JP4465290B2 - Spark plug - Google Patents

Description

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

  Conventionally, with respect to a through-hole formed in the axial direction of an insulator, a terminal fitting is inserted into one end side, and a center electrode is inserted into the other end side, and the terminal fitting is inserted into the through-hole. Spark plugs having a structure in which a central electrode and a central electrode are sealed and fixed with a conductive sealing material layer are widely used.

  In the insulator through-hole, the terminal fitting and the center electrode are directly connected by the conductive sealing material layer, or are connected in such a manner that a resistor is disposed between each conductive sealing material layer. The conductive sealing material layer is generally composed of a mixture of metal particles and base glass, and the metal particles are dispersed in a network-like contact state in the glass matrix so that the conductive glass is electrically conductive with respect to the insulating glass. It has been given a sex.

In recent years, an insulator made of an alumina ceramic having an excellent insulation withstand voltage has been used as an insulator for a spark plug. On the other hand, the terminal fitting or the center electrode is made of metal mainly composed of Fe, Ni, etc., and the difference in linear expansion coefficient (hereinafter also referred to as thermal expansion coefficient) with the insulator is considerably large (for example, alumina is 7.3 × 10 ⁻⁶ / ° C., Fe and Ni are around 12 to 14 × 10 ⁻⁶ / ° C.). Therefore, for example, when a spark plug heated to a high temperature is cooled during use, the terminal metal fitting or the center electrode has a larger contraction amount than the insulator. Therefore, if the conductive sealing material layer cannot follow this, it may cause peeling. There is.

  Therefore, since the conductive sealing material layer using a mixture of metal and glass (inorganic material) can be adjusted to a thermal expansion coefficient intermediate between the terminal fitting or the center electrode and the insulator, the conductive sealing material layer is used. As a result, the difference in contraction displacement between the two can be somewhat reduced.

  On the other hand, the specifications of the engine to which the spark plug is applied have increased in output, and since the compression ratio of the air-fuel mixture is high, the airtight performance of the conductive sealing material layer is required to be higher. It has become to. Further, in recent engines, the mechanism around the cylinder head to which the spark plug is attached is complicated, and it is difficult to secure a mounting space. Therefore, there is a strong demand for downsizing the spark plug.

  If the spark plug is miniaturized, the inner diameter of the insulator and thus the through hole formed in the insulator is also reduced. When the combustion pressure of the engine is applied to the center electrode of such a spark plug, the pressure per unit area applied to the conductive sealing material layer in the through hole becomes higher than before, and the compression ratio of the air-fuel mixture is increased. Combined with the increase, it has become difficult to ensure sufficient durability with the specifications of the conventional conductive sealing material layer.

  That is, when using a conventional terminal fitting or a conductive sealing material layer having a thermal expansion coefficient intermediate between that of the center electrode and the insulator, the conductive sealing material layer is made of an alumina ceramic when cooled from a high temperature. The amount of shrinkage is larger, and the amount of contraction of alumina is small on the joint surface between the sealing material and the insulator on the inner surface of the through hole, so tensile stress is generated on the conductive sealing material layer side. Arise.

  In particular, in a small spark plug having a through-hole inner diameter of 4 mm or less, durability is ensured in combination with the above factors when applied to an engine operated under conditions of high output and high compression ratio. It becomes difficult. In addition, when the radial contraction of the conductive sealing material layer is greatly generated, the conductive sealing material layer is peeled off from the inner surface of the insulator through-hole to form a gap, which may reduce the airtightness and durability of the sealing material itself. is there.

Therefore, for example, an inorganic material having a lower coefficient of thermal expansion than alumina constituting an insulator in the conductive sealing material layer, such as β-eucryptite, β-spodumene, keatite, silica, mullite, cordierite, zircon and titanic acid By containing an insulating filler made of aluminum or the like and making the thermal expansion coefficient of the conductive sealing material layer smaller than the thermal expansion coefficient of the insulator, the compressive stress is applied to the conductive sealing material layer side as opposed to the above. It is known that cracks can be prevented from progressing and peeling (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2003-22886

  However, when the conductive sealing material layer contains an insulating filler as described above, the solid component when the base glass of the conductive sealing material layer is softened increases, so that the hardness of the conductive sealing material layer as a whole increases. . Usually, in order to seal and fix the terminal fitting and the center electrode with the conductive sealing material layer, the terminal fitting is pressed into the insulator while heating the insulator (hereinafter referred to as a glass seal). At this time, the conductive sealing material layer is too hard, and the sealing load on the terminal fitting at the time of glass sealing is not sufficient, so that the terminal fitting is not sufficiently inserted into the insulator, so-called terminal contact may occur. . On the other hand, if the sealing load is simply increased, the insulator may be damaged when the terminal fitting is press-fitted into the insulator.

  The present invention has been made to solve the above-described problems, and reduces the linear expansion coefficient of the insulator while reducing as much as possible the insulating filler that causes the conductive sealing material layer to become hard. It is possible to suppress the occurrence of cracks, peeling, etc. in the conductive sealing material layer by making it smaller than that, and also suppress the occurrence of terminal cracks after the glass seal. The purpose of this is to provide a spark plug that can suppress the occurrence of water and is excellent in productivity and reliability.

