JP5903008B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug used for an internal combustion engine or the like.

  The spark plug is attached to, for example, an internal combustion engine (engine), and is used to ignite an air-fuel mixture or the like in the combustion chamber. In general, a spark plug is welded to an insulator having an axial hole extending in the axial direction, a center electrode inserted into the tip end side of the shaft hole, a metal shell provided on the outer periphery of the insulator, and a tip surface of the metal shell. A rod-shaped ground electrode (see, for example, Patent Document 1).

  The ground electrode is welded to the front end surface of the metal shell, and includes a base portion that extends toward the front end side in the axial direction and is at least partially buried in the metal shell. In addition, the ground electrode is bent back so that the tip of the ground electrode is opposed to the center electrode at a substantially intermediate portion of the ground electrode, and a gap is formed between the tip of the ground electrode and the tip of the center electrode. The A high voltage is applied to the gap, and a spark discharge is generated in the gap, thereby igniting the air-fuel mixture or the like.

  Furthermore, the ground electrode is generally welded in a state of being slightly buried in the metal shell by resistance welding. Along with welding, a so-called melting sag is formed in which the metal shell and the ground electrode are melted together. Here, if the molten sag protrudes from the outer peripheral surface or the inner peripheral surface of the metal shell, troubles may occur when the spark plug is attached to an internal combustion engine or the like, or insulation may occur between the center electrode and the molten sag. There is a risk of abnormal discharge over the surface of the body. For this reason, during welding, it is necessary to adjust the pressing load of the ground electrode against the metal shell and the energizing current flowing through the contact portion between them to prevent the molten sag from protruding to the outer peripheral surface or inner peripheral surface of the metal shell. It is common.

JP2012-89325A

  In recent years, the diameter of the metal shell has been reduced in order to reduce the size (small diameter) of the spark plug (that is, the screw diameter of the screw portion provided on the outer peripheral surface of the metal shell has been made smaller). ) In such a metal shell having a reduced diameter, the width of the tip surface (that is, the surface to be welded of the ground electrode) is small, and the difference between the width of the tip surface of the metal shell and the thickness of the ground electrode is very small. It will be a thing. When the screw diameter is small (M10 or less) and the difference between the width of the tip surface and the thickness of the ground electrode is very small, the ground electrode is a surface on the side of the center electrode such as a rectangular cross section. When the surface opposite to the center electrode is flat, both ends in the width direction of the ground electrode are very close to the inner peripheral surface and outer peripheral surface of the metal shell.

  In such a configuration, in order to prevent the molten sag from protruding from the outer peripheral surface and the inner peripheral surface of the metal shell, it is conceivable to reduce the energization current to suppress the formation of the molten sag. However, in this case, the metal shell and the ground electrode cannot be sufficiently melted, and the welding strength of the ground electrode to the metal shell may be insufficient.

  Further, when the width of the front end surface of the metal shell is small, the cross-sectional area of the ground electrode must be relatively small, and the welding area of the metal shell and the ground electrode is also small. In order to more reliably prevent the ground electrode from falling off the metal shell when an external force such as vibration associated with the operation of the internal combustion engine or the like is applied to the ground electrode in such a small welding area. It is necessary to ensure better welding strength. However, as described above, when the ground electrode is very close to the inner peripheral surface of the metal shell, it is very difficult to improve the welding strength. That is, in the spark plug in which the cross-sectional area of the ground electrode is small and the difference between the width of the front end face of the metal shell and the thickness of the ground electrode is very small, there is a particular concern that the ground electrode may fall off due to external force.

  The present invention has been made in view of the above circumstances, and its purpose is to ensure sufficient welding strength in a spark plug in which the ground electrode is particularly worried due to an external force. It is to prevent more reliably.

  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. The spark plug of this configuration includes a cylindrical insulator having an axial hole penetrating in the axial direction;
A center electrode inserted on the tip side of the shaft hole;
A cylindrical metal shell having a threaded portion on the outer periphery and provided on the outer periphery of the insulator;
A spark plug comprising a ground electrode joined to a front end surface of the metal shell via a welded portion and forming a gap with the center electrode,
The ground electrode is
Together are joined through the weld at the tip surface of the metal shell, extending toward the tip end side in the axial direction, a spark plug having a base portion at least partially buried in the metal shell,
The base portion has a flat surface in the width direction of a surface located on the side of the center electrode and a surface located on the side opposite to the center electrode, and the base portion along a direction perpendicular to the axis. The cross-sectional area is 3 mm ² or less,
The screw diameter of the screw portion is M10 or less, and
Width of the end face of the metal shell along a direction perpendicular to the axis, the While larger than the metal shell to the maximum area to be joined via a weld thickness of the base of the metal shell The difference between the width of the tip surface and the maximum thickness is 0.3 mm or less,
In a cross section that includes a perpendicular bisector of the thickness of the base and extends in parallel with the axis, the maximum burying amount of the base along the axis is 0.10 mm or more,
In a cross section that includes a vertical bisector of a width line segment of the base portion and extends in parallel with the axis , only one of the outer peripheral surface and the inner peripheral surface of the metal shell is the base metal. It is characterized by being buried most with respect to the tip surface .

