Piston rings, booster pumps, and cryogenic fluid supply systems; method for manufacturing piston rings

Abstract

The aim is to improve sealing performance in piston rings, booster pumps, cryogenic fluid supply systems, and piston ring manufacturing methods. [Solution] A piston ring made of resin material, which is attached to the outer circumference of the piston of a booster pump that compresses a low-temperature fluid in a compression chamber, has a main body that has a gap between the main body and forms a ring shape, a first overlapping portion provided at one end of the main body in the circumferential direction, and a second overlapping portion provided at the other end of the main body in the circumferential direction and overlapping the first overlapping portion in the axial direction, wherein when the piston ring wears down, the low-temperature fluid leaks from the gap between the first and second overlapping portions before they break.

Description

Technical Field

[0001] The present disclosure relates to a piston ring, a booster pump, a cryogenic fluid supply system, and a method for manufacturing a piston ring.

Background Art

[0002] As a system for achieving carbon neutrality, application of hydrogen gas as a fuel has been considered. Hydrogen is stored in a tank in a liquid hydrogen state, and the liquid hydrogen stored in the tank is vaporized into hydrogen gas, which is supplied to, for example, a fuel cell, a hydrogen engine, or the like. The hydrogen supply system includes a booster pump that boosts the pressure of liquid hydrogen. The booster pump has a cylinder having a compression chamber, and a piston that compresses the liquid hydrogen in the compression chamber. The piston has a piston ring mounted on its outer peripheral portion, and is movably supported inside the cylinder via the piston ring. The piston ring prevents leakage of high-pressure liquid hydrogen from the compression chamber. An example of such a booster pump is described in Patent Document 1 below.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0004] Because piston rings are ring-shaped and have a joint, there is a risk that liquid hydrogen from the compression chamber may leak to the outside through the joint of the piston ring. Therefore, it is conceivable to overlap the ends that constitute the joint of the piston ring. However, when a piston ring with an overlapping joint is applied to a booster pump that pressurizes cryogenic liquid hydrogen, the following problems arise. When the piston ring is made of resin, the ends overlap properly at room temperature, but when it comes into contact with cryogenic liquid hydrogen, the piston ring spreads outward, and the amount of overlap between the ends decreases. Furthermore, as the piston ring wears down with long-term use, it becomes thinner and spreads outward, further reducing the amount of overlap between the ends. When the amount of overlap between the ends of the piston ring decreases, when pressure is applied from the compression chamber, the bending stress on the ends that constitute the joint of the piston ring increases, and the ends may break. If the ends of the piston ring break, the fragments may get stuck in the sliding part between the piston and the cylinder, potentially interfering with the operation of the booster pump.

[0005] This disclosure aims to solve the aforementioned problems and to provide a piston ring, a booster pump, a cryogenic fluid supply system, and a method for manufacturing a piston ring that improves sealing performance. [Means for solving the problem]

[0006] To achieve the above objective, the piston ring of the present disclosure is a piston ring made of a resin material that is mounted on the outer circumference of a piston of a booster pump that compresses a cryogenic fluid in a compression chamber, and comprises a main body having a gap to form a ring shape, a first overlapping portion provided at one circumferential end of the main body, and a second overlapping portion provided at the other circumferential end of the main body that overlaps the first overlapping portion in the axial direction, wherein when the piston ring wears, the cryogenic fluid leaks from the gap between the first and second overlapping portions before they break.

[0007] Furthermore, the booster pump of this disclosure comprises a cylinder having a compression chamber, a piston that compresses the low-temperature fluid in the compression chamber by reciprocating the cylinder, and a piston ring as described in claim 1 that is mounted on the outer circumference of the piston.

[0008] Furthermore, the cryogenic fluid supply system of this disclosure comprises a compressor, an evaporator for vaporizing the cryogenic fluid compressed by the compressor, and a dispenser for supplying the gas vaporized by the evaporator.

[0009] Furthermore, the present disclosure relates to a method for manufacturing a piston ring, which is mounted on the outer circumference of a piston of a booster pump that compresses a low-temperature fluid in a compression chamber, and comprises a main body made of a resin material with a gap at the joint to form a ring shape, a first overlapping portion provided at one end of the main body in the circumferential direction, and a second overlapping portion provided at the other end of the main body in the circumferential direction and overlapping the first overlapping portion in the axial direction, wherein the amount of overlap between the first overlapping portion and the second overlapping portion in the circumferential direction is set based on an allowable wear amount that does not reach the fracture life set based on the dimensions and shapes of the first overlapping portion and the second overlapping portion. [Effects of the Invention]

[0010] According to the piston ring, booster pump, cryogenic fluid supply system, and piston ring manufacturing method of this disclosure, it is possible to improve sealing performance. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic diagram showing the overall configuration of the hydrogen supply system according to the first embodiment. [Figure 2] Figure 2 is a longitudinal cross-sectional view showing the compressor of the first embodiment. [Figure 3] Figure 3 is a cross-sectional view showing the piston and cylinder. [Figure 4] Figure 4 is a cross-sectional view showing the piston ring mounting area. [Figure 5]Figure 5 is a perspective view showing the piston ring of the first embodiment. [Figure 6] Figure 6 is a perspective view showing the piston ring in use. [Figure 7] Figure 7 is a perspective view showing the piston ring at the time of wear. [Figure 8] Figure 8 is a flowchart showing a method for manufacturing a piston ring. [Figure 9] Figure 9 is a schematic diagram for explaining a method for manufacturing a piston ring. [Figure 10] Figure 10 is a graph showing the relationship between wear life and breakage life. [Figure 11] Figure 11 is a fragmentary perspective view showing the piston ring of the second embodiment. [Figure 12] Figure 12 is a fragmentary perspective view showing a first modification of the piston ring of the second embodiment. [Figure 13] Figure 13 is a fragmentary plan view showing a second modification of the piston ring of the second embodiment. [Figure 14] Figure 14 is a front view showing the piston ring of the third embodiment. [Figure 15] Figure 15 is a cross-sectional view taken along line XV-XV in Figure 14. [Figure 16] Figure 16 is a cross-sectional view showing a modification of the piston ring of the third embodiment. [Figure 17] Figure 17 is a front view showing the piston ring of the fourth embodiment. [Figure 18] Figure 18 is a cross-sectional view taken along line XVIII-XVIII in Figure 17. (Modes for Carrying Out the Invention)

[0012] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited by these embodiments, and in a case where there are a plurality of embodiments, configurations obtained by combining the respective embodiments are also included. Further, the constituent elements in the embodiments include those that can be easily assumed by those skilled in the art, those that are substantially identical, and those within the so-called equivalent scope.

