Spark plug

Abstract

To provide a spark plug capable of improving ignitability while reducing wasting of a chip.SOLUTION: A spark plug comprises: an insulator that is provided with a shaft hole extending along an axis line; a central electrode that is arranged in the shaft hole; a main fitting that is arranged on the outer periphery of the insulator; and a grounding electrode that is connected to the main fitting. At least one of the central electrode and the grounding electrode includes a base material, and a chip that is joined to the base material and that consists primarily of Ru. The chip includes a discharge surface that faces the other one of the central electrode and the grounding electrode. An arithmetic average roughness of the discharge surface is in the range of 0.4-4.8 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a spark plug having a tip containing Ru. [Background technology]

[0002] Patent Document 1 discloses a prior art in which at least one of the center electrode and the ground electrode includes a tip made of simple Ru or a Ru alloy. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-54955 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a need in the prior art for a technology that can improve ignition performance while reducing tip wear due to oxidation.

[0005] The present invention has been made to meet this demand, and an object of the present invention is to provide a spark plug that can improve ignition performance while reducing tip wear. [Means for solving the problem]

[0006] A first aspect for achieving this object includes an insulator having an axial hole extending along an axis, a center electrode disposed in the axial hole, a metallic shell disposed on the outer periphery of the insulator, and a ground electrode connected to the metallic shell, wherein the center electrode includes a base material and a tip joined to the base material, the tip is mainly composed of Ru and includes a discharge surface facing the ground electrode, and the arithmetic mean roughness of the discharge surface is 0.4 μm or more and 4.8 μm or less.

[0007] A second aspect includes an insulator having an axial hole extending along an axis, a center electrode disposed in the axial hole, a metallic shell disposed on the outer periphery of the insulator, and a ground electrode connected to the metallic shell, wherein the ground electrode includes a base material and a tip joined to the base material, the tip is mainly composed of Ru and includes a discharge surface facing the center electrode, and the arithmetic mean roughness of the discharge surface is 0.4 μm or more and 4.8 μm or less.

[0008] A third aspect includes an insulator having an axial hole extending along an axis, a center electrode disposed in the axial hole, a metallic shell disposed on the outer periphery of the insulator, and a ground electrode connected to the metallic shell, wherein the center electrode and the ground electrode include a base material and a tip joined to the base material, the tip is mainly composed of Ru and includes a discharge surface facing the other of the center electrode and the ground electrode, and the arithmetic mean roughness of the discharge surface is 0.4 μm or more and 4.8 μm or less.

[0009] In a fourth aspect, in any one of the first to third aspects, the arithmetic mean roughness of the discharge surface is 3.2 μm or less.

[0010] A fifth aspect is any one of the first to fourth aspects, wherein the arithmetic mean roughness of the discharge surface is 1.1 μm or more.

[0011] In a sixth aspect, in any of the first to fifth aspects, the tip includes a side surface connected to the discharge surface, and the value obtained by dividing the arithmetic mean roughness of the side surface by the arithmetic mean roughness of the discharge surface is 0.5 or more and 2.0 or less.

[0012] In a seventh aspect, in any of the first to sixth aspects, the arithmetic mean roughness of the opposing surface of the ground electrode that faces the discharge surface of the center electrode is smaller than the arithmetic mean roughness of the discharge surface of the center electrode.

[0013] In an eighth aspect, in any of the first to seventh aspects, the base material of the center electrode includes a protrusion that protrudes from the insulator in the axial direction toward the ground electrode, and the arithmetic mean roughness of the side surface of the protrusion is smaller than the arithmetic mean roughness of the discharge surface of the center electrode. [Effects of the Invention]

[0014] According to the present invention, the arithmetic mean roughness of the discharge surface of the Ru-based tip is 4.8 μm or less, which reduces tip wear due to oxidation.Furthermore, the arithmetic mean roughness of the discharge surface of the tip is 0.4 μm or more, which increases the electric field strength of the discharge surface and improves ignition performance. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a half cross-sectional view of a spark plug according to an embodiment; [Figure 2] 2 is a cross-sectional view of a portion where a center electrode and a ground electrode of a spark plug face each other. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a half-sectional view of a spark plug 10 according to one embodiment, taken along axis X. In Fig. 1, the lower side of the drawing is the leading end side of the spark plug 10, and the upper side is the trailing end side of the spark plug 10.

[0017] As shown in Fig. 1, a spark plug 10 includes an insulator 11, a center electrode 13, a metallic shell 15, and a ground electrode 16. The insulator 11 is a substantially cylindrical member made of ceramics such as alumina, which has excellent mechanical properties and insulating properties at high temperatures. The insulator 11 has an axial hole 12 extending therethrough along the axis X. The center electrode 13 is a rod-shaped electrode disposed in the axial hole 12 along the axis X.

