JPH05159857A - Spark plug for gaseous fuel engine - Google Patents

Abstract

PURPOSE:To check any growth of a cohesive grain at an electrode ignition part by forming a noble metal tip with a material made dispersing an oxide of a specified element in platinum, and making the tip and a core to get closer to each other. CONSTITUTION:In a center electrode 4, a noble metal tip 5 is installed in a point 4A of a material 40 made arranging a good conductive metal core 42 in a cylindrical anticorrosion nickel alloyed base material 41. This tip 5 is made to contact the core, or they are drawn nearer within 0.5m and welded together, and this tip is formed with a material made distributing a rare earth element oxide in pure iridium or iridium. An earth electrode 1 is composed of welding the noble metal tip 6 to an ignition face of a point 1A of a compound material 10 made arranging a good conductive metal core 12 in a bar- form anticorrosion nickel alloyed base material 11. The tip 6 is composed dispersing an oxide of an element belonging to a 3A group rare earth elect or 4A group (Ti, Zr, Hf) in platinum. Suppose this material is used, the tip 6 is kept in cold and thereby any occurrence and growth of a cohesive grain can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug suitable for an engine using gas fuel.

[0002]

2. Description of the Related Art A spark plug mounted on an engine that uses a gaseous fuel such as natural gas, city gas, or LPG gas has a long life by welding a precious metal to the ignition part of the electrode in order to reduce the replacement frequency. ing. Further, since the gaseous fuel is easier to ignite than the gasoline, the spark discharge gap may be narrow. Therefore, the gap of the spark plug for a gasoline engine is 0.8 to 1.1 mm, while that of the spark plug for a gas fuel engine is about 0.3 to 0.7 mm. As a result, the spark plug for a gas fuel engine has advantages that the required voltage is low, the withstand voltage design is set low, and electrode consumption due to discharge is small.

[0003]

However, since the spark plug has a narrow spark discharge gap, the spark plug has the following problems. 1) Since a negative high voltage is usually applied to the noble metal on the side of the center electrode, ionization in gas molecules and cations having a large mass collide with the electrode. Therefore, the collision energy repeatedly microscopically melts the surface of the noble metal tip 5 to scatter the noble metal molecules and deposit them on the electrode surface. As a result, as shown in FIG. 3, the noble metal particles Q project from the discharge surface. Sparks are concentrated on the protrusions, and the melting is repeated, and the grains Q grow. 2) Since the gas used as a fuel for the noble metal on the ground electrode side is a reducing atmosphere or a corrosive atmosphere, the grain boundaries of the noble metal tip 6 become brittle as shown in FIG. 4, and grain boundary cracking easily occurs. The noble metal tip 6 is usually formed by cutting a rolled material and has a layered work structure in the rolling direction. For this reason, the corroded surface is easily peeled off along the processing structure of the noble metal tip 6 in the rolling direction, and the curling 8 easily occurs. Alternatively, the heating of the ground electrode causes a phenomenon similar to that of the center electrode (the noble metal is repeatedly melted, scattered, and deposited, and the granular noble metal projects from the discharge surface). 3) According to the above 1) or 2), a bridge is formed in the spark discharge gap, normal spark discharge does not occur, and misfire is caused. An object of the present invention is to provide a spark plug for a gas fuel engine, which can suppress the growth of protruding particles generated in the electrode ignition part by the energy of spark discharge and prevent the formation of a bridge in the spark discharge gap.

