JPH0795465B2 - Glow plug for diesel engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a glow plug used for preheating a sub-combustion chamber or a combustion chamber of a diesel engine. The present invention relates to an improvement of a glow plug for a diesel engine equipped with a ceramic heater having self-saturation capable of achieving glowing.

[Conventional technology]

Generally, diesel engines have poor startability at low temperatures, so a glow plug is installed in the auxiliary combustion chamber or combustion chamber.
It employs a method to improve engine startability by raising the intake air temperature or using it as an ignition source due to energization and heat generation. As a glow plug of this type, a so-called sheath type is generally used in which a heat-resistant insulating powder is conventionally filled in a metal sheath and a coiled heating wire made of iron chromium, nickel or the like is embedded therein. In addition to this, JP-A-57-
As disclosed in Japanese Patent No. 41523, there is also known 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 an insulating property. Such a ceramic heater type is
Compared to the sheath type that heats indirectly through heat-resistant insulating powder and sheath, it can improve heat transfer efficiency and is excellent in heat generation characteristics. Due to its thermal performance, it has been actively used in recent years.

[Problems to be solved by the invention]

However, the above-mentioned ceramic heater type glow plug has a structure in which a heating wire made of metal such as tungsten is embedded inside an insulating ceramic material such as silicon nitride, and the coefficient of thermal expansion between these members is different. For,
In particular, a rapid temperature rise during heat generation and repeated use thereof may reduce the durability of the ceramic heater. Therefore, there is a problem in terms of reliability such as heat resistance, and there is a drawback that the cost is further increased.

In order to solve the above problems, a ceramic heater structure in which a heating wire is made of a conductive ceramic material having a thermal expansion coefficient substantially equal to that of an insulating ceramic material is disclosed in, for example, Japanese Patent Laid-Open No.
It is proposed by the 60-9085 gazette and the 60-60784 gazette. However, both of them still have problems in terms of structure and function 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 to be 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. In addition, there is a problem that the forming process is complicated. In the latter, the heating element is exposed on the surface of the heater and has a function of rapid heating, while the heating element is formed by a laminated structure of members having a U shape.
Moreover, since both ends of the electrode are only led to the rear end of the heater, the structure for taking out the electrode is complicated and the cost is increased.

Further, in recent years, in this kind of glow plug, the startability of the diesel engine is improved and the durability against the high temperature of the usage condition accompanying the turbocharging is further maintained, and the glow plug is kept energized for a certain time after the engine is started. As a result, there is a great market demand for adopting the so-called afterglow method, which is to enable smooth and appropriate combustion inside the engine and take measures against exhaust and noise. Moreover, it is necessary to make this afterglow time as long as possible (for example, about 10 minutes). In order to prolong such afterglow, the electric power supplied to the heating element is self-controlled to significantly improve the heating characteristics, prevent overheating in the heater portion, and maintain its saturation temperature at an appropriate level. It is also necessary to have a self-temperature saturation function that can be maintained below the temperature. Therefore, in consideration of these points, the advent of an inexpensive glow plug that has fast heating property, self-temperature saturation property, and the like, and is excellent in reliability such as heat resistance is desired.

[Means for solving problems]

In order to solve the above problems, in the present invention, A. The ceramic heater is held at the tip of the hollow holder with one end projected to the outside.

B. In this ceramic heater, a U-shaped heat generating portion and a pair of lead portions extending rearward from both ends of the U-shaped heat generating portion are integrally formed of a conductive ceramic material.

C. The outer surface of the one lead portion is electrically conductive, and the outer surface of the other lead portion is joined and held in the holder via an insulating layer.

D. For the composition of β-sialon represented by Si _6-Z Al _Z o _Z N _{8-Z in} which z is more than 0 and less than 1
It is formed by a sialon sintered body to which Ti carbonitride solid solution of more than 5 vol.% And less than 70 vol.% Is added.

It adopted the technical means.

In the present invention, the reason why the Ti carbonitride solid solution is added as the conductive compound is as follows. That is, IV a, V
Sialon sinters with electrical conductivity can be obtained from a, VI a group carbides, nitrides, borides, etc., but the sinterability by normal pressure sintering or gas pressure sintering and the acid resistance of the sintered body can be obtained. This is because Ti is limited to carbides and nitrides in consideration of the chemical conversion property. In this case, the use of a carbonitride solid solution instead of a single carbide or nitride makes it possible to obtain sialon sintered bodies having various electrical resistivities by changing the ratio of C and N in the solid solution. Because.

