JP2015185286A - spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug that has plural insulating members and is enhanced in strength.SOLUTION: A spark plug includes a first insulating member having a first portion having a first hole, a second portion which has a second hole having a larger inner diameter than the first hole and is disposed to be nearer to the rear end side than the first portion, and a shelf portion formed between the first portion and the second portion, a second insulating member having a cylindrical portion which has a through-hole extending in an axial line direction and is disposed in the first hole, and a center electrode having a rod-shaped portion disposed in the through-hole of the cylindrical portion. The second insulating member has a large-diameter portion which is disposed at the rear end side of the cylindrical portion, and has a larger outer diameter than the cylindrical portion. The large-diameter portion is directly or indirectly supported by the shelf portion of the first insulating member.

Description

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

The spark plug generates a spark in the gap formed between the tip of the center electrode and the tip of the ground electrode by applying a voltage to the center electrode and the ground electrode insulated from each other by an insulator. Let Here, a technique is known in which an insulator that insulates between two electrodes is configured by combining a plurality of insulating members. For example, in the technique described in Patent Document 1, the insulator of the spark plug is composed of a main body formed using aluminum nitride having excellent thermal conductivity, and alumina (Al ₂ O ₃ having excellent voltage resistance at high temperatures). And a pipe member formed using The pipe member is disposed in a gap between the main body and the center electrode, and is fixed by an adhesive (also referred to as cement). This improves the heat resistance and voltage resistance of the spark plug.

Japanese Patent Laid-Open No. 2-152186 JP-A-55-113290 JP 2002-246145 A

  However, in the above technique, it cannot be said that a sufficient contrivance has been made for a structure for fixing a plurality of insulating members. For this reason, there is a possibility that the strength of the spark plug cannot be sufficiently ensured.

  An object of the present invention is to improve the strength of a spark plug including a plurality of insulating members as an insulator for insulating between two electrodes.

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

[Application Example 1] A first portion having a first hole extending in the axial direction and a second hole having an inner diameter larger than that of the first hole are arranged on the rear end side of the first portion. A first insulating member comprising a second part and a shelf formed between the first part and the second part;
A second insulating member having a through hole extending in the axial direction and including a cylindrical portion disposed in the first hole;
A center electrode provided with a rod-shaped portion disposed in the through hole of the tubular portion;
A spark plug comprising:
The second insulating member is disposed on a rear end side of the cylindrical portion, and includes a large diameter portion having an outer diameter larger than that of the cylindrical portion,
The spark plug according to claim 1, wherein the large-diameter portion is supported directly or indirectly on the shelf portion of the first insulating member.

  According to the said structure, the large diameter part of the 2nd insulating member is supported by the shelf part of the 1st insulating member. As a result, the second insulating member can be firmly fixed to the first insulating member. Therefore, the strength of the spark plug can be improved.

[Application Example 2] The spark plug according to Application Example 1,
The center electrode is disposed on the rear end side from the cylindrical part, and includes a head having a larger outer diameter than the cylindrical part,
The spark plug, wherein the large-diameter portion of the second insulating member is sandwiched between the shelf portion of the first insulating member and the head portion of the center electrode.

  According to the above configuration, the large-diameter portion of the second insulating member is sandwiched between the shelf portion of the first insulating member and the head portion of the center electrode. As a result, the second insulating member can be more firmly fixed to the first insulating member. Therefore, the strength of the spark plug can be further improved.

[Application Example 3] The spark plug according to Application Example 2, further comprising:
A seal member that seals between the head and the second portion in the second hole;
A spark plug.

  According to the above configuration, the second insulating member can be more firmly fixed to the first insulating member by the sealing member that seals between the head and the second portion. Therefore, the strength of the spark plug can be further improved.

[Application Example 4] The spark plug according to any one of Application Examples 1 to 3,
Each of the first insulating member and the second insulating member includes Al ₂ O ₃ ,
The spark plug according to claim 1, wherein a weight ratio of Al ₂ O ₃ contained in the first insulating member is different from a weight ratio of Al ₂ O ₃ contained in the second insulating member.

The lower the weight ratio of Al ₂ O ₃ (alumina), the better the moldability, but the voltage resistance tends to be inferior. According to the above configuration, by using the first insulating member and the second insulating member weight ratio of Al ₂ O ₃ is different, is compatible with the molding of the spark plug, the voltage resistance, the.

[Application Example 5] The spark plug according to any one of Application Examples 1 to 4,
Each of the first insulating member and the second insulating member includes Al ₂ O ₃ ,
Said second weight ratio of Al ₂ O ₃ contained in the insulating member, a spark plug, characterized in that said at first insulating Al ₂ O ₃ weight ratio or more contained in the member.

  According to the above configuration, it is possible to ensure the voltage resistance of the second insulating member that is required to have higher voltage resistance than the first insulating member because it is closer to the center electrode, and to form the first insulating member. Can be secured. As a result, it is possible to more effectively achieve both the ease of manufacturing the spark plug and the withstand voltage.

[Application Example 6] The spark plug according to any one of Application Examples 1 to 5,
The tip of the second insulating member is located on the tip side from the tip of the first insulating member,
The spark plug according to claim 1, wherein a front end of the center electrode is positioned on a rear end side with respect to a front end of the second insulating member.

  In general, a material called “channeling” that has high resistance to spark consumption (spark wear resistance) has poor voltage resistance. According to the above configuration, the front end of the center electrode is located on the rear end side from the front end of the second insulating member. For this reason, the second insulating member is easily consumed by the spark generated at the tip of the center electrode, and the first insulating member is less likely to be consumed by the spark than the second insulating member. According to the above configuration, the second insulating member that is required to have high spark consumption and the first insulating member that is not required to have high spark consumption are formed of different members. Both flower wear and voltage resistance can be achieved.

[Application Example 7] The spark plug according to Application Example 6,
The second insulating member includes at least one specific compound of La ₂ O ₃ , SiO ₂ , SiC, TiO ₂ , Y ₂ O ₃ , CaO, and MgO,
The spark plug according to claim 1, wherein a total weight ratio of the specific compounds included in the second insulating member is greater than a total weight ratio of the specific compounds included in the first insulating member.

The higher the weight ratio of La ₂ O ₃ , SiO ₂ , TiO ₂ , Y ₂ O ₃ , CaO, and MgO, the lower the surface resistance and the higher the spark consumption. According to the above configuration, the spark wear resistance of the second insulating member can be improved more than that of the first insulating member, so that the spark plug wear resistance of the spark plug can be improved.

[Application Example 8] The spark plug according to any one of Application Examples 1 to 3 and Application Example 6,
The first insulating member is a ceramic mainly composed of Al ₂ O ₃ ,
The spark plug, wherein the second insulating member is a ceramic mainly composed of any one of AlN, ZrO ₂ , SiC, TiO ₂ , and Y ₂ O ₃ .

According to the above configuration, the characteristics of the first insulating member formed using the ceramic mainly composed of Al ₂ O ₃ and any one of AlN, ZrO ₂ , SiC, TiO ₂ , and Y ₂ O ₃ are used. A spark plug having an insulator whose performance is optimized can be realized by the characteristics of the second insulating member formed using ceramics whose main component is.

  The present invention can be realized in various modes. For example, a spark plug, an ignition device using the spark plug, an internal combustion engine equipped with the spark plug, and an ignition device using the spark plug are provided. This can be realized in the form of an internal combustion engine or the like to be mounted.

It is sectional drawing which cut | disconnected the spark plug 100 of 1st Embodiment by the surface where an axis line is included. It is the figure which expanded the vicinity of the center electrode 20 of sectional drawing of FIG. It is sectional drawing of comparative sample AC. The figure which shows the structure of the edge part of the spark plug of a comparison form. It is a 1st figure which shows the example of the inner side insulator of a modification. It is a 2nd figure which shows the example of the inner side insulator of a modification.

