JP2018106807A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug capable of hardly breaking a melting part.SOLUTION: An earth electrode comprises: an electrode base material in which a first end part is bonded to a main metal jig, and a second end part is faced to a center electrode; and an electrode chip formed by being bonded to the second end part of the electrode base material. The electrode chip comprises: a chip main body principally formed by a precious metal; and a medium member surrounding at least one part of a side surface of the chip main body around a whole periphery, and is constructed by having a first melting part crossing over the medium member and the chip main body and a second melting part crossing over the medium member and the electrode base material. A part formed onto the chip main body of the first melting part in a cross section vertical to an axis of the chip main body exists in a first region having a predetermined angle which is formed by two first liners passing through the axis of the chip main body, and is 45 degrees or more. The second melting part only exists in a second region other than a first region.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a spark plug, and more particularly to a spark plug in which an electrode tip containing a noble metal is provided on a ground electrode.

  The tip body mainly composed of noble metal is surrounded by an intermediate member over the entire circumference, the tip body and the intermediate member are joined at the first melting part to form an electrode tip, and the electrode tip is joined to the electrode base material of the ground electrode A spark plug is known (Patent Document 1). In the technique disclosed in Patent Document 1, the intermediate member of the electrode tip is joined to the electrode base material by the second melting portion that does not melt with the first melting portion.

JP 2009-283262 A

  However, in the above-described conventional technology, there is a possibility that the melted portion breaks due to the thermal stress caused by the thermal expansion difference between the chip body and the intermediate member.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a spark plug that can make it difficult to break a melted portion.

  In order to achieve this object, a spark plug according to the present invention includes a center electrode extending along an axis, an insulator having a center electrode disposed in an axial hole formed along the axis, and an outer periphery of the insulator. And a ground electrode joined to the metal shell. The ground electrode includes an electrode base material having a first end joined to the metal shell and a second end facing the center electrode, and an electrode tip joined to the second end of the electrode base. The electrode tip includes a tip body mainly composed of a noble metal, and an intermediate member that surrounds at least a part of a side surface of the tip body over the entire circumference, a first melting portion straddling the intermediate member and the chip body, and an intermediate member And a second molten portion straddling the electrode base material.

  In a cross section perpendicular to the axis of the chip body, a portion of the first melted portion formed in the chip body has a first angle in which an angle formed by two first straight lines passing through the axis of the chip body is 45 ° or more. It exists in an area | region, and a 2nd fusion | melting part exists only in 2nd area | regions other than a 1st area | region.

  According to the spark plug of the first aspect, in the cross section perpendicular to the axis of the chip body, the portion formed in the chip body in the first melting part straddling the intermediate member and the chip body passes through the axis of the chip body. The angle formed by the two first straight lines exists in the first region having a predetermined angle of 45 ° or more. On the other hand, the second melted portion straddling the intermediate member and the electrode base material exists only in the second region other than the first region. As a result, it is possible to secure the circumferential length of the portion of the intermediate member that exists in the first region. The elastic deformation of the intermediate member can relieve the thermal stress caused by the difference in thermal expansion between the chip body and the intermediate member, so that there is an effect that it is difficult to break the first molten part.

  According to the spark plug of the second aspect, since the electrode base material and the intermediate member are made of an alloy mainly composed of Ni or Ni, the thermal stress of the second molten portion straddling the electrode base material and the intermediate member can be alleviated. Since the first melting part contains 30 to 70% by mass of the noble metal component, the linear expansion coefficient of the first melting part in the environment where the spark plug is used can be set between the linear expansion coefficient of the chip body and the linear expansion coefficient of the intermediate member. . Since the first melting part relaxes the thermal stress between the intermediate member and the chip body, the first melting part can be hardly broken. Therefore, in addition to the effect of Claim 1, there exists an effect which can make a 1st fusion | melting part hard to fracture | rupture more.

  According to the spark plug of the third aspect, in the cross section perpendicular to the axis of the chip body, the first straight line is in contact with two adjacent second melted portions. The angle formed by the two second straight lines passing through the axis of the chip body in contact with the portion formed on the chip body in the first melting portion is 70% or less with respect to the angle formed by the two first straight lines. Therefore, it is possible to prevent the ratio of the first melted portion relative to the portion existing in the first region of the intermediate member from becoming excessive. Since the thermal deformation caused by the difference in thermal expansion between the chip body and the intermediate member can be more easily relaxed by the elastic deformation of the intermediate member, in addition to the effect of claim 1 or 2, the first molten portion can be more difficult to break. There is.

  According to the spark plug according to claim 4, at least a part of the first melted portion formed in the chip body is at least partially extended from the first end portion to the second end portion and the shaft of the electrode base material and the tip. A virtual plane perpendicular to a plane including the axis of the main body and present on the first end side of the virtual plane including the axis of the chip main body. A conductive path from the metal shell to the chip body can be secured by the first melted portion present on the first end side. Compared with the case where the 1st fusion part exists in the 2nd end side, since the electric conduction path which goes through the 1st fusion part from a metal shell to a chip body can be shortened, it is in the effect of any one of claims 1 to 3. In addition, there is an effect that it is difficult to cause loss and deterioration of characteristics during discharge.

