JPH07190362A - Ceramic glowing plug - Google Patents

Abstract

PURPOSE:To provide a ceramic glowing plug improving a quickly heating property, having stable strength and abounding in reliability, by forming a thin coat on the surface of a glowing plug body in which a metallic coil is embedded. CONSTITUTION:A metallic coil 3 is formed by connecting a heating coil 5 with an electric current-controlling coil 4 in series, and is embedded in a glowing plug body 1 consisting of a reaction sintered ceramic which includes Si, Ti and has a porosity of 10% or more, and on the surface of the glowing plug body 1, a coat 2 consisting of a ceramic not including oxides between grain boundaries is formed. The ceramic forming the coat 2 is made of Si3N4 and with which the glowing plug body 1 is coated by CVD and spraying methods.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic glow plug used in a diesel engine or the like.

[0002]

2. Description of the Related Art Conventionally, as a glow plug for a diesel engine, there is one disclosed in JP-A-62-141424. The glow plug is a hollow holder provided with a cylindrical ceramics heater at the tip thereof. The ceramics heater is a thin plate insulator made of insulating ceramics and laminated on both side surfaces and one end of the thin plate insulator. A laminated body composed of a thin plate resistor made of conductive ceramics is bent in the width direction to form a tubular body, and a protective pipe made of conductive ceramics is fitted to the outer peripheral portion of the tubular body on the rear end side. It is baked and integrally molded.

Further, as the self-current control type glow plug, rod-shaped ceramics in which a heating wire made of tungsten wire or the like is embedded in a ceramic material is used to improve heat transfer efficiency and self-control the electric power supplied to the heating wire. It is known to improve heat generation characteristics and prevent overheating in the heater portion. For example, there are self-current control type glow plugs disclosed in Japanese Examined Patent Publication No. 4-34052, Japanese Examined Patent Publication No. 60-19404, and Japanese Unexamined Patent Publication No. 59-157423.

Further, in the glow plug disclosed in Japanese Patent Laid-Open No. 2-183718, a heating portion in which a heating element is embedded in a ceramic sintered body is provided on the tip side of the casing, and the heating element is made of tungsten. Then, the ceramics sintered body has a silicon carbide coating layer formed on the surface of an aluminum nitride sintered body by a vapor phase method.

Further, in the ceramic heater disclosed in Japanese Unexamined Patent Publication No. 4-259781, a heating portion for embedding a heating element is made of aluminum nitride ceramics, and a supporting portion for supporting the heating portion is made of silicon nitride ceramics. It is what

[0006]

However, in the conventional glow plug, a structure in which a metal wire having a high melting point such as a tungsten wire is embedded in ceramics such as silicon nitride in a sandwich shape by hot pressing and integrated is formed. Have Therefore, the conventional glow plug has a problem that a temperature gradient is formed at the center, non-uniform thermal stress is generated, and the ceramics in which the metal wire is embedded is cracked and easily cracked.

Alternatively, the conventional metal coil is made of Fe--Cr.
Make a rush coil, that is, a heating element coil with an alloy,
Then, a brake coil, that is, a current control coil is manufactured, and a heating element coil made of a different metal and a current control coil are connected in series. In the conventional glow plug, the metal coil is arranged inside the metal sheath and the space is filled with MgO powder. However, Fe--Cr alloy and Ni have a low eutectic point and are generally burnt integrally with ceramics. It cannot be bonded, has a property of easily forming a silicide by reacting with Si, and has a problem that a difference in thermal expansion coefficient is large.

Further, AlN used in the conventional glow plug has a characteristic that shrinkage of 15 to 20% occurs during firing. Therefore, during hot press firing in the process of manufacturing the glow plug, the shape of the coil is unavoidably two-dimensional, and as a result, the temperature of the glow plug becomes non-uniform and the ceramic cracks and cracks occur. As a result, there is a problem that durability is reduced.

