JP2002349852A - Glow plug and method of manufacturing glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug which can achieve firm coupling without slackness after assembly, by materializing such constitution that the assembly of a heater body, a metallic outer case, a main metal fitting, etc., becomes easy, in a glow plug using a ceramic heater. SOLUTION: The glow plug is equipped with a bar-shaped ceramic heater 1 where a ceramic resistor 10 consisting of conductive ceramic is buried in a ceramic substrate 13 consisting of insulating ceramic, and it is provided with a metallic outer tube 3 which is arranged with the tip of the ceramic heater 1 projected, and a main metal fitting 4 where a mounting part to an internal combustion engine is made. The ceramic heater 1 is tight fitted inside the metallic outer tube 3, while the frictional coefficient between the engaging faces is set to be larger at the front end 101 of the metallic outer tube 3 than at the rear end 103 when defined that the tip side of the ceramic heater 1 is front side, in the case where a sliding material remains in the space (space in engagement section) made by each engaging face of the inner peripheral face of the metallic outer tube and the outer peripheral face of the ceramic heater.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug for preheating diesel engines.

[0002]

2. Description of the Related Art A glow plug using a ceramic heater having a structure in which a resistance heating element made of conductive ceramic is embedded in an insulating ceramic base has been widely known. In such a glow plug, there has been provided a method of holding a ceramic heater including a resistance heating element with a metal shell via a metal outer cylinder. For example, a method of integrally configuring a ceramic heater, a metal outer cylinder, and a metal shell by joining a ceramic heater and a metal shell with a brazing material and bonding the metal outer cylinder and the metal shell by brazing is used. I have.

[0003]

In a glow plug using such a ceramic heater, since the ceramic heater is joined to the metal outer cylinder by the brazing material, preparation of the brazing material, heat treatment accompanying the brazing, and surface treatment are performed. Processing, etc., increase in the number of processes due to structural or process problems,
The complication of manufacturing was inevitable. In addition, when the method of joining the ceramic heater, the metal outer cylinder, and the metal shell by brazing is used, there is also an accuracy problem that it is difficult to ensure the concentricity of the ceramic heater, the metal shell, and the metal shell. .

An object of the present invention is to provide a glow plug using a ceramic heater in which a ceramic heater, a metal outer cylinder, a metal shell and the like can be easily assembled. In addition, the present invention provides a glow plug capable of forming a firm connection without loosening after assembly.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a rod-shaped ceramic heater in which a ceramic resistor made of a conductive ceramic is embedded in a ceramic base made of an insulating ceramic. A glow plug having a metal outer cylinder that surrounds the ceramic heater in a circumferential direction and is arranged in a manner to project a tip portion of the ceramic heater in an axial direction.
When the front end side of the ceramic heater in the axial direction is set to the front side, a metal shell coupled to the axial rear end of the metal outer cylinder and having a mounting portion to the internal combustion engine formed on the outer peripheral surface thereof. In the meantime, the ceramic heater is tightly fitted inside the metal outer cylinder, while the lubricating material is inserted into gaps (fitting portion gaps) formed by respective fitting surfaces of the inner peripheral surface of the metal outer cylinder and the outer peripheral surface of the ceramic heater. A glow plug, wherein the glow plug remains so that the front end of the metal outer cylinder is set to have a larger coefficient of friction between the fitting surfaces than the rear end.

[0006] The fitting of the ceramic heater and the metal outer cylinder and the bonding of the metal outer cylinder and the metal shell are each fitted by fitting, so that the joining by brazing between these members can be eliminated. Simplification can be achieved, and in addition, the load at the time of press-fitting can be reduced by using a sliding material at the time of the interference fit, thereby facilitating assembly. In this manner, if the press-fitting form is such that the lubricating material remains in the fitting portion gap, the misalignment, inclination, and the like of these joined bodies are suppressed, and the shape accuracy is high. In addition, if a thermally decomposable lubricant is used, insertion can be easily performed at the time of press-fitting, and as the use proceeds, the lubricant is decomposed by the heat generated by the ceramic heater, and the tightening force is increased. In particular, when one of the objects to be pressed is such a heating element, it is extremely effective to use a thermally decomposable sliding material.

