Failure detection device

Abstract

This failure detection device (20) for detecting a failure of a pressure-reducing valve in a fuel cell system (10) having: a pressure-reducing valve (38) disposed in a fuel supply path (36) through which hydrogen fuel is supplied to a fuel cell stack (30); a communication path (44) for communicating the fuel supply path in an upstream section (36u) of the pressure-reducing valve; a pressure sensor (46) for measuring the pressure in the communication path; and a concentration sensor (48) for measuring the concentration of hydrogen fuel leaking from a downstream section (36d) of the pressure-reducing valve to the outside of the fuel supply path, the failure detection device (20) comprising a failure detection unit (94) for detecting a failure of the pressure-reducing valve on the basis of a pressure measurement value and a concentration measurement value.

Description

Fault detection device

[0001] The present disclosure relates to a fault detection device.

[0002] In recent years, in order to ensure access to more people to affordable, reliable, sustainable and advanced energy, research and development on fuel cells that contribute to energy efficiency has been carried out. In the fuel cell system disclosed in Japanese Patent Application Laid-Open No. 2019-71183, the number of malfunctioning pressure reducing valves can be determined.

[0003] There is a long-felt need for a fault detection device that can detect a fault in a pressure reducing valve in a fuel cell system well.

[0004] The present disclosure aims to solve the above-described problems, and ultimately contributes to energy efficiency.

[0005] An aspect of the present disclosure is a fault detection device for detecting a fault in a pressure reducing valve in a fuel cell system having a plurality of fuel cell stacks, a plurality of fuel supply paths through which hydrogen fuel is respectively supplied to the plurality of fuel cell stacks, a plurality of pressure reducing valves respectively arranged in the plurality of fuel supply paths, a communication path for communicating the plurality of fuel supply paths in an upstream section of the pressure reducing valve, a pressure sensor for measuring a pressure in the communication path, and a concentration sensor for measuring a concentration of hydrogen fuel leaking from an external portion of the plurality of fuel supply paths from a downstream section of the pressure reducing valve, the fault detection device including a measurement value acquisition unit that acquires a pressure measurement value of the pressure sensor and a concentration measurement value of the concentration sensor, and a fault detection unit that detects the fault of the pressure reducing valve based on the pressure measurement value and the concentration measurement value acquired by the measurement value acquisition unit.

[0006] According to the present disclosure, a fault detection device that can detect a fault in a pressure reducing valve in a fuel cell system well can be provided.

[0007] Figure 1 is a schematic diagram illustrating an example of a fuel cell system and fault detection device. Figures 2A, 2B, 2C, and 2D are diagrams illustrating the failure levels of a pressure reducing valve. Figure 3 is a diagram illustrating an example in which the pressure in the communication passage decreases over time due to a failure of the pressure reducing valve. Figures 4A, 4B, and 4C are diagrams illustrating maps showing the correspondence between the failure level of the pressure reducing valve and the measured pressure and concentration values. Figure 5 is a flowchart illustrating the processing procedure for detecting a failure of a pressure reducing valve. Figure 6 is a schematic diagram illustrating an example of a fuel cell system and fault detection device. Figure 7 is a diagram illustrating an example in which the pressure in the communication passage decreases over time due to a failure of the pressure reducing valve. Figures 8A, 8B, and 8C are diagrams illustrating maps showing the correspondence between the failure level of the pressure reducing valve and the estimated pressure and concentration values. Figure 9 is a flowchart illustrating the processing procedure for detecting a failure of a pressure reducing valve. Figures 10A and 10B illustrate maps showing the correspondence between the number of pressure reducing valves in which a malfunction was detected and the estimated pressure and measured concentration values.

[0008] A fuel cell system in a large vehicle may be equipped with multiple fuel cell stacks. Figure 1 is a schematic diagram showing an example of a fuel cell system 10 and a fault detection device 20. The fuel cell system 10 has multiple fuel cell stacks 30, multiple fuel tanks 32, multiple main shut-off valves 34, and multiple fuel supply lines 36. The fuel cell system 10 further has multiple pressure reducing valves 38, multiple injectors 40, multiple relief valves 42, communication lines 44, a pressure sensor 46, and a concentration sensor 48.

[0009] The fuel cell system 10 is housed in the housing 60. However, it is preferable that the multiple fuel cell stacks 30 are arranged outside the housing 60. The housing 60 may be provided, for example, on the cargo bed of the large vehicle described above.

[0010] The fuel cell stack 30 generates electricity through an oxidation-reduction reaction between hydrogen fuel and air. Figure 1 illustrates two fuel cell stacks 30. Multiple fuel tanks 32 store hydrogen fuel. Multiple main shut-off valves 34 are provided at each outlet from which hydrogen fuel flows out of the multiple fuel tanks 32. Each of the multiple fuel tanks 32 is connected to multiple fuel supply lines 36 via multiple main shut-off valves 34. Figure 1 illustrates two fuel tanks 32, two main shut-off valves 34, and two fuel supply lines 36 corresponding to two fuel cell stacks 30.

[0011] When each main shut-off valve 34 is opened, hydrogen fuel flows out of each fuel tank 32 into the fuel supply passage 36. When each main shut-off valve 34 is closed, the outflow of hydrogen fuel from each fuel tank 32 stops. The hydrogen fuel that flows out of the multiple fuel tanks 32 and into the multiple fuel supply passages 36 is supplied to each of the multiple fuel cell stacks 30.

[0012] Multiple pressure reducing valves 38 are arranged in each of the multiple fuel supply lines 36. Figure 1 illustrates two pressure reducing valves 38, each corresponding to two fuel supply lines 36. In the fuel supply line 36 through which hydrogen fuel flows from the fuel tank 32 to the fuel cell stack 30, the section upstream of the pressure reducing valve 38 is under high pressure. This upstream section is the section from the fuel tank 32 to the pressure reducing valve 38.

[0013] The pressure reducing valve 38 reduces the pressure of the hydrogen fuel that has flowed through the upstream section and entered the pressure reducing valve 38 from high pressure to medium pressure. Therefore, the section of the fuel supply line 36 downstream of the pressure reducing valve 38 is at medium pressure. This downstream section is the section from the pressure reducing valve 38 to the fuel cell stack 30.

