JP2007165291A - Spark plug for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an elongated life of a central electrode and a ground electrode and, at the same time, to improve a fatigue strength at high temperature, in a spark plug for an internal combustion engine. <P>SOLUTION: An alloy constituting the ground electrode 4 contains, nickel (Ni) being a principal component, Ni of ≤70 mass%, chromium (Cr) of 20 to 30 mass%, iron (Fe) of 7 to 20 mass%, aluminum (Al) of 1 to 5 mass%, titanium (Ti) of 0.05 to 0.5 mass%, manganese (Mn) of ≤0.5 mass%, silicon (Si) of ≤0.5 mass%, carbon (C) of 0.12 to 0.5 mass%, and further at least one or more of zirconium (Zr), yttrium (Y), neodymium (Nd), selenium (Se), lanthanum (La), and samarium (Sa), the total amount of contents of the special element group being ≥5 mass% and ≤1 mass% of that of Al. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spark plug used for an internal combustion engine.

  Materials used for the center electrode and ground electrode of spark plugs for internal combustion engines such as automobile engines have good oxidation resistance at high temperatures, low consumption by sparks, good thermal conductivity, high temperature strength Highness, good workability, and particularly good for weldability are required for the ground electrode. As a material that satisfies these requirements, a heat-resistant nickel (Ni) alloy is generally used.

Conventionally, the heat-resistant Ni alloy is, in mass%, chromium (Cr): 10 to 25%, iron (Fe): 0.5 to 10%, aluminum (Al): 0.3 to 3.2%, silicon ( Si): 0.2 to 2.2%, manganese (Mn): 0.1 to 0.8%, magnesium (Mg): less than 0.001%, sulfur (S): less than 0.002% And what has the composition which the remainder consists of Ni and an unavoidable impurity is devised (for example, refer patent document 1). By using such a high Cr Ni alloy material, the oxidation resistance is improved by the Cr oxide film formed on the electrode surface.
JP 2002-235138 A

The improvement in oxidation resistance as described above contributes to the extension of the life of the spark plug. However, even if only the oxidation resistance is improved, if the high-temperature fatigue strength is not sufficient, for example, the ground electrode may be broken.
In particular, when the spark plug is used for a long period of time, there is a possibility that Al nitride is formed at the grain boundary below the oxide film due to nitrogen penetrating the Cr oxide film described above. We are anxious about fatigue strength falling.

  The present invention has been made in order to solve the above-mentioned problems. By using a material having excellent oxidation resistance and sufficient high temperature fatigue strength that can withstand long-term use, the center electrode In order to improve the durability of the ground electrode, the life of the spark plug for the internal combustion engine is extended.

  Hereinafter, each configuration suitable for solving the above-described problems will be described in terms of items. In addition, the effect etc. peculiar to the structure which respond | corresponds as needed are added.

  Configuration 1. The spark plug for an internal combustion engine of this configuration is a spark plug for an internal combustion engine comprising a center electrode and a ground electrode arranged so as to have a discharge gap with the center electrode, and at least one of the center electrode and the ground electrode Is a Ni alloy containing Ni as a main component, Cr containing 20 to 30% by mass, Fe containing 7 to 20% by mass and Al containing 1 to 5% by mass, and further comprising zirconium (Zr) and yttrium (Y). , Neodymium (Nd), cerium (Ce), lanthanum (La), and samarium (Sm) as a specific element group, containing at least one of the specific element groups, and the total content of the specific element group is The nickel content is 5% or more of the Al content. Here, “mainly composed of Ni” means that the nickel alloy contains the most Ni.

  In the above configuration 1, a high Cr Ni alloy material containing Fe and Al is used as a material constituting at least one of the center electrode and the ground electrode. Thus, by making the content of Cr relatively high, as shown below, a dramatic improvement in oxidation resistance is achieved.

  That is, when the Cr content is less than 20% by mass, a strong Cr oxide film is not formed, and sufficient oxidation resistance may not be obtained. On the other hand, if the content of Cr exceeds 30% by mass, the workability is deteriorated and the thermal consumability is deteriorated, which may deteriorate the spark consumption. In this regard, according to the configuration 1, since the Cr content is 20 to 30% by mass, a strong Cr oxide film is formed, and sufficient oxidation resistance can be obtained. In addition, processability and spark consumption are not deteriorated.

