JP2018206621A - Spark plug - Google Patents

Abstract

To provide a spark plug capable of improving endurance of an electric conductor.SOLUTION: A spark plug includes an electric conductor placed between a center electrode and a terminal fitting and connected electrically with the terminal fitting, a conductive glass in contact with the center electrode, the electric conductor and an insulator, and an insulating glass in contact with the conductive glass, the electric conductor and the insulator. In an arbitrary cross-section including the axis line, boundary surface of the insulating glass and the conductive glass is such that a first point, where the boundary surface comes into contact with the insulator, is located farther rear end side than a second point, where the boundary surface comes into contact with the electric conductor, and the boundary surface is located at the same position as the second point in the axial direction, or on the farther rear end side than the second point in the axial direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a spark plug, and more particularly to a spark plug incorporating a conductor such as a resistor or a magnetic material.

  In order to suppress radio noise generated at the time of discharge, there is a spark plug in which a conductor such as a resistor or a magnetic body is built in an insulator (Patent Documents 1 and 2). In the technique disclosed in Patent Document 2, the insulating property that contacts the conductive glass, the conductive material, and the insulator so that the conductive material (resistor) connected to the central electrode via the conductive glass is not damaged by vibration. Glass is built-in.

JP-A-61-208768 JP 2007-122879 A

  However, in the above conventional technique, the electric field concentrates on the portion where the interface between the conductive glass and the insulating glass is in contact with the conductor during discharge, and the conductor may be deteriorated.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a spark plug that can improve the durability of a conductor.

  To achieve this object, a spark plug according to the present invention includes an insulator having an axial hole extending in the axial direction from the front end side to the rear end side, a center electrode disposed on the front end side of the shaft hole, A conductor disposed on the rear end side of the center electrode, a conductive glass that contacts the center electrode, the conductor and the insulator and electrically connects the center electrode and the conductor, and the conductor and the insulator Insulating glass disposed between and in contact with the conductive glass and the conductor and the insulator. In any cross section including the axis, the interface between the insulating glass and the conductive glass is located at the rear end side of the first point where the interface is in contact with the insulator than the second point where the interface is in contact with the conductor. The second point is located at the same position in the axial direction or at the rear end side in the axial direction from the second point.

  According to the spark plug of the first aspect, the concentration of the electric field at the second point on the conductor can be alleviated, so that deterioration of the conductor can be suppressed. Therefore, the durability of the conductor can be improved.

  According to the spark plug according to claim 2, the distance D in the axial direction between the rearmost end position in the axial direction and the most distal position among the boundary lines where the conductor and the interface are in contact is set in the axial direction of the conductor. D / L divided by the maximum length L satisfies 0 ≦ D / L ≦ 0.1. As a result, variation in the circumferential direction of the contact area of the conductive glass contacting the side surface of the conductor can be suppressed. Thus, in addition to the effect of the first aspect, variations in the resistance value of the conductor can be suppressed, and the durability of the conductor can be improved.

It is a half sectional view of the spark plug in the first embodiment of the present invention. (A) is sectional drawing of the spark plug which expanded and showed the part shown by IIa of FIG. 1, (b) is sectional drawing which expanded and showed a part of spark plug in 2nd Embodiment. . It is the perspective view which illustrated the conductor typically. (A) is sectional drawing which expanded and showed a part of spark plug in 3rd Embodiment, (b) is sectional drawing which expanded and showed a part of spark plug in 4th Embodiment. is there. It is sectional drawing which expanded and showed a part of spark plug in the comparative example.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a one-side cross-sectional view with an axis O of a spark plug 10 in the first embodiment of the present invention as a boundary. In FIG. 1, the lower side of the paper surface is referred to as the front end side of the spark plug 10, and the upper side of the paper surface is referred to as the rear end side of the spark plug 10 (the same applies to FIGS. 2 to 5). The spark plug 10 includes an insulator 11, a center electrode 14, and a terminal fitting 15.

  The insulator 11 is a member made of ceramic such as alumina which is excellent in mechanical properties and insulation at high temperature, and has a shaft hole 12 penetrating along the axis O. In the present embodiment, the shaft hole 12 has a circular cross-sectional shape orthogonal to the axis O. The shaft hole 12 is provided with a stepped portion 13 on the distal end side whose inner diameter gradually decreases toward the distal end.