It is a half sectional view of the spark plug in the first embodiment of the present invention. It is a top view of a ground electrode. It is sectional drawing of the ground electrode in the III-III line of FIG. It is sectional drawing of the ground electrode in the IV-IV line | wire of FIG. It is sectional drawing of the ground electrode of the spark plug in 2nd Embodiment. It is a half sectional view of the spark plug in 3rd Embodiment. It is a bottom view of the spark plug seen from the arrow VII direction of FIG. It is sectional drawing of the ground electrode in the VIII-VIII line of FIG.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a one-side cross-sectional view showing an outline view (on the left side of the paper) and a full cross-sectional view (on the right side of the paper) taken along a plane including the axis O with respect to the spark plug 10 in the first embodiment of the present invention. It is. In FIG. 1, the lower side of the drawing is referred to as the front end side of the spark plug 10, and the upper side of the drawing is referred to as the rear 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 metal shell 15, and a ground electrode 16.

  The insulator 11 is a substantially cylindrical member formed of alumina or the like that is excellent in mechanical properties and insulation at high temperatures. The insulator 11 passes through the shaft hole 12 along the axis O. The center electrode 13 is a rod-shaped electrode that is inserted into the shaft hole 12 and held by the insulator 11 along the axis O. The terminal fitting 14 is a rod-like member to which a high voltage cable (not shown) is connected, and the distal end side is disposed in the insulator 11.

  The metal shell 15 is a substantially cylindrical member fixed to a screw hole (not shown) of the internal combustion engine. The metal shell 15 is fixed to the outer periphery of the insulator 11. The ground electrode 16 is joined to a metal (for example, nickel-base alloy) electrode base material 17 whose first end 18 is joined to the tip of the metal shell 15 and a second end 19 of the electrode base material 17. The electrode tip 20 (refer FIG. 2, FIG. 3) is provided. The electrode base material 17 is a rod-shaped member whose second end 19 side is bent toward the center electrode 13 with respect to the first end 18. The electrode tip 20 of the ground electrode 16 faces the center electrode 13 through a spark gap.

  The spark plug 10 is manufactured by the following method, for example. First, the center electrode 13 is inserted into the shaft hole 12 of the insulator 11. The center electrode 13 is disposed such that the tip is exposed to the outside from the shaft hole 12. After the terminal fitting 14 is inserted into the shaft hole 12 and the conduction between the terminal fitting 14 and the center electrode 13 is ensured, the metal shell 15 to which the electrode base material 17 is bonded in advance is assembled to the outer periphery of the insulator 11. After joining the electrode tip 20 to the electrode base material 17, the electrode base material 17 is bent so that the electrode tip 20 faces the center electrode 13 in the direction of the axis O to obtain the spark plug 10.

  With reference to FIG. 2, the electrode base material 17 to which the electrode tip 20 is bonded will be described. FIG. 2 is a plan view of the ground electrode 16 (viewed from the rear end side in the axis O direction of the spark plug 10). In FIG. 2, the second end portion 19 (see FIG. 1) of the electrode base material 17 is illustrated, and the first end portion 18 side of the electrode base material 17 is not illustrated.

  The ground electrode 16 includes an electrode base material 17 and an electrode tip 20. The electrode base material 17 is an alloy mainly composed of Ni or a member made of Ni, and a recess 21 is formed at a position facing the tip of the center electrode 13 (see FIG. 1). The recess 21 is a part into which at least a part of the electrode tip 20 is fitted. The electrode tip 20 fitted in the recess 21 faces the center electrode 13 through the spark gap.

  The electrode chip 20 includes a chip body 22 and an intermediate member 25 that surrounds at least a part of the side surface 24 of the chip body 22 over the entire circumference. The chip body 22 is joined to the intermediate member 25 by the first melting part 26, and the intermediate member 25 is joined to the electrode base material 17 by the second melting part 27. Both the first melting part 26 and the second melting part 27 are provided intermittently in the circumferential direction of the electrode tip 20. In the present embodiment, the first melting part 26 and the second melting part 27 are formed to have a predetermined length by overlapping spots of the pulsed laser beam.

  The chip body 22 is a member made of a noble metal such as platinum, iridium, ruthenium, or rhodium that has a higher spark resistance than the electrode base material 17 or an alloy containing a noble metal as a main component. In the present embodiment, the chip body 22 is a plate material having a circular plan view. Further, the chip body 22 is arranged such that an axis 23 passing through its center coincides with the axis O of the center electrode 13 (see FIG. 1). The intermediate member 25 is an alloy mainly composed of Ni or a member made of Ni. In the present embodiment, the intermediate member 25 is an annular member having the same axial thickness and radial width in the circumferential direction.

  3 is a cross-sectional view of the ground electrode 16 taken along line III-III in FIG. As shown in FIG. 3, the electrode base material 17 has a shaft 28 that extends from the first end portion 18 (see FIG. 1) side to the second end portion 19. The axis 28 of the electrode base material 17 is orthogonal to the axis O (see FIG. 1). The recess 21 is a bottomed recess formed in the electrode base material 17. The electrode tip 20 is accommodated in the recess 21 with the tip body 22 slightly protruding from the electrode base material 17.

  The first melting part 26 straddling the intermediate member 25 and the chip body 22 is formed in a wedge shape (conical shape) whose cross-sectional area gradually decreases from the intermediate member 25 toward the shaft 23 of the chip body 22. The second melting part 27 is a part extending along the axis 23 of the chip body 22, and is formed in a columnar shape straddling the intermediate member 25 and the electrode base material 17. In the present embodiment, the first melting part 26 and the second melting part 27 are respectively formed at three locations.

