JP5751968B2 - Heater and glow plug equipped with the same - Google Patents

Description

  The present invention is, for example, for 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 a glow plug of an automobile engine, and various sensors such as an oxygen sensor. In particular, the present invention relates to a heater used for a heater, a heater for heating a measuring instrument, and a glow plug including the heater.

  A heater used for a glow plug of an automobile engine includes a resistor having a heat generating portion, a lead, and an insulating base. These materials are selected and designed so that the resistance of the lead is smaller than the resistance of the resistor.

  Here, the joint between the resistor and the lead is a point of change in shape or a point of change in material composition, so that it is not affected by the difference in thermal expansion during heat generation or cooling during use. For the purpose of increasing the junction area, as shown in FIG. 8A, the junction between the resistor 3 and the lead 8 is symmetrical between the anode side and the cathode side when viewed in a cross section parallel to the axial direction of the lead. There is known a heater that is disposed in a slanted manner and has a boundary surface bonded obliquely (see, for example, Patent Documents 1 and 2).

JP 2002-334768 A JP 2003-22889 A

  In recent years, in order to optimize the combustion state of the engine, a driving method in which a control signal from the ECU is pulsed has been adopted.

  Here, a rectangular wave is often used as the pulse. There is a high frequency component at the rising edge of the pulse, and this high frequency component is transmitted on the surface of the lead. However, if the seam portion (boundary surface) is formed so that the end surface of the lead having a different impedance and the end surface of the resistor face each other, part of the high-frequency component that cannot be matched in impedance is at the boundary surface. It is reflected or dissipates from the lead surface through the surrounding dielectric by making the boundary surface function as an antenna. In particular, there is a tendency to dissipate much in the direction perpendicular to the boundary surface and in the direction toward the downstream side along the boundary surface.

  In the conventional heater, when viewed in a cross section parallel to the axial direction of the lead, the junction between the resistor 3 and the lead 8 is arranged symmetrically on the anode side and the cathode side, and the boundary surface is joined obliquely. Because of the structure, radio waves emitted from the anode side boundary surface are dissipated toward the cathode side boundary surface and the vicinity of the heat generating part of the resistor, and thus interfere with signals flowing along the resistor. An interference phenomenon (crosstalk phenomenon) occurred.

  Therefore, a signal is transmitted to the cathode side boundary surface while the pulse waveform is distorted, impedance matching is not achieved at this boundary surface, it is dissipated as Joule heat, and the boundary surface generates heat locally. At this time, due to the difference between the thermal expansion coefficient of the lead and the thermal expansion coefficient of the resistor, microcracks are generated at the interface between the lead and the resistor, and along the interface between the lead and the resistor. The crack has progressed all at once, causing a problem that the resistance value changes.

  Similar problems have arisen when DC driving is employed instead of pulse driving. That is, since there is no circuit loss in recent ECUs, a large current flows through the resistor at the start of engine operation for the purpose of rapid temperature rise. Therefore, since the rising of the power inrush becomes steep as in the case of the rectangular wave of the pulse and the high power containing the high frequency component has entered the heater, the same problem has arisen.

  The present invention has been devised in view of the above-mentioned conventional problems, and its purpose is to achieve high-frequency cross-over even when a large current flows through a resistor during pulse driving, DC driving, or rapid temperature rise. By suppressing the talk phenomenon, a highly reliable and durable heater in which the occurrence of microcracks at the boundary surface between the resistor and the lead, the progress of cracks at the boundary surface, and changes in product resistance are suppressed, and the heater Is to provide a glow plug with

The heater of the present invention includes an insulating base, a resistor embedded in the insulating base and having a folded shape, and embedded in the insulating base, connected to the resistor on the front end side and the resistor on the rear end side. A heater comprising a pair of leads led to the surface of an insulating base, wherein the resistor and the pair of leads overlap in a direction perpendicular to a plane including both axes of the pair of leads. A line that connects between the axes of the pair of leads on a cross section perpendicular to a plane that is connected and the arrangement of the resistor and the pair of leads includes both axes of the pair of leads, or the line thereof The line perpendicular to the line is not line symmetric and is point symmetric with respect to the center of the insulating substrate .

