EP0078954B1 - Spark plug for an internal-combustion engine - Google Patents

Spark plug for an internal-combustion engine Download PDF

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Publication number
EP0078954B1
EP0078954B1 EP82109767A EP82109767A EP0078954B1 EP 0078954 B1 EP0078954 B1 EP 0078954B1 EP 82109767 A EP82109767 A EP 82109767A EP 82109767 A EP82109767 A EP 82109767A EP 0078954 B1 EP0078954 B1 EP 0078954B1
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EP
European Patent Office
Prior art keywords
spark plug
insulator
combustion chamber
metal
insulating body
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP82109767A
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German (de)
French (fr)
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EP0078954A1 (en
Inventor
Friedrich Dr. Esper
Karl-Hermann Dr. Friese
Walter Dr. Gohl
Peter Sternad
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OFFERTA DI LICENZA AL PUBBLICO
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Robert Bosch GmbH
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Publication of EP0078954A1 publication Critical patent/EP0078954A1/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
    • H01T13/02—Details
    • H01T13/16—Means for dissipating heat
    • 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

Definitions

  • the invention relates to a spark plug for internal combustion engines according to the type of the main claim - as is already known from US Pat. No. 2,603,200.
  • the longitudinal bore of the insulator contains a liquid metal (e.g.
  • soot are only burned off relatively late on this area of the insulating body, as a result of which misfiring can occur or exist until the free-burning temperature is reached stay. If such spark plugs also have a narrow opening between the liquid metal and the spark gap, a short circuit also frequently occurs because liquid metal grows through the opening, forms a bridge in the direction of the ground electrode and can lead to a short circuit.
  • a spark plug is also described (FIGS. 1 and 6), the metal connecting pin of which extends on the combustion chamber side to the bottom of the insulating body, which contains a narrow opening; the connecting bolt forms the central electrode with its end section on the combustion chamber side, can be cemented in the longitudinal bore of the insulating body and consequently has no desired different effect with regard to heat dissipation during the warm-up phase or during the full load phase of the internal combustion engine.
  • spark plugs are already known which, in connection with their central electrode in the longitudinal bore of the insulating body, have a metal core which is made of copper or silver and which is introduced as a powder or rod into the longitudinal bore of the insulating body, heated and pressed in such that close contact between them the metal core and the insulator is reached; These spark plugs also have the disadvantage with regard to the free-burning temperature at the start or when the internal combustion engine is idling for a long time (British patent 547 119).
  • the spark plug according to the invention with the characterizing features of the main claim has the advantage that it quickly and functionally safely reaches the free-burning temperature of 400/450 ° C in the start-up phase, consequently burning electrically conductive deposits on the combustion chamber-side section of the insulating body, thereby causing misfiring leading, electrically conductive shunts are prevented;
  • glow ignition does not occur at high operating temperatures in the spark plug according to the invention, because in this temperature range they have good heat dissipation from the combustion chamber-side section of the insulating body.
  • a further advantage is that the spark plug according to the invention is suitable for a larger number of different internal combustion engines than is the case with known spark plugs, because the heat flow in the spark plug according to the invention largely adapts to the respective thermal load.
  • the measures listed in the subclaims enable advantageous developments and improvements of the spark plug specified in the main claim; It is particularly advantageous for the free-burning temperature of this spark plug, which is in the start-up phase, to be reached quickly if the end section of the insulating body on the combustion chamber side is thin-walled and / or if an insulating body material with poor thermal conductivity is used at low temperatures. In some applications, it may be expedient to install a separate center electrode made of a material which is inserted into the bottom of the insulating body and which dissipates heat only poorly at low temperatures. -
  • the spark plug according to the invention also allows considerable savings in manufacturing costs (wages, material, systems, energy), enables easier to achieve manufacturing security and has a long service life due to a small change in electrode spacing due to erosion and corrosion.
  • the combustion chamber-side end section of the spark plug 10 according to the invention shown in FIGS. 1 and 2 has a substantially tubular metal housing 11, which has a screw thread 12 on its outside and a key hexagon no longer recorded in FIGS. 1 and 2 for the installation of the spark plug 10 in has an internal combustion engine, not shown.
  • This metal housing 11 carries at its combustion chamber end a wire-shaped ground electrode 13, the free end portion of which is arranged in a hook shape in front of the through hole 14 of the metal housing 11; in certain spark plug designs, the metal housing 11 carries a plurality of ground electrodes 13, in other embodiments the ground electrode is formed by part of the internal combustion engine.
  • a shoulder 15 is formed in the through-bore 14 of the metal housing 11, which shoulder faces away from the combustion chamber of the internal combustion engine and, with the interposition of a sealing ring 16, supports the collar 17 of an essentially rotationally symmetrical insulating body 18.
  • This insulating body 18 is fixed in the metal housing through bore 14 in a known manner by flanging and shrinking, but can also be done in the housing in a different way, such as, for. B. Einkitten be installed. While the head of the insulating body 18, not shown, protrudes from the metal housing 11 on the connection side, the combustion chamber-side section (foot) of the insulating body 18 extends in the direction of the free end section of the ground electrode 13 and tapers in the same direction.
  • This insulating body 18 has an axial longitudinal bore 19, the connection-side region 19/1 merges into the region 19/3 on the combustion chamber side via a frustoconically tapering central region 19/2;
  • This thickness of 0.4 mm of the base 20 also extends over part of the adjoining insulating body 18, namely - measured from the base 20 in the axial direction of the insulating body 18 - over a length of 6 mm;
  • this thickness of the end section of the insulating body 18 with the base 20 on the combustion chamber side can be between 0.2 and 0.9 mm, but this thickness is preferably between 0.3 and 0.6 mm.
  • the length of this thin wall area from the insulating body 18 can, depending on the application, be between 2.5 and 12 mm, but preferably between 5 and 9 mm.
  • the transition from this thin-walled area of the insulating body 18 to the collar 17 must be adapted in length and wall thickness to the respective application - as is the case with known spark plugs.
  • the insulating body 18 consists essentially of aluminum oxide, the 10 weight percent flux (e.g. magnesium and / or calcium silicates) are added; the relatively high proportion of flux compared to conventional spark plug insulators (conventional insulators contain about 5 percent by weight flux) has the effect that the thermal conductivity of the insulator 18 at temperatures below 600 ° C. is lower than with conventional insulators, but that the insulator 18 at temperatures above from 600 to 700 ° C has essentially the same thermal conductivity as conventional material.
  • the lower softening point of the insulating body 18 due to the higher flux content does not hinder the function of the spark plug 10 because the operating temperatures occurring at the spark plug are far below the softening temperature of such a ceramic.
  • the proportion of flux in the insulating body 18 can be in the range between 3 and 20 percent by weight, but is preferably between 8 and 15 percent by weight.
  • connection-side area 19/1 of the insulating body longitudinal bore 19 a metallic connecting bolt 21 protrudes, the end section protruding from the insulating body 18 has a thread or the like (not shown) and at its end section on the combustion chamber side with an anchoring means 22 (e.g. thread, knurling) is provided.
  • This anchoring means 22 of the connecting bolt 21 is firmly and tightly embedded in an electrically conductive sealant 23, which contains the insulating body longitudinal bore 19 in this area.
  • sealants 23 are generally known and are preferably used as an electrically conductive glass melt flow (see, for example, US Pat. No. 3909459).
  • the sealant 23 is followed by a metal core 24 on the combustion chamber side, which - depending on the application - the region 19/3 on the combustion chamber side, possibly also partially the middle region 19/2 of the longitudinal bore 19 of the insulating body, except for a very narrow gap 25 between the metal core 24 and the surface the insulating body longitudinal bore 19 fills.
  • the gap 25 is only present as long as the temperature of the end section of the insulating body 18 on the combustion chamber side is below 450 ° C., and it closes after an operating temperature of 450 to 500 ° C. has been reached.
  • This behavior of the metal core 24 is due to its thermal expansion capacity, which is greater than that of the ceramic of the insulating body 18.
