JP2002257341A - Ceramic glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of a ceramic glow plug employing such a structure as a recess is formed at the end part on the anode side and an electrode take-out metal is secured by pouring solder material therein that boring is required after burning in order to form the recess because a ceramic insulator is normally burned by hot press and thereby a long time is required for machining and the cost can not be reduced. SOLUTION: In the ceramic glow plug where a ceramic heater 2 composed of silicon nitride ceramics and having a heating resistor 4 on the forward end side is provided with an electrode lead-out part 7b being connected with the heating resistor 4, the electrode lead-out part 7b is exposed to the rear end face of the ceramic heater 2 and a nail head pin forming an anode metal 10 is brazed to the rear end face 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-saturated ceramic glow plug for maintaining fuel ignition and stable combustion when starting or idling a diesel engine.

[0002]

2. Description of the Related Art Conventionally, a ceramic glow plug used for assisting starting of a diesel engine has a ceramic heating element, a mounting bracket formed of a tubular housing which is held at a tip end thereof and is mounted on a cylinder head of the engine. A metal outer cylinder for holding the ceramic heating element at the tip of the mounting bracket. In this glow plug, generally, a ceramic heating element and metal are joined by brazing with a silver braze, and furthermore, a metal outer cylinder holding the ceramic heating element is joined by brazing to the tip of a mounting bracket. ing.

Further, since this type of glow plug itself constitutes a part of a pressure partition for shutting off the cylinder of the engine and the outside air, the above-mentioned ceramic heater type glow plug also needs to have a function of maintaining airtightness. Conventionally, as described above, the airtightness can be ensured by depositing silver brazing or the like over the entire circumference and filling the space between the ceramic heating element and the metal outer cylinder.

For example, as shown in FIG. 4, tungsten carbide (WC) or the like is used as a heating resistor 34 in a ceramic heating element 32 mainly composed of silicon nitride (Si ₃ N ₄ ) having high strength and excellent oxidation resistance. Embedded conductive ceramic of
It has been proposed that the ceramic heating element 32 in consideration of the difference in thermal expansion between the ceramic body 33 and the heating resistor 34 made of embedded conductive ceramics is suitable as a ceramic glow plug (Japanese Utility Model Laid-Open No. 2-2003093). reference).

In this ceramic glow plug, a heat generating resistor 34 and a lead pin 36 made of tungsten are embedded in an electrically insulating ceramic heat generating body 32, an electrode lead-out portion 37a on the cathode side is joined to a cathode metal fitting 38, and an anode side electrode is connected. The electrode lead portion 37b was joined to the coil-shaped anode fitting 40, and further joined to the anode terminal 41 and the rod-shaped electrode 42. Further, the rod-shaped electrode 42 is connected to the cathode fitting 3.
In order to secure electrical insulation between the housing 8 and the housing fitting 39 joined thereto, the structure is fixed with mounting screws 45 via insulating seals 44 and 46. A screw part 43 is formed on the outer periphery of the housing fitting 39, and the ceramic glow plug 31 is mounted in the cylinder of the engine by tightening this part.

The glow plug of the type in which the heat generating resistor 34 made of a nickel-chromium alloy high melting point metal wire used before that is embedded is used, the starting time required for heating from room temperature to 800 ° C. is 30 seconds. Was necessary,
In a ceramic glow plug 31 of the type shown in FIG. 4, this was shortened to 4 to 5 seconds. However, recently, it has been demanded that the rise time be 3 seconds or less.

[0007] The mainstream of the ceramic glow plug 31 currently used is a ceramic heating element 32 having an outer diameter of about 3.5 mmφ from the viewpoint of workability. However, when the outer diameter is as large as this, the starting time is inevitably required to be 4 to 5 seconds. If the starting time is further reduced, the durability of the ceramic glow plug 31 is significantly reduced due to excessive temperature rise at the time of starting. I knew it would.

[0008] Further, as another movement for reducing the size of a diesel engine, conventionally, an auxiliary combustion chamber is provided,
Here, a two-stage combustion was adopted in which the fuel was ignited and the combustion was transmitted to a combustion chamber filled with a rich air-rich gas, but the auxiliary combustion chamber was abolished and the combustion chamber was replaced with a combustion chamber. Direct injection engines that directly ignite fuel have been put to practical use. Such an engine is a system in which the fuel injection in the combustion chamber generates a concentration variation, ignites the fuel at a portion having a high concentration, and spreads the fuel over the entirety where the fuel concentration is low. Further, the number of valves has been increased to four in order to improve combustion efficiency and output.

