JP2002098332A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure a sufficient insulation distance between the inner surface of a tube at a tube end part and an inner shaft, in a glow plug formed that a tube to hold in an insulating state a heat generating body to generate heat through energization and the center shaft for energizing a heat generating body at an internal part is securely inserted in a cylindrical mounting fitment having a mounting screw part having an outside size of 8 mm or less. SOLUTION: At an other end 3b of the tube 3 serving as a tube end part, a gap size G between the inside diameter of the tube 3 and the outside diameter of the inner shaft 6 is set to a range of 0.2-0.8 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug in which a heater tube is held in a mounting bracket for mounting an engine, and more particularly, an outer diameter of a mounting screw portion of the mounting bracket is 8 mm.
The following relates to a glow plug having a reduced diameter.

[0002]

2. Description of the Related Art Generally, a glow plug is mounted on a cylindrical mounting bracket having a mounting screw portion for mounting an engine on an outer peripheral surface thereof, with one end protruding from one end of the mounting bracket and the other end inserted into the mounting bracket. A cylindrical tube held by a metal fitting, a heating element housed at one end of the tube and generating heat when energized, and one end side electrically connected to the heating element inside the tube and the other end side attached to the other end of the tube with a mounting bracket It has a rod-shaped central shaft protruding inward, and a heating element in the tube and an electric insulating material filled in a gap between the central shaft and the tube.

[0003]

In recent years, with the direct injection and miniaturization of diesel engines, glow plugs have also been required to be miniaturized. The development of glow plugs in which the outer diameter of the mounting screw portion of the metal fitting is reduced from the conventional 10 mm (M10) to 8 mm or less (that is, the screw size of M8 or less) is underway.

However, as the diameter of the fitting in such a glow plug is reduced, the diameter of the tube (heater tube) inserted into the mounting must also be reduced. Then, at the end of the tube, the insulation distance between the inner surface of the tube and the center shaft that is insulated and held in the tube is reduced, and the tube and the middle shaft are electrically contacted, and a short circuit is likely to occur.

SUMMARY OF THE INVENTION In view of the above problems, the present invention relates to a heating element which generates heat by energizing a cylindrical mounting bracket having a mounting screw portion formed on the outer peripheral surface and having an outer dimension of 8 mm or less. It is an object of the present invention to secure a sufficient insulation distance between the inner surface of the tube at the end of the tube and the center shaft in a glow plug in which a tube having a center shaft for insulation is inserted and fixed.

[0006]

The present inventor conducted an experimental study on the insulation distance at the end of the tube in order to obtain a sufficient insulation distance between the inner surface of the tube and the central shaft.
Here, in order to sufficiently increase the insulation distance, it is necessary to reduce the diameter of the central shaft insulated and held in the tube or to increase the diameter of the tube.

However, since a wiring member (harness or the like) for electrically connecting to the power supply is screw-connected to the center shaft, the center shaft needs to have strength enough to withstand the tightening torque in the screw tightening. There is a limit in reducing the diameter of the central shaft (for example, the outer diameter of the central shaft is 2.2 mm or more).

[0008] Even if the diameter of the tube is increased, in a glow plug in which the outer diameter of the mounting screw portion of the mounting bracket is reduced to 8 mm or less, the diameter of the tube inserted into the mounting bracket is limited to the following. Of course, there is an upper limit (for example, the outer diameter of the insertion portion in the tube is φ4.8 mm or less).

[0009] Therefore, as a result of conducting an experimental study on the insulation distance in consideration of the above restrictions on the center shaft and the tube, if the insulation distance is within a predetermined range, the outer diameter of the mounting screw portion of the mounting bracket is determined. It has been found that a sufficient insulation distance can be appropriately secured in a glow plug whose diameter is reduced to 8 mm or less. The present invention has been created based on the results of such studies.

That is, according to the first aspect of the present invention, a cylindrical mounting bracket (2) and an engine mounting mounting portion (21) formed on the outer peripheral surface of the mounting bracket and having an outer dimension of 8 mm or less. , One end (3a) side is one end (2a) of the mounting bracket.
A cylindrical tube (3) protruding from the other end (3b) and held by the fitting with the other end (3b) side being inserted into the fitting, and a heating element (4, 5) housed at one end of the tube and generating heat when energized. A rod-shaped middle shaft (6) having one end (6a) electrically connected to the heating element in the tube and the other end (6b) projecting from the other end of the tube into the mounting bracket; and a heating element in the tube. A glow plug comprising an electrical insulating material (7, 8) filled in a gap between the central shaft and the tube, wherein at the other end of the tube, a gap size (G) between the inner diameter of the tube and the outer diameter of the central shaft Is set to 0.2 mm or more and 0.8 mm or less.

