Fuel cell system

Abstract

The invention relates to a fuel cell system. When the medium outlet temperature (Tco) of the heat exchange medium is equal to or greater than the threshold temperature (Tth), the heat exchange medium is supplied at a predetermined flow rate to the medium flow path (60) of the fuel cell stack (18), and when the medium outlet temperature (Tco) of the heat exchange medium is less than the threshold temperature (Tth), the heat exchange medium is supplied at a predetermined flow rate to the medium flow path (60) of the fuel cell stack (18) as the medium outlet temperature (Tco) decreases. As a result, the pressure difference between the anode flow path (59) and the medium flow path (60) in the fuel cell stack (18) does not increase, and the fuel cell stack (18) can be appropriately protected.

Description

[0001] This application is a divisional application of an application with a filing date of March 27, 2023, application number 202310304143.0, and invention name “Fuel Cell System”. Technical Field

[0002] The present invention relates to a fuel cell system having a fuel cell stack including a plurality of stacked power generation cells, wherein the power generation cells are formed by sandwiching an electrolyte membrane-electrode structure including a cathode electrode and an anode electrode sandwiching an electrolyte membrane between separators. Background Art

[0003] In recent years, in order to ensure that more people have access to appropriate, reliable, sustainable and advanced energy, research and development of fuel cells (FC) that contribute to energy efficiency has been carried out.

[0004] For example, Patent document 1 discloses the following fuel cell system: the anode pressure of the fuel cell stack is increased together with the increase in the rotation speed of the medium circulation pump, thereby suppressing the pressure of the anode flow path within the fuel cell stack from being lower than the pressure of the cooling water flow path within the fuel cell stack, thereby improving the durability of the cooling water circulation path outside the fuel cell stack (paragraph 0093 of Patent document 1).

[0005] Patent Document 2 Figure 2 2 is a cross-sectional view of a power generation cell of a solid polymer fuel cell as an example.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: JP2014-127452A

[0009] Patent Document 2: JP2018-125258A Summary of the invention

[0010] Problems to be solved by the invention

[0011] However, in a fuel cell stack, it is required that the pressure difference between the pressure in the anode flow path and the pressure in the medium flow path in the fuel cell stack does not increase, so as to prevent the fuel cell stack itself from being damaged.

[0012] However, Patent Document 1 does not disclose protection of the fuel cell stack with respect to the pressure difference between the anode flow path and the medium flow path in the fuel cell stack.

[0013] The object of the present invention is to solve the above-mentioned problems.

[0014] Solutions for solving problems

[0015] One aspect of the present invention relates to a fuel cell system, comprising a fuel cell stack formed by stacking a plurality of power generation cells, wherein the power generation cells are formed by sandwiching an electrolyte membrane-electrode structure consisting of a cathode electrode and an anode electrode sandwiching a solid polymer electrolyte membrane between separators. In the fuel cell system, an anode flow path, a cathode flow path and a medium flow path are formed on the separator, the anode flow path is used to allow fuel gas to flow along the anode electrode, the cathode flow path is used to allow oxidant gas to flow along the cathode electrode, the medium flow path is adjacent to the anode flow path and the cathode flow path, and is used to allow heat exchange medium to flow. The fuel cell system comprises: a medium supply device, which supplies heat to the medium flow path in the fuel cell stack through a medium inlet piping. The heat exchange medium, and recovering and cooling the heat exchange medium circulating in the fuel cell stack through a medium outlet piping; a temperature acquisition unit, which acquires the temperature of the heat exchange medium in the medium outlet piping or a temperature related to the temperature of the heat exchange medium in the medium outlet piping as a medium outlet temperature; and a control device, which controls the medium supply device, when the medium outlet temperature is above a threshold temperature, the control device supplies the heat exchange medium to the medium flow path at a predetermined flow rate, and on the other hand, when the medium outlet temperature is less than the threshold temperature, the control device supplies the heat exchange medium at a predetermined flow rate as the medium outlet temperature decreases.

[0016] Effects of the Invention

[0017] According to the present invention, when the medium outlet temperature is above the threshold temperature, the heat exchange medium is supplied to the medium flow path of the fuel cell stack at a predetermined flow rate. On the other hand, when the medium outlet temperature is lower than the threshold temperature, the heat exchange medium is supplied at a flow rate reduced from the predetermined flow rate as the medium outlet temperature decreases. As a result, the pressure difference between the anode flow path and the medium flow path in the fuel cell stack will not increase, and the fuel cell stack can be properly protected.

[0018] The above-mentioned objects, features and advantages will be easily understood from the following description of the embodiments described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic structural diagram of a fuel cell vehicle in which a fuel cell system according to an embodiment of the present invention is incorporated.

[0020] Figure 2 It is described in a little more detail Figure 1 A cross-sectional view of a power generation cell schematically depicted in FIG.

[0021] Figure 3This is a functional block diagram of the medium supply device control unit in the control device.

[0022] Figure 4 is a mapping relationship showing the characteristics of the first flow rate with respect to the medium outlet temperature.

[0023] Figure 5 This is a flowchart for explaining the operation of the fuel cell system of a fuel cell vehicle while the vehicle is running or idling.

[0024] Figure 6 It is used Figure 5 The flowchart is a timing diagram illustrating an example of the operation.

[0025] Figure 7 It is a timing chart showing an example of the operation of the modification example. DETAILED DESCRIPTION

[0026] [Implementation Method]

[0027] [structure]

[0028] Figure 1 It is a schematic structural diagram of a fuel cell vehicle 12 incorporating a fuel cell system 10 according to an embodiment of the present invention.

