JPH05159855A - Spark plug - Google Patents

Abstract

PURPOSE:To provide a spark plug whose ignitability is improved by lowering the extent of discharge voltage and decreasing a flash reducing action in a way of keeping off any oxidative volatilization and simultaneously installing some jogs on a tip. CONSTITUTION:A spark plug is provided with a center electrode 4 made up of welding a noble metal tip 5 to the tip of a cylindrical nickel alloyed base material 41, and having a good conductive metal core 42 sealed in the center. This noble metal tip 5 is made directly to contact the core 42, or approximated within 0.5mm at the most, and it is joined together as projected out of the base material, while it is made dispersing at least more than one type of a simple substance or oxide belonging to 3A and 4A groups in a periodic table as much as 0.01wt%-1.0 wt.% in a platinum material of the rest. In this connection, the noble metal tip is provided with a recess formed by means of plastic working in advance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention encapsulates a core of a good heat conductive metal in a center electrode, mounts a noble metal having excellent corrosion resistance on the tip, and forms a recess in the noble metal tip to reduce the discharge voltage. The present invention relates to a spark plug that can be used.

[0002]

2. Description of the Related Art In a spark plug for an automobile engine or the like, a center electrode has conventionally been formed by using a two-layer material in which a nickel (Ni) alloy base material and a copper (Cu) core excellent in heat conductivity are embedded. Heat dissipation from a noble metal tip made of platinum (Pt) welded to the tip of the electrode is improved. Further, in order to reduce the discharge voltage of the spark plug, unevenness is provided in the spark discharge ignition part. This unevenness has been conventionally formed by cutting, forging, or electric discharge machining the electrode surface.

[0003]

However, in the conventional spark plug, the noble metal tip, which is the ignition surface of the center electrode, is small, and in the conventional processing method, the unevenness is provided in the subsequent step, so that it cannot be formed uniformly. It was difficult and the uneven shape was likely to vary. Therefore, the effect of reducing the discharge voltage also varies due to the difference in the unevenness, making it difficult to obtain uniform performance. And, in the noble metal tip having unevenness made of Pt of the center electrode, the concentration of spark discharge is remarkable,
The temperature of the electrode rises easily, so oxidation and volatilization at high temperature,
The spark energy causes coarsening of crystal grains of the noble metal tip and intergranular cracking of the coarse particles, which accelerates the consumption of electrodes that melts and scatters the noble metal tip and shortens the life of the spark plug.

Further, a base material layer having poor heat conductivity was interposed between the welded surface of the noble metal tip and the Cu core in a thickness of 1.5 mm or more. Therefore, there is a drawback that heat received from the surface of the noble metal tip exposed in the combustion chamber is released to the rear end side of the center electrode through the Cu core, so-called heat conduction is not sufficient. The problem to be solved by the present invention is to provide a core of a good thermal conductive metal in the vicinity of the oxide-dispersed noble metal tip, reduce the temperature of the tip part to prevent oxidative volatilization, and make the tip uneven. By providing the spark plug, the discharge voltage is reduced, the extinction effect is reduced, and the ignition performance is improved.

[0005]

A spark plug according to the present invention is formed by welding a noble metal tip forming a discharge portion to a tip of a columnar nickel alloy base material without leaving a gap and using a good heat conductive metal at the center. A center electrode enclosing a core is provided. This noble metal tip is in direct contact with one end of the noble metal tip or is within 0.5 mm at most, and the other end is
Bonded so as to project from the base metal, and belong to groups 3A and 4 of the periodic table.
It is formed by dispersing at least one kind of Group A simple substance or its oxide in an amount of 0.01 wt% to 1.0 wt% in the rest of the platinum material. The noble metal tip has a recess, and the recess is previously formed by plastic working.

