JP2012238449A - Method for manufacturing spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a variation in joint strength between a ground electrode and a noble metal tip in a spark plug.SOLUTION: A method for manufacturing a spark plug having a center electrode, an insulator, a main metal fitting, a ground electrode and a noble metal tip arranged at a tip end portion of the ground electrode to form a gap against the center electrode comprises: welding electrode arrangement step of arranging a welding electrode; and step of resistance-welding the noble metal tip to an inner peripheral surface of the ground electrode. The welding electrode arrangement step arranges the welding electrode such that an electrode side tip end contact portion of the welding electrode is positioned at least 0.1 mm longitudinally rearward of a tip side tip end contact portion of the noble metal tip.

Description

  The present invention relates to a method for manufacturing a spark plug.

  As a spark plug used in an internal combustion engine, a spark plug is known which performs a spark discharge in a gap (spark gap) between a noble metal tip welded to a ground electrode and a center electrode. As a method for welding the noble metal tip to the ground electrode, the noble metal tip is arranged at the end of the ground electrode, the ground electrode on which the noble metal tip is arranged is sandwiched between the two welding electrodes, and a voltage is applied between the welding electrodes to precious metal tip. There has been proposed a method of resistance-welding to a ground electrode (Patent Document 1).

JP 2002-246143 A

  In the resistance welding technique in which the ground electrode on which the noble metal tip is arranged is sandwiched between two welding electrodes, the energization area between the welding electrodes (the energization path in the ground electrode) is wide, so the energization path is not constant and the welded state There was a risk that the bonding strength would not reach the target level due to variations. In addition, since the surface of the ground electrode in contact with the welding electrode is not smooth, there is a possibility that the contact state (energization path) between the welding electrode and the ground electrode may vary and the conduction state between the welding electrodes may vary. However, in such resistance welding of noble metal tips, the actual situation is that the size of the current-carrying region and the contact state between the welding electrode and the ground electrode are not fully considered.

  An object of the present invention is to suppress variations in bonding strength between a ground electrode and a noble metal tip in a spark plug.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 A central electrode extending in the axial direction;
An insulator having an axial hole extending in the axial direction and holding the center electrode inside the axial hole;
A cylindrical metal shell disposed on the outer periphery of the insulator;
A ground electrode disposed at an end of the metal shell,
A noble metal tip disposed at the tip of the ground electrode and forming a gap with the center electrode, and a spark plug manufacturing method comprising:
Among the side surfaces of the noble metal tip, the position of the side surface on the front end side of the ground electrode coincides with the position of the end surface of the front end of the ground electrode or is positioned on the front end side in the longitudinal direction from the position of the end surface of the front end. A noble metal tip placement step of placing the noble metal tip on the inner peripheral surface of the ground electrode;
A welding electrode arrangement step of arranging a welding electrode so as to be in contact with the outer peripheral surface which is the opposite surface of the inner peripheral surface at the tip portion;
Resistance welding the noble metal tip to the inner peripheral surface;
With
In the welding electrode arrangement step, of the contact portions with the outer peripheral surface of the welding electrode, the electrode-side tip contact portion located closest to the front end side in the longitudinal direction is the contact portion with the inner peripheral surface of the noble metal tip. Among them, the method for manufacturing a spark plug, wherein the welding electrode is arranged so as to be positioned 0.1 mm or more on the rear end side in the longitudinal direction from the tip side front end contact portion positioned closest to the front end side in the longitudinal direction.

  In the spark plug manufacturing method of Application Example 1, since the welding electrode is disposed so that the electrode-side tip contact portion is positioned at least 0.1 mm longer in the longitudinal direction than the tip-side tip contact portion, the electrode-side tip contact portion A configuration in which the welding electrode is disposed so that the electrode side tip contact portion is positioned on the rear end side in the longitudinal direction by a distance shorter than 0.1 mm from the tip side tip contact portion, or the electrode side tip contact portion is longer in the longitudinal direction than the tip side tip contact portion. Compared to the configuration in which the welding electrode is disposed so as to be positioned on the distal end side, the energization region in the ground electrode can be narrowed. Therefore, since the variation in the energization path can be suppressed and made constant, the variation in welding strength can be suppressed.

Application Example 2 In the spark plug manufacturing method according to Application Example 1,
In the welding electrode arrangement step, the position of the electrode side tip contact portion is the tip side rear end contact portion located closest to the rear end side in the longitudinal direction among the contact portions with the inner peripheral surface of the noble metal tip; A method for manufacturing a spark plug, wherein the welding electrode is disposed so as to coincide with each other in the longitudinal direction or to be located closer to the rear end side in the longitudinal direction than a position of the tip side rear end contact portion.

  With such a configuration, a current-carrying region (a region that can be energized) in the ground electrode can be planar, and the current-carrying region can be further narrowed.

[Application Example 3] In the spark plug manufacturing method according to Application Example 2,
In the welding electrode arrangement step, the spark plug manufacturing method includes arranging the welding electrode such that the electrode side tip contact portion is positioned within 2.0 mm from the tip side rear end contact portion in the longitudinal direction.

  With such a configuration, it is possible to suppress the distance between the electrode-side tip contact portion and the tip-side rear end contact portion from becoming very long. The longer the distance, the longer the energization distance in the ground electrode, and the energization current decreases. Therefore, since the above-described configuration can suppress a decrease in energization current, a decrease in welding strength can be suppressed, and a period required for the resistance welding process can be shortened.

[Application Example 4] In the spark plug manufacturing method according to any one of Application Examples 1 to 3,
In the tip portion, the outer peripheral surface includes a first deforming portion that is recessed in a direction from the outer peripheral surface toward the inner peripheral surface, and a second deforming portion that protrudes in a direction from the inner peripheral surface toward the outer peripheral surface. At least one of
In the welding electrode arrangement step, the position of the electrode side tip contact portion is greater than the position of the rear end in the longitudinal direction of the deformed portion located closest to the rear end among the first deformed portion or the second deformed portion. A method for manufacturing a spark plug, wherein the welding electrode is disposed so as to be positioned at a rear end side in the longitudinal direction of 0.1 mm or more.

  With such a configuration, the welding electrode can be disposed on the outer peripheral surface of the ground electrode while avoiding the deformed portion, so that the shape and size of the contact portion with the ground electrode can be made constant, Variations can be suppressed.

Application Example 5 In the spark plug manufacturing method according to any one of Application Examples 1 to 4,
In the welding electrode placement step, the welding electrode is placed in contact with the outer peripheral surface, and the noble metal tip placed on the inner peripheral surface is opposite to the tip portion with the noble metal tip interposed therebetween. Disposing another welding electrode different from the welding electrode so as to make contact on the side, and a method for manufacturing a spark plug.

  With such a configuration, by applying a voltage between the welding electrode and another welding electrode, the tip portion and the noble metal tip can be energized, and the tip portion and the noble metal tip can be resistance-welded. .

  In addition, this invention can be implement | achieved in various aspects, for example, can also be implement | achieved with forms, such as a spark plug and the joining method of a ground electrode and a noble metal tip.

