Piston and piston ring combination structure and partition ring

Abstract

To provide a technology of a combination structure of a piston and a piston ring, the technology being capable of suppressing troubles due to direct contact between the piston ring and an inner wall of a piston ring groove.SOLUTION: A combination structure of a piston and a piston ring includes a ring groove provided on an outer peripheral surface of the piston for attaching the piston ring, one or multiple piston rings to be attached to the ring groove, and a partition ring to be attached together with the one or multiple piston rings to the ring groove side by side in an axial direction of the piston. The partition ring fits on a bottom groove wall surface that is a bottom face of the ring groove with a predetermined clearance from an inner wall of a cylinder.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a piston and piston ring combination structure and a partition ring. [Background technology]

[0002] The internal combustion engine mounted on a typical automobile employs a configuration in which a combination of piston rings including a compression ring (pressure ring) and an oil ring is fitted in a ring groove formed in the piston. In the axial direction of the piston, the compression ring is provided on the combustion chamber side, and the oil ring is provided on the crank chamber side, and they perform their functions by sliding on the inner wall surface of the cylinder. The oil ring, which is the furthest from the combustion chamber, has an oil seal function that suppresses the outflow of oil to the combustion chamber side (oil rising) by scraping off excess engine oil (lubricating oil) attached to the inner wall surface of the cylinder to the crank side, and a function that prevents the piston from seizing due to the operation of the internal combustion engine by adjusting the amount of oil so that a lubricating oil film is appropriately maintained on the inner wall surface of the cylinder. The compression ring has a gas seal function that suppresses 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 that suppresses oil rising by scraping off excess oil that the oil ring could not scrape off.

[0003] As described above, a piston ring structure for assembling a combination of multiple piston rings to a piston usually employs a structure in which multiple ring grooves, the same number as the number of piston rings, are formed on the outer circumferential surface of the piston, and one piston ring is fitted into each ring groove. Meanwhile, in recent years, with the trend toward reducing the weight of internal combustion engines, efforts have been made to reduce the weight of pistons by shortening the axial length of the piston (hereinafter, axial length). In addition, efforts have been made to reduce the width (i.e., thickness in the axial direction) of piston rings. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Utility Model Application Publication No. 1-21852 [Patent Document 2] Japanese Utility Model Application Publication No. 63-9442 [Patent Document 3] Jpn. Jpn. Published No. 55-2290 [Patent Document 4] Japanese Utility Model Application Publication No. 3-63745 Summary of the Invention [Problem to be solved by the invention]

[0005] In conventional internal combustion engines in which piston rings are assembled to pistons, the piston rings come into direct contact with the inner wall of the ring groove of the piston. As a result, with the recent improvement in thermal efficiency and higher output of engines, there has been a problem that the sliding between the piston rings and the inner wall of the ring groove causes problems such as adhesion between the piston rings and the ring groove and wear of the inner wall of the ring groove. Therefore, a solution to such problems is required.

[0006] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide a technique capable of suppressing defects caused by direct contact between a piston ring and an inner wall of a ring groove of a piston in an assembled structure of a piston and a piston ring mounted in a cylinder. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention adopts the following configuration. That is, the present invention is a combination structure of a piston and a piston ring to be mounted in a cylinder, the outer periphery of the piston the piston has a ring groove for mounting a piston ring provided on a piston surface, one or more piston rings mounted in the ring groove, and a partition ring mounted in the ring groove in line with the one or more piston rings in the axial direction of the piston, the partition ring fitting into a bottom groove wall surface which is the bottom surface of the ring groove with a predetermined gap between the partition ring and the inner wall of the cylinder.

[0008] In the present invention, when a partition ring is attached between the upper groove wall or the lower groove wall of the ring groove and the piston ring, the partition ring functions as a piston land that separates the piston ring from the inner wall of the ring groove. Therefore, compared to a case where a partition ring is not attached between the upper groove wall or the lower groove wall of the ring groove and the piston ring, it is possible to reduce the number of contact points between the piston ring and the inner wall of the ring groove of the piston. Also, in the present invention, when a partition ring is attached between the piston rings, the partition ring functions as a piston land that separates the piston rings. Therefore, compared to a case where the piston rings are separated by a piston land, it is possible to reduce the number of contact points between the piston ring and the inner wall of the ring groove of the piston. As a result, according to the present invention, it is possible to suppress defects caused by direct contact between the piston ring and the inner wall of the ring groove of the piston.

[0009] Furthermore, when a partition ring is fitted between the piston rings, the partition ring functions as a substitute for a piston land that separates the piston rings, and thus it becomes possible to fit a plurality of piston rings in one ring groove. Therefore, according to the present invention, in a device (equipment) in which a plurality of piston rings are assembled to a piston that reciprocates in a cylinder, the number of ring grooves can be reduced compared to a case in which a ring groove is formed for each piston ring. This makes it easier to shorten the axial length of the piston. In addition, since the partition ring is a member separate from the piston, there is less restriction in terms of strength with respect to making the width in the axial direction thin compared to a piston land. Therefore, by increasing the material strength of the partition ring, a partition ring having a thinner width than the piston land can be used in place of the piston land. This also makes it easier to shorten the axial length of the piston. As a result, this can contribute to reducing the weight of the piston, and therefore the weight of the device. In addition, by reducing the number of ring grooves to be formed on the outer circumferential surface of the piston, the strength of the piston can be increased compared to a case in which a ring groove is formed for each piston ring. This can contribute to increasing the output of the internal combustion engine. In addition, by adjusting the width of the partition ring to be fitted in the ring groove, a thin piston ring can be fitted without thinning the ring groove, improving design freedom.

[0010] In addition, in the present invention, the piston may be a piston mounted in the cylinder of an internal combustion engine, and the partition ring may have an upper partition surface facing the upper groove wall surface, which is the groove wall surface on the combustion chamber side of the internal combustion engine, of a pair of inner walls arranged opposite to each other in the ring groove, a lower partition surface facing the lower groove wall surface, which is the groove wall surface on the crank chamber side of the internal combustion engine, of the pair of inner walls arranged opposite to each other in the ring groove, an inner peripheral fitting surface provided on an inner peripheral portion of the partition ring and fitting with the bottom groove wall surface connecting the inner peripheral edge of the upper groove wall surface and the inner peripheral edge of the lower groove wall surface of the ring groove to form a contact state with the bottom groove wall surface, and an outer peripheral separating surface provided on an outer peripheral portion of the partition ring and ensuring a predetermined separation distance between the inner wall of the cylinder of the internal combustion engine.

[0011] In the present invention, the partition ring may have an upper protruding portion that is provided radially inward of the upper partition wall surface of the piston and protrudes toward the combustion chamber, thereby being supported in the axial direction of the piston.

[0012] In the present invention, the partition ring may have a lower protruding portion that is provided radially inward of the lower partition wall surface of the piston and protrudes toward the crank chamber so as to be supported in the axial direction of the piston.

[0013] In the present invention, a plurality of piston rings may be fitted in the ring groove, and the plurality of piston rings may include a top ring fitted between the upper groove wall surface of the ring groove and the upper partition surface of the partition ring, and a second ring fitted between the lower groove wall surface of the ring groove and the lower partition surface of the partition ring.

[0014] In the present invention, a plurality of piston rings may be fitted in the ring groove, and the plurality of piston rings may include a second ring fitted between the upper groove wall surface of the ring groove and the upper partition surface of the partition ring, and an oil ring fitted between the lower groove wall surface of the ring groove and the lower partition surface of the partition ring.

[0015] In the present invention, the crankshaft crankshaft includes a first partition ring as the partition ring, and a second partition ring attached to a position in the ring groove closer to the crank chamber than the first partition ring, wherein the first partition ring has a first upper partition wall surface as the upper partition wall surface, a first lower partition wall surface as the lower partition wall surface, a first inner peripheral fitting surface as the inner peripheral fitting surface, and a first outer peripheral spacing surface as the outer peripheral spacing surface, and the second partition ring has a second upper partition wall surface facing the first lower partition wall surface side of the first partition ring, a second lower partition wall surface facing the lower groove wall surface side of the ring groove, and a second upper partition wall surface provided on an inner peripheral surface of the second partition ring and fitting with the bottom groove wall surface. and a second inner peripheral fitting surface that forms a contact state with the bottom groove wall surface by contacting the bottom groove wall surface with the second partition ring, and a second outer peripheral spacing surface that is provided on the outer peripheral surface of the second partition ring and ensures a predetermined spacing distance between the inner wall of the cylinder, and a plurality of piston rings are fitted in the ring groove, and the plurality of piston rings may include a top ring that is fitted between the upper groove wall surface of the ring groove and the first upper partition surface of the first partition ring, a second ring that is fitted between the first lower partition surface of the first partition ring and the second upper partition surface of the second partition ring, and an oil ring that is fitted between the lower groove wall surface of the ring groove and the second lower partition surface of the second partition ring.

[0016] In the present invention, a plurality of piston rings are fitted in the ring groove, and a partition portion that separates the ring groove is formed by a plurality of partition rings arranged between the plurality of piston rings so as to overlap each other in the axial direction of the piston, and in the partition portion, the partition rings adjacent to each other in the axial direction may have different properties.

[0017] In the present invention, the material of the partition ring disposed closest to the combustion chamber in the partition portion may have higher thermal conductivity than the materials of the other partition rings.

[0018] In the present invention, the material of the partition ring disposed closest to the crank chamber in the partition portion may have a higher heat set resistance than the materials of the other partition rings.

[0019] In the present invention, at least one of the upper partition wall surface of the partition ring arranged closest to the combustion chamber side in the partition portion and the lower partition wall surface of the partition ring arranged closest to the crank chamber side is provided with a void. A gap forming portion may be provided.

[0020] In addition, in the present invention, in at least any of the partition rings of the partition portion, a notch extending in a circumferential direction of the partition ring may be formed between the outer peripheral spacing surface and the lower partition surface, or between the outer peripheral spacing surface and the upper partition surface.

[0021] In the present invention, the partition ring that is second from the combustion chamber side among the multiple partition rings included in the partition portion may have a smaller radial thickness of the piston than the partition ring that is closest to the combustion chamber side.

[0022] In addition, in the present invention, the multiple piston rings installed in the ring groove include a compression ring and an oil ring arranged below the compression ring, the partition portion is arranged between the compression ring and the oil ring, the oil ring has a pair of segments arranged side by side in the axial direction of the piston, and a spacer expander arranged between the pair of segments and biasing the pair of segments radially outward of the piston, and at least a portion of the lower partition surface of the partition ring arranged closest to the crank chamber in the partition portion may be inclined so as to approach the crank chamber as it moves radially outward of the piston.

[0023] In the present invention, an adhesive layer may be provided between the partition rings adjacent to each other in the axial direction in the partition portion.

[0024] The present invention may further include a retaining ring provided between the bottom groove wall surface and the partition portion, which holds at least any of the partition rings of the partition portions from both axial sides of the piston, and the multiple partition rings may be engaged with the bottom groove wall surface via the retaining ring.

[0025] In the present invention, the partition ring may have a pair of abutment ends that face each other to form a abutment.

[0026] In the present invention, the pair of abutment ends may each be formed in a key shape so as to be engaged with each other while overlapping in the radial direction of the partition ring.

[0027] In addition, in the present invention, the piston may have a protrusion protruding into the ring groove, and the joint may include a receiving portion capable of receiving the protrusion, and the protrusion may be received in the receiving portion, thereby regulating the rotation of the partition ring relative to the piston.

[0028] The present invention may also relate to a partition ring that is mounted axially alongside one or more piston rings in a ring groove for mounting a piston ring provided on the outer peripheral surface of a piston that is mounted in a cylinder, and that, when the partition ring is mounted in the ring groove in a use state, fits into a bottom groove wall surface that is the bottom surface of the ring groove with a predetermined gap between it and the inner wall of the cylinder.

[0029] In the present invention, the piston is a piston that is attached to the cylinder of an internal combustion engine, and the partition ring is a piston that is attached to the ring groove and is disposed between a pair of inner walls that are opposed to each other in the ring groove when the partition ring is attached to the ring groove. The partition ring may be provided with an upper partition surface facing the upper groove wall surface, which is the groove wall surface on the combustion chamber side of the internal combustion engine, a lower partition surface facing the lower groove wall surface, which is the groove wall surface on the crank chamber side of the internal combustion engine, of a pair of inner walls arranged opposite to each other in the ring groove in the said state of use, an inner peripheral fitting surface provided on the inner peripheral portion of the partition ring and which, in the said state of use, forms a contact state with the bottom groove wall surface by fitting with the bottom groove wall surface connecting the inner peripheral edge of the upper groove wall surface and the inner peripheral edge of the lower groove wall surface of the ring groove, and an outer peripheral separating surface provided on the outer peripheral portion of the partition ring and which, in the said state of use, ensures a predetermined separation distance between the inner wall of the cylinder of the internal combustion engine. Effect of the Invention

[0030] According to the present invention, in a combined structure of a piston and a piston ring mounted in a cylinder, it is possible to suppress defects caused by direct contact between the piston ring and the inner wall of the ring groove of the piston. [Brief description of the drawings]

[0031] [Figure 1] 1 is a cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a first embodiment. [Diagram 2]1 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a first embodiment. [Diagram 3] FIG. 2 is a top view of a partition ring according to an embodiment. [Figure 4] 1 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a first modified example of the first embodiment. FIG. [Diagram 5] 1 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a second modified example of the first embodiment. FIG. [Figure 6] 10 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a third modified example of the first embodiment. FIG. [Figure 7] FIG. 6 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a second embodiment. [Figure 8] 10 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a first modified example of the second embodiment. FIG. [Figure 9] FIG. 11 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a second modified example of the second embodiment. [Figure 10] FIG. 11 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a third embodiment. [Figure 11] FIG. 11 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a fourth embodiment. [Figure 12] FIG. 13 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a first modified example of the fourth embodiment. [Figure 13] FIG. 13 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a second modified example of the fourth embodiment. [Figure 14] FIG. 13 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a third modified example of the fourth embodiment. [Figure 15] FIG. 13 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a fourth modified example of the fourth embodiment. [Figure 16] FIG. 4 is a diagram showing an example of a gap forming portion. [Figure 17] FIG. 11 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a fifth modified example of the fourth embodiment. [Figure 18]FIG. 13 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a sixth modified example of the fourth embodiment. [Figure 19] FIG. 13 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a seventh modified example of the fourth embodiment. [Figure 20] FIG. 13 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to an eighth modified example of the fourth embodiment. [Figure 21] FIG. 13 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a ninth modified example of the fourth embodiment. [Figure 22] FIG. 11 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a fifth embodiment. [Figure 23] FIG. 13 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a first modified example of the fifth embodiment. [Figure 24] 11A and 11B are diagrams illustrating examples of the shape of a cutout portion. [Diagram 25] FIG. 21 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a second modified example of the fifth embodiment. [Figure 26] FIG. 21 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a third modified example of the fifth embodiment. [Figure 27] FIG. 11 is a partial cross-sectional view of an internal combustion engine equipped with a piston ring structure according to a sixth embodiment. [Figure 28] FIG. 1 is a cross-sectional view showing a variation of the partition ring. [Figure 29] FIG. 2 is a cross-sectional view showing a variation of the partition ring. [Diagram 30] FIG. 3 is a cross-sectional view showing a variation of the partition ring. [Diagram 31] A cross-sectional view (4) showing a variation of the partition ring. [Diagram 32] A cross-sectional view (5) showing a variation of the partition ring. [Diagram 33] A cross-sectional view (6) showing a variation of the partition ring. [Diagram 34] A cross-sectional view (7) showing a variation of the partition ring. [Diagram 35] A cross-sectional view (8) showing a variation of the partition ring. [Diagram 36] A cross-sectional view (9) showing a variation of the partition ring. [Figure 37] A cross-sectional view (10) showing a variation of the partition ring. [Figure 38] FIG. 11 is a cross-sectional view showing a variation of the partition ring. [Figure 39] A cross-sectional view (12) showing a variation of the partition ring. [Diagram 40] A cross-sectional view (13) showing a variation of the partition ring. [Diagram 41] A cross-sectional view (14) showing a variation of the partition ring. [Diagram 42] A cross-sectional view (15) showing a variation of the partition ring. [Diagram 43] 11A to 11C are diagrams showing variations in the shape of the abutment of the partition ring. [Diagram 44] FIG. 1 is a diagram for explaining a piston ring structure equipped with anti-rotation means. [Diagram 45] FIG. 2 is a diagram for explaining a piston ring structure equipped with anti-rotation means. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Note that the configurations described in the following embodiments are not intended to limit the technical scope of the invention unless otherwise specified.