However, in the engine of such a system, the fuel injection nozzle, the intake / exhaust valve and the like are dense, the space for installing the glow plug is narrow, and the conventional ceramic glow plug cannot be used due to its size. There were challenges. The ceramic glow plugs required at present have a large outer diameter, and there is a problem that the engine must be designed with a reduced capacity in order to be installed in an engine cylinder. The currently required ceramic glow plug is 8 mm or less in diameter of the housing fitting, and in consideration of the overall holding strength including the cathode fitting, the outer diameter of the ceramic heating element needs to be 2-3 mm.

However, in the conventional ceramic glow plug, since the anode fitting 40 is connected to the outer periphery of the ceramic insulator 32, the housing fitting 39 is further provided outside the cathode fitting 38 to prevent contact with the housing fitting 39.
To avoid the anode fitting 40. For this reason, the structure of the glow plug could not be reduced.

In order to solve such a problem, Japanese Patent Application Laid-Open No. 2000-356343 discloses a ceramic heating element in which a heating element made of an inorganic conductive material or a high-melting metal material is embedded in ceramic. In a ceramic heater type glow plug having a metal outer cylinder for holding a heating element and a mounting bracket for holding the metal outer cylinder, a ceramic heater type glow plug positioned in the metal outer cylinder has been proposed. . In this glow plug, as shown in FIG. 5, a heating element 34 and two lead wires 36 connected to the heating element 34 are buried in a ceramic insulator 35 made of silicon nitride.
Is exposed on the side surface of the ceramic insulator 35 and connected to the cathode metal fitting 38, and the end of another lead wire 36 is exposed in a concave portion 47 formed on the rear end face side of the ceramic insulator 35, Reference numeral 48 denotes a structure connected to the anode fitting 40. Regarding the method of forming the concave portion 47,
It is shown that a molybdenum wire is buried at a position where the concave portion 47 is to be formed, and after firing, the molybdenum wire is removed by machining such as cutting or dissolving with aqua regia.

With the structure shown in FIG. 5 as described above, it is not necessary to form the housing fitting 39 avoiding the anode fitting 40, so that the diameter of the glow plug can be reduced accordingly.

[0013]

However, in the structure of the ceramic glow plug shown in FIG. 5, a concave portion 46 is formed in the rear end surface of the ceramic heating element 32, and a brazing material is poured into the concave portion to fix the anode fitting 40. Although it has a structure,
Since the ceramic insulator 35 made of silicon nitride is usually heated while applying pressure in a uniaxial direction by hot press firing, in order to form the concave portion 47, molybdenum is temporarily embedded in the concave portion 47, fired, and further cut after firing. It is necessary to form the concave portion 47 by a method such as mechanical processing such as dissolution with aqua regia or the like, and there is a problem that processing takes a very long time and cost cannot be reduced.

[0014]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a ceramic sintered body made of silicon nitride ceramics having a heat-generating resistor at the tip end is provided with an electrode lead connected to the heat-generating resistor. In the ceramic glow plug having a portion, the electrode lead-out portion is exposed at a rear end surface of the ceramic heating element, and a nail head pin forming an anode metal is brazed to the rear end surface to form an electrode. We found that we could solve the problem.

As a result, the diameter of the ceramic glow plug can be reduced, and the temperature rise time from room temperature to 800 ° C. of the ceramic glow plug can be reduced to 3 seconds or less.

[0016]

Embodiments of the present invention will be described with reference to FIG.

FIG. 1A is a sectional view of a ceramic glow plug 1 of the present invention. The ceramic heating element 2 includes a first heating resistor 4, a second heating resistor 5, a lead pin 6, and a cathode electrode lead-out section 7 in a ceramic body 3.
a, an electrode lead-out portion 7b for the anode is embedded. The electrode lead portion 7 a is connected to the cathode metal fitting 8 by a brazing material, and further connected to the housing metal fitting 9. Also,
On the anode side, an electrode lead-out portion 7b is exposed from the rear end face 20 of the ceramic heating element 2. A nail head pin forming the anode fitting 10 is joined to the electrode lead-out portion 7b via a brazing material 7c, and a nail head pin is formed. Is further connected to the rod-shaped electrode 12. The housing metal 9 and the rod-shaped electrode 12 are electrically insulated by insulating seals 14 and 16, and are electrically insulated from the housing metal 9 by the mounting screws 15 via the ring-shaped insulating seals 14 and 16. It is tightened and fixed in the state.

