JP2003017215A - Spark plug and manufacturing method of spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug with excellent heat resistance, ignitability, and durability, especially, a creeping discharge type spark plug one which makes up a structure excellent in anti-channeling property. SOLUTION: The spark plug 1 has a plane part 104 formed at its tip part so that, when projected against a virtual plane parallel with an axis direction concerning a central axis line O, as well as with the opposing direction of an end face of a grounding electrode 4 against a central electrode 2, an outside visible outline 111 is to form a linear shape orthogonal to the central axis line O at the tip part of the grounding electrode among inside and outside visible lines continuing from the tip edge to base end edge of the grounding electrode in an orthogonal projection image. On the other hand, an inside visible outline 110 forms a curved shape inflecting from the base end edge 4m to the tip edge. Then, if the direction orthogonal to the inner visible outline 110 in the orthogonal projection image is in the thickness direction of the grounding electrode 4, the thickness of the grounding electrode is formed so as to be smaller at the tip edge than at the base end edge.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a spark plug and a method for manufacturing the spark plug.

[0002]

2. Description of the Related Art Conventionally, there is provided a so-called multipolar plug in which a plurality of ground electrodes are joined to a metal shell. In this multipolar plug, for example, the end face of the ground electrode is a side peripheral face of the center electrode or an insulator. Is used to face the side peripheral surface of the. Further, in such a spark plug, one having excellent heat resistance, ignitability, antifouling property, channeling resistance, etc. is desirable, and for example, as a spark plug with improved antifouling property, a creeping discharge type spark plug is also used. What is called is configured so that the spark generated in the spark discharge gap propagates in the form of creeping discharge via the surface of the insulator at all times or under certain conditions.

[0003]

By the way, in the above-mentioned creeping discharge type spark plug, sparks that crawl on the surface of the insulator are frequently generated, so that the surface of the insulator is cut into a groove shape. It is known that a ring easily occurs. As the channeling progresses, the heat resistance of the spark plug may be impaired, or the reliability may be deteriorated. In particular, when the tip end surface of the center electrode is in a positional relationship closer to the lower edge than the front edge of the ground electrode, it is easy to concentrate and fire at the lower edge, so crawl on the insulator surface. There was a possibility that the degree would be high and channeling would occur easily.

The problem to be solved by the present invention is to provide a spark plug having excellent heat resistance, ignitability, and durability, and particularly a creeping discharge type spark plug having a structure excellent in channeling resistance. Provide a spark plug.

[0005]

Means for Solving the Problems and Actions / Effects In order to solve the above problems, the present invention provides an insulator having a central through hole, and an insulator held in the central through hole and disposed at the tip of the insulator. Shaped center electrode, a metal shell that holds the tip of the insulator so that it projects from its own tip surface, and a shape in which one end is joined to the metal shell and the other end side bends toward the center axis of the center electrode. And a plurality of ground electrodes arranged so that at least a part of the tip surface faces the side circumferential surface of the center electrode or the side circumferential surface of the insulator, and is parallel to the axial direction of the central axis, and When projected onto a virtual plane parallel to the facing direction of the tip surface of the ground electrode and the center electrode, the outer and outer surface contour lines of the inner and outer surfaces that continue from the tip edge to the base edge of the ground electrode in the orthogonal projection image are projected. Of which, the outer contour line is perpendicular to the central axis When the plane portion is formed at the tip of the ground electrode so as to form a shape, and the direction orthogonal to the inner contour line in the orthogonal projection image is the thickness direction of the ground electrode, the thickness of the ground electrode is Provided is a spark plug characterized in that it is formed so as to become smaller as it approaches the tip edge.

