HEATER AND GLOWPLUG

Abstract

 A heater includes a ceramic body having a rod shape; a heating resistor embedded in the ceramic body; a conductor layer on at least one end surface of the ceramic body, electrically connected to the heating resistor; a metal cap attached to an end portion of the ceramic body at a site near the end surface, the metal cap covering at least a portion of the conductor layer and the end surface with a gap therebetween and including a through hole; and a lead terminal inserted in the through hole and electrically connected to the conductor layer. An end portion of the lead terminal disposed in the gap includes a portion that is outside the through hole when viewed in a penetrating direction of the through hole.

Description

Technical Field

[0001] The present invention relates to heaters for use in, for example, combustion vehicle heating systems, kerosene fan heaters, glow plugs for automobile engines, various sensors such as oxygen sensors, or measurement devices. The present invention also relates to glow plugs including the heaters.

Background Art

[0002] A ceramic heater described in, for example, Patent Document 1 is an example of heaters for use in combustion vehicle heating systems, kerosene fan heaters, glow plugs for automobile engines, various sensors such as oxygen sensors, or measurement devices. The ceramic heater described in Japanese Unexamined Utility Model Registration Application Publication No. 63-80456 (hereinafter referred to as Patent Document 1) includes a rod-shaped ceramic body in which a heating resistor is embedded, and a metal cap provided so as to cover a side surface of the ceramic body. The metal cap is electrically connected to the heating resistor, and serves as an electrode. The metal cap has a through hole at the center thereof. A lead terminal extends through the through hole, and the lead terminal is bonded to the metal cap in this state.

[0003] However, in the ceramic heater described in Patent Document 1, when electricity is supplied to the heating resistor through the lead terminal, the lead terminal may be heated to a high temperature due to an inrush current that flows through the lead terminal. Accordingly, the metal cap may also be heated to a high temperature by heat transmitted from the lead terminal. As a result, there is a possibility that the lead terminal will be pulled out of the metal cap due to thermal expansion of the metal cap. Accordingly, it is difficult to improve the long-term reliability of the ceramic heater in heat cycles.

Summary of Invention

[0004] A heater includes a ceramic body having a rod shape; a heating resistor embedded in the ceramic body; a conductor layer on at least one end surface of the ceramic body, electrically connected to the heating resistor; a metal cap attached to an end portion of the ceramic body at a site near the end surface, the metal cap covering at least a portion of the conductor layer and the end surface with a gap therebetween and including a through hole; and a lead terminal inserted in the through hole and electrically connected to the conductor layer. An end portion of the lead terminal disposed in the gap includes a portion that is outside the through hole when viewed in a penetrating direction of the through hole.

[0005] A glow plug includes the above-described heater and a cylindrical metal member attached to the ceramic body, the cylindrical metal member covering a side surface of the ceramic body at a site near the end surface.

Brief Description of Drawings

[0006] 

Fig. 1 is a sectional view of a heater and a glow plug including the heater.

Fig. 2 is a perspective view of one end of a ceramic body included in the heater illustrated in Fig. 1.

Fig. 3 is a perspective view of a main part of the heater illustrated in Fig. 1.

Fig. 4 is a sectional view of the main part of the heater illustrated in Fig. 1.

Fig. 5 is a sectional view of a modification of the heater illustrated in Fig. 1.

Fig. 6 is a perspective view of a lead terminal illustrating a modification of the heater illustrated in Fig. 1.

Fig. 7 is a perspective view of a lead terminal illustrating a modification of the heater illustrated in Fig. 1.

Fig. 8 is a sectional view of a modification of the heater illustrated in Fig. 1.

Description of Embodiments

[0007] A heater 10 will be described with reference to the drawings. Fig. 1 is a sectional view of the heater 10. As illustrated in Fig. 1, the heater 10 includes a ceramic body 1, a heating resistor 2 embedded in the ceramic body 1, and a metal cap 4 that covers one end of the ceramic body 1. Although not illustrated in Fig. 1, as illustrated in Fig. 2, a conductor layer 3 is provided on the one end of the ceramic body 1. In Fig. 2, the hatched area shows the region in which the conductor layer 3 is provided.

