Method for controlling a fuel cell system

Abstract

To provide a control method for a fuel cell system, the method enabling determination whether or not a detector functions normally to be made.SOLUTION: A control method for a fuel cell system 10 includes detector value determination processing, hydrogen concentration adjustment processing, and determination processing. In the detector value determination processing, whether or not a detector value is smaller than a threshold for a detector is determined. In the hydrogen concentration adjustment processing, following the detector value determination processing determining that the detector value is smaller than the threshold for the detector, a fuel cell unit 11 is controlled in such a way that a concentration of hydrogen gas around the fuel cell unit 11 is higher than that at the time of execution of the detector value determination processing and is adjusted to a concentration after adjustment that is equal to or greater than the threshold for the detector, at the time of next power generation of a fuel cell stack 13 following stop of power generation by the fuel cell stack 13. In the determination processing, whether or not a detector 31 functions normally is determined in a state in which a concentration of hydrogen gas discharged from the fuel cell stack 13 is adjusted to the concentration after adjustment.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for controlling a fuel cell system. [Background technology]

[0002] It is known that in a fuel cell unit that includes a fuel cell, hydrogen gas contained in the fuel gas may be emitted, albeit in small amounts, due to permeation or leakage from each component of the fuel cell unit. For example, Patent Document 1 discloses a hydrogen detection system that detects hydrogen gas leakage.

[0003] The hydrogen detection system disclosed in Patent Document 1 compares the detection value from a hydrogen sensor installed in a fuel cell vehicle with a threshold value to detect hydrogen leaks from the fuel cell stack or hydrogen tank and notify the driver, etc. The hydrogen detection system also uses different threshold values ​​for normal hydrogen leak detection and hydrogen sensor inspection. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4277925 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the hydrogen detection system of Patent Document 1, if the hydrogen sensor does not function properly, it becomes impossible to make a judgment based on the detection value of the hydrogen sensor. As a result, it becomes impossible to detect permeation or leakage of hydrogen gas. For this reason, it is necessary to accurately judge whether the hydrogen sensor is functioning properly. [Means for solving the problem]

[0006] A control method for a fuel cell system for solving the above problems is a control method for a fuel cell system including a fuel cell unit that includes a fuel cell that generates electricity when supplied with a fuel gas containing hydrogen gas and an oxidant gas, and that discharges an exhaust gas containing the hydrogen gas, a detector that detects the concentration of the hydrogen gas around the fuel cell unit as a detector value, and a control device, the control method being executed by the control device, and the control device includes a detector value determination process that, after the fuel cell unit is started, determines whether the detector value is less than a detector threshold value for determining that the detector is abnormal. a hydrogen concentration adjustment process for controlling the fuel cell unit so that the concentration of hydrogen gas around the fuel cell unit is adjusted to a post-adjustment concentration higher than that at the time of execution of the detector value determination process and equal to or higher than the detector threshold at the next power generation by the fuel cell following the stopping of power generation by the fuel cell after the detector value determination process determines that the detector value is less than the detector threshold; and a judgment process for determining whether the detector is functioning normally when the concentration of hydrogen gas around the fuel cell unit has been adjusted to the post-adjustment concentration.

[0007] According to this, before the hydrogen concentration adjustment process is performed, the hydrogen gas concentration around the fuel cell unit is lower than the adjusted concentration, and in this case, the detector value may fall below the detector threshold value even though the detector is functioning normally.

[0008] Therefore, when the detector value determination process determines that the detector value is less than the detector threshold, the control device executes the hydrogen concentration adjustment process. Therefore, the determination process after the hydrogen concentration adjustment process is executed is executed in a state where the concentration of hydrogen gas around the fuel cell unit is higher than before the hydrogen concentration adjustment process. As a result, if the detector is functioning normally, a detector value is more likely to be obtained, and if the detector is abnormal, an abnormal detector value is more likely to be obtained. Therefore, by executing the hydrogen concentration adjustment process, it is possible to prevent the detector value from falling below the detector threshold even when the detector is functioning normally. As a result, it is possible to prevent the detector from being determined to be abnormal even when the detector is functioning normally.

[0009] Regarding a control method for a fuel cell system, the fuel cell unit includes an injector that supplies hydrogen gas to the fuel cell, an anode-side on-off valve that opens and closes an anode off-gas exhaust path connected to the anode of the fuel cell, and a cathode-side on-off valve that opens and closes a cathode off-gas exhaust path connected to the cathode of the fuel cell, and the hydrogen concentration adjustment process is a process that closes the cathode-side on-off valve and the anode-side on-off valve after power generation by the fuel cell unit is stopped, and drives the injector to increase the amount of hydrogen gas supplied from the injector to the fuel cell, and the determination process may be performed the next time the fuel cell unit is started up following the stop of power generation by the fuel cell unit.

[0010] According to this, when the hydrogen concentration adjustment process is performed, the amount of hydrogen gas remaining in the fuel cell increases after power generation by the fuel cell unit is stopped. Then, when the fuel cell unit is started, the amount of hydrogen gas discharged from the fuel cell increases to adjust the concentration after adjustment. The hydrogen concentration adjustment process is a process that increases the amount of hydrogen gas supplied from the injector during the purge process that is performed after power generation by the fuel cell unit is stopped. In other words, the hydrogen concentration adjustment process simply increases the amount of hydrogen gas supplied during the purge process that is already being performed. Therefore, according to this control method for a fuel cell system, it is possible to determine whether the detector is functioning normally without adding any new processes.

[0011] Regarding a control method for a fuel cell system, the fuel cell system is provided with a blower that generates an air flow around the fuel cell unit, and the blower can be set to either a first mode for generating the air flow around the fuel cell unit, or a second mode in which the air flow is less than in the first mode or is zero, and the control method for the fuel cell system includes a setting process for setting the blower to the second mode after the detector value determination process determines that the detector value is less than the detector threshold value and before the determination process, and the determination process may be performed under conditions in which the blower is in the second mode.

[0012] According to this, when the blower is in the second mode, the exhaust gas is less likely to be swept away by the blower. In other words, the hydrogen gas adjusted to the adjusted concentration is less likely to be swept away by the blower. Therefore, the determination process is more likely to be performed when the hydrogen gas concentration around the fuel cell unit is the adjusted concentration. As a result, the exhaust gas is more likely to come into contact with the area around the detector, so if the detector is functioning normally, a normal detector value will be obtained, and if the detector is abnormal, an abnormal detector value will be obtained. [Effects of the Invention]

[0013] According to the present invention, it is possible to accurately determine whether a detector functions normally. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a side view showing a forklift. [Figure 2] FIG. 1 is a schematic diagram showing a fuel cell system. [Figure 3] FIG. 2 is a perspective view showing the fuel cell system from the housing side. [Figure 4] 10 is a flowchart showing a detector determination process. [Figure 5] FIG. 2 is a schematic diagram showing a fuel cell system in a first mode. [Figure 6] FIG. 4 is a schematic diagram showing a fuel cell system in a second mode. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of a control method for a fuel cell system will be described below with reference to FIGS. <Fuel cell system> As shown in Fig. 1, the fuel cell system 10 is mounted on a forklift F. The fuel cell system 10 may be applied to industrial vehicles other than the forklift F, and may also be applied to vehicles other than industrial vehicles, such as passenger cars, buses, and trucks.

