Spark plug

Abstract

To provide a spark plug capable of reducing the generation of falling of an intermediate member.SOLUTION: A spark plug comprises: an intermediate member containing a chip that has a discharge surface and has a precious metal as a main body, a main body part in which both parts of the discharge surface of the chip and a part on the opposite side are bonded to one end part, and a flange part that is expanded to the circumference of the other end part of the main body part; and a ground electrode that includes a base material bonded to the other end part side of the intermediate member via a fusion zone part. When viewing a cross section containing a shaft line of the chip passing through a center of the discharge surface, a gap opening toward a direction where the flange part is expanded is provided between the base material and the flange part.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] As a spark plug for igniting the air-fuel mixture in the combustion chamber, there is known a spark plug having a ground electrode including a tip mainly made of a precious metal, an intermediate member to which the tip is joined, and a base member to which the intermediate member is joined via a fusion zone. In the prior art disclosed in Patent Document 1, the entire end face of the intermediate member, including the flange, is in intimate contact with the base member. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2009 / 084565 Summary of the Invention [Problem to be solved by the invention]

[0004] In the prior art, the deformation of the end face including the flange of the intermediate part is restricted by the base material, so that the intermediate part and the molten part are heated by the combustion of the air-fuel mixture and cooled by the air-fuel mixture flowing into the combustion chamber, which generates thermal stress, and the molten part may crack. If the molten part breaks, the intermediate part falls off from the base material together with the tip.

[0005] The present invention has been made to solve this problem, and has an object to provide a spark plug which can reduce the occurrence of the intermediate member falling off. [Means for solving the problem]

[0006] To achieve this object, the spark plug of the present invention comprises a ground electrode having a tip having a discharge surface and made mainly of a precious metal, an intermediate member including a main body having a portion of the tip opposite the discharge surface joined to one end thereof and a flange extending around the other end of the main body, and a base material joined to the other end side of the intermediate member via a molten portion, and when viewed in a cross section including the axis of the tip passing through the center of the discharge surface, there is a gap between the base material and the flange that opens in the direction in which the flange extends. Effect of the Invention

[0007] According to the first aspect, when a cross section including the axis of the tip passing through the center of the discharge surface is viewed, between the base material of the ground electrode and the flange of the intermediate member, there is a gap that opens toward the direction in which the flange protrudes. Compared to a ground electrode in which the entire end face including the flange of the intermediate member is in close contact with the base material and the deformation of the intermediate member is restricted, the deformation of the intermediate member due to thermal expansion and contraction is permitted by the amount of the gap. This reduces the thermal stress of the intermediate member and the molten part, thereby reducing the occurrence of cracks in the molten part and the occurrence of the intermediate member falling off.

[0008] According to the second aspect, in the first aspect, the gap extends from between the base material and the flange to between the base material and the other end. Since the intermediate part can be deformed by the gap, the thermal stress in the intermediate part and the molten part can be further reduced. Therefore, the occurrence of the intermediate part falling off due to cracks in the molten part can be further reduced.

[0009] According to the third aspect, in the first or second aspect, the gap extends from between the base material and the flange to the fusion zone. Since the intermediate part can be deformed by a large amount corresponding to the gap, the thermal stress of the intermediate part and the fusion zone can be further reduced. Therefore, the occurrence of the intermediate part falling off due to cracks in the fusion zone can be further reduced. [Brief description of the drawings]

[0010] [Figure 1] 1 is a half-sectional view of a spark plug according to a first embodiment. [Diagram 2] FIG. 4 is a cross-sectional view of a ground electrode. [Diagram 3] 1 is a cross-sectional view of a component having a chip joined to an intermediate member and a base material. FIG. [Figure 4] FIG. 11 is a cross-sectional view of a ground electrode of a spark plug according to a second embodiment. [Diagram 5] FIG. 11 is a cross-sectional view of a ground electrode of a spark plug according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 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 O. In Fig. 1, the lower side of the paper surface refers to the leading end side of the spark plug 10, and the upper side of the paper surface refers to the rear end side of the spark plug 10 (the same applies to Figs. 2 to 5). As shown in Fig. 1, the spark plug 10 includes a center electrode 13 and a ground electrode 18. The center electrode 13 is disposed in an insulator 11, and the ground electrode 18 is connected to a metallic shell 16 disposed in the insulator 11.

