JP3497015B2 - Side electrode type spark plug - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a side electrode type spark plug for performing spark discharge between a side surface of a center electrode and an end portion of an outer electrode, and more particularly to a technique using a noble metal for a spark discharge portion of a center electrode. Take

[0002]

2. Description of the Related Art As a conventional technique of this kind, Japanese Patent Laid-Open No. 5-1
The techniques disclosed in JP-A-82741, JP-A-6-68955, and JP-A-6-310256 are known. The technique disclosed in Japanese Unexamined Patent Publication No. 5-182741 discloses a parallel electrode type spark plug (a spark plug that performs spark discharge between an end surface of a center electrode and a side surface of an outer electrode bent in a substantially L shape). This is a technique of using a noble metal for the center electrode, and a technique of embedding and joining a noble metal rod at the end of the center electrode (electrode base material) of a parallel electrode type spark plug.

The technique disclosed in Japanese Unexamined Patent Publication No. 6-68955 uses a noble metal for the center electrode of a side electrode type spark plug, and is used for surrounding the center electrode (electrode base material) of the side electrode type spark plug. This is a technique in which a noble metal ring is arranged and the noble metal is melted into the center electrode by laser welding to form a noble metal alloy part in the spark discharge part of the center electrode.

The technique disclosed in Japanese Unexamined Patent Publication No. 6-310256 also uses a noble metal for the center electrode of the side electrode type spark plug, and is used on the side surface of the center electrode (electrode base material) of the side electrode type spark plug. , A technology for joining flat precious metal chips.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Since the technique disclosed in Japanese Patent No. 2741 is a parallel electrode type spark plug, the outer electrode is long. If the outer electrode is long, the heat of the outer electrode is difficult to transfer to the metal shell quickly,
Easy to overheat. In addition, since the tip side is longer than the bent portion of the outer electrode, there is a problem that the outer electrode easily breaks when it receives an impact during repeated combustion.

Further, since the technique disclosed in the above-mentioned Japanese Patent Laid-Open No. 6-68955 is a technique in which a noble metal is melted into the electrode base material of the spark discharge part, if the electrode base material has a small diameter (for example, diameter 1 0.5 mm or less), the electrode base material itself is melted by the heat at the time of laser welding, which makes it difficult to manufacture a center electrode having a small diameter of the spark discharge portion.

Further, the technique disclosed in the above-mentioned Japanese Patent Laid-Open No. 6-310256 is a technique for joining a flat noble metal tip to a position where the ends of the outer electrodes face each other.
At the time of assembling the spark plug, it was necessary to align the noble metal tip of the center electrode and the end of the outer electrode so that productivity was poor.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a side electrode type spark plug which is excellent in breakage resistance and easy to manufacture.

[0009]

[Means of Claim 1]

The side electrode type spark plug includes a tubular metal shell, a tubular insulator fixed in the metal shell, a center electrode fixed in the insulator, and an end portion of the metal shell. An outer electrode whose end is directed to the side surface of the center electrode, and a spark discharge gap is formed between the side surface of the center electrode and the end of the outer electrode. The center electrode is a nickel alloy rod-shaped electrode base material fixed in the insulator, and is joined to the end portion of the electrode base material by laser welding all around , and between the end portion of the outer electrode. Smaller in diameter than the electrode base material in which the spark discharge gap is formed
In, and a noble metal rod of the rod-shaped made of precious metal, the outer
Cover the tip of the center electrode with the electrode by laser welding all around.
The shortest length A with the joint formed so that
0.3 mm which is the limit gap increase amount to the electric gap G
It is characterized by being longer than the added length .

[Means for Claim 2] In the side electrode type spark plug according to Claim 1, the noble metal rod has a rod shape with a circular cross section and is provided with an outer diameter of 0.5 to 1.5 mm. It is characterized by being done.

[0011]

[0012]

[0013]

According to the side electrode type spark plug of the first aspect, the length of the outer electrode is short because the end portion of the outer electrode faces the side surface of the center electrode. For this reason,
The heat of the outer electrode is quickly transferred to the metal shell, preventing overheating of the outer electrode. Further, since the length of the outer electrode on the tip side is shorter than that of the bent portion, it is possible to prevent breakage of the bent portion of the outer electrode due to the large inertial mass.

