JP5149839B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug.

  There is known a spark plug in which a noble metal tip member such as iridium (Ir) excellent in spark wear resistance and oxidation wear resistance is joined to a spark discharge site in a center electrode or a ground electrode of the spark plug (for example, Patent Document 1). ~ 3).

JP 2002-93547 A JP 2005-183167 A JP-A-8-298178

  In such a spark plug, when the noble metal tip member is attached to the electrode base material via the intermediate member at the center electrode or the ground electrode, the noble metal tip member and the intermediate member are joined by laser welding to form the two-layer member. After the formation, the intermediate member and the laser melting part are buried in the electrode base material, and the noble metal tip member is formed by resistance welding near the tip of the electrode base material so that the upper surface protrudes from the electrode base material. It is joined.

  4 and 5 are cross-sectional views showing a cross section of a portion centering on a two-layer member in a conventional spark plug, respectively. In these drawings, reference numeral 31 denotes an electrode base material.

  When the noble metal tip member 333 and the intermediate member 334 are joined by laser welding to form the two-layer member 332, as shown in FIG. 4 or FIG. 5, first, the lower surface of the noble metal tip member 333 and the intermediate member 334 Then, the outer edge of the boundary surface 336 where the noble metal tip member 333 and the intermediate member 334 are in contact with each other is laser-welded over almost the entire circumference, and laser is applied to the boundary surface 336 portion. A melting part 335 is formed, and the noble metal tip member 333 and the intermediate member 334 are joined by the laser melting part 335. At this time, the tip 335a of the laser melting part 335 does not reach the center of the boundary surface 336, and the laser melting part 335 is formed in a ring shape.

  However, in the past, the laser melting portion 335 was formed at a position as described below, so that the temperature change caused the intermediate member 334 and the noble metal tip member 333 between and the intermediate member 334 and the electrode base material 31. When stress is generated in the meantime, the noble metal tip member 333 may fall off.

  That is, conventionally, in the direction perpendicular to the boundary surface 336, the tip 335a of the laser melting portion 335 is located at the same position as the boundary surface 336 as shown in FIG. 4, or as shown in FIG. The laser melting part 335 was formed so as to be positioned closer to the intermediate member 334 than 336. At this time, at the former position, as shown in FIG. 4, the distance between the opposed tips 335 a of the laser melting portion 335, in other words, the inner diameter φd of the laser melting portion 335 having a ring shape is It becomes equal to the outer diameter φD of the contact portion between the noble metal tip member 333 and the intermediate member 334 (φd = φD). In the latter position, as shown in FIG. 5, the inner diameter φd of the laser melting portion 335 is smaller than the outer diameter φD of the contact portion between the noble metal tip member 333 and the intermediate member 334 on the boundary surface 336 (φd > ΦD).

  Conventionally, since the laser melting portion 335 is formed at the position as described above, it is allowed between the intermediate member 334 and the noble metal tip member 333 and between the intermediate member 334 and the electrode base material 31 due to temperature change. When the above stress is generated, in the case of the former position shown in FIG. 4, as shown in FIG. 6, in the case of the latter position shown in FIG. 5, as shown in FIG. Could fall off.

  6 and 7 are explanatory views showing a state in which the noble metal tip member has dropped off in the conventional spark plug, respectively.

  Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a spark plug in which a noble metal tip member is not easily dropped even when stress due to temperature change occurs in an electrode.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A spark plug having a center electrode and a ground electrode that forms a spark gap between the center electrode, wherein at least one of the center electrode and the ground electrode includes an electrode base material, a noble metal tip member, The first surface is in contact with the noble metal tip member, and the second surface opposite to the first surface is in contact with the electrode base material, and the noble metal tip and the intermediate member are in contact with each other. A laser melting portion formed in the vicinity of the boundary surface by laser welding at least a part of the outer edge of the boundary surface, and the distance φd between the opposed tips of the laser melting portion is 0 The tip of the laser melting portion is located closer to the noble metal tip member than the boundary surface in a direction perpendicular to the boundary surface and the distance φd is equal to the noble metal tip on the boundary surface. A spark plug characterized in that it is smaller than the outer diameter φD of the contact portion between the tip member and the intermediate member.
As described above, in the spark plug of Application Example 1, since the laser melting portion is formed so that the tip of the laser melting portion is located on the noble metal tip member side with respect to the boundary surface, stress due to temperature change is applied to the electrode. Even if it occurs, the noble metal tip member is not easily dropped due to being caught by the laser melting portion.

