JPH07208740A - Ceramic heat generator - Google Patents

Abstract

PURPOSE:To so fill a coiled metal heat generating wire and ceramic powder in an outer shell of a sheath state made of ceramics without generating a volumetric change at the time of burning to be integrated. CONSTITUTION:At least one ceramic film of magnesium oxide and aluminum oxide is provided on a surface of a coiled metal heat generating wire 2 made by coupling two metals having different resistance temperature coefficients, inserted into an outer shell 21 of a sheath state made of silicon nitride, formed at a continued part (matrix) made of silicon, carbon, oxygen and nitrogen, and composite ceramics in which ceramic particles are dispersed as filler is filled in the shell 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug for promoting vaporization and ignition of liquid fuel in an internal combustion engine, a combustor, etc., and more particularly to a ceramic heating element of a glow plug protruding into a combustion chamber.

[0002]

2. Description of the Related Art In a general glow plug of an internal combustion engine, a metal heating wire in the form of a coil made of two kinds of metals is fitted inside a metal tube, and magnesium oxide powder is filled in the inner space of the metal tube. It is structured. On the other hand, in a glow plug using a ceramic, a ceramic heating element is a zigzag metal heating wire made of a refractory metal such as tungsten or W-Re formed from silicon nitride (Si ₃ N ₄ ) in an upper and lower pair. It is sandwiched between the plate-shaped outer shells and baked by the hot pressing method. However, in the ceramic heating element described above, the bond strength of the pair of outer shells cannot be said to be sufficient for vibration and heat history.

Therefore, in order to make the ceramic heating element have a high-strength structure, a coil-shaped metal heating wire made of iron, chromium, nickel alloy or the like is provided inside a sheath-like outer shell formed from silicon nitride and sintered. It is conceivable that the inner shell of the outer shell is filled with magnesium oxide powder, but the outer shell made of silicon nitride is different from the metal tube, and it is swallowed (the outer shell is pressed from the outer peripheral side). Therefore, the outer shell, the metal heating wire inside, and the magnesium oxide powder cannot be consolidated. Further, iron-chromium-nickel alloy and magnesium oxide have lower melting points than silicon nitride and have a large difference in coefficient of thermal expansion from silicon nitride, and therefore cannot be integrally fired.

[0004]

SUMMARY OF THE INVENTION In view of the above problems, the object of the present invention is to provide a sheath-shaped outer shell made of ceramic,
It is an object of the present invention to provide a ceramic heating element excellent in durability, which is formed by filling a coiled metal heating wire and ceramic powder and integrating them so that the volume change does not occur during firing.

[0005]

In order to achieve the above object, the structure of the present invention has a coil-shaped metal heating wire formed by connecting two kinds of metals having different temperature coefficients of resistance, and a sheath-shaped wire made of silicon nitride. Placed inside the outer shell of silicon, carbon, oxygen,
A composite ceramic in which amorphous ceramics made of nitrogen form a continuous portion and ceramic particles are dispersed as a filler is filled in the inner space of the outer shell.

[0006]

In the present invention, the coil-shaped metal heating wire has a surface coated with magnesium oxide (Al2O3) or aluminum oxide. The filler is made into a slurry by kneading polycarbomethylsilazane, silicon nitride powder and titanium powder.

The above-mentioned coil-shaped metal heating wire coated with the slurry-like filler is loaded into the inside of a shell-shaped outer shell formed from silicon nitride and pre-sintered, and further the inside of the outer shell is loaded. Fill the empty space with a slurry-like filler and keep the temperature at about 900 ° C.
The filler is pyrolyzed in the nitrogen atmosphere. That is, polycarbomethylsilazane is converted into silicon / carbon / nitrogen based ceramics, and titanium is converted into titanium nitride (TiN).

The volume of polycarbomethylsilazane contracts by about 0.1% in the process of thermal decomposition, but on the contrary, the volume of titanium expands in the process of conversion to titanium nitride, so that the volume change of the filler as a whole occurs. No As a result, the outer shell made of silicon nitride, the coil-shaped metal heating wire, and the filler are integrated into a high-density composite.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a front sectional view of a glow plug provided with a ceramic heating element according to the present invention, and FIG. 2 is 2A-2A of FIG.
2 is a plan sectional view of a ceramic heating element according to FIG. The glow plug H has a threaded portion 4a of a hollow metal body 4 screwed and supported on the engine body, and the ceramic heating element 1 at the lower end is projected into the pre-combustion chamber of the engine.

