JP2012164457A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system which can perform humidification of the fuel cell appropriately at the next time system start-up.SOLUTION: When a determination is made during system stoppage that the condensed water does not freeze at the next time system start-up, an ECU60 performs water storage operation for storing the condensed water in a reservoir section 42a by controlling a compressor 34 according to the operation pressure determined based on the operation temperature. When a determination is made that the condensed water freezes at the next time system start-up, control of the compressor 34 according to the operation pressure determined based on the operation temperature and drainage of water by a drain valve 47 are performed until the processing time of water removal elapses, thus draining the condensed water from the reservoir section 42a.

Description

  The present invention relates to a fuel cell system.

  As means for improving the operation efficiency of the fuel cell system, for example, techniques described in Patent Document 1 and Patent Document 2 have been proposed. Patent Document 1 describes a technique for improving the energy efficiency of a compressor by spraying water on the rotor of the compressor. Patent Document 2 describes a technique in which water accumulated downstream of an expander is injected downstream of a compressor to humidify a gas supplied to the fuel cell.

JP 2000-294265 A JP 7-14599 A

  However, Patent Document 1 and Patent Document 2 do not discuss any management of water when the system is stopped. For example, when the system is started next time, water is insufficient and the amount of humidification for the fuel cell decreases. There was a problem that humidification was not performed properly by freezing in an environment where the temperature was below freezing when the system was started.

  The present invention solves the above-described conventional problems, and an object thereof is to provide a fuel cell system capable of appropriately humidifying the fuel cell at the next system startup.

  The present invention relates to a fuel cell that generates power by being supplied with fuel and an oxidant, an oxidant supply channel through which the oxidant supplied to the fuel cell flows, and an exhaust oxidant that is discharged from the fuel cell. An oxidant discharge passage through which the exhaust gas flows, an expansion means disposed in the oxidant discharge flow path for expanding the discharged oxidant, a compressor disposed in the oxidant supply flow path, and the expansion means. A water recovery means disposed downstream and for recovering condensed water; and water injection means for injecting the condensed water recovered by the water recovery means into the oxidant supply flow path. If it is determined that the condensed water will not freeze at times, a water storage process is performed in which the condensed water is stored in the water recovery means. If it is determined that the condensed water will freeze at the next system startup, the condensed water is discharged from the water recovery means. Control to remove water Characterized in that it comprises a.

  According to the present invention, when it is determined that the condensed water recovered by the water recovery means at the next system startup does not freeze when the fuel cell system is stopped, the condensed water is stored in the water recovery means next time. When the system is started (for example, when the fuel cell is started in a high temperature state), it is possible to prevent the condensed water from being insufficient, and it is possible to prevent the fuel cell from being insufficiently humidified. In addition, when it is determined that the condensed water collected by the water collecting means at the next system startup is frozen when the fuel cell system is stopped, the condensed water is removed from the water collecting means so that Can be prevented from being frozen and humidified properly.

  In addition, the control unit predicts the next startup temperature at the next system startup, performs the water storage process when the next startup temperature is higher than a predetermined value, and if the next startup temperature is equal to or lower than the predetermined value, A water removal treatment is performed.

  According to this, it is possible to appropriately determine whether or not the condensed water is frozen at the next system startup by making a prediction based on the temperature.

  Further, the expansion means includes an expander turbine and a transmission shaft that obtains regenerative energy of the expander turbine and transmits a driving force to the compressor.

  According to this, by obtaining the regenerative energy of the expander turbine and driving the compressor, the pressure of the exhaust oxidant can be used effectively, and the power consumption of the compressor can be reduced.