  The center electrode 14 is a rod-shaped member extending along the axis O, and copper or a core material mainly composed of copper is covered with nickel or a nickel-based alloy. The center electrode 14 is locked to the step portion 13 of the shaft hole 12, and the tip is exposed from the shaft hole 12.

  The terminal fitting 15 is a rod-like member to which a high voltage cable (not shown) is connected, and is formed of a conductive metal material (for example, low carbon steel). The terminal fitting 15 is fixed to the rear end of the insulator 11 with the tip end inserted into the shaft hole 12.

  The insulator 11 has a metal shell 16 swaged and fixed to the distal end side of the outer periphery with a gap in the direction of the axis O from the terminal metal 15. The metal shell 16 is a substantially cylindrical member formed of a conductive metal material (for example, low carbon steel). The metal shell 16 includes a seat portion 17 that projects in a bowl shape outward in the radial direction, and a screw portion 18 that is formed on the outer peripheral surface on the tip side of the seat portion 17. The metal shell 16 is fixed by fastening a screw portion 18 to a screw hole (not shown) of the internal combustion engine (cylinder head).

  The ground electrode 19 is a metal (for example, nickel-base alloy) member joined to the tip of the metal shell 16. In the present embodiment, the ground electrode 19 is formed in a rod shape, the tip side is bent and faces the center electrode 14. The ground electrode 19 forms a spark gap with the center electrode 14.

  The conductor 20 is a member for suppressing radio noise generated at the time of discharge, and is disposed between the center electrode 14 in the shaft hole 12 and the terminal fitting 15. The conductor 20 is electrically connected to the center electrode 14 by a conductive glass 21 that contacts the center electrode 14 and the conductor 20. In the present embodiment, the conductor 20 is formed in a cylindrical shape. Further, the conductor 20 is electrically connected to the terminal fitting 15 by the conductive glass 22 that contacts the terminal fitting 15 and the conductor 20.

  Examples of the conductor 20 include a magnetic body or a resistor body in which a ferrite and a conductor are combined. The resistor absorbs a component in a frequency band that causes radio noise in the discharge current. The magnetic body blocks or absorbs a component of the frequency band that causes radio noise in the discharge current due to the impedance, magnetic loss, etc. of the ferrite.

  As the resistor, for example, an element (resistor) in which a film of a resistance material such as carbon, metal, metal oxide or the like is bonded to the surface of a base material such as porcelain, a resistance wire such as Ni-Cr is used as a base such as porcelain. An element wound around a material, a molded body in which an aggregate and conductive powder are mixed, or the like is used. The resistance value of the resistor is, for example, preferably 0.1 kΩ to 30 kΩ, and more preferably 1 kΩ to 20 kΩ.

In the resistor formed by mixing aggregate and conductive powder, examples of the aggregate include glass powder and inorganic compound powder. Examples of the aggregate glass powder include B ₂ O ₃ —SiO ₂ system, BaO—B ₂ O ₃ system, SiO ₂ —B ₂ O ₃ —CaO—BaO system, SiO ₂ —ZnO—B ₂ O ₃ system, Examples of the powder include SiO ₂ —B ₂ O ₃ —Li ₂ O and SiO ₂ —B ₂ O ₃ —Li ₂ O—BaO. Examples of the aggregate inorganic compound powder include powders of alumina, silicon nitride, mullite, steatite and the like. These aggregates may use only 1 type and may use 2 or more types together.

Examples of the conductive powder include powder made of a semiconductive oxide, a metal, a non-metallic conductive material, and the like. An example of the semiconductive oxide is SnO ₂ . Examples of the metal include Zn, Sb, Sn, Ag, and Ni. Examples of the nonmetallic conductive material include amorphous carbon (carbon black), graphite, silicon carbide, titanium carbide, titanium nitride, tungsten carbide, and zirconium carbide. These conductive powders may be used alone or in combination of two or more.

  Examples of the magnetic body include an element in which a conductor is bonded to the surface of a ferrite porcelain, an element in which a metal wire is wound around a ferrite porcelain, and an aggregate (molded body) of magnetic particles in which ferrite particles are coated with a conductive substance. Is mentioned. The resistance value of the magnetic material is preferably 0.01Ω to 10Ω, for example.

