JP2009054572A - Spark plug for internal combustion engine and manufacturing method of spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain a rare-metal chip from being peeled off caused by a difference of thermal stresses, and as a result, to aim at elongation of life of a spark plug. <P>SOLUTION: The spark plug 1 is provided with a ground electrode 27, to a tip part of which 27, a rare-metal chip 32 is joined. The ground electrode 27 and the rare-metal chip 32 are joined by a melting part 34 formed by melting a metal material and a rare-metal material. The melting part 34 is provided with a base-end-side melting part A formed at a base end side of the ground electrode 27 and a front-end-side melting part B formed at a front end side of the ground electrode 27. As the melting part 34 is viewed at a cross section including a center axis Y of the rare-metal chip 32 along a longitudinal direction of the ground electrode 27, a sum of a cross-sectional area of the base-end-side melting part A and a cross-sectional area of the front-end-side melting part B is to be 4.0 mm<SP>2</SP>or more, and a cross-sectional area of the front-end-side melting part B is 1.1 to 1.3 times greater than that of the base-end-side meting part A. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a spark plug used for an internal combustion engine and a method for manufacturing the same.

  A spark plug for an internal combustion engine is attached to an internal combustion engine (engine) and used for ignition of an air-fuel mixture in a combustion chamber. In general, a spark plug is composed of an insulator having a shaft hole, a center electrode inserted through the shaft hole, a metal shell provided on the outer periphery of the insulator, and a front end surface of the metal shell. And a ground electrode that forms a spark discharge gap therebetween.

Further, for the purpose of improving the spark wear resistance and the ignitability, a noble metal tip made of a noble metal alloy such as platinum is joined to the tip of a ground electrode made of a heat-resistant and corrosion-resistant metal such as a nickel alloy. In joining the noble metal tip to the ground electrode, a technique has been proposed in which spot welding is performed with a laser beam along the outer edge of the joint surface between the ground electrode and the noble metal tip (see, for example, Patent Document 1).
Japanese Patent No. 3460087

  By the way, in recent years, there has been a tendency to develop an engine with a high compression ratio in order to increase the output of the engine. In such a combustion chamber of the engine, the noble metal tip and the ground electrode are exposed to higher temperature conditions. It is. In addition, the ground electrode is less likely to receive heat toward the tip side, and the closer to the tip side of the ground electrode, the higher the temperature. For this reason, in the noble metal tip, the ground electrode, and the joint portion between them, there is a possibility that a difference occurs between the thermal stress acting on the tip side portion of the ground electrode and the thermal stress acting on the base side portion. As a result, there is a concern that oxide scale, cracks, and the like occur at the boundary portion between the noble metal tip and the ground electrode, and the noble metal tip falls off the ground electrode.

  In recent years, spark plugs have been reduced in size due to the demand for smaller engines, and the metal shell itself tends to be thinner and thinner, and the ground electrode to be bonded to this has a smaller bonding area with the metal shell. The size must be further reduced because it must be done. As a result, the heat-drawing performance of the ground electrode is further deteriorated, and there is a possibility that the above-described problems become more remarkable.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a spark plug for an internal combustion engine that can prevent the noble metal tip from falling off due to a difference in thermal stress, and thereby achieve a long life. And it is providing the manufacturing method.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. A spark plug for an internal combustion engine of this configuration includes a cylindrical insulator having an axial hole penetrating in the axial direction;
A center electrode inserted in the shaft hole;
A cylindrical metal shell provided on the outer periphery of the insulator;
A grounding provided at the distal end portion of the metal shell such that a proximal end of a noble metal tip mainly composed of a noble metal is joined to one side surface of the distal end side of the own metal, and the distal end surface of the noble metal tip faces the distal end surface of the center electrode. Electrodes,
A spark plug for an internal combustion engine comprising:
The noble metal tip is joined by forming a melted part in which the noble metal tip and the ground electrode have melted around itself,
When looking at the melting portion of the cross section along the longitudinal direction of the ground electrode and including the central axis of the noble metal tip,
The total cross-sectional area of the cross-sectional area of the base-end side melted portion A located on the base end side of the ground electrode and the cross-sectional area of the front-end side melted portion B located on the front end side of the ground electrode is 4 mm ² or more, The cross-sectional area of the front end side melted part B is 1.1 to 1.3 times the cross sectional area of the base end side melted part A.

  In some cases, at least one of the base end side melted part A and the front end side melted part B may be formed so as to overlap the center axis of the noble metal tip. In this case, it is desirable to determine the cross-sectional area as follows. That is, along the longitudinal direction of the ground electrode and in a cross section including the central axis of the noble metal tip, an outer shape line forming the outer shape of the proximal end side fusion portion A and an outer shape line forming the outer shape of the distal end side fusion portion B Two melting points are connected by a straight line, the melted part divided on the base end side melted part A side is determined as “base end side melted part A”, and the melted part divided on the front end side melted part B side is “tip side melted” Part B "is determined. Further, the “noble metal material” includes not only a material composed only of a noble metal such as platinum (Pt) or iridium (Ir) but also a material mainly composed of a noble metal.

  According to the above configuration 1, since the noble metal tip is joined to the tip portion of the ground electrode, it is possible to improve the spark resistance and the ignitability.

  On the other hand, as described above, the tip end side of the ground electrode tends to be hard to draw heat. Therefore, under a high temperature condition, a larger heat is generated in a portion closer to the tip end portion of the ground electrode, such as a noble metal tip or a melted portion. Stress is likely to occur. In particular, when focusing on the distal end side and the proximal end side with the center of the noble metal tip as a base point, a relatively large thermal stress is generated on the distal end side, while a relatively small thermal stress is generated on the proximal end side. . The melted part formed by welding between the ground electrode and the noble metal tip absorbs the difference in thermal expansion between the two and suppresses the noble metal tip from peeling off from the ground electrode. If the melted portion on the rear end side has the same area, the difference in thermal stress is not absorbed, and the noble metal tip may peel off at the boundary portion between the ground electrode and the noble metal tip.

  In this regard, in the above-described configuration 1, the cross-sectional area of the distal end side melted portion B is along the longitudinal direction of the ground electrode and when the melted portion of the cross section including the central axis of the noble metal tip is viewed. The cross-sectional area is 1.1 to 1.3 times. For this reason, the length of the boundary between the tip-side molten portion B and the noble metal tip (the contact area between the tip-side molten portion and the noble metal tip) and the length of the boundary between the tip-side molten portion B and the ground electrode (tip) The contact area between the molten portion on the side and the ground electrode) can be further increased. Therefore, since more energy can be absorbed in the melted portion on the tip side, distortion of thermal stress applied to the noble metal tip can be reduced. Thereby, the balance of thermal stress can be prevented from being lost, and the peel resistance (dropout resistance) of the noble metal tip can be improved. As a result, the life of the spark plug can be extended.

Moreover, in the said structure 1, the total cross-sectional area of the cross-sectional area of the base end side fusion | melting part A and the cross-sectional area of the front end side fusion | melting part B shall be 4.0 mm < ² > or more. As a result, sufficient welding strength can be ensured, and the above-described effects can be more reliably exhibited.

