JPS6148225B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a spark plug for improving the fouling resistance of the spark plug in an internal combustion engine.

Normally, when the temperature of the tip of the ignition part of a porcelain insulator in a spark plug is 500℃ or less, conductive substances such as carbon or moisture adhere to the surface of the ignition part, and the insulation resistance between the electrodes drops to 1MΩ or less, causing a spark to ignite. This makes it difficult to produce a normal spark discharge. In particular, this phenomenon occurs from the time the spark plug is installed at the car manufacturer until the car is delivered to the user, or from the time the car is new.
When the engine is cycled for less than 1,000 km and the engine is repeatedly operated for short periods such as adjustment operation, low speed, and low load, the above-mentioned conductive substance adheres to the surface of the ignition part of the porcelain insulator, resulting in a misfire. Easy to do.

Conventionally, in order to prevent this kind of contamination, spark plugs are known in which a heat-resistant insulating material is provided on the inner surface of the metal shell on the side of the combustion chamber to prevent short-circuiting of current from the firing part surface of the porcelain insulator to the metal shell. . It has been proposed to form such a heat-resistant insulating material, for example, silicone oil, on the inner surface of the metal shell and on the surface of the firing part of the porcelain insulator. (Unexamined Japanese Patent Publication 1973-
(No. 45724) However, it has been found that this coating layer made only of silicone oil cannot effectively prevent a decrease in insulation resistance. That is, silicone has a chain bond of -Si-O-Si-O-, and as a result, the silicone film has air permeability. Therefore, even if a silicone film is formed on the inner surface of the metal shell or on the surface of the igniting part of the porcelain insulator, the carbon, moisture, etc. will enter the breathable part and make it conductive, impairing its insulation properties, making it difficult to resist staining. It had the disadvantage of being inferior.

The present invention has been made in view of the above problems, and provides a spark plug that effectively prevents a decrease in insulation resistance even if a conductive substance adheres to the surface of the ignition part of a porcelain insulator and has excellent stain resistance. With the goal.

A feature of the present invention is that a coating layer made of a liquid mixture mainly composed of silicone oil and paraffin is formed on at least the surface of the ignition part of the porcelain insulator surrounded by the inner surface of the metal shell on the side of the combustion chamber, thereby preventing a decrease in insulation resistance. It's a plug.

The present invention will be specifically explained below.

FIG. 1 is a cross-sectional view of the main parts of a spark plug showing an embodiment of the present invention, in which 1 is a main metal fitting with engine mounting screws arranged, 2 is a center electrode, and 3 is a porcelain insulator made of high alumina inside. The center electrode 2 is held at the center. This insulator 3 is housed in the metal shell 1 and sealed and fixed by a known method with a gasket 6 interposed therebetween.
An ignition part 3a is provided on the inner surface 1a of the metal shell 1 on the combustion chamber side.
Equipped with. The coating layer 4 of the present invention is formed on the surface of the firing portion 3a. Reference numeral 5 denotes a spark plug having a ground electrode connected to the lower end surface of the metal shell 1 to form a spark gap with the center electrode 2.

Here, for the coating layer 4 of the present invention, a mixed solution of silicone oil and paraffin is used. The reason for its application is, as mentioned above, that since silicone alone has air permeability, the insulation resistance easily decreases when a conductive substance is attached to it. For this purpose, insulating paraffin is embedded in the air-permeable portion of the silicone to uniformly improve the insulation and waterproof properties of the entire coating. As a result, in the case of conventional spark plugs that do not form a coating layer on the surface of the ignition part of the porcelain insulator, conductive substances such as carbon and moisture tend to adhere, and particles of these substances are not uniformly connected. The insulation resistance decreases rapidly due to the adhesion. On the other hand, in the coating layer 4 of the present invention, it is difficult for such a conductive substance to adhere, and even if it adheres, the particles become spherical on the coating surface and the insulation distance between the particles is maintained, so that the insulation resistance is reduced. This is thought to be due to the effect of significantly inhibiting the decline.

In order to effectively promote the above action and to easily obtain a uniform coating layer, it is necessary to dilute with a solvent that melts both silicone oil and paraffin. Examples of this solvent include trichlorotrifluoroethane, trichlene, chlorobenzene, toluene,
Xylene, ligroin oil, benzene, etc. can be used. The paraffin is preferably a heat-resistant solid paraffin or a eutectic product of polyethylene or polystyrene.

