JP2002246153A - Ceramic heater and glow plug provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly durable ceramic heater, having well-balanced various characteristics, especially mechanical strength and temperature rise characteristics, and provide a manufacturing method of the same and a glow plug provided with the same. SOLUTION: The ceramic heater 1 is provided by injecting kneaded material, which is made by adding a binder to powder mixture containing silicon nitride, erbium oxide, silica, and tungsten carbide and kneading, in a mold provided with a U-shaped recessed part with tungsten lead wires 12a, 12b fixed, where the tungsten lead wires are adjusted to have a fitting area of the lead wire and the heating resistor 11 to exceed 0.1 mm2 and smaller than 20 mm2 by a diameter of a wire and lengths of the lead wires 12a and 12b projected in the mold, obtaining a molded body to be the heating resistor, mounting in split molds which is to become an insulator 13, and hot-pressing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ceramic heater and a glow plug having the same. More specifically,
The present invention relates to a ceramic heater having various characteristics in a well-balanced manner and a glow plug having the ceramic heater. The glow plug of the present invention can be suitably used for a glow plug of a diesel engine.

[0002]

2. Description of the Related Art Conventionally, a conductor formed of a U-shaped heating resistor mainly composed of tungsten carbide or the like, and a lead wire fitted to both ends of the heating resistor and mainly composed of tungsten or the like. However, ceramic heaters having a structure buried in an insulator made of a silicon nitride sintered body or the like are often used.

[0003]

In such a ceramic heater, a reaction layer which is not sufficiently densified at the time of firing may be formed at a fitting portion where a lead wire and a heating resistor are in contact with each other. It is known that this reaction layer has insufficient mechanical strength and is likely to be a starting point for cracks and breaks.
However, on the other hand, it has been found that this reaction layer plays a role in improving the bondability between the lead wire and the heating resistor.
Furthermore, the electrical conductivity changes depending on the fitting area between the lead wire and the heating resistor, and accordingly, the maximum temperature, the rate of temperature rise, and the like change. Therefore, the ceramic heater needs to be provided with a contradictory characteristic that the mechanical strength is improved as the fitting area is smaller and the electric conductivity is improved as the fitting area is larger. Until now, it has not been studied to adjust the balance of each characteristic by such a fitting area when a reaction layer exists.

The present invention solves the above-mentioned problems, and provides a ceramic heater having a structure capable of maintaining all properties such as mechanical strength, bonding property, and electrical conductivity in a well-balanced and maximally advantageous manner, and a ceramic heater having such a structure. An object of the present invention is to provide a glow plug using a heater.

[0005]

SUMMARY OF THE INVENTION A ceramic heater according to the present invention comprises an insulator, and a conductor embedded in the insulator, the conductor being a heating resistor, and one end portion being disposed via a reaction layer. In a ceramic heater having a pair of lead wires fitted to the heating resistor and having the other end exposed from the insulator, a fitting area between the heating resistor and each of the lead wires is 0.
Exceed 1 mm ^2, and less than 20 mm ^2.

[0006] The above-mentioned "insulator" is usually fired integrally with a conductor having a heating resistor and a lead wire, and after firing, these are integrated. The insulator only needs to have sufficient insulation properties at -20 to 1500 ° C. with respect to the heating resistor and the lead wire. In particular, 10 ⁸
It is preferable to have twice or more the insulating property. The constituents of the insulator are not particularly limited. For example, silicon nitride,
It may be composed of only one of sialon and aluminum nitride, and may contain at least one of silicon nitride, sialon and aluminum nitride as a main component. Further, a boride of each metal element constituting the heating resistor may be contained, and a small amount of a conductive component may be contained in order to reduce a difference in a coefficient of thermal expansion from the following conductive component.

