JP2001052845A - Ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic heater capable of suppressing or preventing the occurrence of cracks in a heating resistance element made of a high-melting- point metal or conductive ceramics and the occurrence of breakage of lead wires, by rationally disposing the lead wires. SOLUTION: Assuming the radius of a ceramic substrate 13 to be R and the shortest distance to be L between any surface of lead wires 11, 12 and a surface of the ceramic substrate 13, 0.3<=L/R<=0.8 is established. This enables the lead wires 11, 12 to be disposed close to a center axis of a ceramic heater 1 standing as a neutral line with respect to stresses. Accordingly, during the stage of manufacture or during the stage of use, the occurrence of cracks in a heating resistance element 10 and the occurrence of breakage of the lead wires 11, 12 can be suppressed or prevented without sharply changing a manufacturing process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ceramic heater used for a glow plug, for example.

[0002]

2. Description of the Related Art Conventionally, for example, as shown in FIG.
2 is known and is used to promote starting of a diesel engine or the like. The ceramic heater 102 has, for example, a U-shaped ceramic heating element 104 (resistive heating element) formed of conductive ceramic on the tip of a rod-shaped insulating ceramic base 103.
Is buried, and is energized through lead wires 105 connected to both ends thereof to generate resistance heat. Here, the lead wire 105 is connected to the ceramic heating element 104 by embedding its tip end in each end of the ceramic heating element 104. In addition, a ceramic heater of a type in which a resistance heating element using a high melting point metal such as a tungsten wire is embedded instead of conductive ceramic is also known.

[0003]

In such a ceramic heater 102, cracks K are formed in the ceramic heating element 104 during the manufacturing process or during the use of the heating heater, the glow plug 100 for starting promotion of a diesel engine, or the like. In some cases, or a break S in the lead wire 105 (FIG. 11B). That is, the ceramic heater 102 (ceramic base 1
03) The ceramic heating element 1 receives a mechanical external force during the surface polishing operation or the brazing operation of the outer cylinder 101 in the manufacturing process of the glow plug 100, or during use.
In some cases, the occurrence of crack K and disconnection S may be observed by receiving thermal stress accompanying the cooling / heating cycle of No. 04.

[0004] Such cracks K and disconnections S occur because the residual carbon content contained in the organic binder not removed in the degreasing step during hot press sintering during the manufacturing process of the ceramic heater 102 is caused by the lead wire 105. It is considered that one reason is that a reaction layer T is formed on the surface of the substrate, and the reaction layer T is a region having low mechanical strength. That is, since such a reaction layer is not sintered, a region which is not densified but is in a squat state exists in the ceramic heater 102. It is considered that the presence of such a non-densified region within the limited cross-sectional area in the ceramic heater 102 causes the mechanical strength of the ceramic heater 102 to be insufficient. In addition, it is sufficiently predicted that the difference in thermal expansion coefficient between the lead wire 105 and the ceramic heating element 104 is related to the occurrence of the crack K and the disconnection S due to the difference in the material.

In many cases, W (tungsten) or a W alloy is used as the lead wire 105. Lead wire 10
Although it is conceivable that the metal layer 5 is made of another high melting point metal such as Pt (platinum), the formation of the reaction layer T is not always stopped even if these metals are used.
Since there is still a difference in the coefficient of thermal expansion between the ceramic heating element 104 and the ceramic heating element 104, another effective means capable of suppressing or preventing the occurrence of cracks K and disconnections S is desired. I have.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a ceramic which can reasonably arrange lead wires to suppress or prevent the occurrence of cracks in a resistance heating element made of a high melting point metal or a conductive ceramic and the occurrence of disconnection in a lead wire. It is to provide a heater.

[0007]

In order to solve the above-mentioned problems, a ceramic heater according to the present invention comprises a shaft-shaped insulating ceramic substrate, a resistance heating element embedded in the ceramic substrate, and A pair of leads embedded in the ceramic base and one end of which is connected to both ends of the resistance heating element. R, the shortest distance between any surface of the lead wire and the surface of the ceramic base (hereinafter simply referred to as the shortest distance)
Is defined as L, and 0.3 ≦ L / R ≦ 0.8 is satisfied.

