JPH0719477A - Ceramic glow plug - Google Patents

Abstract

PURPOSE:To provide a ceramic glow plug of self-current controlling type having a stable strength, a high temperature and a high strength against a thermal shock and the like. CONSTITUTION:A low thermal conducting member 4 of Si-Ti-Al-O-N type ceramics is filled in a ceramic sheath 2 having a heat generating part 12 projected from a hollow main body 1. A current controlling heater coil 3 having a small diameter is buried within a low thermal conduction member 4, a heater coil 5 having a large diameter is arranged outside the heater coil and then the current controlling heater coil 3 and the heater coil 5 are connected in series. Upon making an electrical current flow, the current controlling heater coil 3 shows a higher temperature than that of the heater coil 5, resulting in that its resistance value becomes high, the currents flowing in the current controlling heater coil 3 and the heater coil 5 are reduced, a heating amount at the heat generating part 12 of the ceramic sheath 2 is self controlled and it is controlled to be its most suitable value.

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 Heretofore, a glow plug has been constructed by embedding a tungsten W wire in a ceramic such as silicon nitride. For tungsten W wire, as shown in FIG.
With respect to a 2V power source, the resistance value is 0.1Ω at room temperature and the current at that time is 120A. When the temperature of the glow plug rises from room temperature to 900 ° C with the passage of time, the resistance value becomes 0.4Ω, and the current at that time is 30A.
Is. Then, the glow plug is heated to increase the resistance value, and the resistance value becomes 1Ω and becomes stable, and the current at that time is 12A. That is, in the conventional glow plug used in the diesel engine, when the current is supplied from the 12V battery according to the instruction of the controller, it is initially 1
A current of 20 A flows, but as the temperature of the heater coil rises, the resistance value increases and becomes stable when the resistance value becomes 1Ω. Therefore, in order to stabilize the glow plug at a resistance value of 1 Ω, the current is controlled by a controller command so that the heater coil is maintained at 1 Ω.

A conventional glow plug has been developed which can be self-controlled so that the glow plug can be adjusted to 1Ω without using a controller. Tungsten W
As shown in FIG. 3, nickel Ni and nickel Ni have a characteristic that the resistance value Ω increases and increases as the temperature rises. Therefore, with tungsten W wire and nickel Ni wire,
As the temperature rises, the resistance value Ω increases, the current decreases, and the current value is limited. Therefore, the self-regulating glow plug is constructed by burying a tungsten W wire in a ceramic such as Si ₃ N ₄ and connecting a nickel Ni wire coil in series with the W wire. That is, in the self-regulating glow plug, a conductor having a small electric resistance value is arranged in the heating element portion of the heater coil, and a metal wire having a large electric resistance value of the Ni wire coil is connected to the upstream side of the conductor. It was made by. In such a self-regulating glow plug, the Ni coil is overheated by passing an electric current to increase the resistance value, and the electric current is reduced to control the heat generation amount of the heating element portion of the heater coil. .

Conventionally, self-current control type glow plugs have been disclosed in Japanese Examined Patent Publication No. 4-34052 and Japanese Examined Patent Publication No. 60-194.
No. 04, JP-A-59-157423, JP-A-58-106326, and the like.

For example, in the self-control glow plug disclosed in Japanese Examined Patent Publication No. 4-34052, a current control resistor is connected in series to the heating element in order to control the temperature of the heating element at the time of heating by energization. The heating wire coil and the resistor coil are connected in series and embedded in the ceramic sintered body to form an integrated ceramic heater, and the heating wire has a temperature-resistance coefficient of 4 times or less. Such a tungsten W and rhenium Re alloy wire having a positive temperature coefficient of resistance are used, and the resistor is a wire material of pure W or pure molybdenum Mo.

The sheath glow plug disclosed in Japanese Patent Publication No. 19404/1985 directly connects the heating element and the resistor of the winding between the inner bottom of the heat-resistant bottomed metal tube and the center electrode. This is a self-regulating type sheath glow plug having the winding pitch of the resistor formed close to the central electrode side close to the electrode side fitting, and the portion close to the heating element side formed roughly.

