JP4153849B2 - Ceramic heater and glow plug using the same - Google Patents

Description

  The present invention relates to a ceramic heater and a glow plug using the ceramic heater. More specifically, the present invention relates to a ceramic heater used for ignition of an oil fan heater or other heating and a glow plug used for promoting start-up of a diesel engine using the ceramic heater.

  In recent years, in order to comply with exhaust gas regulations, the combustion system of a diesel engine has shifted from a type having a sub-combustion chamber to a direct injection type, so-called direct injection type, and multi-valve has been performed. Since the glow plug used in such a direct injection type diesel engine passes through the wall surface of the cylinder head and faces the main combustion chamber, it has a longer overall length and a smaller diameter than the type that preheats the auxiliary combustion chamber. It is necessary. Furthermore, it is necessary to increase the thickness of the cylinder head in order to ensure the strength of the cylinder head.

  For this reason, the insertion hole for mounting the glow plug is very thin and long, and the glow plug has to be formed to be very long correspondingly.

  Therefore, in order to meet the above-mentioned demand for longer glow plugs and to reduce the overall length of the ceramic heater and reduce the cost, the heat generating part in which the heating element is embedded is externally connected to the ceramic heater. A glow plug having a structure that is fixed to one end of a metal outer cylinder so as to protrude has been proposed.

  For example, FIG. 3 shows a conventional glow plug disclosed in Patent Document 1. The glow plug of Patent Document 1 is configured by holding and fixing the ceramic heater 6 with glass 30 </ b> A from the front end opening of the metal outer cylinder 8.

  This ceramic heater 6 is formed by embedding a coil of a high melting point metal (for example, tungsten) or a heating resistor 64 such as conductive ceramic in a cylindrical ceramic body 6a made of insulating ceramics. Then, a circular protruding portion 6be protruding from the outer peripheral portion 6bf is formed at the central portion of the end surface 6b of the ceramic body 6a, and an anode-side lead wire connected to the heating resistor 64 on the side surface of the protruding portion 6be. The side surface of the tip portion 68a of the 68 is exposed. On the other hand, an anode terminal 50 formed in a cup shape (bottomed cylindrical shape) is connected to the tip of the electrode extraction fitting 12, and this anode terminal 50 is fitted into a protruding portion 6 be formed on the end surface 6 b of the ceramic heater 6. Are joined by brazing. Further, the lead-out part on the cathode side of the heating resistor 64 is exposed from the side surface of the insulating ceramic and connected to the metal outer cylinder 8.

  For the manufacture of the ceramic heater 6, the anode-side lead wire 68 is eccentrically fired during sintering, and the end surface 6b of the sintered ceramic heater 6 is stepped by grinding or the like to form a circular protrusion 6be. The tip 68a of the lead wire 68 is exposed on the side surface of the circular protrusion 6be.

In Patent Document 1, since the cup-shaped anode terminal 50 is fitted and brazed to the circular protrusion 6be at the end of the ceramic heater 30, the strength of the brazed portion 16 is improved. Further, since the brazing portion 16 is protruded from the end face 6b, no brazing material remains in the surrounding portion, and a short circuit between the electrode extraction fitting 12 and the metal outer cylinder 8 can be prevented.
JP 2002-122326 A (page 8, FIG. 1)

  The configuration in which the anode terminal 50 is fitted to the protruding portion 6be and connected by brazing as in Patent Document 1 is excellent in that both can be reliably connected. There is a problem that the energization durability of the ceramic heater deteriorates.

  For this reason, it has been desired that the ceramic heater 6 be provided with energization durability more than ever.

  The present invention has been devised in view of the above-described problems, and suppresses local heat generation at the anode terminal, and a ceramic heater having sufficient energization durability and a rapid temperature increase using this ceramic heater. An object of the present invention is to provide a glow plug that can be used.

