JPS63297918A - Glow plug for diesel engine - Google Patents

Abstract

PURPOSE:To extend lifetime and to improve reliability by decreasing the degree of oxidation, by providing a coating layer composed of an oxide which is a mixture of one or more than two kinds of ingredients on the inner and outer surfaces of a glow part at the top of a ceramic heater. CONSTITUTION:A ceramic heater 11 is constituted in such a manner that conductive sialon powder, for example, is kneaded with such as thermoplastic resin and it is injection-molded into a metal mold which has a specified cavity. The diameter of a glow part 20 is so molded that the thickness of the part 20 is thinner than those of lead parts 21 and 22. As for an oxide composing a coating layer provided on the glow part 20, one or a mixture of more than two kinds of ingredients chosen from among zirconium silicate, chromium oxide, aluminum oxide, magnesium oxide, zirconium oxide, and aluminum silicate can be used. It is necessary for the coating layer to have the thickness more than 2mum, at least, in order to prevent TiN contained in the conductive sialon of a heater from oxidizing, while the thermal capacity of a coating layer will increase if the thickness exceeds 100mum, as a result, the function of a glow plug will be deteriorated.

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.
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. 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 has excellent heat generation characteristics.It becomes red hot in a short time when heated, greatly improving temperature rise characteristics, and is very fast. Because it has thermal performance, it has been widely adopted in recent years.

(Problems to be Solved by the Invention) However, the above-mentioned 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. Since the coefficient of thermal expansion between these two members is different,
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, a ceramic heater structure in which the heating wire is formed of a conductive ceramic material having a coefficient of thermal expansion approximately equal to that of an insulating ceramic material is disclosed, for example, in Japanese Patent Laid-Open No. 60-9085.

This method has been proposed in Publication No. 60-14784 and the like. However, there are still problems in terms of structure and function when using these as glow plugs.

It has not yet 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 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. 1, No. 6 of Patent Application No. 61-256355)
2-32643, etc.), these inventions have been able to solve the problems existing in the above-mentioned prior art, but when a conductive sialon containing TiN is used as a material constituting the ceramic heater.

Due to the oxidizing atmosphere, TiN changes to Ti0z to form an oxide film, and the thickness of this oxide film increases with the passage of time. As a result, a crank occurs between the oxide film and the substrate,
There are still some problems that require improvement, such as the possibility of shortening the life of the ceramic heater as a whole or changing the electric resistance value of the ceramic heater.

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] In order to solve the above problems, there are two aspects of the present 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.

C3: A coating made of an oxide is provided on the surface of the U-shaped heating section.

D. An insulating layer is provided on the outer circumferential surface of at least one of the leads, and the leads are bonded and held in the holder.

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 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 penetrated and embedded in a synthetic resin or other insulating material.
Lead portions 21.22 that fit and support the connection terminals 13.14 and the ceramic heater 11.
The connection is made via a metal wire 4116, 17, such as a flexible wire, and a terminal camp 28,29.

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.
8 external connection terminals 14, an assembly body 15a made of a resin mold that integrates the above connection terminals 13 and 14 and the outer peripheral part so as to insulate them.
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, and is buckled along the axial direction, so that the inner side of the metal tube 15b is made of resin toward 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 contact yA#A is provided on the outer end side of the washer 18b.
Fit it on the child 13 side. Further, 18d and 18s 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. The washer 18b and the insulating member 18
By interposing and sandwiching lead wires (not shown) from the bufftery between L8C and wA edge member L8C and spring washer 18d.

Each of the external connection terminals 13 and 14 is electrically connected to a battery. 16a and 17a are the metal conductive wires, 16.1
It is an insulating member such as a tube coated with 7.

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 this 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 between the 8 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, 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 of the ceramic heater 11 held by the holder 12 can be improved.

As described above, the entire ceramic heater 11 is
When we conducted an experiment by forming the 50 dragon 9 heat generating part 20 into a 3Mφ
The performance was confirmed at approximately 1100° C. under the following conditions.

FIG. 2 is a diagram showing the relationship between oxidation temperature and oxidation weight increase in the heat generating portion of the ceramic heater. In this case, the ceramic heater was formed of conductive sialon containing 40v011% of TINt, and the oxidation was performed for 40 hours. In FIG. 2, curve a indicates that a coating of zirconium silicate (trade name: Glass Power 1500, manufactured by Nichiban Research Institute) is coated on the inner and outer circumferential surfaces of the heat generating part 20 of the ceramic heater 11 shown in FIG. 20-40 depending
The two curved lines are not coated. As is clear from Figure 2.

As the oxidation temperature rises, the weight gain due to oxidation naturally increases, but at the normal temperature of 1000°C or less in diesel engines, the weight gain due to oxidation in curve 1 is A or less than that in curve 1 (f). The thickness of the above film must be at least 2 μm or more in order to prevent the oxidation of TiN contained in the conductive sialon that constitutes the ceramic heater, but if it exceeds 100 μm, This is disadvantageous because the heat capacity becomes large and the function as a glow plug deteriorates.

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 while holding them at the tips of the lead parts 21 and 22, an example is shown in which insulation 7123 and 24 are formed on the outer peripheral surfaces of each lead part 21 and 22. 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 conductive wire 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 shape of each part can be changed. , modify the 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.

In addition to zirconium silicate, chromium oxide, aluminum oxide, magnesium oxide, zirconium oxide, aluminum silicate, etc. can be used as the oxide forming the coating provided on the heat generating part 20 of the ceramic heater 11. More than one species may be mixed or used in multiple layers.

Note that as a means for forming the film, known means other than brush coating, such as dipping and spraying, 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.

(11 Despite the simple structure, the heat generating part is exposed on the outer surface of the heater, so the tip becomes red hot more quickly and reliably than conventional types, allowing it to function as a fast heating type. .

(2) Since the conductive ceramics that form the heat generation 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. It is possible.

(3) Since the heat capacity of the tip heating part is small, it has self-temperature saturation, and as a result, long-term afterglow is easy as a measure against engine exhaust and noise. (4) The overall structure is simple, Molding process 3 Assembly is easy and productivity is extremely high.

(5) Since a coating made of oxide is provided on the inner and outer surfaces of the tip heating section, oxidation weight gain can be reduced, the service life can be significantly extended, and reliability can be dramatically improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical cross-sectional view of a main part showing an embodiment of the present invention. FIG. 2 is a diagram showing the relationship between oxidation temperature and oxidation weight increase in the heat generating portion of the ceramic heater. ll: ceramic heater, 12: holder. 20; heat generating part, 21. zz: lead part, 23°24: insulating layer.

Claims (6)

[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, a coating made of oxide is provided on the surface of the U-shaped heating part, and an insulating layer is provided on the outer peripheral surface of at least one of the lead parts, and the inside of the holder is 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) The thickness of the film made of oxide is 2 μm to 100 μm
The glow plug for a diesel engine according to any one of claims 1 to 4, which is m. (6) The oxide is zirconium silicate, chromium oxide, aluminum oxide, magnesium oxide, zirconium oxide,
The glow plug for a diesel engine according to any one of claims 1 to 5, which is one type or a mixture of two or more types selected from aluminum silicate.