[0007] Further, since the front end of the ceramic heater has a high temperature, the front end of the metal outer cylinder near the high temperature portion tends to expand and contract in the radial direction due to the heat, resulting in deformation and the like. The front end may be easily loosened. Therefore, if the friction coefficient at the front end is set to be larger than that at the rear end in order to compensate for such a situation, such local loosening can be suppressed, and more firm fitting can be realized. Furthermore, if the thermally decomposable lubricant is allowed to remain as described above, the lubricant is more easily decomposed at the front end portion due to heat generated by the ceramic heater. The material will be degraded more. Normally, with the progress of use, loosening between the front end fitting surfaces due to heat may gradually become remarkable, but on the other hand, the sliding material is gradually decomposed and the friction coefficient increases. As a result, the binding force at the front end is effectively supplemented.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a glow plug using the ceramic heater of the present invention together with its internal structure. The glow plug 50 has a ceramic heater 1, a metal outer cylinder 3 covering an outer peripheral surface of the ceramic heater 1 so that a tip portion of the ceramic heater 1 projects, and a cylindrical metal shell 4 covering the metal outer cylinder 3 from outside. Etc. are provided.
On the outer peripheral surface of the metal shell 4, a screw portion 5 as an attachment portion for fixing the glow plug 50 to an engine block (not shown) is formed. The metal shell 4 is brazed to the metal outer cylinder 3 by, for example, filling the gap between the inner and outer peripheral surfaces of the metal outer cylinder 3 or the inner peripheral edge of the opening of the metal shell 4 at the front end side and the outer peripheral surface of the metal outer cylinder 3. Is fixed by laser welding all around. Further, the metal shell 4 and the metal outer cylinder 3 may be tightly fitted.

FIG. 2 is an enlarged sectional view showing the ceramic heater 1. The ceramic heater 1 has a rod-like shape in which a ceramic resistor 10 made of conductive ceramic is embedded in a ceramic base 13 made of insulating ceramic. The ceramic resistor 10 includes a first resistor portion 11 made of a first conductive ceramic disposed at a tip portion of the ceramic heater 1 and the first resistor portion 1.
1 is arranged so as to extend along the direction of the axis O of the ceramic heater 1, and the front ends are respectively joined to both ends of the first resistor portion 11 in the energizing direction, and the first conductive member 11 is connected to the first conductive member 11. A pair of second resistor portions 1 made of a second conductive ceramic having a lower resistivity than the ceramic
2 and 12.

In this embodiment, a silicon nitride ceramic is used as an insulating ceramic constituting the ceramic base 13. The structure of the silicon nitride ceramic has a form in which main phase particles mainly composed of silicon nitride (Si ₃ N ₄ ) are bound by a grain boundary phase derived from a sintering aid component described later. The main phase may be a phase in which Si or N is partially substituted by Al or O, or a phase in which metal atoms such as Li, Ca, Mg, and Y are dissolved in the phase. .

[0011] Silicon nitride-based ceramics include 3 in the periodic table.
A, 4A, 5A, 3B (for example, Al) and 4B (for example, Si) and at least one element selected from the group consisting of Mg and Mg as the above-mentioned cation element, in terms of the content in the whole sintered body, It can be contained in a conversion of 1 to 10% by mass. These components are mainly added in the form of oxides,
In the sintered body, it is mainly contained in the form of an oxide or a composite oxide such as silicate. If the sintering aid component is less than 1% by mass, it is difficult to obtain a dense sintered body, and if it exceeds 10% by mass, insufficient strength, toughness or heat resistance is caused. The content of the sintering aid component is desirably 2 to 8% by mass.
It is good to do. When a rare earth component is used as a sintering aid component, Sc, Y, La, Ce, Pr, Nd, Sm,
Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, L
u can be used. Among them, Tb and D
Since y, Ho, Er, Tm, and Yb have the effect of promoting crystallization of the grain boundary phase and improving the high-temperature strength, they can be suitably used.

Next, the first resistor portion 11 and the second resistor portions 12, 12 constituting the resistance heating element 10 are made of conductive ceramics having different electric resistivity as described above. The method of making the electric resistivity of both conductive ceramics different from each other is not particularly limited. For example, a method of using the same kind of conductive ceramic phase and making the contents different from each other; Various methods can be exemplified, such as a method using a conductive ceramic phase; and a method based on a combination of the following. In this embodiment, the method is used.