[0012] The insulator 11 is a substantially cylindrical member having an axial hole 12 along the axis O. The insulator 11 is made of ceramics such as alumina, which has excellent mechanical properties and insulating properties at high temperatures. The center electrode 13 is disposed in the axial hole 12. The center electrode 13 is a rod-shaped metal member having electrical conductivity. The center electrode 13 is formed by a cylindrical base material with a bottom, the main component of which is, for example, Ni, covering a core material the main component of which is copper. It is possible to omit the core material. A tip made mainly of a precious metal such as Pt, Rh, Ir, or Ru is provided at the tip of the center electrode 13. The tip surface 14 (the discharge surface of the tip) of the center electrode 13 is disposed outside the axial hole 12.

[0013] The center electrode 13 is electrically connected to a terminal fitting 15 in the axial hole 12. The terminal fitting 15 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and is made of a conductive metal material (such as low carbon steel). The terminal fitting 15 is fixed to the rear end of the insulator 11 with its tip side inserted into the axial hole 12.

[0014] The metal shell 16 is a substantially cylindrical member made of a conductive metal material (such as low carbon steel). The metal shell 16 surrounds the tip end side of the insulator 11 and holds the insulator 11 radially inward. A male thread 17 is formed on the outer circumferential surface of the metal shell 16. The male thread 17 is a portion that is screwed into a screw hole of an engine (not shown).

[0015] The ground electrode 18 includes a rod-shaped base material 19 made of a metal material having electrical conductivity (e.g., Ni-based alloy, etc.). The base material 19 extends from one end 19a connected to the metal shell 16 to the other end 19b. The cross section of the base material 19 perpendicular to the extending direction of the base material 19 is, for example, a rectangle, an ellipse, or a semicircle. The base material 19 is bent between the one end 19a and the other end 19b. The base material 19 may be embedded with a core material having high thermal conductivity (e.g., a material mainly composed of copper). Discharge occurs between the ground electrode 18 and the tip surface 14 of the center electrode 13.

[0016] Fig. 2 is a cross-sectional view of the ground electrode 18. A part of the base material 19 is omitted in Fig. 2 (the same applies to Figs. 3 to 5). A tip 20 is connected to the other end 19b (see Fig. 1) of the base material 19 via an intermediate member 22. The material of the tip 20 is mainly made of precious metals such as Pt, Rh, Ir, Ru, etc., and contains one or more of the precious metals such as Pt, Rh, Ir, Ru, etc., and contains 50 wt % or more of one of these precious metals.

[0017] The discharge surface 21 of the tip 20 faces the tip surface 14 of the center electrode 13 (see FIG. 1). The tip 20 extends along an axis A passing through the center 20a of the discharge surface 21. The cross section of the tip 20 perpendicular to the axis A may be, for example, a circle or a square. FIG. 2 is a cross section of the ground electrode 18 including the axis A.

[0018] The intermediate member 22 includes a main body 23 extending along the axis A and a flange 26 extending around the main body 23. The cross section of the main body 23 perpendicular to the axis A may be, for example, a circle or a square. The material of the intermediate member 22 is, for example, an alloy containing Ni as a main component.

[0019] The tip 20 is joined to one axial end 24 of the main body 23 via a first molten zone 27. The first molten zone 27 is formed by melting and solidifying components of the tip 20 and intermediate member 22. In this embodiment, the first molten zone 27 is provided around the entire circumference of the main body 23 and the tip 20, and a molten zone 27 is also formed at the position intersecting with the axis A.

