JPS61284903A - Manufacture of resistor for resistance-contained plug - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a resistor for a spark plug used in a high-voltage ignition circuit of an internal combustion engine, and more particularly, the present invention relates to a method for manufacturing a resistor for a spark plug used in a high-voltage ignition circuit of an internal combustion engine. The present invention relates to a manufacturing method for improving a resistor built into a device.

[Prior Art] High-frequency noise radio waves generated from a spark plug can be suppressed by, for example, inserting a resistor between a terminal fitting fitted into one end of the inner hole of the spark plug and a center electrode fitted at the other end. This can be done by connecting them in series to form a high frequency absorption circuit.

As this type of resistor, a conductive material-glass-filler system is often used. A study of the components and structure of this resistor is described in Japanese Patent Laid-Open No. 144830/1983. That is, this publication discloses a method in which an electrically insulating ceramic filler having a relatively large particle size is added to a resistor to form a zigzag current path in the resistor.

Furthermore, various studies have shown that in order to further improve the radio noise prevention effect, it is sufficient to increase the amount of filler. If the amount of filler is simply increased in this way, the conductive material will decrease, so the resistance value will be 5 Ω ± 30%, 10 Ω ± 30%, 15 Ω ± 30%, as specified by JIs-D-5102.
In order to obtain ±30%, it has been found that carbon, which is fine particles and has a low resistivity, is advantageous as the conductive material.

In addition to the method of directly adding carbon black, there are also known methods of forming carbon by thermally decomposing an organic substance.

[Problems to be Solved by the Invention] In spark plugs with conventional carbon-glass-filler-based resistors, the resistance value changes during spark discharge depending on the selection of carbon black or the selection of organic material. There was a problem that the lifespan was shortened. The reason for this is, for example, when fine particulate carbon black is directly added, the sintering temperature of the carbon itself is extremely high (approximately 2500° C. or higher), so even if they are fixed together with the filler, the bond between the fine particulate carbon and the fine carbon is extremely weak. Therefore, the conductive paths do not form a series of tightly connected network-like conductors, but are separated and simply in contact, which seems to shorten the discharge life.

Further, Japanese Patent Publication No. 57-23363 discloses a method of attaching carbon to the surface of glass powder by thermally decomposing a carbon-containing substance such as dextrin in a non-oxidizing atmosphere. According to this method, a resistor having a uniform resistance value and a long discharge life can be efficiently obtained. However, since this method is carried out in a non-oxidizing atmosphere, the conditions are special and there are problems with the equipment and the number of steps.

The present invention has been made in view of the above-mentioned problems, and provides a method for easily manufacturing a plug resistor that has a long Group 11 life and has little change in resistance due to plug discharge, even in the atmosphere.

Means for Solving Problems] The method for manufacturing a resistor for a resistor-containing plug according to the present invention includes 88 to 96 parts by weight of glass powder, 4 to 12 parts by weight of ceramic powder having an average particle size smaller than that of the glass powder. A solution or dispersion of a carbon-containing substance such as dextrin is brought into contact with 100 parts by weight of the filler powder, and then dried to adhere 0.1 to 1 part by weight of the carbon-containing substance to the surface of the filler powder. a pressurizing step of enclosing the filler powder to which the carbon-containing substance is attached in a predetermined container and applying pressure; and a pressurizing step of pressurizing the filler powder together with the container at a temperature equal to or higher than the glass transition temperature of the glass powder. and heating at a temperature below the melting point of the ceramic powder,
It is characterized by comprising a heating step of forming a carbon conductive layer produced by thermal decomposition of the carbon-containing substance on the surface of the filler powder and integrally sintering the filler powder having the carbon conductive layer.

In view of the manufacturing method disclosed in Japanese Patent Publication No. 57-23363, the inventors of the present invention conducted extensive research and discovered a method for thermally decomposing carbon-containing substances to generate carbon without using a non-oxidizing atmosphere. It is something. That is, by performing a heating process at a temperature higher than the glass transition temperature of the glass powder, preferably at least 100°C higher than the glass transition temperature, the glass powder is melted, and the stress caused by pressure acts uniformly on the entire surface to form voids. decreases, blocking the communication hole with the outside world.

It has been discovered that this results in an extremely low amount of oxygen, which prevents the combustion of carbon-containing substances and effectively sinters the carbon produced.

The filler powder referred to in the present invention acts as an electrical insulator in a resistor, and is composed of glass powder and ceramic powder.

