JPH06188062A - Electrode for spark plug - Google Patents

Abstract

PURPOSE:To provide an electrode for a spark plug having a large durability with which a sufficient weld strength can be obtained only by spot welding of an electrode base material with a precious metal chip by laser beam. CONSTITUTION:An electrode 10 for a spark plug comprises an electrode base material 1 in the form of a rod comprising heat-resistant and corrosion-resistant metal, and a precious metal chip 2 spot welded with an ignition part of the electrode base material 1 by laser beam. A spot welded part is formed as a closed ring alloy belt 30 which is formed continuous covering the whole circumference of a joint surface 20 of the electrode base material 1 with the precious metal chip 2 in which adjacent alloyed spots 3 are partly overlapped with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug electrode in which a noble metal layer is laser-welded to an ignition part of an electrode base material.

[0002]

2. Description of the Related Art In order to improve the spark wear resistance of a spark plug electrode, a noble metal tip such as a platinum alloy is welded to the ignition portion of an electrode base material made of a heat resistant and corrosion resistant metal such as a nickel alloy. Electric resistance welding is generally used as a method for welding the noble metal tip, but it has a drawback that it is weak against thermal stress and has insufficient durability because the alloy layer that can be formed on the joint surface is thin. In order to solve such a drawback, the applicant of the present patent proposes a spark plug in which a noble metal tip is resistance-welded to a center electrode base material and a welding surface is irradiated with a laser beam from the outer periphery in JP-A-57-151183. I am

[0003]

However, the combination of the above resistance welding and laser welding can thicken the alloy layer of the electrode base material and the noble metal tip and significantly increase the welding strength, but the welding work is time-consuming and costly. There was a drawback of becoming expensive. Further, in JP-A-59-191281, a shaft hole is formed at the tip of the center electrode, a noble metal tip is inserted into the shaft hole, and a laser beam is irradiated from the circumferential direction of the center electrode to the fitting surface. An electrode for a spark plug has been proposed which has one or more integrated melting and solidifying portions. But,
In the case of this electrode bonding, if there is a gap between the laser beam spot irradiation portion and the laser beam spot irradiation point, it becomes a starting point of a crack when thermal stress occurs, and the spot may melt and solidify, and a crack may develop and the chip may peel off. there were. An object of the present invention is to provide an electrode for a spark plug, which can obtain sufficient welding strength and dispersion of thermal stress only by spot welding the electrode base material and the noble metal tip with a laser beam and has a high durability.

[0004]

DISCLOSURE OF THE INVENTION The present invention is for a spark plug comprising a rod-shaped electrode base material made of heat-resistant and corrosion-resistant metal and a noble metal tip spot-welded to the ignition part of the electrode base material with a laser beam. The electrode is characterized in that the spot welded portion is formed in a continuous ring-shaped alloy strip that partially overlaps adjacent alloyed spots and covers the entire circumference of the joint surface between the electrode base material and the noble metal tip.

[0005]

According to the present invention, since the electrode base material and the noble metal tip are joined by a thick alloy layer continuous in an annular shape, the thermal stress generated by repeated cold and heat cycles during use is eliminated. Can be relaxed and dispersed. As a result, it is possible to prevent thermal stress due to repeated cooling / heating cycles from being concentrated in a local area such as a joint between a discontinuous portion and a continuous portion, which may cause peeling and chip separation. As a result, the durability of the spark plug is improved. With the configuration according to the second aspect, the annular alloy layer can be formed substantially uniformly and deeply. As a result, the thermal stress dispersion effect can be increased. With the configurations according to claims 3 and 4, the thickness of the annular alloy layer can be increased, and the effect of relaxing the thermal stress can be increased.

