JPH04118882A - Ground electrode for ignition plug and its manufacture - Google Patents

Abstract

PURPOSE:To keep a speak gap suitable between a ground electrode and a center electrode as well as to enhance heat radiation by providing a heat absorbing section with a core section which is extended in the longer direction at its inner side, and is roughly identical in a thermal expansion coefficient to a sheathing body. CONSTITUTION:A ground electrode 5 is a composite electrode composed of a central core section 6, a heat absorbing section 7 sheathing the core section 6, and of a sheathing body 8 sheathing the heat absorbing section. The sheathing body 8 is made of metal excellent in heat resistance and corrosion resistance such as Ni alloys, Inconel and the like. The heat absorbing section 7 is made of Cu excellent in heat radiation. And in the heat absorbing section 7, its circumference is sheathed by the sheathing body 8, its one end is sealed by the sheathing body 8, and the other end is joined with a main body fitting 4. The core section 6 is made of metal such as pure Ni which is roughly identical in a thermal expansion coefficient to the sheathing body 8, and is comparatively excellent in thermal conductivity. The circumference of the core section 6 is sheathed by the heat absorbing section 7. And one end of the core section is sealed together with the heat absorbing section 7 by the sheathing body 8, and the other end is joined with the main body fitting 4.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an outer electrode of a spark plug that is arranged with a spark gap between it and a center electrode, and particularly to a composite electrode of the outer electrode and a method for manufacturing the same. Regarding.

[Prior Art] The outer electrode of a spark plug has a rod-like shape and is joined to an end of a metal shell. The outer electrode is arranged such that the end thereof faces the center electrode with a spark gap interposed therebetween.
It is bent.

In addition, the outer electrode is generally made of 95% or more nickel.
N added with silicon, chromium, aluminum, manganese, etc.
It is made of i-alloy. This Ni alloy has excellent corrosion resistance (particularly spark abrasion resistance) and heat resistance (high temperature strength), as well as relatively excellent heat dissipation (thermal conductivity).

However, in recent years, as the performance of engines has improved, there has been a demand for outer electrodes that have even better heat removal than before.

Therefore, it has been proposed that Cu, which has excellent heat conductivity, is arranged inside the outer electrode as a heat absorbing part.

[Problems to be Solved by the Invention] However, an ignition plug was actually created using Cu for the heat absorbing part and an outer electrode using Ni alloy or Inconel for the coating covering the CU, and it was used in an engine. The shape of the outer electrode changes due to the difference in coefficient of thermal expansion between the heat absorbing part and the covering.

Therefore, there was a problem in that it was difficult to maintain the spark gap between the outer electrode and the center electrode at an appropriate value under the usage conditions.

The present invention was developed in view of the above circumstances, and its purpose is to eliminate the change in the shape of the outer electrode due to temperature changes, and to maintain the spark gap between the outer electrode and the center electrode at an appropriate value even under the usage conditions. The purpose of the present invention is to provide an outer electrode of a spark plug that can retain heat and has excellent heat dissipation.

[Means for Solving the Problems] In order to achieve the above object, the outer electrode of the spark plug of the present invention employs the following technical means.

The outer electrode of the ignition plug includes a heat absorbing part made of Cu that has excellent heat dissipation, and a metal covering with excellent heat and corrosion resistance that covers one end and the surrounding area of this heat absorbing part, and the other end of the outer electrode of the ignition plug is made of copper. It is joined to the main metal fitting using welding technology.

The heat absorbing portion includes a core portion extending in the longitudinal direction on the inside and having a heat absorption rate of 165 approximately the same as that of the covering body.

Further, the above-mentioned outer electrode is manufactured by combining the following steps.

The first step is to form a cladding material covered with Cu on the metal forming the core. A second step of inserting the cladding material into a metal recess forming a cup-shaped covering to form a joined body. A third step of pressing the joined body into a circular die with a circular die hole to form a cylindrical rod. A fourth step of cutting the flange at the end of the cylindrical rod; a fifth step of pushing the cylindrical rod into a rectangular die with a rectangular die hole to form a prismatic rod; cutting the Cu-side cylindrical body of the cylindrical rod; a sixth step of annealing the prismatic bar; and a seventh step of annealing the prismatic bar.

[Operations and Effects of the Invention] In the present invention, the heat absorbing portion made of Cu is sandwiched between the covering body and the core portion having substantially the same thermal expansion rate. As a result, even if a temperature change occurs, thermal stress caused by a difference in expansion rate is alleviated, and changes in the shape of the outer electrode are suppressed.

In other words, even if the outer electrode is placed in a combustion chamber and exposed to high temperature conditions, the shape change of the outer electrode is suppressed.

