JPS63201425A - Glow plug for diesel engine - Google Patents

Abstract

PURPOSE:To obtain a glow plug having quickly heated properties and self- temperature saturating properties at low price, by unitarily constituting a heating part and a lead part of conductive ceramic material. CONSTITUTION:A conductive ceramic material consists of a sintered body of sialon, which is composed of beta-sialon shown by the formula of Si6-zAlzOzN8-z of which 'z' is above 0 and below 1, to which above 20vol.% and below 50vol.% of TiN is added. The ceramic heater of a glow plug 10 is made of the conductive ceramic material, unitarily composed of a heating part 20 and lead parts 21 and 22. A metallized layer 23 is formed on the outer surface of a lead part 21, and an insulating coating layer 24 is formed on the lead part 22. The ceramic heater 11 is fitted and is fixed in a holder 12. A metallic lead wire 15 is connected to the metallized layer 27 plated on the terminal 26 of an electrode, interposed by a terminal cap 15a, and the rear end of a metallic lead wire 15 is connected to the terminal 14 to be connected to an outer part, being held by the rear end of a holder 12 by the intermediary of an insulating bush 13.

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 Application 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 a ceramic material such as silicon nitride having m green property 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 become popular 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,
In particular, the rapid temperature rise during heat generation and its repeated use may reduce the durability of the ceramic heater. Therefore, there were problems in terms of reliability such as heat resistance and strength, and there was also the drawback 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. The m plan 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.

For example, the former has a structure in which a conductive ceramic material serving as a heating element is embedded in an insulating ceramic material.

Although the thermal conductivity is superior to that of the sheath type, since it is indirect heating, the function of the rapid heating type is insufficient, and furthermore, there are problems such as the complicated molding process.

The latter has two heating elements exposed on the surface side of the heater and has a fast heating function, but the heating elements are simply formed of a laminated structure of U-shaped members, and both ends are connected to the rear end of the heater. However, the structure for removing the electric scraper becomes complicated, leading to high costs.

Also, in recent years, this type of glow plug has become more popular.

Improved startability of diesel engines, durability against higher operating conditions associated with turbochargers, and smooth and appropriate combustion within the engine by keeping the globe lugs energized for a certain period of time after the engine has started. There is a strong demand in the market for the adoption of the so-called after-grossing method, which takes measures against exhaust gas and noise by making the after-grossing process possible, and what is more, it is necessary to make this after-grossing time as long as possible (for example, about 10 minutes). has been done.

In order to prolong the afterglow, 1) self-control the power applied to the heating element to greatly improve the heat generation characteristics, prevent overheating in the heater part, and adjust its saturation temperature to an appropriate level. There is also a need to have self-temperature saturation capability that can be maintained below temperature. Therefore, taking these points into consideration, it has rapid heating properties, self-temperature saturation properties, etc.

There is also a demand for an inexpensive glow plug that is excellent in terms of reliability such as heat resistance and strength.

[Means for solving problems]

In order to solve the above problems, there are three 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.

C9 At least the outer surface of the one lead portion is bonded and held within the holder via an insulating layer.

D. 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.

E. The outer surface of the one lead portion is placed through a conductive layer.

The outer surface of the other lead portion is bonded and held within the holder via an insulating layer.

F, the conductive ceramic material is S 16-2Aj! z
O.

For a composition in which 2 of the β-type sialon represented by Nt2 exceeds O and is less than 1, 20vol. % over 50vo1. %
It is formed from a sialon sintered body containing less than 10% of TiN.

This technical method was adopted.

In the present invention, TiN is added as a conductive compound for the following reason. That is, IVa.

Sialon sintered bodies with electrical conductivity can also be obtained by using Va and VIa group carbides, nitrides, borides, etc., but the sinterability and oxidation resistance of the sintered bodies by atmospheric pressure sintering or gas pressure sintering are This is because, considering the properties, it is limited to TiN.

Further, the amount of TiN added was 20vol. Exceeding %509゜1
The reason why it should be less than 0% is 20vo1. % or less, Ti
A conductive path due to mutual contact of N cannot be obtained.

This is disadvantageous because it does not exhibit electrical conductivity. 20 ma. When it exceeds 10%, conductivity due to positive resistance-temperature characteristics is exhibited, and as the amount added increases, the electrical resistivity changes continuously. On the other hand, 50. . At over 19%.

This is disadvantageous because the inherent properties of Sialon, such as oxidation resistance and high-temperature strength, are significantly impaired.

Next, 2 in Si, -zAlzOzN2O□N and 2.

