JP6807660B2 - Ceramic heater element and ceramic glow plug - Google Patents

Description

The present specification relates to a ceramic heater element and a ceramic glow plug.

The ceramic heater element provided in the ceramic glow plug or the like includes, for example, a heat generating resistor and a support made of ceramic (for example, silicon nitride or the like) in which the heat generating resistor is embedded. Further, the heat generating resistor includes a heat generating portion and a lead portion connected to the heat generating portion. The heat generating portion and the lead portion are formed of, for example, a material containing silicon nitride and a conductive substance. When energized, power is supplied to the heat generating portion through the lead portion, and the temperature of the heat generating portion rises.

International Publication No. 2013/047849 International Publication No. 2014/003093 Japanese Unexamined Patent Publication No. 2006-127995 Japanese Unexamined Patent Publication No. 2010-277706

In order to raise the temperature of the heat generating portion when energized, the heat generating portion and the lead portion are configured so that the resistance value of the heat generating portion becomes larger than the resistance value of the lead portion. For example, by making the material composition ratio (for example, the ratio of each of silicon nitride and the conductive substance) different between the heat generating portion and the lead portion, the resistance value of the heat generating portion becomes larger than the resistance value of the lead portion. However, when the material composition ratio differs between the heat generating portion and the lead portion, the strength of the connecting portion between the heat generating portion and the lead portion may decrease.

The present specification discloses a technique capable of suppressing a decrease in strength at a joint surface between a heat generating portion and a lead portion in a ceramic heater element having a heat generating resistor having a material composition ratio different between the heat generating portion and the lead portion. ..

The present specification discloses, for example, the following application examples.

[Application example 1]
A ceramic heater element comprising a heat-generating resistor including a heat-generating portion and a lead portion connected to the heat-generating portion, and a support made of ceramic in which the heat-generating resistor is embedded.
The heat generating portion contains silicon nitride and a first conductive substance.
The lead portion contains silicon nitride and a second conductive substance.
The average value of the maximum outer diameters of the silicon nitride particles including at least a part in the first target region of the 15 μm × 15 μm square on the cross section of the heat generating portion is a 15 μm × 15 μm square on the cross section of the lead portion. Larger than the average value of the maximum outer diameters of the silicon nitride particles containing at least a part in the second target region of
The proportion of the first conductive substance in the first target region of the heat generating portion is smaller than the proportion of the second conductive substance in the second target region of the lead portion.
Ceramic heater element.

As described above, when the ratio of the first conductive substance in the first target region of the heat generating portion is smaller than the ratio of the second conductive substance in the second target region of the lead portion, the resistance value of the heat generating portion is changed to the resistance value of the lead portion. It is possible to increase the temperature of the heat generating portion.

However, if the ratio of the conductive substance is different between the heat generating part and the lead part (that is, the material composition ratio is different between the heat generating part and the lead part), the strength at the joint surface between the heat generating part and the lead part becomes stronger. May decrease. On the other hand, in the configuration of this application example, the average value of the maximum outer diameters of the silicon nitride particles containing at least a part in the first target region is set, and the silicon nitride particles containing at least a part in the second target region. It is larger than the average value of the maximum outer diameter of. As a result, it is possible to suppress a decrease in strength at the joint surface between the heat generating portion and the lead portion.

The inventors presume the following reasons as the reason why the decrease in strength at the joint surface between the heat generating portion and the lead portion can be suppressed. That is, in the vicinity of the joint surface, cracks due to the difference in thermal expansion between the heat generating portion and the lead portion are likely to occur, but if more silicon nitride particles having a long outer diameter are present near the joint surface, these cracks are joined. It is believed that even if it occurs near the surface, the progress of cracks can be suppressed, and as a result, the decrease in strength can be suppressed.
Then, silicon nitride in which at least a part is contained in the first target region of the heat generating portion containing a larger amount of silicon nitride (for example, the proportion of silicon nitride increases by decreasing the proportion of the first conductive substance). By increasing the average value of the maximum outer diameters of the particles of the lead portion containing a relatively small amount of silicon nitride (for example, by relatively increasing the ratio of the second conductive substance, the ratio of silicon nitride becomes relatively small. ), By making it larger than the average value of the maximum outer diameters of the silicon nitride particles containing at least a part of them, a large number of silicon nitride particles having a long outer diameter should be present in the vicinity of this joint surface. I think I can do it.

[Application example 2]
The ceramic heater element according to Application Example 1.
The shape of the ceramic heater element is a rod shape extending in the direction of the axis.
The heat generating portion is arranged on the tip side in the direction of the axis, and the lead portion extends along the direction of the axis.
The heat generating portion and the lead portion are connected so as to overlap in a direction perpendicular to the direction of the axis.
The joint surface between the lead portion and the heat generating portion includes a portion that is inclined obliquely with respect to the direction of the axis.
Ceramic heater element.

As described above, the joint surface between the lead portion and the heat generating portion includes a portion that is inclined obliquely with respect to the direction of the axis. According to this configuration, the area of the joint surface is larger than that when the entire joint surface is perpendicular to the direction of the axis, so that more silicon nitride particles having a long outer diameter may be present near the joint surface. Therefore, the decrease in strength can be further suppressed at the joint surface between the lead portion and the heat generating portion.

[Application example 3]
The ceramic heater element according to Application Example 1 or 2 and
A tubular main metal fitting that accommodates the rear end of the ceramic heater element,
Ceramic glow plug with.

The technique disclosed in the present specification can be realized in various aspects, for example, a ceramic heater element, a method for manufacturing a ceramic heater element, a ceramic heater element, and a metal outer cylinder for holding the ceramic heater element. It can be realized in the form of a ceramic heater module having a ceramic heater, a ceramic glow plug having a ceramic heater element and a main metal fitting, and the like.