[0008] The ceramic body 1 is, for example, a rod-shaped component. The ceramic body 1 includes a tapered portion 11 at the one end thereof. The ceramic body 1 may be made of, for example, electrically insulating ceramics, such as oxide ceramics, nitride ceramics, or carbide ceramics. More specifically, alumina ceramics, silicon nitride ceramics, aluminum nitride ceramics, silicon carbide ceramics, etc., may be used. In particular, the ceramic body 1 is preferably made of a silicon nitride ceramic. Silicon nitride ceramics are advantageous in that silicon nitride, which is the main component, is strong, tough, highly insulative, and highly resistant to heat.

[0009] The ceramic body 1 made of a silicon nitride ceramic may be obtained by, for example, mixing silicon nitride, which is the main component, with 5 to 15 mass% of a rare earth element oxide, such as Y₂O₃, Yb₂O₃, or Er₂O₃, which serves as a sintering additive, and 0.5 to 5 mass% of Al₂O₃; forming the mixture into a predetermined shape; and performing hot-press firing at 1650°C to 1780°C. The length of the ceramic body 1 is set to, for example, 20 to 50 mm, and the diameter of the ceramic body 1 is set to, for example, 2.5 to 5 mm. When the length of the ceramic body 1 is about 20 to 40 mm and the diameter of the ceramic body 1 is about 3 mm, the length of the tapered portion 11 may be set to about 1.5 mm, and the diameter of the end surface of the tapered portion 11 may be set to about 1.5 mm.

[0010] When the ceramic body 1 is made of a silicon nitride ceramic and the heating resistor 2 is made of molybdenum (Mo) or tungsten (W), MoSi₂ or WSi₂, for example, is preferably mixed and dispersed in the ceramic body 1. In this case, the coefficient of thermal expansion of the silicon nitride ceramic, which is the base material, can be set to a value close to the coefficient of thermal expansion of the heating resistor 2, and the durability of the heater 10 can be increased.

[0011] The heating resistor 2 is a resistor for generating heat, and generates heat when a current flows therethrough. The heating resistor 2 is embedded in the ceramic body 1. The heating resistor 2 is provided at the other end of the ceramic body 1. The heating resistor 2 includes a heating portion 21, which is a portion that mainly generates heat, and lead portions 22 that are connected to the heating portion 21. The heating portion 21 has a folded shape, such as a letter 'U' shape, and both ends thereof are separately connected to the respective lead portions 22. The heating portion 21 having the folded shape generates a maximum amount of heat in a central region of the folded portion. The distance from one end of the heating portion 21 to the other end of the heating resistor 2 in the length direction of the ceramic body 1 is set to, for example, 2 to 10 mm.

[0012] The lead portions 22 are components for electrically connecting the heating portion 21 to an external power supply. One end of each lead portion 22 extends to a surface of the ceramic body 1, and the other end is connected to an end portion of the heating portion 21. The lead portions 22 are separately connected to both ends of the heating portion 21. One of the lead portions 22 extends to an end surface of the ceramic body 1 at the one end thereof. In Fig. 2, the location at which the lead portion 22 extends to the end surface is indicated by the broken line. The other lead portion 22 extends to an outer peripheral surface of the ceramic body 1 in a region near the one end thereof.

[0013] The heating resistor 2 may be made be made of a material having, for example, a carbide, nitride, or silicide of W, Mo, titanium (Ti) or the like as the main component. The heating resistor 2 may contain the same material as the material of the ceramic body 1, so that the ceramic body 1 and the heating resistor 2 have close coefficients of thermal expansion. The heating portion 21 has a high resistance, and generates a maximum amount of heat in a region around the folded portion. The resistance per unit length of the lead portions 22 is set to a value smaller than that of the heating portion 21 by, for example, making the content of the material of the ceramic body 1 in the lead portions 22 smaller than that in the heating portion 21, or making the cross section of the lead portions 22 larger than that of the heating portion 21.

