Fuel cell system

Abstract

This system detects a decrease in the flow rate of hydrogen gas supplied to the fuel cell while keeping the number of components in the fuel cell system to a minimum. [Solution] The fuel cell system FCS comprises a pressure sensor Sp that measures the pressure of hydrogen gas supplied to the fuel cell FC, and a control unit Cf that outputs an injection command to the injector INJ, causing the injector INJ to inject hydrogen gas into the ejector EJT. The control unit Cf detects that the flow rate of hydrogen gas supplied to the fuel cell has decreased if the difference between the pressures measured by the pressure sensor Sp at two different timings after the output of the injection command is stopped is below a threshold.

Description

Technical Field

[0007] , , ,

[0001] The present invention relates to a fuel cell system.

Background Art

[0002] As a fuel cell system, there is one provided with a pump that supplies hydrogen gas discharged from a fuel cell back to the fuel cell. As a related technology, there is Patent Document 1.

[0003] However, when a pump is adopted to supply hydrogen gas back to the fuel cell, an inverter or the like is required to drive the motor in the pump, so there is a concern about an increase in manufacturing cost due to an increase in the number of parts.

[0004] Therefore, as another fuel cell system, it is conceivable to adopt an ejector that supplies hydrogen gas discharged from a fuel cell back to the fuel cell by hydrogen gas injected from an injector instead of a pump.

[0005] By the way, in order to reduce the number of parts of a fuel cell system, when a flow sensor for measuring the flow rate of hydrogen gas supplied to a fuel cell is not provided, there is a concern that it may not be possible to detect that the flow rate of hydrogen gas supplied to the fuel cell has decreased.

[0006] Therefore, for example, it is conceivable to detect that the flow rate of hydrogen gas supplied to a fuel cell has decreased due to a decrease in the voltage output from the fuel cell. However, since a decrease in the output voltage of the fuel cell may lead to a decrease in the output power of the fuel cell system or the like, it is desirable to detect that the flow rate of hydrogen gas supplied to the fuel cell has decreased before the output voltage of the fuel cell decreases.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

[0008] One aspect of the present invention is to detect a decrease in the flow rate of hydrogen gas supplied to a fuel cell while suppressing an increase in the number of components in the fuel cell system. [Means for solving the problem]

[0009] One embodiment of the present invention is a fuel cell system comprising a fuel cell, an injector for injecting hydrogen gas, an ejector for supplying hydrogen gas injected from the injector and hydrogen gas discharged from the fuel cell to the fuel cell, a pressure sensor for measuring the pressure of the hydrogen gas supplied to the fuel cell, and a control unit that outputs an injection command to the injector to inject hydrogen gas from the injector to the ejector, wherein the control unit detects that the flow rate of hydrogen gas supplied to the fuel cell has decreased if the difference between the pressures measured by the pressure sensor at two different timings after the output of the injection command is stopped is below a threshold.

[0010] Thus, since an ejector is used instead of a pump to resupply the hydrogen gas emitted from the fuel cell back into the fuel cell, there is no need to include an inverter to drive the electric motor in the pump, thus reducing the number of components in the fuel cell system. Furthermore, for example, when the flow rate of hydrogen gas supplied to the fuel cell decreases, by setting the maximum value of the difference between the pressures measured by the pressure sensors at the two timings mentioned above as the threshold value, it is possible to detect that the flow rate of hydrogen gas supplied to the fuel cell has decreased if the difference between the pressures measured by the pressure sensors at the two timings is less than or equal to the threshold value.

[0011] Furthermore, the control unit may be configured to detect a decrease in the flow rate of hydrogen gas supplied to the fuel cell if the difference between the maximum and minimum values ​​of the pressure measured by the pressure sensor during the period from the time when the pressure measured by the pressure sensor reaches its maximum to the time when it reaches its next maximum is less than or equal to the threshold.

[0012] Furthermore, the control unit may be configured to detect a decrease in the flow rate of hydrogen gas supplied to the fuel cell if the difference between the maximum pressure measured by the pressure sensor during the period from the cessation of the output of the injection command until a certain period of time has elapsed, and the pressure measured by the pressure sensor at the time when the certain period of time has elapsed from the cessation of the output of the injection command is less than or equal to the threshold.

[0013] Furthermore, the aforementioned fixed time may be the time from the cessation of the injection command output until the amount of hydrogen gas supplied to the fuel cell falls below a predetermined value, provided that the flow rate of hydrogen gas supplied to the fuel cell has not decreased.

[0014] Furthermore, the aforementioned fixed time may be determined based on the design information of the ejector and the variation in the time from the cessation of the injection command output until the amount of hydrogen gas supplied to the fuel cell falls below a predetermined value.

[0015] Furthermore, the control unit may be configured to detect a decrease in the flow rate of hydrogen gas supplied to the fuel cell if the difference between the maximum pressure among the pressures measured by the pressure sensor after the output of the injection command has stopped and the pressure measured by the pressure sensor at the timing when the rate of change per unit time of the pressure measured by the pressure sensor changes is less than or equal to the threshold.

[0016] Furthermore, the control unit may be configured to increase the amount of change per unit time of the pressure measured by the pressure sensor after the output of the injection command is stopped, as the output current of the fuel cell increases.

[0017] Further, assume that the fuel cell system does not include an inverter for driving an electric motor in a pump that circulates hydrogen gas discharged from the fuel cell back to the fuel cell.

Advantages of the Invention

[0018] According to the present invention, it is possible to detect that the flow rate of hydrogen gas supplied to the fuel cell is decreasing while suppressing an increase in the number of components of the fuel cell system.

