JP4294332B2 - Spark plug - Google Patents

Description

【００３８】
番号３，４，５，８，９，１０は本発明品のスパークプラグであり、電極母材として、Ｃｒを１４〜１７質量％、Ｍｏを０．８〜３．５質量％、Ｎｉを６８〜８５．２質量％含有するＮｉ合金を用いている。いずれもＣｒの含有量を減少させる代わりに、Ｍｏを上記範囲で添加しているので、Ｃを含有しているにもかかわらず、耐高温酸化性はＣｒの多い番号１の比較例と遜色ない程度に確保できていることがわかる。そして、Ｃｒの含有量が比較的低いので、番号１の比較例よりも電極の加工性が良好であり、Ｃｕ系伝熱促進部の埋設も支障なく行うことができる。該埋設により、熱引きが改善される結果、貴金属チップの耐久性も良好である。また、Ｍｏの添加により高温強度が著しく向上し、耐高温折損性も良好である。さらに、エンジンで長時間使用しても拡散層の厚みの増大を抑えることができ、この拡散層における剥離がない。これに対し、Ｍｏを添加しない番号１の比較例は冷間加工性が悪く、Ｃｕ系伝熱促進部の埋設には面倒な温間加工が必要である。また、耐高温折損性もあまり良好でなく、拡散層における剥離が発生している。そして、番号１２のようにＣｕ系伝熱促進部の埋設を省略すると、高温耐酸化性及び貴金属チップの耐久性が著しく低下する結果を招いている。
【図面の簡単な説明】
【図１】本発明のスパークプラグの一実施例を示す縦断面図。
【図２】図１のスパークプラグの要部を拡大して示す断面図。
【図３】図１のスパークプラグの変形例を示す要部断面図。
【図４】図１のスパークプラグの接地電極の製造工程説明図。
【図５】図３のスパークプラグの接地電極の製造工程説明図。
【符号の説明】
１ 主体金具
２ 絶縁体
２１ 先端部
３ 中心電極
３２ 貴金属チップ
４ 接地電極
４ａ 電極母材
４ｃ Ｃｕ系伝熱促進部
１００ スパークプラグ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spark plug used for ignition of an internal combustion engine.
[0002]
[Prior art]
In recent years, with the aim of improving the performance of internal combustion engines such as automobile engines, or the lean burn of engines for the purpose of strengthening exhaust gas regulations and improving combustion efficiency, the electrode temperature of spark plugs used for ignition tends to increase. . In particular, since the ground electrode is located on the combustion chamber side with respect to the center electrode, the temperature rises rapidly. In particular, a spark plug used for a direct injection engine or the like is particularly likely to cause a temperature rise of the ground electrode. Under the above severe conditions, the sparks of the electrode can easily be consumed. Therefore, in order to suppress the expansion rate of the spark discharge gap, a spark in which a noble metal tip is welded to the portion of the ground electrode facing the spark discharge gap is used. Plugs are popular.
[0003]
When the temperature of the ground electrode rises, high temperature oxidation of the electrode base material to which the noble metal tip is welded becomes a problem. Conventionally, the base material of the ground electrode is often made of a Ni-base heat-resistant alloy such as Inconel 600 (Inconel is a trade name of Inco, UK) in order to ensure high-temperature oxidation resistance. However, since the heat conductivity of Ni-base heat-resistant alloys is generally not so high, so-called heat sinking is bad, and the electrode temperature is particularly likely to rise during high-speed operation. When the heat pulling deteriorates and the electrode temperature rises, the temperature of the metal tip bonded to the electrode base material also rises, causing a decrease in life due to abnormal wear. Therefore, a method has been proposed in which a core material made of a Cu-based metal (Cu-based heat transfer accelerating portion) is arranged in the electrode base material to suppress the temperature rise of the electrode in order to promote improvement in heat dissipation ( For example, Patent Document 1 and Patent Document 2).
