Liquid hydrogen pump

Abstract

To provide a liquid hydrogen pump that can appropriately pressurize liquid hydrogen while preventing unintended leakage of the liquid hydrogen.SOLUTION: A liquid hydrogen pump 30 pressurizes and pumps up liquid hydrogen stored in a hydrogen tank 10, and comprises a cylinder 34 at least partially arranged in the hydrogen tank 10, and a piston 36 to be reciprocated inside the cylinder 34, and partitioning the inside of the cylinder 34 into a pump chamber 44 to be pressurized by the piston 36, and an opposite chamber 46 located on the side opposite to the pump chamber 44 across the piston 36. A back flow opening 70 for returning the liquid hydrogen having flowed into the opposite chamber 46, into the hydrogen tank 10 is formed at a place corresponding to the opposite chamber 46 out of a peripheral wall of the cylinder 34.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This specification discloses a liquid hydrogen pump that pressurizes and pumps liquid hydrogen stored in a tank.

Background Art

[0002] Conventionally, a liquid hydrogen pump that pressurizes and pumps liquid hydrogen in a tank has been known. As such a liquid hydrogen pump, for example, there is a cylinder pump having a cylinder and a piston that reciprocates within the cylinder. In this case, a seal ring that is in close contact with the inner peripheral surface of the cylinder and restricts the passage of liquid hydrogen is provided on the outer peripheral surface of the piston.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, even when a large number of seal rings are provided, when liquid hydrogen is pressurized to a high pressure, a part of the liquid hydrogen to be pressurized may pass through the seal ring and leak outside the tank.

[0005] Note that Patent Document 1 discloses a booster pump having a cylinder having a pressure chamber, a reciprocating piston, and a bellows. The piston has a piston that moves forward and backward in the pressure chamber and a piston rod. Further, a bellows is attached to the piston, and this bellows separates the pressure chamber into a space surrounding the piston rod and a space outside thereof. According to such a configuration, even if the gap between the piston and the cylinder is increased, leakage of the liquid to be boosted can be prevented.

[0006] However, Patent Document 1 provides a highly flexible bellows in the pressure chamber. Therefore, the pressure fluctuations associated with the movement of the piston may be absorbed by the deformation of the bellows, and there is a risk that the target liquid cannot be pressurized to a sufficiently high pressure. That is, conventionally, there has been no liquid hydrogen pump that can appropriately pressurize liquid hydrogen while preventing unintentional leakage of liquid hydrogen.

[0007] Therefore, this specification discloses a liquid hydrogen pump that can appropriately pressurize liquid hydrogen while preventing unintentional leakage of liquid hydrogen.

Means for Solving the Problems

[0008] The liquid hydrogen pump disclosed in this specification is a liquid hydrogen pump that pressurizes and pumps up liquid hydrogen stored in a tank, and includes a cylinder at least partially disposed in the tank, and a piston that reciprocates inside the cylinder. The inside of the cylinder is separated into a pump chamber pressurized by the piston and an opposing chamber located on the opposite side of the pump chamber with the piston interposed therebetween. A piston is provided, and a reflux opening for returning the liquid hydrogen that has flowed into the opposing chamber to the inside of the tank is formed at a location on the peripheral wall of the cylinder corresponding to the opposing chamber.

[0009] With such a configuration, even when liquid hydrogen flows from the pump chamber into the opposing chamber, the liquid hydrogen returns to the inside of the tank through the reflux opening, so that external leakage of liquid hydrogen can be effectively prevented.

[0010] In this case, the reflux opening may be located above the liquid level when the liquid hydrogen is fully filled.

[0011] With such a configuration, it is possible to prevent a large amount of liquid hydrogen from flowing from the tank into the opposing chamber.

[0012] Furthermore, the pump chamber may further include an inlet formed in the pump chamber, an outlet formed in the pump chamber, a first check valve for opening and closing the inlet, which allows the flow flowing into the pump chamber and prohibits the flow flowing out of the pump chamber, and a second check valve for opening and closing the outlet, which allows the flow flowing out of the pump chamber and prohibits the flow flowing into the pump chamber.

