Method for operating fuel cell system, and fuel cell system

Abstract

To provide an operating method for a fuel cell system that can suppress a purge valve from being frozen, and the fuel cell system.SOLUTION: An operation method for a fuel cell system 10 which comprises a fuel cell stack 12, a fuel gas supply passage 40, a circulation passage 45, a purge valve 46a, and a temperature sensor 84, and is mounted on a vehicle 11 includes: a determination process of determining whether a temperature detected by the temperature sensor 84 drops to a predetermined temperature or lower in a state in which the vehicle is stopped from being driven by turning off the ignition of the vehicle; and a purge valve exhaustion processing process of intermittently opening and closing the purge valve 46a a plurality of times while supplying fuel gas through the fuel gas supply passage 40 in the driving stop state if the temperature drops to the predetermined temperature or lower.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for operating a fuel cell system having a purge valve that discharges fuel gas from a circulation path provided in a flow path that supplies fuel gas to a fuel cell stack, and to a fuel cell system. [Background technology]

[0002] A fuel cell system includes a fuel cell stack, a fuel gas system device that supplies a fuel gas (anode gas) such as hydrogen gas to the fuel cell stack, and an oxidant gas system device that supplies an oxidant gas (cathode gas) such as air to the fuel cell stack. The fuel cell stack generates electricity through an electrochemical reaction between the fuel gas and the oxidant gas.

[0003] As disclosed in Patent Document 1, the fuel gas system device includes a circulation path that circulates fuel off-gas (fuel gas) discharged from the fuel cell stack to a fuel gas supply path that supplies fuel gas to the fuel cell stack, a purge path that discharges fuel gas from the circulation path, and a purge valve that opens and closes the purge path. For example, the purge valve closes the purge path in a normal state, and is opened in response to a change in state, such as an increase in the nitrogen gas concentration in the circulation path, thereby discharging the fluid in the circulation path. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-218242 A Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, the fluid (fuel off-gas discharged from the fuel cell stack) flowing through the circulation path of the fuel cell system contains water vapor generated by the power generation of the fuel cell stack. Therefore, when the surroundings of the fuel cell system are in a low-temperature environment (for example, below freezing point), the water vapor freezes, which may cause the orifice of the purge valve to become clogged or the valve body to become stuck. This may cause the purge valve to become unable to open or close.

[0006] The present invention has been made in consideration of the above-mentioned situation, and aims to provide a fuel cell system and an operating method for a fuel cell system that can prevent the purge valve from freezing by properly discharging water that has adhered to the vicinity of the orifice of the purge valve when the environment is low temperature. [Means for solving the problem]

[0007] A first aspect of the present invention is a method for operating a fuel cell system mounted on a vehicle, the method comprising: a fuel cell stack; a fuel gas supply path for supplying fuel gas to the fuel cell stack; a circulation path for circulating fuel off-gas discharged from the fuel cell stack to the fuel cell stack; a purge valve for discharging the fuel off-gas from the circulation path; and a temperature sensor for detecting the temperature of the surrounding environment of the purge valve, the method including a determination step for determining whether the temperature detected by the temperature sensor has dropped below a predetermined temperature when the vehicle is in a drive-stopped state with the ignition of the vehicle turned off; and a purge valve scavenging processing step for, when the temperature is below the predetermined temperature, intermittently opening and closing the purge valve multiple times while supplying fuel gas through the fuel gas supply path in the drive-stopped state.

[0008] A second aspect of the present invention is a fuel cell system mounted on a vehicle, comprising a fuel cell stack, a fuel gas supply path that supplies fuel gas to the fuel cell stack, a circulation path that circulates fuel off-gas discharged from the fuel cell stack to the fuel cell stack, a purge valve that discharges the fuel off-gas from the circulation path, a temperature sensor that detects the temperature of the surrounding environment of the purge valve, and a control unit that, when the vehicle is in a drive-stopped state with the ignition of the vehicle turned off, determines whether the temperature detected by the temperature sensor has dropped below a predetermined temperature, and if the temperature is below the predetermined temperature, intermittently opens and closes the purge valve multiple times while supplying fuel gas through the fuel gas supply path in the drive-stopped state. Effect of the Invention

[0009] The above-mentioned fuel cell system operating method and fuel cell system can properly discharge water near the purge valve in a low-temperature environment where the purge valve may freeze. In particular, by intermittently opening and closing the purge valve multiple times, a pulsation is applied to the fuel gas pressure upstream of the purge valve, which moves the water contained in the circulation path and allows it to be smoothly discharged from the purge valve. Therefore, the fuel cell system can more reliably suppress freezing of the purge valve. [Brief description of the drawings]

[0010] [Figure 1] 1 is an explanatory diagram illustrating a schematic overall configuration of a fuel cell system according to an embodiment of the present invention; [Diagram 2] 4 is a block diagram showing functional parts in an ECU in anti-freezing processing; FIG. [Diagram 3] Fig. 3A is a flow chart showing a method for operating a fuel cell system, and Fig. 3B is a flow chart showing the order of steps in a freeze suppression process. [Figure 4] 4 is a time chart showing an example of a freeze suppression process of a fuel cell system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to preferred embodiments thereof and accompanying drawings.

[0012] 1, a fuel cell system 10 according to one embodiment of the present invention includes a fuel cell stack 12, a fuel gas system device 14, an oxidant gas system device 16, and a cooling device 18. This fuel cell system 10 is mounted in a motor room or the like of a fuel cell automobile (hereinafter simply referred to as a vehicle 11). The fuel cell system 10 supplies power generated by the fuel cell stack 12 to a battery Bt, a driving motor Mt, and the like of the vehicle 11. Note that the fuel cell system 10 is not limited to being mounted on the vehicle 11, and may be used as a stationary system, for example.

[0013] The fuel cell stack 12 includes a plurality of power generating cells 20 that generate electricity through an electrochemical reaction between a fuel gas (hydrogen gas, anode gas) and an oxidant gas (oxygen contained in air, cathode gas). With the fuel cell stack 12 mounted on the vehicle 11, the plurality of power generating cells 20 are stacked along the vehicle width direction with their electrode surfaces in an upright position to form a stack 21. The plurality of power generating cells 20 may also be stacked in the vehicle length direction (front-rear direction) of the vehicle 11 or in the direction of gravity.

