JP6400049B2 - Spark plug - Google Patents

Description

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

  Conventionally, as an ignition plug used in an internal combustion engine, an ignition plug that performs a spark discharge in a gap (spark discharge gap) between a center electrode and a ground electrode has been used. In such a spark plug, various types of ground electrode tips are known. For example, Patent Document 1 discloses a configuration in which the discharge surface of the ground electrode tip is inclined with respect to the discharge surface of the center electrode tip.

JP 2003-17214 A

  Here, in order to improve the fuel efficiency of the internal combustion engine and to purify the exhaust gas, the mixture is diluted and the amount of recirculated gas (EGR gas) is increased, and the accompanying decrease in the flame propagation speed is compensated. For this reason, the flow velocity of the gas flow in the combustion chamber of the internal combustion engine tends to increase. As a result, for example, there is an increasing need to consider a phenomenon in which sparks generated in the gap between the spark plugs are blown into the gas flow (hereinafter also referred to as blowing flow). The ground electrode tip of the above technology does not sufficiently consider the flow of sparks, so when a spark flow occurs, for example, the spark may not be stable and the ignition performance of the spark plug may be reduced. there were.

  The present specification discloses a technique for improving the ignition performance of a spark plug when a spark blow occurs in the spark plug.

  The technology disclosed in the present specification can be realized as, for example, the following application examples.

Application Example 1 An insulator having a through hole;
A center electrode having a first discharge surface and held on a tip side of the through hole;
A metal shell that is disposed around a radial direction of the insulator and holds the insulator;
A rod-shaped ground electrode body having a second end joined to the tip of the metal shell, and a first end closer to the center electrode than the second end;
A ground electrode chip having a second discharge surface that is bonded to a specific side surface of the ground electrode body facing the first discharge surface at the first end of the ground electrode body, and that faces the first discharge surface;
A spark plug comprising:
Passing through the center of gravity of the second discharge surface, and passing through the center of gravity of the second discharge surface when the specific cross section is perpendicular to the second discharge surface and parallel to the axis of the ground electrode body, And in an arbitrary cross section perpendicular to the second discharge surface and having an acute angle of 45 degrees or less with respect to the specific cross section,
Of the two side surfaces of the ground electrode chip, the side surface on the first end side from the center of gravity of the second discharge surface is the first side surface, and the side surface on the second end side is the second side surface,
An acute angle between a straight line connecting the second discharge surface side end of the first side surface and the specific side surface end and a straight line L perpendicular to the second discharge surface is an inclination of the first side surface. Let angle A,
When the acute angle between the straight line L connecting the end on the second discharge surface side of the second side surface and the end on the specific side surface and the straight line L is an inclination angle B of the second side surface,
An end of the first side surface on the specific side surface is positioned closer to the first end portion than an end of the first side surface on the second discharge surface side,
A spark plug satisfying (A / 2)> B.

  According to the above configuration, the first side surface is specified in any cross section that passes through the center of gravity of the second discharge surface, is perpendicular to the second discharge surface, and has an acute angle within 45 degrees with the specific cross section. Since the end on the side surface is located closer to the first end portion than the end on the second discharge surface side of the first side surface, the spark that has flowed to the first end portion side when a spark blowing flow has occurred. It becomes easy for the discharge to move along the first side surface, and it is possible to suppress the spark discharge from moving discontinuously to the ground electrode body. As a result, the stability of the spark discharge is improved. Furthermore, since the inclination angle A of the first side surface and the inclination angle B of the second side surface satisfy (A / 2)> B, when a spark blown flow occurs, the blown spark is converted into the ground electrode. It can suppress spreading to the 2nd end part side of a main part. As a result, the flame extinguishing action by the ground electrode body can be suppressed. Therefore, the ignition performance of the spark plug can be improved when a spark blowing flow occurs.

[Application Example 2] The spark plug according to Application Example 1,
In the specific cross section,
The spark plug having an inclination angle B of the second side surface of 0 degree.

  According to the said structure, when the blowing flow of spark discharge generate | occur | produces, it can suppress more effectively that the discharged spark discharge spreads to the 2nd edge part side of a ground electrode main body.

  The technology disclosed in the present specification can be realized in various modes. For example, an ignition device using an ignition plug or an ignition plug, an internal combustion engine equipped with the ignition plug, or an ignition plug thereof This can be realized in an aspect of an internal combustion engine or the like equipped with an ignition device using the.

1 is a cross-sectional view of a spark plug 100. FIG. The figure which shows the specific cross section CFA near the front-end | tip of the spark plug 100. FIG. The figure which looked at the vicinity of the 2nd discharge surface 395 toward the front end direction FD from the rear end direction BD. It is a figure which shows cross-section CFB and CFC. The figure explaining the blowing flow of the spark discharge of embodiment. The figure explaining the blowing flow of the spark discharge of a comparison form. Sectional drawing of the ground electrode 30b of a modification. Sectional drawing of the ground electrodes 30c-30e of a modification.