  In addition, the water recovery means includes a water storage unit that stores condensed water, and includes a water level sensor that detects a water level of the water storage unit, and a temperature sensor that detects a fuel cell related temperature related to the temperature of the fuel cell, When the water storage process is performed when the system is stopped, the control unit determines whether the relationship between the fuel cell related temperature and the amount of water vapor necessary for the fuel cell, and the pressure of the fuel cell and the amount of water vapor necessary for the fuel cell. Based on the relationship, the operating pressure necessary for the fuel cell is obtained using the detected temperature related to the fuel cell, and the compressor is adjusted so as to be the operating pressure until the water level value by the water level sensor reaches a predetermined value. It is characterized by controlling.

  By the way, the relationship between the temperature related to the fuel cell (hereinafter referred to as the operating temperature) and the amount of water vapor required for the fuel cell (hereinafter referred to as the required water vapor amount), and the required water vapor amount and the pressure of the fuel cell (hereinafter referred to as the operating pressure). )), The required water vapor amount increases as the operating temperature rises. Therefore, the required water vapor amount can be reduced by increasing the operating pressure. Accordingly, it is possible to adjust the amount of condensed water generated by the expansion means by controlling the operating pressure based on the operating temperature.

  By performing the water storage process when the system is stopped based on such a relationship, for example, when the operating temperature is high, the amount of water contained in the exhaust oxidant is large, so the required water vapor amount can be reduced by increasing the operating pressure. The amount of condensed water can be increased. By controlling the amount of condensed water in this way, condensed water can be secured in the water storage section in a short time. Therefore, even if the fuel cell is started in a high temperature state (for example, when the system is started immediately after the system is stopped) at the next system start-up, the condensed water stored in the water storage section at the time of the system stop is used as the oxidant supply channel. Insufficient water (insufficient humidification) can be avoided by spraying on the surface.

  Further, the water recovery means includes a drain valve for discharging the recovered condensed water to the outside, and when the controller performs the water removal process when the system is stopped, the fuel cell related temperature and the water removal process time, The water removal processing time is obtained based on the detected temperature related to the fuel cell, and the relationship between the temperature related to the fuel cell and the amount of water vapor necessary for the fuel cell, and the pressure of the fuel cell Based on the relationship with the amount of water vapor required for the fuel cell, using the detected temperature related to the fuel cell to determine the operating pressure required for the fuel cell, control of the compressor according to the operating pressure, The water is discharged by the drain valve until the water removal treatment time elapses.

  For example, as the operating temperature increases, the amount of water contained in the exhaust oxidant increases. Therefore, by increasing the operating pressure, the required water vapor amount can be reduced and a large amount of condensed water is generated. Therefore, since the amount of condensed water to be removed increases, the water removal processing time is set longer. Thus, by obtaining the operating pressure and the water removal treatment time and opening the discharge valve until the water removal treatment time elapses, a large amount of water contained in the discharge oxidant can be discharged when the system is stopped.

  The controller may predict the next startup temperature using at least one of the outside air temperature, calendar information, and GPS information.

  According to this, the next startup temperature can be appropriately predicted.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell system which can perform humidification of a fuel cell appropriately at the next system starting can be provided.

It is a whole lineblock diagram showing the fuel cell system concerning this embodiment. (A), (b) is sectional drawing which shows the structural example of a water injection mechanism. (A) is a map showing the relationship between the operating temperature and the required water vapor amount, and (b) is a map showing the relationship between the required water vapor amount and the operating pressure. It is a graph which shows the relationship between an operating pressure and the moisture content which generate | occur | produces in an expander. It is the schematic for determining the operating pressure at the time of normal driving | operation. It is a flowchart which shows a water storage process and a water removal process. (A) is a map showing the relationship between operating temperature and operating pressure, and (b) is a map showing the relationship between operating temperature and processing time. It is a whole block diagram which shows the fuel cell system which concerns on the modification of this embodiment.

  Next, the fuel cell system 10 according to the present embodiment will be described with reference to FIGS. 1 to 8. In the following, the fuel cell system 10 will be described by taking a fuel cell vehicle (including a four-wheeled vehicle, a two-wheeled vehicle, etc.) as an example, but is not limited thereto, and is not limited to this. It can be applied to anything that requires electricity, such as stationary ones.