[0018] The terminal fitting 14 is a rod-shaped member to which an ignition device (not shown) is connected, and its tip side is disposed in the axial hole 12 of the insulator 11. The terminal fitting 14 is electrically connected to the center electrode 13 in the axial hole 12.

[0019] The metal shell 15 is a substantially cylindrical metal member that is fixed to a screw hole (not shown) of an internal combustion engine. The metal shell 15 is made of a conductive metal material (such as low-carbon steel). The metal shell 15 is fixed to the outer periphery of the insulator 11. A ground electrode 16 is connected to the metal shell 15.

[0020] 2 is a cross-sectional view of the portion of the spark plug 10 where the center electrode 13 and the ground electrode 16 face each other. The center electrode 13 includes a base material 17 and a tip 20 provided at the tip of the base material 17.

[0021] A core material 18 having excellent thermal conductivity is embedded in the base material 17. The material of the base material 17 is, for example, Ni or an alloy containing Ni as a main component, and the material of the core material 18 is, for example, Cu or an alloy containing Cu as a main component. The core material 18 can be omitted.

[0022] The tip 20 is joined to the base material 17 by a fusion zone 19. The tip 20 and the base material 17 are melted together in the fusion zone 19. The fusion zone 19 is formed by laser welding, resistance welding, diffusion bonding, or the like. The tip 20 includes a discharge surface 21 facing the ground electrode 16 and a side surface 22 connected to the discharge surface 21.

[0023] The base material 17 includes a protruding portion 24 that protrudes from the tip 23 of the insulator 11 in the direction of the axis X (see FIG. 1). The protruding portion 24 is a portion of the base material 17 between the tip 23 of the insulator 11 and the fusion zone 19. The protruding portion 24 includes a side surface 25 that surrounds the axis X.

[0024] The ground electrode 16 includes a base material 26 connected to the metallic shell 15 and a tip 28 provided on the base material 26. A core material (not shown) with excellent thermal conductivity is embedded in the base material 26. The base material 26 is made of an alloy containing Ni as its main component, and the core material is made of Cu or an alloy containing Cu as its main component. The core material can be omitted. An intermediate member protruding toward the center electrode 13 may be provided on the base material 26, and the tip 28 may be joined to the intermediate member. The intermediate member is a part of the base material 26.

[0025] The tip 28 is joined to the base material 26 by a fusion zone 27. The tip 28 and the base material 26 are melted together in the fusion zone 27. The fusion zone 27 is formed by laser welding, resistance welding, diffusion bonding, or the like. The tip 28 includes a discharge surface 29 facing the center electrode 13 and a side surface 30 connected to the discharge surface 29.

[0026] At least one of the chips 20, 28 has Ru as its main component. "Having Ru as its main component" means that Ru is the element with the largest content among the elements constituting the chips 20, 28. The Ru content is preferably 50% by mass or more, more preferably 60% by mass or more or 70% by mass or more, of the total amount of components constituting the chips 20, 28.

[0027] When the tip 20 of the center electrode 13 is primarily composed of Ru, or when the tip 28 of the ground electrode 16 is primarily composed of Ru, the elements other than Ru that make up the tips 20, 28 can be one or more selected from Rh, Pd, Os, Ir, Pt, Ta, W, Mo, Nb, Re, Cr, Mn, Fe, Co, Ni, V, Ti, Zr, Hf, Al, and Sc.

[0028] When the tip 20 of the center electrode 13 is mainly composed of Ru, the ground electrode 16 is either one that includes a tip 28 mainly composed of Ru, one that includes a tip 28 mainly composed of one or more platinum group elements other than Ru (Rh, Pd, Os, Ir, Pt), or one in which the fusion zone 27 and the tip 28 are not provided in the base material 26.

[0029] When the tip 28 of the ground electrode 16 is primarily composed of Ru, the center electrode 13 is either one that includes a tip 20 primarily composed of Ru, one that includes a tip 20 primarily composed of one or more platinum group elements other than Ru (Rh, Pd, Os, Ir, Pt), or one in which the fusion zone 19 and the tip 20 are not provided in the base material 17.

[0030] The spark plug 10 is manufactured, for example, by the following method. First, the center electrode 13 is inserted into the axial hole 12 of the insulator 11. Next, the metal terminal 14 is inserted into the axial hole 12 to ensure electrical continuity between the metal terminal 14 and the center electrode 13, and then the metal shell 15, to which the ground electrode 16 is previously connected, is assembled to the outer periphery of the insulator 11. The ground electrode 16 is bent to form a spark gap between the center electrode 13 and the ground electrode 16, and the spark plug 10 is obtained.