[0033] <Embodiment 1> FIG. 1 is a cross-sectional view of an internal combustion engine 100 equipped with a piston and piston ring combination structure (hereinafter, piston ring structure) 110 according to the first embodiment. FIG. 2 is a partial cross-sectional view of the internal combustion engine 100 equipped with the piston ring structure 110 according to the first embodiment. FIG. 2 illustrates a cross section perpendicular to the circumferential direction of the piston ring. As shown in FIG. 1, the internal combustion engine 100 according to the embodiment has a cylinder 10 and a piston 20 attached to the cylinder 10. In the internal combustion engine 100, the combustion chamber side indicated by reference numeral 30 is the upper side, and the crank chamber side indicated by reference numeral 40 is the lower side. As shown in FIG. 2, the internal combustion engine 100 has two compression rings (pressure rings) including a top ring 1 and a second ring 2, and one oil ring. The piston 20 is fitted with a combination of three piston rings, including the piston ring 3.

[0034] [Overall configuration] As shown in FIG. 2, in the internal combustion engine 100, a piston gap PC1 is formed by ensuring a predetermined separation distance d between the outer peripheral surface 20a of the piston 20 and the inner wall surface 10a of the cylinder 10. In addition, a first ring groove 201 and a second ring groove 202 are formed in the outer peripheral surface 20a of the piston 20 in this order from the upper side (combustion chamber 30 side) with a predetermined interval in the axial direction of the piston 20. The piston ring structure 110 is a structure for assembling a piston ring to the piston 20 of the internal combustion engine 100. The piston ring structure 110 includes a first ring groove 201 and a second ring groove 202 for mounting the piston rings, which are provided in the outer peripheral surface 20a of the piston 20, a top ring 1, a second ring 2, an oil ring 3, and a partition ring 4. In this specification, when the top ring 1, the second ring 2, and the oil ring 3 are described without distinction, they are simply referred to as "piston rings". A piston ring is a sliding member that is assembled to a piston mounted in a cylinder of an internal combustion engine and slides on the inner wall surface of the cylinder with the reciprocating motion of the piston. As shown in FIG. 2, a state in which the piston 20 to which the piston rings and the partition ring 4 are assembled is mounted in the cylinder 10 is referred to as a "use state". As shown in FIG. 2, a direction (axial direction) along the central axis of the piston 20, the piston ring, and the partition ring 4 is defined as an "upper-lower direction". In the axial direction of the piston ring and the partition ring 4, the combustion chamber 30 side in the internal combustion engine 100 (upper side in FIG. 2) is defined as an "upper side", and the opposite side, i.e., the crank chamber side (lower side in FIG. 2) is defined as a "lower side". As shown in FIG. 2, in the piston ring structure 110, a top ring 1, a second ring 2, and a partition ring 4 are mounted in a first ring groove 201, and an oil ring 3 is mounted in a second ring groove 202. Hereinafter, each configuration of the piston ring structure 110 will be described.

[0035] [Ring groove] The first ring groove 201 and the second ring groove 202 are formed on the entire circumference of the outer circumferential surface 20a as grooves with a rectangular cross section extending annularly around the axis of the piston 20. As shown in FIG. 2, the second ring groove 202 is formed at a position lower than the first ring groove 201 on the outer circumferential surface 20a of the piston 20. The first ring groove 201 and the second ring groove 202 are each formed to include a pair of groove walls (inner walls) arranged opposite each other vertically. Of the pair of groove walls, the upper groove wall is referred to as the upper groove wall W1, and the lower groove wall is referred to as the lower groove wall W2. In addition, in each of the first ring groove 201 and the second ring groove 202, the groove wall connecting the inner peripheral edge of the upper groove wall W1 and the inner peripheral edge of the lower groove wall W2 is referred to as the bottom groove wall W3. In this example, the first ring groove 201 corresponds to the "ring groove" according to the present invention. The connection portion (corner) between the upper groove wall W1 and the bottom groove wall W3 and the connection portion (corner) between the lower groove wall W2 and the bottom groove wall W3 may be rounded or C-shaped.

[0036] [Top ring] The top ring 1 is a compression ring that is assembled to the uppermost position of the piston 20 in the axial direction among the three piston rings. The top ring 1 in this example is formed in a so-called rectangular shape, and has a rectangular cross section. 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 outer peripheral surface 11 is formed into a barrel face that is curved so as to protrude radially outward. 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 both end surfaces in the axial direction, faces upward and the lower surface 14, which is the other, faces downward, and the outer peripheral surface 11 is in sliding contact with the inner wall surface 10a of the cylinder 10. The top ring 1 has a self-tension such that the outer peripheral surface 11 presses against the inner wall surface 10a of the cylinder 10 in a used state. This provides a gas seal function and an oil seal function. In addition, the top ring according to the present invention The shape of the top ring is not limited to the above. Various shapes can be used for the top ring. For example, the outer peripheral surface of the top ring may be straight-faced or tapered. The cross-sectional shape of the top ring may be keystone, half keystone, or internal bevel.

[0037] [Second Ring] The second ring 2 is a compression ring that is assembled to the lower side of the top ring 1 in the axial direction of the piston 20. That is, the second ring 2 is assembled between the top ring 1 and the oil ring 3. 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 width of the second ring 2 in the axial direction. The second ring 2 is formed in a so-called rectangular shape, and the outer peripheral surface 21 of the second ring 2 has a tapered shape that is inclined so that the diameter increases toward the lower side. In the internal combustion engine 100, the second ring 2 is assembled to the piston 20 so that the upper surface 23, which is one of both end surfaces in the axial direction, faces upward and the lower surface 24, which is the other, faces downward, and the outer peripheral surface 21 is in sliding contact with the inner wall surface 10a of the cylinder 10. The second ring 2 has a self-tension so that the outer peripheral surface 21 presses against the inner wall surface 10a of the cylinder 10 in a used state. This provides a gas seal function and an oil seal function. The shape of the second ring according to the present invention is not limited to the above. Various shapes can be adopted for the second ring. For example, the outer peripheral surface of the second ring may be a barrel face or a straight face. The second ring may be a scraper ring having an undercut or a napier ring. The cross-sectional shape of the second ring may be a keystone, half keystone, or internal bevel.

[0038] [Oil ring] Of the three piston rings, the oil ring 3 is the piston ring that is assembled to the lowest position in the axial direction of the piston 20. The oil ring 3 is a so-called three-piece type combined oil ring, and includes a pair of segments 31, 31 (an example of a pair of sliding parts) and a spacer expander 32 (an example of an expander), as shown in Fig. 2.

[0039] The pair of segments 31, 31 are formed in an annular shape around the axis of the oil ring 3, and are arranged side by side in the axial direction independently of each other. In the oil ring 3 according to this embodiment, the pair of segments 31, 31 have the same shape. However, in the present invention, the pair of segments may have different shapes. Hereinafter, when the pair of segments 31, 31 are to be distinguished from each other, the segment 31 provided on the upper side (combustion chamber 30 side) is referred to as the upper segment 31U, and the segment 31 provided on the lower side (crank chamber 40 side) is referred to as the lower segment 31L. When there is no need to distinguish between them, they are simply referred to as the segment 31. As shown in FIG. 2, the segment 31 has an outer peripheral surface 311, an inner peripheral surface 312, an upper surface 313, and a lower surface 314. The upper surface 313 and the lower surface 314 define the width of the segment 31 in the axial direction. In the internal combustion engine 100, the segment 31 is assembled to the piston 20 such that an upper surface 313, which is one of both end surfaces in the axial direction, faces upward and a lower surface 314, which is the other, faces downward, and the outer circumferential surface 311 is in sliding contact with the inner wall surface 10a of the cylinder 10. The spacer expander 32 is provided between the pair of segments 31, 31, and has a self-tensioning force so as to expand in diameter when in use. As a result, the upper segment 31U and the lower segment 31L are urged radially outward by the spacer expander 32, and the outer circumferential surface 311 presses the inner wall surface 10a of the cylinder 10. This provides an oil seal function. The shape of the oil ring according to the present invention is not limited to the above. The oil ring may be, for example, a so-called two-piece oil ring. The two-piece oil ring has an oil ring main body formed in an annular shape around the axis and a coil expander (an example of an expander) that urges the oil ring main body radially outward, and the oil ring main body has a coil expander protruding radially outward. The term "oil ring" refers to an oil ring in which a pair of rails (an example of a pair of sliding parts) that are aligned in the axial direction of the oil ring are formed. The oil ring may also be in a form that does not include a spacer expander or a coil expander and functions as a single unit.

[0040] [Partitioning] The partition ring 4 is a ring-shaped member that functions as a substitute for a piston land by being fitted in a ring groove (in this example, the first ring groove 201) together with one or more piston rings (in this example, the top ring 1 and the second ring 2). The partition ring 4 in this example is formed in a so-called rectangular shape, and a cross section perpendicular to the circumferential direction is rectangular. However, the present invention is not limited to this. The partition ring 4 has an outer peripheral separation surface 41, an inner peripheral fitting surface 42, an upper partition wall surface 43, and a lower partition wall surface 44. The upper partition wall surface of the partition ring may be parallel to the upper groove wall of the ring groove, or may be inclined relative to the upper groove wall. Similarly, the lower partition wall surface of the partition ring may be parallel to the lower groove wall of the ring groove, or may be inclined relative to the lower groove wall. In addition, each corner of the partition ring may be chamfered, step cut, or the like.

[0041] As shown in FIG. 2, the upper partition surface 43 faces the upper groove wall W1 of the first ring groove 201 in the use state. As a result, a space in which the top ring 1 can be attached is defined between the upper groove wall W1 and the upper partition surface 43. The lower partition surface 44 faces the lower groove wall W2 of the first ring groove 201 in the use state. As a result, a space in which the second ring 2 can be attached is defined between the lower groove wall W2 and the lower partition surface 44. The inner fitting surface 42 is provided on the inner periphery of the partition ring 4. The inner fitting surface 42 fits with the bottom groove wall W3 in the use state to form a contact state with the bottom groove wall W3. The inner fitting surface 42 in this example is in contact with the bottom groove wall W3 over the entire circumference. However, the present invention is not limited to this, and it is sufficient that at least a part of the inner fitting surface is in contact with the bottom groove wall. In addition, the inner circumferential fitting surface 42 of this example is fitted with the bottom groove wall W3 so that the partition ring 4 can slide on the bottom groove wall W3 along the axial direction. Therefore, the partition ring 4 is movable along the axial direction together with the top ring 1 and the second ring 2. However, the present invention is not limited to this. The inner circumferential fitting surface may be fitted with the bottom groove wall to such an extent that the partition ring cannot move along the axial direction. The outer circumferential separation surface 41 is provided on the outer periphery of the partition ring 4 and connects the outer circumferential edge of the upper partition wall surface 43 and the outer circumferential edge of the lower partition wall surface 44. In addition, the outer circumferential separation surface 41 secures a predetermined separation distance d1 between the inner wall surface 10a of the cylinder 10 in the usage state. In other words, the partition ring 4 is separated from the inner wall surface 10a of the cylinder 10. Here, FIG. 3 is a top view of the partition ring 4 according to the first embodiment (viewed from above in the axial direction). 3, the partition ring 4 includes a pair of joint ends 410, 420 that face each other to form a joint G1. Examples of a method for assembling the partition ring 4 include, but are not limited to, shrink fitting, friction welding, screwing, adhesion, and welding. When friction welding is performed, the partition ring 4 is fitted into the first ring groove 201 and then slid against the bottom groove wall W3 to fix them together.

[0042] The material of the partition ring 4 is not particularly limited, but for example, steel, cast iron, Cu alloy, or aluminum alloy can be used. In addition, the surface of the partition ring 4 can be coated with a resin film, a nitriding film, a Ni-P plating film, a chrome plating film, or the like. Alternatively, a coating may be formed that includes at least one layer selected from the group consisting of a film, a chemical conversion coating, an oxidation coating, a paint film, a PVD coating, and a DLC coating. The term "resin coating" refers to a coating formed from a resin material. The term "nitriding coating" refers to a coating formed by infiltrating nitrogen into the metal surface through nitriding. The term "Ni-P plating coating" refers to a coating formed by permeating nitrogen into the metal surface through nitriding. The term "coating" refers to a coating formed by Ni-P plating. The "Ni-P plating" is, for example, electroless Ni-P plating, but is not limited thereto. Also, the term "chrome plating coating" refers to a coating formed by Ni-P plating. " refers to a coating formed by chrome plating. Chrome plating is also called industrial chrome plating. "Chemical conversion coating" refers to a coating formed by chemical conversion treatment. Examples of chemical conversion treatments include iron oxide treatment (black dye), phosphate treatment, and chromate treatment. "Oxidation treatment coating" refers to a coating formed by oxidizing the metal surface through oxidation treatment. An example of oxidation treatment is anodizing. "Coating" refers to a film formed by applying paint. Examples of "coating" and "resin coating" include resin coating made from water-based or oil-based resin paint. "PVD (physical vapor deposition) treatment coating" refers to a film formed by applying PV This refers to the coating formed by the D method. Also, "DLC (Diamond Like Carbon) Coating" " refers to an amorphous hard carbon film composed mainly of hydrocarbons and carbon allotropes. Such a coating is preferably formed on the inner peripheral fitting surface 42, the upper partition wall surface 43, and the lower partition wall surface 44, which are the contact areas between the partition ring 4 and other members. By forming such a coating, the wear resistance, etc. of the partition ring 4 can be increased, and defects due to direct contact between base materials, such as adhesion between the partition ring 4 and other members, can be prevented.

[0043] As shown in FIG. 2, in the piston ring structure 110, the top ring 1 is fitted between the upper groove wall W1 of the first ring groove 201 and the upper partition wall surface 43 of the partition ring 4, the second ring 2 is fitted between the lower groove wall W2 of the first ring groove 201 and the lower partition wall surface 44 of the partition ring 4, and the oil ring 3 is fitted in the second ring groove 202. In the piston ring structure 110, the lower surface 14 of the top ring 1 faces the upper partition wall surface 43 of the partition ring 4, and the upper surface 23 of the second ring 2 faces the lower partition wall surface 44 of the partition ring 4. Therefore, when the top ring 1 moves downward, the partition ring 4 abuts against the top ring 1, and when the second ring 2 moves upward, the partition ring 4 abuts against the second ring 2. In other words, the partition ring 4 is interposed between the top ring 1 and the second ring 2, and the top ring 1 and the second ring 2 are separated by the partition ring 4. In this way, in the piston ring structure 110, the partition ring 4 functions in place of a piston land separating the top ring 1 and the second ring 2, thereby forming a space surrounded by the lower surface 14 of the top ring 1, the upper surface 23 of the second ring 2, the outer peripheral separating surface 41 of the partition ring 4, and the inner wall surface 10a of the cylinder 10, which can adjust the pressure between the top ring 1 and the second ring 2 and function as an oil reservoir.