The reason for setting the value to be more than 0 and less than 1 is because a sintered body with high strength can be obtained within this range. Specifically, 5i
sN4 powder, AIN polytie powder (crystal type 21R), A
11t02 powder, Y! Os powder is used, TiN powder is added and mixed to these powders, and after molding, the temperature is 1700 to 190
By sintering at 0°C.

A conductive sialon sintered body is obtained.

〔Example〕

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention.

The schematic structure of a glow plug, which is generally designated by the reference numeral 10 in the figure, will be briefly described. The glow plug 10 includes a rod-shaped ceramic heater 11 whose tip side functions as a heating element;
It has a substantially tubular metal holder 12 that holds the ceramic heater 11 at its tip. An external connection terminal 14 is fitted concentrically to the rear end of the holder 12 via an insulating bushing 13 made of synthetic resin or the like, and this external connection terminal 14 is flexible with the lead part 22 inside the ceramic heater 11. Connection is made via a metal conductor 15 such as a wire and a terminal camp 15a. Note 13a
is a metal pipe which is integrally fitted onto the outer circumference of the insulating bushing 13 and is buckled and deformed in the axial direction by a high pressurizing force by caulking the rear end of the holder 12 when attaching 1Mi, and the insulating bushing 13 is integrated with the holder 12 side with the required mechanical strength to eliminate the influence of '/A degrees. Also 16a
, 16b, and 15c are an insulating ring screwed onto the screw portion on the rear end side of the external connection terminal 14, a fixing nand, and a nut for tightening the external lead, and a battery (not shown)
The external connection terminal 14 is electrically connected to one terminal of the battery by sandwiching the lead wire from the nut 16b and 16C between the nuts 16b and 16C. On the other hand, the threaded portion 12 on the outer periphery of the holder 12
By screwing the ceramic heater 11 into a threaded hole (not shown) provided in the cylinder head of the engine, the ceramic heater 11 is electrically connected to the ground, and at the same time, the tip of the ceramic heater 11 is placed so as to protrude into the sub-combustion chamber or the combustion chamber. Note that the external connection terminal 14 is connected to the ceramic heater 11 via a metal 115, which protects the ceramic heater 11 from mechanical external forces such as various vibrations and tightening torques applied to the external connection terminal 14. This is to protect the public. Metal conductor wire 15
It is preferable to use a material having a certain degree of flexibility, such as flexible wire.

Next, FIG. 2 is an enlarged perspective view showing the ceramic heater 11, and the same parts are designated by the same reference numerals as in FIG.
In the figure, the 9 heat generating parts 20 are formed to have a small diameter so that the wall thickness is thinner than the lead parts 21.22, and the 1 heat generating part 20 is connected to the lead parts 21.
A slit 25 is formed in the longitudinal direction between 22 and 22. Also, one of the lead parts 21 and 22 formed integrally with the heat generating part 20 from a conductive ceramic material.
A metallized layer 23 is formed on the outer peripheral surface of the
An insulating coating layer 24 is formed on the other lead portion 22 . Note that a nickel plating layer (not shown) is provided on the surfaces of the metallized layer 23 and the insulating coating layer 24.
Laminate. The above-mentioned two layers 23 and 24 and the nickel plating layer on their surfaces make the ceramic heater 11
As shown in FIG. 1, the holder 12 is bonded and fixed to the tip of the holder 12 through means such as silver soldering. In this case, a nickel plating layer can be formed on the joint surface side of the holder 12 as well, if necessary.

Next, the ceramic heater 11 is formed by kneading conductive sialon powder with a thermoplastic resin or the like, injection molding it into a predetermined mold, and then firing this molded product, or by pre-forming it into a rod shape. A ceramic heater can be formed into a desired shape by electrical discharge machining or cutting. After the above molding, a metal metallized layer 23 and an insulating coating layer 24 (preferably alumina or the like is sprayed)
etc. are formed on the outer circumferential surface of the corresponding lead portions 21 and 22, respectively, and a metal holder 12 shown in FIG.
It is sufficient to form a nickel plating layer as an auxiliary material for connection with the electrode as a post-processing. Note that 27 in FIG.
Of course, the same nickel plating layer as described above is formed on the surface of the metal metallized layer formed on the 6 portions, and the metal &11
15 can be connected to form a heater assembly. Note that the ceramic heater 1 molded as described above
1 into the holder 12 as shown in FIG.
The glow plug 10 is fixed by brazing or the like via the insulating coating layer 24, and the rear end of the metal 'Ma15 is connected to the external connection terminal 14 side held at the rear end of the holder 12. Complete assembly.

Note that the thickness of each part of the ceramic heater 11 can be freely adjusted during molding.

This allows the resistance value to be freely selected, for example 0.

