Patent Application
20170074513
This application claims the benefit of Japanese Patent Application No. 2015-178312, filed Sep. 10, 2015, which is incorporated herein by reference in its entity.
The present invention relates to a ceramic heater and to a glow plug provided with the ceramic heater.
A conventional glow plug used for ignition assistance for internal combustion engines includes a ceramic heater in which a resistor formed of a conductive ceramic is disposed inside a substrate formed of an insulating ceramic. The resistor includes two rod-shaped lead portions, an approximately U-shaped joint portion that joins one end of one of the lead portions to one end of the other lead portion, and electrode portions disposed so as to protrude from the lead portions toward the outer circumferential surface of the substrate. The resistor generates heat when current is supplied to the resistor through the electrode portions. The resistor and substrate used for the ceramic heater are produced from materials each containing a ceramic and a binder (such as a resin). For example, as described in Japanese Patent Application Laid-Open (kokai) No. 2007-240080, a green intermediate molded product that later becomes the resistor in a subsequent step is formed by injection molding of a material powder containing a ceramic and a binder, and the intermediate molded product is subjected to debindering and firing, whereby the resistor is produced.
When a green resistor is placed in a die and then a material such as a ceramic is injected into to the die to form a green substrate such that it surrounds the green resistor, a space not filled with the material may remain near the electrode portions of the lead portions. Such a space becomes a cavity in a completed ceramic heater obtained through the subsequent debindering and firing steps. The presence of such a cavity causes a problem in that cracking starts from the cavity and the ceramic heater is damaged.
This problem is not specific to the case where ceramic heaters are manufactured by injection molding but is common to the cases where ceramic heaters are manufactured by other molding methods usable to form the substrate such as powder press molding in which a powdery material is compressed, sheet laminating molding in which sheet-shaped materials are laminated, and casting. Moreover, this problem is not specific to ceramic heaters used for glow plugs but is common to ceramic heaters used for ignition heaters and various sensors.
The present invention has been made to solve the foregoing problem and can be embodied in the following modes.
(1) According to one mode of the present invention, a ceramic heater is provided. This ceramic heater comprises a substrate containing a ceramic, and a resistor embedded in the substrate and containing another ceramic. The resistor includes two lead portions extending parallel to each other, a joint portion that connects one end of a lead portion to one end of another lead portion, and an electrode portion that is formed integrally with at least one lead portion of the two lead portions and extends in a direction crossing an axial line of the one lead portion. The electrode portion has a base end portion connected to the one lead portion, a distal end portion exposed at an outer surface of the substrate, and a connection portion disposed between the base end portion and the distal end portion and connecting the base end portion and the distal end portion. A cross section of at least one of the base end portion, the distal end portion, and the connection portion has an imaginary plane perpendicular to an extension direction of the electrode portion, and said cross section having a streamline shape. According to the ceramic heater of this mode, the cross section of at least one of the base end portion, the distal end portion, and the connection portion taken along an imaginary plane perpendicular to an extension direction of the electrode portion has a streamline shape. Therefore, during manufacture of the ceramic heater, the molding material of the ceramic heater can be sufficiently distributed to an area in the vicinity of the electrode portion, whereby formation of a cavity in such an area can be suppressed.
(2) The ceramic heater of the above-described mode may be configured such that the cross section has an elongated shape having a longitudinal direction and a lateral direction perpendicular to the longitudinal direction, two end portions of the cross section in the longitudinal direction have curved outlines, and a curvature radius of one end portion is greater than a curvature radius of another end portion. According to the ceramic heater of this mode, during manufacture of the ceramic heater, the molding material of the ceramic heater can be moved smoothly in a direction from the one end portion toward the other end portion, whereby the molding material can be distributed to the area in the vicinity of the electrode portion.
