JPH0650663B2 - Spark plug for internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to a spark plug used in an internal combustion engine.

(Prior Art) Conventionally, in a spark plug used in an internal combustion engine, since the air-fuel mixture is made rich from the start to the end of warming up, carbon generated by combustion of the fuel causes the legs of the insulator to be separated by the liquid fuel. A large amount of carbon may be attached to the legs, and the carbon attached to the insulator legs is arranged along with the electric force (applied voltage), and the carbon path is formed from the ground side of the leg base toward the tip. Since it progresses and causes a decrease in the insulation resistance of the insulator and causes a malfunction of the internal combustion engine, the insulator must be removed in order to remove the attached carbon and promote the self-cleaning action of the insulator itself. By increasing the length of the legs, the insulation resistance is prevented from lowering, and a substance such as highly water-repellent silicon oil is applied to the surface of the insulator and the inner wall of the metal shell to prevent the carbon itself from adhering. There is.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional one, in the case of increasing the leg length so that the surface temperature of the insulator is easily increased, the insulator is prevented from adhering carbon due to combustion of fuel. Since it can maintain the insulation resistance of the insulation, it has an effect on the stain resistance, but if the insulator legs are long, preignition is likely to occur, and there is a limit to the length in terms of heat resistance. It was Furthermore, when applying a substance such as silicone oil with high water repellency to the insulator surface or the inner wall of the metal shell, when exposed to high-temperature combustion gas, it is applied to the insulator leg surface or the inner wall of the metal shell. The substance having high water repellency such as silicone oil has a drawback that the effect on carbon adhesion is lost in a short period of time because the silicone oil or the like is gradually evaporated. Therefore, the present invention is to improve the drawbacks of the above-mentioned conventional ones, by preventing the carbon generated by combustion from adhering to the insulator legs, etc., it is possible to prevent the insulation resistance from decreasing and to ensure the reliability of the spark plug. It is intended to maintain a good ignition.

(Means for Solving the Problem) Therefore, 5 × 10 ² to the base surface of the insulator leg portion
A band made of a semiconductor material having a resistance value of 10 ⁴ MΩ / mm is applied or baked, and the length of the band is set to 1/3 or less of the leg length of the insulator leg. The material band shall be water repellent, and a water repellent material shall be applied to the inner wall of the metal shell facing the insulator leg formed by applying or baking the semiconductor material band, or the metal shell shelf width shall be set. It is made longer in the axial direction.

(Operation) With the above configuration, carbon is generated by combustion, and even if an attempt is made to adhere to the surface of the insulator by raw gas, water, etc. generated during repeated rapid acceleration / deceleration operation, the insulator, especially the insulator leg surface Is 5 × 10 ^{2 to} 5 × 10 ⁴ MΩ / mm
Since a band made of a semiconductor material having a resistance value of is coated or baked, even if water or the like is attached to the insulator surface with carbon, the arrangement of carbon can be electrically inhibited. In addition, the band should have water repellency,
By applying a water-repellent substance to the inner wall of the metal shell, it is possible to improve the waterproof property, improve the stain resistance of the insulator surface due to carbon, and prevent the insulation resistance from decreasing.

