WO2011128589A1 - Spark plug provided with a means for preventing short circuits - Google Patents

Spark plug provided with a means for preventing short circuits Download PDF

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Publication number
WO2011128589A1
WO2011128589A1 PCT/FR2011/050848 FR2011050848W WO2011128589A1 WO 2011128589 A1 WO2011128589 A1 WO 2011128589A1 FR 2011050848 W FR2011050848 W FR 2011050848W WO 2011128589 A1 WO2011128589 A1 WO 2011128589A1
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WO
WIPO (PCT)
Prior art keywords
electrode
spark plug
cavity
plug according
metal
Prior art date
Application number
PCT/FR2011/050848
Other languages
French (fr)
Inventor
Maxime Makarov
Marc Pariente
Original Assignee
Renault S.A.S.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Renault S.A.S. filed Critical Renault S.A.S.
Priority to CN201180023522.8A priority Critical patent/CN102884686B/en
Priority to EP11730372.7A priority patent/EP2559119B1/en
Publication of WO2011128589A1 publication Critical patent/WO2011128589A1/en

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Classifications

    • 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
    • H01T13/50—Sparking plugs having means for ionisation of gap

Definitions

  • the present invention relates to a spark plug, radiofrequency plasma type (RF), for internal combustion engine.
  • RF radiofrequency plasma type
  • the candle of the invention is equipped with means making it possible to avoid short-circuit phenomena.
  • Such a candle which is described, for example, in FR 2,878,086, FR 2,886,776, FR 2,888,421, FR 2 895 169 and FR 2 895 170, comprises:
  • a central electrode formed in a second conductive material and extending along the main axis
  • a body formed in an electrically insulating material, disposed between said base and said electrode, having an internal lateral face in contact with the electrode and beyond which an end portion of the electrode protrudes.
  • This phenomenon is due to the fact that the outer face of the insulating body which is in contact with the gaseous fuel mixture and the flame, clogs with the combustion residues. In addition, a parasitic spark appears on the fouled external face between the central electrode and the peripheral mass pellet.
  • the spurious spark can either consume only a portion of the available energy in the radio frequency (RF) supply, which nevertheless reduces the volume of the main spark, or cause a short circuit which blocks the emission of the main spark.
  • RF radio frequency
  • the origin of the problem lies in the profile of the junction between the outer face of the insulating body and the central electrode where the dielectric-metal-air media are in contact.
  • the body has a central duct in which is housed the central electrode.
  • the intensity of the electric field is enhanced in the local body-electrode junction zone where the threshold of ionization of the air proves to be largely exceeded.
  • the inclined or curvilinear surface of the insulating body in the junction zone generates a tangential component of the field which favors the propagation of an ionization avalanche phenomenon.
  • this phenomenon contributes to the initiation of a spurious surface spark maintained by the presence of a semiconductor layer of carbon bonded to the fouling of the outer face of the body.
  • Radiofrequency candles of the prior art have only sought to reduce the fouling of the body.
  • the present invention aims to solve the technical problem set out above by intervening on the origin of the problem, that is to say, by aiming at avoiding the strengthening of the electric field at the junction between the external face of the body. dielectric and the central electrode.
  • spark plug whose dielectric body comprises at least one annular cavity of central axis, formed on its lateral face of contact with the electrode so as to locally modify the lines of the electrostatic field at the junction between the outer face of said body and the electrode.
  • said cavity is provided with at least one metal lining element extending, at least partially, along the internal lateral face of the body in contact with the electrode and whose thermal expansion coefficient is similar. of that of the dielectric material of said body.
  • said packing element is formed of a metal layer covering the inner wall of said cavity.
  • said metallic lining element is made in one piece with the electrode.
  • said body is made by sintering a ceramic composition around the electrode carrying said lining element.
  • said electrode is made with the metal filling element by casting of metal in situ in said cavity.
  • said metal lining element is soldered.
  • said packing element is an alloy of one or more metals chosen from molybdenum, tungsten, invar and kovar.
  • the junction between the outer face of the body and the electrode has a convex curvature whose radius is less than or equal to half the distance separating said face of said cavity.
  • the wall of said cavity has a semi-elliptical profile whose half small axis is greater than or equal to three times the radius of curvature of the junction between the outer face of the body and the electrode and the half major axis is greater than or six times the radius.
  • the spark plug of the invention makes it possible to protect the radiofrequency candles from fouling by acting on the very cause of the phenomenon.
  • the invention is based on an attenuation of the field at the junction between the external face of the body and the electrode obtained by a modification of their internal interface in contact.
  • Figure 1 shows a sectional side view of an embodiment of the candle of the invention in the ignition phase.
