Spark plug

Abstract

To provide a spark plug that can improve ignitability.SOLUTION: A spark plug includes an insulator having an axial hole, a center electrode disposed in the axial hole, a metallic shell disposed on the outer periphery of the insulator, and a ground electrode connected to the metallic shell. The ground electrode has one end connected to the metallic shell and another end located opposite the one end, and the other end includes a first protrusion protruding toward the center electrode and a second protrusion provided on a portion of the periphery of the first protrusion.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a spark plug. [Background technology]

[0002] The flame kernel generated by the discharge between the center electrode and ground electrode of the spark plug grows and ignites and burns the air-fuel mixture. If the flame kernel is extinguished by the flame quenching action of the ground electrode (the ground electrode absorbing the energy of the flame kernel), ignition will fail. Therefore, the prior art disclosed in Patent Document 1 provides the ground electrode with a protrusion with a small heat capacity that protrudes toward the center electrode, and generates the flame kernel by the discharge between the protrusion and the center electrode, thereby reducing the flame quenching action of the ground electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-86612 Summary of the Invention [Problem to be solved by the invention]

[0004] In the prior art, when the flow of the air-fuel mixture between the center electrode and the ground electrode is fast, the discharge path formed between the center electrode and the ground electrode is stretched by the flow, and if the discharge can no longer be maintained, the discharge path disappears and ignition performance deteriorates.

[0005] The present invention has been made to solve this problem, and has as its object to provide a spark plug that can improve ignition performance. [Means for solving the problem]

[0006] A first aspect for achieving this object comprises an insulator having an axial hole, a center electrode disposed in the axial hole, a metal shell disposed on the outer periphery of the insulator, and a ground electrode connected to the metal shell, wherein the ground electrode has one end connected to the metal shell and another end located opposite the one end, and the other end includes a first protrusion protruding toward the center electrode and having a discharge surface facing the center electrode, and a second protrusion provided at a portion of the circumferential periphery of the first protrusion and protruding toward the center electrode.

[0007] In the second embodiment, in the first embodiment, the second protrusion is located outside the range obtained by projecting the first protrusion perpendicularly onto a plane including the center of gravity of the end face of the other end and the center of gravity of the discharge surface.

[0008] In a third embodiment, in the second embodiment, the second protrusions are present on both sides of the range.

[0009] In a fourth aspect, in any one of the first to third aspects, the height of the second projections is 54% or more of the height of the first projections.

[0010] A fifth aspect is the fourth aspect, wherein the height of the second projections is equal to or less than the height of the first projections.

[0011] In a sixth aspect, in any of the first to fifth aspects, the ground electrode includes a main body portion and a flange portion extending around the main body portion, and the first protrusion is provided on the main body portion and the second protrusion is provided on the flange portion. [Effects of the Invention]

[0012] According to the present invention, the ground electrode is provided with a second protrusion at a portion of the periphery of a first protrusion that protrudes toward the center electrode. The second protrusion weakens the flow between the center electrode and the ground electrode, making it easier to maintain discharge between the center electrode and the ground electrode, thereby improving ignition performance. [Brief explanation of the drawings]

[0013] [Figure 1]1 is a half-sectional view of a spark plug according to a first embodiment. [Figure 2] 2A is a plan view of the other end of the ground electrode, and FIG. 2B is a cross-sectional view of the other end taken along line IIb-IIb. [Figure 3] FIG. 10 is a cross-sectional view of a component in which a tip is joined to an intermediate member and a base material. [Figure 4] 4(a) is a plan view of the other end of the spark plug according to the second embodiment, and FIG. 4(b) is a cross-sectional view of the other end taken along line IVb-IVb. [Figure 5] 10(a) is a plan view of the other end of the spark plug according to the third embodiment, and FIG. 10(b) is a side view of the other end. [Figure 6] 10(a) is a plan view of the other end of the spark plug according to the fourth embodiment, and FIG. 10(b) is a side view of the other end. [Figure 7] 10(a) is a plan view of the other end of the spark plug according to the fifth embodiment, and FIG. 10(b) is a side view of the other end. [Figure 8] 10(a) is a plan view of the other end of the spark plug according to the sixth embodiment, and FIG. 10(b) is a side view of the other end. [Figure 9] 10(a) is a plan view of the other end of the spark plug of the seventh embodiment, and FIG. 10(b) is a side view of the other end. [Figure 10] 13(a) is a plan view of the other end of the spark plug according to the eighth embodiment, and FIG. 13(b) is a side view of the other end. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a half-sectional view of a spark plug 10 according to a first embodiment, taken along an axis C. The lower side of Fig. 1 is the leading end side of the spark plug 10, and the upper side is the trailing end side of the spark plug 10. As shown in Fig. 1, the spark plug 10 includes an insulator 11, a center electrode 13, a metallic shell 15, and a ground electrode 16.

