JP2001241660A - Ceramic heater and glow plug using the ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a ceramic heater capable of preventing a local overheat of a ceramic heating element arranged in the heater and having excellent durability and becoming the highest temperature on a surface of an end of the heater. SOLUTION: The ceramic heater 1 comprises an axial bar-like ceramic base 13 and a ceramic heating element 10 embedded in the base 14 to be resistance- heated. In this case, the element 10 is increased in an area of a bore side by forming a cross sectional shape of a top 10c of a U-shaped directional converter 10a, thereby dispersing a part becoming the highest temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ceramic heater used for a glow plug for a diesel engine and a glow plug using the ceramic heater. More specifically, the present invention relates to a technique for bringing a portion having the highest temperature on the surface of a ceramic heater close to a tip by resistance heat generated by a ceramic heating element disposed in the ceramic heater.

[0002]

2. Description of the Related Art Conventionally, as a ceramic heater used for a ceramic glow plug, a ceramic heater having a U-shaped direction change portion which generates resistance heat by energization is embedded in an insulating ceramic base. Things are known. And the ceramic heating element
One end of a linear electrode is buried on the end side for the current supply. This ceramic heater is manufactured, for example, as follows. That is, first, an integral molded body of a U-shaped conductive ceramic powder molded body that becomes a ceramic heating element after firing and an electrode is formed by injection molding or the like.
At this time, the U-shaped portion is formed in a rod shape having substantially the same outer diameter. On the other hand, separately from this, a concave portion for accommodating the above-mentioned integrally formed body is formed on the mating surface, and a divided preformed body which becomes a ceramic base after firing is produced by press molding or the like using base ceramic powder. Next, after accommodating the integrally formed body in the concave portion, the divided preformed bodies are matched with each other, and then they are pressed and integrated using a mold to obtain a composite formed body. Here, the pressing direction is set substantially perpendicular to the mating surface of the divided preform. The composite molded body thus obtained is subjected to a hot press treatment of baking while pressing in a direction perpendicular to the pressing direction, that is, in the direction of the mating surface, and further polishing the outer peripheral surface of the obtained fired body. Thus, a ceramic heater is obtained.

A ceramic heater manufactured by hot pressing in this way has a shape in which an internal ceramic heating element is crushed in a pressing direction at the time of hot pressing. However, since the pressing direction is perpendicular to the cross section, the top of the U-shaped direction changing portion has a shape similar to the shape of the conductive ceramic powder molded body before firing. That is,
Before baking, it is formed in a U-shaped rod shape, so that it keeps a circular shape even after baking hot press.

[0004]

When the heat generation state of the ceramic heating element inside the conventional ceramic heater as described above was analyzed by FEM, it was found that the heat was concentrated on a local small portion on the inner diameter side at the top of the U-shaped direction changing portion. It was found that heat was generated, and it was found that heat was not generated at all from the middle of the top of the U-shaped direction changing portion to the outer diameter side. For this reason, on the surface of the ceramic heater, the highest temperature is not the tip, but the highest temperature is the portion closer to the end where one end of the linear electrode is embedded. As a result, the temperature rise characteristics of the tip of the ceramic heater are slightly inferior,
Since heat is concentrated in a local minute portion, a crack is likely to be generated in that portion, so that it is expected that a problem will occur in durability.

[0005] As an example, FIG. 1 shows the result of calculating the temperature distribution of the tip of a conventional ceramic heater by FEM analysis.
4 and FIG. FIG. 15 shows a calorific value distribution per unit volume when a cross section of the inside of the ceramic heater is taken, where a low heat generating portion is represented by black, and the whiter the greater the calorific value is. ing. According to this analysis result, it is considered that heat is generated only on the inner diameter side of the top portion, and heat is diffused from this portion to each portion. In FIG. 14, the abscissa indicates the distance along the surface from the position to the end, with the foremost position 0 of the ceramic heater, and the ordinate indicates the temperature at that distance. As described above from this analysis result, the highest temperature portion of the ceramic heater surface is not the tip,
It can be seen that the portion is closer to the end.

