JP3461670B2 - Spark plug and its manufacturing method - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a spark plug used in an internal combustion engine.

[0002]

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

[0003]

When the ignition part is made of Ir in the above-mentioned plug, Ir is 900 to 1000.
Since it has a property of being easily oxidized and volatilized in a high temperature range of ℃, if it is used as it is in the electrode ignition part, there is a drawback that the consumption by oxidation and volatilization becomes a problem rather than the spark consumption. Therefore, the durability is good under the condition of low temperature such as city driving, but there is a problem that the durability is extremely lowered in the case of high speed continuous operation.

According to the present invention, although the ignition part is mainly composed of Ir, the spark is excellent in durability even in city driving and high speed driving because the Ir component is hardly consumed by oxidation and volatilization at high temperature. To provide a plug.

[0005]

In order to solve the above-mentioned problems, the spark plug of the present invention has a central electric power source.
A pole, an insulator provided outside the center electrode thereof, and
The metal shell provided on the outside of the insulator and the metal shell
One end is joined and the other end is bent back to the side.
So that its side faces the tip of the center electrode.
Sparks that are fixed to the ground electrode and the center electrode that are placed
And a firing portion forming a discharge gap, the center electrode
7 to 25 wt% of Rh, mainly Ir, on the tip surface of
A chip made of an alloy having a composition contained in the range of
Hot-rolling a molten alloy of the above composition at a temperature of 700 ° C or higher or
After processing into a linear or rod shape by hot forging,
Stacked by cutting it into a predetermined length in the length direction
Or a molten alloy of the above composition at 700 ° C or higher
Hot rolled at a temperature to form a plate, and then
Manufactured by punching into a predetermined shape by hot stamping
Are piled up, and along the outer edge of the joint surface,
Forming a weld that extends over the tip and the center electrode
As a result, Rh is mainly contained in the range of 7 to 25% by weight.
It is characterized in that an ignition part made of an alloy having a composition contained in the enclosure is formed .

The present inventor constructs the ignition part forming the spark discharge gap from an alloy containing Ir as a main component and Rh in the above range, so that the Ir component is effectively consumed by oxidation and volatilization at high temperatures. It was found that a spark plug that is suppressed by the above, and eventually has excellent durability is realized.

The ignition part can be formed by welding a tip made of a metal having a notational composition to the ground electrode and / or the center electrode by welding. In this case, the term "firing part" used in the present specification refers to, among the joined chips,
It refers to a portion that is not affected by the composition fluctuation due to welding (for example, the remaining portion excluding the portion alloyed with the material of the ground electrode or the center electrode by welding).

When the content of Rh in the above alloy is less than 7 % by weight, the effect of suppressing the oxidation and volatilization of Ir becomes insufficient,
Since the ignition part is easily worn, the durability of the plug is reduced. In this case, the tip surface portion of the tip welded to the center electrode and / or the ground electrode is the first place where the ignition portion is consumed. However, when the Rh content is reduced, the side surface portion of the tip is also consumed. It may progress. In such a situation, the electric current cross-sectional area of the tip for spark discharge is reduced, and as a result, the electric field tends to concentrate on the tip end surface of the tip, wear is accelerated and the life of the plug is rapidly exhausted. It also leads to being lost. Therefore, it can be said that it is desirable to adjust the content of Rh in a range in which not only the tip surface portion of the chip but also the side surface portion is less likely to be consumed. In addition, the molten alloy of that composition is 700
Hot rolled at a temperature above ℃
Is punched into a predetermined shape by hot punching
Forming or forming a molten alloy by hot rolling or hot forging
After processing into a linear or rod shape by manufacturing,
To form a chip by cutting it into a predetermined length in the vertical direction
You can Ir, which is the main component of the chip material, is a single metal
Is poor in ductility or malleability, but adding Rh
The workability is improved with and, for example, by rolling or forging.
Rh is added to the plate, rod, wire, etc.
It will be easier to do compared to the case without. Specifically, rolling
Or cracks and other defects are unlikely to occur in the alloy material during forging
The chip manufacturing efficiency and material yield.
Can be improved. On the other hand, when the content of Rh is 25 % by weight or more, the melting point of the alloy is lowered and the durability of the plug is similarly lowered. From the above, the content of Rh is preferably adjusted within the above range, preferably 15 to 25% by weight, and most preferably 18 to 22% by weight.

[0009]

DETAILED 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 includes a tubular metallic shell 1, an insulator 2 fitted inside the metallic shell 1 so that a tip portion 21 projects, and an ignition portion formed at the tip. One end is joined to the center electrode 3 provided inside the insulator 2 and the metal shell 1 in a state in which 31 is projected, and the other end side is bent back to the side, and the side surface is the center electrode. The ground electrode 4 and the like are provided so as to face the tip portion of 3. In addition, the ground electrode 4 is formed with a firing portion 32 facing the firing portion 31, and these firing portions 31 and
The spark discharge gap g is the gap between the opposing firing parts 32.
It is said that.