[0014] Each power generating cell 20 is composed of a membrane electrode assembly 22 (hereinafter referred to as "MEA 22") and a pair of separators 24 (first separator 24a, second separator 24b) that sandwich the MEA 22. The MEA 22 has an electrolyte membrane 26 (for example, a solid polymer electrolyte membrane (cation exchange membrane)), an anode electrode 28 laminated on one side of the electrolyte membrane 26, and a cathode electrode 30 laminated on the other side of the electrolyte membrane 26. Between the first separator 24a and the MEA 22, a fuel gas flow path 32 is formed for flowing a fuel gas along the separator surface. Between the second separator 24b and the MEA 22, an oxidizer gas flow path 34 is formed for flowing an oxidizer gas along the separator surface. In addition, a refrigerant flow path 36 for flowing a refrigerant along the separator surface is formed between the first separator 24a and the second separator 24b by stacking the multiple power generating cells 20.

[0015] Furthermore, the fuel cell stack 12 has a plurality of communication holes (not shown) (fuel gas communication hole, oxidant gas communication hole, refrigerant communication hole) that allow the fuel gas, oxidant gas, and coolant to flow along the stacking direction of the stack 21. The fuel gas communication hole is connected to the fuel gas flow path 32, the oxidant gas communication hole is connected to the oxidant gas flow path 34, and the refrigerant communication hole is connected to the coolant flow path 36.

[0016] Fuel gas is supplied to the fuel cell stack 12 by the fuel gas system device 14. In the fuel cell stack 12, the fuel gas flows through a fuel gas communication hole (fuel gas inlet communication hole) and enters a fuel gas flow passage 32, and is used for power generation at the anode electrode 28. Fuel gas not used for power generation and fuel off-gas containing water flows from the fuel gas flow passage 32 to the fuel gas communication hole (fuel gas outlet communication hole), and is discharged from the fuel cell stack 12 to the fuel gas system device 14.

[0017] Furthermore, the fuel cell stack 12 is supplied with an oxidant gas by an oxidant gas device 16. In the fuel cell stack 12, the oxidant gas flows through the oxidant gas communication holes (oxidant gas inlet communication holes) and enters the oxidant gas flow passage 34, and is used for power generation at the cathode electrode 30. The oxidant off-gas, which contains oxidant gas and water that is not used for power generation, flows from the oxidant gas flow passage 34 to the oxidant gas communication holes (oxidant gas outlet communication holes), and is discharged from the fuel cell stack 12 to the oxidant gas device 16.

[0018] Furthermore, a coolant is supplied to the fuel cell stack 12 by a cooling device 18. In the fuel cell stack 12, the coolant flows through the coolant communication holes (coolant inlet communication holes) and enters the coolant flow passage 36, appropriately adjusting the temperature of each power generation cell 20. This coolant flows from the coolant flow passage 36 to the coolant communication holes (coolant outlet communication holes), and is discharged from the fuel cell stack 12 to the cooling device 18.

[0019] Next, the fuel gas system 14 that distributes the fuel gas outside the fuel cell stack 12 will be described in detail.

[0020] The fuel gas system 14 has a fuel gas supply path 40 that supplies fuel gas to the fuel cell stack 12, and a fuel gas discharge path 42 that discharges fuel off-gas from the fuel cell stack 12. In addition, a fuel gas circulation path 44 is connected between the fuel gas supply path 40 and the fuel gas discharge path 42, and returns unreacted fuel gas contained in the fuel off-gas in the fuel gas discharge path 42 to the fuel gas supply path 40.

[0021] That is, the downstream side of the fuel gas supply path 40, the fuel gas discharge path 42, and the fuel gas circulation path 44 form a circulation path 45 that circulates the fuel gas between the fuel cell stack 12. A purge path 46 is connected to the fuel gas circulation path 44 to discharge fuel off-gas (fuel gas, water (including water vapor and attached liquid water), nitrogen gas, etc.) from the circulation path 45.

[0022] The upstream end of the fuel gas supply path 40 is connected to a high-pressure tank 47. The high-pressure tank 47 is a supply source that stores and supplies fuel gas, and causes the fuel gas to flow into the fuel gas supply path 40 based on the opening and closing of a supply valve 47a (in-tank solenoid valve) provided in the high-pressure tank 47 itself and a pressure reducing valve 47b provided midway.

[0023] An injector 48 and an ejector 50 are provided in series at a midpoint of the fuel gas supply path 40, and a supply bypass path 52 is connected across the injector 48 and the ejector 50. A BP (bypass) injector 54 is provided in the supply bypass path 52.

[0024] During operation of the fuel cell system 10, the injector 48 and the BP injector 54 open and close upstream (high pressure side) of the fuel gas supply path 40 to discharge a predetermined amount of fuel gas downstream (low pressure side). The injector 48 is a main injector that is mainly used during power generation, and the BP injector 54 is a sub-injector that supplies a large amount of hydrogen when the fuel cell stack 12 is started or when high current power generation is required. The ejector 50 supplies fuel gas to the downstream fuel cell stack 12 while sucking in fuel off-gas from the fuel gas circulation path 44 by using negative pressure generated by the flow of the fuel gas discharged from the injector 48.

[0025] A gas-liquid separator 56 is provided in the fuel gas discharge path 42 to separate gas from liquid (liquid water produced during power generation) contained in the fuel off-gas. The fuel gas circulation path 44 is connected to the top of the gas-liquid separator 56, while one end of a drain path 60 that discharges liquid from the gas-liquid separator 56 is connected to the bottom of the gas-liquid separator 56. This drain path 60 is provided with a drain valve 60a that opens and closes the internal flow path. In addition, the gas-liquid separator 56 is provided with a water level sensor 56a to detect the level of liquid (liquid water) that has been separated from the fuel off-gas and accumulated at the bottom.

[0026] The fuel gas circulation path 44 is provided with a fuel gas pump 58 for circulating the fuel off-gas to the fuel gas supply path 40. One end of the purge path 46 is connected between the gas-liquid separator 56 and the fuel gas pump 58. The other end of the purge path 46 is connected to an oxidant gas discharge path 64 of the oxidant gas system device 16 described below. The other end of the drain path 60 is connected to a midpoint of the purge path 46, and a purge valve 46a for opening and closing the flow path is provided upstream (to the fuel gas circulation path 44) of the connection point of the drain path 60. The purge valve 46a discharges the fuel off-gas (fuel gas) from the circulation path 45. The purge valve 46a may be configured to be provided on the circulation path 45 and discharge the fuel gas to the purge path 46 branched off from the circulation path 45.

