JPH07190361A - Self-control type glow plug - Google Patents

Abstract

PURPOSE:To prevent an over-heating of a heat generating member and improve a uniform heating characteristic and a rapid heating characteristic of the heat generating member. CONSTITUTION:A metallic heat generating wire 19 made of tungsten or tungsten alloy is enclosed within a sheath-like outer shell 18 made of minute silicon nitride together with a filling material 23 made of ceramic material including at least one of silicon, titanium, oxygen and nitrogen. A coil-like resistor 20 and a coil-like heat generating part 24 are formed while a certain space being left at the metallic heat generating wire 19. Then, a sleeve 21 made of non- organic compound such as alumina is externally inserted into the coil-like resistor part 20. The coil-like heat generating part 24 is arranged to be contacted with an inner circumferential surface of an extremity end 18c of the outer shell 18.

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 assisting ignition of fuel in a diesel engine using a liquid fuel, a combustor, etc., and more particularly to a self-regulating glow plug using a ceramic material.

[0002]

2. Description of the Related Art A sheath made of a material having a positive resistance temperature coefficient larger than that of a metal heating wire is used as a power control element for self-controlling the electric power supplied to the heating portion in order to prevent overheating of the heating portion of the metal heating wire. It has been proposed that a mold resistor is connected in series with a metal heating wire and then disposed inside the heating element.

In the above-mentioned self-regulating glow plug, a material having a different resistance temperature coefficient, that is, a material having a small resistance temperature coefficient for the metal heating wire and a material having a large resistance temperature coefficient for the resistor are used in combination by the hot press manufacturing method. The metal heating wire is embedded in a monolithic ceramic material. However, in the above hot press manufacturing method, since the shape of the metal heating wire is limited to a two-dimensional shape, the heating element cannot be said to have sufficient rapid heating, and there is a problem in that the outer surface temperature varies. Remain.

[0004]

In view of the above problems, the object of the present invention is to self-control the electric power supplied to a heating element using a ceramic material in accordance with the temperature of a metal heating wire, and to overheat the heating element ( It is intended to provide a self-regulating glow plug which prevents an excessive temperature rise) and enhances uniform heating property and rapid heating property of a heating element.

[0005]

In order to achieve the above object, the structure of the present invention is such that a metal heating wire made of tungsten or a tungsten alloy is provided inside a sheath-like outer shell made of dense silicon nitride. Encapsulating with a filler made of material, forming a coil-shaped heat generating portion and a coil-shaped resistance portion at intervals in the metal heating wire, and extrapolating a sleeve made of an inorganic compound to the coil-shaped resistance portion, The filler contains at least one element selected from the group consisting of silicon, titanium, oxygen and nitrogen.

[0006]

According to the present invention, the metal heating wire is inserted such that the coil-shaped heating portion is inscribed in the inner peripheral surface of the sheath-like outer shell made of ceramics, and the metal heating wire is provided in the inner space of the outer shell separately. A filler made of ceramic material is inserted. As a result, the heating element has a double structure in which the metal heating wire is sandwiched between the outer shell and the filler. In the metal heating wire, the coil-shaped heating portion is in direct contact with the inner peripheral surface of the outer shell to improve the rapid heating property of the heating element.

The sleeve made of an inorganic compound extrapolated to the coil-shaped resistance portion of the metal heating wire enhances the degree of heat shielding between the outer shell and the resistance portion, suppresses wasteful consumption of electric power, and improves the speed of the heating portion. It improves the heat resistance and stabilizes the temperature resistance characteristic of the resistance part. The coil-shaped resistance portion of the metal heating wire self-controls the electric power supplied to the heating portion due to the increase in the resistance value accompanying the temperature rise, and prevents the heating portion from overheating.

[0008]

1 is a front sectional view of a self-regulating glow plug according to the present invention. The self-regulating glow plug according to the present invention has a heating element 22, a metal heating wire 19 between an outer shell 18 made of dense silicon nitride (SiN) as a ceramic and a filler 23 made of another ceramic. Arranged and configured. Outer shell 1 with a closed bottom or tip
8 is fitted in the metal protection tube 17, and the fitting portion 17a is integrally joined by, for example, a metallizing method. Although not shown, the metal protection tube 17 is fitted to a metal body screwed to the wall of the combustion chamber and is joined by brazing or the like.

The pre-sintered outer shell 18 has therein a metal heating wire 19 made of tungsten, a tungsten alloy, or the like.
Is inserted. Tungsten or a tungsten alloy is used for the metal heating wire 19 in terms of the temperature coefficient of resistance, the specific resistance, the coefficient of thermal expansion, and the heat resistance. The metal heating wire 19 is formed with a coil-shaped resistance portion 20 and a coil-shaped heating portion 24 with a predetermined interval.

