JP2002333136A - 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 is facilitated, whilst after the assembling a strong joint structure is ensured, and further in a joint of a metal lead wire with the heater body joint structure and a conduction state are excellent. SOLUTION: There are provided a metal outer cylinder 3 disposed such that it surrounds a heater body 2 circumferentially, and is made interference fitted to the heater body, and further a tip end of the heater body 2 is protruded axially, and a main metal fitment 4 joined with an axial rear end of the metal outer cylinder 3 and on an external peripheral surface a mounting section to an internal combustion engine is formed. Any one of two metal lead wires connected with a ceramic resistor is welded to the metal external cylinder 3 as a grounding power supply terminal section 16 in order to make the ceramic resistor conductive, and the metal outer cylinder 3 and the heater body 2 are joined at the grounding power supply terminal section 16 in a gap formed between the external peripheral surface of the heater body and the rear end internal peripheral surface.

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, by joining the heater body and the metal outer cylinder by brazing and joining the metal outer cylinder and the metal shell by brazing, the heater body,
A method of integrally configuring the metal outer cylinder and the metal shell is used.

[0003]

By the way, in a glow plug using a ceramic heater as described above,
In order to join the heater body to the metal outer cylinder by brazing,
Preparation of the brazing material, heat treatment associated with brazing, and the like are required, and simplification of assembly and processing is desired. Also, after joining the metal outer cylinder and the heater main body, it is necessary to join a metal lead wire for conducting the resistance heating element from outside the heater, but this joining is also performed while facilitating processing. There is a demand for a structure having high strength and a good conduction state.

[0004] It is an object of the present invention to provide a glow plug using a ceramic heater which has a strong bonding structure after assembly while facilitating assembly, and further has a bonding strength in bonding a metal lead wire to a heater body. Another object of the present invention is to provide a glow plug having a good conduction state.

[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 arranged so as to fit around the heater body so as to surround the heater body in the circumferential direction, and to protrude the tip of the heater body in the axial direction. And a metal shell joined to the rear end in the axial direction of the metal outer cylinder and having an outer peripheral surface formed with a mounting portion to the internal combustion engine, and joined to the heater body to conduct the ceramic resistor. A glow plug characterized in that a metal lead wire is joined to a metal outer cylinder.

As described above, by fitting the heater main body and the metal outer cylinder together, it is possible to facilitate the manufacture and reduce the number of steps as compared with joining by brazing or the like.
Further, the strength can be improved. In addition to this,
If the metal lead wire for grounding is welded to the metal outer cylinder, a good conduction state can be achieved while firmly joining the metal lead wire and the metal outer cylinder. Specifically, the metal lead wire can be configured as a pair of metal lead wires, and one of the metal lead wires is joined to a metal outer cylinder as a grounding current-carrying terminal portion, so that the metal lead and the ground metal are connected via the metal outer cylinder. To the power supply terminal section. The other metal lead wire can be electrically connected to the terminal fitting insulated from the metallic shell.

Further, a gap is formed between the outer peripheral surface of the heater main body and the inner peripheral surface of the rear end portion of the metal outer cylinder, and the other end of the metal lead wire, one end of which is joined to the metal outer cylinder, is placed in the gap. It can be joined to the heater body.
As described above, if a gap is formed between the outer peripheral surface of the heater main body and the inner peripheral surface of the rear end portion of the metal outer cylinder, at least a part of the metal lead wire can be accommodated in the gap, and the compact Can be achieved. In addition, by providing the gap, the outer peripheral surface of the heater body is exposed in a form forming the inner surface of the gap, and the exposed surface can be used as the joining surface of the metal lead wire. It is possible to increase the size and improve the bonding strength.

Further, the metal lead wire may be joined to the metal outer cylinder on the inner peripheral surface of the metal outer cylinder. By doing so, the space for joining the metal lead wire to the metal outer cylinder can be increased, and the joining strength can be improved. A gap is formed as described above, and one end of the metal lead wire is joined to the outer peripheral surface of the heater main body in the gap, and the other end is joined to the inner peripheral surface of the metal outer cylinder inside or outside the gap. In this case, both ends of the metal lead can be firmly joined on their respective surfaces, and at least a part of the metal lead can be housed in the gap to efficiently use the space.

[0009]

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. As shown in FIG. The heater main body 2 is configured as a rod-shaped ceramic heater element in which a ceramic resistor 10 made of conductive ceramic is embedded in a ceramic base 13 made of insulating ceramic. Then, the heater main body 2 is connected to a grounding energizing terminal 1 described later.
6. The ceramic heater 1 is constituted by joining the power supply side energizing terminal portion 17. And the ceramic resistor 10
A first resistor portion 11 made of a first conductive ceramic disposed at a tip end portion of the heater main body 2, and a rear portion of the first resistor portion 11 along the direction of the axis O of the heater main body 2. A pair of second conductive ceramics having a lower end than the first conductive ceramic and having a tip joined to each end of the first resistor portion 11 in the direction of current flow. And the second resistor portions 12, 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. .

[0012] Silicon nitride 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.

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 15%. -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.

