JP2002246145A - Insulator for spark plug, and the spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulator for a spark plug capable of improving durability to a dielectric breakdown and being manufactured at a low cost. SOLUTION: The insulator for a spark plug 2 includes a first part 2p and a second part 2s, respectively formed of alumina ceramic mainly consisting of alumina. The first part 2p on a side of a spark discharge gap g, which is likely to create a problem, such as the dielectric breakdowns resulting from applying a high voltage is formed of the alumina ceramic with higher insulating performance (to be specific, having a high breakdown voltage) than the second part 2s, which is relatively not likely to create the problem, such as dielectric breakdowns. For example a content rate of the alumina in the first part 2p is higher than that of the second part 2s. Or the percent content of a rear earth element component of the alumina ceramic in the first part 2p is higher than that of the second part 2s. Also the percent content of an alkali metal component of the alumina ceramic in the first part 2p is lower than that of the second part 2s.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug insulator and a spark plug using the same.

[0002]

2. Description of the Related Art In recent years, the area occupied by intake and exhaust valves in a combustion chamber has been increasing with the increase in the output of internal combustion engines used in automobiles and the like. Therefore, the spark plug for igniting the air-fuel mixture is required to be downsized, and a supercharger such as a turbocharger is used.
Since the temperature in the combustion chamber also tends to increase, an insulator made of an alumina-based insulating material having excellent heat resistance is generally used. Another important reason why an insulator made of alumina is used as an insulator for a spark plug is that alumina has excellent withstand voltage characteristics at high temperatures. However, in recent years, as the size of the spark plug has been reduced, the thickness of the insulator has also tended to be reduced, and an insulator having excellent withstand voltage characteristics has been demanded.

For example, alumina ceramics using a ternary sintering aid of SiO ₂ —CaO—MgO have been widely used as a material for an insulator for a spark plug. However, since this kind of sintering aid forms a low-melting glassy grain boundary phase in the ceramic, there is a problem that dielectric breakdown easily occurs when a high voltage is applied at a high temperature. Also, in the alumina raw material manufactured by the Bayer method or the like, a considerable amount of Na component is inevitably mixed for reasons of the manufacturing method, but this Na component dissolves in the grain boundary phase and lowers the withstand voltage. It also causes.

Therefore, an insulator whose alumina content is increased to 95 to 98% by mass to improve the withstand voltage characteristic, an insulator whose Na content is reduced by using low soda alumina, and Y _2. An insulator having a high melting point grain boundary phase formed by blending a rare earth element such as O ₃ or La ₂ O ₃ to improve the withstand voltage characteristics (for example, JP-A-63-19063)
No. 753) has been proposed.

[0005]

However, the cost of the production method or the raw material is higher than that of general alumina ceramics, and the price of the final spark plug rises in exchange for the improvement of performance. Inevitable.

An object of the present invention is to provide a spark plug insulator which can be manufactured at a lower cost while improving the durability against dielectric breakdown and the like, and a spark plug using the same.

[0007]

SUMMARY OF THE INVENTION An insulator for a spark plug according to the present invention is composed of two parts, specifically, a second part and a second part which are formed as alumina ceramics having different materials. And a first portion having high insulation performance (specifically, high insulation withstand voltage). In the spark plug according to the present invention, the insulator is arranged between the metal shell and the center electrode, and at the distal end side of the insulator, a ground electrode and a center electrode whose base ends are coupled to the metal shell. A spark discharge gap is formed between them. The main point is that the portion is configured as a first portion and at least a part of the remaining portion is configured as a second portion in order to selectively improve the insulating property of the insulator tip.

[0008] In the present specification, the alumina ceramic is a ceramic containing alumina as a main component. In this specification, “main component” (“mainly”
Alternatively, “mainly the same” means a component having the highest weight content ratio of the substance of interest.

