JP6992017B2 - Spark plug - Google Patents

Description

This specification relates to a spark plug for igniting a fuel gas in an internal combustion engine or the like.

In the electrode of the spark plug, a precious metal electrode tip having excellent spark consumption resistance has been conventionally used for a portion forming a gap where sparks are generated. As a method of joining the electrode tip to the electrode body, for example, a method using laser welding is known (for example, Patent Document 1).

As shown in Patent Document 1, various shapes of a molten portion formed by laser welding on the contact surface between the electrode chip and the electrode body have been proposed. For example, it is known to bond the entire contact surface between the electrode tip and the electrode body in order to increase the bonding strength between the electrode tip and the electrode body. In this spark plug, a layered molten portion is formed between the electrode tip and the electrode body.

JP 2012-74271

In such a spark plug, since the electrode tip and the electrode body are made of different materials, thermal stress is applied to the molten portion due to the difference in the linear expansion coefficient between the two materials. Therefore, there is a demand for a technique for improving the resistance (peeling resistance) against peeling of the electrode tip from the electrode body due to the thermal stress. Further, since the fuel gas explodes in the vicinity of the electrode tip, the impact of the explosion is applied to the electrode tip. Therefore, there is a demand for a technique capable of improving the impact resistance of the electrode tip.

The present specification discloses a technique capable of improving the peeling resistance and impact resistance of the electrode tip in a spark plug in which the electrode tip and the electrode body are joined via a molten portion.

The techniques disclosed herein can be realized as the following application examples.

[Application Example 1] A ground electrode and a center electrode are provided.
At least one of the ground electrode and the center electrode is a spark plug including an electrode body, an electrode tip having a discharge surface, and a molten portion formed between the electrode body and the electrode tip. hand,
In the first cross section that passes through the center of gravity of the discharge surface and is perpendicular to the discharge surface.
The range in the direction parallel to the discharge surface where the molten portion and the electrode tip are in contact and the melted portion and the electrode body are in contact is defined as the first contact range.
Of the contour lines of the molten portion in the first contact range, the portion in contact with the electrode tip is referred to as the first contour line, and the portion in contact with the electrode body is referred to as the second contour line.
Of the directions perpendicular to the discharge surface, the direction from the electrode body toward the electrode chip is defined as the first direction, and the direction opposite to the first direction is defined as the second direction.
The first contact range is divided in the direction parallel to the discharge surface at intervals of 0.05 mm to specify a plurality of first sections.
The position in the direction parallel to the discharge surface is the position of the center of the first section, and the position in the direction perpendicular to the discharge surface is from the end of the first contour line in the first section in the first direction. The point that is the center position of the range up to the end in the second direction is defined as the first point of the first section.
The position in the direction parallel to the discharge surface is the position of the center of the first section, and the position in the direction perpendicular to the discharge surface is the position from the end in the first direction of the second contour line in the first section. The point that is the center position of the range up to the end in the second direction is defined as the second point of the first section.
The line length of the first line connecting the plurality of first points corresponding to the plurality of the first sections is L1, and the number of maximum points and minimum points in the first line is N1.
When the line length of the second line connecting the plurality of the second points corresponding to the plurality of the first sections is L2 and the number of maximum points and minimum points in the second line is N2.
A spark plug characterized by satisfying L1 <L2 and (2 × N1) <N2.

According to the above configuration, the contact area between the molten portion and the electrode body can be sufficiently increased as compared with the contact area between the molten portion and the electrode tip. As a result, the heat transfer property in the vicinity of the electrode tip, which becomes hot during use, is transferred to the electrode body, so that the heat-drawing performance of the spark plug can be improved, and the degree of thermal expansion and contraction of the electrode tip can be improved. Can be made smaller. In addition, since the contact surface between the molten portion and the electrode body has a more uneven shape than the contact surface between the fused portion and the electrode tip, the wedge effect improves the bonding strength between the fused portion and the electrode body. can. As a result, the peeling resistance of the electrode tip can be improved. Furthermore, compared to the contact surface between the molten part and the electrode body, the contact surface between the molten part and the electrode tip has a shape with less unevenness, so the impact due to the explosion of fuel gas generated near the electrode tip is a specific point. Since it is possible to suppress concentration on (for example, the tip and the rear end of the unevenness), the impact resistance of the spark plug can be improved.

[Application Example 2] The spark plug according to Application Example 1.
On the first line
The maximum point located between the two minimum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the first maximum point.
The minimum point located between the two maximum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the first minimum point.
On the second line,
The maximum point located between the two minimum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the second maximum point.
When the minimum point located between the two maximum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the second minimum point,
The total number M1 of the first maximum point and the first minimum point and the total number M2 of the second maximum point and the second minimum point are (5 × M1) <M2. A spark plug characterized by satisfying.

According to the above configuration, the joint strength between the molten portion and the electrode body can be further improved by the wedge effect, and the impact due to the explosion of the fuel gas can be further suppressed from being concentrated at a specific point. Therefore, the peeling resistance and impact resistance of the electrode tip can be further improved.

[Application Example 3] The spark plug according to Application Example 1 or 2.
In a second cross section that passes through the center of gravity of the discharge surface, is perpendicular to the discharge surface, and is perpendicular to the first cross section.
The range in the direction parallel to the discharge surface where the molten portion and the electrode tip are in contact and the melted portion and the electrode body are in contact is defined as the second contact range.
Of the contour lines of the molten portion in the second contact range, the portion in contact with the electrode tip is referred to as a third contour line, and the portion in contact with the electrode body is referred to as a fourth contour line.
The second contact range is divided in the direction parallel to the discharge surface at intervals of 0.05 mm to specify a plurality of second sections.
The position in the direction parallel to the discharge surface is the position of the center of the second section, and the position in the direction perpendicular to the discharge surface is the position from the end in the first direction of the third contour line in the second section. The point that is the center position of the range up to the end in the second direction is defined as the third point of the second section.
The position in the direction parallel to the discharge surface is the position of the center of the second section, and the position in the direction perpendicular to the discharge surface is the position from the end in the first direction of the fourth contour line in the second section. The point that is the center position of the range up to the end in the second direction is defined as the fourth point of the second section.
The line length of the third line connecting the plurality of the third points corresponding to the plurality of the second sections is L3, and the number of maximum points and minimum points in the third line is N3.
When the line length of the fourth line connecting the plurality of the fourth points corresponding to the plurality of the second sections is L4 and the number of maximum points and minimum points in the fourth line is N4.
A spark plug characterized by satisfying L3 <L4 and (2 × N3) <N4.

According to the above configuration, the contact area between the molten portion and the electrode body can be further increased as compared with the contact area between the molten portion and the electrode tip, so that the heat drawing performance of the spark plug can be further improved. can. Further, compared to the contact surface between the molten portion and the electrode tip, the contact surface between the fused portion and the electrode body has a more uneven shape, so that the bonding strength between the fused portion and the ground electrode body is further improved. can. As a result, the peeling resistance of the electrode tip can be improved. Further, since the contact surface between the molten portion and the electrode tip has a shape with less unevenness as compared with the contact surface between the molten portion and the electrode body, the impact resistance of the spark plug can be further improved.

