JP4070228B2 - Manufacturing method of spark plug - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a spark plug.
[0002]
[Prior art]
In many spark plugs used in an internal combustion engine such as an automobile engine, a ground electrode (also referred to as an outer electrode by those skilled in the art) that forms a spark discharge gap with a center electrode has recently been developed. As the output increases, problems such as breakage tend to occur. The cause is considered to be resonance due to engine or combustion vibration and high acceleration (G).
[0003]
[Problems to be solved by the invention]
Therefore, in order to ensure the durability of the ground electrode in a harsher environment, a heat-resistant alloy such as Inconel 600 (trade name of Inco Corporation in the UK) is also used as the material. In view of preventing breakage, there is a problem that the strength is not always sufficient. This is because the ground electrode is bent so that the tip side faces the center electrode side, so that a bending moment is likely to act on the base end side attached to the metal shell, and the shock wave accompanying combustion is directly received. This is probably because it is attached to the position. Although there is a method of increasing the bending rigidity by increasing the material cross-sectional area of the ground electrode, there are limitations due to various restrictions. For example, when increasing the thickness of the material in the electrode bending direction, if the thickness of the metal shell on the outer surface of the mounting screw is too large, when the spark plug is mounted on the cylinder head, the thread of the plug hole and the ground electrode In some cases, the base end portion of the base plate may interfere with normal attachment. On the other hand, if the thickness of the metal shell on the inner surface side of the mounting screw portion is excessively increased, the inner surface of the electrode base end portion is too close to the center electrode, and sparks are likely to occur. In addition, if the thickness of the ground electrode is excessively increased, depending on the position of the spark plug, the ground electrode may prevent the inhaled mixture from flowing into the spark discharge gap, thereby significantly reducing ignitability. .
[0004]
The subject of this invention is providing the manufacturing method of the spark plug which can ensure the intensity | strength with respect to a breakage etc. enough, without making the raw material thickness of a ground electrode so large.
[0005]
[Means for solving the problems and actions / effects]
In order to solve the above problems, a method for manufacturing a spark plug of the present invention includes:
A center electrode, an insulator provided outside the center electrode, a metal shell made of carbon steel provided outside the insulator, one end side coupled to the metal shell, and the other end side of the center electrode A ground electrode that is disposed so as to face the tip and forms a spark discharge gap with the center electrode, and at least a surface layer portion of the ground electrode is 20 at the center of the R-shaped bent portion on the electrode side surface. A Vickers hardness measured at ℃ is 265 to 1300, and a spark plug manufacturing method comprising a metal having a Vickers hardness of 60 to 200 measured at 730 ° C,
As the metal constituting at least the surface layer portion of the ground electrode, the Ni content is 9 to 83% by mass, the total content of Fe and Ni is 50 to 83% by mass, Cr, Mo, W and Using Ni-base heat-resistant alloy or Fe-base heat-resistant alloy containing 16 to 49% by mass in total of one or more types of Co and containing 1 to 10% by mass of one or both of Al and Ti,
One end side is coupled to the metal shell, and at least the surface layer portion is made of the Ni-base heat-resistant alloy or the Fe-base heat-resistant alloy, and the other end side is bent sideways while locally heating with a laser beam. It includes a heat bending process for processing.
[0007]
As a result of intensive studies by the present inventors, the use of a metal having a Vickers hardness of 220 or more measured at 20 ° C. as the material of the ground electrode can break the electrode even if the internal combustion engine to be mounted has a high output. Can be suppressed very effectively, and as a result, sufficient strength against breakage can be ensured without increasing the material thickness of the ground electrode so that the life of the electrode can be extended. It becomes.
[0008]
The ground electrode may be entirely composed of the above-described high-hardness metal, or a metal material for heat dissipation (a metal having a lower hardness than a high-hardness metal, such as Cu or Cu alloy) may be used inside. In the case of disposing, only the main part including the surface layer part (the part occupying 50% or more by volume ratio) may be made of a high-hardness metal.
