JPH0652965A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide a spark plug, in which the airtightness between the housing and the insulator leg part is high, and which has the mounting structure of the airtight member also having excellent heat resistance. CONSTITUTION:A holding part 18 of an insulator 10 is formed into a taper part 18a and a step difference part 18b, and a packing 22 is sandwiched between the holding part 18 and an abutted part 24 of a housing 20. The packing 22 is protected against the heat of a combustion chamber, while the thickness of the packing 22 can be thickened, and the contact area can thus be enlarged and the airtightness is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug for an internal combustion engine.

[0002]

2. Description of the Related Art A conventional spark plug is shown in FIG.
A packing 4 for keeping airtightness is sandwiched between an insulator leg portion 2a exposed to the combustion chamber of an insulator 2 including the center electrode 1 and a housing 3 holding the insulator 2. .

The packing 4 maintains airtightness between the insulator 2 and the housing 3. However, in recent years
In order to maintain the airtightness between the insulator 2 and the housing 3, the engine output of the two or four wheels increases, the influence of the spark plug on the heat damage increases, and the pressure and temperature during combustion in the combustion chamber tend to increase. It has been desired to improve the heat resistance of the packing 4.

[0004]

However, in the prior art, as shown in FIG. 8, the side surface 4a of the packing 4 is exposed in the combustion chamber (not shown), and therefore, for example, the packing material is improved. , By the packing itself,
The heat resistance against the heat in the combustion chamber had to be improved.

However, this packing needs not only to improve heat resistance but also to sufficiently satisfy the airtightness between the insulator 2 and the housing 3, and it is necessary to find such a packing material. Was difficult.

Further, in the case of simply improving the airtightness, the airtightness itself can be achieved by increasing the tightening pressure of the packing. However, it is necessary to increase the tightening force of the packing by using the insulator leg portion. 2a and the housing 3 have a large amount of internal stress, which causes a problem that the durability of the housing is affected.

Therefore, it is an object of the present invention to provide a spark plug having a mounting structure for an airtight member, which has high airtightness between a housing and an insulator leg portion and is also excellent in heat resistance.

[0008]

In order to achieve the above object, according to the present invention, an insulator containing a center electrode, a holding portion formed on the outer peripheral surface of the insulator and having a step shape, and a hollow shape are provided. A housing having an inner peripheral surface having an abutting portion capable of abutting the holding portion of the insulator, and the holding portion of the insulator when holding the insulator with the housing. It is composed of an airtight member sandwiched between the holding portion of the insulator and the abutting portion of the housing so that the distance between the abutting portion of the housing and the abutting portion is greater than 0 and 0.5 mm or less. A spark plug for an internal combustion engine is provided.

[0009]

In the present invention, the step-shaped holding portion of the insulator is formed on the outer surface of the insulator, so that the airtight member is held by the step portion of the holding portion. Therefore, the portion of the airtight member sandwiched between the housing and the insulator is exposed to the outside air with a minute distance of 0.5 mm or less, which is the distance between the contact portion of the housing and the holding portion of the insulator. Therefore, the area of heat received by the airtight member from the outside air can be reduced. Therefore, even if the outside air is hot,
It is possible to prevent the airtight member from deteriorating.

Furthermore, since the airtight member is held by the holding portion having the step shape, the thickness of the airtight member can be increased, and the contact area between the insulator and the airtight member can be greatly increased as compared with the conventional one. Airtightness could also be improved in proportion to this contact area.

[0011]

According to the present invention, it is possible to provide a spark plug for an internal combustion engine having a structure for holding an airtight member having excellent airtightness and heat resistance.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of a spark plug according to a first embodiment of the present invention. Reference numeral 10 is an insulator made of alumina porcelain. This insulator 10 has a shaft hole 1 in the axial direction.
0a is formed. And, in this shaft hole 10a,
A central electrode 12 made of a conductive metal having heat resistance and corrosion resistance, such as a nickel alloy, is included, and one end of the central electrode 12 is exposed to a combustion chamber (not shown). A discharge gap G is formed at one end 12a of the center electrode 12 together with the ground electrode 21 fixed to the housing 20. Further, the other end 12b of the center electrode 12 is electrically connected to a center rod 16 made of carbon steel via a conductive glass seal layer 14. Furthermore, on the outer peripheral portion of the insulator 10,
A holding portion 18 described later is formed.

A housing 20 is made of a conductive metal having heat resistance and corrosion resistance, and contains an insulator 10. The housing 20 is formed on the inner peripheral surface and abuts against the abutment portion 24, which comes into contact with the packing 22 which is an airtight member held by the holding portion 18 of the insulator, and the caulking portion 28 via the caulking packing 26. And, the insulator 10 is fixed.