[0029] The fuel cell system 10 can also be incorporated into other mobile objects besides the fuel cell automobile 12 , such as ships, aircraft, robots, etc.

[0030] The fuel cell vehicle 12 is composed of a control device 15 that controls the entire fuel cell vehicle 12 , the fuel cell system 10 , and an output unit 16 that is electrically connected to the fuel cell system 10 .

[0031] The control device 15 may not be one, and may be divided into two or more control devices, for example, a control device for the fuel cell system 10 and a control device for the output unit 16 .

[0032] The fuel cell system 10 is composed of a fuel cell stack (also simply referred to as a fuel cell) 18 , a hydrogen tank 20 , an oxidant gas supplier 22 , a fuel gas supplier 24 , and a medium supplier (heat exchange medium supplier) 26 .

[0033] The oxidizing gas supply device 22 includes a compressor (CP) 28 and a humidifier (HUM) 30 .

[0034] The fuel gas supply device 24 includes a stop valve 21, an injector (INJ) 32, an ejector 34, and a gas-liquid separator 36. The injector 32 may be replaced by a pressure reducing valve.

[0035] The medium supply device 26 includes a medium pump (WP) 38 and a radiator 40 .

[0036] The output unit 16 includes a drive unit 42, a high voltage power storage device (battery) 44, and a motor (electric motor) 46. The load of the drive unit 42 includes the motor 46 as a main machine and the compressor 28, the medium pump 38, and an air conditioner (not shown) as auxiliary equipment.

[0037] Furthermore, the high-voltage DC voltage of the power storage device 44 is applied to the compressor 28, while the low-voltage DC voltage of the power storage device (not shown) is applied to the other auxiliary devices. The low-voltage power storage device is charged with low-voltage power obtained by stepping down the high voltage of the power storage device 44 by a step-down converter (not shown).

[0038] The fuel cell vehicle 12 travels using the driving force generated by the motor 46 .

[0039] The fuel cell stack 18 is formed by stacking a plurality of power generation cells 50. The power generation cell 50 includes an electrolyte membrane-electrode assembly 52 and separators 53 and 54 that sandwich the electrolyte membrane-electrode assembly 52.

[0040] The electrolyte membrane-electrode structure 52 includes a solid polymer electrolyte membrane 55 which is, for example, a thin film of perfluorosulfonic acid containing water, and a cathode electrode 56 and an anode electrode 57 which sandwich the solid polymer electrolyte membrane 55 .

[0041] Figure 2 It describes in detail Figure 1 2 is a cross-sectional view of a power generation cell 50 schematically depicted in FIG.

[0042] exist Figure 2 In the embodiment, the cathode electrode 56 and the anode electrode 57 respectively have gas diffusion layers 56a and 57a formed of carbon paper, etc. Porous carbon particles carrying platinum alloy on the surface are uniformly coated on the surface of the gas diffusion layers 56a and 57a, thereby forming electrode catalyst layers 56b and 57b on both sides of the solid polymer electrolyte membrane 55.

[0043] The separators 53 and 54 are arranged in such a structure that the concave cross-sectional portions and the convex cross-sectional portions of the separators 53 and 54 sandwich the electrolyte membrane-electrode assembly 52. Figure 2 The lateral direction of the phase is shifted by 180 degrees (inverted state) and is connected. Figure 2 The longitudinal direction of the stack is inverted in phase. Figure 2 In the embodiment, the bottom of the concave cross-sectional portion of the spacer 53 is in contact with the top of the convex cross-sectional portion of the spacer 54, and the spacers 53 and 54 are sealed. The spacers 53 and 54 have a metal protrusion structure.

[0044] A heat exchange medium such as a coolant (denoted as cla in the drawing) flows through a medium flow path 60 having a hexagonal cross section formed by stacking the separators 53 and 54 .

[0045] like Figure 1 as well as Figure 2 As shown, a cathode flow path (oxidant gas flow path) 58 that connects the oxidant gas inlet communication port 101 and the oxidant gas outlet communication port 102 is formed on the surface of one separator 53 that faces the membrane electrode assembly 52 .

[0046] An anode flow path (fuel gas flow path) 59 that connects the fuel gas inlet communication port 103 and the fuel gas outlet communication port 104 is formed on the surface of the other separator 54 that faces the membrane electrode assembly 52 .

[0047] That is, the fuel gas (H 2 ) flows through the anode flow path 59 formed by the anode electrode 57 and the separator 54 stacked on the anode electrode 57 .

[0048] Oxidant gas (air) flows through a cathode flow path 58 formed by a cathode electrode 56 and a separator 53 stacked on the cathode electrode 56 .

[0049] In the anode electrode 57, when fuel gas (hydrogen) is supplied, hydrogen ions are generated from hydrogen molecules due to an electrode reaction via the electrode catalyst layer 57b. The hydrogen ions pass through the solid polymer electrolyte membrane 55 and move to the cathode electrode 56. Meanwhile, electrons are released from the hydrogen molecules.

[0050] The electrons released from the hydrogen molecules move from the negative electrode terminal 106 to the cathode electrode 56 via the positive electrode terminal 108 through the loads such as the drive unit 42 and the motor 46 .

[0051] In the cathode electrode 56 , the hydrogen ions and the electrons react with oxygen included in the supplied oxidant gas due to the action of the electrode catalyst layer 56 b to generate water.

[0052] A voltage sensor 110 for detecting the generated voltage Vfc is provided between the wiring connecting the positive terminal 108 and the drive unit 42 and the wiring connecting the negative terminal 106 and the drive unit 42. In addition, a current sensor 112 for detecting the generated current Ifc is provided in the wiring connecting the positive terminal 108 and the drive unit 42.

