JPH0293209A - Glow-plug for diesel engine - Google Patents

Abstract

PURPOSE:To sharply improve the airtightness and reliability by forming integrally a U-shaped heat generating section of a ceramic heater which is held at the tip end section of a hollow holder and a pair of lead sections by means of a conductive ceramics, and inserting a ceramic insulation sheet into the slit between the lead sections to form a reaction layer through a metallic soldering material and connecting them into one body. CONSTITUTION:A ceramic heater 11 is formed by mixing conductive sialon powder, for instance, with thermoplastic resin, etc., and kneading the mixture. At the central section of the heater 11 a slit 25 is formed from a heat generating section 20 to between the lead sections 21 and 22 and between the lead sections 21 and 22, an insulation sheet which is formed for instance, of an insulating ceramic material is inserted to a section which corresponds to the tip end section of a holder 12 that is substantially tubular and made of metal, and a metallic soldering material 27 is inserted or painted among the lead sections 21 and 22 and insulation sheet 26, and they are heated in vacuum or an inert gas, and a reaction layer is formed by the lead sections 21 and 22 and they are connected as one body. The metallic soldering material 27 contains titanium and the rest is made preferably by a combination of a metal foil that contains more than one kinds of copper, nickel, and silver, paste, and one or more than two kinds of coating materials.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 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 equipped with a ceramic heater that has a fast heating function and can achieve long-term afterglow.

[Conventional technology]

-i Diesel engines have poor startability at low temperatures, so a globe lug is installed in the auxiliary combustion chamber or combustion chamber to generate electricity and heat to raise 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, never-green powder, and a coiled heating wire made of iron chromium, nickel, etc. buried therein. The so-called sheath type is common. In addition, there are also JP-A-57-41
As shown in Japanese Patent No. 523, etc., a ceramic heater type is also known that uses a rod-shaped heater in which a heating wire made of tungsten or the like is embedded in a ceramic material such as silicon nitride which has a non-greening property. This type of ceramic heater is
Compared to the sheath type, which heats indirectly through a heat-resistant green powder and a sheath, it improves heat transfer efficiency and also has superior heat generation characteristics.It generates heat in a short time when heated, greatly improving temperature rise characteristics. Because it has fast heating performance.

It has been widely adopted in recent years.

However, the ceramic heater type glow plug described above has a structure in which a heating wire made of a metal such as tungsten is embedded inside a non-green ceramic material such as silicon nitride, and the coefficient of thermal expansion between these two members is Due to different
In particular, the rapid temperature rise during heat generation and its repeated use may reduce the durability of the ceramic heater. Therefore, there were problems in terms of reliability such as heat resistance strength, and there was also a drawback that it led to higher costs.

To solve the above problems, there is a ceramic heater structure in which the heating wire is made of a conductive ceramic material having a coefficient of thermal expansion approximately equal to that of the non-green ceramic material. , No. 60-14784, etc. However, both of them still have structural and functional problems when used as glow plugs, and have not been put into practical use.

For example, the former has a structure in which a conductive ceramic material serving as a heating element is embedded in a non-greening ceramic material.

Although the thermal conductivity is superior to that of the sheath type, there are problems such as the function of the rapid heating type is insufficient because of indirect heating, and the molding process is complicated.

In the latter case, one heating element is exposed on the surface side of the heater and has a fast heating function, but on the other hand, the heating element is simply formed by a laminated structure of U-shaped members, and both ends are connected to the rear end of the heater. Since the structure of the electrode is only guided to the electrode, the structure for taking out the electrode becomes complicated, leading to an increase in cost.

For this reason, the inventors of the present application have constructed a rod-shaped ceramic chain held at the tip of the holder by connecting a U-shaped heating part and a pair of lead parts extending rearward in parallel from both ends of the U-shaped heating part to a conductive ceramic material. constituted by integrally forming the
In addition, he invented a glow plug for a diesel engine in which the outer surface of one lead part was joined to the holder side through a conductive layer and the other was held to the holder side through an anti-green layer. The proposal was disclosed as a No.

