JP2019212388A - Spark plug - Google Patents

Abstract

To provide a spark plug which allows improvement in durability.SOLUTION: A spark plug comprises: a conductor which is arranged between a center electrode and a terminal fitting; a first conductive glass part which electrically connects the center electrode to the conductor; and a second conductive glass part which electrically connects the terminal fitting to the conductor. The first conductive glass part and the second conductive glass part are made of a mixture containing insulative glass and metal. The conductor has a main phase, a first phase, and a second phase. The main phase, the first phase, and the second phase are each made of a sintered body of a conductive oxide. The main phase is electrically connected to the first conductive glass part via the first phase and is electrically connected to the second conductive glass part via the second phase. Volume resistivities of the first phase and the second phase are lower than that of the main phase.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a spark plug, and more particularly to a spark plug with a built-in conductor.

  In order to suppress radio noise generated during discharge, there is a spark plug in which a conductor such as a resistor is incorporated in an insulator (Patent Document 1). In the technique of Patent Document 1, the conductor incorporated in the cylindrical insulator is in contact with the conductive glass connected to the center electrode.

JP 2007-122879 A

  However, in the above conventional technique, the contact resistance at the interface between the conductor and the conductive glass may be increased. That is, since the conductor and the conductive glass are brought into conduction by the contact between the conductive oxide forming the conductor and the metal contained in the conductive glass, the contact resistance is likely to increase due to the Schottky barrier. As a result, the electric field may concentrate on this interface 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 capable of improving durability.

  To achieve this object, a spark plug according to the present invention comprises an insulator having an axial hole extending in the direction of the axis from the front end side to the rear end side, a center electrode disposed on the front end side of the axial hole, and an axial hole A terminal fitting disposed on the rear end side, a conductor disposed between the center electrode in the shaft hole and the terminal bracket, and a first conductive glass electrically connecting the center electrode and the conductor; And a second conductive glass for electrically connecting the terminal fitting and the conductor. The first conductive glass and the second conductive glass are made of a mixture containing insulating glass and metal. The conductor has a main phase, a first phase that contacts the front end side of the main phase, and a second phase that contacts the rear end side of the main phase, and the main phase, the first phase, and the second phase are conductive, respectively. It consists of a sintered body of a functional oxide. The main phase is electrically connected to the first conductive glass via the first phase, and is electrically connected to the second conductive glass via the second phase. The volume resistivity of the first phase and the second phase is lower than the volume resistivity of the main phase.

  According to the spark plug of the first aspect, each of the first phase and the second phase of the conductor is in contact with the main phase. The main phase is electrically connected to the first conductive glass through the first phase, and is electrically connected to the second conductive glass through the second phase. Since the volume resistivity of the first phase and the second phase is lower than the volume resistivity of the main phase, the contact resistance between the first phase and a member that contacts the first phase and is located on the opposite side of the main phase, and The contact resistance between the second phase and a member that contacts the second phase and is located on the opposite side of the main phase can be reduced. Therefore, it is possible to reduce the concentration of the electric field at these interfaces during discharge. Furthermore, since the main phase, the first phase, and the second phase are each made of a sintered body of conductive oxide, deterioration due to oxidation can be prevented. As a result, the durability of the spark plug can be improved.

According to the spark plug according to claim 2, since the volume resistivity of the first phase and the volume resistivity of the second phase are 1.0 × 10 ⁻¹ Ω · m or less, the member located on the opposite side of the main phase is The effect of suppressing contact resistance between the first phase and the second phase can be improved. Therefore, in addition to the effect of Claim 1, the durability of the spark plug can be further improved.

  According to the spark plug of claim 3, since the minimum value of the thickness in the direction of the axis of the first phase and the second phase is 5 μm or more, in addition to the effect of claim 1 or 2, the first phase and the second phase The effect of reducing the contact resistance due to can be easily expressed. Further, since the maximum value of the thickness is 5 mm or less, the main phase can be relatively lengthened, and the electric characteristics of the main phase can be easily developed.

  According to the spark plug of claim 4, the main phase contains one or more metal elements that are the same as the metal element contained in the first phase, and one or more metal elements that are the same as the metal element contained in the second phase. contains. Thereby, it is possible to make it difficult for the first phase or the second phase to interact with the main phase. Therefore, in addition to the effect of any one of claims 1 to 4, the durability can be further improved.

  According to the spark plug of the fifth aspect, since the main phase, the first phase, and the second phase are composed of a sintered body of complex oxides having the same constituent elements, in addition to the effect of the fourth aspect, The interaction between the second phase and the main phase can be made more difficult to occur.

  According to the spark plug of the sixth aspect, the first buffer layer disposed between the first conductive glass and the conductor is in contact with the first conductive glass and the first phase. The second buffer layer disposed between the second conductive glass and the conductor is in contact with the second conductive glass and the second phase. The first buffer layer and the second buffer layer are made of a mixture of a metal and a conductive oxide or a metal. Therefore, compared with the case where the metal (powder or particle) contained in the first conductive glass and the second conductive glass is in contact with the conductor, the conductive material (metal or metal contained in the first buffer layer and the second buffer layer). The contact area between the conductive oxide) and the conductor can be increased. The first buffer layer and the second buffer layer are electrically connected in so-called point contact with the metals (powder and particles) contained in the first conductive glass and the second conductive glass, respectively. It is also made by the metal contained in the two buffer layers. Thereby, an ohmic contact or a contact close to an ohmic contact can be realized between the first buffer layer and the first conductive glass and between the second buffer layer and the second conductive glass, respectively. As a result, it is possible to further alleviate the concentration of the electric field at these interfaces during discharge, so that the durability of the spark plug can be further improved in addition to the effect of any one of claims 1 to 5.

