Oil ring and method for manufacturing oil ring

Abstract

An oil ring is a multi-piece oil ring which is provided in a piston of an internal combustion engine and which is provided with a ring body having a track and a spiral expander. A coating film formed by physical vapor deposition is formed on the track of the ring main body. The outer peripheral surface of the rail formed by the film has: an actual contact surface which is formed in a belt shape extending in the circumferential direction and slides in contact with the inner wall surface of the cylinder of the internal combustion engine; and an inclined surface which is continuous from the edge of the actual contact surface in the axial direction toward the outer side in the axial direction, and the distance between the inclined surface and the inner wall surface increases toward the outer side in the axial direction. The inclined surface is formed by grinding or grinding the surface of the coating film in the circumferential direction. Therefore, the sliding resistance of the oil ring is reduced, and the fuel efficiency is further improved.

Description

Technical Field

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

[0002] Reducing the friction between the piston ring and the cylinder liner is effective for reducing the fuel consumption of the engine. In recent years, the oil ring, which is one type of piston ring, has been subjected to nitriding treatment, chromium nitride coating based on PVD treatment to become a low friction coefficient material, DLC coating, etc. to achieve friction reduction.

[0003] In addition, by forming the outer peripheral surface of the oil ring in a step land shape and reducing the actual contact width between the sliding surface of the protruding end and the cylinder liner, sufficient contact surface pressure can be ensured even with a small tension. In this case, since the surface pressure of the sliding surface becomes high, the wear resistance is deteriorated by nitriding alone, and PVD treatment is sometimes used to obtain a high hardness film (see Japanese Patent No. 5871277). Summary of the invention

[0004] Technical issues Although this was an unknown topic at the time of this application, it was clear that if a high-hardness film is formed on the sliding surface of the oil ring by physical vapor deposition, a friction reduction effect can be achieved, but there is still room for further improvement. In view of the above actual situation, the present invention aims to provide an oil ring that can further reduce the sliding resistance of the oil ring and achieve improved fuel efficiency.

[0005] Technical Solution The present invention for achieving the above-mentioned purpose is an oil ring, characterized in that it is a multi-piece oil ring, which is arranged on the piston of an internal combustion engine and has a ring body with a track, and a spiral expander that applies tension to the ring body, and a film formed by physical vapor deposition treatment is formed on the track of the ring body, and the outer peripheral surface of the track formed by the film has: an actual contact surface, which is formed in a band shape extending in the circumferential direction and abuts and slides against the inner wall surface of the cylinder of the internal combustion engine; and an inclined surface, which is continuous from the axial edge of the actual contact surface to the axial outside, and the distance between the inclined surface and the inner wall surface increases as it goes to the axial outside, and the inclined surface is composed of a surface of the surface of the film that is ground or grinded along the circumferential direction.

[0006] The present invention related to the above oil ring may be characterized in that the actual contact surface is constituted by a surface of the film that is ground or polished in the axial direction.

[0007] The present invention related to the above-mentioned oil ring may be characterized in that, when a position on the inclined surface where the inclination angle with respect to the axial direction becomes 7° is defined as an evaluation position, a protrusion peak height Rpk measured along the circumferential direction at the evaluation position is 0.15 μm or less.

[0008] The present invention related to the above-mentioned oil ring may also be characterized in that, when a position in the inclined surface where the inclination angle based on the axial direction becomes 7° is defined as an evaluation position, a load length ratio Rmr obtained by measuring the evaluation position along the circumferential direction when a 0.3 μm height reduction is generated with the 0.5% position as the starting point is greater than 35%.

[0009] The present invention related to the above oil ring may be characterized in that the inclined surface has a thin line extending in the circumferential direction formed by the grinding or lapping.

[0010] The present invention related to the above-mentioned oil ring may also be characterized in that the actual contact surface has a fine line extending in the axial direction formed by grinding or lapping.

[0011] The present invention related to the above oil ring may be characterized in that the film is a chromium nitride alloy film or a hard carbon film.

[0012] The present invention for achieving the above-mentioned purpose provides a method for manufacturing an oil ring, characterized in that it is a method for manufacturing a multi-piece oil ring, wherein the oil ring is arranged on a piston of an internal combustion engine and comprises a ring body having a track, and a spiral expander for applying tension to the ring body, the method for manufacturing the oil ring comprising: a step of forming a film on the track of the ring body by physical vapor deposition treatment; a step of forming a circumferential wear surface on the surface of the film by grinding or grinding the outer peripheral surface of the track formed by the film in the circumferential direction; and a step of forming an actual contact surface on the surface of the film that abuts and slides against the inner wall surface of the cylinder of the internal combustion engine by grinding or grinding a part of the circumferential wear surface in the axial direction, wherein the circumferential wear surface is left from the axial edge of the actual contact surface to the axially outer side, thereby making the circumferential wear surface an inclined surface whose distance from the inner wall surface increases as it goes toward the axially outer side.

[0013] Technical Effects According to the present invention, it is possible to achieve excellent effects such as further reducing the sliding resistance of the oil ring and improving fuel efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 (A) 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, Figure 1 (B) is a partially enlarged cross-sectional view showing the piston and the piston ring. Figure 1 (C) is a partial enlarged cross-sectional view of the top ring. Figure 1 (D) is a partial enlarged cross-sectional view of the second ring.

[0015] Figure 2 It is a cross-sectional view of a two-piece oil ring according to the present embodiment.

[0016] Figure 3 It is an axial cross-sectional view showing the vicinity of the outer peripheral surface of the oil ring in an enlarged manner.

[0017] Figure 4 (A) is an axial cross-sectional view showing in enlargement the vicinity of the outer peripheral surface of the oil ring after the physical vapor deposition process in the manufacturing process of the oil ring. Figure 4 (B) is a partial cross-sectional view showing the method of polishing the oil ring. Figure 4 (C) is an enlarged perspective view showing the vicinity of the outer peripheral surface of the oil ring after the polishing process.

[0018] Figure 5 (A) is a partial cross-sectional view showing the method of polishing the oil ring. Figure 5 (B) is an enlarged perspective view showing the vicinity of the outer peripheral surface of the oil ring after the polishing process.

[0019] Figure 6 (A) is a cross-sectional view of a three-piece oil ring which is a modified example of the oil ring of the present embodiment. Figure 6 (B) is an axial cross-sectional view showing the vicinity of the outer peripheral surface of the oil ring in an enlarged manner.

[0020] Figure 7 (A) is a Stribeck curve diagram related to the slip of a general internal combustion engine. Figure 7 (B) is a graph of FMEP related to slip in a general internal combustion engine.

[0021] Figure 8 It is a cross-sectional view along the axial direction of a cylinder liner of an internal combustion engine to which the oil ring is applied.

[0022] Fig. 9 (A) and (B) are development views showing a state where the inner peripheral wall of the cylinder liner is developed in the circumferential direction.

[0023] Fig.10 It is a cross-sectional view of the inner peripheral wall of the cylinder liner in a direction perpendicular to the axis.

[0024] Fig.11 (A) to (C) are graphs showing actual measurement results of surface texture parameters in the circumferential direction of the oil rings according to the first and second embodiments.

[0025] Fig.12(A) and (B) are graphs showing the actual measurement results of the surface texture parameters in the circumferential direction of the oil rings according to the first and second embodiments.

[0026] Fig.13 (A) to (C) are graphs showing actual measurement results of surface texture parameters in the circumferential direction of the oil rings according to the first and second embodiments.

