Spark plug and method for manufacturing the same

Abstract

To provide an ignition plug that improves the bonding strength of a tip in a ground electrode, restrains peeling of the tip caused by a repeated thermal cycling and is excellent in durability, and a method for manufacturing the same.SOLUTION: A spark plug 1 includes a center electrode 3 held inside a housing 2, a ground electrode 4 extending from the tip of the housing 2 and facing the center electrode 3, and a precious metal tip 5 formed integrally with the ground electrode 4. The tip 5 has a base end 51 embedded in the ground electrode 4, and a protruding portion 52 that protrudes further toward the center electrode 3 beyond the surface 41 of the ground electrode 4. A protective layer 6 is provided on the outside of the tip 5 in a direction perpendicular to a plug axis Y so as to cylindrically surround the outer peripheries of the base end 51 and protruding portion 52. The protective layer 6 is made of the same material as the base material of the ground electrode 4, and the maximum height hmax of the protective layer from the surface 41 in the plug axial direction X is equal to the height Ht of the protruding portion 52.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a spark plug and a method for manufacturing the same.

Background Art

[0002] A spark plug is provided with a discharge portion having a center electrode and a ground electrode on the tip side protruding into the engine cylinder, and generates a spark discharge between both electrodes to ignite the fuel gas. A noble metal chip excellent in wear resistance is joined to the surface of the ground electrode facing the center electrode by resistance welding or the like, and it is important to ensure the joinability of the chip in order to maintain the discharge gap formed between the chip and the tip surface of the center electrode.

[0003] In Patent Document 1, paying attention to the fact that when the chip is welded and fixed to the main body portion of the ground electrode, the joining strength decreases if the melted portion flows out, it has been proposed to suppress the outflow depending on the processed shape of the main body portion. Specifically, the end portion of the main body portion is cut from the opposite side toward the one surface side that becomes the chip joining side, and the chip is joined to the portion including the end deformed by the cutting. According to this prior art, the end deformed to protrude toward the center electrode side serves as a protruding portion that improves ignitability and retains the melted portion, and a melted portion is formed around the chip, and it is said that the peel resistance of the chip is improved.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, as a combustion environment in which a spark plug is exposed in an engine cylinder, the flow velocity of the airflow flowing around the spark plug has a tendency to increase. Therefore, the spark discharge generated in the discharge gap of the spark plug is likely to be carried away by the airflow. In the shape of the ground electrode having a protruding portion protruding toward the center electrode side as in the prior art, the spark discharge moves from the tip to the protruding portion side, and the protruding portion is consumed. When the protruding portion is consumed, the consumption due to the spark discharge is accelerated also in the molten portion formed around the tip, and the interface between the tip and the ground electrode is likely to be partially exposed. In such a state, there was a risk that the tip would peel off due to repeated cold and heat cycles caused by fluctuations in the engine speed and the like.

[0006] The present invention has been made in view of such problems, and aims to provide a spark plug with excellent durability and a method for manufacturing the same, which enhance the bonding property of the tip in the ground electrode, suppress the peeling of the tip due to repeated cold and heat cycles.

Means for Solving the Problems

[0007] One aspect of the present invention is a center electrode (3) that is insulated and held inside a cylindrical housing (2) and protrudes beyond the tip of the housing, a ground electrode (4) that extends from the tip of the housing and faces the center electrode in the plug axis direction (X), a spark plug (1) comprising a noble metal tip (5) provided integrally with the ground electrode and forming a discharge gap (G) between the center electrode, wherein the tip has a base end portion (51) embedded in the ground electrode and a protruding portion (52) protruding toward the center electrode side from the surface (41) of the ground electrode on the side facing the center electrode, in a direction (Y) orthogonal to the plug axis direction, a protective layer (6) is provided outside the tip to cylindrically surround the outer circumferences of the base end portion and the protruding portion. In the spark plug, the protective layer is made of the same material as the base material of the ground electrode, and in the axial direction of the plug, the maximum height (Hmax) of the protective layer from the surface is equal to the height (Ht) of the protruding portion.

[0008] Another aspect of the present invention is a method for manufacturing a spark plug having the above-described configuration, which includes a welding step of joining the chip to the ground electrode by resistance welding, in the welding step, a first welding electrode (101) having a recess (103) with an inner diameter larger than the diameter of the chip is used, the first welding electrode and a second welding electrode (102) are opposed to each other in the axial direction of the plug, and the chip and the ground electrode are disposed therebetween such that the chip is located inside the recess, by energizing while sandwiching the chip and the ground electrode between the first welding electrode and the second welding electrode, the base material of the ground electrode is melted, and the melted base material of the ground electrode climbs up and covers the outside of the chip inside the recess, thereby forming the protective layer having a shape along the recess. This is a method for manufacturing a spark plug.

Advantages of the Invention

[0009] In the spark plug having the above-described configuration, the base end portion of the chip is embedded and fixed to the ground electrode, and the outer periphery of the chip including the protruding portion protruding toward the center electrode side is protected by a protective layer made of the same material as the base material of the ground electrode. The protective layer surrounds the outer periphery of the chip in a cylindrical shape such that the maximum height from the surface of the ground electrode is equal to the height of the protruding portion of the chip, and it is possible to increase the substantial chip volume and suppress the consumption of the chip. As a result, even in an environment where the in-cylinder airflow is fast and the engine speed fluctuates greatly, it is possible to prevent the interface between the chip and the ground electrode from being exposed and further prevent the chip from peeling off.

[0010] Further, the spark plug having the above configuration can be manufactured by providing a recess having an inner diameter larger than the chip diameter in the first welding electrode disposed on the chip side in the welding process and performing resistance welding while sandwiching the chip and the ground electrode between the first welding electrode and the second welding electrode. That is, the movement of the base material of the melting ground electrode is restricted by the recess, and a protective layer surrounding the outer periphery of the chip in a cylindrical shape can be formed by the solidification of the base material climbing along the recess.

