JP3050266B2 - Ceramic heating element and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heating element constituting a ceramic glow plug used in, for example, a diesel engine or the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a ceramic glow plug has a structure in which a heat generating portion is formed by integrating a refractory metal such as tungsten with Si ₃ N ₄ during hot pressing.
As a ceramic glow plug, for example,
JP-A-15077 and JP-A-1-157084. 64-15077
The glow plug disclosed in Japanese Patent Application Laid-Open Publication No. H10-209400 includes a heating unit made of a ceramic sintered body in which a heating element coated with a ceramic coating layer by a gas phase method is embedded. In the ceramic heating element disclosed in Japanese Patent Application Laid-Open No. 1-157084, a heating resistance wire made of a refractory metal such as W, Mo, Re or an alloy thereof is embedded in a Si ₃ N ₄ sintered body. And an intermediate layer made of a non-oxide ceramic such as a metal element identical to the main constituent metal element of the resistance wire or a nitride, carbide, silicide, silicide carbide or the like on the surface of the resistance wire. is there.

A self-current control type glow plug is disclosed in Japanese Patent Publication No. 4-34052 and Japanese Patent Publication No. Sho 60-194.
No. 04, JP-A-62-141424 and the like.

For example, in a self-control glow plug disclosed in Japanese Patent Publication No. 4-34052, a current controlling resistor is connected in series to the heating element in order to control the temperature of the heating element during energization. The heating wire coil and the resistor coil are connected in series and buried in a ceramic sintered body to constitute an integrated ceramic heater, and the heating wire has a temperature-resistance coefficient of 4 times or less. It is made of a tungsten W and rhenium Re alloy wire having such a positive temperature coefficient of resistance, and the resistor is made of a wire of pure W or pure molybdenum Mo. Further, the sheathed glow plug disclosed in Japanese Patent Publication No. 60-19404 discloses a self-contained glow plug having a heat-resistant bottomed metal tube in which a heating element and a resistor are directly connected to each other between an inner bottom and a center electrode. This is a control-type sheathed glow plug, in which the winding pitch of the resistor is made denser at the portion near the electrode-side mounting bracket on the center electrode side, and coarsely formed at the portion closer to the heating element.

[0005]

However, the conventional self-current control type glow plug, when used in a high temperature combustion chamber such as a heat shield engine, has sufficient heat resistance, heat shock resistance, and high temperature strength. I could not say it. Further, the self-control glow plug disclosed in the related art connects a heating wire coil manufactured using a tungsten carbide wire and a resistor coil manufactured using a Ni wire coil, and the two are made of materials having different temperature coefficients of resistance. Or the heating element and the resistor of the winding are made in different shapes, so that there is a problem that the Ni wire is broken due to overheating during use and deteriorates due to aging. The structure became complicated, and cost and strength were not satisfactory.

In the conventional self-current control type glow plug, a metal coil such as a tungsten wire is embedded and sintered in ceramics at the time of molding. Pressure sintering is usually performed. Therefore, the shape of the metal coil buried in the ceramic is limited, and it becomes a two-dimensional structure,
The space between the wall of the ceramic outer shell and the metal coil is separated,
There is a problem that the heat transfer efficiency is reduced and the quick heat property of the ceramic heater is reduced. Further, in a ceramic glow plug having a structure in which a tungsten wire and Si ₃ N ₄ are integrated during a hot press, a tungsten wire and a S wire are used.
A gap is formed at the boundary with i ₃ N ₄ , causing a problem that moisture or oxygen invades from the gap and causes corrosion or the like. In particular, in order to prevent moisture or oxygen from entering from the gap between the tungsten wire and Si ₃ N ₄ , the gap between the boundaries must be sealed. Although it is conceivable, there is a problem that the number of manufacturing steps increases and the reliability decreases.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, and to provide a self-current control type ceramic heating element and a method for manufacturing the same. In order to increase the degree of heat insulation in the middle area and arrange a current control coil to form a current control unit, to reduce the degree of heat insulation in the tip area and increase the amount of heat dissipation to form a heating unit, A self-current control type that adjusts the current flowing through the current control unit to ensure the optimal amount of heat generation. Especially, heat transfer is improved by tightly contacting the boundary between the outer shell, the filling member, and the metal coil without any gap. A highly reliable ceramic heating element that prevents moisture or oxygen from entering the boundary between the metal coil and the ceramic in the outer shell in the heating section, reduces manufacturing costs, and ensures stable strength, and its To provide a production method.