  The first melting portion 26 is formed by irradiating a laser beam in a direction perpendicular to the shaft 23 from the side surface (outer periphery) of the intermediate member 25 with the chip body 22 inserted inside the intermediate member 25. By the first melting portion 26, the electrode tip 20 in which the tip body 22 and the intermediate member 25 are joined is produced. Since the intermediate member 25 and the chip body 22 are melted in the first melting part 26, the components of the intermediate member 25 and the chip body 22 are mixed. The component of the first melting part 26 depends on the ratio between the volume of the melted intermediate member 25 and the volume of the chip body 22.

  The second melting portion 27 irradiates a laser beam parallel to the shaft 23 toward the boundary between the intermediate member 25 and the electrode base material 17 in a state where the electrode tip 20 is fitted in the recess 21 of the electrode base material 17. , Formed on the outer periphery of the intermediate member 25. The electrode tip 20 and the electrode base material 17 (concave portion 21) may be resistance-welded before irradiating the laser beam for forming the second melted portion 27. As a laser for forming the first melting part 26 and the second melting part 27, for example, a solid laser such as a YAG laser, a disk laser, or a fiber laser can be used.

  The second melting part 27 is provided at a position separated from the first melting part 26 so as not to melt with the first melting part 26. The second melting portion 27 is formed by melting the outer peripheral portion of the intermediate member 25 and the inner peripheral portion of the recess 21 (electrode base material 17), so that the components of the intermediate member 25 and the electrode base material 17 are mixed. The component of the second melting portion 27 depends on the ratio between the volume of the melted intermediate member 25 and the volume of the electrode base material 17.

  Since the electrode chip 20 is fitted in the recess 21, the first melting part 26 exposed on the side surface of the intermediate member 25 can be accommodated in the recess 21. As a result, the first melting part 26 can be prevented from being directly exposed to the outside air. It is known that an alloy containing a noble metal tends to cause oxidative corrosion when the proportion of the noble metal contained in the component increases. However, since the first melting part 26 can be prevented from being directly exposed to the outside air, the oxidative corrosion of the first melting part 26 can be suppressed.

  The electrode base material 17 and the intermediate member 25 are made of an alloy or Ni mainly containing Ni, and the chip body 22 is made of an alloy or noble metal mainly containing a noble metal. Therefore, the linear expansion coefficient of the chip body 22 in the environment where the spark plug 10 is used is smaller than the linear expansion coefficients of the electrode base material 17 and the intermediate member 25. The 1st fusion | melting part 26 is set so that 30-70 mass% of noble metal components may be contained. Therefore, the linear expansion coefficient of the first melting portion 26 in the above-described use environment can be set between the linear expansion coefficient of the intermediate member 25 and the linear expansion coefficient of the chip body 22. Therefore, since the first melting part 26 relaxes the thermal stress between the intermediate member 25 and the chip body 22, the first melting part 26 can be hardly broken in the environment where the spark plug 10 is used.

  The elemental analysis of the first melting part 26 can be performed by, for example, EDX (energy dispersive X-ray analysis) or EPMA (electron beam microanalyzer). The analysis position of the first melting part 26 by EDX, EPMA or the like is substantially the center of the first melting part 26. This is to prevent the analysis from being performed at a position where the element concentration distribution is non-uniform, such as a portion of the first melting portion 26 close to the axis 23 of the chip body 22.

  FIG. 4 is a cross-sectional view of the ground electrode 16 taken along the line IV-IV in FIG. 3, and shows a cross section perpendicular to the axis 23 of the chip body 22. In the present embodiment, the first melting part 26 is a melting part formed by slightly shifting the irradiation position of the pulsed laser beam twice in the circumferential direction. The first melting part 26 is formed at three locations on the electrode tip 20 with a gap in the circumferential direction. The first melting part 26 includes a part 30 formed on the chip body 22 and a part 31 formed on the intermediate member 25. The boundary between the portion 30 and the portion 31 is a boundary between the chip body 22 and the intermediate member 25 (side surface 24 of the chip body 22) before the first melting portion 26 is formed (before melting).

  A portion 30 formed in the chip main body 22 in the first melting portion 26 is in the first region 33 in which an angle θ1 formed by two first straight lines 32 passing through the shaft 23 of the chip main body 22 has a predetermined angle of 45 ° or more. Exists. On the other hand, the second melting portion 27 exists only in the second region 34 other than the first region 33. In the present embodiment, the first straight line 32 is a straight line that contacts the adjacent second melting portion 27 and passes through the shaft 23 of the chip body 22.

  Since the angle θ1 formed by the two first straight lines 32 defining the first region 33 has a predetermined angle of 45 ° or more, the length of the intermediate member 25 existing in the first region 33 can be ensured. Since the intermediate member 25 between the second melting portions 27 in the first region 33 is elastically deformed and the stress generated in the first melting portion 26 due to the thermal expansion difference between the chip body 22 and the intermediate member 25 is relieved, Breakage of the 1 melting part 26 can be suppressed.

  In the present embodiment, a plurality (three) of first melting portions 26 are formed in the chip body 22, and a plurality of (three) second melting portions 27 are provided between the first melting portions 26 of the intermediate member 25. Is formed. As for the 1st field 33 and the 2nd field 34, a field is set up for every 1st fusion part 26 about each of a plurality of 1st fusion parts 26. Since all the first regions 33 satisfy the above relationship of θ1 ≧ 45 °, and all the second melted portions 27 exist only in the set second regions 34, all the first melted portions 26 are broken. Can be suppressed.

  In the present embodiment, since the chip body 22 is joined to the intermediate member 25 by the three first melting portions 26, the arbitrary first melting portion 26 includes the other two first melting portions 26, the chip body 22, and the like. Under the influence of the thermal stress due to the difference in thermal expansion, the force acting on the first melting portion 26 becomes larger than in the case of one or two first melting portions 26. In such a case, since the force can be relaxed by utilizing the elastic deformation of the intermediate member 25 and the breakage of the first melting portion 26 can be suppressed, it is particularly effective.

