Fuel cell system

Abstract

To accurately detect fuel gas leaks after the operation of a fuel cell is stopped.SOLUTION: A fuel cell system includes a pressure sensor that detects the pressure in an anode flow channel and the pressure in a cathode flow channel, and an ECU that detects fuel gas leakage from the anode flow channel on the basis of the pressure in the anode flow channel and the pressure in the cathode flow channel detected by the pressure sensor. After the fuel cell stops operating, the ECU controls a fuel gas supply / discharge unit and an oxidant gas supply / discharge unit to achieve a flow channel interruption state in which the anode flow channel is interrupted from the fuel gas supply / discharge unit and the cathode flow channel is interrupted from the oxidant gas supply / discharge unit while maintaining the pressure in the anode flow channel and the pressure in the cathode flow channel at predetermined values, respectively, and detects fuel gas leakage on the basis of the amount of change in the pressure in the anode flow channel and the amount of change in the pressure in the cathode flow channel from the flow channel interruption state.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] In recent years, technological developments related to fuel cells that contribute to energy efficiency have been underway to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. One known technology related to this type of fuel cell system is a fuel cell system that detects leaks of fuel gas containing hydrogen after the fuel cell has stopped operating (see, for example, Patent Document 1). The fuel cell system described in Patent Document 1 detects the pressure of the fuel gas within a target pressure maintenance range, and determines that a gas leak has occurred from the target pressure maintenance range when the rate at which the pressure drops is equal to or exceeds a set rate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-181263 Summary of the Invention [Problem to be solved by the invention]

[0004] However, it is difficult to accurately detect gas leaks simply by using the detected pressure value of the fuel gas as in the fuel cell system described in Patent Document 1. [Means for solving the problem]

[0005] A fuel cell system according to one aspect of the present invention includes a fuel cell stack having a cell stack formed by stacking a plurality of power generation cells, and having an anode flow path through which a fuel gas flows and a cathode flow path through which an oxidant gas flows provided inside the cell stack; a fuel gas supply / discharge unit that supplies the fuel gas to the anode flow path and discharges the fuel gas from the anode flow path; an oxidant gas supply / discharge unit that supplies the oxidant gas to the cathode flow path and discharges the oxidant gas from the cathode flow path; a pressure detection unit that detects the pressure in the anode flow path and the pressure in the cathode flow path; and a leak detection unit that detects fuel gas leakage from the anode flow path based on the pressure in the anode flow path and the pressure in the cathode flow path detected by the pressure detection unit. After the fuel cell stops operating, the leak detection unit controls the fuel gas supply / discharge unit and the oxidant gas supply / discharge unit so as to achieve a flow path blocking state in which the anode flow path is blocked from the fuel gas supply / discharge unit and the cathode flow path is blocked from the oxidant gas supply / discharge unit while maintaining the pressure in the anode flow path and the pressure in the cathode flow path at predetermined values, respectively, and further detects a fuel gas leak based on the amount or rate of change in the pressure in the anode flow path and the amount or rate of change in the pressure in the cathode flow path from the flow path blocking state. [Effects of the Invention]

[0006] According to the present invention, fuel gas leakage can be detected with high accuracy. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram showing a schematic configuration of a main part of a fuel cell system according to an embodiment of the present invention; [Figure 2] FIG. 2 is a perspective view showing a schematic overall configuration of a fuel cell stack included in the fuel cell system of FIG. [Figure 3] 3 is a cross-sectional view of a main part of a cell laminate included in the fuel cell stack of FIG. 2. [Figure 4] FIG. 3 is a perspective view showing a schematic configuration of an electrode assembly included in the fuel cell stack of FIG. 2. [Figure 5] FIG. 3 is a rear view of a separator included in the fuel cell stack of FIG. 2. [Figure 6]FIG. 6 is a cross-sectional view taken along line IV-IV in FIG. 5 . [Figure 7] FIG. 2 is a block diagram showing the control configuration of the fuel cell system according to the embodiment of the present invention. [Figure 8] 8 is a flowchart showing an example of processing executed by the ECU of FIG. 7; [Figure 9] FIG. 3 is a diagram showing an example of an operation of the fuel cell system according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to Figs. 1 to 9. Fig. 1 is a block diagram showing a schematic configuration of a main part of a fuel cell system 200 according to an embodiment of the present invention. The fuel cell system 200 is mounted on, for example, a vehicle and generates electric power for driving the vehicle. As shown in Fig. 1, the fuel cell system 200 has a fuel cell stack 100 formed by stacking a plurality of power generation cells, a fuel gas supply / discharge unit 210, an oxidant gas supply / discharge unit 220, and a coolant supply / discharge unit 230. The fuel gas and oxidant gas are sometimes called anode gas and cathode gas, respectively.

[0009] The fuel gas supply / discharge unit 210 has a tank 211 that stores high-pressure fuel gas, an injector 212 that discharges the fuel gas, and an ejector 213. The fuel gas in the tank 211 is supplied to the fuel cell stack 100 via the injector 212, the ejector 213, and a supply pipe 210a. The fuel gas is an anode gas containing hydrogen (e.g., hydrogen gas). The fuel gas (fuel exhaust gas) is discharged from the fuel cell stack 100 via a discharge pipe 210b.

[0010] A gas-liquid separator 214 is provided in the discharge pipe 210b, and moisture contained in the fuel exhaust gas is separated from the fuel exhaust gas by the gas-liquid separator 214. The separated moisture is discharged through a drain pipe 210c. In the ejector 213, a negative pressure is generated by the flow of the fuel gas discharged from the injector 212. Due to this negative pressure, the fuel exhaust gas from which moisture has been separated in the gas-liquid separator 214 is sucked through a circulation pipe 210d and merges with the fuel gas discharged from the injector 212. A portion of the fuel exhaust gas is not returned to the ejector 213, but is discharged through a purge pipe 210e.

