JP2600657B2 - Spark plug - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an improvement in a spark plug for an internal combustion engine, and more particularly, to a spark plug which prevents a decrease in insulation resistance and has excellent carbon fouling resistance.

[Prior Art] Conventionally, as a known spark plug, as shown in FIG. 5, there is a spark plug in which a porcelain insulator holding a center electrode is housed and fixed via a step 8 'of a hollow metal shell. ,
The stepped seat 8 ′ makes the tubular gap 5 ′ between the inner wall surface 1 a ′ on the combustion chamber side and the ignition leg 3 a ′ of the porcelain insulator smaller than the tip end to the extent that the ingress of combustion gas is prevented at the base side. It is known that an electrically insulating oil layer 7 'is formed in the narrow tubular gap 5' (Japanese Utility Model Application Laid-Open No. 57-104481).

[Problems to be Solved by the Invention] In the above-mentioned spark plug, the electric insulating oil such as the silicone oil is held only in the narrow tubular gap 5 ', so that the quantity is limited. Electric insulating oil such as silicone oil gradually drops and stays at the tip of the ignition part even when not exposed to the combustion gas. They evaporate when exposed to combustion gases. When this cycle is repeated, the insulating oil layer disappears in a very short period of time, and there is a disadvantage that the durability of the carbon fouling resistance effect is poor.

An object of the present invention is to overcome the above-mentioned drawbacks and to provide a spark plug having improved droop resistance at normal temperature and improved durability of carbon fouling resistance.

[Means for Solving the Problems] A spark plug according to the present invention includes a porcelain insulator holding a center electrode, a metal shell for housing and fixing the porcelain insulator inside,
Wherein the melting point of the surface of the leg portion of the insulator exposed to the combustion chamber side of the internal combustion engine and the inner surface of the metal shell facing the combustion chamber side of the leg portion is 50 ° C.
It is characterized in that a coating layer made of the above modified silicone oil, which becomes solid at normal temperature and becomes fluid when used, is formed.

Hereinafter, the present invention will be described with reference to specific examples.

The spark plug of the present embodiment is partially cut away and
FIG. 2 is a partially cutaway overall perspective view of FIG.

The spark plug of this embodiment is a spark plug formed by housing and fixing a ceramic insulator 3 holding a center electrode 2 in a metal shell 1. One end of the porcelain insulator 3 on the combustion chamber side of the internal combustion engine is a leg 3a and a tip 3b connected to the leg 3a.
Having. A coating layer (electric insulating layer) 7 made of a modified silicone oil having a melting point of 50 ° C. or more is provided on the surface 3c of the leg 3a and the inner surface 1a of the metal shell 1 facing the surface 3c and on the combustion chamber side. Are formed. The melting point of the compound of this coating layer is about 50 to 300 ° C. Note that 4 in FIG. 1 indicates a packing.

Here, the modified silicone oil is a modified silicone oil (polyalkyl, aminoalkyl, polysiloxane) having a skeleton of a siloxane structure as shown by the following chemical structural formula and having an organic group introduced into a part of the methyl groups of the silicone oil. And higher fatty acids).
It is in a solid state at room temperature and has the property of becoming a fluid at about 50 to 300 ° C. or higher.

(N = 15 to 19) A test was conducted to compare the carbon plug resistance of the above-described spark plug with a conventional spark plug using silicone oil.
Note that dimethylpolysiloxane (1000 cst) was used as a conventional silicone oil.

The test conditions are as follows.
And a pattern operation in which acceleration and deceleration of 10 to 20 km / Hr were repeated 6 times, and after stopping for 5 minutes, the same pattern operation was repeated again, and a test was performed in which one cycle was performed up to this point.
After performing this test, the degree of insulation deterioration between the center electrode 2 and the ground electrode 6 was evaluated.

The result is shown in FIG. According to this result, when the conventional silicone oil was used, the insulation resistance sharply decreased after 7 cycles, but when the modified silicone oil of the present example was used, the reduction rate was remarkably large. Few. As described above, the rate of decrease in insulation resistance is smaller in the spark plug of the present embodiment than in the comparative example.

In addition, a test of the droop resistance of the above-mentioned example product and the above-mentioned comparative example product was conducted. As a condition of this test, a standing test was performed at 50 ° C. and a relative humidity of 80%, and the droop resistance of each test product was examined as a droop rate (number of droop products / number of test products). The results of the droop rate are shown in FIG. According to these results, the comparative product was 17
The droop rate of 5% after leaving for 5 days and 15% after leaving for 20 days is 0% even on the 25th day in the product of the present example, which clearly shows that the product of the present example is different from the comparative product. It has remarkably excellent droop resistance.

