Liquid hydrogen system

Abstract

To provide a liquid hydrogen system capable of appropriately supplying hydrogen to a hydrogen engine.SOLUTION: A liquid hydrogen system 10 comprises: a hydrogen tank 12 that is mounted on a vehicle, and stores liquid hydrogen; a supply circuit 30 that extracts the liquid hydrogen from the hydrogen tank 12, then converts it to hydrogen gas, and supplies it to a hydrogen engine 100; and a return circuit 60 branching off from the supply circuit 30 and connected to the hydrogen tank 12, where the return circuit 60 returns the hydrogen gas to the hydrogen tank 12 so that an internal pressure of the hydrogen tank 12 is equal to or higher than a specified reference pressure Pst.SELECTED DRAWING: Figure 1

Description

Technical Field

[0006] ,

[0001] This specification discloses a liquid hydrogen system that stores hydrogen in a liquid state, converts it to a gaseous state, and supplies it to a hydrogen engine.

Background Art

[0002] Conventionally, a liquid hydrogen system that stores hydrogen to be supplied to a hydrogen engine in a liquid state has been known. For example, Patent Document 1 discloses a system that stores liquid hydrogen in a hydrogen tank, pumps out this liquid hydrogen, and then vaporizes it to supply it to a hydrogen engine. By storing hydrogen in a liquid state in this way, the storage amount of hydrogen can be increased compared to the case of storing it in a gaseous state.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in such a liquid hydrogen system, when the consumption amount of hydrogen by the hydrogen engine suddenly increases, naturally, a large amount of liquid hydrogen is taken out of the hydrogen tank in a short time. And when a large amount of liquid hydrogen is taken out, there is a risk that the internal pressure of the hydrogen tank will drop excessively. If the internal pressure of the hydrogen tank drops excessively, it becomes difficult to discharge the liquid hydrogen by the pump.

[0005] However, in conventional technologies such as Patent Document 1, such a decrease in internal pressure accompanying the extraction of liquid hydrogen has not been studied. As a result, in the conventional technology, there are cases where hydrogen cannot be appropriately supplied to the hydrogen engine.

[0006] Therefore, this specification discloses a liquid hydrogen system that can appropriately supply hydrogen to a hydrogen engine. [Means for solving the problem]

[0007] The liquid hydrogen system disclosed herein is characterized by comprising: a hydrogen tank mounted on a vehicle for storing liquid hydrogen; a supply circuit for taking the liquid hydrogen from the hydrogen tank, converting it into hydrogen gas, and supplying it to a hydrogen engine; and a recirculation circuit branching off from the supply circuit and connected to the hydrogen tank, which recirculates the hydrogen gas back into the hydrogen tank so that the internal pressure of the hydrogen tank is equal to or greater than a specified reference pressure.

[0008] By incorporating a recirculation circuit that circulates hydrogen gas, it is possible to prevent the internal pressure of the hydrogen tank from dropping excessively. This, in turn, prevents malfunctions in the discharge of liquid hydrogen by the pump, and as a result, ensures that hydrogen is properly supplied to the hydrogen engine.

[0009] In this case, the recirculation circuit further includes a pressure sensor that detects the internal pressure of the hydrogen tank as the tank pressure, and a controller, wherein the recirculation circuit includes an electrically openable and closable recirculation gate valve, and the controller may open the recirculation gate valve when the tank pressure is less than the reference pressure.

[0010] This configuration ensures that the internal pressure of the hydrogen tank is reliably maintained above the standard pressure.

[0011] Furthermore, the recirculation circuit may also include a recirculation pressure reducing valve provided on the hydrogen tank side of the recirculation gate valve, which reduces the pressure of the hydrogen gas and outputs it.

[0012] This configuration prevents the internal pressure of the hydrogen tank from becoming excessively high.

[0013] Furthermore, the supply circuit may have a chamber for temporarily storing the hydrogen gas, which is fluidly connected upstream of the branching point of the recirculation circuit.

[0014] With this configuration, any slight excess or deficiency of hydrogen gas can be adjusted by the hydrogen gas stored in the chamber. As a result, pressure fluctuations of the hydrogen gas can be suppressed, and the response delay of the hydrogen supply control can be absorbed by the chamber. Furthermore, with this configuration, problems do not arise even if the hydrogen supply amount is calculated while ignoring the hydrogen gas return rate, thus simplifying the hydrogen supply control.