[0016] 2, the fuel cell system 10 includes a fuel cell unit 11 and a control device 51. The fuel cell system 10 may further include a housing 12 that houses the fuel cell unit 11 and an alarm 52 that notifies of an abnormality in the detector 31.

[0017] <Forklift> As shown in Fig. 1, the forklift F has a seat Fa. The forklift F has a storage compartment Fb below the seat Fa. The storage compartment Fb contains a fuel cell system 10. The forklift F operates using power generated by a fuel cell unit 11 of the fuel cell system 10.

[0018] <Case> 2 and 3, the housing 12 includes a bottom plate 12a, a top plate 12b, a peripheral wall 12c, and a ventilation hole 12f. The peripheral wall 12c is cylindrical and connects the peripheral edge of the bottom plate 12a with the peripheral edge of the top plate 12b. Assuming that the housing 12 is placed on a horizontal plane, the vertical direction is indicated by the Z axis, and directions along the horizontal plane are indicated by the X axis and the Y axis. The X axis, Y axis, and Z axis are perpendicular to one another.

[0019] In the housing 12, the bottom plate 12a and the top plate 12b face each other in the direction extending along the Z axis. The peripheral wall 12c has a first side wall 12d and a second side wall 12e that face each other in the direction extending along the X axis. A plurality of ventilation holes 12f are arranged in the first side wall 12d.

[0020] <Fuel cell unit> 2, the fuel cell unit 11 includes a fuel cell stack 13, a hydrogen tank 14, an air compressor 15, a diluter 16, and a gas-liquid separator 26. The fuel cell unit 11 also includes a hydrogen gas supply channel 17, an air supply channel 18, an anode off-gas discharge channel 19a, a cathode off-gas discharge channel 19b, a hydrogen gas circulation channel 19c, and a gas discharge channel 20. The fuel cell unit 11 also includes a heat exchanger 21, a radiator fan 21a, a circulation channel 22, accessories 23, and an accessory fan 24.

[0021] The fuel cell stack 13 is a fuel cell formed by stacking a plurality of fuel cell cells. The fuel cell cells are solid molecular fuel cells. The fuel cell stack 13 generates electricity when supplied with a fuel gas containing hydrogen gas and an oxidant gas. The oxidant gas is air.

[0022] The hydrogen tank 14 stores hydrogen gas under high pressure. The hydrogen gas supply path 17 connects the hydrogen tank 14 to an anode (not shown) of the fuel cell stack 13. A pressure adjustment valve 17a is provided in the hydrogen gas supply path 17. The pressure adjustment valve 17a reduces the pressure of the hydrogen gas supplied from the hydrogen tank 14. The hydrogen gas supply path 17 also includes an injector 17b. Therefore, the fuel cell unit 11 includes the injector 17b that supplies hydrogen gas to the fuel cell stack 13. The injector 17b supplies the hydrogen gas, the pressure of which has been reduced by the pressure adjustment valve 17a, to the anode of the fuel cell stack 13. More specifically, the injector 17b injects the hydrogen gas toward the fuel cell stack 13. The injector 17b adjusts the amount of hydrogen gas supplied to the anode of the fuel cell stack 13. The injector 17b is signal-connected to the control device 51. The injector 17b is controlled by the control device 51.

[0023] The air compressor 15 compresses air and supplies it to an air supply path 18. The air supply path 18 connects the air compressor 15 to a cathode (not shown) of the fuel cell stack 13. Air discharged from the air compressor 15 flows through the air supply path 18.

[0024] The anode off-gas discharge path 19a connects the anode (not shown) of the fuel cell stack 13 to the diluter 16. The anode off-gas flows through the anode off-gas discharge path 19a from the fuel cell stack 13 toward the diluter 16. The anode off-gas mainly contains unreacted hydrogen gas in the fuel cell stack 13 and water produced when hydrogen reacts with oxygen.

[0025] The gas-liquid separator 26 is provided in the anode off-gas discharge path 19a. The gas-liquid separator 26 separates water from the anode off-gas. The anode off-gas from which the water has been separated flows through the anode off-gas discharge path 19a toward the diluter 16. The anode off-gas that has flowed through the anode off-gas discharge path 19a is supplied to the diluter 16.

[0026] An anode-side on-off valve 19d is provided downstream of the gas-liquid separator 26 and upstream of the diluter 16 in the flow direction of the anode off-gas from the fuel cell stack 13 toward the diluter 16. The anode-side on-off valve 19d opens and closes an anode off-gas discharge path 19a connected to the anode of the fuel cell stack 13. The anode-side on-off valve 19d is signal-connected to the control device 51. The opening and closing of the anode-side on-off valve 19d is controlled by the control device 51.

[0027] The cathode offgas discharge path 19b connects the cathode (not shown) of the fuel cell stack 13 to the diluter 16. Cathode offgas flows through the cathode offgas discharge path 19b from the fuel cell stack 13 toward the diluter 16. The cathode offgas mainly contains air containing oxygen that has not reacted in the fuel cell stack 13, and water that is generated when hydrogen and oxygen react. A cathode side on-off valve 18a is provided in the cathode offgas discharge path 19b. The cathode side on-off valve 18a opens and closes the cathode offgas discharge path 19b, which is connected to the cathode of the fuel cell stack 13. The cathode side on-off valve 18a is signal-connected to the control device 51. The opening and closing of the cathode side on-off valve 18a is controlled by the control device 51. Therefore, the fuel cell unit 11 is equipped with an anode side on-off valve 19d and a cathode side on-off valve 18a.

[0028] The anode off-gas discharged from the gas-liquid separator 26 and the cathode off-gas discharged from the fuel cell stack 13 flow into the diluter 16. The diluter 16 dilutes the anode off-gas that has flowed in with the cathode off-gas. The diluter 16 reduces the concentration of hydrogen gas in the anode off-gas. The diluter 16 discharges the exhaust gas with the reduced hydrogen gas concentration into the gas discharge path 20. The exhaust gas is discharged from the gas discharge path 20. Therefore, the fuel cell unit 11 discharges exhaust gas containing hydrogen gas. The exhaust gas is discharged into the interior of the housing 12.

[0029] The hydrogen gas circulation path 19c connects the gas-liquid separator 26 and the hydrogen gas supply path 17. The hydrogen gas circulation path 19c is connected downstream of the injector 17b in the flow direction of hydrogen gas from the hydrogen tank 14 toward the fuel cell stack 13. The anode off-gas discharged from the gas-liquid separator 26 flows through the hydrogen gas circulation path 19c toward the hydrogen gas supply path 17.