[0027] Next, the oxidizing gas system 16 that distributes the oxidizing gas outside the fuel cell stack 12 will be described in detail.

[0028] The oxidant gas device 16 has an oxidant gas supply channel 62 that supplies oxidant gas to the fuel cell stack 12, and an oxidant gas discharge channel 64 that discharges oxidant off-gas from the fuel cell stack 12. Furthermore, an oxidant gas bypass channel 66 is provided between the oxidant gas supply channel 62 and the oxidant gas discharge channel 64, for directly circulating the oxidant gas in the oxidant gas supply channel 62 to the oxidant gas discharge channel 64. The fuel cell system 10 according to this embodiment also includes an oxidant gas circulation channel 68 between the oxidant gas supply channel 62 and the oxidant gas discharge channel 64, for circulating the oxidant off-gas in the oxidant gas discharge channel 64 to the oxidant gas supply channel 62. Note that the fuel cell system 10 may not be configured to include the oxidant gas circulation channel 68.

[0029] A compressor 70 is provided at a predetermined position of the oxidant gas supply path 62, which compresses air taken in from the atmosphere and supplies the compressed air as oxidant gas. The oxidant gas bypass path 66 is connected to the oxidant gas supply path 62 downstream of the compressor 70 in the flow direction of the oxidant gas. A supply-side on-off valve 72 is provided in the oxidant gas supply path 62 downstream of the connection point of the oxidant gas bypass path 66 in the flow direction of the oxidant gas. The oxidant gas circulation path 68 is connected to the oxidant gas supply path 62 downstream of the supply-side on-off valve 72 in the flow direction of the oxidant gas. Although not shown, the oxidant gas supply path 62 may be provided with an auxiliary device such as an intercooler for cooling the oxidant gas.

[0030] Furthermore, a humidifier 74 is provided in the oxidant gas supply path 62 between the compressor 70 (downstream of the supply-side on-off valve 72 in the flow direction of the oxidant gas) and the fuel cell stack 12. The humidifier 74 is connected to both the oxidant gas supply path 62 and the oxidant gas discharge path 64, and humidifies the oxidant gas in the oxidant gas supply path 62 with moisture contained in the oxidant off-gas in the oxidant gas discharge path 64. A humidifier bypass path 75 that bypasses the humidifier 74 is provided in the oxidant gas supply path 62, and a humidifier bypass valve 75a that opens and closes the flow path is provided in the humidifier bypass path 75.

[0031] The oxidant gas circulation path 68 is connected to the oxidant gas discharge path 64 downstream in the flow direction of the oxidant off-gas from the humidifier 74. The oxidant gas circulation path 68 is provided with an EGR pump 82 for circulating the oxidant off-gas from the oxidant gas discharge path 64 to the oxidant gas supply path 62.

[0032] Further, a discharge side opening / closing valve 76 and an exhaust pressure valve 78 are provided on the oxidant gas discharge channel 64 downstream in the flow direction of the oxidant off-gas from the connection point of the oxidant gas circulation channel 68 .

[0033] The oxidant gas bypass passage 66 is connected to the oxidant gas discharge passage 64 downstream in the flow direction of the oxidant off-gas from the exhaust pressure valve 78. This oxidant gas bypass passage 66 is provided with a flow rate adjustment valve 80 that adjusts the flow rate of the oxidant gas flowing from the oxidant gas supply passage 62 to the oxidant gas discharge passage 64. Furthermore, the purge passage 46 of the fuel gas system device 14 is connected to the oxidant gas discharge passage 64 downstream of the connection point of the oxidant gas bypass passage 66.

[0034] The fuel cell system 10 also includes a temperature sensor 84 for detecting the temperature of the surrounding environment of the purge valve 46a. As the temperature sensor 84, for example, an outside air temperature sensor 84a that detects the air temperature around the fuel cell system 10 (including the outside of the vehicle 11) can be used. Alternatively, the temperature sensor 84 may be attached to the purge valve 46a itself, or, for example, a fuel gas outlet temperature sensor 84b provided in the fuel gas discharge path 42 may be used.

[0035] Furthermore, the fuel cell system 10 is provided with a pressure sensor 86 in the fuel gas supply path 40 for detecting the pressure of the gas (fuel gas, etc.) flowing through the fuel gas supply path 40.

[0036] The above fuel cell system 10 has an ECU (Electronic Control Unit) 90 that controls the operation of each component of the fuel cell system 10 to generate power in the fuel cell stack 12. The ECU 90 is configured as a computer having a processor, memory, and an input / output interface (not shown). Note that the ECU 90 may be configured with multiple ECUs (for example, a power generation ECU that controls the current of the fuel cell stack 12, an ECU for the fuel gas system device 14, an ECU for the oxidant gas system device 16, etc.).

[0037] 2, the ECU 90 is connected to each auxiliary device of the fuel cell system 10 (or a power distribution unit that controls the power supply to each auxiliary device) via an in-vehicle communication line, etc. The water level sensor 56a, the temperature sensor 84, and the pressure sensor 86 are also connected to the ECU 90 via an in-vehicle communication line, etc.

[0038] The ECU 90 operates with low power even when the vehicle 11 is stopped (ignition off), and determines or estimates whether the surroundings of the fuel cell system 10 are in a low temperature environment (for example, below freezing) based on temperature information detected by the temperature sensor 84. If the ECU 90 determines that the surroundings are in a low temperature environment, it performs a purge valve scavenging process to suppress freezing of the purge valve 46a.

[0039] That is, in the fuel cell system 10, as described above, the fuel off-gas contains water vapor, and this water vapor also moves to the purge valve 46a of the purge path 46. In a low-temperature environment, such as below freezing point, this water vapor freezes into ice. At this time, the frozen water may clog the orifice of the purge valve 46a or may cause the valve body (not shown) of the purge valve 46a to adhere to the valve housing. This makes it impossible for the purge valve 46a to discharge the fluid in the circulation path 45.