[0053] The compressor 28 is composed of a mechanical supercharger driven by a compressor motor (not shown). The power of the power storage device 44 is supplied to the compressor motor through the drive unit 42. The compressor 28 has the following functions: drawing external gas (atmosphere, air) from the external gas inlet 113 for pressurization, and supplying it to the fuel cell stack 18 through the humidifier 30.

[0054] The humidifier 30 has a flow path 31A and a flow path 31B. Air (oxidant gas) compressed, heated, and dried by the compressor 28 flows through the flow path 31A. Exhaust gas discharged from the oxidant gas outlet communication port 102 of the fuel cell stack 18 flows through the flow path 31B.

[0055] The humidifier 30 has a function of humidifying the oxidant gas supplied from the compressor 28. That is, the humidifier 30 moves the moisture contained in the exhaust gas (exhaust gas) from the flow path 31B through the internal porous membrane to the supply gas (oxidant gas) flowing in the flow path 31A to humidify it, and supplies the humidified oxidant gas to the fuel cell stack 18 through the oxidant gas inlet 91.

[0056] In the oxidant gas supply flow path 61 (including the oxidant gas supply flow paths 61A and 61B) from the external gas inlet 113 to the oxidant gas inlet 91, a stop valve 114, an air flow sensor (AFS: flow sensor) 116, a compressor 28, an input side sealing valve 118, and a humidifier 30 are provided in order from the external gas inlet 113. In addition, the flow paths such as the oxidant gas supply flow path 61 drawn with double lines are formed by piping (the same applies hereinafter).

[0057] The stop valve 114 is opened and closed to open or shut off the introduction of air into the oxidizing gas supply flow path 61 .

[0058] The air flow sensor 116 measures the mass flow of the oxidant gas supplied to the fuel cell stack 18 by the compressor 28 .

[0059] The input-side sealing valve 118 opens and closes the oxidizing gas supply flow path 61B.

[0060] The outside air inlet 113 is provided with a temperature sensor 73 for detecting (measuring, acquiring) the outside air temperature Tair and a pressure sensor 83 for detecting (measuring, acquiring) the atmospheric pressure Pair.

[0061] In the oxidant exhaust flow path 62 communicating with the oxidant gas outlet communication port 102 through the oxidant exhaust outlet 92 , a humidifier 30 and a discharge-side sealing valve 120 also functioning as a back pressure valve are provided in order from the oxidant exhaust outlet 92 .

[0062] A bypass flow path 64 is provided between the suction port of the input side sealing valve 118 and the discharge port of the discharge side sealing valve 120 to connect the oxidant gas supply flow path 61 with the oxidant exhaust flow path 62. A bypass valve 122 is provided in the bypass flow path 64 to open and close the bypass flow path 64. The bypass valve 122 adjusts the flow rate of the oxidant gas bypassing the fuel cell stack 18.

[0063] The confluence of the bypass flow path 64 and the oxidant exhaust flow path 62 communicates with the exhaust flow path 62A.

[0064] The hydrogen tank 20 is provided with an electromagnetically operated stop valve 21 and is a container for storing high-purity hydrogen compressed at a high pressure.

[0065] The fuel gas ejected from the hydrogen tank 20 is supplied to the inlet of the anode flow path 59 via the shutoff valve 21, the injector 32 and the ejector 34 provided in the fuel gas supply flow path 72, and the fuel gas inlet 93 and the fuel gas inlet connecting port 103 of the fuel cell stack 18. A pressure sensor 82 is provided in the fuel gas supply flow path 72 near the fuel gas inlet 93, and the pressure sensor 82 detects (measures, obtains) the inlet pressure of the anode flow path 59 as the anode inlet pressure Pin.

[0066] The outlet of the anode flow path 59 communicates with the inlet 151 of the gas-liquid separator 36 via the fuel gas outlet communication port 104 , the fuel exhaust outlet 94 , and the fuel exhaust flow path 74 , and the fuel exhaust as hydrogen-containing gas is supplied from the anode flow path 59 to the gas-liquid separator 36 .

[0067] The gas-liquid separator 36 separates the fuel exhaust gas into a gas component and a liquid component (liquid water). The gas component of the fuel exhaust gas (fuel exhaust gas) is discharged from the gas discharge port 152 of the gas-liquid separator 36, and is supplied to the suction port of the ejector 34 through the circulation flow path 77 when the discharge valve 70 is closed.

[0068] On the other hand, when the discharge valve 70 is opened, the fuel exhaust gas is supplied to the suction port of the ejector 34 through the circulation flow path 77 and is also supplied to the oxidant gas supply flow path 61B via the connecting flow path (interconnecting flow path) 78 and the discharge valve 70 .

[0069] The liquid component of the fuel exhaust gas flows from the liquid discharge port 160 of the gas-liquid separator 36 through the discharge flow path 162 provided with a discharge valve 164, mixes with the exhaust gas discharged from the discharge flow path 62A, and is discharged to the outside (atmosphere) through the discharge flow path 99 and the exhaust gas exhaust port 168.

[0070] In reality, part of the fuel exhaust (hydrogen-containing gas) is discharged together with the liquid component to the drain flow path 162. Part of the oxidant gas ejected from the compressor 28 is supplied to the discharge flow path 62A through the bypass flow path 64 in order to dilute the hydrogen in the fuel exhaust and discharge it to the outside.

[0071] During the driving of the fuel cell vehicle 12, in order to prevent the nitrogen gas present in the cathode flow path 58 from penetrating the electrolyte membrane-electrode structure 52 and causing the hydrogen concentration in the anode flow path 59 to decrease, resulting in degradation of the anode electrode 57, the discharge valve 70 provided in the connecting flow path 78 connecting the fuel exhaust circulation flow path 77 with the oxidant gas supply flow path 61B is opened.