An object of the present invention is to prevent local heating of a ceramic heating element provided in a ceramic heater,
It is an object of the present invention to provide a ceramic heater having excellent durability in which the tip surface of the ceramic heater has the highest temperature and a glow plug using such a ceramic heater.

[0007]

The ceramic heater according to the first aspect of the present invention has an axial rod-shaped ceramic base, and is buried inside the ceramic base and is energized from its own end side. A ceramic heating element having resistance heating and a ceramic heating element, wherein the ceramic heating element includes a U-shaped direction changing portion,
The top cross-sectional shape of the direction changing portion has a width b and a thickness c,
It is characterized by satisfying the relationship of b> c.

The reason why the temperature distribution of the conventional ceramic heater has the above-described temperature distribution is considered to be as follows. That is, when a voltage is applied to the electrode portion provided on the ceramic heater, a current flows through the ceramic heating element. However, this current does not flow uniformly over the entire cross section of the ceramic heating element, but flows intensively in a low resistance portion in the ceramic heating element. In the linear heating portion 100b of the ceramic heating element shown in FIG. 15, the current flows almost uniformly. However, in the vicinity of the top 100c of the direction changing portion 100a, since the resistance value becomes high on the outside diameter side because the path is long even in the ceramic heating element, current hardly flows on the outside diameter side. As a result,
It is considered that the current concentrates and flows on the short path, that is, on the inner diameter side where the resistance value is low. The ceramic heating element disposed in the ceramic heater of the conventional structure has a top 10
Since the cross-sectional shape near 0c is circular, the current concentrates on the inner diameter side having the lower resistance value as described above.

Therefore, by forming the top cross-sectional shape of the direction changing portion such that the width b and the thickness c satisfy the relationship of b> c as in the first invention, the resistance value is low. The area on the inner diameter side can be increased. Since the area of this portion can be increased, the concentration of current can be dispersed. As a result, since local heat generation can be reduced, the heat diffusivity is improved, and the temperature rise characteristics at the tip of the ceramic heater can be improved, and wasteful power consumption can be suppressed. In addition, since it is possible to alleviate the heat generated by local minute parts,
Cracks can be prevented from occurring at that portion. In addition, in this specification, when the U-shaped ceramic heating element is viewed from the front as shown in FIG.
H × 3% based on the center of

[0010] A ceramic heater according to a second aspect of the present invention comprises a ceramic base in the form of a rod in the axial direction, and a ceramic heating element buried inside the ceramic base and which generates resistance by being energized from its end. In the ceramic heater, the ceramic heating element includes a U-shaped direction changing portion, and a width b 'on the base side of the direction changing portion on the top side cross-sectional shape in the top cross-sectional shape satisfies the relationship of b>b'. Characterized by having a portion.

As described above, the U-shaped portion of the ceramic heating element disposed in the ceramic heater having the conventional structure has a rod shape having substantially the same diameter before firing, so that the U-shaped portion is maintained even after firing. The width of the part was almost constant. For this reason, at the top part having a circular cross section after firing, local heat is generated on the inner diameter side. As a method of increasing the area on the inner diameter side, a method of forming the shape as in the first invention described above may be used. However, even if the cross-sectional shape at the top is circular, as in the second invention, Alternatively, a method of increasing the area in the method may be used.
As described above, the above-mentioned problem can be solved by satisfying the relationship of b> b ′ where the width b ′ on the noble portion side with respect to the width b at the top portion of the direction change portion. Note that the cross-sectional shape at the top is not necessarily limited to a circular shape, but may be any shape as long as the effects of the present invention are exhibited. For example, the shape may be semicircular or elliptical. Further, the effects of the present invention can be further improved even if the shape is a combination of the first invention and the second invention.