[0008]

The present invention is configured as follows to achieve the above object. That is, the present invention provides an outer shell made of dense ceramics having both open ends, a filling member made of porous ceramics included on both inner sides of the outer shell, and the above-mentioned joined to both end surfaces of the outer shell. A sealing film for sealing the inside of the outer shell, a low thermal conductive ceramic disposed at the center of the outer shell and filled with N ₂ gas, and an inner wall surface on the tip end side of the outer shell filled with the filling member; A metal coil having a portion arranged in a contact state and a portion arranged in a state of being separated from an inner wall surface of the outer shell in which the N ₂ gas is sealed,
And a ceramic heating element characterized by comprising:

Further, in this ceramic heating element,
The metal coil is made of a tungsten wire, and the portion disposed in contact with the inner wall surface of the outer shell constitutes a heating element coil, and is disposed at a distance from the inner wall surface of the outer shell. The part constitutes a current control coil.

In this ceramic heating element,
On the surface of the metal coil, a ceramic film coated by a CVD method or converted from an organic silicon polymer is disposed.

Further, in this ceramic heating element,
The porous ceramic contains Si and Ti.

In the ceramic heating element,
The sealing film is made of glass or ceramics of the same kind as the outer shell.

Further, in this ceramic heating element,
The outer shell is made of Si ₃ N ₄ .

Further, in this ceramic heating element,
The low thermal conductive ceramic is composed of ceramic whiskers and / or ceramic powder.

Further, according to the present invention, an outer shell having both ends opened from dense ceramics is produced, and a surface of a coil made of a high melting point metal wire is coated with ceramics having a thermal expansion coefficient substantially equal to that of the coil. The coil is disposed inside the outer shell so as to contact the inner wall surface at one end side and is spaced at the intermediate inner wall surface, and a material containing Si and Ti is provided at one inner end side of the outer shell. Is filled with a material containing low thermal conductive ceramics and Si and Ti on the other end side, and then fired in a N ₂ atmosphere to be fired.
The raw material containing Ti and Ti is changed to porous ceramics of Si ₃ N ₄ and TiN, and the porous ceramics are brought into close contact with the dense ceramics of the outer shell, and then the interior is sealed at both end surfaces of the outer shell. The present invention relates to a method for manufacturing a ceramic heating element, characterized in that a film is coated.

[0016]

The ceramic heating element and the method of manufacturing the same according to the present invention are constructed as described above, and operate as follows. That is, this ceramic heating element includes a porous ceramic filling member on both sides inside the outer shell of the dense ceramics, and joins a sealing film for sealing the inside to both end surfaces of the outer shell. A low thermal conductive ceramic is disposed in the center and N ₂ gas is sealed, and the metal coil is in contact with the inner wall surface on the tip side of the outer shell filled with the filling member and the N ₂ gas is sealed. Since the metal coil is arranged in a state of being spaced from the inner wall surface of the outer shell, a portion of the metal coil arranged in contact with the inner wall surface of the outer shell constitutes a heating element coil, and the inner shell of the outer shell has The portion of the metal coil arranged at a distance from the wall forms a current control coil.

Therefore, if a current is passed through the metal coil,
While the heat generated by the heating element coil heats the outer shell and radiates heat to the outside, the heat generated by the current control coil is shielded and the temperature rises, and the temperature rises. The current flowing through the current control coil is suppressed, and constitutes a current control unit. That is, if the temperature of the current control coil becomes high, the resistance value increases, the current flowing through the metal coil decreases, the amount of heat generated from the outer shell is self-controlled, and is controlled to an optimum value. Become.

