Piston rings, pistons, and reciprocating compressors

Abstract

The present invention provides piston rings, pistons, and reciprocating compressors that can improve compression efficiency. [Solution] The piston ring comprises an inner annular member extending circumferentially and an outer annular member positioned radially outside the inner annular member and extending circumferentially to surround the inner annular member. Each of the inner and outer annular members has at least one joint gap, which is the gap between a pair of opposing surfaces facing each other along the circumferential direction. The joint gap of the outer annular member is offset circumferentially from the joint gap of the inner annular member so that it does not overlap with the joint gap of the inner annular member when viewed radially from the central axis of the inner annular member.

Description

Technical Field

[0001] The present invention relates to a piston ring, a piston, and a reciprocating compressor.

Background Art

[0002] Liquefied gas is stored in a tank for storage or transportation. Generally, the liquefaction temperature of the gas is lower than the atmospheric temperature. Therefore, the liquefied gas stored in the tank vaporizes inside the tank due to heat input to the tank. This gas is called so-called boil-off gas (BOG). This gas (BOG) increases the internal pressure of the tank. Therefore, by compressing the vaporized gas, the internal pressure of the tank is kept at a predetermined value. Patent Document 1 discloses a system for compressing vaporized gas. In this system, the internal pressure of a tank storing low-temperature liquefied gas is controlled. In Patent Document 1, a reciprocating compressor is exemplified as the compressor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the reciprocating compressor described above, the piston moves back and forth inside the cylinder, compressing the gas inside the cylinder and generating high-pressure gas. In this reciprocating compressor, a piston ring that fits into the ring groove of the piston is used to seal the gap between the piston and the cylinder. When the piston reciprocates, the side surface of the piston ring is pressed axially against the side surface of the ring groove by inertial force. Then, high-pressure gas enters between the inner surface of the piston ring and the bottom surface of the ring groove, pressing the outer surface of the piston ring against the inner surface of the cylinder. This seals the gap between the piston ring and the cylinder.

[0005] Piston rings have a gap formed in the circumferential direction, which is partially open, to suppress the occurrence of problems due to thermal expansion. However, such a gap can form a flow path through which gas leaks along the axial direction. Therefore, to block such flow paths, a piston ring is sometimes used in which two ring members are stacked axially with the circumferential positions of the gaps offset from each other. However, even with such a piston ring, a flow path through which gas leaks can form between one ring member and the side surface of the ring groove in the gap. In this case, gas that has entered between the inner circumferential surface of the piston ring and the bottom surface of the ring groove may leak into another space through the flow path formed by the gap. Such gas leakage can reduce the gas sealing performance inside the cylinder, which can lead to a decrease in compression efficiency.

[0006] The present invention provides a piston ring, a piston, and a reciprocating compressor that can improve compression efficiency. [Means for solving the problem]

[0007] A piston ring according to one embodiment of the present invention comprises an inner annular member extending circumferentially and an outer member positioned radially outside the inner annular member and extending circumferentially to surround the inner annular member. Each of the inner annular member and the outer annular member has at least one joint gap, which is the gap between a pair of opposing surfaces facing each other along the circumferential direction. The joint gap of the outer annular member is offset circumferentially from the joint gap of the inner annular member such that it does not overlap with the joint gap of the inner annular member when viewed radially from the central axis of the inner annular member.

[0008] This piston ring comprises an inner annular member and an outer annular member surrounding the inner annular member. The gap of the outer annular member is offset circumferentially from the gap of the inner annular member so that, when viewed radially from the central axis of the inner annular member, it does not overlap radially with the gap of the inner annular member. In this case, when the piston ring is fitted into the ring groove formed in the piston, the outer annular member can be brought into contact with the side surface of the ring groove at the gap of the inner annular member, thus blocking the flow path through which gas leaks out of the gap of the inner annular member. Similarly, the inner member can be brought into contact with the side surface of the ring groove at the gap of the outer annular member, thus blocking the flow path through which gas leaks out of the gap of the outer annular member. Therefore, at both the gaps of the inner and outer annular members, it is possible to prevent gas that has entered between the inner circumferential surface of the inner annular member and the bottom surface of the ring groove from leaking out into another space through the gap between either annular member and the side surface of the ring groove. This improves the gas sealing performance, making it possible to improve compression efficiency.

[0009] In one embodiment, the outer annular member has a first annular body and a second annular body aligned along the axial direction in which the central axis extends. The outer annular member has a joint gap, a first joint gap provided in the first annular body and a second joint gap provided in the second annular body. The first joint gap may be offset circumferentially from the second joint gap so as not to overlap with the second joint gap in the axial direction. In this case, the flow path through which gas leaks axially through the first joint gap of the first annular body can be blocked by the second annular body. Furthermore, the flow path through which gas leaks axially through the second joint gap of the second annular body can be blocked by the first ring body. Therefore, with the above configuration, in addition to the flow path through which gas leaks from between the inner circumferential surface of the inner annular member and the bottom surface of the ring groove, and between the side surface of the piston ring and the side surface of the ring groove, the flow path through which gas leaks from between the outer circumferential surface of the outer annular member and the inner circumferential wall of the cylinder can also be blocked. This further improves the gas sealing performance, making it possible to further improve compression efficiency.

[0010] In one embodiment, a groove extending in the circumferential direction is formed on one of the circumferential surfaces of the inner annular member and the inner circumferential surface of the outer annular member, and a projection that fits into the groove is formed on the other circumferential surface, and the side surface of the groove and the side surface of the projection may face each other along the axial direction of the inner annular member. In this case, the engagement of the groove and the projection can suppress axial displacement between the inner annular member and the outer annular member. As a result, the inner annular member and the outer annular member can be held together as a single unit, and a configuration in which the flow path through which gas leaks out through the joint gap of one of the inner annular member and the outer annular member is blocked by the other of the inner annular member and the outer annular member can be realized more reliably. As a result, the gas sealing performance can be more reliably improved.

[0011] In one embodiment, a recess is formed on one of the outer circumferential surfaces of the inner annular member and the inner circumferential surface of the outer annular member, and a protrusion that fits into the recess is formed on the other of the outer and inner circumferential surfaces, and the side surface of the recess and the side surface of the protrusion may face each other along the circumferential direction. In this case, the fitting of the recess and the protrusion can suppress rotational displacement in the circumferential direction between the inner annular member and the outer annular member. This makes it possible to more reliably maintain a state in which the joint gap of the outer annular member is shifted in the circumferential direction so as not to overlap radially with the joint gap of the inner annular member. As a result, it is possible to more reliably realize a configuration in which the flow path through which gas leaks out of one of the joint gaps of the inner annular member and the outer annular member is blocked by the other of the inner annular member and the outer annular member. This makes it possible to more reliably improve the gas sealing performance.