[0011] As described above, according to the above aspect, it is possible to provide a spark plug excellent in durability and a method for manufacturing the same by enhancing the joinability of the chip in the ground electrode and suppressing the peeling of the chip due to repeated thermal cycles. Note that the reference numerals in parentheses described in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described later, and do not limit the technical scope of the present invention.

Brief Description of Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

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Figure 8

Figure 9

Figure 10

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Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Modes for Carrying Out the Invention

[0013] (Embodiment 1) Embodiments related to the spark plug will be described with reference to the drawings. As shown in FIGS. 1 and 2, the spark plug 1 has a cylindrical housing 2, a center electrode 3 that is insulated and held inside it, a ground electrode 4 that faces the center electrode 3 in the plug axis direction X, a tip 5 made of a noble metal, and a protective layer 6. The tip 5 made of a noble metal is provided integrally with the ground electrode 4 and forms a discharge gap G between it and the center electrode 3.

[0014] As shown in FIG. 1, in the plug axis direction X, the center electrode 3 protrudes beyond the tip of the housing 2. The ground electrode 4 extends from the tip of the housing 2, and its extended end extends to a position facing the center electrode 3. The center electrode 3 is coaxially arranged inside the housing 2.

[0015] Here, the plug axis direction X is the direction in which the plug central axis extends, and coincides with the central axis C of the cylindrical housing 2 and the direction of the central axis of the shaft-shaped center electrode 3. In addition, the direction orthogonal to the plug axis direction X and in which the extended end of the ground electrode 4 extends will hereinafter be referred to as the plug axis orthogonal direction Y.

[0016] The chip 5 has a base end portion 51 embedded in the ground electrode 4 and a protruding portion 52. The ground electrode 4 has a first surface 41 which is the surface on the side facing the center electrode 3, and the protruding portion 52 protrudes toward the center electrode 3 side from the first surface 41. At this time, a discharge gap G is formed between the protruding end surface 521 of the protruding portion 52 and the tip surface 31 of the center electrode 3. In addition, in the plug axis direction X, the surface located on the side opposite to the first surface 41 of the ground electrode 4 will hereinafter be referred to as the second surface 42.

[0017] The chip 5 has, for example, a flat columnar shape. A part located on the center electrode 3 side across the first surface 41 of the ground electrode 4 becomes the protruding portion 52, and a part located on the second surface 42 side becomes the base end portion 51. For the chip 5, the virtual line shown by the dotted line in FIG. 1 indicates the position of the first surface 41 that partitions the base end portion 51 and the protruding portion 52.

[0018] In the plug axis orthogonal direction Y, a protective layer 6 is provided outside the chip 5. The protective layer 6 cylindrically surrounds the outer circumferences of the base end portion 51 and the protruding portion 52 to protect the outer circumferential side of the chip 5. The protective layer 6 is made of the same material as the base material of the ground electrode 4, and can be formed, for example, as a molten and solidified layer obtained by melting a part of the base material of the ground electrode 4 and then solidifying it.

[0019] Further, as enlarged and shown in FIG. 2, in the protective layer 6, the maximum height hmax of the protective layer 6 from the first surface 41 is equal to the height Ht of the protruding portion 52. Here, the height h of the protective layer 6 is the height from the first surface 41 in the plug axis direction X, and it is sufficient that its maximum height hmax reaches the height Ht of the protruding portion 52. Preferably, throughout the entire outer periphery of the chip 5, the height h of the protective layer 6 from the first surface 41 is equal (i.e., the maximum height hmax) and reaches the height Ht of the protruding portion 52.

[0020] Specifically, the protective layer 6 has a cylindrical layer 61 that covers the outer peripheral surface of the protruding portion 52 of the chip 5. Preferably, the cylindrical layer 61 generally evenly surrounds the entire outer periphery of the protruding portion 52, and an annular end face (hereinafter, appropriately referred to as an annular surface) 611 is formed with a substantially constant width on the side facing the central electrode 3.

[0021] Further, the protective layer 6 has a base portion 60 of the protective layer 6 that covers the outside of the base end portion 51 of the chip 5. The cylindrical layer 61 is preferably located outside the base portion 60 in the direction perpendicular to the plug axis Y. At this time, the portion of the cylindrical layer 61 located outside the base portion 60 is positioned so as to cover the first surface 41 of the ground electrode 4 located outside the protruding portion 52, and the interface between the chip 5 and the ground electrode 4 can be protected.

[0022] Preferably, the protective layer 6 is formed by welding and joining the chip 5 to the ground electrode 4. That is, due to the heat generated during welding and joining, a part of the ground electrode 4 melts, and as the chip 5 sinks, it is extruded to cover the periphery of the chip 5, and the protective layer 6 is formed. In that case, as will be described later, by devising the shape of the electrode used for welding and joining, it is possible to regulate so that a part of the melted ground electrode 4 does not flow out, and the protective layer 6 made of a molten and solidified layer can be made into a desired shape.

[0023] [Configuration of Ignition Plug 1] Hereinafter, the ignition plug 1 of the present embodiment will be described in detail. As shown in FIG. 3, the ignition plug 1 has a substantially cylindrical housing 2 extending in the plug axis direction X. Inside the housing 2, a substantially cylindrical insulator 20 that insulatively holds the central electrode 3 is coaxially accommodated. A ground electrode 4 is disposed on the tip side (for example, the lower end side in FIG. 3) of the housing 2, and an end portion on the base end side (for example, the upper end side in FIG. 3) thereof is fixed to the cylindrical tip surface 21 of the housing 2.

[0024] On the tip side of the housing 2, the central electrode 3 is coaxially disposed inside the insulator 20. The central electrode 3 is supported by a stepped portion formed on the inner peripheral surface of the insulator 20 where a large-diameter head is formed, and is electrically connected to an external power source (not shown) via a resistor 13 and a terminal portion 14 disposed on the base end side thereof. Thereby, a discharge portion is provided in which the central electrode 3 and the ground electrode 4 face each other with a discharge gap G therebetween, and by supplying a high voltage for ignition, a spark discharge can be generated.

