JP6885815B2 - Resistor and spark plug with it - Google Patents

Description

The present invention relates to, for example, a resistor used in a high temperature environment and a spark plug provided with the resistor.

A spark plug for an internal combustion engine is attached to an internal combustion engine (engine) and is used for igniting an air-fuel mixture in a combustion chamber. Generally, the spark plug is provided on the outer periphery of an insulator having a shaft hole, a center electrode inserted on the tip end side of the shaft hole, a terminal electrode inserted on the rear end side of the shaft hole, and an insulator. It is provided with a main metal fitting and a ground electrode provided on the tip surface of the main metal fitting and forming a spark discharge gap between the main metal fitting and the center electrode. Further, in the shaft hole, between the center electrode and the terminal electrode, a resistor for suppressing radio wave noise (noise) generated by the operation of the engine is provided, and both electrodes are provided via the resistor. Are electrically connected (see, for example, Patent Document 1 and the like).

Here, the resistor described in Patent Document 1 has glass particles as a main component, and has a structure in which an electric conduction path by carbon black is provided between the glass particles.

International Publication No. 2009/154070

In recent years, due to the shortening / diameter reduction of spark plugs, there is a restriction that a resistor is placed near the combustion chamber. However, in the above resistor, the glass particles soften or melt in a high temperature environment. There was a problem with heat resistance.

Therefore, if the resistor is configured to have ceramic particles such as alumina as the main component, the bond between the ceramic particles and carbon is weak, and due to repeated application of a high voltage at a high temperature, micro between the ceramic particles and carbon. There was a risk that cracks would occur, the resistance value would increase, and the noise suppression effect would decrease.

It is an object of the present disclosure to provide a resistor capable of suppressing an increase in resistance value for a long period of time in a high temperature environment, and a spark plug provided with the resistor.

The resistor of the present disclosure is characterized by containing a plurality of alumina particles and comprising a sintered body having carbon aggregates and sialon particles at least a part of the grain boundaries of the plurality of alumina particles.

Further, the spark plug of the present disclosure includes a center electrode on the front end side, a terminal electrode on the rear end side, and the above-mentioned resistor arranged between the center electrode and the terminal electrode.

According to the resistor of the present disclosure, an increase in resistance value can be suppressed for a long period of time in a high temperature environment. Further, according to the spark plug of the present disclosure, since the resistor can suppress the increase in the resistance value for a long period of time, the ignition efficiency can be improved for a long period of time.

(A) is a schematic perspective view showing an example of an embodiment of a resistor, and (b) is a schematic view of an enlarged cross section of a main part of an example of a resistor shown in (a). It is the schematic of the main part enlarged cross section of another example of a resistor. It is a schematic vertical sectional view of the spark plug using a resistor.

Hereinafter, an example of the embodiment of the resistor will be described in detail with reference to the drawings.

FIG. 1A is a schematic perspective view showing an example of an embodiment of a resistor, and FIG. 1B is a schematic view of an enlarged cross section of a main part of an example of a resistor shown in FIG. 1A.

The resistor 10 shown in FIG. 1 is composed of a sintered body containing a plurality of alumina particles 1 and having carbon aggregates 2 and sialon particles 3 at least a part of the grain boundaries of the plurality of alumina particles 1.

The resistor 10 is a polycrystalline sintered body containing a plurality of alumina particles 1. Alumina is an oxide ceramic that has excellent thermal shock and can be used even at high temperatures. Since the phase transformation does not occur even if the temperature rises, the volume does not change suddenly, and the valence of the metal ion does not change, so that the reaction with the surrounding metal components does not occur, and the resistor 10 is stable for a long period of time. Contributes to functioning as.

As described above, by forming the resistor 10 from a polycrystalline sintered body (polycrystalline body) containing a large amount of a plurality of alumina particles 1 as a main component, the resistor 10 is softened as compared with a resistor containing glass particles as a main component. It can be made to have excellent heat resistance without melting or melting.

Further, the resistor 10 has carbon aggregates 2 and sialon particles 3 (SiAlON particles) at least a part of the grain boundaries of the plurality of alumina particles 1.

When carbon black is provided at the grain boundaries of a plurality of alumina particles, the resistance value of the resistor is increased due to an increase in lattice vibration due to a temperature rise and an increase in the resistance value of carbon black due to a temperature rise (temperature dependence). Tends to be too high. On the other hand, in order to keep the resistance value of the resistor low even when the temperature rises, the content of carbon black, which is a conductive material, is increased with respect to the amount of the raw material powder of the insulating alumina particles, and the mixing ratio is adjusted. There are ways to change it. However, according to this method, the strength of the resistor is lowered, and the difference in thermal expansion between the alumina particles and the carbon black may cause cracks and sparks between them.

