Compression ring

Abstract

To provide a technique capable of suppressing dilution of lubricating oil due to fuel in an internal combustion engine.SOLUTION: An outer peripheral surface of a compression ring has: an outer peripheral sliding surface including an apex to be a maximum diameter in the compression ring, and sliding on a cylinder wall surface of an internal combustion engine; and a connection surface connecting a top surface as a surface at a combustion chamber side in the internal combustion engine in both edge surfaces in an axial direction of the compression ring, and the outer peripheral sliding surface. When a width of the compression ring in the axial direction of the compression ring is h1 in a cross section orthogonal to a circumferential direction of the compression ring, the apex is P0, a connection point between the outer peripheral sliding surface and the connection surface is P2, an outer peripheral edge of the top surface is P3, and an area of a region surrounded by connecting the apex P0, the connection point P2, and the outer peripheral edge P3 by straight lines is S1, 0.013≤S1 / h1≤0.034 is established.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a compression ring that is assembled to a piston of an internal combustion engine. [Background technology]

[0002] Internal combustion engines installed in typical automobiles use a piston unit in which piston rings, including a compression ring (pressure ring) and an oil ring, are each fitted into a ring groove individually formed in the piston. In the axial direction of the piston, the compression ring is located on the combustion chamber side, and the oil ring is located on the crank chamber side. These piston rings exert their functions by sliding on the inner wall surface of the cylinder. Of these, the compression ring has a gas seal function that prevents combustion gas from leaking from the combustion chamber side to the crank chamber side (blow-by) by maintaining airtightness, and an oil seal function that prevents oil leakage by scraping off excess lubricating oil (engine oil) that the oil ring was unable to scrape off.

[0003] Piston rings used in internal combustion engines are required to have high sliding performance. Meanwhile, biofuels derived from biomass have become widespread as fuel for internal combustion engines in recent years. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5872678 [Patent Document 2] Patent Publication No. 2015-059502 Summary of the Invention [Problem to be solved by the invention]

[0005] However, since biofuels have different properties from conventional fuels, when they are used in internal combustion engines, a new problem may arise in that the lubricating oil is diluted by the fuel. For example, as described in Patent Document 1, among biofuels, biodiesel fuel Biodiesel has a higher and narrower boiling point range than regular diesel fuel, and its molecular structure results in larger droplets being ejected from the fuel injector. The physical properties of biodiesel fuel lead to dilution of the lubricating oil in the crankcase, increasing the potential for engine wear. While the diesel portion of the fuel mixture evaporates and flows into the exhaust stream, the piston is at the bottom of the cylinder. The methyl ester fraction, with its higher and narrower boiling point range and larger droplet size, remains liquid and resides on the inner cylinder wall. As the piston rises, any biodiesel fuel not scraped up by the piston rings flows into the crankcase. Once inside the crankcase, biodiesel does not evaporate like diesel. The heat inside the crankcase can cause oxidation of the lubricating oil and biodiesel mixture, resulting in engine wear due to organic acids. This is no exception for the piston rings, which slide against the inner cylinder wall, and there is a risk of increased wear, particularly on the outer sliding surface of the oil ring. Due to these factors, in internal combustion engines that use biofuels, wear resistance can be insufficient even in piston rings that have wear countermeasures in place, such as providing a nitride layer on the sliding surface as exemplified in Patent Document 2. Furthermore, in diesel engines that use fuels other than biofuels, such as diesel oil, dilution of lubricating oil by the fuel can also be a problem.

[0006] The present invention has been made in view of the above-mentioned problems, and has an object to provide a technique capable of suppressing dilution of lubricating oil by fuel in an internal combustion engine. [Means for solving the problem]