  The heater according to the present invention is characterized in that a boundary surface between the resistor and the pair of leads is a flat surface.

  In addition, the present invention is a glow plug including the heater having the above-described configuration and a metal holding member that is electrically connected to the lead and holds the heater.

  According to the heater of the present invention, since the cathode-side boundary surface and the resistor are not located in the main propagation direction of the high-frequency waves that propagate through the anode-side boundary surface as a transmitting antenna, the occurrence of crosstalk phenomenon in which high-frequency signals interfere with each other. Can be deterred. As a result, it is possible to suppress abnormal heat generation at the boundary surface and generation of microcracks due to abnormal heat generation. Therefore, regardless of pulse driving or DC driving, even if the rising of the power inrush becomes steep, the generation of microcracks at the boundary surface between the resistor and the lead and the progress of cracks at the boundary surface are suppressed, and the long-term Resistance is stable. Thereby, the reliability and durability of the heater are improved.

It is the permeation | transmission schematic which shows an example of embodiment of the heater of this invention. (A) is the expanded schematic of an example which expanded the area | region A containing the connection part of a resistor and a lead shown in FIG. 1, (b) is a cross-sectional view in the XX line shown to (a), (c) is principal part sectional drawing in the YY line shown to (a), (d) is principal part sectional drawing in the ZZ line | wire shown to (a). (A) is the expansion schematic of the other example to which the area | region A containing the connection part of a resistor and a lead shown in FIG. 1 was expanded, (b) is a cross-sectional view in the XX line shown to (a). (C) is principal part sectional drawing in the YY line shown to (a), (d) is principal part sectional drawing in the ZZ line | wire shown to (a). (A) is the expansion schematic of the other example to which the area | region A containing the connection part of a resistor and a lead shown in FIG. 1 was expanded, (b) is a cross-sectional view in the XX line shown to (a). (C) is principal part sectional drawing in the YY line shown to (a), (d) is principal part sectional drawing in the ZZ line | wire shown to (a). (A) is the expansion schematic of the other example to which the area | region A containing the connection part of a resistor and a lead shown in FIG. 1 was expanded, (b) is a cross-sectional view in the XX line shown to (a). (C) is principal part sectional drawing in the YY line shown to (a), (d) is principal part sectional drawing in the ZZ line | wire shown to (a). (A) is the expansion schematic of the other example to which the area | region A containing the connection part of a resistor and a lead shown in FIG. 1 was expanded, (b) is a cross-sectional view in the XX line shown to (a). (C) is principal part sectional drawing in the YY line shown to (a), (d) is principal part sectional drawing in the ZZ line | wire shown to (a). (A) is the expansion schematic of the other example to which the area | region A containing the connection part of a resistor and a lead shown in FIG. 1 was expanded, (b) is a cross-sectional view in the XX line shown to (a). (C) is principal part sectional drawing in the YY line shown to (a), (d) is principal part sectional drawing in the ZZ line | wire shown to (a). (A) is the expansion schematic which expanded the area | region containing the connection part of the resistor of a conventional heater, and a lead, (b) is a cross-sectional view in the XX line shown to (a), (c) is The principal part sectional drawing in the YY line | wire shown to (a), (d) is principal part sectional drawing in the ZZ line | wire shown to (a).

  Hereinafter, examples of embodiments of the heater of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a transmission schematic diagram showing an example of an embodiment of the heater of the present invention, and FIG. 2A is an enlarged schematic example of an example in which a region A including a connection portion between a resistor and a lead shown in FIG. 1 is enlarged. 2 (b) is a cross-sectional view taken along the line XX shown in FIG. 2 (a), FIG. 2 (c) is a cross-sectional view taken along the line YY shown in FIG. 2 (a), and FIG. 2 (d) is a cross-sectional view of the main part along the line ZZ shown in FIG. 2 (a).

