JPS63297920A - Glow plug for diesel engine - Google Patents

Abstract

PURPOSE:To improve insulation properties, by preventing cracks from continuing by incorporating the cracks in other neighboring flow-free layers if some flaws such as micro cracks occur in some layers, by forming insulating layers on the lead parts of a ceramic heater by screen printing and by laminating them in a plurality of layers. CONSTITUTION:A silver paste is used to joint a ceramic heater 11 to a holder 12. Accordingly a material of which properties are not changed by the brazing temperature of a silver paste is needed for the one of insulating layers 23 and 24. A paste is composed by grinding amorphous glass of which softening point is higher than 700 deg.C, and by mixing it with a binder and a solvent to make a paste. The paste is spread on the outer surface of a heater 11 through a wire sheet by screen printing. At that time a brush is used, and the heater 11 is turned round under the wire sheet in order to obtain uniform thickness in the insulating layers 23 and 24. The thickness of a layer is about 15mum, and an insulation layer of specified thickness can be formed by laminating the layers a plurality of times. The starting end 'a' and the last end 'b' of a layer are overlapped, but the difference in the thickness of layers is reduced to the minimum by slipping off the overlapped parts from one to another.

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 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 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 heat generated by tungsten or the like is embedded in an insulating ceramic material such as silicon nitride 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 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 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 structure for removing the electric scraper, and difficulty in extending 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.

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 that the bonding strength between the two is sufficiently large, but also that electrical insulation between the two be ensured. For this purpose, an insulating layer is formed on the outer peripheral surface of the ceramic heater. In this case, in order to improve insulation, it is common to increase the thickness of the insulating layer, but if a thick insulating layer is formed at once, defects such as voids and microcranks may occur in the layer. occurs, impairing insulation properties, and in some cases may even lead to dielectric breakdown. On the other hand, as a conventional means for forming an insulating layer, coating means using a brush or the like is the usual method, and the thickness of the nine layers varies at each position (it is difficult to form uniformly).
There are still problems that require some improvement, such as partial poor bonding between the holder and the holder.

It is an object of the present invention to solve the above problems, perfect the above 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 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 by laminating a plurality of layers.

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. The schematic structure of the glow plug, which is generally designated by the symbol 10 in the figure, will be explained. The glow plug IO 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, which 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 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 penetrated and embedded in 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 metal conductor wires 16, 17, such as flexible wires, and terminal caps 28, 29, for example.

Next, the terminal assembly 15 connects the first external connection terminal 13, which is located on the inner end of the terminal assembly 15, with the rond part 13a, which is disposed on its axis and is to be connected to the metal conductive wire 16, and the first external connection terminal 13, which is located on the inner end side thereof, and 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 main body 15a made of a resin mold which integrates the external connection terminal 14, both connection terminals 13 and 14, and the outer peripheral part so as to insulate it, and one assembly 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, 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. 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 18d and 18s are a spring washer and a tightening nut, respectively, which are fitted and screwed into the 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 18.
1 by interposing lead wires (not shown) from the batteries between each of the external connection terminals 13.1 and 13.d.
4 is electrically connected to the battery. Reference numerals 16a and 17a are insulating members such as tubes that cover the metal conductive wires 1'6 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 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 central part of the ceramic heater 11 in the longitudinal direction between the three heat generating parts 20 and 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
．． Between 22 and 22.

For example, it is preferable that an insulating sheet 27 made of an insulating ceramic material is 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 of the ceramic heater 11 held by the holder 12 can be improved.

Next, the means for 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 For this reason, 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 pre-recorded solder; for example, amorphous glass with a softening point of 700°C or higher It is preferable to use

The amorphous glass is ground and mixed with a binder and solvent, such as ethyl cellulose, to form a paste. Next, the above paste is applied to the outer circumferential surface of the preformed ceramic heater 11 by screen printing via a 300-mesh wire mesh made of stainless steel, for example.

in this case.

By using a brush and rolling 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. Note that the layer thickness of the single-layer insulating layers 23 and 24 formed as described above is approximately 15 μm.

By laminating this multiple times, insulation Ji of a predetermined size can be obtained.
! i23 and 24 are formed. Therefore, even if there are micro defects such as voids and microcranks in each single layer,
Because other healthy single layers are integrated adjacently by lamination,
This makes it possible to prevent the inconvenience caused by the continuous microcranks and ensure overall insulation. The greater the number of laminations, the more desirable it is from the standpoint of improving insulation, but in consideration of productivity, the number of layers is preferably 2 to 5N, preferably 2 to 3 layers. In the above lamination, the starting end a and the ending end b (see FIG. 2) of each single layer overlap.

By sequentially shifting the overlapping locations between adjacent glabellas, variations in the thickness of the nine layers can be suppressed to a minimum. The insulating layers 23 and 24 of the ceramic heater 11 formed as described above are bonded and fixed in the holder 12 shown in FIG. 1 by interposing silver solder, for example, on the outer periphery of the insulating layers 23 and 24. In the above screen printing, when changing the thickness of the paste coating, the viscosity of the paste may be changed or the mesh of the wire gauze may be changed.

As above, the entire Ceramic Heater II is 5m+*
φX50mm+, heat generating part 20 311+Ilφ×101
II11 and assembled as the glow plug 10, an experiment confirmed that it took 3.5 seconds to reach 800°C and that the saturation temperature could be set to about 1100°C within the permissible range of 1200°C.

In this embodiment, the ceramic heater 11 is
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 this is provided and electrically connected to the holder 12, and the metal conductive wire is connected only to the other lead portion, for example, 22. 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.
1 may have a rectangular, square, polygonal, elliptical, etc. shape in addition to a circular cross section, and the effect is the same.

Further, in the case where the insulating layers are formed in a laminated manner, the means for forming each single layer is not limited to the screen printing described in this embodiment, but other known film forming means or coating means may be applied. Note that as the material for forming the insulating layer, glass or other insulating materials other than amorphous can be used.
Any material that does not change in quality even at the baking temperature of the bonding material when bonded to the holder 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 its simple structure, the three heat-generating parts are 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 reliability such as heat resistance strength is ensured. obtain.

(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) Since the insulating layer is formed by laminating multiple layers, even if there are defects such as microcracks in each layer, other healthy layers are adjacent and integrated, so the above defects will not continue. can be prevented and insulation properties can be improved.

(6) By increasing the number of laminated layers, the thickness of the insulating layer can be increased, and the insulation properties are improved.

Reliability can be dramatically improved.

[Brief explanation of the drawing]

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, 227 lead part, 23° 24: Insulating 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 insulating layer is bonded and held in the holder, and the insulating layer is formed by laminating a plurality of layers; 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 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.