In this embodiment, the ceramic heater 11 as a whole has a circular cross section of 5 mmφ, and the 1 heat generating part 20 has a circular cross section of 3 mmφ, and the length is 50+m (the length of the electrode extraction end 26 is 5+s
- is excluded), the length of the 9 exothermic part 20 is 1 (lu+), and the metallized layer 23 and the insulating coating layer 24 are formed over a length of 20 m5+ from a position 25 mm away from the tip. This increases the heat capacity of the heat generating part 20 to the lead parts 21 and 22.
It has been confirmed through experiments that it is possible to obtain the required resistance value and exhibit the required self-temperature saturation property.

Furthermore, although the explanation was omitted in the above embodiment, when the ceramic heater 11 is used in an environment with severe usage conditions, a protective film having oxidation resistance is coated on the outer surface of the ceramic heater 11, especially on the heat generating part 20, by vapor deposition or the like. If it is formed by using the same method, greater durability, etc. can be expected.

When the above-mentioned ceramic heater 11 was assembled as a glow plug 10 and an experiment was carried out, as shown in FIG.
Time to reach 0℃: 3.5 seconds, saturation temperature within its allowable range: 120℃
It was confirmed that the temperature could be lowered to about 1100°C while keeping the temperature below 0°C.

By the way, in the glow plug 10 having the above-described structure, as is clear from FIGS. 1 and 2, the slit 25 formed along the longitudinal direction of the ceramic heater 11 allows the interior space of the holder 12 to be The heater 11 is in communication with the engine combustion chamber and the like. Therefore, it is necessary to prevent combustion pressure from leaking to the outside of the engine in the event of an explosion within the combustion chamber. For this reason, in the third embodiment, as shown in FIG.
For example, asbestos.

A structure is adopted in which this portion is mechanically sealed by interposing a sealing sheet 28 made of rubber or the like. However, there are three possible locations and sealing methods for such a seal portion.

For example, an O-ring or the like may be interposed on the inner end side of the insulating bushing 13 to seal between it and the holder 12.

FIG. 4 is a longitudinal sectional view of main parts showing another embodiment of the present invention, and the same parts are designated by the same reference numerals as in FIGS. 1 and 2. In FIG. 4, 30 is an insulating sheet. And 1
For example, the ceramic heater 1 may be made of an insulating ceramic material.
The lead portions 21 and 22 of at least the portion corresponding to the tip of the holder 12 of the holder 1 are integrally joined to each other. This prevents leakage to the outside. Further, with the above configuration, in the ceramic heater 11, the holder 12
In addition to improving the mechanical strength of the rear end portion that is held in place, it is also possible to omit the sealing sheet 28 as in the above-described embodiment, which has great advantages.

Here, as the above-mentioned insulating ceramic material.

Similar to the conductive ceramic material forming the ceramic heater 11, by adjusting the amount of TiH added, insulation and
It is preferable to use Sialon whose conductivity can be selected. If such a material is selected, the insulating sheet 30 can be formed of the same material with approximately the same coefficient of thermal expansion as the resistor side, increasing the bonding strength. In this way, reliability such as heat resistance strength can also be ensured. In addition, in order to join the members made of the above-mentioned insulating and conductive ceramic material using Sialon, Y! By sintering with an oxide sintering aid such as Ox, it is possible to form a strong bond with a diffusion layer formed in the bonded area, but this is of course a common method for bonding ceramic materials. A halogen compound method, a brazing method, or a solid phase bonding method may be used. Furthermore, insulating sheet 3
The insulating ceramic material forming the 0 may be SiC, Si, Np, AAN, or Al2, which has excellent heat resistance and strength, and also has excellent bonding strength with the conductive ceramic material.
A material containing O as a main component may also be considered, and it may also be an insulating material such as glass. In particular, the above-mentioned insulation sheet 30
This is because the intervening portion is the rear end portion of the ceramic heater 11 that is remote from the heat generating portion 20 .

Even if the reliability of the joint is slightly lowered, there is no practical problem.

Note that the present invention is not limited to the structure of the embodiment described above, and the shape, structure, etc. of each part may be modified or changed as appropriate. For example, the shape of the ceramic heater 11 is not limited to the round bar shape in the above embodiment, but may also be a square bar shape with a rectangular cross section as shown in FIG. 5, or as shown in FIG. 6(a). .

It is clear that the case may have an elliptical shape as shown in (b).

