JPS6024545B2 - spark plug - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spark plug for an internal combustion engine having a center electrode and a ground electrode made of a base metal, an alloy, or a solid solution, in which the center electrode or both electrodes are at least opposed to each other. The ignition part is coated with a metal or alloy, the coating layer having an average atomic weight of more than 100 and a melting point of more than 1500 qo.

Point plugs, which are normally introduced for igniting fuel/air mixtures in internal combustion engines, have electrodes made of base metals such as nickel or nickel alloys.

During operation, burnout of the electrodes occurs, which occurs in the interpolar gap between the electrodes, due to atomization of the electrode surface as well as evaporation of the electrode material. This electrode burnout increases the electrode gap, resulting in a change in ignition characteristics. However, the optimum value for the amount of fuel consumed can only be achieved if no or only small adjustments are made to the electrodes during operation. The degree of burnout of an electrode is determined by the tendency of the electrode material to form a porcelain-like coating in the form of metal oxides or metal carbides by reacting with gases in the combustion chamber or by absorbing compounds from the combustion chamber. Layout of the top electrode layer (Ve pr ung)
) is particularly high when this occurs.

The inert or partially inert dielectric or semiconductor layer is torn away from the pole gap. This is also because layers such as porcelain cannot withstand the stress caused by frequent temperature fluctuations, especially at the interface with metals. This combination of chemical and physical processes results in particularly high burnout values of the support metal. Attempts have been made to solve the above problem by manufacturing spark plugs with electrodes made of platinum or platinum/iridium.

In order to reduce the amount of precious metals required, the electrode tips made of these metals are joined to the fin electrode carrier using welding or soldering techniques or are encapsulated using a platinum plate of the electrode. However, strong thermal stress may cause the welding and soldering to loosen, and eventually the electrode tip may peel off. In order to prevent corrosion phenomena between the electrode tip and electrode material and welding or soldering auxiliary means, an amount several times the amount of precious metal required to reduce the degree of burnout is used for fixing to the haze electrode rod. will be introduced in Because spark plugs of this type require a large amount of precious metal to manufacture, they are expensive and are only introduced in high-power engines as well as special engines. The final drawback is U.S. Patent No. 247.
0033 and 2,391,458, which are coated by conventional wet plating methods at low temperatures.

The coating layer produced by this type of wet plating method has poor bonding with the lightning electrode carrier and microcrystallinity, which leads to deterioration of the structure, which is mostly millet-like. Therefore, the thickness of the coating layer is, for example, 635 mm for the center electrode and 254 mm for the ground electrode (see comparison with U.S. Pat. No. 2,470,033), which is practically necessary. The thickness of the coating layer is more than 100 degrees thick. As a result, such spark plugs have not yet gained general acceptance.
The present invention has been developed in view of the above points, and its object is to provide an ignition system which has the lowest possible burn-out values and which, as a result, ensures optimum combustion or fuel utilization over long operating times. The object of the present invention is to provide a spark plug, and in particular to provide a spark plug which can be produced much more economically than previously known spark plugs and which has such performance.

The spark plug according to the invention has 5 to 100 µm, preferably 15 to 60 µm, grown in the ignition part of the center electrode, using electrodes from molten salt or crystallized using metal vapor deposition or chemical vapor deposition. It is coated with a metal layer the thickness of the skin of a Buddha. The diameter of the axis of the cylindrical center electrode is preferably larger than the diameter of the front surface by an order of magnitude s to IMs, with the frustoconical side wall surface being coated with metal to a height of 0.3s to IWs. Quite unexpectedly, by selecting a suitable metal and producing a coating layer in the form of a tightly bonded ductile layer with a columnar crystalline structure, such as those formed in high temperature coating processes, It has been found that even when the metal coating on the ignition part of the spark plug electrode is very thin, it is already sufficient to prevent burnout quite thoroughly.

Insofar as electrode burnout is due to evaporation of the electrode material, burnout depends on the vapor pressure and indirectly on the melting temperature of the material. 150
Metals and alloys with melting points above 0.000 have outstanding properties in this respect.