(3) The ceramic heater of the above-described mode may be configured such that the cross section has an elongated shape having a longitudinal direction and a lateral direction perpendicular to the longitudinal direction, and a first intersection point, which is a point of intersection between a first line segment extending in the longitudinal direction at a position where the cross section has a maximum length in the longitudinal direction and a second line segment extending in the lateral direction at a position where the cross section has a maximum length in the lateral direction, differs from a second intersection point, which is a point of intersection between a third line segment extending in the longitudinal direction and passing through a center of a line segment extending in the lateral direction in the cross section and a fourth line segment extending in the lateral direction and passing through a center of a line segment extending in the longitudinal direction in the cross section. According to the ceramic heater of this mode, the first intersection point and the second intersection point differ from each other. Therefore, when the molding material is supplied from a position closer to the first intersection point (of the first intersection point and the second intersection point) during manufacture of the ceramic heater, the molding material can flow over a portion of the electrode portion where its cross section has the maximum length in the lateral direction thereof, at a position toward the upstream side with respect to the flow direction of the molding material; i.e., in a state in which the molding material has a larger flow force. Accordingly, the molding material can be sufficiently distributed to the second intersection point side (on the downstream side with respect to the flow direction of the molding material).
(4) The ceramic heater of the above-described mode may be configured such that, among a first cross section which is the cross section at the base end portion, a second cross section which is the cross section at the connection portion, and a third cross section which is the cross section at the distal end portion, the first cross section has the largest area, the second cross section has the second largest area, and the third cross section has the third largest area. According to the ceramic heater of this mode, the first cross section has the largest area, the second cross section has the second largest area, and the third cross section has the third largest area. Therefore, during manufacture of the ceramic heater, the molding material of the ceramic heater can be easily caused to reach an area in the vicinity of the distal end portion, which area is located near the outer surface of the substrate and is a hard-to-reach area for the molding material of the ceramic heater.
(5) The ceramic heater of the above-described mode may be configured such that, at the connection portion, the area of the cross section taken along the imaginary plane decreases from the base end portion toward the distal end portion along the extension direction. According to the ceramic heater of this mode, at the connection portion, the area of the cross section taken along the imaginary plane decreases from the base end portion toward the distal end portion along the extension direction. Therefore, during manufacture of the ceramic heater, the molding material of the ceramic heater can be easily caused to reach an area in the vicinity of the base end portion, which area is a hard-to-reach area for the molding material of the ceramic heater.
(6) The ceramic heater of the above-described mode may be configured such that the centroid of the first cross section which is the cross section at the base end portion deviates from the centroid of the third cross section which is the cross section at the distal end portion as viewed in the extension direction. According to the ceramic heater of this mode, the centroid of the first cross section and the centroid of the third cross section deviate from each other as viewed in the extension direction. Therefore, the side surface (surface extending in the extension direction) of the electrode portion can be made relatively gentle. Accordingly, during manufacture of the ceramic heater, the molding material can be easily caused to move along such a side surface, whereby the molding material can be sufficiently distributed to the vicinity of the electrode portion.
(7) The ceramic heater of the above-described mode may be configured such that, as viewed in the extension direction, the centroid of the third cross section is more remote from the joint portion as compared with the centroid of the first cross section. According to the ceramic heater of this mode, when the molding material is supplied from a position near the centroid of the third cross section as viewed in the extension direction during manufacture of the ceramic heater, movement of the molding material in a region of the side surface of the electrode portion, which region is located near the centroid of the first cross section as viewed in the extension direction, can be made easier, whereby the molding material can be sufficiently distributed to that region.
The present invention can be embodied in various modes other than the ceramic heater. For example, the present invention can be embodied as a glow plug, a method of producing the ceramic heater, a method of producing the glow plug, a resistor for the ceramic heater, a method of producing the resistor, a substrate for the ceramic heater, and a method of producing the substrate.
The metallic shell 2 is a metal-made member having an approximately cylindrical outer shape with an axial hole 9. On the outer circumferential surface of the metallic shell 2, a tool engagement portion 12 is formed at the rear end, and a male screw portion 11 is formed in a central portion. The tool engagement portion 12 has an outer shape (e.g., a hexagonal cross sectional shape) engageable with a prescribed tool and is engaged with the prescribed tool when the glow plug 100 is mounted to, for example, a cylinder head of an unillustrated engine. The male screw portion 11 is used to mount the glow plug 100 to the cylinder head of the unillustrated engine.
