JP2013038003A - Heater and glow plug provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heater having high reliability and durability, in which generation of micro-cracks in the connection between a resistor and a lead and change in product resistance are suppressed even when a large current is flowed through a resistor upon pulse driving, DC driving, rapid heating or the like, and to provide a glow plug provided with the heater.SOLUTION: A heater 1 comprises: an insulation base body 9; a resistor 3 buried in the insulation base body 9 and having a folded shape; and a pair of leads 8 buried in the insulation base body 9 and of which tip sides are connected to the insulation base body 9 and rear end sides are lead out of the insulation base body 9. Two interfaces 2 between the resistor 3 and each of the pair of leads 8 are perpendicular to a plane including both axis of the pair of leads 8, and have the tip sides inclined towards an inner side or outer side in different angles to each other.

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 connection part between the resistor and the lead may be a shape change point or a material composition change point, 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 bonding area, as shown in FIG. 12A, the boundary surface between the resistor 3 and the lead 8 is symmetrically inclined when viewed in a cross section parallel to the axial direction of the lead 8. (For example, refer to Patent Documents 1 and 2).

JP 2002-334768 A JP 2003-22889 A

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

  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 Or the boundary surface functions as an antenna and dissipates from the lead surface via the surrounding dielectric.

  In conventional heaters, when viewed in a cross section parallel to the axial direction of the lead, the two boundary surfaces are symmetrically opposed so as not to be twisted. Two planar antennas are arranged so as to match, and an interference phenomenon (crosstalk phenomenon) occurs from the boundary surface on the power input side (anode side) to the boundary surface on the power output side (cathode side). It was.

  Therefore, impedance matching cannot be achieved at the boundary surface on the power output side (cathode side), and 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, a microcrack occurs at the interface between the lead and the resistor, and the crack progresses along the boundary. As a result, there has been 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.

  Further, since the cathode side lead is always grounded in DC driving, free electrons are dispersed so that the lead and the resistor are equipotential with the ground until power is applied to the anode side lead. . When DC voltage suddenly enters there, free electrons start to move according to the potential difference, and in the transient state at the time of power entry, the resistance value at the interface that connects the lead and resistor instantaneously increases. The boundary surface generates heat rapidly. When the boundary surface generates heat instantaneously, only the boundary surface starts thermal expansion before the surrounding insulating base (ceramics) generates heat. In particular, a resistor with a higher resistance value than a lead generates more heat and the thermal expansion becomes more severe, and the shear stress that tries to tear the ceramic is the boundary between the conductor (lead, resistor) and the ceramic. Arising from. The main direction is the extending direction of the boundary surface. If the boundary surface is obliquely inclined, microcracks are generated at the boundary surface between the lead and the resistor, and at the same time, the anode side and the cathode from the heater center. The stress propagates symmetrically to the side, the stress on the anode side and the stress on the cathode side interfere with each other, and a microcrack is connected, and the crack progresses all at once along the boundary surface between the lead and the resistor. As a result, there has been a problem that the resistance value changes.

  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. Suppressing the talk phenomenon and distributing the stress propagation direction, microcracks are generated at the interface between the resistor and the lead, crack growth at the interface, and high reliability in which changes in product resistance are suppressed And a durable heater and a glow plug including the same.

  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. In a heater including a pair of leads led to the surface of the insulating base, two boundary surfaces between the resistor and the pair of leads are perpendicular to a plane including both axes of the pair of leads. Both of them are characterized in that the tip side is inclined inward or outward and is inclined at different angles.

  Further, in the heater of the present invention, in the above configuration, the inclination angle of the cathode-side boundary surface with respect to the cross section perpendicular to the axial direction is smaller than the inclination angle of the anode-side boundary surface with respect to the cross section perpendicular to the axial direction. It is characterized by.

  Further, in the heater of the present invention, in the above configuration, when viewed in a cross section perpendicular to the axial direction intersecting each boundary surface, the area of the cross section on the cathode side is more than the area of the cross section on the anode side. It is characterized by being large.

  The heater according to the present invention is characterized in that, in the configuration described above, of the cross sections perpendicular to the axial direction intersecting with the respective boundary surfaces, the resistors are respectively surrounded by the pair of leads. It is what.