[0012] One form of piston ring may further include an inner ring positioned radially inward of the inner annular member and extending circumferentially so as to surround the inner annular member. In this case, the inner ring applies tension radially outward relative to the inner surface of the inner annular member, thereby pressing the outer surface of the outer annular member against the inner wall of the cylinder. This reduces the gap between the outer surface of the outer annular member and the inner wall of the cylinder. As a result, the flow path through which gas leaks axially between the outer surface of the outer annular member and the inner wall of the cylinder can be blocked, thereby more reliably improving gas sealing performance.

[0013] In one embodiment, the outer annular member may be made of a material with higher wear resistance than the inner annular member. In this case, significant wear of the outer circumferential surface of the outer annular member in response to the reciprocating motion of the piston can be suppressed, thereby preventing the formation of a gap between the outer circumferential surface of the outer annular member and the inner circumferential wall of the cylinder due to wear. As a result, the flow path through which gas leaks axially through the space between the outer circumferential surface of the outer annular member and the inner circumferential wall of the cylinder can be blocked, thereby more reliably improving the gas sealing performance.

[0014] A piston according to one embodiment of the present invention comprises a piston ring as described above, a piston head including an outer peripheral wall having a ring groove formed therein in which the piston ring fits, and a piston rod connected to the piston head and extending along the axial direction in which the central axis extends.

[0015] Since this piston is equipped with one of the piston rings described above, it produces the same effect as described above.

[0016] A reciprocating compressor according to one embodiment of the present invention comprises the piston described above and a cylindrical cylinder including an inner circumferential wall surrounding the outer circumferential wall, into which the piston is inserted so as to be reciprocally movable along the axial direction, and together with the piston, forms a compression chamber.

[0017] Since this reciprocating compressor is equipped with the piston described above, it produces the same effects as described above. [Effects of the Invention]

[0018] According to one embodiment of the present invention, a piston ring, a piston, and a reciprocating compressor can improve compression efficiency. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is a schematic diagram showing a reciprocating compressor according to an embodiment. [Figure 2] Figure 2 is a perspective view showing the piston in Figure 1. [Figure 3] Figure 3 is a cross-sectional view showing an enlarged view of section A1 of the piston in Figure 1. [Figure 4] Figure 4(a) is a plan view showing the piston ring of the embodiment. Figure 4(b) is a partial cross-sectional view showing the piston ring of Figure 4(a). [Figure 5] Figure 5 is a cross-sectional view showing an enlarged view of section A2 in Figure 4(b). [Figure 6] Figure 6 is a plan view showing an enlarged view of section A3 of Figure 4(a). [Figure 7]FIG. 7 is a cross-sectional view taken along line VII-VII of FIG. 4(a). [Figure 8] FIG. 8 is a cross-sectional view taken along line VIII-VIII of FIG. 4(a). [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX of FIG. 4(a). [Figure 10] FIG. 10(a) is a plan view showing another piston ring. FIG. 10(b) is a partial cross-sectional view showing the piston ring of FIG. 10(a). [Figure 11] FIG. 11(a) is a plan view showing the piston ring of Comparative Example 1. FIG. 11(b) is a cross-sectional view taken along line XI-XI of FIG. 11(a).

MODE FOR CARRYING OUT THE INVENTION

[0020] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0021] <reciprocating compressor> The reciprocating compressor 1 shown in FIG. 1 constitutes, for example, a boil-off gas (BOG) compression system. The BOG compression system is installed in a receiving base and a storage base for hydrogen, etc. The storage base includes a tank for storing liquid hydrogen. Inside the tank, liquid hydrogen vaporizes to generate hydrogen gas. The BOG compression system is used for compressing this hydrogen gas.

[0022] The following description exemplifies a case where the gas to be compressed by the reciprocating compressor 1 is hydrogen gas. However, the gas to be compressed by the reciprocating compressor 1 is not limited to hydrogen gas, but may be other gaseous fuels such as natural gas and propane gas. Therefore, the reciprocating compressor 1 is applicable to systems that compress, for example, BOG, but the gas that the reciprocating compressor 1 compresses is not limited to BOG. ​​For example, the reciprocating compressor 1 can be suitably used in systems that target gases having a liquefaction temperature lower than that of air. Examples of such gases include the aforementioned hydrogen and helium. In this disclosure, the term "gas" in a broad sense means gaseous fuels, including natural gas. Furthermore, the term "gas" in a narrow sense means gaseous fuels, such as hydrogen gas, that have a liquefaction temperature lower than that of air.

[0023] As shown in Figure 1, the reciprocating compressor 1 comprises a piston 5, a cylinder 6, and a housing 3. The reciprocating compressor 1 compresses the supplied gas to a predetermined pressure. The cylinder 6 is covered by the housing 3 and housed inside the housing 3. The cylinder 6 is, for example, cylindrical. The cylinder 6 may have a cylindrical cylinder liner. In that case, the material of the cylinder liner may be, for example, metal, and may have a different thermal shrinkage rate than the piston ring 60 described later. The cylinder 6 and piston 5 form compression spaces P1, P2 (compression chambers) for compressing the gas. The housing 3 is provided with an intake mechanism 3a that can draw gas into the compression spaces P1, P2, and a discharge mechanism 3b that can discharge gas from the compression spaces P1, P2.

[0024] The intake mechanism 3a introduces gas into the cylinder 6. The gas to be inhaled is, for example, hydrogen gas at -245°C. The intake mechanism 3a has an intake valve 2b provided in the cylinder 6. The intake valve 2b switches between a state that allows gas intake (open mode) and a state that does not allow gas intake (closed mode) depending on the internal pressure of the compression spaces P1 and P2. For example, when the internal pressure of the compression spaces P1 and P2 decreases (intake), the intake valve 2b takes the open mode, which allows gas to enter and exit. On the other hand, when the internal pressure of the compression spaces P1 and P2 increases (compression), the intake valve 2b takes the closed mode, which prohibits gas from entering and exiting.

[0025] The discharge mechanism 3b discharges gas from inside the cylinder 6. For example, the discharged gas is hydrogen gas at minus 200°C. The discharge mechanism 3b has a discharge valve 2a located on the opposite side of the intake valve 2b in the cylinder 6. The discharge valve 2a is closed when the internal pressure of the compression spaces P1 and P2 decreases (intake). On the other hand, the discharge valve 2a is open when the internal pressure of the compression spaces P1 and P2 increases (compression).

[0026] In this manner, the reciprocating compressor 1 compresses the gas drawn into the cylinder 6 via the intake valve 2b using the piston 5, and then discharges the compressed gas through the discharge valve 2a.

[0027] An unloader 4 is attached to the intake valve 2b. The unloader 4 functions as a capacity adjustment mechanism for the reciprocating compressor 1. When the internal pressure of the compression spaces P1 and P2 increases, the unloader 4 forcibly releases the closed state. For example, when capacity control is required, the unloader 4 presses the intake valve 2b, opening the intake valve 2b. When the intake valve 2b is open, gas compression does not occur inside the cylinder 6, and the internal pressure does not increase. As a result, the discharge valve 2a, which is opened by the increase in internal pressure of the compression spaces P1 and P2, does not open, and compressed gas is not supplied. Therefore, by using the unloader 4, it is possible to adjust the compression capacity of the reciprocating compressor 1.