Brief Description of the Drawings

[0019] [Figure 1] It is a diagram showing an example of a fuel cell system of an embodiment. [Figure 2] It is a flowchart showing an example of the operation of the control unit after the start of the idle state. [Figure 3] It is a flowchart showing the operation of the control unit in Example 1. [Figure 4] It is a diagram showing an injection command, the flow rate of hydrogen gas, and the pressure of hydrogen gas during normal times. [Figure 5] It is a diagram showing an injection command, the flow rate of hydrogen gas, and the pressure of hydrogen gas when a problem occurs. [Figure 6] It is a flowchart showing an example of the operation of the control unit in Example 2. [Figure 7] It is a diagram showing an injection command, the flow rate of hydrogen gas, and the pressure of hydrogen gas during normal times. [Figure 8] It is a diagram showing an injection command, the flow rate of hydrogen gas, and the pressure of hydrogen gas when a problem occurs. [Figure 9] It is a flowchart showing an example of the operation of the control unit in a modified example of Example 2.

Modes for Carrying Out the Invention

[0020] Hereinafter, embodiments will be described in detail based on the drawings.

[0021] Figure 1 shows an example of a fuel cell system according to an embodiment.

[0022] The fuel cell system (FCS) shown in Figure 1 is installed in the higher-level system (STM) and supplies power to the load (Lo). For example, if the higher-level system (STM) is a vehicle such as a forklift, towing tractor, or automated guided vehicle (AGV), the load (Lo) is expected to be an inverter circuit that drives cargo handling equipment or a drive motor. In this case, the load (Lo) is installed inside the higher-level system (STM) as shown in Figure 1. Alternatively, if the higher-level system (STM) is a stationary generator such as an industrial stationary generator, a household stationary generator, or an emergency stationary generator, the load (Lo) is expected to be industrial machinery or household appliances. In this case, the load (Lo) may be installed outside the higher-level system (STM).

[0023] Furthermore, the higher-level system STM includes a control unit Cs in addition to the fuel cell system FCS.

[0024] The control unit Cs consists of a microcomputer and other components, and sends the power request from the load Lo as a power command value to the fuel cell system FCS.

[0025] A fuel cell system (FCS) comprises a main unit, the fuel cell (FC), and several types of auxiliary equipment for generating electricity using the fuel cell (FC).

[0026] Specifically, the fuel cell system (FCS) includes a fuel tank (HT), injector (INJ), ejector (EJT), pressure sensor (Sp), gas-liquid separator (GLS), exhaust / drain valve (EDV), and diluent (DIL) as auxiliary hydrogen gas system components. To reduce the number of parts, the fuel cell system (FCS) does not include a flow sensor in the hydrogen gas flow path from the fuel tank (HT) to the fuel cell (FC). Furthermore, to reduce the number of parts, the fuel cell system (FCS) does not include an inverter to drive the electric motor in the pump that circulates the hydrogen gas discharged from the fuel cell (FC) back into the fuel cell (FC).

[0027] Furthermore, the fuel cell module (FCM) is equipped with air system auxiliary equipment such as an air compressor (ACP) and an air pressure regulating valve (ARV).

[0028] Furthermore, the fuel cell module (FCM) is equipped with cooling system auxiliary components such as a water pump (WP) and a radiator (R).

[0029] Furthermore, the fuel cell module (FCM) is equipped with electrical auxiliary components such as a DC-DC converter (CNV) and an energy storage device (B).

[0030] Furthermore, the fuel cell module (FCM) includes a memory unit (Str) and a control unit (Cf). Note that the devices and components provided in the fuel cell module (FCM) may vary depending on the type of higher-level system (STM). For example, if the higher-level system (STM) is a vehicle, the energy storage device (B), fuel tank (HT), and radiator (R) are located inside the fuel cell module (FCM) as shown in Figure 1. Alternatively, if the higher-level system (STM) is a stationary generator, the energy storage device (B), fuel tank (HT), and radiator (R) may be located outside the fuel cell system (FCS).

[0031] A fuel cell (FC) consists of multiple fuel cell cells (for example, polymer electrolyte fuel cells (PEFCs)) connected in series with each other, and generates electricity through an electrochemical reaction between hydrogen contained in hydrogen gas and oxygen contained in air.

[0032] The fuel tank (HT) is a storage container for hydrogen gas. The hydrogen gas stored in the fuel tank (HT) is supplied to the fuel cell (FC) via the injector (INJ) and ejector (EJT).

[0033] The injector INJ injects hydrogen gas supplied from the fuel tank HT into the ejector EJT based on injection commands from the control unit Cf. During the period when an injection command is output from the control unit Cf to the injector INJ (for example, when the injection command is at a high level), the on-off valve inside the injector INJ is open, and hydrogen gas supplied from the fuel tank HT continues to be injected into the ejector EJT. Conversely, during the period when no injection command is output from the control unit Cf to the injector INJ (for example, when the injection command is at a low level), the on-off valve inside the injector INJ is closed, and hydrogen gas supplied from the fuel tank HT is not injected into the ejector EJT.

[0034] The ejector EJT draws in hydrogen gas discharged from the fuel cell FC and gas-liquid separator GLS using hydrogen gas injected from the injector INJ. It also mixes the drawn-in hydrogen gas with the hydrogen gas input to the ejector EJT from the injector INJ and outputs it to the fuel cell FC. In other words, the ejector EJT supplies hydrogen gas injected from the injector INJ and hydrogen gas discharged from the fuel cell FC to the fuel cell FC. During the period when hydrogen gas is being injected from the injector INJ to the ejector EJT, the flow rate of hydrogen gas supplied to the fuel cell FC increases, and the pressure of hydrogen gas supplied to the fuel cell FC increases. After that, when hydrogen gas is no longer injected from the injector INJ to the ejector EJT, the flow rate of hydrogen gas supplied to the fuel cell FC decreases, and the pressure of hydrogen gas supplied to the fuel cell FC decreases.

[0035] The pressure sensor Sp measures the pressure of the hydrogen gas supplied to the fuel cell FC and sends the measured pressure P to the control unit Cf.

[0036] The gas-liquid separator (GLS) separates hydrogen gas, which contains unreacted hydrogen, from liquid water emitted from the fuel cell (FC).