A. Embodiment:
A-1. Spark plug configuration:
FIG. 1 is a cross-sectional view of a spark plug 100 of the present embodiment. The dashed line in FIG. 1 indicates the axis CO of the spark plug 100. A direction parallel to the axis CO (vertical direction in FIG. 1) is also referred to as an axis direction. A radial direction of a circle on the plane perpendicular to the axis centered on the axis CO is simply referred to as “radial direction”, and a circumferential direction of the circle is also simply referred to as “circumferential direction”. The lower direction in FIG. 1 is referred to as a front end direction FD, and the upper direction is also referred to as a rear end direction BD. The lower side in FIG. 1 is called the front end side of the spark plug 100, and the upper side in FIG. 1 is called the rear end side of the spark plug 100.

  The spark plug 100 is attached to the internal combustion engine and used to ignite the combustion gas in the combustion chamber of the internal combustion engine. The insulator 10, the center electrode 20, the ground electrode 30, the terminal fitting 40, and the metal shell 50 are provided.

  The insulator 10 is formed by firing alumina or the like. The insulator 10 is a substantially cylindrical member that extends along the axial direction and has a shaft hole 12 that is a through-hole penetrating the insulator 10. The insulator 10 includes a flange part 19, a rear end side body part 18, a front end side body part 17, a step part 15, and a leg length part 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 from the flange portion 19 and has an outer diameter smaller than the outer diameter of the flange portion 19. The long leg portion 13 is positioned on the distal end side from the distal end side body portion 17 and has an outer diameter smaller than the outer diameter of the distal end side body portion 17. The leg 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 long portion 13 and the distal end side body portion 17.

  The metal shell 50 is formed 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 an engine head (not shown) of an internal combustion engine. The metal shell 50 is formed with an insertion hole 59 penetrating along the axis CO. The metal shell 50 is disposed around the insulator 10 in the radial direction (that is, the outer periphery). That is, the insulator 10 is inserted and held in the insertion hole 59 of the metal shell 50. The tip of the insulator 10 protrudes from the tip of the metal shell 50 toward the tip side. The rear end of the insulator 10 protrudes toward the rear end side from the rear end of the metal shell 50.

  The metal shell 50 is formed between a hexagonal column-shaped tool engagement portion 51 with which a spark plug wrench engages, an attachment screw portion 52 for attachment to an internal combustion engine, and the tool engagement portion 51 and the attachment screw portion 52. And a bowl-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 metal shell 50. The gasket 5 seals a 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 metal shell 50 further includes a thin caulking portion 53 provided on the rear end side of the tool engaging portion 51, and a thin compression deformation portion 58 provided between the seat portion 54 and the tool engaging portion 51. And. An annular region formed between the inner peripheral surface of the portion of the metal shell 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 has an annular shape. Ring members 6 and 7 are arranged. Between the two ring members 6 and 7 in the said area | region, the powder of the talc (talc) 9 is filled. The rear end of the crimping portion 53 is bent radially inward and fixed to the outer peripheral surface of the insulator 10. The compression deforming portion 58 of the metal shell 50 is compressed and deformed when the crimping portion 53 fixed to the outer peripheral surface of the insulator 10 is pressed toward the distal end side during manufacture. By the compression deformation of the compression deformation portion 58, the insulator 10 is pressed toward the front end side in the metal shell 50 through the ring members 6, 7 and the talc 9. A step portion 15 (insulator side step portion) of the insulator 10 is formed by a step portion 56 (metal portion side step portion) formed on the inner periphery of the mounting screw portion 52 of the metal shell 50 through the metal annular plate packing 8. ) Is pressed. As a result, the gas in the combustion chamber of the internal combustion engine is prevented by the plate packing 8 from leaking outside through the gap between the metal shell 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 at the tip end portion 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 in the electrode base material 21A. The electrode base material 21A is formed using, for example, nickel (Ni) or an alloy containing Ni as a main component (for example, NCF600, NCF601). The core portion 21B is made of copper, which is superior in thermal conductivity to the alloy forming the electrode base material 21A, or an alloy containing copper as a main component, in this embodiment, copper.

