Boost pump and hydrogen supply system

Abstract

To improve the seal performance of a booster pump and a hydrogen supply system.SOLUTION: A booster pump includes a cylinder having a compression chamber, a suction valve for sucking a low temperature fluid to the compression chamber, a piston supported movably in the cylinder for compressing the low temperature fluid in the compression chamber, a discharge valve for discharging the low temperature fluid in the compression chamber, and a piston ring disposed on an outer peripheral part of the piston. The piston ring includes a piston ring body positioned at the inner peripheral surface side of the cylinder and an inner ring positioned at the center side of the piston with respect to the piston ring body. The hardness of the inner ring is lower than the hardness of the piston ring body.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a booster pump for boosting a cryogenic fluid such as liquid hydrogen, and a hydrogen supply system having the booster pump.

Background Art

[0002] As a conventional booster pump, for example, there is one described in Patent Document 1 below. The booster pump described in Patent Document 1 includes a cylinder block having a compression chamber, a suction valve for sucking a cryogenic fluid into the compression chamber, a piston for compressing the cryogenic fluid in the compression chamber, and a discharge valve for discharging the compressed cryogenic fluid. Further, the piston is movably supported by the cylinder block. The piston has a piston ring mounted on its outer peripheral portion to prevent leakage of high-pressure cryogenic fluid from the compression chamber. As such a piston ring, for example, there is one described in Patent Document 2 below.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventional piston rings use resin materials such as polytetrafluoroethylene (PTFE) and polyether ether ketone (PEEK). The piston ring is required to have high sealing performance with low friction, low wear, and high strength. However, when the pressure of the cryogenic fluid applied in the booster pump becomes ultra-high pressure (for example, 100 MPa), there is a problem that it becomes difficult to ensure sufficient performance.

[0005] The present disclosure solves the above-described problems and aims to provide a booster pump and a hydrogen supply system that improve sealing performance.

Means for Solving the Problems

[0006] The booster pump of the present disclosure for achieving the above object includes a cylinder having a compression chamber, an intake valve for sucking a cryogenic fluid into the compression chamber, a piston movably supported by the cylinder for compressing the cryogenic fluid in the compression chamber, a discharge valve for discharging the cryogenic fluid in the compression chamber, and a piston ring provided on an outer peripheral portion of the piston. The piston ring has a piston ring body located on the inner peripheral surface side of the cylinder and an inner ring located closer to the center of the piston than the piston ring body, and the hardness of the inner ring is lower than the hardness of the piston ring body.

[0007] Further, the hydrogen supply system of the present disclosure includes a compression device having the booster pump for compressing liquid hydrogen as a cryogenic fluid, an evaporation device for vaporizing the liquid hydrogen compressed by the compression device, and a dispenser for supplying the hydrogen gas vaporized by the evaporation device.

Advantages of the Invention

[0008] According to the booster pump and the hydrogen supply system of the present disclosure, it is possible to improve the sealing performance.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0010] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited by this embodiment, and when there are a plurality of embodiments, those configured by combining each embodiment are also included. In addition, the components in the embodiments include those that can be easily assumed by those skilled in the art, substantially the same ones, and those within the so-called equivalent range.

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

[0012] As shown in Figure 1, the hydrogen supply system 10 supplies (refills) the liquid hydrogen stored in the container 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, etc., and is mounted on the vehicle 12. The hydrogen supply system 10 is, for example, a so-called hydrogen stand facility that supplies (refills) hydrogen gas, which is a 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 compresses and supplies cryogenic fluids (e.g., liquid hydrogen, liquid nitrogen, liquid oxygen, liquefied carbon dioxide gas, liquefied natural gas, liquefied propane gas, etc.).

[0013] 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 container 11 to a preset predetermined high pressure (high-pressure state). The evaporation device 22 generates hydrogen gas by vaporizing the high-pressure liquid hydrogen compressed by the compression device 21. The dispenser 23 fills the hydrogen gas generated by the evaporation device 22 into the power source of the vehicle 12.

[0014] Note that although the compression device 21 compresses the liquid hydrogen stored in the container 11 to a predetermined high pressure, it is not limited to this configuration. For example, when the container 11 stores hydrogen gas, the compression device 21 may compress the hydrogen gas stored in the container 11 to a predetermined high pressure.

[0015] The compression device 21 includes a drive motor 31 and a booster pump 32. The drive motor 31 is an electric motor that can be driven by electric power supplied from the outside. The rotational speed of the drive motor 31 is controlled by an inverter (not shown). The drive motor 31 transmits the rotational force to the booster pump 32. The booster pump 32 operates by the rotational force of the drive motor 31.

[0016] <Compression device> FIG. 2 is a schematic configuration diagram showing the compression device.

[0017] As shown in FIG. 2, the drive motor 31 is connected to the booster pump 32 via a speed reducer 33. The speed reducer 33 decelerates the rotational force of the drive motor 31 and transmits it to the booster pump 32. The booster pump 32 is a reciprocating pump. The booster pump 32 converts the rotational force of the drive motor 31 decelerated by the speed reducer 33 into a reciprocating force and operates. The booster pump 32 alternately performs suction and compression (pressure increase) of the liquid hydrogen by the reciprocating force, compresses the sucked liquid hydrogen to a predetermined high-pressure state, and discharges it to the outside.

