JPH077691B2 - Spark plug for internal combustion engine - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a spark plug for an internal combustion engine, and more particularly to a wide range spark plug having improved heat resistance and stain resistance.

(Prior Art) Among the components of a conventional spark plug, a metal shell with a screw for mounting to an engine is made of carbon steel, and an insulator having a center electrode inside is made of alumina porcelain. The physical properties of the spark plug, especially its thermal conductivity, determine the thermal performance of the spark plug, that is, heat resistance, which is the resistance to pre-ignition on the high-temperature side, and resistance to smoldering due to carbon adhesion on the low-temperature side. It had been.

(Problems to be Solved by the Invention) By the way, in recent years, there has been a demand for a wide-range spark plug in which the performance of the spark plug is further improved in accordance with the high performance of the engine such as high output and low fuel consumption.

This invention is intended to improve the heat resistance, which is the thermal performance of the spark plug, by using a material with good thermal conductivity for the metal shell and the insulator, and also to lower the insulator temperature which is the starting point of preignition. This makes it possible to design a longer insulating path, improve smoldering stains on the low temperature side, and provide a spark plug having airtightness and strength as a plug.

(Means for Solving Problems) The present invention relates to a spark plug in which an insulator containing a center electrode is surrounded by a metal shell having a mounting screw, wherein the metal shell is made of a Cu alloy or an Al alloy, and Its tensile strength is 40 to 150 kg / mm ² , thermal conductivity is 0.30 to 0.8 cal / cm ・ sec ℃
Formed from a material that has undergone solution treatment, or this metal shell and the insulator further have a thermal conductivity of 0.20 to 0.59 cal / cm.
-It is a spark plug formed from a material with sec ℃, withstand voltage of 10 to 17 kv / mm, and bending strength of 15 to 50 kg / mm ² .

(Operation) This invention is applied to the metal shell material with the above-mentioned thermal conductivity of 0.30 to 0.8 cal.
/ cm ・ sec ℃, preferably 0.3 ~ 0.8cal / cm ・ sec ℃ Cu alloy or Al alloy, the conventional carbon steel (S10C
However, if the pure copper material has a low tensile strength, sufficient strength cannot be ensured due to insufficient strength when the insulator is assembled, but the above materials cannot be treated by solution treatment (aging treatment). the tensile strength by performing processing) 40 kg / mm ² or more, preferably to eliminate the problem that such by a 40~150kg / mm ^2, can also comprise a sufficient air tightness in the actual machine.

Further, according to the present invention, the withstand voltage against high voltage of the insulator material assembled to the metal shell is 10 kv / mm or more, preferably 14 to 17 k
v / mm is required, the strength is 15 kg / mm ² or more as a minimum that does not cause damage during the assembly of the metal shell, preferably required flexural strength of 15~50kg / mm ^2, further Thermal conductivity is 0.20 cal / cm ・ sec ℃ or more, preferably 0.2-0.59 cal / cm
・ Sec ° C is required, and heat resistance is not improved at less than 0.20 cal / cm ・ sec ° C. The plug of the present invention has improved heat resistance in the metal shell and the insulator, and due to the improvement, the leg length of the insulator (distance 1 from the tip surface to the step of the metal shell) is lengthened to lengthen the insulating path. Therefore, the stain resistance can be improved, and a spark plug having a wide range as a whole can be obtained.

The upper limit of the numerical value indicates the upper limit of the characteristics of the material.

(Examples) The present invention will be described below with reference to examples of the drawings.

FIG. 1 is a spark plug showing an embodiment of the present invention, in which 1 is a center electrode made of a nickel alloy having a copper core 1a arranged therein, 2 is an insulator, and the center electrode 1 is provided at a tip portion of the shaft hole 2a. The center electrode flange 1b is inserted into the stepped portion 2b, and the resistor 4 is sandwiched between the conductive glass 3 and the terminal electrode 5 to seal the center electrode flange 1b. is there. Reference numeral 6 denotes a metal shell equipped with a mounting screw 6a for the engine. A packing 7 is placed on a stepped portion 6b of the inner cavity of the metal shell, and the insulator 2 is inserted and locked, and the upper end 6c of the metal shell 6 is fixed. It is a spark plug which is fixed by a known method of swaging inward and has a spark gap 9 in the air formed between the outer electrode 8 joined to the upper end 6d of the metal shell and the center electrode 1. Next, the plug performance when good thermal conductivity is used for the metal shell material and the insulating material will be described.

As the metal shell material, there are copper alloys of samples A to G shown in Table 1 and aluminum alloys of samples H to K shown in Table 2. Of these, the copper alloys of the present invention are aluminum alloys of samples A to F. The alloys can satisfy the thermal conductivity and tensile strength of the I and K samples. That is, three spark plugs (BPR5ES) of the related art were prepared for comparison with the spark plug of the present invention, which was formed of F and K samples as a representative of the metal shell materials using an alumina insulator, and a heat resistance test was conducted. The test was performed by using a 4-cylinder 2000cc engine and varying the ignition advance angle. As a result, as shown in FIG. 2, the plugs F and K of the present invention were able to improve the heat resistance of 2.5 ° to 7.5 °. The copper alloy and the aluminum alloy can be improved in tensile strength by solution treatment (aging treatment).