As the conductive ceramic phase, for example, tungsten carbide (WC), molybdenum disilicide (MoSi
₂ ) and known materials such as tungsten disilicide (WSi ₂ ). In the present embodiment, WC is adopted.
In order to reduce the difference in linear expansion coefficient from the ceramic base 13 and increase the thermal shock resistance, an insulating ceramic phase which is a main component of the ceramic base 13, here, a silicon nitride ceramic phase can be blended. Therefore, by changing the content ratio between the insulating ceramic phase and the conductive ceramic phase, the electric resistivity of the conductive ceramic constituting the resistor portion can be adjusted to a desired value.

More specifically, the first conductive ceramic, which is the material of the first resistor portion 11 forming the resistance heating portion, has a conductive ceramic phase content of 10 to 25% by volume, and the remainder is an insulating ceramic phase. It is good to do. When the content of the conductive ceramic phase exceeds 25% by volume, the conductivity becomes too high and a sufficient calorific value cannot be expected. When the content is less than 10% by volume, the conductivity becomes too low. Cannot be secured sufficiently.

On the other hand, the second resistor portions 12 and 12 serve as a conduction path to the first resistor portion 11, and the material of the second conductive ceramic has a conductive ceramic phase content of 10%. -30% by volume, with the balance being an insulating ceramic phase. If the content of the conductive ceramic phase exceeds 30% by volume, it becomes difficult to densify by firing, and the strength tends to be insufficient. In addition, even when the temperature reaches the temperature range usually used for preheating the engine, the electric resistivity is low. In some cases, the rise becomes insufficient and the self-saturation function for stabilizing the current density cannot be realized. On the other hand, when the volume is less than 15% by volume, the heat generation in the second resistor portions 12 and 12 becomes too large, and the heat generation efficiency of the first resistor portion 11 is deteriorated. In this embodiment, the content of WC in the first conductive ceramic is 16% by volume (55% by mass), and the content of WC in the second conductive ceramic is 20% by volume (7%).
0% by mass) (all the rest are silicon nitride ceramics (including a sintering aid)).

In this embodiment, the ceramic resistor 10
Are arranged such that the first resistor portion 11 has a U-shape, and the U-shaped bottom portion is located on the tip side of the ceramic heater 1, and the second resistor portions 12 and 12 have a U-shaped shape. Bar-shaped portions extending substantially in parallel with each other in the direction of the axis O from both ends of the one resistor portion 11 are formed.

The first resistor portion 11 of the ceramic resistor 10 has a tip portion 11a which should be at the highest temperature during operation.
In order to concentrate the electric current, the tip 11a has a smaller diameter than both ends 11b, 11b. Then, the joint surface 15 with the second resistor portions 12, 12 has a tip 1
The axial cross-sectional area of the second resistor portions 12, 12 is larger than the cross-sectional area of the distal end portion 11a of the first resistor portion 11, while being formed at both end portions 11b, 11b having a diameter larger than 1a. Is set.

A pair of second resistor portions 12, 12 of the ceramic resistor 10 are respectively exposed at the rear end in the axial direction to the surface of the ceramic heater 1, and the exposed portions 12a, 12a It is a junction area of the current-carrying terminals 16 and 17 to the resistor 10 and functions as an electrical connection. In this structure, it is not necessary to embed a lead wire for energization in the ceramic heater 1, and the ceramic heater 1 can be made of all-ceramic, so that the number of manufacturing steps can be reduced. In a structure in which a metal lead wire is embedded in ceramic, when a heater driving voltage is applied at a high temperature, metal atoms constituting the metal lead wire receive an electrochemical driving force due to the electric field gradient. In some cases, it is consumed by the so-called electromigration effect of forcibly diffusing into the ceramic side, and disconnection or the like is likely to occur. However, in the above structure, the current-carrying terminal portion 1
6, 17 are second resistor portions 12, 1 forming conductive paths.
Since it is only joined to the second exposed portions 12a, 12a and does not become a buried form, there is also an advantage that it is essentially less affected by the electromigration effect.

In this embodiment, at the rear end of the ceramic heater 1 in the direction of the axis O, a part of the ceramic base 13 is cut out, and the rear end of the second resistor portion 12 is exposed in the cutout 13a. ing. Thereby, the exposed portions 12a, 12a can be easily formed. Such a notch 13a may be formed at the stage of the molded body, or may be formed later by grinding or the like after firing.