The ceramic heater of the present invention includes a rod-shaped ceramic body , a heating resistor incorporated in the ceramic body, a lead wire connected to the heating resistor and led out to the surface side of the ceramic body, and the lead wire It includes a lead portion connected exposed on the surface of the ceramic body, and an anode connected to the exposed portion of the cited exit portion terminal and. And while forming a protrusion part in the one end surface of the said ceramic body, the said drawer part is exposed in several places of the side wall of the said protrusion part , and the exposed part of the said drawer part is via the side wall of the said protrusion part. It is formed in the position which opposes, and the said anode terminal can be connected to each of the said exposed part, It is characterized by the above-mentioned.

  Moreover, it is preferable that the ratio of the outer diameter A of the protrusion and the outer diameter B of the ceramic body is 0.4 ≦ A / B ≦ 0.88.

Furthermore, it is preferable that the cross-sectional area of the exposed portion of the lead-out portion is 1 × 10 ^{5 to} 6.8 × 10 ⁵ μm ² .

  And the glow plug characterized by inserting and fixing the above-mentioned ceramic heater in the front-end | tip opening part of a metal outer cylinder is provided.

According to the configuration of the present invention, to expose the lead portion is pulled out from a plurality of locations of the side wall of the projecting portion, the anode terminal is configured to be connected to each of the exposed portions. Therefore, even when a high voltage is applied from the anode terminal, it becomes possible to flow a small current to the lead portion, the heat generation of the lead portions is suppressed. Furthermore, since the exposed part of the drawer part is formed at a position facing the side wall of the protrusion part, the distance between the local heat generation points of the drawer part can be maximized, so that the thermal stress of the protrusion part is suppressed. Energization durability can be improved.
Therefore, it is possible to provide a ceramic heater that is resistant to the thermal shock of the projecting portion when a voltage is applied and has excellent current durability. In addition , a glow plug using a ceramic heater that is resistant to such a thermal shock has no ignition failure and can greatly improve reliability.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a sectional view of a ceramic heater of the present invention, and FIG. 2 is a sectional view of a glow plug using the ceramic heater of the present invention.

  As shown in FIG. 1, a ceramic heater 10 of the present invention includes a heating resistor 12 built in a ceramic body 11, and lead wires connected to one side of the heating resistor 12 and led out to the end face side of the ceramic body 11. 15b, a lead portion 13a connected to the lead wire 15b and exposed to the surface of the ceramic body 11, and an anode terminal 14 connected to the exposed portion of the lead portion 13a are formed. In addition, a lead wire 15a connected to the other side of the heating resistor 12 and led to the side surface side of the ceramic body 11, and a lead portion 13b connected to the tip of the lead wire 15a and exposed to the side surface of the ceramic body 11 are provided. Formed and connectable to the cathode side.

The ceramic body 11 is made of a rod-shaped electrically insulating ceramic, and one end face thereof forms a protrusion 16. In addition, a heating resistor 12 is embedded inside the tip side. The heating resistor 12 is a U-shaped rod-like body, and contains a conductive component, an adjustment component for adjusting a resistance temperature coefficient, and a ceramic component which is an insulating component. Further, as shown in FIG. 1, the lead-out portions 13a and 13b are connected to the tips of the lead wires 15a and 15b. In particular, the lead-out portion 13a is connected to the tip of the lead wire 15b and 2 on the side wall of the protruding portion 16. It is exposed is drawn to the sites.

  The anode terminal 14 is made of SUS304 or the like, and has a tip formed in a cup shape so that a predetermined voltage can be applied from the outside. This anode terminal 14 is formed in order to securely connect the two exposed portions of the side wall drawn from the above-described lead portion 13b, and the anode terminal 14 can be securely connected even if the exposed portion is increased. Can be connected. Although the tip of the anode terminal 14 is formed in a cup shape, the present invention is not limited to this, and the tip may be divided into a plurality of portions corresponding to the exposed portion and connectable.

  When the lead portion 13a is energized from an external power source, power is supplied to the end of the U-shaped heating resistor 12 provided in the ceramic body 11 and the heating resistor 12 starts to generate heat. Conducts through the ceramic body 11 and reaches the surface.

