JP2002359051A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug capable of restraining abnormal consumption in the shape of hollowing out an outer peripheral surface of a noble metal chip in the spark plug for forming a discharge part of the noble metal chip increased in the content of Ir while minimizing the content of Rh. SOLUTION: The central electrode 3 discharge part 31 is formed of the noble metal chip 31' composed of an Ir group alloy. The noble metal chip 31' is constituted by containing Ir of 90 mass % or more as a main component, and also including Rh of 0.5 mass % or more, and Ni of a range of 0.5 to 9 mass %. As a result, consumption resistance of the noble metal chip 31' (the discharge part 31) can be excellently secured, and the abnormal consumption easily caused when restraining the content of Rh can be restrained by adding Ni, in its turn, the high performance spark plug can be inexpensively constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug used as an ignition source for an internal combustion engine such as an automobile engine.

[0002]

2. Description of the Related Art In a spark plug used for igniting an internal combustion engine such as an automobile engine, the temperature in a combustion chamber tends to increase in order to increase the engine output and improve fuel efficiency. Further, in order to improve the ignitability, an engine of a type in which a discharge portion corresponding to a spark discharge gap of a spark plug protrudes into a combustion chamber has been increasingly used. In such a situation, since the discharge portion of the spark plug is exposed to a high temperature, the spark is more likely to be consumed. Therefore, in order to improve the spark erosion resistance of the discharge portion corresponding to the spark discharge gap, there have been proposed many types in which a noble metal tip mainly composed of Pt, Ir or the like is welded to the tip of the electrode.

For example, Japanese Patent Application Laid-Open No. 9-7733 discloses that
By forming the noble metal tip with an Ir-Rh alloy, while adding the advantages of Ir having a high melting point, adding Rh for preventing the oxidation and volatilization of Ir at a high temperature (about 900 ° C or more), There is disclosed a spark plug capable of improving wear resistance at higher temperatures (hereinafter, both spark wear resistance and high-temperature oxidation resistance are collectively referred to as wear resistance).

[0004]

However, Rh is several times more expensive than Ir, and the melting point of Rh is Ir.
Is lower at 1970 ° C. than at 2454 ° C.
If the content is too large, not only does the material cost of the noble metal tip soar, but also the spark erosion resistance becomes insufficient.

Therefore, the present inventors have set a low content of Rh in a noble metal chip composed of an Ir-Rh binary alloy to improve the spark wear resistance while suppressing the wear due to oxidation and volatilization. Tried. However, it has been found that when the content of Rh is set to a relatively small value, the consumption of the discharge portion (noble metal tip) cannot be suppressed on the contrary due to occurrence of abnormal consumption described later.

Specifically, the present inventors have developed a 6-cylinder gasoline engine using a spark plug in which a discharge portion composed of a noble metal tip containing Ir as a main component and 20% by mass of Rh is provided only at a center electrode. (Displacement: 2000 cc), and operation was performed using unleaded gasoline as fuel at a fully opened throttle and an engine speed of 5000 rpm. Then, when the appearance of the noble metal tip was observed after 20 hours, as shown in FIG. 5, the outer peripheral side surface which is not the discharge surface (the upper surface of the discharge portion) facing the ground electrode of the noble metal tip was formed in a circular arc. It was observed that abnormal wear occurred. As can be seen from FIG. 5, this abnormal wear has a special form of wear, and it is considered that the cause of the wear cannot be easily perceived by simply spark discharge or oxidative volatilization. This abnormal wear is not shown, but I
10% by mass of Rh, 5% by mass of Rh and 1% by mass of R
Similarly, when the above-mentioned operation (test) is performed using each of the noble metal chips containing h, the tendency that the lower the Rh content is, the more the degree of digging from the outer peripheral side surface of the discharge part becomes, In other words, there was a tendency for abnormal wear to occur easily. Therefore, by using a noble metal tip with an increased content of Ir while suppressing the content of expensive Rh to a low level, an attempt to suppress the oxidative consumption while improving the spark wear resistance of the discharge portion, a new phenomenon called abnormal consumption. This may cause a phenomenon, and the exhaustion of the discharge part cannot be completely eliminated.