A spark plug according to the present invention has a conductive sealing material layer disposed between a terminal fitting and a center electrode in a through hole formed in an axial direction of an insulator made of alumina ceramic. The conductive sealing material layer has a base glass, a conductive filler, and an insulating filler having a content of 10 wt% or less (including 0), and the base glass contains Si component as SiO _2. 65 wt% 55 wt% or more in terms of oxide constituents below, the B component _B 2 _{O 3} 35 wt% 22 wt% or more in terms of oxide constituents below, in terms of Ca component in CaO oxide component 0.2 wt% or more and 2 wt% or less, Al component converted to Al ₂ O ₃ oxide component, 2 wt% or less, Na component and K component are Na ₂ O oxide component, K ₂ O oxidation, respectively Converted to physical components Comprises 4 wt% or more and 8 wt% or less in Kino total amount, and is characterized in that it is intended to include both the Na component and the K component.

  In the present invention, the content of the insulating filler in the conductive sealing material layer is 10% by weight or less. Thereby, the hardness of the whole electroconductive sealing material when base glass softens can be reduced. Therefore, even if the sealing load at the time of performing the glass seal is relatively small, it is possible to suppress the occurrence of terminal cracks and to suppress the breakage of the insulator. In addition, the said effect cannot be acquired when content of the insulating filler in a conductive sealing material layer exceeds 10 weight%.

  In the present invention, even if the content of the insulating filler in the conductive sealing material layer is reduced by setting the composition of the base glass constituting the conductive sealing material layer of the spark plug to a predetermined composition, the conductive seal The thermal expansion coefficient of the material layer can be made smaller than that of the insulator made of alumina ceramic. Thereby, a compressive stress can be generated on the conductive sealing material layer side, and crack progress, peeling, and the like can be suppressed.

Specifically, as the base glass constituting the conductive sealing material layer, the Si component is converted to a SiO ₂ oxide component in an amount of 55 wt% to 65 wt%, and the B component is converted to a B ₂ O ₃ oxide component. 22 wt% to 35 wt%, Ca component converted to CaO oxide component, 0.2 wt% to 2 wt%, Al component converted to Al ₂ O ₃ oxide component, 2 wt% In addition, the Na component and the K component are contained in a total amount of 4% by weight to 8% by weight in terms of the Na ₂ O oxide component and the K ₂ O oxide component, respectively. Both. Hereinafter, each component which comprises base glass is demonstrated.

When the weight of the Si component converted to the SiO ₂ oxide component is less than 55% by weight, the thermal expansion coefficient of the base glass increases, and peeling or cracking occurs between the conductive sealing material layer and the insulator. There is a fear. On the other hand, if it exceeds 65% by weight, the softening temperature of the base glass becomes high, and there is a risk of terminal cracks occurring when performing glass sealing.

Further, when the weight when the B component is converted to the B ₂ O ₃ oxide component is less than 22% by weight, the softening temperature of the base glass becomes high, and there is a possibility that a terminal crack occurs when performing glass sealing. On the other hand, if it exceeds 35% by weight, the thermal expansion coefficient of the base glass increases, and there is a possibility that peeling or cracking may occur between the conductive sealing material layer and the insulator.

  The Ca component is added to stabilize the resistance value of the resistor in contact with the conductive sealing material layer including the base glass or to reduce the softening temperature of the base glass itself. If the content of the Ca component converted to the CaO oxide component is less than 0.2% by weight, the resistance value of the resistor is not stabilized or the softening temperature of the base glass is not sufficiently reduced, and glass sealing is performed. There is a risk that the terminal terminal will be generated. If it exceeds 2% by weight, the coefficient of thermal expansion becomes large, and there is a risk of peeling or cracking between the conductive sealing material layer and the insulator.

The Al component is contained as an unavoidable impurity in the base glass, and when it exceeds 2% by weight in terms of the Al ₂ O ₃ oxide component, the softening temperature of the base glass increases, so that a terminal for performing glass sealing There is a risk of generating uki. The Al component is preferably as the content in the base glass is close to 0% by weight.

  Both the Na component and the K component are added to reduce the softening temperature of the base glass. By containing both the Na component and the K component in the base glass, an alkali mixing effect occurs, and the softening temperature of the base glass can be effectively reduced.

When the Na component is converted to the Na ₂ O oxide component and the K component is converted to the K ₂ O oxide component, the softening temperature of the base glass is reduced if the total content is less than 4% by weight based on the entire base glass. It is difficult to do so, and there is a risk of generating terminal cracks when performing glass sealing. Moreover, when the total of these contents exceeds 8 weight%, the thermal expansion coefficient will become large and there exists a possibility that peeling and a crack may generate | occur | produce between an electroconductive sealing material layer and an insulator.

