JP6855354B2 - Spark plug - Google Patents

Description

The present invention relates to a spark plug for igniting fuel gas in an internal combustion engine or the like.

A spark plug used in an internal combustion engine, for example, generates a spark discharge in a gap formed between a center electrode and a ground electrode, and ignites a fuel gas in an internal combustion engine or the like. In order to improve wear resistance, ignition with a noble metal electrode tip such as iridium joined by resistance welding or laser welding to a part of the center electrode or ground electrode that forms a gap where spark discharge occurs. The plug is known. When the electrode tips are joined by welding, a welded portion is formed between the electrode body and the electrode tip by welding.

Japanese Unexamined Patent Publication No. 2005-135783

By the way, in recent years, the development of a higher performance and fuel-efficient internal combustion engine has been progressing. Along with this, spark plugs tend to be exposed to higher temperatures. The welded portion is relatively easy to oxidize and has a relatively low thermal conductivity. For this reason, in the above technology, when the spark plug is exposed to a high temperature, the welded portion may be oxidized and the electrode tip may be peeled off or fall off, and the thermal conductivity of the welded portion is low. As a result, the heat drawing performance may deteriorate.

The present specification discloses a technique capable of suppressing peeling or falling off of an electrode tip and improving heat drawing performance in a spark plug.

The techniques disclosed herein can be realized as the following aspects or application examples.
[Aspect] With the center electrode,
A spark plug comprising a ground electrode that forms a gap between the center electrode and the center electrode.
The ground electrode has a chip holding portion having a hole portion penetrating itself and an electrode chip having a discharge surface forming the gap, and at least a part thereof is arranged in the hole portion of the chip holding portion. Prepare,
The portion of the electrode chip arranged in the hole portion includes a press-fitting portion that directly contacts the chip holding portion over the entire circumference at least at the end portion on the discharge surface side .
The portion of the electrode tip from the discharge surface to the press-fitting portion is formed of a single member.
A spark plug in which the entire surface of the electrode tip that is continuous with the surface of the end portion of the press-fitting portion on the discharge surface side is exposed.

[Application Example 1] With the center electrode
A spark plug comprising a ground electrode that forms a gap between the center electrode and the center electrode.
At least one of the center electrode and the ground electrode has a chip holding portion having a hole portion and a discharge surface forming the gap, and at least a part of the electrode is arranged in the hole portion of the chip holding portion. With a tip,
The portion of the electrode chip arranged in the hole is provided with a press-fitting portion that comes into direct contact with the chip holding portion over the entire circumference.
A spark plug in which a portion of the electrode tip from the discharge surface to the press-fitting portion is formed of a single member.

According to the above configuration, the portion of the electrode chip arranged in the hole portion includes a press-fitting portion that comes into direct contact with the chip holding portion over the entire circumference. In such a press-fitted portion, since the chip holding portion and the electrode chip are joined without passing through the welded portion, they are unlikely to be oxidized even when exposed to a high temperature. Therefore, peeling or falling off of the electrode tip can be suppressed. Further, since the portion from the discharge surface to the press-fitting portion is formed of one member, the thermal conductivity is lowered as compared with the case where the welded portion is interposed between the discharge surface and the press-fitting portion, for example. Can be suppressed, and deterioration of heat drawing performance can be suppressed. As described above, according to the above configuration, it is possible to suppress the peeling and falling off of the electrode tip in the spark plug and improve the heat drawing performance.

[Application Example 2] The spark plug according to Application Example 1.
The hole is a spark plug that penetrates the chip holding portion.

According to the above configuration, the electrode tip can be press-fitted from the side opposite to the other electrode. As a result, it is possible to prevent the discharge surface from being deformed during press fitting.

[Application Example 3] The spark plug according to Application Example 2.
A spark plug in which the length of the electrode tip on the discharge surface side of the press-fitting portion in the direction parallel to the discharge surface is smaller than the length of the press-fitting portion in the direction parallel to the discharge surface.

According to the above configuration, when the electrode tip is press-fitted from the side opposite to the other electrode, it is possible to suppress the occurrence of a defect in the portion of the electrode tip on the discharge surface side of the press-fitting portion.

[Application Example 4] The spark plug according to any one of Application Examples 1 to 3.
When the surface of the electrode chip opposite to the discharge surface is referred to as the opposite surface,
A spark plug further comprising a welded portion for joining the chip holding portion and a portion of the electrode chip on the opposite surface side of the press-fitted portion.

According to the above configuration, since the welded portion is provided on the side opposite to the discharge surface, which is not easily damaged, peeling or falling off of the electrode tip can be further suppressed.

[Application Example 5] The spark plug according to any one of Application Examples 1 to 4.
When the length of the electrode tip in the press-fitting portion in the thickness direction is L and the length of the press-fitting portion in the direction perpendicular to the thickness direction is D.
A spark plug, characterized in that (D / L) ≤1.33.

According to the above configuration, the length L of the press-fitting portion in the press-fitting direction is not excessively short with respect to the length D in the direction perpendicular to the press-fitting direction of the press-fitting portion. Can be fixed with.

[Application Example 6] The spark plug according to Application Example 5.
A spark plug, characterized in that (D / L) ≦ 1.

According to the above configuration, since the length L of the press-fitting portion in the press-fitting direction is sufficiently longer than the length D in the direction perpendicular to the press-fitting direction of the press-fitting portion, the electrode tip is further sufficiently strong for the chip holding portion. Can be fixed with.

The present invention can be realized in various aspects, for example, an ignition device using a spark plug or an ignition plug, an internal combustion engine equipped with the spark plug, and an ignition device using the spark plug. It can be realized in the form of an internal combustion engine, an electrode of a spark plug, or the like.