[0028] <Piston> As shown in Figures 1 and 2, the piston 5 comprises a piston rod 53 and a piston head 55. The piston rod 53 is, for example, a rod shape extending along the axial direction D1. The axial direction D1 is the direction in which the central axis C60 of the piston ring 60 (see Figure 4(a)), which will be described later, extends. The central axis C53 of the piston rod 53 coincides with the central axis C60 of the piston ring 60. The piston head 55 is connected to one end of the piston rod 53. The other end of the piston rod 53 is connected to the piston drive unit. The piston rod 53 transmits the reciprocating motion of the piston drive unit to the piston head 55.

[0029] The piston head 55 has a cylindrical shape extending along the axial direction D1 and has a larger outer diameter than the piston rod 53. The piston head 55 includes an end face 55a to which one end of the piston rod 53 is connected, and an outer peripheral wall 55b extending from the end face 55a along the axial direction D1. The outer peripheral wall 55b constitutes the outer peripheral surface of the piston head 55.

[0030] As shown in Figures 1 and 3, the piston 5 is inserted into the cylinder 6 in an axial direction D1. The piston 5 is configured to reciprocate along the axial direction D1 while inserted into the cylinder 6. The outer peripheral wall 55b of the piston head 55 is surrounded by the inner peripheral wall 6a of the cylinder 6. The outer peripheral wall 55b is an outer peripheral surface extending along the circumferential direction D2 (see Figure 2). The outer peripheral wall 55b faces the inner peripheral wall 6a of the cylinder 6 with a gap in the radial direction D3. The circumferential direction D2 is the direction along the ring of the piston ring 60 centered on the central axis C60 (see Figure 4(a)). The radial direction D3 is the direction perpendicular to the central axis C60.

[0031] As shown in Figure 3, the piston 5 further comprises a plurality (three in this embodiment) of piston rings 60 and a pair of piston rings 60A. Note that in Figure 2, the pair of piston rings 60A are omitted. The plurality of piston rings 60 are each fitted into a plurality of ring grooves 56 formed in the outer peripheral wall 55b of the piston head 55, sealing the gap between the outer peripheral wall 55b and the inner peripheral wall 6a of the cylinder 6. The plurality of ring grooves 56 are annular grooves extending along the circumferential direction D2 of the outer peripheral wall 55b and are spaced apart along the axial direction D1. Accordingly, the plurality of piston rings 60 are also arranged to be spaced apart along the axial direction D1.

[0032] A pair of piston rings 60A are positioned in a pair that sandwich the plurality of piston rings 60 in the axial direction D1. The pair of piston rings 60A may have a different configuration from, for example, the plurality of piston rings 60. The pair of piston rings 60A may have the same configuration as the plurality of piston rings 60. A pair of rider rings 80 are provided in the pair that sandwich the pair of piston rings 60A in the axial direction D1. The pair of rider rings 80 are fitted into a pair of ring grooves formed in the outer peripheral wall 55b and slide along the inner peripheral wall 6a to support the piston 5 in the radial direction D3.

[0033] <Piston Rings> Next, the configuration of the piston ring 60 described above will be explained in detail. As shown in Figures 4(a) and 4(b), the piston ring 60 comprises an inner cover 63 (inner annular member), an outer cover 65 (outer annular member), and an inner ring 67. The inner cover 63 and the outer cover 65 are each annular ring members centered on a central axis C60 and extending along the circumferential direction D2. The outer cover 65 is formed separately from the inner cover 63. The central axis C60 coincides with the central axis of the inner cover 63 and the central axis of the outer cover 65. The outer cover 65 is located radially outward D3 from the inner cover 63 and is arranged concentrically with the inner cover 63. In other words, the outer cover 65 extends along the circumferential direction D2 so as to surround the inner cover 63.

[0034] The outer cover 65 is positioned at the same location as the inner cover 63 in the axial direction D1, and is positioned to overlap the inner cover 63 in the radial direction D3. Thus, the piston ring 60 has a structure in which two ring members are divided in the radial direction D3. The width of the outer cover 65 along the axial direction D1 may be the same as the width of the inner cover 63 along the axial direction D1. The thickness T of the outer cover 65 along the radial direction D3 is set to be greater than the gap S between the inner circumferential wall 6a of the cylinder 6 and the outer circumferential wall 55b of the piston head 55 (see Figure 7 described later).

[0035] The outer cover 65 is made of a material with higher wear resistance than the inner cover 63. In this case, the materials of the outer cover 65 and the inner cover 63 are selected such that the amount of wear on the outer cover 65 due to sliding between the outer cover 65 and the inner circumferential wall 6a of the cylinder 6 (see Figure 3) is lower than the amount of wear on the inner cover 63 due to sliding between the inner cover 63 and the inner circumferential wall 6a of the cylinder 6. A parameter that indicates the level of wear resistance may be, for example, the coefficient of friction. For example, a small coefficient of friction indicates high wear resistance. Therefore, the fact that the outer cover 65 is made of a material with higher wear resistance than the inner cover 63 means that the outer cover 65 is made of a material with a smaller coefficient of friction than the inner cover 63, that is, the coefficient of friction of the outer cover 65 is smaller than the coefficient of friction of the inner cover 63.

[0036] As shown in Figure 4(b), the inner cover 63 includes an inner circumferential surface 63a facing inward in the radial direction D3 and an outer circumferential surface 63b facing outward in the radial direction D3. Each of the inner circumferential surface 63a and the outer circumferential surface 63b is a circumferential surface extending along the circumferential direction D2. The outer cover 65 includes an inner circumferential surface 65a facing inward in the radial direction D3 and an outer circumferential surface 65b facing outward in the radial direction D3. Each of the inner circumferential surface 65a and the outer circumferential surface 65b is a circumferential surface extending along the circumferential direction D2. The inner circumferential surface 65a extends along the circumferential direction D2 so as to surround the outer circumferential surface 63b of the inner cover 63. That is, the inner circumferential surface 65a faces the outer circumferential surface 63b and the radial direction D3 over the entire circumference of the circumferential direction D2. The inner circumferential surface 65a may be in contact with the outer circumferential surface 63b and the radial direction D3.

[0037] As shown in Figure 4(a), a joint gap S63 is formed at one location in the circumferential direction D2 of the inner cover 63. The joint gap S63 is a small gap formed between a pair of end faces 63c, 63d (a pair of opposing surfaces) that face each other along the circumferential direction D2. The pair of end faces 63c, 63d are the end faces of the inner cover 63 in the circumferential direction D2. The joint gap S63 can also be described as an opening in which a part of the circumferential direction D2 of the inner cover 63 opens. The joint gap S63 can be defined as the space region sandwiched between the pair of end faces 63c, 63d. The joint gap S63 is formed to prevent defects (e.g., breakage or abnormal wear) caused by deformation of the inner cover 63 during thermal expansion. Multiple joint gaps may be formed at multiple locations on the inner cover 63 along the circumferential direction D2.