  The heater 1 according to the present embodiment includes an insulating base 9, a resistor 3 embedded in the insulating base 9 and having a folded shape, and connected to the resistor 3 on the leading end side and embedded in the insulating base 9, and a rear end. A heater having a pair of leads 8 led out to the surface of the insulating base 9 on the side, wherein the resistor 3 and the pair of leads 8 are perpendicular to a plane including both axes of the pair of leads 8. The resistor 3 and the pair of leads 3 with respect to the boundary line between the resistor 3 and the pair of leads 8 when viewed in a cross section perpendicular to a plane including both axes of the pair of leads 8. The arrangement with the lead 8 is reversed at each connecting portion.

  The insulating base 9 in the heater 1 of the present embodiment is formed in a rod shape, for example. The insulating substrate 9 covers the resistor 3 and the lead 8. In other words, the resistor 3 and the lead 8 are embedded in the insulating substrate 9.

Here, it is preferable that the insulating base 9 is made of ceramics, which can withstand temperatures higher than that of metal, so that it is possible to provide the heater 1 with improved reliability at the time of rapid temperature rise. become. Specifically, ceramics having electrical insulation properties such as oxide ceramics, nitride ceramics, carbide ceramics can be given. In particular, the insulating substrate 9 is preferably made of silicon nitride ceramics. This is because silicon nitride ceramics is excellent in terms of high strength, high toughness, high insulating properties, and heat resistance. This silicon nitride ceramic is, for example, 3 to 12% by mass of a rare earth element oxide such as Y ₂ O ₃ , Yb ₂ O ₃ , Er ₂ O ₃ as a sintering aid with respect to silicon nitride as a main component,
0.5 to 3% by mass of Al ₂ O ₃ and further SiO ₂ are mixed so that the amount of SiO ₂ contained in the sintered body is 1.5 to 5% by mass and molded into a predetermined shape. Thereafter, for example, 1650 to 1780 It can be obtained by hot press firing at 0 ° C.

In the case of using a made of silicon nitride ceramics as the insulating substrate _9, it is preferable to mixing MoSi 2, WSi _2, etc. dispersed. In this case, the coefficient of thermal expansion of the silicon nitride ceramic that is the base material can be brought close to the coefficient of thermal expansion of the resistor 3, and the durability of the heater 1 can be improved.

  The resistor 3 has a heat generating portion 4 that is a region that generates heat in particular, and this region can be used as the heat generating portion 4 by providing a region having a partially reduced cross-sectional area or a spiral region. In the case where the resistor 3 has a folded shape as shown in FIG. 1, the vicinity of the middle point of the folding is the heat generating portion 4 that generates the most heat.

  As this resistor 3, the thing which has a carbide | carbonized_material, nitride, silicide, etc., such as W, Mo, Ti, etc. as a main component can be used. In the case where the insulating base 9 is made of the above-described material, tungsten carbide (WC) is one of the above materials because it has a small difference in thermal expansion coefficient from the insulating base 9, high heat resistance, and low specific resistance. It is excellent as a material for the resistor 3. Furthermore, when the insulating substrate 9 is made of silicon nitride ceramics, the resistor 3 is preferably composed mainly of WC of an inorganic conductor, and the content of silicon nitride added thereto is 20% by mass or more. For example, in the insulating substrate 9 made of silicon nitride ceramics, the conductor component serving as the resistor 3 has a higher coefficient of thermal expansion than silicon nitride, and thus is usually in a state where tensile stress is applied. On the other hand, by adding silicon nitride into the resistor 3, the thermal expansion coefficient of the resistor 3 is brought close to the thermal expansion coefficient of the insulating base 9, and the thermal expansion coefficient when the heater 1 is heated and lowered. The stress due to the difference can be relaxed.

  Further, when the content of silicon nitride contained in the resistor 3 is 40% by mass or less, the resistance value of the resistor 3 can be made relatively small and stabilized. Therefore, the content of silicon nitride contained in the resistor 3 is preferably 20% by mass to 40% by mass. More preferably, the content of silicon nitride is 25% by mass to 35% by mass. Further, as a similar additive to the resistor 3, boron nitride can be added in an amount of 4% by mass to 12% by mass instead of silicon nitride.