It is sectional drawing of the spark plug 100 of this embodiment. It is explanatory drawing of the vicinity of the tip of the spark plug 100. It is a figure explaining the manufacturing method of the ground electrode 30. It is explanatory drawing of the spark plug of 2nd Embodiment. It is sectional drawing in the vicinity of the gap G of the spark plug of the third embodiment. It is sectional drawing in the vicinity of the center electrode tip 29d of the spark plug of 4th Embodiment.

A. First Embodiment:
A-1. Spark plug configuration:
FIG. 1 is a cross-sectional view of the spark plug 100 of the present embodiment. FIG. 2 is an explanatory view of the vicinity of the tip of the spark plug 100. The alternate long and short dash line in FIGS. 1 and 2 indicates the axis AX of the spark plug 100. The direction parallel to the axis AX (vertical direction in FIGS. 1 and 2) is also referred to as an axis direction. The radial direction of the circle on the plane centered on the axis AX and perpendicular to the axis AX is also simply referred to as the "diameter direction", and the circumferential direction of the circle is also simply referred to as the "circumferential direction". The downward direction in FIG. 1 is referred to as a front end direction FD, and the upward direction is also referred to as a rear end direction BD. The lower side in FIGS. 1 and 2 is referred to as the front end side of the spark plug 100, and the upper side in FIGS. 1 and 2 is referred to as the rear end side of the spark plug 100.

The spark plug 100 is attached to the internal combustion engine and is used to ignite the combustion gas in the combustion chamber of the internal combustion engine. The spark plug 100 includes an insulator 10, a center electrode 20, a ground electrode 30, a terminal electrode 40, a main metal fitting 50, a resistor 70, and conductive sealing members 60 and 80.

The insulator 10 is a substantially cylindrical member having a shaft hole 12 which is a through hole extending along the axis AX and penetrating the insulator 10. The insulator 10 is formed by using ceramics such as alumina. The insulator 10 includes a collar portion 19, a rear end side body portion 18, a tip side body portion 17, a reduced outer diameter portion 15, and a leg length portion 13.

The collar portion 19 is a portion of the insulator 10 located substantially in the center in the axial direction. The rear end side body portion 18 is located on the rear end side of the collar portion 19, and has an outer diameter smaller than the outer diameter of the collar portion 19. The front end side body portion 17 is located on the front end side with respect to the flange portion 19, and has an outer diameter smaller than the outer diameter of the rear end side body portion 18. The leg length portion 13 is located on the tip end side of the tip end side body portion 17, and has an outer diameter smaller than the outer diameter of the tip end side body portion 17. The outer diameter of the leg length portion 13 is reduced toward the tip side, and when the spark plug 100 is attached to an internal combustion engine (not shown), it is exposed to the combustion chamber thereof. The reduced outer diameter portion 15 is a portion formed between the leg length portion 13 and the front end side body portion 17 and whose outer diameter is reduced from the rear end side toward the front end side.

From the viewpoint of the configuration on the inner peripheral side, the insulator 10 is located on the tip side of the large inner diameter portion 12L located on the rear end side and the large inner diameter portion 12L, and has a smaller inner diameter than the large inner diameter portion 12L. An inner diameter portion 12S and a reduced inner diameter portion 16 are provided. The reduced inner diameter portion 16 is a portion formed between the large inner diameter portion 12L and the small inner diameter portion 12S, and the inner diameter is reduced from the rear end side to the tip end side. The position of the reduced inner diameter portion 16 in the axial direction is the position of the tip end side portion of the tip end side body portion 17 in the present embodiment.

The main metal fitting 50 is made of a conductive metal material (for example, a low carbon steel material), and is a cylindrical metal fitting for fixing the spark plug 100 to the engine head (not shown) of an internal combustion engine. The main metal fitting 50 is formed with a through hole 59 penetrating along the axis AX. The main metal fitting 50 is arranged around the insulator 10 in the radial direction (that is, the outer circumference). That is, the insulator 10 is inserted and held in the through hole 59 of the main metal fitting 50. The tip of the insulator 10 projects toward the tip side of the tip of the main metal fitting 50. The rear end of the insulator 10 projects toward the rear end side of the rear end of the main metal fitting 50.

The main metal fitting 50 is formed between the hexagonal column-shaped tool engaging portion 51 with which the plug wrench is engaged, the mounting screw portion 52 for mounting on the internal combustion engine, and the tool engaging portion 51 and the mounting screw portion 52. It is provided with a wrench-shaped seat portion 54. The nominal diameter of the mounting screw portion 52 is, for example, M8 to M14.

A metal annular gasket 5 is fitted between the mounting screw portion 52 and the seat portion 54 of the main metal fitting 50. The gasket 5 seals the gap between the spark plug 100 and the internal combustion engine (engine head) when the spark plug 100 is attached to the internal combustion engine.

The main metal fitting 50 further includes a thin-walled compression deformation portion 58 provided between the thin-walled crimping portion 53 provided on the rear end side of the tool engaging portion 51 and the seat portion 54 and the tool engaging portion 51. And have. In the annular region formed between the inner peripheral surface of the portion of the main metal fitting 50 from the tool engaging portion 51 to the crimping portion 53 and the outer peripheral surface of the rear end side body portion 18 of the insulator 10, the annular region is formed. Circular wire packings 6 and 7 are arranged. The powder of talc (talc) 9 is filled between the two wire packings 6 and 7 in the region. The rear end of the crimping portion 53 is bent inward in the radial direction and fixed to the outer peripheral surface of the insulator 10. The compression deformation portion 58 of the main metal fitting 50 is compression-deformation when the crimping portion 53 fixed to the outer peripheral surface of the insulator 10 is pressed toward the tip side during manufacturing. Due to the compression deformation of the compression deformation portion 58, the insulator 10 is pressed toward the tip side in the main metal fitting 50 via the wire packings 6 and 7 and the talc 9. The reduced outer diameter portion 15 (insulator side step) of the insulator 10 is formed by the step portion 56 (metal fitting side step portion) formed at the position of the mounting screw portion 52 on the inner circumference of the main metal fitting 50 via the annular plate packing 8. Part) is pressed. As a result, the plate packing 8 prevents the gas in the combustion chamber of the internal combustion engine from leaking to the outside through the gap between the main metal fitting 50 and the insulator 10.