  In addition, the "maximum burial amount of the base" means that the portion of the base that is most buried with respect to the metal shell in the cross section is the portion of the base that is least buried with respect to the metal shell The value obtained by subtracting the amount of burial (hereinafter the same).

According to Configuration 1, the base has a cross-sectional area of 3 mm ² or less along the direction orthogonal to the axis, and the welding area is relatively small. Further, the thread diameter of the thread portion is set to M10 or less, and the width of the front end surface of the metal shell along the direction orthogonal to the axis is larger than the maximum thickness of the base portion, while the width of the front end surface of the metal shell is The difference from the maximum thickness is 0.3 mm or less. In other words, when an external force is applied, the ground electrode is likely to drop off, and it is difficult to ensure sufficient welding strength with the conventional method to secure a welding strength that can prevent the dropping. Yes.

In this regard, according to the configuration 1, the position where the base is most buried with respect to the distal end surface of the metal shell in the cross section including the vertical bisector of the width of the base and extending parallel to the axis. However, it is comprised so that it may be located only in either one of the outer peripheral surface and inner peripheral surface of a metal shell. That is, when an external force is applied to the ground electrode, stress is particularly applied to the inner periphery and outer periphery of the welded portion of the base and the metal shell. It is configured to be buried most. Therefore, it is possible to more surely secure the welding strength that can sufficiently resist the stress.

  Further, according to the configuration 1, the maximum burying amount of the base portion along the axis (hereinafter, referred to as a cross section including the vertical bisector where the thickness of the base portion is maximum and extending in parallel with the axis line). “Sometimes referred to as“ maximum burying amount MB2 ”) is 0.10 mm or more. That is, it is configured such that a sufficient amount of burial is ensured in a portion other than the outer periphery and the inner periphery in the base portion. Thereby, the further improvement of welding strength can be aimed at and the fall-off of a ground electrode can be prevented more reliably.

  It should be noted that the position where the base metal is most buried with respect to the metal shell is positioned on the outer peripheral surface or the inner peripheral surface of the metal shell. Under such conditions, the ground electrode is welded to the metallic shell. By letting molten sag protrude from the outer peripheral surface and inner peripheral surface of the metal shell, the innermost circumference and outermost circumference of the front end surface of the metal shell can be deformed into a concave shape. The most buried position can be the outer peripheral surface or inner peripheral surface of the metallic shell. In addition, during welding, a relatively large energization current that causes the molten sag to flow out is allowed to flow so that the metal shell and the ground electrode are sufficiently melted, which contributes to an improvement in welding strength.

  It should be noted that by cutting away the molten sag that protrudes from the inner peripheral surface or the like of the metal shell, it is possible to avoid problems associated with the sag of the molten metal.

  Configuration 2. The spark plug of this configuration is the maximum embedment amount of the base portion along the axis in the cross section including the perpendicular bisector of the width of the base portion and extending in parallel with the axis line in the above configuration 1 Is 0.05 mm or more and 0.5 mm or less.

  According to the above configuration 2, the maximum burying amount of the base portion (hereinafter referred to as “maximum burying amount MB1”) in a cross section including the vertical bisector of the width of the base portion and extending in parallel with the axis. Is) 0.05 mm or more. Therefore, the welding strength can be improved more reliably.

  By the way, in order to increase the maximum amount of burying, it is necessary to increase the energization current and hence the heat generation amount. However, if the calorific value is excessively increased, the precipitation state of the components contained in the ground electrode and the like at the welding interface between the metal shell and the ground electrode will be different from the usual, resulting in a decrease in welding strength. There is a risk of being invited.

  In this respect, according to the above-described configuration 2, since the maximum burying amount MB1 is set to 0.5 mm or less, it is possible to suppress an excessive increase in the energization current and thus the heat generation amount. Therefore, it is possible to prevent the change in the precipitation state of components at the welding interface more reliably, and to prevent the welding strength from being lowered. As a result, the effect by making the maximum burying amount MB1 0.05 mm or more can be sufficiently exhibited.

Configuration 3. The spark plug of this configuration is the maximum of the base portion along the axis in a cross section including a perpendicular bisector of the thickness of the base in the configuration 1 or 2 and extending in parallel to the axis. The amount of burial is 0.15 mm or more,
The maximum burying amount of the base along the axis in a cross section including a perpendicular bisector of the width of the base and extending in parallel with the axis is 0.10 mm or more and 0.4 mm or less. It is characterized by.

