Spark plug

Abstract

To provide a spark plug that can avoid premature wear even if Ta is added to an electrode member.SOLUTION: In the spark plug, an angle formed by a central forge flow line (15b) along the longitudinal direction of crystal grains that configure a precious metal tip (15), which is a central electrode tip, and a ground normal (16b), which is the normal of a ground discharge surface (16a), a surface on which a ground electrode 14 faces the precious metal tip (15), is 30 degrees or less.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to spark plugs. [Background technology]

[0002] Conventionally, there is a spark plug that uses an IrRh alloy, in which 3 to 30 wt% of Rh (rhodium) is added to Ir (iridium), for the electrode member of the discharge part. Such a spark plug has excellent high-temperature heat resistance and can improve wear resistance at the same time. Aiming to further improve wear resistance, a spark plug described in the following Patent Document 1 has been proposed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-110114 A Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses a spark plug in which an electrode member in which at least one of Ta (tantalum) and Nb (niobium) is added in a total amount of 0.3 to 7.5 wt % to an IrRh alloy is provided in a discharge portion.

[0005] Adding Ta to an electrode material makes the surface layer brittle, and if a discharge attack occurs in this brittle area, the surface layer may be worn out early. The early wear of the surface layer may also accelerate wear of the center part other than the surface layer.

[0006] An object of the present disclosure is to provide a spark plug capable of preventing early wear even when Ta is added to an electrode member. [Means for solving the problem]

[0007] The present disclosure relates to a spark plug, comprising a discharge portion which discharges when a voltage is applied thereto, the discharge portion being formed by arranging a center electrode (13) and a ground electrode (14) opposite each other, the center electrode being formed by joining a center electrode tip (15) containing Ir, Rh, and Ta to a center electrode base material (13a), and an angle formed between a central grain flow line (15b) extending along the longitudinal direction of crystal grains constituting the center electrode tip and a ground normal (16b) which is a normal to a ground discharge surface (16a) which is the surface of the ground electrode facing the center electrode tip is within 30°.

[0008] The present disclosure relates to a spark plug, comprising a discharge portion which discharges when a voltage is applied thereto, the discharge portion being formed by arranging a center electrode (13) and a ground electrode (14) opposite each other, the center electrode being formed by joining a center electrode tip (15) containing Ir, Pt, and Ta to a center electrode base material (13a), and an angle formed between a central grain flow line (15b) extending along the longitudinal direction of crystal grains constituting the center electrode tip and a ground normal (16b) which is a normal to a ground discharge surface (16a) which is the surface of the ground electrode facing the center electrode tip is within 30°.

[0009] By keeping the angle between the central grain flow line and the ground normal within 30°, wear due to electrical discharge attacks can be reduced. Effect of the Invention

[0010] According to the present disclosure, it is possible to provide a spark plug capable of preventing early wear even when Ta is added to the electrode member. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a half cross-sectional view of a spark plug. [Diagram 2] FIG. 2 is a partially enlarged view of FIG. [Diagram 3] FIG. 3 is an enlarged view of the discharge section. [Figure 4] FIG. 4 is an enlarged view of the discharge section. [Diagram 5] FIG. 5 is an enlarged view of the discharge section. [Figure 6] FIG. 6 is an enlarged view of the discharge section. [Figure 7] FIG. 7 is an enlarged view of the discharge section. [Figure 8] FIG. 8 is an enlarged view of the discharge portion. [Figure 9] FIG. 9 is a diagram for explaining the test results. [Figure 10] FIG. 10 is an enlarged view of the discharge portion. [Figure 11] FIG. 11 is a diagram for explaining the test results. [Figure 12] FIG. 12 is a diagram for explaining the test results. [Figure 13] FIG. 13 is a diagram for explaining the test results. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicated description will be omitted.

[0013] 1, the spark plug 10 includes a housing 11. The housing 11 is cylindrical and made of a metal material such as iron. A threaded portion 11a is formed on the outer periphery of the lower part of the housing 11.