[0072] When the discharge valve 70 is opened, the fuel exhaust gas ejected from the fuel cell stack 18 through the fuel exhaust flow path 74 and via the gas-liquid separator 36 flows to the cathode flow path 58 via the connecting flow path 78, the oxidant gas supply flow path 61B, the oxidant gas inlet 91 and the oxidant gas inlet connecting port 101.

[0073] The fuel gas in the fuel exhaust gas flowing to the cathode flow path 58 is ionized by hydrogen due to the catalyst reaction in the cathode electrode 56, and the hydrogen ions react with the oxidant gas to generate water. The remaining fuel exhaust gas that has not reacted (including nitrogen and a small amount of unreacted hydrogen) is discharged from the oxidant exhaust outlet 92 of the fuel cell stack 18 as oxidant exhaust and flows to the oxidant exhaust flow path 62.

[0074] The oxidant exhaust (including the unreacted remaining fuel exhaust) flowing into the oxidant exhaust flow path 62 is mixed with the oxidant gas supplied through the oxidant gas bypass flow path 64, and the oxidant exhaust in which the concentration of the fuel exhaust (including the fuel gas) is diluted flows into the exhaust flow path 62A.

[0075] The discharge flow path 62A communicates and merges with the drain flow path 162 and communicates with the discharge flow path 99 .

[0076] In the exhaust flow path 99 , the fuel gas in the mixed fluid of liquid water and fuel exhaust ejected from the drain flow path 162 is diluted with the oxidant exhaust gas from the exhaust flow path 62A and discharged to the outside (atmosphere) of the fuel cell vehicle 12 through the exhaust gas exhaust port 168 .

[0077] The medium supply device 26 of the fuel cell system 10 has a medium pipe 138 for circulating the heat exchange medium. The medium pipe 138 is formed with a medium supply flow path 140 and a medium discharge flow path 142. The medium supply flow path 140 is connected to the medium flow path 60 (see FIG. 1 ) inside the fuel cell stack 18. Figure 2) supplies a heat exchange medium, and the heat exchange medium flowing in the medium flow path 60 of the fuel cell stack 18 is discharged to the medium discharge flow path 142.

[0078] A radiator 40 is connected between the medium discharge flow path 142 and the medium supply flow path 140. The radiator 40 cools the heat exchange medium. A medium pump 38 is provided in the medium supply flow path 140. The medium pump 38 circulates the heat exchange medium in the circulation loop of the heat exchange medium. The circulation loop of the heat exchange medium includes the medium supply flow path 140, the medium flow path 60 inside the fuel cell stack 18 (see Figure 2 ), the medium discharge flow path 142 and the radiator 40.

[0079] Temperature sensors (temperature acquisition units) 76 and 86 are provided in the medium supply flow path 140 and the medium discharge flow path 142, respectively. The temperature (medium outlet temperature) Tco of the heat exchange medium detected by the temperature sensor 86 is estimated as the (internal) temperature of the fuel cell stack 18. The temperature sensor 76 detects (measures, acquires) the temperature (medium inlet temperature) Tci of the heat exchange medium.

[0080] The control device 15 comprehensively controls the above-described components of the fuel cell system 10 .

[0081] Moreover, in addition to the stop valves 21 and 114, which are on-off valves controlled by the control device 15, the input side sealing valve 118, the discharge side sealing valve 120, the unloading valve 70, and the drain valve 164 are flow regulating valves whose openings are controlled by the control device 15, but the on-off valves can also be used for occupancy control.

[0082] The control device 15 is composed of an ECU (Electronic Control Unit). The ECU is composed of a computer having one or more processors (CPU), a memory, an input / output interface, and a circuit. The one or more processors (CPU) execute computer-executable instructions such as a program (not shown) stored in the memory.

[0083] The processor (CPU) of the control device 15 performs calculations according to computer-executable instructions such as the program, thereby controlling the operation of the fuel cell vehicle 12 and the fuel cell system 10 .

[0084] Figure 3 The function block diagram shows the structure of the medium supply device control unit 200 , which is a part of the function of the control device 15 that controls the medium supply device 26 by the processor executing calculations according to the computer-executable instructions of the program.

[0085] The medium supply device control unit 200 includes a first flow rate calculation unit 201 , a second flow rate calculation unit 202 , a maximum value selection unit 204 , and a medium pump rotation speed command value calculation unit 206 .

[0086] The first flow calculation unit 201 functions as a medium flow requirement value calculation unit, which is configured to calculate a mapping relationship (form) of the medium flow rate, i.e., the first flow rate Fr1 [L / min], for pressure difference protection between the anode flow path 59 and the medium flow path 60 based on the generated current Ifc [A] and the medium outlet temperature Tco [°C].

[0087] like Figure 4 As shown, the mapping relationship 201m used to calculate the first flow rate Fr1 [L / min] has the following characteristics: when the medium outlet temperature Tco is less than the threshold temperature Tth, a value that decreases in proportion to the decrease in the medium outlet temperature Tco [°C] is used; when the medium outlet temperature Tco is above the threshold temperature Tth, the maximum flow rate Fr1max is used.

[0088] Furthermore, the internal temperature of the fuel cell stack 18 is estimated to be substantially equal to the medium outlet temperature Tco.

[0089] When the maximum value of the internal temperature of a PEFC (solid polymer fuel cell) type fuel cell stack 18 is set to, for example, 100 [°C] or a temperature close to 100 [°C], the threshold temperature Tth is a temperature lower than the set temperature and is set to a predetermined temperature that takes into account the power generation efficiency of the fuel cell stack 18, etc.