As is clear from the above evaluation effects, the product of the present example is compared with the product of the comparative example before and after the engine is mounted, when the engine is stopped, that is, at room temperature, the modified silicone oil is in a solid state, Actively suppresses drooping, while acting as a fluid during engine operation, spreads to the leg side surfaces 3c, 1a of the plug pocket 5 and acts to suppress a decrease in insulation resistance, and maintains durability against drooping and carbon fouling Could be dramatically improved. In the present spark plug, the melting point of the modified silicone oil is 50 to 300 ° C.
Therefore, it has excellent resistance to droop and resistance to carbon fouling at ordinary temperatures in the region, not only in cold regions but also in warm regions. In particular, in the present invention, a coating layer made of a modified silicone oil having a melting point of 50 ° C. or more is formed on the surface of the legs of the insulator as well as on the inner surface of the metal fitting facing the legs. Therefore, it is possible to effectively suppress a side spark that jumps from the plug leg to the inner surface of the metal fitting. As a result, ignition mistakes are less likely to occur, and reliable ignition is enabled.

It should be noted that the present invention is not limited to the above embodiment, but can be variously modified and applied within the scope of the present invention depending on the purpose and application. That is, the electric insulating oil used in the present spark plug is not limited to those exemplified in the above embodiment, and modified silicone oil having a melting point of at least 50 ° C. and serving as a fluid during engine operation can be used. When the engine is stopped, the temperature of the modified silicone oil becomes 50 ° C. or less, so that the modified silicone oil is in a solid state and does not sag.
For this reason, the modified silicone oil according to the present invention is superior in droop resistance and the like as compared with the conventional product. The modified silicone oil preferably has a melting point of 50 to 300 ° C. This is because it is in a solid state at normal temperatures such as a cold region and a warm region. This modified silicone oil is a compound which usually becomes a solid at normal temperature to 300 ° C. by introducing various substituents into a silicone oil having a siloxane skeleton to increase the melting point. For example, carnauba-modified silicone oil (trade name) or the like can be used as a modified silicone oil other than the above examples. The thickness of the coating layer made of the modified silicone oil is not particularly limited, but is usually about 0.001 to 0.01 mm. In the above embodiment, the covering layer 7 is formed except for the tip 3b of the leg 3a. However, the range of the tip 3b can be variously changed, and in some cases, the covering layer 7 is formed on the entire leg 3a. It is also possible to form

[Effects of the Invention] A spark plug of the present invention holds a center electrode, and has a porcelain insulator having a leg at one end on the combustion chamber side and a leading end continuous with the leg, and the porcelain insulator inside the porcelain insulator. A modified silicone oil having a melting point of 50 ° C. or more on the surface of the leg and the inner surface of the metallic shell facing the surface of the leg and facing the surface of the leg. And a coating layer which is solid at room temperature and becomes fluid at the time of use.

Therefore, the modified silicone oil that forms the coating layer used in the present spark plug is in a solid state before the engine is mounted and when the engine is stopped after the mounting, and actively suppresses dripping to the ignited portion, and initial contamination is a problem. During low-speed, low-load engine operation, the fluid spreads over the entire surface of the plug pocket and acts to suppress a decrease in insulation resistance. Therefore, in the present spark plug, the durability of droop resistance and carbon fouling resistance can be remarkably improved, and a decrease in insulation resistance can be effectively prevented.
And, the side spark from the leg surface of the plug to the inner surface of the fitting is effectively suppressed.

[Brief description of the drawings]

FIG. 1 is a partially broken explanatory view showing a main part of a spark plug according to an embodiment. FIG. 2 is an explanatory view showing the entire spark plug according to the embodiment and showing a partially broken state. FIG. 3 is a graph showing the rate of decrease in insulation resistance in the example.
FIG. 4 is a graph showing the droop rate in the example. FIG. 5 is a partially broken explanatory view showing a main part of a conventional ignition plug. DESCRIPTION OF SYMBOLS 1 ... Metal fitting 2 ... Central electrode 3 ... Porcelain insulator 3a ... Leg of porcelain insulator 3b ... Tip part of porcelain insulator 3c ... Surface of leg of porcelain insulator 4 ... Packing 5 Plug pocket 6 Ground electrode 7 Electric insulating layer (coating layer) 8 Step

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-93184 (JP, A) JP-A-50-86599 (JP, A) JP-B-61-48225 (JP, B2)

Claims (2)

(57) [Claims] 1. A spark plug having a porcelain insulator holding a center electrode and a metal shell for accommodating and fixing the porcelain insulator therein, a leg of the insulator exposed to a combustion chamber side of an internal combustion engine. A coating layer made of a modified silicone oil having a melting point of 50 ° C. or higher and fixed at normal temperature and in a fluid state when used, on the surface of the portion and the inner surface of the metal shell facing the surface of the leg facing the combustion chamber. A spark plug, characterized in that a spark plug is formed. 2. The modified silicone oil has a melting point of 50-30.
2. The spark plug according to claim 1, wherein the temperature is 0 ° C.