[0014] Multiple injectors 40 are arranged in each of the multiple fuel supply lines 36. The injectors 40 are located in the section of the fuel supply line 36 downstream of the pressure reducing valve 38. That is, the injectors 40 are located between the pressure reducing valve 38 and the fuel cell stack 30. Figure 1 illustrates two injectors 40 corresponding to two pressure reducing valves 38. The injectors 40 supply or stop the supply of hydrogen fuel at a predetermined flow rate from the section downstream of the pressure reducing valve 38 to the fuel cell stack 30.

[0015] Multiple relief valves 42 are arranged in each of the multiple fuel supply passages 36. The relief valves 42 are located in the section of the fuel supply passage 36 downstream of the pressure reducing valve 38. The relief valves 42 are located between the pressure reducing valve 38 and the injector 40. It is preferable that the relief valves 42 are provided in close proximity to the pressure reducing valve 38. Figure 1 illustrates two relief valves 42, each corresponding to two pressure reducing valves 38.

[0016] The relief valve 42 communicates with the space within the housing 60. The relief valve 42 is normally closed, but opens when the pressure in the downstream section rises due to a malfunction of the pressure reducing valve 38, which will be described later. When the relief valve 42 opens, hydrogen fuel leaks from the downstream section to the outside of the fuel supply passage 36. That is, hydrogen fuel leaks into the space within the housing 60. This reduces the pressure in the downstream section.

[0017] The connecting passage 44 connects multiple fuel supply lines 36 in the upstream section of the pressure reducing valve 38. Figure 1 illustrates a connecting passage 44 that connects two fuel supply lines 36. Through the connecting passage 44, hydrogen fuel flowing out from each of the two fuel tanks 32 can circulate through either of the two fuel supply lines 36. In other words, the hydrogen fuel stored in the two fuel tanks 32 can be supplied to either of the two fuel cell stacks 30.

[0018] As described above, the upstream section of the pressure reducing valve 38 is under high pressure. Therefore, the communication passage 44 is also under high pressure. The pressure sensor 46 measures the pressure in the communication passage 44. A malfunction of the pressure reducing valve 38, which will be described later, releases the pressure in the upstream section of the pressure reducing valve 38 to the downstream section. In this case, the pressure in the upstream section of the pressure reducing valve 38 decreases, while the pressure in the downstream section increases. If this condition continues, the pressure measured by the pressure sensor 46 will decrease over time.

[0019] The concentration sensor 48 measures the concentration of hydrogen fuel leaking from the downstream section of the fuel supply passage 36 to the outside of the multiple fuel supply passages 36. As described above, when the pressure in the downstream section increases due to a malfunction of the pressure reducing valve 38, the relief valve 42 opens. As a result, the hydrogen fuel leaked to the outside is measured by the concentration sensor 48. The outside of the multiple fuel supply passages 36 is covered by the containment section 60. Therefore, the concentration sensor 48 measures the hydrogen concentration inside the containment section 60. If the inside of the containment section 60 is isolated from the atmosphere, the concentration measured by the concentration sensor 48 will increase over time if this leakage of hydrogen fuel to the outside continues.

[0020] The concentration sensor 48 may be placed at any position within the housing 60, but it is preferable to place it near the relief valve 42 or the pressure reducing valve 38. Alternatively, the concentration sensor 48 may be placed near one of the multiple relief valves 42, or near one of the multiple pressure reducing valves 38.

[0021] Furthermore, multiple concentration sensors 48 may be placed near each of the multiple relief valves 42, or near each of the multiple pressure reducing valves 38. In this case, one of the multiple concentration measurements from the multiple concentration sensors 48, or a concentration calculation value obtained based on the multiple concentration measurements, will be used for fault detection of the pressure reducing valve 38, as described later.

[0022] Figure 1 shows a block diagram illustrating the configuration of the fault detection device 20. The fault detection device 20 includes an arithmetic unit 80 and a storage unit 82. The arithmetic unit 80 is a computer and includes a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). In other words, the arithmetic unit 80 includes processing circuitry.

[0023] The storage unit 82 is a recording medium that can be read by a computer. The storage unit 82 includes volatile memory such as RAM (Random Access Memory) and non-volatile memory such as ROM (Read Only Memory) or flash memory. The volatile memory is used as the working memory of the processor. The non-volatile memory stores the computer program executed by the processor, the map M described later, and other necessary data.

[0024] Computer programs (computer software) executed by a processor can also be called computer program products. Computer program products are not limited to computer programs stored on recording media, but also include computer programs transmitted, distributed, or downloaded via the internet, etc.

[0025] The calculation unit 80 includes a fuel supply control unit 90, a measurement value acquisition unit 92, and a fault detection unit 94. The fuel supply control unit 90, the measurement value acquisition unit 92, and the fault detection unit 94 are realized when the calculation unit 80 executes a computer program stored in the storage unit 82. At least a portion of the fuel supply control unit 90, the measurement value acquisition unit 92, and the fault detection unit 94 may be realized by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array), or by an electronic circuit including discrete devices.

[0026] The fuel supply control unit 90 controls the supply and cessation of hydrogen fuel from the downstream section of the pressure reducing valve 38 in the multiple fuel supply lines 36 to the multiple fuel cell stacks 30. The fuel supply control unit 90 controls the supply of hydrogen fuel to the fuel cell stacks 30 by controlling the injectors 40. The injectors 40 supply a predetermined flow rate of hydrogen fuel to the fuel cell stacks 30. The fuel supply control unit 90 controls the cessation of the supply of hydrogen fuel to the fuel cell stacks 30 by controlling the injectors 40. The injectors 40 stop supplying hydrogen fuel to the fuel cell stacks 30.

[0027] A fuel cell stack 30 whose hydrogen fuel supply has been stopped will not generate electricity. A fuel cell stack 30 that is being supplied with hydrogen fuel will generate electricity.

[0028] The fuel supply control unit 90 can control the cessation of hydrogen fuel supply to at least some of the multiple fuel cell stacks 30. The fuel supply control unit 90 may control the cessation of hydrogen fuel supply to some of the multiple fuel cell stacks 30 and control the supply of hydrogen fuel to the remaining stacks. In this embodiment, the fuel supply control unit 90 controls the cessation of hydrogen fuel supply to all of the multiple fuel cell stacks 30. In that case, it is preferable that the fuel supply control unit 90 further closes all of the multiple main shut-off valves 34.