The center electrode 20 includes a rod-shaped center electrode body 21 extending along the axis AX and a center electrode tip 29. The center electrode body 21 is held in a portion on the tip side inside the shaft hole 12 of the insulator 10. That is, the rear end side of the center electrode 20 (the rear end side of the center electrode body 21) is arranged in the shaft hole 12. The center electrode main body 21 is formed by using a metal having high corrosion resistance and heat resistance, for example, nickel (Ni) or an alloy containing Ni as a main component (for example, NCF600, NCF601). The center electrode main body 21 may have a two-layer structure including a base material formed of Ni or a Ni alloy and a core portion embedded inside the base material. In this case, the core portion is formed of, for example, copper or an alloy containing copper as a main component, which is superior in thermal conductivity to the base material.

The center electrode main body 21 has a collar portion 24 provided at a predetermined position in the axial direction, a head portion 23 which is a portion on the rear end side of the collar portion 24, and a leg which is a portion on the front end side of the collar portion 24. A unit 25 and the like are provided. The collar portion 24 is supported from the tip end side by the reduced inner diameter portion 16 of the insulator 10. That is, the center electrode body 21 is locked to the reduced inner diameter portion 16. The tip end side of the leg portion 25, that is, the tip end side of the center electrode body 21, protrudes toward the tip end side of the tip end of the insulator 10.

The center electrode tip 29 is, for example, a member having a substantially cylindrical shape, and is joined to the tip of the center electrode body 21 (the tip of the leg 25) by, for example, laser welding. The tip surface of the center electrode tip 29 is a first discharge surface 295 that forms a spark gap with the ground electrode tip 39, which will be described later. The center electrode tip 29 is formed by using, for example, a noble metal having a high melting point such as iridium (Ir) or platinum (Pt), or an alloy containing the noble metal as a main component.

The terminal electrode 40 is a rod-shaped member extending in the axial direction. The terminal electrode 40 is inserted into the shaft hole 12 of the insulator 10 from the rear end side, and is located in the shaft hole 12 on the rear end side of the center electrode 20. The terminal electrode 40 is made of a conductive metal material (for example, low carbon steel), and the surface of the terminal electrode 40 is formed with plating such as Ni for anticorrosion, for example.

The terminal electrode 40 includes a collar portion 42 formed at a predetermined position in the axial direction, a cap mounting portion 41 located on the rear end side of the collar portion 42, and a leg portion 43 on the tip side of the collar portion 42. I have. The cap mounting portion 41 of the terminal electrode 40 is exposed on the rear end side of the insulator 10. The leg portion 43 of the terminal electrode 40 is inserted into the shaft hole 12 of the insulator 10. A plug cap to which a high-voltage cable (not shown) is connected is attached to the cap attachment portion 41, and a high voltage for generating a discharge is applied.

The resistor 70 is arranged in the shaft hole 12 of the insulator 10 between the tip end of the terminal electrode 40 and the rear end end of the center electrode 20. The resistor 70 has, for example, a resistance value of 1 KΩ or more (for example, 5 KΩ) and has a function of reducing radio wave noise when a spark is generated. The resistor 70 is formed of, for example, a composition containing glass particles as a main component, ceramic particles other than glass, and a conductive material.

The gap between the resistor 70 and the center electrode 20 in the shaft hole 12 is filled with the conductive sealing member 60. The gap between the resistor 70 and the terminal electrode 40 is filled with the sealing member 80. That is, the seal member 60 is in contact with the center electrode 20 and the resistor 70, respectively, and separates the center electrode 20 and the resistor 70 from each other. The seal member 80 is in contact with the resistor 70 and the terminal electrode 40, respectively, and separates the resistor 70 from the terminal electrode 40. In this way, the seal members 60 and 80 electrically and physically connect the center electrode 20 and the terminal electrode 40 via the resistor 70. The sealing members 60 and 80 are formed of a conductive material, for example, _{a composition containing glass particles such as B 2} O _3- SiO ₂ system and metal particles (Cu, Fe, etc.).

As shown in the enlarged cross-sectional view of FIG. 2A, the ground electrode 30 (ground electrode main body 31) is a rod-shaped body having a quadrangular cross section. The ground electrode main body 31 has a connection end portion 312 and a free end portion 311 located on the opposite side of the connection end portion 312 as both end portions. The connection end portion 312 is joined to the tip 50t of the main metal fitting 50 by, for example, resistance welding. As a result, the main metal fitting 50 and the ground electrode main body 31 are electrically and physically connected. The vicinity of the connection end portion 312 of the ground electrode main body 31 extends in the direction of the axis AX, and the vicinity of the free end portion 311 extends in the direction perpendicular to the axis line AX. The rod-shaped ground electrode body 31 is curved by about 90 degrees at the central portion.

The ground electrode main body 31 is formed by using a metal having high corrosion resistance and heat resistance, an alloy containing Ni or Ni as a main component (for example, NCF600, NCF601). Like the center electrode main body 21, the ground electrode main body 31 has a base material and a core portion formed of a metal having higher thermal conductivity than the base material (for example, copper) and embedded in the base material. It may have a two-layer structure including.

A ground electrode tip 39 having a second discharge surface 395 facing the free end portion 311 with a gap G formed between the center electrode 20 and the first discharge surface 295 is fixed to the free end portion 311. The gap G between the first discharge surface 295 and the second discharge surface 395 is a so-called spark gap in which discharge occurs. Like the center electrode tip 29, the ground electrode tip 39 is formed by using, for example, a noble metal or an alloy containing a noble metal as a main component.