The first specific structure of the insulator of the present invention is as follows. In the above insulator, the first portion has a higher alumina content than the second portion (hereinafter referred to as alumina content requirement). Satisfies at least one of the following requirements: high content of rare earth element components (hereinafter referred to as rare earth content requirements); low content of alkali metal components (hereinafter referred to as alkali metal content requirements). Is the gist.

The first portion satisfies the alumina content requirement, that is, the alumina content of the first portion is higher than that of the second portion. Can be improved. Also,
It is only necessary to apply high-alumina ceramic which is costly to the first part only, and the material of the second part can be composed of a less expensive ceramic having a lower alumina content, so that the cost of the entire insulator increases. It is possible to improve the durability against dielectric breakdown and the like while suppressing the occurrence of electric current.

Further, the fact that the first portion satisfies the rare earth content requirement, that is, the content of the rare earth element component of the alumina ceramic is higher in the first portion than in the second portion, provides the following: The effect can be achieved.
The rare earth element components are Sc, Y, La, Ce, Pr, N
d, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
At least one of m, Yb, and Lu is added as a sintering aid, for example, in the form of an oxide. Since the rare earth element component mainly forms a high melting point compound phase in the grain boundary phase, by increasing the rare earth element component content of the first part more than the second part, it is easily affected by high voltage application during spark discharge. The withstand voltage characteristics of the first part can be improved.
Also, increasing the rate of addition of the rare earth element component is expensive in terms of cost, but it is sufficient to add a large amount of the rare earth element component only in the first portion. Durability can be improved.

Furthermore, the following effects can be achieved by the first portion satisfying the alkali metal requirement, that is, the content of the alkali metal component of the alumina ceramic is made lower in the first portion than in the second portion. it can. That is, the alkali metal component is, for example, Li, Na
And one or more of K, all of which have high ionic conductivity, and when they become a component forming a grain boundary phase of the ceramic, if the content thereof is excessive, the withstand voltage characteristics may be reduced. Leads to invitation. Therefore, by making the alkali metal component content of the first portion lower than that of the second portion, it is possible to improve the withstand voltage characteristics of the first portion which is easily affected by the application of a high voltage during spark discharge. On the other hand, an alkali metal element is often inevitably contained in an alumina raw material such as Na, for example, due to manufacturing factors. For example, it is more expensive than medium soda alumina or ordinary soda alumina). While doing
In the above configuration, such an alumina ceramic having a low alkali metal component content may be applied only to the first portion, and the material of the second portion is a less expensive ceramic having a higher alkali metal component content. Can be configured,
It is possible to improve the durability against dielectric breakdown and the like while suppressing an increase in the cost of the entire insulator.

In the first configuration of the insulator according to the present invention, the first portion of the insulator includes the above alumina content requirement (A), rare earth content requirement (B), and alkali metal content requirement (C). May be satisfied independently, or two or more arbitrary ones may be satisfied simultaneously, whereby the withstand voltage characteristic of the first portion can be further improved. Specific combinations are as follows. A + B; B + C; C + A; A + B + C.

Next, a second specific configuration of the insulator according to the present invention is characterized in that, in the insulator, the first portion is made of alumina ceramic having a higher translucency than the second portion. And In order to achieve both mechanical strength and withstand voltage characteristics as an insulator for a spark plug, it is necessary that the alumina ceramic used be dense so that the relative density is 90% or more. The withstand voltage characteristics are further improved by further densifying the ceramic. Further, the abundance of the crystal grain boundaries and the grain boundary phase can also be a factor affecting the withstand voltage characteristics. For example, it is possible to improve the withstand voltage characteristics by reducing the abundance of the crystal grain boundaries and the grain boundary phase. . Alumina ceramics have a property that the translucency gradually increases as the densification progresses or the amount of formation of crystal grain boundaries and / or grain boundary phases decreases. In other words, the withstand voltage characteristic of the alumina ceramic becomes better as the translucency increases. For example, what is generally known as a light-transmitting alumina is polycrystalline alumina that has been densified to almost the theoretical density. It can be manufactured by firing in a medium. Further, it may be manufactured using a high pressure firing method such as a hot isostatic pressing (HIP) method or a hot pressing method. Such an alumina ceramic has excellent withstand voltage characteristics, but is naturally more expensive than ordinary alumina.

