JP2001273965A - Spark plug for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug for an internal combustion engine, that is superior in anti-lead corrosiveness and wherein a chip for outside electrode does not exfoliate or fall off because of a difference of thermal expansion. SOLUTION: Each chip for a central electrode and an outside electrode of 0.9 mm in a diameter and 0.6 mm of thickness is made of Ir alloy containing a specific amount of (1) Rh, (2) Pt, or (3) Rh and Pt or Ru, and chips for an intermediate layer of 1.2 mm in a diameter and 0.3 mm of thickness made of Ir alloy containing 40 wt.% Ni are fabricated by a powder processing method. After that, the chip for the central electrode is welded by laser to the end face of the base body of the central electrode made of Ni alloy (Inconel 600). Further, the chip for the intermediate layer is abutted on a designated position of the outside electrode, and the chip for the outside electrode is abutted on the central part of this chip for the intermediate layer, and while pressed, these are welded with an electric resistance welding. Further, the spark plug is obtained consisting of insulators and metal fittings made of general materials and structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a spark plug for an internal combustion engine. More specifically, the present invention relates to a spark plug for an internal combustion engine that suppresses abnormal corrosion of an electrode tip due to a Pb component contained in gasoline, has excellent spark wear resistance, and has little electrode wear due to high-temperature oxidation.

[0002]

2. Description of the Related Art In order to improve spark wear resistance, a spark plug using an electrode tip containing Pt as a main component has been put to practical use. Further, as a spark plug having more excellent spark erosion resistance, Pt-I containing Pt as a main component is used.
A device using an electrode tip made of an r alloy has also been developed. However, when these electrode tips are joined by electric resistance welding to the base of the center electrode and the base of the outer electrode mainly composed of Ni or Ni alloy, they are separated by thermal stress due to a difference in thermal expansion at a high temperature during use, The electrode tip may fall off.

[0003] Therefore, P
A spark plug in which an intermediate layer containing t and Ni is provided to reduce thermal stress has also been proposed. In particular, in the case of the center electrode, the base and the electrode tip are welded by laser welding,
A spark plug whose thermal stress has been reduced by forming a bonding layer made of an alloy containing t and Ni has also been put to practical use.

As described above, a long-life spark plug which is excellent in spark wear resistance and in which peeling and falling off of an electrode tip due to thermal stress is prevented is being used in many parts of the world with the spread of motorization in recent years. It has become. However, in a spark plug provided with an electrode tip containing Pt as a main component, when gasoline contains Pb, a compound having a low melting point is formed between Pt and Pb.
Then, there is a problem that the electrode tip is abnormally corroded by Pb, and the life of the spark plug, which should have high performance and long life, is rather shortened.

[0005]

As described in detail above, a spark plug which is superior in spark erosion resistance and has a long service life, or a spark plug which prevents peeling and falling off of an electrode chip due to a difference in thermal expansion coefficient. The plug is disclosed in
No. 9284, JP-A-6-45050, JP-A-9-7733 and JP-A-11-3765. However, abnormal corrosion of the electrode tip due to Pb has not been sufficiently studied, and in particular, even when the electrode tip is joined to the outer electrode by electric resistance welding, the electrode tip is peeled or dropped due to thermal stress. There is no description of a spark plug that prevents the occurrence of a spark plug.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, in which Ir or a tip for an outer electrode mainly composed of Ir is provided with a specific thermal expansion coefficient formed at a predetermined position on the outer electrode. Even when joined to an intermediate layer having electric resistance by electric resistance welding, chips are prevented from falling off, and even when gasoline contains Pb, it does not corrode abnormally and has excellent durability for internal combustion engines. It is intended to provide a spark plug.

[0007]

SUMMARY OF THE INVENTION A spark plug for an internal combustion engine according to the present invention has a center electrode including a base, a center electrode tip joined to the base, a base, and a base formed at a predetermined position on the base. And an outer electrode comprising an outer electrode tip joined to the surface of the intermediate layer,
A spark plug in which the center electrode tip and the outer electrode tip are arranged to face each other, wherein the center electrode tip and the outer electrode tip are made of Ir or an alloy containing Ir as a main component. The coefficient of thermal expansion of the layer is between the coefficient of thermal expansion of the base and the coefficient of thermal expansion of the outer electrode tip, the base and the center electrode tip are joined by laser welding, and the intermediate layer The bonding with the outer electrode tip is performed by electric resistance welding.