[0015] Furthermore, the system may also include a booster pump for pressurizing and discharging the liquid hydrogen in order to extract it from the hydrogen tank.

[0016] By using a booster pump, the pressure resistance required for the hydrogen tank can be kept low. However, when using a booster pump, the possibility of the pump becoming unable to discharge increases as the internal pressure of the tank decreases. However, the liquid hydrogen system disclosed in this specification is equipped with a recirculation circuit, so even when a booster pump is used, pump discharge failure can be prevented. [Effects of the Invention]

[0017] The liquid hydrogen system disclosed herein can adequately supply hydrogen to a hydrogen engine. [Brief explanation of the drawing]

[0018] [Figure 1] This is a diagram showing the configuration of a liquid hydrogen system. [Figure 2] Block diagram showing how to control motor rotation speed using a controller. [Figure 3] This is a graph showing the operation of a recirculation gate valve. [Figure 4] This flowchart shows the flow of opening and closing control for a recirculation gate valve. [Figure 5] This flowchart shows another example of the flow for controlling the opening and closing of a recirculation gate valve. [Figure 6] This diagram shows other components of the liquid hydrogen system. [Figure 7] Block diagram showing another example of controlling motor speed using a controller.

Mode for Carrying Out the Invention

[0019] Hereinafter, the configuration of the liquid hydrogen system 10 will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of the liquid hydrogen system 10. This liquid hydrogen system 10 stores hydrogen in a liquid state and converts the hydrogen into a gaseous state to supply it to the hydrogen engine 100. The liquid hydrogen system 10 and the hydrogen engine 100 are mounted on a vehicle. The configuration of the hydrogen engine 100 is not particularly limited. Hereinafter, the hydrogen engine 100 is a direct injection type hydrogen engine that directly injects hydrogen gas into the engine cylinder.

[0020] The liquid hydrogen system 10 has a hydrogen tank 12 for storing liquid hydrogen. The hydrogen tank 12 stores liquid hydrogen in a heat-insulated manner. As such a hydrogen tank 12, for example, a double-structured container can be used. In this case, the hydrogen tank 12 has an inner tank 14 and an outer tank 16 that covers the inner tank 14, and a vacuum insulation layer is formed between the inner tank 14 and the outer tank 16.

[0021] The hydrogen tank 12 is spherical or barrel-shaped in order to keep the pressure applied to the inner wall uniform. In addition, a collector portion 18 recessed from the periphery is provided on the bottom surface of the hydrogen tank 12. The hydrogen pump 26 described later is disposed in this collector portion 18. With such a configuration, even when the remaining amount of liquid hydrogen decreases, the hydrogen pump 26 can be positioned in the liquid, and the liquid hydrogen can be discharged until the end.

[0022] In the hydrogen tank 12, the liquid hydrogen is kept at a low temperature. Also, in the hydrogen tank 12, the pressure of the liquid hydrogen is substantially the same as the atmospheric pressure or slightly higher than the atmospheric pressure, for example, 1 Mpa or less. Here, the inner tank 14 is vacuum-insulated. However, it is not possible to completely prevent heat input, and as time passes, the stored liquid hydrogen naturally vaporizes. The hydrogen gas (i.e., boil-off gas) generated by natural vaporization stays in the upper part of the hydrogen tank 12.

[0023] Liquid hydrogen is supplied to the hydrogen tank 12 from the outside via a refueling circuit 19. The refueling circuit 19 has a refueling channel 20 through which liquid hydrogen flows, and a discharge channel 22 that guides hydrogen gas to the outside. Both the refueling channel 20 and the discharge channel 22 extend from the connector 24 into the interior of the hydrogen tank 12. The refueling circuit 19 is connected via the connector 24 to a refueling hose (not shown) provided at an external hydrogen station. Liquid hydrogen stored at the external hydrogen station is supplied to the hydrogen tank 12 through the refueling channel 20. In addition, boil-off gas generated during the liquid hydrogen refueling process is released to the outside through the discharge channel 22.