[0006]

[Function] By forming the unevenness on the noble metal tip of the center electrode in advance by plastic working, it becomes possible to mass-produce the noble metal tip having unevenness with little variation. In addition, since electrons are likely to collect at sharp points, the electrons are collected at the corners at both ends of the concave portion, which can cause a fire even at a low voltage, thereby lowering the discharge voltage. In addition, since unevenness forms a plurality of locations having a high discharge voltage, it is possible to suppress variations in the discharge voltage.

In order to maintain the above action, unevenness is formed.
It is necessary to make it deeper, but if you make the recess deep,
Cracks easily occur in the
0.01% to 1.0% by weight of zirconia (Zr
O₂) Or yttria (Y ₂O₃), Thoria (Th
O₂), Yttrium (Y), zirconium (Zr), etc.
Of Periodic Table 3A Group, 4A Group simple substance or oxide
When dispersed in the inside, the crystal grains are formed without coarsening of the structure.
Can be made fine and prevents chip cracking at high temperatures
can do. Also, in order to prevent electrode wear,
The metal tip is in direct contact with the core of a good heat conductive metal, or
Exposed in the combustion chamber because they are welded close together within 5 m
The high temperature from the noble metal tip is quickly increased to the center electrode and the insulator.
Conducted by the child, etc., and further diffused to the engine through the metal shell
And prevent an explosive temperature rise of the center electrode
It

[0008]

1 shows a spark plug according to a first embodiment of the present invention. This spark plug has an L
An insulator 2 with a shaft hole 21 is fitted in a tubular metal shell 1 to which a character-shaped outer electrode 11 is welded. The insulator 2 has a packing 12 that is attached to a shoulder 12 provided on the inner circumference of the metal shell 1.
3 is engaged with the seat surface 22 of the insulator 2 through the metal shell 1
It is fixed by caulking the head 14 of the. The center electrode 4 is inserted into the shaft hole 21 of the insulator 2, the front end 4A of the center electrode 4 projects from the end of the insulator 2, and the rear end flange 4B is in contact with the head of the shaft hole 21. .. Shaft hole 21
The terminal electrode 3 having the monolithic resistor 32 sandwiched between the conductive glass seals 31 is heat-sealed to the rear end portion thereof.

As shown in FIG. 2, the center electrode 4 has a cylindrical shape with a small tip, and contains 15.0% by weight of chromium (Cr) and 8.0% by weight of iron (Fe). The distance L between the base material 41 made of Ni alloy, the core 42 of a good heat conductive metal mainly containing copper (Cu) or silver (Ag) embedded in the center of the base material 41, and the distance L between the core 42 and , 0.5 mm
It consists of a noble metal tip 5 welded inside or in contact with the core 42 as shown in FIG.

The noble metal tip 5 has a cylindrical shape, and the diameter thereof is the same as that of the tip end portion 43 of the core 42 which is in contact with the rear end 51 of the noble metal tip 5 or is welded at the distance L, or is slightly smaller in diameter. .. The tip portion 52 of the noble metal tip 5 projects from the base material 41 that projects from the tip of the insulator 2. The noble metal tip 5 is welded at the joint 5A with the base material 41 over the entire circumference. In the welding at the joint 5A, if resistance welding is performed and then laser welding is performed, the welding strength can be increased and the degree of joining between the noble metal tip 5 and the base material 41 can be increased, so that the heat conduction is the best.

The noble metal tip 5 contains 99.99% by weight to 9% by weight.
9.00 wt% Pt and its alloying component 0.0
1% by weight to 1.00% by weight of Y, Zr, ZrO ₂ , Y ₂
It is composed of an oxide of a group 3A or 4A element in the periodic table such as O ₃ and ThO ₂ or an oxide. When the noble metal tip 5 is made of pure Pt, the crystal becomes coarse and grain boundary cracks of coarse particles are likely to occur due to cooling after melting by the spark energy of spark discharge, which may result in loss of the noble metal part. is there. However, as mentioned above, Pt and Y,
When a simple substance such as Zr, lanthanum (La), or thorium (Th) or an alloy containing an oxide thereof is used for the noble metal tip 5, the crystal of the noble metal tip 5 is not coarsened,
The crack generation rate from the coarse grain boundary portion due to thermal stress caused by repeated cold heat of combustion gas and fresh gas during use of the spark plug is reduced.

