JPH09112904A - Glow plug for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high heat resistant sheathed heater which facilitates use in a high temperature area and prolongation of after glow. SOLUTION: An internal space on the tip side of a metal sheath 11 is filled with a conducting ceramic material in the form of powder or a sintered product to arrange a heating body 20 inside. A tip part 15a of an electrode rod 15 inserted to be fitted from a base end part of the sheath is connected to the heating body. Moreover, an insulating ceramic material is packed in the perimeter of the electrode rod in the form of powder or a sintered product on the side of the base part of the sheath to form a heat resistant insulation cylinder body 21. Under such a condition, a swaging is performed to form a sheathed heater 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug provided with a sheath type heater (hereinafter referred to as a sheathed heater) used to improve the startability of a diesel engine, and particularly to a high temperature which has been difficult to use in the past. The present invention relates to a high heat-resistant glow plug that can be used in a diesel engine and is capable of being used in the region and achieving afterglow over a long period of time, and that can be used in a diesel engine that is complying with exhaust gas regulations.

[0002]

2. Description of the Related Art Various types of glow plugs for diesel engines of this type have been known. Most commonly, a sheath made of a heat-resistant metal such as stainless steel is used, and a nickel wire (Ni wire) is used as a heating element (so-called heating coil) in a heat-resistant insulating powder such as magnesia (MgO) filled inside. ), Iron-chromium wire (Fe-Cr-Al alloy wire), nickel-chromium alloy wire (Ni-Cr alloy wire), etc. are used.

An example thereof will be briefly described with reference to FIGS. 8A and 8B. A glow plug for a diesel engine, generally designated by reference numeral 10, is a sheath 11 made of a heat-resistant metal material.
A sheathed heater 12, a cylindrical housing 13 that holds the sheathed heater 12 at the tip, and an electrode rod 15 that is concentrically held at the rear end of the housing 13 via an insulating bush 14. . The tip portion 15a of the electrode rod 15 is inserted into the sheath 11.

Reference numeral 16 denotes a heating element (hereinafter referred to as a heating coil) which is a spiral heating resistor arranged in the inner space on the distal end side of the sheath 11 along the axial direction, and 17 denotes the heating coil 16 inside the sheath 11. A heat-resistant insulating powder such as magnesia to be embedded in the sheath 1 at one end of the heating coil 16
The sheathed heater 12 in the glow plug 10 is constructed by electrically connecting the tip end of the electrode 1 and the other end to the tip of the electrode rod 15 inserted in the sheath 11. There is.

Further, in such a sheathed heater 12, a positive temperature coefficient of resistance is larger than that of the material of the heat generating coil 16 on the rear end side of the heat generating coil 16 assembled in the inner space of the front end side in the sheath 11. For example, a sheathed heater made of so-called two kinds of materials in which a resistance coil as a control spiral resistor formed of a conductive material such as iron (Fe wire) or nickel wire (Ni wire) is connected in series is used. It is proposed by JP-A-57-182026.

When a sheathed heater made of such two kinds of materials is used, a large amount of electric power is supplied to the heating coil immediately after energization to quickly generate heat, and the sheathed heater has a function as a rapid heating type.
After a lapse of a predetermined time, the power supply to the heating coil is kept constant due to the increase in the resistance value due to the temperature rise on the control coil side,
It has a temperature control function to prevent fusing due to overheating in the heating coil.

Further, as a glow plug for a diesel engine, a ceramic heater type glow plug has been proposed as a plug having a function as a rapid heating type. Such a ceramic heater type glow plug is disclosed, for example, in Japanese Patent Laid-Open No.
As disclosed in Japanese Patent Publication No. 7-41523, there is known one using a ceramic heater in which a heating wire made of tungsten (W), rhenium alloy (Re) or the like is embedded in an insulating ceramic material. When such a ceramic heater is used, it is superior in heat transfer efficiency as compared with the case where the sheathed heater described above is used, and heat generation characteristics and temperature rising characteristics are improved to exhibit the performance as a rapid heating type.