[0038] As shown in Figure 4(b), the outer cover 65 has a first ring member 71 (first annular body) and a second ring member 72 (second annular body) arranged along the axial direction D1. Each of the first ring member 71 and the second ring member 72 is an annular ring member extending along the circumferential direction D2 with respect to the central axis C60. The second ring member 72 is formed separately from the first ring member 71. The second ring member 72 has the same outer diameter as the first ring member 71 and is positioned to overlap the first ring member 71 in the axial direction D1. The second ring member 72 may be in contact with the first ring member 71 in the axial direction D1. Thus, the outer cover 65 has a structure in which two ring members are divided along the axial direction D1.

[0039] The first ring member 71 has multiple (three in this embodiment) first joint gaps S71 formed therein. The three first joint gaps S71 are formed at equally spaced positions along the circumferential direction D2. For example, the three first joint gaps S71 are arranged at intervals of 120° around the central axis C60.

[0040] The first ring member 71 is divided into three segmented pieces P71 by the formation of three first joint gaps S71. In other words, the first ring member 71 is composed of three (or more) segmented pieces P71 divided in the circumferential direction D2. Each segmented piece P71 is an arc-shaped member extending along the circumferential direction D2, and they are arranged adjacent to each other along the circumferential direction D2. Each segmented piece P71 includes an end face P71a located at one end along the circumferential direction D2, and an end face P71b located on the opposite side of end face P71a. Of two adjacent segmented pieces P71, the end face P71a of one segmented piece P71 faces the end face P71b of the other segmented piece P71 with a small gap in the circumferential direction D2. The first joint gap S71 is formed between these end faces P71a and P71b (a pair of opposing faces). A single first joint gap may be formed at only one location in the circumferential direction D2 of the first ring member 71.

[0041] The second ring member 72 has multiple (three in this embodiment) second joint gaps S72 formed therein. The three second joint gaps S72 are formed at equally spaced positions along the circumferential direction D2 of the second ring member 72. For example, the three second joint gaps S72 are arranged at intervals of 120° around the central axis C60. Thus, the outer cover 65 has three first joint gaps S71 and three second joint gaps S72 formed therein.

[0042] The second ring member 72 is divided into three segmented pieces P72 by the formation of three second joint gaps S72. In other words, the second ring member 72 is composed of three (or more) segmented pieces P72 divided in the circumferential direction D2. Each segmented piece P72 is an arc-shaped member extending along the circumferential direction D2 and is arranged adjacent to one another along the circumferential direction D2. Each segmented piece P72 includes an end face P72a located at one end along the circumferential direction D2 and an end face P72b located on the opposite side of end face P72a. Of two adjacent segmented pieces P72, the end face P72a of one segmented piece P72 faces the end face P72b of the other segmented piece P72 with a small gap in the circumferential direction D2. The second joint gap S72 is formed between these end faces P72a and P72b (a pair of opposing faces). A single second joint gap may be formed at only one location in the circumferential direction D2 of the second ring member 72.

[0043] In this embodiment, the first joint gap S71 and the second joint gap S72 are offset in the circumferential direction D2 relative to the joint gap S63 of the inner cover 63 so that they do not overlap with the joint gap S63 of the inner cover 63 when viewed along the radial direction D3 from the central axis C60. That is, the first joint gap S71 and the second joint gap S72 are positioned offset along the circumferential direction D2 from a position adjacent to and overlapping with the joint gap S63 in the radial direction D3. Therefore, with respect to the central axis C60, the phase angles of the first joint gap S71 and the second joint gap S72 are set to be different from the phase angle of the joint gap S63. The first joint gap S71 and the second joint gap S72 may be positioned, for example, 180° opposite to the joint gap S63 around the central axis C60.

[0044] The position where the first joint gap S71 is adjacent to and overlaps with the joint gap S63 in the radial direction D3 means a position where the first joint gap S71 and the joint gap S63, which are adjacent to each other in the radial direction D3, have overlapping regions in the radial direction D3. Therefore, the position where the first joint gap S71 is positioned offset along the circumferential direction D2 from the position where it is adjacent to and overlaps with the joint gap S63 in the radial direction D3 means that the entire region of the first joint gap S71 is positioned so that it does not overlap with the joint gap S63 in the radial direction D3. As a result, when viewed along the radial direction D3 from the central axis C60, neither of the pair of end faces P71a and P71b that form the first joint gap S71 is positioned between the pair of end faces 63c and 63d that form the joint gap S63.

[0045] Similarly, the position where the second joint gap S72 is adjacent to and overlaps with the joint gap S63 in the radial direction D3 means that the second joint gap S72 and the joint gap S63, which are adjacent to each other in the radial direction D3, are arranged so that they have overlapping regions in the radial direction D3. Therefore, the position where the second joint gap S72 is positioned offset along the circumferential direction D2 from the position where it is adjacent to and overlaps with the joint gap S63 in the radial direction D3 means that the entire region of the second joint gap S72 is arranged so that it does not overlap with the joint gap S63 in the radial direction D3. As a result, when viewed along the radial direction D3 from the central axis C60, neither of the pair of end faces P72a and P72b that form the second joint gap S72 is located between the pair of end faces 63c and 63d that form the joint gap S63.

[0046] Furthermore, the second joint gap S72 is offset in the circumferential direction D2 so as not to overlap with the first joint gap S71 in the axial direction D1. That is, the second joint gap S72 is positioned at a location offset along the circumferential direction D2 from a position adjacent to and overlapping with the first joint gap S71 in the axial direction D1. The position where the second joint gap S72 is adjacent to and overlapping with the first joint gap S71 in the radial direction D3 means a position where the first joint gap S71 and the second joint gap S72, which are adjacent to each other in the axial direction D1, have regions that overlap with each other in the axial direction D1.

[0047] Therefore, when the second joint gap S72 is positioned at a location offset along the circumferential direction D2 from a position adjacent to and overlapping with the first joint gap S71 in the axial direction D1, it means that the entire area of ​​the second joint gap S72 is positioned so that it does not overlap with the first joint gap S71 in the axial direction D1. As a result, when viewed along the axial direction D1, neither of the pair of end faces P71a and P71b that form the first joint gap S71 is positioned between the pair of end faces P72a and P72b that form the second joint gap S72.

[0048] As shown in Figure 5, a groove 68 is formed in the inner circumferential surface 65a of the outer cover 65. The groove 68 is a rectangular groove that is recessed inward from the inner circumferential surface 65a in the radial direction D3 and is formed to extend along the circumferential direction D2. The groove 68 is formed in areas of the inner circumferential surface 65a other than a portion of area R65 (see Figure 4(a)). In other words, the groove 68 is not formed in area R65 of the inner circumferential surface 65a. Area R65 may be, for example, an area demarcated by a phase angle centered on the central axis C60. The groove 68 includes a bottom surface 68a that is recessed inward from the inner circumferential surface 65a in the radial direction D3, and a pair of side surfaces 68b that connect the bottom surface 68a and the inner circumferential surface 65a in the radial direction D3. The pair of side surfaces 68b are aligned along the axial direction D1 and are arranged to face each other along the axial direction D1. Each of the pair of sides 68b is, for example, a plane that intersects (e.g., orthogonal to) the axial direction D1.