[0009]
In addition, at least the portion of the high-hardness metal constituting the surface layer portion of the ground electrode has a temperature of 20 ° C. in a state where the spark plug is not used (a state in which the heat history associated with the use of the spark plug is not yet applied). It is sufficient that the Vickers hardness measured by measuring 220 or more is secured. The high hardness metal preferably has a Vickers hardness measured at 20 ° C. of 265 or more, and is measured at 730 ° C. in consideration of the actual use environment in which the spark plug is heated. It is preferable to use a metal material having a Vickers hardness of 60 or more, preferably 100 or more. On the other hand, when the Vickers hardness at room temperature exceeds 1300, the ductility of the material is insufficient, and when a strong impact is applied, such as when a spark plug is attached, breakage or the like may easily occur. Therefore, it is preferable to select a material having a Vickers hardness of 1300 or less, more preferably 1200 or less. In addition, in this specification, Vickers hardness means what was measured with the test load of 300 gf in the micro Vickers hardness test method prescribed | regulated to JIS: Z2244.
[0010]
As the metal material, specifically, a Ni-base heat-resistant alloy or a Fe-base heat-resistant alloy having a composition that can ensure the Vickers hardness level after processing can be selected and used. The Ni-base heat-resistant alloy is a heat-resistant alloy containing Ni as a main component, and the Fe-base heat-resistant alloy is a heat-resistant alloy containing Fe as a main component. Further, the “main component” means a metal element component having the highest content rate.
[0011]
In addition, the conventional spark plug uses a metal material that is not so strong at room temperature, such as pure Ni or Inconel 600, but such a metal material generally has a relatively large deformability at room temperature. The bending of the electrode was also performed cold. However, a metal material having a high hardness at room temperature as in the present invention has a low deformability, which may cause a problem such as a work crack in cold working, or a gap adjustment accuracy may decrease due to a large spring back. is there. Therefore, in the spark plug manufacturing method of the present invention, by heating the ground electrode, it is smooth and less likely to be defective while using such a high-hardness material, and the gap adjustment accuracy is reduced due to the spring back. Small bending is possible. In addition, when using Ni-base heat-resistant alloy or Fe-base heat-resistant alloy etc., the standard of processing temperature is about 600-900 degreeC. Further, in order to ensure that bending can be performed by raising the temperature, it is desirable to use a metal having a Vickers hardness of 200 or less measured at 730 ° C. as the ground electrode material.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, some embodiments of the present invention will be described with reference to the drawings.
A spark plug 100 with a resistor as an example of the present invention shown in FIG. 1 has a cylindrical metal shell 1, an insulator 2 fitted into the metal shell 1 so that the tip portion protrudes, and a tip portion protruded. In this state, a center electrode 3 provided inside the insulator 2, a ground electrode 4 and the like that are disposed so that one end is coupled to the metal shell 1 and the other end faces the tip of the center electrode 3. A spark discharge gap g is formed between the ground electrode 4 and the center electrode 3.
[0013]
The insulator 2 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride, and has a through-hole 6 for fitting the center electrode 3 along its own axial direction. A terminal fitting 13 is inserted and fixed on one end side of the through hole 6, and the center electrode 3 is inserted and fixed on the other end side. A resistor 15 is disposed between the terminal fitting 13 and the center electrode 3 in the through hole 6. Both ends of the resistor 15 are electrically connected to the center electrode 3 and the terminal fitting 13 through the conductive glass seal layers 16 and 17, respectively.
[0014]
The metal shell 1 is formed in a cylindrical shape from a metal such as carbon steel, and constitutes a housing of the spark plug 100. On the outer peripheral surface thereof, there is a screw portion 7 for attaching the plug 100 to an engine block (not shown). Is formed. In addition, 1e is a tool engaging part which engages tools, such as a spanner and a wrench, when attaching the metal shell 1, and has a hexagonal axial cross-sectional shape. On the other hand, between the inner surface of the rear opening of the metal shell 1 and the outer surface of the insulator 2, it engages with the rear edge of the flange-shaped protrusion 2 e formed at the intermediate position in the longitudinal direction of the insulator 2. A ring-shaped wire packing 62 is disposed, and a ring-shaped packing 60 is disposed on the further rear side through a filling layer 61 such as talc. Further, the opening edge on the rear side of the metal shell 1 is crimped inward toward the packing 60 to form a crimped portion 1 d, and the metal shell 1 is fixed to the insulator 2.
[0015]
Further, a gasket 30 is fitted into the base end portion of the threaded portion 7 of the metal shell 1. The gasket 30 is a ring-shaped part formed by bending a metal plate material such as carbon steel. By screwing the screw portion 7 into the screw hole on the cylinder head side, the flange-shaped gas seal portion 1f on the metal shell 1 side. Between the screw hole and the periphery of the opening of the screw hole, it is deformed so as to be compressed and crushed in the axial direction, and serves to seal the gap between the screw hole and the screw part 7.