  • FIGS. 2A and 2B show enlarged and sectional detail views respectively of an RF candle according to the prior art and according to the invention with the field lines.
  • FIGS. 3A, 3B and 3C show half-sectional detail views of three embodiments of the candle of the invention.
  • the radiofrequency candle 1 shown in FIG. 1 has a coaxial structure comprising:
  • a central electrode 4 formed in a second conductive material and extending along the central axis X and
  • a body 3 formed in an electrically insulating material (dielectric), disposed between the base 2 and the electrode 4.
  • the body 3 has an internal lateral face 3b of contact with a portion 4b of the electrode and beyond which a pointed end portion 4a of the electrode
  • the electrode 4 is brought to a high RF voltage and is thus isolated by the body 3 of the base 2 which is, in turn, connected to the ground.
  • the body 3 is generally made of a dielectric material such as a ceramic.
  • the outer face 3a of the body 3 which is flat on most of its surface is exposed to the gaseous fuel mixture and the flame and is therefore likely to be fouled by a carbon deposit.
  • Figure 2A shows a detail sectional view of a traditional RF spark plug.
  • the junction of the outer face 3a of the dielectric body 3 with the electrode 4 has an inclined or chamfered profile or more generally, as in the embodiment shown, a curvilinear profile with a radius of curvature R of a hundred microns ( 0.1 mm).
  • Such a profile delimits a restricted and confined empty space where a very intense electric field prevails (of the order of 3.10 7 V / m) favoring the appearance of an air ionization mechanism which is likely to propagate. along the curve and extend along the face 3a by creating a surface parasitic spark.
  • This parasitic phenomenon is all the more likely that the face 3a is strongly exposed to the flame and is gradually covered with a carbon layer.
  • the spark plug shown in FIG. 2B is modified, according to the invention, by the embodiment, on the body 3, of at least one annular cavity 30 of axis X.
  • This cavity is formed on the internal lateral face 3b of the body 3 ensuring contact with the electrode 4.
  • the function of the cavity 30 is to locally modify the lines of the electrostatic field and, in particular, at the junction between the external face 3a of the body 3 and the electrode 4 so as to avoid the increase of the electric field in this zone and to prevent the initiation of ionization.
  • the junction between the outer face 3a of the body 3 and the electrode 4 here has a convex curvature whose radius R is less than or equal to half the distance (c) separating the face 3a of the cavity 30.
  • the wall of the cavity 30 has a semi-elliptical profile whose half small axis (b) is greater than or equal to three times the radius of curvature R of the junction between the outer face 3a of the body 3 and the electrode 4 and the half major axis (a) is greater than or equal to six times said radius.
  • the cavity 30 is provided with at least one metal lining element 5 whose thermal expansion coefficient is close to that of the dielectric material of the body 3.
  • the metallic lining element 5 also extends and, at least partially, along the internal lateral face 3b of the body 3 in contact with the electrode 4 in the form of a coating 53 intended to fill the small interspace between these parts.
  • the gaseous fuel mixture would then be able to penetrate into this space and come into contact with the high walls. temperature before igniting and causing rupture of the body 3.
  • the coating 53 is in electrical contact with the electrode 4 inside the spark plug 1 so that the entire inner surface of the body 3 is equipotential with the electrode which is under high voltage.
  • FIGS 3A to 3C show alternative embodiments of the candle of the invention.
  • the packing element 5 is formed of a metal layer 50 covering the inner wall of the cavity 30 and extending from one side to the other. other of the cavity and along the electrode 4 by the coating 53.
  • the layer 50 and the coating 53 are made from alloys of molybdenum and / or tungsten.
  • a second packing element 51 made by filling the cavity 30 with a metal alloy based on Kovar and / or Invar.
  • the assembly is carried out by soldering in order to ensure good contact between the respective facing faces of the body 3 and the element 51.
  • the second packing member 52 is formed integrally with the electrode 4 and is itself provided with a first packing element in the form of metal coating 53.
  • the body 3 can be made by sintering a ceramic composition around the electrode 4 carrying the metal element 5.
  • An alternative may consist in directly producing the electrode 4 with a metal element 52 by metal casting in situ in the central duct and the cavity 30 of the body 3.

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  • Spark Plugs (AREA)

Abstract

The invention relates to a radio-frequency plasma spark plug which includes: a cylindrical base (2) having a main axis (X) made of a first electrically conductive material; a central electrode (4) made of a second conductive material and extending along the main axis (X) and; a body (3) made of a dielectric material, arranged between said base (2) and said electrode (4), having an internal lateral surface (3b) in contact with the electrode and beyond which an end portion (4a) of the electrode (4) projects, characterised in that said body (3) comprises at least one annular cavity (30) with an axis (X), arranged on the lateral surface (3b) thereof in contact with the electrode (4) such as to modify the lines of the electrostatic field locally at the junction between the outer surface (3a) of said body and the electrode (4).

