Booster pumps and cryogenic fluid supply systems

Abstract

To improve sealing performance in booster pumps and cryogenic fluid supply systems. [Solution] The piston 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 positioned in an annular groove provided on the outer circumference of the piston. The piston ring has a piston ring body located on the inner circumferential surface side of the cylinder and an inner ring located on the center side of the piston relative to the piston ring body. The piston ring body has a high-pressure piston ring body located on the compression chamber side and a low-pressure piston ring body located on the opposite side of the compression chamber relative to the high-pressure piston ring body. The piston has a passage provided in the annular groove on the high-pressure piston ring body side, extending from the outer circumference toward the center.

Description

Technical Field

[0001] The present disclosure relates to a booster pump and a cryogenic fluid supply system.

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, fuel cells, hydrogen engines, and the like. The hydrogen supply system includes a booster pump that pressurizes liquid hydrogen. The booster pump has a cylinder having a compression chamber, and a piston that compresses the liquid hydrogen in the compression chamber. A piston ring is attached to the outer peripheral portion of the piston, and the piston 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 the Invention

Problems to be Solved by the Invention

[0004] The piston ring described in Patent Document 1 is provided on the outer circumference of a piston with multiple rings spaced apart in the axial direction. The piston ring has a piston ring body and an inner ring, and the piston ring has a high-pressure piston ring body and a low-pressure piston ring body. The high-pressure piston ring body and the low-pressure piston ring body have a joint at one location in the circumferential direction, and the joint reduces the pressure difference in the space between each piston ring when the piston moves. However, when the low-pressure piston ring body wears down and its thickness decreases, a leak path is formed on the inner circumference side of the low-pressure piston ring body, and the load pressing the high-pressure piston ring body in the axial direction increases. As a result, the flow rate of liquid hydrogen leaking from the low-pressure side region through the joint of the high-pressure piston ring body to the high-pressure side region decreases, and there is a risk that the low-pressure piston ring body may be damaged.

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

[0006] A booster pump according to the present disclosure for achieving the above objectives comprises a cylinder having a compression chamber, a piston that compresses a low-temperature fluid in the compression chamber by reciprocating the cylinder, and a piston ring disposed in an annular groove provided on the outer circumference of the piston, wherein the piston ring has a piston ring body located on the inner circumferential surface side of the cylinder and an inner ring located on the center side of the piston from the piston ring body, the piston ring body has a high-pressure piston ring body located on the compression chamber side and a low-pressure piston ring body located on the opposite side from the compression chamber from the high-pressure piston ring body, and the piston has a passage provided in the annular groove on the high-pressure piston ring body side extending from the outer circumferential surface toward the center.

[0007] Furthermore, the cryogenic fluid supply system of this disclosure comprises a compressor having the booster pump, an evaporator that vaporizes the cryogenic fluid compressed by the compressor, and a dispenser that supplies the gas vaporized by the evaporator. [Effects of the Invention]

[0008] The booster pump and cryogenic fluid supply system of this disclosure can improve sealing performance. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram showing the overall configuration of the hydrogen supply system of this embodiment. [Figure 2] Figure 2 is a longitudinal cross-sectional view showing the compression device of this 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 body. [Figure 6] Figure 6 is a perspective view of the piston. [Figure 7] Figure 7 is a perspective view showing the main part of the piston (part VII in Figure 6). [Figure 8] Figure 8 is a schematic diagram illustrating the operation of a conventional piston ring. [Figure 9] Figure 9 is a schematic diagram illustrating the action of a conventional piston ring during wear. [Figure 10] Figure 10 is a schematic diagram illustrating the action of the piston ring in this embodiment during wear. [Modes for carrying out the invention]

[0010] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. However, these embodiments do not limit the present disclosure, and where there are multiple embodiments, they may be combinations of these embodiments. Furthermore, the components in the embodiments include those readily conceivable by those skilled in the art, those that are substantially identical, and those that are equivalent.