  The center electrode main body 21 includes a flange portion 24 (also referred to as a flange portion) provided at a predetermined position in the axial direction, a head portion 23 (electrode head portion) that 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 side of the collar portion 24. The flange portion 24 is supported by a step portion 16 formed in the shaft hole 12 of the insulator 10. The distal end portion of the leg portion 25, that is, the distal end of the center electrode main body 21 protrudes toward the distal end side from the distal 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 (tip of the leg portion 25) using, for example, laser welding. The front end surface of the center electrode tip 29 is a first discharge surface 295 that forms a spark gap with a ground electrode tip 39 described later. The center electrode tip 29 is formed of a material mainly composed of a high melting point noble metal. The center electrode tip 29 is formed using, for example, a noble metal such as iridium (Ir) or platinum, 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 metal shell 50, and a ground electrode chip 39 described later in detail. The ground electrode body 31 is a rod-shaped body having a square cross section. The ground electrode main body 31 has a joining end face 312 and a free end face 311 located on the opposite side of the joining end face 312 as both end faces. The joining end surface 312 is joined to the front end surface 50A of the metal shell 50 by, for example, resistance welding. Thereby, the metal shell 50 and the ground electrode body 31 are electrically connected. The vicinity of the joint end surface 312 of the ground electrode body 31 extends in the direction of the axis CO, and the vicinity of the free end surface 311 extends in a direction perpendicular to the axis CO. The rod-shaped ground electrode main body 31 is bent by about 90 degrees in the central portion. The free end surface 311 is located closer to the center electrode 20 (center electrode tip 29) than the joining end surface 312. That is, the second end portion 31B (the end portion on the joining end surface 312 side) of the ground electrode main body 31 is joined to the tip portion (tip surface 50A) of the metal shell 50. The first end 31A (the end on the free end surface 311 side) of the ground electrode main body 31 is closer to the center electrode 20 (the center electrode tip 29) than the second end 31B.

  The ground electrode main body 31 is formed using, for example, Ni or an alloy containing Ni as a main component (for example, NCF600, NCF601). The ground electrode main body 31 is formed using a base material made of a highly corrosion-resistant metal (for example, Ni or Ni alloy) and a metal having a high thermal conductivity (for example, copper), and is embedded in the base material. And a two-layer structure including a core portion.

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

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

A-2. Configuration near the ground electrode tip 39 of the ground electrode 30:
The configuration in the vicinity of the ground electrode tip 39 of the ground electrode 30 will be further described. FIG. 2 is a view showing a specific cross section CFA obtained by cutting the vicinity of the tip of the spark plug 100 along a specific plane. The rear end surface of the ground electrode tip 39 is a second discharge surface 395 that faces the first discharge surface 295 (FIG. 1) of the center electrode tip 29. In the present embodiment, the first discharge surface 295 and the second discharge surface 395 are parallel to each other and are surfaces perpendicular to the axis CO of the spark plug 100. A gap (also referred to as a spark gap) between the first discharge surface 295 and the second discharge surface 395 is a portion where a spark discharge for igniting the combustion gas occurs.

  2 is a cross section that passes through the center of gravity GC1 of the second discharge surface 395, is perpendicular to the second discharge surface 395, and is parallel to the axis of the rod-shaped ground electrode main body 31. In the present embodiment, a line that passes through the center of gravity GC1 of the second discharge surface 395 and is perpendicular to the second discharge surface 395 coincides with the axis CO of the spark plug 100, so that the cross section CFA in FIG. It can also be said that the cross section is parallel to the axis of the rod-shaped ground electrode main body 31.

  FIG. 3 is a view of the vicinity of the second discharge surface 395 of the ground electrode tip 39 as viewed from the rear end direction BD toward the front end direction FD. The dashed line in FIG. 3 indicates the specific cross section CFA in FIG. A direction from the center of gravity GC1 of the second discharge surface 395 toward the free end surface 311 along the second discharge surface 395, that is, the right direction in FIGS. 2 and 3 is defined as a first direction D1. A direction away from the free end surface 311 along the second discharge surface 395 from the center of gravity GC1 of the second discharge surface 395, that is, a direction opposite to the first direction D1 is defined as a second direction D2.

  Of the four side surfaces intersecting the free end surface 311 of the ground electrode main body 31, the side surface facing the first discharge surface 295 is defined as a specific side surface 315. Of the four side surfaces intersecting with the free end surface 311, two side surfaces intersecting with the specific side surface 315, that is, side surfaces positioned in the vertical direction in FIG. 3 are referred to as side surfaces 313 and 314. The direction from the center of gravity GC1 of the second discharge surface 395 toward the side surface 313, that is, the downward direction in FIG. 3, is defined as the third direction D3, and the direction opposite to the third direction D3 is defined as the fourth direction D4.

  The ground electrode tip 39 is joined to the specific side surface 315 in the vicinity of the free end surface 311 of the ground electrode main body 31, that is, at the first end portion 31A. Specifically, the bottom surface 393 of the ground electrode tip 39 opposite to the second discharge surface 395 is resistance welded to the specific side surface 315 of the ground electrode body 31.