An object of the present invention is to provide a spark plug in which a discharge portion is formed by a noble metal tip, wherein the discharge portion is formed by a noble metal tip having an increased Ir content while suppressing a high content of Rh. It is an object of the present invention to provide a spark plug including a noble metal tip having excellent wear resistance, which can suppress occurrence of abnormal wear in a form surrounding an outer peripheral side surface of a noble metal tip.

[0008]

In order to solve the above problems, a spark plug according to the present invention comprises a center electrode held at one end of a through hole in an insulator, and a spark discharge gap between the center electrode and the center electrode. And a ground electrode facing through,
A spark plug in which a noble metal tip is welded to a discharge part corresponding to at least one spark discharge gap between a center electrode and a ground electrode, and the noble metal tip is 90% by mass.
Ir as described above, Rh as 0.5% by mass or more, and 0.5 to 8
It is characterized by containing Ni in a range of mass%.

When the present inventors examined the discharge portion (noble metal tip) in which abnormal wear occurred as shown in FIG. 5, deposits containing Ca and / or P adhered to the surface of the noble metal tip. It became clear. In some cases, the noble metal chip to which the deposit adhered did not cause abnormal wear. However, the deposit caused by the Ca and / or P was attached to all the noble metal chips where abnormal wear was observed. Thus, it is inferred that the above-described abnormal wear is caused by such deposits. On the other hand, it is apparent from FIG. 5 that the abnormal wear proceeds only from a certain direction of the discharge portion (noble metal tip). For this reason, it is considered that some kind of fluid flow exists in the ignition atmosphere in which the discharge unit is ignited, and the flow of the fluid is a cause of abnormal consumption. For example, it can be assumed that the fluid is a mixed gas flow (swirl flow) having a constant flow for uniformly diffusing the fuel in the mixed gas. Further, it can be estimated that the abnormal wear is wear caused by the above two factors. In any case, it can be inferred that such abnormal consumption is caused by a mechanism different from dissolution / separation due to spark discharge, or consumption due to simple oxidation and volatilization of the noble metal tip.

[0010] The present inventors have found that Ir-
In the Rh binary alloy noble metal tip, attention was paid to the fact that the area around the discharge surface of the noble metal tip was hardly abnormally consumed as shown in FIG. Then, component analysis was performed around the discharge surface, and it was found that Ni was contained around the discharge surface. In addition, when the same component analysis was performed on the portion where the abnormal wear occurred (outer peripheral side surface), the presence of Ni was not recognized. That is, the Ni present around the discharge surface is not included in the noble metal tip from the beginning of manufacture, but is included in the process of using the spark plug. That is, it is considered that the Ni component jumps out of the ground electrode made of a Ni-based heat-resistant alloy or the like by repeating the spark discharge, and then the Ni component is injected around the discharge surface of the noble metal tip.
In any case, the present inventors have found that in a noble metal tip where abnormal wear is observed, Ni is contained in a portion where abnormal wear hardly occurs (around the discharge surface).

The present inventors have found that, in the noble metal tip made of the Ir-Rh binary alloy, as the content of Rh decreases, the degree of scouring on the outer peripheral side due to abnormal wear tends to increase. Was. As a result of the above-mentioned intensive studies, the present inventors have found that the discharge portion of the spark plug contains not less than 90% by mass of Ir having a high melting point in order to improve the spark wear resistance, and the oxidation and volatilization of the Ir component. 0.5% by mass or more of Rh for suppressing the consumption by Ni and 0.5 to 8% by mass of Ni.
If it is composed of a noble metal tip containing, it is possible to suppress oxidation consumption while improving spark consumption resistance, and furthermore, it has been found that abnormal consumption as described above can be suppressed, and the present invention has been completed. is there.