Description

Bougie d'allumage équipée de moyens de prévention des courts- circuits Spark plug equipped with means for preventing short circuits
La présente invention concerne une bougie d'allumage, du type plasma à radiofréquence (RF) , pour moteur à combustion interne. The present invention relates to a spark plug, radiofrequency plasma type (RF), for internal combustion engine.
Plus précisément la bougie de l'invention est équipée de moyens permettant d'éviter les phénomènes de court-circuit.  More precisely, the candle of the invention is equipped with means making it possible to avoid short-circuit phenomena.
Pour augmenter les dimensions de l'étincelle produite lors de l'allumage, il est connu d'utiliser une bougie à plasma radiofréquence ayant une électrode centrale à extrémité pointue portée à haute tension et générant une étincelle multifilamentaire de très grande taille.  To increase the dimensions of the spark produced during ignition, it is known to use a radiofrequency plasma candle having a central electrode pointed end carried high voltage and generating a multifilament spark of very large size.
Une telle bougie qui est décrite, par exemple, dans les FR 2 878 086, FR 2 886 776, FR 2 888 421, FR2 895 169 et FR 2 895 170, comporte :  Such a candle which is described, for example, in FR 2,878,086, FR 2,886,776, FR 2,888,421, FR 2 895 169 and FR 2 895 170, comprises:
- un culot cylindrique d'axe principal formé dans un premier matériau électriquement conducteur,  a cylindrical base with a main axis formed in a first electrically conductive material,
- une électrode centrale formée dans un second matériau conducteur et s' étendant selon l'axe principal et,  a central electrode formed in a second conductive material and extending along the main axis, and
- un corps formé dans un matériau électriquement isolant, disposé entre ledit culot et ladite électrode, en présentant une face latérale interne de contact avec l'électrode et au-delà de laquelle une portion d'extrémité de l'électrode fait saillie.  a body formed in an electrically insulating material, disposed between said base and said electrode, having an internal lateral face in contact with the electrode and beyond which an end portion of the electrode protrudes.
Cependant, il a été observé qu'au fur et à mesure de l'utilisation de ces bougies, la taille de l'étincelle diminue progressivement.  However, it has been observed that as and when the use of these candles, the size of the spark gradually decreases.
Ce phénomène est dû au fait que la face externe du corps isolant qui est au contact du mélange gazeux carburé et de la flamme, s'encrasse avec les résidus de combustion. En outre, une étincelle parasite apparaît sur la face externe encrassée entre l'électrode centrale et le culot de masse périphérique. This phenomenon is due to the fact that the outer face of the insulating body which is in contact with the gaseous fuel mixture and the flame, clogs with the combustion residues. In addition, a parasitic spark appears on the fouled external face between the central electrode and the peripheral mass pellet.
En fonction du niveau d'encrassement, l'étincelle parasite peut, soit seulement consommer une partie de l'énergie disponible dans l'alimentation radiofréquence (RF) ce qui réduit néanmoins le volume de l'étincelle principale, soit provoquer un court-circuit qui bloque l'émission de l'étincelle principale.  Depending on the degree of fouling, the spurious spark can either consume only a portion of the available energy in the radio frequency (RF) supply, which nevertheless reduces the volume of the main spark, or cause a short circuit which blocks the emission of the main spark.
L'origine du problème réside dans le profil de la jonction entre la face externe du corps isolant et l'électrode centrale où les milieux diélectrique-métal-air sont en contact.  The origin of the problem lies in the profile of the junction between the outer face of the insulating body and the central electrode where the dielectric-metal-air media are in contact.
Plus précisément, le corps présente un conduit central dans lequel est logée l'électrode centrale.  More specifically, the body has a central duct in which is housed the central electrode.
Pour des raisons de fabrication industrielle, il est impossible de réaliser un conduit à bord vif de sorte que la face externe du corps diélectrique ne peut être orientée perpendiculairement à la paroi de l'électrode et présente alors une légère inclinaison ou une courbure.  For reasons of industrial manufacture, it is impossible to make a conduit with a sharp edge so that the outer face of the dielectric body can not be oriented perpendicular to the wall of the electrode and then has a slight inclination or curvature.