[0024] The hydrogen tank 12 is equipped with a hydrogen pump 26 that discharges the stored liquid hydrogen and sends it to the hydrogen engine 100. In this example, the hydrogen pump 26 is a booster pump that discharges liquid hydrogen while pressurizing it. For example, the hydrogen pump 26 may also be a piston pump that draws in and discharges liquid by reciprocating a plunger in a cylinder placed in the liquid. In this case, check valves are provided at both the intake and discharge ports of the cylinder. This hydrogen pump 26 is driven by a pump motor 28. By providing a hydrogen pump 26 with such a booster function, the pressure resistance required for the hydrogen tank 12 can be reduced.

[0025] In other words, as described above, in this example, the hydrogen engine 100 is a direct-injection type that directly injects hydrogen gas into the engine cylinder. The hydrogen gas that is directly injected is required to be at a very high pressure compared to atmospheric pressure (for example, 5 MPa to several tens of MPa). In order to obtain such high-pressure hydrogen gas, it is required that it be at a sufficiently high pressure before vaporization, i.e., in its liquid state. Therefore, it is conceivable to store high-pressure (for example, several tens of MPa) liquid hydrogen in the hydrogen tank 12. However, in this case, the pressure resistance performance of the hydrogen tank 12 must be increased, which would lead to an increase in the cost and weight of the hydrogen tank 12.

[0026] On the other hand, in this example, the pressure of the liquid hydrogen in the hydrogen tank 12 is set to approximately the same as atmospheric pressure or slightly higher, and when vaporizing the liquid hydrogen, only the necessary amount is sufficiently pressurized by the hydrogen pump 26 before being extracted. With this configuration, it is possible to obtain sufficiently high-pressure hydrogen gas while keeping the pressure resistance performance of the hydrogen tank 12 low. Furthermore, by lowering the required pressure resistance performance, the cost of the hydrogen tank 12 can be reduced. In addition, by lowering the required pressure resistance performance, it becomes possible to adopt shapes other than spherical and cylindrical for the hydrogen tank 12, increasing the degree of freedom in the shape of the hydrogen tank 12.

[0027] Liquid hydrogen discharged from the hydrogen pump 26 is supplied to the hydrogen engine 100 through the supply circuit 30. The supply circuit 30 includes a liquid flow path 32, a gas flow path 33, a vaporizer 34, a pressure chamber 40, and a supply pressure reducing valve 50. The liquid flow path 32 is a flow path that guides the liquid hydrogen discharged from the hydrogen pump 26 to the vaporizer 34. The vaporizer 34 is a heat exchanger that converts liquid hydrogen into hydrogen gas by exchanging heat between liquid hydrogen and a refrigerant. The hydrogen gas produced in the vaporizer 34 is output to the gas flow path 33.

[0028] A refrigerant flow path 36 is provided inside the vaporizer 34. The refrigerant flow path 36 circulates the refrigerant between the vaporizer 34 and the heat source 110. The refrigerant is not particularly limited and may be a gas such as helium or a liquid such as water. The heat source 110 is also not particularly limited. Therefore, the heat source 110 may be, for example, a hydrogen engine 100 or a heater that generates heat using electricity. The refrigerant heated by the heat source 110 heats the liquid hydrogen in the vaporizer 34. As a result, the liquid hydrogen vaporizes and hydrogen gas is generated. When hydrogen vaporizes, its volume increases significantly. The refrigerant is pumped by a refrigerant pump 38.

[0029] The gas flow path 33 is a channel that guides hydrogen gas from the vaporizer 34 to the injector 52. A pressure chamber 40 is connected to the gas flow path 33 via an inlet flow path 42 and an outlet flow path 44. The pressure chamber 40 is a container for temporarily storing hydrogen gas. The capacity of the pressure chamber 40 is sufficient to cover the response delay of the hydrogen gas supply control. For example, the capacity of the pressure chamber 40 is sufficient to cover the maximum hydrogen consumption flow rate of the hydrogen engine 100 for several seconds to 60 seconds. By providing such a pressure chamber 40, a shortage of hydrogen gas can be prevented even if the consumption of the hydrogen engine 100 changes suddenly.