  • Such a metal core 24 preferably consists of aluminum bronze with 8% aluminum, but it can also be made of other materials with appropriate thermal expansion behavior and good thermal conductivity; In addition to aluminum alloys, copper alloys, silver or metal alloys, which mostly contain a considerable proportion of at least one of these substances (eg brass, tin bronze), are also well suited for such a metal core 24.
  • Metals or metal alloys suitable for this purpose preferably have a thermal conductivity of more than 90 W / mK and are liquid or plastically deformable at the melting temperatures used in the spark plug described below such that they melt in the insulating body 18 when the metal core 24 and sealant 23 melt down Fill the affected area 19/3 of the insulating body longitudinal bore 19 without any gaps.
  • this metal core 24 consists of aluminum bronze
  • the insulating body 18, the connecting bolts 21, the sealant 23 and the metal core 24 are mounted in such a way that an aluminum bronze rod of a certain volume is inserted into the combustion chamber-side area 19/3 of the insulating body longitudinal bore 19 , whose end pointing away from the combustion chamber fills the cross-section of the longitudinal bore 19, that a pre-metered amount of a granulated or preformed sealant 23 is then added above the aluminum bronze rod, that in a next step the connecting bolt 21 with its end section carrying the anchoring means 22 above the sealant 23 is inserted into the longitudinal bore 19 of the insulating body, so that in a further step the pre-assembled and upright unit is heated to about the melting temperature of the sealant 23 (e.g.
  • the volume of the metal core 24 can be of different sizes for setting the desired heat dissipation from the combustion chamber-side end section of the insulating body 18 in the direction of the connection side of the spark plug 10 be:
  • the metal core 24 may e.g. B. extend more or less into the area of the sealing ring 16, and / or it can have a different diameter. It should be mentioned that instead of the sealant 23, a combination of sealant 23 known per se with an interference suppressor, not shown, can occur.
  • the insulating body bottom 20 is at a distance 26 (spark gap) opposite the ground electrode 13; this distance 26 is approximately 0.8 mm.
  • the metal core 24 simultaneously serves as the central electrode 27 and the spark jump takes place between this central electrode 27 and the ground electrode 13 via a narrow opening 28 in the insulating body base 20 and the distance 26 between iso serving as an air spark gap lier Economics-bottom 20 and the ground electrode 13.
  • This opening 28 is preferably arranged centrally and has a diameter in the range between about 50 and 300 microns.
  • the insulating body base 20 can be provided with a small depression 29 at the corresponding point; such a depression 29 can be provided on the outside of the insulating body base 20 and / or on the inside of the base 20.
  • a small depression 29 can be provided on the outside of the insulating body base 20 and / or on the inside of the base 20.
  • several such openings 28 can also be present in the base 20. Openings 28 of this type can be produced either by drilling using a laser beam or simply by means of an electrical flashover corresponding voltage between the center electrode 27 and the ground electrode 13, but it can also be pressed into the insulating body 18 using a suitably designed needle (not shown).
  • the end of the insulating body 18 on the combustion chamber side heats up within a very short time, because the insulating body 18 consists of a material that is very poorly heat-conducting at this temperature and because of the gap 25 between Metal core 24 and insulating body 18 heat is dissipated only to a negligible extent; Due to this mode of action, the combustion chamber-side end section of the insulating body 18 quickly reaches the so-called free-burning temperature, which is between 400 and 450 ° C. and at which the insulating body 18 burns electrically conductive deposits on the outside of this area. Electrical shunts as a result of such electrically conductive deposits on the insulating body 18 are consequently avoided, which also contributes to avoiding misfiring.
  • the metal core 24, including its front end section acting as a central electrode 27, has expanded as a result of its thermal expansion behavior in such a way that it comes to bear on the surface of the insulating body longitudinal bore 19/3 with a considerable part of its surface and quickly dissipates heat from the combustion chamber-side region of the insulating body 18 into the rear region of the spark plug.
  • the dimensions and the material of the insulating body 18 are selected so that so much heat is dissipated in the rear part of the spark plug 10 that the metal core 24 remains firm and does not melt. Due to the solid physical state of the metal core 24, the escape of liquid metal parts from the opening 28 of the insulating body 18 and consequently also a short circuit between the center electrode 27 and the ground electrode 13 are avoided.
  • the insulating body 18 has the following dimensions: the outer diameter of the end section on the combustion chamber side is 3.8 mm, over a length of 6 mm; the diameter of the longitudinal bore 19 in the combustion chamber area 19/3 is 3 mm, over a length of 15 mm; the diameter of the collar 17 from the insulating body 18 is 9 mm and begins approximately 13 mm from the bottom 20 of the insulating body 18.
  • the metal core 24 has a length of 15 mm and thus extends somewhat into the central region 19/2 of the longitudinal bore of the insulating body 19.
  • the diameter of the combustion chamber-side region 19/3 of the insulating body longitudinal bore 19 is 1 to 3 mm in most of such spark plugs 10.
  • the metal core 24 consists of aluminum bronze, which is plastically deformed when the insulating body 18, the connecting bolt 21, the sealant 23 and the metal core 24 are assembled in the described method, material is also suitable for the metal core 24 that at the melting temperature of the sealant 23 is molten, but remains firm at the operating temperature of the spark plug, has a corresponding thermal expansion behavior and has good thermal conductivity; These materials also include aluminum, for example.
  • FIG. 3 shows another embodiment of a center electrode 27 'arranged in the insulating body base 20', in the form of a metal pin made of a corrosion and erosion-resistant material, preferably of a noble metal (e.g. platinum metal).
  • This metal pin 27 ' is fixed in an axially arranged opening 30' in the insulating body base 20 ', has a shaft diameter of 0.5 mm and bears a head facing the metal core 24' (without reference numerals);
  • the metal pin 27 'can have a thickness between 0.2 and 1 mm, but preferably has a diameter between 0.3 and 0.6 mm.
  • such a head can also be arranged at the end of the metal pin 27 'on the combustion chamber side, but it can also be omitted in certain applications.
  • the metal pin 27 ' is flush with the insulating body bottom 20', but can also be designed for some applications so that it protrudes up to about 1 mm from the insulating body bottom 20 '.
  • 3 shows such a state of the combustion chamber-side end section of insulating body 18 'and metal core 24', in which the metal core 24 'rests with its surface against the combustion chamber-side region 19' / 3 of the longitudinal bore 19 ', ie in one Temperature range is greater than 450 ° C.
  • this spark plug area had a temperature of less than 400/450 ° C., there would be a gap between the longitudinal insulator bore 19 'and the metal core 24' and thus an interruption in the electrical connection between the metal core 24 'and the metal pin 27'; however, since such a gap is only very narrow, as described, it forms a small spark gap, which is essential for the function of the spark plug known effects.
  • a suitable metal suspension can be introduced and sintered in; A platinum suspension has proven itself for this purpose (see DE-OS 3 132 903).
  • FIG. 4 also shows the combustion chamber-side section of an insulating body 18 "with a metal core 24" built into its longitudinal bore 19 ", but the central electrode 27" built into an opening 28 "is formed from an electrically conductive ceramic part.
  • electrical conductive ceramic part in the bottom 20 "of the insulating body 18" is a porous ceramic with metal in the pores is well suited, such a ceramic can for example consist of aluminum oxide without flux, and aluminum can be chosen as the metal housed in the pores, this in the pores located aluminum can be melted into the longitudinal bore 19 "of the insulating body 18" when the metal core 24 "is melted down;
  • another suitable material eg silver, aluminum bronze, tin bronze
  • the center electrode 27 " which is sintered into the insulating body base 20", cemented or fastened by means of glass, can also contain other metals (see DE-OS 2 854071); such a center electrode 27 "can also consist of semiconductor material (see DE- OS 2 729 099), also e.g. B. made of doped perovskite ceramic (see DE-OS 2824408); metal powder (eg Pt, Ni, Cr, Co) can optionally also be added to the semiconductor material or the Perowski ceramic.
  • substances can also be used which serve as electrical heating elements (see CH-PS 105078). 3 about the small spark gap applies accordingly to this embodiment in FIG. 4.
  • a further exemplary embodiment of a central electrode 27 '" is shown in the figure:
  • a central electrode 27"' is sintered into the bore 28 "'of the insulating body base 20'" and consists of an electrically insulating, ceramic carrier 30 "', which is coated on its surface with an electrically conductive layer 31 "'(e.g. made of platinum);
  • Such a center electrode 27 "' can be provided with a head (without reference number) which rests on the inside of the longitudinal bore 19"' of the insulating body 18 '”or is also arranged on the outside of the insulating body bottom 20"' (see DE- OS 3 038 720).
  • the respective center electrode 27 "or 27” ' is preferably flush with the respective insulating body bottom 20 "or 20"', but it can also be about 1 mm from the bottom 20 "or 20" 'protrude from the combustion chamber.

