JPH09129357A - Spark plug for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a long-life, high-performance spark plug for an internal combustion engine. SOLUTION: A center electrode 2 and a grounding electrode 3 are both made using a nickel alloy as a base material and is jointed noble-metal chips 12, 13 to the discharge parts of their respective ends. The noble-metal chip 12 of the center electrode is made of iridium or an iridium alloy and inserted into a hole 20 axially bored in the end of the center electrode. When the outside diameter of the noble-metal chip 12 is A, the outside diameter of the end 21 of the center electrode 2 is B, and the amount by which the noble-metal chip 12 is projected from the center electrode is C, B-A>=0.8×C is preferable within the range of 0.6<=A<=1.2mm and 0.4mm<=C<=1.0mm. When the axial length of the noble-metal chip 12 is E and the distance from the end of the noble-metal chip to the end of an insulator is D, a relation of E>=D should preferably be met.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a spark plug for an internal combustion engine.

[0002]

2. Description of the Related Art A spark plug for an internal combustion engine is required to have a long life and high performance. In recent years, it is known that the former longer life is improved by using a noble metal tip at the discharge part of the spark plug, and the latter higher performance is improved by using a small-diameter electrode. As the noble metal tip, for example, iridium or iridium alloy is used (Japanese Patent Laid-Open No. 3-17).
6978). Iridium material has a melting point of 2454 ° C
Therefore, it has excellent wear resistance. Therefore, it is promising as a long-lived and high-performance spark plug material.

[0003]

However, in the above-mentioned conventional spark plug for an internal combustion engine, the operating temperature is 900
When the temperature exceeds ℃, the volatility of the noble metal tip tends to increase rapidly. As a result, the life will be greatly shortened in high-temperature environments such as high rotation and high-load continuous operation. Further, in recent years, the heat load on the spark plug has become more and more intense, and a spark plug with higher performance and longer life is required.

In view of the above conventional problems, the present invention aims to provide a spark plug for an internal combustion engine which has a long life and high performance.

[0005]

According to a first aspect of the present invention, there is provided a center electrode held at one end of an insulator, an electric transmission means provided at the other end of the insulator, a housing holding the insulator, The housing has a ground electrode curvedly provided on the front end surface of the housing so as to face the center electrode, and a spark gap provided between the center electrode and the ground electrode. In a spark plug for an internal combustion engine in which a nickel alloy is used as a base material for both the center electrode and the ground electrode, and a noble metal tip is bonded to each of the discharge parts at the tips of the center electrode and the noble metal tip of the center electrode The noble metal tip is inserted into a hole that is open in the axial direction at the tip of the center electrode with its part protruding and is welded, and the noble metal tip is When the outer diameter of the noble metal tip of the pole is A, the outer diameter of the tip of the center electrode is B, and the protrusion amount of the noble metal tip from the center electrode is C, 0.6 mm ≤ A ≤ 1.2 mm, 0.4 mm ≦ C ≦ 1.0
The spark plug for an internal combustion engine is characterized in that a relationship of BA ≧ 0.8 × C is established within a range of mm 2.

The most remarkable thing in this invention is that
The outer diameter A of the noble metal tip provided on the tip of the center electrode, the outer diameter B of the tip of the center electrode, and the protrusion amount C of the noble metal tip from the tip are regulated to fall within the specific ranges as described above. It is that.

When the outer diameter A of the noble metal tip is less than 0.6 mm, or when the protrusion amount C is more than 1.0 mm, there is no problem in the flammability and ignitability, but the noble metal tip is hard and brittle pure iridium. Alternatively, since it is made of an iridium alloy, the workability of the noble metal tip is poor, which causes problems in manufacturability and handleability, which hinders the mass production of spark plugs. vice versa,
When the outer diameter A exceeds 1.2 mm, or the protrusion amount C is 0.
If it is less than 4 mm, the spark plug's ignitability and ignitability are significantly deteriorated.