Il subsiste donc un faible espace libre où les lignes de champ électrostatique traversent un volume d'air dont la constante diélectrique est voisine de l'unité avant de rentrer dans le corps dont la constante diélectrique est plus élevée et de l'ordre de 7 à 9.  There is therefore a small free space where the electrostatic field lines pass through a volume of air whose dielectric constant is close to the unit before entering the body whose dielectric constant is higher and of the order of 7 to 9.
Dans ces conditions, l'intensité du champ électrique se trouve renforcée dans la zone locale de jonction corps-électrode où le seuil d'ionisation de l'air s'avère être largement dépassé.  Under these conditions, the intensity of the electric field is enhanced in the local body-electrode junction zone where the threshold of ionization of the air proves to be largely exceeded.
En conséquence, la surface inclinée ou curviligne du corps isolant dans la zone de jonction génère une composante tangentielle du champ qui favorise la propagation d'un phénomène d'avalanche d'ionisation. Or, ce phénomène contribue à l'amorçage d'une étincelle parasite de surface entretenue par la présence d'une couche semi-conductrice de carbone liée à l'encrassement de la face externe du corps. Consequently, the inclined or curvilinear surface of the insulating body in the junction zone generates a tangential component of the field which favors the propagation of an ionization avalanche phenomenon. However, this phenomenon contributes to the initiation of a spurious surface spark maintained by the presence of a semiconductor layer of carbon bonded to the fouling of the outer face of the body.
Les bougies radiofréquence de l'art antérieur ont seulement cherché à réduire l'encrassement du corps.  Radiofrequency candles of the prior art have only sought to reduce the fouling of the body.
La présente invention a pour but de résoudre le problème technique exposé ci-dessus en intervenant sur l'origine du problème, c'est-à-dire, en visant à éviter le renforcement du champ électrique à la jonction entre la face externe du corps diélectrique et l'électrode centrale.  The present invention aims to solve the technical problem set out above by intervening on the origin of the problem, that is to say, by aiming at avoiding the strengthening of the electric field at the junction between the external face of the body. dielectric and the central electrode.
Ce but est atteint, selon l'invention, au moyen d'une bougie dont le corps diélectrique comporte au moins une cavité annulaire d'axe central, ménagée sur sa face latérale de contact avec l'électrode de façon à modifier localement les lignes du champ électrostatique à la jonction entre la face externe du dit corps et l'électrode.  This object is achieved, according to the invention, by means of a spark plug whose dielectric body comprises at least one annular cavity of central axis, formed on its lateral face of contact with the electrode so as to locally modify the lines of the electrostatic field at the junction between the outer face of said body and the electrode.
Selon une caractéristique avantageuse, ladite cavité est pourvue d'au moins un élément métallique de garnissage s' étendant, au moins partiellement, le long de la face latérale interne du corps en contact avec l'électrode et dont le coefficient de dilatation thermique est voisin de celui du matériau diélectrique du dit corps.  According to an advantageous characteristic, said cavity is provided with at least one metal lining element extending, at least partially, along the internal lateral face of the body in contact with the electrode and whose thermal expansion coefficient is similar. of that of the dielectric material of said body.
Selon une première variante de réalisation ledit élément de garnissage est formé d'une couche métallique recouvrant la paroi interne de ladite cavité.  According to a first variant embodiment, said packing element is formed of a metal layer covering the inner wall of said cavity.
De préférence, ledit élément métallique de garnissage est réalisé d'une seule pièce avec l'électrode.  Preferably, said metallic lining element is made in one piece with the electrode.
Selon une seconde variante de réalisation, ledit corps est réalisé par frittage d'une composition de céramique autour de l'électrode portant ledit élément de garnissage. Selon une autre variante, ladite électrode est réalisée avec l'élément métallique de garnissage par coulée de métal in situ dans ladite cavité. According to a second variant embodiment, said body is made by sintering a ceramic composition around the electrode carrying said lining element. According to another variant, said electrode is made with the metal filling element by casting of metal in situ in said cavity.
