JP5098191B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  Conventionally, since fuel cells have high power generation efficiency and do not emit harmful substances, they have been put into practical use as power generators for industrial and household use, or as power sources for artificial satellites and spacecrafts. Development is progressing as a power source for vehicles such as buses, trucks, passenger carts, and luggage carts. The fuel cell may be of an alkaline aqueous solution type (AFC), phosphoric acid type (PAFC), molten carbonate type (MCFC), solid oxide type (SOFC), direct methanol (DMFC), or the like. Although good, a polymer electrolyte fuel cell (PEMFC) is common.

  In this case, the solid polymer electrolyte membrane is sandwiched between two gas diffusion electrodes and integrated to join. When one of the gas diffusion electrodes is used as a fuel electrode (anode electrode) and hydrogen gas as fuel is supplied to the surface thereof, hydrogen is decomposed into hydrogen ions (protons) and electrons, and the hydrogen ions are converted into a solid polymer electrolyte. Permeates the membrane. Further, when the other of the gas diffusion electrodes is an oxygen electrode (cathode electrode) and air as an oxidant is supplied to the surface, oxygen in the air is combined with the hydrogen ions and electrons to generate water. The An electromotive force is generated by such an electrochemical reaction.

  And when stopping a fuel cell, supply of hydrogen is stopped. In this case, if left as it is, hydrogen continues to be consumed little by little, and the pressure of the hydrogen gas on the fuel electrode side in the fuel cell gradually decreases. Here, when the pressure of the hydrogen gas becomes atmospheric pressure or less, the oxygen electrode side air passes through the MEA (Membrane Electrode Assembly) and moves to the fuel electrode side. And air (oxygen) are mixed. When the oxygen concentration on the fuel electrode side exceeds a certain value, a potential shift occurs in the MEA, resulting in a high potential state of 1.2 [V] or more, catalyst particles are eluted, and the performance of the fuel cell is degraded. End up.

  Therefore, in order to prevent the occurrence of potential shift, purging with an inert gas such as nitrogen may be considered, but in this case, it is necessary to mount an inert gas supply source on the vehicle, and the system is complicated. And it becomes large. For this reason, a technique has been proposed in which the time required for a mixed state of hydrogen and air (oxygen) is shortened by reducing the pressure on the fuel electrode side in the fuel cell and rapidly introducing air (for example, Patent Document 1). reference.).

  FIG. 2 is a diagram showing a configuration of a conventional fuel cell system.

  In the figure, an apparatus for supplying hydrogen gas to the fuel cell stack 111 is shown. Hydrogen gas is supplied from the fuel tank 113 to the fuel cell stack 111 through the first fuel supply line 114 and the second fuel supply line 115. The first fuel supply pipe 114 is provided with a fuel tank original opening / closing valve 121, a pressure reducing valve 122, and a fuel supply electromagnetic valve 123. The second fuel supply line 115 is provided with a safety valve 125 and a pressure sensor 124.

  Then, hydrogen gas discharged as an unreacted component from the outlet of the fuel cell stack 111 is discharged to the outside of the fuel cell stack 111 through the first fuel discharge pipe 116. The first fuel discharge pipe 116 is provided with a water recovery trap 126 attached with a water level gauge. The water recovery trap 126 is connected to a second fuel discharge pipe 117 that discharges hydrogen gas separated from water, and the second fuel discharge pipe 117 is connected to a circulation pressure reduction pump 127 and a hydrogen circulation solenoid valve 128. Is arranged. The end of the second fuel discharge pipe 117 opposite to the water recovery trap 126 side is connected to the second fuel supply pipe 115. Thereby, the hydrogen gas discharged to the outside of the fuel cell stack 111 can be recovered, supplied to the fuel cell stack 111, and reused.

  Further, a third fuel discharge pipe 131 is connected to the water recovery trap 126, and an exhaust electromagnetic valve 141 is provided in the third fuel discharge pipe 131, so that the fuel gas flow is not lost when the fuel cell stack 111 is started. Hydrogen gas discharged from the road can be discharged into the atmosphere. The outlet end of the third fuel discharge pipe 131 is connected to the air exhaust manifold 112, and it is desirable to dilute the hydrogen discharged from the fuel gas circulation path with air.

Further, a fourth fuel discharge line 132 having the other end connected to the third fuel discharge line 131 is connected between the circulation pressure reducing pump 127 and the hydrogen circulation electromagnetic valve 128 in the second fuel discharge line 117. Has been. The fourth fuel discharge line 132 is provided with a reduced-pressure hydrogen discharge valve 142 that is opened when the inside of the fuel cell stack 111 is depressurized. In addition, an outside air introduction line 118 is connected to the second fuel supply line 115. The outside air introduction pipe line 118 is provided with an outside air introduction electromagnetic valve 129 and an air filter 130 so that outside air can be introduced when the fuel cell stack 111 is stopped.
JP 2006-40846 A

  However, in the conventional fuel cell system, when the fuel cell stack 111 is started and stopped, the inside of the fuel cell stack 111 is decompressed by the circulation decompression pump 127. However, the humidity in the pipeline through which hydrogen gas circulates is determined. If the value is high, water droplets may enter the circulation pressure reduction pump 127 and the pressure inside the fuel cell stack 111 may not be sufficiently reduced.