[0011] The fuel gas supply / discharge unit 210 is provided with on-off valves 501 to 503 on the supply side of the fuel gas to the fuel cell stack 100 and on the discharge side of the fuel gas from the fuel cell stack 100. Specifically, the supply-side on-off valve 501 is provided in the pipe 210f between the tank 211 and the injector 212, and the discharge-side on-off valves 502 and 503 are provided in the drain pipe 210c and the purge pipe 210e, respectively.

[0012] The on-off valves 501 to 503 are electromagnetic valves that open and close when a solenoid is energized or deenergized in response to an electrical signal, for example. When the fuel cell is operating (power generation), the on-off valves 501 to 503 are opened or opened at an appropriate timing. When the on-off valves 501 to 503 are closed, the fuel gas supply and discharge pipes 210a, 210b are blocked, allowing the fuel gas to be sealed inside the fuel cell stack 100. Note that the on-off valves may also be provided at other positions on the fuel gas supply and discharge sides.

[0013] The oxidant gas supply / discharge unit 220 has a compressor 221 that compresses the oxidant gas to a high pressure, and a humidifier 222 that humidifies the oxidant gas. The oxidant gas compressed by the compressor 221 is humidified by the humidifier 222 and supplied to the fuel cell stack 100 via a supply pipe 220a. The oxidant gas is a cathode gas (e.g., air) that contains oxygen. Oxidant gas (oxidant exhaust gas) that contains moisture is discharged from the fuel cell stack 100 via a discharge pipe 220b. This oxidant gas is discharged via the humidifier 222 and a pipe 220c.

[0014] The oxidant gas supply / discharge unit 220 is provided with on-off valves 504, 505 on the supply side of the oxidant gas to the fuel cell stack 100 and on the discharge side of the oxidant gas from the fuel cell stack 100. Specifically, the on-off valve 504 on the supply side is provided in the pipe 220d between the compressor 221 and the humidifier 222, and the on-off valve 505 on the discharge side is provided in the pipe 210c downstream of the humidifier 222. Note that the fuel gas and the oxidant gas may sometimes be referred to as reactant gases without distinction between them.

[0015] The on-off valves 504, 505 are electromagnetic valves that open and close by energizing or de-energizing a solenoid in response to an electrical signal, for example. When the fuel cell is operating (power generation), the on-off valves 504, 505 are opened or opened at an appropriate timing. When the on-off valves 504, 505 are closed, the oxidant gas supply and discharge pipes 220a, 220b are blocked, allowing the oxidant gas to be sealed inside the fuel cell stack 100. Note that the on-off valves may also be provided at other positions on the oxidant gas supply and discharge sides.

[0016] The cooling medium supply / discharge unit 230 has a pump (not shown), and the cooling medium discharged from the pump is supplied to the fuel cell stack 100 via a supply pipe 230a. The cooling medium is, for example, water. The cooling medium is discharged from the fuel cell stack 100 via a discharge pipe 230b. The discharged cooling medium is cooled by heat exchange in a radiator and is supplied again to the fuel cell stack 100 via the supply pipe 230a.

[0017] A pressure sensor 51 that detects the pressure of the fuel gas is connected to the fuel gas supply pipe 210a. A pressure sensor 52 that detects the pressure of the oxidant gas is connected to the oxidant gas supply pipe 220a. A hydrogen sensor 53 that detects leakage of fuel gas into the case of the fuel cell stack 100 is connected to the fuel cell stack 100. Although not shown, the fuel cell system 200 is also provided with a temperature sensor that detects the temperature of the reactant gas, etc. The operation of the fuel cell system 200 is controlled based on signals from these sensors.

[0018] FIG. 2 is a perspective view showing a schematic view of the overall configuration of the fuel cell stack 100. For convenience, the three mutually orthogonal axial directions shown in the figure are defined as the front-rear direction, the left-right direction, and the up-down direction, and the configuration of each part will be described in accordance with these definitions. The front-rear direction in FIG. 2 is the stacking direction of the fuel cell stack 100. These directions are not necessarily the same as the front-rear direction, left-right direction, and up-down direction of the vehicle. For example, the front-rear direction in FIG. 2 may be the front-rear direction, the left-right direction, or the up-down direction of the vehicle.

[0019] As shown in Figure 2, the fuel cell stack 100 has a cell stack 10, end units 40 arranged at both the front and rear ends of the cell stack 10, and a case 30 surrounding the cell stack 10, and the entire stack has an approximately rectangular parallelepiped shape.

[0020] The case 30 has four generally rectangular side walls 300 that face the top, right, bottom, and left sides of the cell stack 10. These four side walls 300 form a generally box-shaped storage space SP0 that is open on the front and back. The case 30 is made of a metal such as aluminum or iron. The hydrogen sensor 53 in FIG. 1 is provided in the storage space SP0 outside the cell stack 10.

[0021] Although not shown, the end unit 40 has multiple plates stacked in the front-rear direction. More specifically, the end unit 40 has terminal plates arranged adjacent to both front and rear end surfaces of the cell stack 10, insulating plates arranged on the outside of the terminal plates in the front-rear direction, and end plates arranged on the outside of the insulating plates in the front-rear direction.

[0022] The terminal plate is a generally rectangular metal plate-like member that has a terminal portion for extracting the power generated by the electrochemical reaction in the cell stack 10. The insulating plate is a generally rectangular non-conductive resin or rubber plate-like member that electrically insulates the terminal plate from the end plates. The end plates are metal or high-strength resin plate-like members.

[0023] Part A of Figure 2 shows a cutaway view of a side wall 300 of the case 30. As shown in part A of Figure 2, the cell stack 10 is a stack having a plurality of power-generating cells 1 (for convenience, only a single cell 1 is shown). The power-generating cell 1 has an electrode assembly 2 (UEA; Unitized Electrode Assembly) and separators 3 that are arranged on both the front and rear sides of the electrode assembly 2 and sandwich the electrode assembly 2. The electrode assemblies 2 and the separators 3 are arranged alternately in the front-to-rear direction. The electrode assembly 2 can be called a membrane electrode structure or membrane electrode member.

