JPH02267418A - Glow plug for diesel engine - Google Patents

Abstract

PURPOSE:To improve the reliability and increase the service life by integrally fastening the ceramic heater and the holder with overlapped sections comprising the beginning end and the terminal end of insulation layers and bonding layer disposed nearly equidistantly around the outer circumference of lead sections at the end of the holder. CONSTITUTION:Two layers of insulation 23a, 23b and a bonding layer 23c are superposed around the lead sections 21, 22 at the end of the holder 12 of a ceramic heater 11, and the beginning end and the terminal end are overlapped to form overlapped sections 26a, 26b. It is important to nearly equidistantly dispose these overlapped sections 26a, 26b, 26c in a circle. If the overlapped sections coincide in the same location, the clearance between the ceramic heater 11 and the holder 12 becomes uneven to adversely affect to ensure the electrical insulation and the airtightness. For the material of the bonding layer 23c, palladium silver solder, for instance, is used, and the ceramic heater 11 which has gone through the firing can be fastened in the holder 12 by silver soldering, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a glow plug used for preheating the auxiliary combustion chamber or combustion chamber of a diesel engine.

In particular, the present invention relates to an improvement in a glow plug for a diesel engine, which is equipped with a ceramic heater that has a fast heating function and a self-saturating property that can achieve long-term afterglow.

[Conventional technology]

Diesel engines generally have poor startability at low temperatures, so a glow plug is installed in the auxiliary combustion chamber or combustion chamber to generate heat when energized, raising the intake air temperature or as an ignition source.
A method is used to improve engine startability. Conventionally, this kind of glow plug has a metal sheath filled with heat-resistant insulating powder and a coiled heating wire made of iron chromium, nickel, etc. buried therein. The so-called sheath type is common. In addition, there is also Japanese Patent Application Publication No. 57415
As shown in Japanese Patent No. 23, etc., a ceramic heater type using a rod-shaped heater in which a heating wire made of tungsten or the like is embedded in an insulating ceramic material such as silicon nitride is also known. Compared to sheathed types that heat indirectly through heat-resistant insulating powder and a sheath, these types of ceramic heaters can improve heat transfer efficiency and also have excellent heat generation characteristics. Because it has greatly improved characteristics and has fast heating performance.

It has been widely adopted in recent years.

However, the above ceramic heater type glow plug has a structure in which a heating wire made of metal such as tungsten is embedded inside an insulating ceramic material such as silicon nitride, and the coefficient of thermal expansion between these two materials is different. For,
In particular, the rapid temperature rise during heat generation and its repeated use may reduce the durability of the ceramic heater. Therefore, there is a problem in terms of reliability such as heat resistance strength, and there is also the disadvantage of increasing costs.

In order to solve the above problems, there is a ceramic heater structure in which the heating wire is formed of an insulating ceramic material and a conductive ceramic material having a coefficient of thermal expansion such as between the paths.
This method has been proposed in Japanese Patent No. 0-9085, Japanese Patent No. 6o-14784, and the like. However, both of them still have structural and functional problems when used as glow plugs, and have not been put into practical use.

That is, there are problems such as insufficient function as a rapid heating type, complicated molding process, complicated electrode extraction structure, and difficulty in increasing the afterglow time.

In order to solve the above problems, the present applicant has already filed an invention for a glow plug for diesel engines in which a U-shaped ceramic heater made of conductive ceramic material is bonded and held in a hollow holder. (Patent Application No. 60-299338, No. 60-299339, No. 61-256354, No. 61-256355, No. 62)
-1a3682, 62-134040, Jitsugan Showa 6
2-81651 etc.).

[Problem to be solved by the invention]

Although the above inventions and ideas have solved the problems existing in the prior art, subsequent experiments and research have revealed that there are some problems.

First, when bonding and fixing the ceramic heater to the tip of the holder, an insulating layer made of an insulating material is placed around the outer periphery of the lead part corresponding to the tip of the holder, and a bonding layer made of a metal brazing material is placed around the outer periphery of this insulating layer. By applying and fixing,
It is constructed to ensure airtightness. The above-mentioned insulating layer and bonding layer must be formed to have a uniform thickness around the outer periphery of the lead portion.

Usually, a method such as screen printing is employed.

However, since the starting and ending ends of the thin films that form the insulating layer and bonding layer inevitably overlap, the thickness of the layer becomes larger in one overlapping part than in other parts, resulting in a gap between the outer periphery of the lead part and the inner periphery of the holder. The gap may become uneven and the bonding between the two parts may become incomplete.

There is a problem in that it causes poor airtightness during use of the glow plug, reducing its lifespan.