  FIG. 3 is a schematic diagram showing the configuration of a conventional circulating pressure reducing pump, FIG. 4 is a schematic diagram showing the operation of a check valve when water is high in the conventional circulating pressure reducing pump, and FIG. 5 is a pressure reducing capacity of the conventional circulating pressure reducing pump. It is a graph which shows.

  As shown in FIG. 3, the circulation pressure reduction pump 127 is a reciprocating vacuum pump. A diaphragm 153 is disposed on one side wall of the suction chamber 152, and the volume of the suction chamber 152 is increased by reciprocating the diaphragm 153. Change intake and exhaust. The diaphragm 153 is reciprocated by a connecting rod 155 connected to a crankshaft 154 that is rotated by a motor. An intake pipe 161 and an exhaust pipe 162 are connected to the wall of the suction chamber 152 opposite to the diaphragm 153, and an intake check valve 163 is disposed at the boundary between the intake pipe 161 and the suction chamber 152. An exhaust check valve 164 is provided at the boundary between the exhaust pipe 162 and the suction chamber 152.

  The intake check valve 163 and the exhaust check valve 164 are flexible plate members mainly made of rubber, and one end is fixed to the wall surface of the suction chamber 152 as shown in FIG. The other end, that is, the free end is brought into contact with the first stopper portion 165 and the second stopper portion 166 formed on the wall surface, whereby the intake pipe 161 and the exhaust pipe 162 are selectively closed. 3 and 4, the flow of hydrogen gas flowing through the intake pipe 161 is limited to the direction of flowing into the suction chamber 152, and the hydrogen gas flowing through the exhaust pipe 162 is indicated by the solid arrows in FIGS. 3 and 4. Is limited to the direction of flowing out of the suction chamber 152.

  However, when the humidity in the pipe through which the hydrogen gas circulates is high, water droplets may enter the circulation decompression pump 127 and adhere to the first stopper portion 165 and the second stopper portion 166. Reference numeral 169 in FIG. 4 indicates attached water droplets attached to the first stopper portion 165 and the second stopper portion 166. If the water droplets 169 are present, the adhesion between the intake check valve 163 and the exhaust check valve 164 and the first stopper portion 165 and the second stopper portion 166 cannot be maintained. As indicated by the broken arrow, a backflow occurs. Then, the capacity of the circulation decompression pump 127 is reduced, and the inside of the fuel cell stack 111 cannot be sufficiently decompressed.

  That is, when the moisture is low, as indicated by line A in FIG. 5, the pressure in the fuel cell stack 111 decreases as the operating time of the circulating pressure reducing pump 127 elapses, Become. On the other hand, when the water content is high, the capacity of the circulating pressure reducing pump 127 is reduced, so that the pressure in the fuel cell stack 111 does not become a value equal to or lower than the target pressure reducing level, as shown by the line B in FIG. End up.

  The present invention solves the problems of the conventional fuel cell system, and includes a first decompression pump disposed in a fuel gas circulation path and a second decompression disposed in a pipe line outside the fuel gas circulation path. The fuel gas or the replacement gas in the fuel gas flow path of the fuel cell stack is sucked and discharged by the pump, so that the fuel gas or the replacement gas in the fuel gas flow path can be quickly and reliably at the time of starting or stopping. The start-up time or stop time can be shortened, hydrogen and oxygen are not mixed in the fuel gas flow path, and even if the number of stops is large, no potential shift occurs and the performance It is an object of the present invention to provide a fuel cell system that can prevent the deterioration of the battery and extend the life.

Therefore, in the fuel cell system of the present invention, a fuel cell in which an electrolyte layer is sandwiched between a fuel electrode and an oxygen electrode is laminated with a separator having a fuel gas flow path formed along the fuel electrode. A fuel cell stack; a fuel gas circulation path connected to an inlet and an outlet of the fuel gas flow path for circulating the fuel gas; a first pressure reducing pump disposed in the fuel gas circulation path; and the fuel gas circulation path A second pressure reducing pump disposed in a fuel gas discharge line for branching from the fuel gas into the atmosphere, and operating the first pressure reducing pump during steady operation to circulate the fuel gas. When the start command or the stop command is received, the second pressure reducing pump is operated, and the fuel gas or the replacement gas in the fuel gas flow path is sucked and discharged by the first pressure reducing pump and the second pressure reducing pump. And a control device.

  In another fuel cell system of the present invention, the first pressure reducing pump and the second pressure reducing pump are arranged in series on the flow path of the fuel gas or the replacement gas sucked and discharged from the fuel gas flow path. Is done.

  In still another fuel cell system of the present invention, the first pressure reducing pump and the second pressure reducing pump further include a check valve.