  As shown in FIG. 1, the fuel cell system 10 includes a fuel cell 12, an anode system 14 that supplies and discharges hydrogen (fuel gas, reaction gas) to and from the anode of the fuel cell 12, and a cathode of the fuel cell 12. On the other hand, a cathode system 16 that supplies and discharges air containing oxygen (oxidant gas, reaction gas), a cooling system 17 that cools the fuel cell 12 by circulating a refrigerant, and an ECU (control unit, Control device) 60.

  The fuel cell 12 is a polymer electrolyte fuel cell (PEFC), and a plurality of single cells are formed by sandwiching a MEA (Membrane Electrode Assembly) between separators (not shown). Has been configured. The MEA includes an electrolyte membrane (solid polymer membrane) and a cathode and an anode that sandwich the membrane. Each separator is formed with an anode flow path 18 and a cathode flow path 20 made of grooves and through holes.

  In this case, an electrode reaction occurs when hydrogen (fuel) is supplied to each anode via the anode channel 18, while air (oxidant) is supplied to each cathode via the cathode channel 20. As a result, an electrode reaction occurs, and a potential difference (OCV (Open Circuit Voltage)) is generated in each single cell so that the fuel cell 12 can generate electric power. (For example, a travel motor (not shown) and a motor 35 (electric motor) of the compressor 34 to be described later) are electrically connected to each other, and the fuel cell 12 is configured to generate electric power by taking out current.

  The anode system 14 includes a hydrogen tank 22 in which hydrogen is sealed at a high pressure, an ejector 24, a first gas-liquid separator 26, a drain valve 28, and a purge valve 30.

  The outlet port of the anode is connected to the suction port of the ejector 24 via the pipe a3, the first gas-liquid separator 26, and the pipe a4. In this case, anode off-gas (fuel off-gas) containing unconsumed (unreacted) hydrogen discharged from the anode channel 18 flows through the pipes a3 and a4 to the ejector 24 arranged on the upstream side of the fuel cell 12. Returned and configured to circulate hydrogen.

  That is, a hydrogen circulation line (fuel gas circulation line) is configured by a plurality of pipes a2, a3, and a4 including a pipe a2 that connects the outlet port of the ejector 24 and the inlet port of the anode flow path 18, and this hydrogen circulation line. A first gas-liquid separator 26 is disposed therein. The ejector 24 may be omitted and an electric pump may be arranged.

  The first gas-liquid separator 26 separates moisture (condensation water) contained in the anode off-gas discharged from the outlet of the anode flow path 18 and temporarily stores the separated moisture therein. Note that the gas-liquid separation method in the first gas-liquid separator 26 is, for example, in the first gas-liquid separator 26, by increasing the cross-sectional area of the anode off-gas flow path, and circulating in the first gas-liquid separator 26. By reducing the flow rate of the anode off gas, a method of separating water having a large specific gravity with respect to hydrogen can be employed. Furthermore, a cooling pipe through which a low-temperature refrigerant flows may be provided, and the anode off gas may be cooled by this cooling pipe to separate the moisture.

  The anode off-gas from which the moisture has been separated in the first gas-liquid separator 26 is returned to the ejector 24 via the pipe a4, while the separated and recovered moisture is removed from the bottom of the first gas-liquid separator 26 (for example, And temporarily stored in the tank part).

  The bottom of the first gas-liquid separator 26 is connected to a diluter 32 which will be described later via a pipe a5, a normally closed drain valve 28, and a pipe a6. The drain valve 28 is a valve for discharging the water stored in the first gas-liquid separator 26. When the drain valve 28 is opened by a valve opening signal (control signal) from the ECU 60, the first gas-liquid separator 26 is discharged. The water (reserved water) is discharged to the diluter 32 through the pipe a5, the drain valve 28, and the pipe a6.