[Application Example 2]
The spark plug according to Application Example 1, wherein the laser melting portion is formed so as to be inclined from the intermediate member toward the noble metal tip member with respect to the boundary surface.
Thus, since the laser melting part is formed so as to be inclined, the noble metal tip member becomes more difficult to drop off because the noble metal tip member is caught in the laser melting part.

  Note that the various forms or application examples described above can be combined as appropriate or a part of the configuration can be omitted.

It is explanatory drawing which fractured | ruptured and showed the spark plug 100 as 1st Example of this invention. It is sectional drawing which shows the cross section of the part centering on the two-layer member in the spark plug of FIG. It is sectional drawing which shows the cross section of the part centering on the 2 layer member in the spark plug of 2nd Example of this invention. It is sectional drawing which shows the cross section of the part centering on the two-layer member in the conventional spark plug. It is sectional drawing which shows the cross section of the part centering on the two-layer member in the conventional spark plug. It is explanatory drawing which shows a mode that the noble metal tip member fell in the conventional spark plug. It is explanatory drawing which shows a mode that the noble metal tip member fell in the conventional spark plug.

Hereinafter, embodiments of the present invention will be described in the following order based on examples.
A. First embodiment:
A-1. Spark plug configuration:
A-2.2 Layer member configuration and formation method:
A-3. Effects of the first embodiment:
B. Second embodiment:
B-1.2 Structure and forming method of layer member:
B-2. Effects of the second embodiment:
C. Variations:

A. First embodiment:
A-1. Spark plug configuration:
FIG. 1 is an explanatory view showing a part of a spark plug 100 as a first embodiment of the present invention. A spark plug 100 shown in FIG. 1 includes an insulator 10, a center electrode 20, a ground electrode 30, a terminal fitting 40, and a metal shell 50. The rod-shaped center electrode 20 protruding from one end of the insulator 10 is electrically connected to a terminal fitting 40 provided at the other end of the insulator 10 through the inside of the insulator 10. The outer circumference of the center electrode 20 is insulated by the insulator 10, and the outer circumference of the insulator 10 is held by the metal shell 50 at a position away from the terminal fitting 40. The ground electrode 30 electrically connected to the metal shell 50 forms a spark gap, which is a gap for generating a spark, between the tip of the center electrode 20. The spark plug 100 is attached to a mounting screw hole 201 provided in an engine head 200 of an internal combustion engine (not shown) via a metal shell 50, and a high voltage of 20,000 to 30,000 volts is applied to the terminal fitting 40. Then, a spark is generated in a spark gap formed between the center electrode 20 and the ground electrode 30.

  The insulator 10 of the spark plug 100 is an insulator formed by firing a ceramic material such as alumina. The insulator 10 is a cylindrical body in which the shaft hole 12 that accommodates the center electrode 20 and the terminal fitting 40 is formed at the center. At the center of the insulator 10 in the axial direction, a flange portion 19 having an increased outer diameter is formed. A rear end side body portion 18 that insulates between the terminal metal fitting 40 and the metal shell 50 is formed on the terminal metal fitting 40 side of the flange portion 19. A front end side body portion 17 having an outer diameter smaller than that of the rear end side body portion 18 is formed on the center electrode 20 side with respect to the flange portion 19, and the front end side body portion 17 is further forward than the front end side body portion 17. The leg length portion 13 is formed with a smaller outer diameter, and the outer diameter decreases toward the center electrode 20 side.

