JP4714249B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug.

  Conventional spark plugs are provided with a cylindrical metal shell, and a cylindrical insulator extending in the axial direction of the metal shell and projecting from both ends of the metal shell is fixed in the metal shell. Has been. The central electrode extends in the axial direction of the metal shell, the tip of the center electrode protrudes from the tip of the insulator, and the rear end of the center electrode is fixed in the insulator. On the other hand, one end of the ground electrode is fixed to the metal shell, and a discharge gap is formed between the other end of the ground electrode and the center electrode. The center electrode and the ground electrode are each made of an electrode base material made of Ni alloy or the like such as Inconel (registered trademark) 600 and a chip made of a spark consumable material such as Pt alloy containing Ir at a position forming the discharge gap side. Have. An intermediate member having an intermediate melting point or linear expansion coefficient between the electrode base material and the tip is provided between at least one of the center electrode and the ground electrode and the tip (Patent Document 1). .

  Such a spark plug has been manufactured by the following manufacturing method. That is, in Patent Document 1, first, as a first step, a cylindrical rod-shaped intermediate material having an intermediate melting point or linear expansion coefficient between the electrode base material and the tip is prepared. And as a 2nd process, a cylindrical chip | tip is TIG-welded or laser-welded to the front-end | tip of the intermediate material, and an intermediate material with a chip | tip is obtained. Thereafter, as a third step, the chip-attached intermediate material is cut into a chip-attached intermediate member. The tip-attached intermediate member thus obtained includes a columnar intermediate member and a columnar tip welded to the first surface of the intermediate member. Next, as a fourth step, the second surface of the intermediate member of the intermediate member with tip is resistance-welded to the joint surface on the discharge gap side of the electrode base material to form a center electrode or a ground electrode.

  In this spark plug, the tip made of a spark-resistant consumable material is resistant to wear and exhibits high durability, while the tip based on the thermal stress difference between the tip and the electrode base material is difficult to join to the electrode base material. The problem is solved by the intermediate member.

JP-A-8-298178

  However, in the conventional spark plug described above, stronger bonding between the tip and the electrode base material in at least one of the center electrode and the ground electrode is required.

  That is, in the conventional manufacturing method, the tip-attached intermediate member is obtained by cutting the obtained tip-attached intermediate member after TIG welding or laser welding of the tip to the cylindrical rod-like intermediate member. For this reason, in the spark plug obtained in this way, there is a possibility that a crack is generated in the welded portion when the intermediate material with the tip is cut, and the joining force between the tip and the intermediate member may be weakened by the crack.

  Further, when the intermediate member with the chip is cut to obtain the intermediate member with the chip, it is difficult to cut the tip end surface of the chip and the second surface of the intermediate member with the chip in parallel with each other. For this reason, when an intermediate member with a chip in which the tip end surface of the chip and the second surface of the intermediate member with a chip are not parallel to each other is used as, for example, the center electrode of the spark plug, a discharge gap is formed at the edge of the chip, There is a possibility that the spark wear resistance of the chip itself may be reduced.

  The present invention has been made in view of the above-described conventional situation, and more firmly joining the electrode base material and the chip in at least one of the center electrode and the ground electrode, and maintaining the spark consumption of the chip itself, Providing a spark plug capable of realizing this is an issue to be solved.

The spark plug of the present invention includes a cylindrical metal shell, a cylindrical insulator that extends in the axial direction of the metal shell, protrudes from both ends of the metal shell, and is fixed in the metal shell. A central electrode extending in the axial direction of the metal shell, having a tip projecting from the tip of the insulator and having a rear end fixed in the insulator, one end fixed to the metal shell, and the other end A ground electrode that forms a discharge gap with the center electrode, and the center electrode and the ground electrode are each composed of an electrode base material and a spark consumable material at a position where the discharge gap is formed in the electrode base material. And an intermediate member having an intermediate melting point or a linear expansion coefficient between the electrode base material and the tip is provided between the tip and the electrode base material of at least one of the center electrode and the ground electrode. In the spark plug
The intermediate member has a first surface bonded to the chip and a second surface parallel to the first surface and bonded to the electrode base material ,
The intermediate member is such that the first surface and the second surface are orthogonal to the axis of the intermediate member, and the maximum diameter of the first surface is smaller than the maximum diameter of the second surface. A flange portion that forms the second surface on the bottom surface, and a column portion that rises from the flange portion with a smaller diameter than the flange portion and forms the first surface on the top surface.