Therefore, in the second configuration, the first portion is made of alumina ceramic having higher translucency than the second portion, so that the first portion is easily affected by a high voltage during spark discharge. Voltage characteristics can be improved. In addition, it is sufficient to use an alumina ceramic having an increased light transmittance only in the first portion, so that it is possible to improve the durability against dielectric breakdown and the like while suppressing an increase in the cost of the entire insulator.

A third specific configuration of the insulator according to the present invention has a first portion made of single-crystal alumina and a second portion made of an insulating ceramic material different from the first portion, The spark plug according to the present invention is characterized in that a tip portion of the insulator, which is to be located on the spark discharge gap side of the spark plug, is configured as a first portion, and at least a part of the remaining portion is configured as a second portion. The second portion can be made of a polycrystalline alumina ceramic, but may be made of another insulating ceramic such as aluminum nitride.

The single-crystal alumina includes, for example, artificial ruby, artificial sapphire, and artificial corundum manufactured by a known single crystal growing method such as the Bernoulli method. These are ultimate alumina materials from which the influence of residual pores, crystal grain boundaries or grain boundary phases has been almost completely eliminated, and by applying this as the material of the first portion of the insulator, Withstand voltage characteristics can be dramatically improved. In addition, since the second portion is made of a general-purpose insulating ceramic such as a polycrystalline alumina ceramic, the problem of an increase in the cost of the entire insulator hardly occurs.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. A spark plug 100 as an example of the present invention shown in FIGS. 1 and 2 is formed on a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that a distal end portion 21 protrudes, and a distal end. One end is connected to the center electrode 3 provided inside the insulator 2 and the metal shell 1 by welding or the like while the igniting portion 31 is protruded, and the other end is bent back to the side. Includes a ground electrode 4 and the like arranged so as to face the tip of the center electrode 3. Further, the ground electrode 4 is provided with a firing portion 32 facing the firing portion 31.
The gap between the opposing firing part 32 is the spark discharge gap g.
It has been.

The insulator 2 has a shaft-like shape and, when incorporated into the spark plug 100, forms a tip portion in the direction of the axis O located on the side of the spark discharge gap g.
And a second portion 2s adjacent to the first portion 2p on the rear side in the direction of the axis O are each made of alumina ceramic mainly composed of alumina. The second portion 2s can be made of, for example, alumina ceramics of the same material as the conventional insulator for a spark plug.

The material of the first portion 2p is formed as an alumina ceramic satisfying at least one of the following requirements. The alumina content is higher than the second portion 2s. The specific content of the alumina component can be selected in the range of 95 to 100% by mass in terms of mass in terms of Al ₂ O ₃ .
In this case, for example, Si, Ca, which functions as a sintering aid,
Mg, Ba and B components, Si is SiO ₂ , Ca is C
aO, Mg to MgO, Ba to BaO, B to B ₂ O
₃ to 5 in total in terms of mass in oxide conversion
By containing it in the range of up to mass%, the densification of the sintered body forming the first portion 2p can be promoted. Further, as a sintering aid, it is of course possible to employ a rare earth element component described below. On the other hand, when high-temperature and high-pressure sintering such as hot isostatic pressing is possible, a dense sintered body can be obtained even with the sintering agent almost eliminated.
The relative density of the sintered body forming the first portion 2p is 95% by mass or more, preferably 98% by mass or more, particularly from the viewpoint of improving the withstand voltage characteristics at high temperatures.