FIG. 2B shows an enlarged view of the rectangular region AA of FIG. 2A. FIG. 2C is a view of the portion shown in FIG. 2B as viewed from the front end side toward the rear end direction BD along the axis AX. The ground electrode tip 39 has a substantially cylindrical shape. The surface of the ground electrode chip 39 opposite to the second discharge surface 395 is referred to as an opposite surface 396. The direction along the axis AX of the ground electrode tip 39 (axis direction) is also referred to as the thickness direction of the ground electrode tip 39. The direction perpendicular to the axis AX of the ground electrode tip 39, that is, the direction perpendicular to the thickness direction is also referred to as the width direction.

The ground electrode tip 39 has a small outer diameter portion 391 on the second discharge surface 395 side (rear end side), a large outer diameter portion 393 on the opposite surface 396 side (tip side), and a small outer diameter portion 391 and a large outer diameter. It has an expanded outer diameter portion 392 between the portion 393 and the portion 393. The outer diameter of the large outer diameter portion 393 is larger than the outer diameter of the small outer diameter portion 391. The expanded outer diameter portion 392 is a portion whose outer diameter is expanded from the second discharge surface 395 side (rear end side) to the opposite surface 396 side (tip side).

A hole 34 having a size corresponding to the large outer diameter portion 393 of the ground electrode tip 39 is formed in the free end portion 311 of the ground electrode main body 31. The hole portion 34 is a substantially columnar hole that penetrates the ground electrode main body 31 in the axial direction. The hole portion 34 has an equal inner diameter portion 341 and an enlarged inner diameter portion 342. The inner diameter enlarged portion 342 is a portion whose inner diameter is expanded from the second discharge surface 395 side (rear end side) to the opposite surface 396 side (tip side).

The axial length of the large outer diameter portion 393 of the ground electrode tip 39 is substantially equal to the axial length of the hole portion 34, that is, the axial length of the free end portion 311. The small outer diameter portion 391 and the expanded outer diameter portion 392 project toward the rear end side of the rear end surface 311B of the free end portion 311. The opposite surface 396 of the ground electrode tip 39 is substantially on the same surface as the tip surface 311F of the free end portion 311.

The ground electrode tip 39 is fixed to the free end portion 311 by being press-fitted into the hole portion 34. For this reason, of the large outer diameter portion 393, the portion arranged in the equal inner diameter portion 341 of the hole portion 34 is in direct contact with the inner peripheral surface 34i of the hole portion 34 over the entire circumference in the circumferential direction. .. Of the large outer diameter portion 393, the portion that is in direct contact with the inner peripheral surface 34i of the hole portion 34 over the entire circumference in the circumferential direction is also referred to as a press-fit portion 394. For example, when the ground electrode 30 is cut on an arbitrary surface including the axis of the ground electrode tip 39 (in this embodiment, the axis AX of the spark plug 100), the outer peripheral surface of the ground electrode tip 39 and the hole 34 are formed. When the inner peripheral surface 34i of the ground electrode main body 31 (free end portion 311) to be formed is in contact with the inner peripheral surface 34i without a gap, the portion in contact without the gap can be recognized as the press-fitting portion 394. ..

The length of the press-fitting portion 394 in the thickness direction (length in the axial direction) is defined as the press-fitting length L. The length (outer diameter of the press-fitting portion 394) in the direction perpendicular to the thickness direction of the press-fitting portion 394 is defined as the press-fitting diameter D. The press-fitting length L can also be said to be the length of the ground electrode tip 39 in the press-fitting direction.

The ground electrode tip 39 is a member made of one kind of material (for example, a precious metal). That is, the second discharge surface 395 to the press-fitting portion 394 are formed of one member.

A-2. How to make a spark plug:
The manufacturing method of the spark plug 100 will be described focusing on the manufacturing method of the ground electrode 30. FIG. 3 is a diagram illustrating a method of manufacturing the ground electrode 30. First, a square rod-shaped ground electrode main body 31 and a substantially columnar ground electrode tip 39 are prepared. The inner diameter D2 of the equal inner diameter portion 341 of the hole portion 34 before press fitting is slightly smaller than the outer diameter D1 of the large outer diameter portion 393 of the ground electrode 30 before press fitting. For example, when the outer diameter D1 of the large outer diameter portion 393 before press fitting is Φ1 (tolerance r6) mm, the inner diameter D2 of the equal inner diameter portion 341 of the hole portion 34 before press fitting is Φ1 (tolerance H7) mm. Here, the tolerances r6 and H7 are defined in JIS B 0401 (1998).

The ground electrode tip 39 is press-fitted into the hole 34 of the ground electrode main body 31 fixed with a jig (not shown) from the front end surface 311F side toward the rear end surface 311B. As described above, in the present embodiment, the press-fitting direction of the ground electrode tip 39 is the direction along the axis of the ground electrode tip 39 (in the present embodiment, the axis AX of the spark plug 100). When the ground electrode tip 39 is press-fitted, the opposite surface 396 is pressed by a pressing member (not shown). When press-fitting is performed in the opposite direction, that is, from the rear end surface 311B side toward the front end surface 311F side, it is necessary to press the second discharge surface 395. In this case, there is a high possibility that a flaw will be formed on the small outer diameter portion 391 including the second discharge surface 395 at the time of press fitting. Such a defect may cause breakage of the ground electrode tip 39 or the like. Further, in this case, there is a high possibility that the small outer diameter portion 391 is deformed at the time of press fitting. As a result, the length of the gap G, the area of the second discharge surface 395, and the like can be formed different from the desired values. In the present embodiment, such inconvenience can be suppressed and the product accuracy can be improved.