The center shaft 3 is a metal-made round bar-shaped member and is accommodated within the axial hole 9 of the metallic shell 2 such that a portion of the center shaft 3 on the rear end side protrudes from the rear end of the metallic shell 2. The center shaft 3 has at its forward end a small-diameter portion 17 smaller in diameter than the remaining portion. One end of the metal-made lead wire 19 is connected to the small-diameter portion 17, and the small-diameter portion 17 is electrically connected to the electrode ring 18 through the lead wire 19.
The insulating member 5 has a ring-like outer shape surrounding the center shaft 3 and is disposed within the axial hole 9 of the metallic shell 2. The insulating member 5 fixes the center shaft 3 such that the center axis of the metallic shell 2 and the center axis of the center shaft 3 coincide with the center axis C1 of the glow plug 100. The insulating member 5 electrically insulates the metallic shell 2 and the center shaft 3 from each other and serves as a hermetic seal therebetween. The insulating member 6 includes a tubular portion 13 and a flange portion 14. The tubular portion 13 has a ring-like outer shape, as does the insulating member 5, and is disposed at the rear end of the axial hole 9 so as to surround the center shaft 3. The flange portion 14 has a ring-like outer shape, and has a diameter larger than the outer diameter of the tubular portion 13. The flange portion 14 is disposed rearward of the tubular portion 13 so as to surround the center shaft 3, and electrically insulates the metallic shell 2 and the center shaft 3 from each other and the metallic shell 2 and the crimp member 8 from each other.
The crimp member 8 has an approximately cylindrical outer shape, is disposed so as to be in contact with the flange portion 14, and is then crimped so as to surround the center shaft 3 protruding from the rear end of the metallic shell 2. By crimping the crimp member 8 as described above, the insulating member 6 fitted between the center shaft 3 and the metallic shell 2 is fixed, so that the insulating member 6 is prevented from coming off the center shaft 3.
The outer tube 7 is a metal-made member having an approximately cylindrical outer shape with an axial hole 10 and is joined to the forward end of the metallic shell 2. A thick-walled portion 15 and an engagement portion 16 are formed at the rear end of the outer tube 7. The engagement portion 16 is disposed rearward of the thick-walled portion 15 and has an outer diameter smaller than the outer diameter of the thick-walled portion 15. The outer tube 7 is disposed such that the engagement portion 16 is fitted into the axial hole 9 of the metallic shell 2 and the thick-walled portion 15 is in contact with the forward end of the metallic shell 2. The outer tube 7 holds the heater 4 within the axial hole 10 such that the center axis of the heater 4 coincides with the center axis C1 of the glow plug 100.
The heater 4 has a cylindrical outer shape with a curved forward end surface and is fitted into the axial hole 10 of the outer tube 7. A portion of the heater 4 on the forward end side protrudes from the outer tube 7 and is exposed to an unillustrated combustion chamber. A portion of the heater 4 on the rear end side protrudes from the outer tube 7 and is accommodated within the axial hole 9 of the metallic shell 2. The structure of the heater 4 will be described in detail later. The heater 4 is a so-called ceramic heater formed of ceramic-based materials. The electrode ring 18 is a metal-made member and is fitted onto the rear end of the heater 4. One end of the lead wire 19 is connected to the electrode ring 18.
The resistor 22 is formed of a conductive ceramic. The conductive ceramic of the present embodiment is obtained, for example, by firing a conductive ceramic material containing, as a main component, silicon nitride serving as an insulating material and further containing tungsten carbide serving as an electrically conductive material. Specifically, the resistor 22 contains silicon nitride in an amount of from 56% by volume to 70% by volume inclusive and tungsten carbide in an amount of from 20% by volume to 35% by volume inclusive. The resistor 22 includes a joint portion 32 and a pair of lead portions 31a and 31b. The joint portion 32 has a U-shaped outer shape and connects the forward (the −X direction side) ends of the two lead portions 31a and 31b to each other. The joint portion 32 is a portion which generates heat when energized. To achieve high temperature by concentrating the electric current on a curved portion of the joint portion 32, the diameter of the curved portion is smaller than the diameter of the remaining portion of the joint portion 32 and the diameter of the lead portions 31a and 31b.