[0007] In order to solve the above problems, the connection structure according to the present invention employs the following configuration. That is, the gist of the present invention is as follows. [1] A compression ring assembled to a piston of an internal combustion engine, an outer peripheral surface of the compression ring having an outer peripheral sliding surface that includes a top portion that is the largest diameter of the compression ring and slides on a cylinder wall surface of the internal combustion engine; and a connection surface that connects the outer peripheral sliding surface to an upper surface, which is a surface on the combustion chamber side of the internal combustion engine, of both axial end surfaces of the compression ring, In a cross section perpendicular to the circumferential direction of the compression ring, The width of the compression ring in the axial direction of the compression ring is defined as h1, The top is P0, A connection point between the outer circumferential sliding surface and the connection surface is designated as P2, The outer periphery of the upper surface is P3, When the area of ​​the region enclosed by the apex P0, the connection point P2, and the outer periphery P3, each connected by a straight line, is S1, 0.013≦S1 / h1≦0.034 That is, Compression ring. [2] In a cross section perpendicular to the circumferential direction of the compression ring, The width of the outer peripheral sliding surface in the axial direction is defined as h2, A virtual line passing through the connection point P2 and extending in the radial direction of the compression ring is defined as Lh, The intersection point of an imaginary line L8 passing through the top point P0 and extending in the axial direction with an imaginary line Lh is defined as P20, The intersection point of the imaginary line L3 passing through the top P0 and the outer peripheral edge P3 and the imaginary line Lh is defined as P23, When the area of ​​the region enclosed by the lines connecting the vertex P0, the intersection point P20, and the intersection point P23 is S2, 0.011≦S2 / h2≦0.033 That is, The compression ring described in [1]. [3] In a cross section perpendicular to the circumferential direction of the compression ring, Of the two points where a virtual line L7, which is located 2.5 μm inward from the apex P0 in the radial direction of the compression ring and extends in the axial direction, intersects with the outer peripheral sliding surface, the intersection point on the combustion chamber side is defined as P1, When the area of ​​the region enclosed by the intersection point P1, the connection point P2, and the outer edge P3, each connected by a straight line, is S3, 0≦S3 / h1≦0.011 That is, A compression ring according to [1] or [2]. [4] In a cross section perpendicular to the circumferential direction of the compression ring, Of the two points where a virtual line L7, which is located 2.5 μm inward from the apex P0 in the radial direction of the compression ring and extends in the axial direction, intersects with the outer peripheral sliding surface, the intersection point on the combustion chamber side is defined as P1, The angle between the imaginary line L1 and the imaginary line L7 passing through the intersection point P1 and the connection point P2 is defined as θ1. , The angle formed by the imaginary line L2 passing through the intersection point P1 and the outer peripheral edge P3 and the imaginary line L7 is defined as θ2, When the area of ​​the region enclosed by the intersection point P1, the connection point P2, and the outer edge P3, each connected by a straight line, is S3, 0≦S3 / h1 / (θ1+θ2)≦0.0009; A compression ring according to any one of [1] to [3]. [5] In a cross section perpendicular to the circumferential direction of the compression ring, The width of the outer peripheral sliding surface in the axial direction is defined as h2, Of the two points where a virtual line L7, which is located 2.5 μm inward from the apex P0 in the radial direction of the compression ring and extends in the axial direction, intersects with the outer peripheral sliding surface, the intersection point on the combustion chamber side is defined as P1, The distance in the axial direction between the top point P0 and the intersection point P1 is B2, A virtual line passing through the connection point P2 and extending in the radial direction of the compression ring is defined as Lh, The intersection point of the imaginary line L2 passing through the intersection point P1 and the outer peripheral edge P3 and the imaginary line Lh is defined as P22, When the area of ​​the region enclosed by the lines connecting the intersection point P1, the connection point P2, and the intersection point P22 is S4, 0≦(S4 / h2)×(B2 / h2)≦0.0013 That is, A compression ring according to any one of [1] to [4]. [6] In a cross section perpendicular to the circumferential direction of the compression ring, When the distance in the axial direction between the top point P0 and the connection point P2 is B1, 0.1≦B1 / h1≦0.4, A compression ring according to any one of [1] to [5]. [7] A hard layer including at least one of a PVD coating, a DLC coating, a chrome plating coating, and a nitriding layer is formed on the outer peripheral surface of the compression ring. A compression ring according to any one of [1] to [6]. [8] The internal combustion engine is a compression ignition engine. A compression ring according to any one of [1] to [7]. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress dilution of lubricating oil by fuel in an internal combustion engine. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a partial cross-sectional view of an internal combustion engine equipped with a piston structure according to an embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view of the outer circumferential surface of the top ring according to the embodiment. [Figure 3] FIG. 10 is a diagram showing a partial contour line of a cross section of a top ring according to an embodiment. [Figure 4] FIG. 2 is an enlarged cross-sectional view of the top ring for explaining first to fourth regions. DETAILED DESCRIPTION OF THE INVENTION

[0010] One aspect of the present invention is a compression ring that is assembled to a piston of an internal combustion engine that uses biofuel. Biofuel is a fuel derived from living organisms (plants or animals) and is made from biological resources (biomass). The biofuel according to the present invention is not particularly limited, but examples thereof include biodiesel fuel obtained by methyl esterification of vegetable oils and fats or animal oils and fats. In addition, the use of the internal combustion engine is not particularly limited, but the compression ring according to the present invention can be used in a variety of applications. The cushion ring can be suitably used in, for example, an automobile engine. The internal combustion engine to which the present invention is applied may be a compression ignition engine, such as a diesel engine. The internal combustion engine may use pure biofuel or a blend of biofuel and fossil fuel. The internal combustion engine is not limited to engines that use biofuel as fuel, and may be, for example, a diesel engine that uses diesel as fuel.

[0011] Herein, in this specification, when there is no need to distinguish between compression rings and oil rings, they will be collectively referred to as "piston rings." A piston ring is a sliding member that is attached to a piston mounted in a cylinder of an internal combustion engine and slides on the cylinder wall surface (the inner wall surface of the cylinder) as the piston reciprocates. In addition, in this specification, the term "circumferential direction" refers to the circumferential direction (direction of circumferential length) of the piston ring unless otherwise specified. The term "radial direction" refers to the radial direction of the piston ring unless otherwise specified. The term "axial direction" refers to the direction along the central axis of the piston ring unless otherwise specified. In addition, with regard to a piston ring, the term "outer peripheral surface" refers to the surface connecting the outer peripheral edges of both axial end faces that define the width (axial dimension) of the ring (or segment), and the term "inner peripheral surface" refers to the surface connecting the inner peripheral edges of both axial end faces.