  The ground electrode tip 39 has a truncated cone shape having a second discharge surface 395, a bottom surface 393, and a side surface 392 intersecting with the second discharge surface 395 and the bottom surface 393 (FIGS. 2 and 3). The second discharge surface 395 and the bottom surface 393 are circular, and the outer diameter of the second discharge surface 395 is smaller than the outer diameter of the bottom surface 393 (FIG. 3). For this purpose, the ground electrode tip 39 has a truncated cone shape.

  The outer diameter of the bottom surface 393 is the same as the width H1 of the ground electrode body 31 in the fourth direction D4. The end of the bottom surface 393 in the fourth direction D4 reaches the side surface 314 of the ground electrode main body 31, and the end of the bottom surface 393 in the third direction D3 reaches the side surface 313 of the ground electrode main body 31. The end of the bottom surface 393 in the first direction D1 reaches the free end surface 311 of the ground electrode main body 31.

  Two side surfaces 392 appear in a cross section passing through the center of gravity GC1 and perpendicular to the second discharge surface 395. For example, the specific cross section CFA of FIG. 2 includes a first side surface 3921a on the first end 31A side (first direction D1 side) from the center of gravity GC1 and a second end 31B side (second direction D2 side) from the center of gravity GC1. Of the second side 3922a appears. The inclination angles of the two side surfaces appearing in such a cross section are a straight line connecting the end of the side surface on the second discharge surface 395 side and the end of the side surface on the specific side surface 315 side, and a straight line perpendicular to the second discharge surface 395. It can be defined as an acute angle between L and L.

  For example, in the specific cross section CFA of FIG. 2, the inclination angle Aa of the first side surface 3921a is a straight line connecting the end Pau on the second discharge surface 395 side of the first side surface 3921a and the end Pab on the specific side surface 315 side. An acute angle between the surface 395 and the perpendicular straight line L. The inclination angle Ba of the second side surface 3922a is such that the straight line connecting the end Pbu on the second discharge surface 395 side of the second side surface 3922a and the end Pbb on the specific side surface 315 side, and the straight line L perpendicular to the second discharge surface 395. Is an acute angle between. In the example of FIG. 2, the inclination angle Aa of the first side surface 3921a is about 40 degrees, and the inclination angle Ba of the second side surface 3922a is 0 degrees.

  Here, when viewed along a direction perpendicular to the second discharge surface 395 (that is, the direction of the axis CO), the center of gravity GC1 of the second discharge surface 395 is in the second direction with respect to the center of gravity GC2 of the bottom surface 393. It is shifted to D2 (FIG. 3). For this reason, the inclination angle of the side surface 392 differs depending on the position in the circumferential direction. In FIG. 3, the position in the circumferential direction of the point P0 in the second direction D2 when viewed from the center of gravity GC1 (axis line CO) of the second discharge surface 395 is a 0 degree position, and is viewed from the center of gravity GC1 of the second discharge surface 395. A position in the circumferential direction of the point P1 in the first direction D1 is set to a position of 180 degrees. The inclination angle of the side surface 392 has a minimum value at a position of 0 degrees and a maximum value at a position of 180 degrees. The inclination angle of the side surface 392 sequentially increases as the circumferential position moves from the 0 degree position to the 180 degree position.

  For example, the inclination angle Aa of the first side surface 3921a of the specific cross section CFA in FIG. 2 described above is the inclination angle of the side surface 392 at a position of 180 degrees, and thus is the maximum inclination angle of the side surface 392. Further, the inclination angle Ba of the second side surface 3922a is the minimum inclination angle of the side surface 392 because it is the inclination angle of the side surface 392 at the position of 0 degree.

  In FIG. 3, two cross-sections CFB and CFC that pass through the center of gravity GC1 and are perpendicular to the second discharge surface 395 and whose acute angle to the specific cross-section CFA is 45 degrees are indicated by one-dot broken lines. Has been.

  FIG. 4 is a diagram showing cross sections CFB and CFC. Also in the cross-section CFB of FIG. 4A, as in the specific cross-section CFA of FIG. 2, the first side surface 3921b on the first end portion 31A side (first direction D1 side) from the center of gravity GC1 and the second end from the center of gravity GC1. And the second side surface 3922b on the part 31B side (second direction D2 side) appears. In the cross-section CFB of FIG. 4A, the inclination angle Ab of the first side surface 3921b is the straight line connecting the end Pcu on the second discharge surface 395 side of the first side surface 3921b and the end Pcb on the specific side surface 315 side. An acute angle between the surface 395 and the perpendicular straight line L. The inclination angle Bb of the second side surface 3922b is a straight line connecting the end Pdu on the second discharge surface 395 side of the second side surface 3922b and the end Pdb on the specific side surface 315 side, and a straight line L perpendicular to the second discharge surface 395. Is an acute angle between.

