JP4981746B2 - Spark plug for internal combustion engine - Google Patents

Description

  The present invention relates to a spark plug used for an internal combustion engine.

  A spark plug for an internal combustion engine such as an automobile engine includes, for example, a center electrode, an insulator provided outside the center electrode, a cylindrical metal shell provided outside the insulator, and a base end portion of the metal shell. And a ground electrode joined to the front end surface of the. The ground electrode has a substantially rectangular cross section and is arranged so that the inner side surface of the tip part faces the tip part of the center electrode, thereby forming a spark discharge gap between the tip part of the center electrode and the tip part of the ground electrode. Is done.

  A threaded portion (not shown) is formed on the outer peripheral surface of the metal shell. The spark plug is attached by being screwed into a plug hole provided with a female screw formed in the cylinder head of the engine at the screw portion. By the way, when the air-fuel mixture is in a positional relationship such that it strikes the back surface of the ground electrode when the spark plug is attached, the ground electrode may hinder the inflow of the air-fuel mixture into the spark discharge gap. As a result, the ignitability may vary.

  On the other hand, in a type having two or more ground electrodes, there is a technique in which each ground electrode has a cylindrical shape with a substantially circular cross section (for example, see Patent Document 1). By making the cross section substantially circular in this way, even when the air-fuel mixture hits the back of the ground electrode, it is difficult for the air-fuel mixture to peel off from the ground electrode, and it goes around inside The air-fuel mixture easily reaches the spark discharge gap.

There is also a technique of making the cross section of the ground electrode substantially trapezoidal (see, for example, Patent Document 2). By making the cross section substantially trapezoidal in this way, it can be said that the air-fuel mixture easily reaches the spark discharge gap as compared with the case where the cross section is rectangular.
Japanese Patent Laid-Open No. 11-121142 JP-A-5-13146

  However, for the convenience of joining the ground electrode to the front end surface of the metal shell, if the cross section of the ground electrode is circular, the cross sectional area has to be smaller than when the cross section is rectangular. As a result, so-called heat sinking (heat dissipation) is poor, the electrode temperature is likely to rise during high-speed operation, etc., and the degree of wear of the ground electrode is large, and the durability may be reduced.

  In recent years, it is also conceivable to improve ignitability and spark propagation by bonding a tip made of a noble metal alloy (noble metal tip) to the tip of the center electrode and the tip of the ground electrode. However, when the ground electrode has a circular cross section as in Patent Document 1, there is a concern that it may be difficult to join the noble metal tip on the ground electrode side.

  Furthermore, Patent Document 2 describes that the ground electrode is composed of an outer layer and an inner layer having better thermal conductivity than the outer layer, and although it has been suggested to improve the heat drawing performance, There is no description about the joining technique. Here, for example, if a noble metal tip is welded by resistance welding, sufficient joint strength cannot be obtained. In addition, for example, when welding is performed by laser or electron beam welding, there is a possibility that the melted part may reach the inner layer. In this case, the oxidation resistance is reduced due to the formation of an oxide scale. Is concerned.

  The present invention has been made in view of the above circumstances, and its purpose is to suppress the inhibition of the inflow of the air-fuel mixture into the spark discharge gap, to prevent deterioration of ignitability, and to improve the bonding strength of the noble metal tip, An object of the present invention is to provide a spark plug for an internal combustion engine that can improve durability.

  Hereinafter, each configuration suitable for solving the above-described problems will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The spark plug of this configuration is
A rod-shaped center electrode extending in the axial direction;
A substantially cylindrical insulator provided on the outer periphery of the center electrode;
A cylindrical metal shell provided on the outer periphery of the insulator;
A base electrode is joined to the tip of the metal shell, and the tip is disposed so that the tip faces the tip of the center electrode,
A noble metal tip for center electrode is joined to the tip of the center electrode, and a noble metal tip for ground electrode is joined to a position facing the noble metal tip for center electrode in the tip portion of the ground electrode, A spark plug for an internal combustion engine having a spark discharge gap between a tip of a noble metal tip for a center electrode and a tip of the noble metal tip for a ground electrode,
At least the tip side of the ground electrode has a convex curved surface on the back side opposite to the center electrode side,
The noble metal tip for the ground electrode is bonded to a seat surface of a pedestal portion mainly composed of nickel, and is provided by bonding the pedestal portion to the ground electrode, and the pedestal among the ground electrodes. The part where the part is joined is a flat surface,
At least a portion of the ground electrode that is subjected to a spark discharge includes an outer layer made of a nickel alloy and an inner layer made of a heat conductive material than the outer layer,
In the cross section of the ground electrode viewed from the tip surface side of the ground electrode along the axis,
The shortest distance between the flat surface (including the flat surface before bonding) and the inner layer is A (mm),
When the distance between the farthest point from the center electrode in the inner layer and the farthest point from the center electrode in the outer layer is B (mm),
A / B ≦ 0.7
It is characterized by satisfying.

  According to the configuration 1, the ground electrode has the convex curved surface on the back surface opposite to the center electrode side at least on the tip side of the center of the spark discharge gap. For this reason, even when the air-fuel mixture is in a positional relationship such that it directly contacts the back surface of the ground electrode, the air-fuel mixture tends to enter the inside of the ground electrode, and the air-fuel mixture easily reaches the spark discharge gap. As a result, it is possible to prevent deterioration in ignitability.

  In addition, at least a portion of the ground electrode that is subjected to spark discharge includes an outer layer made of a nickel alloy and an inner layer made of a metal having better heat conductivity than the outer layer. Due to the presence of the outer layer, the durability against oxidation is enhanced, and the presence of the inner layer improves heat sinking, resulting in an increase in the temperature of the ground electrode and the noble metal tip of the ground electrode during high-speed operation. For example, the increase in the spark discharge gap due to the consumption of the ground electrode or the noble metal tip of the ground electrode can be easily suppressed.

  Further, a noble metal tip is joined to each of the center electrode and the ground electrode. For this reason, the spark wear resistance at high temperatures can be improved. That is, consumption is suppressed by the presence of the noble metal tip, and durability can be improved in this sense.

  In Configuration 1, at least a joint surface of the ground electrode to which the noble metal tip for ground electrode is joined has a substantially flat surface. For this reason, compared with the case where the joining surface is curved, it is easy to avoid complication of joining work, and it is possible to improve the joining strength.

