JP3272390B2 - 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 spark plug in which a noble metal tip is welded to a firing surface of an electrode.

[0002]

2. Description of the Related Art To improve spark wear resistance, a plate-shaped noble metal tip is welded to the ignition surface of an outer electrode welded to the tip of a metal shell, and a raised portion of a base material is formed on the outer periphery thereof. (Japanese Patent Publication No. 3-75994) has been proposed.

[0003]

However, in the above-described spark plug, it is difficult to uniformly form the bulge amount of the base metal during welding, and therefore, the edge of the plate-shaped noble metal tip protrudes from the base metal. And the amount of protrusion is small. As a result, there are disadvantages that the required voltage for spark discharge in the discharge gap varies, and the required voltage becomes a high level due to a small electric field intensity. An object of the present invention is to provide a spark plug which has a uniform edge on the surface of a plate-shaped noble metal tip and which can reduce a required voltage required for a spark discharge voltage at a low level and with a small variation.

[0004]

According to the present invention, there is provided a spark plug having an electrode in which a noble metal tip is electrically resistance welded to a firing surface of a base material, wherein the noble metal tip projects from the base material surface, A central portion having an edge, and an edge portion located on the outer periphery of the central portion and welded in a form in which the base material surface around the central portion is recessed in comparison with the other base material surfaces. It is characterized by. A spark plug according to a second aspect is characterized in that, in the first aspect, the top surface of the central portion has unevenness with an edge.

[0005]

According to the present invention, the protruding central portion having an edge in the plane of the noble metal tip welded to the ignition surface of the electrode and the base material surface located on the outer periphery of the central portion and around the central portion are provided. Since the edge to be welded is formed to be recessed in comparison with the other base material surfaces, the height of the edge can be made uniform and the height of the edge can be made higher. This makes it possible to reduce the variation in the required voltage of the spark plug required for spark discharge and to reduce the required voltage to a low level.

[0006]

FIG. 1 shows a spark plug according to the present invention. An insulator 3 having a shaft hole 31 is fitted into a cylindrical metal shell 1 having an outer electrode (ground electrode) 2 welded to a tip 11 thereof. The center electrode 4 is sealed in the shaft hole 31. A spark discharge gap G is formed between the front end surface 41 of the center electrode 4 protruding from the insulator 3 and the ignition surface 21 of the outer electrode 2.

The outer electrode 2 is made of a heat-resistant Ni alloy and is formed by bending a rod-shaped base material 20 having a rectangular cross section into an approximately L-shape, and has a base 22 in the axial direction and a tip 23 bent in the direction of the center electrode. Consists of The center electrode tip surface 4 of the tip portion 23
The surface facing 1 is the ignition surface 21 and the disk-shaped noble metal tip 5 made of a Pt alloy is welded.

The noble metal tip 5 has a central portion 51 protruding in the direction of the central electrode and an outer peripheral edge 52. A top surface 53 of the central portion 51 is formed on the surface 24 of the base material of the surrounding outer electrode 2.
The edge 52 protrudes in the direction of the center electrode by about 0.2 mm to 0.5 mm, and the edge 52 is flush with the surface 24 or is recessed from the surface 24 by about 0.1 mm to 0.2 mm. . The tip of the central portion 51 is an edge E. As a material for the outer electrode 2, a composite material in which a core made of a good heat conductive material such as Cu is embedded in a rod-shaped base material made of a Ni alloy, and a core made of pure Ni or pure Fe is further embedded in the core.
A layer mixture may be used.

FIG. 2 shows a method for welding the noble metal tip 5 to the outer electrode base material 20. The disc-shaped noble metal tip 5 is placed at a predetermined position on the outer electrode base material (material) 20, and the electrode rod 6 having a substantially flat distal end surface 60 is lowered from above to perform electric resistance welding. As a result, as shown in (a), the noble metal tip 5 is welded mainly by melting the base material 20, and the bulge 25 of the molten base material 20 is formed on the outer periphery 50.
Is formed.

Next, as shown in (b), a columnar recess 71 having a diameter somewhat smaller than that of the noble metal tip 5 is provided at the center of a circular tip surface 70 having a diameter slightly larger than the outer diameter of the noble metal tip 5.
Resistance welding is performed again by the electrode rod 7 provided with.
As a result, a central portion 51 protruding in the direction of the center electrode and an outer peripheral edge portion 52 are formed. In addition, only when necessary, as shown in (c), cut the unnecessary end in dimensions,
The outer electrode 2 is manufactured. The outer electrode 2 is welded to the tip of the metal shell 1 and other members such as the insulator 3 and the center electrode 4 are assembled, and the outer electrode 2 is bent into a substantially L-shape to form the noble metal tip 5 and the center electrode tip surface 41. A spark discharge gap G having a predetermined width is set between them to manufacture a spark plug.

