JP2845256B2 - Ceramic heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heater, for example, a ceramic heater used for a ceramic glow plug.

[0002]

2. Description of the Related Art Conventionally, ceramic heaters used for ceramic glow plugs are disclosed in, for example,
As disclosed in Japanese Patent No. 126989, a high-melting point metal such as a tungsten wire is disposed in an insulating ceramic body as a heating element, and heat can be generated by flowing a current as described in Japanese Patent Application Laid-Open No. 1-317170. There is a conductive ceramic body and a lead wire for supplying a current to the conductive ceramic body embedded in an insulating ceramic body.

[0003]

However, the method disclosed in Japanese Patent Application Laid-Open No. 55-126989 has a problem that since the heating element is made of metal, disconnection occurs due to a rapid temperature rise or the like.

[0004] Therefore, as in JP-A-1-317170, it is desired to employ a conductive ceramic body as a heating element. By the way, as a method of molding the ceramic heater, conventionally, the ceramic heater is molded by injection molding.

FIG. 8 is a sectional view showing a state in which the conductive ceramic body set in the injection molding die is set in the injection molding die. That is, in FIG. 8, a heating element including a conductive ceramic body 1 and a lead wire 2 made of tungsten, which is a conductive member electrically connected to the conductive ceramic body 1, is formed by injection molding dies 3a and 3b. Installed in space R. Then, from injection port 4,
The ceramic heater is formed by injecting the slurry-like insulating ceramic. And then
By firing the formed product, a ceramic heater is obtained.

However, when the insulating ceramic is injected, it is injected under high-temperature and high-pressure conditions. Therefore, the insulating ceramic directly collides near the conductive portion 5 between the conductive ceramic body 1 and the lead wire 2. However, there is a problem that the conductive ceramic body 1 is deformed.

FIG. 9 shows how the conductive ceramic body 1 is deformed. That is, as shown in FIG. 9, the conductive ceramic body 1 near the conducting portion 5 is injected by the injection of the insulating ceramic.
The insulating ceramic body 6 around the conductive ceramic body 1 has a very small wall pressure because the peeling part 1a is not formed due to the peeling and the peeling part 1a. 6 is exposed on the surface. Therefore, when this ceramic heater is used, there is a problem that insulation failure occurs.

The present invention has been made in view of the above problems, and has as its object to provide a ceramic heater in which a conductive ceramic body is less deformed and insulation failure does not occur.

[0009]

Therefore, according to the present invention, there is provided an insulating ceramic body, a conductive ceramic body embedded in the insulating ceramic body and capable of generating heat by passing an electric current, and a conductive ceramic body. A ceramic heater comprising an electrically conductive member, wherein the conductive ceramic body is provided with a conductive member near a conductive portion between the conductive ceramic member embedded in the insulating ceramic member and the conductive member. Ceramic body is conductive ceramic body
The ceramic heater is formed in a substantially tapered shape so as to become thinner according to the end surface of the ceramic heater.

[0010]

According to the above construction, the conductive ceramic body at the conductive portion between the conductive ceramic body and the conductive member is electrically conductive.
Tapered so that it becomes thinner according to the end face of the conductive ceramic body
Since the conductive ceramic body is deformed in the conductive portion, the thickness of the insulating ceramic body in the conductive portion can be made larger than when the conductive ceramic body is not tapered. Even if the conductive ceramic body is deformed, the conductive ceramic body is not exposed on the surface of the insulating ceramic body.

[0011]

According to the present invention, since the conductive ceramic body can be prevented from being exposed on the surface of the insulating ceramic body, deformation of the conductive ceramic body is small and insulation failure does not occur. A ceramic heater was obtained.

[0012]

The present invention will be described below with reference to specific examples.
FIG. 1 is a cross-sectional view showing one embodiment in which the ceramic heater of the present invention is used for a ceramic glow plug 10. As shown in FIG.