If B-A <0.8 × C, the amount of the center electrode base material around the noble metal tip becomes too small, and the heat received by the noble metal tip from the spark gap can be efficiently transferred to the center electrode. I can't. Therefore, there is a problem that the temperature of the noble metal tip is kept high during use, and the wear of the noble metal tip becomes severe.

As described above, in the spark plug for an internal combustion engine, the outer diameter A of the noble metal tip at the tip of the center electrode is 0.
6 mm to 1.2 mm, and the protrusion amount C of the noble metal tip from the base material tip of the center electrode is 0.4 mm to 1.0 mm. Therefore, excellent flying and ignitability can be secured. In addition, this size is a size that can be easily processed even if the precious metal tip is pure iridium or iridium alloy which is hard and brittle. Therefore, the manufacturability and handleability of precious metal chips are good.

Further, by setting B-A ≧ 0.8 × C as described above, the amount of the center electrode base material around the noble metal tip becomes a sufficient amount for heat transfer. Therefore, the noble metal tip can efficiently dissipate the heat received from the spark gap to the tip of the center electrode. Therefore, the temperature of the noble metal tip is lowered, and the wear resistance can be greatly improved. Moreover, pure iridium or iridium alloy is used for the noble metal tip of the center electrode, and these have higher melting points than other metal for electrodes. for that reason,
Has excellent wear resistance.

As described above, according to the present invention, it is possible to provide a spark plug for an internal combustion engine having a long life and high performance.

Next, as in the second aspect of the invention, the axial length of the noble metal tip bonded to the center electrode is E, and the distance from the tip of the noble metal tip to the tip of the insulator is D. Then, it is preferable that the relationship of E ≧ D is established. As a result, the noble metal tip is embedded in the hole of the center electrode up to the same position as the tip of the insulator or inward of the tip of the insulator.

Therefore, the portion of the noble metal tip that contributes to heat dissipation to the center electrode can secure a large contact area with the insulator. Therefore, the noble metal tip can efficiently radiate heat to the center electrode. As a result, the temperature of the noble metal tip is reduced, and the wear resistance of the spark plug can be greatly improved.

Next, as in the invention described in claim 3, the precious metal chip is made of pure iridium or pure iridium containing Pt, Pd, Rh, Ru, Ni, W, Si, Y ₂ O ₃ and ZrO _2. It is preferable that the alloy contains one or two or more additives selected from the group. The reason is that by adding the above additives to pure iridium,
This is because the oxidation resistance and wear resistance of the noble metal tip can be improved.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 A spark plug for an internal combustion engine according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. The spark plug 1 for an internal combustion engine of this example has a through hole 5 as shown in FIG.
An insulator 5 having 0, a center electrode 2 held at one end of the insulator 5, a housing 9 holding the insulator 5, and a front surface of the housing 9 facing the center electrode 2. The curved ground electrode 3 and the spark gap 8 provided between the center electrode 2 and the ground electrode 3.
And Both the center electrode 2 and the ground electrode 3 are made of a nickel alloy as a base material, and the noble metal tips 12 and 13 are joined to the discharge portions at the tips thereof.

The noble metal tip 12 of the center electrode 2 is made of pure iridium or iridium alloy. Precious metal tip 12
2 is inserted and welded into a hole 20 opened in the axial direction of the tip portion 21 of the center electrode 2, as shown in FIG. In this example, the outer diameter A of the noble metal tip 12 is 0.8 mm. The outer diameter B of the tip portion 21 of the center electrode 2 is 1.4 mm. The protrusion amount C of the noble metal tip 12 from the center electrode 2 is 0.6 mm. Axial length E of the noble metal tip 12
Is 2.0 mm. The distance D from the tip of the noble metal tip 12 to the tip of the insulator 5 is 1.5 mm.

Next, the above spark plug will be supplementarily described. As shown in FIG. 1, the spark plug 1 includes a cylindrical housing 9 made of a metal material. Inside the housing 9, the tip end side of the cylindrical insulator 5 is coaxially fixed by caulking. A thread groove 511 for mounting on the internal combustion engine is formed on the outer peripheral portion of the insulator 5 near the tip.