[0004]
[Patent Document 1]
JP-A-5-159857 [Patent Document 2]
Japanese Examined Patent Publication No. 6-48629
[Problems to be solved by the invention]
However, when the combustion temperature further rises and the ignition part gets closer to the center of the combustion chamber as in the direct injection engine described above, the temperature rise of the ground electrode becomes more significant. As a result, there arises a problem that the high temperature oxidation of the electrode base material cannot be suppressed with an alloy performance of about Inconel 600. In this case, it is conceivable to replace the material of the electrode base material with a material having better high-temperature oxidation resistance. For example, instead of the conventionally used Inconel 600, a proposal has been made to use Inconel 601 with improved high-temperature oxidation resistance by increasing the content of Cr and Fe. However, this material replacement presents a major obstacle when the embedding of the Cu-based heat transfer promoting portion is selected.
[0006]
That is, an electrode having a Cu-based heat transfer promoting portion is assembled by assembling a Cu material serving as a Cu-based heat transfer promoting portion into a Ni alloy material serving as an electrode base material, and this assembly is drawn or forged, or Manufactured by cold working by rolling to make a clad wire. However, nickel-base heat-resistant alloys with increased Cr content such as Inconel 601 have higher deformation resistance and lower ductility than conventional Inconel 600 and the like as a metal material whose strength has been improved by high alloying. Therefore, when it is going to manufacture a clad wire with a Cu system heat transfer promotion part by the above processes, troubles, such as a crack, are easy to occur and there is a problem which brings about a significant fall of a manufacturing yield. In addition, when a spark plug having a Cu-based heat transfer promoting portion is used in an engine for a Ni-based electrode base material, a diffusion layer in which components are diffused between the electrode base material and the Cu-based heat transfer promoting portion is formed. Is done. In addition, peeling may occur from this diffusion layer by receiving a repeated load due to the difference in thermal expansion between the two. As a result, heat conduction may not be sufficiently performed from the electrode base material to the Cu-based heat transfer promoting portion. On the other hand, if the Cu-based heat transfer promoting portion is omitted, even if the high-temperature oxidation of the electrode base material can be suppressed, the temperature increase of the noble metal tip cannot be suppressed, so the problem of abnormal consumption cannot be solved.
[0007]
The object of the present invention is to provide sufficient resistance to high-temperature oxidation to the electrode base material of the ground electrode, and to be able to manufacture a structure in which a Cu-based heat transfer promoting portion is embedded without any problem by cold working. It is an object of the present invention to provide a spark plug that can prevent abnormal consumption of bonded noble metal tips.
[0008]
[Means for solving the problems and actions / effects]
In order to solve the above problems, a spark plug according to the present invention includes a cylindrical metal shell, an insulator fitted inside the metal shell, a center electrode provided inside the insulator, One end of the bracket is joined by welding or the like and a ground electrode is formed on the other end side to form a spark discharge gap with the center electrode. The ground electrode is embedded in the electrode base material and the electrode base material. And a Cu-based heat transfer promoting portion composed mainly of Cu, and a noble metal tip welded to the electrode base material at a position facing the spark discharge gap. It consists of a Ni alloy containing ˜17% by mass, Mo of 0.8 to 3.5% by mass, and Ni of 68 to 85.2% by mass. In the present specification, “main component” refers to a component having the highest mass content.
[0009]
According to the spark plug of the present invention, the Cu-based heat transfer promoting portion is embedded in the electrode base material that forms the ground electrode, thereby promoting the heat dissipation and suppressing the temperature rise, thereby improving the life of the ground electrode. Can be planned. Moreover, since the temperature rise of the noble metal tip welded to the electrode base material is also suppressed, abnormal wear is prevented and durability can be ensured. And in this invention, what has the said specific composition is employ | adopted as Ni alloy which comprises an electrode base material. As a result, there are the following advantages compared to the case of employing Inconel 601 or the like, which has been problematic in the past. First, when a Ni alloy containing C is employed as in the present invention, the high temperature oxidation resistance of the alloy can be remarkably improved by containing a certain amount of Mo together with Cr. Therefore, combined with the adoption of the Cu-based heat transfer promoting part, even when the spark plug is used under more severe conditions, the durability of the ground electrode can be sufficiently ensured and the life can be improved.
