JPH0648631B2 - Method for manufacturing outer electrode of spark plug - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an outer electrode of a spark plug arranged with a spark gap between a center electrode and the center electrode, and more particularly to a method for manufacturing a composite outer electrode.

[Prior Art] The outer electrode of the spark plug is generally rod-shaped and is joined to the end of the metal shell. Then, the outer electrode is arranged so that the end portion is opposed to the center electrode through the spark gap,
It has been bent.

In addition, the outer electrode is generally 95% or more of nickel,
N added with silicon, chromium, aluminum, manganese, etc.
It is formed of an i alloy. This Ni alloy is excellent in corrosion resistance (especially fire wear resistance) and heat resistance (high temperature strength), and also relatively excellent in heat conduction (heat conductivity).

However, in recent years, as the performance of engines has improved, there has been a demand for an outer electrode that is more excellent in heat dissipation than before.

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

[Problems to be Solved by the Invention] However, Cu is actually used for the heat absorbing portion, and a spark plug is made with an outer electrode using a Ni alloy or Inconel for a covering body that covers the Cu and is used in an engine. Then, the shape of the outer electrode changes due to the difference in thermal expansion coefficient between the heat absorbing portion and the covering.

Therefore, there is a problem that it is difficult to keep the spark gap between the outer electrode and the center electrode at an appropriate value under the use condition.

The present invention has been made in view of the above circumstances, and an object thereof is to eliminate a change in the shape of the outer electrode due to a temperature change,
Another object of the present invention is to provide an outer electrode of a spark plug which is capable of keeping the spark gap between the outer electrode and the center electrode at an appropriate value even under use conditions and which is excellent in heat dissipation.

[Means for Solving the Problems] In order to achieve the above object, the present invention is directed to a heat absorbing part made of metal excellent in heat dissipation, and a metal excellent in heat resistance and corrosion resistance for covering the tip and the periphery of the heat absorbing part. In the method of manufacturing the outer electrode, the rear end of which is joined to the metal shell of the spark plug by welding, in which (a) the metal forming the core having the same coefficient of thermal expansion as that of the cover is heat-extracted. First step of forming a clad material covered with excellent metal, (b) forming a cup-shaped covering body, inserting the clad material into a concave portion of a metal having excellent heat resistance and corrosion resistance, and forming a joined body A second step of forming a small diameter cylindrical rod by pressing the joined body from the closed end side of the cup into a circular die having a circular die hole, and (d) an end of the cylindrical rod. 4th step of cutting the collar portion of the cup, (e) the cylindrical rod from the closed end side of the cup into a die hole Pushing the rectangle of the rectangular die, a fifth step of forming a prismatic rod, adopting the sixth step, the technical means consisting of cleaving (f) bonding side cladding material of the prismatic rod is exposed.

[Operation and Effect of the Invention] In the present invention, the heat absorbing portion made of Cu is sandwiched between the coating body and the core portion having substantially the same thermal expansion coefficient. As a result, even if the temperature changes, the thermal stress caused by the difference in expansion coefficient is relaxed and the shape of the outer electrode is prevented from changing. That is, even if the outer electrode is placed in the combustion chamber and exposed to a high temperature state, the shape change of the outer electrode is suppressed.

In addition, 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 the use condition, and the outer electrode excellent in heat transfer can be obtained.

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

On the other hand, by using a material having excellent jointability with the outer electrode for the core portion, the joint 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.

(Structure of Embodiment) FIG. 1 is a sectional view of a main portion 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 spark plug 1 is roughly composed of 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 a composite electrode in which a Cu core is enclosed in a Ni alloy. The insulator 3 is made of an insulating material such as alumina, and is a cylindrical body that covers the periphery of the center electrode 2 and insulates and holds the center electrode 2. The metal shell 4 is a tubular metal shell made of an iron-based material that is screwed into an internal combustion engine (not shown) while holding the insulator 3, and the outer electrode 5 is provided at the end of the metal shell 4.
It is joined by welding technology.

The outer electrode 5 has a rod shape, and is bent in a substantially L shape so that the end portion is opposed to the center electrode 2 with a spark gap 1 interposed therebetween.

The outer electrode 5 is a composite electrode including a central core portion 6, a heat absorbing portion 7 that covers the core portion 6, and a cover 8 that covers the heat absorbing portion 7.

Since the coating 8 is exposed to the combustion chamber and spark discharge is generated on the surface, the Ni alloy, Inconel, etc.
It is made of a metal having excellent heat resistance (high-temperature strength) and corrosion resistance (especially spark wear resistance), and having a high joint strength with the metal shell 4. The cover 8 covers the end portion (one end) of the heat absorbing portion 7 on the side facing the center electrode 2 and the periphery of the heat absorbing portion 7.
Then, with the outer electrode 5 alone, the metal shell 4
The core portion 6 and the heat absorbing portion 7 are exposed at the end portion (the other end) on the side to be joined to, and the other end is joined to the metal shell 4.

The heat absorbing part 7 is made of Cu which excels in heat dissipation. Then, as described above, the heat absorbing portion 7 has its periphery covered with the cover 8, one end sealed with the cover 8 and the other end joined to the metal shell 4. The cross-sectional area of the heat absorbing portion 7, that is, the cross-sectional area of Cu is
It is provided within the 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 substantially the same coefficient of thermal expansion as that of the covering body 8 and relatively excellent thermal conductivity, and is made of, for example, pure Ni. Core 6
Is surrounded by the heat absorbing portion 7. Then, one end is sealed by the cover 8 together with the heat absorbing part 7, and the other end is joined to the metal shell 4. The core 6 may be pure iron.