[0011] [Embodiment] <Hydrogen supply system> Figure 1 is a schematic diagram showing the overall configuration of the hydrogen supply system of this embodiment.

[0012] As shown in Figure 1, the hydrogen supply system (low-temperature fluid supply system) 10 supplies (replenishes) liquid hydrogen stored in the liquefied hydrogen storage tank 11 as hydrogen gas at a predetermined pressure to the power source of the vehicle 12. Here, the power source is, for example, a fuel cell or a hydrogen engine, which is mounted on the vehicle 12. The hydrogen supply system 10 is, for example, a so-called hydrogen station that supplies (replenishes) hydrogen gas, which is the fuel, to the power source of the vehicle 12. However, the hydrogen supply system 10 is not limited to supplying hydrogen gas to the power source of the vehicle 12, but also includes supplying hydrogen gas to the tank of a trailer for transporting hydrogen. Furthermore, the hydrogen supply system 10 operates similarly when supplying compressed low-temperature fluids (for example, liquid hydrogen, liquid nitrogen, liquid oxygen, liquefied carbon dioxide, liquefied natural gas, liquefied propane gas, etc.) rather than just hydrogen.

[0013] The hydrogen supply system 10 includes a compressor 21, an evaporator 22, and a dispenser 23. The compressor 21 compresses liquid hydrogen (low-temperature fluid) supplied from the liquefied hydrogen storage tank 11 to a predetermined high pressure (high-pressure state). The evaporator 22 generates hydrogen gas by vaporizing the high-pressure liquid hydrogen compressed by the compressor 21. The dispenser 23 fills the power source of the vehicle 12 with the hydrogen gas generated by the evaporator 22.

[0014] The compression device 21 compressed the liquid hydrogen stored in the liquefied hydrogen storage tank 11 to a predetermined high pressure, but the configuration is not limited to this.

[0015] The compression device 21 includes a drive unit 31 and a booster pump 32. Although not illustrated, the drive unit 31 includes a drive motor and a drive mechanism. The drive motor is an electric motor that can be driven by electric power supplied from the outside. The rotation speed of the drive motor is controlled by an inverter (not illustrated). The drive mechanism has a crank mechanism and converts the rotational power of the drive motor into linear reciprocating power. The drive motor transmits rotational power to the drive mechanism, and the drive mechanism transmits linear reciprocating power to the booster pump 32. The booster pump 32 is operated by the drive unit 31 to compress liquid hydrogen. The drive unit 31 may include a speed reducer between the drive motor and the drive mechanism.

[0016] <Compression Device> Figure 2 is a longitudinal sectional view showing the compression device of the present embodiment.

[0017] As shown in Figure 2, the compression device 21 includes a drive unit 31 and a booster pump 32, and the drive unit 31 includes a drive mechanism 34. The compression device 21 (the booster pump 32) is a device for boosting liquid hydrogen, which is an extremely low-temperature liquid, to a high pressure (about 90 MPa).

[0018] <Drive Unit> The drive mechanism 34 includes an eccentric shaft portion 41, a rotating body 42, a link portion 43, a swing shaft portion 44, a crosshead 45, and a housing 46.

[0019] The eccentric shaft portion 41 has a cylindrical shape and is arranged along the horizontal direction. The eccentric shaft portion 41 is supported rotatably around an axis O1 extending in the horizontal direction. The eccentric shaft portion 41 rotates when a rotational force is input from the outside.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] <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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] <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.

[0035] <Piston Rings> Figure 3 is a cross-sectional view showing the piston and cylinder.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] <Specific configuration of piston rings> Figure 4 is a cross-sectional view showing the mounting area of ​​the piston ring, and Figure 5 is a perspective view showing the piston ring body.

[0040] 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.

[0041] The piston 53 has an annular groove 74 formed on its outer circumference along the circumferential direction. The annular groove 84 has a rectangular cross-sectional shape composed 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.

