EP0238520B1 - Surface-discharge spark plug - Google Patents

Surface-discharge spark plug Download PDF

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Publication number
EP0238520B1
EP0238520B1 EP86905220A EP86905220A EP0238520B1 EP 0238520 B1 EP0238520 B1 EP 0238520B1 EP 86905220 A EP86905220 A EP 86905220A EP 86905220 A EP86905220 A EP 86905220A EP 0238520 B1 EP0238520 B1 EP 0238520B1
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EP
European Patent Office
Prior art keywords
electrode
combustion chamber
insulating body
spark plug
central electrode
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP86905220A
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German (de)
French (fr)
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EP0238520A1 (en
Inventor
Walter Benedikt
Gerhard Heess
Werner Herden
Karl-Hermann Friese
Helmut Reum
Jürgen SCHMATZ
Siegbert Schwab
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Robert Bosch GmbH
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Robert Bosch GmbH
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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
    • H01T13/52—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 a spark plug with a spark gap is known from GB-A-1 049 321; it is provided with a central electrode, the end of which is flat on the combustion chamber side, runs perpendicular to the longitudinal axis of the central electrode and ends flush with a sliding spark gap which surrounds the central electrode and is also perpendicular to the longitudinal axis of the central electrode.
  • the annular ground electrode radially adjoining the sliding spark gap which is formed by the end of the metal housing of the spark plug on the combustion chamber side, also closes on the combustion chamber side of the end of the center electrode.
  • the sliding spark gap is represented by the surface of a pane on the combustion chamber side, which is attached as a lower part to a connection-side upper part of an insulating body made of a material commonly used for this purpose, such as aluminum oxide, using an electrically highly insulating material (for example glass); the pane consists of a semiconductor material (copper oxide + chromium oxide, optionally + iron oxide), the dielectric constant of which is greater than the dielectric constant of the material forming the upper part of the insulating body.
  • Spark plugs according to GB-A-1 049 321 have a relatively low ignition voltage requirement, but enable the sparking of high-energy sparks.
  • GB-A-1 049 321 does not provide any information about the polarities of the center or ground electrode.
  • a similar spark plug is also described in GB-A-2 097 467; the lower part of the insulating body on the combustion chamber side in this spark plug essentially consists of silicon nitride, but is not directly connected to the upper part of the insulating body on the connection side, but is separated therefrom by means of an air gap.
  • This publication also does not contain any information about the polarities of the center or the ground electrode.
  • Spark discharge devices which have a conical sliding spark gap and whose central electrode protrudes from an annular body on the combustion chamber side, which forms the ground electrode, are already known and are used to generate brief pressure surges of high energy in a hydraulic working medium surrounding the discharge region; the pressure surges are used for the processing of metals and for other mechanical work purposes (DE-B-12 54 896).
  • the invention is based on the object of developing the above-mentioned spark plugs for internal combustion engines in such a way that the length of the sliding spark gap can be further increased for a given ignition voltage.
  • the shape of the surface of the insulating body and the electrodes can be chosen as desired, while adhering to the teaching according to the invention. It is expedient, with a justifiable ignition voltage, to design the surface in such a way that the longest possible slideway length is achieved in order to achieve the highest possible operating voltage.
  • the energy delivered by the spark plug according to the invention to the combustible fuel-air mixture is approximately ten times as high as in the case of a conventional spark plug.
  • the spark plug according to the invention has a much lower ignition voltage requirement with the same energy transfer to the fuel-air mixture.
  • the spark plug according to the invention is intended for a glow discharge with a burn time of milliseconds;
  • the glow discharge prevents erosion damage to the combustion chamber surface of the insulating body.
  • the formation of the surface discharge is promoted with increasing dielectric constant of the insulating body material
  • a breakdown at the separation point between the lower part and the upper part is prevented by a highly insulating separating layer between the two.
  • An arc discharge after the ignition is avoided according to the embodiment of the invention according to claim 6 by a resistance of about 1 k ⁇ in the lead of the center electrode.
  • the spark plug for an internal combustion engine shown in FIG. 1 has a rotationally symmetrical insulating body 10 which is encompassed on a longitudinal section by a likewise rotationally symmetrical metal housing 11.
  • the metal housing 11 has a thread 13 on an end section 12 with a reduced diameter, with which the spark plug can be screwed into a cylinder head of the internal combustion engine.
  • a hexagon key 14 is used for screwing in.
  • a sealing ring 15 ensures the gas-tight installation of the spark plug in the cylinder head.
  • the metal housing carries an annular ground electrode 16 on the end face of its combustion chamber-side end section 12 provided with the thread 13.