[0090] In the first flow calculation unit 201, the power generation current Ifc is referred to in order to determine whether the power generation of the fuel cell stack 18 is above a predetermined value. Even when the power generation current Ifc is below a predetermined value, it is estimated that the anode inlet pressure Pin can be maintained, and it is set that pressure difference protection may be required. The first flow Fr1 is calculated based on the medium outlet temperature Tco and with reference to the mapping relationship 201m.

[0091] The second flow rate calculation unit 202 is a medium flow rate requirement value calculation unit as a theoretical calculation formula, and calculates the medium flow rate for cooling the fuel cell stack 18, that is, the second flow rate Fr2, corresponding to the power generation amount based on the power generation current Ifc and the medium inlet and outlet temperature difference Tdif (Tdif=Tco-Tci).

[0092] The theoretical calculation formula for calculating the second flow rate Fr2 is as follows: The medium inlet and outlet temperature difference Tdif=Tco-Tci increases in proportion to the generated current Ifc, so the second flow rate Fr2 as the medium flow rate requirement value increases.

[0093] The maximum value selection unit 204 compares the first flow rate Fr1 and the second flow rate Fr2 , selects the larger one as the medium flow rate requirement value Frreq {Frreq(Fr1) or Frreq(Fr2)}, and outputs it to the medium pump rotation speed command value calculation unit 206 .

[0094] The medium pump speed command value calculation unit 206 sets the medium flow requirement value Frreq as the target flow rate Ftar{Frreq(Fr1)→Ftar(Fr1) or Frreq(Fr2)→Ftar(Fr2)} to calculate the target speed command value Ncom{Ftar(Fr1)→Ncom(Fr1) or Ftar(Fr2)→Ncom(Fr2)} of the medium pump 38 corresponding to the target flow rate Ftar and outputs it to the medium pump 38.

[0095] The control device 15 performs feedback control so that the medium pump 38 rotates at the medium pump rotation speed N according to the target rotation speed command value Ncom.

[0096] The control device 15 is connected to a power switch (power SW) 71 of the fuel cell vehicle 12. The power switch 71 starts, continues (ON) or ends (OFF) the power generation operation of the fuel cell stack 18 of the fuel cell system 10. The control device 15 is also connected to an accelerator opening sensor, a vehicle speed sensor, and a SOC (storage capacity) sensor of the power storage device 44, which are not shown.

[0097] The fuel cell stack 18 of the fuel cell vehicle 12 generates electric power in accordance with the electric power required by the motor 46 and loads such as the air conditioner while the vehicle is traveling or idling.

[0098] In order to generate the generated power (Ifc×Vfc) corresponding to the required power, the control device 15 of the fuel cell system 10 supplies an oxidant gas flow corresponding to the required power from the compressor 28 to the fuel cell stack 18, and supplies a fuel gas flow corresponding to the required power from the hydrogen tank 20 to the fuel cell stack 18 through the injector 32.

[0099] The fuel cell stack 18 generates electricity through an electrochemical reaction between the oxidant gas flowing through the cathode flow path 58 and the fuel gas flowing through the anode flow path 59 , and distributes the generated electricity to loads including the motor 46 through the drive unit 42 .

[0100] Furthermore, in the fuel cell stack 18, during power generation, the oxidant gas pressure of the cathode flow path 58 is set to a pressure lower than the fuel gas pressure of the anode flow path 59. Therefore, it is considered to provide pressure difference protection for preventing deformation of the metal protrusion structure of the separators 53 and 54 between the anode flow path 59 through which the fuel gas flows and the medium flow path 60 through which the heat exchange medium flows, which are opposite (adjacent) to each other and sandwich the separator 54.

[0101] [action]

[0102] The fuel cell system 10 according to this embodiment is basically configured as described above. Figure 5 The flowchart of FIG. 1 illustrates the pressure difference protection operation between the anode flow path 59 and the medium flow path 60 in the fuel cell stack 18 when the power switch 71 is turned on (during driving or idling). The control device 15 repeatedly executes the pressure difference protection operation at a predetermined period. Figure 5 Flowchart of the process.

[0103] In step S1, the control device 15 obtains physical quantities related to the current power generation state detected by various sensors, such as the medium outlet temperature Tco detected by the temperature sensor 86, the medium inlet temperature Tci detected by the temperature sensor 76, and the power generation current Ifc detected by the current sensor 112, and advances the processing to step S2.

[0104] In step S2, when the generated current Ifc is below a predetermined value, the first flow calculation unit 201 of the control device 15 calculates the first flow Fr1 using the medium outlet temperature Tco and referring to the mapping relationship 201m of the medium flow for pressure difference protection between the anode flow path 59 and the medium flow path 60, and the processing proceeds to step S3.

[0105] In step S3, the second flow calculation unit 202 of the control device 15 calculates the second flow Fr2 using a theoretical calculation formula (Japanese: theoretical calculation formula) that the second flow Fr2 as the medium flow requirement value increases because the medium inlet and outlet temperature difference Tdif=Tco-Tci increases in proportion to the generated current Ifc, and the processing proceeds to step S4.

[0106] In step S4 , the maximum value selection unit 204 of the control device 15 determines (selects) the larger value of the first flow rate Fr1 related to differential pressure protection or the second flow rate Fr2 related to temperature control as the target flow rate Ftar, and advances the process to step S5 .

[0107] Here, the process of determining the target flow rate Ftar will be described.

[0108] (i) Determination of the first flow rate Fr1

[0109] The medium outlet temperature Tco of the heat exchange medium flowing through the medium flow path 60 in the fuel cell stack 18 changes gradually following the change in the power generated by the fuel cell stack 18 .