The feature of the present invention lies in the structure on the anode side, and the electrode lead-out portion 7b is provided on the rear end face 20 of the ceramic heating element 2.
The rear end face 20 is exposed to a nail head pin which forms the anode fitting 10 so that the cathode fitting 8 is formed.
In addition, the outer diameter of the housing fitting 9 can be reduced, and the diameter of the ceramic glow plug 1 can be reduced, and at the same time, the number of steps can be reduced and the workability thereof can be improved.

It is preferable that the surface roughness (Ra) of the rear end face 20 of the ceramic heating element 2 to be brazed is 0.5 μm or more. By doing so, the joining strength can be improved by the anchor effect.

As for the positional relationship between the outer periphery of the head of the nail head pin forming the anode fitting 10 and the electrode lead-out portion 7b, as shown in FIG. 1B, the electrode lead-out portion 7b is covered by the head of the nail head pin. Preferably, the distance d between the head and the outer periphery of the head is 0.2 mm or more.

If the position of the electrode lead portion 7b protrudes from the outer periphery of the head of the nail head pin, or if the distance d is less than 0.2 mm, the temperature near the nail head pin during use is as high as about 400 to 450 ° C. Therefore, there is a problem that cracks occur around the electrode lead-out portion 7b due to the stress due to the difference in thermal expansion between the brazing material 7c and the ceramic, and the resistance value increases. Once such a tendency is reached, the temperature near the electrode lead-out portion 7b further increases due to the increase in the resistance value, and a vicious cycle of further crack growth is entered, which is not preferable. In particular, when the end of the brazing material 7c has a shape crossing the electrode lead-out portion 7b, a crack is likely to be generated at the end of the brazing material 7c, so care must be taken.

Further, as shown in FIG. 1C, a rear end face 20 on which a nail head pin forming the anode fitting 10 is brazed.
By chamfering a C-plane or an R-plane of 0.2 mm or more on the outer periphery 22 of the brazing material, the brazing material 7c protruding from the brazing portion can be removed, and an effective insulation distance with the housing fitting 9 can be secured. become able to.

As shown in FIG. 2, a ceramic heating element 2 is provided so as to cover a nail head pin forming the anode fitting 10.
By joining the cap 10a to the rear end face 20,
Further, the strength can be improved. By doing so, it is possible to improve the workability of attaching the anode fitting 10 and the fixing strength. The nail head pin and the cap 1 that constitute the anode fitting 10
0a may be brazed at the same time.

FIG. 3 shows another embodiment of the present invention.
As shown in FIG. 2, a small-diameter portion 21 is formed on the rear end face 20 side of the ceramic heating element 2 and a coil-shaped or cap-shaped anode metal fitting 10 is formed thereon and brazed. In addition, it is possible to reduce the outer diameter of the housing fitting 9 and reduce the diameter of the glow plug. At this time, the electrode lead-out portion 7b may be exposed from the rear end face 20 or may be exposed at the outer periphery of the small-diameter portion 21. In addition, the coil-shaped anode fitting 10
Is preferably brazed to the entire rear end face 20 of the ceramic heating element 2.

In the above embodiment, the outer diameter of the portion of the ceramic heating element 2 in which the heating resistor 4 is embedded is 2.
It is preferable to set the thickness to 0 to 3.0 mm. When the outer diameter of the ceramic heating element 2 is less than 2.0 mm, the first heating resistor 4
Undesirably comes close to the cathode fitting 8 and the cathode fitting 8 is directly heated by the first heating resistor 4. Further, if the outer diameter exceeds 3.0 mm, miniaturization cannot be achieved.