[0016]
Even when the ground electrode 4 is applied to a high-power gasoline engine, at least the surface layer, in the present embodiment, the entire Vickers hardness is measured at 20 ° C. so that problems such as breakage can be avoided. The length is 220 or more, preferably 265 or more. As the metal, a material having a Vickers hardness at 730 ° C. of 60 or more, more preferably 100 or more is selected.
[0017]
Specifically, the metal as described above is composed of a Ni-based heat-resistant alloy or a Fe-based heat-resistant alloy whose composition is adjusted so as to have the hardness level. For example, in the precipitation strengthening type material, the content of Ni is 9 to 83% by mass, the total content of Fe and Ni is 50 to 83% by mass, and one of Cr, Mo, W, and Co or Ni group containing 16 to 49% by mass in total of 2 or more types (hereinafter referred to as oxidation resistance-imparting components) and 1 to 10% by mass of one or both of Al and Ti (hereinafter referred to as precipitation forming components) A heat-resistant alloy or Fe-based heat-resistant alloy can be used. This material contains Ni and Al and / or Ti in the above composition range, so that a fine intermetallic compound such as Ni ₃ Al or Ni ₃ Ti is mainly composed of Ni or Fe by appropriate heat treatment. Disperses and precipitates in the matrix, improving high-temperature strength.
[0018]
When the Ni content is less than 9% by mass, the amount of precipitates that can contribute to dispersion strengthening is insufficient. When the Ni content exceeds 83% by mass, the content of the oxidation resistance-imparting component is insufficient and the high-temperature oxidation resistance is poor. May be sufficient. On the other hand, if the content of the oxidation resistance-imparting component is less than 16% by mass, the high-temperature oxidation resistance becomes insufficient, and if it exceeds 49% by mass, the strength and workability may be reduced. Further, if the precipitation forming component is less than 1% by mass, the amount of precipitates that can contribute to dispersion strengthening is insufficient, and if it exceeds 10% by mass, the material may become brittle. Further, if the total content of Fe and Ni is less than 50% by mass, it is difficult to ensure the required strength. If the total content exceeds 83% by mass, the content of the oxidation resistance imparting component is insufficient and the high temperature oxidation resistance is insufficient. It may become.
[0019]
Among the Ni-base heat-resistant alloys having the above composition, the following are particularly suitable for the present invention (however, they are not limited to these):
Inconel 601 (trade name of Inco, UK, standard composition: Ni-23 mass% Cr-1.4 mass% Al-14.1 mass% Fe-0.5 mass% Mn-0.2 mass% Si-0. 05 mass% C);
Inconel X751 (trade name of Inco, UK, standard composition: Ni-15.5 mass% Cr-1.0 mass% Nb-0.7 mass% Al-2.5 mass% Ti-7 mass% Fe-0. 5 mass% Mn-0.2 mass% Si-0.05 mass% C).
[0020]
In addition, the matrix solid solution strengthened Ni-base heat-resistant alloy contains 45 to 70% by mass of Ni, and a total of one or more of Cr, Mo, W, and Co (oxidation imparting component) is 28 to 45. What contains 1 mass% and contains 1-20 mass% of Fe can also be used. If the Ni content is less than 45% by mass, sufficient high-temperature strength may not be ensured. If the Ni content is 70% by mass or more, the content of the component for imparting resistance to oxidation, which is also a solid solution component, is insufficient. May be insufficient. On the other hand, if the content of the oxidation resistance-imparting component is less than 28% by mass, the high temperature strength or the high temperature oxidation resistance may be insufficient, and if it exceeds 45% by mass, the strength and workability may be reduced.
[0021]
Among the Ni-base heat-resistant alloys having the above composition, the following are particularly suitable for the present invention (however, they are not limited to these):
Hastelloy C22 (trade name of US Highness Stellite, standard composition: Ni-21.5 mass% Cr-2.5 mass% Co-13.5 mass% Mo-4 mass% -5.5 mass% Fe-1 0.0 mass% Mn-0.1 mass% Si-0.01 mass% C);
Hastelloy C276 (trade name of US Highness Stellite, standard composition: Ni-15.5 mass% Cr-2.5 mass% Co-16 mass% Mo-3.7 mass% -5.5 mass% Fe-1 0.0 mass% Mn-0.1 mass% Si-0.01 mass% C).
[0022]
The thickness of the ground electrode 4 in the bending direction is preferably set as follows.