[0027] Fig.14 (A) to (D) are photographic diagrams showing the results of three-dimensionally photographing the surface properties in the circumferential direction of the oil ring of the first embodiment.

[0028] Fig.15 (A) to (D) are photographic diagrams showing the results of three-dimensionally photographing the surface properties in the circumferential direction of the oil ring of the second embodiment.

[0029] Fig.16 (A) to (D) are photographic diagrams showing the results of three-dimensionally photographing the surface properties in the circumferential direction of an oil ring serving as a comparative example.

[0030] Fig.17 It is a FMEP graph of an internal combustion engine obtained by actual measurement using oil rings serving as an example and a comparative example.

[0031] Explanation of symbols 10 Cylinder liner 12 Inner wall surface 30 Piston 40 Piston ring 50 Top ring 60 Second Ring 70 Oil ring 73a, 73b Side rails 76C Spiral Expander 76s Septal Dilator 81 Single peripheral surface 81A Upper outer surface 81B Lower outer surface 82 Outer Surface 83A Actual contact surface on the upper side 83B Actual contact surface on the lower side 84A Upper first inclined surface 84B Lower first inclined surface 85A Upper second inclined surface 85B Lower side second inclined surface 90 base material 92 PVD film 92A membrane outer surface 92B Circumferential wear surface 100 Polishing Wheel 120 Grinding tools DETAILED DESCRIPTION

[0032] Hereinafter, an oil ring and a method for manufacturing the same according to an embodiment of the present invention will be described with reference to the drawings.

[0033] First, a sliding structure of an internal combustion engine including an oil ring according to the present embodiment will be described.

[0034] <Structure of Piston and Piston Ring> exist Figure 1 (A) and Figure 1 In (B), as a part of a gasoline engine, a piston 30 and a piston ring 40 (a top ring 50, a second ring 60, and an oil ring 70) provided in a ring groove of the piston 30 are shown. The piston ring 40 reciprocates along the axial direction of the cylinder 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 and prevents gas leakage (blow-by) of compressed gas from escaping from the combustion chamber to the crankcase side. The second ring 60 has both the function of eliminating the gap between the piston 30 and the cylinder liner 10 in the same way as the top ring 50, and the function of scraping off the excess engine oil attached to the inner wall surface 12 of the cylinder liner 10. It should be noted that the top ring 50 and the second ring 60 are sometimes referred to as compression rings.

[0035] The oil ring 70 forms an appropriate oil film by scraping off excess engine oil adhering to the inner wall surface 12 of the cylinder liner 10 , thereby preventing the piston 30 from being seizure-bonded.

[0036] <Top ring shape> like Figure 1 As shown in the enlarged view of (C), the top ring 50 is a separate annular member, and when the cross section of the outer peripheral surface 52 is observed, it is in the shape of a barrel that is gently convex toward the radial outside and is a so-called gently curved line. Figure 1 In (C), for convenience of explanation, the convex shape of the outer peripheral surface is emphasized by greatly exaggerating the radial dimension relative to the axial dimension.

[0037] 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.

[0038] An actual contact surface 53 is formed on a portion of the outer peripheral surface 52 in the axial direction. The actual contact surface 53 is a band-shaped area extending in the circumferential direction of the outer peripheral surface 52. The actual contact surface 53 refers to a sliding area (sliding surface) that contacts and slides with the inner wall surface 12 of the cylinder liner 10. Furthermore, on the outer peripheral surface 52, an inclined surface 54 and a corner portion 55 are formed on the outer peripheral surface 52 from both edges in the axial direction (band width direction) of the actual contact surface 53 toward the outside. The inclined surface 54 and the corner portion 55 are areas away from the inner wall surface 12 of the cylinder liner 10.

[0039] The actual contact surface width f of the actual contact surface 53 before the running-in operation is preferably set to 0.15 mm or more, more preferably set to 0.3 mm or more, further preferably set to be larger than 0.3 mm, and further preferably set to be 0.4 mm or more.

[0040] In order to actively form the collapsed shape by the running-in operation, 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 case.

[0041] <Shape of the Second Ring> like Figure 1 As shown in the enlarged view of (D), the second ring 60 is a separate annular member, and when the cross section of the outer peripheral surface 62 is observed, it is in a so-called tapered shape. The plane on the front end side of the tapered shape is in a so-called barrel shape that is gently convex toward the radial outside and forms a gentle curve. Figure 1 In (D), for convenience of explanation, the convex shape of the outer peripheral surface is emphasized by greatly exaggerating the radial dimension relative to the axial dimension.

[0042] 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.

[0043] Similar to the top ring 50, an actual contact surface 63 is formed on a portion of the axial direction of the outer peripheral surface 62. The actual contact surface 63 is a band-shaped area extending in the circumferential direction of the outer peripheral surface 62. The actual contact surface 63 refers to a sliding area (sliding surface) that contacts and slides with the inner wall surface 12 of the cylinder liner 10. Furthermore, on the outer peripheral surface 62, an inclined surface 64 and a corner portion 65 are formed from both edges in the axial direction (band width direction) of the actual contact surface 63 toward the outside. The inclined surface 64 and the corner portion 65 are areas away from the inner wall surface 12 of the cylinder liner 10.

[0044] The actual contact surface width f of the actual contact surface 63 before the running-in operation is preferably set to 0.15 mm or more, more preferably set to 0.3 mm or more, further preferably set to be larger than 0.3 mm, and further preferably set to be 0.4 mm or more.

[0045] In order to actively form the collapsed shape by the running-in operation, 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 case.

[0046] <Shape of oil ring> exist Figure 2 The two-piece oil ring 70 of this embodiment is shown in an enlarged manner in FIG. The oil ring 70 includes a ring body 72 and a coil expander (Coil expander) 76C in the form of a coil spring.

[0047] The ring body 72 integrally includes an annular upper rail 73A and a lower rail 73B disposed at both ends in the axial direction, and an annular column 75 disposed between and connecting the upper rail 73A and the lower rail 73B. The cross-sectional shape obtained by combining the pair of upper rails 73A and the lower rail 73B and the column 75 is substantially I-shaped or H-shaped, and an inner circumferential groove 79 having a semicircular arc cross-sectional shape for accommodating the spiral expander 76C is formed on the inner circumferential surface side by utilizing this shape.

[0048] The upper rail 73A and the lower rail 73B are provided with an upper annular protrusion 74A and a lower annular protrusion 74B projecting radially outward with reference to the column 75. The upper annular protrusion 74A and the lower annular protrusion 74B have an upper outer peripheral surface 81A and a lower outer peripheral surface 81B near their projecting ends.

[0049] The spiral expander 76C is accommodated in the inner circumferential groove 79 to press and urge the ring body 72 radially outward. In addition, a plurality of oil return holes 77 are formed in the column portion 75 of the ring body 72 along the circumferential direction.

[0050] like Figure 3As shown in the enlarged view, the upper peripheral surface 81A and the lower peripheral surface 81B are respectively the surfaces of a hard film (hereinafter referred to as a PVD film) 92 formed by physically vapor-depositing the surface of a base material 90. The material of the base material 90 is, for example, 8Cr steel, 10Cr steel, 13CrSUS, etc. In addition, the PVD film 92 can be a chromium nitride alloy film such as Cr-N series, Cr-BN series, Cr-BVN series, Cr-B-Ti-V-(Mn,Mo)-N series, or a hard carbon film (also called a diamond-like carbon film or DLC film). It should be noted that the hydrogen content of the hard carbon film is preferably 10 atomic % or less. The surface hardness of the PVD film 92 is preferably set to 2000 Hv or less, and is set to 1800 Hv here.