[0012] The content of Ni contained in the noble metal tip is in the range of 0.5 to 8% by mass. If the content of Ni is less than 0.5% by mass, the effect of suppressing abnormal wear may not be sufficiently exhibited. On the other hand, if the content of Ni exceeds 8% by mass, the content of Ni is excessively large, and the effect of containing 90% by mass or more of Ir to improve spark erosion resistance is not preferable. Therefore, the noble metal tip preferably contains 0.5 to 8% by mass of Ni, and more preferably contains 1 to 4% by mass of Ni. The reason why the Ni content is more preferably in the range of 1 to 4% by mass is as follows. When the content of Ni is 1% by mass or more, the effect of suppressing abnormal wear can be sufficiently exhibited. On the other hand, N
When the content of i exceeds 4% by mass, although the effect of suppressing abnormal wear is obtained, the Ni component in the material is oxidized by the heat applied during the processing of Ni, and cracks start from the oxidized Ni. When a noble metal tip is to be manufactured by processing such as forging, rolling, or punching, good workability may not be obtained in some cases.

The noble metal tip contains 90% by mass of Ir.
It is composed of the Ir-based alloy contained above. Since Ir has a high melting point (2454 ° C.), its content is 90%.
By setting the amount to be not less than mass%, good spark erosion resistance can be obtained. However, since the Ir component has a problem that its consumption tends to increase rapidly due to oxidation and volatilization when it exceeds 900 ° C.,
The noble metal tip of the present invention contains 0.5% by mass or more of Rh in order to suppress the oxidation and volatilization of the Ir component. When the Rh content is less than 0.5% by mass, I
The effect of suppressing the oxidation and volatilization of the r component becomes insufficient, the noble metal tip (discharge part) is easily consumed, and it becomes difficult to ensure the durability of the plug.

That is, in the present invention, a high melting point Ir component is contained in an amount of 90% by mass or more, and Rh which is more expensive than Ir and has a lower melting point than Ir is provided within a range in which the effect of suppressing oxidation and volatilization can be exerted. The noble metal tip is formed by containing the Ni component in the above range while suppressing the content to a small extent. As a result, the wear resistance of the noble metal tip (discharge part) can be ensured well, and the occurrence of abnormal wear that is likely to occur when the content of Rh is suppressed can be suppressed by adding Ni. The spark plug can be configured at low cost.

The noble metal chips are Sr, Y, La,
Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, H
An oxide (including a composite oxide) of an element selected from o, Er, Tm, Yb, Lu, Ti, Zr, and Hf may be contained. As a result, consumption of Ir by oxidation and volatilization at a high temperature is more effectively suppressed. The oxide preferably contains at least one of La ₂ O ₃ and Y ₂ O _{3. In} addition, ThO ₂ ,
ZrO ₂ or the like can be preferably used. The content of the oxide is preferably set in the range of 0.5 to 3% by mass. If the amount is less than 0.5% by mass, the effect of suppressing the oxidation and volatilization of the added metal element component by the addition of the oxide cannot be sufficiently obtained. On the other hand, when the oxide content exceeds 3% by mass, the heat resistance of the noble metal tip may be impaired.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to cross sections. FIG. 1 is a longitudinal sectional view showing an example of a spark plug 100 of the present invention, and FIG. 2A is an enlarged view of the vicinity of a discharge portion of the spark plug 100. A spark plug 100 including a resistor, which is an example of the present invention, is formed at a distal end, and a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that a distal end portion 21 protrudes. The center electrode 3 held at the tip (one end) of the through hole 6 of the insulator 2 with the discharge portion 31 protruded, and one end connected to the metal shell 1 by welding or the like, and the other end 4a side is laterally connected. And a ground electrode 4 arranged so that the side surface 4 c faces the discharge portion 31 formed on the center electrode 3. Further, a discharge portion 32 facing the discharge portion 31 is formed in the ground electrode 4, and a spark discharge gap g is formed in a gap between the discharge portion 31 and the discharge portion 32.

