JPH02155184A - Spark plug having nitride series ceramic insulator - Google Patents

Abstract

PURPOSE:To achieve a nitride series ceramic insulator with a high through voltage not requiring a larger diameter of the insulator by making the difference between the intrinsic diameter of the insulator and the diameter of a central electrode within an axial bore be at least 4.9mm and making the central electrode diameter within the axial bore not less than 0.9mm and not more than 2.0mm. CONSTITUTION:When the diameter of a central electrode within an axial bore is denoted by phiA, and the intrinsic diameter of an insulator by phiB, phiB-phiA is made to be at least 4.9mm and phiA is made to be not less than 0.9mm and not more than 2.0mm. Namely, the wall thickness of the insulator (phiB-phiA)/2 must be at least 2mm, because when it is nearly same as that of alumina ceramic, through current will be generated. Further, because the upper limit value (about 6mm) of the intrinsic diameter phiB of the insulator is determined by the diameter of a screw of a main fitting for spark plug, it is advantageous to reduce the diameter of the central electrode within the axial bore phiA, but the central electrode will be liable to be broken during manufacturing as a result of it. Therefore, phiA is made to be in the range not less than 0.9mm and not more than 2.0mm. Thus, the through voltage can be made higher without making the diameter of the insulator 2 larger.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application] The present invention relates to a spark plug for an internal combustion engine, and more particularly to an improvement in a spark plug using a nitride-based ceramic as an insulator.

BACKGROUND ART Nitride-based ceramics have better thermal resistance and thermal conductivity than alumina, which is normally used as an insulator for spark plugs.

Conventionally, a spark plug having a nitride-based ceramic insulator includes a cylindrical civil engineering metal fitting, a cylindrical insulator formed of a ceramic sintered body fitted into the main metal fitting, and a center electrode fitted into the insulator. A nitride-based ceramic insulator was used for the long leg portion of the insulator.

[Problems to be Solved by the Invention] However, conventional spark plugs having a nitride-based ceramic insulator have the following drawbacks.

(A) Nitride-based ceramics have strong covalent bonding properties, and their insulation properties decrease at high temperatures, making them susceptible to penetration defects.

In order to prevent penetration, increasing the thickness of the insulator will increase the diameter of the long leg part, and making the center electrode thinner will reduce the mechanical strength of the center electrode and cause problems with heat dissipation at the firing part. occurs.

An object of the present invention is to provide a nitride-based ceramic insulator that is excellent in heat removal from the igniting part and has a high through voltage without increasing the diameter of the insulator or reducing the mechanical strength of the center electrode. We provide spark plugs that take care of your needs.

[Means for Solving the Problems] In order to achieve the above problems, a spark plug having a nitride-based ceramic insulator of the present invention has the following configuration.

(2) Consisting of a cylindrical metal shell, a cylindrical insulator fitted into the cylindrical metal shell and formed of a ceramic sintered body, and a center electrode fitted into the insulator, at least the long leg portion of the insulator. In a spark plug in which a nitride-based ceramic insulator is used, if the axial hole center electrode diameter is φA and the insulator is φB, φB - φA is at least 4.
．． 9 mm and a configuration in which φA is 0.9 mm or more and 2.0 mm or less.

■Has the configuration of ■ above, and the center electrode is (a)
The center shaft is formed of a noble metal including a noble metal alloy manufactured by blending complex elements, or is formed by wrapping a nickel alloy with the precious metal, and (a) the center shaft is sealed with a conductive glass sealing material within the shaft hole of the insulator. and (1) the gap between the electrocardiogram in the shaft hole and the shaft hole has a thickness t of 0.1 mm.
Above 1. Structure filled with heat-resistant insulating material of 100 mm or more.

[Action and effect of invention] The present invention has the following functions and effects.

・Regarding claim 1> If the center electrode in the shaft hole is φA and the insulator is φB, the insulator wall thickness (φB - ΦA)/2 is at least as large as that of alumina ceramic because it causes penetration. A thickness of 2 mm is required.