[0030] The heat exchanger 21 exchanges heat between the outside air and the heat exchange medium. The radiator fan 21a blows air toward the heat exchanger 21. The circulation flow path 22 circulates the heat exchange medium between the fuel cell stack 13 and the heat exchanger 21. Cooling water is used as the heat exchange medium, but other media may also be used.

[0031] The heat exchanger 21 is disposed on the second side wall 12e of the housing 12. The heat exchanger 21 is disposed to the side of the fuel cell stack 13. The radiator fan 21a, which is an example of an air blower, is rotated by a motor M. The drive of the motor M of the radiator fan 21a is controlled by a control device 51.

[0032] The circulation flow path 22 has an outward flow path 22a, a return flow path 22b, a pump (not shown), and a heat exchange flow path. The outward flow path 22a is a flow path for flowing cooling water from the heat exchanger 21 toward the fuel cell stack 13. The return flow path 22b is a flow path for flowing cooling water from the fuel cell stack 13 toward the heat exchanger 21. The pump circulates the cooling water through the circulation flow path 22. The heat exchange flow path (not shown) is routed within the fuel cell stack 13 and the heat exchanger 21.

[0033] The cooling water that flows through the outward path 22a into the heat exchange flow path in the fuel cell stack 13 absorbs heat generated in the fuel cell stack 13 and cools the fuel cell stack 13. The cooling water that flows through the return path 22b into the heat exchange flow path in the heat exchanger 21 exchanges heat with outside air and is cooled. As the radiator fan 21a rotates, air is blown toward the heat exchanger 21. The air blown by the radiator fan 21a improves the cooling efficiency of the cooling water in the heat exchange flow path in the heat exchanger 21.

[0034] Furthermore, as the radiator fan 21a rotates, air is drawn into the housing 12 from the outside through the vent 12f, as indicated by the arrow V in Fig. 5. Inside the housing 12, that is, around the fuel cell unit 11, an air flow W is generated that flows from the vent 12f toward the radiator fan 21a.

[0035] The radiator fan 21a is switchable between a first mode M1 and a second mode M2. The first mode M1 is a mode in which the radiator fan 21a rotates to cool the coolant. When the radiator fan 21a rotates in the first mode M1, the above-mentioned air flow W can be generated around the fuel cell unit 11. Therefore, the fuel cell system 10 is provided with the radiator fan 21a that generates the air flow W around the fuel cell unit 11. When the radiator fan 21a rotates in the first mode M1, the air flow W is generated around the fuel cell unit 11 so that air passes through the inside of the housing 12. The motor M rotates the radiator fan 21a. The rotation speed of the motor M is defined as the rotation speed of the radiator fan 21a. The rotation speed of the motor M in the first mode M1 is defined as a first operating amount of the radiator fan 21a.

[0036] The second mode M2 ​​is a mode in which a second operating amount is smaller than the first operating amount, or the operating amount is zero. In this embodiment, the second mode M2 ​​is a mode in which the operating amount is zero. Therefore, in the second mode M2, the radiator fan 21a does not rotate. In the second mode M2, no air flow W is formed around the fuel cell unit 11. Therefore, the radiator fan 21a can be in either the first mode M1 for generating the air flow W around the fuel cell unit 11, or the second mode M2 ​​in which the air flow W is zero.

[0037] An example of the auxiliary device 23 is a secondary battery. In order to prevent deterioration of the auxiliary device 23 due to high temperatures, it is necessary to prevent the auxiliary device 23 from being maintained in a high temperature state. In order to prevent deterioration of the auxiliary device 23, an operating temperature range is set for the auxiliary device 23.

[0038] When the fuel cell unit 11 is started, the auxiliary fan 24, which is an example of an air blower, rotates, generating an air flow W toward the auxiliary 23 inside the housing 12, as shown by the arrow W in Fig. 5. The direction of the air flow toward the auxiliary 23 is the same as or approximately the same as the direction of the air flow toward the heat exchanger 21 due to the rotation of the radiator fan 21a.

[0039] The auxiliary fan 24 has a fan motor 25. The auxiliary fan 24 can be switched between a first mode M1 and a second mode M2 ​​by controlling the fan motor 25. The first mode M1 is a mode in which the auxiliary fan 24 rotates to cool the auxiliary equipment 23. When the auxiliary fan 24 rotates in the first mode M1, an air flow W can be generated around the fuel cell unit 11. Therefore, the fuel cell system 10 is provided with the auxiliary fan 24 that generates the air flow W around the fuel cell unit 11. The rotation speed of the fan motor 25 is defined as the rotation speed of the auxiliary equipment fan 24. The rotation speed of the auxiliary equipment fan 24 in the first mode M1 is defined as a first operating amount of the auxiliary equipment fan 24.

[0040] The second mode M2 ​​is a mode in which a second operating amount is less than the first operating amount, or the operating amount is zero. In this embodiment, the second mode M2 ​​is a mode in which the operating amount is zero. Therefore, the auxiliary fan 24 does not rotate in the second mode M2. In the second mode M2, no air flow W is formed around the fuel cell unit 11. Therefore, the auxiliary fan 24 can be set to either the first mode M1 for generating an air flow W around the fuel cell unit 11, or the second mode M2 ​​in which the air flow W is zero.

[0041] <Detector> As shown in FIGS. 2 and 3, the fuel cell system 10 includes two detectors 31. The two detectors 31 are disposed on the top plate 12b of the housing 12. Each detector 31 includes a detection surface 31a for hydrogen gas. The detection surface 31a is exposed to the inside of the housing 12. One detector 31 is disposed closer to the first side wall 12d of the top plate 12b, and the other detector 31 is disposed closer to the second side wall 12e of the top plate 12b. The detectors 31 detect the concentration of hydrogen gas when the exhaust gas comes into contact with the detection surface 31a. In other words, the detector 31 detects the concentration of hydrogen gas around the fuel cell unit 11 as a detector value. The detector 31 detects the concentration of hydrogen gas that is emitted, even in small amounts, due to permeation and leakage from each component of the fuel cell unit 11.

[0042] The lower the concentration of hydrogen gas in the exhaust gas, the less likely it is that hydrogen gas will be detected by the detector 31. As a result, even if the detector 31 is functioning normally, the detector value is likely to be lower than the normal value.

[0043] On the other hand, the higher the concentration of hydrogen gas in the exhaust gas, the more likely it is that hydrogen gas will be detected by the detector 31. As a result, if the detector 31 is functioning normally, the detector value will be a normal value.

[0044] Furthermore, when the radiator fan 21a and the auxiliary fan 24 rotate in the first mode M1, the exhaust gas is swept away by the air blown from the radiator fan 21a and the auxiliary fan 24. This causes the exhaust gas to diffuse from the periphery of the detector 31, making it difficult for the hydrogen gas in the exhaust gas to come into contact with the detection surface 31a of the detector 31. As a result, the detector value is likely to be lower than the normal value even though the detector 31 is functioning normally.