[0014] A lower end of a cylindrical insulator 12 is coaxially inserted inside the housing 11. The insulator 12 is made of an insulating material such as alumina. An upper end 11b of the housing 11 is crimped to the insulator 12, so that the housing 11 and the insulator 12 are joined together. A through hole 12a is provided at the lower end, which is one end of the insulator 12. A center electrode 13, which is an electrode for a spark plug, is inserted and held in the through hole 12a.

[0015] The center electrode 13 is formed in a cylindrical shape using a Ni alloy having excellent heat resistance as a base material. Specifically, the inner material of the center electrode 13 is formed of copper, and the outer material is formed of a Ni (nickel)-based alloy. A tip portion 13a of the center electrode 13 is exposed from the lower end of the lower part of the insulator 12.

[0016] A ground electrode 14 is disposed at a position facing the tip portion 13a of the center electrode 13, and extends in a curved manner integrally with the lower end surface of the housing 11. The ground electrode 14 is also made of a Ni-based alloy.

[0017] As shown in Fig. 2, the discharge portion of the spark plug 10 is formed by the tip portion 13a of the center electrode 13 and the opposing tip portion 14a of the ground electrode 14. Precious metal tips 15, 16 are attached to the tip portion 13a of the center electrode 13 and the tip portion 14a of the ground electrode 14, respectively. The precious metal tip 15 is provided on the center electrode 13 side and corresponds to the center electrode tip. The precious metal tip 16 is provided on the ground electrode 14 side and corresponds to the ground electrode tip.

[0018] The precious metal tips 15 and 16 are joined to the tip portions 13a and 14a, respectively, by a joining process such as laser welding or resistance welding. The tip portions 13a and 14a correspond to the center electrode base material. In Fig. 2, fusion zones 31 and 32 are formed at the portion where the precious metal tip 15 and the tip portion 13a are joined. The fusion zones 31 and 32 appear to be separated in the cross-sectional view, but are connected along the outer periphery of the precious metal tip 15.

[0019] A spark gap 17 is formed between the noble metal tip 15 and the noble metal tip 16. Discharge occurs between the noble metal tip 15 and the noble metal tip 16 in the spark gap 17, and a spark is generated.

[0020] Both the noble metal tips 15 and 16 are formed in a cylindrical shape. For example, the noble metal tip 15 has an outer diameter A of 1.0 mm and a height B of 1.5 mm. The noble metal tip 16 has an outer diameter C of 1.0 mm and a height D of 0.5 mm.

[0021] 1, as is well known, a central shaft 18 and a terminal portion 19 are electrically connected to the upper portion of the center electrode 13. An external circuit that applies a high voltage for generating sparks is connected to the terminal portion 19. In addition, a gasket 20 used for mounting to an internal combustion engine is provided on the upper end portion of the threaded portion 11a of the housing 11.

[0022] The precious metal tips 15, 16 are formed of an IrRh alloy based on Ir (iridium), which has a high melting point and excellent wear resistance, and containing Rh (rhodium) to suppress the high-temperature volatility of Ir. The IrRh alloy can suppress the oxidation and volatilization of Ir from grain boundaries in high-temperature air or oxidizing atmosphere. An IrRh alloy containing preferably 5 to 50 wt% Rh, and more preferably 5 to 30 wt% Rh, can suppress the oxidation and volatilization of Ir from grain boundaries in high-temperature air or oxidizing atmosphere. In the IrRh alloy, the components other than Rh and Ta are Ir.

[0023] 3, the positional relationship between the precious metal tip 15 provided on the center electrode 13 side and the precious metal tip 16 provided on the ground electrode 14 side will be described. Note that even if the precious metal tip 16 is not provided on the ground electrode 14, the same positional relationship can be established between the precious metal tip 15 and the tip portion 14a of the ground electrode 14.