  According to the configuration 3, the maximum burying amount MB2 is set to 0.15 mm or more, and the maximum burying amount MB1 is set to 0.10 mm or more. Therefore, the welding strength can be further increased.

  Moreover, according to the said structure 3, since the maximum embedment amount MB1 is 0.4 mm or less, an excessive increase in the energization current and thus the calorific value can be more effectively suppressed. Therefore, it is possible to prevent the change in the precipitation state of the components at the welding interface more reliably, and it is possible to very effectively prevent the welding strength from being lowered. As a result, the welding strength can be further improved.

  Configuration 4. The spark plug of this configuration is characterized in that, in any one of the above configurations 1 to 3, the ground electrode is made of nickel or an alloy mainly composed of nickel.

  The “main component” means a component having the highest mass ratio in the material.

  According to Configuration 4, the ground electrode is formed of Ni or an alloy containing Ni as a main component. Therefore, the thermal conductivity of the ground electrode can be improved, and excellent wear resistance can be realized.

  Configuration 5. In the spark plug of this configuration, in any one of the above configurations 1 to 4, the ground electrode is composed of 93 mass% or more of Ni and 0.05 mass% or more and 0.45 mass% or less of a rare earth element containing yttrium (Y). It is characterized by containing.

  As the “rare earth element”, in addition to Y, lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), dysprosium (Dy), erbium (Er), and ytterbium (Yb) Can be mentioned.

  According to the configuration 5, the ground electrode is formed of a metal containing 93 mass% or more of Ni. Therefore, the thermal conductivity of the ground electrode can be improved, and excellent wear resistance can be realized.

  On the other hand, a metal containing a large amount of Ni tends to grow at high temperatures, and when the ground electrode is formed of a metal containing a large amount of Ni as in the configuration 5, the ground electrode is configured at a high temperature. There is concern about the growth of metal grains.

  In this regard, according to the configuration 5, the ground electrode contains one or more rare earth elements, and the rare earth element content is 0.05 mass% or more. Therefore, the grain growth of the metal constituting the ground electrode can be more reliably suppressed, and the wear resistance can be further improved.

  If the rare earth element content is excessively high, sweat particles are likely to be generated on the surface of the ground electrode at high temperatures. If sweat particles are generated, the gap formed between the center electrode and the ground electrode is locally narrowed due to the presence of the sweat particles, which may lead to a decrease in ignitability. In this regard, according to the configuration 5, the rare earth element content is set to a sufficiently small value of 0.45% by mass or less. Therefore, the generation of sweat particles can be effectively suppressed, and the reduction in ignitability can be more reliably prevented.

  In addition, when the ground electrode is formed of a metal containing a large amount of Ni, as described above, the thermal conductivity of the ground electrode is improved, so that the metal shell and the ground electrode are sufficient when welding the ground electrode to the metal shell. Therefore, it is necessary to increase the energization current and thus the heat generation amount to some extent. However, in the case where the ground electrode contains a rare earth element, if the heat generation amount is increased, the precipitation state of the rare earth element at the welding interface may change. As a result, cracks are likely to occur at the weld interface, and the weld strength may be reduced.

  In this regard, by adopting the above configuration 1 or the like, a ground electrode is formed of a metal containing 93 mass% or more of Ni and rare earth elements of 0.05 mass% or more and 0.45 mass% or less as in the above configuration 5. Even when there is a concern about a decrease in welding strength, excellent welding strength can be ensured. In other words, the configuration 1 and the like are particularly effective when the ground electrode is formed of a metal containing 93 mass% or more of Ni and 0.05 mass% or more and 0.45 mass% or less of the rare earth element.

It is a partially broken front view which shows the structure of a spark plug. (A) is an enlarged front view which shows the structure of the front-end | tip part of a spark plug, (b) is a partially broken enlarged side view which shows the structure of the front-end | tip part of a spark plug. It is the JJ sectional view taken on the line of Fig.2 (a). It is a partial expanded sectional view which shows a base etc. FIG. It is the KK sectional view taken on the line of FIG. It is a partial expanded sectional view which shows a base etc. FIG. It is the LL sectional view taken on the line of FIG. It is a partial expanded sectional view which shows the shape of the ground electrode in another embodiment. It is a partial expanded sectional view which shows the embedding aspect of the base with respect to a main metal fitting in another embodiment.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a partially cutaway front view showing a spark plug 1. In FIG. 1, the direction of the axis CL <b> 1 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.

  As is well known, the insulator 2 is formed by firing alumina or the like, and in its outer portion, a rear end side body portion 10 formed on the rear end side, and a front end than the rear end side body portion 10. A large-diameter portion 11 that protrudes radially outward on the side, a middle body portion 12 that is smaller in diameter than the large-diameter portion 11, and a tip portion that is more distal than the middle body portion 12. The leg length part 13 formed in diameter smaller than this on the side is provided. In addition, 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 middle body portion 12 and the long leg portion 13, and the insulator 2 is locked to the metal shell 3 at the step portion 14.

