JPS63297926A - Glow plug for diesel engine - Google Patents

Abstract

PURPOSE:To combine both characteristics of mechanical strength and electrically insulating property in one body by a method wherein a U-shaped heat generating part and a lead part are constituted in one body by electrically conductive ceramic material and an electrically insulating layer placed at the periphery of the lead part is formed into a membrane with a specified thickness by an amorphous glass having a softening point of 700 deg.C or more. CONSTITUTION:A ceramic heater 11 is formed in such a manner that electrically conductive sialon powder and thermoplastic resin are kneaded together, injection- molded, and baked. A heat generating part 20 is formed in a small diameter so that its thickness is thinner than those of lead parts 21, 22 and at the center part of the heater 11 a slit 25 is formed. On the periphery of the parts 21, 22 material having an unchanged property in its quality at the baking temp. of silver solder such as amorphous glass with a softening point of 700 deg.C or more is used and electrically insulating layers 23, 24 with a thickness of 10-100mum are formed. A sheet 30 for sealing composed of rubber, asbestos, etc. is inserted into and attached to the outside edge of an assembled unit 15 for terminals which is equipped with primary and secondary connecting terminals 13, 14 for the outside and placed at the opening part in the rear part of a holder 12 and is constituted to seal this parts mechanically.

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, 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 electricity and generate heat to raise the intake air temperature or serve 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 are also JP-A-57-41
As shown in Japanese Patent No. 523, 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 the sheath type, which heats indirectly through heat-resistant insulating powder and a sheath, the ceramic heater type improves heat transfer efficiency and also has superior heat generation characteristics, generating red heat in a short time when heated, greatly improving the temperature rise characteristics. Because it has improved and fast heating type performance.

It has been widely adopted in recent years.

[Problem that the invention seeks to solve]

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 a drawback that the cost is increased.

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 that is approximately the same as that of an insulating ceramic material. This method has been proposed in Japanese Patent No. 60-14784 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 extending the afterglow time.

In order to solve the above problems, the 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. 62-32643, etc.). These inventions have solved the problems existing in the prior art described above, but the problem is that there is
It is necessary to ensure not only sufficient bonding strength between the two, but also electrical insulation between the two. For this reason, an insulating layer is formed between the holder and the ceramic heater, but there is no material for forming this insulating layer that has both the mechanical strength and electrical insulation properties. There are still problems that require some improvement, such as cracks occurring due to thermal stress due to differences in thermal expansion coefficients between the members, and poor bonding due to insufficient wettability with the joining member.

One object of the present invention is to solve the above-mentioned problems, perfect the above-mentioned invention, and propose a highly reliable glow plug for diesel engines.

[Means for solving problems]

In order to solve the above problem, first of all, in the first invention.

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.

C1 An insulating layer is provided on the outer circumferential surface of at least one of the lead parts and is bonded and held within the holder.

D. The insulating layer is formed of amorphous glass having a softening point of 700° C. or higher to a thickness of 10 to 100 μm.

E. At least the rear end of the one lead portion is connected via a metal conductive wire to an external connection terminal held in an insulated state at the rear end of the holder.

A technical method was adopted.

On the other hand, in the second invention of the present application, in place of the above first invention.

D', the insulating layer is formed from a mixed glass of amorphous glass and crystalline glass to a thickness of 10 to 100 μm.

This technical method was adopted.

〔Example〕

The figure 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 1) 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 1) at its distal end. A threaded portion tZa 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 1) is held in a state protruding 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 penetrated and embedded in a synthetic resin or other insulating material.
Each terminal 13.14 is connected to the lead portion 21.22 constituting the ceramic heater 1) via a metal conductive wire 16.17 such as a flexible wire and a terminal cap 28.29. do.

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.
external connection terminal 14, and both terminals 13. ．． It has an assembly main body 15a made of a resin mold that integrates 14 questions and the outer periphery so as to insulate it, and has a 1Mi three-dimensional main body 15.
A metal tube 15b for connection reinforcement is fitted around the outer periphery of a. 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, so that problems caused by external force or heat shrinkage can be solved.

