JPH06168773A - Ceramic heater - Google Patents

Abstract

PURPOSE:To provide a ceramic heater of high durability capable of continuous operation over a long time at high temperature by electrically connecting and fixing a ceramic heating body to a terminal rod with edges faced to each other via an electrode takeout fitting. CONSTITUTION:When a ceramic heater 1 is used as an assist heater for an internal combustion engine, a cylindrical fitting 5 is first coupled to a ceramic heating body 4 having an exothermic resistor 3 of inorganic conductive material buried in a sintered body 2 of silicon nitride. An electrode takeout fitting 6 is thus connected and fastened, and the heating body 4 is electrically connected and fixed to a terminal rod 8 with edges faced to each other via the fitting 6. Or, constitution is so made that at least the cross sectional area of the heat generation section of the heating body 4 exposed from a fitting 5 is made larger than the minimum cross sectional area of the coupling hole of the fitting 5. As a result, the heating body 4 can be protected against a break due to a travel in an axial direction, regardless of long-time continuos operation at high temperature, thereby enhancing durability and reliability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high temperature ceramic used for a glow plug for starting assistance of a diesel engine, an assist heater for various internal combustion engines using a fuel containing alcohol and an ignition heater for various combustion equipment. It is about heaters.

[0002]

2. Description of the Related Art Conventionally, as a glow plug and various heaters for ignition and heating used for accelerating the starting of a diesel engine, a heat resistant insulating powder is filled in a sheath made of a heat resistant metal, and nickel (Ni) is contained in the heat resistant insulating powder. ) -Chromium (Cr) or the like, a sheathed heater in which a heating resistor made of a high melting point metal wire is embedded, and various ignition devices utilizing high-voltage spark discharge have been used.

However, since the sheathed heater transfers the heat of the heat-generating resistor through the heat-resistant insulating powder filled in the sheath made of heat-resistant metal, it is difficult to rapidly raise the temperature in a short time and, in addition, it has abrasion resistance. In addition to the problem of poor durability, various ignition devices using the spark discharge also cause radio interference such as noise at the time of ignition, lack of reliability from the viewpoint of reliable ignition, in the case of unignition There were drawbacks such as safety issues.

Therefore, the temperature can be rapidly raised in a short time, no radio wave interference occurs, and the ignition is surely performed to ensure safety, and it can be used for a long time regardless of the atmosphere, and is wear-resistant. As a highly reliable and highly reliable heating element, a ceramic heating element in which a heating resistor made of an inorganic conductive material is embedded in a ceramic sintered body has been widely used.

Above all, a silicon nitride sintered body having a heat shock resistance and a high temperature strength remarkably superior to those of other ceramics is used as a substrate of a heater, and in general, tungsten (W) is used.
A heating resistor made of a high melting point metal such as molybdenum (Mo) or a compound thereof is embedded in a substrate, or a heating resistor paste mainly containing the high melting point metal or a compound thereof is pattern-printed on the substrate. The one obtained by firing and integrating is widely used as a heater at about 1000 ° C., such as a glow plug of an internal combustion engine (see JP-A-1-313362).

[0006]

However, the ceramic heating element based on the above-mentioned silicon nitride sintered body is the one shown in FIG.
As compared with a metal member such as a cylindrical metal fitting 26 for connecting and fixing one electrode 25 of the ceramic heating element 24 as shown in FIG. There was a problem of disconnection of the ceramic heater 27 due to the above.

That is, due to the heat conduction from the heat generating portion 28 which is energized by the ceramic heat generating element 24 and becomes red, for example, the cylindrical metal fitting 26 has the ceramic heat generating element 2 as shown by the arrow in FIG.
When the liquid fuel such as petroleum or light oil at a temperature close to room temperature is sprayed on the ceramic heater 27 in such a heated state, the tubular metal fitting is expanded in the radial direction and the axial direction. Reference numeral 26 is a heating portion 28 of the ceramic heating element 24.
Since it is cooled from the side, as shown by the arrow in FIG. 9, the tubular metal member 26 first contracts radially at the tip end to compress and hold the ceramic heating element 24, and subsequently in the axial direction opposite to the direction during heating. It will contract.