  However, immediately after being applied to the anode terminal 14 to the lead portion 13a, the generated heat is not sufficiently transmitted through the ceramic body 11, and the protrusion 16 has a temperature difference from the ceramic body 11 due to heat generated by the lead portion 13a. . Therefore, local heat is generated in the lead-out portion 13a in the protruding portion 16, and the energization durability of the ceramic heater 10 is likely to deteriorate.

  In the ceramic heater 10 of the present invention, two or more lead portions 13a connected to the anode terminal 14 are exposed on the side wall of the protruding portion 16, and the anode terminal 14 is provided so as to be connectable to each of the exposed portions. Therefore, the partial resistance of the protrusion 16 can be reduced, local heat generation of the lead-out part 13a at the time of voltage inrush can be suppressed, and the heat stress of the protrusion 16 can be suppressed to increase the current-carrying durability.

  And as a more preferable form, as shown in FIG. 1, it is good to form the exposed part of the drawer | drawing-out part 13a in the position which opposes via the protrusion part 16. As shown in FIG. By forming in such a position, the distance of the local heat generation part of the drawer | drawing-out part 13a which generate | occur | produces slightly can be maximized, the thermal stress of the protrusion part 16 can be suppressed, and energization durability can be improved.

  Furthermore, the ratio of the outer diameter A of the protrusion 16 and the outer diameter B of the ceramic body 11 is preferably 0.4 ≦ A / B ≦ 0.88. If the ratio A / B of the outer diameter is smaller than 0.4, the distance that exposes the side surface of the lead portion 13a becomes long, so the resistance of the lead portion 13a increases, and local heat generation occurs in the protrusion portion 16 when the voltage enters. However, if the thermal stress accompanying this increases, and the ratio A / B of the outer diameter is greater than 0.88, the diameter of the protruding portion 16 becomes thinner, the load resistance of the protruding portion 16 becomes lower, and cracks occur in the protruding portion 16. To do. This crack is likely to occur when the lead portion 13a is formed only on one side at one location.

Furthermore, the area of the exposed part of the lead-out part 13a is preferably 1 × 10 ^{5 to} 6.8 × 10 ⁵ μm ² . If the cross-sectional area of the lead-out portion 13a is smaller than 1 × 10 ⁵ μm ² , the contact resistance between the side surface of the lead-out portion 13a and the anode terminal 14 becomes high, and local heat generation occurs in the protrusion portion 16 at the time of voltage inrush. Thermal stress increases. In addition, if the area of the exposed portion of the drawn portion 13a is larger than 6.8 × 10 ⁵ μm ² , the drawn portion 13a has a large influence as a foreign substance on the protruding portion 16, and cracks due to thermal stress are caused by the drawn portion 13a and the protruding portion. 16 occurs.

The electrically insulating ceramic constituting the ceramic body 11 is usually fired integrally with the heating resistor 12 and the lead wires 15a and 15b, and these are integrated after firing. This electrically insulating ceramic only needs to have sufficient insulating properties at −20 to 1500 ° C. with respect to the heating resistor 12 and the lead wires 15a and 15b. In particular, it is preferable to have an insulation property of 10 ⁸ times or more with respect to the heating resistor 12.

  The components constituting this electrically insulating ceramic are not particularly limited, but nitride ceramics are desirable. Nitride ceramics has relatively high thermal conductivity, can efficiently transfer heat from the tip of the ceramic body 11 to the other end, and reduce the temperature difference between the tip and the other end of the ceramic body 11. Because you can. For example, it may be composed of only one of silicon nitride ceramics, sialon, and aluminum nitride ceramics, and at least one of silicon nitride ceramics, sialon, and aluminum nitride ceramics may be the main component.

In particular, by using silicon nitride ceramics among nitride ceramics, a ceramic heater and a glow plug that are resistant to thermal shock and excellent in durability can be obtained. This silicon nitride ceramics includes a wide variety of silicon nitride as a main component, and includes not only silicon nitride but also sialon. Furthermore, usually, a sintering aid (each oxide such as Y, Yb, Er, etc.) is blended by several mass% (about 2-10 mass%) and fired. Further, the sintering aid powder is not particularly limited, and powders such as rare earth oxides generally used for firing silicon nitride can be used. In particular, it is more preferable to use a sintering aid powder such as Er ₂ O ₃ in which the grain boundary when sintered is a crystal phase, since the heat resistance is increased.