The above-mentioned "spark plug for an internal combustion engine" includes a center electrode tip joined to the end face of the base and an outer electrode tip joined to the inner side face of the edge of the base via the intermediate layer. A spark plug of a parallel electrode type opposed to the spark plug can be obtained. Further, a multi-electrode type including a plurality of outer electrodes in which a center electrode tip joined to the side surface of the edge of the base and an outer electrode tip joined to the end face of the base via an intermediate layer are opposed to each other. Spark plug.

Here, the end face or side face of the base and the base is not only a flat face, but also has a recess for fitting and joining the center electrode tip or the outer electrode tip, and the bottom face of the recess. Is also meant. In addition, a member constituting another part of the spark plug, that is, an insulator disposed in contact with the peripheral surface of the base, a metal shell provided outside of the insulator, and an insulator connected to the center electrode, The material, structure, and the like of the terminal fittings and the like provided on the other end side may be general ones, and are not particularly limited.

The "base" constituting the center electrode and the "base" constituting the outer electrode are usually composed of Ni alone or I.
It is formed of a Ni alloy such as nconel. Further, the "center electrode tip" bonded to the base and the "outer electrode tip" bonded to the base via an intermediate layer are:
Ir such as Ir alone or Ir-Rh alloy and Ir-Pt alloy
It is formed of an Ir alloy containing r as a main component. Further, the “intermediate layer” is formed of an alloy including Ir, Ni, Rh, Pt, and the like included in the base and the outer electrode tip, and has a “thermal expansion coefficient” of each of the base and the outer electrode tip. Lies between the coefficients of thermal expansion.

The center electrode tip is joined to the base by "laser welding" to form a joint made of an alloy containing components of the base and the components of the center electrode tip, ie, Ni and Ir. The electrode for the center electrode, in which lead corrosion is sufficiently suppressed and excellent durability is required, must be made of a material mainly composed of Ir. On the other hand, in consideration of mass productivity, the substrate is made of a material mainly composed of Ni. preferable. When a chip and a base made of such a material are used, the difference in melting point between the chip and the base becomes very large as compared with a case where a conventional chip mainly composed of Pt is welded to the base.

Further, the center electrode must be made thinner in order to improve the ignitability and reduce the discharge voltage.
When a member made of a material having a very large difference in melting point in such a small-diameter portion is subjected to electric resistance welding, a large bulge occurs or a base buckles. Furthermore, Ir
Since the chip mainly composed of Pt has a very large difference in thermal expansion from the substrate compared with the chip mainly composed of Pt, grinding such a bulge with a cutting tool lowers the welding strength, and the chip becomes in use during use. There is a risk of falling off. Further, if used as it is, the consumption is rapidly accelerated by spark discharge from a swell made of an alloy of Ir and Ni, the welding strength is reduced, and the chip may fall off. Furthermore, when buckling occurs, it is necessary to grind with a cutting tool to repair the base, and if used as it is, depending on the degree of buckling, it is provided on an insulator to mount the center electrode. It cannot be inserted into the through hole.

In contrast, laser welding does not cause such swelling or buckling, so that the above-described problem does not occur, and the chip is firmly joined to the base. The chip does not peel off or fall off the substrate due to the difference in thermal expansion between the chip and the base.

On the other hand, in the outer electrode, the tip for the outer electrode is joined to the surface of the intermediate layer by "electric resistance welding", not by laser welding, for the structural reason. this is,
This is because the chip is bonded to a part of the plane of the base. In other words, when performing laser welding, the laser spot must be aligned with the outer periphery of the bonding surface between the outer electrode tip and the base, so that the laser is obliquely applied to the bonding surface between the chip and the base. Not get. For this reason, it is not possible to form a melted portion by the laser to a depth of the bonding surface, and it is difficult to obtain a sufficient bonding strength.

On the other hand, when the chip is subjected to electric resistance welding via the intermediate layer, the chip can be joined over the entire joining surface of the chip, and sufficient welding strength can be easily obtained. In this case as well, swelling occurs as in the case of the center electrode side, but this swelling is not a serious problem as occurs on the center electrode side. That is, since the outer electrode is normally at a positive potential, only negative ions having a small mass are attracted to the outer electrode during spark discharge. Therefore, even if a spark discharge occurs due to the swelling, the wear does not progress toward the center electrode side, and the welding strength does not easily decrease.