Examples of the conductive material used for the magnetic particles include metals such as Ni, Cu, Sn, Fe, and Inconel (INCONEL is a registered trademark), and conductive or semiconductive complex oxides such as LaMnO ₃ , SrTiO ₃ , and SrCrO ₃ . , Carbon, and carbon compounds such as Cr ₃ C ₂ and TiC. One or more types of ferrite and conductive materials can be appropriately selected and used. In addition to magnetic particles, it is naturally possible to form a magnetic body (aggregate of magnetic particles) by mixing glass powder, inorganic compound powder, or the like. The aggregate of magnetic particles forms a three-dimensional conductive path by bringing conductive materials into contact with each other.

  As means for covering the surface of the ferrite particles with a conductive substance, known means can be appropriately employed. For example, the conductive material is mixed and stirred together with the particles to mechanically adhere to the surface of the particles, the conductive material is adhered to the surface of the particles using a binder or the like, or the conductive material is made particles by electroless plating. And means for depositing on the surface.

As the conductive glasses 21 and 22, those obtained by baking a mixture of glass powder and conductive powder are used. As the glass powder and the conductive powder, the same glass powder and conductive powder as the resistor material are used. The conductive glasses 21 and 22 may contain a semiconductive inorganic compound powder such as TiO ₂ , an insulating powder, or the like as necessary.

  FIG. 2A is a cross-sectional view of the spark plug 10 showing an enlarged portion indicated by IIa in FIG. In FIG. 2A, the arrow F indicates the front end side in the axial direction, the arrow B indicates the rear end side in the axial direction, and the arrow P indicates the inner side in the direction perpendicular to the axis O (see FIG. 1). (The same applies to (b), FIG. 3, FIG. 4 (a), FIG. 4 (b), and FIG. 5).

  As shown in FIG. 2A, in the spark plug 10, an insulating glass 23 is disposed between the side surface 20 b of the conductor 20 and the insulator 11. The insulating glass 23 is in contact with the conductive glass 21, the conductor 20 and the insulator 11. By interposing the insulating glass 23 between the conductor 20 and the insulator 11, the conductor 20 can be prevented from being damaged by vibration.

As a material of the insulating glass 23, a material having a melting point lower than the melting point of the insulator 11, for example, B ₂ O ₃ —SiO ₂ type, BaO—B ₂ O ₃ type, SiO ₂ —B ₂ O ₃ —CaO—BaO. System, SiO ₂ —ZnO—B ₂ O ₃ system, SiO ₂ —B ₂ O ₃ —Li ₂ O system, and SiO ₂ —B ₂ O ₃ —Li ₂ O—BaO system. These may use only 1 type and may use 2 or more types together. The insulating glass 23 may contain an inorganic compound such as alumina, silicon nitride, mullite, and steatite.

  The conductive glass 21 contacts a part of the bottom surface 20 a and the side surface 20 b of the conductor 20 and contacts the insulator 11. When the conductive glass 21 comes into contact with the insulator 11, the combustion gas in the combustion chamber of the internal combustion engine (not shown) to which the spark plug 10 is attached can be prevented from leaking from the shaft hole 12.

  The insulating glass 23 is interposed between the conductive glass 21 and the conductive glass 22. Since the volume resistivity of the insulating glass 23 is larger than the volume resistivity of the conductor 20 and the conductive glass 21, the conductive glasses 21 and 22 can be prevented from being short-circuited through the insulating glass 23.

  The spark plug 10 is manufactured by the following method, for example. First, the center electrode 14 is inserted into the shaft hole 12 of the insulator 11, and the center electrode 14 is locked by the step portion 13. Next, the raw material powder of the conductive glass 21 is put through the shaft hole 12 and filled around the center electrode 14. The raw material powder of the conductive glass 21 filled in the shaft hole 12 is pre-compressed using a compression rod (not shown).