According to the present invention, when the radius of the ceramic base is R and the shortest distance is L, 0.3 ≦ L / R ≦
By setting the ratio to 0.8, the lead wire can be arranged closer to the center axis of the ceramic heater, which is a neutral line with respect to stress. Therefore, in the manufacturing stage or in the use stage, the occurrence of cracks in the resistance heating element and the occurrence of disconnection in the lead wires can be suppressed or prevented without significantly changing the manufacturing process. It has been confirmed that this tendency becomes stronger when the radius R of the ceramic base is 1.5 to 2.5 mm.

Furthermore, since the lead wire of the present invention can be formed of W or W alloy, the occurrence of disconnection in the lead wire during the manufacturing stage or the use stage while maintaining the same heating performance as the existing ceramic heater is maintained. Can be suppressed or prevented, and the yield and quality can be improved.

Further, the resistance heating element of the present invention may be a ceramic heating element formed of conductive ceramics. By using a conductive ceramic having excellent durability (withstanding repeated use), the life of the ceramic heater can be improved. On the other hand, as the lead wire is arranged closer to the center axis of the ceramic heater, at least the resistance heating element at the connection overlapping (embedded) portion of the lead wire also approaches the center axis of the ceramic heater, that is, moves away from the surface of the ceramic heater. May be placed. In this case, it is disadvantageous in view of the heat generation characteristics (heat rise on the heater surface in a short time). But,
These disadvantages can be eliminated by using conductive ceramics having excellent heat generation characteristics.

Here, the conductive ceramics are composed of W, Mo, Ti, Ta, Nb, Cr
At least one carbide, nitride or silicide selected from the group consisting of: By using these conductive ceramics, a ceramic heater having more excellent heat generation characteristics can be obtained.

Further, the end of the lead wire of the present invention is embedded in a ceramic heating element, and the insertion depth H of the lead wire into the ceramic heating element in the axial direction can be set to 0.3 ≦ H ≦ 7 mm. If it is less than 0.3 mm, the possibility of the lead wire dropping off from the ceramic heating element or poor conduction between the lead wire and the ceramic heating element increases. If it exceeds 7 mm, the area of the reaction layer increases because the contact area of the lead wire increases. As the area of the reaction layer increases, the mechanical strength of this part is likely to decrease. Therefore, by embedding the lead wire in the ceramic heating element within the above range, the mechanical strength of the ceramic heater can be ensured, and a conduction failure between the lead wire and the ceramic heating element during the ceramic heater manufacturing process. Since the number of defects that occur or the lead wire is broken can be reduced, the product yield is improved.

Furthermore, the wire diameter φD of the lead wire of the present invention is:
0.2 ≦ φD ≦ 0.8 mm can be set. If it is smaller than 0.2 mm, the electric resistance of the lead wire increases, so that it becomes difficult to supply sufficient power to the heating element, and it is easy to cause disconnection. In addition, when it exceeds 0.8 mm, the contact area of the lead wire becomes large,
The area where the reaction layer is formed increases. An increase in the area of such a non-densified reaction layer within a limited cross-sectional area within the ceramic heater results in a lack of mechanical strength of the ceramic heater. Therefore, by keeping the lead wire diameter within this range, sufficient power can be supplied to the heating element, and the strength of the ceramic heater can be ensured.

Further, the present invention has a semi-cylindrical surface with a radius of 1.5 mm, and is placed on two fulcrums arranged at a distance of 12 mm with the shortest distance facing downward. A load point having a semi-cylindrical surface with a radius of 1.5 mm is contacted from above at the center of the connection overlap length in the axial direction between the resistance heating element and the lead wire above the center between the two fulcrums, and crossed. When a load at a head speed of 0.5 mm / min is applied and the maximum bending stress derived from the maximum load at break is measured as the bending strength σ, σ ≧ 400MP
can be set to a. As a result, a ceramic heater having sufficient mechanical strength (maximum bending stress) for suppressing or preventing the occurrence of cracks in the resistance heating element and the occurrence of disconnection in the lead wires can be reliably obtained.