[0045] On the other hand, in the second mode M2 ​​in which the radiator fan 21a and the auxiliary fan 24 do not rotate, no air flow W is generated around the fuel cell unit 11. As a result, the exhaust gas is less likely to be swept away by the blown air. Because the exhaust gas is relatively likely to come into contact with the area around the detector 31, the hydrogen gas in the exhaust gas is more likely to come into contact with the detection surface 31a of the detector 31. For this reason, in the second mode M2, if the detector 31 is functioning normally, the detector value will be normal.

[0046] <Control device> The control device 51 includes a processor 51a, a storage unit 51b, and a counter 51c. The processor 51a may be, for example, a central processing unit (CPU), a graphics processing unit (GPU), or a digital signal processor (DSP). The storage unit 51b includes a random access memory (RAM) and a read-only memory (ROM). The storage unit 51b stores program code or instructions configured to cause the processor 51a to execute processing. The storage unit 51b, i.e., the computer-readable medium, includes any available medium accessible by a general-purpose or special-purpose computer. The control device 51 may be configured with a hardware circuit such as an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA). The control device 51, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or an FPGA, or a combination thereof.

[0047] The control device 51 executes the purge process when the key of the forklift F is turned off. The key is turned off by an operator in order to stop the forklift F. When the key is turned off, the forklift F cannot travel. In other words, the state in which the forklift F is stopped is the key-off state. When the forklift F is stopped, power generation by the fuel cell stack 13 is stopped. In addition to when the key is turned off, power generation by the fuel cell stack 13 is stopped when the amount of power generation by the fuel cell stack 13 exceeds the amount of power generation command from the upper control device.

[0048] <Purge process> The control device 51 executes a purge process when power generation by the fuel cell stack 13 is stopped as a result of the key being turned off for the forklift F. The purge process is executed to suppress the diffusion of oxygen to the anode of each fuel cell while power generation by the fuel cell stack 13 is stopped. The purge process is a process of replacing the cathode of each fuel cell with hydrogen.

[0049] When the purge process is performed, the control device 51 closes the anode-side on-off valve 19d and the cathode-side on-off valve 18a, thereby restricting the discharge of anode off-gas and cathode off-gas from the fuel cell stack 13 and, ultimately, from each fuel cell unit.

[0050] Then, with the emission of anode offgas and cathode offgas from each fuel cell restricted, the control device 51 drives the injector 17b. This supplies hydrogen gas to the anode of each fuel cell. The amount of hydrogen gas supplied from the injector 17b is set to an amount that consumes all of the oxygen remaining in the fuel cell stack 13 after key-off. The amount of hydrogen gas supplied from the injector 17b during the purge process is determined based on the amount of power generated by the fuel cell stack 13 while the fuel cell system 10 is in operation. While the fuel cell system 10 is in operation, the control device 51 determines the amount of oxygen remaining in the fuel cell stack 13 based on the amount of power generated by the fuel cell stack 13, the amount of hydrogen gas supplied from the hydrogen tank 14, and the amount of air supplied from the air compressor 15. The control device 51 calculates the amount of hydrogen gas to be supplied to the fuel cell stack 13 from the amount of oxygen remaining in the fuel cell stack 13. The control device 51 controls the operation of the injector 17b to supply the calculated amount of hydrogen gas to the fuel cell stack 13. The injector 17 b pressurizes hydrogen gas and supplies it to the fuel cell stack 13 .

[0051] As a result, the oxygen remaining at the cathode of each fuel cell reacts with hydrogen, consuming the oxygen remaining at the cathode. The oxygen at the cathode of each fuel cell is then replaced with hydrogen. As a result, the diffusion of oxygen to the anode of each fuel cell is suppressed.

[0052] The purging process is performed with the anode-side on-off valve 19d and the cathode-side on-off valve 18a closed. Therefore, when the purging process is completed, each fuel cell is filled with hydrogen gas. Then, the more the amount of hydrogen gas supplied to each fuel cell from the injector 17b during the purging process is increased, the more hydrogen gas remains in each fuel cell after the purging process is completed.

[0053] <Detector judgment process> The control device 51 executes a process for determining whether the detector 31 functions normally. In the following description, the "process for determining whether the detector 31 functions normally" will be simply referred to as a "detector determination process."

[0054] If the detector 31 is functioning normally, the detector value will be a normal value. However, if the concentration of hydrogen gas around the fuel cell unit 11 is low, the detector value is likely to be lower than the normal value even if the detector 31 is functioning normally. If the detector value is less than a predetermined detector threshold value Tb, the detector 31 is deemed to be "abnormal." Therefore, the detector threshold value Tb is a threshold value for determining that the detector 31 is abnormal.

[0055] The storage unit 51b of the control device 51 stores program codes or instructions for executing a process for determining whether the detector 31 functions normally. The storage unit 51b of the control device 51 stores a detector threshold value Tb, a determination counter threshold value Ta, and a counter threshold value Tc, which are used when executing the detector determination process.

[0056] An example of the detector threshold value Tb is 100 ppm. If the detector 31 is actually abnormal, the detector value may become zero or an abnormally low value. Taking this into consideration, the detector threshold value Tb is set in advance through experiments. Note that the detector threshold value Tb is not limited to 100 ppm and may be changed depending on the performance of the detector 31 and the arrangement of components around the detector 31. The control device 51 then periodically performs a detector value determination process to determine whether the detector value is less than the detector threshold value Tb.

[0057] Here, the counter 51c will be described. The counter 51c increments the abnormality counter value every time a detector value less than the detector threshold value Tb is detected, that is, every time the detector value is determined to be less than the detector threshold value Tb. Specifically, the counter 51c increments the abnormality counter value by "1" every time the detector 31 is deemed to be abnormal.

[0058] The detector value determination process by the control device 51 is repeatedly performed at a predetermined control period. The control period is, for example, every few milliseconds. Therefore, the integrated value of the control period and the abnormality counter value is the total time during which the detector 31 is considered to be abnormal. The total time during which the detector 31 is considered to be abnormal refers to the total time during which the detector value remains below the detector threshold value Tb.

[0059] While the forklift F is in operation, the abnormality counter value is incremented by "1" each time the detector value falls below the detector threshold value Tb, that is, at each control cycle. When the abnormality counter value measured by the counter 51c reaches or exceeds a predetermined value, the total time during which the detector 31 has been considered abnormal reaches or exceeds the predetermined time. In this case, the control device 51 determines that the detector 31 is abnormal.

[0060] In the detector determination process, the counter threshold value Ta for determination is used to determine whether the detector 31 is abnormal. The counter threshold value Ta for determination is a threshold value for determining whether the detector 31 is abnormal.

[0061] The counter threshold for determination Ta is a threshold for the "total time considered to be abnormal." An example of the counter threshold for determination Ta is 200 hours. In the fuel cell system 10, it is rare that hydrogen gas does not come into contact with the detection surface 31a of the detector 31 for more than 200 hours. In other words, by the time 200 hours have passed, hydrogen gas will have come into contact with the detection surface 31a and the detector value will be detected.