Further, in the conventional self-current control type glow plug, since a heating wire such as a tungsten wire is embedded in the ceramic at the time of molding and is sintered, pressure sintering is required for sintering, and hot sintering, that is, uniaxial sintering is required. Pressure sintering is usually performed. Therefore, the shape of the heating wire embedded in the ceramics is limited, and the heating wire has a two-dimensional structure, so that the heating wire is separated from the inner wall surface of the ceramic outer shell or the ceramics contained therein, and the heat transfer efficiency is reduced. However, there is a problem that the rapid heating property of the ceramics heater is lowered. Further, in the ceramic glow plug having a structure in which the tungsten wire and Si ₃ N ₄ are integrated at the time of hot pressing in the heat generating portion, a gap is formed at the boundary between the tungsten wire and Si ₃ N _4, and water or moisture is discharged from the gap. There is a problem that oxygen penetrates and corrosion occurs. Especially, tungsten wire and Si ₃ N
There is a problem in that the boundary must be sealed in order to prevent water or oxygen from entering through the gap between the boundary and ₄ .

Therefore, an object of the present invention is to solve the above-mentioned problems, and a metal coil such as a tungsten wire composed of a current control coil and a heating element coil is arranged, and a current flowing through the heating section and the current control section is arranged. It is configured as a self-current control type that adjusts the
After forming a slurry of Ti, Si ₃ N ₄ and reaction sintering, a dense ceramic coating such as Si ₃ N ₄ is formed on the surface of the reaction sintered ceramic by CVD or thermal spraying, and the metal coil is three-dimensionally shaped. And a ceramic glow plug that can be manufactured at low cost.

Another object of the present invention is to fabricate an outer shell from a dense ceramic, arrange a current control coil and a metal coil composed of a heating element coil in the outer shell, and flow through the heating section and the current control section. A self-current control type that regulates an electric current to ensure an optimum amount of heat generation, is filled with a reaction-sintered ceramic that does not cause shrinkage in the outer shell during firing, and fills the metal coil with the filling member. And a ceramic film made of a gradient material is coated on the outer peripheral surface of the metal coil by an electrophoretic method in order to alleviate thermal stress of the metal coil against the filling member and prevent reaction, and the metal coil is formed into a three-dimensional shape. The present invention is to provide a ceramic glow plug that can be uniformly heated and can be manufactured at low cost.

[0012]

In order to achieve the above object, the present invention is configured as follows. That is, the present invention relates to a metal coil in which a heating element coil and a current control coil are connected in series and which has a terminal, and the periphery of the metal coil is formed from a reaction-sintered ceramic containing Si and Ti and having a porosity of 10% or more. The present invention relates to a glow plug body, and a ceramic glow plug, characterized in that the glow plug body is formed of a coating film made of ceramics that does not contain oxides at grain boundaries formed on the surface of the glow plug body. Further, in this ceramic glow plug, the ceramic constituting the coating is made of Si ₃ N ₄ , and the glow plug main body is coated by either CVD or thermal spraying.

Alternatively, according to the present invention, an outer shell made of dense ceramics, a metal coil in which a heating element coil contained in the outer shell and a current control coil are connected in series and having a terminal, the outer shell A filling member made of ceramics containing Si and Ti, which is filled in the metal coil and arranged in the gap between the metal coils, and a plurality of layers of ceramic coatings having different thermal expansion coefficients formed on the surface of the metal coil,
The present invention relates to a ceramic glow plug, which is characterized in that Further, in this ceramic glow plug, the ceramic coating is composed of layers of MgO, ZrO ₂ , and Al ₂ O ₃ coated by an electrophoretic method, and the respective layers are arranged so that their thermal expansion coefficients are inclined. Has been done. Further, the ceramic constituting the filling member is composed of non-shrink ceramics formed by reacting and sintering a slurry of Si ₃ N ₄ , Si, and Ti.

[0014]

The function of the ceramic glow plug according to the present invention is as follows.
It is configured as described above and operates as follows. That is, this ceramic glow plug is a metal coil that has a heating element coil and a current control coil connected in series and has a terminal, and the reaction sintering of the periphery of the metal coil containing Si and Ti and having a porosity of 10% or more. Since it is composed of a glow plug body made of ceramics and a coating made of ceramics that does not contain oxides at the grain boundaries formed on the surface of the glow plug body, if a current is applied to the metal coil, it is generated in the heating element coil. The generated heat heats the coating film and radiates the heat to the outside, whereas the current control coil suppresses the current flowing through the current control coil as the temperature rises, and constitutes a current control unit. That is, when the temperature of the current control coil becomes high, its resistance value increases, the current flowing through the metal coil decreases, and the amount of heat generated from the outer shell is self-controlled and controlled to an optimum value. Become.