[0044] [Actions and Effects] As described above, the piston ring structure 110 according to the first embodiment includes the first ring groove 201 formed in the outer peripheral surface 20a of the piston 20, a plurality of piston rings (the top ring 1 and the second ring 2) mounted in the first ring groove 201, and the partition ring 4 mounted in the first ring groove 201 in line with the top ring 1 and the second ring 2 in the axial direction of the piston 20. The partition ring 4 has an upper partition wall surface 43 facing the upper groove wall W1 side of the first ring groove 201, a lower partition wall surface 44 facing the lower groove wall W2 side of the first ring groove 201, an inner peripheral fitting surface 42 that fits with the bottom groove wall W3 of the first ring groove 201 to form a contact state with the bottom groove wall W3, and an outer peripheral separating surface 41 that ensures a predetermined separation distance d1 between the partition ring 4 and the inner wall surface 10a of the cylinder 10.

[0045] In an internal combustion engine in which multiple piston rings are assembled to a piston, if a ring groove is formed for each piston ring, the interval between the ring grooves must be shortened in order to shorten the axial length of the piston. However, if the interval between the ring grooves is shortened, the piston land between adjacent ring grooves in the axial direction becomes thin, making it difficult to maintain the strength of the piston. In addition, from the viewpoint of the machining accuracy of the ring grooves, it is also difficult to shorten the axial length of the piston.

[0046] According to the piston ring structure 110, the partition ring 4 functions as a substitute for a piston land separating the top ring 1 and the second ring 2, so that the top ring 1 and the second ring 2 can be fitted in the first ring groove 201. Therefore, it is not necessary to form a ring groove for fitting the top ring 1 and a ring groove for fitting the second ring 2 separately on the outer circumferential surface 20a of the piston 20. In other words, according to the piston ring structure 110, a plurality of piston rings (the top ring 1 and the second ring 2 in this example) can be fitted in one ring groove. As a result, in an internal combustion engine in which a plurality of piston rings are assembled to a piston, the number of ring grooves can be reduced compared to a case in which a ring groove is formed for each piston ring. This makes it easy to shorten the axial length of the piston 20. As a result, according to the piston ring structure 110, it is possible to contribute to weight reduction of the piston, and therefore to weight reduction of the internal combustion engine. In addition, by reducing the width of the piston ring and the partition ring, it is possible to shorten the axial length of the piston 20. In addition, by reducing the number of ring grooves to be formed on the outer circumferential surface 20a of the piston 20, the strength of the piston can be increased compared to the case where a ring groove is formed for each piston ring, which contributes to increasing the output of the internal combustion engine.

[0047] Furthermore, according to the piston ring structure 110, the design constraints on the land volume can be relaxed. Here, the "land volume" refers to the volume of the space surrounded by the piston rings adjacent in the axial direction, the outer peripheral surface of the piston, and the inner wall surface of the cylinder. In this example, since the partition ring 4 functions as a substitute for the piston land, the volume of the space surrounded by the lower surface 14 of the top ring 1, the upper surface 23 of the second ring 2, and the outer peripheral surface 20a of the piston 20 corresponds to the land volume. Since the partition ring 4 is formed as a member separate from the piston 20, the constraints in terms of strength with respect to making the width in the axial direction thin are smaller than those of the piston land. Therefore, according to the piston ring structure 110, the degree of freedom in designing the land volume can be increased. This can improve the degree of freedom in designing the pressure adjustment function and the function as an oil reservoir.

[0048] In addition, since pistons are usually made of aluminum alloy, aluminum adhesion may occur at the contact points between the piston ring and the inner wall of the ring groove. In addition, the inner wall of the ring groove may be worn due to sliding between the piston ring and the inner wall of the ring groove. In this regard, in the piston ring structure 110, the partition ring 4 is interposed between the top ring 1 and the second ring 2 instead of the piston land, so that the contact points between the top ring 1 and the inner wall of the ring groove and the contact points between the second ring 2 and the inner wall of the ring groove can be reduced compared to the case where the piston rings are separated from each other by the piston land. Therefore, defects due to direct contact between the piston ring and the inner wall of the ring groove of the piston, such as aluminum adhesion, can be suppressed. In addition, by appropriately selecting the material and surface treatment of the partition ring 4, it is possible to prevent the occurrence of defects such as aluminum adhesion at the contact points between the top ring 1 or the second ring 2 and the partition ring 4, and to improve the wear resistance of the partition ring 4.

[0049] In addition, in the piston ring structure 110, a contact state is formed between the bottom groove wall W3 of the first ring groove 201 and the inner fitting surface 42 of the partition ring 4, so that the amount of oil and gas passing between the bottom groove wall W3 of the first ring groove 201 and the inner fitting surface 42 of the partition ring 4 can be reduced. In other words, oil rising and gas outflow from the inner side of the partition ring 4 can be suppressed. In addition, since the bottom groove wall W3 of the first ring groove 201 and the inner fitting surface 42 of the partition ring 4 are in contact with each other, heat of the piston 20 can be transferred from the bottom groove wall W3 to the piston ring via the inner fitting surface 42 of the partition ring 4, and the heat can be released to the cylinder 10 with which the piston ring slides. Note that in the present invention, at least a part of the inner fitting surface It is sufficient that the groove wall is in contact with the bottom groove wall.

[0050] Furthermore, the partition ring 4 has a pair of abutment ends 410, 420 that face each other to form abutment G1. Since the abutment G1 is formed in the partition ring 4, the partition ring 4 can be detached from the ring groove, and the partition ring 4 can also be replaced. In addition, the abutment G1 can absorb the volume expansion of the partition ring 4 due to thermal expansion by stretching in the circumferential direction. Therefore, it is possible to suppress the volume expansion of the partition ring 4 due to thermal expansion proceeding radially inward, causing the inner peripheral fitting surface 42 of the partition ring 4 to bite into the bottom groove wall W3 of the first ring groove 201, and the volume expansion of the partition ring 4 proceeding radially outward, causing a change in the land volume. In addition, it is possible to suppress the application of excessive force to the partition ring 4 due to thermal expansion of the piston 20, and the partition ring 4 from biting into the piston. In addition, since an appropriate abutment gap is formed, it is possible to suppress the abutment of the abutment ends 410, 420 with each other during thermal expansion of the partition ring 4, and as a result, it is possible to prevent the formation of a gap on the inner peripheral side of the partition ring 4.

[0051] The number of piston rings according to the present invention is not limited to three, and the types of piston rings are not limited to the above-mentioned top ring, second ring, and oil ring. For example, the multiple piston rings may be configured to include one compression ring and one oil ring, and the compression ring, the oil ring, and a partition ring may be mounted in one ring groove. In addition, the number of compression rings assembled to the piston may be three or more, and for example, the compression ring may be disposed at a position closer to the crank chamber side than the oil ring. In that case, the oil ring, the compression ring, and the partition ring may be mounted in one ring groove, and the partition ring may be interposed between the oil ring and the compression ring. In addition, the number of oil rings may be two or more, and a partition ring may be interposed between the oil rings.

[0052] [Modification of the first embodiment] The following describes modifications of the embodiment 1. In the following description, differences from the above-described piston ring structure 110 will be mainly described, and similar configurations will be denoted by the same reference numerals and detailed description will be omitted.

[0053] [Variation 1] 4 is a partial cross-sectional view of an internal combustion engine 100A equipped with a piston ring structure 110A according to Modification 1 of Embodiment 1. The piston ring structure 110A according to Modification 1 differs from the piston ring structure 110 in that the partition ring 4 is mounted in a second ring groove 202 in line with the second ring 2 and the oil ring 3 in the axial direction of the piston 20. In this example, the second ring groove 202 corresponds to the "ring groove" according to the present invention.

[0054] As shown in Fig. 4, in the piston ring structure 110A, the upper partition wall surface 43 of the partition ring 4 faces the upper groove wall W1 of the second ring groove 202, so that a space in which the second ring 2 can be fitted is defined between the upper groove wall W1 and the upper partition wall surface 43. In addition, the lower partition wall surface 44 of the partition ring 4 faces the lower groove wall W2, so that a space in which the oil ring 3 can be fitted is defined between the lower groove wall W2 and the lower partition wall surface 44. As shown in Fig. 4, in the piston ring structure 110A, the top ring 1 is fitted in the first ring groove 201, the second ring 2 is fitted between the upper groove wall W1 of the second ring groove 202 and the upper partition wall surface 43 of the partition ring 4, and the oil ring 3 is fitted between the lower groove wall W2 of the second ring groove 202 and the lower partition wall surface 44 of the partition ring 4. In the piston ring structure 110A, the lower surface 24 of the second ring 2 faces the upper partition wall surface 43 of the partition ring 4, and the upper segment 31U faces the lower partition wall surface 44 of the partition ring 4. The upper surfaces 313 of the second ring 2 and the oil ring 3 face each other. Therefore, when the second ring 2 moves downward, the partition ring 4 comes into contact with the second ring 2, and when the oil ring 3 moves upward, the partition ring 4 comes into contact with the oil ring 3. In other words, the partition ring 4 is interposed between the second ring 2 and the oil ring 3.

[0055] The piston ring structure 110A according to the first modification can also provide the same effects as those of the piston ring structure 110 described above. That is, according to the piston ring structure 110A, a plurality of piston rings (the second ring 2 and the oil ring 3 in this example) can be mounted in one ring groove, and the number of ring grooves can be reduced. This makes it easy to shorten the axial length of the piston 20. As a result, the piston ring structure 110A can contribute to reducing the weight of the piston, and therefore the weight of the internal combustion engine. In addition, since the partition ring 4 functions as a substitute for a piston land that separates the piston rings, the number of contact points between the piston rings and the inner wall of the piston ring groove can be reduced compared to the case where the piston rings are separated by a piston land. This can suppress defects caused by direct contact between the piston rings and the inner wall of the piston ring groove.

[0056] [Variation 2] FIG. 5 is a partial cross-sectional view of an internal combustion engine 100B equipped with a piston ring structure 110B according to Modification 2 of the embodiment 1. The piston ring structure 110B according to Modification 2 differs from the piston ring structure 110 in that only a first ring groove 201 is formed on the outer peripheral surface 20a of the piston 20, that a top ring 1, a second ring 2, and an oil ring 3 are attached to the first ring groove 201, and that a partition ring indicated by reference numeral 5 is attached to the first ring groove 201 in addition to the partition ring 4. In Modification 2, the first ring groove 201 corresponds to the "ring groove" according to the present invention. In addition, in Modification 2, the partition ring 4, the outer peripheral separating surface 41, the inner peripheral fitting surface 42, the upper partition wall surface 43, and the lower partition wall surface 44 correspond to the "first partition ring", the "first outer peripheral separating surface", the "first inner peripheral fitting surface", the "first upper partition wall surface", and the "first lower partition wall surface" according to the present invention, respectively. The partition ring 5 has an outer peripheral separating surface 51, an inner peripheral fitting surface 52, an upper partition wall surface 53, and a lower partition wall surface 54. In the second modification, the partition ring 5, the outer peripheral separating surface 51, the inner peripheral fitting surface 52, the upper partition wall surface 53, and the lower partition wall surface 54 correspond to the "second partition ring", the "second outer peripheral separating surface", the "second inner peripheral fitting surface", the "second upper partition wall surface", and the "second lower partition wall surface" according to the present invention, respectively. The partition ring 5 also corresponds to the "partition ring" according to the present invention.

[0057] 5, in the piston ring structure 110B, the partition ring 4 and the partition ring 5 are mounted in the first ring groove 201 together with the top ring 1, the second ring 2, and the oil ring 3 in the axial direction of the piston 20. An upper partition wall surface 43 of the partition ring 4 faces the upper groove wall W1 of the first ring groove 201, thereby defining a space between the upper groove wall W1 and the upper partition wall surface 43 in which the top ring 1 can be mounted. In addition, a lower partition wall surface 44 of the partition ring 4 faces the lower groove wall W2, thereby defining a space between the lower groove wall W2 and the lower partition wall surface 44 in which the second ring 2 and the oil ring 3 can be mounted.

[0058] In the piston ring structure 110B, the partition ring 5 is attached to the first ring groove 201 at a position lower than the partition ring 4. In the piston ring structure 110B, the upper partition wall surface 53 of the partition ring 5 faces the lower partition wall surface 44 of the partition ring 4, so that a space in which the second ring 2 can be attached is defined between the lower partition wall surface 44 of the partition ring 4 and the upper partition wall surface 53 of the partition ring 5. In addition, the lower partition wall surface 54 of the partition ring 5 faces the lower groove wall W2. Thereby, a space in which the oil ring 3 can be attached is defined between the lower groove wall W2 and the lower partition surface 54.

[0059] In addition, the inner circumferential fitting surface 52 provided on the inner circumferential portion of the partition ring 5 is fitted with the bottom groove wall W3 in a use state, thereby forming a contact state between the bottom groove wall W3. The inner circumferential fitting surface 52 of this example is in contact with the bottom groove wall W3 over the entire circumference. However, the present invention is not limited to this, and it is sufficient that at least a part of the second inner circumferential fitting surface is in contact with the bottom groove wall. In addition, the inner circumferential fitting surface 42 of this example is fitted with the bottom groove wall W3 so that the partition ring 4 can slide on the bottom groove wall W3 along the axial direction. Therefore, the partition ring 4 is movable along the axial direction together with the top ring 1 and the second ring 2. However, the present invention is not limited to this. In addition, the outer circumferential separation surface 51 provided on the outer circumferential portion of the partition ring 5 ensures a predetermined separation distance d2 between the inner wall surface 10a of the cylinder 10 in a use state.

[0060] 5, in the piston ring structure 110B, the top ring 1 is fitted between the upper groove wall W1 of the first ring groove 201 and the upper partition wall surface 43 of the partition ring 4, the second ring 2 is fitted between the lower partition wall surface 44 of the partition ring 4 and the upper partition wall surface 53 of the partition ring 5, and the oil ring 3 is fitted between the lower groove wall W2 of the first ring groove 201 and the lower partition wall surface 54 of the partition ring 5. That is, in the piston ring structure 110B, the partition ring 4 is interposed between the top ring 1 and the second ring 2, and the partition ring 5 is interposed between the second ring 2 and the oil ring 3. In this way, in the piston ring structure 110B, the partition ring 4 and the partition ring 5 function as substitutes for piston lands.

[0061] The piston ring structure 110B according to the second modification can also provide the same effect as the piston ring structure 110 described above. That is, according to the piston ring structure 110B, a plurality of piston rings (a top ring 1, a second ring 2, and an oil ring 3 in this example) can be fitted in one ring groove, and the number of ring grooves can be reduced. This makes it easier to shorten the axial length of the piston 20. In particular, in the second modification, three piston rings can be fitted in one ring groove, so that the structure of the piston 20 can be further simplified, and it becomes easier to shorten the axial length of the piston 20. In addition, the partition ring 4 and the partition ring 5 function as a substitute for a piston land that separates the piston rings from each other, and thus defects caused by direct contact between the piston rings and the inner wall of the ring groove of the piston can be suppressed.

[0062] [Variation 3] 6 is a partial cross-sectional view of an internal combustion engine 100C equipped with a piston ring structure 110C according to Modification 3 of Embodiment 1. The piston ring structure 110C according to Modification 3 differs from the piston ring structure 110 in that a retaining portion H1 is formed on a bottom groove wall W3 of the first ring groove 201.

