HEATER AND GLOW PLUG

Description

Technical Field

[0001] The present invention relates to heaters according to the preamble of claim 1 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] 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 is disclosed in, for example, Japanese Unexamined Utility Model Registration Application Publication No. 63-80456 (hereinafter referred to as Patent Document 1). The heater disclosed in Patent Document 1 includes a ceramic body including a heating resistor embedded therein, and a metal cap provided so as to cover an end of the ceramic body. The metal cap is electrically connected to the heating resistor, so that electric power can be supplied to the heating resistor by connecting a lead terminal to the metal cap. Thus, heat can be generated by the heater.

[0003] However, in the heater disclosed in Patent Document 1, thermal stress may be generated between the ceramic body and the metal cap, which are made of different materials. Therefore, there is a problem that it is difficult to improve the long-term reliability of the heater in heat cycles.

[0004] EP 2 247 156 A1 discloses a heater according to the initially-mentioned type.

[0005] The present invention has been made in light of the above-described problems, and an object of the present invention is to provide a heater in which thermal stress generated between a ceramic body and a metal cap can be reduced.

Summary of Invention

[0006] A heater according to an aspect of the present invention includes a rod-shaped ceramic body; a heating resistor embedded in the ceramic body; a conductor layer on at least a surface of the ceramic body at one end of the ceramic body, the conductor layer being electrically connected to the heating resistor; and a metal cap for external connection, the metal cap covering the one end of the ceramic body together with at least a portion of the conductor layer. The metal cap has a slit in a portion of an outer periphery of the metal cap, the slit extending from an outer region toward an inner region.

Brief Description of Drawings

[0007] 

Fig. 1 is a sectional view of a heater and a glow plug according to an embodiment of the present invention.

Fig. 2 is a perspective view of an end of a ceramic body and a conductor layer included in the heater illustrated in Fig. 1.

Fig. 3 is a perspective view of a metal cap included in the heater illustrated in Fig. 1.

Fig. 4 is an enlarged perspective view of a region around the metal cap in the heater illustrated in Fig. 1.

Fig. 5 is an enlarged sectional view of the region around the metal cap in the heater illustrated in Fig. 1. Description of Embodiments

[0008] A heater according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a sectional view of a heater 10 according to the embodiment of the present invention. 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. The heating resistor 2 and the conductor layer 3 are electrically connected to each other by a lead portion 22.

[0009] The ceramic body 1 is, for example, a rod-shaped component. Herein, a rod-shaped object is defined as an object that is long in a certain direction. Therefore, a plate-shaped object that is long in a certain direction may also be regarded as being rod-shaped. The ceramic body 1 has 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.

[0010] 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, 0.5 to 5 mass% of Al₂O₃, and SiO₂ so that the content of SiO₂ in the sintered body is 1.5 to 5 mass%; forming the mixture into a predetermined shape; and performing hot-press firing at 1650°C to 1780°C. In the case where the ceramic body 1 is rod-shaped, 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 50 mm and the diameter of the ceramic body 1 is about 3 mm, the length of the tapered portion 11 may be set to 0.1 to 3 mm, and the diameter of the end surface of the tapered portion 11 may be set to 1 to 2.9 mm.

[0011] 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.

[0012] 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 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 of the heating resistor 2 is provided at the other end of the ceramic body 1. The heating portion 21 has a folded shape, and both ends thereof are connected to the 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 the front end of the heating portion 21 to the rear end of the heating resistor 2 in the length direction of the ceramic body 1 is set to, for example, 2 to 10 mm.

[0013] 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 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 of the ceramic body 1 at the one end thereof is shown 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.

[0014] 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 coefficients of thermal expansion that are close to each other. 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.

[0015] 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 the one end of the ceramic body 1. More specifically, the conductor layer 3 is provided on the end surface of the ceramic body 1 and a portion of the outer peripheral surface of the tapered portion 11. The conductor layer 3 is electrically connected to the heating resistor 2 by the corresponding lead portion 22. 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, and titanium, or a metallized layer containing gold, nickel, and 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 20 to 40 µm. The thickness of the plating layer is preferably greater than or equal to, for example, 1 µm.

