JPH0582235A - Manufacture of spark plug - Google Patents

Abstract

PURPOSE:To provide the manufacture of a spark plug, by which edges of an electrode surface for spark discharge can be industrially and uniformly mass-produced, and by which the reduction in a discharge voltage can be attained with small dispersion. CONSTITUTION:In the manufacture of a spark plug comparing the steps of pressing and forming powdery material mainly composed of a noble metal powder, sintering the press-formed body so as to produce a chip 5 which is to be fixedly mounted to an igniting part predetermined edges 6 are formed on an igniting surface upon the press-forming of the chip followed by sintering them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a spark plug in which a sinter composed mainly of a noble metal is fixedly attached to an ignition part.

[0002]

2. Description of the Related Art Spark plug discharge voltage (required voltage)
It is known that unevenness is provided in the ignition part of the spark discharge in order to reduce the noise. This discharge voltage varies in a normal distribution, and its center value is determined by the size of the electrode diameter. The highest discharge voltage is not significantly affected by the electrode diameter, and can be lowered by providing unevenness on the discharge part (ignition part) of the electrode and forming an edge on the ignition surface. The irregularities (edges, hereinafter referred to as irregularities) are conventionally formed by cutting, forging, or electric discharge machining the electrode surface. Further, there is also proposed a spark plug in which a tip of a sintered metal (including cermet) is welded to the tip of the center electrode so as to wear the electrode and improve ignitability.

[0003]

However, since the ignition surface of the electrode is small and the concavities and convexities are provided in the subsequent process by the conventional processing method, it is difficult to form the concavities and convexities easily and the irregularities are apt to vary. Therefore, the effect of reducing the discharge voltage also varies due to the difference in the unevenness, and it is difficult to obtain uniform performance. An object of the present invention is to provide a method for manufacturing a spark plug which can industrially uniformly produce irregularities on an electrode surface of spark discharge and can achieve reduction of discharge voltage with little variation.

[0004]

A spark plug manufacturing method according to the present invention comprises press-molding a powder raw material mainly composed of a noble metal powder, and fixing a chip obtained by sintering the press-molded body to an ignition part. In the spark plug, the chip was press-molded to form predetermined irregularities on the ignition surface, and then sintered.

[0005]

Since the powder raw material is press-molded to form the chips having the predetermined unevenness on the ignition surface and the chips are sintered, it is possible to mass-produce chips with unevenness with little variation. Since this tip is fixed to the ignition part of the spark plug by welding or the like, the discharge voltage can be reduced with little variation.

[0006]

1 shows a spark plug according to the present invention. In this spark plug 100, an insulator 2 with a shaft hole 21 is fitted in a tubular metal shell 1 having an L-shaped outer electrode 11 welded to its tip surface. The insulator 2 is
The seat surface 22 of the insulator 2 is locked to the stepped seat 12 provided on the inner circumference of the metal shell 1 through the packing 13, and the metal shell head 14 is fixed by caulking. The center electrode 4 is inserted into the shaft hole 21 on the front end side, the front end portion 4A thereof projects from the front end of the insulator 2, and the rear end flange portion 4B of the shaft hole 21.
Is in contact with the stepped portion of. On the rear end side of the shaft hole 21, a monolithic resistor 32 and a center shaft 3 sandwiched by a conductive glass seal 31 are heat-sealed.

As shown in FIG. 2, the center electrode 4 has a diameter of 2.5 mm with a small tip (diameter of 2.0 mm).
And has a columnar shape of 15.0% by weight of chromium (Cr),
A base material 41 made of nickel (Ni) alloy containing 8.0% by weight of iron (Fe), and copper (C) embedded in the shaft core of the base material 41.
u) or a core material 42 mainly made of silver (Ag) and made of a good heat conducting metal, and a two-layered material 40 at the tip thereof, and unevenness 6 is formed on the tip surface.
A columnar noble metal tip 5 including a head portion 51 provided with and a base portion 52 having a small diameter is welded and formed. In this embodiment, the unevenness 6 is one groove 53 provided on the end surface.

In this embodiment, the tip 5 is provided at the center of the tip surface of the base material 41, and the base portion 52 of the tip is fitted into a small hole 43 reaching the tip of the core material 42, and the base portion 52 and the base material 41. The fitting surface 5A (joint surface) is welded over the entire circumference, and the tip end surface 54 is in contact with the tip of the core member 42. When the fitting surface 5A is laser-welded after the tip 5 is applied to the small hole 43 and resistance-welded, the welding strength can be increased, and the degree of bonding between the tip 5 and the core material 42 can be increased, and the heat conduction can be best achieved. ..