  The metal shell 50 of the spark plug 100 is a cylindrical metal fitting that surrounds and holds a portion ranging from a part of the rear end side body portion 18 to the leg long portion 13 of the insulator 10. In this embodiment, the low-carbon steel is used. Consists of. The metal shell 50 includes a tool engaging portion 51, a mounting screw portion 52, a seal portion 54, and a tip surface 57. A tool (not shown) for attaching the spark plug 100 to the engine head 200 is fitted into the tool engaging portion 51 of the metal shell 50. The mounting screw portion 52 of the metal shell 50 has a thread that is screwed into the mounting screw hole 201 of the engine head 200. The seal portion 54 of the metal shell 50 is formed in a hook shape at the base of the mounting screw portion 52, and an annular gasket 5 formed by bending a plate is inserted between the seal portion 54 and the engine head 200. . The distal end surface 57 of the metal shell 50 is a hollow circular surface formed at the distal end of the mounting screw portion 52, and the center electrode 20 wrapped in the leg long portion 13 projects from the center of the distal end surface 57.

  The center electrode 20 of the spark plug 100 is a rod-shaped electrode having a structure in which a core material 25 having better thermal conductivity than the electrode base material 21 is embedded in an electrode base material 21 formed in a bottomed cylindrical shape. The electrode tip 22 is joined to the tip portion of the electrode base material 21 by laser welding. In this embodiment, the electrode base material 21 is made of a nickel alloy containing nickel as a main component such as Inconel (registered trademark), and the core member 25 is made of copper or an alloy containing copper as a main component. In addition, the electrode tip 22 is formed with a high melting point noble metal as a main component in order to improve the spark wear resistance. The center electrode 20 is inserted into the shaft hole 12 of the insulator 10 with the tip of the electrode base material 21 protruding from the shaft hole 12 of the insulator 10, and is electrically connected to the terminal fitting 40 via the ceramic resistor 3 and the seal body 4. Connected.

  The ground electrode 30 of the spark plug 100 is an electrode having a structure in which an electrode base material 31 joined to the front end surface 57 of the metal shell 50 is bent in a direction intersecting the axial center line O. A two-layer member 32 including a noble metal tip member is embedded in the vicinity of the tip, and is disposed so as to face the tip of the center electrode 20. In this embodiment, the electrode base material 31 is made of a nickel alloy containing nickel as a main component such as Inconel (registered trademark).

A-2.2 Layer member configuration and formation method:
FIG. 2 is a cross-sectional view showing a cross-section of a portion around the two-layer member in the spark plug of FIG.

  As shown in FIG. 2, the two-layer member 32 has a noble metal tip member 33 and an intermediate member 34, and is formed by joining both of them by laser welding. For the noble metal tip member 33, for example, Pt (platinum) or an alloy containing Pt as a main component is used. In this embodiment, a Pt-20Ir alloy (a platinum alloy containing 20% by mass of iridium) is used. The intermediate member 34 includes Pd (palladium) or an alloy containing Pd as a main component, Au (gold) or an alloy containing Au as a main component, AuPd alloy, Pt alloy, platinum nickel alloy (for example, Pt-20Ni (20 mass) % Platinum-containing platinum alloy)). In this embodiment, Pd is used. Further, the intermediate member 34 may be formed of the same material as the electrode base material 31 such as a nickel alloy such as INC600.

  When the two-layer member 32 is formed, first, the two-layer member 32 is laminated so that the lower surface of the noble metal tip member 33 and the upper surface of the intermediate member 34 are in contact with each other. Next, the outer edge of the boundary surface 36 where the noble metal tip member 33 and the intermediate member 34 abut is irradiated with laser over almost the entire circumference, and the noble metal tip member 33 and the intermediate portion in the vicinity of the boundary surface 36 are heated by the heat. The member 34 is melted to form a laser melting portion 35 at the boundary surface 36. The noble metal tip member 33 and the intermediate member 34 are joined by such laser welding. At this time, the tip 35a of the laser melting portion 35 does not reach the center of the boundary surface 36, and the laser melting portion 35 is formed in a ring shape. That is, the distance between the opposed tips 35a of the laser melting portion 35, in other words, the inner diameter φd of the laser melting portion 35 having a ring shape is larger than 0 (φd> 0).

