JP2020098801A - Ceramic heater - Google Patents

Abstract

To improve long-term reliability of a ceramic heater.SOLUTION: A ceramic heater 10 is a ceramic heater 10 comprising: a ceramic laminate 1 in which a plurality of ceramic layers are stacked; a belt-shaped heat element 2 that is embedded between the layers of the ceramic laminate 1; and belt-shaped leads 3 that are embedded between the layers of the ceramic laminate 1 and connected to ends of the heat element 2 in an overlapping manner. The heat element 2 protrudes, at connection parts with the leads 3, to both sides in a width direction from the ends of the leads 3, and a thickness of a protruding portion is smaller than a thickness of a portion overlapping the leads 3. This configuration can improve long-term reliability of the ceramic heater 10.SELECTED DRAWING: Figure 2

Description

The present invention relates to a ceramic heater.

A ceramic heater is known as a heater used for a gas stove, a vehicle-mounted heating device, an oil fan heater, a glow plug of an automobile engine, or preheating of fuel. Examples of the ceramic heater include the ceramic heater disclosed in Patent Document 1.

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 to the surface of the ceramic structure. I have it.

JP, 2000-156275, A

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

A ceramic heater according to one aspect of the present invention is a ceramic laminate in which a plurality of ceramic layers are laminated, a strip-shaped heating resistor embedded between layers of the ceramic laminate, and the interlayer of the ceramic laminate. And a strip-shaped lead embedded in and connected to an end portion of the heating resistor so as to overlap with each other, wherein the heating resistor has a width from an end portion of the lead at a connecting portion with the lead. It is characterized in that it overhangs on both sides in the direction, and the thickness of the overhanging portion is smaller than the thickness of the portion overlying the lead.

The ceramic heater according to one aspect of the present invention can improve long-term reliability when it is repeatedly used in a high temperature environment.

It is a longitudinal section showing a ceramic heater of an example of an embodiment of the present invention. It is a cross-sectional view which cut|disconnected the ceramic heater shown in FIG. 1 by the AA' line.

Hereinafter, ceramic heaters 10 according to some embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1, a ceramic heater 10 according to an embodiment of the present invention includes a ceramic laminate 1, a heating resistor 2 provided inside the ceramic laminate 1, and a heating resistor 2 provided inside the ceramic laminate 1. And a lead 3 connected to the heating resistor 2. Such a ceramic heater 10 can be used, for example, for preheating a glow plug or fuel of an automobile engine or for igniting a gas range.

A lead 3 and a heating resistor 2 are embedded inside the ceramic laminate 1. By providing the lead 3 and the heating resistor 2 inside the ceramic laminate 1, the environment resistance of the lead 3 and the heating resistor 2 can be improved. The ceramic laminated body 1 is, for example, a rod-shaped or plate-shaped member (which can be collectively referred to as a column). The ceramic laminated body 1 is formed by laminating a plurality of ceramic layers.

The ceramic laminated body 1 is made of an electrically insulating ceramic such as oxide ceramics, nitride ceramics, or carbide ceramics. Specifically, the ceramic laminate 1 is made of alumina ceramics, silicon nitride ceramics, aluminum nitride ceramics, silicon carbide ceramics, or the like.

The ceramic laminated body 1 made of silicon nitride ceramics can be obtained by the following method. Specifically, for example, 5 to 15% by mass of a rare earth element oxide such as Y ₂ O ₃ , Yb ₂ O ₃ or Er ₂ O ₃ as a sintering aid with respect to silicon nitride as a main component, 0. the amount of SiO ₂ contained in the _Al 2 _{O 3} and sintering of 5-5% by weight amount such that 1.5 to 5 wt% is mixed SiO ₂ that has been adjusted. Then, after being formed into a predetermined shape, it is fired at a temperature of 1650 to 1780° C., whereby the ceramic laminated body 1 made of silicon nitride ceramics can be obtained. For the firing, for example, a hot press method can be used.