[0110] Therefore, in a high load state where the load impedance value of the motor 46 etc. is small, the required generated power (generated current Ifc) increases, the medium outlet temperature Tco increases, and the pressure in the anode flow path 59 in the fuel cell stack 18 increases.

[0111] In this case, in order to prevent the pressure difference between the pressure in the anode flow path 59 in the fuel cell stack 18 and the pressure in the medium flow path 60 from increasing, referring to the mapping relationship 201m, when the medium outlet temperature Tco is above the threshold temperature Tth, the heat exchange medium is supplied to the medium flow path 60 at a predetermined flow rate, here the maximum flow rate Fr1max, thereby ensuring the pressure in the medium flow path 60.

[0112] Thus, when the pressure in the anode flow path 59 is high, the pressure difference between the pressure in the anode flow path 59 and the pressure in the medium flow path 60 can be reduced, thereby achieving pressure difference protection that can prevent deformation of the metal protrusion structure of the separators 53 and 54.

[0113] On the other hand, in a low load state where the load impedance value of the motor 46 is large, the required power generation is reduced. When the medium outlet temperature Tco representing the medium temperature in the medium flow path 60 is less than the threshold temperature Tth, the pressure in the anode flow path 59 in the fuel cell stack 18 is reduced. Therefore, in order to perform pressure difference protection, referring to the mapping relationship 201m, the heat exchange medium is supplied from the maximum flow rate Fr1max as the medium outlet temperature Tco decreases, so that the pressure in the medium flow path 60 is reduced.

[0114] Therefore, when the medium outlet temperature Tco is above the threshold temperature Tth, the heat exchange medium is supplied to the medium flow path 60 at a predetermined flow rate (the maximum flow rate Fr1max in this embodiment). On the other hand, when the medium outlet temperature Tco is lower than the threshold temperature Tth, the heat exchange medium is supplied at a lowered flow rate from the predetermined flow rate as the medium outlet temperature Tco decreases, thereby preventing the pressure difference between the anode flow path 59 and the medium flow path 60 in the fuel cell stack 18 from increasing.

[0115] As a result, deformation of the metal protrusion structure of the spacers 53 and 54 can be prevented, and the fuel cell stack 18 (power generating cells 50 ) can be appropriately protected.

[0116] (ii) Decision on the second flow rate Fr2

[0117] In order to dissipate the heat generated in the fuel cell stack 18 due to the power generation of the fuel cell stack 18 using the radiator 40, the medium flow rate (medium pump speed N) is controlled to increase or decrease proportionally with the generated power (generated current Ifc), so that the medium inlet and outlet temperature difference Tdif = Tco-Tci converges within a predetermined temperature range.

[0118] When the state of large power generation continues, the medium outlet temperature Tco rises, and the medium flow rate is relatively high, for example, consider the situation where the state of the accelerator pedal depression amount decreasing sharply is maintained. In this case, control is performed to reduce the medium flow rate (medium pump speed N), so that the heat release of the radiator 40 is reduced and the medium inlet and outlet temperature difference Tdif = Tco-Tci converges within a predetermined temperature range. In this case, the medium flow rate is maintained at a flow rate at the upper limit temperature protection required speed Nreq so that the deviation between the anode inlet pressure Pin and the medium pressure does not increase. In this way, the second flow rate Fr2 is determined. In this case, deformation of the metal protrusion structure of the separators 53 and 54 can also be prevented, so that the fuel cell stack 18 (power generation cell 50) can be properly protected.

[0119] When the medium pump speed N at the second flow rate Fr2 is maintained at the upper limit temperature protection required speed Nreq, when the medium outlet temperature Tco is lower than the threshold temperature Tth, the medium pump speed N is switched to the first flow rate Fr1 for pressure difference protection.

[0120] Returning to the description of the flowchart, in step S5 , the medium pump rotation speed command value calculation unit 206 of the control device 15 calculates a target rotation speed command value Ncom of the medium pump 38 based on the target flow rate (target medium flow rate) determined (selected) in step S4 .

[0121] In step S6 , the control device 15 controls the medium pump 38 so that the medium pump rotation speed N of the medium pump 38 becomes the target rotation speed command value Ncom calculated in step S5 .

[0122] (Explain based on the timing diagram)

[0123] Reference Figure 6 The timing diagram (timing diagram of the fuel cell vehicle 12 during driving) is used to illustrate the Figure 5 The flowchart is an example of the operation described.

[0124] First, the calculation process of the target rotation speed command value Ncom(Fr2) based on the second flow rate Fr2 indicated by the dotted line will be described.

[0125] At time t1, when the power generation current Ifc of the fuel cell stack 18 decreases sharply due to a sudden deceleration operation such as releasing the accelerator pedal, the target speed command value Ncom (Fr2) decreases in proportion to the medium outlet temperature Tco during the period from time t1 to time t2.

[0126] However, when the target speed command value Ncom(Fr2) decreases to the predetermined upper limit temperature protection required speed Nreq of the fuel cell stack 18, the target speed command value Ncom(Fr2) is set to the upper limit temperature protection required speed Nreq (time point t2 to time point t4).

[0127] At time t4 , when the generated current Ifc rises sharply due to a sudden acceleration operation such as suddenly stepping on the accelerator pedal, the target rotation speed command value Ncom ( Fr2 ) rises in proportion to the medium outlet temperature Tco during a period from time t4 to time t7 .

[0128] However, after time t7 when the target rotation speed command value Ncom(Fr2) reaches the maximum rotation speed Nmax of the medium pump 38, the target rotation speed command value Ncom(Fr2) is set to the maximum rotation speed Nmax.

