JPS5910550B2 - spark plug - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ignition plug that allows unburned carbon attached to the surface of an insulator leg to be easily removed.

When a new gasoline-powered car is completed at a car factory, the car's gasoline engine is loaded into a morch pool or onto a transport truck or export cargo ship before it is sold to a customer. It is activated and moved.

Although the driving for this movement is not uniform, the speed of the vehicle is approximately 30 to 40 bl/hour, the driving distance is about 500 m for each drive, and the driving conditions include low speed,
It is a short distance.

However, under such low-speed, short-distance driving conditions, the ignition plugs installed in automobile engines tend to smolder, and this smoldering reduces the insulation resistance of the ignition plugs, causing misfires and movement. Driving may become impaired.

This smoldering phenomenon is especially common when the outside air gets cold, such as in winter.

Further, such smoldering may occur not only in the case of a new car as described above, but also in the case of a car that has already been used, such as during the winter season.

As shown in Figure 1, this smoldering phenomenon occurs when the ignition plug 1
This is caused by unburned carbon, such as scalpels, produced by combustion of gasoline in the engine, adhering to the surface of the leg part 61 of the insulator 6, which is the part exposed to combustion gas.

In addition, in the drawing, 2 is a housing, 3 is a ground electrode,
4 is a washer, and 5 is a center electrode.

In order to solve the above-mentioned problems, an attempt has been made in the past to provide a spark plug in which a coating layer of alumina particles (a portion indicated by reference numeral 7 in the figure) is formed on the surface of the insulator leg portion 61.

However, when using a product coated with alumina particles, the alumina particles may fall off during use, causing abnormal wear within the engine.

Furthermore, the leg portions 6 cause a temperature rise during engine operation, which may lead to pre-ignition at high speeds and high loads.

The present invention eliminates the drawbacks of the prior art and makes it easier to remove unburned carbon attached to the surface of the insulator legs 61.

The object of the present invention is to provide a spark plug that has excellent self-cleaning properties and is also excellent in the durability of the self-cleaning properties.

That is, the present invention provides a spark plug 1 for an internal combustion engine comprising an insulator 6 holding a center electrode and a housing 2 disposed around the outer periphery of the insulator 6 and having a ground electrode 3. Of these, the leg 6 is exposed to the combustion gas of the internal combustion engine.
A spark plug characterized in that a coating layer 7 comprising a mixture of one or more of alkali metal hydroxides, nitrates and carbonates and one or more sodium silicate or potassium silicate is formed on the surface of the spark plug 1. It is in.

Therefore, according to the present invention, it is possible to provide an ignition plug that has excellent self-cleaning properties and is also excellent in the durability of the self-cleaning properties.

Moreover, even if the coating layer 7 is gradually removed from the surface of the leg after long-term use of the spark plug, it is easily exposed to the outside together with exhaust gases from the engine. It will be released and there is no risk of engine damage.

Further, the spark plug according to the present invention is free from the risk of pre-ignition as described above.

Furthermore, as will be described later, the coating layer 7 can be simply formed by applying it in the form of an aqueous solution and then baking it.

Note that the above-mentioned self-cleaning property means that even if unburned carbon adheres to the surface of the leg portion 61 due to low-temperature, short-distance operation of the engine, the ignition plug will be removed due to the temperature rise in the engine room during the next operation. As the temperature rises, the deposited carbon is naturally removed, meaning that the spark plug itself self-cleans.

Therefore, this self-cleaning is required to be carried out at as low a temperature as possible, preferably 400° C. or lower.

In the present invention, the substances for forming the coating layer 7 include at least one of alkali metal hydroxides, nitrates, and carbonates, and any one of sodium silicate, sodium silicate, and potassium silicate. It is a mixture of the above.

Here, the alkali metal hydroxide is hydroxide li? Um (
LiOH), *sodium oxide (NaOH), potassium hydroxide (KOH), rubidium hydroxide (RbOH) and cesium hydroxide (CsOH), alkali metal carbonates include lithium carbonate (Li2C03), sodium carbonate ( Na2C03), potassium carbonate (K2CO3),
Rubidium carbonate (Rb2C03) and cesium carbonate (
The alkali metal nitrates were lithium nitrate (LI NO3), sodium nitrate (NaNOa), and potassium nitrate (KN0).
3), using rubidium nitrate (RbNO3) and cesium nitrate (CsNO3).