Furthermore, in the embodiment described above, in order to bond and fix the ceramic heater 11 in a state where it is held at the tip of the holder 12, one lead part 21 is coated with metallized N23, and the other lead part is coated with a conductive coating layer 24. Although the present invention is not limited to this, for example, the outer surfaces of the lead portions 21 and 22 of the ceramic heater 11 are each insulated from glass or other insulating material. It is also possible to form layers and fix metal conductive wires to each layer. FIG. 7 is a longitudinal sectional view showing an embodiment constructed in this way, and the same parts are shown in FIGS. 1, 2, and 4. In the rear end of the holder 12, first and second external connection terminals 31 and 32 are inserted through a synthetic resin or other insulating material, indicated by the same reference numerals as in FIGS. The lead portions 21.22 which fit and hold the buried terminal assembly 33 and constitute the ceramic heater 11 with each terminal 31.32 are.

The zero-order terminal assembly 33, which is connected via metal conductive wires 35 and 36 having the same structure as described above, has a first terminal assembly 33 having a rond portion 31a located on its axis and connected to the conductive wire 36 on its inner end side. a second external connection terminal 31 having a cylindrical shape, which is connected to the metal conducting wire 35, and a lead piece 32a arranged around the first external connection terminal 31 at a predetermined interval and extending from a part of the inner end thereof; Connection terminal 32 and both terminals 31.3
It has an assembly body 33a made of resin molding that insulates between the two and integrates them with an insulating layer on the outer periphery thereof, and a metal tube 33b for connection reinforcement is provided on the outer periphery of this main body 33a. It is fitted. and,
This metal tube 33b is caulked with a high pressure at the peripheral edge of the opening at the rear end of the holder 12, and is buckled and deformed along the axial direction, so that the inner side of the metal tube 33b is turned toward the resin assembly main body 33a.

The outside is firmly pressed against the inner wall of the holder 12,
This can solve problems caused by external forces and thermal contraction.

Further, 34a and 34b in FIG. 1 are insulating rings and washers fitted to the second terminal 32 protruding rearward of the holder 12, and 34c is an outer end of the washer 34b fitted to the first terminal 31 side. equipped insulating member, 34d, 34
e is a spring washer screwed onto a threaded portion formed at the outer end of the first terminal 31, and a tightening pad.

And between the washer 34b and the insulating member 34c.

And between the insulating member 34c and the spring washer 34d, a lead wire (not shown) from the bufftery and -
By interposing and holding the side lead wires, each of the terminals 3
1.32 will be electrically connected to the battery terminal side. Furthermore, 35a and 36a in FIG. 1 indicate the metal conductive wires 35.
．． It is an insulating member such as a tube covered with 36. An insulating coating layer 24 is provided as an insulating layer on the outer surface of the lead parts 21 and 22 to bond and hold the tip of the holder 12, and the rear end of each lead part 21 and 22 is connected to the holder through metal conductive wires 35 and 36. First and second external connection terminals 31 and 32 held in an insulated state at the rear end of 12
Connect with. The configuration other than the above is the same as that in the previous embodiment.

The effect is therefore also 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.

(11 Despite the simple structure, the heat generating part is exposed on the outer surface of the heater, so it achieves faster and more reliable tip heating compared to conventional types, and can demonstrate its 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 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.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view showing an embodiment of the present invention, and FIG.
FIG. 3 is a diagram showing the temperature characteristics of the ceramic heater; FIG. 4 is a vertical sectional view of main parts showing another embodiment of the present invention; FIGS.
11: Ceramic Heater, 12: Holder. 20: Heat generating part, 21.22: Lead part, 25 Nislit, 30: Insulating sheet.

Claims (7)

[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 at least the outer surface of the one lead part is bonded and held in the holder via an insulating layer, and at least the rear end part of the one lead part is made of metal. The conductive ceramic material is connected to an external connection terminal held in an insulated state at the rear end of the holder via a conductive wire, and the conductive ceramic material is connected to the Si_6_-_
For a composition in which z of β-type sialon represented by zAl_zO_zN_2_-_z is more than 0 and less than 1, 20 vol.
．． % over 50vol. 1. A glow plug for a diesel engine, characterized in that it is formed of a sialon sintered body to which less than % of TiN is added. (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 glow plug for a diesel engine according to claim 1 or 2, wherein the conductive layer is a metallized layer and the insulating layer is an insulating coating layer. (4) According to any one of claims 1 to 3, an insulating sheet for sealing combustion pressure is integrally interposed between a pair of lead portions of a ceramic heater at least in a portion corresponding to the holder tip portion. Glow plug for the diesel engine listed. (5) A patent 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 conductive wire. A glow plug for a diesel engine according to any one of items 1 to 4. (6) The grain boundary layer of the sialon sintered body is Y, Si, O, N,
The glow plug for a diesel engine according to any one of claims 1 to 5, which is amorphous containing Al. (7) The electrical resistivity of the Sialon sintered body at room temperature is 1Ω・
7. The glow plug for a diesel engine according to any one of claims 1 to 6, which has a temperature coefficient of resistance of less than cm and a positive temperature coefficient of resistance.