[0012] The outer peripheral surface of the compression ring according to the present invention has an outer peripheral sliding surface that includes an apex that is the maximum diameter of the compression ring and slides on the cylinder wall surface of an internal combustion engine. The apex of the outer peripheral sliding surface is a portion located radially outward of other portions of the outer peripheral sliding surface, and the compression ring has the maximum diameter at the apex. The apex may be formed as a peak in a cross section perpendicular to the circumferential direction of the compression ring, or may be formed as a flat surface (straight surface) extending along the axial direction and having a width (contact width) in the axial direction. Furthermore, in this specification, the "axial distance between the combustion chamber-side edge of the outer peripheral sliding surface and the apex" refers to the distance between the combustion chamber-side edge of the outer peripheral sliding surface and the position of the apex closest to the combustion chamber. Therefore, when the apex is formed as a surface with a contact width, the "axial distance between the combustion chamber-side edge of the outer peripheral sliding surface and the apex" refers to the distance between the combustion chamber-side edge of the outer peripheral sliding surface and the combustion chamber-side edge of the apex.

[0013] Preferred embodiments of the present invention will now be described with reference to the drawings. In the embodiments described below, the compression ring configuration according to the present invention is applied to a top ring, which is positioned closest to the combustion chamber among multiple compression rings assembled to a piston. However, the compression ring according to the present invention is not limited to a top ring. The compression ring configuration according to the present invention may also be applied to, for example, a second ring, which is positioned second from the combustion chamber among multiple compression rings. Furthermore, the piston ring combination according to the embodiments described below includes two compression rings and one oil ring positioned closer to the crank chamber than the two compression rings. However, the number of compression rings and oil rings in the piston ring combination is not limited to this. The number of compression rings may be one, or three or more. Furthermore, unless otherwise specified, the configurations described in the following embodiments are not intended to limit the technical scope of the invention to those configurations.

[0014] [Overall configuration] FIG. 1 is a partial cross-sectional view of an internal combustion engine 100 equipped with a piston ring assembly 110 according to an embodiment. FIG. 1 illustrates a cross section along the central axis of the piston. As an example, the internal combustion engine 100 is a diesel engine for an automobile that uses biofuel as fuel. As shown in FIG. 1, the internal combustion engine 100 according to an embodiment includes a cylinder 10, a piston 20 mounted in the cylinder 10, and a plurality of piston rings assembled to the piston 20. 1, in the internal combustion engine 100, a piston gap PC1 is formed by ensuring a predetermined distance between an outer peripheral surface 20a of the piston 20 and a cylinder wall surface 10a (an inner wall surface of the cylinder 10). In the internal combustion engine 100, the combustion chamber side is defined as the upper side, and the crank chamber side is defined as the lower side.

[0015] [piston] 1, a first ring groove 201, a second ring groove 202, and a third ring groove 203 are formed in the outer peripheral surface 20a of the piston 20 in this order from the upper side (combustion chamber side) at a predetermined interval in the axial direction of the piston 20. Hereinafter, when the first ring groove 201, the second ring groove 202, and the third ring groove 203 are not to be distinguished from one another, they will be simply referred to as "ring grooves."

[0016] The ring groove is formed around the entire outer peripheral surface 20a as a groove extending annularly around the axis of the piston 20. As shown in FIG. 1, each ring groove is formed to include a pair of groove walls (inner walls) arranged opposite each other in the axial direction of the piston 20. Of the pair of groove walls, the groove wall on the combustion chamber side is referred to as the upper wall W1, and the groove wall on the crankcase side is referred to as the lower wall W2. In addition, in each ring groove, the groove wall connecting the inner peripheral edge of the upper wall W1 and the inner peripheral edge of the lower wall W2 is referred to as the bottom wall W3. Note that a drain hole may be formed in the bottom wall W3 of the third ring groove 203 to discharge oil flowing into the third ring groove 203 to the crankcase. However, the third ring groove 203 does not necessarily have to have a drain hole.

[0017] [Piston rings] As shown in FIG. 1, in an internal combustion engine 100 according to the embodiment, a piston 20 is fitted with a three-ring assembly 110 including two compression rings (pressure rings) including a top ring 1 and a second ring 2, and one oil ring 3. In the embodiment, the top ring 1 is fitted in a first ring groove 201, the second ring 2 is fitted in a second ring groove 202, and the oil ring 3 is fitted in a third ring groove 203. Hereinafter, the state in which the piston rings are fitted to the piston 20 fitted in the cylinder 10 as shown in FIG. 1 will be referred to as the "used state." Also, as shown in FIG. 1, the direction along the central axis of the piston ring (axial direction) is defined as the "up-down direction" of the piston ring. Also, in the axial direction of the piston ring, the combustion chamber side of the internal combustion engine 100 (upper side in FIG. 1) is defined as the "upper side," and the opposite side, i.e., the crank chamber side (lower side in FIG. 1) is defined as the "lower side." Of the axial end faces of the piston ring, the upper face (combustion chamber side) is referred to as the "upper face" and the lower face (crank chamber side) is referred to as the "lower face."