[0037] The exhaust and drain valve (EDV) sends the liquid water separated by the gas-liquid separator (GLS) to the diluent (DIL). The liquid water sent to the diluent (DIL) is stored in a tank within the diluent (DIL). In addition, the air discharged from the fuel cell (FC) via the air pressure regulating valve (ARV) and the hydrogen gas supplied from the gas-liquid separator (GLS) merge in the diluent (DIL) and are discharged either outside or inside the fuel cell system (FCS).

[0038] The air compressor (ACP) compresses air supplied from outside the fuel cell system (FCS) and delivers it to the fuel cell (FC).

[0039] The air pressure regulating valve (ARV) adjusts the pressure and flow rate of the air supplied to the fuel cell (FC).

[0040] The radiator R exchanges heat between the cold soot (e.g., water) discharged from the fuel cell FC and the outside air, and then sends it to the water pump WP.

[0041] The water pump (WP) supplies cold soot from the radiator (R) to the fuel cell (FC).

[0042] The DC-DC converter CNV converts the voltage output from the fuel cell FC to a predetermined voltage. The power output from the DC-DC converter CNV is supplied to each auxiliary device, load Lo, and energy storage device B.

[0043] Energy storage device B is composed of, for example, a lithium-ion capacitor and is connected between the DC-DC converter CNV and the load Lo, working in cooperation with the fuel cell FC to supply power to the load Lo. When power is supplied from the fuel cell FC to energy storage device B, energy storage device B is charged and its charge rate (the ratio of remaining capacity to the full charge capacity of energy storage device B [%]) increases. Conversely, when power is supplied from energy storage device B to the load Lo, energy storage device B is discharged and its charge rate decreases.

[0044] The memory unit Str is composed of non-volatile memory such as ROM (Read Only Memory) or flash memory. It is assumed that the memory unit Str already has pre-stored threshold values ​​such as threshold ΔP1th and threshold ΔP2th, which will be described later.

[0045] The control unit Cf consists of a microcomputer and other components, and controls the power generation of the fuel cell FC.

[0046] For example, when controlling the power generation of the fuel cell FC, the control unit Cf controls the operation of each auxiliary device so that the output power of the fuel cell FC follows the power command value sent from the control unit Cs.

[0047] Furthermore, for example, when the control unit Cf receives an idling start instruction from the control unit Cs, it transitions the state of the fuel cell FC from the power generation state to the idle state. Once the control unit Cf transitions the state of the fuel cell FC from the power generation state to the idle state, it controls the operation of each auxiliary device so that the fuel cell FC does not output any power, while simultaneously enabling it to quickly return from the idle state to the power generation state.

[0048] Figure 2 is a flowchart showing an example of the operation of the control unit Cf after the idle state begins. Note that a certain time α < a certain time β.

[0049] First, when the idle state begins (Step S11: Yes), the control unit Cf changes the injection command from a low level to a high level (Step S12), and then, after a certain period of time α has elapsed (Step S13: Yes), changes the injection command from a high level to a low level (Step S14).

[0050] Next, the control unit Cf executes the processes from steps S12 to S14 again after a certain period of time β has elapsed (step S15: Yes).

[0051] In other words, when the fuel cell FC transitions from the power generation state to the idle state, the control unit Cf periodically outputs injection commands to the injector INJ, thereby intermittently injecting hydrogen gas from the injector INJ to the ejector EJT, so as to prevent power output from the fuel cell FC while simultaneously enabling the fuel cell FC to quickly return from the idle state to the power generation state.

[0052] Furthermore, when the fuel cell FC is in an idle state, the control unit Cf detects that the flow rate of hydrogen gas supplied to the fuel cell FC has decreased compared to normal conditions if the difference ΔP between the pressures P measured by the pressure sensor Sp at two different timings after the output of the injection command is stopped is less than or equal to the threshold ΔPth. Normal conditions refer to, for example, when there are no malfunctions in the injector INJ or ejector EJT, and the fuel cell FC is in an idle state, and the desired flow rate of hydrogen gas is supplied to the fuel cell FC. The threshold ΔPth is, for example, the maximum value of the difference Δ between the pressures P measured by the pressure sensor Sp at the two timings mentioned above when the flow rate of hydrogen gas supplied to the fuel cell FC has decreased compared to normal conditions, or the minimum value of the difference Δ when it is possible to supply the desired power to the load Lo from the fuel cell system FCS even if the flow rate of hydrogen gas supplied to the fuel cell FC has decreased compared to normal conditions. Furthermore, the control unit Cf may be configured to display a message on a display (not shown) to inform the user that an abnormality has occurred in the injector INJ or ejector EJT when it detects, for example, that the flow rate of hydrogen gas supplied to the fuel cell FC has decreased compared to normal conditions. Alternatively, the control unit Cf may be configured to restore the power generation of the fuel cell FC by increasing the output of the injection command when it detects that the flow rate of hydrogen gas supplied to the fuel cell FC has decreased compared to normal conditions.

[0053] <Example 1> In the control unit Cf of Example 1, when the fuel cell FC is in an idle state, if the difference ΔP1 between the maximum pressure Pmax and the minimum pressure Pmin among the pressures P measured by the pressure sensor Sp between timing T1 when the pressure P measured by the pressure sensor Sp is at its maximum and timing T2 when the next maximum pressure P is at its maximum is less than or equal to the threshold ΔPth1, then it is detected that the flow rate of hydrogen gas supplied to the fuel cell FC has decreased compared to normal.

[0054] Figure 3 is a flowchart showing the operation of the control unit Cf in Example 1.

[0055] First, when the control unit Cf starts in idle state (step S21: Yes), it switches the injection command from high level to low level (step S22: Yes), and then repeatedly acquires the pressure P until it determines that the pressure P has reached its maximum value twice, and stores it in the memory unit Str (steps S23, S24: No).

[0056] Next, when the control unit Cf determines that the pressure P has reached its maximum value twice (step S24: Yes), it selects the maximum pressure Pmax and minimum pressure Pmin from among the pressures P stored in the memory unit Str (step S25), and calculates the difference ΔP1 between the maximum pressure Pmax and the minimum pressure Pmin (step S26). For example, if the two pressures P that reached their maximum value between timings T1 and T2 are different values, the control unit Cf selects the larger of the two pressures P as the maximum pressure Pmax. If the two pressures P that reached their maximum value between timings T1 and T2 are the same value, the control unit Cf selects one of the two pressures P as the maximum pressure Pmax.