The rare earth element component R (= Sc, Y, La,
Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, H
o, Er, Tm, Yb and / or Lu) in which the content is higher than that of the second part. Specifically, the amount of addition is RO ₂ when R is Ce, and R ₆ O when R is Pr.
₁₁ , In other cases, R ₂ O ₃ can be selected in the range of 0.01 to 18% by mass in terms of oxide. These rare earth element components can be blended, for example, in the form of an oxide powder as a sintering aid. It is more effective to use one or both of Pr and Nd among the above rare earth element components, from the viewpoint of improving the withstand voltage characteristics at high temperatures. In addition, if a form in which the Nd component and the Pr component are added in combination is adopted, for example, an oxide of dymium which is a non-separable rare earth mainly composed of Nd and Pr can be adopted, which is effective in reducing the raw material cost. .

It is of course possible to mix other sintering aid components together with the rare earth element component R. For example, one or more of Si, Mg, Ca, Ba and B may be co-added. It can be blended as a binder component. In particular, Si
A high melting point composite oxide can be easily formed with the rare earth element component, and the effect of improving the withstand voltage characteristics at high temperatures can be further enhanced.

The content of the alkali metal component in the second part 2
lower than s. For example, when low-soda alumina powder is used as a raw material and an alkali metal component other than Na is not actively added, the content of the alkali metal component can be kept to 0.05% by mass or less in terms of oxide. It is.

On the other hand, as a specific material of the second portion 2s, for example, a sintering aid component (including the alkali metal component, the same sintering aid may be used as the above type). content is 5 to 15 wt% in terms of oxide, and for example, Na as the alkali metal component _Na 2 O
What is contained in the converted value in the range of 0.07 to 0.5% by mass can be adopted. With such Na content,
Medium soda alumina or ordinary soda alumina can also be used as a raw material without any problem.

Next, the overall shape of the insulator 2 will be described in detail. First, a through-hole 6 is formed in the insulator 2 in the axial direction, and a terminal fitting 13 is inserted and fixed from one end thereof, and the center electrode 3 is inserted and fixed from the other end thereof. ing. Further, a resistor 15 is arranged between the terminal fitting 13 and the center electrode 2 in the through hole 6. Both ends of the resistor 15 are electrically connected to the center electrode 3 and the terminal fitting 13 via conductive glass seal layers 16 and 17, respectively. The resistor 15 is formed of a resistor composition obtained by mixing glass powder and conductive material powder (and ceramic powder other than glass as required) and sintering the mixture by hot pressing or the like. The conductive glass seal layers 16 and 17 are made of Cu, Sn,
It is made of glass mixed with a metal powder mainly composed of one or more metal components such as Fe. Note that the resistor 15 may be omitted, and the terminal fitting 13 and the center electrode 3 may be integrated by a single conductive glass seal layer.

As shown in FIG. 1, a projecting portion 2e projecting outward in the circumferential direction is formed, for example, in a flange shape in the middle of the insulator 2 in the axial direction. The insulator 2 has a main body 2b having a smaller diameter than the protruding portion 2e, with the side facing the tip of the center electrode 3 (FIG. 1) as the front side. On the other hand, on the front side of the protrusion 2e, a first shaft 2g having a smaller diameter than the first shaft 2g and a second shaft 2i having a smaller diameter than the first shaft 2g are formed in this order. A glaze 2d is applied to the outer peripheral surface of the main body 2b, and a corrugation 2c is formed at the rear end of the outer peripheral surface. The outer peripheral surface of the first shaft portion 2g has a substantially cylindrical shape, and the outer peripheral surface of the second shaft portion 2i has a substantially conical surface shape whose diameter decreases toward the distal end.

The axial sectional diameter of the center electrode 3 is equal to the resistance of the resistor 15.
Is set to be smaller than the shaft cross-sectional diameter. The through-hole 6 of the insulator 2 has a substantially cylindrical first portion 6a through which the center electrode 3 is inserted, and a substantially cylindrical portion formed on the rear side (upper side in the drawing) of the first portion 6a with a diameter larger than this. And a second portion 6b. As shown in FIG.
The resistor 3 and the resistor 15 are accommodated in the second portion 6b, and the center electrode 3 is inserted into the first portion 6a.