[0051] (Description of actual contact surface) An upper side actual contact surface 83A and a lower side actual contact surface 83B that actually abut against the inner wall surface 12 of the cylinder liner 10 are formed on a portion of the upper side outer peripheral surface 81A and the lower side outer peripheral surface 81B. The upper side actual contact surface 83A and the lower side actual contact surface 83B are band-shaped areas extending in the circumferential direction. The upper side actual contact surface 83A and the lower side actual contact surface 83B are flat surfaces (see dotted line V) produced by grinding or polishing along the axial direction (band width direction) to wear away a portion of the surface side of the PVD film 92. Figure 5 As shown in FIG. 8B , thin axial thin lines H1 extending in the axial direction (belt width direction) as grinding marks are formed on the surfaces of the upper side actual contact surface 83A and the lower side actual contact surface 83B.

[0052] The radial thickness t1 of the PVD film 92 at the axial center of the upper actual contact surface 83A and the lower actual contact surface 83B is preferably 5 μm or more, more preferably 10 μm or more. The thickness t1 of the PVD film 92 is preferably 50 μm or less, more preferably 40 μm or less. Here, it is set to 20 μm.

[0053] It should be noted that the upper outer peripheral surface 81A and the lower outer peripheral surface 81B are integrally formed in the ring body 72. As a result, the two outer peripheral surfaces 81A and 81B can also be matched to define a single outer peripheral surface 81 (see Figure 2 ). It should be noted that a gap is formed in the center of the single outer peripheral surface 81.

[0054] return Figure 3, the upper side actual contact surface 83A has a concave step 98 that is recessed in a manner that a portion of the upper side outer peripheral surface 81A is reduced in diameter on the axial column portion 75 side (the lower side). Similarly, the lower side actual contact surface 83B has a concave step 98 that is recessed in a manner that a portion of the lower side outer peripheral surface 81B is reduced in diameter on the axial column portion 75 side (the upper side). With these concave steps 98, the upper side outer peripheral surface 81A and the lower side outer peripheral surface 81B become stepped. Thus, the actual contact widths (belt widths) f1 and f2 of the upper side actual contact surface 83A and the lower side actual contact surface 83B can be set smaller. In other words, the upper side annular protrusion 74A and the lower side annular protrusion 74B become a two-stage protrusion shape, which is called a step shape. The concave step 98 can be formed, for example, by grinding the base material 90, but can also be formed in advance during the drawing process of the wire.

[0055] (Description of the inclined surface) On the upper outer peripheral surface 81A, the two edges in the axial direction (band width direction) of the upper actual contact surface 83A are formed with an upper first inclined surface 84A and an upper second inclined surface 85A. The upper first inclined surface 84A is on the distal side from the spacer expander 76C, and the upper second inclined surface 85A is on the proximal side from the spacer expander 76C. The upper first inclined surface 84A becomes an inclined area in which the distance from the inner wall surface 12 of the cylinder liner 10 increases as it moves away from the upper actual contact surface 83A upward. The upper second inclined surface 85A becomes an inclined area in which the distance from the inner wall surface 12 of the cylinder liner 10 increases as it moves away from the upper actual contact surface 83A downward. The upper first inclined surface 84A and the upper second inclined surface 85A each become a belt-shaped area extending in the circumferential direction.

[0056] In addition, an upper first corner portion 86A is formed on the axially outer side (upper side) of the upper first inclined surface 84A. When the axial cross section is observed, the upper first corner portion 86A is a region where the inclination changes sharply from the upper first inclined surface 84A toward the upper side side of the upper annular protrusion 74A.

[0057] The upper second corner 87A is formed on the axially outer side (lower side) of the upper second inclined surface 85A. When the axial cross section is viewed, the upper second corner 87A is a region where the inclination changes sharply from the upper second inclined surface 85A toward the lower side surface of the upper annular protrusion 74A.

[0058] On the lower outer peripheral surface 81B, a lower first inclined surface 84B and a lower second inclined surface 85B are formed on both edges in the axial direction (band width direction) of the lower actual contact surface 83B. The lower first inclined surface 84B is on the distal side from the spacer expander 76C, and the lower second inclined surface 85B is on the proximal side from the spacer expander 76C. The lower first inclined surface 84B becomes an inclined region in which the distance from the inner wall surface 12 of the cylinder liner 10 increases as it moves away from the lower actual contact surface 83B downward. The lower second inclined surface 85B becomes an inclined region in which the distance from the inner wall surface 12 of the cylinder liner 10 increases as it moves away from the lower actual contact surface 83B upward. The lower first inclined surface 84B and the lower second inclined surface 85B each become a band-shaped region extending in the circumferential direction.

[0059] In addition, a lower first corner portion 86B is formed on the axially outer side (lower side) of the lower first inclined surface 84B. When the axial cross section is observed, the lower first corner portion 86B is a region where the slope of the inclination changes sharply from the lower first inclined surface 84B toward the lower side of the lower annular protrusion 74B.

[0060] A lower second corner portion 87B is formed on the axially outer side (upper side) of the lower second inclined surface 85B. When the axial cross section is viewed, the lower second corner portion 87B is a region where the inclination changes sharply from the lower second inclined surface 85B toward the upper side of the lower annular protrusion 74B.

[0061] like Figure 5 As shown in (B), at least the upper first inclined surface 84A and the lower first inclined surface 84B are polished or ground along the circumferential direction by the polishing process described later. As a result, the upper first inclined surface 84A and the lower first inclined surface 84B are smoothed along the circumferential direction. A thin circumferential fine line H2 extending along the circumferential direction (with long side direction) is formed on the surface of the upper first inclined surface 84A and the lower first inclined surface 84B as a grinding mark.

[0062] It should be noted that in the present 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 polished or ground to be smooth, and fine circumferential fine lines H2 are formed on their surfaces.

[0063] return Figure 1 , the combined radial thickness a of the oil ring 70 11 (Reference Figure 1The combined axial width (nominal width) h1 (see Figure 1 The thickness (radial width) a1 of the upper rail 73A or the lower rail 73B is set to 4.0 mm or less, for example, and preferably 3.0 mm or less. Figure 1 (B) is set to, for example, 4.0 mm or less, preferably 3.0 mm or less. The width (axial width) h of the single body 12 (Reference Figure 1 The diameter (B) is set to, for example, 0.40 mm or less, desirably 0.30 mm or less, and more preferably 0.20 mm or less.

[0064] The upper side actual contact width f1 of the upper side actual contact surface 83A and the lower side actual contact width f2 of the lower side actual contact surface 83B before the running-in operation are preferably formed to be 0.05 mm or more. It is more desirable to form them to be 0.10 mm or more, and it is further desirable to set them to be greater than 0.13 mm. In addition, the upper side actual contact width f1 and the lower side actual contact width f2 are preferably formed to be 0.40 mm or less. It is more desirable to form them to be 0.35 mm or less, and it is further desirable to set them to be less than 0.30 mm.

[0065] In addition, the total actual contact width F obtained by summing the actual contact width f1 on the upper side and the actual contact width f2 on the lower side is preferably formed to be greater than 0.10mm. It is more desirable to form it to be greater than 0.20mm, and it is further desirable to be set to be greater than 0.26mm. The total actual contact width F is preferably formed to be less than 0.80mm. It is more desirable to form it to be less than 0.70mm, and it is further desirable to be set to be less than 0.60mm. Furthermore, the surface pressure acting on the actual contact surface 83A on the upper side and the actual contact surface 83B on the lower side is preferably set to be greater than 0.8MPa, and it is more desirable to be set to be greater than 1.0MPa. Furthermore, the surface pressure is preferably set to be less than 2.5MPa, and it is more desirable to be set to be less than 2.2MPa.