Further, since the chip is welded to the flat surface of the base portion, buckling does not occur, and even if buckling occurs, it is not particularly necessary to repair buckling. Furthermore, since the intermediate layer has an intermediate coefficient of thermal expansion between the chip and the base, peeling and falling off of the chip due to the difference in thermal expansion between the chip and the base are sufficiently prevented even with electric resistance welding. You. For the reasons described above, it is necessary to join the center electrode side by laser welding and the outer electrode side by electric resistance welding via an intermediate layer.

The intermediate layer may be joined to the base by laser welding or by electric resistance welding, but it is preferable that this joining is also carried out by electric resistance welding. In particular, if the intermediate layer and the outer electrode tip are simultaneously bonded to the base, the number of steps can be reduced, and the outer electrode can be formed easily and inexpensively.

Each chip for the center electrode and the outer electrode is
The spark plug can be made of Ir or an Ir alloy which is excellent in spark abrasion resistance and hardly corrodes even when Pb is contained in gasoline, and has excellent durability.
r tends to be oxidized at high temperatures. In particular, when the engine is placed in a severe use environment such as high rotation and high output, the temperature near the electrodes, particularly near the outer electrode, becomes 900 ° C.
° C, or even 1000 ° C, and the chip is easily consumed by high-temperature oxidation. Therefore, it is more preferable to use a chip made of an alloy of Ir and Rh, Pt, or the like, which has excellent oxidation resistance at high temperatures.

Each of these chips is (1) 1.5 to 50
% By mass of Rh, (2) 1 to 10% by mass of Pt, or 1.
It is particularly preferable to use an alloy mainly containing Ir containing 5 to 50% by mass of Rh and 1 to 10% by mass of Pt or Ru. When Rh is less than 1.5% by mass or Pt or Ru is less than 1% by mass, the oxidation resistance at high temperatures is not sufficiently improved. On the other hand, when Rh exceeds 50% by mass, the spark erosion resistance tends to slightly decrease. However, since the Rh facilitates the processing of the electrode tip, the amount ratio of Rh is 7 to 40% by mass, particularly 10% by mass.
More preferably, the content is set to 30% by mass. Further, when Pt or Ru exceeds 10% by mass, the melting point of the electrode tip is lowered and processing becomes more difficult than when only Ir is used. Therefore, the amount ratio of Pt or Ru should be 2 to 7% by mass. Is more preferred.

In each of the chips for the center electrode and the outer electrode, the content of Ir is the largest by mass ratio,
When the content of h, Pt or Ru is large and other metals are contained, it is preferable to minimize the content thereof.
Even in the case of an alloy mainly composed of Ir, if the metal having the next highest content is Ni, sufficient lead corrosion resistance cannot always be obtained when gasoline containing Pb is used. Each of these chips has a shape such as a cylinder or a truncated cone, and has a diameter of 0.6 to 1.8 mm, particularly 0.6 to 1.4 mm, and a thickness of 0.2 to 0.7 mm, particularly 0.4. It is preferably about 0.7 mm.

The intermediate layer is preferably formed of an alloy containing Pt or Ir as a main component. Since the intermediate layer does not discharge unlike the respective chips for the center electrode and the outer electrode, Ir is not essential and has sufficient durability even if the metal having the second highest content after the main component is Ni. It has no peeling or falling off from the base. The middle layer is 30-5
Ir alloy containing 0 mass% Ni, 30-50 mass% R
h containing Ir alloy and P containing 10 to 30% by mass of Ni
It can be formed of a t alloy or the like.

The intermediate layer has a coefficient of thermal expansion at 900 ° C. measured by a thermal expansion analyzer of “10 × 10 ⁻⁶ /
To 16 × 10 ⁻⁶ / ° C. ”. When the thermal expansion coefficient of the intermediate layer is less than 10 × 10 ⁻⁶ / ° C., the difference in thermal expansion coefficient between the intermediate layer and the base composed of Ni alone or a Ni alloy increases, and the intermediate layer may peel off or fall off from the base. Therefore, it is not preferable. On the other hand, the thermal expansion coefficient of the intermediate layer is 16 × 1
If it exceeds 0 ^-6 / ° C., the difference in thermal expansion coefficient between the outer electrode tip and the intermediate layer becomes large, and the chip may peel off or fall off from the intermediate layer, which is not preferable. When the thermal expansion coefficient of the intermediate layer is 12 × 10 ⁻⁶ / ° C. to 15 × 10 ⁻⁶ / ° C., the peeling and falling off of the intermediate layer and the outer electrode tip are suppressed, and the spark plug has a sufficient durability. And more preferred.