[0007]

However, the conventional self-current control type glow plug has sufficient heat resistance, strength against heat shock, high temperature strength, etc. when used in a high temperature combustion chamber such as a heat shield engine. It was something I couldn't say. Further, in the conventionally disclosed self-regulating glow plug, a heating wire coil manufactured using a tungsten carbide wire and a resistor coil manufactured using a Ni wire coil are connected to each other, and both are made of materials having different resistance temperature coefficients. Or the heating element and the resistor of the winding are formed in different shapes, there is a problem that the Ni wire is disconnected due to overheating during use or deteriorates due to aging. The structure became complicated, and the cost and strength were not satisfactory.

With respect to the ceramic glow plug, a self current control type glow plug can be constructed by the resistance value extremely increasing in the upstream region of the current path of the heater coil. The relationship between the resistance value and the temperature in the heater coil is expressed by the following equation. ρ _TX = ρ _{T 0} [1 + α (T _X −T ₀ )] where ρ _TX is the resistance value of the heater coil at a certain temperature T _X , ρ _{T 0} is the resistance value of the heater coil at room temperature T ₀ , and α is It is a temperature coefficient of resistance.

Normally, in a glow plug, a saturation current flows at about 1Ω at a power supply voltage of 12 V and the temperature is maintained at about 900 ° C. In order to heat the glow plug instantaneously, about 0.1Ω is required at room temperature. Usually, a heating wire, that is, a W wire used as a heater coil has a temperature coefficient of resistance of about 4 × 10 ⁻³ , so that the current cannot be saturated at 900 ° C.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems, and the heat shield degree of the current control heater coil in the upstream region of the tungsten wire or the like is connected to the current control heater coil in the downstream side. The resistance value of the current control heater coil is set to be larger than the heat shield degree of the heater coil in the side region, and the current control heater coil is overheated due to a difference in heat dissipation amount between the current control heater coil and the heater coil. And a heater coil for current control and a current flowing through the heater coil are controlled to control the amount of heat generated at the tip of the heating element of the ceramic sheath. Ceramic glove that has high strength against heat shock in the environment, rich in oxidation resistance and heat resistance, does not cause strain on electrical connection parts, and can secure stable strength It is to provide a plug.

[0011]

In order to achieve the above object, the present invention is configured as follows. That is, the present invention relates to a hollow main body having an electrode, a ceramic sheath fixed to the main body with a heat generating portion protruding from the main body,
A low thermal conductive member made of ceramics filled in the ceramic sheath, a wire diameter that is connected to the electrode through a power source connecting portion and is embedded inside the ceramic thermal sheath in the longitudinal direction of the low thermal conductive member. Of the current control heater coil, and the current control heater coil connected in series and connected to the main body via an electrical connection portion, and in contact with the inner wall surface of the ceramic sheath in the longitudinal direction of the low thermal conductivity member. The present invention relates to a ceramic glow plug having a heater coil having a large wire diameter arranged outside.

In this ceramic glow plug, the current control heater coil is wound tightly and the heater coil is wound coarsely.

Further, in this ceramic glow plug, the low heat conductive member filled in the ceramic sheath is produced by sintering a powder mixture of Ti, Si and Al ₂ O ₃ in N _2. -Al-O-N based ceramics.

Further, in this ceramic glow plug, the ceramic sheath is made of Si ₃ N ₄ .

In this ceramic glow plug, the current control heater coil and the heater coil are made of a tungsten wire, and the outer surface of the tungsten wire is coated with silicon carbide or tungsten carbide.