The joining between the ceramic heating element 2 and the cathode fitting 8 is preferably performed at 750 to 1000 ° C. in a vacuum using a brazing material containing at least one of Ag and Cu as a main component. Further, between the end portion 20 and the nail head pin forming the anode fitting 10, a brazing material 7 c containing at least one of Ag, Au, Cu, and Ni as a main component is used in vacuum 750.
It is preferable to perform the bonding at a temperature of up to 1000 ° C.

If the resistance ratio of the first heating resistor 4 to the second heating resistor 5 is smaller than 2: 1 and the resistance of the first heating resistor is smaller than 2: 1, the vicinity of the cathode fitting 10 is undesirably heated. . When the resistance of the first heating resistor 4 becomes greater than the resistance ratio of 7: 1, silicon nitride of the same quality as the ceramic body 3 as a buffer material is used to reduce the resistance of the second heating resistor 5. And the amount of boron nitride to be added is not preferable because cracks are generated in the second heating resistor 5 due to thermal shock at the time of temperature rise and fall. Therefore, the resistance ratio is 2: 1 to 1
A range of 7: 1 is preferred.

The ceramic body 3 of the present invention contains silicon nitride as a main component, 3 to 10% by weight of a rare earth element oxide, 0.3 to 3% by weight of aluminum oxide as a sintering aid,
0.5-8.5% by weight molybdenum disilicide and 1-5
Those containing silicon oxide by weight are preferred. The rare-earth element oxide improves the melting point of the grain boundary phase and improves the high-temperature durability of the ceramic glow plug. Further, aluminum oxide greatly promotes sintering of silicon nitride, and greatly affects the increase and decrease of the amount of grain boundary phase. More preferably, the content is preferably 0.5 to 2% by weight. Silicon oxide is composed of oxygen contained as an impurity of a raw material, a substance mixed from an atmosphere during firing, and a substance to be added. Silicon oxide also has the effect of greatly promoting the sintering of silicon nitride. However, if the content exceeds 5% by weight, it tends to collect on the anode side due to the electric field during energization, which deteriorates the durability of the ceramic glow plug.

The above-mentioned raw material is formed into a predetermined structure, and a first heating resistor 4, a second heating resistor 5, and an electrode lead portion 7 are formed on the surface of the molded body. Body 5
It is preferable that a lead pin 6 made of tungsten is installed so as to connect the electrode lead portion 7 and another molded body is stacked, and integrally fired by hot press firing. The reason for installing the second heating resistor 5 is that if the first heating resistor 4 and the lead pin 6 made of tungsten are directly connected, the temperature of the connecting portion becomes extremely high, so that the ceramic heating element 2 and the cathode This is because the brazing portion of the metal fitting 8 is melted and deteriorated, and the reliability of holding the ceramic heating element 2 is reduced. In order to prevent this, a second heating resistor 5 having a lower resistance than the first heating resistor 4 is formed at the connection portion to lower the temperature of the connection portion with the lead pin 6. Also, the first heating resistor 4
And when the second heating resistor 5 is provided in a plurality of layers,
After preparing a plurality of the compacts, they are stacked and baked integrally by hot pressing.

The compact thus prepared is fired by a hot press to obtain a rectangular ceramic heating element 2 having a built-in heating resistor 4. The shrinkage ratio of the heating resistor 4 in the thickness direction is approximately 40 to 60% with respect to the print thickness.
About.

Further, the rectangular ceramic heating element 2 is processed into a columnar shape, the electrode lead portions 7a and 7b are exposed, and the cathode metal fitting 8, the anode metal fitting 10, the rod-shaped electrode 12, and the housing metal fitting 9 are sequentially joined. The rod-shaped electrode was fixed to the housing fitting 9 via an insulating seal with a screw to obtain a ceramic glow plug 1.

The type in which the heating resistor 4 is formed on the surface of the molded body and laminated and fired has been described above. However, the heating resistor 4 is formed by injection molding or the like, and the silicon nitride ceramics is further formed around the heating resistor 4. The same applies to those obtained by forming an insulating layer made of and baking.

[0033]

EXAMPLES Example 1 5% by weight of ytterbium oxide (Yb ₂ O ₃ ), 3% by weight of molybdenum disilicide, 0.8% by weight of aluminum oxide and an appropriate amount of silicon oxide were mixed. Using a granulated powder of silicon nitride, a flat silicon nitride compact is prepared by press molding. The first heating resistor 4 and the second heating resistor 5 and the electrode lead portion 7 are printed on one surface of the molded body, and two sets of molded bodies having lead pins 6 are prepared. At this time, the first heating resistor 4
And a second heating resistor 5 having a resistance ratio of 5: 1 to produce a sample.

