Oil ring, manufacturing method of oil ring

Abstract

To reduce the sliding resistance of an oil ring, and to further improve fuel consumption.SOLUTION: A plural-piece type oil ring 70 is installed in a piston of an internal combustion engine, and has a ring body 72 having a rail and an expander. On the rail of the ring body 72, a coating 92 is formed by physical vapor deposition. Outer peripheral surfaces 81A and 81B of the rail formed by the coating 92 are formed in a band shape extending in a circumferential direction, and have actual contact surfaces 83A and 83B abutting on an inner wall surface of a cylinder of the internal combustion engine and sliding, and inclined surfaces 84A, 84B, 85A, and 85B continuing to an axial outer side from an axial edges of the actual contact surfaces 83A and 83B, and getting distant from the inner wall surface toward the axial outer side. The inclined surfaces 84A, 84B, 85A, and 85B are configured by surfaces of the coating 92 which are polished or ground in the circumferential direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an oil ring for an internal combustion engine having a cylinder and a piston, and a method for manufacturing the same. [Background technology]

[0002] Reducing friction between piston rings and cylinder liners is an effective way to improve engine fuel economy. In recent years, oil rings, a type of piston ring, have been treated with nitriding, PVD chromium nitride coating with a low friction coefficient, DLC coating, etc. to reduce friction.

[0003] In addition, the outer peripheral surface of the oil ring is configured in a step land shape, and the actual contact width between the sliding surface at the tip and the cylinder liner is reduced, thereby ensuring sufficient contact pressure even with a small tension. In this case, the surface pressure on the sliding surface becomes high, so that nitriding alone will not provide sufficient wear resistance, and therefore PVD treatment or the like, which can produce a high-hardness coating, is sometimes adopted (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5871277 Summary of the Invention [Problem to be solved by the invention]

[0005] Although this was an unknown problem at the time of filing this application, it has become clear that although forming a high-hardness coating on the sliding surface of an oil ring by physical vapor deposition can reduce friction, there is still room for further improvement. In view of this situation, the object of the present invention is to provide an oil ring that can further reduce the sliding resistance of the oil ring and achieve improved fuel efficiency. [Means for solving the problem]

[0006] To achieve the above-mentioned object, the present invention provides a multi-piece oil ring that is mounted on a piston of an internal combustion engine and includes a ring body having rails, and an expander that applies tension to the ring body, wherein the rails of the ring body are coated with a coating formed by physical vapor deposition, and the outer peripheral surface of the rail formed by the coating is formed in a band shape that extends in the circumferential direction and has an actual contact surface that abuts and slides against the inner wall surface of a cylinder of the internal combustion engine, and an inclined surface that continues from the axial edge of the actual contact surface outward in the axial direction and whose distance from the inner wall surface increases as it extends axially outward, and wherein the inclined surface is formed by polishing or grinding the surface of the coating along the circumferential direction.

[0007] In relation to the above oil ring, the actual contact surface may be configured by polishing or grinding the surface of the coating along the axial direction.

[0008] In relation to the above oil ring, when the position on the inclined surface where the inclination angle with respect to the axial direction is 7° is defined as the evaluation position, the protruding peak height Rpk obtained by measuring the evaluation position along the circumferential direction may be 0.15 μm or less.

[0009] In relation to the above oil ring, when a position on the inclined surface where the inclination angle with respect to the axial direction is 7° is defined as an evaluation position, the load length ratio Rmr obtained by measuring the evaluation position along the circumferential direction when causing a height reduction of 0.3 μm starting from a 0.5% position may be 35% or more.

[0010] In relation to the oil ring, the inclined surface may have a hairline extending in the circumferential direction, which is formed by the polishing or grinding.

[0011] In relation to the oil ring, the contact surface may be characterized by having a hairline extending in the axial direction, which is formed by polishing or grinding.

[0012] In relation to the oil ring, the coating may be a chromium nitride alloy coating or a hard carbon coating.

[0013] To achieve the above-mentioned object, the present invention provides a method for manufacturing a multi-piece oil ring that is mounted on a piston of an internal combustion engine and that includes a ring body having rails and an expander that applies tension to the ring body, the method comprising the steps of: forming a coating on the rails of the ring body by physical vapor deposition; circumferentially polishing or grinding the outer peripheral surface of the rail formed by the coating to form a circumferential wear surface on the surface of the coating; and axially polishing or grinding a portion of the circumferential wear surface to form an actual contact surface on the surface of the coating that abuts and slides against the inner wall surface of a cylinder of the internal combustion engine, wherein the circumferential wear surface remains axially outward from the axial edge of the actual contact surface, thereby making the circumferential wear surface an inclined surface whose distance from the inner wall surface increases as it extends axially outward. [Effects of the Invention]

[0014] According to the present invention, the sliding resistance of the oil ring can be further reduced, and the excellent effect of improving fuel efficiency can be achieved. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1A is a side view showing a piston and a piston ring to which an oil ring according to an embodiment of the present invention is applied, FIG. 1B is a partially enlarged cross-sectional view showing the piston and the piston ring, FIG. 1C is a partially enlarged cross-sectional view of a top ring, and FIG. 1D is a partially enlarged cross-sectional view of a second ring. [Figure 2] FIG. 2 is a cross-sectional view of a two-piece type oil ring according to the present embodiment. [Figure 3]FIG. 2 is an enlarged axial cross-sectional view of the oil ring in the vicinity of its outer peripheral surface. [Figure 4] 1A is an axial cross-sectional view showing an enlarged view of the vicinity of the outer peripheral surface of the oil ring after physical vapor deposition processing in the manufacturing process of the oil ring, FIG. 1B is a partial cross-sectional view showing how the oil ring is buffed, and FIG. 1C is a perspective view showing an enlarged view of the vicinity of the outer peripheral surface of the oil ring after buffing. [Figure 5] 1A is a partial cross-sectional view showing how the oil ring is subjected to lapping, and FIG. 1B is an enlarged perspective view showing the vicinity of the outer peripheral surface of the oil ring after lapping. [Figure 6] 1A is a cross-sectional view of a three-piece oil ring that is a modified example of the oil ring of this embodiment, and FIG. 1B is an axial cross-sectional view showing an enlarged view of the vicinity of the outer peripheral surface of the oil ring. [Figure 7] (A) Stribeck diagram and (B) FMEP diagram of sliding in a typical internal combustion engine. [Figure 8] 2 is a cross-sectional view taken along the axial direction of a cylinder liner of an internal combustion engine to which the oil ring is applied. FIG. [Figure 9] 4A and 4B are developments showing the inner peripheral wall of the cylinder liner developed in the circumferential direction. [Figure 10] 3 is a cross-sectional view of the inner peripheral wall of the cylinder liner taken along a direction perpendicular to the axis. FIG. [Figure 11] 10(A) to 10(C) are graphs showing the results of measuring the surface texture parameters in the circumferential direction of the oil rings according to the first and second examples. [Figure 12] 10(A) and 10(B) are graphs showing the results of measuring the surface texture parameters in the circumferential direction of the oil rings according to the first and second examples. [Figure 13] 10(A) to 10(C) are graphs showing the results of measuring the surface texture parameters in the circumferential direction of the oil rings according to the first and second examples. [Figure 14] 10(A) to 10(D) are images showing the results of three-dimensional imaging of the surface texture in the circumferential direction of the oil ring according to the first embodiment. [Figure 15]10(A) to 10(D) are images showing the results of three-dimensional imaging of the surface texture in the circumferential direction of the oil ring according to the second embodiment. [Figure 16] 10(A) to 10(D) are images showing the results of three-dimensional imaging of the surface texture in the circumferential direction of an oil ring serving as a comparative example. [Figure 17] FIG. 1 is a diagram showing FMEP curves of an internal combustion engine actually measured using oil rings according to an embodiment and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0016] An oil ring and a method of manufacturing the same according to an embodiment of the present invention will now be described with reference to the accompanying drawings.

