JP3207335B2 - Glow plug - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug used as an auxiliary device for starting an internal combustion engine (for example, a diesel engine).

[0002]

2. Description of the Related Art A conventional glow plug has a heater tube sealing structure in which one O-ring (including a ring-shaped rubber) is provided between the entire metal heater tube and an electrode rod.
And draw the entire heater tube (for example,
Swaging) to increase the density of the insulating powder inside the heater tube and compress the O-ring,
A technique is used in which a ring is brought into close contact with the inner periphery of a heater tube and the outer periphery of an electrode bar. Further, as another sealing structure, a sealing glass having a low softening point is arranged between the mouth of the heater tube and the electrode rod, and the sealing glass is heated to a softening point temperature of the sealing glass to heat the sealing glass. There is known a technique in which the inner circumference of a tube and the outer circumference of an electrode rod are brought into close contact with each other.

[0003]

The heat-generating portion of the glow plug is mounted in a combustion chamber or a pre-combustion chamber of an internal combustion engine, and the upper end portion of the glow plug is exposed to severe conditions such as fuel oil, lubricating oil or moisture. Exposed to the environment. In the conventional seal structure described above, the upper end of the glow plug penetrates into the metal shell, and the fuel oil, lubricating oil, moisture, or the like penetrates into the heater tube from the O-ring or sealing glass. In addition, the insulating powder of the heater tube may be carbonized or conductive, and the heater tube and the electrode rod may be short-circuited. Further, when the heater tube is drawn during the production of the glow plug, there is a possibility that lubricating oil used at the time of working may enter the heater tube.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide fuel oil inside a heater tube.
An object of the present invention is to provide a glow plug with high reliability, in which impurities such as lubricating oil or moisture do not enter.

[0005]

Means for Solving the Problems [Means of Claim 1] The glow plug of the present invention employs the following technical means.
A glow plug, a heating element that generates heat when energized, an electrode rod connected to the heating element and energizing the heating element,
A heater tube that insulates and covers the heating element and the electrode rod. The glow plug has a plurality of O-rings between the electrode rod and the heater tube for shutting off the inside and the outside of the heater tube. It is characterized in that it is thinner than the wire diameter of the O-ring arranged on the side different from the body.

According to a second aspect of the present invention, in the glow plug according to the first aspect, at least one of the plurality of O-rings is made of a heat-resistant material, and at least one of the plurality of O-rings is made of an oil-resistant material. .

[0007]

[0008]

According to the glow plug of the present invention, a plurality of O-rings for shutting off the inside and the outside of the heater tube are arranged between the electrode rod and the heater tube, and the glow plug is provided on the heating element side. The diameter of the O-ring (the O-ring inserted first) is smaller than the diameter of the O-ring (the O-ring inserted later) disposed on a side different from the heating element. With this setting, the O-ring to be inserted earlier can be easily inserted. Further, the eccentricity of the electrode rod is corrected by inserting the O-ring ahead. For this reason, it becomes easy to insert the O-ring having the next largest wire diameter, and as a result, the workability in manufacturing the glow plug can be improved.

The heat generating portion of the glow plug is mounted in a combustion chamber or a pre-combustion chamber of an internal combustion engine, and the upper end of the glow plug is provided with fuel oil, lubricating oil, moisture, or the like. Exposure to impurities. Therefore, by providing at least one O-ring of the plurality of O-rings with a heat-resistant material, high sealing performance can be ensured even when exposed to a high-temperature state. In addition, by providing at least one O-ring of the plurality of O-rings with an oil-resistant material, high sealing performance can be ensured even for oil-based impurities of fuel oil and lubricating oil.

[0010]

[0011]

Next, a glow plug according to the present invention will be described with reference to the drawings. FIGS. 1 and 2 show a first embodiment. FIG. 1 is an enlarged view of a main part of a glow plug, and FIG. 2 is a sectional view of the glow plug. The glow plug 1 includes a substantially cylindrical metal shell 2 fastened to an internal combustion engine, an electrode rod 3 penetrating through the metal shell 2, and an insulator that insulates and holds the electrode rod 3 and the nut 7 on the metal shell 2. 4, a heater tube 5 and the like inserted into the metal shell 2 and partially protruding outside the metal shell 2. In the heater tube 5, the heating element 6 and the electrode rod 3 are arranged, and the insulating powder is provided. 7
Is filled and insulated.