[0024] The precious metal tip 15 includes a surface layer portion 151 and a non-surface layer portion 152. The precious metal tip 15 can be obtained by processing the sintered body into a wire- or rod-shaped material by at least one of hot forging, hot rolling, and hot wire drawing in a hot working process, and then cutting the material into a predetermined length in the length direction. Therefore, the non-surface layer portion 152 in which the crystal grains are stretched into a fiber-like shape and the surface layer portion 151 in which the crystal grains are not stretched into a fiber-like shape are formed. In this embodiment, the portion of the non-surface layer portion 152, particularly the portion near the center, is used as a central tip portion 153.

[0025] A metal flow line along the longitudinal direction of the crystal grains in the central tip portion 153 is defined as a central grain flow line 15b. A surface of the noble metal tip 16 facing the noble metal tip 15 is defined as a ground discharge surface 16a. A normal to the ground discharge surface 16a is defined as a ground normal 16b.

[0026] 3, precious metal tip 15 is arranged so that central discharge surface 15a, which is the surface facing precious metal tip 16, is parallel to ground discharge surface 16a, which is the surface of precious metal tip 16 facing precious metal tip 15. In this state, central grain flow 15b and ground normal 16b are parallel to each other.

[0027] 4 and 5 are diagrams for explaining that the angle between the central grain flow 15b and the ground normal 16b is preferably 30° or less. As shown in Fig. 4, when the precious metal tip 15 is attached to the tip 13a of the center electrode 13, the precious metal tip 15 may be attached at an angle. As shown in Fig. 5, a gap G is formed between the precious metal tip 15 and the precious metal tip 16, and an electric discharge occurs between the precious metal tip 15 and the precious metal tip 16 to form a spark. When a spark is generated in the gap G, the attack by the electric discharge is directed toward the lowest end of the precious metal tip 15, which is the surface layer 151 in Fig. 5.

[0028] As described later, it is preferable that the angle between central grain flow 15b and ground normal 16b be 30° or less. If the angle between central grain flow 15b and ground normal 16b is within this range, the attack of the discharge on surface layer 151 is not excessive, and wear of precious metal tip 15 can be reduced.

[0029] 6, even if the precious metal tip 15 is not tilted when attached to the tip portion 13a of the center electrode 13, the precious metal tip 16 on the ground electrode 14 side may be tilted. In this case as well, it is preferable that the angle between the central grain flow line 15b and the ground normal line 16b is 30° or less.

[0030] 7, the precious metal tip 15 may be tilted when attached to the tip 13a of the center electrode 13, and the precious metal tip 16 may also be tilted when attached to the tip 14a of the ground electrode 14. In this case, the angle between the center grain flow 15b and the ground grain flow 16c that runs along the longitudinal direction of the crystal grains constituting the precious metal tip 16 is preferably within 30°.

[0031] As shown in Fig. 8, when the angle between central grain flow 15b and ground normal 16b exceeds 30° and reaches 45°, the discharge attack is directed toward a wide area of ​​surface layer 151. Fig. 9 shows the results of an engine durability test in which the angle between central grain flow 15b and ground normal 16b is changed.

[0032] Test sample A, in which the angle between central grain flow 15b and ground normal 16b is 0°, corresponds to the example shown in Figure 3. Test sample B, in which the angle between central grain flow 15b and ground normal 16b is 30°, corresponds to the examples shown in Figures 4, 5, 6, and 7. Test sample C, in which the angle between central grain flow 15b and ground normal 16b is 45°, corresponds to the example shown in Figure 8.

[0033] The test conditions for the engine durability test were as follows: a test spark plug 10 was attached to a 2000cc 4-cylinder engine, and the engine was idled for 1 minute, then kept at 5600 r / min for 1 minute (one cycle), and the increase in gap G was confirmed for 200 hours (equivalent to a run of 100,000 km).