  • the insulating body 10 has on its surface a number of annular grooves 17 as a so-called leakage current barrier and is provided with a central axial through hole 18.
  • a connecting pin 19 which has a connector 20 from the insulating body 10 protrudes from the end facing away from the combustion chamber, and a center electrode 21 which extends in the end section of the insulating body 10 on the combustion chamber side and is electrically and mechanically connected to the connecting bolt 19 via a glass melt flow mass formed here as a resistance chipboard 27.
  • the combustion chamber end face of the center electrode 21 is exposed.
  • a sliding spark gap 26 is formed between them along the free surface 22 of the insulating body 10 on the combustion chamber side.
  • the insulating body 10 is cross-divided in its end section on the combustion chamber side and thus has an upper part 23 on the connection side and a lower part 24 on the combustion chamber side.
  • the upper part 23 consists of aluminum oxide (Al203) with a dielectric constant ⁇ r of less than ten, while the material of the lower part 24 has a much higher dielectric constant, here about 50-500.
  • a separating layer 25 made of silicone rubber, epoxy resin or glass.
  • FIGS. 2-11 show different embodiments of the design of the combustion chamber end section of the spark plug.
  • the surface 22 of the insulating body 10 is shaped in such a way that it is from a plurality of the imaginary field lines 30 (FIG. 2) of the electrical field which is formed between the center electrode 21 and the ground electrode 16 when a voltage is applied.
  • the electrode that forms the cathode or a part of this electrode viewed in the direction of the field line, is guided behind the surface 22 at a distance from and at any angle of inclination to this surface 22. The distance is arbitrary, it can be the same or change along the surface 22. Because of its position "behind" the surface 22, this electrode is also called the "rear electrode".
  • the course of the field lines 30 is shown schematically in FIG. 2 as a representative of all of the figures.
  • the electrode representing the cathode is formed by the central electrode 16, while in the exemplary embodiments according to FIGS. 3, 6, 10 and 14 the ground electrode 16 represents the cathode.
  • the cathode is identified by a (-) and the anode by a (+).
  • the holes penetrate from the ring-shaped end face of the ground electrode 16 (in the exemplary embodiments according to FIGS.
  • the electrodes are arranged concentrically with one another, their electrode walls running parallel to one another.
  • the surface 22 of the insulating body 10 rises continuously from the anode (+) to the cathode (-) in such a way that the normals of any small surface elements with the longitudinal axis 29 of the insulating body 10 or the longitudinal axis of the electrodes 16 , 21, enclose an angle that is greater than 0 o and at most 90 o .
  • the increase in the surface can also be discontinuous.
  • the central electrode 21 forming the cathode (-) projects far beyond the end of the ground electrode 16 forming the anode (+).
  • the end section of the insulating body 10 is hat-shaped, in such a way that its longitudinal profile has a rectilinear (Fig. 2.8 and 9) or curved or curved (Fig. 4.5) rising from the ground electrode 16 to the central electrode 21 ) Has a contour. With a discontinuous increase in the surface, a step-like contour results.
  • the end of the center electrode 21 forming the anode (+) is set back to the annular end of the ground electrode 16 forming the cathode (-) and the end section of the insulating body 10 on the combustion chamber side is crater-like , in such a way that in the longitudinal profile from the central electrode 21 to the ground electrode 16 there are rising flanks with a rectilinear (Fig. 3, 10 and 14) or curved or curved (Fig. 6) contour.
  • the central electrode 21 representing the cathode is angled in the insulating body region protruding beyond the ring-shaped ground electrode 16 in relation to the part of the central electrode 21 which is concentric with the ground electrode 16.
  • the ignition spark which is formed between the center electrode 21 and the ground electrode 16 is forced onto a predetermined slideway, as is designated by 26 in FIG. 7.
  • FIGS. 8-11 Embodiments of the spark plugs according to the invention, in which there is a uniform erosion over the entire surface 22 of the insulating body 10 on the combustion chamber side, are shown in FIGS. 8-11.
  • at least one of the electrodes 16, 21 is formed in its end section 161 or 211 such that the shortest distances between the electrodes 16, 22 measured in the sectional areas of the insulating body 10 running parallel to the surface 22 in the region of the end sections 161 and 211 increase with increasing distance of the parallel cut surfaces from the surface 22.
  • the cut surfaces form cone shells.
  • the shortest distance between the electrodes 16, 21 measured along this cut surface 28 increases.
  • the slideway length between the electrodes 16, 21 increases with increasing Burn-off on the surface 22. Since the slideway with the shortest distance from the ignition spark is preferred, the ignition spark is displaced and a uniform burn-off of the surface 22 is achieved on the circumference.
  • the spark plug To achieve a glow discharge discharge, the spark plug must have the lowest possible capacity.
  • the insulating body 10 As described in Figure 1, formed in two parts. If necessary, a spark gap is provided in the plug or in the spark plug.
  • the sliding glow discharge is a relatively cold discharge in terms of gas discharge, since the electrons are released from the electrode surfaces by ion impacts and not thermally. Erosion of the surface 22 of the insulating body 10 does not occur.