The metal shell 2 is provided with fastening screws 2a around it.
And a fastening bolt portion 2b, which is grounded to the vehicle by being fastened to the internal combustion engine. The electrode rod 3 is a rod-shaped metal body made of a steel material, and is provided so as to receive power from a power supply circuit (not shown) via terminal connection means 8 (nut) provided at the end. The insulator 4 is a metal shell 2
It is an insulating material made of a synthetic resin that insulates and maintains the space between the electrode rods 3 disposed therein.

The heater tube 5 is a heater tube 5 made of a heat-resistant metal which covers one end of the heating element 6 and the electrode rod 3 and is provided with its end closed. Is filled. The heater tube 5 has an opening side inserted into the metal shell 2 and is fixed to the metal shell 2 by silver brazing, press fitting, or the like.
The metal shell 2 is grounded. The heating element 6 is an iron-chromium or nickel-based coil having one end connected to the electrode rod 3 and the other end connected to the inside of the heater tube 5, and generates heat when energized from the electrode rod 3. It is.

In this embodiment, two O-rings 11 and 12 are arranged between the electrode rod 3 and the mouth of the heater tube 5 to shut off the inside and outside of the heater tube 5, and the entire heater tube 5 is swaged. Squeezing to a smaller diameter
The two O-rings 11 and 12 are in close contact with the outer periphery of the electrode rod 3 and the inner periphery of the heater tube 5 to block the inside and outside of the heater tube 5.

In this embodiment, the outer O-ring 11
The (O-ring disposed on a side different from the heating element 6) is provided using a fluorine rubber of a material excellent in oil resistance in order to prevent intrusion of impurities including oil which is likely to enter from the outside. I have. On the other hand, the O-ring 12
Since the temperature of the (O-ring disposed on the side of the heating element 6) is higher than that of the O-ring 11 disposed on the outside, the O-ring is provided with a material having excellent heat resistance and using inexpensive silicone rubber. .

As described above, by providing the outer O-ring 11 with an oil-resistant material, it is possible to secure a high sealing property against oil-based impurities such as fuel oil and lubricating oil. In addition, by providing the inner O-ring 12 with a heat-resistant material, a high sealing property can be ensured even when the glow plug is used and exposed to a high temperature.

The dimensions of the two O-rings 11 and 12 will be described. The inner diameter of the heater tube 5 (dimension before drawing) is D1, and the outer diameter of the electrode rod 3 on which the O-rings 11 and 12 are mounted is D2. And O-rings 11, 1
The outer diameter dimension D3 of No. 2 satisfies the following expression.

D3 ≧ D1 The diameter D4 of the O-rings 11 and 12 satisfies the following expression.

## EQU2 ## D4.gtoreq. (D1 -D2) / 2

Here, the wire diameter of the inner O-ring 12 (the O-ring arranged on the side of the heating element 6 and inserted into the heater tube 5 first at the time of assembly) in the present embodiment is equal to the outer diameter. O-ring 11 (an O-ring that is inserted into the heater tube 5 later at the time of assembly) is provided with a smaller diameter.

Since the inner O-ring 12 has a smaller wire diameter than the outer O-ring, the O-ring 12 to be inserted first can be easily inserted at the time of manufacturing the glow plug. In addition, since the eccentricity of the electrode rod 3 is corrected by inserting the O-ring 12, it is easy to insert the O-ring 11 having the next larger wire diameter, and as a result, the workability when manufacturing the glow plug is improved. I do.

[Experimental Results] Next, the sealing results were measured using the glow plug 1 of the embodiment to which the present invention was applied and a conventional glow plug (having a structure sealed with one O-ring). The experimental results obtained are shown. In this experiment, the glow plug 1 of this embodiment and the conventional glow plug were
The electrode rod 3 was immersed in an engine oil at 30 ° C. for 100 hours. As a result, a short circuit occurred in the conventional glow plug, but no short circuit occurred in the glow plug of the present embodiment.