[0034] If the expansion amount of gap G exceeds 0.2 mm, the required voltage increases and affects other components such as the insulator voltage resistance, so a gap G expansion amount of 0.2 mm is set as the NG boundary value. As shown in Fig. 9, when the angle between central grain flow 15b and ground normal 16b is 30° or less, the expansion amount of gap G is 0.2 mm or less in all of the test samples for four cylinders. On the other hand, when the angle between central grain flow 15b and ground normal 16b is 35° or more, the expansion amount of gap G is 0.2 mm or more in all of the test samples for four cylinders.

[0035] As shown in Figure 10(A), when the angle between central grain flow 15b and ground normal 16b is 35° or more, such as 45°, surface layer 151 falls off due to an electrical discharge attack. When surface layer 151 falls off, a chain reaction of burrs occurs in non-surface layer 152, as shown in Figure 10(B), and precious metal tip 15 is worn away. As a result, gap GA between precious metal tip 15 and precious metal tip 16 expands to gap GB. Therefore, by setting the angle between central grain flow 15b and ground normal 16b to 30° or less, wear of precious metal tip 15 can be suppressed.

[0036] Figure 11 shows the test results in which the angle between the central grain flow line 15b and the ground normal 16b is set to 30° and the aspect ratio is changed. The aspect ratio is defined as the ratio between the maximum distance and the minimum distance in a pair of parallel tangents that do not cross the inside of the grain, when the tangents are drawn in various positions to the outline of the grain observed in the field of view on a specified cross section.

[0037] The test conditions for the engine durability test were as follows: a test spark plug 10 was attached to a 2000cc 4-cylinder engine, and the engine was idled for 1 minute, then kept at 5600 r / min for 1 minute (one cycle), and the increase in gap G was confirmed for 200 hours (equivalent to a run of 100,000 km).

[0038] As shown in FIG. 11, if the aspect ratio is 6 or more, the amount of gap expansion is 0.2 mm or less for all components, and it was confirmed that the impact of the gap expansion on other components can be suppressed.

[0039] The spark plug of this embodiment has a discharge portion that discharges when a voltage is applied. The discharge portion is formed by arranging a center electrode 13 and a ground electrode 14 facing each other. The center electrode 13 is formed by joining a precious metal tip 15 containing Ir, Rh, and Ta as a center electrode tip to a tip portion 13a as a center electrode base material, and an angle formed by a central grain flow 15b along the longitudinal direction of crystal grains constituting the precious metal tip 15 and a ground normal 16b that is a normal to a ground discharge surface 16a that is a surface of the ground electrode facing the center electrode tip is within 30°.

[0040] By setting the angle between central grain flow 15b and ground normal 16b to within 30°, wear due to electrical discharge attack can be reduced.

[0041] The ground electrode 14 is formed by joining a precious metal tip 16 serving as a ground electrode tip containing Ir, Rh, or Ta to the tip 14a serving as a ground electrode base material, and the ground discharge surface 16a is formed on the precious metal tip 16. In the present embodiment, an example in which the precious metal tip 16 is provided on the tip 14a of the ground electrode 14 has been described, and therefore the ground discharge surface 16a is formed on the precious metal tip 16. However, the precious metal tip 16 does not have to be provided, and in that case, the surface of the tip 14a facing the precious metal tip 15 becomes the ground discharge surface, and the normal to the ground discharge surface becomes the ground normal.

[0042] In this embodiment, the angle formed by center grain flow 15b and ground grain flow 16c extending along the longitudinal direction of the crystal grains constituting precious metal tip 16 serving as the ground electrode tip can be within 30°.

[0043] In this embodiment, the aspect ratio of the grains forming center grain flow 15b and / or ground grain flow 15c is preferably 6 or more.

