JPS62141424A - Glow plug for diesel engine - Google Patents

Abstract

PURPOSE:To provide an inexpensive ceramic heater with heating rapidity, self- temp. saturability etc. and also excellent reliability in heat resistant strength etc. by forming ceramic material members into one body in such a way that resistances made of conductive ceramic material and a thin-plate-shaped insulator made of insulating ceramic material are formed into lamination layers and bent and they are baked under the condition that a protecting pipe member made of conductive ceramic material is inserted on the bent lamination layers. CONSTITUTION:A cylindrical ceramic heater 11 held at the tip part of a hollow holder 12 is shaped in such a way that a lamination layer body which is formed by a thin-plate-shaped insulator 20 and thin-plate-shaped resistances 21, 22 made of insulating ceramic material and installed at both sides and one end of the insulator 20 is bent into nearly cylindrical form as a whole. Baking under the condition that a protecting pipe member 23 made of conductive ceramic material is inserted on the periphery of the rear end of this cylindrical body causes the heating part to expose on the outer surface of the heater and achieve a quick and sure red hot condition at its tip. Thus, it is possible to manufacture a flow plug 10 for a diesel engine which is able to exhibit function as a rapid heating type one.

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, and particularly to a glow plug that exhibits a function as a fast heating type. The present invention relates to an improvement in a glow plug for a diesel engine, which is equipped with a ceramic heater having self-temperature saturation that improves heat generation characteristics and achieves long-term afterglow.

[Conventional technology]

Generally, diesel engines have poor startability at low temperatures, so glow plugs are installed in the auxiliary combustion chamber or combustion chamber.
A method has been adopted in which a current is passed through this to generate heat, raising the intake air temperature or using it as an ignition source to improve the startability of the engine. By the way, conventionally, this kind of glow plug is commonly called a sheath, which is a metal sheath filled with heat-resistant insulating powder and embedded with a coiled heating wire made of iron chromium, nickel, etc. , In addition, Japanese Patent Application Laid-Open No. 57-41523
As shown in the above publications, a ceramic heater type is also known in which a rod-shaped heater is used in which a heating wire made of tungsten or the like is buried in a ceramic material such as silicon nitride having insulating properties. And, compared to the sheath type, which uses indirect heating through heat-resistant insulating powder and a sheath, the overnight type of ceramics has a higher efficiency when heating the heating body.
It has been widely adopted in recent years as it can heat up quickly and has excellent heat-generating properties.It can become red hot in a short time when heated, greatly improving the temperature rise characteristic, and exhibiting the performance of a fast-heating type. It looks like this.

[Problem that the invention seeks to solve]

However, 1. The ceramic heater type glow plug described above has a heater structure in which a metal (tungsten) heating wire is embedded inside an insulating ceramic material such as silicon nitride.

Moreover, since the coefficient of thermal expansion is different between these two members,
In particular, the rapid temperature rise during heat generation and its repeated use may have a negative effect on the durability of the ceramic heater, causing problems with reliability such as heat resistance strength, and further leading to higher costs. was there.

As a solution to this problem, there is a ceramic heater structure in which the heating wire is made of a conductive ceramic material having a thermal modulus approximately between that of an insulating ceramic material. Although these proposals have already been proposed in 1985-9085 and 1987-14784, there are still problems in terms of structure and function for use as glow plugs. However, it was not possible to put it into practical use.

For example, in the former case, the conductive ceramic material that serves as the heating element is embedded in the insulating ceramic material, so it is superior to the sheath type in terms of thermal conductivity. Since the heating is indirect, there are problems in exerting the function as a rapid heating type, and furthermore, the molding process is troublesome and complicated. In the latter case, the heating element is exposed on the surface side of the heater, and although it can function as a fast heating type, the heating element is exposed to the surface of the heater.
It is formed by a laminated structure of members exhibiting a letter shape, and both ends thereof are only led to the rear end of the heater.
The structure becomes complicated when taking out the electrode, and the cost I.
In addition, the U-shaped heating element had an adverse effect on the vortex flow inside the combustion chamber, which caused problems in practical use.

