JPH10162931A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug where an ignition part is constituted of a material excellent in workability by obstructing consumption due to oxidation or volatilization of Ir components at high temperatures although it is mainly composed of Ir. SOLUTION: A spark plug 100 includes a central electrode 3 and an insulator 2 provided outside the central electrode 3. A main metal fitting 1 is provided outside the insulator 2 in a state wherein the central. electrode 3 projects from one end of the main metal fitting 1. An earthed electrode 4 is disposed in such a manner that its one end is associated with the main metal fitting 1, and that the other end is opposed to the central electrode 3. A tip 31 or 32 is stuck on either one or both of the central electrode 3 and the earthed electrode 4 to form a spark discharge gap (g). In addition, the tip 31 or 32 is constituted of an alloy mainly containing Ir, 3 to 49. 5wt.% of Rh, and 0.5 to 12wt.% of W as well.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug used for an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, as a spark plug for an internal combustion engine such as an automobile engine, a spark plug formed by welding a Pt (platinum) alloy tip to the tip of an electrode to improve spark wear resistance has been used. However, since platinum is expensive, it has been proposed to use inexpensive Ir (iridium) as a chip material.

[0003]

In the above-mentioned plug, when the chip is made of Ir, Ir is 900 to 1000.
Since it has the property of being easily oxidized and volatilized in a high temperature region of ° C., if it is used as it is in the electrode ignition portion, there is a disadvantage that consumption by oxidation and volatilization is more problematic than spark consumption. Therefore, durability is good under low temperature conditions such as running in an urban area, but there is a problem in that durability is extremely reduced in high-speed continuous operation. On the other hand, as another problem, since Ir has poor ductility or malleability at both room temperature and high temperature, it is necessary to manufacture a chip for forming a ignited portion by processing such as forging, rolling or punching. In addition, there is a disadvantage that the material yield and the production efficiency are reduced and mass productivity is deteriorated.

[0004] For example, as one means for improving the durability of the above-mentioned chip, it is conceivable to add a suitable metal component to the alloy to suppress the consumption of Ir by oxidation and volatilization. The workability is not necessarily improved, and the workability may be further deteriorated depending on the type of the added element. Further, in order to avoid the problem of workability, it has been proposed to manufacture chips by a sintering method (for example, Japanese Patent Application Laid-Open No. 61-88479). There is a drawback that the durability is inferior to the above. As described above, a plug using an Ir-based chip, which is excellent in both the durability and the mass productivity of the chip, has not been developed yet, and is a major factor hindering the spread of the plug.

An object of the present invention is to provide a spark plug which is mainly composed of Ir, is less likely to be consumed by oxidation and volatilization of an Ir component at a high temperature, and has an ignition portion made of a material having excellent workability. To provide.

[0006]

In order to solve the above-mentioned problems, a spark plug according to the present invention comprises a center electrode, an insulator provided outside the center electrode, and one end side. A metal shell provided outside the insulator with the center electrode protruding from the insulator, a ground electrode having one end coupled to the metal shell and the other end facing the center electrode; A spark portion that is fixed to at least one of the electrode and the ground electrode to form a spark discharge gap;
9.5% by weight, and W is 0.5 to 12%.
It is characterized by being constituted by an alloy contained in the range of weight%.

The present inventor has proposed that the ignition portion forming the spark discharge gap is made of an alloy mainly containing Ir and containing Rh in the above range, so that the oxidation of the Ir component at a high temperature can be achieved.
It has been found that the wear due to volatilization is effectively suppressed and the workability of the alloy is dramatically improved by further containing W in the above range. This solves all the problems of the conventional spark plug in which the ignition portion is made of an Ir-based metal, and furthermore, its durability (particularly high speed) while using a metal mainly composed of Ir as a constituent material of the ignition portion. It is possible to realize a spark plug that is excellent in both durability during running) and mass productivity.

The ignition portion can be formed by joining a tip made of a metal having the above composition to a ground electrode and / or a center electrode by welding. In this case, the “ignition portion” in this specification refers to
It refers to a portion that is not affected by the composition change due to welding (for example, a remaining portion excluding a portion alloyed with the material of the ground electrode or the center electrode by welding).