  Similarly, also in the cross section CFC of FIG. 4B, the first side surface 3921c on the first end portion 31A side (first direction D1 side) from the center of gravity GC1 and the second end portion 31B side (second direction) from the center of gravity GC1. D2 side) second side surface 3922c appears. In the cross-section CFB of FIG. 4B, the inclination angle Ac of the first side surface 3921c is the straight line connecting the end Peu on the second discharge surface 395 side of the first side surface 3921c and the end Peb on the specific side surface 315 side. An acute angle between the surface 395 and the perpendicular straight line L. The inclination angle Bc of the second side surface 3922c is a straight line connecting the end Pfu on the second discharge surface 395 side of the second side surface 3922c and the end Pfb on the specific side surface 315 side, and a straight line L perpendicular to the second discharge surface 395. Is an acute angle between.

  In the example of FIG. 4, the inclination angles Ab and Ac of the first side surfaces 3921b and 3921c are about 30 degrees, and the inclination angle Bc of the second side surfaces 3922b and 3921c is about 5 degrees.

  In the present embodiment, any cross section that passes through the center of gravity GC1 of the second discharge surface 395, is perpendicular to the second discharge surface 395, and has an acute angle with the specific cross section CFA within 45 degrees, that is, 3, the inclination angle A of the first side surface and the inclination angle B of the second side surface satisfy (A / 2)> B in an arbitrary cross section passing through the hatched region. That is, the inclination angle A of the first side surface is larger than twice the inclination angle B of the second side surface.

  For example, in the specific cross section CFA of FIG. 2, the inclination angle Aa of the first side surface 3921a and the inclination angle Ba of the second side surface 3922a satisfy (Aa / 2)> Ba. In the cross section CFB of FIG. 4A, the inclination angle Ab of the first side surface 3921b and the inclination angle Bb of the second side surface 3922b satisfy (Ab / 2)> Bb. In the cross section CFC in FIG. 4B, the inclination angle Ac of the first side surface 3921c and the inclination angle Bc of the second side surface 3922c satisfy (Ac / 2)> Bc.

  In the present embodiment, in any cross section that passes through the center of gravity GC1 of the second discharge surface 395, is perpendicular to the second discharge surface 395, and has an acute angle of 45 degrees or less with the specific cross section CFA, The end of the first side surface on the specific side surface 315 side is more radial than the end of the first side surface on the second discharge surface 395 side on the first end portion 31A side (first direction D1 side), that is, the center of gravity GC1. It is located outside.

  For example, in the specific cross section CFA of FIG. 2, the end Pab on the specific side 315 side of the first side 3921a is closer to the first end 31A (first side than the end Pau on the second discharge surface 395 side of the first side 3921a. In the direction D1 side).

  For example, in the cross-sections CFB and CFC of FIG. 4, the ends Pcb and Peb on the specific side 315 side of the first side surfaces 3921b and 3921c are more than the ends Pcu and Peu on the second discharge surface 395 side of the first side surfaces 3921b and 3921c. It is located on the first end 31A side (first direction D1 side).

  In the specific cross section CFA in FIG. 2, the inclination angle Ba of the second side surface 3922a is zero. Therefore, the end Pbb on the specific side 315 side of the second side 3922a and the end Pbu on the second discharge surface 395 side of the second side 3922a have the same radial position. On the other hand, in the cross-sections CFB and CFC of FIG. It is located on the second end 31B side (second direction D2 side), that is, on the outside in the radial direction.

  According to the present embodiment described above, an arbitrary angle that passes through the center of gravity GC1 of the second discharge surface 395, is perpendicular to the second discharge surface 395, and has an acute angle of 45 degrees or less with the specific cross section CFA. In the cross section, the end (for example, Pab, Pcb, Peb) of the first side surface (for example, 3921a, 3921b, 3921c) is the second discharge surface of the first side surface (for example, 3921a, 3921b, 3921c). It is located on the first end portion 31A side (that is, on the outside in the radial direction) from the end on the 395 side (for example, Pau, Pcu, Peu). For this reason, when a spark flow occurs, the spark discharge that has flowed toward the first end portion 31 </ b> A side easily moves along the first side surface, and the spark discharge discontinuously moves to the ground electrode body 31. It can suppress moving.

  FIG. 5 is a diagram for explaining the flow of spark discharge according to the embodiment. FIG. 5 shows a cross-sectional view of the specific cross-section CFA as in FIG. In order to improve the fuel efficiency of the internal combustion engine and purify the exhaust gas, the air-fuel mixture is diluted and the EGR gas is increased. To compensate for the decrease in the flame propagation speed, the gas in the combustion chamber of the internal combustion engine The flow velocity tends to increase. Gas flow in various directions such as a tumble flow and a swirl flow can also occur near the spark discharge gap of the spark plug 100.