(Example) The present invention will be further described with reference to an example shown in the drawings. (1)
Is a spark plug for an internal combustion engine which is an embodiment of the present invention. The spark plug (1) for an internal combustion engine comprises an insulator (2) having a center electrode (3) at its tip and the center electrode (3). It is composed of a metal shell (4) having an outer electrode (5) arranged at a position opposite to and surrounding a screw part (6) used when mounting on an internal combustion engine. 5 × 10 ^{2 to} 5 × 1 particularly on the surface of the insulator (2) that holds the electrode (3) on the base side (14) of the leg (7).
This is obtained by applying or baking a strip (8) made of a semiconductor material having a resistance value of 0 ⁴ MΩ / mm (first embodiment). The band (8) made of this semiconductor material contains alumina or silica as a main component and contains 0.1 to 5% of the semiconductor material (Ti
O ₂ , Nb ₂ O ₅ , ZrO ₂ , BaTiO ₃ , IrO ₂
After mixing coated ferrite) represented by like or Fe ₂ O ₃ or the like, air-dried (1hr), is made by baking a further 100 to 300 ° C.. For this reason, even if carbon is generated by combustion and adheres to the surface of the insulator (2) due to fuel, water, etc., the carbon is generated on the surface of the insulator (2), particularly the surface of the insulator leg (7) at the base side (14). 5 × 10 ^{2 to} 5 × 10 ⁴ MΩ /
Since the band (8) made of a semiconductor material having a resistance value of mm is provided, it is possible to prevent carbon that is attached together with water and the like from being electrically arranged by an applied voltage, and the carbon is attached to the surface of the insulator (2). It is possible to prevent a decrease in insulation resistance that occurs. In particular, if the resistance value of the semiconductor material of the strip (8) is smaller than 5 × 10 ² , the insulation resistance is small,
Flashover cannot be prevented, resulting in misfire, and if it is larger than 5 × 10 ⁴ , it becomes the same as an insulator, which obstructs the electrical arrangement of carbon and the effect of preventing carbon fouling cannot be obtained.

The range of the band (8) made of a semiconductor material coated or baked on the surface of the insulator (2) is equal to the leg length (1).
If it is 1/3 or less, the antifouling effect can be maintained, and if it is longer than that, the effect does not occur (second
Example).

Further, as shown in FIG. 3, the band (8) made of a semiconductor material may be formed by coating or baking except the root (17) of the base side (14) (third embodiment). The shape of the strip (8) is such that the carbon path developed from the root (17) is interrupted by the strip (8) and the movement of the carbon path from the strip (8) toward the tip is further delayed. The stain resistance is superior to that of the first embodiment.

Further, a band (8) made of a semiconductor material, which is applied or baked on the surface of the insulator (2), particularly on the base side (14) of the insulator leg (7), contains carbon black in an amount of 2 to 5%. The band (8) is made water repellent by applying a mixture of silicone or silicone varnish and boron nitride to be added, drying, baking, or using Teflon or the like as a base material for improving heat resistance. However, since it is possible to prevent fuel or water generated by combustion from adhering to the surface of the insulator (2), it is possible to prevent contamination of adhering carbon or the like ( Fourth embodiment). Further, as shown in FIG. 4, the inner wall (15) of the metal shell (3) at a position facing the strip (8) formed by coating or baking on the surface of the base (14) of the insulator (2). ) Is coated with a water-repellent substance (9) to prevent water from adhering to the surface of the insulator (2) and to remove carbon adhesion factors (fifth embodiment).

In addition, the band (8) is formed on the surface of the base (14) of the insulator leg (7) by coating or baking, and the metal shell (3) which is the receiving part of the insulator (2) is formed. Shelf (1
The shelf width (S) of 6) is lengthened in the axial direction, so that the invasion of carbon into the base side (14) of the insulator (2) is reduced and the stain resistance can be improved ( Sixth embodiment). Further, in the sixth embodiment, the inner wall (15) of the metallic shell (3) may be coated with a water-repellent substance (9) in the same manner as in the fifth embodiment. A stain resistance effect can be obtained.

In addition, (11) is a resistor (1) with a glass sealant (12) sandwiched in an axial hole (10) formed in an insulator (2).
It is a terminal electrode enclosed together with 3).

Therefore, as shown in the table, with respect to the spark plugs for internal combustion engines of the examples, comparative examples and conventional examples of the present invention, a 4-cycle, 2000 cc commercial vehicle was used, and the vehicle speed was 35 km / h × 6.
When a pre-delivery fouling test was repeated at a low temperature of 10 ° C., the operation pattern of 0 second, idling × 20 seconds and 15 km / h × 40 seconds was repeated as one cycle, and the effect was confirmed as shown in FIG.