  In addition, the noble metal tip for the ground electrode is bonded to the seat surface of the pedestal portion whose main component is nickel, and the pedestal portion is bonded to the flat surface of the ground electrode. Therefore, if the noble metal tip for ground electrode is firmly bonded to the pedestal portion, the pedestal portion mainly composed of the same nickel and the flat surface of the ground electrode can be bonded relatively easily and firmly. Therefore, the bonding strength of the noble metal tip for ground electrode is improved, and the bonding state is further stabilized.

  Moreover, in Configuration 1, the shortest distance between the flat surface (including the flat surface before bonding) and the inner layer is A (mm) in the cross section of the ground electrode viewed from the tip surface side of the ground electrode along the axis. When the distance between the point farthest from the center electrode in the inner layer and the point farthest from the center electrode in the outer layer is B (mm), A / B ≦ 0.7 is satisfied. That is, the shortest distance A between the flat surface and the inner layer is relatively short. As described above, the noble metal tip for ground electrode is joined to the flat surface of the ground electrode via the pedestal portion. In this way, through the pedestal part, it is possible to realize strong bonding without the molten part containing the components of the noble metal tip coming into direct contact with the inner layer, but on the other hand, the presence of the pedestal part Therefore, there is a concern that the distance between the noble metal tip for ground electrode and the inner layer will be increased. In this respect, in Configuration 1, since the shortest distance A between the flat surface and the inner layer is relatively short, the heat from the noble metal tip for the ground electrode is easily transferred to the inner layer made of a metal having good heat conductivity. As a result, it is possible to dramatically improve the heat drawing performance.

  On the other hand, when A / B ≦ 0.7 is not satisfied, it is difficult to perform good heat pulling, and the consumption volume is increased. As a result, the spark discharge gap increases with time, the required voltage increases, and the like.

  As described above, in the configuration 1, the noble metal tip for the ground electrode is joined to the flat surface of the ground electrode via the plate-shaped pedestal portion, but from the viewpoint of securing a stronger joint and the like. It is more desirable to employ configurations 4 to 7 described later.

Configuration 2. The spark plug of this configuration is
A rod-shaped center electrode extending in the axial direction;
A substantially cylindrical insulator provided on the outer periphery of the center electrode;
A cylindrical metal shell provided on the outer periphery of the insulator;
A base electrode is joined to the tip of the metal shell, and the tip is disposed so that the tip faces the tip of the center electrode,
A noble metal tip for center electrode is joined to the tip of the center electrode, and a noble metal tip for ground electrode is joined to a position facing the noble metal tip for center electrode in the tip portion of the ground electrode, A spark plug for an internal combustion engine having a spark discharge gap between a tip of a noble metal tip for a center electrode and a tip of the noble metal tip for a ground electrode,
At least the tip side of the ground electrode has an elliptical cross section,
The noble metal tip for the ground electrode is bonded to a seat surface of a pedestal portion mainly composed of nickel, and is provided by bonding the pedestal portion to the ground electrode, and the pedestal among the ground electrodes. The part where the part is joined is a flat surface,
At least a portion of the ground electrode that is subjected to a spark discharge includes an outer layer made of a nickel alloy and an inner layer made of a heat conductive material than the outer layer,
In the cross section of the ground electrode viewed from the tip surface side of the ground electrode along the axis,
The shortest distance between the flat surface (including the flat surface before bonding) and the inner layer is A (mm),
When the distance between the farthest point from the center electrode in the inner layer and the farthest point from the center electrode in the outer layer is B (mm),
A / B ≦ 0.7
It is characterized by satisfying.

  The “oval shape” is a shape in which a perfect circle is centered, or an ellipse is cut by a long side or a short side and both ends of the cut semicircle or semi-ellipse are connected by a straight line. In other words, it means a shape formed by curving a pair of opposing sides of a rectangle in a protruding manner.

  According to the configuration 2, since the curved surfaces are formed on both side surfaces of the ground electrode, the air-fuel mixture can be easily flown into the spark discharge gap, and as a result, the same effect as the configuration 1 can be obtained. . As in the case of the configuration 1, it is more preferable to adopt the configurations 4 to 7 described later from the viewpoint of securing a stronger bonding of the noble metal tip for the ground electrode.

Configuration 3. The spark plug of this configuration is
A rod-shaped center electrode extending in the axial direction;
A substantially cylindrical insulator provided on the outer periphery of the center electrode;
A cylindrical metal shell provided on the outer periphery of the insulator;
A base electrode is joined to the tip of the metal shell, and the tip is disposed so that the tip faces the tip of the center electrode,
A noble metal tip for center electrode is joined to the tip of the center electrode, and a noble metal tip for ground electrode is joined to a position facing the noble metal tip for center electrode in the tip portion of the ground electrode, A spark plug for an internal combustion engine having a spark discharge gap between a tip of a noble metal tip for a center electrode and a tip of the noble metal tip for a ground electrode,
At least the tip side of the ground electrode has a cross-sectional shape formed by cutting out the four corners of the rectangle into straight or protruding curved shapes, respectively.
The noble metal tip for the ground electrode is bonded to a seat surface of a pedestal portion mainly composed of nickel, and is provided by bonding the pedestal portion to the ground electrode, and the pedestal among the ground electrodes. The part where the part is joined is a flat surface,
At least a portion of the ground electrode that is subjected to a spark discharge includes an outer layer made of a nickel alloy and an inner layer made of a heat conductive material than the outer layer,
In the cross section of the ground electrode viewed from the tip surface side of the ground electrode along the axis,
The shortest distance between the flat surface (including the flat surface before bonding) and the inner layer is A (mm),
When the distance between the farthest point from the center electrode in the inner layer and the farthest point from the center electrode in the outer layer is B (mm),
A / B ≦ 0.7
It is characterized by satisfying.

  In addition, "the cross-sectional shape formed by cutting the four corners of the rectangle in a straight line" is the front side surface located on the center electrode side of the ground electrode and the back side surface located on the back side of the front side surface, It means that a chamfered portion is provided between the front side surface and the both side surfaces located between the back side surface and has an octagonal cross section. In addition, “the cross-sectional shape formed by cutting out the four corners of the rectangle into a projecting curved shape” means that the front side surface and the back side surface and both side surfaces located between the front side surface and the back side surface It means that a curved surface portion is provided between the two.

  According to the configuration 3, the ground electrode has a cross-sectional shape in which the four corners of the rectangle are cut into straight or projecting curved shapes, so that the air-fuel mixture can easily flow into the spark discharge gap. . As a result, the same effects as those of the above configuration 1 are achieved.

