CN106233819B - Ceramic heater and the igniter for having it - Google Patents

Abstract

The ceramic heater has: a ceramic body, a strip-shaped heating resistor embedded in the ceramic body, and a strip-shaped wire embedded in the ceramic body and connected to the end of the heating resistor. The wire has: a first portion covering the end of the heating resistor at the connection with the heating resistor, and a second portion extending to both sides of the end, wherein the thickness of the second portion is thinner than that of the first portion.

Description

Ceramic heater and ignition device having the same

technical field

The present invention relates to a ceramic heater and an ignition device provided with the same.

Background technique

Ceramic heaters are known as heaters used for gas furnaces, vehicle heaters, oil fan heaters, glow plugs of vehicle engines, or preheating of fuel. As a ceramic heater, the ceramic heater disclosed in Unexamined-Japanese-Patent No. 2000-156275 (henceforth, patent document 1) is mentioned, for example.

The ceramic heater disclosed in Patent Document 1 includes a ceramic structure, a heating resistor embedded in the ceramic structure, and a power supply line connected to the heating resistor and drawn out to the surface of the ceramic structure.

When the ceramic heater disclosed in Patent Document 1 is repeatedly used in a high-temperature environment, cracks may occur in the connection portion between the power supply line and the heating resistor due to thermal stress generated in the power supply line and the heating resistor. As a result, it is difficult to improve long-term reliability when the ceramic heater is repeatedly used in a high-temperature environment.

SUMMARY OF THE INVENTION

The ceramic heater includes a ceramic body, a strip-shaped heating resistor embedded in the ceramic body, and a strip-shaped lead wire embedded in the ceramic body and connected to an end of the heating resistor, the lead wire It has: a first part covering the end of the heating resistor at the connection part with the heating resistor, and a second part extending to both sides of the end, and the thickness of the first part In contrast, the thickness of the second portion becomes thinner.

The ignition device includes the ceramic heater, and a flow path through which the gaseous fuel flows through the ceramic body in the ceramic heater.

Description of drawings

FIG. 1 is a vertical cross-sectional view showing a ceramic heater.

Fig. 2 is a cross-sectional view of the ceramic heater shown in Fig. 1 cut along the line A-A'.

FIG. 3 is an enlarged view showing a resistor and a lead wire in the ceramic heater shown in FIG. 2 .

FIG. 4 is a perspective view showing an ignition device using the ceramic heater shown in FIG. 1 .

Detailed ways

Hereinafter, the ceramic heater 10 will be described with reference to the drawings.

As shown in FIG. 1 , the ceramic heater 10 includes a ceramic body 1 , a heating resistor 2 provided in the ceramic body 1 , and a lead wire 3 provided in the ceramic body 1 and connected to the heating resistor 2 . Such a ceramic heater 10 can be used, for example, for a glow plug of an automobile engine or for preliminary heating of fuel, or for ignition of a gas stove, or the like.

The ceramic body 1 is a member in which the lead wire 3 and the heating resistor 2 are embedded. By providing the lead wire 3 and the heating resistor 2 inside the ceramic body 1 , the durability of the lead wire 3 and the heating resistor 2 can be improved. The ceramic body 1 is, for example, a rod-shaped or plate-shaped member (the combination of these may be referred to as a column shape). The ceramic body 1 is formed by laminating a plurality of ceramic layers 11, for example. In the following example, the ceramic heater 10 in which the ceramic body 1 is composed of a laminate of a plurality of ceramic layers 11 will be described, but the present invention is not limited to this. That is, the ceramic body 1 may also be integrally formed. As a method of integrally forming the ceramic body 1, for example, injection molding etc. are mentioned.

The ceramic body 1 is composed of, for example, ceramics having electrical insulating properties, such as oxide ceramics, nitride ceramics, or carbide ceramics. Specifically, the ceramic body 1 is composed of alumina ceramics, silicon nitride ceramics, aluminum nitride ceramics, silicon carbide ceramics, or the like.