[0129] Next, a calculation process of the target rotation speed command value Ncom(Fr1) based on the first flow rate Fr1 indicated by the solid line will be described.

[0130] During the period from time point t0 to time point t3 , the medium outlet temperature Tco is equal to or higher than the threshold temperature Tth, so the target rotation speed command value Ncom ( Fr1 ) is set to the maximum rotation speed Nmax.

[0131] During the period from time t3 to time t5 , the medium outlet temperature Tco is lower than the threshold temperature Tth and is gradually decreasing. Therefore, the target rotation speed command value Ncom ( Fr1 ) is gradually decreased from the maximum rotation speed Nmax in proportion to the decrease in the medium outlet temperature Tco.

[0132] During the period from time t5 to time t6 , the medium outlet temperature Tco is lower than the threshold temperature Tth and is slowly increasing, so the target rotation speed command value Ncom( Fr1 ) is increased in proportion to the increase in the medium outlet temperature Tco.

[0133] After time t6 , the medium outlet temperature Tco is equal to or higher than the threshold temperature Tth, so the target rotation speed command value Ncom ( Fr1 ) is set to the maximum rotation speed Nmax.

[0134] Moreover, in Figure 6In the example shown in the timing chart of , although all selected flow rates are controlled according to the first flow rate Fr1, when the medium outlet temperature Tco decreases and control according to the second flow rate Fr2 is selected, control is switched to control according to the target rotation speed command value Ncom (Fr2).

[0135] In addition, according to Figure 6 In the timing diagram, when the medium outlet temperature Tco is above the threshold temperature Tth, the control device 15 supplies the heat exchange medium to the medium flow path 60 at a predetermined flow rate, i.e., a maximum flow rate (the target speed command value Ncom of the medium pump 38 is set to the maximum speed Nmax). Alternatively, when the rising speed of the anode inlet pressure Pin of the anode flow path 59 becomes above a predetermined speed or the anode inlet pressure Pin becomes above a predetermined pressure Pth (time point t4 to time point t6), the medium supply device 26 is operated at a maximum flow rate (the target speed command value Ncom of the medium pump 38 is set to the maximum speed Nmax to operate).

[0136] In this way, when the anode inlet pressure Pin of the anode flow path 59 is likely to become a large pressure, or when it becomes greater than the predetermined pressure Pth, the medium flow rate supplied from the medium supply device 26 to the medium flow path 60 in the fuel cell stack 18 can be set to the maximum flow rate to increase the pressure of the medium flow path 60, so that the pressure difference protection between the pressure in the anode flow path and the pressure in the medium flow path can be quickly and reliably performed. That is, the deformation of the metal protrusion structure of the separators 53 and 54 can be prevented, so that the fuel cell stack 18 (power generation unit cell 50) can be appropriately protected.

[0137] [Modifications]

[0138] The above-mentioned embodiment can also be modified as follows.

[0139] Figure 7 It is a timing chart showing an example of the operation of the modification example.

[0140] In this modification, the hardware structure is the same as Figure 1 The fuel cell system 10 shown is the same, with only the control being changed.

[0141] In this modification, during the period from time point t0 to time point t3, the medium pump 38 is driven by the target speed command value Ncom (Fr2) indicated by the dashed line with an arrow symbol. During the period from time point t3 to time point t6, the medium pump 38 is driven by the target speed command value Ncom (Fr1) indicated by the solid line with an arrow symbol. After time point t6, the medium pump 38 is driven by the target speed command value Ncom (Fr2) indicated by the dashed line with an arrow symbol.

[0142] That is, during the period from time point t1 to time point t3, even during deceleration, when the medium outlet temperature Tco is above the threshold temperature Tth, in order to ensure a medium pressure above a certain level, the maximum value selection unit 204 controls the medium pump 38 using the target speed command value Ncom (Fr2) related to the second flow rate Fr2.

[0143] During the period from time t3 to time t6, the anode inlet pressure Pin decreases and the medium outlet temperature Tco is below the threshold temperature Tth. Therefore, in order to ensure a certain medium pressure or above, the medium pump 38 is controlled using the target speed command value Ncom(Fr1) related to the first flow rate Fr1.

[0144] In addition, from time point t4 to time point t7 and after time point t7, even when re-accelerating, when the medium outlet temperature Tco is below the threshold temperature Tth, control is performed to ensure a medium pressure of a certain level or higher. Therefore, from time point t4 to time point t6, the medium pump 38 is controlled by the target speed command value Ncom (Fr1) shown by the solid line related to the first flow rate Fr1. After time point t6, the anode inlet pressure Pin increases, so the medium pump 38 is controlled by the target speed command value Ncom (Fr2) shown by the dotted line related to the second flow rate Fr2.

[0145] In the above-mentioned variation example, power generation of the fuel cell stack 18 is controlled based on the load size and the medium outlet temperature Tco so that the pressure difference between the anode inlet pressure Pin and the medium pressure (proportional to the target speed command value Ncom) does not increase, thereby preventing deformation of the metal protrusion structure of the partitions 53 and 54, thereby protecting the fuel cell stack 18.

[0146] [Inventions that can be understood from the embodiments and modifications]

[0147] Here, the invention that can be grasped about the above-mentioned embodiment and modification examples is described as follows. In addition, for easy understanding, the reference numerals used in the above-mentioned embodiment are marked on some of the components, but the components are not limited to the components marked with the reference numerals.