Further, in the spark plug of the present invention, the weight when the Na component in the base glass is converted to a Na ₂ O oxide component is W1, and the weight when the K component is converted to a K ₂ O oxide component is W2. It is preferable that W1 ≧ W2. When the change in the magnitude of the thermal expansion coefficient of the base glass is compared when the Na component and the K component are used, it is recognized that the change in the magnitude of the thermal expansion coefficient of the base glass is smaller when the Na component is used. Therefore, by setting W1 ≧ W2 as described above, it is possible to reduce the thermal expansion coefficient while reducing the softening temperature of the base glass.

  More preferably, it is more preferable that W1 ≧ W2 ≧ W1 / 5. From the viewpoint of the thermal expansion coefficient described above, it is preferable to increase the Na component more than the K component, but from the viewpoint of reducing the softening temperature of the base glass, it is necessary to contain both, and if the K component is too small, It becomes difficult to sufficiently reduce the softening temperature.

  The present invention is characterized by containing the Si component, the B component, the Ca component, the Na component and the K component as the essential components as the base glass as described above, but if necessary and contrary to the spirit of the present invention. Other components such as Zr component, Ti component, MgO component and the like may be included within the range not to be used. In this case, the content of other components is preferably 10% by weight or less with respect to the entire base glass in terms of oxide components.

  Furthermore, in the spark plug of the present invention, it is preferable that the conductive sealing material layer is formed only of a base glass and a conductive filler. Thus, the hardness at the time of softening of the electroconductive sealing material layer which does not contain an insulating filler and has reduced hardness at the time of softening can be further reduced. Therefore, it is possible to further suppress the occurrence of terminal contact during glass sealing.

Furthermore, the spark plug of the present invention has a total weight of 86 when the Si component in the base glass is converted to the SiO ₂ oxide component and the weight when the B component is converted to the B ₂ O ₃ oxide component. It is preferable that it is at least 94% by weight. Thereby, the thermal expansion coefficient of the conductive sealing material layer can be sufficiently reduced.

In another spark plug of the present invention, the center electrode is fixed to the first conductive sealing material layer, and the terminal fitting is fixed to the second conductive sealing material layer in the through hole formed in the axial direction of the insulator, In the spark plug in which a resistor is interposed between the first conductive sealing material layer and the second conductive sealing material layer, the second conductive sealing material layer includes a base glass, a conductive filler, and a content. 10% by weight or less (excluding 0) of an insulating filler, and the first conductive sealing material layer has a base glass, a conductive filler, and a content less than that of the second conductive sealing material layer. An insulating filler (including 0) is included.

  In the present invention, the content of the insulating filler in the first conductive sealing material layer and the second conductive sealing material layer is 10% by weight or less. Thereby, the hardness when the base glass of a 1st conductive sealing material layer and a 2nd conductive sealing material layer softens can be reduced. Therefore, even if the sealing load at the time of performing the glass seal is relatively small, the terminal contact can be suppressed. In addition, due to the reduced sealing load, damage to the insulator can be suppressed when performing glass sealing. If the content of the insulating filler in the first conductive sealing material layer or the second conductive sealing material layer exceeds 10% by weight, the above effect cannot be obtained.

  And the content of the insulating filler in the second conductive sealing material layer is larger than the content of the insulating filler in the first conductive sealing material layer, so that the second conductive sealing material layer The hardness at the time of softening the base glass is larger than the hardness at the time of softening the base glass of the first conductive sealing material layer. Then, the resistor provided between the first conductive sealing material layer and the second conductive sealing material layer is sufficiently pressed by the second conductive sealing material layer and can be sealed and fixed inside. In addition, if content of the insulating filler in a 2nd conductive sealing material layer is below the content of the insulating filler in a said 1st conductive sealing material layer, it will be difficult to acquire the said effect fully. Further, the above effect can be effectively obtained by increasing the content of the insulating filler in the second conductive sealing material layer by 1% by weight or more from the content of the insulating filler in the first conductive sealing material layer. Can do.

  The first embodiment will be described below. FIG. 1 shows an example of a spark plug 100 according to the first embodiment. The spark plug 100 includes a cylindrical metal shell 1, an insulator 2 that is fitted inside the metal shell 1 so that the tip 2 a protrudes, and an ignition body 3 a that is formed at the tip of the insulator 1. 2 is connected to the center electrode 3 and the metal shell 1 by welding or the like, and the other end is bent back to the side so that its side faces the tip of the center electrode 3. A ground electrode 4 and the like are provided. Further, the ground electrode 4 is formed with an ignition part 4a facing the ignition part 3a, and a gap between the ignition part 3a and the opposing ignition part 4a is a spark discharge gap g.

  The metal shell 1 is formed in a cylindrical shape from a metal such as low carbon steel, and constitutes a housing of the spark plug 100, and a screw portion for attaching the spark plug 100 to an engine block (not shown) on the outer peripheral surface thereof. 1a is formed. Reference numeral 1b denotes a tool engaging portion that engages a tool such as a spanner or a wrench when the metal shell 1 is attached to the engine block, and has a hexagonal axial cross-sectional shape.

The insulator 2 has a through hole 5 for fitting the center electrode 3 along its own axial direction inside, and the whole is made of the following insulating material. That is, the insulating material of Al component, 80～98Mol% in terms of value to the _Al 2 _{O 3} (preferably 90~98mol%) alumina ceramic containing.