  A portion 30 formed in the chip main body 22 in the first melting portion 26 exists between two second straight lines 35 that are in contact with the portion 30 and pass through the shaft 23 of the chip main body 22. The angle θ2 formed by the second line 35 with respect to the angle θ1 formed by the first line 32 is set to 95% or less, preferably 70% or less.

  Here, as the volume of the first melting part 26 increases, the force acting on the first melting part 26 due to the difference in thermal expansion between the intermediate member 25 and the chip body 22 increases. However, by setting θ2 / θ1 ≦ 95%, the thermal stress caused by the difference in thermal expansion among the chip body 22, the intermediate member 25, and the electrode base material 17 can be more easily relaxed due to the elastic deformation of the intermediate member 25. As a result, the first melting part 26 and the second melting part 27 can be made more difficult to break. In particular, if θ2 / θ1 ≦ 70%, the first melting portion 26 and the second melting portion 27 can be made more difficult to break.

  The angle θ2 formed by the two second straight lines 35 is set to 20 ° or more. This is to secure a volume of the first melting part 26 that only holds the chip body 22. As a result, the first melting part 26 can hold the chip body 22 on the intermediate member 25 against the force acting on the first melting part 26 due to the thermal expansion difference between the intermediate member 25 and the chip body 22.

  The electrode base material 17 and the intermediate member 25 are made of an alloy or Ni containing Ni as a main component, and the second melting part 27 is made of an alloy or Ni containing Ni as a main component. The expansion coefficient can be made close to the linear expansion coefficient of the electrode base material 17 and the intermediate member 25. Since the thermal stress generated in the second melting part 27 can be reduced, the breakage of the second melting part 27 can be suppressed.

  If a crack occurs at the interface between the first melting part 26 and the chip body 22, the thermal stress of the first melting part 26 and the second melting part 27 is released. As a result, it is possible to suppress the electrode base material 17 from being deformed or the chip body 22 from being broken. Since it is possible to prevent the electrode base material 17 from being deformed by thermal stress, it is possible to prevent a gap from being formed between the electrode tip 20 and the recess 21, and a spark gap between the center electrode 13 (see FIG. 1) and the tip body 22 It can be prevented from becoming narrower or wider.

  The portion 30 formed in the chip body 22 of the first melting part 26 is at least partially virtual with the axis 23 perpendicular to the plane including the axis 28 of the electrode base material 17 and the axis 23 of the chip body 22. It exists on the first end 18 (see FIG. 1) side (left side in FIG. 4) of the electrode base material 17 with respect to the plane 29 (plane perpendicular to the paper surface in FIG. 4). Since the first melting part 26 connects the intermediate member 25 and the chip body 22, a conductive path from the electrode base material 17 to the chip body 22 can be secured by the first melting part 26.

  As a result, as compared with the case where the first melted portion 26 exists only on the second end portion 19 (see FIG. 1) side (right side in FIG. 4) from the virtual plane 39, the first base material 17 to the chip body 22 1 The conductive path passing through the melting portion 26 can be shortened. Since the distance of the conductive path through which the discharge current flows can be shortened, loss and characteristic deterioration can hardly occur. Therefore, it is possible to suppress the occurrence of spark discharge between the chip body 22 and the center electrode 13 (see FIG. 1).

  When the portion 30 of the first melting portion 26 exists on the first end portion 18 (see FIG. 1) side of the virtual plane 29, the first melting portion 26 is the electrode mother in the axial direction of the chip body 22. It is formed at a position overlapping the shaft 28 of the material 17. Thereby, compared with the case where the 1st fusion | melting part 26 does not overlap with the axis | shaft 28, the conductive path | route via the 1st fusion | melting part 26 from the electrode base material 17 to the chip | tip main body 22 can be shortened. Since the distance of the conductive path can be further shortened, loss and characteristic deterioration can be made less likely to occur.

  In the present embodiment, a part of the first melting part 26 exists on the second end 19 (see FIG. 1) side (right side in FIG. 4) from the virtual plane 29. Since the first melting part 26 exists on both sides of the virtual plane 29, even if a crack occurs at the interface between the first melting part 26 and the chip body 22, the first melting part 26 bites into the chip body 22. The chip body 22 can be held by the intermediate member 25.

  Next, a second embodiment will be described with reference to FIG. In the first embodiment, a description will be given of a case where the first melted portion 26 is formed by two-time irradiation of a pulsed laser and the second melted portion 27 is formed by multiple-time irradiation of a pulsed laser. did. In the second embodiment, the number of times of laser beam irradiation is different from that of the first embodiment to form the first melting portion 41, and the continuous wave laser beam is irradiated to form the second melting portion 44. explain. In addition, about the part same as the part demonstrated in 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted.

  FIG. 5 is a cross-sectional view of the ground electrode of the spark plug 40 according to the second embodiment, and shows a cross section perpendicular to the axis 23 of the chip body 22. The first melting part 41 is a melting part formed by one-time irradiation of each pulsed laser beam. In the present embodiment, the first melting part 41 is formed at two locations across the shaft 23 of the chip body 22. The first melting part 41 includes a part 42 formed on the chip body 22 and a part 43 formed on the intermediate member 25. The boundary between the portion 42 and the portion 43 is a boundary (side surface 24) between the chip body 22 and the intermediate member 25 before the first melting portion 41 is formed (before melting). The 1st fusion | melting part 41 contains 30-70 mass% of noble metal components.

