JP2002333135A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug wherein in the glow plug using a ceramic heater assembling of a heater body, a metal outer cylinder, and a main metal fitment, etc., is facilitated, and wherein after the assembling strong coupling without looseness is ensured. SOLUTION: In a glow plug 50, a heater body 2 is closely fitted in a metal outer cylinder 3, whilst at a rear end of the metal outer cylinder 3 there is provided a diameter enlargement section that forms a predetermined gap between an internal peripheral surface of the metal outer cylinder 3 and an external peripheral surface of the heater body 2. The metal outer cylinder 3 and the main metal fitment 4 are closely fitted such that the main metal fitment 4 surrounds the metal outer cylinder 3 at a position corresponding to the gap 60 (diameter enlargement section gap 60) formed by the diameter enlargement section. A smoothing member 70 is provided in the diameter enlargement section 60 and in a gap 62 (fitting section gap 62) adjacent to the former diameter enlargement section gap 60 formed with the respective engagement surfaces of the metal outer cylinder internal peripheral surface and the heater body external peripheral surface. The diameter enlargement section gap 60 serves as a smoothing member accommodating section upon inserting the heater body 2 into the metal outer cylinder 3.

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, a method is provided in which a heater main body including a resistance heating element is held by a metal shell via a metal outer cylinder. For example, a method of integrally configuring the heater main body, the metal outer cylinder, and the metal shell by joining the heater main body and the metal outer cylinder with a brazing material and bonding the metal outer cylinder with the metal shell by brazing is used. I have.

[0003]

In a glow plug using such a ceramic heater, since a heater body is joined to a metal outer cylinder by a brazing material, preparation of the brazing material, heat treatment accompanying the brazing, and surface treatment are performed. Processing, etc.
Due to structural or process problems, an increase in the number of processes and an increase in manufacturing complexity have been unavoidable. Also, the heater body,
When the method of joining the metal outer cylinder and the metal shell by brazing is used, there is also a problem in accuracy that it is difficult to ensure concentricity of the heater body, the metal shell, and the metal shell.

[0004] It is an object of the present invention to provide a glow plug using a ceramic heater in which a heater main body, 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]

In order to solve the above-mentioned problems, the present invention provides a rod-shaped heater body in which a ceramic resistor made of conductive ceramic is embedded in a ceramic base made of insulating ceramic. A metal outer cylinder that surrounds the heater main body in the circumferential direction and is arranged in a manner to protrude the front end portion of the heater main body in the axial direction, and at the rear end in the axial direction of the metal outer cylinder. And a metal shell having an outer peripheral surface formed with a mounting portion to the internal combustion engine, and the heater body is tightly fitted inside the metal outer cylinder, while the rear end of the metal outer cylinder has An enlarged portion that forms a certain amount of gap between the inner peripheral surface of the metal outer cylinder and the outer peripheral surface of the heater body is provided, and a gap formed by the enlarged portion (hereinafter, “enlarged portion gap”)
The glow plug is characterized in that the metal shell and the metal shell are fitted tightly so that the metal shell surrounds the outside in the radial direction with respect to the axis.

The fitting of the heater main body to the metal outer cylinder and the bonding of the metal outer cylinder to the metal shell are each fitted and fitted, so that the joining by brazing between these members can be eliminated and the manufacturing process can be simplified. Can be achieved. That is, as compared with joining by brazing or the like, it is possible to facilitate manufacturing, reduce the number of steps, improve strength, and the like. Further, by forming the enlarged diameter portion as described above, for example, at the time of press-fitting in the interference fit, the lubricating material accumulates in the enlarged diameter portion, and the sliding surface of the heater main body and the metal outer cylinder has a sufficient amount. The amount of the lubricant is applied efficiently. As a result, in joining the heater main body and the metal outer cylinder, a highly accurate shape in which misalignment, inclination, and the like are suppressed is obtained.

A gap between the enlarged diameter portion and a gap following the enlarged diameter portion gap, which is formed by the fitting surfaces of the inner peripheral surface of the metal outer cylinder and the outer peripheral surface of the heater body (the fitting portion clearance) ) May be provided with a lubricating material, respectively. More specifically, the enlarged-diameter portion gap can function as a lubricating material accommodating portion when press-fitting the heater main body into the metal outer cylinder in order to fit tightly, thereby reducing the load at the time of press-fitting. It is possible to reduce the number of the components and facilitate the assembly.