Further, the outer peripheral surface of the connecting portion 2h between the first shaft portion 2g and the second shaft portion 2i is a stepped surface, and this is a stepped surface.
Ridge 1 as a metal shell side engaging portion formed on the inner surface of
By engaging with c via a ring-shaped plate packing 63, axial removal is prevented. On the other hand, between the inner surface of the rear opening of the metal shell 1 and the outer surface of the insulator 2,
A ring-shaped line packing 62 that engages with the rear side peripheral edge of the flange-shaped protrusion 2e is arranged, and further on the rear side, a ring-shaped packing 60 is disposed via a filling layer 61 such as talc.
Is arranged. Then, the insulator 2 is pushed forward toward the metal shell 1 and, in this state, the opening edge of the metal shell 1 is swaged inward toward the packing 60 to form a swaged portion 1d. It is fixed to the insulator 2.

In the embodiment shown in FIG. 1, the first portion 2p and the second portion 2s of the insulator 2 are joined at a position slightly toward the middle of the second shaft portion 2i in the axial direction (toward the first shaft portion 2g). Have been. This joining position is the same as the first part 2p
And the second portion 2s in the direction of the axis О. Specifically, as shown in FIG. 2, the dimension of the first portion 2p in the direction of the axis O increases as the position of the bonding interface is located rearward in the direction of the axis О. 2nd part 2p
Since the material cost is higher than that of the second portion 2s, for example, as shown in FIG. 2 (a), a joining surface is set near the tip of the second shaft portion, and the temperature is easily raised in the combustion chamber, and It is more advantageous to reduce the cost if only the vicinity of the front end, which is close to the spark discharge gap g and easily affected by high voltage application, is the first portion 2p. On the other hand, when stricter withstand voltage characteristics are required, or when the diameter of the entire insulator 2 is small, or when the thickness of the insulator 2 must be reduced, as shown in FIG. 2g or Fig. 2
As shown in (c), the first portion 2 is further moved to the rear position.
It may be p.

Returning to FIG. 1, the metallic shell 1 is formed of a metal such as low carbon steel into a cylindrical shape.
00 and a screw portion 7 for attaching the plug 100 to an engine block (not shown) is formed on the outer peripheral surface thereof. This screw part 7
Has an outer diameter of 18 mm or less (for example, 18 mm, 14 mm,
12 mm, 10 mm, etc.). Reference numeral 1e denotes a tool engagement portion that engages a tool such as a wrench or a wrench when the metal shell 1 is attached, and has a hexagonal axial cross-sectional shape.

Next, the body portions 3a and 4a of the center electrode 3 and the ground electrode 4 are made of a Ni alloy or the like such as Inconel (trade name). Further, a core material 3b made of Cu or Cu alloy or the like is embedded in the center electrode 3 to promote heat radiation. On the other hand, the ignition part 3
1 and the opposing firing part 32 are Ir, Pt and Rh of 1
It is mainly composed of a noble metal alloy containing at least one kind or two or more kinds. The main body 3a of the center electrode 3 has a reduced diameter on the tip end side and a flat tip end face. A disk-shaped chip made of an alloy composition constituting the ignition portion is superimposed on the tip end, and the outer edge of the joining surface is further joined. Laser welding along the part,
The ignition portion 31 is formed by forming a welded portion by electron beam welding, resistance welding, or the like and fixing the welded portion. Further, the opposing firing portion 32 aligns the tip with the ground electrode 4 at a position corresponding to the firing portion 31, and similarly forms a welded portion (not shown) along the outer edge of the joint surface and fixes it. Formed by In addition, these chips are blended with each alloy component so as to have the indicated composition, for example.
It can be composed of a molten material obtained by melting, or a sintered material obtained by molding and sintering alloy powder or a single metal component powder mixed in a predetermined ratio. Note that at least one of the firing part 31 and the opposing firing part 32 may be omitted.