When the nominal size of the mounting screw is M10: 0.8 to 1.3 mm;
When the nominal size of the mounting screw is M12: 0.8 to 1.5 mm;
When the nominal size of the mounting screw is M14: 1.8 to 1.7 mm. In this specification, the name of the mounting screw means a value defined in ISO 2705 (M10), ISO 2704 (M12), and ISO 1919 (M14), and of course, within the range of the dimensional tolerance defined in the standard. Allow fluctuations in
[0023]
The spark plug 100 can be manufactured as follows. First, one end of a linear metal material (eg, manufactured by wire drawing or rolling) to be a ground electrode is welded to the metal shell by resistance welding or the like, and then cut to the required electrode length To do. This is placed outside the insulator on which the center electrode 3 and the like are already assembled, and is crimped, and in the spark plug 100 shown in FIG. Figure 2). Then, the ground electrode 4 (ground electrode material) before bending is bent at the front end side toward the front end surface of the center electrode 3 in the following process, and a spark gap g is formed to form the spark plug 100. This processing can be performed by, for example, a two-stage process including preliminary bending and main bending.
[0024]
As shown in FIG. 2A, in the pre-bending step, a pre-bending spacer 42 is disposed so as to face the front end surface of the center electrode 3 of the assembly 100 ′, and the ground electrode 4 is arranged with respect to the pre-bending spacer 42. The front end side is pressed by using a bending punch 43 from the side opposite to the center electrode 3. Here, as described above, since the ground electrode material to be bent is a relatively hard material having a Vickers hardness of 220 or more at 20 ° C. (normal temperature), the deformation resistance is somewhat too high at normal temperature and bending is performed. In some cases, the yield may be reduced due to cracks or the like during processing.
[0025]
Therefore, it is effective to heat the material to, for example, 700 ° C. or more to reduce the deformation resistance and perform the processing. As a heating method, as shown in FIG. 2B, a method of locally heating only the ground electrode 4 with a laser beam LB can be employed. Since the laser beam LB can be narrowed down by a lens, only an R-shaped bent portion where plastic deformation is particularly large can be selectively heated. In this embodiment, the ground beam 4 is irradiated with the laser beam LB from the side so that the laser beam is not blocked by the pre-bending spacer 42 or the pre-bending punch 43.
[0026]
Next, in this bending process, first, as shown in FIG. 2 (c), a knife for defining a spark gap amount between the front end surface of the center electrode 3 and the front end portion of the ground electrode 4 after completion of the preliminary bending. The spacer 95 is sandwiched. Then, as shown in FIG. 4D, in this state, the end of the ground electrode 4 is inclined upward by a main bending punch 90 provided so as to be able to approach and separate from the side opposite to the spacer 95. The pre-bent ground electrode 4 is subjected to a main bending process so that the tip end portion is substantially parallel to the tip end surface of the center electrode 3. Also at this time, the ground electrode 4 can be locally heated by the laser beam LB.
[0027]
Note that the method of heating the ground electrode is not limited to the method using laser beam irradiation, and direct heating using current-carrying resistance heating can also be performed, for example. FIG. 3 shows some examples. FIGS. 3A and 3B show a heating method at the time of preliminary bending. In FIG. 3A, the preliminary bending punch 43 and the preliminary bending spacer 42 are diverted to energized electrodes, and direct current energization heating ( AC current heating may be used). On the other hand, (b) is a method in which current-carrying electrodes 91 and 91 separate from the pre-bending punch 43 and the pre-bending spacer 42 are brought into contact with the electrode base end portion and the tip end portion, respectively, and are heated by the heating power supply 50. . Note that electricity may be supplied between the preliminary bending punch 43 and the metal shell 1. FIG. 3C shows a state in which the main bending process is performed while the ground electrode 4 is energized and heated through the main bending punch 90 and the metal shell 1.
[0028]
As shown in FIG. 4, the insulator 2 may be assembled to the metal shell 1 after bending the ground electrode 4 in advance.