The center electrode 2 is inserted and fixed to one end of the through hole 50 of the cylindrical insulator 5. An electrical transmission means is provided at the other end of the through hole 50 of the insulator 5. The electric transmission means is, for example, a center shaft 72 made of a conductive material having a terminal 73 on the upper portion. The center rod 72 is inserted into the through hole 50 of the insulator 5, and is heat-fused integrally with the center electrode 2 by a conductive glass sealing material 71.

The center electrode 2 has a columnar shape, and the inner material at the center is made of copper and the outer material covering the outside is N.
It is formed of an i-based alloy. The center electrode 2 is inserted into the through hole 50 of the insulator 5 with the thin end 21 which is the discharge end exposed from the insulator 5. As shown in FIG. 2, the noble metal tip 12 is inserted into a hole 20 that is opened in the axial direction at the tip of the center electrode 2. The center electrode 2 and the noble metal tip 12 are attached by laser welding at least at two points or over the entire circumference. In FIG. 2, reference numeral 10 is the laser welding mark. Resistance welding other than laser welding can also be performed.

The ground electrode 3 is made of a Ni-based alloy and extends integrally from the tip of the housing 9. A noble metal tip 13 is welded to the tip of the ground electrode 3, and a spark gap 8 is provided between the noble metal tip 13 and the noble metal tip 12 of the center electrode 2.

Next, the spark plug was tested for wear resistance. Test conditions are 4 cycle 6 cylinder, 2000
Using a CC engine at a full load of 4000 rpm,
After continuous operation for 50 hours, the presence or absence of wear resistance was determined. Under these test conditions, the consumption of precious metal chips is 4 × 10 ^-2
If it is within mm ³ , there is a track record of ensuring sufficient wear resistance in general driving, and it was judged that there is no problem in actual use. As a result, the amount of consumption of the noble metal tip was as small as 2.1 × 10 ^-2 mm ³ . From this, it can be seen that the precious metal tip has high wear resistance and the spark plug exhibits high performance for a long time.

Embodiment 2 In this example, the relationship between the attachment size of the noble metal tip at the tip of the center electrode and the wear resistance of the spark plug was evaluated. First, the outer diameter A of the noble metal tip, the outer diameter B of the tip of the center electrode, and the protrusion amount C of the noble metal tip from the center electrode were changed. The length E of the noble metal tip in the axial direction was 2 mm, and the distance D from the tip of the noble metal tip to the tip of the insulator was fixed at 1.5 mm.

Pure iridium was used as the noble metal tip at the tip of the center electrode. For such a spark plug,
The wear resistance was tested. The test conditions are the same as in the first embodiment. The results are shown in FIGS. 3 and 4. In FIG. 3, when A is 0.6 mm, (B-
The relationship between A) / C and the amount of wear of the noble metal tip is shown. In FIG. 4, when A is 1.2 mm, (BA) /
The relationship between C and the amount of wear of the noble metal tip is shown.

From the figure, when (B−A) / C is 0.8 or more (B−A ≧ 0.8 × C), the consumption amount of the noble metal tip continues to maintain the minimum value. On the other hand, when (B−A) / C was less than 0.8 (B−A <0.8 × C), the consumption amount increased rapidly.

This means that B-A ≧ 0.8 × C (FIG. 3,
4), the amount of the center electrode base material around the noble metal tip is sufficient for heat transfer, and the noble metal tip 12 receives the heat received from the spark gap 8 in the small diameter area of the center electrode 2. It shows that heat can be efficiently radiated to the tip portion 21. Therefore, it is considered that the temperature of the noble metal tip can be lowered, and the wear resistance is significantly improved.

Further, the dimensions of E and D were variously changed, and the relationship between C and AB was investigated in the same manner as above. Also in this case, the same result as in the case where E was 2 mm and D was 1.5 mm as described above could be obtained.