According to the present invention, the clearance dimension is set to 0.2 m
In the glow plug in which the outer diameter of the mounting screw portion is reduced to 8 mm or less by setting the length to m or more and 0.8 mm or less, a sufficient insulation distance between the inner surface of the tube and the central shaft at the tube end (the other end). Can be appropriately secured.

If the gap is smaller than 0.2 mm, the inner surface of the tube at the end of the tube (the other end) and the central shaft are electrically short-circuited. In addition, if the gap size is to be made larger than 0.8 mm, the central shaft must be made thinner than necessary or the outer diameter of the tube must be made larger than necessary. It is not appropriate from the point of view.

It is preferable that the thickness (t) of the tube at the other end (3b) of the tube (3) be 0.75 mm or less. If the wall thickness of the tube is larger than 0.75 mm, the diameter of the central shaft is reduced more than necessary to secure the gap size, which is not preferable from the viewpoint of maintaining the strength of the central shaft.

According to the third aspect of the present invention, when the other end (3b) of the tube (3) is fixed by being press-fitted into the fitting (2), the press-fitting portion between the tube and the fitting (2). K) to the mounting screw (2
It is characterized in that it is set at a position that does not overlap with 1).

According to the present invention, when the glow plug is screw-connected to the engine via the mounting screw portion, the other end of the tube in the mounting bracket is deformed by the screw tightening force, and the inner surface of the tube at the tube end portion is deformed. This is preferable because it is possible to prevent the insulation distance between the shaft and the center shaft from changing.

Further, as in the fourth aspect of the present invention, it is preferable that the other end (3b) of the tube (3) is set at a position deviated from the press-fitting portion (K) with the fitting (2).
Specifically, it is possible to make the thickness of the other end of the tube thinner than the thickness of the tube in the press-fit portion so that the other end of the tube does not contact the mounting bracket.

According to the present invention, it is possible to prevent the other end of the tube from being deformed by the force applied at the time of press-fitting, thereby preventing a change in the insulation distance between the inner surface of the tube and the central shaft at the end of the tube.

The reference numerals in parentheses of the above means are examples showing the correspondence with specific means described in the embodiments described later.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 1 shows a vertical cross-sectional configuration of a glow plug 1 according to an embodiment of the present invention. This glow plug 1
Is, for example, a plurality of (for example, four cylinders) engine heads (not shown) in a direct injection diesel engine of an automobile.
Each of the holes is attached to a hole formed in the hole, and is applied to promote ignition and combustion of fuel when the engine is started.

The glow plug 1 is a mounting member (housing) 2 having a hollow cylindrical shape and made of a conductive material (for example, an iron-based material).
A mounting screw portion 21 having an outer dimension of 8 mm or less is formed on the outer peripheral surface of the mounting bracket 2.
The glow plug 1 is removably attached to the engine head by being inserted into a hole of the engine head and screw-connecting a screw portion (engine-side screw portion) formed in the hole portion to a mounting screw portion 21. It is supposed to be.

In this embodiment, the mounting bracket 2 is made of carbon steel, and is formed by forming the inner and outer surfaces by cold forging and then forming the mounting screw portion 21 by cutting or the like. In this example, the external dimensions of the mounting screw portion 21 are 8 mm, that is, the size of M8 specified in JIS (Japanese Industrial Standard).

A cylindrical tube (heater tube) 3 is housed in the inner hole 22 of the mounting member 2. The tube 3 has an elongated bottomed cylindrical shape having a closed portion on one end 3a side and an opening on the other end 3b side, and is made of a conductive material (for example, a stainless steel material) having excellent heat resistance and oxidation resistance. Further, in this example, the tube 3 is formed into a stepped cylindrical shape having a small diameter portion 31 on one end 3a side and a large diameter portion 32 on the other end 3b side by narrowing the outer diameter of the tube 3 by swaging. .