Glass powder includes soda lime glass, phosphosilicate glass,
Various glasses such as borosilicate glass and quartz glass can be used. By the way, in the heating step described below, it is necessary to heat at a temperature higher than the glass transition temperature of the glass powder, and in terms of energy saving, it is desirable that the glass transition temperature be lower. However, when used as a normal plug, thermal softening causes various problems, so it is desirable that the glass transition temperature be at least higher than 300°C. Among these, it is desirable to use lithium borosilicate glass, which has a small coefficient of thermal expansion, high electrical insulation properties, and thermal shock resistance.

This glass powder may have a substantially uniform particle size, but it is desirable to use a mixture of large and small particle sizes. The powder with a large diameter creates a zigzag current path in the resistor, improving the radio noise prevention effect, and the powder with a small diameter increases the surface area, which increases the amount of carbon-containing substances deposited (described later), and improves the carbon conductive layer. The amount of formation can be increased. That is, the resistance value can be adjusted by adjusting the ratio of large-diameter powder to small-diameter powder. In addition, since heat is quickly transmitted to the inside of the powder with a small diameter, the heating time can be shortened.

Ceramic powders that do not soften or melt during the heating step described below are used, and various materials such as zirconia, alumina, cordierite, magnesia, and silicon nitride can be used. The ceramic powder used is smaller in average particle size than the glass powder. This is to adjust the amount of carbon conductive layer formed by intervening between the glass powders and prevent the glass powders from fusing together, making it easier to adjust the resistance value. This is sometimes done to minimize the gaps between filler particles.

The ratio of glass powder to ceramic powder is 88 to 96 parts by weight for glass powder and 4 to 12 parts by weight for ceramic powder.
Parts by weight. If the amount of ceramic powder is less than 4 parts by weight, only the glass powder will fuse together to form large particles, making it difficult to secure a current path and resulting in an excessively high resistance value. In addition, if the number of glass powders is more than 12, the effect of relaxing pressure stress during melting and blocking communication holes with the outside world will be reduced due to less glass powder, which will prevent densification and carbon formation. Problems like this occur.

The adhesion step is a step of adhering a carbon-containing substance to the surface of the filler powder. As the carbon-containing substance, soluble starch, thin starch, white dextrin, yellow dextrin, starch, allyl starch, carboxymethyl starch, sucrose, glycerin, polyvinyl alcohol, etc. can be used. Then, these can be dissolved or made into a colloid in water, alcohol, etc., mixed with the filler powder, brought into contact with the filler powder by a method such as spraying, and then allowed to adhere by drying.

Note that it is desirable to use an organic binder such as a cellulose ether such as methyl cellulose, ethyl cellulose, carboxy cellulose, or oxyethyl cellulose in combination with the above carbon-containing material.

Alternatively, this organic binder can be used alone as the carbon-containing material. These cellulose ethers have high viscosity and high film-forming ability when made into an aqueous or alcohol solution. Therefore, the carbon-containing substance is reliably retained as a film on the surface of the filler powder, and is particularly prevented from falling off after drying. Due to this effect, carbon is uniformly formed on the surface of the filler powder in the heating step.

The carbon-containing material is attached to the surface of the filler in an amount of 0.1 to 1 part by weight per 100 parts by weight of the filler.

If Appendix II is outside this range, the discharge life will be shortened and the desired resistance value will not be obtained.

The pressurizing step is a step in which the filler powder having a film of carbon-containing material obtained in the above adhesion step is sealed in a predetermined container and pressurized to reduce the voids between the particles. This container may be of any type as long as it can withstand the heat and applied force of the heating process, but it is generally cylindrical because it is desirable to reduce contact between the filler powder and the atmosphere. In particular, in order to reduce the number of steps, it is desirable to use the inner hole of the spark plug as a container and pressurize the filler powder between the terminal fitting and the center electrode of the plug. Note that it is desirable that the pressing force be 0.5 kQ/c1 or more. If the pressure is lower than this, the particles will not come into close contact with each other, and the produced carbon particles will not be able to make good contact with each other, so the resistance value will vary. Further, the pressurization may be continued during the next heating step. As a result, voids newly created by melting the glass powder are also densely filled. Note that in the case of omitting pressurization during the heating step, it is desirable to apply pressure again after heating to achieve densification.

The most important feature of the present invention is the heating step. In this heating step, the filler powder to which the carbon-containing substance is attached is heated together with the container. The heating temperature is higher than the glass transition temperature of the glass powder in the filler powder and lower than the melting point of the ceramic powder. Desirably, the temperature is 100° C. or more higher than the glass transition temperature of the glass powder. As a result, the glass powder softens and melts during heating, and the filler particles become dense due to the stress of pressurization, closing the communication holes with the outside.

