JPS6016720B2 - Manufacturing method of closed-end porcelain spark plug insulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a closed-end porcelain spark plug insulator.

An advantage of the present invention is that the closed-end porcelain spark plug insulator is advantageously suited for improving spark plug durability and ignitability, and also effectively contributes to lowering the noise level caused by the spark plug. We are proposing a new manufacturing method.

In this invention, the durability of the spark plug is enhanced by eliminating the provision of the corrosion-resistant metal center electrode facing the outer electrode, which was considered indispensable in conventional general spark plugs, thereby eliminating wear and tear. This also improves ignitability.
Similarly, by eliminating the anti-inflammatory effect originating from the center electrode, each of these can be achieved all at once and effectively.

In recent years, the purification of automobile exhaust gas has become a matter of urgent importance.
So-called compliant cars with various exhaust gas countermeasures are actually being put on the market, and on the other hand, radio noise mainly emitted from the ignition system of cars is also becoming increasingly seen as a problem as FM radio and mobile hams become more popular. It is desired to establish countermeasures for this.

Regarding both exhaust pollution and radio wave interference, the performance of the ignition system, especially the spark plug, which is the ignition source, is extremely important, and much effort is currently being put into its research and development.

In other words, the main problems are: 1) alleviation of the flame-extinguishing effect generated at the center electrode of the ignition plug, and 2) suppression of noise current during spark discharge of the ignition plug.

By the way, the flame-extinguishing effect of the center electrode is linked to so-called misfires, so as a concrete means to reduce this, the gap between the electrodes is currently widened, for example, the plug gap of the secondary plug is generally 0.7 to 0.9 m There was 1.1~
Measures were taken to widen the flame to 1.5 ribs, and in fact this significantly improved ignition performance.

However, widening the electrode gap as described above increases the spark voltage between the electrodes almost in proportion to the gap length, which requires a special ignition power source, such as a transistor ignition power source. This may force system design changes and increase costs.

Therefore, attempts were made to coat the tip of the electrode with ceramic or other refractory materials with the intention of alleviating the flame-extinguishing effect of the center electrode and improving ignitability without increasing the discharge voltage. Due to the large difference in expansion coefficients, satisfactory results are not always achieved.

On the other hand, so-called resistor-containing plugs, in which a resistor is inserted or formed inside the shaft hole of the porcelain insulator, suppress the noise radio waves generated when the spark discharges from a spark plug. It is widely used in the United States in particular, and the demand for it is increasing domestically as well.In Canada, among other countries, strong radio wave regulations have been adopted in earnest since September 1977. 1
Resistor-containing plugs with high noise prevention effects up to a high frequency band of about 1,000 MHz are now required.

By the way, in order to increase the noise prevention effect at high frequencies, it is important to place the inserted resistor as close to the ignition point as possible, and it has been found that forming a resistive film on the electrode surface itself is most effective. . Regarding this point, the inventor conducted the following experiment to investigate the cause. When a new spark plug was installed in the engine and the noise level was measured according to the prescribed measurement method, it was discovered that when the measurement was performed again after a period of time had passed, the noise level had significantly decreased. Ta.

Therefore, we applied carbon to the new spark plug electrode.
When I quickly measured it using this, the noise level was significantly reduced.

In other words, although there is no carbon on the electrode surface when it is new,
After the spark plug is installed in the combustion chamber and operated, it becomes contaminated with carbon, and this carbon contributes to lowering the noise level.

Therefore, as a result of forming various resistance films on the discharge surface and similarly measuring the noise level, it was found that the higher the surface resistance, the lower the noise level. That is, if there is a resistive film on the discharge surface itself, this resistive film will particularly remove high frequency components.

However, such carbon and resistive films are immediately oxidized and destroyed by powerful spark energy and high-temperature flames, and have no durability at all.

As a result of detailed research into the process of oxidation loss in order to obtain a highly durable and stable resistive film, it was confirmed that this oxidation loss is caused by exposure to flame at high temperatures, and furthermore, sparks It was also discovered that the effect of electrical discharge was surprisingly small.