Each of the pair of lead portions 31a and 31b is a rod-shaped member formed of a conductive ceramic and is disposed within the substrate 21. The pair of lead portions 31a and 31b are disposed such that their longitudinal directions are parallel to each other and their center axes (axial lines) C11 and C12 are parallel to the center axis C1 of the glow plug 100. The pair of lead portions 31a and 31b are disposed such that the three center axes C1, C11, and C12 are positioned in a single imaginary plane. An electrode portion 27 is disposed on the lead portion 31a to be located at a position close to the rear end thereof. The electrode portion 27 is formed integrally with the lead portion 31a. The electrode portion 27 has one end connected to the lead portion 31a and extends such that its other end is located on the radially outer side. As shown in
As shown in
In the present embodiment, the cross section of the electrode portion 27 taken along the imaginary plane perpendicular to the extension direction has a streamline shape at each of the base end portion 271, the connection portion 272, and the distal end portion 273 and has a streamline shape at any position of each portion along the extension direction.
Also, in the present embodiment, the area of the cross section of the electrode portion 27 taken along the imaginary plane perpendicular to the extension direction is the largest at a portion (connection portion) continuing to the lead portion 31a and decreases toward the outer surface of the substrate 21 along the extension direction of the electrode portion 27. Accordingly, among the cross-sectional area of the base end portion 271, the cross-sectional area of the connection portion 272, and the cross-sectional area of the distal end portion 273, the cross-sectional area of the base end portion 271 is the largest, the cross-sectional area of the connection portion 272 is the second largest, and the cross-sectional area of the distal end portion 273 is the third largest. The above-mentioned “cross-sectional area of the base end portion 271” means the area of a cross section of the base end portion 271 (hereinafter also referred to as the “first cross section”) taken along an imaginary plane which passes through the midpoint of the base end portion 271 in the extension direction, is parallel to the lead portion 31a (the center axis C11), and is perpendicular to the extension direction. Similarly, the above-mentioned “cross-sectional area of the connection portion 272” means the area of a cross section of the connection portion 272 (hereinafter also referred to as the “second cross section”) taken along an imaginary plane which passes through the midpoint of the connection portion 272 in the extension direction, is parallel to the lead portion 31a (the center axis C11), and is perpendicular to the extension direction. Similarly, the above-mentioned “cross-sectional area of the distal end portion 273” means the area of a cross section of the distal end portion 273 (hereinafter also referred to as the “third cross section”) taken along an imaginary plane which passes through the midpoint of the distal end portion 273 in the extension direction, is parallel to the lead portion 31a (the center axis C11), and is perpendicular to the extension direction.
Also, in the present embodiment, as shown in
As described above, in the heater 4 of the present embodiment, the cross section of the electrode portion 27 taken along the imaginary plane perpendicular to the extension direction of the electrode portion 27 has a streamline shape. Therefore, when the material of the substrate 21 is injected for injection molding during the manufacture of the heater to be described later, the flow of the material in the vicinity of the electrode portion 27 (more precisely, the vicinity of a portion corresponding to the electrode portion 27 before firing) can be made smooth, whereby the material can be completely supplied to the vicinity of the electrode portion 27. Notably, as shown in
An intermediate molded product of the resistor 22 is produced by injection molding using the molding material obtained in step S105 (step S115). In the present embodiment, “the intermediate molded product of the resistor 22” means a member that later becomes the resistor 22 through heating steps such as debindering and firing described later.