[0031] The chips 20, 28, which are primarily composed of Ru, are made by sintering a compact of metal powder containing Ru, punching a metal plate containing Ru, cutting a metal wire containing Ru, etc. The shape of the chips 20, 28 is not limited and may be a disk, a truncated cone, an elliptical cylinder, or a polygonal prism such as a triangular prism or a square prism.

[0032] When the tip 20 of the center electrode 13 is primarily composed of Ru, the arithmetic mean roughness of the discharge surface 21 of the tip 20 is 0.4 μm or more and 4.8 μm or less. If the discharge between the center electrode 13 and the ground electrode 16 occurs mainly between the discharge surface 21 of the tip 20 and the ground electrode 16, the flame quenching effect of the center electrode 13 can be reduced, leading to improved ignition performance. The rougher the discharge surface 21, the greater the electric field strength. If the arithmetic mean roughness is 0.4 μm or more, discharge is more likely to occur on the discharge surface 21, improving ignition performance. If the arithmetic mean roughness of the discharge surface 21 is 1.1 μm or more, the effect of improving ignition performance is even greater, making it preferable.

[0033] On the other hand, for a Ru-containing tip 20, the rougher the discharge surface 21, the more susceptible the tip 20 is to wear due to oxidation. If the arithmetic mean roughness of the discharge surface 21 is 4.8 μm or less, wear of the tip 20 due to oxidation can be reduced. If the arithmetic mean roughness of the discharge surface 21 is 3.2 μm or less, the effect of reducing wear of the tip 20 is greater, which is preferable.

[0034] The arithmetic mean roughness of the discharge surface 21 is calculated by scanning the discharge surface 21 with a laser beam and measuring the contour curve (roughness curve) over a reference length using a non-contact 3D laser measuring device, and expressing the average absolute value of the height of the roughness curve. An area of ​​10% of the width of the discharge surface 21 (the length of the line segment passing through the center of gravity of the discharge surface 21) from the edge of the discharge surface 21 is excluded, and the roughness curve of the area inside this area is obtained. The electric field strength is high at the edge of the discharge surface 21 (the corner where the discharge surface 21 intersects with the side surface 22), making it easy for discharge to occur. Therefore, in order to make it easier for discharge to occur in areas other than this area, it is necessary to manage the surface roughness of the area other than this area.

[0035] The reference length is preferably 0.1 mm or more, for example, 25% of the width of the discharge surface 21, in order to ensure measurement accuracy. For example, the arithmetic mean roughness is measured at 12 points on the discharge surface 21 with a scan interval of 2 μm or more, and the five largest arithmetic mean roughnesses are selected from the 12 points, and the discharge surface 21 is fabricated so that the average of the five is in the range of 0.4 μm to 4.8 μm. The five largest arithmetic mean roughnesses are averaged because if the discharge surface 21 has a portion with a large arithmetic mean roughness, that portion is more likely to generate discharge and be more likely to be subject to oxidative wear.

[0036] The value obtained by dividing the arithmetic mean roughness of the side surface 22 of the tip 20 by the arithmetic mean roughness of the discharge surface 21 is preferably 0.5 or more and 2.0 or less. A value of 0.5 or more indicates that the arithmetic mean roughness of the side surface 22 is a certain value, making discharge more likely to occur on the side surface 22 of the tip 20 as well, thereby increasing the electric field strength on the discharge surface 21 and side surface 22 of the tip 20. As a result, discharge is more likely to occur between the discharge surface 21 of the tip 20 closest to the ground electrode 16 and the ground electrode 16, making it less likely for flame quenching to occur, thereby improving ignition performance. A value of 2.0 or less indicates that the side surface 22 is not too rough, which is preferable because it reduces discharge on the side surface 22 due to electric field concentration on the rough side surface 22.

[0037] The arithmetic mean roughness of the side surface 22 is calculated by scanning the side surface 22 in the axial direction with a laser beam and measuring the profile curve (roughness curve) over a reference length with a non-contact 3D laser measuring device, and expressing the average absolute value of the height of the roughness curve. The roughness curve in the axial direction of the side surface 22 is obtained from a point 0.1 mm away from the edge of the side surface 22 that intersects with the discharge surface 21. The edge of the side surface 22 (the corner where the discharge surface 21 and the side surface 22 intersect) has a high electric field strength and is prone to discharge, so in order to make it easier for discharge to occur in areas other than the edge of the side surface 22, it is necessary to control the surface roughness of the area excluding the area within 0.1 mm from the edge of the side surface 22.