Therefore, since flame is the cause of oxidation loss at high temperatures, we decided to consider materials that are less affected by flames.

Now, since ceramic materials have good properties at high temperatures and are widely used as insulating materials, I wonder if this ceramic material can't be used as it is as an electrode for spark plugs?
In addition, as a result of detailed research into whether it is possible to make this ceramic itself conductive, we succeeded in making it conductive using the method described below. Because the specific heat is small, the flame-extinguishing effect is reduced, and in addition, the electrode surface itself has a resistance component, so the noise level is also significantly lower, making this a completely new spark plug that exhibits excellent effects that cannot be expected with metal electrodes. I was able to propose this here.

That is, this invention involves the steps of forming an insulator base of high alumina porcelain into a bottomed hollow shape with the tip of the ignition part of the spark plug insulator porcelain closed, and then calcining the insulator base to create an unglazed firing; By placing a chip of conductivity-imparting material in the bottom of the hollow hole and heating it to the normal sintering temperature,
A method for manufacturing a closed-end porcelain spark plug insulator, which combines the steps of forming a ceramic electrode impregnated with the conductivity imparting substance at the tip of the ignition part of the spark plug insulator porcelain, and at the same time proceeding with the formation of the porcelain. .

Here, the conductivity-imparting substances include Cu, Fe, Mm, and C.
Metals of one or more of O, Cr, Ti, and La, alloy chips, and oxide semiconductor powders of the above metals are suitable.

Next, referring to a diagram of a closed-end porcelain spark plug according to the present invention,
A comparison will be made with a conventional spark plug having a metallic center electrode.

FIG. 1 shows a secondary ignition plug, particularly a resistor-containing ignition plug, in half section, and FIG. 2 similarly illustrates a preferred embodiment of the present invention.

The conventional plug shown in FIG. 1 has a center electrode 1 made of Ni alloy, and a terminal electrode 4 connected to this via a semiconducting sealing material 2 and a resistive material 3, both inside a rattan hole of a hollow insulator 5 made of insulating porcelain. In the figure, 6 is an outer electrode, and 7 is a metal shell.

On the other hand, the spark plug insulator 5' of the present invention shown in FIG. 2 is combined with a metal shell 7 similar to that shown in FIG. It has a hollow shape and is characterized by having a ceramic electrode 1' formed by infiltration of a conductive substance at its tip instead of the center electrode 1. Therefore, the back surface of this ceramic electrode 1', that is, the bottom of the hollow hole. The resistance material 3, which can be placed directly on the inner surface of the end, can be connected to the insulating terminal electrode 4 using a sealing material 2 or the like.

In the spark plug according to the present invention, there is no need for the center electrode g to protrude from the tip of the insulator, so even if the electrode gap g is the same as that of the conventional plug, the specific heat and thermal conductivity of the material constituting the ceramic electrode 1' that controls discharge Due to the significant difference in the properties of the ceramic electrode 1' with respect to the metallic center electrode 1, the quenching effect is advantageously reduced and the ignitability is improved, and the ceramic electrode 1' itself has a large surface resistance, thereby preventing spark discharge. In addition to being able to advantageously prevent noise during spark plug insulator 5', the hollow hole in the spark plug insulator 5' is a blind hole and no seal is required, which simplifies the structure of the spark plug and the manufacturing process. can also be easily realized.

In the present invention, high alumina porcelain can be used as the spark plug insulator porcelain in the same manner as in the prior art.

It is most convenient to use oxygen-free Cu as the conductive material for forming the ceramic electrode 1' at the tip of the ignition part of the ignition plug insulator porcelain.

After considering this, we found that in addition to Cu, Fe
, Cr, Co, Mn, Ca, Tj, and La, alloy chips, and oxide semiconductors of these metal elements have been confirmed to exhibit the same effect. Further, it was confirmed that the thickness of the firing end of the ceramic electrode was within the range of 0.2 to 2.0 Yanagi to meet the purpose of the present invention.