According to the present invention, in a fuel cell system, a fuel cell in which an electrolyte layer is sandwiched between a fuel electrode and an oxygen electrode is laminated with a separator having a fuel gas flow path formed along the fuel electrode. A fuel cell stack; a fuel gas circulation path connected to an inlet and an outlet of the fuel gas flow path for circulating the fuel gas; a first pressure reducing pump disposed in the fuel gas circulation path; and the fuel gas circulation path A second pressure reducing pump disposed in a fuel gas discharge line for branching from the fuel gas into the atmosphere, and operating the first pressure reducing pump during steady operation to circulate the fuel gas. When the start command or the stop command is received, the second pressure reducing pump is operated, and the fuel gas or the replacement gas in the fuel gas flow path is sucked and discharged by the first pressure reducing pump and the second pressure reducing pump. And a location.

  In this case, since the fuel gas or the replacement gas in the fuel gas flow path can be quickly and reliably discharged at the time of starting or stopping, the starting time or stopping time can be shortened. Therefore, hydrogen and oxygen are not mixed in the fuel gas channel, and no potential shift occurs even if the number of stops is large. Accordingly, it is possible to prevent the performance of the fuel cell stack from being lowered, and to extend the life of the fuel cell stack. Moreover, even when the humidity in the fuel gas flow path or the fuel gas circulation path is high, the fuel gas or the replacement gas in the fuel gas flow path can be quickly and reliably discharged.

  In another fuel cell system, the first pressure reducing pump and the second pressure reducing pump are arranged in series on the flow path of the fuel gas or the replacement gas sucked and discharged from the fuel gas flow path.

  In this case, since the flow of the fuel gas or the replacement gas discharged from the first pressure reducing pump flows into the second pressure reducing pump, the backflow in the second pressure reducing pump is suppressed, and rather the pressure reducing by the second pressure reducing pump is accelerated. The Thereby, the decompression capability is improved, and the inside of the fuel gas channel can be sufficiently decompressed even if the humidity in the fuel gas channel is high.

  In still another fuel cell system, the first pressure reducing pump and the second pressure reducing pump further include a check valve.

  In this case, the flow of the fuel gas or the replacement gas can be appropriately controlled by the check valve, and the pressure reduction capability is improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a fuel cell stack according to an embodiment of the present invention.

  In the figure, reference numeral 11 denotes a fuel cell stack as a fuel cell (FC), which is used as a power source for vehicles such as passenger cars, buses, trucks, passenger carts, and luggage carts. Here, the vehicle includes a large number of auxiliary devices that consume electricity, such as a lighting device, a radio, and a power window, which are used even when the vehicle is stopped. Since the required output range is extremely wide, it is desirable to use a fuel cell stack 11 as a power source in combination with a secondary battery, a capacitor or the like as a power storage means (not shown).

  The fuel cell stack 11 may be of an alkaline aqueous solution type, a phosphoric acid type, a molten carbonate type, a solid oxide type, a direct type methanol or the like, but is preferably a solid polymer type fuel cell. .

  More preferably, PEMFC (Proton Exchange Membrane Fuel Cell) type fuel cell or PEM (Proton Exchange Membrane) using hydrogen gas as fuel gas, that is, anode gas, and oxygen or air as oxidant, that is, cathode gas. ) Type fuel cell. Here, the PEM fuel cell is generally a fuel cell in which a catalyst, an electrode, and a separator are combined on both sides of a solid polymer electrolyte membrane as an electrolyte layer that transmits ions such as protons. Are composed of a plurality of stacks connected in series.

  In this case, the solid polymer electrolyte membrane is sandwiched between two gas diffusion electrodes and integrated to join. Then, when one of the gas diffusion electrodes is used as a fuel electrode (anode electrode) and a fuel gas, that is, hydrogen gas as an anode gas, is supplied to the fuel electrode through a fuel gas flow channel in contact with the surface of the fuel electrode, It is decomposed into hydrogen ions (protons) and electrons, and the hydrogen ions permeate the solid polymer electrolyte membrane. Further, when the other of the gas diffusion electrodes is an oxygen electrode (cathode electrode) and an oxidizing gas, that is, air as a cathode gas, is supplied to the oxygen electrode through an air passage in contact with the surface of the oxygen electrode, oxygen in the air The hydrogen ions and electrons combine to produce water. An electromotive force is generated by such an electrochemical reaction.

  In the figure, an apparatus for supplying hydrogen gas as fuel gas to the fuel cell stack 11 is shown. Although hydrogen gas, which is fuel taken out by reforming methanol, gasoline, or the like by a reformer (not shown), can be directly supplied to the fuel cell stack 11, it is stable and sufficient even during high-load operation of the vehicle. In order to be able to supply an amount of hydrogen gas, it is desirable to supply the hydrogen gas stored in the fuel source 13. Thereby, the hydrogen gas is always sufficiently supplied at a substantially constant pressure, so that the fuel cell stack 11 can follow the fluctuation of the load of the vehicle and supply a necessary current. . In this case, the output impedance of the fuel cell stack 11 is extremely low and can be approximated to zero.