Next, the difference (D-E) between the axial length E of the tip of the center electrode in the axial direction of the noble metal tip and the distance D from the tip of the noble metal tip to the tip of the insulator was changed. When C is 0.4 mm, A is 1.2 mm, and B is 1.6 mm, C is 1.0 mm, A is 0.6 mm, and B is 1.4 mm.
In the case of, the D−E was changed as described above. Pure iridium was used as the noble metal tip of the center electrode. The test conditions are the same as above. The result is shown in FIG.
It was shown to.

From the figure, in the case of DE ≦ 0 (hatched area in FIG. 5), the amount of consumption of the noble metal tip hardly changed. On the other hand, when D−E> 0, the consumption amount of the noble metal tip increased sharply. This means that D−E ≦ 0,
That is, when the noble metal tip is embedded in the center electrode inward of the tip of the insulator, the noble metal tip can efficiently dissipate heat to the center electrode, resulting in a decrease in the temperature of the noble metal tip and It is considered that the exhaustiveness has been greatly improved.

From the above test, 0.6 mm ≦ A ≦ 1.2
mm, within the range of 0.4 mm ≦ C ≦ 1.0 mm,
It can be seen that by setting B-A ≧ 0.8 × C, the wear resistance of the noble metal tip is improved, whereby the spark plug can have a long life and high performance. Further, by setting E ≧ D, it can be seen that the wear resistance of the noble metal tip can be greatly improved, and similarly, the spark plug can have a long life and high performance.

[0030]

According to the present invention, it is possible to provide a spark plug for an internal combustion engine having a long life and high performance.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a spark plug according to a first embodiment.

FIG. 2 is an enlarged cross-sectional view of a main part of the spark plug, showing the discharge parts of the center electrode and the ground electrode according to the first embodiment.

FIG. 3 is an outer diameter A of the noble metal tip in the second embodiment.
The graph which shows the relationship between (BA) / C and the amount of consumption of a noble metal tip in the case where is 0.6 mm.

FIG. 4 is an outer diameter A of the noble metal tip in the second embodiment.
The graph which shows the relationship between (BA) / C and the amount of consumption of a noble metal tip in case of 1.2 mm.

FIG. 5 is a diagram showing the relationship between DE and the amount of wear of the noble metal tip in the second embodiment.

[Explanation of symbols]

 1. . . Spark plug, 12, 13. . . Noble metal tip, 2. . . Center electrode, 3. . . Ground electrode, 5. . . Insulator, 8. . . Spark gap, 9. . . housing,

Claims (3)

[Claims] 1. A center electrode held at one end of an insulator,
An electric transmission means provided at the other end of the insulator, a housing for holding the insulator, a ground electrode curvedly provided on the front end surface of the housing so as to face the center electrode, and The center electrode and the ground electrode each have a spark gap provided between the center electrode and the ground electrode, and both of the center electrode and the ground electrode are made of a nickel alloy as a base material. In a spark plug for an internal combustion engine in which chips are joined, the noble metal tip of the center electrode is made of iridium or an iridium alloy, and the noble metal tip has a part of the noble metal tip in an axially opened hole at the tip of the center electrode. The noble metal tip of the center electrode has an outer diameter of A, the outer diameter of the tip of the center electrode is B, and the noble metal tip of the center electrode is noble from the center electrode. When the amount of projection of the genus chip was C, 0.6mm ≦ A ≦ 1.2mm, 0.4mm ≦ C ≦ 1.0
A spark plug for an internal combustion engine, characterized in that a relationship of BA ≧ 0.8 × C is established within a range of mm 2. 2. When the axial length of the noble metal tip bonded to the center electrode is E and the distance from the tip of the noble metal tip to the tip of the insulator is D, E ≧ D A spark plug for an internal combustion engine, characterized in that 3. The noble metal tip of the center electrode according to claim 1, wherein the noble metal tip of the center electrode is pure iridium, or pure iridium containing Pt, Pd, Rh, Ru, Ni, W, Si and Y ₂ O.
_A spark plug for an internal combustion engine, which is an alloy containing one or more additives selected from the group consisting of ₃ and ZrO ₂ .