Further, in the use state, the heat of the outer electrode is conducted to the metal shell through the heat absorbing portion.

As a result, the spark gap between the outer electrode and the center electrode can be maintained at an appropriate value even under usage conditions, and an outer electrode with excellent heat dissipation can be obtained.

Note that the outer electrode of the present invention is manufactured by the above manufacturing method.

On the other hand, by using a material with excellent bondability with the outer electrode for the core portion, the bonding strength between the outer electrode and the metal shell can be increased.

[Example] Next, the outer electrode of the spark plug of the present invention will be described based on an example shown in the drawings.

(Configuration of Example) FIG. 1 is a sectional view of a main part of an ignition plug arranged in a combustion chamber of an internal combustion engine, and FIG. 2 is a sectional view of an outer electrode.

The ignition plug 1 is roughly divided into a center electrode 2, an insulator 3, and a metal shell 4. The center electrode 2 is a metal body to which a high voltage is applied from an ignition device (not shown), and is made of a Ni alloy. Consists of a composite electrode containing a Cu core. The insulator 3 is made of an insulating material such as alumina, and is a cylindrical body that covers the center electrode 2 and holds the center electrode 2 insulated. The metal shell 4 is a cylindrical metal fitting made of an iron-based material that is screwed onto an internal combustion engine (not shown) while holding the insulator 3, and has an outer electrode 5 at the end.
Joined using welding technology.

The outer electrode 5 has a rod shape, and is bent into an abbreviated shape so that the end thereof is opposed to the center electrode 2 with the spark gap 1 interposed therebetween.

This outer electrode 5 is a composite electrode consisting of a central core portion 6, a heat absorbing portion 7 covering the core portion 6, and a covering member 8 covering the heat absorbing portion 7.

The covering 8 is exposed to the combustion chamber and spark discharge occurs on the surface, so it is made of Ni alloy, Inconel, etc.
It is made of a metal that has excellent heat resistance (high temperature strength) and corrosion resistance (especially spark abrasion resistance), and also has high bonding strength with the metal shell 4. This covering 8 covers the end (one end) of the heat absorbing part 7 on the side facing the center electrode 2 and the periphery of the heat absorbing part 7, and is joined to the metal shell 4 when the outer electrode 5 is alone. A core portion 6 and a heat absorption portion 7 are provided at the side end (other end).
is exposed, and the other end is joined to the metal shell 4.

The heat absorbing portion 7 is made of Cu, which has excellent heat removal properties. As described above, the heat absorbing portion 7 is surrounded by the covering 8, one end is sealed by the covering 8, and the other end is joined to the metal shell 4. Note that the cross-sectional area of the heat absorbing portion 7, that is, the cross-sectional area of Cu, is
It is provided within a range of, for example, 20 to 50% of the cross-sectional area of the outer electrode 5.

The core portion 6 is a metal body having approximately the same thermal IUI rate as the covering body 8 and relatively excellent thermal conductivity, and is made of, for example, pure Ni. Core part 6
is surrounded by a heat absorbing section 7. Then, one end is sealed together with the heat absorbing portion 7 in the cover 8, and the other end is joined to the metal shell 4. Note that the core portion 6 may be made of pure iron.

(Manufacturing method) Next, an example of manufacturing the outer electrode 5 is shown in FIGS. 3 to 8.
This will be briefly explained using figures.

First, a clad wire (clad material) covering pure Ni with Cu is formed.

As shown in FIG. 3, this clad wire is formed into a cylindrical body 9 having a flange 9a at the end.

N forming the cup-shaped covering 8 shown in FIG.
The cylindrical body 9 is inserted into the recess 10a of the i-alloy cup 10, and a joined body 11 is formed by joining the cylindrical body 9 and the cup 1G (see FIG. 4).

This joined body 11 is pushed from the Ni alloy side into a circular die 12 with a circular die 6 to form a cylindrical rod 13 with a circular cross section (see FIG. 5).

The flange 14 formed on the Cu side end of the cylindrical rod 13 is cut (see step 6 [i?l).

The cylindrical rod 13 is inserted from the Ni alloy side into a rectangular die 15 with six rectangular dies to form a prismatic frame 16 with a rectangular cross section (see FIG. 7).

This prismatic frame 16 is cut to an appropriate length on the Cu bonding side (see FIG. 8). At this time, the cylindrical body 16a of the Cu bonding side of the prismatic frame 16 is cut. After that, prismatic frame 1
6 is annealed.

Through the above steps, the outer electrode 5 is formed.

Thereafter, the cut portion of the outer electrode 5 is joined to the end of the metal shell 4 by welding.

Then, the end portion on the center electrode 2 side is bent into an abbreviated shape so as to face the center electrode 2 with a predetermined spark gap 1 in between, thereby forming a metal shell 4 having an outer electrode 5. .