[Effects of the Embodiment] The glow plug 1 of this embodiment has an O-ring 11 having excellent oil resistance on the outside and an O-ring having excellent heat resistance on the inside between the electrode rod 3 and the heater tube 5.
Since the ring 12 is disposed, in a normal state, the outer O-ring 11 causes the insulator 4 in which impurities such as fuel oil, lubricating oil, or moisture are interposed between the metal shell 2 and the electrode rod 3. To prevent the water from entering the heater tube 5 from entering the space. However, when a sealing failure occurs in the outer O-ring 11, the inner O-ring 12 can prevent impurities such as fuel oil, lubricating oil, or moisture from entering the heater tube 5.

That is, as can be seen from the above experimental results,
The glow plug 1 of the embodiment to which the present invention is applied has improved sealing performance as compared with a conventional glow plug, and as a result, impurities such as fuel oil, lubricating oil, or moisture enter the inside of the heater tube 5. Can be reliably prevented. For this reason, the glow plug 1 of the present embodiment can obtain high reliability by preventing short circuit.

[Second Embodiment] FIG. 3 shows a second embodiment and is an enlarged view of a main part of the glow plug 1. As shown in FIG. In the present embodiment, an intermediate O-ring 13 is disposed between an outer O-ring 11 and an inner O-ring 12. In addition,
The material of the intermediate O-ring 13 is the outer O-ring 11
Or the same as the inner O-ring 12, or another material (for example, rubber of an inexpensive material)
May be provided. In this embodiment, three O-rings 11, 12, 13 are used for sealing,
Compared with the glow plug 1 of the first embodiment (a structure in which sealing is performed by two O-rings 11 and 12), the sealing performance is further improved and the reliability is increased.

The conventional glow plug has a single O-ring at the mouth of the heater tube 5 and therefore has poor sealing performance.
Sealing means for preventing intrusion of impurities between the mouth of the metal shell 2 and the electrode rod 3 (for example, a ring-shaped sealing material such as silicon).
However, in this embodiment, since the sealing performance is improved by using a plurality of O-rings, the metal shell 2
Can be eliminated. As a result, the number of steps for sealing the mouth of the metal shell 2 is reduced while maintaining the sealing performance equal to or higher than the conventional one, and the manufacturing cost can be reduced.

[Modification] In the above embodiment, an example is shown in which a plurality of O-rings are provided with at least two or more materials (oil-resistant material, heat-resistant material). Alternatively, a plurality of O-rings may be provided with the same material. In the above embodiment, the wire diameter of the O-ring (the inner O-ring 12 in the embodiment) inserted first into the heater tube is smaller than that of the other O-rings (the outer O-ring 11 in the embodiment). Although an example is shown, they may be provided at the same wire diameter.

[Brief description of the drawings]

FIG. 1 is an enlarged view of a main part of a glow plug (first embodiment).

FIG. 2 is a sectional view of a main part of a glow plug (first embodiment).

FIG. 3 is an enlarged view of a main part of a glow plug (second embodiment).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Glow plug 3 Electrode rod 5 Heater tube 6 Heating element 7 Insulating powder 8 Insulator 11 Outer O-ring (oil-resistant material, O-ring on the side different from the heating element) 12 Inner O-ring (heat-resistant material, heating element side) O-ring) 13 Intermediate O-ring

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H05B 3/04 F23Q 7/00 605 H05B 3/18 H05B 3/44-3/48

Claims (2)

(57) [Claims] A heating element connected to the heating element for supplying heat to the heating element; and a heater tube insulated and covering the heating element and the electrode rod. in the glow plug, the electrode rod and between the heater tubes, O-ring multiple placement Then co blocking the inside and outside of the heater tube
The wire diameter of the O-ring arranged on the heating element side is
Than the wire diameter of the O-ring arranged on the side different from the heating element
Glow plug, characterized in that the thin. 2. The glow plug according to claim 1, wherein at least one of the plurality of O-rings is made of a heat-resistant material, and at least one of the plurality of O-rings is made of an oil-resistant material.