The above-mentioned "heating resistor" usually contains a conductive component and an insulating component. The conductive components are W, Ta, N
b, at least one of silicide, carbide or nitride of at least one element selected from Ti, Mo, Zr, Hf, V, Cr and the like, and the insulating component is a silicon nitride sintered body or the like. is there. In particular, when silicon nitride is contained in the insulating component and / or the component forming the insulator, it is preferable to use at least one of tungsten carbide, molybdenum silicide, titanium nitride, and tungsten silicide 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 has a melting point of the operating temperature of the ceramic heater (1400 ° C. or higher, more preferably 1 ° C. or higher).
(500 ° C. or more). Further, the amount ratio of the conductive component to the insulating component contained in the heating resistor is not particularly limited, but when the heating resistor is 100% by volume, the conductive component is preferably 15 to 40% by volume, More preferably, the content is 20 to 30% by volume.

The above-mentioned "lead wire" is for applying a voltage to the heating resistor, and is usually connected to one end of the heating resistor.
A total of two pieces are fitted together. The components constituting the lead wire are not particularly limited, but include W, Re, Ta, Mo, and N.
It is preferable that at least one of the elements selected from b is a main component. Above all, it is more preferable that W is a main component (preferably at least 90% by mass, more preferably at least 95% by mass). The wire diameter of this lead wire is 0.05 to 0.9 mm (more preferably 0.1 to 0.7 mm, and still more preferably 0.2 to 0.5 mm).
m) is preferred. Lead wire diameter is 0.05
If it is less than mm, it is difficult to stably fit the heating resistor during manufacturing. On the other hand, if the wire diameter exceeds 0.9 mm, the mechanical strength of the ceramic heater tends to decrease.

The above-mentioned "reaction layer" is a layer formed by the reaction between the components constituting the heating resistor and the components constituting the lead wire. The “fitting area” is the area of the reaction layer existing between the heating resistor and the lead wire. However, since the thickness of the reaction layer is extremely thin (about 5 μm), it is calculated as the sum of the area of one end face of the lead wire and the area of the side face of the fitting part of the lead wire.

The fitting area exceeds 0.1 mm ² and
Less than 0 mm ^2, preferably a 0.15~18mm ^2. (More preferably 0.3 to 13 mm ² , particularly preferably 0.5 to 8 mm ² ). Fitting area is 0.15m
If it is less than m ² , the electrical resistance tends to increase, and if the applied voltage is constant, it tends to be difficult to raise the temperature sufficiently. On the other hand, if the fitting area exceeds 18 mm ² , it is difficult to obtain sufficient mechanical strength. In particular, when the lead wire diameter is 0.05 to
0.9 mm and fitting area is 0.15-18 mm
² (More preferably, the lead wire diameter is 0.1 to 0.7 mm and the fitting area is 0.3 to 13 mm ² , and further preferably, the lead wire diameter is 0.2 to 0.5 mm and the fitting area is 0.5 to 8 mm.
² ) is preferable.

When the ceramic heater of the present invention is used for a glow plug, it is usually inserted through a ceramic heater protection tube (metal cylinder) for preventing breakage of the ceramic heater due to the effect of heat drawing or the like, and is connected with a silver braze or the like. It is fixed in the ceramic heater protection tube. At the time of this fixing, the temperature between the ceramic heater and the ceramic heater protection tube is kept at 800 to 1200 ° C. for 100 to 300 minutes to melt the silver brazing and the like, and then cooled in the furnace to cool to room temperature. (This fixing method is hereinafter referred to as “shrink fit”).

Therefore, it is necessary to have a mechanical strength capable of withstanding the temperature change, thermal stress, thermal expansion, cooling contraction, and the like generated at the time of shrink fitting. For this reason, when the load point according to JIS R 1601 is one point on the surface of the ceramic heater corresponding to the center of both ends of the fitting portion between one lead wire and the heating resistor, the three-point bending strength is 500 MPa or more. It is preferred that

Since each of the two lead wires has a fitting portion, there are two fitting portions in one ceramic heater. However, usually, this fitting portion has the same position perpendicular to the longitudinal direction of the ceramic heater, so that the load point can be determined to be one point. When used for applications other than the glow plug, the ceramic heater of the present invention is 5 mm.
The three-point bending strength of less than 00 MPa may be used.