[0024] FIG. 3 is a cross-sectional view of a main portion of the cell stack 10. As shown in FIG. 3, the separator 3 has a front plate 3F and a rear plate 3R, which are a pair of front and rear metal thin plates with a corrugated cross section. The front plate 3F extends in the vertical and horizontal directions and has a front surface 3Fa and a rear surface 3Fb. The rear plate 3R extends in the vertical and horizontal directions and has a front surface 3Ra and a rear surface 3Rb. The opposing rear surface 3Fb of the front plate 3F and the front surface 3Ra of the rear plate 3R are joined at their outer peripheral edges by welding or the like. This integrally joins the front plate 3F and the rear plate 3R to form the separator 3. The separator 3 is made of a conductive material with excellent corrosion resistance, such as stainless steel, titanium, or a titanium alloy.

[0025] A refrigerant flow path PAw through which a cooling medium flows is formed inside the separator 3 surrounded by the front plate 3F and the rear plate 3R, that is, between the rear surface 3Fb of the front plate 3F and the front surface 3Ra of the rear plate 3R. The power generation surface of the power generation cell 1 is cooled by the flow of the cooling medium.

[0026] The surfaces of the separator 3 facing the electrode assembly 2 (front surface 3Fa and rear surface 3Rb) are formed unevenly by press molding or the like so as to form a gas flow path between the separator 3 and the electrode assembly 2. More specifically, the separator 3 has a pair of front and rear rib portions 3A that protrude toward the electrode assembly 2, and a pair of front and rear recesses 3B that are connected to the pair of front and rear rib portions 3A and formed in a concave shape.

[0027] The pair of front and rear rib portions 3A abut against the front surface 2a and rear surface 2b of the electrode assembly 2. A compressive load F is applied to the cell stack 10 in the front-to-rear direction during assembly of the fuel cell stack 100, and this compressive load F is maintained after assembly of the fuel cell stack 100 is complete. As a result, a predetermined surface pressure due to the compressive load F acts on the electrode assembly 2 in the front-to-rear direction via the rib portions 3A.

[0028] An anode flow path PAa through which fuel gas flows is formed by the recess 3B between the front surface 2a of the electrode assembly 2 and the rear plate 3R of the separator 3 facing this front surface 2a. A cathode flow path PAc through which oxidant gas flows is formed by the recess 3B between the rear surface 2b of the electrode assembly 2 and the front plate 3F of the separator 3 facing this rear surface 2b.

[0029] Fig. 4 is a perspective view showing a schematic configuration of the electrode assembly 2. As shown in Fig. 4, the electrode assembly 2 has a substantially rectangular assembly 20 and a frame 21 that supports the assembly 20. As shown in the detailed view of part A in Fig. 3, the assembly 20 is a membrane electrode assembly (MEA) that has an electrolyte membrane 23, an anode electrode 24 provided on a front surface 23f of the electrolyte membrane 23, and a cathode electrode 25 provided on a rear surface 23r of the electrolyte membrane 23.

[0030] The electrolyte membrane 23 is, for example, a solid polymer electrolyte membrane, and a thin film of a perfluorosulfonic acid polymer containing water can be used. The electrolyte membrane 23 is not limited to a fluorine-based electrolyte membrane, and a hydrocarbon-based electrolyte membrane can also be used.

[0031] The anode 24 is formed on the front surface 23f of the electrolyte membrane 23 and includes an electrode catalyst layer 241 that serves as a reaction field for an electrode reaction, and a gas diffusion layer 242 that is provided in front of the electrode catalyst layer 241 and diffuses and supplies a fuel gas. The cathode 25 is formed on the rear surface 23r of the electrolyte membrane 23 and includes an electrode catalyst layer 251 that serves as a reaction field for an electrode reaction, and a gas diffusion layer 252 that is provided on the rear surface of the electrode catalyst layer 251 and diffuses and supplies an oxidant gas. An intermediate layer (base layer) may be provided between the electrode catalyst layers 241, 251 and the gas diffusion layers 242, 252.

[0032] The electrode catalyst layers 241, 251 contain a catalytic metal that promotes an electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas, a proton-conductive electrolyte (e.g., ionomer), and electron-conductive carbon particles, etc. The gas diffusion layers 242, 252 are made of a gas-permeable conductive material, such as a porous carbon material.

[0033] At the anode electrode 24, the fuel gas (hydrogen) supplied via the anode flow path PAa is ionized by the action of a catalyst and moves through the electrolyte membrane 23 toward the cathode electrode. The electrons generated at this time pass through an external circuit and are extracted as electrical energy. At the cathode electrode 25, the oxidant gas (oxygen) supplied via the cathode flow path PAc reacts with the hydrogen ions introduced from the anode electrode 24 and the electrons that have moved from the anode electrode 24, producing water. The produced water provides an appropriate humidity to the electrolyte membrane 23, and excess water is discharged to the outside of the electrode assembly 2 along the gas flow.

[0034] As shown in FIG. 4, the frame 21 is a thin plate having a substantially rectangular shape and is made of insulating resin, rubber, or the like. A substantially rectangular opening 21a is provided in the center of the frame 21. The joining body 20 is provided so as to cover the entire opening 21a, and the peripheral edge of the joining body 20 is supported by the frame 21. On the left side of the opening 21a in the frame 21, three through holes 201 to 203 are opened in a vertical line that penetrate the frame 21 in the front-to-rear direction. On the right side of the opening 21a, three through holes 204 to 206 are opened in a vertical line that penetrate the frame 21 in the front-to-rear direction.