  According to another aspect of the present invention, there is provided a glow plug comprising: the heater according to any one of the above configurations; and a metal holding member that is electrically connected to the lead and holds the heater.

  According to the heater of the present invention, the phase of the high frequency propagating from the power input side (anode side) boundary surface and the phase of the high frequency reaching the power output side (cathode side) boundary surface are unlikely to coincide with each other. It is possible to suppress the crosstalk phenomenon that causes interference. As a result, it is possible to suppress abnormal heat generation at the boundary surface and generation of microcracks due to abnormal heat generation. Even if the DC voltage suddenly rushes, the stress direction due to the thermal expansion between the lead and the resistor at the boundary surface is asymmetric between the anode side and the cathode side. The direction can be dispersed.

  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 a longitudinal section showing an example of an embodiment of a heater of the present invention. (A) is the expanded sectional view which expanded the area | region A containing the interface of a resistor and a lead shown in FIG. 1, (b) is a cross-sectional view in the XX line shown to (a). (A) is an expanded sectional view which shows the principal part of the other example of embodiment of the heater of this invention, (b) is a cross-sectional view in the XX line shown to (a). (A) is an expanded sectional view which shows the principal part of the other example of embodiment of the heater of this invention, (b) is a cross-sectional view in the XX line shown to (a). (A) is an expanded sectional view which shows the principal part of the other example of embodiment of the heater of this invention, (b) is a cross-sectional view in the XX line shown to (a). (A) is an expanded sectional view which shows the principal part of the other example of embodiment of the heater of this invention, (b) is a cross-sectional view in the XX line shown to (a). (A) is an expanded sectional view which shows the principal part of the other example of embodiment of the heater of this invention, (b) is a cross-sectional view in the XX line shown to (a). (A) is an expanded sectional view which shows the principal part of the other example of embodiment of the heater of this invention, (b) is a cross-sectional view in the XX line shown to (a). (A) is an expanded sectional view which shows the principal part of the other example of embodiment of the heater of this invention, (b) is a cross-sectional view in the XX line shown to (a). (A) is an expanded sectional view which shows the principal part of the other example of embodiment of the heater of this invention, (b) is a cross-sectional view in the XX line shown to (a). (A) is an expanded sectional view which shows the principal part of the other example of embodiment of the heater of this invention, (b) is a cross-sectional view in the XX line shown to (a). (A) is a longitudinal cross-sectional view which shows the principal part of the conventional heater, (b) is a cross-sectional view in the XX 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 longitudinal sectional view showing an example of an embodiment of the heater of the present invention, and FIG. 2 (a) is an enlarged cross-sectional view in which a region A including a boundary surface between the resistor 3 and the lead 8 shown in FIG. FIG. 2B is a cross-sectional view taken along line XX shown in FIG.

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. The heater is provided with a pair of leads 8 led out to the surface of the insulating base 9 on the side, and the two boundary surfaces 2 between the resistor 3 and the pair of leads 8 are both the axes of the pair of leads 8. Both of them are perpendicular to the plane including, and the tip side is inclined inward or outward and is inclined at different angles.

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 is preferably about 0.5 mm to 1.5 mm, and the width of the resistor 3 is preferably about 0.3 mm to 1.3 mm. By setting it 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 substrate 9 having a laminated structure can be maintained.

  The pair of leads 8 connected to the resistor 3 on the front end side and led to the surface of the insulating base 9 on the rear end side are mainly composed of carbides such as W, Mo, Ti, nitrides, silicides, and the like. A material similar to that of the resistor 3 can be used. 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 two boundary surfaces 2 between the resistor 3 and the pair of leads 8 are perpendicular to a plane including both axes of the pair of leads 8, and both of the tip sides are inside or Inclined toward the outside and inclined at different angles.

  For example, the inclination angle of the boundary surface with respect to the cross section perpendicular to the axial direction is, for example, 10 to 80 degrees. The different angles are the inclination angle a with respect to the cross section perpendicular to the lead 8 axial direction of the anode side boundary surface and the cathode side. It means that the inclination angle b with respect to the cross section perpendicular to the lead 8 axis direction of the boundary surface is different. Specifically, the difference in angle between the inclination angle a of the anode side boundary surface and the inclination angle b of the cathode side boundary surface. Means 5 degrees or more. As shown in FIG. 2, both the inclination angle a and the inclination angle b are angles of less than 90 degrees in relation to the cross section perpendicular to the lead 8 axis direction. Further, the cathode side boundary surface in the present embodiment is the boundary surface 2 located on the lower side of the figure.