The insulator 2 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride. The insulator 2 extends along its own axis and has a through hole 6 for fitting the center electrode 3 therein. ing. The metal shell 1 is formed of a metal such as low-carbon steel in a cylindrical shape, constitutes a housing of the spark plug 100, and has an outer peripheral surface on which the spark plug 100 is attached to an engine block (not shown). A screw portion 7 is formed. The terminal fitting 1 is provided at one end of the through hole 6.
3 is inserted and fixed, and the center electrode 3 is also provided on the other end side.
Is inserted and fixed. A resistor 15 is arranged between the terminal fitting 13 and the center electrode 3 in the through hole 6. Both ends of the resistor 15 are electrically connected to the center electrode 3 and the terminal fitting 13 via conductive glass seal layers 17 and 18, respectively. The discharge unit 31
Alternatively, the configuration may be such that one of the facing discharge unit 32 is omitted. In this case, a spark discharge gap g is formed between the discharge part 31 or the opposite discharge part 32 and the ground electrode 4 or the center electrode 3.

As shown in FIG. 2B, for example, the discharge portion 31 is formed by forming a noble metal tip 31 'on a disk from a Ni-based heat-resistant alloy such as INCONEL600 (trademark of INCO, UK) or a Fe-based heat-resistant alloy. The welded portion W is formed by laser welding, electron beam welding, electric resistance welding, or the like, formed along the outer peripheral edge of the joining surface, and is fixed to the end surface of the tip portion 3a of the center electrode 3 to be formed. It is formed. Also,
For example, when the discharge part 32 is formed on the ground electrode 4 side made of a Ni-based heat-resistant alloy such as INCONEL600 and INCONEL601, the discharge part 32 is located at a position corresponding to the discharge part 31 on the center electrode 3 side. No. 4 is formed by aligning the noble metal tip 32 ′, forming a welded portion W ′ along the outer peripheral edge of the joining surface, and fixing the welded portion W ′.

Here, the discharge portions 31 and 32 contain 90% by mass or more of Ir as a main component, and further contain 0.5% by mass or more of Rh and 0.5% to 8% by mass of Ni. Noble metal chips 31 'and 32' containing The content of Ni is preferably 1 to 4% by mass.

The noble metal tips 31 'and 32' are, for example,
It is formed as follows. That is, a noble metal powder as a raw material is blended in an expected ratio, and this is melted to form an alloy ingot. As a specific melting method, for example, a method such as arc melting, plasma beam melting, or high frequency induction melting is employed. Further, if the alloy solution is cast using a water-cooled mold or the like to form a quenched ingot, segregation of the alloy can be reduced, so that this method may be employed. Further, the ingot may be manufactured by compression-molding a noble metal powder blended with a desired composition and then sintering.

Thereafter, the alloy is processed into a linear or rod-shaped material by one or a combination of two or more of hot forging, hot rolling and hot drawing, and the material is processed to a predetermined length in the length direction. And formed. For example, after being processed into a rod shape by hot forging, the diameter is further reduced by hot rolling with a grooved rolling roll and hot swaging, and finally a wire having a wire diameter of 0.8 mm or less by hot drawing. Process into
Thereafter, the wire is cut to have a desired thickness to obtain noble metal tips 31 'and 32'.

The noble metal chips 31 'and 32' are prepared by hot rolling the molten alloy obtained by blending and melting the respective alloy components, and hot stamping the plate material. It can also be formed by punching into a predetermined chip shape. Further, a spherical noble metal alloy may be prepared by a known atomizing method, and the spherical noble metal alloy may be used as it is as a discharge part, or may be compressed by a press or a flat die to obtain a flat or cylindrical shape. Noble metal tips 31 'and 32'.

