenden sehr heissen Funkens von einigen zehntausend Grad erodieren die Oberflächen der Elektroden und besonders die Gleitbahn der Gleitfunkenstrecke stark, wodurch wiederum die ordnungsgemässe Funktion der Zündkerze und deren Lebensdauer wesentlich beeinträchtigt werden.Such spark plugs with sliding spark gaps, which form on the combustion chamber-side surface of the insulating body between the center and ground electrodes, are distinguished by an ignition voltage that is substantially lower than that of a spark plug with air spark gap. It has been shown that the higher the dielectric constant of the insulating body material, the lower the ignition voltage. However, such an insulating body made of high-dielectric material leads to a relatively high capacity in a spark plug, which causes a breakdown discharge at the sliding spark gap. As a result of the very hot spark of a few tens of thousands of degrees that occurs during the breakdown discharge, the surfaces of the electrodes and especially the slideway of the spark gap are severely eroded, which in turn significantly impairs the proper functioning of the spark plug and its service life.

Bei einer bekannten Zündkerze der eingangs genannten Art wie beschrieben in EP-A-0.236.376 (= WO 87/01876 = DE-A-35 33 123.2) hat man zur Vermeidung der Durchbruchphase mit hoher Energie den Isolierkörper im brennraumseitigen Endbereich quergeteilt und das volumengrössere anschlussseitige Oberteil aus einem Werkstoff mit niedriger Dielektrizitätskonstanten und das volumenkleinere brennraumseitige Unterteil aus einem Werkstoff mit einer sehr viel höheren Dielektrizitätskonstanten gemacht. Die Druckschrift EP-A-0.236.376 bildet einen Stand der Technik nach Artikel 54(3) EPÜ. Insgesamt lässt sich die Gesamtkapazität der Zündkerze jedoch nicht klein genug halten, so dass die Energie in mitunter auftretenden Durchbruchphasen doch noch nennenswerte Erosion in der Isolierkörperoberfläche bewirkt.In a known spark plug of the type mentioned at the outset, as described in EP-A-0.236.376 (= WO 87/01876 = DE-A-35 33 123.2), the insulating body in the end area on the combustion chamber side has been cross-divided to avoid the breakdown phase and that Volume-larger connection-side upper part made of a material with a low dielectric constant and the smaller-volume lower part on the combustion chamber side made of a material with a much higher dielectric constant. EP-A-0.236.376 forms a state of the art according to Article 54 (3) EPC. Overall, however, the total capacity of the spark plug cannot be kept small enough, so that the energy still causes significant erosion in the insulating body surface in breakdown phases that sometimes occur.

Die erfindungsgemässe Zündkerze mit den kennzeichnenden Merkmalen des Anspruchs 1 hat den Vorteil, dass durch den koaxialen Schichtaufbau des Isolierkörpers oder Kerzensteins sich ein koaxialer Kondensator mit geschichtetem Dielektrikum ergibt, dessen Gesamtkapazität durch die kleinere Kapazität der niederdielektrischen Schicht, also der Schicht mit der sehr viel kleineren Dielektrizitätskonstanten, bestimmt wird. Ohne Erhöhung der Kerzenkapazität können daher Keramiken mit einer relativen Dielektrizitätskonstanten bis zu 10000 in der hochdielektrischen Schicht verwendet werden, wenn nur die niederdielektrische Schicht eine relativ kleine Dielektrizitätszahl von ungefähr 10 bis 50 aufweist.The spark plug according to the invention with the characterizing features of claim 1 has the advantage that the coaxial layer structure of the insulating body or candle block results in a coaxial capacitor with a layered dielectric, the total capacity of which is due to the smaller capacitance of the low-dielectric layer, i.e. the layer with the much smaller one Dielectric constant is determined. Without increasing the candle capacity, ceramics with a relative dielectric constant of up to 10,000 can therefore be used in the high-dielectric layer if only the low-dielectric layer has a relatively small dielectric constant of approximately 10 to 50.