[0016]

The ceramic glow plug according to the present invention is
It is configured as described above and operates as follows. That is, in this ceramic glow plug, a heat generating portion of a ceramic sheath is projected from a hollow body, a low heat conductive member made of ceramic is filled in the ceramic sheath, and the electrode is connected to the electrode through a power source connecting portion. A large-diameter large-diameter heater coil for current control is embedded inside the ceramic sheath inside the low-heat-conducting member in the longitudinal direction, and is in contact with the inner wall surface of the ceramic sheath outside the low-heat-conducting member in the longitudinal direction. The heater coil is connected to the current control heater coil in series and is connected to the main body through an electrical connection portion. Therefore, when a current is passed through the current control heater coil and the heater coil, the current control heater The coil is embedded in the low thermal conductive member and has a high degree of heat insulation, and the current control heater coil is larger than the heater coil in comparison with the heater coil. It becomes warm. Therefore, when the temperature of the current control heater coil rises, the resistance value of the current control heater coil increases, the current flowing through the current control heater coil and the heater coil decreases, and the ceramic sheath The amount of heat generated by the heat generating portion is self-controlled and controlled to an optimum value.

In this ceramic glow plug,
The ceramic sheath is formed of Si ₃ N ₄ in a thin-walled tube, one end of which is closed, in which heat-resistant metal wires are doubly arranged, and the inner side of the heat-resistant metal wire is the heater for current control. It is a coil and the outside is the heater coil. Further, S is contained in the ceramic sheath.
Since the low heat conductive member made of i-Ti-Al-O-N ceramics is filled and the current control heater coil is embedded in the low heat conductive member, the current control heater coil is reliably shielded. While being heated, the current control heater coil and the heater coil are firmly fixed in the ceramic sheath. In addition, the heater coil for current control, whose resistance value increases as the temperature rises, is
Since it is embedded in the Ti-Al-O-N ceramics, it is possible to reliably prevent the occurrence of wire breakage. Further, since the ceramic sheath has a tubular shape and a simple structure, The heater coil, the current control heater coil, the hollow main body, and the power source connecting portion can be firmly configured.

The Si-Ti-Al-O-N-based ceramics are prepared by crushing Si, Ti and Al ₂ O ₃ as raw materials and filling the ceramic sheath of Si ₃ N ₄ with N.
Sintering in a ₂ gas atmosphere to produce a composite material of Si ₃ N ₄ and TiN, and then in an O ₂ gas atmosphere at about 1000 ° C.
Then, TiN is oxidized to form TiO ₂ , and the internal density is made uniform to a value close to Si ₃ N ₄ . In this case, since the tungsten W wire is severely oxidized by O ₂ at a high temperature, it can be dealt with by coating with SiC having the same linear expansion coefficient on the outer circumference. At this time, when the powder mixture of Si, Ti, and Al ₂ O ₃ is reacted and sintered with Si ₃ N ₄ and TiN, TiN expands in volume, so that a uniform sintered body is produced without gaps in the glow plug. it can. That is, this sintered body,
Since it does not shrink in the ceramic sheath made of Si ₃ N _4, has a small thermal conductivity and a small linear expansion coefficient, it has ideal characteristics as a low thermal conductive member in the ceramic sheath.

[0019] The heater coil constituting the heat generating portion is greater tungsten W wire diameter and close to the said ceramic sheath Si ₃ N _4, the thermal conductivity of good Si ₃ N ₄ The ceramic sheath is heated. On the other hand, the current control heater coil having a small diameter is a tungsten W wire having a small wire diameter and is embedded in the Si-Ti-Al-O-N ceramics of the low thermal conductive member, and therefore, Along with the heating of the current control heater coil, a high temperature atmosphere is created around the current control heater coil. That, Si-Ti-Al-O -N -based ceramics has a small linear expansion coefficient ^- since ^{(2 × 10 6 / K)} , the occurrence of thermal stress is less, until it reaches the high temperature to destroy even when rapid heating I have little worries. In addition, the resistance value of the tungsten wire inside the low thermal conductive member increases as the temperature rises, and suppresses the current supplied to the glow plug. For the change of thermal stress such as heating and quenching in the combustion chamber of the engine, Si of the ceramic sheath located outside is used.
_{Since 3} N ₄ guarantees sufficient strength, it is possible to provide a glow plug with excellent overall durability.