[0040] For this reason, the fuel cell system 10 according to this embodiment performs a purge valve scavenging process to prevent the purge valve 46a from freezing by discharging water adhering to the purge valve 46a and water vapor present in the circulation path 45. The fuel cell system 10 is also configured to perform a purge valve scavenging process in conjunction with a cathode scavenging process that is performed to suppress freezing of the power generating cells 20 in the fuel cell stack 12 in a low-temperature environment. Hereinafter, a series of processes including the cathode scavenging process and the purge valve scavenging process are also referred to as a freeze suppression process.

[0041] In order to carry out the freeze suppression process, the ECU 90 constructs internally functional blocks as shown in Fig. 2 by having a processor read and execute a program (not shown) stored in memory. The ECU 90 includes a freeze determination unit 92, a cooperative control unit 94, a cathode scavenging control unit 96, and an anode scavenging control unit 98. When the fuel cell system 10 has multiple ECUs, the anode scavenging control unit 98 may be provided in the ECU of the fuel gas system device 14, and the cathode scavenging control unit 96 may be provided in the ECU of the oxidant gas system device 16.

[0042] The freezing determination unit 92 is a functional unit that determines or estimates the possibility of freezing of the purge valve 46a based on temperature information detected by the temperature sensor 84. The freezing determination unit 92 holds in advance a freezing determination threshold Th (predetermined temperature) that defines a low-temperature environment in which the purge valve 46a freezes, and determines whether the temperature information is equal to or lower than the freezing determination threshold Th. An example of the temperature of the freezing determination threshold Th is 0°C, but it may be set to a temperature lower than 0°C taking into account the structure of the purge valve 46a, etc. Furthermore, the freezing determination unit 92 may estimate early that the low-temperature environment will occur before the temperature falls below the freezing determination threshold Th, based on the rate at which the temperature information drops, etc.

[0043] The cooperative control unit 94 is a functional unit that links the control by the cathode scavenging control unit 96 and the control by the anode scavenging control unit 98 in the freeze prevention process. That is, in the freeze prevention process, the operation of each accessory of the fuel gas system device 14 and the operation of each accessory of the oxidant gas system device 16 are appropriately synchronized. This allows the fuel cell system 10 to take measures such as diluting the fuel gas discharged from the purge path 46 with the oxidant gas discharged from the oxidant gas discharge path 64.

[0044] Furthermore, in the freeze suppression process of this embodiment, a plurality of processes (oxidant gas path dilution process, purge valve scavenging process, cathode scavenging process, drain discharge process) are performed sequentially or in parallel, and the cooperative control unit 94 manages the execution timing of each process. The oxidant gas path dilution process is a process in which oxidant gas is supplied to the path of the oxidant gas system device 16, thereby making it possible to dilute the concentration of the fuel gas to be later discharged from the fuel gas system device 14 with the oxidant gas. The drain discharge process is a process in which liquid water accumulated in the gas-liquid separator 56 of the fuel gas system device 14 is drained.

[0045] In the freeze prevention process, the cathode scavenging control unit 96 controls each auxiliary device of the oxidant gas system device 16. The auxiliary devices of the oxidant gas system device 16 that operate in the freeze prevention process include the compressor 70, the exhaust pressure valve 78, and the flow rate control valve 80. In the freeze prevention process, the supply side opening / closing valve 72, the humidifier bypass valve 75a, and the discharge side opening / closing valve 76 (all see FIG. 1) are maintained in an open state.

[0046] The anode scavenging control unit 98 controls each accessory of the fuel gas system device 14 during the freeze inhibition process. Examples of the accessories of the fuel gas system device 14 that operate during the freeze inhibition process include the purge valve 46a, the supply valve 47a, the injector 48, and the drain valve 60a. Although not described here, the BP injector 54 (see FIG. 1) may be operated when increasing the amount of fuel gas discharged during the freeze inhibition process.

[0047] The fuel cell system 10 according to this embodiment is basically configured as described above, and its operation will be described below.

[0048] When the vehicle 11 is in a driving state (ignition on), the ECU 90 of the fuel cell system 10 controls the operation of each auxiliary device of the fuel gas system device 14 and each auxiliary device of the oxidant gas system device 16 in order to generate power using the fuel cell stack 12. The fuel cell stack 12 generates power through an electrochemical reaction of the fuel gas and oxidant gas supplied by the operation of each auxiliary device. Water is produced in the fuel cell stack 12 as a result of power generation, and this produced water is discharged from the fuel cell stack 12 to the fuel gas discharge path 42, the oxidant gas discharge path 64, etc.

[0049] The liquid (liquid water) of the generated water discharged to the fuel gas discharge path 42 is separated from the gas in the gas-liquid separator 56 and is stored in the gas-liquid separator 56. Meanwhile, the gas (water vapor) of the generated water discharged to the fuel gas discharge path 42 circulates through the circulation path 45 (the fuel gas discharge path 42, the fuel gas circulation path 44, and the fuel gas supply path 40). This water vapor also moves from the circulation path 45 to the purge path 46, and is discharged via the purge path 46 when the purge valve 46a, which is normally closed, is opened.

[0050] When the vehicle 11 is stopped (ignition off), the ECU 90 appropriately stops the operation of each auxiliary device and stops power generation in the fuel cell stack 12. In the stopped state, the above-mentioned water vapor or liquid water formed by condensation of water vapor is present in the circulation path 45, purge path 46, and purge valve 46a of the fuel gas system device 14. Therefore, the ECU 90 operates at low power and executes the process flow shown in Fig. 3A (method of operating the fuel cell system 10).

[0051] The freezing determination unit 92 of the ECU 90 receives (acquires) temperature information constantly detected by the temperature sensor 84 (step S1). Then, the freezing determination unit 92 compares the temperature information with a freezing determination threshold Th stored in advance, and determines whether the temperature information is equal to or lower than the freezing determination threshold Th (step S2). If the temperature information is higher than the freezing determination threshold Th (step S2: NO), there is no possibility that the purge valve 46a will freeze, so the process returns to step S1, and the same process flow is repeated thereafter.

[0052] On the other hand, if the temperature information is equal to or lower than the freezing determination threshold value Th (step S2: YES), the purge valve 46a may freeze, so the process proceeds to step S3. In step S3, the cooperative control unit 94 of the ECU 90 causes the cathode scavenging control unit 96 and the anode scavenging control unit 98 to cooperate with each other to carry out the freezing suppression process.