It is a half sectional view of the spark plug in a 1st embodiment. It is sectional drawing of the spark plug which expanded and showed a part of FIG. It is sectional drawing which expanded and showed a part of spark plug in 2nd Embodiment. It is sectional drawing which expanded and showed a part of spark plug in 3rd Embodiment. It is sectional drawing which expanded and showed a part of spark plug in 4th Embodiment. It is sectional drawing which expanded and showed a part of spark plug in 5th Embodiment. 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 half sectional view with an axis O of a spark plug 10 according to the first embodiment 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 7). The spark plug 10 includes an insulator 11, a center electrode 14, and a terminal fitting 15.

  The insulator 11 is a ceramic member such as alumina that is excellent in mechanical properties and insulation at high temperatures, and has a shaft hole penetrating along the axis O. In the present embodiment, the inner peripheral surface 12 of the insulator 11 formed through the shaft hole has a circular cross-sectional shape orthogonal to the axis O. The inner peripheral surface 12 of the insulator 11 is provided with a rear end-facing surface 13 on the front end side, the inner diameter of which gradually decreases toward the front 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 rear end facing surface 13 of the insulator 11, and the tip is exposed from the insulator 11. The center electrode 14 may omit the core material.

  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.

  A metal shell 16 is caulked and fixed to the outer periphery on the distal end side of the insulator 11. 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 during discharge, and is disposed between the center electrode 14 on the inner peripheral surface 12 of the insulator 11 and the terminal fitting 15. The conductor 20 is electrically connected to the center electrode 14 via the first conductive glass 24 disposed between the center electrode 14 and the conductor 20. In the present embodiment, the conductor 20 is formed in a cylindrical shape. The conductor 20 is electrically connected to the terminal fitting 15 via the second conductive glass 25 disposed between the terminal fitting 15 and the conductor 20.

  FIG. 2 is a cross-sectional view including an axis O of the spark plug 10 showing a part of FIG. 1 (in the vicinity of the conductor 20) in an enlarged manner. In FIG. 2, the illustration of the intermediate portion in the axial direction of the conductor 20 is omitted (the same applies to FIGS. 3 to 7).

  As shown in FIG. 2, the conductor 20 includes a main phase 21, a first phase 22 that contacts the front end side of the main phase 21, and a second phase 23 that contacts the rear end side of the main phase 21. The main phase 21, the first phase 22, and the second phase 23 are each made of a sintered body of conductive oxide. The conductor 20 is preferably a single body in which the main phase 21, the first phase 22 and the second phase 23 are integrated by firing, but the sintered bodies of the main phase 21, the first phase 22 and the second phase 23 are made of each. Aggregates in contact with each other may be used. The conductor 20 of the present embodiment is a sintered body in which the main phase 21, the first phase 22, and the second phase 23 are integrated by firing.

  Examples of the conductor 20 include a resistor and a magnetic material. 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. Examples of the conductive oxide constituting the magnetic material include Mn—Zn ferrite.

As the conductive oxide constituting the resistor, for example, a semiconductive sintered body obtained by blending and firing oxides such as Mn, Co, Ni, Fe, and Cr, a general formula A _{2 -X} B _X CuO ₄ or a sintered body containing the composite oxide represented by the general formula CDO ₃ . Element A and element C in the general formula are one or more selected from Group 3 elements in the periodic table based on the IUPAC 1990 recommendation. The element B is at least one selected from Ca, Sr and Ba selected from Group 2 elements of the periodic table based on the IUPAC 1990 recommendation. Element D is one or more of transition elements. The subscript x satisfies 0 ≦ x <2. The subscript x = 0 indicates that the element B is not included.

  Examples of the elements A and C include lanthanoids such as La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb, actinoids such as Ac, and Sc and Y. . In particular, the element A is preferably at least one selected from La, Ce, Pr, Nd, Sm, Gd, Y and Yb, more preferably at least one selected from La, Ce, Nd and Gd. Part of the element C can be replaced with other elements such as Ca, Sr and Ba. Examples of the element D include Cr, Mn, Fe, Ni, and Al.

As the composite oxide represented by the general formula _{A 2-X B X CuO 4} , for example, _{La 2 CuO 4, YBa 2 Cu} 3 O 7, La 1.85 Ba 0.15 CuO 4 , and the like. The composite oxide represented by the general formula CDO ₃ includes YCrO ₃ , YMnO ₃ , La (Fe _0.5 Ni _0.5 ) O ₃ , (Nd _0.7 Ca _0.3 ) (Mn _0.4 Al _0.6 ) O _{3 and the} like.

The conductor 20 can contain a substance having a volume resistivity higher than that of the conductive oxide in order to adjust the resistance value. Examples of this substance (insulating powder) include metal oxides such as Al ₂ O ₃ , Y ₂ O ₃ , ZrO ₂ , mullite and steatite, metal nitrides such as Si ₃ N ₄ , and B ₂ O ₃ —SiO _2. , BaO—B ₂ O ₃ system, 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 — Examples thereof include B ₂ O ₃ —Li ₂ O—BaO-based glasses. These substances may be used alone or in combination of two or more.

The resistance value of the conductor 20 as the resistor is, for example, preferably 0.1 kΩ to 30 kΩ, and more preferably 1 kΩ to 20 kΩ. The volume resistivity at 20 ° C. of the first phase 22 and the second phase 23 is set lower than the deposition resistivity at 20 ° C. of the main phase 21. Preferably, the volume resistivity at 20 ° C. of the first phase 22 and the volume resistivity at 20 ° C. of the second phase 23 are set to 1.0 × 10 ⁻¹ Ω · m or less.

  The conductor 20 is prepared by, for example, mixing starting materials weighed for each of the main phase 21, the first phase 22 and the second phase 23 and pre-baking each, and then pulverizing the pre-fired powder and insulating if necessary. This is a sintered body obtained by mixing and forming and firing the raw material powders in the order of the first phase 22, the main phase 21, and the second phase 23 after mixing the active material (insulating powder). The sintered body is subjected to external processing as necessary.