[0010]
In this case, particularly for the Ni alloy containing C, the effect of improving the high temperature corrosion resistance by adding Mo is high. There are both cases where the C is contained as an impurity and cases where it is positively added (so-called weak precipitation type alloy) in order to enhance precipitation strengthening by carbide formation, and is adjusted to 0.3% by mass or less. Particularly in the latter case, the C content is adjusted within a range of, for example, 0.03 to 0.3% by mass. However, excessive addition reduces the cold workability due to the formation of a large amount of carbide, so it is desirable to make it 0.10% by mass or less. In any case, the contained C mainly forms carbides with Cr when Mo is not added. When a large amount of such Cr carbide is formed, the Cr component, which is an oxidation resistance imparting element, decreases in the form of carbide precipitation, resulting in insufficient formation of a passive oxide film, leading to a decrease in oxidation resistance. . In particular, when Cr carbide is formed at the grain boundary, a Cr-deficient layer is formed near the grain boundary, and the interfacial corrosion is facilitated due to the local battery effect and the like, which further adversely affects the durability of the electrode base material. .
[0011]
However, when an appropriate amount of Mo is added, Mo carbides are preferentially formed and the precipitation of Cr carbides is suppressed, and the effective Cr content contributing to passive oxide film formation can be increased. As a result, even with the same Cr content, a stronger passive oxide film can be formed, which contributes to the improvement of high temperature corrosion resistance. In addition, since Mo carbides generally do not easily cause grain boundary precipitation, a Cr-deficient layer is also unlikely to occur, which is advantageous in terms of suppressing grain boundary corrosion.
[0012]
As a result, high-temperature corrosion resistance equivalent to or higher than that of Inconel 601 and the like having a higher Cr composition can be realized even if the Cr content is set to a relatively low value of 14 to 17% by mass based on the above effect due to the addition of Mo. Accordingly, the cold workability is improved by the amount of Cr content reduced, so that the processing of the clad material in which the Cu-based heat transfer promoting portion is embedded can be performed without any problem. Become.
[0013]
In addition, the addition of Mo can suppress an increase in the thickness of the diffusion layer formed at the boundary between the electrode base material and the Cu-based heat transfer promoting portion even if the engine is used for a long time. Can be prevented. The occurrence of this peeling is presumed to be due to the low ductility that is characteristic of the alloy of Cu and Ni, which is the main component of this diffusion layer.
[0014]
When the Cr content of the Ni alloy constituting the electrode base material is less than 14% by mass, the high temperature oxidation resistance of the electrode base material is insufficient, which causes a problem that the electrode life is reduced. On the other hand, when it exceeds 17 mass%, workability deteriorates, and when a clad material having a Cu-based heat transfer promoting portion embedded therein, which is a ground electrode material, is produced, cracking or the like is likely to occur.
[0015]
If the Mo content is less than 0.8% by mass, the effect of improving the high-temperature oxidation resistance due to the addition of Mo and the effect of preventing peeling in the diffusion layer during long-time use become poor. On the other hand, if it exceeds 3.5 mass%, the hardness of the alloy increases and the deformation resistance increases, leading to deterioration of workability. Furthermore, if the Ni content is less than 68% by mass, the content of subcomponents becomes too high, which tends to cause deterioration in workability.
On the other hand, if the Ni content exceeds 85.2% by mass, the necessary Cr and Mo contents cannot be ensured, leading to deterioration in high-temperature oxidation resistance.
[0016]
The Ni alloy constituting the electrode base material should have an Al content of less than 1% by mass from the viewpoint of securing the weldability and thus the weld joint strength when the ground electrode is welded to the metal shell. When the Al content is 1% by mass or more, the production of aluminum oxide becomes excessive, and weldability or weld joint strength may be impaired. On the other hand, Al can be positively added in the above range for the purpose of improving high-temperature oxidation resistance.
[0017]
Fe can be added to the Ni alloy that forms the electrode base material. Fe functions as a solid solution in a Ni-based matrix to strengthen and strengthen high temperature strength. The Fe content is preferably adjusted in the range of 6 to 10% by mass. If the Fe content is less than 6% by mass, the effect of improving the high-temperature strength is poor, and if it exceeds 10% by mass, sufficient high-temperature oxidation resistance may not be ensured.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a longitudinal cross-sectional view of a spark plug 100 as an example of the present invention. A cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that a tip 21 protrudes, A center electrode 3 provided inside the insulator 2 and a ground electrode 4 having one end coupled to the metal shell 1 by welding or the like and forming a spark discharge gap g between the other end and the center electrode 3 are provided. ing. The spark plug 100 according to the present embodiment is a so-called parallel electrode type, and the front end side of the ground electrode 4 is bent back to the side, and a spark discharge gap g is formed between the side surface and the front end surface of the metal shell 1. Is formed. Further, noble metal tips 31 and 32 made of a Pt alloy or an Ir alloy are welded to the ground electrode 4 and the center electrode 3 at positions facing the spark discharge gap g, respectively.