[0017] First, a sliding structure of an internal combustion engine equipped with the oil ring of this embodiment will be described.

[0018] <Piston and piston ring structure> 1(A) and 1(B) show a piston 30 and piston rings 40 (top ring 50, second ring 60, oil ring 70) installed in the ring groove of the piston 30 as part of a gasoline engine. The piston ring 40 reciprocates in the cylinder axial direction with its outer peripheral surface 42 facing the inner wall surface 12 of the cylinder liner 10. The top ring 50 eliminates the gap between the piston 30 and the cylinder liner 10, preventing gas leakage (blow-by), in which compressed gas escapes from the combustion chamber to the crankcase. The second ring 60, like the top ring 50, serves both to eliminate the gap between the piston 30 and the cylinder liner 10 and to scrape off excess engine oil adhering to the inner wall surface 12 of the cylinder liner 10. The top ring 50 and the second ring 60 are sometimes referred to as compression rings.

[0019] The oil ring 70 scrapes off excess engine oil adhering to the inner wall surface 12 of the cylinder liner 10 and forms an appropriate oil film, thereby preventing the piston 30 from seizing.

[0020] <Top ring shape> As shown enlarged in Fig. 1(C), the top ring 50 is a single annular member, and when viewed in cross section from its outer circumferential surface 52, it has a so-called weak barrel shape that is gently convex radially outward. For ease of explanation, the radial dimension in Fig. 1(C) is greatly exaggerated relative to the axial dimension, thereby emphasizing the convex shape of the outer circumferential surface.

[0021] The thickness (radial width) a1 of the top ring 50 is set to, for example, 6.0 mm or less, preferably 4.5 mm or less, and the width (axial width) h1 is set to, for example, 3.5 mm or less, preferably 3.0 mm or less.

[0022] A contact surface 53 is formed in a portion of the outer peripheral surface 52 in the axial direction. The contact surface 53 is a band-shaped region extending in the circumferential direction of the outer peripheral surface 52. The contact surface 53 is a sliding region (sliding surface) that comes into contact with and slides against the inner wall surface 12 of the cylinder liner 10. Furthermore, on the outer peripheral surface 52, inclined surfaces 54 and corner portions 55 are formed outward from both edges of the contact surface 53 in the axial direction (band width direction). The inclined surfaces 54 and corner portions 55 are regions that are separated from the inner wall surface 12 of the cylinder liner 10.

[0023] The dimension of the actual contact width f of the actual contact surface 53 before the running-in operation is preferably set to 0.15 mm or more, more preferably 0.3 mm or more, even more preferably set to be greater than 0.3 mm, and even more preferably set to be 0.4 mm or more.

[0024] In order to actively form a sagging shape by running-in, the surface hardness of the outer peripheral surface 52 is preferably set to 2000 Hv or less, and is set to 1800 Hv in this example.

[0025] <Second ring shape> As shown enlarged in Figure 1(D), the second ring 60 is a single annular member, and its outer peripheral surface 62 has a tapered cross section. The flat surface at the tip of this tapered shape has a weak barrel shape that is gently convex radially outward. For ease of explanation, the radial dimension in Figure 1(D) is greatly exaggerated relative to the axial dimension, thereby emphasizing the convex shape of the outer peripheral surface.

[0026] The thickness (radial width) a1 of the second ring 60 is set to, for example, 6.0 mm or less, preferably 4.5 mm or less, and the width (axial width) h1 is set to, for example, 3.0 mm or less, preferably 2.5 mm or less.

[0027] Similar to the top ring 50, a contact surface 63 is formed in part of the outer peripheral surface 62 in the axial direction. The contact surface 63 is a band-shaped region extending in the circumferential direction of the outer peripheral surface 62. The contact surface 63 is a sliding region (sliding surface) that comes into contact with and slides against the inner wall surface 12 of the cylinder liner 10. Furthermore, on the outer peripheral surface 62, inclined surfaces 64 and corner portions 65 are formed outward from both edges of the contact surface 63 in the axial direction (band width direction). The inclined surfaces 64 and corner portions 65 are regions that are separated from the inner wall surface 12 of the cylinder liner 10.

[0028] The dimension of the actual contact width f of the actual contact surface 63 before the running-in operation is preferably set to 0.15 mm or more, more preferably 0.3 mm or more, even more preferably set to be greater than 0.3 mm, and even more preferably set to be 0.4 mm or more.

[0029] In order to actively form a sagging shape by running-in, the surface hardness of the outer peripheral surface 62 is preferably set to 1600 Hv or less, and is set to 1400 Hv in this example.

[0030] <Oil ring shape> 2 shows an enlarged view of a two-piece type oil ring 70 according to this embodiment. The oil ring 70 has a ring body 72 and a coil expander 76C in the form of a coil spring.

[0031] The ring body 72 integrally includes annular upper rail 73A and lower rail 73B disposed at both axial ends, and annular pillar portions 75 disposed between and connecting the upper rail 73A and lower rail 73B. The cross section of the pair of upper rail 73A and lower rail 73B and pillar portions 75 combined is generally I-shaped or H-shaped, and by utilizing this shape, an inner circumferential groove 79 having a semicircular cross section for accommodating a coil expander 76C is formed on the inner circumferential surface side.

[0032] An upper annular protrusion 74A and a lower annular protrusion 74B are formed on the outer periphery of each of the upper rail 73A and the lower rail 73B, respectively, and protrude radially outward from the column portion 75. The vicinity of the tip of the upper annular protrusion 74A and the lower annular protrusion 74B has an upper outer peripheral surface 81A and a lower outer peripheral surface 81B.

[0033] The coil expander 76C is housed in the inner circumferential groove 79, thereby pressing and biasing the ring body 72 radially outward. Note that a plurality of oil return holes 77 are formed in the pillar portion 75 of the ring body 72 in the circumferential direction.

[0034] As shown enlarged in FIG. 3, the upper outer peripheral surface 81A and the lower outer peripheral surface 81B each constitute the surface of a hard coating (hereinafter referred to as a PVD coating) 92 formed on the surface of a base material 90 by physical vapor deposition. The base material 90 may be made of, for example, 8Cr steel, 10Cr steel, or 13CrSUS. The PVD coating 92 may be a chromium nitride alloy coating such as a Cr-N, Cr-BN, Cr-BVN, or Cr-B-Ti-V-(Mn,Mo)-N alloy, or a hard carbon coating (also referred to as a diamond-like carbon coating or DLC coating). The hydrogen content of the hard carbon coating is preferably 10 atomic % or less. The surface hardness of the PVD coating 92 is preferably 2000 Hv or less, and is set to 1800 Hv in this example.

[0035] (Explanation of actual contact surface) An upper contact surface 83A and a lower contact surface 83B that actually contact the inner wall surface 12 of the cylinder liner 10 are formed on portions of the upper outer peripheral surface 81A and the lower outer peripheral surface 81B. The upper contact surface 83A and the lower contact surface 83B are band-shaped regions extending in the circumferential direction. The upper contact surface 83A and the lower contact surface 83B are flat surfaces created by wearing away portions of the surface side of the PVD coating 92 through lapping, which polishes or grinds along the axial direction (band width direction) (see dotted line V). As shown in FIG. 5(B), fine axial hairlines H1 that extend in the axial direction (band width direction) and become polishing marks are formed on the surfaces of the upper contact surface 83A and the lower contact surface 83B.