In this case, the chip can be formed of a processed material obtained by subjecting a molten alloy obtained by mixing and melting the raw materials to a predetermined composition to a predetermined processing. Here, “processing” means a process including at least one of rolling, forging, drawing, cutting, cutting, and punching. In this case, processing such as rolling, forging, or punching can be performed by so-called hot working (or warm working) performed by raising the temperature of the alloy to a predetermined temperature. The processing temperature depends on the alloy composition, but is preferably, for example, 700 ° C. or higher.
The chip material in the spark plug of the present invention has particularly good properties for hot stamping, for example, a molten alloy is processed into a plate by hot rolling, and the plate is formed into a predetermined shape by hot stamping. If a chip is formed by punching, the chip manufacturing efficiency is significantly improved, and the chip manufacturing cost can be significantly reduced. Note that a method is also possible in which a molten alloy is worked into a linear shape or a rod shape by hot rolling or hot forging, and then cut into a predetermined length in a length direction to form a chip.

If the content of W in the alloy is less than 0.5% by weight, the effect of improving the workability of the alloy cannot be sufficiently achieved, and for example, cracks and cracks are liable to occur during the processing, and the chip is manufactured. This leads to a decrease in the material yield when performing. Further, when chips are manufactured by hot punching or the like, tools such as punching blades are liable to be worn or damaged, and the manufacturing efficiency is reduced. On the other hand, when the content exceeds 12% by weight, the workability is rather deteriorated, which also leads to a decrease in material yield and a decrease in manufacturing efficiency. Therefore, the content of Rh is preferably adjusted in the above-mentioned range, and more preferably in the range of 2 to 9% by weight. The optimum W content varies depending on the Rh content. When the Rh content is less than 18% by weight, the W content is preferably set to 1.5 to 9.5% by weight. When the content is 18 to 23% by weight, the W content is preferably 0.5 to 9.5% by weight.
When the content is 23% by weight or more, the W content is 0.5 to 1%.
The content is preferably 2% by weight.

Next, when the content of Rh in the alloy is less than 3% by weight, the effect of suppressing the oxidation and volatilization of Ir becomes insufficient, and the chip is easily consumed, so that the durability of the plug is reduced. In this case, the tip of the tip is the first place where the chip is consumed. However, if the Rh content is reduced, the tip may be consumed on the side face. In such a situation, as a result of a decrease in the current-carrying cross-sectional area of the chip for spark discharge, an electric field tends to concentrate on the tip end portion of the chip, and the consumption progresses at an accelerated rate, and the life of the plug is rapidly exhausted. It also leads to getting lost.
Therefore, it can be said that it is desirable to adjust the Rh content not only in the tip surface portion of the chip but also in a range in which wear on the side surface portion is less likely to occur. On the other hand, if the Rh content exceeds 49.5% by weight, the melting point of the alloy decreases, and the durability of the plug similarly decreases. From the above, Rh
Is preferably adjusted within the above-mentioned range, preferably from 7 to 30% by weight, more preferably from 15 to 25% by weight, and most preferably from 18 to 22% by weight.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings. A spark plug 100 as an example of the present invention shown in FIG. 1 has a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that a distal end portion 21 protrudes, and a firing portion formed at the distal end. One end is connected to the center electrode 3 provided inside the insulator 2 and the metal shell 1 by welding or the like while the other end 31 is protruded, and the other end is bent to the side. 3 is provided with a ground electrode 4 and the like arranged so as to face the distal end portion. Further, the ground electrode 4 is provided with a firing portion 32 facing the firing portion 31.
The gap between the opposing firing part 32 is the spark discharge gap g.
It has been.

The insulator 2 is made of a ceramic sintered body such as alumina or aluminum nitride, and has a hole 6 for fitting the center electrode 3 along its own axial direction. . The metal shell 1 is formed of a metal such as low-carbon steel in a cylindrical shape, forms a housing of the spark plug 100, and has a screw on its outer peripheral surface for attaching the plug 100 to an engine block (not shown). The part 7 is formed.

Next, the body portions 3a and 4a of the center electrode 3 and the ground electrode 4 are made of a Ni alloy or the like. On the other hand, the firing part 31 and the opposing firing part 32 set Rh at 3 to 4
9.5% by weight, preferably 7 to 30% by weight, more preferably 15 to 25% by weight, most preferably 18 to 22% by weight, and further contains W 0.5 to 12% by weight, preferably It is composed of an alloy containing from 2 to 9% by weight.