(Manufacturing Method) Next, an example of a manufacturing example of the outer electrode 5 will be described with reference to FIGS.
A brief description will be given with reference to the drawings.

First, a clad wire (clad material) in which pure Ni is covered with Cu is formed.

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

N for forming the cup-shaped covering 8 shown in FIG.
The cylindrical body 9 is inserted into the recess 10a of the cup 10 made of an i alloy to form a bonded body 11 in which the cylindrical body 9 and the cup 10 are bonded (see FIG. 4).

The joined body 11 is pushed into the circular die 12 having a circular die hole from the closed end side of the Ni alloy cup to form a cylindrical rod 13 having a small diameter circular section (see FIG. 5).

The collar portion 14 formed at the Cu side end portion of the cylindrical rod 13 is cut (see FIG. 6).

The cylindrical rod 13 is inserted into the rectangular die 15 having a rectangular die hole from the closed end side of the Ni alloy cup to form a rectangular rod 1 having a rectangular cross section.
6 is formed (see FIG. 7).

This prismatic rod 16 is cut to an appropriate length on the joining side where the cladding material is exposed (see FIG. 8). At this time, the columnar body 16a on the Cu-bonding side of the prismatic rod 16 is cut. Then, the prismatic rod 16 is annealed.

As described above, the outer electrode 5 is formed.

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

Then, the end portion on the side of the center electrode 2 is bent into a substantially L shape so as to face the center electrode 2 via a predetermined spark gap l, and the metal shell 4 provided with the outer electrode 5 is formed. .

(Experimental example) Next, two experiments in which the cross-sectional area of the heat absorbing portion 7 is changed to examine the heat drawing and the joint strength with the metal shell 4 will be described.

In the first experiment, the heat-extraction effect was investigated by changing the ratio of the cross-sectional area of the heat absorbing part 7 to the cross-sectional area of the outer electrode 5, and the experimental result is shown in the graph of FIG.

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

In the second experiment, a core 6 having a constant size was used, and the ratio between the cross-sectional area of the heat absorbing part 7 and the cross-sectional area of the outer electrode 5 was changed to weld the outer electrode 5 to the metal shell 4 by electric resistance welding. Welded by the method and examined the joint strength.
It is shown in the graph of FIG.

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

(Effects of the embodiment) In the present invention, the Cu heat absorbing portion 7 is sandwiched between the coating 8 and the core portion 6 having substantially the same coefficient of thermal expansion. by this,
Even if the temperature changes, the shape of the outer electrode 5 can be prevented from changing. That is, even if the outer electrode 5 is placed in the combustion chamber even at room temperature and exposed to a high temperature state, the shape change of the outer electrode 5 is suppressed.

In addition, as shown in the above two experimental results, the heat absorbing portion 7
By setting the cross-section area of 20 to 50% of the cross-section area of the outer electrode 5, it is possible to obtain the outer electrode 5 having a high heat-extracting effect and a high bonding strength with the metal shell 4.

Further, since the outer electrode 5 can be manufactured by partially diverting the manufacturing method of 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 columnar body (see FIG. 3) having a flange portion at the end was formed from the clad wire and joined to the cup, but in the present embodiment, as shown in FIG. First, the clad wire 17 is directly inserted into the recess 10a of the cup 10 to form the joined body 11 (see FIG. 12) without forming the clad wire 17 into a cylindrical body. The subsequent steps are the same as in the first embodiment.

(Modification) The present invention includes the following embodiments in addition to the above embodiments.

In this embodiment, the spark plug 1 provided with one outer electrode 5 is illustrated, but a plurality of outer electrodes may be used.

The present invention is applied to the outer electrode 5 bent into a substantially L shape,
It may be applied to the outer electrode 5 having another shape such as a C-shape, or the oblique outer linear electrode 5 facing the tip edge of the center electrode.

[Brief description of drawings]

1 to 10 show a first embodiment, FIG. 1 is a sectional view of a main part of an ignition plug, FIG. 2 is a sectional view of an outer electrode, and FIGS. 3 to 8 are outer portions. FIG. 9 and FIG. 10 are process charts showing an example of manufacturing an electrode, and are graphs showing experimental results. 11 to 16 show the second method of manufacturing the outer electrode 5.
This is an example. In the figure, 1 ... Spark plug, 4 ... Metal shell 5 ... Outer electrode, 6 ... Core part, 7 ... Heat absorbing part, 8 ... Cover

Claims (1)

[Claims] 1. A heat absorbing part made of metal which is excellent in heat dissipation, and a metal covering which covers the tip and the periphery of this heat absorbing part and which is excellent in heat resistance and corrosion resistance. In the method of manufacturing an outer electrode to be joined to a metal fitting by welding, (a) a first step of forming a clad material covered with a metal excellent in heat conduction on a metal forming a core having a thermal expansion coefficient substantially the same as that of the coating, (b) A second step of forming a bonded body by inserting the clad material into a concave portion of a metal having excellent heat resistance and corrosion resistance that forms a cup-shaped covering body, and (c) cups the bonded body. The third step of forming a thin cylindrical rod by pushing the circular die from the closed end side into a circular die, (d) the fourth step of cutting the flange portion at the end of the cylindrical rod, (e) The fifth step of forming the prismatic rod by pushing the cylindrical rod into the rectangular die having a rectangular die hole from the closed end side of the cup. , (F) the sixth step, the manufacturing method of the outer electrode become more spark plugs to cut the bonding side of the clad material of the prismatic rod is exposed.