compression ring

Abstract

The outer peripheral surface of the compression ring includes a barrel surface, when a width of the outer peripheral surface in the axial direction of the compression ring is set as L1, a condition of 0.2 mm < 1 / 2 x L1 is satisfied, when a distance in the radial direction of the compression ring of each of two points on the barrel surface at 0.1 mm from the outer peripheral apex in the axial direction of the compression ring and the outer peripheral apex is set as d1, and a distance in the radial direction of the compression ring of each of two points on the barrel surface at 1 / 4 x L1 from the outer peripheral apex in the axial direction of the compression ring and the outer peripheral apex is set as d2, a condition of d1 < d2 is satisfied.

Description

TECHNICAL FIELD

[0001] The present application relates to a compression ring. BACKGROUND

[0002] A general automobile-mounted internal combustion engine (engine) adopts a configuration in which three piston rings of two compression rings (pressure rings) including a top ring and a second ring, and an oil ring are provided to a piston attached to a cylinder. The three piston rings are attached to ring grooves formed in an outer circumferential surface of the piston in the order of the top ring, the second ring, and the oil ring from the upper side (combustion chamber side), and slide on a cylinder inner wall surface. The oil ring, which is farthest from the combustion chamber, has an oil seal function of suppressing the outflow (oil rise) of oil to the combustion chamber side by scraping off excess engine oil (lubricating oil) adhering to the cylinder inner wall surface to the crank side, and a function of preventing seizure of the piston accompanying operation of the internal combustion engine by adjusting the amount of oil to appropriately maintain a lubricating oil film on the cylinder inner wall surface. The compression rings have a gas seal function of suppressing the outflow of combustion gas from the combustion chamber side to the crank chamber side (blow-by) by maintaining airtightness, and an oil seal function of suppressing the oil rise by scraping off excess oil that is not scraped off by the oil ring. By such a combination of the piston rings, reduction of blow-by in the internal combustion engine and reduction of oil consumption are achieved.

[0003] In an internal combustion engine for a four-wheel sedan vehicle used in a high rotation speed region, in order to reduce the friction between the outer circumferential surface of the top ring and the cylinder inner wall, and reduce the friction loss of the internal combustion engine, a top ring having an outer circumferential surface of a cylindrical shape that is symmetrical about the vertical direction is mainly adopted. In relation to this, Patent Literature 1 discloses a top ring in which the curvature radius of the central portions of the upper and lower sides of the outer circumferential surface is larger than the curvature radius of the portions on both sides thereof in an outer circumferential surface having a cylindrical shape.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Publication No. H64-8553

[0007] Patent Literature 2: Japanese Patent Application Publication No. S53-22680

[0008] Patent Literature 3: Japanese Patent Application Publication No. 2005-273583

[0009] Patent Literature 4: Japanese Patent Application Publication No. H02-98262

[0010] Patent Literature 5: Japanese Patent Application Publication No. 2002-39384 SUMMARY

[0011] PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] In recent years, hybridization of internal combustion engines and development of internal combustion engines for range extenders are advancing. These internal combustion engines are often operated intermittently while being repeatedly stopped and started. Therefore, the oil temperature is difficult to rise, and the internal combustion engines are often operated in a state where the viscosity of the oil is high compared with conventional internal combustion engines. Therefore, the performance of the piston ring is required to reduce the friction generated between the cylinder inner wall and the ring outer peripheral surface even in such a condition.

[0013] In a condition of low oil temperature where the viscosity of the oil is large, in order to reduce the friction in a fluid lubrication region where the oil film between the cylinder inner wall and the ring outer peripheral surface is thick, it is effective to reduce the contact area between the cylinder inner wall and the ring outer peripheral surface and to reduce the shear resistance of the oil film. Therefore, in the case of a top ring having a cylindrical outer peripheral surface, by reducing the radius of curvature of the outer peripheral surface, it is possible to reduce the friction in the fluid lubrication region. However, in this case, the surface pressure of the ring outer peripheral surface with respect to the cylinder inner wall becomes high, and therefore in a boundary lubrication region near the top and bottom dead centers of the piston where the oil film is thin and the cylinder inner wall and the outer peripheral surface are in solid contact, it is possible that the oil will be excessively scraped off, thereby causing the oil film to break. In this case, it is feared that the friction will rather increase.