  Moreover, by containing 1 mass% or more of Al, an oxide is formed directly under the Cr oxide film, and the oxidation resistance can be further improved. On the other hand, when the content of Al exceeds 5% by mass, workability and weldability of the noble metal tip are deteriorated. In this regard, according to the configuration 1, since the Al content is 1 to 5% by mass, the oxidation resistance can be improved, and the workability and weldability are not deteriorated. In addition, the content of Al is preferably 1 to 3% by mass.

  Furthermore, if the Fe content is less than 7% by mass, the workability becomes insufficient. On the other hand, if the Fe content exceeds 20% by mass, the high temperature strength is lowered. In this regard, according to the above-described configuration 1, since the Fe content is 7 to 20% by mass, sufficient workability is ensured and the high-temperature strength is not reduced.

  As described above, according to the present configuration 1, the strong Cr oxide film and the Al oxide immediately below the Cr oxide film improve the oxidation resistance as compared with the prior art and contribute to a longer life. However, even if only the oxidation resistance is improved, the ground electrode may be broken, for example, if the high-temperature fatigue strength is not sufficient.

  Therefore, in the configuration 1, at least one of Zr, Y, Nd, Ce, La, and Sm as the specific element group is included in the material. These specific element groups are precipitated at the grain boundaries, and can suppress the formation of the Al nitride. However, if the total content of the specific element group is less than 5% of Al, the effect of suppressing the formation of Al nitride may be insufficient. In this regard, according to the above-described configuration 1, since the total content of the specific element group is 5% or more of the Al content, the formation of Al nitride can be sufficiently suppressed. Therefore, it is possible to suppress a decrease in high-temperature fatigue strength and improve the durability of the center electrode and the ground electrode. As a result, the life of the spark plug for the internal combustion engine can be extended.

  In addition, according to the said structure 1, the result that the weldability of the noble metal tip which comprises the ignition part of a center electrode and a ground electrode was also improved compared with the conventional one.

  Configuration 2. The spark plug for an internal combustion engine of this configuration is characterized in that, in the above configuration 1, the total content of the specific element group is 1% by mass or less.

  If the total content of the specific element group exceeds 1% by mass, the workability of the material may be deteriorated. In this respect, according to the above-described configuration 2, the total content of the specific element group is set to 1% by mass or less, so that the workability is not deteriorated.

  Configuration 3. The spark plug for an internal combustion engine of this configuration is characterized in that, in the above configuration 1 or 2, the Ni alloy further contains 0.05 to 0.5 mass% of titanium (Ti).

  By containing Ti, when nitride and carbon (C) are contained inside the material, carbide is formed, and coarsening of crystal grains is suppressed. If the crystal grains become coarse, for example, the ground electrode may be broken. On the other hand, if the Ti content exceeds 0.5% by mass, weldability is lowered, internal oxidation is promoted, and oxidation resistance is deteriorated. In this regard, according to the above-described configuration 3, since the Ti content is 0.05 to 0.5% by mass, the coarsening of the crystal grains can be suppressed, and the weldability is not deteriorated, and the internal oxidation is promoted. It is hard to be done.

  Configuration 4. The spark plug for an internal combustion engine of this configuration is any one of the above configurations 1 to 3, wherein the Ni alloy further includes at least one of Mn of 0.5% by mass or less and Si of 0.5% by mass or less. It is characterized by containing.

  By containing Mn and Si, it acts as a deoxidizing material at the time of material preparation, and oxygen is removed from the material, thereby contributing to oxidation prevention. Moreover, oxidation resistance improves by containing a trace amount Mn and Si. However, when it contains abundantly (when the content of Mn and Si exceeds 0.5 mass%), workability will deteriorate. According to the configuration 4, since Mn and Si are contained in an amount of 0.5% by mass or less, the effects of preventing oxidation and improving oxidation resistance are exhibited without deteriorating workability. In order to achieve the effect, the content of Mn and Si is preferably 0.05% by mass or more. Further, the content of Mn and Si is preferably 0.1% by mass or less.

  Configuration 5. The spark plug for an internal combustion engine of this configuration is characterized in that, in any one of the above configurations 1 to 4, the Ni alloy further contains 0.12 to 0.5 mass% of carbon (C).