  Further, in this embodiment, as shown in FIG. 2, the tip 35 a of the laser melting portion 35 is more than the boundary surface 36 in the direction perpendicular to the boundary surface 36 (that is, the direction along the axial center line O). A laser melting part 35 is formed so as to be positioned on the noble metal tip member 33 side. Accordingly, the inner diameter φd of the laser melting portion 35 is smaller than the outer diameter φD of the contact portion between the noble metal tip member 33 and the intermediate member 34 on the boundary surface 36 (φd> φD).

  In the two-layer member 32 formed in this way, the intermediate member 34 and the laser melting portion 35 are buried in the electrode base material 31 in the vicinity of the tip of the electrode base material 31 joined to the front end surface 57 of the metal shell 50. The noble metal tip member 33 is joined by resistance welding so that the upper surface protrudes from the electrode base material 31. Thereafter, as shown in FIG. 1, the electrode base material 31 is bent in a direction intersecting the axial center line O, the noble metal tip member 33 is opposed to the electrode tip 22 of the center electrode 20, and between the two. The gap formed (i.e., spark gap) is positioned to the desired dimensions.

A-3. Effects of the first embodiment:
By forming the two-layer member 32 and creating the ground electrode 30 as described above, the following effects can be achieved in this embodiment.

  That is, in the present embodiment, in the two-layer member 32, as shown in FIG. 2, the laser melting portion 35 so that the tip 35a of the laser melting portion 35 is located on the noble metal tip member 33 side with respect to the boundary surface 36. In the ground electrode 30, even if stress is generated between the intermediate member 34 and the noble metal tip member 33 and between the intermediate member 34 and the electrode base material 31 due to temperature change, the noble metal tip The member 33 is caught by the laser melting part 35 and hardly falls off.

B. Second embodiment:
The spark plug of the present embodiment is the same as the spark plug 100 of the first embodiment except that the configuration of the two-layer member is different from the configuration of the two-layer member 32 in the first embodiment. For this reason, only the two-layer member will be described below, and description of other components will be omitted.

B-1.2 Structure and forming method of layer member:
FIG. 3 is a cross-sectional view showing a cross section of a portion centering on a two-layer member in a spark plug according to a second embodiment of the present invention.

  Also in this embodiment, as shown in FIG. 3, the two-layer member 32 ′ has a noble metal tip member 33 and an intermediate member 34, and is formed by joining both of them by laser welding. . The noble metal tip member 33 and the intermediate member 34 are made of the same material as in the first embodiment.

  When forming the two-layer member 32 ′, first, lamination is performed so that the lower surface of the noble metal tip member 33 and the upper surface of the intermediate member 34 are in contact with each other. Next, with respect to the boundary surface 36 where the noble metal tip member 33 and the intermediate member 34 abut, the intermediate member 34 is inclined over the entire circumference of the side surface so as to be inclined from the intermediate member 34 toward the noble metal tip member 33. Irradiate the laser. At this time, the noble metal tip member 33 and the intermediate member 34 in the vicinity of the boundary surface 36 are melted by the heat of the laser, and the laser melting is performed so that the noble metal tip member 33 is inclined from the intermediate member 34 as shown in FIG. A portion 35 is formed. At this time, as in the case of the first embodiment, the tip 35a of the laser melting portion 35 does not reach the center of the boundary surface 36, and the laser melting portion 35 is formed in a ring shape. That is, the inner diameter φd of the laser melting part 35 is larger than 0 (φd> 0). Further, by forming the laser melting portion 35 to be inclined from the intermediate member 34 toward the noble metal tip member 33 as described above, a direction perpendicular to the boundary surface 36 (that is, a direction along the axial center line O). , The tip 35a of the laser melting part 35 is located closer to the noble metal tip member 33 than the boundary surface 36. Accordingly, the inner diameter φd of the laser melting portion 35 is smaller than the outer diameter φD of the contact portion between the noble metal tip member 33 and the intermediate member 34 on the boundary surface 36 (φd> φD).