[0035] FIG. 5 is a rear view (viewed from behind) of the separator 3 disposed in front of the electrode assembly 2, showing the rear surface 3Rb (FIG. 3) of the rear plate 3R. As shown in FIG. 5, although some illustrations are omitted, a plurality of vertical rib portions 3A are formed by pressing in the left-right central portion of the rear surface 3Rb, extending in the left-right direction and facing the assembly 20 of the electrode assembly 2. Recesses 3B are formed between vertically adjacent rib portions 3A, 3A. An anode flow path PAa is formed between the recesses 3B and the front surface 2a of the assembly 20. Although not shown, rib portions 3A and recesses 3B are also formed by pressing on the front surface of the front plate 3F of the separator 3, and a cathode flow path PAc is formed between the recesses 3B and the rear surface 2b of the assembly 20.

[0036] The separator 3 has through holes 301 to 306 that penetrate the separator 3 in the front-rear direction at positions corresponding to the through holes 201 to 206 (FIG. 4) of the frame 21. The through holes 301 to 306 are connected to the through holes 201 to 206 of the frame 21, respectively. A collection of these through holes 201 to 206 and 301 to 306 that are connected to one another forms a plurality of flow paths that penetrate the cell stack 10 and extend in the front-rear direction.

[0037] 2, a plurality of through holes 401 to 406 are formed in the rear end unit (wet side end unit) 40, penetrating the end unit 40 in the front-rear direction, at positions corresponding to the through holes 201 to 206 and 301 to 306. However, the front end unit (dry side end unit) 40 does not have the through holes 401 to 406.

[0038] The through-holes 401 and 406 are a supply port and a discharge port for fuel gas, respectively. The supply pipe 210a and the discharge pipe 210b shown in Fig. 1 are connected to the through-holes 401 and 406, respectively. As shown by the solid arrows in Fig. 2, fuel gas is supplied to the fuel cell stack 100 via the through-hole 401, and the fuel gas is discharged from the fuel cell stack 100 via the through-hole 406.

[0039] The through-holes 404 and 403 are a supply port and a discharge port for the oxidant gas, respectively. The supply pipe 220a and the discharge pipe 220b in Fig. 1 are connected to the through-holes 404 and 403, respectively. As indicated by the dotted arrows in Fig. 2, the oxidant gas is supplied to the fuel cell stack 100 via the through-hole 404, and the oxidant gas is discharged from the fuel cell stack 100 via the through-hole 403.

[0040] The through-holes 405 and 402 are a supply port and a discharge port for the cooling medium, respectively. The supply pipe 230a and the discharge pipe 230b shown in Fig. 1 are connected to the through-holes 405 and 402, respectively. As shown by the dashed-dotted arrows in Fig. 2, the cooling medium is supplied to the fuel cell stack 100 through the through-hole 405, and the cooling medium is discharged from the fuel cell stack 100 through the through-hole 402.

[0041] 5, a weld WP1 (dotted line) is provided around the entire outer periphery of the separator 3, and the rear plate 3R and the front plate 3F are joined together via the weld WP1. Additionally, welds WP2 (dotted line) are provided around the gas supply and discharge through-holes 301, 303, 304, and 306 so as to individually surround the entire periphery of the through-holes 301, 303, 304, and 306. This forms a refrigerant flow space SPw inside the separator 3 (between the rear plate 3R and the front plate 3F), sealing the outer periphery of the separator 3 and the through-holes 301, 303, 304, and 306. A cooling medium is supplied to and discharged from the refrigerant flow space SPw via the through-holes 302 and 305.

[0042] A sealing bead portion 31 is provided on the rear surface 3Rb of the rear plate 3R, outside the anode flow channel PAa, protruding rearward toward the frame 21 of the electrode assembly 2. The bead portion 31 has an outer bead portion 311, an inner bead portion 312, and individual bead portions 313 that extend without intersecting each other.

[0043] The outer bead portion 311 extends in a generally rectangular shape along the outer periphery of the rear plate 3R so as to surround all of the through holes 301 to 306. The inner bead portion 312 extends in a generally rectangular shape so as to surround the anode flow channel PAa, and a portion of the inner bead portion 312 extends close to the outer bead portion 311 so as to surround the through holes 301, 306 for supplying and discharging fuel gas. A plurality of individual bead portions 313 are provided between the outer bead portion 311 and the inner bead portion 312 so as to individually surround the through holes 302 to 305.

[0044] Although not shown, a sealing bead portion 31 protruding forward toward the frame 21 of the electrode assembly is also provided on the front surface 3Fa of the front plate 3F. However, unlike the inner bead portion 312 on the rear surface 3Rb of the rear plate 3R, the inner bead portion 312 on the front surface 3Fa of the front plate 3F extends in a substantially rectangular shape so as to surround the cathode flow path PAc, and a portion of it extends close to the outer bead portion 311 so as to surround the through holes 304 and 303 for supplying and discharging the oxidant gas. In addition, a plurality of individual bead portions 313 are provided on the front surface 3Fa of the front plate 3F between the outer bead portion 311 and the inner bead portion 312 so as to individually surround the through holes 301, 302, 305, and 306.

[0045] By providing the bead portions 31 on the rear surface 3Rb of the rear plate 3R in this manner, a gas flow space SPa is formed with its periphery sealed from the through-hole 301 to the anode flow channel PAa and the through-hole 306. This allows fuel gas to flow in a sealed state through the gas flow space SPa along the rear surface 3Rb of the rear plate 3R. Furthermore, by providing the bead portions 31 on the front surface 3Fa of the front plate 3F, a gas flow space is formed with its periphery sealed from the through-hole 304 to the cathode flow channel PAc and the through-hole 303. This allows oxidant gas to flow in a sealed state through the gas flow space along the front surface 3Fa of the front plate 3F.