  Next, a glass tube made of the material of the insulating glass 23 into which a conductor 20 (element, molded body, etc.) is put is inserted into the shaft hole 12, and a molded body of the raw material powder of the conductive glass 21 is inserted. put on top. After placing the molded body obtained by forming the raw material powder of the conductive glass 22 into a pellet shape on the conductor 20 and the glass tube, the insulator 11 is transferred into the furnace, for example, the raw material powder of the conductive glasses 21 and 22. Or heated to a temperature higher than the softening point of the glass component contained in the material of the insulating glass 23. After the heating, the terminal fitting 15 is press-fitted into the shaft hole 12 of the insulator 11, and the raw material powder of the conductive glasses 21 and 22 and the material of the insulating glass 23 are compressed in the axial direction by the tip of the terminal fitting 15. As a result, they are compressed and sintered, and the conductor 20, the conductive glasses 21 and 22, and the insulating glass 23 are formed inside the insulator 11.

  Next, the insulator 11 is transferred to the outside of the furnace, and the metal shell 16 is assembled to the outer periphery of the insulator 11. After joining the ground electrode 19 to the metal shell 16, the ground electrode 19 is bent so that the tip of the ground electrode 19 faces the center electrode 14 to obtain the spark plug 10.

  In this manufacturing method, instead of inserting the glass tube containing the conductor 20 into the shaft hole 12, the conductor 20 (molded body) is inserted into the shaft hole 12, and then the insulating glass 23 is formed around the conductor 20. It is naturally possible to fill the raw material powder. In addition, instead of firing the conductor 20 (molded body) together with the conductive glasses 21 and 22 and the insulating glass 23, the conductor 20 (element) is placed in the shaft hole 12 and softened in the shaft hole 12. Naturally, the conductive glasses 21 and 22 and the insulating glass 23 can be brought into contact with the conductor 20 (element). Furthermore, instead of inserting the compact of the raw material powder of the conductive glass 22 into the shaft hole 12, it is naturally possible to fill the shaft hole 12 with the raw material powder of the conductive glass 22.

  As shown in FIG. 2A, the conductor 20 has a bottom surface 20 a that contacts the conductive glass 21. In an arbitrary cross section including the axis O (see FIG. 1), the interface 24 between the conductive glass 21 and the insulating glass 23 has a first point 25 in contact with the insulator 11 and a second point on the side surface 20b of the conductor 20. 26 touches. In the present embodiment, the interface 24 is inclined linearly from the first point 25 to the second point 26. The shape of the interface 24 and the positions of the first point 25 and the second point 26 are the pressure when compressing each material in the axial direction using the terminal fitting 15 and the shape of the material of the insulating glass 23 (glass tube). Or by adjusting the amount of the raw material powder of the insulating glass 23 and the like.

  For example, the bottom surface 20 a of the conductor 20 can be embedded in the conductive glass 21 by increasing the pressure when compressing each material in the axial direction using the terminal fitting 15. The softened conductive glass 21 enters the gap between the insulating glass 23 and the insulator 11 through the insulator 11. As a result, the interface 24 between the conductive glass 21 and the insulating glass 23 rises from the conductor 20 toward the insulator 11.

  The interface 24 is such that the first point 25 is located closer to the rear end side in the axial direction (arrow B direction) than the second point 26, and at any two points on the interface 24, the inner side in the direction perpendicular to the axis (arrow P direction). This point is located on the tip end side (arrow F direction) in the axial direction with respect to the point outside the axis perpendicular direction (counter arrow P direction). The angle formed between the interface 24 and the conductor 20 (side surface 20b) (angle on the conductive glass 21 side) is set to 90 ° or more, and the angle formed between the interface 24 and the insulator 11 (shaft hole 12) (conductive glass). 21 side angle) is set to less than 90 °. This relationship is established in any (any case) cross section including the axis O (see FIG. 1). Thereby, the concentration of the electric field at the second point 26 can be alleviated. Since the current density at the time of discharging at the second point 26 can be suppressed and deterioration of the conductor 20 can be suppressed, the durability of the conductor 20 can be improved.

  FIG. 3 is a perspective view schematically showing the conductor 20. Since the interface 24 (see FIG. 2A) is in contact with the side surface 20b of the conductor 20 in any (in any case) cross section including the axis O, in FIG. 3, a boundary line 27 where the conductor 20 and the interface 24 are in contact is shown. , Expressed as a continuous curve. The boundary line 27 is a set of second points 26 (see FIG. 2A).

