Spark plug

Abstract

The invention provides a spark plug capable of reducing consumption of an electrode tip and improving ignitability. A spark plug is provided with: an insulator provided with a shaft hole extending along an axis; a center electrode disposed in the shaft hole; a main body metal housing disposed on the outer periphery of the insulator; and the grounding electrode is connected with the main body metal shell. At least one of the center electrode and the ground electrode includes a base material and an electrode tip bonded to the base material and mainly composed of Ru, the electrode tip includes a discharge surface facing the other of the center electrode and the ground electrode, and the arithmetic average roughness of the discharge surface is 0.4 [mu] m or more and 4.8 [mu] m or less.

Description

Technical Field

[0001] This invention relates to spark plugs having electrodes containing Ru. Background Technology

[0002] Patent document 1 discloses prior art in which at least one of the center electrode and the ground electrode comprises an electrode head made of a Ru monomer or an electrode head made of a Ru alloy.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 5-54955 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In the prior art, there is a need for techniques that can reduce electrode tip consumption caused by oxidation and improve ignition performance.

[0008] This invention was made in response to this requirement, and its purpose is to provide a spark plug that can reduce electrode tip consumption and improve ignition performance.

[0009] Solution for solving the problem

[0010] A first technical solution for achieving this objective provides a spark plug comprising: an insulator having a bore extending along an axis; a center electrode disposed in the bore; a body metal housing disposed on the outer periphery of the insulator; and a ground electrode connected to the body metal housing. The center electrode comprises a base material and an electrode head joined to the base material. The electrode head is mainly composed of Ru and includes a discharge surface opposite to the ground electrode. The arithmetic mean roughness of the discharge surface is 0.4 μm or more and 4.8 μm or less.

[0011] The second technical solution provides a spark plug comprising: an insulator having a bore extending along an axis; a center electrode disposed in the bore; a main metal housing disposed on the outer periphery of the insulator; and a ground electrode connected to the main metal housing. The ground electrode includes a base material and an electrode head joined to the base material. The electrode head is mainly composed of Ru and includes a discharge surface opposite to the center electrode. The arithmetic mean roughness of the discharge surface is 0.4 μm or more and 4.8 μm or less.

[0012] The third technical solution provides a spark plug comprising: an insulator having a bore extending along an axis; a center electrode disposed in the bore; a main metal housing disposed on the outer periphery of the insulator; and a ground electrode connected to the main metal housing. Both the center electrode and the ground electrode include a base material and an electrode head joined to the base material. The electrode head is mainly composed of Ru and includes a discharge surface opposite to 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.

[0013] The fourth technical solution is that, in any of the first to third technical solutions, the arithmetic mean roughness of the discharge surface is less than 3.2 μm.

[0014] The fifth technical solution is that, in any one of the first to fourth technical solutions, the arithmetic mean roughness of the discharge surface is 1.1 μm or more.

[0015] The sixth technical solution is that, in any of the first to fifth technical solutions, the electrode head 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.

[0016] The seventh technical solution is that, in any of the first to sixth technical solutions, the arithmetic mean roughness of the opposing surface of the grounding electrode and the discharge surface of the center electrode is smaller than the arithmetic mean roughness of the discharge surface of the center electrode.

[0017] The eighth technical solution is that, in any of the first to seventh technical solutions, the base material of the center electrode includes a protrusion that protrudes from the insulator along 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.

[0018] The effects of the invention

[0019] According to the present invention, the arithmetic mean roughness of the discharge surface of the electrode tip, which is mainly composed of Ru, is 4.8 μm or less, thereby reducing electrode tip consumption caused by oxidation. Furthermore, since the arithmetic mean roughness of the discharge surface of the electrode tip is 0.4 μm or more, the electric field strength of the discharge surface can be increased, thereby improving ignition performance. Attached Figure Description

[0020] Figure 1 This is a one-sided sectional view of a spark plug in one embodiment.

[0021] Figure 2 This is a cross-sectional view of the part of the spark plug where the center electrode is opposite to the ground electrode.

[0022] Explanation of reference numerals in the attached figures

[0023] 10. Spark plug; 11. Insulator; 12. Shaft hole; 13. Center electrode; 15. Main metal shell; 16. Ground electrode; 17. Base material; 20. Electrode head; 21. Discharge surface; 22. Side; 24. Protrusion; 25. Side; 26. Base material; 28. Electrode head; 29. ​​Discharge surface (opposite surface); 30. Side; X, axis. Detailed Implementation

[0024] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a single-side sectional view of a spark plug 10 according to one embodiment, bounded by the X-axis. Figure 1 In this context, the lower side of the paper is referred to as the front end side of the spark plug 10, and the upper side of the paper is referred to as the rear end side of the spark plug 10.