[0046] 6 is a cross-sectional view (a cross-sectional view taken along line VI-VI in FIG. 5) of a main portion of the separator 3 showing the configuration of the seal portion 33. As shown in FIG. 6, a seal material 32 made of a rubber material or a resin material is fixed to the surface of the bead portion 31 (inner bead portion 312 in FIG. 6), thereby forming the seal portion 33. The bead portion 31 is in close contact with the front and rear surfaces of the frame 21 via the seal material 32. Note that the seal material 32 may be omitted, and the bead portion 31 may be in close contact with the front and rear surfaces of the frame 21.

[0047] However, a defective seal may occur due to bending of the separator 3 or deterioration of the sealing material 32. In this case, as shown by arrow L1 in FIG. 6, fuel gas may leak out of the gas flow space SPa through the bead portion 31 or the sealing material 32, and further out of the cell stack 10. That is, an out-leak may occur, in which fuel gas leaks out of the cell stack 10. Furthermore, a defective weld, such as a defect or damage, may occur in the welds WP1 and WP2 that join the front plate 3F and the rear plate 3R, and fuel gas may leak from the gas flow space SPa to the refrigerant flow space SPw, as shown by arrow L2 in FIG. That is, a cross-leak may occur, in which fuel gas leaks into another flow path.

[0048] To enable accurate detection of such fuel gas leakage, the fuel cell system 200 of this embodiment is configured as follows: Although there is a risk of leakage of not only fuel gas but also oxidant gas, the following will be treated as if there is no leakage of oxidant gas.

[0049] 1 and 7, the fuel cell system 200 includes an ECU 50 as a leak detector, a pressure sensor 51 that detects the fuel gas pressure P1 (referred to as the anode pressure) in the anode flow path PAa, a pressure sensor 52 that detects the oxidant gas pressure P2 (referred to as the cathode pressure) in the cathode flow path PAc, a hydrogen sensor 53 that detects hydrogen outside the cell stack 10 and within the case, a fuel gas supply / discharge unit 210, and an oxidant gas supply / discharge unit 220. The fuel gas supply / discharge unit 210 includes an injector 212 and on-off valves 501-503, and the oxidant gas supply / discharge unit 220 includes a compressor 221 and on-off valves 504 and 505.

[0050] The ECU 50 includes a computer having a calculation unit such as a CPU, a storage unit such as a ROM and a RAM, and other peripheral circuits. The calculation unit functions as a gas flow control unit 50A and a leak determination unit 50B by executing a program stored in advance in the storage unit.

[0051] Fig. 8 is a flowchart showing an example of processing executed by the calculation unit of the ECU. The processing shown in this flowchart is started when the operation (power generation) of the fuel cell is stopped by turning off the vehicle's power switch or ignition switch, for example. For example, it is executed every time the fuel cell is stopped. Note that the processing of Fig. 8 may be executed every time the fuel cell is operated a predetermined number of times, or every time a predetermined period of time has passed. At the start of the processing, the anode pressure P1 and cathode pressure P2 detected by the pressure sensors 51, 52 are at an initial pressure P0 that is sufficiently lower than that during power generation.

[0052] As shown in FIG. 8, first, in step S1, the fuel gas supply / discharge unit 2120 and the oxidant gas supply / discharge unit 220 are controlled to increase the pressure of the fuel gas in the anode flow path PAa and the oxidant gas in the cathode flow path PAc in the fuel cell stack 100. Specifically, control signals are output to on-off valves 501-503 of the fuel gas supply / discharge unit 210 to open on-off valve 501 and close on-off valves 502 and 503. In this state, a control signal is output to the injector 212 to supply the fuel gas to the anode flow path PAa. At the same time, control signals are output to on-off valves 504 and 505 of the oxidant gas supply / discharge unit 220 to open on-off valve 504 and close on-off valve 505. In this state, a control signal is output to the compressor 22 to supply the oxidant gas to the cathode flow path PAc. In this case, the gas supply amount is adjusted so that the anode pressure P1 and the cathode pressure P2 increase at the same rate.

[0053] Next, in step S2, it is determined whether the anode pressure P1 and the cathode pressure P2 detected by the pressure sensors 51 and 52 have reached a pre-stored predetermined value Pa. The predetermined value Pa is a value that generates a pressure difference that easily indicates a fuel gas leak when there is a seal defect in the seal portion 33 or a welding defect in the welded portions WP1 and WP2. If the result in step S2 is negative, the process returns to step S1, and the gas pressure continues to increase. If the result in step S2 is positive, the process proceeds to step S3.

[0054] In step S3, a control signal is output to the on-off valve 501 to close it, and a control signal is output to the injector 212 to stop the supply of fuel gas. This stops the pressure increase in the anode flow path PAa, fuel gas is sealed in the anode flow path PAa, and the anode pressure P1 is maintained at the predetermined value Pa. At the same time, a control signal is output to the on-off valve 504 to close it, and a control signal is output to the compressor 221 to stop the supply of oxidant gas. This stops the pressure increase in the cathode flow path PAc, oxidant gas is sealed in the cathode flow path PAc, and the cathode pressure P2 is maintained at the predetermined value Pa.

[0055] The above is the processing performed by the gas flow control unit 50A in FIG. 7. The gas flow control unit 50A controls the flow of reactant gas to a flow path blocking state in which the anode flow path PAa and the cathode flow path PAc are blocked while maintaining the anode pressure P1 and the cathode pressure P2 at predetermined values Pa, respectively. In the flow path blocking state, the fuel gas and the oxidant gas flow opposite each other via the assembly 20. Therefore, even if there is no fuel gas leakage, the reactant gas is consumed by the electrochemical reaction, and the pressures P1 and P2 decrease. The amount of pressure decrease in this case is a normal amount, which can be determined in advance by experiment, analysis, etc.

[0056] The leak determination unit 50B in FIG. 7 executes the processes from step S4 onward. In step S4, the flow path is blocked and the unit waits for a predetermined time T1. The predetermined time T1 is the time required for a significant drop in fuel gas pressure to occur when there is a seal defect or welding defect. The predetermined time T1 is determined in advance through experiments, analysis, etc., and is stored in the memory unit.