[0063] As shown in FIG. 6, in the piston ring structure 110C, a part of the bottom groove wall W3 of the first ring groove 201 is recessed to form a holding portion H1 that holds the partition ring 4. The holding portion H1 is formed as an inner wall of a groove formed around the entire circumference of the bottom groove wall W3, and holds the partition ring 4 to restrict movement of the partition ring 4 along the axial direction. The holding portion H1 is formed to include an upper restricting wall W31 and a lower restricting wall W32 that are arranged opposite to each other vertically, and a fitting wall W33 that connects the inner peripheral edge of the upper restricting wall W31 and the inner peripheral edge of the lower restricting wall W32. The upper restricting wall W31 abuts against the upper bulkhead surface 43 of the partition ring 4 to restrict upward movement of the partition ring 4. The lower restricting wall W 32 restricts the downward movement of the partition ring 4 by contacting with the lower partition wall surface 44 of the partition ring 4. The fitting wall W33 fits with the inner peripheral fitting surface 42 of the partition ring 4. Here, in the piston ring structure 110C, the distance d3 between the upper limiting wall W31 and the upper groove wall W1 in the axial direction is set to be larger than the width t1 of the top ring 1 in the axial direction. This allows clearances to be formed between the top ring 1 and the upper groove wall W1 and between the top ring 1 and the upper partition wall surface 43. However, the present invention is not limited to this. Also, in the piston ring structure 110C, the distance d4 between the lower limiting wall W32 and the lower groove wall W2 in the axial direction is set to be larger than the width t2 of the second ring 2 in the axial direction. This allows clearances to be formed between the second ring 2 and the lower partition wall surface 44 and between the second ring 2 and the lower groove wall W2. However, the present invention is not limited to this.

[0064] The retaining portion H1 can be combined with other aspects of the present invention. For example, in the piston ring structure 110A, the partition ring 4 may be retained by the retaining portion H1. In the piston ring structure 110B, either the partition ring 4 or the partition ring 5 may be retained by the retaining portion H1, or two retaining portions H1 may be formed, and both the partition ring 4 and the partition ring 5 may be retained by the retaining portion H1, respectively.

[0065] <Embodiment 2> 7 is a partial cross-sectional view of an internal combustion engine 200 equipped with a piston ring structure 120 according to embodiment 2. The piston ring structure 120 according to embodiment 2 will be described below, focusing on the differences from the piston ring structure 110 according to embodiment 1, and similar configurations will be denoted by the same reference numerals and detailed description thereof will be omitted.

[0066] 7, the piston ring structure 120 differs from the piston ring structure 110 in that a partition ring 6 is attached to a first ring groove 201 instead of the partition ring 4. The partition ring 6 differs from the partition ring 4 in that a cross section perpendicular to the circumferential direction is formed into a T-shape. In this example, the first ring groove 201 corresponds to the "ring groove" according to the present invention.

[0067] The partition ring 6 has an outer peripheral spacing surface 61, an inner peripheral fitting surface 62, an upper partition wall surface 63, a lower partition wall surface 64, an upper protruding portion 65, and a lower protruding portion 66. In this example, the partition ring 6 corresponds to the "partition ring" according to the present invention.

[0068] 7, in the piston ring structure 120, the partition ring 6, the top ring 1, and the second ring 2 are mounted in the first ring groove 201 in a line up in the axial direction of the piston 20. An upper partition wall surface 63 of the partition ring 6 faces the upper groove wall W1 of the first ring groove 201, thereby defining a space between the upper groove wall W1 and the upper partition wall surface 63 into which the top ring 1 can be mounted. In addition, a lower partition wall surface 64 of the partition ring 6 faces the lower groove wall W2, thereby defining a space between the lower groove wall W2 and the lower partition wall surface 64 into which the second ring 2 can be mounted.

[0069] In addition, the inner circumferential fitting surface 62 provided on the inner circumferential portion of the partition ring 6 is fitted with the bottom groove wall W3 in the usage state, thereby forming a contact state with the bottom groove wall W3. In this example, the inner circumferential fitting surface 62 is in contact with the bottom groove wall W3 over the entire circumference. However, the present invention is not limited to this, and it is sufficient that at least a portion of the second inner circumferential fitting surface is in contact with the bottom groove wall. In addition, the outer circumferential separating surface 61 provided on the outer circumferential portion of the partition ring 6 ensures a predetermined separation distance d5 between it and the inner wall surface 10a of the cylinder 10 in the usage state.

[0070] As shown in Figure 7, in the piston ring structure 120, the top ring 1 is fitted between the upper groove wall W1 of the first ring groove 201 and the upper partition surface 63 of the partition ring 6, the second ring 2 is fitted between the lower groove wall W2 of the first ring groove 201 and the lower partition surface 64 of the partition ring 6, and the oil ring 3 is fitted in the second ring groove 202.

[0071] The piston ring structure 120 according to the second embodiment can also provide the same effects as the piston ring structure 110 according to the first embodiment. That is, according to the piston ring structure 120, a plurality of piston rings (in this example, the top ring 1 and the second ring 2) can be mounted in one ring groove, and the number of ring grooves can be reduced. This makes it easy to shorten the axial length of the piston 20.

[0072] Further, in the piston ring structure 120, the partition ring 6 has an upper protruding portion 65 and a lower protruding portion 66. As shown in FIG. 7, the upper protruding portion 65 is provided inside the upper partition wall surface 63 in the radial direction of the piston 20, and protrudes toward the combustion chamber 30 with respect to the upper partition wall surface 63. The upper protruding portion 65 is provided inside the top ring 1 in the radial direction of the piston 20, that is, on the inner circumferential surface 12 side of the top ring 1. The upper protruding portion 65 is supported in the axial direction of the piston 20 by abutting against the upper groove wall W1 of the first ring groove 201. This restricts the upward movement of the partition ring 6. Here, in the piston ring structure 120, the protruding amount of the upper protruding portion 65 with respect to the upper partition wall surface 63, that is, the distance h1 between the top of the upper protruding portion 65 and the upper partition wall surface 63 in the axial direction, is set to be larger than the width t1 of the top ring 1 in the axial direction. This allows a clearance to be formed between the top ring 1 and the upper groove wall W1 or between the top ring 1 and the upper partition surface 63. However, the present invention is not limited to this. The upper protrusion 65 only needs to be configured so that a clearance can be formed between the top ring 1 and the upper partition surface 63 by being supported in the axial direction in contact with the inner wall of the first ring groove 201, and h1 may be set smaller than t1 according to the shape of the inner peripheral edge of the ring groove to ensure the clearance. The top of the upper protrusion 65 may be a flat surface parallel to the upper partition surface 63, or may not be a flat surface. The top may be a curved R surface or an inclined surface. The edge may be chamfered. The lower protrusion 66 is provided inside the lower partition surface 64 in the radial direction of the piston 20, and protrudes toward the crank chamber 40 with respect to the lower partition surface 64. The lower protrusion 66 is provided radially inward of the second ring 2, that is, on the inner circumferential surface 22 side of the second ring 2. The lower protrusion 66 is supported in the axial direction of the piston 20 by abutting against the lower groove wall W2 of the first ring groove 201. This restricts the partition ring 6 from moving downward.Here, in the piston ring structure 120, the amount of protrusion of the lower protrusion 66 from the lower partition surface 64, that is, the distance h2 between the top of the lower protrusion 66 and the lower partition surface 64 in the axial direction is set to be larger than the width t2 of the second ring 2 in the axial direction. This allows a clearance to be formed between the second ring 2 and the lower partition surface 64 and between the second ring 2 and the lower groove wall W2. However, the present invention is not limited to this. The lower protrusion 66 only needs to be configured so that a clearance can be formed between the second ring 2 and the lower partition surface 64 by being supported in the axial direction in contact with the inner wall of the first ring groove 201, and h2 may be set to be smaller than t2 according to the shape of the inner peripheral edge of the ring groove to ensure the clearance. In addition, the top of the lower protrusion 66 may be a flat surface parallel to the lower partition surface 64, or may not be a flat surface. The top may be a curved R surface or an inclined surface. In addition, a chamfer may be formed on the edge. Furthermore, the partition ring 6 may be movable in the axial direction, or the movement in the axial direction may be restricted.

[0073] 7, the upper protrusion 65 and the lower protrusion 66 are formed to include a part of the inner peripheral fitting surface 62. Therefore, the axial length of the inner peripheral fitting surface 62 is longer than the axial length of the outer peripheral separating surface 61. As a result, the first ring groove 20 By lengthening the inner peripheral fitting surface 62 in contact with the bottom groove wall W3 of the piston 20 in the axial direction, heat from the piston 20 is easily transferred from the bottom groove wall W3 to the partition ring 6, and the heat can be easily released from the partition ring 6 to the cylinder 10 via the piston ring. The partition ring 6 may have only one of the upper protrusion 65 and the lower protrusion 66. In other words, the cross section of the partition ring 6 perpendicular to the circumferential direction may be formed in an L-shape.

[0074] [Modification of the second embodiment] The following describes a modification of the embodiment 2. In the following description, differences from the above-described piston ring structure 120 will be mainly described, and similar configurations will be denoted by the same reference numerals and detailed description will be omitted.

[0075] [Variation 1] 8 is a partial cross-sectional view of an internal combustion engine 200A equipped with a piston ring structure 120A according to Modification 1 of Embodiment 2. The piston ring structure 120A according to Modification 1 differs from the piston ring structure 120 in that the partition ring 6 is mounted in a second ring groove 202 in line with the second ring 2 and the oil ring 3 in the axial direction of the piston 20. In this example, the second ring groove 202 corresponds to the "ring groove" according to the present invention.

[0076] As shown in Fig. 8, in the piston ring structure 120A, an upper partition wall surface 63 of the partition ring 6 faces the upper groove wall W1 of the second ring groove 202, so that a space in which the second ring 2 can be fitted is defined between the upper groove wall W1 and the upper partition wall surface 63. In addition, a lower partition wall surface 64 of the partition ring 6 faces the lower groove wall W2, so that a space in which the oil ring 3 can be fitted is defined between the lower groove wall W2 and the lower partition wall surface 64. As shown in Fig. 8, in the piston ring structure 120A, the top ring 1 is fitted in the first ring groove 201, the second ring 2 is fitted between the upper groove wall W1 of the second ring groove 202 and the upper partition wall surface 63 of the partition ring 6, and the oil ring 3 is fitted between the lower groove wall W2 of the second ring groove 202 and the lower partition wall surface 64 of the partition ring 6.

[0077] Furthermore, in the piston ring structure 120A, the upper protrusion 65 is supported in the axial direction of the piston 20 by abutting against the upper groove wall W1 of the second ring groove 202. This restricts the upward movement of the partition ring 6. Here, in the piston ring structure 120A, the protrusion amount h1 of the upper protrusion 65 relative to the upper partition surface 63 is set to be larger than the width t2 of the second ring 2 in the axial direction. This allows a clearance to be formed between the second ring 2 and the upper groove wall W1 or between the second ring 2 and the upper partition surface 63. However, the present invention is not limited to this. In order to ensure the clearance, h1 may be set smaller than t2 according to the shape of the inner peripheral edge of the ring groove. Also, in the piston ring structure 120A, the lower protrusion 66 is supported in the axial direction of the piston 20 by abutting against the lower groove wall W2 of the second ring groove 202. This restricts the downward movement of the partition ring 6. Here, in the piston ring structure 120A, the protrusion amount h2 of the lower protruding portion 66 relative to the lower partition surface 64 is set to be larger than the axial width t3 of the oil ring 3. This makes it possible to form clearances between the oil ring 3 and the lower partition surface 64 and between the oil ring 3 and the lower groove wall W2. However, the present invention is not limited to this. In order to ensure the clearance, h2 may be set smaller than t3 depending on the shape of the inner peripheral edge of the ring groove.

[0078] [Variation 2] 9 is a partial cross-sectional view of an internal combustion engine 200B equipped with a piston ring structure 120B according to Modification 2 of the embodiment 2. The piston ring structure 120B according to Modification 2 is different from the piston 20 in that only the first ring groove 201 is formed on the outer circumferential surface 20a of the piston 20. The piston ring structure 120 differs from the piston ring structure 120 in that the top ring 1, the second ring 2, and the oil ring 3 are mounted, and that a partition ring indicated by reference numeral 7 is mounted in the first ring groove 201 in addition to the partition ring 6. In the second modification, the first ring groove 201 corresponds to the "ring groove" according to the present invention. In the second modification, the partition ring 6, the outer peripheral separating surface 61, the inner peripheral fitting surface 62, the upper partition wall surface 63, and the lower partition wall surface 64 correspond to the "first partition ring", the "first outer peripheral separating surface", the "first inner peripheral fitting surface", the "first upper partition wall surface", and the "first lower partition wall surface" according to the present invention, respectively. The partition ring 7 has an outer peripheral separating surface 71, an inner peripheral fitting surface 72, an upper partition wall surface 73, a lower partition wall surface 74, an upper protrusion 75, and a lower protrusion 76. In the second modification, the partition ring 7, the outer peripheral separating surface 71, the inner peripheral fitting surface 72, the upper partition wall surface 73, and the lower partition wall surface 74 correspond to the "second partition ring", "second outer peripheral separating surface", "second inner peripheral fitting surface", "second upper partition wall surface", and "second lower partition wall surface" according to the present invention, respectively. The partition ring 7 also corresponds to the "partition ring" according to the present invention.

[0079] As shown in FIG. 9, in the piston ring structure 120B, the partition ring 6 and the partition ring 7 are mounted in the first ring groove 201 together with the top ring 1, the second ring 2, and the oil ring 3 in the axial direction of the piston 20. The partition ring 7 is mounted in the first ring groove 201 at a position lower than the partition ring 6. The upper partition wall surface 63 of the partition ring 6 faces the upper groove wall W1 of the first ring groove 201, so that a space in which the top ring 1 can be mounted is defined between the upper groove wall W1 and the upper partition wall surface 63. The upper partition wall surface 73 of the partition ring 7 faces the lower partition wall surface 64 of the partition ring 6, so that a space in which the second ring 2 can be mounted is defined between the lower partition wall surface 64 of the partition ring 6 and the upper partition wall surface 73 of the partition ring 7. The lower partition wall surface 74 of the partition ring 7 faces the lower groove wall W2, so that a space in which the oil ring 3 can be mounted is defined between the lower groove wall W2 and the lower partition wall surface 74. This makes it possible to fit three piston rings in one ring groove.

[0080] In addition, the inner circumferential fitting surface 72 provided on the inner circumferential portion of the partition ring 7 fits with the bottom groove wall W3 in the usage state, thereby forming a contact state with the bottom groove wall W3. In this example, the inner circumferential fitting surface 72 contacts the bottom groove wall W3 over the entire circumference. However, the present invention is not limited to this, and it is sufficient that at least a portion of the second inner circumferential fitting surface contacts the bottom groove wall. In addition, the outer circumferential separating surface 71 provided on the outer circumferential portion of the partition ring 7 ensures a predetermined separation distance d6 between itself and the inner wall surface 10a of the cylinder 10 in the usage state.

[0081] 9, the upper protrusion 75 of the partition ring 7 is provided inward of the upper partition wall surface 73 in the radial direction of the piston 20, and protrudes toward the combustion chamber 30 from the upper partition wall surface 73. The lower protrusion 76 is provided inward of the lower partition wall surface 74 in the radial direction of the piston 20, and protrudes toward the crank chamber 40 from the lower partition wall surface 74.