[0015] The insulator 11 is a substantially cylindrical member having an axial hole 12 along the axis C. The insulator 11 is made of ceramics such as alumina, which has excellent mechanical properties and insulating properties at high temperatures. A center electrode 13 is disposed in the axial hole 12 of the insulator 11.

[0016] The center electrode 13 is a rod-shaped conductor. The center electrode 13 has a cylindrical base material with a bottom, mainly composed of Ni, covering a core material mainly composed of copper. It is possible to omit the core material. A tip mainly composed of a precious metal such as Pt, Rh, Ir, or Ru is provided at the tip of the center electrode 13. It is possible to omit the tip. The tip portion of the center electrode 13 protrudes toward the tip side from the tip of the insulator 11.

[0017] The center electrode 13 is electrically connected to a metal terminal 14 inside the axial hole 12. The metal terminal 14 is a rod-shaped member to which an ignition device (not shown) is connected, and is made of a conductive metal material (such as low-carbon steel). The metal terminal 14 is fixed to the insulator 11 with its front end inserted into the axial hole 12, and protrudes from the rear end of the insulator 11. The metal shell 15 is a substantially cylindrical member made of a conductive metal material (such as low-carbon steel). The metal shell 15 is arranged on the outer periphery of the insulator 11.

[0018] The ground electrode 16 is a rod-shaped conductor made of a metal material (for example, a Ni-based alloy). One end 17 of the ground electrode 16 is connected to the metallic shell 15. The ground electrode 16 extends from the one end 17 to the other end 18, and the other end 18 is located on the tip side of the center electrode 13 with a gap therebetween. In this embodiment, the ground electrode 16 is curved between the one end 17 and the other end 18. A core material with high thermal conductivity (for example, a material mainly composed of copper) may be embedded in the ground electrode 16.

[0019] FIG. 2(a) is a plan view of the other end 18 of the ground electrode 16. FIG. 2(b) is a cross-sectional view of the other end 18 taken along line IIb-IIb. The one end 17 of the ground electrode 16 is not shown in FIGS. 2(a) and 2(b) (the same applies to FIGS. 3(a) to 10(b)). The other end 18 includes a base material 19 and a first protrusion 20 provided on a rear end surface 19a of the base material 19 facing the center electrode 13 (rear end). The base material 19 is made of a material mainly composed of Ni, and contains 50 wt% or more of Ni.

[0020] The first protrusion 20 protrudes toward the center electrode 13 (see FIG. 1). The first protrusion 20 includes a tip 21 and an intermediate member 23. The material of the tip 21 is mainly made of a precious metal such as Pt, Rh, Ir, or Ru, and includes one or more of the precious metals such as Pt, Rh, Ir, or Ru, with one of these precious metals accounting for 50 wt% or more. The discharge surface 22 of the first protrusion 20 faces the tip of the center electrode 13. The shape of the discharge surface 22 can be, for example, circular or rectangular. The tip 21 is joined to the intermediate member 23.

[0021] The intermediate member 23 includes a main body 24 and a flange 25 that extends around the main body 24. The cross-sectional shape of the main body 24 is, for example, circular or rectangular. The material of the intermediate member 23 is, for example, an alloy containing Ni as its main component.

[0022] The tip 21 is joined to the main body 24 via a first molten zone 26. The first molten zone 26 is formed by melting and solidifying components of the tip 21 and components of the intermediate member 23. In this embodiment, the first molten zone 26 is provided around the entire periphery of the main body 24 and the tip 21.

[0023] The main body portion 24 is joined to the base material 19 via the second molten zone 27. The second molten zone 27 is formed by melting and solidifying the components of the base material 19 and the components of the intermediate member 23. The first projection 20 is made up of the main body portion 24 joined to the base material 19 by the second molten zone 27, the first molten zone 26, and the tip 21.