In addition, in recent years, glow plugs of this type have been improved in terms of starting performance of diesel engines, durability against high temperature usage conditions associated with the spread of turbo engines, and also durability for a certain period of time after engine start + JIJ. In contrast to adopting the so-called after-glow method, which maintains the energization state M1 to the glow plug during the engine to ensure smooth and appropriate combustion within the engine and to counteract exhaust and noise. There is a strong market demand, and it is considered desirable to make this after-grossing hour as long as possible (for example, about 10 minutes). In order to prolong this afterglow, it is necessary to self-control the power applied to the heating element, greatly improving the heat generation characteristics, preventing overheating in the heater part, and adjusting its saturation temperature appropriately. It is also necessary to have a self-temperature saturation function that can maintain the temperature below a certain temperature state. Taking these points into consideration, the product must have fast heating properties, self-temperature saturation properties, etc., and have high heat resistance strength, etc. There is a demand for a glow plug having an inexpensive ceramic heater that is also superior in terms of reliability.

[Means for solving problems]

-1- In order to meet the above-mentioned demands, the diesel engine glow plug according to the present invention has a cylindrical ceramic heater held at the tip of a hollow holder, and a thin plate-like insulator formed of an insulating ceramic material. Conductive ceramic 7 laminated and attached to the body, both sides and one end
A laminated body made of a thin plate-shaped resistor made of a material is curved in the width direction so that the whole has a substantially cylindrical shape, and
A protective pipe body made of a conductive ceramic material is attached to the outer periphery of the rear end of this cylindrical body, and then fired to form an integral body.

[Effect]

According to the present invention, a ceramic heater is formed by laminating and bending a resistor made of a conductive ceramic material having a coefficient of thermal expansion of about Since the protective pipe body made of ceramic material is baked in a solid state and molded integrally, its reliability such as heat resistance is improved (-), and the outer surface of the heater is softened. The heat-generating part of the resistor, which is arranged in a sloping manner, allows the tip of the heater to quickly become red hot, demonstrating the performance of a fast-heating type. can be appropriately controlled.

〔Example〕

Hereinafter, the present invention will be explained in detail using embodiments shown in the drawings.

Figures 1 to 3 are complete! This figure shows an example of a glow plug for a diesel engine related to I+, and first, in FIG. 1, the glow plug J! To briefly explain the structure, this glow plug 1
0 is equipped with a rod-shaped ceramic heater 11 whose tip side functions as a heating element, and a substantially tubular metal holder 12 that holds the ceramic heater 11 at its tip, and the rear end of this holder 12 is made of a synthetic resin material or the like. An external connection terminal 14 is fitted and held concentrically through an insulating bushing 13 made of connected via. In addition,
In the figure, 13a is integrally fitted to the outer circumference of the insulating bushing 13 and buckled in the axial direction due to the high pressure applied by the rear end of the holder 12 which is swaged during assembly, thereby moving the insulating bushing 13 toward the holder 12. This is a metal pipe that is integrated with the required mechanical strength and has a structure that is less susceptible to temperature effects. Further, 16a, 16b, and 16c are insulating rings screwed onto the threaded portion on the rear end side of the external connection terminal 14;
Use the nuts 16b and 16c to tighten the lead wires from the battery (not shown).
This external connection terminal 14 is electrically connected to the battery terminal by sandwiching it between the two terminals. On the other hand, the holder 12 is electrically connected to ground by having a threaded portion 12a on its outer circumference screwed into a threaded hole formed in a cylinder head of an engine (not shown), and at the same time, the tip of the heater 11 is It is arranged so as to protrude into the chamber or combustion chamber.

Here, in this embodiment, the reason why the external connection terminal 14 is connected to the ceramic heater 11 using the metal conductor wire 15 is as follows.
The purpose of various vibrations and wire drawings applied to the external connection terminal 14 is to protect the heater 11 from mechanical external forces such as torque, and it is preferable to use a material with a certain degree of flexibility for the conductor wire 15. It is.

Now, according to the present invention, 1: In the glow plug 10 having the above-mentioned configuration, the rod-shaped ceramic heater 11 held at the tip of the holder 12 is arranged as shown in Fig. t51 and Fig. 2(a).
(b), and also Figure 4 (a), (b), (
c).

As is clear from (d) and (e), the thin plate insulator 20 formed of an insulating ceramic material, both sides of this thin plate insulator 20, and one of the sides (the end of the heater tip (l11)) The laminate (see FIGS. 4(b) and 4(c)) is curved in the width direction, and the whole is approximately It is formed into a cylindrical shape, and is molded into one piece by firing with a protective pipe body 23 made of a conductive ceramic material fitted to the outer periphery of the rear end of the cylindrical body. It has some characteristics.