In a predetermined section in the axial direction, a fitting portion between the heater main body and the metal outer cylinder may be configured to overlap a fitting portion between the metal outer cylinder and the metal shell. With such an overlapped configuration, a good heat drawing in the metal outer cylinder is achieved, and therefore, a rise in the temperature of the metal outer cylinder due to heat generation from the heater body can be suppressed. Therefore, since the thermal expansion of the metal outer cylinder can be effectively suppressed,
The fitting state between the heater main body and the metal outer cylinder and the fitting state between the metal outer cylinder and the metal shell are maintained, so that the configuration is unlikely to loosen. Also, in addition to the tight fit between the heater body and the metal outer cylinder, a binding force is applied by the metal shell from the outside of the metal outer cylinder, so that the joining of the heater main body, the metal shell, and the metal shell is stronger. This makes the configuration extremely resistant to external loads such as thermal shock and vibration.

Further, by providing a glass-filled layer filled with glass in the gap of the enlarged diameter portion, it is possible to further strengthen the joining between the heater main body and the metal outer cylinder while improving the insulation of necessary portions, and to reduce vibration. A strong configuration can be achieved. More specifically, each of a pair of metal lead wires connected to the ceramic resistor to conduct the ceramic resistor is joined on the inner peripheral surface of the heater main body in the enlarged diameter portion gap, A glass-filled layer can be formed in such a manner that at least a part of each of the pair of metal leads is buried in the enlarged-diameter portion gap. If the metal lead wires are joined in the enlarged diameter portion gap, the joint portion can be accommodated in the gap and the compactness can be achieved, and the joining area can be widened on the inner peripheral surface of the heater main body. It is possible to increase the bonding strength. In addition, when the metal lead wire is buried in the glass-filled layer in this way, a structure in which disconnection, poor contact, and the like hardly occur even when vibration or the like is applied.

[0010]

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 that covers the outer peripheral surface of the main body 2 so that the tip of the heater body 2 projects, and a cylindrical metal shell 4 that covers 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 shell 3 or the inner edge of the opening on the distal end side of the metal shell 4,
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 heater main body 2 has a rod-like form 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 heater body 2, and a first resistor portion 11 on the rear side of the first resistor portion 11. The second conductive member is arranged so as to extend along the direction of the axis O, and has a tip portion joined to each end portion of the first resistor portion 11 in the direction of conduction, and has a lower resistivity than the first conductive ceramic. And a pair of second resistor portions 12, 12 made of conductive ceramic.

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. .

[0013] 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 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, 12 serve as a conduction path to the first resistor portion 11, and the second conductive ceramic, which is a material thereof, 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 heater body 2.
The second resistor portions 12, 12 are bar-shaped portions extending substantially parallel to each other and extending rearward from both ends of the U-shaped first resistor portion 11 along the direction of the axis O.

In the ceramic resistor 10, the first resistor portion 11 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.

The pair of second resistor portions 12, 12 of the ceramic resistor 10 are respectively exposed on the surface of the heater main body 2 at the rear end in the axial direction.
Reference numerals 2a and 12a serve as joining regions of the current-carrying terminal portions 16 and 17 to the ceramic resistor 10 and function as electric connection portions. In this structure, it is not necessary to embed a lead wire for energization in the heater main body 2, and the heater main body 2 can be made of all ceramics, 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 energizing terminal portions 16 and 17 are connected to the exposed portions 12a and
There is also an advantage that it is not easily affected by the above-mentioned electromigration effect because it is not buried just by being joined to the substrate 12a.

In this embodiment, at the rear end of the heater body 2 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 above-mentioned exposed portion 1
2a and 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 terminals 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, 12 of the ceramic resistor 10 is electrically connected to the metal shell 4 via the metal outer cylinder 3 by the grounding energizing terminal portion 16. 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 heater main body 2. The heater main body 2 has a rear end surface 2r positioned 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 heater main body 2,
The rear end of the metal outer cylinder 3 is configured to protrude rearward from the rear end of the heater main body 2. As described above, when the rear end of the metal outer cylinder 3 projects rearward from the rear end of the heater main body 12, when the heater main body 2 is assembled to the metal outer cylinder 3, the grounding energizing terminal portion 16 and the metal The outer cylinder 3 can be easily joined.

The grounding conducting terminal portion 16 constituted by a metal lead wire is arranged so as to connect the exposed portion 12a of the heater main body 2 to the rear end portion of the inner peripheral surface of the metal outer cylinder 3, and furthermore, the metal outer cylinder 3 The inside of the enlarged diameter portion 59 (to be described later) of the glass 3 (specifically, the inside of the portion located rearward from the notch 13a)
0 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 current-carrying terminal 16 for grounding is used.
Is a band-shaped metal member, the front end of one plate surface 16a is joined to the corresponding second resistor portion 12 by brazing, while the rear end of the other plate surface 16b is
Is joined to the rear end of the inner peripheral surface by resistance welding such as brazing or spot welding. Thereby, the joining of the grounding conduction terminal portion 16 can be performed more easily.
The use of spot welding eliminates the need for heat treatment such as brazing, thereby facilitating the processing and increasing the bonding strength.