[Application Example 4] The spark plug according to Application Example 3.
On the third line
The maximum point located between the two minimum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the third maximum point.
The minimum point located between the two maximum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the third minimum point.
On the fourth line,
The maximum point located between the two minimum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the fourth maximum point.
When the minimum point located between the two maximum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the fourth minimum point,
The total number M3 of the third maximum point and the third minimum point and the total number M4 of the fourth maximum point and the fourth minimum point are (5 × M3) <M4. A spark plug characterized by satisfying.

According to the above configuration, the joint strength between the molten portion and the electrode tip can be further improved by the wedge effect, and the impact due to the explosion of the fuel gas can be further suppressed from being concentrated at a specific point. Therefore, the peeling resistance and impact resistance of the electrode tip can be further improved.

The technique disclosed in the present specification can be realized in various aspects, for example, an ignition device using a spark plug or a spark plug, an internal combustion engine equipped with the spark plug, and an electrode of the spark plug. , The method of welding the electrode of the spark plug and the electrode tip, the method of manufacturing the electrode of the spark plug, and the like can be realized.

It is sectional drawing of the spark plug 100 of this embodiment. It is a figure which looked at the vicinity of the 2nd discharge surface 391 from the rear end direction BD toward the tip direction FD along the axial direction. It is sectional drawing which cut the vicinity of the tip of the spark plug 100 at a specific surface. It is an enlarged view of the vicinity of the 1st contour line OL1 in the 1st cross section CF1. It is an enlarged view of the vicinity of the 2nd contour line OL2 in the 1st cross section CF1. It is a flowchart of the manufacturing method of the ground electrode 30. It is 1st explanatory drawing of the manufacturing method of the ground electrode 30. It is a 2nd explanatory drawing of the manufacturing method of the ground electrode 30.

A. Embodiment A-1. Configuration of Spark Plug FIG. 1 is a cross-sectional view of the spark plug 100 of the present embodiment. The alternate long and short dash line in FIG. 1 indicates the axis CO of the spark plug 100. The direction parallel to the axis CO (vertical direction in FIG. 1) is also referred to as the axis direction. The radial direction of the circle centered on the axis CO is also simply referred to as "diametrical direction", and the circumferential direction of the circle centered on the axis CO is also simply referred to as "circumferential direction". The downward direction in FIG. 1 is referred to as a tip direction FD, and the upward direction is also referred to as a rear end direction BD. The lower side in FIG. 1 is referred to as the front end side of the spark plug 100, and the upper side in FIG. 1 is referred to as the rear end side of the spark plug 100.

The spark plug 100 generates a spark discharge in a gap (spark gap) formed between the center electrode 20 and the ground electrode 30, which will be described in detail later. The spark plug 100 is attached to the internal combustion engine and is used to ignite the fuel gas in the combustion chamber of the internal combustion engine. The spark plug 100 includes an insulator 10 as an insulator, a center electrode 20, a ground electrode 30, a terminal fitting 40, and a main fitting 50.

The insulator 10 is formed by firing alumina or the like. The insulator 10 is a substantially cylindrical member having a shaft hole 12 which is a through hole extending along the axial direction and penetrating the insulator 10. The insulator 10 includes a flange portion 19, a rear end side body portion 18, a tip side body portion 17, a step portion 15, and a leg length portion 13. The rear end side body portion 18 is located on the rear end side of the flange portion 19 and has an outer diameter smaller than the outer diameter of the flange portion 19. The distal end side body portion 17 is located on the distal end side of the flange portion 19 and has an outer diameter smaller than the outer diameter of the flange portion 19. The leg length portion 13 is located on the distal end side of the distal end side trunk portion 17 and has an outer diameter smaller than the outer diameter of the distal end side trunk portion 17. The leg length portion 13 is exposed to the combustion chamber when the spark plug 100 is attached to an internal combustion engine (not shown). The step portion 15 is formed between the leg length portion 13 and the tip side body portion 17.

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 CO. 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. In other words, the main metal fitting 50 is arranged around the center electrode 20, and the center electrode 20 is insulated and held via the insulator 10. The tip of the center electrode projects toward the tip from the tip of the main metal fitting 50. The rear end of the insulator 10 projects toward the rear end side from 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 spark 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, one of M8 (8 mm (millimeters)), M10, M12, M14, and M18.

An annular gasket 5 formed by bending a metal plate 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 crimping portion 53 provided on the rear end side of the tool engaging portion 51, and a thin-walled compression deformation portion 58 provided between the seat portion 54 and the tool engaging portion 51. And have. 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 is annular. Ring members 6 and 7 are arranged. The powder of talc (talc) 9 is filled between the two ring members 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 ring members 6, 7 and the talc 9. As a result, the stepped portion 15 (insulation) of the insulator 10 is formed by the stepped portion 56 (metal fitting side stepped portion) formed on the inner circumference of the mounting screw portion 52 of the main metal fitting 50 via the metal annular plate packing 8. The body side step 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 main body 21 extending in the axial direction and a center electrode tip 29. The center electrode main body 21 is held in a portion on the tip side inside the shaft hole 12 of the insulator 10. The center electrode main body 21 has a structure including an electrode base material 21A and a core portion 21B embedded inside the electrode base material 21A. The electrode base material 21A is formed by using, for example, nickel or an alloy containing nickel as a main component (for example, NCF600, NCF601). The core portion 21B is made of copper or an alloy containing copper as a main component, which is superior in thermal conductivity to the alloy forming the electrode base material 21A, and is made of copper in this embodiment.

Further, the center electrode main body 21 has a flange portion 24 (also referred to as a flange portion) provided at a predetermined position in the axial direction and a head portion 23 (electrode head portion) which is a portion on the rear end side of the flange portion 24. And a leg portion 25 (electrode leg portion) which is a portion on the tip end side of the flange portion 24. The flange portion 24 is supported by the step portion 16 of the insulator 10. The tip portion of the leg portion 25, that is, the tip end of the center electrode main body 21, protrudes toward the tip end side from the tip end of the insulator 10.

The center electrode tip 29 is a member having a substantially cylindrical shape, and is joined to the tip of the center electrode main body 21 (the tip of the leg portion 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 described later. The center electrode tip 29 is made of a material containing a high melting point precious metal as a main component. The center electrode chip 29 is, for example, a noble metal chip formed by using a noble metal such as iridium (Ir) or Ir, or an alloy containing the noble metal as a main component.