[0049] A projection 69 is formed on the outer circumferential surface 63b of the inner cover 63, which fits into a groove 68 of the outer cover 65. The projection 69 is a rectangular projection that protrudes radially D3 outward from the outer circumferential surface 63b toward the groove 68 of the inner circumferential surface 65a, and is formed to extend along the circumferential direction D2. The projection 69 is formed on the region of the outer circumferential surface 63b that faces the groove 68 radially D3. The projection 69 includes a top surface 69a that protrudes radially D3 outward from the outer circumferential surface 63b, and a pair of side surfaces 69b that connect the top surface 69a and the outer circumferential surface 63b radially D3. The pair of side surfaces 69b are aligned along the axial direction D1 and are arranged to face opposite each other in the axial direction D1. Each of the pair of side surfaces 69b is, for example, a plane that intersects (e.g., orthogonal to) the axial direction D1.

[0050] When the projection 69 is fitted into the groove 68, the top surface 69a of the projection 69 faces the bottom surface 68a of the groove 68 in the radial direction D3. The top surface 69a may also be in contact with the bottom surface 68a. In addition, the pair of side surfaces 69b of the projection 69 face the pair of side surfaces 68b of the groove 68 in the axial direction D1. The side surfaces 69b may also be in contact with the side surfaces 68b. The contact of the side surfaces 69b with the side surfaces 68b in the axial direction D1 restricts the relative movement of the inner cover 63 and the outer cover 65 along the axial direction D1. Therefore, the groove 68 and the projection 69 constitute a misalignment restricting mechanism that restricts the misalignment of the inner cover 63 and the outer cover 65 along the axial direction D1.

[0051] As shown in Figure 6, a protrusion 75 is further formed on the inner circumferential surface 65a of the outer cover 65. In Figure 6, the protrusion 75 and the recess 73, which will be described later, are hatched for ease of understanding. The protrusion 75 is a rectangular protrusion that projects radially outward in the direction D3 toward the outer circumferential surface 63b of the inner cover 63, and is formed in a portion of the inner circumferential surface 65a, specifically in area R65, where the groove 68 is not formed. The protrusion 75 projects radially outward in the direction D3 from, for example, the bottom surface 68a of the groove 68 formed on the outer circumferential surface 63b. The protrusion 75 includes a top surface 75a that projects radially outward in the direction D3 from the inner circumferential surface 65a, and a pair of side surfaces 75b that connect the top surface 75a and the inner circumferential surface 65a in the direction D3. The pair of side surfaces 75b are aligned along the circumferential direction D2 and are arranged to face opposite each other along the circumferential direction D2. Each of the pair of sides 75b is, for example, a plane intersecting the circumferential direction D2. Each of the pair of sides 75b may be, for example, inclined from a plane perpendicular to the circumferential direction D2.

[0052] A recess 73 is further formed on the outer peripheral surface 63b of the inner cover 63, which fits into the protrusion 75 of the outer cover 65. The recess 73 is a rectangular recess that is recessed inward in the radial direction D3, and is formed on the outer peripheral surface 63b in the region facing the protrusion 75 in the radial direction D3. The recess 73 includes a bottom surface 73a that is recessed inward in the radial direction D3 from the outer peripheral surface 63b, and a pair of side surfaces 73b that connect the bottom surface 73a and the outer peripheral surface 63b in the radial direction D3. The pair of side surfaces 73b are aligned along the circumferential direction D2 and are arranged to face each other along the circumferential direction D2. Each of the pair of side surfaces 73b is, for example, a plane that intersects the circumferential direction D2. Each of the pair of side surfaces 73b may be inclined from a plane perpendicular to the circumferential direction D2, for example, along the inclination direction of the side surface 75b.

[0053] When the recess 73 is fitted into the groove 68, the bottom surface 73a of the recess 73 faces the top surface 75a of the convex portion 75 in the radial direction D3. The bottom surface 73a may also be in contact with the top surface 75a. In addition, the pair of side surfaces 73b of the recess 73 face the pair of side surfaces 75b of the convex portion 75 in the circumferential direction D2. The side surfaces 73b may also be in contact with the side surfaces 75b. The contact of the side surfaces 73b with the side surfaces 75b in the circumferential direction D2 restricts the relative rotation of the inner cover 63 and the outer cover 65 along the circumferential direction D2. Therefore, the convex portion 75 and the recess 73 constitute a rotational misalignment restricting mechanism that restricts the rotational misalignment of the inner cover 63 and the outer cover 65 along the circumferential direction D2.

[0054] An inner ring groove 64 is formed on the inner circumferential surface 63a of the inner cover 63, extending along the circumferential direction D2. The inner ring groove 64 is formed on the inner circumferential surface 63a over the entire circumference in the circumferential direction D2. An inner ring 67 fits into the inner ring groove 64. The inner ring 67 is an annular ring member extending along the circumferential direction D2 centered on the central axis C60. The inner ring 67 is located inside the inner cover 63 in the radial direction D3 and is arranged concentrically with the inner cover 63. In other words, the inner ring 67 extends along the circumferential direction D2 so as to be surrounded by the inner cover 63. The material of the inner ring 67 is a metal such as stainless steel.

[0055] The piston ring 60 does not necessarily have an inner ring 67. The piston ring 60 is removable from the piston ring 60 depending on the situation. The inner ring 67 assists the tension on the inner cover 63 and outer cover 65 in the radial direction D3 from the piston head 55 toward the cylinder 6. In other words, the inner ring 67 applies tension to the inner circumferential surface 63a of the inner cover 63 radially outward in the radial direction D3. This tension causes the outer circumferential surface 65b of the outer cover 65 to press against the inner circumferential wall 6a of the cylinder 6. As a result, the gap between the outer circumferential surface 65b and the inner circumferential wall 6a becomes smaller.

[0056] The outer cover 65 and inner cover 63 are manufactured to dimensions that match the inner diameter of the cylinder 6. However, the outer cover 65 and inner cover 63 have different thermal expansion rates than the cylinder 6. Therefore, when the reciprocating compressor 1 is operated at low temperatures, a gap may occur between the piston ring 60 and the cylinder 6 due to the difference in these thermal expansion rates. By using the inner ring 67, it is possible to reduce this gap.