In addition, the addition amount of Ti carbonitride solid solution exceeds 25 vol.% And 70 vo
Below 1%, it is inconvenient if the content of 25vol.% or less does not show a conductive path due to mutual contact of Ti carbonitride solid solution particles with each other and does not show conductivity. If it exceeds 25 vol.%, It exhibits conductivity due to the positive resistance-temperature characteristic, and the electrical resistivity changes continuously as the amount of addition increases.
On the other hand, when it is 70 vol.% Or more, it is inconvenient because the original properties of Sialon such as oxidation resistance and high temperature strength are significantly impaired. Preferably, it is more than 30 vol.% And less than 50 vol.%.

Next, z in Si _6-Z Al _Z O _Z N _8-Z is set to be more than 0 and less than 1 because a sintered body having a high strength can be obtained within this range. Specifically, Si ₃ N ₄ powder, AlN polytype powder (crystal type 21R), Al ₂ O ₃ powder, and Y ₂ O ₃ powder were used. 70 vol.% Is added and mixed, and after molding, it is sintered at 1700 to 1900 ° C to obtain a conductive sialon sintered body.

〔Example〕

FIG. 1 is a vertical sectional view showing an embodiment of the present invention. In the figure, a schematic structure of a glow plug, generally designated by reference numeral 10, will be briefly described. The glow plug 10 has a rod-shaped ceramic heater 11 whose front end side functions as a heating element, and a substantially tubular metal holder 12 which holds the ceramic heater 11 at the front end. An external connection terminal 14 is concentrically fitted to the rear end of the holder 12 via an insulating bush 13 made of a synthetic resin material or the like, and the external connection terminal 14 is flexible with the lead portion 22 in the ceramic heater 11. Connection is made via a metal conducting wire 15 such as a wire and a terminal cap 15a. Reference numeral 13a is a metal pipe, which is integrally fitted to the outer peripheral portion of the insulating bush 13 and the rear end portion of the holder 12 is caulked at the time of assembly, so that it is buckled and deformed in the axial direction by high pressing force, The insulating bush 13 is integrated on the holder 12 side with a required mechanical strength to eliminate the influence of temperature. Also 16a, 16
b and 16c are an insulating ring screwed to the screw portion on the rear end side of the external connection terminal 14, a nut for fixing, and a nut for tightening the external lead. The lead wire from the battery (not shown) is nutd. By sandwiching between 16b and 16c, the external connection terminal 14 is electrically connected to the battery terminal. On the other hand, by screwing the screw portion 12a of the outer peripheral portion of the holder 12 into a screw hole (not shown) provided in the cylinder head of the engine, the grounding of the ceramic heater 11 is achieved at the same time as the earth connection is made. Alternatively, it is arranged so as to project into the combustion chamber. For the ceramic heater 11, the external connection terminal 14
Are connected via the metal lead wire 15, which is an external connection terminal.
This is to protect the ceramic heater 11 from the mechanical strength such as various vibrations and tightening torque applied to the 14 in terms of strength. As the material of the metal conductor 15, it is preferable to use a material having some 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. In FIG. 2, the heat generating portion 20 is formed to have a smaller diameter than the lead portions 21 and 22 and has a small diameter, and the central portion of the ceramic heater 11 extends in the longitudinal direction from the heat generating portion 20 to the lead portions 21 and 22. A slit 25 is formed in the. Further, the lead portions 21 and 22 formed integrally with the heat generating portion 20 by a conductive ceramic material.
Among these, a metal metallization layer 23 is formed on the outer peripheral surface of one lead portion 21, and an insulating coating layer 24 is formed on the other lead portion 22. The metal metallization layer 23
A nickel plating layer (not shown) is laminated on the surface of the insulating coating layer 24. Thus, the ceramic heater 11 is joined and fixed to the tip of the holder 12 as shown in FIG. 1 by means of, for example, silver brazing by means of the layers 23 and 24 and the nickel plating layer on the surface thereof. Of. In this case, a nickel plating layer can be formed on the joint surface side of the holder 12 if necessary.