[0025] The ignition plug 1 is applied to an internal combustion engine such as various engines. For example, it is attached to the cylinder wall of the engine and is arranged such that the tip side serving as the discharge portion is exposed inside the cylinder. A screw portion 22 for attachment is formed on the outer peripheral surface of the tip side half portion of the housing 2, and is screwed into an attachment hole provided in a cylinder wall (not shown). The tip end portion of the insulator 20 is tapered and reduced in diameter toward the tip side, faces the inner peripheral surface of the housing 2 with a gap therebetween, and protrudes from the tip surface 21 of the housing 2 toward the tip side and faces the ground electrode 4.

[0026] In FIG. 1, the ground electrode 4 is integrally provided on the tip surface 21 of the housing 2, extends toward the tip side and is bent in a substantially L shape, and the extending end portion on the tip side from the bent portion extends in the direction Y perpendicular to the plug axis and faces the tip surface 31 of the central electrode 3. The central electrode 3 can be configured such that, for example, a noble metal chip 30 is joined to a tip end portion that is tapered and reduced in diameter toward the tip side. In that case, the exposed end surface of the chip 30 facing the discharge gap G becomes the tip surface 31 of the central electrode 3.

[0027] The housing 2 is made of a metal material such as an iron-based alloy, and the insulator 20 is made of an insulating ceramic material such as alumina.

[0028] In FIG. 2, on the first surface 41 side of the plate-shaped extended end portion of the ground electrode 4 that faces the tip surface 31 of the center electrode 3, the chip 5 is embedded and joined. For the chip 5, the protruding portion 52 protrudes from the first surface 41 toward the tip surface 31 of the center electrode 3 (see, for example, FIG. 1), and the base end portion 51 is embedded inside the ground electrode 4. Here, the chip 5 is formed in a flat columnar shape, and has a circular protruding end surface 521 and a circular base end surface 511 located at a position facing the protruding end surface 521.

[0029] Note that the plate width direction Z of the ground electrode 4 shown in FIG. 2 is a direction orthogonal to both the plug axis direction X and the direction perpendicular to the plug axis Y. The plug axis direction X coincides with the plate thickness direction of the ground electrode 4, and the direction perpendicular to the plug axis Y coincides with the extending direction of the extended end portion. Here, as an example, for the top view of the extended end portion, the A-A cross section that is the cross section in the plate width direction Z is shown, but the cross-sectional shapes of the chip 5 and the protective layer 6 are the same in other cross sections in the direction perpendicular to the axis Y or the radial direction.

[0030] As the material of the base material of the ground electrode 4, a Ni alloy material having oxidation resistance is preferably used. The content of Ni in the Ni alloy material can be, for example, in the range of 50% by mass to 90% by mass, and the alloying elements added to Ni include elements such as Cr, Fe, Mo, Al, Co, Mn, Si, C, and S. Specifically, a Ni-Cr alloy, a Ni-Cr-Fe alloy, etc. can be used as the Ni alloy material. Note that the ground electrode 4 may be entirely composed of the base material, or may have a configuration including a core material made of a different material inside, but at least the surface layer portion to which the chip is joined is composed of the base material of the same material as the protective layer 6.

[0031] The chip 5 is made of a noble metal alloy material containing noble metals such as Pt, Rh, and Ir. Preferably, a Pt alloy material is used. Since the Pt alloy material has a higher melting point and better oxidation resistance than the material of the ground electrode 4, the wear resistance of the chip 5 can be improved. As the Pt alloy material, an alloy material obtained by adding other noble metals (for example, Rh, Ir, etc.) to Pt, or an alloy material obtained by adding non-noble metals (for example, Ni, etc.) to Pt can be used. The chip 30 of the center electrode 3 can have a similar configuration.

[0032] Specifically, a Pt-Ni alloy can be used as the material of the chip 5. In that case, by containing the same non-noble metal as the material of the ground electrode 4, it not only contributes to cost reduction, but also reduces the difference in the linear expansion coefficient. Thereby, the thermal stress applied to the interface between the chip 5 and the ground electrode 4 due to repeated thermal cycles can be reduced. The content of Ni in the Pt-Ni alloy can be, for example, in the range of 5% by mass to 20% by mass.

[0033] A protective layer 6 is disposed outside the chip 5. The protective layer 6 is formed so as to cover the outer peripheral portion of the base end face 511 and the outer peripheral surfaces of the base end portion 51 and the protruding portion 52. Thereby, only the protruding end face 521 of the chip 5 is exposed, and the chip surface excluding the protruding end face 521 is protected by the protective layer 6. The protective layer 6 has a cylindrical layer 61 surrounding the outer peripheral side of the protruding portion 52 and a base portion 60 embedded inside the ground electrode 4.

[0034] The cylindrical layer 61 generally evenly surrounds the entire outer peripheral surface of the protruding portion 52. In the direction from the outer peripheral surface of the protruding portion 52 toward the outside, the thickness of the cylindrical layer 61 (hereinafter, appropriately referred to as the layer thickness) is the same throughout the circumferential direction, and the end face in the plug axis direction X is an annular surface 611 having a substantially constant width. The cylindrical layer 61 and the protruding portion 52 have the same height in the plug axis direction X, and the annular surface 611 is in substantially the same plane as the protruding end face 521 of the protruding portion 52.

[0035] At this time, the height h of the cylindrical layer 61 from the first surface 41 is substantially constant (i.e., the maximum height hmax) throughout the circumferential direction, from the inner circumferential side in contact with the protruding portion 52 to the outer circumferential side, and is equal to the height Ht of the protruding portion 52 (i.e., Ht≒hmax). The chip thickness T, which is the thickness of the chip 5, is represented by the distance between the protruding end surface 521 and the base end surface 511, and is the sum of the embedding depth Hd of the base end portion 51 and the height Ht of the protruding portion 52 (i.e., T = Hd + Ht).