It is the schematic of an example of the ceramic glow plug of an embodiment. It is an enlarged sectional view of the tip part of the ceramic heater element 40. This is an example of a cross-sectional image of the resistor 220 by a scanning electron microscope (SEM). It is a table which shows the result of the evaluation test. It is explanatory drawing which shows the arrangement of three supports S1, S2, S3 in a bending test.

A. Embodiment:
A1. Ceramic glow plug configuration:
FIG. 1 is a schematic view of an example of a ceramic glow plug of the embodiment. FIG. 1 (A) is a cross-sectional view of a ceramic glow plug 10 (hereinafter, also simply referred to as “glow plug 10”), and FIG. 1 (B) shows a portion of the glow plug 10 including a ceramic heater element 40. It is an enlarged sectional view which shows. The illustrated line CL indicates the central axis of the glow plug 10. The cross section shown is a flat cross section including the central axis CL. Hereinafter, the central axis CL is also referred to as "axis CL", and the direction parallel to the central axis CL is also referred to as "axis direction". The radial direction of the circle centered on the central axis CL is also simply referred to as the "diameter direction", and the circumferential direction of the circle centered on the central axis CL is also referred to as the "circumferential direction". Of the directions parallel to the central axis CL, the downward direction in FIG. 1 is called the first direction D1. The first direction D1 is a direction from the terminal member 80 described later toward the ceramic heater element 40. The second direction D2 and the third direction D3 in the figure are directions perpendicular to each other, and both are directions perpendicular to the first direction D1. Hereinafter, the first direction D1 is also referred to as a tip direction D1, and the direction opposite to the first direction D1 is also referred to as a rear end direction D1r. Further, the front end direction D1 side in FIG. 1 is referred to as the front end side of the glow plug 10, and the rear end direction D1r side in FIG. 1 is referred to as the rear end side of the glow plug 10.

The glow plug 10 includes a main metal fitting 20, a center pole 30, a ceramic heater element 40 (hereinafter, also simply referred to as “heater element 40”), an O-ring 50, an insulating member 60, and a metal outer cylinder 70 (hereinafter, simply referred to as “heater element 40”). It also includes an "outer cylinder 70"), a terminal member 80, and a connecting member 90. The main metal fitting 20 is a tubular member having a through hole 20x extending along the central axis CL. Further, the main metal fitting 20 includes a tool engaging portion 28 formed at the end portion on the rear end direction D1r side and a male screw portion 22 provided on the tip direction D1 side of the tool engaging portion 28. There is. The tool engaging portion 28 is a portion that engages with a tool (not shown) when the glow plug 10 is attached or detached. The male screw portion 22 includes a screw thread for screwing into a female screw of a mounting hole of an internal combustion engine (not shown). The main metal fitting 20 is made of a conductive material (for example, a metal such as carbon steel).

The center pole 30 is housed in the through hole 20x of the main metal fitting 20. The center pole 30 is a round bar-shaped member. The center pole 30 is made of a conductive material (for example, stainless steel). The rear end portion 39, which is the end portion on the rear end direction D1r side of the center pole 30, projects from the opening OPb on the rear end direction D1r side of the main metal fitting 20 toward the rear end direction D1r.

In the vicinity of the opening OPb, an O-ring 50 is provided between the outer surface of the center pole 30 and the inner surface of the through hole 20x of the main metal fitting 20. The O-ring 50 is made of an elastic material (for example, rubber). Further, a ring-shaped insulating member 60 is attached to the opening OPb of the main metal fitting 20. The insulating member 60 includes a tubular portion 62 and a flange portion 68 provided on the D1r side in the rear end direction of the tubular portion 62. The tubular portion 62 is sandwiched between the outer surface of the center pole 30 and the inner surface of the portion of the main metal fitting 20 that forms the opening OPb. The insulating member 60 is made of, for example, a resin. The main metal fitting 20 supports the center pole 30 via these members 50 and 60.

The terminal member 80 is arranged on the D1r side in the rear end direction of the insulating member 60. The terminal member 80 is a cap-shaped member and is made of a conductive material (for example, a metal such as nickel). A flange portion 68 of the insulating member 60 is sandwiched between the terminal member 80 and the main metal fitting 20. The rear end 39 of the center pole 30 is inserted into the terminal member 80. By crimping the terminal member 80, the terminal member 80 is fixed to the rear end portion 39. As a result, the terminal member 80 is electrically connected to the center pole 30.

An outer cylinder 70 is fixed to the opening OPa on the D1 side in the tip direction of the main metal fitting 20 (for example, press fitting or welding). The outer cylinder 70 is a tubular member having a through hole 70x extending along the central axis CL. The outer cylinder 70 is made of a conductive material (for example, stainless steel).

A heater element 40 that generates heat when energized is inserted into the through hole 70x of the outer cylinder 70. The heater element 40 is a rod-shaped member arranged so as to extend along the central axis CL. The outer cylinder 70 holds the outer peripheral surface of the central portion of the heater element 40 in a state where the tip portion 41 of the heater element 40 is exposed. The rear end 49 of the heater element 40 is housed in the through hole 20x of the main metal fitting 20. Hereinafter, the entire heater element 40 and the metal outer cylinder 70 will also be referred to as a “heater module 490”.

A connecting member 90 is fixed to the rear end 49 of the heater element 40. The connecting member 90 is a cylindrical member having a through hole extending along the central axis CL, and is made of a conductive material (for example, stainless steel). The rear end 49 of the heater element 40 is press-fitted into the portion of the connecting member 90 on the D1 side in the tip direction. The tip portion 31 which is the end portion of the center pole 30 on the tip direction D1 side is press-fitted into the portion on the rear end direction D1r side of the connecting member 90. As a result, the center pole 30 is electrically connected to the connecting member 90. The tip 31 of the center pole 30 and the connecting member 90 may be welded together.

