JP6027289B2 - Heater and ignition device - Google Patents

Description

  The present invention relates to a heater and an ignition device.

  A heater (ceramic heater) in which a heating element is provided inside a ceramic body is known as a heater used for a gas range, an in-vehicle heating device, an oil fan heater, a glow plug of an automobile engine, or the like. As a ceramic heater, the ceramic heater disclosed by patent document 1 is mentioned, for example.

  A ceramic heater disclosed in Japanese Unexamined Patent Publication No. 2000-156275 (hereinafter referred to as Patent Document 1) includes a ceramic structure, a heating resistor embedded in the ceramic structure, and a ceramic structure connected to the heating resistor. And a power supply line drawn out on the surface.

  When the ceramic heater described in Patent Document 1 is repeatedly used in a high temperature environment, cracks may occur in the power supply line. In particular, when this crack occurs in a region of the power supply line exposed on the surface of the ceramic structure, outside air may enter the inside of the power supply line. For this reason, when the power supply line reacts with the outside air, the resistance value of the power supply line changes, and abnormal heat generation may occur locally. As a result, it has been difficult to improve long-term reliability when the ceramic heater is repeatedly used in a high temperature environment.

  The heater includes a ceramic laminate formed by laminating a plurality of ceramic layers, a belt-like heating resistor provided between the ceramic layers and having both ends drawn to the side surfaces of the ceramic laminate, and the heating resistor between the ceramic layers. A strip-shaped conductive layer laminated on both ends of the body and having one end drawn to the side surface, the conductive layer including the first conductive layer drawn to the side surface and the first conductive layer. A second conductive layer adjacent to the first conductive layer, wherein the first conductive layer and the second conductive layer are composed of a plurality of particles, and the average particle size of the particles of the first conductive layer is the second conductive layer. Smaller than the average particle size of the particles.

It is a longitudinal cross-sectional view which shows a heater. It is the cross-sectional view which cut | disconnected the heater shown in FIG. 1 by the AA 'line. It is the cross-sectional view which cut | disconnected the heater shown in FIG. 1 by the BB 'line. It is a cross-sectional view showing a modification of the heater. It is a perspective view which shows the ignition device using the heater shown in FIG.

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

  As shown in FIGS. 1 to 3, the heater 10 includes a ceramic laminate 1 in which a plurality of ceramic layers 11 are laminated, a heating resistor 2 provided between adjacent ceramic layers 11, and a heating resistor 2. And a conductive layer 3 laminated thereon. The heater 10 can be used for, for example, a glow plug or a gas range of an automobile engine.

  The ceramic laminate 1 is a member in which a heating resistor 2 and a conductive layer 3 are embedded. By providing the heating resistor 2 and the conductive layer 3 inside the ceramic laminate 1, the durability of the heating resistor 2 and the conductive layer 3 can be improved. The ceramic laminate 1 is, for example, a rod-shaped or plate-shaped member.

  The ceramic laminate 1 is made of ceramics having electrical insulation properties such as insulating ceramics, nitride ceramics or carbide ceramics. Specifically, the ceramic laminate 1 is made of alumina ceramic, silicon nitride ceramic, aluminum nitride ceramic, silicon carbide ceramic, or the like.

The ceramic laminate 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; 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. And the ceramic laminated body 1 which consists of silicon nitride ceramics can be obtained by baking at the temperature of 1650-1780 degreeC after shape | molding in a predetermined shape. For the firing, for example, hot press firing can be used.

  When the shape of the ceramic laminate 1 is a rod shape, more specifically, when the shape is a quadrangular prism shape, the length of the ceramic laminate 1 is set to 20 to 100 mm, for example. Moreover, the cross section of the ceramic laminated body 1 is set to a square with a thickness of 1 to 6 mm and a width of 2 to 40 mm, for example.