The connection end portion 312 of the generated rod-shaped ground electrode 30 is resistance welded to the tip 50t of the main metal fitting 50. After that, an assembly in which the terminal electrode 40, the center electrode 20, the resistor 70 and the like are assembled to the insulator 10 is prepared, and the assembly is fixed to the main metal fitting 50. Specifically, the plate packing 8, the assembly, the wire packings 6 and 7, and the talc 9 are arranged in the through hole 59 of the main metal fitting 50. A plate packing 8 is interposed between the reduced outer diameter portion 15 of the insulator 10 and the step portion 56 of the main metal fitting 50. Then, the main metal fitting 50 and the insulator 10 are assembled by crimping the crimping portion 53 of the main metal fitting 50 so as to bend inward. Then, the rod-shaped ground electrode 30 is bent to form a gap G. This completes the spark plug 100.

In the spark plug 100 of the present embodiment described above, as described above, the large outer diameter portion 393, which is a portion arranged in the hole portion 34 of the ground electrode chip 39, has the ground electrode main body 31 over the entire circumference. It is provided with a press-fitting portion 394 that comes into direct contact with. In such a press-fitting portion 394, for example, since the ground electrode main body 31 and the ground electrode tip 39 are joined without passing through the welded portion, they are not easily oxidized even when exposed to a high temperature. Therefore, peeling or falling off of the ground electrode tip 39 can be suppressed. The weld formed by welding is generally more susceptible to oxidation than the base metal. Further, when the spark plug 100 is joined via a welded portion, it is caused by the difference in linear expansion coefficient between the center electrode tip 29 and the ground electrode body 31 when heating and cooling are repeated when the spark plug 100 is used. Then, thermal stress is generated at the interface between the center electrode tip 29 and the welded portion and the interface between the welded portion and the ground electrode main body 31, and peeling may occur. On the other hand, in the press-fitting portion 394, even if a thermal stress is generated between the ground electrode tip 39 and the inner peripheral surface 34i of the hole portion 34 in the direction parallel to the inner peripheral surface 34i, the bonding by press-fitting becomes weak. Therefore, the ground electrode tip 39 does not peel off or fall off due to the thermal stress.

Further, according to the present embodiment, the portion from the second discharge surface 395 to the press-fitting portion 394 is formed of one member, so that, for example, the welded portion is formed between the second discharge surface 395 and the press-fitting portion 394. Compared with the case of intervening, the decrease in thermal conductivity can be suppressed, and the decrease in heat drawing performance can be suppressed. This is because the welded portion contains the components of the two base materials to be joined, so that the thermal conductivity of the welded portion is generally lower than that of the base metal. As can be seen from the above description, according to the spark plug 100 of the present embodiment, it is possible to suppress peeling and falling off of the ground electrode tip 39 and improve the heat drawing performance of the spark plug 100.

Further, according to the present embodiment, the hole 34 penetrates the ground electrode main body 31. As a result, the ground electrode tip 39 can be press-fitted from the side opposite to the center electrode 20 (the tip surface 311F side). As a result, it is possible to prevent the small outer diameter portion 391 on the second discharge surface 395 side from being flawed and the small outer diameter portion 391 from being deformed at the time of press fitting.

Further, according to the present embodiment, the length of the ground electrode tip 39 on the second discharge surface 395 side of the press-fitting portion 394 in the direction parallel to the second discharge surface 395 (in the present embodiment, the outer diameter is expanded). The outer diameter of the diameter portion 392 and the small outer diameter portion 391) is smaller than the length of the press-fitting portion 394 in the direction parallel to the first discharge surface 295 (in the present embodiment, the outer diameter D of the large outer diameter portion 393). .. As a result, when the ground electrode tip 39 is press-fitted from the opposite side (tip surface 311F side) facing the center electrode 20, the second discharge surface 395 side of the ground electrode tip 39 is closer to the press-fitting portion 394. It is possible to prevent the portions (in the present embodiment, the enlarged outer diameter portion 392 and the small outer diameter portion 391) from coming into contact with the hole portion 34. Therefore, at the time of press-fitting, it is possible to prevent the portion of the ground electrode tip 39 on the second discharge surface 395 side of the press-fitting portion 394 from being scratched or deformed.

B. Evaluation test In the evaluation test, 13 samples 1 to 13 in which at least one of the press-fit length L and the press-fit diameter D are different from each other were prepared for the spark plug 100. Specifically, the press-fitting diameter D of the samples 1 to 13 is any one of 0.6 mm, 0.8 mm, 1 mm, and 1.2 mm. The press-fit lengths L of the samples 1 to 3 having the press-fit diameter D of 0.6 mm are 0.4 mm, 0.6 mm, and 0.8 mm, whereby the value of (D / L) becomes 1.5, 1. It is set to 00 and 0.75. The press-fit lengths L of the samples 4 to 6 having the press-fit diameter D of 0.8 mm are set to 0.6 mm, 0.8 mm, and 1.2 mm, whereby the value of (D / L) is 1.33, 1. It is set to 00 and 0.67. The press-fit length L of the samples 7 to 10 having the press-fit diameter D of 1 mm is 0.6 mm, 1 mm, 1.4 mm, and 1.7 mm, whereby the value of (D / L) is 1.67, 1. It is set to 00, 0.71 and 0.59. The press-fit lengths L of the samples 11 to 13 having the press-fit diameter D of 1.2 mm are set to 0.6 mm, 0.9 mm, and 1.6 mm, whereby the value of (D / L) becomes 2.00, 1. It is set to 33 and 0.75.

The press-fitting length L includes the axial length of the large outer diameter portion 393 of the ground electrode tip 39, the axial length of the hole portion 34 (the axial length of the free end portion 311 of the ground electrode main body 31), and the like. It was adjusted by changing. The press-fitting diameter D was adjusted by changing the outer diameter of the large outer diameter portion 393 and the inner diameter of the hole portion 34.