[0018] The booster pump 32 includes a crank mechanism 34, a crosshead 35, a piston rod 36, a piston 37, and a cylinder block 38.

[0019] The crank mechanism 34 converts the rotational force transmitted from the speed reducer 33 into linear reciprocating force and transmits it to the crosshead 35. The crosshead 35 reciprocates in the vertical direction VD by the reciprocating force in the vertical direction VD transmitted from the crank mechanism 34. The piston rod 36 has its upper end connected to the crosshead 35 and its other end connected to the piston 37. The cylinder block 38 has a hollow shape, and the piston 37 is supported movably along the vertical direction VD inside.

[0020] The booster pump 32 is disposed at the lower part, that is, the cylinder block 38 is disposed inside the container 39. The container 39 is a heat-insulated vacuum container, and the inside is maintained in a vacuum state together with the booster pump 32. The container 39 is supplied with liquid hydrogen inside and filled to the atmospheric pressure state.

[0021] When the booster pump 32 operates, first, in the suction process in which the piston 37 rises, the liquid hydrogen in the container 39 is sucked into the inside of the cylinder block 38. Next, in the compression process in which the piston 37 descends, the liquid hydrogen inside the cylinder block 38 is compressed, and the high-pressure liquid hydrogen is discharged to the outside of the container 39.

[0022] <Booster pump> FIG. 3 is a longitudinal sectional view showing the main part of the booster pump of the first embodiment.

[0023] As shown in FIG. 3, the booster pump 32 includes a piston 37, a cylinder block (cylinder) 38, a suction valve 41, and a discharge valve 42.

[0024] The cylinder block 38 functions as a cylinder, and a fitting hole 51 is formed inside. The piston 37 is supported movably in the axial direction in the fitting hole 51 of the cylinder block 38. The piston 37 and the fitting hole 51 have a circular cross section centered on the axis O. The cylinder block 38 forms a compression chamber 52 when the piston 37 is disposed in the fitting hole 51. When the piston 37 descends, the volume of the compression chamber 52 decreases, and the liquid hydrogen in the compression chamber 52 is compressed.

[0025] The intake valve 41 and the discharge valve 42 are provided in the cylinder block 38 and communicate with the compression chamber 52. The intake valve 41 is opened in the intake process in which the piston 37 ascends, and liquid hydrogen is inhaled into the compression chamber 52 of the cylinder block 38. The discharge valve 42 is opened in the compression process in which the piston 37 descends, and the high-pressure liquid hydrogen compressed in the compression chamber 52 is discharged to the outside.

[0026] Also, the booster pump 32 includes a piston ring 61 and a wear ring 62. That is, the piston 37 is provided with the piston ring 61 and the wear ring 62 on the outer peripheral portion. The piston ring 61 and the wear ring 62 are arranged on the outer peripheral portion of the piston 37 at intervals in the direction of the axis O which is the moving direction of the piston 37. A plurality (three in this embodiment) of piston rings 61 are arranged at intervals in the direction of the axis O. However, the number of piston rings 61 is not limited to three. The wear ring 62 is arranged at intervals on one side in the direction of the axis O of the plurality of piston rings 61. However, the number of wear rings 62 is not limited to one.

[0027] <Piston Ring> FIG. 4 is a cross-sectional view showing the mounting portion of the piston ring.

[0028] As shown in FIG. 4, the piston ring 61 has a piston ring body 71, an inner ring 72, and a backup ring 73. The piston ring body 71, the inner ring 72, and the backup ring 73 are ring-shaped, but the dimensions of the outer diameter and the inner diameter are different from each other.

[0029] The piston 37 has an annular groove 74 formed along the circumferential direction on its outer peripheral surface. The annular groove 74 has a rectangular cross-sectional shape composed of a ceiling surface 74a, a side surface 74b, and a bottom surface 74c, and opens to the inner peripheral surface side of the fitting hole 51. The ceiling surface 74a, the side surface 74b, and the bottom surface 74c of the annular groove 74 are each a plane. The ceiling surface 74a and the bottom surface 74c of the annular groove 74 are parallel and opposed to each other, and the ceiling surface 74a and the bottom surface 74c form a substantially right angle with the side surface 74b. Also, the side surface 74b of the annular groove 74 is parallel and opposed to the inner surface of the fitting hole 51 of the cylinder block 38.

[0030] The piston ring 61 is disposed in the annular groove 74. That is, the piston ring body 71 is disposed in the annular groove 74 on the radially outer side, that is, on the inner peripheral surface side of the fitting hole 51. The inner ring 72 is disposed on the radially inner side of the piston ring body 71, that is, on the center (axis O) side of the piston 37. The backup ring 73 is disposed on the radially inner side of the inner ring 72, that is, on the center (axis O) side of the piston 37. The piston ring 61 is configured by arranging the piston ring body 71, the inner ring 72, and the backup ring 73 in this order from the radially outer side to the radially inner side in the annular groove 74.