On the other hand, the resistor 10 of the present disclosure has a carbon aggregate 2 at least a part of the grain boundaries of the plurality of alumina particles 1. The carbon aggregate 2 extends continuously at least linearly along the particles of the plurality of alumina particles 1, for example. Here, the carbon agglomerates 2 extending continuously in a linear shape refer to a filamentous body, a fibrous body, a tubular body, or the like formed by bonding carbons like a mesh. The carbon agglomerates 2 include a structure in which a plurality of linear (filamentous) bodies are intricately entwined, a shape that continuously extends in a shape (strip shape) that spreads in the width direction, and a shape (membrane) that spreads over a wide range. It may have a shape that extends continuously in a shape). Further, the carbon agglomerates 2 may extend continuously in a three-dimensional network. According to this configuration, even if a plurality of ceramic particles 1 constituting a polycrystal are repeatedly thermally expanded and contracted due to a change in ambient temperature, the carbon agglomerates 2 are entangled with the ceramic particles 1 to maintain adhesion. it can. As the carbon aggregate 2, carbon nanotubes can be preferably used.

Unlike carbon black, the carbon aggregate 2 having such a structure has a property that the resistance value is maintained or decreased as the temperature rises. Therefore, in the resistor 10, an increase in the resistance value due to temperature dependence is suppressed, and rather, the resistance value tends to decrease at a high temperature. Further, the resistor 10 can realize a low resistance value even if the amount is smaller than that of carbon black.

Further, the resistor 10 of the present disclosure has sialon particles 3 (SiAlON particles) at least a part between the particles (grain boundaries) of the plurality of alumina particles 1. The sialon particles 3 are present at the grain boundaries of the alumina particles 1 together with the carbon aggregates 2, and are in contact with the alumina particles 1 and the carbon aggregates 2.

The bond between the alumina particles 1 and the carbon aggregate 2 tends to be weak. _{On the other hand, the sialon particles 3 are bonded to the alumina particles 1 (Al 2} O ₃ ) by aluminum (Al) and oxygen (O), and are bonded to the carbon aggregate 2 (C) by silicon (Si). As a result, the bond between the alumina particles 1 and the carbon aggregate 2 is strengthened, microcracks are less likely to occur, and the resistance value is stabilized. Therefore, it is possible to realize the resistor 10 which can suppress the increase in the resistance value for a long period of time in a high temperature environment and can maintain the noise suppression effect.

The ratio of the plurality of alumina particles 1, the carbon agglomerates 2, and the sialon particles 3 contains the largest amount of the alumina particles 1, for example, the alumina particles 1 are 40 to 80% by volume, and the carbon agglomerates 2 are. 1 to 40% by volume and 0.1 to 25% by volume of sialon particles 3. This ratio can be measured, for example, using an electron probe microanalyzer (EPMA) or an X-ray diffractometer (XRD).

Here, the resistor 10 may have glass in an amount of about 5% by volume or less between the particles (grain boundaries) of the plurality of alumina particles 1 together with the carbon aggregates 2 and the sialon particles 3. Since glass can be softened at a high temperature to reduce the stress of thermal shock, the presence of glass can stably maintain the noise suppression effect for a long period of time.

Further, for the same reason, there may be voids 4 of about 5% by volume or less between the particles (grain boundaries) of the plurality of alumina particles 1.

Further, as shown in FIG. 2, the resistor 10 has a grain boundary having the sialon particle 3 and a grain boundary not having the sialon particle 3 among the grain boundaries of the plurality of alumina particles 1. There may be an alumina particle 1 facing the grain boundary having the grain boundary and an alumina particle 1 having a particle size larger than that of the alumina particle 1 and not facing the grain boundary having the sialon particle 3. For example, the particle size of the alumina particles 1 facing the grain boundaries having the sialon particles 3 is, for example, 2 μm or more, and the particle size of the alumina particles 1 facing the grain boundaries having the sialon particles 3 is, for example, 1 μm or less.

Here, the alumina particles 1 facing the grain boundaries having the sialon particles 3 are the alumina particles 1 in which the sialon particles 3 are present at at least one of the grain boundaries around the alumina particles 1 in terms of cross section. Means that. Further, the alumina particles 1 having the sialon particles 3 and not facing the grain boundaries mean that the sialon particles 3 do not exist at the grain boundaries around the alumina particles 1 when viewed in cross section.