[0030] The inflow channel 42 is equipped with a check valve 46 that prevents flow from the pressure chamber 40 toward the gas channel 33. The outflow channel 44 is equipped with a chamber gate valve 48. The chamber gate valve 48 is, in principle, open while the hydrogen engine 100 is running. The inflow channel 42 is located upstream of the outflow channel 44. Therefore, if the pressure in the gas channel 33 is higher than the internal pressure of the pressure chamber 40, the check valve 46 opens and hydrogen gas flows into the pressure chamber 40. On the other hand, if the internal pressure of the pressure chamber 40 is higher than the pressure in the gas channel 33, the hydrogen gas stored in the pressure chamber 40 is supplied to the gas channel 33 through the outflow channel 44. As a result, the pressure of the hydrogen gas supplied to the supply pressure reducing valve 50 becomes approximately the same as the internal pressure of the pressure chamber 40.

[0031] The pressure sensor 41 detects the internal pressure of the pressure chamber 40. Hereinafter, the value detected by the pressure sensor 41 will be referred to as "hydrogen gas pressure Pgh". As will be explained in detail later, the controller 80 controls the rotational speed of the pump motor 28 so that the hydrogen gas pressure Pgh becomes a predetermined target hydrogen gas pressure Pgh*.

[0032] A supply pressure reducing valve 50 is provided downstream of the outflow channel 44. The supply pressure reducing valve 50 reduces the hydrogen gas pressure to a level suitable for the hydrogen engine 100. The reduced-pressure hydrogen gas is supplied to the hydrogen engine 100 via an injector 52. The flow rate of hydrogen gas supplied to the hydrogen engine 100 is detected by a flow meter 54. Hereinafter, the flow rate of hydrogen gas detected by the flow meter 54 will be referred to as "hydrogen gas flow rate Qgh".

[0033] The recirculation circuit 60 is a circuit that branches off from the supply circuit 30 and recirculates hydrogen gas to the hydrogen tank 12. The recirculation circuit 60 includes a recirculation channel 62, a recirculation gate valve 64, a recirculation pressure reducing valve 66, and a check valve 68. The recirculation channel 62 is a channel that branches off from the gas channel 33 at a position downstream of the outlet channel 44 and upstream of the supply pressure reducing valve 50. After branching off from the gas channel 33, the recirculation channel 62 heads towards the hydrogen tank 12 and communicates with the inside of the hydrogen tank 12.

[0034] The recirculation gate valve 64 is a valve that opens and closes the recirculation passage 62 and is controlled by the controller 80. When the recirculation gate valve 64 is opened, a portion of the hydrogen gas flowing in the supply circuit 30 is returned to the hydrogen tank 12. The recirculation pressure reducing valve 66 is located downstream of the recirculation gate valve 64 (i.e., away from the branching point). The recirculation pressure reducing valve 66 reduces the pressure of the hydrogen gas to a level that is safe to return to the hydrogen tank 12. The check valve 68 is located downstream of the recirculation pressure reducing valve 66. The check valve 68 allows flow only in the direction from the recirculation pressure reducing valve 66 towards the hydrogen tank 12, preventing backflow of hydrogen gas. The reason for providing such a recirculation circuit 60 will be explained later.

[0035] A boil-off passage 72 is further connected to the hydrogen tank 12. The boil-off passage 72 is a passage that is opened when the internal pressure of the hydrogen tank 12 exceeds a specified safety value Psf. When the boil-off passage 72 is opened, some of the hydrogen gas accumulated inside the hydrogen tank 12 is released to the outside. This prevents the internal pressure of the hydrogen tank 12 from becoming excessively high. In other words, as mentioned above, although the inner tank 14 is vacuum-insulated, it is not possible to completely prevent heat input. As a result, some of the stored liquid hydrogen naturally vaporizes, generating hydrogen gas (so-called boil-off gas). If this hydrogen gas is left unchecked, the internal pressure of the hydrogen tank 12 will become excessively high. Therefore, when the internal pressure of the hydrogen tank 12 exceeds a specified safety value Psf, the boil-off passage 72 is opened, and some of the hydrogen gas is released to the outside of the tank.

[0036] Note that Figure 1 shows only one boil-off passage 72. However, multiple boil-off passages 72 may be provided. For example, a first boil-off passage that opens at a first safety value and a second boil-off passage that opens at a second safety value higher than the first safety value may be provided. Furthermore, the boil-off passage 72 may be one that opens and closes repeatedly, or it may be one that cannot be closed once opened. Therefore, the boil-off passage 72 may be equipped with an openable and closable valve, or it may be equipped with a rupture disc that mechanically breaks when the pressure exceeds the safety value Psf to maintain the open state.

