JP3128254B2 - Method of manufacturing composite electrode for 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 method of manufacturing a composite electrode for an ignition plug such as a composite outer electrode for a ignition plug and a composite center electrode for an ignition plug.

[0002]

2. Description of the Related Art Conventionally, an electrode of a spark plug, for example, an outer electrode, is generally formed of a nickel alloy obtained by adding silicon, chromium, aluminum, manganese or the like to 95% or more of nickel. This nickel alloy is excellent in corrosion resistance (particularly, spark wear resistance), heat resistance (high-temperature strength), and relatively excellent in heat removal (thermal conductivity).

However, in recent years, as the performance of internal combustion engines has become higher, there has been a demand for outer electrodes that are more excellent in heat removal than conventional ones. Therefore, a composite outer electrode in which copper having excellent heat dissipation is embedded in a nickel alloy has been proposed.

[0004]

However, when a conventional two-layer composite outer electrode is used to manufacture an ignition plug for use in an internal combustion engine, the difference in the coefficient of thermal expansion between nickel alloy and copper is large. There has been a problem that the shape of the electrode changes, and it is difficult to keep the spark discharge gap between the outer electrode and the center electrode at an appropriate value under use conditions. The present invention
The present invention provides a method for manufacturing a composite electrode for an ignition plug in which a difference in thermal expansion coefficient is reduced by forming the composite electrode into a three-layer structure, and a spark discharge gap between the outer electrode and the center electrode can be maintained at an appropriate value even under use conditions. With the goal.

[0005]

The present invention is manufactured by combining the following steps. (A) A first step of forming a cup-shaped first cover having a first recess at an end from a first metal having excellent thermal conductivity. (B) A second step of forming a cup-shaped second cover having a second recess at an end from a second metal having excellent heat resistance and corrosion resistance. (C) a third metal having excellent heat resistance, wherein the difference between the coefficient of thermal expansion of the first metal and the coefficient of thermal expansion of the third metal is greater than the coefficient of thermal expansion of the second metal and the third metal; A third step of fitting a core material made of a metal having a smaller difference in thermal expansion coefficient into the first recess to form a first composite in which the first covering member covers the core material. (D) a fourth step of fitting the first composite into the second recess to form a second composite covering the first composite with the second covering. (E) a fifth step of extruding the second composite to form an extruded body. (F) a sixth step of forming a composite electrode by cutting the extruded body in a region where the first metal, the second metal, and the third metal are present in the same cross section.

The first cover may be fitted in the second recess of the second cover, and a core made of a third metal may be fitted in the first recess of the first cover. As the first metal, copper, a copper alloy containing copper as a main component, or the like can be considered. As the second metal, nickel or a nickel alloy containing nickel as a main component can be considered. As the third metal, nickel having substantially the same thermal expansion coefficient as the second metal, a nickel alloy containing nickel as a main component, or the like can be considered.

[0007]

The composite electrode for an ignition plug manufactured according to the present invention comprises:
The first metal having excellent thermal conductivity is obtained by comparing the second metal having excellent heat and corrosion resistance with the thermal expansion coefficient of the second metal and the third metal based on the difference between the thermal expansion coefficients of the first metal and the third metal. Is exposed to the outside by being sandwiched by a third metal having a smaller difference (three-layer structure), even if a temperature change occurs, thermal stress caused by a difference in thermal expansion coefficient is reduced, and the shape of the composite electrode is reduced. Change is suppressed. That is, even if the composite electrode is disposed in the combustion chamber of the internal combustion engine and exposed to a high temperature, the shape change of the composite electrode can be suppressed.

In use, the heat of the composite electrode is
It travels along the first covering made of the first metal and is led to the ignition plug component adjacent to the composite electrode. For this reason, under the use conditions, when the composite electrode is used for the outer electrode, the spark discharge gap with the center electrode is kept at an appropriate value, and when the composite electrode is used as the center electrode, the spark discharge gap with the outer electrode is maintained. Is kept at an appropriate value.

[0009]

1 shows a method of manufacturing a composite electrode for an ignition plug according to the present invention.
A description will be given based on an embodiment shown in FIG. FIG. 1 is a process diagram showing an example of manufacturing a composite outer electrode. FIG. 2 and FIG. 3 are views showing an ignition plug assembled to the internal combustion engine.

A spark plug 1 includes a composite center electrode 2 having a copper core sealed in a nickel alloy, an insulator 3 fitted on the outer periphery of the composite center electrode 2, and a main body fitted on the outer periphery of the insulator 3. A metal fitting 4 is provided. A composite outer electrode 5 is joined to the tip of the metal shell 4 by welding.