Furthermore, an insulating sheet is interposed and fixed between the pair of lead parts extending rearward from both ends of the U-shaped heat generating part at the part corresponding to the tip of the holder, as described above. Since the ceramic heater is formed in a U-shape, it is difficult to form the gap size between the lead portions to be constant or with extremely high precision. Further, since the ceramic heater itself has some springiness, the gap size of the lead portion naturally varies. For this reason, even if the insulating sheet is formed with high precision, a gap of an undesired size is created between the two, and the sheet that should be interposed for bonding, such as Ti-C
Variations in thickness occur in the bonding layer made of the u brazing material. If this bonding layer is too thick, it will be difficult to adhere the insulating layer to the outside, resulting in poor insulation. On the other hand, if the bonding layer is too thin, the bonding between the lead part and the insulating sheet will fail. Become complete. The above-mentioned disadvantages have the problem of significantly shortening the lifespan of the glow plug when used repeatedly.

It is an object of the present invention to solve the problems existing in the above-mentioned prior art, to perfect the above-mentioned inventions and ideas, and to provide a glow plug for a diesel engine that is highly reliable and has a long life.

[Means to solve the problem]

In order to achieve the above object, in the first invention, a U-shaped heat generating part and a pair of lead parts extending rearward from both ends of the heat generating part are made of a conductive ceramic material. A ceramic heater integrally constructed by the above is held at the tip of a hollow holder with at least the heat generating part protruding outside, and at least one part of the ceramic heater corresponding to the holder tip is held at the tip of a hollow holder. In a diesel engine glow plug constructed by interposing and fixing an insulating sheet between a pair of lead parts, a plurality of insulating layers made of an insulating material are provided on the outer periphery of the lead part corresponding to the tip of the holder, and this insulating layer At least one bonding layer made of a metal brazing material is applied to the outer periphery of the ceramic heater, and overlapping portions consisting of the respective insulating layers and the starting and ending ends of the bonding layers are arranged approximately equally in the outer circumferential direction. Join and secure the holder together. A technical method was adopted.

Next, in the second invention, a U-shaped heat generating part and a pair of lead parts extending rearward from both ends of the heat generating part are integrally formed of a conductive ceramic material. The ceramic heater is held at the tip of a hollow holder with at least the heat generating part protruding outside, and the ceramic heater is insulated between a pair of lead portions of at least a portion of the ceramic heater corresponding to the holder tip. In a glow plug for a diesel engine constructed by interposing and fixing a sheet, the thickness at the rear end of the insulating sheet is 20 to 100 μm larger than the thickness at the front end.

A technical method was adopted.

[Effect]

With the above configuration, the ceramic heater has sufficient heat resistance strength and can quickly become red hot at the tip of the ceramic heater.

It can fully demonstrate its performance as a fast heating type.

It can function as a highly reliable and long-life glow plug for diesel engines.

〔Example〕

FIG. 1 is a longitudinal sectional view of a main part showing an embodiment of the present invention. A schematic structure of a glow plug, which is generally designated by the reference numeral 10 in the figure, will be explained. The glow plug 10 has a rod-shaped ceramic heater 11 whose distal end functions as a heating element, and a substantially tubular holder 12 made of metal, such as stainless steel, that holds the ceramic heater 11 at its distal end. A threaded portion 12a is formed on the outer periphery of the holder 12, and is screwed into a threaded hole (not shown) on the cylinder head side of the engine.
The tip of the ceramic heater 11 is held in a state in which it projects into the combustion chamber or the auxiliary combustion chamber. At the rear end of the holder 12 is a terminal assembly 1 in which first and second external connection terminals 13 and 14 are embedded through a synthetic resin or other insulating material.
The lead portions 21.22 that fit in and support the terminals 13.14 and the ceramic heater 11.

Connection is made via a metal conductor 16.17, such as a flexible wire, and a terminal cap 28.29. In this case, since the terminal caps 28 and 29 are fixed to the rear ends of the lead parts 21 and 22, the outer diameter of this rear end is made smaller than the outer diameter of the other parts of the lead parts 21 and 22. Then.

This is preferable in order to avoid electrical short circuit accidents caused by the terminal caps 28 and 29 coming into contact with the inner surface of the holder 12.

Next, the terminal assembly 15 includes a first external connection terminal 13 arranged on its axis and having a rod portion 13a on its inner end side to be connected to the metal conductive wire 16, and a first external connection terminal 13 having a predetermined interval around the first external connection terminal 13. A cylindrical second lead piece 14a, which is placed at the same position and extends to a part of the inner end thereof, is connected to the metal conductive wire 17.
It has an assembly body 15a made of a resin mold that integrates the external connection terminal 14, both terminals 13 and 14 and the outer periphery so as to insulate them, and a metal tube for connection reinforcement is provided on the outer periphery of the assembly body 15a. 15b. Then, this metal tube 15b is crimped at the peripheral edge of the opening at the rear end of the holder 12 using a high pressure, and is buckled and deformed along the axial direction, so that the inner side of the metal tube 15b is turned outward toward the resin assembly main body 15a. is firmly pressed against the inner wall of the holder 12, so that problems caused by external force or thermal contraction can be solved.