When the shape of the ceramic laminated body 1 is rod-shaped, more specifically, when it is a quadrangular prism, the length of the ceramic laminated body 1 is set to 20 to 100 mm, for example. Further, the cross section of the ceramic laminate 1 is set to a quadrangle having a thickness of 1 to 6 mm and a width of 2 to 40 mm, for example.

The heating resistor 2 is a strip-shaped member that generates heat when a voltage is applied. The heating resistor 2 is embedded between the plurality of ceramic layers of the ceramic laminate 1. When a voltage is applied to the heating resistor 2, a current flows and the heating resistor 2 generates heat. The heat generated by this heat generation is transmitted inside the ceramic laminated body 1 and the surface of the ceramic laminated body 1 becomes high in temperature. Then, the heat is transferred from the surface of the ceramic laminate 1 to the object to be heated, so that the ceramic heater 10 functions. Examples of the object to be heated to which heat is transferred from the surface of the ceramic laminated body 1 include light oil supplied to a fuel injection device of an automobile diesel engine.

The heating resistor 2 is provided on the tip side of the ceramic laminated body 1. The heating resistor 2 has a vertical cross section (a plane parallel to the length direction of the heating resistor 2) that is, for example, a folded shape. The heating resistor 2 is folded back near the tip of the ceramic laminate 1. The length from the front end of the heating resistor 2 to the rear end of the heating resistor 2 is set to, for example, 2 to 15 mm in the length direction of the heating resistor 2.

The heating resistor 2 contains, for example, a carbide such as tungsten (W), molybdenum (Mo), or titanium (Ti), a nitride, a silicide, or the like as a main component. When the ceramic laminate 1 is made of silicon nitride ceramics, the heating resistor 2 is preferably made of tungsten carbide as a main component. Thereby, the coefficient of thermal expansion of the ceramic laminated body 1 and the coefficient of thermal expansion of the heating resistor 2 can be made close to each other.

The lead 3 is a strip-shaped member that is embedded in the layers of the plurality of ceramic layers inside the ceramic laminated body 1 and has one end pulled out to the side surface of the ceramic laminated body 1. The lead 3 is electrically connected to the heating resistor 2. The lead 3 is used to electrically connect the heating resistor 2 and an external power source.

Two leads 3 are provided along the length direction of the ceramic laminated body 1 corresponding to each of the heating resistors 2, and are bent at the rear end side of the ceramic laminated body 1 so that the lead 3 of the ceramic laminated body 1 is bent. It is pulled out to the side. The lead 3 is bent at 90° on the rear end side of the ceramic laminated body 1 and is drawn out to the side surface of the ceramic laminated body 1.

The lead 3 is made of a metal material having excellent heat resistance such as W or Mo. In particular, from the viewpoint of the coefficient of thermal expansion, it is preferable to use the same tungsten carbide as the heating resistor 2. The lead 3 has, for example, a width of 1 to 20 mm, a length of a portion along the length direction of the heating resistor 2 is 10 to 80 mm, and since the lead 3 is pulled out to the side surface of the ceramic laminate 1, the length of the heating resistor 2 is long. The length of the portion extending in the direction perpendicular to the depth direction is set to 2 to 30 mm and the thickness is set to about 10 to 50 μm.

FIG. 2 is a cross-sectional view of the ceramic heater 10 shown in FIG. 1, taken along the line AA′ passing through the connection between the heating resistor 2 and the lead 3. In addition, in FIG. 2, a part of the boundary of the plurality of ceramic layers is shown by a dotted line. As shown in FIG. 2, the heating resistor 2 projects from the end of the lead 3 to both sides in the width direction at the connecting portion with the lead 3 (projection 20). The thickness of the overhanging portion of the heating resistor 2 is smaller than the thickness of the portion overlapping the lead 3.