A half of an intermediate molded product of the substrate 21 is formed on one side of the intermediate molded product of the resistor 22 obtained in step S115 (step S120). The other half of the intermediate molded product of the substrate 21 is formed on the other side of the intermediate molded product of the resistor 22 to thereby obtain an intermediate molded product of the heater 4 (step S125). In each of steps S120 and S125, the molding material obtained in step S110 is injection-molded.
The cavity 420 formed in the lower die 400 has a shape which allows the lower half of the intermediate molded product 300 of the resistor 22 to be fitted into the cavity 420. The upper die 500 has a hollow approximately rectangular cuboidal shape having an opening on its mating surface which mates with the lower die 400. An injection hole for filling the space inside the upper die 500 with a molding material is provided on one longitudinal end surface S500 of the upper die 500. After the intermediate molded product 300, the lower die 400, and the upper die 500 are disposed as described above, the molding material obtained in step S110 is injected into the upper die 500 to form a half of the intermediate molded product of the substrate 21 on one side (the upper side in
In step S125, the intermediate molded product 700 obtained in step S120 is turned upside down to orient it as shown in
As described above, in step S125, the molding material is injected into the upper die 500 from the end surface S500 of the upper die 500. Therefore, the molding material flows within the upper die 500 in a direction from the end surface S500 toward the surface on the opposite side. As shown by a thick solid arrow FL in
Notably, in the above-described steps S120 and 125, instead of injection molding, powder press molding which compresses a powdery molding material may be used to form the intermediate molded product of the heater 4. Also, instead of injection molding and powder press molding, there may be used sheet laminating molding in which a molding material is formed into sheets, and the sheets of the molding material are laminated.
After the intermediate molded product of the heater 4 is obtained in step S125 as shown in
Then polishing and cutting are performed (step S140). In this step, the outer circumference of the fired product obtained in step S135 is polished, and the forward end portion of the fired product is shaped into a curved surface. As a result of the polishing, the electrode portions 27 and 28 are exposed at the surface of the substrate 21. As a result of the cutting, the rear end portion of the fired product obtained in step S135, i.e., a portion corresponding to the rear-end joint portion 350, is removed. The heater 4 is completed through steps S105 to S140 described above. Then, components of the glow plug 100 shown in
In the glow plug 100 of the embodiment described above, the cross section of the electrode portion 27, 28 taken along the imaginary plane perpendicular to the extension direction of the electrode portion 27, 28 has a streamline shape at any position along the extension direction of the electrode portion 27, 28. Therefore, when the molding material of the substrate 21 is injected in the steps S120 and S125 of the heater manufacturing process, the molding material can be sufficiently distributed to an area near the electrode forming portion 327, 328; in particular, the area AR1 which is an area on the downstream side of the electrode forming portion 327, 328 with respect to the flow direction of the molding material. Therefore, it is possible to suppress formation of a cavity in the area AR1 in the completed heater 4 obtained through subsequent steps such as debindering and firing. Accordingly, it is possible to suppress a drop in the strength of the completed heater 4, which drop occurs as a result of formation of such a cavity.
Also, at any position along the extension direction of the electrode portion 27, 28, the cross section of the electrode portion 27, 28 taken along the imaginary plane perpendicular to the extension direction has longitudinal opposite end portions each having a curved outline, and the curvature radius of one of the end portions is greater than that of the other end portion. Therefore, the molding material can be moved smoothly in the direction from the one end to the other end, whereby the molding material can be sufficiently charged to the area AR1.
Also, at any position along the extension direction of the electrode portion 27, 28, the cross section of the electrode portion 27, 28 taken along the imaginary plane perpendicular to the extension direction has a shape in which the point of intersection p1 between the first line segment and the second line segment and the point of intersection p2 between the third line segment and the fourth line segment differ from each other; i.e., the intersection points p1 and p2 do not coincide with each other. In this case, when the molding material is supplied from a position closer to the intersection point p1, the molding material can flow over a portion of the electrode portion where its cross section has the maximum length in the lateral direction thereof, in a state in which the molding material has a larger flow force. Accordingly, the molding material can be sufficiently distributed to the area AR1, which is an area on the side of the electrode forming portion 327, 328 where the intersection point p2 is present; i.e., an area on the downstream side of the electrode forming portion 327, 328 with respect to the flow direction of the molding material.