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Description

Stand derTechnikState of the art

Die Erfindung geht aus von einer Zündkerze für Brennkraftmaschinen nach der Gattung des Hauptanspruchs - wie sie schon aus der US-Patentschrift 2 603 200 bekannt ist. Bei der in dieser US-Patentschrift (siehe Fig. 10) beschriebenen Zündkerze enthält die Isolierkörper-Längsbohrung ein flüssiges Metall (z. B. Quecksilber) oder ein niedrig schmelzendes Metall (Wismut, Zinn, Blei, Antimon), das während der normalen Betriebstemperatur flüssig ist; Zündkerzen dieser Art erreichen während der Startphase der Brennkraftmaschine am brennraumseitigen Endabschnitt ihres Isolierkörpers erst nach relativ langer Zeit eine Temperatur von 400° bis 450° C (sogenannte Freibrenntemperatur), weil der Wärmeübergang vom Isolierkörper zu dem genannten Metall in der Isolierkörper-Längsbohrung schon in der Warmlaufphase sehr gut ist; dadurch, daß der brennraumseitige Abschnitt des Isolierkörpers relativ lange unterhalb der Freibrenntemperatur bleibt, werden elektrisch leitfähige Ablagerungen (z. B. Ruß) auf diesem Isolierkörperbereich erst relativ spät abgebrannt, wodurch bis zum Erreichen der Freibrenntemperatur zu Zündaussetzern führen könnende elektrische Nebenschlüsse entstehen bzw. bestehen bleiben. Sofern derartige Zündkerzen außerdem eine enge Öffnung zwischen dem flüssigen Metall und der Funkenstrecke aufweisen, tritt zudem häufig dadurch ein Kurzschluß auf, daß flüssiges Metall durch die Öffnung hindurchwächst, eine Brücke in Richtung Masseelektrode bildet und zu einem Kurzschluß führen kann.The invention relates to a spark plug for internal combustion engines according to the type of the main claim - as is already known from US Pat. No. 2,603,200. In the spark plug described in this U.S. patent (see Fig. 10), the longitudinal bore of the insulator contains a liquid metal (e.g. mercury) or a low melting metal (bismuth, tin, lead, antimony) which is present during normal operating temperature is liquid; Spark plugs of this type only reach a temperature of 400 ° to 450 ° C (so-called free-burning temperature) after a relatively long time during the start phase of the internal combustion engine at the end section of their insulating body on the combustion chamber, because the heat transfer from the insulating body to the metal mentioned in the longitudinal body bore in the Warm-up phase is very good; Because the section of the insulating body on the combustion chamber side remains relatively long below the free-burning temperature, electrically conductive deposits (e.g. soot) are only burned off relatively late on this area of the insulating body, as a result of which misfiring can occur or exist until the free-burning temperature is reached stay. If such spark plugs also have a narrow opening between the liquid metal and the spark gap, a short circuit also frequently occurs because liquid metal grows through the opening, forms a bridge in the direction of the ground electrode and can lead to a short circuit.

In der oben bereits genannten US-PS 2 603 200 wird außerdem eine Zündkerze beschrieben (Fig. 1 und 6), deren metallischer Anschlußbolzen brennraumseits bis zum Isolierkörper-Boden reicht, welcher eine enge Öffnung enthält; der Anschlußbolzen bildet dabei mit seinem brennraumseitigen Endabschnitt die Mittelelektrode, kann in der Isolierkörper-Längsbohrung eingekittet sein und hat demzufolge keine erwünscht unterschiedliche Wirkung hinsichtlich der Wärmeableitung bei der Warmlaufphase bzw. bei der Vollastphase der Brennkraftmaschine.In the above-mentioned US Pat. No. 2,603,200, a spark plug is also described (FIGS. 1 and 6), the metal connecting pin of which extends on the combustion chamber side to the bottom of the insulating body, which contains a narrow opening; the connecting bolt forms the central electrode with its end section on the combustion chamber side, can be cemented in the longitudinal bore of the insulating body and consequently has no desired different effect with regard to heat dissipation during the warm-up phase or during the full load phase of the internal combustion engine.

Weiterhin sind bereits Zündkerzen bekannt, die in Verbindung mit ihrer Mittelelektrode in der Isolierkörper-Längsbohrung einen Metallkern haben, welcher aus Kupfer oder Silber besteht und als Pulver oder Stange in die Isolierkörper-Längsbohrung eingebracht, erwärmt und derart eingepreßt wird, daß ein enger Kontakt zwischen dem Metallkern und dem Isolator erreicht wird; auch diese Zündkerzen weisen den Nachteil bezüglich der Freibrenntemperatur bei Start oder lang andauerndem Leerlauf der Brennkraftmaschine auf (britische Patentschrift 547 119).Furthermore, spark plugs are already known which, in connection with their central electrode in the longitudinal bore of the insulating body, have a metal core which is made of copper or silver and which is introduced as a powder or rod into the longitudinal bore of the insulating body, heated and pressed in such that close contact between them the metal core and the insulator is reached; These spark plugs also have the disadvantage with regard to the free-burning temperature at the start or when the internal combustion engine is idling for a long time (British patent 547 119).

Auch ist bereits bei Zündkerzen bekannt, in die Isolierkörper-Längsbohrung einen z. B. aus Silber bestehenden Metallkern mittels Schleuderguß spaltlos einzubringen (DE-PS 1 207 709 = US-PS 3 113 232) oder in die Isolierkörper-Längsbohrung einen aus Kupfer oder Nickel bestehenden Metallkern spaltlos einzupressen, dem Stoffe hinzugefügt wurden, um das Wärmeausdehnungsverhalten von Metallkern und Isolierkörper einander anzupassen (US-PS 3061 756); auch diese beiden Ausführungsformen von Zündkerzen weisen den Nachteil auf, daß sie aufgrund der guten Wärmeableitung während der Startphase oder bei Leerlauf der Brennkraftmaschine erst relativ spät bzw. überhaupt nicht ihre Freibrenntemperatur erreichen. Ferner ist es bei Zündkerzen bekannt, an der Innenseite des brennraumseitigen Abschnitts der Metallgehäuse-Längsbohrung ein aus Wärme gut leitendem Material bestehendes Rohr anzuordnen, welches den brennraumseitigen Abschnitt des Isolierkörpers koaxial mit Abstand umfaßt, nach Überschreiten der Freibrenntemperatur aber am gesamten Abschnitt des Isolierkörpers anliegt und Wärme ableitet (US-PS 3 743 877); eine solche Zündkerze ermöglicht in der Startphase ein relativ schnelles Freibrennen ihres brennraumseitigen Bereichs und verringert Glühzündungen bei hohen Betriebstemperaturen in Brennkraftmaschinen. Es hat sich jedoch gezeigt, daß die vorstehend beschriebene Maßnahme funktionell schwer beherrschbar ist.It is also known in the case of spark plugs that a z. B. existing silver metal core by centrifugal casting without gap (DE-PS 1 207 709 = US-PS 3 113 232) or in the insulating body longitudinal hole a copper or nickel existing metal core without a gap, the substances were added to the thermal expansion behavior of Metal core and insulating body to match each other (US-PS 3061 756); These two embodiments of spark plugs also have the disadvantage that, due to the good heat dissipation during the starting phase or when the internal combustion engine is idling, they reach their free-burning temperature only relatively late or not at all. Furthermore, it is known in the case of spark plugs to arrange on the inside of the combustion chamber-side section of the metal housing longitudinal bore a pipe made of heat-conducting material, which coaxially encloses the combustion chamber-side section of the insulating body, but is present on the entire section of the insulating body after the free-burning temperature has been exceeded and Dissipates heat (U.S. Patent No. 3,743,877); Such a spark plug enables a relatively quick free-burning of its combustion chamber area in the starting phase and reduces glow ignition at high operating temperatures in internal combustion engines. However, it has been shown that the measure described above is difficult to control functionally.

Vorteile der ErfindungAdvantages of the invention

Die erfindungsgemäße Zündkerze mit den kennzeichnenden Merkmalen des Hauptanspruchs hat demgegenüber den Vorteil, daß sie in der Startphase schnell und funktionell sicher auf die Freibrenntemperatur von 400/450° C kommt, demzufolge elektrisch leitfähige Ablagerungen auf dem brennraumseitigen Abschnitt des Isolierkörpers verbrennen, wodurch mit zu Zündaussetzern führende, elektrisch leitfähige Nebenschlüsse verhindert werden; wie auch bei den zum Stand der Technik gehörenden Zündkerzen unterbleibt auch bei der erfindungsgemäßen Zündkerze ein Auftreten von Glühzündungen bei hohen Betriebstemperaturen, weil sie in diesem Temperaturbereich eine gute Wärmeableitung vom brennraumseitigen Abschnitt des lsolierkörpers aufweisen. Als weiterer Vorteil ist anzusehen, daß die erfindungsgemäße Zündkerze für eine größere Anzahl verschiedener Brennkraftmaschinen geeignet ist als es bei bekannten Zündkerzen der Fall ist, weil sich nämlich der Wärmefluß in der erfindungsgemäßen Zündkerze weitgehend der jeweiligen thermischen Belastung anpaßt.The spark plug according to the invention with the characterizing features of the main claim has the advantage that it quickly and functionally safely reaches the free-burning temperature of 400/450 ° C in the start-up phase, consequently burning electrically conductive deposits on the combustion chamber-side section of the insulating body, thereby causing misfiring leading, electrically conductive shunts are prevented; As with the spark plugs belonging to the prior art, glow ignition does not occur at high operating temperatures in the spark plug according to the invention, because in this temperature range they have good heat dissipation from the combustion chamber-side section of the insulating body. A further advantage is that the spark plug according to the invention is suitable for a larger number of different internal combustion engines than is the case with known spark plugs, because the heat flow in the spark plug according to the invention largely adapts to the respective thermal load.

Ein zusätzlicher Vorteil ist bei solchen Zündkerzen gegeben, die im Bereich ihres brennraumseitigen Isolierkörper-Abschnitts eine enge Bohrung aufweisen, weil bei der erfindungsgemäßen Zündkerze kein schmelzflüssiges Metall aus dieser Bohrung austritt und demzufolge keine Brücke in Richtung Masseelektrode gebildet wird.An additional advantage is given in those spark plugs which have a narrow bore in the region of their combustion chamber-side insulating body section, because in the case of the invention According to the spark plug, no molten metal emerges from this hole and consequently no bridge is formed in the direction of the ground electrode.

