JPH0419330Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial field of application] The present invention relates to a glow plug that preheats the sub-combustion chamber or combustion chamber of a diesel engine. This invention relates to improvements in glow plugs for diesel engines equipped with bipolar ceramic heaters.

[Conventional technology]

Glow plugs of various structures have been known as this type of glow plug, but ceramic heater type glow plugs have recently attracted attention because of their ability to function as a rapid heating type.

As such a ceramic heater type glow plug, for example, Japanese Patent Application Laid-open No. 14784/1984 discloses
The heating element is formed integrally with the heater insulating part so as to be exposed on the outer surface of the heater, using a conductive ceramic material having a coefficient of thermal expansion substantially equal to that of the insulating ceramic material forming the heater insulating part. The configuration is shown here, and this enables rapid tip redness to be obtained and exhibits the performance as a fast heating type, while also maintaining the bonding state between the heating element and the heater insulation part properly and reliably, and improving heat resistance strength etc. It was possible to improve reliability to some extent.

[Problem that the invention attempts to solve]

However, the ceramic heater type glow plug with the conventional structure as described above still has problems from both a structural and functional standpoint before it can be put to practical use as a glow plug.

In other words, for this type of glow plug,
While it is desired that the tip rapidly become red hot immediately after energization and be able to exhibit the effect of a rapid heating type,
In recent years, the startability of diesel engines has improved, and with the spread of turbo engines, durability against high-temperature operating conditions has been improved, and combustion within the engine can be improved by keeping the glow plug 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 afterglow method, which allows for smooth and appropriate operation and takes measures against exhaust and noise. degree) is also required. In order to prolong the afterglow, it is necessary to self-control the power applied to the heating element to greatly improve the heat generation characteristics, prevent overheating in the heater part, and adjust the saturation temperature to an appropriate level. It is necessary to have a self-temperature saturation function that can maintain the temperature below the state,
Conventional ceramic heaters have not been able to meet these demands. That is,
In conventional heater structures, it is common practice to form the heating part at the tip of the heater into a thin wall so that it can function as a fast-heating type due to the red-hot property of the tip. It is not possible to obtain such self-temperature saturation properties, and there are also problems in terms of reliability such as heat resistance strength. Taking these points into consideration, it is necessary to take some measures to particularly demonstrate self-temperature saturation properties. It is requested.

[Means for solving problems]

In order to meet the above-mentioned demands, the diesel engine glow plug according to the present invention includes a rod-shaped ceramic heater that is held through the tip of the holder.
A pair of large cross-sectional areas that are connected to each other via a U-shaped heat generating part with a small cross-sectional area and a tapered part formed to gradually increase the cross-sectional area at both ends of the heat generating part and extend parallel to the rear. It is configured by integrally forming the lead part for external connection with a conductive ceramic material, and the cross-sectional area ratio ε (= SH/
SL) is within the range of 0.15≦ε≦0.6,
The thickness of the U-shaped heat generating part is formed thinner than that of the lead part, and the pair of lead parts are held by penetrating the holder tip part with a part of the heat generating part side protruding from the holder tip part. The projecting length of this external connection lead portion is set according to the specifications of the cylinder head to which it is attached.

[Effect]

According to the present invention, the U-shaped heating part on the tip side of the heater is made of only conductive ceramic material that does not contain any foreign matter, and has an appropriate cross-sectional area ratio in comparison with the rear lead part that is penetrated and held by the holder. The U-shaped heat generating part on the tip side of the heater can be heated rapidly and efficiently when electricity is applied. Demonstrates performance as a thermal type,
In addition to improving engine startability, it can also achieve long-term afterglow by appropriately controlling the saturation temperature using its own heat-generating properties.It also allows the non-red-hot reed to be extended to a specified length. By holding the heater at the tip of the holder, you can freely choose to place the red-hot heat-generating part facing the necessary part of the cylinder head, which is the side to which it is installed. By taking out the electrodes in a two-pole, two-wire structure, the thermal influence on the part from which they are taken out can be reduced and reliability can be improved.