As a result, when thermal stress is generated in the heating resistor 2, the thermal stress can be easily concentrated on the protruding portion. Therefore, it is possible to reduce the possibility that a crack will occur in the portion of the heating resistor 2 that overlaps the lead 3. As a result, 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 portion of the heating resistor 2 that overlaps the lead 3 and the thickness of the portion that overhangs can be compared by the following method. Specifically, the average value of the thickness of each of the portion overlapping the lead 3 and the protruding portion may be obtained and compared. The average value of the thickness can be obtained by the following method, for example. First, the portion overlapping the lead 3 and the protruding portion are divided into three equal parts in the width direction. Next, the thickness of each of the three divided parts is obtained. Then, a value calculated by adding the thicknesses of the respective three divided parts and dividing by 3 is regarded as an average value of the thicknesses. In addition, in the above-mentioned example, the target portion for which the average value is to be obtained is divided into three equal parts in the width direction and the average of the respective thicknesses is obtained, but the present invention is not limited to this. Specifically, it may be divided into four equal parts, or five (or more) parts.

Regarding the thickness of the heating resistor 2, the thickness of the central portion can be set to 3 to 5 μm, and the thickness of the protruding portion can be set to 1 to 3 μm. The thickness of the lead 3 can be set to 10 to 15 μm at the center. The width of the heating resistor 2 can be set to 10 to 50 μm including the protruding portion.

Further, in the heating resistor 2, the thickness of the protruding portion is reduced toward the outer side. Since the thickness of the protruding portion is thinner toward the outer side, stress is likely to be concentrated particularly on the tip portion of the protruding portion. Therefore, it is possible to further reduce the possibility of cracks in the portion of the heating resistor 2 that overlaps the lead 3. As a result, it is possible to further improve the long-term reliability when the ceramic heater 10 is repeatedly used in a high temperature environment.

Further, the lead 3 has a thickness that becomes thinner toward the outer sides on both sides at the connection portion with the heating resistor 2. As a result, when the heating resistor 2 and the lead 3 are taken as a unit, the heating resistor 2 and the lead 3 are tapered toward the outer edges on both sides. It becomes easier to concentrate on the side. As a result, cracks are less likely to occur in the main parts of the heating resistor 2 and the leads 3, so that the long-term reliability of the ceramic heater 10 can be improved.

In particular, as shown in FIG. 2, when the ceramic heater 10 is viewed in cross section, the outer periphery of the lead 3 and the portion of the outer periphery of the heating resistor 2 which is not covered by the lead 3 are smoothly continuous. Is preferred. As a result, even if a crack is generated between the ceramic laminate 1 and the protruding portion of the heating resistor 2, the crack propagates and penetrates between the heating resistor 2 and the lead 3. It is possible to reduce the risk of doing so.

1: Ceramic laminate 2: Heating resistor 3: Lead 10: Ceramic heater

Claims (5)

A ceramic laminated body in which a plurality of ceramic layers are laminated, a strip-shaped heating resistor embedded between layers of the ceramic laminated body, and an end portion of the heating resistor embedded between the layers of the ceramic laminated body A ceramic heater having strip-shaped leads connected to each other,
The heating resistor, when viewed in cross section, at the connection portion with the lead,
Overhanging in a direction orthogonal to the stacking direction of the ceramic layers on both sides in the width direction from the ends of the leads,
The thickness of the lead is thicker than the thickness of the heating resistor, and the outer circumference of the lead and a portion of the outer circumference of the heating resistor that is not covered by the lead are smoothly continuous. heater. 2. The ceramic heater according to claim 1, wherein the heating resistor has a projecting portion thinner than a portion overlapping the lead. The ceramic heater according to claim 1, wherein the heating resistor has a projecting portion whose thickness is reduced toward the outer side. The ceramic heater according to claim 1, wherein the lead has a thickness that decreases toward outer edges on both sides at a connection portion with the heating resistor. At the connecting portion between the heating resistor and the lead, when viewed in cross section,
The ceramic heater according to claim 1, wherein, in the heating resistor, a contact surface with the lead has a larger outward protrusion in a stacking direction of the ceramic layers than a surface facing the contact surface.

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