[0057] Next, in step S5, it is determined whether the anode pressure P1 is equal to or less than a predetermined value Pb and whether the cathode pressure P2 is greater than the predetermined value Pb. The predetermined value Pb is a value lower than the predetermined value Pa by a predetermined decrease amount ΔP. The predetermined value Pb is a threshold value for identifying the occurrence of a fuel gas leak, and is determined in advance through experiments, analysis, etc. and stored in a memory unit.

[0058] In step S5, it is determined whether P1≦Pb holds, as well as whether P2>Pb holds. Therefore, it is determined whether the anode pressure P1 has dropped significantly more than the cathode pressure P2, which is assumed to be leak-free, thereby improving the accuracy of the leak determination. Note that instead of the processing of step S5, it may be determined whether the anode pressure P1 is smaller than the cathode pressure P2 by a predetermined value or more.

[0059] If the result in step S5 is negative, the process proceeds to step S6. In this case, it is determined that there is no fuel gas leak, and the process ends. On the other hand, if the result in step S5 is positive, the process proceeds to step S7, where it is determined whether hydrogen has been detected in the storage space SP0 outside the cell stack 10 and inside the case 30, based on the signal from the hydrogen sensor 53. For example, if the hydrogen sensor 53 detects more than a predetermined amount of hydrogen, it is determined that hydrogen has been detected.

[0060] If the result in step S7 is affirmative, the process proceeds to step S8. In this case, it is determined that fuel gas is leaking outside the cell stack 10 (out-leak), and the process ends. On the other hand, if the result in step S7 is negative, the process proceeds to step S9. In this case, it is determined that fuel gas is leaking in the refrigerant flow path PAw (refrigerant flow space SPw) (cross-leak), and the process ends.

[0061] This completes the process for fuel gas leak detection. After the process of FIG. 8 is completed, the ECU 50 may output the determination result. For example, the determination result may be output to a monitor for display, or may be output to memory for storage. After the process of FIG. 8 is completed, the oxidant gas accumulated in the cathode flow path PAc continues to be consumed by the electrochemical reaction with the fuel gas.

[0062] The main operations of this embodiment can be summarized as follows. Figure 9 is a graph showing the changes in anode pressure P1 and cathode pressure P2 over time from the initial time t0 when the operation of the fuel cell is stopped. In the graph, characteristic f1 indicates the change in anode pressure P1, and characteristic f2 indicates the change in cathode pressure P2. At time t0, with discharge-side on-off valves 502, 503, and 505 closed, fuel gas and oxidant gas are simultaneously supplied to the anode flow channel PAa and the cathode flow channel PAc, respectively (step S1). As a result, the anode pressure P1 and the cathode pressure Pc gradually increase from the initial pressure P0, as shown by characteristics f1 and f2.

[0063] At time t1, when the anode pressure P1 and cathode pressure P2 rise to a predetermined value Pa, the supply of fuel gas and oxidant gas is stopped (step S3). As a result, the anode flow path PAa and cathode flow path PAc in the fuel cell stack are maintained in a flow path blocked state, with fuel gas and oxidant gas sealed therein at the predetermined pressure Pa. At time t1, the anode pressure P1 and cathode pressure P2 are equal, so no cross-leak of gas occurs between the anode flow path PAa and the cathode flow path PAc.

[0064] If there is a poor seal or poor welding on the separator 3 on the anode flow channel PAa side, fuel gas will leak from the anode flow channel PAa, and as time passes from time t1, anode pressure P1 will gradually decrease, as shown in Figure 9. In contrast, there is no leakage of oxidant gas from the cathode flow channel PAc, so cathode pressure P2 remains constant. In reality, fuel gas and oxidant gas are consumed through a reaction with each other, and the anode pressure P1 and cathode pressure P2 decrease accordingly; however, for convenience, this is ignored in Figure 6 as characteristics f1 and f2.

[0065] At time t2, when a predetermined time T1 has elapsed since time t1, if the anode pressure P1 is higher than a predetermined value Pb and the cathode pressure P2 is also higher than the predetermined value Pb, it is determined that there is no fuel gas leak (step S6). On the other hand, as shown in Figure 9, if the anode pressure P1 falls below the predetermined value Pb even though the cathode pressure P2 is higher than the predetermined value Pb, it is determined that the pressure drop is not due to a reaction but is due to a leak. In other words, it is determined that there is a cross leak from the anode flow path PAa to the refrigerant flow path PAw or an out leak to the outside of the cell stack 10.

[0066] Furthermore, if hydrogen is detected by the hydrogen sensor 53, it is determined that there is an out-leak of fuel gas, and if hydrogen is not detected, it is determined that there is a cross-leak of fuel gas (steps S8 and S9). This makes it possible to determine not only whether there is a fuel gas leak, but also the type of leak.

[0067] According to this embodiment, the following effects can be achieved. (1) The fuel cell system 200 includes a fuel cell stack 100 having a cell stack 10 formed by stacking a plurality of power generation cells 1, and an anode flow path PAa through which fuel gas flows and a cathode flow path PAc through which oxidant gas flows provided inside the cell stack 10; a fuel gas supply / discharge unit 210 that supplies fuel gas to the anode flow path PAa and discharges the fuel gas from the anode flow path PAa; an oxidant gas supply / discharge unit 220 that supplies oxidant gas to the cathode flow path PAc and discharges the oxidant gas from the cathode flow path PAc; pressure sensors 51, 52 that detect a pressure P1 in the anode flow path PAa and a pressure P2 in the cathode flow path PAc; and an ECU 50 as a leak detection unit that detects fuel gas leakage from the anode flow path PAa based on the anode pressure P1 and cathode pressure P2 detected by the pressure sensors 51, 52 (FIGS. 1, 2, 7). After the fuel cell operation is stopped, the ECU 50 controls the fuel gas supply / discharge unit 210 and the oxidant gas supply / discharge unit 220 to achieve a flow path blocking state in which the anode flow path PAa is blocked from the fuel gas supply / discharge unit 210 and the cathode flow path PAc is blocked from the oxidant gas supply / discharge unit 220 while maintaining the anode pressure P1 and the cathode pressure P2 at predetermined values Pa, respectively, and further detects a fuel gas leak based on the amount of change in the anode pressure P1 and the amount of change in the cathode pressure P2 from the flow path blocking state (Figure 8).