  By containing carbon, the strength of the Ni alloy is improved. Along with this, the high-temperature strength is also improved. Moreover, since the coarsening of a crystal grain is also suppressed, breakage of a ground electrode can be suppressed, for example. But when it contains abundantly (when content of C exceeds 0.5 mass%), workability will deteriorate. According to the configuration 5, since the C content is 0.12 to 0.5% by mass, the effects of improving the high temperature strength and suppressing the coarsening of the crystal grains are exhibited without deteriorating the workability.

  Configuration 6. The spark plug for an internal combustion engine of this configuration is characterized in that, in any of the above configurations 1 to 5, the content of Ni contained in the Ni alloy is 70% by mass or less.

  By setting the Ni content to 70% by mass or less, the spark consumption of the Ni alloy is improved. Among the elements contained in the Ni alloy, in the three elements (Ni, Fe, Cr) having a high content, the content of Fe and Cr having a melting point higher than that of Ni is reduced by decreasing the Ni content having the lowest melting point. Since the amount is relatively increased, the spark consumption of the Ni alloy is improved. The Ni content is preferably 65% by mass or less.

  Configuration 7. The spark plug for an internal combustion engine of this configuration is characterized in that, in any one of the above configurations 1 to 6, the Ni alloy contains at least Y (yttrium) and Zr (zirconium) in the specific element group. .

  By including Y and Zr in the specific element group, formation of Al nitride is effectively suppressed. Therefore, it is possible to suppress a decrease in high-temperature fatigue strength and improve the durability of the center electrode and the ground electrode. As a result, the life of the spark plug for the internal combustion engine can be extended.

  Configuration 8. The spark plug for an internal combustion engine of the present configuration has the above-described configuration 7, when the ratio of the content of Y and Zr contained in the nickel alloy is represented by (Y content) / (Zr content). The content ratio is 0.5 to 2.

  In the case where Y and Zr are included in the Ni alloy in the specific alloy group, the formation of Al nitride is more effectively achieved by adding the Y and Zr so that the ratio of the content of Y and Zr is 0.5-2. It is suppressed. Therefore, it is possible to suppress a decrease in high-temperature fatigue strength and to further improve the durability of the center electrode / ground electrode. As a result, the life of the spark plug for the internal combustion engine can be extended.

  Configuration 9 The spark plug for an internal combustion engine according to this configuration is characterized in that, in any one of the above configurations 1 to 8, the ground electrode is made of the Ni alloy.

  By using the Ni alloy for the ground electrode, the durability of the ground electrode can be improved. In addition, since the ground electrode is exposed to a high temperature atmosphere and is formed to be elongated as compared with the center electrode, breakage is likely to occur when the spark plug is used for a long period of time. In this regard, according to the above configuration 9, since the ground electrode is made of the nickel alloy, breakage of the ground electrode can be suppressed.

  Configuration 10 The spark plug for an internal combustion engine of this configuration is characterized in that, in the above configuration 9, the center electrode is made of a Ni alloy that does not include the specific element in the Ni alloy.

Since the center electrode is not exposed to a high temperature atmosphere as compared with the ground electrode, high temperature fatigue strength is not required as much as the ground electrode. On the other hand, since the Ni alloy contains a specific element, the workability is not so good as compared with an alloy not containing the specific element.
Therefore, when the center electrode is not required to have a high-temperature fatigue strength as high as the ground electrode, the center electrode can be made of a Ni alloy that does not include the specific element among the Ni alloys in consideration of the workability of the center electrode.

  Whether or not the electrode material is within the scope of the present invention can be determined by, for example, EPMA (Electron Probe Microanalysis).

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the spark plug 100 of the present embodiment includes a metal shell 1, an insulator 2, a center electrode 3, and a ground electrode 4. The metal shell 1 has a cylindrical shape, and an insulator 2 is fitted inside thereof. The tip 21 of the insulator 2 protrudes from the metal shell 1. Moreover, the center electrode 3 is provided inside the insulator 2 in a state where the ignition part 31 provided at the tip is protruded. Further, the ground electrode 4 is disposed so that the base end portion thereof is welded to the metal shell 1, the front end side is bent back, and the side surface thereof faces the front end portion of the center electrode 3. The ground electrode 4 is provided with an ignition part 32 that faces the ignition part 31. A gap between the ignition part 31 and the ignition part 32 is a spark discharge gap 33.

