JPH07217884A - Self-controlled type ceramic glow plug - Google Patents

Abstract

PURPOSE:To perform an effective control of a supplying electrical power for a heat generating part and to prevent the heat generating part from being over-heated by a method wherein the heat generating part and a resistor part of the electrical heat generating wire are made of a common material and a peripheral structure at each of the sides is provided with a required characteristic. CONSTITUTION:A cylindrical outer shell 31 and inner shells 32, 34 are made of ceramics having different heat transfer rates. A coil-like heat generating part 24 of the electrical heating wire is buried to be contacted with the inner surface of the extremity end of the outer shell 31, and a coil-like resistor part 22 connected in series with the heat generating part 24 is not contacted with the inner surface at the base end of the outer shell 31. The inner shell 34 enclosing the resistor part 22 is made of ceramics having a low heat transfer rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic glow plug which aids ignition by vaporizing liquid fuel in an internal combustion engine or the like.
In particular, the heat of the heating part of the heating wire is effectively transferred to the outer surface of the ceramic heating element, and the resistance part of the heating wire is adiabatically heated to increase the resistance value, which is related to the temperature of the heating element. The present invention relates to a self-controlled ceramic glow plug in which the power supplied to the heat generating part is controlled.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Laid-Open No. 1-318810, a conventional glow plug has a cylindrical metal body having an upper end portion to which an electrode rod is connected and a lower end portion to which a sheath-like metal sheath is connected. Then, insert a coil-shaped heating wire inside the metal sheath, and then fill the metal sheath with powder with high heat resistance and high thermal conductivity such as magnesium oxide, and seal it. , And the other end is connected to a metal sheath, respectively.

In recent years, in order to obtain a quicker temperature rise of the heating element, a ceramic molded body having a heating wire embedded therein has been put into practical use. That is, as shown in FIGS. 4 and 5, the ceramic heating element 51 is made of silicon nitride (Si ₃ N ₄ ).
A heating wire 53 curved in a corrugated shape is sandwiched between a pair of elongated preformed bodies 51a, 51b having a crescent-shaped cross section formed by, for example, and sintered integrally while pressurizing by a hot press method. One terminal wire 53a of the heating wire 53 is connected to the electrode rod, and the other terminal wire 53b is connected to the tubular metal body.

In the above ceramic glow plug, the heating wire 51 is made of the ceramic material, so that the heating wire 53 is formed.
The heat transfer efficiency from the ceramic heating element 51 to the outer surface 54 of the ceramic heating element 51 is improved. However, as shown by the arrows in FIG. 5, the distance between the heating wire 53 and each part of the outer surface of the ceramic heating element 51 is not uniform. Is not uniform, and variations occur.

Further, the conventional ceramic glow plug is
In order to prevent overheating of the ceramic heating element, a sheath-type resistor made of a material with a positive temperature coefficient of resistance larger than that of the heating wire is connected in series inside the metal body to the heating wire. The power supplied to the heating wire is controlled in relation to the temperature. That is, a material with a small resistance temperature coefficient is used for the heating wire, and a material with a large resistance temperature coefficient is used for the resistor as the energization control element.The resistance of the heating wire is large at room temperature and the resistance of the resistor is large at high temperature. Is designed to be.

From the above points of view, it is desired that the heating wire has a resistance temperature coefficient as small as possible. On the other hand, the heating wire has a high melting point and thermal expansion due to the thermal stress generated during energization and the surrounding structure. A material having a low rate (a material close to a ceramic substrate forming a sheath) is required, and materials satisfying both conditions are limited to materials such as tungsten.

[0007]

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to use a common material for the heat generating portion and the resistance portion of the current-carrying body or heating wire, and to provide the characteristics required for the respective surrounding structures. The purpose of the present invention is to provide a self-control type ceramic glow plug that effectively controls the electric power supplied to the heat generating part and prevents overheating of the heat generating part.

[0008]

In order to achieve the above object, the structure of the present invention comprises a ceramic outer shell having a cylindrical outer shell and an inner shell filled in the outer shell, and a coil of a heating wire. Self-controlled ceramics that are embedded so that the heating element in the shape of a coil contacts the inner surface of the tip of the outer shell, and the coil-shaped resistor connected in series with the heating element does not contact the inner surface of the outer shell on the base end side. In the glow plug, the inner shell that wraps the heat generating portion and the inner shell that wraps the resistance portion are made of ceramics having different thermal conductivities.