A second embodiment of the present invention is shown in FIG.
The noble metal tip 6 made of a simple substance or an oxide of a 3A group or 4A group element in the periodic table has a base portion 61 having the same diameter as the tip portion 43 of the core 42 of a good heat conductive metal and a small diameter, and the base material 4.
1 has a large diameter portion 62 having the same diameter as the outer circumference of the front end portion 4A and a large diameter. The base 61 is in contact with the core 42 of good heat conductive metal,
Alternatively, it is fitted within 0.5 mm and welded by laser welding with the rear end of the large-diameter portion 62 as the joint portion 6A with the front end portion 4A of the base material 41.

In the second embodiment, the large diameter portion 6 of the noble metal tip 6 is attached to the tip portion 4A of the base material 41 protruding from the insulator 2.
Since 2 is welded, the tip of the center electrode 4 can withstand environments such as high temperature, high pressure, and rapid cooling in the combustion chamber of the engine, and can withstand long-term use. Also, precious metal tip 6
Since the area of the joining portion 6A between the large diameter portion 62 and the base material 41 is large, the welding can be performed firmly and the reliability of the center electrode 4 is also increased.

A third embodiment of the present invention is shown in FIG. The noble metal tip 7 of this embodiment includes a base portion 71 having the same diameter and a small diameter as the tip portion 43 of the core 42 of a good heat conductive metal, and a large diameter portion 72 having the same diameter as the outer circumference of the tip portion 4A of the base material 41. Have. Large diameter part 72
A plurality of corners 75 are formed at both ends of the concave portion 74 by providing a cross-shaped concave portion 74 cut to the outer peripheral edge portion on the tip surface 73 thereof. Further, the rear end of the large diameter portion 72 is welded by laser welding as a joint 7A with the front end 4A of the base material 41.

The large-diameter portion 72 having the concave portion 74 is the large-diameter portion 7
Not only the corners 76 of the outer peripheral edge of the second part 2 but also a plurality of corners 75 formed by providing the cross-shaped recesses 74 cause a spark discharge, so that the extinction effect can be reduced. Further, since the corners 75 and 76 form many places where the electric field strength is high during spark discharge, variations in discharge voltage are suppressed and the discharge voltage can be lowered. This recess 74
Is formed by performing plastic working such as header working or press working in advance before welding with the base material 41.
The shape of the recess 74 of the spark plug having a low discharge voltage is stably supplied.

A fourth embodiment of the present invention is shown in FIG. The noble metal tip 8 of this embodiment is provided with a cross-shaped concave portion 84 having an outer peripheral edge portion left on the tip end surface 83 thereof.
Corners 85 having a cross shape are formed at both ends of 4. Also in this embodiment, the corner 86 of the outer peripheral edge and the corner 85 surrounding the concave portion 84 reduce the flame-extinguishing action and lower the discharge voltage.

In Table 1 shown below, in the spark plug in which the noble metal tip 7 shown in FIG. 5 is provided with the cross-shaped recess 74, the composition component of the noble metal tip 7 is changed to 2000c.
c, 6-cylinder engine, 1 minute at 5500 rpm fully open-1
A cold heat pattern test of idling for 100 minutes was performed for 100 hours. In this test, the degree of cracking of the noble metal tip 7 after the test, the degree of spark consumption of the Pt amount, and the plastic workability were evaluated. An example of the crystal grain structure after the test is shown in Fig. 7.
Shown in.

[0018]

[Table 1]

From the above results, if the amount of Y, Zr, La, Th or other simple substance or oxide mixed with Pt of the noble metal tip 7 is 0.01% by weight or less, coarsening of Pt cannot be suppressed. As a result, the crack occurrence rate becomes high. In addition, Y, Z with respect to Pt of the noble metal tip 7
When the mixing amount of r, La, Th, etc. is 1.0% by weight or more, problems such as coarsening, oxidation volatility, and spark consumption do not occur, but it becomes difficult to process the recess 74 of the tip 73. .. From the viewpoint of plastic working, it is desirable that the amount of a simple substance or an oxide mixed is 0.06% by weight to 0.3% by weight.