[0029] The measurement value acquisition unit 92 acquires the pressure measurement value from the pressure sensor 46 and the concentration measurement value from the concentration sensor 48. The measurement value acquisition unit 92 acquires the pressure measurement value and the concentration measurement value at different times. Multiple sets of pressure measurement values ​​and concentration measurement values ​​obtained by acquiring the pressure measurement value and concentration measurement value multiple times at different times are stored in the storage unit 82.

[0030] The fault detection unit 94 detects a fault in the pressure reducing valve 38 based on the pressure measurement value and concentration measurement value acquired by the measurement value acquisition unit 92 and the map M stored by the storage unit 82. As will be described later, the map M shows the correspondence between the fault level of the pressure reducing valve 38 and the pressure measurement value and concentration measurement value mentioned above. The fault level of the pressure reducing valve 38 corresponds to the amount of hydrogen fuel leaking from the section of the fuel supply passage 36 downstream of the pressure reducing valve 38 to the outside of the fuel supply passage 36.

[0031] As described above, the measurement value acquisition unit 92 may obtain multiple sets of pressure and concentration measurements. In that case, the fault detection unit 94 determines the fault level of the pressure reducing valve 38 based on the multiple sets of pressure and concentration measurements obtained. The fault detection unit 94 may also identify the quantity of the pressure reducing valve 38 that has been detected as faulty based on the multiple sets of pressure and concentration measurements obtained.

[0032] Figures 2A, 2B, 2C, and 2D are diagrams illustrating the failure levels of the pressure reducing valve 38. The pressure reducing valve 38 shown in Figure 2A is not malfunctioning. That is, the pressure reducing performance of the hydrogen fuel by the pressure reducing valve 38 is normal. When hydrogen fuel flows into the pressure reducing valve 38 from the upstream section 36u of the fuel supply passage 36, the pressure reducing valve 38 reduces the pressure of the hydrogen fuel from high pressure to medium pressure. The reduced pressure hydrogen fuel flows out into the downstream section 36d of the fuel supply passage 36. Since the pressure reducing valve 38 is normal, the relief valve 42 remains closed. Therefore, hydrogen fuel does not leak outside the fuel supply passage 36.

[0033] In the pressure reducing valve 38 shown in Figure 2B, a malfunction corresponding to a minor failure level has occurred. A malfunction in which a small amount of hydrogen fuel leaks from the pressure reducing valve 38 to the outside of the fuel supply passage 36 via the relief valve 42 corresponds to a minor failure level. A malfunction corresponding to a minor failure level can occur, for example, when a small foreign object F becomes caught in the valve body of the pressure reducing valve 38, as shown in Figure 2B.

[0034] In that case, the pressure regulating performance of the hydrogen fuel by the pressure reducing valve 38 decreases slightly. The pressure of the hydrogen fuel in the upstream section 36u decreases slightly, while the pressure of the hydrogen fuel in the downstream section 36d increases slightly. Consequently, the relief valve 42 opens, and a small amount of hydrogen fuel leaks from inside the fuel supply passage 36 to the outside. Over time, the pressure measured by the pressure sensor 46 in the connecting passage 44 of the upstream section 36u decreases. At the same time, the concentration measured by the concentration sensor 48 located in the storage section 60 beyond the downstream section 36d increases.

[0035] In the pressure reducing valve 38 shown in Figure 2C, a failure corresponding to a moderate failure level, which is more severe than a minor failure level, has occurred. A failure in which a large amount of hydrogen fuel leaks from the pressure reducing valve 38 to the outside of the fuel supply passage 36 via the relief valve 42 corresponds to a moderate failure level. A failure corresponding to a moderate failure level can occur, for example, when the valve body of the pressure reducing valve 38 is tilted with respect to the direction of movement of the valve body, as shown in Figure 2C.

[0036] In that case, the pressure regulating performance of the hydrogen fuel by the pressure reducing valve 38 is greatly reduced. The pressure of the hydrogen fuel in the upstream section 36u decreases, while the pressure of the hydrogen fuel in the downstream section 36d increases. Consequently, the relief valve 42 opens, and a relatively large amount of hydrogen fuel leaks out of the fuel supply passage 36. Over time, the pressure measured by the pressure sensor 46 in the communication passage 44 decreases. At the same time, the concentration measured by the concentration sensor 48 located in the containment section 60 increases.

[0037] In the pressure reducing valve 38 shown in Figure 2D, a failure corresponding to a severe failure level, which is more severe than a moderate failure level, has occurred. If a failure occurs in which a large amount of hydrogen fuel leaks from the pressure reducing valve 38 to the outside of the fuel supply passage 36 via the relief valve 42, then this failure corresponds to a severe failure level. Failures corresponding to a severe failure level can occur, for example, when the valve body of the pressure reducing valve 38 is damaged or bent, as shown in Figure 2D.

[0038] In that case, the pressure regulating performance of the hydrogen fuel by the pressure reducing valve 38 is almost lost. The pressure of the hydrogen fuel in the upstream section 36u drops significantly, while the pressure of the hydrogen fuel in the downstream section 36d rises significantly. Consequently, the relief valve 42 opens, and a considerable amount of hydrogen fuel leaks out of the fuel supply passage 36. Over time, the pressure measured by the pressure sensor 46 in the communication passage 44 decreases. At the same time, the concentration measured by the concentration sensor 48 located in the containment section 60 increases.

[0039] Figure 3 shows an example where the pressure PA in the communication passage 44 decreases over time due to a failure of the pressure reducing valve 38. If the time when the hydrogen fuel supply to the fuel cell stack 30 is stopped is set as zero, the pressure PA in the communication passage 44 at that time is P0. At a subsequent time T1, the pressure PA in the communication passage 44 is A1, which is lower than P0. At a time T2, which is after time T1, the pressure PA in the communication passage 44 is A2, which is lower than A1. At a time T3, which is after time T2, the pressure PA in the communication passage 44 is A3, which is lower than A2.

[0040] Figures 4A, 4B, and 4C illustrate a map M showing the correspondence between the failure levels of the pressure reducing valve 38 and the measured pressure and concentration values. The range represented in map M corresponds to each failure level based on the pressure [MPa] in the communication passage 44 indicated by the measured pressure value and the hydrogen concentration [%] in the containment section 60 indicated by the concentration measurement value. The vertical axis of map M illustrated in Figures 4A, 4B, and 4C shows the pressure PA [MPa] in the communication passage 44, ranging from P0 to P0-D3 [MPa]. The horizontal axis of map M shows the hydrogen concentration [%] in the containment section 60, ranging from 0 to C [%].