[0057] Then, the control unit Cf detects that the flow rate of hydrogen gas supplied to the fuel cell FC has not decreased compared to normal conditions if the difference ΔP1 is greater than the threshold ΔPth1 (step S27: No) (step S28), and detects that the flow rate of hydrogen gas supplied to the fuel cell FC has decreased compared to normal conditions if the difference ΔP1 is less than or equal to the threshold ΔPth1 (step S27: Yes) (step S29).

[0058] The control unit Cf may, after detecting whether the flow rate of hydrogen gas supplied to the fuel cell FC has decreased compared to normal conditions, repeat the processes in steps S22 to S29.

[0059] Furthermore, if the control unit Cf determines in step S24 that the pressure P has reached its maximum value three or more times, it may execute the processing from step S25 onward.

[0060] Figures 4 and 5 show the injection command, hydrogen gas flow rate, and hydrogen gas pressure in Example 1.

[0061] In the two-dimensional coordinates shown in Figures 4(a) and 5(a), the horizontal axis represents time, and the vertical axis represents voltage (level). The solid lines in Figures 4(a) and 5(a) represent injection commands.

[0062] Furthermore, in the two-dimensional coordinates shown in Figures 4(b) and 5(b), the horizontal axis represents time, and the vertical axis represents flow rate. The solid line in Figure 4(b) shows the actual flow rate of hydrogen gas supplied to the fuel cell FC under normal conditions (when there are no malfunctions in the injector INJ, ejector EJT, etc.). The solid line in Figure 5(b) shows the actual flow rate of hydrogen gas supplied to the fuel cell FC when there are malfunctions in the injector INJ, ejector EJT, etc. (for example, when the on-off valve of the injector INJ malfunctions, or when foreign matter is inside the ejector EJT, making it difficult for hydrogen gas to flow in the hydrogen gas flow path from the fuel tank HT to the fuel cell FC).

[0063] Furthermore, in the two-dimensional coordinates shown in Figures 4(c) and 5(c), the horizontal axis represents time, and the vertical axis represents pressure. In Figure 4(c), the solid line represents the pressure P measured by the pressure sensor Sp under normal conditions. In Figure 5(c), the solid line represents the pressure P measured by the pressure sensor Sp when a malfunction occurs in the injector INJ, ejector EJT, etc.

[0064] First, when the idle state begins, the control unit Cf switches the injection command from low level to high level at time t11 or time t21, as shown in Figure 4(a) or Figure 5(a). Then, as shown in Figure 4(b) or Figure 5(b), the actual flow rate of hydrogen gas supplied to the fuel cell FC increases from time t11 or time t21 onwards, and as shown in Figure 4(c) or Figure 5(c), the pressure P measured by the pressure sensor Sp increases from time t11 or time t21 onwards.

[0065] Next, if the idle state continues, the control unit Cf switches the injection command from high level to low level at time t12, a certain time α after time t11, as shown in Figure 4(a), or at time t22, a certain time α after time t21, as shown in Figure 5(a). Then, as shown in Figure 4(b) or Figure 5(b), the actual flow rate of hydrogen gas supplied to the fuel cell FC decreases from time t12' after time t12 or from time t22' after time t22, and as shown in Figure 4(c) or Figure 5(c), the pressure P measured by the pressure sensor Sp decreases from time t12' or from time t22'.

[0066] Next, if the idle state continues, the control unit Cf switches the injection command from low level to high level again at time t13 or t14, after a certain time β has elapsed since switching the injection command from high level to low level, as shown in Figure 4(a) or Figure 5(a). Then, as shown in Figure 4(b) or Figure 5(b), the actual flow rate of hydrogen gas supplied to the fuel cell FC increases from time t13 or time t23 onwards, and as shown in Figure 4(c) or Figure 5(c), the pressure P measured by the pressure sensor Sp increases from time t13 or time t23 onwards.

[0067] Then, if the idle state continues, the control unit Cf switches the injection command from high level to low level at time t14, a certain time α after time t13, or at time t24, a certain time α after time t23. As a result, as shown in Figure 4(b) or Figure 5(b), the actual flow rate of hydrogen gas supplied to the fuel cell FC decreases from time t14' after time t14 or from time t24' after time t24, and as shown in Figure 4(c) or Figure 5(c), the pressure P measured by the pressure sensor Sp decreases from time t14' or from time t24'.

[0068] Thus, in the control unit Cf of Example 1, when the idle state is maintained, the actual flow rate of hydrogen gas supplied to the fuel cell FC is repeatedly increased or decreased by repeatedly outputting injection commands, and the pressure P is repeatedly increased or decreased.

[0069] Furthermore, when a malfunction occurs in the injector (INJ) or ejector (EJT), the increase in the actual hydrogen gas flow rate from the time the injection command is stopped until the actual flow rate of hydrogen gas supplied to the fuel cell (FC) is at its highest is smaller than under normal conditions. Therefore, the increase in pressure P from the time the injection command is stopped until the pressure P is at its highest is also smaller than under normal conditions. Consequently, if the decrease in pressure P from the time the injection command is stopped until the pressure P is at its lowest is the same under normal conditions and when a malfunction occurs in the injector (INJ) or ejector (EJT), the difference between the maximum and minimum values ​​of pressure P obtained when a malfunction occurs in the injector (INJ) or ejector (EJT) is smaller than under normal conditions. In Example 1, this is used to detect whether or not the flow rate of hydrogen gas supplied to the fuel cell (FC) is decreasing.