Die erfindungsgemässe Zündkerze hat bei Vorsehen einer vorteilhaft hochdielektrischen Gleitbahn eine nur kleine Kerzenkapazität und zeigt dadurch bedingt nur geringe Erosionen an der Gleitbahn. Durch die hohe Dielektrizitätskonstante der Isolierkörperoberfläche, auf welcher sich die Gleitbahn ausbildet, ist der Zündspannungsbedarf der Zündkerze niedrig, so dass ein erheblicher Teil der von der Zündanlage zur Verfügung gestellten Energie an das Kraftstoffgemisch übertragen wird. Dadurch sind gute Entflammungsbedingungen auch für magere Kraftstoffgemische geschaffen. Durch den niedrigen Zündspannungsbedarf ergeben sich sämtliche Vorteile einer Niederspannungszündung, wie kleinere Zündspule, gute Entstörwirkung, geringer Aufwand an Hochspannungsisolation.The spark plug according to the invention, if an advantageously high-dielectric slideway is provided, has only a small plug capacity and, as a result, shows only slight erosions on the slideway. Due to the high dielectric constant of the insulating body surface on which the slideway is formed, the ignition voltage requirement of the spark plug is low, so that a considerable part of the energy made available by the ignition system is transferred to the fuel mixture. This creates good ignition conditions even for lean fuel mixtures. Due to the low ignition voltage requirement, all advantages of a low-voltage ignition, such as a smaller ignition coil, good interference suppression, and low expenditure on high-voltage insulation result.

Durch die in den weiteren Ansprüchen aufgeführten Massnahmen sind vorteilhafte Weiterbildungen und Verbesserungen der im Anspruch 1 angegebenen Zündkerze möglich.The measures listed in the further claims allow advantageous developments and improvements of the spark plug specified in claim 1.

Eine vorteilhafte Ausführungsform ergibt sich dabei aus Anspruch 2. Bei Verwendung von Materialien mit sehr hoher relativer Dielektrizitätskonstante, z. B. zwischen 500 bis 10000, wird eine niedrige Zündspannung schon bei relativ dünnen Schichten erzielt, deren Schichtdicke zwischen 0,1 bis 1 mm liegt. Solche Schichten können gemäss der Ausführungsform der Erfindung nach Anspruch 7 durch Plasmaspritzen auf einen Kerzenstein aus z. B. Aluminiumoxid aufgebracht werden. Mit dieser Technik können gemäss der Ausführungsform der Erfindung nach Anspruch 8 mehrere Schichten aus Werkstoff mit hoher Dielektrizitätskonstanten übereinander aufgebracht werden, wobei die Dielektrizitätskonstante der einzelnen Schichten stufig oder kontinuierlich anwachsen kann. Gemäss der Ausführungsform der Erfindung nach Anspruch 9 genügt es dabei, die hochdielektrische Schicht oder Schichten nur im Gleitbahnbereich aufzubringen und im übrigen den Kerzenstein oder Isolierkörper ohne Trennstellen ganz aus Aluminiumoxid-Keramik herzustellen.An advantageous embodiment results from claim 2. When using materials with a very high relative dielectric constant, for. B. between 500 to 10,000, a low ignition voltage is achieved even with relatively thin layers, the layer thickness of which is between 0.1 to 1 mm. Such layers can be according to the embodiment of the invention according to claim 7 by plasma spraying on a candle from z. B. alumina can be applied. With this technique, according to the embodiment of the invention according to claim 8, a plurality of layers of material with a high dielectric constant can be applied one above the other, the dielectric constant of the individual layers being able to increase in stages or continuously. According to the embodiment of the invention according to claim 9, it is sufficient to apply the high-dielectric layer or layers only in the slideway region and, moreover, to manufacture the candle stone or insulating body entirely without separation points from aluminum oxide ceramic.

Eine vorteilhafte Ausführungsform der Erfindung ergibt sich auch aus Anspruch 11. Durch diese Überlappung der Schichten in axialer Richtung wird eine Hochspannungsfestigkeit zwischen den Schichten in axialer Richtung erreicht, wobei durch eine Überlappung bis in den Gleitbahnbereich die Hochspannungsbeanspruchung der hochdielektrischen Schicht klein gehalten wird.An advantageous embodiment of the invention also results from claim 11. This overlap of the layers in the axial direction achieves high-voltage strength between the layers in the axial direction, the high-voltage stress on the high-dielectric layer being kept small by overlapping into the slideway region.