The energizing terminal portions 16 and 17 are, for example, N
i or a metal such as a Ni alloy, and is brazed to the second resistor portions 12 at the exposed portions 12a. In this brazing, for metal-ceramic bonding, an active brazing material suitable for this is used, or the active metal component is adhered to the ceramic side by vapor deposition or the like, metallized, and then joined using a normal brazing material. It is desirable to adopt a technique that does this. Known Ag-based or Cu-based brazing materials can be used, and one, two or more of Ti, Zr and Hf can be used as the active metal component.

As shown in FIG. 1, a metal shaft 6 for supplying electric power to the ceramic heater 1 is provided inside the metal shell 4 from the rear end side in the direction of the axis O in an insulated state with the metal shell 4. Are located. In the present embodiment, a ceramic ring 31 is disposed between the outer peripheral surface on the rear end side of the metal shaft 6 and the inner peripheral surface of the metal shell 4, and the glass-filled layer 3
2 is formed and fixed. A ring-side engaging portion 31a is formed on the outer peripheral surface of the ceramic ring 31 in the form of a large-diameter portion. By engaging with the side engaging portion 4e, the axially forward side is prevented from coming off.
In addition, the outer peripheral surface portion of the metal shaft 6 that comes into contact with the glass-filled layer 32 is provided with unevenness by knurling or the like (a hatched area in the figure). Further, the rear end of the metal shaft 6 extends rearward of the metallic shell 4, and the terminal fitting 7 is fitted into the extended portion via an insulating bush 8. The terminal fitting 7 is fixed in a conductive state to the outer peripheral surface of the metal shaft 6 by a circumferential caulking portion 9.

In the exposed portions 12a, one of the second resistor portions 12 of the ceramic resistor 10 is electrically connected to the metal shell 4 via the metal outer cylinder 3 by the grounding terminal 16 at the exposed portions 12a. The other end is also electrically connected to the metal shaft 6 by the power supply terminal 17. In the present embodiment, as shown in FIG.
Has an exposed portion 12a formed at the rear end portion of the outer peripheral surface of the ceramic heater 1. In the ceramic heater 1, the rear end surface 2r is located forward of the rear end surface 3r of the metal outer cylinder 3 in the axis O direction. I have. In other words, in the axial direction of the ceramic heater 1, the rear end of the metal outer cylinder 3 is configured to protrude rearward from the rear end of the ceramic heater 1. As described above, when the rear end of the metal outer cylinder 3 projects rearward from the rear end of the ceramic heater 12, when the ceramic heater 1 is assembled to the metal outer cylinder 3, the grounding energizing terminal 16
And the metal outer cylinder 3 are easily joined.

The grounding terminal 16 formed of a metal lead wire is arranged to connect the exposed portion 12a of the ceramic heater 1 to the rear end of the inner peripheral surface of the metal outer cylinder 3. The inside of the enlarged diameter portion 59 (FIG. 3: described later) is filled with the glass 30 (specifically, the inside of the portion located rearward from the notch 13a) to form a glass-filled layer. As a result, since the grounding energizing terminal portion 16 is substantially entirely buried in the glass 30, disconnection or poor contact is unlikely to occur even when vibrations or the like are applied. In the present embodiment, the grounding conducting terminal 16 is a band-shaped metal member, and the front end of one plate surface 16a is joined to the corresponding second resistor portion 12 by brazing, while the other plate is The rear end of the surface 16b is joined to the rear end of the inner peripheral surface of the metal outer cylinder 3 by resistance welding such as brazing or spot welding. Thereby, the joining of the grounding conduction terminal portion 16 can be performed more easily. By using spot welding,
Easier processing by eliminating the need for heat treatment such as brazing,
And joining strength can be raised.

The ceramic heater 1 has a metal outer cylinder 3.
At the rear end of the metal outer cylinder 3, a predetermined amount of clearance is formed between the inner peripheral surface 3 a of the metal outer cylinder 3 and the outer peripheral surface of the ceramic heater 1 at the rear end of the metal outer cylinder 3. A diameter portion 59 is provided, and the metal outer cylinder 3 and the metal shell 4 are joined such that the metal shell 4 surrounds the gap radially outward with respect to the axis. The enlarged diameter portion 59 is provided in a shape following the fitting inner peripheral surface 3b of the fitting portion of the metal outer cylinder 3 with the ceramic heater 1.

