JPH0244675A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To stabilize the electromagnetic wave noise preventing effect at high temperature by joining a discharging portion and an intermediate electrode, consisting of a molded sintered body in which alumina particles are used as an aggregate and whose surface is coated with a metal oxide, through simultaneous baking. CONSTITUTION:An alumina powder molded body, whose surface is coated with platinum, iridium, platinum alloy, or noble metal, is used as a discharge portion 4, and an intermediate electrode 2, consisting of a molded sintered body 3 in which alumina particles are used as an aggregate and whose surface is coated with a metal oxide and formed by baking an alumina insulator simultaneously with the discharge portion 4, is provided adjacent the discharge portion 4. In this manner, the molded sintered body 3, in which alumina particles are used as an aggregate and whose surface is coated with a metal oxide, and the discharging portion 4 are jointed together by simultaneous baking, so that semiconductor action is achieved and stable electromagnetic wave noise preventing effect can be obtained even at a high temperature.

Description

[Detailed Description of the Invention] (1) Industrial use! iff: The non-invention relates to the improvement of the pole in the center 1 of the spark plug.Special VC'
L11. This is related to the construction of a spark plug with a resistor, which is excellent in preventing wave noise.

(2) Conventional technology and its problems: Suppressing the departure radio waves generated when the spark plug for an internal combustion engine generates a few sparks. As a second countermeasure, it is known to insert a resistor into the shaft hole of the porcelain insulator, or to use a resistor-containing plug with a resistor formed thereon.

Therefore, in order to effectively suppress the generation of noise radio waves,
A bladder containing a resistor with high noise prevention effect up to a high frequency band of about 100 O is now required. By the way, in order to increase the noise prevention effect at high frequencies, it is important to place the inserted resistor as close to the ignition point as possible.
It turns out that forming a resistive film on the surface itself is most effective. However, it was discovered that such resistive films were not durable as they oxidized and disappeared when exposed to high-temperature flames. Therefore, ceramic materials were selected as flame resistant materials, and the use of ceramic materials as they were in spark plugs was considered, and research was underway to add electrical conductivity to the ceramic itself. In these processes, a product was developed in which metal powder and ceramic powder were mixed and molded and sintered to form a hermitage in the center 1 of nine cermets, but satisfactory results have not yet been obtained.

Predetermined means for solving the problems: The spark plug of the present invention (1) has a surface coated with platinum, iridium, a platinum alloy, or a noble metal as a discharge part, and has a formed body of alumina powder or a sintered body thereof and an entire alumina insulator. The intermediate electrode part of the spark plug is made of alumina particles as an aggregate, the surface of which is coated with a metal oxide, and a t-sintered body is disposed on the intermediate electrode part of the spark plug, which is integrated by simultaneous combustion.

(11) The alumina powder of the sintered body of the intermediate electrode is a high-purity fine powder that can be fired at 1450°C or less (
Specifically, it is a spark plug that uses spark plugs with a primary particle diameter of 1 μm or less.
(1) above, wherein the metal oxide forming the intermediate electrode portion sintered body according to (1) has a melting point of 1450° C. or higher;
fii).

(1v) The metal oxide described in (11) is an alumina with a crystal purity that can be fired at 1450°C or less. After completely covering the oxide, this rL is made into an intermediate γl!
The shape of the pole 1 is formed by extrusion molding, etc., and fired in an oxygen atmosphere to form a pole sintered body in the middle 1. Set spark plug. The invention also includes a spark plug in which such an intermediate electrode sintered body is inserted into an insulator leg section immediately adjacent to a discharge section.

Therefore, the alumina powder used as the alumina aggregate used as the intermediate 'FFL pole has a small primary particle size and has a high purity of 99.9% or more. On the other hand, the metal to be coated is inexpensive, easy to coat, and has an F of 1@ point 1400゛C or higher.
Transition metal groups such as e + N 1 r Cr r Co are preferred. ! The coating thickness is at least 1μ
m is desirably 3 to 10 μm. If the thickness is less than 1 μm, the metal coating will peel off during pressurization, making it difficult to obtain conductivity through the oxidized pattern during sintering. If it is too thick (more than 10μ), the expansion coefficient will be different from the surrounding alumina part after sintering, and residual stress will remain, making it easy to crack.

Effect: As mentioned above, the alumina particles used for the intermediate electrode have a purity of 9.
9.9 or more, the primary particle diameter is about 0.1 μm. The melting points of the metals and their oxides coated on the alumina particles are shown in the table below.

Table 1 metal oxide Ni 1455 “CNi0 Cr’　1560CCr1e3 Fe　153n℃Fern.