[0018] In addition, with regard to the shape of the outer peripheral sliding surface of a piston ring in this specification, the term "barrel shape" refers to an outer peripheral shape having a barrel surface that is curved so as to be convex outward in the radial direction, including an apex that is the maximum diameter of the piston ring.

[0019] The top ring 1 is an example of a "compression ring" according to the present invention. The top ring 1 is a compression ring that is assembled at the position closest to the combustion chamber (the uppermost position) among the multiple piston rings that make up the piston ring combination 110.

[0020] The top ring 1 has an outer peripheral surface 11, an inner peripheral surface 12, an upper surface 13, and a lower surface 14. The upper surface 13 and the lower surface 14 define the width of the top ring 1 in the axial direction. The shape of the outer peripheral surface 11 will be described later. The top ring 1 is assembled to the piston 20 in the internal combustion engine 100 so that the upper surface 13, which is one of its axial end surfaces, faces upward and the other, the lower surface 14, faces downward, and a part of the outer peripheral surface 11 is in sliding contact with the cylinder wall surface 10a. The cross-sectional shape of the top ring 1 according to this embodiment is rectangular. However, the cross-sectional shape of the top ring 1 is not limited to the above. Compression rings of various cross-sectional shapes can be used as the top ring 1. Furthermore, the top ring 1 is The cross-sectional shape may be a bevel shape, a keystone shape, or a half keystone shape.

[0021] The second ring 2 is a compression ring that is assembled in a position next to the top ring 1 closest to the combustion chamber among the plurality of piston rings that make up the piston ring combination 110.

[0022] The cross-sectional shape of the second ring 2 according to this embodiment is rectangular, similar to that of the top ring 1. The second ring 2 has an outer peripheral surface 21, an inner peripheral surface 22, an upper surface 23, and a lower surface 24. The upper surface 23 and the lower surface 24 define the axial width of the second ring 2. The outer peripheral surface 21 has a tapered shape that increases in width toward the bottom. Note that the shape of the second ring 2 is not limited to the above. Compression rings of various shapes can be used as the second ring 2. For example, the outer peripheral surface 21 of the second ring 2 may be barrel-shaped or tapered. Furthermore, the cross-sectional shape of the second ring 2 may be bevel-shaped, keystone-shaped, half-keystone-shaped, or scraper-shaped.

[0023] The top ring 1 and the second ring 2 have a self-tension so that the outer peripheral surfaces thereof press against the cylinder wall surface 10a when in use, thereby achieving a gas sealing function and an oil sealing function.

[0024] The oil ring 3 is assembled at a position farthest from the combustion chamber among the multiple piston rings that make up the piston ring assembly 110. In other words, the oil ring 3 is assembled closer to the crank chamber than the compression rings (top ring 1 and second ring 2). The oil ring 3 according to this embodiment is a so-called two-piece type combined oil ring, and as shown in FIG. 1, includes a main ring 4 having a pair of integrated rail portions 41, 41, and a coil expander 5 that biases the main ring 4 radially outward.

[0025] The pair of rail portions 41, 41 are formed in an annular shape along the circumferential direction of the oil ring 3 and are arranged side by side in the axial direction of the oil ring 3. The coil expander 5 is arranged radially inside the main ring 4 and biases the main ring 4 radially outward. This causes the pair of rail portions 41, 41 to press against the cylinder wall surface 10a, thereby achieving an oil seal function. When the piston 20 reciprocates within the cylinder 10, the pair of rail portions 41, 41 slide against the cylinder wall surface 10a, causing excess oil adhering to the cylinder wall surface 10a to be scraped off into an oil pan (not shown) on the crankcase side.

[0026] The shape of the oil ring according to the present invention is not limited to the above. The rail portions 41 may have the same or different shapes. The shape of the outer circumferential surface of the rail portion is not particularly limited and may be a straight shape, a symmetrical barrel shape, a tapered shape, an eccentric barrel shape, or the like. The outer circumferential end surfaces of the rail portions may have different shapes. Although the embodiment uses a so-called two-piece oil ring, the oil ring may function as a single component without a coil expander. The oil ring may also be a so-called three-piece oil ring, which may include a pair of segments formed annularly along the circumferential direction of the oil ring and arranged independently of each other in the axial direction of the oil ring, and a spacer expander disposed between the pair of segments. Such a three-piece oil ring is suitable for use in a spark ignition engine that uses, for example, bioethanol as fuel.