Next, the ceramic heater 11 is formed by kneading the conductive sialon powder with a thermoplastic resin or the like, injection-molding it into a predetermined mold, and then firing the molded body, or preliminarily forming it into a rod shape. The ceramic heater can be formed into a desired shape by electric discharge machining or cutting. After the above-mentioned molding, a metal metallization layer 23, an insulating coating layer 24 (which may be sprayed with alumina, etc.) are formed on the outer peripheral surfaces of the corresponding lead portions 21 and 22, respectively, and the metal shown in FIG. A nickel plating layer as an auxiliary material for connection with the holder 12 may be formed as a post process. Reference numeral 27 in FIG. 2 denotes a metal metallization layer formed on the electrode extraction end portion 26, and of course a nickel plating layer similar to the above is formed on the surface thereof, and the metal conductor 15 is formed on the metal plating layer through the terminal cap 15a. Can be connected to form a heater assembly. 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 portions 21 and 22 are separated by the metal metallized layer 23 and the insulating coating layer 24, respectively. The glow plug 10 is fixed by attachment and the rear end of the metal conductor 15 is connected to the external connection terminal 14 side held by the rear end of the holder 12 to complete the assembly of the glow plug 10.

The thickness of each part of the ceramic heater 11 can be freely adjusted at the time of molding, and the resistance value can be freely selected by this. For example, in the present embodiment, when the entire ceramic heater 11 has a circular cross section of 5 mmφ and the heating portion 20 has a diameter of 3 mmφ, and the length is 50 mm (excluding the electrode lead-out end 26 having a length of 5 mm) In addition, the length of the heat generating part 20 is 10 mm, and the length 20 mm from the position 25 mm from the tip.
The metal metallization layer 23 and the insulating coating layer 24 are formed over a thickness of mm. It has been confirmed by experiments that the heat capacity of the heat generating portion 20 can be made smaller than that of the lead portions 21 and 22 by this, and the required self-temperature saturation can be achieved by obtaining the required resistance value. Further, although not described in the above-mentioned embodiment, when used in an environment where the usage conditions are severe, the outer surface of the ceramic heater 11 is coated with a protective film having oxidation resistance particularly on the heating portion 20 by vapor deposition or the like. If formed in this way, greater durability can be expected.

As a result of assembling and experimenting with the above-mentioned ceramic heater 11 as the glow plug 10, as shown in FIG. 3A, it is possible to reach 800 ° C. for 3.5 seconds, and to set the saturation temperature to about 1100 ° C. with the allowable range 1200 ° C. It was confirmed.

By the way, in the glow plug 10 having the above-described structure, as is apparent from FIGS. 1 and 2, the slit 25 formed along the longitudinal direction of the ceramic heater 11 allows the internal space of the holder 12 to be made ceramic. The heater 11 is in communication with the engine combustion chamber and the like facing the heater 11. Therefore, it is necessary to prevent the combustion pressure from leaking to the outside of the engine at the time of an explosion in the combustion chamber. Therefore, in this embodiment, the first
As shown in the figure, at the rear end opening portion of the holder 12, an insulating bushing 13 integrally formed with the external connection terminal 14 is provided on the outer end side thereof with a sealing sheet 28 made of, for example, asbestos or rubber interposed therebetween. Is used to mechanically seal. However, various arrangement positions and sealing methods of such a seal portion are conceivable. For example, an O-ring or the like for sealing between the holder 12 and the inner end side of the insulating bush 13 may be interposed. .

FIG. 4 is a longitudinal sectional view of an essential part showing another embodiment of the present invention, in which the same parts are designated by the same reference numerals as those in FIGS. 1 and 2. In FIG. 4, 30 is an insulating sheet,
For example, using an insulating ceramic material, the ceramic heater 11
At least the lead part of the part corresponding to the tip of the holder 12
Join them together between 21,22. With this configuration, the slit 25 is closed and sealed by the holder 12 portion, the combustion pressure of the engine is sealed, and leakage to the outside is prevented. 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-described embodiment can be omitted, which is an advantage. large.

Here, the insulating ceramic material described above is the same as the conductive ceramic material forming the ceramic heater 11,
It is advisable to use a sialon whose insulation and conductivity can be selected by adjusting the amount of i-carbonitride solid solution added. If such a material is selected, the insulating sheet 30 can be formed of the same material that has substantially the same coefficient of thermal expansion as the resistor side, and its bonding strength is increased to ensure reliability such as heat resistance. obtain. In order to join the members made of insulating and conductive ceramic material with Sialon as described above, sintering is performed with an oxide sintering aid such as Y ₂ O ₃ interposed, and It is possible to firmly bond with the diffusion layer formed, but of course the general method of bonding ceramic materials is the halogen compound method, brazing method,
A solid phase bonding method may be used. Further, the insulating ceramic material forming the insulating sheet 30 is mainly made of, for example, SiC, Si ₃ N ₄ , AlN or Al ₂ O _3, which has excellent heat resistance and is excellent in terms of bonding strength with the conductive ceramic material. It may be used as a component, and may be an insulating material such as glass. In particular, since the above-mentioned insulating sheet 30 interposed portion is the rear end side away from the heat generating portion 20 of the ceramic heater 11, even if the reliability of the joint portion is somewhat lowered, there is no practical problem.