[0013] [First Embodiment] <Hydrogen Supply System> FIG. 1 is a schematic diagram illustrating the overall configuration of the hydrogen supply system of the present embodiment.

[0014] As shown in FIG. 1, the hydrogen supply system (cryogenic fluid supply system) 10 supplies (replenishes) liquid hydrogen stored in a liquefied hydrogen storage tank 11 as hydrogen gas at a predetermined pressure to a power source of a vehicle 12. Here, the power source is, for example, a fuel cell or a hydrogen engine, and is mounted on the vehicle 12. The hydrogen supply system 10 is, for example, a so-called hydrogen station that supplies (replenishes) hydrogen gas as fuel to the power source of the vehicle 12. However, the hydrogen supply system 10 is not limited to one that supplies hydrogen gas to the power source of the vehicle 12, and also includes one that supplies hydrogen gas to a tank of a trailer for transporting hydrogen. In addition, the hydrogen supply system 10 operates similarly not only for hydrogen but also when compressing and supplying a cryogenic fluid (for example, liquid hydrogen, liquid nitrogen, liquid oxygen, liquefied carbon dioxide gas, liquefied natural gas, liquefied propane gas, etc.).

[0015] The hydrogen supply system 10 includes a compression device 21, an evaporation device 22, and a dispenser 23. The compression device 21 compresses the liquid hydrogen (cryogenic fluid) supplied from the liquefied hydrogen storage tank 11 to a preset predetermined high pressure (high pressure state). The evaporation device 22 vaporizes the high-pressure liquid hydrogen compressed by the compression device 21 to generate hydrogen gas. The dispenser 23 fills the power source of the vehicle 12 with the hydrogen gas generated by the evaporation device 22.

[0016] Note that although the compression device 21 compresses the liquid hydrogen stored in the liquefied hydrogen storage tank 11 to a predetermined high pressure, the present disclosure is not limited to this configuration.

[0017] The compression device 21 comprises a drive unit 31 and a booster pump 32. The drive unit 31, although not shown, comprises a drive motor and a drive mechanism. The drive motor is an electric motor that can be driven by power supplied from an external source. The rotational speed of the drive motor is controlled by an inverter (not shown). The drive mechanism has a crank mechanism and converts the rotational power of the drive motor into linear reciprocating power. The drive motor transmits the rotational power to the drive mechanism, and the drive mechanism transmits the linear reciprocating power to the booster pump 32. The booster pump 32 is operated by the drive unit 31 and compresses liquid hydrogen. The drive unit 31 may have a reduction gear between the drive motor and the drive mechanism.

[0018] <Compressor> Figure 2 is a longitudinal cross-sectional view showing the compression device of this embodiment.

[0019] As shown in Figure 2, the compressor 21 comprises a drive unit 31 and a booster pump 32, and the drive unit 31 comprises a drive mechanism 34. The compressor 21 (boostering pump 32) is a device for increasing the pressure of liquid hydrogen, which is an extremely cold liquid, to high pressure (approximately 90 MPa).

[0020] <Drive Unit> The drive mechanism 34 includes an eccentric shaft portion 41, a rotating body 42, a link portion 43, a pivot shaft portion 44, a crosshead 45, and a housing 46.

[0021] The eccentric shaft portion 41 is cylindrical in shape and arranged along the horizontal direction. The eccentric shaft portion 41 is rotatably supported about an axis O1 along the horizontal direction. The eccentric shaft portion 41 rotates when a rotational force is applied from the outside.

[0022] The rotating body 42 is disc-shaped, positioned outside the eccentric shaft portion 41, and rotatable integrally with the eccentric shaft portion 41. The rotating body 42 has a center along the axis O2, and the center of the rotating body 42 (axis O2) and the center of the eccentric shaft portion 41 (axis O1) are offset radially. That is, the center of the eccentric shaft portion 41 (axis O1) is located eccentrically with respect to the center of the rotating body 42 (axis O2). When the eccentric shaft portion 41 rotates, the rotating body 42 oscillates around the axis O1.

[0023] The link section 43 constitutes a crank mechanism and converts rotational power into linear reciprocating power, which is then transmitted to the booster pump 32. The link section 43 has an upper annular section 43a, a connecting section 43b, and a lower annular section 43c. The upper annular section 43a is ring-shaped. The upper annular section 43a is positioned on the outside of the rotating body 42 via a bearing section (not shown) and is rotatable relative to the rotating body 42. The lower annular section 43c is ring-shaped. The connecting section 43b is positioned between the upper annular section 43a and the lower annular section 43c and integrally connects the upper annular section 43a and the lower annular section 43c.

[0024] When the eccentric shaft portion 41 rotates and the rotating body 42 oscillates around the axis O1, the link portion 43 is activated. Specifically, the upper annular portion 43a of the link portion 43 oscillates around the axis O1 due to the rotation of the rotating body 42, and the oscillating power of the upper annular portion 43a is transmitted to the lower annular portion 43c via the connecting portion 43b, causing the lower annular portion 43c to reciprocate linearly in the vertical direction while rotating around the axis O3 which is parallel to the axes O1 and O2.

[0025] The upper end of the oscillating shaft portion 44 is connected to the lower end of the lower annular portion 43c of the link portion 43. The lower end of the oscillating shaft portion 44 is connected to the upper end of the piston 53 of the booster pump 32, which will be described later. The oscillating shaft portion 44 is pivotable between the lower annular portion 43c and the piston 53, around an oscillating axis that is horizontally aligned with respect to the lower annular portion 43c and the piston 53.

[0026] The crosshead 45 has a bottomed cylindrical shape that covers the lower annular portion 43c from the outside. The housing 46 is positioned on the outer circumference of the crosshead 45. The housing 46 is supported by a frame (not shown), and the crosshead 45 is supported so as to be movable along the vertical direction relative to the housing 46. The lower annular portion 43c of the link portion 43 is rotatably supported by the crosshead 45. When the eccentric shaft portion 41 and the rotating body 42 rotate and the link portion 43 reciprocates along the vertical direction, the lower annular portion 43c and the crosshead 45 reciprocate along the vertical direction relative to the housing 46.

[0027] <Booster pump> As shown in Figure 2, the booster pump 32 comprises a casing 51, a cylinder 52, a piston 53, and a discharge pipe 54.