[0008]

In the conventional glow plug 10 described above, in which the sheath heater 12 made of one kind or two kinds of materials is used, the metallic sheath 11 is used.
The deterioration of the heat generating coil 16 due to the high temperature oxidation due to the iron-chromium wire, the nickel-chromium alloy wire, and the like embedded in the heat-resistant insulating powder 17 determines the entire life of the sheathed heater 12. Therefore, the surface temperature of the sheath 11 is about 110.
The use limit was set to be 0 ° C. That is, the iron-chromium wire or the nickel-chromium alloy wire as the material of the heating coil 16 has a maximum operating temperature of 1300
The limit was 1350 ° C., and thus the surface temperature of the sheath 11 was 1100 to 1150 ° C. as the limit of performance.

Therefore, the glow plug 10 using the conventional sheathed heater 12 as described above has a heat generation characteristic and a heat generation characteristic when it is adopted in a diesel engine which meets exhaust gas regulations which are required to be taken in recent years. Problems have been raised in terms of durability. That is, in a diesel engine, in order to comply with exhaust gas regulations, there is a decrease in engine startability, occurrence of a so-called blow-up phenomenon that the engine rotation does not increase when it is not warm immediately after engine startup, and further when the engine does not warm up. There is white smoke. Then, in order to solve the problem in the case of complying with these exhaust gas regulations, the heat generation characteristics of the glow plug, especially the saturation temperature on the sheath surface is maintained at, for example, about 1200 to 1250 ° C., and after the engine is started for a certain period of time. During that time, it is necessary to keep the saturation temperature and generate heat.

However, in the conventional general sheathed heater 12 described above, the use limit temperature of the heating coil 16 is too low as described above, and the above-mentioned 1200 to 1250 ° C.
There is a problem in terms of heat resistance, oxidation resistance, and eventually durability when used in a high temperature range, and it was not possible to obtain a satisfactory diesel engine that complies with exhaust gas regulations.

In other words, in order to improve the characteristics of a diesel engine that meets the exhaust gas regulations,
In the conventional sheathed heater 12, it is possible to set the saturation temperature, which has been a constraint from heat resistance, to a high temperature of a predetermined temperature or higher, and to maintain the high temperature state for a certain period of time even after the engine is started. It is necessary to prevent the above, secure the durability and heat resistance strength of the heating coil, etc., and make the life as long as possible, and such points must be taken into consideration.

Further, in the ceramic heater type glow plug which is one of the conventional examples described above, it is possible to raise the above-mentioned use limit temperature to some extent, but in the state where the heating wire is embedded in the insulating ceramic material. Manufacturing cost increases due to reasons such as sintering and the addition of a terminal member for electrical connection around it, and there is a problem in strength, and it is necessary to avoid hitting the ceramic part when mounting it on the engine. There has been an annoyance that the assembly work must be performed while paying attention.

Particularly, in recent years, in this kind of glow plug, the glow plug is kept energized for a certain period of time after the engine is started so that combustion inside the engine can be smoothly and appropriately performed. That is, there is a great demand for adopting the so-called afterglow method, and it is necessary to make the afterglow time as long as possible. That is, even after the engine is started, the engine is too cold, for example, in a cold region, and it takes a long time to idle, producing a lot of noise, and there is a problem of exhaust and noise such as white smoke and engine stall. It is necessary to prevent this to occur, and such points must be taken into consideration.

The present invention has been made in view of the above circumstances, and is used from the operating temperature limit of the maximum heat generation temperature of a conventional heat generation coil by filling a conductive sheath ceramic powder as a heat generation element in a metal sheath. To obtain a glow plug having a highly heat-resistant sheathed heater, which is suitable for use in a diesel engine that is compatible with exhaust gas regulations and that can be used in a high temperature range that was difficult to achieve. It is an object.

[0015]

In order to meet such demands, a glow plug for a diesel engine according to the present invention has a heating element inside by filling the inner space of the distal end side of a metal sheath with a conductive ceramic material. A heat-resistant insulating tubular body made of an insulating ceramic material, which is provided with the distal end portion of the electrode rod fitted from the proximal end portion of the sheath connected to the heating element, and around the electrode rod on the proximal end side of the sheath. A sheathed heater is configured by filling the sheath heater. Such a sheathed heater is formed by performing a swaging process after filling the sheath with a conductive ceramic material or an insulating ceramic material. At this time, the conductive ceramic material and the insulating ceramic material may be filled in the sheath as powder or may be incorporated in the state of a sintered product.