The diameter of the center electrode in the spark discharge portion is the diameter of the noble metal rod, and the diameter of the electrode base material is larger than the diameter of the spark discharge portion. Therefore, even when the diameter of the center electrode in the spark discharge part is small, by increasing the diameter of the electrode base material, when the precious metal rod is joined to the electrode base material, the electrode base material is melted and damaged by laser welding. It can prevent defects and has excellent manufacturability.

Further, since the noble metal rod is joined to the end portion of the electrode base material and the side surface of the noble metal rod faces the end portion of the outer electrode, the noble metal rod and the outer electrode are aligned in the rotational direction. It becomes unnecessary. That is, when assembling the spark plug, it is not necessary to align the center electrode with the end portion of the outer electrode in the rotational direction, and the assembling is easy and the productivity is excellent.

Also, by the outer electrode and the entire circumference laser welding
Shortest distance to the joint formed so as to cover the center electrode tip surface
Limit A to the spark discharge gap G
It is provided longer than the total length of 0.3 mm. this
As a result, when the precious metal rod is consumed, its consumption length is 0.3 m.
Spark discharge is not generated at the joint until it is consumed more than m.
This is to prevent it.

In claim 2, the outer diameter of the noble metal rod is
The reason for providing within the range of 0.5 to 1.5 mm is the outer diameter dimension
If the thickness is smaller than 0.5 mm, the heat of the precious metal rod will be quickly generated by the electrode mother.
It is difficult to transmit to the material, the precious metal rod overheats and spark consumption increases
It In addition, the precious metal rods are exhausted before reaching the endurance life.
The reason is that On the other hand, the outer diameter is 1.5 mm
If thicker, ignitability in the lean fuel region (excess air region)
Because it is bad.

[0018]

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a side electrode type spark plug of the present invention will be described with reference to the drawings. [Structure of First Embodiment] FIGS. 1 to 4 are drawings for explaining a first embodiment of a side electrode type spark plug of the present invention, and FIG. 1 is a side view showing a tip of the side electrode type spark plug. is there.

The side electrode type spark plug 1 has a substantially cylindrical metal shell 2 which is fastened to an internal combustion engine such as a gasoline engine, a substantially cylindrical insulator 3 fixed inside the metal shell 2, and this insulation. It is composed of a substantially rod-shaped center electrode 4 fixed inside the body 3, and two outer electrodes 5 and the like joined to the ends of the metal shell 2 and having the ends directed to the side surfaces of the center electrode 4.

The metal shell 2 is grounded to the engine by being fastened to an internal combustion engine (not shown), around which a screw portion 2a screwed into the internal combustion engine and the metal shell 2 are fastened. A bolt portion (not shown) into which the tool is fitted is formed. The insulator 3 is a ceramic insulator such as alumina, and insulates and holds the center electrode 4 inside the metal shell 2.

The center electrode 4 is a rod-shaped member arranged on the combustion chamber side of the insulator 3, and has a terminal electrode (not shown) connected to the ignition device and a resistor (not shown) for reducing noise generation. Is connected to the ignition device via the, and receives the high voltage generated by the ignition device.

The center electrode 4 is made of a nickel alloy having excellent heat resistance and corrosion resistance and has a rod-shaped electrode base material 4a, and a rod-shaped noble metal rod 4b joined to the end surface of the electrode base material 4a by laser welding. Consists of.

The electrode base material 4a is provided so that the diameter to be joined to the noble metal rod 4b is larger than the diameter of the noble metal rod 4b (described later). The electrode base material 4a has a good heat conductive metal core (not shown) such as copper or silver excellent in heat conductivity embedded in the axial center portion thereof.

The noble metal rod 4b is mainly composed of platinum and has a circular cross section and is rod-shaped, for example, Pt-20Ir (20 wt%).
The alloy is joined to the electrode base material 4a by abutting the end surface of the noble metal rod 4b on the center portion of the end surface of the electrode base material 4a and irradiating the joining portion with a laser beam. The diameter of the noble metal rod 4b is within the range of 0.5 to 1.5 mm in outer diameter dimension in order to secure the durability of the noble metal rod 4b and the ignitability in the lean region (excess air region) below the stoichiometric air-fuel ratio. It is provided in.