  As another method for manufacturing the conductor 20, for example, the raw material powder of the main phase 21 is molded and fired to obtain a sintered body, and then an outer shape process is performed as necessary. Then, a paste containing the raw material powder of the first phase 22 is applied to one end face of the sintered body of the main phase 21, and a paste containing the raw material powder of the second phase 23 is applied to the other end face, followed by baking. Can be mentioned.

As the first conductive glass 24 and the second conductive glass 25, those obtained by firing a mixture containing insulating glass powder and metal powder are used. Glasses included in the first conductive glass 24 and the second conductive glass 25 are B ₂ O ₃ —SiO ₂ type, BaO—B ₂ O ₃ type, SiO ₂ —B ₂ O ₃ —CaO—BaO type, SiO 2 _2- ZnO—B ₂ O ₃ system, SiO ₂ —B ₂ O ₃ —Li ₂ O system, SiO ₂ —B ₂ O ₃ —Li ₂ O—BaO system, and the like can be given.

Examples of the metal contained in the first conductive glass 24 and the second conductive glass 25 include Zn, Sb, Sn, Ag, Ni, Fe, and Cu. The first conductive glass 24 and the second conductive glass 25 are made of conductive materials such as amorphous carbon (carbon black), graphite, SiC, TiC, TiN, WC and ZrC, and semiconductive inorganic materials such as ZnO and TiO _2. You may contain a compound powder, insulating powder, etc.

  An insulating glass 26 is disposed between the side surface 20 c of the conductor 20 and the inner peripheral surface 12 of the insulator 11. The insulating glass 26 is interposed between the first conductive glass 24 and the second conductive glass 25. Since the volume resistivity of the insulating glass 26 is higher than the volume resistivity of the conductor 20, the first conductive glass 24 and the second conductive glass 25 are not short-circuited via the insulating glass 26. it can. By interposing the insulating glass 26 between the conductor 20 and the insulator 11, the conductor 20 can be prevented from being damaged by vibration.

Examples of the material of the insulating glass 26 include those having a melting point lower than that of the insulator 11, such as 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 26 may contain an inorganic compound such as alumina, silicon nitride, mullite, and steatite.

  In the spark plug 10, the first conductive glass 24 is in contact with the end surface 20 a (first phase 22) in the axial direction of the conductor 20, and the end surface 20 b (second phase 23) on the rear end side of the conductor 20. The second conductive glass 25 comes into contact. The first phase 22 separates the main phase 21 and the first conductive glass 24, and the second phase 23 separates the main phase 21 and the second conductive glass 25. The minimum value of the thickness T1 in the axial direction of the first phase 22 and the minimum value of the thickness T2 in the axial direction of the second phase 23 are each 5 μm or more. The maximum value of the thicknesses T1 and T2 is 5 mm or less. The thicknesses T1 and T2 are obtained by observing a cross section including the axis O of the spark plug 10 using a microscope such as SEM, and the thickness of the thinnest part (minimum value) and the thickness of the thickest part (maximum value). Measured.

  Specifically, the spark plug 10 is divided into four along two virtual planes that intersect substantially perpendicularly such that the axis O of the spark plug 10 intersects, and the obtained cross section is observed with a microscope such as SEM. The first phase 22 and the second phase 23 manufactured by the above-described method can have a substantially uniform thickness. Therefore, the minimum value and the maximum value of the thickness of the first phase 22 and the second phase 23 observed in the cross section are estimated as the minimum value and the maximum value of the thicknesses T1 and T2.

  The spark plug 10 is manufactured by the following method, for example. First, the center electrode 14 is inserted into the shaft hole of the insulator 11, and the center electrode 14 is locked by the rear end facing surface 13. Next, the raw material powder of the first conductive glass 24 is put through the shaft hole and filled around the center electrode 14. The raw material powder of the first conductive glass 24 filled around the center electrode 14 is pre-compressed using a compression rod (not shown).

  Next, a glass tube made of the material of the insulating glass 26 with the conductor 20 (sintered body) placed therein is inserted into the shaft hole with the first phase 22 facing down, and the first conductive glass Place on 24 raw powders. Next, a molded body in which the raw material powder of the second conductive glass 25 is formed into a pellet shape is placed on the conductor 20 and the glass tube. The insulator 11 is transferred into the furnace and heated to a temperature higher than the softening point of the glass component contained in the raw material powder of the first conductive glass 24 and the second conductive glass 25 and the material of the insulating glass 26, for example.

  After the heating, the terminal fitting 15 is inserted into the shaft hole of the insulator 11, and the raw material powder of the first conductive glass 24 and the second conductive glass 25 and the material of the insulating glass 26 are axially moved by the tip of the terminal fitting 15. Compress. As a result, they are compressed and sintered, and the first conductive glass 24, the conductor 20, the insulating glass 26, and the second conductive glass 25 are integrated into 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, the conductor 20 (sintered body) is put into the shaft hole, and then the raw material of the insulating glass 26 around the conductor 20. It is of course possible to fill with powder. Furthermore, instead of inserting the compact of the raw material powder of the second conductive glass 25 into the shaft hole, it is naturally possible to fill the raw material powder of the second conductive glass 25 into the shaft hole.

  According to the spark plug 10, the main phase 21 made of a conductive oxide is in contact with the first phase 22 and the second phase 23 made of a conductive oxide, and the first conductive glass 24 and the second conductive glass 25. And away. The volume resistivity of the first phase 22 and the second phase 23 is lower than the volume resistivity of the main phase 21. Thereby, the difference between the volume resistivity of the first phase 22 and the volume resistivity of the metal contained in the first conductive glass 24 in contact with the first phase 22 can be reduced. The difference between the volume resistivity of the second phase 23 and the volume resistivity of the metal contained in the second conductive glass 25 in contact with the second phase 23 can be reduced. Achieves ohmic contact or contact close to ohmic contact between the metal contained in the first conductive glass 24 and the first phase 22 and between the metal contained in the second conductive glass 25 and the second phase 23, respectively. it can.