Next, a ceramic heater according to a third aspect of the present invention comprises:
In a ceramic heater having an axial rod-shaped ceramic base and a ceramic heater buried inside the ceramic base and generating resistance heat when energized from its own end, the ceramic heater is a U-shaped ceramic heater. An end-side contour in a range of 60% of the center of the width b in the top cross-sectional shape of the direction changing unit,
An area A formed by a tangent at the center of the end side contour line;
When an imaginary circle having a width b as a diameter is drawn so as to be in contact with the center of the end-side outline, the area A ′ formed by the imaginary circle and the tangent in a range of 60% of the center is A ′> It has a portion that satisfies the relationship of A. With such a configuration, it is possible to increase the area on the inner diameter side particularly in the range of 60% at the center where local heat is easily generated. The cross-sectional shape at the top may be any shape as long as the effects of the present invention are exhibited. For example, the shape may be a rectangle, a square, or an ellipse. Further, the shape may be as shown in FIG. Further, the effect of the present invention can be further improved even if the shape is a combination of any two of the first to third inventions.

Next, a ceramic heater according to a fourth aspect of the present invention comprises:
The top-side cross-sectional shape is such that when the end-side contour line in the range of 60% of the center of the width is formed by one or two straight lines, and when it is constituted by two straight lines, the included angle α Is 160 ° ≦ α <180 °. In the present invention, the included angle α of a straight line when the rhombus is formed into an R-shape as shown in FIG. 7 or a shape as shown in FIG. 9 is defined. When the end-side outline is formed by a single straight line, it is considered that the included angle α is 180 °, and thus α may be considered as 160 ° ≦ α ≦ 180 °. With such a configuration, the area on the inner diameter side of the top portion that locally generates heat can be further increased, so that the effects of the present invention can be more easily achieved. In addition, since the integrally formed body of the U-shaped conductive ceramic powder compact and the electrode, which becomes the ceramic heating element after firing, is molded by injection molding or the like, it is preferable to form a taper from the viewpoint of work problems. Since it is considered that this draft taper needs to be about 1 °, it is preferable that the opening angle α of the end side contour line is α ≦ 178 °. The effects of the present invention can be further improved even if the shape is a combination of any two or more of the first to fourth inventions.

Next, a ceramic heater according to a fifth aspect of the present invention comprises:
The thickness c ′ on the end side with respect to the thickness c at the top is c <c ′
Is satisfied. With such a configuration, it is possible to eliminate a portion on the top outer diameter side where no heat is generated. Therefore, the heat-generating portion on the inner diameter side of the top portion can be arranged at a more distal end side of the ceramic heater. As a result, the position of the highest temperature can be brought closer to the tip as compared with the ceramic heater having the conventional structure, so that the temperature rising characteristic of the tip of the ceramic heater can be improved.

In the ceramic heater having a small diameter at the tip, the portion having the small diameter has the highest temperature on the surface of the ceramic heater due to the resistance heating of the ceramic heating element as described above. Therefore, it is possible to improve the temperature rise characteristics of the tip of the ceramic heater and to suppress unnecessary power consumption.

If the ceramic heater as described above is used for a glow plug for a diesel engine, it becomes possible to improve the ignition characteristics of the diesel engine.
It is more preferable that the highest temperature portion of the ceramic heater surface be the most advanced.

[0017]

Embodiments of the present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 shows a glow plug using a ceramic heater according to the present invention, together with its internal structure. That is, the ceramic glow plug 50 is connected to the ceramic heater 1 provided at one end thereof.
A metal outer cylinder 3 that covers the outer peripheral surface of the ceramic heater 1 so that the curved front end 2 protrudes, and a cylindrical metal housing 4 that covers the outer cylinder 3 from outside. ing. The ceramic heater 1 and the outer cylinder 3 and the outer cylinder 3 and the metal housing 4 are respectively joined by brazing. In addition, one end of a coupling member 5, both ends of which are formed in a helical spring shape by a metal wire, is fitted from the outside to the rear end of the ceramic heater 1, and the other end is inserted into the metal housing 4. It is fitted to one end of the metal shaft 6. The other end of the metal shaft 6 extends to the outside of the metal housing 4, and a nut 7 is screwed into a screw portion 6 a formed on the outer peripheral surface of the metal shaft 6. The metal shaft 6 is fixed to the metal housing 4. An insulating bush 8 is fitted between the nut 7 and the metal housing 4. And
Screws 5 a for fixing the ceramic glow plug 50 to an engine block (not shown) are formed on the outer peripheral surface of the metal housing 4.