In addition, when the total cross-sectional area of the cross-sectional area of the base end side melted part A and the cross-sectional area of the front end side melted part B is less than 4.0 mm ² , the welding strength becomes insufficient, and the above-described action There is a risk that the effect will not be sufficiently achieved. Further, when the cross-sectional area of the distal end side melted portion B is less than 1.1 times the cross sectional area of the proximal end side melted portion A, the thermal stress from the distal end side of the ground electrode is not sufficiently relaxed, and the above-described effects May not be fully played. On the other hand, when the cross-sectional area of the distal end side melted portion B is greater than 1.3 times the cross sectional area of the proximal end side melted portion A, the thermal stress applied from the distal end side of the ground electrode to the noble metal tip is extremely relaxed. There is a risk of being overkill. As a result, the thermal stress applied to the noble metal tip from the distal end side of the ground electrode becomes smaller than the thermal stress applied to the noble metal tip from the proximal end side of the ground electrode, and the balance of thermal stress is as described above. There is a risk of collapse in the opposite direction.

Configuration 2. The spark plug for an internal combustion engine of this configuration is the above-described configuration 1, wherein the noble metal tip has its base end embedded in the ground electrode,
The proximal end side fusion part A and the distal end side fusion part B are each
The noble metal tip-side melted portion C on the noble metal tip side of the region partitioned by the rectangular first virtual outline of the noble metal tip before the melted portion is formed,
Of the area defined by the first virtual outline, the area on the ground electrode side, and further, the ground electrode side defined by the second virtual outline of the ground electrode before formation of the melting portion And the ground electrode side melting part D of
In at least one of the proximal end side fusion part A and the distal end side fusion part B,
The cross-sectional area of the ground electrode side melted portion D in the cross section along the longitudinal direction of the ground electrode and including the central axis of the noble metal tip is 1.0 to 2 times the cross sectional area of the noble metal tip side melted portion C. It is characterized by being set to 0 times.

  According to the configuration 2, the cross-sectional area of the ground electrode-side melted portion D is 1.0 times the cross-sectional area of the noble metal tip-side melted portion C for at least one of the base end-side melted portion A and the distal end-side melted portion B. It is set to -2.0 times. As a result, the linear expansion coefficient of the melted part does not become too close to the linear expansion coefficient of either the noble metal material or the metal material. That is, the volume change of the melted part and the volume change of the noble metal material are not greatly different due to thermal expansion, and the volume change of the melted part and the volume change of the metal material are also greatly different. Disappear. As a result, it is possible to suppress an increase in shearing force due to thermal expansion at the boundary portion between the molten portion and the noble metal tip or at the boundary portion between the molten portion and the ground electrode, and as a result, oxide scales and cracks at each boundary. Etc. can be suppressed. As a result, it is possible to further improve the peel resistance.

  In addition, when the cross-sectional area of the ground electrode side melted part D is less than 1 times the cross-sectional area of the noble metal tip side melted part C, the linear expansion coefficient of the melted part is closer to the linear expansion coefficient of the noble metal material. As a result, the difference in linear expansion coefficient between the fusion zone and the ground electrode becomes larger. As a result, the shear force at the boundary portion between the melted portion and the ground electrode increases with thermal expansion, and there is a risk that cracks or the like may occur between the melted portion and the ground electrode. On the other hand, when the cross-sectional area of the ground electrode-side melted portion D is larger than twice the cross-sectional area of the noble metal tip-side melted portion C, the linear expansion coefficient of the melted portion approaches the linear expansion coefficient of the metal material. End up. For this reason, an increase in shearing force between the melted part and the noble metal tip is caused, and as a result, cracks and the like may occur between the melted part and the noble metal tip.

Configuration 3. The spark plug for the internal combustion engine of the present configuration has the longitudinal direction of the ground electrode in the configuration 1 or 2, and a cross section including the central axis of the noble metal tip.
E (mm) is the shortest distance from the tip of the noble metal tip to the base side melted portion A,
When the shortest distance from the tip of the noble metal tip to the tip side melted portion B is F (mm),
The following expressions (1) and (2) are satisfied.

1.05 ≦ E / F ≦ 1.25 (1)
0.3 mm ≦ E ≦ 0.5 mm (2)
Generally, when a noble metal tip is placed under a high temperature condition, the oxidation resistance is lowered, and consequently the wear resistance is lowered. Here, as described above, the tip of the ground electrode is less likely to draw heat, and the portion closer to the tip side of the ground electrode is likely to have a higher temperature. Therefore, the tip of the ground electrode is also connected to the noble metal tip bonded to the ground electrode. The part located on the side tends to be hot. Therefore, the portion of the noble metal tip that is located on the distal end side of the ground electrode is more easily consumed by the discharge than the portion that is located on the proximal end side, and the noble metal tip may be consumed unevenly. If the noble metal tip is consumed in an uneven manner, the discharge position becomes unstable, causing variations in the way the flame spreads, which may lead to a reduction in combustion efficiency.

  In this regard, according to the above-described configuration 3, the shortest distance from the tip of the noble metal tip to the base side melted portion A is E (mm), and the shortest distance from the tip of the noble metal tip to the tip side melted portion B is F (mm). ), The melted part is formed so as to satisfy 1.05 ≦ E / F ≦ 1.25. In other words, the surface area of the portion of the noble metal tip located on the distal end side of the ground electrode is made smaller than the surface area of the portion located on the proximal end side of the ground electrode. Therefore, it is possible to reduce the amount of heat received at the tip side of the ground electrode of the noble metal tip, which tends to be higher in temperature, and as a result, the portion of the noble metal tip located at the tip side of the ground electrode and the base end side. The temperature difference from the part to be performed can be reduced. As a result, uneven consumption of the noble metal tip can be effectively prevented, the discharge position can be stabilized, and the combustion efficiency can be improved.

  By the way, if the surface area of the part located on the tip side of the ground electrode in the noble metal tip is reduced, the surface area of the part located on the tip side of the ground electrode in the melted part is increased. For this reason, there is a concern that the amount of heat received at the site increases, and the peel resistance and durability are reduced. However, generally, a metal material (for example, Ni alloy) that forms a ground electrode has a lower thermal conductivity than a noble metal material that forms a noble metal tip. The thermal conductivity of the melted portion that is melted is smaller than the thermal conductivity of the noble metal tip. Therefore, the heat from the combustion gas is relatively difficult to be transmitted to the melted part, and even if the surface area of the melted part increases, it is unlikely that the amount of heat received by the melted part will increase extremely, and the peel resistance It is also difficult to happen such as deterioration of durability.

  Note that when 1.05> E / F, the amount of heat received at the portion of the noble metal tip located on the tip side of the ground electrode cannot be sufficiently reduced, and the above-described effects are sufficiently achieved. There is a risk that it will not be. Further, when E / F> 1.25, the amount of heat received at the portion of the noble metal tip located on the tip side of the ground electrode is extremely reduced, and the base end side of the ground electrode of the noble metal tip. There is a possibility that the wear at the part located in the region is likely to proceed. In addition, when 0.3 mm> E, the melted portion is formed at a position relatively close to the spark discharge gap, and thus discharge is likely to occur between the melted portion. As a result, the discharge position may not be sufficiently stabilized. At the same time, when E> 0.5 mm, the noble metal tip protrudes further from the ground electrode, and the amount of heat received by the noble metal tip increases. The balance of the temperature difference with the part located on the end side may be lost, and as a result, the above-described effects may not be sufficiently achieved.