B-2. Effects of the second embodiment:
As described above, by forming the two-layer member 32 ′ and forming the ground electrode 30, the effect similar to or more than that of the first example can be obtained in this example.

  That is, in this embodiment, in the two-layer member 32 ′, as shown in FIG. 3, the laser melting portion 35 is formed so as to be inclined from the intermediate member 34 toward the noble metal tip member 33. Since the portion of the tip member 33 that is caught by the laser melting portion 35 increases, the noble metal tip member 33 is more difficult to drop off.

C. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the scope of the invention.

  In each of the embodiments described above, the two-layer members 32 and 32 ′ formed by joining the noble metal tip member 33 and the intermediate member 34 are attached to the ground electrode 30 side. However, the present invention is not limited to this. However, it may be attached to the center electrode 20 side. Specifically, the two-layer members 32 and 32 ′ may be attached in place of the electrode chip 22. Further, the two-layer members 32, 32 'may be attached to both the center electrode 20 side and the ground electrode 30 side.

  In each of the above-described embodiments, when the noble metal tip member 33 and the intermediate member 34 are joined by laser welding in the two-layer members 32 and 32 ′, laser welding is performed over substantially the entire circumference of the two-layer members 32 and 32 ′. However, there may be a portion where laser welding is not performed in a part of the periphery.

  In each of the above-described embodiments, in the two-layer members 32 and 32 ′, the noble metal tip member 33 and the intermediate member 34 are joined by laser welding, but the present invention is not limited to this, You may make it join by electron beam welding.

DESCRIPTION OF SYMBOLS 3 ... Ceramic resistance 4 ... Sealing body 5 ... Gasket 10 ... Insulator 12 ... Shaft hole 13 ... Leg long part 17 ... Front end side trunk | drum 18 ... Rear end side trunk | drum 19 ... Ridge part 20 ... Center electrode 21 ... Electrode base material 22 ... Electrode tip 25 ... Core material 30 ... Ground electrode 31 ... Electrode base material 32, 32 '... Double layer member 33 ... Precious metal tip member 34 ... Intermediate member 35 ... Laser melting part 35a ... Tip 36 ... Boundary surface 40 ... Terminal fitting 50 ... Metal shell 51 ... Tool engaging part 52 ... Mounting screw part 54 ... Sealing part 57 ... End face 100 ... Spark plug 200 ... Engine head 201 ... Mounting screw hole 332 ... Two-layer member 333 ... Precious metal tip member 334 ... Intermediate member 335 ... laser melting part 335a ... tip 336 ... interface

Claims (2)

A center electrode;
A ground electrode that forms a spark gap with the center electrode;
A spark plug having
At least one of the center electrode and the ground electrode is
An electrode base material;
A precious metal tip member;
An intermediate member in which a first surface is in contact with the noble metal tip member, and a second surface opposite to the first surface is in contact with the electrode base material;
By laser welding at least a part of the outer edge of the boundary surface where the noble metal tip member and the intermediate member abut, a laser melting portion formed in the vicinity of the boundary surface,
With
The distance φd between the opposite ends of the laser melting portion is greater than 0, and the tip of the laser melting portion is located closer to the noble metal tip member than the boundary surface in a direction perpendicular to the boundary surface. The spark plug is characterized in that the distance φd is smaller than an outer diameter φD of a contact portion between the noble metal tip member and the intermediate member on the boundary surface. The spark plug according to claim 1, wherein
The spark plug is characterized in that the laser melting portion is formed so as to be inclined from the intermediate member toward the noble metal tip member with respect to the boundary surface.

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