  Hydrogen gas is stored in a container containing a hydrogen storage alloy, a container containing a hydrogen storage liquid such as decalin, a first fuel supply line 14 as a fuel supply line from a fuel source 13 such as a hydrogen gas cylinder, and the like The fuel is supplied to an inlet of a fuel gas flow path of the fuel cell stack 11 through a second fuel supply pipe 15 as a fuel supply pipe connected to the first fuel supply pipe 14. The first fuel supply line 14 is provided with a fuel source source opening / closing valve 21, a pressure reducing valve 22 as a regulator, a fuel supply electromagnetic valve 23, and a pressure sensor 24. The second fuel supply line 15 is provided with a safety valve 25 as a purge valve. In this case, the fuel source 13 has a sufficiently large capacity and is capable of always supplying a sufficiently high pressure of hydrogen gas.

  Then, hydrogen gas discharged as an unreacted component from the outlet of the fuel gas flow path of the fuel cell stack 11 is discharged to the outside of the fuel cell stack 11 through the first fuel discharge pipe 16 as the fuel gas discharge pipe. Is done. The first fuel discharge pipe 16 is provided with a water recovery trap 26 as a recovery container for recovering and storing water from hydrogen gas. The water recovery trap 26 is provided with a water level meter and can measure the amount of recovered water. The water recovery trap 26 is connected to a second fuel discharge pipe 17 as a fuel gas discharge pipe for discharging hydrogen gas separated from water, and the second fuel discharge pipe 17 has a first pressure reduction. A hydrogen circulation decompression pump 27 is provided as a pump. A hydrogen circulation electromagnetic valve 28 is disposed in the second fuel discharge pipe 17. The end of the second fuel discharge pipe 17 opposite to the water recovery trap 26 side is connected to the second fuel supply pipe 15. Thereby, the hydrogen gas discharged to the outside of the fuel cell stack 11 can be recovered, supplied to the fuel gas flow path of the fuel cell stack 11 and reused. That is, the second fuel supply line 15, the first fuel discharge line 16, and the second fuel discharge line 17 constitute a fuel gas circulation path. The hydrogen circulation decompression pump 27 is disposed in the fuel gas circulation path, like the water recovery trap 26 and the hydrogen circulation electromagnetic valve 28.

  The water recovery trap 26 is connected to a third fuel discharge pipe 31 as a fuel gas discharge pipe, and an exhaust electromagnetic valve 41 is provided in the third fuel discharge pipe 31 so as to form a fuel cell stack. The hydrogen gas discharged from the fuel gas flow path at the time of starting 11 can be discharged into the atmosphere. The outlet end of the third fuel discharge pipe 31 is connected to the air exhaust manifold 12, and it is desirable to dilute the hydrogen discharged from the fuel gas circulation path with air. The air exhaust manifold 12 is a passage that is supplied to the air flow path of the fuel cell stack 11 and discharges air as an oxidant from the air flow path. In addition, a hydrogen combustor can be provided in the third fuel discharge conduit 31 as necessary. The hydrogen gas discharged by the hydrogen combustor can be combusted to form water, and then discharged into the atmosphere.

  Further, the other end of the second fuel discharge conduit 17 is connected to the downstream side of the exhaust solenoid valve 41 in the third fuel discharge conduit 31 between the hydrogen circulation pressure reducing pump 27 and the hydrogen circulation solenoid valve 28. A fourth fuel discharge pipe 32 as a fuel gas discharge pipe is connected. The fourth fuel discharge pipe 32 has a reduced-pressure hydrogen discharge valve 42 that is opened when the pressure inside the fuel gas flow path of the fuel cell stack 11 is reduced, and a decompression dedicated pump 43 as a second decompression pump. It is arranged. That is, the depressurizing pump 43 is disposed outside the fuel gas circulation path and in a fuel gas discharge line connected to the fuel gas circulation path.

  In addition, an outside air introduction line 18 is connected between the connection portion of the second fuel discharge line 17 to the second fuel supply line 15 and the hydrogen circulation electromagnetic valve 28. The outside air introduction pipe line 18 is provided with an outside air introduction electromagnetic valve 29 and an air filter 30 so that outside air can be introduced into the fuel gas flow path when the fuel cell stack 11 is stopped.

  Here, the pressure reducing valve 22 is a butterfly valve, a regulator valve, a diaphragm valve, a mass flow controller, a sequence valve, or the like. The pressure of the hydrogen gas flowing out from the outlet of the pressure reducing valve 22 is set to a preset pressure. Any type can be used as long as it can be adjusted. The pressure adjustment may be performed manually, but is preferably performed by an actuator including an electric motor, a pulse motor, an electromagnet, or the like.

  The fuel supply solenoid valve 23, the hydrogen circulation solenoid valve 28, the exhaust solenoid valve 41, the pressure-reducing hydrogen discharge valve 42, and the outside air introduction solenoid valve 29 are so-called on-off type, and are an electric motor, a pulse motor, The actuator is operated by an electromagnet or the like. The fuel source source opening / closing valve 21 is operated manually or automatically using an electromagnet.