  The spark plug 10 has a point 28 (rear end position) located on the most rear end side (arrow B direction) and a point located on the most front end side (arrow F direction) of the boundary line 27 on the side surface 20b of the conductor 20. D / L obtained by dividing the distance D in the direction of the axis O with respect to 29 (the most advanced position) by the maximum length L in the direction of the axis O of the conductor 20 satisfies 0 ≦ D / L ≦ 0.1. .

  The maximum length L of the conductor 20 refers to a distance between two planes when the conductor 20 is sandwiched in the direction of the axis O by two planes orthogonal to the axis O. Further, the shape of the interface 24, the positions of the first point 25 and the second point 26, the distance D and the length L are determined by non-destructive inspection using a microscope observation of a cut surface of the sample or a CT scanner (X-ray fluoroscope). It can be measured.

  By satisfying 0 ≦ D / L ≦ 0.1, variation in the circumferential direction of the contact area of the conductive glass 21 in contact with the side surface 20b of the conductor 20 can be suppressed. Therefore, variation in the resistance value of the conductor 20 can be suppressed.

  Further, by satisfying 0 ≦ D / L ≦ 0.1, variation in the current density of the side surface 20b of the conductor 20 can be suppressed, so that deterioration of the conductor 20 can be suppressed. Therefore, the durability of the conductor 20 can be further improved.

  Next, a second embodiment will be described with reference to FIG. In the first embodiment, the case where the interface 24 contacts the side surface 20b of the conductor 20 has been described. In contrast, in the second embodiment, a case where the interface 34 is in contact with the corners of the bottom surface 20a and the side surface 20b of the conductor 20 will be described. In addition, about the part same as 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted. FIG. 2B is an enlarged cross-sectional view showing a part of the spark plug 30 in the second embodiment.

  As illustrated in FIG. 2B, the bottom surface 20 a of the conductor 20 is in contact with the conductive glass 31. In an arbitrary cross section including the axis O (see FIG. 1), the interface 34 between the conductive glass 31 and the insulating glass 33 is such that the first point 35 is in contact with the insulator 11, and the bottom surface 20a and the side surface 20b of the conductor 20 The second point 36 touches the corner or side surface 20b. In the present embodiment, in at least one of the arbitrary cross sections, the interface 34 between the conductive glass 31 and the insulating glass 33 has a second point 36 at the corner between the bottom surface 20a and the side surface 20b of the conductor 20. Touch. The interface 34 is linearly inclined from the first point 35 to the second point 36.

  The interface 34 is such that the first point 35 is located on the rear end side (arrow B direction) in the axial direction with respect to the second point 36, and at any two points on the interface 34, the inner side in the direction perpendicular to the axis (arrow P direction). This point is located on the tip end side (arrow F direction) in the axial direction with respect to the point outside the axis perpendicular direction (counter arrow P direction). The angle formed by the interface 34 and the conductor 20 (the bottom surface 20a or the side surface 20b) (the angle on the conductive glass 31 side) is set to 90 ° or more, and the angle formed by the interface 34 and the insulator 11 (the shaft hole 12) ( The angle on the conductive glass 31 side) is set to less than 90 °. This relationship is established in any (any case) cross section including the axis O (see FIG. 1). Therefore, the concentration of the electric field at the second point 36 can be alleviated, and deterioration of the conductor 20 can be suppressed.

  A third embodiment will be described with reference to FIG. In addition, about the part same as 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted. FIG. 4A is an enlarged cross-sectional view showing a part of the spark plug 40 according to the third embodiment.

  As shown in FIG. 4A, the conductor 20 has a bottom surface 20 a in contact with the conductive glass 41. In an arbitrary cross section including the axis O (see FIG. 1), the interface 44 between the conductive glass 41 and the insulating glass 43 has a first point 45 in contact with the insulator 11 and a second point on the side surface 20b of the conductor 20. 46 touches. In the present embodiment, in at least one of the arbitrary cross-sections, the interface 44 is a curved curve convex toward the tip side (in the direction of arrow F).

