JPS59951B2 - Spark plug for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spark plug for an internal combustion engine that has heat resistance that is almost the same as that of the conventional spark plug and has better stain resistance than the conventional spark plug.

A conventionally known spark plug for an internal combustion engine, for example, as shown in FIG. 1, has a grounding electrode fixed by welding or the like to a housing for installation in an internal combustion engine, and an insulator 1 with a center electrode 2 inside the housing. They are fixed by tightening or the like, forming a spark gap between the center electrode 2 and the ground electrode,
The structure was such that the air-fuel mixture was ignited by sending a spark through this spark gap.

Furthermore, the gap between the insulator leg 1a and the center electrode 2, which is directly exposed to the air-fuel mixture, is left empty or is sometimes filled with a filler such as ceramic powder, cement, or foamed glass.

However, under no-load or light-load operating conditions due to an overly rich air-fuel mixture, the spark plug having the above-mentioned structure may deposit carbon, oil, etc. on the surface of the leg portion 1a of the insulator 1 that is exposed inside the combustion chamber of the internal combustion engine. Due to the accumulation of conductive matter, the insulation resistance drops to the bottom and the fuel cannot be ignited without sparking in the spark gap.This condition occurs especially in the winter when the spark plug is not fully closed, starting, or short-circuited. Most of the problems occur as a result of repeated distance driving.

The reason why the conductive material is deposited is because the temperature of the leg portion 1a of the insulator 1 is too low under the above usage condition.

For this improvement, it is desirable to use a spark plug with a structure that prevents the temperature of the leg 1a from decreasing, that is, a low heat value spark plug, but this plug poses a problem of early ignition and cannot withstand all usage conditions. .

In the present invention, the surface of the legs of the insulator has a low thermal conductivity in a low temperature range where conductive substances such as carbon are deposited on the legs, and a low thermal conductivity in a high temperature range where premature ignition occurs compared to the low temperature range. It is characterized by forming an inorganic film with a high thermal conductivity.

According to the present invention, the inorganic film having the above characteristics reduces heat dissipation to the legs of the insulator in low-temperature regions where conductive substances such as carbon are deposited on the legs of the insulator. In high temperature ranges where the temperature of the insulator legs increases and conductive substances such as carbon deposited on the insulator legs are burned out, and premature ignition occurs, heat dissipation from the insulator legs increases, causing the legs to burn out. The temperature does not drop and premature ignition does not occur, and the plug has heat resistance comparable to that of conventional plugs, so the plug of the present invention can be used over a wide range of temperatures from low to high temperatures.

The present invention will be explained below with reference to Examples.

In FIG. 2, the ignition part of a spark plug is shown, and a center electrode 2 is held on a leg part 1a of an insulator 1 that is exposed in a combustion chamber C of an internal combustion engine E. As shown in FIG.

A ground electrode 5 is fixed to a housing 4 fixed to the outer periphery of the insulator 1 via a backing washer 3 by welding or the like.

A spark gap 6 is provided between the ground electrode 5 and the center electrode 2.
is formed.

The housing 4 is provided with a threaded portion 4a that is screwed into the cylinder block 7 of the internal combustion engine E.

8 is a center shaft, and this center shaft 8 and the center electrode 2 are electrically connected through a conductive glass seal 9.

10 is an inorganic film in the present invention, and this film 10 is formed on the surface of the leg portion 1a of the insulator 1.

Here, the method for forming the inorganic film 10 and the film 1
The effects of 0 are summarized in Table 1.

In Table 1, conventional plug A and conventional plug B have the structures shown in Figure 1, where plug A shows a plug with a lower heat value, and plug B shows a plug with a higher heat value than plug A. There is.

In addition, in Table 1, the lower limit of the operating temperature range indicates the temperature in the combustion chamber C of the internal combustion engine E that can burn out the carbon deposited on the legs 1a of the insulator 1, and the upper limit of the operating temperature range indicates the It shows the temperature in the combustion chamber C of the internal combustion engine E where ignition occurs, and each temperature was measured by a temperature measuring plug installed in parallel with the test plug.

Note that an inorganic film 10 is formed on the leg portion 1a of the insulator 1,
Carbon is attached to the surface of this membrane 10 in advance by low-speed operation, and the internal combustion engine E is heated with the carbon attached.
The above operating temperature range was measured by attaching it to the

Sodium silicate (sodium silicate) in Table 1 is JIS
Sodium silicate No. 1 to No. 3 specified in I 408-66 was used.

In addition, in Table 1, the leg portion 1 in the application range of the coating agent
The entire surface a refers to the area indicated by the dashed line X in FIG.