  The insulator 2 is made of, for example, a ceramic sintered body such as alumina or Al nitride, and has a hole 6 for fitting the center electrode 3 along its own axial direction. 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. On the outer peripheral surface thereof, the spark plug 100 is attached to a cylinder head of an engine (not shown). A threaded portion 7 is formed.

  As shown in FIG. 2, the main body portions 3a and 4a of the center electrode 3 and the ground electrode 4 are made of Ni alloy. This embodiment is characterized by the composition of the alloy constituting the main body 4a of the ground electrode 4, and this point will be described in detail later. On the other hand, the ignition part 31 and the opposing ignition part 32 are made of an alloy or the like mainly containing iridium (Ir).

  The main body 3a of the center electrode 3 is reduced in diameter on the front end side, and the front end surface thereof is formed flat, and a disk-shaped chip made of an alloy composition constituting the ignition part 31 is overlapped on the main body 3a. The ignition portion 31 is formed by forming the welded portion B1 along the outer edge portion by laser welding, electron beam welding, resistance welding or the like and fixing it. Further, the ignition part 32 opposite to this is formed by aligning the chip on a predetermined position of the ground electrode 4, and similarly forming the welded part B2 along the outer edge part of the joining surface and fixing it. The In addition, it is good also as a structure which abbreviate | omits any one among the ignition part 31 and the ignition part 32 facing this. In this case, a spark discharge gap 33 is formed between the ignition part 31 and the ground electrode 4 or between the opposing ignition part 32 and the center electrode 3.

  In the present embodiment, in particular, the main body portion 4a of the ground electrode 4 is formed through die drawing or the like using a molten alloy obtained by blending and melting each alloy component. The alloy constituting the main body portion 4a of the ground electrode 4 is mainly composed of Ni, Ni is 70 mass% or less, Cr is 20-30 mass%, Fe is 7-20 mass%, and Al is 1-5 mass%. Ti: 0.05 to 0.5 mass%, Mn: 0.5 mass% or less, Si: 0.5 mass% or less, C: 0.12 to 0.5 mass%, Zr, Y , Nd, Ce, La, and Sm. In this embodiment, Zr, Y, Nd, Ce, La, and Sm are specified element groups, and the total content of the specified element group is 5% or more of the Al content and 1 mass. % Or less.

  Here, if the content of Cr is less than 20% by mass as the composition of each alloy component in the ground electrode 4, a strong Cr oxide film is not formed, and sufficient oxidation resistance may not be obtained. On the other hand, if the content of Cr exceeds 30% by mass, the workability is deteriorated and the thermal consumability is deteriorated, which may deteriorate the spark consumption. On the other hand, in the spark plug 100 of the present embodiment, the material constituting the main body portion 4a of the ground electrode 4 contains 20 to 30% by mass of Cr, so that a strong Cr oxide film is formed on the surface of the main body portion 4a. Thus, sufficient oxidation resistance can be obtained. Further, the workability and spark consumption of the main body 4a are not deteriorated.

  On the other hand, when Al is less than 1% by mass, an oxide is hardly formed directly under the Cr oxide film, and there is a possibility that the oxidation resistance is lowered. On the other hand, when the content of Al exceeds 5% by mass, workability and weldability of the noble metal tip are deteriorated. On the other hand, in the spark plug 100 of this embodiment, since the Al content is 1 to 5% by mass, the oxidation resistance of the main body portion 4a of the ground electrode 4 can be improved. There is no deterioration in weldability. In addition, the content of Al is preferably 1 to 3% by mass.

  Furthermore, if the Fe content is less than 7% by mass, the workability becomes insufficient. On the other hand, if the Fe content exceeds 20% by mass, the high temperature strength is lowered. On the other hand, in the spark plug 100 of this embodiment, since the Fe content is 7 to 20% by mass, sufficient workability of the main body 4a of the ground electrode 4 is ensured and the high temperature strength is reduced. Will not be invited.

  Moreover, by containing Ti, when nitride and C are contained inside the material, carbide is formed, and coarsening of crystal grains is suppressed. The coarsening of crystal grains may cause breakage of the ground electrode 4. On the other hand, if the Ti content exceeds 0.5% by mass, weldability is lowered, internal oxidation is promoted, and oxidation resistance is deteriorated. On the other hand, in the spark plug 100 of the present embodiment, since the Ti content is 0.05 to 0.5% by mass, the coarsening of the crystal grains in the main body portion 4a of the ground electrode 4 can be suppressed, Moreover, the weldability is not deteriorated and internal oxidation is not promoted. Thereby, the further improvement of the oxidation resistance of the main body part 4a is realized, which contributes to a longer life.

