JPS6148223B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a built-in electrode type spark plug.

This is an attempt to propose an improvement to a spark plug that can advantageously improve the durability and ignitability of the spark plug, and in addition can advantageously contribute to reducing the noise level caused by the spark plug. .

In recent years, the purification of exhaust gas from automobiles has become an urgent matter, and so-called compliant cars with various exhaust gas countermeasures are actually being sold on the market.At the same time, radio noise mainly emitted from the ignition system of automobiles has been reduced by FM radio. With the spread of mobile hams and mobile hams, this is becoming more and more of a problem, and it is desired to establish countermeasures against these problems.

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. That is, the main problems are: 1. Mitigation of the flame-extinguishing effect generated at the center electrode of the ignition plug. 2. Suppression of noise current during spark discharge of the ignition plug.

Regarding item 1 above, since the flame-extinguishing effect of the center electrode leads to so-called misfires, current concrete measures to reduce this are widening the electrode gap, for example, the conventional plug gap is 0.7
Measures have been taken to widen the range from ~0.9 mm to around 1.1 to 1.5 mm, and in fact, this significantly improves ignition performance. However, if the electrode gap is widened as described above, the spark voltage between the electrodes increases almost in proportion to the length of the electrode gap, so a special ignition system, such as a transistor ignition power supply, is required. There is a risk that this will require design changes and increase costs.

Therefore, with the intention of relaxing the quenching effect of the center electrode and improving ignitability without increasing the discharge voltage,
Attempts have been made to coat the tip of the center electrode with ceramic or other refractory materials, but this has not always yielded satisfactory results because of the significant difference in coefficient of thermal expansion between these coatings and metals.

On the other hand, regarding 2 above, 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 during spark discharge of the spark plug. It has been widely used in the United States in particular, and the demand for it is increasing domestically. Among other countries, Canada has implemented strong radio wave regulations in earnest in September 1977. This requires a plug with a resistor that is highly effective in preventing noise up to a high frequency band of around 1000MHz.

In this regard, numerous experiments have shown that it is useful to position the resistor inserted into the hollow shaft hole of the spark plug porcelain insulator as close to the ignition point as possible in order to increase the effect of preventing high-frequency noise. It became.

The present invention advantageously overcomes the problems in the prior art as described above, and achieves improved spark plug durability and ignitability, as well as a more useful reduction in noise level.

In this invention, the porcelain insulator of the spark plug has a bag-shaped hollow shaft hole with the tip of the ignition part facing the outer electrode closed, and in this hollow shaft hole, from the bottom, metal plates or metal A built-in device comprising a built-in electrode made of a sintered layer of powder or a mixture of metal powder and porcelain powder, a semiconducting resistor, and a terminal shaft, the terminal shaft being sealed in a hollow shaft hole. This is an electrode type spark plug, and the insulator here has a thick wall at the tip of the ignition part.
Preferably, it is in the range of 0.2 to 1.0 mm.

By the way, the wear of the center electrode in conventional spark plugs is usually 15,000 yen even when using highly corrosion-resistant metal materials such as Ni-based alloys, which are currently most commonly used.
Since the spark gap expands and the discharge voltage increases after driving for ~20,000km, the general useful life has been thought to be just under 20,000km. On the other hand, as mentioned above, attempts to coat the center electrode with ceramic or the like tended to cause peeling of the coating due to the difference in thermal expansion between the center electrode and the metal, and did not have much of an effect on increasing durability. It is.

In this invention, the durability of the spark plug is firstly enhanced by eliminating the exposed facing of the center electrode facing the outer electrode, which is made of a highly corrosion-resistant metal material and is indispensable in conventional general spark plugs. By eliminating its consumption, the ignitability can also be improved.
Similarly, by fundamentally eliminating the anti-inflammatory effect originating from the center electrode, this can be achieved all at once and effectively.

In other words, as described above, the porcelain insulator of the spark plug has a hollow shaft hole closed in a bag-like manner at the tip of the ignition part, and by providing a built-in electrode in this hollow shaft hole, the central electrode There is no need to use highly corrosion-resistant metal materials, and there is no risk of oxidation wear and tear, as would be the case when the spark plug is exposed to the high-temperature combustion atmosphere of the engine, thus greatly improving the durability of the spark plug. Also, the ignitability is significantly improved by eliminating the disadvantage of the anti-inflammatory effect caused by the center electrode itself.

Here, the built-in electrode located at the bottom of the hollow shaft hole that closes the ignition end of the spark plug porcelain insulator in a bag shape is closed by a high voltage of about 20kV applied between it and the outer electrode. As a result of the electric discharge penetrating the thickness of the tip of the firing part of the porcelain insulator housed in the hollow axial hole, extremely fine perforations are created, creating a discharge path with a fine hole diameter of about 50 to 100 μm.