Also, the area of the cross section of the electrode portion 27 is the largest in a region where the electrode portion 27 continues to the lead portion 31a and gradually decreases toward the surface of the substrate 21 along the extension direction of the electrode portion 27. Therefore, in step S125, the molding material can be easily caused to reach the hard-to-reach area in the vicinity of the base end portion 271.
A plurality of samples of the heater 4 of the above-described embodiment were manufactured, and a strength measurement test was carried out for each sample. Also, a plurality of samples of a heater of a comparative example (Comparative Example) were manufactured, and the strength measurement test was carried out for each sample. Table 1 shows the results of the test. Samples 1 and 3 correspond to the heater 4 of the embodiment (Example). Accordingly, the cross-sectional shape (the shape of a cross section taken along an imaginary plane perpendicular to the extension direction) of the electrode portion 27, 28 in each of Samples 1 and 3 was streamline. In steps S120 and S125 of the process of preparing Sample 1, the intermediate molded product of the heater 4 was formed by powder press molding. In contrast, in steps S120 and S125 of the process of preparing Sample 3, the intermediate molded product of the heater 4 was formed by injection molding. Samples 2 and 4 correspond to the heater of Comparative Example. The cross-sectional shape of the electrode portion in each of Samples 2 and 4 was rectangular. During preparation of Sample 2, the intermediate molded product of the heater was formed by powder press molding. During preparation of Sample 4, the intermediate molded product of the heater was formed by injection molding. As each of Samples 1 to 4, 10 heaters having the same shape were prepared by the same manufacturing method.
The three-point bending strength of each of the prepared heaters was measured with a span of 12 mm. In this measurement, the surface on which the distal end portion of the electrode portion 28 was disposed was used as a tensile surface. The strength of each sample shown in Table 1 is the lowest strength among the measured strengths of the 10 heaters of the sample. In the results of the evaluation of strength in Table 1, “AA” (a good rating) is given when the strength is 1,000 MPa or more, and “XX” (a poor rating) is given when the strength is less than 1,000 MPa.
As shown in Table 1, since the strengths of Samples 2 and 4 of Comparative Example were 920 MPa or less, Samples 2 and 4 were evaluated to be poor (XX). The presumed reason for the relatively low strengths of Samples 2 and 4 of Comparative Example is that since in Samples 2 and 4 of Comparative Example, the cross-sectional shape of the electrode portion was rectangular, when the intermediate molded product of the heater was formed, a hard-to-reach space for the molding material was present in the vicinity of the electrode forming portion, and such a space appeared as a cavity in the completed heater.
In contrast, since the strengths of Samples 1 and 3 of Example were 1000 MPa or more, Samples 1 and 3 of Example were evaluated to be good (AA). In Samples 1 and 3 of Example, since the cross-sectional shape of the electrode portion 27, 28 is streamline, as described above, the molding material can be sufficiently charged to the area in the vicinity of the electrode forming portion when the intermediate molded product of the heater 4 is formed. Therefore, it is presumed that formation of a cavity in the vicinity of the electrode portion 27, 28 of the completed heater 4 was restrained, and therefore, Samples 1 and 3 were high in strength.
In the above-described embodiment and example, the cross-sectional shape of the electrode portion 27, 28 is oval as shown in
In the first mode of the modification 1 shown in
In the second mode of the modification 1 shown in
In the above-described embodiment and example, the shapes of cross sections of the electrode portion 27 at different positions in the extension direction of the electrode portion 27 are approximately similar to one another. However, the present invention is not limited thereto.
The electrode portion 27c according to the modification 2 differs from the electrode portion of the above-described embodiment and example in that the electrode portion 27c has a distal end portion 273c in place of the distal end portion 273 and a connection portion 272c instead of the connection portion 272. The unillustrated other electrode portion in the modification 2 has a structure similar to that of the electrode portion 27c. The structures of a heater and a glow plug according to the modification 2 are the same as the structures of the heater 4 and the glow plug 100 of the embodiment and the example, except for the structure of the above-mentioned electrode portion.