A. First embodiment:
A-1. Spark plug configuration:
Hereinafter, embodiments of the present invention will be described based on the embodiments. FIG. 1 is a cross-sectional view of the spark plug 100 according to the first embodiment cut along a plane including an axis. The dashed line in FIG. 1 indicates the axis CO (also referred to as axis CO) of the spark plug 100. A direction parallel to the axis CO (vertical direction in FIG. 1) is also referred to as an axis direction. The radial direction of the circle centered on the axis CO is simply referred to as “radial direction”, and the circumferential direction of the circle centered on the axis CO is also simply referred to as “circumferential direction”. The lower direction in FIG. 1 is referred to as a front end direction FD, and the upper direction is also referred to as a rear end direction BD. The lower side in FIG. 1 is called the front end side of the spark plug 100, and the upper side in FIG. 1 is called the rear end side of the spark plug 100. The spark plug 100 includes an outer insulator 10 as a first insulating member, a center electrode 20, a ground electrode 30, a terminal fitting 40, a metal shell 50, and an inner insulator 90 as a second insulating member. .

Although the details will be described later, the outer insulator 10 is formed by using, for example, ceramics mainly composed of Al ₂ O ₃ (alumina). The outer insulator 10 is a substantially cylindrical member having a through hole 12 (axial hole) extending along the axial direction and penetrating the outer insulator 10. The outer insulator 10 includes a flange part 19, a rear end side body part 18, a front end side body part 17, a step part 15, and a leg length part 13. The rear end side body portion 18 is located on the rear end side of the flange portion 19 and has an outer diameter smaller than the outer diameter of the flange portion 19. The distal end side body portion 17 is located on the distal end side from the flange portion 19 and has an outer diameter smaller than the outer diameter of the flange portion 19. The long leg portion 13 is positioned on the distal end side from the distal end side body portion 17 and has an outer diameter smaller than the outer diameter of the distal end side body portion 17. The leg portion 13 is exposed to the combustion chamber when the spark plug 100 is attached to an internal combustion engine (not shown). The step portion 15 is formed between the leg long portion 13 and the distal end side body portion 17.

  The metal shell 50 is formed of a conductive metal material (for example, a low carbon steel material) and is a cylindrical metal fitting for fixing the spark plug 100 to an engine head (not shown) of an internal combustion engine (FIG. 1). The metal shell 50 is formed with an insertion hole 59 penetrating along the axis CO. The metal shell 50 is disposed on the outer periphery of the outer insulator 10. That is, the outer insulator 10 is inserted and held in the insertion hole 59 of the metal shell 50. The tip of the outer insulator 10 protrudes from the tip of the metal shell 50 to the tip side. The rear end of the outer insulator 10 protrudes toward the rear end side from the rear end of the metal shell 50.

  The metal shell 50 is formed between a hexagonal column-shaped tool engagement portion 51 with which a spark plug wrench engages, an attachment screw portion 52 for attachment to an internal combustion engine, and the tool engagement portion 51 and the attachment screw portion 52. And a bowl-shaped seat portion 54. The nominal diameter of the mounting screw portion 52 is, for example, one of M8 (8 mm (millimeters)), M10, M12, M14, and M18.

  An annular gasket 5 formed by bending a metal plate is fitted between the mounting screw portion 52 and the seat portion 54 of the metal shell 50. The gasket 5 seals a gap between the spark plug 100 and the internal combustion engine (engine head) when the spark plug 100 is attached to the internal combustion engine.

  The metal shell 50 further includes a thin caulking portion 53 provided on the rear end side of the tool engaging portion 51, and a thin compression deformation portion 58 provided between the seat portion 54 and the tool engaging portion 51. And. In the annular region formed between the inner peripheral surface of the portion of the metal shell 50 from the tool engaging portion 51 to the crimping portion 53 and the outer peripheral surface of the rear end side body portion 18 of the outer insulator 10, Annular ring members 6 and 7 are arranged. Between the two ring members 6 and 7 in the region, talc (talc) 9 powder is filled. The rear end of the crimped portion 53 is bent radially inward and fixed to the outer peripheral surface of the outer insulator 10. The compression deformation portion 58 of the metal shell 50 is compressed and deformed when the crimping portion 53 fixed to the outer peripheral surface of the outer insulator 10 is pressed toward the distal end side during manufacture. The outer insulator 10 is pressed toward the front end side in the metal shell 50 through the ring members 6 and 7 and the talc 9 by the compression deformation of the compression deformation portion 58. A step portion 15 (insulator side) of the outer insulator 10 is formed by a step portion 56 (metal portion step portion) formed on the inner periphery of the mounting screw portion 52 of the metal shell 50 through the metal annular plate packing 8. The step) is pressed. As a result, the gas in the combustion chamber of the internal combustion engine is prevented by the plate packing 8 from leaking outside through the gap between the metal shell 50 and the outer insulator 10.

  The terminal fitting 40 is a rod-shaped member extending in the axial direction. The terminal fitting 40 is formed of a conductive metal material (for example, low carbon steel), and a metal layer (for example, Ni layer) for corrosion protection is formed on the surface of the terminal fitting 40 by plating or the like. The terminal fitting 40 includes a collar part 42 (terminal jaw part) formed at a predetermined position in the axial direction, a cap mounting part 41 located on the rear end side of the collar part 42, and a leg part 43 on the distal side of the collar part 42. (Terminal leg). The cap mounting portion 41 of the terminal fitting 40 is exposed to the rear end side from the outer insulator 10. The leg portion 43 of the terminal fitting 40 is inserted into the through hole 12 of the outer insulator 10. A plug cap to which a high voltage cable (not shown) is connected is attached to the cap attaching portion 41, and a high voltage for generating a spark discharge is applied.

  The ground electrode 30 includes a ground electrode body 31 and a cylindrical ground electrode tip 39. The ground electrode main body 31 is a rod-shaped body having a square cross section. The rear end portion of the ground electrode main body 31 is joined to the front end surface of the metal shell 50 by welding. Thereby, the metal shell 50 and the ground electrode body 31 are electrically connected. The tip of the ground electrode body 31 is a free end. The ground electrode tip 39 is welded to the surface facing the center electrode 20 near the tip of the ground electrode body 31 (surface on the rear end side). As the material of the ground electrode tip 39, for example, Pt (platinum) or an alloy mainly containing Pt is used. In this embodiment, a Pt-20Rh alloy (a platinum alloy containing 20 wt% rhodium) is used.

  Although details will be described later, the inner insulator 90 is formed using a material different from that of the outer insulator 10. Although the details will be described later, the inner insulator 90 is a substantially cylindrical member, and is disposed at a tip side portion inside the through hole 12 of the outer insulator 10.

  As will be described in detail later, the center electrode 20 includes a substantially rod-shaped center electrode body 25 and a columnar center electrode chip 29 joined to the tip of the center electrode body 25 (FIG. 1). Most of the center electrode body 25 is inserted into an inner insulator 90 which will be described in detail later. A spark gap is formed between the center electrode tip 29 and the ground electrode tip 39 described above.

In the through-hole 12 of the outer insulator 10, there is a radio wave at the time of spark generation between the tip of the terminal fitting 40 (tip of the leg 43) and the rear end of the center electrode 20 (back end of the center electrode body 25). A resistor 70 for reducing noise is disposed. The resistor 70 is formed of, for example, a composition including glass particles that are main components, ceramic particles other than glass, and a conductive material. In the through hole 12, a gap between the resistor 70 and the center electrode 20 is filled with a conductive seal member 60. A gap between the resistor 70 and the terminal fitting 40 is filled with a conductive seal member 80. The seal members 60 and 80 are formed of a composition containing glass particles such as B ₂ O ₃ —SiO ₂ and metal particles (Cu, Fe, etc.), for example.