[0025] like Figure 1 As shown, the spark plug 10 includes an insulator 11, a center electrode 13, a main metal housing 15, and a ground electrode 16. The insulator 11 is a generally cylindrical component made of alumina or other ceramic with excellent mechanical properties and high-temperature insulation. The insulator 11 has a shaft hole 12 extending along the axis X. The center electrode 13 is a rod-shaped electrode disposed along the axis X in the shaft hole 12.

[0026] The terminal metal housing 14 is a rod-shaped component that connects to an ignition device (not shown), and the front end of the terminal metal housing 14 is disposed in the shaft hole 12 of the insulator 11. The terminal metal housing 14 is electrically connected to the center electrode 13 in the shaft hole 12.

[0027] The main metal housing 15 is a generally cylindrical metal component fixed to a threaded hole (not shown) in an internal combustion engine. The main metal housing 15 is formed of a conductive metallic material (e.g., low-carbon steel). The main metal housing 15 is fixed to the outer periphery of the insulator 11. A grounding electrode 16 is connected to the main metal housing 15.

[0028] Figure 2 This is a cross-sectional view of the portion of the spark plug 10 opposite the center electrode 13 and the ground electrode 16. The center electrode 13 includes a base material 17 and an electrode head 20 located at the front end of the base material 17.

[0029] The base material 17 has a core material 18 embedded therein, which has excellent thermal conductivity. The material of the base material 17 is, for example, Ni or an alloy with Ni as the main component, and the material of the core material 18 is, for example, Cu or an alloy with Cu as the main component. The core material 18 can be omitted.

[0030] The electrode head 20 is joined to the base material 17 via a molten section 19. The molten section 19 fuses the electrode head 20 and the base material 17 together. The molten section 19 is formed by laser welding, resistance welding, diffusion bonding, etc. The electrode head 20 includes a discharge surface 21 opposite to the ground electrode 16 and a side surface 22 connected to the discharge surface 21.

[0031] The base material 17 includes a portion extending from the front end 23 of the insulator 11 along the axis X (see reference). Figure 1 The protrusion 24 is a portion of the base material 17 located between the front end 23 of the insulator 11 and the molten portion 19. The protrusion 24 includes a side 25 surrounding the axis X.

[0032] The grounding electrode 16 includes a base material 26 connected to the main metal housing 15 and an electrode head 28 disposed 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 a Ni-based alloy, and the core material is made of Cu or a Cu-based alloy. The core material can be omitted. Alternatively, an intermediate member protruding towards the central electrode 13 can be disposed on the base material 26, and the electrode head 28 can be joined to the intermediate member. The intermediate member is part of the base material 26.

[0033] The electrode head 28 is joined to the base material 26 via a molten section 27. The molten section 27 fuses the electrode head 28 and the base material 26 together. The molten section 27 is formed by laser welding, resistance welding, diffusion bonding, etc. The electrode head 28 includes a discharge surface 29 opposite to the center electrode 13 and a side surface 30 connected to the discharge surface 29.

[0034] At least one of electrode head 20 and electrode head 28 is primarily composed of Ru. Being primarily composed of Ru means that Ru is the most abundant element among the elements constituting electrode head 20 and electrode head 28. The content of Ru relative to the total amount of components constituting electrode head 20 and electrode head 28 is preferably 50% by mass or more, more preferably 60% by mass or more, or 70% by mass or more.

[0035] When the electrode head 20 of the center electrode 13 is mainly composed of Ru or the electrode head 28 of the ground electrode 16 is mainly composed of Ru, for elements other than Ru constituting the electrode head 20 and the electrode head 28, 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 can be cited as examples.

[0036] When the electrode head 20 of the center electrode 13 is mainly composed of Ru, the ground electrode 16 is any one of the following: an electrode containing an electrode head 28 mainly composed of Ru; an electrode containing an electrode head 28 mainly composed of one or more platinum group elements (Rh, Pd, Os, Ir, Pt) other than Ru; or an electrode on the base material 26 that does not have a molten part 27 and an electrode head 28.

[0037] When the electrode head 28 of the ground electrode 16 is mainly composed of Ru, the center electrode 13 is any one of the following: an electrode containing an electrode head 20 mainly composed of Ru; an electrode containing an electrode head 20 mainly composed of one or more platinum group elements (Rh, Pd, Os, Ir, Pt) other than Ru; or an electrode on the base material 17 that does not have a molten part 19 and an electrode head 20.

[0038] Spark plug 10 is manufactured, for example, by the following method: First, the center electrode 13 is inserted into the shaft hole 12 of the insulator 11. Next, the terminal metal housing 14 is inserted into the shaft hole 12. After ensuring conductivity between the terminal metal housing 14 and the center electrode 13, the main body metal housing 15, pre-connected with the ground electrode 16, is assembled onto 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, thus obtaining spark plug 10.

