JP2001284013A - Grounded electrode and spark plug to use this spark plug and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable to prevent exposure of core materials after welding at a low cost in a manufacturing method of a grounded electrode for a spark plug having a structure in which core materials are enclosed in coating materials. SOLUTION: In the coating materials 11 made of a metal superior in corrosion resistance and oxidation resistance of Ni alloy or the like, a compound material 13 in which core materials are enclosed being made of a metal superior in thermal conductivity of Cu, Cu alloy or a compound of Cu and Ni or the like are cut off into an appointed length, and in a cut-off end 14a of a cut compound 14, the cross-sectional area is made smaller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grounding structure having a structure in which a core material made of a metal having better heat conductivity than a coating material is enclosed inside a coating material made of a metal having excellent corrosion resistance and oxidation resistance. The present invention relates to an electrode, a spark plug using the ground electrode, and a method of manufacturing the same, and is applied to, for example, a spark plug for an internal combustion engine used in an automobile, cogeneration, a gas pressure pump, and the like.

[0002]

2. Description of the Related Art When a spark plug is used in an environment having a severe thermal load, the temperature of a ground electrode rises and exceeds a heat-resistant temperature. Therefore, in order to improve the heat dissipation of the ground electrode and reduce the electrode temperature, Cu or a Cu alloy or a composite of Cu and Ni is coated in a coating material made of a metal having excellent corrosion resistance and oxidation resistance such as a Ni alloy. There has been proposed a ground electrode for a spark plug having a structure in which a core material made of a metal having excellent heat conductivity such as that described above is enclosed.

[0003]

However, in such a ground electrode, a metal such as Cu having excellent thermal conductivity (thermally conductive metal) is inferior in corrosion resistance. If the core material made of a thermally conductive metal is exposed, oxidative corrosion proceeds during use in a combustion chamber of an internal combustion engine. Therefore, there is a danger that the ground electrode will fall off the housing.

As means for avoiding this problem, Japanese Patent Laid-Open No.
A production method described in JP-A-320176 has been proposed. This is to seal the core material before welding the composite body including the core material in the covering material to the housing to prevent the core material from being exposed after welding. However, in this manufacturing method, in order to completely seal the core material, bending the opening edge of the coating material using a molding die, etc.
The process is complicated and the cost is very high.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a spark plug having a ground electrode having a structure in which a core material is sealed in a coating material, so that exposure of the core material after welding can be prevented at low cost. I do.

[0006]

First, the invention according to claim 1 relates to a ground electrode for a spark plug, and a core material (12) is covered with a covering material (11) at one end (11b).
The cross-sectional area on the other end (14a) side is reduced toward the other end.

The other end (14a) of the spark plug ground electrode (14) is welded to the mating member (2) of the spark plug. At this time, since the cross-sectional area of the other end is smaller toward the other end, even if the core material (12) is exposed from the coating material (11) at the end face of the other end, it is melted. At the time of joining, the coating material is bent toward the core material side at the other end and the core material is involved, so that finally the joining surface (2a)
Are joined by the covering material over the entire circumference, and the core material is not exposed. As described above, if the ground electrode for a spark plug of the present invention is used, the step of sealing the core material, which has been conventionally required, becomes unnecessary, and the exposure of the core material after welding can be prevented at low cost.

[0008] The invention according to claims 2 to 4 is:
The present invention relates to a method for manufacturing a ground electrode for a spark plug, comprising cutting a composite (13) in which a core material (12) is sealed in a covering material (11) into a predetermined length, and cutting the composite (1).
4) The end (14a) on the cutting side in (4) is characterized in that the cross-sectional area decreases toward the tip of the end.

According to this manufacturing method, the cut composite (14) serves as a spark plug ground electrode, and the cut end (14a) of the composite is welded to the mating member (2) of the spark plug. Then, for the same reason as in the first aspect of the present invention, the step of sealing the core material, which has been conventionally required, becomes unnecessary, and the exposure of the core material after welding can be prevented at low cost.

[0010] The cut end (14a) of the cut composite (14) may be as follows.
It can be tapered. When this tapered shape is adopted, if the taper angle θ at the end portion (14a) is 15 ° or more as in the invention of claim 4, the welding strength is reliably ensured even if the welding displacement is considered. Yes, it is.