  Further, the insulator 2 is formed with a shaft hole 4 extending along the axis CL <b> 1, and a center electrode 5 is inserted and fixed to the tip side of the shaft hole 4. The center electrode 5 includes an inner layer 5A made of a metal having excellent thermal conductivity (for example, copper, copper alloy, pure nickel (Ni), etc.) and an outer layer 5B made of an alloy containing Ni as a main component. The center electrode 5 has a rod shape (cylindrical shape) as a whole, and a tip portion of the center electrode 5 projects from the tip of the insulator 2.

  In addition, a terminal electrode 6 is inserted and fixed on the rear end side of the shaft hole 4 in a state of protruding from the rear end of the insulator 2.

  Further, a cylindrical resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 of the shaft hole 4. Both ends of the resistor 7 are electrically connected to the center electrode 5 and the terminal electrode 6 through conductive glass seal layers 8 and 9, respectively.

  In addition, the metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel (for example, S25C), and a spark plug 1 is attached to the outer peripheral surface of the metal such as an internal combustion engine or a fuel cell reformer. A threaded portion (male threaded portion) 15 is formed for attachment to the apparatus. Further, a seat portion 16 is formed on the rear end side of the screw portion 15 so as to protrude toward the outer peripheral side, and a ring-shaped gasket 18 is fitted into the screw neck 17 at 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 combustion device, and bent inward in the radial direction. A caulking portion 20 is provided. In the present embodiment, in order to reduce the size of the spark plug 1, the metal shell 3 is reduced in diameter, and the screw diameter of the screw portion 15 is set to M10 or less.

  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 step 14 of the metal shell 3 is locked to the step 21 of the metal shell 3. It is fixed to the metal shell 3 by caulking the rear end side opening portion radially inward, that is, by forming the caulking portion 20. An annular plate packing 22 is interposed between the step portions 14 and 21. Thereby, the airtightness in the combustion chamber is maintained, and the fuel gas 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 talc 25 powder. 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, as shown in FIGS. 2A and 2B, a rod-shaped ground electrode 27 is welded to the distal end surface 26 of the metal shell 3. The ground electrode 27 is welded to the distal end face 26 by energizing the contact portion between the ground electrode 27 and the distal end face 26 while pressing the base end face against the distal end face 26 of the metal shell 3. In addition, a so-called melting sag (not shown) is formed when the metal in which the metal shell 3 and the ground electrode 27 are melted with each other is welded to the outside of the contact portion. Here, when the molten sag protrudes from the outer peripheral surface of the metal shell 3, there is a possibility that trouble may occur when the spark plug 1 is attached to an internal combustion engine or the like. When it protrudes, there is a possibility that an abnormal discharge is generated over the surface of the insulator 2 between the center electrode 5 and the molten sag. Therefore, in the past, the pressing load and energization current when welding the ground electrode 27 to the metal shell 3 are set to values that can prevent the overflow of molten sag from the inner peripheral surface of the metal shell 3 as much as possible. It is common.

  In addition, the ground electrode 27 is formed of Ni or an alloy containing Ni as a main component. In this embodiment, the ground electrode 27 contains 93% by mass or more of Ni and 0.05% of a rare earth element including yttrium (Y). It is formed from a metal containing from mass% to 0.45 mass%. In addition to Y, examples of rare earth elements include lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), dysprosium (Dy), erbium (Er), and ytterbium (Yb). it can.

  In addition, when the energization current at the time of welding the ground electrode 27 to the metal shell 3 is increased and the heat generation amount is increased, it is contained in the ground electrode 27 and the like at the welding interface between the metal shell 3 and the ground electrode 27. Change occurs in the deposited state of the components to be applied (rare earth elements in the present embodiment). When a change occurs in the precipitation state, cracks are likely to occur at the weld interface, and the weld strength is likely to decrease.

  Returning to the description of the ground electrode 27, the ground electrode 27 is bent back at an approximately middle portion of the ground electrode 27, and a spark discharge gap as a gap is provided between the tip side surface of the ground electrode 27 and the tip portion of the center electrode 5. 28 is formed. By applying a voltage to the spark discharge gap 28, spark discharge is performed in the spark discharge gap 28 in a direction substantially along the axis CL1. The ground electrode 27 is bent back at a substantially intermediate portion of the ground electrode 27 after being welded to the distal end surface 26 of the metal shell 3.