The ground electrode 30 includes a ground electrode main body 31 joined to the tip of the main metal fitting 50, and a square pillar-shaped ground electrode tip 39. The ground electrode main body 31 is a rod-shaped body having a quadrangular cross section. One end of the ground electrode main body 31 is a free end 313, and the other end is a connection end 312. The connection end 312 is joined to the tip surface 50A 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 ground electrode main body 31 includes a free end 313 and includes a tip portion 31a extending in a direction perpendicular to the axis CO, and a rear end portion 31b including a connecting end 312 and extending in the axis direction. The portion between the front end portion 31a and the rear end portion 31b is a curved portion.

The ground electrode main body 31 is formed by using, for example, nickel or an alloy containing nickel as a main component (for example, NCF600, NCF601). The ground electrode main body 31 is formed of a base material made of a metal having high corrosion resistance (for example, nickel alloy) and a metal having high thermal conductivity (for example, copper), and has a core embedded in the base material. It may have a two-layer structure including a portion and a portion. The ground electrode tip 39 can be a noble metal tip formed by using the same alloy as the center electrode tip 29. However, preferably, it is a noble metal chip formed by using an alloy containing iridium (Ir) or Ir as a main component or an alloy containing Pt as a main component and containing Ir.

The terminal fitting 40 is a rod-shaped member extending in the axial direction. The terminal fitting 40 is made of a conductive metal material (for example, low carbon steel), and a metal layer for corrosion protection (for example, Ni layer) is formed on the surface of the terminal fitting 40 by plating or the like. The terminal fitting 40 includes a flange portion 42 (terminal jaw portion) formed at a predetermined position in the axial direction, a cap mounting portion 41 located on the rear end side of the flange portion 42, and a leg portion 43 on the tip side of the flange portion 42. (Terminal legs) and. The cap mounting portion 41 of the terminal fitting 40 is exposed on the rear end side of the insulator 10. The leg portion 43 of the terminal fitting 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 spark discharge is applied.

In the shaft hole 12 of the insulator 10, radio noise at the time of spark generation is generated between the tip of the terminal fitting 40 (the tip of the leg 43) and the rear end of the center electrode 20 (the rear end of the head 23). A resistor 70 for reduction is arranged. 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. In the shaft hole 12, the gap between the resistor 70 and the center electrode 20 is filled with the conductive seal 60. The gap between the resistor 70 and the terminal fitting 40 is filled with the conductive seal 80. The conductive seals 60 and 80 are formed of, for example, a composition containing glass particles such as B ₂ O ₃ -SiO ₂ system and metal particles (Cu, Fe, etc.).

A-2. Configuration of the ground electrode 30 in the vicinity of the ground electrode tip 39 The configuration of the ground electrode 30 in the vicinity of the ground electrode tip 39 will be described in more detail. FIG. 2 is a view of the vicinity of the second discharge surface 391 of the ground electrode tip 39 as viewed from the rear end direction BD to the front end direction FD along the axial direction. FIG. 3 is a cross-sectional view in which the vicinity of the tip of the spark plug 100 is cut at a specific surface.

The rear end surface of the ground electrode chip 39 is a second discharge surface 391 facing the first discharge surface 295 (FIG. 1) of the center electrode chip 29. The first cross section CF1 of FIG. 3A is a cross section that passes through the center of gravity GC of the second discharge surface 391, is perpendicular to the second discharge surface 391, and is parallel to the axis of the rod-shaped ground electrode main body 31. .. The second cross section CF2 of FIG. 3B is a cross section that passes through the center of gravity GC of the second discharge surface 391, is perpendicular to the second discharge surface 391, and is perpendicular to the first cross section CF1. In the present embodiment, the line passing through the center of gravity GC of the second discharge surface 391 and perpendicular to the second discharge surface 391 coincides with the axis CO of the spark plug 100.

The center of gravity of the second discharge surface 391 is the center of gravity when it is assumed that the mass is evenly distributed on the second discharge surface 391. The second discharge surface 391 is determined, for example, as follows. The second discharge surface 391 is photographed from the rear end direction BD side toward the front end direction FD to acquire a digital image. In the digital image, the average coordinates of the coordinates of the plurality of pixels constituting the second discharge surface 391 are calculated. The position indicated by the average coordinates is defined as the center of gravity of the second discharge surface 391.

The first direction is the thickness direction of the ground electrode chip 39, that is, the direction perpendicular to the second discharge surface 391 and from the ground electrode main body 31 toward the ground electrode chip 39 (rear end direction BD in this embodiment). Let D1 be, and let the opposite direction of the first direction D1 (the tip direction FD in this embodiment) be the second direction D2.

The direction from the center of gravity GC of the second discharge surface 391 toward the free end 313 along the second discharge surface 391, that is, the left direction in FIG. 2, is referred to as the third direction D3. The direction away from the free end 313 along the second discharge surface 391 from the center of gravity GC of the second discharge surface 391, that is, the direction opposite to the third direction D3 is defined as the fourth direction D4.

Of the four side surfaces connected to the free end 313 (free end surface) of the ground electrode main body 31, the side surface facing the first discharge surface 295 is referred to as an inner side surface 311. Of the four side surfaces of the ground electrode main body 31, the two side surfaces that are connected to the inner side surface 311, that is, the side surfaces located in the vertical direction in FIG. 2 are referred to as side surfaces 315 and 316. Then, the direction from the center of gravity GC of the second discharge surface 391 toward the side surface 315, that is, the upper direction of FIG. 2 is the fifth direction D5, and the opposite direction of the fifth direction D5 is the sixth direction D6.

The ground electrode tip 39 is a member having a square columnar shape. That is, the ground electrode tip 39 includes a quadrangular (square in this embodiment) second discharge surface 391 and four side surfaces 393 to 396 connected to the second discharge surface 391. Of these four sides, the side surface 393 faces the side of the free end 313 (third direction D3) and the side surface 394 faces the side of the connecting end 312 (fourth direction D4). The ground electrode tip 39 has a length W of one side of the second discharge surface 391 of the square, that is, the length of the ground electrode chip 39 in the third direction D3 and the length of the fifth direction D5 are, for example, 2. It is 0.0 mm or more, preferably 2.5 mm or more. The average thickness of the ground electrode tip 39 (average length in the axial direction) is, for example, 0.2 mm to 1.0 mm.

The ground electrode tip 39 is arranged along the inner side surface 311 at the tip portion 31a of the ground electrode main body 31. The ground electrode tip 39 is joined to the ground electrode main body 31 by laser welding. For this purpose, a molten portion 35 formed by laser welding is arranged between the ground electrode tip 39 and the ground electrode main body 31. The molten portion 35 is a portion where a part of the ground electrode tip 39 before welding and a part of the ground electrode main body 31 are melted and solidified. For this purpose, the melting portion 35 includes a component of the ground electrode tip 39 and a component of the ground electrode main body 31. It can be said that the ground electrode tip 39 is joined to the inner surface 311 of the ground electrode main body 31 via the melting portion 35.