To explain this in detail, in this example, the ceramic heater t
i is a thin plate-shaped insulator 2 in a raw state formed in a strip shape of an insulating ceramic material so as to have a long thin plate shape;
As shown in FIGS. 4(a) and 4(b), thin plate-shaped resistors 21, 22, etc., which are also in raw form, are placed on both sides of the 0, the end face on the heater tip side, and both end faces in the longitudinal direction. After laminating and adhering, these laminates are curved in the width direction to form a substantially cylindrical shape as a whole, as shown in FIG. A protective pipe body 23 formed in advance from a raw conductive ceramic material so as to have a cylindrical shape as shown in the figure is fitted and joined, and the whole is fired in this state. Thus, a cylindrical ceramic heater 11 which is entirely integrated is obtained.

Here, the resistor 21 located outside the thin plate-like resistors 21 and 22 made of the conductive ceramic material described above functions as a heating element at the tip of the heater 11. resistor 22 located at
so that the cross-sectional area is smaller (resistance value is larger) than
It is formed so that the wall thickness is as thin as possible. This means that when the entire laminate described above is curved into a cylindrical shape, both paper antibodies 21 and 22 are the same or the resistor 2 is
If the second side is made thinner, the surface area of the resistor 21 on the outside of the heater 11 becomes larger, and the cross-sectional area becomes larger.
This is easily understood because first, the resistance value on the inner resistor 22 side increases, and this side functions as a heating element.

In addition, a metal metallized layer 24 is formed on a part of the outer peripheral surface of the protective pipe body 23 on the rear end side of the ceramic heater 11 fired as described in -1-.
A single solder joint is made on the second side for ground connection. Here, it is preferable to form a nickel plating layer on the surface of the metallized layer 24 as a post-processing so that the bonding state when holding the ceramic heater 11 on the holder 12 side can be made more securely.

On the other hand, an anode electrode rod 25 is fitted and fixed into the inner hole of the ceramic heater 11 from the rear end side, and a conductive wire 15 such as the flexible wire is connected to the rear end of the electrode rod 25. A terminal cap 26 which is anode-connected to the power supply side through the terminal cap 26 is fitted and fixed.

In the ceramic heater 11 having such a configuration, a protective pipe break 23 is provided at the tip of the heater 11.
The part of the thin plate resistor 21 formed on the outer circumferential part that protrudes further than the main body functions as a heat generating part, and the part integrated with the protective pipe body 23 on the rear end side serves as a ground side with respect to the holder 12 side. Functions as a lead part,
In addition, the thin plate resistor 22 in the inner hole of the heater 11 is connected to the electrode rod 25.
This is the anode side lead part connected to the power supply side via the anode side lead part.

Here, as the insulating and conductive ceramic material forming the double ceramic heater 11, for example, β sialon or sialon having a mixed phase of α and β (Si
l NO・-40%, Ar103・・30%, Y2O
Addition of titanium nitride (Tie) to (30.30%)
When using SiAION, etc., whose insulation and conductivity can be selected by adjusting the coefficient of thermal expansion of 0% or less or 1-), This has the advantage of being able to be formed of substantially the same material, increasing the bonding strength, and improving reliability such as heat resistance strength. In other words, it has been confirmed that when approximately 30% or more (40% or more is desirable in practice) of TiN is added to a double-stranded sialon, it has conductivity due to positive resistance-temperature characteristics (so-called conductive sialon). It is known that adding more than that will cause the specific resistance value to change continuously.
It is obvious that the above-mentioned TiN content may be changed as appropriate. In addition, in order to join members made of the insulating and conductive ceramic material of Sialon mentioned above, sintering is performed with an oxide sintering aid such as Y2O3 (Ittria), which creates a diffusion layer in the joint part. It is firmly joined in the state where it is formed. Of course, general ceramic bonding methods such as a halogen compound method, a brazing method, and a solid phase bonding method may also be used.

