JPH09306636A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug with small dispersion of resistance values of a resistor and stable load life characteristics after assembled to prevent the generation of electric wave noise. SOLUTION: In a spark plug 100, a resistor 15 is constituted as a sintered body formed by sintering a mixture of glass powder and conductive material powder. The glass powder contains fine glass having a particle size of 100μm or less and coarse glass having a particle size of 100-800μm, and the ratio Wf/Wc of the weight Wf of the fine glass to the weight Wc of the coarse glass is set in the range of 2/98-50/50. The particle distribution of the coarse glass is specified such that when the total weight of the coarse glass is 100wt.%, the content ratio of particles having a particle size of 100-248μm is 10-60wt.%, that of particles having a particle size of 248-352μm is 10-60wt.%, and that of particles having a particle size of 352-800μm is 10-50wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug used in an internal combustion engine, and more particularly to a spark plug incorporating a resistor for preventing generation of radio noise.

[0002]

2. Description of the Related Art Conventionally, as a spark plug as described above, a terminal fitting is fixed to one end of a through hole formed in the axial direction of an insulator and the other end is also centered. There is known a structure in which an electrode is fixed and a resistor is arranged between the terminal fitting and the center electrode in the through hole. This resistor is disclosed, for example, in Japanese Patent Laid-Open No. 61-10.
After mixing a conductive material powder such as carbon black with glass powder and / or insulating ceramic powder, as disclosed in Japanese Patent No. 4580, Japanese Patent Application Laid-Open No. 61-253786, and Japanese Patent Application Laid-Open No. 2-126584. What is sintered by hot pressing or the like is used. In such a resistor, a mixture of coarse glass powder and fine glass powder is used, and a conductive path having a structure in which conductive material powder is dispersed in fine glass powder is formed,
The effect of preventing radio noise is enhanced by circumventing this conductive path everywhere by interposing coarse glass powder particles and lengthening its execution length.

[0003]

In the case of manufacturing the above-mentioned resistor of the plug, since the glass powder contained in the raw material powder is a mixture of coarse glass powder and fine glass powder, the fluidity is not good. When the preform for hot pressing is produced by a die press, for example, the packing density of the powder in the die, and consequently the density of the preform obtained, tends to be nonuniform or uneven. And
When hot pressing is performed using such a molded body, there is a problem that the resistance value of the obtained resistor varies or the load life characteristic of the plug becomes unstable.

An object of the present invention is to provide a spark plug in which the resistance value of a resistor does not fluctuate and load life characteristics are not unstable.

[0005]

Means for Solving the Problems and Actions / Effects In order to solve the above problems, the spark plug of the present invention is characterized in that it is constructed as follows. That is, with respect to the through hole formed in the axial direction of the insulator, the terminal metal fitting is fixed to one end side of the through hole, and the center electrode is fixed to the other end side of the through hole. A resistor is arranged between the terminal fitting and the center electrode. The resistor is configured as a sintered body obtained by mixing and sintering glass powder and conductive material powder. Further, the glass powder has a particle size of 10
It contains fine glass of 0 μm or less and coarse glass having a particle diameter of 100 to 800 μm, and the ratio Wf / Wc of the weight Wf of the fine glass and the weight Wc of the coarse glass is 2/98 to 50.
It is set in the range of / 50. When the particle size distribution of the coarse glass is 100% by weight, the content ratio of the powder particles belonging to the particle size range 100 to 248 μm is 10 to 60% by weight and the particle size range is 248. ~ 35
The content ratio of the powder particles belonging to 2 μm is 10 to 60% by weight, and the content ratio of the powder particles belonging to the particle size range 352 to 800 μm is 10 to 50% by weight.

FIG. 2 schematically shows the structure of the resistor, which is formed by melting and solidifying at least a part of fine glass particles and in which particles of conductive material powder are dispersed. The phase (bonded glass phase) has a structure surrounding glass particles (block particles) derived from coarse glass powder (hereinafter, such a structure is referred to as a block structure). In this case, at least a part of the bonded glass phase forms a continuous portion extending from the end portion on the terminal metal fitting side to the end portion on the center electrode side, and this continuous portion forms an electric field between particles of the conductive material powder. The conductive path of the resistor is formed based on the physical contact. Then, the continuous portion, that is, the conductive path is diverted everywhere due to the interposition of the block particles, the execution length becomes long, and a good effect of preventing radio wave noise is achieved.