  The heating resistor 2 is a layered member that generates heat when a voltage is applied thereto. The heating resistor 2 is provided between the adjacent ceramic layers 11. 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 laminate 1 and the surface of the ceramic laminate 1 becomes high temperature. The heater 10 functions when heat is transferred from the surface of the ceramic laminate 1 to the object to be heated. As a to-be-heated material which can transmit heat from the surface of the ceramic laminated body 1, the light oil etc. which are supplied into the inside of the diesel engine for motor vehicles, etc. are mentioned, for example.

  Both ends of the heating resistor 2 are drawn out to the side surface on the rear end side of the ceramic laminate 1. The heating resistor 2 has a vertical cross section (a cross section parallel to the length direction of the heating resistor 2), for example, a folded shape. Specifically, the heating resistor 2 has two adjacent linear portions and a connecting portion that has an outer periphery and an inner periphery that are substantially semicircular or semi-elliptical and that folds and connects the two linear portions. doing. The heating resistor 2 is folded back near the tip of the ceramic laminate 1. The total length of the heating resistor 2 is set to 35 to 100 mm, for example.

  The heating resistor 2 is designed to generate a large amount of heat at the tip side of the ceramic laminate 1. Specifically, the conductive layer 3 is laminated on both ends of the heating resistor 2 on the rear end side of the ceramic laminate 1. Therefore, current flows through the heating resistor 2 and the conductive layer 3 on the rear end side of the ceramic laminate 1. As a result, heat generation of the heating resistor 2 is reduced on the rear end side of the ceramic laminate 1. On the contrary, current flows only through the heating resistor 2 on the tip side of the ceramic laminate 1. As a result, heat generation of the heating resistor 2 is increased on the tip side of the ceramic laminate 1.

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

  The conductive layer 3 is a member for adjusting the amount of heat generated by the heating resistor 2 at the rear end side of the ceramic laminate 1, that is, in the vicinity of the portion where the heating resistor 2 is drawn to the side surface of the ceramic laminate 1. In FIG. 1, the conductive layer 3 is indicated by a broken line. In FIG. 1, in order to make the drawing easier to see, the broken line indicating the conductive layer 3 and the solid line indicating the heating resistor 2 are shifted from each other. Have substantially the same width, and the conductive layer 3 and the heating resistor 2 are laminated so as to have the same width. As shown in FIGS. 2 and 3, the conductive layer 3 is laminated between the ceramic layers 11 on both ends of the heating resistor 2, and one end is drawn out to the side surface of the ceramic laminate 1. Yes. Thus, by covering the both ends of the heating resistor 2 to be connected to the external circuit with the conductive layer 3, the heat generation on the rear end side of the ceramic laminate 1 can be reduced. . Therefore, the reliability of connection between the external circuit and the heater 10 can be improved.

  The conductive layer 3 has a first conductive layer 31 drawn to the side surface of the ceramic laminate 1 and a second conductive layer 32 adjacent to the first conductive layer 31. The first conductive layer 31 and the second conductive layer 32 are composed of a plurality of particles. The average particle size of the particles of the first conductive layer 31 is smaller than the average particle size of the particles of the second conductive layer 32. Thus, the density of the 1st conductive layer 31 can be raised because the 1st conductive layer 31 located in the outer side consists of a particle | grain with a small average particle diameter. As a result, since the porosity of the first conductive layer 31 is reduced, it is possible to reduce the outside air from entering the conductive layer 3.

  Further, not only the conductive layer 3 but also the heating resistor 2 is drawn out to the side surface of the ceramic laminate 1, so that the portion drawn out to the side surface can have a two-layer structure. Therefore, even if a crack occurs in one of the conductive layer 3 or the heating resistor 2, the risk of the crack developing in the other can be reduced.

  In addition, since the second conductive layer 32 is made of particles having a large average particle diameter, the grain boundaries of the particles in the second conductive layer 32 can be reduced, so that the resistance value of the second conductive layer 32 can be reduced. . Thereby, unnecessary heat generation occurring in the conductive layer 3 can be reduced.

  As a result, the heater 10 has improved long-term reliability when used under a heat cycle.