[0028] The casing 51 is a pressure vessel for storing liquid hydrogen and is also an insulated vacuum vessel. The support plate 61 is arranged horizontally and installed on a frame (not shown). The support plate 61 has a through hole 61a located on the axis O along the vertical direction. The casing 51 has a casing body 51a, an intermediate flange portion 51b, a support cylinder portion 51c, and an upper flange portion 51d. The casing body 51a is an insulated structure with a bottomed cylindrical shape, forming an internal liquid storage chamber 62. The intermediate flange portion 51b is disc-shaped, with a circular hole formed at its center. The intermediate flange portion 51b is integrally fastened to the upper end of the casing body 51a. The intermediate flange portion 51b has a support cylinder portion 51c, which has a smaller diameter than the casing body 51a, integrally provided at its upper part. The support cylinder portion 51c has an upper flange portion 51d integrally provided at its upper end, which is larger in diameter than the support cylinder portion 51c, and a circular hole is formed in the center of the upper flange portion 51d. The casing 51 is fastened with bolts so that the upper flange portion 51d is in close contact with the lower surface of the support plate 61. In other words, the upper end of the casing 51 is suspended and supported by the support plate 61.

[0029] The casing 51 has a supply pipe 63 and a gas discharge pipe 64 connected to the side of the casing body 51a. The supply pipe 63 is a pipe for supplying liquid hydrogen from an external source to the liquid storage chamber 62 of the casing 51. The supply pipe 63 is located near the bottom of the casing 51. The gas discharge pipe 64 is a pipe for discharging the vaporized components (hydrogen gas) in the liquid storage chamber 62 to the outside. The gas discharge pipe 64 is located above and spaced apart from the supply pipe 63. The liquid storage chamber 62 stores liquid hydrogen, and the liquid level of the liquid hydrogen is adjusted to be below the level of the gas discharge pipe 64.

[0030] The cylinder 52 is a container for compressing liquid hydrogen. The cylinder 52 has a cylinder body 52a and a flange portion 52b. The cylinder body 52a has a bottomed cylindrical shape, and a compression chamber 65 is provided on the lower side inside. The cylinder body 52a has a flange portion 52b that is larger in diameter than the cylinder body 52a integrally provided at its upper end, and the flange portion 52b is open in the center. The cylinder 52 is fitted into a through hole 61a of the support plate 61 and placed on the upper surface of the upper flange portion 51d of the casing 51. That is, the upper end of the cylinder 52 is suspended and supported by the support plate 61. In addition, a sealing member (not shown) is provided between the flange portion 52b of the cylinder 52 and the upper flange portion 51d of the casing 51.

[0031] A suction valve 66 is provided at the bottom of the cylinder 52. The suction valve 66 is for introducing liquid hydrogen from the liquid storage chamber 62 into the compression chamber 65. In other words, the suction valve 66 is a check valve and opens when the pressure in the compression chamber 65 is lower than the pressure in the liquid storage chamber 62, allowing liquid hydrogen from the liquid storage chamber 62 to be introduced into the compression chamber 65. On the other hand, it closes when the pressure in the compression chamber 65 is higher than the pressure in the liquid storage chamber 62, preventing liquid hydrogen from the compression chamber 65 from flowing back into the liquid storage chamber 62. In Figure 2, the suction valve 66 is shown exposed outside the cylinder 52, but Figure 2 is a schematic diagram, and in reality, the suction valve 66 is provided inside the cylinder 52.

[0032] A discharge valve 67 is provided on the lower side of cylinder 52. The discharge valve 67 is for discharging (releasing) the high-pressure liquid water compressed in the compression chamber 65 to the outside. In other words, the discharge valve 67 is a check valve and opens when the pressure in the compression chamber 65 becomes higher than the pressure on the discharge side, discharging the high-pressure liquid hydrogen from the compression chamber 65 to the outside. On the other hand, it closes when the pressure in the compression chamber 65 becomes lower than the pressure on the discharge side, preventing the high-pressure liquid hydrogen from the discharge side from flowing back into the compression chamber 65. In Figure 2, the discharge valve 67 is shown exposed to the outside of cylinder 52, but Figure 2 is a schematic diagram, and in reality, the discharge valve 67 is provided inside cylinder 52.

[0033] The piston 53 has an elongated cylindrical shape and is positioned along an axis O that runs vertically. The outer diameter of the piston 53 is constant throughout the entire direction of axis O. The upper end of the piston 53 is connected to the drive unit 31, and the lower end is positioned inside the cylinder 52. A piston ring 71 is provided at the lower end of the piston 53.

[0034] The cylinder 52 has a piston 53 positioned inside, which divides the lower end into a compression chamber 65. The piston 53 reciprocates inside the cylinder 52 along the direction of axis O by the drive unit 31. When the piston 53 moves upward inside the cylinder 52, the volume of the compression chamber 65 expands, the pressure decreases, and liquid hydrogen is drawn in. When the piston 53 moves downward inside the cylinder 52, the volume of the compression chamber 65 contracts, the pressure increases, and the liquid hydrogen is compressed. The cylinder 52 is provided with a sealing member on the inner circumferential surface of the opening of the flange portion 52b to seal the gap between it and the outer circumferential surface of the piston 53.

[0035] The discharge pipe 54 is a pipe for discharging the high-pressure liquid hydrogen compressed in the compression chamber 35 to the outside. The discharge pipe 54 is located inside the casing 51, adjacent to the cylinder 52. The discharge pipe 54 is arranged vertically, its lower end is connected to the bottom of the cylinder 52, and it communicates with the compression chamber 65 via the discharge valve 67. The upper end of the discharge pipe 54 extends to the outside through the top of the casing 51 and is supported on the top of the casing 51.

[0036] <Operation of the compression device> As shown in Figure 2, when the eccentric shaft 41 rotates, the rotating body 42 oscillates. This activates the link 43, which converts the rotational power into linear reciprocating power and transmits it to the booster pump 32 via the oscillating shaft 44. When the booster pump 32 operates, first, in the suction phase in which the piston 53 rises, liquid hydrogen from the casing 51 is drawn into the compression chamber 65. Next, in the compression phase in which the piston 53 descends, the liquid hydrogen in the compression chamber 65 is compressed, and high-pressure liquid hydrogen is discharged into the discharge pipe 54.

[0037] <Piston Rings> Figure 3 is a cross-sectional view showing the piston and cylinder.

[0038] As shown in Figure 3, the cylinder 52 has a fitting hole 70 formed inside. The piston 53 is supported in the fitting hole 70 of the cylinder 52 so as to be movable in the axial direction. The piston 53 and the fitting hole 70 have a circular cross-sectional shape centered on axis O. The outer diameter of the piston 53 is slightly smaller than the inner diameter of the fitting hole 70. The piston 53 is provided with piston rings 71. Multiple piston rings 71 (three in this embodiment) are mounted on the outer circumference of the piston 53 at intervals in the direction of axis O. However, the number of piston rings 71 is not limited. The piston rings 71 are mounted in an annular groove formed on the outer circumference of the piston 53. The piston rings 71 have an annular shape centered on axis O and are made of resin material. The piston ring 71 contains predetermined amounts of materials such as polytetrafluoroethylene (PTFE), polyether ether ketone (PEEK), carbon fiber (PAN-based, etc.), and zinc oxide whiskers, but other materials are inevitably mixed in. The piston ring 71 can maintain liquid-tightness and airtightness with respect to the inner circumferential surface of the fitting hole 70 of the cylinder 52.