Further, the porous ceramic constituting the filling member on both sides of the outer shell is formed by filling a raw material containing Si and Ti into an outer shell made of dense Si ₃ N _4, and forming an N ₂ gas. By reacting and firing inside, the Si and Ti are changed into Si ₃ N ₄ and TiN. If the outer shell is made of dense Si ₃ N ₄ ,
Since N expands, Si ₃ N ₄ of the outer shell and the reaction Si ₃ N ₄ can be in close contact with each other, and both ends of the outer shell are open. N ₂ gas can be sealed.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a ceramic heating element and a method of manufacturing the same according to the present invention will be described below with reference to the drawings.
FIG. 1 is a sectional view showing an embodiment of a ceramic heating element according to the present invention.

This ceramic heating element is mainly used by being incorporated in a ceramic glow plug incorporated in a diesel engine or the like, and has a pipe-shaped outer shell 1 made of dense ceramics and having open ends. Filling members 2 and 3 made of porous ceramics included on both sides inside the outer shell 1, a sealing film 4 for sealing the inside of the outer shell 1 joined to both end surfaces 15 of the outer shell 1, an outer shell 1
Disposed within the central and N ₂ gas and a metal coil 10 disposed in the low thermal conductivity ceramics 5, and the filling members 2 and 3 and the low thermal conductive ceramic 5 is sealed in. The filling members 2 and 3 are filled in the outer shell 1 in a state of being in close contact with the inner wall surfaces 7 and 14 of the outer shell 1.

The metal coil 10 is a resistance wire made of a metal having a high melting point such as tungsten, and is disposed in contact with the inner wall surface 7 on the distal end side of the outer shell 1 filled with the filling member 2. , And a current control coil 9 located at a position spaced apart from the inner wall surface 8 of the outer shell 1 in which N ₂ gas is sealed. Further, the metal coil 10 includes a connection line 11 that connects one end of the heating element coil 6 and one end of the current control coil 9,
A connection wire 12 extending in the outer shell 1 connected to the other end of the heating element coil 6 and protruding from the porous ceramic filling member 3;
And a connection line 13 connected to the other end of the current control coil 9 and extending inside the outer shell 1 and protruding from the porous ceramic filling member 3.

In this ceramic heating element, the surface of the metal coil 10 is coated with a ceramic film. The porous ceramics constituting the filling members 2 and 3 contain Si and Ti, and change to Si ₃ N ₄ and TiN by firing, and change to TiO ₂ and TiON by oxidizing TiN. It is stable. The sealing film 4 bonded to both end surfaces 15 of the outer shell 1 and the end surfaces of the filling members 2 and 3 is made of a glass material made of a polymer precursor or the like or a ceramic material of the same kind as the outer shell 1. The outer shell 1 is made of dense Si
It is prepared from ₃ N ₄ ceramics. The low thermal conductive ceramics 5 is made of any one of SiC whisker, Si ₃ N ₄ whisker, Al ₂ O ₃ whisker, Al ₂ O ₃ —SiO ₂ whisker, ceramic powder or Si ₃ N ₄ porous material. It is preferable that the ceramics around the current control coil 9 be made of a material having a low thermal conductivity equivalent to that of air from the viewpoint of a heat shielding structure. _Two
The gas is sealed at the time of firing, and the structure is such that oxidation of the metal coil 10 does not occur.

The ceramic heating element is incorporated in a ceramic glow plug, and the end of the outer shell 1 has a hollow body with an electrode mounted in the hollow part through an insulator such as an insulating bush. It is fixed to.
In this case, the hollow main body is made of a metal such as a heat-resistant alloy, and has a screw or the like for attachment to another component. The end of the connection line 13 is connected to the electrode, and the end of the connection line 12 is connected to the hollow body. Therefore,
In this ceramic heating element, the current flows from the electrode to the connection line 1
3 → current control coil 9 → connection wire 11 → heating element coil 6
The connection line 12 is configured to flow through the hollow body.