Co 1490℃Co0 1950℃ 2:310~2330''C 1560℃ 800C Since the metal oxides in Table 1 above exhibit semiconducting properties, they exhibit excellent radio noise suppression effects when uniformly coated on the surface of the alumina particles of the aggregate. In addition, the alumina insulator and the discharge part have an integral structure that is fired at the same time, and the intermediate electrode part is a sintered body in which the surface of the alumina particles is coated with a metal oxide and fired. This is a so-called wide-range spark plug with a protruding ring, which has the effect of dissipating the received heat by transmitting it to the insulator in addition to the above-mentioned quasi-wave noise prevention effect. Table 2 shows a comparison of the thermal properties of the conventional structure product and the product of the present invention.

Table 2 Examples: Figure 1 is a vertical cross-sectional view of the main part of the spark plug insulator of the present invention.
2 is an insulator, 2 is an intermediate part that penetrates the inside, and 2 is a discharge part, which is a sintered body of platinum, iridium, platinum alloy, or alumina powder coated on the entire surface of a precious metal. The intermediate plate part 2 to be connected is made of homogeneous single-particle alumina powder with a high purity of 99.9% or more and a primary particle size of about 0.1 μm (for example, Chiimicron TM-D manufactured by Daimei Chemical Co., Ltd.).
The powder is granulated to a particle size of 10 to 40 μm, and the surface of the granulated powder is coated with at least 1 μm or more, preferably 3 μm.
Fe, Ni*Cr* so that the film thickness is ~10μm
After being coated with a metal such as Co, it is formed into a cylindrical shape by press molding, injection molding, extrusion molding, etc., as in the case of chips. This molded product was produced at a temperature of 1850 while adjusting the oxygen partial pressure.
Fire at ~1400'O. Usually alumina powder is 160
Although it is necessary to sinter at a temperature of 0 to 1,650°C, the alumina powder can be sintered at a temperature of 1,300°C as shown in Figure 2, and therefore can be sintered at a lower temperature than that of Fe, Ni+Cr, Co, etc. By appropriately adjusting the oxygen partial pressure, the metal components are oxidized to produce metal oxides, and after firing, as shown in Figure 3, the structure becomes a structure in which the metal oxides surround the alumina particles, which exhibits semiconductor properties. Since it is a sintered body having a sintered body, the radio noise prevention effect can be improved by disposing and bonding it as a resistor to the mediograph pupil immediately near the discharge part.

Effects of the invention: The present invention uses a molded body of alumina powder whose surface is coated with platinum, iridium, a platinum alloy, or a noble metal as a discharge part, and is formed by simultaneously firing the alumina insulator and the alumina insulator. The surface is coated with metal oxide using alumina particles as aggregate, and the molded sintered body is placed close to the discharge part and bonded by simultaneous firing, so it exhibits a semiconductor effect and is stable even at high temperatures and has a radio noise prevention effect. Since there are no voids, the heat transfer effect to the insulator is large and a wide range of spark plugs can be provided.

[Brief explanation of the drawing]

Figure 1 is a longitudinal sectional front view of the main parts of the spark plug of the present invention, Figure 2 is a graph showing the firing temperature of the intermediate electrode of the present invention, and Figure I3 is a graph showing the firing temperature of the intermediate electrode of the present invention. An enlarged view of the shaped ft7/V mina particle, Fig. 4 is a graph showing insulator leg fittings for product numbers manufactured by the applicant, and Fig. 5 shows the noise radio wave suppression effect of the conventional plug (BCPR5EY) and the plug of the present invention. It is a graph showing a comparison. 1... Insulator 2... Intermediate electrode part 3... Metal oxide coated sintered alumina intermediate electrode 4... Discharge part 5.
...Glass Sea/v 6...Terminal 1!1 Figure Patent Applicant: NGK SPARK PLUG Co., Ltd.

Claims (5)

[Claims] (1) The intermediate electrode of a spark plug is made by co-firing an alumina powder molded body whose surface is coated with platinum, iridium, a platinum alloy, or a noble metal and an alumina insulator as a discharge part, and alumina particles are used as an aggregate to coat the surface of the spark plug. A spark plug equipped with a sintered body coated with metal oxide. (2) The alumina powder of the sintered body of the intermediate electrode section mentioned above is 145
A spark plug characterized by being made of high-purity fine powder that can be fired at temperatures below 0°C. (3) The spark plug according to item 1 or 2, wherein the metal element of the metal oxide forming the intermediate electrode sintered body according to item 1 has a melting point of 1450° C. or higher. (4) The metal oxide mentioned above is made of high-purity alumina powder that can be fired at temperatures below 1450°C and has a melting point of 145°C for the intermediate electrode.
A spark plug that is coated with a metal element having a temperature of 0°C or higher, then formed into the shape of an intermediate electrode, and fired in an oxygen atmosphere to form a sintered intermediate electrode. (5) A spark plug in which the intermediate electrode sintered body described in the preceding paragraph is inserted into the long leg portion of the insulator immediately adjacent to the discharge portion.