Moreover, since it contains Mn and Si, it acts as a deoxidizing material at the time of material preparation, oxygen is removed from the material, and it contributes to oxidation prevention. Moreover, oxidation resistance improves by containing trace amount Mn and Si. However, if it is contained in a large amount (when the contents of Mn and Si exceed 0.1% by mass), the workability deteriorates. On the other hand, since the spark plug 100 according to the present embodiment contains 0.5% by mass or less of Mn and Si, the effects of preventing oxidation and improving oxidation resistance can be obtained without degrading workability.
In order to achieve the effect, the content of Mn and Si is preferably 0.05% by mass or more. Further, the content of Mn and Si is preferably 0.1% by mass or less.

  And high temperature intensity | strength improves by containing carbon. Moreover, since the coarsening of a crystal grain is also suppressed, breakage of the ground electrode 4 can be suppressed. But when it contains abundantly (when content of C exceeds 0.5 mass%), workability will deteriorate. On the other hand, since the spark plug 100 of the present embodiment contains 0.12 to 0.5% by mass of C, the high temperature strength is improved without degrading workability, and the main body of the ground electrode 4 The effect of suppressing the coarsening of crystal grains in 4a can be obtained.

  Moreover, in the spark plug 100 of this embodiment, since content of Ni was 70 mass% or less, the effect of an improvement in spark consumption is obtained. Among the elements contained in the Ni alloy, in the three elements (Ni, Fe, Cr) having a high content, the content of Fe and Cr having a melting point higher than that of Ni is reduced by decreasing the Ni content having the lowest melting point. Since the amount is relatively increased, the spark consumption of the Ni alloy is improved. The Ni content is preferably 65% by mass or less.

  As described above, according to the present embodiment, the strong Cr oxide film and the Al oxide immediately below the Cr oxide film improve the oxidation resistance compared to the conventional case and contribute to a longer life. However, even if only the oxidation resistance is improved, the ground electrode may be broken if the high temperature fatigue strength is not sufficient.

  Therefore, in the present embodiment, the main body portion 4a of the ground electrode 4 contains at least one element among Zr, Y, Nd, Ce, La, and Sm as the specific element group. These specific element groups are precipitated at the grain boundaries, and can suppress the formation of the Al nitride. However, if the total content of the specific element group is less than 5% of Al, the effect of suppressing the formation of Al nitride may be insufficient. Moreover, when the sum total of content of a specific element group exceeds 1 mass%, there exists a possibility that the workability of material may be deteriorated.

In this regard, according to the present embodiment, since the total content of the specific element group is set to 5% or more of the Al content, the formation of Al nitride can be sufficiently suppressed. Therefore, it is possible to suppress a decrease in the high temperature fatigue strength of the main body portion 4a of the ground electrode 4, and it is possible to improve the durability of the main body portion 4a. As a result, the life of the spark plug 100 for the internal combustion engine can be extended. Moreover, since the sum total of content of a specific element group shall be 1 mass% or less, the workability of the main-body part 4a is not deteriorated.
Moreover, when the material having the above composition was used, the result was obtained that the weldability of the disk-shaped tip constituting the ignition part 32 to the main body part 4a of the ground electrode 4 was improved as compared with the conventional case.

  In the present embodiment, the main body 3a of the center electrode 3 is formed through die drawing or the like using a molten alloy obtained by blending and melting each alloy component. The alloy constituting the main body portion 3a of the center electrode 3 does not contain the specific element among the Ni alloys constituting the main body portion 4a of the ground electrode 4. That is, the alloy contains Ni as a main component, contains 20-30% by mass of Cr, 7-20% by mass of Fe, and 1-5% by mass of Al, and contains Zr, Y, Nd, Ce, La, and , Does not contain Sm.