  The thickness of the resistor 3 (vertical thickness in FIG. 2) is preferably 0.5 mm to 1.5 mm, for example, and the width of the resistor 3 (horizontal thickness in FIG. 2) is preferably 0.3 mm to 1.3 mm, for example. By setting the width within this range, the resistance of the resistor 3 is reduced and heat is efficiently generated, and the adhesion at the laminated interface of the insulating base 9 having a laminated structure can be maintained.

  The lead 8 whose tip side is connected to the end of the resistor 3 can use the same material as that of the resistor 3 mainly composed of carbide, nitride, silicide, etc. such as W, Mo, Ti. In particular, WC is suitable as a material for the lead 8 in that the difference in coefficient of thermal expansion from the insulating base 9 is small, the heat resistance is high, and the specific resistance is small. When the insulating substrate 9 is made of silicon nitride ceramics, the lead 8 is preferably composed mainly of WC, which is an inorganic conductor, and silicon nitride is added thereto so that the content is 15% by mass or more. . As the silicon nitride content increases, the thermal expansion coefficient of the lead 8 can be made closer to the thermal expansion coefficient of the insulating substrate 9. Further, when the content of silicon nitride is 40% by mass or less, the resistance value of the lead 8 becomes small and stable. Therefore, the content of silicon nitride is preferably 15% by mass to 40% by mass. More preferably, the content of silicon nitride is 20% by mass to 35% by mass. The lead 8 may have a resistance value per unit length lower than that of the resistor 3 by making the content of the forming material of the insulating base 9 smaller than that of the resistor 3. The resistance value per unit length may be lower than that of the resistor 3 by increasing the cross-sectional area.

  As shown in FIG. 2, the resistor 3 and the pair of leads 8 are connected so as to overlap each other in a direction perpendicular to a plane including both axes of the pair of leads 8. When viewed in a cross section perpendicular to the plane including both of the axes, the arrangement of the resistor 3 and the pair of leads 8 with respect to the boundary line between the resistor 3 and the pair of leads 8 is reversed at each connection portion. ing.

  Thus, the cathode side boundary surface and the resistor are not positioned in the main propagation direction of the high frequency waves that propagate through the anode side boundary surface as the transmitting antenna, so that the anode 3 side of the resistor 3 and the lead 8 is on the anode side. Even if a part of the high frequency component whose impedance is not matched at the boundary surface is dissipated from the surface of the lead 8 through the surrounding dielectric by causing the boundary surface on the anode side to function as an antenna, the boundary surface on the cathode side It is possible to suppress the interference phenomenon (crosstalk phenomenon). As a result, it is possible to suppress abnormal heat generation at the boundary surface and generation of microcracks due to abnormal heat generation.

  In other words, regardless of whether the control signal from the ECU is pulse drive or DC drive, the occurrence of microcracks at the boundary surface between the resistor and the lead and the progress of cracks at the boundary surface, even if the rise of power entry becomes steep Is suppressed, and the resistance is stabilized for a long time. Thereby, the reliability and durability of the heater are improved.

  Here, in the heater of the form shown in FIG. 2, the end portions of the resistor 3 and the lead 8 in each connecting portion are rounded as shown in FIG. 2A, as shown in FIG. Further, the arrangement of the resistor 3 and the pair of leads 8 with respect to the boundary line between the resistor 3 and the pair of leads 8 is reversed at each connection portion, and a cross-section of the main part of the YY line in FIG. As shown in the cross-sectional view of the principal part of the line ZZ in FIG. 2 and FIG. 2D, the boundary surface in each connection portion is a plane, and the area of this boundary surface is different in each connection portion. The heater may have the following configuration.

  In the heater shown in FIG. 3, the resistor 3 and the end of the lead 8 at each connecting portion are rounded as shown in FIG. 3 (a), and the resistor is shown in FIG. 3 (b). 3 and the pair of leads 8 with respect to the boundary line between the pair 3 and the pair of leads 8, the arrangement of the lead 3 and the pair of leads 8 is reversed in each connection portion, and a cross-sectional view of the main portion of FIG. As shown in the sectional view of the principal part of line ZZ in 3 (d), the boundary surface in each connecting portion is a plane, and the area of this boundary surface is the same in each connecting portion.