[0004]

A spark plug for a gas fuel engine according to the present invention comprises a tubular metal shell having a ground electrode welded to its tip, and an insulator having a shaft hole and fitted to the metal shell. A spark plug having a center electrode fitted to the shaft hole with its tip protruding, and forming a spark discharge gap between the center electrode tip and the ground electrode tip, the center electrode is circular. A noble metal tip is brought into contact with the tip and the core at the tip of a composite material in which a good heat conductive metal core is arranged on a base material made of a corrosion-resistant Ni alloy having a columnar shape, or 0.5 m
The precious metal tips are welded and joined together within m
The ground electrode is made of pure Ir or a material in which a rare earth element oxide is dispersed in Ir, and the ground electrode has a firing surface at the tip of a composite material in which a corrosion-resistant Ni alloy base material having a rod shape is provided with a good heat conductive metal core. A noble metal tip is welded and joined to the noble metal tip in Pt, and the noble metal tip is placed in Pt 3A group rare earth element oxide or 4A group (T
i, Zr, Hf, etc.). In the second aspect, the noble metal tip to be welded to the ignition surface of the ground electrode is welded so that the surface cut perpendicular to the parallel work structure generated in the rolled material becomes the ignition surface. In the third aspect, the core made of pure Fe or pure Ni is embedded in the center of the good heat conductive metal core of the ground electrode.

[0005]

In the present invention, P which has been conventionally used as a noble metal tip forming the ignition part of the center electrode.
The t-Ir-based alloy is changed to pure iridium (Ir) having a higher melting point or a material in which a rare earth element oxide is added to Ir to suppress grain growth caused by spark energy. Further, the good thermal conductive metal core is brought close to the noble metal tip to keep the noble metal tip at a low temperature to reduce the generation and growth of protruding particles. Furthermore, Pt, which was conventionally used for the ground electrode,
Instead of a chip made of -Ir (platinum-iridium) alloy or Pt-Ni (platinum-nickel) alloy, oxides such as zirconium (Zr) (group 4A) and yttrium (group 3A, rare earth element) are dispersed in Pt. The selected material is used.

[0006] This is because the Pt-Ir-based material generates protruding particles.
Since the additive element Ni is easily oxidized in the Pt-Ni-based material because it is easy to grow, deposition is unlikely to occur when it is melted and scattered, and the growth of protruding particles is slow but the melting point is low, so spark consumption is large. This is because the noble metal tip in which an oxide of a rare earth element or the like is dispersed in Pt has significantly less generation and growth of protruding particles.

According to the second aspect of the present invention, since the noble metal tip to be welded to the ground electrode is welded so that the cut surface perpendicular to the rolling direction (processing direction) becomes the spark discharge surface, the noble metal corroded or deteriorated. It is possible to prevent a phenomenon in which the surface of the chip is peeled off in a thin film shape and is turned down along the processing structure in the rolling direction. According to the configuration of claim 3, the core of the ground electrode is provided with a pure iron (Fe) or pure Ni core, and the core has a thermal expansion larger than that of the base material. It is possible to prevent the ground electrode from being deformed with time.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a spark plug 1 according to the present invention.
00, the insulator 3 with a shaft hole 31 is fitted inside a cylindrical metallic shell 2 having a ground electrode 1 welded to the front end surface,
The center electrode 4 is fitted into the shaft hole 31 with the tip 4A protruding. In this spark plug 100, the tip portion 4A of the center electrode and the tip portion 1A of the ground electrode 1 serve as an ignition portion that forms a spark discharge gap SG.

The ground electrode 1 is made of a Ni alloy containing 15.0% by weight of chromium (Cr) and 8.0% by weight of Fe, and is made of a corrosion-resistant Ni alloy base material 11 having a rectangular cross section.
The composite material 10 having the metal core 12 with good heat conductivity is bent into a substantially L shape, and the base portion 1B is welded to the tip surface of the metal shell 2.

The center electrode 4 contains 15.0% by weight of Cr,
A cylindrical base material 41 having a diameter of 2.5 mm, which is made of a Ni alloy containing 8.0% by weight of Fe and has a small tip portion 4A (diameter of 1.0 mm), and an axial center portion of the base material 41. A composite material 40 composed of a core 42 made of a good heat conductive metal and having a diameter of 1.3 mm and mainly made of copper (Cu) or silver (Ag) embedded concentrically in the core, and the center of the tip surface of the composite material 40. Hole 4
3 and a cylindrical noble metal tip 5 in which a base 51 is embedded and welded.