[0041] As time progresses, the failure level of the pressure reducing valve 38 can be determined more clearly using map M. Therefore, multiple maps M corresponding to changes in time are generated in advance through experiments and stored in the memory unit 82.

[0042] Figure 4A shows the map M corresponding to time T1. In the map M, a range Rv of pressure measurement values and concentration measurement values corresponding to the severe failure level illustrated in FIG. 2D is defined. Therefore, by using the map M, it is possible to determine whether or not a failure of the pressure reducing valve 38 corresponding to the severe failure level has occurred. That is, the failure detection unit 94 can detect a failure of the pressure reducing valve 38 corresponding to the severe failure level based on the pressure measurement value and the concentration measurement value acquired by the measurement value acquisition unit 92 and the map M corresponding to time T1.

[0043] Figure 4B shows the map M corresponding to time T2 after time T1. In the map M, a range Rm of pressure measurement values and concentration measurement values corresponding to the moderate failure level illustrated in FIG. 2C and the range Rv corresponding to the above-described severe failure level are defined. The pressure PA in the communication path 44 corresponding to the range Rv corresponding to the severe failure level at time T2 is lower than the pressure PA at time T1. The range Rm and the range Rv in the map M are different ranges.

[0044] Therefore, by using the map M, it is possible to determine whether or not a failure of the pressure reducing valve 38 corresponding to the severe or moderate failure level has occurred. That is, the failure detection unit 94 can detect a failure of the pressure reducing valve 38 corresponding to the severe or moderate failure level based on the pressure measurement value and the concentration measurement value acquired by the measurement value acquisition unit 92 and the map M corresponding to time T2.

[0045] Figure 4C shows the map M corresponding to time T3 after time T2. In the map M, a range Ri of pressure measurement values and concentration measurement values corresponding to the mild failure level illustrated in FIG. 2B and the ranges Rv and Rm corresponding to the above-described severe and moderate failure levels are defined.

[0046] The pressure PA in the communication passage 44 corresponding to the range Rv corresponding to the severe failure level at time T3 is further lower than the pressure PA at time T2. The pressure PA in the communication passage 44 corresponding to the range Rm corresponding to the moderate failure level at time T3 is lower than the pressure PA at time T2. The range Ri, the range Rm, and the range Rv in the map M are different ranges respectively.

[0047] Therefore, by using the map M, it is possible to determine whether a failure of the pressure reducing valve 38 corresponding to a severe, moderate, or mild failure level has occurred. That is, the failure detection unit 94 can detect a failure of the pressure reducing valve 38 corresponding to a severe, moderate, or mild failure level based on the pressure measurement value and the concentration measurement value acquired by the measurement value acquisition unit 92 and the map M corresponding to time T3.

[0048] Since the pressure measurement value and the concentration measurement value are acquired a plurality of times corresponding to times T1, T2, and T3, a plurality of sets of pressure measurement values and concentration measurement values are obtained. The failure detection unit 94 may determine the failure level of the pressure reducing valve 38 based on the plurality of sets of pressure measurement values and concentration measurement values. For example, based on the pressure measurement value and the concentration measurement value acquired at the latest time among the plurality of sets of pressure measurement values and concentration measurement values, the failure level of the pressure reducing valve 38 is determined. Thereby, the failure of the pressure reducing valve 38 can be detected in more detail.

[0049] FIG. 5 is a flowchart illustrating a processing procedure related to the failure detection of the pressure reducing valve 38. This processing procedure is performed by the arithmetic unit 80 executing a computer program stored in the storage unit 82 of the failure detection device 20. When this processing procedure is started, in step S1, the fuel supply control unit 90 performs supply stop control of hydrogen fuel to at least a part of the plurality of fuel cell stacks 30. In the present embodiment, as described above, the fuel supply control unit 90 performs supply stop control of hydrogen fuel to all of the plurality of fuel cell stacks 30. The fuel supply control unit 90 may further close all of the plurality of main stop valves 34.

[0050] In step S2, the measurement value acquisition unit 92 acquires the pressure measurement value from the pressure sensor 46 and the concentration measurement value from the concentration sensor 48. In step S3, the fault detection unit 94 reads the map M from the storage unit 82. In step S4, the fault detection unit 94 determines whether or not a fault has been detected in the pressure reducing valve 38 based on the pressure measurement value and concentration measurement value acquired in step S2 and the map M read in step S3. If the result in step S4 is YES, the process proceeds to step S5. If the result in step S4 is NO, the process ends.

[0051] In step S5, the fault detection unit 94 notifies a notification device (not shown) of the detected fault of the pressure reducing valve 38 and the fault level of the pressure reducing valve 38. This allows the operator to understand the fault of the pressure reducing valve 38 and the fault level of the pressure reducing valve 38. Once the processing in step S5 is completed, this processing procedure is terminated. According to this embodiment, a fault detection device 20 that can reliably detect a fault of the pressure reducing valve 38 in the fuel cell system 10 can be provided.

[0052] The embodiments described above may be modified as follows. In the following modifications, explanations that overlap with the embodiments described above will be omitted.

[0053] (Modification 1) In the above-described embodiment, the fuel supply control unit 90 controls the cessation of hydrogen fuel supply to all of the multiple fuel cell stacks 30. In this modification 1, the fuel supply control unit 90 controls the cessation of hydrogen fuel supply to some of the multiple fuel cell stacks 30, and controls the supply of hydrogen fuel to the remaining ones. Fuel cell stacks 30 from which the hydrogen fuel supply has been stopped do not generate electricity. Fuel cell stacks 30 from which hydrogen fuel is being supplied generate electricity.

[0054] Figure 6 is a schematic diagram illustrating an example of a fuel cell system 10 and a fault detection device 20. Figure 6 illustrates two fuel cell stacks 30. The fuel supply control unit 90 controls the supply of hydrogen fuel to fuel cell stack 30A, one of the two fuel cell stacks 30. That is, fuel cell stack 30A does not generate electricity. The fuel supply control unit 90 controls the supply of hydrogen fuel to fuel cell stack 30B, one of the two fuel cell stacks 30. That is, fuel cell stack 30B generates electricity.