The invention according to claims 5 and 6 relates to a spark plug, in which one end (10b) faces the center electrode (4) and a discharge gap (5) and faces the other end (10a). Has a ground electrode (10) welded to the housing (2), the ground electrode having a core material (12) sealed in a coating material (11). And an end portion of the covering material is wound around the core material at a welding portion between the covering material and the housing.

[0012] The structure for winding the ground electrode in the spark plug of the present invention can be appropriately formed by applying the spark plug ground electrode of the first aspect, and the exposure of the core material after welding can be prevented at low cost. A spark plug can be provided. Here, as in the invention of claim 6,
If the winding length (t) of the end of the coating material (11) toward the core material (12) side is 0.1 mm or more, the welding strength can be reliably ensured even if the welding displacement is taken into account. preferable.

[0013] The invention according to claims 7 to 10 relates to a method for manufacturing a spark plug, which is a rod-like material in which a core material (12) is sealed in a covering material (11). The core material is embedded in the covering material at the end face of one end (11b), and the cross-sectional area of the other end (14a) becomes smaller toward the other end.
4) is prepared, and the other end of the material body is welded to the housing (2).

According to the present manufacturing method, for the same reason as in the first aspect of the present invention, the step of sealing the core material which has been required conventionally becomes unnecessary, and the exposure of the core material after welding can be prevented at low cost.

Note that the reference numerals in parentheses of the above means are examples showing the correspondence with specific means described in the embodiments described later.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention. The sectional view shown in FIG. 1 shows a state in which a ground electrode 10 for a spark plug according to the present embodiment is welded to an end surface 2a of a cylindrical housing (mounting fitting) 2 made of low carbon steel or the like in the spark plug 1. Things.

An insulator 3 is fixed in the housing 2, and a center electrode 4 is fixed to the insulator 3 so as to expose a tip end thereof. Here, the insulator 3 is made of, for example, alumina ceramic (Al ₂ O ₃ ), and the center electrode 4 is made of a metal material having excellent heat conductivity such as Cu, for example, and a heat-resistant material such as Ni-based alloy as the outer material. It can be made of a metal material having excellent resistance and corrosion resistance.

The ground electrode 10 has a rod shape and has one end 10.
The b side faces the center electrode 4 held by the insulator 3 with a discharge gap 5 therebetween, and the middle part is bent, and the other end 10a is bent.
Is fixed to the end face 2a of the housing 2 by resistance welding. The ground electrode 10 has a structure in which a core material 12 made of a metal having excellent thermal conductivity such as Cu or Cu alloy is enclosed in a coating material 11 made of a metal having excellent corrosion resistance and oxidation resistance such as a Ni alloy. .

Next, a method of manufacturing the spark plug 1 will be described with reference to FIGS. First, FIG.
(A) As shown as a cross-sectional shape, a cold-forged core material 1 having a large diameter head 12a and a small diameter rod portion 12b.
2 and an open end 1 as shown in FIG.
A cold-forged cup-shaped covering material 11 having 1a and a closed end 11b is prepared.

Next, as shown in FIG. 2C, the rod portion 12b of the core material 12 is inserted from the opening end 11a side of the coating material 11, and the pressure is applied from the head portion 12a of the core material 12 or the like. The covering material 11 and the core material 12 are integrated (integration step).

Next, as shown in FIG. 2 (d) as a cross-sectional shape, the integrated covering material 11 and core material 12 are extruded using a molding tool (not shown) to form the shape of the ground electrode 10 ( However, it is not bent as shown in FIG. 1 and has a straight rod shape). FIG. 2 (e) is the same as FIG.
FIG. 4D is a view taken in the direction of the arrow A. In this example, the ground electrode 10 has a quadrangular prism shape (a cross-sectional size is, for example, 1.6 mm × 2.8 m).
m). This extrusion process (composite formation process)
The rod-shaped member formed by
Corresponds to the complex 13 in which.

Next, as shown as a sectional shape in FIG. 3A, the composite 13 is cut into a predetermined length by a cutter (not shown) or the like. In addition, in FIG. 3, (b) is a view as viewed from an arrow B in (a), and (c) is a view as viewed from an arrow C in (a). At this time, of the two cut composites 13, the one on the closed end 11 b side of the covering material 11 is the raw material 14 of the ground electrode 10.