[0082] In the piston ring structure 120B, the upper protrusion 65 of the partition ring 6 abuts against the upper groove wall W1 of the first ring groove 201, thereby supporting the piston 20 in the axial direction. This restricts the partition ring 6 from moving upward. In the piston ring structure 120B, the protrusion amount h1 of the upper protrusion 65 is set to be larger than the width t1 of the top ring 1 in the axial direction, and a clearance can be formed between the top ring 1 and the upper groove wall W1 and between the top ring 1 and the upper partition wall surface 63. However, the present invention is not limited to this. In order to ensure the clearance, h1 may be set to be smaller than t1 depending on the shape of the inner peripheral edge of the ring groove. Also, in the piston ring structure 120B, the lower protrusion 66 of the partition ring 6 abuts against the upper protrusion 75 of the partition ring 7. The lower protrusion 66 and the upper protrusion 75 are supported in the axial direction of the piston 20 by the protrusions W2 of the first ring groove 201. This restricts the partition ring 6 from moving downward and the partition ring 7 from moving upward. Here, in the piston ring structure 120B, the sum of the protrusion amount h2 of the lower protrusion 66 and the protrusion amount h3 of the upper protrusion 75 is set to be larger than the width t2 of the second ring 2 in the axial direction. This allows clearances to be formed between the second ring 2 and the lower partition wall surface 64 and between the second ring 2 and the upper partition wall surface 73. However, the present invention is not limited to this. Also, in the piston ring structure 120B, the lower protrusion 76 of the partition ring 7 is supported in the axial direction of the piston 20 by abutting against the lower groove wall W2 of the first ring groove 201. This restricts the partition ring 7 from moving downward. Here, in the piston ring structure 120B, the protrusion amount h4 of the lower protrusion 76 is set to be larger than the width t3 of the oil ring 3 in the axial direction. This makes it possible to form clearances between the oil ring 3 and the lower protrusion 76 and between the oil ring 3 and the lower groove wall W2. However, the present invention is not limited to this. In order to ensure clearances, h4 may be set smaller than t3 depending on the shape of the inner peripheral edge of the ring groove.

[0083] Note that the second embodiment can be combined with the other embodiments described above. For example, in the above-described piston ring structure 120B, the partition ring 4 of the piston ring structure 110B may be used instead of the partition ring 6. Also, the partition ring 5 of the piston ring structure 110B may be used instead of the partition ring 7. Also, when the partition ring 4 or the partition ring 6 is applied, it may be held by the holding portion H1 of the piston ring structure 110C.

[0084] <Embodiment 3> 10 is a partial cross-sectional view of an internal combustion engine 300 equipped with a piston ring structure 130 according to embodiment 3. The piston ring structure 130 according to embodiment 3 will be described below, focusing on the differences from the piston ring structure 110 according to embodiment 1, and similar configurations will be denoted by the same reference numerals and detailed description thereof will be omitted.

[0085] The piston ring structure 130 includes a first ring groove 201, a second ring groove 202, and a third ring groove 203 for mounting piston rings provided on the outer peripheral surface 20a of the piston 20, a top ring 1, a second ring 2, an oil ring 3, and a partition ring 4. As shown in FIG. 10, the third ring groove 203 is formed at a position lower than the second ring groove 202 on the outer peripheral surface 20a of the piston 20. In the piston ring structure 130, the top ring 1 and the partition ring 4 are mounted in the first ring groove 201, the second ring 2 is mounted in the second ring groove 202, and the oil ring 3 is mounted in the third ring groove 203. In this example, the first ring groove 201 corresponds to the "ring groove" according to the present invention.

[0086] As shown in FIG. 10, in the piston ring structure 130, the partition ring 4 and the top ring 1 are mounted in the first ring groove 201 in line with each other in the axial direction of the piston 20. The upper partition wall surface 43 of the partition ring 4 faces the upper groove wall W1 of the first ring groove 201, so that the upper partition wall surface 43 is in contact with the upper groove wall W1. The lower partition wall surface 44 of the partition ring 4 faces the lower groove wall W2, so that a space in which the top ring 1 can be mounted is defined between the lower groove wall W2 and the lower partition wall surface 44. As shown in FIG. 10, in the piston ring structure 130, the top ring 1 is mounted between the lower groove wall W2 of the first ring groove 201 and the lower partition wall surface 44 of the partition ring 4. Therefore, when the top ring 1 moves upward, the partition ring 4 comes into contact with the top ring 1. In other words, the partition ring 4 is interposed between the upper groove wall W1 of the first ring groove 201 and the top ring 1.

[0087] The piston ring structure 130 according to the third embodiment can also provide the same effects as those of the above-described piston ring structure 110. That is, the partition ring 4 functions as a substitute for a piston land that separates the upper groove wall W1 of the first ring groove 201 and the top ring 1, thereby reducing the number of contact points between the top ring 1 and the inner wall of the ring groove. This makes it possible to suppress defects caused by direct contact between the piston ring and the inner wall of the piston ring groove.

[0088] The third embodiment can be modified as appropriate. For example, the partition ring 4 may be interposed between the lower groove wall W2 of the first ring groove 201 and the top ring 1. The partition ring 4 may be interposed between the upper groove wall W1 of the second ring groove 202 and the second ring 2, or between the lower groove wall W2 and the second ring 2. The partition ring 4 may be interposed between the upper groove wall W1 of the third ring groove 203 and the oil ring 3, or between the lower groove wall W2 and the oil ring 3. The third embodiment can be combined with the other embodiments described above. For example, in the piston ring structure 110 described above, the partition ring 4 may be interposed between the upper groove wall W1 of the first ring groove 201 and the top ring 1, or between the lower groove wall W2 and the second ring 2. In the piston ring structure 110A described above, the partition ring 4 may be interposed between the upper groove wall W1 of the second ring groove 202 and the second ring 2, or between the lower groove wall W2 and the oil ring 3. In the above-described piston ring structure 110B, a partition ring 4 may be interposed between the upper groove wall W1 of the first ring groove 201 and the top ring 1 or between the lower groove wall W2 and the oil ring 3.

[0089] <Embodiment 4> Hereinafter, a piston ring structure according to the fourth embodiment will be described with reference to Figs. 11 to 21. As shown in Figs. 11 to 21, the fourth embodiment differs from the above-described embodiments in that a plurality of partition rings are arranged between a plurality of piston rings (specifically, between piston rings adjacent in the axial direction of the piston) so as to overlap each other in the axial direction. Moreover, in the fourth embodiment, the properties of the partition rings adjacent in the axial direction are made different from each other. That is, in the fourth embodiment, a plurality of partition rings having different properties are used in combination. Here, in this specification, "properties of the partition ring" refers to the nature and state of the partition ring. The properties of the partition ring include, for example, the material, shape, surface treatment, surface roughness, strength, etc. of the partition ring.

[0090] In the following description, a structure formed by a plurality of partition rings mounted in the ring groove so as to overlap each other in the axial direction of the piston and disposed between the plurality of piston rings is referred to as a partition portion, and is indicated by the reference symbol P1 in the drawings. The partition portion P1 is disposed between the plurality of piston rings, and the partition ring of the partition portion P1 is fitted into the bottom groove wall W3 of the ring groove with a predetermined gap between it and the inner wall surface 10a of the cylinder 10, thereby partitioning the ring groove. The number of partition rings constituting the partition portion P1 is not limited as long as there are a plurality of them. The fourth embodiment is an aspect in which the partition portion P1 is disposed between the top ring 1 and the second ring 2 mounted in the first ring groove 201. In the fourth embodiment, the first ring groove 201 corresponds to the "ring groove" according to the present invention. Hereinafter, the piston ring structures 140 to 140I according to the fourth embodiment will be described, focusing on the differences from the piston ring structure 110 according to the first embodiment, and detailed descriptions thereof will be omitted by assigning the same reference symbols to similar configurations.

[0091] 11 is a partial cross-sectional view of an internal combustion engine 400 including a piston ring structure 140 according to embodiment 4. As shown in FIG. 11, the piston ring structure 140 according to embodiment 4 has two partition rings (partition rings 4 and 5) pistoned in a first ring groove 201. The piston ring structure 110 of the present embodiment differs from that of the piston ring structure 110 of the first embodiment in that the pistons 20 are mounted so as to overlap in the axial direction of the pistons 20.

[0092] As shown in FIG. 11, in the piston ring structure 140, a partition portion P1 is disposed between the top ring 1 and the second ring 2, thereby dividing the first ring groove 201. The partition portion P1 of the piston ring structure 140 is configured to include two partition rings (partition rings 4 and 5). The partition ring 4 and the partition ring 5 are mounted in the first ring groove 201 so as to overlap each other in the axial direction of the piston 20, and the partition ring 5 is disposed lower (closer to the crank chamber 40) than the partition ring 4. Specifically, the lower partition wall surface 44 of the partition ring 4 and the upper partition wall surface 53 of the partition ring 5 are in contact with each other. Therefore, no piston ring is interposed between the partition ring 4 and the partition ring 5. 11, in the piston ring structure 140, the top ring 1 is fitted between the upper groove wall W1 of the first ring groove 201 and the upper partition wall surface 43 of the partition ring 4, and the second ring 2 is fitted between the lower groove wall W2 of the first ring groove 201 and the lower partition wall surface 54 of the partition ring 5. That is, in the piston ring structure 140, the two partition rings 4 and 5 are fitted in the ring grooves so as to overlap between the top ring 1 and the second ring 2. In this way, in the piston ring structure 140, the partition ring 4 and the partition ring 5 cooperate to function in place of one piston land.

[0093] The piston ring structure 140 according to the fourth embodiment can also provide the same effects as the piston ring structure 110 according to the first embodiment. That is, according to the piston ring structure 140, a plurality of piston rings (in this example, the top ring 1 and the second ring 2) can be mounted in one ring groove, and the number of ring grooves can be reduced. This makes it easy to shorten the axial length of the piston 20.

[0094] Here, in the piston ring structure 140 according to the fourth embodiment, the partition ring 4 and the partition ring 5 have different properties. More specifically, in this example, the partition ring 4 and the partition ring 5 are made of different materials.

[0095] In the partition portion P1 of the piston ring structure 140, the material of the partition ring 4 has higher thermal conductivity than the material of the partition ring 5. The partition ring 4 of this embodiment is formed of a material with high thermal conductivity. The material with high thermal conductivity used for the partition ring 4 is not particularly limited, but examples thereof include Cu, Cu-based alloys, Al-Si-based alloys (preferably anodized), and Cu clad materials (clad materials containing Cu as a material). The thermal conductivity of the material used for the partition ring 4 is not particularly limited, but is preferably 40 W / mK to 400 W / mK, more preferably 40 W / mK to 200 W / mK, more preferably 40 W / mK to 150 W / mK, and even more preferably 40 W / mK to 100 W / mK.

[0096] In addition, in the partition portion P1 of the piston ring structure 140, the material of the partition ring 5 has higher heat set resistance than the material of the partition ring 4. The partition ring 5 of this example is formed of a material with high heat set resistance. The material with high heat set resistance used for the partition ring 5 is not particularly limited, but a material with excellent heat resistance and excellent creep resistance with little decrease in strength even at high temperatures is preferable, and examples of such a material include Ni-based alloys and steel materials.

[0097] In this way, in the piston ring structure 140 according to the fourth embodiment, the partition ring (i.e., the partition The material of the partition ring 4) has a higher thermal conductivity than the material of the other partition rings (i.e., the partition ring 5). Here, the flow of heat conduction in the internal combustion engine 400 equipped with the piston ring structure 140 is considered to be in the order of piston, partition ring, piston ring, and cylinder. At this time, due to the combustion of gas in the combustion chamber 30, the temperature of the piston 20 tends to be higher the closer to the combustion chamber 30 (i.e., the higher). Therefore, in the piston ring structure 140 according to the fourth embodiment, the partition ring 4 arranged at the uppermost side in the partition portion P1 is formed from a material with high thermal conductivity, thereby improving the cooling effect of the piston 20. Note that only a part of the partition ring 4 may be formed from a material with high thermal conductivity. Also, instead of forming the partition ring 4 from a material with high thermal conductivity, a coating formed from a material with high thermal conductivity may be provided on the surface of the partition ring 4. For example, in the partition ring 4, only the upper partition surface 43 that contacts the top ring 1 may be made of a high thermal conductivity material, or only the upper partition surface 43 may be coated with a high thermal conductivity material.

[0098] Furthermore, in the piston ring structure 140 according to the fourth embodiment, the material of the partition ring (i.e., the partition ring 5) arranged at the lowest side in the partition portion P1 has a higher heat set resistance than the material of the other partition rings (i.e., the partition ring 4). Here, the partition ring has a self-tension so as to press the bottom groove wall in a usage state in order to fit into the bottom groove wall of the ring groove. However, if the self-tension decreases due to the partition ring being set under high temperature, there is a risk that the fit cannot be maintained. In contrast, in the piston ring structure 140 according to the fourth embodiment, by increasing the heat set resistance of the partition ring 5, the self-tension of the partition ring 5 is maintained even under high heat, and the fit (contact state) between the inner circumferential fitting surface 52 and the bottom groove wall W3 of the first ring groove 201 is firmly maintained. This prevents the partition ring 5 from being displaced in the axial direction, and the inner circumferential sealing property of the partition ring 5 (sealing property between the inner circumferential fitting surface 52 and the bottom groove wall W3) can be maintained. In particular, in the case of this example, the partition ring 4 arranged on the upper side is made of a material with high thermal conductivity in order to enhance the cooling effect of the piston 20, which may result in a decrease in the heat settling resistance of the partition ring 4, but this can be compensated for by making the partition ring 5 arranged on the lower side of the partition ring 4 out of a material with high heat settling resistance. As a result, the partition portion P1 as a whole can be prevented from shifting in position and can maintain the inner periphery sealing performance.

[0099] At least one of the partition rings constituting the partition portion P1 may be made of a material lighter than aluminum. This allows the weight of the partition ring to be reduced. Examples of materials lighter than aluminum that can be used for the partition ring include Mg alloys and FRP (Fiber Reinforced Plastics). When FRP is used for the partition ring, it is preferable to use a material having excellent heat resistance. It is preferable to use PEEK (Polyether ether ketone) resin as the material.

[0100] At least one of the partition rings constituting the partition portion P1 may be hollow, which also reduces the weight of the partition ring.

[0101] By reducing the weight of the partition ring, it is possible to reduce the inertial force of the piston ring structure 140 during operation of the internal combustion engine 400. This makes it easier to design the strength of the connecting rod and metal (bearing) system. For example, the strength and seizure resistance load required for the connecting rod and metal system are reduced, allowing for greater freedom in designing these parts.

[0102] In this embodiment, the material of the partition ring 4 arranged on the upper side is made of a material having high thermal conductivity, and the material of the partition ring 5 arranged on the lower side is made of a material having high heat resistance. However, in the present invention, the combination of properties of the plurality of partition rings is not limited to this. Furthermore, the number of partition rings constituting the partition portion P1 may be three or more.

[0103] [Modification of the fourth embodiment] The following describes a modification of the embodiment 4. In the following description, differences from the above-described piston ring structure 140 will be mainly described, and similar configurations will be denoted by the same reference numerals and detailed description will be omitted.

[0104] [Variation 1] FIG. 12 is a partial cross-sectional view of an internal combustion engine 400A including a piston ring structure 140A according to a first modification of the fourth embodiment. As shown in FIG. 12, in the piston ring structure 140A according to the first modification of the fourth embodiment, an adhesive layer 50 is provided between the partition rings (partition rings 4, 5) adjacent to each other in the axial direction of the piston 20 in the partition portion P1 to bond them together. That is, the adhesive layer 50 is provided between the lower partition wall surface 44 of the partition ring 4 and the upper partition wall surface 53 of the partition ring 5. The material of the adhesive layer 50 is not particularly limited, and examples thereof include soft metals such as Sn. The adhesive layer 50 may be provided, for example, by coating one or both of the lower partition wall surface 44 of the partition ring 4 and the upper partition wall surface 53 of the partition ring 5 with a soft metal. The adhesive layer 50 may be formed, for example, from a thermally conductive paste such as silicone. In the present invention, an adhesive layer may be provided on the surface of the partition ring that comes into contact with the piston (for example, the inner peripheral surface).

