JPS63297919A - Glow plug for diesel engine - Google Patents

Abstract

PURPOSE:To improve hermetic and electrical insulating properties, by joining a heater to a holder for certain, by forming insulating layers on the outer surfaces of lead parts of a ceramic heater by screen printing, and by specifying the difference in the thickness of coating layers. CONSTITUTION:A silver paste is used in order to join a ceramic heater 11 to a holder 12. Accordingly the material of which properties will not be changed by the brazing temperature of a silver paste is needed to form insulating layers 23 and 24. A paste is prepared by grinding amorphous glass of which softening point is higher than 700 deg.C and by mixing it with a binder and a solvent. It is spread on the outer surfaces of a heater 11 through a wire sheet of stainless steel by screen printing. At that time a brush is used, and the heater 11 is turned round under the wire sheet in order to make the thickness of insulating layers 23 and 24 uniform. The thickness of layer is about 15mum, but plural times of screen printing must be performed in order to assure the necessary thickness as insulating layers. The difference in the thickness of layers must be below 100mum in order to assure joint strength and electrical insulation properties.

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]

- Since diesel engines have poor starting performance at low temperatures, a glow plug 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 insulating powder and a coiled heating wire made of iron chrome 9 nickel or the like buried therein. The so-called sheath type is common. In addition, there are also JP-A-57-41
As shown in Japanese Patent Application No. 523, etc., a ceramic heater type using a rod-shaped heater embedded in a ceramic material such as silicon nitride having an insulating property to prevent heat generation by tungsten or the like is also known. This type of ceramic heater is
Compared to the sheath type, which heats indirectly through heat-resistant insulating powder and a sheath, it improves heat transfer efficiency and also has superior heat generation characteristics. Because it has thermal type performance,
It has been widely adopted in recent years.

[Problem that the invention seeks to solve]

However, the ceramic heater type glow plug described above 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 members 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 approximately equal to that of an insulating ceramic material. This method has been proposed in Publication No. 60-14784. 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 diesel engine glow plug 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.

62-32643, etc.), these inventions were able to solve the problems existing in the above-mentioned prior art, but in the joint holding part between the holder and the ceramic heater,
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 on the outer circumferential surface of the ceramic heater, and the conventional means for forming the insulating layer is usually coating means using a brush or the like, so that the thickness of one layer does not vary at each position.

It is difficult to form uniformly, and there may be a partial bonding failure, and there are still problems that require some improvement.

The 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]

One aspect of the present invention is to solve the above problems.

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 part and a pair of lead parts extending rearward from both ends of the U-shaped heat generating part 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. Forming the insulating layer so that the difference in layer thickness is 100 pm or less.

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.

This technical method was adopted.

〔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 tapped hole (not shown) on the cylinder head side of the engine.
The tip of the ceramic heater 11 is held in a state protruding into the combustion chamber or sub-combustion chamber. 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 insulating material is fitted and supported in the rear end of the holder 12, and each terminal 13. 14 and the lead portions 21 and 22 that constitute the ceramic heater 11.

Connection is made via metal conductor wires 16, 17, such as flexible wires, and terminal caps 28, 29, for example.

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 terminal 14, both connection terminals 13 and 14 and the outer peripheral part so as to insulate it,
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, and the structure is such 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. 1 on the external connection terminal 13 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 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 battery (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 1?, respectively.
An insulating member such as a tube coated with

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 first 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 21 forming the slit 25
．． It is preferable that an insulating sheet 27 made of, for example, an insulating ceramic material be integrally joined to the holder 12 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.

Next, the materials forming the insulating layers 23 and 24 will be described. The connection between the ceramic heater 11 and the holder 12 shown in FIG. Use a meltable bonding material such as Therefore, the material for forming the insulating layers 23 and 24 must be one that does not change in quality even at the baking temperature (700 to 850°C) of the silver solder. For example, amorphous glass with a softening point of 700°C or higher It is preferable to use
This amorphous glass is crushed and mixed with a binder and a solvent such as ethyl cellulose to form a paste. Next, the paste is preformed by screen printing through a 300 mesh wire mesh made of stainless steel, for example. The coating is applied to the outer circumferential surface of the ceramic heater 11.

in this case.

By using a brush and moving the ceramic heater 11 on the lower surface of the wire mesh, the thickness of the insulating layers 23 and 24 can be formed uniformly. The thickness of the insulating layers 23 and 24 formed as described above is 15p.
Although it is around m.

As shown in FIG. 2, the starting end a and the ending end are superposed.

However, in order to ensure the necessary thickness for the insulating layers 23 and 24, what is required? JI It is necessary to perform screen printing several times. The insulating layer 23 in the ceramic heater 11 formed as described above is preferably disposed so that the overlapping portions between adjacent eyebrows are sequentially shifted.
．． For example, silver solder 2 is interposed around the outer periphery of the holder 24, and the holder 24 is bonded and fixed inside the holder 12 shown in FIG. In addition, in the above-mentioned screen printing, when changing the thickness of the paste coating film.

You can either change the viscosity of the paste or change the mesh of the wire mesh.

As described above, the entire ceramic heater 11 is
lφX50m5. When the heat generating part 20 was formed into a size of 3-φ x 10 mm and assembled as a glow plug IO, an experiment was conducted.
Time to reach 800℃ 3.5 seconds, saturation temperature within its tolerance range 1
It was confirmed that the temperature could be lowered to about 1100°C with a temperature of 200°C or lower.

In this embodiment, the ceramic heater 11 is mounted on 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. 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 the above embodiment, and the structure of each part may be Change the shape, structure, etc. as appropriate.

You are free to change 1.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.

〔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) Although it has a simple structure, one heat generating part is exposed on the outer circumferential surface of the heater, so the tip becomes red hot more quickly and reliably than conventional types, demonstrating its function as a fast heating type. can.

(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 reliable properties such as heat resistance and strength are ensured. It is possible.

(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) Because the overall structure is simple, molding process, m
It is easy to set up and has extremely high productivity.

(5) The difference in thickness of the insulating layer is extremely small.

The ceramic heater and the holder can be bonded extremely easily and reliably, and the airtightness and electrical insulation can be greatly improved, as well as the reliability can be dramatically 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 is an enlarged cross-sectional view showing the polymerization state of the insulating layer in FIG. 1. 11: Ceramic heater, 12: Holder. 20: Heat generating part, 21.22: Lead part, 23°242 insulation layer.

Claims (5)

[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, 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 difference in layer thickness of the insulating layer is 100 pm or less. 1. A glow plug for a diesel engine, characterized in that the rear end of at least one of the leads is connected via a metal conductive wire to an external connection terminal held in an insulated state at the rear end of the holder. (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 glow plug for a diesel engine according to any one of claims 1 to 4, wherein the insulating layer is formed by screen printing.