Further, in the spark plug 100 of the present embodiment, as shown in FIG. 3, the discharge portion 31 has a reduced diameter. Specifically, the tip diameter D of the noble metal tip constituting the discharge part 31 is 0.3 to 0.8 mm, and the thickness H of the discharge part is 0.4 to 2 mm. The tip diameter D and the discharge portion thickness H are defined as shown in FIG. That is, the tip diameter D is the outer diameter D of the discharge part 31 and the discharge part thickness H
From the outer edge of the discharge surface 31t of the discharge portion 31 to the center electrode 3
Is the shortest distance in the axial direction to the corresponding edge of the welded portion W for welding the noble metal tip 31 ′ to the noble metal tip 31 ′. Although only the discharge part 31 on the center electrode 3 side has been described above, the tip diameter D and the discharge part thickness H can be similarly defined in the discharge part 32 on the ground electrode 4 side.

When the tip diameter D is less than 0.3 mm, it is not possible to maintain sufficient durability against ordinary wear due to spark discharge, oxidative volatilization, and the like. On the other hand, when the tip diameter D is 0.8
If it exceeds mm, the effect of reducing the discharge voltage may not be sufficiently obtained. Further, when the thickness H of the discharge portion is less than 0.4 mm, the weld portion W is likely to be exposed to the discharge surface due to repetition of spark discharge, and it may not be possible to provide sufficient spark wear resistance. On the other hand, the discharge portion thickness H is 2.0 m
If m is exceeded, the heat storage in the discharge part tends to be excessive, and the discharge part is consumed and the durability of the noble metal tip cannot be sufficiently satisfied.

The spark plug 1 according to the present embodiment
00 has a structure in which the temperature of the discharge portion 31 on the side of the center electrode 3 is likely to be high. For example, as shown in FIG. 3, a core 35 having relatively higher thermal conductivity than an electrode base material 36 forming a surface layer is formed at the center of the center electrode 3, and the core 35 in the axial direction is formed. The shortest distance L1 between the tip 35a (hereinafter, also simply referred to as the tip of the core) of the spark discharge gap g and the discharge part 31 is 1 to 3 mm. Here, the core body 35 is formed to draw heat from the discharge part 31 to the center electrode 3 side, and is formed of Cu or a Cu alloy or the like. In this configuration, if L1 is less than 1 mm, the tip 35a of the core 35 must be closer to the discharge portion 31 than the tip 21a of the insulator. May expand and break the insulator 2 from the inside. Further, the electrode base material 36 constituting the surface layer may be consumed, and the core 35 may be exposed. On the other hand, L
If 1 exceeds 3 mm, the temperature of the discharge part 31 becomes too high, and the discharge part 31 cannot withstand wear due to repeated spark discharge. L1 is desirably 1.5 to 2.5 mm.

The welded portion W for welding the noble metal tip 31 'and the center electrode 3 may be formed continuously in the radial direction of the noble metal tip 31' as shown in the sectional view of FIG. Also in this case, as in the case of FIG. 3, the shortest distance between the discharge portion 31 and the tip 35a of the core body 35 is L1.

As shown in FIG. 3, the discharge surface 31t and the tip 21a of the insulator 2 on the side of the spark discharge gap g (hereinafter, referred to as "g").
When the shortest distance in the axial direction with respect to the tip of the insulator is simply defined as J, the range of J is preferably 1.5 mm or more. By setting the value of J to 1.5 mm or more, the discharge voltage is reduced. When the value of J is 1.
If it is less than 5 mm, it is difficult for the electric field to concentrate on the discharge surface 31t, and the discharge voltage increases, so that the effect of reducing the diameter of the discharge portion 31 is lost.