This ceramic heating element can be manufactured as follows. In the method of manufacturing the ceramic heating element, first, an outer shell is formed from dense ceramics, and a surface of the metal coil 10 made of tungsten wire or the like is coated with SiC having substantially the same thermal expansion coefficient as that of the metal coil 10.
Is coated with a CVD method or the like. Then, S
A metal coil 10 such as a tungsten wire coated with a ceramic such as iC is disposed inside the outer shell 1 so as to contact the inner wall surface 7 on one end side of the outer shell 1 and be spaced apart from the inner inner wall surface 8. At the same time, a material containing Si and Ti is filled into one end of the inside of the outer shell 1, a low thermal conductive ceramic 9 such as a SiC whisker or Si ₃ N ₄ porous material is filled in the middle, and a material containing Si and Ti is filled into the other end. Thereafter, the shell 1 filled with the raw material containing Si and Ti and the low thermal conductive ceramic member is fired in a N ₂ atmosphere by reaction firing, and the raw material containing Si and Ti is converted into Si ₃ N ₄ ,
The porous ceramics of TiN, TiO ₂ , and TiON are converted into the filling members 2 and 3 and the porous ceramics are brought into close contact with the dense ceramics forming the inner wall surfaces 7 and 14 of the outer shell 1. The coil 6 can be brought into close contact with the inner wall surface 7 of the outer shell 1. Further, since both ends of the outer shell 1 are open, the N ₂ gas is sealed in the outer shell 1 during firing, especially in the low thermal conductive ceramics 5 in the middle thereof. Further, a sealing film 4 made of the same type of ceramics as the outer shell 1 is coated on both end surfaces 15 of the outer shell 1 by a CVD method, and the inside of the outer shell 1 is sealed to produce a ceramic heating element. Therefore, this ceramic heating element improves the adhesion between the heating element coil 6 and the filling member 2 and the inner wall surface 7 of the outer shell 1 at the heating section, and improves heat transfer, as compared with the conventional ceramic heating element. The temperature can be raised immediately, the number of manufacturing steps is simple, the manufacturing cost can be reduced, and a ceramic heating element to be incorporated in a ceramic glow plug with high stability and high reliability can be manufactured.

Next, specific examples of the ceramic heating element will be described. [Example 1] First, tungsten W having a wire diameter of φ0.2 mm was used.
The wire is wound into a coil having an outer diameter of 3.5 mm to produce a metal coil. C on the surface of this tungsten wire coil
SiC was coated by the VD method. A coil of a tungsten wire coated with SiC is placed in a porous mold such as a gypsum mold for slip casting, and in this state, Si and Ti are mixed at 85:
A predetermined amount of the raw material, that is, the slurry, mixed at a ratio of 15 was injected into the porous mold. Next, with the slurry solidified to a certain degree, Si is added into the porous mold on the slurry filled in the porous mold.
C whiskers were slurried and poured. With the SiC whiskers solidified to some extent, the SiC whiskers are
A predetermined amount of the above slurry of Si and Ti was injected into the porous mold on the whiskers. The water content of the slurry was sufficiently absorbed through the porous mold and solidified. According to the above process, a raw material of Si and Ti was thickened around the tungsten wire coil, and a molded body in which SiC whiskers were arranged in an intermediate portion could be produced.

Next, the compact was taken out of the porous mold, and the compact was dried in an N ₂ gas atmosphere.
9% or more dense Si ₃ N ₄ pipe-shaped outer cylinder, that is, outer shell 1
The dried molded body was inserted into the inside. At this time, the outer diameter of the molded body and the inner diameter of the outer shell 1 were substantially the same, and there was substantially no gap between them. In a setting state in which the molded body is inserted into the outer shell 1, the material is heated to a maximum of 1400 ° C. and fired in a firing furnace in an N ₂ gas atmosphere of 5 atm, and the raw material components of Si and Ti are Si ₃ N ₄ , A low-thermal-conductivity ceramic member 5 in which a sintered body of a nitride such as TiN, that is, a porous ceramic filling member 2 or 3 was changed, and N ₂ gas was sealed with SiC whiskers was formed. In this firing step, about 0.2% of expansion was caused by TiN, so that no void was generated at the boundary between the fired body and the outer shell 1. Next, Si ₃ N ₄ was applied to both end surfaces 15 of the outer shell 1 and the end surfaces of the porous ceramic filling members 2 and ₃ by CVD.
And N ₂ gas was completely sealed in the middle of the outer shell 1.