[0013] With such a configuration, liquid hydrogen can be appropriately pumped.

[0014] In this case, the tank may have a collector portion that is locally sunken at its bottom, and the inlet may be located within the collector portion.

[0015] With such a configuration, even when the remaining amount of liquid hydrogen in the tank decreases, the liquid hydrogen pump can pump up the liquid hydrogen.

Advantages of the Invention

[0016] According to the technology disclosed in this specification, the liquid hydrogen that has flowed into the counter chamber beyond the piston is returned into the tank from the reflux opening. As a result, it is possible to effectively prevent the liquid hydrogen from leaking outside the tank. As a result, while preventing the unintended leakage of liquid hydrogen, the liquid hydrogen can be appropriately pressurized.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0018] The configuration of the liquid hydrogen pump 30 will be described below with reference to the drawings. FIG. 1 is a schematic diagram of a hydrogen tank 10 to which the liquid hydrogen pump 30 is attached. FIG. 2 is a cross-sectional view of the main part of the liquid hydrogen pump 30.

[0019] The hydrogen tank 10 and the liquid hydrogen pump 30 in this example are mounted on a vehicle using hydrogen as an energy source, for example, a hydrogen engine vehicle or a fuel cell vehicle. The hydrogen tank 10 is a tank for storing hydrogen in a liquid state. The hydrogen tank 10 stores liquid hydrogen at a pressure equal to or slightly higher than atmospheric pressure, for example, 1 Mpa or less. The hydrogen tank 10 has a heat insulation structure in order to maintain the liquid hydrogen in a low temperature state (below -253 degrees). Specifically, the hydrogen tank 10 has an inner tank 12 for storing the liquid hydrogen pump 30 and an outer tank 14 that covers the inner tank 12 from the outside. The gap between the inner tank 12 and the outer tank 14 is evacuated, and this gap functions as a vacuum insulation layer. Both the inner tank 12 and the outer tank 14 are made of a metal that is less likely to cause low temperature brittleness, for example, stainless steel or the like.

[0020] A collector portion 22 that is recessed from the surroundings is provided at the bottom of the hydrogen tank 10. The cylinder head 42 of the liquid hydrogen pump 30, which will be described later, is located in this collector portion 22. The reason for such a configuration will be described later.

[0021] A safety port 16 and a pump port 20 are formed at the top of the hydrogen tank 10. The safety port 16 is a port to which the boil-off valve 18 is connected. The boil-off valve 18 is a valve for discharging boil-off gas. That is, although the hydrogen tank 10 has high heat insulation, over time, liquid hydrogen vaporizes due to natural heat ingress, generating hydrogen gas, that is, boil-off gas. If the boil-off gas is left unattended, the internal pressure of the hydrogen tank 10 will rise excessively. Therefore, when the internal pressure of the hydrogen tank 10 reaches a certain level or higher, the boil-off valve 18 is opened, and the boil-off gas is discharged outside the tank.

[0022] The cylinder 34 of the liquid hydrogen pump 30 is inserted into the pump port 20. The liquid hydrogen pump 30 is a booster pump that pressurizes and pumps up liquid hydrogen. The pumped-up liquid hydrogen is vaporized in a vaporizer (not shown) provided outside the hydrogen tank 10 and converted into hydrogen gas, and then directly injected into the cylinders of the hydrogen engine. In this example, the liquid hydrogen pump 30 boosts the liquid hydrogen in the tank to a high pressure (for example, 5 Mpa to 30 Mpa). In this way, pressurizing with the liquid hydrogen pump 30 to a high pressure is to obtain high-pressure hydrogen gas. That is, the hydrogen gas injected into the direct injection type hydrogen engine is required to be at a very high pressure. In order to obtain such high-pressure hydrogen gas, it is necessary to vaporize high-pressure liquid hydrogen. However, when storing liquid hydrogen in the hydrogen tank 10 in a high-pressure state, it is necessary to increase the pressure resistance performance of the hydrogen tank 10, which leads to an increase in weight and cost. On the other hand, in this example, the configuration is such that liquid hydrogen is stored in the hydrogen tank 10 at a low pressure, and the necessary liquid hydrogen is pressurized by the liquid hydrogen pump 30 and sent to the vaporizer. By adopting such a configuration, while keeping the required pressure resistance performance of the hydrogen tank 10 low, high-pressure liquid hydrogen can be supplied to the vaporizer, and high-pressure hydrogen gas can be obtained.