As shown in FIG. 2, the main body 3 of the center electrode 3
As for a, the tip side is reduced in diameter and the tip end surface is flattened, a disk-shaped chip made of an alloy composition constituting the ignition portion is superimposed thereon, and laser welding is performed along the outer edge of the joining surface. The welding portion B is formed by electron beam welding, resistance welding, or the like, and is fixed to form the ignition portion 31. Further, the opposing firing portion 32 is formed by aligning the tip with the ground electrode 4 at a position corresponding to the firing portion 31, forming a welded portion B along the outer edge of the joint surface, and fixing the same. It is formed. Note that a configuration may be employed in which one of the firing portion 31 and the facing firing portion 32 is omitted. In this case, the firing part 3
1 or opposing firing part 32 and ground electrode 4 or center electrode 3
And a spark discharge gap g is formed. For these chips, for example, each alloy component is blended so as to have the indicated composition.
A material formed by processing a molten alloy obtained by melting into a plate by hot rolling and punching the plate into a predetermined chip shape by hot punching is used. The chip may be formed by processing the alloy into a linear shape or a rod shape by hot rolling or hot forging, and then cutting the alloy into a predetermined length in the length direction.

The operation of the spark plug 100 will be described below. That is, the spark plug 100 is attached to the engine block at the screw portion 7 and used as an ignition source for the air-fuel mixture supplied to the combustion chamber.
Here, the ignition portion 31 forming the spark discharge gap g
And since the opposing ignition part 32 is made of the above-mentioned alloy, the consumption of the ignition part due to the oxidation and volatilization of Ir is suppressed, so that the spark discharge g does not expand for a long time and the plug 10
0 life can be extended. Further, by setting the alloy composition in the above-described range, the chips constituting the ignition portions 31 and 32 can be manufactured extremely efficiently by hot rolling and hot punching.

[0017]

【Example】

(Example 1) By mixing and dissolving predetermined amounts of Ir, Rh and W, Rh is contained in respective proportions of 15, 20, and 25% by weight, and W is further contained in an amount of 0 to 13% by weight (0% by weight and 0% by weight). 13% by weight was prepared in various ratios of Comparative Example), and the balance was substantially Ir. This alloy is subjected to hot rolling (at a temperature of 700 ° C. or higher) to a thickness of 0.5 mm.
It was processed into a plate material of mm. During rolling, the sample temperature was always 7
The sample was heated using a predetermined furnace for each fixed pass so as to be maintained at a temperature of 00 ° C. or higher. Next, the obtained plate material was
The temperature was maintained at 00 ° C. or higher, and in this state, a process of punching out a disk-shaped chip having a diameter of 0.7 mm and a thickness of 0.5 mm using a predetermined mold was continuously performed. Then, a sample which was able to be normally punched even when the punching was repeated 1,000 times or more was evaluated as "O", 80
"△" indicates that the chip was broken or chipped or the mold was damaged in about 0 times, and "x" was the chip that was cracked or chipped or was damaged in less than 100 times. evaluated. Table 1 shows the results.

[0018]

[Table 1]

When an alloy having a W content within the scope of the claims of the present invention is used as a chip material, it is understood that the hot stamping workability is good.

Next, of the alloys of the respective compositions, Ir-1
5% by weight Rh-9% by weight W and Ir-25% by weight Rh
Using two kinds of -11% by weight W and an Ir metal containing no Rh and W as a comparative example, this was subjected to hot rolling and punching in the same manner as described above to obtain a diameter of 0.7 mm and a thickness of 0.5 mm.
Into a disk-shaped test piece, and
After holding at 20 ° C. for 20 hours, the weight loss of each test piece was measured. The result is shown in FIG. That is, it can be seen that, since the oxidation and volatilization of Ir is suppressed in the test piece of the alloy containing Rh and W in the indicated composition, the weight loss is smaller than that of the test piece of the comparative example. This means that if you make a spark plug tip with such an alloy,
This suggests that even in a high-speed / high-load operation state in which the temperature of the plug increases, chip consumption is suppressed, and the durability of the plug is improved.

(Example 2) By mixing and dissolving predetermined amounts of Ir, Rh and W, W is 6% by weight and Rh is 0 to 0%.
An alloy containing 60% by weight in various proportions and the balance being substantially composed of Ir (Rh = 0 and 60% by weight is a comparative example) was prepared, and the same hot working as in Example 1 was performed using this. A disk-shaped chip having a diameter of 0.7 mm and a thickness of 0.5 mm was produced by rolling and punching. In addition, as a comparative example, Pt
A chip using a -13 wt% Ir molten alloy was also manufactured.
The spark plug 10 shown in FIG.
A sparking portion 31 of 0 and an opposing firing portion 32 were formed (the width of the spark discharge gap g was 1.1 mm), and a performance test of each plug was performed under the following conditions. Condition A (assuming continuous high-speed operation): 6-cylinder gasoline engine (displacement 3000
cc) with those plugs, throttle fully open,
The engine was operated continuously at an engine speed of 6000 rpm for 300 hours (center electrode temperature: about 900 ° C.), and the amount of expansion of the spark discharge gap g of the plug after the operation was measured. FIG. 4 shows the results in relation to the content of Rh in the alloy and the increase in the spark discharge gap. Condition B (assuming city driving): 4-cylinder gasoline engine (displacement 2000 cc)
The engine is operated for 1000 hours with one cycle of idling 1 minute → engine speed 3500 rpm, fully open state for 30 minutes → engine speed 2000 rpm, half open state for 20 minutes as one cycle (center electrode temperature about 780).
° C), and the amount of expansion of the spark discharge gap g of the plug after the operation was completed was measured. FIG. 5 shows the results in the relationship between the content of Rh in the alloy and the increase in the spark discharge gap.