[Embodiment 2] In this method of manufacturing a ceramic heating element, instead of coating the surface of the coil of tungsten wire with SiC by CVD, a coil of tungsten wire was replaced with polycarbo, which is an organosilicon polymer. The organic silicon polymer was immersed in a toluene solution of silane and heated to a predetermined temperature in an N ₂ gas atmosphere to convert the organosilicon polymer to Si ₃ N ₄ . This processing step was repeated five times to form a ceramic coating of about 50 μm on the outer surface of the tungsten wire coil. The same ceramic heating element was manufactured in the same process as in the first embodiment using the coil of the tungsten wire having the ceramic coating.

[Embodiment 3] In this method for manufacturing a ceramic heating element, a raw material, ie, a slurry consisting of only Si is used for the outer shell 1 instead of a raw material consisting of Si and Ti, and the outer shell 1 is used for the intermediate part. A ceramic heating element was produced in the same process as in Example 1 by using the same SiC whiskers as in Example 1 and using the slurry. In this case, the porous ceramics constituting the filling members 2 and 3 are porous Si
Consisted ₃ N _4.

Example 4 In the method of manufacturing a ceramic heating element, Si and Si ₃ N ₄ were mixed in the outer shell 1 in a ratio of 80:20 instead of the raw material composed of Si and Ti. A ceramic heating element was manufactured in the same process as in Example 1 using the raw material, that is, the slurry. In this case, the porous ceramics constituting the filling members 2 and 3 were composed of porous Si ₃ N ₄ .

Embodiment 5 Further, in this method for manufacturing a ceramic heating element, a raw material of Si, ie, a slurry is used for the outer shell 1 instead of the raw material composed of Si and Ti, and SiC whiskers are used instead of the slurry. Using a raw material of Si, ie, a slurry, a ceramic heating element was manufactured in the same process as in Example 1. In this case, the porous ceramics constituting the filling members 2 and 3 are porous Si ₃
Low thermal conductive ceramic member 5 composed of N ₄
Was composed of a porous Si ₃ N ₄ material.

The ceramic heating element according to the present invention can be manufactured as shown in each of the above-mentioned embodiments, and although there is a slight difference in the temperature rise time of the ceramic heating element with respect to the current supply time, Almost the same effects can be achieved.

[0032]

The ceramic heating element and the method of manufacturing the same according to the present invention are configured as described above and have the following effects. That is, this ceramic heating element
A porous ceramic filling member is enclosed on both sides of the outer shell of the dense ceramic, and a sealing film for sealing the inside of the outer shell is joined to both end faces of the outer shell. And N ₂ gas is sealed therein, and the metal coil is in contact with the inner wall surface on the tip side of the outer shell filled with the filling member, and the inside of the outer shell filled with the N ₂ gas is filled. Since the metal coil is disposed apart from the wall surface, the portion of the metal coil disposed in contact with the inner wall surface of the outer shell constitutes a heating element coil, and is separated from the inner wall surface of the outer shell. The portion of the metal coil arranged in the above constitutes a current control coil. Therefore, when an electric current is applied to the metal coil, the heating element coil constitutes a heating portion and heats the outer shell to radiate heat, whereas the current control coil is made of the low thermal conductive ceramic. The temperature is increased by the heat shield, and when the temperature of the current control coil rises, the resistance value increases, the current flowing through the metal coil decreases, and the amount of heat generated from the outer shell is self-controlled. Is controlled to the optimum value.

In this ceramic heating element, the heating element coil constitutes a heating section by the above configuration, but since the heating element coil is disposed in contact with the inner wall surface of the outer shell, the entire outer shell is formed. Temperature rises uniformly. Since the heating element coil is in close contact with the inner wall surface of the outer shell and the filling member is filled so as to fill the heating element coil,
The heat conductivity of the heat generating portion becomes extremely good.