Further, the entire surface of the intermediate layer is preferably covered with the outer electrode tip. In particular, 30
In an intermediate layer made of an alloy containing at least one of Pt and Ni in an amount of at least 40% by mass, more preferably at least 40% by mass,
When gasoline containing b is used, as shown in FIG. 3, by covering the entire surface with an outer electrode tip,
Abnormal corrosion due to Pb can be prevented. Since the intermediate layer does not discharge, abnormal corrosion due to Pb is not further accelerated by spark consumption, but nevertheless, the entire surface is covered with the outer electrode tip to ensure more durability. An excellent spark plug can be obtained. The intermediate layer has a diameter that is 0.1 to 0.5 mm larger than a diameter of 0.1 to 0.3 mm below the diameter of the outer electrode tip, and has a thickness of 0.1 to 0.6 mm, particularly 0.2 mm.
The size is preferably about 0.5 mm.

In the case of an internal combustion engine, the temperature near the electrodes may be as high as over 800-900 ° C., or as high as 1000 ° C. in some cases at high rotation and high output. At such a high temperature, Ir is oxidized and easily vaporized. Therefore, as in the fifth invention, the above-mentioned "good heat conductive core" made of a metal having high thermal conductivity is disposed inside the base of the outer electrode. Is preferred.

This good heat conductive core is made of pure Ni or iron material as a core and is formed so as to surround the periphery with Cu or Ag as shown in FIG. It is arranged even to the metal shell. Thus, heat in the vicinity of the tip of the outer electrode including the tip is transmitted to the metal shell via the good heat conducting core and further transmitted to the cylinder head of the engine. The chip is oxidized by the so-called heat pulling, and the chip is sufficiently prevented from being heated to a temperature of 900 ° C. or more, which is easily vaporized, and the heat between the base and the intermediate layer and between the intermediate layer and the outer electrode chip. The thermal stress due to the difference in expansion is also reduced, and a spark plug having more excellent durability can be obtained. If the good heat conducting core is disposed up to the tip of the base, the base may be cracked due to thermal expansion and contraction of the good heat conducting core. For this reason, the good heat conducting core is usually provided up to the vicinity of the outer electrode tip as shown in FIG.

The method for producing each of the chips for the center electrode and the outer electrode and the chip for forming the intermediate layer is not limited. In particular, the chip for the outer electrode and the chip for forming the intermediate layer are prepared by a rolling method. Is preferred.
This is because each chip is pressed in the thickness direction during electric resistance welding, and if a chip has a flat crystal structure in a direction perpendicular to the pressing direction, welding cracks are unlikely to occur. is there. The center electrode tip may be manufactured by a rolling method, but is not particularly required. Each of the chips for the center electrode and the outer electrode and the chips for forming the intermediate layer are formed by various methods such as a hot rolling method, a hot drawing method, a powder sintering method, and a hot header processing method. Can be produced.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail by way of examples. [1] Influence of composition of each chip for center electrode and outer electrode on lead corrosion resistance Experimental Examples 1-21 (1) Production of spark plug From Ir alone or an alloy containing each metal described in Table 1 Each tip for the center electrode and the outer electrode having a diameter of 0.9 mm and a thickness of 0.6 mm, and an Ir alloy containing 40% by mass of Ni, and having a diameter of 1.2 mm and a thickness of 0.1 mm. 3mm
Was manufactured by a powder processing method. Then, the tip for the center electrode is made of Ni alloy (Inconel 6).
00) was joined to the end face of the base of the base electrode by laser welding. In addition, the chip for the intermediate layer is also
The outer electrode chip made of EL600 was brought into contact with a predetermined position on the base, and the outer electrode chip was brought into contact with the center of the intermediate layer chip. Note that the respective chips for the center electrode, the outer electrode, and the intermediate layer may be manufactured by a dissolution method.

Except for forming the center electrode and the outer electrode in this manner, the material and the overall structure of the other parts of the spark plug, such as the insulator and the metal shell, are the same as those of the conventional general spark plug. Thus, the spark plugs of Experimental Examples 1 to 21 were manufactured.