Further, by applying pressure using a jig (not shown), as shown in FIG. 3 (b), the cut end of the ground electrode material body (cut composite) 14 is cut. The end portion 14a is tapered so that the cross-sectional area decreases toward the tip (cutting and tapering end forming step). The material body 14 thus completed corresponds to the spark plug ground electrode 14 according to the present invention.

In this material body 14, a core material 12 is embedded in the covering material 11 at one end (closed end) 11b, and a core material 12 is embedded at the other end (cut end) 14a. It is exposed from the coating material 11 and has a shape in which the cross-sectional area on the cut end 14a side decreases toward the tip of the cut end 14a.

Next, the tapered cut end (corresponding to the other end 10a of the ground electrode 10) 14a of the material body 14 is resistance-welded to the end face 2a of the housing (partner member) 2 (welding step). Thereafter, the ground electrode 10 attached to the housing 2 is formed in a shape as shown in FIG.

Here, FIG. 4 is a schematic sectional view for explaining the operation of the welding step in the above manufacturing method. According to the above manufacturing method, the ground electrode material (cut composite) 14
The cutting end 14a is tapered as described above, and the cutting end 14a is welded to the end face 2a of the housing 2.

As a result, as shown in FIG. 4, when the cut end portion 14a is melted and joined, the outer coating material 11 is bent toward the inner core material 12 at the cut end portion 14a, and the core material 12 is bent. In the final step, the material body 14 is formed over the entire periphery of the end face 2a of the housing 2 which is the joining surface.
1 joined. For this reason, before welding, the core 12 is not exposed to the outside after welding, whether or not the core 12 is exposed at the tip end surface of the cut end portion 14a.

The thickness of the coating material 11 is preferably at least 0.3 mm in consideration of spark consumption and oxidation consumption. Also, as the thickness of the coating material 11 is larger, the exposure of the core material 12 at the time of welding can be prevented, but if it is too thick, the volume of the core material 12 relatively decreases, and the effect of reducing the electrode temperature is reduced. Therefore, the thickness of the coating material 11 is preferably 0.5 mm or less. From these, the thickness of the coating material 11 is 0.3 to 0.5 in consideration of manufacturing variations.
mm is a preferred range.

Next, an example in which the taper angle of the cut end portion 14a of the material body 14 was examined when the covering material 11 was made of a Ni-based alloy and the core material 12 was made of Cu, which is a good heat conductive material, in the material body 14 Is shown. In addition, the thickness of the coating material 11 in the material body 14 was 0.3 mm, which is the lower limit value, as the strictest value for preventing the exposure of the core material 12 in the above preferred range. Further, as a comparative example, a case where the cut end portion 14a of the material body 14 had a flat shape without being tapered was also examined.

First, in the comparative example, welding is performed as shown in FIG. 5A. However, due to manufacturing, as shown in FIG. is there. This deflection F occurs in a width of about 0.2 mm at the maximum in manufacturing. When the deflection F occurs, not only the covering material 11 but also the core material 12 is protruded from the end face (joining face) 2a of the housing 2 and welded, that is, the joining is performed by the covering material 11 over the entire circumference of the joining face 2a. It has not been shaped.

When the unnecessary portion (weld burr) K1 of the protruding portion is removed, as shown in FIG. 5C, the core material 12 is exposed, and the ground electrode drops due to the oxidative corrosion as described above. There is a danger. In this regard, according to the present embodiment, as described with reference to FIG. 4, the core material 12 does not protrude outside the end surface 2 a of the housing 2 at the joint due to the effect of the tapered shape. Is removed, the core material 12 is not exposed.

In the present study, the taper angle θ of the cut end (weld side end) 14a of the material body 14 is considered in consideration of the occurrence of such “deflection” and the exposure of the core material accompanying the removal of welding burrs. The relationship between the weldability and weldability was studied.

Here, as shown in FIG. 6, the taper angle θ is the angle of the tapered portion that widens with respect to the axial direction when viewed in the axial section of the material body 14. After cutting to a flat surface, various taper angles θ were produced by adjusting the angles by applying a load from both sides of the cut end as shown by the outlined arrows in the figure. In the case where the cut end portion 14a has the above tapered tapered shape, if the tapered portion remains after welding, the cross-sectional area of the joined portion becomes small and the electrode strength is reduced. 1.0mm)
The length was as follows.