The composite outer electrode 5 has a rectangular rod shape, and is bent into a substantially L-shape so that the distal end thereof is opposed to the distal end surface of the composite center electrode 2 via a spark discharge gap 6. ing.

The composite outer electrode 5 includes a core member 7 disposed at the center, a first covering member 8 covering the outer periphery of the core member 7, and a second covering member covering the outer periphery of the first covering member 8. 9.

The core 7 is made of a third metal having substantially the same thermal expansion coefficient as the second cover 9 and having relatively excellent thermal conductivity, and is made of, for example, pure nickel (Ni) or pure iron (Fe).
Note that pure nickel has a thermal expansion coefficient of 1.3 (10 ⁻⁵ / de).
g) and the thermal conductivity is 68 (kcal / m · h · deg). Pure iron has a coefficient of thermal expansion of 1.2 (10 ⁻⁵ / de).
g), and the thermal conductivity is 68 (kcal / m · h · deg). One end of the core 7 is sealed together with the first covering 8 in the second covering 9, and the other end is joined to the tip of the metal shell 4 together with the first covering 8 and the second covering 9.

The first cover 8 is formed of a first metal having excellent thermal conductivity, and is made of, for example, copper (Cu). Copper has a thermal expansion coefficient of 1.7 (10 ^-5 / deg) and a thermal conductivity of 340 (kcal / m · h · deg). The cross-sectional area of the first coating 8 is, for example, 20
% To 50%.

The second coating 9 is exposed to the combustion chamber of the internal combustion engine and generates a spark discharge on the surface. The second coating 9 is made of a Ni—Mn—Si alloy, Ni—Mn—
It is made of a second metal, such as a nickel alloy such as a Si-Cr alloy or a Ni-Mn-Si-Cr-Al alloy, or Inconel 600, which has excellent heat resistance and corrosion resistance and has high bonding strength with the metal shell 4. Inconel 600 (trade name) has a thermal expansion coefficient of 1.6 (10 ⁻⁵ / deg) and a thermal conductivity of 25 (kca).
l / m · h · deg).

Next, an example of a method for manufacturing the composite outer electrode 5 will be briefly described with reference to FIG. First, by extruding a third metal such as pure nickel or pure iron, as shown in FIG. 1A, a round bar-shaped core portion 71 and a circular flange having a larger outer diameter than the core portion 71 are formed. The core material 7 having the portion 72 is formed.

As shown in FIG. 1A, a first metal such as copper is extruded backward to form a circular closed end 81 at one end and a core material 7 having an inner diameter at the other end. The cup-shaped first cover 8 having a circular first recess 82 substantially the same as the outer diameter of the core portion 71 is formed.

Next, as shown in FIG. 1B, the core 71 of the core 7 is sealed in the first recess 82 of the first cover 8.
The first composite body 10 in which the outer periphery of the core portion 71 of the core material 7 is covered with the first covering body 8 is formed.

Next, by extruding the first composite 10, as shown in FIG. 1C, a round bar-shaped core 11 made of a third metal and a first metal and the core 1
A circular flange 12 having an outer diameter larger than 1 is formed.

Further, the second metal such as a nickel alloy or Inconel is extruded backward to form a second metal as shown in FIG.
As shown in (C), one end has a circular closed end 91 and the other end has a circular second recess 92 whose inner diameter is substantially the same as the outer diameter of the core 11 of the first composite body 10. To form a cup-shaped second cover 9 having

Next, as shown in FIG. 1D, the core 11 of the first composite 10 is sealed in the second recess 92 of the second cover 9, and the core of the first composite 10 is formed. A second composite body 20 in which the outer periphery of 11 is covered with a second covering body 9 is formed.

Next, the second composite 20 is extruded. That is, as shown in FIG.
The second composite body 20 is inserted into a die 31 having a square die hole by a punch 32, with the tip end of the rectangular head 41 being the top, and the cross-sectional shape is larger than the square pillar portion 41 and the outer diameter of the square pillar portion 41. Then, an extruded body 40 having a columnar portion 42 having a circular cross section is formed.

Next, as shown in FIG. 1 (F), the extruded body 40 is cut into an appropriate length on the side where the extruded body 40 is joined to the metal shell 4. At this time, the cylindrical portion 42 that is to be joined to the metal shell 4 is cut. Thereafter, the prism 41 of the extruded body 40 is annealed. As described above, the composite outer electrode 5
Is manufactured.