A-2. Configuration near the center electrode 20 of the spark plug 100:
The configuration in the vicinity of the center electrode 20 of the spark plug 100 will be described in more detail. FIG. 2 is an enlarged view of the vicinity of the center electrode 20 in the cross-sectional view of FIG. The through-hole 12 (FIG. 1) of the outer insulator 10 has a first hole 121 having a diameter R1 and a diameter R2 (R1 <R2) larger than the diameter R1 and located on the rear end side of the first hole 121. And a second hole 122 (FIG. 2). That is, the outer insulator 10 includes a first portion 101 having a first hole 121 and a second portion 102 having a second hole 122 and disposed on the rear end side from the first portion. You can say.

  The first hole 121 is formed in a portion from the distal end of the leg long portion 13 (the distal end of the outer insulator 10) to the distal end side portion of the distal end side trunk portion 17. The second hole 122 is formed in a portion from the front end side portion of the front end side body portion 17 to the rear end (rear end of the outer insulator 10) of the rear end side body portion 18. The through hole 12 of the outer insulator 10 is reduced in diameter from the front end of the second hole 122 toward the rear end of the first hole 121. As a result, the shelf 16 is formed between the first portion having the first hole 121 and the second portion having the second hole 122 inside the outer insulator 10. In addition, the outer diameter of the leg long part 13 is reduced from the rear end diameter Rb to the front end diameter Ra from the rear end side toward the front end side. 2, the intersection of the straight line L1 along the inner peripheral surface of the long leg portion 13 and the straight line L2 along the contact surface with the plate packing 8 of the step portion 15 is P1 (enlarged view of FIG. 2). ), A similar point located on the opposite side across the axis with respect to the intersection P1 is defined as P2 (not shown). The rear end diameter Rb of the leg long portion 13 is the length of a line segment connecting the points P1 and P2. The same applies to the rear end diameter R2b (FIG. 4) of the leg long portion 13D in the second embodiment to be described later.

  The inner insulator 90 includes a cylindrical portion 91 having a through-hole 911 having a diameter R4 extending in the axial direction, and a collar-shaped large-diameter portion 92 disposed on the rear end side of the cylindrical portion 91. ing. The tubular portion 91 is disposed in the first hole 121 of the outer insulator 10. The outer diameter R3 of the cylindrical portion 91 is slightly smaller (for example, 0.04 to 0.06 mm) than the diameter R1 of the first hole 121 (the inner diameter R1 of the first portion 101). That is, a slight gap (for example, a gap of 0.02 to 0.03 mm) is formed between the inner peripheral surface of the first portion 101 and the outer peripheral surface of the cylindrical portion 91. The length of the cylindrical portion 91 in the axial direction is substantially equal to the length of the first hole 121 in the axial direction. For this reason, the positions in the axial direction of the distal end of the outer insulator 10 (the distal end of the long leg portion 13) and the distal end of the cylindrical portion 91 are substantially the same.

  The outer diameter R5 of the large diameter portion 92 is smaller than the diameter R2 of the second hole 122 (the inner diameter R2 of the second portion 102) and larger than the inner diameter R1 of the first portion 101. The outer diameter of the front end portion of the large diameter portion 92 is reduced from the rear end side toward the front end side. Further, the inner diameter of the rear end side portion of the large diameter portion 92 is also reduced from the rear end side toward the front end side. That is, the large diameter portion 92 includes a reduced diameter outer surface 92a on the front end side and a reduced diameter inner surface 92b on the rear end side. The reduced diameter outer surface 92 a of the large diameter portion 92 is in contact with the shelf portion 16 of the outer insulator 10. As a result, the large-diameter portion 92 of the inner insulator 90 is supported by the shelf 16 of the outer insulator 10.

  As described above, the center electrode 20 includes the rod-shaped center electrode body 25 extending in the axial direction and the columnar center electrode tip 29 joined to the tip of the center electrode body 25 (FIG. 2). In the example of FIG. 2, since the electrode tip 29 and the center electrode body 25 are joined using laser welding, the center electrode 20 is interposed between the electrode tip 29 and the tip of the center electrode body 25 during laser welding. A formed melted portion 26 is provided.

  The material of the center electrode tip 29 is, for example, iridium (Ir) or an alloy containing Ir as a main component. In this embodiment, an Ir-11Ru-8Rh-1Ni alloy (11 wt% ruthenium, 8% Iridium alloy containing 1% by weight of rhodium and 1% by weight of nickel) is used.

  The center electrode main body 25 has a two-layer structure including an electrode base material 22 and a core portion 23 embedded in the electrode base material 22. The electrode base material 22 is made of, for example, nickel or an alloy containing nickel as a main component, and in this embodiment, Inconel 600 (“INCONEL” is a registered trademark). The core portion 23 is made of copper, which is superior in thermal conductivity to the alloy forming the electrode base material 22, or an alloy containing copper as a main component, in this embodiment, copper. In the drawings subsequent to FIG. 3, the two-layer structure of the center electrode body 25 is omitted in order to avoid complication of the drawing.

  The center electrode body 25 includes a rod-shaped portion 251 extending along the axial direction, a flange-shaped portion 252 disposed on the rear end side of the rod-shaped portion 251, and a columnar portion 253 disposed on the rear-end side of the flange-shaped portion 252. It is equipped with. The portion on the rear end side from the rod-shaped portion 251, that is, the whole of the flange-shaped portion 252 and the columnar portion 253 is also referred to as a head. The rod-shaped part 251 is disposed in the through hole 911 of the cylindrical part 91 of the inner insulator 90. The outer diameter R6 of the rod-shaped portion 251 of the rod-shaped portion 251 is slightly smaller (for example, 0.04 to 0.06 mm) than the diameter R4 of the through hole 911 (the inner diameter R4 of the tubular portion 91). That is, a slight gap (for example, a gap of 0.02 to 0.03 mm) is formed between the inner peripheral surface of the cylindrical portion 91 and the outer peripheral surface of the rod-shaped portion 251. The length of the rod-shaped portion 251 in the axial direction is longer than the length of the cylindrical portion 91 in the axial direction. For this reason, the tip of the rod-like portion 251 protrudes to the tip side from the tip of the inner insulator 90 and the tip of the outer insulator 10.

  The outer diameter R7 of the hook-shaped portion 252 is larger than the outer diameter R6 of the rod-shaped portion 251 and is substantially the same as the outer diameter R5 of the large-diameter portion 92 of the inner insulator 90 described above. The outer diameter of the portion on the front end side of the bowl-shaped portion 252 is reduced from the rear end side toward the front end side. That is, the bowl-shaped portion 252 includes a reduced diameter outer surface 252a on the distal end side. The reduced diameter outer surface 252a of the bowl-shaped portion 252 and the reduced diameter inner surface 92b of the large diameter portion 92 are in contact with each other. As a result, the large diameter portion 92 of the inner insulator 90 is sandwiched between the shelf portion 16 of the outer insulator 10 and the flange portion 252 of the center electrode body 25. The outer diameter R8 of the columnar part 253 is smaller than the outer diameter R7 of the bowl-shaped part 252.

  As shown in FIG. 2, the sealing member 60 that seals between the resistor 70 and the central electrode body 25 described above includes the outer peripheral surface of the head (the hook-shaped portion 252 and the columnar portion 253) of the central electrode main body 25, The space between the inner peripheral surface of the second portion 102 of the outer insulator 10 is also sealed. Furthermore, the seal member 60 also seals between the large diameter portion 92 of the inner insulator 90 and the inner peripheral surface of the second portion 102 of the outer insulator 10.