Next, the details of the heater module 490 will be described. FIG. 1B shows a more detailed cross-sectional view of the metal outer cylinder 70, the connecting member 90, and the heater element 40. The heater element 40 includes a round bar-shaped substrate 210 extending along the axis CL and a substantially U-shaped heat generating resistor 220 (hereinafter, simply referred to as “resistor 220”) embedded inside the substrate 210. Includes. The substrate 210 is made of an insulating ceramic material (details will be described later). The resistor 220 is made of a conductive ceramic material (details will be described later). The substrate 210 supports the resistor 220 while covering the resistor 220 (the substrate 210 is an example of a "support" in the claims). The heater element 40 is formed by firing the material. The tip of the substrate 210 (that is, the tip 41 of the heater element 40) is rounded. The electrical conductivity of the resistor 220 is higher than the electrical conductivity of the substrate 210. The resistor 220 generates heat when energized.

The resistor 220 includes two lead portions 221 and 222, a heat generating portion 223 connected to the lead portions 221 and 222, and electrode extraction portions 281 and 282. The lead portions 221 and 222 extend from the rear end portion 49 of the heater element 40 to the vicinity of the front end portion 41 along the extending direction of the axis CL (here, parallel to the axis CL). The first lead portion 221 and the second lead portion 222 are arranged at positions substantially symmetrical with respect to the central axis CL. The third direction D3 is a direction from the second lead portion 222 to the first lead portion 221.

The heat generating portion 223 is embedded in the tip portion 41 of the heater element 40, and connects the end of the first lead portion 221 on the tip direction D1 side and the end of the second lead portion 222 on the tip direction D1 side. That is, the lead portions 221 and 222 are connected to the rear end direction D1r side of the heat generating portion 223. The shape of the heat generating portion 223 is a substantially U shape that curves along the round shape of the tip portion 41 of the heater element 40. The cross-sectional area of the heat generating portion 223 is smaller than the cross-sectional area of each of the lead portions 221 and 222. Further, the electric resistance per unit length of the heat generating portion 223 is larger than the electric resistance per unit length of the lead portions 221 and 222. As a result, when energized, the temperature of the heat generating portion 223 rises more rapidly than the temperature of the lead portions 221 and 222.

The first electrode take-out portion 281 is connected to the portion on the D1r side in the rear end direction of the first lead portion 221. The first electrode take-out portion 281 extends along the radial direction. The inner end of the first electrode take-out portion 281 is connected to the first lead portion 221 and the outer end of the first electrode take-out portion 281 is exposed to the outer surface of the heater element 40. The exposed portion of the first electrode extraction portion 281 is in contact with the inner peripheral surface of the outer cylinder 70. As a result, the outer cylinder 70 and the first lead portion 221 are electrically connected.

A second electrode take-out portion 282 is connected to a portion on the D1r side in the rear end direction of the second lead portion 222. The second electrode take-out portion 282 extends along the radial direction, and is arranged on the rear end direction D1r side of the first electrode take-out portion 281. The inner end of the second electrode take-out portion 282 is connected to the second lead portion 222, and the outer end of the second electrode take-out portion 282 is exposed to the outer surface of the heater element 40. The exposed portion of the second electrode extraction portion 282 is in contact with the inner peripheral surface of the connecting member 90. As a result, the connecting member 90 and the second lead portion 222 are electrically connected.

When the glow plug 10 is used, a voltage is applied between the main metal fitting 20 and the terminal member 80. As described above, the first lead portion 221 is electrically connected to the main metal fitting 20 via the second electrode extraction portion 282 and the metal outer cylinder 70. The second lead portion 222 is electrically connected to the terminal member 80 via the second electrode extraction portion 282, the connecting member 90, and the center pole 30. Therefore, the electric power supplied through the main metal fitting 20 and the terminal member 80 is supplied to the heat generating portion 223 through the lead portions 221 and 222. As a result, the heat generating portion 223 generates heat.

FIG. 2 is an enlarged cross-sectional view of the tip end portion of the heater element 40. In the figure, a flat cross section including the axis CL is shown. In the figure, hatching of each element 210, 221 222, 223 of the heater element 40 is omitted in order to make the figure easier to see. The first joint surface 241 in the drawing shows the joint surface between the first lead portion 221 and the heat generating portion 223, and the second joint surface 242 shows the joint surface between the second lead portion 222 and the heat generating portion 223. .. As shown in the figure, in the present embodiment, these joint surfaces 241 and 242 include inclined portions 241x and 242x that are inclined obliquely with respect to the axis CL, respectively. That is, the heat generating portion 223 and the lead portions 221 and 222 are connected in a state of overlapping along the direction perpendicular to the axis CL. Therefore, the area of the first joint surface 241 is larger than that in the case where the entire first joint surface 241 is perpendicular to the axis CL. As a result, more silicon nitride particles having a long outer diameter, which will be described later, can be present in the vicinity of the first joint surface 241 and have a strength at the first joint surface 241 of the first lead portion 221 and the heat generating portion 223. The decrease can be further suppressed. Similarly, the area of the second joint surface 242 is larger than that in the case where the entire second joint surface 242 is perpendicular to the axis CL. As a result, more silicon nitride particles having a long outer diameter, which will be described later, can be present in the vicinity of the second joint surface 242, and the strength of the strength of the strength of the second lead portion 222 and the heat generating portion 223 at the second joint surface 242. The decrease can be further suppressed. In the present embodiment, the inclined portions 241x and 242x extending from the inner peripheral side toward the outer peripheral side (that is, toward the direction away from the axis CL) are inclined toward the rear end side (rear end direction D1r side). doing.

In this embodiment, the substrate 210 is made of an insulating ceramic material containing silicon nitride. Further, the lead portions 221 and 222 and the heat generating portion 223 are each formed of a conductive ceramic material containing silicon nitride and a conductive substance. As the conductive substance, for example, tungsten carbide is used. The material composition ratio of silicon nitride and the conductive substance is different between the conductive ceramic material of the heat generating portion 223 and the conductive ceramic material of the lead portions 221 and 222.