[0036] The radial thickness t1 of the PVD coating 92 at the axial center portions of the upper contact surface 83A and the lower contact surface 83B is preferably 5 μm or more, and more preferably 10 μm or more. The thickness t1 of the PVD coating 92 is preferably 50 μm or less, and more preferably 40 μm or less. Here, it is set to 20 μm.

[0037] The upper outer peripheral surface 81A and the lower outer peripheral surface 81B are integrally formed with the ring body 72. As a result, the two outer peripheral surfaces 81A, 81B can be defined together as a single outer peripheral surface 81 (see FIG. 2). A gap is formed in the center of the single outer peripheral surface 81.

[0038] Returning to FIG. 3 , the upper contact surface 83A has a recessed step 98 on the axial side (lower side) of the column portion 75, where a portion of the upper outer peripheral surface 81A is recessed so as to reduce its diameter. Similarly, the lower contact surface 83B has a recessed step 98 on the axial side (upper side) of the column portion 75, where a portion of the lower outer peripheral surface 81B is recessed so as to reduce its diameter. These recessed steps 98 form the upper outer peripheral surface 81A and the lower outer peripheral surface 81B in a stepped shape. This allows the actual contact widths (band widths) f1 and f2 of the upper contact surface 83A and the lower contact surface 83B to be set small. In other words, the upper annular protrusion 74A and the lower annular protrusion 74B have a two-step protrusion shape, which is referred to as a step-land shape. The recessed step 98 can be formed, for example, by grinding the base material 90, but can also be formed in advance during the wire drawing process.

[0039] (Explanation of the inclined surface) Upper outer peripheral surface 8 1 At A, an upper first inclined surface 84A and an upper second inclined surface 85A are formed on both axial (band width) edges of the upper contact surface 83A. The upper first inclined surface 84A is located distal to the spacer expander 76C, and the upper second inclined surface 85A is located proximal to the spacer expander 76C. The upper first inclined surface 84A is an inclined region in which the distance from the inner wall surface 12 of the cylinder liner 10 increases with increasing upward distance from the upper contact surface 83A. The upper second inclined surface 85A is an inclined region in which the distance from the inner wall surface 12 of the cylinder liner 10 increases with increasing downward distance from the upper contact surface 83A. The upper first inclined surface 84A and the upper second inclined surface 85A each form a band-shaped region extending in the circumferential direction.

[0040] Furthermore, an upper first corner portion 86A is formed on the axial outer side (upper side) of the upper first inclined surface 84A. In an axial cross section, the upper first corner portion 86A is a region where the gradient of the slope changes sharply from the upper first inclined surface 84A toward the upper side surface of the upper annular protrusion 74A.

[0041] An upper second corner portion 87A is formed on the axial outer side (lower side) of the upper second inclined surface 85A. In an axial cross section, the upper second corner portion 87A is a region where the gradient of the slope changes sharply from the upper second inclined surface 85A toward the lower side surface of the upper annular protrusion 74A.

[0042] Lower side outer peripheral surface 8 1 At B, a lower first inclined surface 84B and a lower second inclined surface 85B are formed on both axial (band width) edges of the lower contact surface 83B. The lower first inclined surface 84B is located distally from the spacer expander 76C, and the lower second inclined surface 85B is located proximal to the spacer expander 76C. The lower first inclined surface 84B is an inclined region in which the distance from the inner wall surface 12 of the cylinder liner 10 increases with increasing downward distance from the lower contact surface 83B. The lower second inclined surface 85B is an inclined region in which the distance from the inner wall surface 12 of the cylinder liner 10 increases with increasing upward distance from the lower contact surface 83B. The lower first inclined surface 84B and the lower second inclined surface 85B each form a band-shaped region extending in the circumferential direction.

[0043] Furthermore, a lower first corner portion 86B is formed on the axial outer side (lower side) of the lower first inclined surface 84B. In an axial cross section, the lower first corner portion 86B is a region where the gradient of the slope changes sharply from the lower first inclined surface 84B toward the lower side surface of the lower annular protrusion 74B.

[0044] A lower second corner portion 87B is formed on the axial outer side (upper side) of the lower second inclined surface 85B. In an axial cross section, the lower second corner portion 87B is a region where the gradient of the slope changes sharply from the lower second inclined surface 85B toward the upper side surface of the lower annular protrusion 74B.

[0045] 5(B), at least the upper first inclined surface 84A and the lower first inclined surface 84B are subjected to buffing, which will be described later, to polish or grind a portion of the surface of the PVD coating 92 along the circumferential direction. As a result, the upper first inclined surface 84A and the lower first inclined surface 84B are smoothed along the circumferential direction. Fine circumferential hairlines H2 that extend in the circumferential direction (the strip longitudinal direction) and become polishing marks are formed on the surfaces of the upper first inclined surface 84A and the lower first inclined surface 84B.

[0046] In this embodiment, the upper first inclined surface 84A and the lower first inclined surface 84B, as well as the upper second inclined surface 85A and the lower second inclined surface 85B, are all smoothed by polishing or grinding using buffing, and fine circumferential hairlines H2 are formed on the surfaces.

[0047] Returning to FIG. 1, the combined radial thickness a of the oil ring 70 11 The combined axial width (nominal width) h1 (see FIG. 1(B)) is set to, for example, 5.0 mm or less, preferably 4.5 mm or less. The combined axial width (nominal width) h1 (see FIG. 1(B)) is set to, for example, 4.0 mm or less, preferably 3.0 mm or less. The thickness (radial width) a1 (see FIG. 1(B)) of the upper rail 73A or the lower rail 73B alone is set to, for example, 4.0 mm or less, preferably 3.0 mm or less. The width (axial width) h 12 (See FIG. 1(B)) is set to, for example, 0.40 mm or less, preferably 0.30 mm or less, and more preferably 0.20 mm or less.

[0048] Before the running-in operation, the upper contact width f1 of the upper contact surface 83A and the lower contact width f2 of the lower contact surface 83B are preferably set to 0.05 mm or more, more preferably 0.10 mm or more, and even more preferably set to greater than 0.13 mm. The upper contact width f1 and the lower contact width f2 are preferably set to 0.40 mm or less, more preferably 0.35 mm or less, and even more preferably set to less than 0.30 mm.

[0049] Furthermore, the total contact width F, which is the sum of the upper contact width f1 and the lower contact width f2, is preferably set to 0.10 mm or more, more preferably 0.20 mm or more, and even more preferably greater than 0.26 mm. The total contact width F is preferably set to 0.80 mm or less, more preferably 0.70 mm or less, and even more preferably less than 0.60 mm. Furthermore, the surface pressure acting on the upper contact surface 83A and the lower contact surface 83B is preferably set to 0.8 MPa or more, and more preferably 1.0 MPa or more. Furthermore, this surface pressure is preferably set to 2.5 MPa or less, and more preferably 2.2 MPa or less.

[0050] (Evaluation of surface roughness in the circumferential direction of an inclined surface) In this embodiment, an evaluation position W is defined to evaluate the surface roughness of the upper first inclined surface 84A and the lower first inclined surface 84B along the circumferential direction. As shown in FIG. 3 , in an axial cross-sectional view, the evaluation position W is defined as the point where the inclination angle θ of the upper first inclined surface 84A and the lower first inclined surface 84B relative to the axial direction J of the oil ring 70 is 7°. The surface texture value obtained by measuring this evaluation position W along the circumferential direction using a stylus-type surface roughness measuring instrument (JIS B 0651:2001) is defined as the "circumferential surface texture parameter of the inclined surface." Note that the measurement was performed using a stylus with a standard tip radius of 2 μm and a 60° knife-edge tip shape, with the cutoff wavelength λc for the cross-sectional curve selected to be 0.8 mm.