The glow plug for a diesel engine according to the present invention has a positive temperature coefficient of resistance, which is higher than that of the conductive ceramic material, in addition to the heating element made of the conductive ceramic material with which the inner space of the distal end of the metal sheath is filled. Is provided in the state of being connected in series with the heating element.

According to the present invention, a voltage is applied to the heating element made of a conductive ceramic material on the distal end side of the sheath via the electrode rod to heat the heating element, and the heating element is grounded via the sheath. It

Further, according to the present invention, by applying a voltage to the resistor provided in the sheath via the electrode rod and further to the heating element, a large electric power is applied to the heating element on the tip side of the heater at the initial stage of energization. Is supplied to rapidly generate heat to exhibit the performance as a rapid heating type, and after a predetermined time has elapsed, the power supplied to the heating element is controlled by the power control function of the resistor to prevent heat generation in the heating element. Maintains a predetermined saturation temperature and allows afterglow for a long time.

Here, the conductive ceramic material or the heat-resistant insulating cylinder which is the heating element may be in the powder state or in the sintered state. As the heat-resistant insulating cylindrical body, alumina,
Other insulating ceramic materials may be used. The resistor made of a conductive material may be a spiral resistor made of a metal material or a sintered product made of a conductive ceramic material. The point is that the resistance temperature coefficient is more positive than the material of the heating element. Any material with a large

[0020]

1 to 4 show one embodiment of a glow plug for a diesel engine according to the present invention. In these figures, FIG. 8 (a),
The same or corresponding parts as in (b) are designated by the same reference numerals and detailed description thereof will be omitted.

According to the present invention, as shown in FIGS. 1 (a) and 1 (b), the heating element 2 is formed by filling the inner space of the distal end side of the metallic sheath 11 with powder of a conductive ceramic material.
0 is internally provided, the distal end portion 15a of the electrode rod 15 inserted from the proximal end portion of the sheath 11 is exposed to the inside of the heating element 20 and is connected, and the electrode rod is provided on the proximal end side of the sheath 11. Heat-resistant insulating cylindrical body 2 made of an insulating ceramic material around 15
The sheathed heater 12 is configured by filling 1 into the sheathed heater 12.

Here, such a sheathed heater 12 is
It is formed by filling the inside of the sheath 11 with a conductive ceramic material serving as the heating element 20 and the insulating ceramic material serving as the heat-resistant insulating tubular body 21 and performing a swaging process in the radial direction of the sheath 11. Reference numeral 22 in FIG. 1 denotes a hermetically sealed portion for sealing the proximal end portion of the sheath 11. The sheath 11 is filled with a conductive ceramic material or an insulating ceramic material, and This is a portion that prevents the insulating ceramic material and the electrode rod 15 from falling out from the inside even if the opening of the base end portion is sealed and swaging is performed. Of course, such a sealing portion 22 is not limited to a hermetic seal.

The sheathed heater 1 having the above-mentioned structure
In 2, the conductive ceramic material serving as the heating element 20 is a conductive ceramic material that is stable in performance even in a high temperature state (for example, up to about 1150 to 1200 ° C.) and has excellent thermal shock resistance. Well, for example, by increasing or decreasing the content of titanium nitride (TiN) as a conductivity-imparting material in β sialon containing silicon nitride (Si3 N4) as a main component or sialon having a mixed phase of α and β, It is preferable to use sialon (SiAlON) or the like, which can be used by arbitrarily selecting the specific resistance. That is, it has been confirmed that if TiN is added in an amount of about 20% or more to the above-described sialon, it has conductivity (so-called conductive sialon), and that if added more than that, the specific resistance value changes continuously. Is known, and the above-mentioned selected TiN content may be appropriately used.

However, the present invention is not limited to this, and a non-oxide conductive material such as SiC or a 4a group, 5a group or 6a group element of the periodic table and having conductivity, such as a carbide, boride, nitride or carbonitride. One or more selected from the group of, and silicon nitride,
A conductive ceramic material obtained by mixing an insulating ceramic material such as silicon carbide or magnesia (MgO) at a ratio of 20 to 100% may be used. Here, the insulating ceramic material is mixed in order to obtain a required resistance value. The optimum carbides, borides and nitrides include zirconium boride (ZrB2), chromium carbide (Cr3 C2), titanium boride (TiB2), titanium carbide (TiC) and titanium nitride (TiN). It may be used selectively.