The insulator 2 can be manufactured, for example, by the following method. First, as a raw material powder, an alumina powder and a sintering aid powder are blended so as to have a composition determined for each of the first portion 2p and the second portion 2s, and a hydrophilic binder (for example, PVA) and water are mixed. Add and mix to make a molding base slurry.

The molding base slurry is spray-dried by a spray drying method or the like to form a molding base granule PG1 (for the first part 2p) and a molding base granule PG2 (for the second part 2p).
s). These molding base granules PG1 and P
G2 is subjected to rubber press molding to produce a press molded body serving as a prototype of the insulator. FIG. 4 schematically shows a process of rubber press molding. Here, a rubber mold 300 having a cavity 301 penetrating in the axial direction is used, and an upper punch 304 is fitted into an upper opening of the cavity 301. Further, on the punch surface of the lower punch 302, a press pin 303 that extends in the axial direction within the cavity 301 and that defines the shape of the through hole 6 (FIG. 1) of the insulator 2 is integrally formed. .

In this state, the cavity 301 is filled with a predetermined amount of the base granules PG1 and PG2 for molding, and the upper opening of the cavity 301 is closed with an upper punch 304 to be sealed. At this time, one of the green body granules for molding PG1 and PG2 is first filled on the lower side in the axial direction of the press pin 303, and then the other is filled on the upper side. Thereby, the granulated material PG1 for the first portion 2p and the granulated material PG2 for the second portion 2p are 2 in the axial direction in the cavity 301.
Filled in layers.

In this state, a liquid pressure is applied to the outer peripheral surface of the rubber mold 300, and the granules PG1 and PG2 of the cavity 301 are removed.
By compressing through the rubber mold 300, FIG.
As shown in (a), a pressed compact 202 is obtained in which powder compacts 202s and 202p made of the granules PG1 and PG2 are joined in the axial direction. The outer surface side of the press-formed body 202 is processed by grinder cutting or the like to finish the outer shape corresponding to the insulator 2 in FIG.
As shown in (b), the molded body to be fired 152 having a powder molded portion 152p having a shape corresponding to the first portion 2p and a powder molded portion 152s having a shape also corresponding to the second portion 2s.
Is obtained. By firing the molded body 152 at a predetermined temperature and further applying a glaze to finish firing, FIG.
Is completed.

The form of the joint surface between the first part 2p and the second part 2s of the insulator 2 is a plane form substantially orthogonal to the axis О in FIG. 1, but the joint strength of both parts is improved. For example, as shown in FIG. 3 (a), for example, as shown in FIG. 3 (a), a joining surface 103 having a tapered surface shape protruding in any direction along the axis О, or a stepped portion as shown in FIG. The bonding surface 104 may have a planar shape. Alternatively, the two portions 2p and 2s can be joined in a positional relationship such that the rear end portion 107 of the first portion 2p is housed in the concave portion 106 opened on the tip side of the second portion 2s. In this case, for example, the molded body of the first part is first formed separately by a rubber press or the like, and when the molded body of the second part is formed by another rubber pressing step, simultaneously with the molded body of the first part, 162p (FIG. 6 (a)), and thereafter, the outer peripheral surface is finished by grinding or the like.
It is possible to employ a method of obtaining the molded body to be fired 162 shown in FIG.

When the firing conditions or shrinkage during firing of the first portion 2p and the second portion 2s are significantly different, for example, a method as shown in FIG. 6B is also possible.
That is, the first portion 2p is first formed as a fired body, and a semi-molded body 172 in which the second portion formed body 172s is integrated is formed, and this is fired to form the first portion 2p and the second portion 2s. To obtain the insulator 2 integrated.

As shown in FIG. 7A, the first part 2p and the second part 2s are separately manufactured as sintered bodies, and these sintered bodies are joined to form the insulator 2. It is possible. For example, in the embodiment shown in FIG.
And the second portion 2s are joined by the glass joining layer 2w. Specifically, it is possible to employ a method in which a joining glass material is sandwiched between joining positions of the first portion 2p and the second portion 2s, and the joining is performed by heating to a joining temperature equal to or higher than the glass softening point.