[0009]

According to the present invention, the electric conductor and the resistor are made of a common material such as tungsten having a positive temperature coefficient of resistance. That is, a coil-shaped resistance part and a coil-shaped heat generating part are composed of a single heating wire, and self-control of the temperature of the heating part of the heating wire is achieved by balancing the amount of heat generated from the heating part with the amount of heat dissipation. This is done by increasing the temperature of the part to increase the resistance value and controlling the energizing power. Therefore, the area around the heat generating portion of the heating wire is designed to easily radiate heat, and the area around the resistance portion of the heating wire for controlling energization has a heat insulating structure.

The inner shell enclosing the heating part of the heating wire and the inner shell enclosing the resistance part are made of ceramics containing both silicon and titanium, but the inner shell enclosing the heating part has a small content of titanium. The thermal conductivity is increased, and the inner shell that encloses the resistance portion is increased in titanium content to reduce the thermal conductivity. As a result, the temperature of the resistance portion of the heating wire during energization becomes higher than the temperature of the heat generating portion, the resistance value of the resistance portion increases, and the power supplied to the heat generating portion at high temperature is limited.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a self-controlled ceramic glow plug according to the present invention has a cylindrical metal plug body 7 with an electrode rod 2 at the base end or the upper end thereof and ceramic heat generation at the tip or the lower end thereof. The bodies 30 are fitted together, and the lower ends of the electrode rods 2 are connected to the terminals of the heating wires 20 of the ceramic heating element 30 inside the metal plug body 7. The metal plug body 7 has a threaded portion 7b formed at an intermediate portion, which is fastened to a screw hole in a wall portion of a pre-combustion chamber of an engine by engaging a tool with a hexagonal head portion 7a, and a ceramic heating element 30 at a lower end. Is projected into the pre-combustion chamber. The electrode rod 2 has a threaded portion 2a at its upper end, and is fitted and inserted into an insulating cylinder 6 made of Bakelite or the like, and then fitted into an upper end portion of a metal plug body 7.
The flange 6a at the upper end of the insulating cylinder 6 is reinforced by the metal ring 5, and is superposed on the head portion 7a of the metal plug body 7, and by the nut 3 screwed to the screw portion 2a via the insulating seat plate 4. It is concluded.

The ceramic heating element 30 has a cylindrical outer shell 31 fitted to the lower end of the metal plug body 7 and joined by a metallizing method or the like. The outer shell 31 has the heating wire 20 made of tungsten or the like inserted therein, and has the inner shell 3 inside.
2,34,35 silicon nitride-titanium nitride ceramic powders are filled and sintered together.

The heating wire 20 is connected to the small diameter shaft portion 2b at the lower end of the electrode rod 2 at the upper end of the lead portion 25 passing through the axis of the ceramic heating element 30. The lower end of the lead portion 21 of the heating wire 20 is folded back upward at the tip of the outer shell 31 to form a coil-shaped heat generating portion 24. An upper end of the heat generating portion 24 is formed with a coil-shaped resistance portion 22 covered with a cylindrical heat insulating cover 33 through the lead portion 23, and an upper end of the resistance portion 22 is fitted into the metal plug body 7 through the lead portion 25. Is connected to the metal ring 15.

According to the present invention, the coil-shaped heat generating portion 24 of the heating wire 22 is fitted and inserted so as to come into contact with the inner surface of the outer shell 31,
The heat transfer property to the outer shell 31 is enhanced. The inner shell 32 that encloses the heat generating portion 24 is formed by densely filling the inside of the outer shell 31 with a silicon nitride-titanium nitride-based ceramic in order to increase the thermal conductivity, and increases the content of titanium. Preferably, the weight ratio of titanium nitride in the inner shell 32 is set to 20 to 35%. Specifically, the weight ratio of titanium nitride was set to 30%. Outer shell 31
The inner shell 35, which constitutes the base end portion of, is configured similarly to the inner shell 32.

In order to suppress heat transfer from the resistance portion 22 of the heating wire 20 to the outer shell 31, the coiled resistance portion 22 is formed in the outer shell 31.
It is inserted so as not to contact the inner surface of the. In order to improve the vibration resistance of the resistance portion 22, the resistance portion 22 is formed by winding alumina paper having heat resistance and low thermal conductivity as a heat insulating cover 33, and then fitting the alumina paper inside the outer shell 31. Resistance part 2
The inner shell 34 that encloses 2 is formed by filling silicon nitride-titanium nitride ceramics into the outer shell 31 more coarsely than in the case of the inner shell 32 in order to reduce the thermal conductivity, and is made of titanium. Reduce the content. Preferably, the weight ratio of titanium nitride in the inner shell 34 is 5 to 20%. Specifically, the weight ratio of titanium nitride was set to 10%.