  With such a configuration, a part of the high frequency component whose impedance is not matched at the boundary surface 2 between the resistor 3 and the lead 8 causes the boundary surface 2 to function as an antenna, Even if it is dissipated from the lead surface, the two planar antenna surfaces (boundary surfaces) are placed in an asymmetrical position. Interference phenomenon (crosstalk phenomenon) can be suppressed from the boundary surface 2 on the side (anode side) to the boundary surface 2 on the power output side (cathode side). As a result, abnormal heat generation at the boundary surface and generation of microcracks due to abnormal heat generation can be suppressed.

  Furthermore, even if a direct current voltage suddenly enters due to DC driving, the direction of stress due to thermal expansion between the lead 8 and the resistor 3 at the boundary surface is asymmetric between the anode side and the cathode side. Therefore, the propagation direction of stress can be dispersed.

  Therefore, regardless of pulse driving or DC driving, even if the rising of the power entry becomes steep, the generation of microcracks on the boundary surface between the resistor 3 and the lead 8 and the progress of cracks on the boundary surface are suppressed, The resistance stabilizes for a long time. Thereby, the reliability and durability of the heater are improved.

Here, the inclination angle with respect to the cross section perpendicular to the axial direction of the boundary surface 2 on the cathode side is preferably smaller than the inclination angle with respect to the cross section perpendicular to the axial direction of the boundary surface 2 on the anode side. For example, it is preferable that the inclination angle of the boundary surface 2 on the cathode side is smaller than the inclination angle of the boundary surface 2 on the anode side by 5 degrees or more. As a result, the area of the boundary surface 2 on the cathode side connected to the ground (the contact area between the resistor 3 and the lead 8) is reduced and the resistance is reduced, so that inrush power can be easily flowed to the ground.

  In the heater shown in FIG. 2, the two boundary surfaces 2 between the resistor 3 and the pair of leads 8 are perpendicular to a plane including both axes of the pair of leads 8, and both end sides are inward. The inclination angle with respect to the cross section perpendicular to the axial direction of the boundary surface 2 on the cathode side is smaller than the inclination angle with respect to the cross section perpendicular to the axial direction of the boundary surface 2 on the anode side. Not only such a configuration but also the following configuration may be used.

  In the heater shown in FIG. 3, the two boundary surfaces 2 between the resistor 3 and the pair of leads 8 are perpendicular to a plane including both axes of the pair of leads 8, and both tip sides are directed outward. It is the form which inclines and inclines at each different angle. In this embodiment, the inclination angle of the anode side boundary surface with respect to the cross section perpendicular to the lead 8 axis direction is indicated by a, and the inclination angle of the cathode side boundary surface with respect to the cross section perpendicular to the lead 8 axis direction is indicated by b.

  In the heater shown in FIG. 4, the two boundary surfaces 2 between the resistor 3 and the pair of leads 8 are both inclined so that the tip side is directed inward, and the width of the lead 8 is the anode side cathode side. The width of the lead 3 is wider than that of the resistor 3, and the area of the cross section of the lead 8 is larger than the area of the cross section of the resistor 3.

  Further, in the heater shown in FIG. 5, the two boundary surfaces 2 between the resistor 3 and the pair of leads 8 are both inclined so that the tip side is directed inward, and the cathode-side lead 8 and the resistor 3 The thickness (the vertical thickness in FIG. 5B) is the same as the thickness of the anode-side lead 8 and resistor 3 (the vertical thickness in FIG. 5B), and the cathode-side lead 8 and The width of the resistor 3 (horizontal width in FIG. 5B) is wider than the width of the lead 8 on the anode side and the resistor 3 (horizontal width in FIG. 5B). is there.

  Further, in the heater shown in FIG. 6, the two boundary surfaces 2 between the resistor 3 and the pair of leads 8 are both inclined so that the tip side is directed inward, and the cathode-side lead 8 and the resistor 3 The thickness (vertical thickness in FIG. 6B) is larger than the thickness of the anode-side lead 8 and resistor 3 (vertical thickness in FIG. 6B), and the cathode-side lead 8 and resistor. 3 (the horizontal width in FIG. 6B) is wider than the width of the lead 8 on the anode side and the resistor 3 (the horizontal width in FIG. 6B).