[0024] A second protrusion 28 is provided on a portion of the periphery of the first protrusion 20. In this embodiment, one second protrusion 28 is provided on the flange portion 25, and protrudes from the flange portion 25 in the same direction as the first protrusion 20. The material of the second protrusion 28 is the same as the material of the intermediate member 23.

[0025] An example of a manufacturing method for the ground electrode 16 will be described with reference to Figure 3. Figure 3 is a cross-sectional view of a component 31 in which a tip 21 is joined to an intermediate member 23, and a base material 19. In the component 31, the tip 21 is joined to a main body 24 of the intermediate member 23 via a fusion zone 26. The fusion zone 26 is formed by laser welding. The component 31 has a protrusion 32 provided in the center of the main body 24. There may be multiple protrusions 32.

[0026] The fusion zone 27 (see FIG. 2(b)) is created by resistance welding. The part of the part 31 excluding the flange 25 is gripped with a chuck (not shown), the protrusion 32 of the part 31 is placed against the rear end surface 19a of the base material 19, and the flange 25 is pressed with the chuck to press the protrusion 32 against the base material 19. When electricity is turned on, current flows between the part 31 and the base material 19, and the protrusion 32 heats up and softens due to Joule heat. As it softens, the protrusion 32 collapses, creating the fusion zone 27.

[0027] The flange 25 pressed against the base material 19 by the chuck also softens due to the heat generated when the molten zone 27 is formed, and is deformed by the force applied by the chuck to the flange 25, causing the portion not subjected to the force of the chuck to rise along the chuck. The raised portion is the second protrusion 28. The shape and size of the second protrusion 28 can be set by controlling the shape and size of the chuck, the thickness and size of the flange 25, the magnitude of the force applied by the chuck to the flange 25, the magnitude of the current flowing between the part 31 and the base material 19, etc. The number of second protrusions 28 can be set by controlling the number of gaps in the chuck.

[0028] Returning to Figures 2(a) and 2(b), the explanation will be given. Plane 29 includes the center of gravity of end face 19b of the other end 18 of ground electrode 16 (see Figure 1) and the center of gravity 22a of discharge surface 22, and intersects with one end 17. The position of the center of gravity of end face 19b is the geometric center when end face 19b is considered as a plane figure. The position of the center of gravity 22a of discharge surface 22 is the geometric center when discharge surface 22 is considered as a plane figure. Second protrusion 28 exists outside range 30 obtained by projecting first protrusion 20 perpendicularly onto plane 29. Second protrusion 28 exists at the position where plane 29 intersects.

[0029] When the secondary voltage of the ignition coil (not shown) of the ignition device connected to the metal terminal 14 of the spark plug 10 (see FIG. 1) rises and breaks the insulation between the center electrode 13 and the ground electrode 16, a spark (hereinafter referred to as a "capacitive spark") is first generated between the center electrode 13 and the other end 18 of the ground electrode 16 by the electrical energy stored in the secondary circuit. Next, a long-lasting spark (hereinafter referred to as an "induction spark") is generated by the electromagnetic energy of the ignition coil. The generation of the induction spark continues until the energy of the ignition coil is consumed. The discharge path connecting the center electrode 13 and the other end 18 is extended by the flow of the air-fuel mixture between the center electrode 13 and the other end 18. If the flow is too strong, the discharge path cannot be maintained and disappears, resulting in a decrease in ignition performance.

[0030] According to the spark plug 10, the second projection 28 can weaken the flow perpendicular to the plane 29 between the center electrode 13 and the other end 18. In addition, a vortex is formed in the portion shaded by the second projection 28. As a result, the length of the discharge path extended by the flow can be shortened compared to when the second projection 28 is not provided, thereby reducing the loss of the discharge path and improving ignition performance.

[0031] There is no limit to the height T2 of the second protrusions 28 from the rear end face 19a relative to the height T1 of the first protrusions 20 from the rear end face 19a. However, it is preferable that the height T2 of the second protrusions 28 be 54% or more of the height T1 of the first protrusions 20, as this significantly reduces the effect of weakening the flow between the center electrode 13 and the other end 18. If the height T2 of the second protrusions 28 is less than the height T1 of the first protrusions 20, discharge between the center electrode 13 and the second protrusions 28, which occurs in preference to discharge between the center electrode 13 and the first protrusions 20, can be reduced, thereby reducing wear of the second protrusions 28 due to discharge.