  Further, a boride of each metal element constituting the heating resistor 12 may be contained, and a small amount of a conductive component may be contained in order to reduce a difference in thermal expansion coefficient from the following conductive component.

  The heating resistor 12 usually contains a conductive component and an insulating component. This conductive component is at least one of silicide, carbide or nitride of one or more elements selected from W, Ta, Nb, Ti, Mo, Zr, Hf, V, and Cr, etc. Is a silicon nitride sintered body or the like. In particular, when silicon nitride is contained in the insulating component and / or the component constituting the insulator, it is preferable to use at least one of tungsten carbide, molybdenum silicide, titanium nitride, tungsten silicide, and the like as the conductive component.

  The conductive component preferably has a small difference in thermal expansion between the insulating component and the component constituting the insulator, and the melting point preferably exceeds the operating temperature of the ceramic heater (1400 ° C. or higher, more preferably 1500 ° C. or higher). Moreover, the quantity ratio between the conductive component and the insulating component contained in the heating resistor 12 is not particularly limited, but when the heating resistor 12 is 100% by volume, the conductive component may be 15-40% by volume. Preferably, it is more preferable to set it as 20-30 volume%.

  The glow plug 26 shown in FIG. 2 is configured by inserting and fixing the ceramic heater 10 from the tip opening of the metal outer cylinder 22 held at the tip of the housing 25.

The lead-out portion 13b exposed by being connected to the cathode side of the ceramic heater 10 is electrically connected to the inner side of the metal outer cylinder 22 by brazing. The metal outer cylinder 22 is formed of a conductive material such as stainless steel, and the ceramic body 11 is fitted and fixed by brazing or the like. Moreover, since the drawer | drawing-out part 13b and the metal outer cylinder 22 mutually contact electrically, and the metal outer cylinder 22 itself has the effect | action as a ground electrode, the metal outer cylinder 22 was attached to another member. Sometimes, power can be supplied through the metal outer cylinder 22 itself.

  A ceramic heater of the present invention and a method of manufacturing a glow plug using the same will be described.

  In order to manufacture the ceramic heater 10, first, a paste containing the conductive component and the insulating component shown as the components constituting the heating resistor 12 is prepared, and this is embedded in the electrically insulating ceramic. .

  First, the paste usually contains a conductive component and an insulating component in a total amount of 75 to 90% by mass when the entire paste is 100% by mass. This paste can be obtained, for example, by wet mixing predetermined amounts of these components as raw material powders, then drying, and further mixing with a predetermined amount of a binder such as polypropylene or wax. The paste may further be in the form of pellets that are appropriately dried and molded so as to be easy to handle.

  The embedding may be performed in any way, for example, by adjusting and fixing the length of the lead wire protruding into the mold and pouring the paste into the mold. Furthermore, the contact length can be adjusted and embedded so that the lead wire is inserted into the paste formed into a predetermined shape.

  In addition, a raw material powder of a rod-shaped substrate is obtained by a press molding method, and the above paste in which an appropriate binder is prepared on the upper surface of the molded body is made, and this is screen-printed into a conductor shape of a heating part lead part and an electrode part May be formed by printing.

  In this way, the heating resistor 12 is press-molded together with the raw material for the ceramic body 11 and pressed together to obtain a powder molded body having the shape of the base. And further, this ceramic heater molded body is housed in a pressing die such as graphite, and this is housed in a firing furnace, and after calcination as necessary to remove the binder, the required time at a predetermined temperature, The ceramic heater 10 can be obtained by hot press firing.

  A circular protruding portion 16aa protruding from the outer peripheral portion 16ab is formed at the central portion of the end surface 16a of the ceramic heater 10, and an anode side lead wire 15b connected to the heating resistor 12 is formed on a side surface of the protruding portion 16aa. The side surface of the lead-out part 13a is exposed through the gap. On the other hand, the anode terminal 14 formed in a cup shape (bottomed cylindrical shape) and the lead-out portion 13a are fitted to the protruding portion 16aa formed on the end surface 16b of the ceramic heater 10 and joined by brazing.