  The drain valve 28 is operated using electric power from the fuel cell 12, a battery (not shown) to which power generated by the fuel cell 12 is charged, or a step-down converter (not shown). In addition, the purge valve 30 and a drain valve 47, which will be described later, also operate using the fuel cell 12 and the like as a power source.

  A diluter 32 is connected to a part in the middle of the pipe a4 through a pipe a7, a normally closed purge valve 30, and a pipe a8. The purge valve 30 is a valve for discharging (purging) impurities (such as nitrogen) contained in the anode off-gas (hydrogen) circulating through the hydrogen circulation line (pipes a2 to a4) when the fuel cell 12 generates power. In the anode system 14, the pipes a3, a4 (up to the branch portion), a7, a8 function as fuel off-gas discharge passages.

  The cathode system 16 is provided with a compressor (compressor) 34 that forcibly takes in and sends out air by being given a driving force, a humidifier 38, and a transmission shaft 40 a that transmits a rotational driving force to the compressor 34. The connected expander turbine (expansion means) 40, the diluter 32, the second gas-liquid separator (water recovery means) 42 configured integrally with the diluter 32, and the upstream side of the compressor 34. The water injection mechanism 44a (44b) which injects water in this piping b1 is provided.

  The compressor 34 is driven by obtaining the power of the motor 35 or by obtaining the power of the motor 35 and the regenerative energy (power) of the expander turbine 40 and is transmitted through the transmission shaft 40a. A turbine blade (not shown) is rotationally driven by the force. When the turbine blades of the compressor 34 are driven to rotate, air containing oxygen is taken in and supplied to the fuel cell 12. The transmission shaft 40a is rotatably supported via a bearing (not shown). The compressor 34 is connected to a humidifier 38 via a downstream pipe b2.

  The compressor 34 is connected to the motor 35 via an electromagnetic clutch (not shown), and the rotational speed of the motor 35 is controlled by the ECU 60. The transmission shaft 40a that connects the compressor 34 and the expander turbine 40 is also provided with an electromagnetic clutch 41 so that the compressor 34 and the expander turbine 40 can be connected and disconnected. That is, the regenerative energy of the expander turbine 40 can be recovered as the power of the compressor 34 by connecting the electromagnetic clutch 41. Moreover, the regenerative energy of the expander turbine 40 can be interrupted by disconnecting the electromagnetic clutch 41. In this embodiment, the electromagnetic clutch 41 is provided on the transmission shaft 40a. However, the compressor 34 and the expander turbine 40 may be directly connected by the transmission shaft 40a without providing the electromagnetic clutch 41. Good. In addition, although the case where the expander turbine 40 and the compressor 34 are arrange | positioned coaxially via the transmission shaft 40a is illustrated in FIG. 1, you may be comprised in a different axis | shaft.

  The humidifier 38 is disposed so as to straddle the pipe b3 connected to the inlet port of the cathode flow path 20 of the fuel cell 12 and the pipe b4 connected to the outlet port of the cathode flow path 20. It is configured to humidify the air that faces it. The humidifier 38 includes a hollow fiber membrane (not shown) capable of exchanging moisture, and the moisture can be exchanged between the air toward the cathode channel 20 and the humid cathode offgas via the hollow fiber membrane. Yes. The cathode off-gas outlet port of the humidifier 38 is connected to the upstream side of the expander turbine 40 via a pipe b5. In the cathode system 16, the pipes b1 to b3 function as oxidant supply channels.

  The expander turbine 40 functions as a regenerative turbine (expansion means) that absorbs (depressurizes) the pressure of the cathode offgas (exhaust oxidant) discharged from the fuel cell 12. That is, the expander turbine 40 (regenerative turbine) is rotationally driven by the exhaust energy of the cathode offgas (relatively high pressure) discharged from the fuel cell 12, and the rotational force (regenerative energy) of the expander turbine 40 is transmitted to the transmission shaft 40a. Is transmitted to the compressor 34 via.