According to the above-mentioned invention, since one heat generating part is formed only from conductive ceramic material that does not contain foreign matter, reliability such as heat resistance strength is high despite repeated thermal stress during use.
It has excellent durability and heat generation properties. It is also advantageous in terms of formability, etc., and can reduce manufacturing costs.Furthermore, the heat generating part made of conductive ceramic material exposed on the heater surface allows the tip of the heater to quickly become red hot. It can demonstrate its performance as a mold.

[Problem to be solved by the invention]

In the glow plug with the above-mentioned configuration, the slit formed along the long direction of the ceramic heater allows
The holder internal space is in communication with the engine combustion chamber, etc., which the ceramic heater faces.

Therefore, it is necessary to prevent combustion pressure from leaking to the outside of the engine in the event of an explosion within the combustion chamber.

Therefore, in this ceramic heater, a closing member made of a ceramic material such as alumina or mullite is inserted and bonded as a means for closing and sealing the gap or slit formed between the constituent parts. That is, a closing member made of a ceramic material such as alumina or mullite is inserted into the slit and integrated using glass paste as an adhesive. However, when such a joining method is used, bores may occur due to the glass paste, so the airtightness of the bonded part is not necessarily complete, and therefore carbon, oil, fuel, etc. may enter the holder internal space, causing internal damage. This may lead to corrosion of the metal conductor and even a short circuit. Furthermore, the high viscosity of glass paste makes it difficult to automate one operation, which is also an obstacle to improving productivity. On the other hand, in recent years, glow plugs of this type have been required to have improved startability of diesel engines and durability against the high temperatures that accompany the use of turbo engines. Therefore, depending on the slit closing and sealing means as described above, there is a problem in that the above-mentioned strict specifications cannot be completely satisfied.

SUMMARY OF THE INVENTION An object of the present invention is to provide a glow plug for a diesel engine that can solve the problems existing in the above-mentioned prior art and can significantly improve airtightness and reliability.

[Means to solve the problem]

In order to achieve the above object, one aspect of the present invention is as follows.

A. A ceramic heater is held at the tip of a hollow holder with one end protruding to the outside.

B. In this ceramic heater, a U-shaped heat generating section and a pair of lead sections extending rearward from both ends of the U-shaped heat generating section are integrally constructed using a conductive ceramic material.

C0 A never-green sheet made of a never-green ceramic material is inserted into the slit formed between the lead parts.

The lead portion and the evergreen sheet are integrally joined via a metal brazing material to form a reaction layer, and the tip of the hollow holder is closed and sealed.

D6: At least the outer surface of the one lead portion is bonded and held within the holder via an insulating layer.

E. This is explained as an external connection terminal in which at least the rear end of one of the leads is held at the rear end of the holder through a metal conductive wire in a completely green state.

A technical method was adopted.

In the present invention, as the metal brazing material, one or a combination of two or more of foils, pastes, and coating materials containing titanium and the remainder containing one or more of copper, nickel, and silver may be used. This is desirable because the titanium in the metal brazing material forms a reaction layer on the lead portion and the green sheet portion, respectively, so that the two are reliably joined.

〔Example〕

(Example 1) FIG. 1 is a longitudinal sectional view of a main part showing an example of the present invention. In the same figure, the glow plug, which is designated as a whole by the symbol IO, has a rod-shaped ceramic heater 11 whose tip side functions as a heating element.
and 5. It has a substantially tubular holder 12 made of metal, such as stainless steel, which holds the ceramic heater 11 at its tip.

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 15 in which first and second external connection terminals 13 and 14 are penetrated and embedded in a synthetic resin or other non-green material.
The lead portion 21゜2 that constitutes each external connection terminal 13, 14 and the ceramic heater 11.
2 means 2 metal conductor wires such as flexible wires 16.
17 and terminal caps 28 and 29.