The content of titanium in the silicon nitride-titanium nitride ceramics constituting the inner shells 32 and 34 is determined by adjusting the thermal conductivity and the following circumstances during sintering. Each inner shell 3
The silicon nitride-titanium nitride ceramics constituting Nos. 2 and 34 have characteristics that the higher the titanium content, the lower the thermal conductivity, and the denser the ceramics, the lower the thermal conductivity. The volume change during sintering of the silicon nitride-titanium nitride ceramic is absorbed by the expansion of titanium during nitriding and the contraction of silicon during nitriding. Therefore, if the amount of titanium is too small, the inner shells 32 and 34 will contract during sintering and will not adhere to the outer shell 31.

Since the present invention has the above-mentioned structure, even if a material having different temperature coefficient of resistance is not used for the heating portion and the resistance portion of the heating wire, as shown by the line 41 in FIG. The excellent self-control type ceramic glow plug of is obtained. Line 42 in FIG. 3 shows the temperature rise characteristics of a conventional ceramic glow plug having no energization controller designed for a saturation temperature of 1000 ° C.

In the above embodiment, the resistance portion 2 of the heating wire 20 is used.
In order to prevent heat from flowing out of the resistance portion 22 to the outer shell 31 due to the contact between the outer shell 31 and the outer shell 31, the inner diameter of the outer shell 31 on the base end side is increased.
The winding diameter of 2 may be smaller than that of the heat generating portion 24.

[0019]

As described above, according to the present invention, the inside of the outer shell is filled with the silicon nitride-titanium nitride ceramics, which expands slightly during sintering. The expansion of the constituent ceramics itself sinters the inside of the outer shell in a sealed state. An increase in volume during sintering of a silicon nitride-titanium nitride ceramic is suppressed by expansion of titanium during nitriding and contraction of silicon during nitriding, and problems such as cracking due to excessive expansion do not occur.

Since the coil-shaped heat generating portion of the heating wire is fitted in contact with the inner surface of the outer shell, the heat of the heat generating portion is efficiently transmitted to the outer shell and the outer surface of the outer shell is uniformly heated. .

Around the resistance portion of the heating wire for controlling energization is a heat insulating structure, and the inner shell enclosing the resistance portion has a high content of titanium to reduce the thermal conductivity. Since the temperature of is higher than the temperature of the heat generating part, the resistance value of the resistance part is increased, the power supplied to the heat generating part at high temperature is limited, and the heat generating part is kept at a predetermined temperature.

[Brief description of drawings]

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

FIG. 2 is an enlarged front sectional view showing a main part of the ceramic glow plug.

FIG. 3 is a diagram showing heat generation characteristics of a ceramic glow plug according to the present invention and a conventional one.

FIG. 4 is a front sectional view showing a main part of a conventional ceramic glow plug.

FIG. 5 is a plan sectional view of the ceramic glow plug.

[Explanation of symbols]

2: Electrode rod 7: Metal plug body 20: Heating wire 2
2: Resistance part 24: Heating part 30: Ceramic heating element
31: Outer shell 32, 34, 35: Inner shell

Claims (2)

[Claims] 1. A cylindrical outer shell and an inner shell filled in the outer shell are made of different ceramics, and heat is generated so that a coil-shaped heat generating portion of a heating wire is in contact with the inner surface of the tip of the outer shell. In the self-control type ceramic glow plug, in which the coil-shaped resistance part connected in series to the inner part is embedded so as not to contact the inner surface of the outer shell at the base end side, the inner shell enclosing the heating part and the inner part enclosing the resistance part A self-regulating ceramic glow plug, characterized in that and are composed of ceramics having different thermal conductivities. 2. The inner shell enclosing the heat generating portion and the inner shell enclosing the resistance portion are both made of ceramics containing silicon and titanium, and the weight ratio of titanium nitride contained in the ceramics of the inner shell enclosing the heating portion is 5. ˜20%, and the weight ratio of titanium nitride contained in the ceramic of the inner shell that wraps the resistance part is 20 to 35%,
The self-regulating ceramic glow plug according to claim 1.