(Experimental Examples) Next, two experiments in which the cross-sectional area of the heat absorbing portion 7 was changed and the heat removal and the bonding strength with the metal shell 4 were investigated will be described.

In the first experiment, the heat removal effect was investigated by changing the ratio of the cross-sectional area of the heat absorbing portion 7 and the cross-sectional area of the outer electrode 5, and the experimental results are shown in the graph of FIG.

As can be seen from this graph, by making the cross-sectional area of the heat absorbing portion 7 20% or more of the cross-sectional area of the outer electrode 5, a sufficient heat removal effect can be obtained.

In the second experiment, the ratio of the cross-sectional area of the heat-absorbing part 7 to the cross-sectional area of the outer electrode 5 was changed using a core part 6 of a certain size, and the outer electrode 5 was electrically resistance welded to the metal shell 4. The results of the experiment were reported in the 10th
Shown in the graph of Figure.

As can be seen from this graph, sufficient bonding strength can be obtained by making the cross-sectional area of the heat absorbing portion 7 50% or less of the cross-sectional area of the outer electrode 5.

(Effects of Examples) In the present invention, the heat absorption part 7 made of Cu is sandwiched between the covering body 8 and the core part 6, which have substantially the same heat mrM ratio.

This prevents the shape of the outer electrode 5 from changing due to temperature changes.In other words, the shape of the outer electrode 5 does not change even at room temperature or when placed inside the combustion chamber and exposed to high temperatures. It can be suppressed.

In addition, as shown in the above two experimental results, the heat absorption part 7
By setting the cross-sectional area of the outer electrode 5 to 20 to 50% of the cross-sectional area of the outer electrode 5, it was possible to obtain an outer electrode 5 with a high heat removal effect and a high bonding strength with the metal shell 4.

Furthermore, since the outer electrode 5 can be manufactured by reusing part of the method for manufacturing the center electrode, the composite outer electrode 5 can be manufactured at low cost.

(Second Embodiment) FIGS. 11 to 16 show a second method of manufacturing the outer electrode 5.
An example is shown.

In the first embodiment, an example was shown in which a cylindrical body with a flange at the end (see Fig. 3) was formed from the clad wire and joined to the cup, but in this embodiment, as shown in Fig. 11, Second, the clad wire 17 is directly inserted into the recess 10a of the cup 10 to form the bonded body 11 (see FIG. 12) without forming the clad wire 17 into a cylindrical body. Note that the subsequent steps are the same as in the first embodiment.

(Modified example) In addition to the above embodiments, the present invention includes the following embodiments.

In this embodiment, the ignition plug 1 is provided with one outer electrode 5, but the present invention is applied to the outer electrode 5 bent in an abbreviated shape, in which a plurality of outer electrodes may be used.
The present invention may be applied to an outer electrode 5 having another shape such as a C-shape, or may be applied to an oblique-shaped straight outer electrode 5 facing the periphery of the tip of the center electrode.

[Brief explanation of drawings]

Figures 1 to 10 show the first embodiment, in which Figure 1 is a sectional view of the main part of the spark plug, Figure 2 is a sectional view of the outer electrode, and Figures 3 to 8 are the outer side. A process diagram showing an example of manufacturing an electrode, and FIGS. 9 and 10 are graphs showing experimental results. 11 to 16 show a second method of manufacturing the outer electrode 5.
This is an example. In the diagram 1... Spark plug 4... Metal shell 5...
Outer electrode 6... Core part 7... Heat absorption part 8... Covering body

Claims (1)

[Claims] 1) A heat absorbing part made of Cu with excellent heat removal, and a metal covering with excellent heat and corrosion resistance that covers one end and the surroundings of this heat absorbing part, and the other end is ignited. An outer electrode of a spark plug joined to a main metal fitting of a plug by a welding technique, wherein the heat absorbing part extends in the longitudinal direction on the inner side and includes a core part having approximately the same coefficient of thermal expansion as the covering body. . 2) The outer electrode of the spark plug is made by combining the following steps. (a) A first step of forming a cladding material covered with Cu on the metal forming the core. (b) A second step in which the cladding material is inserted into a metal recess forming a cup-shaped covering to form a bonded body.
Process. (c) A third step of pressing the joined body into a circular die with a circular die hole to form a cylindrical rod. (d) A fourth step of cutting the flange at the end of the cylindrical rod. (e) A fifth step of pressing the cylindrical rod into a rectangular die with a rectangular die hole to form a prismatic rod. (f) Sixth step of cutting the Cu-side cylindrical body of this prismatic rod. (g) A seventh step of annealing the prismatic bar.