Configuration 4. A manufacturing method of the spark plug of this configuration includes a cylindrical insulator having an axial hole penetrating in the axial direction;
A center electrode inserted in the shaft hole;
A cylindrical metal shell provided on the outer periphery of the insulator;
A base end of a noble metal tip mainly composed of a noble metal is bonded to one side surface of its own tip side, and the tip end surface of the noble metal tip is provided at the tip end portion of the metal shell so as to face the tip end surface of the center electrode. A ground electrode,
The noble metal tip is a method of manufacturing a spark plug formed by bonding a melted portion in which the noble metal tip and the ground electrode are melted around itself.
Forming the melted portion by irradiating a laser beam to the outer peripheral portion of the ground electrode and the joint surface of the noble metal tip, and including a joining step of joining the noble metal tip to the ground electrode;
In the joining step, the laser beam is adjusted so that the melting energy for the portion located on the distal end side of the ground electrode is larger than the melting energy for the portion located on the proximal end side of the ground electrode. Irradiating.

  According to the configuration 4, the portion of the melting portion located on the distal end side of the ground electrode (the distal end side fusion portion B) is made larger than the portion located on the proximal end side (the proximal end side fusion portion A). For this reason, it is possible to relatively easily and more reliably manufacture a spark plug having the same effects as those of the above-described configuration 1 or the like.

Configuration 5. A method for manufacturing a spark plug of this configuration is a method for manufacturing a spark plug for an internal combustion engine according to any one of the above configurations 1 to 3,
Forming the melted portion by irradiating a laser beam to the outer peripheral portion of the ground electrode and the joint surface of the noble metal tip, and including a joining step of joining the noble metal tip to the ground electrode;
In the joining step, the laser beam is adjusted so that the melting energy for the portion located on the distal end side of the ground electrode is larger than the melting energy for the portion located on the proximal end side of the ground electrode. Irradiating.

  According to the said structure 5, the effect similar to the said structure 4 will be show | played fundamentally.

  Configuration 6. The spark plug manufacturing method of this configuration is configured to increase the melting energy from the portion located on the proximal end side of the ground electrode to the portion located on the distal end side of the ground electrode in the configuration 4 or 5. And irradiating with a laser beam.

  According to the said structure 6, the effect similar to the said structure 4 etc. will be show | played fundamentally. In addition, according to the present configuration 6, the melting portion is formed so as to gradually increase from a portion located on the proximal end side of the ground electrode to a portion located on the distal end side. Thereby, the balance of the thermal stress applied to the noble metal tip can be further suppressed, and the peel resistance of the noble metal tip can be further improved.

Configuration 7. The manufacturing method of the spark plug of this configuration is any one of the above configurations 4 to 6, and in the joining step,
After fixing the direction of laser beam irradiation,
Of the central axis of the noble metal tip, the axis located on the noble metal tip side is based on the intersection of the central axis of the noble metal tip and a plane including one side surface of the ground electrode, toward the base end side of the ground electrode. The melting part is formed by rotating the noble metal tip and the ground electrode with an inclined axis as a rotation axis.

  As a method for realizing the configuration 3, for example, it is conceivable to change the irradiation direction of the laser beam (position where the laser beam strikes) between a portion located on the distal end side and a portion located on the proximal end side of the ground electrode. . However, when this method is used, it is necessary to separately provide a means for changing the irradiation direction, which may lead to situations such as complication of the apparatus and a decrease in production efficiency.

  In this regard, as in the above configuration 7, by rotating the noble metal tip and the ground electrode about the axis inclined the central axis of the noble metal tip, the irradiation direction of the laser beam remains fixed, The configuration 3 can be realized. That is, according to the present configuration 7, the above-described configuration 3 can be realized without any particular difficulty, and the complication of the apparatus and the reduction in production efficiency can be more reliably prevented.

Embodiments will be described below with reference to the drawings.
[First Embodiment]
FIG. 1 is a partially cutaway front view showing a spark plug 1. In FIG. 1, the axis X direction of the spark plug 1 is the vertical direction in the drawing, the lower side is the front end side of the spark plug 1, and the upper side is the rear end side.

  The spark plug 1 includes an insulator 2 as a cylindrical insulator, a cylindrical metal shell 3 that holds the insulator 2, and the like.

  A shaft hole 4 is formed through the insulator 2 along the axis X. A center electrode 5 is inserted and fixed on the front end side of the shaft hole 4, and a terminal electrode 6 is inserted and fixed on the rear end side. A resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 in the shaft hole 4, and both ends of the resistor 7 are centered via conductive glass seal layers 8 and 9. The electrode 5 and the terminal electrode 6 are electrically connected to each other.

  The center electrode 5 protrudes from the tip of the insulator 2, and the terminal electrode 6 is fixed in a state of protruding from the rear end of the insulator 2. Further, a noble metal tip 31 is joined to the tip of the center electrode 5 by welding (this will be described later).

  On the other hand, the insulator 2 is formed by firing alumina or the like as is well known, and in its outer portion, the rear end side body portion 10 formed on the rear end side, and the rear end side body portion 10 A large-diameter portion 11 that protrudes outward in the radial direction on the distal end side, a middle trunk portion 12 that is smaller in diameter than the large-diameter portion 11 on the distal end side, and the middle trunk portion 12. Is also provided with a leg length portion 13 formed to have a smaller diameter on the distal end side. Of the insulator 2, the large-diameter portion 11, the middle trunk portion 12, and most of the leg long portions 13 are accommodated inside the metal shell 3. A tapered step portion 14 is formed at the connecting portion between the leg length portion 13 and the middle trunk portion 12, and the insulator 2 is locked to the metal shell 3 at the step portion 14.

  The metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a screw portion (male screw portion) 15 for attaching the spark plug 1 to the engine head is formed on the outer peripheral surface thereof. In addition, a seat portion 16 is formed on the outer peripheral surface on the rear end side of the screw portion 15, and a ring-shaped gasket 18 is fitted on the screw neck 17 on the rear end of the screw portion 15. Further, on the rear end side of the metal shell 3, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 3 is attached to the engine head is provided. A caulking portion 20 for holding the insulator 2 is provided.

  A tapered step portion 21 for locking the insulator 2 is provided on the inner peripheral surface of the metal shell 3. The insulator 2 is inserted from the rear end side to the front end side of the metal shell 3, and the rear end of the metal shell 3 is engaged with the step portion 14 of the metal shell 3. It is fixed by caulking the opening on the side radially inward, that is, by forming the caulking portion 20. An annular plate packing 22 is interposed between the step portions 14 and 21 of both the insulator 2 and the metal shell 3. Thereby, the air tightness in the combustion chamber is maintained, and the fuel air entering the gap between the leg long portion 13 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 is prevented from leaking outside.

  Further, in order to make the sealing by caulking more complete, annular ring members 23 and 24 are interposed between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3, and the ring member 23 , 24 is filled with powder of talc (talc) 25. That is, the metal shell 3 holds the insulator 2 via the plate packing 22, the ring members 23 and 24, and the talc 25.