  From the viewpoint of facilitating the air-fuel mixture to reach the spark discharge gap, the chamfered portion has a length along the thickness direction of the ground electrode in the cross section orthogonal to the central axis of the ground electrode, and the ground electrode. It is preferable that each length along the width direction is 0.3 mm or more. In addition, for the curved surface portion, it is preferable that the radius of curvature in a cross section orthogonal to the central axis of the ground electrode is 0.3 mm or more.

  Further, similarly to the configuration 1, it is more desirable to employ the configurations 4 to 7 described later from the viewpoint of securing stronger bonding of the noble metal tip for ground electrode.

Configuration 4. In the spark plug for the internal combustion engine according to Configurations 1 to 3, when the thickness of the pedestal portion in the axial direction is T (mm),
T ≧ 0.25
It is characterized by satisfying.

  From the viewpoint of improving the bonding strength, the noble metal tip for the ground electrode and the pedestal portion are melted together by a predetermined welding or the like to form the noble metal tip for the ground electrode and the nickel-based metal constituting the pedestal portion. It is desirable to form a melted part by mixing and to be joined through the melted part. In this respect, in the configuration 4, the thickness T in the axial direction of the pedestal portion is sufficiently secured to be 0.25 mm or more. For this reason, it is possible to ensure a sufficient size with respect to the melting portion. As a result, a sufficient bonding strength can be ensured between the noble metal tip for ground electrode and the pedestal, and as a result, the bonding state can be further stabilized.

Configuration 5. In the spark plug for an internal combustion engine according to any one of configurations 1 to 4,
The ground electrode noble metal tip is bonded to the seating surface of the pedestal portion by laser welding or electron beam welding.

  Configuration 6. The spark plug for an internal combustion engine according to any one of configurations 1 to 5, wherein the pedestal portion is joined to the flat surface by resistance welding.

  According to the configuration 5, the metal constituting the noble metal tip for ground electrode and the nickel metal constituting the pedestal portion are melted and mixed with each other between the noble metal tip for ground electrode and the pedestal portion. It joins through a fusion | melting part. Since the melted part is formed in this way, the joint strength between the two can be improved.

  Moreover, according to the said structure 6, while the base part has nickel as a main component, the outer layer which comprises a flat surface is also formed with the nickel alloy. That is, since both are made of the same type of metal, sufficient bonding strength can be ensured even if resistance welding is performed, that is, even if a melted part is not formed as in laser welding or the like. In addition, even if the inner layer is a material that is inferior in oxidation resistance, it does not come out on the surface by forming a relatively large melted part, as in other laser welding, etc. Also, it is possible to ensure the bonding strength.

Configuration 7. In the spark plug for an internal combustion engine according to any one of configurations 1 to 6,
The noble metal tip for ground electrode is joined to the seating surface of the pedestal portion to form a composite, and the pedestal portion of the composite is joined to the flat surface. .

  According to the configuration 7, the joining operation can be performed smoothly.

  Furthermore, it is even more desirable to employ the following configurations 8 to 13.

Configuration 8. In the spark plug for an internal combustion engine according to any one of configurations 1 to 7,
The pedestal is in contact with the inner layer.

  According to the configuration 8, the distance between the noble metal tip for ground electrode and the inner layer can be further shortened, and the heat-drawing performance can be further improved. On the other hand, since a pedestal is interposed between the noble metal tip for ground electrode and the inner layer, a malfunction due to contact between the noble metal tip for ground electrode and the inner layer, that is, an oxide scale is formed. Therefore, it is possible to suppress a decrease in oxidation resistance due to the occurrence.

Configuration 9 In the spark plug for an internal combustion engine according to any one of configurations 1 to 8,
At least a part of the inner layer is mainly composed of copper.

  As in configuration 9, by providing the inner layer mainly composed of copper, it is possible to ensure good heat dissipation and to more reliably suppress problems caused by the rise in the ground electrode temperature. The ground electrode is not limited to a simple two-layer structure and may have a three-layer structure or more. However, the inner layer needs to contain a better heat conductive metal than the outer layer. Therefore, for example, when there is an intermediate layer made of copper alloy or pure copper inside the outer layer and there is an innermost layer made of pure nickel inside the intermediate layer, the inner layer is constituted by the intermediate layer and the innermost layer. Can be seen as being.

Configuration 10 In the spark plug for an internal combustion engine according to any one of configurations 1 to 9,
In the cross section of the ground electrode viewed from the tip surface side of the ground electrode along the axis,
When the distance between the flat surface and the point farthest from the center electrode of the outer layer is C (mm),
C ≦ 1.3 is satisfied.

Configuration 11 In the spark plug for an internal combustion engine according to any one of configurations 1 to 10,
In the cross section of the ground electrode viewed from the tip surface side of the ground electrode along the axis,
When the width of the ground electrode in the direction orthogonal to the axis is D (mm),
D ≦ 1.5 is satisfied.

  According to the configurations 10 and 11, the air-fuel mixture goes around inside the ground electrode, and the air-fuel mixture easily reaches the spark discharge gap. As a result, it is possible to further improve the ignitability. Further, even when the screw diameter is relatively small and the joint area is easily restricted, the metal shell can be reliably joined.

Configuration 12 In the spark plug for an internal combustion engine according to any one of configurations 1 to 11,
In the cross section of the ground electrode viewed from the tip surface side of the ground electrode along the axis,
When the length from the flat surface to the tip of the noble metal tip for the ground electrode is E (mm),
E ≧ 0.4 is satisfied.

  According to the structure 12, since the length E from the flat surface to the tip of the noble metal tip for ground electrode is 0.4 mm or more, the ignitability can be further improved.

Configuration 13 In the spark plug for an internal combustion engine according to any one of configurations 1 to 12,
The flat surface is formed by cutting out the outer layer.

  As in the configuration 13, the flat surface is formed by cutting out the outer layer of the ground electrode. For this reason, compared with the case where a flat surface is formed using a mold or the like, the flat surface can be formed relatively easily. In addition, “notching” includes, for example, performing a cutting process. In this case, “A / B ≦ 0.7” defined in the configuration 1 or the like is simply performed by cutting. Can be realized without much difficulty.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a partially cutaway front view showing a spark plug 1. In FIG. 1, the direction of the axis CL <b> 1 of the spark plug 1 is the vertical direction in the drawing, the lower side is the front end side of the spark plug 1, and the upper side is the rear end side.

  The spark plug 1 includes an insulator 2 as an elongated insulator, a cylindrical metal shell 3 that holds the insulator 2, and the like.