As shown in FIG. 1, this glow plug 10
Is provided with a ceramic heater 12 at one end.
The ceramic heater 12 has a substantially U-shaped conductive ceramic body 16 inside a distal end of an insulating ceramic body 14 having a substantially circular cross section.
Are embedded at one end of lead wires 18a and 18b made of tungsten as a conductive member.

An outer peripheral surface of the ceramic heater 12 is joined to one end of a cylindrical metal housing 22 via a metal pipe 20. Here, the ceramic heater 12
The outer peripheral surface of the insulating ceramic body 14 and the metal pipe 20 are joined by nickel plating on the outer surface of the insulating ceramic body 14 and then brazing. The metal pipe 20 and the metal housing 22 are connected by brazing.

The other end of the lead wire 18a extends to the base end of the insulating ceramic body 14 and is fitted to the base end.
4, the lead wire 18a is connected to a power source (not shown) via the metal cap 24, the nickel wire 26, and the center shaft 28.

The other end of the lead wire 18b is connected to the metal pipe 20 to be grounded. FIG. 2 is an enlarged view of a main part of the ceramic heater 12 of the first embodiment. FIG. 3 is a sectional view taken along the line AA of FIG.

The ceramic heater 12 includes a conductive ceramic body 16 made of, for example, molybdenum silicide or the like and a lead wire 18 made of a conductive member in an insulating ceramic body 14 made of, for example, silicon nitride or the like having a substantially circular cross section.
a and 18b are embedded.

The conductive ceramic body 16 is made of a conductive ceramic having a substantially U-shaped cross section having a semicircular shape, and ends 16a and 16b which are substantially U-shaped conductive portions of the conductive ceramic body 16. One ends of lead wires 18a and 18b made of tungsten are buried.

In the first embodiment, the end portions 16a and 16b, which are conductive portions between the conductive ceramic body 16 and the lead wires 18a and 18b, have conductive portions as shown in FIGS. Tapered portions 30a, 30a, 3
0b is formed.

Next, a method of manufacturing the ceramic heater of the first embodiment will be described. First, as shown in FIG. 5, the tapered portion 3 of the U-shaped conductive ceramic body 16 before firing is formed.
Ends 16a and 16b at which 0a, 30b are formed
Heating element 3 in which one ends of lead wires 18a and 18b are embedded
2 is set in the space R formed by the molds 3a and 3b.

Next, a ceramic heater before firing is formed in the space R by injecting the insulating ceramic from the injection port 4. Thereafter, the formed ceramic heater before firing is fired to obtain the ceramic heater 12 employed in the first embodiment.

As described above, in the first embodiment, the tapered portion 30 is provided at the end of the conductive ceramic body 16.
Since the a and 30b are provided, the following effects can be obtained.

That is, as shown by arrows A in FIGS. 5 and 6, when the insulating ceramic injected from the injection port 4 collides with the ends 16a, 16b of the conductive ceramic body 16, the ends 16a, 16b Have tapered portions 30a, 30b
Is formed, so that it flows smoothly. For this reason, it is possible to suppress the insulating ceramic from peeling off a part of the conductive ceramic body 16. Furthermore,
By forming the tapered portions 30a and 30b in the conductive ceramic body 16, the end 1 of the conductive ceramic body 16 is formed.
Since the thickness of the insulating ceramic body 14 in 6a and 16b could be increased, even if the peeled part 16c was generated at a part of the end portions 16a and 16b of the conductive ceramic body 16, it would be possible to obtain FIG. As shown, the insulating ceramic body 1
4 could be prevented from reaching the outer surface, and insulation failure during the operation of the ceramic heater 12 could be prevented.

Next, the molding states of the ceramic heater of the first embodiment and the conventional ceramic heater are compared, and the results are shown in Table 1. As a configuration of a conventional ceramic heater,
As shown in FIG. 8, the end of the conductive ceramic body 1 has a shape in which the taper is not formed and the insulating ceramic directly collides with the end face of the conductive ceramic body 1. Example.