Therefore, the carbon-containing substance inside the system becomes a steamed state, and carbon is generated. If this heating temperature is lower than the glass transition temperature of the glass powder, densification will be insufficient and there will be no effect of closing the communicating holes with the outside, so the carbon-containing substance will be burned out and no carbon will be produced. When the heating temperature is higher than the melting point of the ceramic powder, the glass powder and the ceramic powder all melt and become large particles, which reduces the area on which carbon is attached and increases the resistance value.

The heating time is set according to the desired resistance value. The longer the heating time is, the higher the probability that the produced 7J-bond will come into contact with the atmosphere, which will cause it to burn out and the resistance value will gradually increase.

This heating step may be carried out in a non-oxidizing atmosphere such as nitrogen gas, or in the atmosphere; however, by carrying out the heating step in the atmosphere, it is possible to easily manufacture the product without requiring equipment for special conditions.

[Function] In the manufacturing method of the present invention, the glass powder is melted in the heating step, and the filler particles are densely solidified by the stress of pressurization, and most of the internal voids are closed.

This significantly reduces the number of communication holes communicating with the outside (atmosphere). Further, even if voids remain inside, the amount thereof is small, and the oxygen within the voids is consumed by combustion of a portion of the carbon-containing material. Therefore, most of the carbon-containing substances attached to the filler particles are thermally decomposed without coming into contact with oxygen, and carbon is formed. This carbon is then sintered by melting the glass powder while maintaining good contact with the ceramic powder.

[Effects of the Invention] According to the manufacturing method of the present invention, carbon is easily generated in the atmosphere without the need for a conventional device for creating a non-oxidizing atmosphere, and therefore manufacturing can be performed at low cost. Further, the carbon is uniformly fixed to the surface of the filler powder. Therefore, in the resistor obtained, as shown in FIG. 1, the carbon 3 on the surfaces of the ceramic powder 1 and the glass powder 2 are in uniform and reliable contact at each part, and a series of conductive paths are formed in the form of a network. . Furthermore, the internal voids are closed by the molten glass 2a, the carbon 3 is reliably held, and problems such as disconnection of the electric circuit do not occur.

This makes it possible to manufacture a resistor-containing plug with a long discharge life.

[Example] This will be explained in detail below using examples.

FIG. 2 shows a spark plug containing a resistor manufactured by the manufacturing method of the present invention.

Zirconia as ceramic powder (average particle size 5, [>1
1.8 parts by weight, 5iOz50% by weight, Bz0340% by weight, LixO3
% by weight, lithium borosilicate glass consisting of 7% by weight of Ca (average particle size 30 μm, glass transition temperature 520°C>
58.2 parts by weight were ground and mixed using a vibration mill. This mixture was further mixed with 30 parts by weight of lithium borosilicate glass If ('average particle size: 250 μm) having the same composition as above. Next, prepare an aqueous solution A in which 100 g of water is added to 2 q of carboxymethyl cellulose (CMC), and an aqueous solution B and water C in which 1009 g of water is added to 15 Q of yellow dextrin, and A:B:C is 2:3: 1, prepare a solution containing 109, take the solution 109, and make the above mixture 100.
mixed with g. Thereafter, it was held for 30 minutes to dry the water content and obtain a resistor filling.

The surface of the obtained packing was uniformly covered with a film of the above CMC and yellow dextrin. Next, the center electrode 5 is inserted into the lower end of the inner hole of the alumina insulator 4 shown in Fig. 2, and copper powder and glass powder (weight ratio: 50:50) are inserted into the inner hole.
0.20 of the mixture was filled. On top of that, 0°6g of the resistor filler prepared above was filled, and 0°4q of copper powder and glass powder (weight ratio: 50+50>) were sequentially filled.Next, the stem 6 was inserted into the inner hole, A pressure of 250 kg/C1 was applied from the upper end of the stem 2 to compress the resistor filling and the mixture between it and the center electrode 5.

In this state, each alumina insulator 4 was heated to 700°C to 90°C.
Heat to 0°C and hold for 30 minutes. Through this operation, the d compound of copper powder and glass powder became the conductive glass layer 7, and the resistor filling became the resistor 8. Then, a ground electrode 9 and a housing 10 were fixed around this alumina insulator 4 to produce a resistor-containing plug A.

Subsequently, plugs D to R of Examples were manufactured using the compositions shown in the table and in the same manner as above.

