JP2018073778A - Resistor and spark plug including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resistor excellent in heat resistance and capable of suppressing an increase in resistance value even in a high temperature environment and a spark plug including the same.SOLUTION: A resistor 10 includes: a plurality of ceramic particles 11; and a polycrystalline body having carbon aggregates 2 extending at least linearly along spaces between the particles of the plurality of ceramic particles 11. This makes it possible to realize a resistor excellent in heat resistance and capable of suppressing an increase in a resistance value even in a high temperature environment.SELECTED DRAWING: Figure 1

Description

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

  A spark plug for an internal combustion engine is attached to an internal combustion engine (engine) and used for ignition of an air-fuel mixture in a combustion chamber. Generally, a spark plug is provided on the outer periphery of an insulator having an axial hole, a center electrode inserted through the front end of the axial hole, a terminal electrode inserted through the rear end of the axial hole, and the insulator. The metal shell includes a metal shell and a ground electrode that is provided on the front end surface of the metal shell and forms a spark discharge gap with the center electrode. In addition, a resistor is provided in the shaft hole between the center electrode and the terminal electrode to suppress radio noise (noise) generated with the operation of the engine, and both electrodes are connected via the resistor. Are electrically connected (see, for example, Patent Document 1).

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

International Publication No. 2009/154070

  In recent years, spark plugs have become shorter / smaller and there are restrictions on the placement of resistors near the combustion chamber, and the combustion temperature rises due to lean burn, leading to further heat resistance and noise suppression at high temperatures. An effect is sought.

  Conventional resistors have a problem in heat resistance because glass particles soften or melt in a high temperature environment.

  Further, in the conventional resistor, the resistance value of carbon black tends to increase as the temperature rises (temperature dependency). If such a resistor is used for a spark plug, the resistance value becomes too high. There are problems that the effect of noise reduction becomes small and the ignition efficiency decreases.

  The resistor of the present disclosure has been made in view of the above circumstances, and provides a resistor that is excellent in heat resistance and can suppress an increase in resistance value due to a temperature rise, and a spark plug including the resistor. Objective.

  The resistor according to the present disclosure includes a polycrystalline body having a plurality of ceramic particles and a carbon aggregate extending continuously at least linearly along the particles of the plurality of ceramic particles.

  The spark plug according to the present disclosure includes a center electrode on the front end side, a terminal electrode on the rear end side, and the resistor disposed between the center electrode and the terminal electrode.

  According to the resistor of the present disclosure, heat resistance is excellent, and an increase in resistance value accompanying a temperature increase can be suppressed. Moreover, according to the spark plug provided with this resistor, since the resistance value increase of the resistor is suppressed even when the temperature rises, the effect of noise removal can be maintained and the ignition efficiency can be improved.

(A) is a principal part expanded sectional view which shows an example of embodiment of a resistor, (b) is an enlarged view of an example of the carbon aggregate shown to (a), (c) is a carbon aggregate shown to (a). It is an enlarged view of another example. It is an enlarged view of an example of a carbon aggregate. It is a principal part expanded sectional view which shows the other example of embodiment of a resistor. It is a principal part expanded sectional view which shows the other example of embodiment of a resistor. It is a longitudinal cross-sectional view of the spark plug using a resistor.

  Hereinafter, an exemplary embodiment of a resistor according to the present disclosure will be described in detail with reference to the drawings.

  1A is an enlarged cross-sectional view of a main part showing an example of an embodiment of a resistor, FIG. 1B is an enlarged view of the carbon aggregate shown in FIG. 1A, and FIG. It is an enlarged view of the other example of the carbon aggregate shown to a).

  A resistor 10 according to the present disclosure shown in FIG. 1 includes a plurality of ceramic particles 1 and a carbon aggregate 2 continuously extending at least linearly along the particles of the plurality of ceramic particles 1. Is included.