  The hydrogen circulation decompression pump 27 and the decompression dedicated pump 43 can suck the hydrogen gas in the fuel gas flow path of the fuel cell stack 11 and reduce the pressure in the fuel gas flow path to below atmospheric pressure. Any type of pump may be used, but here, a reciprocating vacuum having a configuration similar to that of the circulating pressure reducing pump 127 as shown in FIG. 3 described in “Problems to be Solved by the Invention”. It shall be a pump. Further, the hydrogen circulation decompression pump 27 and the decompression dedicated pump 43 may have different configurations, but here, it is assumed that they have the same configuration.

  On the other hand, air as an oxidant is supplied to an air flow path of the fuel cell stack 11 from an oxidant supply source (not shown). Note that oxygen can be used as the oxidizing agent instead of air. And the air discharged | emitted from an air flow path is discharged | emitted in air | atmosphere through the air exhaust manifold 12 as a manifold.

  In the present embodiment, the fuel cell system has an FC control ECU (Electronic Control Unit) (not shown) as a control device. The control device includes a calculation means such as a CPU and MPU, a storage means such as a magnetic disk and a semiconductor memory, an input / output interface, and the like. From various sensors such as the pressure sensor 24, the fuel gas flow path and air of the fuel cell stack 11 are provided. By detecting the flow rate, temperature, output voltage, etc. of hydrogen, oxygen, air, etc. supplied to the flow path, the oxidant supply source, pressure reducing valve 22, fuel supply solenoid valve 23, hydrogen circulation solenoid valve 28, hydrogen circulation pressure reduction The operations of the pump 27, the outside air introduction solenoid valve 29, the exhaust solenoid valve 41, the decompression hydrogen discharge valve 42, the decompression dedicated pump 43, and the like are controlled. Further, the FC control ECU cooperates with other sensors provided in the vehicle and an EV (Electric Vehicle) control ECU (not shown) as a vehicle control means to supply fuel and oxidant to the fuel cell stack 11. Centrally control the operation of all equipment supplied.

  Next, the operation of the fuel cell system having the above configuration will be described. First, the operation in steady operation will be described.

  During steady operation in the fuel cell system of the present embodiment, the fuel supply solenoid valve 23 is opened, the hydrogen circulation decompression pump 27 is operated, the hydrogen circulation solenoid valve 28 is opened, the outside air introduction solenoid valve 29 is closed, and the exhaust solenoid valve 41 is closed. Is closed, the vacuum hydrogen discharge valve 42 is closed, and the vacuum pump 43 is stopped. Then, after adjusting the pressure of the hydrogen gas flowing out from the outlet of the pressure reducing valve 22 to a constant pressure set in advance, the pressure reducing valve 22 is not adjusted during the operation of the fuel cell system, and remains as it is. Retained. The oxidant supply source operates so as to be supplied with air set in advance according to the output current of the fuel cell. In this case, the amount of air supplied is an amount sufficiently larger than the amount of air necessary for the output of the fuel cell stack 11 to be maximized.

  When the fuel cell stack 11 starts operation, reverse diffusion water is generated in each unit cell constituting the fuel cell stack 11, and the reverse diffusion water permeates the solid polymer electrolyte membrane and enters the fuel gas flow path. Until the fuel electrode side of the solid polymer electrolyte membrane is humidified. As a result, the fuel electrode side of the solid polymer electrolyte membrane becomes wet, and hydrogen ions generated from hydrogen by the electrochemical reaction can move smoothly in the solid polymer electrolyte membrane.

  Further, the hydrogen gas as an unreacted component that is supplied to the fuel gas flow path and surplus is mixed with the back-diffused water that has permeated into the fuel gas flow path and becomes surplus, and a gas-liquid mixture Become. The hydrogen gas that has become the gas-liquid mixture is sucked by the hydrogen circulation decompression pump 27, and discharged to the outside of the fuel cell stack 11 through the first fuel discharge pipe 16 connected to the fuel cell stack 11. Then, the gas-liquid mixture passes through the first fuel discharge pipe 16 and is introduced into the water recovery trap 26. Then, by staying in the water recovery trap 26 having a relatively wide space, heavy moisture falls downward due to gravity, and the reverse diffusion water is separated from the hydrogen gas. The hydrogen gas separated from the reverse diffusion water is discharged from the second fuel discharge pipe 17 to the outside of the water recovery trap 26.

  In steady operation, the hydrogen gas discharged out of the water recovery trap 26 passes through the open hydrogen circulation solenoid valve 28 and is introduced into the second fuel supply line 15. It is supplied to the fuel gas flow path of the fuel cell stack 11 and reused.

  Next, the operation when starting the fuel cell system will be described.

  FIG. 6 is a schematic diagram showing the operation of the check valve of the decompression dedicated pump in the embodiment of the present invention. FIG. 7 is a diagram showing the decompression capability of the hydrogen circulation decompression pump and the decompression dedicated pump in the embodiment of the present invention. 8 is a flowchart showing an operation when starting the fuel cell system according to the embodiment of the present invention.

