JPS63297917A - Glow plug for diesel engine - Google Patents

Abstract

PURPOSE:To prevent a trouble such as cracking when a heater is glowing, by unitarily molding a glow part and lead parts of conductive ceramics, and also to increase dielectric strength, to prevent cracking caused by thermal stress, and to solve the dispersion of thickness, by fixing an insulation pipe made of insulating ceramic material on the outer surface of lead parts. 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 determined that the thickness of the glow part 20 is thinner than those of lead parts 21 and 22. An insulating pipe 23 is made of insulating ceramic material so that its thickness is 0.5-1mm, and it is fixed on the outer surfaces of lead parts 21 and 22 by a paste for joining, and then is joined to a holder 12. As for a ceramic material consisting of the insulating pipe 23, its thermal expansion coefficient must be approximate to that of a ceramic material constituting the ceramic heater 11.

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 a heating wire made of tungsten or the like is embedded in an insulating ceramic material such as silicon nitride is also known. This kind of ceramic heater type is 5
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.

[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 are problems in terms of reliability such as heat resistance strength, and there is also the disadvantage of increasing 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 an insulating ceramic material. This method has been proposed in Publication 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
For example, although a dielectric strength of LMΩ or more is required at 500V, there are some that are insufficient.

In addition, if the insulating layer is formed thickly to improve the dielectric strength mentioned above, 9 cracks and other problems may occur, or there may be variations in the thickness dimension of the insulating layer, resulting in a lack of stability, and other problems that still require some improvement. There is.

The object of the present invention is to solve the above-mentioned problems, perfect the above-mentioned invention, and propose a glow plug for a diesel engine with high reliability.

[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.

C0 An insulating tube made of an insulating ceramic material is provided on the outer circumferential surface of the lead portion and is bonded and held within the holder.

D. Connect at least the rear end of the one lead portion to an external connection terminal held in an insulated state at the rear end of the holder via a metal conductor wire.

This technical method was adopted.

[Embodiment] FIG. 1 is a vertical 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.
What are the lead portions 21.22 that fit 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 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 terminals 13 and 14 and the outer peripheral part 4 so as to insulate them, and a metal tube for connection reinforcement is provided on the outer periphery of the two assembly main bodies 15a. 15b. 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, 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 between the washer 18b and the insulating member 18c, and between the insulating member taC and the spring washer 18.
d by interposing lead wires (not shown) from the batteries.

Each of the external connection terminals 13 and 14 is electrically connected to a battery. 16a and L7a are the metal conductive wires 16 and 17, 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 that the wall thickness is thinner than that of the lead parts 21.22, and the inner part of the ceramic heater 11 has a slit in the longitudinal direction from the arcing part 20 to the lead part 21.22. Form 25.

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.

FIG. 2 is an enlarged longitudinal sectional view of the joint between the ceramic heater 11 and the holder 12 in FIG. 1.

Identical parts are designated by the same reference numerals as in FIG. 1 above.

In FIG. 2, 23 is an insulating tube made of insulating ceramic material with a wall thickness of 0.5 to 1 mm+, and is attached to the outer circumferential surface of the lead portions 21 and 22 through a soldering material (not shown) for joining. It is fixed and further joined to the holder 12. In addition, the insulation tube 23
As the ceramic material constituting the ceramic heater 1,
It is preferable that the coefficient of thermal expansion be approximated to that of the ceramic material constituting No. 1. The ceramic material constituting the ceramic heater 11 is, for example, Si&-mA12zOzNs
For a composition in which Z of β-type sialon represented by -z is more than 0 and less than 1, 20vol. % and less than 50νo1.5 of a conductive sialon sintered body.

When the insulating tube 23 is made of an insulating sialon sintered body obtained by adding 5 to 15% TiN to the above composition as the ceramic material constituting the insulating tube 23, the coefficients of thermal expansion of both can be made very similar. Further, as a brazing material for fixing or joining, for example, BA8PC specified in JIS Z 3263 can be used. Note that if the brazing filler metal or bonding material for bonding has electrical conductivity, it is necessary to bond the insulating tube 23 so that the inner and outer circumferential surfaces of the insulating tube 23 are completely electrically isolated. Note that 24 is an insulating sheet, which is made of an insulating ceramic material similarly to the insulating tube 23, and is provided at least in the holder 12 of the ceramic heater 11.
It is integrally joined between the lead parts 21 and 22 of the portion corresponding to the tip part. 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. Furthermore, with the above configuration, the holder 12 of the ceramic heater 11
It is possible to improve the mechanical strength of the rear end portion that is held in place.

As described above, the entire ceramic heater 11 is 5+lφ×50mm, and the heat generating part 20 is 3IIIlφ×1O1lI.
- and assembled it as a glow plug lO and conducted an experiment, and it was confirmed that it took 3.5 seconds to reach 800°C and that the saturation temperature could be set to about 1io0°C within the permissible range of 1200°C.

Note that the insulating tube 23 and the insulating sheet 24 may be formed integrally, which has the advantage of facilitating one assembly operation. Further, the present invention is not limited to the structure of the above embodiment.

The shape, structure, etc. of each part may be modified (1) or changed as appropriate. (2) For example, the ceramic heater 11 may have a rectangular, square, polygonal, or elliptical cross section 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.

(Despite the 11 hour wheel 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 the function of 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. It is possible.

(3) Since the heat capacity of the tip heating section 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 an insulating tube made of an insulating ceramic material is fixed to the outer peripheral surface of the lead part, it has high dielectric strength and eliminates the variation in thickness of conventional products, increasing stability. Because I will.

Credibility 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 vertical sectional view of the joint between the ceramic heater and the holder in FIG. 1. ll: Ceramic Heek, 12: Holder. 20: Heat generating part, 21, 22: Lead part, 23: Insulating tube.

Claims (4)

[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, and an insulating tube made of an insulating ceramic material is provided on the outer peripheral surface of the lead part to be connected and held in the holder, and at least the rear end of one of the lead parts 1. A glow plug for a diesel engine, wherein the glow plug is connected to an external connection terminal held in an insulated state at the rear end of the holder via a metal conductive wire. (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 glow plug for a diesel engine according to claim 3, in which an insulating tube and an insulating sheet are integrally formed.