[0037] The internal pressure and temperature of the hydrogen tank 12 are detected by the pressure sensor 78 and the temperature sensor 76. Hereinafter, the internal pressure of the hydrogen tank 12 detected by the pressure sensor 78 will be referred to as "tank internal pressure Pt".

[0038] The controller 80 controls the operation of the liquid hydrogen system 10. Physically, the controller 80 is a computer having a processor 82 and memory 84. This "computer" also includes a microcontroller that incorporates a computer system into a single integrated circuit. Furthermore, the controller 80 is not limited to a single computer, but may be configured by combining multiple mechanically separated computers. Based on values ​​detected by various sensors, the controller 80 controls the operation of multiple valves and pumps provided in the liquid hydrogen system 10.

[0039] Specifically, the controller 80 controls the hydrogen gas supply flow rate to the hydrogen engine 100 in response to a request from the engine control unit (not shown). The hydrogen gas supply flow rate is proportional to the liquid hydrogen discharge flow rate Qlh, and the discharge flow rate Qlh is proportional to the rotational speed Nm of the pump motor 28. Therefore, the controller 80 uses the hydrogen gas flow rate Qgh detected by the flow meter 54 as a feedback value to feedback control the motor rotational speed Nm. In addition, in order to properly drive the hydrogen engine 100, the hydrogen gas pressure must also be at an appropriate value. Therefore, the controller 80 also feeds back the hydrogen gas pressure Pgh detected by the pressure sensor 41 to control the motor rotational speed Nm.

[0040] Figure 2 is a block diagram showing the control of the motor rotation speed Nm by the controller 80. The controller 80 functions as a control block as shown in Figure 2. In Figure 2, the flow rate controller 86 is a calculator that performs a predetermined control calculation on the input value. The control calculation is not particularly limited, but may include at least one of the following: a proportional calculation that multiplies the input value by a proportional gain, an integral calculation that multiplies the integral value of the input value by an integral gain, and a differential calculation that multiplies the differential value of the input value by a differential gain. Similarly, the pressure controller 88 also performs a predetermined control calculation on the input value.

[0041] As shown in Figure 2, in this example, the flow rate deviation is calculated by subtracting the hydrogen gas flow rate Qgh detected by the flow meter 54 from the target hydrogen gas flow rate Qgh*. The flow controller 86 takes the flow rate deviation as input and outputs the first command value C1. Here, the target hydrogen gas flow rate Qgh* is determined, for example, based on the accelerator opening of the vehicle.

[0042] Furthermore, the pressure deviation is calculated by subtracting the hydrogen gas pressure Pgh detected by the pressure sensor 41 from the target hydrogen gas pressure Pgh*. The pressure controller 88 takes the pressure deviation as input and outputs a second command value C2. Here, the target hydrogen gas pressure Pgh* is a value determined according to the characteristics of the hydrogen engine 100 and is, in principle, a fixed position that does not change. The controller 80 controls the drive of the pump motor 28 by using the sum of the first command value C1 and the second command value C2 as the motor rotation speed command Nm*.

[0043] As is clear from the above explanation, the controller 80 drives the pump motor 28 in response to a request from the hydrogen engine 100 to discharge liquid hydrogen from the hydrogen tank 12. When the hydrogen consumption by the hydrogen engine 100 increases and the liquid hydrogen discharge flow rate Qlh increases, the internal pressure of the hydrogen tank 12 may decrease.

[0044] In other words, a small amount of boil-off gas (i.e., hydrogen gas) is constantly being generated inside the hydrogen tank 12. When the liquid hydrogen discharge flow rate Qlh becomes greater than the amount of boil-off gas generated (hereinafter referred to as "boil-off amount Qbf"), the tank internal pressure Pt gradually decreases.

[0045] If the tank pressure Pt becomes excessively low, the hydrogen pump 26 cannot properly discharge liquid hydrogen. In particular, if the hydrogen pump 26 is a booster pump that pressurizes liquid hydrogen, it is necessary to pressurize the liquid hydrogen to a high discharge pressure in order to discharge it. However, if the tank pressure Pt decreases, and consequently the pressure of the liquid hydrogen decreases, the liquid hydrogen cannot be pressurized to a high discharge pressure, and the liquid hydrogen cannot be properly discharged. Therefore, in this example, the recirculation circuit 60 is opened as needed to recirculate a portion of the hydrogen gas flowing in the supply circuit 30 back to the hydrogen tank 12, so that the tank pressure Pt is maintained above the specified reference pressure.