  Thereby, the contact resistance between the 1st phase 22 and the 1st conductive glass 24 and the contact resistance between the 2nd phase 23 and the 2nd conductive glass 25 can be reduced. Therefore, it is possible to reduce the concentration of the electric field at these interfaces during discharge. Furthermore, since the main phase 21, the first phase 22 and the second phase 23 are each made of a sintered body of a conductive oxide, deterioration due to oxidation can be prevented. As a result, the durability of the spark plug 10 can be improved. The main phase 21 can ensure the necessary characteristics for the conductor 20.

Depending on the relationship between the metal contained in the conductive glass and the conductive oxide contained in the conductor 20, the interface between the first conductive glass 24 and the first phase 22 or the second conductive glass 25 and the second phase 23. May increase the Schottky barrier at the interface. However, since the volume resistivity at 20 ° C. of the first phase 22 and the volume resistivity at 20 ° C. of the second phase 23 are 1.0 × 10 ⁻¹ Ω · m or less, the depletion layer width is reduced even if a Schottky barrier is formed. It can be made small, and current can easily flow through the interface. Thereby, the contact resistance between the first conductive glass 24 and the first phase 22 and between the second conductive glass 25 and the second phase 23 is further reduced, and the electric field concentration at these interfaces is suppressed. Easy to do.

  Since the minimum values of the thicknesses T1 and T2 of the first phase 22 and the second phase 23 are 5 μm or more, it is easy to secure the characteristics of the first phase 22 and the second phase 23, respectively, even if mass transfer occurs during sintering. it can. As a result, the effect of reducing the contact resistance by the first phase 22 and the second phase 23 can be easily developed. Moreover, since the maximum value of thickness T1, T2 is 5 mm or less, the main phase 21 can be lengthened relatively. As a result, the electrical characteristics of the main phase 21 for suppressing radio noise can be easily developed.

  A second embodiment will be described with reference to FIG. In the first embodiment, the case where the first phase 22 of the conductor 20 is in contact with the first conductive glass 24 and the second phase 23 is in contact with the second conductive glass 25 has been described. In contrast, in the second embodiment, the first buffer layer 33 is interposed between the first phase 22 and the first conductive glass 31, and the second phase 23 is interposed between the second conductive glass 32 and the second phase. A case where the buffer layer 34 is interposed will be described. 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. FIG. 3 is a cross-sectional view including an axis O showing an enlarged part of the spark plug 30 (in the vicinity of the conductor 20) in the second embodiment. The spark plug 30 is obtained by replacing a part of the spark plug 10 of the first embodiment with the portion shown in FIG.

  In the spark plug 30, the first buffer layer 33 is disposed between the end surface 20 a on the front end side of the conductor 20 and the first conductive glass 31. The first buffer layer 33 is in contact with the first conductive glass 31 and the first phase 22. The first buffer layer 33 separates the conductor 20 and the first conductive glass 31 from each other. A second buffer layer 34 is disposed between the end surface 20 b on the rear end side of the conductor 20 and the second conductive glass 32. The second buffer layer 34 is in contact with the second phase 23 and the second conductive glass 32. The conductor 20 and the second conductive glass 32 are separated by the second buffer layer 34. In the present embodiment, the first buffer layer 33 and the second buffer layer 34 are also in contact with the inner peripheral surface 12 of the insulator 11.

  An insulating glass 35 is disposed between the inner peripheral surface 12 of the insulator 11 and the side surface 20 c of the conductor 20. The first conductive glass 31 and the second conductive glass 32 are separated from the insulating glass 35 by the first buffer layer 33 and the second buffer layer 34.

  The first buffer layer 33 and the second buffer layer 34 are made of a mixture or metal containing a metal and a conductive oxide. Examples of the metal contained in the first buffer layer 33 and the second buffer layer 34 include Cu, Ni, Co, Pt, Rh, and Pd. Examples of the conductive oxide contained in the first buffer layer 33 and the second buffer layer 34 are the same as the conductive oxide contained in the conductor 20.

  In the present embodiment, the first buffer layer 33 and the second buffer layer 34 are formed using a plate material made of metal. However, it is not limited to this. For example, the first buffer layer 33 and the second buffer layer 34 are a plate made of a mixture containing a metal and a conductive oxide, a deposit of a mixture containing a metal powder and a conductive oxide powder, and a deposit of a metal powder. It can form suitably from these.

  In the present embodiment, in the cross section including the axis O, the length L1 in the direction orthogonal to the axis O of the interface 36 between the first conductive glass 31 and the first buffer layer 33, and the second conductive glass 32 and the first The length L3 in the direction perpendicular to the axis O of the interface 37 with the two buffer layers 34 is longer than the lengths L2 and L4 in the direction perpendicular to the axis O of the end faces 20a and 20b of the conductor 20.

  For example, the spark plug 30 is manufactured in the same manner as the method described in the first embodiment. However, a metal plate material for forming the first buffer layer 33 is disposed on the raw material powder of the first conductive glass 31. Further, after placing a metal plate for forming the second buffer layer 34 on the conductor 20 and the glass tube, the raw material powder of the second conductive glass 32 was formed into a pellet shape thereon. Place the compact. In addition, when forming the 1st buffer layer 33 and the 2nd buffer layer 34 with deposits, such as a metal powder, it replaces with arrange | positioning a board | plate material to a shaft hole, and the 1st conductive glass 31 and a 2nd conductive layer. Similar to the glass 32, these raw material powders are filled into the shaft holes, or a compact of the raw material powders is inserted into the shaft holes.