The length of the precious metal rod 4b (dimension in the axial direction)
Is longer than 2 mm in order to provide the shortest length A between the outer electrode 5 and the laser-welded joint 4c longer than the length of the spark discharge gap G plus the limit gap increase amount of 0.3 mm. It is provided. A> G +
The reason for setting 0.3 mm is that the side electrode type spark plug 1
This is because when the precious metal rod 4b is consumed due to long-term use, spark discharge is prevented from being generated at the joint portion 4c until the consumption length is consumed by 0.3 mm or more.

The two outer electrodes 5 are noble metal rods 4b each having a substantially rectangular cross section bent in a substantially L shape. One end of each of the two outer electrodes 5 is joined to the end of the metal shell 2 by a welding technique, and the other end of each is noble metal. It is arranged opposite to the side surface of the rod 4b,
A predetermined spark discharge gap G is formed between the side surface of the noble metal rod 4b and the other ends of the two outer electrodes 5.

[Experimental Data] (Comparison by Durability Test) The side electrode type spark plug 1 of this embodiment (product of the embodiment), the center electrode 4 (made of nickel alloy) without the noble metal rod 4b, and two outer sides. An endurance test was conducted using a side electrode type spark plug α (first comparative product) which performs spark discharge with the electrode 5. The relationship between the distance traveled and the amount of increase in the spark discharge gap is shown in the graph of FIG. The solid line A1 shows the measurement result of the side electrode type spark plug 1 of the example product, and the solid line B1 shows the measurement result of the side electrode type spark plug α of the first comparative product. As is clear from the experimental results, the outer electrode 5 and the noble metal rod 4b
Compared to the side electrode type spark plug α of the first comparative product, the side electrode type spark plug 1 of the example product that performs a spark discharge between and suppresses an increase in the spark discharge gap during long-term use. To be

(Comparison by a breakability test of the outer electrode 5)
The side electrode type spark plug 1 of the example product, the side electrode type spark plug α of the first comparison product, and the parallel electrode type spark plug β (the second comparison product, which is substantially L-shaped with the end face of the center electrode 4). The outer electrode 5 was subjected to a breakage test by using a spark plug which performs spark discharge between the bent outer electrode 5 and the side surface thereof. The spark plugs 1, α, β have the same length from the tip surface of the metal shell to the spark discharge portion. The result of measuring the time until breakage is shown in the graph of FIG. The measurement result of the side electrode type spark plug 1 of the example product is shown in a graph A2, the measurement result of the side electrode type spark plug α of the first comparison product is shown in a graph B2, and the parallel electrode of the second comparison product is shown. The measurement result of the spark plug β is shown in graph C2.

In the side electrode type spark plugs 1, α, the length of the outer electrode 5 is short because the end portion of the outer electrode 5 faces the side surface of the center electrode 4. Therefore, the outer electrode 5
The stress received by the outer electrode 5 is reduced, and the heat of the outer electrode 5 is quickly transferred to the metal shell 2 to prevent the outer electrode 5 from overheating. Therefore, as compared with the parallel electrode type spark plug β of the second comparative product, breakage of the outer electrode 5 can be prevented for a long period of time.

(Comparison by Ignition Test) Noble Metal Rod 4b
The diameter dimension and the ignitable air-fuel ratio are changed, the ignitable air-fuel ratio is measured, and the measurement result is shown in the graph of FIG. As is clear from this experimental result, when the diameter dimension of the noble metal rod 4b is larger than 1.5 mm, the ignitability in the fuel lean region is poor and the diameter dimension of the noble metal rod 4b is 2.0 m.
By making it smaller than m, the ignitability in the fuel lean region is excellent. If the diameter of the noble metal rod 4b is smaller than 0.5 mm, the heat of the noble metal rod 4b will be quickly generated.
It is difficult to be transmitted to a, the precious metal rod 4b is overheated, spark consumption increases, and the precious metal rod is exhausted before the end of its durable life.

[Effects of Embodiment] In the side electrode type spark plug 1 of this embodiment, since the end portion of the outer electrode 5 faces the side surface of the center electrode 4, the length of the outer electrode 5 is short. The heat of the outer electrode 5 is quickly transferred to the metal shell 2, overheating of the outer electrode 5 is prevented, and breakage of the outer electrode 5 can be prevented.

Since the diameter of the spark discharge portion is the diameter of the noble metal rod 4b and the diameter of the electrode base material 4a is larger than the diameter of the noble metal rod 4b for spark discharge, when the noble metal rod 4b is joined to the electrode base material 4a, the electrode There is no problem that the base material 4a is broken by laser welding, and the manufacturability is excellent.