〔Example〕

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

1 to 7 show an embodiment of a glow plug for a diesel engine according to the present invention. First, the general structure of the glow plug, generally designated by the reference numeral 10 in FIG. 4, will be briefly described.
The glow plug 10 includes a rod-shaped ceramic heater 11 whose distal end functions as a heat generating portion, and a substantially tubular metal holder 12 that holds the heater 11 at its distal end. A terminal assembly 15, which is formed by penetrating and embedding first and second external connection terminals 13 and 14 in an insulating material such as a synthetic resin material, is fitted and held in the rear end of the holder 12. , and each terminal 13, 14 is connected to a lead portion (described later) made of a conductive ceramic material constituting the heater 11 via metal conductive wires 16, 17 such as a flexible wire.
These metal conductive wires 16 and 17 are used to forcibly protect the heater 11 from mechanical external forces such as various vibrations and tightening torques applied to the respective external connection terminals 13 and 14, and are made with a certain degree of flexibility. Good. Note that 12a is a threaded portion formed on the outer periphery of the holder 12 to be screwed into a threaded hole on the cylinder head side of an engine (not shown).

Further, the terminal assembly 15 has a rod portion 13a disposed on its axis and connected to the conductive wire 16.
a first external connection terminal 13 having on its inner end side
, a second external connection terminal 14 having a cylindrical shape and having a lead piece 14a extending from a part of the inner end thereof and connected to the conductive wire 17; It has an assembly body 15a made of resin molding that insulates between the children 13 and 14 and also has an insulating layer on the outer periphery to integrate them, and this body 15a
A metal tube 15b for connection reinforcement is fitted around the outer periphery of. Then, this metal tube 15b is connected to the holder 12.
The peripheral edge of the rear end opening is caulked with high pressure and buckled along the axial direction, so that the inner side faces the resin main body 15a and the outer side faces the holder 1.
2. It is in a state where it is firmly pressed against the inner wall, and problems caused by external force and thermal contraction can be solved.

Furthermore, 18a and 18b are insulating rings and washers fitted to the second terminal 14 protruding rearward of the holder 12, and 18c is this washer 18b.
Insulating members 18d and 18e fitted on the outer end of the first terminal 13 are spring washers and tightening nuts screwed onto the threaded portion of the outer end of the first terminal 13. And Washiya 18b
By inserting lead wires (not shown) from the battery between the insulating member 18c and between the insulating member 18c and the spring washer 18d, the terminals 13 and 14 are electrically connected to the battery terminal side. connected to. Furthermore, 16a, 17a
is an insulating tube for covering the conducting wires 16 and 17.

Now, according to the present invention, in the glow plug 10 having the above-described structure, the rod-shaped ceramic heater 11 held at the tip of the holder 12 is arranged in a U-shape having a small cross-sectional area, as is clear from FIGS. 1 and 5. A shaped heat generating part 20 and a tapered part 20 formed at both ends thereof so that the cross-sectional area gradually increases.
A pair of external connection lead portions 21 and 22 having a large cross-sectional area and extending parallel to each other via a and 20b are formed integrally with a conductive ceramic material, so that the entire structure is approximately It is configured to have a U-shape, and the cross-sectional area ratio ε (=SH/SL) of the cross-sectional area SH of the U-shaped heat generating part 20 and the cross-sectional area SL of the lead parts 21 and 22 is 0.15≦ The thickness of the U-shaped heat generating part 20 is formed to be thinner than the rear lead parts 21 and 22 so that ε≦0.6, and the pair of lead parts 21 and 22 are formed on the heat generating part 20 side. A part of the heat generating part protrudes from the tip of the holder 12 and is held through the tip of the holder 12, and the length of the protrusion depends on the specifications of the cylinder head (not shown) to which it is attached. 20 is characterized in that it is configured so that it faces the area that requires the highest temperature heating state. In this embodiment, the outer surfaces of both the lead parts 21 and 22 are used as insulating layers to be bonded and held to the tip of the holder 12 via the insulating coating layers 23 and 24, and the rear ends of each lead part 21 and 22 are Metal conductor wire 1
First and second external connection terminals 13, which are held in an insulated state at the rear end of the holder 12 via terminals 6 and 17,
14 is shown.