[0014] The present application has been achieved in view of the above-described problems, and an object thereof is to provide a technology capable of reducing the friction in a compression ring.

[0015] Solution to the problem

[0016] In order to solve the above-described problems, the present application adopts the following configuration. That is, the present application is a compression ring provided at a ring groove formed in a piston of an internal combustion engine, wherein an outer peripheral surface of the compression ring includes a cylindrical curved surface that includes an outer peripheral apex that becomes a maximum diameter of the compression ring in a cross section of the compression ring orthogonal to a circumferential direction and is curved in a convex manner toward a radially outer side of the compression ring, and the cylindrical curved surface is formed symmetrically in an axial direction of the compression ring with the outer peripheral apex as a boundary in the cross section, and when a width of the outer peripheral surface in the axial direction of the compression ring is set as L1, a condition of 0.2 mm < 1 / 2 x L1 is satisfied, and when a distance of each of two points on the cylindrical curved surface in the axial direction of the compression ring from the outer peripheral apex by 0.1 mm in the cross section is set as d1, and a distance of each of two points on the cylindrical curved surface in the axial direction of the compression ring from the outer peripheral apex by 1 / 4 x L1 in the cross section is set as d2, a condition of d1 < d2 is satisfied.

[0017] Here, the "outer peripheral surface" means a surface connecting the outer peripheries of the axial both end surfaces that define the width (axial dimension) of the piston ring. The "circumferential direction" means the circumferential direction of the piston ring, unless otherwise specified. The "radial direction" means the radial direction of the piston ring, unless otherwise specified. The "axial direction" means the direction along the center axis of the piston ring, unless otherwise specified. Further, the "cylindrical shape" means a shape of a surface that is curved in a convex manner toward the radial direction outer side with a top portion included in the piston ring that becomes the largest diameter, and the "symmetrical cylindrical shape" means a shape of a surface that is a cylindrical shape and is symmetrical in the axial direction (up-down direction) with the top portion as a boundary.

[0018] According to the present application, the fall dl of the position in the region near the outer peripheral top and 0.1 mm above and below from the outer peripheral top is reduced, thereby ensuring the contact area of the cylinder inner wall and the outer peripheral surface, whereby the increase in friction in the boundary lubrication region can be suppressed, and on the other hand, the fall of the position in the oil film formation range in the fluid lubrication region and 1 / 4 x LI above and below from the outer peripheral top is increased, thereby reducing the shear resistance of the oil film, whereby the friction in the fluid lubrication region can be reduced. That is, the increase in friction in the boundary lubrication region can be suppressed and the friction in the fluid lubrication region can be reduced.

[0019] Further, in the present application, it can also be configured that, in the cross section, the cylindrical curved surface is divided into a large diameter region including the outer peripheral top and curved with a first curvature radius, and small diameter regions located on both sides of the large diameter region in the axial direction of the compression ring and curved with a second curvature radius smaller than the first curvature radius, and when the width of the large diameter region in the axial direction of the compression ring is set as L2, the condition of 0.2 mm ≤ L2 ≤ 1 / 2 x LI is satisfied.

[0020] Further, in the present application, it can also be that dl < d2, and 0.05 μm ≤ dl ≤ 0.7 μm and 4.0 μm ≤ d2 ≤ 15.0 μm.

[0021] Further, in the present application, it can also be that, in the cross section, the distance between the midpoint of the outer peripheral surface in the axial direction of the compression ring and the outer peripheral top in the axial direction of the compression ring is 0.05 mm or less.

[0022] Further, in the present application, it can also be that 0.8 mm ≤ LI ≤ 2.5 mm.

[0023] Further, in the present application, it can also be that the internal combustion engine is a gasoline engine.

[0024] Effects of the Invention

[0025] According to the present application, the friction in the compression ring can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a cross-sectional enlarged view of the top ring groove of the internal combustion engine provided with the embodiment of the top ring.

[0027] Figure 2 is a cross-sectional enlarged view of the vicinity of the top ring groove of the internal combustion engine provided with the embodiment of the top ring.