[0062] Therefore, if the detector 31 is functioning normally, a detector value equal to or greater than the detector threshold value Tb will be detected within 200 hours. Therefore, if a detector value equal to or greater than the detector threshold value Tb is not detected within 200 hours, it can be said that the detector 31 is not functioning normally, that is, is abnormal.

[0063] Although the counter threshold value Ta for determination is set to 200 hours, the counter threshold value Ta for determination can be changed as appropriate. If it is desired to determine in a short time whether the detector 31 is functioning normally through the detector determination process, the counter threshold value Ta for determination may be set to be shorter than 200 hours. On the other hand, if it is desired to determine more accurately whether the detector 31 is functioning normally through the detector determination process, the counter threshold value Ta for determination may be set to be longer than 200 hours.

[0064] In order to determine that the detector 31 is abnormal, the detector value must be less than the detector threshold value Tb. However, in the fuel cell unit 11, for example, as the amount of power generation increases, the amount of hydrogen gas remaining in each fuel cell may decrease, resulting in a low concentration of hydrogen gas in the exhaust gas.

[0065] Due to a low hydrogen gas concentration, the detector value may remain below the detector threshold value Tb for a period of time equal to or longer than the determination counter threshold value Ta. In such cases, it is preferable to avoid determining that the detector 31 is abnormal even though it is actually normal. Therefore, in the detector determination process, the control device 51 executes a hydrogen concentration adjustment process to increase the concentration of hydrogen gas discharged from the fuel cell stack 13 in order to accurately determine whether the detector 31 is functioning normally before the abnormality counter value reaches the determination counter threshold value Ta.

[0066] <Hydrogen concentration adjustment treatment> The hydrogen concentration adjustment process is a process for adjusting the concentration of hydrogen gas during the next power generation by the fuel cell stack 13 following the halt of power generation by the fuel cell stack 13 after the detector value determination process determines that the detector value is less than the detector threshold value Tb. The hydrogen concentration adjustment process is a process for controlling the fuel cell unit 11 so that the concentration of hydrogen gas around the fuel cell unit 11 is adjusted to a post-adjustment concentration that is higher than when the detector value determination process was performed and is equal to or greater than the detector threshold value Tb.

[0067] The hydrogen concentration adjustment process is a process in which the control device 51 controls the injector 17b so that the amount of hydrogen gas supplied from the injector 17b to the fuel cell stack 13 during the purge process is increased compared to the normal purge process. Specifically, in the hydrogen concentration adjustment process, the control device 51 controls the injector 17b so that a larger amount of hydrogen gas is supplied to each fuel cell during the purge process than the amount of hydrogen gas calculated by the control device 51. When this hydrogen concentration adjustment process is performed, approximately 1.2 times more hydrogen gas is supplied to the fuel cell stack 13 than during the normal purge process. As a result, after the fuel cell unit 11 is started up, the concentration of hydrogen gas discharged from the fuel cell stack 13 is adjusted to a post-adjustment concentration that is higher than the concentration before the hydrogen concentration adjustment process was performed.

[0068] When the hydrogen concentration adjustment process is performed, a larger amount of hydrogen gas remains in each fuel cell compared to when a normal purge process is performed. Therefore, when the cathode-side on-off valve 18a and the anode-side on-off valve 19d are opened during startup of the fuel cell unit 11, a larger amount of hydrogen gas is discharged from the fuel cell stack 13 compared to after a normal purge process is performed. As a result, the concentration of hydrogen gas in the exhaust gas discharged from the gas discharge path 20 via the diluter 16 is higher than after a normal purge process is performed. Therefore, during power generation by the fuel cell stack 13 following startup of the fuel cell unit 11, the hydrogen gas concentration around the fuel cell unit 11 is adjusted to a post-adjustment concentration that is higher than when the detector value determination process was performed and is equal to or greater than the detector threshold value Tb.

[0069] <Settings process> The setting process is a process for making it easier for exhaust gas to come into contact with the detection surface 31a of the detector 31. In the setting process, the control device 51 switches the radiator fan 21a and the accessory fan 24 from the first mode M1 to the second mode M2.

[0070] <Alarm> The alarm 52 is a device for notifying the operator of the forklift F of an abnormality in the detector 31 when an abnormality in the detector 31 is confirmed. The alarm 52 is connected to the control device 51 by signal. There are no particular limitations on the type of alarm 52 as long as it can notify the operator of an abnormality in the detector 31. Examples of the alarm 52 include a buzzer, a display that can indicate an abnormality, an audio output device that indicates the abnormality by voice, and an indicator light that lights up or flashes when an abnormality occurs.

[0071] <Control method of fuel cell system> The detector determination process is repeatedly performed at a predetermined control period after the forklift F is started. "The forklift F is started" means that the forklift F is in a state where it can travel. The state where the forklift F is started is also called a key-on state. When the forklift F is started, the fuel cell system 10 is started. When the fuel cell system 10 is started, the control device 51 starts the fuel cell unit 11 to periodically open the anode side on-off valve 19d and keep the cathode side on-off valve 18a always open. The control device 51 also controls the injector 17b.

[0072] The hydrogen gas supplied from the hydrogen tank 14 is then pressure-regulated by the pressure regulation valve 17a and then supplied to the fuel cell stack 13 by the injector 17b. Air compressed by the air compressor 15 is supplied to the fuel cell stack 13 through the cathode-side on-off valve 18a. The fuel cell stack 13 then generates electricity.

[0073] The anode off-gas discharged from the fuel cell stack 13 is supplied to the gas-liquid separator 26. A portion of the anode off-gas from which water has been separated by the gas-liquid separator 26 is supplied to the hydrogen gas supply channel 17 via the hydrogen gas circulation channel 19c.

[0074] When the anode-side on-off valve 19d is periodically opened by the control device 51, anode off-gas is discharged from the fuel cell stack 13. The anode off-gas discharged from the fuel cell stack 13 is supplied to the diluter 16. In addition, the cathode off-gas discharged from the fuel cell stack 13 is supplied to the diluter 16. The diluter 16 dilutes the anode off-gas with the cathode off-gas and discharges it.

[0075] When the forklift F is stopped, the forklift F cannot travel. When the forklift F is stopped, the fuel cell unit 11 is stopped. When the fuel cell unit 11 is stopped, power generation by the fuel cell stack 13 is stopped. When power generation by the fuel cell stack 13 is stopped, the control device 51 executes a purge process.

[0076] When the forklift F is started as described above, the control device 51 starts the detector determination process. Furthermore, when the forklift F is started, the control device 51 rotates the radiator fan 21a and the accessory fan 24 in the first mode M1.

[0077] 5, air is sent from the radiator fan 21a toward the heat exchanger 21, and from the accessory fan 24 toward the accessory 23. As a result, an air flow W is generated around the fuel cell unit 11 inside the housing 12. Therefore, the exhaust gas discharged from the diluter 16 is pushed toward the heat exchanger 21 by the air flow W.