[0023] The liquid hydrogen pump 30 includes a cylinder 34, a piston 36 that reciprocates inside the cylinder 34, and a pump motor 32 that reciprocates the piston 36. As shown in FIG. 2, the cylinder 34 has a cylindrical cylinder body 40 and a cylinder head 42 attached to the lower end of the cylinder body 40. A recess 42a communicating with the internal space of the cylinder body 40 is formed in the cylinder head 42.

[0024] The piston 36 is a member having an outer diameter substantially the same as the inner diameter of the cylinder 34. This piston 36 divides the internal space of the cylinder 34 into a pump chamber 44 and an opposing chamber 46. Specifically, the lower side of the piston 36 becomes the pump chamber 44 pressurized by the piston 36, and the upper side of the piston 36 becomes the opposing chamber 46. As the piston 36 reciprocates, the volume of the pump chamber 44, and thus the pressure of the pump chamber 44, changes. Thereby, the liquid hydrogen in the tank is sucked into the pump chamber 44, and the sucked liquid hydrogen is pumped out from the pump chamber 44 to the outside.

[0025] The configuration of the piston 36 is not particularly limited as long as it can slide in a liquid-tight contact with the inner surface of the cylinder 34. The piston 36 of this example has an adapter ring 64, an end plate 60, a nut 62, a seal ring 66, and a spacer 68. The adapter ring 64 is a cylindrical member through which the piston rod 38 is inserted, and a flange portion is formed at its upper end. The end plate 60 is an annular disc member through which the piston rod 38 can be inserted, and is disposed below the adapter ring 64. Two seal rings 66 and a spacer 68 are attached to the outer peripheral surface of the adapter ring 64. The seal ring 66 adheres to the inner peripheral surface of the cylinder 34 and inhibits the passage of liquid hydrogen. The seal ring 66 and the spacer 68 are sandwiched vertically between the flange portion of the adapter ring 64 and the end plate 60. The nut 62 is screwed onto the male thread formed at the lower end of the piston rod 38, and tightens the end plate 60 in the direction of closely contacting the adapter ring 64. Note that all the configurations described here are examples, and the piston 36 may have other configurations as long as it can appropriately pressurize and depressurize the pump chamber 44.

[0026] A piston rod 38 is connected to the piston 36. The piston rod 38 extends to the outside of the hydrogen tank 10. Upper bearings 39U and lower bearings 39L are provided in the upper portion above the piston 36, that is, in the opposing chamber 46. The piston rod 38 is supported by the upper bearings 39U and the lower bearings 39L so as to be able to advance and retreat.

[0027] The pump motor 32 is a motor that reciprocates the piston rod 38 and, thus, the piston 36. A cam (not shown) is attached to the output shaft of the pump motor 32, and the cam rotates as the pump motor 32 is driven. Further, the piston rod 38 is biased by a spring (not shown) in a direction to contact the cam. Therefore, as the pump motor 32 is driven, the height of the contact point between the cam and the piston rod 38 changes, and thereby, the piston 36 reciprocates. Note that such a configuration is also an example, and the configuration of the actuator that reciprocates the piston 36 may be appropriately changed. For example, instead of the actuator having a motor and a cam, an actuator having a ball screw mechanism, a hydraulic mechanism, an electromagnetic cylinder, or the like may be employed.

[0028] As described above, a pump chamber 44 is formed at the lower part of the cylinder 34. An inlet 48 and an outlet 50 are formed in the pump chamber 44. The inlet 48 is an opening that communicates with the inside of the tank via an inflow passage 52. Further, the outlet 50 is an opening that communicates with the outside of the tank via an outflow passage 54. Both the inlet 48 and the outlet 50 are located below the piston 36 at the bottom dead center and are formed at positions not blocked by the piston 36. Further, in this example, the pump chamber 44 and, thus, the inlet 48 are located inside the collector portion 22. With such a configuration, even when the remaining amount of liquid hydrogen in the hydrogen tank 10 decreases, liquid hydrogen can be pumped up from the inlet 48.