[0029]
[Experimental example]
In order to confirm the effect of the present invention, the following experiment was conducted. In the spark plug shown in FIG. 1, the mounting screw portion 7 is called M14, the axial distance l ₁ between the base end portion of the ground electrode 4 and the center electrode 3 is 5.1 mm, and the center electrode 3 is protruded from the metal shell 1. The dimension l ₂ is 3 mm, the interval of the spark discharge gap g is 1.1 mm, and the cross-sectional shape and dimensions of the ground electrode 4 are rectangular as shown in FIG. 5A (bending direction thickness h × width w is 1.3 mm). × 2.7 mm, 1.2 mm × 2.2 mm, and 1.5 mm × 2.8 mm) and a circular shape (φ1.1 mm) shown in FIG. The materials used for the ground electrode 4 were Inconel 601, Inconel X750, Inconel 600 (trade name of Inco, UK, standard composition: Ni-15.5 mass% Cr-8 mass% Fe-0.5 mass% Mn- 0.2% by mass Si-0.08% by mass C: Comparative example), Ni-5% by mass W alloy (comparative example), both of which were used as a raw material after annealing after cold drawing (however, Inconel 601 and Inconel X750 are subjected to the necessary age hardening treatment). In addition, the raw material with a wire diameter of 4 mm was separately manufactured by the same method, a tensile test was performed with a test piece prepared using the same, and the tensile strength was separately measured.
[0030]
The bending process of the ground electrode using the above-mentioned material is performed by performing each step of preliminary bending and main bending shown in FIG. 2 using a laser beam (CW-YAG laser, beam diameter 1.0 mm, energy 10 J). This was performed by heating to 730 ° C. In addition, as shown in FIG. 1, the Vickers hardness of the electrode after bending was measured under two conditions of 20 ° C. and 730 ° C. at substantially the center MP of the R-shaped bent portion on the side surface of the electrode.
[0031]
Each spark plug is attached to a 1800cc 4-cycle DOHC gasoline engine and continuously operated with the load adjusted so that the engine speed is 6000 rpm when the throttle is fully open. The endurance time until it became was measured. The above results are shown in FIG.
[0032]
According to this result, those in which the ground electrode is composed of a metal having a Vickers hardness of 220 or more measured at 20 ° C. exhibit excellent durability, and especially at room temperature, the Vickers hardness is 265 or more and 730 ° C. It can be seen that Inconel X750 having a Vickers hardness of 100 or more can sufficiently maintain the durability even if the electrode cross-sectional dimension is considerably reduced.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing an example of a spark plug according to the present invention.
FIG. 2 is a process explanatory view showing an example of a bending process of a ground electrode.
FIG. 3 is a process explanatory view showing a modified example of the bending process.
FIG. 4 is an explanatory view showing a method of assembling the metal shell and the insulator after bending the ground electrode.
FIG. 5 is an explanatory diagram showing experimental results.
[Explanation of symbols]
1 Metal shell 2 Insulator 3 Center electrode 4 Ground electrode g Spark discharge gap

Claims (4)

A center electrode, an insulator provided outside the center electrode, a metal shell made of carbon steel provided outside the insulator, one end side coupled to the metal shell, and the other end side of the center electrode A ground electrode that is disposed so as to face the tip and forms a spark discharge gap with the center electrode, and at least a surface layer portion of the ground electrode is 20 at the center of the R-shaped bent portion on the electrode side surface. A Vickers hardness measured at ℃ is 265 to 1300, and a spark plug manufacturing method comprising a metal having a Vickers hardness of 60 to 200 measured at 730 ° C,
As the metal constituting at least the surface layer portion of the ground electrode, the Ni content is 9 to 83% by mass, the total content of Fe and Ni is 50 to 83% by mass, Cr, Mo, W and Using Ni-base heat-resistant alloy or Fe-base heat-resistant alloy containing 16 to 49% by mass in total of one or more types of Co and containing 1 to 10% by mass of one or both of Al and Ti,
One end side is coupled to the metal shell, and at least the surface layer portion is made of the Ni-base heat-resistant alloy or the Fe-base heat-resistant alloy, and the other end side is bent sideways while locally heating with a laser beam. A method for manufacturing a spark plug, comprising a heat bending process for processing.   As the metal constituting at least the surface layer portion of the ground electrode, it contains 45 to 70% by mass of Ni, 28 to 45% by mass in total of one or more of Cr, Mo, W and Co, and The method for producing a spark plug according to claim 1, wherein a Ni-base heat-resistant alloy containing 1 to 20% by mass of Fe is used.   The spark plug manufacturing method according to claim 2, wherein the ground electrode material is heated to 700 ° C. or higher in the heating bending process.   The ground electrode material is made of a metal having a Vickers hardness of 200 or less measured at the surface layer portion in the heated state and a Vickers hardness of 220 or more measured at 20 ° C. after bending. The method for manufacturing a spark plug according to any one of claims 1 to 3, wherein a spark plug is used.

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