[0039] The piston ring 71 mounted on the piston 53 divides the piston 53 into a high-pressure side region 201 and a low-pressure side region 202. Here, the high-pressure side region 201 is the region below the piston ring 71 in the direction of axis O, that is, the region on the compression chamber 65 side, and the low-pressure side region 202 is the region above the piston ring 71 in the direction of axis O, that is, the region on the opposite side from the compression chamber 65.

[0040] In cylinder 52, a compression chamber 65 is partitioned by the placement of a piston 53 in a fitting hole 70. The compression chamber 65 is equipped with an intake valve 66 and a discharge valve 67. When the piston 53 rises, the volume of the compression chamber 65 increases, and the intake valve 66 opens, drawing liquid hydrogen into the compression chamber 56. On the other hand, when the piston 53 descends, the volume of the compression chamber 65 decreases, compressing the liquid hydrogen in the compression chamber 65. When a predetermined pressure is reached, the discharge valve 67 opens, discharging the high-pressure liquid hydrogen to the outside.

[0041] <Specific configuration of piston rings> Figure 4 is a cross-sectional view showing the piston ring mounting area.

[0042] As shown in Figure 4, the piston ring 71 has a piston ring body 81, an inner ring 82, and a backup ring 83. The piston ring body 81 and the inner ring 82 are ring-shaped, but their outer and inner diameters are different.

[0043] The piston 53 has an annular groove 84 formed on its outer surface along the circumferential direction. The annular groove 84 has a rectangular cross-sectional shape consisting of a top surface 84a, a side surface 84b, and a bottom surface 84c, and opens toward the inner circumferential surface of the fitting hole 70. The top surface 84a, side surface 84b, and bottom surface 84c of the annular groove 84 are all flat. The top surface 84a and bottom surface 84c are parallel to each other and face each other, and the top surface 84a and bottom surface 84c are approximately perpendicular to the side surface 84b. In addition, the side surface 84b of the annular groove 84 is parallel to and faces the inner surface of the fitting hole 70 of the cylinder 52.

[0044] The piston ring 71 is positioned in the annular groove 84. Specifically, the piston ring body 81 is made of resin and has a rectangular cross-section, positioned radially outward in the annular groove 84, that is, on the inner circumferential surface side of the fitting hole 70. The inner ring 82 is made of resin and has a rectangular cross-section, positioned radially inward from the piston ring body 81, that is, on the side of the center (axis O) of the piston 53. The backup ring 83 is made of metal (stainless steel) and has a circular cross-section, positioned radially inward from the inner ring 82, that is, on the side of the center (axis O) of the piston 37. The piston ring 71 is constructed by arranging the piston ring body 81, inner ring 82, and backup ring 83 in the annular groove 84 in the order from radially outward to radially inward. The piston ring body 81 is positioned in the annular groove 84, and the piston ring body 81, inner ring 82, and backup ring 83 are movable in response to the pressure from the high-pressure side region 201 or low-pressure side region 202 acting on the annular groove 84.

[0045] <Piston ring body> Figure 5 is a perspective view showing the piston ring of the first embodiment, Figure 6 is a perspective view showing the piston ring during use, and Figure 7 is a perspective view showing the piston ring when worn.

[0046] As shown in Figures 4 and 5, the piston ring body 81 has a main body portion 91, a first overlapping portion 92, and a second overlapping portion 93.

[0047] The main body portion 91 has a ring shape with gaps 94a and 94b. The main body portion 91 has an outer circumferential surface 91a, an upper surface 91b, an inner circumferential surface 91c, and a lower surface 91d. The piston ring body 81 has its outer circumferential surface 91a facing the inner circumferential surface of the fitting hole 70 of the cylinder 52, its upper surface 91b facing the ceiling surface 84a of the annular groove 84 of the piston 53, its inner circumferential surface 91c located on the side surface 84b of the annular groove 84, and its lower surface 91d facing the bottom surface 84c of the annular groove 84.

[0048] The first overlapping portion 92 is provided at one end of the main body portion 91 in the circumferential direction. The first overlapping portion 92 is provided on the lower surface 91d side of one end of the main body portion 91. The second overlapping portion 93 is provided at the other end of the main body portion 91 in the circumferential direction. The second overlapping portion 93 is provided on the upper surface 91b side of the other end of the main body portion 91. The first overlapping portion 92 and the second overlapping portion 93 have the same shape and are arranged to overlap the piston ring body 81 in the axial direction.

[0049] The piston ring body 81 forms a ring shape when the first overlapping portion 92 at one end of the main body portion 91 and the second overlapping portion 93 at the other end are combined. However, the piston ring body 81 has a first joint gap 94a between the first overlapping portion 92 at one end of the main body portion 91 and the other end, and a second joint gap 94b between the second overlapping portion 93 at the other end of the main body portion 91 and the one end.

[0050] As shown in Figure 5, when the piston ring body 81 is assembled to the booster pump 32 (see Figure 3), at room temperature, the gap between the first joint 94a and the second joint 94b are at their minimum values, and the circumferential overlap amount C between the first overlapping portion 92 and the second overlapping portion 93 (hereinafter referred to as the joint engagement amount) is at its maximum value. On the other hand, as shown in Figure 6, when the piston ring body 81 is assembled to the booster pump 32 (see Figure 3) and comes into contact with liquid hydrogen in a cold state, the body portion 91 expands outward, the gap between the first joint 94a and the second joint 94b increases, and the joint engagement amount C between the first overlapping portion 92 and the second overlapping portion 93 decreases.

[0051] Furthermore, as shown in Figure 7, when the piston ring body 81 is assembled to the booster pump 32 (see Figure 3) and used for a long period of time in contact with liquid hydrogen, the outer surface 91a wears down, and the thickness T decreases. When the thickness T decreases due to wear, the body portion 91 expands further outward, the gap between the first joint 94a and the second joint 94b becomes larger, the first overlapping portion 92 and the second overlapping portion 93 no longer overlap, and leakage occurs.