As described above, if the tip of the ground electrode is sharpened so that the tip becomes thinner as it approaches the tip edge, the ignitability can be effectively improved. Further, the tip of the ground electrode can be improved. Since the volume in the vicinity of the portion is small, the effect of promoting cooling in the vicinity of the tip portion is obtained, and the structure has excellent heat resistance. Further, in the tip surface of the ground electrode, when the rear edge is closer to the center electrode tip surface than the front edge in the axial direction, the rate of flying at the rear edge is high and channeling is likely to occur. However, if a flat surface is formed so that the distance between the tip of the center electrode and the front edge is reduced, the rate of flying to the front edge will increase. The fire that crawls on the body surface is suppressed, and the channeling is effectively suppressed. In particular, if the tip surface of the center electrode and the outer surface of the flat portion are formed on the same plane, the outer peripheral edge of the tip surface of the center electrode and the front edge of the ground electrode are much closer to each other, which is extremely effective. Is.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described with reference to the examples shown in the drawings. A spark plug 1 as an example of the present invention shown in FIG. 1 is configured as a so-called semi-creeping discharge type spark plug, and has a tubular metal shell 5 and an insulator 3 fitted into the metal shell 5 so that a tip portion thereof protrudes. , The center electrode 2 provided inside the insulator 3 and the metal shell 5 are coupled at the base end side, and the side face and the tip side of the center electrode 2 are opposed to each other with the tip end of the insulator 3 interposed therebetween. The ground electrode 4 and the like are provided. The insulator 3 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride. As shown in FIG. 2, the insulator 3 has a hole (through-hole) for fitting the center electrode 2 along its own axial direction. Hole 3d. Further, the metal shell 5 is formed of a metal such as low carbon steel into a cylindrical shape and constitutes a housing of the spark plug 1, and the spark plug 1 is illustrated on the outer peripheral surface thereof as shown in FIG. A threaded portion 6 for attaching to the cylinder head is formed. As shown in FIG. 2, two ground electrodes 4 are provided, one on each side of the center electrode 2. Each end face (ignition surface) 4a has a cylindrical tip 2a of the center electrode 2. Is formed by being curved so as to face the side peripheral surface 2b (igniting surface) of the metal shell 5 substantially in parallel, while the other end side is formed of the metal shell 5
Is fixed and integrated by welding or the like.

The insulator 3 is arranged such that the tip portion 3a is located between the side peripheral surface 2b of the center electrode 2 and the ignition surface 4a of the ground electrode 4. In FIG. 2, in the axial direction of the center electrode 2, the front end surface 2e side of the center electrode 2 is the front side and the opposite side is the rear side, and the front end surface 3 of the insulator 3 is shown.
e is located on the front side of the rear edge 4f of the tip surface 4a of the ground electrode 4. On the other hand, the tip surface 2 of the center electrode 2
e is arranged so as to project from the tip surface 3e of the insulator 3 by a predetermined height.

Returning to FIG. 1, in the hole 3d of the insulator 3, the terminal metal fitting 13 is inserted and fixed at one end side thereof, and the center electrode 2 is similarly inserted and fixed at the other end side thereof. There is.
A resistor 15 is arranged between the terminal fitting 13 and the center electrode 2 in the through hole 3d. This resistor 1
Both ends of 5 are electrically connected to the center electrode 2 and the terminal fitting 13 via conductive glass seal layers 16 and 17, respectively. Further, the terminal fitting 13 is made of low carbon steel or the like, and a Ni plating layer (layer thickness: 5 μm, for example) for corrosion protection is formed on the surface. The resistor 15 is made of glass powder, ceramic powder, metal powder (for example, Zn, Sb,
Sn, Ag, and Ni, which are mainly one or more of Ni), non-metallic conductive material powder (for example, amorphous carbon or graphite), an organic binder, and the like in a predetermined amount,
It is manufactured by sintering by a known method such as hot pressing.

As shown in FIG. 2, the center electrode 2 is composed of an electrode base material 2n which constitutes the surface layer of the electrode (in this embodiment, Cu or C inserted in the center of the electrode for improving heat transfer).
The portion excluding the core material 2m composed of u alloy) is Ni
Containing Cr as a main component and having a thermal conductivity of 17 to 3
It is composed of a metal of 0 W / m · K.
If sufficient heat conduction can be achieved due to the heat conduction performance of the electrode base material 2n, the core material 2m may be omitted and the entire center electrode 2 may be formed of the electrode base material 2n. Electrode base material 2
The constituent metal of n contains Ni, for example, in an amount of 80% by mass or more,
Those containing 1.5 to 9% by mass of Cr (desirably 2 to 5% by mass) or 1 to 5% by mass of Fe, and Fe
It is possible to use those containing 2 to 9 mass% of Cr and Cr in total. On the other hand, the ground electrode 4 can be made of the same material as the center electrode 2, but the material is not limited to this. For example, if the main component is Ni, a Ni-based material having a composition outside the above range is used. Metals can also be used.

