JP3226294B2 - 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 an improvement in the durability of a spark plug in which a platinum tip is welded to an outer electrode.

[0002]

2. Description of the Related Art In a gasoline engine such as an automobile engine, an operation with a lean air-fuel mixture for purifying exhaust gas and improving fuel efficiency is aimed at, and an outer electrode of a spark plug tends to be exposed to a higher temperature due to an increase in combustion temperature. is there. In addition, the demand for spark plugs that can travel 100,000 km or more without replacement requires not only the tip of the center electrode, but also the surface of the tip of the outer electrode to improve the durability of the spark plug. A platinum spark plug in which a Pt alloy tip (referred to as a platinum tip) is welded has been proposed. Further, composite outer electrodes in which a Cu core is passed through a Ni alloy are known.

[0003]

However, since the outer electrode is more affected by the high temperature of the combustion chamber than the center electrode, peeling occurs at the welding portion between the platinum chip and the base material of the outer electrode. Easy to occur. Particularly, in the protruding spark plug, since the ignition portion protrudes into the combustion chamber, the electrode tip is exposed to a high temperature, and the degree of cooling is high by directly contacting the new air-fuel mixture flowing during the suction stroke. For this reason,
When a Ni-based alloy (containing 10 to 20% by weight of Cr to prevent peeling due to thermal stress) commonly used as an outer electrode base material and a platinum tip are directly welded, the thermal stress at the welded portion is reduced to a normal spark. It is larger than a plug, and the platinum chip is easily peeled off. An object of the present invention is to provide a spark plug that can improve the heat stress resistance of a welded portion between a base material of an outer electrode and a platinum chip and can prevent peeling of the platinum chip for a long time.

[0004]

The spark plug according to the present invention has an outer electrode composed of a composite base in which a highly heat conductive metal core is covered with a base material made of a Ni alloy containing 10 to 20% by weight of Cr. A spark plug including an axially long outer electrode welded so that a Pt alloy tip that forms an air discharge gap with a center electrode is not in contact with the good heat conductive metal core. , Of the outer electrodes
The shortest distance in the axial direction between the welding surface of the Pt alloy tip and the good heat conductive metal core was set to 0 to 2 mm.

[0005]

In the present invention, the shortest distance in the axial direction between the welding surface of the outer electrode Pt alloy tip and the good heat conductive metal core is set to 0 to 2 mm. The heat at the tip of the metal member is smoothly transmitted to the metal shell by the core material. For this reason, a rise in the temperature of the outer electrode tip is suppressed, the thermal stress generated between the platinum tip and the outer electrode base material is small, the oxidation resistance of the welded portion is improved, and the occurrence of peeling can be prevented. If the welded part of the platinum tip and the core material overlap, the core material is softened at the time of welding the platinum tip and the tip of the outer electrode is easily deformed. It was 2 mm.

[0006]

FIG. 1 shows a spark plug according to the present invention, in which an insulator 3 having a shaft hole 31 is fitted into a cylindrical metal shell 2 to which a base end of an L-shaped outer electrode 1 is welded to a distal end surface. The shaft 4 is provided through the shaft hole 31. The center shaft 4 has a center electrode 5 at the front end, a terminal 41 to which the high-voltage cord of the ignition circuit is connected at the rear end, and an electric resistance glass seal 42 at the middle. A front end surface 5A of the center electrode 5;
Between the opposing surface 1A of the tip of the outer electrode 1 and
It is an air discharge gap. In this spark plug, the tip surface 5A of the center electrode 5 is 1.5 m from the tip of the insulator 3.
and 15 mm from the inner wall of the combustion chamber when inserted into the engine.

The outer electrode 1 is welded to a base material 11 made of a Ni alloy containing 10 to 20% by weight of Cr and a composite base 10 made of a metal core 12 having good heat conductivity, and to the facing surface 1A at the tip of the base 10. And a platinum chip 6 formed.
The oxidation resistance of the base material 11, which is the outer skin, increases as the Cr content increases. However, the hardness increases and the thermal conductivity decreases, so the upper limit of the content is set to 20% by weight. Also C
If the content of r is less than 10% by weight, the oxidation resistance decreases, so the lower limit was set as described above. The core 12 is C
Although u, Ag, or alloys thereof can be used, the core 12 is used to prevent the outer electrode 1 from rising due to the thermal cycle and to improve the weldability with the metal shell 2.
It is desirable to arrange a core material made of pure Ni or pure Fe at the center of the composite base 10 and make the composite base 10 have a three-layer structure. As the platinum chip 6, a platinum alloy containing 20% by weight of Ir can be suitably used.