To explain this in detail, the ceramic heater 11 is
As is clear from FIG. 1, the heating section 20 is U-shaped and is made of a conductive ceramic material that has a small diameter and a thinner wall than the rear lead sections 21 and 22 as described above. is provided at the tip portion through tapered portions 20a and 20b whose cross-sectional area gradually changes, and it is possible to obtain a concentrated and rapid red-hot glow only at the tip side (heating portion 20) of the heater 11. be. The resulting rapid temperature rise enables it to demonstrate its performance as a fast-heating type, improving the engine's startability, as well as appropriately controlling the saturation temperature with its own heat generation characteristics, allowing it to last for a long time. Afterglow can also be achieved. Further, the tapered portion 20a described above,
Reference numeral 20b is for gradually lowering the thermal distribution gradient and connecting the heat generating portions 20 to the lead portions 21 and 22 held on the holder 12 side, thereby improving heat resistance strength and the like. Furthermore, the lead portion 21,
22 is the heat generating part 20 without itself becoming red hot.
is held with a required amount of protrusion from the tip of the holder 12, and these lead portions 21, 22
Appropriately select the holding position at the tip of the holder 12,
By adjusting the protruding length of the heat generating part 20, the red-hot heat generating part 20 can be freely selected to face the necessary part according to the specifications and installation condition on the cylinder head side, which is the side to which it is installed, and it can be used for secondary combustion. This makes it possible to efficiently and reliably raise the temperature of areas that require heating, such as indoors. Of course, these lead parts 21 and 22 do not contribute to the heat generation characteristics of the heater 11, and there is no problem in the function of the heater 11 no matter which position the lead parts 21 and 22 are held on the holder 12 side. In addition, in such a heater 11, the heat generating part 20 on the tip side, the tapered part 20
a, 20b, the range of the rear lead parts 21, 22,
In this embodiment, the heat generating part 20 is Protrusion length (A+B+D)
The case is shown below. This protrusion length can be freely changed by arbitrarily selecting the above-mentioned D.

Here, in such a heater 11, a slit 25 is formed in the center thereof from the heat generating part 20 to between the lead parts 21 and 22 along the longitudinal direction. Further, within this slit 25, at least the holder 1 between the lead portions 21 and 22 on the rear end side
An insulating sheet 26 made of, for example, an insulating ceramic material is interposed in a portion corresponding to the tip end of the holder 12, and is integrally joined to the lead portions 21 and 22 made of a conductive ceramic material. The structure is such that the combustion pressure and combustion heat are reliably sealed and prevented from leaking.

Further, tapered portions 20a are provided at both ends of the heat generating portion 20,
An insulating coating layer 2 is provided on the outer circumferential surface of the lead portions 21 and 22, which are integrally formed of a conductive ceramic material via the conductive ceramic material 20b, at approximately the center in the longitudinal direction.
3 and 24 (formed by laminating a silver/palladium layer on the surface), and both these layers 23 and 2
4 and a silver/palladium layer formed on its surface, this ceramic heater 11 is bonded and fixed to the tip of the holder 12 by silver brazing or the like. In this case, it is preferable to form a silver/palladium layer on the bonding surface side of the holder 12 as well, if necessary, but it goes without saying that this is not limiting.

On the other hand, each lead part 21, 22 has electrode extraction ends 21a, 22a extending rearward from the rear end part.
and each of these electrode extraction ends 21a, 22a
The first and second external connection terminals 13 and 14
The ends of the metal conductive wires 16, 17 drawn out from the heater 11 are electrically connected via the terminal caps 27, 28, thereby causing current to flow within the heater 11 as indicated by the arrows in FIG. In addition, 21
Terminal caps 27, 22b and 22b are fitted to the respective electrode extraction ends 21a and 22a, respectively.
28. By applying nickel paste to the surface of the metallized layer and baking it at high temperature, the metal material can be properly and reliably joined to the ceramic material. That is, terminal cap 27,2
8 is formed to match the shape etc. of the electrode lead-out ends 21a, 22a at the rear end of the heater 11, and is welded and joined by silver brazing etc. while being fitted into each electrode lead-out end 21a, 22a. Ru. In addition, the conductor 1 connected to each of these caps 27 and 28
As shown in FIG. 1, caps 6 and 17 are simultaneously joined during brazing with their tip flange portions locked inside the end surfaces of caps 27 and 28, thereby forming a heater assembly. Of course, the other ends of these conductive wires 16 and 17 are connected and fixed to the rod portions 13a and lead pieces 14a of the first and second external connection terminals 13 and 14 of the terminal assembly 15 by spot welding or the like. . In addition, 29 in the figure
is a sealing sheet made of asbestos, rubber, etc., which is interposed on the outer end side of the terminal assembly 15 at the rear end opening portion of the holder 12 and mechanically seals this portion.

According to the two-pole, two-wire type glow plug 10 having such a configuration, the electrode lead-out portion from the ceramic heater 11 is connected to the holder 12 which is remote from the heat generating portion 20.
Since this extraction portion can be maintained at a relatively low temperature, reliability such as heat resistance strength can be significantly improved compared to the conventional method.
In addition, the ceramic heater 11 and holder 1 described above are also included.
2 does not require an electrical ground connection and only requires a simple mechanical connection, so reliability such as bonding strength can be improved.