Moreover, water glass is used for sodium silicate, and potassium water glass is used for potassium silicate.

For sodium water glass, sodium orthosilicate (2N
a20-SiO), sodium metasilicate (Na20・S
iO), sodium sesquisilicate (Na20.2SiO2
) and its crystal water, and potassium water glass also contains potassium metasilicate (K20・SiO2) and potassium disilicate (K20・SiO2).
There are some that are made of potassium silicate such as 2Si02) and its crystal water.

Note that these sodium silicate and potassium silicate are usually a mixture of several of the above.

The coating layer is formed by applying an aqueous solution of the coating layer forming substance to the surface of the legs 61 of the insulator 6, and after drying, heating and baking at 100 to 200°C for about 0.5 to 2 hours. This is done by attaching.

The above coating is performed by dipping the leg portion 61 into an aqueous solution of the substance for forming the coating layer, or by brushing or spraying this portion.

Further, the concentration of the alkali metal compound and sodium silicate or potassium silicate in the aqueous solution is in the range of 2 to 20% (weight ratio, the same applies hereinafter).

Among these, it is more preferable that both of the above ratios are in the range of 5 to 10 from the viewpoint of the amount of adhesion of the coating layer and the adhesion force.

The reason why the spark plug according to the present invention exhibits the above-mentioned excellent self-cleaning properties is presumed to be due to the following reasons.

That is, the deposits on the surface of the leg portions 61 are unburned gasoline mainly composed of carbon.

A portion of the volatile matter in this deposit evaporates at a relatively low temperature (approximately 150° C. or lower) when the engine is started.

The deposits become residual volatile matter and a large amount of carbon black.

Next, when the temperature of the leg portion 61 reaches 300 to 400° C., the substance of the coating layer 7 on the leg portion 61 enters into the pores of the carbon black, and the pores of the carbon black are enlarged. Eventually, it will lead to a rapid collapse.

The ultrafine pieces of collapsed carbon black are agitated by the airflow in the engine compartment and are scattered and removed from the surfaces of the legs 61 and the coating layer 7.

Some of the fine particles removed are burned, and some are emitted outside the engine by exhaust gas.

Therefore, even if unburned carbon is deposited on the leg portion 61 again due to engine operation, the deposit will be removed due to the presence of the coating layer 7 in the same manner as described above during the next engine operation.

Furthermore, since the material of the coating layer in the present invention is a mixture of an alkali metal compound and sodium silicate or potassium silicate, as is known from the comparative data in Examples, the material of the coating layer is a mixture of an alkali metal compound, sodium silicate, or potassium silicate.
Alternatively, it exhibits self-cleaning properties superior to those of potassium silicate alone, and also exhibits excellent durability regarding self-cleaning properties.

Example 1 Fifteen commercially available spark plugs on which no coating layer 7 was formed were prepared, and an aqueous solution of the coating layer forming substance according to the present invention was applied to the surface of the legs 61 of these insulators 6. The coating layer-forming substance was applied at the rate of one kind per piece, and after drying, it was baked in an electric furnace at 100°C for 1 hour.
EXAMPLE 1 An ignition plug was manufactured in which a coating layer according to the present invention was formed on the surface of No. 1.

The above coating was performed by dipping the leg portion 61 once in the aqueous solution.

Further, the coating was performed from the tip of the leg portion 61 to 10 il side.

As shown in FIG. 2, as the substance for forming the coating layer, a mixture of an alkali metal compound and potassium water glass is used, and one part each of the alkali metal compound and potassium silicate are present in the aqueous solution. The aqueous solution was applied as above.

Next, the above-mentioned spark plug is attached to the automobile engine by a conventional method, and the engine is operated while cooling the engine wall with cooling water so that the temperature of the leg portion 61 of the insulator 6 of the spark plug is 150°C or less. A large amount of carbon was deposited on the surface of the leg portion 61.

Next, the spark plug was removed from the engine, placed in an electric furnace, and the temperature at which deposits were removed was measured.

The engine was operated at an air-fuel ratio of 5 to 6, a rotational speed of 1000 rpm, and an operating time of 8 minutes.

The results are shown in FIG. 2 for each material of each coating layer.

In the figure, the shaded area is the removable temperature.

The above measurements were conducted while increasing the temperature in the electric furnace, so the lowest temperature in the shaded area (for example,
350° C. in House 1) is the lowest temperature at which deposits can be removed.