Also, as shown in FIG. 3, the metal outer cylinder inner peripheral surface 3a
In a gap 60 (hereinafter, also referred to as an enlarged-diameter portion gap 60) between the metal heater 3 and the ceramic heater outer peripheral surface 2a, the other end of the grounding conductive terminal portion 16 (metal lead wire), one end of which is joined to the metal outer cylinder 3, is ceramic. The heater 1 (specifically, the exposed portion 12a of the second resistor portion 12) is joined by brazing as described above. In addition, a gap 60 between the enlarged-diameter portion and the gap 60 following the enlarged-diameter portion,
a and the outer peripheral surface 2a of the ceramic heater (specifically, the inner peripheral surface 3b (simply referred to simply as the inner peripheral surface 3b) of the metal outer cylinder side fitting portion) and the outer peripheral surface 2b of the ceramic heater fitting portion. (Simply, also referred to as the fitting portion outer peripheral surface 2b)), the sliding members 70 are provided in the gaps 62 (hereinafter, also referred to as “fitting portion gaps 62”). In FIG. 3, the sliding material is conceptually indicated by a thick line. Further, as described above, the reduced diameter portion is formed on the rear end side by making a part of the ceramic base 13 into a cutout form, while the diameter of the reduced diameter portion in the axial direction is formed on the rear end portion of the metal outer cylinder 3. The enlarged diameter portion is positioned corresponding to the position of the enlarged diameter portion.
Is configured.

The term "sliding material" used herein refers to a material having a function of improving the lubricity of a metal member (ie, lowering the coefficient of friction). Therefore, it includes those that lose lubricity under predetermined conditions (for example, when heat treatment is performed under predetermined temperature conditions), and further includes those that lose lubricity (ie,
The product after decomposition by heat treatment is also referred to in a broad sense as a lubricant.

After the joining, CO—O is used as a lubricant.
It is possible to adopt a configuration in which a substance containing at least one of a bond, a CC bond and a C ＝ O bond remains.
For this lubricant, for example, stearic acid, carboxylic acid, sodium fatty acid which is a substance containing a carboxylate,
A substance such as oxidized microwax, which is decomposed, volatilized or changed to a low lubricating substance by heat treatment to increase friction coefficient, is desirable. By using such a thermally decomposable substance, the lubricating material 70 after assembly as shown in FIG.
Can be changed or eliminated with low lubricity by the heat generated by the ceramic heater 1, and the coefficient of friction between the fitting surfaces can be extremely increased.

As shown in FIG. 2, in the metal outer cylinder 3, the front end portion 101 located on the front end side in the axial direction is set to have a larger coefficient of friction than the rear end portion 103 located on the rear end side. You. In the present invention, when the axial overall length of the fitting portion and the L _1, the rear end portions of the portion from the front end to a distance L ₂ in the axial direction front end portion 101, similarly from the rear end to a distance L ₃ Defined as 103. The distance _{L 2} and _{L 3} is assumed to be equal, the distance _{L 2} and _{L 3} together with 10% of the total length _{L 1} (i.e., 0.1 × L
And _{1 = L 2 = L 3)} . The front end 101 and the rear end 103 defined as described above are set so that the front end 101 has a higher coefficient of friction. The coefficient of friction at the front end 101 is set in the range of 0.1 to 0.5, and the coefficient of friction at the rear end 103 is set in the range of 0.01 to 0.2. The coefficient of friction of the front end 101 is preferably set to be 2 to 10 times the coefficient of friction of the rear end 103.
Further, the friction coefficient of the entire fitting portion is set in a range of 0.01 to 0.5.

In order to set the friction coefficient of the front end portion 101 to be large as described above, the amount of the remaining sliding material in the fitting portion gap 62 is determined by the front end portion 101 and the rear end portion 103.
It is effective to set the number to be smaller. For example, in the finished product of the glow plug, the amount of the lubricating material existing in the fitting portion gap 62 in the section corresponding to the front end portion 101 in the axial direction indicates that the glow plug exists in the fitting portion gap 62 in the section corresponding to the rear end portion 103. It is desirable to make the amount of the sliding material larger.