[0039] Electrode heads 20 and 28, with Ru as the main component, are manufactured by sintering a shaped body containing Ru metal powder, punching a sheet of Ru metal, or cutting a wire containing Ru metal. The shapes of electrode heads 20 and 28 are not limited to circular plates, frustums, elliptical cylinders, triangular prisms, or quadrangular prisms or other polygonal prisms.

[0040] When the electrode head 20 of the center electrode 13 is mainly composed of Ru, the arithmetic mean roughness of the discharge surface 21 of the electrode head 20 is 0.4 μm or more and 4.8 μm or less. When the discharge between the center electrode 13 and the ground electrode 16 mainly occurs between the discharge surface 21 of the electrode head 20 and the ground electrode 16, the flame extinguishing effect of the center electrode 13 can be reduced, thus helping to improve 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 easily generated on the discharge surface 21, thus improving ignition performance. When the arithmetic mean roughness of the discharge surface 21 is 1.1 μm or more, the effect of improving ignition performance becomes even greater, and this is preferred.

[0041] On the other hand, the rougher the discharge surface 21 of the Ru-containing electrode tip 20, the more easily the electrode tip 20 is consumed due to oxidation. If the arithmetic mean roughness of the discharge surface 21 is 4.8 μm or less, the consumption of the electrode tip 20 caused by oxidation can be reduced. When the arithmetic mean roughness of the discharge surface 21 is 3.2 μm or less, the effect of reducing the consumption of the electrode tip 20 becomes even greater, and therefore it is preferred.

[0042] The arithmetic mean roughness of the discharge surface 21 is obtained by scanning the discharge surface 21 with a laser beam and measuring the reference length using a non-contact three-dimensional laser measuring machine, showing the average of the absolute values ​​of the heights of the roughness curves. A range excluding the area at which the distance from the edge of the discharge surface 21 is 10% of the span of the discharge surface 21 (the length of the line segment passing through the centroid of the discharge surface 21) is obtained for the portion inside this range. This is because the electric field intensity is higher at the edge of the discharge surface 21 (the angle where the discharge surface 21 intersects the side surface 22), making it easier for discharge to occur. Therefore, to facilitate discharge in the portion outside this range, it is necessary to manage the surface roughness of the portion outside this range.

[0043] The reference length is preferably set to 0.1 mm or more, for example, 25% of the span of the discharge surface 21. This is to ensure measurement accuracy. For example, the arithmetic mean roughness at 12 points on the discharge surface 21 is measured with a scanning interval of 2 μm or more. Five arithmetic mean roughnesses are selected from the 12 points in descending order, and the discharge surface 21 is fabricated such that the average of these five arithmetic mean roughnesses falls within the range of 0.4 μm or more and 4.8 μm or less. The reason for averaging the five arithmetic mean roughnesses selected in descending order is that if there is a region on the discharge surface 21 with a large arithmetic mean roughness, discharge is more likely to occur in that region, and oxidation consumption is more likely to occur.

[0044] The value obtained by dividing the arithmetic mean roughness of the side surface 22 of the electrode head 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 at a certain level, making it easier for discharge to occur on the side surface 22 of the electrode head 20, thus increasing the electric field strength of the discharge surface 21 and the side surface 22 of the electrode head 20. As a result, discharge is easily generated between the discharge surface 21 of the electrode head 20 closest to the ground electrode 16 and the ground electrode 16, and flame extinguishing is less likely to occur, thus improving ignition performance. A value of 2.0 or less indicates that the side surface 22 is not too rough, reducing discharge at the side surface 22 caused by the electric field concentration on the rougher side surface 22, which is therefore preferable.

[0045] The arithmetic mean roughness of side surface 22 is obtained by scanning the profile curve (roughness curve) of side surface 22 along the axial direction with a laser beam and measuring the reference length using a non-contact three-dimensional laser measuring machine, showing the average of the absolute values ​​of the roughness curve heights. The roughness curve along the axial direction of side surface 22 is obtained from a position 0.1 mm away from the edge of side surface 22 intersecting with the discharge surface 21. This is because the electric field intensity at the edge of side surface 22 (the angle where discharge surface 21 intersects side surface 22) is high, making it easy to generate discharge. Therefore, in order to facilitate discharge in the portion of side surface 22 other than the edge, it is necessary to manage the surface roughness of the portion of side surface 22 other than the range within 0.1 mm from the edge.

[0046] The reference length is preferably set to 0.1 mm or more. This is to ensure measurement accuracy. For example, the arithmetic mean roughness at 12 equally spaced points on the side surface 22 is measured. Five arithmetic mean roughnesses are selected from these 12 points in descending order, and the average of these five arithmetic mean roughnesses is calculated. The reason for averaging the five arithmetic mean roughnesses selected in descending order is that if there is a region on the side surface 22 with a large arithmetic mean roughness, electrical discharge is likely to occur in that region, and oxidation consumption is also likely to occur.