The ceramic heater 1 has a cylindrical straight rod 14.
By forming the tip 2 of the portion into a curved surface, the straight rod 1
The four parts are formed to have a small diameter. Further, as shown in FIG. 2, the ceramic heater 1 has a direction changing portion 10a extending from one end and changing direction to reach the other end.
U-shaped ceramic heating element 1 having two linear portions 10b extending in the same direction from each end of the direction changing portion 10a.
And rod-shaped electrode portions 11 and 1 at both ends thereof.
2 are buried. On the other hand, the ceramic heating element 10
3 has a shape as shown in the overall view of FIG. 3 and a half cross-sectional view in which a cross section is taken at the top portion 10c in FIG. 7, and has the largest cross-sectional area at the connection portion between the direction changing portion 10a and the straight portion 10b. Is getting smaller. The width b ′ and the thickness c ′ at the connection between the direction changing portion 10a and the straight portion 10b are shaped such that the width increases and the thickness decreases toward the top 10c. The top portion 10c has a substantially diamond-shaped apex in an R-shaped cross section.

In this embodiment, the direction changing unit 10a
B ′ and thickness c ′ at the connection between the wire and the straight portion 10b
Are set to b ′ = 1.2 mm and c ′ = 0.8 mm, respectively. The width b ″ and the thickness c ″ of the linear portion 10b are set to b ″ = 2 mm and c ″ = 1.2 mm, respectively. Further, in the present embodiment, the cross-sectional shape at the top 10c is formed in a substantially rhombic shape with an R-shaped apex, but may be elliptical. The cross-sectional area of the direction changing portion 10a is smaller than that of the straight portion 10b so that the temperature on the surface of the ceramic heater 1 has an overshoot characteristic at the initial stage of voltage application.
b can also be formed so that the cross-sectional areas are equal to each other.

The ceramic heating element 10 has a top 1
0c is disposed in the curved front end 2 of the ceramic base 13 of the ceramic heater 1. The top 10c is set in a range of 1 to 3 mm, preferably 0.5 to 3 mm, from the forefront of the ceramic base 13. Further, each of the electrode portions 11 and 12 is
It extends in the direction away from the ceramic heating element 10 in the ceramic base 13 and one of them (1
2) is inside the outer cylinder 3, the other (11) is near the other end of the ceramic base 13, and its rear end is exposed on the surface of the ceramic base 13, and the exposed portion 1 is exposed.
2a and 11a are formed. The tips 11 b and 12 b buried in the ceramic heating element 10 are arranged so as to enter the outer cylinder 3 from the end surface 3 a of the outer cylinder 3. The distance between the tip and the end face 3a of the outer cylinder 3 is 2
２０20 mm, preferably 3-20 mm.

The ceramic heating element is made of a conductive ceramic, for example, a low-resistance material such as tungsten carbide (WC), molybdenum silicide (MoSi ₂ ), tungsten (W), tungsten silicide (WSi ₂ ), and silicon nitride (S).
Although it is composed of a composite with an insulating material such as i ₃ N ₄ ), a semiconductor ceramic such as silicon carbide (SiC) can also be used. The electrode portions 11 and 12 are made of a refractory metal alloy such as tungsten (W) or tungsten-rhenium (Re). In addition,
The electrode portions 11 and 12 may be made of the above-described low-resistance material selected from a material group forming the ceramic heating element 10. In this case, the resistance of the electrode portions 11 and 12 is set to be lower than at least the ceramic heating element 10. In the present embodiment, the electrode portions 11 and 12 are connected to both ends of the ceramic heating element 10.
0 may be directly exposed to the surface of the ceramic base 13 to conduct electricity. On the other hand, the ceramic base 13 is mainly made of insulating ceramics, for example, alumina (Al ₂ O ₃ ), silica (SiO ₂ ), zirconia (Z
rO ₂ ), titania (TiO ₂ ), magnesia (Mg
O), mullite _{(3Al 2 O 3 · 2SiO 2} ), zircon _(ZrO 2 · _SiO 2), cordierite (2MgO
.2Al ₂ O ₃ .5SiO ₂ ), silicon nitride (Si
₃ N _4), constituted by aluminum nitride (AlN) or the like.