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

Abstract

In a surface-discharge spark plug, in order to lengthen the path of the discharge surface with a given ignition voltage, the upper surface (22) of the insulating body (10) facing the combustion chamber is designed so that it is crossed by a plurality of field lines (30) forming parts of an electric field generated between the central electrode (21) and the insulating body (10) and the annular mass electrode (16) fitted to the metal casing (11) which surrounds the central electrode (21). Part of the electrode (16 or 21) which represents the cathode (-) is arranged at a certain distance behind the surface (22), when seen in the direction of the field lines, forming an angle with the latter surface.

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.

Eine derartige Zündkerze mit Gleitfunkenstrecke ist aus der GB-A-1 049 321 bekannt; sie ist mit einer Mittelelektrode versehen, deren brennraumseitiges Ende eben ist, senkrecht zur Längsachse der Mittelelektrode verläuft und bündig mit einer die Mittelelektrode ringförmig umfassenden, auch senkrecht zur Längsachse der Mittelelektrode stehenden Gleitfunkenstrecke abschließt. Die sich der Gleitfunkenstrecke radial anschließende ringförmige Masseelektrode, die vom brennraumseitigen Ende des Metallgehäuses der Zündkerze gebildet wird, schließt brennraumseitig auch mit dem brennraumseitigen Ende der Mittelelektrode ab. Die Gleitfunkenstrecke wird dabei von der brennraumseitigen Oberfläche einer Scheibe dargestellt, die als Unterteil an ein anschlußseitiges Isolierkörper-Oberteil eines aus hierfür üblicherweise verwendeten Materials wie Aluminiumoxid mittels eines elektrisch hochisolierenden Werkstoffes (zum Beispiel Glas) befestigt ist; die Scheibe besteht aus einem Halbleitermaterial (Kupferoxid + Chromoxid, gegebenenfalls + Eisenoxid), dessen Dielektrizitätszahl größer ist als die Dielektrizitätszahl des das Isolierkörper-Oberteil bildenden Materials. Zündkerzen gemäß der GB-A-1 049 321 haben einen relativ geringen Zündspannungsbedarf, ermöglichen jedoch den Überschlag energiereicher Funken. Angaben über die Polaritäten von Mittel- bzw. Masseelektrode sind der GB-A-1 049 321 nicht zu entnehmen.Such a spark plug with a spark gap is known from GB-A-1 049 321; it is provided with a central electrode, the end of which is flat on the combustion chamber side, runs perpendicular to the longitudinal axis of the central electrode and ends flush with a sliding spark gap which surrounds the central electrode and is also perpendicular to the longitudinal axis of the central electrode. The annular ground electrode radially adjoining the sliding spark gap, which is formed by the end of the metal housing of the spark plug on the combustion chamber side, also closes on the combustion chamber side of the end of the center electrode. The sliding spark gap is represented by the surface of a pane on the combustion chamber side, which is attached as a lower part to a connection-side upper part of an insulating body made of a material commonly used for this purpose, such as aluminum oxide, using an electrically highly insulating material (for example glass); the pane consists of a semiconductor material (copper oxide + chromium oxide, optionally + iron oxide), the dielectric constant of which is greater than the dielectric constant of the material forming the upper part of the insulating body. Spark plugs according to GB-A-1 049 321 have a relatively low ignition voltage requirement, but enable the sparking of high-energy sparks. GB-A-1 049 321 does not provide any information about the polarities of the center or ground electrode.

Eine ähnliche Zündkerze ist auch in der GB-A-2 097 467 beschrieben; das brennraumseitige Isolierkörper-Unterteil besteht bei dieser Zündkerze im wesentlichen aus Siliziumnitrid, ist aber mit dem anschlußseitigen Isolierkörper-Oberteil nicht direkt verbunden, sondern davon mittels eines Luftspaltes getrennt. Auch diese Druckschrift enthält keine Angaben über die Polaritäten der Mittel- bzw. der Masseelektrode.A similar spark plug is also described in GB-A-2 097 467; the lower part of the insulating body on the combustion chamber side in this spark plug essentially consists of silicon nitride, but is not directly connected to the upper part of the insulating body on the connection side, but is separated therefrom by means of an air gap. This publication also does not contain any information about the polarities of the center or the ground electrode.

Funkenentladungseinrichtungen, die eine konische Gleitfunkenstrecke aufweisen und deren Mittelelektrode aus einem brennraumseitigen, die Masseelektrode bildenden ringförmigen Körper hervorragt, sind bereits bekannt und dienen zur Erzeugung kurzzeitiger Druckstöße hoher Energie in einem das Entladungsgebiet umgebenden hydraulischen Arbeitsmedium; die Druckstöße werden für die Bearbeitung von Metallen und zu sonstigen mechanischen Arbeitszwecken ausgenutzt (DE-B-12 54 896).Spark discharge devices which have a conical sliding spark gap and whose central electrode protrudes from an annular body on the combustion chamber side, which forms the ground electrode, are already known and are used to generate brief pressure surges of high energy in a hydraulic working medium surrounding the discharge region; the pressure surges are used for the processing of metals and for other mechanical work purposes (DE-B-12 54 896).

Der Erfindung liegt demgegenüber die Aufgabe zugrunde, die obengenannten Zündkerzen für Brennkraftmaschinen derart weiterzubilden, so daß die Länge der Gleitfunkenstrecke bei vorgegebener Zündspannung weiter vergrößert werden kann.In contrast, the invention is based on the object of developing the above-mentioned spark plugs for internal combustion engines in such a way that the length of the sliding spark gap can be further increased for a given ignition voltage.

Diese Aufgabe wird erfindungsgemäß durch die im Kennzeichen des Anspruchs 1 aufgeführten Merkmale gelöst.This object is achieved by the features listed in the characterizing part of claim 1.

Aufgrund des Vorsehens einer die Katode darstellenden sog. Hinterelektrode hinter der brennraumseitigen Oberfläche des Isolierkörpers, bildet sich beim Spannungsanstieg an der Zündkerze infolge der dielektrischen Verschiebung eine Oberflächenladung längs der Oberfläche des Isolierkörpers aus. Diese Oberflächenladung, die proportional der Feldstärke sowie der relativen Dielektrizitätskonstanten (Dielektrizitätszahl) des Oberflächenmaterials des Isolierkörpers ist, bewirkt eine gegenüber der reinen Gasentladung stark reduzierte und vom Druck wenig abhängige Zündspannung. Mit den von den heute üblicherweise in Kraftfahrzeugen verwendeten Zündanlagen zur Verfügung gestellten Zündspannungen lassen sich bei der erfindungsgemäßen Zündkerze Gleitbahnlängen im cm-Bereich mit dem Zündfunken überbrücken. Da mit der möglichen großen Gleitbahnlänge auch die Brennspannung ansteigt, läßt sich sehr leicht Energie übertragen, die auf der langen Wegstrecke der Gleitfunkenstrecke überwiegend dem gasförmigen Kraftstoff-Luft-Gemisch zugeführt wird. Die Form der Oberfläche des Isolierkörpers und der Elektroden kann bei Einhaltung der erfindungsgemäßen Lehre beliebig gewählt werden. Zweckmäßig ist es, bei einer vertretbaren Zündspannung die Oberfläche so auszubilden, daß zur Erzielung einer möglichst hohen Brennspannung eine möglichst große Gleitbahnlänge erreicht wird.Due to the provision of a so-called rear electrode, which represents the cathode, behind the surface of the insulating body on the combustion chamber side, when the voltage on the spark plug rises due to the dielectric displacement, a surface charge forms along the surface of the insulating body. This surface charge, which is proportional to the field strength and the relative dielectric constant (dielectric constant) of the surface material of the insulating body, causes an ignition voltage which is greatly reduced compared to pure gas discharge and is not dependent on the pressure. With the ignition voltages provided by the ignition systems commonly used today in motor vehicles, slideway lengths in the cm range can be bridged with the ignition spark in the spark plug according to the invention. Since the operating voltage increases with the possible large slideway length, it is very easy to transfer energy which is predominantly supplied to the gaseous fuel-air mixture over the long distance of the sliding spark gap. The shape of the surface of the insulating body and the electrodes can be chosen as desired, while adhering to the teaching according to the invention. It is expedient, with a justifiable ignition voltage, to design the surface in such a way that the longest possible slideway length is achieved in order to achieve the highest possible operating voltage.