FIG. 2 is an enlarged view of a contact portion between the insulator 10 and the housing 20, which is a characteristic portion of the first embodiment. A stepped holding portion 18 is formed on the outer peripheral surface of the insulator 10. As shown in FIG. 2, the holding portion 18 is formed at the boundary between the middle step portion 10a of the insulator 10 and the insulator leg portion 10b, and has a tapered portion 18a and a step portion 18b.
It consists of and. The packing 22 is sandwiched between the holding portion 18 of the insulator 10 and the housing 20. In the first embodiment, the height h of the stepped portion 18b of the holding portion 18 is 0.8 mm, and the gap l between the holding portion 18 of the insulator 10 and the contact portion 24 of the housing 20 when the packing 22 is interposed. Was 0.1 mm.

Next, a method of manufacturing the spark plug for an internal combustion engine of the first embodiment will be described. In the first embodiment, the insulator 1
The diameter of the base body 10a of 0 is a, the height of the step portion 18b of the holding portion 18 of the insulator 10 is h, the diameter of the step portion 18b is b, the inner diameter of the packing 22 is c, the outer diameter of the packing 22 is d, and the packing is When the thickness of 22 is t and the inner diameter of the housing 20 is e, the following dimensional conditions are satisfied.

A = φ9.15 mm b = φ7.2 mm
h = 0.8 mm c = φ7.4 mm d = φ9.1 mm t = 1.0 mm e = φ9.
After preparing the holding portion 18, the packing 22 and the housing 20 of the insulator 10 having a shape of 2 mm or more, the packing 22 is inserted into the abutting portion 24 in the housing 20, and then,
The insulator 10 is inserted into the housing 20, and the insulator 10 is fixed in the housing 20.

FIG. 4 shows an insulator 1 in the housing 20.
It is explanatory drawing which shows the fixing method of 0. In order to fix the insulator 10 in the housing 20, the insulator 10 is inserted into the housing 20, and the holding portion 18 of the insulator 10 and the contact portion 24 of the housing 20 are brought into contact with each other via the packing 22. , At the caulking portion 28, caulking packing 2
Fix through 6. As shown in FIG. 4, the fixing by the caulking portion 28 brings the jig 30a into contact with the caulking portion 28, and further, the jig 30b is attached to the bottom surface 20b of the housing 20.
And the jig 30a and the jig 30b are sandwiched therebetween, so that the caulking portion 28 is caulked. further,
At the time of caulking, the caulking is advanced while the adjusting portion 32 of the housing 20 is electrically heated, and as soon as the caulking of the caulking portion 28 is completed, the electric heating is stopped and cooled. By this cooling, the packing 22 is further sandwiched in the space formed by the contact portion 24 of the housing 20 and the holding portion 18 of the insulator 10, and the packing 22 is filled in this space.

The holding portion 18 of the insulator 1 is formed simultaneously with the spark plug molding and grinding. According to the first embodiment, the packing 22 includes the holding portion 1
The stepped portion 18b of 8 is isolated from the combustion chamber (not shown), and only the gap l between the stepped portion 18b and the contact portion 24 is exposed to the heat of the combustion chamber. Therefore, even if the temperature of the combustion chamber becomes high, only a very small range of the packing 22 need be exposed to the high temperature of the combustion chamber as compared with the case where the stepped holding portion 18 is not provided. Therefore, the heat received by the entire packing 22 can be far less than in the conventional case. Therefore, even if the temperature of the combustion chamber is extremely high, the packing 22 made of a conventional material can sufficiently withstand.

FIG. 5 shows a comparative diagram comparing the heat resistance between the spark plug packing of the first embodiment and the conventional spark plug packing shown in FIG. The size of the packing used in the conventional spark plug and the size of the packing used in the first embodiment were the same. The numerical value showing the heat resistance is indicated by the spark ignition timing.

As is apparent from FIG. 5, by adopting the first embodiment, the heat resistance could be greatly improved for the above reason. As described above, in the first embodiment, since the step-shaped holding portion 18 is adopted, the thermal influence from the outside air is related to the size of the gap l, and the thicker the packing as in the conventional case, The area exposed to the outside air became larger and the heat resistance did not deteriorate.

Furthermore, since it is possible to increase the thickness of the packing 22 for the first time, it is possible to increase the contact area between the packing and the holding portion of the insulator and between the packing and the abutting portion of the housing. It has an excellent configuration.

Furthermore, in the first embodiment, the taper portion 18a, the step portion 18b and the contact portion 24 of the holding portion 18 are provided.
Packing 2 in an almost closed space composed of
Since 2 can be filled, the elastic force of the packing 22 can be effectively used as the sealing force between the insulator 10 and the housing 20.