Eine vorteilhafte Ausführungsform der Erfindung ergibt sich auch aus Anspruch 16. Durch die ringförmigen Isolierscheiben werden die radialen kreisringförmigen Trennstellen zwischen den Schichten hochspannungsfest abgedichtet.An advantageous embodiment of the invention also results from claim 16. Due to the annular insulating disks, the radial annular separating points between the layers are sealed against high voltage.

Die Erfindung ist anhand von in der Zeichnung dargestellten Ausführungsbeispielen in der nachfolgenden Beschreibung näher erläutert. Dabei zeigenThe invention is explained in more detail in the following description with reference to exemplary embodiments shown in the drawing. Show

Fig. 1 bis 6 jeweils eine Zündkerze zur Hälfte in Seitenansicht und zur Hälfte längsgeschnitten gemäss sechs verschiedenen Ausführungsbeispielen.Fig. 1 to 6 each have a spark plug half in side view and half cut longitudinally according to six different embodiments.

Die in der Zeichnung dargestellten Zündkerzen für Brennkraftmaschine weisen alle einen Isolierkörper 10 auf, der auf einem Längsabschnitt von einem metallischen Kerzengehäuse 11 umfasst ist. Das Kerzengehäuse 11 trägt auf einem im Durchmesser reduzierten Endabschnitt 12 ein Aussengewinde 13 mittels dessen die Zündkerze in einen nicht dargestellten Zylinderkopf der Brennkraftmaschine eingeschraubt wird. Zum Einschrauben dient in bekannter Weise ein Schlüsselsechskant 14. Der Endabschnitt 12 trägt auf seiner in den Brennraum der Brennkraftmaschine hineinragenden Stirnseite eine ringförmige Masseelektrode 15.The spark plugs for internal combustion engines shown in the drawing all have an insulating body 10, which is enclosed on a longitudinal section by a metallic plug housing 11. The plug housing 11 carries an external thread 13 on an end section 12 with a reduced diameter by means of which the spark plug is inserted into a cylinder head of the internal combustion engine, not shown, is screwed in. In a known manner, a hexagon key 14 is used for screwing in. The end section 12 carries an annular ground electrode 15 on its end face projecting into the combustion chamber of the internal combustion engine.

Der eine zentrale axiale Durchgangsbohrung 16 aufweisende rotationssymmetrische Isolierkörper 10 ragt auf beiden Seiten des Kerzengehäuses 11 aus diesem heraus. Innerhalb der Durchgangsbohrung 16 ist ein metallischer Anschlussbolzen 17 angeordnet, der an seinem brennraumfernen Endabschnitt ein Anschlussstück 18 zum elektrischen Anschluss der Zündkerze an die Zündanlage trägt. Im unteren Bereich der Durchgangsbohrung befindet sich eine Mittelelektrode 19, die an der brennraumseitigen Stirnfläche des Isolierkörpers 10 freiliegt. Der Anschlussbolzen 17 und die Mittelelektrode 19 sind durch eine Glasschmelzflussmasse 20 leitend miteinander verbunden.The rotationally symmetrical insulating body 10, which has a central axial through bore 16, projects out of the candle housing 11 on both sides thereof. A metallic connecting bolt 17 is arranged within the through bore 16 and carries a connecting piece 18 for the electrical connection of the spark plug to the ignition system at its end section remote from the combustion chamber. In the lower area of the through hole there is a central electrode 19 which is exposed on the end face of the insulating body 10 on the combustion chamber side. The connecting bolt 17 and the center electrode 19 are conductively connected to one another by a glass melt flow mass 20.