As can be seen from FIG. 2, the shape of the molten portion 35 seen along the axial direction is a substantially similar figure (square in this embodiment) slightly larger than the shape of the ground electrode tip 39 seen along the axial direction. be. The side surfaces 353 to 356 of the four directions D3 to D6 of the molten portion 35 are located radially outside the corresponding side surfaces 393 to 356 of the ground electrode tip 39 and are exposed to the outside.

The melting portion 35 has a melting sagging 35n that covers the portion of the side surface 393 to 396 of the ground electrode chip 39 on the FD side in the tip direction (FIG. 3). The molten dripping 35n is formed over the entire circumference of the ground electrode tip 39.

The contact surface 351 (FIG. 3) on the BD side in the rear end direction of the melting portion 35 is a contact surface with the surface (the surface in the tip direction FD) opposite to the second discharge surface 391 of the ground electrode tip 39. All of the surfaces of the ground electrode tip 39 on the opposite side of the second discharge surface 391 (the surface in the tip direction FD) are in contact with the molten portion 35. The contact surface 352 (FIG. 3) on the FD side in the tip direction of the melting portion 35 is entirely in contact with the ground electrode main body 31. The contact surface 351 is also referred to as a chip contact surface, and the contact surface 352 is also referred to as a main body contact surface.

The main body contact surface 352 has more irregularities and a rough surface as compared with the chip contact surface 351. In FIG. 3, in order to conceptually show this, the chip contact surface 351 is shown by a straight line, and the main body contact surface 352 is shown by a jagged line.

Here, in the first cross section CF1 of FIG. 3A, the range of the third direction D3 in which the molten portion 35 and the ground electrode tip 39 are in contact with each other and the molten portion 35 and the ground electrode main body 31 are in contact with each other is defined. 1 Contact range is RG1. It can also be said that the first contact range RG1 is the range of the third direction D3 in which both the chip contact surface 351 and the contact surface 352 exist.

Of the contour lines of the molten portion 35 in the first contact range RG1, the portion in contact with the center electrode tip 29 is referred to as the first contour line OL1, and the portion in contact with the center electrode main body 21 is referred to as the second contour line OL2. The first contour line OL1 is a portion of the chip contact surface 351 within the first contact range RG1, and the second contour line OL2 is a portion of the contact surface 352 within the first contact range RG1. I can say.

FIG. 4 is an enlarged view of the vicinity of the first contour line OL1 in the first cross section CF1. FIG. 5 is an enlarged view of the vicinity of the second contour line OL2 in the first cross section CF1. In the first cross section CF1, the division specified by dividing the first contact range RG1 in the direction parallel to the second discharge surface 391 (for example, the third direction D3) at intervals of 0.05 mm is referred to as a division division CL. FIG. 4 shows the division division CL11 to the division division CL18. FIG. 5 shows the division divisions CL21 to CL28. The length L of FIGS. 4 and 5 is 0.05 mm as described above.

In each division division CL, the position of the third direction D3 is the position of the center of the division division CL, and the position of the first direction D1 is from the end of the first direction D1 of the first contour line OL1 in the division division CL. The point at the center of the range up to the end of the second direction D2 is designated as the representative point P1 of the first contour line OL1 of the division division CL. FIG. 4 shows representative points P11 to P18 of the first contour line OL1 of the division divisions CL11 to CL18.

Similarly, in each division division CL, the position in the direction parallel to the second discharge surface 391 (for example, the third direction D3) is the center position of the division division CL, and the position in the first direction D1 is the division. The point at the center of the range from the end of the first direction D1 of the second contour line OL2 in the division CL to the end of the second direction D2 is designated as the representative point P2 of the second contour line OL2 of the division division CL. FIG. 5 shows representative points P21 to P28 of the second contour line OL2 of the division divisions CL21 to CL28.

For example, in FIG. 5, the position of the third direction D3 of the representative point P21 of the second contour line OL2 of the division division CL21 is the center of the third direction D3 of the division division CL21. Therefore, the distance from the representative point P21 to the end of the third direction D3 of the division division CL21 and the distance from the representative point P21 to the end of the fourth direction D4 of the division division CL21 are (L / 2), that is, 0. It is .025 mm. Further, the position of the representative point P21 in the first direction D1 is the center of the range from the end Pa1 of the first direction D1 of the second contour line OL2 to the end Pb1 of the second direction D2 in the division division CL21. Therefore, assuming that the distance of the first direction D1 from the end Pa1 of the first direction D1 to the end Pb1 of the second direction D2 is Ha, the distance of the first direction D1 from the representative point P21 to the end Pa1 of the first direction D1. The distance of the first direction D1 from the representative point P21 to the end Pb1 of the second direction D2 is (Ha / 2).

A virtual line connecting a plurality of representative points of the first contour line OL1 (for example, representative points P11 to P18 in FIG. 4) is referred to as an evaluation virtual line VL1 (FIG. 4) of the first contour line OL1. Similarly, a virtual line connecting a plurality of representative points of the second contour line OL2 (for example, representative points P21 to P28 in FIG. 5) is combined with an evaluation virtual line VL2 (FIG. 5) of the second contour line OL2. do.

In FIGS. 4 and 5, the representative points P11, P14, P18, P21, P23, P25, and P26 circled are the maximum points or the minimum points of the evaluation virtual lines VL1 and VL2. For example, the representative point P23 in FIG. 5 is a maximum point because both of the two representative points P22 and P24 sandwiching themselves on the evaluation virtual line VL2 are located in the second direction D2 with respect to themselves. Further, the representative point P25 in FIG. 5 is a minimum point because both the two representative points P24 and P26 sandwiching themselves on the evaluation virtual line VL2 are located in the first direction D1 with respect to themselves.

Here, the line length of the evaluation virtual line VL1 is L1, and the number of maximum points and minimum points in the evaluation virtual line VL1 is N1. The line length of the evaluation virtual line VL2 is L2, and the number of maximum points and minimum points in the evaluation virtual line VL2 is N2. In this embodiment, since the main body contact surface 352 is sufficiently coarser than the chip contact surface 351, L1, L2, N1 and N2 satisfy L1 <L2 and (2 × N1) <N2.

Here, on the evaluation virtual line (for example, VL1, VL2, and VL3, VL4 described later), the maximum point located between the two minimum points where the distance of the third direction D3 is 0.5 mm or less. Is a specific maximum point SPb. Further, on the evaluation virtual line, the minimum points located between the two maximum points where the distance of the third direction D3 is 0.5 mm or less are defined as the specific minimum points SPs.

For example, on the evaluation virtual line VL1 of FIG. 4, the minimum point P14 is located at the nearest maximum point P18 located in the fourth direction D4 as seen from the minimum point P14 and in the third direction D3 as viewed from the minimum point P14. It is sandwiched between the nearest maximum point P11 and. The distance La of the third direction D3 between the two maximum points P11 and P18 sandwiching the minimum point P14 is (7 × 0.05) = 0.35 mm, so that it is 0.5 mm or less. Therefore, the minimum point P14 is a specific minimum point SPs.