[0042] 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.

[0043] The piston ring body 81 and the inner ring 82 are made of different materials, resulting in differences in hardness. Specifically, the inner ring 82 has a lower hardness than the piston ring body 81. In other words, the inner ring 82 is softer than the piston ring body 81.

[0044] <Piston ring body> The piston ring body 81 comprises a high-pressure piston ring body 91 and a low-pressure piston ring body 92. The high-pressure piston ring body 91 is located on the side of the compression chamber 65 (see Figure 3) (lower side in Figure 4). The low-pressure piston ring body 92 is located on the opposite side of the compression chamber 65 from the high-pressure piston ring body 91 (upper side in Figure 4).

[0045] The high-pressure piston ring body 91 and the low-pressure piston ring body 92 are ring-shaped and have the same outer and inner diameters. The piston ring body 81 is positioned with the high-pressure piston ring body 91 on the side facing the compression chamber 65, and the low-pressure piston ring body 92 on the opposite side from the compression chamber 65.

[0046] The high-pressure piston ring body 91 has an outer circumferential surface 91a, an upper surface 91b, an inner circumferential surface 91c, and a lower surface 91d. The low-pressure piston ring body 92 has an outer circumferential surface 92a, an upper surface 92b, an inner circumferential surface 92c, and a lower surface 92d. The outer circumferential surfaces 91a and 92a of the high-pressure piston ring body 91 and the low-pressure piston ring body 92 face the inner circumferential surface of the fitting hole 70, and the inner circumferential surfaces 91c and 92c face the outer circumferential surface of the inner ring 82. In addition, the upper surface 91b of the high-pressure piston ring body 91 faces the ceiling surface 84a of the annular groove 84, and the lower surface 92d of the low-pressure piston ring body 92 faces the bottom surface 84c of the annular groove 84. Furthermore, the lower surface 91d of the high-pressure piston ring body 91 and the upper surface 92b of the low-pressure piston ring body 92 face each other.

[0047] The high-pressure piston ring body 91 and the low-pressure piston ring body 92 are made of the same material and therefore have the same hardness. However, the high-pressure piston ring body 91 and the low-pressure piston ring body 92 may be made of different materials and therefore have different hardnesses. For example, the hardness of the low-pressure piston ring body 92 may be lower than that of the high-pressure piston ring body 91. In other words, the low-pressure piston ring body 92 may be softer than the high-pressure piston ring body 91.

[0048] Furthermore, as shown in Figure 5, the high-pressure piston ring body 91 has a joint portion 93 at one location in the circumferential direction. The low-pressure piston ring body 92 has a joint portion 94 at one location in the circumferential direction. When the high-pressure piston ring body 91 and the low-pressure piston ring body 92 are assembled, it is preferable that the joint portion 93 of the high-pressure piston ring body 91 and the joint portion 94 of the low-pressure piston ring body 92 are positioned at different locations in the circumferential direction.

[0049] <Piston> Figure 6 is a perspective view of the piston, and Figure 7 is a perspective view of the main part of the piston.

[0050] As shown in Figures 4, 6, and 7, the piston 53 has multiple annular grooves 84 along its outer circumference, spaced apart in the axial direction. The piston ring body 81, inner ring 82, and backup ring 83 that constitute the piston ring 71 are arranged in the multiple annular grooves 84. The piston ring body 81 consists of a high-pressure piston ring body 91 located on the high-pressure side region 201 and a low-pressure piston ring body 92 located on the low-pressure side region 202.

[0051] The piston 53 has a passage 101 provided in the annular groove 84 on the high-pressure piston ring body 91 side, extending from the outer circumferential surface towards the center (axis O). That is, the passage 101 is provided in the bottom surface 84c of the annular groove 84 along the radial direction of the piston 53. The passage 101 has a groove shape that is recessed relative to the bottom surface 84c of the annular groove 84.