The relationship between the tip of the core 12 and the welding position (welding surface) of the platinum chip 6 is as follows.
2 is set so that the shortest distance L in the axial direction is 0 to 2 mm. As described above, the base material 11 made of a Ni alloy containing 10 to 20% by weight of Cr is excellent in oxidation resistance and high-temperature strength as compared with a Ni alloy containing 90% by weight or more of Ni usually used for an outer electrode. However, the thermal conductivity is low. For this reason, in the present invention, the tip of the core 12 is extended to within 2 mm from the welding position of the platinum tip 6 to compensate for the insufficient heat conduction of the base material 11. As a result, it is possible to prevent the temperature of the tip of the outer electrode 1 from becoming excessively high, thereby preventing an increase in thermal stress.
The peeling of the platinum chip 6 can be prevented. The reason that the lower limit of the distance L was set to 0 and the state where the tip of the core 12 and the welding position of the platinum tip 6 overlapped was excluded is that the platinum tip 6 has the outer electrode material formed in a straight rod shape on the tip end surface of the metal shell 2. After welding, the insulator 3 having the central shaft 4 incorporated in the metal shell 2 in this state is assembled, and then welded by electric resistance welding.
Thereafter, the outer electrode 1 is bent into an L shape. Therefore, when the welding position overlaps the core 12, Cu or Ag as the core material is softened at the time of welding the platinum chip 6, and buckling deformation occurs due to the pressure of resistance welding.

The center electrode 5 comprises a Cu core 51 and the Cu core 5
1 and a composite base 50 composed of a Ni alloy base material 52 containing 90% by weight or more of Ni and containing 20 to 25% by weight of Cr, which is excellent in oxidation resistance and high-temperature strength, which is resistance-welded to the tip end surface thereof. A middle layer 53 made of a Ni alloy;
And a platinum tip 7 which is resistance-welded to the Pt. The platinum tip 7 includes a large-diameter portion 71 welded to the intermediate layer 53 and a tip-end small-diameter portion 72 that forms an air discharge gap between the platinum tip 6 welded to the outer electrode 1. The outer shapes of the intermediate layer 53 and the platinum chip 7 are preferably formed after resistance welding in order to prevent deformation due to softening during resistance welding. The center electrode 5 does not have to be a protruding spark plug that protrudes into the combustion chamber.

Next, durability data will be shown together with Examples. In FIG. 3, in a four-cylinder, 2000 cc, four-cycle engine, in a cooling / heating cycle operation in which idling and full opening are repeated, the distance L between the tip of the core 12 and the welding position of the platinum tip 6 and the base metal 11 when the spark plug is loaded. An experimental result of the relationship between the progress of corrosion of the welded portion and the platinum tip 6 is shown. As a result, when the outer electrode 1 does not include the core 12 having thermal conductivity, or when the distance L is 5 mm and 3 mm in a three-layer structure having the center material on the core 12, rapid corrosion progresses at the joint. I do. In the case of a two-layer structure having no center material at the center of the core 12, when the distance L is set to 0 mm, the outer electrode 1 is slightly corroded but slightly rises and a phenomenon occurs. For this reason, the distance L between the tip of the core 12 and the welding position of the platinum tip 6 is desirably 0 mm to 2 mm.

[Brief description of the drawings]

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

FIG. 2 is an enlarged sectional view of an outer electrode.

FIG. 3 is a graph showing data of a durability test of the spark plug of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Outer electrode 2 Metal shell 3 Insulator 4 Center shaft 5 Center electrode 6 Platinum chip 7 Platinum chip 11 Base material 12 core

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-60-41785 (JP, A) JP-A-61-45584 (JP, A) JP-A-63-55880 (JP, A) JP-A-1- 100887 (JP, A) JP 48-15531 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01T 13/00-21/06

Claims (1)

(57) [Claims] 1. A good heat conductive metal core is added in an amount of 10 to 20% by weight.
Composite base covered with a base material made of Ni alloy containing Cr
Together constituted by aerial discharge gap between the center electrode
Pt alloy tip to form a can, and the good heat conductive metal core
With axially long outer electrodes welded against each other
A spark plug, wherein, of the outer electrode, a welding surface of the Pt alloy tip and the good heat conductive metal core
The shortest distance in the axis direction is set to 0~2mm between
Spark plug that is.