[0038] The reference length is preferably 0.1 mm or more to ensure measurement accuracy. For example, the arithmetic mean roughness is measured at 12 equally spaced locations on the side surface 22, and the five largest arithmetic mean roughnesses are selected from the 12 locations and the average of the five is calculated. The five largest arithmetic mean roughnesses are averaged because if the side surface 22 has a portion with a large arithmetic mean roughness, that portion is more likely to experience discharge and oxidation wear.

[0039] The arithmetic mean roughness of the discharge surface 21 and side surface 22 of the tip 20 can be set by blasting processes such as shot blasting and sand blasting, or by ball milling, whereby projectiles or balls are collided with the surface of the tip 20. When the tip 20 is manufactured by sintering a metal powder compact, the arithmetic mean roughness of the discharge surface 21 and side surface 22 can also be set by adjusting the particle size distribution of the metal powder. When the tip 20 is manufactured by punching a plate material, the surface roughness is set by colliding projectiles with the surface of the plate material, and then the plate material is punched out, whereby the arithmetic mean roughness of the discharge surface 21 of the tip 20 can be set.

[0040] The arithmetic mean roughness of the opposing surface of the ground electrode 16 (discharge surface 29 of tip 28 in this embodiment) that faces the discharge surface 21 of the tip 20 is preferably smaller than the arithmetic mean roughness of the discharge surface 21. Because the opposing surface of the ground electrode 16 is more likely to become hotter than the discharge surface 21 of the center electrode 13, by making the arithmetic mean roughness of the opposing surface of the ground electrode 16 smaller than the arithmetic mean roughness of the discharge surface 21, it is possible to reduce pre-ignition caused by rough portions of the opposing surface of the ground electrode 16 acting as sparks.

[0041] The measurement of the arithmetic mean roughness of the opposing surface of the ground electrode 16 is performed in the same manner as the measurement of the arithmetic mean roughness of the discharge surface 21, and therefore a description thereof will be omitted. When the fusion zone 27 and the tip 28 are not provided on the base material 26, the opposing surface of the ground electrode 16 is the surface (a surface of the same size as the discharge surface 21) obtained by projecting the discharge surface 21 of the center electrode 13 onto the base material 26 of the ground electrode 16 perpendicular to the discharge surface 21.

[0042] The arithmetic mean roughness of the side surface 25 of the protrusion 24 is preferably smaller than that of the discharge surface 21. This is because, when the arithmetic mean roughness of the side surface 25 of the protrusion 24 is smaller than that of the discharge surface 21, irregular discharge (so-called side sparks) occurring between the side surface 25 of the protrusion 24 and the metallic shell 15 can be reduced.

[0043] The arithmetic mean roughness of the side surface 25 of the protrusion 24 is calculated by scanning the side surface 25 in the axial direction with a laser beam and measuring the profile curve (roughness curve) over a reference length using a non-contact 3D laser measuring device, and expressing the average absolute value of the height of the roughness curve. The axial roughness curve of the side surface 25 is obtained from a point 0.1 mm axially away from the tip 23 of the insulator 11. This is because the portion of the protrusion 24 near the tip 23 of the insulator 11 is in the shadow of the insulator 11, making it less likely for irregular discharge to occur. The reference length is preferably 0.1 mm or more to ensure measurement accuracy. For example, the arithmetic mean roughness is measured at 12 equally spaced locations on the side surface 25, and the average is calculated.

[0044] In this embodiment, the side surface 25 of the protrusion 24 at the tip 23 of the insulator 11 is a conical surface that tapers toward the tip, but this is not limited to this. Depending on the length of the base material 17 of the center electrode 13 and the insulator 11 and the shape of the base material 17, the side surface 25 of the protrusion 24 at the tip 23 of the insulator 11 may be a cylindrical surface. When the side surface 25 of the protrusion 24 at the tip 23 of the insulator 11 is a cylindrical surface, the arithmetic mean roughness is measured in the same way as when it is a conical surface.

[0045] When the tip 28 of the ground electrode 16 is primarily composed of Ru, the arithmetic mean roughness of the discharge surface 29 of the tip 28 is 0.4 μm or more and 4.8 μm or less, and preferably 1.1 μm or more and 3.2 μm or less, similar to the tip 20 of the center electrode 13. Furthermore, the value obtained by dividing the arithmetic mean roughness of the side surface 30 of the tip 28 by the arithmetic mean roughness of the discharge surface 29 is preferably 0.5 or more and 2.0 or less. The reasons why these ranges are preferable and the method for measuring the arithmetic mean roughness are the same as those explained for the center electrode 13. [Example]

[0046] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0047] (Test 1) The tester prepared plates made of a Ru-Pt alloy (15% by mass Pt, the remainder Ru), a Ru-Ni alloy (10% by mass Ni, the remainder Ru), and a Ru-Co alloy (10% by mass Co, the remainder Ru), and then shot a projectile onto the surfaces of the plates to obtain plates with various surface roughnesses.The plates were then punched out to obtain disc-shaped chips with a diameter of 0.8 mm and a thickness of 0.6 mm and with various discharge surface roughnesses.