  Further, in the heater shown in FIG. 7, the two boundary surfaces 2 between the resistor 3 and the pair of leads 8 are both inclined so that the tip end faces outward, and the cathode-side lead 8 and the resistor 3 The thickness (vertical thickness in FIG. 7B) is the same as the thickness of the anode-side lead 8 and resistor 3 (vertical thickness in FIG. 7B), and the cathode-side lead 8 and The width of the resistor 3 (the horizontal width in FIG. 7B) is wider than the width of the lead 8 on the anode side and the resistor 3 (the horizontal width in FIG. 7B). is there.

  Further, in the heater shown in FIG. 8, the two boundary surfaces 2 between the resistor 3 and the pair of leads 8 are both inclined so that the tip end faces outward, and the cathode-side lead 8 and the resistor 3 The thickness (vertical thickness in FIG. 8B) is larger than the thickness of the anode-side lead 8 and resistor 3 (vertical thickness in FIG. 8B), and the cathode-side lead 8 and resistor. 3 (width in the horizontal direction in FIG. 8B) is wider than the width of the lead 8 on the anode side and the resistor 3 (width in the horizontal direction in FIG. 8B).

Further, in the heater shown in FIG. 9, the two boundary surfaces 2 between the resistor 3 and the pair of leads 8 are both inclined so that the tip end faces outward, and the width of the lead 8 on the cathode side is the resistor. The cross-sectional area of the lead 8 on the cathode side is larger than the width of the resistor 3 and is larger than the cross-sectional area of the resistor 3.

  Further, in the heater shown in FIG. 10, the two boundary surfaces 2 between the resistor 3 and the pair of leads 8 are both inclined so that the tip end faces outward, and the width of the lead 8 is the anode side cathode side. The width of the resistor 3 is wider, and the area of the cross section of the lead 8 is larger than the area of the cross section of the resistor 3 on both the anode side and the cathode side.

  In addition, the heater shown in FIG. 11 has a configuration in which the resistor 3 is surrounded by a pair of leads 8 among the cross sections perpendicular to the axial direction that intersect the respective boundary surfaces 2.

In addition, the distance from end to end in the axial direction of the lead on the boundary surface 2 in each form is, for example, 0.1 to 10 mm. 2 to 11 all have the boundary surface 2 on the cathode side.
The inclination angle with respect to the cross section perpendicular to the axial direction of the anode is smaller than the inclination angle with respect to the cross section perpendicular to the axial direction of the boundary surface 2 on the anode side, but the present invention is not limited to this form.

  Further, as shown in FIGS. 5 to 9, when viewed in a cross section perpendicular to the axial direction intersecting each boundary surface 2, the area of the cross section on the cathode side is larger than the area of the cross section on the anode side. preferable. Specifically, as shown in the drawing, at least the cathode-side lead 8 is made thicker than the anode-side lead 8 or the cathode-side lead 8 is made wider than the anode-side lead 8. By increasing the width, the area of the cross section on the cathode side is made larger than the area of the cross section on the anode side. By doing so, the cathode-side boundary surface 2 connected to the ground can be further reduced in resistance, so that inrush power can easily flow to the ground.

  This is because the cathode-side lead 8 is always grounded, and free electrons are dispersed so that the lead 8 and the resistor 3 are equipotential with the ground until power is applied to the anode-side lead 8. However, when a DC voltage suddenly enters there, free electrons start to move according to the potential difference.At this time, by increasing the area on the cathode side connected to the ground, free electrons flow from the ground. Since it can be easily performed, even in a transient state when power is applied, heat generation at the cathode side boundary surface is suppressed, and furthermore, free electrons can flow into the anode side boundary surface, and heat generation at the anode side boundary surface is also suppressed. Because it can.

  Further, since the cathode-side lead 8 is always grounded, the high-frequency signal propagated by the crosstalk phenomenon from the boundary surface 2 on the power input side (anode side) by increasing the area of the cathode side connected to the ground. Is immediately absorbed by the ground, and as a result, the abnormal heat generation at the boundary surface 2 and the generation of microcracks due to the abnormal heat generation can be suppressed.