  The circular protrusion 16 may be formed by grinding with a protruding female-shaped diamond grindstone, or the ceramic heater 10 may be cut into a molded body to form a shape. Further, the shape may be formed by a mold used for press-molding the molded body of the ceramic heater 10.

  The ceramic heater 10 produced by the above-described method is fitted into the stainless steel outer cylinder 22 and brazed, and then fixed to the housing 25 by brazing and caulking, whereby the glow plug 26 is completed.

  In the ceramic heater 10 of the present invention, the anode-side lead wire 15b is decentered during sintering, and the end surface 16b of the sintered ceramic heater 10 is stepped to form a stepped portion 16 by grinding or the like. In addition, both side surfaces of the drawn portion 13a drawn from the lead wire 15b are directly exposed on the side wall of the protruding portion 16. With this configuration, since the tip of the anode terminal 14 is branched and connected to the side surface of the lead wire 15b, the connection area can be increased and the connection can be made more reliable. Further, since the tip of the anode terminal 14 is formed in a cup shape and is fitted to the protruding portion 16 and brazed, the strength of the brazed portion 16 is improved.

  Next, examples of the present invention will be described.

  The ceramic heater 10 shown in FIG. 1 was produced by the following method.

  90 to 92 mol% of silicon nitride as a main component of the electrically insulating ceramic constituting the ceramic body 11, 2 to 10 mol% of rare earth element oxide as a sintering aid, aluminum oxide, silicon oxide as silicon nitride and rare earth element The raw material powder was prepared by adding and mixing 0.2 to 2.0 mass% and 1 to 5 mass%, respectively, with respect to the total amount of oxide.

  Thereafter, a raw material powder is obtained by a press molding method to obtain a molded body, and a heating element paste in which an appropriate organic solvent and solvent are added and mixed with tungsten is formed on the upper surface of the molded body. Was printed by the screen printing method.

  Furthermore, a ceramic body 11 is obtained by sandwiching a conductive material mainly composed of tungsten between the heating resistor 12 and the drawn portion 13 and performing hot press firing at a temperature of about 1650 to 1800 ° C. The heating resistor 12 was fired at once.

  Next, at the center of the end face 16a of the ceramic heater 10, a circular protruding portion 16aa protruding from the outer peripheral portion 16ab is formed by grinding, and the side of the protruding portion 16aa is connected to the heating resistor 12 on the anode side. The side surface of the lead portion 13a was exposed through the lead wire 15b. On the other hand, the anode terminal 14 formed in a cup shape and the lead-out portion 13a were fitted to the protruding portion 16aa formed on the end surface 16b of the ceramic heater 10 and joined by brazing.

  The lead portions 13a are four places, two places, and one place, and the directions of the lead portions 13a are opposite and one side. In order to arrange the lead-out portions 13a so as to face each other, in the case of four places, the two sets of the opposite lead-out portions 13a are made evenly every 90 ° in the circumferential direction of the protruding portion 16, and in the case of two places, the circumferential direction of the protruding portion 16 is 180 °. One pair of opposing drawing portions 13a was used. In order for the drawer portions 13a to be arranged to face each other, the adjacent drawer portions need only be 90 ° apart or more.

  Further, in order to arrange the drawing portion 13a on one side, all the drawing portions 13a are gathered and arranged in a range within 30 ° in the circumferential direction of the protruding portion 16.

  Furthermore, samples of the ceramic heater 10 were prepared in which the ratio A / B between the outer diameter A of the protrusion 16 and the outer diameter B of the ceramic body 11 was variously changed.

  Further, samples of the ceramic heater 10 in which the cross-sectional area of the lead-out portion 13a was variously changed were prepared.