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

Next, the main body portions 3a and 4a of the center electrode 3 and the ground electrode 4 are made of Ni alloy or the like. On the other hand, the ignition part 31 and the opposing ignition part 32 are composed of an alloy mainly containing Ir and containing Rh in the range of 3 to 50% by weight (not including 50% by weight). In addition, R in the alloy
The content of h is preferably adjusted in the range of 7 to 30% by weight, more preferably 15 to 25% by weight, and most preferably 18 to 22% by weight.

As shown in FIG. 2, the main body 3 of the center electrode 3 is formed.
In a, the tip side is reduced in diameter and the tip surface is made flat, and a disk-shaped tip made of an alloy composition that constitutes the ignition part is superposed on the tip side, and laser welding is further performed along the outer edge of the joint surface. The ignition portion 31 is formed by forming the welded portion W by electron beam welding, resistance welding or the like and fixing the welded portion W. Further, in the opposing firing portion 32, the tip is aligned with the ground electrode 4 at a position corresponding to the firing portion 31, and a welding portion W is similarly formed along the outer edge portion of the joint surface to fix the tip. It is formed. In addition, these chips are prepared by, for example, melting / melting material obtained by blending / melting each alloy component so as to have a notational composition, or alloy powder or metal simple substance component powder blended in a predetermined ratio by molding / sintering. It can be composed of the obtained sintered material.

For example, when the chip is made of a molten alloy, a predetermined chip shape is obtained by subjecting the molten alloy material to at least one of the steps of rolling, forging, drawing, cutting, cutting and punching. be able to. Here, processing such as rolling, forging, or punching can be performed by raising the temperature of the alloy to a predetermined temperature (so-called hot or warm working). The processing temperature depends on the alloy composition, but is preferably 700 ° C. or higher.

More specifically, the molten alloy is processed into a plate shape by hot rolling, and the plate material is further punched into a predetermined shape by hot punching to form chips, or the molten alloy is hot rolled. Alternatively, it is possible to employ a method in which a wire or rod is processed by hot forging and then cut into a predetermined length in the length direction to form a chip. here,
Ir, which is the main component of the chip material, is poor in ductility or malleability as a simple metal, but its workability is improved by adding Rh. It becomes easier to perform compared to the case where is not added. Specifically, defects such as cracks are less likely to occur in the alloy material during rolling or forging, which in turn can improve chip manufacturing efficiency and material yield. The workability of the alloy material becomes better as the amount of Rh added increases.

It is also possible to omit either one of the ignition part 31 and the opposing ignition part 32. In this case,
A spark discharge gap g is formed between the ignition part 31 or the opposing ignition part 32 and the ground electrode 4 or the center electrode 3.

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 thereof and is used as an ignition source for the air-fuel mixture supplied to the combustion chamber.
Here, the ignition part 31 forming the spark discharge gap g.
Also, since the opposing ignition part 32 is made of the above alloy, the consumption of the ignition part due to the oxidation and volatilization of Ir is suppressed, so that the spark discharge gap g does not expand for a long period of time, and the life of the plug 100 is reduced. Can be extended.

[0017]

【Example】

(Example 1) By mixing and dissolving predetermined amounts of Ir and Rh, an alloy containing Rh in various ratios of 0 to 60% by weight and the balance being substantially Ir (provided that Rh = 0 and 60% by weight was prepared as a comparative example, and this was hot-rolled into a plate material, and a disk-shaped chip having a diameter of 0.7 mm and a thickness of 0.5 mm was cut out from the plate material by electric discharge machining. As a comparative example, a chip using a Pt-13 wt% Ir melting alloy was also manufactured. With those chips,
While forming the ignition part 31 and the opposed ignition part 32 of the spark plug 100 shown in FIG. 1 (width of the spark discharge gap g: 1.1 mm), the performance test of each plug was performed under the following conditions. Condition A (assuming continuous high-speed operation): Attach these plugs to a 6-cylinder gasoline engine (displacement 3000cc), fully open the throttle, and continuously operate for 300 hours at an engine speed of 6000rpm (center electrode temperature of about 900 ° C). The amount of expansion of the spark discharge gap g of the plug after completion was measured. FIG. 3 shows the result in relation to the content of Rh in the alloy and the increase amount of the spark discharge gap. Condition B (assuming urban driving): Attaching these plugs to a 4-cylinder gasoline engine (displacement 2000cc), idling 1 minute → engine speed 3500 rpm, fully open state 30 minutes → engine speed 2000 rpm, half open state 20 minutes One cycle was operated for 1000 hours (center electrode temperature of about 780 ° C.), and the expansion amount of the spark discharge gap g of the plug after the operation was measured. FIG. 4 shows the result in relation to the content of Rh in the alloy and the increase amount of the spark discharge gap.

Under the condition B, the increase in spark discharge gap g is small for the plugs whose alloy composition range falls within the range of the present invention, whereas the comparative example (Rh 60 wt% or more, and Pt-Ir alloy). It can be seen that the spark discharge gap of the plug is markedly expanded. Further, under the condition A under a higher load than that, the difference in the spark discharge gap increase amount between the example and the comparative example becomes more remarkable. Further, the content range of Rh is 3 to 50% by weight.
To 7 to 30% by weight, and further to 15 to 25% by weight, the amount of increase in the gap gradually decreased, and in particular, chips having an Rh content of 15 to 25% by weight were used. It can be seen that the plug exhibits very good durability despite the severe operating conditions.