In FIG. 2, glass (not shown) is baked on the surface of the ceramic substrate 13 except for the region including the exposed portion 12a of the electrode portion 12, and the ceramic substrate 13 is baked through the glass layer. And the outer cylinder 3 are joined by brazing. On the other hand, the electrode part 12
Since the exposed portion 12a and the brazing material are directly joined, the outer cylinder 3
It is conducting. The joining member 5 is also brazed to a region including the exposed portion 11a of the electrode portion 11. With this configuration, power is supplied from a power source (not shown) to the ceramic heating element 10 via the metal shaft 6 (FIG. 1), the coupling member 5, and the electrode section 11, and further, the electrode section 12, the outer cylinder 3, It is grounded via a metal housing 4 (FIG. 1) and an engine block (not shown). This energization causes the ceramic heating element 10 to generate resistance heat. In the present embodiment, the exposed portion 12a of the electrode portion 12 is formed inside the outer tube 3. However, the exposed portion 12a is formed at the center of the ceramic base 13 outside the outer tube 3, and the exposed portion 12a is formed via a coil-shaped coupling member. The electrical connection may be made by brazing to the outer cylinder 3.

Here, each tip 11 of the electrode portions 11 and 12
By arranging the electrodes b and 12b so as to enter the outer tube 3 side from the end surface 3a of the outer tube 3, the interface portion P between the electrode portions 11 and 12 and the ceramic heating element 10 can reduce the generation of heat generated by the ceramic heater. The outer cylinder 3 is located away from the vicinity of the end face of the outer cylinder 3 which is easily expanded / contracted by heat from the engine, and the compressive stress from the outer cylinder 3 accompanying the expansion / contraction is:
It becomes difficult to act on the interface portion P. As a result, it is possible to prevent or suppress the occurrence of cracks and the like in the ceramic heating element 10 in the vicinity of the interface portion P. Here, if the distance 1 from each of the tips 11b and 12b of the electrode portions 11 and 12 to the end surface 3a of the outer cylinder 3 is less than 2 mm, the above-described effect may not be achieved. The distance 1 is more desirably set to 3 mm or more. on the other hand,
If the distance l exceeds 20 mm, the length of the ceramic heating element 10 existing in the outer cylinder 3 becomes longer, and the brazing material joining the outer cylinder 3 and the ceramic heater 1 becomes the heating element 1
Problems such as melting and flowing out due to excessive heat generation from 0 may occur. Therefore, the distance 1 is set to 20 mm or less.

The ceramic heater 1 can be manufactured, for example, by the following method. First, FIG.
As shown in FIG. 3, the electrode material 3 is placed on a mold 31 having a U-shaped cavity 32 corresponding to the ceramic heating element 10.
0 is positioned such that its end enters the cavity 32. Then, in this state, by injecting a compound 33 containing the conductive ceramic powder and the binder, the electrode material 30 and the U-shaped conductive ceramic powder molding part 34 are formed as shown in FIG. Is formed into an integrated injection molded body 35. The section 34b that becomes the straight section 10b after firing has a substantially circular cross section.

On the other hand, separately from the above, by pre-press-molding the ceramic powder for forming the ceramic base 13, pre-formed bodies 36 and 37 formed separately as shown in FIG. Have prepared. These preformed bodies 36 and 37 are formed in shapes corresponding to the respective divided portions, assuming that the ceramic base 13 is divided into two by a cross section substantially parallel to the axis thereof. A concave portion 38 having a shape corresponding to the integral molded body 35 is formed in a corresponding portion. Then, the integrated injection molded body 35 is accommodated in the concave portion 38, and the upper and lower preformed bodies 36 and 37 are matched with each other. In this state, the preformed bodies 36 and 37 and the integrated injection molded body 35 are combined.
By further pressing and integrating using a mold,
A composite molded body 39 as shown in FIG.