Further, when the ceramic heater of the present invention is used for a glow plug, a voltage (11 to 36 V) is applied from a lead wire.
) To generate heat. However, when the fitting area between the heating resistor and the lead wire is small, a sufficient voltage cannot be applied, and it is difficult to raise the temperature to a predetermined temperature, and the maximum temperature may decrease. In addition, the rate of temperature rise may be slow, which may make it unsuitable for practical use.

Therefore, a temperature of 850 to 1100 ° C.
In order to obtain a glow plug whose temperature can be raised in 7 seconds, it is preferable that the electric resistance between different lead wires of the ceramic heater be 400 to 600 mΩ at a temperature of 23 ° C. This makes it possible to raise the temperature at the tip of the ceramic heater (one end of the internal combustion engine facing the combustion chamber) to 1200 to 1300 ° C. when a voltage of 11 V DC is applied between different lead wire terminals. When used in applications other than the glow plug, the ceramic heater of the present invention may have other electric resistance values.

Further, this ceramic heater is manufactured according to JIS.
A load point according to R 1601 is a point on the surface corresponding to the center of both ends of the fitting portion between one lead wire and the heating resistor (C in FIG. 1, and the arc-shaped dotted lines have the same length on the left and right. ) And the three-point bending strength is 500 MPa or more (further 600 MPa or more, especially 700 MPa or more,
(Typically 1500 MPa or less).

It is preferable that the ceramic heater of the present invention has both the above-mentioned temperature raising characteristics and strength characteristics. That is, the three-point bending strength at the same load point as above is 500 MPa.
11 V DC between different lead wire terminals
It is preferable that the temperature of the tip of the ceramic heater rises to 1200 to 1300 ° C. when the above voltage is applied.

In order to obtain such a ceramic heater, the contact area between the lead wire and the paste should be more than 0.1 mm ² and 20 mm It is preferable to adjust so as to be less than ² .

The above-mentioned paste contains the conductive component shown as a component constituting the heating resistor and the insulating component, and is usually 100% by mass of the whole paste.
, The conductive component and the insulating component are 75 to 9 in total.
0% by mass. This paste is, for example, wet-mixing these components in a predetermined amount as each raw material powder,
It can be obtained by drying and further mixing with a predetermined amount of a binder such as polypropylene or wax.
This paste may be in the form of pellets or the like, which are appropriately dried and formed so as to be easily handled.

The implantation may be performed in any manner.
For example, it can be performed by adjusting and fixing the length of the lead wire protruding into the mold, and injecting 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. Further, the contact area is an area where the molded body made of the paste that becomes the heating resistor when fired is in contact with the lead wire, and is in contact with the area of one end surface of the lead wire and the heating resistor. This is the sum of the area of the side surface of the lead wire and the same as the above. This area can be adjusted by the wire diameter of the lead wire and the embedded length of the lead wire.

A glow plug according to the present invention includes the ceramic heater according to the present invention. An example of the glow plug of the present invention is shown in FIG. 2 as a longitudinal sectional view. The glow plug G includes a ceramic heater 1, a ceramic heater protection tube 21 holding the ceramic heater 1, an outer tube 2 holding the ceramic heater protection tube 21, and a center shaft 3 made of a conductive rod or the like. Prepare. The lead wires 12a and 12b of the ceramic heater are connected to the lead coils 41 and 42 at lead terminal portions 121a and 121b exposed from the ceramic heater. The lead coil is composed of the ceramic heater protection tube 21 and the outer tube 2.
Connected to the outside through This glow plug is an outer tube 2
The tip portion of the ceramic heater is disposed so as to protrude into the internal combustion engine by the screw portion 22 formed in the internal combustion engine.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the ceramic heater of the present invention and a glow plug having the same will be described in more detail with reference to examples. (1) Production of ceramic heater 86 mass% of silicon nitride raw material powder, 10 mass% of erbium oxide powder (Er ₂ O ₃ ) as a sintering aid and silica powder 4
% By mass to obtain a raw material powder for an insulating component. On the other hand, tungsten carbide powder was used as a raw material powder for conductive components. This insulating component raw material powder 40% by mass and the conductive component raw material powder 6
After 0% by mass and wet mixing for 72 hours, the mixture was dried to obtain a mixed powder. Thereafter, the mixed powder and the binder were put into a kneader and kneaded for 4 hours, and the obtained kneaded product was formed into a pellet.