The current control heater coil and the heater coil are made of a tungsten wire, and the outer surface of the tungsten wire is coated with silicon carbide or tungsten carbide. It can be prevented, the corrosion resistance can be improved, and the durability of the heater coil can be improved. Moreover, the coefficient of linear expansion of both tungsten and silicon carbide is 4 × 10.
^-6 / ° C, which is the same, S due to the difference in thermal expansion
The coating layer of iC does not peel off from the W line and is firmly coated. Since silicon carbide SiC has a negative temperature coefficient of resistance, its self-heating property deteriorates at high temperature, and heat generation inside becomes large. In addition, silicon nitride that constitutes the ceramic sheath and S that constitutes the low thermal conductive member.
Since the i-Ti-Al-O-N material has almost the same linear expansion coefficient and good compatibility with both, the low thermal conductive member does not have a gap in the ceramic sheath, and is good. It is joined and arranged.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a ceramic glow plug according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic explanatory view showing an embodiment of a ceramic glow plug according to the present invention.

The ceramic glow plug is mainly composed of a hollow body 1 to which terminals or electrodes 10 are attached via an insulator (not shown), a ceramic sheath 2, a current control heater coil 3, and the current control. The heater coil 5 is connected in series to the heater coil 3 for heating, and the low thermal conductive member 4 filled in the ceramic sheath 2. The hollow body 1 is made of a metal such as a heat resistant alloy,
It has a screw 11 and a nut 14 for attachment. The ceramic sheath 2 is made of silicon nitride Si ₃ N _{4, which} has excellent heat resistance and high temperature and high strength, into a thin-walled tube. The tip is closed in an arc shape, and the other end is partially hollow body 1. The inner wall surface 17 is fixed in contact with the inner wall surface 17. The ceramic sheath 2 has a heating portion 12 protruding from the hollow main body 1. Further, in order to fix the ceramic sheath 2 to the hollow main body 1, the outer peripheral surface of the ceramic sheath 2 is metalized and joined.
Both can be electrically bonded extremely strongly. Further, the heat generating portion 12 of the ceramic sheath 2 is the end portion 1 of the hollow main body 1.
It is arranged in a protruding state from 5.

In this ceramic glow plug,
The current control heater coil 3 has a power supply connecting portion 8 on the electrode 10.
And a connecting wire 7 provided at the tip of the ceramic sheath 2. Further, the current control heater coil 3 is a heat resistant metal wire having a small wire diameter embedded in the ceramic sheath 2 inside the low thermal conductivity member 4 in the longitudinal direction. The heater coil 5 is connected in series to the current controlling heater coil 3 via a connecting wire, that is, a connecting portion 7, and is hollow via an electric connecting portion 6 fixed to the inner wall surface 17 of the hollow body 1. Connected to the main body 1. Further, the heater coil 5 is a heat-resistant metal wire having a large wire diameter arranged outside the low thermal conductive member 4 in the ceramic sheath 2 in the longitudinal direction, and arranged in contact with the inner wall surface 13 of the ceramic sheath 2. The heat conduction from the heater coil 5 to the ceramic sheath 2 is improved. The current control heater coil 3 is wound tightly, and the heater coil 5 is wound coarsely.

In this ceramic glow plug,
The current control heater coil 3 and the heater coil 5 are made of a heat-resistant metal material such as tungsten W wire coated with silicon carbide SiC or tungsten carbide WC, and extend in the longitudinal direction inside the ceramic sheath 2. Moreover, the current control heater coil 3 and the heater coil 5 are electrically disconnected by the low heat conductive member 4. By coating the tungsten W wire forming the current control heater coil 3 and the heater coil 5 with SiC or WC, the tungsten W can be prevented from being oxidized and the durability can be improved.

In this ceramic glow plug, the low thermal conductive member 4 filled in the ceramic sheath 2 is a low thermal conductive ceramic made of Si-Ti-Al-O-N ceramics. Si-Ti-Al
-O-N-based _{ceramics, Si 3 N 4 + TiO 2} + A
It is a composite material of l ₂ O ₃ and has a thermal conductivity of about 2 W.
/ H · m ^{2 It} is an extremely low ceramic.