  The resistor 10 is a polycrystalline body having a plurality of ceramic particles 1. Examples of the plurality of ceramic particles 1 constituting the polycrystal include oxide ceramics such as alumina, zirconia, zircon, and mullite. In particular, alumina is an oxide that has excellent thermal shock and can be used even at high temperatures. Since the phase transformation does not occur even when the temperature rises, a sudden volume change does not occur, and the valence of the metal ion does not change. Therefore, the reaction with the surrounding metal component does not occur, and the resistor 10 is stably stable for a long time. It contributes to function as.

  Thus, by comprising the resistor 10 with the oxide ceramic polycrystal, it is superior in heat resistance without being softened or melted compared to a resistor mainly composed of glass particles. can do.

  And the resistor 10 which comprises a polycrystal body has the carbon aggregate 2 extended continuously at least linearly along the particle | grains of several ceramic particle | grains 1. As shown in FIG.

  In the vicinity of the surface of the polycrystal body having a plurality of ceramic particles 1, free electrons are generated because the crystal lattice is disordered or non-stoichiometric. Therefore, the movement of free electrons between adjacent ceramic particles is restricted.

  Therefore, it is necessary that a conductive material be present between the plurality of ceramic particles 1 to have an electric conduction path.

However, in the structure having carbon black between a plurality of ceramic particles, the resistance of the resistor is increased due to an increase in lattice vibration accompanying a temperature rise, an increase in the resistance value of carbon black accompanying the temperature rise (temperature dependence), and the like. The resistance value tends to be too high. On the other hand, in order to keep the resistance value low even with a temperature rise, the content of carbon black, which is a conductive material, is increased with respect to the raw material powder of insulating ceramic particles, and the mixing ratio is changed. The resistance of the resistor is reduced, cracks are generated between the ceramic particles and the carbon black due to the difference in thermal expansion, and the resistor 10 does not function stably over a long period of time due to sparking.

  On the other hand, the resistor 10 according to the present disclosure includes the carbon aggregate 2 that continuously extends at least linearly along the plurality of ceramic particles 1. Here, the carbon aggregate 2 continuously extending linearly refers to a filamentous body, a fibrous body, a cylindrical body or the like formed by bonding carbon atoms like a network as shown in FIG. This is the case with so-called carbon nanotubes. Unlike the carbon black, the carbon aggregate 2 having such a structure has a property that the resistance value is maintained or lowered as the temperature rises.

  Therefore, the resistance value of the resistor 10 is suppressed from increasing due to temperature dependence, and rather the resistance value becomes small. Further, even if the amount is smaller than that of carbon black, a low resistance value can be realized, and cracking between the ceramic particles 1 and the carbon aggregate 2 can be suppressed, and the resistor 10 can be stably stabilized for a long period of time. Can function as.

  In addition to the carbon aggregates 2, a matrix 4 exists between the plurality of ceramic particles 1. The matrix 4 is formed as a liquid phase during high-temperature firing, and is formed at the grain boundaries of the plurality of ceramic particles 1 as the main component after cooling, and is mainly composed of a glass component. Here, what is recrystallized is also contained as a glass component.

  Here, FIG. 1B shows a structure in which the carbon aggregates 2 are linear (thread-like), and a plurality of the carbon aggregates 2 are intertwined in a complicated manner. Not limited to. For example, as shown in FIG. 1 (c), the carbon aggregate 2 may have a shape extending continuously in a shape (band shape) extending in the width direction. Further, as shown in FIG. 3, the carbon aggregate 2 may have a shape that continuously extends in a shape (film shape) that spreads over a wider range. FIG. 3 shows an example in which a film-like carbon aggregate 2 is provided at the neck portion between adjacent ceramic particles 1 so as to straddle the surfaces of these particles. FIG. 4 shows an example in which a film-like carbon aggregate 2 is also provided at the interface between adjacent ceramic particles 1.