Bei allen Zündkerzen gemäss Fig. 1 bis 6 weist der Isolierkörper 10 zumindest im brennraumseitigen Endabschnitt zwei in Radialrichtung ganz oder teilweise aneinanderliegende koaxiale Materialschichten mit stark unterschiedlichen Dielektrizitätskonstanten auf. Die relative Dielektrizitätskonstante der dabei verwendeten Materialien liegt zwischen 10 und 10000, vorzugsweise zwischen 50 und 5000. Die in den beiden Materialschichten verwendeten Materialien werden dabei so gepaart, dass die Differenz zwischen ihren Dielektrizitätskonstanten möglichst gross ist.In all spark plugs according to FIGS. 1 to 6, the insulating body 10 has, at least in the end section on the combustion chamber side, two coaxial material layers with completely different dielectric constants which lie completely or partially against one another in the radial direction. The relative dielectric constant of the materials used is between 10 and 10,000, preferably between 50 and 5000. The materials used in the two material layers are paired in such a way that the difference between their dielectric constants is as large as possible.

Bei den Zündkerzen in Fig. 1 und 2 besteht der Isolierkörper 10 im wesentlichen aus einem ganz durchgehenden Grundkörper 21 aus Aluminiumoxid-Keramik mit relativ kleiner Dielektrizitätskonstanten (kleiner 15), und einer vom brennraumseitigen Ende des Grundkörpers 21 her aufgeschobene Hülse 22 aus hochdielektrischem Werkstoff, z. B. Bariumtitanoxid (Ba2 Ti03), mit einer relativen Dielektrizitätskonstanten von ca. 5000. Zur Aufnahme der Hülse 22 ist der Grundkörper 21 über einen brennraumseitigen Endabschnitt im Durchmesser reduziert. Bei der Zündkerze in Fig. 1 erstreckt sich die Hülse 22 vom stirnseitigen Ende des Grundkörpers 21 über nahezu den gesamten Übergreifungsbereich des Kerzengehäuses 11, während in Fig. 2 die Hülse 22 den Grundkörper 21 nur in dem brennraumseitigen Ende des Isolierkörpers 10 abdeckt und etwa in der Mitte des Endabschnitts 12 des Kerzengehäuses 11 endet. Die brennraumferne ringförmige Stirnfläche der Hülse 22 ist von einer radial vorstehenden Schulter des Grundkörpers 21 überdeckt. In dieser radialen Trennstelle zwischen Grundkörper 21 und Hülse 22 ist eine hochspannungsfeste ringförmige lsolierscheibe 23 aus Silikon oder Epoxidharz eingelegt. Die brennraumseitigen Stirnflächen von Grundkörper 21 und Hülse 22 sind von einem Stirnkopf 24 abgedeckt, der aus dem gleichen Material gefertigt ist wie die Mittelelektrode 19 und mit dieser leitend verbunden ist.1 and 2, the insulating body 10 consists essentially of a completely continuous base body 21 made of aluminum oxide ceramic with a relatively low dielectric constant (less than 15), and a sleeve 22 made of high-dielectric material pushed open from the end of the base body 21 on the combustion chamber side. e.g. B. barium titanium oxide (Ba2 Ti03), with a relative dielectric constant of approx. 5000. To accommodate the sleeve 22, the base body 21 is reduced in diameter via an end section on the combustion chamber side. In the spark plug in FIG. 1, the sleeve 22 extends from the front end of the base body 21 over almost the entire overlap area of the candle housing 11, while in FIG. 2 the sleeve 22 covers the base body 21 only in the combustion chamber end of the insulating body 10 and approximately in the middle of the end section 12 of the candle housing 11 ends. The annular end face of the sleeve 22 remote from the combustion chamber is covered by a radially projecting shoulder of the base body 21. In this radial separation point between base body 21 and sleeve 22, a high-voltage-resistant annular insulating disk 23 made of silicone or epoxy resin is inserted. The end faces of the base body 21 and the sleeve 22 on the combustion chamber side are covered by an end face 24, which is made of the same material as the central electrode 19 and is conductively connected to it.