  FIG. 5 illustrates how the spark discharge is blown by such a gas flow. A path E1 indicates the path of the spark discharge immediately after the spark discharge is generated. Since the generated spark discharge is caused to flow by the gas flow (spark discharge flow), the path of the spark discharge changes, for example, to paths E2 to E4 with the passage of time. As shown in FIG. 5, at the end of the second discharge surface 395 of the ground electrode tip 39, the spark discharge is more likely to occur as the angle θ formed by the second discharge surface 395 and the side surface 392 exceeds 90 degrees. The spark discharge path tends to move continuously and smoothly from the end of the discharge surface 395 to the side surface 392. The term “spark discharge moves continuously” means that once a spark discharge disappears (also referred to as a blow-out of a spark discharge), the spark discharge does not occur again (also referred to as a multiple discharge). It means that the discharge moves. In the present embodiment, the end (for example, Pab, Pcb, Peb) on the specific side surface 315 side of the first side surface (for example, 3921a, 3921b, 3921c) is the second side of the first side surface (for example, 3921a, 3921b, 3921c). It is located on the first end portion 31A side (that is, on the outside in the radial direction) from the end on the discharge surface 395 side (for example, Pau, Pcu, Peu). For this reason, since the angle between the second discharge surface 395 and the first side surface exceeds 90 degrees, the spark discharge that has flowed to the first end portion 31A side is the first side surface (for example, FIG. 5). 3921a). As a result, the spark discharge that has flowed is stabilized and easily spread in the direction of the first side surface (for example, 3921a in FIG. 5) (that is, the first end portion 31A side).

  FIG. 6 is a diagram for explaining the blowing flow of the spark discharge of the comparative form. In the example of FIG. 6, a cross-sectional view corresponding to the specific cross-section CFA of FIG. 5 is shown for the comparative example. In the comparative embodiment, the inclination angle of the first side surface 3921x is 0 degree. That is, the end Pxb on the specific side 315 side of the first side surface 3921x has the same radial position as the end Pxu on the second discharge surface 395 side of the first side surface 3921x. Other configurations of the comparative form are the same as those of the embodiment. In the comparative embodiment, compared with the embodiment, the spark discharge that has flowed toward the first end portion 31A cannot smoothly move to the first side surface 3921x. For example, the multiple discharge described above occurs and the spark discharge does not occur. It will be continuous. Specifically, as shown in the example of FIG. 6, the flow of the spark discharge that has flowed is from the paths Ex1 and Ex2 connecting the first discharge surface 295 and the second discharge surface 395 to the first discharge surface 295 and the ground. It moves to the path Ex5 connecting with the specific side surface 315 of the electrode body 31. When the spark discharge becomes discontinuous, the spark discharge is not stable, and the spark discharge that has flowed is not sufficiently elongated, and the ignition performance may be lowered. In addition, when the spark discharge is generated, the consumption amount of the electrode is large, and therefore, when multiple discharge is generated, the wear resistance of the electrode may be reduced. According to this embodiment, such inconvenience can be suppressed.

  Furthermore, according to the present embodiment, any cross section that passes through the center of gravity GC1 of the second discharge surface 395, is perpendicular to the second discharge surface 395, and has an acute angle of 45 degrees or less with the specific cross section CFA. Inclination angle A (for example, Aa, Ab, Ac) of the first side surface (for example, 3921a, 3921b, 3921c) and inclination angle B (for example, Ba, for 3922a, 3922b, 3922c) of the second side surface (for example, 3922a, 3922b, 3922c). Bb, Bc) satisfies (A / 2)> B. For this reason, when the blowing flow of the spark occurs, it is possible to suppress the blown-up spark from spreading to the second end portion 31B side of the ground electrode main body 31. As a result, the flame extinguishing action by the ground electrode body 31, that is, the thermal energy of spark discharge can be suppressed from being absorbed by the ground electrode body 31.

  The reason for this will be explained. The spark discharge is easily moved to a side surface having a large inclination angle as compared to a side surface having a small inclination angle. This is because, as described above, the spark discharge can move more smoothly as the tilt angle increases. According to the present embodiment, by satisfying (A / 2)> B, the spark discharge is caused by the blowing flow to center on a position in the circumferential direction of 0 degrees as viewed from the second end portion 31B side, that is, the center of gravity GC1. The movement within the range of ± 45 degrees is suppressed. And by satisfying (A / 2)> B, the spark discharge is caused by the blowing flow to be ± 45 degrees centered on the circumferential position of 180 degrees as viewed from the first end portion 31A side, that is, from the center of gravity GC1. Can be moved to the range. As a result, it is possible to suppress the spark discharge from colliding with the ground electrode body 31, so that the flame extinguishing action by the ground electrode body 31 can be suppressed.