The composite molded body 39 thus obtained is first calcined to remove the binder component from the conductive ceramic powder molded part 34 or the preformed bodies 36 and 37 by injection molding, and then FIG. As shown in FIG. 3, hot press firing is performed at a predetermined temperature while pressurizing between molding machines 40 made of graphite or the like to obtain a fired body 41 as shown in FIG. At this time, FIG.
The conductive ceramic powder molding machine 34 shown in (b) shows the ceramic heating element 10, the preforms 36 and 37 the ceramic base 13, and the electrode material 30 the electrode parts 11 and 12.
Are formed respectively. Then, by performing processing such as polishing on the outer surface of the fired body 41 as necessary,
A ceramic heater 1 as shown in FIG. 2 is obtained.

[0027]

Next, an experimental example for showing the effect of the present invention will be described. Sample No. Are examples according to the present invention. Is a comparative product for confirming the difference in effect from the present embodiment. Sample No. Are examples in which the cross-sectional shape of the top 10c is elliptical. ~
Is an example in which the cross-sectional shape shown in FIG. Shows an example in the case of a cross-sectional shape in which the vertices of a rhombus are substantially R-shaped. The width b and the thickness c, and in the case of the sample 〜, various shapes were prepared for the included angle α of the base side contour line in the range of 60% of the center of the width b.
The sample No. Are the sample Nos. In FIG. ~
FIG. FIG. 8 shows an enlarged view of the cross-sectional shape at the top. In these drawings, the tangent line 20 and the imaginary circle 21 and the imaginary line 22 indicating the range of 60% of the center of the width are shown so as to be in contact with the center of the base end side contour line 10d.
Is indicated by a dotted line.

Sample No. In the case of, the cross-sectional shape of the top portion 10c is such that the base side contour line 10d in the range of 60% of the center of the width is formed by two straight lines. This 2
The included angle α of the straight line of the sample No. -And sample No.
Is formed at 160 ° ≦ α <180 °.
Are formed at α = 156 ° <160 °.

In addition, the sample No. Has a circular cross-sectional shape as shown in FIG.
Therefore, both the width b and the thickness c are equal to the diameter.
Further, the width b in this cross section, that is, the diameter and the width b ′ on the base side are the same, and the thickness c in this cross section, that is,
The diameter and the thickness c 'on the base side are the same. FIG. 12 shows the results of tests on the temperature rise characteristics, power consumption, and endurance of current conducted on these samples. Further, FIG. 12 shows an area A surrounded by an imaginary line 22 indicating the range of the center 60% of the tangent line 20 and the width b and the base end side contour line 10d, and a range of the center 60% of the tangent line 20 and the width b. , And the area A ′ surrounded by the virtual circle 21 are shown at the same time.

From these test results, it can be seen that a sample having a large width b and a small thickness c shows the best results in each test. In addition, the test method of each test is shown below. Temperature rising characteristic test: When a voltage at which the temperature of the curved tip 2 becomes 1350 ° C. is applied 60 seconds after the start of energization, the temperature of the tip 2 3 seconds after the start of application is measured. . In this case, at least 800 ° C. and 850
The range below ℃ was acceptable (△), the range between 850 ° C and 900 ° C was good (良), and the range above 900 ° C was excellent (優). Power consumption test: The power consumption at the time of steady temperature when a voltage at which the temperature of the tip 2 formed into a curved surface becomes 1350 ° C. is applied at the time of steady temperature is measured. In this case,
80W or more average (×), 75W or more and less than 80W possible (△), 70W or more and less than 75W good (範 囲), 7
A range of less than 0 W was judged as excellent (（). Energization endurance test: When the temperature is steady, at a voltage at which the temperature of the tip 2 formed into a curved surface becomes 1350 ° C., energize for 1 minute, cut off energization for 1 minute
When an endurance test is performed with a cycle of forced cooling by air at the time of energization interruption as one cycle, the number of cycles until the temperature of the tip 2 becomes 1300 ° C. or less due to factors such as an increase in the resistance value of the ceramic heating element is measured. . In this case,
A range of 15,000 cycles to less than 20,000 cycles is average (x), a range of 20,000 cycles to less than 25,000 cycles is acceptable (サ イ ク ル), 25,000 cycles to 30
A range of less than 000 cycles was judged as good (○), and a sample without abnormality even after 30,000 cycles was judged as excellent (◎).