[0048] The tester placed the center electrode, with the tip bonded to the base metal, on the insulator, and then attached the metal shell with the ground electrode connected to it to the outer periphery of the insulator. Before bending the ground electrode, a non-contact three-dimensional shape measurement device (Bruker-Alicona INFINITE FOCUS G4) was used to measure the surface profile of a circular area with a diameter of 0.64 mm, excluding an area 0.08 mm inward from the edge of the tip's discharge surface. The tester randomly drew a normal line to the circle within the circular area and measured the surface profile every 2 μm along the normal line, 0.2 mm long, between the center and circumference of the circle. Eleven normal lines were drawn radially from this normal line at 30° intervals, and the surface profile every 2 μm along each normal line, 0.2 mm long, to obtain a total of 12 arithmetic mean roughness values. The five largest arithmetic mean roughness values ​​were selected from the 12 points, and the average of these five was used as the representative value.

[0049] After measuring the arithmetic mean roughness of the tip discharge surface, the ground electrode was bent so as not to touch the discharge surface, and a spark gap was created between the tip of the center electrode and the ground electrode to obtain spark plug sample No. 1-20. The size of the spark gap (the distance between the discharge surface of the center electrode and the opposing surface of the ground electrode) for the sample was 1.3 mm.

[0050] After installing the spark plug in a pressure chamber equipped with a high-speed camera capable of capturing images of the interior, the chamber was filled with air and the air pressure in the pressure chamber was set to 2 MPa. A voltage was applied between the center electrode and the ground electrode using an ignition device, and the discharge was captured by the high-speed camera.

[0051] Images taken with a high-speed camera were examined, and the number of discharges that occurred between the discharge surface of the center electrode tip and the ground electrode (regular discharges) and the number of discharges that occurred between the center electrode and the ground electrode other than the discharge surface of the tip (irregular discharges) were counted out of 100 discharges. Samples with a regular discharge rate of 80% or more were rated A, samples with a regular discharge rate of 70% to less than 80% were rated B, and samples with a regular discharge rate of less than 70% were rated C. The arithmetic mean roughness (representative value) of the discharge surface and the results are shown in the regular discharge column in Table 1.

[0052] [Table 1]

[0053] (Test 2) The tester installed each of Samples No. 1-20 in a 1.3L gasoline-fueled engine and ran the engine at 5,000 rpm for 100 hours with the intake throttle valve fully open. The tip temperature was 700°C. The tip temperature was measured before the test by using a spark plug with a hole drilled to reach close to the tip and placing a thermocouple hot junction near the tip of the base metal.

[0054] After the test, the samples were removed and the size of the gap (spark gap) between the discharge surface of the center electrode tip and the ground electrode was measured using a pin-type gauge, and the increase in the spark gap before and after the test was calculated. Samples with a spark gap increase of less than 0.03 mm were rated A, samples with a spark gap increase of 0.03 mm or more but less than 0.05 mm were rated B, and samples with a spark gap increase of 0.05 mm or more were rated C. The results are shown in the wear resistance column in Table 1.

[0055] As shown in Table 1, sample No. 3-20 was judged as A or B for normal discharge. In particular, sample Nos. 6-12, 14-16, and 18-20 were judged as A for normal discharge. In addition, sample Nos. 1-10 and 13-20 were judged as A or B for wear resistance. In particular, sample Nos. 1-9, 13-15, and 17-19 were judged as A for normal discharge.

[0056] This revealed that if the arithmetic mean roughness of the discharge surface is 0.4 μm or more, the rate of regular discharge can be increased to 70% or more. In particular, if the arithmetic mean roughness of the discharge surface is 1.1 μm or more, the rate of regular discharge can be increased to 80% or more. When irregular discharge occurs, there is a high possibility that the flame kernel generated by the discharge will be extinguished by the flame quenching effect. Therefore, making the arithmetic mean roughness of the discharge surface 0.4 μm or more and increasing the rate of regular discharge will lead to improved ignition performance.