The first resistor portion 11 of the ceramic resistor 10 has a tip portion 11a which is to be heated to 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 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 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 heater main body 2 is provided inside a metal shell 4 from the rear end side in the direction of the axis O thereof.
A metal shaft 6 for supplying electric power to the metal shell 4 is disposed in an insulated state from the metal shell 4. In this embodiment, the ceramic ring 31 is arranged 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 32 is formed and fixed on the rear side. . The outer peripheral surface of the ceramic ring 31 has a large-diameter ring-side engaging portion 31a.
Is formed near the rear end of the inner peripheral surface of the metal shell 4, and is engaged with the metal fitting side engaging portion 4e formed in the form of a circumferential step to prevent the metal fitting 4 from slipping forward in the axial direction. I have. 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 tube 3 by the grounding 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 2, the joining between the grounding energizing terminal portion 16 and the metal outer cylinder 3 is facilitated.

The grounding conduction terminal portion 16 constituted by a metal lead wire is arranged so as to connect the rear end portion of the outer peripheral surface of the heater main body 2 to the rear end portion of the inner peripheral surface of the metal outer cylinder 3. The inside of a portion of the cylinder 3 located rearward from a notch 13 a described later is filled with glass 30. This allows
Since the grounding current terminal portion 16 is substantially entirely buried in the glass 30, disconnection and poor contact hardly occur even when vibration or the like is 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. 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 is surrounded by the metal shell 4 so as to overlap a position corresponding to the gap in the axial direction (i.e.,
The metal outer cylinder 3 and the metal shell 4 are joined so that the metal shell 4 surrounds the gap radially outward with respect to the axis).

Further, 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 referred to as an "increased diameter portion gap 60").
), The other end of the grounding conducting terminal portion 16 (metal lead wire), one end of which is joined to the metal outer cylinder 3, is connected to the heater main body 2 (specifically, the exposed portion 12a of the second resistor portion 12). Are joined by brazing as described above.
Also, a gap 62 (hereinafter referred to as a gap 62) formed by the fitting surfaces of the inner peripheral surface 3a of the metal outer cylinder and the outer peripheral surface 2a of the heater main body. , "Fitting portion gap 62"), respectively. Note that, in FIG. 3, the sliding material is conceptually indicated by a thick line, and a reduced diameter portion is formed on the rear end side by partially cutting the ceramic base 13 as described above. On the other hand, at the rear end of the metal outer cylinder 3, the enlarged diameter portion is located corresponding to the position of the reduced diameter portion in the axial direction, and the reduced diameter portion and the enlarged diameter portion are enlarged. The gap 60 is configured. As used herein, the term “slipper” refers to a material having a function of improving the lubricity of a metal member (that is, lowering the coefficient of friction). Under the conditions (for example, when the heat treatment is performed at a predetermined temperature condition), those which lose lubricity are included, and those in which lubricity is lost are also broadly referred to as lubricating materials. For the lubricant, for example, stearic acid, carboxylic acid, fatty acid sodium, which is a substance containing a carboxylate,
A substance, such as oxidized microwax, whose lubricity is reduced and the coefficient of friction is increased by heat treatment is desirable. In this embodiment, after the assembly as shown in FIG. 3, the sliding member 70 changes to low lubricity due to the heat generated by the heater main body 2, and the coefficient of friction between the fitting surfaces is extremely high.

The enlarged-diameter portion gap 60 also functions as a sliding material accommodating portion when the heater main body 2 is fitted into the metal outer cylinder 3 by fitting. In other words, by performing the interference fit while accommodating the sliding material in the enlarged diameter portion gap 60,
Since the fitting can be performed while suppressing the load, and after the assembly, it can be formed as a housing portion for housing a part of the grounding conductive terminal portion 16, so that an extremely effective configuration is obtained.

[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.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic heater 2 Heater main body 3 Metal outer cylinder 4 Metal shell 5 Screw part (attachment part) 10 Ceramic resistor 12, 12 Second resistor part 12a, 12a Exposed part 13 Ceramic base 50 Glow plug

Claims (5)

[Claims] 1. A glow plug having a rod-shaped heater body in which a ceramic resistor made of conductive ceramic is embedded in a ceramic base made of insulative ceramic, wherein the heater has a shape surrounding the heater body in a circumferential direction. A metal outer cylinder which is fitted to the main body and fitted so as to protrude the front end of the heater main body in the axial direction, and which is coupled to an axial rear end of the metal outer cylinder and has an outer peripheral surface; And a metal shell formed with an attachment portion to the internal combustion engine, wherein a metal lead wire joined to the heater main body for conducting the ceramic resistor is joined to the metal outer cylinder. And glow plug. 2. A gap is formed between an outer peripheral surface of the heater main body and an inner peripheral surface of a rear end portion of the metal outer cylinder, and the other end of a metal lead wire whose one end is joined to the metal outer cylinder is the gap. The glow plug according to claim 1, wherein the glow plug is joined to the heater main body inside. 3. The glow plug according to claim 1, wherein a rear end of the metal outer cylinder projects rearward from a rear end of the heater main body in an axial direction of the heater main body. 4. The glow plug according to claim 1, wherein the metal lead wire is joined to the metal outer cylinder by spot welding. 5. The glow plug according to claim 1, wherein the metal lead wire is joined to the metal outer cylinder on an inner peripheral surface of the metal outer cylinder.