[0057] Figure 7 is a cross-sectional view along the line VII-VII in Figure 4. In this cross-section, since the joint gap S63, the first joint gap S71, and the second joint gap S72 are not formed, both the inner cover 63 and the outer cover 65 are present. Therefore, both the side surface 63e of the inner cover 63 and the side surface 65c of the outer cover 65 can be in contact with the side surface 56b of the ring groove 56. In this case, gas that enters between the inner circumferential surface 63a of the inner ring 67 and the bottom surface 56a of the ring groove 56 is blocked at the side surface 56b of the ring groove 56. Therefore, the gas flow path R1 that would otherwise leak from between the inner circumferential surface 63a of the inner ring 67 and the bottom surface 56a of the ring groove 56 through the sides 63e,65c of the piston ring 60 and the side surface 56b of the ring groove 56 to another space is blocked. Furthermore, the outer peripheral surface 65b of the outer cover 65 contacts the inner peripheral wall 6a of the cylinder 6, thereby blocking the flow path of gas leaking axially D1 through the gap between the outer peripheral surface 65b and the inner peripheral wall 6a.

[0058] Figure 8 is a cross-sectional view along the line VIII-VIII in Figure 4. In this cross-section, the second ring member 72 is absent because it is the location where the second joint gap S72 of the second ring member 72 is formed, while the inner cover 63 is present. Therefore, the side surface 63e of the inner cover 63 can be brought into contact with the bottom surface 56a of the ring groove 56. In this case, gas that enters between the inner circumferential surface 63a of the inner ring 67 and the bottom surface 56a of the ring groove 56 is blocked at the side surface 56b of the ring groove 56. Therefore, the gas flow path R2 that would otherwise leak from between the inner circumferential surface 63a of the inner ring 67 and the bottom surface 56a of the ring groove 56 through the sides 63e,65c of the piston ring 60 and the side surface 56b of the ring groove 56 to another space is blocked.

[0059] Furthermore, in the second joint gap S72, the second ring member 72 is absent, while the first ring member 71 is present. Therefore, the outer circumferential surface 65b of the first ring member 71 can be brought into contact with the inner circumferential wall 6a of the cylinder 6, thus blocking the flow path through which gas leaks axially D1 through the gap between the outer circumferential surface 65b and the inner circumferential wall 6a. In addition, in the first joint gap S71, the first ring member 71 is absent, while the second ring member 72 is present. Therefore, the outer circumferential surface 65b of the second ring member 72 can be brought into contact with the inner circumferential wall 6a of the cylinder 6, thus blocking the flow path through which gas leaks axially D1 through the gap between the outer circumferential surface 65b and the inner circumferential wall 6a.

[0060] Figure 9 is a cross-sectional view along the line IX-IX in Figure 4. In this cross-section, there is a gap S63 in the inner cover 63. In the gap S63, the inner cover 63 is absent, but the outer cover 65 is present. Therefore, gas that enters the space between the inner circumferential surface 65a of the outer cover 65 and the bottom surface 56a of the ring groove 56 (gap S63) is blocked at the side surface 56b of the ring groove 56. As a result, the gas flow path R3 that would otherwise leak from the space between the inner circumferential surface 65a of the outer cover 65 and the bottom surface 56a of the ring groove 56, through the space between the side surfaces 63e,65c of the piston ring 60 and the side surface 56b of the ring groove 56, to another space is blocked. Furthermore, in the gap S63, since the outer cover 65 is present, the outer circumferential surface 65b of the outer cover 65 contacts the inner circumferential wall 6a of the cylinder 6, thereby blocking the gas flow path that would otherwise leak axially D1 through the gap between the outer circumferential surface 65b and the inner circumferential wall 6a.

[0061] The configuration of the piston ring 60 of the present disclosure has been described above. As described above, the reciprocating compressor 1 of the present disclosure also includes another piston ring 60A, which is different from the piston ring 60. As shown in Figures 10(a) and 10(b), the piston ring 60A comprises a first ring member 91 and a second ring member 92 superimposed in the axial direction D1. Each of the first ring member 91 and the second ring member 92 is an annular ring member extending along the circumferential direction D2 centered on the central axis C60A. The central axis C60A coincides with the central axis C60 of the piston ring 60. As shown in Figure 10(a), the first ring member 91 includes three segmented pieces P91 divided in the circumferential direction D2. Similarly, the second ring member 92 includes three segmented pieces P92 divided in the circumferential direction D2.

[0062] One end face P91a of two adjacent segmented pieces P91 faces the other end face P91b in the circumferential direction D2, and a joint gap is formed between these end faces P91a and P91b. The opposing end faces P91a and P91b are inclined from a plane perpendicular to the circumferential direction D2. One end face P92a of two adjacent segmented pieces P92 faces the other end face P92b in the circumferential direction D2, and a joint gap is formed between these end faces P92a and P92b. The opposing end faces P92a and P92b are inclined from a plane perpendicular to the circumferential direction D2. The joint gap of the second ring member 92 is offset in the circumferential direction D2 relative to the joint gap of the first ring member 91 so as not to overlap in the axial direction D1. This suppresses gas leakage in the axial direction D1.

[0063] The effects and advantages obtained by the piston ring 60, piston 5, and reciprocating compressor 1 of this embodiment, as described above, will be explained along with the problems of the comparative example.

[0064] Figure 11(a) is a front view showing the piston ring 100 of Comparative Example 1. Figure 11(b) is a cross-sectional view along the line XI-XI in Figure 11(a). Figure 11(b) shows a cross-section of the piston ring 100 and its surroundings when the piston ring 100 is inserted into the cylinder 106. As shown in Figure 11(a), the piston ring 100 comprises two ring members 101 and 102 that are stacked on top of each other in the axial direction D1. The ring members 101 and 102 each have gaps S101 and S102 formed in a portion of the circumferential direction D2. The ring members 101 and 102 are stacked with their respective gaps S101 and S102 offset by 180° from each other. Such a piston ring 100 is generally called a one-cut double ring.

[0065] As shown in Figure 11(b), since the ring member 102 is absent at the joint gap S102, a gas flow path R100 is formed between the side surface 101a of the ring member 101 and the side surface 107b of the ring groove 107 of the piston head 105. In this case, there is a concern that gas that has entered between the inner circumferential surface 101b of the piston ring 100 and the bottom surface 107a of the ring groove 107 may leak out into other spaces through the flow path R100.

[0066] In such a piston ring 100, a gas leakage path R100 is formed, which can reduce the gas sealing performance inside the cylinder 106 and potentially decrease compression efficiency. Hydrogen gas, in particular, with a small molecular weight, is prone to causing such gas leakage. Furthermore, in low-temperature environments, the piston ring itself hardens, and due to differences in thermal expansion and contraction between the piston ring and the cylinder, a gap is more likely to form between the outer surface of the piston ring and the inner wall of the cylinder.

[0067] In contrast, the piston ring 60 of this embodiment comprises an inner cover 63 and an outer cover 65 surrounding the inner cover 63. The first gap S71 and the second gap S72 of the outer cover 65 are offset in the circumferential direction D2 so as not to overlap in the radial direction D3 with respect to the gap S63 of the inner cover 63. In this case, as shown in Figure 9, the side surface 65c of the outer cover 65 can be brought into contact with the side surface 56b of the ring groove 56 at the gap S63 of the inner cover 63, so that the flow path R3 through which gas leaks out of the gap S63 of the inner cover 63 can be blocked by the outer cover 65.