Here, the material which forms the outer insulator 10 and the inner insulator 90 will be described. The outer insulator 10 is formed using ceramics whose main component is Al ₂ O ₃ . The main component of the ceramic is a component having the highest weight ratio among components (for example, a compound or a single metal) contained in the ceramic. Ceramics mainly composed of Al ₂ O ₃ include Al ₂ O ₃ and components used as sintering aids (for example, La ₂ O ₃ , SiO ₂ , SiC, TiO ₂ , Y ₂ O ₃ , CaO, MgO). ) And. It is known that the higher the Al ₂ O ₃ weight ratio, the worse the moldability but the higher the voltage resistance. Specifically, the weight ratio of Al ₂ O ₃ of the material forming the outer insulator 10 is preferably 80% by weight or more, and more preferably 90% by weight or more.

The inner insulator 90 is formed using a ceramic different from that of the outer insulator 10. Specifically, the inner insulator 90 is formed using a ceramic having an excellent voltage resistance, although the formability is inferior to the ceramic forming the outer insulator 10. More specifically, the outer insulator 10 is formed using a ceramic mainly composed of Al ₂ O ₃ and having a higher weight ratio of Al ₂ O ₃ than the ceramic forming the inner insulator 90. For example, specifically, the weight ratio of Al ₂ O ₃ of the material forming the outer insulator 10 is preferably 90% by weight or more, and more preferably 95% or more. In this specification, ceramics mainly composed of _Al 2 _{O 3} is, _Al 2 _{O 3} containing no component as sintering aids, i.e., the weight ratio of _Al 2 _{O 3} is a 100 wt% ceramic Shall be included.

  If the entire insulator is made using ceramics that are relatively superior in voltage resistance and relatively inferior in formability, the voltage resistance can be ensured, but the formability cannot be ensured, resulting in decreased productivity or production. It may be impossible. On the other hand, if the entire insulator is made using ceramics that are relatively excellent in formability and relatively inferior in voltage resistance, the formability can be ensured, but the voltage resistance cannot be ensured, and the insulator breaks through. Etc. may occur. Here, the vicinity of the center electrode main body 25 becomes high temperature during operation. Further, in the vicinity of the center electrode main body 25, the radial thickness of the insulator tends to be thin. For this reason, the material forming the portion in the vicinity of the center electrode body 25 of the insulator, that is, the tip side and the inner peripheral portion of the insulator is higher in resistance than the other portions of the insulator. Voltage characteristics are required. Therefore, in the present embodiment, the insulator is constituted by two members, that is, the outer insulator 10 and the inner insulator 90, and the ceramic that forms the outer insulator 10 is used as described above. Although it is inferior in formability, it is formed using ceramics with excellent voltage resistance. As a result, the withstand voltage of the inner insulator 90 requiring higher withstand voltage can be secured, and the moldability of the outer insulator 10 having a larger volume than the inner insulator 90 can be secured. As a result, it is possible to achieve both voltage resistance and formability of the spark plug 100.

  Here, if the insulator is configured by using two members, the overall strength of the insulator may be concerned. In the present embodiment, as described above, the large-diameter portion 92 of the inner insulator 90 is supported by the shelf portion 16 of the outer insulator 10. As a result, the inner insulator 90 can be firmly fixed to the outer insulator 10. Accordingly, the overall strength of the insulator, and consequently the strength of the spark plug 100 can be improved.

  Further, the large-diameter portion 92 of the inner insulator 90 is sandwiched between the shelf portion 16 of the outer insulator 10 and the head of the center electrode body 25 of the center electrode 20 (the hook-like portion 252 and the rod-like portion 251). Yes. As a result, the inner insulator 90 can be more firmly fixed to the outer insulator 10. Therefore, the strength of the spark plug 100 can be further improved.

  Further, a seal member 60 that seals between the head of the center electrode main body 25 and the second portion 102 of the outer insulator 10 is provided. As a result, the inner insulator 90 can be more firmly fixed to the outer insulator 10 by the seal member. Therefore, the strength of the spark plug 100 can be further improved.

Further, as described above, each of the outer insulator 10 and the inner insulator 90, includes _Al 2 _{O 3,} and the weight ratio of _Al 2 _{O 3} contained in the outer insulator 10, contained inside the insulator 90 The weight ratio of Al ₂ O ₃ is different. Thus, by using the outer insulator 10 and the inner insulator 90 having different weight ratios of Al ₂ O ₃ , it is possible to achieve both the formability of the spark plug 100 and the voltage resistance. More specifically, the weight ratio of Al ₂ O ₃ contained in the inner insulator 90 is larger than the weight ratio of Al ₂ O ₃ contained in the outer insulator 10. As a result, it is possible to improve the withstand voltage of the inner insulator 90 that requires higher withstand voltage than the outer insulator 10 and to improve the moldability of the outer insulator 10 larger than the inner insulator 90. As a result, the moldability (ease of fabrication) of the spark plug 100 and the voltage resistance can be more effectively achieved.

A-3: First Evaluation Test In the first evaluation test, in order to confirm the strength of the spark plug 100 of the first embodiment, a sample of the spark plug 100 of the first embodiment (also referred to as an evaluation sample), The strength test of comparative samples A to C was performed.

The main dimensions of the evaluation sample used in the test are as follows.
Inner diameter of first portion 101 of outer insulator 10 (diameter of first hole 121) R1: 2.54 mm
Inner diameter of second portion 102 of outer insulator 10 (diameter of first hole 121) R2: 4 mm
Outer diameter R3 of the cylindrical portion 91 of the inner insulator 90: 2.5 mm
Inner diameter R4 of the cylindrical portion 91 of the inner insulator 90: 1.5 mm
Outer diameter R5 of the large diameter portion 92 of the inner insulator 90: 3.8 mm
Outer diameter R6 of the rod-like portion 251 of the center electrode body 25: 1.46 mm
The outer diameter R7 of the bowl-shaped part 252 of the center electrode body 25: 3.8 mm
The outer diameter R8 of the columnar part 253 of the center electrode body 25: 2.5 mm
Rear end diameter Rb of the long leg portion 13 of the outer insulator 10: 5.5 mm
Tip diameter Ra of leg portion 13 of outer insulator 10: 4 mm

  Comparative samples A to C will be described. FIG. 3 is a cross-sectional view of comparative samples A to C. A comparative sample A in FIG. 3A includes an inner insulator 90A instead of the inner insulator 90 of the evaluation sample. The inner insulator 90A is a cylindrical member that does not include the bowl-shaped large-diameter portion 92. The inner insulator 90A is half the length in the axial direction of the inner insulator 90, and has an outer diameter of 2.8 mm and an inner diameter of 2.54 mm. In the first portion 101A of the outer insulator 10A of the comparative sample A, a hole 121A (diameter 1.5 mm) into which the rod-shaped portion 251 of the center electrode body 25 is inserted, and the inner insulator is located at the tip of the hole 121A. A hole 123A (2.84 mm) into which 90A is inserted is formed. A gap between the outer peripheral surface of the inner insulator 90A and the inner peripheral surface of the first portion 101A is filled with a heat-resistant inorganic adhesive (Aron Ceramics, Toagosei Co., Ltd.). Thus, the inner insulator 90A is fixed to the outer insulator 10A. The center electrode body 25 of the comparative sample A is the same as the center electrode body 25 of the evaluation sample. The tip half of the rod-like portion 251 of the center electrode body 25 of the comparative sample A is inserted into the inner insulator 90A. Since the other structure of the comparative sample A is the same as that of the evaluation sample, its description is omitted.

  A comparative sample B in FIG. 3B includes an inner insulator 90B instead of the inner insulator 90 of the evaluation sample. The inner insulator 90B does not include the large diameter portion 92 of the inner insulator 90 of the evaluation sample. The inner insulator 90B is a cylindrical member having the same shape and dimensions as the cylindrical portion 91 of the inner insulator 90 of the evaluation sample. A gap between the outer peripheral surface of the inner insulator 90B and the inner peripheral surface of the first portion 101 of the outer insulator 10 is filled with the above-described heat-resistant inorganic adhesive. Thus, the inner insulator 90B is fixed to the outer insulator 10. Since the other structure of the comparative sample B is the same as that of the evaluation sample, the description thereof is omitted.