It should be noted 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 appropriately modified or changed. For example, the shape of the ceramic heater 11 is not limited to the round bar shape in the above-mentioned embodiment, and the rectangular bar body having a rectangular cross section shown in FIG. Obviously, it may have an elliptical shape as shown in (b).

Furthermore, in the above-described embodiment, in order to bond and fix the ceramic heater 11 while holding it at the tip of the holder 12,
The case where a metal metallization layer 23 is formed on one lead portion 21 and an insulating coating layer 24 is formed on the other as a conductive layer and an insulating layer, respectively, and brazing is performed, but the present invention is not limited to this. A glass layer may be formed on each of the outer peripheral surfaces of the lead portions 21 and 22 of the ceramic heater 11 so as to be brazed to the holder 12 side. When the above-described joining method using the glass layer and the brazing material layer is adopted, a part of the glass layer is exposed on the lead portion side electrically connected to the holder 12 side so as to expose the part. It may be formed by removing it, and a conductive state may be secured through the brazing material layer.

〔The invention's effect〕

Since the glow plug for a diesel engine of the present invention has the configuration as described above, the following effects can be obtained.

(1) Despite the simple structure, the heat-generating part is exposed on the outer surface of the heater, so it achieves quicker and more reliable red heat at the tip compared to the conventional type, and exhibits the function as a quick-heat type. it can.

(2) Since the thermal expansion coefficient of the resistor and the insulator forming the heat generating portion and the lead portion can be made substantially equal, the joint strength of the resistor can be increased and even if the temperature rises rapidly when the heater heats up, cracks occur. No accidents such as these occur, and reliability such as heat resistance is secured.

(3) Since the heat capacity of the exothermic part 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 entire structure is simple, molding and assembly are easy, and productivity is extremely high.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, and FIG.
FIG. 3 is an enlarged perspective view showing the ceramic heater in the drawing, FIG. 3 is a view showing temperature characteristics of the ceramic heater, FIG. 4 is a longitudinal sectional view of an essential part showing another embodiment of the present invention, FIG. 5 and FIG.
(A) and (b) are respectively a perspective view and a cross-sectional view of a ceramic heater showing still another embodiment. 11: Ceramic heater, 12: Holder, 20: Heat generating part, 21, 22: Lead part, 25: Slit, 30: Insulation sheet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koji Hatanaka, 2-8-2, Hachiman, Kawashima-cho, Hiki-gun, Saitama Prefecture (56) References JP-A-60-254586 (JP, A) JP-A-59-96692 (JP) , A) Japanese Unexamined Patent Publication No. 59-58773 (JP, A) Actual development No. 62-202792 (JP, U)

Claims (7)

[Claims] 1. A ceramic heater is held at the tip of a hollow holder with one end protruding outward, and the ceramic heater extends rearward from a U-shaped heating portion and both ends of the U-shaped heating portion. The pair of lead portions provided are integrally formed of a conductive ceramic material, and the outer surface of the one lead portion is joined and held in the holder by the conductive layer and the other lead portion outer surface by an insulating layer. Together with the conductive ceramic material, a z-type β-sialon represented by Si _6-Z Al _Z O _Z N _8-Z
70vol over 25vol.% For the composition of over 0 and under 1.
A glow plug for a diesel engine, which is formed of a sialon sintered body to which a carbonitride solid solution containing less than 1% of Ti is added. 2. The glow plug for a diesel engine according to claim 1, wherein the thickness of the U-shaped heat generating portion constituting the ceramic heater is smaller than the 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 metal metallized layer and the insulating layer is an insulating coating layer. 4. The ceramic sheet according to claim 1, wherein an insulating sheet for sealing combustion pressure is integrally interposed between a pair of lead portions of at least a portion corresponding to the tip of the holder of the ceramic heater. A glow plug for a diesel engine according to Crab. 5. A method in which one lead portion is electrically connected to a holder through a conductive layer, and the other lead portion and an external connection terminal held at a rear end portion of the holder are connected through a metal conductor wire. A glow plug for a diesel engine according to any one of claims 1 to 4. 6. The grain boundary layer of the sialon sintered body is Y, Si, O, N, Al.
The glow plug for a diesel engine according to any one of claims 1 to 5, wherein the glow plug is amorphous and contains. 7. The diesel engine according to claim 1, wherein the sialon sintered body has an electric resistivity at room temperature of 1 Ω · cm or less and a positive temperature coefficient of resistance. Glow plug.