Mit den heute zur Verfügung stehenden Zündspannungen ist die von der erfindungsgemäßen Zündkerze an das brennbare Kraftstoff-Luft-Gemisch abgegebene Energie etwa zehnmal so hoch wie bei einer herkömmlichen Zündkerze. Umgekehrt besteht bei der erfindungsgemäßen Zündkerze bei gleicher Energieübertragung an das Kraftstoff-Luft-Gemisch ein sehr viel kleinerer Zündspannungsbedarf.With the ignition voltages available today, the energy delivered by the spark plug according to the invention to the combustible fuel-air mixture is approximately ten times as high as in the case of a conventional spark plug. Conversely, the spark plug according to the invention has a much lower ignition voltage requirement with the same energy transfer to the fuel-air mixture.

Die erfindungsgemäße Zündkerze ist für eine Gleit-Glimmentladung mit einer Brenndauer von Millisekunden vorgesehen; bei der Gleit-Glimmentladung werden Erosionsschäden an der brennraumseitigen Oberfläche des Isolierkörpers verhindert.The spark plug according to the invention is intended for a glow discharge with a burn time of milliseconds; The glow discharge prevents erosion damage to the combustion chamber surface of the insulating body.

Bei dieser Gleit-Glimmentladung wird eine hohe Brennspannung erreicht (typischerweise 1 kV), wodurch sich - da die Wärmeverluste über den schlecht wärmeleitenden Isolierkörper und die Energieabfuhr über die Elektroden (Quenching-Verluste) wegen des großen Elektrodenabstandes sehr gering sind - ein der Gleit-Durchbruchentladung nahezu vergleichbarer hoher Wirkungsgrad bei der Energieübertragung an das Kraftstoff-Luft-Gemisch ergibt.With this sliding glow discharge, a high operating voltage is reached (typically 1 kV), which - because the heat losses through the poorly heat-conducting insulating body and the energy dissipation via the electrodes (quenching losses) are very low due to the large electrode spacing - is one of the sliding Breakthrough discharge results in almost comparable high efficiency in the energy transfer to the fuel-air mixture.

Da wie einangs erwähnt, die Ausbildung der Oberflächenentladung mit zunehmender Dielektrizitätszahl des Isolierkörper-Werkstoffes begünstigt wird, ist es zweckmäßig, den Isolierkörper aus einem Werkstoff mit hoher Dielektrizitätszahl herzustellen. Damit würde aber die Zündkerze zugleich eine relativ große Kapazität erhalten, was die Neigung zu einer Gleit-Durchbruchentladung fördert. Um trotz hoher Dielektrizitätszahl des Isolierkörper-Werkstoffes eine Gleit-Glimmentladung zu gewährleisten, ist es zweckmäßig, die Zündkerze gemäß der Ausführungsform der Erfindung in Anspruch 1 auszubilden: Durch das hochdielektrische brennraumseitige Isolierkörper-Unterteil wird die Ausbildung einer Oberflächenladung an der Oberfläche des Isolierkörpers gefördert, was zu einer besonders niedrigen Zündspannung führt. Durch die Zweiteiligkeit des Isolierkörpers, dessen volumenkleineres Unterteil nur die hohe Dielektrizitätszahl aufweist, ist die Kapazität der Zündkerze jedoch relativ niedrig, wodurch eine heiße erosionsverursachende Durchbruchentladung verhindert wird. Ein Durchschlag an der Trennstelle zwischen Unterteil und Oberteil wird durch eine zwischen beiden angebrachte hochisolierende Trennschicht verhindert. Eine Bogenentladung nach der Zündung wird gemäß der Ausführungsform der Erfindung nach Anspruch 6 durch einen Widerstand von etwa 1 kΩ in der Zuleitung der Mittelelektrode vermieden.Since, as mentioned at the beginning, the formation of the surface discharge is promoted with increasing dielectric constant of the insulating body material, it is expedient to produce the insulating body from a material with a high dielectric constant. However, this would also give the spark plug a relatively large capacity, which promotes the tendency to slide breakdown discharge. In order to ensure a glow discharge in spite of the high dielectric constant of the insulating material, it is expedient to design the spark plug according to the embodiment of the invention in claim 1. which leads to a particularly low ignition voltage. Due to the two-part design of the insulating body, the lower-volume part of which has only the high dielectric constant, the capacity of the spark plug is relatively low, which prevents hot erosion-causing breakdown discharge. A breakdown at the separation point between the lower part and the upper part is prevented by a highly insulating separating layer between the two. An arc discharge after the ignition is avoided according to the embodiment of the invention according to claim 6 by a resistance of about 1 kΩ in the lead of the center electrode.