[0031] The piston ring body 71 has an outer peripheral surface 71a, an upper surface 71b, an inner peripheral surface 71c, and a lower surface 71d. For the piston ring body 71, the outer peripheral surface 71a faces the inner peripheral surface of the fitting hole 51, the upper surface 71b faces the ceiling surface 74a of the annular groove 74, the inner peripheral surface 71c is located on the side of the side surface 74b of the annular groove 74, and the lower surface 71d faces the bottom surface 74c of the annular groove 74. The inner ring 72 has an outer peripheral surface 72a, an upper surface 72b, an inner peripheral surface 72c, and a lower surface 72d. For the inner ring 72, the outer peripheral surface 72a faces the inner peripheral surface 71c of the piston ring body 71, the upper surface 72b faces the ceiling surface 74a of the annular groove 74, the inner peripheral surface 72c is located on the side of the side surface 74b of the annular groove 74, and the lower surface 72d faces the bottom surface 74c of the annular groove 74. The backup ring 73 has an outer peripheral surface 73a, an upper surface 73b, an inner peripheral surface 73c, and a lower surface 73d. For the backup ring 73, the outer peripheral surface 73a faces the inner peripheral surface 72c of the inner ring 72, the upper surface 73b faces the ceiling surface 74a of the annular groove 74, the inner peripheral surface 73c faces the side of the side surface 74b of the annular groove 74, and the lower surface 73d faces the bottom surface 74c of the annular groove 74.

[0032] The piston ring body 71 is disposed in the annular groove 74, and the piston ring body 71, the inner ring 72, and the backup ring 73 are movable according to the pressure of liquid hydrogen from the compression chamber 52 (see FIG. 3) acting on the annular groove 74.

[0033] The piston ring body 71, the inner ring 72, and the backup ring 73 are made of different materials, so their hardnesses are different. That is, the hardness of the inner ring 72 is lower than that of the piston ring body 71. That is, the inner ring 72 is softer than the piston ring body 71. The piston ring body 71 is formed of a PEEK-based material mainly composed of polyether ether ketone. The inner ring 72 is formed of a PTFE material mainly composed of polytetrafluoroethylene.

[0034] Here, the hardness refers to the durometer hardness, and the durometer is a rubber hardness tester. The durometer measures the hardness by pressing a needle of a determined shape onto the surface of the sample with the force of a spring to cause deformation, and based on the depth of penetration of the needle into the sample in a state where the resistance force of the sample and the force of the spring are balanced. The larger the force required to push the needle back, the larger the numerical value of the durometer, indicating that it is harder. Note that the durometer is a product name of Shore in the United States. In this embodiment, the durometer hardness of the piston ring body 71 is preferably 1.1 times to 1.6 times that of the inner ring 72.

[0035] <Piston ring body> The piston ring body 71 contains PEEK as the main component, 5 wt% or more and 25 wt% or less of polytetrafluoroethylene (PTFE), 5 wt% or more and 25 wt% or less of carbon fiber, and 5 wt% or more and 20 wt% or less of zinc oxide whisker. These are the basic compositions, and the rest are unavoidably mixed materials.

[0036] The piston ring body 71 is a base material using PEEK having a strength greater than that of PTFE as the main component. Since PEEK does not have a solid lubrication function, PTFE having a solid lubrication function is added. If the amount of PTFE is less than 5 wt%, the solid lubrication effect will not be manifested, so 5 wt% or more is preferred. On the other hand, if the amount of PTFE exceeds 25 wt%, a significant improvement in the solid lubrication effect cannot be expected, so 25 wt% or less is preferred. Note that about 20 wt% of PTFE is most preferred.

[0037] If the amount of carbon fiber is less than 5 wt%, an improvement in strength cannot be obtained, so 5 wt% or more is preferred. On the other hand, if the amount of carbon fiber exceeds 25 wt%, there will be more shedding, and the shed carbon fibers will wear the wear-resistant material for extremely low temperatures, so 25 wt% or less is preferred. Note that about 20 wt% of carbon fiber is most preferred. As the carbon fiber, PAN-based or pitch-based is preferably used, the fiber length is 10 - 1000 μm, preferably 50 - 200 μm, and the fiber diameter is 1 - 50 μm, preferably 7 - 15 μm.

[0038] When the zinc oxide whisker is less than 5% by weight, the function of preventing the carbon fiber from falling off cannot be obtained, so 5% by weight or more is preferable. On the other hand, even if the zinc oxide whisker exceeds 20% by weight, no significant improvement can be expected in terms of strength and adhesion effect, so 20% by weight or less is preferable. Incidentally, about 10% by weight of the zinc oxide whisker is most preferable. The zinc oxide whisker preferably has a tetrapod shape composed of a core part and needle-like crystal parts extending in the four-axis direction from the core part. The zinc oxide whisker can be obtained as a product under the trade name of Panatetra. The length of the needle-like crystal part is 3 to 200 μm, preferably 5 to 50 μm, and the diameter of the core part is 0.1 to 10 μm, preferably 0.3 to 3 μm.

[0039] Furthermore, it may also contain approximately 10% by weight of bronze powder. By adding bronze powder, which can be expected to promote the adhesion effect of PTFE, the wear resistance is improved. Also, by suppressing the bronze powder to about 10% by weight, the mixing with PEEK as the base material is optimized. The composition of the bronze powder is 2 to 15% by weight of Sn, preferably 3 to 12% by weight, and 85 to 98% by weight of Cu, preferably 88 to 92% by weight.