[0066] (Evaluation of Surface Roughness in the Peripheral Direction of the Inclined Surface) In this embodiment, in order to evaluate the surface roughness of the upper first inclined surface 84A and the lower first inclined surface 84B along the circumferential direction, an evaluation position W is defined. Figure 3As shown in the figure, when observing the cross section in the axial direction, the point where the inclination angle θ of the upper first inclined surface 84A and the lower first inclined surface 84B becomes 7° based on the axial direction J of the oil ring 70 is defined as the evaluation position W. The surface property value obtained by measuring the evaluation position W along the circumferential direction using a stylus surface roughness measuring machine (JIS B 0651: 2001) is defined as the "circumferential surface property parameter of the inclined surface". It should be noted that the tip radius of the measuring needle is a standard 2μm, the tip shape is a 60° knife edge shape, and the cutoff wavelength λc for the cross-sectional curve is selected to be 0.8mm for measurement.

[0067] In the present embodiment, the arithmetic mean roughness Ra (JIS B 0601:2013), which is a circumferential surface property parameter, of the upper first inclined surface 84A and the lower first inclined surface 84B is preferably less than 0.18 μm, more preferably 0.10 μm or less.

[0068] In the present embodiment, the maximum height Rz (JIS B 0601:2013), which is a circumferential surface property parameter, of the upper first inclined surface 84A and the lower first inclined surface 84B is preferably less than 1.40 μm, more preferably 1.00 μm or less.

[0069] In the present embodiment, the ten-point average roughness RzJIS (JIS B 0601:2013), which is a peripheral surface property parameter, of the upper first inclined surface 84A and the lower first inclined surface 84B is preferably 1.10 μm or less, more preferably 0.80 μm or less.

[0070] In the present embodiment, in the upper first inclined surface 84A and the lower first inclined surface 84B, the protruding peak height Rpk (JIS B 0671-2: 2002), which is a circumferential surface property parameter, is preferably set to 0.15 μm or less, more preferably 0.10 μm or less.

[0071] In the present embodiment, the center level difference Rk (JIS B 0671-2: 2002), which is a peripheral surface property parameter, of the upper first inclined surface 84A and the lower first inclined surface 84B is preferably 0.50 μm or less, more preferably 0.30 μm or less.

[0072] In the present embodiment, the load length ratio Rmr (JIS B0601:2013) at which a 0.3 μm height reduction occurs starting from the 0.5% position, which is a circumferential surface property parameter, is preferably set to 35% or more, more preferably 75% or more.

[0073] In the present embodiment, the load length ratio Rmr (JIS B0601:2013) at which a 0.4 μm height reduction occurs starting from the 0.5% position, which is a circumferential surface property parameter, is preferably set to 55% or more, more preferably 80% or more.

[0074] In the present embodiment, the load length ratio Rmr (JIS B0601:2013) at which a 0.5 μm height reduction occurs starting from the 0.5% position, which is a circumferential surface property parameter, is preferably set to 70% or more, more preferably 85% or more.

[0075] It should be noted that the radial thickness t2 of the PVD film 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, more preferably 10 μm or more. The thickness t2 of the PVD film 92 is preferably 50 μm or less, more preferably 40 μm or less. Here, it is set to 20 μm.

[0076] (Slight correction based on actual contact surface during running-in) Incidentally, the upper side actual contact surface 83A and the lower side actual contact surface 83B refer to the state when the manufacturing is completed. If the oil ring 70 is installed on the piston 30 and the actual running-in operation is carried out together with the cylinder liner 10, the shape of the upper side actual contact surface 83A and the lower side actual contact surface 83B is slightly modified due to the contact wear. Specifically, the upper side actual contact surface 83A and the lower side actual contact surface 83B are barrel-shaped and slightly tilted from the center of the cylinder axial direction toward both outer sides due to the wear of the running-in operation. These inclinations formed in the upper side actual contact surface 83A and the lower side actual contact surface 83B are called so-called collapsed edge shapes, and their inclinations are extremely small, ranging from 1 / 2000 to 1 / 500. After the running-in operation, the upper side actual contact surface 83A and the lower side actual contact surface 83B are accompanied by slight inclinations and / or deformations, and essentially become sliding areas (sliding surfaces) that contact and slide with the inner wall surface 12 of the cylinder liner 10.

[0077] <Method for Manufacturing Oil Ring Main Body> (Preparation of parent material) Next, a method for manufacturing the ring body 72 of the oil ring 70 of the present embodiment will be described. First, a linear wire having a desired cross-sectional shape is bent into a ring shape by a bending machine (not shown) to produce the base material 90 .

[0078] (Polishing of base material) Next, the outer peripheral surface of the annular base material 90 is polished to grind or grind the outer peripheral surface along the circumferential direction. Thus, the base that becomes the outer peripheral surface of the base material 90 is smoothed. It should be noted that the outer peripheral surface of the base material 90 may also be nitrided.

[0079] (Physical vapor deposition treatment) Then, if Figure 4 As shown in (A), a PVD film 92 is formed on the outer peripheral surface (the future upper peripheral surface 81A and the lower peripheral surface 81B) of the base material 90 by physical vapor deposition, and this time a chromium nitride film is applied. It should be noted that although not particularly shown here, the outer peripheral surface 92A of the PVD film 92 after the physical vapor deposition process is in a state where fine irregularities are randomly formed as a whole. The fine irregularities are caused by the structure of the deposition material deposited by the physical vapor deposition process.

[0080] (Polishing of PVD film) Then, if Figure 4 As shown in (B), the outer peripheral surface 92A (the upper peripheral surface 81A and the lower peripheral surface 81B in the future) of the PVD film 92 is polished. In this embodiment, a plurality of ring bodies 72 are centrally arranged on a rotating tool not particularly shown in the figure, and they are forced to rotate around the central axis E. In addition, the polishing wheel 100, which is a cylindrical grinding tool made of cotton and / or felt, is arranged in parallel with the ring body 72 in a posture in which its own rotation axis Z is parallel to the central axis E of the ring body 72.

[0081] While pressing the outer peripheral surface 100A of the polishing wheel 100 against the outer peripheral surface 92A of the membrane of the ring body 72, the polishing wheel 100 is forced to rotate around the central axis Z. At the same time, the polishing wheel 100 and the ring body 72 are relatively moved along the central axis E and Z directions. It should be noted that by making the ring body 72 and the polishing wheel 100 rotate in the same direction, the outer peripheral surface 100A of the polishing wheel 100 and the outer peripheral surface 92A of the membrane of the ring body 72 at the contact point move in opposite directions, thereby improving the grinding efficiency.

[0082] As a result, if Figure 4 As shown in (C), all or part of the outer peripheral surface 92A of the PVD film 92 (the range that the polishing wheel 100 can contact) is worn due to grinding or grinding. Here, the surface generated by the wear is defined as a circumferential wear surface 92B. A circumferential fine line H2 extending in the circumferential direction is formed on the surface of the circumferential wear surface 92B. Due to the circumferential wear surface 92B, a first inclined surface 84A on the upper side and a second inclined surface 85A on the upper side, a first inclined surface 84B on the lower side and a second inclined surface 85B on the lower side are formed.

[0083] An upper polishing target region 83A' is formed between the upper first inclined surface 84A and the upper second inclined surface 85A. Similarly, a lower polishing target region 83B' is formed between the lower first inclined surface 84B and the lower second inclined surface 85B.