The ceramic body 1 made of silicon nitride ceramics can be obtained by the following method. Specifically, for example, 5 to 15 mass % of rare earth element oxides such as Y ₂ O ₃ , Yb ₂ O ₃ or Er ₂ O ₃ and 0.5 to 5 mass % of Al ₂ are mixed with silicon nitride as the main component. O ₃ and SiO ₂ are used as sintering aids, and the amount of SiO ₂ is adjusted so that the amount of SiO ₂ contained in the sintered body is 1.5 to 5 mass %. Then, the ceramic body 1 made of silicon nitride ceramics can be obtained by firing at a temperature of 1650 to 1780° C. after molding into a predetermined shape. For the firing, for example, a hot press firing method can be used.

When the shape of the ceramic body 1 is a rod shape, more specifically, when it is a square prism shape, the length of the ceramic body 1 is set to, for example, 20 to 100 mm. In addition, the cross section of the ceramic body 1 is set to be, for example, a quadrangle with a thickness of 1 to 6 mm and a width of 2 to 40 mm.

The heating resistor 2 is a strip-shaped member that generates heat when a voltage is applied thereto. The heating resistor 2 is embedded between the adjacent two ceramic layers 11 of the ceramic body 1 . When a voltage is applied to the heating resistor 2 and a current flows, the heating resistor 2 generates heat. The heat generated by this heat generation is conducted to the inside of the ceramic body 1, and the surface of the ceramic body 1 becomes high temperature. Then, the ceramic heater 10 functions by conducting heat to the object to be heated from the surface of the ceramic body 1 . As a to-be-heated object which can conduct heat from the surface of the ceramic body 1, the light oil etc. which are supplied to the fuel injection apparatus of the diesel engine for automobiles are mentioned, for example.

The heating resistor 2 is provided on the front end side of the ceramic body 1 . The shape of the longitudinal cross-section (surface parallel to the longitudinal direction of the heating resistor 2 ) of the heating resistor 2 is, for example, a folded-back shape. Specifically, the heating resistor 2 has two parallel linear portions 21 , and a connecting portion 22 in which the outer periphery and the inner periphery are substantially semicircular or substantially semielliptical, and the two linear portions 21 are folded back and connected. The heating resistor 2 is folded back in the vicinity of the front end of the ceramic body 1 . The length from the front end of the heating resistor 2 (the portion on the frontmost side of the connection portion 22 ) to the rear end of the heating resistor 2 (the rear end of the straight portion 21 ) is set, for example, in the longitudinal direction of the heating resistor 2 2 to 15mm.

The heating resistor 2 is mainly composed of, for example, carbide, nitride, silicide, or the like of tungsten (W), molybdenum (Mo), or titanium (Ti). When the ceramic body 1 is composed of silicon nitride ceramics, the main component of the heating resistor 2 is preferably composed of tungsten carbide. Thereby, the thermal expansion coefficient of the ceramic body 1 can be brought close to the thermal expansion coefficient of the heating resistor 2 .

The lead wire 3 is a strip-shaped member embedded in the ceramic body 1 and having one end drawn out to the side surface of the ceramic body 1 . The conducting wire 3 is located between the adjacent two ceramic layers 11 . The lead wire 3 is electrically connected to the heating resistor 2 . The lead wire 3 is used to electrically connect the heating resistor 2 to an external power source.

Two lead wires 3 are provided along the longitudinal direction of the ceramic body 1 respectively corresponding to the two linear portions 21 of the heating resistor 2 , are bent at the rear end side of the ceramic body 1 , and are led out to the side of the ceramic body 1 . side. The lead wire 3 is bent at 90° on the rear end side of the ceramic body 1 and drawn out to the side surface of the ceramic body 1 .