The heater main body 2 is tightly fitted inside the metal outer cylinder 3, while the inner peripheral surface 3 a of the metal outer cylinder 3 and the heater main body 2 are fitted at the rear end of the metal outer cylinder 3.
The metal outer cylinder 3 and the metal shell 4 are joined so that the metal shell 4 surrounds the gap in the radial direction with respect to the axis. Is done. The enlarged diameter portion 59 is provided in a shape following the fitting portion inner peripheral surface 3b in the fitting portion of the metal outer cylinder 3 with the heater main body 2.

In a gap 60 between the inner peripheral surface 3a of the metal outer cylinder and the outer peripheral surface 2a of the heater main body (hereinafter, also referred to as an enlarged-diameter portion gap 60), one end is connected to the metal outer cylinder 3 for grounding. The other end of the terminal portion 16 (metal lead wire) is connected to the heater body 2 (specifically, the exposed portion 12 of the second resistor portion 12).
a) and brazing as described above. Also, a gap 60 between the enlarged diameter portion and a gap following the enlarged diameter portion gap 60, and each fitting surface of the metal outer cylinder inner peripheral surface 3a and the heater main body outer peripheral surface 2a (specifically, the metal outer cylinder A gap 62 (hereinafter, simply referred to as a fitting portion outer peripheral surface 2b) formed by the side fitting portion inner peripheral surface 3b (simply, also referred to as the fitting portion inner peripheral surface 3b) and a heater main body fitting portion outer peripheral surface 2b (simply, also referred to as the fitting portion outer peripheral surface 2b). A sliding member 70 is provided in each of the “fitting portion gaps 62”. In FIG. 3, the sliding material is conceptually indicated by a thick line. In addition, as described above, the reduced diameter portion is formed on the rear end side by forming a part of the ceramic base 13 into a cutout form, while the axis of the reduced diameter portion is formed on the rear end portion of the metal outer cylinder 3. The enlarged diameter portion is positioned corresponding to the position in the direction, and the reduced diameter portion and the enlarged diameter portion 59 constitute the enlarged diameter portion gap 60.

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. As the lubricating material, for example, a substance whose lubricity is reduced by heat treatment and whose coefficient of friction is increased, such as sodium fatty acid, which is a substance containing stearic acid, carboxylic acid and carboxylate, and oxidized microwax, is desirable. In the present embodiment, after assembly as shown in FIG.
Due to the heat generated by the heater main body 2, the lubricity changes to low lubricity, and the friction coefficient between the fitting surfaces becomes extremely high.

FIG. 5 illustrates the fitting process. As shown in FIG. 5, the enlarged-diameter portion gap 60 has a function as a sliding material accommodating portion when the heater main body 2 is fitted into the metal outer cylinder 3 by interference fitting. That is, the heater body 2
In the state where the sliding material 70 is applied to the outer peripheral surface 2b of the fitting portion, the sliding material is easily deposited on the front end surface 3h of the enlarged diameter portion, and the sliding material can effectively flow between the fitting surfaces. . 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 outer peripheral surface 2a of the heater main body 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.

The fitting portion between the heater main body 2 and the metal outer cylinder 3 and the fitting portion between the metal outer cylinder 3 and the metal shell 4 overlap each other in a predetermined section in the axial direction. Specifically, the fitting surface of the heater main body 2 and the metal outer cylinder 3 (the outer peripheral surface 2b of the heater main body fitting portion and the inner peripheral surface 3b of the metal outer cylinder fitting portion)
The fitting surfaces of the metal outer cylinder 3 and the metal shell 4 (the outer peripheral surface 3c of the metal outer cylinder fitting portion and the inner peripheral surface 4c of the metal shell fitting portion) overlap in a predetermined section in the axial direction. With such an overlapping configuration, a fitting portion with the metal shell 4 is provided at a position corresponding to the fitting portion with the heater body 2 in the metal outer cylinder 3 (specifically, on the back side of the fitting surface). As a result, 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 heater main body 2 can be extremely effectively suppressed. Therefore, the thermal expansion of the metal outer cylinder can be suppressed, and the fitting state between the heater main body 2 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 heater main body 2 and the metal outer cylinder 3, a binding force by the metal shell 4 is applied from the outside of the metal outer cylinder 3, so that the heater main body 2, the metal shell 3, and the metal shell 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.