  In this case, the expander turbine 40 is rotationally driven by the cathode off gas, so that the cathode off gas expands and is cooled. That is, the cathode offgas passing through the expander turbine 40 expands and the pressure decreases, whereby the temperature of the cathode offgas decreases, and a part of the cathode offgas becomes condensed water (condensed water on the cathode side). The condensed water and the cathode off-gas that has passed through the expander turbine 40 are discharged to the diluter 32 connected downstream via the pipe b7.

  The diluter 32 is composed of, for example, box bodies stacked in multiple stages, and a dilution space that communicates between the layers is formed. For example, the second gas-liquid separator 42 is integrally provided in the lowermost dilution space that constitutes the diluter 32. Further, the diluter 32 dilutes hydrogen in the anode off-gas introduced from the pipe a8 at the time of purging (when the purge valve 30 is in an open state) with the cathode off-gas discharged through the expander turbine 40. The diluted anode off gas is discharged into the atmosphere together with the cathode off gas via the second gas-liquid separator 42, the pipe b8, a silencer (silencer) (not shown), and the like. Therefore, the downstream of the expander turbine 40 is close to atmospheric pressure by communicating with the atmosphere.

  The second gas-liquid separator 42 includes a water storage part 42a (water recovery means) for storing condensed water, and water contained in the anode off-gas diluted in the dilution space of the diluter 32 is separated and recovered to store water. Stored in the part 42a. Thus, the fuel cell system 10 can be reduced in size by disposing and integrating the second gas-liquid separator 42 and the water reservoir 42a in the diluter 32. In addition, when the drain valve 28 is in the open state, the water reservoir 42a stores water (anode-side condensed water) stored in the first gas-liquid separator 26 via the pipes a5 and a6. .

  In the present embodiment, the second gas-liquid separator 42 provided with the water storage part 42a in the diluter 32 has been described as an example. However, the present invention is not limited to this, and the diluter 32 and the water storage part You may comprise the 2nd gas-liquid separator 42 provided with 42a separately. In the present embodiment, the case where the water storage unit 42a is provided in the second gas-liquid separator 42 has been described as an example. However, the diluter 32, the second gas-liquid separator 42, and the water storage unit 42a are separately provided. You may comprise. Moreover, the 2nd gas-liquid separator 42 provided with the water storage part 42a may be provided in the piping b7 between the diluter 32 and the expander turbine 40, and only the water storage part 42a is the diluter 32 and the expander. It may be provided in the pipe b7 between the turbine 40.

  The water (condensed water) separated by the second gas-liquid separator 42 and collected in the water storage section 42a is introduced into the water injection mechanisms 44a and 44b (water injection means) via the pipe b9. The water injection mechanisms 44a and 44b inject condensed water stored in the water storage section 42a to the upstream side of the compressor 34, and humidify the air flowing through the pipe b1. In the cathode system 16, the pipes b4 to b7 function as oxidant discharge channels.

  A water injection mechanism 44a shown in FIG. 2 (a) is of an orifice type, and is provided with an orifice portion 50 in a pipe b1 on the upstream side of the compressor 34, and a compressor provided on the downstream side of the pipe b1. The air taken in by the action 34 is passed through the orifice portion 50. And when the said taken-in air passes through the orifice part 50, the flow velocity increases, the pressure of the exit side of the orifice part 50 falls, and a negative pressure generate | occur | produces. The water stored in the water storage part 42a of the second gas-liquid separator 42 is drawn out through the pipe b9 by the suction action by the negative pressure, and water can be suitably injected to the pipe b1 through which air flows. .

  Moreover, the water injection mechanism 44b shown in FIG. 2 (b) shows a pump type, and the water in the water storage part 42a in the second gas-liquid separator 42 is sucked up by the electric pump 56 and faces the pipe b1. The water sucked up by the electric pump 56 is ejected from the tip of the injector 58.