The spark discharge gap SG is formed between the tip of the tip 5 and the ignition surface 13, which is the side surface of the center electrode of the tip 1A. The size of the gap SG is set in the range of 0.3 to 0.7 mm depending on the type of fuel gas. The ignition surface 13 has a diameter of 0.7 mm and a thickness of 0.1.
A 5 mm disc-shaped noble metal tip 6 is welded. The noble metal tip 6 is formed by dispersing 5.0 to 15.0% by weight of rare earth element oxides of the 3A group or oxides of elements belonging to the 4A group (Ti, Zr, Hf, etc.) in Pt.

The noble metal tip 6 is formed by punching a rolled noble metal plate into a predetermined shape. At this time, if the ignition surface 13 is the same as the rolling direction, the internal structure of the noble metal plate becomes layered, and the noble metal plate corroded or deteriorated by the spark discharge is likely to be peeled into a thin layer. When this delamination occurs, a bridge is formed in the narrow spark discharge gap SG, which prevents normal spark discharge from occurring and causes a misfire. In order to prevent this, the ignition surface 13 is preferably a surface cut perpendicularly to the rolling direction, and can be obtained by cutting a wire drawn in the longitudinal direction to a predetermined size.

The composite material 40 has a tip 4A having a diameter of 1.0 m.
The chip 5 is formed to have a small diameter of m to 1.8 mm, and the chip 5 has a diameter of 0.3 mm to 1.2 mm protruding by 0.3 mm or more. The chip 5 has a mating surface 52 with the base material 41.
Is welded over the entire circumference, and the tip 5 and the core 4 are
2 are in contact with each other, or are arranged close to each other so that the distance L between them is within 0.5 mm.

Chip 5 is made of Ir powder 85.0% by volume.
When yttria is rare-earth element oxide (Y ₂ 0 ₃₎
15.0% by volume of the powder of (1) is sintered and has a cylindrical shape. The amount of yttria added must be 5.0 to 15.0% by volume.
Around 0.0% by volume is the most desirable. In addition to yttria, other rare earth element oxides such as thoria (ThO ₂ ) and lanthanum oxide (La ₂ O ₃ ) may be used, and oxides of elements belonging to Group 4A (Ti, Zr, Hf, etc.) of the periodic table. It is also possible to use. Furthermore, the chip 5 may be made of pure Ir.

The tip 5 is provided with a hole 43 reaching the tip surface of the core 42 at the center of the tip surface of the composite material 40, and the column-shaped tip 5 is fitted into the hole 43 with the axes aligned and the fitting surface. 52 is laser beam welded or electron beam welded. At this time, the chip 5 and the base material 41 are eutectic and strongly welded. In this example, the tip 5 before welding
And the size of the hole 43 are such that the tip 5 has a diameter of 0.65.
It is a cylinder with a length of 1.0 mm and a hole 43 with a diameter of 0.
The depth is 7 mm and the depth is 0.5 mm. Chip 5
Undergoes thermal stress due to the difference in thermal expansion between the base material 41 and the core 42 during use (at high temperature). Therefore, it is desirable that the welding be performed along the entire circumference of the fitting surface 52 and deep as described above.

FIG. 2 shows a second embodiment. In this embodiment, a pure Fe or pure Ni core 73 is provided at the center of the core 72 of the ground electrode 7. The ground electrode 1 formed by bending the composite material 10 in which the core 12 is arranged in the base material 11 has a larger thermal expansion than the base material 11 which is the outer cover, and therefore is subjected to repeated cold heat due to the difference in thermal expansion between the two. The radius of curvature of the bent portion gradually increases, and the so-called ground electrode is likely to rise. As in this embodiment, by using the composite material 70 in which the center core 73 is provided at the axial center of the core 72 of the base material 74, the deformation due to repeated cold and heat of the ground electrode 7 is reduced without impairing heat conduction. it can. The reason why pure Fe or pure Ni is used for the core 73 is to prevent this because the thermal conductivity decreases when alloyed.