  First, when a vehicle driver rotates a key inserted in a key insertion slot of a main switch (not shown) and turns the rotation position to ON, a system start command is transmitted to the control device of the fuel cell system, and the fuel cell system is The starting operation is started. In the state before starting, the fuel supply solenoid valve 23 is closed, the hydrogen circulation decompression pump 27 is turned off, that is, stopped, the hydrogen circulation solenoid valve 28 is closed, the outside air introduction solenoid valve 29 is closed, and the exhaust solenoid valve 41 is closed. The depressurized hydrogen discharge valve 42 is closed, and the depressurizing pump 43 is OFF, that is, stopped. Further, the fuel gas flow path of the fuel cell stack 11 is filled with air used as a hydrogen gas replacement gas when the system is stopped.

  The control device first opens the decompression hydrogen discharge valve 42 (step S1), turns on and operates the hydrogen circulation decompression pump 27 (step S2), and turns on and operates the decompression dedicated pump 43 (step S3). ). Thereby, the air in the fuel gas flow path of the fuel cell stack 11 is discharged via the third fuel discharge pipe 31 and the fourth fuel discharge pipe 32. Further, the air in the second fuel supply line 15, the first fuel discharge line 16, the second fuel discharge line 17, the hydrogen circulation solenoid valve 28 and the water recovery trap 26 is also discharged. That is, along with the air in the fuel gas flow path, the air in the fuel gas circulation path is also discharged by the hydrogen circulation decompression pump 27 and the decompression dedicated pump 43. In this case, the hydrogen circulation depressurization pump 27 and the depressurization dedicated pump 43 operate in a state of being arranged in series on the flow path of the air sucked and discharged from the fuel gas flow path.

  By the way, when the humidity in the fuel gas flow path and the fuel gas circulation path is high, water droplets enter the hydrogen circulation decompression pump 27 and the decompression dedicated pump 43 and adhere to the stopper portion as the valve seat of the check valve. May end up. Here, since the hydrogen circulation decompression pump 27 and the decompression dedicated pump 43 have the same configuration, only the case of the decompression dedicated pump 43 will be described.

  As shown in FIG. 6, the decompression dedicated pump 43 has a suction chamber 43a, and an intake pipe 43b and an exhaust pipe 43c are connected to the suction chamber 43a. An intake check valve 43d is disposed at the boundary between the intake pipe 43b and the suction chamber 43a, and an exhaust check valve 43e is disposed at the boundary between the exhaust pipe 43c and the suction chamber 43a. . Here, the intake check valve 43d and the exhaust check valve 43e are plate members having flexibility mainly made of rubber, and one end is fixed to the wall surface of the suction chamber 43a and swings. The other end, that is, the free end is brought into contact with the first stopper portion 43f and the second stopper portion 43g as valve seats formed on the wall surface, thereby selectively closing the intake pipe 43b and the exhaust pipe 43c. As a result, as indicated by solid arrows in FIG. 6, the flow of gas such as air and hydrogen gas flowing through the intake pipe 43b is limited to the direction of flowing into the suction chamber 43a, and the inside of the exhaust pipe 43c. The flow of the flowing gas is limited to the direction of flowing out of the suction chamber 43a.

  However, when the humidity in the fuel gas flow path and the fuel gas circulation path is high, the attached water droplet 46 may adhere to the first stopper portion 43f and the second stopper portion 43g. As a result, it becomes impossible to maintain the adhesion between the intake check valve 43d and the exhaust check valve 43e and the first stopper portion 43f and the second stopper portion 43g, as shown by broken arrows in FIG. , Backflow will occur.

  However, in this embodiment, since the reduced pressure hydrogen discharge valve 42 is opened and both the hydrogen circulation decompression pump 27 and the decompression dedicated pump 43 are operating, the hydrogen circulation decompression pump 27 and the decompression dedicated pump 43 are connected in series. The fuel gas or the replacement gas in the fuel gas flow path and the fuel gas circulation path, that is, the gas is discharged. Therefore, the flow of the gas discharged from the hydrogen circulation decompression pump 27 flows in from the intake pipe 43b as shown by an arrow α in FIG. 6, so that the backflow in the intake pipe 43b is suppressed. The decompression due to will be accelerated. Therefore, even if the humidity in the fuel gas passage and the fuel gas circulation path is high, the pressure in the fuel gas passage and the fuel gas circulation path can be sufficiently reduced.

  Lines A and B in FIG. 7 are the same as the lines A and B in FIG. 5, and are curves showing the decompression capability in the conventional fuel cell system. As shown by the line B, it can be seen that the pressure does not become a value equal to or lower than the target decompression level when the water content is high. On the other hand, the decompression capability of the fuel cell system in the present embodiment is indicated by lines C and D. That is, when the moisture is low, the pressure in the fuel gas flow path and the fuel gas circulation path rapidly decreases as indicated by line C, and becomes a value equal to or lower than the target pressure reduction level in a short time. Moreover, even when there is a lot of moisture, as indicated by the line D, it becomes a value equal to or lower than the target decompression level in a short time.