[0052] Incidentally, when the piston ring body 81 wears down due to long-term use from a cold state and its thickness T decreases, the amount of engagement C at the joint between the first overlapping portion 92 and the second overlapping portion 93 decreases. Stress acts on the piston ring body 81 from the compression chamber 65, which is the high-pressure side region 201. The stress from the compression chamber 65 also acts on the first overlapping portion 92 and the second overlapping portion 93. When stress acts from the compression chamber 65 with a small amount of engagement C at the joint, the bending stress on the first overlapping portion 92 and the second overlapping portion 93 increases. And when the bending stress becomes large, there is a risk that the first overlapping portion 92 and the second overlapping portion 93 will break. If the first overlapping portion 92 and the second overlapping portion 93 break, fragments may get stuck in the sliding parts between the cylinder 52 and the piston 53, causing interference with the operation of the booster pump 32.

[0053] Therefore, in this embodiment, the piston ring body 81 is configured such that when the piston ring body 81 wears down due to long-term use, the gap between the first joint 92 and the second joint 93 becomes larger, reducing the gap between the joint 94a and the second joint 94b, before the first joint 92 or the second joint 93 breaks, causing a leak to occur as the gap between the first joint 94a and the second joint 94b communicates.

[0054] <Manufacturing method for piston rings> Figure 8 is a flowchart illustrating the manufacturing method of piston rings, Figure 9 is a schematic diagram illustrating the manufacturing method of piston rings, and Figure 10 is a graph showing the relationship between wear life and fracture life.

[0055] The target lifespan of the piston ring body 81 is determined, for example, by the allowable wear amount of the piston ring body 81 and the number of piston ring bodies 81 to be mounted on the piston 53. As shown in Figure 8, in step S11, the allowable wear amount (wear life) of the piston ring body 81 is set by setting the target lifespan of the piston ring body 81 and the number of piston ring bodies 81. In step S12, the shape of the piston ring body 81, that is, the initial gap S1 between the first overlapping portion 92 and the second overlapping portion 93 (see Figure 9(a)), is set based on the allowable wear amount. In step S13, the gap S when wear occurs and leakage occurs (see Figure 9(c)) is calculated from the gap S2 and gap engagement amount C (see Figure 9(b)) at cold temperatures (-253°C) based on the initial gap S1.

[0056] In step S14, the bending stress (beam calculation) acting on the first overlap 92 and second overlap 93 of the piston ring body 81 is calculated. In step S15, the fracture life evaluation (SN diagram) of the first overlap 92 and second overlap 93 is performed and the fracture life is calculated. In step S16, it is determined whether the fracture life is longer than the wear life. If it is determined that the fracture life is longer than the wear life (Yes), in step S17, the amount of leakage and manufacturability are checked. On the other hand, if it is determined that the fracture life is not longer than the wear life, the process is repeated, returning to step S11 (or step S12). That is, when it is determined that the fracture life is not longer than the wear life, the allowable wear amount is changed in step S11, or the initial joint engagement amount C1 is changed in step S12, and the process is repeated.

[0057] Specifically, the fracture life is calculated based on the dimensions and shape of the first overlapping portion 92 and the second overlapping portion 93 of the piston ring body 81, and then the allowable wear amount is set so as not to reach the fracture life. Then, the initial gap S1 is calculated based on the allowable wear amount that does not reach the fracture life, and the engagement amount C is calculated based on the initial gap S1.

[0058] As the gap S between the piston ring body 81 increases, the bending stress in the first overlapping portion 92 and the second overlapping portion 93 increases. Based on this relationship, the allowable wear amount of the piston ring body 81 is set. In other words, as shown in Figure 10, in the relationship between the allowable wear amount and life of the piston ring body 81, a larger allowable wear amount results in a longer wear life and a shorter fracture life. Therefore, in the relationship between wear life and fracture life, by setting the allowable wear amount in a region where the wear life is smaller than the intersection point of wear life and fracture life, leakage occurs in the piston ring body 81 before the first overlapping portion 92 and the second overlapping portion 93 fracture.

[0059] In the first embodiment, when the piston ring body 81 wears down, liquid hydrogen leaks from the gap between the first and second overlapping portions 92 and 93 before they break. Therefore, breakage of the first and second overlapping portions 92 and 93 during the operation of the booster pump 32 is suppressed, and sealing performance can be improved. Furthermore, it is possible to prevent fragments of the first and second overlapping portions 92 and 93 from entering the sliding parts between the cylinder 52 and the piston 53.

[0060] [Second Embodiment] Figure 11 is a perspective view of the main part of the piston ring of the second embodiment. Note that components having the same function as those in the first embodiment described above are denoted by the same reference numerals, and detailed descriptions are omitted.

[0061] As shown in Figure 11, the piston ring body 81A has a main body portion 91, a first overlapping portion 92A, and a second overlapping portion 93A.

[0062] The main body portion 91 has a ring shape. The first overlapping portion 92A is provided at one end of the main body portion 91 in the circumferential direction. The first overlapping portion 92A is provided on the lower surface 91d side and the outer peripheral surface 91a side of one end of the main body portion 91. The first overlapping portion 92A has a first opposing surface 92a perpendicular to the axial direction and a second opposing surface 92b along the axial direction.

[0063] The second overlapping portion 93A is provided at the other end of the main body portion 91 in the circumferential direction. The second overlapping portion 93A is provided on the upper surface 91b side and the outer peripheral surface 91a side of the other end of the main body portion 91. The second overlapping portion 93A has a first opposing surface 93a perpendicular to the axial direction and a second opposing surface 93b along the axial direction.

[0064] The first overlapping portion 92A and the second overlapping portion 93A have the same shape and are arranged to overlap the piston ring body 81A in the axial and radial directions. That is, the first opposing surface 92a of the first overlapping portion 92A and the first opposing surface 93a of the second overlapping portion 93A are in contact in the axial direction. Also, the second opposing surface 92b of the first overlapping portion 92A and the second opposing surface 93b of the second overlapping portion 93A are in contact in the radial direction.

[0065] The piston ring body 81A forms a ring shape when the first overlapping portion 92A at one end of the main body portion 91 and the second overlapping portion 93A at the other end are combined. However, a gap is provided between the first overlapping portion 92A and the second overlapping portion 93A of the piston ring body 81A. Since the piston ring body 81A is in contact with the first overlapping portion 92A and the second overlapping portion 93A in the axial and radial directions, the surface pressure is increased and the sealing performance is improved.

[0066] <First variation> Figure 12 is a perspective view of the main part of a first modified example of the piston ring of the second embodiment.

[0067] The piston ring body 81B has a main body portion 91, a first overlapping portion 92B, and a second overlapping portion 93B.

