JPS63110588A - Glow-plug for diesel engine - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 electricity and generate heat to raise the intake air temperature or serve 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 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,
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, 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.

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 the heating is done indirectly, the function of the rapid heating type is insufficient, and furthermore, the molding process is complicated.

In the latter case, nine heating elements are exposed on the surface side of the heater, and while it has a fast heating function, the heating element is simply formed by a laminated structure of U-shaped members, and both ends are connected to the rear end of the heater. Since the structure of the electrode is only guided to the electrode, the structure for taking out the electrode becomes complicated, leading to an increase in cost.

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-gross method, which takes measures against exhaust gas and noise. Moreover, it is necessary to make this afterglow time as long as possible (for example, about 10 minutes).

In order to prolong the afterglow, we can self-control the power applied to the 9 heating elements to significantly improve the heat generation characteristics, prevent heat filtration in the heater part, and lower its saturation temperature. There is also a need to have self-temperature saturation capability that can maintain the temperature below a suitable 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]

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.

C8 The outer surface of the one lead part is interposed through a conductive layer.

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

D, the conductive ceramic material is S 1h-z Adz
For a composition in which 2 of β-type sialon represented by OsN s-z exceeds O and is less than 1, +25 vol,% exceeds 70
Shiol.

% of a carbonitride solid solution of TI is added.

This technical method was adopted.

In the present invention, the reason why a carbonitride solid solution of Ti is added as a conductive compound is as follows.

That is, carbides and nitrides of lVa, Va, and VIa groups.

Sialon sintered bodies with electrical conductivity can also be obtained using boride, etc., but considering the sinterability by normal pressure sintering or gas pressure sintering and the oxidation resistance of the sintered bodies, titanium carbides and nitrides are preferable. This is because it is limited to things. and,
In this case a single carbide.

Why use carbonitride solid solution instead of nitride?

This is because sialon sintered bodies having various electrical resistivities can be obtained by changing the ratio of C and N in the solid solution.

Further, the amount of Ti carbonitride solid solution added was 25νo1. To make it more than 70vol and less than 10%, first of all, 25vol,
% or less, a conductive path through mutual contact between the Ti carbonitride solid solution particles cannot be obtained and no conductivity is exhibited, which is disadvantageous. If it exceeds 25 vol.%, it exhibits conductivity due to positive resistance-temperature characteristics, and as the amount added increases, the electrical resistivity changes continuously. If the amount is more than 70 vol.%, it is disadvantageous because the inherent characteristics of SiAlON, such as oxidation resistance and high temperature strength, are significantly impaired. Preferably 3
0vol, exceeds 50vol. It is better to set it to less than %.

Next, 2 in S i 6-z A 12 z Oz N5-z.

The reason why the value is greater than O and less than 1 is because a sintered body with high strength can be obtained within this range. Specifically, St.
+N4 powder, AAN polytype powder (crystal type 21 R)
, using A Az Os powder and Yz O+ powder,
To these, 25 to 70% of Ti carbonitride solid solution powder was added.
A conductive sialon sintered body is obtained by adding and mixing VO11%, molding, and sintering at 1,700 to 1,900°C.

〔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 conducting wire 15 such as a wire and a terminal cap 15a. Note that 13a is a metal pipe, which is integrally fitted to the outer circumferential portion of the insulating bushing 13, and is buckled in the axial direction by a high pressing force by caulking the rear end of the holder 12 during assembly.
The insulating bushing 13 is integrated with the holder 12 side with the required mechanical strength to eliminate the influence of temperature. Also 16a, 16b
, 15c is an insulating ring screwed onto the screw portion on the rear end side of the external connection terminal 14, a fixing nut, and a nut for tightening the external lead, and the lead wire from the battery (not shown) is connected to the nut 16b. .

160, the external connection terminal 14 is electrically connected to one terminal of the battery. - holder 12
By screwing the threaded portion 12a on the outer periphery of the ceramic heater 11 into a threaded hole (not shown) provided in the cylinder head of the engine, electrical ground connection is established, and at the same time, the tip of the ceramic heater 11 is inserted into the auxiliary combustion chamber or the combustion chamber. Place it so that it sticks out.

Note that the external connection terminal 14 is connected to the ceramic heater 11 via a metal conductor wire 15, 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. As the material of the metal conductive wire 15, it is preferable to use a material having a certain degree of flexibility, such as a 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. 1. Second
In the figure, the 5 heat generating parts 20 are formed to have a small diameter so as to be thinner than the lead parts 21.22, and the 9 heat generating parts 20 to 9 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, it 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-described forming, a metal metallized layer 23, an insulating coating layer 24 (preferably alumina or the like is sprayed), etc. are formed on the outer circumferential surfaces of the corresponding lead parts 21 and 22, and furthermore, the metal layer 23 and the insulating coating layer 24 (preferably coated with alumina or the like) as shown in FIG. made holder 1
A nickel plating layer as an auxiliary material for connection with 2 may be formed as a post-processing. In addition, 27 in FIG. 2 is a metal metallized layer formed on the electrode extraction end 26 portion, and of course, the same nickel plating layer as described above is formed on the surface, and the metal conductor 1 is connected to this through the terminal cap 15a.
5 can be connected to form a heater assembly. Note that the ceramic heater 11 molded as described above
is fitted into the holder 12 as shown in FIG. 1, and the outer peripheral surfaces of the lead parts 21 and 22 are fixed by brazing or the like via the metallized layer 23 and the insulating coating layer 24, respectively.