From the results of these tests, the following was confirmed. 1. Sample N whose width b and thickness c satisfy the relationship of b> c
o. -And sample No. Is a sample No. as a comparative example.
It turns out that it is excellent in energization durability compared with. 2. Sample No. in which the width b ′ on the base side with respect to the width b satisfies the relationship of b> b ′. And sample no. Is a sample No. as a comparative example. It turns out that it is excellent in energization durability compared with. 3. Sample No. in which the area A and the area A ′ satisfy the relationship of A ′> A. -Are sample Nos. Which are comparative examples. It turns out that it is excellent in energization durability compared with. 4. Sample No. 1 in which the base side contour line in the range of 60% at the center of the width b is formed by one or two straight lines.
In the sample No., the included angle α is 160 ° ≦ α ≦ 180 °. -And sample No. Is that the included angle α is 154
It can be seen that the current-carrying durability is further improved as compared with the sample of ゜. 5. The sample No. whose thickness c ′ on the base side with respect to the thickness c satisfies the relationship of c <c ′. -And sample No. Is a sample No. as a comparative example. Compared with, since it has excellent current-carrying durability and the highest temperature part of the ceramic heating element can be arranged at the most advanced side of the ceramic base,
It can be seen that the temperature rise characteristics are also improved. Further, power consumption can be further reduced. 6. The width b and the thickness c satisfy the relationship of b> c, the width b ′ on the base side of the width b satisfies the relationship of b> b ′, and the area A
And the area A ′ satisfy the relationship of A ′> A, and the included angle α
Is 160 ° ≦ α ≦ 180 °, and the thickness of the sample No. satisfies the relationship of c <c ′ with respect to the thickness c ′ on the base side of the thickness c.
It can be seen that is the best in all of the temperature rise characteristics, power consumption, and energization durability.

Next, Sample No. 1 having the best current-carrying durability, power consumption, and temperature rising characteristics was used. And sample N as a comparative example
o. FIG. 13 shows the results of measuring the temperature distribution at the time of steady temperature when a voltage at which the temperature of the tip 2 formed into a curved surface becomes 1350 ° C. at the time of steady temperature is applied. In FIG. 13, the horizontal axis indicates the distance along the surface in the base direction from this position with the leading end position of the ceramic heater being 0, and the vertical axis indicates the temperature at that distance. The symbol P in FIG. 13 indicates the position of the boundary between the tip 2 and the straight rod 14 in the ceramic heater 1.
As a result, the sample No. It can be seen that the highest temperature of the ceramic heater is highest, and the temperature decreases toward the base side. On the other hand, the sample No. It can be seen that is the position where the highest temperature of the ceramic heater surface is not at the front end 2 but closer to the base side.

[Brief description of the drawings]

FIG. 1 is a front partial sectional view showing an example of a glow plug of the present invention.

FIG. 2 is a front sectional view of the ceramic heater.

FIG. 3 is an overall view of a ceramic heating element.

FIG. 4 is an explanatory diagram of a manufacturing process of the ceramic heater.

FIG. 5 is an explanatory view of the process following FIG. 4;

FIG. 6 is an explanatory view of the process following FIG. 5;

FIG. 7 is a half sectional view when the ceramic heating element according to the present invention is sectioned at the top.

FIG. 8 is an enlarged top view of the ceramic heating element according to the present invention.

FIG. 9 is an enlarged top view of a ceramic heating element according to another embodiment of the present invention.