Bei Verwendung von Materialien mit einer sehr hohen relativen Dielektrizitätskonstanten wird eine niedrige Zündspannung schon bei relativ dünnen Schichten von 0,1 bis 1 mm erreicht. In diesem Fall kann die Hülse 22 entfallen und die hochdielektrische Schicht unmittelbar auf den aus Aluminiumoxid-Keramik bestehenden Isolierkörper 10, z. B. durch Plasmaspritzen, aufgebracht werden. Mit dieser Technik ist es auch möglich, mehrere Schichten mit kontinuierlichem bzw. stufigem Übergang der Dielektrizitätskonstanten zwischen der Keramik und der letzten hochdielektrischen Schicht (z. B. Bariumtitanoxid) übereinander aufzubringen. Dabei ist es auch möglich, die hochdielektrische Schicht bzw. Schichten ausschliesslich im Gleitbahnbereich zwischen Stirnkopf 24 der Mittelelektrode 19 und der Masseelektrode 15 am Isolierkörper 10 vorzusehen.When using materials with a very high relative dielectric constant, a low ignition voltage is achieved even with relatively thin layers of 0.1 to 1 mm. In this case, the sleeve 22 can be omitted and the high-dielectric layer directly on the insulating body 10 made of aluminum oxide ceramic, for. B. be applied by plasma spraying. With this technique it is also possible to apply several layers with a continuous or step-wise transition of the dielectric constant between the ceramic and the last high-dielectric layer (e.g. barium titanium oxide). It is also possible to provide the high-dielectric layer or layers on the insulating body 10 exclusively in the slideway area between the end face 24 of the center electrode 19 and the ground electrode 15.

Bei den in Fig. 3 und 4 dargestellten Zündkerzen verlaufen der Grundkörper 21 und die Hülse 22 nicht koaxial zueinander bis an das brennraumseitige Stirnende des Isolierkörpers 10, sondern überlappen sich nur in Axialrichtung, wobei der Grundkörper 21 in Abstand vor dem brennraumseitigen Ende des Isolierkörpers 10 innerhalb des Umgreifungsbereiches des Kerzengehäuses 11 endet, während die Hülse 22 bis hin zum freien Stirnende reicht. An der Austrittsstelle aus der im Grundkörper 21 verlaufenden Durchgangsbohrung 16 ist die Mittelelektrode 19 bis auf die Hülse 22 verbreitert, so dass die Hülse 22 auf einem Längsabschnitt den Grundkörper 21 und auf einem sich zum Brennraum hin anschliessenden weiteren Längsabschnitt unmittelbar die Mittelelektrode 19 umgibt. Während bei der Zündkerze in Fig. 3 die Hülse 22 sich weit in das Kerzengehäuse 11 hinein erstreckt und erst nahe dem Schlüsselsechskant 14 endet, endet die Hülse 22 bei der Zündkerze in Fig. 4 bereits im Endabschnitt 12 des Kerzengehäuses 11. Die ringförmige Stirnfläche der Hülse 22 liegt in Fig. 4 frei, während sie in Fig. 3 wiederum von dem mit der Mittelelektrode 19 verbundenen Stirnkopf 24 abgedeckt wird.In the spark plugs shown in FIGS. 3 and 4, the base body 21 and the sleeve 22 do not run coaxially to one another as far as the front end of the insulating body 10 on the combustion chamber side, but only overlap in the axial direction, the base body 21 being at a distance from the end of the insulating body 10 on the combustion chamber side ends within the encompassing area of the candle housing 11, while the sleeve 22 extends to the free end. At the exit point from the through bore 16 running in the base body 21, the central electrode 19 is widened down to the sleeve 22, so that the sleeve 22 directly surrounds the base body 21 on a longitudinal section and directly surrounds the central electrode 19 on a further longitudinal section adjoining the combustion chamber. While the sleeve 22 in the spark plug in FIG. 3 extends far into the plug housing 11 and only ends near the key hexagon 14, the sleeve 22 in the spark plug in FIG. 4 already ends in the end section 12 of the plug housing 11. The annular end face of the Sleeve 22 is exposed in FIG. 4, while in FIG. 3 it is in turn covered by the end head 24 connected to the center electrode 19.