[0032] The size of the second protrusions 28 in a plan view (see FIG. 2(a)) is desirably smaller than the size of the first protrusions 20 (the size of the discharge surface 22). This is to extend the life of the first protrusions 20. For example, the length of the second protrusions 28 in a direction perpendicular to the plane 29 is equal to or less than the diameter of the discharge surface 22, and the length of the second protrusions 28 in a direction parallel to the plane 29 is equal to or less than the radius of the discharge surface 22. In this embodiment, there is a gap between the top of the second protrusions 28 and the side of the first protrusions 20, but this is not limited to this. The top of the second protrusions 28 and the side of the first protrusions 20 may also be in contact.

[0033] Because the intermediate member 23 is provided at the other end 18, the distance between the discharge surface 22 of the tip 21 and the base material 19 can be increased by the thickness of the intermediate member 23 without increasing the length of the tip 21. Therefore, the amount of tip 21 used can be reduced while the flame quenching effect of the base material 19 is reduced, improving ignition performance.

[0034] Since the first protrusion 20 is provided on the main body 24 of the intermediate member 23 and the second protrusion 28 is provided on the flange 25, the flow around the first protrusion 20 can be weakened by the flange 25. As a result, the ignition performance can be further improved.

[0035] A second embodiment will be described with reference to Fig. 4. In the first embodiment, the first protrusion 20 is described as being composed of a main body 24, a first fusion zone 26, and a tip 21. In contrast, in the second embodiment, the first protrusion 33 is described as being composed of a single material. In the second embodiment, the same parts as those described in the first embodiment are denoted by the same reference numerals, and the following description will be omitted (the same applies to Figs. 5(a) to 10(b)).

[0036] FIG. 4(a) is a plan view of the other end 18 of the spark plug 10 according to the second embodiment, and FIG. 4(b) is a cross-sectional view of the other end 18 taken along line IVb-IVb. The first projection 33 is joined to the base material 19 by a fusion zone 35. The material of the first projection 33 is primarily made of a precious metal such as Pt, Rh, Ir, or Ru, and contains one or more of these precious metals, with 50 wt% or more of these precious metals. The discharge surface 34 of the first projection 33 faces the tip of the center electrode 13. The shape of the discharge surface 34 may be, for example, circular or rectangular.

[0037] A second protrusion 36 is provided around the first protrusion 33. In this embodiment, one second protrusion 36 is provided, and it protrudes from the rear end face 19a in the same direction as the first protrusion 33. The material of the second protrusion 36 is the same as the material of the base material 19.

[0038] The fusion zone 35 is created by resistance welding. The tip that will become the first protrusion 33 is gripped with a chuck (not shown), a protrusion (not shown) on the tip is placed against the rear end surface 19a of the base material 19, and the tip is pressed with the chuck to press the protrusion against the base material 19. When current begins to flow, current flows between the tip and the base material 19, and the protrusion heats up and softens due to Joule heat. As it softens, the protrusion collapses, creating the fusion zone 35.

[0039] The surface of the base material 19 against which the tip is pressed also softens due to the heat generated when the molten zone 35 is formed, and is deformed by the force applied by the chuck to the tip, rising up along the chuck. The raised portions are second protrusions 36. The shape and size of the second protrusions 36 can be set by controlling the shape and size of the chuck, the strength of the force pressing the tip against the base material 19, the strength of the current flowing between the tip and the base material 19, etc. The number of second protrusions 36 can be set by controlling the number of gaps in the chuck.

[0040] The second protrusion 36 is located outside the range 30 formed by projecting the first protrusion 33 perpendicularly onto a plane 29 that includes the center of gravity of the cross section of one end 17 of the ground electrode 16 (see FIG. 1), the center of gravity of the cross section of the other end 18, and the center of gravity 34a of the discharge surface 34. The second protrusion 36 is located at the position where the plane 29 intersects. The second protrusion 36 can weaken the flow perpendicular to the plane 29 between the center electrode 13 and the other end 18. Compared to when the second protrusion 36 is not present, the length of the discharge path generated between the center electrode 13 and the other end 18 that extends due to the flow can be shortened, thereby ensuring discharge and improving ignition performance.