[0036] The base portion 60 has a substantially L-shaped cross-sectional shape, covers the entire outer peripheral surface of the base end portion 51 of the chip 5, and bends radially inward from its lower end side to cover the outer peripheral side of the base end surface 511. On the outer peripheral side of the base end portion 51, the thickness of the base portion 60 does not necessarily have to be uniform. Here, the thickness of the base portion 60 becomes thinner from the first surface 41 side toward the second surface 42 side. The same applies to the outside of the base end surface 511 in the plug axis direction X, and the thickness of the base portion 60 becomes thinner from the outer peripheral side of the base end surface 511 toward the inner peripheral side.

[0037] Also, the outer peripheral side portion of the cylindrical layer 61 projects outward in a flange shape from the base portion 60. Here, the layer thickness of the cylindrical layer 61 is thicker than the thickness of the base portion 60 as a whole, and substantially covers the vicinity of the boundary between the base portion 60 and the first surface 41 in an annular shape. Specifically, the outer peripheral side surface 612 of the cylindrical layer 61 is located outside the base portion 60 on the outer peripheral side of the chip 5 and is a vertical wall rising from the first surface 41 in the plug axis direction X. The outer peripheral side surface 612 intersects at a substantially right angle with the annular surface 611 that is substantially parallel to the protruding end surface 521 of the chip 5, and the cylindrical layer 61 has a shape with a corner portion on the outer peripheral side portion facing the center electrode 3. As a result, the chip area facing the center electrode 3 is substantially expanded, and an effect of suppressing the consumption of the chip 5 is obtained.

[0038] Since such a cylindrical layer 61 protects the entire exposed outer peripheral surface of the chip 5 with a predetermined thickness, the volume of the cylindrical layer 61 that protects the chip 5 increases. Therefore, even if the spark discharge is flowed laterally by the air current, the consumption of the protective layer 6 is suppressed, and the bonding interface between the chip 5 and the ground electrode 4 is less likely to be exposed. Thereby, the bonding property between the chip 5 and the ground electrode 4 can be improved, and the peel resistance can be enhanced.

[0039] Also, it is desirable that the protective layer 6 is made of the same material as the base material of the ground electrode 4, and the base portion 60 and the cylindrical layer 61 are integrally formed by a part of the base material of the ground electrode 4. Specifically, the protective layer 6 can be formed as a molten and solidified layer obtained by melting and then solidifying a part of the first surface 41 side of the ground electrode 4 around the chip 5. In that case, depending on the chip 5 (for example, diameter Lt) and the size of the extended end portion of the ground electrode 4 (for example, plate width Lg), etc., the cylindrical layer 61 (for example, outer diameter Lw) located around the chip 5 has an appropriate layer thickness and projects outward, and the protective layer 6 is preferably formed so as to protect the outer periphery of the chip 5 together with the base portion 60.

[0040] (Modification example) As shown in FIG. 4, as long as the protective layer 6 surrounds the entire circumference of the outer periphery of the chip 5, the thickness on the outer peripheral side of the protruding portion 52 does not necessarily have to be uniform throughout, and the outer peripheral shape of the cylindrical layer 61 covering the protruding portion 52 may be a shape along a substantially circle. Here, in a part of the circumferential direction of the cylindrical layer 61, a thin portion 613 in which a part of the outer peripheral portion is missing is formed, and the outer peripheral side surface 612 has an irregular outer peripheral shape that enters the inside of the circle.

[0041] Also in that case, it is desirable that in the entire circumferential direction, the height h of the cylindrical layer 61 reaches the maximum height hmax and covers the entire protruding portion 52. Even in this way, the same effect of increasing the chip volume by the protective layer 6 surrounding the chip 5 and suppressing the consumption of the chip 5 can be obtained. And the exposure of the bonding interface between the chip 5 and the ground electrode 4 can be prevented, and the peel resistance can be improved.

[0042] (Comparative form 1) Taking the configuration of the above-described prior art as Comparative Form 1, as shown in FIG. 5, when a protruding portion 410 that protrudes toward the center electrode 3 is provided at the extended end portion of the ground electrode 4, the discharge path changes due to a high-speed air flow, and the spark discharge P easily moves to the protruding portion 410 on the side of the chip 5. As a result, when the protruding portion 410 is consumed, the spark discharge moves to the side surface or the base end side of the chip 5, and even if it is configured to suppress the outflow of the base material of the ground electrode 4 during bonding, the consumption due to the spark discharge occurs acceleratively. As a result, as shown in an enlarged view of the state after consumption in FIG. 5, the bonding interface between the chip 5 and the ground electrode 4 is exposed. In this state, when the temperature in the vicinity of the ground electrode 4 fluctuates due to fluctuations in the engine speed or the like, thermal stress concentrates on the exposed bonding interface (indicated by an arrow in FIG. 5), and there is a risk that the chip 5 may peel off.

[0043] Note that the effect of retaining the molten base material of the ground electrode 4 around the chip 5 by providing the protruding portion 410 is limited, and it is difficult to form a molten portion around the entire circumference of the chip 5. Further, since the discharge path of the spark discharge changes depending on the direction of the air flow, it is difficult to obtain a sufficient effect for preventing the peeling of the chip 5. On the other hand, by providing the protective layer 6 that surrounds the outer periphery of the chip 5 in a cylindrical shape as in this embodiment, the outer periphery of the chip 5 can be more reliably protected and the peel resistance can be improved.

[0044] [Resistance welding method for chip 5] The protective layer 6 composed of such a base portion 60 and a cylindrical layer 61 can be formed by using, for example, the shape of an electrode used for resistance welding in the process of bonding the chip 5 to the ground electrode 4. Next, with reference to FIGS. 6 and 7, a method of bonding the chip 5 and the ground electrode 4 by resistance welding and a method of forming the protective layer 6 will be described.