FIG. 1 is a partial cross-sectional view of a spark plug. FIG. 2 is an enlarged view of the vicinity of a tip portion of a center electrode shown in FIG. 1. It is explanatory drawing which shows the joining procedure of the noble metal chip | tip to the front-end | tip part in 1st Embodiment. It is explanatory drawing which shows the detailed arrangement position of two welding electrodes in the spark plug manufacturing method of 1st Embodiment. It is explanatory drawing which shows the detailed arrangement position of two welding electrodes in the comparative example of 1st Embodiment. It is explanatory drawing which shows the preferable arrangement position of the 2nd welding electrode in 2nd Embodiment. It is explanatory drawing which shows the detailed arrangement position of two welding electrodes in the comparative example of 2nd Embodiment. It is the 1st explanatory view showing the desirable arrangement position of the 2nd welding electrode in a 3rd embodiment. It is the 2nd explanatory view showing the desirable arrangement position of the 2nd welding electrode in a 3rd embodiment. It is explanatory drawing which shows the variation of the deformation | transformation part in 3rd Embodiment. It is 1st explanatory drawing which shows typically the front-end | tip part vicinity in the noble metal tip joining process at the time of producing 8 types of samples in 1st Example. It is the 2nd explanatory view showing typically the tip part neighborhood in precious metal tip joining processing at the time of creating eight kinds of samples in the 1st example. It is 1st explanatory drawing which shows the result obtained by the joining strength evaluation test in 1st Example. It is the 2nd explanatory view showing the result obtained by the joint strength evaluation test in the 1st example. It is explanatory drawing which shows the simulation result for pinpointing the preferable magnitude | size of the distance d2 in 1st Example. It is explanatory drawing which shows the method of the evaluation test in 2nd Example. It is explanatory drawing which shows the result obtained by the joining strength evaluation test in 2nd Example. It is explanatory drawing which shows the detailed arrangement position of the 2nd welding electrode in the spark plug manufacturing method of the modification.

A. First embodiment:
A1. Spark plug configuration:
FIG. 1 is a partial cross-sectional view of a spark plug. FIG. 2 is an enlarged view of the vicinity of the tip of the center electrode shown in FIG. 1 and 2, the axis O indicates the axis of the spark plug 100.

  As shown in FIG. 1, the spark plug 100 includes an insulator 10, a center electrode 20, a terminal fitting 40, a metal shell 50, and a ground electrode 30. The insulator 10 has a cylindrical shape extending along the axial direction OD, and an axial hole 12 extending in the axial direction OD is formed at the axial center. The insulator 10 has a cylindrical shape having an axial hole 12 extending along the axial direction OD. The metal shell 50 has a cylindrical shape extending along the axial direction OD. In the spark plug 100, the insulator 10 holding the center electrode 20 in the shaft hole 12 on the front end side and the terminal fitting 40 in the shaft hole 12 on the rear end side is arranged around the radial direction of the insulator 10 (axis line A side surface in a direction perpendicular to the direction OD) is surrounded and held by the metal shell 50. One end of the ground electrode 30 is joined to the front end surface 57 of the metal shell 50. The ground electrode 30 extends from the one end along the axial direction OD, then bends toward the axial line O, and reaches the other end (tip 31).

  Hereinafter, each component of the spark plug 100 will be described in detail. The insulator 10 is formed by firing alumina or the like, and has a cylindrical shape in which an axial hole 12 extending in the axial direction OD is formed at the axial center. A flange portion 19 having the largest outer diameter is formed in the approximate center of the axial direction OD. A rear end side body portion 18 is formed on the rear end side (upper side in FIG. 1) from the flange portion 19. A front end side body portion 17 having a smaller outer diameter than the rear end side body portion 18 is formed on the front end side (lower side in FIG. 1) from the flange portion 19. A long leg portion 13 having an outer diameter smaller than that of the front end side body portion 17 is formed on the front end side of the front end side body portion 17. The long leg portion 13 is reduced in diameter toward the distal end side, and is exposed to the combustion chamber when the spark plug 100 is attached to the engine head (not shown) of the internal combustion engine. A step portion 15 is formed between the long leg portion 13 and the front end side body portion 17.

  The center electrode 20 is mainly composed of copper or copper, which is superior in thermal conductivity to the base material 21 inside the base material 21 formed of nickel such as Inconel (trade name) or an alloy containing nickel as a main component. This is a rod-shaped electrode having a structure in which a core material 25 made of an alloy is embedded. The center electrode 20 is held on the distal end side in the shaft hole 12 of the insulator 10, and the distal end portion 22 of the center electrode 20 protrudes further toward the distal end side than the distal end of the insulator 10. The distal end portion 22 of the center electrode 20 is formed so as to have a smaller diameter toward the distal end side, and a noble metal tip 90 made of a noble metal for improving spark wear resistance is joined to the distal end surface.

  The noble metal tip 90 extends along the axial direction OD. Further, the noble metal tip 90 extends to a position facing the end face 31 e of the ground electrode 30. However, there is a gap between the tip 31 and the noble metal tip 90. The entire noble metal tip 90 and the center electrode 20 correspond to a “center electrode” in the claims.

  Further, a slight gap is provided between the inner peripheral surface of the shaft hole 12 near the tip of the insulator 10 and the outer peripheral surface of the center electrode 20 facing the inner peripheral surface (see FIG. 2). By generating a corona discharge in this gap at the time of turning, the carbon adhering to the vicinity of the tip of the insulator 10 is burned out and the insulation resistance is restored. Further, the center electrode 20 extends toward the rear end side in the shaft hole 12 of the insulator 10, and passes through the seal body 4 and the ceramic resistor 3, and is located at the rear (upper side in FIG. 1) terminal. It is electrically connected to the metal fitting 40. A high voltage cable (not shown) is connected to the terminal fitting 40 via a plug cap (not shown) so that a high voltage is applied.

  The metal shell 50 is a cylindrical metal fitting for fixing the spark plug 100 to an engine head (not shown) of the internal combustion engine, and is formed of a low carbon steel material. The metal shell 50 inserts and holds the insulator 10 so as to surround a portion from a part of the rear end body part 18 to the leg long part 13. Further, the metal shell 50 includes a tool engaging portion 51 into which a spark plug wrench (not shown) is fitted, and a mounting screw portion 52 in which a screw thread that is screwed into a mounting hole (not shown) of the engine head is formed. ing.

  Between the tool engaging portion 51 and the mounting screw portion 52, a bowl-shaped seal portion 54 is formed. Further, an annular gasket 5 formed by bending a plate is fitted into a screw neck 59 between the attachment screw portion 52 and the seal portion 54. The gasket 5 is deformed by being crushed between the seat surface 55 of the seal portion 54 and the opening peripheral edge of the attachment hole when the spark plug 100 is attached to the attachment hole (not shown) of the engine head. Thereby, since the space between the seat surface 55 and the opening peripheral edge of the mounting hole is sealed, airtight leakage in the engine via the mounting hole is prevented.

  A thin caulking portion 53 is provided on the rear end side of the metal shell 50 with respect to the tool engaging portion 51. A thin buckled portion 58 is provided between the seal portion 54 and the tool engaging portion 51 in the same manner as the caulking portion 53. Further, annular ring members 6 and 7 are interposed between the inner peripheral surface from the tool engaging portion 51 to the crimping portion 53 and the outer peripheral surface of the rear end side body portion 18 of the insulator 10. Yes. Between the ring members 6 and 7, powder of talc (talc) 9 is filled.

  In such a metal shell 50, the insulator 10 is pressed toward the front end side in the metal shell 50 through the ring members 6, 7 and the talc 9 by crimping the caulking portion 53 inwardly. Is done. Thus, the step portion 15 of the insulator 10 is supported by the step portion 56 formed at the position of the mounting screw portion 52 on the inner periphery of the metal shell 50 via the annular plate packing 8. The insulator 10 is integrated. Moreover, since the airtightness between the metal shell 50 and the insulator 10 is maintained by the plate packing 8, the outflow of combustion gas is prevented. Further, the buckling portion 58 is configured to bend outwardly and deform as the compressive force is applied during caulking. Further, the compression length of the talc 9 in the axial direction OD is increased to improve the airtightness in the metal shell 50.