[0057] It was also found that when the arithmetic mean roughness of the discharge surface is 4.8 μm or less, the increase in the spark gap can be kept to less than 0.05 mm. In particular, it was found that when the arithmetic mean roughness of the discharge surface is 3.2 μm or less, the increase in the spark gap can be kept to less than 0.03 mm. Therefore, it was found that in order to ensure the rate of regular discharge and further improve the wear resistance of the tip, the arithmetic mean roughness of the discharge surface of the tip must be 0.4 μm or more and 4.8 μm or less. It was found that to further increase the rate of regular discharge, the arithmetic mean roughness of the discharge surface is preferably 1.1 μm or more, and to improve wear resistance, the arithmetic mean roughness of the discharge surface is preferably 3.2 μm or less.

[0058] (Test 3) The tester prepared a circular tip made of a Ru-Pt alloy containing 15% Pt by mass and the remainder Ru, measuring 0.8 mm in diameter and 0.6 mm thick. Then, he bombarded the discharge surface and side of the tip with projectile material to obtain tip samples with various surface roughnesses. The tester placed the center electrode, which was bonded to the base metal, on an insulator, and attached the metal shell connected to the ground electrode to the outer periphery of the insulator. Before bending the ground electrode, he used a non-contact three-dimensional shape measurement device (Bruker-Alicona INFINITE FOCUS G4) to measure the arithmetic mean roughness of a circular area 0.64 mm in diameter, excluding an area 0.08 mm inward from the edge of the tip's discharge surface, and the arithmetic mean roughness in the axial direction of the area excluding an area 0.1 mm inward from the edge of the side of the tip. The tester measured the arithmetic mean roughness of the tip's discharge surface in the same manner as in Test 1, and selected the five largest arithmetic mean roughnesses from the 12 locations, and used the average of these five as the representative value.

[0059] The tester arbitrarily drew a straight line parallel to the axis of the chip on the side of the chip, measured the surface shape of a 0.2 mm length on the line including the center of the chip height at 2 μm intervals, and calculated the arithmetic mean roughness of the side. The arithmetic mean roughness was calculated at 12 equally spaced locations around the circumference, and the five with the largest arithmetic mean roughness were selected from the 12 locations and the average of these five was used as the representative value.

[0060] After measuring the arithmetic mean roughness of the discharge surface and side of the tip, the ground electrode was bent so as not to touch the tip, and a spark gap was created between the center electrode tip and the ground electrode to obtain a spark plug sample (No. 21-43). The spark gap size of the sample was 1.3 mm, and a test similar to Test 1 was conducted.

[0061] Samples with a normal discharge rate of 90% or more were rated as S, samples with a normal discharge rate of 80% or more but less than 90% were rated as A, and samples with a normal discharge rate of 70% or more but less than 80% were rated as B. Table 2 shows the arithmetic mean roughness (representative value) of the discharge surface and side surface, Q / P, the value obtained by dividing the arithmetic mean roughness Q of the side surface by the arithmetic mean roughness P of the discharge surface, and the results.

[0062] [Table 2]

[0063] As shown in Table 2, among samples with an arithmetic mean roughness of the discharge surface of 0.4 μm, Nos. 22-24 were judged as having normal discharges with an A rating, and among samples with an arithmetic mean roughness of the discharge surface of 1.1 μm, Nos. 28-30 were judged as having normal discharges with an S rating. Among samples with an arithmetic mean roughness of the discharge surface of 1.6 μm, Nos. 33-35 were judged as having normal discharges with an S rating, and among samples with an arithmetic mean roughness of the discharge surface of 3.2 μm, Nos. 38 and 39 were judged as having normal discharges with an S rating. Among samples with an arithmetic mean roughness of the discharge surface of 4.8 μm, Nos. 42 and 43 were judged as having normal discharges with an S rating. According to the examples, it was revealed that the rate of normal discharge can be further increased and ignition performance can be improved when the value Q / P obtained by dividing the arithmetic mean roughness Q of the tip side by the arithmetic mean roughness P of the discharge surface is 0.5 or more and 2.0 or less.

[0064] (Test 4) The tester prepared a disk-shaped tip made of a Ru-Pt alloy (15% by mass of Pt, the remainder Ru) with a diameter of 0.8 mm and a thickness of 0.6 mm, and a base material (for the center electrode). Afterward, the tester struck the discharge surface and side of the tip with projectile material to obtain tip with various surface roughnesses. Furthermore, the tester struck the tip near the tip end with projectile material to obtain base materials with various surface roughnesses. The tester placed the center electrode, which had each tip bonded to the base material, on an insulator, and then attached a metal shell connected to the ground electrode to the outer periphery of the insulator. Before bending the ground electrode, the tester used a non-contact three-dimensional shape measurement device (INFINITE FOCUS G4, manufactured by Bruker Alicona) to measure the arithmetic mean roughness of a circular area with a diameter of 0.64 mm, excluding an area 0.08 mm inward from the edge of the discharge surface of the tip, and the arithmetic mean roughness of the side of the protruding portion of the base material.