Under the condition B, the spark discharge gap g of the plug whose alloy composition range falls within the range of the present invention is small, whereas the comparative example (Rh 60% by weight or more and Pt-Ir alloy) It can be seen that the spark discharge gap of the plug is significantly widened. Further, under the higher load condition A, the difference in the spark discharge gap increase amount between the embodiment and the comparative example is further remarkable. Further, the content range of Rh is 3 to 40% by weight.
From 7 to 30% by weight, and further from 15 to 25% by weight, the amount of increase in the gap is gradually reduced, and in particular, a chip having a Rh content of 15 to 25% by weight was used. It can be seen that the plug shows very good durability despite severe operating conditions.

(Example 3) A predetermined amount of Ir, Rh and W are blended and dissolved to obtain 6% by weight of W and 1% of Rh.
5, 18, 20, 22, and 25% by weight of each alloy were prepared, and the balance was substantially composed of Ir. An alloy was prepared as a chip material, and a plug similar to that of Example 1 was manufactured. did. The first embodiment is applied to these plugs.
The performance test was performed under the following condition C, which is more severe than the condition A. Condition C: 4-cylinder gasoline engine (displacement 16
00 cc), the throttle was fully opened, and the engine was continuously operated at an engine speed of 6250 rpm for 300 hours (center electrode temperature: about 950 ° C.). FIG.
The results are shown in the relationship between the content of Rh in the alloy and the increase in spark discharge gap.

According to the results, the content range of Rh was 18
In a plug using a chip having a content of ２２22% by weight, the gap increase amount is smaller even under the condition C which is more severe than the condition B as compared with a plug using a chip whose Rh content is out of the above range, and the better. It turns out that it shows durability.

[Brief description of the drawings]

FIG. 1 is a front partial sectional view showing a spark plug of the present invention.

FIG. 2 is an enlarged sectional view showing a main part thereof.

FIG. 3 is a graph showing the value of weight loss due to oxidation of each test piece of the example.

FIG. 4 is a graph showing the relationship between the Rh content in the alloy constituting the ignition portion and the amount of expansion of the spark discharge gap (Example 2: Condition A).

FIG. 5 is a graph showing the relationship between the Rh content in the alloy constituting the ignition portion and the amount of expansion of the spark discharge gap (Example 2: Condition B).

FIG. 6 is a graph showing the relationship between the Rh content in the alloy constituting the ignition portion and the amount of expansion of the spark discharge gap (Example 3: Condition C).

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 metal shell 2 insulator 3 center electrode 4 ground electrode 31 firing part (tip) 32 opposing firing part (tip) g spark discharge gap

Claims (6)

[Claims] 1. A center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, one end of the metal shell is coupled to the metal shell, and the other end is connected to the center electrode. A spark electrode that is fixed to at least one of the center electrode and the ground electrode to form a spark discharge gap. A spark plug characterized by comprising an alloy containing up to 49.5% by weight and further containing W in a range of 0.5 to 12% by weight. 2. An alloy constituting the ignition portion, wherein W is 2 to 2.
The spark plug according to claim 1, which is contained in a range of 9% by weight. 3. The alloy constituting the ignition part has a Rh of 7
The spark plug according to claim 1, wherein the content of the spark plug is in the range of about 30% by weight. 4. The alloy constituting the ignition portion has a Rh of 1
The spark plug according to claim 1, wherein the content of the spark plug is 5 to 25% by weight. 5. The alloy constituting the ignition portion has a Rh of 1
The spark plug according to claim 1, wherein the content of the spark plug is in a range of 8 to 22% by weight. 6. The igniter is formed by rolling and rolling a molten alloy obtained by mixing and melting a raw material so as to have a predetermined composition.
The spark plug according to any one of claims 1 to 5, wherein the spark plug is formed of a work material obtained by performing a process including at least one of forging, drawing, cutting, cutting, and punching.