  The ground electrode 30 is made of a metal having high corrosion resistance. As an example, a nickel-based alloy such as Inconel (trade name) is used. The ground electrode 30 is formed using a square bar whose cross section perpendicular to its longitudinal direction is substantially rectangular. Further, the ground electrode 30 is bent and formed in a substantially L shape. The ground electrode 30 includes a distal end portion 31 to which a noble metal tip 95, which will be described later, is joined, a proximal end portion 32 that is resistance-welded to the distal end surface 57 of the metal shell 50, and a portion between the distal end portion 31 and the proximal end portion 32. And a bent portion 35 bent into an L shape.

  The proximal end portion 32 extends from the distal end surface 57 along the axial direction OD. The bent portion 35 is bent so as to go from the base end portion 32 toward the noble metal tip 90. The distal end portion 31 extends from the bent portion 35 toward the noble metal tip 90. However, as shown in FIGS. 1 and 2, the tip 31 does not reach the noble metal tip 90. That is, there is a gap between the tip 31 and the noble metal tip 90. The first direction FD shown in FIGS. 1 and 2 is a direction along the longitudinal direction of the tip portion 31 and means a direction from the tip portion 31 toward the noble metal tip 90. The second direction BD is a direction along the longitudinal direction of the tip portion 31 and means a direction from the noble metal tip 90 toward the tip portion 31. In this embodiment, the first direction FD and the second direction BD are both directions perpendicular to the axial direction OD.

  A noble metal tip 95 protruding from the tip 31 toward the side surface of the noble metal tip 90 is resistance-welded to the inner peripheral surface 33 of the tip 31. The noble metal tip 95 faces the side surface of the noble metal tip 90 and forms a spark discharge gap G (spark gap) between the two noble metal tips 90 and 95. The noble metal tip 95 is made of a noble metal with high resistance to spark consumption, such as Pt, Ir, Rh, for example. The shape is a square bar shape extending along a direction (first direction FD) perpendicular to the axial direction OD. A part of the noble metal tip 95 protrudes toward the noble metal tip 90 from the end surface 31 e of the tip 31. In this way, the noble metal tip 90 protrudes from the center electrode 20 toward the axial direction OD, and further, the noble metal tip 95 protrudes from the ground electrode 30 toward the side surface of the noble metal tip 90. Spark discharge is actively performed. Then, since a flame nucleus is formed in the spark discharge gap G, it is suppressed in an initial stage of the growth process of the flame nucleus that the flame nucleus contacts the ground electrode 30 and heat is taken away. The shape of the noble metal tip 95 is not limited to a square bar shape, and various shapes (for example, a round bar shape or a triangular bar shape) can be adopted. Further, the cross-sectional shape of the noble metal tip 95 (the shape of the cross section perpendicular to the extending direction of the noble metal tip 95) may be changed according to the position in the extending direction.

  The inner peripheral surface 33 of the ground electrode 30 is a side surface on the inner peripheral side of the bend. The outer peripheral surface 34 of the ground electrode 30 is a side surface on the outer peripheral side of the bend. In the present embodiment, the ground electrode 30 has a rectangular cross section, and one side (one surface) of the rectangle corresponds to the inner peripheral surface 33 and the outer peripheral surface 34. In the tip portion 31, the inner peripheral surface 33 and the outer peripheral surface 34 are both substantially perpendicular to the axial direction OD (that is, substantially parallel to the first direction FD and the second direction BD).

A2. Spark plug manufacturing method:
The manufacturing procedure of the spark plug 100 is divided into a “preparation process” in which the component parts of the spark plug 100 are produced and prepared, and an “assembly process” in which the component parts produced in the preparation process are assembled together.

  Since the preparation process is the same as the conventional method, it will be schematically described. In the preparation step, the insulator 10, the center electrode 20, and the ground electrode 30 are respectively produced. Alumina is used as the main raw material for the insulator 10. And the insulator 10 is produced by cutting etc. so that it may become a predetermined shape, and baking at high temperature. The center electrode 20 and the ground electrode 30 are made in a rod shape using the nickel-based alloy described above. A core material 25 made of copper or an alloy containing copper as a main component is inserted into the base material of the center electrode 20, which is superior in thermal conductivity to the base material. Next, the center electrode 20, the seal body 4, the resistor 3, the terminal fitting 40 previously produced by plastic working or the like are sequentially inserted into the produced insulator 10, and a heating compression process called a glass seal is performed. These are integrally formed. On the other hand, a steel material is used for the metal shell 50. Then, the metal shell 50 is manufactured by performing plastic working, cutting, thread forming process, and the like so as to have a predetermined shape. The metal fitting 50 is formed with the above-described tool engaging portion 51, seal portion 54, and the like.

  The assembling process includes the step of joining the ground electrode 30 to the front end surface 57 of the metal shell 50, the step of plating the metal shell 50, the step of holding the insulator 10, the step of bending the ground electrode 30, and the tip 31. Joining the noble metal tip 95.

  In the joining step of the ground electrode 30, the base end portion 32 of the ground electrode 30 is joined to the distal end surface 57 of the metal shell 50 before the insulator 10 is assembled by resistance welding. The ground electrode 30 is in a rod-like state before being bent. That is, the ground electrode 30 is in a state extending in parallel to the axial direction of the metal shell 50 (that is, the axial direction OD).

  In the plating process of the metal shell 50, the ground electrode 30 is masked or the like, or after plating the metal shell 50 without masking, the plating attached to the ground electrode 30 is peeled off. As a result, it is possible to prevent the plating from adhering to the position where the noble metal tip 95 of the ground electrode 30 is welded and the welding strength of the noble metal tip 95 from being lowered. Hereinafter, a member in which the ground electrode 30 is welded to the metal shell 50 and the ground electrode 30 and the metal shell 50 after the plating process is referred to as a “metal assembly”.

  In the holding process of the insulator 10, first, the insulator 10 in which the center electrode 20 is integrated with a glass seal is inserted inside the metal fitting assembly. Next, the crimping portion 53 (see FIG. 1) is crimped so as to be bent inward. Then, the insulator 10 is pressed toward the front end side in the metal shell 50 through the ring members 6 and 7 and the talc 9 (see FIG. 1). As a result, insulation is provided to the stepped portion 56 (see FIG. 1) formed at the position of the mounting screw portion 52 (see FIG. 1) on the inner periphery of the metal shell 50 via the annular plate packing 8 (see FIG. 1). The step portion 15 of the insulator 10 is supported. The insulator 10 is integrally held by the metal shell 50 with the tip of the center electrode 20 protruding from the tip side of the metal shell 50.

  In the bending process of the ground electrode 30, the rod-shaped ground electrode 30 is processed into a predetermined bent shape. As a method of bending the ground electrode 30, various known methods can be employed. For example, the ground electrode 30 may be transformed into a plurality of stages using a plurality of types of molding molds (not shown). Further, the ground electrode 30 may be deformed once. In either case, the bending process changes the shape of the ground electrode 30 to a predetermined final shape.

  FIG. 3 is an explanatory diagram showing a procedure for joining the noble metal tip to the tip in the first embodiment. The joining process of the noble metal tip 95 to the tip portion 31 in the present embodiment includes three processes F1 to F3 including a noble metal tip 95 placement process F1, a welding electrode placement process F2, and a resistance welding process F3. In FIG. 3, a perspective view and a side view of the tip portion of the spark plug 100 in these two steps are shown for steps F1 and F2, and a side view of the spark plug 100 is shown for step F3. In addition, the side view in process F3 is the side view seen along 2nd direction BD.

  In the arrangement process F1 of the noble metal tip 95, first, the direction of the ground electrode 30 (that is, the direction of the metal shell 50) is set so that the axial direction OD is vertically downward. Then, the metal shell 50 is fixed by a holding member (not shown). Thereby, the ground electrode 30 is fixed. This fixing is maintained until the welding of the noble metal tip 95 is completed.