The operation of the spark plug 1 will be described below. The spark plug 1 is attached to an internal combustion engine such as a gasoline engine at its screw portion 6 (FIG. 1) and is used as an ignition source for an air-fuel mixture supplied to a combustion chamber.
The spark plug 1 may be applied with a high voltage for discharge so that, for example, the center electrode 2 side is negative and the ground electrode 4 side is positive. However, when the center electrode side is a positive electrode, the wear resistance on the center electrode side is improved. Can be expected, and is more effective when the center electrode is a thin axis. Then, in FIG. 2, sparks are generated by discharge between the ignition surface 4a of the ground electrode 4 and the side peripheral surface (ignition surface) 2b of the tip 2a of the center electrode 2, and the mixture is ignited. Here, the tip 3a of the insulator 3 is arranged so as to enter between the ignition surface 4a and the side peripheral surface 2b of the center electrode 2, and the spark propagates along a path along the tip surface of the insulator 3. Functions as a semi-creeping discharge spark plug. As shown in FIG. 2, the spark plug 1 of the present embodiment.
Then, the tip portion 2a of the center electrode 2 is the tip surface 3a of the insulator 3.
By protruding from the side peripheral surface 2b and the ground electrode 4
The first gap g ₁ between the ignition surface 4a and the second gap g between the outer peripheral surface of the insulator 3 and the ignition surface 4a.
₂ is formed. As a result, the spark plug 1
Is the first gap g when the pollution does not progress so much.
_The frequency of spark discharge in ₁ is high, and the frequency of spark discharge in the second gap g ₂ is high when the pollution progresses, so that the progress of the pollution on the surface of the insulator 3 is automatically detected and the pollution detection / purification for burning it off. It can be seen as having a function.

A plurality of (two in FIG. 2) ground electrodes 4 are also provided.
Is the side peripheral surface 2b of the center electrode 2 and the side peripheral surface 3b of the insulator 3.
It is arranged so as to face. On the front side in the axial direction of the tip portion 4k of the ground electrode 4, the flat surface portion 104 is formed so as to reach the tip surface (ignition surface 4a) of the ground electrode 4.
Are formed. The thickness of the leading edge is formed to be smaller than the thickness of the base edge 4m.

FIG. 3 shows an orthogonal projection image when projected onto a virtual plane parallel to both the direction of the central axis O of the center electrode 2 and the opposite direction of the end face of the ground electrode 4 and the center electrode 2. Shows. The opposing direction of the tip end surface (ignition surface 4a) of the ground electrode 4 and the center electrode 2 is defined as follows. That is, as shown in FIGS. 2A and 2B, when a virtual line PV passing through the base edge 4m of the ground electrode 4 is set in the direction orthogonal to the central axis O of the central electrode 2, the virtual line PV is set. The direction parallel to PV is the opposite direction. More specifically, “passing through the base edge” means that a cross section orthogonal to the axis O is taken at the base edge 4m of the ground electrode 4 as shown in FIG. ), The cross-sectional shape is broken line 121
(Indicated by), and means passing through the center of gravity G of the cross-sectional figure.

In the orthographic image shown in FIG. 3, the outer contour line 110 of the inner and outer outer contour lines continuing from the leading edge (outer edge of the ignition surface 4a) to the base edge 4m of the ground electrode 4 is grounded. The flat portion 104 is formed at the tip 4k of the electrode 4 so as to have a linear shape orthogonal to the central axis O at the tip 4k. On the other hand, on the inner side, the inner outer shape line 111 is formed to have a curved shape that bends from the base edge 4m to the tip edge. Then, when the direction orthogonal to the tangent line TL in the inner outline 111 in the orthogonal projection image is the thickness direction of the ground electrode 4, the thickness W _n of the ground electrode 4 becomes smaller as it approaches the tip edge. It is formed.

Also, the scent on the base end portion side following the flat surface portion 104
The outer contour line 110 has a curved shape that continuously bends.
As described above, the curved surface portion 105 having the curved outer main surface 4i has a shape.
Is made. Then, the curved surface portion 105 and the flat surface portion 1
04 boundary (ie, transition point P _s) Outside contour line 1
Can be formed so that the shape of 10 is discontinuous
It Note that the discontinuity here means that the orthogonal projection image is a two-dimensional
It cannot be differentiated at the boundary when it is considered as a standard plane (ie,
The rate of change is discontinuous).

Specifically, the ground electrode 4 is formed by bending a thin plate-shaped electrode member (described later), and the main surface outside the ground electrode 4 (outer main surface 4i: FIG. 2) is a base. A curved surface is formed by continuously bending on the end side.
On the tip end side, the outer main surface 4 in the flat surface portion 104
i (FIG. 2) has a planar shape. The curved surface portion 105 and the flat surface portion 104 are adjacent to each other so as to be discontinuous.

Further, the outer main surface 4 of the plane portion 104 is
i is a plane orthogonal to the axis O (may be a plane substantially orthogonal to each other), and the outer main surfaces 4i of the plane portions 104, 104 of the ground electrodes 4, 4 are located on the same plane. It is supposed to do. In addition, in FIG. 3, a portion to be removed by the later-described removal processing is shown as a removed portion R _e , and by using such removal processing, the outer surfaces of both flat surface portions 104, 104 (that is, the outer main surface 4i). Will be formed on the same plane with high precision.