In particular, this ceramic glow plug is
Since the coating film on the outermost peripheral portion is a thin film, its heat capacity is small, and since the coating film has a high thermal conductivity, it is possible to rapidly raise the temperature. In addition, the reaction-sintered ceramics constituting the glow plug body does not shrink during firing, the degree of freedom of the coil shape of the metal coil is increased, and the most stable shape is formed into a coiled three-dimensional shape. The temperature distribution during heat generation is uniform, cracks and the like do not occur, and it is possible to manufacture at low cost.

In particular, in the non-shrinkable ceramics filled in the outer shell, a raw material containing Si, Ti and Si ₃ N ₄ is filled in the outer shell made of dense Si ₃ N ₄ and N ₂ gas is added. Si and Ti are converted to Si by
₃ N _4, TiN, is intended to be changed to TiO _2, TiON, if by making the shell with dense Si ₃ N _4, TiN expands during firing, react with Si ₃ N ₄ of the outer shell Si ₃ N ₄ can be adhered to the metal coil, and even if it is fired without pressure, the expansion action of TiN does not cause a gap at the boundary between the outer shell and the filling member, and the metal coil is Even if formed in the original shape, the contact state between the metal coil and the outer shell is not deteriorated, and heat transfer efficiency can be improved,
Enables rapid temperature rise in the heat generating part.

[0017]

Embodiments of the ceramic glow plug according to the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing an embodiment of a ceramic glow plug according to the present invention, and FIG. 2 is a graph showing the relationship between the energization time and the surface temperature of the heat generating portion for the ceramic glow plug.

This ceramic glow plug is mainly used in a diesel engine or the like and is used as a start-up assisting device. The heating element coil 5 and the current control coil 4 are connected in series and serve as terminals. A metal coil 3 having wires 6 and 7, a glow plug body 1 made of a reaction-sintered ceramic containing Si and Ti and having a porosity of 10% or more around the metal coil 3, and an outer surface of the glow plug body 1. It is composed of a coating film 2 formed on the surface 9 and made of ceramics containing no oxide at the grain boundaries. The ceramic constituting the coating film 2 is made of Si ₃ N ₄ , and forms a thin film in which the surface 9 of the glow plug body 1 is coated by either the CVD method or the thermal spraying method. In this ceramic glow plug, a heat generating portion 8 is formed on the tip side of a glow plug body 1 coated with a coating 2.

The glow plug body 1 in which the metal coil 3 is embedded is made of ceramics that expands during firing, and the coating 2 is made of dense ceramics. The coating 2 is the entire surface 9 of the glow plug body 1.
Coated on one side to form a closed end 10 at one end,
Silicon nitride Si ₃ N _{4 with the} other end formed on the open end 11
Etc. are made from dense ceramics.

Further, in this ceramic glow plug, the reaction-sintered ceramics constituting the glow plug main body 1 is formed by firing raw materials of Si and Ti to form S.
i ₃ N ₄ , TiN, TiO ₂ , and TiO are converted into porous ceramics, and Si before firing is used.
Of the raw materials of Si and Ti and Si ₃ N ₄ , TiN after firing,
The volumes of TiO ₂ and TiO are substantially the same and do not cause sintering shrinkage. Therefore, dense Si ₃
No gap in the boundary between the inner surface 12 of the film 2 N ₄ glow plug surface 9 of the body 1 of the non-shrinkage ceramic.

Further, the metal coil 3 is made of a tungsten wire of a refractory metal or the like into a coil having a three-dimensional shape.
The portion arranged in contact with the inner surface 12 of the above constitutes the heating element coil 5, and the portion arranged in a spaced state from the inner surface 12 of the coating 2 constitutes the current control coil 4. is there. Further, the metal coil 3 is the heating element coil 5
Connection wire 13 that connects one end of the current control coil 4 to one end of the current control coil 4, a connection wire 7 that extends inside the coating 2 connected to the other end of the heating element coil 5 and projects from the glow plug body 1, and a current control coil. It has a connecting wire 6 that is connected to the other end of the glow plug 4, extends through the inside of the coating 2, and projects from the glow plug body 1.