Since the center electrode 3 is not exposed to a high temperature atmosphere as compared with the ground electrode 4, high temperature fatigue strength is not required as much as the ground electrode. On the other hand, since the alloy constituting the main body 4a of the ground electrode 4 contains a specific element, the workability is not so good as compared with an alloy not containing the specific element.
Therefore, according to this embodiment, when the center electrode 3 is not required to have a high temperature fatigue strength as high as that of the ground electrode 4, the workability of the center electrode 3 is taken into consideration and the alloy constituting the main body 3a of the center electrode 3 is grounded. Of the alloys constituting the main body 4a of the electrode 4, an alloy that does not contain a specific element can be used.

  In addition, this embodiment has a technical feature in containing a specific element group. Therefore, experimental results obtained by changing the content ratio of the specific element are shown below. Here, Cr is 25.00 mass%, Al is 2.50 mass%, Fe is 10.00 mass%, Si is 0.10 mass%, Mn is 0.08 mass%, and C is 0.17 mass%. Using high-temperature fatigue strength and workability, a material containing 0.10% by mass of Ti and the balance of Ni was used to contain the specific element group.

  In Table 1, for the evaluation of the high temperature fatigue strength, a suitably prepared ground electrode test piece is subjected to a rotating bending fatigue test in accordance with JIS Z2274. The tester used an axial load fatigue test, setting the temperature to 700 ° C., the stress amplitude condition to 120 MPa tension / compression, the repetition rate to 3000 rpm, and the number of repetitions to 10 8 cycles. After the test, the ground electrode was shown as “◯” when it was not broken, and “x” when it was broken.

  On the other hand, the evaluation of workability was carried out by whether or not cold working with a 15 mm diameter round bar having a cross-sectional dimension of 1.5 mm × 2.8 mm was possible. Those that could be cold worked were indicated as “◯”, and those that could not be cold worked or cracked were indicated as “x”.

  No. No. 1 does not contain a specific element group, so to speak, corresponds to the prior art. In this case, the high temperature fatigue strength was “x” and the workability was “◯”. This is presumably because Al nitride is formed at the grain boundaries as described above.

  No. Nos. 2 to 7 are cases in which 1.00 mass% of one kind of different specific element is contained. No. 2 contains Y. 3 contains Zr. Similarly, no. 4, Nd, No. In Ce, No. 5 In La, No. 6 7 contains Sm. In this case, both high temperature fatigue strength and workability were obtained as “◯”. It can be seen that the formation of Al nitride is sufficiently suppressed by the inclusion of the specific element corresponding to the upper limit (1% by mass).

  In contrast, no. No. 8 contains 1.20% by mass of Y. No. 9 contains 1.20% by mass of Zr. In this case, the result of workability “x” was obtained. Thereby, it turns out that workability deteriorates by containing the specific element exceeding an upper limit (1 mass%).

  No. 10 to 12 are cases in which 0.08% by mass of two kinds of specific elements are contained. No. No. 10 contains Y and Zr. No. 11 contains Zr and Ce. No. 12 contains Nd and La. In both cases, the results of high-temperature fatigue strength “◯” and workability “◯” were obtained. In these cases, the total content of the two specific elements is 0.16% by mass, and is 0.125% by mass or more, which is 5% of the Al content of 2.50% by mass. It can be said that the formation of Al nitride is sufficiently suppressed by the content. In addition, before and after the high temperature fatigue test (rotary bending fatigue test), No. No. 10-12 ground electrode specimens were observed. The shape (thickness or length) of 10 test pieces hardly changed. From this, it can be seen that the inclusion of Y and Zr in the specific element group sufficiently suppresses the formation of Al nitride and further suppresses the decrease in high-temperature fatigue strength.

  No. 13 is a case containing 0.055% by mass of Y and 0.07% by mass of Zr, and the total content of the specific element group is just 5% of the Al content of 2.50% by mass. It is 0.125% by mass. Also in this case, the results of “◯” were obtained for both high temperature fatigue strength and workability. In contrast, no. No. 14 is a case containing 0.05% by mass of Y and 0.05% by mass of Zr. The total content of the specific element group is 0.10% by mass, and the Al content is 2.50. It is less than 0.125 mass% which is 5% of mass%. In this case, the result of high temperature fatigue strength “×” was obtained. Thereby, when the total content of the specific element group is less than 5% of the Al content, the formation of Al nitride is not sufficiently suppressed, and as a result, the high temperature fatigue strength is reduced.