[0019]
The insulator 2 is made of a ceramic sintered body such as alumina or aluminum nitride, for example, and has a hole 6 for fitting the center electrode 3 and the terminal fitting 8 along its own axial direction. Yes. The metal shell 1 is formed in a cylindrical shape from a metal such as low carbon steel, and constitutes a housing of the spark plug 100, and a screw for attaching the plug 100 to an engine block (not shown) on its outer peripheral surface. Part 7 is formed.
[0020]
As shown in FIG. 2, the ground electrode 4 includes an electrode base material 4a forming an outer surface portion, and a Cu-based heat transfer promoting portion 4c embedded in the electrode base material 4a. The electrode base material 4a is made of a Ni alloy containing 14 to 17% by mass of Cr, 0.8 to 3.5% by mass of Mo, and 68 to 85.2% by mass of Ni. Further, the Cu-based heat transfer promoting portion 4c is composed of pure Cu or a Cu alloy. In the present embodiment, the Cu-based heat transfer promoting portion 4 c is disposed in the longitudinal direction of the ground electrode 4. The Cu-based heat transfer promoting portion 4c is tapered, and its tip is set so as to deviate from the position of the spark discharge gap g. This is because the temperature of the tip of the ground electrode 4 where the spark discharge gap g is located is particularly high, and when the Cu-based heat transfer promoting portion 4c enters this portion, the linear expansion coefficient with the electrode base material 4a is increased. This is because problems such as electrode swelling and delamination may occur based on the difference.
[0021]
In the present embodiment, the center electrode 3 is also configured to have an electrode base material 3a and a Cu-based heat transfer promoting portion 3c embedded therein. The electrode base material 3a can also be made of the same Ni alloy as that of the ground electrode 4 side. However, since the temperature is less likely to rise than the ground electrode 4, the Mo content is lower than that of the electrode base material 4a on the ground electrode 4 side. (Although it does not contain Mo), the Cr content can be the same as or lower than that of the electrode base material 4a.
[0022]
FIG. 4 shows an example of a method for manufacturing the ground electrode 4. That is, as shown in FIG. 4 (a), a Ni-based molded body 104a having a gap 104h is produced by plastic working such as cutting or deep drawing with a Ni alloy that is a constituent material of the electrode base material 4a. On the other hand, a Cu-based molded body 104c having a shape corresponding to the gap 104a is made of pure Cu (for example, oxygen-free copper material) or a Cu alloy as a constituent material of the Cu-based heat transfer promoting portion 4. Then, this Cu-based molded body 104c is fitted into the gap 104h of the Ni-based molded body 104a to produce the assembly 104 in FIG. 4B.
[0023]
Next, as shown in FIG. 4C, the assembly 104 is subjected to die drawing, forging, or rolling at room temperature to reduce and extend the clad wire 4 ′. Thereby, the Cu-based molded body 104c becomes the Cu-based heat transfer promoting portion 4c, and the Ni-based molded body 104a becomes the electrode base material 4a. The ground electrode 4 is completed by welding the exposed end of the Cu-based heat transfer promoting portion 4c of the clad wire 4 'to the end face of the metal shell 1 (FIG. 2) and bending it.
[0024]
The Ni alloy forming the Ni-based molded body 104a has good workability because the Cr content is reduced as described above, and is performed by cold working at room temperature or by raising the temperature to 900 ° C. or lower. Thus, the clad material 4 ′ can be obtained without any problems without causing defects such as cracks. And, instead of reducing the Cr content, Mo in the above range is contained, so even when compared with Ni-based heat-resistant alloys such as Inconel 601 having a high Cr content, the high temperature corrosion resistance is inferior, and the ground electrode Can greatly extend the service life. In addition, the Cu-based heat transfer promoting portion 4c can be easily arranged, and further, even if it is used for a long time in an engine, the diffusion layer does not peel off. Can be secured.