As shown in FIGS. 3 and 4, when the shortest distance in the axial direction between the tip 21a of the insulator 2 and the tip 35a of the core 35 is L2, the tip 35a of the core 35 is insulated. L2 is 1 mm or less when it is closer to the discharge surface 31t than the tip 21a of the body 2 (in the case of FIG. 4),
On the other hand, when the tip 21a of the insulator 2 is closer to the discharge surface 31t than the tip 35a of the core 35 (in the case of FIG. 3), L2
Is 1.5 mm or less. By defining the range of L2 in this manner, it becomes easy to set L1 defined as described above to a suitable range.

The spark plug 100 as described above is attached to the engine block at the screw portion 7 thereof.
It is used as an ignition source for the air-fuel mixture supplied to the combustion chamber.
In use, a discharge voltage is applied between the discharge unit 31 and the discharge unit 32, and a spark is generated in the spark discharge gap g (see FIG. 1 for each code). When the spark plug 100 of the present invention is used in an ignition atmosphere in which Ca and / or P is present, the effect of using the discharge portions 31 and 32 is effectively exhibited by the noble metal tip having the above-described configuration. Will be done. Further, since Ca and / or P present in these ignition atmospheres are contained in the engine oil used for the internal combustion engine, the present invention relates to an internal combustion engine using such an engine oil. The spark plug 100 can be suitably used.

In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof. Nor. For example, in the above-described embodiment, the noble metal tip 31 ′ is overlapped on the end face of the tip 3 a of the center electrode 3, and the welded portion W is formed along the outer peripheral edge of the joint surface by laser welding or the like. However, noble metal tip 3
In order to facilitate the positioning and fixing of the center electrode 3 of the tip 1 'to the tip 3a, a positioning groove corresponding to the outer shape of the chip is formed on the end face of the tip 3a, and the noble metal tip 31' is placed in the groove for positioning. The welded portion W may be formed after fitting. In this case, in order to reliably perform the welding, the laser beam may be applied to the intersection edge between the opening peripheral edge of the positioning groove and the chip outer peripheral surface to form the welded portion W. Further, although the spark plug 100 of the above embodiment is a so-called single-pole type in which only one ground electrode 4 is formed, the present invention may be applied to a multi-pole type having a plurality of ground electrodes.

[0031]

[Experimental Examples] In order to investigate the effects of the present invention, the following experiments were conducted. (Experimental Example 1) First, a noble metal tip used for a discharge portion of a spark plug was manufactured as follows. In order to form various noble metal chips having different compositions shown in Table 1, desired element components were mixed and mixed in various ratios to obtain various raw material powders. Next, this raw material powder was 20 mm in diameter,
It was press-formed into a columnar shape having a length of 130 mm. The compact was placed in an arc melting furnace and subjected to arc melting to obtain alloy ingots of various compositions. Further, the alloy was subjected to hot forging, hot rolling and hot swaging at about 1500 ° C., and further hot-drawn to obtain an outer diameter of 0.1 mm.
A 6 mm alloy wire was obtained. By cutting this in the longitudinal direction, the diameter (tip diameter D) of each composition is 0.6 m.
A disc-shaped noble metal tip having a thickness of 0.8 mm and a thickness of 0.8 mm was obtained. In the production of various noble metal chips having different compositions shown in Table 1, those which could be produced without cracks during the processing were evaluated as “good”. The processability of the noble metal tip was evaluated as “△”, which was produced as a noble metal tip although its existence was confirmed. Table 1 shows the evaluation results of workability.

Then, various noble metal chips obtained by the above-described method are welded by laser welding while being mounted on the front end face of the center electrode base material made of INCONEL600, and are formed as shown in FIGS. Manufactured spark plugs. In addition,
After the laser welding, each composition was set such that the shortest distance (discharge portion thickness H) from the outer edge of the discharge surface to the corresponding edge of the welded portion for welding the center electrode and the noble metal tip was 0.5 mm. The above laser welding was carried out by appropriately adjusting the laser welding conditions suitable for the noble metal tip. In this experiment, the discharge portion on the ground electrode side of each spark plug was formed of a noble metal tip having a tip diameter of 0.9 mm, a thickness of 0.6 mm, and a component of Pt-20 mass% Ni.