[0014] The conductor layer 3 is a component for electrically connecting the heating resistor 2 to an external electrode. The conductor layer 3 is provided on at least one end surface of the ceramic body 1. More specifically, the conductor layer 3 is provided on the outer peripheral surface and end surface of the tapered portion 11. The conductor layer 3 is electrically connected to the heating resistor 2. The conductor layer 3 includes a metallized layer and a plating layer stacked on the metallized layer. The metallized layer may be, for example, a metallized layer containing silver, copper, or titanium, or a metallized layer containing gold, nickel, or palladium (Pd). The plating layer may be, for example, a nickel boron plating layer, a gold plating layer, or a nickel plating layer. The thickness of the metallized layer may be set to, for example, about 5 to 40 µm. The thickness of the plating layer is preferably greater than or equal to, for example, 1 µm.

[0015] The metal cap 4 is a meal component including a bottom portion 41 and a side portion 42. The metal cap 4 may be made of, for example, a metal material such as a stainless steel or an iron-nickel-cobalt (Fe-Ni-Co) alloy. In particular, from the viewpoint of thermal expansion, an iron-nickel-cobalt (Fe-Ni-Co) alloy is preferably used. The metal cap 4 is a component for strongly connecting the conductor layer 3 to the external electrode. As illustrated in Fig. 3, the metal cap 4 is arranged so as to cover the one end of the ceramic body 1 and at least a portion of the conductor layer 3, and is electrically connected to the conductor layer 3. The metal cap 4 has a shape corresponding to the tapered shape of the one end of the ceramic body 1. More specifically, the bottom portion 41 has the shape of a substantially circular plate having a through hole 7 in a central region thereof. The side portion 42 is shaped such that the side portion 42 is substantially annular in cross section perpendicular to the axial direction of the ceramic body 1, and such that the side portion 42 expands as the distance from the bottom portion 41 increases. The metal cap 4 is attached to the ceramic body 1 such that the bottom portion 41 faces the one end of the ceramic body 1 and the side portion 42 extends from the one end so as to cover a portion of the side surface of the tapered portion 11 over an annular region. The side portion 42 has a slit 43. Accordingly, the possibility that thermal stress will be generated in the metal cap 4 due to a difference in the amount of thermal expansion between the metal cap 4 and the ceramic body 1 can be reduced. The shape of the metal cap 4 can be changed in accordance with the shape of the ceramic body 1 as appropriate.

[0016] The heater 10 further includes a lead terminal 5 that extends through the through hole 7 and that is bonded to the metal cap 4. The lead terminal 5 is a component for electrically connecting the conductor layer 3 to the external electrode. The lead terminal 5 is made of, for example, a metal material such as nickel or a stainless steel. The lead terminal 5 is a linear component, and an end portion 9 thereof, which is disposed in a gap between the bottom portion 41 of the metal cap 4 and the conductor layer 3 provided on the end surface of the ceramic body 1, is bonded to the metal cap 4. Accordingly, the metal cap 4 and the lead terminal 5 can be more strongly bonded together than when the lead terminal 5 is simply bonded to the outer surface of the bottom portion 41 of the metal cap 4.

[0017] In addition, in the heater 10, as illustrated in Figs. 3 and 4, the end portion 9 of the lead terminal 5, which is disposed in the gap, includes a part that is outside the through hole 7 when viewed in a penetrating direction of the through hole 7. More specifically, the end portion 9 of the lead terminal, which is disposed in the gap between the metal cap 4 and the end surface of the ceramic body 1, extends over an area greater than the through hole 7. Therefore, even when there is a risk that the lead terminal 5 will be pulled out of the metal cap 4, such a risk can be reduced because the end portion 9 of the lead terminal 5 engages with the bottom portion 41 of the metal cap 4. As a result, the long-term reliability of the heater 10 in heat cycles can be improved.

[0018] In the heater 10, the end portion 9 of the lead terminal 5 extends over a disc-shaped region. Accordingly, the risk of occurrence of local stress concentration in the end portion 9 of the lead terminal 5 can be reduced. As a result, the durability of the lead terminal 5 can be increased.