[0148] (1) The fuel cell system 10 of the present invention comprises a fuel cell stack 18 formed by stacking a plurality of power generation cells 50, wherein the power generation cells are formed by sandwiching an electrolyte membrane-electrode structure 52 composed of a cathode electrode 56 and an anode electrode 57 sandwiching a solid polymer electrolyte membrane 55 between separators 53 and 54. In the fuel cell system, an anode flow path 59, a cathode flow path 58 and a medium flow path 60 are formed on the separator, wherein the anode flow path is used to allow fuel gas to flow along the anode electrode, and the cathode flow path is used to allow oxidant gas to flow along the cathode electrode. The medium flow path 60 is adjacent to the anode flow path and the cathode flow path and is used to allow heat exchange medium to flow. The fuel cell system comprises: a medium supply device 26, which supplies heat to the fuel cell through a medium inlet piping. The medium flow path in the stack supplies the heat exchange medium, and the heat exchange medium circulating in the fuel cell stack is recovered and cooled through the medium outlet piping; a temperature acquisition unit 86, which acquires the temperature of the heat exchange medium in the medium outlet piping or a temperature related to the temperature of the heat exchange medium in the medium outlet piping as the medium outlet temperature; and a control device 15, which controls the medium supply device, and when the medium outlet temperature is above a threshold temperature, the control device supplies the heat exchange medium to the medium flow path at a predetermined flow rate, and on the other hand, when the medium outlet temperature is lower than the threshold temperature, the control device supplies the heat exchange medium at a predetermined flow rate as the medium outlet temperature decreases.

[0149] In this way, when the medium outlet temperature is above the threshold temperature, the heat exchange medium is supplied to the medium flow path of the fuel cell stack at a predetermined flow rate. On the other hand, when the medium outlet temperature is lower than the threshold temperature, the heat exchange medium is supplied at a flow rate reduced from the predetermined flow rate as the medium outlet temperature decreases, thereby preventing the pressure difference between the anode flow path and the medium flow path in the fuel cell stack from increasing, thereby properly protecting the fuel cell stack.

[0150] (2) Alternatively, in a fuel cell system, the control device compares a first flow rate Fr1 obtained by a first flow rate control with a second flow rate Fr2 obtained by a second flow rate control, and controls the medium supply device so that the supply flow rate of the heat exchange medium becomes the larger of the first flow rate and the second flow rate, wherein the first flow rate control is a control as follows: when the medium outlet temperature is above the threshold temperature, the control device supplies the heat exchange medium to the medium flow path at the predetermined flow rate, and on the other hand, when the medium outlet temperature is lower than the threshold temperature, the control device reduces the supply flow rate from the predetermined flow rate as the medium outlet temperature decreases, and the second flow rate control is a control for increasing or decreasing the supply flow rate according to an increase or decrease in the power generated by the fuel cell stack.

[0151] Therefore, with the help of controlling the medium supply device, the following first flow control and second flow control can be taken into account, that is, the first flow control related to pressure difference protection so that the pressure difference between the pressure in the anode flow path and the pressure in the medium flow path in the fuel cell stack will not expand too much, thereby protecting the fuel cell stack, and the second flow control related to temperature protection of the fuel cell stack.

[0152] (3) Alternatively, in a fuel cell system, the control device may set the predetermined flow rate supplied to the medium flow path to a maximum flow rate, and when the rising speed of the anode inlet pressure Pin of the anode flow path becomes greater than a predetermined speed or the inlet pressure becomes greater than a predetermined pressure, the medium supply device may be set to the maximum flow rate.

[0153] In this way, when the inlet pressure of the anode flow path is likely to become a high pressure or become above a predetermined pressure, the medium flow rate supplied from the medium supply device to the medium flow path can be set to a maximum flow rate to increase the pressure of the medium flow path, thereby enabling rapid and reliable protection of the pressure difference between the pressure in the anode flow path and the pressure in the medium flow path.

[0154] Furthermore, the present invention is not limited to the above-described embodiment, and various configurations can be employed without departing from the gist of the present invention.

Claims

1. A fuel cell system comprising a fuel cell stack formed by stacking a plurality of power generation cells, wherein the power generation cells are formed by sandwiching an electrolyte membrane-electrode structure composed of a cathode electrode and an anode electrode sandwiching a solid polymer electrolyte membrane between separators, wherein in the fuel cell system, An anode flow path, a cathode flow path, and a medium flow path are formed in the separator, wherein the anode flow path is used to allow fuel gas to flow along the anode electrode, the cathode flow path is used to allow oxidant gas to flow along the cathode electrode, and the medium flow path is adjacent to the anode flow path and the cathode flow path and is used to allow heat exchange medium to flow. The fuel cell system comprises: a medium supply device that supplies the heat exchange medium to the medium flow path in the fuel cell stack through a medium inlet pipe, and recovers and cools the heat exchange medium flowing in the fuel cell stack through a medium outlet pipe; a temperature acquisition unit that acquires the temperature of the heat exchange medium in the medium outlet pipe or a temperature related to the temperature of the heat exchange medium in the medium outlet pipe as a medium outlet temperature; as well as a control device for controlling the medium supply device, When the medium outlet temperature is above the threshold temperature, the control device supplies the heat exchange medium to the medium flow path at a predetermined flow rate in such a manner that the pressure difference between the pressure in the anode flow path and the pressure in the medium flow path does not increase. On the other hand, when the medium outlet temperature is lower than the threshold temperature, the control device supplies the heat exchange medium at a flow rate reduced from the predetermined flow rate as the medium outlet temperature decreases.

2. The fuel cell system according to claim 1, characterized in that: The control device sets the predetermined flow rate supplied to the medium flow path as a maximum flow rate, and sets the medium supply device to the maximum flow rate when the rising speed of the inlet pressure of the anode flow path becomes higher than a predetermined speed or the inlet pressure becomes higher than a predetermined pressure.

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