[0053] 3B, the cooperative control unit 94 sequentially performs an oxidant gas path dilution process (step S3-1), a purge valve scavenging process (step S3-2), a cathode scavenging process, and a drain discharge process (step S3-3). Hereinafter, the operation contents of the freeze suppression process (steps S3-1 to S3-3) will be specifically described with reference to the time chart of FIG.

[0054] At time t1 after the start of the freeze prevention process, the cathode scavenging control unit 96 of the ECU 90 outputs a valve open command to the flow rate control valve 80, which is closed in the drive-stop state. As a result, the flow rate control valve 80 is opened 100% between time t1 and time t2 (see the dotted line in FIG. 4), allowing a large amount of oxidant gas to flow through the oxidant gas bypass passage 66. In addition, at time t1, the cathode scavenging control unit 96 closes the exhaust pressure valve 78, which is open in the drive-stop state, for a short period of time, and checks the operating state of the exhaust pressure valve 78. After checking the operation of the exhaust pressure valve 78, the exhaust pressure valve 78 is opened again.

[0055] Then, at time t2 when the flow rate regulating valve 80 actually opens, the cathode scavenging control unit 96 starts rotating the compressor 70 and supplies the oxidant gas to the oxidant gas supply passage 62 downstream of the compressor 70. At this time t2, the cathode scavenging control unit 96 sets the required rotation speed of the compressor 70 to a first required rotation speed (e.g., 50,000 rpm). The actual rotation speed of the compressor 70 gradually increases based on this first required rotation speed, and after time t3 when the actual rotation speed reaches the first required rotation speed, the actual rotation speed is controlled according to the first required rotation speed.

[0056] The oxidant gas supplied to the oxidant gas supply channel 62 by the rotation of the compressor 70 flows through the oxidant gas supply channel 62 toward the fuel cell stack 12 and also flows through the oxidant gas bypass channel 66 because the exhaust pressure valve 78 and the flow rate control valve 80 are open. As a result, the inside of the fuel cell stack 12 (oxidant gas flow channel 34), the oxidant gas exhaust channel 64, and the oxidant gas bypass channel 66 are filled with oxidant gas.

[0057] Further, under the command of the cooperative control unit 94, the anode scavenging control unit 98 increases the target value of the fuel gas pressure in the circulation path 45 to a predetermined pressure value at time t2, thereby starting the operation of the fuel gas system device 14. That is, the anode scavenging control unit 98 opens the supply valve 47a and the pressure reducing valve 47b on the upstream side (high-pressure tank 47 side) of the fuel gas supply path 40, which were closed when the fuel gas supply path 40 was not driven. As a result, the fuel gas system device 14 supplies the high-pressure fuel gas in the high-pressure tank 47 to the downstream side of the fuel gas supply path 40 while reducing the pressure in the pressure reducing valve 47b. However, at time t2, since the injector 48 is not driven, the fuel gas is not discharged downstream of the injector 48, and the fuel gas pressure in the circulation path 45 (pressure sensor 86) does not increase.

[0058] Then, the anode scavenging control unit 98 operates the injector 48 at time t2a, which is slightly before time t3. The injector 48 discharges the fuel gas with the flow rate adjusted to the downstream fuel gas supply path 40. As a result, from time t3 onwards, the fuel cell stack 12 (fuel gas flow path 32) and the circulation path 45 (fuel gas discharge path 42, fuel gas circulation path 44, and fuel gas supply path 40 downstream of the ejector 50) are filled with fuel gas. Therefore, the pressure sensor 86 detects the fuel gas pressure (actual pressure value) that has increased in response to the operation of the injector 48.

[0059] The cooperative control unit 94 ends the oxidant gas path dilution process (step S3-1 in FIG. 3B) at time t4 when the oxidant gas fills the path of the oxidant gas system device 16, and after this end (i.e., from time t4), the cooperative control unit 94 transitions to the purge valve scavenging process. In the purge valve scavenging process, the cathode scavenging control unit 96 sets the rotation speed of the compressor 70 to a second required rotation speed (e.g., 40,000 rpm) that is lower than the first required rotation speed. The actual rotation speed of the compressor 70 decreases according to this second required rotation speed.

[0060] Furthermore, the cathode scavenging control unit 96 keeps the flow rate adjustment valve 80 open even at time t4, while closing the exhaust pressure valve 78, which was open until time t4. This closure of the exhaust pressure valve 78 stops the oxidant gas from flowing through the fuel cell stack 12, and all of the oxidant gas supplied by the compressor 70 flows toward the oxidant gas bypass path 66. Therefore, a large amount of oxidant gas flows through the oxidant gas discharge path 64 downstream of the connection point of the oxidant gas bypass path 66.

[0061] Meanwhile, in the purge valve scavenging process after time t4, the anode scavenging control unit 98 performs an operation of intermittently (discontinuously) opening and closing the purge valve 46a, which was closed in a drive-stopped state, multiple times. Also, at time t4, the anode scavenging control unit 98 increases the discharge amount of the fuel gas discharged from the injector 48. In other words, the anode scavenging control unit 98 makes the second discharge amount of the injector 48 from time t4 to time t5 larger than the first discharge amount of the injector 48 from time t3 to time t4.

[0062] As a result, a large amount of fuel gas flows into the purge passage 46 and the purge valve 46a from the circulation passage 45. The purge valve 46a can pulsate the fuel gas pressure upstream of the purge valve 46a by repeatedly opening and closing the valve intermittently, thereby moving the water in the circulation passage 45 and the purge passage 46. For example, the fuel gas pressure applied to the purge valve 46a is increased in the closed state of the purge valve 46a, and the water (steam or liquid water) inside the purge valve 46a is repelled under this fuel gas pressure in the open state. Therefore, the water present near the orifice and the valve body of the purge valve 46a is significantly reduced. In particular, the anode scavenging control unit 98 can effectively discharge the water in the circulation passage 45 to the purge passage 46 downstream of the purge valve 46a by repeatedly opening and closing the purge valve 46a multiple times.

[0063] When the purge valve 46a is open, gas containing fuel gas is discharged together with water into the purge path 46 downstream of the purge valve 46a. The fuel gas discharged into the purge path 46 mixes with the oxidant gas in the oxidant gas discharge path 64 to which the purge path 46 is connected. That is, since the oxidant gas discharge path 64 is filled with the oxidant gas, the fuel gas can be diluted in the oxidant gas discharge path 64. The oxidant gas discharge path 64 then discharges the fuel gas diluted with the oxidant gas to the outside of the vehicle 11.