[0046] More specifically, in this example, when the internal tank pressure Pt detected by the pressure sensor 78 falls below the specified reference pressure Pst, the reflux gate valve 64 is opened, and hydrogen gas is directed to the hydrogen tank 12. Note that the hydrogen gas passing through the reflux gate valve 64 is at a higher pressure than the internal pressure of the hydrogen tank 12. Therefore, in this example, a reflux pressure reducing valve 66 is provided downstream of the reflux gate valve 64 to reduce the pressure of the hydrogen gas to a level suitable for inflow into the hydrogen tank 12. For example, the reflux pressure reducing valve 66 reduces the pressure of the hydrogen gas to a level higher than the reference pressure Pst and lower than the safety value Psf. By refluxing a portion of the hydrogen gas flowing through the supply circuit 30 to the hydrogen tank 12, it is possible to prevent the internal pressure of the hydrogen tank 12 from dropping excessively, and the discharge of liquid hydrogen by the hydrogen pump 26 can be properly continued.

[0047] Naturally, the reference pressure Pst is sufficiently lower than the safety value Psf for opening the boil-off passage 72. Furthermore, the reference pressure Pst may not be a single value but may have a certain degree of hysteresis. Figure 3 is a graph showing the operation of the reflux gate valve 64. In Figure 3, the horizontal axis represents the tank internal pressure Pt, and the vertical axis represents the state of the reflux gate valve 64. Figure 4 is a flowchart showing the flow of opening and closing control of the reflux gate valve 64.

[0048] In the examples in Figures 3 and 4, two reference pressures, a lower reference pressure Pst_lw and an upper reference pressure Pst_up which is higher than the lower reference pressure Pst_lw, are set as reference pressures Pst. The controller 80 constantly monitors the tank internal pressure Pt. If the tank internal pressure Pt crosses the lower reference pressure Pst_lw during the process of decreasing (Yes in S10), the controller 80 opens the recirculation gate valve 64 (S12).

[0049] After opening the reflux gate valve 64, the controller 80 monitors whether the tank internal pressure Pt crosses the upper reference pressure Pst_up during the process of increasing (S14). If the tank internal pressure Pt does not exceed the upper reference pressure Pst_up (No in S14), the controller 80 keeps the reflux gate valve 64 open. With the reflux gate valve 64 open, hydrogen gas flows into the hydrogen tank 12, and the tank internal pressure Pt gradually rises. Then, if the tank internal pressure Pt exceeds the upper reference pressure Pst_up (Yes in S14), the controller 80 closes the reflux gate valve 64 (S16). After that, the process returns to step S10 and the same process is repeated.

[0050] Note that the control described here is just one example. The opening and closing control of the recirculation channel 62 may be modified as appropriate, as long as the tank pressure Pt is kept above the reference pressure Pst. For example, in the above description, the recirculation gate valve 64 is controlled by feeding back the tank pressure Pt detected by the pressure sensor 78. However, the recirculation gate valve 64 may also be controlled based on parameters other than the tank pressure Pt. For example, the recirculation gate valve 64 may be controlled based on the liquid hydrogen discharge flow rate Qlh.

[0051] Figure 5 is a flowchart showing the flow of opening and closing control of the reflux gate valve 64 based on the discharge flow rate Qlh. In this case, the controller 80 calculates the discharge flow rate Qlh of liquid hydrogen based on the motor rotation speed command Nm* output to the pump motor 28 (S20). Typically, the discharge flow rate Qlh is a proportional value to the motor rotation speed command Nm*.

[0052] Next, the controller 80 subtracts the boil-off amount Qbf from the discharge flow rate Qlh to calculate the hydrogen increase / decrease amount ΔQ (S22). The boil-off amount Qbf may be a preset fixed value or a variable value that changes according to the temperature detected by the temperature sensor 76.