Since the noble metal rod 4b having a circular cross section is joined to the end of the electrode base material 4a and the side surface of the noble metal rod 4b faces the end of the outer electrode 5, the noble metal rod 4b and the outer electrode 5 are connected to each other. The alignment in the rotation direction of is unnecessary. Therefore, when assembling the spark plug 1, the center electrode 4 and
Positional alignment with the end of the outer electrode 5 in the rotational direction is unnecessary, assembly is easy, and productivity is excellent.

The outer diameter of the precious metal rod 4b is 0.5 to 1.5.
When it is provided within the range of mm, the ignitability in the fuel lean region is excellent and the durability of the precious metal rod 4b is also excellent. By providing the shortest length A between the outer electrode 5 and the laser welded joint 4c to be longer than the length of the spark discharge gap G plus the limit gap increase amount of 0.3 mm (A> G + 0.3 mm), Spark discharge can be generated between the outer electrode 5 and the noble metal rod 4b for a long period of time, and as a result, a sharp increase in the spark discharge gap can be prevented for a long period of time.

[0036]

[Modification] In the above embodiment, the outer electrode 5 is used.
Although the side electrode type spark plug 1 provided with two side electrodes is shown as an example, the present invention may be applied to the side electrode type spark plug having one outer electrode 5 or three or more outer electrodes 5. Precious metal rod 4
Although the example in which the outer diameter of b is set within the range of 0.5 to 1.5 mm is shown, the noble metal rod 4 may be used depending on the internal combustion engine used.
The outer diameter dimension of b may be provided outside the range of 0.5 to 1.5 mm.

The length of the precious metal rod 4b (dimension in the axial direction)
Is set to be longer than 2 mm, so that the shortest length A between the outer electrode 5 and the joining portion 4c by laser welding is set to be longer than the length obtained by adding the spark discharge gap G to the limit gap increase amount of 0.3 mm. Although an example is shown, the length of the noble metal rod 4b may be set to 2 mm or less depending on the size of the end portion of the outer electrode 5 and the internal combustion engine used. Further, as the material of the noble metal rod 4b, in addition to the materials shown in the above embodiment, a Pt-In-Ni alloy, a Pt-Ni alloy, Ir.
Other noble metal materials such as --Y2 O3 alloy may be used.

[Brief description of drawings]

FIG. 1 is a side view of a tip of a side electrode type spark plug (first embodiment).

FIG. 2 is a graph showing the results of a durability test.

FIG. 3 is a graph showing the results of a breakability test.

FIG. 4 is a graph showing the results of an ignitability test.

[Explanation of symbols]

1 Side electrode type spark plug 2 metal shell 3 insulator 4 Center electrode 4a Electrode base material 4b precious metal rod 4c joint 5 Outer electrode G spark discharge gap

─────────────────────────────────────────────────── --Continued from the front page (56) Reference JP-A-7-22156 (JP, A) JP-A-3-176989 (JP, A) JP-A-57-15382 (JP, A) JP-A-60- 232679 (JP, A) JP 61-171080 (JP, A) JP 60-220586 (JP, A) JP 61-253785 (JP, A) Actual development S50-145929 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01T 13/20 H01T 21/02

Claims (2)

(57) [Claims] 1. A tubular metal shell, a tubular insulator fixed in the metal shell, a center electrode fixed in the insulator, and an end portion of the metal shell provided at the center. A side electrode type spark plug comprising: an outer electrode having an end portion directed to a side surface of the electrode, wherein a spark discharge gap is formed between the side surface of the center electrode and the end portion of the outer electrode, wherein the center electrode Is a rod-shaped electrode base material made of nickel alloy fixed in the insulator, and is joined to the end portion of the electrode base material by laser welding all around , and the spark discharge gap is formed between the end portion of the outer electrode. center electrode destination smaller diameter than the electrode base material but formed, and a noble metal rod of the rod-shaped made of noble metal, and the outer electrode, wherein the entire circumference laser welding
The shortest length A with the joint formed so as to cover the end face is
The spark discharge gap G has a limit gap increase amount of 0.
A side electrode type spark plug characterized by being longer than the length obtained by adding 3 mm . 2. The side electrode type spark plug according to claim 1, wherein the noble metal rod has a rod shape with a circular cross section, and the outer dimension is provided within a range of 0.5 to 1.5 mm. A side electrode type spark plug.