[0034] The weldability was evaluated by a commonly used tensile test. A tensile test was performed while holding the tip of the housing 2 and the ground electrode 10 to evaluate the breaking strength and the location of the break. As a result, if the entire periphery of the joint surface is not completely joined by the covering material 11, the tensile strength is lower than the strength of the ground electrode itself (base metal strength), and the broken portion is also located at the interface between the housing 2 and the ground electrode 10. And it was confirmed that weldability was not ensured.

FIG. 7 shows various taper angles θ (unit: °) and a welding strength (unit: N) as the above-mentioned tensile strength when the deflection between the housing and the ground electrode is 0.2 mm. 6 is a graph showing the relationship of. As can be seen from FIG. 7, when the taper angle θ is 15 ° or more, the welding strength can be reliably ensured even if the deflection is taken into consideration, which is preferable.
This is because when the taper angle θ is less than 15 °, the material 14
This is because the cut end portion 14a becomes close to a flat shape as in the above comparative example, and the entire circumference joining by the covering material 11 on the joining surface 2a is not achieved, and the core material 12 is easily exposed after the removal of welding burrs. .

As described above, according to the present embodiment, in the method of manufacturing a ground electrode for a spark plug having a structure in which a core material is enclosed in a covering material, a conventionally required core material for completely sealing the core material is provided. No process is required. And by devising the step of cutting the composite 13, even if the core material 12 is exposed at the cut end portion 14 a before welding, or even if there is deflection, the core material 12 after welding is removed. Exposure can be prevented at low cost, and the weldability of the ground electrode 10 can be ensured.

Further, according to the present embodiment, one end 11b
In the end face, a core member 12 is buried in the coating material 11, and a material body (spark plug ground electrode) 14 having a shape in which the cross-sectional area on the other end 14a side becomes smaller toward the other end is provided. be able to. The use of the material body 14 can prevent the exposure of the core material 12 after welding at low cost.

As shown in FIGS. 1 and 4,
In the present embodiment, at the welded portion of the ground electrode 10 to the housing 2 after welding, the end of the outer coating material 11 is wound around the inner core material 12 and the core material 12 is wound. . The winding configuration of the ground electrode 10 can be appropriately formed by applying the above manufacturing method. Therefore, according to the present embodiment, it is possible to provide the spark plug 1 that can prevent the exposure of the core material after welding at low cost.

Here, the winding length (wraparound amount) of the end portion of the coating material 11 shown in FIG.
It is preferable that t is 0.1 mm or more. This basis is shown in the graph shown in FIG. This graph shows the wraparound amount t (unit: mm) when the taper angle θ (unit: °) of the material body 14 is variously changed and welded by the above-described manufacturing method. The wraparound amounts t at ten locations were measured for five material bodies (n = 5).

From this graph, when the taper angle is set to 15 ° or more to ensure the welding strength even when the welding displacement is considered, the wraparound amount t is 0.1 mm or more. In other words, in the case of a spark plug in which the wraparound amount t is 0.1 mm or more, the welding strength can be reliably ensured even in consideration of the welding displacement.

(Other Embodiments) In the above embodiment, once the complex 13 is cut flat,
By applying a load with a jig or the like, the cutting-side end 14a of the material body (cut composite) 14 is tapered, but has a desired tapered shape as shown in FIG. By cutting the composite 13 using a cutter (cutting jig) 100 or the like, a tapered shape may be formed at the same time as cutting (first modified example).

Further, the tapered shape of the cut end portion 14a of the material body 14 does not have to be a tapered shape such that the cross-sectional area decreases continuously toward the tip end. For example, as shown in FIG. 10, by applying a load to a cut portion of the composite 13 using a jig 110, the portion is constricted, and the constricted portion K <b> 2 is cut. (A second modification). Also according to this method, the cut end portion 14a has a shape in which the cross-sectional area decreases toward the tip end. In these modified examples, the same effects as those of the above embodiment can be obtained.

In the above-described embodiment, in the composite forming step, the shape of the ground electrode 10 is extruded to obtain the final shape of the ground electrode 10 (however, the shape of the straight electrode). You don't have to. For example, by extruding the raw material (cut composite) 14 after the cutting and the tapered end forming step, the final shape (length,
Thickness, etc.).