[0052] The passage 101 has a bottom surface 102, a pair of side surfaces 103, and an inclined surface 104 that connects the side surfaces 103 to the bottom surface 84c of the annular groove 84. The bottom surface 102 is substantially parallel to the bottom surface 84c of the annular groove 84, offset in the axial direction of the piston 53. The pair of side surfaces 103 are substantially perpendicular to the bottom surface 102 on both sides of the piston 53 in the circumferential direction. The inclined surface 104 connects each side surface 103 to the bottom surface 84c of the annular groove 84 and is inclined with respect to the bottom surface 102 and the side surfaces 103. The inclined surface 104 may be composed of multiple inclined surfaces with different angles, or it may be composed of a curved surface.

[0053] The length of passage 101 from the outer surface of piston 53 toward the center (axis O) is longer than the combined thickness of the piston ring body 81 and the inner ring 82. Also, the length of passage 101 from the outer surface of piston 53 toward the center (axis O) is shorter than the depth of the annular groove 84.

[0054] <The action of piston rings> Figure 8 is a schematic diagram illustrating the operation of a conventional piston ring.

[0055] As shown in Figure 8, a conventional piston ring has a piston ring body 81 and an inner ring 82, and the piston ring body 81 has a high-pressure piston ring body 91 and a low-pressure piston ring body 92. Multiple piston rings (two in Figure 8) are provided at intervals in the axial direction of the piston 53. When the piston 53 descends relative to the cylinder 52 and pressurizes the liquid hydrogen in the compression chamber 65, the pressure in the compression chamber 65 (cylinder pressure) increases and is maintained at a constant high pressure. At this time, the high-pressure piston ring body 91, which is positioned in the annular groove 84 of the piston 53, is subjected to pressure from the high-pressure liquid hydrogen on the compression chamber 65 side below, which acts downward through the gap between the outer surface of the piston 53 and the inner surface of the fitting hole 70. The pressure acts on the inner surface of the low-pressure piston ring body 92 through the gap between the high-pressure piston ring body 91 and the annular groove 84, and the low-pressure piston ring body 92 seals by pressing its outer surface against the inner surface of the fitting hole 70.

[0056] Furthermore, some of the high-pressure liquid hydrogen on the compression chamber 65 side flows through the joint 93 (see Figure 5) of the high-pressure piston ring body 91 to the inner circumferential surface of the high-pressure piston ring body 91, and leaks upward through the joint 94 (see Figure 5) of the low-pressure piston ring body 92. In other words, when the piston 53 descends and the liquid hydrogen in the compression chamber 65 is pressurized, the high-pressure liquid hydrogen leaks through the joint 93 of the high-pressure piston ring body 91 and the joint 94 of the low-pressure piston ring body 92 into the interstage between them and the upper piston ring, and the interstage pressure gradually increases.

[0057] Subsequently, when the piston 53 reaches bottom dead center and rises relative to the cylinder 52, the pressure in the compression chamber 65 (cylinder pressure) decreases. At this time, because the pressure on the lower side of the compression chamber 65 becomes low, some of the liquid hydrogen at a predetermined pressure in the interstage of the piston ring leaks through the joint 94 of the low-pressure piston ring body 92 and the joint 93 of the high-pressure piston ring body 91 into the interstage between them and the lower piston ring. As a result, the axial stress acting on the high-pressure piston ring body 91 and the low-pressure piston ring body 92 is relieved.

[0058] Figure 9 is a schematic diagram illustrating the action of a conventional piston ring during wear.

[0059] As shown in Figure 9, the piston ring is sealed when the pressure from the lower compression chamber 65 side acts on the inner surface of the low-pressure piston ring body 92 through the gap between the high-pressure piston ring body 91 and the annular groove 84, causing the low-pressure piston ring body 92 to press against the inner surface of the fitting hole 70. Therefore, with long-term use, the low-pressure piston ring body 92 wears down and becomes thinner, forming a leak path on the inner surface of the low-pressure piston ring body 92. Then, when the piston 53 descends and pressurizes the liquid hydrogen in the compression chamber 65, the high-pressure liquid hydrogen leaks into the interstage between the upper piston ring and the joint portion 93 of the high-pressure piston ring body 91 and the joint portion 94 of the low-pressure piston ring body 92. However, the amount of leakage increases, the interstage pressure becomes as high as the in-cylinder pressure, and is maintained at a constant high pressure.