Specifically, components other than Al can be contained in one or more types within the following range:
Si component: 1.50~5.00mol% in terms of SiO ₂ values;
Ca component: 1.20 to 4.00 mol% in terms of CaO;
Mg component: 0.05 to 0.17 mol% in terms of MgO;
Ba component: 0.15-0.50 mol% in terms of BaO;
Component _{B: 0.15~0.50mol%} in terms _of B 2 _{O 3} value.

  In the middle of the insulator 2 in the axial direction, a protruding portion 2b protruding outward in the circumferential direction is formed in a flange shape, for example. And the rear-end side is made into the main-body part 2c formed more narrowly than this from the protrusion part 2b. On the other hand, a first shaft portion 2d having a smaller diameter and a second shaft portion 2e having a smaller diameter than the first shaft portion 2d are formed in this order on the distal end side of the protruding portion 2b.

  A corrugation 2f is formed at the rear end of the outer peripheral surface of the main body 2c, and a glaze layer 2g is formed on the outer peripheral surface. Further, the outer peripheral surface of the first shaft portion 2d is substantially cylindrical, and the outer peripheral surface of the second shaft portion 2e is substantially conical, whose diameter decreases toward the tip.

  The through hole 5 of the insulator 2 includes a substantially cylindrical first portion 5a through which the center electrode 3 is inserted, and a substantially cylindrical second portion 5b formed with a larger diameter at the rear end side of the first portion 5a. And have. The terminal fitting 10 and the resistor 11 are accommodated in the second portion 5b, and the center electrode 3 is inserted into the first portion 5a.

At the rear end portion of the center electrode 3, an electrode fixing convex portion 3 b is formed protruding outward from the outer peripheral surface thereof. Then, a first portion 5a and second portion 5b of the through hole 5, are connected to each other in the first front portion 2d, the connection position, Keru receive the electrode fixing convex portion 3b of the center electrode 3 The convex receiving surface 5c is formed in a tapered surface or a rounded surface.

  Moreover, the connection part 2h in the outer peripheral surface of the 1st axial part 2d and the 2nd axial part 2e is made into the stepped surface, and this is the protruding item | line part 1c as a metal fitting side engaging part formed in the inner surface of the metal fitting 1 And the ring-shaped plate packing 20 are engaged to prevent axial removal.

  On the other hand, a ring-shaped wire packing 30 that engages with the rear peripheral edge of the flange-shaped protrusion 2b is disposed between the inner surface of the rear end side opening of the metal shell 1 and the outer surface of the insulator 2, Further, a ring-shaped wire packing 32 is disposed on the rear side through a filling layer 31 such as talc. Then, the insulator 2 is pushed toward the front end side toward the metal shell 1, and in this state, the crimping portion 1d is formed by crimping the opening edge of the metal shell 1 toward the ring-shaped wire packing 32, The metal shell 1 is fixed to the insulator 2.

  A terminal fitting 10 is inserted and fixed on the rear end side of the through hole 5 of the insulator 2, and the center electrode 3 is inserted and fixed on the distal end side. A resistor 11 is disposed between the terminal fitting 10 and the center electrode 3 in the through hole 5. Both ends of the resistor 11 are electrically connected to the center electrode 3 and the terminal fitting 10 via the first conductive sealing material layer 12 and the second conductive sealing material layer 13, respectively.

  The resistor 11 is a resistor composition obtained by using, as a raw material, a mixed powder of glass powder and conductive material powder (and ceramic powder other than glass if necessary), and heating and pressing it in a glass sealing step described later. Composed of things. The resistor 11 may be omitted, and the terminal fitting 10 and the center electrode 3 may be integrated with a single conductive sealing material layer.

  The terminal fitting 10 is made of low carbon steel or the like, and a Ni plating layer (layer thickness: for example, 5 μm) for corrosion prevention is formed on the surface. And this terminal metal fitting 10 has the seal | sticker part 10a (front-end | tip part), the terminal part 10c which protrudes from the rear-end edge of the insulator 2, and the rod-shaped part 10b which connects the terminal part 10c and the seal | sticker part 10a.

  The seal portion 10a is formed in a cylindrical shape that is long in the axial direction, and has a convex portion in the form of a screw or a rib on its outer peripheral surface, and is disposed so as to be immersed in the conductive sealing material layer 13 so as to penetrate therethrough. A space between the inner surfaces of the holes 5 is sealed with a conductive sealing material layer 13.

  The main body portions of the ground electrode 4 and the center electrode 3 are made of Ni alloy, Fe alloy or the like. A core material 3c made of Cu or Cu alloy is embedded in the main body of the center electrode 3 to promote heat dissipation. Note that a core material may also be embedded in the ground electrode 4. On the other hand, the ignition part 3a and the opposing ignition part 4a are mainly composed of a noble metal alloy mainly containing one or more of Ir, Pt and Rh. Note that one or both of the ignition part 3a and the opposing ignition part 4a can be omitted.

  The 1st conductive sealing material layer 12 and the 2nd conductive sealing material layer 13 make the principal part of the spark plug 100 of 1st Embodiment, and consist of base glass and a conductive filler.