[0055] A pressure reducing valve 38A corresponding to a fuel cell stack 30A that does not generate electricity is located in a fuel supply passage 36A that can supply hydrogen fuel to the fuel cell stack 30A when the fuel cell stack 30A is generating electricity. A pressure reducing valve 38B corresponding to a fuel cell stack 30B that generates electricity is located in a fuel supply passage 36B that can supply hydrogen fuel to the fuel cell stack 30B.

[0056] The fuel cell system 10 further includes a temperature sensor 110. The temperature sensor 110 measures the fuel temperature of the hydrogen fuel supplied to the fuel cell stack 30 by the fuel supply passage 36. The temperature sensor 110 is placed, for example, on the surface of each fuel tank 32. Alternatively, the temperature sensor 110 may be placed in a layer below the surface layer described above. The temperature sensor 110 may also be placed inside each fuel tank 32, or in a main shut-off valve 34 provided at the hydrogen fuel outlet from each fuel tank 32.

[0057] The calculation unit 80 of the fault detection device 20 shown in Figure 6 includes, in addition to the parts shown in Figure 1, a temperature acquisition unit 120 and a hydrogen consumption calculation unit 122. The temperature acquisition unit 120 and the hydrogen consumption calculation unit 122 are also realized by the calculation unit 80 executing a computer program stored in the storage unit 82. The temperature acquisition unit 120 and the hydrogen consumption calculation unit 122 may also be realized by an integrated circuit such as an ASIC or FPGA, or by an electronic circuit including discrete devices.

[0058] The temperature acquisition unit 120 acquires the temperature measurement value from the temperature sensor 110. The hydrogen consumption calculation unit 122 acquires the current value of the power generation current output from the power-generating fuel cell stack 30. The fuel cell stack 30 generates power through hydrogen fuel supply control by the fuel supply control unit 90. The fuel cell stack 30 uses hydrogen fuel for power generation. Based on the power generation current output from the fuel cell stack 30, the hydrogen consumption amount of the hydrogen fuel used by the fuel cell stack 30 for power generation is calculated by the hydrogen consumption calculation unit 122.

[0059] The fault detection unit 94 calculates a pressure equivalent value of the hydrogen consumption based on the temperature measurement value obtained by the temperature acquisition unit 120 and the hydrogen consumption amount calculated by the hydrogen consumption calculation unit 122. The ideal gas law is used to calculate the pressure equivalent value. The fault detection unit 94 obtains a pressure estimate value by subtracting the above-mentioned pressure equivalent value from the pressure measurement value obtained by the measurement value acquisition unit 92. The pressure drop associated with hydrogen consumption in normal power generation is different from the pressure drop due to a failure of the pressure reducing valve 38. Therefore, the pressure estimate value is obtained by subtracting the pressure equivalent value corresponding to hydrogen consumption in normal power generation from the pressure measurement value.

[0060] The fault detection unit 94 detects a fault in the pressure reducing valve 38 based on the pressure estimate obtained in this way, the concentration measurement value obtained by the measurement value acquisition unit 92, and the map M.

[0061] Figure 7 shows an example where the pressure PA in the communication passage 44 decreases over time due to a failure of the pressure reducing valve 38. If the time when the hydrogen fuel supply to the fuel cell stack 30 is stopped is set as zero, the pressure PA in the communication passage 44 at that time is P0. At the time T11 thereafter, the pressure PA in the communication passage 44 is A11, which is lower than P0. At the time T12 after time T11, the pressure PA in the communication passage 44 is A12, which is lower than A11. At the time T13 after time T12, the pressure PA in the communication passage 44 is A13, which is lower than A12.

[0062] The decrease in pressure PA in the communication passage 44 shown in Figure 7 includes the decrease in pressure PL due to the failure of the pressure reducing valve 38 and the decrease in pressure PG due to hydrogen consumption during normal power generation. As described above, pressure PL can be estimated by subtracting pressure PG from pressure PA.

[0063] For example, the pressure PA = A11 at time T11 is obtained as the pressure measurement value of the pressure sensor 46. The pressure PG = G11 at time T11 is obtained as the pressure conversion value described above, based on the hydrogen consumption amount obtained based on the power generation current output from the fuel cell stack 30 and the temperature measurement value of the temperature sensor 110. The pressure PL at time T11 is obtained as the pressure estimate value described above, based on the value obtained by subtracting the pressure PG = G11 from the pressure PA = A11 and the value P0 described above. This makes it possible to more accurately estimate the amount of pressure PL decrease due to hydrogen fuel leakage outside the fuel supply line 36.

[0064] Figures 8A, 8B, and 8C illustrate a map M showing the correspondence between the failure levels of the pressure reducing valve 38 and the estimated pressure and measured concentration values. The range represented in map M corresponds to each failure level based on the pressure drop [MPa] due to the failure of the pressure reducing valve 38 indicated by the estimated pressure value and the hydrogen concentration [%] in the containment section 60 indicated by the measured concentration value. In the map M illustrated in Figures 8A, 8B, and 8C, the vertical axis shows P0 to P0-D13 [MPa] as the pressure [MPa] due to the failure of the pressure reducing valve 38. The horizontal axis of the map M shows 0 to C [%] as the hydrogen concentration [%] in the containment section 60.

[0065] As time progresses, the failure level of the pressure reducing valve 38 can be more clearly determined using map M. Therefore, multiple maps M corresponding to changes in time are generated in advance through experiments and stored in the memory unit 82. Furthermore, the range represented in map M differs depending on whether the pressure reducing valve 38A corresponding to the non-power-generating fuel cell stack 30A fails or the pressure reducing valve 38B corresponding to the power-generating fuel cell stack 30B fails. This is because, when the pressure reducing valve 38B fails, the amount of hydrogen fuel leaking outside the fuel supply passage 36 can be suppressed compared to when the pressure reducing valve 38A fails, because the hydrogen fuel is consumed for power generation.

[0066] Figure 8A shows map M corresponding to time T11. Map M defines ranges Rvs and Rvg for pressure estimates and concentration measurements corresponding to the severe failure levels illustrated in Figure 2D. In map M, ranges Rvs and Rvg do not overlap. Range Rvs corresponds to the case where the pressure reducing valve 38A corresponding to the non-generating fuel cell stack 30A fails. Range Rvg corresponds to the case where the pressure reducing valve 38B corresponding to the generating fuel cell stack 30B fails. The hydrogen concentration corresponding to range Rvg is lower than the hydrogen concentration corresponding to range Rvs.