  A shaft hole 4 is formed through the insulator 2 along the axis CL1. A center electrode 5 is inserted and fixed on the front end side of the shaft hole 4, and a terminal electrode 6 is inserted and fixed on the rear end side. A resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 in the shaft hole 4, and both ends of the resistor 7 are connected to the center electrode via conductive glass seal layers 8 and 9. 5 and the terminal electrode 6 are electrically connected to each other.

  The center electrode 5 protrudes from the tip of the insulator 2, and the terminal electrode 6 is fixed in a state of protruding from the rear end of the insulator 2. Further, a noble metal tip (noble metal tip for center electrode) 31 mainly composed of iridium is joined to the tip of the center electrode 5 by welding.

  On the other hand, the insulator 2 is formed by firing alumina or the like, as is well known, and has a flange-shaped large-diameter portion 11 that is formed to protrude outward in the radial direction at a substantially central portion in the axis CL1 direction. And an inner body portion 12 having a smaller diameter on the distal end side than the large diameter portion 11, and an inner body portion 12 having a smaller diameter on the distal end side than the intermediate body portion 12, and an internal combustion engine (engine). And a leg length portion 13 exposed to the combustion chamber. Of the insulator 2, the distal end side including the large-diameter portion 11, the middle trunk portion 12, and the leg long portion 13 is accommodated in a metal shell 3 formed in a cylindrical shape. A step portion 14 is formed at the connecting portion between the leg long portion 13 and the middle trunk portion 12, and the insulator 2 is locked to the metal shell 3 at the step portion 14.

  The metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a screw portion (male screw portion) 15 for attaching the spark plug 1 to the cylinder head of the engine is formed on the outer peripheral surface thereof. A seat portion 16 is formed on the outer peripheral surface on the rear end side of the screw portion 15, and a ring-shaped gasket 18 is fitted on the screw neck 17 on the rear end of the screw portion 15. Further, on the rear end side of the metallic shell 3, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the metallic shell 3 is attached to the cylinder head is provided. A caulking portion 20 for holding the insulator 2 is provided.

  Further, a step portion 21 for locking the insulator 2 is provided on the inner peripheral surface of the metal shell 3. The insulator 2 is inserted from the rear end side to the front end side of the metal shell 3, and the rear end of the metal shell 3 is engaged with the step portion 14 of the metal shell 3. It is fixed by caulking the opening on the side radially inward, that is, by forming the caulking portion 20. An annular plate packing 22 is interposed between the step portions 14 and 21 of both the insulator 2 and the metal shell 3. Thereby, the airtightness in the combustion chamber is maintained, and the fuel air entering the gap between the leg long portion 13 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 is prevented from leaking outside.

  Further, in order to make the sealing by caulking more complete, annular ring members 23 and 24 are interposed between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3, and the ring member 23 , 24 is filled with powder of talc (talc) 25. That is, the metal shell 3 holds the insulator 2 via the plate packing 22, the ring members 23 and 24, and the talc 25.

  A ground electrode 27 having a substantially L shape is joined to the front end surface 26 of the metal shell 3. That is, the ground electrode 27 is welded at its proximal end to the distal end surface 26 of the metal shell 3, and the distal end side is bent back, and one side surface of the distal end side is the distal end portion (noble metal tip) of the center electrode 5. 31). The ground electrode 27 is provided with a noble metal tip (a noble metal tip for ground electrode) 32 so as to face the noble metal tip 31. The noble metal tips 31 and 32 are provided on the axis line CL 1, and a gap between the noble metal tips 31 and 32 is a spark discharge gap 33.

  As shown in FIG. 2, the center electrode 5 includes an inner layer 5A made of copper or a copper alloy and an outer layer 5B made of a nickel (Ni) alloy. The center electrode 5 is reduced in diameter at the tip side, has a rod shape (cylindrical shape) as a whole, and has a flat tip surface. The noble metal tip 31 having a cylindrical shape is overlapped therewith, and further, laser welding, electron beam welding, or the like is performed along the outer edge of the joining surface, whereby the noble metal tip 31 and the center electrode 5 are melted together, and the melting portion 41 Is formed. That is, the noble metal tip 31 is bonded to the tip of the center electrode 5 by being fixed at the melting portion 41.

  On the other hand, the ground electrode 27 has a two-layer structure including an inner layer 27A and an outer layer 27B. The outer layer 27B in the present embodiment is made of a nickel alloy such as Inconel 600 or Inconel 601 (both are registered trademarks). On the other hand, the inner layer 27A is made of a copper alloy or pure copper, which is a better heat conductive metal than the nickel alloy. The presence of the inner layer 27A improves the heat drawability (this will be described in detail later). In the present embodiment, for the sake of convenience of explanation, a simple two-layer structure is described. However, a three-layer structure or a multilayer structure of four or more layers may be used. However, the inner layer of the outer layer 27B needs to contain a better heat conductive metal than the outer layer 27B. Therefore, for example, an intermediate layer made of copper alloy or pure copper may be provided inside the outer layer 27B, and an innermost layer made of pure nickel may be provided inside the intermediate layer. In this case, the inner layer 27A is constituted by the intermediate layer and the innermost layer.

  In the present embodiment, the ground electrode 27 basically has a circular cross section. In particular, the tip portion including at least the portion to which the noble metal tip 32 is joined (the tip portion rather than the bent portion in the present embodiment) of the ground electrode 27 is cut so as to be substantially flat. ing. That is, the flat surface F1 is formed by cutting the outer layer 27B by the cutting process.

  The noble metal tip 31 on the side of the center electrode 5 has been referred to as containing iridium as a main component, but the noble metal tip 32 on the side of the ground electrode 27 contains, for example, platinum as a main component and contains 20% by mass of rhodium. It is composed of a noble metal alloy. However, these material configurations are merely examples, and are not limited to the above description. For example, as another example, it is good also as improving weldability with the base part 52 mentioned later which has nickel as a main component as Pt-10Ni. These noble metal tips 31 and 32 are manufactured as follows, for example. First, an ingot whose main component is iridium or platinum is prepared, and each alloy component is blended and melted so as to have the predetermined composition described above, and an ingot is formed again with respect to the molten alloy. Forging and hot rolling (groove roll rolling) are performed. Then, after drawing a rod-shaped raw material by performing a drawing process, the cylindrical noble metal tips 31 and 32 are obtained by cutting it into a predetermined length.

