JP4914023B2 - Method for fabricating the center electrode of a spark plug - Google Patents

Description

  The present invention relates to a method for fabricating a center electrode of a spark plug by fabricating a substantially cylindrical base body and depositing a local protective layer of a ruthenium based alloy on the base body.

  The electrode of the spark plug is exposed in the combustion chamber of the internal combustion engine at the assembly position, and in this case is exposed to spark erosion, oxidation and corrosion and thus severe wear. In connection with the energy transferred to the electrode by the discharge produced during operation of the spark plug, the electrode material is melted, evaporated and / or oxidized.

  In order to extend the life of the spark plug, not only structural means but also material technical means can be taken. In order to produce a spark plug electrode, a material having a high melting point and a high boiling point is generally used. In this case, the material selection is performed in such a way that the arc rate of the post-discharge generated during the operation of the spark plug is reduced for a glow discharge which is more advantageous against spark erosion. In particular for spark plug electrodes, materials are used which have a slight oxidation tendency, a slight corrosion tendency and / or a high wear resistance against spark erosion.

  In particular, nickel-based materials constitute a sufficiently popular material for producing spark plug electrodes. In particular, a platinum-based material or an iridium-based material may be used to produce a long-life spark plug electrode. It is also known to produce a spark plug with a center electrode consisting of a base body made of a nickel-based material and a local reinforcement made of platinum. However, the use of platinum as an electrode material makes spark plugs very expensive.

  A spark plug is known from EP-A-0 660 475. This known spark plug has a ground electrode and a center electrode. The center electrode is composed of a base body and an insert or attachment portion made of a ruthenium / aluminum alloy. In order to fabricate the center electrode, first a base body is molded, and then an insert forming a local protective layer is applied to the end surface of the base body facing the ground electrode.

However, the insert known from EP-A-0 660 475 is used for spark plugs formed as so-called “surface discharge plugs” having a central electrode which cooperates with a plurality of ground electrodes over the circumferential surface. I can't.
European Patent Application No. 0660475

  The object of the present invention is to improve the method for producing the center electrode of the spark plug so that the center electrode cooperating with at least one ground electrode over the circumferential surface of the spark plug has a high spark erosion resistance and / or It is to be able to be manufactured with oxidation resistance.

  In order to solve this problem, in the method of the present invention, an alloy for forming a protective layer is applied to the base body in the form of a slurry and bonded to the base body after the remelting process.

  The method according to the invention has the advantage that the central electrode can be provided with a protective layer which is wear-resistant, i.e. spark erosion-resistant and oxidation-resistant, at any location, i.e. its peripheral surface. . This protective layer cannot be deformed and shaped according to its fragile nature. The protective layer is applied to the substantially cylindrical base body, particularly in the region of local discharge action.

  The center electrode made according to the present invention is a center electrode which cooperates with at least one ground electrode, especially over the circumference. In this case, the slurry is advantageously applied to the peripheral surface of the base body. For example, in this case, the center electrode of a so-called “surface discharge plug” is considered.

  According to the method according to the invention, the center electrode of a spark plug with a higher wear resistance than a base body made, for example, of a nickel-based alloy, although certainly less than a platinum-reinforced center electrode. Can be produced. Furthermore, the center electrode fabricated in accordance with the present invention provides significant cost advantages over the center electrode with platinum reinforcement.

  Since the method according to the invention requires only a small amount of alloy to produce the protective layer, there is now only a small material cost for the protective layer.

  In an advantageous embodiment of the process according to the invention, alloys containing elements: nickel, aluminum and / or chromium in addition to ruthenium are used. In this case, the nickel proportion of the alloy is advantageously about 30% to 40% by volume, and the aluminum and chromium proportions of the alloy are about 10% to 30% by volume. Thus, a sufficiently high melting point can be produced for each use case in relation to the ratio of each alloying element: nickel, aluminum and chromium. This melting point ensures high wear resistance of the center electrode. Furthermore, the aluminum / chromium ratio of the alloy is centered on a stable and rapidly increasing aluminum oxide / chromium oxide layer in the combustion chamber of the internal combustion engine where an oxidizing atmosphere is formed and the central electrode is exposed during operation. It is guaranteed to be formed on the electrode. This layer prevents severe oxidation of the center electrode. Even in the case of exfoliation of the oxide layer due to thermal shock or discharge, the oxide layer continues to grow so that the effect of protecting the electrode material continues to exist. In this case, however, it is advantageous to use a material containing a sufficient amount of aluminum and chromium to post-supply the oxide layer to fabricate the base body.

  Advantageously, a slurry which is applied to the base body only in the region of the discharge action which takes place during operation of the spark plug is preferably between 5% and 9% by volume in a preferred embodiment of the method according to the invention. It comprises a binder having a proportion, preferably a solvent having a proportion between 31% and 45% by volume, and preferably an alloy having a proportion between 50% and 60% by volume. With regard to the composition of the slurry, different layer thicknesses of the alloy can be achieved with good quality.

  As the slurry binder, for example, ethyl cellulose can be used. This ethylcellulose can be easily evaporated during the remelting process.

  An organic solvent is particularly suitable as the slurry solvent. This solvent may comprise a mixed solution of benzyl alcohol and ethanol, for example. The selected mixing ratio of the solvent components is advantageously related to the layer thickness of the protective layer that it is desired to produce. Thus, ethanol has a lower boiling point than, for example, benzyl alcohol. Thus, when making larger layer thicknesses that require more time to remove the solvent, a solvent mixture having a higher benzyl alcohol ratio is selected. An excessively high ethanol ratio can result in cavity formation in the protective layer based on a rapid evaporation process.

  In order to be able to make the central electrode easily with a substantially cylindrical peripheral surface, it is advantageous if a slurry is fed into the annular groove of the base electrode.