This discharge path is
Since the generated voltage is 20 to 30 kV and the spark energy is about 20 to 50 mj, if the thickness of the tip of the ignition part of the porcelain insulator is 0.2 to 1.0 mm, it can be easily formed when using a spark plug. Of course, depending on the case, the holes may be pre-drilled at the plug manufacturing factory.

As mentioned above, this perforation is minute, so even if the flame generated during spark discharge is at high temperature and pressure, it will not pass through the pores of porcelain, which has much higher thermal conductivity than gas. The rapid cooling does not cause the built-in electrode in the hollow shaft hole to oxidize and wear out, and the flow of high-temperature gas generated by the ignition of the air-fuel mixture is effectively blocked, which also prevents the built-in electrode from being consumed by oxidation. It does not cause consumption and does not increase the required discharge voltage.

In this way, the spark energy generated by the spark discharge between the built-in electrode and the outer electrode, which are placed inside the bag-shaped hollow shaft hole with the tip of the ignition part of the porcelain insulator closed, can be used to ignite the air-fuel mixture. Therefore, the built-in electrode is virtually not exposed to the high temperature of the combustion generated gas, and there is no oxidation consumption due to this, and only the consumption of spark energy is much smaller than that, so the spark plug has a significantly longer lifespan. Furthermore, since the tip of the ignition part, which is exposed to combustion gas, is made of ceramic, which has a much lower thermal conductivity than metal, the quenching effect that occurs on the exposed center electrode is significantly alleviated, which should be seen as an improvement in ignitability. There is something.

Now, FIG. 1 shows a conventional type ignition plug with a so-called resistor, and FIG. 2 shows an embodiment of the ignition plug of the present invention.

In the figure, 1 is a porcelain insulator made of high alumina porcelain as a plug insulator, 2 is a terminal shaft inserted and fixed inside a hollow hole penetrated by the plug insulator 1, and 3 is an internal resistor. In 4 is
Exposed center electrode, typically made of Ni alloy;
5 and 5' are conductive sealing glasses.

As shown in Fig. 2, in the present invention, the plug insulator 1 is shaped like a bag with the tip of the firing part facing the outer electrode (see Fig. 3) 6, which is normally provided integrally with the metal shell to be combined with the plug insulator 1, closed with a thin bottom. It has a hollow shaft hole 7, and a built-in electrode 9 is placed at the bottom of the hollow shaft hole 7 so as to be in close contact with the bottom wall 8 at the tip of the thin firing part, and a semiconductor resistor 10 is placed on top of the built-in electrode 9. A terminal shaft 2 is disposed with a sealing glass 11 interposed therebetween. The conductive sealing glass 11 serves to seal the terminal shaft 2 inside the hollow shaft hole 7.

In this example, plug insulator 1 is made of high alumina porcelain (95
%AI ₂ O ₃ ) after press molding at approximately 1600℃
If the thickness of the bottom wall 8 at the tip of the ignition part becomes too thick by sintering, the discharge voltage required to form the discharge path will become high, so to avoid this,
In addition, in order to suppress the required voltage in spark discharge from increasing, it is most preferable to have a diameter of about 0.5 mm in consideration of ease of manufacture, and the withstand voltage in oil is approximately 15 kV/
mm, but when the spark gap between the metal shell and the ground electrode 6 is set to 0.7 mm after assembly, it is approximately 20 kV.
With a voltage of
A pore with a pore diameter of 50 μm was created.

As the semiconductor resistor 3, a composition similar to that used in conventional resistor-containing spark plugs is used, for example, in the following manner.

For example, the composition of the semiconductor resistor 10 is as follows.

Barium borate glass: 40 parts by weight Zirconia powder: 60 parts by weight Glycerin (after carbonization): 1 to 4 parts by weight One or more of TiC, TiO ₂ and Nb ₂ O ₅ as additives: 1 to 10 parts by weight Depending on the case In this case, metal powders such as Fe and B, and aggregates such as Si ₃ N ₄ may be included in the mixture, and AI ₂ O may be added as necessary to improve the heat resistance of glass as mentioned above. ₃ , SiO ₂ may be included.

Prior to encapsulating the semiconductor resistor 10, the built-in electrode 9
Precious metals with high heat resistance, such as Pt,
A small disk of a metal such as Cr, Ni or Fe or an alloy thereof or a sintered layer of powder of these metals or a mixture of powder and porcelain powder is placed at the bottom of the hollow shaft hole 7. The small disks or sintered layers are sealed with the hollow shaft hole 7 by the conductive sealing glass 11 by sequentially inserting the terminal shaft 2 thereon under pressure through the semiconducting resistor 3 .

The built-in electrode 9 is made of metal or alloy powder such as Pt, Cr, Ni, Fe, etc. in the hollow shaft hole 7 instead of a small disk so that it can be more closely joined to the inner surface of the tip wall of the firing part of the plug insulator 1. The plug insulator 1 may be filled and fired at the same time as the plug insulator 1 is fired.