Durch die in den Unteransprüchen aufgeführten Maßnahmen sind vorteilhafte Weiterbildungen und Verbesserungen der im Hauptanspruch angegebenen Zündkerze möglich; besonders vorteilhaft ist es für ein schnelles Erreichen der Freibrenntemperatur dieser in der Startphase befindlichen Zündkerze, wenn der brennraumseitige Endabschnitt des Isolierkörpers dünnwandig gestaltet ist und/oder ein Isolierkörper-Material mit bei niedrigen Temperaturen schlechter Wärmeleitfähigkeit verwendet wird. Bei einigen Anwendungsfällen kann der Einbau einer in den Boden des Isolierkörpers eingefügten, separaten Mittelelektrode aus einem derartigen Material zweckmäßig sein, das bei niedrigen Temperaturen Wärme nur schlecht abführt. - Die erfindungsgemäße Zündkerze erlaubt außerdem erhebliche Fertigungskosteneinsparungen (Lohn, Stoff, Anlagen, Energie), ermöglicht eine einfacher zu erzielende Fertigungssicherheit und hat eine hohe Lebensdauer infolge von geringer, auf Erosion und Korrosion zurückzuführende Änderung des Elektrodenabstandes.The measures listed in the subclaims enable advantageous developments and improvements of the spark plug specified in the main claim; It is particularly advantageous for the free-burning temperature of this spark plug, which is in the start-up phase, to be reached quickly if the end section of the insulating body on the combustion chamber side is thin-walled and / or if an insulating body material with poor thermal conductivity is used at low temperatures. In some applications, it may be expedient to install a separate center electrode made of a material which is inserted into the bottom of the insulating body and which dissipates heat only poorly at low temperatures. - The spark plug according to the invention also allows considerable savings in manufacturing costs (wages, material, systems, energy), enables easier to achieve manufacturing security and has a long service life due to a small change in electrode spacing due to erosion and corrosion.

Zeichnungdrawing

Ausführungsbeispiele der Erfindung sind in der Zeichnung dargestellt und in der nachfolgenden Beschreibung näher erläutert; es zeigt

  • Fig. 1 einen vergrößert dargestellten Längsschnitt durch den brennraumseitigen Abschnitt einer im kalten Zustand befindlichen Zündkerze (Isolierkörper-Metallkern dient gleichzeitig als Mittelelektrode),
  • Fig. einen vergrößert dargestellten Längsschnitt durch den brennraumseitigen Abschnitt der im betriebswarmen Zustand befindlichen Zündkerze nach Fig. 1,
  • Fig. 3 einen vergrößert dargestellten Längsschnitt durch den brennraumseitigen Endabschnitt eines Zündkerzen-Isolierkörpers mit Metallkern und einer in den Boden des Isolierkörpers eingefügten separaten metallischen Mittelelektrode,
  • Fig. 4 einen vergrößert dargestellten Längsschnitt durch den brennraumseitigen Endabschnitt eines Zündkerzen-Isolierkörpers mit Metallkern und einer in den Boden des Isolierkörpers eingefügten separaten, elektrisch leitfähigen Mittelelektrode, die keramische Anteile hat, und
  • Fig. 5 einen vergrößert dargestellten Längsschnitt durch den brennraumseitigen Endabschnitt eines Zündkerzen-Isolierkörpers mit Metallkern und einer in den Boden des Isolierkörpers eingefügten separaten Mittelelektrode, die aus einem keramischen Träger und einer elektrisch leitfähigen Schicht besteht.
Embodiments of the invention are shown in the drawing and explained in more detail in the following description; it shows
  • 1 shows an enlarged longitudinal section through the section on the combustion chamber side of a spark plug which is in the cold state (insulator-metal core also serves as a central electrode),
  • 1 shows an enlarged longitudinal section through the section on the combustion chamber side of the spark plug according to FIG. 1 which is in the warm operating state,
  • 3 shows an enlarged longitudinal section through the end section on the combustion chamber side of a spark plug insulator with a metal core and a separate metallic center electrode inserted into the bottom of the insulator,
  • Fig. 4 is an enlarged longitudinal section through the combustion chamber end portion of a spark plug insulating body with a metal core and a separate, electrically conductive center electrode inserted into the bottom of the insulating body, which has ceramic components, and
  • 5 shows an enlarged longitudinal section through the combustion chamber end section of a spark plug insulating body with a metal core and a separate center electrode inserted into the bottom of the insulating body and consisting of a ceramic carrier and an electrically conductive layer.

Beschreibung der AusführungsbeispieleDescription of the embodiments

Der in den Fig. 1 und 2 gezeigte brennraumseitige Endabschnitt der erfindungsgemäßen Zündkerze 10 besitzt ein im wesentlichen rohrförmiges Metallgehäuse 11, das an seiner Außenseite ein Einschraubgewinde 12 und ein nicht mehr in den Fig. 1 und 2 erfaßtes Schlüsselsechskant für den Einbau der Zündkerze 10 in eine nicht dargestellte Brennkraftmaschine aufweist. Dieses Metallgehäuse 11 trägt an seinem brennraumseitigen Ende eine drahtförmige Masseelektrode 13, deren freier Endabschnitt hakenförmig vor der Durchgangsbohrung 14 des Metallgehäuses 11 angeordnet ist; bei bestimmten Zündkerzen-Ausführungen trägt das Metallgehäuse 11 mehrere Masseelektroden 13, bei anderen Ausführungsformen wird die Masseelektrode von einem Teil der Brennkraftmaschine gebildet. In der Durchgangsbohrung 14 des Metallgehäuses 11 ist eine Schulter 15 eingeformt, die dem Brennraum der Brennkraftmaschine abgewendet ist und unter Zwischenschaltung eines Dichtringes 16 den Bund 17 eines im wesentlichen rotationssymmetrischen Isolierkörpers 18 trägt. Dieser Isolierkörper 18 ist in der Metallgehäuse-Durchgangsbohrung 14 in bekannter Weise durch Bördein und Schrumpfen dichtend festgelegt, kann im Gehäuse jedoch auch auf andere Art wie z. B. Einkitten eingebaut sein. Während der nicht dargestellte Kopf des Isolierkörpers 18 anschlußseits aus dem Metallgehäuse 11 herausragt, erstreckt sich der brennraumseitige Abschnitt (Fuß) des Isolierkörpers 18 in Richtung auf den freien Endabschnitt der Masseelektrode 13 und verjüngt sich in der gleichen Richtung. Dieser Isolierkörper 18 besitzt eine axiale Längsbohrung 19, deren anschlußseitiger Bereich 19/1 über einen kegelstumpfförmig sich verjüngenden mittleren Bereich 19/2 in den brennraumseitigen Bereich 19/3 übergeht; an dem brennraumseitigen Endabschnitt des Isolierkörpers 18 ist ein kuppenförmiger Boden 20 mit angeformt, der nur 0,4 mm dick ist. Diese Dicke von 0,4 mm des Bodens 20 erstreckt sich auch noch über einen Teil des sich anschließenden Isolierkörpers 18, und zwar - gemessen vom Boden 20 in Axialrichtung des Isolierkörpers 18 - auf 6 mm Länge; je nach Anwendungsfall kann diese Dicke des brennraumseitigen Endabschnitts des Isolierkörpers 18 mit dem Boden 20 im Bereich zwischen 0,2 und 0,9 mm liegen, bevorzugt liegt diese Dicke jedoch zwischen 0,3 und 0,6 mm. Auch die Länge dieses dünnen Wandbereiches vom Isolierkörper 18 kann je nach Anwendungsfall zwischen 2,5 und 12 mm, jedoch bevorzugt zwischen 5 und 9 mm liegen. Der Übergang von diesem dünnwandigen Bereich des Isolierkörpers 18 zum Bund 17 hin muß in Länge und Wanddicke dem jeweiligen Anwendungszweck angepaßt sein - wie es auch bei bekannten Zündkerzen der Fall ist.The combustion chamber-side end section of the spark plug 10 according to the invention shown in FIGS. 1 and 2 has a substantially tubular metal housing 11, which has a screw thread 12 on its outside and a key hexagon no longer recorded in FIGS. 1 and 2 for the installation of the spark plug 10 in has an internal combustion engine, not shown. This metal housing 11 carries at its combustion chamber end a wire-shaped ground electrode 13, the free end portion of which is arranged in a hook shape in front of the through hole 14 of the metal housing 11; in certain spark plug designs, the metal housing 11 carries a plurality of ground electrodes 13, in other embodiments the ground electrode is formed by part of the internal combustion engine. A shoulder 15 is formed in the through-bore 14 of the metal housing 11, which shoulder faces away from the combustion chamber of the internal combustion engine and, with the interposition of a sealing ring 16, supports the collar 17 of an essentially rotationally symmetrical insulating body 18. This insulating body 18 is fixed in the metal housing through bore 14 in a known manner by flanging and shrinking, but can also be done in the housing in a different way, such as, for. B. Einkitten be installed. While the head of the insulating body 18, not shown, protrudes from the metal housing 11 on the connection side, the combustion chamber-side section (foot) of the insulating body 18 extends in the direction of the free end section of the ground electrode 13 and tapers in the same direction. This insulating body 18 has an axial longitudinal bore 19, the connection-side region 19/1 merges into the region 19/3 on the combustion chamber side via a frustoconically tapering central region 19/2; A dome-shaped bottom 20, which is only 0.4 mm thick, is integrally formed on the end section of the insulating body 18 on the combustion chamber side. This thickness of 0.4 mm of the base 20 also extends over part of the adjoining insulating body 18, namely - measured from the base 20 in the axial direction of the insulating body 18 - over a length of 6 mm; Depending on the application, this thickness of the end section of the insulating body 18 with the base 20 on the combustion chamber side can be between 0.2 and 0.9 mm, but this thickness is preferably between 0.3 and 0.6 mm. The length of this thin wall area from the insulating body 18 can, depending on the application, be between 2.5 and 12 mm, but preferably between 5 and 9 mm. The transition from this thin-walled area of the insulating body 18 to the collar 17 must be adapted in length and wall thickness to the respective application - as is the case with known spark plugs.