[0040] <Inner ring> The inner ring 72 contains 35% by weight or more of PTFE as the main component, 5% by weight or more and 30% by weight or less of bronze powder, 5% by weight or more and 15% by weight or less of carbon fiber, and 5% by weight or more and 20% by weight or less of zinc oxide whisker. These are the basic compositions, and the rest are materials that are inevitably mixed in.

[0041] The inner ring 72 is made of a base material mainly using PTFE having a function as a solid lubricant. Necessary strength is ensured by adding bronze powder to PTFE. Further, the bronze powder promotes the adhesion of PTFE to the metal material that is the sliding friction partner. When PTFE adheres to the metal material, wear is reduced. In order to achieve even greater strength, carbon fiber was added. Further, zinc oxide whisker is added to prevent the carbon fiber from falling off. This zinc oxide whisker further has a function of promoting the adhesion effect of PTFE to the metal material more than the bronze powder even in an extremely low temperature environment such as liquid hydrogen temperature (20K).

[0042] If the bronze powder is less than 5% by weight, the desired strength cannot be obtained, so it is preferably added in an amount of 5% by weight or more. On the other hand, even if the bronze powder exceeds 30% by weight, no significant improvement can be expected in terms of strength and adhesion effect, so it is preferably 30% by weight or less. Incidentally, about 20% by weight of the bronze powder is most preferable. The composition of the bronze powder is 2 to 15% by weight of Sn, preferably 3 to 12% by weight, and 85 to 98% by weight of Cu, preferably 88 to 92% by weight.

[0043] If the carbon fiber is less than 5% by weight, improvement in strength cannot be obtained, so it is preferably 5% by weight or more. On the other hand, if the carbon fiber exceeds 15% by weight, the amount of shedding increases, and the shed carbon fiber will wear the wear-resistant material for extremely low temperatures, so it is preferably 15% by weight or less. Incidentally, about 10% by weight of the carbon fiber is most preferable. As the carbon fiber, a pitch-based one is preferably used, and the fiber length is 10 to 1000 μm, preferably 50 to 200 μm, and the fiber diameter is 1 to 50 μm, preferably 7 to 15 μm.

[0044] When the zinc oxide whisker is less than 5% by weight, the function of preventing the carbon fiber from falling off cannot be obtained, so 5% by weight or more is preferable. On the other hand, even if the zinc oxide whisker exceeds 20% by weight, a significant improvement in strength and deposition effect cannot be expected, so 20% by weight or less is preferable. Incidentally, about 10% by weight of the zinc oxide whisker is most preferable. The zinc oxide whisker preferably has a tetrapod shape composed of a core part and needle-shaped crystal parts extending from this core part in four axial directions. The zinc oxide whisker can be obtained as a product under the trade name of Panatetra. The length of the needle-shaped crystal part is 3 to 200 μm, preferably 5 to 50 μm, and the diameter of the core part is 0.1 to 10 μm, preferably 0.3 to 3 μm.

[0045] The weight ratio of the carbon fiber to the zinc oxide whisker is 1.0 or more and 1.5 or less. Since the zinc oxide whisker has a function of preventing the carbon fiber from falling off, if the weight ratio of the carbon fiber to the zinc oxide whisker exceeds 1.5, the carbon fiber will fall off more and the wear will increase. Therefore, the weight ratio of the carbon fiber to the zinc oxide whisker is preferably 1.5 or less. On the other hand, considering the improvement in strength by the carbon fiber, it is preferable that at least an amount of carbon fiber equivalent to that of the zinc oxide whisker is added. Therefore, the weight ratio of the carbon fiber to the zinc oxide whisker is preferably 1.0 or more.

[0046] <Backup ring> The backup ring 73 is formed of stainless steel. For the backup ring 73, for example, any of SUS304, SUS304L, SUS316, and SUS316L is preferably used, but it is not limited thereto.

[0047] <Wearing ring> The wearing ring 62 functions as a bearing such as a piston 37 supported by the fitting hole 51 of the cylinder block 38, and prevents seizure and eccentricity. The wearing ring 62 is formed of a PITE material mainly composed of polytetrafluoroethylene. The PTFE material used for the wearing ring 62 is the same as that of the inner ring 72.

[0048] <Stress Distribution of Piston Ring> FIG. 5 is a schematic diagram for explaining the pressure distribution acting on the piston ring.

[0049] As shown in FIG. 4, the piston ring 61 disposed in the annular groove 74 of the piston 37 receives a pressure P from the high-pressure liquid hydrogen in the lower compression chamber 52 (see FIG. 3). The pressure P acts on the lower part of the piston ring 61 through the gap between the outer peripheral surface of the piston 37 and the inner peripheral surface of the fitting hole 51. Then, the pressure P acts on the inner peripheral surface side (the inner peripheral surface 73c of the backup ring 73) of the piston ring 61 through the gap between the piston ring 61 and the annular groove 74, and presses the outer peripheral surface (the outer peripheral surface 71a of the piston ring body 71) of the piston ring 61 against the inner peripheral surface of the fitting hole 51 to seal.