FIG. 3 shows another manufacturing process of the outer electrode 2. In this embodiment, an electrode rod 8 having a shallow cylindrical recess 81 smaller in diameter than the plate-shaped noble metal tip 5 is used at the center of a circular tip surface 80 having a diameter slightly larger than the outer diameter of the noble metal tip 5. The noble metal tip 5 is fixed to the outer electrode base material 20 by one-time resistance welding,
1 and a recessed edge 52 at the outer periphery thereof are formed.
Thus, the manufacturing process can be simplified, and the manufacturing cost can be reduced.

FIG. 4 shows still another embodiment. In this embodiment, as shown in (a), by electric resistance welding using an electrode rod 9 having a cross-shaped ridge 92 in a cylindrical recess 91 provided at the center of the distal end face 90, (b) As shown, the outer electrode 2 with the noble metal tip 5 having the uneven surface 54 having the edge E is formed. By providing unevenness having an edge E on the top surface of the central portion 51 as in this embodiment, the required voltage for spark discharge can be further reduced. In addition, the pattern of the unevenness having the edge E can be arbitrarily selected.

FIG. 5A shows an outer diameter of 0.8 mm and a thickness of 0.8 mm.
A 2 mm disc-shaped noble metal tip 5 is welded to the outer electrode base material 20 having a rectangular cross section of 2.8 mm in width and 1.0 mm in thickness. The spark discharge voltage (required voltage) of the type A in which the plate-shaped noble metal tip 5 is welded flush to the electrode base material 20, the type B in which the outer peripheral surface is half buried, and the type C according to the present invention are as follows: 5 is a graph measured in a pressurized chamber with a gauge pressure of 6 kgf / cm ² . From this measurement result, it can be seen that the required voltage of the spark plug according to the present invention of type C can be remarkably reduced when the center electrode 4 indicated by the hatched bar graph has a positive characteristic (power supply characteristic has a positive polarity) as compared with the comparative product.

FIG. 5B shows a case where a spark plug using the above type B and type C outer electrodes is mounted on a 2000 cc, 6 cylinder gasoline engine, and idling operation at 700 rpm is performed while changing the air-fuel ratio. 5 shows the results of measuring the frequency of HC spikes (due to the occurrence of misfire) in the exhaust gas. It has been proved that the type C of the present invention has a low number of misfires and excellent ignitability in a lean fuel operation range.

FIG. 6 shows that the spark plug of the present invention having the type C outer electrode 2 is mounted on a 2000 cc, 6-cylinder gasoline engine under the conditions of 5500 rpm, full load operation for 1 minute and idling operation for 1 minute. The progress degree of the oxide scale S on the welded surface of the noble metal tip 5 with the base material 20 after 3000 cycles of the thermal cycle durability test is shown. The progress of the oxidized scale S was only the outer peripheral portion 52 (stopped at 10 to 20% with respect to the diameter D of the noble metal tip) and did not progress to the central portion 51, indicating that the peeling resistance was high. This is because the edge portion 52 is deeply melted in the base material 20 and the diffusion layer is formed thick, which contributes to strengthening of welding strength such as relaxation of thermal stress, prevention of crack generation, and improvement of corrosion resistance. Guessed.

[Brief description of the drawings]

FIG. 1 is a perspective view of a tip portion of a spark plug according to one embodiment of the present invention.

FIG. 2 is a manufacturing process diagram of an outer electrode.

FIG. 3 is a manufacturing process diagram of an outer electrode according to another embodiment.

FIG. 4 is a manufacturing process diagram of an outer electrode according to still another embodiment.

FIG. 5 is a graph showing the relationship between the structure of the outer electrode and ignitability.

FIG. 6 is a cross-sectional view showing the progress of the oxidation scale of the welded portion of the noble metal tip after the durability test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal shell 2 Outer electrode 3 Insulator 4 Center electrode 5 Noble metal tip 20 Base material 21 Firing surface 24 Surface 51 Central part 52 Edge E Edge

Claims (2)

(57) [Claims] 1. A spark plug having an electrode in electrical resistance <br/> welding a noble metal tip to the firing surface of the base material, together with the noble metal tip protrudes from the front Kihaha material surface, a central portion having an edge , Located on the outer periphery of the central part
And other base material tables along with the base material surface around the central portion.
A spark plug having an edge welded in a recessed shape relative to a surface . 2. The method according to claim 1, wherein
Is a spark plug characterized by having irregularities with edges .