Table 1 shows the contact area between the holding portion and the packing of the insulator and the contact portion of the housing and the packing in the case of the spark plug of the first embodiment and the conventional spark plug (see FIG. 8). . The thickness of each packing is also shown.

(Margin below) As is clear from Table 1, in the first embodiment, a larger contact area could be obtained as compared with the conventional one, so that the packing holding structure having a better airtightness than the conventional one could be obtained. I understand.

Further, even if the insulator leg portion 10b of the insulator 10 exposed to the combustion chamber (not shown) becomes high in temperature, the contact area where the insulator 10 contacts the housing 20 through the packing 22 is as described above. In addition, since it can be made larger than the conventional one, heat can be easily conducted,
It was possible to improve the heat resistance of the insulator and also the heat resistance of the spark plug itself.

In the first embodiment, the gap 1 between the holding portion 18 and the contact portion 24 is 0.1 mm, and the height of the stepped portion 18b of the holding portion 18 is 0.8 mm. The size is not limited, and other sizes may be used. The dimensions will be examined below.

FIG. 6 is a characteristic diagram showing the relationship between the gap 1 and heat resistance. As the index showing heat resistance, the same index as the heat resistance of FIG. 5 was used. As is clear from FIG. 6, the gap 1 is
It can be seen that when the thickness is 0.5 mm or less, high heat resistance is obtained.

When the gap 1 is 0, the holding portion of the insulator and the abutting portion of the housing come into contact with each other, which causes a problem that the holding portion or the abutting portion is damaged, which is not preferable.

FIG. 7 is a characteristic diagram showing the relationship between the airtightness limit temperature and the airtight leakage amount with respect to the packing initial thickness and the packing thickness after assembly under the same assembling force. here,
The airtight limit temperature is a temperature at which the amount of leakage is 1 cc / min or more. Further, α is the initial packing thickness and β is the packing thickness after assembly.

As is apparent from FIG. 7, it can be seen that the airtight limit temperature can be increased and the leakage amount can be decreased by increasing the packing thickness. That is, it can be seen that the packing thickness is 0.3 mm, preferably 0.6 mm in consideration of the airtight leakage amount, as the packing thickness after assembly.

However, if the packing thickness can be made thicker than the conventional one, both the airtight limit temperature and the airtight leakage amount can be improved, so that the packing thickness can be made thicker than the conventional one. It can be seen that the step h of the holding portion, which is a characteristic part of the above, may be formed even a little. However, in forming the step h, it is very difficult to manufacture unless it is at least 0.1 mm or more.
It is preferably 0.1 mm or more.

As described above, in the present invention, the structure of the insulator holding portion is made into the tab portion and the step portion, and the packing is sandwiched between the holding portion and the abutting portion of the housing. Since the packing can be protected from the heat of 1 and the packing thickness can be increased for the first time, the contact area can be increased and the airtightness can be improved. Furthermore, by increasing the contact area, the contact area between the housing and the insulator was also increased, and the heat of the insulator could be effectively transferred to the housing.

The airtight member in the present invention may be a metal packing of iron, copper, nickel or the like having a hardness before use of Hv = 100 to 150.

[Brief description of drawings]

FIG. 1 is a sectional view of a spark plug according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a contact portion between the insulator and the housing of the spark plug of the present invention.

FIG. 3 is an explanatory view showing the dimensions of the insulator and the housing of the spark plug of the present invention.

FIG. 4 is an explanatory view illustrating assembly of the spark plug of the present invention.

FIG. 5 is a comparative diagram comparing the heat resistances of the present invention and a conventional spark plug.

FIG. 6 is a relationship diagram showing the relationship between the heat resistance of the packing and the gap 1 of the present invention.

FIG. 7 is a relationship diagram showing a relationship between a packing thickness, an airtight limit temperature, and an airtight leak amount.

FIG. 8 is an enlarged view of a contact portion between an insulator and a housing in a conventional spark plug.

[Explanation of symbols]

 10 Insulator 18 Holding Part 20 Housing 22 Packing (Airtight Member) 24 Abutting Part

Claims (1)

[Claims] 1. An insulator including a center electrode, a holding portion formed on an outer peripheral surface of the insulator and having a step shape, and a hollow member having a hollow shape and capable of contacting with the holding portion of the insulator. A housing having a contact portion formed on an inner peripheral surface, and a distance between the holding portion of the insulator and the contact portion of the housing is greater than 0 and 0 when the insulator is fixed by the housing. A spark plug for an internal combustion engine, comprising an airtight member sandwiched between the holding portion of the insulator and the abutting portion of the housing so that the spark plug has a thickness of 0.5 mm or less.