The items common to each sample are as follows.
Material of ground electrode tip 39: Platinum alloy Material of ground electrode body 31: NCF600

In the vibration test conducted as an evaluation test, each sample was attached to a vibration tester and vibrated in the axial direction at an acceleration of 50 G and 100 Hz for 100 hours. The vibration test was performed in a state where the vicinity of the ground electrode tip 39 of each sample was heated to 1000 degrees Celsius using a burner.

Then, the evaluation of the sample in which the ground electrode tip 39 fell off during the test was set to "C", and the sample in which the ground electrode tip 39 did not fall off at the end of the test but the ground electrode tip 39 was displaced in the axial direction was observed. The evaluation was "B". At the end of the test, the evaluation of the sample in which neither the ground electrode tip 39 fell off nor slipped was evaluated as "A". The evaluation results are shown in Table 1 below.

The evaluation of samples 1, 7, and 11 having a value of (D / L) larger than 1.33 was "C" regardless of the press-fit diameter D. On the other hand, the evaluation of the samples 2 to 6, 8 to 10, 12, and 13 in which the value of (D / L) is 1.33 or less is "B" or more regardless of the press-fitting diameter D. It was.

The reason for this is considered as follows. The larger the press-fitting diameter D, that is, the larger the size of the ground electrode tip 39, the heavier the weight of the ground electrode tip 39, and therefore the greater the force applied during vibration. On the other hand, the larger the press-fitting length L, the greater the force for joining the ground electrode tip 39 and the ground electrode main body 31. Therefore, if the press-fitting length L is excessively short with respect to the press-fitting diameter D, a sufficient bonding force cannot be obtained, and if the press-fitting length L is sufficiently long with respect to the press-fitting diameter D, a sufficient bonding force can be obtained.

When (D / L) is larger than 1.33, the press-fitting length L is excessively short with respect to the press-fitting diameter D, so that sufficient bonding force cannot be obtained and the ground electrode tip 39 falls off. When (D / L) is 1.33 or less, the press-fitting length L is not excessively short with respect to the press-fitting diameter D, so that the ground electrode tip 39 can be fixed to the ground electrode main body 31 with sufficient strength.

As described above, it was found by the evaluation test that it is preferable to satisfy (D / L) ≦ 1.33.

Further, among the samples 2 to 6, 8 to 10, 12 and 13 having a (D / L) value of 1.33 or less, the evaluation of the samples 4 and 12 having a (D / L) value of more than 1 is , "B". On the other hand, the evaluation of samples 2, 3, 5, 6, 8 to 10 and 13 in which the value of (D / L) was 1 or less was "A".

The reason for this is that when (D / L) is 1 or less, the press-fitting length L is sufficiently longer than the press-fitting diameter D as compared with the case where (D / L) is larger than 1, so that the ground electrode This is because the chip 39 can be fixed to the ground electrode body 31 with sufficient strength. As described above, it was found by the evaluation test that it is more preferable to satisfy (D / L) ≦ 1.

C. 2nd Embodiment FIG. 4 is an explanatory view of the spark plug of the 2nd embodiment. FIG. 4A is a cross-sectional view of the region AAb corresponding to the rectangular region AA illustrated in FIG. 2B of the first embodiment. FIG. 4B is a view of the portion shown in FIG. 4A as viewed from the front end side toward the rear end direction BD along the axis AX.

The ground electrode tip 39b of the second embodiment has a small outer diameter portion 391b and a large outer diameter portion 393b located on the tip side of the small outer diameter portion 391b, similarly to the ground electrode tip 39 of the first embodiment. It has an enlarged outer diameter portion 392b located between the small outer diameter portion 391b and the large outer diameter portion 393b. The small outer diameter portion 391b is a portion having a second discharge surface 395b. The large outer diameter portion 393b is a portion having an outer diameter larger than that of the small outer diameter portion 391b and having an opposite surface 396b.

The large outer diameter portion 393b has a press-fitting portion 394b and a welding target portion 397b which is a portion on the opposite surface 396b side of the press-fitting portion 394b. The press-fitting portion 394b is a portion that is in direct contact with the inner peripheral surface 34bi of the hole portion 34b over the entire circumference in the circumferential direction, similarly to the press-fitting portion 394 of the first embodiment. The weld target portion 397b is a portion joined to the ground electrode main body 31b (free end portion 311b) via the welded portion WP. The welded portion WP is formed by melting and solidifying the component of the ground electrode main body 31b and the component of the ground electrode tip 39b by laser welding.

As shown in FIG. 4C, the welded portion WP is formed over the entire circumference along the contact surface between the ground electrode tip 39b and the hole portion 34b. As a modification, the welded portion WP may not be formed over the entire circumference. For example, the welded portion WP may be formed at a plurality of locations along the contact surface between the ground electrode tip 39b and the hole portion 34b at intervals.

The ground electrode of the second embodiment is manufactured as follows. First, similarly to the ground electrode 30 of the first embodiment, the ground electrode tip 39b having a substantially cylindrical shape is press-fitted into the hole portion 34b of the ground electrode main body 31b (free end portion 311b). After that, the laser is irradiated from the opposite surface 396b side along the contact surface between the ground electrode tip 39b and the hole 34b, perpendicular to the opposite surface 396b, over the entire circumference. As a result, the welded portion WP is formed.

According to the second embodiment described above, similarly to the first embodiment, the press-fitting portion 394b is provided, and the portion from the second discharge surface 395b to the press-fitting portion 394b is formed of one member. It is possible to suppress peeling and falling off of 39b and improve the heat drawing performance of the spark plug.

