JPH0432178A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the second precious metal piece from falling off an outside electrode and improve durability by providing a plane ceiling portion, to which the second precious metal piece is joined by electric welding, in an area opposite to the end of a center electrode as the first precious metal piece. CONSTITUTION:A platinum-alloy-made precious chip 6 is joined to the end of a center electrode 4 by electric welding. An outside electrode 5 made of Ni alloy mainly containing Ni has the plane ceiling portion 51 placed corresponding to the end of the center electrode 4 and the leg portions 52 to connect the ceiling portion 51 to the end side of a metal shell 2. The ceiling portion 51 has a circular hole 53 made in an area opposite and parallel to the end face of the precious metal chip 6 so as to pass through the opposite area. The platinum-alloy-made precious metal chip 7 is joined into the hole 53 by resistance welding. The precious metal chip 6 as the first precious metal piece is made in a circular or inverse T shape in cross section and welded to the end of the center electrode 4. The precious metal chip 7 as the second precious metal piece has the axial portion 71 cylindrically formed, the first collar portion 72 and the second collar portion 73 disc-formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spark plug used in internal combustion engines such as automobiles.

[Prior Art] Spark plugs used in internal combustion engines such as automobiles have traditionally had a center electrode with a platinum tip bonded to its tip in order to improve ignitability, durability, and breakage resistance of the outer electrode. Then, a flat platinum tip is joined by electric welding to the opposing part facing the tip of this center electrode.
A device has been proposed that includes a ceiling portion in which one or more holes are formed, and an outer electrode made of a Ni alloy and having a plurality of legs connecting the ceiling portion and the tip of the metal shell. [Problem to be solved by the invention] When the above-mentioned spark plug is used in an internal combustion engine, the temperature of the outer electrode repeatedly rises and falls, so the temperature of the welded part of the platinum tip also decreases. , rise and fall repeatedly. Therefore, if this spark plug is used for a long period of time, the difference in thermal expansion coefficient between the outer electrode and the platinum tip may cause the platinum tip to lift up from the opposing part of the ceiling of the outer electrode, or the platinum tip may crack due to wear due to oxidation. could have occurred. As a result, the platinum chip partially peels off from the opposing part of the ceiling.
Eventually, the platinum chip will fall off the outer electrode.

Therefore, corrosion and wear of the outer electrode due to spark discharge are accelerated, resulting in a problem that the life of the spark plug is shortened.

An object of the present invention is to provide a spark plug for an internal combustion engine that can further improve durability by preventing the second precious metal piece from falling off the outer electrode.

[Means for Solving the Problems] (Claim 1) A spark plug for an internal combustion engine of the present invention comprises a cylindrical metal shell, a cylindrical insulator fixed within the metal shell, and a cylindrical insulator fitted into the insulator. is held by the insulator, and
A flat plate having a center electrode having a first noble metal piece whose main component is a precious metal fixed to its tip, and a second noble metal piece whose main component is a precious metal joined by electric welding to an opposing portion facing the tip of the first noble metal piece. The device includes a shaped ceiling portion, and an outer electrode having a plurality of legs connecting the ceiling portion and the metal shell.

The ceiling part has a hole penetrating the opposing part, and the second precious metal piece is provided on a shaft part fitted into the hole and on both ends of the shaft part, and the second precious metal piece is provided on both ends of the shaft part, and It has a flange-like part that sandwiches the part.

(Claim 2) The flange-shaped portion is formed by applying current to both ends of the second noble metal piece and simultaneously applying a pressing force to deform the second noble metal piece.

[Function] (Claim 1) Even when the second noble metal piece is joined to the opposing portion of the ceiling by electric welding, the second noble metal piece is attached to the outer electrode due to the difference in thermal expansion coefficient between the outer electrode and the second noble metal piece. Even if a crack occurs in the second precious metal piece due to floating or oxidation of the second precious metal piece, the second precious metal piece is caught on the opposite part of the ceiling part by the brim, so the second precious metal piece can be removed from the opposite part of the ceiling part. will not fall off.

(Claim 2) It becomes possible to easily form flanges at both ends of the second noble metal piece. Further, the shaft portion of the second precious metal piece is adhered to the inner peripheral surface of the resistance portion of the ceiling portion, and the brim-like portion of the second precious metal piece is attached to the wall surface of the opposite portion of the ceiling portion so as to sandwich the opposite portion of the ceiling portion. Since the second noble metal piece is bonded, the adhesion strength of the second noble metal piece to the outer electrode is high.