[0068] Furthermore, as shown in Figure 8, at the second joint gap S72 of the outer cover 65, the side surface 63e of the inner cover 63 can be brought into contact with the side surface 56b of the ring groove 56, so that the flow path R2 through which gas leaks out of the outer cover 65 via the second joint gap S72 can be blocked by the inner cover 63. The same applies at the location where the first joint gap S71 of the outer cover 65 is formed.

[0069] Therefore, in any of the gaps of the inner cover 63 (S63), the first gap of the outer cover 65 (S71), and the second gap of the outer cover 65 (S72), it is possible to suppress the leakage of gas that has entered between the inner circumferential surface 63a of the inner cover 63 and the bottom surface 56a of the ring groove 56 into another space through the space between the inner cover 63 or outer cover 65 and the side surface 56b of the ring groove 56. This improves the gas sealing performance, thereby improving compression efficiency. Furthermore, when the piston ring 60 is divided radially D3 in this way, the rigidity of the inner cover 63 and outer cover 65 can be reduced compared to when the piston ring 60 is composed of a single component, making it easier to press the inner cover 63 and outer cover 65 against the inner circumferential wall 6a of the cylinder 6 using the tension of the inner ring 67. In other words, it is possible to make the shapes of the inner cover 63 and outer cover 65 conform to the shape of the inner circumferential wall 6a of the cylinder 6. This prevents the formation of a gap between the outer peripheral surface 65b and the inner peripheral wall 6a of the outer cover 65, thereby further improving the gas sealing performance.

[0070] Furthermore, the formation of the first joint gap S71 divides the first ring member 71 into three segmented pieces P71. Similarly, the formation of the second joint gap S72 divides the second ring member 72 into three segmented pieces P72. Since these segmented pieces P71 and P72 can move independently, it becomes easier to make the first ring member 71 and the second ring member 72 conform to the shape of the inner circumferential wall 6a of the cylinder 6. In other words, the conformability of the outer cover 65 to the inner circumferential wall 6a of the cylinder 6 is further improved. As a result, the formation of a gap between the outer circumferential surface 65b of the outer cover 65 and the inner circumferential wall 6a can be avoided more reliably, thus further improving the gas sealing performance.

[0071] As in this embodiment, the first joint gap S71 of the outer cover 65 may be offset in the circumferential direction D2 relative to the second joint gap S72 so as not to overlap with the second joint gap S72 in the axial direction D1. In this case, the flow path through which gas leaks axially D1 through the first joint gap S71 of the first ring member 71 can be blocked by the second ring member 72, and the flow path through which gas leaks axially D1 through the second joint gap S72 of the second ring member 72 can be blocked by the first ring member 71. As a result, in addition to the gas flow paths R1, R2, and R3 described above, the gas flow path passing axially D1 between the outer peripheral surface 65b of the outer cover 65 and the inner peripheral wall 6a of the cylinder 6 can also be blocked. This further improves the gas sealing performance, making it possible to further improve the compression efficiency.

[0072] As in this embodiment, a groove 68 extending along the circumferential direction D2 may be formed on the inner circumferential surface 65a of the outer cover 65, and a projection 69 that fits into the groove 68 may be formed on the outer circumferential surface 63b of the inner cover 63. In this case, by fitting the projection 69 into the groove 68, the side surface 68b of the groove 68 and the side surface 69b of the projection 69 can be brought into contact with each other in the axial direction D1, thereby restricting the misalignment of the inner cover 63 and the outer cover 65 in the axial direction D1. As a result, the inner cover 63 and the outer cover 65 can be held together as a single unit, making it possible to more reliably achieve the configuration in which the outer cover 65 blocks the gas flow path passing through the gap S63 of the inner cover 63. This makes it possible to more reliably improve the gas sealing performance.

[0073] As in this embodiment, a recess 73 may be formed on the outer peripheral surface 63b of the inner cover 63, and a protrusion 75 that fits into the recess 73 may be formed on the inner peripheral surface 65a of the outer cover 65. In this case, the protrusion 75 fitting into the recess 73 restricts rotational displacement in the circumferential direction D2 between the inner cover 63 and the outer cover 65. This makes it possible to more reliably maintain a state in which the first joint gap S71 and the second joint gap S72 of the outer cover 65 are offset in the circumferential direction D2 so as not to overlap with the joint gap S63 of the inner cover 63 in the radial direction D3. As a result, it is possible to more reliably suppress gas that has entered between the inner peripheral surface 63a of the inner cover 63 and the bottom surface 56a of the ring groove 56 from leaking out into another space through any of the joint gaps S63, the first joint gap S71, and the second joint gap S72. This makes it possible to more reliably improve the gas sealing performance.

[0074] As in this embodiment, the piston ring 60 may include an inner ring 67 positioned radially D3 inward relative to the inner cover 63 and extending circumferentially D2 so as to surround the inner cover 63. In this case, the inner ring 67 applies tension radially D3 outward relative to the inner circumferential surface 63a of the inner cover 63, thereby pressing the outer circumferential surface 65b of the outer cover 65 against the inner circumferential wall 6a of the cylinder 6. This ensures that even if the outer circumferential surface 65b of the outer cover 65 wears down due to the reciprocating motion of the piston 5, the outer circumferential surface 65b of the outer cover 65 remains in contact with the inner circumferential wall 6a of the cylinder 6 more reliably. As a result, the gas flow path between the outer circumferential surface 65b of the outer cover 65 and the inner circumferential wall 6a of the cylinder 6 can be more reliably blocked, thereby improving the gas sealing performance.

[0075] As in this embodiment, the outer cover 65 may be made of a material with higher wear resistance than the inner cover 63. In this case, the excessive wear of the outer peripheral surface 65b of the outer cover 65 in response to the reciprocating motion of the piston 5 can be suppressed, and the state in which the outer peripheral surface 65b of the outer cover 65 is in contact with the inner peripheral wall 6a of the cylinder 6 can be maintained more reliably. As a result, the gas flow path passing between the outer peripheral surface 65b of the outer cover 65 and the inner peripheral wall 6a of the cylinder 6 can be more reliably blocked, thereby improving the gas sealing performance more reliably.

[0076] Furthermore, worn outer covers 65 can be replaced during inspection. By replacing only the worn outer cover 65, it is possible to maintain the piston rings 60 without replacing the inner cover 63. This simplifies the replacement process and reduces costs.

[0077] The reciprocating compressor 1, piston 5, and piston ring 60 of this disclosure have been described above. However, the reciprocating compressor 1, piston 5, and piston ring 60 of this disclosure may be implemented in various forms without being limited to the above embodiments.

[0078] For example, the inner cover 63 has an annular shape, but the inner cover 63 may have a distorted shape in part of its annular form. The outer cover 65 also has an annular shape, but similar to the inner cover 63, the outer cover 65 may have a distorted shape in part of its annular form.