[0015]

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 is connected to the ceramic heater 1 provided at one end thereof.
And a metal outer cylinder 3 that covers the outer peripheral surface of the ceramic heater 1 so that the tip 2 protrudes, and a cylindrical metal housing 4 that covers the outer cylinder 3 from the outside. 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 having both ends formed in a helical spring shape by a metal wire is fitted into the rear end of the ceramic heater 1 from the outside, 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 outside the metal housing 4, and a nut 7 is screwed into a screw portion 6a formed on the outer peripheral surface.
The metal shaft 6 is fixed to the metal housing 4 by tightening the nut 7 toward the metal housing 4. An insulating bush 8 is fitted between the nut 7 and the metal housing 4. On the outer peripheral surface of the metal housing 4, a screw portion 5a for fixing the glow plug 50 to an engine block (not shown) is formed.

As shown in FIG. 2, the ceramic heater 1 extends from one base end into an axially insulative ceramic base 13 having a substantially circular cross section, and then changes its direction to form the other base end. Direction changing part 10a reaching the part, and two straight parts 1 extending in the same direction from each base end of the direction changing part 10a.
0b, a U-shaped ceramic heating element 10 (resistance heating element). Further, the ends of a pair of linear or rod-shaped lead wires 11 and 12 are embedded in both ends of the ceramic heating element 10. The ceramic heating element 1
Numeral 0 is embedded in the tip portion 2 of the ceramic heater 1 so that the direction changing portion 10a faces the tip side of the ceramic heater 1.

Each of the lead wires 11 and 12 extends in the ceramic base 13 in a direction away from the ceramic heating element 10. And one of them (1
2) is inside the outer cylinder 3, and 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 to form exposed portions 12a and 11a. ing.

The ceramic heating element 10 is made of a ceramic having conductivity, for example, W, M as a component having conductivity.
at least one selected from o, Ti, Ta, Nb, Cr
It can be formed from ceramics containing various carbides, nitrides or silicides. Specifically, it is composed of tungsten carbide (WC), molybdenum silicide (MoSi ₂ ), a composite of tungsten carbide and silicon nitride (Si ₃ N ₄ ), and uses a semiconductor ceramic such as silicon carbide (SiC). You can also. In addition, lead wire 11
And 12 are tungsten (W) or tungsten-
It is composed of a high melting point metal material such as a rhenium (Re) alloy. On the other hand, the ceramic base 13 is mainly made of insulating ceramics, for example, alumina (Al ₂ O ₃ ), silica (Si
O ₂ ), zirconia (ZrO ₂ ), titania (Ti
O ₂ ), magnesia (MgO), mullite (3Al ₂ O)
₃ · 2SiO _2), zircon _(ZrO 2 · _SiO 2),
Cordierite _{(2MgO · 2Al 2 O 3 ·} 5Si
O ₂ ), silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN) and the like.

In FIG. 2, the surface of the ceramic base 13 is covered with a region including the exposed portion 12a of the lead wire 12.
A thin metal layer (not shown) of nickel or the like is formed by a predetermined method (for example, plating or vapor deposition). The ceramic base 13 and the outer cylinder 3 are interposed via the thin metal layer.
Are joined by brazing, and the lead wire 12
Are electrically connected to the outer cylinder 3 through the exposed portion 12a. Similarly, a thin metal layer is formed in a region including the exposed portion 11a of the lead wire 11, and the joining member 5 is brazed to the thin metal layer. 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 lead wire 11,
Furthermore, it is grounded via a lead wire 12, an outer cylinder 3, a metal housing 4 (FIG. 1), and an engine block (not shown). This energization causes the ceramic heating element 10 to generate resistance heat.