  Next, the noble metal tip 95 is disposed on the tip portion 31 (on the inner peripheral surface 33). At this time, in this embodiment, the jig J1 is disposed between the noble metal tip 95 and the noble metal tip 90. The jig J1 is a flat insulator (for example, ceramic), and the size (thickness) of the jig J1 in the first direction FD is set in advance to be equal to a predetermined desired distance of the spark discharge gap G. Has been. Such a jig J1 is used to fix the arrangement position of the noble metal tip 95 so that the distance between the noble metal tip 90 and the noble metal tip 95, that is, the spark discharge gap G is a predetermined distance. In addition, the jig | tool J1 is abbreviate | omitted, For example, an operator can determine a preferable position by measurement and the method of arrange | positioning the noble metal chip | tip 95 in that position is also employable.

  In the welding electrode arrangement step F2, the first welding electrode E1 and the second welding electrode E2 are arranged so as to sandwich the tip portion 31 therebetween. In the present embodiment, the first welding electrode E1 is disposed on the upper side (rear end side) of the distal end portion 31. That is, the first welding electrode E1 is located between the metal shell 50 (mounting screw portion 52) and the ground electrode 30 (tip portion 31) at a position facing the ground electrode 30 (tip portion 31) with the noble metal tip 95 interposed therebetween. Be placed. The second welding electrode E2 is disposed on the lower side (tip side) of the tip portion 31.

  The first welding electrode E1 is a square bar-shaped electrode, and is disposed above the distal end portion 31 so that the longitudinal direction thereof is along the third direction PD. At this time, one end e11 of the first welding electrode E1 protrudes in the third direction PD side of the mounting screw portion 52, and the other end e12 protrudes in the direction opposite to the third direction PD. Note that the third direction PD is a direction perpendicular to the axial direction OD, the first direction FD, and the second direction BD, as shown in FIG. The second welding electrode E2 is a flat electrode, and is arranged so that the longitudinal direction thereof coincides with the longitudinal direction of the first welding electrode E1 (that is, parallel to the third direction PD). In the present embodiment, the second welding electrode E2 is used as a ground electrode.

  In the resistance welding process F3, the noble metal tip 95 is joined to the tip portion 31 by resistance welding. In this step, one end e11 of the first welding electrode E1 is held by the holding members H1 and H2, and the other end e12 of the first welding electrode E1 is held by the holding members H3 and H4. The holding members H1 to H4 apply a predetermined load in the direction toward the second welding electrode E2 (in the present embodiment, the axial direction OD) to the first welding electrode E1. On the other hand, a predetermined load is applied to the second welding electrode E2 in the direction toward the first welding electrode E1 (in the present embodiment, the direction opposite to the axial direction OD). As a result, the first welding electrode E1 contacts the noble metal tip 95, the second welding electrode E2 contacts the tip portion 31, and the noble metal tip 95 and the tip portion 31 are sandwiched by the welding electrodes E1 and E2. Further, the noble metal tip 95 is pressed toward the tip 31 with a predetermined force. Conversely, the tip 31 is pressed toward the noble metal tip 95 with a predetermined force.

  In a state where a load is applied, a voltage for resistance welding is applied between the two welding electrodes E1 and E2. By applying this voltage, a current flows through the noble metal tip 95 and the tip portion 31. By this electric current, the noble metal tip 95 and the tip 31 are melted and the noble metal tip 95 and the tip 31 are joined. Specifically, the portion of the noble metal tip 95 that contacts the tip 31 (inner peripheral surface 33) and the portion of the tip 31 that contacts the noble metal tip 95 are joined.

  In the method for manufacturing the spark plug 100 according to the present embodiment, as will be described later, by narrowing the energization region between the two welding electrodes E1 and E2, that is, by making the energization path constant, the variation in energization is suppressed, Variations in the bonding strength of the noble metal tip 95 are suppressed. The noble metal tip 95 corresponds to the noble metal tip in the claims. The second welding electrode E2 corresponds to the welding electrode in the claims, and the first welding electrode E1 corresponds to the other welding electrode in the claims.

  FIG. 4 is an explanatory view showing detailed arrangement positions of two welding electrodes in the spark plug manufacturing method of the first embodiment. In FIG. 4, for the convenience of explanation, it is shown upside down from FIGS.

  In the first embodiment, the foremost portion P1 in the first direction FD of the contact portion T2 between the second welding electrode E2 and the tip portion 31 is in the first direction FD of the contact portion T1 between the noble metal tip 95 and the tip portion 31. It is located in the longitudinal direction rear end side (namely, 2nd direction BD side) rather than the most advanced part P2. Further, the forefront portion P1 is located on the front end side in the longitudinal direction (that is, the first direction FD) with respect to the rearmost end portion P3 in the second direction BD of the contact portion T1.

  The contact portion T1 corresponds to the “contact portion with the inner peripheral surface of the noble metal tip” in the claims. Further, the contact portion T2 corresponds to a “contact portion with the outer peripheral surface of the welding electrode” in the claims. Further, the forefront portion P1 corresponds to the electrode side tip contact portion in the claims, the tip portion P2 corresponds to the tip side tip contact portion in the claims, and the rearmost end portion P3 corresponds to the tip side rear end contact portion in the claims. To do.

  In the present embodiment, the foremost part P1 is set to be positioned at the rear end side in the longitudinal direction by 0.1 mm or more than the foremost part P2. In other words, the distance d1 along the second direction BD to the most distal portion P1 is set to be 0.1 mm or more with reference to the position of the most distal portion P2. With such a configuration, the current-carrying region Ar1 between the second welding electrode E2 and the first welding electrode E1 includes a distal end portion P1 and a rearmost end portion P3 as ends as shown in FIG. Ar1. Accordingly, in the tip portion 31, the region Ar2 including the most distal portion P1 and the most distal portion P2 as ends does not correspond to the energization region. A part of the contact portion T1 is not included in the energization region (region Ar1). Therefore, the energization region is narrower than the configuration in which all of the contact portions T1 are included in the energization region.

  In addition, although the most advanced part P1 was located in the 1st direction FD side rather than the back end part P3, it replaces with this and the structure located in the 2nd direction BD side rather than the back end part P3 is employable. The distance d1 can be obtained by measuring using, for example, a micrometer. Therefore, in the welding electrode arrangement step F2, the second welding electrode E2 is arranged at a position where the distance d1 is 0.1 mm or more. By doing so, the distance d1 can be set to 0.1 mm or more. This distance d1 can also be specified in the manufactured spark plug 100. Specifically, for example, when the trace of the second welding electrode E2 remains on the outer peripheral surface 34 of the manufactured spark plug 100, the position of the most advanced portion P1 is determined based on the shape of the trace. By specifying, the distance d1 can be specified. As described above, since a load is applied to the second welding electrode E2 in the resistance welding step F3, there is a possibility that an arrangement trace of the second welding electrode E2 remains on the outer peripheral surface 34.

  FIG. 5 is an explanatory diagram showing detailed arrangement positions of two welding electrodes in the comparative example of the first embodiment.

  In the comparative example shown in FIG. 5, the second welding electrode E2 is arranged so as to be shifted in the first direction FD direction as compared with the first embodiment. And the most advanced part P1 in this comparative example is a part corresponding to the end surface 31e of the front-end | tip part 31, unlike the most advanced part P1 (end surface of the 2nd welding electrode E2) of 1st Embodiment.