[0045] In FIG. 6, in the resistance welding apparatus 100, a first welding electrode 101, which is a movable electrode, and a second welding electrode 102, which is a fixed electrode, are arranged to face each other in the vertical direction of the figure, and are configured to be energizable between both electrodes by a welding power source 10. The welding power source 10 can be, for example, a commercial AC power source. On the upper surface of the second welding electrode 102, a ground electrode 4 and a tip 5 are placed in this order, and the first welding electrode 101 is arranged above them so as to be relatively movable. The first welding electrode 101 is connected to a driving device (not shown) and is provided so as to be able to apply pressure while sandwiching the ground electrode 4 and the tip 5 between both electrodes.

[0046] The first welding electrode 101 has a recess 103 on the side facing the second welding electrode 102, which restricts the shape of a protective layer 6 formed around the tip 5. The recess 103 consists of a contact surface 111 that contacts the tip 5 and applies a predetermined load, and a restricting wall 112 that surrounds the periphery of the contact surface 111. The restricting wall 112 is located at an interval on the outer peripheral side of the tip 5, and an annular end face 113 of the first welding electrode 101 located outside the restricting wall 112 faces a part of the ground electrode 4 placed on the second welding electrode 102.

[0047] By using such a first welding electrode 101, during welding, the contact surface 111 of the recess 103 presses the tip 5 toward the ground electrode 4 side, and the restricting wall 112 of the recess 103 restricts the movement of the base material of the ground electrode 4 that softens and melts. The depth Dd of the recess 103 (in other words, the height of the restricting wall 112) is the depth of the contact surface 111 from the annular end face 113, and is thicker than the tip thickness T of the tip 5 (that is, T > Dd). The depth Dd of the recess 103 can be appropriately set within a range where the annular end face 113 does not contact the ground electrode 4, according to the amount of sinking of the tip 5 during welding, the shape of the protective layer 6, etc.

[0048] Note that the amount of the tip 5 sinking during welding corresponds to the embedding depth Hd of the base end portion 51 shown in FIG. 2 above. Further, the inner diameter of the recess 103 (that is, the diameter of the contact surface 111) corresponds to the outer diameter Lw of the cylindrical layer 61 and is larger than the diameter Lt of the tip 5. Further, the outer diameter of the recess 103 is larger than the plate width Lg of the extending end portion of the ground electrode 4, and the plate width Lg is larger than the outer diameter Lw of the cylindrical layer 61 (that is, Lg > Lw > Lt).

[0049] Specifically, as shown in FIG. 7 as step (1), first, the tip 5 and the ground electrode 4 to be welded are set in the resistance welding apparatus 100 (setting step). That is, the extending end portion of the ground electrode 4 is placed on the upper surface of the second welding electrode 102, and further, the tip 5 is placed at a predetermined position on the first surface 41 (that is, the state shown in FIG. 6 above), and from that state, the first welding electrode 101 located above the tip 5 is lowered.

[0050] Next, as shown in step (2), while applying a pressing force to the tip 5 and the ground electrode 4 via the first welding electrode 101, an alternating current is supplied from the welding power source 10 between both electrodes (pressing and energizing step). As a result, a welding current flows in a state where the tip 5 and the ground electrode 4 are sandwiched between the first welding electrode 101 and the second welding electrode 102, and Joule heat is generated at the interface between the tip 5 and the ground electrode 4. Along with this, a part of the base material of the ground electrode 4 having a melting point lower than that of the tip 5 is softened and melted, and the tip 5 sinks into the base material of the ground electrode 4.

[0051] At that time, as shown in step (3), the movement of the melted base material is restricted by the recess 103 of the first welding electrode 101, and the protective layer 6 is formed (protective layer forming step). Specifically, on the outer peripheral side where the amount of current flowing is larger than that inside the tip 5, the temperature of the ground electrode 4 in contact with the tip 5 becomes high, and the melted base material is pushed out from the outer peripheral edge portion of the base end surface 511 to the outside while crawling along the outer peripheral surface of the tip 5. At this time, due to the sinking of the tip 5, the annular end surface 113 of the first welding electrode 101 descends to a position close to the first surface 41 of the ground electrode 4 with a gap d, and restricts the melted base material from moving outward.

[0052] As a result, the molten base material is filled into the space surrounded by the contact surface 111 and the restricting wall 112 of the recess 103 and the first surface 41 facing the contact surface 111, and a cylindrical layer 61 that covers the protruding portion 52 of the chip 5 is formed. At the proximal end side of the cylindrical layer 61, around the outer peripheral corner of the proximal end portion 51 of the chip 5, the base material of the ground electrode 4 melts to form a base portion 60 integral with the cylindrical layer 61.

[0053] Thereafter, when the energization is stopped, the molten base material is cooled and solidified (cooling step). That is, a protective layer 6 composed of a cylindrical layer 61 having a predetermined thickness corresponding to the shape of the recess 103 and a base portion 60 following it is formed. Note that the amount of energization in the pressure energization step is maintained at a temperature at which only the base material of the ground electrode 4 having a lower melting point melts and the noble metal chip 5 does not melt around the welding interface. For example, for a Pt alloy material mainly containing Pt (melting point: 1770 °C) and a Ni alloy material mainly containing Ni (melting point: 1455 °C), the alloy elements and their content ratios can be adjusted respectively to be appropriately adjusted to a desired melting point.

[0054] In this way, when the chip 5 is joined to the ground electrode 4 by resistance welding, a recess 103 is provided in the first welding electrode 101 on the chip 5 side, and a protective layer 6 surrounding the chip 5 is formed as a configuration in which the molten burrs generated during welding are accommodated in the space formed on the outer periphery of the chip 5. As a result, the molten base material extruded from the proximal end side of the chip 5 to the first surface 41 remains inside the recess 103 and surrounds the welding interface between the chip 5 and the ground electrode 4 where a part thereof is embedded in the base material of the ground electrode 4 over the entire circumference of the edge portion in contact with the first surface 41. That is, the restricting wall 112 suppresses the outflow of the molten base material, and the molten base material that climbs up to the contact surface 111 solidifies to form a cylindrical layer 61 having the same height as the protruding end surface 521 of the chip 5.