[0064] The cooperative control unit 94 performs the above-described purge valve scavenging process over a period from time t4 to time t5. The period during which the purge valve scavenging process is performed (the interval from time t4 to time t5) is not particularly limited, but is set, for example, to be longer than the period during which the oxidant gas path dilution process is performed (times t1 to t4).

[0065] The cooperative control unit 94 ends the purge valve scavenging process (step S3-2 in FIG. 3B) at time t5, and after the end (i.e., from time t5), performs the cathode scavenging process and the drain discharge process. In the cathode scavenging process, the cathode scavenging control unit 96 sets the rotation speed of the compressor 70 to a third requested rotation speed (e.g., 24,000 rpm) that is lower than the second requested rotation speed. The actual rotation speed of the compressor 70 decreases according to this third requested rotation speed.

[0066] Furthermore, at time t5, the cathode scavenging control unit 96 closes the flow rate control valve 80 while opening the exhaust pressure valve 78, which was closed until time t5. Closing the flow rate control valve 80 blocks the flow of the oxidant gas in the oxidant gas bypass passage 66, and all of the oxidant gas supplied by the compressor 70 is directed toward the fuel cell stack 12. Therefore, in the fuel cell stack 12, the supplied oxidant gas removes moisture remaining in the MEA 22. Also, a portion of the supplied oxidant gas is discharged to the oxidant gas discharge passage 64, while another portion permeates (cross leaks) the MEA 22 and moves to the fuel gas flow passage 32 and the fuel gas discharge passage 42 (circulation path 45). Drying is promoted in the fuel cell stack 12 by the movement of the oxidant gas.

[0067] The cathode scavenging control unit 96 may shift the closing timing of the flow rate control valve 80 to a timing (time t5a) later than time t5, as indicated by the two-dot chain line in Fig. 4. This allows the oxidant gas to be discharged to the oxidant gas discharge path 64 via the oxidant gas bypass path 66 until time t5a, thereby making it possible to satisfactorily dilute the fuel gas discharged in association with the drain water discharge treatment.

[0068] On the other hand, in the drain discharge process after time t5, the anode scavenging control unit 98 closes the purge valve 46a that has been intermittently opened and closed. Also, at time t5, the anode scavenging control unit 98 opens the drain valve 60a of the drain path 60 while monitoring the liquid water by the water level sensor 56a of the gas-liquid separator 56.

[0069] Furthermore, at time t5, the anode scavenging control unit 98 reduces the discharge amount (supply pressure) of the fuel gas discharged from the injector 48. In other words, the anode scavenging control unit 98 makes the third discharge amount of the injector 48 from time t5 to time t6 smaller than the second discharge amount of the injector 48 from time t4 to time t5.

[0070] The opened drain path 60 and drain valve 60a can smoothly discharge the water (liquid water) accumulated in the gas-liquid separator 56. At this time, the fuel gas pressure in the circulation path 45 is appropriately adjusted by the operation of the injector 48, thereby suppressing the outflow of fuel gas to the drain path 60 and promoting the discharge of liquid water from the gas-liquid separator 56. The liquid water and fuel gas that have flowed into the drain path 60 downstream of the drain valve 60a flow into the oxidant gas discharge path 64 via the purge path 46, are diluted with the oxidant gas in the oxidant gas discharge path 64, and are then discharged to the outside of the vehicle 11.

[0071] The drain valve 60a is opened (drainage process) while the water level sensor 56a monitors the liquid water level, and ends at time t6 when the water level becomes approximately zero and the absence of liquid water continues for a predetermined time. At the end of the drainage process (time t6), the anode scavenging control unit 98 reduces the target value of the fuel gas pressure to the pressure value before the freeze suppression process. As a result, the anode scavenging control unit 98 closes the supply valve 47a and the pressure reducing valve 47b and stops the operation of the injector 48, so that the fuel gas pressure (actual pressure value) in the circulation path 45 gradually decreases. In addition, the anode scavenging control unit 98 closes the drain valve 60a that was open at time t6. That is, at this timing, scavenging on the fuel gas system device 14 side ends.

[0072] In response to this, the cathode scavenging control unit 96 continues the cathode scavenging process at time t6. That is, the process of thoroughly drying the power generating cells 20 in the fuel cell stack 12 with the oxidant gas takes longer than the drain water discharge process, so the process is also performed after the drain water discharge process. Note that the execution time of the cathode scavenging process is preferably set appropriately based on the temperature of the surrounding environment, and for example, when the temperature of the fuel cell stack 12 is high, the process may be configured to be performed for a shorter period of time than the purge valve scavenging process.

[0073] Even after time t6, the cathode scavenging control unit 96 rotates the compressor 70 at the third required rotation speed, while maintaining the flow rate control valve 80 in the closed state and the exhaust pressure valve 78 in the open state. This allows the inside of the fuel cell stack 12 to be sufficiently dried, and makes it possible to prevent freezing of the power generating cells 20 when the environment becomes a low temperature environment after the freeze prevention process.

[0074] Then, at time t7 when a predetermined time has elapsed since the start of the cathode scavenging process (time t5), the cathode scavenging control unit 96 ends the cathode scavenging process (step S3-3 in FIG. 3B). At this time, the cathode scavenging control unit 96 sets the required rotation speed of the compressor 70 to zero to stop the rotation of the compressor 70. The cathode scavenging control unit 96 also maintains the exhaust pressure valve 78 in an open state and the flow rate control valve 80 in a closed state. As a result, the fuel cell system 10 ends the freeze inhibition process and transitions to a standby state.

[0075] In the fuel cell system 10 in which the above-mentioned freeze suppression process has been carried out, even in a low-temperature environment, there will be almost no water in the circulation path 45. Therefore, the fuel cell system 10 can suppress freezing of the purge valve 46a, and reduce the inconvenience of the purge valve 46a freezing and being unable to discharge fluid from the circulation path 45. Furthermore, the fuel cell system 10 does not need to install a heater or the like in the purge valve 46a, making it possible to suppress increases in manufacturing costs and power consumption.