[0016] 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. 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 ceramic body 1. More specifically, the bottom portion 41 has the shape of a substantially circular plate. The side portion 42 is shaped such that the side portion 42 is substantially annular in in cross section perpendicular to the axial length 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 covers part of the tapered portion 11.

[0017] As illustrated in Figs. 3 and 4, the metal cap 4 has a slit 43 formed in a portion of the outer periphery of the metal cap 4. The slit 43 extends from an outer region, that is, the rim, toward an inner region, that is, the central region. More specifically, the slit 43 extends from the bottom edge of the side portion 42 toward the center of the bottom portion 41. Accordingly, when the thermal expansion of the metal cap 4 occurs, the metal cap 4 can be deformed such that the width of the slit 43 decreases. Thus, the difference between the amount of thermal expansion of the metal cap 4 and the amount of thermal expansion of the ceramic body 1 can be reduced. This leads to a reduction in the thermal stress generated between the metal cap 4 and the ceramic body 1. As a result, the long-term reliability of the heater 10 can be improved.

[0018] In addition, as illustrated in Fig. 5, the inclination angle α of the inner peripheral surface of the side portion 42 of the metal cap 4 is greater than the inclination angle β of the tapered portion 11. Herein, the inclination angle α shows how much the inner peripheral surface of the side portion 42 is inclined with respect to the plane including the inner surface of the bottom portion 41. The inclination angle β shows how much the outer peripheral surface of the tapered portion 11 is inclined with respect to a plane perpendicular to the axial direction of the ceramic body 1.

[0019] Since the inclination angle α is greater than the inclination angle β, when the metal cap 4 is attached to the tapered portion 11, the bottom surface of the side portion 42 of the metal cap 4 comes into contact with the tapered portion 11, and a gap can be provided between the inner surface of the bottom portion 41 of the metal cap 4 and a portion of the conductor layer 3 that is provided on the end surface of the tapered portion 11. By placing a solder material 7 in this gap, as illustrated in Fig. 5, the metal cap 4 and the conductor layer 3 can be strongly bonded to each other. The inclination angle α of the inner peripheral surface of the side portion 42 may be set to, for example 40° to 80°. The inclination angle β of the tapered portion 11 may be set to, for example, 45° to 75°. In Figs. 1 and 4, the solder material 7 is omitted to simplify the drawings.

[0020] The metal cap 4 is formed such that the slit 43 extends to the center of the metal cap 4. In other words, the slit 43 extends from the bottom edge of the side portion 42 of the metal cap 4 to the central region of the bottom portion 41. Accordingly, the thermal expansion of the bottom portion 41 in the circumferential direction can be reduced in a balanced manner, so that a change in the shape of the bottom portion 41 after the thermal expansion from that before the thermal expansion can be reduced. Accordingly, the thermal stress generated in the metal cap 4 can be further reduced.

[0021] In the heater 10 according to the present embodiment, the slit 43 is formed such that the slit 43 has a circular-hole-shaped end portion in the central region. A slit having such a shape is also regarded as a single slit 43. The slit 43 may, of course, instead be formed so as to have a constant width to the center of the bottom portion 41, or such that the width thereof changes at an intermediate position.

[0022] With regard to the dimensions of the metal cap 4, when the diameter of the ceramic body 1 is about 3 mm, for example, the inner diameter of the bottom portion 41 may be set to about 1.5 to 2 mm, and the thickness of the bottom portion 41 may be set to about 0.1 to 0.5 mm. In addition, the inner diameter of the side portion 42 at the bottom end thereof may be set to about 1.5 to 2.5 mm, the thickness of the side portion 42 may be set to about 0.1 to 0.5 mm, and the height of the side portion 42 may be set to 1 to 1.2 mm. The length of the slit 43 may be set to 1 to 2 mm.

[0023] The heater 10 further includes a lead terminal 5 having an end portion connected to the conductor layer 3. The lead terminal 5 is a component for electrically connecting the metal cap 4 and 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 terminal 5 is a linear component, and the end portion thereof is disposed in the slit 43 in the metal cap 4 and bonded to the metal cap 4. Accordingly, the metal cap 4 and the lead terminal 5 can be more strongly bonded together than in the case where the lead terminal 5 is bonded to the outer surface of the bottom portion 41 of the metal cap 4. The above-described solder material 7 spreads over a portion of the slit 43 that is formed in the bottom portion 41, and surrounds the lead terminal 5.