Insulator 12 for closing the upper end of the metal body 4
The electrode rod 8 is screwed and supported, and the nut 13 is screwed and fastened to the screw portion 8a. The metallic protective cylinder 3 is fitted and fixed to the lower end of the metallic main body 4. The protective cylinder 3 is previously joined to the ceramic heating element 1 at the fitting portion 3a by a metallizing joining method or the like. The ceramic heating element 1 has a metal cap 5 coupled to the upper end thereof. Preferably, the metal cap 5 is integrally formed with a terminal 5a that contacts the electrode rod 8. The lower end of the ceramic heating element 1 is projected downward from the protective cylinder 3. A metal heating wire 2 is embedded in the ceramic heating element 1.

As shown in FIGS. 1 and 2, for example, a diameter of about 0.
The metal heating wire 2 made of 2 mm of iron / chromium / nickel alloy or the like has the upper end portion 19 a of the lead portion 19 joined to the metal cap 5. The metal heating wire 2 extends straight down substantially along the axis of the protective cylinder 3 and forms a coil-shaped energization controller 17 inside the protective cylinder 3. Further, the energization controller 17 is provided.
The lead portion 19b is extended downward from the above to form a heat generating portion 14 by being coiled outside the protective cylinder 3. The metal heating wire 2 is folded back upward at the lower end of the coil-shaped heating portion 14 to form the lead portion 18. The lead portion 18 extends straight through the inside of the coil-shaped heat generating portion 14 and the energization control portion 17, and the upper end portion 18 a is joined to the upper end portion of the protective cylinder 3.

As shown in FIG. 2, the metal heating wire 2 has a surface coated beforehand with at least one of magnesium oxide and aluminum oxide. The metal heating wire 2 includes a coil-shaped heating portion 14 and an energization control portion 17, which are formed in a sheath-like outer shell 21 formed from ceramic silicon nitride and pre-sintered.
The metal heating wire 2 is loaded so as to contact the inner surface 30 of the outer shell 21. The inner space of the outer shell 21 is filled with a filler 16 which is a non-shrinkable ceramic for sintering, more specifically, an amorphous ceramic composed of silicon, carbon, oxygen, and nitrogen which forms a continuous portion (mother phase). . The filler 16 is a mixture of polycarbomethylsilazane, silicon nitride and titanium in a slurry form, and is filled in the inner space of the outer shell 21. Next, if the metal heating wire 2 and the filler 16 are inserted into the sheath-shaped outer shell 21 and sintered, the metal heating wire 2 and the filler 16 do not change in volume inside the outer shell 21, The outer shell 21 is not cracked or a void is not formed in the inner space of the outer shell 21, and the three are integrally connected.

The ceramic heating element according to the present invention is manufactured as follows. On the surface of the coil-shaped metal heating wire 2 made of iron / chromium / nickel alloy, magnesium oxide (MgO) and aluminum oxide (Al
₂ O ₃ ) was applied. As the filler 16, a polycarbomethylsilazane solution was kneaded with a silicon nitride powder having a particle size of about 0.3 μm and a titanium powder having a particle size of about 10 μm to form a slurry.

A coil-shaped metal heating wire 2 coated with magnesium oxide and aluminum oxide is inserted into the inside of a sheath-like outer shell 21 having an inner diameter of 3.5 mm formed and sintered from silicon nitride in advance, and the outside. The slurry-like filler 16 was pressure-injected into the inner space of the shell 21 and filled without gaps.

The outer shell 21 containing the metal heating wire 2 and the filler 16 was heated in a nitrogen atmosphere at 900 ° C. It was confirmed that polycarbomethylsilazane was converted into completely amorphous silicon, carbon, oxygen and nitrogen in the heating process, and titanium was converted into titanium nitride (TiO ₂ and TiO).