[0105] According to the piston ring structure 140A of the first modification, the adhesive layer 50 can improve the adhesion between adjacent partition rings. This can suppress the passage of gas and oil between adjacent partition rings, that is, between the lower partition wall surface 44 of the partition ring 4 arranged on the upper side and the upper partition wall surface 53 of the partition ring 5 arranged on the lower side. As a result, blow-by gas and oil consumption can be reduced. In addition, the adhesive layer 50 can improve the thermal conductivity between adjacent partition rings, so that the cooling effect of the piston 20 can be improved. From the viewpoint of improving the adhesion, it is preferable that the lower partition wall surface 44 of the partition ring 4 and the upper partition wall surface 53 of the partition ring 5 are smooth surfaces.

[0106] [Variation 2] Fig. 13 is a partial cross-sectional view of an internal combustion engine 400B equipped with a piston ring structure 140B according to Modification 2 of Embodiment 4. As shown in Fig. 13, the piston ring structure 140B according to Modification 2 of Embodiment 4 further includes a retaining ring 60 that is provided between the bottom groove wall W3 of the first ring groove 201 and the partition portion P1 and retains the partition rings 4, 5 of the partition portion P1 from both sides in the axial direction of the piston 20.

[0107] The retaining ring 60 is a ring-shaped member, and its inner peripheral surface 602 fits into the bottom groove wall W3 of the first ring groove 201. A portion of the outer peripheral surface 601 of the retaining ring 60 is recessed to form a fitting portion 605 into which the partition rings 4 and 5 fit. The fitting portion 605 is formed as an inner wall of a groove formed over the entire circumference of the outer peripheral surface 601, and holds the partition rings 4 and 5, thereby restricting movement of the partition rings 4 and 5 along the axial direction. The fitting portion 605 is formed to include an upper wall W10 and a lower wall W20 arranged opposite each other vertically, and a connecting wall W30 that connects the inner peripheral edge of the upper wall W10 and the inner peripheral edge of the lower wall W20.

[0108] In this example, the upper surface 603 of the retaining ring 60 abuts against the upper groove wall W1 of the first ring groove 201. The surface 604 abuts against the lower groove wall W2 of the first ring groove 201, so that the retaining ring 60 is supported in the axial direction of the piston 20, and the axial movement of the retaining ring 60 is restricted. Furthermore, the upper wall W10 abuts against the upper partition wall surface 43 of the partition ring 4, so that the upward movement of the partition portion P1 is restricted, and the lower wall W20 abuts against the lower partition wall surface 54 of the partition ring 5, so that the downward movement of the partition portion P1 is restricted. In addition, the connection wall W30 is fitted with the inner peripheral fitting surface 42 of the partition ring 4 and the inner peripheral fitting surface 52 of the partition ring 5. In this way, the partition rings 4 and 5 are held by the retaining ring 60 and are fitted with the bottom groove wall W3 of the first ring groove 201 via the retaining ring 60. The axial movement of the retaining ring 60 is restricted, so that the partition portion P1 can be prevented from being displaced in the axial direction. In addition, since the axial width of the retaining ring 60 is larger than the axial width of the partition portion P1, the self-tension of the retaining ring 60 is larger than the self-tension of the partition rings 4 and 5. The partition rings 4 and 5 are fitted into the bottom groove wall W3 of the first ring groove 201 via such a retaining ring 60, so that the partition portion P1 can be prevented from being displaced in the axial direction. In order to restrict the retaining ring 60 from moving in the axial direction, a recessed groove may be formed in the connecting wall W30 of the first ring groove 201, and the retaining ring 60 may be fitted into the recessed groove. In addition, the retaining ring 60 may be formed of a pair of rings arranged to sandwich the partition portion P1 from both sides (from above and below) in the axial direction of the piston 20.

[0109] [Variation 3] FIG. 14 is a partial cross-sectional view of an internal combustion engine 400C including a piston ring structure 140C according to Modification 3 of the embodiment 4. As shown in FIG. 14, the piston ring structure 140C according to Modification 3 of the embodiment 4 is different from the piston ring structure 140B according to Modification 2 in that only the partition ring 5 arranged on the lower side of the partition portion P1 is held by the retaining ring 60. Specifically, in this example, the upper wall W10 abuts against the upper partition wall surface 53 of the partition ring 5, the lower wall W20 abuts against the lower partition wall surface 54 of the partition ring 5, and the connecting wall W30 and the inner peripheral fitting surface 52 of the partition ring 5 are fitted together. Even in such Modification 3, it is possible to prevent the partition portion P1 from being displaced in the axial direction. Note that only the partition ring 4 may be held by the retaining ring 60.

[0110] [Variation 4] 15 is a partial cross-sectional view of an internal combustion engine 400D equipped with a piston ring structure 140D according to Modification 4 of Embodiment 4. In the piston ring structure 140D according to Modification 4 of Embodiment 4, the partition ring 4 and the partition ring 5 have different surface shapes.

[0111] 15, in a piston ring structure 140D according to a fourth modified example of the fourth embodiment, a gap forming portion indicated by reference symbol V1 is provided on an upper partition wall surface 43 of the partition ring 4 arranged on the uppermost side (combustion chamber 30 side) in the partition portion P1 and on a lower partition wall surface 54 of the partition ring 5 arranged on the lowermost side (crank chamber 40 side). A gap for retaining oil is formed in the gap forming portion V1.

[0112] By providing the gap forming portion V1 on the upper partition wall surface 43 of the partition ring 4, a gap is secured between the lower surface 14 of the top ring 1 and the gap forming portion V1 even when the lower surface 14 of the top ring 1 and the upper partition wall surface 43 of the partition ring 4 are in contact with each other, and oil is held in the gap. This reduces friction between the lower surface 14 of the top ring 1 and the upper partition wall surface 43 of the partition ring 4, and makes it possible to reduce wear of the top ring 1 and the partition ring 4.

[0113] Furthermore, by providing the gap forming portion V1 on the lower partition surface 54 of the partition ring 5, it is possible to reduce the contact area between the upper surface 23 of the second ring 2 and the lower partition surface 54 of the partition ring 5. This makes it possible to suppress adhesion between the upper surface 23 of the second ring 2 and the lower partition surface 54 of the partition ring 5.

[0114] As shown in FIG. 15, when the gap forming portion V1 is provided on the upper partition wall surface 43 of the partition ring 4, it is preferable that the gap forming portion V1 is provided on the upper partition wall surface 43 except for the end region 43a on the radially outer side. The end region 43a on the radially outer side is a region located at the end of the upper partition wall surface 43 on the radially outer side and having a predetermined width. By leaving the end region 43a on the upper partition wall surface 43 where no gap is formed, when the lower surface 14 of the top ring 1 and the upper partition wall surface 43 of the partition ring 4 are in contact with each other, a gap is secured between the lower surface 14 and the gap forming portion V1, while a sealability is secured between the lower surface 14 and the end region 43a. Therefore, gas is prevented from passing between the lower surface 14 of the top ring 1 and the upper partition wall surface 43 of the partition ring 4 and escaping to the outer periphery side. As a result, an increase in blow-by gas can be suppressed. For the same reason, when the gap forming portion V1 is provided on the lower partition wall surface 54 of the partition ring 5, it is preferable that the gap forming portion V1 is provided in a region of the lower partition wall surface 54 excluding the end region 54a on the radially outer side. Note that the present invention is not limited to this, and the gap forming portion may be provided on the entire region of the upper partition wall surface or the lower partition wall surface of the partition ring.

[0115] 16(A) to (D) are diagrams showing an example of the void forming portion V1. The void forming portion V1 shown in FIG. 16(A) forms voids by a plurality of holes V11 arranged at equal intervals in the circumferential direction. The holes V11 may be through holes or non-through holes. The holes V11 are formed as long holes elongated in the circumferential direction. The size of the holes V11 is not limited, but for example, the length L1 in the longitudinal direction is preferably 4 mm to 8 mm. In the embodiment shown in FIG. 16(A), the arithmetic mean roughness Ra of the area on the surface excluding the holes V11 is preferably 1.0 μm or less. The void forming portion V1 shown in FIG. 16(B) forms voids by a plurality of dimples (depressions) V12 formed on the surface. The plurality of dimples V12 are arranged in a certain pattern, so that the void forming portion V1 has a textured shape. The void forming portion V1 shown in Fig. 16(C) forms voids by a plurality of grooves V13 arranged at equal intervals in the circumferential direction. The grooves V13 are formed as grooves elongated in the radial direction. The void forming portion V1 shown in Fig. 16(D) forms voids by making the surface roughness rougher than other portions (end regions). In the example shown in Fig. 16(D), the voids may be formed by roughening the surface by, for example, sintering or surface spraying.

[0116] As shown in Figures 16(A) to (D), it is preferable that the gap forming portion V1 has gaps formed discontinuously (intermittently). This makes it possible to prevent oil from passing through the gaps and to retain the oil in the gaps. Note that the gap forming portion V1 may be a combination of the aspects shown in Figures 16(A) to (D).

[0117] The void forming portion V1 may be formed of a member separate from the partition ring. In that case, the void forming portion V1 may be formed of, for example, a Cu-based porous material or a sintered material.

[0118] The gap forming portion V1 may be impregnated with a resin material, which can suppress adhesion between the partition ring and the piston ring.

[0119] In this embodiment, the gap forming portion V1 is provided on both the partition ring 4 and the partition ring 5, but the present invention is not limited to this. The gap forming portion is provided on at least one of the upper partition wall surface of the partition ring arranged closest to the combustion chamber in the partition portion and the lower partition wall surface of the partition ring arranged closest to the crank chamber. This may also be the case.

[0120] [Variation 5] Fig. 17 is a partial cross-sectional view of an internal combustion engine 400E equipped with a piston ring structure 140E according to Modification 5 of Embodiment 4. As shown in Fig. 17, in the piston ring structure 140E according to Modification 5 of Embodiment 4, a surface treatment coating indicated by reference symbol S1 is provided on an upper partition wall surface 43 of the partition ring 4 arranged at the uppermost position in the partition portion P1 and a lower partition wall surface 54 of the partition ring 5 arranged at the lowermost position. The surface treatment coating S1 may be, for example, a resin coating, a nitriding coating, a Ni-P plating coating, a chrome plating coating, a chemical The surface treatment coating S1 may be a coating containing at least one layer selected from the group consisting of a chemical treatment coating, an oxidation treatment coating, a paint film, a PVD treatment coating, and a DLC coating. For example, by making the surface treatment coating S1 a coating containing a DLC coating, adhesion between the piston ring and the partition ring can be suppressed. In addition, by making the material of the partition ring SUS and making the surface treatment coating S1 a coating containing a nitriding treatment coating, wear of the piston ring and the partition ring can be reduced.

[0121] In this example, the surface treatment coating S1 is provided on both the partition ring 4 and the partition ring 5, but the present invention is not limited to this. The surface treatment coating may be provided on at least one of the upper partition wall surface of the partition ring that is disposed closest to the combustion chamber in the partition portion and the lower partition wall surface of the partition ring that is disposed closest to the crank chamber.

[0122] [Variation 6] 18 is a partial cross-sectional view of an internal combustion engine 400F including a piston ring structure 140F according to Modification 6 of Embodiment 4. In the piston ring structure 140F according to Modification 6 of Embodiment 4, the partition ring 4 and the partition ring 5 have different shapes.

[0123] As shown in FIG. 18, the partition ring 4 of the piston ring structure 140F has an upper protruding portion UP1 in addition to an outer peripheral separating surface 41, an inner peripheral fitting surface 42, an upper partition wall surface 43, and a lower partition wall surface 44. As a result, the cross-sectional shape of the partition ring 4 is substantially L-shaped. The upper protruding portion UP1 is provided on the inside of the upper partition wall surface 43 in the radial direction of the piston 20, and protrudes toward the combustion chamber 30 side relative to the upper partition wall surface 43. The upper protruding portion UP1 is supported in the axial direction of the piston 20 by abutting against the upper groove wall W1 of the first ring groove 201 on the inner peripheral surface 12 side of the top ring 1. As a result, the partition ring 4 (and therefore the partition portion P1) is restricted from moving upward.

[0124] 18, the partition ring 5 of the piston ring structure 140F has a lower protruding portion LP2 in addition to the outer peripheral separating surface 51, the inner peripheral fitting surface 52, the upper partition wall surface 53, and the lower partition wall surface 54. As a result, the cross-sectional shape of the partition ring 5 is substantially L-shaped. The lower protruding portion LP2 is provided on the inner side of the lower partition wall surface 54 in the radial direction of the piston 20, and protrudes toward the crank chamber 40 with respect to the lower partition wall surface 54. The lower protruding portion LP2 is supported in the axial direction of the piston 20 by abutting against the lower groove wall W2 of the first ring groove 201 on the inner peripheral surface 22 side of the second ring 2. As a result, the partition ring 5 (and thus the partition portion P1) is restricted from moving downward.

[0125] [Variation 7] 19 is a partial cross-sectional view of an internal combustion engine 400G equipped with a piston ring structure 140G according to a seventh modification of the embodiment 4. In the piston ring structure 140G according to the seventh modification of the embodiment 4, the partition ring 4 and the partition ring 5 have different shapes. .

[0126] As shown in FIG. 19, in the piston ring structure 140G according to the seventh modified example of the fourth embodiment, of the two partition rings 4, 5 included in the partition portion P1, the partition ring 5 arranged on the lower side has a smaller radial thickness than the partition ring 4 arranged on the upper side. In other words, of the two partition rings 4, 5 included in the partition portion P1, the partition ring 5 arranged second from the combustion chamber side has a smaller radial thickness of the piston than the partition ring 4 arranged closest to the combustion chamber side. As a result, the outer peripheral separation surface 51 of the partition ring 5 is located inside the outer peripheral separation surface 41 of the partition ring 4 in the radial direction of the piston 20. In other words, the outer diameter of the partition ring 5 is smaller than the outer diameter of the partition ring 4. Therefore, the separation distance d2 between the outer peripheral separation surface 51 of the partition ring 5 and the inner wall surface 10a of the cylinder 10 is larger than the separation distance d1 between the outer peripheral separation surface 41 of the partition ring 4 and the inner wall surface 10a of the cylinder 10.

[0127] In the piston ring structure 140G according to the seventh modification of the fourth embodiment, the radial thickness of the partition ring 5 is reduced, so that the land volume can be ensured. This makes it possible to reduce the pressure (land pressure) in the space (second land space) surrounded by the lower surface 14 of the top ring 1, the upper surface 23 of the second ring 2, the outer peripheral separating surfaces 41, 51 of the partition rings 4, 5, and the inner wall surface 10a of the cylinder 10. On the other hand, by increasing the radial thickness of the partition ring 4, it is possible to ensure a large area of ​​the upper partition wall surface 43 that comes into contact with the lower surface 14 of the top ring 1 in the partition ring 4. That is, it is possible to ensure a large contact area between the lower surface 14 of the top ring 1 and the upper partition wall surface 43. This makes it possible to stabilize the posture of the top ring 1. In addition, it is possible to ensure a sealability (side sealability) between the lower surface 14 of the top ring 1 and the upper partition wall surface 43 of the partition ring 4.

[0128] In this manner, in the piston ring structure 140G according to the seventh modification of the fourth embodiment, the partition rings 4, 5 constituting the partition portion P1 have different thicknesses, which increases the degree of freedom in designing the land volume.