[0068] The main body portion 91 has a ring shape. The first overlapping portion 92B is provided at one end of the main body portion 91 in the circumferential direction. The first overlapping portion 92B is provided on the lower surface 91d and the inner circumferential surface 91c side of one end of the main body portion 91. The first overlapping portion 92B has an inclined surface (opposing surface) 92c that is inclined with respect to the axial direction and the radial direction.

[0069] The second overlapping portion 93B is provided at the other end of the main body portion 91 in the circumferential direction. The second overlapping portion 93B is provided on the upper surface 91b and the outer peripheral surface 91a side of the other end of the main body portion 91. The second overlapping portion 93B has an inclined surface (opposing surface) 93c that is inclined with respect to the axial direction and the radial direction.

[0070] The first overlapping portion 92B and the second overlapping portion 93B have substantially the same shape and are arranged to overlap in a direction inclined with respect to the axial and radial directions of the piston ring body 81B. That is, the inclined surface 92c of the first overlapping portion 92B and the inclined surface 93c of the second overlapping portion 93B are in contact with each other in a direction inclined with respect to the axial and radial directions.

[0071] The piston ring body 81B forms a ring shape when the first overlapping portion 92B at one end of the main body portion 91 and the second overlapping portion 93B at the other end are combined. However, a gap is provided between the first overlapping portion 92B and the second overlapping portion 93B of the piston ring body 81B. Since the piston ring body 81B is in contact with the first overlapping portion 92B and the second overlapping portion 93B in directions inclined in the axial and radial directions, the surface pressure is increased and the sealing performance is improved.

[0072] <Second variation> Figure 13 is a plan view of the main part showing a second modified example of the piston ring of the second embodiment.

[0073] As shown in Figure 13, the piston ring body 81C has a main body portion 91, a first overlapping portion 92C, and a second overlapping portion (not shown).

[0074] The main body portion 91 has a ring shape. The first overlapping portion 92C is provided at one end of the main body portion 91 in the circumferential direction. The first overlapping portion 92C is provided on the lower surface 91d side of one end of the main body portion 91. The first overlapping portion 92C has an opposing surface 92d perpendicular to the axial direction. The first overlapping portion 92C also has a recess 92e on the opposing surface 92d. The recess 92e is provided over a predetermined length from one end of the opposing surface 92d. The length of the recess 92e is shorter than the circumferential length of the opposing surface 92d.

[0075] The second overlapping portion, although not shown in the figures, is the second overlapping portion 93 of the first embodiment (see Figure 3), i.e., the second overlapping portion is provided at the other end of the main body portion 91 in the circumferential direction. The second overlapping portion is provided on the upper surface 91b side of the other end of the main body portion 91. The second overlapping portion has opposing surfaces perpendicular to the axial direction. A recess may also be provided on the opposing surface of the second overlapping portion.

[0076] The first overlapping portion 92C and the second overlapping portion have substantially the same shape and are arranged to overlap the piston ring body 81C in the axial direction. That is, the opposing surface 92d of the first overlapping portion 92C and the opposing surface of the second overlapping portion are in contact with each other in the axial direction. When the amount of overlap between the first overlapping portion 92C and the second overlapping portion of the piston ring body 81C, which is the amount of overlap in the circumferential direction, falls below a predetermined value, the recess 93e communicates with the outside. That is, leakage occurs through the recess 92e, and the high-pressure side region and the low-pressure side region communicate with each other. Since the piston ring body 81C has a recess 92e on the opposing surface 92d, the timing of liquid hydrogen leakage can be adjusted by adjusting the length of the recess 92e. The piston ring body 81C maintains liquid-tightness and airtightness with the inner circumferential surface of the cylinder fitting hole until the high-pressure side region and the low-pressure side region are connected by the recess 92e. When the gap between the rings widens due to long-term use, the engagement amount C decreases and becomes shorter than the length of the recess 92e, causing leakage. This makes it easy to induce leakage while avoiding breakage.

[0077] [Third Embodiment] Figure 14 is a front view showing the piston ring of the third embodiment, and Figure 15 is a cross-sectional view taken along line XV-XV in Figure 14. Note that components having the same function as those in the first embodiment described above are denoted by the same reference numerals, and detailed descriptions are omitted.

[0078] As shown in Figures 14 and 15, the piston ring body 81D is ring-shaped, with a first overlapping portion (not shown) at one end and a second overlapping portion (not shown) at the other end. The piston ring body 81D has a recess 101 on its outer circumferential surface 81a on the high-pressure side (lower side in Figure 14) where high-pressure liquid hydrogen acts. Multiple recesses 101 are provided at intervals in the circumferential direction. The recesses 101 are rectangular parallelepipeds and open to the outer circumferential surface 81a and the lower surface 91d of the piston ring body 81D.

[0079] The piston ring body 81D is mounted on the outer circumference of the piston 53, and its outer surface 91a contacts the inner surface of the fitting hole 70 of the cylinder 52. As the piston 53 moves relative to the cylinder 52, the piston ring body 81D slides against the cylinder 52, causing the outer surface 91a to generate heat. However, since the piston ring body 81D has a recess 101 on its outer surface 81a, the contact area between the outer surface 91a of the piston ring body 81D and the inner surface of the fitting hole 70 of the cylinder 52 is reduced, and the amount of heat generated is also reduced. Therefore, deterioration over time is suppressed for the piston ring body 81D, and its lifespan is extended.

[0080] <Variation> Figure 16 is a cross-sectional view showing a modified example of the piston ring of the third embodiment.

[0081] As shown in Figure 16, the piston ring body 81E has a ring shape, with a first overlapping portion (not shown) at one end and a second overlapping portion (not shown) at the other end. The piston ring body 81E has a recess 102 on the outer circumferential surface 81a on the high-pressure side region (lower side in Figure 16) where high-pressure liquid hydrogen acts. Multiple recesses 102 are provided at intervals in the circumferential direction. The recesses 102 have a triangular prism shape and open to the outer circumferential surface 81a and the lower surface 91d side of the piston ring body 81D.

[0082] Furthermore, the recesses 101 and 102 are not limited to a rectangular parallelepiped or triangular prism shape, but can be set as appropriate.

[0083] [Fourth Embodiment] Figure 17 is a front view showing the piston ring of the fourth embodiment, and Figure 18 is a cross-sectional view taken along line XVIII-XVIII in Figure 17. Note that components having the same function as those in the first embodiment described above are denoted by the same reference numerals, and detailed descriptions are omitted.

[0084] As shown in Figures 7 and 8, the piston ring body 81F is ring-shaped, with a first overlapping portion (not shown) at one end and a second overlapping portion (not shown) at the other end. The piston ring body 81F has a groove 111 along the circumferential direction on the outer circumferential surface of the intermediate portion in the axial direction, and a recess 112 is provided on the outer circumferential surface 81a on the high-pressure side region (lower side in Figure 17) where high-pressure liquid hydrogen acts. The groove 111 and the recess 112 of the piston ring body 81F are in communication with each other.