[0044] In the above description, the precious metal tips 15 and 16 are made of an IrRh alloy containing Ir (iridium), which has a high melting point and excellent wear resistance, and Rh (rhodium) to suppress the high-temperature volatility of Ir. The material of the precious metal tips 15 and 16 is not limited to this, and may be made of an IrPt alloy containing Ir (iridium), which has a high melting point and excellent wear resistance, and Pt (platinum), to suppress the high-temperature volatility of Ir. The IrPt alloy can suppress the oxidation and volatilization of Ir from the grain boundaries in the air or an oxidizing atmosphere at high temperatures. An IrPt alloy containing preferably 5 to 50 wt% Pt, and more preferably 5 to 30 wt% Pt, can suppress the oxidation and volatilization of Ir from the grain boundaries in the air or an oxidizing atmosphere at high temperatures. In the IrPt alloy, the components other than Pt and Ta are Ir.

[0045] The results of an engine durability test using IrPt metal are shown in Fig. 12. Fig. 12 shows the results of an engine durability test in which the angle between central grain flow 15b and ground normal 16b was changed.

[0046] Test sample A, in which the angle between central grain flow 15b and ground normal 16b is 0°, corresponds to the example shown in Figure 3. Test sample B, in which the angle between central grain flow 15b and ground normal 16b is 30°, corresponds to the examples shown in Figures 4, 5, 6, and 7. Test sample C, in which the angle between central grain flow 15b and ground normal 16b is 45°, corresponds to the example shown in Figure 8.

[0047] The test conditions for the engine durability test were as follows: a test spark plug 10 was attached to a 2000cc 4-cylinder engine, and the engine was idled for 1 minute, then kept at 5600 r / min for 1 minute (one cycle), and the increase in gap G was confirmed for 200 hours (equivalent to a run of 100,000 km).

[0048] If the expansion amount of gap G exceeds 0.2 mm, the required voltage increases and affects other components such as the insulator withstand voltage, so a gap G expansion amount of 0.2 mm is set as the NG boundary value. As shown in Fig. 12, when the angle between central grain flow 15b and ground normal 16b is 30° or less, the expansion amount of gap G is 0.2 mm or less in all of the test samples for four cylinders. On the other hand, when the angle between central grain flow 15b and ground normal 16b is 35° or more, the expansion amount of gap G is 0.2 mm or more in all of the test samples for four cylinders.

[0049] As shown in Figure 10(A), when the angle between central grain flow 15b and ground normal 16b is 35° or more, such as 45°, surface layer 151 falls off due to an electrical discharge attack. When surface layer 151 falls off, a chain reaction of burrs occurs in non-surface layer 152, as shown in Figure 10(B), and precious metal tip 15 is worn away. As a result, gap GA between precious metal tip 15 and precious metal tip 16 expands to gap GB. Therefore, by setting the angle between central grain flow 15b and ground normal 16b to 30° or less, wear of precious metal tip 15 can be suppressed.

[0050] Figure 13 shows the test results in which the angle between the central grain flow 15b and the ground normal 16b is 30° and the aspect ratio is changed. The aspect ratio is defined as the ratio between the maximum and minimum distances between pairs of parallel tangents that do not cross the grain interior, when the pairs of tangents are drawn in various positions to the outline of the grain observed in the field of view on a specified cross section.

[0051] The test conditions for the engine durability test were as follows: a test spark plug 10 was attached to a 2000cc 4-cylinder engine, and the engine was idled for 1 minute, then kept at 5600 r / min for 1 minute (one cycle), and the increase in gap G was confirmed for 200 hours (equivalent to a run of 100,000 km).

[0052] As shown in FIG. 13, if the aspect ratio is 6 or more, the amount of gap expansion is 0.2 mm or less for all components, and it was confirmed that the impact of the gap expansion on other components can be suppressed.

[0053] The spark plug of this embodiment has a discharge portion that discharges when a voltage is applied. The discharge portion is formed by arranging a center electrode 13 and a ground electrode 14 facing each other. The center electrode 13 is formed by joining a precious metal tip 15 containing Ir, Pt, and Ta as a center electrode tip to a tip portion 13a as a center electrode base material, and an angle formed between a central grain flow 15b along the longitudinal direction of crystal grains constituting the precious metal tip 15 and a ground normal 16b that is a normal to a ground discharge surface 16a that is the surface of the ground electrode facing the center electrode tip is within 30°.