  According to the spark plug 30, the first phase 22 of the conductor 20 is separated from the first conductive glass 31, and the first buffer layer 33 is in contact with the first phase 22 and the first conductive glass 31. Further, the second phase 23 of the conductor 20 is separated from the second conductive glass 32, and the second buffer layer 34 is in contact with the second phase 23 and the second conductive glass 32. Therefore, compared to the case where the metal (powder or particles) contained in the first conductive glass 31 or the second conductive glass 32 is in contact with the first phase 22 or the second phase 23, the first buffer layer 33 or the second buffer layer. The contact area between the conductive material (metal or conductive oxide) contained in the layer 34 and the first phase 22 or the second phase 23 can be increased. The first buffer layer 33 and the second buffer layer 34 are brought into contact with the first conductive glass 31 and the second conductive glass 32, respectively. The conduction is included in the first buffer layer 33 and the second buffer layer 34. It is also made by metal. As a result, ohmic contact or contact close to ohmic contact can be realized between the first buffer layer 33 and the first conductive glass 31, and between the second buffer layer 34 and the second conductive glass 32, respectively.

  Thereby, the contact resistance between the first buffer layer 33 and the first phase 22, the contact resistance between the second buffer layer 34 and the second phase 23, the first buffer layer 33 and the first conductive glass 31 And the contact resistance between the second buffer layer 34 and the second conductive glass 32 can be further reduced. Therefore, it is possible to further alleviate the concentration of the electric field at these interfaces during discharge. As a result, the durability of the spark plug 30 can be further improved.

  Since the insulating glass 35 is disposed between the inner peripheral surface 12 of the insulator 11 and the side surface 20c of the conductor 20, the movement of the conductor 20 inside the inner peripheral surface 12 of the insulator 11 can be suppressed. Thereby, the contact between the end surface 20a of the conductor 20 and the first buffer layer 33 and the contact between the end surface 20b of the conductor 20 and the second buffer layer 34 can be strengthened. Therefore, the contact resistance between the end surface 20a of the conductor 20 and the first buffer layer 33 and the increase due to the vibration of the contact resistance between the end surface 20b of the conductor 20 and the second buffer layer 34 can be suppressed.

  As shown in FIG. 3, when the insulating glass 35 is brought into contact with not only the conductor 20 but also the first buffer layer 33 and the second buffer layer 34, their integrity can be further enhanced. Thereby, the contact between the end surface 20a of the conductor 20 and the first buffer layer 33 and the contact between the end surface 20b of the conductor 20 and the second buffer layer 34 can be further strengthened.

  The length L1 in the direction perpendicular to the axis O of the interface 36 and the length L3 in the direction perpendicular to the axis O of the interface 37 are the lengths L2 and L4 in the direction perpendicular to the axis O of the end faces 20a and 20b of the conductor 20. The contact area between the first conductive glass 31 and the first buffer layer 33 (area of the interface 36) and the contact area between the second conductive glass 32 and the second buffer layer 34 (area of the interface 37). Can be made larger inside the inner peripheral surface 12 of the insulator 11. That is, the area of the interface 36 can be increased as compared with the case where the length L1 of the interface 36 in the direction orthogonal to the axis O is equal to the length L2 of the end face 20a of the conductor 20 in the direction orthogonal to the axis O. The area of the interface 37 can be increased as compared with the case where the length L3 of the interface 37 in the direction orthogonal to the axis O is equal to the length L4 of the end face 20b of the conductor 20 in the direction orthogonal to the axis O. As a result, since the resistance of the interfaces 36 and 37 can be reduced, electric field concentration at the interfaces 36 and 37 can be relaxed, and the durability can be further improved.

  Since the first buffer layer 33 is disposed only on the front end side of the conductor 20, and the second buffer layer 34 is disposed only on the rear end side of the conductor 20, the first buffer layer 33 and the second buffer layer 34 are electrically conductive. The body 20 contacts the end surfaces 20a and 20b without contacting the side surface 20c. Thereby, the resistance value of the conductor 20 is made to depend on the area of the end surfaces 20a and 20b of the conductor 20 that the first buffer layer 33 and the second buffer layer 34 are in contact with, and the length between the end surfaces 20a and 20b. Can do. As a result, a part of the first buffer layer 33 and the second buffer layer 34 wraps around the side surface 20c of the main phase 21 and the distance between the first buffer layer 33 and the second buffer layer 34 varies. The variation in the electrical characteristics of the conductor 20 can be suppressed.

  A third embodiment will be described with reference to FIG. In the second embodiment, the case where the first conductive glass 31 and the second conductive glass 32 are separated from the insulating glass 35 has been described. On the other hand, 3rd Embodiment demonstrates the case where the 1st conductive glass 41 and the 2nd conductive glass 42 contact the insulating glass 45. FIG. 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. FIG. 4 is a cross-sectional view including an axis O showing a part of the spark plug 40 (in the vicinity of the conductor 20) in the third embodiment in an enlarged manner. The spark plug 40 is obtained by replacing a part of the spark plug 10 of the first embodiment with the part shown in FIG.

  As shown in FIG. 4, the spark plug 40 has a first buffer layer 43 that contacts the first phase 22 of the conductor 20. An insulating glass 45 is disposed between the side surface 20 c of the conductor 20 and the inner peripheral surface 12 of the insulator 11. The first conductive glass 41 is in contact with the first buffer layer 43 and the insulating glass 45. The conductor 20 and the first conductive glass 41 are separated by the first buffer layer 43. The second buffer layer 44 contacts the second phase 23 of the conductor 20. The second conductive glass 42 contacts the second buffer layer 44 and the insulating glass 45. The conductor 20 and the second conductive glass 42 are separated by the second buffer layer 44.