For the lead wire 3, a metal material having excellent heat resistance such as W or Mo is used. In particular, from the viewpoint of the thermal expansion coefficient, it is preferable to use the same tungsten carbide as the heating resistor 2 . The lead wire 3 is set, for example, to have a width of 1 to 20 mm and a length of a portion along the longitudinal direction of the heating resistor 2 to be 10 to 80 mm. The length of the part extending in the direction perpendicular to the longitudinal direction is 2 to 30 mm, and the thickness is about 10 to 50 μm.

Fig. 2 is a transverse cross-sectional view of the ceramic heater 10 shown in Fig. 1 , which is cut along the line A-A' passing through the connection portion between the heating resistor 2 and the lead wire 3. FIG. 2 shows a cross section perpendicular to the main surface of the heating resistor 2 . In addition, in FIG. 2, a part of the boundary of the some ceramic layer 11 is shown by a dotted line. In addition, FIG. 3 is an enlarged view of the resistor 2 and the lead wire 3 in FIG. 2 . As shown in FIGS. 2 and 3 , the lead wire 3 has a first portion 31 covering the end portion of the heating resistor 2 and a second portion 32 extending to both sides of the end portion. In this way, the lead wire 3 covers the end of the heating resistor 2 and protrudes on both sides of the end, so that the boundary between the lead wire 3 and the heating resistor 2 is not flat, so the boundary between the lead wire 3 and the heating resistor 2 is not flat , cracks can be difficult to propagate. In particular, the protruding length W of the protruding portion (the second portion 32 ) is preferably larger than the thickness T of the lead wire 3 at the end of the portion (the first portion 31 ) where the lead wire 3 overlaps the heating resistor 2 (in FIG. 3 ). indicated by the dotted line) is large. Thereby, the end of the lead wire 3 can be sufficiently far away from the heating resistor 2 , and when a crack occurs at the end of the second portion 32 , the possibility of the crack spreading between the lead wire 3 and the heating resistor 2 can be reduced. In particular, the protruding length W of the second portion 32 may be equal to or greater than twice the thickness T of the lead wire 3 at the end of the first portion 31 . Thereby, the second portion 32 can be thinly expanded in the ceramic body 1 . As a result, when the second portion 32 thermally expands, the thermal stress generated in the ceramic body 1 can be reduced.

Furthermore, among the lead wires 3 , the thickness of the protruding portion (the second portion 32 ) is thinner than the thickness of the portion (the first portion 31 ) overlapping the heating resistor 2 . Accordingly, when thermal stress occurs in the heating resistor 2, the thermal stress can be easily concentrated on the protruding portion.

Therefore, it is possible to reduce the possibility of cracks occurring in the portion (the first portion 31 ) of the lead wire 3 that overlaps with the heating resistor 2 . As a result of these, it is possible to improve long-term reliability when the ceramic heater 10 is repeatedly used in a high-temperature environment. The thickness of the lead wire 3 can be set, for example, as follows: the thickness of the first portion 31 can be set to 5 to 50 μm, and the thickness of the second portion 32 can be set to 0.5 to 10 μm.

The comparison between the thickness of the first portion 31 and the thickness of the second portion 32 can be performed, for example, by comparing the average thickness of the first portion 31 and the average thickness of the second portion 32 . The average thickness of the first portion 31 and the second portion 32 can be obtained, for example, by the following method. Specifically, three imaginary lines that divide the first portion 31 and the second portion 32 into four equal parts in the width direction are drawn from the first portion 31 and the second portion 32 . Then, the average value of each of the thicknesses at the positions where the three imaginary lines are drawn in the first part 31 and the second part 32 is obtained. The respective average values can be regarded as the average thickness of the first portion 31 and the average thickness of the second portion 32 .

Further, as shown in FIGS. 2 and 3 , it is preferable that the thickness of the second portion 32 be thinned toward the outside at the connection portion between the lead wire 3 and the heating resistor 2 . In this way, since the second portion 32 is thinned outward, thermal stress tends to be concentrated in the second portion 32, particularly in the vicinity of the front end. Thereby, even if thermal stress occurs in the lead wire 3 , cracks can be generated in the lead wire 3 at a position away from the heating resistor 2 and the first portion 31 . Therefore, it is possible to reduce the possibility that the connection reliability of the lead wire 3 and the heating resistor 2 is lowered.