That is, Pt which is less likely to be oxidized and volatilized at high temperature
In addition, the secondary workability is improved by using, for the noble metal tip 7, an alloy in which one or more kinds of 3A group and 4A group elements or oxides are mixed and 0.01 wt% to 1.0 wt% is mixed. In addition, coarsening of crystal grains due to repeated high temperature and cooling during use is suppressed. In addition, iridium (Ir) having a high melting point is used as a crystal grain refining element of the noble metal tip 7.
Alternatively, even if ruthenium (Ru) or rhodium (Rh) is used, coarsening progresses, the noble metal tip 7 deteriorates, or consumption due to oxidative volatilization occurs, and an optimal noble metal tip 7 cannot be obtained.

In order to suppress the quenching action and to reduce the discharge voltage, the noble metal tip 7 is provided with the concave portion 74, but this processing makes the shape of the noble metal tip 7 complicated and easily causes cracks as shown in FIG. .. However, as described above, the noble metal tip 7 is made of Pt which is less likely to be oxidized and volatilized at high temperature.
To be formed from a simple substance or an oxide of a 3A group or 4A group element,
Moreover, since the core 42 of the good heat conductive metal is embedded in the center axis of the base material 41, heat is quickly drawn from the tip end portion 43 of the center electrode 2 and the durability of the noble metal tip 7 is improved.

In the above embodiment, the embodiment in which the noble metal tip is attached to the ignition part has been described. However, the noble metal tip may be attached to the ignition part of the outer electrode 11, and it is difficult to attach the noble metal tip to both of them. Most desirable from a perspective. Noble metal tip is 3A group or 4A as alloy material of Pt
The group may be formed of a plurality of elements instead of a simple substance, and the shape of the recess is not limited to the cross shape, and may be any shape such as a straight line or a circle that is easy to process.

[0023]

EFFECTS OF THE INVENTION The noble metal tip of the spark plug of the present invention can prevent the noble metal tip from dropping during use, and can suppress the discharge voltage at the time of spark generation to a low level, thus reliably improving ignition performance and durability. Therefore, the life of the spark plug can be extended.

[Brief description of drawings]

FIG. 1 is a sectional view of a spark plug according to a first embodiment.

FIG. 2 is a sectional view of a tip portion of the spark plug of the first embodiment.

FIG. 3 is a sectional view of a tip portion of the spark plug of the first embodiment.

FIG. 4 is a sectional view of a front end surface of a spark plug according to a second embodiment.

FIG. 5 is a sectional view of a front end surface of a spark plug according to a third embodiment.

FIG. 6 is a sectional view of a front end surface of a spark plug according to a fourth embodiment.

FIG. 7 is a structural example of crystal grains of a noble metal tip in a cold heat test.

FIG. 8 is a cross-sectional view of a tip surface of a spark plug in which a crack has occurred.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal shell 2 Insulator 3 Terminal electrode 4 Center electrode 41 Base material 42 Core of good heat conductive metal 5, 6, 7, 8 Noble metal tip 74, 84 Recess

Claims (2)

[Claims] 1. A tip of a columnar nickel alloy base material,
In a spark plug having a center electrode in which a noble metal tip forming a discharge part is welded without a gap and a core made of a good heat conductive metal is sealed in the center, the noble metal tip has one end of the core made of the good heat conductive metal. Direct contact with or close to within 0.5 mm at the most, the other end protruding from the base material and joined, 3A of the periodic table
A spark plug formed by dispersing at least one kind of Group 4A group or oxide thereof in an amount of 0.01 wt% to 1.0 wt% in the rest of the platinum material. 2. The spark plug according to claim 1, wherein the noble metal tip has a recess, and the recess is previously formed by plastic working.