Furthermore, 18a and 18b are an insulating ring and a warsha, respectively, and 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, reference numerals 1'8d and 18s are respective spring washers and tightening nuts, which are fitted and screwed into threaded portions formed on the outer end side of the first external connection terminal 13. The washer 18b and the insulating member 18c
and between the insulating member 18c and the spring washer 1.
8d and lead wires from the bufftery (not shown).
By sandwiching the interposition.

Each of the external connection terminals 13 and 14 is electrically connected to a battery. 16a and 17a are the metal conductive wires 16 and 17, respectively.
An insulating member such as a tube coated with

Ceramic heaters 1) are formed by kneading conductive sialon powder with thermoplastic resin, etc., injection molding into a mold having a predetermined cavity, and firing this molded body, or by pre-forming into a rod shape. The material 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 that the wall thickness is thinner than that of the lead parts 21.22, and a slit 25 is formed in the center of the ceramic heater 1) in the longitudinal direction from the heat generating part 20 to the lead parts 21.22. form. Note that lead part 2
Insulating layers 23 and 24 are provided on the outer peripheral surface of 1.22.

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. Note that the lead portion 2 forming the slit 25
Between 1.22 and 1.22.

For example, an insulating sheet formed of an insulating ceramic material may be integrally joined to the holder 12 at least in a portion corresponding to the tip end thereof.

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 held by the holder 12 of the ceramic heater 1) can be improved.

Next, the materials forming the insulating layers 23 and 24 will be described. The bonding strength between the ceramic heater 1) and the holder 1'2 shown in the figure is sufficient.

Since it is necessary to ensure airtightness to prevent external leakage of engine combustion pressure, a meltable bonding material such as silver solder is usually used. Therefore, as the material for forming the insulating layers 23 and 24, the baking temperature of the silver solder (700 to 800
It is necessary to have properties that do not change even at a temperature of 50°C. For example, an amorphous glass with a softening point of 700°C or higher is used. This amorphous glass is crushed and mixed with, for example, an ethyl cellulose-based binder and a solvent to form a paste, which is coated on the outer periphery of a pre-formed ceramic heater 1) and baked to form an insulating layer 23 of 10 to 100 μm. Form 24. Ceramic heater 1 formed as above
), for example, silver solder is interposed on the outer periphery of the insulating layers 23 and 24, and the insulating layers 23 and 24 are bonded and fixed in a holder 12 shown in FIG.

The insulating layers 23 and 24 are the ceramic heater 1) and the holder 12.
However, if the thickness is less than 10 μm, it is inconvenient because a predetermined insulation resistance cannot be secured. Also, the thickness is 100μm
If it exceeds, not only the degree of dielectric strength improvement will be saturated, but also the ceramic heater 1) and the insulating layer 23 .
Insulating layer 23 due to a slight difference in thermal expansion coefficient from 24
This is disadvantageous because it tends to cause cracks or cracks within the angle 24° and increases the number of man-hours due to the increase in the number of multilayer coatings.

As described above, the entire ceramic heater 1) was made to a diameter of 5 mm.
x5Qmm, and the heat generating part 20 was formed to 3mmφ x lQmm, and when assembled as a glow plug 10 and tested, 8
Time to reach 00℃ 3.5 seconds, saturation temperature within its allowable range 12
It was confirmed that the temperature could be reduced to about 1) 00°C after the temperature was set to 00°C or lower. It was confirmed that the airtightness between the ceramic heater 1) and the holder 12 was perfect, and that the electrical insulation between the two was also perfect in the heat resistance durability test and the intermittent durability test.

Next, as a material for forming the insulating layers 23 and 24.

Select a mixed glass of amorphous glass and crystalline glass,
A paste was formed in the same manner as in the case of the amorphous glass having a high softening point, and the glow plug 10 was assembled. Note that the mixing volume ratio of amorphous glass and crystalline glass is preferably 5% or more and 70% or less of amorphous glass. Performance as a glow plug was similar to that in the previous example.