Further, according to the second embodiment, since the welded portion WP for joining the ground electrode main body 31b and the welding target portion 397b is provided, peeling or falling off of the ground electrode tip 39b can be further suppressed. For example, even if the welded portion is provided on the second discharge surface 395b side of the press-fitted portion 394b, the welded portion is damaged by the impact of the discharge because it comes into contact with the discharge, so that it is easily consumed by oxidation. In the present embodiment, since the welded portion WP is provided on the side opposite to the second discharge surface 395b, which is hard to be damaged, peeling or falling off of the ground electrode tip 39b can be further suppressed.

D. Third Embodiment In the first embodiment and the second embodiment, the chip holding portions for holding the ground electrode chip are the ground electrode bodies 31, 31b. Instead of this, the chip holding portion may be another member. An example in which the chip holding portion is the main metal fitting will be described as the third embodiment.

FIG. 5 is a cross-sectional view of the vicinity of the gap G of the spark plug of the third embodiment. The tip of the main metal fitting 50c (the tip of the mounting screw portion 52c) of the third embodiment is located closer to the tip side than the tip of the insulator 10c (the tip of the leg length portion 13c). The tip of the main metal fitting 50c is further located on the tip side of the tip of the center electrode 20c, that is, the first discharge surface 295c of the center electrode tip 29c joined to the tip of the leg portion 25c. A hole 34c that penetrates the mounting screw 52 is formed in a portion of the mounting screw 52c that is closer to the tip than the first discharge surface 295c in a direction perpendicular to the axis AX of the spark plug.

The hole portion 34c has a large inner diameter portion 342c on the outer peripheral surface side of the mounting screw portion 52c and a small inner diameter portion 341c on the inner peripheral surface side of the mounting screw portion 52c.

The ground electrode tip 39c of the third embodiment has a substantially cylindrical shape extending in a direction perpendicular to the axis AX. That is, in the third embodiment, the axis AX of the spark plug and the axis AXc of the ground electrode tip 39c are perpendicular to each other. The ground electrode tip 39c is an expansion located between the small outer diameter portion 391c, the large outer diameter portion 393c located on the outer peripheral side of the small outer diameter portion 391c, and the small outer diameter portion 391c and the large outer diameter portion 393c. It has an outer diameter portion of 392c. The small outer diameter portion 391c is a portion having a second discharge surface 395c. The large outer diameter portion 393c is a portion having an outer diameter larger than that of the small outer diameter portion 391b and having an opposite surface 396c. The outer diameter of the large outer diameter portion 393c is substantially equal to the inner diameter of the small inner diameter portion 341c of the mounting screw portion 52c. In the third embodiment, the second discharge surface 395c is a side surface of a substantially cylindrical ground electrode tip 39c.

As shown by an arrow in FIG. 5, the ground electrode tip 39c is press-fitted into the hole 34c of the main metal fitting 50c from the outer peripheral side to the inner peripheral side. For this purpose, the large outer diameter portion 393c of the ground electrode tip 39c includes a press-fit portion 394c that directly contacts the small inner diameter portion 341c of the hole portion 34c over the entire circumference in the circumferential direction centered on the axis AXc. ..

In the third embodiment described above, the mounting screw portion 52c of the main metal fitting 50c has a hole portion 34c and functions as a tip holding portion of the ground electrode for holding the electrode tip 39c. According to the third embodiment, as in the first embodiment, the press-fitting portion 394c is provided, and the portion from the second discharge surface 395c to the press-fitting portion 394c is formed of one member, so that the ground electrode tip 39c It is possible to suppress the peeling and falling off of the spark plug and improve the heat drawing performance of the spark plug.

E. Fourth Embodiment In the first to third embodiments, the ground electrode tips 39, 39b, 39c are fixed to the tip holding portion (ground electrode main body 31, 31b or main metal fitting 50c) by press fitting. Instead of the ground electrode tip, or together with the ground electrode tip, the center electrode tip may be fixed to the tip holding portion (for example, the center electrode body) by press fitting.

FIG. 6 is a cross-sectional view of the vicinity of the center electrode tip 29d of the spark plug of the fourth embodiment. In the center electrode 20d of the fourth embodiment, a hole portion 251d extending along the axis AX is formed at the tip of the leg portion 25d of the center electrode main body 21d. The hole 251d has a bottom 252d. That is, the hole portion 251d does not penetrate the center electrode main body 21d and is open only to the tip end side.

The center electrode tip 29d has a small outer diameter portion 293d on the rear end side and a large outer diameter portion 291d on the front end side. The outer diameter of the small outer diameter portion 293d is substantially equal to the inner diameter of the hole portion 251d of the center electrode body 21d. The outer diameter of the large outer diameter portion 291d is larger than the outer diameter of the small outer diameter portion 293d. The surface on the tip end side of the large outer diameter portion 291d is the first discharge surface 295d that forms a gap for discharge with the second discharge surface of the ground electrode (not shown).

As shown by an arrow in FIG. 6, the center electrode tip 29d is press-fitted into the hole 251d of the center electrode body 21d from the first discharge surface 295d (tip side) to the opposite surface 296d side (rear end side). There is. For this purpose, the small outer diameter portion 293d of the center electrode tip 29d includes a press-fitting portion 294d that directly contacts the hole portion 251d over the entire circumference in the circumferential direction centered on the axis AX.

According to the fourth embodiment described above, since the press-fitting portion 294d is provided and the portion from the first discharge surface 295d to the press-fitting portion 294d is formed of one member, peeling or falling off of the center electrode tip 29d is suppressed. At the same time, the heat drawing performance of the spark plug can be improved.

F. Modification Example (1) In the first embodiment, the hole 34 penetrates the ground electrode main body 31 along the axis AX (FIG. 2). Instead of this, the hole 34 may be opened only on the rear end side (rear end surface 311B side) without penetrating the ground electrode main body 31. In this case, the ground electrode tip 39 may be press-fitted into the hole 34 from the rear end side toward the front end side, for example. Similarly, also in the second embodiment, the hole portion 34b does not have to penetrate the ground electrode main body 31b. Also in the third embodiment, the hole portion 34c does not have to penetrate the mounting screw portion 52c.