  Returning to FIG. 1, a pipe b10 provided with a normally closed drain valve 47 is connected to the water reservoir 42a. The drain valve 47 discharges the condensed water stored in the water storage section 42a to the outside (outside the vehicle), and discharges the water stored in the water storage section 42a by opening the drain valve 47. The water in the water reservoir 42a can be removed.

  The cooling system 17 circulates a refrigerant to cool the fuel cell 12, is connected to a refrigerant flow path (not shown) formed in the fuel cell 12, and an outlet port of the refrigerant flow path is connected via a pipe c1. It is connected to the inlet port of the radiator 36, and the outlet port of the radiator 36 is connected to the inlet port of the refrigerant flow path via the pipe c2, the refrigerant pump 37, and the pipe c3. Although not shown, the cooling system 17 includes a bypass pipe that bypasses the radiator 36, and a switching valve (thermostat valve) that switches the flow path between the radiator 36 and the bypass pipe.

  In such a cooling system 17, for example, when the temperature of the fuel cell 12 becomes high (a predetermined temperature or higher), the switching valve is switched so that the refrigerant flows through the radiator 36, so that the radiator 36 radiates heat. The cooled refrigerant is introduced into the fuel cell 12, and the fuel cell 12 is cooled.

  The ECU 60 (control unit) includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory) storing a program, and the like. The motor 35 of the compressor 34 and the motor ( (Not shown), the water injection mechanism 44b (electric pump, injector) is controlled, and the drain valve 47, the drain valve 28, and the purge valve 30 are opened and closed.

  In addition, the ECU 60 sets the refrigerant temperature sensor 61 (temperature sensor) for detecting the refrigerant outlet temperature (fuel cell related temperature) of the fuel cell 12 provided in the pipe c1, and the intake air temperature (fuel cell related temperature) of the compressor 34. Intake temperature sensor 62 (temperature sensor) to detect, outside air temperature sensor 63 (temperature sensor) to detect outside air temperature (fuel cell related temperature), and detected value (refrigerant temperature, coolant temperature, water level sensor 64) (Intake air temperature, outside air temperature, water level).

  Further, the ECU 60 acquires from the IG 65 an IG-ON signal for starting the fuel cell system 10 (system start) and an IG-OFF signal for stopping the fuel cell system 10 (system stop). The ECU 60 is connected to a timer 66 that measures the time for removing the water in the water storage section 42a, and is configured to acquire the time (water removal processing time) measured by the timer 66.

  In addition, when the ECU 60 determines that the condensed water does not freeze at the next system startup (at the next IG-ON) when the system is stopped (IG-OFF), the water storage process stores the condensed water in the water storage unit 42a. And a means for performing a water removal process for discharging the condensed water from the water storage section 42a when it is determined that the condensed water will be frozen at the next system startup. For example, the next startup temperature is predicted based on a predetermined value (for example, 0 ° C. which is a freezing point of pure water under 1 atm) for predicting the next startup temperature at the next system startup and determining whether or not to freeze. If the temperature exceeds a predetermined value, it can be determined that the water is not frozen, and the water storage process can be performed. If the temperature is equal to or lower than the predetermined value, it is determined that the water is frozen.

  The next startup temperature can be predicted using, for example, at least one of the outside air temperature, calendar information, and GPS information. The outside air temperature is, for example, the temperature outside the vehicle when the system is stopped (current), and can be detected by the outside air temperature sensor 63. The detection of the outside air temperature is not limited to the outside air temperature sensor 63, but may be detected by the intake air temperature sensor 62. The calendar information is the current date, day of the week, time, etc. For example, the presence or absence of freezing can be determined based on the season (for example, whether it is summer or winter). The GPS information includes, for example, information (for example, longitude and latitude) sent from an artificial satellite for GPS. For example, the own vehicle is based on information calculated by a car navigation device mounted on the vehicle. A position (for example, whether it is Okinawa or Hokkaido) is calculated.