Next, an embodiment of the method for producing the ceramic glow plug according to the present invention will be described. In this ceramic glow plug manufacturing method, one tungsten wire, which is a refractory metal, has a wire diameter of 0.2 m.
The metal coil 3 was produced by winding the coil in a coil shape of m, forming a portion to be the heating element coil 5 with an inner diameter of φ3.5 mm, and forming a portion to be the current control coil 4 with a slightly smaller inner diameter.
The metal coil 3 was placed in a gypsum mold having a hole with an inner diameter of 3.5 mm, and the gypsum mold was filled with a slurry of Si and Ti, and the slurry was solidified. The solidified molded body is taken out of the gypsum mold, dried, and then the molded body is fired at 1400 ° C. in N ₂ gas to form the glow plug body 1.
A sintered body, that is, a porous ceramics was obtained. In this porous ceramic, a slurry made of a raw material containing Si and Ti is converted into a non-shrinkable ceramic made of Si ₃ N ₄ , TiN, TiO ₂ , and TiO. Further, in this state, the metal coil 3 of the portion to be the heating element coil 5 is exposed on the surface of the porous ceramics, and the metal coil 3 of the portion to be the current control coil 4 is inside the porous ceramics. It is embedded.

Next, in order to form the coating 2 on the surface 9 of the glow plug body 1, a CVD method or a thermal spraying method can be applied. In this embodiment, the coating 2 was formed by the CVD method. That is, SiCl ₄ , NH ₃ , N ₂ , H ₂ (carrier gas)
Is used as a source gas in the CVD furnace at 1500 ° C., and the surface 9 of the porous ceramics containing the metal coil 3 is approximately 150
A coating 2 of dense Si ₃ N ₄ which is a CVD-Si ₃ N ₄ film was formed so as to have a thickness of μm to produce a ceramic glow plug.

With respect to this ceramic glow plug, the glow plug body 1 and the coating 2 are brought into close contact with each other by the above-mentioned CVD treatment step, and the porous ceramic is sealed with dense Si ₃ N ₄ . The O ₂ gas concentration existing in the porous ceramics becomes almost zero, oxidation of the tungsten wire forming the metal coil 3 can be prevented, and extremely small holes existing on the surface of the porous ceramics are blocked by the CVD reaction. Also, it is possible to prevent water from entering the porous ceramics. Further, the CVD-Si ₃ N ₄ film, that is, the coating film 2 has a structure in which the grain boundary does not include an oxide.

Regarding this ceramic glow plug,
The results of measuring the temperature rising characteristics are shown in FIG. This ceramic glow plug (product of the present invention) has the same temperature rising characteristic as the conventional Al
Comparison was made with the temperature rise characteristics of a glow plug (conventional product) in which the surface of N was coated with SiC. In FIG. 2, the horizontal axis represents the energization time (sec) and the vertical axis represents the surface temperature (° C.) of the heat generating portion 8. As can be seen from FIG. 2, the product of the present invention has a shorter energization time than the conventional product and immediately rises to a predetermined temperature, indicating that it has excellent rapid heating properties.
That is, in the ceramic glow plug according to the present invention, since the outermost peripheral portion is formed of the thin film of the coating film 2, the heat capacity is small and the thermal conductivity is high, so that the temperature can be rapidly raised. Further, the Si ₃ N ₄ formed by CVD that constitutes the coating film 2 does not contain an oxide such as an auxiliary agent at the grain boundary, phonon scattering is unlikely to occur at this portion, and heat is easily transmitted. Further, the crystal grains of CVD-Si ₃ N ₄ are as large as 50 μm, while the sintered Si ₃ N ₄ has a size of about 10 μm, which is considered to be a factor for increasing the thermal conductivity. However, the heat transfer coefficient K of CVD-Si ₃ N ₄ is 50 W / m · K.
On the other hand, the heat transfer coefficient K of hot pressing, that is, sintering Si ₃ N ₄ is 27 W / m · K.

Next, another embodiment of the ceramic glow plug according to the present invention will be described with reference to FIGS. 3, 4 and 5. The ceramic glow plug of this example is
Mainly, an outer shell 22 made of dense ceramics,
A metal coil 23 having a heating element coil 25 and a current control coil 24, which are contained in the outer shell 22, connected in series and having terminals 26 and 27, and a gap filled with the metal coil 23 in the outer shell 22. Filling member 21 made of ceramics containing Si and Ti and metal coil 23 arranged
It is composed of a plurality of layers of ceramic coatings 32, 33, 34 (generally indicated by reference numeral 30) having different thermal expansion coefficients formed on the surface thereof. In this embodiment, the heating element coil 25 is in contact with the outer shell 22 on the tip side of the outer shell 22 to form a heat generating portion 28. The outer shell 22 has an end portion on the heat generating portion 28 side formed in the closed end portion 35 and the other end formed in the open end portion 31, and the connecting wires 26, 27 extend.