More specifically, the lead portion 19a on one end side of the metal heating wire 19 is arranged at the axial center of the outer shell 18 and is a portion located inside the metal protection tube 17 on the way and wound in a spiral or coil shape. The resistance portion 20 is formed. The metal heating wire 19 is connected to the tip portion 1 of the outer shell 18 from the resistance portion 20 through the lead portion 18b.
The heating portion 24 is formed by winding it in a coil shape at 8c. The other end of the metal heating wire 19 is folded upward from the heating portion 24 to form a lead portion 19c. The resistance portion 20 of the metal heating wire 19 is fitted with a sleeve 21 by winding a sleeve made of an inorganic compound, for example, alumina paper, in order to enhance the heat shielding degree. That is, the sleeve 21
Is sandwiched between the outer shell 18 and the resistance portion 20 of the metal heating wire 19 to thermally shield the periphery of the resistance portion 20. In the outer shell 18, the inner diameter of the step portion 18b to the tip portion 18c is made smaller than the inner diameter of the base end portion 18a, and the coil-shaped heat generating portion 24 at the tip of the metal heating wire 19 is directly attached to the inner peripheral surface of the outer shell 18. Arranged to contact.

As the filler 23 filled in the outer shell 18, a silicon nitride / titanium nitride (SiN-TiN) -based ceramic powder that can be fired without pressurization and that is slightly expanded by firing is used. To be In this manner, the metal shell 19 filled with the metal heating wire 19 and the filler 23 made of ceramic powder is fired at a predetermined temperature (about 1400 ° C.) to solidify the filler 23 made of ceramic powder, It is integrally connected to the outer shell 18.

The lead portion 19a of the metal heating wire 19 is connected to the metal terminal 14 connected to the center of the annular body 13 made of an insulator through the insulator 16 at the center of the metal terminal 15, and the lead portion 19c is connected to the metal protective tube. It is connected to an annular metal terminal 15 fitted in 17. The metal terminal 14 is connected to the well-known electrode rod 12, and the metal terminal 15 is connected to the metal protection tube 17.

With the above-described structure, when the coil-shaped heat generating portion 24 of the metal heat generating wire 19 is energized, the heat generating portion 24 is heated by the outer shell 1.
8 to heat the outer surface of the outer shell 18, that is, the outer surface of the heating element 22 rapidly and uniformly. On the other hand, the metal heating wire 19
The coil-shaped resistance portion 20 is thermally shielded by the sleeve 21 around the periphery thereof, suppresses wasteful consumption of electric power, assists rapid heat generation of the heat generating portion 24, and stabilizes the temperature resistance characteristic of the resistance portion 20. When the heating portion 24 of the metal heating wire 19 reaches a predetermined temperature (900 to 1000 ° C.), the temperature of the resistance portion 20 is shielded by heat and rises above the heating portion, and the resistance value of the resistance portion 20 increases. The electric power supplied to the heat generating portion 24 is reduced by itself to suppress an excessive temperature rise of the heat generating portion 24, and the metal heating wire 19 is prevented from being burnt or the heat generating element 22 is thermally destroyed.

Since the self-regulating glow plug according to the present invention has the above-mentioned structure, its rapid heating property and self-temperature controllability, as shown by the solid line in FIG. 2, are superior to those without the conventional sleeve shown by the broken line. There is.

[0015]

As described above, according to the present invention, the coil-shaped heat generating portion of the metal heating wire is inserted so as to be inscribed in the inner peripheral surface of the sheath-shaped outer shell made of ceramic, and is made of another ceramic. Since the filling material is inserted into the inner space of the outer shell, the outer shell is directly heated by the coil-shaped heat generating portion, and a rapid and uniform temperature rise of the outer surface of the heating element can be obtained.

The coil-shaped resistance portion of the metal heating wire is externally fitted with a sleeve made of an inorganic compound, so that the surroundings are shielded from heat and wasteful consumption of electric power in the resistance portion is suppressed, thereby facilitating rapid heating of the heating portion. . Since the heat transfer from the resistance part to the outer shell is suppressed, the temperature resistance characteristic of the resistance part is stabilized, the power supplied to the coil-shaped heat generating part of the metal heating wire is stably controlled, and overheating of the heat generating part is prevented. It

[Brief description of drawings]

FIG. 1 is a front sectional view showing a main part of a self-regulating glow plug according to the present invention.

FIG. 2 is a diagram showing a rapid heating property of a self-regulating glow plug according to the present invention, as compared with a conventional one.

[Explanation of symbols]

17: Metal protective tube 18: Outer shell 19: Metal heating wire 2
0: Resistance part 21: Sleeve 22: Heating element 23: Filler 24: Heating part

Claims (3)

[Claims] 1. A metal heating wire made of tungsten or a tungsten alloy is enclosed in a sheath-like outer shell made of dense silicon nitride together with a filler made of a ceramic material, and a space is provided between the metal heating wires. A coil-shaped heat generating portion and a coil-shaped resistance portion are formed, and a sleeve made of an inorganic compound is externally inserted to the coil-shaped resistance portion, and the filler is at least one of silicon, titanium, oxygen and nitrogen. A self-regulating glow plug, characterized in that it contains two elements. 2. The self-regulating glow plug according to claim 1, wherein the coil-shaped heat generating portion of the metal heat generating wire is in contact with the inner peripheral surface of the outer shell. 3. The self-regulating glow plug according to claim 1, wherein the sleeve having the coiled resistance portion of the metal heating wire inserted therein is made of a ceramic material having a thermal conductivity of 3 W / m · K or less.