Furthermore, as shown in FIG. 2 and FIG. 3 , the heating resistor 2 and the lead wire 3 may also be provided between two adjacent ceramic layers 11 . Thereby, the cracks which generate|occur|produce in the ceramic body 1 can be reduced. In the ceramic body 1 , stress is likely to concentrate particularly between the ceramic layers 11 . By providing such an interlayer between the ceramic layers 11 , the stress can be concentrated on the heating resistor 2 and the lead wire 3 in the second portion 32 as described above, and the second portion 32 can absorb the heat generated between the layers of the ceramic layer 11 . stress. Therefore, it is possible to reduce the occurrence of cracks in the ceramic body 1 from the interlayers of the ceramic layers 11 .

In addition, at the connection portion between the lead wire 3 and the heating resistor 2 , the heating resistor 2 and the second portion 32 may be in contact with one surface of one ceramic layer 11 of the two ceramic layers 11 . Accordingly, when the heating resistor 2 and the second portion 32 are in contact with the same surface, when thermal stress occurs in the ceramic body 1 , the heating resistor 2 and the lead wire 3 can absorb the force. In other words, it is possible to reduce the case where the force is applied only to the heating resistor 2 or the force is applied only to the lead wire 3 . Therefore, for example, it is possible to reduce the occurrence of cracks at the interface between the heating resistor 2 and the lead wire 3 .

Furthermore, the heating resistor 2 and the second portion 32 may be continuous on one surface. The term "continuous on one surface" here means that when viewing a cross section passing through the heating resistor 2 and the lead wire 3, on one surface of one ceramic layer 11 among the two adjacent ceramic layers 11, The heating resistor 2 is connected to the wire 3 . Thereby, since the gap which becomes the origin of a crack can be reduced in the interface of the heating resistor 2 and the 2nd part 32, it can reduce the occurrence of a crack in the interface of the heating resistor 2 and the lead wire 3.

Further, as shown in FIG. 2 and FIG. 3 , in the second part 32 of the lead wire 3 , one main surface may be connected to the heating resistor 2 and one ceramic layer 11 of the two adjacent ceramic layers 11 . The two surfaces are in contact with each other, and the other main surface is an arc shape concave inward. Thereby, the stress can be more easily concentrated on the distal end portion of the second portion 32 . As a result, even if thermal stress occurs in the second portion 32 , cracks can be generated in the lead wire 3 at a position away from the first portion 31 . Therefore, the reliability of the connection between the lead wire 3 and the heating resistor 2 can be improved.

Further, the lead wire 3 and the heating resistor 2 may also be composed of a metal material and a ceramic material mixed with the metal material. As such a metal material, WC etc. are mentioned. Moreover, as a ceramic material, Si3N4, BN, etc. are _{mentioned .} At this time, the content of the ceramic material in the second part 32 may be made larger than the content of the ceramic material in the first part 31 . Thereby, when stress is applied to the entire wire 3 , cracks can be more easily generated in the second portion 32 than in the first portion 31 . This is because in the second part 32 , the ratio of the metal material is reduced and the ratio of the ceramic material is increased compared with the first part 31 , so that the second part 32 is more difficult to elastically deform than the first part 31 . As a method for changing the composition of the first part 31 and the second part 32, for example, a method of forming the first part 31 and the second part 32 from separate green sheets is exemplified.