In this ceramic glow plug,
The heating element coil 25 is made of Fe—Cr, and the current control coil 24 is made of Ni. Metal coil 2
3 connects the heating element coil 25 and the current control coil 24 in series, and the ceramic coatings 32, 3 are formed on the surfaces thereof.
3, 34 are coated. Fe-C
The melting point of r is 1516 ° C., and the thermal expansion coefficient α is 15 × 1.
0 ^- is a ⁶ / ℃. The melting point of Ni is 1455 ° C., and the thermal expansion coefficient α is 13 × 10 ⁻⁶ / ° C. In addition, the internal ceramic coating 3 coated on the surface of the metal coil 23
2 is MgO, and the intermediate ceramic coating 33 is Zr.
O ₂ and the external ceramic coating 34 is Al
₂ O ₃ . The thermal expansion coefficient α of MgO is 13 × 10 ⁻⁶
/ ° C., and the coefficient of thermal expansion α of ZrO ₂ is 9.5 × 10
^-6 / ° C, and the coefficient of thermal expansion α of Al ₂ O ₃ is 7.5 ×
It is ^10-6 / ° C. The ceramics forming the filling member 21 is made of non-shrinkable ceramics formed by reacting and sintering a slurry of Si ₃ N ₄ , Si, and Ti. The coefficient of thermal expansion α of this non-shrinkable ceramic is 3 × 1
0 ^- is a ⁶ / ℃. The dense ceramics forming the outer shell 22 is dense Si ₃ N ₄ , and its coefficient of thermal expansion α is 3.5 × 10 ⁻⁶ / ° C.

This ceramic glow plug has the above-mentioned structure, and the metal coil 23 is electrophoresed by the ceramic coating 30 in which the thermal expansion coefficient changes in an inclined manner with respect to the non-shrinkable ceramic forming the filling member 21. Method, or the sol-gel method, the non-shrinkable ceramics has reduced thermal stress, excellent durability, and good temperature rising characteristics. Further, MgO has the effect of suppressing the reaction between the metal part and other materials.

Next, this ceramic glow plug is
It can be manufactured as follows. First, the rush coil or heating element coil 25 is made of Fe-Cr, and the brake coil or current control coil 24 is made of Ni (having a positive temperature coefficient of resistance). Current control coil 2
4 and the heating element coil 25 are connected in series to form the metal coil 2
3 was produced. Next, the outer peripheral surface of the metal coil 23 is coated with MgO, ZrO ₂ and Al ₂ O ₃ in this order by electrophoresis, and the ceramic coatings 32, 33 are formed on the surface of the metal coil 23 so that the coefficient of thermal expansion changes in an inclined manner. , 34 were coated to a thickness of 50 μm. on the other hand,
The outer shell 22 is made of Si ₃ N ₄ having a relative density of 99% or more and is φ3.5.
Formed.

Therefore, the ceramic coating 3 is provided in the outer shell 22.
The metal coil 23 coated with 2, 33, and 34 was put in, and the space portion of the outer shell 22 was filled with a slurry composed of Si, Ti, and Si ₃ N ₄ powder. After drying the slurry, 1 in N ₂ gas
Reaction-sintering was performed at 300 ° C. to form a non-shrinkable ceramic. Therefore, the surface 29 of the filling member 21 filled in the outer shell 22 is in close contact with the inner wall surface 32 of the outer shell 22, and the heating element coil 25 of the metal coil 23 is also in close contact with the inner wall surface 20 of the outer shell 22. Therefore, no gap is generated at the boundary between the outer shell 22 and the filling member 21, and the heat generated in the heating element coil 25 is satisfactorily conducted to the heat generating portion 28 of the outer shell 22 to improve the rapid heating property.