As a result of earnest studies, the present inventors set the particle size and the mixing ratio of the coarse-grained glass and the fine-grained glass used for the resistor within the above-mentioned ranges, and thus the effect of preventing the generation of radio noise is particularly improved. It has been found that, by setting the particle size distribution of the coarse glass as described above, the fluidity and the filling property of the raw material powder are enhanced and the density of the molded product is less likely to be nonuniform or uneven. . As a result, problems such as variations in the resistance value of the resistor and instability in the load life characteristic of the plug can be avoided or suppressed.

At least a part of the fine glass melts during the sintering process such as hot pressing, and fills the gaps formed between the coarse glass particles. However, if the particle size exceeds 100 μm, the melting is insufficient and voids are easily generated in the conductive path, which leads to impaired load life characteristics of the plug. The particle size of the fine glass is preferably set in the range of 70 to 100 μm. On the other hand, the coarse glass has a particle size of 100 μm.
If it is less than the above range, the particles are likely to be softened or melted during hot pressing, and the above-mentioned block structure is impaired, so that a good effect of preventing radio wave noise is not achieved. If the particle size exceeds 800 μm, voids are likely to remain between the glass particles, which leads to impaired load life characteristics of the plug.

If the ratio Wf / Wc of the weight Wf of fine glass to the weight Wc of coarse glass is less than 2/98, the glass hardly melts during hot pressing and a large amount of voids are formed between the glass particles. As a result, the load life characteristic of the plug is impaired. On the other hand, when Wf / Wc exceeds 50/50, the content ratio of the block particles decreases, the formation of the block structure becomes insufficient, and the good effect of preventing radio wave noise cannot be achieved. Note that Wf / Wc is preferably 2
It is preferable to set it in the range of / 98 to 10/90.

Next, when coarse-grained glass having a particle size distribution deviating from the above-mentioned one is used, the fluidity and filling property of the raw material powder are deteriorated, and the density of the molded product is apt to be nonuniform or uneven. There arises a problem that the resistance value of the resistor varies or the load life characteristic of the plug becomes unstable. The particle size distribution is more preferably 100 to 2 in the particle size range.
The content ratio of powder particles belonging to 48 μm is 20 to 40% by weight, the content ratio of powder particles belonging to particle size range 248 to 352 μm is 15 to 25% by weight, particle size range 352 to 800 μm.
It is preferable to set the content ratio of the powder particles belonging to m to be 45 to 55% by weight.

The glass powder is specifically B ₂ O ₃ --SiO _2.
2 system, BaO-B ₂ O _{3 based, SiO 2 -B 2 O 3 -CaO} -B
It is possible to use one containing at least one of aO-based and SiO ₂ —ZnO—B ₂ O ₃ -based glass powders. In this case, by using a material having a softening temperature of 800 ° C. or lower, the fluidity of the glass at the time of melting is increased,
The bonded glass phase spreads sufficiently into the gaps between the block particles, making it difficult to form gaps or the like. As a result, the load life characteristics of the plug are improved. Here, the softening temperature of the glass is
It means the temperature at which the viscosity is 4.5 × 10 ⁷ poise. If the softening temperature is lower than 300 ° C., the heat resistance of the resistor is impaired, so the softening temperature is 300 to 8
It is preferable to use glass at 00 ° C, more preferably 600 to 800 ° C. In addition, with coarse grain glass and fine grain glass,
The glass material may be different.

Further, more specifically, it is desirable to use a glass powder having a difference between the softening temperature of fine glass and the softening temperature of coarse glass of 100 ° C. or less. That is, it is desirable that | TC−TF | ≦ 100 ° C. when the softening temperatures of the fine glass and the coarse glass are respectively TC and TF. In this case, even if TC> TF, T
Either C <TF or both may be used. The reason will be described below. First, the fine-grained glass and the coarse-grained glass have the property that the former is more likely to be deformed during hot pressing than the latter, even if the viscosity is the same. And
In the case of TC> TF, if | TC−TF | ≦ 100 ° C., even if the softening temperature of the fine glass is slightly higher than that of the coarse glass,
The fine glass is sufficiently deformed by the pressure at the time of hot pressing and fills the gaps between the coarse glass, so that the load life characteristics of the plug are maintained good. However, | TC-TF |> 10
When it reaches 0 ° C., the deformation of the fine glass particles becomes insufficient, a gap is formed between the coarse glass particles, and the load life characteristics deteriorate.
On the other hand, in the case of TC <TF, the fine glass particles are more likely to be deformed and gaps are less likely to be formed.
If −TF│> 100 ° C., the viscosity of the glass becomes too low, and there is a concern that the glass may flow into unnecessary portions such as the gap between the center electrode and the insulator. ｜ TC
−TF | is preferably 50 ° C. or lower.