  Further, a ground electrode 27 having a substantially L shape is joined to the distal end portion 26 of the metal shell 3. That is, the ground electrode 27 is welded at its rear end to the front end portion 26 of the metal shell 3, and the front end side is bent back so that the side surface faces the front end portion (the noble metal tip 31) of the center electrode 5. Are arranged as follows. In the present embodiment, the ground electrode 27 is made of Ni-23Cr-14.4Fe-1.4Al (Inconel 601 (registered trademark)), and the thermal conductivity of the metal material is about 0.111 W. / Cm · K.

  Further, a noble metal tip 32 is joined to the ground electrode 27 so as to face the noble metal tip 31 (this will be described later). A gap between the noble metal tips 31 and 32 is a spark discharge gap 33. In the present embodiment, the noble metal tip 31 is made of a known noble metal material (for example, a Pt—Ir alloy), and the noble metal tip 32 is made of a Pt-20Ir-5Rh alloy. . The thermal conductivity of the metal material is about 0.262 W / cm · K, which is larger than that of the metal material constituting the ground electrode 27.

  The center electrode 5 includes an inner layer 5A made of copper or a copper alloy and an outer layer 5B made of a nickel (Ni) alloy. The ground electrode 27 is made of a Ni alloy.

  The center electrode 5 is reduced in diameter at the tip side, has a rod shape (cylindrical shape) as a whole, and has a flat tip surface. The noble metal tip 31 and the center electrode 5 are joined by superimposing the columnar noble metal tip 31 and performing laser welding, electron beam welding, resistance welding or the like along the outer edge of the joining surface. ing.

  On the other hand, the noble metal tip 32 facing the noble metal tip 31 is aligned on a predetermined position of the ground electrode 27 and the end of the noble metal tip 32 is embedded in the ground electrode 27 by resistance welding. Spot welding is performed with a laser beam along the part. As a result, a melted portion 34 in which the noble metal material and the Ni alloy are melted is formed, and the ground electrode 27 and the noble metal tip 32 are joined. The noble metal tip 31 on the center electrode 5 side may be omitted. In this case, a spark discharge gap 33 is formed between the noble metal tip 32 and the tip of the center electrode 5.

In addition, in the present embodiment, the melting portion 34 is located on the distal end side (right side in the drawing) of the ground electrode 27 from the proximal end melting portion A located on the proximal end side (left side in the drawing) of the ground electrode 27. The volume (melting amount) is formed so as to gradually increase toward the distal end side melting portion B. More specifically, as shown in FIG. 2, the cross-sectional area of the front end side melted portion B is along the longitudinal direction of the ground electrode 27 and includes the central axis Y of the noble metal tip 32 (referred to as “central axis cross section”). The cross-sectional area of the base end side melted part A is 1.1 to 1.3 times (for example, 1.2 times). In addition, the total cross-sectional area of the cross-sectional area of the base end side melted part A and the cross-sectional area of the front end side melted part B is 4.0 mm ² or more (for example, 5.0 mm ² ).

  Further, as shown in FIG. 3, the base end side melted portion A and the tip end side melted portion B are each before the melted portion 34 is formed (the end portion of the noble metal tip 32 is embedded in the ground electrode 27). Among the regions defined by the rectangular first virtual outline N1 of the noble metal tip 32, the noble metal tip side melted portions C1 and C2 on the noble metal tip 32 side and the regions defined by the first virtual outline N1 The ground electrode 27 side melted portions D1 and D2 on the ground electrode 27 side, which are the regions on the ground electrode 27 side and further divided by the second virtual outline N2 of the ground electrode 27 before the melted portion 34 is formed. It is divided into and. Note that the noble metal tip side melted portions C1 and C2 are shown with an upward slanted diagonal line, and the ground electrode side melted portions D1 and D2 are shown with a downward right oblique line.

  In addition, in the cross section of the central axis, the cross-sectional area of the ground electrode side melted portion D1 is 1.0 to 2.0 times (for example, 1.5 times) the cross-sectional area of the noble metal tip side melted portion C1. At the same time, the cross-sectional area of the ground electrode-side melted portion D2 is set to 1.0 to 2.0 times (for example, 1.7 times) the cross-sectional area of the noble metal tip-side melted portion C2.

  Next, the manufacturing method of the spark plug 1 comprised as mentioned above is demonstrated. First, the metal shell 3 is processed in advance. That is, a cylindrical metal material (for example, an iron-based material such as S17C or S25C or a stainless steel material) is formed by forming a through-hole by cold forging to produce a rough shape. Thereafter, the outer shape is adjusted by cutting to obtain a metal shell intermediate.

  Subsequently, a ground electrode 27 made of a Ni alloy (for example, an Inconel alloy) is resistance-welded to the front end surface of the metal shell intermediate. When the welding is performed, so-called “sag” is generated. After the “sag” is removed, the threaded portion 15 is formed by rolling at a predetermined portion of the metal shell intermediate body. Thereby, the metal shell 3 to which the ground electrode 27 is welded is obtained. In addition, after providing the noble metal chip | tip 32 mentioned later to the ground electrode 27, it is good also as welding the ground electrode 27 to a metal shell intermediate body. The metal shell 3 to which the ground electrode 27 is welded is galvanized or nickel plated. In order to improve the corrosion resistance, the surface may be further subjected to chromate treatment.

  Further, the above-described noble metal tip 32 is joined to the tip portion 26 of the ground electrode 27. More specifically, first, the end portion of the noble metal tip 32 is temporarily fixed to a predetermined portion of the ground electrode 27 by resistance welding in a state where the end portion is embedded in the ground electrode 27. Then, the laser beam is intermittently applied to the outer edge of the joint surface between the ground electrode 27 and the noble metal tip 32 while rotating the noble metal tip 32 relative to the laser irradiation means with the central axis Y of the noble metal tip 32 as the rotation axis. Is irradiated. More specifically, the laser beam is irradiated a predetermined number of times (for example, 8 times) so that the distances between the centers of the melting points irradiated with the laser beam are substantially equal. As a result, a large number of melting points (melting portions 34) that are annularly connected when viewed from the front end side of the noble metal tip 32 are formed, and the ground electrode 27 and the noble metal tip 32 are joined (spot welding method). Further, when irradiating the laser beam, the laser beam is irradiated at a predetermined angle with respect to the outer edge portion of the joint surface while increasing or decreasing the output energy stepwise. Specifically, a relatively low energy laser beam is irradiated to a portion located on the proximal end side of the ground electrode 27 in the outer edge portion of the joint surface, while being located on the distal end side of the ground electrode 27. The region is irradiated with a relatively high energy laser beam. As a result, the melting amount of the distal end side melting portion B formed on the distal end side of the ground electrode 27 is made larger than the melting amount of the proximal end side melting portion A formed on the proximal end side of the ground electrode 27. The In addition, by changing the focal length of the laser beam without increasing / decreasing the output energy as described above, or by increasing / decreasing the output energy, the melting amount of the proximal end side melting portion A and the distal end side melting portion B can be reduced. It may be increased or decreased.

  Further, in order to make the welding more reliable, prior to the welding, the plating of the welded part is removed, or the planned welding part is masked during the plating process. Further, the precious metal tip 32 may be welded after a combination described later.