[0006]

1 shows a spark plug center electrode 10 according to an embodiment of the present invention. The center electrode 10 has a center electrode base material 1 in which a copper core 12 is embedded in the shaft center of a nickel alloy center electrode skin material 11, and a disc-shaped noble metal tip 2 welded to a tip end surface 13 thereof. . Base material 1 is
It is a round bar with a diameter of 2.5 mm, and its tip portion 14 is formed into a small diameter portion with a diameter of 2.0 mm. The noble metal tip 2 has a disk shape with a diameter of 2.0 mm and a thickness of 0.6 mm, and Pt-20Ir is used in this embodiment.
The base material 1 and the noble metal tip 2 are welded to each other at the joint surface 20.
It is made by intermittently irradiating a laser beam on the two and spot welding them at multiple points. By this spot welding, along the joint surface 20, a large number of alloy portions (spots 3) having a circular or elliptical surface and having a conical shape toward the center are lined up in a strip shape.

According to the present invention, the spots 3 are formed such that the center-to-center distance L between the adjacent spots 3 and 3 and the width (diameter in the arranging direction) D of the respective spots 3 are continuous such that D> L. is doing. As a result, the rows of the spots 3 partially overlap each other between the adjacent spots 3 ... 3 of the alloyed spots 3,
The continuous ring-shaped alloy strip 30 covers the entire circumference of the joint surface 20 between the electrode base material 1 and the noble metal tip 2. In addition, spots 3 and 3
If the center-to-center distance L and the width D of each spot 3 are D> 2L, the ring-closed alloy zone 30 can be formed in an alloy layer having less unevenness in the depth direction.

2A, 2B, and 2C show a manufacturing process of the spark plug center electrode 10. Center electrode base material 1
Disc-shaped precious metal tip 2 made of platinum alloy on the tip surface of
Place it as shown in. Next, as shown in (b), while rotating the center electrode 10 at a constant speed, the laser beam B is intermittently applied to the joint surface 20 between the noble metal tip 2 and the base material 1 toward the center of the electrode at regular intervals. Irradiate. As a result,
By the laser beam B, the base material 1 and the noble metal tip 2 in the irradiated portion are melted and permeated with each other to form a pyramidal alloy portion (spot 3). The surface of the spot 3 is a circle or an ellipse as described above. Spot 3 next to Spot 3
As shown in (c), the alloy parts are continuously formed in a ring shape without interruption so that the ring-closed alloy band 30 is formed. As a result, even when the spark plug is exposed to the cooling and heating cycle of the engine, the thermal stress applied to the welding surface is uniformly dispersed by the ring-closing alloy band 30, a stress concentration causes a crack, and the chip 2 is peeled off. Can be prevented.

FIG. 3 shows a second embodiment. In this embodiment, the center electrode 10 is rotated twice to perform spot welding with a laser beam so that the center-to-center distance L of the spots 3 is D> L with respect to the width D of the spots 3, preferably D.
It is formed to> 2L. According to this method, the residual stress generated during spot welding can be welded while the entire circumference is uniformly dispersed. Note that the center electrode 10 may be rotated three times or more to perform spot welding, and the center-to-center distance L of the spots 3 may be set to 1/2 or less of the width D of the spots 3.

FIG. 4 shows a third embodiment. In this embodiment, spot welding is performed in two rows in the circumferential direction. This structure has an advantage that the thickness of the ring-closing alloy strip 30 (the length of the alloy layer in the axial direction) can be extremely increased. In this case, the distance H between the adjacent closed ring alloy bands 30 is equal to the spot 3
From the viewpoint of welding strength and thermal stress dispersion, it is desirable that the axial width G is 1/2 or less.

FIG. 5 shows a fourth embodiment. In this embodiment, two spot rows (ring-closing alloy strip 30) composed of a large number of spots 3 in the circumferential direction are formed by rotating the central electrode 10 twice, that is, four times in total. In this example.
The effect of the second embodiment and the effect of the third embodiment are combined.

