JP2020041573A - Piston ring and method of manufacturing piston ring - Google Patents

Abstract

An object of the present invention is to provide a piston ring capable of suppressing abrasion of a sliding partner material even if the outer peripheral surface has an uneven structure.
The piston ring is a piston ring in which a concave / convex structure having grooves and land portions extending in a predetermined direction alternately formed on an outer peripheral surface, wherein the outer peripheral surface has a central axis of the piston ring. In a contour shape having a cross section including: an outermost diameter portion having the largest outer diameter dimension, the uneven structure is not formed at the outermost diameter portion.
[Selection diagram] FIG. 3B

Description

  The present invention relates to a piston ring and a method for manufacturing the piston ring.

  As a sliding member used in an internal combustion engine, there is a piston ring. The piston ring is mounted in a ring groove provided along the circumferential direction on the outer periphery of a piston made of metal or the like. The outer peripheral surface of the piston ring slides against the cylinder inner wall when the piston reciprocates in the axial direction. Therefore, sliding resistance occurs between the outer peripheral surface of the piston ring and the inner wall of the cylinder.

  Therefore, in order to reduce the sliding resistance between the outer peripheral surface of the piston ring and the inner wall of the cylinder, a piston ring in which an uneven structure capable of holding lubricating oil is formed on the outer peripheral surface has been developed (for example, Patent Document 1). 1-3).

JP-A-5-340473 JP 2016-200246 A Japanese Patent No. 5620794

  According to the piston rings described in Patent Literatures 1 to 3, the lubricating oil is held in the uneven structure formed on the outer peripheral surface, so that the sliding resistance between the lubricating oil and a mating member such as a cylinder is formed. Can be reduced. However, repetition of sliding of the concavo-convex structure formed on the sliding surface with respect to the mating material further wears the mating material. In particular, in the piston ring, the inner wall of the cylinder may be worn. When the inner wall of the cylinder is worn, the inner diameter of the cylinder increases, so that the diameter of the piston ring increases and the gap at the abutment may increase. When the gap at the abutment of the piston ring becomes large, there is a problem that the sealing function is reduced, and an increase in the amount of blow-by gas or an increase in oil consumption occurs.

  An object of the present invention is to solve such a problem, and an object of the present invention is to provide a piston ring capable of suppressing wear of a mating material even if the outer peripheral surface has an uneven structure, and An object of the present invention is to provide a method for manufacturing a piston ring.

  The piston ring of the present invention is a piston ring in which a concave-convex structure having grooves and land portions extending in a predetermined direction alternately formed on an outer peripheral surface, wherein the outer peripheral surface defines a central axis of the piston ring. In the contour shape including the cross section, an outermost diameter portion having a maximum outer diameter is provided, and the uneven structure is not formed on the outermost diameter portion.

  According to the present invention, in the above-described configuration, the outer peripheral surface is formed of the outermost diameter portion and the vicinity thereof, in which the uneven structure is not formed, in which the uneven structure is not formed, and the upper or lower side of the uneven structure non-formed region. And a concavo-convex structure forming region in which the concavo-convex structure is formed adjacent to at least one of the side surfaces.

  According to the present invention, in the above structure, preferably, the uneven structure forming region is provided only on the lower surface side of the uneven structure non-forming region.

  The present invention, in the above configuration, the contour shape of the cross-section of the outer peripheral surface has a shape such that the outer diameter gradually decreases as going from the outermost diameter portion toward the upper surface side or the lower surface side, It is preferable that the region where the uneven structure is not formed is at least 0.5 μm or more from the outermost diameter portion to the region where the outer peripheral surface is located radially inward.

  According to the present invention, in the above configuration, it is preferable that the groove structure and the land portion are periodically formed in the outer peripheral surface in the circumferential direction.

  In the present invention, in the above-described configuration, it is preferable that a repeating unit in which the groove portions and the land portions are formed alternately has a size of 100 μm or less.

  According to the present invention, in the above structure, it is preferable that a height difference from a deepest portion of the groove portion of the concavo-convex structure to the land portion is 0.01 μm or more and 100 μm or less.

  According to the present invention, in the above structure, a fine uneven structure having a height difference smaller than a height difference from a deepest portion of the groove portion of the uneven structure to the land portion is formed on at least one surface of the groove portion and the land portion. It is preferred that

  According to the present invention, in the above configuration, it is preferable that the groove portion and the land portion extend along a central axis direction.

  In the present invention, in the above configuration, at least a part of the uneven structure is formed in a part of the outer peripheral surface at a position not exceeding 100 μm radially inward from the outermost diameter portion. Is preferred.

  The present invention, in the above configuration, the outer peripheral surface, the inclined portion inclined so as to approach radially inward as going from the outermost diameter portion toward the upper surface side or the lower surface side, with respect to the outermost diameter portion It is preferable to provide on both sides in the central axis direction.

  The present invention, in the above configuration, the outer peripheral surface, the inclined portion inclined so as to approach radially inward as going from the outermost diameter portion toward the upper surface side or the lower surface side, with respect to the outermost diameter portion It is preferable to provide only one side in the central axis direction.

  Preferably, in the above configuration, the outermost diameter portion is located in a region not including the center of the outer peripheral surface in the central axis direction.

  According to the present invention, in the above configuration, the outer peripheral surface is connected to the barrel-shaped portion including the outermost diameter portion and the barrel-shaped portion at one end in a central axis direction, and is 17 ° or more to the central axis direction. And a tapered portion inclined at an angle of not more than °.

  According to the present invention, in the above configuration, it is preferable that the outer peripheral surface is formed of a hard coating.

  The method for manufacturing a piston ring according to the present invention includes a step of forming a hard coating on an outer peripheral surface of the piston ring, and a step of forming an outer peripheral surface after the hard coating is formed in a contour shape including a cross section including a central axis of the piston ring. Forming a concavo-convex structure at a position other than the outermost diameter portion having the largest outer diameter.

  ADVANTAGE OF THE INVENTION According to this invention, even if it has an uneven | corrugated structure on an outer peripheral surface, the piston ring which can suppress abrasion of a partner material, and a manufacturing method of a piston ring can be provided.

It is the top view of the piston ring seen from the upper surface side as one embodiment of the present invention. FIG. 2 is a cross-sectional view showing the piston ring of FIG. 1 mounted on a piston and inserted into a cylinder. FIG. 3 is an overall sectional view of a section including a central axis in a state where the piston ring of FIG. 2 is housed in a bore of a cylinder. It is sectional drawing which expands and shows a part of FIG. 3A. It is a side view which shows the outer peripheral surface containing the uneven | corrugated structure of the piston ring of FIG. FIG. 4B is a side view showing the outer peripheral surface of the piston ring of FIG. 1 in a case where the uneven structure has a different arrangement from the uneven structure shown in FIG. 4A. FIG. 4B is a side view showing the outer peripheral surface of the piston ring of FIG. 1 in a case where the uneven structure shown in FIG. 4A and the uneven structure shown in FIG. 4B are included. FIG. 2 is an enlarged perspective view showing an uneven structure formed on an outer peripheral surface of the piston ring of FIG. 1. It is sectional drawing which shows the uneven structure shown in FIG. It is sectional drawing which shows the 1st modification of the uneven structure shown in FIG. It is sectional drawing which shows the 2nd modification of the uneven structure shown in FIG. It is sectional drawing which shows the 3rd modification of the uneven structure shown in FIG. FIG. 4 is a cross-sectional view illustrating a first modification of the piston ring of FIG. 1. FIG. 9 is a cross-sectional view illustrating a second modification of the piston ring of FIG. 1. It is a side view which shows the outer peripheral surface of the piston ring of FIG. FIG. 8 is a cross-sectional view illustrating a third modification of the piston ring of FIG. 1. FIG. 13 is a cross-sectional view illustrating a fourth modification of the piston ring of FIG. 1. It is sectional drawing which expands and shows the land part of the piston ring of FIG. It is a flowchart which shows some processes of the manufacturing method of the piston ring as one Embodiment of this invention. FIG. 4 is a diagram for explaining a test method of Example 1. FIG. 13 is a partial cross-sectional view of a single reciprocating motion tester used in a third embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same reference numerals are given to the common components in each drawing.