The tube 3 has one end 3a side protruding from one end 2a of the mounting bracket 2 and the tube 3
Is fixed to and held by the mounting bracket 2 in a state where the other end 3b side is inserted into the mounting bracket 2. One end 3a of tube 3
Are exposed to the combustion chamber of the engine with the glow plug 1 attached to the engine head.

Here, the tube 3 and the mounting bracket 2 can be fixed by brazing, joining by press fitting, or the like. In this example, the tube 3 and the mounting bracket 2 are fixed by press fitting which is non-thermal bonding from the viewpoint of securing the strength of the mounting bracket and productivity. By this press-fitting, the tube 3 is inserted at the portion where the tube 3 is inserted into the fitting 2.
And the mounting bracket 2 are contacted and fixed with a predetermined surface pressure.

Further, inside the tube 3 on one end 3a side, first and second coil-shaped resistors (heating elements in the present invention) 4 and 5 which generate heat when energized are provided in the longitudinal direction of the tube 3. It is provided along. The first of the two resistors 4 and 5
The resistor 4 is incorporated near one end (closed portion) 3 a of the tube 3, and the second resistor 5 is incorporated closer to the other end (opening) 3 b of the tube 3 than the first resistor 4.

One end 4a of the first resistor 4 is welded and electrically connected to one end 3a of the tube 3, and the other end 4b of the first resistor 4 is connected to one end 5a of the second resistor 5. The two resistors 4 and 5 are electrically connected by welding.

The resistance change rate of the first resistor 4 at normal temperature (20 ° C.) and 1000 ° C. (temperature of the first resistor 4 of the glow plug 1 during preheating) (resistance value at 1000 ° C./20)
For example, the first conductive material (for example, an iron-chromium alloy or a nickel-chromium alloy) having a resistance value of about 1 ° C. is small.

The second resistor 5 is made of a second conductive material (for example, nickel, low carbon steel or cobalt iron alloy) having the above-mentioned rate of change of resistance of about 5 to 14, for example. The resistance temperature coefficient is a slope of a graph obtained by plotting temperature on the horizontal axis and resistance value on the vertical axis. Therefore, the second conductive material is a material having a larger positive temperature coefficient of resistance than the first conductive material.

A rod-shaped center shaft 6 made of carbon steel processed by cutting and cold forging is accommodated in the inner hole 22 of the mounting bracket 2. One end 6a of the center shaft 6 is electrically connected to the other end 5b of the second resistor 5 in the tube 3 by welding or the like, and the other end 6b is connected from the other end 3b of the tube 3 to the inner hole of the mounting member 2. 22. Also,
The center shaft 6 is made of a carbon steel material (for example, S45C or the like) having a Vickers hardness of 200 Hv or more in terms of securing strength.

In the tube 3, gaps between the resistors 3 and 5 and the end 6a of the center shaft 6 and the tube 3 are filled with electric insulating members 7 and 8, respectively. As a result, the resistors 4, 5 buried in the electrical insulating members 7, 8 and the one end 6 a side of the center shaft 6 are insulated from portions other than the one end (closed portion) 3 a of the tube 3.

In this embodiment, the electric insulating members 7 and 8 are provided with a heat-resistant material filled in the gap between the resistors 4 and 5 and the tube 3 and the gap between most of the one end 6 a side of the center shaft 6 and the tube 3. Insulating powder 7 made of an insulating material (such as magnesia)
And a sealing member 8 made of insulating liquid silicon that fills a gap between the central shaft 6 and the tube 3 and seals the insulating powder 7 at the other end (opening) 3b of the tube 3. .

In the present embodiment, the tube 3 for partitioning the main body and the two resistors 4, 5 housed in the tube 3 are provided.
An electrical insulating member 7 filled between the resistors 4 and 5 and the tube 3 to insulate the resistors 4 and 5 from the tube 3;
8 constitutes a sheath heater 9 having a columnar shape (in this example, a stepped columnar shape). And this sheath heater 9
Are electrically connected to the center shaft 6 and are held in the mounting bracket 2.

The other end 6b of the center shaft 6 projects from the other end 2b of the mounting bracket 2, and the other end 6b of the center shaft 6 has an external wiring electrically connected to a power source (not shown). A terminal screw portion 61 to which a member (not shown) is screwed is formed. The terminal screw portion 61 is made in accordance with the standard of the external wiring member, and has an outer dimension of 4 mm (M
It is usually 4) or 5 mm (M5).