[0028] Figure 3 is a cross-sectional enlarged view of the vicinity of the outer peripheral surface of the top ring.

[0029] Figure 4 is a graph showing the distribution of the oil pressure of Experimental Examples 1 to 3. DETAILED DESCRIPTION

[0030] Hereinafter, a preferred embodiment of the compression ring of the present application will be described with reference to the accompanying drawings. In the embodiment described below, the compression ring of the present application is applied to a top ring, but this is only an example, and the present application is not limited to the top ring. The present application can also be applied to a second ring. Note that the configuration described in the following embodiment is not intended to limit the technical scope of the present application to this alone, unless otherwise specified.

[0031] Figure 1 is a cross-sectional enlarged view of the internal combustion engine provided with the embodiment of the top ring. As shown in Figure 1 , the internal combustion engine 1000 of the embodiment has a cylinder 200, and a piston 100 attached to the cylinder 200.

[0032] As shown in Figure 1 , in the internal combustion engine 1000, a piston clearance PCI is formed by reserving a prescribed separation distance between the outer peripheral surface 110 of the piston and the inner wall 210 of the cylinder. Further, in the outer peripheral surface 110 of the piston, a top ring groove 101, a second ring groove 102, and an oil ring groove 103 are formed in this order at prescribed intervals in the axial direction of the piston 100 from the combustion chamber side. The outer peripheral surface 110 of the piston is divided by the top ring groove 101, the second ring groove 102, and the oil ring groove 103. As shown in Figure 1 , the top ring 10, the second ring 20, and the oil ring 30 are attached to the top ring groove 101, the second ring groove 102, and the oil ring groove 103, respectively. As shown in Figure 1 , the state in which each piston ring is attached to the corresponding ring groove of the piston 100 attached to the cylinder 200 is referred to as the "use state". In the use state, each piston ring has its own tension that presses the outer peripheral surface thereof against the inner wall 210 of the cylinder.

[0033] Further, in the following description, "circumferential direction" means the circumferential direction of the piston ring, unless otherwise specified. "Radial direction" means the radial direction of the piston ring, unless otherwise specified. "Axial direction" means the direction along the central axis of the piston ring, unless otherwise specified. Further, for the piston ring, "outer peripheral surface" means the surface connecting the outer peripheral edges of the axial both end surfaces defining the width (axial dimension) of the ring (or segment), and "inner peripheral surface" means the surface connecting the inner peripheral edges of the axial both end surfaces.

[0034] Here, Figure 1 The arrow in the above indicates the upward and downward direction. In the present specification, for the internal combustion engine 1000, the combustion chamber side is defined as the "upper side", and the crank chamber side is defined as the "lower side". Further, for the piston 100, the cylinder 200, the top ring 10, the second ring 20, and the oil ring 30, the respective axial directions are defined as the upward and downward directions, and the combustion chamber side when they are in the state of use is defined as the respective "upper side", and the opposite side thereof (i.e., the side away from the combustion chamber, the crank chamber side) is defined as the respective "lower side".

[0035] Further, in the present specification, "cylindrical shape" means a surface shape including the top portion which becomes the largest diameter in the piston ring and curved in a convex manner toward the radial direction outer side, and "symmetrical cylindrical shape" means a surface shape which is the cylindrical shape and symmetrical in the axial direction (upward and downward direction) with the top portion as a boundary. As Figure 1 indicated in the above, the internal combustion engine 1000 of the embodiment adopts a combination of the piston ring constituted by the top ring 10 having the outer peripheral surface of the symmetrical cylindrical shape, the second ring 20 having the lower portion of the outer peripheral portion of the undercut shape in which the bottom is cut away, and the oil ring 30 including a pair of segments (side rails) 30a, 30a and a spreader / dispenser 30b which applies a force to the pair of segments toward the radial direction outer side (cylinder inner wall 210). However, the present application is not limited thereto.