[0041] The size of the second protrusion 36 in a plan view (see FIG. 4(a)) is desirably smaller than the size of the first protrusion 33 (the size of the discharge surface 34). This is to extend the life of the first protrusion 33. For example, the length of the second protrusion 36 in a direction perpendicular to the plane 29 is equal to or less than the diameter of the discharge surface 34, and the length of the second protrusion 36 in a direction parallel to the plane 29 is equal to or less than the radius of the discharge surface 34. This is because the second protrusion 36 can prevent the flow between the center electrode 13 and the other end 18 from being too weak, and the extension of the discharge path due to the flow can improve ignition performance.

[0042] A third embodiment will be described with reference to Fig. 5. In the first and second embodiments, the case where there is one second protrusion 28, 36 has been described. In contrast, in the third embodiment, the case where there are two second protrusions 37, 38 will be described.

[0043] 5(a) is a plan view of the other end 18 of the spark plug 10 in the third embodiment, and FIG. 5(b) is a side view of the other end 18. The other end 18 has two second projections 37, 38 on the flange 25 around the first projection 20. The second projections 37, 38 are made of the same material as the intermediate member 23.

[0044] The second protrusions 37, 38 are located on both sides of the first protrusion 20, outside the range 30 formed by projecting the first protrusion 20 perpendicularly to the plane 29. The second protrusions 37, 38 are located at the intersection of the plane 29. Because the second protrusions 37, 38 are located on both sides of the range 30, the flow perpendicular to the plane 29 between the center electrode 13 and the other end 18 can be further weakened compared to when there is only one second protrusion. This ensures discharge between the center electrode 13 and the other end 18, further improving ignition performance.

[0045] A fourth embodiment will be described with reference to Fig. 6. In the first to third embodiments, cases where second protrusions 28, 36, 37, and 38 are present outside of range 30 have been described. In contrast, in the fourth embodiment, a case where second protrusions 39 and 40 are present within range 30 will be described.

[0046] 6(a) is a plan view of the other end 18 of the spark plug 10 in the fourth embodiment, and FIG. 6(b) is a side view of the other end 18. The other end 18 has two second projections 39, 40 on the flange 25 around the first projection 20. The second projections 39, 40 are made of the same material as the intermediate member 23.

[0047] The second protrusions 39, 40 are present within the range 30. Because the second protrusions 39, 40 are present within the range 30, the flow parallel to the plane 29 between the center electrode 13 and the other end 18 can be weakened compared to when the second protrusions are not present within the range 30. This makes it possible to shorten the length of the discharge path due to the flow parallel to the plane 29, thereby ensuring discharge and improving ignition performance.

[0048] Because the second protrusions 39, 40 are provided on both sides of the first protrusion 20, the flow parallel to the plane 29 between the center electrode 13 and the other end 18 can be further weakened compared to when there is only one second protrusion. Since discharge between the center electrode 13 and the other end 18 can be ensured, ignition performance can be further improved.

[0049] A fifth embodiment will be described with reference to Fig. 7. In the first to third embodiments, cases where second protrusions 28, 36, 37, and 38 are present outside of range 30 are described, and in the fourth embodiment, a case where second protrusions 39 and 40 are present within range 30 is described. In contrast, in the fifth embodiment, a case where second protrusion 41 is present within range 30 and second protrusion 42 is present outside range 30 is described.

[0050] 7(a) is a plan view of the other end 18 of the spark plug 10 in the fifth embodiment, and FIG. 7(b) is a side view of the other end 18. The other end 18 has two second projections 41, 42 on the flange 25 around the first projection 20. The second projections 41, 42 are made of the same material as the intermediate member 23.

[0051] The second protrusion 41 is located within the range 30, and the second protrusion 42 is located outside the range 30. This makes it possible to weaken both the flow parallel to the plane 29 and the flow perpendicular to the plane 29 between the center electrode 13 and the other end 18. This makes it possible to shorten the length of the discharge path due to the flow in two directions, thereby ensuring discharge and improving ignition performance.

[0052] A sixth embodiment will be described with reference to Fig. 8. In the fifth embodiment, a case was described in which second protrusion 41 exists within range 30 but second protrusion 42 does not exist, and second protrusion 42 exists outside range 30 but second protrusion 41 does not exist. In the sixth embodiment, a case in which second protrusions 43 and 44 exist at the boundary of range 30 will be described.

