JPS63297916A - 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 prevent cracking caused by thermal stress, by brazing the lead parts to a holder with a metallic pipe provided around the outer surfaces of insulating layers in the 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 having a specified cavity. The diameter of a glow part 20 is to be determined so that the thickness of a glow part 20 is thinner than those of lead parts 21 and 22. A metallic pipe 26 is made of the same stainless steel, for example, as of a holder 12, and it is fixed on the outer surfaces of lead parts 21 and 22. That is, high softening point glass containing much silicic acid, for example, is used as a material to form insulating layers 23 and 24, and the metallic pipe 26 is fixed on the layers by baking. Both the holder 12 and the metallic pipe 26 are fixed to each other by heating with a binder such as silver paste being interposed between both parts.

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 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 excellent heat generation characteristics.It becomes red hot in a short time when heated, greatly improving temperature rise characteristics, and is fast. 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, 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 is proposed, for example, as disclosed in JP-A-60-9085. , No. 60-14784, etc. 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. Cracks may occur due to thermal stress, and bonding defects may occur due to insufficient wettability with the bonding member.

There are still problems that require some improvement.

It is an object of the present invention 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]

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.

C1 An insulating layer is provided on the outer peripheral surface of at least one of the leads.

D. A metal tube is interposed on the outer peripheral surface of the lead portion, and the lead portion is bonded and held in the holder.

E. Small (both the rear end of the one lead portion is connected via a metal conductor 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 configuration of a glow plug, the entirety of which is indicated by the symbol IO 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) in an example cylinder head of an 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 embedded through 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 a metal conductor 16.17, such as a flexible wire, and a terminal cap 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.
There is an assembly body 15a made of a resin mold that integrates the external connection terminal 14, both terminals 13 and 14 and the outer periphery so as to insulate them, and a metal tube for connection reinforcement is provided on the outer periphery of the two assembly bodies 15a. 15b. Then, by buckling and deforming the metal tube 15b along the axial direction of the caulking 9 through high pressure at the rear end opening peripheral portion of the holder 12, 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 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 pad, 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 18C and the spring washer 18.
d and the battery vA (not shown).
By sandwiching the interposition.

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

Ceramic heater 11 is 2 (for example, conductive sialon)
The powder is kneaded with a thermoplastic resin, etc., injection molded into a mold with a predetermined cavity, and this molded body is fired to form the product, or a material previously formed into a rod shape is molded into a predetermined shape by electrical discharge machining or cutting. Can be molded into any shape. 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 insulating layers 23 and 24 are provided on the outer peripheral surfaces of the lead portions 21 and 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.

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, 26 is a metal tube 2, for example, a holder 12.
Made of the same stainless steel as the material that makes up the wall, the wall thickness is 0.
05~O, l+w-, and is fixed to the outer peripheral surface of the lead portion 21°22. That is, the metal tube 26 is fixed by baking using, for example, high softening point glass with a high silicic acid content as the material for forming the insulating layers 23 and 24. A bonding material such as silver solder is interposed between the holder 12 and the metal tube 26, and the two are fixed by heating. Note that 27 is an insulating sheet 1 made of, for example, an insulating ceramic material, and has lead portions 21.2 of at least a portion of the ceramic heater 11 corresponding to the tip of the holder 12.
2 and join them together.

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
IφX5 (1+m, heat generating part 20 311 uglyφX10mm
When the glow plug 10 was assembled and tested, it was 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 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, electrically connected to the holder 12 via the metal tube 26, and a metal conductor is connected only to the other lead part, for example, 22. Not limited to the shape of each part.

You are free to modify and change the structure etc. as appropriate.

For example, the ceramic heater 11 has a cross section other than circular.

The effect is the same even if the shape is rectangular, square, polygonal, elliptical, etc. Furthermore, the material constituting the metal tube interposed on the outer peripheral surface of at least one lead part with an insulating layer interposed therein is as follows:
It is preferable that the material is the same as the material constituting the holder, but
It may be composed of different materials, in addition to stainless steel, copper 1wA alloy 5 Kovar, Fe-Ni, Ni, Ni alloy,
Metal materials such as steel 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 5 heat-generating parts are exposed on the outer circumferential surface of the heater, so compared to conventional types, the tip becomes red hot more quickly and reliably, and can function as 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 in terms of heat resistance and strength is 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) Since the overall structure is simple, molding and assembly are easy, and productivity is extremely high.

(5) A metal tube is interposed on the outer circumferential surface of the insulating layer provided on the outer circumferential surface of at least one lead portion.

By completely brazing and absorbing 28 stress, cracking can be prevented and 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 vertical sectional view of the joint between the ceramic heater and the holder in FIG. 1. 11F ceramic heater, 12; holder. 20: Heat generating part, 21. 22F lead part, 23° 24: Insulating layer, 26 Two metal tubes.

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 a metal tube is interposed on the outer peripheral surface of the lead part to be bonded and held in the holder; 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 metal tube and the holder are made of the same metal material.