FIG. 6 shows a fifth embodiment. In this embodiment, a shaft hole 15 is formed in the tip surface 13 of the center electrode base material 1,
The end portion of the round rod-shaped chip 2 is fitted into the shaft hole 15, and the laser beam B is irradiated obliquely from above to form the ring-closing alloy strip 30 on the joint surface 20. Incidentally, as shown in the drawing, the laser beam B may be irradiated from the side to perform spot welding from the outer periphery of the base material 1. This embodiment also has the same effect as that of the first embodiment.

FIGS. 7A, 7B and 7C show the sixth embodiment. In this embodiment, the tip portion 1 of the center electrode base material 1 is
4. A peripheral groove 16 is formed on the outer circumference, and a noble metal ring 21 having a rounded wire or band is fitted into the peripheral groove 16, the laser beam B is irradiated from the outer circumference, and a ring-closing alloy band 30 is formed on the fitting surface. Also in this configuration, it is natural that the ring-closing alloy strip 30 may be formed in two or more upper and lower stages. In addition, although the spot shape of the laser welding is substantially circular in Examples 1 to 6, it may be square.

FIG. 8 shows the result of a durability test of the center electrode 10 of the present invention. Center electrode 1 shown in the first to fourth examples
A center electrode in which the spark plugs P1 to P4 in which 0 is incorporated and the noble metal tip 2 and the tip surface of the nickel alloy base material 1 are welded by an electric resistance welding with an alloy layer 4 having a thickness of 20 μm as shown in (a). (Comparative Example 1) incorporated spark plug P5, and as shown in (b), the center-to-center distance L of the spot 3 is 2D = L with respect to the width D of the spot 3.
A spark plug P6 incorporating a center electrode (Comparative Example 2) intermittently formed so that it was mounted on a 2000-cc, 6-cylinder engine and subjected to a repeated durability test at 5000 rpm for 1 minute at full load and 1 minute at idle. Done,
The time at which the welded portion of the noble metal tip 2 cracked was measured. According to this data, the center electrode welded with the noble metal tip of the present invention shows no cracking even after 200 hours have passed, but in Comparative Example 2 of the spark plug P6, cracking occurred at 80 hours, and the spark plug P5 had no cracking. 1 in Comparative Example 1
After 90 hours, cracks were generated.

[Brief description of drawings]

FIG. 1 is a perspective view of a spark plug center electrode according to a first embodiment of the present invention.

FIG. 2 is a manufacturing process diagram of the spark plug center electrode shown in FIG.

FIG. 3 is a perspective view of a spark plug center electrode according to a second embodiment.

FIG. 4 is a perspective view of a spark plug center electrode according to a third embodiment.

FIG. 5 is a perspective view of a spark plug center electrode according to a fourth embodiment.

FIG. 6 is a perspective view of a spark plug center electrode according to a fifth embodiment.

FIG. 7 is a manufacturing process diagram of a spark plug center electrode according to a sixth embodiment.

FIG. 8 is a graph showing the results of durability tests of the first to fourth examples.

[Explanation of symbols]

 1 Electrode base material 2 Noble metal tip 3 Spot 10 Center electrode of spark plug 20 Bonding surface 30 Ring-closing alloy strip

Claims (4)

[Claims] 1. A spark plug electrode comprising a rod-shaped electrode base material made of heat-resistant and corrosion-resistant metal and a noble metal tip spot-welded with a laser beam to the ignition portion of the electrode base material, wherein the spot-welded portion is An electrode for a spark plug formed in a continuous ring-shaped alloy band in which alloyed spots partially overlap each other between adjacent spots and cover the entire circumference of the joint surface between the electrode base material and the noble metal tip. 2. The spark plug electrode according to claim 1, wherein a center-to-center distance L between adjacent spots is 1/2 or less of a width D of each spot. 3. The electrode for a spark plug according to claim 1, wherein a plurality of the ring-closing alloy bands are provided in the axial direction, and the ring-closing alloy bands are continuous in the axial direction. 4. The electrode for a spark plug according to claim 3, wherein a distance H between adjacent closed ring alloy strips is 1/2 or less of an axial width G of the spot.