[0076] The present invention is not limited to the above-described embodiment, and various modifications are possible in accordance with the gist of the invention. For example, the fuel cell system 10 may perform a cathode scavenging process when performing a purge valve scavenging process in which the purge valve 46a is intermittently opened and closed. The fuel cell system 10 may perform a purge valve scavenging process without performing a cathode scavenging process or an oxidant gas path dilution process. Alternatively, the timing of performing the oxidant gas path dilution process may be set to be during or after the purge valve scavenging process.

[0077] The technical ideas and effects that can be understood from the above-described embodiments will be described below.

[0078] A first aspect of the present invention is a method for operating a fuel cell system 10 including a fuel cell stack 12, a fuel gas supply path 40 that supplies fuel gas to the fuel cell stack 12, a circulation path 45 that circulates fuel off-gas discharged from the fuel cell stack 12 to the fuel cell stack 12, a purge valve 46a that discharges the fuel off-gas from the circulation path 45, and a temperature sensor 84 that detects the temperature of the surrounding environment of the purge valve 46a, and includes a determination step of determining whether the temperature detected by the temperature sensor 84 has dropped below a predetermined temperature (freezing determination threshold Th), and a purge valve scavenging processing step of intermittently opening and closing the purge valve 46a multiple times while supplying fuel gas via the fuel gas supply path 40 when the temperature is below the predetermined temperature.

[0079] As described above, the operating method of the fuel cell system 10 includes the determination step and the purge valve scavenging process step, and thus can appropriately discharge water near the purge valve 46a in a low-temperature environment where the purge valve 46a may freeze. In particular, in the purge valve scavenging process step, the purge valve 46a is intermittently opened and closed multiple times to impart pulsation to the fuel gas pressure upstream of the purge valve 46a, thereby moving the water in the circulation path 45 and the purge path 46, and allowing the water to be smoothly discharged from the purge valve 46a. Therefore, the fuel cell system 10 can more reliably suppress freezing of the purge valve 46a.

[0080] The system also includes an oxidant gas supply passage 62 that supplies oxidant gas to the fuel cell stack 12, an oxidant gas discharge passage 64 to which the purge passage 46 is connected, through which the oxidant off-gas discharged from the fuel cell stack 12 flows and through which fluid discharged from the purge valve 46a flows, an oxidant gas bypass passage 66 that connects the oxidant gas supply passage 62 and the oxidant gas discharge passage 64 and directly flows the oxidant gas in the oxidant gas supply passage 62 to the oxidant gas discharge passage 64, and an exhaust pressure valve 78 that is provided in the oxidant gas discharge passage 64 between the point at which the oxidant gas bypass passage 66 is connected and the fuel cell stack 12 and that opens and closes the oxidant gas discharge passage 64, and in the purge valve scavenging processing step, the exhaust pressure valve 78 is closed and the oxidant gas is caused to flow through the oxidant gas bypass passage 66 to the oxidant gas discharge passage 64 to dilute the fuel gas discharged from the purge valve 46a. As a result, the fuel cell system 10 can effectively dilute the fuel gas discharged in response to the opening of the purge valve 46a with the oxidant gas in the oxidant gas discharge path 64. Furthermore, the fuel cell system 10 can prevent the fuel cell stack 12 from drying out by closing the exhaust pressure valve 78 in the purge valve scavenging process.

[0081] Furthermore, the oxidant gas supply passage 62 is provided with a compressor 70 that supplies the oxidant gas to the fuel cell stack 12, and after the purge valve scavenging process step, the compressor 70 is rotated while the exhaust valve 78 is opened to perform a cathode scavenging process step in which the oxidant gas is supplied to the fuel cell stack 12 through the oxidant gas supply passage 62 and the amount of water in the fuel cell stack 12 is reduced. This enables the fuel cell system 10 to perform the purge valve scavenging process step and the cathode scavenging process step together, thereby reducing power consumption of the battery Bt due to the execution of the purge valve scavenging process step and improving fuel efficiency.

[0082] Furthermore, the rotation speed of the compressor 70 in the purge valve scavenging process is higher than the rotation speed of the compressor 70 in the cathode scavenging process. As a result, the fuel cell system 10 can reduce noise during the freeze suppression process and improve marketability by changing the flow rate of the oxidant gas by the compressor 70 from a high flow rate to a low flow rate.

[0083] Furthermore, before the purge valve scavenging process is performed, an oxidant gas path dilution process is performed in which the compressor 70 is rotated to cause the oxidant gas to flow through the oxidant gas discharge path 64. This allows the fuel cell system 10 to fill the oxidant gas discharge path 64 with oxidant gas before the purge valve scavenging process is performed, thereby reliably diluting the fuel gas in the purge valve scavenging process.

[0084] Also, the oxidant gas bypass path 66 is provided with a flow rate adjustment valve 80 for adjusting the flow rate of the oxidant gas bypass path 66, and the flow rate adjustment valve 80 is opened in the purge valve scavenging process step, while the flow rate adjustment valve 80 is closed in the cathode scavenging process step. This enables the fuel cell system 10 to smoothly guide the oxidant gas to the oxidant gas discharge path 64 in the purge valve scavenging process step, while smoothly guide the oxidant gas to the fuel cell stack 12 in the cathode scavenging process step.

[0085] The circulation path 45 also includes a gas-liquid separator 56 that separates the liquid and gas contained in the fuel off-gas discharged from the fuel cell stack 12, and a drain path 60 that discharges the separated liquid is connected to the gas-liquid separator 56, and the drain path 60 includes a drain valve 60a that opens and closes the drain path 60, and in a purge valve scavenging process, the drain valve 60a is closed, and after the purge valve scavenging process, the drain valve 60a is opened to discharge the liquid. This allows the fuel cell system 10 to effectively discharge the liquid from the gas-liquid separator 56 as well.

[0086] Furthermore, in the drain water treatment process, the pressure of the fuel gas in the circulation path 45 is reduced below the pressure of the fuel gas in the circulation path 45 during the purge valve scavenging process. This allows the fuel cell system 10 to suppress the discharge of fuel gas in the drain water treatment process, thereby improving the fuel efficiency of the fuel gas.

[0087] The fuel cell system 10 is mounted on a vehicle 11 and performs a determination process and a purge valve scavenging process when the vehicle 11 is stopped. This allows the fuel cell system 10 to prevent the purge valve 46a from freezing when the vehicle 11 is stopped and in a low temperature environment.