Selon encore une autre variante, ledit élément métallique de garnissage est rapporté par brasage.  According to yet another variant, said metal lining element is soldered.
Selon une autre caractéristique avantageuse, ledit élément de garnissage est un alliage d'un ou plusieurs métaux choisis parmi le molybdène, le Tungstène, l'Invar et le Kovar .  According to another advantageous characteristic, said packing element is an alloy of one or more metals chosen from molybdenum, tungsten, invar and kovar.
Selon l'invention, il est aussi prévu que la jonction entre la face externe du corps et l'électrode présente une courbure convexe dont le rayon est inférieur ou égal à la moitié de la distance séparant ladite face de ladite cavité.  According to the invention, it is also provided that the junction between the outer face of the body and the electrode has a convex curvature whose radius is less than or equal to half the distance separating said face of said cavity.
De préférence, la paroi de ladite cavité a un profil semi-elliptique dont le demi petit axe est supérieur ou égal à trois fois le rayon de courbure de la jonction entre la face externe du corps et l'électrode et le demi grand axe est supérieur ou égal à six fois ledit rayon.  Preferably, the wall of said cavity has a semi-elliptical profile whose half small axis is greater than or equal to three times the radius of curvature of the junction between the outer face of the body and the electrode and the half major axis is greater than or six times the radius.
La bougie d'allumage de l'invention permet de protéger les bougies radiofréquence de l'encrassement en agissant sur la cause même du phénomène.  The spark plug of the invention makes it possible to protect the radiofrequency candles from fouling by acting on the very cause of the phenomenon.
L' invention repose sur une atténuation du champ à la jonction entre la face externe du corps et l'électrode obtenu par une modification de leur interface interne en contact .  The invention is based on an attenuation of the field at the junction between the external face of the body and the electrode obtained by a modification of their internal interface in contact.
En conséquence, le fonctionnement et la fiabilité des bougies (RF) sont améliorés et leur durée de vie est notablement prolongée.  As a result, the operation and reliability of the candles (RF) are improved and their service life is significantly extended.
L'invention sera mieux comprise à la lecture de la description qui va suivre, en se référant aux dessins annexés sur lesquels : La figure 1 représente une vue latérale en coupe d'un mode de réalisation de la bougie de l'invention en phase d' allumage . The invention will be better understood on reading the description which follows, with reference to the appended drawings in which: Figure 1 shows a sectional side view of an embodiment of the candle of the invention in the ignition phase.
Les figures 2A et 2B représentent des vues de détail agrandies et en coupe respectivement d'une bougie RF selon l'art antérieur et selon l'invention avec les lignes de champ .  FIGS. 2A and 2B show enlarged and sectional detail views respectively of an RF candle according to the prior art and according to the invention with the field lines.
Les figures 3A, 3B et 3C représentent des demi-vues de détail en coupe de trois variantes de réalisation de la bougie de l'invention.  FIGS. 3A, 3B and 3C show half-sectional detail views of three embodiments of the candle of the invention.
La bougie radiofréquence 1 représentée sur la figure 1 a une structure coaxiale comprenant :  The radiofrequency candle 1 shown in FIG. 1 has a coaxial structure comprising:
- un culot cylindrique 2 d'axe principal X formé dans un premier matériau électriquement conducteur,  a cylindrical base 2 of main axis X formed in a first electrically conductive material,
- une électrode centrale 4 formée dans un second matériau conducteur et s' étendant selon l'axe central X et,  a central electrode 4 formed in a second conductive material and extending along the central axis X and
- un corps 3 formé dans un matériau électriquement isolant (diélectrique) , disposé entre le culot 2 et l'électrode 4.  a body 3 formed in an electrically insulating material (dielectric), disposed between the base 2 and the electrode 4.
Le corps 3 présente une face latérale interne 3b de contact avec une portion 4b de l'électrode et au-delà de laquelle une portion d'extrémité en pointe 4a de l'électrode The body 3 has an internal lateral face 3b of contact with a portion 4b of the electrode and beyond which a pointed end portion 4a of the electrode
4 fait saillie. 4 protrudes.