FIG. 4 shows some examples of the shape of the enlarged diameter portion. For example, as shown in FIG. 4A, the enlarged diameter portion may be configured to have a tapered inclined portion 3c following the fitting portion inner peripheral surface 3b of the metal outer cylinder 3. . In the vertical cross-section about the axis O shown in FIG. 4A, the outer peripheral line of the inner peripheral surface of the metal outer cylinder 3 is such that the inclination angle of the inclined portion 3c with respect to the inner peripheral surface 3b of the fitting portion is a predetermined angle (for example, 40 ° to 80 °). °). When the inclined portion is provided in such a tapered shape, the heater main body 2 can be smoothly inserted into the metal outer cylinder 3. Further, as shown in FIG. 4 (b), a round portion 3d which is continuously bent may be formed so as to continue to the rear side of the inner peripheral surface 3b of the fitting portion. When the round portion 3d is formed in this manner, the heater main body 2 can be easily press-fitted into the metal outer cylinder 3, and the smooth material can smoothly flow into the fitting surface at the time of press-fitting. Further, as shown in FIG. 4C, an end face (orthogonal face 3
The stepped portion may be formed in the form provided with e).
Further, as shown in FIG. 4C, in a shape having the orthogonal surface 3e, a chamfer or a radius may be formed at a corner 3g following the inner peripheral surface 3b of the fitting portion. Such a chamfer or radius can be similarly applied to a case where the chamfer or the radius follows the fitting portion inner peripheral surface 3b as shown in FIG. 3 or FIG. The corners can likewise be chamfered or rounded.

[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 a view showing some examples of a metal outer cylinder shape.

FIG. 5 is an explanatory diagram for explaining an interference fitting process of the heater main body and the metal outer cylinder.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic heater 2 Heater main body 2a Heater main body outer peripheral surface 3 Metal outer cylinder 3a Metal outer cylinder inner peripheral surface 4 Metal shell 5 Screw part (mounting part) 10 Ceramic resistor 13 Ceramic base 16 Grounding conduction terminal part (metal lead wire) 17 Power supply side energizing terminal part (metal lead wire) 30 Glass 50 Glow plug 59 Large diameter part 60 Large diameter part gap 62 Fitting part gap 70 Slipper

Claims (6)

[Claims] 1. A glow plug having a rod-shaped heater body 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 heater body in a circumferential direction and extends in an axial direction. And a metallic shell connected to an axial rear end of the metal outer cylinder so as to protrude a front end of the heater main body, and having a mounting portion for an internal combustion engine formed on an outer peripheral surface thereof. And wherein the heater body is tightly fitted inside the metal outer cylinder, and at the rear end of the metal outer cylinder, the inner peripheral surface of the metal outer cylinder and the outer peripheral surface of the heater main body. A large diameter portion that forms a certain amount of gap is provided between the metal shells and the gap formed by the large diameter portion (hereinafter, also referred to as a “large diameter portion gap”). To surround Ri, glow plugs, characterized in that they metal outer cylinder and the metal shell is fitted interference fit. 2. A gap (hereinafter, referred to as a gap) formed between the enlarged-diameter portion gap and a gap following the enlarged-diameter portion gap, the gap being formed by a fitting surface of each of the inner peripheral surface of the metal outer cylinder and the outer peripheral surface of the heater main body. ,
The glow plug according to claim 1, wherein a lubricating material is provided in each of the “fitting portion gaps”. 3. A glass-filled layer filled with glass is provided in the enlarged-diameter portion gap.
The glow plug according to 1. 4. A pair of metal lead wires connected to the ceramic resistor for conducting the ceramic resistor are joined on the inner peripheral surface of the heater main body in the enlarged-diameter portion gap. 4. The glow plug according to claim 3, wherein the glass-filled layer is formed such that at least a part of each of the pair of metal leads is buried in the enlarged-diameter portion gap. 5. In a predetermined section in the axial direction, a fitting portion between the heater main body and the metal outer cylinder is configured to overlap a fitting portion between the metal outer cylinder and the metal shell. 5. The glow plug according to any one of 1 to 4. 6. A glow plug having a rod-shaped heater body 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 heater body in a circumferential direction and has an axial direction. And a metallic shell connected to an axial rear end of the metal outer cylinder so as to protrude a front end of the heater main body, and having a mounting portion for an internal combustion engine formed on an outer peripheral surface thereof. And the heater main body is fitted and coupled inside the metal outer cylinder, and at the rear end of the metal outer cylinder, an inner peripheral surface of the metal outer cylinder and an outer peripheral surface of the heater main body are provided. A large-diameter portion that forms a certain amount of gap is provided therebetween, and a gap formed by the large-diameter portion (hereinafter, also referred to as a “large-diameter portion gap”)
The metal outer cylinder and the metal shell are fitted so that the metal shell surrounds the outside in the radial direction with respect to the axis, the fitting portion between the heater body and the metal shell, the metal shell and the metal shell. The fitting portion of the glow plug is configured to overlap in a predetermined section in the axial direction.