[0029] Here, the inlet 48 is opened and closed by a first check valve 56. The first check valve 56 allows the flow into the pump chamber 44 and prohibits the flow out of the pump chamber 44. Further, the outlet 50 is opened and closed by a second check valve 58. The second check valve 58 allows the flow out of the pump chamber 44 and prohibits the flow into the pump chamber 44. Note that the second check valve 58 allows the flow out of the pump chamber 44, but when the pressure in the pump chamber 44 is low, it is not opened, and no flow in the outflow direction occurs. The second check valve 58 is opened only when the pressure in the pump chamber 44 reaches the target boost pressure.

[0030] Among such liquid hydrogen pumps 30, the parts that come into contact with liquid hydrogen are made of materials that do not cause low-temperature brittleness. Specifically, the cylinder 34, the adapting 64, the end plate 60, the nut 62, the spacer 68, and the piston rod 38 are made of metals such as stainless steel, and the seal ring 66 is made of a resin that does not cause low-temperature brittleness.

[0031] The operation of the liquid hydrogen pump 30 with the above configuration will be described. As the piston 36 rises with the drive of the pump motor 32, the volume of the pump chamber 44 expands, and the liquid hydrogen inside the hydrogen tank 10 flows into the pump chamber 44. Then, as the piston 36 descends with the drive of the pump motor 32, the volume of the pump chamber 44 shrinks. At this time, since the second check valve 58 is closed until a predetermined target boost pressure is reached, the liquid hydrogen cannot flow out of the pump chamber 44 and will be pressurized. After that, when the liquid hydrogen in the pump chamber 44 is pressurized to the target boost pressure, the second check valve 58 is opened, and the pressurized liquid hydrogen is pumped out of the tank through the outflow passage 54.

[0032] By the way, in this example, the target boost pressure is extremely high (for example, 5 Mpa to 30 Mpa). Therefore, when pressurizing the liquid hydrogen, a part of the piston 36 may be deformed because it cannot withstand the pressure of the liquid hydrogen, and the liquid hydrogen may flow from the pump chamber 44 into the counter chamber 46. That is, some liquid hydrogen may flow into the counter chamber 46 through the route of arrow A in FIG. 3. And various problems will occur when the liquid hydrogen flowing into the counter chamber 46 finally leaks out of the hydrogen tank 10.

[0033] To avoid such problems, it is also conceivable to increase the number of seal rings 66. However, if the number of seal rings 66 is increased, it will cause other problems such as an increase in cost and an increase in the size of the pump. Also, as described above, liquid hydrogen is pressurized to a very high pressure. Further, since liquid hydrogen is at a very low temperature, the elasticity of the seal ring 66 in contact with it is likely to decrease, and it is difficult to maintain high seal performance of the seal ring 66. Therefore, even if the number of seal rings 66 is increased, it has been difficult to surely prevent the flow of liquid hydrogen into the counter chamber 46.

[0034] Therefore, in this example, a reflux opening 70 for returning the liquid hydrogen flowing into the counter chamber 46 to the inside of the hydrogen tank 10 is provided in the cylinder 34. As shown in FIG. 2, the reflux opening 70 is an opening formed on the circumferential surface of the cylinder 34. This reflux opening 70 is located above the liquid level (hereinafter referred to as the "uppermost liquid level HL") that mimics the state where the liquid hydrogen is fully filled. Also, the reflux opening 70 is located at a height inside the hydrogen tank 10. Therefore, the reflux opening 70 is located inside the tank, but is not located in the liquid of the liquid hydrogen and is always located in the gas. Therefore, the inflow of liquid hydrogen from the reflux opening 70 into the counter chamber 46 is prevented.