[0065] The tester measured the arithmetic mean roughness of the discharge surface of the tip in the same way as in Test 1, selected the five largest arithmetic mean roughnesses from the 12 locations, and used the average of these five as the representative value. The tester then measured the arithmetic mean roughness of the side of the protrusion on the tip side from a position 0.1 mm axially toward the tip from the point where the side of the protrusion intersects with the tip of the insulator, in the same way as the arithmetic mean roughness of the side of the tip in Test 3, and found the arithmetic mean roughness of 12 locations equally spaced circumferentially. The average of the 12 arithmetic mean roughnesses was used as the representative value for the protrusion.

[0066] After measuring the arithmetic mean roughness of the tip and protrusion, the ground electrode was bent so as not to touch the tip and protrusion, and a spark gap was created between the center electrode tip and the ground electrode to obtain spark plug sample No. 44-51. The spark gap size of the sample was 1.3 mm. In addition to the conditions of Test 1, an air flow (flow rate 5 L / min) across the spark gap was created in the pressure chamber, and a test similar to Test 1 was conducted.

[0067] Samples with a normal discharge rate of 90% or more were rated as S, samples with a normal discharge rate of 80% or more but less than 90% were rated as A, and samples with a normal discharge rate of 70% or more but less than 80% were rated as B. Table 3 shows the arithmetic mean roughness (representative values) and results for the discharge surface of the tip and the side surface of the protrusion.

[0068] [Table 3]

[0069] As shown in Table 3, samples Nos. 45, 47, 49, and 51, in which the arithmetic mean roughness of the side surface of the protrusion was smaller than the arithmetic mean roughness of the discharge surface of the tip, had a higher proportion of regular discharges than samples Nos. 44, 46, 48, and 50, in which the arithmetic mean roughness of the side surface of the protrusion was larger than the arithmetic mean roughness of the discharge surface of the tip. It was found that the proportion of regular discharges could be further increased and ignition performance could be improved by making the arithmetic mean roughness of the discharge surface of the tip smaller than the arithmetic mean roughness of the side surface of the protrusion.

[0070] (Test 5) The tester prepared a disk-shaped tip made of a Ru-Pt alloy containing 15% Pt by mass and the remainder Ru, measuring 0.8 mm in diameter and 0.6 mm in thickness, and a ground electrode. Then, the tester struck a projectile on the discharge surface of the tip to obtain tip pieces with various surface roughnesses. The tester then struck a projectile on the opposing surface of the ground electrode to obtain ground electrodes with various surface roughnesses. The tester then placed the center electrode, in which the tip was bonded to the base metal, on an insulator, and assembled a metal shell connected to the ground electrode to the outer periphery of the insulator. Before bending the ground electrode, a non-contact three-dimensional shape measuring device (INFINITE FOCUS G4 manufactured by Bruker-Alicona) was used to measure the arithmetic mean roughness of a circular area with a diameter of 0.64 mm, excluding an area 0.08 mm inward from the edge of the discharge surface of the chip, and the arithmetic mean roughness of a circular area with a diameter of 0.64 mm, excluding an area 0.08 mm inward from the edge of the opposing surface of the ground electrode, in the same manner as in Test 1.The five largest arithmetic mean roughnesses were selected from the 12 locations, and the averages of these five were used as representative values.

[0071] After measuring the arithmetic mean roughness, the ground electrode was bent so that the discharge surface of the tip did not come into contact with the opposing surface of the ground electrode, and a spark gap was created between the tip of the center electrode and the ground electrode to obtain spark plug samples No. 52-58. The spark gap size of the sample was 1.3 mm.

[0072] Testers mounted each sample on a 1.5L inline 4-cylinder supercharged engine and operated it at 2000 rpm and an indicated mean effective pressure (NMEP) of 1000 kPa. The test engine's ignition timing was advanced by 1° in increments from the normal ignition timing of the original spark plugs, and the occurrence of pre-ignition was investigated based on the waveform of the ionic current, identifying the ignition timing at which pre-ignition occurred. Samples where pre-ignition occurred at a crank angle advanced by 2° or more from the crank angle of the original spark plugs were rated as A, while samples where pre-ignition occurred at an angle less than 2° were rated as B. The results are shown in the pre-ignition column in Table 4.

[0073] [Table 4]

[0074] As shown in Table 4, samples Nos. 53, 55, 57, and 58, in which the arithmetic mean roughness of the facing surface of the ground electrode was smaller than that of the discharge surface of the tip, were less likely to experience pre-ignition than samples in which the arithmetic mean roughness of the facing surface of the ground electrode was larger than that of the discharge surface of the tip. The examples revealed that by making the arithmetic mean roughness of the facing surface of the ground electrode smaller than that of the discharge surface of the tip, pre-ignition caused by the discharge surface of the ground electrode can be reduced.