  According to the configuration in which the carbon aggregates 2 extending at least linearly between the ceramic particles 1 and the matrix 4 are included, the temperature is higher than that in the configuration in which carbon black is filled. Is less susceptible to changes in electrical conductivity due to free electrons generated from the ceramic particles 1 when rises. Further, since the carbon aggregate 2 is in the form of a band or a film, an instantaneous current is easily transmitted only on the surface of the carbon aggregate 2, and is less susceptible to changes in electrical conductivity. The resistor 10 functions stably.

  Moreover, the carbon aggregate 2 may extend continuously in a three-dimensional network. According to this configuration, even if the plurality of ceramic particles 1 constituting the polycrystal body repeat thermal expansion and contraction due to a change in ambient temperature, the carbon aggregate 2 can be entangled with the ceramic particles 1 to maintain adhesion. it can. Thereby, it can further suppress that a crack arises between the ceramic particle 1 and the carbon aggregate 2, and can function as the resistor 10 more stably for a long period of time.

Further, as shown in FIGS. 1, 3, and 4, there may be voids 3 together with the carbon aggregates 2 between the plurality of ceramic particles 1. According to this configuration, even if the plurality of ceramic particles 1 constituting the polycrystal body repeat thermal expansion and contraction due to a change in ambient temperature, the void 3 relaxes the stress, and the carbon aggregate 2 and the ceramic particles 1 Adhesion with can be maintained. Thereby, it can further suppress that a crack arises between the ceramic particle 1 and the carbon aggregate 2, and can function as the resistor 10 more stably for a long period of time.

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

  First, a precursor of the carbon aggregate 2 is obtained by dissolving a phenol resin in a solvent such as toluene or methyl ethyl ketone and dispersing it as a colloid having a particle size of about 10 nm. Here, the phenol resin is soluble in a solvent and can be uniformly dispersed in the ceramic raw material powder, and the carbon aggregate 2 after firing can be formed into a thread-like (linear) structure. In addition, as a precursor of the carbon aggregate 2, in addition to a phenol resin, a filamentous or fibrous carbon source such as a carbon nanotube may be used alone or in combination as the second precursor. In other words, instead of a part or all of the precursor of the carbon aggregate 2, carbon nanotube powder may be added in advance as the second precursor.

(Method 1)
Next, oxide ceramic raw material powders such as alumina, zirconia, zircon, mullite, sintering aids such as CaO, SiO ₂ , ZnO, TiO ₂ , ZrO _2, etc., for example, polyvinyl alcohol, paraffin wax, acrylic resin, etc. The binder and the precursor and / or the second precursor are mixed, dried, pressed, and fired at 1450 to 1650 ° C. At this time, filling is performed in the carbon powder so that the carbon does not react with surrounding oxygen and volatilize. In addition, a precursor and a 2nd precursor are mixed in the ratio of 1-20 mass% with respect to 100 mass% of oxide ceramic raw material powders, for example.

  The precursor does not diffuse into the ceramic particles 1, but the sintering proceeds while clinging together in a linear (thread-like or fiber-like) manner between the ceramic particles 1 together with the surrounding liquid phase components. Thereby, as shown in FIG. 1A, a carbon aggregate 2 extending continuously at least linearly along the ceramic particles 1 can be formed.

  Here, in order to form a film so as not to form a lump, it is necessary that the thread-like or fibrous precursors adhered to the particle surface are overlapped, so that the colloid becomes a carbon film, so that the oxide In order to suppress the crystal growth, it is preferable to carry out the firing at a maximum temperature of 1 hour or less. In order to obtain 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 aggregates are torn into a network). Note that this is not limited to some devices and facilities.

(Method 2)
Further, as shown in FIG. 3, in order to obtain a carbon aggregate 2 in which carbon is agglomerated in a matrix at a neck portion between adjacent ceramic particles 1 and ceramic particles 1, It is necessary for the carbon to agglomerate. For this reason, the sintering aid is covered so as to cover the sintering aids CaO, SiO ₂ , ZnO, TiO ₂ and ZrO ₂ so that the colloid can move together with the liquid phase. After coating the colloid, the binder is added. Then, after the liquid phase becomes a matrix so that the colloid becomes the carbon aggregate 2, it is preferable to perform baking at a maximum temperature of 1 hour or less so as to suppress crystallization. In order to obtain a three-dimensional network structure, it is preferable to cool the carbon film within 3 hours in order to apply stress. Note that this is not limited to some devices and facilities.