  The control device repeatedly determines whether or not the pressure detected by the pressure sensor 24 has become less than a predetermined value (step S4), and monitors the pressure in the fuel gas flow path and the fuel gas circulation path. When the pressure detected by the pressure sensor 24 becomes less than a predetermined value, the control device closes the reduced-pressure hydrogen discharge valve 42 (step S5), and stops discharging air in the fuel gas flow path and the fuel gas circulation path. . Subsequently, the control device opens the fuel supply electromagnetic valve 23 (step S6) and introduces hydrogen gas into the fuel gas flow path of the fuel cell stack 11. In this case, since the outside air introduction solenoid valve 29 is in a closed state, air does not flow in. Then, the control device opens the exhaust electromagnetic valve 41 (step S7), purges the water in the water recovery trap 26, and removes the hydrogen gas flowing out from the fuel gas flow path of the fuel cell stack 11 to the third fuel discharge pipe. Discharge through path 31.

  Subsequently, the control device repeatedly determines whether the fuel cell voltage, that is, the terminal voltage of the fuel cell stack 11 exceeds a predetermined value (step S8), and monitors the terminal voltage of the fuel cell stack 11. When the terminal voltage of the fuel cell stack 11 exceeds a predetermined value, the control device closes the exhaust electromagnetic valve 41 (step S9), turns off the decompression dedicated pump 43 and stops it (step S10), and hydrogen circulation electromagnetic The valve 28 is opened (step S11). As a result, the hydrogen gas circulates in the fuel gas flow path of the fuel cell stack 11, the hydrogen gas is filled in the fuel gas flow path of the fuel cell stack 11, and the steady operation is started.

  Next, an operation when stopping the fuel cell system will be described.

  FIG. 9 is a flowchart showing the operation when stopping the fuel cell system in the embodiment of the present invention.

  First, when a vehicle driver rotates a key inserted in a key insertion slot of a main switch (not shown) and turns the rotational position to OFF, a system stop command is transmitted to the control device of the fuel cell system, and the vehicle is in steady operation. The operation for stopping the fuel cell system is started. As described above, in the state of steady operation, the fuel supply solenoid valve 23 is opened, the hydrogen circulation decompression pump 27 is turned on, that is, operates, the hydrogen circulation solenoid valve 28 is opened, and the outside air introduction solenoid valve 29 is closed. The exhaust solenoid valve 41 is closed, the decompression hydrogen discharge valve 42 is closed, and the decompression dedicated pump 43 is OFF, that is, is stopped.

  Then, the control device first closes the fuel supply electromagnetic valve 23 (step S21), and stops the supply of hydrogen gas from the fuel source 13. Subsequently, the hydrogen circulation electromagnetic valve 28 is closed (step S22), and the circulation of hydrogen gas in the fuel gas circulation path is stopped. Further, the exhaust solenoid valve 41 is opened (step S23), the water in the water recovery trap 26 is discharged, and the hydrogen gas flowing out from the fuel gas flow path of the fuel cell stack 11 is discharged through the third fuel discharge pipe 31. .

  Subsequently, the control device repeatedly determines whether or not the pressure detected by the pressure sensor 24 has become approximately 0 [kPaG] (step S24), and monitors the pressure in the fuel gas flow path and the fuel gas circulation path. . When the pressure detected by the pressure sensor 24 becomes approximately 0 [kPaG], the control device closes the exhaust electromagnetic valve 41 (step S25), opens the decompression hydrogen discharge valve 42 (step S26), and performs the decompression dedicated pump 43. Is turned on and operated (step S27). Thereby, the hydrogen gas in the fuel gas flow path of the fuel cell stack 11 is discharged through the third fuel discharge pipe 31 and the fourth fuel discharge pipe 32 by the hydrogen circulation pressure reduction pump 27 and the pressure reduction dedicated pump 43. . Further, hydrogen gas in the fuel gas circulation path is also discharged.

  Subsequently, the control device repeatedly determines whether or not the pressure detected by the pressure sensor 24 has become less than a predetermined value (step S28), and monitors the pressure in the fuel gas flow path and the fuel gas circulation path. When the pressure detected by the pressure sensor 24 becomes less than a predetermined value, the control device opens the outside air introduction electromagnetic valve 29 (step S29) and introduces air as a replacement gas into the fuel gas flow path. In this case, since the fuel supply electromagnetic valve 23 is in a closed state, the introduced air does not flow toward the fuel source 13. Thereby, the fuel gas flow path of the fuel cell stack 11 is filled with air. Since the air passes through the air filter 30 and is filtered, it does not contain dust, impurities, harmful gases, etc. that exist in the atmosphere. Therefore, members such as a catalyst in the fuel gas flow path of the fuel cell stack 11 are not contaminated or altered by the dust, impurities, harmful gas, or the like.

