JP6878116B2 - Heater and glow plug with it - Google Patents

Description

The present invention is for, for example, a heater for ignition or flame detection in a combustion type in-vehicle heating device, a heater for ignition of various combustion devices such as an oil fan heater, a heater for glow plugs of an automobile engine, and various sensors such as an oxygen sensor. It relates to a heater used for a heater, a heater for heating a measuring device, and the like.

As a heater used for a glow plug of an automobile engine or the like, for example, the heater described in Patent Document 1 is known. The heater described in Patent Document 1 includes a rod-shaped ceramic body, a heat generating resistor embedded in the tip of the ceramic body, and a lead connected to the heat generating resistor. The heat generating resistor has a resistance value set to be larger than that of the lead and has a folded shape. In such a heater, the interface between the lead and the heat generating resistor is linear. In recent years, glow plugs have been required to have both rapid temperature rise and durability.

Japanese Unexamined Patent Publication No. 2003-22889

When such a heater is rapidly heated, the heat generating resistor and the lead are rapidly expanded. At this time, since the boundary between the heat generating resistor and the lead is linear, there is a possibility that shear stress may occur along the boundary between the heat generating resistor and the lead. In particular, stress tends to be particularly concentrated on the portion of the boundary between the heat generating resistor and the lead that is in contact with the ceramic body. As a result, when the heater was used repeatedly, cracks were generated in the portion of the boundary between the heat generating resistor and the lead in contact with the ceramic body, and this crack might grow along the boundary between the heat generating resistor and the lead. .. As a result, it has been difficult to improve the long-term reliability of the heater.

The heaters of the present disclosure include a rod-shaped ceramic body, a heat generating resistor located inside the ceramic body and having a folded shape, and a pair of heat generating resistors located inside the ceramic body and connected to the heat generating resistor. A lead is provided, and the heat generating resistor and the pair of leads are overlapped and connected in a direction perpendicular to the axial direction of the ceramic body, and the heat generating resistor and the pair of leads are overlapped and connected. When the cross section perpendicular to the axial direction of the ceramic body is viewed through the region, the lead is located inside the heat generating resistor and sandwiches the heat generating resistor. It has a portion that wraps around the outer peripheral side of the heat generation resistor, and the outer circumference of the wraparound portion and the outer circumference of the heat generation resistor have a continuous curve, and the wraparound portion is along the axial direction of the ceramic body. It becomes smaller from the lead side toward the heat generating resistor side .

According to the heater of the present invention, the reed has a portion that wraps around the outer peripheral side of the heat-generating resistor so as to sandwich the heat-generating resistor, so that a shear stress is generated between the heat-generating resistor and the lead. Can be reduced. Further, since the outer circumference of the wraparound portion and the outer circumference of the heat generation resistor have a continuous curve, it is possible to reduce the concentration of stress on either the outer circumference of the wraparound portion or the outer circumference of the heat generation resistor.

It is sectional drawing which shows an example of a heater. (A) is a partially enlarged view of the area A of the heater shown in FIG. 1, and (b) is a cross-sectional view taken along the line XX. (A) is a partially enlarged view of the area A of the heater shown in FIG. 1, and (b) is a cross-sectional view taken along the YY line. (A) is a partially enlarged view of the area A of the heater shown in FIG. 1, and (b) is a cross-sectional view taken along the line ZZ. It is sectional drawing which shows an example of a glow plug. It is sectional drawing which shows a part of the manufacturing process of a heater. It is sectional drawing which shows a part of the manufacturing process of a heater.

As shown in FIGS. 1 and 2, the heater 10 is located inside the ceramic body 1 and the heat generating resistor 2 located inside the ceramic body 1, and is connected to the heat generating resistor 2 while being located inside the ceramic body 1. It includes a pair of leads 3. The heater 10 is used, for example, as a heater 10 for a glow plug.

The ceramic body 1 in the heater 10 has, for example, a rod shape having a longitudinal direction (axial direction). A heat generating resistor 2 and a lead 3 are embedded in the ceramic body 1. Here, the ceramic body 1 is made of ceramics. This makes it possible to provide the heater 10 with high reliability at the time of rapid temperature rise. Examples of the ceramics include electrically insulating ceramics such as oxide ceramics, nitride ceramics and carbide ceramics. The ceramic body 1 may be made of silicon nitride ceramics. Silicon nitride, which is the main component of silicon nitride ceramics, is excellent in strength, toughness, insulation, and heat resistance.