The heater element 40 is manufactured, for example, as follows. First, the insulating ceramic material of the substrate 210, the conductive ceramic material of the lead portions 221 and 222, and the conductive ceramic material of the heat generating portion 223 are prepared. The insulating ceramic material of the substrate 210 is prepared, for example, as follows. A powder is produced by spray-drying from a slurry containing a silicon nitride powder. By kneading the produced powder and the binder, a mixture of the substrate 210 as an insulating ceramic material is produced. The conductive ceramic materials of the lead portions 221 and 222 are prepared, for example, as follows. A powder is produced by spray-drying from a slurry containing a silicon nitride powder and a conductive substance powder. By kneading the produced powder and the binder, a mixture of the lead portions 221 and 222 as a conductive ceramic material is produced. The conductive ceramic material of the heat generating portion 223 is prepared in the same manner as the conductive ceramic material of the lead portions 221 and 222. However, in the present embodiment, the particle size of the silicon nitride powder contained in the conductive ceramic material of the heat generating portion 223 is larger than the particle size of the silicon nitride powder contained in the conductive ceramic material of the lead portions 221 and 222. large. Further, the proportion of the conductive substance contained in the conductive ceramic material of the heat generating portion 223 (for example, weight percent) is lower than the proportion of the conductive substance contained in the conductive ceramic material of the lead portions 221 and 222.

Next, the unfired resistor 220 is molded, for example, as follows. First, the unfired reed portions 221 and 222 are molded by injection molding using the materials of the reed portions 221 and 222. Then, with the unfired lead portions 221 and 222 arranged at predetermined positions in the molding mold for the heat generating portion 223, the heat generating portion 223 is molded by injection molding using the material of the heat generating portion 223. As a result, the unfired lead portions 221 and 222 and the heat generating portion 223 connected to each other, that is, the unfired resistor 220 is formed. In addition, in a state where the unfired heat generating portion 223 is injection-molded first and the unfired heat generating portion 223 is arranged at a predetermined position in the molding mold for the lead portions 221 and 222, the lead portions 221 and 222 are formed. It may be molded by injection molding.

Next, the substrate 210 is molded as follows, for example. With the unfired resistor 220 placed at a predetermined position in the molding die for the heater element 40, the material of the substrate 210 is molded so as to cover the unfired resistor 220 by injection molding. As described above, the unfired substrate 210 and, by extension, the unfired heater element 40 are formed.

Next, the unfired heater element 40 is fired. Then, the heater element 40 is completed by adjusting the outer shape of the fired member (also referred to as a fired body) by polishing.

FIG. 3 is an example of a cross-sectional image of the resistor 220 by a scanning electron microscope (SEM). This cross-sectional image IM is an image obtained by mirror-polishing the cross-section of the heater element 40 shown in FIG. 2 and photographing the mirror-polished cross-section with a scanning electron microscope (SEM) (magnification is 3000 times). .. The brightly colored portion in the cross-sectional image IM indicates the portion of the conductive material (here, tungsten carbide). The dark colored part in the cross-sectional image IM shows the silicon nitride particles. The light-colored lines that separate the dark-colored areas indicate the grain boundaries. The white dotted line shown in the cross-sectional image IM shows the outline of one silicon nitride particle G. As shown in the figure, the shape of the silicon nitride particles is elongated rod-like (also called needle-shaped particles). In the resistor 220, a large number of particles of silicon nitride are formed. Such silicon nitride particles are formed during firing.

At the bottom of the cross-sectional image IM, the major axis length L of one particle G of silicon nitride is shown. The major axis length L indicates the maximum outer diameter of the particles in the cross-sectional image IM. As shown, the outer diameter of the particle G varies depending on the direction. The major axis length L is the maximum outer diameter among the outer diameters that differ depending on the direction. The major axis length L is used in an evaluation test described later.

A2. Evaluation test of heater element:
FIG. 4 is a table showing the results of the evaluation test. In the evaluation test, the toughness and bending strength of the heater element 40 were evaluated using a sample of the heater element 40. The table of FIG. 4 shows the sample numbers, the average value L1 of the major axis length L in the heat generating portion 223 (referred to as the first average major axis length L1), and the average value L2 of the major axis length L in the lead portion 222 (the first). 2 Average major axis length L2), the ratio L1 / L2, the conductive material ratio R1 in the heat generating portion 223, the conductive material ratio R2 in the lead portion 222, the toughness value, and the bending strength.

The average major axis lengths L1 and L2 are average values of the major axis lengths L described with reference to FIG. As described with reference to FIG. 3, the cross section of the heater element 40 including the axis CL of the sample was mirror-polished. Then, the mirror-polished cross section was photographed with a scanning electron microscope (SEM) at a magnification of 3000 times. The average major axis lengths L1 and L2 were calculated by analyzing the images obtained by photographing (also referred to as SEM images). The average major axis lengths L1 and L2 are both average values of the major axis lengths L of the particles in which at least a part is included in the target region of the 15 μm × 15 μm square in the SEM image. When a part of the particle is located outside the target area and the rest of the particle is located inside the target area, the major axis length L of the particle was used to calculate the average major axis lengths L1 and L2. The first target area A1 shown in FIG. 2 indicates a target area for calculating the first average major axis length L1 of the heat generating portion 223, and the second target area A2 is the second average major axis length L2 of the lead portion 222. The target area for the calculation of is shown. As shown in the figure, the first target region A1 is arranged at a position away from the joint surfaces 241 and 242 on the heat generating portion 223. Further, the second target region A2 is arranged at a position away from the joint surface 242 on the lead portion 222.