[0025]
When the ground electrode 4 is manufactured by cold working, as shown in FIG. 4D, a structure in which crystal grains extend in the longitudinal direction of the electrode is observed in the electrode base material 4a. When the clad wire 4 'is annealed from the finished state, component diffusion occurs between the Cu-based heat transfer promoting portion 4c and the electrode base material 4a made of Ni alloy, thereby improving the binding force between the two. Can do. This annealing may be performed after processing or before processing, but when the temperature of annealing performed after processing is high, the stretched structure of crystal grains shown in FIG. May change to the organization.
[0026]
In addition, as shown in FIG. 3, you may arrange | position the Ni type expansion | swelling adjustment layer 4d which consists of pure Ni or Ni alloy further inside the Cu type heat transfer promotion part 4c. The electrode base material 4a made of an Ni alloy and the Cu-based heat transfer promoting portion 4c have a large difference in linear expansion coefficient, and there is a concern that electrode swelling, delamination, and the like are likely to occur particularly when a severe cooling / heating cycle is applied. However, by forming the Ni-based expansion adjustment layer 4d as described above, the thickness of the Cu-based heat transfer promoting portion 4c is reduced, and the Cu-based heat transfer promoting portion 4c is sandwiched between Ni-based metals, It is possible to make the above-mentioned problem difficult to occur.
[0027]
【Example】
In order to confirm the effect of the present invention, the following experiment was conducted.
Various prototypes of the spark plug 100 shown in FIG. 1 were manufactured. The ground electrode 4 was manufactured by the method shown in FIG. That is, Ni alloys having various compositions shown in Table 1 were prepared as electrode base material, and a Ni-based molded body 104a to be the electrode base material 4a was measured with an outer diameter of 4.5 mm and a length of 5.4 mm. Produced. Further, a Cu-based molded body 104c to be the Cu-based heat transfer promoting portion 4c was manufactured using oxygen-free copper as a material with a base end outer diameter of 2.9 mm and a length of 5 mm. Then, this was fitted into the gap 104h formed in the Ni-based molded body 104a to form an assembly 104. This assembly 104 was cold-extruded so that the area reduction rate per pass was 55%, and the cross-section was a rectangle with a length of 1.5 mm and a width of 2.8 mm, and the length was 19 mm. A wire was obtained. For comparison, a ground electrode having the composition of No. 1 was prepared by omitting the Cu heat transfer promoting portion 4c (No. 13).
[0028]
Each of the above ground electrodes was subjected to workability evaluation according to the following criteria.
Good (O): No cracks or peeling were observed between the electrode base material 4a and the Cu-based heat transfer promoting portion 4c, and cold working was possible without problems.
Possible (Δ): Cracks or peeling was observed between the electrode base material 4a and the Cu-based heat transfer promoting portion 4c. However, when the assembly was annealed at 930 ° C. for 1 hour, cold working was not possible. Is solved.
Impossibility (x): An assembly was annealed at 930 ° C. for 1 hour, but the failure was not eliminated (a ground electrode having no failure was obtained separately by warm extrusion at a temperature of 730 ° C.).
[0029]
Moreover, the high temperature fatigue test of the obtained ground electrode is performed on the following conditions. That is, the tester used an axial load fatigue test, setting the temperature to 600 ° C., the stress amplitude condition to ± 900 N tension / compression, and the repetition rate to 10 Hz. Then, the fatigue strength, JIS: Z2273 in compliance with the method defined in, a test number of goods N = 2, obtains the time-intensity at the time of setting the fatigue life of 10 ⁶ times, was evaluated by the following criteria ( Confirmation of high temperature breakability).
Good (◯): Time strength is 220 MPa or more.
Possible (Δ): Time strength is 200 MPa or more and less than 220 MPa.
Impossible (x): Time strength is less than 200 MPa.
[0030]
Next, with respect to the center electrode 3, the cross section of the center electrode 3 is externally formed by cold extrusion similar to the ground electrode 4 in the form in which the electrode base material 3 a is composed of Inconel 600 and the Cu-based heat transfer promoting portion 3 c is composed of oxygen-free copper. It was manufactured to have a circular shape with a diameter of 2.5 mm and a length of 24 mm.