Regarding the alloy material having a Rh content of 15 to 25% by weight, cracks were less likely to occur when hot-rolled into a plate shape, as compared with an Ir simple metal material containing no Rh. .

(Example 2) A predetermined amount of Ir and Rh were mixed.
By melting, an alloy containing Rh in the proportions of 15, 18, 20, 22 and 25% by weight and the balance substantially composed of Ir was prepared. A similar plug was made. Then, a performance test was performed on these plugs under the following condition C, which is more severe than the condition A of the first embodiment. Condition C: 4-cylinder gasoline engine (displacement 1600cc) with those plugs attached, throttle fully open, engine speed 6250rp
continuous operation for 300 hours (center electrode temperature about 950
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 result in relation to the content of Rh in the alloy and the increase amount of the spark discharge gap.

According to the results, the Rh content range is 18
In a plug using a chip having a content of ˜22% by weight, the gap increase amount is small even in the condition C, which is more severe than the condition B, and is better than that in the plug using the chip having an Rh content outside the range. It can be seen that it shows durability.

[Brief description of drawings]

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

FIG. 2 is an enlarged cross-sectional view showing the main part thereof.

FIG. 3 is a graph showing the relationship between the Rh content in the alloy forming the ignition part and the expansion amount of the spark discharge gap (Example 1: Condition A).

FIG. 4 is a graph showing the relationship between the Rh content in the alloy forming the ignition part and the expansion amount of the spark discharge gap (Example 1: Condition B).

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

[Explanation of symbols]

1 metal shell 2 insulator 3 Center electrode 4 ground electrode 31 Firing part (chip) 32 Opposing ignition part (chip) g Spark discharge gap

Continuation of front page (56) Reference JP-A-7-37674 (JP, A) JP-A-4-329286 (JP, A) JP-A-7-268574 (JP, A) JP-A-7-37673 (JP , A) JP-A-7-37677 (JP, A) JP-A-6-112261 (JP, A) JP-A-9-7733 (JP, A) JP-A-10-32076 (JP, A) JP-B 61-31945 (JP, B2) European publication 702093 (EP, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01T 13 / 00-13 / 56

Claims (5)

(57) [Claims] 1. A center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, one end coupled to the metal shell, and the other end sideways. And a ground electrode arranged so that its side surface faces the tip of the center electrode, and an ignition part that is fixed to the center electrode to form a spark discharge gap. the distal end surface, the Rh mainly of Ir 15
A chip made of an alloy having a composition contained in the range of up to 25% by weight , the molten alloy having the composition is processed into a linear or rod shape by hot rolling or hot forging at a temperature of 700 ° C. or higher, Are cut to a predetermined length in the longitudinal direction and are overlapped with each other, and a welded portion extending over the tip and the center electrode is formed along the outer edge of the joint surface, whereby Rh is mainly composed of Ir. 15 to 25% by weight
A spark plug formed by forming an ignition part made of an alloy having a composition contained in the range. 2. A center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, one end coupled to the metal shell, and the other end sideways. And a ground electrode arranged so that its side surface faces the tip of the center electrode, and an ignition part that is fixed to the center electrode to form a spark discharge gap. the distal end surface, the Rh mainly of Ir 15
A chip made of an alloy having a composition contained in the range of up to 25% by weight , the molten alloy having the composition described above is processed into a plate shape by hot rolling at a temperature of 700 ° C. or higher, and the plate material is further hot stamped. 15h to 25wt with Rh mainly composed of Ir by stacking products manufactured by punching into a predetermined shape, and forming a welded portion extending over the tip and the center electrode along the outer edge of the joint surface. A spark plug formed by forming an ignition part made of an alloy having a composition contained in the range of % . 3. The alloy forming the ignition part has Rh of 1 or less.
The spark plug according to claim 1 or 2, wherein the spark plug is contained in a range of 8 to 22% by weight. 4. A center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and one end coupled to the metal shell, the other end side being the center electrode. In order to manufacture a spark plug provided with a ground electrode arranged to face with the spark plug and a sparking part fixed to the center electrode to form a spark discharge gap, 15 to 25% by weight of Rh is mainly composed of Ir. The molten alloy contained in the range of is processed into a linear or rod shape by hot rolling or hot forging at a temperature of 700 ° C. or higher, and then cut into a predetermined length in the length direction to form a chip. A method for manufacturing a spark plug, characterized in that a tip is welded to the center electrode to form the ignition part. 5. A center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and one end coupled to the metal shell, the other end side being the center electrode. In order to manufacture a spark plug provided with a ground electrode arranged to face with the spark plug and a sparking part fixed to the center electrode to form a spark discharge gap, 15 to 25% by weight of Rh is mainly composed of Ir. The molten alloy contained in the range of 1) is processed into a plate shape by hot rolling at a temperature of 700 ° C. or higher, and the plate material is punched into a predetermined shape by hot punching to form a chip. A method for manufacturing a spark plug, characterized in that the ignition part is formed by welding and joining to a spark plug.