[0068] In this way, after the fuel cell operation is stopped, fuel gas and oxidant gas are supplied to the anode flow path PAa and the cathode flow path PAc, respectively, and fuel gas leak detection is performed, eliminating the need to add a dedicated flow path for leak detection and enabling leak detection with a simple configuration. Furthermore, since fuel gas leaks are determined not only based on the amount of change in anode pressure P1 but also based on the amount of change in cathode pressure P2, the occurrence of a fuel gas leak can be accurately determined even if the anode pressure P1 drops due to a reaction between the fuel gas and oxidant gas.

[0069] (2) The ECU 50 determines whether a leak has occurred in the anode flow path PAa based on the amount of change in the anode pressure P1 relative to the amount of change in the cathode pressure P2 from the flow path shut-off state, i.e., when the anode pressure P1 is equal to or lower than the predetermined value Pb even though the cathode pressure P2 is higher than the predetermined value Pb (FIG. 8). This allows for accurate determination of the presence or absence of a fuel gas leak.

[0070] (3) The fuel cell system 200 further includes a coolant supply / discharge unit 230 that supplies a coolant to a refrigerant flow path PAw adjacent to the anode flow path PAa via a rear plate 3R (partition wall) and discharges the coolant from the refrigerant flow path PAw (FIGS. 1 and 2). When the degree of decrease in anode pressure P1 over time from the flow path blocked state is greater than the degree of decrease in cathode pressure P2, the ECU 50 determines that fuel gas is leaking from the anode flow path PAa to the outside of the cell stack 10 or from the anode flow path PAa to the refrigerant flow path PAw (FIG. 8). This makes it possible to determine that the fuel gas is leaking either out of the cell stack 10 or cross-leaking into the refrigerant flow path PAw.

[0071] (4) The fuel cell system 200 further includes a hydrogen sensor 53 that detects fuel gas outside the cell stack 10 (FIG. 1). When the hydrogen sensor 53 detects fuel gas in a state in which the degree of decrease in anode pressure P1 over time from the flow path shutoff state is greater than the degree of decrease in cathode pressure P2, the ECU 50 determines that fuel gas is leaking from the anode flow path PAa to the outside of the cell stack 10. When the hydrogen sensor 53 does not detect fuel gas, the ECU 50 determines that fuel gas is leaking from the anode flow path PAa to the refrigerant flow path PAw (FIG. 8). This makes it possible to identify the nature of the fuel gas leak with a simple configuration. The hydrogen sensor 53 is provided in the storage space SP0 in the case rather than in the refrigerant flow path, making installation of the hydrogen sensor 53 easy.

[0072] (5) After the fuel cell stops operating, the ECU 50 controls the fuel gas supply / discharge unit 210 and the oxidant gas supply / discharge unit 220 so as to simultaneously increase the anode pressure P1 and the cathode pressure P2 to a predetermined value Pa (FIG. 8). This allows the system to quickly transition to a flow path blocking state in which the gas pressure has increased to the predetermined value Pa, and allows the leak detection process to be completed in a short time. Furthermore, because the anode pressure P1 and the cathode pressure P2 are simultaneously increased to equal values, cross leaks due to the pressure difference between the anode pressure P1 and the cathode pressure P2 can be suppressed.

[0073] The above fuel cell system 200 can also be used as a method for detecting gas leaks in a fuel cell, including the steps of increasing the anode pressure P1 and the cathode pressure P2 to a predetermined value Pa after the fuel cell has stopped operating to block the flow path (steps S1 to S3), waiting for a predetermined time T1 while keeping the flow path blocked (step S4), and detecting a fuel gas leak based on the amount of change in the anode pressure P1 and the amount of change in the cathode pressure P2 after the predetermined time T1 has elapsed (steps S5 to S9).

[0074] The above embodiment can be modified in various ways. Some modifications will be described below. In the above embodiment, pressure sensors 51 and 52 serving as pressure detection units are connected to pipes 210f and 220a. However, the locations of the pressure detection units are not limited to those described above, as long as the pressures P1 and P2 in the anode flow path and the cathode flow path are detected. The anode pressure P1 and the cathode pressure P2 may be calculated using the detection values of other sensors that detect other physical quantities that have a correlation with these pressures P1 and P2. The configuration of the pressure detection units is not limited to those described above. Leak detection may be performed by detecting the differential pressure between the anode pressure P1 and the cathode pressure P2 and determining whether the anode pressure P1 is lower than the cathode pressure P2 and whether the differential pressure is equal to or greater than a predetermined value. In the above embodiment, the predetermined values Pa and Pb are constant. However, the predetermined values Pa and Pb may be changed, for example, based on a detected temperature value.

[0075] In the above embodiment, the ECU 50 as a leak detector detects a fuel gas leak by determining whether the pressures P1 and P2 have decreased by a predetermined amount or more after the predetermined time T1 has elapsed since the passage blocking state was established. However, the ECU 50 may also detect a fuel gas leak by determining whether the pressures P1 and P2 have decreased by a predetermined amount or more within a predetermined time without waiting for the predetermined time T1 (e.g., when P1≦Pb and P2>Pb are established). In the above embodiment, the ECU 50 detects a fuel gas leak based on the amount of change (decrease) in the pressures P1 and P2. However, the ECU 50 may also detect a fuel gas leak based on the rate of change in the pressures P1 and P2 (e.g., the rate of change in the pressures P1 and P2 per unit time, more specifically, the rate of decrease), i.e., whether the rate of pressure decrease is equal to or greater than a predetermined value. Therefore, the configuration of the leak detector that determines whether the degree of decrease in the anode pressure P1 over time from the passage blocking state is greater than the degree of decrease in the cathode pressure P2 is not limited to the above.