Die Erfindung ist anhand von in der Zeichnung dargestellten Ausführungsbeispielen in der nachfolgenden Beschreibung näher erläutert. Es zeigen:

Fig. 1
eine teilweise geschnittene Zündkerze einer Brennkraftmaschine,
Fig. 2 bis Fig. 14
jeweils eine schematische Darstellung des brennraumseitigen Endabschnittes der Zündkerze in Fig. 1 gemäß zehn verschiedenen Ausführungsbeispielen.
The invention is explained in more detail in the following description with reference to exemplary embodiments shown in the drawing. Show it:
Fig. 1
a partially cut spark plug of an internal combustion engine,
2 to 14
in each case a schematic representation of the combustion chamber end section of the spark plug in FIG. 1 according to ten different exemplary embodiments.

Die in Fig. 1 dargestellte Zündkerze für eine Brennkraftmaschine weist einen rotationssymmetrischen Isolierkörper 10 auf, der auf einem Längsabschnitt von einem ebenfalls rotationssymmetrischen Metallgehäuse 11 umfaßt wird. Das Metallgehäuse 11 trägt auf einem im Durchmesser reduzierten Endabschnitt 12 ein Gewinde 13, mit welchem die Zündkerze in einen Zylinderkopf der Brennkraftmaschine eingeschraubt werden kann. Zum Einschrauben dient ein Schlüsselsechskant 14. Ein Dichtring 15 sorgt für den gasdichten Einbau der Zündkerze im Zylinderkopf. Das Metallgehäuse trägt auf der Stirnseite seines brennraumseitigen, mit dem Gewinde 13 versehenen Endabschnittes 12 eine ringförmige Masseelektrode 16.The spark plug for an internal combustion engine shown in FIG. 1 has a rotationally symmetrical insulating body 10 which is encompassed on a longitudinal section by a likewise rotationally symmetrical metal housing 11. The metal housing 11 has a thread 13 on an end section 12 with a reduced diameter, with which the spark plug can be screwed into a cylinder head of the internal combustion engine. A hexagon key 14 is used for screwing in. A sealing ring 15 ensures the gas-tight installation of the spark plug in the cylinder head. The metal housing carries an annular ground electrode 16 on the end face of its combustion chamber-side end section 12 provided with the thread 13.

Der Isolierkörper 10 besitzt auf seiner Oberfläche eine Anzahl von Ringnuten 17 als sog. Kriechstrombarriere und ist mit einer zentralen axialen Durchgangsbohrung 18 versehen. In der Durchgangsbohrung 18 liegt ein Anschlußbolzen 19, der mit einem Anschlußstück 20 aus dem Isolierkörper 10 an dessen vom Brennraum abgekehrten Ende herausragt, und eine Mittelelektrode 21, die sich in dem brennraumseitigen Endabschnitt des Isolierkörpers 10 erstreckt und über eine hier als Widerstandspanat 27 ausgebildete Glasschmelzflußmasse mit dem Anschlußbolzen 19 elektrisch und mechanisch verbunden ist. Die brennraumseitige Stirnseite der Mittelelektrode 21 liegt frei. Beim Anlegen einer Hochspannung zwischen der Mittelelektrode 21 und der Masseelektrode 16 entsteht zwischen diesen eine Gleitfunkenstrecke 26 längs der brennraumseitigen freien Oberfläche 22 des Isolierkörpers 10.The insulating body 10 has on its surface a number of annular grooves 17 as a so-called leakage current barrier and is provided with a central axial through hole 18. In the through hole 18 is a connecting pin 19, which has a connector 20 from the insulating body 10 protrudes from the end facing away from the combustion chamber, and a center electrode 21 which extends in the end section of the insulating body 10 on the combustion chamber side and is electrically and mechanically connected to the connecting bolt 19 via a glass melt flow mass formed here as a resistance chipboard 27. The combustion chamber end face of the center electrode 21 is exposed. When a high voltage is applied between the center electrode 21 and the ground electrode 16, a sliding spark gap 26 is formed between them along the free surface 22 of the insulating body 10 on the combustion chamber side.

In dem in Figur 1 zu sehenden Ausführungsbeispiel der Zündkerze ist der Isolierkörper 10 in seinem brennraumseitigen Endabschnitt quergeteilt und weist dadurch ein anschlußseitiges Oberteil 23 und ein brennraumseitiges Unterteil 24 auf. Das Oberteil 23 besteht aus Aluminiumoxid (Al₂0₃) mit einer Dielektrizitätszahl ε r von kleiner als zehn, während der Werkstoff des Unterteils 24 eine sehr viel höhere Dielektrizitätszahl, hier etwa 50 - 500, aufweist. In der Trennebene zwischen Oberteil 23 und Unterteil 24 ist eine Trennschicht 25 aus Silikongummi, Epoxydharz oder Glas vorhanden.In the embodiment of the spark plug shown in FIG. 1, the insulating body 10 is cross-divided in its end section on the combustion chamber side and thus has an upper part 23 on the connection side and a lower part 24 on the combustion chamber side. The upper part 23 consists of aluminum oxide (Al₂0₃) with a dielectric constant ε r of less than ten, while the material of the lower part 24 has a much higher dielectric constant, here about 50-500. In the parting plane between the upper part 23 and lower part 24 there is a separating layer 25 made of silicone rubber, epoxy resin or glass.