[Configuration of piston ring]
FIG. 1 is a plan view of a piston ring 1 as viewed from the upper side surface 80 as one embodiment of the present invention. FIG. 2 is a cross-sectional view showing the piston ring 1 inserted into the bore of the cylinder 200 with the piston 100 being inserted into the piston ring groove 101 of the piston 100 inserted into the bore of the cylinder 200 for an internal combustion engine. is there. Specifically, FIG. 2 is a diagram illustrating a contour shape of the piston ring 1 in a cross section including the central axis O (see FIG. 1) of the piston ring 1.

  Hereinafter, when the piston ring 1 is viewed from the upper surface 80 side, when the curve drawn by the outer peripheral surface of the piston ring 1 is approximated by a circle, the center of the circle is set to the central axis of the piston ring 1 and “O”. The circumferential direction is “A”, the central axis direction along the central axis O is “B”, and the radial direction of the piston ring 1 is “C”. The radial direction C is a direction orthogonal to the central axis direction B. In the central axis direction B, the side (upper side in FIG. 2) where the combustion chamber is located relative to the piston ring 1 is defined as the combustion chamber side (upper side 80 side) D, and the side where the crankcase is located relative to the piston ring 1 ( The lower side in FIG. 2 is referred to as a crankcase side (lower side 90 side) E. The inner side in the radial direction C when viewed from the outer peripheral surface 10 of the piston ring 1 described later is referred to as a radially inner side F, and the opposite direction is referred to as a radially outer side G. 2 shows a partial cross section of the piston 100. The piston 100 is provided with a piston ring groove other than the piston ring groove 101 shown in FIG. The piston ring grooves other than the piston ring groove 101 are on the opposite side of the piston ring groove 101 from the side where the space on the combustion chamber side D surrounded by the bore of the cylinder 200 and the top surface of the piston 100 is located, It is provided on the crankcase side E. A piston ring of another form is also mounted in the piston ring groove.

  As shown in FIGS. 1 and 2, the piston ring 1 includes an outer peripheral surface 10, an inner peripheral surface 70 located radially inward F from the outer peripheral surface 10, an upper side surface 80 of the combustion chamber side D, and a crankcase side. E lower surface 90. The upper side surface 80 of the present embodiment is a surface on the combustion chamber side D located between the outer peripheral surface 10 and the inner peripheral surface 70 when mounted on the piston 100. Further, the lower side surface 90 of the present embodiment is a surface on the crankcase side E located between the outer peripheral surface 10 and the inner peripheral surface 70 when mounted on the piston 100. As shown in FIG. 1, an abutment 6 is formed in the piston ring 1. As shown in FIG. 2, the outer peripheral surface 10 of the piston ring 1 of the present embodiment is formed in a convex curved surface (barrel face) shape. The inner peripheral surface 70 of the piston ring 1 is formed in a cylindrical shape substantially parallel to the central axis direction B. The upper surface 80 and the lower surface 90 of the piston ring 1 are each formed in a flat surface shape substantially parallel to the radial direction C.

  The piston 100 shown in FIG. 2 reciprocates repeatedly in the cylinder 200 along the central axis direction B toward the combustion chamber D and the crankcase E during operation of the internal combustion engine. The piston ring 1 follows the piston 100 and reciprocates repeatedly along the central axis direction B while sliding within the cylinder 200 against the inner wall of the cylinder 200. When the piston ring 1 slides on the inner wall of the cylinder 200, it slides on a part of the outer peripheral surface 10 including an outermost diameter portion 11 (see FIG. 3B and the like) described later.

  The base material of the piston ring 1 according to the present embodiment may be any of a cast iron material, a steel material, and a resin material. The resin material is polytetrafluoroethylene (PTFE), polyether ether ketone (PEEK), polyphenylene sulfide (PPS), polyimide (PI), polyamide imide (PAI), polybenzimidazole (PBI), polyamide (PA), poly At least one resin component selected from the group consisting of ether ketone (PEK), polyether ketone ether ketone ketone (PEKEKK), and liquid crystal polymer (LCP), and selected from the group consisting of glass fiber, synthetic fiber, and carbon fiber It is preferable that the resin composition contains at least one kind of fiber. The steel is preferably steel selected from, for example, spring steel such as SUP, silicon chrome steel SWOSC-V, carbon steel, low alloy steel, bearing steel, and martensitic stainless steel. The carbon steel is preferably high carbon steel having a carbon content of about 0.6 to 0.8 mass%, the spring steel is preferably SUP9, SUP10, SUP12, and the like, and the bearing steel is SUJ2. Preferably, the martensitic stainless steel is SUS420J2 or SUS440B.

  FIGS. 3A and 3B show a state in which the abutment 6 of the piston ring 1 of the present embodiment shown in FIGS. 1 and 2 is narrowed down to the nominal diameter of the piston ring 1 in the bore of the cylinder 200. It is a figure showing a state. Specifically, FIG. 3A is an overall cross-sectional view including a cross section including the center axis O of the piston ring 1. FIG. 3B is a cross-sectional view showing a part of FIG. 3A in an enlarged manner.

  As shown in FIG. 3A, the outer peripheral surface 10 has a contour shape of a cross section including the central axis O of the piston ring 1 and includes an outermost diameter portion 11 in which the outer diameter D1 of the piston ring 1 is maximum. In FIG. 3A, the outer diameter D1 of the piston ring 1 at the outermost diameter portion 11 is shown as the outer diameter D1max. Here, in the present specification, the “outer diameter D1 of the piston ring 1” means the diameter of the outer peripheral surface 10 of the piston ring 1 at each position in the central axis direction B. In addition, in the present specification, the “outermost diameter portion 11 of the piston ring 1” is a region of the outer peripheral surface 10 corresponding to a position in the central axis direction B where the outer diameter D1 of the piston ring 1 is maximum. In the present embodiment, the outermost diameter portion 11 is the same as the position of the outer peripheral surface 10 at which the dimension in the thickness direction (radial direction C) from the inner peripheral surface 70 to the outer peripheral surface 10 of the piston ring 1 is maximum. Has become. The outer diameter D1 is smaller than the outermost diameter portion 11 at the position of the outer peripheral surface when the outer peripheral surface 10 moves along the central axis direction B from the outermost diameter portion 11. That is, the cross-sectional shape of the outer peripheral surface 10 has a shape such that the outer diameter D <b> 1 decreases gradually from the outermost diameter portion 11 toward the upper surface D or the lower surface E.