  The second melting part 44 is a series of melting parts formed by scanning a continuous wave laser beam in the circumferential direction. In the present embodiment, the second melting part 44 is formed at two locations across the shaft 23 of the chip body 22.

  A portion 42 formed in the chip body 22 of the first melting portion 41 is in the first region 46 where an angle θ1 formed by two first straight lines 45 passing through the shaft 23 of the chip body 22 has a predetermined angle of 45 ° or more. Exists. On the other hand, the second melting portion 44 exists only in the second region 47 other than the first region 46. In the present embodiment, the first straight line 45 is a straight line that contacts the adjacent second melting portion 44 and passes through the shaft 23 of the chip body 22.

  A portion 42 formed on the chip main body 22 in the first melting portion 41 exists between two second straight lines 48 that are in contact with the portion 42 and pass through the shaft 23 of the chip main body 22. The angle θ2 formed by the second line 48 with respect to the angle θ1 formed by the first line 45 is set to 95% or less, preferably 70% or less.

  At least a portion 42 of the first melting portion 41 formed on the chip body 22 is at least partly closer to the first end portion 18 (FIG. 1) of the electrode base material 17 than the virtual plane 29 (plane perpendicular to the plane of FIG. 5). Reference) side (left side of FIG. 5). According to the second embodiment, the same operational effects as those of the first embodiment can be realized.

  Next, a third embodiment will be described with reference to FIGS. In the first embodiment and the second embodiment, the case where the electrode tip 20 is bonded to one electrode base material 17 of the ground electrode 16 has been described. On the other hand, in the third embodiment, in the spark plug 50 in which the two electrode base materials 56 are arranged on the ground electrode 55, the electrode tip 60 is joined to the second end portion 58 of the electrode base material 56. explain. In addition, about the part same as the part demonstrated in 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted.

  6 is a half sectional view of the spark plug 50 according to the third embodiment, FIG. 7 is a bottom view of the spark plug 50 viewed from the direction of arrow VII in FIG. 6, and FIG. 8 is a line VIII-VIII in FIG. It is sectional drawing of the ground electrode 55 in. In FIG. 6, the rear end side of the metal shell 15 is not shown.

  As shown in FIG. 6, the center electrode 51 of the spark plug 50 is joined to the rod-shaped main body 52 inserted into the shaft hole 12 and held by the insulator 11 along the axis O, and the tip of the main body 52. Chip 53. The chip 53 is a columnar member formed of a noble metal such as platinum, iridium, ruthenium, or rhodium or an alloy containing a noble metal as a main component. The tip 53 is joined to the tip of the main body 52 by a welded portion 54.

  Two ground electrodes 55 are arranged at positions that are point-symmetric with respect to the axis O at the front end of the metal shell 15. The ground electrode 55 is joined to an electrode base material 56 made of metal (for example, a nickel base alloy) whose first end portion 57 is joined to the tip of the metal shell 15 and a second end portion 58 of the electrode base material 56. The electrode tip 60 is provided. The electrode base material 17 is a rod-shaped member whose second end 19 side is bent toward the center electrode 51 with respect to the first end 18.

  The electrode chip 60 includes a chip body 61 and an intermediate member 64 that surrounds the side surface 63 of the chip body 61 over the entire circumference. The chip body 61 is a member formed of a noble metal such as platinum, iridium, ruthenium, or rhodium that has a higher resistance to spark consumption than the electrode base material 56 or an alloy containing a noble metal as a main component. In the present embodiment, the chip body 61 is an annular plate material.

  The intermediate member 64 is an alloy mainly made of Ni or an annular member made of Ni. The intermediate member 64 has a bottom portion 65 that extends inward in the radial direction and has a hole in the center, and is provided at the tip in the axis O direction. The chip body 61 is supported by the bottom portion 65 while being inserted into the intermediate member 64.

  The chip body 61 is joined to the intermediate member 64 by the first melting part 66, and the intermediate member 64 is joined to the electrode base material 56 by the second melting part 67. The second melting portion 67 is a portion extending along the axis O, and is formed in a columnar shape straddling the intermediate member 64 and the electrode base material 56. In the present embodiment, the first melting part 66 and the second melting part 67 are formed by irradiation with a pulsed laser beam.

  The chip body 61 is arranged such that an axis 62 (see FIG. 8) passing through the center of the chip body 61 coincides with the axis O of the center electrode 51 (see FIG. 6). The tip 53 of the center electrode 51 passes through the center of the tip body 61. The chip body 61 faces the side surface of the chip 53 of the center electrode 51 via a spark gap.

  As shown in FIG. 7, the electrode base material 56 has a shaft 68 extending from the first end portion 57 (see FIG. 6) side to the second end portion 58. The axis 68 of the electrode base material 56 is orthogonal to the axis O (see FIG. 6). The first melting portion 66 straddling the intermediate member 64 and the chip body 61 is formed in a wedge shape (conical shape) whose cross-sectional area gradually decreases from the intermediate member 64 toward the axis O. In the present embodiment, the first melting part 66 is formed at 10 places with a gap in the circumferential direction of the electrode tip 60, and the second melting part 67 is at 2 places in contact with the two electrode base materials 56. Is formed.

  As shown in FIG. 8, the first melting portion 66 includes a portion 70 formed on the chip body 61 and a portion 71 formed on the intermediate member 64. The boundary between the portion 70 and the portion 71 is a boundary (side surface 63) between the chip body 61 and the intermediate member 64 before the first melting portion 66 is formed (before melting). The 1st fusion | melting part 66 contains 30-70 mass% of noble metal components.