FIG. 10 is an enlarged top view of a ceramic heating element according to another embodiment of the present invention.

FIG. 11 is an enlarged top view of a ceramic heating element according to a comparative example of the present invention.

FIG. 12 is a drawing showing experimental results of the present invention.

FIG. 13 is a drawing showing a temperature distribution of ceramic heaters according to an example of the present invention and a comparative example.

FIG. 14 is a diagram showing a temperature distribution of a conventional ceramic heater.

FIG. 15 is a drawing showing a temperature distribution in a cross section of a conventional ceramic heater obtained by FEM analysis.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic heater 2 Front end 10 Ceramic heating element 10a Direction conversion part 10b Linear part 10c Top part 10d Base end side contour line 11 Electrode part 12 Electrode part 13 Ceramic base 20 Tangent line 21 Virtual circle 22 Virtual line (line indicating 60% of width center) ) 50 Ceramic glow plug α Included angle b Width c Thickness

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masahiro Konishi 14-18, Takatsuji-cho, Mizuho-ku, Nagoya-shi Inside Japan Special Ceramics Co., Ltd. Ceramics Co., Ltd.

Claims (9)

[Claims] 1. A ceramic heater comprising: an axial rod-shaped ceramic base; and a ceramic heating element buried inside the ceramic base and configured to generate resistance heat by being energized from an end of the ceramic base. A ceramic heater, wherein the body includes a U-shaped direction changing portion, and a width b and a thickness c of a top cross-sectional shape of the direction changing portion satisfy a relationship of b> c. 2. A ceramic heater comprising: an axial rod-shaped ceramic base; and a ceramic heating element buried inside the ceramic base and configured to generate heat by resistance when energized from an end of the ceramic base. The body is provided with a U-shaped direction change portion, and the width b in the top cross-sectional shape of the direction change portion is provided.
A width b ′ closer to the end than the end portion satisfies the relationship of b> b ′. 3. A ceramic heater comprising: an axial rod-shaped ceramic base; and a ceramic heating element buried inside the ceramic base and configured to generate resistance heat when energized from an end thereof. The body is provided with a U-shaped direction change portion, and the width b in the top cross-sectional shape of the direction change portion is provided.
, An area A defined by an end-side contour line in a range of 60% of a center thereof, a tangent line at the center of the end-side contour line, and a width b.
When an imaginary circle having a diameter of is drawn so as to be tangent at the center of the end side contour line, an area A ′ formed by the imaginary circle and the tangent line within a range of 60% of the center is A ′ >
A ceramic heater having a portion satisfying the relationship of A. 4. The top cross-sectional shape has a center 6
In the case where the end side contour line in the range of 0% is formed by one or two straight lines and is constituted by two straight lines, the included angle α is 160 ° ≦ α <180.
The ceramic heater according to claim 3, wherein? 5. A ceramic heater comprising: an axial rod-shaped ceramic base; and a ceramic heating element buried inside the ceramic base and configured to generate resistance heat when energized from an end thereof. A ceramic heater provided with a U-shaped direction changing portion, wherein the thickness c 'on the end side of the direction changing portion satisfies a relationship of c <c' with respect to a thickness c at a top portion of the direction changing portion. . 6. The ceramic heater, wherein a tip is formed to have a small diameter, and a portion of the surface of the ceramic heater at which a maximum temperature is obtained by resistance heating of the ceramic heating element is the tip. Claims 1 to 5
The ceramic heater according to any one of the above. 7. The ceramic heater according to claim 1, wherein a portion of the surface of the ceramic heater at which the temperature is highest is a front end. 8. A ceramic heater comprising: an axially rod-shaped ceramic base; and a ceramic heating element buried inside the ceramic base and configured to generate resistance heat when energized from an end of the ceramic base. Has a small diameter tip,
The ceramic heater is characterized in that a portion of the surface of the ceramic heater at which the temperature becomes the highest by resistance heating of the ceramic heating element is the tip. 9. A glow plug comprising the ceramic heater according to claim 1.