The ceramic body 1 made of silicon nitride ceramics can be produced, for example, by the following method. Specifically, a sintering aid, Al ₂ O ₃ and SiO ₂ are mixed with silicon nitride as the main component to obtain a mixture. The mixture is molded into a predetermined shape to obtain a molded product. Then, the ceramic body 1 can be obtained by hot-press firing the molded body at 1650 to 1780 ° C. The sintering aid can be used 3-12% by weight of _{Y 2 O 3, Yb 2 O} 3 or a rare earth element oxides such as _Er 2 _{O 3.} Al ₂ O ₃ can be used, for example, 0.5 to 3% by mass. SiO _{2 can be mixed so that the amount of SiO 2} contained in the ceramic body 12 is, for example, 1.5 to 5% by mass. The length of the ceramic body 12 is set to, for example, 20 to 50 mm, and the diameter of the ceramic body 12 is set to, for example, 3 to 5 mm.

When a silicon nitride ceramic is used as the ceramic body 1, MoSiO ₂ or WSi ₂ or the like may be mixed and dispersed. In this case, the coefficient of thermal expansion of the silicon nitride ceramics as the base material can be brought close to the coefficient of thermal expansion of the heat generating resistor 2. As a result, the durability of the heater 10 can be improved.

The heat generating resistor 2 is provided inside the ceramic body 1. The heat generating resistor 2 is provided on the tip end side (one end side) of the ceramic body 1. The heat generation resistor 2 is a member that generates heat by passing an electric current. The heat generating resistor 2 has a folded shape.

As the material for forming the heat generating resistor 2, a material containing a carbide such as W, Mo or Ti, a nitride or a silicified material as a main component can be used.

Further, when the ceramic body 1 is made of silicon nitride ceramics, the heat generating resistor 2 is
The WC of the inorganic conductor may be the main component, and the content of silicon nitride added thereto may be 20% by mass or more. For example, in the ceramic body 1 made of silicon nitride ceramics, the conductor component to be the heat generating resistor 2 has a larger coefficient of thermal expansion than silicon nitride, so that it is usually in a state where tensile stress is applied. On the other hand, by adding silicon nitride to the heat generating resistor 2, the coefficient of thermal expansion is brought closer to that of the ceramic body 1, and the stress due to the difference in the coefficient of thermal expansion when the heater 10 is raised and lowered is relaxed. can do.

Further, when the content of silicon nitride contained in the heat-generating resistor 2 is 40% by mass or less, the variation in the resistance value of the heat-generating resistor 2 can be reduced. Therefore, the content of silicon nitride contained in the heat generating resistor 2 may be 20 to 40% by mass. Further, as a similar additive to the heat generating resistor 2, boron nitride can be added in an amount of 4 to 12% by mass instead of silicon nitride. The total length of the heat generating resistor 2 can be set to 3 to 15 mm, and the cross-sectional area ^{can be set to 0.15 to 0.8 mm 2.}

The lead 3 is a member for electrically connecting the heat generating resistor 2 and an external power source. The lead 3 is connected to the heat generating resistor 2 and is drawn out to the surface of the ceramic body 1. Specifically, the leads 3 are joined to both ends of the heat generating resistor 2. One lead 3 is connected to one end of the heat generating resistor 2 on one end side, and is led out from the side surface near the rear end of the ceramic body 1 on the other end side. The other lead 3 is connected to the other end of the heat generating resistor 2 on one end side, and is led out from the rear end portion of the ceramic body 1 on the other end side.

The lead 3 is formed, for example, by using the same material (main component) as the heat generating resistor 2. The lead 3 has a larger cross-sectional area than the heat generating resistor 2, and the content of the material for forming the ceramic body 1 is smaller than that of the heat generating resistor 2, so that the resistance value per unit length is lowered. ing. Further, the reed 3 contains WC, which is an inorganic conductor, as a main component, and silicon nitride may be added thereto so that the content is 15% by mass or more. As a result, the coefficient of thermal expansion of the reed 3 can be brought close to the coefficient of thermal expansion of silicon nitride constituting the ceramic body 1.

Then, as shown in FIG. 2, the heater 10 is located inside the rod-shaped ceramic body 1, the heat generating resistor 2 which is located inside the ceramic body 1 and has a folded shape, and is located inside the ceramic body 1 and generates heat. It includes a pair of leads 3 connected to the resistor 2. Then, the heat generating resistor 2 and the pair of leads 3 are overlapped and connected in a direction perpendicular to the axial direction of the ceramic body 1, and the region where the heat generating resistor 2 and the pair of leads 3 are overlapped and connected is formed. As you can see, when looking at the cross section perpendicular to the axial direction of the ceramic body 1, the lead 3 is located inside the heat generating resistor 2 and the outer circumference of the heat generating resistor 2 so as to sandwich the heat generating resistor 2. It has a portion that wraps around to the side, and the outer circumference of the wraparound portion and the outer circumference of the heat generating resistor 2 form a continuous curve.