[Embodiments] Specific embodiments of the ceramic heater 1 according to the present invention will be described below together with a method of manufacturing the same. First, as shown in FIG. 3A, the lead wire 30 is inserted into a mold 31 having a U-shaped cavity 32 corresponding to the ceramic heating element 10 so that the end thereof enters the cavity 32. Deploy. Then, in this state, the compound 33 containing the WC-Si ₃ N ₄ -based conductive ceramic powder and the binder is injected, so that the lead wires 30 and the U
An integrated injection molded body 35 in which the conductive ceramic powder molded part 34 having a U-shape is integrated is produced.

On the other hand, separately from the above, the ceramic powder forming the ceramic base 13 is pre-press-molded to form pre-formed bodies 36 and 37 formed separately as shown in FIG. Have prepared. Here, the ceramic powder forming the ceramic base 13 may be, for example, an Si ₃ N ₄ powder having an average particle diameter of 0.5 to 1.5 μm
95% by weight, and Er ₂ having an average particle size of 0.5 to 1.5 μm.
1 to 15% by weight of O ₃ powder and an average particle size of 0.5 to 1.5
It is prepared by mixing 0.5 to 10% by weight of a μm SiO ₂ powder and 0.5 to 10% by weight of a MoSi ₂ powder having an average particle diameter of 0.5 to 1.5 μm. Note that instead of Er ₂ O ₃ , other rare earth element oxides such as Y ₂ O ₃ and Yb ₂ O ₃ may be used. Also, instead of SiO _2, SiO ₂ and A
A mixture with l ₂ O ₃ may be used, or only Al ₂ O ₃ may be used. 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. In a corresponding portion, a concave portion 38 having a shape corresponding to the integral injection molded body 35 is provided.
Are formed. Then, the integrated injection molded body 35 is accommodated in the recess 38, and the upper and lower preformed bodies 36 and 37 are matched with each other.
The composite molded body 39 as shown in FIG. 4B is prepared by further pressing and integrating the molded bodies 6, 37 and the integrated injection molded body 35 using a mold.

The composite molded body 39 thus obtained is first embedded in a Si ₃ N ₄ ceramic powder in order to remove a binder component and the like from the conductive ceramic powder molded part 34 or the preformed bodies 36 and 37 by injection molding. In this state, calcination is performed in an N ₂ atmosphere to perform degreasing. continue,
As shown in FIG. 5A, the degreased composite molded body 39 to which the release agent has been applied is set between the upper and lower molds (carbon molds) 40, and pressed at 300 kgf / cm ² at 1800 ° C.
By performing hot press firing for 90 minutes, a fired body 41 as shown in FIG. At this time, FIG.
The conductive ceramic powder molding section 34 shown in FIG. 2B shows the ceramic heating element 10, the preformed bodies 36 and 37 show the ceramic base 13, and the lead wire 30 shows the lead wires 11 and 12.
Are formed respectively. Thereafter, the outer surface of the fired body 41 is subjected to centerless polishing, so that the ceramic substrate outer diameter 2R as shown in FIG. 6 is, for example, 2R = 3.5.
mm ceramic heater 1 is obtained.

FIG. 6 shows a typical cross-sectional structure example of the ceramic heater 1 manufactured by injection molding. In FIG. 6, the ceramic heating element 10 of the ceramic heater 1 is:
In a cross section orthogonal to the axis, it has a pseudo-elliptical shape on both sides of the central axis. On the other hand, in the axial section, the linear portion 10b has a cross-sectional area larger than that of the tip-side linear portion 10b1 having substantially the same cross-sectional area as the direction changing portion 10a (having substantially the same width in the drawing) and the direction changing portion 10a. Then the tip side straight part 1
0b1 only on the central axis side, and is wider than the direction changing portion 10a).