4mrIL refers to the range indicated by the broken line Y in FIG.

As understood from Table 1, for example, Example numbers 1-1 to
In the comparison of Example No. 1-5, in the conventional plug A of Example No. 1-1, the lower limit temperature at which the carbon deposited on the leg portion 1a of the insulator 1 can be burned out is 145 ° C. For example, in the plug of the present invention of Example No. 1-2, in which the film 10 is formed on the surface of the leg portion 1a of the insulator 1, the lower limit temperature at which the deposited carbon can be burned out is 1.
15° C., indicating that the plug of the present invention can be used even at low temperatures where conventional plug A would misfire due to carbon contamination.

In other words, the stain resistance is good.

Further, in the plug of the present invention of Example No. 1-2, the upper limit temperature that causes early ignition is 568°G, which is almost the same as the upper limit temperature that causes early ignition of the conventional plug A, which is 570°C. It can be seen that it has almost the same heat resistance as A.

The plugs of the present invention of Example No. 1-3 to Example No. 1-5 also have a lower usable lower limit temperature than the conventional plug A, and are superior in that the usable upper limit temperature is the same as the conventional plug A. It is.

In addition, the same thing applies to Example No. 2-1 to Example No. 2
The same can be said about the comparison of the -8 plug.

As understood from the above explanation, the leg portion 1a of the insulator 1
The film 10 formed on the surface of the combustion engine E has a characteristic of having a small thermal conductivity with respect to temperature when the temperature in the combustion chamber C of the internal combustion engine E is low enough to cause carbon deposition on the leg portion 1a.
It can also be seen that in a high temperature range where the temperature inside the combustion chamber C causes early ignition, the thermal conductivity with respect to temperature is higher than in a low temperature range.

. In other words, in the plug of the present invention, the internal combustion engine E
In a low temperature range where the temperature in the combustion chamber C is such that conductive substances such as carbon and oil are deposited on the leg portion 1a, the thermal conductivity of the film 10 formed on the surface of the leg portion 1a is small, and the By providing resistance to heat dissipation, the temperature of the leg portion 1a increases, and even if conductive material such as carbon or oil is deposited on the leg portion 1a, this conductive material can be burned out.

On the other hand, in a high temperature range where the temperature in the combustion chamber C of the internal combustion engine E causes early ignition, the thermal conductivity of the membrane 10 is high, which promotes heat dissipation to the leg 1a. The temperature decreases, and even with the film 10 formed, the same heat resistance as the conventional plug can be maintained.

In addition, as can be understood from Table 1, even if the concentration of sodium silicate in the coating agent that is the material of the membrane 10 is low, the effect will be slightly lower than if it is concentrated, but it can still be used compared to conventional plugs. The minimum temperature limit is low and the maximum usable temperature is almost the same as that of conventional plugs.

For example, conventional plug A and embodiment numbers 1-2 and 1-
This can be seen from the comparison with the plug of the present invention in No. 4 and the comparison between the conventional plug B and the plugs of the present invention in Example Nos. 2-2 and 2-4.

Furthermore, as can be seen from the comparison between the plug of the present invention of Example No. 2-2 and the plug of the present invention of Example No. 2-6, for example,
It can be seen that in a composite composition in which lead chloride is added in addition to the main component, sodium silicate, in the coating agent that is the material of the membrane 10, the usable lower limit temperature becomes even lower.

The same can be said of the plug of the present invention of Example No. 2-7 in which the film 10 was formed by applying a coating agent containing lead sulfate.

The effect varies depending on the range of application of the coating agent to the leg portions 1a.

This can be seen by comparing Example numbers 1-3 and 1-5.

It has been confirmed that the leg portion 10, which is mainly made of sodium silicate, does not peel off from the surface of the leg portion 1a even if it is used for a long time at high temperatures.

Furthermore, according to confirmation experiments conducted by the present inventors, when a coating agent is applied to the leg portion 1a and the leg portion 1a is heat-treated at a high temperature after drying, as in the case of the plug of the present invention of Example No. 1-3, a film is formed. 10 becomes vitrified and firmly adheres to the surface of the leg portion 1a,
It has been found that the film 10 does not peel off easily even when subjected to mechanical shock such as vibration.

Therefore, post-drying heat treatment is beneficial.

Further, the effect of the film 10 formed on the surface of the leg portion 1a of the insulator 1 becomes better as the thickness increases, but the film 10 is
When the membrane is composed of sodium silicate, the sodium silicate contains water of crystallization, so if the amount of sodium silicate is increased to increase the thickness of the film 10, more water of crystallization will scatter during drying. , many pores are formed on the surface of the membrane 10, giving it an unsightly appearance.