Furthermore, 18a and 18b are an insulating ring and a washer, respectively, which are fitted into the second external connection terminal 14 protruding rearward of the holder 12. 18c is an insulating member, and the first external connection terminal 1 is connected to the outer end of the washer 18b.
Fit on the 3rd side. Further, 18d and 18e are a spring washer and a tightening nut, respectively, which are fitted and screwed into a threaded portion formed on the outer end side of the first external connection terminal 13. and between the washer 18b and the insulating member 18c, and between the insulating member 18c and the spring washer la.
By interposing lead wires (not shown) from the batteries between each of the external connection terminals 13.1 and d,
4 is electrically connected to the battery. Reference numerals 16a and 17a are insulating members such as tubes covering the metal conductive wires 16 and 17, respectively.

The ceramic heater 11 is formed by, for example, kneading conductive sialon powder with a thermoplastic resin or the like, injection molding it into a mold having a predetermined cavity, and firing the molded body, or by forming the material into a rod shape in advance. can be formed into a predetermined shape by electrical discharge machining or grinding. The heat generating part 20 is formed to have a small diameter so as to be thinner than the lead parts 21.22, and a slit 25 is formed in the center of the ceramic heater 11 in the longitudinal direction between the two heat generating parts 20 and the lead parts 21.22. Form. The ceramic heater 11 is fitted into the holder 12 with an insulating sheet 24 interposed in the slit 25 and an intermediate layer 23 coated on the outer periphery of the lead portions 21 and 22.

The sealing sheet 30 is made of rubber, asbestos, etc.
The external connection terminals 13 and 14 are interposed on the outer end side of the terminal assembly 15, and this portion is mechanically sealed.

2 is an enlarged vertical sectional view of the joint between the ceramic heater 11 and the holder 12 in FIG. 1, and FIG. 3 is a sectional view taken along the line A-A in FIG. 2, and the same parts are the same as in FIG. 1. Indicated by the reference symbol. In both figures, 23 is the middle layer,
21M insulating layer 23a.

23b and the junction 7123c are sequentially stacked.

That is, these layers ensure electrical insulation between the ceramic heater 11 and the holder 12.

Since it is necessary to ensure airtightness to prevent the combustion pressure inside the engine from leaking to the outside, the material for forming the insulating layer 23a23b is 1, for example, amorphous glass with a softening point of 700°C or higher, and the bonding layer is For example, silver palladium solder is used as the material for forming 23c. Next, the intermediate layer 23
To describe the means for forming the
The above amorphous glass is crushed and mixed with a binder and a solvent, such as ethyl cellulose, to form a paste.

Next, the paste is applied to the outer periphery of the preformed ceramic heater 11 by screen printing through a 300-mesh wire mesh made of stainless steel, for example. In this case, if a brush is used and the ceramic heater 11 is moved under the wire mesh, the insulating layer 23a,
The layer thickness dimension of 23b can be formed uniformly. The thickness of the insulating layers 23a and 23b formed as described above is approximately 15 μm, and as shown in FIG. 3, the starting ends and the ending ends overlap to form overlapping portions 26a and 26b. Such overlapping parts 26a, 26b and bonding layer 23c
If the overlapping portions 26C of the overlapping portions 26C of

It is important that 26b and 26c are arranged approximately equally in the circumferential direction. With the above configuration, the ceramic heater 11 which has been baked at 700 to 850''C can be fixed in the holder 12 by means such as silver brazing (not shown). If you change the thickness of the paste, do you change the viscosity of the paste?

All you have to do is change the wire mesh.

Note that an insulating sheet 24 is made of an insulating ceramic material and is integrally joined between the lead portions 21 and 22 of the ceramic heater 11 at least in a portion corresponding to the tip of the holder 12.

With this configuration, the slit 25 can be closed and sealed at the tip of the holder 12 to prevent the combustion pressure of the engine from leaking to the outside. Further, with the above configuration, the mechanical strength of the rear end portion of the ceramic heater 11 held by the holder 12 can be improved. In this case, the ceramic material constituting the insulating sheet 24 includes the ceramic heater 11
It is preferable to have a coefficient of thermal expansion close to that of the ceramic material constituting the ceramic heater 11. For example, the ceramic material constituting the ceramic heater 11 is
- For a composition in which Z of β-sialon indicated by * is greater than O and less than 1, the Z is greater than 20vol,% and is less than 50νo1. An insulating sialon is formed by adding 5 to 15 vol.% of TiN to the above composition as a ceramic material constituting the intermediate layer 23 when the conductive sialon sintered body is made of a conductive sialon sintered body to which less than 5% of TiN is added. When constructed from a sintered body, the coefficients of thermal expansion of the two can be brought close to each other.