A nut 12 is tightened to the terminal screw portion 61 via an O-ring 10 as a sealing member made of an insulating elastic material such as rubber and a bush 11 made of an insulating resin. The other end 6b is
It is insulated and fixed to the other end 2 b side of the mounting bracket 2. The O-ring 10 seals between the center shaft 6 and the mounting bracket 2.

The glow plug 1 has the following characteristic configuration in addition to the above configuration. First, in this example, the other end 3b side of the tube 3, that is, the large diameter portion 32
Is fixed by being press-fitted into the mounting fitting 2, at this time, as shown in FIG. 1, a press-fit portion between the tube 3 and the mounting fitting 2 (both portions 2, 3 having a predetermined surface pressure). The contacting portion K is located closer to the one end 2a of the mounting bracket 2 than the mounting screw portion 21, and is located at a position where the press-fitting portion K and the mounting screw portion 21 do not overlap.

Further, as shown in FIG. 1, the other end 3b of the tube 3 is set at a position separated from the press-fitting portion K. This is because the thickness of the other end 3b of the tube 3 is made smaller than the thickness of the tube 3 (the large-diameter portion 32) in the press-fit portion K by cutting the outer peripheral surface of the other end 3b of the tube 3 or the like. This is achieved by preventing the other end 3b of 3 from coming into contact with the inner surface of the mounting bracket 2.

FIG. 2 is an enlarged view of a portion on the other end 3b (opening) side of the tube 3 and its peripheral portion in FIG. As described above, at the other end 3 b of the tube 3, the gap between the center shaft 6 and the tube 3 is filled with the sealing member 8, but the other end 3 b of the tube 3 is most insulated from the tube 3. This is a site where destruction, that is, a short circuit is likely to occur.

In the present embodiment, the gap G between the inner diameter of the tube 3 and the outer diameter of the center shaft 6 shown in FIG. Is set to

By setting the gap size G within the above range,
A sufficient insulation distance between the inner surface of the tube 3 and the central shaft 6 at the end (the other end 3b) of the tube 3 is supported while the glow plug 1 is reduced in diameter so that the outer diameter of the mounting screw portion 21 is 8 mm or less. Can be secured appropriately.

The above range of the gap size G was found as a result of the present inventor's experimental study including the diameter and wall thickness of the mounting bracket 2, the tube 3 and the center shaft 6 in the glow plug 1. Although not limited, an example of a study result that is the basis of the above range regarding the gap dimension G will be described below.

In order to increase the gap size G and sufficiently increase the insulation distance, it is necessary to reduce the diameter of the central shaft 6 that is insulated and held in the tube 3 or to increase the diameter of the tube 3.

Here, the center shaft 6 needs to have enough strength to withstand the tightening torque when the terminal screw portion (screw size is M4 or M5) 61 and the external wiring member are screw-connected. The tightening torque is determined by a standard, and the screw size of the terminal screw portion 61 is, for example, M4 × 0.
In the case of 7, the maximum is 1.5 N · m.

In order to secure such a tightening torque, there is a limit in reducing the diameter of the central shaft 6, and according to the study of the present inventors, in the case of the central shaft 6 having a material strength of Vickers hardness of 200 Hv or more, the tube The outer diameter D2 of the center shaft 6 at the other end 3b of the shaft 3 needs to be φ2.2 mm or more. If the outer diameter D2 is less than φ2.2 mm, the breaking torque of the center shaft 6 due to screw tightening becomes smaller than the maximum value of the tightening torque (for example, 1.5 N · m).

Even if the diameter of the tube 3 is increased, in the glow plug 1 in which the outer diameter of the mounting screw portion 21 of the mounting bracket 2 is reduced to 8 mm or less, the tube inserted into the mounting bracket 2 3 (the outer diameter D1 of the large diameter portion 32 in the press-fit portion K in this example) has an upper limit as a matter of course. This is because the outer diameter D1 of the large diameter portion 32 substantially corresponds to the inner diameter of the mounting member 2 (the diameter of the inner hole 22).