The above-described ceramic heater 11 can be formed by injecting a conductive ceramic material into a mold in the form of a paste and then firing it, or by electrical discharge machining of a ceramic heater that has been previously formed into a rod shape. After this molding, insulating coating layers 23, 24 (preferably sprayed with alumina, etc.), metallized layers 21b, 22b, etc. are applied to the corresponding lead portions 21, 22b, etc., respectively. 22, the electrode extraction end 2
1a, 22a, and further, a silver/palladium layer may be formed as a post-processing material on the surface thereof as an auxiliary material for connection with the metal holder 12.

Furthermore, as is well known, the ceramic heater 11 molded as described above is fitted into the holder 12 and the outer peripheral surfaces of the lead parts 21 and 22 are fixed by brazing or the like via the insulating layers 23 and 24, respectively. At the same time, the rear ends of the conductors 16 and 17 are attached to the holder 1.
The glow plug 10 is assembled by being connected to the first and second external connection terminals 13 and 14 held at the rear end of the glow plug 2 .

Here, as a conductive ceramic material forming the ceramic heater 11 having a generally U-shaped overall shape, for example, β-sialon (Si ₃ N ₄ . . . 88
%, Al ₂ O ₃ ... 5%, Y ₂ O ₃ ... 7%) or by adjusting the amount of titanium nitride (TiN) added to SiAlON, which has a mixed phase of α and β, conductivity can be obtained. It is preferable to use SiAlON or the like.
In other words, it has been confirmed that when approximately 20% or more of TiN is added to the above-mentioned sialon, it has conductivity due to positive resistance temperature characteristics (so-called conductive sialon), and when more than that is added, the specific resistance value decreases. It is known that the content rate of TiN changes continuously, and the above-mentioned content rate of TiN may be appropriately selected. However, the conductive ceramic material serving as the resistor in the ceramic heater 11 described above is not limited to the above-mentioned Sialon, but the point is that it has stable performance even in high temperature conditions (for example, up to about 1200°C), and has thermal shock resistance etc. Any ceramic material having excellent properties may be used, for example selected from the group of non-oxide conductive materials such as SiC and carbides, borides, nitrides or carbonitrides of elements of group 4a, 5a or 6a of the periodic table. A sialon sintered body containing one or more types of sintered materials and A1 or an A1 compound as a sintering binder is considered.

Further, as the insulating ceramic material forming the above-mentioned insulating sheet 26, similar to the conductive ceramic material forming the ceramic heater 11, by adjusting the amount of titanium nitride (TiN) added, the insulating property can be improved.
The use of SiAlON, which has selectable conductivity, is effective in increasing the bonding strength with the resistor side. However, it is effective in increasing the bonding strength with the resistor side. For example, materials mainly composed of Si ₃ N ₄ , AlN or Al ₂ O ₃ are also conceivable, and of course, insulating materials such as glass may also be used.

According to the configuration according to the present invention described above,
Since the heat generating part 20 made of conductive ceramic material does not contain any foreign matter and is formed to be exposed on the outer surface of the heater 11, the heat generation characteristics are improved and the tip of the heater 11 can quickly become red hot, making it possible to use it as a fast heating type. In addition to being able to demonstrate the functions of This method is advantageous, and has advantages such as being able to be mass-produced and reducing costs.

Furthermore, according to the ceramic heater 11 according to the present invention, the heat generating part 20 and the tapered part 2
Since the specific resistance of the conductive sialon forming the pair of lead parts 21 and 22 that are connected via 0a and 20b can be adjusted by adjusting the amount of titanium nitride added, its thickness can be set freely, and especially in the heat generating part. Reduce the width dimension (cross-sectional area) at the 20th part,
In addition to obtaining rapid heat generation characteristics, it is also possible to achieve long-term afterglow by appropriately controlling the saturation temperature. That is, according to the present invention, the heat generating portion 20 and the tapered portions 20a, 2
By setting the cross-sectional area ratio of the lead parts 21 and 22, which are connected to each other via the lead parts 0b, to a certain range as described above, the saturation temperature can be properly controlled and the saturation temperature can be maintained for a long period of time in addition to the rapid heat generation as described above. This allows for long-lasting afterglow. To explain this in detail, such self-temperature saturation is determined by the cross-sectional area ratio ε( =SH/SL)
is preferably determined within a range that satisfies the conditions required for the heater 11, such as ceramic heater strength, engine startability, temperature increase characteristics, etc. Here, if the heat capacity of the heat generating part 20 described above is reduced, the temperature rise characteristic {see Figure 3 a} will improve, but if the heat capacity is too small, the engine will be cooled by the fuel sprayed at the time of startup, swirl, etc. When the heat capacity is increased, the temperature decreases significantly, deteriorating startability, and the strength is also adversely affected.
The time it takes to reach ℃ is 10 seconds or more, and the temperature rise characteristics deteriorate. Furthermore, if the saturation temperature exceeds 1100°C in Figure b, it will cause a problem in terms of strength. Considering these conditions, the above-mentioned cross-sectional area ratio ε is 0.15≦ε(=SH/SL)≦0.6 It is good if the relationship is satisfied. Considering the various conditions described above within this range, ε=0.3 (indicated by P in FIG. 3) becomes an ideal value.