The temperature for reaction sintering is 120.
The temperature is 0 ° C. to 1400 ° C., and in this embodiment, the reaction sintering is performed at 1300 ° C. Actually, 3Si + 2N ₂ →
Since it is a reaction of Si ₃ N ₄ and is accompanied by heat generation, the internal temperature is unknown. In addition, the amount of heat generated during sintering can be reduced by mixing Si ₃ N ₄ powder with the slurry. In other words, the calorific value can be lowered by mixing the Si ₃ N ₄ powder to reduce the substantial amount of Si and Ti forming the slurry. At this time, since the metal coil 23 is covered with the ceramic coatings 32, 33 and 34, when the metal coil 23 is included in the non-shrinkable ceramic filling member 21, the ceramic coatings 32, 33 and 34 are filled. The function of alleviating the coefficient of thermal expansion of 21 is exerted, and the occurrence of cracks or cracks in the filling member 21 can be prevented.

FIG. 5 shows the results of measuring the temperature rise characteristics of the ceramic glow plug of this example. The temperature rising characteristics of this ceramic glow plug (product of the present invention) were compared with the temperature rising characteristics of a glow plug (conventional product) using a conventional tungsten coil. In FIG. 5, the horizontal axis represents the energization time (sec) and the vertical axis represents the surface temperature (° C.) of the heat generating portion 8. As can be seen from FIG. 5, the product of the present invention has a shorter energization time than the conventional product and has a predetermined temperature (10
It can be seen that the temperature is similarly increased up to 00 ° C., and the rapid heating property is excellent.

In order to evaluate the durability of the product of the present invention and the conventional product using the Fe-Cr coil not coated with a ceramic film, after repeating heating and cooling from room temperature to 1000 ° C. for 500 cycles. The observation of the ceramics and the metal coil forming the filling member was performed. In the product of the present invention, no damage such as cracks was found in the filling member 21. No reaction layer was found on the coil surface of the metal coil 23 of the present invention. On the other hand, it was confirmed that cracks were generated in the ceramics constituting the conventional filling member. In addition, in the Fe-Cr coil not coated with the ceramic coating, generation of a silicide reaction layer was observed on the coil surface. The thickness of silicide is 50
was μm. That is, it can be seen that the product of the present invention is more durable than the conventional product.

[0034]

The ceramic glow plug according to the present invention is constructed as described above and has the following effects. That is, this ceramic glow plug is a metal coil in which a heating element coil and a current control coil are connected in series and which has a terminal, and the reaction sintering with a porosity of 10% or more containing Si and Ti around the metal coil. Since the glow plug body made of ceramics and the coating made of ceramics that does not contain oxides at the grain boundaries formed on the surface of the glow plug body, the outermost peripheral portion is a thin film of the coating and contacts the heating element coil. It will be in the state of doing. Therefore, the heat capacity of the heat generating portion can be rapidly raised because the heat capacity of the coating is small and the heat conductivity is high. In addition, the coating itself is C of Si ₃ N ₄ .
It can be composed of a VD film, does not contain an oxide such as an auxiliary agent in the grain boundary, is less likely to cause phonon scattering in the film portion, and has a structure in which heat is easily transmitted. Further, the coating has a large crystal grain size of 50 μm, so that the thermal conductivity is high.

Regarding this ceramic glow plug,
When a current is applied to the metal coil, the heat generated in the heating element coil heats the coating film and radiates the heat to the outside, whereas in the current control coil, the heat flows to the current control coil as the temperature rises. The current is suppressed and constitutes a current controller. That is, if the current control coil becomes hot,
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,
The heat generating part is controlled to the optimum value.

Further, this ceramic glow plug is
Since the coating film on the outermost peripheral portion is a thin film, its heat capacity is small, and since the coating film has a high thermal conductivity, it is possible to rapidly raise the temperature. In addition, the reaction-sintered ceramics constituting the glow plug body does not shrink during firing, the degree of freedom of the coil shape of the metal coil is increased, and the most stable shape is formed into a coiled three-dimensional shape. The heating element coil is formed in a coil shape and is in close contact with the inner wall surface of the coating, so that the temperature does not become non-uniform when energized, and the temperature distribution during heat generation becomes uniform. The main body is not cracked and has excellent durability and can be manufactured at low cost.