  In the comparative sample C in FIG. 3C, the insulator is constituted by a rear end side insulator 10C and a front end side insulator 90C. That is, the rear end side insulator 10 </ b> C is a member corresponding to the rear end half of the first portion 101 of the evaluation sample and the second portion 102. The tip side insulator 90C is a member corresponding to the tip side half of the first portion 101 of the evaluation sample. Since the comparative sample C does not include the inner insulator 90, the inner diameter of the first portion 101C of the rear-end-side insulator 10C and the inner diameter of the front-end-side insulator 90C are outside the rod-shaped portion 251 of the center electrode body 25. The value is slightly larger than the diameter (1.5 mm). The rear end side insulator 10C and the front end side insulator 90C are bonded by the heat-resistant inorganic adhesive described above. Thereby, the front end side insulator 90C is fixed to the rear end side insulator 10C. Since the other structure of the comparative sample C is the same as the structure of the evaluation sample, the description thereof is omitted.

The materials of the outer insulator 10 of the evaluation sample, the outer insulators 10A and 10 of the comparative sample, and the rear end side insulator 10C are 90% by weight of Al ₂ O ₃ and 10% by weight of sintering aid. A ceramic made of an agent (SiO ₂ , CaO, MgO, BaO) was used.

Further, the materials of the inner insulator 90 of the evaluation sample, and the inner insulators 90A and 90B and the tip side insulator 90C of the comparative sample are 95% by weight of Al ₂ O ₃ and 5% by weight of a sintering aid. A ceramic composed of (SiO ₂ , CaO, MgO, BaO) was used.

  In the first evaluation test, three samples of each type were prepared, and an impact resistance test defined in 7.4 of JIS B8031: 2006 (internal combustion engine-spark plug) was performed. After the test, the insulator was checked for abnormalities. The evaluation of the sample in which there was no abnormality in the insulator was “◯”, and the evaluation of the sample in which the insulator was abnormal was “x”. The test results were as shown in Table 1 below.

  The evaluations of the three evaluation samples were all “◯”. Of the three comparative samples A, one evaluation was “◯”, and the remaining two evaluations were “x”. Among the three comparative samples B, one evaluation was “◯”, and the remaining two evaluations were “x”. The evaluations of the three comparative samples C were all “x”. In Comparative Samples A and B with an evaluation of “x”, an abnormality was observed in which the inner insulators 90A and 90B were peeled off from the outer insulators 10A and 10 in the portion bonded with the inorganic adhesive. In the comparative sample C having an evaluation of “x”, an abnormality in which the front end side insulator 90C was peeled off from the rear end side insulator 10C was observed in the portion bonded with the inorganic adhesive.

  According to the first evaluation test, in the spark plug 100 of the embodiment, as described above, the inner insulator 90 can be firmly fixed to the outer insulator 10, and the strength of the spark plug 100 can be improved. Was confirmed.

A-4: Second Evaluation Test In the second evaluation test, as shown in Table 2 below, 10 samples of 8 types 1 to 8 were prepared. Sample 1 is a sample (comparative sample) of a spark plug of a comparative form. Samples 2 to 8 are samples (evaluation samples) of the spark plug 100 of the first embodiment. The configurations of the evaluation samples 2 to 8 are the same as the evaluation samples of the first evaluation test except for the materials that form the outer insulator 10 and the inner insulator 90. In the comparative sample 1, the outer insulator 10 and the inner insulator 90 of the evaluation sample are formed of an integral insulator. The other structure of the comparative sample 1 is the same as the evaluation sample.

As the insulator material of Comparative Sample 1, ceramics composed of 90 wt% Al ₂ O ₃ and 10 wt% sintering aid (SiO ₂ , CaO, MgO, BaO) was used.

Further, the material of the outer insulator 10 of the evaluation samples 2 to 8 includes 90% by weight of alumina and 10% by weight of a sintering aid (SiO ₂ , CaO, MgO, BaO) was used. The material of the inner insulator 90 of the evaluation samples 2 to 8 is a ceramic composed of 80 to 100% by weight of alumina and 0 to 20% by weight of a sintering aid (SiO ₂ , CaO, MgO, BaO). Used. Specifically, the weight percentages of Al ₂ O ₃ contained in the inner insulator 90 of the evaluation samples 2 to 8 are 80%, 85%, 88%, 90%, 92%, 95%, and 100%, respectively. is there. Here, the difference between the weight percent (referred to as Wta) of Al ₂ O ₃ contained in the outer insulator 10 and the weight percent (referred to as Wtb) of Al ₂ O ₃ contained in the inner insulator 90 is expressed as ΔWt. (ΔWt = Wtb−Wta). The weight percent differences ΔWt of the Al ₂ O ₃ of the evaluation samples 2 to 8 are −10%, −5%, −2%, 0%, 5%, 2%, and 10%, respectively (Table 2).

  In the second evaluation test, a withstand voltage test was performed using ten samples of each type. Specifically, using a withstand voltage test apparatus defined in 7.3 of JIS B8031: 2006 (internal combustion engine-spark plug), the test is performed while increasing the voltage to be applied step by step by 1 kV. The lower limit value of the voltage at which penetration breakdown occurs (referred to as the withstand voltage value) was examined. Then, an average value Va and a variance σ of withstand voltage values of 10 samples of the same type are calculated, and a value of (Va-3σ) is calculated as an evaluation value Ve (unit is kV) of withstand voltage. did. And among the evaluation samples 2 to 8, the evaluation of the sample whose evaluation value Ve exceeds the evaluation value Ve (= 42 kV) of the comparative sample 1 is “◯”, and the evaluation value Ve is equal to or lower than the evaluation value Ve of the comparative sample 1 The evaluation of the sample was “Δ”. The test results were as shown in Table 2 below.

As shown in Table 2, the evaluation of the evaluation samples 2 to 4 in which the difference ΔWt in weight percent of Al ₂ O ₃ is negative is “Δ”, and the difference ΔWt in weight percent of Al ₂ O ₃ is 0. The evaluation of a certain evaluation sample 5 and evaluation samples 6 to 8 in which the difference ΔWt in weight percent of Al ₂ O ₃ is a positive value was “◯”.

According to the second evaluation test, as described above, when the weight ratio of Al ₂ O ₃ contained in the inner insulator 90 is equal to or higher than the weight ratio of Al ₂ O ₃ contained in the outer insulator 10, the voltage resistance is improved. It was confirmed that it could be improved. In addition, the evaluation sample 5 in which the difference ΔWt in weight percent of Al ₂ O ₃ is 0 is superior to the comparative sample 1 in that the withstand voltage is superior to the inner peripheral surface of the outer insulator 10 and the outer periphery of the outer insulator 10. It is thought that there is a gap between the surface.

In addition, as shown in Table 2, in the evaluation samples 2 to 8, the larger the difference ΔWt in the weight percent of Al ₂ O ₃ , in other words, the weight percent of Al ₂ O ₃ contained in the inner insulator 90 is, It was found that the higher the weight percent of Al ₂ O ₃ contained in the outer insulator 10, the better the voltage resistance.

B. Second embodiment:
B-1. Spark plug configuration:
Unlike the spark plug 100 of the first embodiment, the spark plug of the second embodiment is a type of spark plug called a plasma jet plug. Note that the plasma jet plug differs from the spark plug 100 of the first embodiment in the configuration in the vicinity of the tip. FIG. 4 is a cross-sectional view in which the vicinity of the tip of the spark plug according to the second embodiment is cut along a plane including an axis. Among the configurations of the spark plug of the second embodiment, for the configurations different from the spark plug 100 of the first embodiment, “D” is added to the end of the reference numerals, and the same configurations as the spark plug 100 of the first embodiment are described. The same reference numerals as those of the spark plug 100 of the first embodiment are used.