[0024] In the heater 10 illustrated in Fig. 5, the solder material 7 spreads not only in the portion of the slit 43 that is formed in the bottom portion 41 but also to the region outside the bottom portion 41. The portion of the solder material 7 that spreads to the region outside the bottom portion 41 surrounds the end portion of the lead terminal 5. Accordingly, the metal cap 4 and the lead terminal 5 can be more strongly bonded together.

[0025] The width of the end portion of the slit 43 is greater than the width of a portion of the slit 43 that extends from the outer region toward the inner region. More specifically, the end portion of the slit 43 has a circular shape in plan view at the central region of the bottom portion 41 of the metal cap 4, and the diameter (width) of the end portion of the slit 43 is greater than the width of the portion of the slit 43 that extends from the outer region toward the inner region. Accordingly, when the metal cap 4 and the lead terminal 5 are bonded together while the lead terminal 5 is disposed in the end portion of the slit 43, the risk that the lead terminal 5 will be shifted to the portion of the slit 43 that extends from the outer region toward the inner region can be reduced. The lead terminal 5 may have a diameter that is greater than the width of the portion of the slit 43 that extends from the outer region toward the inner region and smaller than the diameter (width) of the end portion of the slit 43. In this case, the risk that the lead terminal 5 will be shifted to the portion of the slit 43 that extends from the outer region toward the inner region can be further reduced.

[0026] Although the end portion of the slit 43 has a circular shape in the present embodiment, the shape of the end portion is not limited to this. More specifically, the end portion of the slit 43 may instead have a polygonal shape, such as a rectangular shape. Alternatively, the end portion of the slit 43 may have, for example, an elliptical shape or an oval shape. When the end portion of the slit 43 has a polygonal shape, the length of the longest one of the diagonal lines that connect the corners may be regarded as the width. When the end portion of the slit 43 has an elliptical shape or an oval shape, the length of the major axis may be regarded as the width.

[0027] The solder material 7 may be applied such that the solder material 7 spreads over the portion of the slit 43 that is formed in the bottom portion 41 but does not spread into a portion of the slit 43 that is formed in the side portion 42. In this case, the metal cap 4 and the lead terminal 5 can be strongly bonded together while the thermal stress generated between the metal cap 4 and the ceramic body 1 is suppressed.

[0028] The solder material 7 may be applied such that the solder material 7 spreads not only over a portion of the conductor layer 3 provided on the end surface of the ceramic body 1 but also over a portion of the conductor layer 3 provided on a portion of the outer peripheral surface of the tapered portion 11. In addition, the portion of the conductor layer 3 provided on a portion of the outer peripheral surface of the tapered portion 11 may be bonded to the side portion 42 of the metal cap 4. In this case, the metal cap 4 and the lead terminal 5 can be more strongly bonded together.

[0029] The metal cap 4 includes the bottom portion 41 and the side portion 42, and the conductor layer 3 is located on a surface of the ceramic body 1 in a region closer to the bottom portion 41 of the metal cap 4 than the open end of the side portion 42 is. More specifically, the end of the side portion 42 of the metal cap 4 opposite the end at which the bottom portion 41 is provided is in contact with the outer peripheral surface of the tapered portion 11, and the conductor layer 3 is provided on the outer peripheral surface of the tapered portion 11 in a region closer to the end surface of the ceramic body 1 than a portion of the outer peripheral surface of the tapered portion 11 that is in contact with the side portion 42 is. In other words, the conductor layer 3 may be arranged such that the conductor layer 3 is not provided on a portion of the outer peripheral surface of the tapered portion 11 that is in contact with the side portion 42. Accordingly, when the conductor layer 3 and the metal cap 4 are bonded together with the solder material 7, the solder material 7 may be easily introduced into the space between the conductor layer 3 and the metal cap 4.