However, the insulating and conductive ceramic material forming the above-mentioned thin plate insulator 20 and the resistor 21.22 is not limited to the above-mentioned sialon; Any ceramic material may be used as long as it is stable in performance and has excellent thermal shock resistance. In this case, resistor 21.22
As the conductive ceramic material forming the , for example, one or more types obtained from 1"I of J1 oxide conductive materials such as carbides, borides, or nitrides of elements of group 4a, group 5a, or group 6a of the periodic table. and SiG and its sintered bonding material AI
Alternatively, a sintered body consisting of an A1 compound can be considered. In addition, the insulating ceramic material forming the thin plate insulator 20 has excellent heat resistance, W, etc., and also has excellent bonding strength and IW with the resistors 21 and 22. fSiG, Si3N
+, AIN, or ^1z03 as a main component can be considered.

According to the configuration according to the present invention described in -, the conventional glow plug has an internal heating type in which a gold 1+6911 heating wire is embedded in a sheath or an insulating ceramic material, so it functions as a fast heating type. It is easy to understand that the problem of lack of heat can be solved by placing the resistor 21, which becomes the heat generating part, on the outer surface of the ceramic heater 11, thereby improving its heat generation characteristics and functioning as a fast heating type. It will be. Further, according to the present invention, the resistors 21 and 22 and the thin plate insulator 20 are properly and reliably joined together using a ceramic material such as sialon having substantially the same coefficient of thermal expansion (small difference). This eliminates the adverse effects on durability, such as cracks caused by rapid temperature increases, unlike conventional ceramic heaters, and significantly improves reliability such as heat resistance strength. In particular, the ceramic heater II, which has excellent reliability such as heat resistance strength, has superior bonding strength between the two components compared to the conventional case where a metal heating wire is embedded in the ceramic material. Further, there is no need for a lead portion exposed to the outside of the heater so as to take out the heating wire from the surface of the ceramic material, which is a great advantage.

Furthermore, according to the ceramic heater 11 according to the present invention,
Since the specific resistance of the conductive sialon forming the resistors 21 and 22 can be adjusted by adjusting the amount of titanium nitride, its thickness can be freely set, and the width dimension (cross-sectional area) of the heat generating part can be particularly reduced. In addition to obtaining rapid heat generation characteristics, it is also possible to appropriately control the saturation temperature to enable long-term afterglow. That is,
The 1゛-1 self-temperature saturation as shown in 1 is obtained by the relationship between the volume (cross-sectional area) of the heat generating portion of the resistor 21 and the volume of its lead portion (22゜23). Moreover, since these resistors 21, 22 and the protective pipe body 23 are made of conductive ceramic material, they are superior in terms of moldability and durability compared to conventional metal heating wires. There are also advantages. Note that the above-mentioned resistor 21,
The thickness etc. of each part of 22 and 23 can be freely adjusted during molding, thereby allowing the resistance value to be freely selected.

Here, in the above-mentioned ceramic heater tt, in this embodiment, the entire outer diameter is 3φ, and the inner hole is 1φ.
When the resistor 21, which becomes the heat generating part, is formed into a thin plate shape having a thickness of Q and 1 wu+, and the heat generating part is formed into a protective pipe body. Length 10 from 23 to the tip of heater 11
■The resistor 22 which becomes the lead part on the anode side is formed with a thickness of 0.4+w■, and the thin plate-like insulator 20 is formed with a thickness of 0.5 mm. In addition, if the protective pipe body 23 that functions as the ground side lead part is formed with a diameter of 5φ, the heat capacity at the heat generating part due to the resistor 21 is made smaller than that at the lead part.
It has been confirmed through experiments that it is possible to obtain the required resistance value and exhibit the required self-temperature saturation property.

Note that this embodiment shows a case in which the ceramic heater 11 is formed so that its cross-sectional shape is approximately cylindrical, and this provides advantages such as being advantageous in terms of shaping and processing. However, it is of course not limited to this, and various modifications such as an elliptical shape and a angular shape are possible.

In addition, although the explanation was omitted in the embodiment described in 1-1, when used in an environment with severe usage conditions, the heater 1
If a protective film having oxidation resistance is coated on the outer surface, particularly on the heat generating portion, by vapor deposition or the like, greater durability can be expected.

As described in 1-1, if a ceramic heater 11 is used which is integrally formed with a thin plate-like insulator 20 made of insulating and conductive ceramic material and resistors 21 and 22, the result shown in FIG. The glow plug 10 can exhibit excellent characteristics.

That is, according to the glow plug IO according to the present invention, as shown by a in the figure, the time to reach noo°C is 3.5 seconds, and the saturation temperature is set to about 1200°C or less, with an allowable range of 1200°C or less.
It has been confirmed through experiments that the temperature can be set to about 100°C.