Atomization of the electrode surface, which causes burnout, can be significantly suppressed by metals or alloys with an average atomic weight of more than 100. This is because the exchange of kinetic energy between the atoms on the metal surface in the ignition region and the ions in the gas in the combustion chamber is extremely small, especially compared to nickel (atomic weight: 7.7). The metal used in the layer also has a high thermal conductivity, thus helping to prevent overheating at the electrode tip due to heat concentration. The success of this invention further requires that the coating metal be chemically inert so that it does not react with compounds inherently present in the combustion chamber to form oxides or carbides. It is important that there be.

Furthermore, the metal must practically not absorb the gases occurring in the combustion chamber, so as not to cause the surface layer to become hardened. Finally, the electrode material acts advantageously as a fixed contact means acting as a catalyst during the ignition process and the start of combustion, such as by catalytic cracking of hydrocarbon fuels or oxidation of said fuels.

In particular, metals of the platinum group are known as preferred decomposition and oxidation catalysts. The same can be said about rhenium. In summary, the coating must combine the following properties:

That is, {a' 1500? 'b) a high thermal conductivity; {cl an atomic weight on average above 100; and 'd) as long as possible to react with the constituent parts of the fuel/air mixture and with the combustion gases. (e) as little as possible to the decomposition due to the absorption of compounds from the combustion chamber; {f') the decomposition and/or oxidation of hydrocarbon groups; It has catalytic activity for

Suitable metals are first of all the elements of the platinum group, namely platinum, palladium, ruthenium, rhodium, iridium, osmium and rhenium.

Alloys of these with each other and with other metals are also contemplated. Although alloys have a reduced thermal conductivity compared to pure metals, they have the advantage that the melting point, and therefore indirectly also the vapor pressure, can be precisely adjusted. Iridium and osmium are extremely expensive compared to platinum, but
This can be compensated for by using thinner layer thicknesses, or by using less expensive osmium/iridium alloys without separating into pure single metals. The electrode itself advantageously consists of a base metal carrier material with as good a thermal conductivity as possible, such as an electrode consisting of a core of copper or other suitable material and covered with nickel or a nickel electrode. is suitable. Since burnout at the center electrode is usually very high, it is particularly important to coat the firing part of the center electrode with a noble metal according to the invention. Of course, the ground electrode may be similarly coated, but the ground electrode functions as an electron acceptor, is substantially unaffected by heavy cations in the gaseous atmosphere, and is further structurally provided with favorable conditions for heat dissipation. have. As a result, the thermal load on the ground electrode is less than the thermal load on the center electrode, which is at a negative potential and high pressure relative to the ground electrode and is surrounded by an isolator. Therefore, mainly the burnout of the center electrode limits the life of the spark plug in particular, and there is therefore an urgent need to solve the problem in order to reduce the burnout. The metal layer in the region of the ignition part of the electrode is located at the bottom of the polar gap (Fu8punk
It should be formed as far away as possible from the region te).

To save on the amount of layer metal used, the layer metal can be assembled onto the electrode carrier without welding and soldering means.The present invention uses a coating method.

By this method, a flat and very tightly bonded, crystalline but non-dendritic layer can be formed into complex shapes with a desired thin layer thickness of about 5 to 100 mm, preferably 15 to 60 mm. It is also possible to coat the tip of the electrode. This crystallinity is produced by vapor deposition from the gas phase or by electrolysis from molten salts at high temperatures. In particular, this type of coating method makes it possible to coat the electrode tip with a cap-like noble metal layer, which will be described in detail below. This coating layer is grown by crystallization, so that the spark on the coating metal layer can be supported by a relatively wide electrode end surface, and the thermal conductivity of the coating metal layer is high, so the coating Atomization or evaporation of the electrode surface of the ignition part of the layer can be virtually avoided. The crystallized and grown coating layer has the desired catalytic activity,
In order to have thermal resistance and mechanical strength against thermal stress, a thickness of 5 mounds or more is required, preferably 15 mounds or more, and on the other hand, the type, concentration, combustion temperature, pressure of the combustion chamber, etc. of the fuel gas, etc. By having a skin thickness of 60 mm under various combustion conditions, it can have properties such as catalytic ability, thermal stability, and mechanical stability. If the thickness is more than 100 mm, the thermal resistance may increase, and the above-mentioned properties will not be improved further in practice, and a maximum layer thickness of 100 mm is sufficient.