[0084] (Polishing) Then, if Figure 5 As shown in (A), a plurality of ring bodies 72 are collectively arranged on a fixing tool not particularly shown, and then inserted into the inner peripheral grinding surface 120A of a cylindrical grinding tool (grinding disc) 120 so as to slide relative to each other in the axial direction. By making the inner diameter of the inner peripheral grinding surface 120A approximate to that of the ring body 72 and placing predetermined abrasive grains therebetween, the upper side outer peripheral surface 81A and the lower side outer peripheral surface 81B of the ring body 72 are ground or polished. Specifically, the upper side polishing processing target area 83A' and the lower side polishing processing target area 83B' of the circumferential wear surface 92B are worn. If restoration is performed, the circumferential wear surface 92B is left intact on the outer sides of the upper side polishing processing target area 83A' and the lower side polishing processing target area 83B' of the circumferential wear surface 92B.

[0085] As a result, if Figure 5 As shown in (B), the upper actual contact surface 83A and the lower actual contact surface 83B are formed by using the area worn by the grinding process. Axial fine lines H1 that become grinding marks are formed on the upper actual contact surface 83A and the lower actual contact surface 83B.

[0086] <Surface pressure setting of oil ring> Next, the setting of the surface pressure between the oil ring 70 and the cylinder liner 10 is described. Here, the surface pressure of the oil ring 70 refers to the surface pressure acting on the sliding surface constituting 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).

[0087] In the present 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. Furthermore, the surface pressure is preferably set to 2.5 MPa or less, more preferably 2.2 MPa or less.

[0088] <Deformation of Oil Ring> It should be noted that the oil ring 70 of the above embodiment is exemplified as a two-piece type, but the present invention is not limited to this. Figure 6A three-piece oil ring can be used, such as the oil ring 70 shown in (A) in an enlarged manner. The oil ring 70 has annular side rails 73a and 73b separated from each other in the upper and lower parts, and a spacer expander 76s disposed between the side rails 73a and 73b. A pair of side rails 73a and 73b form a set to constitute a ring body.

[0089] The spacer expander 76s is formed by plastic working a steel material into a wave shape that is repeatedly concave and convex in the axial direction of the cylinder. The wave shape forms an upper side support surface 78a and a lower side support surface 78b, and supports a pair of side rails 73a and 73b in the axial direction, respectively. The inner peripheral side end of the spacer expander 76s has an ear portion 74m that is erected and arranged in an arc shape toward the axial outside. The ear portion 74m abuts against the inner peripheral surface of the side rails 73a and 73b. It should be noted that the spacer expander 76s is assembled to the annular groove of the piston 30 in a state where the joint is joined and contracted in the circumferential direction. As a result, the ear portion 74m presses the side rails 73a and 73b radially outward by the restoring force of the spacer expander 76s. If subjected to this force, as shown by the dotted line, the side rails 73a and 73b are inclined to the inside of the axial direction (combined nominal width direction) of the oil ring 70. That is, the pair of outer peripheral surfaces 82 , 82 are brought closer to each other.

[0090] The combined radial thickness a of the oil ring 70 11 For example, it is set to 4.0 mm or less, preferably 3.0 mm or less. The combined axial width (nominal width) h1 is set to 4.0 mm or less, preferably 2.0 mm or less. The thickness (radial width) a1 of the side rails 73a and 73b is set to 4.0 mm or less, preferably 3.0 mm or less. The width (axial width) h1 of the side rails 73a and 73b is set to 4.0 mm or less, preferably 3.0 mm or less. 12 For example, it is set to 1.0 mm or less, desirably 0.5 mm or less, and more preferably 0.4 mm or less.

[0091] like Figure 6 As further enlarged in (B), the outer peripheral surface 82 of each of the side rails 73a and 73b is formed into a barrel shape that is gently convex toward the radial outside, so-called a gently curved barrel shape. It should be noted that for the sake of convenience of explanation, the radial dimension is greatly exaggerated relative to the axial dimension, thereby emphasizing the convex shape of the outer peripheral surface.

[0092] The outer peripheral surface 82 is the surface of a hard film (hereinafter referred to as a PVD film) 92 formed by physically vapor-depositing the base material 90. An actual 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 actual contact surface 83B is a flat surface (see dotted line V) produced by grinding or polishing along the axial direction (belt width direction) to wear away a portion of the surface side of the PVD film 92. The actual contact surface 83 is a belt-shaped area extending in the circumferential direction of the outer peripheral surface 82. A thin axial fine line H1 extending in the axial direction (belt width direction) is formed on the surface of the actual contact surface 83, which becomes a grinding mark.

[0093] Furthermore, the outer peripheral surface 82 has inclined surfaces 84 formed at both edges in the axial direction (band width direction) of the actual contact surface 83. The inclined surface 84 is an inclined region away from the inner wall surface 12 of the cylinder liner 10. The inclined surface 84 is a band-shaped region extending in the circumferential direction.

[0094] Furthermore, a corner portion 86 is formed further outward in the axial direction of each inclined surface 84. When the axial cross section is viewed, the corner portion 86 is a region where the gradient of the inclination changes sharply from the inclined surface 84 toward the side surfaces of the side rails 73a, 73b.

[0095] The inclined surface 84 is a surface formed by grinding or polishing a portion of the surface side of the PVD film 92 along the circumferential direction. As a result, the inclined surface 84 is smoothed along the circumferential direction. A thin circumferential fine line extending along the circumferential direction (belt length direction) is formed on the surface of the inclined surface 84 as a grinding mark.

[0096] The actual contact width f of the actual contact surface 83 before the running-in operation is preferably formed to be 0.05 mm or more. It is more desirable to be formed to be 0.10 mm or more, and it is further desirable to be set to be greater than 0.13 mm. In addition, the actual contact width f is preferably formed to be 0.40 mm or less. It is more desirable to be formed to be 0.35 mm or less, and it is further desirable to be set to be less than 0.30 mm.

[0097] The total actual contact width F obtained by summing the actual contact widths f of the pair of outer peripheral surfaces 82, 82 is preferably formed to be greater than 0.10 mm. It is more desirable to form it to be greater than 0.20 mm, and it is further desirable to set it to be greater than 0.26 mm. The total actual contact width F is preferably formed to be less than 0.80 mm. It is more desirable to form it to be less than 0.70 mm, and it is further desirable to set it to be less than 0.60 mm. Furthermore, the surface pressure acting on the actual contact surface 83 is preferably set to be greater than 0.8 MPa, and it is more desirable to set it to be greater than 1.0 MPa. Furthermore, the surface pressure is preferably set to be less than 2.5 MPa, and it is more desirable to set it to be less than 2.2 MPa.

[0098] <Friction form between cylinder liner and oil ring> Next, the friction between the cylinder liner and the oil ring is described. The change in the friction coefficient during sliding is usually expressed as Figure 7 The Stribeck curve diagram shown in (A). In the Stribeck curve diagram, the friction form of the solid contact area 110 with direct contact sliding, the friction form of the boundary lubrication area 112 with sliding through the oil film, and the friction form of the fluid lubrication area 114 with sliding through the viscous lubricating oil film are distinguished. In addition, between the boundary lubrication area 112 and the fluid lubrication area 114, there is a friction form of the mixed lubrication area 113 where both states exist. It should be noted that the horizontal axis of the Stribeck curve diagram is a graph that logarithmically represents "kinematic viscosity (dynamic viscosity) μ" × "speed Q" / "contact load W", and the vertical axis is the friction coefficient (f). Therefore, the area where the friction force can be minimized is the fluid lubrication area 114 or the mixed lubrication area 113, and the effective use of the areas 114 and 113 is effective for low friction, that is, low oil consumption. On the other hand, when the boundary lubrication region 112 cannot be shifted to the fluid lubrication region 114 even when the speed Q increases, the boundary lubrication region 112 continues as it is to the high speed region as shown by the dotted line.