In the spark plug of the present invention, the intermediate member has a first surface bonded to the chip and a second surface parallel to the first surface and bonded to the electrode base material . The intermediate member is such that the first surface and the second surface are orthogonal to the axis of the intermediate member, and the maximum diameter of the first surface is smaller than the maximum diameter of the second surface. The intermediate member includes a flange portion that forms the second surface on the bottom surface, and a column portion that rises from the flange portion with a smaller diameter than the flange portion and forms the first surface on the top surface. For this reason, the 2nd surface of an intermediate member is welded with the joining surface by the side of the discharge gap of an electrode base material with a large area, and the joining force of an intermediate member and an electrode base material improves reliably.

  Further, in this spark plug, since the first surface and the second surface of the intermediate member are parallel to each other, the tip end surface of the chip and the second surface of the intermediate member can be easily maintained in parallel with each other. And the joint surface of the electrode base material are easily maintained parallel to each other. For this reason, it is difficult to form a discharge gap at the edge of the chip, and it is easy to maintain the spark wear resistance of the chip itself.

  Therefore, the spark plug of the present invention realizes stronger bonding between the electrode base material and the chip in at least one of the center electrode and the ground electrode and maintenance of the spark wear resistance of the chip itself. For this reason, this spark plug can maintain the durability exhibited by the chip for a long period of time.

  The intermediate member includes a flange portion that forms the second surface on the bottom surface, and a cylindrical portion that rises from the flange portion with a smaller diameter than the flange portion and forms the first surface on the top surface. For this reason, the weldability between the intermediate member and the tip can be improved by the cylindrical portion while the area of the second surface is increased by the flange portion. In that case, it is more preferable that the flange portion has a tapered surface protruding to the first surface side. Since the flange portion has a tapered surface protruding to the first surface side, the strength of the intermediate member can be ensured.

  In the spark plug of the present invention, it is preferable that the chip has a cylindrical shape, the first surface is a circle including the bottom surface of the chip, and the diameter of the first surface is larger than the diameter of the chip. In particular, when the diameter of the first surface is d1 and the diameter of the chip is D1, it is preferable that D1 <d1 ≦ D1 + 0.6 (mm). In this case, it is easy to firmly join the tip and the intermediate member by melting the bottom surface of the tip and the first surface of the intermediate member by laser welding. According to the test results of the inventors, when the diameter of the first surface is equal to or smaller than the diameter of the chip (when d1 ≦ D1), the melting balance between the chip and the intermediate member is deteriorated, and the chip and the intermediate member are strengthened. It is hard to join to. Further, when the diameter of the first surface is larger than the diameter of the chip by 0.6 mm (D1 + 0.6 <d1), it is difficult to secure the focal point of the laser and it is difficult to firmly bond the chip and the intermediate member. .