  On the other hand, the insulator 2 is formed separately from the metal shell 3. For example, by using a raw material powder mainly composed of alumina and containing a binder or the like, a green granulated material for molding is prepared, and rubber press molding is used to obtain a cylindrical molded body. The obtained molded body is ground and shaped. Then, the shaped one is put into a firing furnace and fired. The insulator 2 is obtained by performing various grinding | polishing processes after baking.

  Separately from the metal shell 3 and the insulator 2, the center electrode 5 is manufactured. That is, the Ni alloy is forged, and an inner layer 5A made of a copper alloy is provided at the center of the Ni alloy to improve heat dissipation. And the noble metal tip 31 mentioned above is joined to the front-end | tip part by resistance welding, laser welding, etc.

  Then, the insulator 2 and the center electrode 5, the resistor 7, and the terminal electrode 6 obtained as described above are sealed and fixed by the glass seal layers 8 and 9. The glass seal layers 8 and 9 are generally prepared by mixing borosilicate glass and metal powder, and the prepared material is injected into the shaft hole 4 of the insulator 2 with the resistor 7 interposed therebetween. Then, the terminal electrode 6 is pressed from the rear and then baked in a firing furnace. At this time, the glaze layer may be fired simultaneously on the surface of the rear end side body portion 10 of the insulator 2 or the glaze layer may be formed in advance.

  Thereafter, the insulator 2 provided with the center electrode 5 and the terminal electrode 6 and the metal shell 3 provided with the ground electrode 27 are assembled as described above. More specifically, it is fixed by caulking the opening on the rear end side of the metal shell 3 formed relatively thin inward in the radial direction, that is, by forming the caulking portion 20.

  Finally, the ground electrode 27 is bent to adjust the spark discharge gap 33 between the noble metal tip 31 provided at the tip of the center electrode 5 and the noble metal tip 32 provided on the ground electrode 27. Is done.

  Thus, the spark plug 1 having the above-described configuration is manufactured through a series of steps.

  Next, in order to confirm the operational effects achieved by the present embodiment, the following test was performed. That is, the noble metal tip is joined to the ground electrode, and along the longitudinal direction of the ground electrode, the cross-sectional area of the base-side melted portion (hereinafter referred to as the melted portion of the cross section passing through the central axis of the noble metal tip) "SA") and the total cross-sectional area (hereinafter referred to as "SB") of the cross-sectional area (hereinafter referred to as "SB") of the tip side melted portion, and the cross-sectional area ratio of SA and SB (hereinafter referred to as "SB / SA"). The cross-sectional area ratio (hereinafter referred to as “SC”) of the noble metal tip side melted portion on the tip side melted portion side and the cross sectional area of the ground electrode side melted portion on the tip side melted portion side (hereinafter referred to as “SD”) ( Samples of spark plugs having various modifications (hereinafter referred to as “SD / SC”) were prepared, and a peel resistance evaluation test was performed on each sample. The results of the test are shown in the line graphs and contour graphs of FIGS. Here, the outline of the peel resistance evaluation test is as follows. In other words, each spark plug sample is attached to a 2000 cc in-line 6-cylinder engine and brought to a full load state for 1 minute (engine speed = 5000 rpm), and then idled for 1 minute as one cycle. The number of cycles until the occurrence of (chip peeling cycle number) was measured. Moreover, in the said test, it was judged that it has sufficient peeling-proof performance, when the chip | tip peeling cycle number becomes 10,000 cycles or more.

4 and 5, when SA + SB is 3 mm ² , FIGS. 6 and 7 are when SA + SB is 4 mm ^2, and FIGS. 8 and 9 are broken lines when SA + SB is 6 mm ^2. A graph and a contour graph are shown respectively.

  In each line graph (FIGS. 4, 6, and 8), the vertical axis represents the number of chip peeling cycles, the horizontal axis represents SD / SC, and the sample with SB / SA of “1.0” is a black circle. The “1.1” sample is a black triangle, the “1.2” sample is a black diamond, the “1.3” sample is a black square, and the “1.4” sample is a cross. Each is plotted. In addition, 10000 cycles, which is a limit value (peeling limit) that can be evaluated as having sufficient peeling resistance, is indicated by a bold line.

  Furthermore, in each contour graph (FIGS. 5, 7, and 9), the vertical axis is SB / SA, the horizontal axis is SD / SC, and the area where the number of chip peeling cycles is 10,000 cycles or more is displayed in white. Yes. Here, when the number of chip peeling cycles is 13,000 cycles or more, it is recognized that the chip has extremely excellent peeling resistance, and therefore, the crossing line in the region is particularly indicated by a dotted line. On the other hand, when the number of chip peeling cycles is less than 10,000 cycles, the area is indicated by dotted dots because the peeling resistance is not sufficient. In this case, the higher the dot density (the higher the concentration), the less the peel resistance is.

  As shown in FIG. 4 to FIG. 9, SB / SA is set to “1.0” or “1.4” by setting SB / SA to “1.1 to 1.3” without depending on the value of SA + SB. It was confirmed that the number of chip peeling cycles was increased as compared with the case. This is because the area of the boundary between the tip-side melted part and the noble metal tip and the area of the boundary between the tip-side melted part and the ground electrode are further increased. This is considered to be because the thermal stress applied to the noble metal tip from the portion to be relaxed is relaxed, and as a result, the balance between the thermal stress from the distal end side of the ground electrode and the thermal stress from the proximal end side of the ground electrode is maintained.

  Furthermore, it was revealed that the number of chip peeling cycles is further increased by setting SD / SC to “1.0 to 2.0”. This is because the linear expansion coefficient of the melted part is not too close to only the linear expansion coefficient of one of the noble metal material or the metal material, so at the boundary part between the melted part and the noble metal tip or the boundary part between the melted part and the ground electrode. It is considered that an increase in shearing force can be suppressed, and as a result, generation of oxide scales and cracks at each boundary can be suppressed.

On the other hand, as shown in FIGS. 4 and 5, when SA + SB is 3 mm ² , SB / SA is set to “1.1 to 1.3”, and SD / SC is set to “1.0 to 2.0. However, it was not recognized that the film had sufficient peel resistance. It is considered that this is because the weld strength was insufficient because the melting amount of the melted portion was too small.

On the other hand, as shown in FIGS. 6 and 7, when SA + SB is 4 mm ² , SB / SA is “1.1 to 1.3”, and SD / SC is “1.0 to 2.0 ”(in the region surrounded by the thick line in FIG. 7), it was confirmed that the number of chip peeling cycles exceeded 10,000 cycles and sufficient peeling resistance performance was realized.

Further, as shown in FIGS. 8 and 9, when SA + SB is 6 mm ² , SB / SA is “1.1 to 1.3” and SD / SC is “1.0 to 2. In the region “0” (in the region surrounded by the thick line in FIG. 9), the portion where the number of chip peeling cycles exceeds 13,000 occupies most of the region, and very excellent peeling resistance performance can be realized. It was confirmed.