[0070] Specifically, as shown in Figure 4(a), the control unit Cf of Embodiment 1 switches the injection command from high level to low level at time t12, and then, as shown in Figure 4(c), if it determines at time t12' that the pressure P measured by the pressure sensor Sp has reached its maximum value, it acquires the pressure P measured by the pressure sensor Sp at time t12' as the first maximum pressure Pmax. Furthermore, as shown in Figure 4(a), the control unit Cf of Embodiment 1 switches the injection command from high level to low level at time t14, and then, as shown in Figure 4(c), if it determines at time t14' that the pressure P measured by the pressure sensor Sp has reached its maximum value, it acquires the pressure P measured by the pressure sensor Sp at time t14' as the second maximum pressure Pmax. For example, if the control unit Cf of Embodiment 1 determines that the sign of the change in pressure P per unit time has changed from positive to negative at time t12' and time t14', it stores the pressure P measured by the pressure sensor Sp at time t12' as the first maximum pressure Pmax in the storage unit Str, and stores the pressure P measured by the pressure sensor Sp at time t14' as the second maximum pressure Pmax in the storage unit Str.

[0071] Next, when the control unit Cf of Example 1 determines that the pressure P has reached its maximum value twice, it selects the maximum pressure P (the pressure P acquired at time t12' in the example shown in Figure 4(c)) from among the pressures P stored in the memory unit Str during the period from time t12' to time t14' as the maximum pressure Pmax, and selects the minimum pressure P (the pressure P acquired at time t13 in the example shown in Figure 4(c)) as the minimum pressure Pmin.

[0072] Furthermore, the control unit Cf of Example 1 detects that the flow rate of hydrogen gas supplied to the fuel cell FC has not decreased if the difference ΔP1 between the maximum pressure Pmax and the minimum pressure Pmin is greater than the threshold ΔP1th.

[0073] On the other hand, as shown in Figure 5(a), the control unit Cf of Example 1 switches the injection command from high level to low level at time t22, and then, as shown in Figure 5(c), if it determines at time t22' that the pressure P measured by the pressure sensor Sp has reached its maximum value, it acquires the pressure P measured by the pressure sensor Sp at time t22' as the first maximum pressure Pmax. Also, as shown in Figure 5(a), the control unit Cf of Example 1 switches the injection command from high level to low level at time t24, and then, as shown in Figure 5(c), if it determines at time t24' that the pressure P measured by the pressure sensor Sp has reached its maximum value, it acquires the pressure P measured by the pressure sensor Sp at time t24' as the second maximum pressure Pmax. For example, if the control unit Cf of Embodiment 1 determines that the sign of the change in pressure P per unit time has changed from positive to negative at time t22' and time t24', it stores the pressure P measured by the pressure sensor Sp at time t22' as the first maximum pressure Pmax in the storage unit Str, and stores the pressure P measured by the pressure sensor Sp at time t24' as the second maximum pressure Pmax in the storage unit Str.

[0074] Next, when the control unit Cf of Embodiment 1 determines that the pressure P has reached its maximum value twice, it selects the first or second maximum pressure Pmax, and also selects the minimum pressure P (the pressure P obtained at time t23 in the example shown in Figure 5(c)) among the pressures P stored in the memory unit Str during the period from time t22' to time t24' as the minimum pressure Pmin.

[0075] Furthermore, the control unit Cf of Example 1 detects that the flow rate of hydrogen gas supplied to the fuel cell FC is decreasing when the difference ΔP1 between the maximum pressure Pmax and the minimum pressure Pmin is less than or equal to the threshold ΔP1th.

[0076] <Example 2> In the control unit Cf in Embodiment 2, when the fuel cell FC is in an idle state, if the difference ΔP2 between the maximum pressure Pmax among the pressures P measured by the pressure sensor Sp during the period from the cessation of the injection command output until a certain time t has elapsed, and the pressure Pt measured by the pressure sensor Sp at the time when a certain time t has elapsed from the cessation of the injection command output, is less than or equal to the threshold ΔPth2, then it is detected that the flow rate of hydrogen gas supplied to the fuel cell FC has decreased. The certain time t is a value determined in advance by experiment or simulation, and under normal circumstances, it is the time from the cessation of the injection command output until the flow rate of hydrogen gas supplied to the fuel cell FC falls below a predetermined value (for example, zero or approximately zero). Alternatively, the certain time t may be determined based on the design information of the ejector EJT or the variation in the time it takes for the flow rate of hydrogen gas supplied to the fuel cell FC to fall below a predetermined value from the cessation of the injection command output.

[0077] Figure 6 is a flowchart showing the operation of the control unit Cf in Example 2.

[0078] First, when the idle state begins (step S31: Yes), the control unit Cf switches the injection command from high level to low level (step S32: Yes), and then repeatedly acquires the pressure P measured by the pressure sensor Sp and stores it in the memory unit Str until a certain time t has elapsed (steps S33, S34: No).

[0079] Next, when a certain time t has elapsed (step S34: Yes), the control unit Cf acquires the pressure P measured by the pressure sensor Sp and stores the acquired pressure P as pressure Pt in the storage unit Str (step S35).

[0080] Next, the control unit Cf selects the maximum pressure Pmax from among the multiple pressures P stored in the memory unit Str (step S36), and calculates the difference ΔP2 between the maximum pressure Pmax and the pressure Pt (step S37).

[0081] Then, the control unit Cf detects that the flow rate of hydrogen gas supplied to the fuel cell FC has not decreased compared to normal conditions if the difference ΔP2 is greater than the threshold ΔPth2 (step S38: No), and detects that the flow rate of hydrogen gas supplied to the fuel cell FC has decreased compared to normal conditions if the difference ΔP2 is less than or equal to the threshold ΔPth2 (step S38: Yes).

[0082] The control unit Cf may, after detecting whether the flow rate of hydrogen gas supplied to the fuel cell FC has decreased compared to normal conditions, repeat the processes in steps S32 to S40.

[0083] Figures 7 and 8 show the injection command, hydrogen gas flow rate, and hydrogen gas pressure in Example 2.

[0084] In the two-dimensional coordinates shown in Figures 7(a) and 8(a), the horizontal axis represents time, and the vertical axis represents voltage (level). The solid lines in Figures 7(a) and 8(a) represent injection commands.