  The first buffer layer 43 and the second buffer layer 44 are formed on the end surfaces 20a and 20b of the conductor 20 by, for example, plating, baking coating, physical vapor deposition, chemical vapor deposition, or the like. Since the conductor 20 and the first buffer layer 43 and the second buffer layer 44 are integrated by these treatments, when the first conductive glass 41 and the like are integrated with the insulator 11, the second embodiment The work of inserting the plate material or the like for forming the first buffer layer 33 and the second buffer layer 34 into the shaft hole of the insulator 11 separately from the conductor 20 as described can be omitted.

  Note that the shape of the interface between the first conductive glass 41 and the insulating glass 45 and the shape of the interface between the second conductive glass 42 and the insulating glass 45 are the same as those of the first conductive glass 41 and the insulator 11. Can be set as appropriate depending on the magnitude of the axial load caused by the terminal fitting 15 when it is integrated with the metal, the temperature at which the insulator 11 is heated, the length of the insulating glass 45 in the axial direction, and the like.

  In the present embodiment, in the cross section including the axis O, the length L1 in the direction orthogonal to the axis O of the interface 46 between the first conductive glass 41 and the first buffer layer 43, and the second conductive glass 42 and the first The length L3 in the direction orthogonal to the axis O of the interface 47 with the two buffer layers 44 is substantially equal to the lengths L2 and L4 in the direction orthogonal to the axis O of the end faces 20a and 20b of the conductor 20. Thereby, in 3rd Embodiment, the effect similar to 2nd Embodiment except the effect by L1 = L3> L2 = L4 demonstrated in 2nd Embodiment is realizable.

  A fourth embodiment will be described with reference to FIG. In the second embodiment and the third embodiment, the case where the first buffer layers 33 and 43 and the second buffer layers 34 and 44 are in contact with the end surfaces 20a and 20b of the conductor 20 but not the side surface 20c has been described. In contrast, in the fourth embodiment, a case where the first buffer layer 53 and the second buffer layer 54 are in contact with the end surfaces 20a and 20b and the side surface 20c of the conductor 20 will be described. 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. FIG. 5 is a cross-sectional view including an axis O showing a part of the spark plug 50 (in the vicinity of the conductor 20) in the fourth embodiment in an enlarged manner. The spark plug 50 is obtained by replacing a part of the spark plug 10 of the first embodiment with the part shown in FIG.

  As shown in FIG. 5, the spark plug 50 includes a first buffer layer 53 that contacts the end surface 20 a and the side surface 20 c of the conductor 20. An insulating glass 55 is disposed between the side surface 20 c of the conductor 20 and the inner peripheral surface 12 of the insulator 11. The first conductive glass 51 contacts the first buffer layer 53 and the insulating glass 55. The conductor 20 and the first conductive glass 51 are separated by the first buffer layer 53. The second buffer layer 54 is in contact with the end surface 20 b and the side surface 20 c of the conductor 20. The second conductive glass 52 is in contact with the second buffer layer 54 and the insulating glass 55. The conductor 20 and the second conductive glass 52 are separated by the second buffer layer 54. In FIG. 5, the first buffer layer 53 and the second buffer layer 54 are separated from the inner peripheral surface 12 of the insulator 11, but they may be in contact with each other.

  The first buffer layer 53 and the second buffer layer 54 of the spark plug 50 are formed on the end surfaces 20a and 20b of the conductor 20 by plating, coating film baking, physical vapor deposition, chemical vapor deposition, or the like, for example. The first buffer layer 53 and the second buffer layer 54 can also be formed of a plate material made of metal, a plate material made of a mixture containing a metal and a conductive oxide, or the like. When forming the 1st buffer layer 53 and the 2nd buffer layer 54 using a board material, the shape in which the edge of the 1st buffer layer 53 and the 2nd buffer layer 54 bent bent the 1st conductive glass 51 grade | etc., To the insulator 11. Can be set as appropriate depending on the magnitude of the axial load caused by the terminal fitting 15 when it is integrated with the metal, the temperature at which the insulator 11 is heated, the length of the insulating glass 55 in the axial direction, and the like.

  In the present embodiment, in the cross section including the axis O, the length L1 in the direction perpendicular to the axis O of the interface 56 between the first conductive glass 51 and the first buffer layer 53, and the second conductive glass 52 and the first The length L3 in the direction perpendicular to the axis O of the interface 57 with the two buffer layers 54 is longer than the lengths L2 and L4 in the direction perpendicular to the axis O of the end faces 20a and 20b of the conductor 20.

  In the fourth embodiment, since the first buffer layer 53 and the second buffer layer 54 are in contact with the end surfaces 20a and 20b and the side surface 20c of the conductor 20, the buffer layer is in contact only with the end surfaces 20a and 20b of the conductor 20. As compared with the above, the contact area between the first buffer layer 53 and the conductor 20 and the contact area between the second buffer layer 54 and the conductor 20 can be increased. Thus, the resistance of the interface between the first buffer layer 53 and the conductor 20 and the resistance of the interface between the second buffer layer 54 and the conductor 20 are equivalent to the amount of contact of the buffer layer with the side surface 20c of the conductor 20. Can be reduced. Therefore, the electric field concentration at the interface between the first buffer layer 53 and the conductor 20 and the interface between the second buffer layer 54 and the conductor 20 can be reduced, and the durability can be further improved.

  A fifth embodiment will be described with reference to FIG. In the second to fourth embodiments, the case where the first conductive glasses 31, 41, 51 and the second conductive glasses 32, 42, 52 are separated from the conductor 20 has been described. On the other hand, in the fifth embodiment, the first conductive glass 61 and the second conductive glass 62 are separated from the main phase 21, but the first conductive glass 61 and the second conductive glass 62 are separated from the first phase 22 and The case where it contacts each of the second phase 23 will be described. 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. FIG. 6 is a cross-sectional view including an axis O showing a part of the spark plug 60 (in the vicinity of the conductor 20) in the fifth embodiment in an enlarged manner. The spark plug 60 is obtained by replacing a part of the spark plug 10 of the first embodiment with the part shown in FIG.