Bei den Zündkerzen in Fig. 5 und 6 weist der Isolierkörper 10 wiederum einen Grundkörper 25 aus Aluminiumoxid-Keramik auf, der die Durchgangsbohrung 16 enthält und innerhalb des metallischen Kerzengehäuses 11 endet. Mit Abstand vor dem brennraumseitigen Ende des Grundkörpers 25 ist die Durchgangsbohrung im Durchmesser erweitert. In diesen dadurch zwischen der Mittelelektrode 19 und dem Grundkörper 25 verbleibenden Zylinderring ist ein Hohlzapfen 26 aus hochdielektrischem Material eingeschoben, so dass er einerseits den Endbereich der Mittelelektrode 19 umgibt und andererseits über einen Längsabschnitt von dem Grundkörper 25 umschlossen ist.In the spark plugs in FIGS. 5 and 6, the insulating body 10 in turn has a base body 25 made of aluminum oxide ceramic, which contains the through-bore 16 and ends within the metallic plug housing 11. At a distance from the end of the base body 25 on the combustion chamber side, the diameter of the through hole is enlarged. A hollow pin 26 made of highly dielectric material is inserted into this cylinder ring, which remains between the center electrode 19 and the base body 25, so that it surrounds the end region of the center electrode 19 on the one hand and is enclosed by the base body 25 over a longitudinal section.

Bei der Zündkerze in Fig. 5 ist die Mittelelektrode 19 und der Anschlussbolzen 17 nicht über eine Glasschmelzflussmasse miteinander verbunden, sondern durch eine hochisolierende Trennschicht 27 voneinander getrennt, die zur elektrisch leitenden Verbindung von Anschlussbolzen 17 und Mittelelektrode 19 von einem Kontaktstift 28 durchstossen ist.5, the central electrode 19 and the connecting pin 17 are not connected to one another via a glass melt flow mass, but are separated from one another by a highly insulating separating layer 27, which is pierced by a contact pin 28 for the electrically conductive connection of connecting pin 17 and central electrode 19.

Im Unterschied zu Fig. 5 ist in Fig. 6 die Mittelelektrode im brennraumseitigen Endbereich ähnlich wie bei der Zündkerze in Fig. 3 ausgebildet. Der Durchmesser der Mittelelektrode 19 vergrössert sich wiederum im brennraumseitigen Endabschnitt. Der Hohlzapfen 26 ist hier trichterartig ausgebildet und umgibt wiederum die Mittelelektrode 19 bis hin zu deren brennraumseitigem Ende. Sein Aussenumfang fluchtet mit dem Aussenumfang des Grundkörpers 25. Am brennraumseitigen Stirnende wird der Hohlzapfen 26 wiederum von dem mit der Mittelelektrode 19 verbundenen Stirnkopf 24 abgedeckt.In contrast to FIG. 5, the mean in FIG. 6 is Electrode in the end area on the combustion chamber is similar to that of the spark plug in FIG. 3. The diameter of the center electrode 19 in turn increases in the end section on the combustion chamber side. The hollow pin 26 is here funnel-shaped and in turn surrounds the center electrode 19 up to its end on the combustion chamber side. Its outer circumference is aligned with the outer circumference of the base body 25.

Claims (16)