The alumina particles 1 facing the grain boundaries having the sialon particles 3 tend to have smaller grain sizes due to suppressed grain growth than the alumina particles 1 having the sialon particles 3 not facing the grain boundaries. The larger the number of alumina particles 1 having a small particle size, the easier it is to disperse the stress of thermal shock and the less likely it is that microcracks will occur. Further, due to the presence of the alumina particles 1 having a large particle size and the alumina particles 1 having a small particle size, even if cracks occur, they are more resistant to fracture due to the deflection and the pinning effect of the coarse particles.

Further, although not shown, a large amount of sialon particles 3 may be distributed on the surface of the sintered body. On the surface of the sintered body, the bond between the alumina particles 1 and the carbon aggregate 2 is particularly strengthened. Further, since the Sialon particles 3 have a small coefficient of thermal expansion, compressive stress is likely to occur on the surface of the sintered body. Therefore, microcracks are less likely to occur on the surface of the sintered body. Here, the surface of the sintered body means a region within 10% from the end in the cross section of the sintered body. Whether or not a large amount of sialon particles 3 are distributed on the surface of the sintered body can be determined by analyzing the cross section of the sintered body with an electron probe microanalyzer (EPMA) and observing the distribution of Si and N. ..

Further, the alumina particles 1 may be distributed on the surface of the sintered body so that the particle size is smaller than that inside. Here, when the particle size of the alumina particles 1 inside the sintered body is, for example, 1 to 10 μm, the particle size of the alumina particles 1 on the surface of the sintered body is the alumina particles 1 inside the sintered body. For example, it is 0.01 to 0.5 times the particle size of. As a result, breakage is less likely to occur on the surface of the sintered body, and stress is dispersed throughout the sintered body.

Further, the sialon particles 3 are preferably smaller than the alumina particles 1. Whether or not it has such a configuration is compared by calculating the average particle size of the same number of particles as viewed from a scanning electron microscope (SEM) or transmission electron microscope (TEM) image of an arbitrary cross section. By doing so, it can be determined. The carbon aggregates 2 can be continuously present at the grain boundaries of the alumina particles 1, and the sialon particles 3 can be dispersed and present. Therefore, the bond between the alumina particles 1 and the carbon aggregate 2 can be further strengthened. Further, even if microcracks occur, their progress can be suppressed.

Next, an example of the method for manufacturing the resistor 10 described above will be described.

First, a phenol resin dissolved in a solvent such as toluene or methyl ethyl ketone and dispersed as a colloid having a particle size of about 10 nm is used as a precursor of carbon aggregate 2. Here, the phenol resin is soluble in a solvent and can be added and dispersed in the ceramic raw material powder uniformly, and the carbon aggregate 2 after firing can be at least a filamentous (linear) structure. .. As the precursor of the carbon aggregate 2, in addition to the phenol resin, a filamentous or fibrous carbon source such as carbon nanotubes can be used alone or in combination as the second precursor. In other words, instead of part or all of the precursor of carbon agglomerates 2, carbon nanotube powder can be added in advance as a second precursor.

Next, the alumina raw material powder, a raw material powder of sialon (SiAlON) or silicon nitride _(Si 3 _{N 4), CaO} of sintering aid, and _{SiO 2, ZnO, TiO 2,} ZrO 2 or the like, for example polyvinyl alcohol , Paraffin wax, acrylic resin and other binders are mixed with the precursor and / or the second precursor, dried and pressed, and then fired at 1450 ° C to 1650 ° C. At this time, in order to prevent carbon from reacting with surrounding oxygen and volatilizing, it is buried with carbon powder in a forming gas (mixed gas of hydrogen and nitrogen) atmosphere. The precursor and the second precursor are mixed at a ratio of, for example, 1 to 20% by mass with respect to 100% by mass of the alumina raw material powder.

Here, the precursor does not diffuse into the alumina particles 1, but proceeds with sintering while clinging linearly (filamentally or fibrously) between the particles of the alumina particles 1 together with the surrounding liquid phase components. As a result, a carbon agglomerate 2 extending at least linearly and continuously along the particles of the alumina particles 1 can be formed, and a sintered body having the sialon particles 3 between the particles of the alumina particles 1 can be obtained. ..

In order to form the carbon aggregate 2 into a film, it is preferable to bake it so that the colloid becomes a carbon film and the keep time at the maximum temperature is set to 1 hour or less so as to suppress the crystal growth of alumina. Further, in order to form a three-dimensional network structure, it is preferable to cool the carbon film within 3 hours in order to apply stress (the film-like carbon aggregate 2 is torn to form a network). It should be noted that some devices and equipment are not limited to this. For example, the alumina raw material powder coated with colloid surface, and the raw material powder of sialon (SiAlON) or silicon nitride (Si 3 _{N 4),} and sintering aid, and a binder are mixed, may be fired.