[0051] In this embodiment, the arithmetic mean roughness Ra (JIS B 0601:2013), which is a circumferential surface quality parameter, of the upper first inclined surface 84A and the lower first inclined surface 84B is preferably less than 0.18 μm, and more preferably 0.10 μm or less.

[0052] In this embodiment, the maximum height Rz (JIS B 0601:2013), which is a circumferential surface texture parameter, of the upper first inclined surface 84A and the lower first inclined surface 84B is preferably less than 1.40 μm, and more preferably 1.00 μm or less.

[0053] In this embodiment, the ten-point average roughness RzJIS (JIS B 0601:2013), which is a circumferential surface quality parameter, of the upper first inclined surface 84A and the lower first inclined surface 84B is preferably 1.10 μm or less, and more preferably 0.80 μm or less.

[0054] In this embodiment, the protruding peak height Rpk (JIS B 0671-2:2002), which is a circumferential surface quality parameter, of the upper first inclined surface 84A and the lower first inclined surface 84B is preferably 0.15 μm or less, and more preferably 0.10 μm or less.

[0055] In this embodiment, the core level difference Rk (JIS B 0671-2:2002), which is a circumferential surface texture parameter, is preferably 0.50 μm or less, and more preferably 0.30 μm or less, on the upper first inclined surface 84A and the lower first inclined surface 84B.

[0056] In this embodiment, the load length ratio Rmr (JIS B 0601:2013) of the upper first inclined surface 84A and the lower first inclined surface 84B, which is a circumferential surface texture parameter, when a height reduction of 0.3 μm is caused starting from the 0.5% position, is preferably 35% or more, and more preferably 75% or more.

[0057] In this embodiment, the load length ratio Rmr (JIS B 0601:2013) of the upper first inclined surface 84A and the lower first inclined surface 84B, which is a circumferential surface texture parameter, when a height reduction of 0.4 μm occurs starting from the 0.5% position, is preferably 55% or more, and more preferably 80% or more.

[0058] In this embodiment, the load length ratio Rmr (JIS B 0601:2013) of the upper first inclined surface 84A and the lower first inclined surface 84B, which is a circumferential surface texture parameter, when a height reduction of 0.5 μm is caused starting from the 0.5% position, is preferably 70% or more, and more preferably 85% or more.

[0059] The radial thickness t2 of the PVD coating 92 at the evaluation position W of the upper first inclined surface 84A and the lower first inclined surface 84B is preferably 5 μm or more, and more preferably 10 μm or more. The thickness t2 of the PVD coating 92 is preferably 50 μm or less, and more preferably 40 μm or less. Here, it is set to 20 μm.

[0060] (Fine adjustment of the actual contact surface by running in) Incidentally, the upper and lower contact surfaces 83A and 83B represent the states at the time of completion of manufacturing. When this oil ring 70 is attached to the piston 30 and subjected to actual break-in operation together with the cylinder liner 10, the shapes of the upper and lower contact surfaces 83A and 83B are minutely modified by contact wear. Specifically, the upper and lower contact surfaces 83A and 83B each assume a barrel shape that is slightly inclined from the center in the cylinder axial direction to both outer sides due to wear during break-in. These inclinations formed in the upper and lower contact surfaces 83A and 83B are referred to as sagging shapes, and their gradients are extremely small, on the order of 1 / 2000 to 1 / 500. After the running-in operation, the upper contact surface 83A and the lower contact surface 83B become a sliding area (sliding surface) that substantially contacts and slides against the inner wall surface 12 of the cylinder liner 10 while being slightly inclined or deformed.

[0061] <Manufacturing method of the ring body of the oil ring>

[0062] (Making base material) Next, a method for manufacturing the ring body 72 of the oil ring 70 of this embodiment will be described. First, a linear wire having a desired cross-sectional shape is bent into a ring shape using a bending machine (not shown) to produce a base material 90.

[0063] (Buffing of base material) Next, the outer peripheral surface of the ring-shaped base material 90 is buffed to polish or grind the outer peripheral surface in the circumferential direction. This smooths the base that will become the outer peripheral surface of the base material 90. The outer peripheral surface of the base material 90 may also be subjected to nitriding treatment.

[0064] (Physical vapor deposition process) 4(A), a PVD coating 92 was then formed by physical vapor deposition on the outer peripheral surfaces (future upper outer peripheral surface 81A and lower outer peripheral surface 81B) of the base material 90, in this case a chromium nitride coating. Although not specifically shown here, immediately after the physical vapor deposition process, the outer peripheral surface 92A of the PVD coating 92 has fine irregularities formed randomly all over it. These fine irregularities result from the structure in which the vapor deposition material is deposited during the physical vapor deposition process.

[0065] (Buffing of PVD coating) Next, as shown in FIG. 4(B), the outer circumferential surface 92A of the PVD coating 92 (future upper outer circumferential surface 81A and lower outer circumferential surface 81B) is buffed. In this embodiment, a plurality of ring bodies 72 are set together on a rotating tool (not shown), and these are forcibly rotated around a central axis E. A buff 100, which is a cylindrical polishing tool made of cotton or felt, is placed next to the ring body 72 with its rotation axis Z parallel to the central axis E of the ring body 72.

[0066] The buff 100 is forcibly rotated about the central axis Z while the outer peripheral surface 100A of the buff 100 is pressed against the coating outer peripheral surface 92A of the ring body 72. At the same time, the buff 100 and the ring body 72 are moved relative to each other in the direction of the central axis E and Z. By aligning the rotation directions of the ring body 72 and the buff 100, the outer peripheral surface 100A of the buff 100 and the coating outer peripheral surface 92A of the ring body 72 move in opposite directions at their contact points, improving polishing efficiency.

[0067] As a result, as shown in FIG. 4(C), all or part of the outer circumferential surface 92A of the PVD coating 92 (the area that can be contacted by the buff 100) is worn away by polishing or grinding. The surface resulting from this wear is defined here as a circumferential wear surface 92B. A circumferential hairline H2 extending in the circumferential direction is formed on the surface of this circumferential wear surface 92B. The circumferential wear surface 92B forms an upper first inclined surface 84A, an upper second inclined surface 85A, and a lower first inclined surface 84B, a lower second inclined surface 85B.

[0068] An upper lapping target region 83A' is formed between the upper first inclined surface 84A and the upper second inclined surface 85A. Similarly, a lower lapping target region 83B' is formed between the lower first inclined surface 84B and the lower second inclined surface 85B.

[0069] (lapping) Next, as shown in FIG. 5(A), the plurality of ring bodies 72 are set together in a fixture (not shown), and then inserted into the inner grinding surface 120A of a cylindrical grinding tool (lapping machine) 120, and slid relatively in the axial direction. The inner diameter of the inner grinding surface 120A and the ring body 72 are made to approximate each other, and a predetermined amount of abrasive grains are interposed between them, so that the upper outer peripheral surface 8 of the ring body 72 is ground. 1 The upper and lower outer peripheral surfaces 81A and 81B are ground or polished. Specifically, the upper and lower lapping target regions 83A' and 83B' of the circumferential wear surface 92B are worn away. In other words, the circumferential wear surface 92B is left as it is outside the upper and lower lapping target regions 83A' and 83B' of the circumferential wear surface 92B.