Further, as described above, the inner main surface of the ground electrode 4 (the inner main surface 4j (FIG. 2)) has its outer surface contour line 111 continuously bent from the base edge to the tip edge. Specifically, as shown in FIG. 3, the inner outline 111 on the inner main surface 4j (FIG. 2) extends from the base edge 4m to the tip edge (that is, the outer edge of the ignition surface 4a). , Has a curved shape with a continuous rate of change. If it is continuous, a straight line portion may exist in a part of the inner outline 111.

Further, FIG. 3 illustrates the dimensional relationship of each part. In this embodiment, the thickness of the base edge 4 m is W
_1, and the thickness of the leading edge is W ₂ , the flat portion is formed so that the value of W ₂ / W ₁ is set in the range of 0.3 to 0.8. If this value exceeds 0.8, heat resistance,
If the effect of improving the ignitability is reduced and, conversely, if it is less than 0.3, the tip may be too sharp and the spark wear resistance may be impaired.

The distance from the center electrode tip surface 2e is
The distance from the front edge 4e is set smaller than the distance from the rear edge 4f of the ground electrode 4.
In FIG. 3, the leading end surface 2e and the outer main surface 4i of the flat portion 104 are formed on the same plane, and the front edge 4e is located on the same plane.

In order to improve the anti-channeling property of the spark plug, an operating environment in which the attack of the creeping discharge spark on the insulator 3 is not excessive is formed.
For example, it is effective to suppress the tendency of sparks to concentrate at one location as much as possible and disperse the sparks. As the method, it is effective to provide a plurality of ground electrodes 4,
For example, three ground electrodes or four ground electrodes 4 may be arranged at substantially equal angular intervals around the axis of the center electrode 2. In particular, when the number of ground electrodes is 3 or more, the channeling resistance is significantly improved. Note that such setting of the number of ground electrodes can be applied to any form of spark plug shown in the present embodiment.

Although the embodiment of the present invention has been described above by taking the semi-creeping discharge type spark plug as an example, the present invention is not limited to this. In the spark plug 1 of FIG. 4, the tip of the insulator 3 is the tip 2a of the center electrode 2.
It does not enter into the space (first gap g ₁ ) between the side peripheral surface 2b and the tip surface (ignition surface 4a) of the ground electrode 4. Note that FIG. 4 shows an orthographic image projected on a virtual plane similar to FIG. Then, the tip portion 2 of the center electrode 2
With respect to the distance between the side peripheral surface 2b of a and the tip surface 4a of the ground electrode 4, the tip surface 3e of the insulator 3 and the tip surface 4a of the ground electrode 4 are provided.
The distance from the rear edge 4f is set to be small (second gap g ₂ ). That is, the tip 2a of the center electrode 2 is arranged so as to project from the insulator 3, and the tubular metal shell 5 is provided so as to cover the outside of the insulator 3. The ground electrode 4 has its base end side joined to the end of the metal shell 5 and its tip end side bent back to the center electrode 2 side.
The tip surface 4a is arranged so as to face the side circumferential surface 2b of the tip portion 2a of the protruding center electrode 2, and the first gap g is provided.
₁ , the inner surface of the tip 4k of the ground electrode 4 is opposed to the tip 3e of the insulator 3 and the first gap g _{1 is formed.}
And a smaller second gap g ₂ is formed. This is a so-called intermittent creeping discharge type spark plug in which a spark discharge is generated in the second gap g ₂ only when the insulator 3 is contaminated.

The spark plugs of the above embodiments are
In all of the types, the tip surfaces of all the ground electrodes were opposed to the side surfaces of the center electrode, but in the present invention, some of the plurality of ground electrodes are not necessarily opposed to the side surfaces of the center electrode. It also includes non-embodiment. An example thereof is shown in the sectional view of FIG. In this spark plug 1, similarly to the spark plug 1 of FIG. 2 and the like, a tubular metal shell 5 is provided so as to cover the outside of the insulator 3. Further, the base end side is joined to the end portion of the metallic shell 5, while the tip end side is provided with a plurality of ground electrodes 4 and 114 that are bent back toward the center electrode 2 side. Then, one of the ground electrodes, that is, the electrode member 114 is arranged such that the side surface faces the tip surface 2e of the center electrode 2, while at least one of the remaining ground electrodes 4 is disposed.
One (two in this case) is arranged such that the tip surface (ignition surface 4a) faces the side peripheral surface 2b of the center electrode 2.
A noble metal tip 115 is joined to the tip of the center electrode 2 via a welded portion 116.