  Now, the noble metal tip 32 on the ground electrode 27 side in the present embodiment is not directly joined to the tip portion of the ground electrode 27 but indirectly joined via the pedestal 51. That is, the noble metal tip 32 is bonded to the seat surface 52 of the plate-like pedestal portion 51 containing nickel as a main component, and the pedestal portion 52 (the surface opposite to the seat surface 52) is connected to the ground electrode 27. Of these, it is bonded to the flat surface F1. More specifically, first, with the noble metal tip 32 in contact with the seating surface 52 of the pedestal 51, laser welding or electron beam welding is performed along the outer edge of the contact surface. As a result, the noble metal tip 32 and the pedestal portion 51 are melted and the melted portion 42 is formed, thereby obtaining a composite 61 in which the noble metal tip 32 and the pedestal portion 51 are firmly bonded and fixed (FIG. 6C). reference). The pedestal 51 of the composite 61 is joined to the flat surface F1 of the ground electrode 27 by resistance welding. Since both the pedestal 51 and the outer layer 27B of the ground electrode 27 are made of a nickel alloy, sufficient bonding strength can be obtained even by resistance welding. Note that the thickness T (see FIG. 5) of the pedestal 51 in this embodiment is 0.25 m or more (for example, 0.45 mm), which is sufficient for laser welding or electron beam welding. Welding can be performed (a sufficiently deep (thick) melting portion 42 can be formed).

In the present embodiment configured as described above, as shown in FIG. 5, in the cross section of the ground electrode 27 viewed from the front end side of the ground electrode 27 along the axis CL1, the flat surface F1, the inner layer 27A, Is the shortest distance of A (mm), and the distance between the farthest point from the center electrode 5 in the inner layer 27A and the farthest point from the center electrode 5 in the outer layer 27B is B (mm),
It is configured to satisfy A / B ≦ 0.7.

In the present embodiment, when the distance between the flat surface F1 of the ground electrode 27 and the point farthest from the center electrode 5 in the outer layer 27B is C (mm),
It is configured to satisfy C ≦ 1.3.

Further, when the width of the ground electrode 27 in the direction orthogonal to the axis CL1 is D (mm),
It is configured to satisfy D ≦ 1.5.

In addition, when the length from the flat surface F1 to the tip of the noble metal tip 32 is E (mm),
It is configured to satisfy E ≧ 0.4.

  As described above, in the present embodiment, the ground electrode 27 has a projecting curved surface on the back surface opposite to the center electrode 5 side. For example, as shown in FIG. Alternatively, the ground electrode 27 may be configured to have a projecting curved surface on both side surfaces adjacent to the side surface facing the center electrode 5 (that is, in an elliptical cross section). Further, the ground electrode 27 may be configured to have a cross-sectional shape formed by cutting four corners of a rectangle. That is, as shown in FIG. 10, it is good also as comprising a chamfer part MB between each side surface of the ground electrode 27, and as shown in FIG. 11, it curves between each side surface of the ground electrode 27. It is good also as comprising so that it may have surface part WB. Moreover, it is good also as comprising so that it may have either the said chamfer part MB or the curved surface part WB between each side surface of the said ground electrode 27. FIG. In providing the chamfered portion MB or the curved surface portion WB, the chamfered portion MB has a ground electrode in a cross section orthogonal to the central axis of the ground electrode 27 from the viewpoint of making the air-fuel mixture easily reach the spark discharge gap 33. Preferably, the length along the thickness direction of 27 and the length along the width direction of the ground electrode 27 are each 0.3 mm or more. In addition, for the curved surface portion WB, it is preferable that the radius of curvature in the cross section orthogonal to the central axis of the ground electrode 27 is 0.3 mm or more.

  Next, a method for manufacturing the spark plug 1 configured as described above will be described focusing on the manufacturing process of the ground electrode 27 and the like. First, the metal shell 3 is processed in advance. That is, a metal material (for example, an iron-based material such as S15C or S25C or a stainless steel material) formed in a cylindrical shape is formed through holes by cold forging to produce a rough shape. Thereafter, the outer shape is adjusted by cutting to obtain a metal shell intermediate.

  On the other hand, the intermediate body of the ground electrode 27 is manufactured. That is, the intermediate body of the ground electrode 27 is still a straight rod-like shape before bending. The ground electrode 27 before bending is obtained as follows, for example.

  That is, a core material made of a metal material constituting the inner layer 27A and a bottomed cylindrical body made of a metal material constituting the outer layer 27B are prepared (both not shown). And a cup material is formed by inserting a core material with respect to the recessed part of a bottomed cylindrical body. Next, the cup material having the two-layer structure is subjected to a thinning process in the cold. Examples of cold thinning include wire drawing using a die or the like, extrusion forming using a female die, and the like. Thereafter, by performing swaging, as shown in FIG. 6A, a rod-like body 271 having a circular cross section and a reduced diameter is formed.

  Then, the flat surface F1 is formed on the rod-shaped body 271 as shown in FIG.

  Subsequently, the ground electrode 27 before bending and before chip bonding is bonded to the front end surface of the metal shell intermediate body by resistance welding. It should be noted that so-called “sagging” occurs during resistance welding, and an operation of removing the “sagging” is performed. Further, in this example, after performing swaging processing, cutting processing, etc., the ground electrode 27 before bending is joined by resistance welding, but after thinning, the rod-like body was joined to the metal shell intermediate body. Thereafter, swaging may be performed, and then cutting may be performed. In this case, at the time of swaging, the rod-like body joined to the front end surface of the metal shell intermediate body can be introduced from the front end side into the swaged portion (swaging die) while holding the metal shell intermediate body. Therefore, it is not necessary to set the rod-like body to be long in order to secure a portion for holding during swaging.

  Thereafter, the threaded portion 15 is formed by rolling at a predetermined portion of the metal shell intermediate. Thereby, the metal shell 3 to which the ground electrode 27 before bending is welded is obtained. The metal shell 3 or the like is galvanized or nickel plated. In order to improve the corrosion resistance, the surface may be further subjected to chromate treatment.

  On the other hand, the composite body 61 of the noble metal tip 32 is formed as described above. That is, in a state where the noble metal tip 32 is in contact with the seating surface 52 of the pedestal portion 51, by performing laser welding or electron beam welding along the outer edge of the contact surface, the melting portion 42 is formed, Thereby, the composite body 61 in which the noble metal tip 32 and the pedestal portion 51 are firmly bonded and fixed is obtained.