Also, the upper limit of the insulator φB is determined by the thread diameter of the main metal fitting of the spark plug (approximately 0 + nm), so
The smaller the axial center electrode diameter φA is, the more advantageous it is, but the more likely it is to break during manufacturing. Therefore, the range of φA is 0.
It is 9 mm or more and 2.0 mm or less.

Within the above range, a spark plug having a nitride-based ceramic insulator can have a high through voltage withstand voltage without increasing the diameter of the insulator.

Regarding Claim 2> A nitride-based ceramic insulator is used for the long leg portion of the insulator. Here, (a) it is formed of a noble metal including a noble metal alloy manufactured by blending complex elements, or it is formed by wrapping a nickel alloy with this precious metal, and (b) it is conductive within the shaft hole of the insulator. It is joined to the center shaft by a glass sealing material, and (a) the gap between the center electrode inside the shaft hole and the shaft hole is
(2) It is filled with a heat-resistant insulator with a diameter of 0.1 mm or more and 1.0 mm or less.

A spark plug having a nitride-based ceramic insulator has a thin center electrode due to its structure, and if left as is, the T4 pole is likely to wear out. To compensate for this, the above-mentioned configuration (a) is adopted.

In order to compensate for the decrease in mechanical strength due to the reduction in the diameter of the center electrode and to effectively remove heat, the above-mentioned configurations are adopted. Here, if this numerical limitation is less than 0°1 mm, it is difficult to compensate for the decrease in mechanical strength of the center electrode;
This is because if it exceeds 0 mm, it will be too thick and the heat transfer will be poor.

The above-mentioned configuration (a) is adopted so that the bonding strength between the center shaft and the center electrode is maintained.

With the configurations (a) to (v), the heat from the firing part at the tip of the center electrode can be conducted through the heat-resistant insulator, the long legs of the insulator, and the backing, and can be released to the metal shell.

Therefore, a spark plug with a nitride-based ceramic insulator takes advantage of the advantages of excellent thermal conductivity and thermal shock resistance, and also has excellent heat dissipation from the ignition part without reducing the mechanical strength of the center electrode. , high penetration voltage can be achieved.

[Example] Next, an example of the present invention (corresponding to claim 1.2) will be described as a first example.
This will be explained based on the diagram and FIG.

Spark plug A having a nitride-based ceramic insulator is
As shown in FIG. 1, a cylindrical metal shell 1, a leg insulator 2 fitted into the cylindrical metal shell 1 and made of aluminum nitride (thermal conductivity 170 to 180 W/m −k; room temperature), It consists of a center electrode 3 fitted into a shaft hole 20 of the insulator 2.

The main metal fitting 1 is made of a heat-resistant metal, and the tip is coated with platinum-20.
% iridium alloy is welded.

The leg insulator 2 (insulator light diameter φB=5.5) is fixed inside the metal shell 1 via a packing 13 arranged on the tapered rIII 112 inside the metal shell 1.

Further, the outer diameter of the insulator 2 is formed to have a small diameter on the front end side and a large diameter on the rear end side. Correspondingly, the shaft hole 20 has a tip side 21.
has a small diameter (φ1.5), and the rear end side 22 has a large diameter.

The center electrode 3 has a small diameter tip (axial hole center electrode diameter φA=1
．． 2), and the rear end becomes a flange-like portion 31 and is locked to the conical surface 23 inside the insulator 2.

This center electrode 3 has an electrode body 32 made of a nickel alloy.
The outer periphery of the is wrapped with a platinum-20% iridium alloy 33, and at the tip that is fitted into the shaft hole 20, a heat-resistant insulator is used in the gap with the shaft hole 20. In this embodiment, an alumina cement 24 (thickness t=0. The rear end surface 34 of the flanged portion 31 is joined to the resistor 41 fixed to the center shaft 4 by means of a conductive glass sealing material 35.

The spark plug A having the nitride-based ceramic insulator of this embodiment has the following functions and effects.