As described above, SA + SB is set to 4 mm ² or more, SB / SA is set to “1.1 to 1.3”, and SD / SC is set to “1.0 to 2.0”. It can be said that the peelability can be sufficiently improved.
[Second Embodiment]
Next, a second embodiment will be described with reference to FIGS. In the present embodiment, the structure of the melting portion 34 and the method for joining the ground electrode 27 and the noble metal tip 32 are different from those in the first embodiment. In the present embodiment as well, as in the first embodiment, the cross-sectional area of the distal end-side melted portion B is 1.1 times to 1.-1. The total cross-sectional area of the cross-sectional area of the base end side melted part A and the cross-sectional area of the front end side melted part B is 4.0 mm ² or more. Further, in the cross section of the central axis, the cross-sectional area of the ground electrode side melted portions D1 and D2 is 1.0 to 2.0 times the cross sectional area of the noble metal tip side melted portions C1 and C2.

  Now, the structure of the melting part 34 peculiar to the second embodiment will be described. As shown in FIG. 11, in the present embodiment, the melting portion 34 has an edge located on the distal end side of the noble metal tip 32 from a portion located on the proximal end side of the ground electrode 27 to a portion located on the distal end side. It is formed so as to gradually approach the tip of the noble metal tip 32. That is, as shown in FIG. 12, the distal end side molten portion B is formed closer to the distal end of the noble metal tip 32 than the proximal end side molten portion A. More specifically, the shortest distance from the tip of the noble metal tip 32 to the base side melted portion A in the cross section of the central axis is E (mm), and the shortest distance from the tip of the noble metal tip 32 to the tip side molten portion B is F. (Mm), the melted portion 34 is formed so as to satisfy 1.05 ≦ E / F ≦ 1.25. Further, in the present embodiment, the melting part 34 is formed so as to satisfy 0.3 mm ≦ E ≦ 0.5 mm.

  Further, as shown in the figure, the noble metal tip 32 is bonded so that the tip end face 32f thereof is parallel to the end face 27b of the ground electrode 27 on the center electrode 5 side. That is, the distance (tip-side protruding length) L1 along the central axis Y of the noble metal tip 32 between the tip-side end 32f1 positioned on the tip-side of the ground electrode 27 and the end surface 27b of the tip-face 32f of the ground electrode 27. And the distance along the central axis Y of the noble metal tip 32 between the base end side end portion 32f2 located on the base end side of the ground electrode 27 in the tip end surface 32f of the ground electrode 27 and the end surface 27b of the ground electrode 27. (Base end side protrusion length) L2 is made equal.

  In addition, the noble metal tip 32 is joined such that the tip end face 32 f protrudes 0.8 mm along the central axis Y from the end face 27 b of the ground electrode 27.

  Next, a method for joining the ground electrode 27 and the noble metal tip 32 will be described. First, the end portion of the noble metal tip 32 is temporarily fixed to a predetermined portion of the ground electrode 27 by resistance welding in a state where the end portion is embedded in the ground electrode 27. As shown in FIGS. 13 and 14, the base axis side of the ground electrode 27 is based on the central axis Y of the noble metal tip 32 and the intersection BP between the central axis Y and a plane including one side surface of the ground electrode 27. While rotating the ground electrode 27 and the noble metal tip 32 relative to each other about the axis AR inclined at a predetermined angle to the rotation axis, the outer edge of the contact surface between the ground electrode 27 and the noble metal tip 32 is irradiated with the laser beam (LB) fixed in the irradiation direction. Irradiate the part intermittently. As a result, the laser beam (LB) is irradiated at a position relatively close to the tip of the noble metal tip 32 at a portion located on the tip side of the ground electrode 27, while being located on the base end side of the ground electrode 27. In the part, the laser beam (LB) is irradiated to a position relatively separated from the tip of the noble metal tip 32. As a result, the distal end side molten portion B is formed in a state closer to the distal end of the noble metal tip 32, and the proximal end side molten portion A is formed at a position relatively separated from the distal end of the noble metal tip 32.

  As described above, by using the above-described manufacturing method, the edge located on the distal end side of the noble metal tip 32 of the melting portion 34 is located on the proximal end side of the ground electrode 27 without complicating the apparatus and reducing the production efficiency. The melted portion 34 can be formed so as to gradually approach the tip of the noble metal tip 32 from the portion located to the portion located on the tip side.

  Next, in order to confirm the operational effect achieved by the present embodiment, as shown in FIG. 15, the noble metal tip of the noble metal tip with respect to the shortest distance “SF” between the tip of the noble metal tip on the ground electrode side and the tip side melted portion is shown. Samples of spark plugs in which the ratio of the shortest distance “SE” between the front end and the base end side melted part (“SE / SF”) and the shortest distance “SE” were variously manufactured were prepared, and durability evaluation was performed on each sample. A test was conducted. The outline of the durability evaluation test is as follows. That is, each sample was attached to a 2000 cc in-line 6-cylinder engine, and the engine was operated for 100 hours under a full load condition (engine speed = 5000 rpm). Thereafter, for the noble metal tip on the center electrode side and the noble metal tip on the ground electrode side, the distance “G1” between the parts located on the proximal end side of the ground electrode and the distance between the parts located on the distal end side of the ground electrode While measuring "G2", the absolute value (| G1-G2 |) of the difference between the two was calculated. FIG. 16 is a graph showing the relationship between SE / SF and | G1-G2 |. In the figure, the test results when SE is 0.3 mm are plotted with white diamonds, the test results when SE is 0.4 mm are plotted with white triangles, and SE is 0.5 mm. The test results were plotted with white circles, and the test results when SE was 0.6 mm were plotted with cross marks. Further, the noble metal tip was formed of a Pt-20Ir-5Rh alloy, and the ground electrode was formed of Inconel 601 (registered trademark).

  As shown in FIG. 16, for samples in which SE is 0.3 mm or more and 0.5 mm or less and SE / SF is 1.05 or more and 1.25 or less, | G1-G2 | is 0.05 mm or less. It was found that uneven consumption of the noble metal tip can be effectively suppressed. This is because SE / SF is set to 1.05 or more and 1.25 or less, and the surface area of the portion located on the tip side of the ground electrode in the noble metal tip on the ground electrode side is located on the base end side of the ground electrode. Since it is smaller than the surface area of the part, it is possible to reduce the amount of heat received at the part located on the distal end side of the ground electrode, which is likely to become higher temperature, and as a result, the part located on the distal end side of the ground electrode and the proximal end side. This is considered to be because the temperature difference with the part could be reduced.

  On the other hand, for samples with an SE / SF of less than 1.05 and samples with an SE / SF of over 1.25, | G1-G2 | exceeds 0.05 mm, resulting in uneven wear on the noble metal tip. It became clear. This is considered to be due to the following reason. That is, when the SE / SF is less than 1.05, the amount of heat received at the portion of the noble metal tip located on the tip side of the ground electrode has not been sufficiently reduced, so that the consumption at that portion is likely to proceed. This is considered to be caused by this. On the other hand, when SE / SF exceeds 1.25, the amount of heat received at the portion of the noble metal tip located on the tip side of the ground electrode has been extremely reduced, so that it is located on the base end side of the ground electrode. This is thought to be due to the fact that consumption at the site has become easier to proceed.