[0060] Subsequently, when the piston 53 reaches bottom dead center and rises relative to the cylinder 52, the pressure in the compression chamber 65 (cylinder pressure) decreases. At this time, because the pressure on the lower compression chamber 65 side is low, some of the liquid hydrogen at a predetermined pressure in the interstage of the piston ring leaks through the joint 94 of the low-pressure piston ring body 92 and the joint 93 of the high-pressure piston ring body 91 into the interstage between the lower piston ring. However, because the interstage pressure is high, the high-pressure interstage pressure acts on the high-pressure piston ring body 91 through the leak path, pressing and deforming the high-pressure piston ring body 91 against the lower surface 84C of the annular groove 84. As a result, the joint 93 of the high-pressure piston ring body 91 narrows, and the amount of leakage into the interstage between it and the lower piston ring decreases. Consequently, the decrease in the amount of leakage delays the decrease in interstage pressure, increasing the load acting on the low-pressure piston ring body 92, which may damage the low-pressure piston ring body 92.

[0061] Figure 10 is a schematic diagram illustrating the action of the piston ring in this embodiment during wear.

[0062] As shown in Figure 10, the piston ring 71 of this embodiment has a piston ring body 81 and an inner ring 82, the piston ring body 81 has a high-pressure piston ring body 91 and a low-pressure piston ring body 92, and a passage 101 is provided on the bottom surface 84c side of the annular groove 84 in the piston 53.

[0063] Over time, the piston ring 71's low-pressure piston ring body 92 wears down, becoming thinner and forming a leak path on the inner circumference side of the low-pressure piston ring body 92. When the piston 53 descends and pressurizes the liquid hydrogen in the compression chamber 65, the high-pressure liquid hydrogen leaks through the joint 93 of the high-pressure piston ring body 91 and the joint 94 of the low-pressure piston ring body 92 into the interstage between them and the upper piston ring. This leakage increases, causing the interstage pressure to rise to a level similar to the in-cylinder pressure.

[0064] Subsequently, when the piston 53 reaches bottom dead center and rises relative to the cylinder 52, the pressure in the compression chamber 65 (cylinder pressure) decreases. At this time, because the pressure on the lower side of the compression chamber 65 becomes low, some of the liquid hydrogen at a predetermined pressure in the interstage of the piston ring 71 leaks through the joint 94 of the low-pressure piston ring body 92 and the joint 93 of the high-pressure piston ring body 91 into the interstage between it and the lower piston ring. In addition, some of the liquid hydrogen at a predetermined pressure in the interstage flows from the joint 94 of the low-pressure piston ring body 92 into the leak path and leaks through the passage 101 from the inner circumference side of the high-pressure piston ring body 91 and the inner circumference side of the inner ring 82 into the interstage between it and the lower piston ring 71.

[0065] Therefore, although the interstage pressure is high, the high-pressure interstage pressure leaks from the leak path through the passage 101 to the lower interstage section, so the amount of leakage to the interstage section between the lower piston ring and the lower piston ring does not decrease. As a result, the necessary amount of leakage is ensured, the interstage pressure decreases in accordance with the in-cylinder pressure, the increase in load acting on the low-pressure piston ring body 92 is suppressed, and the risk of damaging the low-pressure piston ring body 92 is reduced.