Similarly, on the evaluation virtual line VL2 of FIG. 5, the maximum point P23 is located at the nearest minimum point P26 located in the fourth direction D4 when viewed from the maximum point P23 and the third direction D3 when viewed from the maximum point P23. It is sandwiched between the nearest local minimum point P21. The distance Lb in the third direction D3 between the two minimum points P21 and P26 sandwiching the maximum point P23 is (4 × 0.05) = 0.2 mm, so that it is 0.5 mm or less. Therefore, the maximum point P23 is the specific maximum point SPb. Further, the minimum point P25 is sandwiched between the nearest maximum point P26 located in the fourth direction D4 when viewed from the minimum point P25 and the closest maximum point P23 located in the third direction D3 when viewed from the minimum point P25. ing. The distance Lc of the third direction D3 between the two maximum points P23 and P26 sandwiching the minimum point P25 is (3 × 0.05) = 0.15 mm, so that it is 0.5 mm or less. Therefore, the minimum point P25 is a specific minimum point SPs.

Here, the total number M1 of the specific maximum point SPb and the specific minimum point SPs in the evaluation virtual line VL1 and the total number M2 of the specific maximum point SPb and the specific minimum point SPs in the evaluation virtual line VL2 are (5 × M1) <M2 is satisfied.

Here, in the second cross section CF2 of FIG. 3B, the range of the fifth direction D5 in which the molten portion 35 and the ground electrode tip 39 are in contact with each other and the fused portion 35 and the ground electrode main body 31 are in contact with each other is defined. 2 Contact range RG2. It can also be said that the second contact range RG2 is the range of the fifth direction D5 in which both the chip contact surface 351 and the contact surface 352 exist.

Of the contour lines of the molten portion 35 in the second contact range RG2, the portion in contact with the center electrode tip 29 is referred to as the third contour line OL3, and the portion in contact with the center electrode main body 21 is referred to as the fourth contour line OL4 (FIG. 3). (B)). The third contour line OL3 is a portion of the chip contact surface 351 within the second contact range RG2, and the fourth contour line OL4 is a portion of the contact surface 352 within the second contact range RG2. I can say.

The evaluation virtual line VL3 of the third contour line OL3 is specified by the same method as the method for specifying the evaluation virtual line VL1 of the first contour line OL1 described with reference to FIG. 4 (not shown). That is, in the second cross section CF2, the division division CL is specified by dividing the second contact range RG2 in the direction parallel to the second discharge surface 391 (for example, the fifth direction D5) at intervals of 0.05 mm. In each division division CL, the position of the fifth direction D5 is the position of the center of the division division CL, and the position of the first direction D1 is from the end of the first direction D1 of the third contour line OL3 in the division division CL. The point at the center of the range up to the end of the second direction D2 is taken as the representative point of the third contour line OL3 of the division division CL. A virtual line connecting a plurality of representative points of the third contour line OL3 is referred to as an evaluation virtual line VL3 (not shown) of the third contour line OL3.

The evaluation virtual line VL4 of the fourth contour line OL4 is specified by the same method as the method for specifying the evaluation virtual line VL2 of the second contour line OL2 described with reference to FIG. 5 (not shown). That is, in each division division CL in the second cross section CF2, the position of the fifth direction D5 is the position of the center of the division division CL, and the position of the first direction D1 is the position of the fourth contour line OL4 in the division division CL. The point at the center of the range from the end of the first direction D1 to the end of the second direction D2 is designated as the representative point of the fourth contour line OL4 of the division division CL. A virtual line connecting a plurality of representative points of the fourth contour line OL4 is referred to as an evaluation virtual line VL4 (not shown) of the fourth contour line OL4.

The line length of the evaluation virtual line VL3 is L3, and the number of maximum points and minimum points in the evaluation virtual line VL3 is N3. The line length of the evaluation virtual line VL4 is L4, and the number of maximum points and minimum points in the evaluation virtual line VL4 is N4. In this embodiment, since the main body contact surface 352 is sufficiently coarser than the chip contact surface 351, L3, L4, N2, and N4 satisfy L3 <L4 and (2 × N3) <N4.

Further, also in the evaluation virtual lines VL3 and VL4, the specific minimum point SPs and the specific maximum point SPb described with reference to FIGS. 4 and 5 can be specified. The total number M3 of the specific maximum point SPb and the specific minimum point SPs in the evaluation virtual line VL3 and the total number M4 of the specific maximum point SPb and the specific minimum point SPs in the evaluation virtual line VL4 are (5 × M3) <Satisfy M4.

A-3. Manufacturing Method A manufacturing method of the spark plug 100 will be described focusing on a manufacturing method of the ground electrode 30. FIG. 6 is a flowchart of a method for manufacturing the ground electrode 30. 7 and 8 are explanatory views of a method for manufacturing the ground electrode 30. First, the rod-shaped ground electrode main body 31 before being bent is prepared. Then, the ground electrode tip 39 before being welded to the ground electrode main body 31 is prepared.

In S10, the ground electrode main body 31 is fixed to the fixing base 400. Specifically, as shown in FIG. 8, the ground electrode main body 31 is arranged on the upper surface of the fixing base 400 with the inner side surface 311 facing upward. Then, the portion of the inner side surface 311 in the fourth direction D4 is pressed by the pressing member 500 in the second direction D2 (downward in FIG. 8) than the portion to which the ground electrode tip 39 should be joined. The holding member 500 and the fixing base 400 are made of a metal material (for example, iron) having a relatively high thermal conductivity.

In S20, as shown in FIGS. 7 (A) and 8 (A), a square columnar ground electrode tip 39 before welding is arranged on the inner side surface 311 of the ground electrode main body 31. In this state, the surface 39S on the tip end side of the ground electrode chip 39 and the inner surface surface 311 come into contact with each other. The contact surface between the front end side surface 39S and the inner side surface 311 of the ground electrode main body 31, that is, the surface to be joined between the ground electrode tip 39 and the ground electrode main body 31, is also referred to as a chip joint surface BS.

In S30, the laser for laser welding is scanned and output, and about half of the chip joint surface BS on the fifth direction D5 side is welded. In this embodiment, a fiber laser is used as the laser. Since the fiber laser has a higher light-collecting property than the YAG laser, for example, the degree of freedom in the shape of the molten portion 35 that can be formed is high, and therefore, as shown in FIG. 2, the thickness is relatively thin and the fiber laser has a high degree of freedom. , The molten portion 35 having a relatively long length in the direction perpendicular to the axis (for example, the fifth direction D5) can be formed.