[0085] Furthermore, in the two-dimensional coordinates shown in Figures 7(b) and 8(b), the horizontal axis represents time, and the vertical axis represents flow rate. The solid line in Figure 7(b) shows the actual flow rate of hydrogen gas supplied to the fuel cell (FC) under normal conditions, while the solid line in Figure 8(b) shows the actual flow rate of hydrogen gas supplied to the fuel cell (FC) when a malfunction occurs in the injector (INJ), ejector (EJT), etc.

[0086] Furthermore, in the two-dimensional coordinates shown in Figures 7(c) and 8(c), the horizontal axis represents time, and the vertical axis represents pressure. In Figure 7(c), the solid line represents the pressure P measured by the pressure sensor Sp under normal conditions, while in Figure 8(c), the solid line represents the pressure P measured by the pressure sensor Sp when a malfunction occurs in the injector INJ, ejector EJT, etc.

[0087] In Example 2, the changes in hydrogen gas flow rate and pressure P in response to changes in the injection command level are the same as in Example 1.

[0088] First, when the idle state begins, the control unit Cf switches the injection command from low level to high level at time t31 or time t41, as shown in Figure 7(a) or Figure 8(a). Then, as shown in Figure 7(b) or Figure 8(b), the actual flow rate of hydrogen gas supplied to the fuel cell FC increases from time t31 or time t41 onwards, and as shown in Figure 7(c) or Figure 8(c), the pressure P measured by the pressure sensor Sp increases from time t31 or time t41 onwards.

[0089] Next, if the idle state continues, the control unit Cf switches the injection command from high level to low level at time t32, a certain time α after time t31, as shown in Figure 7(a), or at time t42, a certain time α after time t41, as shown in Figure 8(a). Then, as shown in Figure 7(b) or Figure 8(b), the actual flow rate of hydrogen gas supplied to the fuel cell FC decreases from time t32' after time t32 or from time t42' after time t42, and as shown in Figure 7(c) or Figure 8(c), the pressure P measured by the pressure sensor Sp gradually decreases from time t32' or from time t42'.

[0090] Next, if the idle state continues, the control unit Cf switches the injection command from low level to high level again at time t33 or t34, after a certain time β has elapsed since switching the injection command from high level to low level, as shown in Figure 7(a) or Figure 8(a). Then, as shown in Figure 7(b) or Figure 8(b), the actual flow rate of hydrogen gas supplied to the fuel cell FC increases from time t33 or time t43 onwards, and as shown in Figure 7(c) or Figure 8(c), the pressure P measured by the pressure sensor Sp increases from time t33 or time t43 onwards.

[0091] Then, if the idle state continues, the control unit Cf switches the injection command from high level to low level at time t34, a certain time α after time t33, or at time t44, a certain time α after time t43. As a result, as shown in Figure 7(b) or Figure 8(b), the actual flow rate of hydrogen gas supplied to the fuel cell FC decreases from time t34' after time t34 or from time t44' after time t44, and as shown in Figure 7(c) or Figure 8(c), the pressure P measured by the pressure sensor Sp gradually decreases from time t34' or from time t44'.

[0092] Thus, in the control unit Cf of Example 2, similar to the control unit Cf of Example 1, when the idle state is maintained, the actual flow rate of hydrogen gas supplied to the fuel cell FC is repeatedly increased or decreased by repeatedly outputting injection commands, and the pressure P is repeatedly increased or decreased.

[0093] Furthermore, when a malfunction occurs in the injector (INJ) or ejector (EJT), the increase in the actual hydrogen gas flow rate from the time the injection command is stopped until the actual flow rate of hydrogen gas supplied to the fuel cell (FC) reaches its maximum is smaller than under normal circumstances. Therefore, the increase in pressure P from the time the injection command is stopped until the pressure P reaches its maximum is also smaller than under normal circumstances. Consequently, if the decrease in pressure P during the period from the time the injection command is stopped until a certain time t has elapsed is the same under normal circumstances as when a malfunction occurs in the injector (INJ) or ejector (EJT), the difference between the maximum pressure P obtained when a malfunction occurs in the injector (INJ) or ejector (EJT) and the pressure P at the time a certain time t has elapsed since the injection command was stopped will be smaller than under normal circumstances. In Example 2, this is used to detect whether or not the flow rate of hydrogen gas supplied to the fuel cell (FC) is decreasing.

[0094] In other words, as shown in Figures 7(b) and 7(c), the control unit Cf of Embodiment 2 acquires the pressure P measured by the pressure sensor Sp as pressure Pt at time t32', which is a certain time t after time t32. Furthermore, as shown in Figure 7(c), the control unit Cf of Embodiment 2 selects the largest pressure P among the pressures P stored in the memory unit Str during the period from time t32 to time t32' as the maximum pressure Pmax.

[0095] Then, the control unit Cf in Example 2 calculates the difference ΔP2 between the maximum pressure Pmax and the pressure Pt, and if the calculated difference ΔP2 is greater than the threshold ΔP2th, it detects that the flow rate of hydrogen gas supplied to the fuel cell FC has not decreased.

[0096] On the other hand, as shown in Figures 8(b) and 8(c), the control unit Cf of Embodiment 2 acquires the pressure P measured by the pressure sensor Sp as pressure Pt at time t42', which is a certain time t after time t42. Furthermore, as shown in Figure 8(c), the control unit Cf of Embodiment 2 selects the largest pressure P among the pressures P stored in the memory unit Str during the period from time t42 to time t42' as the maximum pressure Pmax.

[0097] Then, the control unit Cf in Example 2 calculates the difference ΔP2 between the maximum pressure Pmax and the pressure Pt, and if the calculated difference ΔP2 is less than or equal to the threshold ΔP2th, it detects that the flow rate of hydrogen gas supplied to the fuel cell FC has decreased.

[0098] <Modified Example 2> In the modified example of Embodiment 2, the control unit Cf detects that the flow rate of hydrogen gas supplied to the fuel cell FC has decreased if the difference ΔP2 between the maximum pressure Pmax among the pressures measured by the pressure sensor Sp after the output of the injection command has stopped and the pressure Pt measured by the pressure sensor Sp at the timing when the rate of change per unit time of the pressure P measured by the pressure sensor Sp changes is less than or equal to the threshold ΔP2th.