[0078] <Details of detector judgment process> 4, in step S1 of the detector determination process, the control device 51 determines whether each of the detector values ​​acquired from the two detectors 31 is less than the detector threshold value Tb. Therefore, step S1 is a detector value determination process that determines whether the detector value is less than the detector threshold value Tb. This step S1 is executed after the fuel cell unit 11 has been started up and in a state where the concentration of hydrogen gas around the fuel cell unit 11 is lower than the adjusted concentration.

[0079] In step S1, if both of the two detector values ​​are equal to or greater than the detector threshold value Tb (NO in step S1), the control device 51 proceeds to step S6. In step S6, the control device 51 resets the abnormality counter value of the counter 51c and proceeds to step S1. At this time, since the two detectors 31 detect values ​​greater than the detector threshold value Tb, the detectors 31 are functioning normally.

[0080] On the other hand, in step S1, if both of the acquired detector values ​​are less than the detector threshold value Tb (YES in step S1), the control device 51 executes the process of step S2. In step S2, the control device 51 determines whether the abnormal counter value measured by the counter 51c is equal to or greater than the counter threshold value Tc. Step S2 is a process for determining whether the result of the counter 51c is equal to or greater than the counter threshold value Tc when the detector value is less than the detector threshold value Tb in step S1.

[0081] If the abnormal counter value is less than the counter threshold value Tc (NO in step S2), the control device 51 executes the process of step S5. In step S5, the control device 51 determines whether the abnormal counter value is equal to or greater than the counter threshold value Ta for determination. If the abnormal counter value is less than the counter threshold value Ta for determination (NO in step S5), the control device 51 executes the process of step S7. In step S7, the control device 51 adds "1" to the abnormal counter value to the counter 51c. Thereafter, the control device 51 proceeds to step S1. Therefore, if the detector value is less than the detector threshold value Tb, the control device 51 repeats the processes of steps S1, S2, S5, and S7 until the abnormal counter value becomes equal to or greater than the counter threshold value Tc. Therefore, if the detector value is less than the detector threshold value Tb, the abnormal counter value is incremented by "1" in the counter 51c. In other words, the time during which the detector 31 is considered to be abnormal increases. At this time, the state in which the detector value is less than the detector threshold value Tb continues.

[0082] Thereafter, if the forklift F continues to operate and the fuel cell stack 13 continues to generate electricity while the detector value remains below the detector threshold Tb, the abnormality counter value becomes equal to or greater than the counter threshold Tc (YES in step S2). In other words, the total time during which the detector 31 is considered to be abnormal becomes equal to or greater than the counter threshold Tc. Then, the control device 51 executes the process of step S3. In step S3, the control device 51 turns on the hydrogen concentration adjustment process flag in the memory unit 51b.

[0083] Even if the control device 51 transitions to step S4 while the hydrogen concentration adjustment process flag is on, the control device 51 does not close the cathode-side on-off valve 18a or the anode-side on-off valve 19d, and does not increase the amount of hydrogen gas supplied by the injector 17b. The hydrogen concentration adjustment process flag is turned off when the purge process is executed after key-off.

[0084] After step S3, in step S4, the control device 51 turns on a fan stop flag in the storage unit 51b so that the motor M and the fan motor 25 are not driven. Even if the control device 51 transitions to step S5 with the fan stop flag on, it does not set the radiator fan 21a and the auxiliary fan 24 to the second mode M2. The fan stop flag is turned off when the mode of the radiator fan 21a and the auxiliary fan 24 is changed from the first mode M1 to the second mode M2.

[0085] After step S4, the control device 51 executes the processes of steps S5 and S7. After step S4, the control device 51 repeats the processes of steps S1, S2, S5, and S7 until the abnormal counter value becomes equal to or greater than the determination counter threshold Ta. Therefore, if the detector value is less than the detector threshold Tb, the abnormal counter value in the counter 51c is incremented by "1". In other words, the time during which the detector 31 is considered to be abnormal increases. At this time, the state in which the detector value is less than the detector threshold Tb continues.

[0086] Thereafter, when the forklift F is stopped with the abnormality counter value below the determination counter threshold Ta, the detector determination process ends. Then, when the forklift F is stopped and power generation by the fuel cell stack 13 in the fuel cell unit 11 is stopped, the control device 51 executes the hydrogen concentration adjustment process in accordance with the hydrogen concentration adjustment process flag. The control device 51 closes the cathode side on-off valve 18a and the anode side on-off valve 19d. Furthermore, the control device 51 drives the injector 17b to supply an increased amount of hydrogen gas to the fuel cell stack 13 compared to when a normal purge process is executed. Therefore, the hydrogen concentration adjustment process is a process in which, after power generation by the fuel cell unit 11 is stopped, the cathode side on-off valve 18a and the anode side on-off valve 19d are closed and the injector 17b is driven to increase the amount of hydrogen gas supplied from the injector 17b to the fuel cell stack 13. When such a hydrogen concentration adjustment process is performed, a purge process is performed in each fuel cell, and in addition, a larger amount of hydrogen gas remains in the fuel cell stack 13 than when a normal purge process is performed.

[0087] When the forklift F is started again after the forklift F has been stopped, the control device 51 stops the radiator fan 21a and the accessory fan 24 in accordance with the fan stop flag. That is, the control device 51 executes a setting process for setting the radiator fan 21a and the accessory fan 24 to the second mode M2. Therefore, the setting process is a process for setting the radiator fan 21a and the accessory fan 24 to the second mode M2 ​​after the detector value determination process determines that the detector value is less than the detector threshold value Tb and before the subsequent detector determination process. The setting process is executed when the fuel cell unit 11 is started again after the fuel cell unit 11 has been stopped. In the setting process, the control device 51 sets the radiator fan 21a and the accessory fan 24 to the second mode M2. After the setting process, the radiator fan 21a and the accessory fan 24 do not rotate, and therefore, no air flow W is generated around the fuel cell unit 11.

[0088] When the fuel cell unit 11 is started, the control device 51 periodically opens the anode-side on-off valve 19d and keeps the cathode-side on-off valve 18a constantly open. This causes a larger amount of hydrogen gas to be discharged from the fuel cell stack 13 than after a normal purge process is performed. As a result, the hydrogen gas concentration in the exhaust gas discharged from the gas discharge path 20 via the diluter 16 becomes a post-adjustment concentration that is higher than after a normal purge process is performed. In other words, by performing the hydrogen concentration adjustment process, the hydrogen gas concentration around the fuel cell unit 11 is adjusted to a post-adjustment concentration that is higher than when the detector value determination process was performed and is equal to or higher than the detector threshold value Tb when the fuel cell stack 13 next generates electricity after the fuel cell stack 13 has stopped generating electricity.