If the amount of the coating agent applied is adjusted so that the thickness of the membrane 10 is 0.2 mm or less, no pores will be formed on the surface of the membrane 10.

Next, Fig. 3 shows the results of the actual vehicle test.

FIG. 3 shows the relationship between the type of coating agent that is the material of the film 10 formed on the surface of the leg portion 1a of the plug, the carbon burnout vehicle speed, and the premature ignition point for a conventional plug.

In this figure 3, the coating agent sodium silicate is JIS 1
No. 2 was used, and the coating area of the coating agent was set to the area indicated by X in FIG.

The conventional plug used was the same as plug A in Table 1.

Carbon burnout vehicle speed was measured by attaching carbon in advance, using a car equipped with a 4-stroke, 4-cylinder, 1200cc internal combustion engine, and driving at a constant speed on a flat road, and the vehicle speed at which carbon was burned off was taken as the carbon burnout vehicle speed.

Regarding premature ignition point, the ignition timing of the internal combustion engine is advanced by +5 degrees from the standard timing (STD) using a crank ampoule, and the power generated by the internal combustion engine is rapidly reduced (
The advance point at which the pre-ignition phenomenon occurred was defined as the pre-premature ignition point.

As is clear from FIG. 3, it can be seen that in the plugs in which the lubricant is applied to the leg portions 1a of the plugs, that is, in the plugs in which the film 10 is formed, the carbon burnout vehicle speed is much lower than in the conventional plugs.

This means that carbon can be burned off even at low temperatures at relatively low vehicle speeds.

It can also be seen that the premature ignition point is the same as that of conventional plugs, and that there is almost no difference from conventional plugs in terms of heat resistance.

Note that the present invention can be modified in various ways as shown below.

(1) Film 10 formed on the surface of leg portion 1a of insulator 1
The material of the film is not limited to one mainly composed of sodium silicate, but any film material may be used as long as it can obtain properties comparable to those of a film made of sodium silicate.

(2) In order to make it easier to apply the coating agent as described above to the leg portions 1a of the insulator 1, the coating agent may be in the form of an aqueous solution or dissolved in an organic solvent such as alcohol. .

(3) The film-forming substance in the above-mentioned coating agent, that is, the above-mentioned sodium silicate, for example, may contain substances that disappear upon heating, such as ammonia groups and hydroxyl groups.

(4) Even if an organic glue is added to the above-mentioned coating agent in order to make it easier to coat, there is no problem as long as it is heated and burnt out.

(5) Since the temperature at the time of welding the conductive glass seal 9 of the plug is generally 750°C to 950°C,
If the aforementioned coating agent is applied to the leg portions 1a of the insulator 1 in advance, the drying and heat treatment steps can be omitted due to the high temperature during welding.

As described above, according to the plug of the present invention, by forming the film 10 on the surface of the leg portion 1a of the insulator 1, it maintains the same heat resistance as the conventional one, and has better resistance to staining by conductive materials such as carbon than the conventional one. can be significantly improved.

Therefore, the plug of the present invention can be used under a wide range of usage conditions.

Note that the film 10 does not peel off, and the above effects can be reproduced.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the main parts of a conventional plug, Fig. 2 is a sectional view of the main parts of an embodiment of the present plug installed in an internal combustion engine, and Fig. 3 is an embodiment of the present plug. It is a characteristic diagram for explaining the effect in. 1... Insulator, 1a... Leg, 2...
... Center electrode, 4 ... Housing, 5 ...
...Ground electrode, 10...Membrane, E...
・Internal combustion engine, C... Combustion chamber.

Claims (1)

[Scope of Claims] 1. A spark plug for an internal combustion engine comprising an insulator holding a center electrode and a housing having a ground electrode disposed on the outer peripheral surface of the insulator, in which a spark plug for an internal combustion engine that Thermal conductivity is low in a low temperature range where the temperature inside the combustion chamber causes the accumulation of conductive parts such as carbon on the legs, and the temperature inside the combustion chamber causes premature ignition. 1. A spark plug for an internal combustion engine, characterized by forming an inorganic film having lower thermal conductivity in a high temperature range that causes . 2. The spark plug for an internal combustion engine according to claim 1, wherein the film is made of only sodium silicate. 3. The spark plug for an internal combustion engine according to claim 1, wherein the membrane is made of a composite composition of sodium silicate as a main component and additives. 4. The spark plug for an internal combustion engine according to claim 3, wherein the additive is lead sulfate. 5. The spark plug for an internal combustion engine according to claim 3, wherein the additive is lead chloride.