Next, the terminal assembly 15 includes a first external connection terminal 13 which is disposed on its axis and has a rond part 13a on its inner end side to be connected to the metal conductive wire 16, and a predetermined interval around the first external connection terminal 13. A cylindrical second lead piece 14a, which is arranged at the same position and extends to a part of the inner end side, is connected to the metal conductive wire 17.
It has an assembly main body 15a made of a resin mold that integrates the external connection terminals 14, the external connection terminals 13 and 14, and the outer periphery so as to be completely green, and also has &! A metal tube 15b for connection reinforcement is fitted around the outer periphery of the three-dimensional main body 15a. Then, this metal tube 15b is caulked at the peripheral edge of the opening at the rear end of the holder 12 using a high pressure force, and is buckled and deformed along the axial direction, so that the inner side thereof is made of resin and is attached to the assembly main body 15a. The outer side is firmly pressed against the inner wall of the holder 12, and the structure is such that problems caused by external force or thermal contraction can be solved.

Next, 18a and 18b are an anti-green ring and a washer, respectively, which are fitted into the second external connection terminal 14 protruding rearward of the holder 12. Reference numeral 18c denotes a green-proofing member, which is fitted on the first external VT terminal 13 side on the outer end side of the washer 18b. Reference numerals 18d and 18e are a subring 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. The washer 18b and the green-proofing member 18
The external connection terminals 13 are connected to each other by interposing and sandwiching a glue board vA (not shown) from the battery between the battery 18c and the spring washer 18d.
．． 14 is electrically connected to the battery. 16a, 17a
are respectively insulating members such as tubes that cover the metal conductive wires 16 and 17.

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 cutting. 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 from the 5 heat generating parts 20 to the lead parts 21.22. do. Then, a never-green sheet 26 made of a never-green ceramic material, for example, is inserted between the lead parts 21 and 22 forming the slit 25 into at least a portion corresponding to the tip of the holder 12 and joined. That is, a metal brazing material 27 is inserted or coated between the lead portions 21.22 and the evergreen sheet 26, and heated in a vacuum or in an inert gas, thereby bonding the lead portions 21.22 and the nevergreen sheet 26 to the metal brazing material 27. A reaction layer, which will be described later, is formed via 27 and integrally joined.

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.

Next, the connection between the ceramic heater 11 and the holder 12 will be described. When joining the two, it is most common to use a molten metal material such as silver solder. In order to improve the wettability of the zero-order wettability, an Ag-Pd paste is applied to the outer peripheral surface of the non-green layer 23.24, and baked at 750 to 850°C. After forming a 20 μm metallized layer, the holder 12 and the ceramic heater 11 are bonded and fixed using silver solder, and the glow plug 10 as shown in FIG. 1 is assembled.

In the above description, the ceramic heater 11 is attached to the holder 1.
In order to bond and fix the lead parts 21 and 22 in a state where they are held at the tip end, we have shown an example in which the never-green layers 23 and 24 are formed on the outer circumferential surfaces of the lead parts 21 and 22, respectively. It is also possible to provide a structure in which a conductive layer is provided to electrically connect to the holder 12, and a metal conductor is connected only to the other lead part, for example, 22.The present invention is not limited to the structure of this embodiment, and each part may be Change the shape, structure, etc. as appropriate.

You are free to change 5. For example, ceramic heater 1.
1 may have a rectangular, square, polygonal, elliptical, etc. shape in addition to a circular cross section, and the effect is the same.

Next, the connection between the lead portions 21, 22 and the evergreen sheet 2G will be explained with reference to FIGS. 2(a) to 2(C). Figure 2 (
a) is an enlarged cross-sectional view showing the green sheet 26 and the metal brazing material 27 before joining, and FIG. 2 0)) shows the lead part 21 before joining.
．． FIG. 2C is an enlarged cross-sectional view showing the lead portions 21 and 22 after bonding.