[0099] Figure 9 is a flowchart showing the operation of the control unit Cf in a modified example of Example 2.

[0100] First, when the idle state begins (step S41: Yes), the control unit Cf switches the injection command from high level to low level (step S42: Yes), and then repeatedly acquires the pressure P measured by the pressure sensor Sp and stores it in the memory unit Str until the rate of change of pressure P per unit time changes (steps S43, S44: No).

[0101] Next, when the rate of change of pressure P per unit time changes (step S44: Yes), the control unit Cf acquires the pressure P measured by the pressure sensor Sp at the timing when the rate of change of pressure P per unit time changes, and stores the acquired pressure P as pressure Pt in the storage unit Str (step S45).

[0102] Next, the control unit Cf selects the maximum pressure Pmax from among the pressures P stored in the memory unit Str (step S46), and calculates the difference ΔP2 between the maximum pressure Pmax and the pressure Pt (step S47).

[0103] Then, the control unit Cf detects that the flow rate of hydrogen gas supplied to the fuel cell FC has not decreased compared to normal conditions if the difference ΔP2 is greater than the threshold ΔPth2 (step S48: No), and detects that the flow rate of hydrogen gas supplied to the fuel cell FC has decreased compared to normal conditions if the difference ΔP2 is less than or equal to the threshold ΔPth2 (step S48: Yes).

[0104] The control unit Cf may, after detecting whether the flow rate of hydrogen gas supplied to the fuel cell FC has decreased compared to normal conditions, repeat the processes in steps S42 to S50.

[0105] In the modified control unit Cf of Example 2, similar to the control unit Cf of Example 1 and Example 2, when the fuel cell FC is in an idle state, the actual flow rate of hydrogen gas supplied to the fuel cell FC is repeatedly increased or decreased by repeatedly outputting injection commands, thereby repeatedly increasing or decreasing the pressure P.

[0106] Furthermore, when a malfunction occurs in the injector INJ or ejector EJT, the increase in the actual hydrogen gas flow rate from the time the injection command is stopped until the actual flow rate of hydrogen gas supplied to the fuel cell FC is at its highest is smaller than under normal circumstances. Therefore, the increase in pressure P from the time the injection command is stopped until the pressure P is at its highest is also smaller than under normal circumstances. In addition, if the period from the time the injection command is stopped until the rate of change of pressure P per unit time (for example, the slope of pressure P between time t32 and time t32' shown in Figure 7(c)) changes is the same as the period from the time the injection command is stopped until the actual flow rate of hydrogen gas is at its lowest (a certain time t), then the pressure P acquired at the timing when the rate of change of pressure P per unit time changes will be the same as the pressure Pt acquired after a certain time t has elapsed from the time the injection command is stopped. In the modified example of Embodiment 2, this is used to detect whether or not the flow rate of hydrogen gas supplied to the fuel cell FC is decreasing.

[0107] In other words, as shown in Figures 7(b) and 7(c), the control unit Cf in the modified example of Embodiment 2 acquires the pressure P measured by the pressure sensor Sp as pressure Pt at time t32', when the rate of change of pressure P per unit time changes after time t32. Furthermore, as shown in Figure 7(c), the control unit Cf in the modified example of Embodiment 2 selects the largest pressure P among the pressures P stored in the memory unit Str during the period from time t32 to time t32' as the maximum pressure Pmax.

[0108] In the modified example of Embodiment 2, the control unit Cf calculates the difference ΔP2 between the maximum pressure Pmax and the pressure Pt, and if the calculated difference ΔP2 is greater than the threshold ΔP2th, it detects that the flow rate of hydrogen gas supplied to the fuel cell FC has not decreased.

[0109] On the other hand, in the modified example of Embodiment 2, as shown in Figures 8(b) and 8(c), the control unit Cf acquires the pressure P measured by the pressure sensor Sp as pressure Pt at time t42', when the rate of change of pressure P per unit time changes after time t42. Furthermore, as shown in Figure 8(c), the control unit Cf in the modified example of Embodiment 2 selects the largest pressure P among the pressures P stored in the memory unit Str during the period from time t42 to time t42' as the maximum pressure Pmax.

[0110] In the modified example of Embodiment 2, the control unit Cf calculates the difference ΔP2 between the maximum pressure Pmax and the pressure Pt, and detects that the flow rate of hydrogen gas supplied to the fuel cell FC has decreased if the calculated difference ΔP2 is less than or equal to the threshold ΔP2th.

[0111] In the fuel cell system FCS of this embodiment, if the difference between the pressures P measured by the pressure sensor Sp at two different timings after the output of the injection command is stopped is below a threshold, the system is configured to detect that the flow rate of hydrogen gas supplied to the fuel cell FC has decreased.

[0112] Thus, by employing an ejector (EJT) instead of a pump to resupply hydrogen gas emitted from the fuel cell (FC) back into the fuel cell (FC), there is no need for an inverter or other components to drive the electric motor in the pump, thus reducing the number of parts in the fuel cell system (FCS). This reduces the manufacturing cost of the fuel cell system (FCS).

[0113] Furthermore, for example, when the flow rate of hydrogen gas supplied to the fuel cell (FC) decreases, by setting the maximum value of the difference between each pressure P measured by the pressure sensor Sp at the two timings mentioned above as a threshold, it is possible to detect that the flow rate of hydrogen gas supplied to the fuel cell (FC) is decreasing if the difference between each pressure P measured by the pressure sensor Sp at the two timings is less than or equal to the threshold.

[0114] Furthermore, in the fuel cell system FCS of this embodiment, the system is configured to detect whether or not the hydrogen gas flow rate is decreasing when the output current of the fuel cell FC is relatively small during idle conditions. This allows for accurate measurement of the pressure P, thereby improving the accuracy of detecting whether or not the hydrogen gas flow rate is decreasing.