Thereafter, the obtained pellet-shaped kneaded material is put into an injection molding machine, and the kneaded material is injection-injected into a mold having a U-shaped concave portion to which two tungsten lead wires are fixed, respectively. Was obtained as a U-shaped heat generating resistor fitted at both ends. By adjusting the wire diameter of the lead wire and the length of the lead wire fixed to the mold and projecting into the mold, eight types of molded bodies having different contact areas were obtained.

On the other hand, 84% by mass of silicon nitride raw material powder
10% by mass of erbium oxide powder (Er
₂ O ₃ ), 4% by mass of silica powder and 2% by mass of molybdenum disilicide powder were blended and wet-mixed for 40 hours and granulated by a spray drier method. The granulated product was compacted to prepare two half molds in which a molded body serving as a heat generating resistor would fit. Next, the compact was placed between two half molds, pressed, and then pressed together with a pressure of 7 MPa to obtain an unfired ceramic heater. Thereafter, the unsintered ceramic heater was calcined at 600 ° C. to remove the binder to obtain a calcined body. Then, the calcined body was set on a pressing die made of graphite, and heated at 1800 ° C. under a nitrogen atmosphere. Table 1. Hot press firing for 1.5 hours
Eight different types of ceramic heaters having the lead wire diameter, the fitting length (A in FIG. 1), the distance from the lead wire tip to the ceramic heater tip (D in FIG. 1), and the fitting area are obtained.

[0026]

[Table 1]

(2) Evaluation of Ceramic Heater 1.3 Measurement of Three-Point Bending Strength The mechanical strength was evaluated based on the three-point bending strength. Ten ceramic heaters of eight types obtained in (1) are taken out, and according to JIS R 1601, C shown in FIG. 1 (surface corresponding to the center position at both ends of the fitting portion between one lead wire and the heating resistor) The three points of bending strength were measured three times at a crosshead speed of 0.5 mm / min, and the average value of the three points of bending strength was calculated and also shown in Table 1.

(3) Measurement of Electric Resistance and Tip Temperature The electric resistance between the lead terminal portions 121a and 121b was measured three times at a temperature of 23 ° C. using a resistance meter. Further, a voltage of DC 11 V was applied between the same lead terminal portions, and the tip temperature of the ceramic heater was measured. Table 1 also shows the results.

FIG. 3 is a graph of the results in Table 1. From FIG. 3, the three-point bending strength is 50 when the fitting area is 6.2 mm ² or less.
It can be seen that a ceramic heater having a pressure of 0 MPa or more can be obtained, and further, when the fitting area is 0.8 to ⁵ mm ² , the tip temperature can be 1250 to 1300 ° C. Therefore, it is understood that the fitting area is preferably set to 1.4 to 5.0 mm ^{2 in} order to obtain a ceramic heater having both of the above two characteristics.

(4) Production of Glow Plug A rod 31 made of low carbon steel was coaxially fitted and held in a metal inner tube 32, and one end of the inner tube was closed with a rubber stopper. Thereafter, magnesia powder was filled between the rod and the inner tube as the filler powder 33, and the magnesia powder was compacted by swaging the inner tube from the outside in the radial direction.
Thereafter, the rubber stopper was removed to obtain the center shaft 3.

On the other hand, the ceramic heater 1 obtained in (1) is attached so as to pass through a predetermined position of the silver heater.
Next, the wire was inserted into the ceramic heater protection tube 21 so as to cover the wound silver solder. Then, at a temperature of 1000 ° C
For 120 minutes, then cooled, brazed and fixed so that the ceramic heater protruded from the lower end of the ceramic heater protection tube using shrinkage of the ceramic heater protection tube (shrink fit).