  A portion 70 formed in the chip main body 61 of the first melting portion 66 has a predetermined angle in which an angle θ1 formed by two first straight lines 72 passing through the shaft 62 (overlapping the axis O) of the chip main body 61 is 45 ° or more. It exists in the 1st area | region 73 which has. On the other hand, the second melting portion 67 exists only in the second region 74 other than the first region 73. In the present embodiment, the first straight line 72 is a straight line passing through the shaft 62 of the chip body 61 in contact with the adjacent second melting portion 67.

  A portion 70 formed in the chip body 61 of the first melting portion 66 exists between two second straight lines 75 that are in contact with the portion 70 and pass through the shaft 62 of the chip body 61. The angle θ2 formed by the second straight line 75 with respect to the angle θ1 formed by the first straight line 72 is set to 95% or less, preferably 70% or less.

  The portion 70 formed in the chip main body 61 of the first melting portion 66 is at least partly hypothesized including the axis 62 perpendicular to the plane including the axis 68 of the electrode base material 56 and the axis 62 of the chip main body 61. It exists on the first end portion 57 (see FIG. 6) side (the left and right outer sides in FIG. 8) of the electrode base material 56 with respect to the plane 69 (a plane perpendicular to the plane of FIG. 8). According to the third embodiment, the same function and effect as those of the first embodiment can be realized.

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

Example 1
The intermediate member 25 was made of a nickel alloy (Inconel 600 (registered trademark)) and had an annular shape with dimensions of an inner diameter of 2.5 mm, an outer diameter of 3.3 mm, and a thickness of 0.85 mm. The chip body 22 was made of a noble metal alloy having a composition of 80Ir-11Ru-8Rh-1Ni (numerical value is mass%), and had a disk shape with an outer diameter of 2.5 mm and a thickness of 1 mm. Various types of the first melting portion 26 (three melting portions) described in the first embodiment are formed by irradiating a plurality of locations on the outer periphery of the intermediate member 25 into which the chip body 22 is fitted with a pulsed laser beam. The electrode tip 20 was obtained. The laser beam (typical example) which formed the 1st fusion | melting part 26 was energy 1200W, and irradiation rate 24Hz.

  The ratio (mass%) of the noble metal component of the 1st fusion | melting part 26 was measured by EDX. The melting amount of the first melting part 26 was adjusted so that the ratio of the noble metal component in the first melting part 26 was changed from 25 mass% to 75 mass%.

  Next, an electrode base material 17 made of a rod-shaped nickel alloy (Inconel 600 (registered trademark)) having a rectangular section and having a first end 18 and a second end 19 is prepared, and an inner diameter 3 is provided at the second end 19. A recess 21 having a depth of 3 mm and a depth of 0.85 mm was formed. After fitting the electrode tip 20 into the recess 21 with the portion where the first melted portion 26 is formed facing the first end 18 side of the electrode base material 17, the boundary between the intermediate member 25 and the electrode base material 17 is formed. The intermediate member 25 and the electrode base material 17 were welded by the second melting part 27 formed by irradiating the laser beam, and various samples were obtained.

  The cross section of the electrode tip 20 perpendicular to the axis 23 of the tip body 22 was observed with an X-ray fluoroscope, and the angle θ of the first region 33 where the first melting part 26 was formed was determined. In this embodiment, an angle θ1 formed by two first straight lines 32 that are in contact with the second melting portion 27 and pass through the shaft 23 of the chip body 22 is defined as the angle θ of the first region 33.

  Similarly, an angle θ <b> 2 formed by two second straight lines 35 in contact with a portion 30 formed in the chip main body 22 in the first melting portion 26 and passing through the axis 23 of the chip main body 22 was obtained by an X-ray fluoroscope. In the second melting part 27, the ratio (θ2 / θ1) of the angle θ2 formed by the second straight line 35 to the angle θ1 formed by the first straight line 32 was set to 70%. From these samples, samples shown in Table 1 in which the angle θ of the first region 33 (the angle θ1 formed by the first straight line 32) is 35 ° to 80 ° were extracted.

  For all the samples, heating with a burner for 2 minutes so that the temperature of the second end 19 of the electrode base material 17 holding the first end 18 becomes 950 ° C., and letting it cool for 1 minute. As a cycle, a cooling test in which 1000 cycles were applied to the electrode base material 17 was performed.

  After the cooling test, the cross section of the electrode tip 20 perpendicular to the axis 23 of the tip body 22 was observed with a metal microscope, and the length of the cracks existing in the first melting part 26 was measured. The starting point of the crack present in the first melting part 26 is located at a position where the circumferential end of the first melting part 26 and the boundary between the chip body 22 and the intermediate member 25 (side surface 24 of the chip body 22) intersect. It was.

  A sample in which a crack was connected from one end to the other in the circumferential direction of one first melting portion 26 was evaluated as “broken (x)”. Cracks are not connected from end to end in the circumferential direction of the first melting portion 26, and cracks propagated to the boundary between the first melting portion 26 and the chip body 22 or the boundary between the first melting portion 26 and the intermediate member 25. The sample was evaluated as “not broken (Δ)”. Even if the crack exists in the 1st fusion | melting part 26, the crack is not connected from the end of the circumferential direction of the 1st fusion | melting part 26 to the end, and the sample which the crack progressed in the 1st fusion | melting part 26 is "preferable ( ○) ”. The results are shown in Table 1.