Furthermore, the thermal expansion coefficient of the heating resistor 2 may be made smaller than the thermal expansion coefficient of the lead wire 3 . Thereby, after firing, residual stress remains, so that the lead wire 3 sandwiches the heating resistor 2 . Therefore, the occurrence of peeling between the heating resistor 2 and the lead wire 3 can be reduced. Moreover, in order to make the thermal expansion coefficient of the heating resistor 2 smaller than the thermal expansion coefficient of the lead wire 3, the following method can be used, for example. Specifically, the main component of the lead wire 3 and the heating resistor 2 is WC, and Si ₃ N ₄ having a thermal expansion coefficient smaller than that of WC is added as a sub-component. At this time, the thermal expansion coefficient of the heating resistor ₂ can be made smaller than that of the lead wire _{3 by making the amount of Si 3 N 4} added to the heating resistor 2 larger than that of the lead wire 3 .

The above-mentioned ceramic heater 10 can be produced by, for example, a hot pressing method. Specifically, first, a paste to be the heating resistor 2 and the lead wire 3 is laminated on the green sheet that is a part of the ceramic layer 11 . At this time, since the second portion 32 of the lead wire 3 protrudes to both sides of the heating resistor 2, a slight pressure is applied to the portion serving as the second portion 32 in the lead wire 3, so that the portion serving as the second portion 32 is different from the original one. Green paste sticks. Then, another green sheet was laminated on the above-mentioned green sheet with the heating resistor 2 and the lead wire 3 sandwiched therebetween to obtain a laminated body. Then, the ceramic heater 10 can be produced by firing the laminate using a hot press firing method.

The ceramic heater 10 is used, for example, as the ignition device 100 shown in FIG. 4 . The ignition device 100 includes a ceramic heater 10 and a flow path 20 through which gas fuel flows to the ceramic heater 10 . The flow path 20 is constituted by, for example, an air valve 21 and a ventilation pipe 22 having a discharge port 23 . The gas valve 21 has a function of controlling the flow rate of the gaseous fuel. Examples of the gas fuel supplied from the gas valve 21 include natural gas, propane gas, and the like. The ventilation duct 22 ejects the gaseous fuel supplied from the gas valve 21 to the ceramic heater 10 from the ejection port 23 . Then, by heating the ejected gas fuel using the heater 10, the gas fuel can be ignited. Since the ignition device 100 has the ceramic heater 10 with improved long-term reliability, the stability of ignition of the gaseous fuel is improved.

-Symbol Description-

1: Ceramic body

11: Ceramic layer

2: heating resistor

21: Straight Parts

22: Links Section

3: Wire

31: Part 1

32: Part 2

10: Ceramic heater

100: Ignition device

Claims (8)

1. a kind of ceramic heater, comprising:

The ceramic body that multiple ceramic layers are laminated；

It is embedded in the band-like heat generating resistor of an interlayer of the ceramic layer；With

The band-like conducting wire for being embedded in the ceramic body and being connect with the end of the heat generating resistor,

The conducting wire includes

In cross-sectional apparent time, the part 1 of the end of the heat generating resistor is covered in the interconnecting piece with the heat generating resistor；With

In the part 2 that two sides of the end are stretched out to the direction orthogonal with the stacking direction of the ceramic layer,

Compared with the thickness of the part 1, the thickness of the part 2 is thinning.

2. ceramic heater according to claim 1, wherein

It is thinning outward in the thickness of the interconnecting piece of the conducting wire and the heat generating resistor, the part 2.

3. ceramic heater according to claim 1 or 2, wherein

Compared with the thickness of the end of the part 1, the extension elongation of the part 2 is larger.

4. ceramic heater according to claim 1 or 2, wherein

The ceramic body is made of the laminated body of multiple ceramic layers.

5. ceramic heater according to claim 4, wherein

The heat generating resistor and the conducting wire are arranged at the interlayer of 2 adjacent ceramic layers.

6. ceramic heater according to claim 5, wherein

The heat generating resistor and the part 2 connect with 1 face of a ceramic layer among 2 ceramic layers.

7. ceramic heater according to claim 6, wherein

The heat generating resistor and the part 2 are continuous on 1 face.

8. a kind of igniter, has:

Ceramic heater described in any one of the claim 1 to claim 7；With

Gaseous fuel is flowed to the flow path of the ceramic body among the ceramic heater.