  No. 15 to 19 are cases in which two types of specific elements Y and Zr are contained. The total content of the specific elements is 0.27% by mass, whereas Y is 0.06% by mass, and 0.0. The content ratio of Y and Zr is changed by adding 09 mass%, 0.13 mass%, 0.18 mass%, and 0.20 mass%. That is, no. No. 15 is Y / Zr = 0.29. 16, Y / Zr = 0.5. No. 17, Y / Zr = 0.93. 18 is Y / Zr = 2. In 19, Y / Zr = 2.9. In this case, the results of high temperature fatigue strength “◯” and workability “◯” were obtained. In addition, before and after the high temperature fatigue test (rotary bending fatigue test), No. When the test pieces of ground electrodes 15 to 19 were observed, The shape (thickness or length) of the test pieces of 16 to 18 is No. Compared to 15 and 19, there was no change. From this, by forming the ratio of Y content to Zr content (Y / Zr) to 0.5-2, the formation of Al nitride is sufficiently suppressed and the high temperature fatigue strength is further reduced. It turns out that it can suppress.

In addition, it is not limited to the description content of embodiment mentioned above, For example, you may implement as follows.
(A) In the experiment in the above embodiment, one type or two types of specific elements are included, but three or more types of specific elements may be included. In that case, it is desirable to contain each specific element in a proportion close to equality.
(B) In the above embodiment, the material having the above composition is used as the material constituting the ground electrode 4 (main body portion 4a). However, instead of or in addition to this, the material constituting the center electrode 3 (main body portion 3a). A material having the above composition may be used.
(C) Instead of the ground electrode 4 (main body part 4a) of the above embodiment, a heat transfer promoting part made of a copper alloy or the like may be embedded in the ground electrode (main body part).

It is explanatory drawing which shows the structure of a spark plug. It is explanatory drawing which shows formation of the ignition part with respect to the main-body part of a center electrode and a ground electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Metal fitting, 2 ... Insulator, 3 ... Center electrode, 4 ... Ground electrode, 3a, 4a ... Main-body part, 6 ... Hole part, 7 ... Screw part, 21 ... Tip part, 31, 32 ... Ignition part, 33 ... spark discharge gap, 100 ... spark plug, B1, B2 ... weld.

Claims (10)

In a spark plug for an internal combustion engine comprising a center electrode, and a ground electrode arranged to have a discharge gap with the center electrode,
At least one of the center electrode and the ground electrode is
Nickel as the main component,
20-30% by mass of chromium,
7-20% by mass of iron,
A nickel alloy containing 1 to 5% by mass of aluminum,
further,
Zirconium, yttrium, neodymium, cerium, lanthanum, and samarium as a specific element group, containing at least one or more of the specific element group,
A spark plug for an internal combustion engine, characterized in that the total content of the specific element group is made of a nickel alloy having a content of 5% or more of the aluminum content. The spark plug for an internal combustion engine according to claim 1, wherein the total content of the specific element group is 1% by mass or less. The spark plug for an internal combustion engine according to claim 1 or 2, wherein the nickel alloy further contains 0.05 to 0.5 mass% of titanium. The spark plug for an internal combustion engine according to any one of claims 1 to 3,
The nickel alloy further includes
0.5% by mass or less of manganese,
Silicon of 0.5 mass% or less,
Among them, a spark plug for an internal combustion engine comprising at least one of them. The spark plug for an internal combustion engine according to any one of claims 1 to 4,
The spark plug for an internal combustion engine, wherein the nickel alloy further contains 0.12 to 0.5% by mass of carbon. The spark plug for an internal combustion engine according to any one of claims 1 to 5,
A spark plug for an internal combustion engine, wherein the nickel content in the nickel alloy is 70% by mass or less. The spark plug for an internal combustion engine according to any one of claims 1 to 6,
The spark plug for an internal combustion engine, wherein the nickel alloy contains at least yttrium and zirconium in the specific element group. The spark plug for an internal combustion engine according to claim 7,
When the ratio of the content of yttrium and zirconium contained in the nickel alloy is expressed by (content of yttrium) / (content of zirconium), the content ratio is 0.5-2. A spark plug for an internal combustion engine. The spark plug for an internal combustion engine according to any one of claims 1 to 8,
The spark plug for an internal combustion engine, wherein the ground electrode is made of the nickel alloy. The spark plug for an internal combustion engine according to claim 9,
The spark plug for an internal combustion engine, wherein the center electrode is made of a nickel alloy that does not include the specific element in the nickel alloy.

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