表１に示すように、第１領域３３の角度θが４５°以上の第１溶融部２６は破断しなかった。第１領域３３の角度θが４５°以上に設定されると、第２溶融部２７間の中間部材２５の周方向の長さを確保できるので、中間部材２５の弾性変形により、チップ本体２２と中間部材２５との熱膨脹差により第１溶融部２６に生じる応力を緩和できるものと推察される。第１領域３３の角度θが大きくなるにつれて、中間部材２５の弾性変形量は大きくなるので、中間部材２５による熱応力の緩和効果は増大する。第１溶融部２６によってチップ本体２２が中間部材２５に固定されるので、第１溶融部２６によって放電電流の導電経路を確保できることも明らかであった。

As shown in Table 1, the 1st fusion part 26 whose angle theta of the 1st field 33 is 45 degrees or more did not fracture. If the angle θ of the first region 33 is set to 45 ° or more, the circumferential length of the intermediate member 25 between the second melting portions 27 can be secured. It is presumed that the stress generated in the first melting portion 26 can be relaxed due to the difference in thermal expansion with the intermediate member 25. As the angle θ of the first region 33 increases, the amount of elastic deformation of the intermediate member 25 increases, so that the effect of mitigating thermal stress by the intermediate member 25 increases. Since the chip body 22 is fixed to the intermediate member 25 by the first melting part 26, it was also clear that the first melting part 26 can secure a conductive path for the discharge current.

  Moreover, in the 1st fusion | melting part 26 which contains 30-70 mass% of noble metal components among the samples whose angle (theta) of the 1st area | region 33 is 45 degrees or more, the crack progressed in the 1st fusion | melting part 26. FIG. When the first melting part 26 has a composition containing 30 to 70% by mass of a noble metal component, the stress generated in the first melting part 26 due to the difference in thermal expansion between the chip body 22 and the intermediate member 25 can be relaxed to such an extent that no breakage occurs. Inferred.

  In the first melting part 26 containing 25% by mass of the noble metal component, the interface between the chip body 22 and the first melting part 26 was mainly broken. It is presumed that the linear expansion coefficient of the first melting portion 26 is closer to the linear expansion coefficient of the intermediate member 25 than the linear expansion coefficient of the chip body 22. Further, in the first melting part 26 containing 75% by mass of the noble metal component, a part mainly close to the intermediate member 25 was broken. It is presumed that the linear expansion coefficient of the first melting portion 26 is closer to the linear expansion coefficient of the chip body 22 than the linear expansion coefficient of the intermediate member 25.

  Thus, when a crack progresses to the boundary of the site | parts from which a linear expansion coefficient differs, we are anxious about the rate of progress of a crack being larger than the speed which a crack progresses in the 1st fusion | melting part 26. FIG. Therefore, in order to make it difficult for cracks to propagate to the boundary between portions having different linear expansion coefficients, it is more preferable that the first melting portion 26 has a composition containing 30 to 70% by mass of a noble metal component.

(Example 2)
The angle θ of the first region 33 (the angle θ1 formed by the first straight line 32) is fixed to 60 °, and the shaft 23 of the chip body 22 is in contact with the portion 30 formed in the chip body 22 of the first melting part 26. A sample in Example 2 was obtained in the same manner as in Example 1 except that the ratio of the angle θ2 formed by the two passing second straight lines 35 to the angle θ1 formed by the first straight line 32 was varied. In addition, the ratio (mass%) of the noble metal component of the 1st fusion | melting part 26 was fixed to 50 mass%.

  All the samples were subjected to the same cooling test as in Example 1. After the thermal test, the cross section of the electrode tip perpendicular to the axis of the tip body was observed with a metal microscope. Although evaluated using the same evaluation criteria as in Example 1, among the samples evaluated as “preferable (◯)” in the evaluation, the sample in which no cracks existed in the first melting portion 26 was “excellent ( ◎) ”. The results are shown in Table 2.

表２に示すように、θ２／θ１が７０％以下の第１溶融部２６は、第１溶融部２６にクラックが存在しなかった。中間部材２５の弾性変形によって、第１溶融部２６に生じる熱応力を緩和できたと推察される。

As shown in Table 2, the first melted portion 26 having θ2 / θ1 of 70% or less had no cracks in the first melted portion 26. It is presumed that the thermal deformation generated in the first melting part 26 can be alleviated by the elastic deformation of the intermediate member 25.

  According to Example 1 and Example 2, since the intermediate member 25 relieves thermal stress, the breakage of the first melting portion 26 can be suppressed, and the chip body 22 can be stably held on the intermediate member 25. it is obvious.

  The present invention has been described above based on the embodiments. However, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It can be easily guessed. For example, the shape and number of the first melting parts 26, 41, 61 and the second melting parts 27, 44, 67, and the size and length of the first melting parts 26, 41, 61 and the second melting parts 27, 44, 67 Etc. are examples and can be set as appropriate.

  In the first embodiment, the case where the shape of the chip body 22 is a disk shape (columnar shape) has been described. However, the shape is not necessarily limited to this, and other shapes can naturally be adopted. Examples of the shape of the other chip body include a truncated cone shape, an elliptical column shape, and a polygonal column such as a triangular column and a quadrangular column.

  In the first and second embodiments, the chip body 22 is cylindrical, and in the third embodiment, the chip body 61 is annular. Therefore, the intermediate members 25 and 64 that surround the side surfaces 24 and 63 of the chip bodies 22 and 61. The case where is an annular shape has been described. However, the shape is not necessarily limited to this, and naturally, various shapes such as a cylindrical shape, an annular shape, and a rectangular tube shape can be adopted according to the shape of the chip body.