The composite material of Si-Ti-Al-O-N ceramics can be manufactured as follows. Additives, binders, etc. are added to a mixed powder of Si, Ti and Al ₂ O ₃ to prepare a slurry, and the mixture is converted into Si ₃ N ₄ and TiN by reaction sintering in an N ₂ gas atmosphere. . Since TiN is unstable, Si ₃ N ₄
When TiN and TiN are reacted in O ₂ gas, TiN becomes TiO 2.
₂ , and Si-Ti-Al-O-N based ceramics are produced. Here, TiO ₂ itself is extremely stable against oxidation, and TiN is used as an intermediate product in the manufacturing process.
Since the reaction volume becomes large because of the inclusion of the above, the gap between the ceramic sheath 2 and the wire for the current control heater coil 3 and the heater coil 5 does not occur, and they are in close contact with each other. In this state, the low thermal conductive member 4 made of Si—Ti—Al—O—N ceramics is arranged inside the ceramic sheath 2.

The ceramic sheath 2 is formed as a thin tube made of Si ₃ N ₄ and closed at one end. For manufacturing the ceramic sheath 2, for example, a tungsten wire serving as the heater coil 5 is arranged in a gypsum mold, and the raw material slurry of Si ₃ N ₄ is inlaid on the wall surface of the gypsum mold by a mud discharging method to form a molded body. After manufacturing, the molded body is fired to produce Si ₃
A ceramic sheath 2 made of N ₄ is produced. Also,
A refractory metal wire is arranged in a ceramic sheath 2 and a current control heater coil 3 is arranged therein. Next, in order to form Si—Ti—Al—O—N ceramics in the ceramic sheath 2, Ti, Si as raw materials are used.
By mixing the powders of ₃ N ₄ and Al ₂ O ₃ and filling the ceramic sheath 2 with a slurry to which a binder, an additive, etc. have been added, and performing reaction sintering in N ₂ gas, the ceramic sheath 2 while being converted into Si ₃ N ₄ and TiN therein, an O ₂ gas atmosphere, to oxidize the TiN at about 1000 ° C., and TiO _2, a uniform internal density, Si ₃ N
Set a value close to ₄ . In this case, since the tungsten W wire is severely oxidized by O ₂ at a high temperature, it can be dealt with by coating with SiC having the same linear expansion coefficient on the outer circumference. Moreover, a powder mixture of Si, Ti, and Al ₂ O ₃ is added to Si.
_When reaction sintering is performed with ₃ N ₄ and TiN, TiN expands in volume, so that a uniform sintered body can be produced without gaps in the glow plug. At this time, this sintered body does not shrink in the ceramic sheath 2 made of Si ₃ N ₄ , has a small thermal conductivity, and has a small linear expansion coefficient, so that it is ideal as a low thermal conductive member in the ceramic sheath 2. Have the following characteristics.

The heater coil 5 forming the heating element is a tungsten W wire having a large diameter and is close to the ceramic sheath 2 of Si ₃ N ₄ , so that the S having good thermal conductivity is used.
The ceramic sheath 2 of i ₃ N ₄ is heated. On the other hand, the current control heater coil 3 having a small diameter is a tungsten W wire having a small diameter, and the Si-T of the low thermal conductive member 4 is used.
Since it is embedded in the i-Al-O-N ceramics, the heating of the current control heater coil 3 causes a high temperature atmosphere around the current control heater coil 3. That is,
Since the Si-Ti-Al-O-N based ceramics has a small linear expansion coefficient, thermal stress is less likely to occur, and there is less concern that the ceramics will be destroyed even when rapidly heated until reaching a high temperature. Further, the resistance value of the tungsten wire inside the low thermal conductive member 4 increases as the temperature rises, and suppresses the current supplied to the glow plug. Since Si ₃ N ₄ of the ceramic sheath 2 located outside guarantees sufficient strength against changes in thermal stress such as heating and quenching in the combustion chamber of the engine,
It is possible to provide a glow plug having excellent overall durability.