  FIG. 4A is a side view showing the outer peripheral surface 10 including the uneven structure 30 of the piston ring 1 of the present embodiment. As shown in FIGS. 3B and 4A, the outermost diameter portion 11 of the piston ring 1 of the present embodiment is located at the center of the outer peripheral surface 10 in the central axis direction B (in other words, in the width dimension of the piston ring, from one side surface). (Corresponding to half the width). Further, the outermost diameter portion 11 of the piston ring 1 of the present embodiment exists at each position in the circumferential direction A of the piston ring 1 so as to be continuous in the circumferential direction A. However, the outermost diameter portion 11 of the piston ring 1 may have a cylindrical surface substantially parallel to the central axis direction B, or may have an upper surface side D and a lower surface from the center of the outer peripheral surface 10 in the central axis direction B. The side E may have a predetermined width. The outermost diameter portion 11 of the piston ring 1 in such a case is constituted by an annular band.

  As shown in FIG. 3B, the outer peripheral surface 10 of the piston ring 1 of the present embodiment has a cross-sectional shape including the central axis O of the piston ring 1. Alternatively, the inclined portion 12 having the inclined surface such that the position of the outer peripheral surface 10 in the radial direction C approaches the radially inner side F than the outermost diameter portion 11 toward the lower side surface 90), and the upper and lower sides of the outermost diameter portion 11 In preparation. As shown in FIG. 3B, the outer peripheral surface 10 of the piston ring 1 is entirely in the contour shape of the cross section including the central axis O of the piston ring 1 in the direction in which the cylinder 200 is located (radially outward G in the radial direction C). ) Is constituted by a barrel-shaped portion 14 having a convex curved surface shape. That is, the barrel-shaped part 14 includes the outermost diameter part 11 and the inclined part 12. In the cross section including the central axis O like the barrel-shaped part 14, the inclined part 12 is not limited to the shape whose contour is formed by a curve, but is the shape whose contour is formed in a straight line. You may.

  As shown in FIGS. 3B and 4A, an uneven structure 30 is formed on the outer peripheral surface 10 of the piston ring 1. As shown in FIG. 4, the concavo-convex structure 30 has a groove 31 and a land 41, and each has a shape extending in a predetermined direction. Further, it is preferable that the groove portions 31 and the land portions 41 are formed on the outer peripheral surface 10 alternately in the circumferential direction A periodically. Thereby, the function of the concavo-convex structure 30 described later can be exerted uniformly in the circumferential direction A. Details of the groove 31 and the land 41 will be described later.

  The concavo-convex structure 30 is not formed at least on the outermost diameter part 11, as shown in FIG. 3B. In particular, the outermost diameter portion 11 is a place where the piston 100 is most easily slid with the bore of the cylinder 200 due to the vertical movement. Since the concavo-convex structure 30 is not formed at this location, the aggressiveness of the bore of the cylinder 200 can be reduced, and the increase in the gap size of the joint 6 of the piston ring 1 due to the wear of the bore of the cylinder 200 can be suppressed.

  In the piston ring 1 according to the present embodiment, as shown in FIG. 3B, the uneven structure 30 has an outer peripheral surface region (hereinafter, referred to as a region within a first distance L1 from the outermost diameter portion 11 toward the radially inner side F). , "The outermost diameter portion 11 and its vicinity" are also not formed. As shown in FIG. 3B, a band-shaped region including the outermost diameter portion and the vicinity thereof and continuing in the circumferential direction A of the piston ring 1 on the outer peripheral surface 10 of the piston ring 1, where the uneven structure 30 is not formed. Is referred to as an uneven structure non-forming region S. The first distance L1 in the radial direction C from the position of the outermost diameter to the position of the radially innermost F in the uneven structure non-forming region S is preferably 0.5 μm or more, and more preferably 1 μm or more. Is more preferably 3 μm or more, further preferably 10 μm or more. Note that the first distance L1 is smaller than a second distance L2 described later. As described above, since the concavo-convex structure 30 is not formed in the outermost diameter portion 11 and the vicinity thereof, there is an opportunity for the concavo-convex structure 30 to slide against the inner wall of the cylinder 200 which is a sliding partner of the piston ring 1. It can be further suppressed. Thereby, the diameter expansion of the piston ring 1 due to the expansion of the inner diameter of the cylinder 200 can be suppressed, and the reduction of the sealing function due to the expansion of the gap between the joints 6 of the piston ring 1 can be more reliably suppressed.

  In the present embodiment, as shown in FIG. 3B, the end of the concave-convex structure 30 closest to the outermost diameter portion 11 (that is, the end of the concave-convex structure 30 on the radially outer side G) is, as shown in FIG. It is located on the upper surface side D or the lower surface side E, and is formed in a region of the outer peripheral surface within a second distance L2 from the outermost diameter portion 11 toward the radially inner side F. In addition, as shown in FIG. 3B, in the present embodiment, an end portion on the radially outer side G of the uneven structure 30 is formed on the lower side surface E. The second distance L2 is preferably equal to or less than 100 μm, and more preferably equal to or less than 50 μm. As shown in FIG. 3B, the end of the concavo-convex structure 30 on the radially outer side G was located at a point of 0.5 μm from the outermost diameter part 11 toward the radially inner side F. Here, an oil film made of lubricating oil such as engine oil is formed in the bore of the cylinder 200, and the film thickness of the oil film is about 50 μm or more and about 100 μm or less. Therefore, the end of the radially outer side G of the concavo-convex structure 30 is within the second distance L2 from the outermost diameter portion 11 to the upper surface side D or the lower surface side E, and from the outermost diameter portion 11 to the radially inner side F. If the oil film is formed in the area of the oil film near the surface of the oil film formed in the bore of the cylinder 200, a part of the uneven structure 30 is immersed. Thereby, oil can be efficiently supplied to the groove 31 of the uneven structure 30.

  Further, the lubricating oil flowing into and held in the groove portion 31 of the uneven structure 30 is subjected to inertia or capillary action due to reciprocating movement of the piston ring 1 along the central axis direction B, thereby preventing the outermost diameter portion 11 and the uneven structure near the outermost portion 11. It is supplied to the formation region S. Therefore, the lubricating state between the piston ring 1 and the bore of the cylinder 200 is maintained in a good state, so that the sliding resistance of the piston ring 1 can be reduced. Further, since the end of the concave-convex structure 30 on the radially outer side G (the non-concavo-convex structure non-forming region S side) can always be in contact with the oil film, the oil film dams the combustion gas entering the groove 31 of the concave-convex structure 30. The effect occurs. Therefore, the state in which the combustion gas leaks along the groove 31 of the uneven structure 30 can be reduced, and the improvement of the sealing performance between the piston ring 1 and the cylinder bore can be expected.

  Further, in the piston ring 1 of the present embodiment, the extending direction of the groove portion 31 and the land portion 41 included in the uneven structure 30 is set so as to be substantially equal to the central axis direction B of the piston ring 1. According to such a configuration, the lubricating oil held in the groove portion 31 of the uneven structure 30 is easily discharged to the uneven structure non-formation region S by the reciprocating motion along the central axis direction B of the piston ring 1. In the piston ring 1 of the present embodiment, the uneven structure 30 is formed adjacent to the lower surface side E of the uneven structure non-formed area S. A region where the uneven structure 30 is formed adjacent to at least one of the upper surface side D and the lower surface side E of the uneven structure non-formed region S in this way is referred to as an uneven structure forming region P.