  Then, as shown in FIG. 6C, the pedestal 51 of the composite 61 is joined to the flat surface F1 of the rod-like body 271 by resistance welding. In addition, in order to make welding more reliable, plating removal of a welding site is performed prior to the welding, or masking is performed on a planned welding site during a plating process. Further, the composite 61 may be welded after assembling described later.

  On the other hand, the insulator 2 is formed separately from the metal shell 3. For example, a raw material powder containing alumina as a main component and containing a binder or the like is used to prepare a green granulated material for molding, and rubber press molding is used to obtain a cylindrical molded body. The obtained molded body is ground and shaped. And the insulator 2 is obtained by throwing the shaped thing into a baking furnace and baking.

  Separately from the metal shell 3 and the insulator 2, the center electrode 5 is manufactured. That is, a Ni-based alloy is forged, and a copper core is provided at the center to improve heat dissipation. And the noble metal tip 31 mentioned above is joined to the front-end | tip part by laser welding etc.

  The center electrode 5 to which the noble metal tip 31 obtained as described above is joined and the terminal electrode 6 are sealed and fixed to the shaft hole 4 of the insulator 2 by a glass seal (not shown). As the glass seal, one prepared by mixing borosilicate glass and metal powder is generally used. First, the center electrode 5 is inserted into the shaft hole 4 of the insulator 2, and the terminal electrode 6 is pressed from behind after the prepared sealing material is injected into the shaft hole 4 of the insulator 2. Then, it is baked and hardened in a firing furnace. At this time, the glaze layer may be fired simultaneously on the body surface on the rear end side of the insulator 2, or the glaze layer may be formed in advance.

  Thereafter, the insulator 2 including the center electrode 5 and the terminal electrode 6 manufactured as described above, and the metal shell 3 including the straight rod-shaped ground electrode 27 are assembled. More specifically, a part of the insulator 2 is formed on the metal shell 3 from the circumferential direction by performing cold crimping or hot crimping on the rear end portion of the metal shell 3 formed relatively thin. It is held so that it is surrounded.

  Finally, a process of adjusting the spark discharge gap 33 between the center electrode 5 (the noble metal tip 31) and the ground electrode 27 (the noble metal tip 32) is performed by bending the straight rod-like ground electrode 27. The

  Thus, the spark plug 1 having the above-described configuration is manufactured through a series of steps.

  As described above in detail, according to the present embodiment, with respect to the spark plug 1 to be obtained, at least the tip side of the ground electrode 27 from the center of the spark discharge gap 33 and the back surface opposite to the center electrode 5 side. It has a convex curved surface (having a substantially circular cross section). For this reason, for example, as shown in FIGS. 3 and 4, even when the air-fuel mixture directly contacts the back surface of the ground electrode 27, the air-fuel mixture wraps around the ground electrode 27, The air-fuel mixture easily reaches the spark discharge gap 33. As a result, a reduction in ignitability can be prevented.

  The ground electrode 27 includes an outer layer 27B made of a nickel alloy or the like and an inner layer 27A made of a metal having a better thermal conductivity than the outer layer 27B. For this reason, in the inner layer 27A, heat is actively released, and so-called “heat drawing” is improved. Accordingly, it is possible to suppress problems caused by the temperature rise of the ground electrode 27 and the noble metal tip 32 for the ground electrode during high-speed operation, that is, deterioration of durability such as oxidation resistance and spark wear resistance.

  In the present embodiment, the noble metal tip 32 of the ground electrode 27 is bonded to a flat surface F1 having a substantially planar shape. For this reason, compared with the case where the joining surface is curved, it is easy to avoid complication of joining work, and it is possible to improve the joining strength.

  In addition, the noble metal tip 32 is bonded to the seat surface of the plate-like pedestal portion 51 containing nickel as a main component, and the pedestal portion 51 is bonded to the flat surface F 1 of the ground electrode 27. Therefore, if the noble metal tip 32 is firmly joined to the pedestal 51 by laser welding or the like, the pedestal 51 containing the same nickel as the main component and the flat surface F1 of the ground electrode 27 can be joined relatively easily. Can do. Therefore, the bonding strength of the noble metal tip 32 is improved, and the bonding state is further stabilized.

  Moreover, in the present embodiment, in the cross section of the ground electrode 27 viewed from the front end surface side of the ground electrode 27 along the axis CL1, the shortest distance between the flat surface F1 and the inner layer 27A is A (mm), and the inner layer 27A When the distance between the point farthest from the center electrode 5 and the point farthest from the center electrode 5 in the outer layer 27B is B (mm), A / B ≦ 0.7 is satisfied. That is, the shortest distance A between the flat surface F1 and the inner layer 27A is relatively short. As described above, the noble metal tip 32 is bonded to the flat surface F1 of the ground electrode 27 via the pedestal 51, and the molten part 42 is directly connected to the inner layer 27A through the pedestal 51 as described above. While it is possible to achieve strong bonding without contact, the distance between the noble metal tip 32 and the inner layer 27A is also increased by the presence of the pedestal 51. There is concern. In this regard, in the present embodiment, since the shortest distance A between the flat surface F1 and the inner layer 27A is relatively short, heat from the noble metal tip 32 is easily transferred to the inner layer 27A made of a metal having good heat conductivity. As a result, it is possible to dramatically improve the heat drawing performance.

  Here, in order to confirm the above effects, various samples were prepared by changing A / B, and various evaluations were attempted. The experimental results are described below.

  First, as a sample, the screw diameter M12, the protruding length from the combustion chamber to the tip surface of the noble metal tip 31 for the center electrode is 3.5 mm, the spark discharge gap is 1.05 mm, the noble metal tip 31 for the center electrode is 0.6 mm in diameter, and the height. A spark plug sample obtained by joining a 0.8 mm Ir-5Pt alloy and joining a Pt-20Rh alloy having a diameter of 0.7 mm as E = 0.8 mm as the noble metal tip 32 for the ground electrode, A spark plug sample (samples 1 to 16) with various changes in the shortest distance A to the noble metal tip 32 for the ground electrode is mounted on an engine with a displacement of 660 cc and an inline 3-cylinder engine, and the 4000 rpm throttle is fully opened and the ignition timing is 5 ° BTDC. , And operated for a total of 300 hours under the test condition of A / F (air-fuel ratio) 10.7 (however, each spark plug sample is By 0 hours rotation was (cylinder also rotation) is not). And the consumption volume and the side-fire ratio of the noble metal tip 32 for the ground electrode of the spark plug sample after the test were measured. The consumed volume means the amount of decrease after the test from the initial volume of the noble metal tip 32. More specifically, the volume of the noble metal tip 32 was measured using a CT scanner before the test, and the volume of the noble metal tip 32 was similarly measured after the test. And the consumption volume was computed by subtracting the volume after a test from the volume before a test. In addition, the side fire rate is calculated by loading the spark plug sample after operation under the above test conditions on the same engine, operating at a constant idle speed (1500 rpm), and taking 100 discharge waveform data. The discharge waveform is calculated on the basis of the operator discriminating whether the discharge is a normal discharge or a side fire. Samples 1 to 4 have curved surfaces on the back surface of the ground electrode, and Samples 5 to 8 have curved surfaces on both side surfaces of the ground electrode. Samples 9 to 12 have chamfered portions between the front and back surfaces of the ground electrode and both side surfaces. Samples 13 to 16 have chamfered portions between the front and back surfaces of the ground electrode and both side surfaces. It has a curved surface part.