(Force) Axial hole center electrode diameter φA is 1.2, insulator light diameter φB
is assumed to be 5.5 mm, and the insulator wall thickness (φB-φA)/
2 becomes 2.15, which makes it difficult for the insulation 111g1t to cause penetrating. Furthermore, since φA is 1.2 mm, it is not too thin and is unlikely to break during manufacturing.

Therefore, the spark plug A can maintain a high through voltage withstand voltage without increasing the diameter of the insulator.

(g) Due to the above-mentioned reason, the shaft hole center electrode diameter φA is 1.2
If left as is, the electrode will easily wear out. However, the center electrode 3 has an electrode body 3 made of a nickel alloy.
Since the outer periphery of the electrode 2 is wrapped with a platinum-20% iridium alloy 33, electrode wear is less likely to occur.

(i) The rear end surface 34 of the flange-shaped portion 31 is joined to the resistor 41 fixed to the center shaft 4 by a conductive glass sealing material 35. Further, at the tip that is fitted into the shaft hole 20, the gap between the shaft hole 20 and the shaft hole 20 is filled with alumina cement 24 having a thickness t=0.15 mm. Therefore, the strength of the bond between the resistor 41 and the center electrode 3 can be increased. In addition, since the alumina cement 24 is firmly fixed in the insulator 2, breakage is unlikely to occur even when subjected to combustion gas vibrations or mechanical vibrations.
0W/m・k (room temperature) is made of alumina and has a thickness of 0.
Since the diameter is 15 mm, the heat is removed quickly, and the state of the heat removal is shown in FIG.

For reference, FIG. 3 shows how heat is removed from a spark plug B having an insulator 200 made of alumina and a center electrode 100 made of nickel 110 and copper 120.

(k) The long leg insulator 2 made of aluminum nitride has a small coefficient of thermal expansion (4.9X10-'/deg).The center electrode 3 fitted into the insulator 2 has an electrode body 32 made of a nickel alloy. Its outer periphery is wrapped with platinum-20% iridium alloy 33.

Here, this center electrode 3 is not easily oxidized and has a small coefficient of thermal expansion, so it is suitable for being fitted into the insulator 2.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a main part showing an embodiment of a spark plug having a nitride-based ceramic insulator of the present invention, FIG. 2 is a cross-sectional view of a main part showing how the spark plug heats up, and FIG. FIG. 2 is a cross-sectional view of a main part showing how heat is removed from a spark plug having an alumina insulator. In the diagram: 1... Cylindrical metal shell 2... Long leg insulator 3
... Center electrode 4 ... Center shaft 20 ... Shaft hole 33
...Platinum-20% iridium alloy (noble metal including IL metal alloy) 35... Conductive glass sealing material φA...
・Shaft hole circle center electrode diameter φB...Insulator joke t...
Thickness (thickness of heat-resistant insulator) A...Spark plug with nitride-based ceramic insulator

Claims (1)

[Scope of Claims] 1) Consisting of a cylindrical metal shell, a cylindrical insulator formed of a ceramic sintered body and fitted into the cylindrical metal shell, and a center electrode fitted into the insulator, In a spark plug in which a nitride-based ceramic insulator is used for at least the long leg portion of the insulator, where φA is the diameter of the central electrode in the shaft hole and φB is the original diameter of the insulator, φB−φA is at least 4.9 mm, A spark plug having a nitride-based ceramic insulator, characterized in that φA is 0.9 mm or more and 2.0 mm or less. 2) The center electrode is (a) formed of a noble metal including a noble metal alloy produced by blending complex elements, or formed by wrapping a nickel alloy with the noble metal, and (b) an insulator shaft. It is connected to the center shaft in the hole by a conductive glass sealant, and (c) the gap between the center electrode in the shaft hole and the shaft hole is made of heat-resistant insulator with a thickness t of 0.1 mm or more and 1.0 mm or less. A spark plug having a nitride-based ceramic insulator according to claim 1, wherein the spark plug is filled with a nitride-based ceramic insulator.