  The second end portion 31B of the ground electrode main body 31 is approximately located within a range of ± 30 degrees centered on a position in the circumferential direction of 0 degrees as viewed from the center of gravity GC1. Therefore, the above-described (A / 2)> B is satisfied in a range of ± 45 degrees that is slightly wider than a range of ± 30 degrees where the second end portion 31B of the ground electrode body 31 is located. Thereby, it is possible to appropriately suppress the spark discharge from colliding with the ground electrode main body 31.

  As can be seen from the above description, according to the present embodiment, the stability of spark discharge can be improved and the flame extinguishing action by the ground electrode body 31 can be suppressed, so that the ignition performance of the spark plug 100 can be improved.

  Furthermore, according to the present embodiment, the inclination angle Ba of the second side surface 3922a is 0 degree in the specific cross section CFA of FIG. For this reason, when the blowing flow of the spark discharge occurs, it is possible to more effectively suppress the blown-off spark discharge from spreading to the second end portion 31B side (second direction D2 side) of the ground electrode body 31. . As a result, the ignition performance of the spark plug 100 can be further improved.

  Furthermore, according to the present embodiment, the inclination angle Aa of the first side surface 3921a in the specific cross section CFA of FIG. 2 is the maximum inclination angle of the side surface 392. For this reason, when the blowing flow of the spark discharge is generated, it is possible to effectively promote the spread of the spark discharge that has flowed to the first end portion 31 </ b> A side of the ground electrode body 31. As a result, the ignition performance of the spark plug 100 can be further improved.

B. Variation:
(1) FIG. 7 is a cross-sectional view of a modified ground electrode 30b. FIG. 7 shows a cross section corresponding to the cross section CFB in FIG. In the above embodiment, the ground electrode tip 39 is joined to the ground electrode main body 31 by resistance welding. However, in a modification, the ground electrode tip 39 is joined to the ground electrode main body 31 by laser welding, for example. Yes. For this reason, in the ground electrode 30 b of FIG. 7, the welded portion 35 is formed at the boundary portion between the specific side surface 315 of the ground electrode body 31 and the bottom surface 393 of the ground electrode 30. The welded 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 welded portion 35 includes a component of the ground electrode tip 39 and a component of the ground electrode main body 31. The welded portion 35 can also be referred to as a joint portion that joins the ground electrode tip 39 and the ground electrode body 31, and can also be referred to as a bead that joins the ground electrode tip 39 and the ground electrode body 31.

  Also in the ground electrode 30b of the modified example, two side surfaces appear in a cross section that passes through the center of gravity GC1 like the cross section CFB and is perpendicular to the second discharge surface 395. Similar to the embodiment, the inclination angles of the two side surfaces are a straight line connecting the end of the side surface on the second discharge surface 395 side and the end of the side surface on the specific side surface 315 side, and a straight line perpendicular to the second discharge surface 395. It can be defined as an acute angle between L and L. For example, in the cross section CFB of FIG. 7, the inclination angle Ab of the first side surface 3921b is a straight line connecting the end Pcu on the second discharge surface 395 side and the end Pcb on the specific side surface 315 side of the first side surface 3921b. And an acute angle between the second discharge surface 395 and a straight line L perpendicular to the second discharge surface 395. The inclination angle Bb of the second side surface 3922b is a straight line connecting the end Pdu on the second discharge surface 395 side of the second side surface 3922b and the end Pdb on the specific side surface 315 side, and a straight line L perpendicular to the second discharge surface 395. Is an acute angle between.

  Also in the modified example, similar to the embodiment, in the present embodiment, the acute angle between the second discharge surface 395 and the specific cross section CFA is 45 degrees through the center of gravity GC1 of the second discharge surface 395 and perpendicular to the second discharge surface 395. In an arbitrary cross-section (for example, cross-section CFB in FIG. 7), the inclination angle A of the first side surface and the inclination angle B of the second side surface preferably satisfy (A / 2)> B. In this way, the ignition performance of the spark plug can be improved.

(2) In the above embodiment, two side surfaces (for example, the first side surface 3921a and the second side surface 3922a in FIG. 2) appearing in a cross section that passes through the center of gravity GC1 like the cross section CFB and is perpendicular to the second discharge surface 395. Is linear. However, the present invention is not limited thereto, and two or more of the two side surfaces appearing in the cross section may be curved. For example, the two side surfaces may be curved curves that protrude outward in the radial direction, or may be curved curves that protrude inward in the radial direction. Even in this case, the inclination angle of the side surface is perpendicular to the second discharge surface and the straight line connecting the second discharge surface side end of the side surface and the specific side surface end of the side surface, as in the embodiment. An acute angle between the straight line L and the straight line L.