[0115] It should be noted that the present invention is not limited to the embodiments described above, and various improvements and modifications are possible without departing from the spirit of the invention.

[0116] <Example 1> In the fuel cell system FCS of the above embodiment, the system is configured to detect whether the hydrogen gas flow rate has decreased when the fuel cell FC is in an idle state. However, it may also be configured to detect whether the hydrogen gas flow rate has decreased when the power generation of the fuel cell FC is being controlled.

[0117] Generally, as the output current of the fuel cell (FC) increases, the amount of hydrogen gas consumed by the fuel cell increases, and therefore the pressure P measured by the pressure sensor Sp decreases. In other words, as the output current of the fuel cell (FC) increases, the rate of change (slope) of pressure P per unit time, as shown in Figures 4(c), 5(c), 7(c), or 8(c), becomes smaller.

[0118] Therefore, when the control unit Cf is controlling the power generation of the fuel cell FC, it may correct each pressure P stored in the memory unit Str so that the rate of change (slope) of each pressure P stored in the memory unit Str increases as the output current of the fuel cell FC increases. For example, the amount of hydrogen gas consumed per unit time corresponding to the increase in the output current of the fuel cell FC may be determined, the amount of pressure P decrease corresponding to the determined amount of hydrogen gas consumed per unit time may be determined, and the determined amount of pressure P decrease may be used as a correction value to be added to each pressure P stored in the memory unit Str.

[0119] This allows for accurate detection of whether the hydrogen gas flow rate is decreasing due to pressure P, without being affected by fluctuations in the output current of the fuel cell (FC), thereby reducing the likelihood of false detections regarding whether the hydrogen gas flow rate is decreasing.

[0120] <Modification 2> For example, under normal conditions, as shown in Figure 4(c) or Figure 7(c), the rate of change of pressure P per unit time changes between the time the output of an injection command stops and the time the next injection command is output. On the other hand, when a malfunction occurs in the injector INJ or ejector EJT, as shown in Figure 5(c) or Figure 8(c), the rate of change of pressure P per unit time does not change, or hardly changes, between the time the output of an injection command stops and the time the next injection command is output. Using this, the control unit Cf in change example 2 detects whether or not the flow rate of hydrogen gas supplied to the fuel cell FC has decreased.

[0121] In other words, in Change Example 2, if the rate of change per unit time of pressure P measured by the pressure sensor Sp changes between the time the injection command is stopped and the next injection command is issued, the control unit Cf detects that the flow rate of hydrogen gas supplied to the fuel cell FC has not decreased. On the other hand, in Change Example 2, if the rate of change per unit time of pressure P measured by the pressure sensor Sp does not change between the time the injection command is stopped and the next injection command is issued, the control unit Cf detects that the flow rate of hydrogen gas supplied to the fuel cell FC has decreased.

[0122] Even with this configuration, there is no need to include an inverter or other components to drive the electric motor inside the pump, thus reducing the number of parts in the fuel cell system (FCS) and lowering the manufacturing cost of the fuel cell system (FCS). [Explanation of symbols]

[0123] FCS Fuel Cell System Lo load FC fuel cell HT fuel tank INJ Injector EJT Ejector GLS gas liquid separator EDV Exhaust Drain Valve ACP Air Compressor ARV Air Pressure Regulating Valve DIL Diluent R Radiator WP Water Pump CNV DC-DC converter B Energy storage device sp pressure sensor Str storage Cf, Cs control unit

Claims

1. Fuel cells and An injector that sprays hydrogen gas, An ejector that supplies hydrogen gas injected from the injector and hydrogen gas discharged from the fuel cell to the fuel cell, A pressure sensor for measuring the pressure of hydrogen gas supplied to the fuel cell, A control unit that outputs an injection command to the injector, thereby causing the injector to inject hydrogen gas into the ejector, Equipped with, The control unit detects that the flow rate of hydrogen gas supplied to the fuel cell has decreased if the difference between the pressures measured by the pressure sensor at two different timings after the output of the injection command is stopped is below a threshold. Fuel cell system.

2. A fuel cell system according to claim 1, The control unit detects that the flow rate of hydrogen gas supplied to the fuel cell is decreasing if the difference between the maximum and minimum values ​​of the pressure measured by the pressure sensor during the period from the time when the pressure measured by the pressure sensor is at its maximum to the time when it is at its next maximum is less than or equal to the threshold. Fuel cell system.

3. A fuel cell system according to claim 1, If the difference between the maximum pressure measured by the pressure sensor during the period from the cessation of the output of the injection command until a certain period of time has elapsed, and the pressure measured by the pressure sensor at the time when the cessation of the output of the injection command has elapsed, is less than or equal to the threshold, then it is detected that the flow rate of hydrogen gas supplied to the fuel cell has decreased. Fuel cell system.

4. A fuel cell system according to claim 3, The aforementioned fixed time is the time from the cessation of the injection command output until the amount of hydrogen gas supplied to the fuel cell falls below a predetermined value, provided that the flow rate of hydrogen gas supplied to the fuel cell has not decreased. Fuel cell system.

5. A fuel cell system according to claim 3, The aforementioned fixed time is determined based on the design information of the ejector and the variation in the time from the cessation of the injection command output until the amount of hydrogen gas supplied to the fuel cell falls below a predetermined value. Fuel cell system.

6. A fuel cell system according to claim 1, The control unit detects that the flow rate of hydrogen gas supplied to the fuel cell has decreased if the difference between the maximum pressure among the pressures measured by the pressure sensor after the output of the injection command has stopped and the pressure measured by the pressure sensor at the time when the rate of change per unit time of the pressure measured by the pressure sensor changes is less than or equal to the threshold. Fuel cell system.

7. A fuel cell system according to claim 1, The control unit increases the rate of change per unit time of the pressure measured by the pressure sensor after the output of the injection command is stopped, as the output current of the fuel cell increases. Fuel cell system.

8. A fuel cell system according to claim 1, It does not include an inverter for driving the electric motor in the pump that circulates the hydrogen gas discharged from the fuel cell back into the fuel cell. Fuel cell system.

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