(Method 3)
Further, as shown in FIG. 4, in order to obtain a carbon aggregate 2 in which carbon is aggregated at the interface between adjacent ceramic particles 1 and ceramic particles 1, the carbon aggregates in the liquid phase component during sintering. After that, when sintering proceeds, the matrix component is pushed out from between the crystals, and only the carbon needs to remain. Therefore, after coating the oxide ceramic raw material powder with colloid so as to cover the oxide ceramic raw material powder such as alumina, zirconia, zircon, mullite, etc., the sintering aids CaO, SiO ₂ , ZnO, TiO which become the liquid phase _2, addition of a binder together with ZrO _2. Here, the particle size of the precursor aggregate and the particle size of the oxide ceramic raw material powder of alumina, zirconia, zircon, mullite, etc. are the same size so that the liquid phase oozes into the aggregates of the surrounding precursors It is good to do. To make the particle size of the precursor agglomerates the same as the particle size of the oxide ceramic raw material powder, put the mixture of the binder and precursor agglomerates in a container such as a platinum crucible or an alumina mortar and heat-treat in advance. Thus, the particle size may be confirmed to design an optimal precursor aggregate. When the particle size is large, if the raw material is carbon nanotubes, change to a smaller particle size, and if the phenol resin is the raw material, change the concentration of the phenol resin in the solvent so that the colloid diameter is small. Increase and mix. On the other hand, when the particle size is small, the particle size may be changed to a larger one or the concentration of the phenol resin may be increased. Then, after the liquid phase between the crystals begins to saturate, the sintering proceeds while the carbon left behind is aggregated. Here, in order to obtain a three-dimensional network structure, it is preferable to cool within 3 hours in order to apply stress to the carbon film.

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

  The spark plug 20 shown in FIG. 5 includes a center electrode 21 on the front end side, a terminal electrode 22 on the rear end side, and the above-described resistor 10 disposed between the center electrode 21 and the terminal electrode 22. .

  Specifically, in the embodiment shown in FIG. 5, the center electrode 21 is inserted and fixed on the tip end side of the shaft hole of the spark plug 20. More specifically, a bulging portion 211 that bulges toward the outer periphery of the center electrode 21 is formed at the rear end portion of the center electrode 21, and the bulging portion 211 is engaged with the step portion of the shaft hole. In the stopped state, the center electrode 21 is fixed. The center electrode 21 is comprised by the inner layer which consists of copper or a copper alloy, and the outer layer which consists of nickel alloy which has nickel (Ni) as a main component. Furthermore, the center electrode 21 has a rod-like shape (cylindrical shape) as a whole, its tip end surface is formed flat, and protrudes from the tip end of the insulator 23.

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

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

  In addition, the metal shell 24 is formed in a cylindrical shape from a metal such as low carbon steel, and a screw portion (male screw portion) 241 for attaching the spark plug 20 to the engine head is formed on the outer peripheral surface thereof. . In addition, 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 metal shell 24, a tool engaging portion 243 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 24 is attached to the engine head is provided. A caulking portion 244 for holding the insulator 23 is provided.

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

  An annular plate packing (not shown) is interposed between the step portions of both the insulator 23 and the metal shell 24. Thereby, the airtightness in the combustion chamber is maintained, and the fuel air entering the gap between the leg long part 232 of the insulator 23 exposed to the combustion chamber and the inner peripheral surface of the metal shell 24 is prevented from leaking outside. Furthermore, in order to make the sealing by caulking more complete, an annular ring member 26 is interposed between the metal shell 24 and the insulator 23 on the rear end side of the metal shell 24, and between the ring members 26. Is filled with talc 27 powder. That is, the metal shell 24 holds the insulator 23 via the plate packing (not shown), the ring member 26 and the talc 27.