In the latter case, the difference in thermal expansion between the metal and the porcelain may cause the plug insulator to crack during firing, so in order to avoid this, alumina similar to the porcelain base used for the plug insulator 1 is used. It is more preferable to mix the porcelain base powder in an amount of approximately 50% or less by volume and perform firing in the same manner. In this case, the metal or alloy powder forms a partial oxide film during firing to achieve strong adhesion with the alumina, and also to form a strong bond with the glass during subsequent sealing of the semiconducting resistor 3. When combined, a more durable spark plug is obtained.

The results of comparing the performance of the spark plug according to the present invention with that of a conventional spark plug are as follows.

(1) Durability In conventional spark plugs, the center electrode exposed in the high-temperature combustion atmosphere wears out, causing an increase in the electrode gap and an increase in the discharge voltage, which determines the useful life of the plug. In the case of the ignition plug, the wear of the built-in electrode is significantly reduced because oxidation wear, which is a major factor in electrode wear, is protected by the bottom wall at the tip of the closed ignition part. However, due to the lengthening of the discharge path by adding the thickness of the bottom wall at the tip of the firing part to the gap with the outer electrode, when comparing the spark gap with the spark gap of 0.7 to 0.8 mm as before, the discharge voltage when new is higher than that of the conventional product. One example of the results was as shown in FIG. 4.

The results shown in Figure 4 are a comparison of the maximum required voltage when accelerating from 40 km/h according to the distance traveled, using a passenger car equipped with a 2000 c.c. 4-cylinder engine.

(2) Ignitability The tip of the ignition part of the spark plug, which is exposed to combustion gas, has a higher temperature at 800 to 1000°C than the Ni-based alloy center electrode of the conventional plug.
Since the thermal conductivity is quite low at 1 to 2 x 10 ^-2 cal/cm・sec・℃, the flame-extinguishing effect of the spark is alleviated and the ignitability is improved. The test results were as shown in FIG. FIG. 5 shows the relationship between the air-fuel ratio and the ignition error rate using a 2000 c.c. four-cylinder electronic fuel injection engine, and compares the conventional plug with the plug of the present invention.

(3) Noise prevention effect Figure 6 shows the results of measuring the noise electric field intensity in accordance with the JRTC regulations, comparing the plug of the present invention with a sealed semiconducting resistor to a conventional resistor-containing spark plug. As shown, the noise level is significantly reduced because the semiconductor resistor is located closer to the firing point of the present invention.

During repeated experiments on the above-mentioned ignition plug, we found that the tip of the ignition part of the ignition plug was sometimes exposed to the semiconducting resistor 3 under severe test conditions, such as overheating due to premature ignition. Depending on the glass composition used, the elution may travel through the discharge path and form a bridge between it and the outer electrode 6.
It has been experienced that misfires may occur. It was found that it was necessary to use glass with a fairly high softening point, particularly over 900°C.

In other words, the above compositional combination is also useful as a means for preventing the above-mentioned elution, which is a concern when using a glass composition of the semiconducting resistor 3 having a low softening point that is particularly advantageous in terms of workability.

As described in detail above, in the spark plug according to the present invention, the built-in electrode is protected by the bottom wall of the ignition part tip of the porcelain insulator, so wear and tear on the built-in electrode is significantly reduced, and it can be used for a long period of time. Also, the increase in discharge voltage is much smaller than with conventional exposed metal center electrodes, and durability can be improved. Similarly, since the heat conduction of the ignition part is lower than that of conventional metal center electrodes, the extinguishing effect of the spark is alleviated and the ignitability is improved. Furthermore, since the semiconducting resistor is enclosed in a position closer to the ignition part, remarkable effects such as excellent noise prevention effects can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the electrode structure of a conventional spark plug, FIG. 2 is a similar cross-sectional view showing an embodiment of the spark plug of the present invention, FIG. 3 is a partially detailed view of FIG. 2, and FIG. is a durability performance comparison graph, FIG. 5 is an ignition performance comparison graph, and FIG. 6 is a noise reduction effect comparison graph. DESCRIPTION OF SYMBOLS 1...Porcelain insulator, 2...Terminal shaft, 6...Outer electrode, 7...Hollow shaft hole, 8...Bottom wall at the tip of firing part, 9...Built-in electrode, 10...Semiconductor resistor .

Claims (1)

[Scope of Claims] 1. The porcelain insulator of the spark plug has a bag-shaped hollow shaft hole with the tip of the ignition part facing the outer electrode closed, and within this hollow shaft hole, the metal A built-in electrode made of a plate or a sintered layer of metal powder or a mixture of metal powder and porcelain powder, a semiconducting resistor, and a terminal shaft are arranged, and the terminal shaft is sealed in the hollow shaft hole. Built-in electrode type spark plug. 2. The spark plug according to claim 1, wherein the thickness of the tip of the porcelain insulator firing portion is 0.2 to 1.0 mm.