  In such a comparative example, the foremost part P1 has the same position along the first direction FD (and the second direction BD) with respect to the foremost part P2, and thus the aforementioned distance d1 is 0 mm. ing. In such a configuration, as shown in FIG. 5, the energization region between the second welding electrode E2 and the first welding electrode E1 includes the most distal end portion P2 (the most distal end portion P1) and the rearmost end portion P3. , The region Ar30 is included as an end. This region Ar30 is a region including a region Ar2 that is not a current-carrying region in the first embodiment. That is, the region Ar30 of the comparative example is wider by the region Ar2 than the region Ar1 of the first embodiment. Therefore, in the comparative example, since the energization region is wide, the energization path is likely to vary.

  On the other hand, in the spark plug manufacturing method of the first embodiment, the energization region can be narrowed, so that the energization path can be made constant. Therefore, the occurrence of variations in the welding strength of the noble metal tip 95 can be suppressed.

B. Second embodiment:
FIG. 6 is an explanatory view showing a preferred arrangement position of the second welding electrode in the second embodiment. The spark plug manufacturing method according to the second embodiment is that the spark plug according to the first embodiment is further imposed on the arrangement of the second welding electrode E2 in addition to the condition for the distance d1 (d1 ≧ 0.1 mm). Unlike the method for manufacturing the plug, the other configuration (the configuration of the spark plug 100 and each manufacturing process) is the same as that of the first embodiment.

  In the second embodiment, the most distal end portion P1 of the contact portion T2 in the second welding electrode E2 is positioned within 2.0 mm along the second direction BD from the rearmost end portion P3 of the contact portion T2 in the noble metal tip 95. Is set to In other words, the distance d2 along the second direction BD to the most distal end portion P1 is set to be 2.0 mm or less with the position of the rearmost end portion P3 as a reference.

  As shown in FIG. 6, in the second embodiment, the foremost portion P1 is located on the second direction BD side as compared to the rearmost end portion P3. Therefore, the energization region is a region (surface) connecting the most distal end portion P1 and the rearmost end portion P3, and is very narrow compared to the energization region (volume) in the first embodiment shown in FIG. Therefore, in the second embodiment, the variation in the bonding strength of the noble metal tip 95 can be further suppressed. In addition, in the first embodiment, the most advanced portion P1 is set to be located within 2.0 mm along the second direction BD from the rearmost end portion P3 of the contact portion T2 in the noble metal tip 95. It can suppress that the distance (energization distance) between the most advanced part P1 and the last end part P3 becomes very long.

  FIG. 7 is an explanatory diagram showing detailed arrangement positions of two welding electrodes in a comparative example of the second embodiment.

  In the comparative example shown in FIG. 7, the foremost portion P1 is disposed away from 2.0 mm along the second direction BD from the rearmost end portion P3 of the contact portion T1 in the noble metal tip 95. In other words, the distance d2 is set to be longer than 2.0 mm. As in the second embodiment, the energization region in this comparative example is a region Ar31 that connects the most distal end portion P1 and the rearmost end portion P3. However, the distance between the most distal end portion P1 and the rearmost end portion P3 in this comparative example is very long compared to the second embodiment. Therefore, a decrease in energization current occurs due to a very long distance between the most distal end portion P1 and the rearmost end portion P3, resulting in a low welding strength or a long time for the resistance welding process. It will be.

  On the other hand, in the spark plug manufacturing method of the second embodiment described above, the energization region can be narrowed and the distance between the most distal end portion P1 and the rearmost end portion P3 can be shortened. Therefore, since a decrease in energization current can be suppressed, a decrease in welding strength can be suppressed, and a period required for the resistance welding process can be shortened.

C. Third embodiment:
FIG. 8 is a first explanatory view showing a preferred arrangement position of the second welding electrode in the third embodiment. The manufacturing method of the spark plug according to the third embodiment relates to the arrangement of the second welding electrode E2, a point that imposes other conditions instead of the condition of the distance d1 (d1 ≧ 0.1 mm), the shape of the tip 31,
However, unlike the spark plug manufacturing method of the first embodiment, the other configuration (the configuration of the spark plug 100 and each step of the manufacturing method) is the same as that of the first embodiment.

  The tip portion 31a of the third embodiment has a deformed portion G1 at the tip portion. The deformed portion G1 has a smaller thickness (length in the axial direction OD) than other portions of the tip portion 31a. In other words, the deformed portion G1 has a configuration that is recessed in the direction from the outer peripheral surface 34 toward the inner peripheral surface 33 (in the direction opposite to the axial direction OD). Such a deformed portion G1 of the distal end portion 31a may occur due to a processing error at the time of cutting the square bar in the manufacturing process of the member (square bar) of the ground electrode 30. In the spark plug manufacturing method of the third embodiment, the second welding electrode E2 is a portion where the most distal end portion P1 of the second welding electrode E2 is located in the second direction BD of the deformed portion G1 (the rearmost end). Part) From P4, it arrange | positions so that it may be located 0.1 mm or more in a longitudinal direction rear end side (namely, 2nd direction BD side). In other words, the distance d3 along the second direction BD to the most distal end portion P1 is set to be 0.1 mm or more with reference to the position of the rearmost end portion P4.

  With such a configuration, as in the first embodiment, part of the contact portion T1 in the noble metal tip 95 does not become an energization region, and thus the energization region can be narrowed. In addition, since the second welding electrode E2 can be disposed avoiding the deformation part G1, the contact state between the second welding electrode E2 and the tip part 31a (the ground electrode 30) does not have the deformation part G1. It is possible to suppress the difference from a spark plug or a spark plug having a deformed portion having a shape different from that of the deformed portion G1. Accordingly, variations in the energized state can be suppressed, and variations in the bonding strength of the noble metal tip 95 can be suppressed.

  FIG. 9 is a second explanatory view showing a preferred arrangement position of the second welding electrode in the third embodiment. The example of FIG. 9 is different from the example of FIG. 8 in the shape of the deformed portion, and the other configuration is the same as the example of FIG. The deformation part G2 in FIG. 9 has a larger thickness (length in the axial direction OD) than the other part of the tip part 31b. In other words, the deforming part G2 has a configuration protruding in the direction from the inner peripheral surface 33 toward the outer peripheral surface 34 (in the direction opposite to the axial direction OD). Also in this example, the second welding electrode E2 is disposed such that the most distal end portion P1 of the second welding electrode E2 is located on the second direction BD side by 0.1 mm or more from the rearmost end portion P5 of the deformation portion G2. (That is, arranged so as to satisfy d3 ≦ 0.1 mm).

  FIG. 10 is an explanatory diagram showing variations of the deforming portion in the third embodiment. FIG. 10 shows three variations of the deformed portion at the tip. The deformed portion of the uppermost case 1 is the same as the deformed portion G1 in FIG. That is, the thickness of the deformed portion of the case 1 is smaller than the thickness F of other portions. And in this case 1, compared with the thickness F of the other part in the front-end | tip part, the front end side is regarded as a deformation | transformation part rather than the part (thickness G part) whose thickness is 0.5% smaller.

  The deformed portion of the middle case 2 is the same as the deformed portion G2 in FIG. That is, the thickness of the deformed portion of the case 2 is larger than the thickness F of other portions. And in this case 2, compared with the thickness F of the other part in the front-end | tip part, the front end side is regarded as a deformation | transformation part rather than the part (thickness H part) whose thickness is only 0.5% smaller.

  The deformed portion of the lowermost case 3 is formed by combining the deformed portion of the case 1 and the deformed portion of the case 2. Specifically, the distal end portion of the case 3 includes a deformed portion having a thickness larger than that of the other portion, and a deformed portion positioned on the distal end side of the deformable portion and having a thickness smaller than that of the other portion. . And between these two deformation | transformation parts, although the part of the same thickness as the thickness F of another part exists, in case 3, in the deformation | transformation part (thickness larger thickness compared with another part) in the rear end side. The portion on the tip side of the portion) is regarded as a deformed portion.