[0067] Therefore, by using the map M, it is possible to determine whether or not a failure of a pressure reducing valve 38 corresponding to a severe failure level has occurred. It is also possible to identify which pressure reducing valve 38 is experiencing a failure corresponding to a severe failure level. In other words, the failure detection unit 94 can detect a failure of a pressure reducing valve 38 corresponding to a severe failure level based on the pressure estimate, the concentration measurement, and the map M corresponding to time T11.

[0068] Figure 8B shows map M corresponding to time T12, which is after time T11. Map M defines ranges Rms and Rmg for pressure estimates and concentration measurements corresponding to the moderate failure level illustrated in Figure 2C. Map M also defines ranges Rvs and Rvg corresponding to the severe failure level described above. The pressure PL corresponding to ranges Rvs and Rvg at time T12 is lower than the pressure PL at time T11. The ranges Rms and Rvs in map M are different ranges.

[0069] In map M, ranges Rms and Rmg do not overlap. Range Rms corresponds to the case where the pressure reducing valve 38A corresponding to the non-generating fuel cell stack 30A fails. Range Rmg corresponds to the case where the pressure reducing valve 38B corresponding to the generating fuel cell stack 30B fails. The hydrogen concentration corresponding to range Rmg is lower than the hydrogen concentration corresponding to range Rms.

[0070] In map M, ranges Rvs and Rvg do not overlap. Range Rvs corresponds to the case where the pressure reducing valve 38A corresponding to the non-power-generating fuel cell stack 30A fails. Range Rvg corresponds to the case where the pressure reducing valve 38B corresponding to the power-generating fuel cell stack 30B fails. The hydrogen concentration corresponding to range Rvg is lower than the hydrogen concentration corresponding to range Rvs.

[0071] Therefore, by using the map M, it is possible to determine whether or not a failure of a pressure reducing valve 38 corresponding to a severe or moderate failure level has occurred. It is also possible to identify which pressure reducing valve 38 is experiencing a failure corresponding to a severe or moderate failure level. In other words, the failure detection unit 94 can detect a failure of a pressure reducing valve 38 corresponding to a severe or moderate failure level based on the pressure estimate, the concentration measurement, and the map M corresponding to time T12.

[0072] Figure 8C shows map M corresponding to time T13, which is after time T12. Map M defines ranges Ris and Rig for pressure estimates and concentration measurements corresponding to the mild failure levels illustrated in Figure 2B. Map M also defines ranges Rvs and Rvg corresponding to the severe failure levels mentioned above, and ranges Rms and Rmg corresponding to the moderate failure levels mentioned above.

[0073] The pressure PL corresponding to ranges Rvs and Rvg, which correspond to severe failure levels at time T13, is even lower than the pressure PL at time T12. The pressure PL corresponding to ranges Rms and Rmg, which correspond to moderate failure levels at time T13, is also lower than the pressure PL at time T12. Ranges Ris, Rms, and Rvs in map M are all different ranges. Also, ranges Rig, Rmg, and Rvg in map M are all different ranges.

[0074] In map M, ranges Ris and Rig do not overlap. Range Ris corresponds to the case where the pressure reducing valve 38A corresponding to the non-power-generating fuel cell stack 30A fails. Range Rig corresponds to the case where the pressure reducing valve 38B corresponding to the power-generating fuel cell stack 30B fails. The hydrogen concentration corresponding to range Rig is lower than the hydrogen concentration corresponding to range Ris.

[0075] In map M, ranges Rms and Rmg do not overlap. Range Rms corresponds to the case where the pressure reducing valve 38A corresponding to the non-generating fuel cell stack 30A fails. Range Rmg corresponds to the case where the pressure reducing valve 38B corresponding to the generating fuel cell stack 30B fails. The hydrogen concentration corresponding to range Rmg is lower than the hydrogen concentration corresponding to range Rms.

[0076] In map M, ranges Rvs and Rvg do not overlap. Range Rvs corresponds to the case where the pressure reducing valve 38A corresponding to the non-power-generating fuel cell stack 30A fails. Range Rvg corresponds to the case where the pressure reducing valve 38B corresponding to the power-generating fuel cell stack 30B fails. The hydrogen concentration corresponding to range Rvg is lower than the hydrogen concentration corresponding to range Rvs.

[0077] Therefore, by using the map M, it is possible to determine whether or not a failure of a pressure reducing valve 38 corresponding to a severe, moderate, or minor failure level has occurred. It is also possible to identify which pressure reducing valve 38 is experiencing a failure corresponding to a severe, moderate, or minor failure level. In other words, the failure detection unit 94 can detect a failure of a pressure reducing valve 38 corresponding to a severe, moderate, or minor failure level based on the pressure estimate, concentration measurement, and the map M corresponding to time T13.

[0078] Since pressure and concentration measurements are acquired multiple times corresponding to times T11, T12, and T13, multiple sets of pressure and concentration measurements are obtained. The fault detection unit 94 may determine the fault level of the pressure reducing valve 38 based on the multiple sets of pressure and concentration measurements. For example, the fault level of the pressure reducing valve 38 may be determined based on the pressure and concentration measurements acquired at the most recent time from among the multiple sets of pressure and concentration measurements.

[0079] Figure 9 is a flowchart illustrating the processing procedure for fault detection of the pressure reducing valve 38. This processing procedure is performed by the arithmetic unit 80 executing a computer program stored in the memory unit 82 of the fault detection device 20. Using Figure 5, steps similar to those described above are denoted by the same reference numerals, and explanations are omitted as appropriate.

[0080] When this processing procedure is started, steps S1 and S2 are performed. When step S2 is completed, in step S21, the temperature acquisition unit 120 acquires the temperature measurement value of the temperature sensor 110. In step S22, the hydrogen consumption calculation unit 122 calculates the amount of hydrogen consumed by the fuel cell stack 30 for power generation based on the power generation current output from the fuel cell stack 30 that is generating power.

[0081] In step S23, the fault detection unit 94 calculates a pressure equivalent value of the hydrogen consumption based on the temperature measurement value obtained in step S21 and the hydrogen consumption amount calculated in step S22. The fault detection unit 94 then calculates an estimated pressure value using the pressure equivalent value thus calculated and the pressure measurement value obtained in step S2.