  Further, in the heater of the form shown in FIG. 4, the ends of the resistor 3 and the lead 8 in each connecting portion are rounded as shown in FIG. 4A, and as shown in FIG. 4B. The arrangement of the resistor 3 and the pair of leads 8 with respect to the boundary line between the resistor 3 and the pair of leads 8 is reversed at the respective connecting portions, and a cross-sectional view of the main part of the YY line in FIG. And as shown in the ZZ line principal part sectional view of Drawing 4 (d), the boundary surface in each connection part is a curved surface, and the area of this boundary surface is the same composition in each connection part.

  Further, in the heater of the form shown in FIG. 5, as shown in FIG. 5A, the end portions of the resistor 3 and the lead 8 in each connecting portion are linear and perpendicular to the axial direction of the lead 8. As shown in FIG. 5 (b), the arrangement of the resistor 3 and the pair of leads 8 with respect to the boundary line between the resistor 3 and the pair of leads 8 is reversed at each connection portion. As shown in the cross-sectional view of the main portion of the YY line and the cross-sectional view of the main portion of the line ZZ in FIG. 5 (d), the boundary surface at each connecting portion is formed in a step shape. The configuration is the same for each part.

Further, as shown in FIG. 6A, the heater of the form shown in FIG. 6 is such that the end portions of the resistor 3 and the lead 8 in each connecting portion are linearly perpendicular to the axial direction of the lead 8. 6 (b)
As shown in FIG. 6, the arrangement of the resistor 3 and the pair of leads 8 with respect to the boundary line between the resistor 3 and the pair of leads 8 is reversed at each connection portion, and the YY line in FIG. As shown in the cross-sectional view of the main part and the cross-sectional view of the main part of the line ZZ in FIG. 6 (d), the boundary surface at each connection part is formed in a complicated and fitted shape. The configuration is the same for each part.

  Further, in the heater of the form shown in FIG. 7, as shown in FIG. 7A, the end portions of the resistor 3 and the lead 8 in the respective connecting portions are linear shapes perpendicular to the axial direction of the lead 8. As shown in FIG. 7B, the arrangement of the resistor 3 and the pair of leads 8 with respect to the boundary line between the resistor 3 and the pair of leads 8 is reversed at each connection portion. As shown in the cross-sectional view of the main part of the YY line and the cross-sectional view of the main part of the line ZZ in FIG. 7 (d), the boundary surface at each connecting part is shaped so that the step shown in FIG. The area of this boundary surface is the same in each connecting portion.

  In addition, the distance from the end to the end in the axial direction of the lead of each connection portion is, for example, 0.1 to 10 mm.

  According to the heater as shown in FIGS. 2 and 3, since the boundary surface between the resistor 3 and the pair of leads 8 is a flat surface, a high frequency propagates with stronger directivity in the extending direction of the inclined boundary surface. Therefore, since neither the cathode-side interface nor the cathode lead 8 exists in the high-frequency propagation direction from the cathode-side interface, no crosstalk occurs at all. As a result, abnormal heat generation at the boundary surface and generation of microcracks caused by abnormal heat generation can be effectively suppressed.

  On the other hand, according to the heater as shown in FIGS. 4 to 7, the bonding strength between the resistor 3 and the lead 8 can be improved.

  As shown in FIGS. 3 to 7, the intermediate point in the length direction of the connecting portion (the axial direction of the lead 8) is seen in a cross section perpendicular to the plane including both the axes of the pair of leads 8, and the resistance The arrangement of the body 3 and the pair of leads 8 is preferably point-symmetric with respect to the center of the insulating base 9. This is because, when the heater 1 is heated for a long time, the resistor 3 generates heat more than the lead 8, so that the cross section is point symmetric, and the heat distribution in the axial cross section is also point symmetric with respect to the axial center. Therefore, the heat distribution direction of the heater 1 becomes uniform around the axis, and no place for abnormal heating occurs, so that the resistance is stabilized for a long time. The location of the resistor 3 and the pair of leads 8 is point-symmetric with respect to the center of the insulating base in all the cross sections of the connecting portion, so that places where abnormal heating occurs at all positions of the connecting portion occur. It is more preferable because it is not present. The point symmetry means that the boundary line between one resistor 3 and the lead 8 in the anode side cross section and the cathode side cross section may be inclined by an angle of 5 degrees or less.