[0047] By using shot peening, sandblasting, or ball milling to collide the projected material or ball with the surface of the electrode head 20, the arithmetic mean roughness of the discharge surface 21 and side surface 22 of the electrode head 20 can be set. When the electrode head 20 is manufactured by sintering a metal powder molded body, 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 electrode head 20 is manufactured by punching a sheet metal, the arithmetic mean roughness of the discharge surface 21 of the electrode head 20 can be set by punching the sheet metal after setting the surface roughness by colliding the projected material with the surface of the sheet metal.

[0048] The arithmetic mean roughness of the opposing surface of the ground electrode 16 (in this embodiment, the discharge surface 29 of the electrode head 28) opposite the discharge surface 21 of the electrode head 20 is preferably smaller than the arithmetic mean roughness of the discharge surface 21. Since the opposing surface of the ground electrode 16 is more prone to temperature rise 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, premature ignition caused by the rough portion of the opposing surface of the ground electrode 16 becoming a spark can be reduced.

[0049] The arithmetic mean roughness measurement of the opposite surface of the ground electrode 16 is performed in the same manner as the arithmetic mean roughness measurement of the discharge surface 21, so the description is omitted. When the molten part 27 and the electrode head 28 are not provided on the base material 26, the opposite surface of the ground electrode 16 is the surface obtained by projecting the discharge surface 21 of the center electrode 13 onto the base material 26 of the ground electrode 16 in a manner perpendicular to the discharge surface 21 (a surface of the same size as the discharge surface 21).

[0050] The arithmetic mean roughness of the side surface 25 of the protrusion 24 is preferably smaller than the arithmetic mean roughness of the discharge surface 21. This is because if the arithmetic mean roughness of the side surface 25 of the protrusion 24 is smaller than the arithmetic mean roughness of the discharge surface 21, non-standard discharges (so-called lateral sparking) generated between the side surface 25 of the protrusion 24 and the main metal casing 15 can be reduced.

[0051] The arithmetic mean roughness of the side surface 25 of the protrusion 24 is obtained by scanning the side surface 25 along the axial direction with a laser beam and measuring the reference length using a non-contact three-dimensional laser measuring machine, showing the average of the absolute values ​​of the height of the roughness curve. The roughness curve in the axial direction of the side surface 25 is obtained from a position 0.1 mm away from the front end 23 of the insulator 11 in the axial direction. This is because the portion of the protrusion 24 close to the front end 23 of the insulator 11 is shielded by the insulator 11, making it less prone to non-standard discharge. The reference length is preferably 0.1 mm or more. This is to ensure measurement accuracy. For example, the arithmetic mean roughness at 12 equally spaced points on the side surface 25 is measured, and its average value is calculated.

[0052] In this embodiment, the side surface 25 of the protrusion 24 at the front end 23 of the insulator 11 is a conical surface that tapers towards the front end, but it is not limited to this. Depending on the length of the base material 17 of the center electrode 13 and the shape of the base material 17, there may be a case where the side surface 25 of the protrusion 24 at the front end 23 of the insulator 11 is a cylindrical surface. In the case where the side surface 25 of the protrusion 24 at the front end 23 of the insulator 11 is a cylindrical surface, the arithmetic mean roughness is measured in the same way as in the case of a conical surface.

[0053] When the electrode head 28 of the ground electrode 16 is mainly composed of Ru, similarly to the electrode head 20 of the center electrode 13, the arithmetic mean roughness of the discharge surface 29 of the electrode head 28 is 0.4 μm or more and 4.8 μm or less, preferably 1.1 μm or more and 3.2 μm or less. Furthermore, the value obtained by dividing the arithmetic mean roughness of the side surface 30 of the electrode head 28 by the arithmetic mean roughness of the discharge surface 29 is preferably 0.5 or more and 2.0 or less. The reasons for these favorable ranges and the method for measuring the arithmetic mean roughness are the same as those explained for the center electrode 13.

[0054] [Example]

[0055] The invention is illustrated in more detail by way of examples, but the invention is not limited to these examples.

[0056] (Experiment 1)

[0057] The experimenters prepared plates made of Ru-Pt alloy (containing 15% Pt by mass, with the remainder being Ru), Ru-Ni alloy (containing 10% Ni by mass, with the remainder being Ru), and Ru-Co alloy (containing 10% Co by mass, with the remainder being Ru). The projected material was then collided with the surfaces of these plates to obtain plates with various surface roughnesses. The plates were then punched to obtain circular electrode heads with various discharge surface roughnesses, a diameter of 0.8 mm, and a thickness of 0.6 mm.