The first conductive substance ratio R1 is the ratio of the area of the portion representing the conductive substance (here, tungsten carbide) in the first target region A1 to the area of the first target region A1 on the SEM image. The second conductive substance ratio R2 is the ratio of the area of the portion representing the conductive substance in the second target region A2 to the area of the second target region A2 on the SEM image.

The toughness value was specified as follows according to the IF method specified in JIS R1607. A cross section (FIG. 2) of the heater element 40 including the axis CL of the sample was mirror-polished, and an indentation was formed on the cross section of the sample using a Vickers hardness tester. The indentation VI of FIG. 2 gives an overview of the indentation VI formed in this evaluation test. In FIG. 2, an enlarged view of a portion including the indentation VI is shown at the lower part of the cross section of the heater element 40. The Vickers hardness tester forms a rectangular indentation on the sample. Here, the relative positions of the sample with respect to the indenter of the Vickers hardness tester were adjusted so that the two diagonals C1 and C2 of the indentation VI were located on the joint surface 242. The formation of the indentation VI was performed under the condition that the load was 5 kgf and the holding time of the load was 15 seconds. By applying such a load, cracks CR1 and CR2 were generated from the indentation VI angles C1 and C2 along the joint surface 242.

The crack length C is the end of the first crack CR1 extending from the first corner C1 (the end opposite to the corner C1) and the end of the second crack CR2 extending from the second corner C2 (the end opposite to the corner C2). ) And half of the straight line distance 2C. The indentation length k is half of the linear distance 2k between the two diagonals C1 and C2 of the indentation VI. Using such a crack length C and an indentation length k, the toughness value Kc was calculated according to the following formula.
Kc = 0.026 x E ^1/2 x P ^1/2 x k / (C ^3/2 )
Here, E is the elastic modulus of the resistor 220. Since the elastic modulus was the same between the lead portion 222 and the heat generating portion 223, the same elastic modulus was adopted as the elastic modulus E of the resistor 220 (here, E = 400 GPa). P is a load (here, P = 5 kgf).

The bending strength shows the maximum bending stress when the sample is broken by performing a bending test of three-point support using the sample of the heater element 40. FIG. 5 is an explanatory view showing the arrangement of the three supports S1, S2, and S3 in the bending test. In the figure, the same cross section of the heater element 40 as in FIG. 2 is shown. As shown in the figure, the first support tool S1 supports the sample of the heater element 40 at the first position P1 which is a position near the joint surface 242 on the outer peripheral surface of the heater element 40. The second support tool S2 supports the sample of the heater element 40 at the second position P2 on the outer peripheral surface of the heater element 40, which is opposite to the first position P1 and on the tip direction D1 side of the first position P1. To do. The third support S3 is a sample of the heater element 40 at the third position P3 on the outer peripheral surface of the heater element 40, which is opposite to the first position P1 and on the rear end direction D1r side of the first position P1. To support. The distance between the second position P2 and the third position P3 was the same regardless of the type of sample. Then, the first support S1 applies a load in the direction toward the other supports S2 and S3 perpendicular to the axis CL to the sample of the heater element 40. The supports S2 and S3 apply a load in the direction toward the first support S1 perpendicular to the axis CL to the sample of the heater element 40. Then, the load was gradually increased until the sample broke.

In this evaluation test, the distance T between the outer peripheral surface of the substrate 210 and the joint surfaces 241 and 242 (that is, the distance between the outer peripheral surface of the substrate 210 and the lead portions 221 and 222) is 0. The outer peripheral surface of the sample of the heater element 40 was polished so as to have a thickness of .2 mm. Then, in the bending test, the maximum bending stress of the sample whose origin of fracture of the sample is one of the joint surfaces 241 and 242 was adopted. If the origin of the fracture was neither of the joint surfaces 241 or 242 (for example, the joint surfaces 241 and 242 were not cracked and the other parts were cracked), the bending stress of the sample was not adopted. Then, using another sample having the same configuration, the bending test was repeated until the origin of the fracture of the sample was one of the joint surfaces 241 and 242.

As shown in the table of FIG. 4, three types of samples No. 1, No. 2, No. 3 were evaluated. Among these samples, at least one of the first average major axis length L1 of the heat generating portion 223 and the first conductive substance ratio R1 of the heat generating portion 223 is different from each other. The change between the first average major axis length L1 and the first conductive substance ratio R1 is the change in the conductive ceramic material of the heat generating portion 223 (specifically, the particle size of the material particles of silicon nitride and the content of the conductive substance (for example). , Weight percent)) was achieved by changing. The configuration of the other parts of the heater element 40 was common among the three types of samples. For example, the conductive ceramic materials of the leads 221 and 222 were common among the three types of samples. Also, the insulating ceramic material of the substrate 210 was common among the three types of samples. Further, the shape of the heater element 40, the outer diameter of the heater element 40, the shape of the heat generating portion 223, the shape of the first lead portion 221 and the shape of the second lead portion 222, and each of these elements 40, 221, 222, 223. The size was common among the three samples.

The change of the first average major axis length L1 was realized by changing the particle size of the material particles of silicon nitride contained in the material of the heat generating portion 223. The larger the particle size of the silicon nitride material particles, the longer the first average major axis length L1 after firing. Specifically, the first average major axis length L1 was 1.3 mm, 1.8 mm, and 2.2 mm in the order of Nos. 1, 2, and 3. The second average major axis length L2 of the lead portion 222 is approximately the same among the three types of samples, and specifically, 1.8 μm, 1.7 μm, and 1 in the order of No. 1, No. 2, No. 3, and 1. It was 0.7 μm. The difference (0.1 μm) in the second average major axis length L2 among the three types of samples is an error due to manufacturing variation. The ratios L1 / L2 were 0.7, 1.1, and 1.3 in the order of No. 1, No. 2, No. 3, and No. 1. As described above, in the first sample, the first average major axis length L1 of the heat generating portion 223 was smaller than the second average major axis length L2 of the lead portion 222. In the No. 2 and No. 3 samples, the first average major axis length L1 of the heat generating portion 223 was larger than the second average major axis length L2 of the second lead portion 222. The average major axis length of the first lead portion 221 is approximately the same as the first average major axis length L1 of the second lead portion 222.