  A voltage is applied to the heating resistor 12 of each prepared sample to cause the heating resistor 12 to generate Joule heat, voltage A is applied so that the saturation temperature of the ceramic heater is 1400 ° C., the voltage application time is 5 minutes, and then An evaluation was conducted to examine the temperature change after a 10000 cycle energization endurance test in a thermal cycle in which the time for forced cooling was set to 3 minutes by cutting the voltage and blowing and cooling normal temperature compressed air onto the ceramic heater's highest heat generating portion.

  The results are shown in Table 1.

  In addition, about the temperature change, it was set as the temperature change at the time of applying the voltage A that the saturation temperature of the ceramic heater before an endurance test becomes 1400 degreeC after an energization endurance test of 10,000 cycles.

Then, as a judgment, ◎ (very good) when the temperature change is within −25 ° C., ○ (good) when it is within −45 ° C., Δ (within the allowable range) within −100 ° C., −100 ° C. A sample exceeding x was marked as x (impossible).

  From the results shown in Table 1, No. 1 is within the scope of the present invention. With respect to the samples 1 to 33, the results within the allowable range could be obtained in the temperature change after 10,000 cycles. However, sample no. Samples outside the scope of the present invention shown in 34 to 42 did not give good results in temperature changes after 10,000 cycles.

  No. 2-8, no. Samples 14 to 20 are provided with a plurality of lead portions, the lead portion directions are opposite, the diameter ratio is 0.4 ≦ A / B ≦ 0.88, and the cross-sectional area of the lead portion is 1 × 10 5 to 6 Since it was .8 × 105 μm 2, the temperature change after 10,000 cycles was very good within −25 ° C.

  Furthermore, as a comparative example, no. 36, no. In the samples 39 to 42, cracks were also observed in the lead-out portion 3a or the protruding portion 16.

  In addition, good results were obtained according to the present example. The metal outer cylinder 22 and the housing 25 are fixed by brazing and caulking to the ceramic heater 10 manufactured under the conditions of 1 to 33, and the glow plug 26 is manufactured. Thermal cycle in which the saturation temperature at the tip of the glow plug is 1400 ° C., the voltage application time is 5 minutes, and then the forced cooling time is 3 minutes by cutting the voltage and blowing the normal temperature compressed air to the highest heat generating part and cooling. In 10,000 cycles, the temperature change after 10000 cycles gave a very good result within −25 ° C., and the contact points between the metal outer cylinder 22 and the ceramic body 21 were completely different. No damage was observed, and it was found that the glow plug exhibited excellent thermal shock resistance.

It is sectional drawing of the ceramic heater of this invention. It is sectional drawing of the glow plug using the ceramic heater of this invention. It is sectional drawing of the glow plug using the conventional ceramic heater.

Explanation of symbols

10: Ceramic heater 11: Ceramic body 12: Heating resistor 13: Leader 14: Anode terminal 15: Lead wire 16: Protruding part 20: Ceramic heater
22 : Metal outer cylinder
24 : Anode terminal 25: Housing 26: Glow plug

Claims (4)

A rod-shaped ceramic body , a heating resistor built in the ceramic body, a lead wire connected to the heating resistor and led out to the surface side of the ceramic body, and connected to the lead wire, In a ceramic heater comprising a drawn portion exposed on the surface and an anode terminal connected to the exposed portion of the drawn portion, a protruding portion is formed on one end surface of the ceramic body, and the drawn portion is formed of the protruding portion. Exposed at a plurality of locations on the side wall, and the exposed portion of the lead-out portion is formed at a position facing the side wall of the protruding portion, and the anode terminal can be connected to each of the exposed portions. A ceramic heater characterized by having 2. The ceramic heater according to claim 1 , wherein a ratio of an outer diameter A of the protrusion and an outer diameter B of the ceramic body is 0.4 ≦ A / B ≦ 0.88. ^2. The ceramic heater according to claim 1 , wherein an area of the exposed portion of the lead-out portion is 1 × 10 ^{5 to} 6.8 × 10 ⁵ μm ² . A glow plug, wherein the ceramic heater according to any one of claims 1 to 3 is inserted and fixed in a front end opening of a metal outer cylinder.

Images