  In the second embodiment, the axial length of the leg portion 13D of the outer insulator 10D is shorter than the axial length of the inner insulator 90D. For this reason, the tip of the inner insulator 90D is located on the tip side of the tip of the outer insulator 10D.

  The inner insulator 90D includes a cylindrical portion 91D and a large diameter portion 92, like the inner insulator 90 in the first embodiment. In the example of FIG. 4, the inner diameter R24 of the cylindrical portion 91D is smaller than the inner diameter 4 of the cylindrical portion 91 of the first embodiment. Accordingly, the length (thickness) of the cylindrical portion 91D in the radial direction is thicker than the cylindrical portion 91 of the first embodiment.

  Furthermore, the center electrode 20D does not include a center electrode tip at the tip. The center electrode 20D includes a rod-shaped portion 251D, a flange-shaped portion 252 and a columnar portion 253, similarly to the center electrode main body 25 in the first embodiment. The outer diameter R26 of the rod-shaped portion 251D is smaller than the outer diameter R6 of the rod-shaped portion 251 of the first embodiment. The tip of the rod-shaped portion 251D (that is, the tip of the center electrode 20D) is located on the rear end side from the tip of the inner insulator 90D. As a result, a cavity CV defined by the inner peripheral surface of the cylindrical portion 91 of the inner insulator 90D and the tip of the center electrode 20D is formed at the tip of the spark plug.

  The front end of the metal shell 50D is located on the front end side from the front end of the cylindrical portion 91D (the front end of the inner insulator 90D). A disc-shaped ground electrode 30D is joined to the tip of the metal shell 50D. The ground electrode 30D has a plasma ejection hole 35D opened on the axis CO. The axial position of the rear end surface of the ground electrode 30D and the axial position of the distal end surface of the cylindrical portion 91D are substantially the same. Further, the diameter of the ejection hole 35D and the inner diameter of the cylindrical portion 91D are substantially the same. As shown in FIG. 4, the spark gap G of the spark plug according to the second embodiment includes a tip of the center electrode 20D (tip of the rod-like portion 251D) and a portion where the ejection hole 35D is formed in the ground electrode 30D. Between.

  Furthermore, the spark plug according to the second embodiment does not include the resistor 70 (FIG. 1). For this reason, in the spark plug of the second embodiment, the gap between the tip of the terminal fitting 40D (tip of the leg 43D) and the rear end of the center electrode 20D (back of the columnar portion 253) is the seal member 60D. Is sealed by.

  Other configurations of the spark plug of the second embodiment are the same as those of the spark plug 100 of the first embodiment.

  The spark plug (plasma jet plug) of the second embodiment operates as follows. When a spark discharge is generated in the spark gap G by supplying a high voltage by an ignition device (not shown), the gas in the cavity CV is excited by the energy of the spark discharge, and plasma is formed in the cavity CV. When the plasma formed in the cavity CV expands and the pressure in the cavity CV increases, the plasma in the cavity CV is ejected from the ejection hole 35D formed in the ground electrode 30D in a fire column shape. The air-fuel mixture in the combustion chamber of the internal combustion engine is ignited by the ejected plasma.

  Here, of the inner peripheral surface of the cylindrical portion 91D of the inner insulator 90D, the tip portion defining the cavity CV is melted and consumed by the energy of the spark discharge. As a result, a groove-like scratch called channeling occurs at the tip of the inner peripheral surface of the cylindrical portion 91D. If such channeling occurs excessively, the tubular portion 91D may be chipped, and the spark plug may not be able to exhibit its original performance. For this reason, the material of the inner insulator 90D is required to have resistance to channeling, that is, spark wear resistance.

Here, in ceramics whose main component is an insulator such as Al ₂ O ₃ , the amount of specific compounds such as La ₂ O ₃ , SiO ₂ , SiC, TiO ₂ , Y ₂ O ₃ , CaO, and MgO increases. As the surface resistance of the ceramic decreases, the spark wear resistance is improved. On the other hand, as the added amount of these specific compounds is increased, the resistance of the ceramic is lowered, so that the withstand voltage is deteriorated.

  If the entire insulator is made of ceramics with relatively high voltage resistance and relatively low spark wear resistance, the voltage resistance can be secured, but the spark wear resistance cannot be ensured and the life of the spark plug is reduced. May be shorter. Conversely, if the entire insulator is made of ceramics that are relatively excellent in spark erosion resistance and relatively inferior in voltage resistance, the spark erosion resistance can be secured, but the voltage resistance cannot be ensured, and the insulator There is a possibility of the occurrence of through breakage. A material that forms a portion where channeling occurs, that is, a tip side portion and an inner peripheral side portion of the insulator is required to have higher spark erosion resistance than other portions of the insulator. Therefore, in the present embodiment, the insulator is constituted by two members, that is, the outer insulator 10D and the inner insulator 90D, and the inner insulator 90D has a higher withstand voltage than the ceramic forming the outer insulator 10D. Although it is inferior, it is formed using ceramics having excellent spark wear resistance.

Specifically, the outer insulator 10D has Al ₂ O ₃ as a main component and one of La ₂ O ₃ , SiO ₂ , SiC, TiO ₂ , Y ₂ O ₃ , CaO, and MgO as an additive. The specific compound is formed of ceramics containing a predetermined amount (for example, 3% by weight). Specifically, the weight ratio of Al ₂ O ₃ of the material forming the outer insulator 10D is preferably 80% by weight or more, more preferably 90% by weight or more, and 95% by weight or more. Most preferred.

The inner insulator 90D has Al ₂ O ₃ as a main component and, as an additive, one specific compound of La ₂ O ₃ , SiO ₂ , SiC, TiO ₂ , Y ₂ O ₃ , CaO, and MgO. Is made of ceramics containing more than the material forming the outer insulator 10D. That is, the weight% of the specific compound contained in the inner insulator 90D is larger than the weight% of the specific compound contained in the outer insulator 10D. As a result, it is possible to achieve both spark resistance and voltage resistance of the spark plug.

  As in the first embodiment, the large diameter portion 92 of the inner insulator 90D is supported by the shelf 16 of the outer insulator 10D. As a result, the inner insulator 90D can be firmly fixed to the outer insulator 10D. Further, similarly to the first embodiment, the large-diameter portion 92 of the inner insulator 90D is constituted by the shelf portion 16 of the outer insulator 10D and the head (the hook-like portion 252 and the rod-like portion 251) of the center electrode 20D. It is sandwiched. As a result, the inner insulator 90D can be more firmly fixed to the outer insulator 10D. Furthermore, as in the first embodiment, a seal member 60 that seals between the head of the center electrode 20D and the second portion 102 of the outer insulator 10D is provided. As a result, the inner insulator 90D can be more firmly fixed to the outer insulator 10D by the seal member. Therefore, the strength of the spark plug 100 can be improved.

B-2: Evaluation Test In the evaluation test, a spark consumption test of the spark plug sample of the second embodiment was performed.

The main dimensions of the evaluation sample used in the test are as follows.
Inner diameter R21 of the first portion 101D of the outer insulator 10D: 2.54 mm
Inner diameter R22 of the second portion 102 of the outer insulator 10D: 4 mm
Outer diameter R23 of the cylindrical portion 91D of the inner insulator 90D: 2.5 mm
Inner diameter R4 of the cylindrical portion 91D of the inner insulator 90D: 0.8 mm
Outer diameter R25 of the large diameter portion 92 of the inner insulator 90D: 3.8 mm
Outer diameter R26 of the rod-like portion 251D of the center electrode 20D: 0.76 mm
The outer diameter R27 of the flange-shaped part 252 of the center electrode 20D: 3.8 mm
The outer diameter R28 of the columnar part 253 of the center electrode 20D: 2.5 mm
Rear end diameter R2b of leg long portion 13D of outer insulator 10D: 5.5 mm
Tip diameter R2a of leg long portion 13D of outer insulator 10D: 4 mm

In addition, as a material for the outer insulator 10D of the evaluation sample, ceramics including 97% by weight of Al ₂ O ₃ and 3% by weight of a specific compound was used. As a material for the inner insulator 90D of the evaluation sample, ceramics composed of 95 to 99% by weight of Al ₂ O ₃ and 1 to 5% by weight of a specific compound was used. Specifically, as shown in Table 3 below, five samples each of seven specific compounds of La ₂ O ₃ , SiO ₂ , SiC, TiO ₂ , Y ₂ O ₃ , CaO, and MgO are used. Was prepared. In five samples for one specific compound, the weight percentage of the specific compound was changed to 1%, 2%, 3%, 4%, 5%, respectively, and accordingly, Al ₂ O ₃ The weight percentages of these are changed to 99%, 98%, 97%, 96%, and 95%.