[0058] The experimenter positioned the center electrode, formed by attaching the electrode head to the base material, on an insulator, and assembled the main metal housing, connected to the ground electrode, onto the outer periphery of the insulator. Before bending the ground electrode, a non-contact three-dimensional shape measuring device (Bruker Alicona INFINITE FOCUS G4) was used to measure the surface shape of a circular area with a diameter of 0.64 mm on the discharge surface of the electrode head, excluding the area from the edge to a distance of 0.08 mm from the edge. The experimenter arbitrarily drew the normal to the circle within the circular area, and measured the surface shape at a length of 0.2 mm on the normal between the center and the circumference of the circle every 2 μm, calculating the arithmetic mean roughness. Using this normal as a reference, 11 normals were drawn radially at 30° intervals, and the surface shape at a length of 0.2 mm on each normal was measured every 2 μm, calculating the arithmetic mean roughness at a total of 12 locations. From the 12 arithmetic mean roughness values, select 5 arithmetic mean roughness values ​​in descending order, and use the average of these 5 arithmetic mean roughness values ​​as the representative value.

[0059] After measuring the arithmetic mean roughness of the discharge surface of the electrode tip, the grounding electrode was bent without contacting the discharge surface to obtain spark plug samples No.1 to No.20 with a spark gap between the electrode tip of the center electrode and the grounding electrode. The size of the spark gap (the distance between the discharge surface of the center electrode and the opposite surface of the grounding electrode) of the sample was set to 1.3 mm.

[0060] After installing a spark plug in the pressure chamber equipped with a high-speed camera capable of capturing internal images, air is filled into the pressure chamber, and the air pressure is set to 2 MPa. A voltage is applied between the center voltage and the ground electrode using an ignition device, and the discharge process is captured by the high-speed camera.

[0061] This study analyzed images captured by a high-speed camera and counted the number of discharges (standard discharges) occurring between the discharge surface of the central electrode tip and the ground electrode in 100 discharge cycles, and the number of discharges (non-standard discharges) occurring between the portion of the central electrode excluding the discharge surface of the electrode tip and the ground electrode. Samples with a standard discharge ratio of 80% or higher were classified as A, samples with a standard discharge ratio of 70% or higher but less than 80% were classified as B, and samples with a standard discharge ratio of less than 70% were classified as C. The arithmetic mean roughness (representative value) of the discharge surface and the results are recorded in the standard discharge column of Table 1.

[0062] [Table 1]

[0063]

[0064] (Experiment 2)

[0065] The experimenter conducted the following test: After installing samples No. 1 to No. 20 into a 1.3L gasoline-powered engine, the intake throttle valve was fully open, and the engine was run at 5000 rpm for 100 hours. The electrode tip temperature was 700℃. Before starting the test, a spark plug with a hole extending to the vicinity of the electrode tip was used, and a thermocouple contact was placed near the front end of the base material near the electrode tip to measure the electrode tip temperature.

[0066] After the test, the samples were removed, and the gap (spark gap) between the discharge surface of the center electrode tip and the ground electrode was measured using a pin gauge. The increase in spark gap before and after the test was calculated. Samples with a spark gap increase of less than 0.03 mm were classified as A, samples with a spark gap increase of 0.03 mm or more but less than 0.05 mm were classified as B, and samples with a spark gap increase of 0.05 mm or more were classified as C. The results were recorded in the wear resistance column of Table 1.

[0067] As shown in Table 1, the standard discharge performance of samples No. 3 to No. 20 is judged as either A or B. In particular, the standard discharge performance of samples No. 6 to No. 12, No. 14 to No. 16, and No. 18 to No. 20 is judged as A. Furthermore, the wear resistance performance of samples No. 1 to No. 10 and No. 13 to No. 20 is judged as either A or B. In particular, the standard discharge performance of samples No. 1 to No. 9, No. 13 to No. 15, and No. 17 to No. 19 is judged as A.

[0068] Therefore, it can be seen that when the arithmetic mean roughness of the discharge surface is 0.4 μm or higher, the proportion of standard discharges can be above 70%. In particular, when the arithmetic mean roughness of the discharge surface is 1.1 μm or higher, the proportion of standard discharges can be above 80%. If a non-standard discharge occurs, the possibility of the flame nucleus generated by the discharge disappearing due to flame extinguishing increases. Therefore, setting the arithmetic mean roughness of the discharge surface to 0.4 μm or higher to increase the proportion of standard discharges helps to improve ignition performance.

[0069] Furthermore, it is known that if the arithmetic mean roughness of the discharge surface is 4.8 μm or less, the increase in spark gap can be less than 0.05 mm. In particular, it is known that when the arithmetic mean roughness of the discharge surface is 3.2 μm or less, the increase in spark gap can be less than 0.03 mm. Therefore, it is known that in order to ensure the standard discharge ratio and improve the wear resistance of the electrode tip, the arithmetic mean roughness of the discharge surface of the electrode tip needs to be 0.4 μm or more and 4.8 μm or less. It is known that, in order to further improve the standard discharge ratio, the arithmetic mean roughness of the discharge surface is preferably 1.1 μm or more, and in order to improve wear resistance, the arithmetic mean roughness of the discharge surface is preferably 3.2 μm or less.