Test Example 1 In FIG. 3A, a first test product was prepared by changing the position of the lead wire 30 relative to the cavity 32. Specifically, in the section perpendicular to the axis of the embedded portion of the lead wires 11 and 12 when the ceramic heater 1 is completed as shown in FIG.
Is R, the shortest distance is L, and L / R is 0.
It was varied from 1 to 0.9. Note that three test articles were prepared for each L / R.

Next, the following durability test was carried out on test specimens (three for each L / R) obtained by hot press firing and surface polishing. That is, a repetitive durability test of 20,000 cycles was performed, in which the lead wires 11 and 12 of the ceramic heater 1 were energized for 60 seconds and then stopped for 60 seconds as one cycle. Thereafter, a three-point bending test shown in FIG. 6 was performed to determine a bending strength σ. The test procedure is performed as follows. First, the two fulcrums 21 and 22 of the three-point bending test apparatus 20 are arranged in a substantially horizontal direction at an interval of a span 1 = 12 mm.
2 has a semi-cylindrical surface 21 with a radius r = 1.5 mm.
a, 22a. Surface roughness 0.8μmR
The semi-cylindrical surfaces 21a, 2 of the fulcrums 21, 21 with the tip 2 of the ceramic heater 1 whose surface is polished to not more than max (maximum height) with the direction of forming the shortest distance L facing downward.
It is placed so as to straddle 2a. Next, the radius r
= Load point 23 at which a semi-cylindrical surface 23a of 1.5 mm is formed
Are located above the center between the fulcrums 21 and 22 and are connected to the lead wires 11 and 1 for the ceramic heating element 10 (resistance heating element).
At the midpoint of the insertion depth H (connection overlap length) in the axial direction of No. 2, the ceramic heater 1 comes into contact with the ceramic heater 1 from above. Then, a crosshead speed of 0.5 is applied to the ceramic heater 1.
A load of mm / min is applied, and the maximum bending stress derived from the maximum load P at the time of fracture of the ceramic heater 1 is measured (or calculated and obtained) as the bending strength σ.

That is, the maximum load at break is P, and the fulcrum 2
When the distance between 1 and 22 is 1 and the radius of the ceramic base 13 is R, the bending strength σ is obtained by the following equation. σ = (P · l) / (π · R ³ ) (1) As shown in FIG. 6, with respect to the set position of the ceramic heater 1 with respect to the three-point bending bending test apparatus 20, the shortest distance L where breakage is most likely to occur is formed. When the ceramic heater 1 is placed in the vertical direction with the direction in which the load is applied downward and in the same direction as the direction in which the load P is applied, the bending strength σ of the ceramic heater 1 obtained here is regarded as a design allowable stress against bending. Can be That is, the ceramic fired body is generally strong in compression but weak in tension. In the case of the three-point bending test, in the cross section orthogonal to the axis of the ceramic heater 1, a tensile stress is generated on a lower side of the cross section, and a compressive stress is generated on an upper side. Therefore, when the direction in which the shortest distance L is formed is directed downward, the reaction layer is located at the lowest position, and thus the destruction starts from the portion in which the shortest distance L is formed. For example, if the bending strength σ ≧ 400 MPa is set, the ceramic heating element 1
Whether the ceramic heater 1 has sufficient mechanical strength (maximum bending stress) to suppress or prevent the occurrence of cracks at 0 (resistance heating element) and the occurrence of disconnection at the lead wires 11 and 12 is described above. The three-point bending test enables reliable and easy inspection.

The test apparatus 20 used for the three-point bending test in [Test Example 1] is an AG-5000 type autograph (500 kgf load cell, manufactured by Shimadzu Corporation). The horizontal distance M from the tip of the ceramic heater 1 to the load point 23 is M = 7.5 in the embodiment of FIG.
mm, and in FIG.
Are set on the upper side (the side where the load point 23 is located). The fulcrums 21 and 22 and the load points 23 may be in the form of a column or a semi-column in addition to the tunnel shape shown in FIG. 6, and may have the semi-column surfaces 21a, 22a and 23a. Furthermore, other measurement conditions are based on JIS
R1601 (Bending strength test method for fine ceramics).