Further, since the current control heater coil 3 and the heater coil 5 are coated with silicon carbide SiC or tungsten carbide WC, the current control heater coil 3 is provided.
Also, the tungsten W forming the heater coil 5 can be prevented from being oxidized, the corrosion resistance can be improved, and the durability of the current control heater coil 3 and the heater coil 5 can be improved. Since silicon carbide SiC has a negative temperature coefficient of resistance, its self-heating property deteriorates at high temperature, and heat generation inside becomes large.

In this ceramic glow plug, the electrode 10 extends in a non-contact state with the hollow portion 9 of the hollow main body 1 and is connected to the power source connecting portion 8. Since the tungsten W wire has a small diameter inside the ceramic sheath 2 and a large diameter outside the ceramic sheath 2, the heater coil 5 can be formed inside the ceramic sheath 2. Further, the ceramic sheath 2 can be manufactured by forming a molded body from silicon nitride Si ₃ N ₄ by a mud discharge method or the like and firing it. In order to electrically connect the heater coil 5 and the hollow main body 1 to each other, the electric connection portion 6 is fixed to the inner wall surface 17 of the hollow main body 1, and the heater coil 5 is connected to the electric connection portion 6 by vapor deposition of a heat-resistant metal. can do. Further, the electric connection between the heater coil 5 and the connecting portion 7 and the electric connection between the electric resistance wire 3 and the power source connecting portion 8 are firmly and surely connected by vapor deposition with a heat-resistant metal.

Since this ceramic glow plug is constructed as described above, it operates as follows. That is, in this ceramic glow plug, when a current is passed from the electrode 10 to the current control heater coil 3 and the heater coil 5, since the low thermal conductive member 4 is filled in the ceramic sheath 2, the current control heater coil 3 is filled. The temperature of the central portion of the ceramic sheath 2 where 3 is located is extremely higher than that of the outer periphery where the heater coil 5 is located. And
When the temperature inside the low heat conductive member 4 becomes high, the resistance value of the current control heater coil 3 increases, and the current flowing through the current control heater coil 3 and the heater coil 5 decreases.
The heat generation amount of the heat generating portion 12 of the ceramic sheath 2 is self-controlled. Further, when the temperature inside the low thermal conductive member 4 decreases, a current again flows through the current control heater coil 3 and the heater coil 5 and the heater coil 3 heats the heat generating portion 12 of the ceramic sheath 2. Heating part 1
2 is always maintained at the optimum calorific value. For example, as shown in FIG. 2, since the heat generating portion 12 of the ceramic sheath 2 is exposed to the outside of the combustion chamber or the like, heat is dissipated from the heat generating portion 12, and the temperature of the heat generating element of the heat generating portion 12 rises to 900 ° C. While being maintained, the resistance value of the heater coil 5 becomes 0.4Ω. However, since the current control heater coil 3 inside the low thermal conductive member 4 is embedded in the low thermal conductive member 4 and is shielded from heat, the low thermal conductive member is Four
The temperature of the central portion of the current controller becomes 1800 ° C., and the resistance value of the current control heater coil 3 becomes 0.6Ω. Therefore, in this ceramic glow plug, the current control heater coil 3 is used.
The total resistance value of the heater coil 5 and the total resistance value of the heater coil 5 is 1Ω, and the stable state is achieved.

[0032]