[0070] (Experiment 3)

[0071] The experimenter prepared a circular electrode head with a diameter of 0.8 mm and a thickness of 0.6 mm, made of a Ru-Pt alloy containing 15% Pt and the remainder Ru. The projected material was then impacted with the discharge surface and side surface of the electrode head to obtain electrode heads with various surface roughnesses. A center electrode, formed by bonding the electrode head to the base material, was placed in an insulator, and a main metal housing with a ground electrode attached was assembled onto the outer periphery of the insulator. Before bending the ground electrode, the arithmetic mean roughness of the discharge surface of the electrode head (excluding the area from the edge to 0.08 mm from the edge) was measured using a non-contact three-dimensional shape measuring device (Bruker Alicona INFINITE FOCUS G4) in a circular area with a diameter of 0.64 mm, and the arithmetic mean roughness of the side surface of the electrode head (excluding the area from the edge to 0.1 mm from the edge) in the axial direction was measured. The experimenter measured the arithmetic mean roughness of the discharge surface of the electrode head in the same manner as in Experiment 1. Five arithmetic mean roughnesses were selected from the 12 arithmetic mean roughnesses in descending order, and the average value of these five arithmetic mean roughnesses was taken as the representative value.

[0072] The experimenter arbitrarily drew a straight line parallel to the axis of the electrode head on its side. Every 2 μm, a 0.2 mm length of surface shape along this line, including the exact midpoint of the electrode head's height, was measured, and the arithmetic mean roughness of the side surface was calculated. The arithmetic mean roughness at 12 equally spaced points along the circumference was then calculated. From these 12 points, five arithmetic mean roughnesses were selected in descending order, and the average of these five roughnesses was taken as the representative value.

[0073] After measuring the arithmetic mean roughness of the discharge surface and side surface of the electrode head, the grounding electrode was bent without contacting the electrode head to obtain spark plug samples No. 21 to No. 43 with a spark gap between the electrode head of the center electrode and the grounding electrode. The spark gap of the samples was 1.3 mm, and the same test as in Experiment 1 was performed.

[0074] Samples with a standard discharge ratio of 90% or higher are classified as S, samples with a standard discharge ratio of 80% or higher but less than 90% are classified as A, and samples with a standard discharge ratio of 70% or higher but less than 80% are classified as B. Table 2 records the arithmetic mean roughness (representative value) of the discharge surface and the side surface, as well as the value Q / P obtained by dividing the arithmetic mean roughness Q of the side surface by the arithmetic mean roughness P of the discharge surface, and the result.

[0075] [Table 2]

[0076]

[0077] As shown in Table 2, in samples with an arithmetic mean roughness of 0.4 μm on the discharge surface, the standard discharges No. 22 to No. 24 are judged as A; in samples with an arithmetic mean roughness of 1.1 μm on the discharge surface, the standard discharges No. 28 to No. 30 are judged as S; in samples with an arithmetic mean roughness of 1.6 μm on the discharge surface, the standard discharges No. 33 to No. 35 are judged as S; in samples with an arithmetic mean roughness of 3.2 μm on the discharge surface, the standard discharges No. 38 and No. 39 are judged as S; and in samples with an arithmetic mean roughness of 4.8 μm on the discharge surface, the standard discharges No. 42 and No. 43 are judged as S. According to the examples, if the value Q / P obtained by dividing the arithmetic mean roughness Q of the electrode head side surface by the arithmetic mean roughness P of the discharge surface is 0.5 or more and 2.0 or less, the proportion of standard discharges can be further increased, thus improving ignition performance.

[0078] (Experiment 4)

[0079] The experimenter prepared a circular electrode head with a diameter of 0.8 mm and a thickness of 0.6 mm, made of a Ru-Pt alloy containing 15% Pt and the remainder Ru, and a base material (for the center electrode). The projected material was then impacted with the discharge surface and side surface of the electrode head to obtain electrode heads with various surface roughnesses. Furthermore, the projected material was impacted with the vicinity of the front end of the base material to obtain base materials with various surface roughnesses. The experimenter then placed the center electrode, formed by bonding the electrode head to the base material, onto an insulator, and assembled the main metal housing with the ground electrode attached to it onto the outer periphery of the insulator. Before bending the ground electrode, the arithmetic mean roughness of the discharge surface of the electrode head (excluding the area from the edge to a distance of 0.08 mm from the edge) and the arithmetic mean roughness of the side surface of the protrusion of the base material were measured using a non-contact three-dimensional shape measuring device (Bruker Alicona INFINITE FOCUS G4).