  Specifically, for example, unlike the above-described heater 10, there is the following problem when the average particle size of the conductive layer is constant regardless of the part. That is, when the average particle size of the conductive layer is simply reduced, the resistance of the conductive layer itself is increased even if the outside air can be reduced from entering the conductive layer. In this case, unnecessary heat is generated. On the other hand, when the average particle size of the conductive layer is simply increased, it is easy for outside air to enter the conductive layer even if unnecessary heat generation in the conductive layer can be reduced. On the other hand, like the heater 10 described above, the average particle size of the particles of the first conductive layer 31 is made smaller than the average particle size of the particles of the second conductive layer 32, thereby reducing the entry of outside air. Unnecessary heat generation in the conductive layer 3 can be reduced.

  Furthermore, as shown in FIG. 2, it is preferable that the first conductive layer 31 and the second conductive layer 32 partially overlap. Thereby, compared with the case where the 1st conductive layer 31 and the 2nd conductive layer 32 have not overlapped, when the conductive layer 3 is seen in the length direction, the thermal expansion coefficient of the conductive layer 3 is changed stepwise. Can be made. As a result, it is possible to reduce the possibility that the conductive layer 3 is cracked under a heat cycle.

  Further, the first conductive layer 31 is positioned between the second conductive layer 32 and the heating resistor 2, and the first conductive layer 31 is positioned between the second conductive layer 32 and the heating resistor 2 in the first It is preferable that the conductive layer 31 becomes thinner toward the other end. Thereby, the thermal expansion coefficient of the conductive layer 3 can be changed gently. As a result, it is possible to further reduce the possibility that the conductive layer 3 is cracked under a heat cycle.

  In the heater 10 described above, the conductive layer 3 includes only the first conductive layer 31 and the second conductive layer 32, but is not limited thereto. The conductive layer 3 may have a portion other than the first conductive layer 31 and the second conductive layer 32. For example, as shown in FIG. 4, the conductive layer 3 may include a third conductive layer 33 in addition to the first conductive layer 31 and the second conductive layer 32. The third conductive layer 33 is adjacent to the second conductive layer 32 on the side opposite to the first conductive layer 31.

  The layer used as the third conductive layer 33 is not particularly limited. For example, the average particle diameter of the particles of the third conductive layer 33 may be smaller than the average particle diameter of the particles of the second conductive layer 32. As a result, the grain boundaries of the particles in the third conductive layer 33 increase. Therefore, the resistance value in the third conductive layer 33 can be made larger than the resistance value in the second conductive layer 32. Thereby, the emitted-heat amount of the heating resistor 2 can be changed in steps. Therefore, the temperature of the surface of the heater 10 can be changed stepwise. As a result, generation of a large thermal stress locally in the ceramic laminate 1 can be reduced.

The first conductive layer 31 to the third conductive layer 33 are made of a metal material having excellent heat resistance such as molybdenum (Mo), tungsten (W), or rhenium (Re), for example. In particular, in order to bring the coefficient of thermal expansion close to that of the ceramic laminate 1, it is preferable to mix MoSi ₂ and WSi ₂ or the like. The length of the first conductive layer 31 is set such that the length of the portion along the length direction of the heating resistor 2 is about 2 to 10 mm. The thickness of the first conductive layer 31 is set to about 5 to 30 μm. The length of the second conductive layer 32 is set such that the length of the portion along the length direction of the heating resistor 2 is about 5 to 20 mm. The thickness of the second conductive layer 32 is set to about 25 to 75 μm. When the first conductive layer 31 and the second conductive layer 32 overlap, the length of this region is set to about 500 μm, for example.

  The particle sizes of the first conductive layer 31 and the second conductive layer 32 can be adjusted as follows. Specifically, in the case where both the first conductive layer 31 and the second conductive layer 32 are made of W, the first conductive layer 31 and the second conductive layer are made different by changing the particle diameter of the starting W powder. The particle size of 32 can be adjusted. For example, the average particle size of the W powder used for the first conductive layer 31 may be set to 0.2 μm, and the average particle size of the W powder used for the second conductive layer 32 may be set to 1.2 μm. Thereby, the average particle diameter of the 1st conductive layer 31 can be set to 0.2-2 micrometers, and the average particle diameter of the 2nd conductive layer 32 can be set to 1.2-12 micrometers.