[0055] As a result, the protective layer 6 surrounds the entire circumference of the welding interface between the chip 5 and the ground electrode 4 to suppress its exposure, and while the cylindrical layer 61 that protrudes outward from the base portion 60 protects the protruding portion 52 of the chip 5, it functions as a part thereof. That is, the larger the volume of the cylindrical layer 61, the greater the substantial electrode volume, and it is possible to prevent the chip 5 from being consumed or peeled off and extend the electrode life.

[0056] It is desirable that the depth Dd of the recess 103 satisfies the following formula 1 with respect to the chip thickness T of the chip 5 and the embedding depth Hd of the base end portion 51. Formula 1: Dd < T - Hd Since the resistance welding proceeds with the protruding end face 521 of the chip 5 in contact with the contact surface 111 of the first welding electrode 101, when the recess 103 becomes deeper, the height Ht (= T - Hd) of the protruding portion 52 or more, and at the end of the welding process, there is a possibility that the annular end face 113 of the first welding electrode 101 contacts the first surface 41 of the ground electrode 4.

[0057] In that case, as shown in FIG. 8, sputtering due to energization occurs on the first surface 41, sputter holes 411 are formed, and there is a possibility that cracks progress from the sputter holes 411 and lead to damage to the ground electrode 4. Alternatively, sputter burrs 412 are likely to adhere to the periphery of the sputter holes 411, and it becomes necessary to add a process for removing the sputter burrs 412. Therefore, while appropriately setting the embedding depth Hd, within the range of the above-described formula 1 (Dd < T - Hd), it is advisable to set the depth Dd of the recess 103 so as to prevent the outflow of the molten base material and prevent sputtering.

[0058] The inner diameter of the recess 103 can be appropriately set so that the molten base material extruded during resistance welding fills the recess 103 and a cylindrical layer 61 having a desired shape is formed. At this time, the height h of the cylindrical layer 61 is substantially constant over the entire circumference, becomes the maximum height hmax from the first surface 41 of the protective layer 6, and is equivalent to the height Ht of the protruding portion 52 (h ≒ hmax ≒ Ht).

[0059] Note that the height h of the cylindrical layer 61 satisfies the following formula 2 with respect to the depth Dd of the recess 103 and the gap d between the first welding electrode 101 and the first surface 41 at the end of welding. Formula 2: h (hmax) = Dd + d Here, the gap d can be arbitrarily set according to the chip shape, the desired height h of the cylindrical layer 61, etc. For example, it can be set to 0.01 mm or more. Within the range where the first welding electrode 101 and the ground electrode 4 do not come into contact, the smaller the gap d, the larger and deeper the depth Dd of the recess 103 can be made, making it easier to suppress the outflow of the molten base material to the outside of the recess 103. Preferably, the gap d is set to be larger than 0.01 mm. For example, by setting it to about 0.02 mm or more, it is possible to prevent shunting and spatter generation due to the contact between the first welding electrode 101 and the ground electrode 4.

[0060] Also, the embedding depth Hd of the base end portion 51, which is the amount of sinking of the chip 5, can be arbitrarily set according to the chip shape, size, etc. For example, it can be set so that the chip peeling rate in the combustion environment inside the engine cylinder is at the minimum level. Specifically, at an embedding depth Hd of about 1 / 10 or more of the chip thickness T, the chip peeling rate is significantly reduced. Preferably, the embedding depth Hd is set to be deeper than 1 / 10 of the chip thickness T. For example, by setting it to about 1 / 5 to 1 / 2 of the chip thickness T, it is possible to almost prevent the peeling of the chip 5. On the other hand, the larger the embedding depth Hd, the relatively lower the height h of the cylindrical layer 61, and the volume functioning as the chip 5 decreases. Therefore, within the range where peeling in the use environment can be suppressed, it is advisable to appropriately set the embedding depth Hd so that the height h of the cylindrical layer 61 surrounding the protruding portion 52 becomes higher.

[0061] Preferably, as in the test examples described later, a predetermined thermal cycle test can be performed according to the chip shape, size, etc., to optimize the embedding depth Hd. Specifically, in the chip 5 with a chip diameter (diameter Lt) of about 1 mm to 1.5 mm, when the chip thickness T is about 0.2 mm, the embedding depth Hd should be made larger than 0.02 mm. Preferably, by setting the embedding depth Hd to, for example, 0.03 mm or more, the effect of suppressing the peeling of the chip 5 due to thermal cycles can be enhanced.

[0062] Thus, by appropriately controlling the electrode shape and resistance welding conditions constituting the resistance welding apparatus 100, the protective layer 6 that surrounds and protects the outer periphery of the chip 5 in a cylindrical shape can be formed into a desired shape.

[0063] (Evaluation Test 1) Regarding the spark plug 1 configured as in the above-described Embodiment 1, a noble metal chip 5 was joined to the ground electrode 4 using the resistance welding apparatus 100 shown in FIG. 6 above, and a protective layer 6 was formed to evaluate the peel resistance of the chip 5. First, for the columnar chip 5 used in the evaluation test, the optimal embedding depth Hd was examined from the relationship between the embedding depth Hd of the base end portion 51 after joining and the chip peeling rate, and based on the result, the depth Dd of the recess 103 of the first welding electrode 101 was determined. Then, a test sample in which the chip 5 was welded to the ground electrode 4 was produced using the resistance welding apparatus 100 having the determined recess 103 shape, and evaluation was performed by an engine durability evaluation test.