As the insulating ceramic material which is the heat-resistant insulating cylindrical body 21, magnesia (MgO) and the above-mentioned sialon used as an insulating material by reducing the content of titanium nitride are used. Good.

Further, the sheath 11 and the electrode rod 15 constituting the above-mentioned sheathed heater 12 are subjected to a surface treatment as necessary for the purpose of suppressing high temperature oxidation or securing the conductivity of the generated oxide film. Good. Such surface treatment includes nickel plating, chromium plating, CVD treatment with titanium carbide (TiC), titanium nitride (TiN), etc., that is, organometallic compounds, metal halides, hydrocarbon compounds, hydrogen, oxidation, water, etc. A process of depositing a target substance on a substrate by a chemical reaction of a mixed gas of volatile precursors or tungsten (W)
It is advisable to perform thermal spraying, in which is melted in a high temperature air stream and sprayed onto the target to form a film.

When manufacturing the sheathed heater 12 described above, the sheath 11 is filled with the conductive ceramic material serving as the heating element 20 and the insulating ceramic material serving as the heat-resistant insulating tubular body 21 in the powder state. Alternatively, it may be assembled in the state of a sintered product which is formed into a desired shape in advance. Here, when filling the inside of the sheath 11 in a powder state, the positive atmosphere of the sheath 11 can be positively controlled by mixing an appropriate mixture (for example, titanium (Ti) is a metal substance) in the powder. Therefore, it is necessary to prevent deterioration of conductivity between the electrode rod 15 and the powder that becomes the heating element 20. Note that the above-mentioned mixture of titanium is for reducing the oxygen concentration in the sheath 11, and is a material that is more likely to combine with oxygen than chromium oxide (Cr2 O3) generally formed on the stainless steel surface of the sheath 11. Good to add.

Further, when the conductive ceramic powder is filled, the conductive ceramic powder and the insulating ceramic powder are adjusted to have appropriate particle sizes and mixing ratios so that the desired resistance value of the heating element 20 can be satisfied. It is good to adjust. Here, for the purpose of performing such mixing more uniformly, a binder such as PVA (polyvinyl alcohol) is used, mixed in a ball mill or the like, and then filled in a sheath, and after a degreasing step by high temperature heating, You may make it apply a swaging process.

In the above-mentioned FIG. 1, the end face of the electrode rod 15 facing the inside of the heating element 20 and electrically connected is formed as a flat surface. In order to secure it, you may form as a hemispherical end surface or a conical end surface, as shown to FIG. 2 (a), (b).

In the sheath heater 12 described above, in order to secure the conductivity between the electrode rod 15 and the sheath 11 on the ground side, the coefficient of linear expansion is made to match that of the conductive ceramic powder to be the heating element 20. As described above, the material of the conductive ceramic material may be adjusted as necessary. That is, it is advisable to select a conductive ceramic material or an insulating ceramic material that is as close as possible to the linear expansion coefficient of 12 to 15 × 10 ⁻⁶ / K of the iron forming the sheath 11. For example, a conductive ceramic material has a linear expansion coefficient of 11.
Cr3 C2 of 2 × 10 ^-6 / K is magnesia having a linear expansion coefficient of 12.8 × 10 ^-6 / K as an insulating ceramic material.

According to such a heating element 20, the maximum operating temperature is 1450 due to the use of the conductive ceramic material.
The temperature is about 1500 ° C., and as a result, as is clear from the heat generation characteristics indicated by a in FIG.
An exothermic saturation temperature of about 50 to 1200 ° C can be secured. In particular, according to the present invention, the above-mentioned heating element 20 has sufficient oxidation resistance at high temperature and can be used in a high temperature range.
In addition, it is possible to obtain a highly heat resistant sheathed heater 12 having a long life and excellent durability. And
According to the glow plug 10 having such high heat resistance,
It is possible to improve driving characteristics that have deteriorated when a diesel engine is made to comply with exhaust gas regulations, such as improvement in engine startability, and reduction of blowing up and white smoke immediately after starting.