The change of the first conductive substance ratio R1 was realized by changing the ratio of the conductive substance contained in the material of the heat generating portion 223. The higher the ratio of the conductive material contained in the material (for example, the weight percentage), the higher the ratio of the first conductive material R1. Specifically, the first conductive substance ratio R1 was 26%, 29%, and 26% in the order of Nos. 1, 2, and 3. The first conductive substance ratio R1 was the same between No. 1 and No. 3. The second conductive substance ratio R2 of the lead portion 222 was the same 42% among the three types of samples. As described above, the ratio of the first conductive substance R1 of the heat generating portion 223 is lower than the ratio of the second conductive substance R2 of the lead portion 222 (note that the proportion of the conductive substance of the first lead portion 221 is the second of the second lead portion 222. 2 Conductive substance ratio is approximately the same as R2). Therefore, the electric resistance value of the heat generating portion 223 is larger than the electric resistance value of the lead portions 221 and 222. As a result, the temperature of the heat generating portion 223 can be raised even when the power is turned on.

As shown in FIG. 4, the toughness values were 4.7, 5.1, and 6.6 in the order of Nos. 1, 2, and 3 (unit: MPa · m ^0.5 ). As described above, the higher the ratio L1 / L2, the better the toughness value. In particular, the first toughness value at which the first average major axis length L1 of the heat generating portion 223 is smaller than the second average major axis length L2 of the lead portion 222 was less than 5, but the first average length of the heat generating portion 223 was less than 5. The toughness values of Nos. 2 and 3 in which the shaft length L1 is larger than the second average major shaft length L2 of the lead portion 222 exceeded 5. As described above, the reason why the toughness value is improved when the first average major axis length L1 of the heat generating portion 223 is longer than the second average major axis length L2 of the lead portion 222 is that the heat generating portion 223 and the lead portions 221, 222. This is because a large number of silicon nitride particles having a long outer diameter can be present in the vicinity of the joint surfaces 241 and 242 with the joint surface, and as a result, even if cracks occur in the vicinity of the joint surface, the progress of the cracks is suppressed. Presumed.

Further, the first average major axis length L1 is longer than the second toughness value (5.1 in this case) in which the first average major axis length L1 is approximately the same as the second average major axis length L2. The toughness value of No. was 6.6, which was significantly improved. As described above, the longer the first average major axis length L1, the more the toughness value can be improved.

The bending strength was 1027 and 1084 in the order of No. 1 and No. 3 (unit: MPa. No bending strength was measured for the sample No. 2). As described above, the higher the ratio L1 / L2, the better the bending strength. In particular, the first toughness value at which the first average major axis length L1 of the heat generating portion 223 is smaller than the second average major axis length L2 of the lead portion 222 was less than 1030 MPa, but the first average length of the heat generating portion 223 was less than 1030 MPa. The toughness value of No. 3 having a shaft length L1 larger than the second average length shaft length L2 of the lead portion 222 exceeded 1080 MPa. As described above, the reason why the bending strength is improved when the first average major axis length L1 of the heat generating portion 223 is longer than the second average major axis length L2 of the lead portion 222 is that the heat generating portion 223 and the lead portions 221 and 222 A large number of silicon nitride particles having a long outer diameter can be present in the vicinity of the joint surfaces 241, 242 of the above, and as a result, even if cracks occur in the vicinity of the joint surface, the long silicon nitride particles will be cracked. It is presumed that this is because the progress is suppressed, and thus the decrease in strength at the joint surfaces 241 and 242 is suppressed.

The lead portions 221 and 222 and the heat generating portion 223 each contain a conductive substance in addition to silicon nitride. The growth of silicon nitride particles during firing is suppressed by the conductive material present around the silicon nitride particles. The higher the content of the conductive substance, the more difficult it is for the silicon nitride particles to grow. Further, in order to raise the temperature of the heat generating portion 223 when energized, the ratio of the second conductive substance R2 (that is, the content of the conductive substance) in the lead portions 221 and 222 is the ratio of the first conductive substance in the heat generating portion 223. It is higher than R1 (that is, the content of the conductive substance). Therefore, at the time of firing, the silicon nitride particles are less likely to grow in the lead portions 221 and 222 as compared with the heat generating portion 223. Under such conditions, the balance of the major axis length L of the silicon nitride particles is allowed to be uneven between the heat generating portion 223 and the lead portions 221, 222, and the silicon nitride particles grow relatively. By making the first average major axis length L1 in the easily generating portion 223 longer than the second average major axis length L2 in the lead portion 222, the toughness value and the bending strength could be improved.

Further, as described with reference to FIG. 2, the joint surfaces 241 and 242 of the lead portions 221 and 222 and the heat generating portion 223 include inclined portions 241x and 242x that are inclined obliquely with respect to the axial direction. Therefore, the area of the joint surfaces 241 and 242 can be increased as compared with the case where the joint surfaces 241 and 242 are perpendicular to the axis CL. As a result, even if cracks such as the cracks CR1 and CR2 in FIG. 2 occur on the joint surface (joint surface 241 or joint surface 242), silicon nitride particles having a long outer diameter are present near the joint surface. Since the ratio of the crack area to the total area of the joint surface can be reduced, the decrease in strength at the joint surface can be suppressed.