The fitting portion between the ceramic heater 1 and the metal outer tube 3 and the fitting portion between the metal outer tube 3 and the metal shell 4 are configured to overlap in a predetermined section in the axial direction. Specifically, the fitting surface of the ceramic heater 1 and the metal outer cylinder 3 (the outer peripheral surface 2b of the ceramic heater fitting portion and the inner peripheral surface 3b of the metal outer cylinder fitting portion), and the fitting of the metal outer cylinder 3 and the metal shell 4 The surfaces (the outer peripheral surface 3c of the metal outer cylinder fitting portion and the inner peripheral surface 4c of the metal shell fitting portion) are configured to overlap in a predetermined section in the axial direction. With such an overlapping configuration, the ceramic heater 1 in the metal outer cylinder 3 can be used.
Position corresponding to the mating part (specifically, the back side of the mating surface)
In addition, since a fitting portion with the metal shell 4 is provided, a good heat drawing configuration is achieved, and a rise in the temperature of the metal outer cylinder 3 due to heat generation from the ceramic heater 1 can be extremely effectively suppressed. Therefore, the thermal expansion of the metal outer cylinder can be suppressed, and the fitting state between the ceramic heater 1 and the metal outer cylinder 3 and the fitting state between the metal outer cylinder 3 and the metal shell 4 are favorably maintained. It becomes a difficult configuration. Further, in addition to the interference fit between the ceramic heater 1 and the metal outer cylinder 3, a tightening force is applied from the outside of the metal outer cylinder 3 by the metal shell 4, so that the ceramic heater 1, the metal outer cylinder 3, and the metal shell 3 4 becomes stronger and has a structure that is extremely resistant to external loads such as thermal shock and vibration. As in the present embodiment, when the fitting portion gap 60 is provided and a configuration in which the fitting surfaces are overlapped is adopted, a sufficient fitting area (press-fit length in the axial direction) can be obtained while reducing the fitting area. Since the bonding strength can be exhibited, it is more effective. In addition, if the rear end is overlapped in this way to improve the tightening force, the effect of improving the tightening force can be obtained at both the front end and the rear end. Is realized.

Next, a method for manufacturing a glow plug will be described. As shown in FIG. 4, after forming a rod-shaped ceramic heater 1 in which a ceramic resistor 10 made of a conductive ceramic is embedded in a ceramic base 13 made of an insulating ceramic, the formed ceramic heater 1 and a metal outer cylinder are formed. An application step of applying a thermally decomposable lubricant to at least one of the outer peripheral surface of the ceramic heater 1 and the inner peripheral surface of the metal outer cylinder 3 is performed on at least any one of the three. In the present embodiment, the lubricant 70 made of the above-described substance is applied to the outer peripheral surface of the ceramic heater 1.

After the application step, a press-fitting step of forming the joined body 100 (see FIG. 5) by press-fitting the ceramic heater 1 into the metal outer cylinder 3 is performed. As shown in FIG. 4, the enlarged-diameter portion gap 60 functions as a sliding material accommodating portion when the ceramic heater 1 is fitted into the metal outer cylinder 3 in this press-fitting step. That is, in a state in which the lubricant 70 is applied to the outer peripheral surface 2b of the fitting portion of the ceramic heater 1, the lubricant easily accumulates on the front end face 3h of the enlarged diameter portion, and the lubricant is effectively removed between the fitting surfaces. Can flow in. In particular, in the insertion state as indicated by the broken line, the lubricant is further accumulated inside the enlarged-diameter portion gap 60, and the application state of the ceramic heater outer peripheral surface 2a at the time of press-fitting is extremely good. As described above, the fitting can be performed while the load is suppressed by performing the interference fit while accommodating the sliding material in the enlarged-diameter portion gap 60. Since this can be a housing section for housing the section, the configuration is extremely effective.

Then, a heat treatment step is performed to reduce the lubricity of the lubricating material by performing a heat treatment on the joined body 100 obtained after the press-fitting step. As the heat treatment step, an energization heating step in which the ceramic heater 1 is energized and heated by the energizing means 201 (a voltage application device or the like) in the joined body 100 joined as shown in FIG. 5A can be performed.
In this heat treatment step, the front end portion of the ceramic heater 1 is set to a particularly high temperature so that the front end portion 101 (FIG. 2)
Is locally decomposed, volatilized, or changed into a low-sliding substance so that the friction coefficient after the treatment is within the above range. Further, the temperature or the energizing time of the ceramic heater may be adjusted so as to affect the sliding material at the rear end.
By adjusting the energization time to such an extent that a difference in the slipperiness between the front end portion 101 and the rear end portion 103 is obtained (that is, to an extent in which a difference in the coefficient of friction between the front end portion 101 and the rear end portion 103 is obtained), the fitting force of the front end portion 101 is improved While the object is achieved, the energization time can be shortened. It is to be noted that the sliding material may be entirely removed by decomposition, volatilization or the like without making a difference.