(2) In each of the above embodiments, the shapes of the ground electrode chips 39, 39b, 39c and the center electrode chip 29d are examples, and other shapes and dimensions may be used. For example, the shape and dimensions may not satisfy (D / L) ≦ 1.33. Further, the ground electrode tip is not limited to the cylindrical shape, and may have another shape such as a quadrangular prism shape.

The spark plug is a type of plug that forms a gap for discharge between the cylindrical ground electrode tip extending in the direction perpendicular to the axis AX and the side surface of the cylindrical center electrode tip. Is also good. In this case, for example, a hole penetrating in the direction perpendicular to the axis AX is formed in the vicinity of the tip of the ground electrode body extending in the direction parallel to the axis AX, and the hole extends in the direction perpendicular to the axis AX. A cylindrical ground electrode tip may be press-fitted.

(3) In each of the above embodiments, the configurations of the ground electrode chips 39, 39b, 39c and the center electrode chip 29d have been mainly described, but other elements such as the center electrode 20, the terminal electrode 40, and the ground electrode 30 have been described. The material and dimensions of the above can be changed in various ways. For example, in the first to third embodiments, the center electrode may be configured not to include a chip made of a precious metal. In the fourth embodiment, the ground electrode may be configured not to include a chip made of a precious metal. Further, as for the configurations of the main metal fittings 50 and 50b, various known configurations can be adopted for the configurations and materials. For example, the material of the main metal fitting 50 may be low carbon steel plated with zinc, nickel, or the like, or low carbon steel not plated with these.

Although the present invention has been described above based on the embodiments and modifications, the above-described embodiments of the invention are for facilitating the understanding of the present invention and do not limit the present invention. The present invention may be modified or improved without departing from the spirit and claims, and the present invention includes an equivalent thereof.

5 ... gasket, 6 ... wire packing, 7 ... sample, 8 ... plate packing, 9 ... talc, 10, 10c ... insulator, 10c ... insulator, 12 ... shaft hole, 12L ... large inner diameter part, 12S ... small inner diameter part , 13 ... Leg length part, 13c ... Leg length part, 15 ... Reduced outer diameter part, 16 ... Reduced inner diameter part, 17 ... Tip side body part, 18 ... Rear end side body part, 19 ... Collar part, 20, 20c, 20d ... Center electrode, 21, 21d ... Center electrode body, 23 ... Head, 24 ... Collar, 25, 24d, 25d ... Leg, 29, 29c, 29d ... Center electrode tip, 30 ... Ground electrode, 31, 31b ... Ground Electrode body, 34, 34b, 34c ... Hole, 39, 39b, 39c ... Ground electrode tip, 40 ... Terminal electrode, 41 ... Cap mounting part, 42 ... Collar, 43 ... Leg, 50, 50c ... Main metal fittings, 51 ... Tool engaging part, 52, 52c ... Mounting screw part, 53 ... Clamping part, 54 ... Seat part, 56 ... Step part, 58 ... Compression deformation part, 59 ... Through hole, 60 ... Seal member, 70 ... Resistance Body, 80 ... Seal member, 100 ... Ignition plug, 251d ... Hole, 252d ... Bottom, 291d ... Large outer diameter part, 293d ... Small outer diameter part, 294d ... Press-fitting part, 295, 295c, 295d ... First discharge surface , 296d ... Opposite surface, 311 and 311b ... Free end, 312 ... Connection end, 341 ... Equal inner diameter, 341c ... Small inner diameter, 342 ... Expanded inner diameter, 342c ... Large inner diameter, 391, 391b, 391c ... Small outer diameter part, 392, 392b, 392c ... Expanded outer diameter part, 393, 393b, 393c ... Large outer diameter part, 394, 394b, 394c ... Press-fitting part, 395, 395b, 395c ... Second discharge surface, 396, 396b 396c ... Opposite surface, 397b ... Welding target part, 1000 degrees ... ° C., L ... Press-fit length, D ... Press-fit diameter, D1 ... Outer diameter, FD ... Tip direction, BD ... Rear end direction, WP ... Welding part, AX ... Axis

Claims (5)

With the center electrode
A spark plug comprising a ground electrode that forms a gap between the center electrode and the center electrode.
The ground electrode has a chip holding portion having a hole portion penetrating itself and an electrode chip having a discharge surface forming the gap, and at least a part thereof is arranged in the hole portion of the chip holding portion. Prepare,
The portion of the electrode chip arranged in the hole portion includes a press-fitting portion that directly contacts the chip holding portion over the entire circumference at least at the end portion on the discharge surface side .
The portion of the electrode tip from the discharge surface to the press-fitting portion is formed of a single member.
A spark plug in which the entire surface of the electrode tip that is continuous with the surface of the end portion of the press-fitting portion on the discharge surface side is exposed. The spark plug according to claim 1.
A spark plug in which the length of the electrode tip on the discharge surface side of the press-fitting portion in the direction parallel to the discharge surface is smaller than the length of the press-fitting portion in the direction parallel to the discharge surface. The spark plug according to claim 1 or 2.
When the surface of the electrode chip opposite to the discharge surface is referred to as the opposite surface,
A spark plug further comprising a welded portion for joining the chip holding portion and a portion of the electrode chip on the opposite surface side of the press-fitted portion. The spark plug according to any one of claims 1 to 3.
When the length of the electrode tip in the press-fitting portion in the thickness direction is L and the length of the press-fitting portion in the direction perpendicular to the thickness direction is D.
A spark plug, characterized in that (D / L) ≤1.33. The spark plug according to claim 4.
A spark plug, characterized in that (D / L) ≦ 1.

Images