  As shown in FIG. 6, the first plug layer 63 that contacts the first phase 22 of the conductor 20 is disposed in the spark plug 60. An insulating glass 65 is disposed between the side surface 20 c of the conductor 20 and the inner peripheral surface 12 of the insulator 11. The first conductive glass 61 contacts the first buffer layer 63, the first phase 22, and the insulating glass 65, and the main phase 21 and the first conductive glass 61 are separated from each other. The second buffer layer 64 is in contact with the second phase 23 of the conductor 20. The second conductive glass 62 is in contact with the second buffer layer 64, the second phase 23 and the insulating glass 65, and the main phase 21 and the second conductive glass 62 are separated from each other.

  The first buffer layer 63 and the second buffer layer 64 are formed on the end surfaces 20a and 20b of the conductor 20 by, for example, plating, baking coating, physical vapor deposition, chemical vapor deposition, or the like. The shape of the interface between the first conductive glass 61 and the insulating glass 65 and the shape of the interface between the second conductive glass 62 and the insulating glass 65 are such that the first conductive glass 61 and the like are integrated with the insulator 11. It can be set as appropriate depending on the magnitude of the axial load caused by the terminal fitting 15 when heated, the temperature at which the insulator 11 is heated, the length of the insulating glass 65 in the axial direction, and the like.

  In the present embodiment, in the cross section including the axis O, the length L1 in the direction perpendicular to the axis O of the interface 66 between the first conductive glass 61 and the first buffer layer 63, and the second conductive glass 62 and the first The length L3 in the direction orthogonal to the axis O of the interface 67 with the two buffer layers 64 is substantially equal to the lengths L2 and L4 in the direction orthogonal to the axis O of the end faces 20a and 20b of the conductor 20. Thereby, in 5th Embodiment, the effect similar to 2nd Embodiment except the effect by L1 = L3> L2 = L4 demonstrated in 2nd Embodiment is realizable.

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

  A spark plug sample in the first embodiment and the second embodiment was prepared and a discharge test was performed. Tables 1 and 2 show the forms of Samples 1 to 13, the chemical formulas of the conductive oxides constituting the conductors (main phase, first phase and second phase), and the volume resistivity at 20 ° C. of each conductive oxide. The minimum values of the thicknesses T1 and T2 of the first phase and the second phase, the substances constituting the first buffer layer and the second buffer layer, and the determination of the discharge test are shown in a list.

なお、サンプル１〜１３は、緩衝層の有無、導電体および緩衝層の材質の違いによる特性を評価するため、それらの違い以外の、導電体の寸法、第１導電性ガラス、第２導電性ガラス及び絶縁性ガラスの材質、スパークプラグの各部の寸法や形状等は一定にした。

In addition, since samples 1 to 13 evaluate the characteristics depending on the presence or absence of the buffer layer and the difference in the materials of the conductor and the buffer layer, the dimensions of the conductor, the first conductive glass, and the second conductivity other than those differences. The material of glass and insulating glass, the size and shape of each part of the spark plug, etc. were made constant.

  Samples 1 to 5 and 8 to 10 were formed by stacking raw material powders of the first phase, the main phase, and the second phase when manufacturing the conductors, thereby obtaining sintered bodies. When samples 6, 7, and 11 were manufactured, the main phase sintered body was obtained and then the paste containing the first phase 22 raw material powder and the second phase raw material powder were sintered. Each was applied to the end face of the body (main phase) and baked to obtain a sintered body.

  Samples 1 and 3 to 11 are spark plug samples according to the first embodiment. Sample 2 is a sample of a spark plug in the second embodiment. The first buffer layer and the second buffer layer of sample 2 were formed of a plate material made of Pt.

The main phase of Samples 1 to 8, the first phase and the second phase, the first phase and the second phase of Samples 10 and 11, and the main phase of Sample 12 are each composed of a complex oxide. The main phase of sample 9, the first phase and the second phase, and the main phases of samples 10, 11, and 13 are made of a mixture of a composite oxide and insulating powder (Y ₂ O ₃ ). The numerical value in parentheses in the mixture of Samples 9, 10, 11, and 13 is a volume ratio of the composite oxide and the insulating powder. In Samples 1 to 11, the main phase contains one or more metal elements that are the same as the metal elements contained in the first phase, and contains one or more metal elements that are the same as the metal elements contained in the second phase.

  Samples 12 and 13 are comparative examples. In the spark plug 70 in the comparative example, unlike the samples 1 to 11, the first phase and the second phase of the conductor are omitted. FIG. 7 is a cross-sectional view including an axis O showing an enlarged part of the spark plug 70 (samples 12 and 13) in the 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. 7, in the spark plug 70, a conductor 71, a first conductive glass 72, a second conductive glass 73, and an insulating glass 74 are disposed inside the inner peripheral surface 12 of the insulator 11. The first conductive glass 72 is in contact with the end surface 71 a of the conductor 71 and the insulating glass 74, and the second conductive glass 73 is in contact with the end surface 71 b of the conductor 71 and the insulating glass 74.

  About each sample of 1-13, a DC voltage of 5V was applied between the terminal metal fitting 15 and the center electrode 14, the resistance value was measured, and the measured value at that time was 20 degreeC using the resistance temperature characteristic measured beforehand. It was corrected to the resistance value at. The resistance value at this time was 1 kΩ for each sample.

  Next, each sample was placed in an environment of 425 ° C., a discharge voltage was set to 45 kV, and a test was performed in which a spark was blown between the center electrode 14 and the ground electrode 19 at a rate of 100 times per second for 500 hours. . After the test, it was left for 1 hour, and the resistance value was measured in the same manner as before the test, and the measured value at that time was corrected to the resistance value at 20 ° C. Samples with a resistance change rate of less than ± 10% before and after the test are A, samples with a change rate of ± 10% or more and less than ± 20% are B, and samples with a change rate of ± 20% or more and less than ± 30% C, and samples having a change rate of ± 30% or more were determined as D. The results are shown in Table 2.