The same figure also shows similar measurement results for a spark plug without the coating layer according to the present invention (A C 1 ), that is, a commercially available spark plug.

As can be seen from FIG. 2, the spark plug (A
1 to 15), deposits can be removed at a temperature 125 to 225°C lower than that of a commercially available spark plug (AC1) on which no coating layer is formed.

Among these, it can be seen that when KOH is used, it can be removed at a low temperature of about 300° C., demonstrating excellent performance.

It is also found that all the coating layers have the ability to remove deposits at temperatures below 400°C.

Example 2 As an aqueous solution of a substance for forming a coating layer, alkali metal compound 5 and sodium silicate (sodium water glass were used).

5%) is prepared, one type of each of these aqueous solutions is applied to the leg part 61 of the spark plug in the same manner as in Example 1, dried and baked, and carbon is adhered in the same manner.
The temperature at which the deposits were removed was then measured.

After measuring the removal temperature, carbon was deposited on the spark plug again in the same manner, and the removal temperature was then measured, which was repeated five times.

During each carbon deposition operation, it was confirmed that the carbon deposited in the previous cycle had been removed.

Table 1 shows the minimum temperature for removing carbon deposits for each coating layer material.

The minimum temperature for removing deposits herein refers to the lowest temperature at which deposits can be removed, and for example, in jl6.1 shown in Example 1, 850° C. is suitable.

For comparison, Table 1 shows sodium silicate, KO
Ignition plugs were prepared in the same manner as above using an aqueous solution containing only 5% of H, K2CO3, or KNO3, and the results were measured in the same manner (AC2 to C5).

As can be seen from Table 1, the spark plugs (houses 16 to 22) according to the present invention have a minimum removal temperature of 350°C or 400°C even after repeated deposition and removal operations five times, and are self-cleaning. It can be seen that it has excellent properties as well as durability.

On the other hand, spark plugs having a coating layer of only sodium silicate, KOH, K2CO3, or KNO3 have a higher minimum deposit removal temperature than the spark plug according to the present invention even at the first time, and at the fifth time. Similarly, the spark plug according to the present invention shows an even higher temperature (AC2 and boiling 16-2 2 , 116.C 3
and situation 16, AC 4 and A17, AC5 and A1
8).

Example 3 An aqueous solution containing 20% of an alkali metal compound and 20 parts of sodium silicate was prepared as an aqueous solution of a material for forming a coating layer, and a spark plug with a coating layer formed thereon was prepared in the same manner as in Example 2, The measurement of the minimum temperature for removing deposits was similarly repeated five times.

The minimum temperature for removing deposits in each round is shown in Table 2 in the same manner as in Table 1.

The same table also shows the measurement results for spark plugs prepared using an aqueous solution containing only 20 parts of sodium silicate (116.C 6).

As can be seen from Table 2, the spark plug according to the present invention has excellent self-cleaning properties and durability.

Example 4 An aqueous solution containing 5 parts of an alkali metal compound and 5 parts of potassium silicate (using potassium water glass) was prepared as an aqueous solution of a substance for forming a coating layer, and a coating layer was formed in the same manner as in Example 2 except for the following. A spark plug was prepared, and the minimum temperature for removing deposits was repeatedly measured in the same manner.

The results are shown in Table 8 in the same manner as in Table 1.

Also, 20% alkali metal compounds and 20% potassium silicate
Create a spark plug in the same manner as above using an aqueous solution containing
Similar measurements were made.

The results are shown in Table 4.

As can be seen from Tables 3 and 4, the spark plug according to the present invention has excellent self-cleaning properties and durability.

In addition, apart from the above examples, the spark plug according to the present invention was mounted on an engine and repeatedly driven at low speeds and short distances in the same manner as in the actual case, but the spark plug with any coating layer did not cause smoldering. It has been shown that it is an excellent spark plug.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of a spark plug, and FIG. 2 is a diagram showing measurement results in Example 1. 1... Spark plug, 2... Housing, 6
...Insulator, 61...Legs, 7...
...Covering layer. 166

Claims (1)

[Claims] 1. In a spark plug for an internal combustion engine comprising an insulator holding a center electrode and a housing disposed around the outer periphery of the insulator and having a ground electrode, the insulator is exposed to the combustion gas of the internal combustion engine. A coating layer made of a mixture of one or more of alkali metal hydroxides, nitrates and carbonates and one or more of sodium silicate or potassium silicate is formed on the surface of the legs. A spark plug featuring