[0053] 8(a) is a plan view of the other end 18 of the spark plug 10 in the sixth embodiment, and FIG. 8(b) is a side view of the other end 18. The other end 18 has two second projections 43, 44 on the flange 25 around the first projection 20. The second projections 41, 42 are made of the same material as the intermediate member 23.

[0054] At the other end 18, second protrusions 43, 44 are present on both sides of the first protrusion 20. Parts of the second protrusions 43, 44 are present within the range 30. Furthermore, parts of the second protrusions 43, 44 are present within the range 30a obtained by projecting the first protrusion 20 parallel to the plane 29. This makes it possible to weaken not only the flow parallel to the plane 29 and the flow perpendicular to the plane 29, but also the flow oblique to the plane 29, among the flows between the center electrode 13 and the other end 18. The length of the extension of the discharge path can be shortened by the flows in various directions, thereby ensuring discharge and improving ignition performance.

[0055] A seventh embodiment will be described with reference to Fig. 9. In the first to sixth embodiments, the cases where the height of the second protrusions 28, 36, 37, 38, 39, 40, 41, 42, 43, 44 is 54% or more of the height of the first protrusion 20 will be described. In the seventh embodiment, the case where the height of the second protrusions 45, 46 is less than 50% of the height of the first protrusion 20 will be described.

[0056] 9(a) is a plan view of the other end 18 of the spark plug 10 in the seventh embodiment, and FIG. 9(b) is a side view of the other end 18. The other end 18 has two second projections 45, 46 on the flange 25 around the first projection 20. The second projections 45, 46 are made of the same material as the intermediate member 23.

[0057] The other end 18 has second protrusions 45, 46 on both sides of the range 30. The height of the second protrusions 45, 46 relative to the height of the first protrusions 20 is less than 50%, for example, 25% or more. The flow perpendicular to the plane 29 between the center electrode 13 and the other end 18 can be weakened compared to when the second protrusions are not present, thereby ensuring discharge between the center electrode 13 and the other end 18 and improving ignition performance.

[0058] An eighth embodiment will be described with reference to Fig. 10. In the first to seventh embodiments, the height of the second protrusions 28, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, and 46 is less than 100% of the height of the first protrusion 20. In the eighth embodiment, the height of the first protrusion 20 and the height of the second protrusions 47 and 48 are equal to each other.

[0059] 10(a) is a plan view of the other end 18 of the spark plug 10 in the eighth embodiment, and FIG. 10(b) is a side view of the other end 18. The other end 18 has two second projections 47, 48 on the flange 25 around the first projection 20. The second projections 47, 48 are made of the same material as the intermediate member 23.

[0060] The other end 18 has second protrusions 47, 48 on both sides of the range 30. The second protrusions 47, 48 are the same height as the first protrusions 20. Compared to when the second protrusions are lower than the first protrusions 20, the flow perpendicular to the plane 29 between the center electrode 13 and the other end 18 can be weakened, thereby reducing the occurrence of loss of the discharge path between the center electrode 13 and the other end 18 and improving ignition performance. [Example]

[0061] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0062] The flow velocity of the mixture flowing between the center electrode and the first protrusion was calculated using a computer simulation. The main assumptions for the simulation were as follows: first protrusion height T1: 0.88 mm, first protrusion width: 1.0 mm, second protrusion width: 0.25 mm, second protrusion thickness: 0.05 mm. The second protrusion was placed adjacent to the first protrusion, and the flow velocity was 1.40 m / s when the second protrusion height T2 was 0 mm (when there was no second protrusion). The flow velocity was calculated by changing the ratio of the second protrusion height T2 to the first protrusion height T1 (T2 / T1 (%)). The calculated flow velocity and the rate of decrease in flow velocity compared to the flow velocity when T2 = 0 mm are shown in Table 1.

[0063] [Table 1]

[0064] According to Table 1, the flow velocity decreased as T2 / T1 increased. When T2 / T1 = 25%, the flow velocity reduction rate was 2.1%, while when T2 / T1 = 54%, the flow velocity reduction rate was 4.3%. When T2 / T1 = 54%, a reduction rate of over 4.0% was obtained, so it can be said that the effect of reducing flow velocity is remarkable.

[0065] Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments, and it is easily understood that various improvements and modifications are possible within the scope of the present invention. For example, the number and height of the second protrusions are merely examples and may be set as appropriate.