  In addition, the second surface is a circle within the width of the electrode base material in the center electrode or the width of the electrode base material in the ground electrode, and the diameter of the second surface is the diameter of the electrode base material in the center electrode or the electrode base in the ground electrode. It is preferably smaller than the width of the material. The diameter of the electrode base material is intended when the intermediate member with the tip is welded to the center electrode. The width of the electrode base material is intended when the intermediate member with a tip is welded to the ground electrode. This is because the second surface of the intermediate member can be utilized to the maximum. In particular, when the diameter of the first surface is d1, the diameter of the second surface is d2, and the diameter of the electrode base material at the center electrode or the width of the electrode base material at the ground electrode is D2, d1 + 0.3 <d2 ≦ D2 (mm ) Is preferable. If it is this, the 2nd surface of the intermediate member in the case of resistance welding can be utilized to the maximum, and the intermediate member with a chip | tip and an electrode base material can be joined firmly. According to the test results of the inventors, when the difference between the diameter of the second surface and the diameter of the first surface is 0.3 mm or less, the joint surface becomes small, so that the intermediate member with the chip is firmly attached to the electrode base material. It is difficult to join. In addition, when the intermediate member with the tip is pressed in the axial direction by the side surface of the intermediate member with the tip, it is difficult to press the intermediate member with the tip, so that it is difficult to firmly join the intermediate member with the tip to the electrode base material. . Further, when the diameter of the second surface is larger than the diameter of the electrode base material in the center electrode or the width of the electrode base material in the ground electrode, the second surface of the intermediate member after resistance welding protrudes from the center electrode or the ground electrode, Spark plug ignitability is reduced.

  In addition to the above-mentioned Patent Document 1, spark plug manufacturing methods described in Japanese Patent Application Laid-Open Nos. 2000-277231 and 2001-273965 are also known.

  In the manufacturing method described in Japanese Patent Application Laid-Open No. 2000-277231, first, a disk-shaped intermediate member having an intermediate melting point or linear expansion coefficient between the electrode base material and the tip is prepared. Then, a spherical tip is brought into contact with the first surface of the intermediate member, and in this state, the second surface of the intermediate member is resistance-welded to the joint surface on the discharge gap side of the electrode base material, and the center electrode or ground The electrode. In the spark plug thus obtained, the intermediate member has a disk shape in which the first surface and the second surface have the same diameter and are parallel to each other, although the chip is recessed into the first surface. Resistance welding is performed in a state where the tip is indented into the first surface of the intermediate member, and the second surface of the intermediate member is resistance-welded to the joint surface on the discharge gap side of the electrode base material.

  In the manufacturing method described in Japanese Patent Application Laid-Open No. 2001-273965, first, a center electrode tip having a columnar shape is laser-welded to the joint surface on the discharge gap side of the electrode base material of the center electrode to form a center electrode. In addition, a cylindrical intermediate member having an intermediate melting point or linear expansion coefficient between the electrode base material and the tip is prepared. Then, the ground electrode tip having a columnar shape is brought into contact with the first surface of the intermediate member, and in this state, the second surface of the intermediate member is resistance welded to the joint surface on the discharge gap side of the electrode base material. The ground electrode. Also in the spark plug thus obtained, the intermediate member of the ground electrode has a cylindrical shape in which the first surface and the second surface have the same diameter and are parallel to each other. Resistance welding is performed in a state where the tip is indented into the first surface of the intermediate member, and the second surface of the intermediate member is resistance-welded to the joint surface on the discharge gap side of the electrode base material.

  However, in these known manufacturing methods, the intermediate member has a cylindrical shape or a disk shape in which the first surface and the second surface have the same diameter and are parallel to each other, and the second surface of the intermediate member is the electrode mother. It is merely welded to the joint surface on the discharge gap side of the material with a small area. For this reason, in the spark plug obtained by these manufacturing methods, there is a concern about the bonding force between the intermediate member and the electrode base material. In particular, it is considered that this tendency is large when the second surface of the intermediate member and the electrode base material of the ground electrode are joined by resistance welding due to the limitation of the incident angle of the laser.