Alternatively, the ceramic glow plug according to the present invention is a metal coil having an outer shell made of dense ceramics, a heating element coil contained in the outer shell and a current control coil connected in series and having a terminal. A filling member made of ceramics containing Si, Ti, and Si ₃ N ₄ which is filled in the outer shell and arranged in a gap between the metal coils, and a thermal expansion coefficient formed on the surface of the metal coil. Since the ceramic coating is composed of a plurality of different layers, the ceramic coating functions as a thermal expansion gradient function material that absorbs a thermal expansion difference between the metal coil and the filling member, that is, a thermal expansion difference relaxing material, It is possible to prevent the occurrence of cracks and the like, improve durability, and improve temperature rising characteristics. Furthermore, since Si ₃ N ₄ powder is included when the filling member is produced, the amount of heat generated during sintering can be reduced, and the filling member can be formed into a desired porous non-shrinkable ceramic.

The ceramic coating is composed of layers of MgO, ZrO ₂ and Al ₂ O ₃ coated by an electrophoretic method, and the layers are arranged so that their thermal expansion coefficients are inclined. Therefore, the ceramic coating can be formed to have a desired thermal expansion gradient function. Although the heating element coil constitutes a heating portion, since the heating element coil is arranged in contact with the inner wall surface of the outer shell, the temperature of the entire outer shell 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 in a state of filling the heating element coil, the heat conductivity of the heating portion becomes extremely good, and immediately rises when energized. It can be heated and the rapid heating property can be improved.

In the non-shrinkable ceramics filled in the outer shell, a raw material containing Si, Ti and Si ₃ N ₄ is filled in the outer shell made of dense Si ₃ N _4, and N ₂ gas is added. Si and Ti are converted to Si by
₃ N _4, TiN, is intended to be changed to TiO _2, TiON, if by making the shell with dense Si ₃ N _4, TiN expands during firing, react with Si ₃ N ₄ of the outer shell Si ₃ N ₄ can be adhered to the metal coil, and even if it is fired without pressure, the expansion action of TiN does not cause a gap at the boundary between the outer shell and the filling member, and the metal coil is Even if formed in the original shape, the contact state between the metal coil and the outer shell is not deteriorated, and heat transfer efficiency can be improved,
Enables rapid temperature rise in the heat generating part.

[Brief description of drawings]

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

FIG. 2 is a graph showing the relationship between the energization time and the surface temperature of the heat generating part in the ceramic glow plug of FIG.

FIG. 3 is a sectional view showing another embodiment of the ceramic glow plug according to the present invention.

FIG. 4 is an enlarged cross-sectional view for explaining a boundary between a metal coil and a filling member of the ceramic glow plug of FIG.

5 is a graph showing the relationship between the energization time and the surface temperature of the heat generating portion in the ceramic glow plug of FIG.

[Explanation of reference numerals] 1 glow plug body 2 coating 3,23 metal coil 4,24 current control coil 5,25 heating element coil 6,7,26,27 connection wire 8,28 heating portion 9 surface of glow plug body 10 , 35 Closed end portion 11, 31 Open end portion 12 Inner surface of coating 21 Filling member 22 Outer shell 29 Surface of filling member 30 Ceramics coating 32 Ceramics coating of MgO 33 Ceramics coating of ZrO ₂ 34 Al ₂ O ₃ ceramics coating

Claims (5)

[Claims] 1. A metal coil in which a heating element coil and a current control coil are connected in series and which has a terminal, and the periphery of the metal coil is made of reaction sintered ceramics containing Si and Ti and having a porosity of 10% or more. A ceramic glow plug comprising: a glow plug body; and a film formed on the surface of the glow plug body and made of a ceramic containing no oxide at grain boundaries. 2. The ceramic constituting the coating is Si
The ceramic glow plug according to claim 1, wherein the glow plug body is made of ₃ N ₄ and is coated on the glow plug body by either CVD or thermal spraying. 3. An outer shell made of dense ceramics,
A metal coil having a terminal in which a heating element coil and a current control coil included in the outer shell are connected in series, and Si and Ti filled in the outer shell and arranged in a gap between the metal coils , A ceramic glow plug comprising a filling member made of ceramics containing Si ₃ N ₄ and a plurality of layers of ceramic coatings having different thermal expansion coefficients formed on the surface of the metal coil. 4. The ceramic coating is composed of layers of MgO, ZrO ₂ , and Al ₂ O ₃ coated by an electrophoretic method, and the layers are arranged so that their thermal expansion coefficients are inclined. The ceramic glow plug according to claim 3, characterized in that 5. The ceramic constituting the filling member is composed of non-shrink ceramics formed by reacting and sintering a slurry of Si ₃ N ₄ , Si, and Ti. The described ceramic glow plug.