[0033]

[Table 1]

The durability test of each spark plug obtained as described above was performed under the following conditions. That is, the displacement 2
These spark plugs were attached to a 000 cc gasoline engine (six cylinders), and the operation was performed for a total of 300 hours at a throttle fully opened state and an engine speed of 5000 rpm. The fuel used was unleaded gasoline, and the temperature at the tip of the center electrode was 900 ° C. Also, the spark discharge gap of each spark plug was set to 1.1 mm,
This durability test was performed.

In each of the spark plugs after the above-mentioned durability test, the degree of abnormal wear occurring in such a manner as to surround one side of the discharge portion (noble metal tip) was visually evaluated. ○: No abnormal wear was observed, △: Abnormal wear occurred, but endurance test was completed to the last, ×: Endurance test could not be continued due to abnormal wear, ×, worn regardless of abnormal wear Those that did were evaluated as-. Table 1 shows the results of the evaluation of abnormal wear. Also,
Regarding the evaluation results (evaluation results of wear resistance) obtained by measuring the amount of increase in the gap of each spark plug after the operation was performed until the endurance time, the amount of expansion of the spark discharge gap was 0.1%.
Those with less than 5 mm were evaluated as ○, those with 0.15-0.3 mm as Δ, and those with more than 0.3 mm were evaluated as x. In cases where the durability test could not be continued due to abnormal wear, the gap increase was not measured and evaluated as-. Table 1 also shows the evaluation results of the wear resistance. And Table 1
In consideration of the evaluation results of abnormal wear, all of the evaluation results of wear resistance and workability, all evaluation results are evaluated as ◎, two evaluation results are evaluated as が, but one evaluation result is evaluated as ○ A comprehensive evaluation was made with Δ being ○ and X being otherwise.

According to the results shown in Table 1, while containing 90% by mass or more of Ir, 0.5% by mass or more of Rh is contained.
Metal plug containing 0.5 to 8% by mass of a noble metal and a spark plug using the noble metal chip as a discharge part (Example N
o. In Nos. 1 to 15), it is found that the occurrence of abnormal wear is suppressed and the wear resistance and workability are excellent. In particular, Example N in which the content of Ni is in the range of 1 to 4% by mass.
o. With respect to Nos. 1 to 4, 7 to 9, and 11 to 15, it can be seen that the occurrence of abnormal wear is more reliably suppressed, and good processability of the noble metal tip can be obtained.

On the other hand, in Comparative Example No. containing no Ni. 1
Comparative Examples Nos. 6, 17, and in which the content of Ni is less than 0.5% by mass. In No. 19, the occurrence of abnormal wear could not be suppressed. In Comparative Example No. which contained Ni but had an Ir content of less than 90% by mass. In Nos. 20 to 22, satisfactory wear resistance was not obtained due to reduced spark wear resistance, and sufficient evaluation results were not obtained in any of abnormal wear and workability. Further, when the content of Rh is 0.1.
Comparative Example No. less than 5% by mass. In No. 18, it was found that the effect of suppressing the oxidation and volatilization of Ir was not sufficiently exhibited, and that the wear resistance was deteriorated.

(Experimental Example 2) Next, the composition of the noble metal tip constituting the discharge part was measured in Example No. 1 of Table 1. 3 or Comparative Example No. 16 and L1 and L2 defined in the above-described embodiment (FIGS. 3 and 4).
The spark plugs were manufactured by changing the length of each of the spark plugs as shown in Table 3. Note that the tip diameter D and the discharge part thickness H were D: 0.3 to 0.8 mm and H: 0.4 to 2 mm, respectively. Then, in each of the spark plugs, the above experimental example 1
A durability test similar to that described above was performed, and the degree of abnormal wear at the discharge portion after the durability test was evaluated. Table 2 shows the obtained results. It should be noted that, in the value of L2 in this experimental example, the sign of minus (-) indicates that the tip of the core is located closer to the discharge part than the tip of the insulator as shown in FIG. The shortest distance between the tip of the core body and the tip of the insulator in the above is indicated. In other cases, as shown in FIG. 3, the tip of the insulator is closer to the discharge part than the tip of the core body. It indicates the shortest distance between the tip of the core and the tip of the insulator when located.