On the other hand, the lead wire 1
The electrical resistance value between the lead wires 11 and 12 was measured.
It was confirmed that there was no contact between them.

FIG. 7 shows the measurement results of the bending strength and the electric resistance value. When the resistance strength σ did not reach 400 MPa and when the electric resistance value did not reach 400 mΩ, the product was determined to be defective, and the result of the durability test was determined based on whether there was a defective product (×) or not (○). As shown in FIG. 7, when L / R is 0.3 or more, sufficient mechanical strength with a bending strength σ of 400 MPa or more is secured. On the other hand, when L / R is 0.8 or less,
Sufficient insulation with an electric resistance value of 400 mΩ or more is maintained. If L / R is less than 0.3, the axially inserted portions of the lead wires 11 and 12 with respect to the ceramic heating element 10 approach the surface of the ceramic base 13, so that sufficient bending strength σ cannot be obtained. And L / R is 0.8
When the distance exceeds, the insertion portion is too close to the center, and the possibility of short-circuit (dielectric breakdown) increases.

[Test Example 2] Referring again to FIG.
A second test sample was prepared by changing the position of the lead wire 30 relative to the cavity 32. Specifically, in FIG. 3B, the conductive ceramic powder molding unit 34
Lead wires 30, 3 for (ceramic heating element 10)
0 (lead wires 11 and 12) in the axial direction
It was varied from 0.2 to 8 mm. Note that ten test articles were prepared for each insertion depth H.

Next, the test pieces (10 pieces at each insertion depth H) obtained in this manner were connected to the lead wires 30, 30.
A conduction test was performed between the (lead wires 11 and 12) and the conductive ceramic powder molded portion 34 (the ceramic heating element 10), and the number of conduction failures was counted. On the other hand, each test sample was subjected to hot press baking to produce a ceramic heater 1 shown in FIG. Then, a three-point bending test shown in FIG. 6 was performed to determine the bending strength σ.
The number that was less than 0 MPa was counted. The method of performing the three-point bending test is based on [Test Example 1].

Here, the threshold value of the bending strength σ is 400 M
The reason for setting Pa was that it was confirmed that sufficient mechanical strength (bending strength) could be secured in [Test Example 1]. In addition, out of 10 test samples, defective (excellent when the bending strength σ is less than 400 MPa or when the number of conduction failures is 0, excellent (）), acceptable when 1-2, acceptable (△), 3 or more In some cases, it is evaluated as impossible (x).

FIG. 8 shows the measurement results of the bending strength and the conduction state. As shown in FIG. 8, in the case of the ceramic heater 1 manufactured by the injection molding of FIG.
mm or less, the bending strength σ substantially secures the mechanical strength of 400 MPa or more, while the insertion depth H is 0.3 m
Above m, good conduction is almost maintained. In addition, when the insertion depth H is less than 0.3 mm, the lead wire 11,
12 increases the possibility of falling off or poor conduction from the ceramic heating element 10 (or injection molded article), and if the insertion depth H exceeds 7 mm, the contact area between the lead wires 11 and 12 and the ceramic heating element 10 The number of reaction layers increases as the value increases, and the possibility of weakening in mechanical strength increases. By the way, in the case of the ceramic heater 1B manufactured by thick-film printing of FIG. 10B described later, since the processing can be performed more precisely than injection molding, the lower limit value of the insertion depth H is increased to 0.3 mm or less. Is possible.

[Test Example 3] Referring again to FIG.
A third test product was prepared by changing the wire diameter φD of the lead wire 30 with respect to the cavity 32. Specifically, the wire diameter φD of the lead wire 30 (lead wires 11 and 12) is set to 0.1
０．９0.9 mm. The test product has a wire diameter φD
10 were created for each.