[0070] 5(B), the area worn away by the lapping process forms an upper contact surface 83A and a lower contact surface 83B. Axial hairlines H1, which are grinding marks, are formed on the upper contact surface 83A and the lower contact surface 83B.

[0071] <Oil ring surface pressure setting> Next, we will explain how to set the surface pressure between the oil ring 70 and the cylinder liner 10. Here, the surface pressure of the oil ring 70 means the surface pressure acting on the sliding surfaces that define the actual contact widths f1 and f2 on the outer peripheral surface 42 of the piston ring 40. Specifically, the surface pressure is calculated by (2 × tension) / (cylinder liner diameter × actual contact width f).

[0072] In this embodiment, the surface pressure of the oil ring 70 is preferably set to 0.8 MPa or more, more preferably 1.0 MPa or more, and is preferably set to 2.5 MPa or less, more preferably 2.2 MPa or less.

[0073] <Modified oil ring> Although the oil ring 70 in the above embodiment is a two-piece type, the present invention is not limited to this. For example, a three-piece oil ring can be used, as shown in the enlarged view of oil ring 70 in FIG. 6(A). This oil ring 70 has annular side rails 73a and 73b separated into upper and lower sections, and a spacer expander 76s disposed between these side rails 73a and 73b. The pair of side rails 73a and 73b together constitutes the ring body.

[0074] The spacer expander 76s is formed by plastic processing a steel material into a corrugated shape with repeated concave and convex portions in the axial direction of the cylinder. This corrugated shape forms an upper support surface 78a and a lower support surface 78b, which support the pair of side rails 73a and 73b in the axial direction. The inner peripheral end of the spacer expander 76s has ears 74m that extend axially outward in an arched shape. These ears 74m abut the inner peripheral surfaces of the side rails 73a and 73b. The spacer expander 76s is fitted into the ring groove of the piston 30 in a circumferentially contracted state with its butt joints butted together. As a result, the restoring force of the spacer expander 76s causes the ears 74m to press and urge the side rails 73a and 73b radially outward. This urging causes the side rails 73a and 73b to tilt inward in the axial direction (the combined nominal width direction) of the oil ring 70, as shown by the dotted lines. In other words, the pair of outer circumferential surfaces 82, 82 come closer to each other by that amount.

[0075] Combined radial thickness of oil ring 70 a 11 is set to, for example, 4.0 mm or less, preferably 3.0 mm or less. The combined axial width (nominal width) h1 is set to, for example, 4.0 mm or less, preferably 2.0 mm or less. The thickness (radial width) a1 of each of the side rails 73a, 73b alone is set to, for example, 4.0 mm or less, preferably 3.0 mm or less. The width (axial width) h 12 is set to, for example, 1.0 mm or less, preferably 0.5 mm or less, and more preferably 0.4 mm or less.

[0076] As shown in a further enlarged view in Figure 6(B), the outer peripheral surface 82 of each side rail 73a, 73b has a so-called weak barrel shape that is gently convex radially outward. For ease of explanation, the radial dimension is greatly exaggerated relative to the axial dimension to emphasize the convex shape of the outer peripheral surface.

[0077] The outer peripheral surface 82 is the surface of a hard coating (hereinafter referred to as a PVD coating) 92 formed on the base material 90 by physical vapor deposition. A contact surface 83 that actually contacts the inner wall surface 12 of the cylinder liner 10 is formed on a portion of the outer peripheral surface 82 in the axial direction. The contact surface 83B is a flat surface created by wearing away a portion of the surface side of the PVD coating 92 through lapping, which polishes or grinds along the axial direction (band width direction) (see dotted line V). The contact surface 83 is a band-shaped region extending in the circumferential direction of the outer peripheral surface 82. Fine axial hairlines H1 that extend in the axial direction (band width direction) and become polishing marks are formed on the surface of the contact surface 83.

[0078] Furthermore, on the outer peripheral surface 82, an inclined surface 84 is formed on each of both edges in the axial direction (band width direction) of the contact surface 83. The inclined surface 84 is an inclined region that is separated from the inner wall surface 12 of the cylinder liner 10. The inclined surface 84 is a band-shaped region that extends in the circumferential direction.

[0079] Corners 86 are formed further axially outward from each inclined surface 84. When viewed in axial cross section, corners 86 are regions where the gradient of the inclination changes sharply from inclined surface 84 toward the side surfaces of side rails 73a, 73b.

[0080] The inclined surface 84 is formed by buffing a portion of the surface side of the PVD coating 92 polished or ground in the circumferential direction. As a result, the inclined surface 84 is smoothed in the circumferential direction. Fine circumferential hairlines that extend in the circumferential direction (the band longitudinal direction) and become polishing marks are formed on the surface of the inclined surface 84.

[0081] The actual contact width f of the actual contact surface 83 before the running-in operation is preferably set to 0.05 mm or more, more preferably 0.10 mm or more, and even more preferably set to greater than 0.13 mm. The actual contact width f is preferably set to 0.40 mm or less, more preferably 0.35 mm or less, and even more preferably set to less than 0.30 mm.

[0082] The total contact width F, which is the sum of the contact widths f of the pair of outer peripheral surfaces 82, 82, is preferably set to 0.10 mm or more, more preferably 0.20 mm or more, and even more preferably greater than 0.26 mm. The total contact width F is preferably set to 0.80 mm or less, more preferably 0.70 mm or less, and even more preferably less than 0.60 mm. Furthermore, the surface pressure acting on the contact surface 83 is preferably set to 0.8 MPa or more, and more preferably 1.0 MPa or more. Furthermore, this surface pressure is preferably set to 2.5 MPa or less, and more preferably 2.2 MPa or less.

[0083] <Friction between cylinder liner and oil ring> Next, we will explain the friction behavior between a cylinder liner and an oil ring. The change in the friction coefficient during typical sliding is expressed as a Stribeck diagram shown in Figure 7(A). This Stribeck diagram distinguishes between the friction behavior in the solid contact region 110 (direct contact), the friction behavior in the boundary lubrication region 112 (sliding through an oil film), and the friction behavior in the hydrodynamic lubrication region 114 (sliding through a viscous lubricant film). Between the boundary lubrication region 112 and the hydrodynamic lubrication region 114, there exists a friction behavior in the mixed lubrication region 113, where both conditions coexist. In this Stribeck diagram, the horizontal axis represents the logarithmic representation of kinematic viscosity μ × velocity Q / contact load W, and the vertical axis represents the friction coefficient (f). Therefore, the hydrodynamic lubrication region 114 or the mixed lubrication region 113 has the smallest frictional force. Effective utilization of these regions 114 and 113 is effective for reducing friction and, therefore, fuel consumption. On the other hand, if the speed Q increases but the boundary lubrication region 112 cannot transition to the fluid lubrication region 114, the boundary lubrication region 112 continues into the high speed region, as shown by the dotted line.

[0084] Incidentally, most of the friction force in the fluid lubrication region 114 is the shear resistance of the oil, and this shear resistance is defined as (viscosity) x (velocity) x (area) / (oil film thickness). As a result, reducing the shear area directly leads to a reduction in friction force.

[0085] Therefore, in this embodiment, oil is actively directed into the upper solid contact surface 83A and the lower solid contact surface 83B of the oil ring 70 from the upper first inclined surface 84A, the upper second inclined surface 85A, the lower first inclined surface 84B, and the lower second inclined surface 85B formed on both sides thereof, thereby quickly transitioning to the fluid lubrication region 114 and achieving low friction. In addition, as will be described in detail later, by applying so-called dimple liner technology to the cylinder liner 10, recesses are formed in the stroke center region of the cylinder liner 10, reducing the effective area where shear resistance of the oil occurs, thereby achieving a more efficient reduction in frictional force.