[0039]

[Table 2]

According to Table 2, in the case of the comparative example containing no Ni, L1: 1-3 mm and L2: -1 to 1.5 mm were obtained. In the spark plugs Nos. 1 to 8, the discharge portion easily became high in temperature, so that the discharge portion particularly abnormally consumed. Further, when the values of L1 and L2 are outside the above range, although the occurrence of abnormal wear has been confirmed, it is because the heat of the ignition portion is satisfactorily removed and the temperature is hardly increased.
The degree of wear was smaller than when L1 and L2 were within the above range (Comparative Example No. 9). On the other hand, in this embodiment No.
In Nos. 10 to 18, in addition to the case where L1 and L2 are out of the above specified range, even if the discharge part where L1 and L2 are in the above specified range tends to be relatively high in temperature, the abnormality due to the addition of Ni is abnormal. It can be seen that the effect of reducing wear is sufficiently obtained.

From the results of the above two experiments, it was found that the high melting point Ir
In addition to containing 90% by mass or more of the component, Rh, which is more expensive than Ir and has a melting point lower than that of Ir, is contained in a range where the effect of suppressing oxidation and volatilization can be exhibited, and then the Ni component is contained in the above range. By using the noble metal tip contained in the discharge part, the wear resistance of the noble metal tip (discharge part) can be ensured well, and the occurrence of abnormal wear that tends to occur when the content of Rh is suppressed is suppressed. Can be
As a result, it can be seen that a high-performance spark plug can be configured at low cost.

[Brief description of the drawings]

FIG. 1 is an overall front sectional view showing an embodiment of a spark plug of the present invention.

FIG. 2 is a partial cross-sectional view and an enlarged cross-sectional view showing a main part of the spark plug of FIG. 1;

FIG. 3 is an enlarged view of a periphery of a discharge portion and a description of definitions of a chip diameter D, a discharge portion thickness H, and the like.

FIG. 4 is a view for explaining definitions of a chip diameter D, a discharge portion thickness H, and the like, following FIG. 3;

FIG. 5 is an observation diagram showing a state of a discharge portion on a center electrode side due to abnormal wear.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 spark plug 1 metal shell 2 insulator 3 center electrode 4 ground electrode 6 through hole g spark discharge gap 31, 32 discharge part 31 ', 32' precious metal tip 35 core W welded part

Continuation of front page (72) Inventor Osamu Yoshimoto 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi F-term (reference) 5G059 AA04 DD11 EE11

Claims (4)

[Claims] 1. A center electrode held at one end of a through hole of an insulator, and a ground electrode opposed to the center electrode via a spark discharge gap, wherein at least one of the center electrode and the ground electrode is provided. A spark plug in which a noble metal tip is welded to a discharge part corresponding to the spark discharge gap, wherein the noble metal tip has an Ir of 90% by mass or more, and 0.5% or less.
A spark plug containing at least Rh by mass and Ni in a range of 0.5 to 8% by mass. 2. The spark plug according to claim 1, wherein the noble metal tip contains Ni in a range of 1 to 4% by mass. 3. The noble metal tip is composed of La ₂ O ₃ and Y
_3. The composition according to claim 1, wherein the composition contains at least one of ₂ O _3.
Spark plug according to 1. 4. The precious metal tip is 0.5 to 3% by mass.
La within the range₂O ₃And Y₂O₃At least one of
The spark plug according to claim 3, which contains a spark plug.