1. Spark plug with surface discharge section for internal combustion engines, comprising a spark plug housing which, with a housing section, projects into the combustion chamber of the internal combustion engine and has an annular earth electrode at its end on the combustion chamber side, an insulating body which is enclosed by the spark plug housing over a longitudinal section and, on the combustion chamber side, protrudes beyond the spark plug housing, and a centre electrode which lies in a through bore in the insulating body and is exposed on the combustion chamber side, the surface discharge section being formed between centre and earth electrode along a surface-discharge path on the surface of the insulating body, and the insulating body (10), at least in the end section on the combustion chamber side, having at least two coaxial material coatings (21, 22; 25, 26) which bear completely or partly against one another in the radial direction and have greatly different dielectric constants.
2. Spark plug according to Claim 1, characterized in that the relative dielectric constant of the materials used lies between 10 and 10,000, preferably between 50 and 5,000, and in that materials are paired which are as far apart as possible in their dielectric constants.
3. Spark plug according to Claim 1 or 2, characterized in that the coatings (21, 22) run coaxially to one another down to thefrontend of the insulating body (10) on the combustion chamber side.
4. Spark plug according to Claim 3, characterized in that the low-dielectric coating (21 ) surrounds the centre electrode (19) and is enclosed by the high-dielectric coating (22) over a longitudinal section extending down to the front end of the insulating body (10).
5. Spark plug according to Claim 3 or 4, characterized in that the low-dielectric coating (21) is in one piece with the insulating body (10) made of the same material, and in that the high-dielectric coating (22) is applied to the insulating body (10).
6. Spark plug according to Claim 5, characterized in that the coating thickness of the high-dielectric coating, atvery high dielectric constants, is selected to be between 0.1 and 1 mm.
7. Spark plug according to Claim 5 or 6, characterized in that the high-dielectric coating is applied to the insulating body (10) by means of plasma spraying.
8. Spark plug according to any of Claims 3 to 5, characterized in that a plurality of high-dielectric coatings having dielectric constants increasing continuously or in a graduated manner lie one above the other in the radial direction.
9. Spark plug according to any of Claims 3 to 8, characterized in that the high-dielectric coating or coatings are provided solely in the surface- discharge path area of the surface discharge section.
10. Spark plug according to any of Claims 3 to 9, characterized in that the centre electrode (19), with a preferably one-piece front head (24), protrudes beyond the end of the insulating body (10) on the combustion chamber side, and in that the front head (24) covers the annular front end of the material coatings (21, 22).
11. Spark plug according to Claim 1 or 2, characterized in that the material coatings (21,22; 25, 26) overlap in the axial direction and only the high-dielectric coating (22; 26) protrudes from the spark plug housing (11) at the end on the combustion chamber side.
12. Spark plug according to Claim 11, characterized in that the high-dielectric coating (22) encloses the low-dielectric coating (21) in the overlapping area and surrounds the centre electrode (19) at least in the end section protruding from the spark plug housing (11).
13. Spark plug according to Claim 11, characterized in that the high-dielectric coating (26) surrounds the centre electrode (19) at least in the end section on the combustion chamber side and is enclosed in the overlapping area by the low-dielectric coating (25).
14. Spark plug according to any of Claims 11 to 13, characterized in that the overlapping area of the coatings (21, 22; 25, 26) is placed inside the spark plug housing (11).
15. Spark plug according to any of Claims 3 to 14, characterized in that the front end of the high-dielectric coating (22) remote from the end of the insulating body (10) on the combustion chamber side is covered by the low-dielectric coating (21).
16. Spark plug according to Claim 15, characterized in that a high-voltage-stable insulating disc (23), e. g. of silicone or epoxy resin, is inserted between the insulating body (10) and the annular front end of the high-dielectric coating (22) remote from the end on the combustion chamber side.
EP87902423A 1986-05-16 1987-05-06 Spark plug with surface discharge section Expired EP0268598B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19863616668 DE3616668A1 (en) 1986-05-16 1986-05-16 SPARK PLUG WITH GLIDING RANGE
DE3616668 1986-05-16

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EP0268598A1 EP0268598A1 (en) 1988-06-01
EP0268598B1 true EP0268598B1 (en) 1989-12-20

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US (1) US4870319A (en)
EP (1) EP0268598B1 (en)
JP (1) JPS63503418A (en)
KR (1) KR880701479A (en)
BR (1) BR8707310A (en)
DE (2) DE3616668A1 (en)
ES (1) ES2005229A6 (en)
WO (1) WO1987007094A1 (en)

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Also Published As

Publication number Publication date
JPS63503418A (en) 1988-12-08
DE3616668A1 (en) 1987-11-19
EP0268598A1 (en) 1988-06-01
KR880701479A (en) 1988-07-27
BR8707310A (en) 1988-09-13
US4870319A (en) 1989-09-26
ES2005229A6 (en) 1989-03-01
WO1987007094A1 (en) 1987-11-19
DE3761239D1 (en) 1990-01-25

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