[0050] At this time, as shown in FIG. 5, a pressure distribution occurs on the outer peripheral surface and the inner peripheral surface of the piston ring 61. That is, the lower side of the piston ring 61, which is the compression chamber 52, is at high pressure and the upper side is at low pressure. Therefore, the outer peripheral surface of the piston ring 61 has a pressure distribution such that the pressure on the lower side is higher than that on the upper side with respect to the pressure on the upper side. Also, the inner peripheral surface of the piston ring 61 has a pressure distribution such that the pressure on the upper side and the pressure on the lower side are equal. Specifically, the outer peripheral surface 71a of the piston ring body 71 has a pressure distribution such that the pressure on the lower side is higher than that on the upper side with respect to the pressure on the upper side. Also, the inner peripheral surface of the backup ring 73 has a pressure distribution such that the pressure on the upper side and the pressure on the lower side are equal.

[0051] <Operation of Piston Ring> FIG. 6 is a schematic diagram for explaining the operation of the piston ring.

[0052] As shown in FIGS. 5 and 6, when the pressure distribution is such that the pressure on the lower side is higher than the pressure on the upper side on the outer peripheral surface 71a of the piston ring body 71, a rotational moment M in the counterclockwise direction in FIG. 6 acts on the piston ring body 71. Then, the piston ring body 71 rotates in the counterclockwise direction in FIG. 6 due to the rotational moment M. When the piston ring body 71 rotates, only the upper surface 71b side of the outer peripheral surface 71a comes into contact with the inner peripheral surface of the fitting hole 51, and only the lower surface 71d side of the inner peripheral surface 71c comes into contact with the outer peripheral surface 72a of the inner ring 72. When the piston ring body 71 is in a state of single contact with the inner peripheral surface of the fitting hole 51 and the outer peripheral surface 72a of the inner ring 72, the sealing performance deteriorates. Further, if the state of single contact of the piston ring body 71 continues, local wear progresses due to the movement of the piston 37, and it becomes difficult to maintain the long-term sealing performance.

[0053] However, in the first embodiment, the hardness of the inner ring 72 is lower than the hardness of the piston ring body 71. Therefore, when the piston ring body 71 rotates in the counterclockwise direction in FIG. 6 due to the rotational moment M, the inner ring 72 deforms under stress received from the lower surface 71d side of the inner peripheral surface 71c in the piston ring body 71. That is, the inner ring 72 deforms such that the middle part in the vertical direction warps toward the backup ring 73 side. The backup ring has a pressure P acting on the inner peripheral surface 73c side, and the inner ring 72 transmits the pressure P from the backup ring 73 to the piston ring body 71. That is, the upper part (upper surface 72b side) of the outer peripheral surface 72a of the inner ring 72 comes into contact with and presses the upper part (upper surface 71b side) of the inner peripheral surface 71c in the piston ring body 71, and the lower part (lower surface 72d side) of the outer peripheral surface 72a comes into contact with and presses the lower part (lower surface 71d side) of the inner peripheral surface 71c in the piston ring body 71.

[0054] As a result, the rotational moment M is canceled by the pressing force of the deformed inner ring 72, and as shown in Fig. 4, the entire area along the axis O on the outer peripheral surface 71a can come into contact with the inner peripheral surface of the fitting hole 51. Therefore, for the piston ring 61, the entire outer peripheral surface 71a of the piston ring body 71 can press the inner peripheral surface of the fitting hole 51, preventing single-sided contact and ensuring sealing performance.

[0055] [Second Embodiment] <Piston Ring> Fig. 7 is a cross-sectional view showing the mounting portion of the piston ring applied to the pressure boosting pump of the second embodiment. Members having the same functions as those in the first embodiment described above are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

[0056] As shown in Fig. 7, the piston ring 61A includes a piston ring body 71A, an inner ring 72, and a backup ring 73. The piston ring body 71A includes a high-pressure piston ring body 81 and a low-pressure piston ring body 82. The high-pressure piston ring body 81 is located on the side of the compression chamber 52 (the lower side in Fig. 7). The low-pressure piston ring body 82 is located on the side opposite to the compression chamber 52 with respect to the high-pressure piston ring body 81 (the upper side in Fig. 7).

[0057] The high-pressure piston ring body 81 and the low-pressure piston ring body 82 are ring-shaped and have the same outer diameter and inner diameter dimensions. The piston ring 61A is disposed in the annular groove 74. The piston ring 61A is configured to be disposed in the annular groove 74 in the order of the piston ring body 71A, the inner ring 72, and the backup ring 73 from the outer side to the inner side in the radial direction. And the high-pressure piston ring body 81 is located on the compression chamber 52 side of the piston ring body 71A, and the low-pressure piston ring body 82 is located on the side opposite to the compression chamber 52.

[0058] The high-pressure piston ring body 81 has an outer peripheral surface 81a, an upper surface 81b, an inner peripheral surface 81c, and a lower surface 81d. The low-pressure piston ring body 82 has an outer peripheral surface 82a, an upper surface 82b, an inner peripheral surface 82c, and a lower surface 82d. For the high-pressure piston ring body 81 and the low-pressure piston ring body 82, the outer peripheral surfaces 81a, 82a face the inner peripheral surface of the fitting hole 51, and the inner peripheral surfaces 81c, 82c face the outer peripheral surface 72a of the inner ring 72. Further, for the high-pressure piston ring body 81, the upper surface 81b faces the ceiling surface 74a of the annular groove 74, and for the low-pressure piston ring body 82, the lower surface 82d faces the bottom surface 74c of the annular groove 74. Then, the lower surface 81d of the high-pressure piston ring body 81 faces the upper surface 82b of the low-pressure piston ring body 82.