[0019] In addition, in the heater 10, as illustrated in Fig. 4, the end portion 9 of the lead terminal 5 is apart from the metal cap 4, and a conductive bonding agent 8, with which the metal cap 4, the conductor layer 3, and the end portion 9 of the lead terminal 5 are bonded together, is in the gap. Since the conductive bonding agent 8 is provided, when an external force that pulls the lead terminal 5, that is, an external force that presses the end portion 9 of the lead terminal 5 against the metal cap 4, is applied to the lead terminal 5, the bonding agent 8 serves as a layer that absorbs the external force. Therefore, the risk that the lead terminal 5 will be damaged can be reduced.

[0020] In addition, as illustrated in Fig. 4, the bonding agent 8 may be provided so as to spread over the space between the bottom portion 41 and the conductor layer 3 but not over the space between the side portion 42 and the conductor layer 3. In such a case, the thermal stress generated between the metal cap 4 and the ceramic body 1 can be reduced. As illustrated in Fig. 4, the through hole 7 may be filled with the bonding agent 8. In such a case, the lead terminal 5 and the metal cap 4 can be strongly bonded together. The bonding agent 8 is preferably provided so as to not only fill the through hole 7 but also spread along the lead terminal 5 in a region outside the metal cap 4. In such a case, the lead terminal 5 and the metal cap 4 can be more strongly bonded together.

[0021] The conductive bonding agent 8 may be, for example, a brazing material. In Figs. 1 to 3, the bonding agent 8 is omitted to simplify the drawings.

[0022] As illustrated in Fig. 4, in the heater 10, the end portion 9 of the lead terminal 5 is spaced from the conductor layer 3. Accordingly, even when the lead terminal 5 is heated to a high temperature due to the inrush current that flows while electricity is being supplied, the possibility that the stress will be generated between the lead terminal 5 and the conductor layer 3 can be reduced. As a result, the possibility that the conductor layer 3 will crack can be reduced. The end portion 9 of the lead terminal 5 is preferably separated from the conductor layer 3 by, for example, about 0.05 to 0.2 mm.

[0023] The dimensions of the end portion 9 of the lead terminal 5 may be set, for example, as follows. For example, when the diameter of the ceramic body 1 is 3 mm, the inner diameter of the bottom portion 41 of the metal cap 4 is about 1.8 mm, the length of the side portion 42 of the metal cap 4 in the longitudinal direction of the ceramic body 1 is about 1.2 mm, the thickness of the bottom portion 41 and the side portion 42 is about 0.3 mm, and the diameter of the through hole 7 is about 0.1 to 0.7 mm, the diameter of the end portion 9 of the lead terminal 5 may be set to a value in the range of about 0.2 to 1.7 mm that is greater than the diameter of the through hole 7, and the thickness of the end portion 9 of the lead terminal 5 may be set to about 0.1 to 1 mm.

[0024] Referring to Fig. 1 again, a glow plug 100 includes the above-described heater 10 and a cylindrical metal member 6 attached to a portion of the side surface of the heater 10 that is adjacent to the tapered portion 11.

[0025] The metal member 6 is a component for holding the ceramic body 1. The metal member 6 is a cylindrical component, and is provided so as to surround the one end of the ceramic body 1. In other words, the ceramic body 1 is inserted in the metal member 6. The metal member 6 is electrically connected to the other lead portion 22 that extends to the region near the one end of the ceramic body 1. The metal member 6 is made of, for example, a stainless steel, an iron-nickel-cobalt (Fe-Ni-Co) alloy, or a nickel alloy.

[0026] The metal member 6 and the ceramic body 1 are bonded together with a brazing material. The brazing material is provided so as to surround the end portion of the ceramic body 1. In other word, the brazing material is provided in the form of a layer over the entire circumference of the end portion of the ceramic body 1. Accordingly, the metal member 6 and the ceramic body 1 are strongly bonded together.