  The evaluation results are shown in Table 1 and FIG. In FIG. 7, samples 1 to 4 are plotted with white circles, samples 5 to 8 are plotted with white triangles, samples 9 to 12 are plotted with white squares, and samples 13 to 16 are marked with a cross. And plotted.

表１及び図７に示すように、内層２７Ａと貴金属チップ３２との最短距離をＡ（ｍｍ）、前記内層２７Ａのうち中心電極５から最も遠い点と、外層２７Ｂのうち中心電極５から最も遠い点との距離をＢ（ｍｍ）とするときの、Ａ／Ｂの値が０．７を超えるサンプル１，５，９，１３に関しては、消耗体積が０．０８ｍｍ³を超え、Ａ／Ｂ≦０．７を満たす他のサンプル（サンプル２〜４，６〜８，１０〜１２，１４〜１６）に比べて大きいものとなってしまった。また、当該消耗体積が大きいサンプル１，５，９，１３に関しては、他のサンプルでは発生しなかった横飛火が発生してしまった。これらのことから、平坦面Ｆ１と内層２７Ａとの最短距離Ａを比較的短くすることで、熱引き性能の飛躍的な向上を図ることができるといえる。これに対し、Ａ／Ｂ≦０．７を満たさない場合には、良好な熱引きが行われにくくなり、消耗体積の増大を招いてしまうとともに、横飛火等が起こりやすくなってしまうことが明らかとなった。

As shown in Table 1 and FIG. 7, the shortest distance between the inner layer 27A and the noble metal tip 32 is A (mm), the point farthest from the center electrode 5 in the inner layer 27A, and the farthest from the center electrode 5 in the outer layer 27B. For samples 1, 5, 9, and 13, where the A / B value exceeds 0.7 when the distance from the point is B (mm), the consumption volume exceeds 0.08 mm ³ and A / B ≦ It was larger than other samples satisfying 0.7 (samples 2 to 4, 6 to 8, 10 to 12, and 14 to 16). Further, with respect to samples 1, 5, 9, and 13 having a large consumption volume, a side fire that did not occur in other samples occurred. From these facts, it can be said that the heat pulling performance can be drastically improved by relatively shortening the shortest distance A between the flat surface F1 and the inner layer 27A. On the other hand, when A / B ≦ 0.7 is not satisfied, it is difficult to perform good heat pulling, which leads to an increase in the consumption volume, and it is easy to cause side fire or the like. It became.

  In addition, it is not limited to the description content of embodiment mentioned above, For example, you may implement as follows.

  (A) In the above embodiment, as the ground electrode 27, a round bar is used as a whole. For example, as shown in FIG. 8, the ground electrode 27 is joined to the front end surface of the metal shell 3 and has a certain width. A base 71 having a substantially rectangular cross section, a small-diameter portion 72 having a circular cross-section (provided with a flat surface) located on the tip side of the base 71, and a cross-section located between the 71 and the small-diameter portion 72 You may employ | adopt the ground electrode 27 which comprises the taper part 73 in which a shape changes gradually along a longitudinal direction (however, the center electrode etc. are abbreviate | omitted in the figure). In this case, the bonding area between the ground electrode 27 and the metal shell 3 can be increased, and consequently the bonding strength can be increased.

  In short, the shape of the ground electrode 27 is particularly limited as long as it has a convex curved surface on the back side opposite to the center electrode 5 side at least on the tip side of the center of the spark discharge gap 33. It is not a thing.

  (B) Moreover, in the said embodiment, the cutting process is given so that the front-end | tip part may become substantially planar shape rather than the bending part of the ground electrode 27. FIG. On the other hand, at least only the portion to which the noble metal tip 32 is bonded may be cut by cutting, or if the inner layer 27A is not exposed to the outside, cutting is performed in the entire longitudinal direction. May be.

  (C) The part to which the noble metal tip 32 is joined may be substantially planar, and need not be a plane in a strict sense. Therefore, there may be some unevenness.

  (D) In the above embodiment, the case where the outer layer 27B is present between the inner layer 27A and the pedestal portion 51 is embodied. However, the embodiment may be embodied when the outer layer 27B is not interposed. In this case, the pedestal 51 is in direct contact with the inner layer 27A, and the distance between the inner layer 27A and the noble metal tip 32 can be further shortened.

  (E) In the above embodiment, a cross section in which the melting part 42 is not connected to one side and the other side is shown, but it may be connected.

It is a partially broken front view which shows the structure of the spark plug of this embodiment. It is a partial expanded sectional view of a spark plug. It is a side view which shows the spark plug seen from the direction orthogonal to FIG. It is a top view which shows the state which looked at the spark plug from the front end side. It is a cross-sectional schematic diagram of the said ground electrode etc. visually recognized from the front end surface side of the ground electrode along the axis line. (A)-(c) is a cross-sectional schematic diagram which shows the manufacturing process of a ground electrode. It is a graph which shows the relationship of the consumption volume with respect to A / B. It is a perspective view which shows typically the ground electrode in another embodiment. It is an expanded sectional view which shows the shape of the ground electrode in another embodiment. It is an expanded sectional view which shows the shape of the ground electrode in another embodiment. It is an expanded sectional view which shows the shape of the ground electrode in another embodiment.