As a result of the fouling test, the spark plug of the conventional example in which the semiconductor strip is not provided has a sharp decrease in the insulation resistance value from 3 cycles and decreases to 1 MΩ in 6 cycles to cause misfire. The spark plugs of the third, fourth, fifth and sixth embodiments show a slow decrease in insulation resistance and exhibit good stain resistance. In particular, the semiconductor resistance value is 5 x 1
It is preferably 0 ^{2 to} 5 × 10 ⁴ MΩ / mm, and as shown in the comparative example, when it is 100 MΩ / mm, the insulation resistance value gradually decreases with the number of cycles, and sufficient stain resistance cannot be exhibited. Further, as shown in the comparative product of the second embodiment, the strip (8)
If the length (t) is about 50% of the leg length (1), the insulation resistance value will suddenly decrease and the stain resistance will not be effective, and t will be 1/3, 1
The following is appropriate, and as shown in the third embodiment, it is more resistant that the strip (8) is provided in a ring shape within the range (t) except the root (17) on the base side (14). Effective against fouling. Further, it is more effective for the semiconductor to have water repellency on the strip as in the fourth embodiment, and also to have water repellency on the inner wall of the metal shell (3) as in the fifth embodiment. It is more effective for the stain resistance to lengthen the shelf width (S) of the metal shell (3) as in the case of the first embodiment and the sixth embodiment. Particularly, the sixth embodiment is easy to manufacture and useful because only the processing size of the shelf is changed.

(Effects of the Invention) As described above, by coating and baking the semiconductor material on the legs of the insulator, the electrical arrangement of carbon adhering to the insulator surface is hindered, and the water repellent substance is further arranged on the insulator surface. By doing so, since it is possible to eliminate the water or the like that is the cause of the electrical arrangement of the carbon, it is possible to prevent a decrease in the insulation resistance value, it is possible to remove the carbon contamination that causes preignition excellent effect Is to have.

[Brief description of drawings]

FIG. 1 is a partial sectional view of a spark plug for an internal combustion engine which is an embodiment of the present invention, and FIG. 2 is a first sectional view of the present invention.
FIG. 3 is an enlarged sectional view of an essential part of an embodiment, FIG. 3 is an enlarged sectional view of an essential part of a third embodiment of the present invention, and FIG. 4 is an enlarged sectional view of an essential part of a fifth embodiment of the present invention. FIG. 6 is an enlarged cross-sectional view of an essential part of a sixth embodiment of the present invention, and FIG. 6 is a graph showing a stain test result. 1 ... Spark plug for internal combustion engine, 2 ... Insulator, 3 ...
… Center electrode, 4 …… Metal fitting, 5 …… Outer electrode, 6 ……
Screw part, 7 ... leg part, 8 ... band, 9 ... water repellent material,
10 ... Shaft hole, 11 ... Terminal electrode, 12 ... Glass sealing material, 13 ... Resistor, 14 ... Base side, 15 ... Metal shell inner wall, 16 ... Shelf section, 17 ... Root

Front page continuation (72) Inventor Eigogo Goto 14-18 Takatsuji-cho, Mizuho-ku, Nagoya, Aichi Nihon Special Ceramics Co., Ltd. (72) Inventor Makoto Sugimoto 14-18 Takatsuji-cho, Mizuho-ku, Aichi Nihon Special Ceramics Co., Ltd. (72) Inventor Toru Moriya 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Nihon Special Ceramics Co., Ltd.

Claims (4)

[Claims] 1. The surface of the insulator leg portion on the base side is 5 × 10 ² to.
A strip of semiconductor material having a resistance value of 5 × 10 ⁴ MΩ / mm is applied or baked, and the length (t) of the strip is 1/3 or less of the leg length (1) of the insulator leg. Spark plug for internal combustion engine. 2. The spark plug for an internal combustion engine according to claim 1, wherein the band made of a semiconductor material coated or baked on the surface of the insulator leg is water-repellent. 3. The internal combustion engine according to claim 1, wherein a water-repellent substance is applied to the inner wall of the metal shell facing the insulator leg formed by applying or baking a band made of a semiconductor material. Spark plug for engine. 4. The spark plug for an internal combustion engine according to claim 1, wherein the metal shell shelf width as the insulator receiving portion is lengthened in the axial direction.