[0086] The Stribeck diagram in Figure 7(A) shows the dynamic change in the friction coefficient (f) during one stroke of the piston 30. Another index for evaluating friction behavior is the friction mean effective pressure (FMEP). This friction mean effective pressure is calculated by dividing the friction work per cycle by the stroke volume. Figure 7(B) shows a diagram of this friction mean effective pressure (FMEP diagram). In the FMEP diagram, the horizontal axis represents the rotational speed (N) and the vertical axis represents the friction mean effective pressure (kPa). As the rotational speed (N) increases, the proportion of the hydrodynamic lubrication region 114 during one stroke increases. On the other hand, as the rotational speed (N) decreases, the proportion of the hydrodynamic lubrication region 114 during one stroke decreases, and the proportion of the mixed lubrication region 113 (or boundary lubrication region 112) increases. Therefore, the shape of the FMEP diagram in FIG. 7(B) is relatively similar to the shapes of the hydrodynamic lubrication region 114 and the mixed lubrication region 113 in the Stribeck diagram in FIG. 7(A).

[0087] <Cylinder liner dimple technology> Next, a cylinder liner 10 suitable for use with the oil ring 70 of this embodiment will be described. As shown in FIG. 8, a plurality of recesses 14 are formed in the inner wall surface 12 of the cylinder liner 10. The recesses 14 are formed in a mid-stroke region 20 of the inner wall surface 12. This mid-stroke region 20 refers to the entire or partial region extending from the bottom surface of the ring groove of the lowest piston ring at top dead center T of the piston 30 to the top surface of the ring groove of the highest piston ring at bottom dead center U of the piston 30 (here, the entire region is the mid-stroke region 20, and the recesses 14 are formed throughout this region is illustrated). If the region outside the mid-stroke region 20 is defined as an outer region 25, this outer region 25 is composed of an upper outer region 25A adjacent to the top dead center side of the mid-stroke region 20 and a lower outer region 25B adjacent to the bottom dead center side of the mid-stroke region 20. As the piston 30 reciprocates within the cylinder liner 10, it repeatedly passes through the upper outer region 25A, the mid-stroke region 20, the lower outer region 25B, the mid-stroke region 20, and the upper outer region 25A in this order. The boundary between the upper outer region 25A and the mid-stroke region 20 is defined as an upper boundary 27A, and the boundary between the lower outer region 25B and the mid-stroke region 20 is defined as a lower boundary 27B.

[0088] Of course, it is possible to form multiple recesses 14 beyond the mid-stroke region 20, but from the perspective of oil consumption (LOC), it is preferable to form recesses 14 limited to within the mid-stroke region 20.

[0089] <Dimples formed on the cylinder liner> The recesses 14 are arranged so that at least one recess 14 exists in any cross section taken in the axis-perpendicular direction on the inner wall surface 12 of the mid-stroke region 20. That is, the recesses 14 are arranged so as to overlap in the axial direction. As a result, the outer circumferential surface of a piston ring passing through the mid-stroke region 20 always faces at least one recess 14. On the other hand, no recesses 14 are formed in the upper outer region 25A and the lower outer region 25B.

[0090] The recesses 14 are shaped like quadrangles (squares or rectangles) that are arranged diagonally relative to the axial direction, resulting in a diagonal grid arrangement of the recesses 14. As shown in the development view of FIG. 9(A), when focusing on a specific recess 14, the axial lowest point 14b of that recess 14 is located axially lower than the axial highest points 14a of the other recesses 14. Because the recesses 14 overlap in the axial direction, a recess 14 can always be present in the cross section perpendicular to the axis at any location (e.g., arrows A, B, and C) in the stroke center region 20. Here, the recesses 14 with the same area are uniformly arranged in the planar directions (axial and circumferential directions) in the stroke center region 20.

[0091] 9(B), multiple recesses 14 having the same area may be arranged non-uniformly in the planar direction. In this example, the area occupied by the multiple recesses 14 is smaller in a circumferential band-like region 20P at the axial end of the stroke mid-region 20, and the area occupied by the multiple recesses 14 is larger in a circumferential band-like region 20Q at the axial center of the stroke mid-region 20.

[0092] The dimensions and shape of the recesses 14 are not particularly limited, but are appropriately selected depending on the dimensions and purpose of the cylinder and piston ring. For example, the recesses 14 can be formed in a slit or strip shape so as to penetrate (or extend) through the stroke mid-region 20 in the axial direction of the cylinder. From the viewpoint of airtightness of the cylinder, it is preferable that the maximum average length D (see FIG. 9(A)) of the recesses 14 in the axial direction of the cylinder be equal to or less than the length (width) of the piston ring (top ring) located at the top of the piston, specifically, approximately 5 to 100% of that length. When there is variation in the maximum axial dimensions of multiple recesses 14, the average length D of the recesses 14 refers to the average value.

[0093] The maximum average length S of the recesses 14 in the cylinder circumferential direction is preferably in the range of 0.1 mm to 15 mm, and more preferably in the range of 0.3 mm to 5 mm. If it is smaller than these ranges, the effect of reducing the sliding area by the recesses 14 themselves may not be sufficiently obtained. On the other hand, if it is larger than these ranges, part of the piston ring may easily get into the recess, which may cause problems such as deformation of the piston ring.

[0094] As shown in FIG. 10, the maximum average length R (maximum average depth R) of the recesses 14 in the cylinder diameter direction is preferably in the range of 0.1 μm to 1000 μm, more preferably in the range of 0.1 μm to 500 μm. It is more preferably set to 0.1 μm to 50 μm. If the maximum average length R of the recesses 14 in the cylinder diameter direction is smaller than this range, the effect of reducing the sliding area of ​​the recesses 14 themselves may not be sufficiently obtained. On the other hand, if it is attempted to be larger than this range, processing becomes difficult and problems such as the need to increase the cylinder wall thickness may arise. Note that, for ease of explanation, the recesses 14 in FIG. 10 are drawn with the cylinder diameter direction greatly exaggerated relative to the cylinder circumferential direction.

[0095] Returning to Figure 9, the average value of the minimum distance Hc in the cylinder circumferential direction between circumferentially adjacent recesses 14 at the same axial position is preferably in the range of 0.05 mm to 15 mm, and particularly preferably in the range of 0.1 mm to 5.0 mm. If it is smaller than these ranges, the contact area (sliding area) between the piston ring and the cylinder liner may be too small to allow stable sliding. On the other hand, if it is larger than these ranges, the effect of reducing the sliding area of ​​the recesses 14 itself may not be sufficiently obtained.

[0096] The average value of the minimum distance Ha in the cylinder axial direction between axially adjacent recesses 14 at the same circumferential position is preferably in the range of 0.05 mm to 15 mm, and particularly preferably in the range of 0.1 mm to 5.0 mm. If it is smaller than these ranges, the contact area (sliding area) between the piston ring and the cylinder liner may be too small to allow stable sliding. On the other hand, if it is larger than these ranges, the effect of reducing the sliding area of ​​the recesses 14 itself may not be sufficiently obtained.

[0097] Furthermore, regardless of the direction, the average value of the minimum distance Hm between adjacent recesses 14 is preferably in the range of 0.001 mm to 15 mm, and particularly preferably in the range of 0.001 mm to 5.0 mm. If it is greater than these ranges, the effect of reducing the sliding area of ​​the recesses 14 itself may not be sufficiently obtained.