[Effects of the Invention] Since it is possible to prevent the second noble metal piece from falling off from the opposing portion of the ceiling, it is possible to suppress the progress of corrosion and wear of the outer electrode. Therefore, the durability of the spark plug for an internal combustion engine can be further improved.

[Example] A spark plug for an internal combustion engine according to the present invention will be described based on an example shown in the drawings.

1 to 6 show a first embodiment of the invention. 1st
1 and 2 show the main parts of a spark plug for an internal combustion engine.

A spark plug 1 for an internal combustion engine includes a cylindrical metal shell 2, a cylindrical insulator 3, a center electrode 4, and an outer electrode 5.

The metal shell 2 has an outer electrode 5 joined to the side surface of the tip portion by laser welding, resistance welding, etc., and a threaded portion 21 for attachment to an internal combustion engine is formed on the outer periphery. An insulator 3 is attached inside the metal shell 2 by a fixing method such as caulking.
is fixed.

The insulator 3 has a shaft hole 32 formed therein in the axial direction and opening at a front end surface 31 and a rear end surface (not shown). A center electrode 4 is fitted into a shaft hole 32 of a long leg portion 33 of the insulator 3 that projects into the combustion chamber of the internal combustion engine.

The center electrode 4 is held in the long leg portion 33 of the insulator 3 by being fitted into the shaft hole 32 of the insulator 3 with its tip portion protruding from the shaft hole 32 . A noble metal tip 6 made of platinum alloy is joined to the tip of the center electrode 4 by electric welding or the like.

The outer electrode 5 is made of a Ni alloy containing Ni as a main component (for example, Inconel 600, etc.), and includes a flat plate-shaped ceiling part 51 disposed opposite to the tip of the center electrode 4, and this ceiling part 51.
It has a plurality of (three in this embodiment) legs 52 that connect the side surface of the tip of the metal shell 2.

The ceiling portion 51 has a circular hole 5 extending through the opposing portion parallel to the tip surface of the noble metal chip 6.
It has 3. Further, around the hole 53, a plurality of circular shapes (
In this embodiment, three holes 54 are formed. A noble metal tip 7 made of a platinum alloy is joined in the hole 53 by resistance welding or the like. The noble metal tip 6 is the first noble metal piece of the present invention and has a circular or inverted T-shaped cross section. and is welded to the tip of the center electrode 4.

The noble metal chip 7 is a second noble metal piece of the present invention, and has a cylindrical shaft portion 71, a disk-shaped first flange portion 72, and a second flange portion 73.

The shaft portion 71 is fitted into the hole 53 and joined to the inner peripheral surface of the ceiling portion 51 .

The first flange-shaped portion 72 is formed at one end of the noble metal chip 7 protruding from the opening on one side of the hole 53, and is joined to one wall surface of the ceiling portion 51 while being locked. Conversely, the second brim-shaped portion 73 is formed at the other end side portion of the noble metal chip 7 protruding from the opening portion on the other side of the hole 53, and is
It is joined while being locked to the other wall surface of 1.

These first flange-shaped portion 72 and second flange-shaped portion 73 are deformed into a disc-shaped flange shape by supplying electricity from a power source 8 to both end portions of the round bar-shaped noble metal chip 7 and applying pressing force at the same time. formed by

A method of manufacturing a spark plug 1 for an internal combustion engine according to this embodiment will be explained based on FIGS. 1 to 6.

Before joining the outer electrode 5 to the tip of the metal shell 2 by welding or the like, a circular hole 53 is formed in the opposing portion of the outer electrode 5 opposite to the tip of the first electrode 6 as shown in FIG. A columnar noble metal chip 7 is inserted or press-fitted.

The noble metal tip 6 is made of a platinum alloy (Pt20Ir) whose main component is platinum, iridium, or an iridium alloy, and has a diameter of, for example, φ0.8, and the noble metal tip 7 is made of a platinum alloy (Pt2ONi, The outer electrode 5 is made of a Ni alloy (9ONi) containing Ni as a main component and the diameter of the hole 53 is, for example, φ0.8. Then, as shown in FIG. 4, by applying a large current to both end portions 701 and 702 of the shaft portion 71 of the noble metal tip 7 and applying pressure at the same time, resistance welding is performed, as shown in FIG. Both end portions 701.7
02 into a disc-shaped flange shape to form a first flange-shaped portion 72 and a second flange-shaped portion 73. At this time, the contact portions of the shaft portion 71 of the noble metal chip 7, the first flanged portion 72, and the second flanged portion 73 with the opposing portion of the ceiling portion 51 are melted, and the ceiling portion 51 is melted.
The noble metal chip 7 is adhered to the wall surface of the hole 53 and the inner peripheral surface of the hole 53. Moreover, since a pressing force is applied to the first flange-like portion 72 and the second flange-like portion 73, the noble metal chip 1 is
Ceiling part 5 so as to sandwich the wall surface of the opposite part of 1 from both sides.
1.