[0080] Similar to Experiment 1, the experimenter measured the arithmetic mean roughness of the discharge surface of the electrode head. From the 12 arithmetic mean roughness measurements, five were selected in descending order, and the average of these five roughness measurements was taken as the representative value. Similar to Experiment 3, the experimenter measured the arithmetic mean roughness of the side surface of the protrusion on the front end side, starting 0.1 mm away from the point where the side surface of the protrusion intersects with the front end of the insulator, and calculated the arithmetic mean roughness at 12 equally spaced points in the circumferential direction. The average of these 12 arithmetic mean roughness measurements was taken as the representative value of the protrusion.

[0081] After measuring the arithmetic mean roughness of the electrode head and protrusion, the grounding electrode was bent without contacting the electrode head and protrusion to obtain spark plug samples No. 44 to No. 51 with a spark gap between the electrode head of the center electrode and the grounding electrode. The spark gap size of the samples was set to 1.3 mm. In addition to the conditions of Test 1, the same test as Test 1 was conducted with air flowing across the spark gap (flow rate 5 L / min) in the pressure chamber.

[0082] Samples with a standard discharge ratio of 90% or higher are classified as S, samples with a standard discharge ratio of 80% or higher but less than 90% are classified as A, and samples with a standard discharge ratio of 70% or higher but less than 80% are classified as B. Table 3 records the arithmetic mean roughness (representative value) and results of the discharge surface and the side surface of the protrusion of the electrode head.

[0083] [Table 3]

[0084]

[0085] As shown in Table 3, it can be seen that, compared with samples No. 44, No. 46, No. 48, and No. 50, where the arithmetic surface roughness of the side of the protrusion is greater than the arithmetic mean roughness of the discharge surface of the electrode head, samples No. 45, No. 47, No. 49, and No. 51, where the arithmetic surface roughness of the side of the protrusion is smaller than the arithmetic mean roughness of the discharge surface of the electrode head, have a larger proportion of standard discharge. It can be concluded that by making the arithmetic mean roughness of the discharge surface of the electrode head greater than the arithmetic mean roughness of the side of the protrusion, the proportion of standard discharge can be further increased, thus improving ignition performance.

[0086] (Experiment 5)

[0087] The experimenter prepared a circular plate-shaped electrode head with a diameter of 0.8 mm and a thickness of 0.6 mm, made of a Ru-Pt alloy containing 15% Pt and the remainder Ru, and a grounding electrode. The projected material was then impacted with the discharge surface of the electrode head to obtain electrode heads with various surface roughnesses. Furthermore, the projected material was impacted with the opposing surface of the grounding electrode to obtain grounding electrodes with various surface roughnesses. The experimenter then positioned a center electrode, formed by bonding the electrode head to the base material, within an insulator, and assembled a main metal shell connected to the grounding electrode onto the outer periphery of the insulator. Before bending the grounding electrode, a non-contact three-dimensional shape measuring device (Bruker Alicona INFINITE FOCUS G4) was used to measure the arithmetic mean roughness of the discharge surface of the electrode head, excluding the area from the edge to a position 0.08 mm from the edge, and the arithmetic mean roughness of the opposite surface of the grounding electrode, excluding the area from the edge to a position 0.08 mm from the edge, in the same manner as in Experiment 1. Five arithmetic mean roughnesses were selected from the 12 arithmetic mean roughnesses in descending order, and the average value of these five arithmetic mean roughnesses was used as the representative value.

[0088] After measuring the arithmetic mean roughness, the grounding electrode was bent in a manner that did not contact the discharge surface of the electrode tip or the opposing surface of the grounding electrode, thus obtaining spark plug samples No. 52 to No. 58 with a spark gap between the electrode tip of the center electrode and the grounding electrode. The spark gap size of the samples was 1.3 mm.

[0089] The testers installed each sample in a 1.5L inline four-cylinder turbocharged engine and operated the engine at 2000 rpm and an indicated mean effective pressure (NMEP) of 1000 kPa. The ignition timing was advanced by 1° relative to the standard ignition timing of the genuine spark plug for each test engine. Based on the waveform of the ion current, the occurrence of pre-ignition (early ignition) was studied, and the ignition timing that caused pre-ignition was determined. Samples that showed pre-ignition with a crankshaft angle more than 2° advanced relative to the genuine spark plug were classified as A, and samples that showed pre-ignition with an angle less than 2° advanced were classified as B. The results are recorded in the pre-ignition column of Table 4.

[0090] [Table 4]

[0091]

[0092] As shown in Table 4, it can be seen that, compared with samples where the arithmetic mean roughness of the opposite surface of the ground electrode is greater than the arithmetic mean roughness of the discharge surface of the electrode head, samples No. 53, No. 55, No. 57, and No. 58 where the arithmetic mean roughness of the opposite surface of the ground electrode is smaller than the arithmetic mean roughness of the discharge surface of the electrode head are less prone to premature ignition. According to the embodiments, by making the arithmetic mean roughness of the opposite surface of the ground electrode smaller than the arithmetic mean roughness of the discharge surface of the electrode head, premature ignition of the discharge surface of the ground electrode as a spark can be reduced.