[0031]
The ground electrode 4 was made of a Pt-10 mass% Ni alloy, and a disc-shaped noble metal tip 32 having a diameter of 0.9 mm and a thickness of 0.4 mm was joined by resistance welding. In addition, a disc-shaped noble metal tip 32 made of a Pt-13 mass% Ir alloy and having a diameter of 0.8 mm and a thickness of 0.6 mm was joined to the center electrode 3 by laser welding. The center electrode 3 is assembled to the insulator 2 made of alumina, and the metal shell 1 to which the ground electrode 4 is welded is assembled to the insulator 2, and the ground electrode 4 is bent, whereby the noble metal tips 31, 32 are assembled. A spark discharge gap g with a spacing of 0.9 mm was formed therebetween.
[0032]
The following tests were performed on the test pieces of each spark plug using the ground electrode obtained by the manufacturing method described above. In addition, the ground electrode which was tested by the following engine was previously annealed at 930 ° C. for 1 hour, and a diffusion layer of 10 to 20 μm was formed between the Cu-based heat transfer promoting portion 4c and the electrode base material 4a. It is.
A spark plug was attached to a 4-cylinder gasoline engine (displacement 2000 cc), and an actual machine test was performed in which the throttle was fully opened and continuously operated at an engine speed of 6000 rpm for 250 hours (estimated temperature of the noble metal tip 32 on the ground electrode side: about 1000 ° C. ). After the test, the cross section of the ground electrode 4 was observed with a scanning electron microscope, and the thickness of the formed oxide scale layer was measured and evaluated according to the following criteria (confirmation of high temperature oxidation resistance of the ground electrode).
Good (O): Oxide scale layer thickness less than 0.05 mm.
Possible (Δ): Oxide scale layer thickness of 0.05 mm or more and less than 0.15 mm.
Impossible (x): Oxide scale layer thickness of 0.15 mm or more.
[0033]
Further, the wear thickness of the noble metal tip on the ground electrode side after the test was measured in the gap interval direction and evaluated according to the following criteria (confirmation of durability of the noble metal tip).
Good (O): Consumed thickness is less than 0.3 mm.
Possible (Δ): Consumed thickness is 0.3 mm or more and less than 0.35 mm.
Impossible (x): Consumed thickness is 0.35 mm or more.
[0034]
Further, the welding strength between the ground electrode 4 and the metal shell 1 was performed as follows. The strength test consists of a tensile test in which the metal shell 1 and the tip of the ground electrode 4 (before bending) (at a position 5 mm from the tip) are held and pulled in the axial direction of the ground electrode 4, and the metal shell 1 is cantilevered. A bending test was performed in which a fixed bending load was repeatedly applied to the ground electrode 4 in a direction orthogonal to the axial direction of the ground electrode 4 at a position 5 mm from the end surface of the metal fitting until breakage occurred. And it evaluated on the following conditions (confirmation of weldability).
Good (O): Does not break at the welded part in either the tensile test or the bending test.
Possible (Δ): Only the tensile test does not break at the weld.
Impossible (x): Breaks at the welded part in both the tensile test and the bending test.
[0035]
Furthermore, after the test, the observation of the ground electrode 4 by X-ray and the cross section thereof were observed with a scanning electron microscope, whereby the occurrence of peeling in the diffusion layer and the thickness of the diffusion layer were measured and evaluated according to the following criteria (grounding) Confirmation of peelability of electrode heat transfer promotion part).
Good (O): The Cu-based heat transfer promoting portion 4c and the electrode base material 4a are not separated and the width of the diffusion layer is 50 μm or less.
Possible (Δ): The Cu-based heat transfer promoting portion 4c and the electrode base material 4a are not separated, but the diffusion layer has a width of 50 μm or more.
Impossible (x): The peeling has occurred between the Cu-based heat transfer promoting portion 4c and the electrode base material 4a.
[0036]
The results are shown in Table 1.