That is, the outer diameter D3 of the mounting bracket 2 is, for example, φ
The upper limit is about 6.6 mm. Here, if the outer diameter D1 of the large-diameter portion 32 is excessively large, the thickness of the mounting bracket 2 (substantially corresponds to a value obtained by subtracting the outer diameter D1 of the large-diameter portion 32 from the outer diameter D3 of the mounting bracket 2). When the glow plug 1 is screw-connected to the engine head, the mounting bracket 2 may buckle so as to expand in the radial direction.

When this buckling occurs, the mounting bracket comes into contact with the inner surface of the hole of the engine head at the buckled portion, and the glow plug 1 cannot be removed from the engine head. Therefore, the inner diameter (outer diameter D1 of the large-diameter portion 32) of the mounting bracket 2 that realizes the thickness of the mounting bracket 2 such that buckling does not occur is determined.

When the screw size of the mounting screw portion 21 is M8, the tightening torque generated at the time of screw connection to the engine head is, for example, about 13 N · m at the maximum. Normal,
The Vickers hardness of the mounting bracket is 200 Hv or more,
When the mounting bracket 2 having such a material strength was examined, when the inner diameter of the mounting bracket 2 was larger than φ4.8 mm, the buckling was reduced by a torque equal to or less than the tightening torque generated when the screw was connected to the engine head. Occurred.

Therefore, the inner diameter of the mounting bracket 2, that is, the large diameter portion 32
Needs to be φ4.8 mm or less. Further, since the terminal screw portion 61 of the center shaft 6 is M4 or M5, the inner diameter of the mounting bracket 2 for housing the center shaft 6 is φ4.0 mm.
Since the above is necessary, the outer diameter D1 of the large diameter portion 32 is also φ
It is necessary to be 4.0 mm or more.

From the above discussion, the dimensions of each part in the glow plug 1 of the present embodiment are not limited, but can be as follows. That is, the outer diameter D3 of the mounting bracket 2 is φ6.4 mm to φ6.6 mm (in this example, φ3 mm).
6.6 mm), and the outer diameter D1 of the large diameter portion 32 of the tube 3 is φ
4.0 mm to φ4.8 mm (φ4.3 mm in this example),
The outer diameter D2 of the center shaft 6 at the other end 3b of the tube 3 is φ
It is 2.2 mm or more (φ2.6 mm in this example). The outer diameter of the small diameter portion 31 of the tube 3 can be set to φ4.3 mm or less (φ3.5 mm in this example).

Incidentally, in the conventional glow plug in which the thread size of the mounting screw portion is M10, for example, the outer diameter D3 of the mounting bracket is φ8.2 mm, the outer diameter D1 of the large diameter portion of the tube is φ5 mm, and Outer diameter D of center shaft at end
2 is φ2.9 mm, the outer diameter of the small diameter portion of the tube is φ3.5
mm. On the other hand, the glow plug 1 according to the present embodiment adopts the above-described dimensions, so that the mounting screw 21
Is smaller than M8, the mounting bracket 2
And the structure taking into consideration the strength of the shaft 6 and the like.

FIG. 3 shows the results of an experimental study of the gap dimension G taking into account the dimensional restrictions on the center shaft 6 and the tube 3 as described above. FIG. 3 shows the thickness t (tube thickness, thickness at the other end 3b of the tube 3).
By changing the gap size G by changing the gap size (see FIG. 2), whether or not a short circuit occurs in each gap size G is examined. In FIG. 3, a black square plot indicates a short circuit, and a white square plot indicates no short circuit.

In this embodiment, as described above, the thickness t of the other end 3b of the tube 3 is made smaller than the thickness of the tube 3 at the press-fit portion K by cutting or the like. At this time,
Outer diameter D of other end 3b of tube 3 having tube thickness t
1 ′ is about 0.2 mm thinner than the outer diameter D1 of the large diameter portion 32 in the press-fit portion K.

The results of the study shown in FIG.
The outer diameter D1 of the tube 3 was φ4.3 mm, the outer diameter D1 ′ of the other end 3b of the tube 3 was φ4.1 mm, and the outer diameter D2 of the center shaft 6 at the other end 3b of the tube 3 was φ2.6 mm. In this dimension, the tube thickness t was changed, and the gap size G was changed. The short circuit measurement of the glow plug 1 is performed at DC60V.
Was charged to the capacitor, the glow plug 1 was instantaneously energized, and the glow plug resistance was measured from the discharge waveform based on the time constant when an electrical shock was applied.