In contrast, the spark plug of the present invention has a first surface where the intermediate member is bonded to the chip and a second surface which is parallel to the first surface and bonded to the electrode base material . The intermediate member is such that the first surface and the second surface are orthogonal to the axis of the intermediate member, and the maximum diameter of the first surface is smaller than the maximum diameter of the second surface. The intermediate member includes a flange portion that forms the second surface on the bottom surface, and a column portion that rises from the flange portion with a smaller diameter than the flange portion and forms the first surface on the top surface. For this reason, compared with the conventional spark plug whose intermediate member is cylindrical or disk-shaped, the durability exhibited by the tip made of the spark-resistant consumable material can be maintained for a long time.

  Hereinafter, an embodiment in which the spark plug of the present invention is embodied will be described with reference to FIGS.

  First, as shown in FIG. 1, in the first step S10, an intermediate member 10 made of an Ir alloy containing 40% by mass of Ni is manufactured. As shown in FIG. 2, the intermediate member 10 rises from a flange portion 12 having a diameter of 1.5 (mm) and a surrounding thickness of 0.2 (mm), and an upper surface of the flange portion 12, and has a diameter of 0.8 ( mm) and a cylindrical portion 14 having a thickness of 0.2 (mm). The bottom surface of the flange portion 12 is the second surface 12a, and the top surface of the cylindrical portion 14 is the first surface 14a. The first surface 14 a and the second surface 12 a are orthogonal to the axis of the intermediate member 10. The upper surface of the flange portion 12 forms a tapered surface 12b that protrudes toward the first surface 14a.

Next, in the second step S20 shown in FIG. 1, as shown in FIG. 3, a refractory spark made of an Ir alloy containing 20% by mass of Rh, 5% by mass of Pt or 1.7% by mass of Y ₂ O ₃ is used. A chip 16 made of a consumable material is manufactured. The chip 16 has a cylindrical shape with a diameter of 0.6 (mm) and a thickness of 0.8 (mm), and the tip surface and the bottom surface of the chip 16 are parallel to each other and orthogonal to the axis of the chip 16. .

  And this chip | tip 16 is mounted on the 1st surface 14a of the intermediate member 10, and these are welded with the laser which is not shown in figure. At this time, whether it is bonded to the center electrode 30 shown in FIG. 7 or to the ground electrode 40, the intermediate member 20 with a chip shown in FIG. 3 is obtained without being limited by the incident angle of the laser. Can do. Further, since the intermediate member 10 and the chip 16 are bonded by the laser, their bonding force is high. In particular, since the relationship between the diameter d1 of the first surface 14a of the intermediate member 10 and the diameter D1 of the chip 16 is D1 <d1 ≦ D1 + 0.6 (mm), it is easy to secure the focal point of the laser, and the chip 16 Can be firmly bonded to the intermediate member 10. Moreover, since the intermediate member 10 contains Ir which is a component of the chip 16, the intermediate member 20 with the chip is a member in which the intermediate member and the chip 16 are mixed and firmly bonded.

  Next, in a third step S30 shown in FIG. 1, the tip-attached intermediate member 20 is resistance-welded to the center electrode 30 as shown in FIG. The center electrode 30 has a diameter of 2.5 (mm) using a Ni alloy of Inconel (registered trademark) 600 as an electrode base material. At that time, first, the second surface 12a of the intermediate member 10 of the intermediate member 20 with the tip is disposed on the joint surface 32 of the center electrode 30 on the discharge gap side. Then, an electric resistance welder 50 is provided on the flange portion 12 of the intermediate member 10, and a predetermined current is applied under a predetermined pressure. Thus, as shown in FIG. 5, the tip-attached intermediate member 20 is resistance-welded to the center electrode 30. After that, as shown in FIG. 7, the center electrode 30 is incorporated into the insulator 62 so that the tip protrudes, and the terminal 63 is inserted into the rear end of the center electrode 30 in the insulator 62. These are incorporated into the metal shell 60.