[0036] Hereinafter, the top ring 10 of the embodiment will be described in detail. Figure 2 is an enlarged view of the vicinity of the top ring groove 101 of the internal combustion engine 1000 provided with the top ring 10 of the embodiment. As Figure 2 indicated in the above, the top ring groove 101 is formed by a pair of inner walls opposed to each other, and in the pair of inner walls, the inner wall on the upper side is referred to as the upper wall W1, and the inner wall on the lower side is referred to as the lower wall W2. As Figure 2 indicated in the above, the top ring 10 has an upper surface 1 provided on the upper side, a lower surface 2 provided on the lower side, an outer peripheral surface 3 connecting the outer peripheral edge E1 of the upper surface 1 and the outer peripheral edge E2 of the lower surface 2, and an inner peripheral surface 4 connecting the inner peripheral edge E3 of the upper surface 1 and the inner peripheral edge E4 of the lower surface 2. In the state in which the top ring 10 is attached to the top ring groove 101, i.e., in the state of use, the upper surface 1 is located on the upper side and opposed to the upper wall W1 of the top ring groove 101, the lower surface 2 is located on the lower side and opposed to the lower wall W2, and the outer peripheral surface 3 is in sliding contact with the cylinder inner wall 210.

[0037] Figure 3 is an enlarged view of a cross section near the outer peripheral surface 3 of the top ring 10. Figure 3 The reference sign CL1 indicates a straight line (center line) passing through the center of the width in the up-down direction (axial direction) of the top ring 10. As shown in Figure 3 the outer peripheral surface 3 includes a cylindrical surface S1 provided at the outer peripheral end portion of the top ring 10, and a pair of connecting surfaces S2, S2 connecting the cylindrical surface S1 and the upper surface 1 and the lower surface 2, respectively. The outer peripheral edge (hereinafter, referred to as upper edge) E11 of one connecting surface S1 of the pair of connecting surfaces S2, S2 on the upper side (combustion chamber side) connects the cylindrical surface S1 and the outer peripheral edge E1 of the upper surface 1. The outer peripheral edge (hereinafter, referred to as lower edge) E12 of the other connecting surface S2 of the pair of connecting surfaces S2 on the lower side (crank chamber 40 side) connects the cylindrical surface S1 and the outer peripheral edge E2 of the lower surface 2. The pair of connecting surfaces S2, S2 are formed symmetrically with respect to the center line CL1.

[0038] As shown in Figure 3 the cylindrical surface S1 is formed in a cylindrical shape. That is, the cylindrical surface S1 includes an outer peripheral apex P1 which becomes the largest diameter in the top ring 10 and is curved in a prescribed curvature radius in a convex manner toward the radially outer side in a cross section of the top ring 10 orthogonal to the circumferential direction. The outer peripheral apex P1 of the cylindrical surface S1 is located on the radially outermost side of the top ring 10 on the outer peripheral surface 3, and the cylindrical surface S1 is in sliding contact with the cylinder inner wall 210 in the use state. In the present embodiment, the outer peripheral apex P1 is located on the center line CL1 and coincides with the midpoint C1 of the outer peripheral surface 3 in the up-down direction (axial direction). Further, the cylindrical surface S1 is formed in a symmetrical cylindrical shape. That is, the cylindrical surface S1 is formed symmetrically with respect to the outer peripheral apex P1 in a cross section orthogonal to the circumferential direction. Here, the width of the outer peripheral surface 3 in the up-down direction is set to L1. At this time, the top ring 10 is configured to satisfy the condition of 0.2 mm < 1 / 2 x L1.

[0039] As shown in Figure 3 the cylindrical surface S1 is divided into a large-diameter region S11 and a pair of small-diameter regions S12, S12 having different curvature radii in a cross section of the top ring 10 orthogonal to the circumferential direction. The large-diameter region S11 includes the outer peripheral apex P1 and is curved in a first curvature radius R1. The pair of small-diameter regions S12, S12 are located on both sides of the large-diameter region S11 in the up-down direction in a manner sandwiching the large-diameter region S11, and are curved in a second curvature radius R2 smaller than R1. That is, R2 < R1. Here, the width of the large-diameter region S11 in the up-down direction is set to L2. At this time, the top ring 10 is configured to satisfy the condition of 0.2 mm ≤ L2 ≤ 1 / 2 x L1.