Next, as the conductive material powder, one containing at least either carbon black or graphite powder can be used. As the conductive material powder, one having a particle diameter smaller than that of fine glass can be used, and in the production of the resistor, fine glass particles are used in the form of a composite powder covered with particles of the conductive material powder. be able to. In this case, the compounding ratio of the composite powder in the resistor is preferably adjusted in the range of 10 to 40% by weight. When the content of the composite powder is less than 10% by weight, the absolute amount of the conductive material powder becomes insufficient, and as a result, the continuous portion of the bonded glass phase, that is, the conductive path is divided by the welding of the coarse-grained glasses to each other, and The electrical resistivity increases and the plug does not work properly. On the other hand, if it exceeds 40% by weight, the bound glass phase becomes insufficient, and a gap is apt to be formed between the block particles, so that the load life characteristic of the plug is deteriorated.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some 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 FIG. 1 has a tubular metal shell 1, an insulator 2 fitted in the metal shell 1 so that a tip portion 21 projects, and an ignition part 31 in a projected state. The center electrode 3 provided inside the insulator 2 and the ground electrode 4 and the like, one end of which is coupled to the metal shell 1 and arranged to face the side surface of the ignition part 31 (center electrode 3), are provided. Ground electrode 4
Is formed by bending so that its front end face 21 faces the side surface of the ignition part 31 substantially in parallel, and a spark gap g is formed between the tip surface 21 and the outer surface of the ignition part 31. On the other hand, the base end side of the ground electrode 4 is fixed and integrated with the metal shell 1 by welding or the like. Further, the metal shell 1 is formed of carbon steel or the like, and as shown in FIG. 1, a screw portion 12 for attachment to an engine is formed on the outer peripheral surface of the ignition portion 31 side. The center electrode 3 is made of Ni alloy or the like. Furthermore, the insulator 2 is made of a ceramics sintered body such as alumina.

A through hole 2a is formed in the insulator 2 in the axial direction, and a terminal fitting 13 is fixed to one end of the through hole 2a and the other end is also provided. Has the center electrode 3 fixed. A resistor 15 is arranged between the terminal fitting 13 and the center electrode 3 in the through hole 2a. Both ends of the resistor 15 are electrically connected to the terminal fitting 13 and the center electrode 3 via the conductive glass layers 16 and 17, respectively.

The resistor 15 is formed as a sintered body obtained by mixing glass powder and conductive material powder and sintering by hot pressing or the like. The glass powder is composed of fine glass particles having a particle diameter of 100 μm or less and a particle diameter. 100 to 800 μm of coarse glass is contained, and the ratio Wf / Wc between the weight Wf of the fine glass and the weight Wc of the coarse glass is set in the range of 2/98 to 50/50. And, when the particle size distribution of the coarse glass is 100% by weight of the total amount of the coarse glass,
The content ratio of the powder particles belonging to the particle size range 100 to 248 μm is 10 to 60% by weight, the content ratio of the powder particles belonging to the particle size range 248 to 352 μm is 10 to 60% by weight, and the powder particles belonging to the particle size range 352 to 800 μm Content ratio is 1
It is set to 0 to 50% by weight. The glass powder is, for example, B
₂ O ₃ -SiO ₂ system, BaO-B ₂ O ₃ based, SiO ₂ -B ₂ O ₃
One containing at least one of each of —CaO—BaO based and SiO ₂ —ZnO—B ₂ O ₃ based glass powders and having a softening temperature in the range of 300 to 800 ° C. is used. The conductive material powder is composed of, for example, carbon black. The structure of the resistor 15 is as already described in FIG.

[0017]

EXAMPLE A glass powder and carbon black as a conductive material were blended in a predetermined amount and wet mixed, and then dried to prepare a raw material powder. Next, this was hot-press molded into a predetermined shape to form a resistor, and various plugs shown in FIG. 1 were prepared using this resistor. The glass powder used was a mixture of fine glass powder and coarse glass powder in various proportions. Among them, the fine glass powder has a particle size of 100 μm or less, and the coarse glass powder is A shown in Table 1,
Those having particle size distributions of B, C and D were used (Fig. 3
Is a graph of those particle size distributions). Table 3
Shows the mixing ratio of the fine glass powder and the coarse glass powder in the resistor of each plug, and the particle size distribution of the adopted coarse glass powder (however, those marked with * are those of the present invention. It is out of range). Also,
Table 2 shows the composition and softening point of the glass powder used (~). Of these, sample numbers 1 to 10 and 1 in Table 3
In the plugs 3 to 16, both fine-grain glass and coarse-grain glass were used. Further, in the 11 plug, fine glass was used as glass and coarse glass was used as glass. Further, in the 12 plugs, fine glass was used as glass and coarse glass was used as glass.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

The following evaluations were made for each of the above plugs. (1) Fillability The resistor of each plug was cut in the axial direction, the cross section was observed using a scanning electron microscope, and the judgment was made according to the following four stages. ⊚: No holes (gaps) are observed in the bonded glass phase. ◯: Porosity is hardly observed in the bonded glass phase. Δ: A few holes are observed in the bonded glass phase. X: Many pores are observed in the bonded glass phase.