[0053] Next, the controller 80 inputs the hydrogen increase / decrease amount ΔQ and zero into the MAX function to calculate the hydrogen decrease amount Qd = MAX(ΔQ, 0) (S24). The MAX function is a function that outputs the largest value among the multiple variables that have been input. In step S24, if the hydrogen increase / decrease amount ΔQ is greater than 0, Qd = ΔQ, and if the hydrogen increase / decrease amount ΔQ is 0 or less, Qd = 0. If the hydrogen decrease amount Qd is greater than 0, the tank pressure Pt will gradually decrease. Therefore, the controller 80 opens the reflux gate valve 64 for (Qd × Kt) seconds (S26). Here, the coefficient Kt is a predetermined fixed value. After (Qd × Kt) seconds have elapsed, the controller 80 closes the reflux gate valve 64 and returns to step S20. Furthermore, if Qd=0, the recirculation gate valve 64 will naturally remain closed, and hydrogen gas will not be recirculated.

[0054] In this way, by varying the opening time of the reflux gate valve 64 based on the discharge flow rate Qlh, hydrogen gas can be refluxed before the tank pressure Pt decreases, and the operation of the hydrogen pump 26 can be kept more appropriate.

[0055] Furthermore, in another configuration, the return flow path 62 may be opened and closed as needed by utilizing the opening pressure of the check valve 68. For example, as shown in Figure 6, the return gate valve 64 and the return pressure reducing valve 66 may be omitted in the return flow path 62, and only the check valve 68 may be provided. In this case, the opening pressure Pvo of the check valve 46 is set to be equivalent to the differential pressure between the target hydrogen gas pressure Pgh* and the reference pressure Pst. That is, Pvo = Pgh* - Pst.

[0056] Here, the pressure on the primary side of the check valve 68 is approximately the same as the hydrogen gas pressure Pgh detected by the pressure sensor 41. The controller 80 also performs feedback control to ensure that the hydrogen gas pressure Pgh matches the target hydrogen gas pressure Pgh*. Therefore, the pressure on the primary side of the check valve 68 is approximately the same as the target hydrogen gas pressure Pgh*. When the internal pressure of the hydrogen tank 12 decreases to below the reference pressure Pst, a pressure greater than or equal to the opening pressure Pvo acts on the check valve 68, causing the check valve 68 to open. As a result, hydrogen gas is returned to the hydrogen tank 12, and the tank internal pressure Pt increases. When the tank internal pressure Pt increases and the differential pressure between the primary and secondary sides of the check valve 68 falls below the opening pressure Pvo, the check valve 68 automatically closes, and the return of hydrogen gas stops. In this way, by using the check valve 68 to open and close the return passage 62 as needed, the control by the controller 80 can be simplified.

[0057] By the way, if a portion of the hydrogen gas is recirculated to the hydrogen tank 12, an additional amount of hydrogen gas will be required. For example, if hydrogen gas at a recirculation rate Qr is recirculated to the hydrogen tank 12, the entire liquid hydrogen system will require an amount of hydrogen gas equal to the target hydrogen gas flow rate Qgh* supplied to the hydrogen engine 100 plus the recirculation rate Qr. Therefore, ideally, in Figure 2, this added value Qgh* + Qr should be set as the target flow rate. However, considering the recirculation rate Qr complicates the control and increases the amount of computation required.

[0058] Here, the return flow rate Qr is significantly smaller than the hydrogen gas flow rate Qgh supplied to the hydrogen engine 100. In this example, a pressure chamber 40 is provided in the middle of the supply circuit 30 to temporarily store hydrogen gas. Any slight excess or shortage of hydrogen gas can be absorbed by the hydrogen gas temporarily stored in this pressure chamber 40. Therefore, in this example with a pressure chamber 40, the motor rotation speed command Nm* is calculated while ignoring the return flow rate Qr. Because this example has a pressure chamber 40, even if the return flow rate Qr is ignored, a shortage of hydrogen gas can be prevented. Also, by ignoring the return flow rate Qr in the calculation of the motor rotation speed command Nm*, the amount of computation required for control can be reduced.

[0059] However, naturally, the return flow rate Qr can be incorporated into the motor speed control. That is, the parameter Qgh* in Figure 2 can be replaced with Qgh* + Qr. In this case, the return flow rate Qr is calculated, for example, by the formula Qr = MAX(ΔQ, 0).

[0060] Alternatively, as shown in Figure 7, the tank pressure Pt may be fed back to calculate the motor speed command Nm*. Specifically, the controller 80 calculates the tank pressure deviation ΔPt by subtracting the tank pressure Pt from the reference pressure Pst. The controller 80 then inputs this tank pressure deviation ΔPt and a value of 0 into the function MAX(), and calculates a third command value C3 by multiplying the output value by a predetermined gain Kn. The controller 80 then outputs the motor speed command Nm* as the sum of the three command values ​​C1, C2, and C3.