In den Figuren 2 - 11 sind verschiedene Ausführungsformen der Ausbildung des brennraumseitigen Endabschnittes der Zündkerze dargestellt. In allen Ausführungsbeispielen ist die Oberfläche 22 des Isolierkörpers 10 derart geformt, daß sie von einer Mehrzahl der gedachten Feldlinien 30 (Fig.2)des zwischen der Mittelelektrode 21 und der Masseelektrode 16 bei Anlegen einer Spannung sich ausbildenden elektrischen Feldes durchstoßen wird. Dabei ist bei jedem Ausführungsbeispiel die Elektrode, welche die Katode bildet bzw. ein Teil dieser Elektrode, in Richtung des Feldlinienverlaufs gesehen, hinter der Oberfläche 22 mit Abstand von und in einem beliebigen Neigungswinkel zu dieser Oberfläche 22 entlang geführt. Der Abstand ist dabei beliebig , er kann längs der Oberfläche 22 gleich sein oder sich verändern. Wegen ihrer Lage "hinter" der Oberfläche 22 wird diese Elektrode auch "Hinterelektrode" genannt. Der Verlauf der Feldlinien 30 ist in Fig. 2 stellvertretend für alle Fig. schematisch eingezeichnet.FIGS. 2-11 show different embodiments of the design of the combustion chamber end section of the spark plug. In all exemplary embodiments, the surface 22 of the insulating body 10 is shaped in such a way that it is from a plurality of the imaginary field lines 30 (FIG. 2) of the electrical field which is formed between the center electrode 21 and the ground electrode 16 when a voltage is applied. In each embodiment, the electrode that forms the cathode or a part of this electrode, viewed in the direction of the field line, is guided behind the surface 22 at a distance from and at any angle of inclination to this surface 22. The distance is arbitrary, it can be the same or change along the surface 22. Because of its position "behind" the surface 22, this electrode is also called the "rear electrode". The course of the field lines 30 is shown schematically in FIG. 2 as a representative of all of the figures.

In den Ausführungsbeispielen gemäß Fig. 2,4,5 und 7 - 9 wird die die Katode darstellende Elektrode von der Mittelelektrode 16 gebildet, während in den Ausführungsbeispielen gemäß Fig. 3,6,10 und 14 die Masseelektrode 16 die Katode darstellt. In den einzelnen Figuren ist die Katode durch ein (-) und die Anode durch ein (+) gekennzeichnet. Wie ohne weiteres aus diesen Darstellungen zu erkennen ist, durchstoßen die von der ringförmigen Stirnseite der Masseelektrode 16 (in den Ausführungsbeispielen gemäß Fig. 2,4,5 und 7 - 9) bzw. von der Stirnseite der Mittelelektrode 21 (in den Ausführungsbeispielen gemäß Fig. 3,6,10 und 14) ausgehenden Feldlinien in ihrer Mehrzahl die Oberfläche 22 in einem spitzen oder rechten Winkel und enden in der hinter der Oberfläche 22 und mit Abstand von dieser liegenden Katode. Durch diese zu den elektrischen Feldlinien schräg oder senkrecht gestellten Oberflächenelemente der Oberfläche 22 bildet sich beim Spannungsanstieg zwischen den Elektroden 16,21 infolge der dielektrischen Verschiebung im Isolierkörper 10 eine Elektronenladung an der Oberfläche 22 aus, die proportional der Feldstärke sowie der relativen Dielektrizitätskonstanten bzw. Dielektrizitätszahl des Isolierkörpers 10 ist. Durch diese Oberflächenladung kann der Zündfunke zwischen den Elektroden 16,21 schon bei einer sehr viel niedrigeren Zündspannung überspringen als dies bei einer reinen Gasentladung oder nicht in dieser Weise gestaltetenGleitentladungen der Fall ist.In the exemplary embodiments according to FIGS. 2, 4, 5 and 7 - 9, the electrode representing the cathode is formed by the central electrode 16, while in the exemplary embodiments according to FIGS. 3, 6, 10 and 14 the ground electrode 16 represents the cathode. In the individual figures, the cathode is identified by a (-) and the anode by a (+). As can be easily seen from these representations, the holes penetrate from the ring-shaped end face of the ground electrode 16 (in the exemplary embodiments according to FIGS. 2, 4, 5 and 7 - 9) or from the end face of the center electrode 21 (in the exemplary embodiments according to FIG 3, 6, 10, and 14) the majority of the field lines emanating from the surface 22 at an acute or right angle and end in the cathode lying behind the surface 22 and at a distance from this. As a result of these surface elements of the surface 22, which are inclined or perpendicular to the electrical field lines, an electron charge is formed on the surface 22 when the voltage rises between the electrodes 16, 21 due to the dielectric shift in the insulating body 10, which charge is proportional the field strength and the relative dielectric constant or dielectric constant of the insulating body 10. As a result of this surface charge, the ignition spark between the electrodes 16, 21 can jump at a much lower ignition voltage than is the case with a pure gas discharge or sliding discharges not designed in this way.

Bei den Ausführungsbeispielen der Zündkerze gemäß Fig.2 - 6 und Fig. 8 - Fig. 14 sind die Elektroden konzentrisch zueinander angeordnet, wobei ihre Elektrodenwände parallel zueinander verlaufen. Die Oberfläche 22 des Isolierkörpers 10 steigt in allen Ausführungsbeispielen von der Anode (+) zur Katode (-) hin kontinuierlich an, und zwar derart, daß die Normalen von beliebig kleinen Oberflächenelementen mit der Längsachse 29 des Isolierkörpers 10 bzw. der Längsachse der Elektroden 16,21, einen Winkel einschließen, der größer 0o und höchstens 90o ist. Der Anstieg der Oberfläche kann aber auch diskontinuierlich sein.In the exemplary embodiments of the spark plug according to FIGS. 2-6 and 8-14, the electrodes are arranged concentrically with one another, their electrode walls running parallel to one another. In all exemplary embodiments, the surface 22 of the insulating body 10 rises continuously from the anode (+) to the cathode (-) in such a way that the normals of any small surface elements with the longitudinal axis 29 of the insulating body 10 or the longitudinal axis of the electrodes 16 , 21, enclose an angle that is greater than 0 o and at most 90 o . The increase in the surface can also be discontinuous.