Thereafter, the lead coil 41 was fitted into a ceramic heater and brazed so as to be electrically connected to the lead wire 12a. Next, the lead coil 42 was fitted into a ceramic heater and brazed so as to be electrically connected to the lead wire 12b. Then, lead coil 4
One end of the center shaft 3 obtained above was fitted to the side not connected to the ceramic heater 2 and welded to obtain an assembly.

Further, an outer tube 2 having a screw portion 22 for screwing the cylinder head and a tool engaging portion 23 for engaging a tool for screwing is prepared. The assembly obtained by electrically connecting the central shaft and the ceramic heater obtained earlier to this outer tube 2 is inserted and coaxially held, and the upper end of the ceramic heater protection tube and the lower end of the outer tube are connected. It was brazed and crimped from the outside to fix the center shaft in the outer tube. Thereafter, glass powder was filled from the upper end of the outer tube, melted and solidified, and sealed with glass. Next, a nut 7 was attached from the upper end of the bar 11 via the insulating pad 6 to obtain a glow plug G.

(5) Evaluation of breakage in shrink fitting process The glow plug made of the eight types of ceramic heaters obtained in (4) is disassembled, the ceramic heater and the ceramic heater protection tube are removed, and the ceramic heater is visually observed. Was confirmed to be broken. As a result, the broken ratio is shown in Table 2.

[0035]

[Table 2]

(6) Evaluation by Cooling / Heat Cycle Endurance Test Of the glow plugs obtained in (4), three of each type were taken out, and the temperature at the tip of the ceramic heater was 140
A cycle of energizing for 1 minute so as to reach 0 ° C. and then cutting off for 1 minute was repeated 5000 times. as a result,
Glow plugs with broken lead wires are indicated by "x", and glow plugs without disconnection are indicated by "O" in Table 2.

From the results shown in Tables 1 and 2, the fitting area is 20
It can be seen that if it exceeds mm ² , the shrink-fitting breakage rate, which is considered to be caused by a decrease in strength at the fitting portion, increases, and the durability in the thermal cycle durability test tends to decrease. On the other hand, when the fitting area is less than 0.1 mm ² , the electric resistance increases, and the electric power required to raise the temperature to a certain temperature increases. It can be seen that the temperature rise of the lead wire of the fitting portion and the like at the time of the thermal cycle durability test increases and the durability tends to decrease.

[0038]

According to the present invention, it is possible to obtain a ceramic heater which is particularly excellent in balance between mechanical strength and temperature raising performance. In addition, a glow plug including the above ceramic heater can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a ceramic heater of the present invention.

FIG. 2 is a cross-sectional view of an example of the glow plug of the present invention.

FIG. 3 is a graph showing a correlation between a fitting area of the ceramic heater of the present embodiment, a three-point bending strength, and a tip temperature when the ceramic heater is energized.

[Explanation of symbols]

1; ceramic heater, 11; heating resistor, 12a, 1
2b: Lead wire, 121a, 121b; Lead wire terminal portion, 13: Insulator, A: Fitting portion, C: Outer peripheral position corresponding to the center of both ends of the fitting portion of the lead wire, D: Ceramic from the tip of the lead wire Distance to the tip of the heater, G; glow plug, 2; outer tube, 21; ceramic heater protection tube, 22;
Screw portion, 23; tool engaging portion, 3; center shaft, 31; bar, 3
2; inner tube, 33; filler powder, 41, 42; lead coil, 5; glass seal, 6; insulating pad, 7;

Claims (2)

[Claims] 1. An insulator comprising: an insulator; and a conductor buried in the insulator, wherein the conductor is fitted to the heating resistor at one end via a reaction layer, and the other end is connected to the heating resistor. in the ceramic heater and a pair of leads part is exposed from the insulator, characterized in that the engagement area between the heat generating resistor and the the lead wire exceeds 0.1 mm ^2, less than 20 mm ² Ceramic heater. 2. A glow plug comprising the ceramic heater according to claim 1.