Der Isolierkörper 18 besteht im wesentlichen aus Aluminiumoxid, dem 10 Gewichtsprozent Flußmittel (z. B. Magnesium- und/oder Calciumsilikate) hinzugefügt sind; der gegenüber herkömmlichen Zündkerzen-Isolierkörpern relativ hohe Anteil an Flußmittel (herkömmliche Isolierkörper enthalten etwa 5 Gewichtsprozent Flußmittel) bewirkt, daß die Wärmeleitfähigkeit des Isolierkörpers 18 bei Temperaturen unterhalb von 600°C geringer ist als bei herkömmlichen Isolierkörpern, daß jedoch der Isolierkörper 18 bei Temperaturen oberhalb von 600 bis 700°C im wesentlichen die gleiche Wärmeleitfähigkeit hat wie herkömmliches Material. Der infolge des höheren Flußmittelsgehaltes bedingte niedrigere Erweichungspunkt des Isolierkörpers 18 behindert nicht die Funktion der Zündkerze 10, weil die an der Zündkerze auftretenden Betriebstemperaturen weit unter der Erweichungstemperatur einer solchen Keramik liegen. Der Anteil an Flußmittel im Isolierkörper 18 kann im Bereich zwischen 3 und 20 Gewichtsprozenten liegen, beträgt bevorzugt jedoch zwischen 8 und 15 Gewichtsprozent.The insulating body 18 consists essentially of aluminum oxide, the 10 weight percent flux (e.g. magnesium and / or calcium silicates) are added; the relatively high proportion of flux compared to conventional spark plug insulators (conventional insulators contain about 5 percent by weight flux) has the effect that the thermal conductivity of the insulator 18 at temperatures below 600 ° C. is lower than with conventional insulators, but that the insulator 18 at temperatures above from 600 to 700 ° C has essentially the same thermal conductivity as conventional material. The lower softening point of the insulating body 18 due to the higher flux content does not hinder the function of the spark plug 10 because the operating temperatures occurring at the spark plug are far below the softening temperature of such a ceramic. The proportion of flux in the insulating body 18 can be in the range between 3 and 20 percent by weight, but is preferably between 8 and 15 percent by weight.

In den anschlußseitigen Bereich 19/1 der lsolierkörper-Längsbohrung 19 ragt ein metallischer Anschlußbolzen 21, dessen aus dem Isolierkörper 18 herausragender Endabschnitt ein nicht dargestelltes Gewinde oder ähnliches besitzt und an seinem brennraumseitigen Endabschnitt mit einem Verankerungsmittel 22 (z. B. Gewinde, Rändelung) versehen ist. Dieses Verankerungsmittel 22 des Anschlußbolzens 21 ist fest und dicht in einem elektrisch leitfähigem Dichtmittel 23 eingebettet, das die Isolierkörper-Längsbohrung 19 in diesem Bereich enthält. Derartige Dichtmittel 23 sind allgemein bekannt und finden bevorzugt als elektrisch leitfähiger Glasschmelzfluß Anwendung (siehe z. B. US-Patentschrift 3909459). Dem Dichtmittel 23 schließt sich brennraumseits ein Metallkern 24 an, der - je nach Anwendungsfall - den brennraumseitigen Bereich 19/3, gegebenenfalls auch teilweise den mittleren Bereich 19/2 der Isolierkörper-Längsbohrung 19 bis auf einen sehr engen Spalt 25 zwischen Metallkern 24 und Oberfläche der lsolierkörper-Längsbohrung 19 ausfüllt. Der Spalt 25 ist jedoch nur dann vorhanden, solange die Temperatur des brennraumseitigen Endabschnitts vom Isolierkörper 18 unterhalb 450°C liegt, und er schließt sich nach Erreichen einer Betriebstemperatur von 450 bis 500°C. Dieses Verhalten des Metallkerns 24 ist auf sein Wärmeausdehnungsvermögen zurückzuführen, das gegenüber dem der Keramik des Isolierkörpers 18 größer ist. Ein solcher Metallkern 24 besteht vorzugsweise aus Aluminiumbronze mit 8% Aluminium, er kann aber auch aus anderen Stoffen mit entsprechendem Wärmeausdehnungsverhalten und guter Wärmeleitfähigkeit hergestellt sein; gut geeignet sind für einen solchen Metallkern 24 außer Aluminiumlegierungen auch Kupferlegierungen, Silber oder Metallegierungen, die zumeist einen erheblichen Anteil von mindestens einem dieser Stoffe enthalten (z. B. Messing, Zinnbronze). Für diesen Zweck geeignete Metalle bzw. Metallegierungen haben bevorzugt eine Wärmeleitfähigkeit von mehr als 90 W/mK und sind bei den nachfolgend beschriebenen, bei der Zündkerze angewendeten Einschmelztemperaturen flüssig oder derart plastisch verformbar, daß sie beim Einschmelzen von Metallkern 24 und Dichtmittel 23 im Isolierkörper 18 den betroffenen Bereich 19/3 der Isolierkörper-Längsbohrung 19 spaltfrei ausfüllen. Bei der bevorzugten Ausführungsform, bei der dieser Metallkern 24 aus Aluminiumbronze besteht, erfolgt die Montage von Isolierkörper 18, Anschlußbolzen 21, Dichtmittel 23 und Metallkern 24 derart, daß in den brennraumseitigen Bereich 19/3 der Isolierkörper-Längsbohrung 19 ein Aluminiumbronzestab bestimmten Volumens eingefügt wird, dessen vom Brennraum wegweisendes Ende den Querschnitt der Längsbohrung 19 ausfüllt, daß anschließend eine vordosierte Menge eines granulierten oder als Tablette vorgeformten Dichtmittels 23 oberhalb des Aluminiumbronzestabes hineingegeben wird, daß in einem nächsten Schritt der Anschlußbolzen 21 mit seinem das Verankerungsmittel 22 tragenden Endabschnitt oberhalb des Dichtmittels 23 in die Isolierkörper-Längsbohrung 19 eingesteckt wird, daß in einem weiteren Schritt die derart vormontierte und senkrecht stehende Baueinheit etwa auf die Einschmelztemperatur des Dichtmittels 23 erwärmt wird (z. B. 900°C), daß dann Druck auf den Anschlußbolzen 21 in Richtung auf das Dichtmittel 23 so stark ausgeübt wird, so daß sich der bei dieser Temperatur warmverformbare Aluminiumbronzestab mit seiner gesamten Oberfläche im entsprechenden Bereich in der Längsbohrung 19 anlegt, daß die Baueinheit anschließend gekühlt wird, wobei der Druck auf den Anschlußbolzen 21 bevorzugt erst kurz vor Erreichen des Transformationspunkts (z. B. 500° C) des Dichtmittels 23 entfernt wird. Beim Abkühlen der Baueinheit bildet sich infolge des unterschiedlichen Wärmeausdehnungsverhaltens von Isolierkörper 18 und Metallkern 24 zwischen diesen beiden den Spalt 25. Für die Einstellung der gewünschten Wärmeableitung vom brennraumseitigen Endabschnitt des Isolierkörpers 18 in Richtung Anschlußseite der Zündkerze 10 kann das Volumen des Metallkernes 24 verschieden groß gestaltet sein: Der Metallkern 24 kann z. B. mehr oder weniger bis in den Bereich des Dichtringes 16 reichen, und/oder er kann einen unterschiedlichen Durchmesser haben. Es sei erwähnt, daß anstelle des Dichtmittels 23 auch eine an sich bekannte Kombination von Dichtmittel 23 mit einem nicht dargestellten Entstörwiderstand treten kann.In the connection-side area 19/1 of the insulating body longitudinal bore 19 a metallic connecting bolt 21 protrudes, the end section protruding from the insulating body 18 has a thread or the like (not shown) and at its end section on the combustion chamber side with an anchoring means 22 (e.g. thread, knurling) is provided. This anchoring means 22 of the connecting bolt 21 is firmly and tightly embedded in an electrically conductive sealant 23, which contains the insulating body longitudinal bore 19 in this area. Such sealants 23 are generally known and are preferably used as an electrically conductive glass melt flow (see, for example, US Pat. No. 3909459). The sealant 23 is followed by a metal core 24 on the combustion chamber side, which - depending on the application - the region 19/3 on the combustion chamber side, possibly also partially the middle region 19/2 of the longitudinal bore 19 of the insulating body, except for a very narrow gap 25 between the metal core 24 and the surface the insulating body longitudinal bore 19 fills. However, the gap 25 is only present as long as the temperature of the end section of the insulating body 18 on the combustion chamber side is below 450 ° C., and it closes after an operating temperature of 450 to 500 ° C. has been reached. This behavior of the metal core 24 is due to its thermal expansion capacity, which is greater than that of the ceramic of the insulating body 18. Such a metal core 24 preferably consists of aluminum bronze with 8% aluminum, but it can also be made of other materials with appropriate thermal expansion behavior and good thermal conductivity; In addition to aluminum alloys, copper alloys, silver or metal alloys, which mostly contain a considerable proportion of at least one of these substances (eg brass, tin bronze), are also well suited for such a metal core 24. Metals or metal alloys suitable for this purpose preferably have a thermal conductivity of more than 90 W / mK and are liquid or plastically deformable at the melting temperatures used in the spark plug described below such that they melt in the insulating body 18 when the metal core 24 and sealant 23 melt down Fill the affected area 19/3 of the insulating body longitudinal bore 19 without any gaps. In the preferred embodiment, in which this metal core 24 consists of aluminum bronze, the insulating body 18, the connecting bolts 21, the sealant 23 and the metal core 24 are mounted in such a way that an aluminum bronze rod of a certain volume is inserted into the combustion chamber-side area 19/3 of the insulating body longitudinal bore 19 , whose end pointing away from the combustion chamber fills the cross-section of the longitudinal bore 19, that a pre-metered amount of a granulated or preformed sealant 23 is then added above the aluminum bronze rod, that in a next step the connecting bolt 21 with its end section carrying the anchoring means 22 above the sealant 23 is inserted into the longitudinal bore 19 of the insulating body, so that in a further step the pre-assembled and upright unit is heated to about the melting temperature of the sealant 23 (e.g. 900 ° C.), so that pressure on the connecting bolt 21 in the direction au f the sealant 23 is exerted so strongly that the aluminum bronze rod, which can be thermoformed at this temperature, rests with its entire surface in the corresponding area in the longitudinal bore 19 that the assembly is then cooled, the pressure on the connecting bolt 21 preferably only shortly before reaching the transformation point (e.g. B. 500 ° C) of the sealant 23 is removed. When the structural unit cools down, the gap 25 forms between the two due to the different thermal expansion behavior of the insulating body 18 and the metal core 24. The volume of the metal core 24 can be of different sizes for setting the desired heat dissipation from the combustion chamber-side end section of the insulating body 18 in the direction of the connection side of the spark plug 10 be: The metal core 24 may e.g. B. extend more or less into the area of the sealing ring 16, and / or it can have a different diameter. It should be mentioned that instead of the sealant 23, a combination of sealant 23 known per se with an interference suppressor, not shown, can occur.