Deposition from the gas phase is carried out either by vapor deposition of noble metals or by thermal decomposition and reduction of suitable volatile noble metal compounds, ie chemical vapor deposition (so-called CVD method). The coating is however U.S. Patent No. 209 I06, 2292766
No. 3,309,292 and No. 354,778y' is preferably carried out using a melt electrolysis method as described herein.

A particularly advantageous method is described in Patent Application Publication No. 24 of the Federal Republic of Germany.
No. 17424. For melt electrolysis in the process it is possible to use solutions of noble metal salts in alkali cyanamide and/or rhodanide and/or monocyanide and/or halide melts, which are In a given case it may also contain alkali carbonates and/or cyanates, in which case, depending on the reaction conditions, substances forming CN- or CNO- groups may be added to the melt for the dissolution of the metal. Add to. There are a number of substantial advantages to using melt electrolysis for coating spark plug electrodes.

That is, 'a-- An extremely pure metal layer is deposited without forming any non-metallic additives inside, and [b'] Because the working temperature in the manufacturing method is relatively high, The metal can be produced as a very tightly bonded layer on the electrode, 'c-
The degree of bonding of the layers is further increased by increasing the operating temperature to a temperature at which the layer metal diffuses into the carrier.

On the other hand, this diffusion may also be carried out by tempering after coating, [d) Patent Application Publication No. 2 of the Federal Republic of Germany.
The method of No. 417,424 allows virtually all metals to be deposited in crystalline layer shapes appropriate to the respective desired layer thicknesses over a wide range of operating temperatures.

The use of this coating method provides the ability to rationally manufacture large numbers of pieces with a minimum amount of precious metal, and these are dependent on the thickness of the layer, the degree of bonding of the layer on the metallic carrier, and the adhesion. The purity of the metal layer produced, the flexibility of the coating process when used on complex electrode tips,
The requirements regarding high coating rates and the possibility of using a wide range of pallets made of various coating metals or their alloys are met.

In certain cases, after coating, further polishing may be carried out by forging, grinding, polishing or similar mechanical post-treatments. The coating of the center electrode of the present invention is preferably formed in the shape of a hat or a cap.

As a result, the coating extends not only over the entire front surface but also onto the side walls of the electrode. The shape of this metal layer ensures very good thermal conductivity when compared to electrode tips consisting of large amounts of platinum or platinum/iridium wire or platinum/iridium bands, even when alloyed instead of pure precious metals. Provided to. This is primarily due to the large heat-conducting cross section provided between the metal layer and the carrier. Providing a bevel-like or cap-like metal coating on the center electrode is particularly advantageous if the firing part of the center electrode is formed in the shape of a vice-cone.

In this case, the shaft can also be of cylindrical design as usual. Preferably, the head conical tip is coated over a portion of its height, viewed from the small diameter front side, with a cap of platinum, another platinum metal, rhenium or an alloy of these metals. At this time, the cap is shaped conically to a depth equal to at least half the thickness of the layer coating the front surface, usually one to one diagonal of the thickness of the layer, measured from the front surface. It is formed by coating the side wall surface. As a result, the closed interface between the layer and the carrier metal is well separated from the area of highest thermal load. The three-dimensional shape of the vice principal's conical tip is
After coating the layered metal cap, it is advantageous to shape its diameter and height in such a way that it does not exceed the size of the cylindrical cross-section of the electrode shaft in any position. This makes it easier to coat the electrode when applying partial coatings to form a cap, and also makes it easier to remove the center electrode from the support used during the coating operation. The invention will now be described with reference to the accompanying drawings.

This drawing shows two specific examples of the center electrode for a spark plug according to the present invention, and the lower part of the center electrode is omitted in each case. The center electrode shown in FIGS. 1 and 2 has a cylindrical shaft 1 with a diameter D, and in the ignition part 2, which is also surrounded by the isolator of the spark plug, a diameter D.
2. The diameter is 4.

The tip 3 of the electrode is formed in the shape of a warhead cone, and as a result, the electrode diameter at the front face 5 of the warhead cone is D3=D2-a.
Reduce the diameter to ds. The factor a, which indicates a multiple of the thickness of the layer and is the degree to which D2 at least increases to 3, has a value of 2 to 10. At this time, the lower limit of the diameter in the coating process is determined by D3 and D2, and the small diameter portion is the coating D3 and D2. Forming the cap of the present invention on the electrode tip d. The value is between 0.5 and 1 s, where ds is the thickness of the layer on the front surface 5. The height of the battle cone tip is determined by the selection of the values of ds and d. The embodiments in FIGS. 1 and 2 differ in that in FIG. 1 the cap 4 partially covers the principal's conical side wall surface 6, whereas in FIG. 2 it completely covers it.