Example 1 First, make a saturated solution by scraping solid paraffin and dissolving it in a solvent of trichlorotrifluoroethane. To 100 c.c. of this saturated solution, add 0.1 cc of silicone oil.
Make a mixture of A, B, C, D, E, and F by adding cc, 3c.c., 10c.c., 25c.c., and 50c.c. These liquid mixtures are applied to the surface of the ignition part of the porcelain insulator to form a coating layer, and the insulator is left to stand for 24 hours, after which spark plugs A to F are assembled into the metal shell. Next, as comparison products, a spark plug G in which a solution prepared by diluting only paraffin with the above solvent was similarly applied to the ignition part surface, and a solution prepared by diluting only silicone oil (10 c.c.) in the above solvent were ignited in the same way. FIG. 2 shows the results of a comparison experiment of stain resistance using a spark plug H coated on the surface of the spark plug H and a conventional spark plug I without coating.

The engine used in the experiment was a 4-stroke single-cylinder engine, and the test conditions were to run for 50 seconds with a rich mixture at idle (2070 rpm) with the throttle 3/4 closed, followed by racing 5 times with the throttle fully open, and then stop for 2 minutes. This cycle is repeated.

As shown in the figure, spark plugs G and H have a coating layer made of paraffin alone and silicone, compared to conventional uncoated spark plugs.
Although silicone H is more effective, neither of them has reached the point where it has a practical effect. In comparison, spark plugs A to F in which a coating layer made of a silicone oil and paraffin mixture of the present invention is formed have a higher number of cycles and improved stain resistance than the comparative products. The liquid mixture of the present invention can be sufficiently effective if 0.5% or more of silicone oil is mixed with 100% of paraffin saturated solution, but it is preferable to mix 5 to 50% of silicone oil, and do not add more than 50% of silicone oil. The coating is thick and cannot be formed uniformly, which is economically wasteful.

Note that the spark plug of Example 1 above was used for commercially available vehicles.
Idle and low speed (10-20Km/H) at a low temperature of 10℃
It has been confirmed that a similar tendency exists under conditions where the driving pattern is repeated.

Further, in the present invention, as shown in FIG. 3, the mixed liquid 4 of the present invention may be formed on both the ignition portion 3a of the porcelain insulator 3 and the inner surface 1a of the metal shell 1. 1st above
As shown in the figure, only the surface of the ignition part 3a of the porcelain insulator 3 is effective, but by forming it also on the inner surface 1a of the metal shell 1, short circuit to the metal shell is prevented, which improves the stain resistance. can be further improved. In this case, the coating can be formed by injecting the liquid mixture into the annular space of the ignition part after the porcelain insulator is assembled to the metal shell.

As described above, the present invention forms a coating layer made of a mixture of silicone oil and paraffin on at least the surface of the igniting part of the porcelain insulator, so that carbon and moisture remain on the surface even after repeated low-speed and low-load operation. It is difficult for conductive substances to adhere to it, and even if it does adhere, it can maintain high insulation resistance, and has an excellent effect of effectively preventing rapid fouling of spark plugs in new cars.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a main part of a spark plug showing one embodiment of the present invention, Fig. 2 is a graph showing comparison results of stain resistance, and Fig. 3 is a spark plug ignition showing another embodiment of the present invention. FIG. DESCRIPTION OF SYMBOLS 1... Metal shell, 1a... Inner surface, 2... Center electrode, 3... Porcelain insulator, 3a... Firing part, 4...
Coating layer.

Claims (1)

[Scope of Claims] 1. In a spark plug comprising a ceramic insulator holding a center electrode in a metal shell, at least the firing part surface of the ceramic insulator surrounded by the inner surface of the metal shell on the combustion chamber side, A spark plug with excellent stain resistance that is characterized by forming a film layer made of a liquid mixture mainly composed of silicone oil and paraffin to prevent a decrease in insulation resistance. 2 The above mixture contains at least 0.1% silicone oil per 100% saturated solution of paraffin.
% or more of the spark plug having excellent stain resistance according to claim 1.