[0027] [Hard layer] Here, the outer circumferential surface of the piston ring (compression ring or oil ring) according to the present invention is coated with at least one of a PVD coating, a DLC coating, a chrome plating coating, and a nitrided layer. A hard layer containing at least one of these may be formed. This reduces friction on the outer peripheral surface of the piston ring and improves wear resistance. The term "PVD (Physical Vapor Deposition) coating" refers to a coating formed by the PVD method. The PVD method is also called physical vapor deposition. The term "DLC (Diamond-Like Carbon) coating" refers to an amorphous hard carbon film composed mainly of hydrocarbons and carbon allotropes. The term "chrome-plated coating" refers to a coating formed by chrome plating. The term "nitrided layer" refers to a layer formed by diffusing nitrogen into a metal surface by nitriding. For example, a hard layer containing a PVD coating may be formed on the outer peripheral surface 11 of the top ring 1 and the outer peripheral surface of the oil ring 3 (i.e., the outer peripheral surfaces of the pair of rail portions 41, 41), and a hard layer containing a chrome-plated coating or a nitrided layer may be formed on the outer peripheral surface 21 of the second ring. In the case of a three-piece oil ring, the above-mentioned hard layer may also be formed on its outer circumferential surface (the outer circumferential surfaces of a pair of segments).

[0028] [Outer surface of top ring] As shown in FIG. 1, the outer peripheral surface 11 of the top ring 1 includes an outer peripheral sliding surface 111 provided at the outer peripheral end of the top ring 1 and sliding on the cylinder wall surface 10a of the internal combustion engine 100, a connecting surface 112 connecting the upper surface 13 to the outer peripheral sliding surface 111, and a connecting surface 113 connecting the lower surface 14 to the outer peripheral sliding surface 111. FIG. 2 is an enlarged cross-sectional view of the outer peripheral surface 11 and its vicinity of the top ring 1 according to this embodiment. FIG. 2 shows a cross section perpendicular to the circumferential direction of the top ring 1. The outer peripheral sliding surface 111 includes a top portion having the largest diameter on the top ring 1. When the top ring 1 is in use, the top portion contacts the cylinder wall surface 10a. As shown in FIG. 2, the top portion is designated as P0 in the cross section perpendicular to the circumferential direction of the top ring 1.

[0029] The outer peripheral sliding surface 111 is curved so as to be convex radially outward, including the apex P0, in a cross section perpendicular to the circumferential direction of the top ring 1. The outer peripheral sliding surface 111 according to this embodiment is formed in an arc shape, and is curved so as to decrease in diameter as it moves away from the apex P0 in the axial direction. The outer peripheral sliding surface 111 may be formed by a single arc in a cross section perpendicular to the circumferential direction of the top ring 1, or may be formed by a series of multiple arcs with different curvatures. The apex P0 according to this embodiment is formed as an apex in a cross section perpendicular to the circumferential direction of the top ring 1. The connecting surfaces 112 and 113 may be arc-shaped or linear in cross section. Normally, the connecting surfaces 112 and 113 do not contact (slide) with the cylinder wall surface 10a.

[0030] 2, in a cross section perpendicular to the circumferential direction of the top ring 1, the outer peripheral edge of the upper surface 13 is designated as P3. That is, P3 is the connection point between the upper surface 13 and the outer peripheral surface 11 (specifically, the upper connecting surface 112), and is the upper edge of the outer peripheral surface 11. Also, in a cross section perpendicular to the circumferential direction of the top ring 1, as shown in FIG. 2, the connection point between the outer peripheral sliding surface 111 and the upper connecting surface 112 (i.e., the upper edge of the outer peripheral sliding surface 111) is designated as P2, and the connection point between the outer peripheral sliding surface 111 and the lower connecting surface 113 (i.e., the lower edge of the outer peripheral sliding surface 111) is designated as PL. Here, the positions of the connection points P2, P3, and PL in the cross section perpendicular to the circumferential direction of the top ring 1 will be described in detail with reference to FIG. 3. FIG. 3 is a diagram showing the contour of a portion of the cross section perpendicular to the circumferential direction of the top ring 1. In FIG. 3, the vertical axis (y-axis) is aligned with the radial direction of the top ring 1. The horizontal axis (x-axis) is in the same direction as the axial direction of the top ring 1. In this case, the contour line includes the outer peripheral surface 11, at least a part of the upper surface 13, and at least a part of the lower surface 14. When the cross section of the top ring is rectangular or keystone (full keystone), the center line of the top ring in the width direction is parallel to the vertical axis. In a diagram showing the contour line of a part of a cross section perpendicular to the circumferential direction of the top ring 1, as shown in FIG. 3, Then, a first auxiliary line and a second auxiliary line are drawn, each inclined at a first predetermined angle θa (for example, θa=80°). At this time, the first auxiliary line is a line inclined at the first predetermined angle θa in the positive direction (downward direction in the axial direction) of the horizontal axis (x-axis) with respect to the vertical axis (y-axis), and the second auxiliary line is drawn. is a line inclined at a first predetermined angle θa in the negative direction (upward in the axial direction) of the horizontal axis (x axis) with respect to the vertical axis (y axis). The points of contact between the first and second auxiliary lines and the contour line of the outer peripheral surface 11 of the top ring 1 are determined by translating the first and second auxiliary lines in the direction of the axis. The position of the point of contact between the first auxiliary line and the contour line of the outer peripheral surface 11 of the top ring 1 is the position of the connection point P2 between the outer peripheral sliding surface 111 and the upper connecting surface 112, and the position of the point of contact between the second auxiliary line and the contour line of the outer peripheral surface 11 of the top ring 1 is the position of the connection point PL between the outer peripheral sliding surface 111 and the lower connecting surface 113. The inclination angles of the first and second auxiliary lines are basically 80°, but if the intersections of the outer peripheral surface 11 and the first and second auxiliary lines fall within the outer peripheral sliding surface 111, the inclination angles of the first and second auxiliary lines may be set to 70°, or if this does not change the situation, the inclination angle may be set to 60°.