  Further, the heater 1 of the present embodiment is a metal holding that holds the heater 1 while being electrically connected to the heater 1 according to any of the above-described configurations and a terminal portion (not shown) of the lead 8. It is preferable to use it as a glow plug provided with a member. Specifically, in the heater 1, a resistor 3 having a folded shape is embedded in a rod-shaped insulating base 9, and a pair of leads 8 are electrically connected to both ends of the resistor 3, respectively. The glow plug includes a metal holding member (sheath fitting) electrically connected to one lead 8 and a wire electrically connected to the other lead 8. preferable.

The metal holding member (sheath fitting) is a metal cylindrical body that holds the heater 1, and is joined to one lead 8 drawn to the side surface of the ceramic base 9 with a brazing material or the like. Further, the wire is joined to the other lead 8 drawn out to the rear end of the other ceramic base 9 with a brazing material or the like. As a result, the resistance of the heater 1 does not change even if it is used for a long time while being repeatedly turned on and off in a high-temperature engine, so that a glow plug having excellent ignitability can be provided at any time.

  Next, the manufacturing method of the heater 1 of this Embodiment is demonstrated.

  The heater 1 of the present embodiment can be formed by, for example, an injection molding method using a die having the shape of the resistor 3, the lead 8, and the insulating base 9.

  First, a conductive paste to be the resistor 3 and the lead 8 including the conductive ceramic powder and the resin binder is manufactured, and a ceramic paste to be the insulating base 9 including the insulating ceramic powder and the resin binder is manufactured.

  Next, a conductive paste molded body (molded body a) having a predetermined pattern to be the resistor 3 is formed by an injection molding method or the like using the conductive paste. Then, in a state where the molded body a is held in the mold, the conductive paste is filled in the mold to form a conductive paste molded body (molded body b) having a predetermined pattern to be the leads 8. Thereby, the molded product a and the molded product b connected to the molded product a are held in the mold.

  Next, in a state where the molded body a and the molded body b are held in the mold, a part of the mold is replaced with one for molding the insulating base 9, and then the ceramic paste that becomes the insulating base 9 in the mold Fill. Thereby, the molded body (molded body d) of the heater 1 in which the molded body a and the molded body b are covered with the molded body of the ceramic paste (molded body c) is obtained.

  Next, the obtained molded body d is fired at, for example, a temperature of 1650 ° C. to 1780 ° C. and a pressure of 30 MPa to 50 MPa, whereby the heater 1 can be manufactured. The firing is preferably performed in a non-oxidizing gas atmosphere such as hydrogen gas.

  The heater of the Example of this invention was produced as follows.

First, a conductive paste containing 50% by mass of tungsten carbide (WC) powder, 35% by mass of silicon nitride (Si ₃ N ₄ ) powder, and 15% by mass of a resin binder is injection-molded into a mold to form a resistor. A formed product a was produced.

  Next, with the molded body a held in the mold, the conductive paste to be the lead is filled in the mold to form the molded body b to be connected to the molded body a. did. At this time, as shown in Tables 1 and 2, four types of leads and connecting portions between the resistors and the leads were formed using molds having various shapes. In addition, the inclination of the anode side interface shown in the table is the angle a shown in the figure, and the inclination of the cathode side interface shown in the table is the angle b shown in the figure.

Next, 85% by mass of silicon nitride (Si ₃ N ₄ ) powder and ytterbium (Yb) oxide (Yb ₂ ) as a sintering aid while the molded product a and the molded product b are held in the mold. A ceramic paste containing 10% by mass of O ₃ ) and 5% by mass of tungsten carbide (WC) for bringing the coefficient of thermal expansion close to the resistor and the lead was injection molded into a mold. As a result, a molded body d having a configuration in which the molded body a and the molded body b were embedded in the molded body c serving as an insulating base was formed.