In the modification 2, the distal end portion 273c has a circular columnar external shape, and the shape of the cross section of the distal end portion 273c at any position along the extension direction (the +Y direction) is an approximately perfect circular shape. The cross-sectional shape of the connection portion 272c is an approximately perfect circular shape in a region where the connection portion 272c continues (is connected) to the distal end portion 273c. The cross-sectional shape of the connection portion 272c is a streamline shape (oval shape), as in the embodiment, in a region where the connection portion 272c continues (is connected) to the base end portion 271. A heater and a glow plug according to the modification 2 each of which includes an electrode having such a structure have advantageous effects similar to those of the heater 4 and the glow plug 100 of the above-described embodiment and example. Notably, in the above-described structure of the modification 2, instead of or in addition to the distal end portion 273c, the base end portion 271 may have a cross section of a perfect circular shape. Also, in the structure of the modification 2, instead of the perfect circular shape, any shape other than streamline may be employed. As can be understood from the above-described embodiment, example, and modifications 1 and 2, the structure in which the cross section of at least one of the base end portion, the distal end portion, and the connection portion taken along the imaginary plane perpendicular to the extension direction of the electrode portion has a streamline shape can be applied to the present invention. The “cross section of at least one of the base end portion, the distal end portion, and the connection portion taken along the imaginary plane perpendicular to the extension direction of the electrode portion” means at least one of the first cross section, the second cross section, and the third cross section in the above-described embodiment.
Also, as can be understood from the above-described structure of the modification 2, at least one of the base end portion and the distal end portion may be formed such that the area of the cross section taken along the imaginary plane perpendicular to the extension direction does not decrease gradually toward the surface of the substrate 21 along the extension direction. In the modification 2, the cross-sectional areas of the distal end portion 273c at different positions along the extension direction are equal to one another. Like the distal end portion 273c, the connection portion 272, 272c or the base end portion 271 may be formed such that the cross-sectional areas at different positions along the extension direction are equal to one another. Also, the connection portion 272 may be formed such that the cross-sectional area of the connection portion 272 is the largest at the center position in the extension direction of the connection portion 272, and decreases toward the base end portion 271 and toward the distal end portion 273. However, the connection portion 272, 272c is preferably formed such that the area of the cross section taken along the imaginary plane perpendicular to the extension direction decreases gradually toward the surface of the substrate 21 along the extension direction. In this case, in step S125, the molding material can be easily caused to flow from the base end 271 side toward the distal end portion 273, 273c side.
In the above-described embodiment and example, the centroid g1 of the base end portion 271, the centroid g2 of the connection portion 272, and the centroid g3 of the distal end portion 273 deviate from one another as viewed in the extension direction. However, the present invention is not limited thereto. The electrode portion may be formed such that, of the three centroids g1, g2, and g3, two centroids g1 and g3 deviate from each other as viewed in the extension direction as in the case shown in
In the above embodiments and examples, the electrically conductive material in the molding material of the resistor 22 is tungsten carbide. However, any electrically conductive material such as molybdenum silicide or tungsten silicide may be used instead of tungsten carbide.
In the above embodiments, the heater 4 is a ceramic heater used for the glow plug 100. The heater 4 may be used for components other than the glow plug 100. Specifically, the heater 4 may be an ignition heater for a burner, a heater for heating a gas sensor, or a ceramic heater used for a DPF (diesel particulate filter).
The present invention is not limited to the above described embodiment, example, and modifications and may be embodied in various other forms without departing from the spirit of the invention. For example, the technical features in the embodiment and modifications corresponding to the technical features in the modes described in Summary of the Invention can be appropriately replaced or combined to solve some of or all the foregoing problems or to achieve some of or all the foregoing effects. A technical feature which is not described as an essential feature in the present specification may be appropriately deleted.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-178312 | Sep 2015 | JP | national |