[0059] The high-pressure piston ring body 81 and the low-pressure piston ring body 82 are made of different materials, so their hardnesses are different. That is, the hardness of the low-pressure piston ring body 82 is lower than that of the high-pressure piston ring body 81. That is, the low-pressure piston ring body 82 is softer than the high-pressure piston ring body 81. The high-pressure piston ring body 81 is formed of a PEEK-based material mainly composed of polyether ether ketone, and the low-pressure piston ring body 82 is formed of a PTFE material mainly composed of polytetrafluoroethylene. In the present embodiment, the durometer hardness of the high-pressure piston ring body 81 is preferably 1.0 times to 1.5 times the durometer hardness of the low-pressure piston ring body 82.

[0060] Also, the hardness of the inner ring 72 is equal to or lower than the hardness of the low-pressure piston ring body 82. That is, the inner ring 72 has the same hardness as the low-pressure piston ring body 82 or is softer than the low-pressure piston ring body 82. In the present embodiment, the durometer hardness of the low-pressure piston ring body 82 is preferably 1.0 times to 1.6 times the durometer hardness of the inner ring 72.

[0061] <Stress distribution of piston ring> FIG. 8 is a schematic diagram for explaining the pressure distribution acting on the piston ring.

[0062] As shown in FIG. 7, the piston ring 61A disposed in the annular groove 74 of the piston 37 receives the pressure P from the high-pressure liquid hydrogen in the lower compression chamber 52 (see FIG. 7). The pressure P acts on the lower part of the piston ring 61A through the gap between the outer peripheral surface of the piston 37 and the inner peripheral surface of the fitting hole 51. Then, the pressure P acts on the inner peripheral surface side (the inner peripheral surface 73c of the backup ring 73) of the piston ring 61A through the gap between the piston ring 61A and the annular groove 74, and presses the outer peripheral surface (the outer peripheral surfaces 81a, 82a of the piston ring main bodies 81, 82) of the piston ring 61A against the inner peripheral surface of the fitting hole 51 to seal it.

[0063] At this time, as shown in FIG. 8, a pressure distribution is generated on the outer peripheral surface and the inner peripheral surface of the piston ring 61A. That is, in the piston ring 61A, the lower side, which is the compression chamber 52, is at high pressure and the upper side is at low pressure. Therefore, the outer peripheral surface of the piston ring 61A has a pressure distribution such that the pressure on the lower side is higher than the pressure on the upper side. Also, the inner peripheral surface of the piston ring 61A has a pressure distribution such that the pressure on the upper side and the pressure on the lower side are equal. Specifically, the outer peripheral surfaces 81a, 82a of the high-pressure piston ring main body 81 and the low-pressure piston ring main body 82 have a pressure distribution such that the pressure on the lower side is higher than the pressure on the upper side. Also, the inner peripheral surface of the backup ring 73 has a pressure distribution such that the pressure on the upper side and the pressure on the lower side are equal.

[0064] <Operation of the piston ring> FIG. 9 is a schematic diagram for explaining the operation of the piston ring.

[0065] As shown in FIGS. 8 and 9, when the pressure distributions of the outer peripheral surfaces 81a and 82a of the high-pressure piston ring body 81 and the low-pressure piston ring body 82 are such that the pressure on the lower side is higher than the pressure on the upper side with respect to the pressure on the upper side, rotational moments M1 and M2 in the counterclockwise direction in FIG. 9 act on the high-pressure piston ring body 81 and the low-pressure piston ring body 82. Then, the high-pressure piston ring body 81 rotates in the counterclockwise direction in FIG. 9 due to the rotational moment M1. When the high-pressure piston ring body 81 rotates, only the upper surface 81b side of the outer peripheral surface 81a comes into contact with the inner peripheral surface of the fitting hole 51, and only the lower surface 81d side of the inner peripheral surface 81c comes into contact with the outer peripheral surface 72a of the inner ring 72. Similarly, the low-pressure piston ring body 82 rotates in the counterclockwise direction in FIG. 9 due to the rotational moment M2. When the low-pressure piston ring body 82 rotates, only the upper surface 82b side of the outer peripheral surface 82a comes into contact with the inner peripheral surface of the fitting hole 51, and only the lower surface 82d side of the inner peripheral surface 82c comes into contact with the outer peripheral surface 72a of the inner ring 72.

[0066] When the high-pressure piston ring body 81 and the low-pressure piston ring body 82 are in a state of single contact with the inner peripheral surface of the fitting hole 51 and the outer peripheral surface 72a of the inner ring 72, the sealing performance deteriorates. Further, when the state of single contact of the high-pressure piston ring body 81 and the low-pressure piston ring body 82 continues, local wear progresses due to the movement of the piston 37, and it becomes difficult to maintain the long-term sealing performance.