Furthermore, it has been confirmed that when the resistance value of the electrode is in the range of 0.1 to 10 .mu.MQ, it exhibits an effective noise prevention effect without increasing the spark discharge voltage.

As for the resistor 3 which is sealed and formed in the hollow hole of the plug insulator in direct contact with the ceramic electrode 1', the following materials used in conventional resistor-containing spark plugs can be used as they are.

4 parts by weight of barium shelf acid glass, 6 parts by weight of zirconia powder, and glycerin
Add 1 to 4 parts by weight (after carbonization) of the mixture to 1 to 4 parts by weight of TIC, Ti02, NQ05, etc. as resistance stabilizing components.
The composition is 1 part by weight, but depending on the case, metal powder such as Fe-B or aggregate such as Sj3N4 may be mixed.

Furthermore, in order to improve heat resistance, glass containing A203 and Si02 may be used. By the way, when looking at the existing technology of spark plugs, in addition to using a metal center shaft made of Ni alloy, W, or Pt as the center electrode as in the general conventional spark plug mentioned above, the center electrode is also made of a non-metallic semiconductor. There are various ideas for forming electrodes using materials, such as electrodes formed by adding metals such as Pt, Ni, Cr, and W or metal carbides such as SIC and WC to ceramics such as alumina, clay, and glass, and electrodes made of oxide semiconductors. It is.

However, these electrodes generally need to be made in a separate process from the spark plug insulator, which is made of high alumina porcelain, and must be combined with the spark plug insulator and further bonded in a process similar to that of conventional metal koji. However, in this case, it is extremely troublesome to manufacture and has not been put into practical use due to problems such as instability of performance. Other attempts have been made to form electrode parts at the same time as the porcelain is formed, but in this case, the forming conditions are difficult to match the conditions for producing semiconductor ceramics, so it is difficult to achieve the desired goal. was difficult to obtain.

We have thoroughly considered this problem and continued research on a method to easily create a ceramic electrode with low resistivity.As a result, we have found that the electrode part is attached to the tip of the firing part of insulated porcelain, as previously thought. Rather than making it from a separate material, we have developed a method in which it is integrated with porcelain, and only the tip of the ignition part of the porcelain is made into a semiconductor in the process of joining the porcelain.

The method is to mold the ignition plug's insulator porcelain into a thin bag-like hollow shape at the tip of the ignition part using a high alumina porcelain insulator base, and then heat the ignition plug with metal at the bottom of the hole during bisque firing with temporary phosphorus. This method involves infiltration in the form of an oxide semiconductor and competitive bonding, and at the same time as this sintering, the desired ceramic semiconductor ferrule was formed, making it possible to create a new plug insulator. An example of implementing this invention is shown in FIG.

That is, a hollow structure element 8 with a bag-shaped tip of the firing part is press-molded from a high alumina insulator base material, and this is
At 0xlh, the pieces were temporarily placed in an unglazed state. In contact with the inner surface of the closed bottom 10 of the unglazed central hole 9, as shown in Fig. 4a, 0.05% oxygen-free steel (99.9%) is applied.
A lumpy chip 11 was placed in the chamber, and with the lumpy chip 11 enclosed, the temperature was raised to 1,600qo at a heating rate of 80 qo and then cooled. Using. By this heating, the lumpy chip 11 is gradually oxidized from the surface as shown in FIG. 4b, and the melting point is about 110
At 0:00, it melted and penetrated into the pores of the bisque as shown in Figure 4c. Here, the leakage of molten copper (Weta
Looking at the contact angle, copper leaks very easily from the inner surface of the bisque in the air, and furthermore, part of the oxidized surface becomes Cu○, C0 and reacts with alumina, forming spinel. form.

Here, in the process from FIG. 4b to FIG. 4c, that is, around 1000 oo, the unglazed heating sintering reaction does not proceed sufficiently, so it remains quite porous, and copper easily penetrates.