Explanation of symbols

1 ... Spark plug 2 ... Insulator (insulator)
3 ... metal shell 5 ... center electrode 27 ... ground electrode 27A ... inner layer 27B ... outer layer 31 ... (for center electrode) noble metal tip 32 ... (for ground electrode) noble metal tip 33 ... spark discharge gap 42 ... melting part 51 ... pedestal part 52 ... Sitting surface 61 ... Composite F1 ... Flat surface CL1 ... Axis

Claims (13)

A rod-shaped center electrode extending in the axial direction;
A substantially cylindrical insulator provided on the outer periphery of the center electrode;
A cylindrical metal shell provided on the outer periphery of the insulator;
A base electrode is joined to the tip of the metal shell, and the tip is disposed so that the tip faces the tip of the center electrode,
A noble metal tip for center electrode is joined to the tip of the center electrode, and a noble metal tip for ground electrode is joined to a position facing the noble metal tip for center electrode in the tip portion of the ground electrode, A spark plug for an internal combustion engine having a spark discharge gap between a tip of a noble metal tip for a center electrode and a tip of the noble metal tip for a ground electrode,
At least the tip side of the ground electrode has a convex curved surface on the back side opposite to the center electrode side,
The noble metal tip for the ground electrode is bonded to a seat surface of a pedestal portion mainly composed of nickel, and is provided by bonding the pedestal portion to the ground electrode, and the pedestal among the ground electrodes. The part where the part is joined is a flat surface,
At least a portion of the ground electrode that is subjected to a spark discharge includes an outer layer made of a nickel alloy and an inner layer made of a heat conductive material than the outer layer,
In the cross section of the ground electrode viewed from the tip surface side of the ground electrode along the axis,
The shortest distance between the flat surface (including the flat surface before bonding) and the inner layer is A (mm),
When the distance between the farthest point from the center electrode in the inner layer and the farthest point from the center electrode in the outer layer is B (mm),
A / B ≦ 0.7
A spark plug for an internal combustion engine characterized by satisfying A rod-shaped center electrode extending in the axial direction;
A substantially cylindrical insulator provided on the outer periphery of the center electrode;
A cylindrical metal shell provided on the outer periphery of the insulator;
A base electrode is joined to the tip of the metal shell, and the tip is disposed so that the tip faces the tip of the center electrode,
A noble metal tip for center electrode is joined to the tip of the center electrode, and a noble metal tip for ground electrode is joined to a position facing the noble metal tip for center electrode in the tip portion of the ground electrode, A spark plug for an internal combustion engine having a spark discharge gap between a tip of a noble metal tip for a center electrode and a tip of the noble metal tip for a ground electrode,
At least the tip side of the ground electrode has an elliptical cross section,
The noble metal tip for the ground electrode is bonded to a seat surface of a pedestal portion mainly composed of nickel, and is provided by bonding the pedestal portion to the ground electrode, and the pedestal among the ground electrodes. The part where the part is joined is a flat surface,
At least a portion of the ground electrode that is subjected to a spark discharge includes an outer layer made of a nickel alloy and an inner layer made of a heat conductive material than the outer layer,
In the cross section of the ground electrode viewed from the tip surface side of the ground electrode along the axis,
The shortest distance between the flat surface (including the flat surface before bonding) and the inner layer is A (mm),
When the distance between the farthest point from the center electrode in the inner layer and the farthest point from the center electrode in the outer layer is B (mm),
A / B ≦ 0.7
A spark plug for an internal combustion engine characterized by satisfying A rod-shaped center electrode extending in the axial direction;
A substantially cylindrical insulator provided on the outer periphery of the center electrode;
A cylindrical metal shell provided on the outer periphery of the insulator;
A base electrode is joined to the tip of the metal shell, and the tip is disposed so that the tip faces the tip of the center electrode,
A noble metal tip for center electrode is joined to the tip of the center electrode, and a noble metal tip for ground electrode is joined to a position facing the noble metal tip for center electrode in the tip portion of the ground electrode, A spark plug for an internal combustion engine having a spark discharge gap between a tip of a noble metal tip for a center electrode and a tip of the noble metal tip for a ground electrode,
At least the tip side of the ground electrode has a cross-sectional shape formed by cutting out the four corners of the rectangle into straight or protruding curved shapes, respectively.
The noble metal tip for the ground electrode is bonded to a seat surface of a pedestal portion mainly composed of nickel, and is provided by bonding the pedestal portion to the ground electrode, and the pedestal among the ground electrodes. The part where the part is joined is a flat surface,
At least a portion of the ground electrode that is subjected to a spark discharge includes an outer layer made of a nickel alloy and an inner layer made of a heat conductive material than the outer layer,
In the cross section of the ground electrode viewed from the tip surface side of the ground electrode along the axis,
The shortest distance between the flat surface (including the flat surface before bonding) and the inner layer is A (mm),
When the distance between the farthest point from the center electrode in the inner layer and the farthest point from the center electrode in the outer layer is B (mm),
A / B ≦ 0.7
A spark plug for an internal combustion engine characterized by satisfying When the thickness in the axial direction of the pedestal portion is T (mm),
T ≧ 0.25
The spark plug for an internal combustion engine according to any one of claims 1 to 3, wherein:   The spark plug for an internal combustion engine according to any one of claims 1 to 4, wherein the noble metal tip for ground electrode is joined to the seating surface of the pedestal portion by laser welding or electron beam welding.   The spark plug for an internal combustion engine according to any one of claims 1 to 5, wherein the pedestal portion is joined to the flat surface by resistance welding.   The noble metal tip for ground electrode is joined to the seating surface of the pedestal portion to form a composite, and the pedestal portion of the composite is joined to the flat surface. The spark plug for an internal combustion engine according to any one of claims 1 to 6.   The spark plug for an internal combustion engine according to any one of claims 1 to 7, wherein the pedestal portion is in contact with the inner layer.   9. The spark plug for an internal combustion engine according to claim 1, wherein at least a part of the inner layer is mainly composed of copper. In the cross section of the ground electrode viewed from the tip surface side of the ground electrode along the axis,
When the distance between the flat surface and the point farthest from the center electrode of the outer layer is C (mm),
The spark plug for an internal combustion engine according to claim 1, wherein C ≦ 1.3 is satisfied. In the cross section of the ground electrode viewed from the tip surface side of the ground electrode along the axis,
When the width of the ground electrode in the direction orthogonal to the axis is D (mm),
The spark plug for an internal combustion engine according to claim 1, wherein D ≦ 1.5 is satisfied. In the cross section of the ground electrode viewed from the tip surface side of the ground electrode along the axis,
When the length from the flat surface to the tip of the noble metal tip for the ground electrode is E (mm),
The spark plug for an internal combustion engine according to claim 1, wherein E ≧ 0.4 is satisfied.   The spark plug for an internal combustion engine according to any one of claims 1 to 12, wherein the flat surface is formed by cutting out the outer layer.

Images