Further, the first portion 2p may be made of an insulating ceramic having a higher translucency than the second portion 2s, for example, a translucent alumina. Also, the first part 2p
May be made of single crystal alumina such as artificial ruby, artificial sapphire or artificial corundum. The first portion 2p made of these materials has a large difference in manufacturing method from the second portion 2s made of ordinary alumina ceramic, and a method of integrally firing the second portion 2s in a powder compact state is in principle. Impossible. Therefore, a part to be the first part 2p is separately manufactured, and thereafter, FIG.
(B) Or it is appropriate to adopt a method of joining by a method as shown in FIG.

[0040]

EXAMPLES In order to confirm the effects of the present invention, the following experiments were conducted. As the raw material alumina powder, the following 2
Were prepared Type: Normal Soda Alumina: Na content (Na ₂ O equivalent)
0.3 mass%, average particle diameter 1 μm; low soda alumina: Na content (in terms of Na ₂ O)
05% by mass, average particle size 0.5 μm.

The sintering aid powder has an average particle size of 0.1.
6 μm SiO ₂ powder, CaCO with average particle size 0.8 μm
₃ powder, MgO powder having an average particle diameter of 0.3 μm, and various rare earth powders having an average particle diameter of 0.1 μm (Nd ₂ O ₃ , Dy ₂ O
₃ , Pr ₆ O ₁₁ ) were blended such that the target composition of the sintered body was as shown in Table 1. The total amount of this blended powder is 1
3 parts by weight of PVA as a hydrophilic binder.
Parts by mass and 103 parts by mass of water were added and wet-mixed by a ball mill for 16 hours to prepare a forming base slurry. Next, these slurries having different compositions were dried by a spray-drying method, respectively, to prepare spherical molding base granules. The granules are sieved to a particle size of 50 to 100 μm.

[0042]

[Table 1]

Various insulators shown in Table 2 were produced by using the above four types of base granules. In the table, 〜 corresponds to the number of each base granulated material in Table 1, and the numerical value in each column indicates how many% by mass of each corresponding forming base granulated material was used.

[0044]

[Table 2]

Numbers 1 to 4 in Table 2 are comparative examples, and a molded article made entirely by rubber plus using the base granulated material in any one of Table 1 was fired in air at 1625 ° C. for 2 hours. It was done. On the other hand, Nos. 5 to 8 are examples, and the green compact of the second portion 152s of FIG. 5 is formed by the base granulated product, and the green compact 152p of the first portion is formed by any of the base granulated products. A molded body produced by integral molding using the method shown in FIG. 4 is fired at 1625 ° C. for 2 hours in the air.

Also, reference numerals 9 to 12 are examples, and FIG.
The molded body 152s of the second part is formed by a separate granule press, and the molded body 152p of the first part is formed by a separate rubber press. Each of the compacts was fired at 1600 ° C. for 2 hours in the air in a state where the compacts were abutted in the axial direction.

Further, reference numerals 13 to 16 are examples.
The molded body 152s of the second part in FIG. 5 is produced by a separate green press, and the molded body 152p of the first part is produced by a separate rubber press. Each of the compacts was fired in air at 1625 ° C. for 2 hours, and then the sintered compacts were joined by the glass joining layer 2w. In addition, about the test goods of No. 9-16,
Al, S for each formed part by the base granulated material
The contents of i, Ca, Mg, the rare earth element (RE) and Na were measured by ICP emission spectroscopy, and converted into the corresponding oxide contents to determine the sintered body composition. As a result, it was found that the composition was substantially the same as the target composition in Table 1.

On the other hand, No. 17 and No. 18 show that the second part 2s shown in FIG. 7B is produced by rubber-pressing the base granulated material of No. 17 and 18, followed by firing at 1600 ° C. for 2 hours in the air. , The first portion 2p is made of translucent alumina and single-crystal alumina, respectively, and is joined by the glass joining layer 2w.