  The conductive filler contained in the conductive sealing material layers 12 and 13 is a metal powder mainly composed of one or more metal components such as Cu and Fe.

Thus, the content of the insulating filler in the first conductive sealing material layer 12 and the second conductive sealing material layer 13 is 10% by weight or less. Thereby, the hardness at the time of base glass softening of the 1st conductive sealing material layer 12 and the 2nd conductive sealing material layer 13 can be reduced. Therefore, it is possible to suppress the occurrence of terminal cracks when performing glass sealing. Further, it is not necessary to simply increase the sealing load, and it is possible to suppress damage to the insulator 2 when performing glass sealing.

Furthermore, the base glass in the first conductive sealing material layer 12 and the second conductive sealing material layer 13 has a Si component converted to an SiO ₂ oxide component of 55 wt% or more and 65 wt% or less, and a B component is B _2. 22 to 35% by weight in terms of O ₃ oxide component, 0.2 to 2% by weight in terms of Ca component to CaO oxide component, and Al ₂ O ₃ oxide component in terms of Al component 2% by weight or less in terms of Na, and 4 parts by weight or more and 8% by weight or less in total when Na component and K component are converted into Na ₂ O oxide component and K ₂ O oxide component, respectively, and In addition, both the Na component and the K component are included.

  By making the composition of the base glass in the first conductive sealing material layer 12 and the second conductive sealing material layer 13 as described above, the first conductive sealing material layer 12 including the base glass, the second conductive property. The thermal expansion coefficient of the sealing material layer 13 can be made lower than the thermal expansion coefficient of the insulator 2, and the progress and separation of cracks in the first conductive sealing material layer 12 and the second conductive sealing material layer 13 are suppressed. can do.

Next, an example of a method for manufacturing the spark plug 100 according to the first embodiment will be described. First, the insulator 2 is, for example, an alumina powder as a raw material powder and each component source powder of Si component, Ca component, Mg component, Ba component, and B component after firing, in a predetermined composition that becomes the above-mentioned composition in terms of oxide The mixture is blended at a ratio, and a predetermined amount of a binder (for example, PVA) and water are added and mixed to form a molding base slurry. Each component source powder, for example, the Si component is SiO ₂ powder, Ca components CaCO ₃ powder, Mg components MgO powder, Ba components BaCO ₃ powder, B components can be blended in the form of _H 3 BO ₃ powder. _{Incidentally,} H 3 BO ₃ may be added in the form of a solution.

  The forming substrate slurry is spray-dried by a spray drying method or the like to form a forming substrate granulated product. And the press molding body used as the original form of an insulator is made by carrying out the rubber press molding of the base granulation material for a shaping | molding. Here, a rubber mold having a cavity penetrating in the axial direction is used, and a lower punch is fitted into the lower opening of the cavity. A press pin that extends in the axial direction in the cavity and that defines the shape of the through hole 5 of the insulator 2 is integrally projected on the punch surface of the lower punch.

  In this state, the cavity is filled with a predetermined amount of the molded granulated material, and the upper opening of the cavity is closed with an upper punch and sealed. In this state, a hydraulic pressure is applied to the outer peripheral surface of the rubber mold, and the granulated product of the cavity is compressed through the rubber mold to obtain a press-molded body. In addition, the green base granulated material for molding is 0.7-1... In which the weight of the green base granulated material is 100 parts by weight so that crushing of the granulated material into powder particles during pressing is promoted. After the addition of 3 parts by weight of water, the press molding is performed. The molded body is processed by grinder cutting or the like on the outer surface side, and finished to an outer shape corresponding to the insulator 2. Then, the molded body is heated to 1400 to 1600 ° C. in the atmosphere and fired for 1 to 8 hours to become the insulator 2.

  The conductive sealing material powder is prepared as follows. That is, a base glass powder and a conductive filler powder containing each component described above in a predetermined composition are blended in a predetermined composition to form a raw material for mixing, and an aqueous solvent and a mixing medium (for example, ceramics such as alumina) ) And the mixture is prepared by uniformly mixing and dispersing the raw materials by rotating the pot.

  Next, the assembly of the center electrode 3 and the terminal fitting 10 to the insulator 2 and the formation of the resistor 11 and the conductive sealing material layers 12 and 13 are performed by a glass sealing process described below.

  First, a glaze slurry coating layer 2ga (FIG. 2) to be the glaze layer 2g in FIG. 1 is formed by spraying and coating the glaze slurry from the spray nozzle onto the required surface of the insulator 2, and this is dried. Next, as shown in FIG. 2, the central electrode 3 is inserted into the first portion 5a of the through-hole 5 of the insulator 2 in which the glaze slurry coating layer 2ga is formed, and then conductive as shown in FIG. The sealing material powder H is filled. Then, as shown in FIG. 4, the powder H filled by inserting the pressing rod 40 into the through hole 5 is pre-compressed to form the first conductive sealing material powder layer 12a.