[0067] However, in the second embodiment, the piston ring 61A is composed of a high-pressure piston ring body 81 and a low-pressure piston ring body 82, and the hardness of the inner ring 72 is lower than that of the high-pressure piston ring body 81. Therefore, when the high-pressure piston ring body 81 and the low-pressure piston ring body 82 rotate counterclockwise in FIG. 9 due to the rotational moments M and M2, the inner ring 72 deforms under stress received from the lower surface 81d side of the inner peripheral surface 81c of the high-pressure piston ring body 81. That is, the inner ring 72 deforms such that the middle part in the vertical direction bends toward the backup ring 73 side. The backup ring 73 has a pressure P acting on the inner peripheral surface 73c side, and the inner ring 72 transmits the pressure P from the backup ring to the high-pressure piston ring body 81 and the low-pressure piston ring body 82. That is, the upper part (upper surface 72b side) of the outer peripheral surface 72a of the inner ring 72 contacts and presses against the low-pressure piston ring body 82, and the lower part (lower surface 72d side) of the outer peripheral surface 72a contacts and presses against the lower part (lower surface 81d side) of the inner peripheral surface 81c of the high-pressure piston ring body 81.

[0068] As a result, the rotational moments M1 and M2 of the high-pressure piston ring body 81 and the low-pressure piston ring body 82 are canceled out by the pressing force of the deformed inner ring 72, and as shown in FIG. 7, the entire area along the axis O on each outer peripheral surface 81a and 82a can contact the inner peripheral surface of the fitting hole 51. Therefore, the piston ring 61A can press the entire inner peripheral surface of the fitting hole 51 with the entire outer peripheral surfaces 81a and 82a of the high-pressure piston ring body 81 and the low-pressure piston ring body 82, preventing single-sided contact and ensuring sealing performance.

[0069] [Operation and Effect of this Embodiment] The boost pump according to the first aspect includes a cylinder block (cylinder) 38 having a compression chamber 52, an intake valve 41 for sucking liquid hydrogen (cryogenic fluid) into the compression chamber 52, a piston 37 movably supported by the cylinder block 38 for compressing the liquid hydrogen in the compression chamber 52, a discharge valve 42 for discharging the liquid hydrogen in the compression chamber 52, and piston rings 61, 61A provided on the outer peripheral portion of the piston 37. The piston rings 61, 61A have piston ring bodies 71, 71A located on the inner peripheral surface side of the fitting hole 51 and inner rings 72 located closer to the center of the piston 37 than the piston ring bodies 71, 71A, and the hardness of the inner rings 72 is lower than the hardness of the piston ring bodies 71, 71A.

[0070] According to the boost pump according to the first aspect, since the hardness of the inner ring 72 is lower than the hardness of the piston ring bodies 71, 71A, when rotational moments M, M2 act due to the pressure acting on the piston ring bodies 71, 71A, the inner ring 72 deforms, and a pressure that pushes back the piston ring bodies 71, 71A acts. Then, the rotational moments M1, M2 of the piston ring bodies 71, 71A are canceled out, and the outer peripheral surfaces 71a, 81a, 82a can appropriately contact the inner peripheral surface of the fitting hole 51. As a result, the sealing performance of the piston rings 61, 61A can be improved, and sufficient sealing performance can be ensured even when the pressure of the applied cryogenic fluid is ultra-high pressure.

[0071] The boost pump according to the second aspect is the boost pump according to the first aspect, and further, the piston ring bodies 71, 71A are formed of a PEEK-based material mainly composed of polyether ether ketone, and the inner rings 72 are formed of a PTFE material mainly composed of polytetrafluoroethylene. Thereby, high sealing performance having low friction, low wear, and high strength can be maintained.

[0072] The pressure boosting pump according to the third aspect is the pressure boosting pump according to the first aspect or the second aspect, and further, the piston ring body 71A has a high-pressure piston ring body 81 located on the compression chamber 2 side and a low-pressure piston ring body 82 located on the side opposite to the compression chamber 52 with respect to the high-pressure piston ring body 81, and the hardness of the low-pressure piston ring body 82 is lower than the hardness of the high-pressure piston ring body 81. Thereby, due to the deformation of the inner ring 72 and the low-pressure piston ring body 82, the outer peripheral surface 81a of the high-pressure piston ring body 81 can be appropriately contacted with the inner peripheral surface of the fitting hole 51, and the sealing performance by the piston ring 61A can be improved.

[0073] The pressure boosting pump according to the fourth aspect is the pressure boosting pump according to the third aspect, and further, the hardness of the inner ring 72 is equal to or lower than the hardness of the low-pressure piston ring body 82. Thereby, due to the deformation of the inner ring 72, the outer peripheral surface 82a of the low-pressure piston ring body 82 can be appropriately contacted with the inner peripheral surface of the fitting hole 51, and the sealing performance by the piston ring 61A can be improved.

[0074] The pressure boosting pump according to the fifth aspect is the pressure boosting pump according to the third aspect or the fourth aspect, and further, the high-pressure piston ring body 81 is formed of a PEEK-based material mainly composed of polyether ether ketone, and the low-pressure piston ring body 82 is formed of a PTFE material mainly composed of polyether ether ketone. Thereby, high sealing performance having low friction, low wear, and high strength can be maintained.