The laser LZ1 in FIG. 7A shows a laser at the start of the welding process (also referred to as a first welding step) of S30, and the laser LZ2 shows a laser at the end of the first welding step. As shown in FIG. 7A, the laser is irradiated from the side surface 395 to the fifth direction D5 side to the sixth direction D6. As shown in FIGS. 7A and 8, in the first welding step, the portion of the side surface 395 on the first direction D1 side slightly from the tip joint surface BS is formed from the end point P1 of the fourth direction D4 to the third direction D3. The laser is continuously irradiated while moving the irradiation position in the third direction D3 to the end point P2 of. Between the end point P3 in the third direction D3 and the end point P4 in the fourth direction D4, the moving speed of the irradiation position and the energy of laser irradiation are appropriately adjusted according to the size and melting point of the ground electrode tip 39.

In FIG. 7B, the hatched molten portion 35A is a fused portion formed in the first welding step. By the first welding step, about half of the chip joint surface BS on the fifth direction D5 side is welded.

In S40 after the first welding step, the laser is scanned and output again, and the remaining half of the chip joint surface BS, that is, about half on the sixth direction D6 side is welded.

The laser LZ3 in FIG. 7B shows a laser at the start of the welding step (also referred to as a second welding step) of S40, and the laser LZ4 shows a laser at the end of the second welding step. As shown in FIG. 7B, the laser is irradiated from the side surface 396 to the fifth direction D5 from the sixth direction D6 side. In the second welding step, the irradiation position is moved from the end point P3 in the third direction D3 to the end point P4 in the fourth direction D4 in the fourth direction D4 on the portion of the side surface 396 on the BD side in the rear end direction slightly from the tip joint surface BS. Meanwhile, the laser is continuously irradiated. Between the end point P3 in the third direction D3 and the end point P4 in the fourth direction D4, the moving speed of the irradiation position and the energy of laser irradiation are appropriately adjusted according to the size and melting point of the ground electrode tip 39.

By the two steps of the first welding step and the second welding step described above, the molten portion 35 described with reference to FIGS. 2 and 3 is formed, and the ground electrode main body 31 and the ground electrode tip 39 are welded to each other. Is completed.

When the molten portion 35 is formed in the first welding step and the second welding step, the ground electrode main body 31 is in contact with the holding member 500 and the fixing base 400. Therefore, in the first welding step and the second welding step, the heat of the ground electrode main body 31 is transferred to the holding member 500 and the fixing base 400 as shown by the arrows AR1 and AR2 in FIG. On the other hand, when the molten portion 35 is formed, the ground electrode tip 39 is only in contact with air having a lower thermal conductivity than the metal holding member 500 and the fixing base 400. Therefore, the heat of the ground electrode chip 39 is difficult to escape to the outside. As described above, in the molten portion 35, the amount of heat drawn on the ground electrode chip 39 side is smaller than that on the ground electrode main body 31 side. Further, the thermal conductivity of the noble metal ground electrode tip 39 is generally higher than that of the nickel alloy ground electrode body 31. As a result, at the time of forming the melting portion 35, the vicinity of the interface between the melting portion 35 and the ground electrode tip 39 becomes uniform at a higher temperature than the vicinity of the interface between the melting portion 35 and the ground electrode main body 31, and the melting portion 35 is melted. The vicinity of the interface between the portion 35 and the ground electrode main body 31 becomes non-uniform at a lower temperature than the vicinity of the interface between the molten portion 35 and the ground electrode tip 39. As a result, as shown in FIG. 3, the main body contact surface 352 of the melting portion 35 becomes rougher than the chip contact surface 351 of the melting portion 35. It is considered that this difference in roughness is easily obtained when the tip joint surface BS of the ground electrode tip 39 is large. Therefore, the length of the ground electrode tip 39 in the third direction D3 and the length of the fifth direction D5 are preferably 2.5 mm or more.

The ground electrode main body 31 and the ground electrode tip 39 may be welded, for example, after the rod-shaped ground electrode main body 31 is welded to the main metal fitting 50. Further, after the ground electrode main body 31 and the ground electrode tip 39 are welded, the ground electrode main body 31 may be welded to the main metal fitting 50.

Further, an assembly having an insulator 10, a center electrode 20, a conductive seal 60, a resistor 70, a conductive seal 80, and a terminal fitting 40 is produced by a known method. For example, the center electrode 20, the material of the conductive seal 60, the material of the resistor 70, and the material of the conductive seal 80 are inserted into the shaft hole 12 of the insulator 10 in this order from the BD side in the rear end direction. Then, the assembly is manufactured by inserting the terminal fitting 40 into the shaft hole 12 from the rear end direction BD side in a state where the insulator 10 is heated.

After that, the assembly is fixed to the main metal fitting 50. Specifically, the assembly, the talc 9, and the ring members 6 and 7 are arranged in the through hole 59 of the main metal fitting 50. A plate packing 8 is interposed between the stepped portion 15 of the insulator 10 and the stepped 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 between the center electrode tip 29 and the ground electrode tip 39. With the above, the spark plug 100 is completed.

According to the spark plug 100 of the present embodiment described above, in the first cross section CF1 (FIG. 3A), the line length of the evaluation virtual line VL1 is set to L1, and the maximum point and the minimum point in the evaluation virtual line VL1. When the number of points is N1, the line length of the evaluation virtual line VL2 is L2, and the number of maximum points and minimum points in the evaluation virtual line VL2 is N2, then L1 <L2 and (2 × N1) <N2. Meet.

As a result, the contact area between the molten portion 35 and the ground electrode main body 31 (that is, the area of the main body contact surface 352) is compared with the contact area between the molten portion 35 and the ground electrode tip 39 (that is, the area of the chip contact surface 351). Area) can be made large enough. As a result, the heat transfer property in the vicinity of the ground electrode tip 39, which becomes hot during use, is transferred to the ground electrode main body 31, so that the heat drawing performance of the spark plug 100 can be improved, and eventually the ground electrode tip 39. The degree of thermal expansion and contraction can be reduced. Further, since the contact surface 352 has a shape with many irregularities (a rough surface) as compared with the contact surface between the molten portion 35 and the ground electrode tip 39 (that is, the chip contact surface 351), the fused portion is due to the wedge effect. The bonding strength between the 35 and the ground electrode main body 31 can be improved. As a result, the peeling resistance of the ground electrode tip 39 can be improved. Further, when the spark plug 100 is used, a spark is generated in the vicinity of the second discharge surface 391 of the ground electrode chip 39, and the spark causes an explosion of fuel gas. Therefore, an impact due to the explosion of the fuel gas is applied to the second discharge surface 391 of the ground electrode tip 39. At this time, if the chip contact surface 351 has irregularities, the impact due to the explosion of the fuel gas is concentrated on specific points such as the front end and the rear end of the irregularities, and the molten portion 35 is easily damaged. According to the present embodiment, the chip contact surface 351 has a shape with less unevenness (smooth surface) as compared with the main body contact surface 352, so that the fuel gas explodes in the vicinity of the ground electrode chip 39. Since it is possible to prevent the impact from concentrating on a specific point (for example, the tip or the rear end of the unevenness), the impact resistance of the spark plug 100 can be improved. As described above, according to the spark plug 100 of the present embodiment, the peeling resistance and the impact resistance of the ground electrode tip 39 can be improved. When the length of the ground electrode chip 39 in the third direction D3 and the length of the fifth direction D5 are 2.5 mm or more, the area of the chip contact surface 351 and the area of the main body contact surface 352 are sufficiently large. Therefore, the above effect becomes remarkable.