In this way, it is particularly effective to use bulk Cu chips to cause impregnation in the form of Cu, Cu20, and Cu○ into the alumina porcelain that has been sintered as shown in Figure 4d. On the other hand, if the same steel is in powder form, the specific surface area is too large and oxidation progresses quickly, resulting in almost 0 and ○, so it is difficult to reduce the specific resistance sufficiently by penetrating into the alumina. be.

The spark plug insulator porcelain created by simultaneous sintering of the ceramic electrode and the spark plug insulator in this way has a thickness of 0.1 when the thickness of the ceramic electrode 1' is set to the 0.5 side.
I was able to keep it within the range of MQ to insect MO.

However, when this resistance exceeds 10 MQ, the electrode no longer functions as a semiconductor, and during use of the ignition plug, it suffers through-hole damage, rendering the electrode useless. It is extremely easy to fill the hollow hole of the above-mentioned plug insulator with the resistor powder 3 by the same method as before, pressurize it, and further heat it to form a resistor-filled plug. Filled with 0.4 ta of semi-solid resistance material made of glass, semiconductor material, metal powder, and carbon, it was heated at 900 to 1000°C for about 1
After heating for 0 minutes, the terminal shaft 4 was pressed from above to seal.

In this example, the terminal shaft 4 is spaced five distances from the bottom 10 in consideration of heat dissipation between the terminal shaft 4 and the insulator.

The ignition plug in which this assembled body was attached to the metal shell 7 as shown in Fig. 2 was subjected to a JRTC prescribed test together with the secondary type resistor-filled ignition plug shown in Fig. 1, and the noise electric field strength was compared and measured. It is shown in Figure 5.

The results shown in Figure 5 are data obtained with a two-cylinder 125cc four-stroke engine. Furthermore, the results of comparing the ignitability are shown in FIG. Figure 6 shows a conventional plug with a gap of 0 for a 2000cc, 4-cylinder electronic fuel injection engine for a passenger car.
．． The relationship between the air-fuel ratio and ignition errors was investigated using 8 sails and 1.1 pigs, and the plug of the present invention was set to 0.8 legs, and is shown as a solid line and a broken line, respectively. As shown in FIGS. 5 and 6, the spark plug having the ceramic semiconductor electrode of the present invention has significantly lower noise electric field strength than conventional spark plugs, exhibits a remarkable prevention effect, and has improved ignition performance. The electrode gap of the conventional spark plug is 1.
It has been found that an effect equivalent to that of side 1 can be obtained with a sail gap of 0.8 in this invention.

As mentioned above, in this invention, the entrance of the hollow hole at the tip of the firing part of the insulating porcelain is abolished, and a ceramic electrode is formed by locally penetrating the conductive substance into the relatively thin bottom part of the closed hole. By forming it during the development of porcelain, it is possible to advantageously achieve the desired improvement in ignitability and durability, as well as a reduction in noise level.

Thus, according to the present invention, the ignitability of the spark plug is improved;
It is possible to advantageously manufacture a closed-end porcelain spark plug insulator that can advantageously improve durability and reduce noise all at once.

[Brief explanation of the drawing]

Fig. 1 is a side view showing a secondary spark plug in cross section, Fig. 2 is a side view of the same according to an embodiment of the invention, Fig. 3 is a sectional view of the spark plug insulator of the invention, and Fig. 4a Figure ~ 4b
The figure is an explanatory diagram of the procedure for forming the discharge electrode, and FIGS. 5 and 6 are effect diagrams. 1'... discharge electrode, 5' porcelain insulator. Figure 1 Figure 2 Figure 3 Figure 4a Figure 4b Figure 4c Figure 4d Figure 5 Figure 6

Claims (1)

[Claims] 1. A stage of forming an insulator base of high alumina porcelain into a bottomed hollow shape with the tip of the ignition part of the spark plug insulator porcelain closed, and then calcining it to create a bisque; A chip of conductivity-imparting material is placed in the
By heating to a normal sintering temperature, a ceramic electrode impregnated with the conductivity imparting substance is formed at the tip of the ignition part of the spark plug insulator porcelain, and at the same time, the porcelain is sintered. A manufacturing method for a closed-end porcelain spark plug insulator.