That is, various studies have been conducted on the heater 11.
As a result of the development, by setting the heat generating part 20 on the tip side to have the cross-sectional area ratio ε obtained as described above with respect to the rear lead parts 21 and 22, only the heat generating part 20 can be used when electricity is applied. By concentrating on the heater 11 and making only that part red hot, rapid temperature rise characteristics are obtained, and the required saturation temperature characteristics are obtained with a simple structure. , heater 11 to holder 12
The holding positions of the lead parts 21 and 22 can be arbitrarily selected, and even if the parts that require high-temperature heating differ depending on the type of engine when installed on the cylinder head, it can be easily handled. This makes it possible to achieve the following advantages.

In addition, in the ceramic heater 11 according to the present invention, since the resistor is integrally formed with conductive ceramic material, it has better moldability and durability than conventional metal heating wires. Furthermore, the conductive sialon mentioned above is
It also has advantages such as having a large positive temperature coefficient of resistance and being advantageous in terms of self-temperature saturation.

Note that the heat generating section 2 constituting the heater 11 described above
The thickness of each part such as 0, lead parts 21, 22, etc. can be freely adjusted during molding, and thereby the resistance value can be freely selected. For example, in this embodiment, as is clear from FIGS. 2a and 2b, the heater 11 as a whole has a circular cross section of 5φ, the heat generating part 20 has a circular cross section of 3φ (the slit 25 is 1 mm), and the length is 50 mm (the electrode Take-out end 26
(excluding the length of 5 mm), the length of the heat generating part 20 is 10 mm, and the insulating coating layers 23 and 24 are formed over a length of 20 mm from a position 25 mm from the tip. This reduces the heat capacity of the heat generating part 20 to the lead parts 21 and 2.
It has been confirmed through experiments and the like that it is possible to obtain the required resistance value and exhibit the required self-temperature saturation property by making the resistance smaller than that of 2. In this case, the cross-sectional area ratio ε mentioned above is 0.27, which is the ideal value mentioned above.
The value is close to 0.3.

As described above, if the ceramic heater 11 is integrally formed with a conductive ceramic material so as to have a substantially U-shape as a whole, the seventh
The glow plug 10 shown in the figure can exhibit excellent characteristics. That is, according to the glow plug 10 according to the present invention, as shown by the solid line in the figure, the time to reach 800°C is 5 seconds, and the saturation temperature can be approximately 1050°C with the permissible range of 1200°C or less. has been confirmed by experiment.

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 and changed as appropriate. For example, ceramic heater 1
The shape of 1 is not limited to the round bar shape of the above-mentioned embodiment, but various modifications including a square bar shape etc. can be considered.In short, the heat generating part 20 at the tip thereof is connected to the tapered parts 20a, 20b. In comparison with the lead parts 21 and 22 which are connected to each other via the lead parts 21 and 22, the lead parts 21 and 22 may be formed to have a small diameter or a thin wall and have a cross-sectional area ratio within the above-mentioned range.

Further, in the above-described embodiment, the glow plug 10 having the bipolar ceramic heater 11 is
The first terminal assembly 15 provided at the rear end of the holder 12
Although a case has been described in which the structure is connected to the outside using the second external connection terminals 13 and 14, the present invention is not limited to this, and as shown in FIG.
External connection terminal 1 with only one lead portion 21 held at the rear end of holder 12 via insulating bushing 60
It will be easily understood that the glow plug 10 may have a structure in which the lead portion 3 is externally connected and the other lead portion 22 is grounded to the holder 12 side. Here, in this embodiment, the metal conductor wire 17
is fitted onto the outer periphery of the insulating bushing 60 and the holder 1
Although the terminal piece 61 extending from the metal pipe 60a connected to the holder 12 is used for connection, the connection is not limited to this, and various modifications can be considered as the means for connecting to the holder 12. .