  Here, the difference between the weight percent (referred to as Wtc) of the specific compound included in the outer insulator 10D and the weight percent (referred to as Wtd) of the specific compound included in the inner insulator 90D is referred to as ΔWt2 (ΔWt2). = Wtd-Wtc). In Table 3, the weight% of the specific compound contained in the inner insulator 90D of each sample is shown using the value of ΔWt2 based on the weight% of the specific compound contained in the outer insulator 10D.

  In the evaluation test, each sample was subjected to a discharge test in which a spark discharge was generated 60 times per second in a chamber pressurized to 1.0 MPa for 300 hours. Each sample was disassembled after the discharge test, and the depth of channeling was measured over the entire circumference of the inner circumferential surface of the inner insulator 90D that defined the cavity CV. A non-contact laser type shape measuring instrument was used for measuring the channeling depth. Of the channeling measured in each sample, the deepest channeling depth was adopted as the channeling depth of each sample. The shallower the channeling depth, the better the spark wear resistance. The test results were as shown in Table 3 below.

  As shown in Table 3, the channeling depth of the sample in which the difference ΔWt2 in the weight% of the specific compound is a negative value is 0 in the difference ΔWt2 in the weight% of the specific compound regardless of the type of the specific compound. Compared to the sample, it was found deeper. In addition, the channeling depth of the sample in which the difference ΔWt2 in the weight% of the specific compound is a positive value is compared with the sample in which the difference ΔWt2 in the weight% of the specific compound is 0 regardless of the type of the specific compound. I found out that it was shallow.

As described above, when the weight ratio of the specific compound contained in the inner insulator 90D is larger than the weight ratio of Al ₂ O ₃ contained in the outer insulator 10, it is possible to improve the spark wear resistance. It could be confirmed.

  In addition, as shown in Table 3, when the same specific compound is added, the larger the difference ΔWt2 in the weight% of the specific compound, in other words, the weight% of the specific compound contained in the inner insulator 90D is It was found that the greater the weight percent of the specific compound contained in the insulator 10D, the better the spark wear resistance.

As shown in Table 3, among the seven specific compounds of La ₂ O ₃ , SiO ₂ , SiC, TiO ₂ , Y ₂ O ₃ , CaO, and MgO, the difference ΔWt2 in weight percent of the specific compound is positive. It was found that SiC can improve the spark erosion resistance most in the range. Then, TiO ₂ and La ₂ O ₃ can improve the spark wear resistance after SiC, and SiO ₂ , Y ₂ O ₃ , CaO, and MgO are refractory next to TiO ₂ and La ₂ O _3. It has been found that flower exhaustion is improved.

C. Variation:
(1) FIG. 5 is a first diagram illustrating an example of a modified inner insulator. Only the parts different from those of the second embodiment will be described with respect to the modified examples of FIGS. The outer diameter of the large diameter portion 92F of the inner insulator 90F in FIG. 5A is larger than the outer diameter of the flange portion 252D of the center electrode. The outer diameter of the large diameter portion 92G of the inner insulator 90G of FIG. 5B is smaller than the outer diameter of the flange portion 252D of the center electrode. As described above, the outer diameter of the large diameter portion of the inner insulator may be different from the outer diameter of the flange portion 252D of the center electrode.

  The outer diameter of the large diameter portion 92H of the inner insulator 90H of FIG. 5C is smaller than the outer diameter of the flange portion 252H of the center electrode. An annular groove DP is formed on the reduced diameter surface on the tip side of the flange portion 252H of the center electrode. The portion on the rear end side of the large diameter portion 92H is fitted in a groove DP formed in the flange portion 252H of the center electrode. As a result, the inner insulator 90H and the center electrode are firmly fixed.

  FIG. 6 is a second diagram illustrating an example of a modified inner insulator. The outer diameter of the large diameter portion 92I of the inner insulator 90I in FIG. 6A is larger than the outer diameter of the flange portion 252D of the center electrode. Further, the inner insulator 90I includes an annular side wall portion 96I extending from the rear end of the large diameter portion 92I toward the rear end. Then, the tip side portion of the flange portion 252D of the center electrode is fitted into a recess defined by the reduced diameter surface 92Ib on the rear end side of the large diameter portion 92I and the inner peripheral surface 96Ia of the side wall portion 96I. ing. As a result, the inner insulator 90H and the center electrode are firmly fixed.

  The head 253J of the center electrode in FIG. 6B is not divided into a bowl-shaped portion and a columnar portion. The head portion 253J has a columnar shape, and the distal end side has a reduced diameter. The outer diameter of the large-diameter portion 92J of the inner insulator 90J in FIG. 6B is larger than the outer diameter of the head 253J of the center electrode, as in the example of FIG. Furthermore, the inner insulator 90J includes an annular side wall portion 96J extending from the rear end of the large-diameter portion 92J toward the rear end, as in the example of FIG. 6 (A). Then, as in the example of FIG. 6A, the portion on the front end side of the head 253J of the center electrode includes a reduced diameter surface 92Jb on the rear end side of the large diameter portion 92J, an inner peripheral surface 96Ja of the side wall portion 96I, Is fitted into a recess defined by. As a result, the inner insulator 90J and the center electrode are firmly fixed.

  As described above, the configuration of the large-diameter portion of the inner insulator is not limited to the configurations of the first embodiment and the second embodiment, and can take various configurations. For example, the large-diameter portion of the inner insulator is arranged in a bowl shape over the entire circumference in the circumferential direction, but is not necessarily arranged over the entire circumference in the circumferential direction, and a part in the circumferential direction. May be missing.

(2) In the first embodiment and the second embodiment, the inner insulator is formed using ceramics mainly composed of Al ₂ O ₃ , but instead, the inner insulator is made of other materials. You may form using the ceramics which have this compound as a main component. As a result, according to the characteristics of the outer insulator formed using a ceramic mainly composed of Al ₂ O ₃ and the characteristics of the inner insulator formed using a ceramic mainly composed of another compound, A spark plug having an insulator with optimized performance can be realized. For example, the inner insulator may be formed using ceramics whose main component is any one of AlN, ZrO ₂ , SiC, TiO ₂ , and Y ₂ O ₃ . For example, a ceramic mainly composed of AlN has higher thermal conductivity than a ceramic mainly composed of Al ₂ O ₃ . For this reason, when the inner insulator is formed using ceramics mainly composed of AlN, the heat-drawing performance of the tip portion of the spark plug that is likely to become high temperature can be improved. Further, ceramics mainly composed of ZrO ₂ or SiC have a lower surface resistance than ceramics mainly composed of Al ₂ O ₃ . For this reason, when the inner insulator is formed using ceramics mainly composed of ZrO ₂ or SiC, the spark wear resistance of the spark plug can be improved as in the second embodiment described above.