[0064] <Determination of the depth Dd of the recess 103> As the material of the noble metal chip 5, a Pt-Ni alloy (90 mass% Pt - 10 mass% Ni) was used, and a chip 5 formed into a flat columnar shape (diameter φ1.3 mm × thickness 0.2 mm) was prepared to investigate the relationship between the embedding depth Hd and the chip peeling rate. The embedding depth Hd was changed in the range of about 0.005 mm to about 0.12 mm by changing the resistance welding conditions using the resistance welding apparatus 100 for a plurality of chips 5 having the same shape. Also, as the ground electrode 4, a plate-shaped Ni alloy material (Ni-Cr alloy plate) having a predetermined cross-sectional dimension (thickness 1.3 mm × width 2.6 mm) was used. The resistance welding apparatus 100 had the first welding electrode 101 as a W electrode and the second welding electrode 102 as a Cu-W electrode, and the welding power source 10 was a single-phase AC power source.

[0065] As shown in FIG. 9, for a plurality of samples in which the chip 5 was resistance welded at various embedding depths Hd, a total thermal stress equivalent to 100,000 km of engine running was applied, and then the state of the samples was observed to calculate the chip peeling rate. The thermal stress test was performed under the following conditions. That is, in a thermostatic heat bench capable of controlling the temperature, after the sample was heated to 950°C and held for 6 minutes, it was cooled and held at 150° for 6 minutes, which was defined as one cycle, and this was repeated 200 cycles. Then, the sample was taken out into the room and air-cooled.

[0066] As shown in FIG. 10, the chip peeling rate is the ratio of the peeling length H (=H1 + H2) at the base end face 511 (diameter Lt) of the chip 5 when the sample of the thermal stress test is cut along the central axis of the chip, and can be calculated based on the following formula 3. Formula 3: [(H1 + H2) / Lt] × 100 H1 and H2 in Formula 3 are the lengths of the peeled portions generated between the base end face 511 and the base 60 of the protective layer 6 and the ground electrode 4 located on the base end side thereof on the cut surface of the chip 5, and the peeling length H is represented by the sum of the lengths of the peeled portions with respect to the chip diameter.

[0067] In Fig. 9, the chip peeling rate exceeds 80% when the embedding depth Hd of chip 5 is 0.01 mm or less, and decreases rapidly as the embedding depth Hd increases. Specifically, when it exceeds 0.02 mm, it greatly decreases from around 30% to 20% or less, and becomes around 10% or less when it is 0.04 mm or more, and converges approximately at about 0.12 mm. From these results, the embedding depth Hd at which the chip peeling rate becomes approximately the minimum level is set to 0.03 mm or more where the slope of the graph of the chip peeling rate changes abruptly, and it is assumed that the embedding depth Hd is set to 0.03 mm or more.

[0068] Then, the depth Dd of the recess 103 is set from the embedding depth Hd and the chip thickness T so as to satisfy the relationship of the above-described formula 1 (Dd < T - Hd). Here, for example, assuming that the embedding depth Hd is set to 0.04 mm and the chip thickness T is 0.2 mm, the depth Dd of the recess 103 is set to 0.15 mm (<T - Hd = 0.2 mm - 0.04 mm).

[0069] <Engine Durability Evaluation Test> Next, at the depth Dd (0.15 mm) of the recess 103 determined in this way, the chip 5 was welded and joined to the ground electrode 4 using the resistance welding apparatus 100 so that the embedding depth Hd was a predetermined value (0.04 mm) (experimental example). By observing the shape and cross-section of the chip after the welding and joining, it was confirmed that a protective layer 6 was formed surrounding the entire circumference of the outer periphery of the chip 5 as shown in the right figure of Fig. 11. In this sample, as shown as a modified example in Fig. 4 above, the outer peripheral shape of the cylindrical layer 61 covering the protruding portion 52 was approximately circular, and a thin portion 613 was observed in part.

[0070] Also, the chip 5 was welded and joined to the ground electrode 4 under the same conditions except that the first welding electrode 101 in which the recess 103 was not formed was used (comparative example). By observing the chip shape and cross-section after welding, as shown in the left figure of Fig. 11, it was confirmed that in the comparative example, a molten and solidified layer 61a was formed around about half of the outer circumference of the chip 5. In this sample, the maximum height of the molten and solidified layer 61a did not reach the protruding end face 521 of the chip 5, and it did not have a shape with a corner at the outer peripheral side portion on the central electrode 3 side.

[0071] A plurality of ignition plugs 1 each including a chip 5 having a protective layer 6 formed in this way were prepared for the experimental example and the comparative example respectively (n = 4), and an engine durability evaluation test was conducted. That is, under the conditions shown in Fig. 12, in the ignition plug 1 attached to the engine, a full-open mode in which the throttle valve is fully opened and fuel injection is performed so that the thermal stress applied to the ground electrode 4 becomes maximum, and a stop mode in which the engine is then stopped and held were repeated. Specifically, in the full-open mode, the engine was operated at an engine speed of 6000 rpm for 120 seconds, and in the stop mode, the engine stop was set to 60 seconds. Taking this as one cycle, 3000 cycles were performed.

[0072] At this time, due to engine operation, the ground electrode 4 reached almost the maximum temperature, and by stopping the engine from here, the temperature difference became the largest and the maximum thermal stress was applied. The chip peeling rates were calculated for the experimental example and the comparative example respectively, and the results are shown in Fig. 13. As a result, as shown in Fig. 13, in the comparative example, all the chip peeling rates exceeded 30%, and their average was 33%. On the other hand, in the experimental example, all the chip peeling rates were less than 10%, and their average was greatly reduced to 3%.

[0073] Further, when observing the cross-section of the sample after the test, as shown in the left figure of Fig. 14, in the sample of the comparative example, in the portion of the extension end where the molten solidified layer 61a was not formed, the consumption of the base material of the ground electrode 4 advanced to the base of the chip 5, and it was confirmed that the adjacent chip 5 was partially peeled off. When such partial peeling occurs, the discharge gap G may become too narrow compared to the predetermined interval and misfire. Also, when the peeling progresses and the chip 5 falls off, the discharge gap G becomes too large and spark discharge does not occur, resulting in misfire.