  With such a configuration, even if the tip has a plurality of deformed portions, the second welding electrode E2 can be brought into contact with the tip 31 (the ground electrode 30) while avoiding any deformed portions. The shape and width of the contact portion between the second welding electrode E2 and the ground electrode 30 can be made constant, and variations in the energized state of the ground electrode 30 can be suppressed.

  Note that the shape of the deformed part (measurement of the thickness in the axial direction OD) can be measured, for example, by a micrometer, by analyzing a projection image obtained by a projector, or by a shape measuring instrument using a laser or the like. This can be achieved.

D. Example:
D1. First embodiment:
In the first embodiment, eight types of spark plugs (samples) having different arrangement states of the second welding electrode E2 in the noble metal tip joining process are manufactured, and the noble metal tip 95 and the tip 31 (grounding) are prepared using these eight types of samples. A test was conducted to evaluate the bonding strength with the electrode 30).

  FIG. 11 is a first explanatory view schematically showing the vicinity of the tip in the noble metal tip joining process when preparing eight types of samples in the first embodiment. FIG. 12 is a second explanatory view schematically showing the vicinity of the tip in the noble metal tip joining process when preparing eight types of samples in the first embodiment.

  11 and 12, the position along the second direction BD of the end surface on the distal end side in the longitudinal direction of the second welding electrode E <b> 2 is represented as a position L with the end surface 31 e of the distal end portion 31 as a reference. Further, the position along the second direction BD of the rear end in the longitudinal direction of the deformed portion is represented as a position K with the end surface 31e of the tip portion 31 as a reference. Further, the position along the second direction BD of the rear end in the longitudinal direction of the noble metal tip 95 is represented as a position J with reference to the end face 31e of the tip 31. Note that the position in the second direction BD is positive and the position in the first direction FD is negative with respect to the end face 31e.

  As shown in FIGS. 11 and 12, the position K in the first sample S1, the second sample S2, the third sample S3, the fourth sample S4, the fifth sample S5, and the sixth sample S6 was +0.5 mm. As shown in FIG. 12, the position K in the seventh sample S7 and the eighth sample S8 was +1.0 mm. Moreover, as shown in FIGS. 11 and 12, the position J in any of the samples S1 to S8 was +0.8 mm.

  At the time of manufacturing the first sample S1, the second welding electrode E2 was disposed so as to cover the entire tip portion 31, and the position L was −0.3 mm. At this time, the most distal portion of the contact portion T2 (the contact portion between the second welding electrode E2 and the tip portion 31) coincides with the rear end of the deformed portion. Further, the most distal portion of the contact portion T1 (the contact portion between the noble metal tip 95 and the tip portion 31) is a portion corresponding to the end surface 31e of the tip portion 31. Therefore, the aforementioned distance d1 is +0.5 mm, which satisfies the condition of the first embodiment (distance d1 ≧ 0.1 mm). In addition, the most distal portion of the contact portion T2 is located on the front end side in the longitudinal direction (first direction FD) with respect to the rear end of the contact portion T1, and the condition of the second embodiment (distance d2 ≦ 2.0 mm). Meet. However, since the most distal portion of the contact portion T2 coincides with the rear end of the deformed portion, the condition of the third embodiment (distance d3 ≧ 0.1 mm) is not satisfied.

  At the time of manufacturing the second sample S2, the second welding electrode E2 was disposed such that the end surface in the first direction FD coincided with the end surface 31e of the distal end portion 31, and the position L was 0 mm. In addition, when the third sample S3 was created, the position L was +0.1 mm. At the time of manufacturing the fourth sample S4, the position L was +0.3 mm. In producing these three samples S2, S3, and S4, the distance d1 is the condition of the first embodiment (distance d1 ≧ 0.1 mm), and the distance d2 is the condition of the second embodiment (distance d2 ≦ 2). 0.0 mm), respectively. However, when these three samples S2, S3, and S4 were produced, the distance d3 did not satisfy the condition of the third embodiment (distance d3 ≧ 0.1 mm).

  As shown in FIG. 12, the second welding electrode E2 was disposed so as not to cover a part of the outer peripheral surface 34 on the front end side in the longitudinal direction when the fifth sample S5 was produced. At this time, the position L was +0.6 mm. During the production of the fifth sample S5, the distance d1 is the condition of the first embodiment (distance d1 ≧ 0.1 mm), and the distance d2 is the condition of the second embodiment (distance d2 ≦ 2.0 mm). I met. In addition, at the time of producing the fifth sample S5, the most distal portion of the contact portion T2 was separated by 0.1 mm from the rear end of the deformed portion to the rear end in the longitudinal direction. d3 ≧ 0.1 mm).

  At the time of producing the sixth sample S6, the second welding electrode E2 is such that the end surface in the first direction FD is positioned on the rear end side in the longitudinal direction along the second direction BD from the rear end of the noble metal tip 95. Arranged. In this case as well, all the conditions of the first to third embodiments were satisfied, as in the production of the fifth sample S5.

  At the time of manufacturing the seventh sample S7, the second welding electrode E2 is disposed at the same position as the third sample S3 and the fourth sample S4 shown in FIG. +0.6 mm. At this time, the condition of the third embodiment (distance d3 ≧ 0.1 mm) was not satisfied. Here, since the deformed portion is relatively large when the seventh sample S7 is manufactured, the most distal portion of the contact portion T2 is positioned at the rear end in the longitudinal direction along the second direction BD rather than the rearmost end portion of the contact portion T1. Was. At this time, the distance d2 was +0.2 mm, which satisfied the conditions of the second embodiment (distance d2 ≦ 2.0 mm). Note that the distance d1 satisfied the condition of the first embodiment (distance d1 ≧ 0.1 mm).

  At the time of producing the eighth sample S8, the second welding electrode E2 was disposed at the same position as the fifth sample S5 with respect to the tip portion 31, and the position L was +1.1 mm. At the time of manufacturing the eighth sample S8, the distance d1 satisfied the condition of the first embodiment (distance d1 ≧ 0.1 mm). Further, at the time of manufacturing the eighth sample S8, the distance d2 was +0.3 mm, so the condition of the second embodiment (distance d2 ≦ 2.0 mm) was satisfied. Further, when the eighth sample S8 was manufactured, the distance d3 was +0.1 mm, so that the condition of the third embodiment (distance d3 ≧ 0.1 mm) was satisfied.

  After making the above eight types of samples S1 to S8 by five, a test for repeatedly heating and cooling the joint portion between the ground electrode 30 and the noble metal tip 95 was performed. And the dimensional change of the joining location before and after the test which repeats this heating and cooling was measured, and the joining strength of the ground electrode 30 (tip part 31) and the noble metal tip 95 was evaluated based on the obtained dimensional change. By repeating the heating and cooling, the ground electrode 30 and the noble metal tip 95 are repeatedly expanded and contracted, respectively, so that the joint portion may be deteriorated. Here, the dimension of the joint portion means the length of the joint portion with the noble metal tip 95 along the first direction FD and the second direction BD at the tip portion 31. When heating and cooling as described above are repeatedly performed, if the welding strength is low, peeling of the joint portion occurs and the joint dimension becomes small, so that the dimensional change becomes large. On the other hand, when the bonding strength is high, peeling of the bonded portion is suppressed, and the change in the bonding dimension is reduced.

  In addition, the test which repeats a heating and cooling was performed on the conditions whose heating temperature is 1100 degreeC, the heating period per time is 2 minutes, the cooling period per time is 1 minute, and the repetition frequency is 1000 times.