[0040] Here, Figure 3Reference signs P2 and P3 indicate two points on the cylindrical surface S1 which are 0.1 mm apart from the outer peripheral apex P1 in the up-down direction. Point P2 is the point on the upper side (combustion chamber side) of the two points, and point P3 is the point on the lower side (crank chamber side) of the two points. Points P2 and P3 are located on the large-diameter region S11. Further, Figure 3 Reference signs P4 and P5 indicate two points on the cylindrical surface S1 which are 1 / 4 x L1 apart from the outer peripheral apex P1 in the up-down direction. Point P4 is the point on the upper side of the two points, and point P5 is the point on the lower side of the two points. Point P4 is located on the small-diameter region S12 on the upper side, and point P5 is located on the small-diameter region S12 on the lower side. Further, the distance of each of points P2 and P3 from the outer peripheral apex P1 in the radial direction is set as a drop d1, and the distance of each of points P4 and P5 from the outer peripheral apex P1 in the radial direction is set as a drop d2. At this time, the top ring 10 is configured to satisfy the condition of d1 < d2.

[0041] Here, generally, in a condition of low oil temperature in which the viscosity of oil becomes large, the friction in the fluid lubrication region in which the oil film between the cylinder inner wall and the ring outer peripheral surface is thick becomes large. In order to reduce the friction in the fluid lubrication region, it is effective to reduce the contact area of the cylinder inner wall and the ring outer peripheral surface, and to reduce the shear resistance of the oil film. On the other hand, if the contact area of the cylinder inner wall and the ring outer peripheral surface is reduced, the surface pressure of the ring outer peripheral surface with respect to the cylinder inner wall becomes high. If the surface pressure is too high, in the boundary lubrication region in which the oil film is thin and solid contact of the cylinder inner wall and the outer peripheral surface occurs, near the top and bottom dead centers of the piston, it is possible that the oil is excessively scraped off, and thus the oil film is broken. Therefore, in the top ring having the outer peripheral surface of a cylindrical shape, in a case where the contact area of the cylinder inner wall and the ring outer peripheral surface is reduced, and the friction in the fluid lubrication region is reduced, by similarly reducing the radius of curvature of the outer peripheral surface, it is feared that the friction due to the oil film breakage of the boundary lubrication region is increased.

[0042] In this regard, the present inventors found that in the fluid lubrication region, the oil film formation range (range in which the oil pressure is high) is reduced to the periphery of the outer peripheral apex rather than the entire region of the outer peripheral surface, and the oil pressure becomes maximum in the vicinity of the outer peripheral apex. Based on this, the present inventors made the difference in the region adjacent to the region in the vicinity of the outer peripheral apex larger than the difference in the region in the vicinity of the outer peripheral apex. Specifically, in the present embodiment, the top ring 10 is configured so as to satisfy the condition of 0.2 mm < 1 / 2 x LI, and the distance dl in the radial direction between each of two points P2, P3 on the cylindrical surface SI that is 0.1 mm apart from the outer peripheral apex PI in the up-down direction (axial direction) and the outer peripheral apex PI, and the distance d2 between each of two points P4, P5 on the cylindrical surface SI that is 1 / 4 x LI apart from the outer peripheral apex PI in the up-down direction and the outer peripheral apex PI satisfy the condition of dl < d2. Accordingly, the difference dl at a position that is 0.1 mm apart from the outer peripheral apex PI in the up-down direction within the region in the vicinity of the outer peripheral apex PI is reduced, and thus the contact area of the cylinder inner wall 210 with the outer peripheral surface 3 is ensured, whereby an increase in friction in the boundary lubrication region can be suppressed, and on the other hand, the difference at a position that is 1 / 4 x LI apart from the outer peripheral apex PI in the up-down direction within the oil film formation range in the fluid lubrication region is increased, and thus the shear resistance of the oil film is reduced, whereby the friction in the fluid lubrication region can be reduced. That is, an increase in friction in the boundary lubrication region can be suppressed and the friction in the fluid lubrication region can be reduced.