That is, the shaft portion 71 of the noble metal chip 7 is inserted or press-fitted into the hole 53 of the opposing portion of the ceiling portion 51, and the shaft portion 71 of the noble metal chip 7 is bonded to the inner peripheral surface of the opposing portion of the ceiling portion 51. The precious metal chip 7
The first flange-like portion 12 and the second flange-like portion 73 are bonded to the wall surface of the opposing portion of the ceiling portion 51 so as to sandwich the opposing portion of the ceiling portion 51 . Therefore, when the noble metal tip 7 is joined to the opposing part of the ceiling part 51 by resistance welding and used in an internal combustion engine, cracks may occur due to the difference in coefficient of thermal expansion between the outer electrode 5 and the noble metal tip 7 or due to wear and tear of the noble metal tip 7. Due to the generation of
Even if it rises from the opposing part of the first brim-shaped part γ2
The noble metal chip 7 is attached to the ceiling portion 5 by the second brim portion 73.
Since the noble metal chip 7 is caught on the opposing portion of the ceiling portion 51, it will not fall off from the opposing portion of the ceiling portion 51.

The graph in FIG. 6 shows the results of a continuous durability test (a cold/hot cycle test in which the internal combustion engine is alternately idling and the throttle opening is fully open for one minute each) of the spark plug 1 for an internal combustion engine.

As can be confirmed from this graph, the conventional product
Hr) When the test was continued, the noble metal tip was lifted up or dropped from the opposing part of the ceiling due to consumption due to oxidation, and the gap between the center electrode 4 and the outer electrode fi5 increased. However, in Example y, even if the noble metal chip 7 was lifted from the opposing portion of the ceiling portion due to wear due to oxidation, it did not fall off from the opposing portion of the ceiling portion 51. Therefore, the gap between the center electrode 4 and the outer electrode 5 does not increase much even after 500 hours (Hr) has elapsed.

Therefore, even if the precious metal chip 7 rises, the ceiling M5
Since it is possible to prevent the outer electrode 5 from falling off from the facing portion of the spark plug 1, corrosion and wear of the outer electrode 5 can be suppressed, thereby increasing the durability of the spark plug 1 for an internal combustion engine with good ignitability and breakage resistance of the outer electrode 5. can be further improved.

FIG. 7 shows a second embodiment of a spark plug for an internal combustion engine according to the present invention.

In this embodiment, the shaft portion 71 of the noble metal chip 7 having a T-shaped cross section is inserted or press-fitted into the hole 53 in the opposing portion of the ceiling portion 51, and the end portions 703.
By energizing 704 and applying pressure to the one end portion 703 to deform the one end portion 703 into a disc-shaped flange shape, the first flange portion 7 is formed on both end portions 703 and 704 of the shaft portion 71.
2 and a second flange-shaped portion 73 are formed.

8 to 11 show a third embodiment of a spark plug for an internal combustion engine according to the present invention.

As shown in FIG. 8, the T-shaped noble metal tip 7 of this embodiment has a length aImII (for example, 1.2 mm), a shaft portion 71 that has a diameter of φb (for example, φ0.8), and has a second flange shape. Part 73
The thickness of the second brim portion 73 is cWm (for example, 0.2 mm).
The diameter is φd (for example, φ11). Further, the hole 53 in the ceiling part 51 is stepped, and as shown in FIG. The diameter of the portion 56 is φC (for example, φ1.15), and the length of the large diameter portion 56 is DIIIflI.
(for example, 0.15+m).

Then, the noble metal chip 7 is inserted or press-fitted into the hole 53 of the ceiling portion 51, and as in the second embodiment, electricity is applied and pressing force is applied at the same time, so that the both end portions 70 of the shaft portion 71 are
5.706, the first flange-shaped portion 72 and the second flange-shaped portion 73 are formed. In this embodiment, since the amount of material for the noble metal tip 7 can be reduced compared to the first embodiment, the cost is lower than that of the first embodiment.