  FIG. 13 is a first explanatory view showing a result obtained by the bonding strength evaluation test in the first example. FIG. 14 is a second explanatory diagram showing a result obtained by the bonding strength evaluation test in the first example. In FIG. 13, the horizontal axis indicates each sample number, and the vertical axis indicates the dimensional change rate (%) of the joint. Since each of the samples S1 to S8 was subjected to the bonding strength test described above for five samples, FIG. 13 shows the maximum value, the minimum value, and the average value based on the five dimensional changes obtained for each sample S1 to S8. ing. Here, the maximum value means the dimensional change rate of the case that has not changed most, and the minimum value means the dimensional change rate of the case that has changed most. In FIG. 14, for each sample, the position J, the position K, the position L, the maximum and minimum values of the joint dimension non-change ratio, the joint dimension non-change ratio difference (the maximum and minimum values of the dimension non-change ratio, Difference).

  As shown in FIG. 13, in each sample S1-S8, all the maximum values were substantially the same. This is presumed to be because welding can be performed in a preferable state depending on the energization path in any environment. However, the difference (variation) between the maximum value and the minimum value is greatly different depending on the sample as shown in FIGS. Specifically, as shown in FIG. 14, in the first sample S1, the maximum value of the joint dimension non-change ratio was 76.00 and the minimum value was 59.30. The difference (difference between the maximum value and the minimum value) was 16.69%. In addition, in the sixth sample S6, the maximum value of the joint dimensional non-change ratio was 76.54 and the minimum value was 69.04, so the joint dimensional change ratio difference was 7.498%. .

  Here, among the six samples S1 to S6 whose position K is +0.5 mm, in the fifth sample S5 and the sixth sample S6 that satisfy the condition of the third embodiment (distance d3 ≧ 0.1 mm), the joint size change The ratio difference is less than 10%, and it can be seen that the variation in bonding strength between products is suppressed compared to the other four samples S1 to S4. Note that, in the two samples S5 and S6, the difference in the change rate is small because the minimum value is higher than in the other four samples S1 to S4. Since the maximum values in the samples S1 to S8 are substantially the same, the average value of the two samples S5 and S6 is higher than the average value of the other four samples S1 to S4 as shown in FIG. It was. This means that these two samples S5 and S6 have an average higher bonding strength than the other four samples S1 to S4.

  Moreover, the same tendency as the samples S1 to S6 was confirmed for the two samples S7 and S8 whose position K is +1.0 mm. That is, in the eighth sample S8 that satisfies the condition of the third embodiment (distance d3 ≧ 0.1 mm), the joint size change rate difference is 2% or more compared to the seventh sample S7 that does not satisfy the condition of the third embodiment. It was low. Therefore, it can be understood that the variation in the bonding strength is suppressed by satisfying the condition of the third embodiment (distance d3 ≧ 0.1 mm).

  FIG. 15 is an explanatory diagram showing a simulation result for specifying a preferable size of the distance d2 in the first embodiment. In FIG. 15, the upper part shows the simulation result, and the lower part shows the data used as the basis of the simulation. In the upper part of FIG. 15, the horizontal axis indicates the position L (mm), and the vertical axis indicates the bonding dimension unchanged rate (%). The items shown in the lower part of FIG. 15 are the same as the items shown in FIG. In the first example, a bonding strength evaluation test was performed on the three types of samples S11 to S13 in the same manner as the samples S1 to S8 described above, and the test results shown in the lower part of FIG. 15 were obtained. In all the samples S11 to S13, the position J was +0.8 mm, and the position K was +0.5 mm. Further, the position L of the sample S11 was +0.7 mm, the position L of the sample S12 was +1.2 mm, and the position L of the sample S13 was +1.6 mm. In addition, the manufacturing method of each sample S11-S13 was the same as sample S1-S8.

  Based on the test results shown in the lower part of FIG. 15 (position L (mm), joint size non-change ratio (%)), the relationship between the position L and the joint size non-change ratio was approximated by a quadratic curve. As shown in the upper part of FIG. 15, in the obtained quadratic curve, the position L when the joint unchanged ratio was 60% was +2.8 mm. That is, if the position L is +2.8 mm or less, the joint unchanged ratio is 60% or more. Here, since the position J is +0.8 mm, the distance d2 when the position L satisfies +2.8 mm or less is +2.0 mm or less. That is, it can be understood that the joint unchanged ratio can be suppressed to 60% or less by satisfying the condition (d2 ≦ + 2.0 mm) of the second embodiment described above.

D2. Second embodiment:
In the second example, the state of welding droop in each sample was evaluated. In this second embodiment, in addition to the five types of samples S1 to S5 of the first embodiment, ten ninth samples S9 each having a position L of +0.8 mm are prepared, and the state of welding of each sample is created. Evaluated.

  FIG. 16 is an explanatory diagram showing a method of an evaluation test in the second example. In FIG. 16, the noble metal tip 95 and the tip portion 31 are shown as viewed from the inner peripheral surface 33 side in the direction opposite to the axial direction OD. As shown in FIG. 16, welding dripping occurs around the noble metal tip 95 on the inner peripheral surface 33. In general, the shape of the welding droop varies depending on the energization path and the like, and the larger the welding dripping, the stronger the joint strength. Further, in the case where weld welds are formed evenly around the noble metal tip 95, the joint strength is higher than in the case where weld welds are formed unevenly. In the example of FIG. 16, the welding on the right side is large and the welding on the left side is small across the noble metal tip 95.

  In the second embodiment, the length A along the first direction FD of the welding droop on the right side (opposite direction to the third direction PD) across the noble metal tip 95 and the left side (third At least one of the lengths B along the first direction FD of the welding droop on the direction PD side is the length M of the contact portion T1 in the first direction FD (that is, the size of the position J in the first embodiment). In the case where it is less than or equal to ½), it was evaluated that a so-called flaking occurred and the bonding strength was low. On the contrary, when both the length A and the length B are larger than ½ of the length M, it was evaluated that the so-called sag does not occur and the joint strength is high. . The lengths A and B can be measured for each sample using, for example, a micrometer.

  FIG. 17 is an explanatory diagram showing the results obtained by the bonding strength evaluation test in the second example. In FIG. 17, the confirmation results and the evaluation results are shown for each of the samples S1 to S5 and S9. In FIG. 17, for convenience, positions L, K, and J for each of the samples S1 to S5 and S9 are also shown. The “confirmation result” in FIG. 17 means the number of pieces in which one of the ten samples S1 to S5 and S9 has occurred. In the “evaluation”, a case where the rate of occurrence of a piece is 0% is a star shape, and a case where the rate of occurrence of a piece is more than 0% and less than 25% is a double circle. A case where the percentage of occurrence is higher than 25% and not more than 50% is represented as a single circle, and a case where the percentage of occurrence of dripping is higher than 50% is represented as a cross.

  Also in the bonding strength evaluation test of the second example, it was found that the larger the position L, the higher the bonding strength. In particular, in the fifth sample S5 and the ninth sample S9, the occurrence rate of the piece is less than 25%, and it can be seen that the bonding strength is higher than the other samples. In the fifth sample S5 and the ninth sample S9, the position L is +0.6 mm or more, and both satisfy the condition of the third embodiment (d3 ≧ 0.1 mm). Therefore, it can be seen that satisfying the conditions of the third embodiment improves the bonding strength.

E. Variations:
In addition, elements other than the elements claimed in the independent claims among the constituent elements in the above embodiments are additional elements and can be omitted as appropriate. The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

E1. Modification 1:
In each embodiment and example, the second welding electrode E2 is a plate-shaped electrode, and the most distal portion in the contact portion T2 (contact portion with the tip portion 31) corresponds to the end surface of the second welding electrode E2. However, the present invention is not limited to this.