  A ground electrode 25 made of a nickel (Ni) alloy is joined to the front end surface of the metal shell 24. That is, the ground electrode 25 is disposed so that the rear end portion thereof is welded to the front end surface of the metal shell 24, the front end side is bent back, and the side surface thereof faces the front end portion of the center electrode 21.

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

  Examples will be described below.

  First, a resistor for a spark plug was produced. A phenol resin as a precursor and / or a carbon nanotube as a second precursor dispersed in a solvent, an oxide ceramic raw material powder made of alumina, zirconia, zircon or mullite, a sintering aid, The mixture was mixed with the binder, dried and pressed, and then fired at 1450 ° C. to 1650 ° C. At this time, filling was performed in carbon powder so that carbon would not react with surrounding oxygen and volatilize.

  Here, more specifically, three different methods were used as the construction method.

  As the construction method 1, a precursor and / or a second precursor dispersed in a solvent, a ceramic raw material powder, a sintering aid, and a binder are mixed and fired as they are (sample No. 1). -5, 8-10).

  In Method 2, the sintering aid is coated with a colloid obtained by dispersing the precursor and / or the second precursor in a solvent, and then the oxide ceramic raw material powder and the binder are mixed and fired (sample) No. 6).

  As Method 3, the oxide ceramic raw material powder is coated with a colloid obtained by dispersing a precursor and / or a second precursor in a solvent, and then a sintering aid and a binder are mixed and fired (sample) No. 7).

  In addition, Table 1 shows the addition amount of the precursor or the second precursor with respect to 100 parts by mass of the oxide ceramic raw material powder in each sample.

  And it measured about the resistance value of each sample. The results are shown in Table 1.

  According to Table 1, in any sample, the resistance value does not increase due to temperature rise, but rather decreases, and a practical resistor within the range of 0.1 to 10 kΩ can be created at 1000 ° C. I understand that.

Moreover, the spark plug using each said resistor was prepared, the load life test was performed by the method prescribed | regulated to 6.10 of Japanese Industrial Standard B8031, and load life (long-term stability) was evaluated. The load life (long-term stability) was evaluated according to the following four levels based on the resistance change rate ΔR of the resistance value after the test with respect to the resistance value before the test.
A: ΔR is within ± 15%.
○: ΔR is within ± 25%.
Δ: ΔR is within ± 30%.
X: ΔR exceeds ± 30%.

  As a result, it is understood that good results can be obtained for the load life evaluation in the spark plug using the resistor of any sample.

  Although not shown in the table, in the sample added with carbon black 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 further 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, as soon as the load was applied, cracks occurred and sparks were generated.

10: resistor 1: ceramic particle 2: carbon aggregate 3: void 4: matrix 20: spark plug 21: center electrode 211: bulge 212: noble metal tip 22: terminal electrode 23: insulator 231: step 232: Leg long part 24: metal shell 241: screw part (male screw part)
242: Seat portion 243: Tool engaging portion 244: Caulking portion 245: Step portion 25: Ground electrode 26: Ring member 27: Talc

Claims (6)

  A resistor comprising a polycrystal having a plurality of ceramic particles and a carbon aggregate extending at least linearly along the plurality of ceramic particles.   The resistor according to claim 1, wherein the carbon aggregate continuously extends in a band shape or a film shape.   The resistor according to claim 1, wherein the carbon aggregate continuously extends in a three-dimensional network.   The resistor according to any one of claims 1 to 3, wherein there is a gap between the plurality of ceramic particles together with the carbon aggregates.   5. The resistor according to claim 1, wherein the plurality of ceramic particles are made of alumina. A center electrode on the front end side, a terminal electrode on the rear end side, and the resistor according to any one of claims 1 to 5 disposed between the center electrode and the terminal electrode. A spark plug characterized by

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