L'électrode 4 est portée à une haute tension RF et est donc isolée par le corps 3 du culot 2 qui est, quant à lui, relié à la masse.  The electrode 4 is brought to a high RF voltage and is thus isolated by the body 3 of the base 2 which is, in turn, connected to the ground.
Le corps 3 est en général réalisé en un matériau diélectrique tel qu'une céramique.  The body 3 is generally made of a dielectric material such as a ceramic.
Dans des conditions normales d'excitation électrique RF, le diamètre A de l'étincelle à multi filaments Under normal conditions of RF electrical excitation, the diameter A of the multi-filament spark
5 est de l'ordre du centimètre. La face externe 3a du corps 3 qui est plane sur la plus grande partie de sa surface est exposée au mélange gazeux carburé et à la flamme et est donc susceptible d'être encrassée par un dépôt de carbone. 5 is of the order of one centimeter. The outer face 3a of the body 3 which is flat on most of its surface is exposed to the gaseous fuel mixture and the flame and is therefore likely to be fouled by a carbon deposit.
Les propriétés semi-conductrices de ce dépôt de surface entraînent un risque important de court-circuit entre le culot 2 et l'électrode 4.  The semiconducting properties of this surface deposit cause a significant risk of short circuit between the base 2 and the electrode 4.
La figure 2A représente une vue de détail en coupe d'une bougie d'allumage RF traditionnelle.  Figure 2A shows a detail sectional view of a traditional RF spark plug.
La jonction de la face externe 3a du corps diélectrique 3 avec l'électrode 4 a un profil incliné ou chanfreiné ou plus généralement, comme dans le mode de réalisation représenté, un profil curviligne avec un rayon de courbure R d'une centaine de microns (0,1 mm) .  The junction of the outer face 3a of the dielectric body 3 with the electrode 4 has an inclined or chamfered profile or more generally, as in the embodiment shown, a curvilinear profile with a radius of curvature R of a hundred microns ( 0.1 mm).
Un tel profil délimite un espace vide restreint et confiné où règne un champ électrique très intense (de l'ordre de 3.107 V/m) favorisant l'apparition d'un mécanisme d'ionisation de l'air qui est susceptible de se propager le long de la courbe et de se prolonger le long de la face 3a en créant une étincelle parasite de surface. Such a profile delimits a restricted and confined empty space where a very intense electric field prevails (of the order of 3.10 7 V / m) favoring the appearance of an air ionization mechanism which is likely to propagate. along the curve and extend along the face 3a by creating a surface parasitic spark.
Ce phénomène parasite est d'autant plus probable que la face 3a est fortement exposée à la flamme et est progressivement recouverte d'une couche de carbone.  This parasitic phenomenon is all the more likely that the face 3a is strongly exposed to the flame and is gradually covered with a carbon layer.
La bougie représentée sur la figure 2B est modifiée, selon l'invention, par la réalisation, sur le corps 3, d'au moins une cavité annulaire 30 d'axe X.  The spark plug shown in FIG. 2B is modified, according to the invention, by the embodiment, on the body 3, of at least one annular cavity 30 of axis X.
Cette cavité est ménagée sur la face latérale interne 3b du corps 3 assurant le contact avec l'électrode 4.  This cavity is formed on the internal lateral face 3b of the body 3 ensuring contact with the electrode 4.
La cavité 30 a pour fonction de modifier localement les lignes du champ électrostatique et, en particulier, à la jonction entre la face externe 3a du corps 3 et l'électrode 4 de façon à éviter l'augmentation du champ électrique dans cette zone et à prévenir l'amorçage de l'ionisation. La jonction entre la face externe 3a du corps 3 et l'électrode 4 présente ici une courbure convexe dont le rayon R est inférieur ou égal à la moitié de la distance (c) séparant la face 3a de la cavité 30. The function of the cavity 30 is to locally modify the lines of the electrostatic field and, in particular, at the junction between the external face 3a of the body 3 and the electrode 4 so as to avoid the increase of the electric field in this zone and to prevent the initiation of ionization. The junction between the outer face 3a of the body 3 and the electrode 4 here has a convex curvature whose radius R is less than or equal to half the distance (c) separating the face 3a of the cavity 30.