Further, as shown in FIG. 5B, a heating step of heating the whole joined body 100 from outside using an external heat source 202 may be performed as a heat treatment step. That is, the entire joined body 100 is heated by the external heat source 202 to decompose, volatilize, or change the lubricating material remaining in the fitting gap 62 into a low-lubricity substance. Regarding the heating, the temperature, time and the like may be adjusted to such an extent that a part remains, and all the lubricant may be decomposed or volatilized. These heat treatment steps (electric heating step and heating step) may be performed when the ceramic heater 1 and the metal outer cylinder 3 are joined as shown in FIG. 5, or as shown in FIG. It may be performed after the metal shell 4 is joined in addition to the joined body 100 made of the metal outer cylinder 3.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of a glow plug of the present invention.

FIG. 2 is an enlarged longitudinal sectional view showing the ceramic heater.

FIG. 3 is an enlarged view of a main part of FIG.

FIG. 4 is an explanatory view illustrating some steps in a method for manufacturing a glow plug.

FIG. 5 is an explanatory diagram illustrating a heat treatment step.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic heater 2a Ceramic heater outer peripheral surface 3 Metal outer cylinder 3a Metal outer cylinder inner peripheral surface 4 Metal shell 10 Ceramic resistor 13 Ceramic base 50 Glow plug 62 Fitting gap 70 Sliding material 100 Joint

Claims (6)

[Claims] 1. A glow plug having a rod-shaped ceramic heater in which a ceramic resistor made of a conductive ceramic is embedded in a ceramic base made of an insulating ceramic, wherein the glow plug surrounds the ceramic heater in a circumferential direction and has an axial direction. And a metal outer cylinder disposed so as to protrude a front end portion of the ceramic heater, and an axial rear end portion of the metal outer cylinder when a front end side of the ceramic heater in the axial direction is a front side. And a metal shell having an outer peripheral surface formed with a mounting portion to the internal combustion engine. The ceramic heater is fitted tightly inside the metal outer cylinder while the metal outer cylinder inner peripheral surface is fitted. And a lubricant remains in a gap formed by each fitting surface of the ceramic heater outer peripheral surface (hereinafter, also referred to as a “fitting portion gap”),
Further, the glow plug is characterized in that the front end of the metal outer cylinder is set to have a larger friction coefficient between the fitting surfaces than the rear end. 2. The remaining amount of the lubricating material remaining in the fitting portion gap is smaller in an axial section corresponding to the front end than in an axial section corresponding to the rear end of the metal outer cylinder. The glow plug according to claim 1, wherein 3. In a predetermined section in the axial direction, a fitting portion between the ceramic heater and the metal outer cylinder is configured to overlap a fitting portion between the metal outer cylinder and the metal shell. The glow plug according to 1 or 2 4. A ceramic heater in which a ceramic resistor made of conductive ceramic is embedded in a ceramic base made of insulative ceramic, and the ceramic heater surrounds the ceramic heater in a circumferential direction, and a tip end of the ceramic heater is arranged in an axial direction. Manufactures a glow plug having a metal outer cylinder arranged in a projecting manner and a metal shell coupled to an axial rear end of the metal outer cylinder and having a mounting portion for an internal combustion engine formed on an outer peripheral surface. A method of applying a thermally decomposable lubricant to an outer peripheral surface of the ceramic heater and / or an inner peripheral surface of the metal outer cylinder; Press-fitting the ceramic heater to form a joined body, and performing a heat treatment on the joined body to reduce the lubricity of the lubricating material. And a method of manufacturing a glow plug. 5. The method for manufacturing a glow plug according to claim 4, wherein the heat treatment step includes an energization heat generation step of energizing the ceramic heater to generate heat. 6. The heat treatment step includes a heating step of heating the entire joined body using an external heat source.
3. The method for manufacturing a glow plug according to item 1.