In the above structure, the spark discharge gap gα similar to that of a so-called parallel facing type spark plug is provided in the electrode member 1.
A spark discharge gap gβ, which is formed between the side surface of 14 and the tip surface of the center electrode 2 and is similar to that of a multi-pole spark plug, is formed between the tip surface of the ground electrode 4 and the side surface of the center electrode 2. When the size of the gap gα is set to be larger than the gap gβ, normally, it is easy to fly in the gap gα and easy to fly in the gap gβ when the tip surface of the insulator 3 is soiled. The gap gα, which has a shape close to that of the parallel-opposing spark plug, has a high concentration of sparks (especially when a voltage is applied with the side of the center electrode 2 being negative), and the ignitability can be improved. In this embodiment, the ground electrode 4 arranged so that the side surface thereof faces the tip end surface of the center electrode 2 has its end surface opposed to the side surface of the center electrode with the tip end portion of the insulator 3 interposed therebetween. It is located in. That is, the flying form at the gap gβ is a semi-creeping flying form similar to that of the spark plug 1 shown in FIG.

In the above embodiment, the creeping discharge type spark plug has been described, but it may have a structure as shown in FIG. The spark plug of FIG. 6 shows an example in which the tip end surface (ignition surface 4a) of the ground electrode 4 directly faces the side peripheral surface 2b of the center electrode 2 without the insulator 3. 6 shows an example in which the tip surface 2e of the center electrode 2 and the outer main surface 4i of the plane portion 104 are located on the same plane as in the case of FIG. The side peripheral surface 2b may be opposed to an imaginary side peripheral surface (the side peripheral surface 200 indicated by a broken line portion) that extends to the front side in the axial direction,
Only part of the tip surface (ignition surface 4a) may be opposed to the side peripheral surface 2b.

Next, a method for manufacturing the spark plug of the present invention will be described. When manufacturing the above-mentioned multipolar plug, as shown in FIG. 7 (a), a spare (for example, a rectangular rod-shaped) electrode member 4'to be a ground electrode is attached to the metal shell 5 by welding or the like. A joining step of forming the body W _P is performed, and then, a bending step of pressing both electrode members 4 ′ (all electrode members if 3 or more) at the same time by pressing them against the molding recess 120 of the punching die K is performed. In this bending step, in the joined body (preliminary body W _P ) obtained in the joining step, the tip end surface of the joined electrode member 4 ′ faces the central axis O ₅ of the metal shell 105. Then, the electrode member 4 ′ is bent, and the bent electrode member 4 ′ becomes the ground electrode 4. After that, FIG.
As shown in (c), the center electrode 2 mounted on the insulator 3 is inserted into the metal shell 5 to form a gap g between the ground electrode 4 and the bent ground electrode 4. When forming a cylindrical surface along the insulator 3 or the center electrode 2 on the tip end surface of the ground electrode 4 after bending, a punching step with a cylindrical punch may be performed before the center electrode or the like is assembled. Become.

Next, the tip forming step will be described. In the tip end forming step, the tip end surface of the electrode member (ground electrode) to be bent is thinner than the base end side at the same time as the bending step or as a step different from the bending step. To form. As the tip portion forming step, as shown in FIG. 7 or 8, for example, a flat surface portion is formed on the front side in the axial direction of the tip portion 4k by performing removal processing such as grinding and polishing to remove a predetermined portion to form a flat portion. A forming step can be performed. The flat surface forming step using such removal processing is performed as a step different from the bending step.
Further, as shown in FIG. 8, it may be performed after the bending step, or may be performed before the bending step in advance.

8 (a) to 8 (c) and FIG. 9 (a),
It shows a flat portion forming step in the semi-creeping discharge type spark plug as shown in FIG. In the flat surface forming step using the removal processing as shown in FIGS. 7 and 8, after the bending processing, a part of the tip portion 4k of the ground electrode 4 is removed to form a flat surface on the front side in the axial direction. Although the plane portion 104 can be formed, the ground electrode 4 may be removed only, or both the ground electrode 4 and the center electrode 2 may be removed.

FIG. 8 (a) shows that after the bending process, the ground voltage is changed.
A part of the tip 4k of the pole 4 is attached to the center electrode 2
When projecting to the front side in the axial direction from the tip surface 2e of
Is shown. In this case, the tip surface of the center electrode 2
2e, which is a portion projecting to the front side (that is, the tip of the ground electrode 4)
The removed portion R shown as a shaded portion at the end 4k_e)
Is removed by a removal process, and the same as the tip surface 2e of the center electrode 2 is removed.
A flat surface portion having a flat surface 109 located on one plane.
Form 104. By forming in this way, FIG.
The final product like
Thickness W of the tip of the ground electrode 4_TwoIs 0.5
The removal process should be performed so that the thickness becomes 1.0 mm to 1.0 mm.
It It should be noted that the tip is also used in other tip forming steps described later.
Edge thickness W _TwoThe range can be set to the above range.