[0082] Subsequently, once the processing in step S3 is complete, in step S4, the fault detection unit 94 determines whether or not it has detected a fault in the pressure reducing valve 38 based on the pressure estimate calculated in step S23, the concentration measurement value acquired in step S2, and the map M read out in step S3. If the answer in step S4 is YES, the process proceeds to step S5. If the answer in step S4 is NO, the process ends.

[0083] In step S5, the fault detection unit 94 notifies a notification device (not shown) of the detected fault in the pressure reducing valve 38, the identification result of the faulty pressure reducing valve 38, and the fault level of the pressure reducing valve 38. This allows the operator to understand the fault in the pressure reducing valve 38, the identification result of the faulty pressure reducing valve 38, and the fault level of the pressure reducing valve 38. Once the processing in step S5 is completed, this processing procedure is finished. According to this modified example 1, it is not necessary to stop the power generation of all of the multiple fuel cell stacks 30 in order to detect a fault in the pressure reducing valve 38.

[0084] (Modification 2) In Modification 1 described above, it is possible to identify which of the two pressure reducing valves 38 has failed. In this Modification 2, the failure detection unit 94 can identify the number of pressure reducing valves 38 that have failed. As described above, Figure 6 illustrates two pressure reducing valves 38: pressure reducing valve 38A corresponding to a fuel cell stack 30A that does not generate power, and pressure reducing valve 38B corresponding to a fuel cell stack 30B that does generate power. If one or both of the two pressure reducing valves 38 fail, the map M shown in Figures 10A and 10B is used.

[0085] Figures 10A and 10B illustrate a map M showing the correspondence between the number of faulty pressure reducing valves 38 and the estimated pressure and concentration measurements. As shown in Figures 10A and 10B, multiple maps M are generated in advance through experiments to correspond to changes in time and stored in the memory unit 82. The vertical and horizontal axes of the maps M shown in Figures 10A and 10B are the same as those of the maps M shown in Figures 8A and 8B.

[0086] Figure 10A shows the ranges Rvs and Rvg for the estimated pressure and measured concentration values ​​corresponding to the case when one of the two pressure reducing valves 38 shown in Figure 8A fails. Figure 10A also defines the range RVd for the estimated pressure and measured concentration values ​​corresponding to the case when both of the two pressure reducing valves 38 fail. The range RVd in map M is different from both range Rvs and range Rvg.

[0087] The pressure drop when both pressure reducing valves 38 fail is equivalent to the sum of the pressure drops when one of the two pressure reducing valves 38 fails. Therefore, the pressure PL corresponding to range Rvd is lower than the pressure PL in ranges Rvs and Rvg.

[0088] Figure 10B shows the ranges Rvs, Rvg, Rms, and Rmg of the pressure estimates and concentration measurements corresponding to the case when one of the two pressure reducing valves 38 shown in Figure 8B fails. Figure 10B further defines the ranges Rvd and Rmd of the pressure estimates and concentration measurements corresponding to the case when both of the two pressure reducing valves 38 fail. Ranges Rvd and Rmd in map M are different ranges. Range Rvd in map M is different from both range Rvs and range Rvg. Range Rmd in map M is different from both range Rms and range Rmg.

[0089] The pressure drop when both pressure reducing valves 38 fail is equivalent to the sum of the pressure drops when one of the two pressure reducing valves 38 fails. Therefore, the pressure PL corresponding to range Rvd is lower than the pressure PL in ranges Rvs and Rvg. Also, the pressure PL corresponding to range Rmd is lower than the pressure PL in ranges Rms and Rmg.

[0090] Therefore, by using the map M, it is possible to detect that one or both of the two pressure reducing valves 38 have failed. In other words, the failure detection unit 94 can identify the number of pressure reducing valves 38 that have failed.

[0091] Since pressure and concentration measurements are acquired multiple times corresponding to times T11, T12, and T13, multiple sets of pressure and concentration measurements are obtained. The fault detection unit 94 may identify the number of faulty pressure reducing valves 38 based on the multiple sets of pressure and concentration measurements. For example, the number of faulty pressure reducing valves 38 is identified based on the pressure and concentration measurements acquired at the first time from among the multiple sets of pressure and concentration measurements. This allows for more detailed detection of faults in the pressure reducing valves 38.

[0092] In this modified example 2, the number of faulty pressure reducing valves 38 out of two is specified. However, it is also possible to specify the number of faulty pressure reducing valves 38 out of three or more pressure reducing valves 38. For example, the pressure drop when two of three pressure reducing valves 38 fail is equivalent to the sum of the pressure drops when one of the two faulty pressure reducing valves 38 fails individually. For example, the pressure drop when all three pressure reducing valves 38 fail is equivalent to the sum of the pressure drops when one of the three faulty pressure reducing valves 38 fails individually.

[0093] Therefore, the ranges of pressure estimates and concentration measurements corresponding to the failure of one of the three pressure reducing valves 38, the ranges corresponding to the failure of two valves, and the ranges corresponding to the failure of all three valves are all different. As a result, it is possible to identify the number of pressure reducing valves 38 that have been detected to be faulty. The same applies to four or more pressure reducing valves 38.

[0094] With regard to the embodiments and modifications described above, the following additional information is disclosed.

[0095] (Note 1) The fault detection device (20) of the present disclosure is a fault detection device for detecting a fault in a fuel cell system (10) having a plurality of fuel cell stacks (30), a plurality of fuel supply lines (36) through which hydrogen fuel is supplied to each of the plurality of fuel cell stacks, a plurality of pressure reducing valves (38) arranged in each of the plurality of fuel supply lines, a communication passage (44) that connects the plurality of fuel supply lines in the upstream section (36u) of the pressure reducing valves, a pressure sensor (46) that measures the pressure in the communication passage, and a concentration sensor (48) that measures the concentration of hydrogen fuel leaking from the downstream section (36d) of the pressure reducing valves to the outside of the plurality of fuel supply lines, and comprises a measurement value acquisition unit (92) that acquires the pressure measurement value of the pressure sensor and the concentration measurement value of the concentration sensor, and a fault detection unit (94) that detects the fault of the pressure reducing valve based on the pressure measurement value and the concentration measurement value acquired by the measurement value acquisition unit. With such a configuration, a fault detection device that can reliably detect a failure in a pressure reducing valve in a fuel cell system can be provided.