In this way, since the lead 3 has a portion that wraps around the outer peripheral side of the heat generating resistor 2 so as to sandwich the heat generating resistor 2, a shear stress is generated between the heat generating resistor 2 and the lead 3. Can be reduced. Further, since the outer circumference of the wraparound portion and the outer circumference of the heat generation resistor 2 have a continuous curve, it is possible to reduce the concentration of stress on either the outer circumference of the wraparound portion or the outer circumference of the heat generation resistor 2. Thereby, the long-term reliability of the heater 10 can be improved.

In particular, since the pinching position (the crotch portion of the lead 3) is on the outer peripheral side, heat is dissipated to the surface of the heater 10. By bringing the crotch portion of the lead 3 (the portion sandwiching the heat generating resistor 2) in which the stress is confined close to the surface of the heater 10, the heat can be easily dissipated to the surface of the heater 10 and the stress can be reduced.

Further, as shown in FIG. 2, the tip of the sandwiched heat generating resistor 2 has an acute angle. Since the tip of the heat generating resistor 2 has an acute angle and is sandwiched between the leads 3, the lead 3 can be formed into a shape in which the heat generating resistor 2 is held. As a result, the possibility that the heat generating resistor 2 will come off from the lead 3 can be reduced.

Further, the outer circumference of the wraparound portion and the outer circumference of the heat generating resistor 2 may be arcuate. As a result, even if thermal expansion and contraction are repeated under the heat cycle, the stress is dispersed along the arc because the boundary portion between the lead 3 in contact with the ceramic body 1 and the heat generating resistor 2 is arcuate. It will be easier to do. As a result, the possibility of cracks in the reed 3 and the heat generating resistor 2 can be reduced.

At this time, the inner circumference of the wraparound portion of the heat generating resistor 2 may also be arcuate. As a result, it is possible to reduce the possibility that thermal stress is locally concentrated in the wraparound portion. In particular, the inner circumference of the wraparound portion may have an arc shape that is convex in the same direction as the outer circumference. As a result, even if thermal stress is received from the ceramic body 1 and the heat generating resistor 2 at the wraparound portion, the thermal stress can be easily dispersed in the wraparound direction.

Further, the wraparound portion may become thinner toward the tip of the wraparound portion. As a result, the distribution of thermal stress applied to the wraparound portion can be gradually changed. As a result, the possibility of cracks due to local thermal stress can be reduced.

Further, when looking at the respective boundary lines between the heat generating resistor 2 and the pair of leads 3, each boundary line other than the wraparound portion may be inclined with respect to one. This is because when the heater 10 is viewed in cross section, the heat distribution has a high central temperature and a low surface temperature. Since the boundary line is inclined with respect to one side, it is possible to easily concentrate the thermal stress on the portion where the lead 3 sandwiches the heat generating resistor 2 when the central side having a high temperature expands thermally. As a result, the possibility that the lead 3 will come off from the heat generating resistor 2 can be reduced.

Further, as shown in FIGS. 2 and 3, the wraparound portion may become smaller from the lead 3 side toward the heat generating resistor 2 side along the axial direction of the ceramic body. Since the temperature of the heat generating resistor 2 side is higher than that of the lead 3 side, the thermal stress can be reduced by reducing the wraparound portion accordingly.

Further, as can be seen from the comparison between FIGS. 2 (b) and 3 (b), the angle at which the lead 3 sandwiches the heat generating resistor 2 (the angle of the portion of the heat generating resistor 2 sandwiched between the leads 3) is The angle may be larger on the heat generating resistor 2 side than on the lead 3 side. Since the temperature of the heat generating resistor 2 side is higher than that of the lead 3 side, the force applied can be made gentle by making the angle of the portion of the lead 3 sandwiching the heat generating resistor 2 obtuse.

Further, as shown in FIG. 4, at the tip of the lead 3 (the most heat-generating resistor 2 side portion of the lead 3), the lead 3 does not have to sandwich the heat-generating resistor 2. Since the thermal stress generated between the tip of the lead 3 and the heat generating resistor 2 is the largest, in this portion, the lead 3 is moved by the force applied from the heat generating resistor 2 because the lead 3 does not sandwich the heat generating resistor 2. The risk of cracks in the splitting direction can be reduced.