Next, the test specimens (10 for each wire diameter φD) obtained by hot press firing and surface polishing were
A three-point bending bending test shown in FIG.
And the number of specimens having a bending strength σ of less than 400 MPa was counted. On the other hand, the lead wires 11 and 1
An energization test was performed between the two, and the number of disconnected wires was counted. The method of performing the three-point bending test is based on [Test Example 1] and [Test Example 2].

Out of the ten test articles, a defective one (deflecting strength σ)
(Less than 400 MPa or in a disconnected state) is evaluated as excellent (○) when the number is 0, acceptable (△) when the number is 1 or 2, and unacceptable (x) when the number is 3 or more.

FIG. 9 shows the measurement results of the bending strength and the disconnection check. As can be seen from FIG. 9, when the lead wire diameter φD is 0.8 mm or less, mechanical strength with a bending strength σ of 400 MPa or more is almost secured, while the lead wire diameter φD
Is greater than or equal to 0.2 mm, a state in which there is almost no break in the lead wire is maintained. Note that the lead wire diameter φD is 0.2 m
If it is less than m, the lead wires 11 and 12 are too thin and the risk of disconnection increases. If the lead wire diameter φD exceeds 0.8 mm, the contact area between the lead wires 11 and 12 and the ceramic heating element 10 increases. The number of reaction layers increases, and the possibility of mechanical strength weakening increases.

FIG. 10 shows another embodiment of the ceramic heater according to the present invention. FIG. 10 (a) is a front sectional view and a BB transverse section of a second embodiment which is an alternative to the first embodiment of FIG. Figure,
FIG. 10B is a C2-C2 longitudinal sectional view and a C1-C1 transverse sectional view of still another third embodiment. FIG. 10A shows an example of a cross-sectional structure instead of FIG. 6 of a ceramic heater manufactured by injection molding. In FIG. 10A, the ceramic heating element 10 'of the ceramic heater 1' has a pseudo-half-moon shape on both sides of the central axis in a cross section orthogonal to the axis. On the other hand, in the axial section, the linear portion 10b '
However, the tip-side linear portion 10b1 'having substantially the same cross-sectional area (the width is substantially equal in the drawing) as the direction changing portion 10a' and the direction changing portion 1
The cross-sectional area gradually decreases toward the base end side from 0a '(in the figure, the width decreases only from the front-side linear portion 10b1' to the front side, and gradually narrows toward the base end side from the direction changing portion 10a '). ) Base end side linear portion 10b2 '. Also, the setting of the ceramic heater 1 ′ with respect to the three-point bending test apparatus 20 is performed with the direction of forming the shortest distance L facing downward and in the same direction as the application direction of the load P, as in FIG. 6.

FIG. 10B shows an example of a cross-sectional structure of a ceramic heater 1 "(heater main body) manufactured by thick-film printing. For example, a pattern is formed by screen printing using a conductive ceramic paste such as WC. The ceramic heating element 10 "is embedded in an insulating ceramic base 13", and four lead wires 11 ", 11", 12 ", and 12" are embedded in the ceramic heating element 10 "and fired. Thus, a ceramic heater 1 ″ is obtained. In FIG. 10B, the ceramic heater 1 ″ is obtained.
Of the ceramic heating element 10 ″ is 4
The lead wires 11 ", 11", 12 ", 12" have a tangential form. On the other hand, in the axial cross section, the linear portion 10b "has a cross-sectional area substantially equal to the direction changing portion 10a" (the width is substantially equal in the drawing). (In the figure, the width is increased on both sides from the distal-side linear portion 10b1 ″ and is wider than the direction changing portion 10a ″). The proximal-side linear portion 10b2 ″ is formed as shown in FIG. The ceramic heater 1 "shown has a four-pole structure provided with two sets of heaters, each of which is composed of one ceramic heating element 10" and a pair of lead wires 11 "and 12". As in FIG. 6, the setting of the ceramic heater 1 ″ with respect to the bending test apparatus 20 is performed with the direction of forming the shortest distance L facing downward and in agreement with the direction in which the load P is applied. Some parts have been omitted.