In this embodiment, the ceramic heater 1) is placed in the holder 1.
In order to bond and fix the lead parts 21 and 22 in a state where they are held at the tips of the lead parts 21 and 22, an example is shown in which the insulating layers 23 and 24 are formed on the outer circumferential surfaces of the lead parts 21 and 22, respectively. A configuration may also be adopted in which a conductive layer such as the one shown in FIG. Further, the present invention is not limited to the structure of the above embodiment, but the shape and structure of each part can be modified as appropriate.

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

Furthermore, as a means of forming the insulating layer, application with a brush is used.

Known means of forming paste or slurry coatings can be used, including spraying. Furthermore, the bonding material used to bond the ceramic heater and the holder depends on the material forming the insulating layer and the material forming the holder.

Bonding materials other than solder can be freely selected.

〔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) f! Although it has a simple structure, the three heat-generating parts are exposed on the outer circumferential surface of the heater, so compared to the conventional type, the tip becomes red hot more quickly and reliably, and it can perform the function of a fast heating type.

-(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 do not occur even when the temperature rises rapidly when the heater generates heat, and reliability such as heat resistance strength is maintained. Can be secured.

(3) Since the heat capacity of the tip heat generating part is small, it has self-temperature saturation, and as a result, long-term afterglow as a measure against engine exhaust and noise is facilitated.

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

(5) The material forming the insulating layer does not change in quality even at the bonding processing temperature of the bonding material, ensuring electrical insulation, and does not crack due to thermal stress, significantly improving airtightness and electrical insulation. In addition, reliability can be dramatically improved.

[Brief explanation of drawings]

The figure is a longitudinal sectional view of a main part showing an embodiment of the present invention. 1): Ceramic heater, 12: Holder. 20: Heat generating part, 21.22 = Lead part, 23° 24: Insulating layer.

Claims (8)

[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 constructed of a conductive ceramic material, an insulating layer is provided on the outer peripheral surface of at least one of the lead parts, and the lead part is bonded and held in the holder, and the insulating layer is heated to a softening point of 700° C. or more. The holder is formed of amorphous glass having a film thickness of 10 to 100 μm, and at least the rear end of one of the leads is connected to an external connection terminal held in an insulated state at the rear end of the holder via a metal conductive wire. Glow plug for diesel engines. (2) A glow plug for a diesel engine according to claim 1, wherein the wall thickness of the U-shaped heat generating portion constituting the ceramic heater is formed to be smaller than the wall thickness of the lead portion. (3) The diesel according to claim 1 or 2, wherein an insulating sheet for sealing combustion pressure is integrally interposed between a pair of lead portions of the ceramic heater at least in a portion corresponding to the holder tip portion. Glow plug for engine. (4) A claim in which one lead part is electrically connected to the holder via a conductive layer, and the other lead part and an external connection terminal held at the rear end of the holder are connected via a metal conductor wire. The glow plug for a diesel engine according to any one of items 1 to 3. (5) A ceramic heater was held at the tip of the hollow holder with one end protruding outside, and the ceramic heater was extended rearward from the U-shaped heating section and both ends of the U-shaped heating section. A pair of lead parts are integrally constructed of a conductive ceramic material, an insulating layer is provided on the outer peripheral surface of at least one of the lead parts, and the lead parts are bonded and held in the holder, and the insulating layer is made of amorphous glass and crystalline glass. The holder is formed of a mixed glass with a film thickness of 10 to 100 μm, and the rear end of at least one of the leads is connected to an external connection terminal held in an insulated state at the rear end of the holder via a metal conductive wire. Glow plug for diesel engines. (6) A glow plug for a diesel engine according to claim 5, wherein the wall thickness of the U-shaped heat generating portion constituting the ceramic heater is formed to be smaller than the wall thickness of the lead portion. (7) The diesel according to claim 5 or 6, wherein an insulating sheet for sealing combustion pressure is integrally interposed between a pair of lead portions of the ceramic heater at least in a portion corresponding to the holder tip portion. Glow plug for engine. (8) A claim in which one lead part is electrically connected to the holder via a conductive layer, and the other lead part and an external connection terminal held at the rear end of the holder are connected via a metal conductor wire. The glow plug for a diesel engine according to any one of items 5 to 7.