[0099] Incidentally, the friction force of the fluid lubrication area 114 is mostly the shear resistance of the oil, which is defined by (viscosity) x (speed) x (area) / (oil film thickness). As a result, reducing the shear area directly leads to a reduction in friction force.

[0100] Therefore, in the present embodiment, the oil is actively flowed into 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 of the oil ring 70, thereby rapidly transferring to the fluid lubrication area 114 to achieve low friction. In addition, by applying the so-called dimple liner technology to the cylinder liner 10, a recess is formed in the stroke center area of ​​the cylinder liner 10 to reduce the substantial area of ​​the shear resistance of the oil, thereby more effectively achieving the reduction of friction, which will be described in detail later.

[0101] Figure 7 The Stribeck curve diagram (A) shows the dynamic change of the friction coefficient (f) in one stroke of the piston 30. However, as another indicator for evaluating the friction form, there is the friction loss mean effective pressure (FMEP: Friction Mean Effective Pressure). The friction loss mean effective pressure represents the value obtained by dividing the friction work per cycle by the stroke volume. Figure 7(B) shows a graph of the friction loss mean effective pressure (FMEP graph). In the FMEP graph, the horizontal axis is the rotation speed (N) and the vertical axis is the friction loss mean effective pressure (kPa). The higher the rotation speed (N), the greater the proportion of the fluid lubrication area 114 in one stroke. On the other hand, if the rotation speed (N) becomes lower, the proportion of the fluid lubrication area 114 in one stroke decreases, and the proportion of the mixed lubrication area 113 (or boundary lubrication area 112) increases. Therefore, Figure 7 (B) The shape of the FMEP curve diagram is Figure 7 The shapes of the fluid lubrication region 114 and the mixed lubrication region 113 of the Stribeck curve diagram (A) are relatively similar.

[0102] <Dimple technology for cylinder liners> Next, a cylinder liner 10 which is preferred when the oil ring 70 of this embodiment is combined will be described. Figure 8 As shown in FIG. 1 , a plurality of recesses 14 are formed on the inner wall surface 12 of the cylinder liner 10. The recesses 14 are formed in a stroke center region 20 in the inner wall surface 12. The stroke center region 20 is a region that is the entire or a part of the range from the lower surface position of the ring groove of the piston ring located at the bottom dead center T of the piston 30 to the upper surface position of the ring groove of the piston ring located at the top dead center U of the piston 30 (here, an example is given in which the entire range is the stroke center region 20 and the recesses 14 are formed in the entire region). If the region outside the stroke center region 20 is defined as an outer region 25, the outer region 25 is composed of an upper outer region 25A adjacent to the top dead center side of the stroke center region 20 and a lower outer region 25B adjacent to the bottom dead center side of the stroke center region 20. When the piston 30 reciprocates in the cylinder liner 10, it repeatedly passes through the upper outer region 25A, the stroke center region 20, the lower outer region 25B, the stroke center region 20, and the upper outer region 25A in sequence. It should be noted that the boundary between the upper outer region 25A and the stroke center region 20 is defined as the upper boundary 27A, and the boundary between the lower outer region 25B and the stroke center region 20 is defined as the lower boundary 27B.

[0103] Of course, a plurality of recessed portions 14 may be formed beyond the stroke mid-portion region 20 , but from the viewpoint of fuel economy (LOC), it is preferable to form the recessed portion 14 in a restricted manner within the stroke mid-portion region 20 .

[0104] <Pits formed in the cylinder liner> The recessed portion 14 is arranged so that no matter which part of the cross section in the direction perpendicular to the axis is taken in the inner wall surface 12 of the stroke center region 20, at least one recessed portion 14 exists in the cross section. That is, the recessed portions 14 are arranged so as to overlap each other in the axial direction. As a result, the outer peripheral surface of the piston ring passing through the stroke center region 20 is always opposite to at least one recessed portion 14. On the other hand, the recessed portion 14 is not formed in the upper outer region 25A and the lower outer region 25B.

[0105] The shape of the recessed portion 14 is a square (square or rectangular) arranged obliquely with respect to the axial direction. As a result, the plurality of recessed portions 14 are arranged in an inclined grid shape as a whole. Fig. 9 As shown in the development view of (A), when focusing on a specific concave portion 14, the lowest point 14b of the concave portion 14 in the axial direction is located axially below the highest point 14a of the other concave portions 14 in the axial direction. In this way, since the plurality of concave portions 14 overlap each other in the axial direction, the concave portion 14 can always be present in the cross section in the direction perpendicular to the axis at all positions (for example, arrows A, arrows B, and arrows C) in the stroke center region 20. Here, in the stroke center region 20, the plurality of concave portions 14 having the same area are uniformly arranged in the surface direction (axial and circumferential directions).

[0106] It should be explained, such as Fig. 9 As shown in the development view of (B), multiple recesses 14 of the same area may be unevenly arranged in the plane direction. Here, the area occupied by the multiple recesses 14 in the circumferential band-shaped area 20P at the axial end of the stroke center area 20 becomes smaller, and the area occupied by the multiple recesses 14 in the circumferential band-shaped area 20Q at the axial center of the stroke center area 20 becomes larger.

[0107] The size and / or shape of the recess 14 are not particularly limited, but can be appropriately selected according to the size and / or purpose of the cylinder and / or piston ring. For example, the recess 14 can be formed in a slit or strip shape so as to penetrate (or extend) in the axial direction of the cylinder in the stroke center region 20. On the other hand, from the perspective of the airtightness of the cylinder, it is preferred that the maximum average length D of the recess 14 in the axial direction of the cylinder (see Fig. 9 (A) is set to be less than the cylinder axial length (width) of the piston ring (top ring) located at the top of the piston, specifically, to be 5 to 100% thereof. When there is a deviation in the maximum axial dimensions of the plurality of recesses 14, the average length D of the recesses 14 refers to the average value thereof.

[0108] The maximum average length S of the recess 14 in the cylinder circumferential direction is preferably within the range of 0.1 mm to 15 mm, and desirably within the range of 0.3 mm to 5 mm. If it is smaller than these ranges, the effect of reducing the sliding area brought about by the recess 14 itself may not be fully obtained. On the other hand, if it is larger than these ranges, a part of the piston ring may easily enter the recess, causing defects such as deformation of the piston ring.

[0109] like Fig.10 As shown, the maximum average length R (maximum average depth R) of the recess 14 in the cylinder radial direction is preferably in the range of 0.1μm~1000μm, and desirably in the range of 0.1μm~500μm. It is more desirably set to 0.1μm~50μm. If the maximum average length R of the recess 14 in the cylinder radial direction is smaller than these ranges, the effect of reducing the sliding area brought by the recess 14 itself may not be fully obtained. On the other hand, if it is larger than these ranges, processing becomes difficult, and there may be disadvantages such as the need to thicken the wall thickness of the cylinder. It should be noted that for the sake of convenience, Fig.10 The recessed portion 14 is depicted in a cylinder radial direction greatly exaggerated relative to the circumferential direction of the cylinder.