As the resistance heating element of the present invention, a heating element made of metal such as W or W-Re alloy or a heating coil may be used in addition to the ceramic heating element formed of conductive ceramics. In addition, as shown in FIG. 6, FIG. 10, etc., the ceramic heaters 1, 1 '
The internal structure of 1 "can be visualized by an X-ray transmitting device without using a destruction means such as cutting.

[Brief description of the drawings]

FIG. 1 is a partial front sectional view showing an example of a glow plug using a ceramic heater according to the present invention.

FIG. 2 is a front sectional view of the ceramic heater of FIG. 1;

FIG. 3 is an explanatory view of a manufacturing process of a ceramic heater.

FIG. 4 is a process explanatory view following FIG. 3;

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

FIG. 6 is a front sectional view and an AA transverse sectional view showing a first embodiment of the ceramic heater according to the present invention.

FIG. 7 is a table showing measurement results of Test Example 1.

FIG. 8 is a table showing measurement results of Test Example 2.

FIG. 9 is a table showing measurement results of Test Example 3.

FIG. 10 shows another embodiment of the ceramic heater according to the present invention. FIG. 10 (a) is a front sectional view of the second embodiment and FIG.
FIG. 10 (b) is a vertical sectional view of C2-C2 and a horizontal sectional view of C1-C1 of the third embodiment.

FIG. 11 is a schematic view showing the structure of a ceramic heater of a conventional glow plug.

[Explanation of symbols]

Reference Signs List 1 ceramic heater 2 tip 10 ceramic heating element (resistance heating element) 11, 12 lead wire 13 ceramic base 21, 22 fulcrum 23 load point φD lead wire diameter H insertion depth of lead wire to ceramic heating element in axial direction (Connection overlap length) L Shortest distance between the surface of any lead wire and the surface of the ceramic substrate R Radius of the ceramic substrate σ Flexural strength

Claims (7)

[Claims] 1. A shaft-shaped insulating ceramic base, a resistance heating element embedded in the ceramic base, and one end of itself embedded in the ceramic base connected to both ends of the resistance heating element. A pair of lead wires, and a radius of the ceramic base is R, and a shortest distance between an arbitrary surface of the lead wire and a surface of the ceramic base (hereinafter, referred to as a cross section perpendicular to the axis at a connection portion of the lead wires)
Let L be the shortest distance), and 0.3 ≦ L / R ≦
A ceramic heater satisfying 0.8. 2. The ceramic heater according to claim 1, wherein said lead wire is formed of W or a W alloy. 3. The ceramic heater according to claim 1, wherein said resistance heating element is a ceramic heating element formed of conductive ceramics. 4. The conductive ceramic according to claim 3, wherein the conductive ceramic contains at least one kind of carbide, nitride or silicide selected from W, Mo, Ti, Ta, Nb, and Cr. Ceramic heater. 5. An end portion of the lead wire is embedded in the ceramic heating element, and an insertion depth H of the lead wire into the ceramic heating element in an axial direction is 0.3 ≦ H ≦ 7 mm. Or the ceramic heater according to 4. 6. The lead wire having a diameter φD of 0.2 ≦ φ
The ceramic heater according to any one of claims 1 to 5, wherein D ≤ 0.8 mm. 7. It has a semi-cylindrical surface with a radius of 1.5 mm, and
A load point having a semi-cylindrical surface with a radius of 1.5 mm is placed on two fulcrums arranged at a distance of 2 mm with the direction forming the shortest distance facing downward. A load at a crosshead speed of 0.5 mm / min is applied from above at a center of the connection overlap length of the resistance heating element and the lead wire in the axial direction above the center, and a load at a crosshead speed of 0.5 mm / min is applied. 7. The ceramic heater according to claim 1, wherein σ ≧ 400 MPa when a maximum bending stress derived from a maximum load is measured as a bending strength σ.