The chip 5 is made of iridium (Ir) powder 9
It is composed of a sintered body obtained by sintering 5.0% by weight and 5.0% by weight of a powder of yttria (Y ₂ O ₃ ) which is a rare earth metal oxide, and has a columnar shape. This sintered body is a cermet in which yttria enters the grain boundary of Ir. The amount of yttria added is required to be 0.1 to 15.0% by weight, and preferably 1.0 to 10.0% by weight. Further, ruthenium (Ru) can be used as the other metal for Ir, and a ternary system containing both of these may be used. In addition to yttria, thoria (ThO) can be used.
₂ ), other rare earth metal oxides such as lanthanum oxide (La ₂ O ₃ ) can also be used.

A method of manufacturing the chip 5 will be described with reference to FIG. After formulating the powder Ir-Y ₂ 0 ₃ as shown in (a), after the granulated powders are dispersed, is filled into the mold 61. Next, as shown in FIG.
Pressure molding is performed by the lower punch 63. The molded body 50 is sintered to manufacture the chip 5. This sintering is performed by performing secondary sintering by hot isostatic pressing after primary sintering. Note Ir-Y ₂ 0 ₃ cermet platinum (Pt), compared with other noble metals such as palladium (Pd), wear resistance is advantageous less expensive with comparable.

FIG. 4 shows the results of measuring the degree of variation in the discharge voltage between the spark plug 100 and a comparative product 200 having the same shape as the spark plug 100 and having the concavities and convexities on the tip surface of the center electrode 4 formed by cutting. Experiment is 6 cylinders, 30
1 spark plug for each 00cc gasoline engine
00 pieces were mounted and arranged by the maximum voltage under the operating conditions from idling to 5500 rpm and full load. The bar graph shows the experimental results with the spark plug 100, and the broken line shows the comparative product 200. It can be seen that the product of the present invention, in which the chip 5 having the unevenness is formed by press molding and sintering, has a lower discharge voltage than the comparative product 200 having the unevenness formed by cutting and there is little variation.

FIG. 5 shows another embodiment of the chip 5 having the unevenness 6. In (a), two V-grooves 55 are formed in parallel on the tip surface. In (b), a groove is provided in a cross-shaped recess 56 on the tip surface. (C) is a circular recess 5 in the center of the tip surface.
7 is provided. As for these unevenness 6, the upper punch 6
It is easy to mass-produce a desired shape with a small variation only by providing the convex portions corresponding to the recesses 55, 56, 57 on the second portion.

FIG. 6 shows another embodiment of the spark plug of the present invention. In this embodiment, alumina (Al ₂
The base portion 51 of the press-molded chip molded body 50 is directly fitted to the tip of the shaft hole 21 of the O ₃ ) insulator 2 and simultaneously sintered, and the high conductivity of the conductive material filled in the shaft hole 21 is obtained. It is heat-sealed with a melting point conductive glass seal 44. As a result, the center electrode 4 and the insulator 2 can be sintered at once, and the assembling can be facilitated. FIG. 7 shows another embodiment of the spark plug of the present invention. In this embodiment, the noble metal tip 5 has a cylindrical shape with the same outer shape. In this embodiment, the shape of the noble metal tip 5 is simple, press moldability and sintering are easy, and the productivity is excellent. If the axial length of the noble metal tip 5 is shorter than the diameter, cracking may occur, so it is preferable that the length> diameter.

In the above embodiment, a cermet is used for the noble metal tip 5, but an alloy of Pt and Pd, etc.
It is also possible to use a powder sintered body of another noble metal having excellent heat resistance and spark wear resistance. Further, the chip 5 and the core material 41 do not necessarily have to be in contact with each other, but the closer they are, the better the heat dissipation of the chip 5, and at least. It is desirable to be close to each other within 05 mm.

[Brief description of drawings]

FIG. 1 is a sectional view of a spark plug of the present invention.

FIG. 2 is an enlarged sectional view of a tip portion of a center electrode.

FIG. 3 is a manufacturing process diagram of a cermet chip.

FIG. 4 is a graph showing an experimental result of a variation degree of discharge voltage.

FIG. 5 is a perspective view showing another embodiment of the chip.

FIG. 6 is a sectional view of a main part of a spark plug according to another embodiment.

FIG. 7 is a sectional view of a main part of a spark plug according to still another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal shell 2 Insulator 3 Middle shaft 4 Center electrode 40 2 layer material 41 Center electrode base material 42 Center electrode core material 5 Noble metal tip

Claims (1)

[Claims] 1. A spark plug obtained by press-molding a powder raw material mainly composed of a noble metal powder, and sintering a press-molded body to fix a chip to an ignition part, wherein the chip has a predetermined surface on the ignition surface at the time of press-molding. Forming irregularities,
A method of manufacturing a spark plug which is then sintered.