As can be seen from FIG.
If it is 2 mm or more and 0.8 mm or less, the inner surface of the tube 3 at the other end 3 b of the tube 3 and the central shaft 6 do not short-circuit. If the gap G is to be larger than 0.8 mm, the tube thickness t becomes too thin and the tube 3
This is not appropriate because the strength of the tube cannot be secured, or the center shaft 6 must be made thinner than necessary or the outer diameter of the tube 3 must be made larger than necessary.

The above is one example of the result of the study which became the basis of the above range for the gap dimension G. In order to realize the gap G, the tube thickness t is preferably set to 0.75 mm or less. If the tube thickness t is larger than 0.75 mm, the diameter of the central shaft 6 is reduced more than necessary to secure the clearance G,
This is not preferred from the viewpoint of maintaining strength.

Next, a method for manufacturing the glow plug 1 will be described. First, the center shaft 6 is connected to the connected resistors 4 and 5.
Is connected to the tube 3 by welding or the like, and the first resistor 4 and one end 3a of the tube 3 are welded. Next, the tube 3 is filled with the insulating powder 7, and the sealing member 8 is injected after the insulating powder 7.

Next, the tube 3 is subjected to swaging to form a stepped cylindrical shape having a small diameter portion 31 and a large diameter portion 32, so that the electric insulating members 7, 8 in the tube 3 are firmly tightened, and the electric insulation is performed. Resistors 4, 5 are provided by members 7 and 8.
And the center shaft 6 is insulated and held. Then, in this example, after the swaging process, the outer peripheral surface of the other end 3b of the tube 3 is cut to make the tube thickness t smaller than the tube thickness at the press-fit portion K.

The gap G is adjusted by adjusting the thickness of the tube 3 before swaging, the outer diameter D1 of the large diameter portion 32,
This is possible by adjusting the outer diameter D2 of the center shaft 6 and the like, and adjusting the pressure in the swaging processing, whereby a desired gap dimension G can be formed.

Thus, the sheath heater 9 to which the center shaft 6 is connected is completed. Then, the sheath heater 9 and the center shaft 6 are inserted into the mounting bracket 2, and the tube 3 and the mounting bracket 2 are inserted.
And are fixed by press fitting or brazing. In this example,
Press fitting is adopted, and mainly the mounting bracket 2 side is deformed,
At the press-fitting portion, the two members 2 and 3 are contacted and fixed with a predetermined surface pressure.

Subsequently, the seal member 10 and the bush 11 are inserted and arranged from the other end 6b side of the center shaft 6. Then, by tightening the nut 12 along the terminal screw portion 61, the glow plug 1 shown in FIG. 1 is completed. As described above, the glow plug 1 is screwed and attached to the hole of the engine head via the attachment screw 21.

When the glow plug 1 is mounted in the hole of the engine head, the external wiring member electrically connected to the power supply tightens a terminal nut (not shown) in the terminal screw portion 61. It is assembled by doing. As a result, power can be supplied from the power supply to the resistors 4 and 5 via the external wiring member and the center shaft 6.

The glow plug 1 can supply a large current to the first resistor 4 immediately after energization,
In addition to causing the resistor 4 to generate heat, after a lapse of a predetermined time,
Due to the temperature rise on the second resistor 5 side, the resistance value of the second resistor 5 is increased, the power supplied to the first resistor 4 is reduced, and the first resistor 4 is disconnected due to overheating. Can be prevented. Thus, ignition and combustion of fuel at the time of starting the engine are promoted.

By the way, according to the present embodiment, the glow plug 1 in which the thread size of the mounting screw portion 21 is reduced to M8 or less by setting the gap size G to be 0.2 mm to 0.8 mm, Without reducing the strength and various functions of the glow plug 1 as compared with the prior art, the other end 3 of the tube 3
A sufficient insulation distance between the inner surface of the tube 3 and the center shaft 6 in b can be appropriately secured.

At a portion other than the other end 3 b of the tube 3, a seal member 8 is provided between the center shaft 6 and the tube 3.
By filling with the insulating powder 7 having relatively higher insulating properties, sufficient insulating properties can be ensured.