Here, in the sheathed heater 12 of this embodiment, the thickness of the heating element 20 provided around the distal end portion 15a of the electrode rod 15 and the sheath 11 is, for example, 1 m.
m. Further, in such a structure, the resistance at the tip portion 15a of the electrode rod 15 is extremely different from the resistance at the heating element 20 made of the conductive ceramic material, and the potential on the electrode rod 15 side is substantially uniform. Can be considered to be That is, even if the cross section is irregular, the potential is uniquely determined by the shape. Furthermore, the heating element 20
Since the conductive ceramic material that has a positive temperature coefficient of resistance, even if there is a portion where the resistance decreases locally, that portion preferentially heats up and the resistance of that portion apparently improves. However, the energization is performed so that uniform heat generation can be performed as a whole, and the heat generation as the sheath heater 12 can be performed in a required state.

The sheath heater 12 in the glow plug 10 described above is shown in FIGS. 3 (a), 3 (b), 3 (c) and 3 (d) or 4 (a), 4 (b), 4 (c) and 4 (d). As shown, the conductive ceramic powder and the insulating ceramic powder are filled with the electrode rod 15 inserted in the sheath 11 and swaging is performed, or the insulating ceramic is formed as a sintered product or a temporary sintered product, respectively. It can be manufactured by assembling the molded body of (1) and the molded body of conductive ceramic to the electrode rod 15, covering the electrode rod 15 with the sheath 11, and then performing swaging. Here, the former part of the conductive ceramic material is filled with a powder-based material such as Si or Ti, which is a raw material for the reaction sintering, and then the reaction sintering is performed in a nitrogen gas atmosphere. A similar sheath heater 12 can be obtained by forming a conductive ceramic sintered body inside 11.

Further, according to the present invention, the metallic sheath 11
Apart from the heating element 20 made of a conductive ceramic material that fills the inner space of the tip side of the spiral resistor 30 made of a conductive material having a larger positive temperature coefficient of resistance than the conductive ceramic material, as shown in FIG. May be provided in a state of being connected to the heating element 20 in series. Here, reference numeral 31 in FIG. 6 is an insulating rod made of an insulating ceramic material or the like for connecting the electrode rod 15 inserted from the proximal end portion of the sheath 11 and the electrode rod distal end portion 15a in an insulated state, which facilitates assembly. Become. Further, both ends of the spiral resistor 30 are connected to the electrode rod 1
5 and the electrode rod tip portion 15a, which are connected in series with the heating element 20 with a predetermined gap. With such a configuration, the sheathed heater 12 can be of a two-material type, and a self-temperature control function can be added.

A sheathed heater 12 made of the above-mentioned two materials.
As shown in FIGS. 7 (a) and 7 (b), the electrode rod 1
A resistor 32 formed of a sintered body of a conductive ceramic material is interposed in the middle of 5, or a heating element 20 and a resistor formed as a sintered body in a cap-shaped inner space in the distal end side of the sheath 11 and a resistor. It is also conceivable to provide the body 33 with a two-layer structure. That is, the resistor made of a conductive material may be the spiral resistor 30 made of a metal material or the resistors 32, 33 made by sintering of a conductive ceramic material. A material having a positive temperature coefficient of resistance larger than that of the material may be used.

The present invention is not limited to the structure described in the above embodiment, and the shape, structure, etc. of each part of the glow plug 10 having the sheath heater 12 can be appropriately modified or changed. Further, the sheath heater 12 may be manufactured by either filling ceramic powder or assembling it after forming it as a sintered product in advance.

[0037]

EXAMPLE The sheath heater 12 remains in a powder state in a cap-shaped space formed between the distal end portion 15a of the electrode rod 15 inserted from the proximal end portion of the sheath 11 in the inner space of the distal end portion of the sheath 11. , Or a heat-resistant insulating cylindrical body 21 made of an insulating ceramic material that is filled around the electrode rod 15 with the sheath 11 is provided. And is formed by performing a swaging process. Also,
The opening at the proximal end of the sheath 11 is sealed by a hermetically sealing portion 22.

[0038]

As described above, according to the glow plug for a diesel engine of the present invention, a heating element is internally provided by filling the inner space of the distal end side of the metal sheath with a conductive ceramic material. By connecting the distal end portion of the electrode rod fitted from the proximal end portion of the sheath to the heating element, and filling the heat-resistant insulating cylindrical body made of an insulating ceramic material around the electrode rod at the proximal end portion side of the sheath. Since the sheathed heater is configured, it has excellent effects as described below.