B. Modification example:
(1) As the configuration of the heat generating resistor 220, various other configurations can be adopted instead of the above configuration. For example, the conductive substance contained in the lead portions 221 and 222 and the heat generating portion 223 is not limited to tungsten carbide, and various conductive substances can be adopted. For example, tungsten may be adopted, or a compound containing tungsten (for example, a carbide of tungsten, a silicified product of tungsten, a nitride of tungsten, etc.) may be adopted. Further, molybdenum may be adopted, or a compound containing molybdenum (for example, a carbide of molybdenum, a silicified product of molybdenum, a nitride of molybdenum, etc.) may be adopted. In general, as the conductive substance, various substances containing at least one metal component of tungsten and molybdenum can be adopted. For example, at least one of the above three compounds containing tungsten and tungsten and the above three compounds containing molybdenum and molybdenum may be adopted. The conductive substance (referred to as the first conductive substance) contained in the heat generating portion 223 may be different from the conductive substance (referred to as the second conductive substance) contained in the first lead portion 221 and is referred to as the second conductive substance. It may be the same. The first conductive substance contained in the heat generating portion 223 may be different from the conductive substance (referred to as the third conductive substance) contained in the second lead portion 222, or may be the same as the third conductive substance. The second conductive substance contained in the first lead portion 221 may be different from the third conductive substance contained in the second lead portion 222, or may be the same as the third conductive substance.

The material of the heat generating portion 223 may contain various substances in addition to the silicon nitride and the conductive substance. The material of the heat generating portion 223 may include, for example, a sintering aid such as an oxide of a rare earth element. Similarly, the materials of the lead portions 221 and 221 may also contain various substances such as a sintering aid in addition to the silicon nitride and the conductive substance. Similarly, the material of the substrate 210 may contain various substances such as a sintering aid in addition to silicon nitride.

(2) As the first target region A1 used for calculating the first average major axis length L1 and the first conductive substance ratio R1, 15 μm × 15 μm square regions at various positions on the cross section of the heat generating portion 223 are defined. It can be adopted. Similarly, the second target region A2 used for calculating the second average major axis length L2 and the second conductive substance ratio R2 is a 15 μm × 15 μm square at various positions on the cross sections of the lead portions 221 and 222. Areas can be adopted. For example, the cross section may be inclined obliquely with respect to the axis CL.

In general, it is preferable that the first target region A1 is arranged in a portion of the heat generating portion 223 having substantially the same structure as the portion forming the joint surfaces 241 and 242. When the entire heat generating portion 223 is formed of the same material as in the above embodiment, it is estimated that the structure is substantially the same over the entire heat generating portion 223. Therefore, as the first target region A1, Regions of various parts of the heat generating portion 223 can be adopted.

Further, it is preferable that the second target region A2 is arranged in a portion of the lead portions 221 and 222 having substantially the same structure as the portion forming the joint surfaces 241 and 242. When the entire first lead portion 221 is made of the same material as in the above embodiment, regions of various portions of the first lead portion 221 can be adopted as the second target region A2. .. Further, as in the above embodiment, when the entire second lead portion 222 is formed of the same material, regions of various portions of the second lead portion 222 can be adopted as the second target region A2. Is.

The first average major axis length L1 and the first conductive substance ratio R1 calculated from at least one first target region A1 on the cross section of the heat generating portion 223, and at least one second target on the cross section of the first lead portion 221. When the second average major axis length L2 and the second conductive substance ratio R2 calculated from the region A2 satisfy the conditions of "L1> L2" and "R1 <R2", the heat generating portion 223 It can be said that the combination of the first lead portion 221 and the first lead portion 221 satisfies two conditions. The same applies to the combination of the heat generating portion 223 and the second lead portion 222. Here, the second average major axis length L2 may be different between the first lead portion 221 and the second lead portion 222. Further, the second conductive substance ratio R2 may be different between the first lead portion 221 and the second lead portion 222. In either case, at least one of the two lead portions 221 and 222 connected to the rear end side of the heat generating portion 223 and the heat generating portion 223 are referred to as "L1> L2" and "R1 <R2". It is preferable that the conditions are satisfied.

The first average major axis length L1, the second average major axis length L2, the first conductive substance ratio R1 and the second conductive substance ratio R2 are various other values, respectively, instead of the values of the sample of FIG. It can be a value. Generally, in order to raise the temperature of the heat generating portion 223, it is preferable that the conductive substance ratio R1 of the heat generating portion 223 is smaller than any of the conductive substance ratios R2 of the two lead portions 221 and 222. .. Further, in order to improve the strength of the heater element 40, the first average major axis length L1 of the heat generating portion 223 must be larger than any of the second average major axis lengths L2 of the two lead portions 221 and 222, respectively. Is preferable.

(3) As a method for increasing the first average major axis length L1 of the heat generating portion 223, various other methods are used instead of the method for increasing the particle size of the silicon nitride particles contained in the material of the heat generating portion 223. It can be adopted. When firing the heater element 40, silicon nitride particles tend to grow when the firing temperature is high. Further, since the content of the conductive substance in the lead portions 221 and 222 is higher than the content of the conductive substance in the heat generating portion 223, the silicon nitride particles in the lead portions 221 and 222 are higher than those in the heat generating portion 223 at the time of firing. Is hard to grow. Therefore, by raising the firing temperature, the growth of silicon nitride particles in the heat generating portion 223 can be promoted more than in the lead portions 221, 222, that is, the first average major axis length L1 is higher than the second average major axis length L2. Can also grow. If the firing temperature becomes excessively high, the silicon nitride particles are decomposed and become smaller. The appropriate firing temperature differs depending on the respective materials of the heat generating portion 223 and the lead portions 221 and 222. The firing temperature is preferably determined experimentally.