Since the spark plug according to the invention has the characteristics detailed above, it is already surprising that the electrode burnout is extremely low at layer thicknesses in the range from 10 to 50 μm.

As a result, the electrode spacing remains practically constant over the unusually long operating life of the engine. In addition, since the consumption of precious metals is extremely small (compared to known platinum spark plugs with electrodes having metal tips of platinum or platinum metal or known spark plugs manufactured by wet electrolytic coating, the consumption of layer metals is very low). The amount is 1/5 to 1/1
The production of spark plugs is economical. As a result, the spark plug according to the invention may be used not only in special engines, but also in ordinary internal combustion engines. In this case, the stability of the electrode spacing and the catalytic properties of the electrodes make it possible to optimize the fuel consumption rate. In the spark plug for an internal combustion engine of the present invention, since the coating layer is made of a metal or alloy having an average atomic weight of 100 or more and a melting point of 1,500 or more, the ignition portion of the center electrode can be atomized and evaporated at temperatures of 100,000 or more. is unlikely to occur.

In addition, since the coating layer is formed by electrolysis or vapor deposition of molten salt, the coating layer has relatively high crystallinity, and the metal or alloy is immediately crystal-grown on the carrier metal of the center electrode. Therefore, not only is this coating layer strongly adhered to the base metal of the center electrode, but also the thermal conduction of the coating layer and the thermal conduction between the coating layer and the carrier metal of the center electrode are improved. Better yet, the heat generated in the coating layer by the spark can be quickly dissipated to the carrier metal.

Therefore, there is no possibility that the coating layer will be overheated, and there is little possibility that the coating layer will be peeled off from the carrier metal due to thermal stress due to thermal expansion or the like.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a specific example of the center electrode for a spark plug according to the present invention, and FIG. 2 is an explanatory diagram of another specific example of the center electrode for a spark plug according to the present invention. 1... shaft, 2... ignition part, 3...
...Tip, 4...Cap, 5...
・Front. Fig. lFig. 2

Claims (1)

[Scope of Claims] 1 At least the ignition portion has a center electrode coated with a metal or alloy having an average atomic weight of 100 or more and a melting point of 1500°C or more, and the coating layer of the metal or alloy is a molten salt. The ignition plug for an internal combustion engine is a layer deposited on the ignition part with a thickness ds of 5 to 100 μm by electrolytic crystal growth. 2. The spark plug according to claim 1, wherein the coating layer has a thickness of 15 to 60 μm. 3. The center electrode has a front surface and a truncated conical side wall surface, and the diameter of the axis of the cylindrical center electrode is 2 times larger than the diameter of the front surface.
2. The spark plug according to claim 1, wherein the spark plug has a height of 0.5 ds to 10 ds, and the entire front surface and truncated conical side wall surface are coated with metal at a height of 0.5 ds to 10 ds. 4. The spark plug according to claim 1, wherein the coating layer is fixed to the electrode by an alloy layer formed by diffusion. 5. The spark plug according to claim 1, wherein the surface of the coating layer is smoothed by mechanical post-treatment. 6. At least the ignition part has a center electrode coated with a metal or alloy having an average atomic weight of 100 or more and a melting point of 1500°C or more, and the coating layer of the metal or alloy is formed by crystal growth by vapor deposition. 5
A spark plug for an internal combustion engine, wherein the layer is deposited on the ignition portion with a thickness of ~100 μm. 7. The spark plug according to claim 6, wherein the coating layer has a thickness of 15 to 60 μm. 8. The center electrode has a front surface and a truncated conical side wall surface, and the diameter of the axis of the cylindrical center electrode is 2 times larger than the diameter of the front surface.
7. The spark plug according to claim 6, wherein the spark plug has a height of ds to 10 ds, and the entire front surface and truncated conical side wall surface are coated with metal at a height of 0.5 ds to 10 ds. 9. The spark plug according to claim 6, wherein the coating layer is fixed to the electrode by an alloy layer formed by diffusion. 10. The spark plug according to claim 6, wherein the surface of the coating layer is smoothed by mechanical post-treatment.