[0098] In other words, these intervals Hc, Ha, and Hm are synonymous with the minimum width in each direction of the inner wall surface 12 remaining between adjacent recesses 14.

[0099] In this embodiment, the average value of the distance Ha in the cylinder axial direction is preferably set in the range of 0.05 mm to 15 mm, and more preferably in the range of 0.1 mm to 5.0 mm. When widening the range of the fluid lubrication region 114 of the piston ring 40 sliding in the cylinder axial direction shown in Fig. 7(A) relative to the recess 14 and the inner wall surface 12 around it, by ensuring the distance Ha of the inner wall surface 12 in the cylinder axial direction, it is possible to suppress local fluctuations in the surface pressure acting on the piston ring 40. [Example]

[0100] The ring body 72 of the two-piece oil ring 70 of this embodiment was manufactured using two different manufacturing conditions for buffing the PVD coating 92, and the circumferential surface texture parameters of the upper first inclined surface 84A, the upper second inclined surface 85A, the lower first inclined surface 84B, and the lower second inclined surface 85B were measured. The oil ring 70 manufactured under the first manufacturing conditions is referred to as Example 1, and the oil ring 70 manufactured under the second manufacturing conditions is referred to as Example 2. An oil ring in which the PVD coating 92 was not buffed at all is referred to as a Comparative Example.

[0101] In the first manufacturing conditions for the first example, a soft buff 100 was used, with alumina (Al2O3) abrasive grains and a flap-type structure in which the polishing material was fixed radially around the rotating shaft. The buffing process was completed by moving the buff 100 back and forth in the axial direction, with the axial feed speed kept constant. The rotation speed of both the buff 100 and the ring body 72 was set to 300 rpm, and the rotation direction was reversed on the outward and return passes. The pressing force of the buff 100 against the ring body 72 was set to a level that increased the current supplied to the motor and applied a certain load compared to when the buff 100 was not in contact with the ring body 72.

[0102] Under the second manufacturing conditions for the second example, a buff 100 with a hardness and a standard structure in which the abrasive material is spirally wound around the rotating shaft and silicon carbide (SiC) abrasive grains was used. The buffing process was completed by moving the buff 100 back and forth in the axial direction, and the axial feed speed was the same as that of the first manufacturing conditions. The rotation speed of both the buff 100 and the ring body 72 was 300 rpm, and the rotation direction on the forward and return passes was reversed. The pressing force of the buff 100 against the ring body 72 was set to a level that increased the current supplied to the motor and applied a certain load compared to when the buff 100 was not in contact.

[0103] For all of the first and second examples and the comparative example, the lapping conditions involved using a honing sleeve with a spiral groove on its inner surface, and grinding or polishing by moving it back and forth in the up and down axial direction a predetermined number of times while interposing abrasive grains.

[0104] (Measurement of circumferential surface texture parameters) Circumferential surface texture parameters were measured for the first example, the second example, and the comparative example. Measurements were performed three times for each inclined surface. The upper and lower limit values ​​and average values ​​of the 12 measurement results for the upper first inclined surface 84A, the upper second inclined surface 85A, the lower first inclined surface 84B, and the lower second inclined surface 85B are shown in Figs. 11 to 13.

[0105] 11(A), the arithmetic mean roughness Ra was measured to be 0.14 μm or less for Examples 1 and 2. Specifically, the average value for Example 1 was 0.10 μm, and the average value for Example 2 was 0.06 μm. On the other hand, the average value for the comparative example was 0.23 μm.

[0106] 11(B), the measured values ​​of the maximum height Rz were 1.16 μm or less for Examples 1 and 2. Specifically, the average value for Example 1 was 0.95 μm, and the average value for Example 2 was 0.68 μm. On the other hand, the average value for the comparative example was 1.62 μm.

[0107] 11(C), the ten-point average roughness RzJIS measured values ​​were 0.92 μm or less for Examples 1 and 2. Specifically, the average value for Example 1 was 0.78 μm, and the average value for Example 2 was 0.54 μm. On the other hand, the average value for the comparative example was 1.29 μm.

[0108] 12(A), the measured values ​​of the protruding peak height Rpk were 0.10 μm or less for Examples 1 and 2. Specifically, the average value for Example 1 was 0.09 μm, and the average value for Example 2 was 0.06 μm. On the other hand, the average value for the comparative example was 0.24 μm.

[0109] 12(B), the core level difference Rk was measured to be 0.40 μm or less for Examples 1 and 2. Specifically, the average value for Example 1 was 0.32 μm, and the average value for Example 2 was 0.17 μm. On the other hand, the average value for the comparative example was 0.57 μm.

[0110] 13(A), the load length ratio Rmr measured when a height reduction of 0.3 μm was caused starting from the 0.5% position was 41.7% or more for Examples 1 and 2. Specifically, the average value for Example 1 was 60.4%, and the average value for Example 2 was 95.2%. On the other hand, the average value for the comparative example was 12.2%.

[0111] 13(B), the load length ratio Rmr measured when a height reduction of 0.4 μm was caused starting from the 0.5% position was 67.6% or more for Examples 1 and 2. Specifically, the average value for Example 1 was 81.6%, and the average value for Example 2 was 99.0%. On the other hand, the average value for the comparative example was 21.6%.

[0112] 13(C), the load length ratio Rmr measured when a height reduction of 0.5 μm was caused starting from the 0.5% position was 84.8% or more for Examples 1 and 2. Specifically, the average value for Example 1 was 92.5%, and the average value for Example 2 was 99.7%. On the other hand, the average value for the comparative example was 33.8%.

[0113] (3D imaging of surface texture) Next, three-dimensional images were taken of the surface texture of the ring body 72 for the first example, the second example, and the comparative example. A confocal microscope OPTELICS HYBRID C3 (100x objective lens) manufactured by Lasertec Corporation was used as the imaging device.

[0114] Figures 14(A) to (D) show the three-dimensional imaging results of the first embodiment, where (A) shows the upper first inclined surface 84A and upper actual contact surface 83A of the ring body 72, (B) shows the upper second inclined surface 85A and upper actual contact surface 83A of the ring body 72, (C) shows the lower second inclined surface 85B and lower actual contact surface 83B of the ring body 72, and (D) shows the lower first inclined surface 84B and lower actual contact surface 83B.

[0115] Circumferential hairlines are formed on all of the upper first inclined surface 84A, the upper second inclined surface 85A, the lower second inclined surface 85B, and the lower first inclined surface 84B, making them smooth in the circumferential direction. As a result, the boundary between the upper contact surface 83A and the upper first inclined surface 84A, the boundary between the upper contact surface 83A and the upper second inclined surface 85A, the boundary between the lower contact surface 83B and the lower second inclined surface 85B, and the boundary between the lower contact surface 83B and the lower first inclined surface 84B are also linear. This allows oil to easily penetrate into the contact surface from each inclined surface, resulting in a structure that makes it easy to maintain an oil film.

[0116] Figures 15(A) to (D) show the three-dimensional imaging results of the second embodiment, where (A) shows the upper first inclined surface 84A and upper actual contact surface 83A of the ring body 72, (B) shows the upper second inclined surface 85A and upper actual contact surface 83A of the ring body 72, (C) shows the lower second inclined surface 85B and lower actual contact surface 83B of the ring body 72, and (D) shows the lower first inclined surface 84B and lower actual contact surface 83B.