Further, in order to obtain a sintered body in which a large amount of sialon particles 3 are distributed on the surface, the sialon particles 3 may be coated or impregnated in a slurry form on the surface of the molded product before firing.

Further, to sialon particles 3 smaller configuration than alumina particles 1 may be used a raw material powder of alumina raw material powder particle size less than sialon (SiAlON) or silicon nitride (Si 3 _{N 4).}

Next, the spark plug of the present disclosure will be described.

The spark plug 20 shown in FIG. 3 includes a center electrode 21 on the front end side, a terminal electrode and 22 on the rear end side, and the above-mentioned resistor 10 arranged between the center electrode 21 and the terminal electrode 22. ..

Specifically, in the form shown in FIG. 3, the center electrode 21 is inserted and fixed to the tip end side of the shaft hole of the spark plug 20. More specifically, at the rear end portion of the center electrode 21, a bulging portion 211 that bulges toward its outer peripheral direction is formed, and the bulging portion 211 engages with the stepped portion of the shaft hole. The center electrode 21 is fixed in the stopped state. The center electrode 21 is composed of an inner layer made of copper or a copper alloy and an outer layer made of a Ni alloy containing nickel (Ni) as a main component. Further, the center electrode 21 has a rod shape (cylindrical shape) as a whole, the tip surface thereof is formed flat, and the center electrode 21 protrudes from the tip of the insulator 23.

Further, the terminal electrode 22 is inserted and fixed to the rear end side (large diameter portion) of the shaft hole in a state of protruding from the rear end of the insulating insulator 23.

Further, a columnar resistor 10 is arranged between the center electrode 21 of the shaft hole (large diameter portion) and the terminal electrode 22. Both ends of the resistor 10 are electrically connected to the center electrode 21 and the terminal electrode 22 via a conductive glass seal layer.

In addition, the main metal fitting 24 is formed of a metal such as low carbon steel in a tubular shape, and a threaded portion (male threaded portion) 241 for attaching the spark plug 20 to the engine head is formed on the outer peripheral surface thereof. .. Further, a seat portion 242 is formed on the outer peripheral surface on the rear end side of the screw portion 241. Further, on the rear end side of the main metal fitting 24, a tool engaging portion 243 having a hexagonal cross section for engaging a tool such as a wrench when attaching the main metal fitting 24 to the engine head is provided, and at the rear end portion. A crimping portion 244 for holding the insulating insulator 23 is provided.

Further, a tapered step portion 245 for locking the insulating insulator 23 is provided on the inner peripheral surface of the main metal fitting 24. Then, the insulating insulator 23 is inserted from the rear end side to the tip end side of the main metal fitting, and is fixed in a state where its own step portion 231 is locked to the step portion 245 of the main metal fitting 24.

An annular plate packing (not shown) is provided on both the insulating insulator 23 and the main metal fitting 24.
Is intervened. As a result, the airtightness of the combustion chamber is maintained, and the fuel air that enters the gap between the leg length portion 232 of the insulating insulator 23 exposed to the combustion chamber and the inner peripheral surface of the main metal fitting 24 is prevented from leaking to the outside. Further, in order to make the sealing by crimping more complete, on the rear end side of the main metal fitting 24, an annular ring member 26 is interposed between the main metal fitting 24 and the insulating insulator 23, and the ring member 26 is provided between the ring members 26. Is filled with talc 27 powder. That is, the main metal fitting 24 holds the insulating insulator 23 via a plate packing (not shown), a ring member 26, and a talc 27.

Further, a ground electrode 25 made of a nickel (Ni) alloy is bonded to the tip surface of the main metal fitting 24. That is, the ground electrode 25 is arranged so that the rear end portion is welded to the tip end surface of the main metal fitting 24, the tip end side is bent back, and the side surface thereof faces the tip end portion of the center electrode 21.

In addition, a columnar noble metal chip 212 made of a noble metal alloy (for example, platinum alloy, iridium alloy, etc.) is bonded to the tip surface of the center electrode 21. Further, a columnar noble metal chip 251 is bonded to the surface of the ground electrode 25 facing the noble metal chip. A spark discharge gap is formed between the tip of the noble metal chip 212 and the tip of the noble metal chip 251.

According to the spark plug 20 having such a configuration, the above-mentioned resistor is used, and the resistor can suppress an increase in the resistance value for a long period of time and can maintain the noise suppression effect. The ignition efficiency can be improved over a long period of time.

Hereinafter, examples will be described.