[0020] The other end 25 of the main body 23 in the axial direction is joined to the base material 19 via a second molten portion 28. The flange 26 protrudes around the other end 25 of the main body 23. In the second molten portion 28, a component of the base material 19 and a component of the intermediate member 22 are melted and solidified. In this embodiment, the molten portion 28 is located at a position intersecting with the axis A. The flange 26 does not have a molten portion 28.

[0021] Between the base material 19 and the flange 26, a gap 29 is provided that opens toward the direction in which the flange 26 projects. In this embodiment, the gap 29 extends from between the base material 19 and the flange 26 to between the base material 19 and the other end 25. In a cross section including the axis A, the gap 29 appears on both sides of the axis A. Furthermore, the gap 29 extends from between the base material 19 and the flange 26 to the fusion zone 28. The gap 29 is provided around the entire circumference of the flange 26.

[0022] An example of a manufacturing method for the ground electrode 18 will be described with reference to Fig. 3. Fig. 3 is a cross-sectional view of a component 30 in which the tip 20 is joined to the intermediate part 22, and the base material 19. In the component 30, the tip 20 is joined to the main body 23 of the intermediate part 22 via a fusion zone 27. The fusion zone 27 is produced by laser welding. In the component 30, a protrusion 31 is provided at the center of an axial end face 25a of the other end 25 of the main body 23. There may be a plurality of protrusions 31.

[0023] The fusion zone 28 (see FIG. 2) is created by resistance welding. When the protrusion 31 of the part 30 is pressed against the base material 19 and electricity is started, a current flows between the part 30 and the base material 19, and the temperature of the protrusion 31 rises due to Joule heat and it softens. As it softens, the protrusion 31 collapses and the fusion zone 28 is formed. By controlling the position and size of the protrusion 31, the magnitude of the current flowing between the part 30 and the base material 19, the pressure force pressing the part 30 against the base material 19, etc., it is possible to set the distance between the outer periphery of the flange 26 and the inner end of the gap 29 and the size of the fusion zone 28.

[0024] Returning to Fig. 2, the explanation will be given. Because the ground electrode 18 has the intermediate member 22, it is possible to increase the distance between the discharge surface 21 of the tip 20 and the base material 19 by the axial length of the intermediate member 22 without lengthening the tip 20. The intermediate member 22 can reduce the flame quenching effect of the base material 19, so that the extinction of the flame kernel caused by the discharge between the center electrode 13 and the discharge surface 21 of the tip 20 can be reduced. This can improve the ignition performance of the spark plug 10.

[0025] On the other hand, since the spark plug 10 has the intermediate member 22 and the tip 20 protruding from the base material 19, the temperature changes of the intermediate member 22 and the tip 20 caused by heating due to combustion of the air-fuel mixture in the combustion chamber of the engine (not shown) and cooling due to the air-fuel mixture flowing into the combustion chamber, and the temperature difference between the tip 20 and the base material 19 are larger and more severe than those of a spark plug without the intermediate member 22. Therefore, the thermal stress generated in the intermediate member 22 and the molten portion 28 due to the thermal expansion and contraction of the ground electrode 18 is larger than that of a ground electrode without the intermediate member 22.

[0026] In the spark plug 10, a gap 29 is provided between the flange 26 of the intermediate member 22 and the base material 19 in a harsh environment, the gap 29 being open toward the direction in which the flange 26 protrudes. This allows the intermediate member 22 to deform due to thermal expansion and contraction by the gap 29, as compared with a ground electrode in which the flange 26 and the end face 25a (see FIG. 3) of the intermediate member 22 are entirely (except for the fusion portion 28) in close contact with the base material 19, restricting the deformation of the intermediate member 22. Since the thermal stress of the intermediate member 22 and the fusion portion 28 can be reduced, the occurrence of cracks in the fusion portion 28 can be reduced. As a result, the occurrence of the intermediate member 22 falling off due to the destruction of the fusion portion 28 can be reduced.