In the present invention, it is necessary that the tip 5 and the tip of the core 42 are in contact with each other or that the distance L between them is within 0.5 mm. This distance L is
1.5 mm for the center electrode where the tip is resistance welded
It is set above. However, Ni which is the base material 41
The alloy has a relatively low thermal conductivity, which prevents the core 42 from conducting heat. As in this embodiment, when in contact with or in close proximity, the temperature of the tip 5 should be kept low by several tens of degrees Celsius to 100 degrees Celsius during high load and high speed operation of the engine, compared to when the distance L is 1.0 mm. You can

Next, in the structure of the spark plug shown in FIG. 2, the material shown in FIG.
FIG. 5 shows the result of a 200-hour durability test performed on a city gas engine with a cylinder and a rated output of 3000 ps / 1000 rpm. Test result, No. 5 (Ir100
%) And No. The chip material of 6 (Ir-2.5% Y ₂ O ₃ ) for the center electrode is good because the crystal grains are not coarsened and the electrode wear is small. In addition, No. Ir-2.5 at 7
% Even if a Y ₂ O ₃ material is used, the distance L between the chip 5 and the core 42
If the value is 1.0 mm, the electrode will be consumed more.

FIG. 6 shows the results of a durability test conducted on the ground electrode material under the same conditions as in FIG. Test result, N
o. 13 (Pt-0.3ZrO ₂ ) having a work structure in a direction perpendicular to the discharge surface is good without cracking or turning over. In addition, No. 14 (Ir-2.5% Y ₂ O ₃ ) is also good, but there is a problem in workability due to the use of a laser for welding. Pt-based alloys such as 13 are excellent in mass productivity because resistance welding can be used.

[Brief description of drawings]

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

FIG. 2 is a perspective view of a spark plug according to a second embodiment of the present invention.

FIG. 3 is an enlarged view of a main part of a conventional spark plug.

FIG. 4 is an enlarged view of a main part of a conventional spark plug.

FIG. 5 shows a result of a durability test of a center electrode.

FIG. 6 shows a result of a durability test of a ground electrode.

[Explanation of symbols]

 1, 7 Ground electrode 2 Metal shell 3 Insulator 4 Center electrode 5, 6 Noble metal tip 1A, 4A Tip 10 Composite material 11 Ground electrode base material 12 Good heat conductive metal core 40 Composite material 41 Center electrode base material 42 Good heat Conductive metal core

Claims (3)

[Claims] 1. A tubular metal shell having a ground electrode welded to its tip, an insulator having a shaft hole and fitted in the metal shell, and a metal shell fitted with the tip portion projecting into the shaft hole. In a spark plug that has a center electrode and forms a spark discharge gap between the tip of the center electrode and the tip of the ground electrode, the center electrode has a columnar shape and has good thermal conductivity in a corrosion-resistant Ni alloy base material. The noble metal tip is brought into contact with the tip and the core or welded to each other by welding within 0.5 mm to the tip of the composite material having the metal core.
It is made of a material in which a rare earth element oxide is dispersed in r or Ir, and the ground electrode is on the ignition surface of the tip of a composite material in which a rod-shaped corrosion-resistant Ni alloy base material and a good thermal conductive metal core are arranged. Noble metal chips are welded and joined to each other, and the noble metal chips are made of Pt containing 3A group rare earth element oxide or 4A group (Ti, Zr, H
A spark plug for a gas fuel engine, which is formed of a material in which an oxide of an element belonging to (f) or the like is dispersed. 2. The noble metal tip according to claim 1, which is welded to the ignition surface of the ground electrode, is welded so that the surface cut perpendicular to the parallel work structure generated in the rolled material becomes the ignition surface. Spark plug for gas fuel engine. 3. The spark plug for a gas fuel engine according to claim 1 or 2, wherein a core made of pure Fe or pure Ni is embedded in the center of the good heat conductive metal core of the ground electrode.