  As shown in FIGS. 3B and 4A, the uneven structure 30 of the present embodiment is formed only on one side in the central axis direction B with respect to the outermost diameter portion 11. Specifically, the piston ring 1 of the present embodiment is a top ring in which the uneven structure 30 is formed only on the crankcase side E in the center axis direction B with respect to the outermost diameter portion 11. If the concavo-convex structure 30 is formed on the combustion chamber side D in the central axis direction B with respect to the outermost diameter portion 11, the lubricating oil held in the concavo-convex structure 30 becomes oil droplets due to inertia at the top dead center. There is a possibility of scattering to the combustion chamber side D. In the piston ring 1 of the present embodiment, since the uneven structure 30 is not formed on the combustion chamber side D in the central axis direction B with respect to the outermost diameter portion 11, the lubricating oil scatters as oil droplets on the combustion chamber side D. Is suppressed. Therefore, an increase in consumption of lubricating oil can be suppressed.

  When the piston ring 1 is used as a top ring, the piston ring 1 is mounted near the end of the piston 100 on the combustion chamber side D. When the piston 100 (see FIG. 2) reciprocates along the central axis direction B with respect to the cylinder 200 (see FIG. 2), the piston 100 has a piston ring groove during the upward stroke (particularly, the exhaust stroke). The lower surface 90 or the upper surface 80 of the piston ring 1 does not completely contact the lower surface or the upper surface of the piston ring 101 (see FIG. 2). May move. Therefore, when the piston 100 slides on the cylinder 200 while being inclined with respect to the cylinder 200, the outer peripheral surface 10 of the piston ring 1 is positioned on the crankcase side E in the center axis direction B with respect to the outermost diameter portion 11. The combustion chamber side D more easily hits the inner wall of the cylinder 200 than the combustion chamber side D. Therefore, in the piston ring 1 of the present embodiment, since the uneven structure 30 is formed only on the crankcase side E in the central axis direction B with respect to the outermost diameter portion 11, the uneven structure 30 is hardly worn, It is easy to exhibit functions over a wide range.

  The direction in which the groove portion 31 and the land portion 41 extend is not limited to the central axis direction B as described above, and may extend in a direction between the central axis direction B and the circumferential direction A. However, as shown in FIG. 4A, if the groove portion 31 extends along the central axis direction B, the lubricating oil accumulated in the groove portion 31 is more easily supplied to the outermost diameter portion 11 and the vicinity thereof. preferable.

  On the other hand, FIG. 4B is a side view showing the outer peripheral surface 10 of the piston ring 1 having the uneven structure 30 ′ extending in a direction different from the uneven structure 30 shown in FIG. 4A. As shown in FIG. 4B, the extending direction of the groove portion 31 or the land portion 41 included in the uneven structure 30 ′ may be set to have an angle with respect to the central axis direction B of the piston ring 1. It is preferable that the angle formed by the extending direction of the groove portion 31 or the land portion 41 with respect to the central axis direction B is 45 ° or less, since lubricating oil is easily supplied to the outermost diameter portion 11 and its vicinity.

  FIG. 4C is a side view showing the outer peripheral surface 10 of the piston ring 1 in the case of including the uneven structure 30 and the uneven structure 30 ″ arranged differently from the uneven structure 30 ′. As shown in FIG. 4C, the groove 31 of the uneven structure 30 ″ does not necessarily have to communicate with the upper surface 80 (see FIG. 3B) or the lower surface 90 (see FIG. 3B) of the piston ring 1. Even in this case, since the oil has the function of retaining the oil in the groove 31, the accumulated oil can be supplied to the outermost diameter portion 11 by the reciprocating motion of the piston 100. However, as shown in FIGS. 4A and 4B, if the groove 31 communicates with the upper surface 80 or the lower surface 90, the wear powder is easily discharged from the groove 31, and the life of the piston ring 1 is easily extended.

  Further, as shown in FIG. 4C, the groove 31 may be interrupted in the extending direction in the uneven structure forming region P. However, as shown in FIGS. 4A and 4B, if the groove 31 is not interrupted in the middle of the extending direction, the lubricating oil held in the groove 31 can easily move along the extending direction of the groove 31. This is preferable because it is easily supplied to the outermost diameter portion 11 and its vicinity.

  Further, as shown in FIG. 4C, the extending direction of the plurality of grooves 31 in the uneven structure forming region P does not necessarily have to be the same in all the grooves 31. In the example illustrated in FIG. 4C, the extending direction of the groove 31 changes with the boundary line X1, the boundary line X2, the boundary line X3, and the boundary line X4 as boundaries.

  Further, as shown in FIG. 8 described later, the uneven structure forming region P in which the uneven structure 30 is formed is located on both the combustion chamber side D and the crankcase side E in the central axis direction B with respect to the outermost diameter portion 11. It may be formed. However, when the piston ring 1 is used as a top ring, it is preferable that the piston ring 1 is formed only on the crankcase side E from the viewpoint of obtaining the above-described effects.

  If the uneven structure 30 is formed on the combustion chamber side D in the central axis direction B with respect to the uneven structure non-forming region S including the outermost diameter portion 11 and its vicinity, the piston 100 (see FIG. 2) When the cylinder rises with respect to the cylinder 200 (see FIG. 2), it is easy to supply the lubricating oil to the outermost diameter portion 11 and its vicinity. Therefore, in an internal combustion engine in which increase in consumption of lubricating oil is unlikely to become a problem, such as a ship or a generator, a piston ring in which the uneven structure 30 is formed on the combustion chamber side D in the central axis direction B with respect to the outermost diameter portion 11. It may be preferable to use as a top ring.

  FIG. 5 is an enlarged perspective view showing the concavo-convex structure 30 formed on the outer peripheral surface 10 of the piston ring 1. FIG. 6 is a sectional view showing the concavo-convex structure 30. As shown in FIG. 5 and FIG. 6, in the concavo-convex structure 30 of the present embodiment, the groove portions 31 and the land portions 41 extending in the predetermined direction are formed alternately in the width direction of the groove portion 31, and the periodicity is improved. It has a concavo-convex structure. 4A, when the piston ring 1 is attached to the piston 100, the sliding direction of the piston ring 1 to the cylinder 200 and the extending direction of the groove 31 are substantially the same. It is formed so as to be parallel. The groove 31 is formed by, for example, laser processing. The plurality of groove portions 31 are formed apart from each other in the width direction of the groove portion 31. Therefore, the land portion 41 is formed between two adjacent groove portions 31. In the uneven structure 30 of the present embodiment, since the groove portions 31 and the land portions 41 extending in the central axis direction B are formed alternately in the circumferential direction A, as described above, the central axis direction of the piston ring 1 is changed. The lubricating oil flows into the groove 31 by the reciprocating movement along B, and the lubricating oil is supplied to the outermost diameter portion 11 and its vicinity through the groove 31 by the inertia force and the capillary phenomenon caused by the reciprocating movement of the piston ring 1. easy. As a result, the lubricating oil stored in the concave-convex structure 30 is easily supplied to the outermost diameter portion 11 and its vicinity by the movement of the piston. Therefore, even if a low-viscosity oil or the like is used as the lubricating oil, the lubricating state is maintained well. It becomes possible. In particular, when the piston ring 1 is used as a top ring, the sliding resistance particularly near the top dead center is reduced.

  The repeating unit I in which the groove portions 31 and the land portions 41 are alternately formed in the width direction is preferably 100 μm or less, and more preferably 10 μm or less. Further, the height difference between the groove 31 and the land 41 as the height difference J of the uneven structure 30 is preferably 0.01 μm or more and 100 μm or less, more preferably 0.05 μm or more and 10 μm or less. When the repeating unit I or the height difference J is within the above range, the lubricating oil is easily held by the groove portion 31 and the capillary phenomenon is more likely to occur. The width of the groove 31 is preferably larger than the width of the land 41. As the width of the groove 31 is wider, lubricating oil is more easily supplied to the outermost diameter portion 11 and the vicinity thereof, and as the width of the land portion 41 is smaller, seizure is less likely to occur.