  Next, the raw material powder of the resistor composition is filled into the through-hole 5 from the rear end side of the insulator 2 and preliminarily compressed in the same manner, and further filled with the conductive sealing material powder H, By performing the pre-compression, as shown in FIG. 5, the first conductive sealing material powder layer 12a, the resistor composition powder layer 11a, and the first conductive material powder layer 12a are formed in the through hole 5 from the center electrode 3 side (lower side). The second conductive sealing material powder layer 13a is laminated.

  Then, as shown in FIG. 6, an assembly PA in which the terminal fitting 10 is arranged in the through hole 5 from the rear end side is formed. In this state, it is inserted into a heating furnace and heated to a predetermined temperature of 700 to 950 ° C., and then the terminal fitting 10 is pressed into the through hole 5 in the axial direction from the side opposite to the center electrode 3 to form each layer 12a in a laminated state, 11a and 13a are pressed in the axial direction. Thereby, as shown in FIG. 7, each layer is compressed and sintered to become the conductive sealing material layer 12, the resistor 11, and the conductive sealing material layer 13, respectively (the sealing process). In addition, the glaze slurry application layer 2ga applied at the time of the glass sealing process is simultaneously glazed to become a glaze layer 2g.

  The metal shell 1, the ground electrode 4, and the like are assembled to the assembly PA in which the glass sealing process is completed in this way, and the spark plug 100 shown in FIG. 1 is completed. The spark plug 100 is attached to the engine block at its screw portion 1a, and is used as an ignition source for the air-fuel mixture supplied to the combustion chamber.

  Next, the spark plug 200 of 2nd Embodiment is demonstrated. The spark plug 200 of the second embodiment is different only in the materials of the first conductive sealing material layer 12 and the second conductive sealing material layer 13 of the spark plug 100 of the first embodiment. The other parts will be omitted.

In the spark plug 200 of the second embodiment, the first conductive sealing material layer 212 is made of a base glass and a conductive filler. On the other hand, the second conductive sealing material layer 213 is made of a base glass, a conductive filler, and 1% by weight of an insulating filler. This insulating filler is made of TiO ₂ crystals.

Thus, the content of the insulating filler in the first conductive sealing material layer 212 and the second conductive sealing material layer 213 is set to 10% by weight or less. Thereby, the hardness at the time of softening the base glass of the 1st conductive sealing material layer 212 and the 2nd conductive sealing material layer 213 can be reduced. Therefore, it is possible to suppress the occurrence of terminal cracks when performing glass sealing. Further, it is not necessary to simply increase the sealing load, and it is possible to suppress damage to the insulator 2 when performing glass sealing.

And the content of the insulating filler in the second conductive sealing material layer 213 is larger than the content of the insulating filler in the first conductive sealing material layer 212, so that the second conductive sealing material The hardness of the layer 213 when the base glass is softened is larger than the hardness of the first conductive sealing material layer 212 when the base glass is softened. Then, the resistor 11 provided between the first conductive sealing material layer 212 and the second conductive sealing material layer 213 is sufficiently pressed by the second conductive sealing material layer 213 to be sealed and fixed inside. be able to.

Hereinafter, the present invention will be described with reference to examples.
Example 1
First, the insulator 2 was produced as follows. As a raw material powder, SiO ₂ (purity 99.5%, average particle size 1. .mu.m) relative to alumina powder (alumina 95 mol%, Na content (Na ₂ O conversion value) 0.1 mol%, average particle size 3.0 μm). 5 μm), CaCO ₃ (purity 99.9%, average particle size 2.0 μm), MgO (purity 99.5%, average particle size 2 μm), BaCO ₃ (purity 99.5%, average particle size 1.5 μm) , H ₃ BO ₃ (purity 99.0%, average particle size 1.5 μm) is blended at a predetermined ratio, and the total amount of the blended powder is 100 parts by weight, and PVA as a hydrophilic binder is 3 parts by weight. Then, 103 parts by weight of water was added and wet-mixed to prepare a molding base slurry.

  Subsequently, the slurry having different compositions was dried by a spray drying method to prepare a spherical molding base granulated product. The granulated product was sized by a sieve to a particle size of 50 to 100 μm. And this granulated material is shape | molded by the pressure of 50 Mpa by the rubber press method already demonstrated, and it grinds the outer peripheral surface of the molded object, processes it into a predetermined insulator shape, and is 2 hours at the temperature of 1550 degreeC. The insulator 2 was obtained by firing. Note that, by fluorescent X-ray analysis, the insulator 2 was found to have the following composition:

Al component: 94.9mol% in terms _{of Al} 2 _{O 3} value;
Si component: 2.4 mol% in terms of SiO ₂ ;
Ca component: 1.9 mol% in terms of CaO;
Mg component: 0.1 mol% in terms of MgO;
Ba component: 0.4 mol% in terms of BaO;
Component _B: 0.3 mol% in terms _of B 2 _{O 3} value.

Next, a metal powder composed of Cu powder and Fe powder mixed in a mass ratio of 1: 1 (both having an average particle diameter of 30 μm), an insulating powder composed of TiO _2, and a base glass powder (average particle diameter of 150 μm) Were mixed so that the content of the metal powder was about 50% by weight, to prepare a conductive sealing material powder.