[0029]

[Table 1]

(2) Evaluation of Lead Corrosion Resistance Using a 6-cylinder gasoline engine with a displacement of 3000 cc, 5000 rpm, WOT (wide open)
A 100-hour endurance test was performed under the conditions of (hrottle), and the amount of increase in the gap between the chips for the center electrode and the outer electrode was measured with a pin gauge. As a fuel, 0.1.
Gasoline containing 4 g / l tetraethyl lead was used. The maximum temperature of the substrate was 850-900 ° C. in each case. The results are also shown in Table 1.

According to the results in Table 1, Experimental Examples 3 and 5 to 5
In 12 and 17 to 20, the increase in the gap between the center electrode tip and the outer electrode tip due to corrosion was 0.05
mm or less, indicating that abnormal corrosion due to Pb is extremely small and there is no problem in practical use. On the other hand, in Experimental Example 1 using the chip containing Pt as the main component, the increase in the gap exceeded 0.4 mm, and similarly in Experimental Example 2 using the chip containing Pt as the main component, it exceeded 0.2 mm. Abnormal corrosion due to Pb was remarkable. Also, Rh relative to Ir
Or Experimental Examples 4 and 16 using chips with too little Pt and Experimental Examples 13 to 15 and 2 using chips with too much Pt
1, the increase in gap is 0.1 mm or more, and Pb
It can be seen that they are easily corroded. These results indicate that Ir
Alternatively, it supports the effectiveness of a chip made of an alloy containing Ir as a main component and containing an appropriate amount of Rh, Pt, or the like with respect to the lead corrosion resistance.

[2] Investigation of the effect of the presence or absence of the intermediate layer on the peeling and falling off of the chip Example 1 (1) Production of spark plugs An Ir alloy containing 40% by mass of Rh or 5% by mass of Pt was used. Are 0.9 mm and the thickness is 0.6 mm, each tip for the center electrode and the outer electrode, and 40% by mass of N
An intermediate layer chip made of an Ir alloy containing i and having a diameter of 1.2 mm and a thickness of 0.3 mm was produced by a powder processing method. Then, the tip for the center electrode was replaced with a Ni alloy (Incon).
el 600) was joined to the end face of the base by laser welding. Also, the chip for the intermediate layer is
The tip of the outer electrode made of nconel 600 was brought into contact with a predetermined position on the base, and the tip of the outer electrode was brought into contact with the center of the tip for the intermediate layer.

Other than the fact that the center electrode and the outer electrode are formed as described above, other materials such as insulators and metal shells and the general structure of the other parts of the spark plug are the same as conventional spark plugs. I did the same.

Comparative Example 1 A spark plug was manufactured in the same manner as in Example 1 except that the tip for the outer electrode was directly joined to a predetermined position of the base of the outer electrode by electric resistance welding without using the tip for the intermediate layer. .

The spark plug 100 of the first embodiment is similar to that of FIG.
As shown in the figure, the center electrode 1, the outer electrode 2, and the terminal electrode 3
And an insulator 4 for fixing and holding each of these electrodes, and a metal shell 5 for containing and protecting the insulator 4
Is provided. Further, the metal shell 5 is formed with a screw portion 51 for attaching a plug to an engine block (not shown).

FIG. 2 is an enlarged longitudinal sectional view showing the vicinity of the center electrode and the outer electrode of the spark plug having an intermediate layer between the tip and the base of the outer electrode. The center electrode 1 includes a base 11 and a center electrode tip 12, and the outer electrode 2 includes a base 21, an intermediate layer 22, and an outer electrode tip 23. The outer electrode 2 is connected to a part of the end face of the metal shell 4, and is arranged so that the other end faces the center electrode 1. The spark plug of Comparative Example 1 has the same configuration as that of Example 1 except that no intermediate layer is formed.

(2) Inspection of whether or not the tip for the outer electrode has fallen Using a gasoline engine with a displacement of 3000 cc and 6 cylinders, a cycle of 5,000 rpm, WOT × 1 minute, idling (about 600 rpm) × 1 minute, 300 hours A thermal endurance test was performed. Unleaded gasoline was used as fuel. After this test, the spark plug was disassembled, and it was inspected whether the outer electrode tip had fallen off the base.