[0129] [Variation 8] 20 is a partial cross-sectional view of an internal combustion engine 400H including a piston ring structure 140H according to an eighth modification of the embodiment 4. In the piston ring structure 140H according to the eighth modification of the embodiment 4, the partition ring 4 and the partition ring 5 have different shapes.

[0130] As shown in Fig. 20, in a piston ring structure 140H according to an eighth modification of the fourth embodiment, a notch indicated by reference symbol N1 is formed in the outer circumferential lower portion of the partition ring 4 and the outer circumferential upper portion of the partition ring 5. More specifically, the notch N1 of the partition ring 4 is formed between the outer circumferential spacing surface 41 and the lower partition wall surface 44. Moreover, the notch N1 of the partition ring 5 is formed between the outer circumferential spacing surface 51 and the upper partition wall surface 53. The notch N1 is formed by recessing a part of the outer circumferential portions of the partition rings 4, 5, and extends in the circumferential direction of the partition rings 4, 5.

[0131] In the piston ring structure 140H according to the eighth modification of the fourth embodiment, the notch portion N1 is formed in the lower outer periphery of the partition ring 4 and the upper outer periphery of the partition ring 5, so that the land volume can be secured. This makes it possible to reduce the land pressure in the second land space. As a result, according to the eighth modification of the fourth embodiment, like the seventh modification, the degree of freedom in designing the land volume can be increased.

[0132] In this example, the notch N1 is formed on both the lower outer periphery of the partition ring 4 and the upper outer periphery of the partition ring 5, but the position where the notch is formed is not limited to this in the present invention. For example, the notch N1 may be formed on only one of the lower outer periphery of the partition ring 4 and the upper outer periphery of the partition ring 5. Also, the notch N1 may be formed on both the upper outer periphery of the partition ring 4 and the lower outer periphery of the partition ring 5.

[0133] However, as shown in Fig. 20, it is preferable that the positions where the notches are formed do not include the upper outer periphery of the partition ring arranged at the uppermost position in the partition part and the lower outer periphery of the partition ring arranged at the lowermost position. In other words, it is preferable to form the notches in the lower outer periphery or upper outer periphery where an adjacent partition ring exists (i.e., the lower outer periphery or upper outer periphery that is not adjacent to a piston ring). By doing so, it is possible to ensure a large contact area between the piston ring and the partition ring.

[0134] [Variation 9] 21 is a partial cross-sectional view of an internal combustion engine 400I equipped with a piston ring structure 140I according to a ninth modified example of the fourth embodiment. The partition portion P1 according to the piston ring structure 140I is configured to include three partition rings (partition rings 4, 5, and 70). The partition ring 4, the partition ring 5, and the partition ring 70 are mounted in the first ring groove 201 so as to overlap one another in the axial direction of the piston 20, and are arranged in this order from the top: the partition ring 4, the partition ring 70, and the partition ring 5.

[0135] In a piston ring structure 140I according to a ninth modification of the fourth embodiment, adjacent partition rings have different shapes. That is, the shape of the partition ring 4 is different from the shape of the partition ring 70, and the shape of the partition ring 70 is different from the shape of the partition ring 5.

[0136] The partition ring 70 of the piston ring structure 140I has an outer peripheral separation surface 701, an inner peripheral fitting surface 702, an upper partition wall surface 703, and a lower partition wall surface 704. As shown in FIG. 21, in the piston ring structure 140I, the partition ring 70 arranged second from the combustion chamber side among the three partition rings 4, 5, and 70 included in the partition portion P1 has a smaller thickness in the radial direction of the piston than the partition ring 4 arranged closest to the combustion chamber side and the partition ring 5 arranged closest to the crank chamber side. As a result, the outer peripheral separation surface 701 of the partition ring 70 is located inside the outer peripheral separation surfaces 41 and 51 of the partition rings 4 and 5 in the radial direction of the piston 20. In other words, the outer diameter of the partition ring 70 is smaller than the outer diameters of the partition rings 4 and 5.

[0137] In the piston ring structure 140I according to the ninth modification of the fourth embodiment, the radial thickness of the partition ring 70 is reduced, so that the land volume can be secured. This allows the land pressure in the second land space to be reduced. On the other hand, by increasing the radial thickness of the partition rings 4 and 5, the areas of the upper partition wall surface 43 and the lower partition wall surface 54 can be secured large. That is, the contact area between the lower surface 14 of the top ring 1 and the upper partition wall surface 43 of the partition ring 4 and the contact area between the upper surface 23 of the second ring 2 and the lower partition wall surface 54 of the partition ring 5 can be secured large. This allows the attitudes of the top ring 1 and the second ring 2 to be stabilized, and also ensures the side sealing properties of the top ring 1 and the second ring 2. Another advantage is that the land volume can be secured without cutting the piston land.

[0138] In addition, in the piston ring structure 140I, by setting the number of partition rings included in the partition portion P1 to three, the tension per partition ring can be reduced compared to when the number of partition rings is two. This makes it easier to assemble the partition rings.

[0139] In the piston ring structure 140I, the partition rings that come into contact with the piston ring in the partition portion P1, i.e., the uppermost partition ring 4 and the lowermost partition ring 5, may be made to have high seizure resistance and adhesion prevention properties. For example, as in the above-mentioned modified example 4 and modified example 5, the upper partition wall surface 43 of the partition ring 4 and the lower partition wall surface 54 of the partition ring 5 may be provided with the gap forming portion V1 and the surface treatment coating S1.

[0140] [Other variations] The various aspects of the above-mentioned embodiment 4 can be combined as much as possible. Although the partition portion P1 according to the piston ring structures 140 to 140I is configured to include two partition rings (partition rings 4 and 5), these aspects can also be applied to the case where the number of partition rings included in the partition portion P1 is three or more.

[0141] <Embodiment 5> Hereinafter, a piston ring structure according to the fifth embodiment will be described with reference to Figs. 22 to 26. As shown in Figs. 22 to 26, the fifth embodiment is an aspect in which a partition portion P1 is disposed between a second ring 2 (compression ring) mounted in a second ring groove 202 and an oil ring 3. In the fifth embodiment, the second ring groove 202 corresponds to the "ring groove" according to the present invention. In the fifth embodiment, the partition rings adjacent to each other in the axial direction have different properties in the partition portion P1. Hereinafter, piston ring structures 150 to 150C according to the fifth embodiment will be described, focusing on differences from the piston ring structure 140 according to the fourth embodiment, and similar configurations will be denoted by the same reference numerals and detailed description thereof will be omitted.

[0142] FIG. 22 is a partial cross-sectional view of an internal combustion engine 500 including a piston ring structure 150 according to the fifth embodiment. As shown in FIG. 22, in the piston ring structure 150, a partition portion P1 is disposed between the second ring 2 and the oil ring 3, thereby partitioning the second ring groove 202. The partition portion P1 according to the piston ring structure 150 includes two partition rings (partition rings 4 and 5) as in the fourth embodiment. As shown in FIG. 22, in the piston ring structure 150, the second ring 2 is fitted between the upper groove wall W1 of the second ring groove 202 and the upper partition surface 43 of the partition ring 4, and the oil ring 3 is fitted between the lower groove wall W2 of the second ring groove 202 and the lower partition surface 54 of the partition ring 5. That is, in the piston ring structure 150, the two partition rings 4 and 5 are fitted in the ring groove so as to overlap between the second ring 2 and the oil ring 3.

[0143] The piston ring structure 150 according to the fifth embodiment can also provide the same effects as the piston ring structure 110 according to the first embodiment. That is, according to the piston ring structure 150, a plurality of piston rings (in this example, the second ring 2 and the oil ring 3) can be mounted in one ring groove, and the number of ring grooves can be reduced. This makes it easy to shorten the axial length of the piston 20.

[0144] In the piston ring structure 150 according to the fifth embodiment, the partition ring 4 and the partition ring 5 are made of different materials. In the partition portion P1, for example, the material of the partition ring 4 may have higher thermal conductivity than the material of the partition ring 5. The partition ring 4 is made of a material with high thermal conductivity as described in the fourth embodiment.

[0145] In addition, in the partition portion P1 of the piston ring structure 140, the material of the partition ring 5 may have higher heat set resistance than the material of the partition ring 4. The partition ring 5 is formed of the material having high heat set resistance as described in the fourth embodiment.

[0146] In this way, in the piston ring structure 150 of embodiment 5, the material of the partition ring 4 that is located at the top of the partition portion P1 is made to have a higher thermal conductivity than the material of the other partition rings (i.e., partition ring 5), thereby enhancing the cooling effect of the piston 20, as in embodiment 4.

[0147] Furthermore, in the piston ring structure 150 of embodiment 5, the material of the partition ring 5, which is located at the lowest position in the partition portion P1, is made to have a higher heat settling resistance than the material of the other partition rings (i.e., partition ring 4), thereby making it possible to prevent displacement of the partition portion P1 and maintain inner peripheral sealing performance.

[0148] [Modification of the fifth embodiment] The following describes modifications of the embodiment 5. In the following description, differences from the above-described piston ring structure 150 will be mainly described, and similar configurations will be denoted by the same reference numerals and detailed description will be omitted.

[0149] [Variation 1] 23 is a partial cross-sectional view of an internal combustion engine 500A including a piston ring structure 150A according to Modification 1 of Embodiment 5. In the piston ring structure 150A according to Modification 1 of Embodiment 5, the partition ring 4 and the partition ring 5 have different shapes.

[0150] 23, in a piston ring structure 150A according to the first modification of the fifth embodiment, a notch N1 is formed on an upper outer periphery of the partition ring 4. More specifically, the notch N1 is formed between the outer periphery separating surface 41 and the upper partition wall surface 43 of the partition ring 4. Moreover, the second ring 2 according to the first modification of the fifth embodiment has an undercut shape in which a lower portion of the outer periphery is cut out.

[0151] In the piston ring structure 150A according to the first modification of the fifth embodiment, a notch N1 is formed on the upper outer periphery of the partition ring 4, thereby ensuring a land volume. This makes it possible to reduce the land pressure in the space (third land space) surrounded by the lower surface 24 of the second ring 2, the upper surface 313 of the upper segment 31U of the oil ring 3, the outer periphery separating surfaces 41, 51 of the partition rings 4, 5, and the inner wall surface 10a of the cylinder 10. Furthermore, by forming the second ring 2 into an undercut shape, a larger land volume can be ensured. As a result, according to the first modification of the fifth embodiment, the degree of freedom in designing the land volume can be increased.

[0152] 24 is a diagram showing an example of the shape of the cutout portion N1. The cutout portion N1 may have a shape as shown in FIG.

[0153] [Variation 2] FIG. 25 is a schematic diagram of an internal combustion engine equipped with a piston ring structure 150B according to a second modification of the fifth embodiment. 13 is a partial cross-sectional view of a piston ring structure 150B according to a second modification of the fifth embodiment, the partition ring 4 and the partition ring 5 have different shapes.

[0154] As shown in FIG. 25, in the piston ring structure 150B according to the second modification of the fifth embodiment, the lower partition wall surface 54 of the partition ring (i.e., the partition ring 5) arranged at the lowest side (the crank chamber 40 side) in the partition portion P1 is inclined so as to approach the crank chamber 40 as it approaches the radially outward side of the piston 20. That is, the lower partition wall surface 54 that abuts against the upper segment 31U of the oil ring 3 is inclined downward toward the radially outward side. More specifically, the lower partition wall surface 54 of the partition ring 5 includes an inclined surface 541 that is inclined downward toward the radially outward side and a flat surface 542 that is perpendicular to the axial direction. The flat surface 542 is arranged radially outward from the inclined surface 541. Therefore, as shown in FIG. 25, the inclined surface 541 of the lower partition wall surface 54 of the partition ring 5 abuts against the upper surface 313 of the upper segment 31U of the oil ring 3, so that the upper segment 31U is maintained in a position inclined downward toward the radially outward side. This improves the sealing performance (side sealing performance) between the upper surface 313 of the upper segment 31U and the lower partition wall surface 54 of the partition ring 5. Furthermore, since the posture of the upper segment 31U is stabilized, sagging of the shape of the outer peripheral surface 311 of the upper segment 31U is suppressed, and therefore the sealing performance (outer peripheral sealing performance) between the outer peripheral surface 311 of the upper segment 31U and the inner wall surface 10a of the cylinder 10 can also be improved. As in the second modification, by making at least a part of the lower partition wall surface of the partition ring arranged closest to the crank chamber in the partition section inclined downward radially outward, the upper segment can be maintained in a downwardly inclined posture.

[0155] [Variation 3] 26 is a partial cross-sectional view of an internal combustion engine 500C equipped with a piston ring structure 150C according to Modification 3 of Embodiment 5. The piston ring structure 150C according to Modification 3 of Embodiment 5 differs from Modification 2 in that a partition ring 80 is provided.

[0156] The partition ring 80 according to the piston ring structure 150C has an outer peripheral separation surface 801, an inner peripheral fitting surface 802, an upper partition wall surface 803, and a lower partition wall surface 804. As shown in FIG. 26, in the piston ring structure 150C, the partition ring 80 is disposed between the oil ring 3 and the lower groove wall W2 of the second ring groove 202. As a result, the upper partition wall surface 803 of the partition ring 80 contacts the lower surface 314 of the lower segment 31L of the oil ring 3, and the lower partition wall surface 804 contacts the lower groove wall W2. Here, in the piston ring structure 150C according to the third modification of the fifth embodiment, the upper partition wall surface 803 of the partition ring 80 is inclined so as to approach the combustion chamber 30 (i.e., to move away from the crank chamber 40) as it moves toward the outside in the radial direction of the piston 20. That is, the upper partition wall surface 803 that abuts against the lower segment 31L of the oil ring 3 is inclined upward toward the outside in the radial direction. 26, the upper partition wall surface 803 of the partition ring 80 abuts against the lower surface 314 of the lower segment 31L of the oil ring 3, so that the lower segment 31L is maintained in a position inclined upward and radially outward. This improves the sealing performance (side sealing performance and outer periphery sealing performance) of the lower segment 31L.

[0157] [Other variations] The various aspects of the above-mentioned embodiment 5 can be combined as much as possible. Although the partition portion P1 according to the piston ring structures 150 to 150C is configured to include two partition rings (partition rings 4 and 5), these aspects can also be applied to the case where the number of partition rings included in the partition portion P1 is three or more.

[0158] <Embodiment 6> FIG. 27 is a partial cross-sectional view of an internal combustion engine 600 including a piston ring structure 160 according to the sixth embodiment. In the piston ring structure 160 according to the sixth embodiment, a top ring 1, a second ring 2, and an oil ring 3 are mounted in a first ring groove 201. In the piston ring structure 160, a partition ring 4 having an upper protrusion UP1 is disposed between the top ring 1 and the second ring 2, and a partition ring 5 having an upper protrusion UP2 is disposed between the second ring 2 and the oil ring 3. Furthermore, the piston ring structure 160 includes a spacer ring 90 that fits into a bottom groove wall W3 of the first ring groove 201. As shown in FIG. 27, an upper surface 901 of the spacer ring 90 abuts against the lower partition wall surface 54 of the partition ring 5 on the inner circumferential side of the oil ring 3, and a lower surface 902 abuts against the lower groove wall W2 of the first ring groove 201, whereby the partition ring 5 is supported in the axial direction of the piston 20.