  In the case where the area of the cross section on the cathode side is larger than the area of the cross section on the anode side as shown in FIGS. 5 to 9, the cathode side boundary surface is particularly formed as shown in FIGS. 6 (b) and 8 (b). By increasing the thickness (by increasing the length in the vertical direction), the position of the starting point when the boundary surface 2 is heated to generate stress can be made asymmetric between the anode side and the cathode side. Therefore, the stress distribution when viewed in cross section is also asymmetrical, which is preferable because mutual interference between stresses on the anode side and the cathode side can be suppressed.

  Also, as shown in FIGS. 4, 9, and 10, the cross-section of the lead 8 is made larger than that of the resistor 3 and bonded to dissipate heat toward the lead 8 when the boundary surface 2 is heated. Therefore, heating of the boundary surface 2 can be suppressed. Furthermore, since the volume of the resistor 3 that increases thermal expansion can be reduced and the generated thermal stress can also be reduced, the generation of microcracks at the boundary surface 2 between the resistor 3 and the lead 8 and the progress of cracks at the boundary surface. Is suppressed, and the resistance is stabilized for a long time. Thereby, the reliability and durability of the heater are improved.

Further, in the cross section perpendicular to the axial direction intersecting each boundary surface 2 as shown in FIG.
Since the cross section is surrounded by the pair of leads 8, the stress can be completely confined even if the resistor 3 is thermally expanded. Further, a part of the high frequency component propagating along the surface of the lead 8 where impedance matching cannot be achieved at the connection with the resistor 3 is reflected, and the rest is dissipated as Joule heat through the surrounding dielectric. The connection part is locally heated. At this time, if the resistor 3 is wrapped in the lead 8 on the rear end side of the connection part, the high frequency reflected by the connection part is concentrated in this region, Since it can be converted into Joule heat, reflection of high frequency components can be eliminated. As a result, micro cracks are less likely to occur at the connecting portion between the lead 8 and the resistor 3, and the crack is prevented from progressing along the boundary surface, and the resistance value is stabilized for a long time.

  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. 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.

  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 Table 1 and Table 2, the connection parts of the four types of resistors and the leads were formed using molds having various shapes.

  Since the boundary surface is slanted, the cross-sectional area of the resistor and the cross-sectional area of the lead in Tables 1 and 2 are the cross-sectional area of the resistor at the end of each boundary surface on the anode side and the cathode side. And the area of the cross section of the lead.

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 boundary surface 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, regarding the fact that the most heat-generating part of the heater is on the cathode side particularly at the interface between the lead and the resistor, the interface 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, the resistance change before and after energization of sample No. 1 was very large at 55%. After pulse energization, the boundary surface between the lead and resistor of sample No. 1 was observed with a scanning electron microscope. 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 interface 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, the interface 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.

  As shown in Table 2, since the resistance change before and after the energization of Sample No. 1 was as large as 55%, the interface between the lead and the resistor of Sample No. 1 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 toward 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 interface between the lead of these sample numbers and the resistor was observed with a scanning electron microscope after DC energization. There was no.

1: Heater 2: Boundary surface 3: Resistor 4: Heat generating part 8: Lead 9: Insulating substrate

Claims (5)

An insulating substrate;
A resistor embedded in the insulating substrate and having a folded shape;
In a heater embedded in the insulating base and connected to the resistor on the front end side and a pair of leads led to the surface of the insulating base on the rear end side,
Two boundary surfaces of the resistor and the pair of leads are perpendicular to a plane including both axes of the pair of leads, both of which have tip ends inclined inward or outward and at different angles. A heater characterized by being inclined at.   2. The heater according to claim 1, wherein an inclination angle with respect to a cross section perpendicular to the axial direction of the boundary surface on the cathode side is smaller than an inclination angle with respect to a cross section perpendicular to the axial direction of the boundary surface on the anode side.   2. The heater according to claim 1, wherein when viewed in a cross section perpendicular to the axial direction that intersects each of the boundary surfaces, the area of the cross section on the cathode side is larger than the area of the cross section on the anode side. .   2. The heater according to claim 1, wherein among the cross sections perpendicular to the axial direction intersecting with the respective boundary surfaces, there are cross sections in which the resistor is surrounded by the pair of leads.   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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