As a result, in the case of the spark plug having the intermediate layer, regardless of the composition of the chip, the outer electrode chip does not peel off or fall off due to the thermal stress due to the repetition of cooling and heating. It was firmly joined to the base. On the other hand, in the case of the outer electrode having no intermediate layer, the test was disassembled and inspected after the test. As a result, the outer electrode tip was peeled off and dropped off from the base. As described above, even when the good heat conductive core is not provided and the chip is peeled or dropped under severe conditions, the formation of the intermediate layer surely prevents the chip from being peeled or dropped. It can be understood that it can be done.

Table 1 shows the coefficients of thermal expansion at 900 ° C. of the chips for the center electrode and the outer electrode. As described above, the coefficient of thermal expansion at 900 ° C. (13.58 × 10 ⁻⁶ / ° C.) of the chip for the intermediate layer is the same as the coefficient of thermal expansion of each of the chips for the center electrode and the outer electrode, and In.
Cone 600 at 900 ° C. (1
6.10 × 10 ⁻⁶ / ° C.), and it can be understood that this also reliably prevents the chip from peeling and falling off.

It should be noted that the present invention is not limited to the above-described specific embodiments, but can be variously modified within the scope of the present invention depending on the purpose and application.
For example, as shown in FIG. 3, the entire surface of the intermediate layer is covered with the outer electrode tip, and a spark plug having more excellent lead corrosion resistance can be obtained. Further, a spark plug in which the good heat conducting core 24 is disposed inside the outer electrode 2 can be provided. By doing so, the maximum temperature of the outer electrode tip periphery can be kept very low at 800 to 850 ° C., and peeling and falling off of the tip can be more reliably prevented.

[0041]

According to the present invention, there is no abnormal corrosion due to Pb of each tip of the center electrode and the outer electrode, and the tip of the outer electrode is prevented from dropping due to a difference in thermal expansion between the tip and the base, thereby improving durability. An excellent spark plug for an internal combustion engine having a long life can be obtained. In addition, by using the alloy of the specific composition of the present invention, and by using a specific configuration or the like, a spark plug having more excellent durability can be obtained.

[Brief description of the drawings]

FIG. 1 is a front view of a spark plug.

FIG. 2 is an enlarged longitudinal sectional view showing the vicinity of a center electrode and an outer electrode of a spark plug in which an intermediate layer is provided between a tip and a base in the outer electrode.

FIG. 3 is an enlarged view of the vicinity of a center electrode and an outer electrode of a spark plug in which the entire surface of an intermediate layer is covered with an outer electrode tip, and a good heat conducting core is disposed inside the outer electrode. FIG.

[Explanation of symbols]

100; spark plug, 1; center electrode, 11; substrate,
12; center electrode tip; 13; junction; 2; outer electrode; 21; base; 22; intermediate layer; 23; outer electrode tip;
5: metal shell, 51: screw part.

Claims (5)

[Claims] 1. A center electrode comprising a base, a center electrode tip bonded to the base, a base, an intermediate layer formed at a predetermined position on the base, and a surface bonded to the intermediate layer. An outer electrode comprising an outer electrode tip,
A spark plug in which the center electrode tip and the outer electrode tip are arranged to face each other, wherein the center electrode tip and the outer electrode tip are made of Ir or an alloy containing Ir as a main component. The coefficient of thermal expansion of the layer is between the coefficient of thermal expansion of the base and the coefficient of thermal expansion of the outer electrode tip, the base and the center electrode tip are joined by laser welding, and the intermediate layer A spark plug for an internal combustion engine, wherein the connection with the outer electrode tip is made by electric resistance welding. 2. The center electrode tip and the outer electrode tip are: (1) 1.5 to 50% by mass of Rh, (2)
1 to 10% by mass of Pt, or 1.5 to 50% by mass of Rh
And an alloy mainly containing Ir containing 1 to 10% by mass of Pt or Ru, and the intermediate layer is made of Pt or Ir.
The spark plug for an internal combustion engine according to claim 1, comprising an alloy containing: 3. The spark plug for an internal combustion engine according to claim 1, wherein the intermediate layer has a coefficient of thermal expansion at 900 ° C. of 10 × 10 ⁻⁶ / ° C. to 16 × 10 ⁻⁶ / ° C. 4. The spark plug for an internal combustion engine according to claim 1, wherein the entire surface of the intermediate layer is covered with the outer electrode tip. 5. The spark plug for an internal combustion engine according to claim 1, wherein a good heat conductive core is provided inside the base of the outer electrode.