  The groove portions 31 and the land portions 41 are preferably formed alternately over the entire circumference including the abutment end adjacent to the abutment 6 in the circumferential direction A of the outer peripheral surface 10. With such a configuration, the above-described effect of forming the groove portion 31 and the land portion 41 can be obtained over the entire circumference of the outer peripheral surface 10 in the circumferential direction A. Needless to say, the above-described effects can be obtained even if the groove 31 and the land 41 are not necessarily formed in the circumferential direction A up to the abutment end.

  7A to 7C are cross-sectional views showing a modification of the concavo-convex structure 30. FIG. Specifically, FIG. 7A is a cross-sectional view illustrating a concavo-convex structure 30a as a first modified example of the concavo-convex structure 30. FIG. 7B is a cross-sectional view showing a concavo-convex structure 30b as a second modified example of the concavo-convex structure 30. FIG. 7C is a cross-sectional view illustrating a concavo-convex structure 30c as a third modification of the concavo-convex structure 30.

  In the example shown in FIGS. 7A to 7C, at least one surface of the groove portion 31 and the land portion 41 has a height difference K smaller than the height difference J of the uneven structure 30 shown in FIG. 6 and the uneven structure 30 shown in FIG. And a fine uneven structure 50 having a repeating unit smaller than the repeating unit I. The fine concave-convex structure 50 includes a fine concave portion 51 and a fine convex portion 61. Specifically, in the concavo-convex structure 30a shown in FIG. 7A, the fine concavo-convex structure 50 is formed on the bottom surface as the surface of the groove 31. In the concavo-convex structure 30b shown in FIG. 7B, a fine concavo-convex structure 50 is formed on the surface of the land portion 41. In the concavo-convex structure 30c shown in FIG. 7C, the fine concavo-convex structure 50 is formed on the bottom surface as the surface of the groove 31 and on the surface of the land portion 41. When the fine concavo-convex structure 50 is formed, the height difference J of the concavo-convex structure 30 is preferably 0.1 μm or more, and the height difference K of the fine concavo-convex structure 50 is preferably less than 0.1 μm. As described above, if the fine uneven structure 50 is formed on at least one surface of the groove portion 31 and the land portion 41, the function of supplying the lubricating oil by the capillary phenomenon can be improved. 7A to 7C, the height difference J of the concave-convex structure 30 means a length based on the fine convex portion 61 of the fine concave-convex structure 50. Specifically, the height difference J of the concavo-convex structure 30 in FIG. 7A means the height difference from the surface of the land portion 41 to the fine protrusion 61 of the fine concavo-convex structure 50 of the groove 31. The height difference J of the concave-convex structure 30 in FIG. 7B means a vertical difference from the fine convex portion 61 of the fine concave-convex structure 50 of the land portion 41 to the surface of the groove portion 31. Further, a height difference J of the uneven structure 30 in FIG. 7C means a height difference from the fine convex portion 61 of the fine uneven structure 50 of the land portion 41 to the fine convex portion 61 of the fine uneven structure 50 of the groove portion 31. Although not shown, when the cross-sectional shape of the groove 31 is U-shaped, the height difference between the deepest part of the groove 31 and the land 41 is the height difference J of the uneven structure 30.

  The fine concave portion 51 is formed by, for example, laser processing or the like. The minute convex portions 61 are formed in two adjacent minute concave portions 51. The shapes of the fine concave portions 51 and the fine convex portions 61 are not particularly limited, but the fine concave portions 51 and the fine convex portions 61 respectively extend in a direction parallel to the groove portions 31 and are formed alternately in the width direction of the fine concave portions 51. It may be. Further, the extending direction of the minute concave portion 51 and the minute convex portion 61 may be different from the extending direction of the groove portion 31 and the land portion 41, or may be the same. For example, the fine concavo-convex structure 50 is formed on the bottom surface of the groove portion 31 like the concavo-convex structure 30a shown in FIG. 7A or the concavo-convex structure 30c shown in FIG. If the extending direction is different from the extending direction of the groove 31, the lubricating oil in the groove 31 is easily held by the fine uneven structure 50. Note that the fine uneven structure 50 is preferably a periodic uneven structure in which unevenness periodically appears in a predetermined direction. Further, since the fine uneven structure 50 is formed on the hard coating described later, when the cylinder bore and the fine uneven structure 50 are slid, the formation of the tribo coating is easily promoted, which contributes to low friction. be able to.

  The outer peripheral surface 10 of the piston ring 1 of the present embodiment is formed of a hard coating. Specifically, for example, after a hard film is directly formed on the outer peripheral surface of the base material of the piston ring, any of the above-described uneven structures (the uneven structures 30, 30 ′, and 30 ″) is formed on the outer peripheral surface 10 formed of the hard film. , 30a, 30b, 30c), the piston ring 1 having the uneven structure is obtained. By configuring the outer peripheral surface 10 of the piston ring 1 with a hard coating, it is possible to suppress wear of the outer peripheral surface 10.

  The hard coating may be, for example, an amorphous hard carbon coating (DLC coating). The amorphous hard carbon film may be a hydrogen-containing amorphous hard carbon film or a hydrogen-free amorphous hard carbon film having a hydrogen content of 10 at% or less. The hard coating may be other than the amorphous carbon coating, for example, electroless plating, a combination of electroless plating and electrolytic plating, hard paint coating, physical vapor deposition (PVD), chemical vapor deposition (CVD), It may be a film formed by a sputtering method or the like. As the material of the film, chromium nitride film (CrN), titanium nitride film (TiN), titanium carbide (TiC), aluminum titanium nitride (TiAlN), chromium nitride (CrN), TiCN, AlCrN, TiC, or nickel (Ni) Alternatively, plating made of a nickel alloy such as nickel phosphorus (NiP) may be used. Further, the hard coating may be a polymer coating such as polyimide, other than the coating made of an inorganic material. The polymer film may be one in which a filler such as carbon fiber or glass fiber is mixed. In the piston ring 1 of the present embodiment, the uneven structure 30 may be formed before forming the hard coating on the base material.

  FIG. 8 is a sectional view showing a piston ring 1a as a first modification of the piston ring 1. As shown in FIG. As shown in FIG. 8, the contour shape of the outer peripheral surface 10 a by a cross section including the central axis O (see FIG. 1 and the like) of the piston ring 1 a is in the direction in which the cylinder 200 is located (radially outward G in the radial direction C). A barrel-shaped part 14a having a convex curved surface shape and tapered parts 15a located on both sides of the barrel-shaped part 14a in the central axis direction B are provided. The barrel-shaped portion 14a includes the outermost diameter portion 11. The inclined portion 12a in the first modification of the present embodiment is provided on the upper surface 80 side and the lower surface 90 side of the outermost diameter portion 11, and includes a part of the barrel-shaped portion 14a and the tapered portion 15a. . The uneven structure forming region P in which the uneven structure 30 is formed is formed on the upper surface side D and the lower surface side E of the inclined portion 12a. S is set. Note that the first distance L1 in the radial direction C from the outermost diameter portion 11 to the uneven structure forming region P is set in a range from 0.5 μm to 100 μm. The piston ring 1a is a top ring in which the uneven structure 30 is formed on both sides of the combustion chamber side D and the crankcase side E in the central axis direction B with respect to the outermost diameter portion 11. That is, the piston ring 1a has the uneven structure forming region P adjacent to both the upper surface side D and the lower surface side E of the uneven structure non-forming region S. The other configuration of the piston ring 1a is the same as the configuration of the piston ring 1 described above, and thus the description is omitted.