First, a resistor for a spark plug was prepared. To that of carbon nanotubes as phenolic resin and the second precursor as a precursor dispersed in a solvent, and the alumina raw material powder, a raw material powder of sialon (SiAlON) or silicon nitride (Si 3 _{N 4),} baked The aid and the binder were mixed, dried, pressed and then fired at 1450 ° C to 1650 ° C. At this time, the sample No. was buried in carbon powder so that the carbon would not react with the surrounding oxygen and volatilize. 1-No. 8 resistors were made.

Here, the sample No. 1-No. Regarding 5, a precursor (phenol resin) and a second precursor (carbon nanotube) dispersed in a solvent, an alumina raw material powder, a raw material powder of Sialon (SiAlON), a sintering aid, and the like. It was mixed with a binder and fired.

In addition, sample No. Regarding 6 to 8, a precursor (phenol resin) and a second precursor (carbon nanotube) dispersed in a solvent, an alumina raw material powder, and a silicon nitride (Si ₃ N ₄ ) raw material powder were used. The sintering aid and the binder were mixed and fired.

In each sample (Samples No. 1 to No. 8), the amount of the raw material powder of Sialon (SiAlON) or the raw material powder of silicon nitride (Si ₃ N ₄ ) added was different with respect to 100 parts by mass of the raw material powder of alumina. I prepared a sample. The amounts of the precursor and the second precursor added to 100 parts by mass of the alumina raw material powder in each sample were 5% phenol resin and 5% carbon nanotubes.

Then, in the sintered resistor (each sample), it is confirmed by electron probe microanalyzer (EPMA) and X-ray that at least a part of the grain boundaries of the plurality of alumina particles contains carbon aggregates and sialon particles. Confirmation was performed using a diffractometer (XRD).

In addition, the amount of sialone in each sample was measured using an X-ray diffractometer (XRD).

In addition, the resistance value of each sample was measured using a digital multimeter. Further, a spark plug using a resistor of each sample was prepared, and a load life test was conducted by a method specified in 6.10 of Japanese Industrial Standard B8031 to evaluate the load life (long-term stability). The load life (long-term stability) was evaluated in the following four stages based on the resistance change rate ΔR of the resistance value after the test with respect to the resistance value before the test.
⊚: ΔR is within ± 15%.
◯: ΔR is within ± 25%.
Δ: ΔR is within ± 30%.
X: ΔR exceeds ± 30%.

The results are shown in Table 1.

According to Table 1, in any of the samples, the resistance value does not increase due to the temperature rise, but rather decreases, and a practical resistor within the range of 0.1 to 10 kΩ can be prepared at 1000 ° C. You can see that. From this, it can be seen that the resistor of the present disclosure has excellent heat resistance and can suppress an increase in resistance value for a long period of time in a high temperature environment.

Although not shown in the table, in the sample to which carbon black was added as a conductor component, the resistance value at 1000 ° C. was 1 MΩ or more even when the addition ratio was 10%. Furthermore, even if the amount of carbon black added to the ceramic powder was increased to lower the resistance value of the resistor, the resistance value was 1 MΩ or more, and the ratio of carbon black in the resistor increased and the strength decreased. As a result, cracks were generated as soon as the load was applied, resulting in sparks.

10: Resistor 1: Alumina particles 2: Carbon agglomerates 3: Sialon particles 20: Spark plug 21: Center electrode 211: Swelling part 212: Precious metal chip 22: Terminal electrode 23: Insulator 231: Step part 232: Leg length part 24: Main metal fitting 241: Threaded part (male threaded part)
242: Seat 243: Tool engaging part 244: Clamping part 245: Step part 25: Ground electrode 26: Ring member 27: Talc

Claims (6)

A resistor containing a plurality of alumina particles and comprising a sintered body having carbon aggregates and sialon particles in at least a part of the grain boundaries of the plurality of alumina particles. The resistor according to claim 1, wherein the resistor has glass at the grain boundaries of the plurality of alumina particles. The resistor according to claim 1 or 2, wherein the carbon aggregate is a carbon nanotube. Among the grain boundaries of the plurality of alumina particles, there are grain boundaries having the sialon particles and grain boundaries not having the sialon particles.
The alumina particles facing the grain boundaries having the sialon particles and the alumina particles having a larger particle size than the alumina particles and not facing the grain boundaries having the sialon particles are present. The resistor according to any one of claims 1 to 3. The resistor according to any one of claims 1 to 4 , wherein the sialon particles are smaller than the alumina particles. The resistor according to any one of claims 1 to 5 , which is provided with a center electrode on the front end side, a terminal electrode on the rear end side, and a resistor arranged between the center electrode and the terminal electrode. A spark plug characterized by being present.

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