(3) Various shapes can be adopted as the shape of the ground electrode tip 39. FIG. 8 is a cross-sectional view of a modified example of the ground electrodes 30c to 30e. FIG. 8A shows a cross section corresponding to the specific cross section CFA of FIG. 2 for the ground electrode 30c of the modification. In the ground electrode 30c of FIG. 8A, the end of the second side surface 3922a on the specific side surface 315 side is closer to the second end 31B side (second direction D2) than the end of the second side surface 3922a on the second discharge surface 395 side. Side). For this reason, the inclination angle Ba of the second side surface 3922a is not 0 degrees.

  FIG. 8B shows a cross section corresponding to the specific cross section CFA of FIG. 2 for the ground electrode 30d of the modification. In the ground electrode 30d in FIG. 8B, the end of the second side surface 3922a on the specific side surface 315 side is closer to the first end portion 31A side (first direction D1) than the end of the second side surface 3922a on the second discharge surface 395 side. Side). For this reason, the inclination angle Ba of the second side surface 3922a is not 0 degrees.

  FIG. 8C illustrates a modification of the ground electrode 30e as viewed from the rear end direction BD toward the front end direction FD. In the ground electrode 30e in FIG. 8C, the shape of the second discharge surface 395 and the shape of the bottom surface 393 are elliptical in which the length in the fourth direction D4 is shorter than the length in the first direction D1.

(4) In the spark plug 100, the materials and dimensions of the ground electrode 30, the metal shell 50, the center electrode 20, the insulator 10, and the like can be variously changed. For example, the material of the metal shell 50 may be low-carbon steel plated with zinc or nickel, or low-carbon steel that is not plated. The material of the insulator 10 may be various insulating ceramics other than alumina.

  As mentioned above, although this invention was demonstrated based on embodiment and a modification, embodiment mentioned above is for making an understanding of this invention easy, and does not limit this invention. The present invention can be changed and improved without departing from the spirit and scope of the claims, and equivalents thereof are included in the present invention.

  5 ... Gasket, 6 ... Ring member, 8 ... Plate packing, 9 ... Talc, 10 ... Insulator, 12 ... Shaft hole, 13 ... Leg length, 15 .. Step part, 16 ... Step part, 17 ... Front end side body part, 18 ... Rear end side body part, 19 ... Gutter part, 20 ... Center electrode, 21 ... Center electrode Main body, 21A ... electrode base material, 21B ... core, 23 ... head, 24 ... buttock, 25 ... leg, 29 ... center electrode tip, 30, 30b- 30e ... ground electrode, 31 ... ground electrode body, 35 ... weld, 39 ... ground electrode tip, 40 ... terminal fitting, 41 ... cap mounting part, 42 ... ４２ Part, 43 ... leg part, 50 ... metal shell, 50A ... tip surface, 51 ... tool engaging part, 52 ... mounting screw part, 53 ... caulking part, 54. .. Seat part, 56 ... Step part, 58 ... Compression deformation part, 59 ... Insertion hole, 60 ... Conductive seal, 70 ... Resistor, 80 ... Conductive seal, 100 ... spark plug, 295. .. First discharge surface, 311 ... Free end surface, 31A ... First end, 312 ... Join end surface, 31B ... Second end, 315 ... Specific side surface, 392 ... Side surface, 393 ... bottom surface, 395 ... second discharge surface, 3921a to 3921c ... first side surface, 3922a to 3922c ... second side surface

Claims (2)

An insulator having a through hole;
A center electrode having a first discharge surface and held on a tip side of the through hole;
A metal shell that is disposed around a radial direction of the insulator and holds the insulator;
A rod-shaped ground electrode body having a second end joined to the tip of the metal shell, and a first end closer to the center electrode than the second end;
A ground electrode chip having a second discharge surface that is bonded to a specific side surface of the ground electrode body facing the first discharge surface at the first end of the ground electrode body, and that faces the first discharge surface;
A spark plug comprising:
Passing through the center of gravity of the second discharge surface, and passing through the center of gravity of the second discharge surface when the specific cross section is perpendicular to the second discharge surface and parallel to the axis of the ground electrode body, And in an arbitrary cross section perpendicular to the second discharge surface and having an acute angle of 45 degrees or less with respect to the specific cross section,
Of the two side surfaces of the ground electrode chip, the side surface on the first end side from the center of gravity of the second discharge surface is the first side surface, and the side surface on the second end side is the second side surface,
An acute angle between a straight line connecting the second discharge surface side end of the first side surface and the specific side surface end and a straight line L perpendicular to the second discharge surface is an inclination of the first side surface. Let angle A,
When the acute angle between the straight line L connecting the end on the second discharge surface side of the second side surface and the end on the specific side surface and the straight line L is an inclination angle B of the second side surface,
An end of the first side surface on the specific side surface is positioned closer to the first end portion than an end of the first side surface on the second discharge surface side,
A spark plug satisfying (A / 2)> B. The spark plug according to claim 1,
In the specific cross section,
The spark plug having an inclination angle B of the second side surface of 0 degree.

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