Further, FIG. 8B shows an example in which both the ground electrode 4 and the center electrode 2 are subjected to removal processing after the bending processing. In FIG. 8B, after bending, the tip end surface of the center electrode 2 projects forward from the front end in the axial direction of the ground electrode 4, and both outer surfaces are removed so as to be located on the same plane. Apply processing. Figure 8
In (b), the portions to be removed by the removal process at the tip portions of the ground electrode 4 and the center electrode 2 are shown as shaded portions (removed portions _Re ), and the surfaces exposed after the removal are the tip ends of the center electrode 2, respectively. The surface 2e serves as the outer main surface (flat surface 109) of the flat surface portion 104.

Further, as shown in FIG. 8C, when the spark-depleting member 130 (for example, a noble metal member of Pt, Ir, etc.) is provided in a part of the center electrode 2, FIG.
Removal processing can be performed in the same manner as in (a) and (b). Further, when the spark consumable member 130 is provided in the circumferential direction so as to be exposed on the side peripheral surface of the center electrode as shown in FIG. 9A, the front side of the spark consumable member 130 is removed. The removal processing may be performed in a shape.

9 (b) and 9 (c) show a step of forming a flat portion in the intermittent creeping discharge type spark plug as shown in FIG. 4, and the same method as in FIGS. 8 and 9 (a) is used. An example is shown in which the removal processing is performed. In addition,
FIG. 9B shows an example in which both the ground electrode 4 and the center electrode 2 are subjected to removal processing similarly to FIG. 8B, and FIG. 9C shows
Similar to FIG. 8C, this is an example in which the spark consumable member 130 exposed on the side peripheral surface of the center electrode 2 is provided. In addition, in the removal processing of FIG. 9C, the spark consumable member 130 is not removed, but a part of the spark consumable member 130 is removed by using the same method as in FIG. 9A. It may be done. 9 (b) and 9 (c) show an example in which both the ground electrode 4 and the center electrode 2 are subjected to removal processing, but as shown in FIGS. 8 (a) and 8 (c), Needless to say, the tip end portion 4k of 4 may be assembled so as to project forward from the tip end surface 2e of the center electrode 2 in the axial direction, and only the ground electrode 4 may be removed.

Further, as shown in FIGS. 10 and 11, as the tip forming step, a press working step of pressing the tip of the ground electrode may be performed. In this press working step, pressing is performed using a mold K ₂ adjusted to a predetermined shape so that the thickness of the ground electrode 4 in the final product (see FIG. 2) as described above becomes smaller as it approaches the tip edge. Perform processing. In the mold K ₂ , a groove 201 in which the electrode members are fitted is formed, and as in FIG. 7, the groove 2 is formed.
The electrode member 4'is pressed against 01 to perform bending. Then, 'by pressing in a form sandwiching the electrode member 4' This bending at the same time the groove 201 of the die K ₂ bottom and the pressing member P ₁ of the outer surface by the electrode member 4 tip of the groove 20
It will be extended in the form of 1. Then, after performing this way the press working to form the desired length and desired tip surface shaped tip portion of the electrode member 4 'by the punch P ₂ punching, the ground electrode 4 obtained as shown in FIG. 11 .
Further, as in FIG. 7C, the center electrode 2, the insulator 3, etc. are assembled to the metal shell 5.

The following experiments were conducted to confirm the effects of the present invention. First, a seismic resistance confirmation test was performed to confirm the seismic resistance of the ground electrode. Two stroke, water-cooled single cylinder, two-wheeled vehicle engine, engine speed 9500
A cycle operation in which the throttle was fully opened at 20 seconds and the engine rotational speed was 3500 rpm at a partial speed of 20 seconds (corresponding to 30 km / h) was repeated in rpm and evaluated. The test plug is a two-pole semi-creeping type shown in FIGS. 2 and 3 (ground electrode size: electrode thickness _Le = 1.5 mm, width _Lw = 2.8 m).
m) without ground electrode grinding (tip edge thickness W ₂ = 1.5
mm, hereinafter referred to as “1.5 mm product”), and a product with ground electrode grinding. With respect to the dimensions shown in FIG. 3, this test plug has a center electrode projecting dimension L _c = 0.5 mm, an axial distance L _d = 0.5 mm between the insulator tip surface 3 e and the edge 4 f on the rear side of the ground electrode, and the center electrode. The diameter L _b was adjusted to 2.0 mm. In addition, with the thickness W ₂ of the leading edge, it was performed by adjusting the value of L _a white shaving. For the ground electrode grinding there products, referred to ground electrode tip 0.3mm grinding the plug (sharpener white _L a = 0.3mm, the tip edge thickness of _W 2 = 1.2mm, hereinafter the "1.2mm product" ), A plug whose ground electrode tip is ground by 0.7 mm (shaving margin L
_a = 0.7 mm, tip edge thickness W ₂ = 0.8 mm, and hereinafter referred to as "0.8 mm product"). Table 1 shows the result of the seismic resistance confirmation test.