(4) As the configuration of the joint surfaces 241 and 242 of the heat generating portion 223 and the lead portions 221 and 222, various other configurations can be adopted instead of the configuration described with reference to FIG. For example, when the inclined portions 241x and 242x are traced from the inner peripheral side to the outer peripheral side, the inclined portions 241x and 242x are not inclined toward the rear end side (rear end direction D1r side), but are inclined toward the front end side (tip direction D1). It may be tilted toward the side). Further, the inclined portions 241x and 242x may include both a portion inclined toward the front end side and a portion inclined toward the rear end side. Further, the shapes may be different between the two joint surfaces 241 and 242. Further, the inclined portions 241x and 242x may be omitted from at least one of the two joint surfaces 241 and 242. In general, it is preferable that at least one of the two joint surfaces 241 and 242 includes a portion inclined at an angle with respect to the axis CL.

(5) The configuration of the heater element may be various other configurations instead of the configurations described in FIGS. 1, 2, and the like. For example, a terminal connected to the second lead portion 222 may be fixed to the heater element. The terminal may be fixed to, for example, the end face on the D1r side in the rear end direction of the heater element 40. Then, the terminal and the center pole 30 may be connected by a wire. In this case, the second electrode take-out portion 282 is omitted.

(6) The configuration of the glow plug may be various other configurations instead of the configuration described with reference to FIG. For example, a male screw is formed on the outer peripheral surface of the rear end portion 39 of the center pole 30, a female screw is formed on the terminal member 80, and the terminal member 80 is screwed into the rear end portion 39 of the center pole 30 to form the center pole 30. The terminal member 80 may be fixed. Here, as the terminal member 80, a nut may be used instead of the cap-shaped member. Further, as a method of fixing the heater element 40 to the main metal fitting 20, any other method can be adopted instead of the method of fixing the outer cylinder 70 holding the heater element 40 to the main metal fitting 20. For example, the rear end 49 of the heater element 40 may be press-fitted directly into the through hole 20x of the main metal fitting 20. In either case, the tubular main metal fitting 20 preferably accommodates the rear end 49 of the heater element 40. According to this configuration, a configuration in which the main metal fitting 20 holds the heater element 40 can be easily realized. Further, it is preferable that the heat generating portion 223 is provided in a portion of the heater element 40 arranged outside the through hole 20x of the main metal fitting 20. According to this configuration, the heater element 40 can appropriately superheat an object to be overheated (for example, a gas in a combustion chamber).

(7) The above-mentioned heater is applicable not only to glow plugs used for assisting the start of an internal combustion engine, but also to various glow plugs. For example, an exhaust gas heater device for raising the temperature of exhaust gas, a burner system for activating a catalyst or a diesel particle filter (DPF), a water heater device for raising the temperature of cooling water, etc. The heater of the above embodiment can be applied to the glow plug used in various devices of the above.

Although the present invention has been described above based on the embodiments and modifications, the above-described embodiments of the invention are for facilitating the understanding of the present invention and do not limit the present invention. The present invention can be modified and improved without departing from the spirit and claims, and the present invention includes equivalents thereof.

10 ... Glow plug, 20 ... Main bracket, 20x ... Through hole, 22 ... Male screw part, 28 ... Tool engagement part, 30 ... Central shaft, 31 ... Tip part , 39 ... rear end, 40 ... ceramic heater element (heater element), 41 ... front end, 49 ... rear end, 50 ... O ring, 60 ... insulating member, 62 ... Cylindrical part, 68 ... Flange part, 70 ... Metal outer cylinder (outer cylinder), 70x ... Through hole, 80 ... Terminal member, 90 ... Connection member, 210. .. Base (support), 220 ... Heat-generating resistor (resistor), 221 ... 1st lead part, 222 ... 2nd lead part, 223 ... Heat-generating part, 241 ... 1 Joint surface, 242 ... 2nd joint surface, 241x, 242x ... Inclined part, 281 ... 1st electrode extraction part, 282 ... 2nd electrode extraction part, 490 ... Heater module, G ... particles, L ... major axis length, C ... crack length, k ... indentation length, T ... distance, R1 ... first conductive material ratio, R2 ... second conductive Material ratio, L1 ... 1st average major axis length, L2 ... 2nd average major axis length, A1 ... 1st target area, A2 ... 2nd target area, C1 ... 1st angle , C2 ... 2nd corner, S1 ... 1st support, S2 ... 2nd support, S3 ... 3rd support, P1 ... 1st position, P2 ... 2nd Position, P3 ... 3rd position, D1 ... 1st direction (tip direction), D1r ... rear end direction, D2 ... 2nd direction, D3 ... 3rd direction, VI ... Indentation, CL ... central axis (axis), IM ... cross-sectional image, CR1 ... 1st crack, CR2 ... 2nd crack, OPa ... opening, OPb ... opening

Claims (3)

A ceramic heater element comprising a heat-generating resistor including a heat-generating portion and a lead portion connected to the heat-generating portion, and a support made of ceramic in which the heat-generating resistor is embedded.
The heat generating portion contains silicon nitride and a first conductive substance.
The lead portion contains silicon nitride and a second conductive substance.
The average value of the maximum outer diameters of the silicon nitride particles including at least a part in the first target region of the 15 μm × 15 μm square on the cross section of the heat generating portion is a 15 μm × 15 μm square on the cross section of the lead portion. Larger than the average value of the maximum outer diameters of the silicon nitride particles containing at least a part in the second target region of
The proportion of the first conductive substance in the first target region of the heat generating portion is smaller than the proportion of the second conductive substance in the second target region of the lead portion.
Ceramic heater element. The ceramic heater element according to claim 1.
The shape of the ceramic heater element is a rod shape extending in the direction of the axis.
The heat generating portion is arranged on the tip side in the direction of the axis, and the lead portion extends along the direction of the axis.
The heat generating portion and the lead portion are connected so as to overlap in a direction perpendicular to the direction of the axis.
The joint surface between the lead portion and the heat generating portion includes a portion that is inclined obliquely with respect to the direction of the axis.
Ceramic heater element. The ceramic heater element according to claim 1 or 2,
A tubular main metal fitting that accommodates the rear end of the ceramic heater element,
Ceramic glow plug with.