As the test conditions, the temperature of the insulating ceramic from the injection port 4 was increased from 155 ° C. by 5 ° C., and the occurrence rate of defects at that time was investigated. In addition, as a defective product, a product that cannot be used as a ceramic heater was determined as a defective product.

[0026]

[Table 1] As is clear from the table, when the injection temperature is lower than 165 ° C., defects occur in both the first embodiment and the comparative example. This is probably because the injection temperature is low and the insulating ceramic is not sufficiently filled in the mold.

When the temperature is further increased, in the case of the comparative example, a peeling portion 1a starts to be generated at the end of the ceramic heating element 1 from about 175 ° C., and a defect starts to be generated when the injection temperature is 180 ° C. . On the other hand, in the case of the first embodiment, at about 185 ° C., at the end of the ceramic heating element, a peeling portion 16c is generated, and the injection temperature is 1 °.
Defects begin to occur at 90 ° C.

Accordingly, the settable temperature condition range at the time of injection of the insulating ceramic is from 165 ° C. to 175 ° C. in the comparative example.
In contrast to about 10.degree. C., which is about 10.degree.
It was about 20 ° C. from 165 ° C. to 185 ° C., which was about twice as large as that of the conventional comparative example.

The specific state of the peeled portion is as shown in FIGS. In the above embodiment, the shape of the tapered portion formed at the end of the conductive ceramic body was a linear tapered shape as shown in FIG. 2, but the present invention is not limited to this. The conductive ceramic body 32 may have tapered portions 34a and 34b having steps at the ends as shown in FIG. That is, any shape of the tapered portion may be used as long as the thickness of the insulating ceramic body can be increased at the end of the conductive ceramic body.

However, when considering the time of injection of the insulating ceramic, the injected insulating ceramic is
It is preferable that the end of the conductive ceramic body has a tapered shape that smoothly flows, for example, a straight line or an inward curved line.

Further, the angle θ of the tapered portion is preferably 15 ° C. to 60 ° C. as shown in FIG. If the temperature is 15 ° C. or lower, the conductive member cannot be sufficiently held only by the conductive ceramic body, and if the temperature is 60 ° C. or higher, when the insulating ceramic collides with the conductive ceramic body, This is because the insulating ceramic cannot be flowed smoothly, and the end of the conductive ceramic body is greatly deformed, so that a sufficient effect of the present invention cannot be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a ceramic glow plug employing a ceramic heater according to a first embodiment of the present invention.

FIG. 2 is a partially enlarged view of the ceramic heater according to the first embodiment of the present invention.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a side view of FIG. 2;

FIG. 5 is a schematic diagram showing a state where the ceramic heater of the first embodiment is installed in a molding die during injection molding.

FIG. 6 is an explanatory view showing a state of deformation of the conductive ceramic during injection molding of the first embodiment.

FIG. 7 is a partially enlarged view showing another embodiment of the present invention.

FIG. 8 is a schematic diagram showing a state in which a conventional ceramic heater is installed in a molding die during injection molding.

FIG. 9 is an explanatory view showing a state of deformation of a conductive ceramic during conventional injection molding.

[Explanation of symbols]

 Reference Signs List 12 ceramic heater 14 insulating ceramic body 16 conductive ceramic body 16a end 16b end 18a lead 18b lead 30a taper 30b taper

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F23Q 7/00

Claims (1)

(57) [Claims] An insulating ceramic body, a conductive ceramic body embedded in the insulating ceramic body and capable of generating heat by passing an electric current, and a conductive member electrically connected to the conductive ceramic body. in the ceramic heater comprising the electrically conductive ceramic material, wherein said conductive ceramic body is electrically conductive canceller conducting the vicinity of the insulating ceramic said conductive is embedded in the body of the ceramic member and said conductive member
A ceramic heater characterized in that it is formed in a substantially tapered shape so as to become thinner in accordance with an end surface of the mix body .