  FIG. 9 is a cross-sectional view showing a piston ring 1b as a second modification of the piston ring 1. FIG. 10 is a side view showing the outer peripheral surface 10b of the piston ring 1b. As shown in FIGS. 9 and 10, the contour shape of the outer peripheral surface 10 b in a cross section including the central axis O (see FIG. 1 and the like) of the piston ring 1 b includes an outermost diameter portion 11, and a central axis extending from the outermost diameter portion 11. An inclined portion 12b that is inclined so as to approach the radially inner side F as going in the direction B. The inclined portion 12b has a contour that can be represented on a straight line in the sectional view shown in FIG. The inclined portion 12b shown in FIGS. 9 and 10 is located on only one side in the central axis direction B with respect to the outermost diameter portion 11. More specifically, the inclined portion 12b shown in FIGS. 9 and 10 is located only on the combustion chamber side D in the central axis direction B with respect to the outermost diameter portion 11, and on the other hand, the crankcase is larger than the outermost diameter portion 11. The side E is a lower side surface 90. The piston ring 1b according to the second modified example of the present embodiment includes the outermost diameter portion 11 and a part of the inclined portion 12b in the vicinity thereof in the uneven structure non-forming region S, and is located above the uneven structure non-forming region S. The inclined portion 12b adjacent to the side surface D has a concavo-convex structure forming region P. The first distance L1 in the radial direction C from the outermost diameter portion 11 to the uneven structure forming region P is set in a range of 0.5 μm or more and 100 μm or less, and the uneven structure 30 is adjacent to the uneven structure non-forming region S. (The uneven structure forming region P).

  As shown in FIGS. 9 and 10, the piston ring 1 b is a second ring in which the uneven structure 30 is formed only on the combustion chamber side D in the center axis direction B with respect to the outermost diameter portion 11. Accordingly, the piston ring 1b is mounted in the piston ring groove located second from the combustion chamber side D among the piston ring grooves of the piston in which three or more piston ring grooves capable of accommodating the piston ring are formed on the side surface. . It is assumed that a piston ring different from the piston ring 1b is mounted in the piston ring groove located closest to the combustion chamber D of the piston on which the piston ring 1b is mounted. When the piston 100 (see FIG. 2) particularly rises relative to the cylinder 200 (see FIG. 2), the piston ring 1b easily supplies the lubricating oil to the outermost diameter portion 11 and its vicinity. Further, since the piston ring 1b is a second ring, even if an inertial force acts on the lubricating oil held in the uneven structure 30 at the top dead center, scattering is suppressed by the top ring located on the combustion chamber side D. The other configuration of the piston ring 1b is similar to the configuration of the piston ring 1 described above, and thus the description is omitted.

  FIG. 11 is a cross-sectional view showing a piston ring 1c as a third modification of the piston ring 1. Note that, in FIG. 11, the configuration of the same reference numerals as in FIG. 9 is the same as the configuration of the piston ring 1b shown in FIG. The piston ring 1c according to the third modification has an inclined portion 12c formed also on the lower side E as compared with the piston ring 1b according to the second modification. And the uneven structure 30 different from the uneven structure 30 formed in the inclined part 12b is formed in the inclined part 12c. The end of the concave-convex structure 30 formed on the inclined portion 12c on the radially outer side G is formed at a first distance L1 from the outermost diameter portion 11 toward the radially inner side F. Therefore, in the piston ring 1c as the third modification, the uneven structure forming region P is formed on both the upper surface side D and the lower surface side E of the uneven structure non-forming region S including the outermost diameter portion 11. I have. Even the piston ring 1c having such a cross-sectional shape has the same effect as the above-described piston ring 1b. It is preferable that the first distance L1 and the second distance L2 in the piston ring 1c according to the third modification have the same dimensional values as those of the piston ring 1b according to the second modification. Further, the piston ring 1c as the third modification is preferably used as a second ring, similarly to the piston ring 1b as the second modification.

  FIG. 12 is a sectional view showing a piston ring 1d as a fourth modification of the piston ring 1. As shown in FIG. 12, the piston ring 1 d is a two-piece type oil ring, and includes a ring main body 2 and a coil expander 3. The coil expander 3 urges the ring main body 2 toward the outside G in the radial direction.

  The ring body 2 has a web portion 4 formed on an inner peripheral surface thereof, and a pair of rail portions 5 formed on an outer peripheral surface thereof. Holes 8 are formed in the ring body 2 at certain intervals. Although not shown, an abutment is provided on a part of the ring main body 2. The pair of rail portions 5 are provided integrally with the ring main body 2 on the combustion chamber side D and the crankcase side E in the central axis direction B with respect to the web portion 4, respectively. Land portions 7 are formed in the outermost regions of the pair of rail portions 5, respectively. The land portion 7 is formed in a region surrounded by a broken line shown in FIG. Each of the lands 7 is formed in a ring shape that protrudes radially outward from the outer peripheral end of the corresponding rail 5 and extends over the entire periphery of the rail 5. Further, an outer peripheral surface located between the land portion 7 formed on the combustion chamber side D and the upper side surface 80 and an outer peripheral surface located between the land portion 7 formed on the crankcase side E and the lower side surface 90. On each of the surfaces, an inclined surface 40 is formed so as to increase in diameter from the side surface toward the land portion 7.

  FIG. 13 is an enlarged sectional view showing one land 7 of the piston ring 1d shown in FIG. The land 7 provided on the rail section 5 on the combustion chamber side D and the land section 7 provided on the rail section 5 on the crankcase side E have basically the same shape. Description will be made based on the land portion 7 provided on the rail portion 5 on the room side D.

  As shown in FIG. 13, the land portion 7 includes an upper axial side portion 80c on the combustion chamber side D in the central axial direction B and a lower axial side portion 90c on the crankcase side E in the central axial direction B. A tapered portion 15c and a barrel-shaped portion 14c are provided between the upper side axial portion 80c and the lower axial side portion 90c. The upper axial side portion 80c and the lower axial side portion 90c are tapered so as to position the tapered portion 15c and the barrel-shaped portion 14c on the outer peripheral side (radially outer side G) of the inclined surface 40. It is formed so as to increase in diameter toward the portion 15c and the barrel-shaped portion 14c, and the inclination angle with respect to the central axis direction B is larger than the inclined surface 40 and the tapered portion 15c. As shown in FIG. 13, the tapered portion 15c also has an inclined surface that increases in diameter toward the crankcase side E, and the barrel-shaped portion 14c protrudes more outward than the tapered portion 15c. It is in a positional relationship.

  As shown in FIG. 13, the outermost diameter portion 11 of the piston ring 1d according to the fourth modification is a barrel-shaped portion 14c. A tapered portion 15c is formed so as to be continuous with the barrel-shaped portion 14c in the central axis direction B (the combustion chamber side D in the example shown in FIG. 13). The barrel-shaped part 14c is formed in a convex curved surface (barrel face) shape. The inclination angle α of the tapered portion 15c with respect to the central axis direction B is 17 ° or more and 27 ° or less.