  The interface 44 is such that the first point 45 is located on the rear end side (arrow B direction) in the axial direction with respect to the second point 46, and at any two points on the interface 44, the inner side in the direction perpendicular to the axis (arrow P direction). Is located at the same position in the axial direction or on the tip side in the axial direction (in the direction of arrow F) with respect to the point outside the direction perpendicular to the axis (in the direction of the arrow P). The angle formed by the interface 44 and the conductor 20 (side surface 20b) (angle on the conductive glass 41 side) is set to 90 ° or more, and the angle formed by the interface 44 and the insulator 11 (shaft hole 12) (conductive glass). 41 side angle) is set to less than 90 °. This relationship is established in any (any case) cross section including the axis O (see FIG. 1). Therefore, the concentration of the electric field at the second point 46 can be alleviated, and the deterioration of the conductor 20 can be suppressed.

  A fourth embodiment will be described with reference to FIG. In addition, about the part same as 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted. FIG. 4B is an enlarged cross-sectional view showing a part of the spark plug 50 according to the fourth embodiment.

  As shown in FIG. 4B, the bottom surface 20a of the conductor 20 is in contact with the conductive glass 51. In an arbitrary cross section including the axis O (see FIG. 1), the interface 54 between the conductive glass 51 and the insulating glass 53 has a first point 55 in contact with the insulator 11 and a second point on the side surface 20b of the conductor 20. 56 touches. In the present embodiment, in at least one of the arbitrary cross sections, the interface 54 is a curve in which the uneven state is changed near the center.

  The interface 54 has the first point 55 positioned on the rear end side in the axial direction (arrow B direction) with respect to the second point 56, and at any two points on the interface 54, on the inner side in the direction perpendicular to the axis (arrow P direction). Is located at the same position in the axial direction or on the tip side in the axial direction (in the direction of arrow F) with respect to the point outside the direction perpendicular to the axis (in the direction of the arrow P). The angle formed by the interface 54 and the conductor 20 (side surface 20b) (angle on the conductive glass 51 side) is set to 90 ° or more, and the angle formed by the interface 54 and the insulator 11 (shaft hole 12) (conductive glass). 51 side angle) is set to less than 90 °. This relationship is established in any (any case) cross section including the axis O (see FIG. 1). Therefore, the concentration of the electric field at the second point 56 can be mitigated, and deterioration of the conductor 20 can be suppressed.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1
A spark plug sample described in the embodiment was prepared and a discharge test was performed. In the sample, first, the center electrode 14 is inserted into the shaft hole 12 of the insulator 11, and then the raw material powder of the conductive glass 21 mixed with the conductive powder and the glass powder is put through the shaft hole 12. Filled around. Next, a conductor 20 formed by mixing a powder of a conductive substance and glass powder in advance and placed in a glass tube made of the material of the insulating glass 23 is inserted into the shaft hole 12 to conduct electricity. The glass was placed on the raw material powder of the functional glass 21. Next, a molded body obtained by forming the raw material powder of the conductive glass 22 into a pellet shape was placed on the conductor 20 and the glass tube, and then the insulator 11 was heated to soften the glass powder and the glass tube. Next, glass powder or the like was pressed by the terminal fitting 15 press-fitted into the shaft hole 12, and the conductor 20, the conductive glasses 21, 22 and the insulating glass 23 were sintered. The metal shell 16 to which the ground electrode 19 was joined was assembled to the insulator 11 to obtain a spark plug sample.

  The form of the interface between the conductive glass and the insulating glass of the obtained sample was observed using an X-ray fluoroscope. Moreover, D and L were measured using the X-ray fluoroscope, and D / L was calculated.

  Table 1 shows the form of the interface of Samples 1 to 8, the conductive substance contained in the conductor 20, the value obtained by dividing the distance D by the length L (D / L), and the test time. As in the first embodiment, the interface between the conductive glass and the insulating glass is linear, and the interface is in contact with the side surface of the conductor. As described above, the case where the interface between the conductive glass and the insulating glass is in contact with the corners of the conductor is referred to as form 2. Further, as in the third embodiment, the interface between the conductive glass and the insulating glass is curved, and the interface is in contact with the side surface of the conductor is referred to as form 3. The interface of the sample classified into any one of the forms 1 to 3 was the form classified in the range of 70% or more of the entire circumference (360 °).