[0076] In the above embodiment, whether or not a leak has occurred in the anode flow path PAa is determined based on whether P1≦Pb and P2>Pb hold after a predetermined time T1 has elapsed since the flow path closed state. However, in other aspects, whether or not a leak has occurred in the anode flow path PAa may be determined based on the amount or rate of change in anode pressure P1 relative to the amount or rate of change in cathode pressure P2 since the flow path closed state. For example, the amount of decrease in anode pressure P1 may be divided by the amount of decrease in cathode pressure P2 to obtain a pressure decrease ratio, and whether or not a leak has occurred in the anode flow path PAa may be determined by determining whether this ratio is equal to or greater than a predetermined value. In the above embodiment, the hydrogen sensor 53 serving as a gas detector is provided in the housing space SP0 within the case. However, the gas detector may also be provided in another location, such as within the motor case.

[0077] In the above embodiment, after the fuel cell operation is stopped, the fuel gas and the oxidant gas are supplied to the anode flow channel PAa and the cathode flow channel PAc, respectively, to detect gas leaks. However, gas leak detection may also be performed by supplying either the fuel gas or the oxidant gas to the anode flow channel PAa and the cathode flow channel PAc, respectively. For example, a connecting line may be provided to connect the fuel gas supply line 210a and the oxidant gas supply line 220a in FIG. 1, and an on-off valve may be provided in the connecting line. When a gas leak is detected after the fuel cell operation is stopped, the on-off valve may be opened to supply either the fuel gas or the oxidant gas to the anode flow channel PAa and the cathode flow channel PAc, respectively, thereby maintaining the gas pressure in each flow channel PAa, PAc at a predetermined value Pa, thereby establishing a flow channel blocking state.

[0078] In the above embodiment, an example of applying the fuel cell system 200 to a vehicle has been described, but the fuel cell system of the present invention can also be applied to moving bodies other than vehicles, such as aircraft and ships, robots, and various industrial machines.

[0079] The above description is merely an example, and the present invention is not limited to the above-described embodiment and modifications as long as the features of the present invention are not impaired. One or more of the above-described embodiment and modifications can be arbitrarily combined, and modifications can also be combined with each other. [Explanation of symbols]

[0080] 1 power generation cell, 10 cell stack, 50 ECU, 51, 52 pressure sensors, 53 hydrogen sensor, 100 fuel cell stack, 200 fuel cell system, 210 fuel gas supply / discharge section, 220 oxidant gas supply / discharge section, 230 coolant supply / discharge section, PAa anode flow path, PAc cathode flow path

Claims

1. a fuel cell stack having a cell stack formed by stacking a plurality of power generation cells, the cell stack having an anode flow path through which a fuel gas flows and a cathode flow path through which an oxidant gas flows, disposed inside the cell stack; a fuel gas supply / discharge unit that supplies a fuel gas to the anode flow channel and discharges the fuel gas from the anode flow channel; an oxidant gas supply / discharge unit that supplies an oxidant gas to the cathode flow channel and discharges the oxidant gas from the cathode flow channel; a pressure detection unit that detects the pressure in the anode flow channel and the pressure in the cathode flow channel; a leak detection unit that detects a leak of fuel gas from the anode flow channel based on the pressure in the anode flow channel and the pressure in the cathode flow channel detected by the pressure detection unit, a leakage detection unit that controls the fuel gas supply / discharge unit and the oxidant gas supply / discharge unit after the operation of the fuel cell is stopped to achieve a flow path blocked state in which the anode flow path is blocked from the fuel gas supply / discharge unit and the cathode flow path is blocked from the oxidant gas supply / discharge unit while maintaining the pressure in the anode flow path and the pressure in the cathode flow path at predetermined values, respectively, and further detects a fuel gas leak based on the amount or rate of change in the pressure in the anode flow path and the amount or rate of change in the pressure in the cathode flow path from the flow path blocked state.

2. 2. The fuel cell system according to claim 1, the leak detection unit determines whether or not a leak has occurred in the anode flow path based on the amount or rate of change in pressure in the anode flow path relative to the amount or rate of change in pressure in the cathode flow path from the flow path blocked state.

3. 3. The fuel cell system according to claim 2, a cooling medium supply / discharge unit that supplies a cooling medium to a cooling medium flow path adjacent to the anode flow path via a partition wall and discharges the cooling medium from the cooling medium flow path, the leak detection unit determines that a fuel gas leak is occurring from the anode flow path to the outside of the cell stack or from the anode flow path to the refrigerant flow path when the degree of pressure decrease in the anode flow path over time from the flow path blocked state is greater than the degree of pressure decrease in the cathode flow path.

4. 4. The fuel cell system according to claim 3, Further, a gas detector that detects a fuel gas outside the cell stack is provided. the leak detection unit determines that fuel gas is leaking from the anode flow path to the outside of the cell stack when the gas detection unit detects fuel gas in a state in which the degree of pressure decrease in the anode flow path over time from the flow path blocked state is greater than the degree of pressure decrease in the cathode flow path, and determines that fuel gas is leaking from the anode flow path to the refrigerant flow path when the gas detection unit does not detect fuel gas.

5. 5. The fuel cell system according to claim 1, a leakage detection unit that controls the fuel gas supply / discharge unit and the oxidant gas supply / discharge unit so as to simultaneously increase the pressure in the anode flow path and the pressure in the cathode flow path to the predetermined value after the operation of the fuel cell is stopped.

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