[0027] Gap 29 between base material 19 and intermediate member 22 extends from between base material 19 and flange 26 to between base material 19 and the other end 25. This allows intermediate member 22 to deform more by the amount of gap 29, compared to a case in which the gap between base material 19 and flange 26 does not extend to between base material 19 and the other end 25. Since the thermal stress of intermediate member 22 and fusion portion 28 due to thermal expansion and contraction can be further reduced, the occurrence of cracks in fusion portion 28 can be further reduced.

[0028] Gap 29 extends from between base material 19 and flange 26 to fusion zone 28. This allows intermediate member 22 to deform more by the amount of gap 29, compared to a case in which the gap between base material 19 and flange 26 does not extend to fusion zone 28. Since the thermal stress of intermediate member 22 and fusion zone 28 due to thermal expansion and contraction can be further reduced, the occurrence of cracks in fusion zone 28 can be further reduced.

[0029] Since gap 29 extends from between base material 19 and flange 26 to fusion zone 28, residual stress due to resistance welding is released by gap 29. Since the tensile residual stress in intermediate member 22 and fusion zone 28 can be reduced, it is possible to prevent cracks in fusion zone 28 from being promoted by the tensile residual stress.

[0030] The gap 29 exists between the two flanges 26 appearing on both sides of the axis A in a cross section including the axis A and the base material 19, and extends from between the base material 19 and the flanges 26 to the fusion zone 28, so that the intermediate member 22 can swing by the gap 29, centered on the fusion zone 28. This makes it possible to reduce cracks in the fusion zone 28 and the intermediate member 22 that may occur when engine vibrations are transmitted to the spark plug 10.

[0031] The gap 29 is provided around the entire circumference of the flange portion 26. Since the thermal stress can be reduced around the entire circumference of the fusion portion 28, the occurrence of cracks in the fusion portion 28 can be further reduced.

[0032] A second embodiment will be described with reference to Fig. 4. In the first embodiment, a case was described in which the gap 29 between the base material 19 and the intermediate member 22 extends from between the base material 19 and the flange portion 26 to the molten portion 28. In the second embodiment, a case will be described in which the gap 29 extends from between the base material 19 and the flange portion 26 to between the other end portion 25 of the intermediate member 22 and the base material 19. In the second embodiment, the same parts as those described in the first embodiment are denoted by the same reference numerals as in the first embodiment, and the following description will be omitted.

[0033] 4 is a cross-sectional view of a ground electrode 40 of a spark plug according to the second embodiment, the cross-sectional view including an axis A. The ground electrode 40 is connected to the metallic shell 16 (see FIG. 1) in place of the ground electrode 18 of the spark plug 10 according to the first embodiment.

[0034] Between the base metal 19 of the ground electrode 40 and the flange portion 26 of the intermediate member 22, a gap 29 is provided that opens in the direction in which the flange portion 26 protrudes. In this embodiment, the gap 29 extends from between the base metal 19 and the flange portion 26 to between the base metal 19 and the other end portion 25 of the main body portion 23. The gap 29 appears on one side of the axis A in a cross section including the axis A. The gap 29 is not in contact with the molten portion 28.

[0035] Since the ground electrode 40 has the gap 29, the deformation of the intermediate member 22 due to thermal expansion and contraction is permitted by the amount of the gap 29. This reduces the thermal stress in the intermediate member 22 and the fusion zone 28, reducing the occurrence of cracks in the fusion zone 28. This reduces the occurrence of the intermediate member 22 falling off due to the destruction of the fusion zone 28.

[0036] A third embodiment will be described with reference to Fig. 5. In the second embodiment, a case was described in which the gap 29 between the base material 19 and the intermediate member 22 extends from between the base material 19 and the flange portion 26 to the main body portion 23. In the third embodiment, a case in which the gap 29 is provided between the base material 19 and the flange portion 26 will be described. In the third embodiment, the same parts as those described in the first embodiment are denoted by the same reference numerals as in the first embodiment, and the following description will be omitted.