That is, according to the present invention, since the heating element is made of the conductive ceramic material, the practically allowable maximum heating temperature when using this type of sheath heater is higher than that of the conventional sheath surface. The temperature can be improved to, for example, about 1150 ° C. Further, according to the present invention, unlike the conventional sheathed heater, since there is no adiabatic insulating portion around the heating element, rapid heating is possible.

Further, according to the present invention, since the metal sheath is used, the troublesome work of assembling the ceramic sintered product so as not to damage it, which is a problem in the conventional ceramic heater, is unnecessary, and the assembling work is not required. Easy to do. In particular, according to the present invention, since the conventional heating coil is not necessary, the connection work by welding the coil and the sheath and the coil and the electrode rod is unnecessary, which improves the assemblability as compared with the conventional method and the manufacturing cost. Can be reduced.

Further, according to the present invention, by incorporating a heating element in the sheath together with a resistor connected in series to the heating element, a large amount of power is supplied to the heating element on the tip side of the heater at the initial stage of energization, and the heating element is rapidly supplied. It is possible to generate heat to exhibit the performance as a rapid heating type, and after a lapse of a predetermined time, the electric power supplied to the heating element is controlled by the power control function of the resistor to appropriately saturate the heat generation in the heating element. Maintains the temperature and can perform afterglow for a long time.

In particular, according to the present invention, the heating element is formed of a conductive ceramic material, but since the outer side thereof is protected by a metal sheath, it is excellent in terms of mechanical strength,
Durability can be improved.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a glow plug for a diesel engine according to the present invention, (a) is a cross-sectional view showing a sheath heater part which is a main part, and (b) is a perspective view of a sheath tip side part. is there.

2 (a) and 2 (b) are explanatory views showing a modification of the electrode rod in the sheathed heater in FIG.

FIG. 3 shows a method for manufacturing a sheath heater in a glow plug for a diesel engine according to the present invention, (a),
(B), (c), (d) is a figure which shows a manufacturing process.

4 (a), (b), (c), and (d) are views for explaining a method for manufacturing a sheathed heater different from FIG.

FIG. 5 is a characteristic diagram for explaining heat generation characteristics of the glow plug for a diesel engine according to the present invention.

FIG. 6 is a sectional view of a sheath heater tip portion showing another embodiment of the present invention.

7 (a) and 7 (b) are cross-sectional views of the tip portion of the sheath heater showing a modification of FIG. 6, respectively.

FIG. 8 shows a conventional glow plug for a diesel engine, (a) is a cross-sectional view of the entire glow plug, and (b) is an enlarged view of a tip portion of a sheath heater.

[Explanation of symbols]

10 ... Ceramic heater type glow plug, 11 ... Sheath, 12 ... Sheath heater, 13 ... Cylindrical housing, 14
... Insulation bush, 15 ... Electrode rod, 15a ... Tip part, 20
... heating element made of conductive ceramic material, 21 ... heat-resistant insulating cylindrical body made of insulating ceramic material, 22 ... hermetically sealed portion, 30 ... spiral resistor made of metal material, 3
1 ... Insulating rods, 32, 33 ... Resistors made of conductive ceramic material.

Claims (3)

[Claims] 1. A heating element is internally provided by filling a conductive ceramic material into the inner space of the distal end side of a metal sheath, and the distal end portion of an electrode rod fitted from the proximal end portion of the sheath is used to generate the heat. A glow plug for a diesel engine, characterized in that a sheathed heater is constituted by connecting to the body and filling a heat-resistant insulating cylindrical body made of an insulating ceramic material around the electrode rod on the proximal end side of the sheath. 2. A heating element is internally provided by filling a conductive ceramic material in the inner space on the tip side of a metal sheath, and a resistance element made of a conductive material having a positive resistance temperature coefficient larger than that of the heating element. Is provided in a state of being connected in series to the heating element, and the tip side of the electrode rod fitted from the base end portion of the sheath is connected to the resistor body, and the periphery of the electrode rod is connected at the base end side of the sheath. A glow plug for a diesel engine, characterized in that a sheath heater is formed by filling an insulating ceramic material into the sheath heater. 3. The glow plug for a diesel engine according to claim 1 or 2, wherein the sheathed heater is formed by filling a metallic sheath with a heating element and a heat-resistant insulating tubular body and then performing a swaging process. A glow plug for diesel engines that is characterized by.