Further, according to the spark plug 100 of the present embodiment, the total number M1 of the specific maximum point SPb and the specific minimum point SPs in the evaluation virtual line VL1 and the specific maximum point SPb and the specific minimum point SPb in the evaluation virtual line VL2. The total number M2 with SPs satisfies (5 × M1) <M2. It can be said that the specific minimum points SPs and the specific maximum points SPb are sharper points than the other minimum points and the minimum points. Therefore, since the impact due to the explosion of the fuel gas tends to concentrate on the specific minimum point SPs and the specific maximum point SPb, it is preferable that the amount is small on the chip contact surface 351. Further, since the specific minimum point SPs and the specific maximum point SPb contribute to the improvement of the joint strength due to the wedge effect, it is preferable that the specific minimum point SPs and the specific maximum point SPb are large in the main body contact surface 352. According to the present embodiment, the specific minimum point SPs and the specific maximum point SPb can be sufficiently reduced on the chip contact surface 351 and the specific minimum point SPs and the specific maximum point SPb can be sufficiently increased on the main body contact surface 352. .. Therefore, the wedge effect can further improve the joint strength between the molten portion 35 and the ground electrode main body 31, and further suppress the impact of the explosion of the fuel gas from concentrating on a specific point on the chip contact surface 351. Therefore, the peeling resistance and impact resistance of the ground electrode tip 39 can be further improved.

Further, according to the spark plug 100 of the present embodiment, in the second cross section CF2 (FIG. 3B), the line length of the evaluation virtual line VL3 is set to L3, and the maximum point and the minimum point of the evaluation virtual line VL4 are set to L3. When the number is N3, the line length of the evaluation virtual line VL4 is L4, and the number of maximum points and minimum points in the evaluation virtual line VL4 is N4, L3 <L4 and (2 × N3) <N4. Fulfill.

According to the above configuration, the area of the main body contact surface 352 can be further increased as compared with the area of the chip contact surface 351 so that the heat drawing performance of the spark plug 100 can be further improved, and eventually the grounding. The degree of thermal expansion and contraction of the electrode tip 39 can be reduced. Further, since the main body contact surface 352 has a shape with more unevenness as compared with the chip contact surface 351, the bonding strength between the molten portion 35 and the ground electrode chip 39 can be further improved. As a result, the peeling resistance of the ground electrode tip 39 can be improved. Further, since the chip contact surface 351 has a shape with less unevenness as compared with the main body contact surface 352, the impact resistance of the spark plug 100 can be further improved.

Further, according to the spark plug 100 of the present embodiment, the total number M3 of the specific maximum point SPb and the specific minimum point SPs in the evaluation virtual line VL3, and the specific maximum point SPb and the specific minimum point SPb in the evaluation virtual line VL4. The total number M4 with SPs satisfies (5 × M3) <M4. Therefore, the wedge effect can further improve the joint strength between the molten portion 35 and the ground electrode main body 31, and further suppress the impact of the explosion of the fuel gas from concentrating on a specific point on the chip contact surface 351. Therefore, the peeling resistance and impact resistance of the ground electrode tip 39 can be further improved.

As can be seen from the above description, the evaluation virtual line VL1 of the present embodiment is an example of the first line, the evaluation virtual line VL2 is an example of the second line, and the evaluation virtual line VL3 is the first line. It is an example of 3 lines, and the virtual line VL4 for evaluation is an example of the 4th line. Further, the specific minimum point SPs and the specific maximum point SPb on the evaluation virtual line VL1 are examples of the first minimum point and the first maximum point, and the specific minimum point SPs and the specific maximum point on the evaluation virtual line VL2. The point SPb is an example of the second local minimum point and the second local maximum point, and the specific local minimum point SPs and the specific local maximum point SPb on the evaluation virtual line VL3 are the third local minimum point and the third local maximum point. As an example, the specific local minimum point SPs and the specific local maximum point SPb on the evaluation virtual line VL4 are examples of the fourth local minimum point and the fourth local maximum point.

B. Modification example:
(1) In the spark plug 100 of the above embodiment, L1 <L2 and (2 × N1) <N2 are satisfied in the first cross section CF1, and L3 <L4 and (2 ×) in the second cross section CF2. N3) <N4 is satisfied. Instead, L1 <L2 and (2 × N1) <N2 are satisfied in the first cross-section CF1, and L3 <L4 and (2 × N3) <N4 are satisfied in the second cross-section CF2. It doesn't have to be. Further, even if L1 <L2 and (2 × N1) <N2 are not satisfied in the first cross-section CF1, and L3 <L4 and (2 × N3) <N4 are satisfied in the second cross-section CF2. good.

(2) In the spark plug 100 of the above embodiment, L1 <L2, (2 × N1) <N2, and (5 × M1) <M2 are satisfied in the first cross section CF1. , (5 × M1) <M2 may not be satisfied. Similarly, in the spark plug 100 of the above embodiment, in the second cross section CF2, L3 <L4 and (2 × N3) <N4 are satisfied, and further, (5 × M3) <M4 is satisfied. , (5 × M3) <M4 may not be satisfied.

(3) The shape of the ground electrode tip 39 and the ground electrode main body 31 of the ground electrode 30 of the spark plug 100 of the above embodiment is an example, and is not limited thereto. For example, the ground electrode tip 39 may have a cylindrical shape or an octagonal pillar shape. Further, in the above embodiment, the first discharge surface 295 and the second discharge surface 391 are vertically discharge type spark plugs facing each other in the axial direction, but instead of this, the first discharge surface and the second discharge surface are It may be a lateral discharge type spark plug facing in a direction perpendicular to the axis line.

(4) When the center electrode main body 21 and the center electrode tip 29 are joined by laser welding and a fused portion is formed between the center electrode main body 21 and the center electrode tip 29, the present invention relates to the center electrode 20. May be applied to. In this case, the main body contact surface where the molten portion and the center electrode main body 21 are in contact is formed coarser than the fused portion, the center electrode tip 29, and the chip contact surface. Then, regarding the contour line of the molten portion at the portion where the center electrode tip 29 and the fused portion come into contact with each other in the cross section perpendicular to the first discharge surface 295 through the center of gravity of the first discharge surface 295, the above-mentioned virtual line VL1 for evaluation is described. The same evaluation virtual line as above is specified, the line length of the evaluation virtual line is L1, and the number of maximum points and minimum points in the evaluation virtual line is N1. Further, regarding the contour line of the molten portion at the portion where the center electrode main body 21 and the fused portion are in contact with each other, an evaluation virtual line similar to the above-mentioned evaluation virtual line VL2 is specified, and the line length of the evaluation virtual line is set to L2. Let N2 be the number of maximum points and minimum points in the evaluation virtual line. In this case, L1 <L2 and (2 × N1) <N2 may be satisfied.