In den Ausführungsbeispielen gemäß Fig. 2,4,5,8 und 9 steht dabei die die Katode (-) bildende Mittelelektrode 21 weit über das Ende der die Anode (+) bildenden Masseelektrode 16 vor. In diesen Ausführungsbeispielen ist der Endabschnitt des Isolierkörpers 10 hutartig ausgebildet, und zwar derart, daß sein Längsprofil eine von der Masseelektrode 16 zur Mittelelektrode 21 hin ansteigende geradlinige (Fig.2,8 und 9 ) oder kurven- oder bogenförmige (Fig.4,5) Kontur aufweist. Bei einem diskontinuierlichen Anstieg der Oberfläche ergibt sich eine treppenartige Kontur.In the exemplary embodiments according to FIGS. 2, 4, 5, 8 and 9, the central electrode 21 forming the cathode (-) projects far beyond the end of the ground electrode 16 forming the anode (+). In these exemplary embodiments, the end section of the insulating body 10 is hat-shaped, in such a way that its longitudinal profile has a rectilinear (Fig. 2.8 and 9) or curved or curved (Fig. 4.5) rising from the ground electrode 16 to the central electrode 21 ) Has a contour. With a discontinuous increase in the surface, a step-like contour results.

Bei den Ausführungsbeispielen der Zündkerze gemäß Fig.3,6, 10 und 14 ist das Ende der die Anode (+) bildenden Mittelelektrode 21 zum ringförmigen Ende der die Katode (-) bildenden Masseelektrode 16 weit zurückversetzt und der brennraumseitige Endabschnitt des Isolierkörpers 10 kraterartig ausgebildet, und zwar derart, daß im Längsprofil von der Mittelelektrode 21 zur Masseelektrode 16 hin ansteigende Flanken mit geradliniger (Fig.3,10 und 14) bzw. kurven- oder bogenförmiger (Fig.6) Kontur entstehen.In the exemplary embodiments of the spark plug according to FIGS. 3, 6, 10 and 14, the end of the center electrode 21 forming the anode (+) is set back to the annular end of the ground electrode 16 forming the cathode (-) and the end section of the insulating body 10 on the combustion chamber side is crater-like , in such a way that in the longitudinal profile from the central electrode 21 to the ground electrode 16 there are rising flanks with a rectilinear (Fig. 3, 10 and 14) or curved or curved (Fig. 6) contour.

Bei der Ausführungsform der Zündkerze gemäß Fig.7 ist die die Katode darstellende Mittelelektrode 21 in dem über die ringförmige Masseelektrode 16 vorstehenden Isolierkörperbereich gegenüber dem mit der Masseelektrode 16 konzentrisch verlaufenden Teil der Mittelelektrode 21 abgewinkelt. Hierdurch wird der zwischen der Mittelelektrode 21 und der Masseelektrode 16 sich ausbildende Zündfunke auf eine vorbestimmte Gleitbahn gezwungen wie sie in Fig. 7 mit 26 bezeichnet ist.In the embodiment of the spark plug according to FIG. 7, the central electrode 21 representing the cathode is angled in the insulating body region protruding beyond the ring-shaped ground electrode 16 in relation to the part of the central electrode 21 which is concentric with the ground electrode 16. As a result, the ignition spark which is formed between the center electrode 21 and the ground electrode 16 is forced onto a predetermined slideway, as is designated by 26 in FIG. 7.

Die bei der beschriebenen Zündkerze auftretende Gleitentladung soll als Glimmentladung im Millisekundenbereich realisiert werden. Ausführungsformen der erfindungsgemäßen Zündkerzen, bei denen über die gesamte brennraumseitige Oberfläche 22 des Isolierkörpers 10 ein gleichmäßiger Abbrand erfolgt, sind in den Figuren 8 - 11 dargestellt. In diesen Ausführungsformen ist mindestens eine der Elektroden 16, 21 in ihrem Endabschnitt 161 bzw. 211 derart ausgebildet, daß die in zur Oberfläche 22 parallel verlaufenden Schnittflächen des Isolierkörpers 10 gemessenen kürzesten Entfernungen zwischen den Elektroden 16, 22 im Bereich der Endabschnitte 161 bzw. 211 mit wachsendem Abstand der parallelen Schnittflächen von der Oberfläche 22 zunehmen. Die Schnittflächen bilden in den Ausführungsbeispielen der Figuren 2, 3, 8 - 11 Kegelmäntel. In den Figuren 8 - 11 ist von den parallelen Schnittflächen jeweils eine Schnittfläche 28 strichliniert eingezeichnet. Wie deutlich zu erkennen ist, verlängert sich bei einem Abbrand der Oberfläche 22 bis auf die Schnittfläche 28 die längs dieser Schnittfläche 28 gemessene kürzeste Entfernung zwischen den Elektroden 16, 21. An dieser Stelle verlängert sich dabei die Gleitbahnlänge zwischen den Elektroden 16, 21 mit zunehmendem Abbrand auf der Oberfläche 22. Da die Gleitbahn mit der kürzesten Entfernung von dem Zündfunken bevorzugt wird, verlagert sich der Zündfunke, und ein am Umfang gleichmäßiger Abbrand der Oberfläche 22 wird erzielt.The sliding discharge occurring in the spark plug described is to be realized as a glow discharge in the millisecond range. Embodiments of the spark plugs according to the invention, in which there is a uniform erosion over the entire surface 22 of the insulating body 10 on the combustion chamber side, are shown in FIGS. 8-11. In these embodiments, at least one of the electrodes 16, 21 is formed in its end section 161 or 211 such that the shortest distances between the electrodes 16, 22 measured in the sectional areas of the insulating body 10 running parallel to the surface 22 in the region of the end sections 161 and 211 increase with increasing distance of the parallel cut surfaces from the surface 22. In the exemplary embodiments in FIGS. 2, 3, 8-11, the cut surfaces form cone shells. FIGS. 8-11 each show a cut surface 28 of the parallel cut surfaces. As can be clearly seen, when the surface 22 burns down to the cut surface 28, the shortest distance between the electrodes 16, 21 measured along this cut surface 28 increases. At this point, the slideway length between the electrodes 16, 21 increases with increasing Burn-off on the surface 22. Since the slideway with the shortest distance from the ignition spark is preferred, the ignition spark is displaced and a uniform burn-off of the surface 22 is achieved on the circumference.