  In addition, for samples with an SE of 0.6 mm, it is clear that | G1-G2 | becomes larger than 0.05 mm regardless of the value of SE / SF, resulting in uneven consumption of the noble metal tip. It became. This is because the noble metal tip on the ground electrode side protrudes further from the ground electrode, so that the amount of heat received by the noble metal tip increases, and as a result, the portion of the noble metal tip located on the distal side of the ground electrode and the proximal side This is thought to be due to the fact that the balance of the temperature difference with the part located at the position has collapsed.

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the above embodiment, the base end side melting portion A and the tip end side melting portion B are formed without exceeding the central axis Y of the noble metal tip 32, but the base end side melting portion A and the tip end side melting portion are formed. At least one of the portions B may be formed beyond the central axis Y. At this time, as shown in FIG. 10A, the base end side melted portion A and the tip end side melted portion B may overlap each other. In such a case, the base end side is performed as follows. It is desirable to determine the cross-sectional area of the melted part A and the cross-sectional area of the front end side melted part B. That is, as shown in FIG. 10 (b), in the cross section of the central axis, the outline G1 that forms the outer shape of the proximal end melted part A and the outer line G2 that forms the outer shape of the distal end melted part B are two. Intersection points K1 and K2 are connected by a virtual straight line S. Then, as shown in FIG. 10 (c), the melted part A1 divided on the base end side melted part A side is determined as “base end side melted part A”, and the melt divided on the front end side melted part B side The portion B1 is determined as the “tip-side melted portion B”.

  (B) In the above embodiment, the cross-sectional area of the ground electrode-side melted part D1 in the base end-side melted part A is 1.0 to 2.0 times the cross-sectional area of the noble metal tip-side melted part C1, The cross-sectional area of the ground electrode side melted part D2 in the front end side melted part B is 1.0 to 2.0 times the cross sectional area of the noble metal tip side melted part C2. On the other hand, the cross-sectional area of the ground electrode side melted part D1 (D2) in either one of the base end side melted part A and the distal end side melted part B is equal to the cross sectional area of the noble metal tip side melted part C1 (C2). It may be 1.0 to 2.0 times.

(C) Although not particularly mentioned in the above embodiment, in view of the recent demand for downsizing of the spark plug, the ground electrode 27 has a relatively small cross-sectional area (for example, 2.0 mm ^2). It is good also as what uses above 3.5mm < ² >. When the cross-sectional area is relatively small as described above, the heat-drawing performance of the ground electrode 27 is lowered, so that the ground electrode 27 is likely to be at a higher temperature, and as a result, the balance of thermal stress applied to the noble metal tip 32 is increased. There is a concern that it will be more likely to collapse. In this regard, by adopting the above configuration, it is possible to stably suppress the balance of thermal stress balance. That is, under the condition where the ground electrode 27 is likely to be at a higher temperature, the operational effect of the above configuration is more effectively achieved.

  (D) In the above embodiment, the noble metal tip 32 is made of a Pt-20Ir-5Rh alloy, but the noble metal tip 32 may be made of another noble metal or a noble metal alloy. Therefore, for example, it may be formed of a Pt-20Rh alloy.

  By the way, by changing the composition of the noble metal tip 32, the thermal conductivity of the melting portion 34 can be changed. Therefore, in order to confirm whether the effects of the above-described embodiment are achieved when the composition of the noble metal tip 32 is changed, the noble metal tip made of a Pt-20Rh alloy is provided, and the tip and tip of the noble metal tip on the ground electrode side are provided. Various ratios ("SE / SF") of the shortest distance "SE" between the front end and base end side molten parts of the noble metal tip to the shortest distance "SF" between the side melted parts and the shortest distance "SE" The sample of the changed spark plug was produced, and the above-described durability evaluation test was performed on each sample. The results of the evaluation test are shown in FIG. The thermal conductivity of the Pt-20Rh alloy is about 0.372 W / cm · K. The ground electrode was formed of Inconel 601 (registered trademark).

  As shown in FIG. 17, for the noble metal tip made of a Pt-20Rh alloy, the SE is set to 0.3 mm or more and 0.5 mm or less and the SE / SF is set to 1.05 or more and 1.25 or less as in the above embodiment. For the sample, | G1-G2 | was 0.05 mm or less, and it was revealed that uneven consumption of the noble metal tip can be effectively suppressed. That is, it is considered that the effect of the above embodiment is achieved by forming the noble metal tip with a noble metal material having a thermal conductivity larger than that of the metal material forming the ground electrode. Therefore, as long as such a relationship is satisfied, not only the above-described alloy containing Pt as a main component but also a noble metal tip formed of an alloy containing Ir as a main component has the same effects. It can be said.

  (E) In the above embodiment, the ground electrode 27 is formed of Inconel 601 (registered trademark), but the metal material constituting the ground electrode 27 is not limited to this. From the viewpoint of effectively suppressing uneven consumption of the noble metal tip 32, the ground electrode 27 may be formed of a metal material having a thermal conductivity smaller than that of the metal material constituting the noble metal tip 32. preferable. Therefore, for example, the ground electrode 27 may be formed of a Ni-15.5Cr-8Fe alloy [Inconel 600 (registered trademark)] which is a relatively small metal material having a thermal conductivity of about 0.149 W / cm · K. .

  (F) In the second embodiment, the noble metal tip 32 is joined to the ground electrode 27 so that the end surface 27b of the ground electrode 27 and the tip end surface 32f of the noble metal tip 32 are parallel to each other, and the tip side protruding length L1. Although the base end side protruding lengths L2 are equal, the noble metal tip 32 may be joined to the ground electrode 27 so that the end surface 27b and the front end surface 32f are substantially parallel to each other. Therefore, the noble metal tip 32 may be bonded to the ground electrode 27 so that the difference between the distal end side protruding length L1 and the proximal end side protruding length L2 is within a predetermined range (for example, 0.05 mm). Good.

  (G) In the above embodiment, the case where the ground electrode 27 is joined to the tip of the metal shell 3 is embodied. However, a part of the metal shell (or one of the metal tips previously welded to the metal shell is used. The present invention can also be applied to the case where the ground electrode is formed by cutting out the portion (for example, Japanese Patent Laid-Open No. 2006-236906).

  (H) In the above embodiment, the tool engagement portion 19 has a hexagonal cross section, but the shape of the tool engagement portion 19 is not limited to such a shape. For example, it may be a Bi-HEX (deformed 12-angle) shape [ISO 22777: 2005 (E)].

It is a partially broken front view which shows the spark plug in this embodiment. It is a partial expanded sectional view which shows the cross section of the fusion | melting part etc. in this embodiment. It is a partial expansion schematic diagram which shows the noble metal tip side fusion | melting part and ground electrode side fusion | melting part in this embodiment. In a peeling resistance evaluation test, it is a line graph which shows the test result in case the total cross-sectional area of the cross-sectional area of a noble metal tip side fusion | melting part and the cross-sectional area of a ground electrode side fusion | melting part is 3 mm < ² >. In a peeling resistance evaluation test, it is a contour graph which shows a test result in case the total cross-sectional area of the cross-sectional area of a noble metal tip side fusion | melting part and the cross-sectional area of a ground electrode side fusion | melting part is 3 mm < ² >. In a peel resistance evaluation test, it is a line graph which shows a test result in case the total cross-sectional area of the cross-sectional area of a noble metal tip side fusion | melting part and the cross-sectional area of a ground electrode side fusion | melting part is 4 mm < ² >. In a peeling resistance evaluation test, it is a contour graph which shows a test result in case the total cross-sectional area of the cross-sectional area of a noble metal chip side fusion | melting part and the cross-sectional area of a ground electrode side fusion | melting part is 4 mm < ² >. It is a line graph which shows the test result in the peeling resistance evaluation test when the total cross-sectional area of the cross-sectional area of the noble metal tip side melted part and the cross-sectional area of the ground electrode side melted part is 6 mm ² . In a peeling resistance evaluation test, it is a contour graph which shows a test result in case the total cross-sectional area of the cross-sectional area of a noble metal tip side fusion | melting part and the cross-sectional area of a ground electrode side fusion | melting part is 6 mm < ² >. (A) is a partial expanded sectional view which shows the front end side fusion | melting part in another embodiment, a base end side fusion | melting part, etc., (b) and (c) are the cutting | disconnections of the front end side fusion | melting part in another embodiment. It is a schematic diagram explaining the determination method of the cross-sectional area of an area and a base end side fusion | melting part. It is a partial enlarged front view which shows the structure of the fusion | melting part of the ground electrode and noble metal tip in 2nd Embodiment. It is a fragmentary sectional view which shows the positional relationship of the base end side fusion | melting part in 2nd Embodiment, a front end side fusion | melting part, and a noble metal tip. It is a cross-sectional schematic diagram for demonstrating the joining method of the ground electrode and noble metal chip | tip in 2nd Embodiment. It is a cross-sectional schematic diagram for demonstrating the joining method of the ground electrode and noble metal chip | tip in 2nd Embodiment. It is a sectional end view for explaining the concept of the sample used in the durability evaluation test (however, hatching is omitted for convenience). It is a graph which shows the result of a durability evaluation test about the sample in which SE and SE / SF were changed variously. It is a graph which shows the result of the durability evaluation test of the sample in which SE and SE / SF were variously changed in different noble metal tips.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Spark plug for internal combustion engines, 2 ... Insulator, 3 ... Main metal fitting, 4 ... Shaft hole, 5 ... Center electrode, 26 ... End surface of main metal fitting, 27 ... Ground electrode, 32 ... Precious metal tip, 33 ... Spark discharge Gap 34, melting portion, A, proximal side melting portion, B, tip side melting portion, C 1, C 2, precious metal tip side melting portion, D 1, D 2, ground electrode side melting portion, N 1, first virtual outline, N2 ... second virtual outline, X ... axis, Y ... central axis.

Claims (7)

A cylindrical insulator having an axial hole penetrating in the axial direction;
A center electrode inserted in the shaft hole;
A cylindrical metal shell provided on the outer periphery of the insulator;
A grounding provided at the distal end portion of the metal shell such that a proximal end of a noble metal tip mainly composed of a noble metal is joined to one side surface of the distal end side of the own metal, and the distal end surface of the noble metal tip faces the distal end surface of the center electrode. Electrodes,
A spark plug for an internal combustion engine comprising:
The noble metal tip is joined by forming a melted part in which the noble metal tip and the ground electrode have melted around itself,
When looking at the melting portion of the cross section along the longitudinal direction of the ground electrode and including the central axis of the noble metal tip,
The total cross-sectional area of the cross-sectional area of the base-end side melted portion A located on the base end side of the ground electrode and the cross-sectional area of the front-end side melted portion B located on the front end side of the ground electrode is 4 mm ² or more, A spark plug for an internal combustion engine, characterized in that a cross-sectional area of the distal end side melted portion B is 1.1 to 1.3 times larger than a cross sectional area of the proximal end side melted portion A. The noble metal tip has its proximal end embedded in the ground electrode,
The proximal end side fusion part A and the distal end side fusion part B are each
The noble metal tip-side melted portion C on the noble metal tip side of the region partitioned by the rectangular first virtual outline of the noble metal tip before the melted portion is formed,
Of the area defined by the first virtual outline, the area on the ground electrode side, and further, the ground electrode side defined by the second virtual outline of the ground electrode before formation of the melting portion And the ground electrode side melting part D of
In at least one of the proximal end side fusion part A and the distal end side fusion part B,
The cross-sectional area of the ground electrode side melted portion D in the cross section along the longitudinal direction of the ground electrode and including the central axis of the noble metal tip is 1.0 to 2 times the cross sectional area of the noble metal tip side melted portion C. The spark plug for an internal combustion engine according to claim 1, wherein the spark plug is set to 0.0 times. Along the longitudinal direction of the ground electrode, and in a cross section including the central axis of the noble metal tip,
E (mm) is the shortest distance from the tip of the noble metal tip to the base side melted portion A,
When the shortest distance from the tip of the noble metal tip to the tip side melted portion B is F (mm),
The spark plug for an internal combustion engine according to claim 1 or 2, wherein the following expressions (1) and (2) are satisfied.
1.05 ≦ E / F ≦ 1.25 (1)
0.3 mm ≦ E ≦ 0.5 mm (2) A cylindrical insulator having an axial hole penetrating in the axial direction;
A center electrode inserted in the shaft hole;
A cylindrical metal shell provided on the outer periphery of the insulator;
A base end of a noble metal tip mainly composed of a noble metal is bonded to one side surface of its own tip side, and the tip end surface of the noble metal tip is provided at the tip end portion of the metal shell so as to face the tip end surface of the center electrode. A ground electrode,
The noble metal tip is a method of manufacturing a spark plug formed by bonding a melted portion in which the noble metal tip and the ground electrode are melted around itself.
Forming the melted portion by irradiating a laser beam to the outer peripheral portion of the ground electrode and the joint surface of the noble metal tip, and including a joining step of joining the noble metal tip to the ground electrode;
In the joining step, the laser beam is adjusted so that the melting energy for the portion located on the distal end side of the ground electrode is larger than the melting energy for the portion located on the proximal end side of the ground electrode. Irradiating, a method for manufacturing a spark plug. A method for producing a spark plug for an internal combustion engine according to any one of claims 1 to 3,
Forming the melted portion by irradiating a laser beam to the outer peripheral portion of the ground electrode and the joint surface of the noble metal tip, and including a joining step of joining the noble metal tip to the ground electrode;
In the joining step, the laser beam is adjusted so that the melting energy for the portion located on the distal end side of the ground electrode is larger than the melting energy for the portion located on the proximal end side of the ground electrode. Irradiating, a method for manufacturing a spark plug.   6. The laser beam irradiation according to claim 4, wherein the laser beam is irradiated so as to increase melting energy from a portion located on the proximal end side of the ground electrode to a portion located on the distal end side of the ground electrode. The manufacturing method of the spark plug of description. In the joining step,
After fixing the direction of laser beam irradiation,
Of the central axis of the noble metal tip, the axis located on the noble metal tip side is based on the intersection of the central axis of the noble metal tip and a plane including one side surface of the ground electrode, toward the base end side of the ground electrode. The spark plug manufacturing method according to any one of claims 4 to 6, wherein the melting portion is formed by rotating the noble metal tip and the ground electrode with an inclined axis as a rotation axis. .

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