[0075] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0076] In the embodiment, the ground electrode 16 is bent, but the present invention is not limited to this. Naturally, a straight ground electrode 16 can be used instead of the bent ground electrode 16. In this case, the tip end side of the metallic shell 15 is extended in the axial direction, and the straight ground electrode 16 is joined to the metallic shell 15. The number of ground electrodes 16 is also set appropriately.

[0077] In the embodiment, the center electrode 13 and the ground electrode 16 are arranged so that the discharge surface 21 of the tip 20 of the center electrode 13 faces the leading end in the axial direction. However, this is not necessarily limited to this. The positional relationship between the center electrode 13 and the ground electrode 16 can be set as appropriate. Another example of a positional relationship between the center electrode 13 and the ground electrode 16 is to arrange the tip 20 and the ground electrode 16 so that a spark gap is formed between the side surface 22 of the tip 20 of the center electrode 13 and the ground electrode 16. In this case, the side surface 22 of the tip 20 facing the ground electrode 16 corresponds to the discharge surface in claim 1, and the discharge surface 21 of the tip 20 corresponds to the side surface connected to the discharge surface. The arithmetic mean roughness of the discharge surface is measured in the same manner as the arithmetic mean roughness of the side surface 22, and the arithmetic mean roughness of the side surface is measured in the same manner as the arithmetic mean roughness of the discharge surface 21. [Explanation of symbols]

[0078] 10 Spark Plugs 11 Insulators 12 Shaft hole 13 Center electrode 15 Metal body 16 Ground electrode 17 Base material 20 chips 21 Discharge surface 22 Side 24 Protrusion 25 Side 26 Base material 28 chips 29 Discharge surface (opposing surface) 30 Side X axis

Claims

1. an insulator provided with an axial hole extending along an axis; a center electrode disposed in the axial hole; a metallic shell disposed on the outer periphery of the insulator; a ground electrode connected to the metallic shell, the center electrode includes a base material and a tip joined to the base material, The tip is made of Ru as a main component and includes a discharge surface facing the ground electrode, The arithmetic mean roughness of the discharge surface is 0.4 μm or more and 4.8 μm or less.

2. an insulator provided with an axial hole extending along an axis; a center electrode disposed in the axial hole; a metallic shell disposed on the outer periphery of the insulator; a ground electrode connected to the metallic shell, the ground electrode includes a base material and a tip joined to the base material, The tip is made of Ru as a main component and includes a discharge surface facing the center electrode, The arithmetic mean roughness of the discharge surface is 0.4 μm or more and 4.8 μm or less.

3. an insulator provided with an axial hole extending along an axis; a center electrode disposed in the axial hole; a metallic shell disposed on the outer periphery of the insulator; a ground electrode connected to the metallic shell, the center electrode and the ground electrode each include a base material and a tip joined to the base material, the tip is made mainly of Ru and includes a discharge surface facing the other of the center electrode and the ground electrode, The arithmetic mean roughness of the discharge surface is 0.4 μm or more and 4.8 μm or less.

4. 4. The spark plug according to claim 1, wherein the arithmetic mean roughness of the discharge surface is 3.2 μm or less.

5. 4. The spark plug according to claim 1, wherein the arithmetic mean roughness of the discharge surface is 1.1 μm or more.

6. the tip includes a side surface that is connected to the discharge surface; 4. The spark plug according to claim 1, wherein a value obtained by dividing the arithmetic mean roughness of the side surface by the arithmetic mean roughness of the discharge surface is 0.5 or more and 2.0 or less.

7. 2. The spark plug according to claim 1, wherein the arithmetic mean roughness of the surface of said ground electrode facing said discharge surface is smaller than the arithmetic mean roughness of said discharge surface.

8. 4. The spark plug according to claim 3, wherein the arithmetic mean roughness of the surface of said ground electrode facing the discharge surface of said center electrode is smaller than the arithmetic mean roughness of the discharge surface of said center electrode.

9. the base material includes a protrusion that protrudes from the insulator in the axial direction toward the ground electrode, 2. The spark plug according to claim 1, wherein the arithmetic mean roughness of the side surface of said protrusion is smaller than the arithmetic mean roughness of said discharge surface.

10. a base material of the center electrode includes a protrusion protruding from the insulator in the axial direction toward the ground electrode, 4. The spark plug according to claim 3, wherein the arithmetic mean roughness of the side surface of said protrusion is smaller than the arithmetic mean roughness of the discharge surface of said center electrode.

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