  Similarly, as shown in FIG. 7, the ground electrode 40 previously welded to the metal shell 60 is produced. The ground electrode 40 has a width of 2.5 (mm) using a Ni alloy of Inconel (registered trademark) 600 as an electrode base material, like the center electrode 30. And as shown in FIG. 4, the 2nd surface 12a of the intermediate member 10 of the intermediate member 20 with a tip is resistance-welded to the ground electrode 40. In that case, first, the second surface 12a of the intermediate member 10 of the intermediate member 20 with the tip is disposed on the joint surface 42 of the ground electrode 40 on the discharge gap side, and resistance welding is similarly performed. At this time, since the intermediate member with tip 20 may be resistance-welded to the electrode base material of the ground electrode 40, the tip 16 can be provided on the side of the ground electrode 40 without being limited by the incident angle of the laser.

  Then, as shown in FIG. 6, one end of the electrode base material of the ground electrode 40 welded to the tip-attached intermediate member 20 is bent toward the center electrode 30 side. In this way, the spark plug shown in FIG. 7 is obtained.

  In these cases, the intermediate member 10 has an intermediate melting point or linear expansion coefficient between the electrode base material of the center electrode 30 and the ground electrode 40 and the chip 20. For this reason, in this spark plug, the difference between the thermal stress generated in the electrode base material of the center electrode 30 and the ground electrode 40 due to the thermal stress generated in the intermediate member 10 and the thermal stress generated in the chip 16 is reduced. For this reason, the intermediate member 10 itself is hardly distorted, and peeling between the electrode base material of the center electrode 30 or the ground electrode 40 and the intermediate member 10 or between the intermediate member 10 and the chip 16 is difficult to occur. Further, in the intermediate member 10 having an intermediate melting point or linear expansion coefficient between the electrode base material and the tip 16, a general-purpose resistance can be obtained without performing laser welding, which is a large facility, in the third step S30. Sufficient weld strength can be secured by welding.

  Further, in the intermediate member with tip 20 obtained in the second step S20, the tip 16 is welded to the first surface 14a of the intermediate member 10 by laser. For this reason, the joining force between the tip 16 and the intermediate member 10 in the tip-attached intermediate member 20 is high. In the third step S30, the tip-attached intermediate member 20 is directly welded to the electrode base material of the center electrode 30 and the ground electrode 40, and the tip-attached intermediate member obtained by cutting the tip-attached intermediate member is welded as in the prior art. Not to do. For this reason, in the spark plug obtained in this way, a crack is not generated in the welded portion between the tip 16 and the intermediate member 10, and the joining force between the tip 16 and the intermediate member 10 is maintained.

  Furthermore, in order to produce the intermediate member 10 having the first surface 14a and the second surface 12a parallel to the first surface 14a in the first step S10, the intermediate member 20 with a chip obtained in the second step S20 is the chip 16 It is easy to maintain the front end surface of the chip and the second surface 12a of the intermediate member 20 with the chip parallel to each other, and in turn, maintain the front end surface of the chip 16 and the bonding surface of the electrode base material in parallel with each other. For this reason, even when this tip-attached intermediate member 20 is used as the center electrode 30 of the spark plug, it is difficult to form a discharge gap at the edge of the tip 16, and it is easy to maintain the spark wear resistance of the tip 16 itself.

  In particular, in this manufacturing method, the relationship between the diameter d1 of the first surface 14a and the diameter d2 of the second surface 12a of the intermediate member 10 and the diameter of the electrode base material at the center electrode 30 or the width D2 of the electrode base material at the ground electrode 40. Since d1 + 0.3 <d2 ≦ D2 (mm), the second surface 12a of the intermediate member 10 at the time of resistance welding can be utilized to the maximum, and the intermediate member 20 with the tip, the electrode base material, Can be firmly joined. Further, since the intermediate member 10 contains Ni which is a component of the electrode base material of the ground electrode 40, the intermediate member 20 with the tip is obtained by mixing and firmly joining the intermediate member and the electrode base material of the ground electrode 40. It becomes.