[0035]

[Table 1]

The seismic resistance judgment condition is that the ground electrode is broken (severe), the ground electrode is cracked is moderate (Δ), and the ground electrode is not damaged (mild). ○). From the above results, it was confirmed that the thinning of the tip edge has an effect of improving the earthquake resistance, and it was found that damage is not accompanied particularly when it is 0.8 mm or less.

Next, a heat resistance confirmation test was conducted to confirm the heat resistance of the ground electrode. Using the above test plug, 4-cylinder gasoline engine (displacement 1800 cc),
DOHC, 4-valve engine with 4 valves per cylinder, throttle fully open, engine speed 6500
The degree of thermal oxidation of the ground electrode was evaluated under the condition of rpm.
The results are shown in Table 2. The same three types of test plugs as those described above were used.

[0038]

[Table 2]

Regarding the judgment of the heat resistance of the ground electrode, the one with severe heating and oxidation degree is severe (x), and the one with loose heating degree is mild (○).
And As shown in Table 2, it was confirmed that the thermal oxidation can be suppressed by making the leading edge thin.

Next, using an L-type 6-cylinder gasoline engine (displacement 2000 cc), only one cylinder was used as a test cylinder, the fuel mixture ratio of the test cylinder was changed to the lean side, and the air-fuel ratio was varied under idling conditions. , I made a misfire decision. The results are shown in Table 3. The same three types of test plugs were used. Then, according to this result, it was confirmed that the lean limit air-fuel ratio becomes larger as the tip edge becomes thinner, and the ignitability can be improved.

[0041]

[Table 3]

Next, a channeling resistance test was conducted using the above test plug. A high voltage with a peak voltage of about 20 kV was applied intermittently at a frequency of 60 kHz with a polarity with the center electrode side as negative, and was applied in an air pressure atmosphere of about 5 atm.
The voltage was applied for 0 hour, and the depth of the channeling groove formed on the surface of the tip of the insulator was measured with an electron microscope. The results are shown in Table 4. The same three types of test plugs as described above were used.

[0043]

[Table 4]

The conditions for determining the channeling level are that the depth of the trenches formed by the channeling is less than 0.2 mm, the degree is mild, and the depth from 0.2 mm to 0.4 mm is moderate, and the degree is more than 0.4 mm. X is attached as a severity. From this result, it was confirmed that the channeling can be effectively suppressed by thinning the tip edge of the ground electrode.

A similar test was conducted on the intermittent creeping discharge type spark plug shown in FIG. As the test plug, the electrode thickness L _e = 1.6 mm, the center electrode protruding dimension L _c
= 1.7 mm and the center electrode diameter L _b = 2.5 mm. In addition, the first gap g1 is 1.1 mm
The second gap g2 was set to 0.45 mm. In addition, with the thickness W ₂ of the leading edge was adjusted by changing the value of the sharpener white L _a. And even in the case of such an intermittent creeping discharge type spark plug, as in the case of the semi-creeping discharge type spark plug, by thinning the tip edge, the seismic resistance, heat resistance, ignition resistance and channeling resistance are improved. It was confirmed to get.

The embodiment of the present invention has been described above.
The present invention is not limited to this, and is not limited to the wording of each claim without departing from the scope described in each claim, and extends to a range easily replaced by those skilled in the art, and Further, improvements based on the knowledge that those skilled in the art usually have can be added as appropriate.

[Brief description of drawings]

FIG. 1 is an overall view of a spark plug showing an embodiment of the present invention.

FIG. 2 is a vertical sectional view and a plan view of the main part of the same.

FIG. 3 is a diagram showing an orthogonal projection image of FIG.

FIG. 4 is a diagram showing an orthogonal projection image of the present invention applied to an intermittent creeping discharge spark plug.

FIG. 5 is a front cross-sectional view of an essential part showing an example of a spark plug provided with both a ground electrode facing a tip end surface of a center electrode and a ground electrode facing the same side surface.

FIG. 6 is a side view showing an example of a spark plug in which ground electrodes facing each other without an insulator are provided on the peripheral surface of the center electrode side.

FIG. 7 is an explanatory diagram illustrating a bending process.

FIG. 8 is a diagram showing some examples of a tip forming step using removal processing.

9 is a diagram showing some examples different from FIG. 7. FIG.

FIG. 10 is an explanatory diagram illustrating an example in which the bending step and the tip end forming step are simultaneously performed by press working.