[0043] Further, in the present embodiment, the cylindrical surface SI is divided into a large-diameter region SIl that includes the outer peripheral apex PI and is curved with a first curvature radius Rl, and small-diameter regions S12 that are located on both sides of the large-diameter region SIl in the up-down direction (axial direction) and are curved with a second curvature radius R2 that is smaller than the first curvature radius Rl, and the top ring 10 is configured so as to satisfy the condition of 0.2 mm ≤ L2 ≤ 1 / 2 x LI for the width L2 of the large-diameter region SIl in the up-down direction. That is, by setting the up-down width of the large-diameter region SIl, which has a large curvature radius, to be 0.2 mm or more and 1 / 2 x LI or less, the top ring 10 is configured so that the measurement positions of dl, i.e., the two points P2, P3 on the cylindrical surface SI that are 0.1 mm apart from the outer peripheral apex PI, are located on the large-diameter region SIl, and the measurement positions of d2, i.e., the two points P4, P5 on the cylindrical surface SI that are 1 / 4 x LI apart from the outer peripheral apex PI, are located on the small-diameter region S12. Thereby, dl < d2 can be achieved, and thus the friction can be reduced. However, the present application is not limited thereto, and Rl and R2 can be the same or substantially the same.

[0044] Further, on the condition that d1 < d2 is satisfied, it is also possible that 0.05 μm ≤ d1 ≤ 0.7 μm and 4.0 μm ≤ d2 ≤ 15.0 μm, preferably 0.05 μm ≤ d1 ≤ 0.7 μm and 6.0 μm ≤ d2 ≤ 15.0 μm, further preferably 0.05 μm ≤ d1 ≤ 0.7 μm and 8.0 μm ≤ d2 ≤ 15.0 μm. In this way, the friction can be further reduced. However, the present application is not limited thereto.

[0045] Further, in the present embodiment, in the cross section of the top ring 10 orthogonal to the circumferential direction, the midpoint Cl of the outer peripheral surface 3 coincides with the outer peripheral vertex Pl, but the midpoint Cl and the outer peripheral vertex Pl can be offset in the up-down direction. However, the distance between the midpoint Cl and the outer peripheral vertex Pl in the up-down direction (axial direction) is preferably 0.05 mm or less, further preferably 0.02 mm or less.

[0046] Further, it is preferable that 0.8 mm ≤ L1 ≤ 2.5 mm, further preferably 1.0 mm ≤ L1 ≤ 1.5 mm. However, the present application is not limited thereto.

[0047] Further, for the outer peripheral surface of the compression ring of the present application, a hard coating film including at least any one layer of a PVD-treated film, a DLC film, and a chrome-plated film can be provided on the outer peripheral surface of the compression ring. In this way, the friction on the outer peripheral surface of the compression ring can be reduced, and the wear resistance can be improved. Note that the "PVD (physical vapor deposition) -treated film" refers to a coating film formed by a PVD method. The PVD method is one of evaporation methods in which a film is formed by causing particles emitted from a target to adhere to the surface of an object material, and is also called physical vapor deposition. Further, the "DLC (Diamond Like Carbon) film" refers to an amorphous hard carbon film mainly composed of hydrocarbon, an allotrope of carbon. Further, the "chrome-plated film" refers to a coating film formed by plating with chromium.

[0048] Further, the compression ring of the present application is preferably provided in a gasoline engine. However, the internal combustion engine to which the compression ring of the present application is applied is not limited to a gasoline engine. The internal combustion engine can also be a diesel engine.

[0049] [Oil pressure experiment]

[0050] An experiment was performed to measure the oil pressure between the inner wall of the cylinder and the outer peripheral surface of the top ring in the fluid lubrication region. The test machine used in this experiment was provided with an internal combustion engine configuration having a bore of 86 mm and a stroke of 60 mm. In this experiment, the test machine was operated for each of Experimental Example 1 to Experimental Example 3 described below, and the distribution of the oil pressure between the inner wall of the cylinder and the outer peripheral surface of the top ring was measured. The experimental conditions were set to a crank speed of 1200 rpm and an oil temperature of 80°C.