  Further, as shown in FIG. 2, the intermediate member 10 has the first surface 14a and the second surface 12a orthogonal to the axis of the intermediate member 10, and the maximum diameter of the first surface 14a is that of the second surface 12a. The shape is smaller than the maximum diameter. And as shown in FIG. 3, the intermediate member 20 with a chip | tip has the discharge gap of the electrode base material of the center electrode 30 and the ground electrode 40 rather than the 1st surface 14a of the intermediate member 10 with which the cylindrical chip | tip 16 was welded. The second surface 12a of the intermediate member 10 welded to the side has a large diameter. For this reason, since the second surface 12a of the intermediate member 10 is resistance-welded in a large area with the joint surfaces 32 and 42 on the discharge gap side of the electrode base material of the center electrode 30 and the ground electrode 40, the intermediate member 10 and The joining force with the electrode base material is reliably improved.

  Furthermore, in this manufacturing method, the intermediate member 10 has a flange portion 12 that forms the second surface 12a on the bottom surface, and a cylindrical portion 14 that rises from the flange portion 12 with a smaller diameter than the flange portion 12 and forms the first surface 14a on the top surface. Therefore, the weldability between the intermediate member 10 and the tip 16 can be improved by the cylindrical portion 14 while the area of the second surface 12 a is increased by the flange portion 12. In particular, since the flange portion 12 has a tapered surface 12b that protrudes toward the first surface 14a, the strength of the intermediate member 10 is ensured.

  Therefore, in this manufacturing method, it is possible to realize stronger bonding between the electrode base material in the center electrode 30 and the ground electrode 40 and the chip 16 and maintenance of the spark wear resistance of the chip 16 itself.

  As shown in FIG. 7, the spark plug thus obtained includes a cylindrical metal shell 60. The metal shell 60 extends in the axial direction of the metal shell 60, and both ends are connected to the metal shell 60. A cylindrical insulator 62 protruding from both ends is fixed. Further, the center electrode 30 extends in the axial direction of the metal shell 60, the tip of the center electrode 30 protrudes from the tip of the insulator 62, and the rear end of the center electrode 30 is fixed in the insulator 62. On the other hand, one end of the ground electrode 40 is fixed to the metal shell 60, and a discharge gap is formed between the other end of the ground electrode 40 and the center electrode 30. The center electrode 30 and the ground electrode 40 are provided with the chip-attached intermediate member 20 facing each other while forming a discharge gap.

  In this spark plug, the intermediate member 10 has a first surface 14a and a second surface 12a parallel to the first surface 14a. The intermediate member 10 is such that the first surface 14a and the second surface 12a are orthogonal to the axis of the intermediate member 10, and the maximum diameter of the first surface 14a is smaller than the maximum diameter of the second surface 12a. It is. The intermediate member 10 includes a flange portion 12 that forms the second surface 12a on the bottom surface, and a cylindrical portion 14 that rises from the flange portion 12 with a smaller diameter than the flange portion 12 and forms the first surface 14a on the top surface. For this reason, the second surface 12a of the intermediate member 10 is welded with a large area to the joint surface on the discharge gap side of the electrode base material, and the joint force between the intermediate member 10 and the electrode base material of the center electrode 30 and the ground electrode 40 is ensured. Has improved. Further, in this spark plug, since the first surface 14a and the second surface 12a of the intermediate member 10 are parallel to each other, the tip surface of the chip 16 and the second surface 12a of the intermediate member 10 can be easily maintained parallel to each other. As a result, the tip surface of the chip 16 and the bonding surface of the electrode base material can be easily maintained in parallel with each other. For this reason, it is difficult to form a discharge gap at the edge of the chip 16, and it is easy to maintain the spark wear resistance of the chip 16 itself.

  Therefore, this spark plug can maintain the durability exhibited by the chip 16 over a long period of time.