Next, two experiments in which the cross-sectional area of the first cover 8 is changed and the heat conduction efficiency and the joint strength with the metal shell 4 are examined will be described. In the first experiment, the heat conduction efficiency was investigated by changing the ratio of the cross-sectional area of the first coating 8 to the cross-sectional area of the composite outer electrode 5, and the experimental results are shown in the graph of FIG. . As can be confirmed from the graph of FIG. 4, sufficient heat conduction efficiency can be obtained by setting the cross-sectional area of the first coating 8 to be 20% or more of the cross-sectional area of the composite outer electrode 5.

In the second experiment, the ratio of the cross-sectional area of the first coating 8 to the cross-sectional area of the composite outer electrode 5 was changed by using the core material 7 having a fixed size, The electrode 5 was joined to the metal shell 4 by electric resistance welding, and the joining strength was investigated. The experimental results are shown in the graph of FIG. As can be confirmed from the graph of FIG. 5, a sufficient bonding strength can be obtained by setting the cross-sectional area of the first coating 8 to 50% or less of the cross-sectional area of the composite outer electrode 5.

The composite outer electrode manufactured according to this embodiment comprises a first coating 8 made of copper, a second coating 9 having excellent heat resistance and corrosion resistance, and a heat treatment of the first coating 8 and the core 7. Since the difference in the coefficient of thermal expansion between the second covering 9 and the core 7 is smaller than the difference in the coefficient of expansion, the core is sandwiched by the core 7 made of metal.
Even when the composite outer electrode 5 is arranged in the combustion chamber of the internal combustion engine and is exposed to a high temperature, the thermal stress caused by the difference in thermal expansion coefficient is reduced, and the change in the shape of the composite outer electrode 5 is suppressed.

In use, the heat of the composite outer electrode 5 is transmitted to the metal shell 4 through the first cover 8. For this reason, the spark discharge gap 6 between the composite outer electrode 5 and the center electrode 2 is maintained at an appropriate value even under use conditions.

Further, as shown in the results of the above two experiments, by setting the cross-sectional area of the first covering member 8 to 20% or more and 50% or less of the cross-sectional area of the composite outer electrode 5, high heat conduction efficiency is obtained. In addition, the composite outer electrode 5 having a high bonding strength with the metal shell 4 can be obtained.

It is conceivable to use a clad wire (cladding material) in which a core material 7 of pure nickel is covered with a first covering body 8 made of copper from the beginning, but since the cladding material is an expensive product, it is expensive. Therefore, the method for manufacturing the composite outer electrode 5 becomes complicated. Therefore, as in the present embodiment, the composite outer electrode 5 manufactured by covering the core material 7 with the first covering body 8 during the manufacturing process is as expensive as the one using the clad material by an inexpensive manufacturing method. Can be obtained.

(Modification) In the present embodiment, the present invention is used for a method of manufacturing a composite outer electrode, but the present invention may be used for a method of manufacturing a composite center electrode.

[0031]

According to the present invention, a spark discharge gap between the outer electrode and the center electrode can be maintained at an appropriate value even under use conditions, and a composite having high heat conduction efficiency, that is, excellent heat removal can be obtained. An electrode can be obtained.

[Brief description of the drawings]

FIG. 1 is a process chart showing an example of manufacturing a composite outer electrode.

FIG. 2 is a sectional view showing a main part of an ignition plug.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a graph showing a relationship between a temperature of a tip portion of a composite outer electrode and an area ratio of a first coating.

FIG. 5 is a graph showing the relationship between the tensile strength and the area ratio of the first coating.

DESCRIPTION OF SYMBOLS 1 Spark plug 5 Composite outer electrode 6 Spark discharge gap 7 Core material 8 First coating 9 Second coating 10 First composite 20 Second composite 40 Extruded body 82 First recess 92 First 2 recesses

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01T 13/00-21/06

Claims (1)

(57) [Claims] (1) From a first metal having excellent thermal conductivity,
A first step of forming a cup-shaped first cover having a first recess at the end; and (b) a cup having a second recess at the end from a second metal having excellent heat and corrosion resistance. The second forming the second covering of the shape
(C) a third metal excellent in heat resistance , wherein the first metal
Before the difference between the coefficient of thermal expansion of the third metal and the coefficient of thermal expansion of the third metal.
The coefficient of thermal expansion of the second metal and the coefficient of thermal expansion of the third metal
A third step of fitting a core material made of a metal having a smaller difference into the first recess to form a first composite covering the core material with the first covering body; A fourth step of fitting the first composite into the second recess to form a second composite covering the first composite with the second covering; and (e) extruding the second composite. A fifth step of molding to form an extruded body; and (f) cutting the extruded body in a region where the first metal, the second metal, and the third metal are present in the same cross section. A method for producing a composite electrode for an ignition plug, comprising: a sixth step of forming a composite electrode.