First, as shown in FIG. 2(a), 16% Ti-Cu alloy foils with a thickness of 60μ are formed on the top and bottom sides of the never-green sheet 26 to have substantially the same width and length as the never-green sheet 26. The green-free sheet 26 and the metal brazing material 27 formed as shown in FIG.
Slit 2 between lead parts 21 and 22 shown in FIG. 2(b)
Insert within 5.

Next, in a vacuum of 2 × 10-' Torr, 11
Heat treatment is performed for 30 minutes at 30°C. As shown in FIG. 2077m of reaction layers 21a, 22a.

26a is formed, completing the integral bonding.

With this configuration, the slit 25 between the lead parts 21 and 22 is closed and sealed by the tip of the holder 12 shown in FIG. 1, and the combustion pressure of the engine is sealed to prevent leakage to the outside. .

FIG. 3 is a micrograph showing the metal structure of part A in FIG. 2(C). In FIG. 3, there are reaction layers 2 between the metal brazing material 27, the lead portion 21, and the evergreen sheet 26, respectively.
It is recognized that 1a and 26a are formed. As a result of analyzing the reaction layers 21a and 26a with a scanning analytical electron microscope, it was found that the titanium contained in the metal brazing material 27, the conductive sialon that forms the lead portion 21, and the alumina that forms the never-green sheet 26, etc. It was confirmed that this is the middle layer. That is, the metal brazing material 27 and the lead portion 2
1 and the interface with the Evergreen sheet 26.

Titanium in the metal brazing material 27 is particularly selectively adsorbed to form the intermediate layer. Note that a reaction layer 22a, which is completely similar to the lead part 21 described above, is also formed on the lead part 22 side.

Next, the material and thickness of the metal brazing filler metal were varied to evaluate bondability and airtightness. Table 1 also lists the material and thickness of the metal brazing filler metal, as well as the evaluation results of bondability and airtightness. The bondability and airtightness in this case were evaluated as follows. First, regarding bondability, see Figure 2 (C).
After the lead portions 21 and 22 and the everlasting sheet 26 are joined as shown in FIG.

For zero-order airtightness, which was obtained by dividing this and measuring the bonded area ratio (%), insert the lead portions 21, 22 and the outer periphery of the never-green sheet 26 into a test jig via an O-ring. , 15 kgf/c from one end of the evergreen sheet 26
The lead portion 21 is submerged in water by applying an air pressure of d.
．． The amount of air leakage between the sheet 22 and the never-green sheet 26 was measured. The results of evaluation from the above measurement results according to the criteria shown in Table 2 are also listed in Table 1. Note that Sample 5 is a comparative example in which glass paste was used in the conventional method. Moreover, the heat treatment at Nα2-4 is as follows.

This is the same as the heat treatment in step 1 above.

As is clear from Table 1, Table 2, and Table 1, the bondability is good in the glass paste of Nα5, but there is a problem in airtightness. On the other hand, for Nα1 to Nα4, as shown in FIG. 2(C) and FIG. Reaction layers 21a, 22a, 26a
was formed, and it was confirmed that the bonding and airtightness were good.

(Example 2) Next, as a means for forming reactions 1121a, 22a, and 26a between the lead portions 21 and 22 and the never-green sheet 26, instead of the metal brazing material 27 in the previous example, as shown in Table 3, A powder paste was used for bonding, and the same evaluation as in the above example was performed.

Table 3 In Table 3, Inhibitor 6 uniformly mixes 10 parts by weight of Ti powder (purity 99.5%) of 350 mesh or less and 90 parts by weight of Cu powder (purity 99.5%) of 350 mesh or less. A paste was prepared by adding a binder consisting of 10% ethyl cellulose and 90% diethylene glycol 7-ethylene ether. Also, the paste in numbers 7 and 8.

10% Ti-Cu alloy powder of 350 mesh or less each (
(purity 99.5%) or 3 parts by weight of T1 powder (purity 99.5%) with a purity of 350 mesh or less and 7 parts by weight of a powder with a purity of 350 mesh or less
It was prepared by uniformly mixing 97 parts by weight of 2% Ag-Cu alloy powder (purity 99.5%) and adding the same binder as Nα6.