The volume of titanium expands in the process of conversion to titanium nitride, while the volume of polycarbomethylsilazane contracts in the process of conversion to ceramics, so that the volume of the filler 16 does not change as a whole. Therefore, even if the outer shell 21 that encloses the metal heating wire 2 and the filler 16 does not expand or contract in volume as a whole, the outer shell 21, the metal heating wire 2 and the filler 16 are in close contact with each other. A complex was obtained.

As shown in FIG. 3, when the filler 16 is sintered, titanium is titanium nitride particles 31 and silicon is silicon nitride particles 32.
In addition, polycarbomethylsilazane is converted into an amorphous ceramic (continuous layer) 33, and the amorphous ceramic (continuous layer) 33 is converted into titanium nitride particles 31 as a filler.
And silicon nitride particles 32 are integrally bonded. The strength of the filler 16 is 124 MPa at room temperature and 131 at 1200 ° C.
MPa, the dimensional change rate during thermal decomposition is + 0.2%
Is. Titanium converts to titanium nitride at a temperature of 600 ° C.

In the ceramic heating element 1 according to the present invention, as described above, the metal heating wire 2 is loaded in contact with the inner surface 30 of the sheath-like outer shell 21, so that it generates heat when energized, as shown in FIG. The surface temperature of the outer shell 21 reaches 1000 ° C. in about 2 seconds. Since the outer shell 21 made of silicon nitride has heat resistance and is formed into a sheath shape, there is no risk of separation from the metal heating wire 2 due to heat history or vibration.

[0019]

As described above, according to the present invention, a coil-shaped metal heating wire formed by coupling two kinds of metals having different temperature coefficients of resistance is inserted and arranged inside a sheath-like outer shell made of silicon nitride. ,
A composite ceramic in which amorphous ceramics composed of silicon, carbon, oxygen, and nitrogen form a continuous part (matrix) and ceramic particles are dispersed as a filler is filled in the inner space of the outer shell. The outer shell made of is heat-resistant and is molded into a sheath, so there is no risk of peeling between the metal heating wire and heat history or vibration, and durability and reliability are improved. An excellent ceramic heating element can be obtained.

In the filler filled in the sheath-like outer shell, the volume expansion due to the conversion of titanium into titanium nitride during sintering is absorbed by the volume contraction due to the conversion of polycarbomethylsilazane into ceramic. As a whole, there is no volume expansion / contraction, and a composite body is obtained in which the outer shell, the metal heating wire and the filler are in close contact with each other.

Since the surface of the metal heating wire is coated with at least one ceramic film of magnesium oxide and aluminum oxide, deterioration of the metal heating wire is suppressed, and a strong bond with the outer shell made of ceramic and the filler. Is obtained.

[Brief description of drawings]

FIG. 1 is a front sectional view of a glow plug including a ceramic heating element according to the present invention.

2 is a plan sectional view of a ceramic heating element according to 2A-2A in FIG. 1. FIG.

FIG. 3 is a schematic view after sintering of a filler in the ceramic heating element.

FIG. 4 is a diagram showing heat generation characteristics of the ceramic heating element.

[Explanation of Codes] 1: Ceramic heating element 2: Metal heating wire 16: Filler 21: Outer shell 31: Titanium nitride particles 32: Silicon nitride particles 33: Amorphous ceramics

Claims (4)

[Claims] 1. A coil-shaped metal heating wire formed by combining two kinds of metals having different temperature coefficients of resistance is inserted and arranged inside a sheath-like outer shell made of silicon nitride, and silicon, carbon, oxygen and nitrogen are provided. A ceramic heating element, characterized in that the amorphous ceramics are formed into a continuous part and the composite ceramics in which ceramic particles are dispersed as filler are filled in the inner space of the outer shell. 2. The ceramic heating element according to claim 1, wherein the surface of the metal heating wire is coated with at least one ceramic coating of magnesium oxide and aluminum oxide. 3. The ceramic heating element according to claim 1, wherein the ceramic particles are silicon nitride. 4. The ceramic heating element according to claim 1, wherein the ceramic particles are silicon nitride and titanium nitride.