  Next, after putting the obtained compact d in a cylindrical carbon mold, hot pressing is performed in a non-oxidizing gas atmosphere made of nitrogen gas at a pressure of 1700 ° C. and 35 MPa to sinter the heater. Was made. A glow plug was produced by brazing a cylindrical metal holding member (sheath fitting) to the lead end portion (terminal portion) exposed on the surface of the obtained sintered body.

  A pulse pattern generator was connected to the electrode of the glow plug, and a rectangular pulse having an applied voltage of 7 V, a pulse width of 10 μs, and a pulse interval of 1 μs was continuously energized. After 1000 hours, the rate of change in resistance value before and after energization ((resistance value after energization−resistance value before energization) / resistance value before energization) was measured. The results are shown in Table 1.

  As shown in Table 1, in Sample No. 1, the most heat-generating portion was the connection portion between the lead and the resistor. In order to confirm the energization state, the pulse waveform flowing through the heater of sample number 1 was confirmed using an oscilloscope. Unlike the input waveform, the rise of the pulse did not become steep, and it took 1 μs to reach 7V. Waving while overshooting.

  This is considered to be because the waveform of the high frequency component included in the rising portion of the pulse is synthesized by the crosstalk phenomenon in the heater of sample number 1. Also, the most heated part of the heater is the connection part between the lead and the resistor, especially on the cathode side. The connection part between the cathode side lead and the resistor is caused by an abnormal pulse caused by crosstalk. It is considered that local heat generation was caused by the fact that impedance matching could not be achieved.

  Furthermore, since the resistance change before and after energization of sample number 1 was as large as 55%, the connection between the lead and resistor of sample number 1 was observed with a scanning electron microscope after pulse energization. It was confirmed that microcracks were generated from the outer peripheral direction to the inner side.

  On the other hand, with respect to sample numbers 2 to 4, the most heat generating portion was the resistor heating portion at the tip of the heater. Then, in order to confirm the energization state, the pulse waveform flowing through the heater was confirmed using an oscilloscope, and the waveform was almost the same as the input waveform.

  This indicates that energization was possible without abnormal heating at the connection between the lead and the resistor.

  In addition, the resistance change before and after the energization of sample numbers 2 to 4 was as small as 5% or less. After the pulse energization, when the connecting portion between the lead of these sample numbers and the resistor was observed with a scanning electron microscope, There was no.

  Next, connect the DC power supply to the heater and set the applied voltage so that the temperature of the resistor is 1400 ° C. 1) Energize for 5 minutes and 2) Deenergize for 2 minutes 1), 2) 10,000 cycles were repeated. The rate of change in the resistance value of the heater before and after energization was measured. The results are shown in Table 2.

  As shown in Table 2, since the resistance change before and after the energization of Sample No. 1 was as large as 55%, the connection between the lead of Sample No. 1 and the resistor was observed with a scanning electron microscope after the DC energization. However, it was confirmed that microcracks were generated on the boundary surface from the outer peripheral direction to the inner side.

  On the other hand, with respect to sample numbers 2 to 4, the resistance change before and after energization was as small as 5% or less, and the connection between the lead and resistor of these sample numbers was observed with a scanning electron microscope after DC energization. There was no.

1: Heater 3: Resistor 4: Heat generating part 8: Lead 9: Insulating substrate

Claims (3)

An insulating substrate;
A resistor embedded in the insulating substrate and having a folded shape;
A heater comprising a pair of leads embedded in the insulating base, connected to the resistor on the front end side and led to the surface of the insulating base on the rear end side,
The resistor and the pair of leads are connected so as to overlap in a direction perpendicular to a plane including both axes of the pair of leads,
An arrangement of the resistor and the pair of leads is a line connecting the axes of the pair of leads on a cross section perpendicular to a plane including both axes of the pair of leads or a line perpendicular to the line. A heater which is not line-symmetric and is point-symmetric with respect to the center of the insulating substrate .   The heater according to claim 1, wherein a boundary surface between the resistor and the pair of leads is a flat surface.   A glow plug comprising: the heater according to claim 1; and a metal holding member that is electrically connected to one of the pair of leads and holds the heater.

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