The composition herein based glass powder, a SiO ₂ 60 _wt%, B 2 _{O 3} 32 wt%, 0.5 wt% of CaO, the _Al 2 _{O 3} 1 wt%, 3.5 weight Na ₂ O %, K ₂ O 1 wt%, ZrO ₂ 1 wt%, and MgO 1 wt%. Further, the insulating powder was adjusted to have the content shown in Table 1.

The resistor material powder was prepared as follows. First, 30% by mass of fine glass powder (average particle size of 80 μm), 66% by mass of ZrO ₂ (average particle size of 3 μm) as ceramic powder, 1% by mass of carbon black, and 3% by mass of dextrin as an organic binder A preliminary material was prepared by blending, wet mixing with a ball mill using water as a solvent, and then drying the mixture. Then, 80 parts by weight of coarse glass powder (average particle size 250 μm) was blended with 20 parts by weight of the preliminary material to obtain a resistor material powder. The material of the glass powder is lithium borosilicate glass obtained by mixing and dissolving 50 mass% of SiO ₂ , 29 mass% of B ₂ O ₅ , 4 mass% of Li ₂ O and 17 mass% of BaO. The softening temperature was 585 ° C.

  Next, using the conductive sealing material powder and the resistor composition powder, 100 spark plugs 100 each including the resistor shown in FIG. 1 are produced by the spark plug manufacturing method (FIGS. 2 to 7) as described above. Manufactured one by one.

The filling amount of the conductive sealing material powder for forming the first conductive sealing material powder layer 12a is 0.15 g, and the filling amount of the resistor raw material powder for forming the resistor composition powder layer 11a is 0. .40 g and the conductive glass powder filling amount for forming the second conductive sealing material powder layer 13a was 0.15 g, the heating temperature of the hot press treatment was 900 ° C., and the applied pressure was 100 kg / cm ² . .

  And the spark plug sample produced on the said conditions and the spark plug sample No. produced by reducing the heating temperature of a hot press process by 50 degreeC. About 1-7, the sealing property evaluation was performed, respectively. The sealability was evaluated by visually observing the presence or absence of the metal terminal 10 from the insulator 2.

  No spark of the terminal fitting 10 from the insulator 2 was observed for any spark plug sample produced at a heating temperature of 900 ° C. in the hot press treatment. The results shown in Table 1 below were obtained when the heating temperature of the hot press treatment was lowered by 50 ° C. (850 ° C.). In Table 1, “100” indicates that there are no 100 metal terminals 10 from the insulator 2, and “Δ” indicates that there are 1 metal terminal 10 and there are 2 terminals. The thing was shown by "x".

  As is apparent from Table 1, the first conductive sealing material layer 12 and the second conductive sealing material layer 13 having an insulating filler content of 10% by weight or less have sufficient sealing properties. It was recognized that

(Example 2)
Next, in the spark plug 100 of Example 1, the composition of the base glass powder of the first conductive sealing material layer 12 and the second conductive sealing material layer 13 is as follows. Spark plug samples prepared to have a composition as shown in Table 2 were prepared. In Table 2, the composition is shown in wt%. In Table 2, Sample No. Nos. 8 to 11 show that the composition of the base glass is within the range of the composition of the base glass in the present invention. Nos. 12 to 22 are those in which the content of at least one component constituting the base glass deviates from the range of the composition of the base glass in the present invention. The content of the insulating filler was 0% by weight.

  The spark plug samples thus obtained (for each condition, 100 manufactured) were evaluated for airtightness. As shown in FIG. 8, the spark plug sample mounting screw 1a is attached to the female cavity 51 of the pressurizing cavity formed in the pressurizing test stand 50, and the compressed air in the pressurizing cavity is 1.5 MPa. (Standard test) and 2.5 MPa (acceleration test) were introduced at two levels, and the amount of air leakage from the terminal fitting 10 side was measured.

  When the compressed air in the pressurized cavity was 1.5 MPa (standard test), no air leakage was observed for any spark plug sample. When the compressed air in the pressurized cavity was 2.5 MPa (accelerated test), the results shown in Table 1 below were obtained. In Table 1, “○” indicates that there was no leakage, “△” indicates that there was leakage of 0.05 ml / min or less, and the leakage amount was 0.05 ml / min or more. Is indicated by “×” as a leaked product.

  Moreover, the same sealing performance as Example 1 was evaluated about the spark plug sample produced like Example 1, and the spark plug sample produced by making the heating temperature of a hot press process low 50 degreeC, respectively. In addition, no spark of the terminal fitting 10 from the insulator 2 was observed in any spark plug sample produced at a heating temperature of 900 ° C. in the hot press treatment. The results shown in Table 2 below were obtained when the heating temperature of the hot press treatment was lowered by 50 ° C. (850 ° C.).

As is apparent from Table 2, the conductive sealing material having the base glass composition within the range of the base glass composition of the present invention has sufficient airtightness and sealing properties. Admitted. In particular, when W1 is the weight when the Na component is converted to the Na ₂ O oxide component and W2 is the weight when the K component is converted to the K ₂ O oxide component, W1 ≧ W2 Even when the temperature at the time of sealing was lowered, it was confirmed that both were excellent in airtightness and sealing property.