[0031] Next, as shown in FIG. 3, the second predetermined angle θb (for example, θ b = 5°) and draw the third auxiliary line. At this time, the third auxiliary line is inclined relative to the vertical axis (y-axis). Then, a second predetermined angle θ is formed in the positive direction of the horizontal axis (x-axis) (downward in the axial direction). b is a tilted line. And by translating the third auxiliary line in the horizontal (x) direction, Then, a point of contact between the third auxiliary line and the contour line of the outer peripheral surface 11 of the top ring 1 is found. At this time, the position of the point of contact between the third auxiliary line and the contour line of the outer peripheral surface 11 of the top ring 1 is the position of the connection point P3 between the upper connecting surface 112 and the top surface 13.

[0032] If the cross section of the top ring is half-keystone or tapered, the flat surfaces (i.e., both axial end surfaces) that were polished during the top ring manufacturing process are aligned parallel to the vertical axis, and the connection points P2, P3, and PL are determined in the same manner. The flat surfaces are located on the outer peripheral surface of the top surface 13 or bottom surface 14.

[0033] As shown in FIG. 2, in a cross section perpendicular to the circumferential direction of the top ring 1, an imaginary line L7 is located 2.5 μm inward from the top point P0 in the radial direction of the top ring 1 and extends in the axial direction. This imaginary line is referred to as the seventh imaginary line. As shown in FIG. 2, the seventh imaginary line L7 intersects with the outer peripheral sliding surface 111 at two points. Of the two points where the seventh imaginary line L7 intersects with the outer peripheral sliding surface 111, the upper intersecting point is referred to as P1 and the lower intersecting point is referred to as P4. The imaginary line passing through the intersecting point P1 and the connecting point P2 is referred to as L1 and is referred to as the first imaginary line. The imaginary line passing through the intersecting point P1 and the outer peripheral edge P3 is referred to as L2 and is referred to as the second imaginary line. The imaginary line passing through the top point P0 and the outer peripheral edge P3 is referred to as L3 and is referred to as the third imaginary line. The imaginary line passing through the connecting point P2 and the outer peripheral edge P3 is referred to as L4 and is referred to as the fourth imaginary line. Furthermore, the imaginary line passing through the apex P0 and the connection point P2 is designated L5 and is referred to as the fifth imaginary line. Furthermore, the imaginary line passing through the outer peripheral edge P3 and extending in the radial direction is designated L6 and is referred to as the sixth imaginary line. Furthermore, the imaginary line passing through the apex P0 and extending in the axial direction is designated L8 and is referred to as the eighth imaginary line. Furthermore, the imaginary line passing through the connection point P2 and extending in the radial direction is designated Lh.

[0034] 2, in a cross section perpendicular to the circumferential direction of the top ring 1, the intersection of the eighth imaginary line L8 and the imaginary line Lh is designated as P20, the intersection of the eighth imaginary line L8 and the sixth imaginary line L6 is designated as P30, the intersection of the second imaginary line L2 and the imaginary line Lh is designated as P22, and the intersection of the third imaginary line L3 and the imaginary line Lh is designated as P23.

[0035] As shown in FIG. 1, the width of the top ring 1 in the axial direction (axial width) in a cross section perpendicular to the circumferential direction of the top ring 1 is defined as h1. h1 is determined by the upper and lower surfaces of the top ring 1. Specifically, h1 is the maximum width in the axial direction, and is the axial distance between the point on the top ring 1 closest to the combustion chamber and the point on the top ring 1 closest to the crank chamber. As shown in FIG. 2, the axial width of the outer peripheral sliding surface 111 in a cross section perpendicular to the circumferential direction of the top ring 1 is defined as h2. The axial distance between the top point P0 and the connection point P2 is defined as B1, the axial distance between the top point P0 and the intersection point P1 is defined as B2, and the axial distance between the intersection point P1 and the intersection point P4 is defined as B3. The distance in the axial direction is B3. The angle between the first imaginary line L1 and the seventh imaginary line L7 is θ1, and the angle between the second imaginary line L2 and the seventh imaginary line L7 is θ2.

[0036] When determining P0, P1, P2, P4, B1, B2, θ1, and θ2, a form coder may be used, or a photograph of a cross section perpendicular to the circumferential direction of the piston ring may be taken and enlarged in the vertical direction.

[0037] Fig. 4 is an enlarged cross-sectional view of the top ring 1 to explain the first region A1 to the fourth region A4. Figs. 4(A) to 4(D) illustrate a cross section perpendicular to the circumferential direction of the top ring 1, and the first region A1 to the fourth region A4 are respectively represented by dot patterns. In detail, Fig. 4(A) represents the first region A1, Fig. 4(B) represents the second region A2, Fig. 4(C) represents the third region A3, and Fig. 4(D) represents the fourth region A4.