[0075] The boost pump according to the sixth aspect is the boost pump according to any one of the first to fifth aspects, and further, an annular groove 74 is formed on the outer peripheral portion of the piston 37, and piston ring bodies 71, 71A are disposed on the outermost radially of the annular groove 74. An inner ring 72 is disposed radially inward of the piston ring bodies 71, 71A in the annular groove 74, and a backup ring 73 is disposed radially inward of the inner ring 72 in the annular groove 74. The backup ring 73 is formed of stainless steel. Thereby, the pressure P acting on the backup ring 73 can be appropriately transmitted to the inner ring 72.

[0076] The boost pump according to the seventh aspect is the boost pump according to any one of the first to sixth aspects, and further, a plurality of piston ring bodies 71, 71A are provided at intervals in the moving direction of the piston 37. Wear rings 62 are provided on one axial side and the other axial side of the plurality of piston ring bodies 71, 71A of the piston 37, respectively. The wear ring 62 is formed of a PTFE material mainly composed of polytetrafluoroethylene. Thereby, it is possible to maintain high sealing performance having low friction, low wear, and high strength.

[0077] The hydrogen supply system according to the eighth aspect includes a compression device 21 that has a boost pump 32 according to any one of the first to seventh aspects and compresses liquid hydrogen as a cryogenic fluid, and an evaporation device 22 that vaporizes the liquid hydrogen compressed by the compression device 21. And a dispenser 23 that supplies the hydrogen gas vaporized by the evaporation device 22. Thereby, the boost pump 32 can improve the sealing performance by the piston rings 61, 61A, and sufficient sealing performance can be ensured even when the pressure of the cryogenic fluid to be applied is ultra-high pressure.

[0078] In the above-described embodiment, the number of the piston ring bodies 71, 71A is one or two, but it may be three or more.

[0079] In the above-described embodiment, the booster pump 32 has been described as being applied to the compressor 21 of the hydrogen supply system 10. However, the present invention is not limited to this field, and it can be applied to any device that applies a cryogenic fluid.

Explanation of Reference Numerals

[0080] 10 Hydrogen supply system 11 Container 12 Vehicle 21 Compressor 22 Evaporator 23 Dispenser 31 Drive motor 32 Booster pump 34 Crank mechanism 35 Crosshead 36 Piston rod 37 Piston 38 Cylinder block (cylinder) 39 Container 41 Suction valve 42 Discharge valve 51 Fitting hole 52 Compression chamber 61, 61A Piston ring 62 Wear ring 71, 71A Piston ring body 72 Inner ring 73 Backup ring 74 Annular groove 81 High-pressure piston ring body 82 Low-pressure piston ring body

Claims

1. A cylinder having a compression chamber, An intake valve for sucking a cryogenic fluid into the compression chamber, A piston having an annular groove formed along the circumferential direction on the outer peripheral surface, movably supported by the cylinder, and compressing the cryogenic fluid in the compression chamber, A discharge valve for discharging the cryogenic fluid in the compression chamber, A piston ring provided in the annular groove of the piston, Comprising, The piston ring, A piston ring body located on the inner peripheral surface side of the cylinder, An inner ring located on the center side of the piston from the piston ring body, A metallic backup ring located on the center side of the piston from the inner ring, Having, The hardness of the inner ring is lower than the hardness of the piston ring body, The piston ring body has a high-pressure piston ring body with a rectangular cross-sectional shape located on the compression chamber side and a low-pressure piston ring body with a rectangular cross-sectional shape located on the side opposite to the compression chamber from the high-pressure piston ring body, The axial thickness of the low-pressure piston ring body is thinner than the axial thickness of the high-pressure piston ring body, A booster pump.

2. The piston ring body is formed of a PEEK-based material mainly composed of polyetheretherketone, and the inner ring is formed of a PTFE material mainly composed of polytetrafluoroethylene, The booster pump according to Claim 1.

3. The hardness of the low-pressure piston ring body is lower than the hardness of the high-pressure piston ring body, The booster pump according to Claim 1 or Claim 2.

4. The hardness of the inner ring is less than or equal to the hardness of the low-pressure piston ring body, The booster pump according to Claim 1 or Claim 2.

5. The high-pressure piston ring body is formed of a PEEK-based material mainly composed of polyetheretherketone, and the low-pressure piston ring body is formed of a PTFE material mainly composed of polytetrafluoroethylene, The booster pump according to Claim 3.

6. The piston has an annular groove formed on the outer peripheral portion, the piston ring body is disposed at the outermost radial position of the annular groove, the inner ring is disposed radially inward of the piston ring body in the annular groove, the backup ring is disposed radially inward of the inner ring in the annular groove, and the backup ring is formed of stainless steel. The boost pump according to claim 1.

7. A plurality of the piston rings are provided at intervals in the moving direction of the piston, wear rings are provided on one axial side and the other axial side of the plurality of piston rings, respectively, and the wear rings are formed of a PTFE material mainly composed of polytetrafluoroethylene. The boost pump according to claim 1.

8. A compression device that has the boost pump according to claim 1 and compresses liquid hydrogen as a cryogenic fluid, An evaporation device that vaporizes the liquid hydrogen compressed by the compression device, A dispenser that supplies hydrogen gas vaporized by the evaporation device, A hydrogen supply system comprising the above.

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