[0088] A second aspect of the present invention is a fuel cell system 10 including a fuel cell stack 12, a fuel gas supply path 40 that supplies fuel gas to the fuel cell stack 12, a circulation path 45 that circulates fuel off-gas discharged from the fuel cell stack 12 to the fuel cell stack 12, a purge valve 46a that discharges the fuel off-gas from the circulation path 45, and a temperature sensor 84 that detects the temperature of the environment surrounding the purge valve 46a, and the system determines whether the temperature detected by the temperature sensor 84 has dropped below a predetermined temperature, and if the temperature is below the predetermined temperature, intermittently opens and closes the purge valve 46a multiple times while supplying fuel gas via the fuel gas supply path 40. This allows the fuel cell system 10 to appropriately discharge water near the purge valve 46a when the environment is low temperature, thereby preventing the purge valve 46a from freezing. [Explanation of symbols]

[0089] 10...Fuel cell system 11...Vehicle 12... fuel cell stack 40... fuel gas supply path 45...Circulation path 46...Purge path 46a... Purge valve 56... Gas-liquid separator 60...Drain path 60a...Drain valve 62: Oxidizing gas supply passage 64: Oxidizing gas exhaust passage 66: Oxidant gas bypass passage 70: Compressor 78...Exhaust pressure valve 80...Flow control valve 84...Temperature sensor 90...ECU Th…Freezing threshold

Claims

1. A fuel cell stack; a fuel gas supply passage for supplying a fuel gas to the fuel cell stack; a circulation path for circulating a fuel off-gas discharged from the fuel cell stack to the fuel cell stack; a purge valve that discharges the fuel off-gas from the circulation path; a temperature sensor for detecting a temperature of an environment surrounding the purge valve, a determination step of determining whether or not the temperature detected by the temperature sensor has dropped to a predetermined temperature or lower while the vehicle is in a drive-stop state due to an ignition being turned off; a purge valve scavenging process step of intermittently opening and closing the purge valve a plurality of times while supplying the fuel gas through the fuel gas supply path in the drive-stop state when the temperature is equal to or lower than the predetermined temperature; Including, the circulation path includes a gas-liquid separator that separates liquid and gas contained in the fuel off-gas discharged from the fuel cell stack, a drain path for discharging the separated liquid is connected to the gas-liquid separator, and the drain path includes a drain valve for opening and closing the drain path; In the purge valve scavenging process, the drain valve is closed, After the purge valve scavenging process, a drain discharge process is performed in which the drain valve is opened to discharge the liquid. A method for operating a fuel cell system.

2. 2. The method for operating a fuel cell system according to claim 1, an oxidant gas supply passage for supplying an oxidant gas to the fuel cell stack; an oxidant gas discharge passage connected to a purge passage through which the oxidant off-gas discharged from the fuel cell stack flows and through which the fluid discharged from the purge valve flows; an oxidant gas bypass passage that connects the oxidant gas supply passage and the oxidant gas discharge passage and allows the oxidant gas in the oxidant gas supply passage to directly flow into the oxidant gas discharge passage; a pressure relief valve that is provided in the oxidant gas discharge path between a point to which the oxidant gas bypass path is connected and the fuel cell stack, and that opens and closes the oxidant gas discharge path, In the purge valve scavenging process, the exhaust pressure valve is closed, and the oxidant gas is caused to flow through the oxidant gas bypass passage into the oxidant gas discharge passage to dilute the fuel gas discharged from the purge valve. A method for operating a fuel cell system.

3. 3. The method for operating a fuel cell system according to claim 2, a compressor that supplies the oxidant gas to the fuel cell stack is provided in the oxidant gas supply path; After the purge valve scavenging process, a cathode scavenging process is performed in which the compressor is rotated and the exhaust valve is opened to supply the oxidant gas to the fuel cell stack through the oxidant gas supply passage, thereby reducing the amount of water in the fuel cell stack. A method for operating a fuel cell system.

4. 4. The method for operating a fuel cell system according to claim 3, The rotation speed of the compressor in the purge valve scavenging process is higher than the rotation speed of the compressor in the cathode scavenging process. A method for operating a fuel cell system.

5. 5. The method for operating a fuel cell system according to claim 3, further comprising the steps of: Before the purge valve scavenging process is performed, an oxidant gas passage dilution process is performed in which the compressor is rotated to cause the oxidant gas to flow through the oxidant gas discharge passage. A method for operating a fuel cell system.

6. The method for operating a fuel cell system according to any one of claims 3 to 5, a flow rate regulating valve for regulating a flow rate of the oxidant gas bypass passage is provided in the oxidant gas bypass passage, In the purge valve scavenging process, the flow rate control valve is opened, while In the cathode scavenging process, the flow rate control valve is closed. A method for operating a fuel cell system.

7. 2. The method for operating a fuel cell system according to claim 1, In the drainage treatment step, the pressure of the fuel gas in the circulation path is reduced to a level lower than the pressure of the fuel gas in the circulation path during the purge valve scavenging treatment step. A method for operating a fuel cell system.

8. A fuel cell system mounted on a vehicle, A fuel cell stack; a fuel gas supply passage for supplying a fuel gas to the fuel cell stack; a circulation path for circulating a fuel off-gas discharged from the fuel cell stack to the fuel cell stack; a purge valve that discharges the fuel off-gas from the circulation path; a temperature sensor for detecting a temperature of an environment surrounding the purge valve; a control unit that, in a drive-stopped state of the vehicle due to an ignition being turned off, determines whether or not the temperature detected by the temperature sensor has dropped to a predetermined temperature or lower, and, if the temperature is equal to or lower than the predetermined temperature, in the drive-stopped state, intermittently opens and closes the purge valve a plurality of times while supplying the fuel gas through the fuel gas supply path; Equipped with the circulation path includes a gas-liquid separator that separates liquid and gas contained in the fuel off-gas discharged from the fuel cell stack, a drain path for discharging the separated liquid is connected to the gas-liquid separator, and the drain path includes a drain valve for opening and closing the drain path; the control unit closes the drain valve in the drive-stop state when the temperature is equal to or lower than the predetermined temperature, and intermittently opens and closes the purge valve a plurality of times while supplying the fuel gas through the fuel gas supply path, The control unit opens the drain valve to discharge the liquid after closing the purge valve. Fuel cell system.

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