(Example 3)
Next, a spark plug 200 was produced in the same manner as the spark plug 100 of Example 1 and Example 2. In addition, the base glass of Example 1 is used as the base glass of the first conductive sealing material layer 212 and the second conductive sealing material layer 213, and the second conductive sealing material layer 213 further contains insulating properties. As shown in Table 3, the filler content was adjusted to be samples N0.23 to 27. The content of the insulating filler in the first conductive sealing material layer 212 is 0% by weight.

  And said sample NO. About 23-27, the insertion resistor load life test shown to JISB8031-1995 was done. Then, “◯” indicates a value that is greater than ± 20% and is ± 30% or less, and “、” indicates that the value is ± 20 or less. The results are shown in Table 3.

According to this, by making the content of the insulating filler in the second conductive sealing material layer 213 larger than the content of the insulating filler in the first conductive sealing material layer 212 , the load life characteristics are particularly effective. Can be improved.

Sectional drawing which showed an example of the spark plug of this invention Sectional drawing which showed an example of the manufacturing process of the spark plug of this invention Sectional drawing which showed an example of the manufacturing process of the spark plug of this invention Sectional drawing which showed an example of the manufacturing process of the spark plug of this invention Sectional drawing which showed an example of the manufacturing process of the spark plug of this invention Sectional drawing which showed an example of the manufacturing process of the spark plug of this invention Sectional drawing which showed an example of the manufacturing process of the spark plug of this invention Schematic showing the evaluation device for sealability evaluation

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Main metal fitting, 2 ... Insulator, 3 ... Center electrode, 4 ... Ground electrode, 10 ... Terminal metal fitting, 11 ... Resistor, 12, 212 ... 1st electroconductive sealing material layer, 13, 213 ... 2nd electroconductivity Sealing material layer, 100, 200 ... spark plug

Claims (9)

In the spark plug having a conductive sealing material layer disposed between the terminal fitting and the center electrode in the through hole formed in the axial direction of the insulator made of alumina ceramic,
The conductive sealing material layer includes a base glass, a conductive filler, and an insulating filler having a content of 10% by weight or less (including 0), and the base glass includes:
55 wt% or more and 65 wt% or less in terms of Si component converted to SiO ₂ oxide component,
The B component is converted to a B ₂ O ₃ oxide component and is 22 wt% to 35 wt%.
Converting Ca component to CaO oxide component, 0.2 wt% or more and 2 wt% or less,
2% by weight or less in terms of Al component converted to Al ₂ O ₃ oxide component, and
The total amount of Na component and K component when converted into Na ₂ O oxide component and K ₂ O oxide component, respectively, is 4 to 8% by weight, and includes both the Na component and K component. Spark plug characterized by being W1 ≧ W2 where W1 is the weight when the Na component in the base glass is converted to the Na ₂ O oxide component, and W2 is the weight when the K component is converted to the K ₂ O oxide component. The spark plug according to claim 1.   The spark plug according to claim 1 or 2, wherein the conductive sealing material layer is formed of only a base glass and a conductive filler. The total of the weight when the Si component in the base glass is converted to a SiO ₂ oxide component and the weight when the B component is converted to a B ₂ O ₃ oxide component is 86 wt% or more and 94 wt% or less. The spark plug according to any one of claims 1 to 3, wherein: In the through-hole formed in the axial direction of the insulator, the center electrode is fixed to the first conductive sealing material layer, and the terminal fitting is fixed to the second conductive sealing material layer, and the first conductive sealing material layer and In the spark plug in which a resistor is interposed between the second conductive sealing material layer,
The second conductive sealing material layer includes a base glass, a conductive filler, and an insulating filler having a content of 10% by weight or less (excluding 0),
The first conductive sealing material layer includes a base glass, a conductive filler, and an insulating filler whose content is less (including 0) than the second conductive sealing material layer.   The spark plug according to claim 5, wherein the first conductive sealing material layer is formed of only a base glass and a conductive filler. The insulator is made of alumina ceramic,
The base glass of the first and second conductive sealing layers is
55 wt% or more and 65 wt% or less in terms of Si component converted to SiO ₂ oxide component,
The B component is converted to a B ₂ O ₃ oxide component and is 22 wt% to 35 wt%.
Converting Ca component to CaO oxide component, 0.2 wt% or more and 2 wt% or less,
2% by weight or less in terms of Al component converted to Al ₂ O ₃ oxide component, and
The total amount of Na component and K component when converted into Na ₂ O oxide component and K ₂ O oxide component, respectively, is 4 to 8% by weight, and includes both the Na component and K component. 7. The spark plug according to claim 5 or 6, wherein the spark plug is a waste plug. W1 ≧ W2 where W1 is the weight when the Na component in the base glass is converted to the Na ₂ O oxide component, and W2 is the weight when the K component is converted to the K ₂ O oxide component. The spark plug according to claim 7. The total of the weight when the Si component in the base glass is converted to a SiO ₂ oxide component and the weight when the B component is converted to a B ₂ O ₃ oxide component is 86 wt% or more and 94 wt% or less. 9. The spark plug according to claim 7 or 8, wherein: