JPH09190874A - Ceamic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heater having a heat emitting element of ceamic, which excels in the durability to current and is unlikely to generate unevenness in the temp. distribution. SOLUTION: A ceramic heater 1 is equipped with a ceramic base body 13 having a circular section and a heat emitting element 10 which is embedded in the base body 13 and makes resistance heat emission when current is fed through electrodes connected with the two ends. The heat emitting element 10 is equipped with a direction changing part 10a extending from one of its base ends, changing the heading at the foremost, and leading to the other end, and two straight portions 10b stretching in the same direction from the base ends of the direction changing part, wherein the section of each straight portion 10b assumes an ellipse inscribing with a virtual circular region 13a set in the section of the base 13. The ratio of the diameter ϕX of the circular region 13a to the section diameter ϕY of the base should range between 0.3 and 0.7. On the elliptical section of the straight portion 10b, the ratio of the length of long axis P to the length Q of short axis should range between 1.2 and 2.5.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a ceramic heater used for a glow plug for a diesel engine, a heating element for burner ignition or an oxygen sensor, and the like.

[0002]

2. Description of the Related Art Heretofore, as a ceramic heater used for a ceramic glow plug, there has been known a ceramic heater having a structure in which an insulating ceramic substrate is embedded with a ceramic heating element which generates heat by resistance. For such a ceramic heater, for example, a plurality of plate-shaped or sheet-shaped insulating ceramic powder compacts on which a pattern is printed using a paste prepared by adding a solvent to a conductive ceramic powder and kneading the surface are prepared. It is manufactured by stacking these and firing the stacked body by hot pressing or the like. In this case, the printed conductive ceramic powder pattern is sintered to form a ceramic heating element.

[0003]

As shown in FIG.
In the ceramic heater 100 as described above, the thickness of the ceramic heating element 101 based on pattern printing is 10
Since the thickness is as thin as ˜30 μm and the volume ratio of the ceramic heating element 101 to the ceramic substrate 102 is small, the temperature distribution on the surface of the ceramic heater 100 is likely to be uneven. Further, since the ceramic heating element 101 is formed to be extremely thin as described above, the thickness thereof tends to be nonuniform due to the influence of variation in dimensional shrinkage during firing. Therefore, uneven heating is likely to occur in the ceramic heating element 101, and long-term energization durability may not be ensured.

An object of the present invention is to provide a ceramic heater which is excellent in durability against electricity flow of a ceramic heating element.

[0005]

A ceramic heater according to the present invention has a ceramic base having a cross section in which at least a part of its outer circumference is formed in an arc shape, and is embedded in the ceramic base and connected to both ends thereof. In order to solve the above problems, a ceramic heating element that generates resistance resistance by being energized via the electrode part is provided.
It has the following features. That is, the ceramic heating element
A direction changing part extending from one base end part to change direction at the tip part to reach the other base end part, and two straight line parts extending in the same direction from each base end part of the direction changing part, The cross section of the straight line portion has an elliptical shape inscribed in a virtual circular region (hereinafter also referred to as a heat generating body existing region) set in the cross section of the ceramic base. Also, the diameter φ of the virtual circular area
The ratio φX / φY between X and the cross-sectional diameter φY of the ceramic substrate is set within the range of 0.3 to 0.7. Further, the elliptical cross section of the straight line portion is set such that the ratio P / Q of the major axis length P and the minor axis length Q thereof is in the range of 1.2 to 2.5. In addition,
The cross-sectional diameter φY of the ceramic base is defined by the diameter of the circular outer circumference when the entire outer circumference of the ceramic base is formed in an arc shape, that is, when the outer circumference of the cross-section is formed in a circular shape. And Further, when only a part is formed in an arc shape, φY is defined as the diameter of the circular area that gives the arc-shaped outer peripheral portion.

That is, P / Q is 1.2 to while securing the heating element existence region so that φX / φY is 0.3 to 0.7.
By setting 2.5, the surface of the ceramic heater can be rapidly and uniformly heated. P / Q is 1.
If it is set out of the range of 2 to 2.5, uneven heating may occur on the surface of the ceramic heater. Also, φX /
If φY is less than 0.3, the distance from the surface of the ceramic heating element to the surface of the ceramic substrate becomes too large, which causes a problem that the temperature rise on the surface of the ceramic heater becomes dull. On the other hand, since the strength of the ceramic heating element is generally not so high, the ceramic base body also plays a role of reinforcing the ceramic heating element. However, φX / φY
When the value exceeds 0.7, the distance from the surface of the ceramic heating element to the surface of the ceramic substrate becomes too small, and the above reinforcing effect may be insufficient. Therefore, φX / φ
Y is set within the above range. In addition, more desirably,
P / Q is 1.6 to 2.0 and φX / φY is 0.5 to
It is good to set it to 0.6.

Next, in the ceramic heating element, the volume ratio of the heating element to the ceramic substrate is increased by setting the minor axis length Q of the elliptical cross section of the linear portion to 0.1 mm or more, and the ceramic heater is increased. The temperature distribution can be made uniform. Further, since the influence of variation in dimensional shrinkage during firing is reduced, uneven heating is less likely to occur in the ceramic heating element, and consequently, long-term electrical durability of the ceramic heating element can be secured. Minor axis length Q
Is more preferably set to 0.5 mm or more.

The cross section of each linear portion of the ceramic heating element can be formed into an elliptical shape compressed in the direction in which the linear portions face each other. Thereby, the temperature distribution on the heater surface can be made more uniform. As a method for manufacturing such a ceramic heater, a method including the following steps can be adopted. First molding step: An integrally molded body having a conductive ceramic powder molding portion having a shape corresponding to the above-mentioned ceramic heating element and electrode portions connected to both ends thereof is manufactured. Second molding step: The outside of the integrally formed body is covered with the base ceramic powder and then compressed to produce a composite formed body in which the integrally formed body is embedded and integrated in the base ceramic powder forming portion. Firing step: By firing the composite molded body while pressurizing it in the opposite direction of the two straight portions of the conductive ceramic powder molded portion, the conductive ceramic powder molded portion having a circular cross section has an elliptical cross section. To obtain a fired body having a base ceramic powder molding portion as a ceramic base.

According to the above method, the electrically conductive ceramic powder molded portion having a circular cross section is fired while applying a pressing force along the opposing direction of its straight line portion, thereby facilitating the ceramic heating element having an elliptical cross section. Can be obtained.

More specifically, the second molding step may include the following steps. A divided preformed body that is formed on a mating surface with each other and has a concave portion for accommodating an integrally molded body such that two linear portions of the conductive ceramic powder molding portion are arranged on the mating surface is formed into a substrate. It is made of ceramic powder. The divided preforms are matched with each other in a state where the integrally formed body is accommodated in the recess. A composite powder compact is formed by pressurizing and integrating the integrated compact and the divided pre-molded body in a direction substantially orthogonal to the mating surface. In this case, in the firing step, the composite formed body is pressed in the direction along the mating surface of the divided preformed body.

According to the above method, by using the divided preform, the positioning of the ceramic powder compact with respect to the base ceramic powder compact can be carried out very easily, which contributes to the improvement of the manufacturing efficiency of the ceramic heater.

[0012]

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 glow plug 50 includes a 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 a tip end portion 2 of the ceramic heater 1 projects, and further includes the outer cylinder 3. A cylindrical metal housing 4 and the like, which are covered from the outside, are provided. 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, at the rear end of the ceramic heater 1,
Coupling member 5 whose ends are formed in a spiral spring shape by metal wires
While one end of is fitted from the outside, the other end is fitted to the corresponding end of the metal shaft 6 inserted in the metal housing 4. The other end portion side of the metal shaft 6 extends to the outside of the metal housing 4, and a nut 7 is screwed into a screw portion 6a formed on the outer peripheral surface of the metal shaft 4, and the nut 7 is tightened toward the metal housing 4. The shaft 6 is fixed to the metal housing 4. Also, nut 7
An insulating bush 8 is fitted between the housing and the metal housing 4. Then, on the outer peripheral surface of the metal housing 4,
A screw portion 5a for fixing the glow plug 50 is formed on an engine block (not shown).

As shown in FIG. 2, the ceramic heater 1 includes a direction changing portion 10a which extends from one base end portion and changes direction at the tip end portion to reach the other base end portion, and the direction changing portion 10a.
A U-shaped ceramic heating element 10 having two linear portions 10b extending in the same direction from the respective base end portions of a is provided, and the tip portions of the linear or rod-shaped electrode portions 11 and 12 are provided at both ends thereof. And the entire ceramic heating element 10 and the electrode portions 11 and 12 are embedded in a rod-shaped ceramic substrate 13 having a circular cross section. The ceramic heating element 10 is arranged such that the direction changing portion 10 a is located on the tip side of the ceramic base 13. In addition, each electrode unit 1
Reference numerals 1 and 12 extend in the ceramic base 13 in a direction away from the ceramic heating element 10, and one of them (12) is inside the outer cylinder 3 and the other one (11) is the other end of the ceramic base 13. In the vicinity of the portions, the rear ends thereof are exposed on the surface of the ceramic base 13 to form exposed portions 11a and 12a.

Further, as shown in FIG. 3, the cross-sectional shape of each linear portion 10b of the ceramic heating element 10 is an elliptical shape compressed in the opposing direction. In addition, the cross section of the ceramic base 13 is formed in a circular shape having its center at a position O that divides the distance between the axes of the two linear portions 10b of the ceramic heating element 10 into substantially equal parts. In addition, straight part 1
The cross section of 0b is set within the cross section of the ceramic base, and is a virtual circular area (heating element existing area) 1 with O as the center.
3a is inscribed in each. In addition, the heating element existence area 13
Ratio of diameter a of φa and cross-sectional diameter φY of ceramic substrate φX /
φY is 0.3 to 0.7 (preferably 0.5 to 0.6)
It is set within the range of. Furthermore, the ceramic heating element has a ratio P / Q of the major axis length P to the minor axis length Q of 1.2 to 2.5 (desirably 1.6 to It is set within the range of 2.0) and Q is set to 0.1 mm or more (desirably 0.5 mm or more).

The ceramic heating element is a ceramic having conductivity such as tungsten carbide (WC), molybdenum silicate (Mo ₂ Si ₃ ), tungsten carbide and silicon nitride (S).
i ₃ N ₄ ) and the like, but semiconductor ceramics such as silicon carbide (SiC) can also be used. The electrode parts 11 and 12 are made of tungsten (W).
Alternatively, it is made of a refractory metal material such as a tungsten-rhenium (Re) alloy. On the other hand, the ceramic base 13
Are mainly insulating ceramics such as alumina (Al
₂ O ₃ ), silica (SiO ₂ ), zirconia (ZrO ₂ ),
Titania (TiO ₂ ), magnesia (MgO), mullite (3Al ₂ O ₃ .2SiO ₂ ), zircon (ZrO ₂ .S)
iO ₂ ) and cordierite (2MgO · 2Al ₂ O ₃ · 5)
SiO ₂ ), silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN) and the like.

In FIG. 2, a thin metal layer (not shown) of nickel or the like is formed on the surface of the ceramic substrate 13 in a region including the exposed portion 12a of the electrode portion 12 by a predetermined method (for example, plating or vapor deposition). The ceramic base 13 and the outer cylinder 3 are joined by brazing through the thin metal layer, and the electrode part 12 is electrically connected to the outer cylinder 3 through these joints. . Similarly, a thin metal layer is formed in a region including the exposed portion 11a of the electrode portion 11, and the joining member 5 is brazed to the thin metal layer. With this configuration, the ceramic heating element 10 is energized from the power source (not shown) through the metal shaft 6 (FIG. 1), the coupling member 5 and the electrode portion 11, and further the electrode portion 12, the outer cylinder 3, It is grounded through the metal housing 4 (FIG. 1) and an engine block (not shown).

The method of manufacturing the ceramic heater 1 will be described below. First, as shown in FIG. 4A, an electrode material 30 is inserted into a mold 31 having a U-shaped cavity 32 corresponding to the ceramic heating element 10, and one end of the electrode material 30 is inserted into the cavity 32. To arrange. Then, in this state, a compound 33 containing a conductive ceramic powder and a binder is injected, so that the electrode material 30 and the U-shaped conductive ceramic powder molding portion 34 are formed as shown in FIG. Integrally molded body 35 in which
Create The conductive ceramic powder molding part 34 is formed to have a substantially circular cross section.

On the other hand, separately from this, the ceramic powder for forming the ceramic substrate 13 is press-molded in advance by a die to form the divided preforms 36 separately formed in the upper and lower parts as shown in FIG. Prepare 37. Each of the divided preformed bodies 36 and 37 has a concave portion 38 having a shape corresponding to that of the integrated molded body 35 on its mating surface 39a. Then, the integral injection molded body 35 is placed in the recess 38.
And the divided preforms 36 and 37 are matched with each other on the mold matching surface 39a. Then, as shown in FIG. 6A, in this state, these divided preforms 36, 37 are formed.
And the integral injection-molded body 35 into the cavity 61 of the mold 61.
By accommodating it in a and pressing and compressing it by using the punches 62 and 63, as shown in FIGS. 5B and 7A, a composite molded body 39 in which these are integrated is formed. . Here, the pressing direction is set substantially perpendicular to the mating surface 39a of the divided preforms 36 and 37.

The composite molded body 39 thus obtained is first calcined at a predetermined temperature (for example, about 800 ° C.) in order to remove the binder component and the like, and the calcined body 39 'shown in FIG. 7 (b).
It is said. Subsequently, as shown in FIG. 6 (b), the calcined body 39 'is set in the cavities 65a and 66a of the hot pressing molds 65 and 66 made of graphite or the like. The calcined body 39 ′ is placed in the furnace 64 in both molds 65.
And 66 while being pressurized to a predetermined temperature (eg about 1
By being fired at 800 ° C., a fired body 70 as shown in FIG. 7C is obtained. At this time, the conductive ceramic powder molding portion 34 shown in FIG.
0, the divided preforms 36 and 37 are the ceramic base 1
3 will be formed respectively. In addition, each electrode material 30
Are the electrode parts 11 and 12, respectively.

Here, the calcined body 39 'is, as shown in FIG. 6B, a mating surface 39 of the divided preformed bodies 36 and 37.
While being compressed in the direction along a, the fired body 70 (FIG.
(C)). Then, as shown in FIG. 7C, the linear portion 34b of the conductive ceramic powder molding portion 34 is deformed so that its circular cross section collapses in the compression direction, so that the ceramic heat generation having the elliptical cross section is generated. It becomes the straight part 10b of the body 10. Then, as shown in FIG.
By performing processing such as polishing on the outer peripheral surface of the fired body 70,
The cross section of the ceramic base 13 is shaped into a circle to form the final ceramic heater 1.

As shown in FIG. 9, the flat portion 13a can be formed by partially cutting out both sides of the ceramic base 13 in the direction of the ellipse major axis of the cross section of the straight portion 10b. Thereby, the variation in the distance from the surface of the linear portion 10b to the surface of the ceramic substrate 13 is further corrected, and the temperature distribution on the heater surface can be made more uniform.

The ceramic heater of the present invention can be used not only for glow plugs but also for heating elements for burner ignition or oxygen sensors.

[0023]

【Example】

Example 1 A ceramic heater 1 produced by the above method and a ceramic heater 100 as shown in FIG. 10 were prepared as comparative examples. Ceramic heater 1
In No. 00, the thin-layer ceramic heating element 101 is formed by pattern printing to form a total of four layers, two layers vertically and horizontally with the axis of the heater 100 interposed therebetween. Each of these ceramic heaters has a maximum surface temperature of 1400 ° C.
The temperature distribution on the heater surface was examined when the temperature was raised so that As shown in FIG. 8, the temperature measurement point is, in the ceramic heater of the embodiment, a straight line connecting the axes of the two straight line portions 10b as a reference line H, and A: the vicinity of the intersection of the reference line H and the heater surface. , B: near the intersection of the heater surface with a straight line J passing through the center O of the heater cross section and orthogonal to the reference line H, and C: near the midpoint of the line segment connecting A and B on the heater surface. did. Regarding the ceramic heater 100 of the comparative example, A: near the intersection of the heater surface with a straight line passing through the center O of the heater cross section and along the layer surface of each ceramic heating element 101, and B: passing through the center O of the heater cross section for each ceramic heat generation. Three points were set: near the intersection of a straight line orthogonal to the layer surface of the body 101 and the heater surface, and C: near the midpoint of the line segment connecting A and B on the heater surface. In the ceramic heater 1 of the embodiment, the temperature at each measurement point is A>B>
The temperature decreased in the order of C, and the temperature difference between A and C was as small as 10 ° C., and a relatively uniform temperature distribution was obtained. On the other hand, in the ceramic heater 100 of the comparative example, the temperature was lowered in the order of C>B> A, and the temperature difference between C and A was 30 ° C., showing a fairly nonuniform temperature distribution.

(Embodiment 2) According to the above method, Q, P /
Ceramic heaters having various values of Q and φX / φY were manufactured, and their electric durability was examined. Current durability is
A cycle of energizing the ceramic heater at a constant voltage for 5 minutes after the temperature is equilibrated, then cooling to room temperature and holding for 3 minutes is set as one cycle, and this is repeated 10,000 times for each ceramic heater. When the heat generation temperature was 150 ° C or more lower than that during the first energization in the stage, it was judged as bad (x), and when not, it was judged as good (○).
It was judged by The energization voltage was set so that the maximum temperature reached by the heater during the first energization was 1400 ° C. The results are shown in Table 1.

[0025]

[Table 1]

It can be seen that each of the ceramic heaters in which the respective values of Q, P / Q and φX / φY satisfy the requirements of the present invention exhibit good electrical durability.

[Brief description of the drawings]

FIG. 1 is a front partial cross-sectional view showing an example of a glow plug adopting a ceramic heater of the present invention.

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

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

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

FIG. 5 is a process explanatory view following FIG. 4;

FIG. 6 is a process explanatory view following FIG. 5;

FIG. 7 is a schematic diagram showing changes in cross-sectional shape of a composite molded body and a fired body in the method for manufacturing a ceramic heater of the present invention.

FIG. 8 is a schematic diagram showing the positions of temperature measurement points of the ceramic heater in the first embodiment.

FIG. 9 is a sectional view showing an example of a ceramic heater in which flat portions are formed on both sides of a ceramic base.

FIG. 10 is a sectional view of a conventional ceramic heater.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic heater 10 Ceramic heating element 11, 12 Electrode part 10b Straight part 13 Ceramic base 13a Virtual circular area (heating element existence area)

Claims (3)

[Claims] 1. A ceramic base having a cross section in which at least a part of its outer periphery is formed in an arc shape, and resistance heating is generated by being energized through electrode parts embedded in the ceramic base and connected to both ends of the ceramic base. In a ceramic heater including a ceramic heating element, the ceramic heating element extends from one base end portion and changes direction at a tip portion to the other base end portion, and each base of the direction changing portion. Two straight portions extending in the same direction from the end portion are provided, and the cross sections of the straight portions are elliptical shapes inscribed in virtual circular regions set in the cross section of the ceramic base, respectively. The ratio φX / φY of the diameter φX of a typical circular region and the cross-sectional diameter φY of the ceramic substrate is set within the range of 0.3 to 0.7, and the elliptical cross section of the linear portion is The major axis length P and the minor axis length A ceramic heater characterized in that a ratio P / Q to the height Q is set within a range of 1.2 to 2.5. 2. The ceramic heater according to claim 1, wherein the value of Q of the ceramic heating element is set to 0.1 mm or more. 3. The ceramic heater according to claim 1, wherein a cross section of each linear portion of the ceramic heating element is formed in an elliptical shape compressed in a direction in which the linear portions face each other.