JP2835209B2 - Ceramic heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug for accelerating the start of a diesel engine, a ceramic heater used as an ignition heater for various combustion equipment and a heater for heating a heating equipment.

[0002]

2. Description of the Related Art Conventionally, nickel (Ni) -chromium (Cr) has been used in a heat-resistant insulating powder filled in a heat-resistant metal sheath as a glow plug used for accelerating the start of a diesel engine and various heaters for ignition and heating. A sheathed heater in which a heat-generating resistor made of a high-melting-point metal wire mainly composed of, for example, is embedded, and various ignition devices using high-voltage spark discharge have been used.

[0003] However, the sheathed heater is difficult to rapidly raise the temperature in a short time, and is inferior in wear resistance and durability.
The igniter and the like utilizing the spark discharge have drawbacks such as causing radio wave interference at the time of ignition and a problem in safety when not ignited.

[0004] Therefore, it is possible to rapidly raise the temperature for a short time, to prevent radio interference, to reliably ignite and to use safely and for a long time regardless of the atmosphere. As a high heater, a ceramic heater in which a heating resistor made of an inorganic conductive material is embedded in a ceramic sintered body has been widely used.

As shown in FIG. 2, for example, the ceramic heater is generally made of tungsten (W) or molybdenum (M).
o) a heating resistance wire made of a high melting point metal or a compound thereof is embedded in a base, or a heating resistor paste mainly containing the high melting point metal or a compound thereof is pattern-printed on the base and fired. The integrated ceramic heating element 19 is joined to the cylindrical fitting 20, one end of the heating resistance wire buried in the ceramic heating element 19 is electrically connected, and the tubular fitting 20 is joined to the mounting fitting 21. To form a negative electrode.

On the other hand, the other end of the heating resistance wire is connected to a terminal rod 25 via a lead wire 24 welded to a metal cap 23 attached to a rear end 22 of the ceramic heating element 19 so as to become a positive electrode. Is configured.

In this case, the ceramic heating element 19 is generally brazed to a cylindrical fitting 20 using a high melting point brazing material so as to withstand a high temperature combustion gas or a high temperature atmosphere of an engine or various kinds of combustion heating equipment. 20 is brazed to the mounting bracket 21 using a low melting point brazing material so as not to be directly exposed to the high-temperature combustion gas or high-temperature atmosphere.
-29426).

[0008]

However, regardless of whether the ceramic heater uses a high melting point brazing material or a low melting point brazing material, the ceramic heating element 19 and the cylindrical fitting 20, and the cylindrical fitting 20 and the mounting fitting are used. Since the brazing of 21 is locally heated and joined, a tensile stress acts on the ceramic heating element 19 due to a difference in thermal expansion between the cylindrical metal fitting 20 or the mounting metal 21 and the ceramic heating element 19, and the ceramic heating element 1 is heated.
There was a risk that 9 would break. In addition, even if the ceramic heating element 19 does not have a large crack at the time of joining, there is a possibility that a minute crack existing inside during use may develop and the heating resistance wire in the ceramic heating element 19 may be broken.

Further, in order to make a brazing contact, the ceramic heating element 19 and the cylindrical fitting 20, and the cylindrical fitting 20 and the mounting fitting 2
1, a gap for pouring a brazing material is required, and there is a possibility that the ceramic heating element 19 may be mounted eccentrically. And the ceramic heating element 19
There was also a problem that it was damaged.

[0010]

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 prevent the ceramic heating element from being cracked or eccentric due to the joining of the ceramic heating element with the cylindrical metal fitting and the mounting metal. A highly durable ceramic heater that can be used continuously for a long time without hitting and damaging the ceramic heating element or breaking the heating resistance wire in the ceramic heating element during use. It is in.

[0011]

According to the ceramic heater of the present invention, a cylindrical heating element having a step is joined to a ceramic heating element in which a heating resistor made of an inorganic conductive material is embedded in a silicon nitride sintered body. The stepped portion of the cylindrical fitting is brought into contact with a stepped seat provided inside the distal end of the mounting fitting via a conductive gasket, and the terminal rod inserted through an insulator having a compressive strength of 50 kg / cm ² or more is connected to the ceramic. A cylindrical metal fitting and a mounting metal, which are connected to a rear end of the heating element, crimp a rear end peripheral edge of the mounting metal with an end face of the insulator, and press a rear end of the ceramic heating element with a terminal rod, and The rear end portion of the ceramic heating element is electrically connected to the terminal rod.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a ceramic heater according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view of a main part showing an embodiment in which the ceramic heater of the present invention is applied to a glow plug used in a diesel engine. In the figure, reference numeral 1 denotes a ceramic heater forming a glow plug formed by a ceramic heating element 2 in which a heating resistor made of an inorganic conductive material is embedded in a silicon nitride sintered body.