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a state in which a ground electrode according to an embodiment of the present invention is welded to a housing of a spark plug.

FIG. 2 is a process chart showing a method for manufacturing a ground electrode according to the embodiment.

FIG. 3 is a process drawing illustrating a method for manufacturing the ground electrode, following FIG. 2;

FIG. 4 is an operation explanatory view of the manufacturing method according to the embodiment.

FIG. 5 is a schematic sectional view showing a comparative example of the present invention.

FIG. 6 is a schematic cross-sectional view showing a taper angle θ of a cut end in a material body.

FIG. 7 is a graph showing a relationship between a taper angle θ and welding strength.

FIG. 8 is a graph showing a relationship between a wraparound amount (wraparound length) t and a taper angle θ.

FIG. 9 is a schematic sectional view showing a first modification of the present invention.

FIG. 10 is a schematic sectional view showing a second modification of the present invention.

[Explanation of symbols]

2 ... Housing, 2a ... Housing end face, 4 ... Center electrode, 5 ... Discharge gap, 11 ... Coating material, 12 ... Core material, 1
3 ... composite, 14 ... material body (cut composite), 14
a: Cut end of the material body.

Claims (10)

[Claims] 1. A structure in which a core material (12) made of a metal having higher thermal conductivity than the coating material is enclosed in a coating material (11) made of a metal having excellent corrosion resistance and oxidation resistance. A ground electrode for a spark plug, wherein at one end (11b), the core material is embedded in the coating material, and the cross-sectional area at the other end (14a) becomes smaller toward the other end. A ground electrode for a spark plug. 2. A structure in which a core material (12) made of a metal having better heat conductivity than the coating material is enclosed in a coating material (11) made of a metal having excellent corrosion resistance and oxidation resistance. In a method of manufacturing a ground electrode for a spark plug, a composite (13) in which the core material is sealed in the covering material is cut into a predetermined length, and an end (14a) on the cut side is cut into a predetermined length. A method for manufacturing a ground electrode for a spark plug, wherein the cross-sectional area decreases toward the tip. 3. The spark plug ground electrode according to claim 2, wherein the cut-side end (14a) of the cut composite (14) has a tapered shape. Method. 4. The ground electrode for a spark plug according to claim 3, wherein the tapered angle θ of the cut-side end (14a) of the cut composite (14) is 15 ° or more. Manufacturing method. 5. One end (10b) is opposed to the center electrode (4) with a discharge gap (5) therebetween, and the other end (10a) has a ground electrode (10) welded to the housing (2).
The ground electrode is formed by enclosing a core material (12) made of a metal having higher thermal conductivity than the coating material inside a coating material (11) made of a metal having excellent corrosion resistance and oxidation resistance. In the spark plug described above, an end of the covering material is wound around the core material at a welding portion between the ground electrode and the housing. 6. A winding length (t) of the end of the coating material (11) toward the core material (12) is 0.1 mm.
The spark plug according to claim 5, wherein: 7. One end (10b) is opposed to the center electrode (4) with a discharge gap (5) therebetween, and the other end (10a) has a ground electrode (10) welded to the housing (2).
The ground electrode is formed by enclosing a core material (12) made of a metal having higher thermal conductivity than the coating material inside a coating material (11) made of a metal having excellent corrosion resistance and oxidation resistance. A method for manufacturing a spark plug, comprising: a rod-shaped member in which the core material (12) is sealed in the coating material (11), wherein the core material is formed in the coating material at one end surface (11b). And a material body (14) of the ground electrode having a shape in which the cross-sectional area on the other end (14a) side decreases toward the other end, and the other end of the material body is welded to the housing. A method for manufacturing a spark plug. 8. The ground electrode material body (14) cuts a composite (13) in which the core material (12) is sealed in the covering material (11) into a predetermined length, End (1
The method according to claim 7, wherein 4a) is formed by reducing the cross-sectional area toward the tip of the end. 9. The method for manufacturing a spark plug according to claim 8, wherein an end (14a) of the ground electrode material on the cut side of the material body (14) is tapered. 10. The method for manufacturing a spark plug according to claim 9, wherein a taper angle θ of a cut-side end (14a) of the ground electrode material body (14) is 15 ° or more. .