Dem Isolierkörper-Boden 20 steht mit Abstand 26 (Funkenstrecke) die Masseelektrode 13 gegenüber; dieser Abstand 26 beträgt etwa 0,8 mm. Bei der vorliegenden bevorzugten Ausführungsform einer erfindungsgemäßen Zündkerze 10 dient der Metallkern 24 gleichzeitig als Mittelelektrode 27 und der Funkenübersprung erfolgt zwischen dieser Mittelelektrode 27 und der Masseelektrode 13 über eine enge Öffnung 28 im Isolierkörper-Boden 20 und den als Luftfunkenstrecke dienenden Abstand 26 zwischen lsolierkörper-Boden 20 und der Masseelektrode 13. Diese Öffnung 28 ist bevorzugt zentral angeordnet und hat einen Durchmesser im Bereich zwischen etwa 50 und 300 µm. Zur Vorfixierung dieser Öffnung 28 kann der Isolierkörper-Boden 20 an der entsprechenden Stelle mit einer kleinen Einsenkung 29 versehen sein; eine solche Einsenkung 29 kann an der Außenseite des Isolierkörper-Bodens 20 und/oder an der Innenseite des Bodens 20 angebracht sein. Anstelle einer einzigen Öffnung 28 können auch mehrere derartiger Öffnungen 28 im Boden 20 vorhanden sein. Die Herstellung derartiger Öffnungen 28 kann entweder durch Bohren mittels Laserstrahl oder auch einfach durch einen elektrischen Überschlag entsprechender Spannung zwischen der Mittelelektrode 27 und der Masseelektrode 13 erfolgen, sie kann aber auch mit einer entsprechend ausgebildeten Nadel (nicht dargestellt) in den Isolierkörper 18 eingepreßt werden.The insulating body bottom 20 is at a distance 26 (spark gap) opposite the ground electrode 13; this distance 26 is approximately 0.8 mm. In the present preferred embodiment of a spark plug 10 according to the invention, the metal core 24 simultaneously serves as the central electrode 27 and the spark jump takes place between this central electrode 27 and the ground electrode 13 via a narrow opening 28 in the insulating body base 20 and the distance 26 between iso serving as an air spark gap lierkörper-bottom 20 and the ground electrode 13. This opening 28 is preferably arranged centrally and has a diameter in the range between about 50 and 300 microns. To pre-fix this opening 28, the insulating body base 20 can be provided with a small depression 29 at the corresponding point; such a depression 29 can be provided on the outside of the insulating body base 20 and / or on the inside of the base 20. Instead of a single opening 28, several such openings 28 can also be present in the base 20. Openings 28 of this type can be produced either by drilling using a laser beam or simply by means of an electrical flashover corresponding voltage between the center electrode 27 and the ground electrode 13, but it can also be pressed into the insulating body 18 using a suitably designed needle (not shown).

Wird eine kalte Brennkraftmaschine mittels einer erfindungsgemäßen Zündkerze 10 in Betrieb genommen, dann erwärmt sich das brennraumseitige Ende des Isolierkörpers 18 innerhalb sehr kurzer Zeit, und zwar, weil der Isolierkörper 18 aus einem bei dieser Temperatur sehr schlecht wärmeleitenden Material besteht und infolge des Spaltes 25 zwischen Metallkern 24 und lsolierkörper 18 Wärme nur im vernachlässigbarem Umfange abgeleitet wird; aufgrund dieser Wirkungsweise erreicht der brennraumseitige Endabschnitt des Isolierkörpers 18 schnell die sogenannte Freibrenntemperatur, die zwischen 400 und 450° C liegt und bei der das Verbrennen von elektrisch leitfähigen Ablagerungen auf der Außenseite dieses Bereiches vom Isolierkörper 18 erfolgt. Elektrische Nebenschlüsse infolge solcher elektrisch leitfähiger Ablagerungen auf dem Isolierkörper 18 werden demzufolge vermieden, was auch zum Vermeiden von Zündaussetzern beiträgt.If a cold internal combustion engine is put into operation by means of a spark plug 10 according to the invention, then the end of the insulating body 18 on the combustion chamber side heats up within a very short time, because the insulating body 18 consists of a material that is very poorly heat-conducting at this temperature and because of the gap 25 between Metal core 24 and insulating body 18 heat is dissipated only to a negligible extent; Due to this mode of action, the combustion chamber-side end section of the insulating body 18 quickly reaches the so-called free-burning temperature, which is between 400 and 450 ° C. and at which the insulating body 18 burns electrically conductive deposits on the outside of this area. Electrical shunts as a result of such electrically conductive deposits on the insulating body 18 are consequently avoided, which also contributes to avoiding misfiring.

Bei Erreichen eines Temperaturbereiches von 450 bis 500°C hat sich der Metallkern 24 einschließlich seines vorderen als Mittelelektrode 27 wirkenden Endabschnitts infolge seines Wärmeausdehnungsverhaltens derart ausgedehnt, daß er mit einem erheblichen Teil seiner Oberfläche an der Oberfläche der Isolierkörper-Längsbohrung 19/3 zur Anlage kommt und Wärme aus dem brennraumseitigen Bereich des Isolierkörpers 18 schnell in den hinteren Bereich der Zündkerze ableitet. Die Abmessungen und das Material des Isolierkörpers 18 sind so gewählt, daß soviel Wärme in den hinteren Teil der Zündkerze 10 abgeführt wird, daß der Metallkern 24 fest bleibt und nicht schmilzt. Aufgrund des festen Aggregatzustandes vom Metallkern 24 wird das Austreten von flüssigen Metallteilen aus der Öffnung 28 des Isolierkörpers 18 und demzufolge auch ein Kurzschluß zwischen der Mittelelektrode 27 und der Masseelektrode 13 vermieden.When a temperature range of 450 to 500 ° C has been reached, the metal core 24, including its front end section acting as a central electrode 27, has expanded as a result of its thermal expansion behavior in such a way that it comes to bear on the surface of the insulating body longitudinal bore 19/3 with a considerable part of its surface and quickly dissipates heat from the combustion chamber-side region of the insulating body 18 into the rear region of the spark plug. The dimensions and the material of the insulating body 18 are selected so that so much heat is dissipated in the rear part of the spark plug 10 that the metal core 24 remains firm and does not melt. Due to the solid physical state of the metal core 24, the escape of liquid metal parts from the opening 28 of the insulating body 18 and consequently also a short circuit between the center electrode 27 and the ground electrode 13 are avoided.