(Conventional example) As a conventional method, 167.5% by weight of the same borosilicate glass as in the example, borosilicate glass [26,
5% by M and 5.511% of zirconia were used and mixed in exactly the same manner as in the example. And more carbon black 0.5
The mixture of % by weight was used as a resistor filling, which was similarly filled into an alumina insulator, and heated at the same pressure, heating temperature, and heating time as in the example to produce a resistor-filled plug W.

(Comparative Example) Using raw materials with the composition shown in the table, 2.250 Q of aqueous solution A and 1.2 Q of aqueous solution B were added per 100 of the composition, and a resistor-containing plug X-Z of a comparative example was prepared in the same manner as in the example. (Produced by the method of the present invention).

(Evaluation) The resistance values of the obtained resistor-containing plugs of Examples, Conventional Examples, and Comparative Examples were measured and the results are shown in FIGS. 3 and 4. Further, the plug of the example was discharged continuously for 250 hours, and the resistance change rate before and after that was measured, and some of the results are shown in FIGS. 5 to 7. Note that FIG. 7 is a rearrangement of FIGS. 5 and 6. Furthermore, the plugs of the conventional example and the comparative example were continuously discharged, and the resistance change rate was 30.
% was measured, and the results are shown in FIG. As is clear from FIGS. 3 and 4, the resistance value can be freely adjusted by adjusting the amount of carbon-containing material and the particle size of the glass powder.

It is clear from FIG. 7 that within the scope of this example, 0.1 Og of yellow dextrin was added to 1°Og of filler powder.
Q9~0763Q 1. ffi and CMCt-0,14
By attaching 7CI to 0.0829, the rate of change in resistance during continuous discharge for 250 hours can be suppressed to within ±10%, and the release! ! A resistor with significantly improved lifespan can be obtained. Also, from FIG. 8, it is clear that the conventional addition of carbon black has an adverse effect on the life span, and that the combined use of the method of the present invention is effective.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the structure of a resistor obtained by the manufacturing method of the present invention. FIG. 2 is a partially sectional front view of a plug encapsulating a resistor obtained by the manufacturing method of the present invention. Figures 3 to 8 show the results of evaluating the resistors obtained in Examples, Conventional Examples, and Comparative Examples. Figure 4 is a graph showing the change in resistance value with respect to the amount of carbon black. Figures 5 and 6 are graphs showing the change in resistance value with respect to the amount of lithium borosilicate glass added with a large particle size. Figure 7 is a graph showing the relationship between the amount of carbon-containing material deposited and the rate of change in resistance, and Figure 8 is a graph showing the relationship between the amount of carbon black added and the discharge time at which the rate of change in resistance is 30%. 1... Ceramic powder 2... Glass powder 2a.
...Fused glass 3...Carbon 8...Resistor patent applicant Nippondenso Co., Ltd. Agent Patent attorney Hirodo Okawa Patent attorney Shudo Fujitani Patent attorney Akio Maruyama Figure 1 Figure 2 Figure 15 Presentation $5 Figure Houkei Rebutsu Chiu A Force゛'tsusu I (It'/,) No. 8
figure

Claims (5)

[Claims] (1) A solution or dispersion of a carbon-containing substance such as dextrin is added to 100 parts by weight of filler powder consisting of 88 to 96 parts by weight of glass powder and 4 to 12 parts by weight of ceramic powder whose average particle size is smaller than that of the glass powder. an adhesion step in which 0.1 to 1 part by weight of the carbon-containing substance is adhered to the surface of the filler powder by drying after contact; and pressurizing the filler powder to which the carbon-containing substance is attached after sealing it in a predetermined container. a pressurizing step, heating the pressurized filler powder together with the container at a temperature above the glass transition temperature of the glass powder and below the melting point of the ceramic powder, and applying heat of the carbon-containing substance to the surface of the filler powder; A method for manufacturing a resistor for a resistor-containing plug, comprising a heating step of forming a carbon conductive layer produced by decomposition and integrally sintering the filler powder having the carbon conductive layer. (2) The heating process is 10° below the glass transition temperature of the glass powder.
A method for manufacturing a resistor for a resistor-containing plug according to claim 1, which is carried out at a temperature higher than 0°C. (3) The method for manufacturing a resistor for a resistor-containing plug according to claim 1, wherein the carbon-containing substance contains an organic binder such as cellulose ether. (4) The method for manufacturing a resistor for a resistor-containing plug according to claim 1, wherein the glass powder is a mixture of a powder with a large particle size and a powder with a small particle size. (5) The method for manufacturing a resistor for a resistor-containing plug according to claim 1, wherein the predetermined container is a plug.