JPS63297923A - Glow plug for diesel engine - Google Patents

Abstract

PURPOSE:To enable complete hermetic sealing by joining, by unitarily providing an interposing insulating sheet to seal combustion pressure, made of sintered mullite, between lead parts corresponding to the end of the holder, at least, of a ceramic heater, of which U-shaped glow part and lead parts are unitarily molded of conductive ceramic material. CONSTITUTION:An insulating sheet 27 is made of sintered mullite formed nearly in the state of a sheet. It is unitarily joined to the parts corresponding to the end of a holder 12, at least, being interposed by a binding agent such as glass paste. After that insulating layers 23 and 24 are provided on the outer surfaces of lead pars 21 and 22 and also that of an insulating sheet 27 to fix the parts in the holder 12. With such a structure, a slit 25 can be closed and sealed at the end of a holder 12, and the combustion pressure of an engine can be prevented from leaking outside. Besides the mechanical strength of the rear end of a ceramic heater 11 which is held by the holder 12 can be increased.

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]

-II Since diesel engines have poor starting performance at low temperatures, glow plugs are installed in the auxiliary combustion chamber or combustion chamber.
A method is adopted to improve the startability of the engine by generating electricity and generating heat, which increases intake air temperature or serves as an ignition source.

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-57-4
As shown in Japanese Patent No. 1523, 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. Compared to sheathed types that heat indirectly through heat-resistant insulating powder and a sheath, these types of ceramic heaters can improve heat transfer efficiency and also have excellent heat generation characteristics. Because it has greatly improved characteristics and has fast heating 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 a 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 I/I is high.

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, a person familiar with the invention 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. (Japanese Patent Application No. 60-299338, No. 60-299339, No. 61-256354, No. 61-256355).

No. 62-32643, etc.). Although these inventions were able to solve the problems existing in the prior art described above, the wettability of the bonding material with the lead portion constituting the ceramic heater and the insulating sheet interposed between the lead portions was insufficient. There may be poor bonding caused by this.

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.

Measures to solve problem C] 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. An insulating sheet made of mullite sintered body for sealing combustion pressure is integrally interposed between a pair of lead parts of the ceramic heater (both corresponding to the holder tip part).

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.

The mullite sintered body constituting the insulating sheet in the present invention has a chemical composition of A1) x 0371.809A.

Si0□28.20%, but depending on the physical and chemical formation conditions, 2Aj! □03 ・Sin, abbreviation A l
zOs・310. change between. Also, the above A
1 z Oz ' S I Besides Ox, Ti0g
* It may contain a small amount of Few Os and other components. Note that the above-mentioned mullite sintered body can be produced by the same manufacturing process as other oxide ceramics.

〔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 1) 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 1) 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, so that the tip of the ceramic heater 1'1 protrudes into the combustion chamber or sub-combustion chamber. hold in condition. Two first and second external connection terminals 13 and 14 are provided at the rear end of the holder 12.
Lead portions 21.2 which fit and support the terminal assembly 15 formed by penetrating and embedded in a synthetic resin or other insulating material, and constitute each terminal 13.14 and the ceramic heater 1).
What is 2?

For example, connect with a 16° 17# metal conductor wire such as a flexible wire and a terminal camp.

Next, the terminal assembly 15. A first external connection terminal 13 is arranged on its axis and has a rond part 13a on its inner end side to be connected to the metal conducting wire 16, and a first external connection terminal 13 is arranged at a predetermined interval around the periphery of the first external connection terminal 13 and has a rond part 13a on its inner end side to be connected to the metal conductor wire 16. A cylindrical second connecting lead piece 14a extending from a part of the end side to the metal conducting wire 17
It has 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 on the outer periphery of the assembly body 15a. 15b. Then, this metal tube 15b is crimped at the peripheral edge of the opening at the rear end of the holder 12 using high pressure, and is buckled and deformed 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.

Further, 18a and 18b are an insulating ring and a washer, respectively, and 18c is an insulating member fitted into the second external connection terminal 14 protruding rearward of the holder 12. The outer end of the washer 18b is fitted onto the first external connection terminal 13 side. Also 18d. Reference numerals 18e denote a spring washer and a tightening nut, 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
Between c. and by interposing lead wires (not shown) from the battery between the insulating member 18C and the spring washer 18d.

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

Ceramic heater 1). For example, conductive sialon powder is kneaded with thermoplastic resin, etc., injection molded into a mold with a predetermined cavity, and the molded body is fired. Alternatively, a material that has been previously formed into a rod shape 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 and 22. A slit 25 is formed in the longitudinal direction from the heat generating part 20 to between the lead parts 21 and 22. Note that lead part 2
1. An insulating layer 23 is provided on the outer peripheral surface of 22.

24 will be provided.

Note that 30 is a sealing sheet made of rubber, asbestos, etc. The first and second
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.

Figure 2 is an enlarged cross-sectional view of the tip of the holder 12 compared to Figure 1. Identical parts are indicated by the same reference numerals as in Figure 1. In Fig. 2, 27 is an insulating sheet, which is made of mullite sintered body and formed into a substantially plate shape. at least holder 12
At a portion corresponding to the tip end of 5, they are joined together via a joining material 26 such as glass paste. After fixing the insulating sheet 27, insulation 1)i23.24(
As described above, the material constituting the insulating layers 23 and 24 is bonded and fixed to the lead portions 21 and 22 of the insulating sheet 27. It may also be a glass paste, by configuring it as above.

By closing and sealing the slit 25 shown in FIG. 1 at the tip of the holder 12, it is possible 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 held by the holder 12 of the ceramic heater 1) can be improved.

As described above, the entire ceramic heater 1) was made to a diameter of 5 mm.
X 5 Q mm, the heat generating part 20 was formed to 3 mmφ x 10 mm, and was assembled as a glow plug 10, and when it was assembled as a glow plug 10, it took 3.5 seconds to reach 800 degrees Celsius, and the saturation temperature was set to below the allowable range of 1200 degrees Celsius, and about 1 ) The performance that can be achieved at 00°C was confirmed.

In this embodiment, the ceramic heater 1) is placed in 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.
) has a rectangular, square, polygonal, elliptical, etc. shape 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.

Although it has a fil II car 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 it can perform the function of 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 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) The mullite sintered body constituting the insulating sheet interposed and bonded between the lead parts has extremely good wettability with the bonding material, so complete airtightness can be maintained by five bondings.

(6) Since sintered mullite is easier to process than other ceramic materials, it can be formed into a shape that matches the shape of the lead part and holder, contributing to maintaining the airtightness mentioned above, and reducing the time and time required for processing. Man-hours can be significantly reduced.

[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 of the tip of the holder in FIG. 1. 1): Ceramic heater, 12: Holder. 20: Heat generating part, 21, 22: Lead part, 23° 24: Insulating layer, 27: Insulating sheet.

Claims (3)

[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 is provided on the outer peripheral surface of at least one of the lead parts, and the lead part is bonded and held in the holder, and the lead part corresponds to at least the tip of the holder of the ceramic heater. An insulating sheet made of mullite sintered body for sealing combustion pressure is integrally interposed between the pair of lead parts of the part, and at least the rear end of one of the lead parts is connected to the rear end of the holder through a metal conductor. A glow plug for a diesel engine, characterized in that the end is connected to an external connection terminal held in an insulated state. (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) Claims 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 item 1 or 2.