[0037]
[Table 1]

[0038]
Numbers 3, 4, 5, 8, 9, and 10 are spark plugs according to the present invention. As an electrode base material, Cr is 14 to 17% by mass, Mo is 0.8 to 3.5% by mass, and Ni is 68. Ni alloy containing ˜85.2% by mass is used. In either case, Mo is added in the above range instead of reducing the Cr content, so that the high-temperature oxidation resistance is comparable to the comparative example of No. 1 with a large amount of Cr even though it contains C. It can be seen that it has been secured to the extent. And since content of Cr is comparatively low, the workability of an electrode is better than the comparative example of No. 1, and embedding of a Cu type heat transfer promotion part can also be performed without trouble. As a result of improving the heat sinking by the burying, the durability of the noble metal tip is also good. Further, the addition of Mo significantly improves the high-temperature strength, and the high-temperature fracture resistance is also good. Further, even if the engine is used for a long time, an increase in the thickness of the diffusion layer can be suppressed, and there is no peeling in the diffusion layer. On the other hand, the comparative example of No. 1 in which Mo is not added has poor cold workability, and the embedding of the Cu-based heat transfer promoting portion requires troublesome warm working. Moreover, the high temperature fracture resistance is not very good, and peeling occurs in the diffusion layer. And if the embedding of the Cu-based heat transfer promoting part is omitted as in the case of No. 12, the result is that the high temperature oxidation resistance and the durability of the noble metal tip are remarkably lowered.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing an embodiment of a spark plug according to the present invention.
2 is an enlarged cross-sectional view showing a main part of the spark plug of FIG. 1. FIG.
FIG. 3 is a cross-sectional view of an essential part showing a modification of the spark plug of FIG.
4 is an explanatory diagram of a manufacturing process of the ground electrode of the spark plug of FIG. 1. FIG.
5 is an explanatory diagram of a manufacturing process of the ground electrode of the spark plug of FIG. 3;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Main metal fitting 2 Insulator 21 Tip part 3 Center electrode 32 Noble metal tip 4 Ground electrode 4a Electrode base material 4c Cu system heat transfer promotion part 100 Spark plug

Claims (7)

A cylindrical metal shell (1), an insulator (2) fitted inside the metal shell (1), a center electrode (3) provided inside the insulator (2), and the metal shell A ground electrode (4) having one end coupled to (1) by welding or the like and forming a spark discharge gap (g) with the center electrode (3) on the other end side;
The ground electrode (4) includes an electrode base material (4a), a Cu-based heat transfer promoting portion (4c) embedded in the electrode base material and mainly composed of Cu, and the spark discharge gap ( a noble metal tip (32) welded to the electrode base material (4a) at a position facing g), and
In the electrode base material (4a), Cr is 14 to 16 % by mass, Mo is 0.8 to 3 % by mass, Al is 1.1% by mass or less, C is 0.03 to 0.1% by mass, Fe is A spark plug comprising a Ni alloy containing 5 to 12% by mass, further containing Mn and Si, and the remaining 68 to 85.2% by mass of Ni . A cylindrical metal shell (1), an insulator (2) fitted inside the metal shell (1), a center electrode (3) provided inside the insulator (2), and the metal shell A ground electrode (4) having one end coupled to (1) by welding or the like and forming a spark discharge gap (g) with the center electrode (3) on the other end side;
The ground electrode (4) includes an electrode base material (4a), a Cu-based heat transfer promoting portion (4c) embedded in the electrode base material and mainly composed of Cu, and the electrode base material ( 4a) and a diffusion layer formed at the boundary between the Cu-based heat transfer promoting portion (4c) and a noble metal tip (4a) welded to the electrode base material (4a) at a position facing the spark discharge gap (g) 32), and
In the electrode base material (4a), Cr is 14 to 16 % by mass, Mo is 0.8 to 3 % by mass, Al is 1.1% by mass or less, C is 0.03 to 0.1% by mass, Fe is A spark plug comprising a Ni alloy containing 5 to 12% by mass, further containing Mn and Si, and the remaining 68 to 85.2% by mass of Ni .   The spark plug according to claim 1 or 2, wherein the Ni alloy constituting the electrode base material has an Al content of less than 1 mass%.   The spark plug according to any one of claims 1 to 3, wherein the Ni alloy constituting the electrode base material has a Fe content of 6 to 10 mass%. The spark plug according to any one of claims 1 to 4, wherein the position of the Cu-based heat transfer promoting part (4c) is set so that a tip of the Cu-based heat transfer promoting part (4c) is out of a position of the spark discharge gap (g) . The spark according to any one of claims 1 to 5, wherein the Cu-based heat transfer promoting portion (4c) has a Ni-based expansion adjustment layer (4d) made of pure Ni or a Ni alloy disposed therein. plug. The spark plug according to any one of claims 1 to 6, wherein the noble metal tip (32) is made of a Pt-Ni alloy .

Images