Above all, as an ignition source, 1100 to 150
In the assist heaters of various internal combustion engines that use a fuel containing alcohol such as methanol that requires a high temperature of 0 ° C, the expansion and contraction described above become remarkable, and continuous operation was performed for a long time under such circumstances. In this case, the ceramic heating element 24 gradually moves in the tubular metal fitting 26 in the axial direction shown by the arrow in FIG. 10, and eventually one electrode 25 of the ceramic heating element 24 comes out of the tubular metal fitting 26, and The connection between the electrode 25 of the heating element 24 and the tubular metal fitting 26 is broken, and the ceramic heater 27 is broken.

[0009]

SUMMARY OF THE INVENTION The present invention has been developed in view of the above-mentioned drawbacks, and an object of the present invention is to provide a ceramic heater which is capable of continuous operation at a high temperature for a long time and is excellent in durability.

[0010]

In the ceramic heater of the present invention, a cylindrical metal fitting is fitted to a ceramic heating element in which a heating resistor made of an inorganic conductive material is embedded in a silicon nitride sintered body, and an electrode is taken out. In the ceramic heater in which the metal fitting is connected and fixed, and the metal fitting for mounting the ceramic heater to the main body and the tubular metal fitting, and the terminal rod forming one electrode and the electrode lead-out metal fitting are electrically connected, The end faces of the terminal rod are butted and electrically connected and fixed by the metal fittings for taking out the electrodes, and the ceramic heating element and the terminal rod are connected, or at least the ceramic heating element on the heating portion side exposed from the tubular metallic member is disconnected. The area is a shape larger than the minimum cross-sectional area of the fitting hole of the tubular metal fitting.

[0011]

In the ceramic heater of the present invention, the end faces of the ceramic heating element and the terminal rod are butted against each other and electrically connected and fixed by the electrode lead-out metal fittings, and the ceramic heating element and the terminal rod are connected, or at least a cylinder. Since the cross-sectional area of the ceramic heating element on the heating part side exposed from the metal fitting is larger than the minimum cross-sectional area of the fitting hole of the tubular fitting, the ceramic heating element moves axially inside the tubular fitting. It acts to prevent you from doing so.

[0012]

The ceramic heater of the present invention will be described in detail below with reference to the drawings. 1 to 3 are partially broken ceramic heaters applied to an assist heater used in an internal combustion engine that uses alcohol as a fuel and a glow plug used to assist starting of a diesel engine according to an embodiment of the present invention. FIG. 2 shows a sectional view, and FIG. 2 shows a partially broken sectional view in which an essential part of the assist heater of FIG. 1 is enlarged.

In FIGS. 1 and 2, reference numeral 1 is a ceramic heating element 4 in which a heating resistor 3 is embedded in a silicon nitride sintered body 2.
Then, the tubular metal fitting 5 and the electrode lead-out metal fitting 6 are connected and fixed, and the tubular metal fitting 5 and the attachment metal fitting 7, and the end faces 9, 10 of the ceramic heating element 4 and the terminal rod 8 are abutted to each other and the electrode lead-out metal fitting 6 is used for electrical connection. It is a ceramic heater that is fixedly connected.

A cylindrical metal fitting 5 having a step portion 15 is externally fitted to the ceramic heating element 4, and the lead wire 1 of the heating resistor 3 is fitted.
6 is led out as one electrode terminal by brazing so as to be connected to 6, and the tubular fitting 5 and the fitting 7 are brought into contact with each other via the conductive gasket 17 to electrically connect and fix them.

At the rear end of the ceramic heating element 4,
An electrode lead-out metal fitting 6 connected to the other lead wire 18 of the heating resistor 3 brazed together with the tubular metal fitting 5 is fixed, and one end of the electrode lead-out metal fitting 6 connects the ceramic heating element 4 and the end faces 9, 10 to each other. It is electrically connected and fixed to the abutted terminal rod 8 by spot welding or the like.

Next, the insulator 19 is inserted through the terminal rod 8,
The rear end peripheral edge of the mounting member 7 is caulked and fixed to the end surface of the insulator 19, and the tubular member 5 and the mounting member 7 are pressure-connected to each other without brazing to form a negative electrode. The terminal rod 8 in which the end faces 9 and 10 are butted against each other is used as a positive electrode,
By fixing the insulating washer 20 such as bakelite to the terminal rod 8 with the nut 21, the negative electrode of the mounting bracket 7 and
The positive electrode of the terminal rod 8 is insulated from the ceramic heater 1
Is configured.