[0110] return Fig. 9 The average value of the minimum spacing Hc in the cylinder circumferential direction between the concave portions 14 that are at the same position in the axial direction and adjacent in the circumferential direction 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 less than these ranges, the contact area (sliding area) between the piston ring and the cylinder liner may be too small, and stable sliding may not be possible. On the other hand, if it is greater than these ranges, the effect of reducing the sliding area brought by the concave portion 14 itself may not be fully obtained.

[0111] The average value of the minimum interval Ha in the cylinder axial direction between the concave portions 14 that are at the same position in the circumferential direction and adjacent in the axial direction 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 less than these ranges, the contact area (sliding area) between the piston ring and the cylinder liner may be too small, and stable sliding may not be possible. On the other hand, if it is greater than these ranges, the effect of reducing the sliding area brought about by the concave portion 14 itself may not be fully obtained.

[0112] Furthermore, regardless of the direction, the average value of the minimum interval Hm between adjacent recesses 14 is preferably within the range of 0.001 mm to 15 mm, particularly preferably within the range of 0.001 mm to 5.0 mm. If it is larger than these ranges, the effect of reducing the sliding area brought by the recesses 14 themselves may not be fully obtained.

[0113] In other words, these intervals Hc, Ha, and Hm are synonymous with the minimum widths in each direction of the inner wall surface 12 remaining between the adjacent recessed portions 14 .

[0114] It should be noted that in this embodiment, the average value of the interval Ha in the axial direction of the cylinder is preferably set to a range of 0.05 mm to 15 mm, and more preferably set to a range of 0.1 mm to 5.0 mm. Figure 7 In the range of the fluid lubrication region 114 of the piston ring 40 sliding in the cylinder axial direction as shown in (A), by ensuring the interval Ha of the inner wall surface 12 in the cylinder axial direction, the local surface pressure fluctuation acting on the piston ring 40 can be suppressed.

[0115] Example 1 The ring body 72 of the two-piece oil ring 70 of the present embodiment was manufactured under two manufacturing conditions for polishing the PVD film 92, and the circumferential surface property 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 condition was taken as the first example, and the oil ring 70 manufactured under the second manufacturing condition was taken as the second example. In addition, the oil ring that was not polished for the PVD film 92 was taken as a comparative example.

[0116] In the first manufacturing condition of the first embodiment, a polishing wheel 100 with a soft hardness and an airfoil structure with a grinding base radially fixed to the rotation axis is used, using aluminum oxide (Al2O3) as abrasive grains. The polishing process is completed by reciprocating the polishing wheel 100 once in the axial direction, and the axial feed speed is kept constant. The rotation speed of both the polishing wheel 100 and the ring body 72 is set to 300 rpm, and the rotation direction of the outward path and the rotation direction of the return path are reversed. The pressing force of the polishing wheel 100 on the ring body 72 is set to a level that increases the current supplied to the motor compared to the non-contact state and applies a certain load.

[0117] In the second manufacturing condition, which is the second embodiment, a polishing wheel 100 of a common structure and hardness is used, which uses silicon carbide (SiC) as abrasive grains and has a grinding base wound spirally around the rotating shaft. The polishing process is completed by reciprocating the polishing wheel 100 once in the axial direction, and the axial feed speed is the same as that of the first manufacturing condition. The rotation speed of both the polishing wheel 100 and the ring body 72 is set to 300 rpm, and the rotation direction of the outward path and the rotation direction of the return path are reversed. The pressing force of the polishing wheel 100 on the ring body 72 is set to a level that increases the current supplied to the motor compared to the non-contact state and applies a certain load.

[0118] It should be noted that for all the first embodiment, the second embodiment and the comparative example, as the condition for the polishing process, a honing sleeve having a spiral groove on the inner circumference is used, and grinding or polishing is performed by reciprocating a predetermined number of times in the axial direction up and down while abrasive grains are interposed therebetween.

[0119] (Determination of circumferential surface properties parameters) The circumferential surface property parameters were measured for the first embodiment, the second embodiment, and the comparative example. Three measurements were performed on each inclined surface. A total of 12 measurements were performed on 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. Figure 11~Figure 13 The upper limit and lower limit values ​​and the average value are shown in FIG.

[0120] like Fig.11 As shown in (A), the measured value of the arithmetic mean roughness Ra is 0.14 μm or less for Examples 1 and 2. Specifically, the average value of Example 1 is 0.10 μm, and the average value of Example 2 is 0.06 μm. On the other hand, the average value of the comparative example is 0.23 μm.

[0121] like Fig.11 As shown in (B), the measured value of the maximum height Rz is 1.16 μm or less for Examples 1 and 2. Specifically, the average value of Example 1 is 0.95 μm, and the average value of Example 2 is 0.68 μm. On the other hand, the average value of the comparative example is 1.62 μm.

[0122] like Fig.11 As shown in (C), the measured value of the ten-point average roughness RzJIS was 0.92 μm or less for Examples 1 and 2. Specifically, the average value of Example 1 was 0.78 μm, and the average value of Example 2 was 0.54 μm. On the other hand, the average value of the comparative example was 1.29 μm.

[0123] like Fig.12 As shown in (A), the measured value of the protrusion peak height Rpk is 0.10 μm or less for Examples 1 and 2. Specifically, the average value of Example 1 is 0.09 μm, and the average value of Example 2 is 0.06 μm. On the other hand, the average value of the comparative example is 0.24 μm.

[0124] like Fig.12 As shown in (B), the measured value of the center level difference Rk is 0.40 μm or less for Examples 1 and 2. Specifically, the average value of Example 1 is 0.32 μm, and the average value of Example 2 is 0.17 μm. On the other hand, the average value of the comparative example is 0.57 μm.

[0125] like Fig.13As shown in (A), for Examples 1 and 2, the measured value of the load length ratio Rmr when a 0.3 μm height reduction occurs starting from the 0.5% position is 41.7% or more. Specifically, the average value of Example 1 is 60.4%, and the average value of Example 2 is 95.2%. On the other hand, the average value of the comparative example is 12.2%.

[0126] like Fig.13 As shown in (B), for Examples 1 and 2, the measured value of the load length ratio Rmr when a 0.4 μm height reduction occurs starting from the 0.5% position is 67.6% or more. Specifically, the average value of Example 1 is 81.6%, and the average value of Example 2 is 99.0%. On the other hand, the average value of the comparative example is 21.6%.

[0127] like Fig.13 As shown in (C), for Examples 1 and 2, the measured value of the load length ratio Rmr when a 0.5 μm height reduction occurs starting from the 0.5% position is 84.8% or more. Specifically, the average value of Example 1 is 92.5%, and the average value of Example 2 is 99.7%. On the other hand, the average value of the comparative example is 33.8%.

[0128] (3D photography of surface texture) Next, for the first embodiment, the second embodiment, and the comparative example, the surface properties of the ring body 72 were three-dimensionally photographed. A confocal microscope OPTELICS HYBRID C3 (objective lens 100 times) manufactured by Lasertec was used as the photographing device.

[0129] Fig.14 (A) to (D) are the three-dimensional shooting results of the first embodiment. Fig.14 (A) is the upper first inclined surface 84A and the upper actual contact surface 83A of the ring body 72, Fig.14 (B) is the upper second inclined surface 85A and the upper actual contact surface 83A of the ring body 72. Fig.14 (C) is the lower second inclined surface 85B and the lower actual contact surface 83B of the ring body 72, Fig.14 (D) represents the lower first inclined surface 84B and the lower actual contact surface 83B.