  FIG. 18 is an explanatory view showing a detailed arrangement position of the second welding electrode in the spark plug manufacturing method of the modification. In FIG. 18, two modified examples are shown in the upper and lower stages. In FIG. 18, the configuration of the second welding electrode is different from the respective embodiments and examples, and other configurations are the same as those of the respective embodiments and examples.

  In the example in the upper part of FIG. 18, the second welding electrode E2a includes a portion D1 having a large thickness in the axial direction OD and a portion D2 having a small thickness in the axial direction OD. In the example in the upper part of FIG. 18, the thickness in the axial direction OD of each of the portion D1 and the portion D2 is constant. In such an example in the upper part of FIG. 18, the most distal portion P1 of the contact portion T2 becomes a boundary portion between the portion D1 and the portion D2, and the most distal portion P8 of the entire second welding electrode E2a (that is, the portion corresponding to the end face). ) Is different.

  In the example in the lower part of FIG. 18, the second welding electrode E2b includes a portion D1 having a large thickness in the axial direction OD and a part D3 having a small thickness in the axial direction OD, as in the upper part of FIG. The lower part D1 in FIG. 18 is the same as the upper part D1 in FIG. In the portion D3, the thickness in the axial direction OD is gradually reduced toward the first direction FD. In such an example in the lower part of FIG. 18, the most distal end portion P1 of the contact portion T2 becomes a boundary portion between the portion D1 and the portion D2, and the most distal end portion P9 of the entire second welding electrode E2b (that is, the portion corresponding to the end face) ) Is different.

  Even in the configuration of such a modification, variations in the bonding strength of the noble metal tip 95 can be suppressed by satisfying the conditions of each embodiment based on the most distal portion P1 of the contact portion T2 specified by the above-described method.

E2. Modification 2:
As a manufacturing procedure of the spark plug 100, not only the procedure of each embodiment mentioned above but the arbitrary procedures including a noble metal chip joining process are employable. For example, the ground electrode 30 may be bent before joining to the metal shell 50. For example, the noble metal tip 95 may be bonded to the ground electrode 30 before the center electrode 20 is assembled.

E3. Modification 3:
The configuration of the spark plug 100 is not limited to the configuration illustrated in FIG. 1, and any configuration in which the noble metal tip 95 is bonded to the ground electrode 30 can be employed. For example, a configuration in which the noble metal tip 90 is not disposed at the tip of the center electrode 20 can be employed. Further, for example, in each embodiment, the noble metal tip 95 is arranged such that the end surface in the first direction FD protrudes in the first direction FD from the end surface 31e of the tip portion 31. The position along the first direction FD of the end surface in the one direction FD may be arranged so as to coincide with the position along the first direction FD of the end surface 31e.

DESCRIPTION OF SYMBOLS 3 ... Resistor 4 ... Sealing body 5 ... Gasket 6 ... Ring member 8 ... Plate packing 9 ... Talc 10 ... Insulator 12 ... Shaft hole 13 ... Leg long part 15 ... Step part 17 ... Front end side body part 18 ... Rear end side trunk Part 19 ... Bridge 20 ... Center electrode 21 ... Base material 22 ... Tip part 25 ... Core material 30 ... Ground electrode 31, 31a, 31b ... Tip part 31e ... End face 32 ... Base end part 33 ... Inner peripheral face 34 ... Outer peripheral face 35 ... Bending part 40 ... Terminal metal fitting 50 ... Metal fitting 51 ... Tool engaging part 52 ... Mounting screw part 53 ... Clamping part 54 ... Sealing part 55 ... Seating surface 56 ... Step part 57 ... Tip surface 58 ... Buckling part 59 ... Screw neck 90,95 ... Precious metal tip 100 ... Spark plug O ... Axis G ... Spark discharge gap OD ... Axis direction FD ... First direction BD ... Second direction PD ... Third direction Ar1, Ar2, Ar3, Ar30, Ar31 ... Region J, K, L Position F1 ... Precious metal tip placement process J1 ... Jig E1 ... First welding electrode E2, E2a, E2b ... Second welding electrode H1, H2, H3, H4 ... Holding member P1 ... Most advanced part T1, T2 ... Contact part d1, d2, d3 ... distance G1, G2 ... deformation part S1 ... first sample D1, D2, D3 ... part P2 ... most advanced part F2 ... welding electrode arrangement process F3 ... resistance welding process P3 ... last end part P4 ... last end part P5 ... last end part P8 ... most advanced part P9 ... most advanced part e11 ... one end part e12 ... other end part

Claims (5)

A central electrode extending in the axial direction;
An insulator having an axial hole extending in the axial direction and holding the center electrode inside the axial hole;
A cylindrical metal shell disposed on the outer periphery of the insulator;
A ground electrode disposed at an end of the metal shell,
A noble metal tip disposed at the tip of the ground electrode and forming a gap with the center electrode, and a spark plug manufacturing method comprising:
Among the side surfaces of the noble metal tip, the position of the side surface on the front end side of the ground electrode coincides with the position of the end surface of the front end of the ground electrode or is positioned on the front end side in the longitudinal direction from the position of the end surface of the front end. A noble metal tip placement step of placing the noble metal tip on the inner peripheral surface of the ground electrode;
A welding electrode arrangement step of arranging a welding electrode so as to be in contact with the outer peripheral surface which is the opposite surface of the inner peripheral surface at the tip portion;
Resistance welding the noble metal tip to the inner peripheral surface;
With
In the welding electrode arrangement step, of the contact portions with the outer peripheral surface of the welding electrode, the electrode-side tip contact portion located closest to the front end side in the longitudinal direction is the contact portion with the inner peripheral surface of the noble metal tip. Among them, the method for manufacturing a spark plug, wherein the welding electrode is arranged so as to be positioned 0.1 mm or more on the rear end side in the longitudinal direction from the tip side front end contact portion positioned closest to the front end side in the longitudinal direction. In the spark plug manufacturing method according to claim 1,
In the welding electrode arrangement step, the position of the electrode side tip contact portion is the tip side rear end contact portion located closest to the rear end side in the longitudinal direction among the contact portions with the inner peripheral surface of the noble metal tip; A method for manufacturing a spark plug, wherein the welding electrode is disposed so as to coincide with each other in the longitudinal direction or to be located closer to the rear end side in the longitudinal direction than a position of the tip side rear end contact portion. In the spark plug manufacturing method according to claim 2,
In the welding electrode arrangement step, the spark plug manufacturing method includes arranging the welding electrode such that the electrode side tip contact portion is positioned within 2.0 mm from the tip side rear end contact portion in the longitudinal direction. In the manufacturing method of the spark plug in any one of Claims 1 thru | or 3,
In the tip portion, the outer peripheral surface includes a first deforming portion that is recessed in a direction from the outer peripheral surface toward the inner peripheral surface, and a second deforming portion that protrudes in a direction from the inner peripheral surface toward the outer peripheral surface. At least one of
In the welding electrode arrangement step, the position of the electrode side tip contact portion is greater than the position of the rear end in the longitudinal direction of the deformed portion located closest to the rear end among the first deformed portion or the second deformed portion. A method for manufacturing a spark plug, wherein the welding electrode is disposed so as to be positioned at a rear end side in the longitudinal direction of 0.1 mm or more. In the manufacturing method of the spark plug in any one of Claims 1 thru | or 4,
The welding electrode arrangement step includes the step of arranging the welding electrode so as to contact the outer peripheral surface, and the tip portion sandwiching the noble metal tip with respect to the noble metal tip arranged on the inner peripheral surface. Disposing another welding electrode different from the welding electrode so as to contact on the opposite side, and a method for manufacturing a spark plug.

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