In this ceramic heating element, the heating element coil and the current control coil are made of a continuous metal coil such as a tungsten wire.
For example, it can be easily manufactured using a ceramic coil manufacturing jig having a through hole in the center and a spiral groove on the outer peripheral surface, and since there is no connection part on the way, the reliability is improved electrically. The metal coil rich in durability can be provided at low cost.

Further, Si and Ti are used for producing porous ceramics constituting the filling member on both sides of the outer shell.
Is filled in a shell made of dense Si ₃ N _4, and ceramic whiskers or porous ceramics are filled in the center of the shell to produce a low heat conductive member in the center, By reacting and firing in an N ₂ gas atmosphere, Si and Ti are converted into Si ₃ N ₄ , Ti
N, TiO ₂ , and TiON are converted to porous ceramics, and the outer shell is made of dense Si ₃ N
If it is made in ₄ , the TiN expands at the time of firing, and the Si ₃ N _{4 of the} outer shell and the reaction Si ₃ N ₄ can be in close contact with each other, and since both ends of the outer shell are open, at the same time the shell during firing, the N ₂ gas can be easily encapsulated in particular in the intermediate section, if blocked both end faces in sealing membrane such as ceramics, can be encapsulated N ₂ gas completely the outer inner shell.
In addition, since N ₂ gas can be sealed in the outer shell during firing, the number of manufacturing steps can be reduced and the cost can be reduced. Moreover, the N ₂ gas filled in the outer inner shell, can improve the corrosion resistance of the metal coil of tungsten wire or the like, the durability can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a ceramic heating element according to the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 outer shell 2, 3 filling member 4 sealing film 5 low thermal conductive ceramics (ceramic whisker or ceramic powder) 6 heating element coil 7, 8, 14 inner wall surface 9 current control coil 10 metal coil 11, 12, 13 connection wire 15 end face

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F23Q 7/00

Claims (8)

(57) [Claims] 1. An outer shell made of dense ceramics having open ends, a filling member made of porous ceramics included on both inner sides of the outer shell, and an outer shell joined to both end faces of the outer shell. A sealing film for sealing the inside of the shell, a low thermal conductive ceramic disposed in the center of the inside of the outer shell and filled with N ₂ gas, and an inner wall on the distal end side of the outer shell filled with the filling member; A ceramic heating element comprising: a portion disposed in a contact state; and a metal coil having a portion disposed apart from an inner wall surface of the outer shell in which the N ₂ gas is sealed. . 2. The metal coil is made of a tungsten wire, and the portion disposed in contact with the inner wall surface of the outer shell forms a heating element coil and is separated from the inner wall surface of the outer shell. The ceramic heating element according to claim 1, wherein the portion arranged in a state forms a current control coil. 3. The ceramic heating element according to claim 1, wherein a ceramic film coated by a CVD method or converted from an organic silicon polymer is disposed on a surface of the metal coil. 4. The porous ceramic is made of Si and Ti.
The ceramic heating element according to claim 1, comprising: 5. The ceramic heating element according to claim 1, wherein the sealing film is made of glass or a ceramic of the same kind as the outer shell. 6. The ceramic heating element according to claim 1, wherein the outer shell is made of Si ₃ N ₄ . 7. The ceramic heating element according to claim 1, wherein the low thermal conductive ceramic is made of ceramic whiskers and / or ceramic powder. 8. A shell having open ends at both ends is made of dense ceramics, and a surface of a coil made of a high melting point metal wire is coated with ceramics having a thermal expansion coefficient substantially equal to that of the coil. The coil is disposed inside the outer shell so as to be in contact with the inner wall surface and to be spaced from the intermediate inner wall surface.
feed containing i, after filling a raw material containing Si and Ti inside middle low thermal conductivity ceramic and internal other end, which react fired in a N ₂ atmosphere, a raw material containing the Si and Ti Si ₃ N ₄ and TiN are converted into porous ceramics, the porous ceramics are brought into close contact with the dense ceramics of the outer shell, and then both end surfaces of the outer shell are coated with a sealing film for sealing the inside. Manufacturing method of ceramic heating element.