[0037] 5 is a cross-sectional view of a ground electrode 50 of a spark plug according to the third embodiment, the cross-sectional view including the axis A. The ground electrode 50 is connected to the metallic shell 16 (see FIG. 1) in place of the ground electrode 18 of the spark plug 10 according to the first embodiment.

[0038] Between the base material 19 of the ground electrode 50 and the flange portion 26 of the intermediate member 22, a gap 29 is provided that opens toward the protruding direction of the flange portion 26. In this embodiment, the gap 29 that exists between the base material 19 and the flange portion 26 does not extend to between the base material 19 and the other end portion 25. The gap 29 appears on one side of the axis A in a cross section including the axis A.

[0039] Since the ground electrode 50 is provided with the gap 29, the intermediate member 22 is allowed to deform due to thermal expansion or contraction by the amount of the gap 29. This reduces the thermal stress in the intermediate member 22 and the fusion zone 28, reducing the occurrence of cracks in the fusion zone 28. This reduces the occurrence of the intermediate member 22 falling off due to destruction of the fusion zone 28.

[0040] Although the present invention has been described above based on the embodiment, the present invention is not limited to the above embodiment, and it can be easily assumed that various improvements and modifications are possible without departing from the spirit of the present invention. For example, the shapes of the ground electrodes 18, 40, and 50 are merely examples and may be set appropriately.

[0041] In the embodiment, the case where the discharge surface 21 of the tip 20 of the ground electrode 18, 40, 50 and the center electrode 13 face each other in the direction of the axis O has been described, but this is not necessarily limited to this. It is of course possible to provide the ground electrode such that the discharge surface 21 of the tip 20 of the ground electrode and the center electrode 13 face each other in a direction intersecting with the axis O.

[0042] In the embodiment, a case has been described in which the fusion zone 28 that joins the base material 19 and the intermediate part 22 is provided in the main body part 23 of the intermediate part 22, and is not provided in the flange part 26, but this is not necessarily limited to this. Depending on the size and position of the fusion zone 28 provided in the main body part 23, it is acceptable for a part of the fusion zone 28 to protrude into the flange part 26.

[0043] In the first embodiment, a case has been described in which the gap 29 appears on both sides of the axis A in a cross section including the axis A, but this is not necessarily limited to this. The gap 29 extending from between the base material 19 and the flange portion 26 to the fusion zone 28 may appear only on one side of the axis A. The gap 29 may or may not appear on the other side of the axis A. When the gap 29 appears on the other side of the axis A, the gap 29 may extend between the base material 19 and the main body portion 23, or may exist only between the base material 19 and the flange portion 26.

[0044] In the second and third embodiments, a case has been described in which the gap 29 appears only on one side of the axis A in a cross section including the axis A, but this is not necessarily limited to this. The gap 29 may appear on the other side of the axis A. When the gap 29 appears on the other side of the axis A, the gap 29 may extend to between the base material 19 and the main body portion 23, or may exist only between the base material 19 and the flange portion 26. [Explanation of symbols]

[0045] 10 Spark plug 18,40,50 ground electrode 19 Base material 20 Chip 21 Discharge surface 22 Intermediate parts 23 Main body 24 One end 25 Other end 26 Flange 28 Second fusion zone (fusion zone) 29 Gap A axis

Claims

1. A tip having a discharge surface and mainly made of a precious metal; an intermediate member including a main body portion having one end portion joined to a portion of the tip opposite to the discharge surface, and a flange portion extending around the other end portion of the main body portion; a base material joined to the other end side of the intermediate member via a fusion zone, When a cross section including an axis of the tip passing through the center of the discharge surface is viewed, a gap is present between the base material and the flange portion, the gap opening toward a direction in which the flange portion protrudes, The gap extends from between the base material and the flange portion to between the base material and the other end portion.

2. 2. The spark plug according to claim 1, wherein the gap extends from between the base material and the flange portion to the fusion zone.

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