[0030] As described above, one lead portion 22 of the heating resistor 2 extends to the end surface of the ceramic body 1 at the one end thereof. The region to which the lead portion 22 extends overlaps the slit 43, and the lead terminal 5 is placed in the slit 43. Also, the lead terminal 5 is located so as to overlap the region to which the lead portion 22 extends. Accordingly, the lead portion 22 and the lead terminal 5 may be arranged near each other, so that the length of the path along which the electricity flows between the lead portion 22 and the lead terminal 5 can be reduced. As a result, unnecessary resistance between the lead portion 22 and the lead terminal 5 can be reduced.

[0031] Referring to Fig. 1 again, a glow plug 100 according to the present embodiment includes the above-described heater 10 and a cylindrical metal member 6 attached to the heater 10 at the tapered-portion-11 side of the heater 10.

[0032] 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 or an iron-nickel-cobalt (Fe-Ni-Co) alloy.

[0033] The metal member 6 and the ceramic body 1 are bonded together with a solder material (not shown). The solder material is provided so as to surround the end portion of the ceramic body 1. In other word, the solder 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.

[0034] The solder material 7 and the solder material with which the metal member 6 and the ceramic body 1 are bonded together 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 according to the present embodiment includes the heater 10 in which the thermal stress generated between the metal cap 4 and the ceramic body 1 is reduced, and therefore the long-term reliability of the heater 10 is increased. As a result, the long-term reliability of the glow plug 100 is increased.

Reference Signs List

[0035] 

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

solder material

10

heater

100

glow plug

Claims

1. A heater (10) comprising a rod-shaped ceramic body (1); a heating resistor (2) embedded in the ceramic body (1); a conductor layer (3) on at least a surface of the ceramic body (1) at one end of the ceramic body (1), the conductor layer (3) being electrically connected to the heating resistor (2); and a metal cap (4) for external connection, the metal cap (4) covering the one end of the ceramic body (1) together with at least a portion of the conductor layer (3),
characterized in that the metal cap (4) has a slit (43) in a portion of an outer periphery of the metal cap (4), the slit (43) extending from an outer region toward an inner region.

2. The heater (10) according to Claim 1, wherein an end portion of the slit (43) reaches a center of the metal cap (4) .

3. The heater (10) according to Claim 1 or 2, wherein a width of an end portion of the slit (43) is greater than a width of a portion of the slit (43) that extends from the outer region toward the inner region.

4. The heater (10) according to any one of Claims 1 to 3, further comprising a lead terminal (5) including an end portion connected to the conductor layer (3), the end portion of the lead terminal (5) being located in the slit (43) and bonded to the metal cap (4).

5. The heater (10) according to Claim 4, wherein the heating resistor (2) extends to an end surface of the ceramic body (1) at the one end, and a portion of the heating resistor (2) that extends to the end surface overlaps the slit (43).

6. The heater (10) according to any one of Claims 1 to 5, wherein the metal cap (4) includes a bottom portion (41) and a side portion (42), and the conductor layer (3) is located on a surface of the ceramic body (1) in a region closer to the bottom portion (41) of the metal cap (4) than an open end of the side portion (42) is.

7. A glow plug (100) comprising the heater (10) according to any one of Claims 1 to 6, and a cylindrical metal member (6) attached to the heater (10) at the one-end side of the heater (10).

Ansprüche

1. Eine Heizvorrichtung (10), aufweisend einen stabförmigen Keramikkörper (1), einen Heizwiderstand (2), der in den Keramikkörper (1) eingebettet ist, eine Leiterschicht (3) auf mindestens einer Fläche des Keramikkörpers (1) an einem Ende des Keramikkörpers (1), wobei die Leiterschicht (3) elektrisch mit dem Heizwiderstand (2) verbunden ist, und eine Metallkappe (4) für eine externe Verbindung, wobei die Metallkappe (4) das eine Ende des Keramikkörpers (1) zusammen mit mindestens einem Abschnitt der Leiterschicht (3) bedeckt,
dadurch gekennzeichnet, dass die Metallkappe (4) einen Schlitz (43) in einem Abschnitt eines Außenumfangs der Metallkappe (4) hat, wobei sich der Schlitz (43) von einem äußeren Bereich in Richtung zu einem inneren Bereich erstreckt.

2. Die Heizvorrichtung (10) gemäß Anspruch 1, wobei ein Endabschnitt des Schlitzes (43) eine Mitte der Metallkappe (4) erreicht.