Further, as shown in FIG. 5, the glow plug 100 is a metal cylinder attached so as to cover the heater 10 in which the heat generating resistor 2 is located on one end side of the ceramic body 1 and the other end side of the ceramic body 1. It is equipped with 4. Since the glow plug 100 includes the heater 10 described above, long-term reliability is improved.

<Manufacturing method 1>
Next, the method for manufacturing the heater 10 described above will be described. In the heater 10, for example, the heat generating resistor 2, the lead 3, and the ceramic body 1 can be formed by injection molding.

First, a conductive paste for the heat generating resistor 2 and a conductive paste for the reed 3 containing the conductive ceramic powder and the resin binder are prepared. In addition, an insulating paste for the ceramic body 1 containing the insulating ceramic powder and the resin binder is produced.

Next, the molded body 21 for the heat generating resistor 2 is formed by using the conductive paste for the heat generating resistor 2. Further, as shown in FIG. 6, the molded body 21 is held in the mold 5 and filled with the conductive paste for the reed 3 to form the molded body 31 for the reed 3. At this time, by adjusting the gap between the molded body 21 and the mold 5, the shape can be formed so that the lead 3 has a portion that wraps around the outer peripheral side of the heat generating resistor 2. In FIG. 6, (a) shows a state before filling the conductive paste for the lead 3, and (b) shows a state after filling the conductive paste for the lead 3.

As a result, the molded body 21 and the molded body 31 are held in the mold. Next, while the molded body 21 and the molded body 31 are held in the mold, a part of the mold is replaced with one for molding the ceramic body 1, and then the insulation for the ceramic body 1 is provided in the mold. Fill with sex paste. As a result, a molded body of the heater 10 can be obtained. Next, the heater 10 can be manufactured by firing the obtained molded product of the heater 10.

<Manufacturing method 2>
Another manufacturing method of the heater 10 will be described. In another manufacturing method, the heater 10 can form, for example, the heat generating resistor 2, the lead 3, and the ceramic body 1 by press molding. First, each molded body to be the heat generating resistor 2, the lead 3, and the ceramic body 1 is formed. At this time, as shown in FIG. 7A, the molded body 31 for the lead 3 does not necessarily have a portion that wraps around the outer peripheral side of the heat generating resistor 2, but the molded body for the heat generating resistor 2 does not necessarily have a portion. A gap is formed between the 21 and the molded body 11 for the ceramic body 1. By arranging the molded body 21 for the heat generating resistor 2 and the molded body 31 for the lead 3 in the molded body 11 for the ceramic body 1 and firing while applying pressure, the molded body 31 for the lead 3 Spreads in the gap between the molded body 21 for the heat generating resistor 2 and the molded body 11 for the ceramic body 1, so that the lead 3 is on the outer peripheral side of the heat generating resistor 2 as shown in FIG. 7 (b). It can be shaped to have a wraparound portion. In FIG. 7, (a) shows the state of the molded body before firing, and (b) shows the state after firing.

1: Ceramic body 2: Heat generation resistor 3: Lead 4: Metal cylinder 10: Heater 100: Glow plug

Claims (5)

It includes a rod-shaped ceramic body, a heat-generating resistor located inside the ceramic body and having a folded shape, and a pair of leads located inside the ceramic body and connected to the heat-generating resistor. ,
The heat generating resistor and the pair of reeds are connected so as to overlap each other in a direction perpendicular to the axial direction of the ceramic body.
When the cross section perpendicular to the axial direction of the ceramic body is viewed through the region where the heat generating resistor and the pair of reeds are overlapped and connected.
The lead is located inside the heat-generating resistor and has a portion that wraps around the heat-generating resistor so as to sandwich the heat-generating resistor, and has a portion that wraps around the outer periphery of the heat-generating resistor and the heat-generating portion. A heater in which the outer periphery of the resistor has a continuous curve, and the wraparound portion becomes smaller from the lead side toward the heat generating resistor side along the axial direction of the ceramic body . The heater according to claim 1, wherein the outer circumference of the wraparound portion and the outer circumference of the heat generating resistor are arcuate. The heater according to claim 1 or 2, wherein the wraparound portion becomes thinner toward the tip of the wraparound portion. Claim that when looking at the respective boundary lines between the heat generating resistor and the pair of leads, the entire boundary line other than the wraparound portion is inclined with respect to one. The heater according to any one of 1 to 3. The heater according to any one of claims 1 to 4 , wherein the heat generating resistor is attached so as to cover one end side of the ceramic body and the other end side of the ceramic body. Glow plug with metal cylinder.

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