The rear end of the metal conductor 15 is connected to the external connection terminal 14 held at the rear end of the holder 12 to complete the assembly of the glow plug 10.

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.

In this embodiment, the entire ceramic heater 11 is 5 ++n
7 heat generating parts 20 portions have a circular cross section with 3 dragons φ,
And when the length is 50 mm (excluding the length 5 mm of the electrode extraction end 26), the length of 1 heat generating part 20 is lQ.
1 layer, and the length is 20 from the position 25 long from the tip.
The metallized layer 23 and the insulating coating layer 24 are formed over a length of m. This makes the heat capacity of the heat generating part 20 smaller than that of 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 configuration, as is clear from FIGS. 1 and 2, the slit 25 formed along the longitudinal direction of the ceramic heater 11 allows the space in the holder 12 to be The ceramic 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 this embodiment, as shown in FIG. 1, two sealing sheets made of, for example, asbestos, rubber, etc. are attached to the outer end side of an insulating bushing 13 that is integrally provided with the external connection terminal 14 at the rear end opening of the holder 12. 28 is used to mechanically seal this part. However, there are 9 different possible installation positions and sealing methods for such a sealing portion. .

FIG. 4 is a longitudinal sectional view of a main part 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 Figure 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 thereto. By configuring in this way, the slit 25 can be connected to the holder 1.
The two parts are closed and sealed, sealing the engine's combustion pressure and preventing leakage to the outside. Further, with the above configuration, in the ceramic heater 11, the mechanical strength of the rear end portion held by the holder 12 can be improved, and the sealing sheet 28 as in the above-mentioned embodiment can be omitted. big.

Here, as the above-mentioned insulating ceramic material.

Similar to the conductive ceramic material forming the ceramic heater 11, it is preferable to use Sialon whose insulating properties and conductive properties can be selected by adjusting the amount of Tt carbonitride solid solution added. If such a material is selected, the insulating sheet 30 can be formed of the same material with substantially the same coefficient of thermal expansion as the resistor side, increasing the bonding strength and ensuring reliability such as heat resistance strength. obtain. In addition, in order to bond the members made of the insulating and conductive ceramic material using Sialon mentioned above, a diffusion layer is formed at the bonded portion by sintering with an oxide sintering aid such as Y2O3. The halogen compound method and brazing method are of course common methods for joining ceramic materials, which can be firmly joined in the formed state.

A solid phase bonding method may also be used. Furthermore, as the insulating ceramic material forming the insulating sheet 30, 1, which has excellent heat resistance and strength and also has excellent bonding strength with the conductive ceramic material, is used.
For example, S i C, 5t3N4゜AβN or Al2O
It is also possible to use an insulating material such as glass.

In particular, since the intervening portion of the insulating sheet 30 described above is on the rear end side away from the heat generating part 20 of the ceramic heater 11,
The reliability of the joints is somewhat low (even if it is).

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-described embodiment, but may also be a square bar shape with a rectangular cross section as shown in FIG.
It is clear that the case may have an elliptical shape as shown in Figures (a) and (bl).

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, a metallized layer 23 is applied to one lead part 21, and an insulating coating layer 24 is applied to the other lead part 21, respectively. Although the case where they are formed as a layer and an insulating layer and joined by brazing has been shown, the present invention is not limited thereto. , brazing may be performed on the holder 12 side. Note that when the above-described bonding method using the glass layer and the brazing material layer is adopted, the holder 12
On the side of the lead part that is electrically connected to the side, a part of the glass layer may be removed to expose a part of 2 to ensure conduction through the brazing material layer. .

〔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 its simple structure, the 9 heat-generating parts are exposed on the outer surface of the heater, allowing the tip to become red hot more quickly and reliably than conventional types, demonstrating its function as a fast-heating type. can.

(2) Since the thermal expansion coefficients of the resistor and insulator that form the heat generating part and the lead part can be made approximately equal, the bonding strength is increased and there is no possibility of cracking due to a sudden temperature rise when the heater generates heat. It is possible to ensure reliability such as heat resistance and strength without causing such accidents.

(3) Since the heat capacity of the tip heating section is small, it has self-temperature saturation, and as a result, long-term afterglow is possible as a measure against engine exhaust and noise.

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

[BRIEF DESCRIPTION OF THE DRAWINGS] 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.
Figures (a) and (fb) are a perspective view and a cross-sectional view of a ceramic heater showing still other embodiments, respectively. 11: Ceramic heater, 12: Holder. 20: Heat generating part, 21.22: Lead part, 25 Nislit, 30: Insulating sheet. $ 3 Enshi crystal hammer (t)

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 portions are integrally formed of a conductive ceramic material, and the outer surface of one of the lead portions is bonded and held within the holder via a conductive layer and the outer surface of the other lead portion is via an insulating layer; The conductive ceramic material was prepared by using 25 vol. Ti over 70vol, less than %
A glow plug for a diesel engine, characterized in that it is formed from a sialon sintered body added with a carbonitride solid solution. (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 the ceramic heater at least in a portion corresponding to the holder tip portion. Glow plug for the diesel engine listed. (5) 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 any one of items 1 to 4. (6) The grain boundary layer of the sialon sintered body is Y, Si, O, N,
A glow plug for a diesel engine according to any one of claims 1 to 5, which is amorphous and contains A. (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.