[0038] As shown in FIG. 4A, in a cross section perpendicular to the circumferential direction of the top ring 1, an area A1 bounded by lines connecting the apex P0, the connection point P2, and the outer peripheral edge P3 is defined as A1 and is referred to as the first area. More specifically, the first area A1 is defined as an area bounded by the third imaginary line L3, the fourth imaginary line L4, and the fifth imaginary line L5. The area of ​​the first area A1 is defined as S1. As shown in FIG. 4B, an area A2 bounded by lines connecting the apex P0, the intersection point P20, and the intersection point P23 is defined as A2 and is referred to as the second area. More specifically, the second area A2 is defined as an area bounded by the third imaginary line L3, the eighth imaginary line L8, and the imaginary line Lh. The area of ​​the second area A2 is defined as S2. As shown in FIG. 4(C), the area surrounded by lines connecting the intersection point P1, the connection point P2, and the outer periphery P3 is designated A3 and referred to as the third area. More specifically, the third area A3 is the area surrounded by the first imaginary line L1, the second imaginary line L2, and the fourth imaginary line L4. The area of ​​the third area A3 is designated S3. As shown in FIG. 4(D), the area surrounded by lines connecting the intersection point P1, the connection point P2, and the intersection point P22 is designated A4 and referred to as the fourth area. More specifically, the fourth area A4 is the area surrounded by the first imaginary line L1, the second imaginary line L2, and the imaginary line Lh. The area of ​​the fourth area A4 is designated S4.

[0039] In this case, the compression ring (top ring 1) according to the embodiment is configured to satisfy the following formula (1). 0.013≦S1 / h1≦0.034...Equation (1) This prevents unburned biofuel from volatilizing and adhering to the cylinder wall surface 10a from flowing from the combustion chamber to the crankcase, and also helps to thin the lubricating oil film left behind by the top ring 1 during the upward stroke. This prevents the unburned biofuel from mixing with the lubricating oil (engine oil) and diluting the lubricating oil. Since the oil that forms the lubricating oil film on the cylinder wall surface 10a is prevented from being diluted by the biofuel, a decrease in the oil's kinematic viscosity is prevented. As a result, peripheral wear of the piston rings can be suppressed. Furthermore, the compression ring according to the present invention can achieve similar effects in engines that use diesel fuel, in which oil dilution is a problem, in addition to biofuel.

[0040] Similarly, from the viewpoint of suppressing dilution of the lubricating oil by the fuel, it is preferable that the compression ring is configured to satisfy any one of the following formulas (2) to (6). 0.011≦S2 / h2≦0.033...Equation (2) 0≦S3 / h1≦0.011...Equation (3) 0≦S3 / h1 / (θ1+θ2)≦0.0009...Equation (4) 0≦(S4 / h2)×(B2 / h2)≦0.0013...Equation (5) 0.1≦B1 / h1≦0.4...Equation (6)

[0041] Furthermore, from the viewpoint of reducing friction of the compression ring, it is preferable that the compression ring be configured to satisfy the following formula (7). B3 / h1≦0.4 Equation (7)

[0042] [simulation] The oil film thickness on the cylinder wall surface when the compression rings according to the examples are used in an internal combustion engine was calculated by simulation. The simulation evaluated Examples 1 to 13 and Comparative Examples 1 to 3. The compression rings according to the examples correspond to the top ring 1 according to the above-described embodiment. Note that the present invention is not limited to the examples described below.

[0043] Table 1 shows the h1 [mm], h2 [mm], and S1 [mm] for Examples 1 to 13 and Comparative Examples 1 to 3. 2 ], S2 [mm 2 ], S3 [mm 2 ], S4 [mm 2 ], B1 [mm], B2 [mm], θ1 [°], and θ2 [°] are shown. Table 2 also shows S1 / h1, S2 / h2, S3 / h1, S3 / h1 / (θ1+θ2), (S4 / h2)×(B2 / h2), and B1 / h1 for Examples 1 to 13 and Comparative Examples 1 to 3, calculated from the values ​​in Table 1. [Table 1] [Table 2]

[0044] In the simulation, assuming that Examples 1 to 13 and Comparative Examples 1 to 3 were used in an internal combustion engine, the oil film thickness of the lubricating oil remaining after the piston passed the top ring was calculated for each 1° crank angle from -180° to 0°, with the compression top dead center being 0°. The simulation results are shown in Table 3. [Table 3] The "oil film thickness" in Table 3 shows the relative value of the oil film thickness for each example and comparative example, with the oil film thickness for Comparative Example 1 set at 1.00. The smaller this value, the more unburned biofuel is prevented from flowing into the crankcase, and the more dilution of the lubricating oil is suppressed. The pass / fail criterion for the oil film thickness was a calculated value (0.80) that was 20% lower than that of Comparative Example 1, with an oil film thickness of 0.80 or less being marked "Good" and an oil film thickness greater than 0.80 being marked "Poor."