[0093] The present invention has been described above based on the embodiments, but the present invention is not limited to any of the above embodiments, and it is easy to deduce that various modifications and variations can be made without departing from the spirit of the present invention.

[0094] In this embodiment, the case of a bent grounding electrode 16 has been described, but it is not limited to this. Of course, a straight grounding electrode 16 can be used instead of a bent grounding electrode 16. In this case, the front end of the main metal housing 15 extends along the axial direction, and the straight grounding electrode 16 is joined to the main metal housing 15. The number of grounding electrodes 16 can also be appropriately set.

[0095] In this embodiment, the central electrode 13 and the ground electrode 16 are described in such a way that the discharge surface 21 of the electrode head 20 of the central electrode 13 faces the front end side in the axial direction, but this is not a limitation. The positional relationship between the central electrode 13 and the ground electrode 16 can be appropriately set. As another positional relationship between the central electrode 13 and the ground electrode 16, for example, the case in which the electrode head 20 is positioned opposite the ground electrode 16 such that there is a spark gap between the side surface 22 of the electrode head 20 of the central electrode 13 and the ground electrode 16. In this case, the surface of the side surface 22 of the electrode head 20 that faces the ground electrode 16 corresponds to the discharge surface of technical solution 1, and the discharge surface 21 of the electrode head 20 corresponds to the side surface connected to the discharge surface. The measurement of the arithmetic mean roughness of the discharge surface is performed in the same way as the measurement of the arithmetic mean roughness of the side surface 22, and the measurement of the arithmetic mean roughness of the side surface is performed in the same way as the measurement of the arithmetic mean roughness of the discharge surface 21.

Claims

1. A spark plug, wherein, This spark plug has the following features: An insulator having a axial hole extending along its axis; The center electrode is disposed in the shaft hole; A main metal casing, which is disposed on the outer periphery of the insulator; as well as The grounding electrode is connected to the main metal casing. The central electrode comprises a base material and an electrode head that is coupled to the base material. The electrode head is mainly composed of Ru and includes a discharge surface opposite to the grounding electrode. The arithmetic mean roughness of the discharge surface is greater than 0.4 μm and less than 4.8 μm.

2. A spark plug, wherein, This spark plug has the following features: An insulator having a axial hole extending along its axis; The center electrode is disposed in the shaft hole; A main metal casing, which is disposed on the outer periphery of the insulator; as well as The grounding electrode is connected to the main metal casing. The grounding electrode comprises a base material and an electrode head that is bonded to the base material. The electrode head is mainly composed of Ru and includes a discharge surface opposite to the central electrode. The arithmetic mean roughness of the discharge surface is greater than 0.4 μm and less than 4.8 μm.

3. A spark plug, wherein, This spark plug has the following features: An insulator having a axial hole extending along its axis; The center electrode is disposed in the shaft hole; A main metal casing, which is disposed on the outer periphery of the insulator; as well as The grounding electrode is connected to the main metal casing. Both the center electrode and the ground electrode comprise a base material and an electrode head that is coupled to the base material. The electrode head is mainly composed of Ru and includes a discharge surface opposite to the center electrode and the ground electrode. The arithmetic mean roughness of the discharge surface is greater than 0.4 μm and less than 4.8 μm.

4. The spark plug according to any one of claims 1 to 3, wherein, The arithmetic mean roughness of the discharge surface is below 3.2 μm.

5. The spark plug according to any one of claims 1 to 3, wherein, The arithmetic mean roughness of the discharge surface is greater than 1.1 μm.

6. The spark plug according to any one of claims 1 to 3, wherein, The electrode head includes a side surface connected to the discharge surface. 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.

7. The spark plug according to claim 1, wherein, The arithmetic mean roughness of the surface opposite the discharge surface of the grounding electrode is smaller than the arithmetic mean roughness of the discharge surface.

8. The spark plug according to claim 3, wherein, The arithmetic mean roughness of the surface opposite the discharge surface of the grounding electrode to the center electrode is smaller than the arithmetic mean roughness of the discharge surface of the center electrode.

9. The spark plug according to claim 1, wherein, The base material includes a protrusion extending from the insulator toward the grounding electrode along the axis, the arithmetic mean roughness of the side surface of the protrusion being smaller than the arithmetic mean roughness of the discharge surface.

10. The spark plug according to claim 3, wherein, The base material of the center electrode includes a protrusion that extends from the insulator toward the ground electrode along the axis, the arithmetic mean roughness of the side surface of the protrusion being smaller than the arithmetic mean roughness of the discharge surface of the center electrode.

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