Bei einem Ausführungsbeispiel hat der Isolierkörper 18 die folgenden Abmessungen: Der Außendurchmesser des brennraumseitigen Endabschnitts beträgt 3,8 mm, und zwar über eine Länge von 6 mm; der Durchmesser der Längsbohrung 19 im brennraumseitigen Bereich 19/3 beträgt 3 mm, und zwar über eine Länge von 15 mm; der Durchmesser des Bundes 17 vom Isolierkörper 18 beträgt 9 mm und beginnt etwa 13 mm vom Boden 20 des Isolierkörpers 18. Der Metallkern 24 hat bei diesem Ausführungsbeispiel eine Länge von 15 mm und reicht damit etwas in den mittleren Bereich 19/2 der Isolierkörper-Längsbohrung 19. Der Durchmesser des brennraumseitigen Bereichs 19/3 der Isolierkörper-Längsbohrung 19 beträgt 1 bis 3 mm bei den meisten derartigen Zündkerzen 10.In one embodiment, the insulating body 18 has the following dimensions: the outer diameter of the end section on the combustion chamber side is 3.8 mm, over a length of 6 mm; the diameter of the longitudinal bore 19 in the combustion chamber area 19/3 is 3 mm, over a length of 15 mm; the diameter of the collar 17 from the insulating body 18 is 9 mm and begins approximately 13 mm from the bottom 20 of the insulating body 18. In this exemplary embodiment, the metal core 24 has a length of 15 mm and thus extends somewhat into the central region 19/2 of the longitudinal bore of the insulating body 19. The diameter of the combustion chamber-side region 19/3 of the insulating body longitudinal bore 19 is 1 to 3 mm in most of such spark plugs 10.

Während beim vorliegenden Ausführungsbeispiel der Metallkern 24 aus Aluminiumbronze besteht, welche beim Zusammenbau von Isolierkörper 18, Anschlußbolzen 21, Dichtmittel 23 und Metallkern 24 bei dem beschriebenen Verfahren plastisch verformt wird, ist für den Metallkern 24 auch Material geeignet, daß bei der Einschmelztemperatur des Dichtmittels 23 schmelzflüssig ist, bei der Betriebstemperatur der Zündkerze jedoch fest bleibt, ein entsprechendes Wärmeausdehnungsverhalten aufweist und gute Wärmeleitfähigkeit besitzt; zu diesen Materialien gehört auch beispielsweise Aluminium.While in the present exemplary embodiment the metal core 24 consists of aluminum bronze, which is plastically deformed when the insulating body 18, the connecting bolt 21, the sealant 23 and the metal core 24 are assembled in the described method, material is also suitable for the metal core 24 that at the melting temperature of the sealant 23 is molten, but remains firm at the operating temperature of the spark plug, has a corresponding thermal expansion behavior and has good thermal conductivity; These materials also include aluminum, for example.

In der Fig. 3 ist eine andere Ausführungsform einer im Isolierkörper-Boden 20' angeordneten Mittelelektrode 27' dargestellt, und zwar in Form eines Metallstifts aus einem korrosions- und abbrandfestem Material, vorzugsweise aus einem Edelmetall (z. B. Platinmetall). Dieser Metallstift 27' ist in einer axial angeordneten Öffnung 30' im Isolierkörper-Boden 20' festgelegt, hat einen Schaftdurchmesser von 0,5 mm und trägt einen zum Metallkern 24' weisenden Kopf (ohne Bezugszeichen); je nach Anwendungsfall kann der Metallstift 27' eine Dicke zwischen 0,2 und 1 mm haben, hat bevorzugt jedoch einen Durchmesser zwischen 0,3 und 0,6 mm. Anstelle des zum Metallkern 24' weisenden Kopfes des Metallstiftes 27' kann ein solcher Kopf auch an dem brennraumseitigen Ende des Metallstiftes 27' angeordnet sein, er kann bei gewissen Anwendungsfällen jedoch auch entfallen. Der Metallstift 27' schließt bündig mit dem Isolierkörper-Boden 20' ab, kann jedoch für manche Anwendungsfälle auch so ausgebildet werden, daß er bis zu etwa 1 mm aus dem Isolierkörper-Boden 20' hervorragt. - In der Fig. 3 ist ein solcher Zustand des brennraumseitigen Endabschnitts von Isolierkörper 18' und Metallkern 24' gezeigt, bei dem der Metallkern 24' mit seiner Oberfläche an den brennraumseitigen Bereich 19'/3 der Längsbohrung 19' anliegt, d. h. sich in einem Temperaturbereich von größer als 450°C befindet. Im Falle, daß dieser Zündkerzenbereich eine Temperatur von weniger als 400/450° C hätte, befände sich zwischen der Isolierkörper-Längsbohrung 19' und dem Metallkern 24' ein Spalt und damit eine Unterbrechung der elektrischen Verbindung zwischen Metallkern 24' und Metallstift 27'; da ein solcher Spalt jedoch nur - wie beschrieben - sehr eng ist, bildet er eine kleine Vorfunkenstrecke, welche für die Funktion der Zündkerze bekannterweise Vorteile bewirkt. Es sei erwähnt, daß anstelle eines solchen, im Isolierkörper-Boden 20' eingesinterten Metallstiftes 27' eine geeignete Metallsuspension eingebracht und eingesintert werden kann; bewährt hat sich für diesen Zweck eine Platinsuspension (siehe DE-OS 3 132 903).3 shows another embodiment of a center electrode 27 'arranged in the insulating body base 20', in the form of a metal pin made of a corrosion and erosion-resistant material, preferably of a noble metal (e.g. platinum metal). This metal pin 27 'is fixed in an axially arranged opening 30' in the insulating body base 20 ', has a shaft diameter of 0.5 mm and bears a head facing the metal core 24' (without reference numerals); Depending on the application, the metal pin 27 'can have a thickness between 0.2 and 1 mm, but preferably has a diameter between 0.3 and 0.6 mm. Instead of the head of the metal pin 27 'facing the metal core 24', such a head can also be arranged at the end of the metal pin 27 'on the combustion chamber side, but it can also be omitted in certain applications. The metal pin 27 'is flush with the insulating body bottom 20', but can also be designed for some applications so that it protrudes up to about 1 mm from the insulating body bottom 20 '. 3 shows such a state of the combustion chamber-side end section of insulating body 18 'and metal core 24', in which the metal core 24 'rests with its surface against the combustion chamber-side region 19' / 3 of the longitudinal bore 19 ', ie in one Temperature range is greater than 450 ° C. In the event that this spark plug area had a temperature of less than 400/450 ° C., there would be a gap between the longitudinal insulator bore 19 'and the metal core 24' and thus an interruption in the electrical connection between the metal core 24 'and the metal pin 27'; however, since such a gap is only very narrow, as described, it forms a small spark gap, which is essential for the function of the spark plug known effects. It should be mentioned that instead of such a metal pin 27 'sintered into the insulating body base 20', a suitable metal suspension can be introduced and sintered in; A platinum suspension has proven itself for this purpose (see DE-OS 3 132 903).