[0117] Circumferential hairlines are formed on all of the upper first inclined surface 84A, the upper second inclined surface 85A, the lower second inclined surface 85B, and the lower first inclined surface 84B, making them smooth in the circumferential direction. As a result, the boundary between the upper contact surface 83A and the upper first inclined surface 84A, the boundary between the upper contact surface 83A and the upper second inclined surface 85A, the boundary between the lower contact surface 83B and the lower second inclined surface 85B, and the boundary between the lower contact surface 83B and the lower first inclined surface 84B are also linear. This allows oil to easily penetrate into the contact surface from each inclined surface, resulting in a structure that makes it easy to maintain an oil film.

[0118] Figures 16(A) to (D) show the three-dimensional imaging results of the comparative example, where (A) shows the upper first inclined surface 84A and upper actual contact surface 83A of the ring body 72, (B) shows the upper second inclined surface 85A and upper actual contact surface 83A of the ring body 72, (C) shows the lower second inclined surface 85B and lower actual contact surface 83B of the ring body 72, and (D) shows the lower first inclined surface 84B and lower actual contact surface 83B.

[0119] Physical vapor deposition is a technique for forming a film by evaporating metals or compounds and depositing them on the oil ring. This results in random fine irregularities on the surfaces of the upper first inclined surface 84A, the upper second inclined surface 85A, the lower second inclined surface 85B, and the lower first inclined surface 84B. This results in a less smooth surface compared to the first and second embodiments. As a result, the boundary between the upper contact surface 83A and the upper first inclined surface 84A, the boundary between the upper contact surface 83A and the upper second inclined surface 85A, the boundary between the lower contact surface 83B and the lower second inclined surface 85B, and the boundary between the lower contact surface 83B and the lower first inclined surface 84B have a random sawtooth pattern. This results in a structure in which the oil film is easily destroyed when oil penetrates the contact surfaces from each inclined surface.

[0120] (FMEP diagram) Next, Fig. 17 shows the results of measuring FMEP using an oil ring 70 employing the oil body 72 of the second embodiment, and the results of measuring FMEP using an oil ring using the oil body of the comparative example. During the measurements, a tension of 22.6 N was applied to the oil ring 70 by the coil expander 76C (the actual contact surface pressure was 1.75 MPa). The cylinder liner 10 used was one employing the dimple liner technology shown in Fig. 10.

[0121] 17, when the oil ring 70 of the second embodiment is used, the FMEP is reduced by about 1 kPa to 2 kPa on average compared to the comparative example. In particular, since the value is reduced even in the low rotation speed range, it is estimated that the mixed lubrication region 113 (or boundary lubrication region 112) is wider on the low rotation speed side, and the lubrication state is such that the oil film is less likely to be destroyed than in the comparative example.

[0122] As described above, according to the oil ring 70 of this embodiment, the upper first inclined surface 84A, the upper second inclined surface 85A, the lower first inclined surface 84B, and the lower second inclined surface 85B, which are formed by the PVD coating 92, are buffed in the circumferential direction to smooth their surfaces. This reduces frictional resistance when sliding against the cylinder liner 10. Furthermore, these inclined surfaces make it difficult for the oil film to be destroyed, which also reduces shear resistance of the oil film.

[0123] Furthermore, in this embodiment, the PVD coating 92 is buffed in the circumferential direction and then partially lapped in the axial direction to form the upper contact surface 83A and the lower contact surface 83B. As a result, the boundaries between the upper first inclined surface 84A, the upper second inclined surface 85A, the lower first inclined surface 84B, and the lower second inclined surface 85B and the upper contact surface 83A and the lower contact surface 83B extend linearly in the circumferential direction. Improved linearity of these boundaries reduces frictional resistance during sliding contact with the cylinder liner 10.

[0124] In this embodiment, a chromium nitride alloy coating is used as an example of the coating formed by physical vapor deposition, but the present invention is not limited to this and can be applied to other physical vapor deposition coatings such as hard carbon coatings. Furthermore, while this oil ring is preferably applied to diesel engines, it can also be applied to gasoline engines that employ cylinder bores. Furthermore, the present invention is not limited to this and can be applied to other internal combustion engines.

[0125] The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0126] 10 Cylinder liner 12 Inner wall surface 30 pistons 40 Piston rings 50 Top Ring 60 Second Ring 70 Oil Ring 73a, 73b Side rails 76C Coil Expander 76s Spacer Expander 81 Single outer surface 8 1 A Upper outer peripheral surface 8 1 B Lower side outer circumferential surface 82 Outer surface 83A Upper contact surface 83B Lower contact surface 84A Upper first slope 84B Lower first slope 85A Upper second slope 85B Lower second slope 90 Base material 92 PVD coating 92A outer surface of coating 92B Circumferential wear surface 100 buffs 120 Grinding Tools

Claims

1. A multi-piece oil ring is installed on a piston of an internal combustion engine and includes a ring body having a rail, and an expander that applies tension to the ring body, a coating formed by physical vapor deposition processing is formed on the rail of the ring body; The outer circumferential surface of the rail formed by the coating is a contact surface formed in a band shape extending in a circumferential direction and contacting and sliding on an inner wall surface of a cylinder of the internal combustion engine; an inclined surface that continues from the axial edge of the actual contact surface to the axially outward side, and the distance from the inner wall surface increases as the inclined surface moves toward the axially outward side, the inclined surface is formed by polishing or grinding the surface of the coating along a circumferential direction, The actual contact surface is formed by polishing or grinding the surface of the coating along the axial direction. Oil ring.

2. When a position on the inclined surface where the inclination angle with respect to the axial direction is 7° is defined as an evaluation position, a protruding peak height Rpk obtained by measuring the evaluation position along the circumferential direction is 0.15 μm or less.

2. The oil ring according to claim 1.

3. When a position on the inclined surface where the inclination angle with respect to the axial direction is 7° is defined as an evaluation position, the load length ratio Rmr obtained by measuring the evaluation position along the circumferential direction when causing a height reduction of 0.3 μm starting from a 0.5% position is 35% or more.

2. The oil ring according to claim 1.

4. A multi-piece oil ring is installed on a piston of an internal combustion engine and includes a ring body having a rail, and an expander that applies tension to the ring body, a coating formed by physical vapor deposition processing is formed on the rail of the ring body; The outer circumferential surface of the rail formed by the coating is a contact surface formed in a band shape extending in a circumferential direction and contacting and sliding on an inner wall surface of a cylinder of the internal combustion engine; an inclined surface that continues from the axial edge of the actual contact surface to the axially outward side, and the distance from the inner wall surface increases as the inclined surface moves toward the axially outward side, the inclined surface is configured by polishing or grinding the surface of the coating along a circumferential direction, and the inclined surface has a hairline extending in a circumferential direction formed by the polishing or grinding, The contact surface has a hairline extending in the axial direction formed by polishing or grinding. Oil ring.

5. The coating is a chromium nitride alloy coating or a hard carbon coating.

5. The oil ring according to claim 1 or 4.

6. A method for manufacturing a multi-piece oil ring that is installed on a piston of an internal combustion engine and has a ring body having a rail, and an expander that applies tension to the ring body, comprising: forming a coating on the rails of the ring body by a physical vapor deposition process; a step of polishing or grinding the outer peripheral surface of the rail formed by the coating in a circumferential direction to form a circumferential wear surface on the surface of the coating; and a step of polishing or grinding a portion of the circumferential wear surface along the axial direction to form an actual contact surface on the surface of the coating that contacts and slides against an inner wall surface of a cylinder of the internal combustion engine, The circumferential wear surface is left on the axially outer side from the axial edge of the actual contact surface, so that the circumferential wear surface is an inclined surface whose distance from the inner wall surface increases as it goes axially outward. Manufacturing method of oil ring.

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