  In addition, the next startup temperature may be predicted by combining a plurality of outside air temperatures, calendar information, and GPS information. Further, as another means for predicting the next startup temperature, it may be predicted based on the operation pattern so far, or may be predicted based on weather information.

  When performing the water storage treatment, as shown in FIG. 3 (a), a map showing the relationship between the operating temperature (fuel cell related temperature) and the required water vapor amount (water vapor amount necessary for the fuel cell 12), and As shown in FIG. 3B, the detected operating temperature (operating temperature) based on a map showing the relationship between the operating pressure (pressure of the fuel cell 12) and the required water vapor amount (water vapor amount required for the fuel cell 12). The operating pressure (the operating pressure necessary for the fuel cell 12) can be obtained from the fuel cell related temperature). The operating pressure means a pressure (target pressure) required for the air flowing through the cathode channel 20.

  The map shown in FIG. 3A shows the fuel cell 12 when the pressure of the air flowing through the fuel cell 12 (pressure of the fuel cell 12) is constant when the fuel cell 12 generates predetermined power. The relationship between the temperature of the fuel cell (temperature related to the fuel cell) and the amount of water vapor necessary for the air introduced into the fuel cell 12 to have a relative humidity of 100% (the amount of water vapor necessary for the fuel cell 12: g / min) is shown. Yes. This is because the saturated water vapor pressure increases as the temperature rises. The map shown in FIG. 3B shows the pressure of the air flowing through the fuel cell 12 when the fuel cell 12 generates a predetermined electric power when the temperature of the fuel cell 12 is constant (the fuel cell 12 Pressure) and the amount of water vapor required for the air introduced into the fuel cell 12 to have a relative humidity of 100% (the amount of water vapor required for the fuel cell 12: g / min). This is because the saturated water vapor pressure decreases when the pressure is increased.

  Therefore, it is necessary to increase the operating pressure according to the maps shown in FIGS. 3A and 3B to bring the air supplied to the fuel cell 12 (cathode channel 20) to 100% relative humidity. It is possible to reduce the amount of water vapor. In other words, even if the operating temperature rises, increasing the operating pressure can suppress an increase in saturated water vapor pressure and bring the relative humidity closer to 100%. That is, the amount discharged from the fuel cell 12 as condensed water can be adjusted by adjusting the operating pressure with reference to the maps of FIGS. 3 (a) and 3 (b). Therefore, the amount of condensed water can be adjusted by controlling the operating pressure based on the operating temperature (see FIG. 7A). Each map shown in FIG. 3A and FIG. 3B is appropriately changed according to the type of the electrolyte membrane of the fuel cell 12 and is obtained in advance by experiments, simulations, or the like.

  FIG. 4 is a graph showing the relationship between the operating pressure of the fuel cell 12 and the amount of water generated by the expander turbine 40 (condensed water amount). That is, as shown in FIG. 4, when the operating pressure increases, the differential pressure across the expander turbine 40 increases, so the temperature drop after passing through the expander turbine 40 increases, and the water vapor contained in the cathode off-gas increases. The amount of condensed water increases. Therefore, the amount of condensed water generated in the expander turbine 40 increases by increasing the operating pressure. Thereby, the amount of water injection supplied to the compressor 34 via the water storage part 42a can be increased.

  FIG. 5 is a schematic diagram for determining the operating pressure during normal operation (when the system is started and when IG-ON). As shown in FIG. 5, the ECU 60 can determine the operating pressure from the operating temperature based on a map that shows the relationship between the operating temperature and the operating pressure. The operating temperature is, for example, an FC (fuel cell) refrigerant temperature detected by the refrigerant temperature sensor 61.

  Further, as shown in FIG. 5, the ECU 60 includes a plurality of maps (IFC: one of large, medium, and small) corresponding to the current command value (IFC (A)) taken out from the fuel cell 12. The operating pressure can be determined by appropriately selecting from the above. Thus, at the time of system startup, control is performed so that the operating pressure increases as the operating temperature increases.