Thereafter, the above-mentioned molded bodies were stacked in two stages, another silicon nitride-based molded body was further laminated on the upper molded body, and further hot-fired to obtain a ceramic heating element 2 having a square cross section. .

Thereafter, the ceramic heating element 2 having a square cross section was rounded to an outer diameter of 2.9 mm. Then, the cathode metal fitting 8 is set on the cathode side electrode lead-out part 7a,
The cathode metal 8 was fixed by melting the brazing material made of Au-Cu. Further, as for the anode, a nail head pin forming the anode fitting 10 was integrated on the electrode lead-out portion 7 on the anode side end face 10a via a brazing material mainly composed of Ag-Cu.

Further, the housing fitting 9 is placed on the cathode fitting 8.
After mounting, this was brazed by high-frequency heating, and a mounting screw 15 installed at the end of the anode fitting 10 was fixed via insulating seals 14 and 16 to obtain a ceramic glow plug.

Further, as shown in FIG. 3, the ceramic heating element 2 manufactured as described above is cut so that the outer diameter near the anode-side rear end becomes 2.4 mm, and the cut portion is formed. Then, a coil-shaped anode metal fitting 10 was brazed to form a ceramic glow plug 1 connected to the anode outlet at the end face 10a.

As shown in FIG. 5, for the purpose of comparison, a recess 47 is formed in the anode side end surface 20 of the ceramic heating element 2 having an outer diameter of 2.9 mm.
Similarly, a ceramic glow plug 1 brazed using a brazing material 48 containing Cu as a main component and a coil-shaped anode fitting 10 on the outer periphery of the anode of a conventional ceramic heating element 2 having an outer diameter of 3.4 mmφ shown in FIG. The ceramic glow plug fixed using the brazing material 48 was manufactured.

Then, the outer diameter, workability and heating time of the ceramic glow plug 1 were compared.

The results are shown in Table 1.

[0041]

[Table 1]

As can be seen from Table 1, in Comparative Example 1, it is necessary to machine the recess 47 in order to mount the anode fitting 10, and it is necessary to pour the brazing material 48 into the recess 47. It is difficult to form the small concave portions 47 by a method such as melting with aqua regia or the like, and the brazing material 4
There was a problem in workability such as difficulty in filling of No. 8.

In Comparative Example 2, which is a conventional ceramic glow plug, the outer diameter of the ceramic glow plug is 12 m.
There was a problem that it would be as large as m.

On the other hand, in the ceramic glow plug of the present invention shown in FIG. 1, the nail head pin constituting the anode fitting 10 is joined by brazing at the rear end face 20 of the ceramic heating element 2, so that the outer diameter of the ceramic glow plug is 8m
It is possible to reduce the thickness to about m, and at the same time, there is no need to drill holes, so that the workability can be remarkably improved.

The same effect can be obtained in the other embodiment of the present invention shown in FIG.

Embodiment 2 Here, the surface roughness of the rear end face 10a of the ceramic heating element 2 to which the anode fitting 10 is brazed and the outer diameter of the head part forming the anode fitting 10 are 2.4 mm and the wire diameter is 0.7 mm. The nail head pin is replaced with a brazing material 7c containing Ag-Cu as a main component.
And the tensile strength of the nail head pin was measured. Brazing was performed at 1000 ° C. in a vacuum. The level of surface roughness (Ra) is less than 0.1 μm, 0.3, 0.
The values were changed to 5, 0.7, and 1.0 μm Ra, and ten samples were prepared, and the average value of the tensile strength was used as data. The outer diameter of the ceramic heating element 2 was 3.0 mm.

Further, as shown in FIG. 2, a cap-shaped metal fitting 10a is put on the outer side of
850 in vacuum using brazing material 7c containing Cu as a main component
A sample brazed at a temperature of ° C. was prepared, and the same evaluation was performed.

The results are shown in Table 2.