Eine Vorbehandlung der Oberfläche 22 durch Anschmelzen, z. B. durch Laseranwendung oder Gasentladung, verbessert die Widerstandsfähigkeit gegen Erosion.A pretreatment of the surface 22 by melting, e.g. B. by laser application or gas discharge, improves resistance to erosion.

Zur Erzielung einer Gleit-Glimmentladung muß die Zündkerze eine möglichst niedrige Kapazität aufweisen. Bei Verwendung von hochdielektrischen Materialien (Dielektrizitätszahl ε r = 50 - 500) zur Verbesserung der Oberflächenentladung wird der Isolierkörper 10 wie in Figur 1 beschrieben, zweiteilig ausgebildet. Gegebenenfalls wird eine Vorfunkenstrecke im Stecker oder in der Zündkerze vorgesehen. Die Gleit-Glimmentladung ist gasentladungsphysikalisch eine relativ kalte Entladung, da die Elektronen durch Ionenstöße und nicht thermisch aus den Elektrodenoberflächen freigesetzt werden. Eine Erosion der Oberfläche 22 des Isolierkörpers 10 tritt nicht auf.To achieve a glow discharge discharge, the spark plug must have the lowest possible capacity. When using high-dielectric materials (dielectric constant ε r = 50 - 500) to improve the surface discharge, the insulating body 10 as described in Figure 1, formed in two parts. If necessary, a spark gap is provided in the plug or in the spark plug. The sliding glow discharge is a relatively cold discharge in terms of gas discharge, since the electrons are released from the electrode surfaces by ion impacts and not thermally. Erosion of the surface 22 of the insulating body 10 does not occur.

Claims (6)

  1. Spark plug for internal combustion engines having a rotation-symmetrical insulating body (10) which is composed of a connection-side upper part (23) and a combustion chamber-side lower part (24), the end faces of upper part (23) and lower part (24) which are located near to one another being connected to an electrically highly insulating dividing layer (25), and the lower part (24) consisting of a material which has a higher dielectric constant than the material forming the upper part (23) and has an exposed combustion chamber-side surface (22), the insulating body (10) additionally has a central axial continuous bore (17) in whose combustion chamber-side section a central electrode (21) is surrounded laterally and is left uncovered at the end sides and is electrically connected on the connection side to a connecting bolt (19) which protrudes axially out of the insulating body (10, 23), and having a metal housing (11) which surrounds the insulating body (10) at least over a longitudinal section and forms with its combustion chamber-side end an earth electrode (16) which surrounds the central electrode (21) coaxially at a distance, the combustion chamber-side surface (22) of the lower part (24) of the insulating body adjoining on the one hand the combustion chamber-side end of the earth electrode (16) and on the other hand the exposed end of the central electrode (21), characterised in that the upper part (23) of the insulating body (10) consists of a material with a dielectric constant of less than 10 and the lower part (24) of the insulating body (10) consists of a material with a dielectric constant of approximately 50 to 500, and in that the electrode (16 or 21) which operates as cathode (-) protrudes further on the combustion chamber-side than the other electrode (21 or 16, respectively).
  2. Spark plug according to Claim 1, characterised in that the central electrode (21) protrudes further on the combustion chamber side than the annular earth electrode (16).
  3. Spark plug according to Claim 1, characterised in that the annular earth electrode (16) protrudes further on the combustion chamber side than the central electrode (21).
  4. Spark plug according to one of Claims 1 to 3, characterised in that at least one of the electrodes (16, 21) is constructed in its end section (161, 211) in such a way that the shortest distance, measured in this end section area, from the other electrode (21, 16) increases with increasing distance in cut edges (28) which extend in this end section area in the longitudinal direction and parallel to the combustion chamber-side surface (22) of the insulating body (10).
  5. Spark plug according to one of Claims 1 to 4, in which the central electrode is electrically conductively connected to a connecting bolt, characterised in that the electrical connection (27) between the central electrode (21) and connecting bolt (19) is constructed to have high impedance with a resistance value in the kiloohm range.
  6. Spark plug according to one of Claims 1 to 5, characterised in that the dividing layer (25) consists of silicone rubber, epoxy resin or glass.
EP86905220A 1985-09-17 1986-09-13 Surface-discharge spark plug Expired - Lifetime EP0238520B1 (en)

Applications Claiming Priority (2)

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DE19853533124 DE3533124A1 (en) 1985-09-17 1985-09-17 SPARK PLUG WITH GLIDING RANGE
DE3533124 1985-09-17

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EP0238520A1 EP0238520A1 (en) 1987-09-30
EP0238520B1 true EP0238520B1 (en) 1992-12-02

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US (1) US4798991A (en)
EP (1) EP0238520B1 (en)
JP (1) JPS63500970A (en)
DE (2) DE3533124A1 (en)
ES (1) ES2002159A6 (en)
WO (1) WO1987001877A1 (en)

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JPS63500970A (en) 1988-04-07
EP0238520A1 (en) 1987-09-30
ES2002159A6 (en) 1988-07-16
DE3687225D1 (en) 1993-01-14
DE3533124A1 (en) 1987-03-26
US4798991A (en) 1989-01-17
WO1987001877A1 (en) 1987-03-26

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