[0096] (Note 2) The fault detection device described in Note 1 further comprises a fuel supply control unit (90) capable of controlling the supply and cessation of hydrogen fuel from the downstream section of the pressure reducing valve to a plurality of fuel cell stacks, wherein the fuel supply control unit may control the cessation of hydrogen fuel supply to at least a portion of the plurality of fuel cell stacks. With such a configuration, it is not necessary to stop the power generation of all of the plurality of fuel cell stacks in order to detect a fault in the pressure reducing valve.

[0097] (Note 3) The fault detection device described in Note 2, wherein the fuel cell system further includes a temperature sensor (110) for measuring the fuel temperature of hydrogen fuel that can be supplied to the fuel cell stack by the fuel supply path, and the fault detection device further includes a temperature acquisition unit (120) for acquiring the temperature measurement value of the temperature sensor, and a hydrogen consumption calculation unit (122) for calculating the amount of hydrogen consumed by the fuel cell stack used for power generation based on the power generation current output from the fuel cell stack which is generating power due to the hydrogen fuel supply control performed by the fuel supply control unit, and the fault detection unit may calculate a pressure equivalent value of the hydrogen consumption based on the temperature measurement value and the hydrogen consumption, and detect the fault of the pressure reducing valve based on the pressure estimate value obtained by subtracting the pressure equivalent value from the pressure measurement value and the concentration measurement value. With such a configuration, the decrease in pressure in the communication passage due to hydrogen fuel leakage to the outside of the fuel supply path can be estimated more accurately.

[0098] (Note 4) A fault detection device according to any one of Notes 1 to 3, further comprising a storage unit (82) that stores a map (M) showing the correspondence between the fault level of the pressure reducing valve corresponding to the amount of hydrogen fuel leaking to the outside from the downstream section of the pressure reducing valve, and the pressure measurement value and the concentration measurement value, wherein the fault detection unit may detect the fault of the pressure reducing valve based on the pressure measurement value, the concentration measurement value and the map. With such a configuration, the fault of the pressure reducing valve can be detected more accurately.

[0099] (Note 5) A fault detection device described in any one of Notes 1 to 3, wherein the fault detection unit determines the fault level of the fault of the pressure reducing valve according to the amount of hydrogen fuel leaking to the outside from the downstream section of the pressure reducing valve, or identifies the number of pressure reducing valves in which the fault has been detected, based on multiple sets of pressure measurement values ​​and concentration measurement values ​​obtained by acquiring the pressure measurement value and the concentration measurement value multiple times. With such a configuration, the fault of the pressure reducing valve can be detected in more detail.

[0100] While this disclosure has been described in detail, it is not limited to the individual embodiments described above. These embodiments can be added, replaced, modified, partially deleted, etc., in any way that does not depart from the gist of this disclosure or from the spirit of this disclosure derived from the claims and their equivalents. These embodiments can also be implemented in combination. For example, the order of operations and processes in the embodiments described above are given as examples only and are not limited thereto. The same applies when numerical values ​​or mathematical formulas are used in the description of the embodiments described above.

[0101] 10...Fuel cell system 20...Fault detection device 30...Fuel cell stack 32...Fuel tank 34...Main shut-off valve 36...Fuel supply line 38...Pressure reducing valve 40...Injector 42...Relief valve 44...Connecting passage 46...Pressure sensor 48...Concentration sensor 60...Housing unit 80...Calculation unit 82...Storage unit 90...Fuel supply control unit 92...Measurement value acquisition unit 94...Fault detection unit 110...Temperature sensor 120...Temperature acquisition unit 122...Hydrogen consumption calculation unit

Claims

1. A fault detection device (20) for detecting a fault in a fuel cell system (10) having a plurality of fuel cell stacks (30), a plurality of fuel supply lines (36) for supplying hydrogen fuel to each of the plurality of fuel cell stacks, a plurality of pressure reducing valves (38) arranged in each of the plurality of fuel supply lines, a communication passage (44) for connecting the plurality of fuel supply lines in the upstream section (36u) of the pressure reducing valves, a pressure sensor (46) for measuring the pressure in the communication passage, and a concentration sensor (48) for measuring the concentration of hydrogen fuel leaking from the downstream section (36d) of the pressure reducing valves to the outside of the plurality of fuel supply lines, comprising: a measurement value acquisition unit (92) for acquiring the pressure measurement value of the pressure sensor and the concentration measurement value of the concentration sensor; and a fault detection unit (94) for detecting the fault in the pressure reducing valve based on the pressure measurement value and the concentration measurement value acquired by the measurement value acquisition unit.

2. A fault detection device according to claim 1, further comprising a fuel supply control unit (90) capable of controlling the supply and cessation of hydrogen fuel from the downstream section of the pressure reducing valve to a plurality of fuel cell stacks, wherein the fuel supply control unit controls the cessation of the supply of hydrogen fuel to at least a portion of the plurality of fuel cell stacks.

3. A fault detection device according to claim 2, wherein the fuel cell system further includes a temperature sensor (110) for measuring the fuel temperature of hydrogen fuel that can be supplied to the fuel cell stack by the fuel supply path, the fault detection device further includes a temperature acquisition unit (120) for acquiring the temperature measurement value of the temperature sensor, and a hydrogen consumption calculation unit (122) for calculating the amount of hydrogen consumed by the fuel cell stack for power generation based on the power generation current output from the fuel cell stack which is generating power due to the power supply control of hydrogen fuel by the fuel supply control unit, the fault detection unit calculates a pressure-converted value of the hydrogen consumption based on the temperature measurement value and the hydrogen consumption, and detects the fault of the pressure reducing valve based on a pressure estimate obtained by subtracting the pressure-converted value from the pressure measurement value and the concentration measurement value.

4. A fault detection device according to any one of claims 1 to 3, further comprising a storage unit (82) that stores a map (M) showing the correspondence between a fault level of the pressure reducing valve corresponding to the amount of hydrogen fuel leaking to the outside from the downstream section of the pressure reducing valve, and the pressure measurement value and the concentration measurement value, wherein the fault detection unit detects the fault of the pressure reducing valve based on the pressure measurement value, the concentration measurement value and the map.

5. A fault detection device according to any one of claims 1 to 3, wherein the fault detection unit determines the fault level of the fault of the pressure reducing valve according to the amount of hydrogen fuel leaking to the outside from the downstream section of the pressure reducing valve, or identifies the number of pressure reducing valves in which the fault has been detected, based on a plurality of sets of pressure measurement values ​​and concentration measurement values ​​obtained by acquiring the pressure measurement value and the concentration measurement value a plurality of times.

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