FIG. 11 is a view following FIG. 10;

[Explanation of symbols]

1 spark plug 2 Center electrode 2b Side surface of center electrode 3 insulator 3b Side surface of insulator 4 ground electrode 4a Ignition surface (tip surface of the ground electrode) 4k ground electrode tip 4m base edge 5 metal shell 104 Plane 110 Outside outline 111 Inside outline O central axis

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01T 13/52 H01T 13/52 21/02 21/02 (72) Inventor Hiroaki Kuki Takatsuji-cho, Mizuho-ku, Nagoya-shi No. 14 No. 18 F term in Japan Special Ceramics Co., Ltd. (reference) 3G019 CA01 KA03 5G059 AA01 AA03 AA04 CC03 EE15 EE19 EE23

Claims (7)

[Claims] 1. An insulator having a center through hole, a center electrode held in the center through hole and provided at a tip portion of the insulator, and a tip portion of the insulator protruding from its tip surface. And a metal shell having one end joined to the metal shell, the other end side being bent in a direction toward the central axis of the center electrode, and at least a part of the tip surface of which is the side peripheral surface of the center electrode. Or a plurality of ground electrodes disposed so as to face the side circumferential surface of the insulator, parallel to the axial direction of the central axis, and the facing direction of the tip surface of the ground electrode and the central electrode When projected onto a virtual plane parallel to, the outer contour line of the inner and outer outer contour lines continuing from the front edge to the base edge of the ground electrode in the orthogonal projection image is orthogonal to the central axis line. To make a straight line shape A plane portion is formed at the tip of the ground electrode, and when the direction orthogonal to the inner contour line in the orthogonal projection image is the thickness direction of the ground electrode, the thickness of the ground electrode is the tip edge. The spark plug is characterized in that it is formed to be smaller than the base edge. 2. When the thickness of the ground electrode at the base edge is W ₁ and the thickness of the tip edge is W ₂ , the value of W ₂ / W ₁ is 0.3 to 0.8. The spark plug according to claim 1, wherein the spark plug is set to have a range of. 3. The spark plug according to claim 1, wherein the front end surface of the center electrode and the outer surface of the flat surface portion are formed on the same plane. 4. An insulator having a center through hole, a center electrode having a noble metal tip at its tip end, which is held in the center through hole and disposed at the tip end of the insulator, and a tip end of the insulator. And a metal shell that holds the portion so as to project from the front end surface of the metal shell, one end of which is joined to the metal shell, and the other end side is bent so as to approach the center axis of the center electrode and the side of the center electrode. A method for manufacturing a spark plug comprising a plurality of ground electrodes arranged so as to face at least one of a peripheral surface and a side peripheral surface of the insulator, wherein in the metal shell, the ground electrode and A joining step of joining a wire electrode member to be formed to form a joined body of the metal shell and the ground electrode, and in the joined body obtained by the joining step, the tip surface of the joined ground electrode is A bending step of bending the ground electrode so as to have a positional relationship facing the central axis of the metal shell, and a step of bending the ground electrode tip portion at the same time as the bending step or separately from the bending step. A thin-walled tip portion forming step, wherein the tip portion forming step is an imaginary plane parallel to the axial direction of the central axis and parallel to the opposing direction of the distal end surface of the ground electrode and the central electrode. In the orthogonal projection image when projected to, of the inner and outer outer contour lines continuing from the leading edge to the base edge of the ground electrode, the direction orthogonal to the inner contour line is the thickness direction of the ground electrode. In this case, the tip portion of the ground electrode is formed so that the tip edge has a smaller thickness than the base edge. 5. The removal process for partially removing the front side in the axial direction of the tip portion of the ground electrode when the front side of the center electrode in the axial direction is the front side in the tip portion forming step. By applying the outer surface contour line outside the ground electrode in the orthogonal projection (hereinafter, also referred to as “outer contour line”), a flat surface is formed at the tip of the ground electrode so as to form a straight line shape orthogonal to the central axis. The method of manufacturing a spark plug according to claim 4, further comprising a step of forming a flat portion for forming the portion. 6. A center electrode assembly for assembling the center electrode with respect to the metal shell so that at least a part of a tip end surface of the ground electrode that has been bent faces a side circumferential surface of the center electrode. In the bonded body obtained by the center electrode assembling step, the flat surface forming step includes the step of forming the ground electrode so that the front end surface of the center electrode and the outer surface of the flat surface portion are located on the same plane. The method for manufacturing a spark plug according to claim 5, wherein at least the ground electrode of the center electrode is subjected to the removing process. 7. The tip forming step includes a press working step of subjecting the ground electrode so that the thickness of the tip of the ground electrode is smaller than that of the base edge. Item 4. A method for manufacturing a spark plug according to Item 4.