[0085] The groove 111 may be provided continuously along the entire circumference of the piston ring body 81F in the circumferential direction, or it may be provided intermittently in the circumferential direction. There may be one recess 112, or there may be multiple recesses spaced apart in the circumferential direction. The groove 111 and the recess 112 are preferably of the same depth, but they may be different.

[0086] [Effects of this embodiment] The piston ring according to the first embodiment is a piston ring body 81, 81A, 81B, 81C, 81D, 81E, 81F (piston ring 71) made of resin material that is attached to the outer circumference of the piston 53 of a booster pump 32 that compresses liquid hydrogen (low-temperature fluid) in a compression chamber 65, and comprises a main body portion 91 that has a ring shape with joint gaps 94a, 94b, and first overlapping portions 92, 92A, 92B, 92C provided at one end of the main body portion 91 in the circumferential direction, and the main body portion 91 The piston ring has a second overlapping portion 93, 93A, 93B provided at the other end in the circumferential direction, which overlaps the first overlapping portion 92, 92A, 92B, 92C in the axial direction. When the piston ring body 81, 81A, 81B, 81C, 81D, 81E, 81F wears down, the amount of engagement C at the joint decreases, and the joint gaps 94a, 94b communicate, causing liquid hydrogen to leak from the joint gaps 94a, 94b before the ring breaks.

[0087] According to the piston ring of the first embodiment, when the piston ring bodies 81, 81A, 81B, 81C, 81D, 81E, and 81F wear out due to long-term use, liquid hydrogen leaks from the gaps 94a and 94b before they break. This suppresses breakage of the first overlapping portions 92, 92A, 92B, and 92C and the second overlapping portions 93, 93A, and 93B during the operation of the booster pump 32, thereby improving sealing performance.

[0088] The piston ring according to the second embodiment is a piston ring according to the first embodiment, further comprising the amount of overlap between the first overlapping portions 92, 92A, 92B, 92C and the second overlapping portions 93, 93A, 93B in the circumferential direction, which is the amount of engagement at the joint, set based on the allowable wear amount that does not reach the fracture life set based on the dimensions and shapes of the first overlapping portions 92, 92A, 92B, 92C and the second overlapping portions 93, 93A, 93B. This makes it possible to set the first overlapping portions 92, 92A, 92B, 92C and the second overlapping portions 93, 93A, 93B to an appropriate shape.

[0089] The piston ring according to the third embodiment is a piston ring according to the second embodiment, further comprising the following features: the fracture life of the first overlapping portions 92, 92A, 92B, 92C and the second overlapping portions 93, 93A, 93B is calculated based on the dimensions and shapes of the first overlapping portions 92, 92A, 92B, 92C and the second overlapping portions 93, 93A, 93B, an allowable wear amount that does not reach the fracture life is set, an initial joint gap is calculated based on the set allowable wear amount, and the joint engagement amount, which is the circumferential overlap amount between the first overlapping portions 92, 92A, 92B, 92C and the second overlapping portions 93, 93A, 93B, is calculated based on the initial joint gap. This makes it possible to set the first overlapping portions 92, 92A, 92B, 92C and the second overlapping portions 93, 93A, 93B to an appropriate shape.

[0090] The piston ring according to the fourth embodiment is a piston ring according to any one of the first to third embodiments, further comprising a first overlapping portion 92A and a second overlapping portion 93A, each having first opposing surfaces 92a and 93a facing each other in the axial direction and second opposing surfaces 92b and 93b facing each other in the radial direction. As a result, contact occurs between the first overlapping portion 92A and the second overlapping portion 93A in the axial and radial directions, increasing the surface pressure and improving sealing performance.

[0091] The piston ring according to the fifth embodiment is a piston ring according to any one of the first to third embodiments, further comprising inclined surfaces 92c and 93c that are inclined with respect to the axial and radial directions, respectively, of the first overlapping portion 92B and the second overlapping portion 93B. This increases the surface pressure between the first overlapping portion 92B and the second overlapping portion 93B, thereby improving sealing performance.

[0092] The piston ring according to the sixth embodiment is a piston ring according to any one of the first to fifth embodiments, further comprising: first overlapping portions 92, 92A, 92B, 92C and second overlapping portions 93, 93A, 93B, each having opposing surfaces 92a, 92b, 92c, 92d, 93a, 93b, 93c, and at least one of the opposing surfaces 92a, 92b, 92c, 92d of the first overlapping portions 92, 92A, 92B, 92C and the opposing surfaces 93a, 93b, 93c of the second overlapping portions 93, 93A, 93B is provided with a recess 92e that communicates with the outside when the amount of overlap between the first overlapping portions 92, 92A, 92B, 92C and the second overlapping portions 93, 93A, 93B, which is the amount of overlap in the circumferential direction, falls below a predetermined value. As a result, a recess 92e is provided on the opposing surface 92d, and by adjusting the length of the recess 92e, the timing of liquid hydrogen leakage can be adjusted.

[0093] The piston ring according to the seventh embodiment is a piston ring according to any one of the first to sixth embodiments, further comprising recesses 101, 102, and 112 on the outer circumferential surface on the side where high-pressure liquid hydrogen acts. This reduces the contact area between the outer circumferential surface 91a of the piston ring body 81D, 81E, 81F and the inner circumferential surface of the fitting hole 70 of the cylinder 52, and also reduces the amount of heat generated, thereby suppressing deterioration of the piston ring body 81D, 81E, 81F over time and extending its lifespan.

[0094] The piston ring according to the eighth embodiment is a piston ring according to the seventh embodiment, further comprising a plurality of recesses 101, 102, 112 spaced apart in the circumferential direction. This reduces the contact area between the outer circumferential surface 91a of the piston ring body 81D, 81E, 81F and the inner circumferential surface of the fitting hole 70 of the cylinder 52, thereby reducing the amount of heat generated.

[0095] The piston ring according to the ninth embodiment is a piston ring according to the seventh or eighth embodiment, further comprising a groove 111 extending circumferentially along the outer circumferential surface of the intermediate portion in the axial direction, and a recess 112 communicating with the groove 111. This allows high-pressure liquid hydrogen to enter the groove 111, thereby maintaining stable sealing performance.

[0096] The booster pump according to the tenth embodiment comprises a cylinder 52 having a compression chamber 65, a piston 53 that compresses liquid hydrogen (low-temperature fluid) in the compression chamber 65 by reciprocating the cylinder 52, and a piston ring 71 according to any one of the first to ninth embodiments that is mounted on the outer circumference of the piston 53. With these components, the sealing performance can be improved by the piston ring 71, and broken fragments can be prevented from interfering with the operation of the booster pump.