サンプル８は比較例である。比較例におけるスパークプラグ６０は、サンプル１〜７と異なり、絶縁性ガラスが省略されている。図５は比較例におけるスパークプラグ６０（サンプル８）の一部を拡大して示した軸線Ｏ（図１参照）を含む断面図である。なお、第１実施の形態で説明した部分と同一の部分については、同一の符号を付して以下の説明を省略する。

Sample 8 is a comparative example. Unlike the samples 1-7, the spark plug 60 in the comparative example omits the insulating glass. FIG. 5 is a cross-sectional view including an axis O (see FIG. 1) showing an enlarged part of a spark plug 60 (sample 8) in a comparative example. In addition, about the part same as the part demonstrated in 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted.

  As shown in FIG. 5, in the spark plug 60, a conductive glass 61 and a conductor 62 are disposed in the shaft hole 12 of the insulator 11. The interface 63 between the conductive glass 61 and the conductor 62 has a curved shape that is convex toward the tip side (in the direction of arrow F), and contacts the insulator 11 at the intersection 64. An angle formed by the interface 63 and the insulator 11 (shaft hole 12) (an angle on the conductive glass 61 side) is set to be less than 90 °. This relationship is established in any (any case) cross section including the axis O (see FIG. 1).

  In the test, a voltage of 45 kV was applied between the terminal fitting 15 and the metal shell 16 at a cycle of 1/100 second in a state where the samples 1 to 8 were stored in a bath at 425 ° C. For the conductors built in Samples 1 to 8, the resistance value (initial value) was set to 1 kΩ, and the test time was measured when the rate of change in resistance value before and after the test exceeded ± 50%.

  As shown in Table 1, Samples 1 to 7 (Examples) had a test time of 200 hours or more until the rate of change in resistance value exceeded ± 50%, whereas Sample 8 (Comparative Example) The change rate of the resistance value exceeded ± 50% in 36 hours after the start of the test. In sample 8 (comparative example), the angle formed by the interface 63 and the insulator 11 (shaft hole 12) (angle on the side of the conductive glass 61) is less than 90 °, so the electric field concentrates at the intersection 64 and the conductor 62 Is presumed to have deteriorated early. On the other hand, samples 1 to 7 were able to alleviate the concentration of the electric field at the second points 26, 36, and 46, so it is assumed that the deterioration of the conductor 20 was suppressed.

  According to Samples 1 to 3, it was found that as the D / L value increased, the test time until the rate of change in resistance value exceeded ± 50% was shortened. When the value of D / L is increased, the variation in current density on the side surface 20b of the conductor 20 is increased, and it is assumed that the conductor 20 is likely to deteriorate.

(Example 2)
Samples having different D / L values were prepared. After the conductive material powder and glass powder were mixed and molded, the conductor was placed in a glass tube made of insulating glass material, and inserted into the shaft hole together with the glass tube. . The conductor was baked in the shaft hole together with the conductive glass and the insulating glass. The conductive substance contained in the conductor was La (Fe _0.5 Ni _0.5 ) O ₃ and the average resistance value of the conductor was set to 1 kΩ.

  Similarly to Example 1, samples of the first embodiment and the third embodiment (forms 1 and 3) are prepared, D and L of the sample are measured using an X-ray fluoroscopic apparatus, and D / L is calculated. Calculated. Further, the resistance value (resistance value of the conductor) of the sample was measured, and the standard deviation (σ) was calculated. Note that a sufficient number of samples to evaluate the standard deviation were prepared and measured. The evaluation of the variation is 3σ ≦ 0.20 kΩ is “excellent (）)”, 0.2 <3σ ≦ 0.35 kΩ is “good” (◯), and 3σ> 0.35 kΩ is “inferior (Δ)”. did.

表２に示すように０≦Ｄ／Ｌ≦０．１を満たすことで、抵抗値のばらつきを小さくできることがわかった。特に０≦Ｄ／Ｌ≦０．０５を満たすことで、抵抗値のばらつきを特に小さくできることがわかった。

As shown in Table 2, it was found that the variation in resistance value can be reduced by satisfying 0 ≦ D / L ≦ 0.1. In particular, it was found that by satisfying 0 ≦ D / L ≦ 0.05, the variation in resistance value can be particularly reduced.