In der Fig. 4 ist ebenfalls der brennraumseitige Abschnitt eines Isolierkörpers 18" mit in seiner Längsbohrung 19" eingebautem Metallkern 24" dargestellt, wobei jedoch die in einer Öffnung 28" eingebaute Mittelelektrode 27" aus einem elektrisch leitfähigem Keramikteil gebildet wird. Als ein solches elektrisch leitfähiges Keramikteil im Boden 20" des Isolierkörpers 18" ist eine poröse Keramik mit in den Poren befindlichem Metall gut geeignet; eine derartige Keramik kann beispielsweise aus Aluminiumoxid ohne Flußmittel bestehen, und als in den Poren untergebrachtes Metall kann Aluminium gewählt werden. Dieses in den Poren befindliche Aluminium kann gleichzeitig beim Einschmelzen des Metallkernes 24" in die Längsbohrung 19" des Isolierkörpers 18" eingeschmolzen werden; anstelle des Materials, aus dem der Metallkern 24" besteht, kann auch ein anderes geeignetes Material (z. B. Silber, Aluminiumbronze, Zinnbronze) hierfür Verwendung finden, es muß jedoch zumeist in einem separaten Arbeitsgang in das Keramikteil eingebracht werden. Bei weiteren Varianten kann die Mittelelektrode 27", welche in den lsolierkörper-Boden 20" eingesintert, eingekittet oder mittels Glas befestigt ist, auch andere Metalle enthalten (siehe DE-OS 2 854071); eine solche Mittelelektrode 27" kann auch aus Halbleitermaterial bestehen (siehe DE-OS 2 729 099), auch z. B. aus dotierter Perowskit-Keramik (siehe DE-OS 2824408); dem Halbleitermaterial bzw. der Perowski-Keramik kann gegebenenfalls auch noch Metallpulver (z. B. Pt, Ni, Cr, Co) zugegeben werden. Es können für diesen Zweck aber auch Stoffe Verwendung finden, welche als elektrische Heizstäbe dienen (siehe CH-PS 105078). Das zu dem Ausführungsbeispiel gemäß Fig. 3 über die kleine Vorfunkenstrecke Gesagte gilt für dieses Ausführungsbeispiel in Fig. 4 entsprechend.4 also shows the combustion chamber-side section of an insulating body 18 "with a metal core 24" built into its longitudinal bore 19 ", but the central electrode 27" built into an opening 28 "is formed from an electrically conductive ceramic part. As such, it is electrical conductive ceramic part in the bottom 20 "of the insulating body 18" is a porous ceramic with metal in the pores is well suited, such a ceramic can for example consist of aluminum oxide without flux, and aluminum can be chosen as the metal housed in the pores, this in the pores located aluminum can be melted into the longitudinal bore 19 "of the insulating body 18" when the metal core 24 "is melted down; Instead of the material from which the metal core 24 "is made, another suitable material (eg silver, aluminum bronze, tin bronze) can also be used for this purpose, but it usually has to be introduced into the ceramic part in a separate operation. For further variants The center electrode 27 ", which is sintered into the insulating body base 20", cemented or fastened by means of glass, can also contain other metals (see DE-OS 2 854071); such a center electrode 27 "can also consist of semiconductor material (see DE- OS 2 729 099), also e.g. B. made of doped perovskite ceramic (see DE-OS 2824408); metal powder (eg Pt, Ni, Cr, Co) can optionally also be added to the semiconductor material or the Perowski ceramic. For this purpose, however, substances can also be used which serve as electrical heating elements (see CH-PS 105078). 3 about the small spark gap applies accordingly to this embodiment in FIG. 4.

In der Fig. ist ein weiteres Ausführungsbeispiel für eine Mittelelektrode 27'" dargestellt: In der Bohrung 28"' des Isolierkörper-Bodens 20'" ist eine Mittelelektrode 27"' eingesintert, die aus einem elektrisch isolierendem, keramischen Träger 30"' besteht, welcher auf seiner Oberfläche mit einer elektrisch leitenden Schicht 31"' (z. B. aus Platin) beschichtet ist; eine solche Mittelelektrode 27"' kann mit einem Kopf (ohne Bezugszeichen) versehen sein, welcher auf der Innenseite der Längsbohrung 19"' des Isolierkörpers 18'" aufliegt oder auch auf der Außenseite des Isolierkörper-Bodens 20"' angeordnet ist (siehe DE-OS 3 038 720). Auch bei dieser Ausführungsform einer Mittelelektrode 27"' gilt für die Vorfunkenstrecke zwischen dem Metallkern 24"' und der Mittelelektrode 27 das zu dem Beispiel in Fig. 3 Gesagte.A further exemplary embodiment of a central electrode 27 '"is shown in the figure: A central electrode 27"' is sintered into the bore 28 "'of the insulating body base 20'" and consists of an electrically insulating, ceramic carrier 30 "', which is coated on its surface with an electrically conductive layer 31 "'(e.g. made of platinum); Such a center electrode 27 "'can be provided with a head (without reference number) which rests on the inside of the longitudinal bore 19"' of the insulating body 18 '"or is also arranged on the outside of the insulating body bottom 20"' (see DE- OS 3 038 720). In this embodiment of a center electrode 27 "', the same applies to the spark gap between the metal core 24"' and the center electrode 27 as for the example in FIG. 3.

Auch bei den Ausführungsbeispielen gemäß der Fig. 4 und 5 schließt die jeweilige Mittelelektrode 27" bzw. 27"' bevorzugt bündig mit dem jeweiligen Isolierkörper-Boden 20" bzw. 20"' ab, sie kann jedoch auch um etwa 1 mm aus dem Boden 20" bzw. 20"' brennraumseits hervorragen.4 and 5, the respective center electrode 27 "or 27" 'is preferably flush with the respective insulating body bottom 20 "or 20"', but it can also be about 1 mm from the bottom 20 "or 20" 'protrude from the combustion chamber.

Claims (14)

1. Spark plug having a tubular metal casing which 1) on its outside has means for installation in an internal combustion engine, 2) in a through bore sealingly encloses a usually rotationally symmetrical, heat-resistant insulator which in its end portion at the combustion chamber end has a thin-walled end face provided with an opening, and 3) in its end portion at the combustion chamber end usually has at least one earth electrode facing and spaced (by the spark gap) from a centre electrode disposed in the portion of the insulator at the combustion chamber end and connected, at the connection end, in series with a metal core situated in the longitudinal bore of the insulator and made of a material which is solid in all operating conditions of the internal combustion engine, characterised in that the metal core (24 to 24"') forms a gap (25) with the surface of the longitudinal bore (19 to 19"') in the insulator at operating temperatures below 450 to 500° C, but because of its expansion behaviour at operating temperatures above 450 to 500° C lies against the surface of the longitudinal bore (19 to 19"') in the insulator.
2. Spark plug according to Claim 1, characterised in that the metal core (24 to 24"') is made of a material having a thermal conductivity of at least 90 W/mk.
3. Spark plug according to Claim 1 or 2, characterised in that the end face (20 to 20"') of the insulator (18 to 18"') has a thickness in the range from 0.2 to 0.9 mm, preferably between 0.3 and 0.6mm.
4. Spark plug as claimed in one of Claims 1 to 3, characterised in that the thin-walled end face (20 to 20"') of the insulator extends over a height between 2.5 mm and 12 mm, preferably between 5 and 9 mm, at the combustion chamber end of the insulator (18 to 18"'), and that the end face (20 to 20"') is preferably in the shape of a dome.
5. Spark plug as claimed in one of Claims 1 to 4, characterised in that the insulator (18 to 18"') consists substantially of aluminium oxide and has a flux content in the range between 3 and 20% by weight, preferably between 8 and 15% by weight.
6. Spark plug according to one of Claims 1 to 5, characterised in that the metal core (24 to 24"') is made of a material which is plasically deformable or molten at the melting temperature of an electrically conductive sealant (23) disposed be- .tween the connection pin (21) and the metal core (24 to 24"').
7. Spark plug according to one of Claims 1 to 6, characterised in that the metal core (24 to 24"') consists of aluminium, copper, silver, or metal alloys containing a considerable proportion of at least one of these substances (for example brass, aluminium bronze, tin bronze).
8. Spark plug according to one of Claims 1 to 7, characterised in that the combustion chamber end of the metal core (24) itself forms the centre electrode (27).
9. Spark plug according to Claim 8, characterised in that the opening (28) in the end face (20) of the insulator (18) has a diameter in the range from 50 to 300 µ.
10. Spark plug according to one of Claims 12 to 7, characterised in that the centre electrode (27') is formed by a thin metal pin or a conductor path secured in an opening (28') in the end face (20') of the insulator.
11. Spark plug according to Claim 10, characterised in that the diameter of the metal pin (27') is in the range from 0.2 to 1 mm, preferably in the range from 0.3 to 0.6 mm.
12. Spark plug according to Claim 10 or 11, characterised in that the metal pin (27') consists of a precious metal, preferably of a metal of the platinum group.
13. Spark plug according to one of Claims 1 to 7, characterised in that the centre electrode (27", 27"') is formed by an electrically conductive ceramic part secured in an opening (28", 28"') in the end face (20", 20"') of the insulator.
14. Spark plug according to one of Claims 10 to 13, characterised in that the centre electrode (27' to 27"') projects to a maximum length of about 1 mm from the combustion chamber end of the insulator (18' to 18"'), but preferably lies flush with the combustion chamber end of the insulator (18'to 18"').
EP82109767A 1981-11-07 1982-10-22 Spark plug for an internal-combustion engine Expired EP0078954B1 (en)

Applications Claiming Priority (2)

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DE3144253 1981-11-07
DE19813144253 DE3144253A1 (en) 1981-11-07 1981-11-07 SPARK PLUG FOR INTERNAL COMBUSTION ENGINES

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EP0078954A1 EP0078954A1 (en) 1983-05-18
EP0078954B1 true EP0078954B1 (en) 1985-05-29

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EP (1) EP0078954B1 (en)
JP (1) JPS5887791A (en)
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US9337624B2 (en) * 2012-10-12 2016-05-10 Federal-Mogul Ignition Company Electrode material for a spark plug and method of making the same
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ES517155A0 (en) 1983-08-01
DE3263919D1 (en) 1985-07-04
DE3144253A1 (en) 1983-05-19
US4539503A (en) 1985-09-03
EP0078954A1 (en) 1983-05-18
ES8308167A1 (en) 1983-08-01
JPS5887791A (en) 1983-05-25

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