[0061] In this way, by adding the hydrogen gas return flow rate Qr to the target flow rate, or by feeding back the tank internal pressure Pt, a more appropriate amount of liquid hydrogen can be discharged, and pressure fluctuations of the hydrogen gas in the gas flow path 33 can be suppressed.

[0062] Furthermore, the configurations described so far are all examples. As long as the liquid hydrogen system 10 has a recirculation circuit 60 that recirculates a portion of the hydrogen gas flowing through the supply circuit 30 back to the hydrogen tank 12, other configurations may be changed. For example, in Figure 1, a check valve 68 is provided in the recirculation circuit 60, but if a recirculation gate valve 64 is provided, the check valve 68 is not necessary. Also, in the explanations so far, a pressure chamber 40 and a supply pressure reducing valve 50 are provided in the recirculation circuit 60, but these are not necessary. In addition, in this example, the hydrogen pump 26 is a booster pump that pressurizes and discharges liquid hydrogen, but the hydrogen pump 26 may be one that cannot pressurize liquid hydrogen. Furthermore, the hydrogen engine 100 is not limited to a direct injection engine, but may be of other forms, such as a port injection engine. [Explanation of symbols]

[0063] 10 Liquid hydrogen system, 12 Hydrogen tank, 14 Inner tank, 16 Outer tank, 18 Collector unit, 19 Filling circuit, 20 Filling channel, 22 Discharge channel, 24 Connector, 26 Hydrogen pump (boost pump), 28 Pump motor, 30 Supply circuit, 32 Liquid channel, 33 Gas channel, 34 Vaporizer, 36 Refrigerant channel, 38 Refrigerant pump, 40 Pressure chamber, 41 Pressure sensor, 42 Inflow channel, 44 Outflow channel, 46 Check valve, 48 Chamber gate valve, 50 Supply pressure reducing valve, 52 Injector, 54 Flow meter, 60 Refrigeration circuit, 62 Refrigeration channel, 64 Refrigeration gate valve, 66 Refrigeration pressure reducing valve, 68 Check valve, 72 Boil-off channel, 76 Temperature sensor, 78 Pressure sensor, 80 Controller, 82 Processor, 84 Memory, 86 Flow controllers, 88 pressure controllers, 100 hydrogen engines, 110 heat sources.

Claims

1. A hydrogen tank mounted on the vehicle that stores liquid hydrogen, A supply circuit that, after extracting the liquid hydrogen from the hydrogen tank, converts it into hydrogen gas and supplies it to the hydrogen engine, A recirculation circuit that branches off from the supply circuit and is connected to the hydrogen tank, the recirculation circuit that recirculates the hydrogen gas to the hydrogen tank so that the internal pressure of the hydrogen tank is equal to or greater than a specified reference pressure, Equipped with, The aforementioned return circuit is An electrically operated return gate valve, A reflux pressure reducing valve is provided on the hydrogen tank side of the aforementioned reflux gate valve and reduces the pressure of the hydrogen gas before outputting it, A liquid hydrogen system characterized by including

2. A liquid hydrogen system according to claim 1, further, A pressure sensor that detects the internal pressure of the hydrogen tank as the tank internal pressure, Controller and Equipped with, The controller opens the return gate valve when the internal pressure of the tank is less than the reference pressure. A liquid hydrogen system characterized by the following features.

3. A liquid hydrogen system according to claim 1, The liquid hydrogen system is characterized in that the supply circuit is fluidly connected upstream of the branching point of the recirculation circuit and has a chamber for temporarily storing the hydrogen gas.

4. A liquid hydrogen system according to claim 1, further, A liquid hydrogen system characterized by comprising a booster pump for pressurizing and discharging the liquid hydrogen in order to extract the liquid hydrogen from the hydrogen tank.

5. A liquid hydrogen system according to claim 2, The controller controls the amount of hydrogen gas supplied to the hydrogen engine based on the difference between the detected flow rate and the target flow rate, and the difference between the detected pressure and the target pressure. The target flow rate of the hydrogen gas is a value that ignores the return flow rate to the hydrogen tank. A liquid hydrogen system characterized by the following features.

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