De préférence, la paroi de la cavité 30 a un profil semi-elliptique dont le demi petit axe (b) est supérieur ou égal à trois fois le rayon de courbure R de la jonction entre la face externe 3a du corps 3 et l'électrode 4 et le demi grand axe (a) est supérieur ou égal à six fois ledit rayon.  Preferably, the wall of the cavity 30 has a semi-elliptical profile whose half small axis (b) is greater than or equal to three times the radius of curvature R of the junction between the outer face 3a of the body 3 and the electrode 4 and the half major axis (a) is greater than or equal to six times said radius.
La cavité 30 est pourvue d'au moins un élément métallique de garnissage 5 dont le coefficient de dilatation thermique est voisin de celui du matériau diélectrique du corps 3.  The cavity 30 is provided with at least one metal lining element 5 whose thermal expansion coefficient is close to that of the dielectric material of the body 3.
L'élément métallique de garnissage 5 s'étend aussi et, au moins partiellement, le long de la face latérale interne 3b du corps 3 en contact avec l'électrode 4 sous forme d'un revêtement 53 destiné à combler le faible espace intercalaire entre ces pièces.  The metallic lining element 5 also extends and, at least partially, along the internal lateral face 3b of the body 3 in contact with the electrode 4 in the form of a coating 53 intended to fill the small interspace between these parts.
En effet, si l'espace intercalaire entre la face latérale interne 3b du corps 3 et l'électrode 4 n'était pas hermétique, le mélange gazeux carburé serait alors susceptible de pénétrer dans cet espace et de venir en contact avec les parois à haute température avant de s'enflammer et de provoquer la rupture du corps 3.  Indeed, if the intermediate space between the internal lateral face 3b of the body 3 and the electrode 4 was not hermetic, the gaseous fuel mixture would then be able to penetrate into this space and come into contact with the high walls. temperature before igniting and causing rupture of the body 3.
En outre, le revêtement 53 est en contact électrique avec l'électrode 4 à l'intérieur de la bougie 1 de façon à ce que toute la surface interne du corps 3 soit équipotentielle avec l'électrode qui est sous haute tension.  In addition, the coating 53 is in electrical contact with the electrode 4 inside the spark plug 1 so that the entire inner surface of the body 3 is equipotential with the electrode which is under high voltage.
Les figures 3A à 3C représentent des variantes de réalisation de la bougie de l'invention.  Figures 3A to 3C show alternative embodiments of the candle of the invention.
Dans la variante de la figure 3A, l'élément de garnissage 5 est formé d'une couche métallique 50 recouvrant la paroi interne de la cavité 30 et se prolongeant de part et d'autre de la cavité et le long de l'électrode 4 par le revêtement 53. In the variant of FIG. 3A, the packing element 5 is formed of a metal layer 50 covering the inner wall of the cavity 30 and extending from one side to the other. other of the cavity and along the electrode 4 by the coating 53.
La couche 50 et le revêtement 53 sont réalisés à partir d'alliages de Molybdène et/ou de Tungstène.  The layer 50 and the coating 53 are made from alloys of molybdenum and / or tungsten.
Dans la variante de la figure 3B, au revêtement 53 est ajouté un second élément de garnissage 51 réalisé par remplissage de la cavité 30 avec un alliage métallique à base de Kovar et/ou d'Invar.  In the variant of FIG. 3B, to the coating 53 is added a second packing element 51 made by filling the cavity 30 with a metal alloy based on Kovar and / or Invar.
L'assemblage est effectué par brasage afin d'assurer un bon contact entre les faces en regard respectives du corps 3 et de l'élément 51.  The assembly is carried out by soldering in order to ensure good contact between the respective facing faces of the body 3 and the element 51.
Dans la variante de la figure 3C qui correspond à celle de la figure 2B, le second élément de garnissage 52 est réalisé d'une seule pièce avec l'électrode 4 et est lui-même pourvu d'un premier élément de garnissage sous forme du revêtement métallique 53.  In the variant of Figure 3C which corresponds to that of Figure 2B, the second packing member 52 is formed integrally with the electrode 4 and is itself provided with a first packing element in the form of metal coating 53.
Dans ce cas, le corps 3 peut être réalisé par frittage d'une composition de céramique autour de l'électrode 4 portant l'élément métallique 5.  In this case, the body 3 can be made by sintering a ceramic composition around the electrode 4 carrying the metal element 5.
Une alternative peut consister à réaliser directement, l'électrode 4 avec un élément métallique 52 par coulée de métal in situ dans le conduit central et la cavité 30 du corps 3.  An alternative may consist in directly producing the electrode 4 with a metal element 52 by metal casting in situ in the central duct and the cavity 30 of the body 3.