A cylindrical fitting 3 having a stepped portion 4 is brazed to the ceramic heating element 2 so that the ceramic heating element 2
One end of the heat-generating resistance wire buried in the base is led out as an electrode terminal, and the stepped portion 4 of the cylindrical metal fitting 3 is brought into contact with a stepped seat 6 provided inside the front end of the mounting fitting 5 via a conductive gasket 7. I have. On the other hand, at the rear end 8 of the ceramic heating element 2, the opening 1
4, a terminal rod 9 having a flange 16 inserted through the insulator 10 via a conductive buffer material 15 such as a washer is inserted thereinto and connected thereto.
The cylindrical metal fitting 3 and the mounting metal fitting 5
Are joined by pressure without brazing to form a negative electrode, and the electrode extraction metal fitting 13 and the terminal rod 9 brazed to the rear end 8 of the ceramic heating element 2 are similarly joined by pressure to form a positive electrode. By fixing an insulating washer 17 such as a bakelite to the terminal rod 9 with a nut 18, the negative electrode of the mounting bracket 5 and the positive electrode of the terminal rod 9 are insulated to constitute the ceramic heater 1.

[0014] The conductive gasket 7 and the conductive buffer material 15, the resistivity in order to reduce the contact resistance 10 ^{- 2} .omega.c
For example, a copper product made of a material having a characteristic of m or less and a Brinell hardness of 100 or less is suitably used, and airtightness can be ensured by interposing such a soft conductive gasket 7.

The terminal rod 9 is inserted into the insulator 10 and the rear end 11 of the mounting bracket 5 is swaged with the end face 12 of the insulator 10 to ensure electrical insulation.

The insulator 10 through which the terminal rod 9 is inserted is made of an insulating insulator having a compressive strength of 50 kg / cm ² or more, such as an alumina insulator, so as to withstand caulking of the rear edge 11 of the mounting bracket 5. Is preferably used.

Further, by fixing between the terminal rod 9 and the insulator 10 with an adhesive, for example, an anaerobic adhesive, the fixing can be further strengthened.

In the ceramic heater of the present invention,
Examples of the heating resistor made of an inorganic conductive material include tungsten carbide (W) in addition to high melting point metals such as tungsten (W), molybdenum (Mo), and rhenium (Re).
C), Group 4a, Group 5a, Group 6a carbides or nitrides such as titanium nitride (TiN), molybdenum silicide (MoSi ₂ ), and zirconium boride (ZrB ₂ ) are also preferably used.

With respect to the ceramic heater assembled by pressure bonding under the above conditions, the ceramic heater is fastened to a jig by clamping an O-ring, and a gas pressure of 15 kg / cm ² is applied from the ceramic heating element side to leak. Gas leakage was measured with a tester, and there was no abnormality in the airtightness. The mounting strength of the ceramic heater was fixed and the tightening torque strength was measured. However, even at a torque strength of 3.0 kg · m, no abnormality was found in the joint. Did not. Further, in the X-ray fluoroscopic inspection, no crack was observed in the ceramic heating element, and it was confirmed that the eccentricity of the ceramic heating element with the mounting bracket was extremely small. Further, a temperature characteristic test was performed by applying a voltage of 11 V so that the temperature after 3.5 seconds became 800 ° C., and it was confirmed that the heating rate was equivalent to that of a conventional ceramic heater.

[0020]

As described above, in the ceramic heater according to the present invention, the ceramic heating element joined to the cylindrical fitting is brought into contact with the step portion of the cylindrical fitting via the conductive gasket at the step of the mounting fitting, and the ceramic heater is connected to the ceramic heater. A terminal rod inserted into the insulator is connected to the rear end of the heating element, and the rear edge of the mounting bracket is crimped on the end surface of the insulator, and the cylindrical fitting and the mounting bracket are pressure-bonded without brazing. In addition to the negative electrode, the rear end of the ceramic heating element and the terminal rod were similarly pressed and joined to form a positive electrode.
Extremely few cracks in the ceramic heating element and eccentricity after assembling processing, no damage to the ceramic heating element due to one side of the insertion hole at the time of installation, and finishing of the mounting bracket tip that will be the seat surface when mounting to equipment The work process is greatly simplified, the work efficiency is greatly improved, and the production cost can be significantly reduced. As a result, it is possible to provide an inexpensive ceramic heater which has sufficient airtightness and has excellent durability and can be used continuously for a long time.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part showing an embodiment in which a ceramic heater of the present invention is applied to a glow plug used in a diesel engine.

FIG. 2 is a sectional view showing a main part when a conventional ceramic heater is applied to a glow plug used in a diesel engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic heater 2 Ceramic heating element 3 Cylindrical fitting 4 Step part 5 Mounting bracket 6 Step seat 7 Conductive gasket 8 Rear end part 9 Terminal rod 10 Insulator 11 Rear end peripheral edge 12 End face

Claims (1)

(57) [Claims] 1. A cylindrical metal fitting having a stepped portion is joined 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 the stepped portion of the cylindrical metal fitting is attached to a mounting metal. A terminal bar inserted into an insulator having a compressive strength of 50 kg / cm ² or more is connected to a rear end of the ceramic heating element while being in contact with a step seat provided on the inner side of the front end through a conductive gasket. By pressing the rear end of the metal fitting with the end face of the insulator and pressing the rear end of the ceramic heating element with the terminal rod, the cylindrical metal fitting and the mounting metal, and the rear end and the terminal rod of the ceramic heating element are pressed. And a ceramic heater electrically connected to each other.