3. Die Heizvorrichtung (10) gemäß Anspruch 1 oder 2, wobei eine Breite eines Endabschnitts des Schlitzes (43) größer als eine Breite eines Abschnitts des Schlitzes (43) ist, der sich von dem äußeren Bereich in Richtung zu dem inneren Bereich erstreckt.

4. Die Heizvorrichtung (10) gemäß irgendeinem der Ansprüche 1 bis 3, ferner aufweisend einen Zuleitungsanschluss (5), der einen Endabschnitt aufweist, der mit der Leiterschicht (3) verbunden ist, wobei der Endabschnitt des Zuleitungsanschlusses (5) in dem Schlitz (43) angeordnet ist und mit der Metallkappe (4) verbunden ist.

5. Die Heizvorrichtung (10) gemäß Anspruch 4, wobei sich der Heizwiderstand (2) zu einer Endfläche des Keramikkörpers (1) an dem einen Ende erstreckt und ein Abschnitt des Heizwiderstandes (2), der sich zu der Endfläche erstreckt, mit dem Schlitz (43) überlappt ist.

6. Die Heizvorrichtung (10) gemäß irgendeinem der Ansprüche 1 bis 5, wobei die Metallkappe (4) einen Bodenabschnitt (41) und einen Seitenabschnitt (42) aufweist und die Leiterschicht (3) sich auf einer Fläche des Keramikkörpers (1) in einem Bereich befindet, der näher bei dem Bodenabschnitt (41) der Metallkappe (4) ist als ein offenes Ende des Seitenabschnitts (42).

7. Eine Glühkerze (100), aufweisend die Heizvorrichtung (10) gemäß irgendeinem der Ansprüche 1 bis 6 und ein zylinderförmiges Metallelement (6), das an der einen Endseite der Heizvorrichtung (10) an der Heizvorrichtung (10) angebracht ist.

Revendications

1. Un dispositif de chauffage (10) comportant un corps céramique en forme de tige (1), une résistance chauffante (2) intégrée dans le corps céramique (1), une couche conductrice (3) sur au moins une surface du corps céramique (1) à une extrémité du corps céramique (1), la couche conductrice (3) étant reliée électriquement à la résistance chauffante (2), et un capot métallique (4) pour une connexion externe, le capot métallique (4) recouvrant ladite une extrémité du corps céramique (1) avec au moins une partie de la couche conductrice (3),
caractérisé en ce que le capot métallique (4) a une fente (43) dans une partie d'une périphérie extérieure du capot métallique (4), la fente (43) s'étendant d'une région extérieure vers une région intérieure.

2. Le dispositif de chauffage (10) selon la revendication 1, dans lequel une partie terminale de la fente (43) atteint un centre du capot métallique (4).

3. Le dispositif de chauffage (10) selon la revendication 1 ou 2, dans lequel une largeur d'une partie terminale de la fente (43) est supérieure à une largeur d'une partie de la fente (43) qui s'étend de la région extérieure vers la région intérieure.

4. Le dispositif de chauffage (10) selon l'une quelconque des revendications 1 à 3, comportant en outre une borne de raccordement (5) comprenant une partie terminale reliée à la couche conductrice (3), la partie terminale de la borne de raccordement (5) étant située dans la fente (43) et reliée au capot métallique (4).

5. Le dispositif de chauffage (10) selon la revendication 4, dans lequel la résistance chauffante (2) s'étend à une surface terminale du corps céramique (1) à ladite une extrémité, et une partie de la résistance chauffante (2) qui s'étend à la surface terminale chevauche la fente (43).

6. Le dispositif de chauffage (10) selon l'une quelconque des revendications 1 à 5, dans lequel le capot métallique (4) comprend une partie de fond (41) et une partie latérale (42), et la couche conductrice (3) est disposée sur une surface du corps céramique (1) dans une région qui est plus proche de la partie de fond (41) du capot métallique (4) qu'une extrémité ouverte de la partie latérale (42).

7. Une bougie de préchauffage (100) comportant le dispositif de chauffage (10) selon l'une quelconque des revendications 1 à 6 et un élément métallique cylindrique (6) attaché au dispositif de chauffage (10) dudit un côté d'extrémité du dispositif de chauffage (10).

Drawing