[0045] The results shown in Table 3 show that Examples 1 to 13, which satisfy the above formula (1), can make the lubricating oil film on the cylinder wall thinner than Comparative Examples 1 to 3, which do not satisfy the formula (1). In other words, it was found that satisfying formula (1) can suppress dilution of the lubricating oil by unburned biofuel.

[0046] Although the preferred embodiments of the present invention have been described above, the various embodiments described above can be combined as much as possible. [Explanation of symbols]

[0047] 100: Internal combustion engine 110: Piston ring combination 10: Cylinder 20: Piston 1: Top ring 2: Second Ring 3: Oil ring

Claims

1. A compression ring assembled to a piston of an internal combustion engine, an outer peripheral surface of the compression ring having an outer peripheral sliding surface that includes a top portion that is the largest diameter of the compression ring and slides on a cylinder wall surface of the internal combustion engine; and a connection surface that connects the outer peripheral sliding surface to an upper surface, which is a surface on the combustion chamber side of the internal combustion engine, of both axial end surfaces of the compression ring, In a cross section perpendicular to the circumferential direction of the compression ring, The width of the compression ring in the axial direction of the compression ring is defined as h1, The top is P0, A connection point between the outer circumferential sliding surface and the connection surface is defined as P2, The outer periphery of the upper surface is P3, When the area of ​​the region surrounded by the apex P0, the connection point P2, and the outer peripheral edge P3, which are connected by straight lines, is S1, 0.013≦S1 / h1≦0.034; Compression ring.

2. In a cross section perpendicular to the circumferential direction of the compression ring, The width of the outer peripheral sliding surface in the axial direction is defined as h2, A virtual line passing through the connection point P2 and extending in the radial direction of the compression ring is defined as Lh, An intersection point P20 is defined as a virtual line L8 that passes through the top point P0 and extends in the axial direction and an imaginary line Lh. The intersection point of the imaginary line L3 passing through the top point P0 and the outer peripheral edge P3 and the imaginary line Lh is defined as P23. When the area of ​​the region enclosed by the straight lines connecting the apex P0, the intersection point P20, and the intersection point P23 is S2, 0.011≦S2 / h2≦0.033; The compression ring of claim 1 .

3. In a cross section perpendicular to the circumferential direction of the compression ring, Of the two points at which a virtual line L7, which is located 2.5 μm inward from the top point P0 in the radial direction of the compression ring and extends in the axial direction, intersects with the outer peripheral sliding surface, the intersection point on the combustion chamber side is defined as P1, When the area of ​​the region enclosed by the intersection point P1, the connection point P2, and the outer periphery P3, each connected by a straight line, is S3, 0≦S3 / h1≦0.011; 3. The compression ring according to claim 1 or 2.

4. In a cross section perpendicular to the circumferential direction of the compression ring, Of the two points at which a virtual line L7, which is located 2.5 μm inward from the top point P0 in the radial direction of the compression ring and extends in the axial direction, intersects with the outer peripheral sliding surface, the intersection point on the combustion chamber side is defined as P1, The angle formed by the imaginary line L1 and the imaginary line L7 passing through the intersection point P1 and the connection point P2 is defined as θ1, The angle formed by the imaginary line L2 passing through the intersection point P1 and the outer peripheral edge P3 and the imaginary line L7 is defined as θ2, When the area of ​​the region enclosed by the intersection point P1, the connection point P2, and the outer periphery P3, each connected by a straight line, is S3, 0≦S3 / h1 / (θ1+θ2)≦0.0009, 3. The compression ring according to claim 1 or 2.

5. In a cross section perpendicular to the circumferential direction of the compression ring, The width of the outer peripheral sliding surface in the axial direction is defined as h2, Of the two points at which a virtual line L7, which is located 2.5 μm inward from the top point P0 in the radial direction of the compression ring and extends in the axial direction, intersects with the outer peripheral sliding surface, the intersection point on the combustion chamber side is defined as P1, The distance in the axial direction between the top point P0 and the intersection point P1 is B2, A virtual line passing through the connection point P2 and extending in the radial direction of the compression ring is defined as Lh, The intersection point of the imaginary line L2 passing through the intersection point P1 and the outer peripheral edge P3 and the imaginary line Lh is defined as P22, When the area of ​​the region enclosed by the intersection point P1, the connection point P2, and the intersection point P22 connected by lines is S4, 0≦(S4 / h2)×(B2 / h2)≦0.0013; 3. The compression ring according to claim 1 or 2.

6. In a cross section perpendicular to the circumferential direction of the compression ring, When the distance in the axial direction between the top point P0 and the connection point P2 is B1, 0.1≦B1 / h1≦0.4; 3. The compression ring according to claim 1 or 2.

7. a hard layer including at least one of a PVD coating, a DLC coating, a chrome plating coating, and a nitriding layer formed on an outer circumferential surface of the compression ring; 3. The compression ring according to claim 1 or 2.

8. The internal combustion engine is a compression ignition engine.

3. The compression ring according to claim 1 or 2.

Images