Note that the diameter of the first brim portion 72 is preferably 1 to 2 times the diameter of the tip of the center electrode 4.

12 to 14 show a fourth embodiment of a spark plug for an internal combustion engine according to the present invention.

In this embodiment, a T-shaped noble metal tip 7 is used, and as shown in FIG.
A ceiling part 51 having a hole 53 provided with 7 is used.

Then, the noble metal chip 7 is inserted or press-fitted into the hole 53 of the ceiling portion 51, and as in the second embodiment, electricity is applied and pressing force is applied at the same time, so that the both end portions 70 of the shaft portion 71 are
At 7.708, the first flange-shaped portion 72 and the second flange-shaped portion 73 are formed. In this embodiment, the amount of material for the noble metal tip 7 can be further reduced than in the second embodiment, resulting in even lower costs.

(Modification) As the material of the first noble metal piece or the second noble metal piece, metals other than those used in this embodiment may be used as long as the main component is noble metal.

The center electrode and the first noble metal piece may be fixed by electric welding as in this embodiment, or by other welding methods, fixing methods using an adhesive, or the like.

In addition to resistance welding as in this embodiment, the outer electrode and the second noble metal piece may be joined by other electric welding methods such as arc welding while applying pressure to both ends of the second noble metal piece. .

In this embodiment, a plurality of holes 54 are provided in the ceiling portion 51 of the outer electrode 5.
However, it is not necessary to provide the plurality of holes 54 in the ceiling portion 51.

[Brief explanation of drawings]

1 to 6 show a first embodiment of the invention. 1st
The figure is a sectional view showing the main parts of a spark plug for an internal combustion engine.
FIG. 2 is a perspective view showing the main parts of a spark plug for an internal combustion engine. Fig. 3 is a sectional view showing the opposing parts of the ceiling of the outer electrode, Fig. 4 is a sectional view showing the outer electrode and the noble metal tip during resistance welding, and Fig. 5 is the outer electrode and the noble metal tip at the end of resistance welding. FIG. 6 is a graph showing the results of a continuous durability test. FIG. 7 shows a second embodiment of the present invention, and is a sectional view showing an outer electrode and a noble metal tip during resistance welding. 8 to 11 show a third embodiment of the present invention. Fig. 8 is a sectional view showing the noble metal tip, Fig. 9 is a sectional view showing the opposing parts of the ceiling of the outer electrode, Fig. 10 is a sectional view showing the outer electrode and the noble metal tip during resistance welding, and Fig. 11. FIG. 3 is a cross-sectional view showing the outer electrode and the noble metal tip after resistance welding is completed. 12 to 14 show a fourth embodiment of the present invention. FIG. 12 is a sectional view showing the opposing parts of the ceiling part of the outer electrode;
FIG. 13 is a sectional view showing the outer electrode and the noble metal tip during resistance welding, and FIG. 14 is a sectional view showing the outer electrode and the noble metal tip after resistance welding. In the figure 1... Spark plug for internal combustion engine 2... Metal shell 3... Cylindrical insulator 4... Center electrode 5... Outer electrode 6... Precious metal tip (first noble metal piece) 7・・・
・Precious metal chip (second precious metal piece) 51...Ceiling part 5
2... Leg portion 53... Hole 71... Shaft portion 72.
...First brim-like part 73...Second brim-like part

Claims (1)

[Scope of Claims] 1) A cylindrical metal shell, a cylindrical insulator fixed within the metal shell, and a cylindrical insulator that is fitted into the insulator and held by the insulator, and whose tip portion is mainly made of precious metal. a center electrode to which a first precious metal piece as a component is fixed; a flat ceiling part in which a second noble metal piece, the main component of which is a noble metal, is joined by electric welding to an opposing portion facing the tip of the first noble metal piece; an outer electrode having a plurality of legs connecting the ceiling part and the metal shell, the ceiling part having a hole penetrating the opposing part, and the second precious metal piece being fitted into the hole. What is claimed is: 1. A spark plug for an internal combustion engine, characterized in that the spark plug has a shaft portion, and a flange-shaped portion provided at both ends of the shaft portion to sandwich the ceiling portion. 2) The spark plug for an internal combustion engine according to claim 1, wherein the flange-shaped portion is formed by deforming both ends of the second noble metal piece by applying current and applying pressing force at the same time.