(2) Variation in resistance value Each of 50 plugs is prepared, the resistance value between the terminal metal fitting and the metal shell (that is, the resistance value of the resistor in the conduction direction) is measured, and the measured value Judgment was carried out in the following four stages according to the value of 3σ where the standard deviation is σ. ⊚: 3σ <0.6 (very uniform resistance values). Good: 0.6 ≦ 3σ <1.2 (resistance values are uniform). Δ: 1.2 ≦ 3σ <1.8 (resistance value is slightly varied). X: 3σ ≧ 1.8 (large variation in resistance value).

(3) Load life A load life test of each plug was conducted by the method specified in 6.10 of Japanese Industrial Standard B8031, and the following 4 was obtained according to the resistance change rate ΔR after the test with respect to the resistance value before the test. The grade was evaluated. ⊚: ΔR is within ± 15%. ◯: ΔR is within ± 25%. Δ: ΔR is within ± 30%. X: ΔR exceeds ± 30%.

Table 3 shows the above evaluation results. That is,
It can be seen that, with regard to the plug using the resistor satisfying the conditions of the present invention, good results are obtained with respect to all evaluation items such as filling property, resistance value variation and load life.

[Brief description of drawings]

FIG. 1 is a front partial cross-sectional view showing an example of a spark plug of the present invention.

FIG. 2 is a schematic diagram showing the structure of a resistor.

FIG. 3 is a graph showing a particle size distribution of coarse glass used in Examples.

[Explanation of symbols]

 1 metal shell 2 insulator 2a through hole 3 center electrode 4 ground electrode 15 resistor 100 spark plug

Claims (6)

[Claims] 1. A terminal metal fitting is fixed to one end of the through hole formed in the axial direction of the insulator, and a center electrode is fixed to the other end of the through hole. A resistor is disposed between the terminal metal fitting and the center electrode, and the resistor is configured as a sintered body obtained by mixing and sintering glass powder and a conductive material powder, and the glass powder is It contains fine glass having a particle size of 100 μm or less and coarse glass having a particle size of 100 to 800 μm, and the ratio Wf / Wc of the weight Wf of the fine glass and the weight Wc of the coarse glass is 2/98 to 50/50. And the particle size distribution of the coarse glass is 100 to 24% when the total amount of the coarse glass is 100% by weight.
The content ratio of the powder particles belonging to 8 μm is 10 to 60% by weight, the content ratio of the powder particles belonging to particle size range 248 to 352 μm is 10 to 60% by weight, the particle size range 352 to 800 μm.
A spark plug characterized in that the content ratio of the powder particles belonging to m is 10 to 50% by weight. 2. A glass phase (hereinafter, referred to as a resistor) formed by melting and solidifying at least a part of the fine glass particles and dispersing the particles of the conductive material powder.
The bonded glass phase) has a structure surrounding glass particles (hereinafter, referred to as block particles) derived from the coarse glass powder, and at least a part of the bonded glass phase is reached by the interposition of the block particles. While forming a detour, a continuous portion is formed from the end portion side on the terminal metal fitting side to the end portion on the center electrode side, and this continuous portion makes electrical contact between particles of the conductive material powder. The spark plug according to claim 1, wherein a conductive path of the resistor is formed based on the above. 3. The glass powder is B ₂ O ₃ —SiO _2.
2 system, BaO-B ₂ O _{3 based, SiO 2 -B 2 O 3 -CaO} -B
The spark plug according to claim 1 or 2, containing at least one of aO-based and SiO ₂ -ZnO-B ₂ O ₃ -based glass powders. 4. The softening temperature of the glass powder is 30.
The spark plug according to claim 3, wherein a spark plug having a temperature of 0 to 800 ° C is used. 5. The glass powder has a difference of 100 ° C. between the softening temperature of the fine glass and the softening temperature of the coarse glass.
The spark plug according to claim 4, wherein the following is used. 6. The spark plug according to claim 1, wherein the conductive material powder contains at least one of carbon black and graphite powder.