  In addition, the ground electrode 27 includes a base portion 271 that is welded to the distal end surface 26, extends toward the distal end side in the direction of the axis CL <b> 1, and is at least partially embedded in the metal shell 3. As shown in FIG. 3 (FIG. 3 is a cross-sectional view taken along the line JJ of FIG. 2A), the base 271 has a surface 27C located on the center electrode 5 side and a side opposite to the center electrode 5. The located surface 27B has a flat surface in its width direction. That is, the outlines of the surfaces 27B and 27C are configured to be linear in a cross section passing through the base 271 and orthogonal to the central axis of the ground electrode 27. In particular, in the present embodiment, at least the base 271 (in this embodiment, the entire area of the ground electrode 27) of the ground electrode 27 is configured to have a rectangular cross section.

Furthermore, in the present embodiment, as described above, since the metal shell 3 is reduced in diameter, the width W1 of the front end surface 26 of the metal shell 3 along the direction orthogonal to the axis CL1 is relatively small. (In this embodiment, the width W1 is constant in the circumferential direction of the metal shell 3). In addition, since the width W1 is relatively small, that is, the area of the surface to be welded is relatively small, the base 271 has a cross-sectional area of 3 mm ² or less along the direction orthogonal to the axis CL1. That is, the welding area between the metal shell 3 and the ground electrode 27 is relatively small, and it is difficult to ensure sufficient welding strength.

  The ground electrode 27 has a certain thickness to prevent deformation due to an external force, and the maximum thickness T1 of the base 271 is smaller than the width W1, but the width W1 and the maximum thickness. The difference from T1 is 0.3 mm or less. As described above, since the surfaces 27B and 27C have flat surfaces in the width direction of the ground electrode 27, the ground electrode 27 has a width direction of the base portion 271 with respect to the inner peripheral surface and the outer peripheral surface of the metal shell 3. Both ends are closest.

  By the way, as in this embodiment, the screw diameter of the screw portion 15 is set to M10 or less, and the difference between the width W1 and the maximum thickness T1 is set to 0.3 mm or less. When the ground electrode 27 is welded to the metallic shell 3, the molten sagging may occur on the inner circumferential surface or the outer circumferential surface of the metallic shell 3. In order to prevent protrusion of molten sag, it is necessary to make the pressing load and the energization current during welding relatively small. However, if the pressing load and the energization current are reduced, the amount of burying of the base portion 271 with respect to the metal shell 3 and the amount of penetration of both are reduced, so that the welding strength of both may be insufficient.

Further, when the cross-sectional area of the base portion 271 is 3 mm ² or less as in the present embodiment, the welding strength tends to be insufficient, and the ground electrode 27 can be removed from the metal shell 3 relatively easily. There is a risk that. That is, in the spark plug 1 according to the present embodiment, considering the cross-sectional area of the base portion 271, it is necessary to ensure better welding strength, but the screw diameter of the screw portion 15 and the width W1 and thickness T1 of the tip surface 26. Therefore, it is difficult to ensure sufficient welding strength.

Therefore, in the present embodiment, the ground electrode 27 is welded to the metal shell 3 without significantly reducing the pressing load or energization current during welding, so that the inner metal surface or the outer peripheral surface of the metal shell 3 is melted. The sag protrudes, and the innermost peripheral part and the outermost peripheral part of the tip surface 26 are deformed as the molten sag protrudes. Accordingly, as shown in FIG. 4, when a cross section including the vertical bisector PM1 of the line segment SG1 having the width of the base 271 and extending in parallel with the axis CL1 is taken, FIG. 5 (FIG. 4), the position 271M where the base 271 is most buried with respect to the distal end surface 26 of the metal shell 3 is the outer peripheral surface 3G or the inner peripheral surface 3 N of the metal shell 3. (In this embodiment, it is comprised so that it may be located in the outer peripheral surface 3G of the metal shell 3). That is, the base portion 271 is sufficiently buried in the metal shell 3 at a portion where stress is concentrated when an external force is applied, and a very excellent welding strength is ensured.

  In the present embodiment, after the ground electrode 27 is welded to the metal shell 3, the molten sag that protrudes from the outer peripheral surface and the inner peripheral surface of the metal shell 3 is cut out by a predetermined jig.

  Furthermore, in the present embodiment, in order to ensure good welding strength at the portions other than the outer periphery and inner periphery of the base portion 271, as shown in FIG. 6, the vertical segment of the line segment SG2 where the thickness of the base portion 271 is maximum is shown. When taking a cross section including the segment PM2 and extending in parallel with the axis CL1, as shown in FIG. 7 (FIG. 7 is a cross-sectional view taken along line LL in FIG. 6), the base along the axis CL1 The maximum burying amount MB2 of 271 is 0.10 mm or more (more preferably, 0.15 mm or more).

  Further, in the present embodiment, in order to realize even better welding strength, as shown in FIG. 5, the vertical bisector PM1 of the line segment SG1 of the width of the base portion 271 is included and extends in parallel with the axis CL1. The maximum burying amount MB1 of the base portion 271 along the axis CL1 in the cross section is 0.05 mm or more (more preferably, 0.10 mm or more). Note that “the maximum amount of burying of the base portion 271” means that the portion of the base portion 271 that is most buried with respect to the metallic shell 3 is the most buried portion of the base portion 271 with respect to the metallic shell 3. A value obtained by subtracting the amount of burial of no part.