Next, the pastes 6 and 7 above are applied to both sides of the never-green sheet 26 by brush coating or screen printing, and then dried. After that, insert it between the lead parts 21 and 22,
11 in a vacuum of 2 x 10'' Torr
Heat treatment is performed at 30° C. for 30 minutes. Through this process as well, reaction layers 21a, 22a, and 26a of approximately 20 μm can be formed on the joint surfaces of the lead portions 21.22 and the evergreen sheet 26, and
6 can be integrally joined.

As is clear from Table 3, although the bondability was slightly low in case 6, the airtightness was good. It was confirmed that Black 7.8 had good bondability and airtightness.

In this embodiment, an example was shown in which the metal brazing material was made of foil and paste, but the same effect can be expected even if a coating material made of powder or fluid is used. In addition, as with the conductive ceramic material forming the ceramic heater, the amount of titanium nitride or carbonitride solid solution added is adjusted to make the non-green ceramic material constituting the above-mentioned non-green sheet. It is recommended to use Sialon selected for this purpose. If such a material is selected, the never-green sheet can be made of the same material with approximately the same coefficient of thermal expansion as the lead part, increasing the bonding strength and ensuring reliability such as heat resistance strength. obtain. Further, examples of the non-green ceramic material for forming the non-green sheet include SiAlON, 31.1, which has excellent heat resistance and strength, and also has excellent bonding strength with the conductive ceramic material. A permanent material such as nitride ceramics such as N, AffiN or oxide ceramics such as Al z Os or mullite can be used.

〔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) Despite the simple structure of l'iJ, the 5 heat-generating parts are exposed on the outer surface of the heater, so the tip becomes red hot more quickly and reliably than conventional types, making it a fast-heating type. You can develop functions.

(2) Since the conductive ceramics that form the heat generating part and the lead part are made of the same material, accidents such as cracking will not occur even if the temperature rises dangerously or drastically when the heater generates heat.
Reliability such as heat resistance strength can be improved by 6'.

(3) Conductive ceramics have excellent heat resistance and strength, and facilitate long-term afterglow as a measure against engine exhaust and noise.

(4) Since the overall structure is simple, molding and assembly are easy, and productivity is extremely high4).

(5) Since a metal brazing material is used, the bonding between the ceramic components is perfect, and airtightness and reliability can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a main part showing an embodiment of the present invention. FIG. 2(a) is an enlarged cross-sectional view showing the green sheet and the metal brazing material before bonding, FIG. 2(b) is an enlarged cross-sectional view showing the lead portion before bonding, FIG. 2(C) 3 is an enlarged cross-sectional view showing the lead portion after bonding, and FIG. 3 is a microphotograph showing the metal structure of portion A in FIG. 2(C). 11: Ceramic heater, 12: Holder. 20: Heat generating part, 21.22: Lead part. 25 Nisrit, 26: Absolute green sheet. 27: Metal brazing material. 21a, 22a, 26a: reaction layer.

Claims (2)

[Claims] (1) A ceramic heater is held at the tip of a hollow holder with one end protruding outside, and this ceramic heater is installed rearward from a U-shaped heating section and both ends of this U-shaped heating section. A pair of lead parts are integrally formed of a conductive ceramic material, a never-green sheet made of a never-green ceramic material is inserted into a slit formed between the lead parts, and the lead part and the never-green sheet are connected to each other. are integrally joined by forming a reaction layer through a metal brazing material, the tip of the hollow holder is closed and sealed, and the outer surface of at least one of the leads is joined into the holder through an insulating layer. In addition to holding
A glow plug for a diesel engine, characterized in that a rear end of at least one of the leads is connected via a metal conductive wire to an external connection terminal held in a completely green state at the rear end of the holder. (2) Claim (1) in which the metal brazing filler metal contains one or more of foils, pastes, and coating materials containing titanium and the balance containing one or more of copper, nickel, and silver (1)
) glow plugs for diesel engines.