[0097] The hydrogen supply system (low-temperature fluid supply system) according to the 11th embodiment comprises a compressor 21 having a booster pump 32 according to the 10th embodiment, an evaporator 22 that vaporizes the liquid hydrogen (low-temperature fluid) compressed by the compressor 21, and a dispenser 23 that supplies the hydrogen gas vaporized by the evaporator 22. This makes it possible to improve the sealing performance of the booster pump 32.

[0098] A piston ring manufacturing method according to the twelfth embodiment includes a main body portion 91 made of resin material, which is attached to the outer circumference of the piston 53 of a booster pump 32 that compresses liquid hydrogen (low-temperature fluid) in a compression chamber 65, and has a ring shape with joint gaps 94a and 94b, a first overlapping portion 92, 92A, 92B, 92C provided at one end of the main body portion 91 in the circumferential direction, and a second overlapping portion provided at the other end of the main body portion 91 in the circumferential direction that overlaps the first overlapping portion 92, 92A, 92B, 92C in the axial direction In a method for manufacturing piston ring bodies 81, 81A, 81B, 81C, 81D, 81E, 81F (piston rings 71) having overlapping portions 93, 93A, 93B, the overlapping amount of the joint between the first overlapping portions 92, 92A, 92B, 92C and the second overlapping portions 93, 93A, 93B is set based on the allowable wear amount that does not reach the fracture life set based on the dimensions and shape of the first overlapping portions 92, 92A, 92B, 92C and the second overlapping portions 93, 93A, 93B. As a result, the first overlapping portions 92, 92A, 92B, 92C and the second overlapping portions 93, 93A, 93B reduce the amount of engagement C at the joint before they break due to wear on the piston ring bodies 81, 81A, 81B, 81C, 81D, 81E, 81F. This causes the joint gaps 94a, 94b to communicate, allowing liquid hydrogen to leak from the joint gaps 94a, 94b, thereby improving sealing performance and preventing broken fragments from interfering with the operation of the booster pump. [Explanation of Symbols]

[0099] 10. Hydrogen supply system (low-temperature fluid supply system) 11. Liquefied hydrogen storage tank 12 vehicles 21 Compressor 22 Evaporator 23 Dispensers 31 Drive unit 32. Booster pump 34 Drive mechanism 41 Eccentric shaft part 42. Solids of revolution 43 Link section 44. Pivoting shaft 45 Crosshead 46 Housing 51 Casing 52 cylinders 53 Pistons 54 Discharge piping 61 Support plate 62 Liquid storage chamber 63 Supply pipe 64 Gas discharge pipe 65 Compression Chamber 66 Intake valve 67 Discharge valve 71 Piston Rings 81, 81A, 81B, 81C, 81D, 81E, 81F Piston ring body 82 Inner Ring 83 Backup ring 84 Annular groove 91 Main body 92, 92A, 92B, 92C First overlapping section 93, 93A, 93B Second overlapping section 94a First joint gap 94b Second joint gap 101, 102, 112 recesses 111 Groove

Claims

1. In a piston ring made of a resin material, which is attached to the outer circumference of the piston of a booster pump that compresses a low-temperature fluid in a compression chamber, The main body has a ring shape with a gap at the joint, A first overlapping portion is provided at one end in the circumferential direction of the main body, A second overlapping portion is provided at the other end in the circumferential direction of the main body portion and overlaps the first overlapping portion in the axial direction, It has, The first and second overlapping portions are designed so that when the piston ring wears out, low-temperature fluid leaks from the gap between them before it breaks. Piston rings.

2. The amount of overlap between the first overlapping portion and the second overlapping portion in the circumferential direction, which is the joint engagement amount, is set based on the allowable wear amount that does not reach the fracture life set based on the dimensions and shapes of the first overlapping portion and the second overlapping portion. The piston ring according to claim 1.

3. Based on the pre-set dimensions and shapes of the first and second overlapping portions, the fracture life of the first and second overlapping portions is calculated, an allowable wear amount that does not reach the fracture life is set, the initial joint gap is calculated based on the set allowable wear amount, and the joint engagement amount, which is the circumferential overlap amount between the first and second overlapping portions, is calculated based on the initial joint gap. The piston ring according to claim 2.

4. The first overlapping portion and the second overlapping portion each have a first opposing surface facing each other in the axial direction and a second opposing surface facing each other in the radial direction. The piston ring according to claim 1.

5. The first overlapping portion and the second overlapping portion each have inclined surfaces that are inclined with respect to the axial direction and the radial direction, The piston ring according to claim 1.

6. The first overlapping portion and the second overlapping portion each have opposing surfaces, and at least one of the opposing surfaces of the first overlapping portion and the opposing surface of the second overlapping portion is provided with a recess that communicates with the outside when the amount of overlap between the first overlapping portion and the second overlapping portion, which is the amount of overlap in the circumferential direction, falls below a predetermined value. The piston ring according to claim 1.

7. A recess is provided on the outer surface of the side to which the high-pressure, low-temperature fluid acts. The piston ring according to claim 1.

8. Multiple recesses are provided at intervals in the circumferential direction. The piston ring according to claim 7.

9. A groove is provided on the outer circumferential surface of the intermediate portion in the axial direction, and the recess communicates with the groove. The piston ring according to claim 7.

10. A cylinder having a compression chamber, A piston that compresses the low-temperature fluid in the compression chamber by reciprocating the cylinder, A piston ring according to claim 1, which is mounted on the outer circumference of the piston, A booster pump equipped with a pressure booster.

11. A compressor having a boost pump as described in claim 10, An evaporator for vaporizing the low-temperature fluid compressed by the aforementioned compressor, A dispenser that supplies the gas vaporized by the aforementioned evaporator, A cryogenic fluid supply system equipped with the following features.

12. It is attached to the outer circumference of the piston of a booster pump that compresses a low-temperature fluid in a compression chamber, and is made of resin material. The main body has a ring shape with a gap at the joint, A first overlapping portion is provided at one end in the circumferential direction of the main body, A second overlapping portion is provided at the other end in the circumferential direction of the main body portion and overlaps the first overlapping portion in the axial direction, In a method for manufacturing a piston ring having, The amount of overlap between the first overlapping portion and the second overlapping portion in the circumferential direction, which is the joint engagement amount, is set based on the allowable wear amount that does not reach the fracture life set based on the dimensions and shapes of the first overlapping portion and the second overlapping portion. A method for manufacturing piston rings.

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