  In the tapered portion 15c of the piston ring 1d, a concavo-convex structure forming region P in which the concavo-convex structure 30 is formed is formed similarly to the above-described piston ring 1. The details of the region of the piston ring 1d where the uneven structure 30 is formed are the same as those of the piston ring 1 of the embodiment shown in FIG. In the shape of the piston ring 1d shown in FIG. 13, since the step dH between the outermost diameter position of the tapered portion 15c and the outermost diameter portion 11 is set to 1 μm or more and 100 μm or less, only the tapered portion 15c is used. The uneven structure forming region P is used. If the step dH is smaller, the concavo-convex structure 30 may be formed on a part of the upper side D of the barrel-shaped portion 14c.

  The same effect can be achieved by applying the outer peripheral surface shape and structure shown in FIG. 13 to both upper and lower rail members of a three-piece type oil control ring set. In this case, it is not always necessary to form the inclined surface 40 between the upper surface and the land 7 or between the lower surface and the land 7. Therefore, from the upper surface of the rail member to the lower surface via the outer peripheral surface, the outer peripheral surface is formed by the arrangement relationship of the upper surface side axial side portion 80c, the tapered portion 15c, the barrel-shaped portion 14c, and the lower surface side axial side portion 90c. It is preferable that the surface shape is configured. Further, only one land portion 7 formed on the outer peripheral surface of each of the upper and lower rail members is required in the sectional direction.

  By the way, the preferred contour shape of the outer peripheral surface in the embodiment of the present invention is the outer diameter at the outermost diameter portion 11 and the position of the inclined portion 12 which is 0.3 mm away from the outermost diameter portion 11 in the central axis direction B. Is preferably 0.002 mm or more and 0.050 mm or less. When the outermost diameter portion 11 has a predetermined width in the central axis direction B, “the position of the inclined portion 12 that is 0.3 mm away from the outermost diameter portion 11 in the central axis direction B” means the outermost diameter. It means the position of the inclined portion 12 that is 0.3 mm away from the center of the portion 11 in the central axis direction B in the central axis direction B.

  The structure of the outer peripheral surface in the present embodiment can be applied to a sliding member other than the piston ring. For example, it has an outer peripheral surface including a region that slides with a counterpart material during sliding, and a side surface oriented in a direction different from the surface direction of the outer peripheral surface in a sliding direction of the outer peripheral surface and a direction opposite to the sliding direction. By setting or forming the uneven structure non-forming region and the uneven structure forming region on the outer peripheral surface of the sliding member as described above, it is possible to obtain good sliding characteristics while preventing the mating material from being worn. Can be. In addition, even with such a sliding member, the sliding area of the outer peripheral surface that slides with the mating material is smaller than the area adjacent to one of the side surfaces during sliding. It is good to have a shape which is close to. Thus, in a shape that is closer to the mating material than the outer circumferential surface adjacent to the side surface, for example, in a portion having a convex shape in the outer circumferential surface, a convex portion that is close to the mating material when sliding. It is preferable that an uneven structure is not provided on the top of and in the vicinity thereof, and an uneven structure forming region is provided in a region adjacent to the sliding region which is a convex portion thereof.

[Production method of piston ring]
FIG. 14 is a flowchart showing some steps of a method of manufacturing a piston ring as one embodiment of the present invention. As shown in FIG. 14, the method for manufacturing a piston ring of the present embodiment includes a film forming step S1 and an unevenness forming step S2.

  The film forming step S1 is a step of forming a hard film on the outer peripheral surface of the piston ring before forming the hard film. The hard coating of the present embodiment may be made of the same material as the hard coating forming the outer peripheral surface 10 of the piston ring 1 described above, and by the same forming method as the hard coating forming the outer peripheral surface 10 of the piston ring 1. Can be formed.

  The unevenness forming step S2 is a step of forming an uneven structure at a position other than the outermost diameter portion having the largest outer diameter on the outer peripheral surface after the hard film is formed and the vicinity thereof after the film forming step S1. The concavo-convex structure of the present embodiment may have the same configuration as the concavo-convex structure 30 of the piston ring 1 described above, and can be formed by the same forming method as the concavo-convex structure 30.

  As described above, in the piston ring manufacturing method of the present embodiment, after forming the hard coating on the outer peripheral surface of the piston ring, the uneven structure is formed on the outer peripheral surface. Thereby, a desired uneven structure can be formed more finely on the outer peripheral surface. By adjusting the thickness of the hard film and the method of film formation so that the uneven structure appears even when the hard film is formed on the uneven structure, the hard film is formed after forming the uneven structure on the outer peripheral surface of the piston ring. May be formed. The manufacturing method of the piston ring of the present embodiment can be applied to any of the manufacturing methods of the piston ring 1 and the piston rings 1a to 1d of the above embodiment.

  In order to confirm the effects of the present invention, Examples 1 to 3 of the present invention were prepared and the following evaluation tests were performed. Note that the present invention is not limited to these examples.

(Example 1)
First, a ring having an outer peripheral surface in a barrel face shape was prepared, and an amorphous hard carbon film was formed as a hard film. Next, as shown in FIG. 3B, the concavo-convex structure 30 (see FIG. 5 and the like) is formed on the hard carbon coating at a position on the lower side E side of the concavo-convex structure non-forming region S including the outermost diameter portion 11 and its vicinity. Formed. The first distance in the radial direction C between the position where the outer diameter is largest on the outer peripheral surface 10 where the uneven structure 30 is formed and the outermost diameter portion 11 (see FIG. 3B etc.) in the uneven structure non-formed area S. L1 was 0.004 mm. In the piston ring, the difference between the outer diameter at the outermost diameter portion 11 and the outer diameter at a position 0.3 mm away from the outermost diameter portion 11 in the central axis direction B (see FIG. 3B and the like) is 0. 005 mm. The outer diameter of the piston ring at the outermost diameter portion 11 was 86 mm, the length in the central axis direction B was 1.2 mm, and the length in the radial direction C was 3.3 mm.

  FIG. 15 is a diagram illustrating the test method of the first embodiment. As shown in FIG. 15, the obtained piston ring was cut along the radial direction C to obtain a ring piece Q. A sliding test was performed on the surface of the cylinder cut piece 200 'while applying a load W to the outer peripheral surface of the ring piece Q toward the cylinder cut piece 200' as a sliding partner. At this time, the viscosity of the dropped oil was set to 0W-20, the sliding time was set to 10 hours, and the load W was set to 100N. In Comparative Example 1, the uneven structure 30 includes the outermost diameter portion 11 in addition to the region formed in Example 1 and the region in which the uneven structure is not formed as the uneven structure non-formed region S in Example 1. Also formed. Note that the grooves of the concavo-convex structure were formed so as to extend along the sliding direction. For other conditions, a ring piece prepared in the same manner as the ring piece Q was prepared. The above-described sliding test was also performed on the ring piece of Comparative Example 1. As a result, in Example 1, the wear amount of the mating member was about 60% as compared with Comparative Example 1.

(Example 2)
A piston ring was obtained in the same manner as in Example 1. Regarding the size of the piston ring, the outer diameter of the outermost diameter portion 11 was 78 mm, the length of the central axis direction B was 1.2 mm, and the length of the radial direction C was 2.5 mm. It was similar to the piston ring of Example 1. The blow-by amount after the internal combustion engine incorporating the piston ring of the present embodiment was operated for a long time by a gasoline engine was measured under the following conditions. That is, using a water-cooled 4-cycle gasoline engine (displacement 1.5 L, 4 cylinders), the operation was performed for 10 hours under the conditions of a rotation speed of 4000 rpm and a full load (Wide Open Throttle). Further, as Comparative Example 2, the concavo-convex structure 30 is also formed between the outermost diameter portion 11 and the point of 0.004 mm inward in the radial direction F, and other conditions are the same as those of the piston ring of the present embodiment. The prepared piston ring was prepared. The above measurement was also performed on an internal combustion engine incorporating the piston ring of Comparative Example 1. From the measurement results, the amount of blow-by after aging was calculated. As a result, in Example 2, the blow-by amount was about 70% of Comparative Example 2.