[0159] <Other> 28 to 42 are cross-sectional views showing variations of the partition ring. In FIG. 28 to FIG. 42, cross sections perpendicular to the circumferential direction of the partition ring are shown. The outer peripheral separation surface 41 of the partition ring 4a shown in FIG. 28 is formed by connecting a tapered surface inclined so as to widen from the upper partition wall surface 43 toward the lower side and a tapered surface inclined so as to widen from the lower partition wall surface 44 toward the upper side. The outer peripheral separation surface 41 of the partition ring 4b shown in FIG. 29 is formed by a tapered surface inclined so as to widen toward the lower side. The outer peripheral separation surface 41 of the partition ring 4c shown in FIG. 30 is formed by connecting a tapered surface inclined so as to narrow from the upper partition wall surface 43 toward the lower side and a tapered surface inclined so as to narrow from the lower partition wall surface 44 toward the upper side. The inner peripheral fitting surface 42 of the partition ring 4d shown in FIG. 31 is formed to be curved so as to be concave. The inner peripheral fitting surface 42 of the partition ring 4e shown in FIG. 32 is formed by connecting a tapered surface inclined so as to widen from the upper partition wall surface 43 toward the lower side and a tapered surface inclined so as to widen from the lower partition wall surface 44 toward the upper side. The upper partition wall surface 43 of the partition ring 4f shown in FIG. 33 is curved so as to bulge upward. The lower partition wall surface 44 of the partition ring 4f shown in FIG. 34 is formed with a groove 45 extending along the circumferential direction of the partition ring 4g. In the partition ring 4h shown in FIG. 35, the groove 45 is formed in the upper partition wall surface 43. In the partition ring 4i shown in FIG. 36, the groove 45 is formed in the outer peripheral separation surface 41. In the partition ring 4j shown in FIG. 37, the groove 45 is formed in the inner peripheral fitting surface 42. In addition, in the partition ring 4j, holes 46 communicating with the grooves 45 penetrate in the radial direction from the outer circumferential side to the inner circumferential side of the partition ring 4j. In the partition ring 4k shown in Fig. 38, grooves 45 are formed in both the outer circumferential separating surface 41 and the inner circumferential fitting surface 42. In addition, in the partition ring 4k, holes 46 penetrate in the radial direction from the grooves 45 on the outer circumferential side to the grooves 45 on the inner circumferential side.The upper partition wall surface 43 of the partition ring 4l shown in FIG. 39 is inclined downward toward the radially outer side. The lower partition wall surface 44 of the partition ring 4m shown in FIG. 40 is inclined upward toward the radially outer side. The partition ring 4l and the partition ring 4m can be combined with a compression ring having a keystone shape. The upper partition wall surface 43 may be inclined upward toward the radially outer side, or the lower partition wall surface 44 may be inclined downward toward the radially outer side. In addition, both the upper partition wall surface 43 and the lower partition wall surface 44 may be inclined. A chamfer 47 is formed at the lower corner on the outer periphery side of the partition ring 4n shown in FIG. 41. The chamfer 47 may be formed at the upper corner on the outer periphery side. In addition, the chamfer 47 may be formed at the upper corner or lower corner on the inner periphery side. A chamfer step 48 is formed at the lower corner on the outer periphery side of the partition ring 4o shown in FIG. 42. The chamfer step 48 may be formed at the upper corner on the outer periphery side. Also, a chamfer step 48 is provided on the inner circumference side. It may be formed at a corner or a lower corner.

[0160] FIG. 43 is a diagram showing variations in the shape of the joint of the partition ring. FIG. 43 shows a state in which the partition ring 4p in use is viewed along the axial direction. As shown in FIG. 43, the joint G1 of the partition ring 4p has a so-called key step shape. A pair of joint ends 410, 420 of the partition ring 4p are each formed in a key shape so that they are locked to each other in a state where they overlap in the radial direction of the partition ring. More specifically, the first joint end 410 has a first convex portion 430 that protrudes toward the second joint end 420 in the circumferential direction, and the second joint end 420 has a second convex portion 440 that protrudes toward the first joint end 410 in the circumferential direction, and in a use state, the first convex portion 430 and the second convex portion 440 overlap in the radial direction. In the example of FIG. 43, the first convex portion 430 is disposed outside the second convex portion 440 in the radial direction, but these may be disposed inversely. Furthermore, a first protrusion 430a protruding radially inward is provided at the tip side of the first protrusion 430, and a second protrusion 440a protruding radially outward is provided at the tip side of the second protrusion 440. The first protrusion 430a and the second protrusion 440a engage with each other, so that the pair of joint ends 410, 420 are locked to each other. By forming the joint G1 in a hook step shape in this way, the partition ring 4p can be easily attached to the piston 20, and the blow-by gas passing through the joint G1 can be reduced. Furthermore, the adhesion between the partition ring 4p and the wall surface of the ring groove can be improved.

[0161] 44 and 45 are diagrams for explaining a piston ring structure having a rotation prevention means. FIG. 44 illustrates a state in which the partition ring 4q in use is viewed from the outside in the radial direction. Reference numeral 204 in FIG. 44 indicates a protrusion that the piston 20 has. The protrusion 204 is, for example, a substantially cylindrical pin that protrudes into the ring groove. As shown in FIG. 44, the upper portion of the tip of the pair of joint ends 410, 420 is cut out, so that the joint G1 of the partition ring 4q includes a receiving portion 49 in its upper portion that can receive (fit) the protrusion 204. The protrusion 204 and the receiving portion 49 form a rotation prevention means. In use, the protrusion 204 is received in the receiving portion 49, so that the protrusion 204 restricts the partition ring 4q from rotating relative to the piston 20 in the circumferential direction. This makes it possible to prevent the partition ring 4q from rotating independently. Fig. 45 shows the partition ring 4r in use as viewed along the axial direction. As shown in Fig. 45, the inner periphery of the tip of the pair of joint ends 410, 420 is cut out, so that the joint G1 of the partition ring 4r includes a receiving portion 49 on its inner periphery that can receive the protrusion 204. This makes it possible to prevent the partition ring 4r from rotating independently.

[0162] Although the preferred embodiments of the present invention have been described above, the above-mentioned various aspects can be combined as much as possible. For example, the fourth embodiment and the fifth embodiment can be combined. Specifically, the top ring 1, the second ring 2, and the oil ring 3 can be mounted in the first ring groove 201, the partition part P1 can be disposed between the top ring 1 and the second ring 2, and another partition part P1 can be disposed between the second ring 2 and the oil ring 3. That is, the present invention may include a plurality of partition parts. Also, for example, in the fourth embodiment, the partition part P1 is disposed between the top ring 1 and the second ring 2, but the partition part P1 of the fourth embodiment shown in Figs. 11 to 21 may be disposed between the second ring 2 and the oil ring 3. Also, in the above-mentioned embodiment, the technology according to the present invention is applied to an internal combustion engine, which is an example of a reciprocating engine, but the technology according to the present invention is not limited to an internal combustion engine and can be applied to any mechanism in which a piston reciprocates in a cylinder. Examples of the application of the technology according to the present invention include a reciprocating engine exemplified as an internal combustion engine and a pneumatic device exemplified as a compressor. [Explanation of symbols]

[0163] 100, 200, 300, 400, 500, 600: Internal combustion engine 110, 120, 130, 140, 150, 160: Combination structure of piston and piston ring 10: Cylinder 20: Piston 201, 202: Ring groove 30: Combustion chamber 40: Crankcase 1: Top ring 2: Second Ring 3: Oil ring 4, 4A, 4B, 4C, 4D, 4E, 4F, 5, 6, 7: Partition ring

Claims

1. A piston and piston ring combination structure that is attached to a cylinder, a ring groove for mounting a piston ring provided on an outer peripheral surface of the piston; One or more piston rings mounted in the ring groove; a partition ring that is mounted in the ring groove together with the one or more piston rings in the axial direction of the piston, The partition ring is fitted to a bottom groove wall surface, which is the bottom surface of the ring groove, with a predetermined gap between the partition ring and the inner wall of the cylinder, The piston is a piston that is attached to the cylinder of an internal combustion engine, the partition ring has: an upper partition surface facing the upper groove wall surface, which is a groove wall surface on the combustion chamber side of the internal combustion engine, of a pair of inner walls arranged opposite to each other in the ring groove; a lower partition surface facing the lower groove wall surface, which is a groove wall surface on the crank chamber side of the internal combustion engine, of the pair of inner walls arranged opposite to each other in the ring groove; an inner peripheral fitting surface provided on an inner peripheral portion of the partition ring and fitting with the bottom groove wall surface connecting an inner peripheral edge of the upper groove wall surface and an inner peripheral edge of the lower groove wall surface of the ring groove to form a contact state with the bottom groove wall surface; and an outer peripheral separating surface provided on an outer peripheral portion of the partition ring, which ensures a predetermined separation distance between the partition ring and an inner wall of a cylinder of the internal combustion engine; The partition ring has an upper protruding portion that is provided on the inside of the upper partition wall surface in the radial direction of the piston and protrudes toward the combustion chamber to be supported in the axial direction of the piston. A combination structure of piston and piston ring.

2. A combination structure of a piston and a piston ring to be mounted in a cylinder, a ring groove for mounting a piston ring provided on an outer peripheral surface of the piston; One or more piston rings mounted in the ring groove; a partition ring that is mounted in the ring groove together with the one or more piston rings in the axial direction of the piston, The partition ring is fitted to a bottom groove wall surface, which is the bottom surface of the ring groove, with a predetermined gap between the partition ring and the inner wall of the cylinder, The piston is a piston that is attached to the cylinder of an internal combustion engine, The partition ring is one of a pair of inner walls disposed opposite to each other in the ring groove. an upper partition surface facing an upper groove wall surface which is a groove wall surface on the combustion chamber side of the internal combustion engine; a lower partition surface facing a lower groove wall surface which is a groove wall surface on the crank chamber side of the internal combustion engine, of a pair of inner walls arranged opposite to each other in the ring groove; an inner peripheral fitting surface which is provided on an inner peripheral portion of the partition ring and which fits with the bottom groove wall surface which connects an inner peripheral edge of the upper groove wall surface and an inner peripheral edge of the lower groove wall surface of the ring groove to form a contact state with the bottom groove wall surface; and an outer peripheral separating surface which is provided on an outer peripheral portion of the partition ring and which ensures a predetermined separation distance from an inner wall of a cylinder of the internal combustion engine, The partition ring has a lower protruding portion that is provided on the inside of the lower partition wall surface in the radial direction of the piston and protrudes toward the crank chamber to be supported in the axial direction of the piston. A combination structure of piston and piston ring.

3. a first partition ring as the partition ring, and a second partition ring attached to a position in the ring groove closer to the crank chamber than the first partition ring, the first partition ring has a first upper partition wall surface as the upper partition wall surface, a first lower partition wall surface as the lower partition wall surface, a first inner peripheral fitting surface as the inner peripheral fitting surface, and a first outer peripheral spacing surface as the outer peripheral spacing surface, the second partition ring has a second upper partition surface facing the first lower partition surface of the first partition ring, a second lower partition surface facing the lower groove wall surface of the ring groove, a second inner peripheral fitting surface provided on an inner peripheral surface of the second partition ring and fitting with the bottom groove wall surface to form a contact state with the bottom groove wall surface, and a second outer peripheral spacing surface provided on an outer peripheral surface of the second partition ring to ensure a predetermined spacing distance between the second partition ring and an inner wall of the cylinder, A plurality of piston rings are fitted in the ring groove, The plurality of piston rings include a top ring mounted between the upper groove wall surface of the ring groove and the first upper partition wall surface of the first partition ring, a second ring mounted between the first lower partition wall surface of the first partition ring and the second upper partition wall surface of the second partition ring, and an oil ring mounted between the lower groove wall surface of the ring groove and the second lower partition wall surface of the second partition ring.

3. A combined structure of a piston and a piston ring according to claim 1 or 2.

4. A plurality of piston rings are fitted in the ring groove, A partition portion that divides the ring groove is formed by a plurality of the partition rings that are arranged between the plurality of piston rings so as to overlap each other in the axial direction of the piston, In the partition portion, the partition rings adjacent to each other in the axial direction have different properties.

3. A combined structure of a piston and a piston ring according to claim 1 or 2.

5. The partition ring has a pair of joint ends that face each other to form a joint, The pair of joint ends are each formed in a key shape so that they are engaged with each other while overlapping in the radial direction of the partition ring.

3. A combined structure of a piston and a piston ring according to claim 1 or 2.

6. The partition ring has a pair of joint ends that face each other to form a joint, The piston has a protrusion protruding into the ring groove, The joint includes a receiving portion capable of receiving the protrusion, When the protrusion is received in the receiving portion, the rotation of the partition ring relative to the piston is restricted.

3. A combined structure of a piston and a piston ring according to claim 1 or 2.

7. A partition ring is mounted in a ring groove for mounting a piston ring provided on an outer circumferential surface of a piston mounted in a cylinder, together with one or more piston rings, in an axial direction, In a use state in which the partition ring is attached to the ring groove, the partition ring is fitted to a bottom groove wall surface, which is the bottom surface of the ring groove, with a predetermined gap between the partition ring and the inner wall of the cylinder, The piston is a piston that is attached to the cylinder of an internal combustion engine, The partition ring is an upper partition wall surface that faces an upper groove wall surface, which is a groove wall surface on the combustion chamber side of the internal combustion engine, of a pair of inner walls that are opposed to each other in the ring groove when the partition ring is attached to the ring groove in use; a lower partition wall surface that faces a lower groove wall surface, which is a groove wall surface on a crank chamber side of the internal combustion engine, of a pair of inner walls that are opposed to each other in the ring groove in the use state; an inner peripheral fitting surface provided on an inner peripheral portion of the partition ring, the inner peripheral surface fitting into the bottom groove wall surface that connects an inner peripheral edge of the upper groove wall surface and an inner peripheral edge of the lower groove wall surface of the ring groove in the usage state, thereby forming a contact state with the bottom groove wall surface; an outer peripheral separation surface that is provided on an outer peripheral portion of the partition ring and that ensures a predetermined separation distance between the outer peripheral surface and an inner wall of a cylinder of the internal combustion engine in the usage state; The partition ring has an upper protruding portion that is provided on the inside of the upper partition wall surface in the radial direction of the piston and protrudes toward the combustion chamber to be supported in the axial direction of the piston. Partition ring.

8. A partition ring that is mounted in an axial direction together with one or more piston rings in a ring groove for mounting a piston ring provided on the outer peripheral surface of a piston mounted in a cylinder, In a use state in which the partition ring is attached to the ring groove, the partition ring is fitted to a bottom groove wall surface, which is the bottom surface of the ring groove, with a predetermined gap between the partition ring and the inner wall of the cylinder, The piston is a piston that is attached to the cylinder of an internal combustion engine, The partition ring is an upper partition wall surface that faces an upper groove wall surface, which is a groove wall surface on the combustion chamber side of the internal combustion engine, of a pair of inner walls that are opposed to each other in the ring groove when the partition ring is attached to the ring groove in use; a lower partition wall surface that faces a lower groove wall surface, which is a groove wall surface on a crank chamber side of the internal combustion engine, of a pair of inner walls that are opposed to each other in the ring groove in the use state; an inner peripheral fitting surface provided on an inner peripheral portion of the partition ring, the inner peripheral surface fitting into the bottom groove wall surface that connects an inner peripheral edge of the upper groove wall surface and an inner peripheral edge of the lower groove wall surface of the ring groove in the usage state, thereby forming a contact state with the bottom groove wall surface; an outer peripheral separation surface that is provided on an outer peripheral portion of the partition ring and that ensures a predetermined separation distance between the outer peripheral surface and an inner wall of a cylinder of the internal combustion engine in the usage state; The partition ring has a lower protruding portion that is provided on the inside of the lower partition wall surface in the radial direction of the piston and protrudes toward the crank chamber to be supported in the axial direction of the piston. Partition ring.

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