  The present invention has been described above based on the embodiments. However, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It can be easily guessed.

  In each of the above-described embodiments, the interfaces 24, 34, 44, and 54 are located at any two points on the interfaces 24, 34, 44, and 54. Although the case where it is located at the same position in the axial direction or the tip side in the axial direction (in the direction of arrow F) with respect to the point on the outer side (counter arrow P direction) has been described, it is not necessarily limited thereto. For example, the interfaces 24, 34, 44, and 54 have a point on the inner side in the direction perpendicular to the axis (in the direction of the arrow P) and a point on the rear end side in the axial direction (in the direction of the arrow P). You may have the part located in a B direction.

  That is, the first points 25, 35, 45, and 55 where the interfaces 24, 34, 44, and 54 contact the insulator 11, and the second points 26, 36, and 46 where the interfaces 24, 34, 44, and 54 contact the conductor 20. , 56 is located on the rear end side (arrow B direction), and the interfaces 24, 34, 44, 54 are in the same axial position as the second points 26, 36, 46, 56 or the second points 26, 36, What is necessary is just to be located in the back end side (arrow B direction) rather than 46,56. If the interfaces 24, 34, 44, 54 are positioned in this way, the angle formed between the interfaces 24, 34, 44, 54 and the side surface 20b of the conductor 20 is set to 90 ° or more, and the interfaces 24, 34, The angle between 44 and 54 and the insulator 11 is set to be less than 90 °. Therefore, the concentration of the electric field at the second points 26, 36, 46, and 56 can be alleviated and deterioration of the conductor 20 can be suppressed.

  In each of the above embodiments, the case where the conductor 20 is connected to the terminal fitting 15 by the conductive glass 22 has been described, but the present invention is not necessarily limited thereto. For example, instead of the conductive glass 22, an elastic body such as a conductive spring is interposed between the conductor 20 and the terminal fitting 15 to electrically connect the conductor 20 and the terminal fitting 15. Is of course possible.

  In each of the above embodiments, the case where the conductor 20 is formed in a columnar shape has been described, but the present invention is not necessarily limited thereto. Since the conductor 20 may be any size and shape that can be inserted into the shaft hole 12, it is naturally possible to employ, for example, the conductor 20 formed in a rectangular parallelepiped shape.

  In each of the embodiments described above, the spark plugs 10, 30, 40, 50 in which the ground electrode 19 faces the tip of the center electrode 14 have been described. However, the structure of the spark plug is not necessarily limited to this. Examples of other structures of the spark plug include a spark plug in which the ground electrode 19 faces the side surface of the center electrode 14 and a multipolar spark plug in which a plurality of ground electrodes 19 are joined to the metal shell 16.

10, 30, 40, 50 Spark plug 11 Insulator 12 Axial hole 14 Center electrode 20 Conductor 20b Side surface 21, 31, 41, 51 Conductive glass 23, 33, 43, 53 Insulating glass 24, 34, 44, 54 Interface 25, 35, 45, 55 First point 26, 36, 46, 56 Second point 27 Boundary line 28 points (end position)
29 points (the most advanced position)
D Distance L Length O Axis

Claims (2)

An insulator having an axial hole extending in the axial direction from the front end side to the rear end side;
A center electrode disposed on the tip side of the shaft hole;
A conductor disposed on a rear end side of the center electrode in the shaft hole;
A conductive glass in contact with the central electrode, the conductor and the insulator, and electrically connecting the central electrode and the conductor;
A spark plug that is disposed between the conductor and the insulator and includes the conductive glass, the insulating glass contacting the conductor and the insulator;
In any cross section including the axis, the interface between the insulating glass and the conductive glass is such that the first point where the interface is in contact with the insulator is the rear end of the second point where the interface is in contact with the conductor. Located on the side
The interface is the spark plug located at the same position in the axial direction as the second point or on the rear end side in the axial direction from the second point.   Of the boundary line between the conductor and the interface, the distance D in the axial direction between the rearmost position and the most distal position in the axial direction is the maximum length L in the axial direction of the conductor. The spark plug according to claim 1, wherein D / L divided by 1 satisfies 0 ≦ D / L ≦ 0.1.

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