[0066] In the embodiment, the number of second protrusions is two or less, but this is not necessarily limited to this. Note that the number of second protrusions is preferably four or less around the first protrusions 20, 33. When there are multiple second protrusions, the intervals between the second protrusions (the distance in the circumferential direction of the first protrusions) may be equal or unequal.

[0067] In the embodiment, a case has been described in which the fusion zone 27 that joins the base material 19 and the intermediate member 23 is provided in the main body 24 of the intermediate member 23, and not in the flange 25, but this is not necessarily limited to this. Depending on the size and position of the fusion zone 27 provided in the main body 24, it is acceptable for a part of the fusion zone 27 to protrude into the flange 25.

[0068] In the embodiment, a case has been described in which the intermediate member 23 has a flange 25, but this is not necessarily limited to this. It is of course possible to omit the flange 25 of the intermediate member 23. When an intermediate member 23 without a flange 25 is resistance welded to the base material 19, a second projection protruding from the base material 19 can be provided around the first projection 20.

[0069] In the embodiment, the case where the second protrusion is formed by resistance welding has been described, but this is not necessarily limited to this. It is of course possible to omit the flange portion 25 of the intermediate member 23 and, instead of the flange portion 25, provide a second protrusion protruding from the side surface of the main body portion 24 in advance on the main body portion 24. In this case, when the first protrusion 20 including the intermediate member 23 is joined to the base material 19, the second protrusion protrudes from the periphery (base) of the first protrusion 20. Because the second protrusion is provided around the first protrusion 20, the flow between the first protrusion 20 and the center electrode 13 can be weakened, as described in the embodiment.

[0070] Alternatively, it is of course possible to provide in advance second protrusions that protrude from the flange 25 of the intermediate member 23 on the flange 25. In this case as well, when the first protrusion 20 including the intermediate member 23 is joined to the base material 19, the second protrusions protrude from the periphery of the first protrusion 20. Because the second protrusions are provided around the first protrusion 20, the flow between the first protrusion 20 and the center electrode 13 can be weakened, as described in the embodiment.

[0071] In the embodiment, the first protrusions 20, 33 and the second protrusions are provided by resistance welding on the other end 18 of the ground electrode 16, but this is not necessarily limited to this. As with the technology disclosed in Patent Document 1, it is of course possible to deform the ground electrode 16 by press forming and provide the first protrusions and the second protrusions on the rear end surface 19a of the other end 18 of the ground electrode 16.

[0072] In the embodiment, when there are multiple second protrusions, the heights of the second protrusions are the same, but this is not necessarily limited to this. When there are multiple second protrusions, it is of course possible to make the heights of the second protrusions different from each other. In this case, the height of the second protrusion is defined as the distance between the apex of the highest protrusion among the second protrusions and the rear end surface 19a. [Explanation of symbols]

[0073] 10 Spark Plugs 11 Insulators 12 Shaft hole 13 Center electrode 15 Metal body 16 Ground electrode 17 One end 18 Other end 19b End face of the other end 20,33 First protrusion 22,34 Discharge surface 22a, 34a Center of gravity of discharge surface 24 Main body 25 Tsuba 28, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48 Second protrusion 29 plane 30 range T1 Height of the first protrusion T2 Height of the second protrusion

Claims

1. an insulator having an axial hole; a center electrode disposed in the axial hole; a metallic shell disposed on the outer periphery of the insulator; a ground electrode connected to the metallic shell, the ground electrode has one end connected to the metallic shell; and an opposite end portion located opposite the one end portion, a first projection provided at the other end portion of the spark plug, the first projection protruding toward the center electrode and having a discharge surface facing the center electrode, The other end includes a second projection provided at a portion of the circumferential periphery of the first projection and projecting toward the center electrode.

2. 2. The spark plug according to claim 1, wherein the second projection is located outside a range obtained by projecting the first projection perpendicularly onto a plane including the center of gravity of the end face of the other end and the center of gravity of the discharge surface.

3. 3. The spark plug according to claim 2, wherein said second projections are present on both sides of said range.

4. 4. The spark plug according to claim 1, wherein the height of said second projections is 54% or more of the height of said first projections.

5. 5. The spark plug according to claim 4, wherein the height of said second projection is equal to or less than the height of said first projection.

6. the ground electrode includes a main body portion and a flange portion extending around the main body portion, 4. The spark plug according to claim 1, wherein the first projection is provided on the body portion, and the second projection is provided on the flange portion.

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