It should be noted that, at a portion where the end surface 9 of the ceramic heating element 4 and the end surface 10 of the terminal rod 8 are abutted with each other, a maximum of 5 mm is provided as long as the connection between the electrode 22 and the tubular metal fitting 5 is not broken.
There may be some gap.

In addition, FIG. 3A shows a ceramic heating element 4 in which a heating resistor is embedded in a silicon nitride sintered body, a cylindrical metal fitting 5 and an electrode lead-out metal fitting 6, and a cylindrical metal fitting 5 and a mounting metal fitting 7.
Is fixed by brazing, the electrode take-out fitting 6 and the terminal rod 8 are connected via the connecting wire 23, and the tubular fitting 5
The side surface of the ceramic heating element 4 is ground so that the cross-sectional area 12 of the ceramic heating element 4 on the side of the heating portion 11 exposed from is larger than the minimum cross-sectional area 14 of the fitting hole 13 of the tubular fitting 5. It is a ceramic heater electrically connected and fixed to the metal fitting 5.

The ceramic heating element 4 of FIG. 3 is the ceramic heating element 4 on the side of the heating portion 11 exposed from the ground side surface.
And are connected by a curved surface, and the radius of curvature is 0.1 mm
In the following, stress may be concentrated on the ceramic heating element 4, and if it is more than that, it is possible to provide a radius of curvature within a range in which the electrode 22 does not come off from the tubular metal fitting 5 due to the movement of the ceramic heating element 4. The range of 0.2 to 0.5 mm is preferable.

Further, in the ceramic heating element of the present invention, the heating resistor made of an inorganic conductive material may be a refractory metal such as tungsten (W), molybdenum (Mo), rhenium (Re), or tungsten carbide (W).
C), titanium nitride (TiN), molybdenum silicide (MoSi ₂ ), zirconium boride (ZrB ₂ ), etc. 4a, 5a, 6a carbide or nitride wire or thin layer What was formed is used suitably.

Further, for connecting the respective parts constituting the negative electrode and the positive electrode, any known method such as pressure joining, brazing, welding or the like may be used.

In evaluating the ceramic heater of the present invention, first, a rod-shaped silicon nitride material is formed by a press molding method using a granulated body made of a mixture of raw material powders containing silicon nitride (Si ₃ N ₄ ) as a main component. A molded body is produced.

Next, a heating resistor composed of a substantially U-shaped coiled tungsten wire and a tungsten wire forming a lead wire portion connected to the coiled tungsten wire is placed on the molded body, Another silicon nitride compact having the same shape as described above was stacked so as to sandwich the heating resistor and pressure-fired.

After the side surface of the thus obtained sintered body is polished to expose a part of the lead wire and a metal coating film of nickel (Ni) or the like is formed on at least the exposed portion by a metallizing method or a plating method. , Fit the tubular metal fittings outside, and join them with silver solder in a reducing gas atmosphere.

On the other hand, the lead wire exposed at the end of the sintered body is similarly joined to the lead-out metal fitting made of a wire material or a cap-shaped metal fitting with silver solder, and then inserted into the tip of the mounting fitting. Each member constituting the positive and negative electrodes by abutting and connecting the respective end surfaces of the ceramic heating element and the terminal rod through the attachment metallic member, the tubular metallic member, and an electrode extraction metallic member brazed to the rear end of the ceramic heating element. Pressure bonding or
Alternatively, the electrode lead-out metal fitting and the terminal rod were connected via a connecting wire, and the respective members constituting the positive and negative electrodes were brazed to produce a ceramic heater for evaluation.

Using the ceramic heater for evaluation, a high load endurance test was carried out for 10000 cycles, which consisted of a step of rapidly heating to a temperature of 1400 ° C., then stopping energization and blowing compressed air to force cooling. However, in all cases, one of the electrodes of the ceramic heating element did not come out from the tubular metal fitting, or the electrode of the ceramic heating element and the tubular metal fitting were disconnected, and the ceramic heater did not break. No damage to the heating element was observed.