  Subsequently, the control device repeatedly determines whether or not the fuel cell voltage, that is, the terminal voltage of the fuel cell stack 11 has become less than a predetermined value (step S30), and monitors the terminal voltage of the fuel cell stack 11. The predetermined voltage is such that no hydrogen gas remains in the fuel gas flow path of the fuel cell stack 11, the air is filled, and no substantial potential difference occurs between the fuel electrode and the air electrode. The voltage corresponds to the state. When the terminal voltage of the fuel cell stack 11 becomes less than a predetermined value, the control device stops all the auxiliary machines (step S31). In this case, the hydrogen circulation decompression pump 27 and the decompression dedicated pump 43 are also stopped, and the oxidant supply source is also stopped. As a result, the output of the fuel cell stack 11 is stopped, and the stop of the fuel cell system is completed.

  As described above, in the present embodiment, the fuel cell system is disposed in the hydrogen circulation decompression pump 27 disposed in the fuel gas circulation path and the fourth fuel discharge pipe 32 connected to the fuel gas circulation path. In the normal operation, the hydrogen circulation decompression pump 27 is operated to circulate hydrogen gas, and when the system start command or stop command is received, the decompression dedicated pump 43 is operated to The hydrogen gas or air in the fuel gas flow path of the fuel cell stack 11 is sucked and discharged by the pump 27 and the decompression dedicated pump 43.

  Therefore, hydrogen gas or air in the fuel gas channel can be quickly discharged at the time of starting or stopping, and the starting time or stopping time can be shortened. As a result, hydrogen and oxygen are not mixed in the fuel gas flow path, and no potential shift occurs even if the number of stops is large. Therefore, it is possible to prevent the performance of the fuel cell stack 11 from being deteriorated, and to extend the life of the fuel cell stack 11.

  Further, even when the humidity in the fuel gas flow path or the fuel gas circulation path is high, the hydrogen gas or air in the fuel gas flow path can be quickly and reliably discharged.

  Furthermore, since only the pressure reducing pump 43 is provided in the fourth fuel discharge pipe 32, the configuration of the fuel cell system is not complicated and the cost does not increase. Furthermore, since the dedicated decompression pump 43 is disposed outside the fuel gas circulation path, it is not necessary to operate the dedicated decompression pump 43 during steady operation. For this reason, it is possible to suppress energy consumption for operating the vacuum pump 43. Note that during the steady operation, the hydrogen circulation decompression pump 27 only needs to exhibit the function of circulating the hydrogen gas, and high decompression capacity is not required. For this reason, even if the humidity in the fuel gas flow path or the fuel gas circulation path is high, a reduction in pressure reduction capacity does not become a problem.

  In addition, this invention is not limited to the said embodiment, It can change variously based on the meaning of this invention, and does not exclude them from the scope of the present invention.

It is a figure which shows the structure of the fuel cell stack in embodiment of this invention. It is a figure which shows the structure of the conventional fuel cell system. It is a schematic diagram which shows the structure of the conventional circulation pressure reduction pump. It is a schematic diagram which shows operation | movement of a non-return valve when there is much water | moisture content in the conventional circulation pressure reduction pump. It is a graph which shows the pressure reduction capability in the conventional circulation pressure reduction pump. It is a schematic diagram which shows operation | movement of the non-return valve of the pump for pressure reduction in embodiment of this invention. It is a figure which shows the decompression capability of the hydrogen circulation decompression pump and the decompression-dedicated pump in the embodiment of the present invention. It is a flowchart which shows the operation | movement at the time of starting the fuel cell system in embodiment of this invention. It is a flowchart which shows the operation | movement at the time of stopping the fuel cell system in embodiment of this invention.

Explanation of symbols

11 Fuel cell stack 15 Second fuel supply line 16 First fuel discharge line 17 Second fuel discharge line 27 Hydrogen circulation depressurization pump 31 Third fuel discharge line 32 Fourth fuel discharge line 43 Depressurization dedicated pump

Claims (3)

A fuel cell stack in which an electrolyte layer is sandwiched between a fuel electrode and an oxygen electrode, and is stacked with a separator having a fuel gas flow path formed along the fuel electrode;
A fuel gas circulation path connected to the inlet and outlet of the fuel gas flow path for circulating the fuel gas;
A first pressure reducing pump disposed in the fuel gas circulation path;
A second pressure reducing pump disposed in a fuel gas discharge line for branching from the fuel gas circulation path and discharging the fuel gas into the atmosphere ;
During the steady operation, the first pressure reducing pump is operated to circulate the fuel gas. When a system start command or a stop command is received, the second pressure reducing pump is operated, and the first pressure reducing pump and the second pressure reducing pump perform the operation. And a control device for sucking and discharging the fuel gas or the replacement gas in the fuel gas flow path.   2. The fuel cell system according to claim 1, wherein the first pressure reducing pump and the second pressure reducing pump are arranged in series on the flow path of the fuel gas or the replacement gas that is sucked and discharged from the fuel gas flow path.   The fuel cell system according to claim 1 or 2, wherein the first pressure reducing pump and the second pressure reducing pump include a check valve.

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