In the present embodiment, as shown in the drawing,
It is preferable that the press-fitting portion K between the tube 3 and the mounting bracket 2 is set at a position where the press-fitting portion K does not overlap with the mounting screw portion 21 in the mounting bracket 2. As a result, when the glow plug 1 is screwed to the engine head via the mounting screw portion 21, the screw tightening force is not directly applied to the other end 3 b of the tube 3 in the mounting bracket 2, so that the other end of the tube 3 It is possible to prevent the gap 3b from changing due to deformation of the gap 3b.

In the present embodiment, the press-fitting portion K is positioned closer to the one end 2a of the mounting bracket 2 than the mounting screw portion 21, so that the press-fitting portion K and the mounting screw portion 21 do not overlap. The press-fit portion K may be positioned closer to the other end 2b of the mounting bracket 2 than the mounting screw portion 21.

However, in this example, since the press-fitting portion K is located closer to the one end 2a of the mounting bracket 2 than the mounting screw portion 21, the mounting screw portion 21 is not deformed at the time of press-fitting. If the mounting screw portion 21 is deformed, the screw size will not be constant and will vary, or it will be necessary to correct the mounting screw portion 21 using a screw corrector or the like after press-fitting, thus reducing productivity. I do. From that point, it is preferable that the position of the press-fitting portion K is set as in this example.

Further, in the present embodiment, it is preferable that the other end 3b of the tube 3 is set at a position deviated from the press-fitting portion K as in the illustrated example. According to this, it is possible to prevent the other end 3b of the tube 3 from being deformed by the force applied at the time of press-fitting, and to prevent the insulation distance (gap dimension G) between the inner surface of the tube and the central shaft at the tube end from changing.

[Brief description of the drawings]

FIG. 1 is a view showing a vertical cross-sectional configuration of a glow plug according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a portion at the other end of the tube in FIG. 1 and a peripheral portion thereof.

FIG. 3 is a diagram showing a result of examining a situation of occurrence of a short circuit due to a gap size G;

[Explanation of symbols]

2 ... Mounting bracket, 2a ... One end of the mounting bracket, 3 ... Tube,
3a: One end of the tube, 3b: The other end of the tube, 4: First resistor, 5: Second resistor, 6: Middle shaft, 6a: One end of middle shaft, 6b: Other end of middle shaft, 7: Insulating powder, 8 ... Seal member, 21 ... Mounting screw part, D1 ... Outer diameter of large diameter part, K ... Press-fit part.

Claims (6)

[Claims] 1. A mounting bracket (2) having a cylindrical shape, a mounting screw portion (21) formed on an outer peripheral surface of the mounting bracket and having an outer dimension of 8 mm or less, and one end (3a) of the mounting bracket being attached to the mounting bracket. A cylindrical tube (3) that protrudes from one end (2a) of the fitting and is held by the fitting with the other end (3b) side inserted into the fitting; A heating element (4, 5) that generates heat due to the above, one end (6a) side is electrically connected to the heating element in the tube, and the other end (6b) side enters the mounting bracket from the other end of the tube. A glow plug comprising: a protruding rod-shaped central shaft (6); and an electric insulating material (7, 8) filled in the tube with the heating element and a gap between the central shaft and the tube. At the other end of the The gap (G) between the inner diameter of the tube and the outer diameter of the center shaft is 0.2 mm or more.
A glow plug characterized by being 8 mm or less. 2. The other end (3b) of the tube (3).
The glow plug according to claim 1, wherein the wall thickness (t) of the tube in (1) is 0.75 mm or less. 3. The other end (3b) of the tube (3).
The side is fixed by being press-fitted into the mounting bracket (2), and a press-fit portion (K) between the tube and the mounting bracket is at a position that does not overlap with the mounting screw portion (21) in the mounting bracket. The glow plug according to claim 1, wherein: 4. The other end (3b) of the tube (3).
The glow plug according to claim 3, wherein the plug is located at a position separated from the press-fitting portion (K). 5. An outer diameter (D1) of a portion of the tube (3) to be inserted into the fitting (2) is φ4.8 m.
The glow plug according to any one of claims 1 to 4, wherein m is equal to or less than m. 6. An outer diameter (D1) of a portion of the tube (3) to be inserted into the fitting (2) is φ4.0 m.
The glow plug according to claim 5, wherein m is not less than m.