[Effect of idea]

As explained above, according to the present invention, the rod-shaped ceramic heater which is held through the tip of the holder is formed with a U-shaped heat generating part having a small cross-sectional area and a gradually increasing cross-sectional area at both ends thereof. A pair of external connection lead parts having a large cross-sectional area are connected to each other via a tapered part and extend parallel to the rear, and are integrally formed of a conductive ceramic material. Cross-sectional area ratio ε between the cross-sectional area SH at the U-shaped heating part and the cross-sectional area SL at the lead part
(=SH/SL) is within the range of 0.15≦ε≦0.6. A portion of the lead protrudes from the holder tip and is held through the holder tip, and the protruding length of this external connection lead is set according to the specifications of the cylinder head to which it is attached. Despite the simple and inexpensive configuration, the U-shaped heat generating part exposed on the surface of the heater tip side can be appropriately compared with the rear lead part that is penetrated and held by the holder. Since it is made of conductive ceramic material with a high cross-sectional area ratio, it has sufficient heat resistance, and when electricity is applied, the U-shaped heat generating part on the tip side of the heater can be heated quickly and efficiently. If done well, this rapid temperature rise will demonstrate the performance of a fast heating type, improving engine startability, and reducing the heat capacity of the heat generating part at the tip made of this conductive ceramic material will reduce self-temperature saturation. It has various excellent practical effects, such as achieving long-term afterglow performance as a countermeasure against engine exhaust and noise, and improving the durability of heat-generating parts. be. In addition, according to the present invention, by holding the lead part that does not heat up at the tip of the holder with the required protrusion length set according to the specifications of the cylinder head to which it is attached, the heat generating part that becomes red hot can be You can freely choose to expose the electrode to the required area, and by taking out the electrode in a two-pole, two-wire structure from the rear end of the heater inside the holder, the thermal effect on the extraction part can be reduced and reliability can be improved. There are also other advantages.

[Brief explanation of the drawing]

Fig. 1 is an enlarged cross-sectional view of essential parts showing an embodiment of a glow plug for a diesel engine according to the present invention, and Fig. 2 a and b are lines a-a and b-b of Fig. 1.
Line sectional view, Figures 3a and 3b are characteristic diagrams for selecting the cross-sectional area ratio between the heat generating part and the lead part in the ceramic heater, Figure 4 is a schematic longitudinal sectional view of the whole, and Figure 5
The figure is a schematic perspective view showing the main part of the ceramic heater, and Figures 6a and b are a-a in Figure 5,
FIG. 7 is a characteristic diagram showing the temperature characteristics of the ceramic heater, and FIG. 8 is a diagram showing another embodiment of the present invention. 10...Glow plug for diesel engine,
DESCRIPTION OF SYMBOLS 11... Rod-shaped ceramic heater, 12... Hollow holder, 13, 14... First and second external connection terminals, 15... Terminal assembly, 16, 17... Metal conductor wire, 20... Conductive ceramic Heat generating part made of material, 21, 22... External connection lead part made of conductive ceramic material, 21a, 22a... Electrode extraction end, 23, 24... Insulating coating layer (insulating layer), 25... Slit, 26... …Insulating sheet,
27, 28...Terminal cap.

Claims (1)

[Claims for Utility Model Registration] (1) A rod-shaped ceramic heater is provided which is held by penetrating the tip of a hollow holder. A pair of external connection lead parts having a large cross-sectional area are integrally formed from a conductive ceramic material, and are connected through a tapered part formed to gradually increase and extend parallel to the rear. In addition, the cross-sectional area ratio ε (=SH/SL) of the cross-sectional area SH of the U-shaped heating part and the cross-sectional area SL of the lead part is 0.15.
≦ε≦0.6, and the pair of external connection lead portions are inserted into the hollow holder tip portion with a portion of the heat generating portion side thereof protruding from the tip portion of the hollow holder. A glow plug for a diesel engine, characterized in that the protruding length of the external connection lead portion is set according to the specifications of the cylinder head to which it is attached. (2) Ceramic heaters are βsialon or α
A request for registration of a utility model characterized in that the product is integrally formed of a ceramic material whose insulation and conductivity can be selected by adjusting the amount of titanium nitride added to sialon, which is a mixed phase of β and β. A glow plug for a diesel engine according to item 1.