[0049]

[Table 2]

As shown in Table 2, the surface roughness (Ra) of the rear end face 20 was less than 0.5 μm. 1, 2 is 6
No. 0N, but the surface roughness (Ra) was 0.5 μm or more. 3 to 5 showed values of 60 N or more. It was presumed that the surface roughness (Ra) improved the anchor effect and further improved the tensile strength.

In addition, as shown in FIG. 2, a cap was put on the nail head pin and brazed. In No. 6, the strength could be further improved.

Example 3 Here, the correlation between the outer diameter of the nail head pin forming the anode fitting 10, the interval between the pattern of the electrode extraction portion 7b of the anode, and the durability was examined. The outer diameter of the head portion of the nail head pin was set to 2.4 mm, and 20 samples each in which the distance d between the outer periphery of the head and the pattern of the electrode extraction portion 7b of the anode was changed from 0 to 0.4 mm were prepared. Tensile strengths were measured for each of the initial and nail head pin mounting portions after 5,000 cycles of heating to 400 ° C. in 2 minutes and forced cooling to 50 ° C. or less in 2 minutes. In addition,
The ceramic heating element 2 used had an outer diameter of 3.0 mm.

Table 3 shows the average intensities of the respective components.

[0054]

[Table 3]

As can be seen from Table 3, the distance d is 0.2
mm. In Nos. 1 and 2, the tensile strength after the durability test was 30 N or less, but the distance d was 0.2 mm or more. Nos. 3 to 5 had a tensile strength of 40 N or more even after the durability test.

[0056]

According to the present invention, there is provided a ceramic glow plug comprising a ceramic sintered body made of silicon nitride ceramics having a heating resistor on a tip end side and having an electrode lead portion connected to the heating resistor. An electrode lead-out portion is exposed on the rear end face of the ceramic heating element, and a nail head pin serving as an anode fitting is brazed to the rear end face, so that workability can be improved and cost can be reduced.

[Brief description of the drawings]

1A is a longitudinal sectional view of a ceramic glow plug of the present invention, FIG. 1B is a sectional view taken along line XX of FIG.
(C) is a partial enlarged view of the joint part of the anode fitting.

FIG. 2 is a sectional view showing another embodiment of the ceramic glow plug of the present invention.

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

FIG. 4 is a sectional view showing a conventional ceramic glow plug.

FIG. 5 is a sectional view showing a conventional ceramic glow plug.

[Explanation of symbols]

 1: ceramic glow plug 2: ceramic heating element 3: ceramic body 4: first heating resistor 5: second heating resistor 6: lead pin 7: electrode lead portion 8: cathode metal fitting 9: housing metal fitting 10: anode metal fitting 11: anode terminal 12: rod-shaped electrode 13: screw part 14, 16: insulating seal 15: mounting screw

Claims (7)

[The claims] 1. A ceramic glow plug comprising: a ceramic heating element made of silicon nitride ceramics having a heating resistor on a tip side; and an electrode leading section connected to the heating resistor. A ceramic glow plug, which is exposed at a rear end surface of a heating element and has a nail head pin serving as an anode fitting brazed to the rear end surface. 2. The ceramic glow plug according to claim 1, wherein a surface roughness (Ra) of a rear end face of said ceramic heating element is 0.5 μm or more. 3. The ceramic glow plug according to claim 1, wherein a cap-shaped fitting is joined so as to cover the nail head pin forming the anode fitting. 4. An electrode lead portion exposed on a rear end face of the ceramic heating element is covered by a nail head pin serving as an anode metal fitting, and a distance between an outer periphery of the nail head pin and the electrode lead portion is 0.2 mm or more. 2. The ceramic glow plug according to claim 1, wherein: 5. The glow plug according to claim 1, wherein the outer periphery of the rear end face of the ceramic heating element is chamfered to a C surface or an R surface of 0.2 mm or more. 6. A ceramic glow plug, comprising a ceramic heating element made of silicon nitride ceramics having a heating resistor on a front end side and having an electrode lead portion connected to the heating resistor, a rear end of the ceramic heating element. The side has a small diameter, and the electrode lead-out part is exposed on the outer periphery or the rear end face,
A ceramic glow plug, wherein an anode fitting is attached to the drawer. 7. The ceramic glow plug according to claim 1, wherein an outer diameter of the ceramic heating element in a portion in which the heating resistor is embedded is 2.0 to 3.0 mm.