[0054] By setting the angle between central grain flow 15b and ground normal 16b to within 30°, wear due to electrical discharge attack can be reduced.

[0055] The ground electrode 14 is formed by joining a precious metal tip 16 serving as a ground electrode tip containing Ir, Pt, or Ta to the tip 14a serving as a ground electrode base material, and the ground discharge surface 16a is formed on the precious metal tip 16. In the present embodiment, an example in which the precious metal tip 16 is provided on the tip 14a of the ground electrode 14 has been described, and therefore the ground discharge surface 16a is formed on the precious metal tip 16. However, the precious metal tip 16 does not have to be provided, and in that case, the surface of the tip 14a facing the precious metal tip 15 becomes the ground discharge surface, and the normal to the ground discharge surface becomes the ground normal.

[0056] In this embodiment, the angle formed by center grain flow 15b and ground grain flow 16c extending along the longitudinal direction of the crystal grains constituting precious metal tip 16 serving as the ground electrode tip can be within 30°.

[0057] In this embodiment, the aspect ratio of the grains forming center grain flow 15b and / or ground grain flow 15c is preferably 6 or more.

[0058] The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Any design modifications made by a person skilled in the art to these specific examples are also included within the scope of the present disclosure as long as they have the features of the present disclosure. The elements of each of the above-mentioned specific examples and their arrangements, conditions, shapes, etc. are not limited to those exemplified and can be changed as appropriate. The combination of each of the elements of each of the above-mentioned specific examples can be changed as appropriate as long as no technical contradiction occurs. [Explanation of symbols]

[0059] 10: Spark plug 11: Housing 11a: Threaded part 11b: Upper end 12: Insulator 13: Center electrode 13a:Tip 14: Ground electrode 14a: Tip 15: Precious metal chip 16: Precious metal chip 17: Spark Gap 18: Central axis 19:Terminal section 20: Gasket

Claims

1. A spark plug, A discharge unit that discharges when a voltage is applied to the discharge unit; The discharge portion is formed by arranging a center electrode (13) and a ground electrode (14) opposite each other, The center electrode is formed by joining a center electrode tip (15) containing Ir, Rh, and Ta to a center electrode base material (13a), The angle between a central grain flow (15b) extending along the longitudinal direction of the crystal grains constituting the center electrode tip and a ground normal (16b) that is a normal to a ground discharge surface (16a) that is a surface of the ground electrode facing the center electrode tip is within 30°, and the central grain flow and the ground normal are not parallel to each other.

2. 2. The spark plug of claim 1, The ground electrode is formed by joining a ground electrode tip (16) containing Ir, Rh, and Ta to a ground electrode base material (14a), The ground discharge surface is formed on the ground electrode tip.

3. A spark plug, A discharge unit that discharges when a voltage is applied to the discharge unit; The discharge portion is formed by arranging a center electrode (13) and a ground electrode (14) opposite each other, The center electrode is formed by joining a center electrode tip (15) containing Ir, Pt, and Ta to a center electrode base material (13a), The angle between a central grain flow (15b) extending along the longitudinal direction of the crystal grains constituting the center electrode tip and a ground normal (16b) that is a normal to a ground discharge surface (16a) that is a surface of the ground electrode facing the center electrode tip is within 30°, and the central grain flow and the ground normal are not parallel to each other.

4. 4. The spark plug according to claim 3, The ground electrode is formed by joining a ground electrode tip (16) containing Ir, Pt, and Ta to a ground electrode base material (14a), The ground discharge surface is formed on the ground electrode tip.

5. 5. A spark plug according to claim 2 or 4, The angle between the central grain flow and a ground grain flow (16c) extending along the longitudinal direction of the crystal grains constituting the ground electrode tip is within 30°, and the central grain flow and the ground grain flow are not parallel to each other.

6. 6. The spark plug according to claim 5, The aspect ratio of the grains forming the center grain flow and / or the ground grain flow is 6 or more.

Images