[0074] On the other hand, as shown in the right figure of Fig. 14, in the sample of the experimental example, the base material of the ground electrode 4 remained, and almost no peeling occurred on the entire circumference of the chip 5. Thus, it was confirmed that in the portion protected by the protective layer 6, the consumption of the base material of the ground electrode 4 was suppressed and the peeling of the chip 5 could be suppressed.

[0075] (Embodiment 2) Embodiment 2 of the spark plug for an internal combustion engine will be described with reference to Figs. 15 and 16. In this embodiment, the shape of the protective layer 6 surrounding the outer periphery of the chip 5 is different from that of the above Embodiment 1. The basic configuration of the spark plug 1, the center electrode 3, and the chip 5 provided on the ground electrode 4 is the same as that of the above Embodiment 1, and the description thereof will be omitted. Among the reference numerals used in and after Embodiment 2, those the same as the reference numerals used in the previously described embodiments represent the same components and the like as those in the previously described embodiments unless otherwise specified.

[0076] In the above Embodiment 1, in the protective layer 6, the cylindrical layer 61 covering the protruding portion 52 of the chip 5 has a shape in which the height h is substantially constant over the entire circumference of the chip 5 and becomes the maximum height hmax from the first surface 41, but it is not limited thereto.

[0077] For example, as shown in FIG. 15, in a part of the outer periphery of the chip 5, a corner is not formed on the outer peripheral side portion of the cylindrical layer 61, and a portion 614 may be provided in which the height h of the cylindrical layer 61 is lower than the maximum height hmax (i.e., the height Ht of the protruding portion 52) from the inner peripheral side to the outer peripheral side as a whole. In that case, the outer peripheral surface of the protruding portion 52 will be exposed in a part on the side of the central electrode 3, but it is sufficient that the cylindrical layer 61 is formed so as to have a sufficient volume as a whole, and the effect of suppressing the exposure of the bonding interface between the chip 5 and the ground electrode 4 can be obtained as in the first embodiment.

[0078] Alternatively, as shown in FIG. 16, the cylindrical layer 61 may have a shape without corners on the outer peripheral side portion in the entire circumferential direction, and the height h of the cylindrical layer 61 may change from the inner peripheral side in contact with the protruding portion 52 to the outer peripheral side. In that case, for example, the cylindrical layer 61 has an inclined surface 615 in which the height h of the cylindrical layer 61 becomes lower as it moves away from the chip 5 on the entire outer periphery of the chip 5, and the maximum height hmax is obtained on the inner peripheral side in contact with the chip 5.

[0079] Thus, the shape of the protective layer 6 can be appropriately changed as long as it surrounds the entire outer periphery of the chip 5 in a cylindrical shape and the maximum height hmax is within the range of the height Ht of the protruding portion 52, and the effect of improving the bondability of the chip 5 can be obtained.

[0080] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist thereof.

Explanation of Reference Numerals

[0081] 1 Spark plug 2 Housing 3 Central electrode 4 Ground electrode 5 Chip 51 Base end portion 52 Protruding portion 511 Base end face 521 Protruding end face 6 Protective layer 61 Cylindrical layer 60 Base

Claims

1. A center electrode (3) that is insulated and held inside a cylindrical housing (2) and protrudes beyond the tip of the housing, and A ground electrode (4) that extends from the tip of the housing and faces the center electrode in the plug axis direction (X), and A noble metal chip (5) that is provided integrally with the ground electrode and forms a discharge gap (G) between the center electrode, and an ignition plug (1) comprising: The chip has a base end portion (51) embedded in the ground electrode and a protruding portion (52) that protrudes toward the center electrode side from the surface (41) of the ground electrode on the side facing the center electrode, In a direction (Y) orthogonal to the plug axis direction, a protective layer (6) that cylindrically surrounds the outer peripheries of the base end portion and the protruding portion is provided outside the chip, The protective layer is made of the same material as the base material of the ground electrode, and in the plug axis direction, the maximum height (hmax) of the protective layer from the surface is equal to the height (Ht) of the protruding portion. An ignition plug.

2. The ignition plug according to claim 1, wherein the protective layer has a height equal to the height of the protruding portion over the entire outer periphery of the chip.

3. The ignition plug according to claim 2, wherein the protective layer has a cylindrical layer (61) that covers the outer peripheral surface of the protruding portion, and the cylindrical layer has an annular end face (611) on the side facing the center electrode.

4. The ignition plug according to claim 3, wherein the cylindrical layer is located outside the base portion (60) of the protective layer that covers the outside of the base end portion in a direction (Y) orthogonal to the plug axis direction.

5. The ignition plug according to claim 1, wherein the protective layer is a melt-solidified layer obtained by melting and solidifying the base material of the ground electrode.

6. The ignition plug according to any one of claims 1 to 5, wherein the chip has an embedded depth (Hd) of the base end portion that is 1 / 10 or more of the chip thickness (T), which is the distance between both end faces in the plug axis direction.

7. A method for manufacturing an ignition plug according to any one of claims 1 to 5, comprising A welding step of joining the chip to the ground electrode by resistance welding, In the welding step, a first welding electrode (101) having a recess (103) with an inner diameter larger than the diameter of the chip is used. The first welding electrode and the second welding electrode (102) are opposed to each other in the plug axis direction, and the chip and the ground electrode are disposed therebetween such that the chip is positioned inside the recess. By energizing while sandwiching the chip and the ground electrode between the first welding electrode and the second welding electrode, the base material of the ground electrode is melted. A method of manufacturing an ignition plug, wherein the molten base material of the ground electrode climbs up and covers the outside of the chip inside the recess, thereby forming the protective layer having a shape along the recess. **Claim 8** The depth (Dd) of the recess and the embedding depth (Hd) of the base end portion of the chip are set such that Dd < T - Hd with respect to the chip thickness (T) which is the distance between both end faces of the chip in the plug axis direction. The method of manufacturing an ignition plug according to claim 7.

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