(5) The specific configuration of the spark plug 100 of the above embodiment is an example and can be appropriately modified. For example, the materials, dimensions, shapes, etc. of the ground electrode tip 39, the ground electrode 30, the main metal fitting 50, the center electrode 20, the insulator 10, and the like can be variously changed. For example, the material of the main metal fitting 50 may be galvanized or nickel-plated low-carbon steel, or unplated low-carbon steel. Further, the material of the insulator 10 may be various insulating ceramics other than alumina.

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 ... Ring member, 8 ... Plate packing, 9 ... Tarku, 10 ... Insulator, 12 ... Shaft hole, 13 ... Leg length, 15 ... Step, 16 ... Step, 17 ... Tip side body, 18 ... rear end side body, 19 ... flange, 20 ... center electrode, 21 ... center electrode body, 21A ... electrode base material, 21B ... core, 23 ... head, 24 ... flange, 25 ... legs, 29 ... Center electrode tip, 30 ... Ground electrode, 31 ... Ground electrode body, 31a ... Tip, 31b ... Rear end, 35 ... Melted part, 35A ... Melted part, 35n ... Melted sagging, 39 ... Ground electrode tip, 39S ... surface, 40 ... terminal metal fittings, 41 ... cap mounting part, 42 ... flange part, 43 ... leg part, 50 ... main metal fittings, 50A ... tip surface, 51 ... tool engaging part, 52 ... mounting screw part, 53 ... Tightening part, 54 ... Seat part, 56 ... Step part, 58 ... Compression deformation part, 59 ... Through hole, 60 ... Conductive seal, 70 ... Resistor, 80 ... Conductive seal, 100 ... Spark plug, 295 ... First Discharge surface, 311 ... Inner side surface, 312 ... Connection end, 313 ... Free end, 351 ... Chip contact surface, 352 ... Main body contact surface, 353 to 356 ... Side surface, 391 ... Second discharge surface, 393 to 396 ... Side surface, 400 ... Fixed base, 500 ... Holding member, BS ... Chip joint surface, CF1 ... 1st cross section, CF2 ... 2nd cross section, RG1 ... 1st contact range, RG2 ... 2nd contact range, OL1 to OL4 ... Contour line, VL1 to VL4 ... Virtual line for evaluation

Claims (4)

Equipped with a ground electrode and a center electrode,
At least one of the ground electrode and the center electrode is a spark plug including an electrode body, an electrode tip having a discharge surface, and a molten portion formed between the electrode body and the electrode tip. hand,
In the first cross section that passes through the center of gravity of the discharge surface and is perpendicular to the discharge surface.
The range in the direction parallel to the discharge surface where the molten portion and the electrode tip are in contact and the melted portion and the electrode body are in contact is defined as the first contact range.
Of the contour lines of the molten portion in the first contact range, the portion in contact with the electrode tip is referred to as the first contour line, and the portion in contact with the electrode body is referred to as the second contour line.
Of the directions perpendicular to the discharge surface, the direction from the electrode body toward the electrode chip is defined as the first direction, and the direction opposite to the first direction is defined as the second direction.
The first contact range is divided in the direction parallel to the discharge surface at intervals of 0.05 mm to specify a plurality of first sections.
The position in the direction parallel to the discharge surface is the position of the center of the first section, and the position in the direction perpendicular to the discharge surface is from the end of the first contour line in the first section in the first direction. The point that is the center position of the range up to the end in the second direction is defined as the first point of the first section.
The position in the direction parallel to the discharge surface is the position of the center of the first section, and the position in the direction perpendicular to the discharge surface is the position from the end in the first direction of the second contour line in the first section. The point that is the center position of the range up to the end in the second direction is defined as the second point of the first section.
The line length of the first line connecting the plurality of first points corresponding to the plurality of the first sections is L1, and the number of maximum points and minimum points in the first line is N1.
When the line length of the second line connecting the plurality of the second points corresponding to the plurality of the first sections is L2 and the number of maximum points and minimum points in the second line is N2.
A spark plug characterized by satisfying L1 <L2 and (2 × N1) <N2. The spark plug according to claim 1.
On the first line
The maximum point located between the two minimum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the first maximum point.
The minimum point located between the two maximum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the first minimum point.
On the second line,
The maximum point located between the two minimum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the second maximum point.
When the minimum point located between the two maximum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the second minimum point,
The total number M1 of the first maximum point and the first minimum point and the total number M2 of the second maximum point and the second minimum point are (5 × M1) <M2. A spark plug characterized by satisfying. The spark plug according to claim 1 or 2.
In a second cross section that passes through the center of gravity of the discharge surface, is perpendicular to the discharge surface, and is perpendicular to the first cross section.
The range in the direction parallel to the discharge surface where the molten portion and the electrode tip are in contact and the melted portion and the electrode body are in contact is defined as the second contact range.
Of the contour lines of the molten portion in the second contact range, the portion in contact with the electrode tip is referred to as a third contour line, and the portion in contact with the electrode body is referred to as a fourth contour line.
The second contact range is divided in the direction parallel to the discharge surface at intervals of 0.05 mm to specify a plurality of second sections.
The position in the direction parallel to the discharge surface is the position of the center of the second section, and the position in the direction perpendicular to the discharge surface is the position from the end in the first direction of the third contour line in the second section. The point that is the center position of the range up to the end in the second direction is defined as the third point of the second section.
The position in the direction parallel to the discharge surface is the position of the center of the second section, and the position in the direction perpendicular to the discharge surface is the position from the end in the first direction of the fourth contour line in the second section. The point that is the center position of the range up to the end in the second direction is defined as the fourth point of the second section.
The line length of the third line connecting the plurality of the third points corresponding to the plurality of the second sections is L3, and the number of maximum points and minimum points in the third line is N3.
When the line length of the fourth line connecting the plurality of the fourth points corresponding to the plurality of the second sections is L4 and the number of maximum points and minimum points in the fourth line is N4.
A spark plug characterized by satisfying L3 <L4 and (2 × N3) <N4. The spark plug according to claim 3.
On the third line
The maximum point located between the two minimum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the third maximum point.
The minimum point located between the two maximum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the third minimum point.
On the fourth line,
The maximum point located between the two minimum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the fourth maximum point.
When the minimum point located between the two maximum points whose distance in the direction parallel to the discharge surface is 0.5 mm or less is defined as the fourth minimum point,
The total number M3 of the third maximum point and the third minimum point and the total number M4 of the fourth maximum point and the fourth minimum point are (5 × M3) <M4. A spark plug characterized by satisfying.

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