[0079] In the above embodiment, one joint gap S63 is formed in the inner cover 63. However, two or more joint gaps may be formed in the inner cover 63. Similarly, two or fewer or four or more joint gaps may be formed in the outer cover 65.

[0080] In the above embodiment, a groove 68 extending along the circumferential direction D2 is formed on the inner circumferential surface 65a of the outer cover 65. However, a groove extending along the circumferential direction D2 may also be formed on the outer circumferential surface 63b of the inner cover 63. In the above embodiment, a projection 69 that fits into the groove 68 is formed on the outer circumferential surface 63b of the inner cover 63. However, a projection that fits into the groove may also be formed on the inner circumferential surface 65a of the outer cover 65.

[0081] In the above embodiment, a recess 73 is formed on the outer peripheral surface 63b of the inner cover 63, and a protrusion 75 that fits into the recess 73 is formed on the inner peripheral surface 65a of the outer cover 65. However, a recess may also be formed on the inner peripheral surface 65a of the outer cover 65, and a protrusion that fits into the recess may be formed on the outer peripheral surface 63b of the inner cover 63.

[0082] In the above embodiment, the first ring member 71 is divided into three segments P71 by three first joint gaps S71. However, the first ring member 71 may be divided into two or four or more segments by providing two or four or more first joint gaps. Similarly, the second ring member 72 is divided into three segments P71 by three second joint gaps S72. However, the second ring member 72 may be divided into four or more segments by providing two or four or more joint gaps.

[0083] <Note> This disclosure comprises [1] an inner annular member extending circumferentially, and an outer annular member disposed radially outside the inner annular member and extending circumferentially so as to surround the inner annular member. Each of the inner annular member and the outer annular member has at least one joint gap formed between a pair of opposing surfaces that face each other along the circumferential direction. A piston ring in which the gap of the outer annular member is offset in the circumferential direction from the gap of the inner annular member so that it does not overlap with the gap of the inner annular member when viewed along the radial direction from the central axis of the inner annular member.

[0084] This disclosure includes [2] "the outer annular member having a first annular body and a second annular body aligned along the axial direction in which the central axis extends, The outer annular member has a first joint gap provided in the first annular body and a second joint gap provided in the second annular body, as the joint gap. The piston ring described in [1] above, wherein the first gap is offset in the circumferential direction relative to the second gap so as not to overlap with the second gap in the axial direction.

[0085] This disclosure includes [3] "A groove extending along the circumferential direction is formed on one of the circumferential surfaces of the inner annular member and the inner annular member, The other of the outer and inner surfaces has a projection that fits into the groove. The piston ring according to [1] or [2] above, wherein the side surface of the groove and the side surface of the projection face each other along the axial direction of the inner annular member.

[0086] This disclosure includes [4] "A recess is formed on one of the circumferential surfaces of the inner annular member and the inner annular member, The other of the outer and inner circumferential surfaces has a protrusion that fits into the recess. The piston ring according to any one of [1] to [3] above, wherein the side surface of the recess and the side surface of the convex portion face each other along the circumferential direction.

[0087] The present disclosure is [5] "a piston ring according to any one of [1] to [4] above, further comprising an inner ring disposed radially inward with respect to the inner annular member and extending circumferentially so as to be surrounded by the inner annular member."

[0088] This disclosure is [6] "The piston ring according to any one of [1] to [5] above, wherein the outer annular member is formed of a material that has higher wear resistance than the inner annular member."

[0089] The present disclosure is [7] "a piston comprising a piston ring as described in any of [1] to [6] above, a piston head including an outer peripheral wall having a ring groove formed therein in which the piston ring fits, and a piston rod connected to the piston head and extending along the axial direction in which the central axis extends."

[0090] The present disclosure is a reciprocating compressor comprising [8] "a piston as described in [7] above, and a cylindrical cylinder including an inner wall surrounding the outer wall, into which the piston is reciprocally inserted along the axial direction, and together with the piston, forming a compression chamber." [Explanation of Symbols]

[0091] 1. Reciprocating compressor 5 pistons 6 cylinders 6a Inner wall 53 Piston Rod 55 Piston Head 55b Outer wall 56 Ring groove 56a Bottom 56b Side 60, 60A piston rings 63 Inner cover (inner annular member) 63a Inner surface 63b Outer surface 63c, 63d end face 63e Side view 65 Outer cover (outer annular member) 65a Inner surface 65b Outer surface 67 Inner Ring 68 Groove 68a Bottom 68b side 69 Protrusion 69a top surface 69b Side view 71 First ring member (first annular body) 72 Second ring member (second annular body) 73 recess 73a Bottom 73b side 75 Convex part 75a top surface 75b Side view C60 center axis D1 Axial direction D2 Circumferential direction D3 radial direction S63 Joint Gap S71 First joint gap S72 Second joint gap

Claims

1. An inner annular member extending along the circumferential direction, An outer annular member is positioned radially outside the inner annular member and extends along the circumferential direction so as to surround the inner annular member, Equipped with, Each of the inner annular member and the outer annular member has at least one joint gap formed between a pair of opposing surfaces that face each other along the circumferential direction. A piston ring in which the gap of the outer annular member is offset in the circumferential direction from the gap of the inner annular member such that it does not overlap with the gap of the inner annular member when viewed along the radial direction from the central axis of the inner annular member.

2. The outer annular member has a first annular body and a second annular body arranged along the axial direction in which the central axis extends, The outer annular member has a first joint gap provided in the first annular body and a second joint gap provided in the second annular body, as the joint gap. The piston ring according to claim 1, wherein the first gap is offset in the circumferential direction with respect to the second gap so as not to overlap with the second gap in the axial direction.

3. A groove extending along the circumferential direction is formed on one of the circumferential surfaces, the outer surface of the inner annular member and the inner surface of the outer annular member. The other of the outer and inner surfaces has a projection that fits into the groove. The piston ring according to claim 1, wherein the side surface of the groove and the side surface of the projection face each other along the axial direction of the inner annular member.

4. A recess is formed on one of the circumferential surfaces, the outer circumferential surface of the inner annular member and the inner circumferential surface of the outer annular member. The other of the outer and inner circumferential surfaces has a protrusion that fits into the recess. The piston ring according to claim 3, wherein the side surface of the recess and the side surface of the convex portion face each other along the circumferential direction.

5. The piston ring according to claim 1, further comprising an inner ring disposed radially inward of the inner annular member and extending circumferentially so as to be surrounded by the inner annular member.

6. The piston ring according to claim 1, wherein the outer annular member is formed of a material that has higher wear resistance than the inner annular member.

7. A piston ring according to any one of claims 1 to 6, A piston head including an outer peripheral wall having a ring groove formed in which the piston ring fits, A piston rod connected to the piston head and extending along the axial direction from which the central axis extends, A piston equipped with a piston.

8. The piston according to claim 7, A cylindrical cylinder including an inner circumferential wall surrounding the outer circumferential wall, into which the piston is reciprocally inserted along the axial direction and together with the piston forms a compression chamber, A reciprocating compressor equipped with the following features.

Images