Claims

REVENDICATIONS
1. Bougie d'allumage du type plasma à radiofréquence comprenant : A radiofrequency plasma type spark plug comprising:
- un culot cylindrique (2) d'axe principal (X) formé dans un premier matériau électriquement conducteur,  a cylindrical base (2) of main axis (X) formed in a first electrically conductive material,
- une électrode centrale (4) formée dans un second matériau conducteur et s' étendant selon l'axe principal (X) et,  a central electrode (4) formed in a second conductive material and extending along the main axis (X) and,
- un e orps (3) , formé dans un matériau diélectrique, disposé entre ledit culot (2) et ladite électrode (4), en présentant une face latérale interne (3b) de contact avec l'électrode et au-delà de laquelle une portion d'extrémité (4a) de l'électrode (4) fait saillie, ledit corps (3) comportant au moins une cavité annulaire (30) d'axe (X), ménagée sur sa face latérale (3b) de contact avec l'électrode (4) de façon à modifier localement les lignes du champ électrostatique à la jonction entre la face externe (3a) du dit corps et l'électrode (4), ladite cavité (30) étant pourvue d'au moins un élément de garnissage métallique (5, 50, 51, 52, 53) s'étendant au moins partiellement le long de la face latérale interne (3b) du corps en contact avec l'électrode (4) et dont le coefficient de dilatation thermique est voisin de celui du matériau diélectrique du dit corps  - An orps (3), formed in a dielectric material, disposed between said base (2) and said electrode (4), having an inner lateral face (3b) of contact with the electrode and beyond which a end portion (4a) of the electrode (4) protrudes, said body (3) having at least one annular cavity (30) with axis (X), formed on its lateral face (3b) of contact with the electrode (4) so as to locally modify the lines of the electrostatic field at the junction between the outer face (3a) of said body and the electrode (4), said cavity (30) being provided with at least one element of metal packing (5, 50, 51, 52, 53) extending at least partially along the inner lateral face (3b) of the body in contact with the electrode (4) and whose thermal expansion coefficient is close to that of the dielectric material of the said body
caractérisée en ce que la jonction entre la face externe (3a) du corps (3) et l'électrode (4) présente une courbure convexe dont le rayon (R) est inférieur ou égal à la moitié de la distance (c) séparant ladite face de ladite cavité (30). characterized in that the junction between the outer face (3a) of the body (3) and the electrode (4) has a convex curvature whose radius (R) is less than or equal to half the distance (c) separating said face of said cavity (30).
2. Bougie d'allumage selon la revendication 1 caractérisée en ce que ledit élément de garnissage (5) est formé d'une couche métallique (50) recouvrant la paroi interne de ladite cavité (30) . 2. Spark plug according to claim 1 characterized in that said packing element (5) is formed of a metal layer (50) covering the inner wall of said cavity (30).
3. Bougie d'allumage selon la revendication 1 ou 2 caractérisée en ce que ledit élément métallique de garnissage est réalisé d'une seule pièce avec l'électrode (4). 3. Spark plug according to claim 1 or 2 characterized in that said metal lining element is made in one piece with the electrode (4).
4. Bougie d'allumage selon la revendication 3 caractérisée en ce ledit corps (3) est réalisé par frittage d'une composition de céramique autour de l'électrode (4) portant ledit élément métallique.  4. Spark plug according to claim 3 characterized in that said body (3) is made by sintering a ceramic composition around the electrode (4) carrying said metal element.
5. Bougie d'allumage selon la revendication 3 caractérisée en ce que ladite électrode (4) est réalisée avec l'élément métallique de garnissage (5) par coulée de métal in situ dans ladite cavité (30) .  5. Spark plug according to claim 3 characterized in that said electrode (4) is formed with the metal lining element (5) by casting metal in situ in said cavity (30).
6. Bougie d'allumage selon la revendication 1 ou 2 caractérisée en ce que ledit élément métallique de garnissage (5) est rapporté par brasage.  6. Spark plug according to claim 1 or 2 characterized in that said metal lining element (5) is attached by brazing.
7. Bougie d'allumage selon l'une des revendications précédentes caractérisée en ce que ledit élément de garnissage (5) est un alliage d'un ou plusieurs métaux choisis parmi le Molybdène, le Tungstène, l'Invar et le Kovar .  7. Spark plug according to one of the preceding claims characterized in that said packing element (5) is an alloy of one or more metals selected from molybdenum, Tungsten, Invar and Kovar.
8. Bougie d'allumage selon l'une des revendications précédentes caractérisée en ce que la paroi de ladite cavité (30) a un profil semi-elliptique dont le demi petit axe (b) est supérieur ou égal à trois fois le rayon de courbure (R) de la jonction entre la face externe (3a) du corps et l'électrode et le demi grand axe (a) est supérieur ou égal à six fois ledit rayon (R) .  8. Spark plug according to one of the preceding claims characterized in that the wall of said cavity (30) has a semi-elliptical profile whose half small axis (b) is greater than or equal to three times the radius of curvature (R) of the junction between the outer face (3a) of the body and the electrode and the half major axis (a) is greater than or equal to six times said radius (R).
PCT/FR2011/050848 2010-04-16 2011-04-14 Spark plug provided with a means for preventing short circuits WO2011128589A1 (en)

Priority Applications (2)

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CN201180023522.8A CN102884686B (en) 2010-04-16 2011-04-14 Spark plug provided with a means for preventing short circuits
EP11730372.7A EP2559119B1 (en) 2010-04-16 2011-04-14 Spark plug provided with a means for preventing short circuits

Applications Claiming Priority (2)

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FR1052908A FR2959071B1 (en) 2010-04-16 2010-04-16 SPARK PLUG EQUIPPED WITH MEANS FOR PREVENTING SHORT CIRCUITS
FR1052908 2010-04-16

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CN (1) CN102884686B (en)
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EP3382830A1 (en) * 2017-03-31 2018-10-03 NGK Spark Plug Co., Ltd. Spark plug
US10581226B2 (en) 2017-03-31 2020-03-03 Ngk Spark Plug Co., Ltd. Spark plug

Also Published As

Publication number Publication date
EP2559119A1 (en) 2013-02-20
EP2559119B1 (en) 2014-12-17
FR2959071A1 (en) 2011-10-21
CN102884686B (en) 2014-06-18
FR2959071B1 (en) 2012-07-27
CN102884686A (en) 2013-01-16

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