(Example 3)
FIG. 16 is a partial cross-sectional view of a single reciprocating motion tester 300 for measuring a friction coefficient used in the third embodiment. A piston ring similar to that of the first embodiment was prepared as the piston ring 301 of the present embodiment. Further, as the piston ring of Comparative Example 3, a piston ring was prepared in which the same hard coating as that of Example 1 was formed on the base material of the piston ring, and thereafter, no irregular structure was formed on the outer peripheral surface. As shown in FIG. 16, an evaluation test was performed by attaching the piston ring 301 of the present example and the piston ring of Comparative Example 3 to the piston 302 of the single-unit reciprocating tester 300, respectively. Specifically, the piston ring 301 of this embodiment or the piston 302 having the piston ring of Comparative Example 3 mounted thereon is inserted into the inner peripheral surface of a cylindrical cylinder liner 303 using a single reciprocating motion tester 300 shown in FIG. Then, the piston 302 was reciprocated vertically. The friction coefficient was calculated by detecting the displacement of the block 304 fixed to the cylinder liner 303 or the load applied to the block 304 at that time by a load sensor 306. The test conditions of the single reciprocating motion tester 300 shown in FIG. 16 were bore x stroke φ86 × 86 mm, rotation speed 500 rpm, lubricating oil viscosity 0W-20, and ring single evaluation. As a result, in Example 3, the friction coefficient near the top dead center was about 60% as compared with Comparative Example 3.

  The present invention is not limited to the above embodiment, and it goes without saying that various changes can be made without departing from the spirit of the present invention. For example, the shape of the outer peripheral surface of the piston ring is not limited to the above-described embodiments, and may be any other shape. Further, the shapes of the inner peripheral surface, the upper surface, and the lower surface of the piston ring are not limited to the shapes of the above-described embodiments.

  The present invention relates to a piston ring and a method for manufacturing the piston ring.

1, 1a, 1b, 1c, 1d: Piston ring 2: Ring body 3: Coil expander 4: Web part 5: Rail part 6: Abutment 7: Land part 8: Hole part 10, 10a, 10b, 10c: Outer peripheral surface 11 : Outer diameter portion 12, 12a, 12b, 12c: Inclined portion 14a, 14c: Barrel shaped portion 15a, 15c: Tapered portion 30, 30 ', 30'', 30a, 30b, 30c: Concavo-convex structure 31: Groove portion 40 : Slope 41: Land 50: Fine concave and convex structure 51: Fine concave 61: Fine convex 70: Inner peripheral surface 80: Upper surface 80 c: Upper surface side axial direction 90: Lower surface 90 c: Lower surface side axial direction Side part 100: Piston 101: Piston ring groove 200: Cylinder 200 ': Cylinder cut piece 300: Single reciprocating motion tester 301: Piston ring 302: Piston 303: Siri Daraina 304: Block 306: Load Sensor A: circumferentially B: central axis direction C: radial D: a combustion chamber side (upper side surface)
E: Crankcase side (lower side)
F: Radial inner side G: Radial outer side I: Repetition unit of groove and land J: Height difference of uneven structure K: Height difference of fine uneven structure L1: First distance L2: Second distance D1: Piston ring Outer diameter D1max: Outer diameter at outermost diameter part dH: Step between outermost diameter position and outermost diameter part of tapered part O: Central axis P: Uneven structure forming area Q: Ring piece S: Uneven structure not formed Areas X1, X2, X3, X4: boundary line α: inclination angle of tapered portion with respect to central axis direction

Claims (16)

A piston ring having an uneven structure having grooves and land portions extending alternately in a predetermined direction formed on an outer peripheral surface,
The outer peripheral surface, in a contour shape by a cross-section including the central axis of the piston ring, includes an outermost diameter portion having a maximum outer diameter dimension,
The said uneven structure is not formed in the said outermost diameter part, The piston ring characterized by the above-mentioned.   The outer peripheral surface is adjacent to at least one of the upper surface side or the lower surface side of the concave-convex structure-free region in which the concave-convex structure is not formed, which is composed of the outermost diameter portion and the vicinity thereof, where the concave-convex structure is not formed. The piston ring according to claim 1, further comprising: an uneven structure forming area in which the uneven structure is formed.   3. The piston ring according to claim 2, wherein the uneven structure forming region is provided only on a lower surface side of the uneven structure non-forming region. The contour shape by the cross section of the outer peripheral surface has a shape such that the outer diameter is gradually reduced as going from the outermost diameter portion toward the upper surface side or the lower surface side,
4. The piston ring according to claim 2, wherein the uneven structure non-forming region extends to a region where the outer peripheral surface is located at least 0.5 μm or more radially inward from the outermost diameter portion. 5.   5. The piston ring according to claim 1, wherein in the uneven structure, the groove and the land are formed periodically in the circumferential direction on the outer peripheral surface.   The piston ring according to claim 5, wherein a repeating unit in which the groove and the land are alternately formed has a size of 100 m or less.   The piston ring according to claim 6, wherein a height difference between a deepest portion of the groove and the land portion of the concave-convex structure is 0.01 μm or more and 100 μm or less.   On at least one surface of the groove and the land, a fine uneven structure having a height difference smaller than the height difference from the deepest portion of the groove of the uneven structure to the land is formed. The piston ring according to any one of claims 5 to 7.   The piston ring according to any one of claims 5 to 8, wherein the groove portion and the land portion extend along a central axis direction.   At least a part of the concavo-convex structure is formed in a partial region of the outer peripheral surface at a position not exceeding 100 μm radially inward of the outermost diameter portion. The piston ring according to any one of claims 1 to 9.   The outer peripheral surface is provided on both sides in the center axis direction with respect to the outermost diameter portion, with inclined portions inclined so as to approach radially inward from the outermost diameter portion toward the upper surface side or the lower surface side. The piston ring according to any one of claims 1 to 10, characterized in that:   The outer peripheral surface has an inclined portion inclined so as to approach radially inward from the outermost diameter portion toward the upper surface side or the lower surface side, only on one side in the central axis direction with respect to the outermost diameter portion. The piston ring according to claim 1, wherein the piston ring is provided.   The piston ring according to claim 11, wherein the outermost diameter portion is located in a region not including a center position of the outer peripheral surface in the central axis direction.   The outer peripheral surface is connected to the barrel-shaped portion including the outermost diameter portion and the barrel-shaped portion at one end in a central axis direction, and is tapered at an angle of 17 ° or more and 27 ° or less with respect to the central axis direction. A piston ring according to any one of claims 1 to 11, characterized by comprising:   The piston ring according to any one of claims 1 to 14, wherein the outer peripheral surface is formed of a hard coating. Forming a hard coating on the outer peripheral surface of the piston ring;
A step of forming a concavo-convex structure at a position other than the outermost diameter portion where the dimension of the outer diameter is the largest among the outer peripheral surfaces after the hard coating is formed, in the contour shape by the cross section including the central axis of the piston ring,
A method for manufacturing a piston ring including:

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