  For applying the slurry to the central electrode, a micrometering device which is advantageously pneumatically controlled is particularly suitable. The micrometering device preferably has an application needle with an inner diameter of 1.1 mm to 1.3 mm and is loaded with an air pressure of about 2 bar to 3 bar. The inner diameter of the application needle and the air pressure can be selected in relation to the viscosity of the slurry and the particle size of the alloy powder used to make the slurry. The average grain size of the alloy is, for example, 22 μm. The micrometering device may be a standard laboratory device with a reservoir and an application needle, for example made of polyethylene, preferably of a conical shape.

  In order to carry out the remelting process, a laser is advantageously used. This laser may be formed as a diode laser or a YAG laser. In this case, in order to achieve high wear resistance, the degree of mixing of the alloy and the base body material is adjusted to a maximum of 35%. A higher degree of mixing can even lead to a reduction in wear resistance compared to a center electrode without a protective layer. The degree of mixing is related to the process guide of the laser remelting process. In order to optimize the remelting process, for example, the power of the laser, the time for rotating the laser once around the circumference of the base body, and the number of rotations can be varied. The degree of mixing is also related to the heat capacity of the base body. Furthermore, this heat capacity is related to the geometry or dimensions of the base body and the ability of the alloy powder used for the slurry to absorb the radiation emitted by the laser.

  Primarily, the material applied to the base body is remelted twice in succession to produce a uniformly remelted protective layer that does not have a point characterizing the start or end point of the remelt process. It is advantageous if This can be achieved by rotating the base body twice about its own axis during the remelting process, especially in stationary laser beams.

  Further advantages and advantageous embodiments of the object according to the invention can be seen from the best mode for carrying out the invention, the brief description of the drawings and the claims.

  In the following, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a central electrode 10 during the production of a creeping discharge plug, which is formed in a conventional manner, anyway, for mounting on an engine block of an automotive internal combustion engine.

  The center electrode 10 has a substantially cylindrical base body 11 made of a NiAlSiY alloy. The base body 11 has a copper core 12 for improving its thermal conductivity. The base body 11 is manufactured with a groove 13 formed on the peripheral surface, and then installed on a rotary tool.

  The groove 13 is then filled with slurry by a micrometering device 15 having a reservoir 16 for the slurry and a conical needle 17 made of polyethylene with an inner diameter of 1.19 mm. This slurry consists of 5% by volume ethylcellulose, 45% by volume solvent formed from benzyl alcohol and ethanol, and 50% by volume alloy. This alloy is made on a ruthenium base and has 50 volume percent ruthenium, 30 volume percent nickel, and 20 volume percent chromium and aluminum. The micro metering device 15 is time / pneumatically controlled. During filling of the groove 13, the base body 11 is rotated by the arrow X.

  Next, the slurry supplied into the groove 13 is dried at room temperature, whereby the solvent is removed and a pre-coating layer 18 composed of an alloy and a binder is formed.

  After drying, a laser remelting process is performed by the diode laser 19, whereby an intermetallic layer 20 is formed in the groove 13. The intermetallic layer 20 is made of a slurry alloy and a material of the base body 11. In this case, the mixing of the slurry alloy and the material of the base body 11 is a maximum of 35%. To accomplish this, the diode laser 19 is adjusted to have a fiber diameter of 600 μm, a focal length of 200 mm, a rotational speed of 80 rpm, and a focal position of −10 mm. The laser power is adjusted to a maximum of 800 watts.

  During the remelting process in which the slurry binder is evaporated, the base body 11 is rotated twice about its axis.

  Finally, the center electrode 10 is provided with an annular coating layer or protective layer at the location of the discharge effect that occurs during operation of the spark plug. Accordingly, the life extension of the spark plug can be achieved by up to 50%.

It is a figure which shows the center electrode at the time of manufacture of the spark plug formed as a creeping discharge plug.

Explanation of symbols

  10 central electrode, 11 base body, 12 copper core, 13 groove, 15 micrometering device, 16 storage container, 17 needle, 18 pre-coating layer, 19 diode laser, 20 intermetallic layer

Claims (9)

-Producing a substantially cylindrical base body (11);
In a method for producing a central electrode of a spark plug by applying a local protective layer (20) made of an alloy made of ruthenium base to a base body (11),
An alloy for forming the protective layer (20) is applied to the base body (11) in the form of a slurry and bonded to the base body (11) after the remelting process, and the slurry comprises a binder, a solvent, and the alloy. and it consists with, characterized that you supplied to the annular groove (13) in the slurry-based body (11), a method for fabricating the center electrode of the spark plug.   The method according to claim 1, wherein the alloy contains nickel, aluminum and / or chromium.   The method of claim 2, wherein the nickel percentage of the alloy is about 30% to 40% by volume and the percentage of aluminum and chromium of the alloy is about 10% to 30% by volume.   In the slurry, the binder has a proportion between 5 vol% and 9 vol%, the solvent has a proportion between 31 vol% and 45 vol%, and the alloy The method of claim 1 having a proportion between 50% and 60% by volume.   The method according to claim 4, wherein the binder contains ethylcellulose.   The method according to claim 4 or 5, wherein the solvent contains benzyl alcohol and / or ethanol. The slurry preferably has a coating needle having an internal diameter of between 1.1Mm～1.3Mm, advantageously be applied by micro-metering device (15) which is pneumatically controlled, of claims 1 to 6 The method of any one of Claims. Done by laser (19) remelting process, in this case, advantageously, alloy and the degree of mixing with the material of the base body is adjusted by 35%, any one process as claimed in claims 1 to 7. Rotating about the axis of the at least two base body between the base body of the reflow process, any one process of claim 1 to 8.

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