JPS63297921A - Glow plug for diesel engine - Google Patents

Abstract

PURPOSE:To secure hermetic properties, by improving wetting properties between a heater and a binder by forming insulating layers and metallized layers in series on the outer surfaces of lead parts, and by joining the ceramic heater, of which U-shaped glow part and lead parts are unitarily molded of conductive ceramic material, to a holder by a metallic binder to hold it in the holder. CONSTITUTION:A melt metallic material such as silver paste is used in order to join a ceramic heater 11 to a holder 12 of stainless steel. But insulating layers 23 and 24, made of glass for example, are formed on the outer surfaces of lead parts 21, and 22. In this case a trouble such as joint failure occurs sometimes because of the insufficient wetting properties of a silver paste with the layers. In order to improve this kind of failure, the ceramic heater 11 is assembled in the holder 12 as a glow plug 10 after forming a metallized layers of 5-20mum thick by baking such as Ag-Pd paste or Ni paste at 750-850 deg.C on the outer surfaces of insulating layers 23 and 24.

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 of a glow plug for a diesel engine equipped with a ceramic double 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 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 materials is different. For,
There is a risk that the durability of the ceramic heater may be reduced, especially due to the rapid increase in temperature during heat generation and its repeated use. 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 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. Cracks may occur due to thermal stress, and bonding defects may occur due to insufficient wettability with the bonding material.

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 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.

C9: An insulating layer and a metallized layer are sequentially formed on the outer peripheral surface of at least one of the lead parts.

D. Bonded and held within the holder via a bonding material made of a metal material.

E, at least the rear end of one of the leads is made of metal -R
It is connected to an external connection terminal held in an insulated state at the rear end of the holder via cotton.

This technical method was adopted.

〔Example〕

The figure 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, 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.
Each terminal 13.14 and the lead portion 21.22 constituting the ceramic heater 11 are connected via a metal conducting wire 16.17 such as a flexible wire and a terminal camp 28.29. .

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 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 tSa 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 the two assembly main bodies 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.

Further, 18a and 18b are an insulating ring and a washer, respectively, and 8c is an insulating member fitted into the second external connection terminal 14 protruding rearward of the holder 12, and the outer end of the washer 18b is connected to the second external connection terminal 14. 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. The washer 18b and the insulating member 18
C, and between the insulating member 18C and the spring washer 18d, lead wires (not shown) from the battery are interposed between the external connection terminals 13 and
．． 14 is electrically connected to the battery. i6a, 17a
are insulating members such as tubes covering the metal conductive wires 16 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 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 part 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
lφX5 (1m1m, heat generating part 20 3ms+φX10m
5+ and assembled as glow plug 10, it was confirmed that it took 3.5 seconds to reach 800°C and the saturation temperature could be set to about 1100°C with the permissible range t-1200°C or less.

Next, the connection between the ceramic heater 11 and the holder 12 will be described. When joining the two.

For example, it is most common to use a molten metal material such as wax, but the lead portion 21 of the ceramic heater 11
．． Since insulating layers 23 and 24 made of an insulating material such as glass are provided on the outer peripheral surface of 22, bonding defects may occur due to insufficient wettability with a 1 m solder.
This has the disadvantage of impeding airtightness. In the present invention, a metallized layer is formed on the outer peripheral surface of the insulating layers 23 and 24 in order to improve the wettability. Ag-Pd paste Ni paste, Ni coating, Ag
We selected five types: paste, N1 plating, and Ag paste, and baked them at 750'' to 850℃.

After forming a metallized layer of 5 to 20 μm, a glow plug 10 as shown in FIG. 3 was assembled.

In this case, the holder 12 is made of stainless steel, for example, and is bonded and fixed to the ceramic heater 11 using silver solder.

The table shows the results of the airtightness test of the glow plug 10, which was conducted on 10 samples each by immersion in water to which IO atmospheric pressure was applied.

As is clear from the margin table below, in the case where a metallized layer is not formed, the holder 12 has a special wettability with the insulating layers 23 and 24 provided on the lead portions 21 and 22 of the ceramic heater 11 and the bonding material wax. Since the bonding is insufficient, the bonding is not completed completely.

Therefore, airtightness cannot be ensured. On the other hand, in the case where the metallized layer according to the present invention is provided, wettability with respect to the wax is ensured.

It was observed that the bonding state was good, and that the airtightness was perfect, especially in those in which the metallized layer was formed using Ag-Pd paste and Ni paste.

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.

Furthermore, as the bonding material interposed between at least one lead part and the holder, in addition to a melt bonding material such as silver solder, it is also possible to use a solid bonding material such as a diffusion bonding material. It can be selected as appropriate depending on the metal material to be formed.

〔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 the simple structure, the two 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 the function of a fast-heating type. can.

(2) Because the conductive ceramics that form the heat generating part and the lead part are made of the same material, 1. Accidents such as cracking will not occur even when the temperature rises rapidly when the heater generates heat.
It can ensure reliability such as heat resistance strength.

(3) Since the heat capacity of the heat generating part at the tip is small, it has self-temperature saturation, and as a result, long-term afterglow as a measure against engine exhaust and noise becomes easy.

(4) Since the overall structure is simple, molding and machining are easy, and productivity is extremely high.

(5) Since sufficient wettability between the ceramic heater and the bonding material can be ensured, airtightness can be made perfect and reliability can be dramatically improved.

[Brief explanation of drawings]

The figure is a longitudinal sectional view of a main part showing an embodiment of the present invention. ll: ceramic heater, 12: holder. 20: Heat generating part, 21.22: 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, an insulating layer and a metallized layer are sequentially formed on the outer peripheral surface of at least one of the lead parts, and the lead parts are bonded and held in the holder via a bonding material made of a metal material. A glow plug for a diesel engine, wherein 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 at least a portion of the ceramic heater 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 metallized layer is formed by baking Ag-Pd paste. (6) A glow plug for a diesel engine according to any one of claims 1 to 4, wherein the metallized layer is formed by baking Ni paste.