[0066] [Effects of this embodiment] The first embodiment of the booster pump 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 positioned in an annular groove 84 provided on the outer circumference of the piston 53. The piston ring 71 has a piston ring body 81 located on the inner circumferential surface side of the cylinder 52 and an inner ring 82 located on the piston center side of the piston than the piston ring body 81. The piston ring body 81 has a high-pressure piston ring body 91 located on the compression chamber 65 side and a low-pressure piston ring body 92 located on the opposite side of the compression chamber 65 from the high-pressure piston ring body 91. The piston 53 has a passage 101 in the annular groove 84 on the high-pressure piston ring body 91 side, extending from the outer circumference towards the center.

[0067] According to the first embodiment of the booster pump, even if the low-pressure piston ring body 92 wears down and becomes thinner due to long-term use, and a leak path is formed on the inner circumference side of the low-pressure piston ring body 92, the pressure in the interstage section leaks appropriately through the passage 101 to the interstage section between it and the lower piston ring 71. Therefore, the reduction in the amount of leakage to the interstage section between it and the lower piston ring is suppressed, the increase in the load acting on the low-pressure piston ring body 92 is suppressed, the risk of damaging the low-pressure piston ring body 92 is reduced, and the sealing performance can be improved.

[0068] The boost pump according to the second embodiment is the boost pump according to the first embodiment, further comprising a groove shape in which the passage 101 is recessed relative to the inner surface of the annular groove 84. This simplifies the formation of the passage 101.

[0069] The third embodiment of the booster pump is the same as the second embodiment, further comprising a bottom surface 102, a pair of side surfaces 103, and an inclined surface 104 or curved surface that connects the side surfaces 103 with the bottom surface (inner surface) 84c of the annular groove 84. This allows for a smooth flow of liquid hydrogen through the passage 101.

[0070] The fourth embodiment of the boost pump is a boost pump according to any one of the first to third embodiments, and further, the length of the passage 101 from the outer circumferential surface of the piston 53 toward the center (axis O) is longer than the combined length of the thickness of the piston ring body 81 and the thickness of the inner ring 82. This allows the pressure in the interstage to be appropriately leaked from the inner circumferential side of the inner ring 82 into the passage 101.

[0071] The fifth embodiment of the boost pump is the same as the fourth embodiment, and further, the length of the passage 01 from the outer surface of the piston 53 toward the center is shorter than the depth of the annular groove 84. This makes it possible to simplify the passage 101.

[0072] The hydrogen supply system (low-temperature fluid supply system) according to the sixth embodiment comprises a compressor 21 having a booster pump 32 according to any one of the first to fifth embodiments, 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. [Explanation of Symbols]

[0073] 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 Piston ring body 82 Inner Ring 83 Backup ring 84 Annular groove 91 High-pressure piston ring body 92 Low-pressure piston ring body 93,94 Joint part 101 Passage 102 Bottom 103 Side view 104 Slope

Claims

1. 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 is positioned in an annular groove provided on the outer circumference of the piston, Equipped with, The aforementioned piston ring is The piston ring body located on the inner circumferential surface side of the cylinder, An inner ring located on the center side of the piston from the piston ring body, It has, The piston ring body comprises a high-pressure piston ring body located on the compression chamber side and a low-pressure piston ring body located on the opposite side of the compression chamber from the high-pressure piston ring body. The piston has a passage provided in the annular groove on the high-pressure piston ring body side, extending from the outer surface toward the center. Booster pump.

2. The passage has a groove shape that is recessed relative to the inner surface of the annular groove. The boost pump according to claim 1.

3. The passage has a bottom surface, a pair of side surfaces, and an inclined or curved surface that connects the side surfaces to the inner surface of the annular groove. The boost pump according to claim 2.

4. The length of the passage extending from the outer surface of the piston toward the center is longer than the combined length of the thickness of the piston ring body and the thickness of the inner ring. The boost pump according to claim 1.

5. The passage has a length from the outer surface of the piston toward the center that is shorter than the depth of the annular groove. The booster pump according to claim 4.

6. A compressor having a boost pump as described in claim 1, 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.

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