(3) As described above, the spark plug inner insulator 90D of the second embodiment includes one of La ₂ O ₃ , SiO ₂ , SiC, TiO ₂ , Y ₂ O ₃ , CaO, and MgO. Although the specific compound is included, two or more specific compounds of La ₂ O ₃ , SiO ₂ , SiC, TiO ₂ , Y ₂ O ₃ , CaO, and MgO may be included. In this case, the total weight ratio of the two or more specific compounds included in the inner insulator 90D is preferably larger than the total weight ratio of the two or more specific compounds included in the outer insulator 10D. . In this way, the spark plug wear resistance of the spark plug can be improved as in the second embodiment.

(4) In the first embodiment, the reduced diameter outer surface 92 a of the large diameter portion 92 of the inner insulator 90 is in direct contact with the shelf portion 16 of the outer insulator 10. That is, the large-diameter portion 92 of the inner insulator 90 is directly supported by the shelf portion 16 of the outer insulator 10. Instead, between the reduced diameter outer surface 92a of the large diameter portion 92 and the shelf portion 16 of the outer insulator 10, an inorganic adhesive (so-called cement) or a material similar to the seal member 60 of FIG. For example, B ₂ O ₃ —SiO ₂ based glass particles and metal particles (Cu, Fe, etc.) may be filled. That is, the large-diameter portion 92 of the inner insulator 90 may be indirectly supported by the shelf portion 16 of the outer insulator 10. The same applies to the second embodiment.

(6) In the first embodiment, an inorganic adhesive may be filled between the inner peripheral surface of the inner insulator 90 and the outer peripheral surface of the rod-shaped portion 251 of the center electrode main body 25. Similarly, an inorganic adhesive may be filled between the inner peripheral surface of the first portion 101 of the outer insulator 10 and the outer peripheral surface of the inner insulator 90.

(7) In the first embodiment, the head (the hook-like portion 252 and the columnar portion 253) of the center electrode main body 25 may be omitted. In this case, for example, the outer peripheral surface of the rod-shaped portion 251 of the center electrode main body 25 is bonded to the inner peripheral surface of the inner insulator 90 with an inorganic adhesive, so that the center electrode main body 25 is fixed to the inner insulator 90. Is done. The large diameter portion 92 of the inner insulator 90 is sandwiched between the shelf portion 16 of the outer insulator 10 and the seal member 60. As a result, the inner insulator 90 is fixed to the outer insulator 10.

(8) In each of the embodiments described above, the configuration of the inner insulator, the outer insulator, and the center electrode has been mainly described. However, other elements such as the material of the metallic shell 50, the terminal fitting 40, the ground electrode 30, and the like, Various dimensions can be changed. For example, the material of the metal shell 50 may be low carbon steel plated with zinc or nickel, or may be low carbon steel not plated with these. The ground electrode 30 may have a two-layer structure including a base material made of a nickel alloy and a core portion made of copper. Further, the ground electrode 30 may be opposed to the tip portion of the center electrode in a direction perpendicular to the axial direction to form a spark gap in a direction perpendicular to the axial direction.

(9) The center electrode 20 of the second embodiment does not include a chip (FIG. 4), but instead, the tip of the center electrode 20 has a noble metal such as platinum or iridium as a main component. A chip formed of an alloy, tungsten (W), or the like may be disposed.

(10) In the second embodiment, the axial position of the rear end surface of the ground electrode 30D coincides with the axial position of the distal end surface of the cylindrical portion 91D (FIG. 4). A slight gap (for example, 0.05 mm to 0.2 mm) may be provided between the rear end surface of 30D and the front end surface of the cylindrical portion 91D.

  As mentioned above, although this invention was demonstrated based on embodiment and a modification, embodiment mentioned above is for making an understanding of this invention easy, and does not limit this invention. The present invention can be changed and improved without departing from the spirit and scope of the claims, and equivalents thereof are included in the present invention.

    5 ... gasket, 6 ... ring member, 8 ... plate packing, 9 ... talc, 10, 10A, 10D ... outer insulator, 10A ... outer insulator, 10C ... Rear end side insulator, 13, 13D ... Long leg part, 15 ... Step part, 16 ... Shelve part, 17 ... Front end side body part, 18 ... Rear end side body part, 19. .. Saddle, 20, 20D ... center electrode, 22 ... electrode base material, 23 ... core, 23 ... head, 25 ... center electrode body, 26 ... melting part 29 ... Electrode tip, 29 ... Center electrode tip, 30, 30D ... Ground electrode, 31 ... Ground electrode body, 35D ... Ejection hole, 39 ... Ground electrode tip, 40, 40D ... terminal fitting, 40D ... terminal fitting, 41 ... cap mounting part, 42 ... collar part, 43, 43D ... leg part, 50, 50D ... main metal fitting, 50D ... .Metal fitting, 51 ... Tool engaging part, 52 ... Mounting screw part, 53 ... Casting part, 54 ... Seat part, 56 ... Step part 58 ... compression deformation part, 59 ... insertion hole, 60, 60D ... seal member, 70 ... resistor, 80 ... seal member, 90 ... inner insulator, 90A, 90B, 90D, 90F to 90J ... inner insulator, 90C ... tip insulator insulator, 91,91D ... cylindrical part, 92,92F-92J ... large diameter part, 96I, 96J ... side wall Part, 100 ... spark plug, 101 ... first part, 251, 252D ... rod-like part, 252, 253D, 252H ... bowl-like part, 253, 253J ... columnar part

Claims (8)

A first part having a first hole extending in the axial direction, a second part having a second hole having an inner diameter larger than that of the first hole, and disposed on a rear end side of the first part; A first insulating member comprising: a shelf formed between the first part and the second part;
A second insulating member having a through hole extending in the axial direction and including a cylindrical portion disposed in the first hole;
A center electrode provided with a rod-shaped portion disposed in the through hole of the tubular portion;
A spark plug comprising:
The second insulating member is disposed on a rear end side of the cylindrical portion, and includes a large diameter portion having an outer diameter larger than that of the cylindrical portion,
The spark plug according to claim 1, wherein the large-diameter portion is supported directly or indirectly on the shelf portion of the first insulating member. The spark plug according to claim 1,
The center electrode is disposed on the rear end side from the cylindrical part, and includes a head having a larger outer diameter than the cylindrical part,
The spark plug, wherein the large-diameter portion of the second insulating member is sandwiched between the shelf portion of the first insulating member and the head portion of the center electrode. The spark plug according to claim 2, further comprising:
A seal member that seals between the head and the second portion in the second hole;
A spark plug. The spark plug according to any one of claims 1 to 3,
Each of the first insulating member and the second insulating member includes Al ₂ O ₃ ,
The spark plug according to claim 1, wherein a weight ratio of Al ₂ O ₃ contained in the first insulating member is different from a weight ratio of Al ₂ O ₃ contained in the second insulating member. The spark plug according to any one of claims 1 to 4,
Each of the first insulating member and the second insulating member includes Al ₂ O ₃ ,
Said second weight ratio of Al ₂ O ₃ contained in the insulating member, a spark plug, characterized in that said at first insulating Al ₂ O ₃ weight ratio or more contained in the member. The spark plug according to any one of claims 1 to 5,
The tip of the second insulating member is located on the tip side from the tip of the first insulating member,
The spark plug according to claim 1, wherein a front end of the center electrode is positioned on a rear end side with respect to a front end of the second insulating member. The spark plug according to claim 6, wherein
The second insulating member includes at least one specific compound of La ₂ O ₃ , SiO ₂ , SiC, TiO ₂ , Y ₂ O ₃ , CaO, and MgO,
The spark plug according to claim 1, wherein a total weight ratio of the specific compounds included in the second insulating member is greater than a total weight ratio of the specific compounds included in the first insulating member. The spark plug according to any one of claims 1 to 3 and claim 6,
The first insulating member is a ceramic mainly composed of Al ₂ O ₃ ,
The spark plug, wherein the second insulating member is a ceramic mainly composed of any one of AlN, ZrO ₂ , SiC, TiO ₂ , and Y ₂ O ₃ .

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