  In particular, the average particle diameter of the first conductive layer 31 is preferably less than 1 μm. Thereby, since it can reduce that external air penetrate | invades between particle | grains, possibility that external air will enter into the 1st conductive layer 31 can be reduced. At this time, the porosity of the first conductive layer is preferably less than 20%. Thereby, the approach of the outside air to the first conductive layer 31 can be reduced.

  The average particle diameter of the conductive layer 3 can be confirmed, for example, by the following method. Specifically, after the heater 10 is cut with a diamond cutter in a plane perpendicular to the conductive layer 3 passing through the conductive layer 3, the surface is polished with diamond powder. Then, what is necessary is just to observe the 1st conductive layer 31 and the 2nd conductive layer 32 using a scanning electron microscope or a metal microscope. More specifically, arbitrary five straight lines are drawn on the image obtained by the scanning electron microscope or the metal microscope. And the average value of the distance for 10 particles crossing these five straight lines is obtained. By dividing this average value by 10 which is the number of particles, the average particle diameter can be obtained. Moreover, you may calculate an average particle diameter using an image-analysis apparatus (The Nireco company make: LUZEX-FS). The above image analysis apparatus can also be used when measuring the porosity of the first conductive layer 31.

  The heater 10 is used, for example, as an ignition device 100 as shown in FIG. The ignition device 100 includes a heater 10 and a flow path 20 through which gaseous fuel flows through the heater 10. The flow path 20 is comprised by the ventilation pipe 22 which has the gas valve 21 and the jet nozzle 23, for example. The gas valve 21 has a function of controlling the flow rate of the gaseous fuel. Examples of the gaseous fuel supplied from the gas valve 21 include natural gas or propane gas. The ventilation pipe 22 ejects the gaseous fuel supplied from the gas valve 21 toward the heater 10 from the ejection port 23. And it can ignite by heating the heater 10 with respect to the gaseous fuel currently injected. Since the ignition device 100 includes the heater 10 with improved long-term reliability, the stability of ignition of gaseous fuel is improved.

1: Ceramic laminate 11: Ceramic layer 2: Heating resistor 3: Conductive layer 31: First conductive layer 32: Second conductive layer 10: Heater 20: Channel 21: Gas valve 22: Ventilation pipe 23: Jet outlet 100: Ignition device

Claims (6)

Both a ceramic laminate in which a plurality of ceramic layers are laminated, a belt-like heating resistor provided between the ceramic layers and having both ends drawn to the side surfaces of the ceramic laminate, and the heating resistor between the ceramic layers And a strip-shaped conductive layer that is laminated on the end of each of the layers and one end of which is drawn to the side surface,
The conductive layer has a first conductive layer drawn out to the side surface and a second conductive layer adjacent to the first conductive layer, and the first conductive layer and the second conductive layer are formed of a plurality of particles. And a heater in which the average particle size of the particles of the first conductive layer is smaller than the average particle size of the particles of the second conductive layer.   The heater according to claim 1, wherein the first conductive layer and the second conductive layer partially overlap. In the portion where the first conductive layer and the second conductive layer overlap, the first conductive layer is located between the second conductive layer and the heating resistor,
The heater according to claim 2, wherein the first conductive layer becomes thinner toward the other end in a portion located between the second conductive layer and the heating resistor.   The average particle diameter of the particles of the first conductive layer is 0.2 to 2 µm, and the average particle diameter of the particles of the second conductive layer is 1.2 to 12 µm. The heater described.   The heater according to any one of claims 1 to 4, wherein the porosity of the first conductive layer is less than 20%.   An ignition device comprising: the heater according to any one of claims 1 to 5; and a flow path for allowing gaseous fuel to flow through the ceramic laminate of the heater.

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