Further, FIGS. 4 and 6 show a portion where the tubular metal fitting 5 is connected and fixed to the ceramic heating element 4, and the shape of the fitting hole 13 of the ceramic heating element 4 and the tubular metal fitting 5 is at least partially. FIG. 7 is a partially broken cross-sectional view of a main part showing another embodiment in which the cross-sectional area 12 is gradually reduced from the heat generating portion 11 side to form a minimum cross-sectional area 14 in a similar shape.

On the other hand, in FIG. 5, only a part of the ceramic heating element 4 exposed from the tubular fitting 5 is fitted into the fitting hole 13 of the tubular fitting 5.
FIG. 7 is a partially broken cross-sectional view of a main part showing another embodiment configured to have a cross-sectional area 12 larger than the minimum cross-sectional area 14 of
Any of the ceramic heaters can effectively prevent the ceramic heating element 4 from moving in the tubular metal fitting 5 in the axial direction as in the above-described embodiments.

[0029]

As described above, according to the ceramic heater of the present invention, the cylindrical metal fitting is fitted to the ceramic heating element in which the heating resistor made of the inorganic conductive material is embedded in the silicon nitride sintered body, and the electrode Connect and fix the take-out metal fitting, butt the end faces of the ceramic heating element and the terminal rod, and electrically connect and fix the electrode heating metal fitting to connect the ceramic heating element and the terminal rod, or at least the heating part side exposed from the tubular metallic fitting. Since the cross-sectional area of the ceramic heating element is configured to be larger than the minimum cross-sectional area of the fitting hole of the tubular metal fitting, the ceramic heating element can be operated even if it is continuously operated at high temperature for a long time. It is possible to provide a ceramic heater having excellent durability and reliability, which never moves in the tubular metal member in the direction and is not broken.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view in which a ceramic heater of the present invention is applied to an assist heater used in an internal combustion engine that uses alcohol as a fuel.

FIG. 2 is a partially broken cross-sectional view showing an enlarged main part of the assist heater shown in FIG.

FIG. 3 is a partially broken cross-sectional view showing a main part in which the ceramic heater of the present invention is applied to a glow plug used for starting assistance of a diesel engine.

FIG. 4 is a partially broken cross-sectional view showing a main part which is another embodiment of the ceramic heater of the present invention.

FIG. 5 is a partial cross-sectional view showing a main part of another embodiment of the ceramic heater of the present invention.

FIG. 6 is a partial cross-sectional view showing a main part of another embodiment of the ceramic heater of the present invention.

FIG. 7 is a partially broken cross-sectional view showing a main part in which a conventional ceramic heater is applied to a glow plug used in a diesel engine.

FIG. 8 is a partial cross-sectional view showing a main part for explaining the behavior of a conventional ceramic heater during heating.

FIG. 9 is a partial cross-sectional view showing a main part for explaining a behavior of a conventional ceramic heater when it is cooled.

FIG. 10 is a partial cross-sectional view showing a main part for explaining a state in which a conventional ceramic heater is broken.

[Explanation of symbols]

 1 Ceramic Heater 2 Silicon Nitride Sintered Body 3 Heating Resistor 4 Ceramic Heating Body 5 Cylindrical Metal Fitting 6 Electrode Extraction Metal Fitting 7 Mounting Hardware 8 Terminal Rod 9, 10 End Face 11 Heat Generation Part 12 Cross Section 13 Fitting Hole 14 Minimum Cross Section

Claims (2)

[Claims] 1. A cylindrical metal fitting and an electrode lead-out metal fitting are connected and fixed to a ceramic heating element in which a heating resistor made of an inorganic conductive material is embedded in a silicon nitride sintered body.
Also, in the ceramic heater in which the electrode lead-out metal fitting and the terminal rod are electrically connected, the ceramic heat-generating body and the terminal rod are connected to each other by abutting the respective end faces of the ceramic heat-generating body and the terminal rod and fixing them by the electrode lead-out metal fitting. Characteristic ceramic heater. 2. A tubular metal fitting and an electrode fitting are connected and fixed to a ceramic heating element in which a heating resistor made of an inorganic conductive material is embedded in a silicon nitride sintered material,
Also, in the ceramic heater in which the electrode lead-out metal fitting and the terminal rod are electrically connected, at least the cross-sectional area of the ceramic heating element on the heat generating portion side exposed from the tubular metal fitting is larger than the minimum cross-sectional area of the fitting hole of the tubular metal fitting. Ceramic heater characterized by