[0035] By providing such a reflux opening 70, the liquid hydrogen that has flowed into the counter chamber 46 returns from the reflux opening 70 into the tank through the route of arrow B in FIG. 3 before flowing out of the tank. That is, according to this example, while pressurizing the liquid hydrogen to a high pressure, the leakage of the liquid hydrogen to the outside of the tank can be effectively prevented. Note that a lower bearing 39L is located between the piston 36 and the reflux opening 70. However, the lower bearing 39L is for the purpose of preventing the inclination of the piston rod 38, and the gaps between the lower bearing 39L and the piston rod 38 and between the lower bearing 39L and the inner circumferential surface of the cylinder 34 are hardly sealed. Therefore, the liquid hydrogen that has flowed into the counter chamber 46 beyond the piston rod 38 can relatively easily reach the reflux opening 70 even beyond the lower bearing 39L.

[0036] In this example, the reflux opening 70 is located above the uppermost liquid level HL. However, as long as the reflux opening 70 is located above the piston 36 at top dead center, it may also be located below the uppermost liquid level HL. That is, as shown in FIG. 4, the reflux opening 70 may be located in the liquid. Even in this case, the liquid hydrogen that has flowed into the counter chamber 46 can return to the inside of the hydrogen tank 10 through the reflux opening 70, so external leakage of the liquid hydrogen can be prevented. In this case, a sealing mechanism may be provided between the lower bearing 39L and the piston 36 and between the lower bearing 39L and the cylinder 34 to prevent the liquid hydrogen from moving above the lower bearing 39L. Since the space between the piston 36 and the lower bearing 39L is at a low pressure, if there is a certain degree of sealing performance, it is possible to prevent this liquid hydrogen from moving upward beyond the lower bearing 39L.

[0037] Also, all of the above descriptions are examples. As long as the reflux opening 70 is formed at a location corresponding to the counter chamber 46 on the peripheral wall of the cylinder 34, other configurations may be appropriately changed.

Explanation of Reference Numerals

[0038] 10 Hydrogen tank, 12 Inner tank, 14 Outer tank, 16 Safety port, 18 Boil-off valve, 20 Pump port, 22 Collector section, 30 Liquid hydrogen pump, 32 Pump motor, 34 Cylinder, 36 Piston, 38 Piston rod, 39L Lower bearing, 39U Upper bearing, 40 Cylinder body, 42 Cylinder head, 42a Recess, 44 Pump chamber, 46 Counter chamber, 48 Inlet, 50 Outlet, 52 Inflow passage, 54 Outflow passage, 56 First check valve, 58 Second check valve, 60 End plate, 62 Nut, 64 Adapter ring, 66 Seal ring, 68 Spacer, 70 Reflux opening.

Claims

1. A liquid hydrogen pump for pressurizing and pumping liquid hydrogen stored in a tank, a cylinder at least partially disposed within the tank, a piston reciprocating inside the cylinder, the piston separating the inside of the cylinder into a pump chamber pressurized by the piston and an opposing chamber located on the side opposite to the pump chamber with the piston interposed therebetween, wherein a reflux opening for returning the liquid hydrogen flowing into the opposing chamber to the inside of the tank is formed at a location on the peripheral wall of the cylinder corresponding to the opposing chamber, the reflux opening is located above the liquid level when the liquid hydrogen is full, furthermore, a piston rod connected to the piston and extending from the piston to the outside of the tank, two bearings for supporting the piston rod so as to be able to move forward and backward with respect to the cylinder, wherein the reflux opening is located above the liquid level when the liquid hydrogen is full and is located inside the tank, one bearing is located between the piston and the reflux opening, the sealing performance of the gap between the one bearing, the piston rod and the cylinder is lower than the sealing performance of the gap between the piston and the cylinder, characterized in that it is a liquid hydrogen pump.

2. The liquid hydrogen pump according to claim 1, further comprising an inlet formed in the pump chamber, an outlet formed in the pump chamber, a first check valve for opening and closing the inlet, which allows the flow flowing into the pump chamber and prohibits the flow flowing out of the pump chamber, a second check valve for opening and closing the outlet, which allows the flow flowing out of the pump chamber and prohibits the flow flowing into the pump chamber, characterized in that it is provided with.

3. The liquid hydrogen pump according to claim 2, the tank has a collector portion locally sunken at its bottom, the inlet is located inside the collector portion, characterized in that it is a liquid hydrogen pump.

Images