It should be noted that the present invention is not limited to the structure of two consecutive embodiments, and the shape, structure, etc. of each part may be modified or changed as appropriate. For example, in the embodiment described in -1-1, the ceramic heater 11 is formed by curving a laminated body of the thin plate-like insulator 20 and the resistor 21, 22 into a substantially C-shape.
However, the present invention is not limited to this, and FIG. 5(a)
, as shown in (b), is curved into a cylindrical shape and its [,I
Various modifications are conceivable, such as connecting the four ends via a connecting part made of conductive ceramic material, or directly connecting both ends of the insulator 20 made of insulating ceramic material. It is something.

〔Effect of the invention〕

As explained above-1-, according to the glow plug for a diesel engine according to the present invention, the cylindrical ceramic heater held at the tip of the hollow holder is replaced by a thin plate-like insulating material formed of an insulating ceramic material. The laminate consisting of the body and a thin plate-shaped resistor made of conductive ceramic material laminated on both sides and one end of the body is curved in the width direction to form an almost cylindrical shape as a whole! In addition to forming the cylindrical body, a protective pipe body made of conductive ceramic material is fitted to the outer periphery of the rear end of the cylindrical body and then fired, making it easy to mold the cylindrical body into one piece. Despite its low cost structure, the heat generating part is exposed on the outer surface of the heater, achieving faster and more reliable tip heating compared to conventional types, allowing it to function as a fast heating type, and allowing the heat generating part and leads to be exposed to the outer surface of the heater. Since the thermal expansion coefficients of the resistor and the thin plate insulator can be made almost equal, the bonding strength can be increased, and it will not be affected by the sudden temperature increase when the heater generates heat. This ensures reliability such as heat resistance and strength, and also prevents the heating plate 1 of the tip heat generating part from occurring.
By reducing 11-, it has self-humidity saturation, and as a result, long-term afterglow is possible as a countermeasure against engine exhaust and noise, and it is possible to demonstrate the performance as a glow plug, and the overall The structure is excellent in molding and assembly in a cylinder, and is advantageous in terms of productivity.
Furthermore, it has various excellent effects such as excellent heat resistance strength and durability that can sufficiently withstand severe usage conditions.

[Brief explanation of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a diesel engine glow plug according to the present invention, and FIGS. 2(a) and (b)
3 is an enlarged sectional view of the main part and a side view showing the main part in cross section as seen from the tip side, FIG. 3 is a characteristic diagram showing the temperature characteristics of the ceramic heater which is the main part, and FIG. 4(a), (
b), (c), (d), and (e) are process diagrams for explaining the molding state of the ceramic heater that characterizes the present invention, and Fig. 5 (a) and (b) are process diagrams for explaining the molding state of the ceramic heater that characterizes the present invention. FIG. 3 is a cross-sectional view of main parts showing the flow side. 1011... Glow plug for diesel engine, i
t: Cylindrical ceramic heater, 12: Hollow holder, 14: External connection terminal, 15: Fist/metal conductor, 20: Thin plate insulator made of insulating ceramic material , 21, 22・φ・Resistor made of electrically conductive ceramic material, 23... Protective pipe body made of electrically conductive ceramic material, 25... Anode electrode rod, 26... Terminal cap Patent applicant Automotive Equipment Co., Ltd. Hitachi Metals Co., Ltd.

Claims (2)

[Claims] (1) Equipped with a cylindrical ceramic heater held at the tip of a hollow holder with one end protruding outside, this ceramic heater consists of a thin plate-shaped insulator made of an insulating ceramic material, and A laminate consisting of both sides of a thin plate insulator and a thin plate resistor made of a conductive ceramic material laminated on one end thereof is curved in the width direction to form a substantially cylindrical shape as a whole, A glow plug for a diesel engine, characterized in that the cylindrical body is integrally molded by firing a protective pipe body made of a conductive ceramic material fitted to the outer periphery of the rear end side of the cylindrical body. (2) The insulating and conductive properties of the thin plate insulator and resistor that make up the ceramic heater can be selected by adjusting the amount of titanium nitride added to β-sialon or sialon with a mixed phase of α and β. The glow plug for a diesel engine according to claim 1, characterized in that the glow plug is integrally formed of a ceramic material obtained from the above.