[0089] Then, the detector determination process is executed again. This detector determination process corresponds to the determination process in the control method for the fuel cell system 10. In other words, the detector determination process is executed when the fuel cell stack 13 in the next fuel cell unit 11 is started up after power generation by the fuel cell stack 13 of the fuel cell unit 11 has been stopped. This detector determination process is a process for determining whether the detector 31 is normal or not in a state in which the concentration of hydrogen gas in the exhaust gas from the diluter 16, i.e., the concentration of hydrogen gas around the fuel cell unit 11, has been increased to a post-adjustment concentration equal to or higher than the detector threshold value Tb. Furthermore, the detector determination process is executed when the radiator fan 21a and the accessory fan 24 are in the second mode M2.

[0090] In this detector determination process, the determination in step S1 is made in a state where the concentration of hydrogen gas around the fuel cell unit 11 has been increased to the adjusted concentration, compared to when the hydrogen concentration adjustment process has not been performed. Furthermore, the determination in step S1 is made in a state where no air flow W is occurring. In other words, as shown in Fig. 6, the determination in step S1 is made in a state where the exhaust gas is more likely to come into contact with the detection surface 31a of the detector 31. In more detail, the determination is made in a state where the hydrogen contained in the exhaust gas is relatively likely to come into contact with the periphery of the detection surface 31a of the detector 31.

[0091] Therefore, if the detector 31 is functioning normally, both detector values ​​acquired from the two detectors 31 will be equal to or greater than the detector threshold value Tb. When both detector values ​​acquired from the two detectors 31 are equal to or greater than the detector threshold value Tb (NO in step S1), the control device 51 proceeds to step S6. In step S6, the control device 51 resets the abnormality counter value of the counter 51c and proceeds to step S1. In other words, the detector 31 is functioning normally.

[0092] On the other hand, if both of the acquired detector values ​​are less than the detector threshold value Tb (YES in step S1), the control device 51 repeats the processes of steps S1, S2, S5, and S7 while the forklift F is in operation.

[0093] Thereafter, when the abnormality counter value becomes equal to or greater than the counter threshold value for determination Ta (YES in step S5), an abnormality in the detector 31 is confirmed. If the state in which the detector value is less than the detector threshold value Tb continues for a period equal to or greater than the counter threshold value for determination Ta even when the hydrogen gas concentration in the exhaust gas is increased to the adjusted concentration and the radiator fan 21a and the accessory fan 24 are in second mode M2, there is an obvious abnormality in the detector 31. Then, when the abnormality counter value becomes equal to or greater than the counter threshold value for determination Ta (YES in step S5), the control device 51 outputs a signal to the alarm 52 indicating that the detector 31 is abnormal. The alarm 52 notifies the operator of the abnormality in the detector 31 as an error.

[0094] <effect> When the detector value changes from being less than the detector threshold value Tb to being equal to or greater than the counter threshold value Tc, the control device 51 executes the hydrogen concentration adjustment process. Therefore, when the forklift F is turned off and power generation by the fuel cell stack 13 in the fuel cell unit 11 is stopped, the hydrogen concentration adjustment process is executed. As a result, the concentration of hydrogen gas remaining in each fuel cell of the fuel cell stack 13 becomes higher than when a normal purge process is executed. Therefore, when the fuel cell unit 11 is started again after being shut down, the concentration of hydrogen gas in the exhaust gas discharged from the gas discharge path 20 will be higher than when a normal purge process is executed. As a result, the detector 31 can more easily detect the concentration of hydrogen gas contained in the exhaust gas.

[0095] According to the above embodiment, the following effects can be obtained. (1) If the detector value determination process determines that the detector value is less than the detector threshold value Tb, the control device 51 executes the hydrogen concentration adjustment process. Therefore, the detector determination process after the hydrogen concentration adjustment process is executed is performed in a state where the concentration of hydrogen gas around the fuel cell unit 11 is increased. As a result, if the detector 31 is functioning normally, the detector value will not be less than the detector threshold value Tb and will be a normal value.

[0096] In the control method for the fuel cell system 10, the concentration of hydrogen gas around the fuel cell unit 11 is increased to above the detector threshold Tb before the time during which the detector value is below the detector threshold Tb reaches the determination counter threshold Ta. In this state, it is determined whether the detector value is below the detector threshold Tb. This prevents the detector value from becoming an abnormal value even when the detector 31 is functioning normally. In other words, the determination in step S1 is performed accurately. As a result, it prevents the detector 31 from being determined to be abnormal even when the detector 31 is functioning normally.

[0097] (2) After executing the hydrogen concentration adjustment process, the control device 51 executes the setting process. Therefore, the detector determination process is performed under conditions in which the radiator fan 21a and the auxiliary fan 24 are not rotating. This prevents the state in which the hydrogen gas concentration is increased by the hydrogen concentration adjustment process from being disrupted by the air blown from the radiator fan 21a and the auxiliary fan 24. In other words, the detector determination process is performed while maintaining the state in which the hydrogen gas concentration is increased by the hydrogen concentration adjustment process. This prevents the detector value from becoming an abnormal value even when the detector 31 is functioning normally. In other words, the determination in step S1 is performed accurately. As a result, it is possible to prevent the detector 31 from being determined to be abnormal even when the detector 31 is functioning normally.

[0098] (3) The hydrogen concentration adjustment process is a process for increasing the amount of hydrogen gas supplied from the injector 17b compared to when a normal purge process is being performed. In other words, the hydrogen concentration adjustment process simply increases the amount of hydrogen gas supplied during a purge process that is already being performed. Therefore, according to the control method for the fuel cell system 10, it is possible to determine whether the detector 31 is functioning normally without adding any new process.

[0099] (4) The fuel cell system 10 is equipped with two detectors 31. A determination is made for each of the two detectors 31 as to whether the detector 31 is functioning normally. For example, compared to a case where a determination is made as to whether one of the two detectors 31 is functioning normally, this leads to securing as many detectors 31 as possible that function normally. As a result, the detector 31 that functions normally can be left, and a state in which hydrogen gas leaks in the fuel cell system 10 can be detected can be maintained.

[0100] (5) The detector 31 of the fuel cell system 10 is provided to detect the concentration of hydrogen gas emitted, however small, due to permeation or leakage from each component of the fuel cell unit 11. The detector 31's function of detecting the concentration of hydrogen gas is used to determine whether the detector 31 is functioning normally. The detector determination process can determine whether the detector 31 is functioning normally simply by executing the hydrogen concentration adjustment process. In other words, it can be determined whether the detector 31 is functioning normally without adding any hardware to the fuel cell system 10.

[0101] The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the spirit of the invention. For example, the following modifications may be made. The hydrogen concentration adjustment process may be the process described below instead of the process of increasing the amount of hydrogen gas supplied by the injector 17b.

[0102] This form of hydrogen concentration adjustment processing is performed when the fuel cell unit 11 is next started up after power generation by the fuel cell stack 13 in the fuel cell unit 11 has been stopped, or when power generation by the fuel cell stack 13 begins after the amount of power generation by the fuel cell stack 13 has been set to zero.