[0051] [Experimental Examples]

[0052] Experimental Examples 1 to 3 use a top ring having an outer peripheral surface with a symmetrical cylindrical shape. The outer peripheral apex P1 of Experimental Examples 1 to 3 is located at the upper and lower center of the outer peripheral surface 3. In Experimental Examples 1 to 3, L1 is set to 1.2 mm, and the size of d2 is made different. d2 becomes a drop at a position 0.3 mm (1 / 4 x L1) above and below the outer peripheral apex P1 located at the upper and lower center of the outer peripheral surface 3. In Experimental Example 1, d2 is set to 15 μm, in Experimental Example 2, d2 is set to 8 μm, and in Experimental Example 3, d2 is set to 4 μm. Note that the present application is not limited to the experimental examples.

[0053] [Experimental Results]

[0054] Figure 4 is a graph showing the distribution of the oil pressure of Experimental Examples 1 to 3. In Figure 4 , the oil pressure distribution at the middle point of the piston stroke at which the piston speed is the maximum speed in the descending stroke, that is, at a crank angle of 77° is shown. Figure 4 The vertical axis of the graph of Figure 4 Experimental Examples 1 to 3 shows that the oil pressure in the fluid lubrication region is confirmed to be in the oil film formation range narrower than the upper and lower width of the ring at 0.6 MPa or more. Further, by comparing Experimental Examples 1 to 3, it is confirmed that the oil film formation range becomes narrower by increasing d2. Thus, it is confirmed that in the fluid lubrication region, the shear resistance of the oil film can be reduced by increasing the drop at a position 1 / 4 x L1 above and below the outer peripheral apex P1.

[0055] The above describes a preferred embodiment of the present application, but the above-described various modes can be combined as much as possible.

[0056] Explanation of Reference Numerals

[0057] 1000: internal combustion engine;

[0058] 100: piston;

[0059] 200: cylinder;

[0060] 10: top ring;

[0061] 3: outer peripheral surface;

[0062] P1: outer peripheral apex;

[0063] S1: cylindrical surface;

[0064] S11: large diameter region;

[0065] S12: small diameter region.

Claims

1. A compression ring which is provided at a ring groove formed at a piston of a cylinder of an internal combustion engine, wherein an outer peripheral surface of the compression ring includes a barrel surface which becomes an outer peripheral apex of a maximum diameter of the compression ring in a cross section of the compression ring orthogonal to a circumferential direction and which is curved in a convex manner toward a radially outer side of the compression ring, and which is formed symmetrically in an axial direction of the compression ring with the outer peripheral apex as a boundary in the cross section, a condition of 0.2 mm < 1 / 2 x Ll is satisfied when a width of the outer peripheral surface in the axial direction of the compression ring is set as Ll, a condition of dl < d2 is satisfied when a distance in a radial direction of the compression ring of each of two points on the barrel surface at 0.1 mm from the outer peripheral apex in the axial direction of the compression ring in the cross section and a distance in the radial direction of the compression ring of each of two points on the barrel surface at 1 / 4 x Ll from the outer peripheral apex in the axial direction of the compression ring in the cross section are set as dl and d2, respectively, in the cross section, the barrel surface is divided into a large-diameter region including the outer peripheral apex and curved with a first radius of curvature and small-diameter regions located on both sides of the large-diameter region in the axial direction of the compression ring and curved with a second radius of curvature smaller than the first radius of curvature, a condition of 0.2 mm ≤ L2 ≤ 1 / 2 x Ll is satisfied when a width of the large-diameter region in the axial direction of the compression ring is set as L2, the two points on the barrel surface at 0.1 mm from the outer peripheral apex in the axial direction of the compression ring are located on the large-diameter region, and the two points on the barrel surface at 1 / 4 x Ll from the outer peripheral apex in the axial direction of the compression ring are located on the small-diameter region.

2. The compression ring according to claim 1, wherein dl < d2, and 0.05 μm ≤ dl ≤ 0.7 μm and 4.0 μm ≤ d2 ≤ 15.0 μm.

3. The compression ring according to claim 1 or 2, wherein in the cross section, a distance in the axial direction of the compression ring of a midpoint of the outer peripheral surface from the outer peripheral apex is 0.05 mm or less.

4. The compression ring according to claim 1 or 2, wherein 0.8 mm ≤ Ll ≤ 2.5 mm.

5. The compression ring according to claim 1 or 2, wherein the internal combustion engine is a gasoline engine. ​

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