  As shown in Table 2, the determinations of Samples 1 to 11 (Examples) were A to C, whereas the determinations of Samples 12 and 13 (Comparative Example) were D. Samples 1 to 11 in which the first phase is interposed between the main phase and the first conductive glass and the second phase is interposed between the main phase and the second conductive glass are the first phase and the second phase. The resistance change rate before and after the test could be reduced as compared with the comparative example in which no exists. It is inferred that Samples 1 to 11 were able to relax the electric field concentration at the interface between the conductor and the conductive glass.

  In particular, Samples 1, 3, 6, 9, 10, and 11 were able to further reduce the rate of change in resistance before and after the test compared to Samples 4, 5, 7, and 8. Unlike Samples 4 and 8, Samples 1, 3, 6, 9, 10, and 11 were composite oxide sintered bodies having the same constituent elements in the main phase, the first phase, and the second phase. It is inferred that these samples can further reduce the interaction between the first phase and the second phase and the main phase, and can further reduce the resistance change rate.

Unlike Sample 5, Samples 1, 3, 6, 9, and 10 had a volume resistivity of the first phase and a volume resistivity of the second phase of 1.0 × 10 ⁻¹ Ω · m or less. These samples can further reduce the contact resistance between the first phase and the first conductive glass and the contact resistance between the second phase and the second conductive glass. It is inferred that it could be made smaller.

  Samples 1, 3, 6, 9, 10, and 11 were different from sample 7 in that the minimum values of the thicknesses T1 and T2 of the first phase and the second phase were 5 μm or more. Since these samples were able to secure the characteristics of the first phase and the second phase even when mass transfer accompanied by sintering occurred, the contact resistance between the first phase and the first conductive glass, and It is presumed that the contact resistance between the two phases and the second conductive glass could be further reduced, and the rate of change in resistance could be further reduced.

  Compared with samples 1, 3, 6, 9, 10, and 11, sample 2 was able to further reduce the rate of resistance change before and after the test. In sample 2, the first buffer layer is brought into contact with the first phase, and the second conductive glass is brought into contact with the second phase, whereby the interface between the first phase and the first conductive glass, and the second phase This is presumably because the electric field concentration at the interface with the second conductive glass could be further relaxed.

  The present invention has been described based on the embodiments and examples. However, the present invention is not limited to these embodiments, and various modifications can be easily made without departing from the spirit of the present invention. Can be inferred.

  In the embodiment, the sample in which the first buffer layer and the second buffer layer are formed of the same type of member has been described, but the present invention is not necessarily limited thereto. Of course, it is possible to vary the materials of the first buffer layer and the second buffer layer and the method of forming the first buffer layer and the second buffer layer.

  In the embodiment, 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 arranged inside the inner peripheral surface 12 of the insulator 11, it is naturally possible to employ the conductor 20 formed in a rectangular parallelepiped shape, for example.

  In the embodiment, the case where the insulating glasses 26, 35, 45, 55, and 65 are disposed between the inner peripheral surface 12 of the insulator 11 and the conductor 20 has been described. However, the present invention is not necessarily limited thereto. . It is naturally possible to omit the insulating glass by managing the size of the gap between the inner peripheral surface 12 of the insulator 11 and the conductor 20.

  In the embodiment, the spark plugs 10, 30, and 40 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 thereto. 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, 60 Spark plug 11 Insulator 14 Center electrode 15 Terminal fitting 20 Conductor 21 Main phase 22 First phase 23 Second phase 24, 31, 41, 51, 61 First conductive glass 25, 32, 42, 52, 62 Second conductive glass 33, 43, 53, 63 First buffer layer 34, 44, 54, 64 Second buffer layer O Axis T1, T2 Thickness

Claims (6)

An insulator having an axial hole extending in the direction of the axis from the front end side to the rear end side;
A center electrode disposed on the tip side of the shaft hole;
A terminal fitting disposed on the rear end side of the shaft hole;
A conductor disposed between the center electrode in the shaft hole and the terminal fitting;
A first conductive glass electrically connecting the center electrode and the conductor;
A spark plug comprising: a second conductive glass that electrically connects the terminal fitting and the conductor;
The first conductive glass and the second conductive glass are made of a mixture containing insulating glass and metal,
The conductor has a main phase, a first phase in contact with a leading end side of the main phase, and a second phase in contact with a rear end side of the main phase, and the main phase, the first phase, and the Each second phase consists of a sintered body of conductive oxide,
The main phase is electrically connected to the first conductive glass via the first phase, and electrically connected to the second conductive glass via the second phase;
A spark plug in which the volume resistivity of the first phase and the second phase is lower than the volume resistivity of the main phase. 2. The spark plug according to claim 1, wherein the volume resistivity of the first phase and the volume resistivity of the second phase are 1.0 × 10 ⁻¹ Ω · m or less.   3. The spark plug according to claim 1, wherein a minimum value of a thickness in the direction of the axis of the first phase and the second phase is 5 μm or more, and a maximum value of the thickness is 5 mm or less.   The main phase contains at least one metal element the same as the metal element contained in the first phase, and contains at least one metal element the same as the metal element contained in the second phase. The spark plug according to any one of the above.   The spark plug according to claim 4, wherein the main phase, the first phase, and the second phase are composed of a sintered body of complex oxides having the same constituent elements. A first buffer layer disposed between the first conductive glass and the conductor and in contact with the first conductive glass and the first phase;
A second buffer layer disposed between the second conductive glass and the conductor and in contact with the second conductive glass and the second phase;
The spark plug according to any one of claims 1 to 5, wherein the first buffer layer and the second buffer layer are made of a mixture of a metal and a conductive oxide or a metal.

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