  In the spark plug according to the embodiment, for example, as shown in FIGS. 8A to 8D, various shapes of the intermediate member 10 can be employed. The intermediate member 71 shown in FIG. 8A has a tapered surface 12b having a larger inclination than that of the above embodiment. The intermediate member 72 shown in FIG. 8B is one in which the flange portion 12 does not have a surrounding thickness. The intermediate member 75 shown in FIG. 8C is composed of a flange portion 12 having a flat upper surface and a cylindrical portion 14 rising from the upper surface of the flange portion 12. The intermediate member 76 shown in FIG. 8D has a thickness of the cylindrical portion 14 smaller than that in FIG. Even with such intermediate members 71, 72, 75, 76, the effects of the present invention can be achieved.

  The present invention is applicable to a spark plug.

It is process drawing of the manufacturing method of a spark plug concerning embodiment. FIG. 6 is a side view of the intermediate member according to the embodiment. It is a side view of the intermediate member with a chip according to the embodiment. It is a side view of the intermediate member with a tip at the time of resistance welding according to the embodiment. It is a partial expanded sectional view of a center electrode or a ground electrode concerning an embodiment. FIG. 4 is a partially enlarged side view of the spark plug according to the embodiment. It is a side view of a partial cross section of the spark plug according to the embodiment. FIG. 10 is a side view of another intermediate member according to the embodiment.

Explanation of symbols

60 ... metal shell 62 ... insulator 30 ... center electrode 40 ... ground electrode 16 ... tip 10, 71, 72, 75, 76 ... intermediate member S10 ... first step 14a ... first surface 20 ... intermediate member with tip S20 ... first 2 processes 32, 34 ... joint surface 12a ... 2nd surface S30 ... 3rd process 12 ... flange part 14 ... cylindrical part 12b ... taper surface

Claims (6)

A cylindrical metal shell, a cylindrical insulator that extends in the axial direction of the metal shell, protrudes from both ends of the metal shell, and is fixed in the metal shell, and an axial direction of the metal shell A center electrode with a tip projecting from the tip of the insulator and a rear end fixed in the insulator, and one end fixed to the metal shell, between the other end and the center electrode. A ground electrode that forms a discharge gap, the center electrode and the ground electrode each having an electrode base material and a tip made of a spark-resistant consumable material at a position where the discharge gap of the electrode base material is formed, In a spark plug in which an intermediate member having an intermediate melting point or a linear expansion coefficient of the electrode base material and the tip is provided between the tip and at least one of the center electrode and the ground electrode.
The intermediate member has a first surface bonded to the chip and a second surface parallel to the first surface and bonded to the electrode base material ,
The intermediate member has a shape in which the first surface and the second surface are orthogonal to the axis of the intermediate member, and the maximum diameter of the first surface is smaller than the maximum diameter of the second surface. A spark plug comprising: a flange portion that forms the second surface on the bottom surface; and a pillar portion that rises from the flange portion with a smaller diameter than the flange portion and forms the first surface on the top surface.   The spark plug according to claim 1, wherein the flange portion has a tapered surface protruding toward the first surface.   3. The spark according to claim 1, wherein the tip has a cylindrical shape, the first surface is a circle including a bottom surface of the tip, and the diameter of the first surface is larger than the diameter of the tip. plug.   4. The spark plug according to claim 3, wherein D1 <d1 ≦ D1 + 0.6 (mm), where d1 is a diameter of the first surface and D1 is a diameter of the tip.   The second surface is a circle within the width of the electrode base material in the center electrode or the width of the electrode base material in the ground electrode, and the diameter of the second surface is the diameter of the electrode base material in the center electrode. The spark plug according to any one of claims 1 to 4, wherein the spark plug is smaller than a width of the electrode base material in the ground electrode.   When the diameter of the first surface is d1, the diameter of the second surface is d2, and the diameter of the electrode base material at the center electrode or the width of the electrode base material at the ground electrode is D2, d1 + 0.3 <d2 The spark plug according to claim 5, wherein ≦ D2 (mm).

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