  In the first embodiment, the case where the intermediate member 25 is a bottomless annular ring has been described, but the present invention is not necessarily limited thereto. Since the intermediate member 25 only needs to surround the side surface 24 of the chip body 22, it is naturally possible to employ the bottomed intermediate member 25 provided with a bottom portion that covers the bottom of the chip body 22.

  In each of the above-described embodiments, the case where the cross section of the electrode base materials 17 and 56 is rectangular has been described. However, the present invention is not necessarily limited to this, and it is naturally possible to employ an electrode base material having another cross-sectional shape. is there. Examples of other cross-sectional shapes of the electrode base material include a circular shape, an elliptical shape, a polygonal shape such as a triangular shape and a pentagonal shape, and the like.

  In each of the above-described embodiments, the second melting portions 27, 44, 67 are formed to a certain length on the outer periphery of the intermediate members 25, 64 by superimposing pulsed laser spots or using a continuous wave laser. However, the present invention is not necessarily limited to this. It is naturally possible to form the second melted portions 27, 44, and 67 by spot welding at one or more places using a pulsed laser.

  In each of the above-described embodiments, the case where the second melting portions 27, 44, and 67 for joining the electrode tip 20 to the electrode base materials 17 and 56 are formed by laser welding is described, but the present invention is not necessarily limited thereto. It is naturally possible to join the electrode tip 20 to the electrode base materials 17 and 56 by other means. Examples of other means include arc welding and resistance welding.

  In the above embodiments, the case where the second end portions 19 and 58 of the electrode base materials 17 and 56 in which the first end portions 18 and 57 are joined to the metal shell 15 is bent has been described. However, it is not necessarily limited to this. Naturally, instead of using the bent electrode base materials 17 and 56, it is possible to use a linear electrode base material. In this case, the front end side of the metal shell 15 is extended in the direction of the axis O, the first end portion of the linear electrode base material is joined to the metal shell 15, and the second end portion of the electrode base material is connected to the center electrode 13. , 51.

  In the first and second embodiments described above, the electrode base material 17 is placed so that the axis O of the center electrode 13 and the axis 23 of the chip body 22 coincide with each other and the electrode tip 20 faces the center electrode 13 in the direction of the axis O. The case of arranging has been described. However, the present invention is not necessarily limited to this, and the positional relationship between the electrode tip 20 and the center electrode 13 can be set as appropriate. As another positional relationship between the electrode tip 20 and the center electrode 13, for example, the electrode base material 17 is arranged so that the axis O of the center electrode 13 and the axis 23 of the tip body 22 intersect, For example, the electrode base material 17 may be disposed so that the side surface and the electrode tip 20 face each other, and the electrode base material 17 may be disposed such that the shaft 28 and the axis O of the electrode base material 17 cross each other at an angle.

  In the third embodiment, the case where two electrode base materials 56 of the ground electrode 55 are joined to the metal shell 15 has been described, but the present invention is not necessarily limited thereto. Of course, the number of the electrode base materials 56 may be three or more. Also in this case, the second end portion 58 of the electrode base material 56 is joined to the outer periphery of the intermediate member 64 by the second melting portion 67.

10, 40, 50 Spark plug 11 Insulator 12 Axial hole 13, 51 Center electrode 15, Metal shell 16, 55 Ground electrode 17, 56 Electrode base material 18, 57 First end 19, 58 Second end 20, 60 Electrode tip 22, 61 Tip body 23, 62 Axis 25, 64 Intermediate member 26, 41, 66 First melting part 27, 44, 67 Second melting part 28, 68 Axis 29, 69 Virtual plane 30, 42, 70 Part 32 , 45, 72 First straight line 33, 46, 73 First region 34, 47, 74 Second region 35, 48, 75 Second straight line O Angle formed by axes θ1, θ2

Claims (4)

A center electrode extending along an axis;
An insulator in which the center electrode is disposed in an axial hole formed along the axis;
A metal shell disposed on the outer periphery of the insulator;
A ground electrode joined to the metal shell,
The ground electrode includes an electrode base material having a first end joined to the metal shell and a second end facing the center electrode, and an electrode tip joined to the second end of the electrode base. With
The electrode tip includes a tip body mainly composed of a noble metal, and an intermediate member that surrounds at least a part of a side surface of the tip body over the entire circumference,
A spark plug formed by forming a first melting portion straddling the intermediate member and the chip body, and a second melting portion straddling the intermediate member and the electrode base material,
In a cross section perpendicular to the axis of the chip body,
The portion formed in the chip body of the first melting part exists in a first region having an angle formed by two first straight lines passing through the axis of the chip body of 45 ° or more, The spark plug according to claim 1, wherein the second melting portion exists only in a second region other than the first region. The electrode base material and the intermediate member are made of Ni-based alloy or Ni,
2. The spark plug according to claim 1, wherein the first melting part contains 30 to 70 mass% of a noble metal component. In a cross section perpendicular to the axis of the chip body,
The two first straight lines are in contact with two adjacent second melted portions,
A ratio of an angle formed by two second straight lines passing through the axis of the chip main body in contact with a portion formed in the chip main body of the first melting portion to an angle formed by the two first straight lines is 70% or less. The spark plug according to claim 1 or 2, wherein:   A portion of the first melted portion formed on the chip body is at least partially extended from the first end portion to the second end portion, the electrode base material axis, and the tip body axis. 4. The spark plug according to claim 1, wherein the spark plug is located on the first end side of a virtual plane that is perpendicular to a plane that includes the axis and includes the axis of the chip body. 5. .

Images