Using the insulator obtained as described above, a spark plug shown in FIG. 1 was assembled, and a withstand voltage test of an actual machine was performed under the following conditions. That is, the spark plug was attached to a 4-cylinder gasoline engine (displacement: 2000 cc), the throttle was fully opened, and the engine speed was 6
At 000 rpm, the discharge voltage is 35 kV and 37.5 k
Continuous operation was performed while controlling to any value of V, and evaluation was made after 50 hours passed by whether or not spark penetration occurred. Table 2 shows the results. That is, the test pieces of Examples (numbers 5-1)
8) is superior in the withstand voltage characteristics to the test product of Comparative Example 1 in which the entire insulator is made of the base granulated material. In addition, even though only the first portion 2p of the insulator 2 is made of the high withstand voltage material, it is also compared with the test products of Comparative Examples 2 to 4 in which the whole is made of the high withstand voltage material. It can be seen that the same or better performance was obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a spark plug according to an embodiment of the present invention.

FIG. 2 is a longitudinal cross-sectional view showing various examples of a bonding mode of a first portion and a second portion in the insulator of FIG. 1;

FIG. 3 is a partial vertical cross-sectional view showing various examples of the joining surface shapes of a first portion and a second portion.

FIG. 4 is an explanatory view of a manufacturing process of the insulator of FIG. 1;

FIG. 5 is a process explanatory view following FIG. 4;

FIG. 6 is an explanatory view showing some modified examples of the manufacturing process of the insulator of FIG. 1;

FIG. 7 is an explanatory view showing still another modified example of the manufacturing process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal shell 2 Insulator 2p 1st part 2s 2nd part 3 Center electrode 4 Ground electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Katsura Matsubara 14-18, Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Prefecture Inside Nihon Toku Toki Co., Ltd. No. 18 Japan Special Ceramics Co., Ltd. (72) Inventor Hiroto Ito 14-18 Takatsujicho, Mizuho-ku, Nagoya City, Aichi Prefecture Inside Japan Special Ceramics Co., Ltd. (72) Inventor Kenji Nunome Mizuho-ku, Nagoya City, Aichi Prefecture 14-18 Takatsuji-cho F-term in Japan Special Ceramics Co., Ltd. (reference) 4G030 AA01 AA11 AA36 BA12 5G059 AA05 AA08 CC02 FF02 FF10 FF14

Claims (5)

[Claims] 1. A second part made of alumina ceramic, and a second part made of alumina ceramic,
A first portion that satisfies at least one of the following A, B, and C, and an insulator tip portion that is scheduled to be located on the spark discharge gap side of the spark plug is configured as the first portion; An insulator for a spark plug, wherein at least a part of the portion is configured as the second portion; A: a high alumina content; B: a high content of a rare earth element component; and C: an alkali metal Low component content. 2. A spark plug having a second portion made of an alumina ceramic and a first portion made of an alumina ceramic and having a higher translucency than the second portion, which is located on the spark discharge gap side of the spark plug. The insulator for a spark plug is characterized in that a scheduled insulator tip is configured as the first portion, and at least a part of the remaining portion is configured as the second portion. 3. A first portion made of single-crystal alumina and a second portion made of an insulating ceramic made of a different material, wherein the first portion is to be located on the spark discharge gap side of the spark plug. An insulator for a spark plug, wherein an insulator front end portion is configured as the first portion, and at least a part of a remaining portion is configured as the second portion. 4. The insulator for a spark plug according to claim 1, wherein the second portion is formed adjacent to the first portion. 5. The insulator according to claim 1, wherein the insulator is disposed between the metal shell and the center electrode, and a base end of the insulator is connected to the metal shell at a distal end side of the insulator. A spark plug, wherein a spark discharge gap is formed between the ground electrode and the center electrode.