  Note that when the maximum burying amount MB1 is set to 0.05 mm or more, for example, when the ground electrode 27 is welded to the metal shell 3, it is conceivable to increase the heat generation amount, but the heat generation amount is excessively increased. If it does, it will change in the precipitation state of the component (rare earth element) contained in the ground electrode 27 in the welding interface. In this case, there is a possibility that the effect of improving the welding strength due to the maximum burying amount MB1 being 0.05 mm or more may not be sufficiently exhibited.

  Therefore, in the present embodiment, the maximum burying amount MB1 is 0.5 mm or less (more preferably 0.4 mm or less), and an increase in the amount of heat generated during welding is suppressed.

  As described above in detail, according to the present embodiment, the position 271M where the base 271 is most buried with respect to the distal end surface 26 of the metal shell 3 is configured to be located on the outer peripheral surface of the metal shell 3. . That is, when an external force is applied to the ground electrode 27, stress is particularly applied to the inner periphery and the outer periphery of the welded portions of the base 271 and the metal shell 3, and the base 271 is mainly used in the portion to which this stress is particularly applied. It is comprised so that it may embed most with respect to the metal fitting 3. Therefore, it is possible to more surely secure the welding strength that can sufficiently resist the stress.

  In addition, the maximum burying amount MB2 is set to 0.10 mm or more, and a sufficient amount of burying is ensured in a portion of the base portion 271 other than the outer periphery and the inner periphery. Thereby, the welding strength can be further improved, and the ground electrode 27 can be more reliably prevented from falling off.

  Furthermore, in the present embodiment, the maximum burying amount MB1 is set to 0.05 mm or more. Therefore, the welding strength can be improved more reliably.

  In addition, since the maximum burying amount MB1 is set to 0.5 mm or less, it is possible to suppress an excessive increase in the energization current and thus the calorific value. Therefore, it is possible to prevent the change in the precipitation state of components at the welding interface more reliably, and to prevent the welding strength from being lowered. As a result, the effect by making the maximum burying amount MB1 0.05 mm or more can be sufficiently exhibited.

  Further, the ground electrode 27 is made of a metal containing 93 mass% or more of Ni. Therefore, the thermal conductivity of the ground electrode 27 can be improved, and excellent wear resistance can be realized.

  On the other hand, in the case where the ground electrode 27 is formed from a metal containing a large amount of Ni, there is a concern about the grain growth of the metal constituting the ground electrode 27 at a high temperature. One or more elements are contained, and the rare earth element content is 0.05% by mass or more. Therefore, the grain growth of the metal constituting the ground electrode 27 can be more reliably suppressed, and the wear resistance can be further improved.

  In addition, the content of rare earth elements in the ground electrode 27 is set to a sufficiently small value of 0.45 mass% or less. Therefore, the generation of sweat particles can be effectively suppressed, and the reduction in ignitability can be more reliably prevented.

  Next, in order to confirm the effect achieved by the above embodiment, in the cross section including the perpendicular bisector of the width of the base portion and extending in parallel with the axis, the front end surface of the metal shell of the base portion In contrast, the most buried position (most buried position) is the outer peripheral surface, inner peripheral surface, or other than that of the metal shell, and the maximum thickness of the base from the screw diameter of the threaded portion and the width W1 of the distal end surface of the metal shell At least five spark plug samples in which the value (W1-T1) obtained by subtracting the thickness T1, the cross-sectional area of the base, and the maximum burial amounts MB1 and MB2 are changed are prepared, and a weld strength evaluation test is performed on each sample. went.

  The outline of the weld strength evaluation test is as follows. That is, in each sample, the ground electrode was repeatedly bent, and the number of times that the ground electrode was broken at the welded portion (the ground electrode was dropped from the metal shell) (number of breaks) was measured, and the average number of times of breakage (average number of breaks) Was calculated. Here, the sample whose average number of breaks was 4.5 times or more was rated as “☆” as having an extremely excellent weld strength, and the average number of breaks was 3.5 times or more and less than 4.5 times. The sample with the excellent fracture strength was evaluated as “◎”, and the sample with an average number of fractures of 2.5 times or more and less than 3.5 times was considered to have good weld strength. It was decided to give an “O” evaluation. On the other hand, a sample having an average number of fractures of less than 2.5 was evaluated as “x” because it was inferior in welding strength. Tables 1 and 2 show the test results of the test.

  The most buried position, the maximum buried amount MB1, MB2, etc. were changed by adjusting the energizing current and the pressing load when welding the ground electrode to the metal shell. For example, by making the energization current relatively small, the formation of melting sag (that is, the protrusion of molten sag to the outer peripheral surface or inner peripheral surface of the metal shell) is suppressed, and the most buried position is set to the outer peripheral surface of the metal shell. And it can be set as positions other than an internal peripheral surface. In addition, by making the energization current relatively large, it is possible to actively form a molten sag (extinguish the molten sag from the outer peripheral surface or inner peripheral surface of the metal shell), and the main burying position is mainly It can be the inner peripheral surface or the outer peripheral surface of the metal fitting. Furthermore, the maximum burying amounts MB1 and MB2 can be increased or decreased by increasing or decreasing the energization current or the pressing load.

  In each sample, a ground electrode was formed of a metal containing 93% by mass of Ni and 0.05% by mass or more and 0.45% by mass or less of rare earth elements. In addition, the base has a rectangular cross section.

  As shown in Table 1 and Table 2, among samples (samples 1 to 11) in which the most buried position is a position other than the inner peripheral surface and the outer peripheral surface of the metallic shell, It was found that the samples (samples 1 to 5) with W1-T1 exceeding 0.3 mm had good welding strength. This is because the screw diameter of the threaded portion and W1-T1 are relatively large, and the distance between the outer periphery and inner periphery of the base and the inner peripheral surface and outer peripheral surface of the metal shell is relatively large. This is also considered to be because the metal shell and the ground electrode could be sufficiently melted without causing melt sag to protrude from the inner and outer peripheral surfaces of the metal shell.

  On the other hand, among the samples (samples 1 to 11) in which the most buried position is a position other than the inner peripheral surface and the outer peripheral surface of the metal shell, the screw diameter of the screw portion is M10 or less, and W1-T1 is set to 0. It was revealed that the samples (samples 6 to 11) having a size of 3 mm or less were inferior in welding strength. This is because the screw diameter and W1-T1 were relatively small, and in order to prevent melting sag from protruding on the inner peripheral surface and outer peripheral surface of the metal shell, the energizing current had to be reduced, and as a result, This is probably because the metal shell and the ground electrode are not sufficiently melted.

  Moreover, it was confirmed that the samples (samples 12 to 17) having the maximum burying amount MB2 of less than 0.10 mm have insufficient welding strength.

In contrast, the only one of the inner and outer peripheral surfaces of the metal shell of the uppermost buried position, and sample the maximum buried amount MB2 was above 0.10 mm (Sample 18-6 5) Screw diameter Even when the thickness was set to M10 or less and W1-T1 was set to 0.3 mm or less, it was revealed that the steel had good welding strength. This is considered to be caused by the following (1) and (2).

  (1) When the energizing current is relatively large, and the molten sag protrudes from the outer peripheral surface and inner peripheral surface of the metal shell, the base portion is located at a location where stress is particularly concentrated when an external force is applied to the ground electrode. Welding strength that is most buried in the metal shell and sufficiently resists stress is secured.

  (2) By making the energizing current relatively large, the metal shell and the ground electrode were sufficiently melted.

  Furthermore, it turned out that the sample (samples 30-65) which made maximum burying amount MB1 0.05 mm or more and 0.5 mm or less has the further outstanding welding strength. This is because when the maximum burying amount MB1 is set to 0.05 mm or more, the welding strength is further improved, and the maximum burying amount MB1 is set to 0.5 mm or less. It is thought that this is because the excessive increase in the amount of) was prevented, and the change in the precipitation state of the components at the weld interface was more reliably prevented.

  In addition, it is clear that the samples (samples 48 to 65) having the maximum burying amount MB1 of 0.10 mm or more and 0.4 mm or less and the maximum burying amount MB2 of 0.15 mm or more have extremely excellent welding strength. It became. This is because the maximum burying amount MB1 is set to 0.10 mm or more and the maximum burying amount MB2 is set to 0.15 mm or more, so that the welding strength is further improved, and the maximum burying amount MB1 is set to 0.4 mm or less. This is considered to be due to the fact that heat generation during welding can be further suppressed and the change in the precipitation state of components at the welding interface can be prevented very effectively.

As a result of the above test, the cross-sectional area of the base is 3 mm ² or less, and it is necessary to ensure better welding strength. On the other hand, the screw diameter of the thread is M10 or less, and W1-T1 is In the spark plug, it is difficult to ensure sufficient welding strength with the conventional method, in order to achieve good welding strength and more reliably prevent the ground electrode from falling off due to external force. It can be said that it is preferable that the maximum burying amount MB2 is set to 0.10 mm or more and that the most burying position of the base is only one of the inner peripheral surface and the outer peripheral surface of the metal shell.

  In order to further improve the welding strength, it can be said that the maximum burying amount MB1 is more preferably 0.05 mm or more and 0.5 mm or less.

  Furthermore, from the viewpoint of further improving the welding strength, it can be said that it is even more preferable that the maximum burying amount MB1 is set to 0.10 mm to 0.4 mm and the maximum burying amount MB2 is set to 0.15 mm or more.

  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) The shape of the base 271 in the above embodiment is an exemplification, and the base 271 has a surface 27C located on the center electrode 5 side and a surface 27B located on the opposite side to the center electrode 5 in its width direction. Any shape having a flat surface may be used. Therefore, for example, as shown in FIG. 8, the surface 37 </ b> C on the side of the center electrode 5 and the surface 37 </ b> B located on the opposite side of the center electrode 5 have a flat surface in the width direction, and the outer peripheral surface of the base 371. Of these, the surface positioned between the surface 37B and the surface 37C may be configured to form a curved surface convex outward. In this case, when the spark plug 1 is attached to an internal combustion engine or the like with the ground electrode 37 positioned between the spark discharge gap 28 and the fuel injection device, the ground electrode 37 is wrapped around. The fuel gas easily enters the spark discharge gap 28. Accordingly, it is possible to more reliably prevent an extreme decrease in ignitability due to a difference in mounting position.

(B) In the above embodiment, the position 271M where the base 271 is most buried is configured to be located on the outer peripheral surface 3G of the metal shell 3. However, as shown in FIG. It is configured so as to be located on the inner circumferential surface 3N of not good.

  (C) In the above embodiment, the ground electrode 27 is formed of a single metal whose main component is Ni. However, the ground electrode 27 is composed of an outer layer made of a metal whose main component is Ni, It is good also as a multilayer structure provided with the inner layer which is arrange | positioned inside and is excellent in heat conductivity (for example, copper, copper alloy, pure Ni etc.).

  (D) In the above embodiment, the spark discharge gap 28 is formed between the tip of the center electrode 5 and the tip of the ground electrode 27. On the other hand, a chip made of a metal having excellent wear resistance (for example, platinum alloy or iridium alloy) is joined to one or both of the electrodes 5 and 27, and the spark discharge gap 28 is connected to one electrode 5 (27 ) And the other electrode 27 (5), or between both chips provided on the electrodes 5 and 27.

  (E) In the above embodiment, the tool engaging portion 19 has a hexagonal cross section, but the shape of the tool engaging 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)].

  DESCRIPTION OF SYMBOLS 1 ... Spark plug, 2 ... Insulator (insulator), 3 ... Main metal fitting, 4 ... Shaft hole, 5 ... Center electrode, 15 ... Screw part, 27 ... Ground electrode, 28 ... Spark discharge gap (gap), 271 ... Base, CL1 ... axis.

Claims (5)

A cylindrical insulator having an axial hole penetrating in the axial direction;
A center electrode inserted on the tip side of the shaft hole;
A cylindrical metal shell having a threaded portion on the outer periphery and provided on the outer periphery of the insulator;
A spark plug comprising a ground electrode joined to a front end surface of the metal shell via a welded portion and forming a gap with the center electrode,
The ground electrode is
Together are joined through the weld at the tip surface of the metal shell, extending toward the tip end side in the axial direction, a spark plug having a base portion at least partially buried in the metal shell,
The base portion has a flat surface in the width direction of a surface located on the side of the center electrode and a surface located on the side opposite to the center electrode, and the base portion along a direction perpendicular to the axis. The cross-sectional area is 3 mm ² or less,
The screw diameter of the screw portion is M10 or less, and
Width of the end face of the metal shell along a direction perpendicular to the axis, the While larger than the metal shell to the maximum area to be joined via a weld thickness of the base of the metal shell The difference between the width of the tip surface and the maximum thickness is 0.3 mm or less,
In a cross section that includes a perpendicular bisector of the thickness of the base and extends in parallel with the axis, the maximum burying amount of the base along the axis is 0.10 mm or more,
In a cross section that includes a vertical bisector of a width line segment of the base portion and extends in parallel with the axis , only one of the outer peripheral surface and the inner peripheral surface of the metal shell is the base metal. A spark plug characterized by being buried most with respect to the tip surface .   The maximum burying amount of the base along the axis in a cross section including a perpendicular bisector of the width of the base and extending parallel to the axis is 0.05 mm or more and 0.5 mm or less. The spark plug according to claim 1. In a cross section that includes a perpendicular bisector of the thickness of the base and extends in parallel with the axis, the maximum burying amount of the base along the axis is 0.15 mm or more,
The maximum burying amount of the base along the axis in a cross section including a perpendicular bisector of the width of the base and extending in parallel with the axis is 0.10 mm or more and 0.4 mm or less. The spark plug according to claim 1 or 2.   The spark plug according to any one of claims 1 to 3, wherein the ground electrode is made of nickel or an alloy mainly composed of nickel.   5. The ground electrode according to claim 1, wherein the ground electrode contains 93 mass% or more of nickel and a rare earth element containing yttrium of 0.05 mass% or more and 0.45 mass% or less. Spark plug.

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