In addition, this invention uses samples I to V shown in Table 3 as insulators.
BeO and AlN have better thermal conductivity, dielectric strength, and bending strength than conventional Al ₂ O ₃ materials. The same heat resistance test was conducted for the case where the copper alloy metal shell of the F sample and the metal shell using the conventional steel material (S10C) were combined with this insulator without causing ceramic damage. As a result, as shown in FIG. 3, the combination of the AlN insulator having good thermal conductivity and the Cu metal shell showed a remarkable effect more than the combination of the steel metal shell. Therefore, as shown in Fig. 4, the insulator leg length is changed from l ₁ to
to l ₂ can cursory, it is possible to obtain a spark plug having a wide range from excellent fouling resistance by appropriately selecting the dimensions. The stain resistance test is a combination of racing-idling-vehicle speeds of 15 km / H and 35 km / H, which is evaluated as a stain cycle when the engine cannot be stopped or restarted as one cycle.

Further, as shown in FIG. 5, the spark plug of the present invention has a tip end small hole 12c of a leg portion 12a of a green body of an insulator of BeO, AlN.
Pt or Pt such as Pt-Ir, Pt-Ph, etc.
A thin wire made of an alloy is inserted, this is sintered together with an insulator to form a center electrode 11, an intermediate electrode 13 is connected to the center electrode, and a conductive glass 3 is sealed. This is a spark plug in which the insulator 12 is combined with the copper alloy or aluminum alloy metal shell 6 shown in Tables 1 and 2. In general, a spark plug in which an insulator and a center electrode are integrally sintered has a lower thermal conductivity than the center electrode with a copper core shown in FIG. In the present invention, such a drawback can be compensated by using an insulator and a metal shell having good thermal conductivity in combination, and the heat resistance can be improved even if the diameter of the insulator is reduced due to the thin center electrode. This is useful for small plugs with a mounting screw diameter of 10 to 8 mm.

The present invention is not limited to the spark plugs of the embodiments, but can be applied to various discharge shapes such as a semi-creeping discharge plug and a full creeping discharge plug within the scope of the present invention.

(Effects of the Invention) As described above, the spark plug of the present invention has a tensile strength of 40 kg / mm ^{2 when} the metal shell material is subjected to solution treatment with good thermal conductivity (0.3 to 0.8 cal / cm · Sec ° C). By forming it from a copper alloy or an aluminum alloy having, it is possible to improve the heat resistance by maintaining the airtightness, and it is also possible to improve the fouling resistance because the insulator leg length can be lengthened by the heat resistance improvement. A spark plug with a wider range can be obtained as compared with a conventional metal shell of low thermal conductivity using carbon steel. In addition, the above metal shell has an insulator with good thermal conductivity (0.2 to 0.59 cal / cm · Sec ° C) and withstand voltage of 10 to 17 kv / m.
By combining materials with m and bending strength of 15 to 50 kg / mm ² , heat resistance and stain resistance can be further improved, flashover resistance can be prevented, and insulator when assembling the insulator It is possible to prevent damage to the plug and maintain stable plug performance. And since it has such performance, it is especially useful for a small plug having a small mounting screw diameter.

[Brief description of drawings]

FIG. 1 is a front view showing a half cross section of a typical spark plug of an embodiment of the present invention, and FIG. 2 is a graph showing heat resistance when using an Al ₂ O ₃ insulator and various metal shell materials, Fig. 3 is a graph showing the heat resistance when a carbon steel or copper alloy metal shell is combined with an AlN, BeO insulator, and Fig. 4 is a graph showing the relationship between the insulator leg length and stain resistance, Fig. 5 FIG. 6 is a sectional view of an ignition part of a spark plug showing another embodiment of the present invention.

Claims (3)

[Claims] 1. A spark plug in which an insulator containing a center electrode is surrounded by a metal shell having a mounting screw,
The metal shell is made of Cu alloy or Al alloy, and its tensile strength is 40 to 150 kg / mm ² , thermal conductivity is 0.30 to 0.8 cal / cm ・ sec.
A spark plug for an internal combustion engine, characterized by being subjected to a solution treatment at ℃. 2. A spark plug in which an insulator containing a center electrode is surrounded by a metal shell equipped with a mounting screw,
The metal shell is made of Cu alloy or Al alloy, and its tensile strength is 40 to 150 kg / mm ² , thermal conductivity is 0.30 to 0.8 cal / cm ・ sec.
It is made of a material that has been subjected to solution treatment at ℃, and the insulator has a thermal conductivity of 0.20 to 0.59 cal / cm ・ sec ℃ and a withstand voltage of 10 to 1
7kv / mm. A spark plug for an internal combustion engine, which is made of a material having a bending strength of 15 to 50 kg / mm ² . 3. The spark plug for an internal combustion engine according to claim 2, wherein the center electrode and the insulator are integrally sintered.