The ceramic glow plug according to the present invention is constructed as described above and has the following effects. That is, in this ceramic glow plug, a heat generating portion of a ceramic sheath is projected from a hollow main body provided with an electrode, and a low heat conductive member made of ceramic is filled in the ceramic sheath to control a current with a small wire diameter. Heater coil is embedded inside the ceramic sheath in the longitudinal direction of the low thermal conductive member and connected to the electrode via a power supply connection portion, and a large diameter heater coil is provided in the ceramic sheath with the low thermal conductive member. Since it is arranged on the outer side in the longitudinal direction of and is connected to the current control heater coil in series and is connected to the main body through an electric connection portion, a current flows through the current control heater coil and the heater coil. The heater coil in which the region of the current control heater coil located inside the low thermal conductive member is located outside the low thermal conductive member Heat degree is increased shielding as compared to the region, the internal side of the low thermal conductive member is likely to become hot. Therefore, when the temperature of the current control heater coil becomes high, the resistance value of the current control heater coil increases, the current flowing through the current control heater coil and the heater coil decreases, and the current control heater coil decreases. When the temperature of the heater coil is lowered, current again flows through the current control heater coil to heat the heat generating portion, and the heat generating portion is always self-controlled to the optimum heat generation amount.

The current control heater coil has a small wire diameter and the heater coil is formed to have a large diameter.
Since the winding method of the current control heater coil is tightly wound and the winding method of the heater coil is roughly wound, the current control heater coil reliably responds to the temperature in the low thermal conductive member. Moreover, the current can be controlled with a good response, and the heater coil can appropriately control the heat generation amount of the ceramic sheath.

Further, Si is contained in the ceramic sheath.
Since the low thermal conductive member made of —Ti—Al—O—N ceramics is filled, the current control heater coil is embedded inside the low thermal conductive member, and the heater coil is disposed outside, The current control heater coil is surely shielded from heat, and the current control heater coil and the heater coil are firmly positioned and fixed in the ceramic sheath. Moreover, since the silicon nitride that constitutes the ceramic sheath and the Si-Ti-Al-O-N material that constitutes the low thermal conductivity member have substantially the same linear expansion coefficient, and the two are well compatible, The low thermal conductive member is well bonded and arranged in the ceramic sheath without a gap.

Further, since the current control heater coil and the heater coil are made of a tungsten wire and the outer surface of the tungsten wire is coated with silicon carbide or tungsten carbide, it is possible to prevent the tungsten wire from being oxidized.
Corrosion resistance can be improved, and durability of the heater coil can be improved.

[Brief description of drawings]

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

FIG. 2 is a graph for explaining a relationship between a resistance value and a temperature of an electric resistance wire and a heater coil in this ceramic glow plug.

FIG. 3 is a graph illustrating the relationship between the resistance values of Ni and W with respect to temperature.

FIG. 4 is a graph showing the relationship of current control with respect to time in a conventional ceramic glow plug.

[Explanation of symbols]

 1 Hollow Body 2 Ceramic Sheath 3 Current Control Heater Coil 4 Low Heat Conduction Member 5 Heater Coil 6 Electrical Connection 7 Connection 8 Power Connection 9 Hollow 10 Electrode 12 Heat Generation 13 Inner Wall of Ceramic Sheath

Claims (5)

[Claims] 1. A hollow main body having an electrode, a ceramic sheath fixed to the main body with a heat generating portion protruding from the main body, a low thermal conductive member made of ceramics filled in the ceramic sheath, and the electrode. And a current control heater coil having a small wire diameter embedded in the longitudinal direction of the low thermal conductive member in the ceramic sheath and connected in series to the current control heater coil. And a heater coil having a large wire diameter, which is connected to the main body via an electric connection portion and is arranged outside the longitudinal direction of the low thermal conductive member in contact with the inner wall surface of the ceramic sheath. A characteristic glow plug made of ceramic. 2. The ceramic glow plug according to claim 1, wherein the current control heater coil is wound tightly and the heater coil is wound coarsely. 3. The low thermal conductive member filled in the ceramic sheath is a Si—Ti—Al—O—N-based material prepared by sintering a powder mixture of Ti, Si and Al ₂ O ₃ in N _2. The ceramic glow plug according to claim 1, wherein the glow plug is made of ceramics. 4. The ceramic glow plug according to claim 1, wherein the ceramic sheath is made of Si ₃ N ₄ . 5. The ceramic according to claim 1, wherein the current control heater coil and the heater coil are made of a tungsten wire, and the outer surface of the tungsten wire is coated with silicon carbide or tungsten carbide. Made glow plug.