Next, the axial lengths 11, 2□ of the insulating sheet 24 and late edge layers 23a, 23b and the length of the joint 12b of the holder 12! , is 2. 〉ρ2〉! ,year.

and! 3 is! , and I12 is preferably within the range of 11. Furthermore, the bond 123c to be attached to the outer periphery of the insulating layer 23b also needs to be kept within the range of the insulating layer 23b, as described above. be.

FIG. 4 is an enlarged side view showing the ceramic heater 11 and the insulating sheet 24 in FIG.
Indicated by the same reference numerals as in the figure. In FIG. 4, an insulating sheet 2 is placed between the lead parts 21 and 22 corresponding to the tip of the holder (not shown) in the slit 25 of the ceramic heater 11.
The difference W+-w between the thickness W1 of the front end 24a of the insulating sheet 24 and the thickness W2 of the rear end 24b is set to 20 to 100 μm. do.

With the above configuration, the insulating sheet 24 and the lead part 2122
In the case where a bonding layer (not shown) made of, for example, Ti-Cu brazing material is used for bonding between the two, the thickness of this bonding layer is the minimum necessary thickness.

and can be formed uniformly. Therefore, not only the bonding between the two is perfect, but also the insulating layer 23a can be easily and reliably deposited as shown in FIG. 3.

As described above, the entire ceramic heater 11 is heated to 5Ils.
φ×50III11 heat generating part 20 3a+mφ×101I
II11 and assembled as glow plug 10, it took 3.5 seconds to reach 800°C, and the saturation temperature was set to below the allowable range of 1200"C, and the temperature reached approximately 1100°C.
We confirmed the performance that can be achieved at °C.

In this embodiment, the case where the cross-sectional shape of the ceramic heater is circular is described, but it can be made into a shape other than a circle, such as a rectangular square, a polygon, an ellipse, etc., and the shape, structure, etc. of each component part can be changed. It is free to change it as appropriate, and one effect is the same.

【Effect of the invention〕

The glow plug for a diesel engine of the present invention is a glow plug for a diesel engine.

With the configuration as described above, the following effects can be achieved.

(1) Electrical insulation between the ceramic heater and the holder can be ensured, and the bonding between the two can be ensured, thereby preventing poor airtightness and poor insulation, and increasing the lifespan of the glow plug.

(2) It is possible to ensure the bonding between the lead part and the insulating sheet, and also to easily and reliably adhere the insulating layer to the outer periphery of the lead part, and as in (2) above, the glow plug can increase the lifespan of

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a main part showing an embodiment of the present invention. Figure 2 is an enlarged vertical sectional view of the joint between the ceramic heater and holder in Figure 1, and Figure 3 is an A-A in Figure 2.
A line sectional view and FIG. 4 are enlarged side views showing the ceramic heater and insulating sheet in FIG. 1. 11: Ceramic heater, 12: Holder, 20 Two heat generating parts, 21.21 Lead parts, 23a, 23b = Insulating layer, 23
c: bonding layer, 24: insulation sheet. Condolence 3

Claims (2)

[Claims] (1) A ceramic heater that is integrally formed with a U-shaped heat generating part and a pair of lead parts extending rearward from both ends of the heat generating part from a conductive ceramic material is used to generate at least one heat generating part. The ceramic heater is held at the tip of a hollow holder with the part protruding outward, and an insulating sheet is interposed and fixed between a pair of lead parts of at least a part of the ceramic heater corresponding to the holder tip. In the glow plug for diesel engines, a plurality of insulating layers made of an insulating material are bonded to the outer periphery of the lead portion corresponding to the tip of the holder, and at least one layer made of a metal brazing material is bonded to the outer periphery of the insulating layer. The ceramic heater and the holder are bonded and fixed together by depositing the layers and arranging the overlapping portions consisting of the starting and ending ends of each insulating layer and bonding layer approximately equally in the outer circumferential direction. Glow plug for diesel engines. (2) A ceramic heater that is integrally formed of a U-shaped heat generating part and a pair of lead parts extending rearward from both ends of the heat generating part using a conductive ceramic material is capable of generating at least The ceramic heater is held at the tip of a hollow holder with the part protruding outward, and an insulating sheet is interposed and fixed between a pair of lead parts of at least a part of the ceramic heater corresponding to the holder tip. In a glow plug for a diesel engine constructed with
A glow plug for diesel engines characterized by being formed into m size.