[0130] A circumferential fine line is formed in all 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, and becomes smooth along the circumferential direction. As a result, the boundary between the upper actual contact surface 83A and the upper first inclined surface 84A, the boundary between the upper actual contact surface 83A and the upper second inclined surface 85A, the boundary between the lower actual contact surface 83B and the lower second inclined surface 85B, and the boundary between the lower actual contact surface 83B and the lower first inclined surface 84B also become straight lines. Thus, the oil easily intrudes from each inclined surface to the actual contact surface, and the structure is easy to maintain the oil film.

[0131] Fig.15 (A) to (D) are the three-dimensional shooting results of the second embodiment. Fig.15 (A) is the upper first inclined surface 84A and the upper actual contact surface 83A of the ring body 72, Fig.15 (B) is the upper second inclined surface 85A and the upper actual contact surface 83A of the ring body 72. Fig.15 (C) is the lower second inclined surface 85B and the lower actual contact surface 83B of the ring body 72, Fig.15 (D) represents the lower first inclined surface 84B and the lower actual contact surface 83B.

[0132] A circumferential fine line is formed in all 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, and becomes smooth along the circumferential direction. As a result, the boundary between the upper actual contact surface 83A and the upper first inclined surface 84A, the boundary between the upper actual contact surface 83A and the upper second inclined surface 85A, the boundary between the lower actual contact surface 83B and the lower second inclined surface 85B, and the boundary between the lower actual contact surface 83B and the lower first inclined surface 84B also become straight lines. Thus, the oil easily intrudes from each inclined surface to the actual contact surface, and the structure is easy to maintain the oil film.

[0133] Fig.16 (A) to (D) are the 3D imaging results of the comparative example. Fig.16 (A) is the upper first inclined surface 84A and the upper actual contact surface 83A of the ring body 72, Fig.16 (B) is the upper second inclined surface 85A and the upper actual contact surface 83A of the ring body 72. Fig.16 (C) is the lower second inclined surface 85B and the lower actual contact surface 83B of the ring body 72, Fig.16 (D) represents the lower first inclined surface 84B and the lower actual contact surface 83B.

[0134] Since the physical vapor deposition process is a method of evaporating metal and / or compounds and depositing them on the oil ring to form a film, random fine concave-convex surfaces are formed on all 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. As a result, the smoothness is poor compared with the first embodiment and the second embodiment. As a result, the boundary between the upper actual contact surface 83A and the upper first inclined surface 84A, the boundary between the upper actual contact surface 83A and the upper second inclined surface 85A, the boundary between the lower actual contact surface 83B and the lower second inclined surface 85B, and the boundary between the lower actual contact surface 83B and the lower first inclined surface 84B become random sawtooth shapes. As a result, the oil film is easily destroyed when the oil invades the actual contact surface from each inclined surface.

[0135] (FMEP curve chart) Then, in Fig.17 The results of measuring FMEP using the oil ring 70 using the oil body 72 of the second embodiment and the results of measuring FMEP using the oil ring using the oil body of the comparative example are shown in FIG. 1 . It should be noted that during the measurement, a tension of 22.6 N was applied to the oil ring 70 using the spiral expander 76C (the surface pressure of the actual contact surface was set to 1.75 MPa). Fig.10 Cylinder liner with dimple liner technology shown.

[0136] according to Fig.17 It is known that, if 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 band, the mixed lubrication region 113 (or the boundary lubrication region 112) expands toward the low rotation speed side, and it is estimated that the oil film is in a lubrication state that is more difficult to be broken than in the comparative example.

[0137] As described above, according to the oil ring 70 of the present 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 formed by the PVD film 92 are polished along the circumferential direction, and the surfaces thereof are smoothed. As a result, the friction resistance is reduced when sliding relative to the cylinder liner 10. In addition, the oil film is not easily broken by these inclined surfaces, so the shear resistance of the oil film is also reduced.

[0138] Furthermore, in the present embodiment, after the PVD film 92 is polished in the circumferential direction, a part of it is grinded in the axial direction, thereby forming the upper side actual contact surface 83A and the lower side actual contact surface 83B. As a result, the boundary between the upper side first inclined surface 84A and the upper side actual contact surface 83A, the boundary between the upper side second inclined surface 85A and the upper side actual contact surface 83A, the boundary between the lower side first inclined surface 84B and the lower side actual contact surface 83B, and the boundary between the lower side second inclined surface 85B and the lower side actual contact surface 83B extend in a straight line in the circumferential direction. By improving the linear accuracy of the boundary, the friction resistance is reduced when sliding relative to the cylinder liner 10.

[0139] It should be noted that in this embodiment, a chromium nitride alloy film is exemplified as a film formed by physical vapor deposition, but the present invention is not limited to this and can be applied to other physical vapor deposition films such as hard carbon films. In addition, the present oil ring is preferably applied to a diesel engine, but can also be applied to a gasoline engine using a cylinder bore. Furthermore, the present invention is not limited to this and can also be applied to other internal combustion engines.

[0140] It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit and scope of the present invention.

Claims

1. An oil ring, characterized in that: The invention relates to a multi-piece oil ring, which is provided on a piston of an internal combustion engine and comprises a ring body having a track and a spiral expander for applying tension to the ring body. A film formed by physical vapor deposition is formed on the track of the ring body. The outer peripheral surface of the track formed by the film has: an actual contact surface formed in a band shape extending in the circumferential direction and abutting and sliding against an inner wall surface of a cylinder of the internal combustion engine; as well as an inclined surface which is continuous from an axial edge of the actual contact surface toward the axial outer side, and the distance between the inclined surface and the inner wall surface increases toward the axial outer side, The inclined surface is formed by grinding or polishing the surface of the film along the circumferential direction.

2. The oil ring according to claim 1, characterized in that: The actual contact surface is formed by grinding or lapping the surface of the film in the axial direction.

3. The oil ring according to claim 2, characterized in that: When a position in the inclined surface where the inclination angle with respect to the axial direction is 7° is defined as an evaluation position, a protrusion peak height Rpk measured along the circumferential direction at the evaluation position is 0.15 μm or less.

4. The oil ring according to claim 2, characterized in that: When a position where the inclined surface has an inclination angle of 7° based on the axial direction is defined as an evaluation position, a load length ratio Rmr when a height reduction of 0.3 μm occurs starting from a 0.5% position measured along the circumferential direction at the evaluation position is 35% or more.

5. The oil ring according to claim 1, characterized in that: The inclined surface has a thin line extending in the circumferential direction formed by the grinding or the lapping.

6. The oil ring according to claim 5, characterized in that: The actual contact surface has a thin line extending in the axial direction formed by grinding or lapping.

7. The oil ring according to claim 1, characterized in that: The film is a chromium nitride alloy film or a hard carbon film.

8. A method for manufacturing an oil ring, characterized in that: The invention relates to a method for manufacturing a multi-piece oil ring, wherein the oil ring is provided on a piston of an internal combustion engine and comprises a ring body having a track and a spiral expander for applying tension to the ring body. The manufacturing method of the oil ring comprises: a step of forming a film on the track of the ring body by physical vapor deposition; a step of grinding or lapping the outer peripheral surface of the track formed by the film in the circumferential direction to form a circumferential wear surface on the surface of the film; and A process of grinding or lapping a portion of the circumferential wear surface in the axial direction to form an actual contact surface on the surface of the film that abuts and slides against an inner wall surface of a cylinder of the internal combustion engine, The circumferential wear surface is left from the axial edge of the actual contact surface to the axially outer side, so that the circumferential wear surface becomes an inclined surface in which the distance between the circumferential wear surface and the inner wall surface increases toward the axially outer side.

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