[0103] When the hydrogen concentration adjustment process is performed, the control device 51 keeps the cathode-side on-off valve 18a closed. The control device 51 also opens the anode-side on-off valve 19d. Then, hydrogen gas is supplied from the injector 17b to the fuel cell stack 13. The supply amount may be the same as that in the normal purging process, or may be an amount of hydrogen gas supplied that corresponds to the amount of power generated by the fuel cell stack 13.

[0104] Because the cathode-side on-off valve 18a is closed, air is not supplied to the fuel cell stack 13. Therefore, the hydrogen gas supplied from the injector 17b to the fuel cell stack 13 does not react with the oxygen in the air. Therefore, the hydrogen gas is discharged as exhaust gas from the diluter 16 via the anode off-gas discharge path 19a, the gas-liquid separator 26, and the anode-side on-off valve 19d. Because air is not supplied to the fuel cell stack 13, almost no cathode off-gas is discharged from the fuel cell stack 13. Therefore, the diluter 16 only slightly dilutes the anode off-gas with the cathode off-gas. Therefore, the hydrogen gas concentration in the exhaust gas discharged from the diluter 16 is relatively high. Therefore, the concentration of hydrogen gas discharged from the fuel cell stack 13 is adjusted to a post-adjustment concentration that is higher than the pre-adjustment concentration and equal to or greater than the detector threshold Tb. As a result, the detector determination process after the hydrogen concentration adjustment process is performed is performed in a state where the hydrogen gas concentration around the fuel cell unit 11 is increased. As a result, if the detector 31 is functioning normally, the detector value will not be less than the detector threshold value Tb and will be a normal value.

[0105] The hydrogen concentration adjustment process may be performed by both increasing the amount of hydrogen gas supplied by the injector 17b and stopping the supply of air to the fuel cell stack 13 to relatively increase the hydrogen gas concentration.

[0106] The processing order of steps S3 and S4 may be reversed. After the fuel cell unit 11 is started, the radiator fan 21a and the auxiliary fan 24 may be stopped, and then the hydrogen concentration adjustment process may be performed.

[0107] The detector determination process may be performed without stopping the radiator fan 21a and the auxiliary fan 24. In the second mode M2, the second operating amount, which is the rotation speed of the radiator fan 21a and the accessory fan 24, may be greater than zero and less than the first operating amount. In this case, in the second mode M2, the air flow W generated around the fuel cell unit 11 is smaller than in the first mode M1.

[0108] The fuel cell system 10 does not have to include the housing 12. In this case, the fuel cell unit 11 and the detector 31 are directly accommodated in the accommodation portion Fb of the forklift F. The fuel cell system 10 may be a stationary fuel cell system. In this case, the fuel cell system 10 may include an exterior panel as a housing, or may not include the housing 12.

[0109] The fuel cell system 10 does not necessarily have to include the auxiliary fan 24. In this case, the radiator fan 21a is the only fan, which is an example of a blower. There may be only one detector 31, or three or more detectors 31. When there are three or more detectors 31, it is preferable that the determination in step S1 be YES when each of the three or more detector values ​​is less than the detector threshold value Tb.

[0110] In step S1, the determination may be YES when only one of the two detector values ​​is less than the detector threshold value Tb. After the determination in step S1 becomes YES, the hydrogen concentration adjustment process flag may be set in the memory unit 51b without determining whether the abnormal counter value is equal to or greater than the counter threshold value Tc (step S2). In this case, the abnormal counter value is not measured by the counter 51c. The detector determination process is performed by only comparing the detector value with the detector threshold value Tb, without comparing the abnormal counter value with the counter threshold value Tc or the determination counter threshold value Ta.

[0111] A timer may be used instead of the counter 51c. The timer may measure the time until the detector 31 is deemed to be abnormal. The air blower may be a door that opens and closes the ventilation opening 12f. In the first mode M1, the ventilation opening 12f is opened. This causes a natural air flow W to be generated within the housing 12 through the ventilation opening 12f. In the second mode M2, the ventilation opening 12f is closed or has an opening area smaller than that of the first mode M1.

[0112] The fuel cell of the fuel cell unit 11 does not have to be a stack of multiple fuel cells, but may be a single fuel cell. Next, the technical ideas that can be understood from the above-described embodiment and other examples will be described below.

[0113] (i) The air blower is a fan that generates a flow of air around the fuel cell system so that the air flows through the inside of the housing. (b) The fuel cell system includes a plurality of detectors, and the detector value determination process determines whether each of the plurality of detector values ​​is less than the detector threshold value. [Explanation of symbols]

[0114] 10... fuel cell system, 11... fuel cell unit, 13... fuel cell stack as fuel cell, 17b... injector, 18a... cathode side opening / closing valve, 19a... anode off-gas discharge path, 19b... cathode off-gas discharge path, 19d... anode side opening / closing valve, 21a... radiator fan as blower, 24... auxiliary fan as blower, 31... detector, 51... control device.

Claims

1. a fuel cell unit including a fuel cell that generates electricity when supplied with a fuel gas containing hydrogen gas and an oxidant gas, and that discharges an exhaust gas containing the hydrogen gas; a detector that detects the concentration of the hydrogen gas around the fuel cell unit as a detector value; A control method for a fuel cell system, the control method being executed by the control device in a fuel cell system including the control device, a detector value determination process for determining whether or not the detector value is less than a detector threshold value for determining that the detector is abnormal after the fuel cell unit is started; a hydrogen concentration adjustment process for controlling the fuel cell unit so that the concentration of hydrogen gas around the fuel cell unit is adjusted to a post-adjustment concentration higher than that at the time of execution of the detector value determination process and equal to or higher than the detector threshold value during the next power generation by the fuel cell following the stop of power generation by the fuel cell after the detector value determination process has determined that the detector value is less than the detector threshold value; a determination process for determining whether the detector functions normally when the concentration of the hydrogen gas around the fuel cell unit is adjusted to the adjusted concentration.

2. the fuel cell unit includes an injector that supplies the hydrogen gas to the fuel cell, an anode-side on-off valve that opens and closes an anode off-gas exhaust passage connected to an anode of the fuel cell, and a cathode-side on-off valve that opens and closes a cathode off-gas exhaust passage connected to a cathode of the fuel cell; the hydrogen concentration adjustment process is a process of closing the cathode side on-off valve and the anode side on-off valve and driving the injector to increase the amount of the hydrogen gas supplied from the injector to the fuel cell after power generation by the fuel cell unit is stopped, 2. The control method for a fuel cell system according to claim 1, wherein the determination process is executed when the fuel cell unit is next started up following a halt in power generation by the fuel cell unit.

3. the fuel cell system includes a blower that generates an air flow around the fuel cell unit; the blower can be set to either a first mode for generating the air flow around the fuel cell unit or a second mode for reducing the air flow to less than that in the first mode or to zero, The control method for the fuel cell system includes: a setting process of setting the blower unit to the second mode after it is determined in the detector value determination process that the detector value is less than the detector threshold value and before the determination process; 3. The control method for a fuel cell system according to claim 1, wherein the determination process is performed when the blower is in the second mode.

Images