[0027] The brazing material may be, for example, silver-copper (Ag-Cu) solder, Ag solder, or Cu solder containing 5 to 30 mass% of glass component. The glow plug 100 includes the heater 10 in which the possibility that the lead terminal 5 will be pulled out is reduced, and therefore has an improved long-term reliability in heat cycles.

[0028] The lead terminal 5 may have various shapes depending on the use thereof. More specifically, as illustrated in Fig. 5, the lead terminal 5 may have a shape obtained by bending a single lead wire. More specifically, the lead terminal 5 may be L-shaped such that the end portion 9 thereof extends in a direction that crosses the penetrating direction of the through hole 7. In the case where the lead terminal 5 is shaped as illustrated in Fig. 5, when a stress that pulls the lead terminal 5 in the penetrating direction of the through hole 7 is applied, the lead terminal 5 may be deformed so as to absorb the stress.

[0029] Alternatively, as illustrated in Fig. 6, the lead terminal 5 may be T-shaped such that the end portion 9 thereof extends in a direction that crosses the penetrating direction of the through hole 7. Also in this case, the possibility that the lead terminal 5 will be pulled out of the metal cap 4 can be reduced.

[0030] Alternatively, as illustrated in Fig. 7, the end portion 9 of the lead terminal 5 may be X-shaped such that two linear parts thereof intersect. In such a case, even when the lead terminal 5 is pulled in various directions, the stress generated between the lead terminal 5 and the metal cap 4 can be distributed over a plurality of parts. Therefore, the possibility that the lead terminal 5 will be damaged can be reduced. In addition, the surface area of the end portion 9 of the lead terminal 5 is smaller than that in the case where the end portion 9 of the lead terminal 5 is disc-shaped. As a result, the amount of heat generated by the heating resistor 2 and transmitted to the lead terminal 5 can be reduced.

[0031] The portion of the lead terminal 5 that extends in the axial direction and the disc-shaped end portion 9 may be formed either integrally, as illustrated in Fig. 1, or separately. More specifically, as illustrated in Fig. 8, the portion of the lead terminal 5 that extends in the axial direction may be formed in the shape of a nail, and the end portion 9 that extends over a region broader than a head 51 of the nail-shaped portion may be disposed between the through hole 7 and the head of the nail-shaped portion. In this case, when the lead terminal 5 is used in heat cycles, the possibility that the portion of the lead terminal 5 that extends in the axial direction and the end portion 9 will be separated from each other can be reduced.

Reference Signs List

[0032] 

1

ceramic body

11

tapered portion

2

heating resistor

21

heating portion

22

lead portion

3

conductor layer

4

metal cap

41

bottom portion

42

side portion

43

slit

5

lead terminal

6

metal member

7

through hole

8

bonding agent

9

end portion

10

heater

100

glow plug

Claims

1. A heater comprising:

a ceramic body having a rod shape;

a heating resistor embedded in the ceramic body;

a conductor layer on at least one end surface of the ceramic body, electrically connected to the heating resistor;

a metal cap attached to an end portion of the ceramic body at a site near the end surface, the metal cap covering at least a portion of the conductor layer and the end surface with a gap therebetween and including a through hole; and

a lead terminal inserted in the through hole and electrically connected to the conductor layer,

wherein an end portion of the lead terminal disposed in the gap comprises a portion that is outside the through hole when viewed in a penetrating direction of the through hole.

2. The heater according to Claim 1, wherein the end portion of the lead terminal is disc-shaped.

3. The heater according to Claim 1 or 2, wherein the end portion of the lead terminal is apart from the metal cap, and a conductive bonding agent that bonds the metal cap, the conductor layer, and the end portion of the lead terminal together is disposed in the gap.

4. The heater according to any one of Claims 1 to 3, wherein the end portion of the lead terminal is apart from the conductor layer.

5. A glow plug comprising:

the heater according to any one of Claims 1 to 4; and

a cylindrical metal member attached to the ceramic body, the cylindrical metal member covering a side surface of the ceramic body at a site near the end surface.

Drawing