  FIG. 5 is a map showing three levels (IFC: large, medium, small), but is not limited to this, and maps corresponding to a large number of current command values (10 levels, 20 levels, etc.) ) May be determined based on. Further, the current command value (IFC) is not set based only on the throttle opening (the amount of depression of the accelerator pedal), but is used to charge the power generated by the fuel cell 12 to a high voltage battery (not shown). It is set by comprehensively judging necessary electric power, electric power necessary to supply generated electric power to auxiliary machines, and the like.

  FIG. 6 is a flowchart showing the water storage process and the water removal process. In the fuel cell system 10 of the present embodiment, it is assumed that the electromagnetic clutch 41 provided on the transmission shaft 40 a is connected and the regenerative energy of the expander turbine 40 is transmitted to the compressor 34.

  In step S101, the ECU 60 determines whether or not the IG 65 is turned off (IG-OFF) based on the IG-OFF signal. If it is determined that the IG 65 is not turned off (No), the ECU 60 proceeds to step S101. If the process is repeated and it is determined that IG-OFF (system stop) has been made (Yes), the process proceeds to step S102.

  In step S102, the ECU 60 predicts the temperature at the next activation (next activation temperature). Note that the next startup temperature is predicted based on at least one of the outside air temperature, calendar information, and GPS information as described above.

  Proceeding to step S103, the ECU 60 determines whether or not the predicted next startup temperature is equal to or lower than a predetermined value A. The predetermined value A is a threshold value for determining whether or not the condensed water is frozen, and is set to 0 ° C., for example. Note that the next startup temperature is not limited to the temperature at the next system startup, but based on the lowest predicted temperature (temperature assuming the worst situation) between the system shutdown and the next system startup. It may be set. As a result, it is possible to prevent the IG-ON (system activation) from being performed at 0 ° C. or lower.

  In step S103, if the ECU 60 determines that the next startup temperature exceeds the predetermined value A (No), the ECU 60 determines that the condensed water in the water storage section 42a is not frozen and proceeds to step S104.

<Water storage treatment>
In step S104, the ECU 60 determines the operating pressure based on the operating temperature. The operating pressure is determined based on a map (a water storage processing map) indicated by a broken line in FIG. FIG. 7A is a map for determining the operating pressure based on the operating temperature, and is obtained in advance by the maps of FIG. 3A and FIG. The amount of condensed water generated in the expander turbine 40 can be controlled by determining the operation pressure based on the map shown in FIG. For example, as the operating temperature rises, the moisture contained in the cathode offgas increases, so the amount of condensed water generated in the expander turbine 40 can be increased by increasing the operating pressure. Therefore, it is possible to secure the amount of water required at the next system startup.

  Then, in step S105, the ECU 60 determines whether or not the water level (water level value) from the water level sensor 64 has reached a predetermined water level (predetermined value) B. For example, the predetermined water level B is set to a water level at which the water storage section 42a becomes full. In step S105, when the ECU 60 determines that the detected water level has not reached the predetermined water level B (No), the ECU 60 repeats the process of step S105 and determines that the detected water level has reached the predetermined water level B. (Yes), the process proceeds to step S112, and the operation of the compressor 34 is stopped.

  As described above, when the water storage process is performed, when the operating temperature is high, the cathode off gas contains a large amount of water. Therefore, by increasing the operating pressure, a large amount of condensed water generated in the expander turbine 40 can be generated. Further, when the operating temperature is low, the cathode off gas contains a small amount of water. Therefore, it is possible to prevent the power consumption of the compressor 34 from being wasted by reducing the operating pressure.

<Water removal treatment>
In step S103, when the ECU 60 determines that the next startup temperature is equal to or lower than the predetermined value A (Yes), the ECU 60 determines that the condensed water stored in the water storage section 42a is frozen, and proceeds to step S106.

  In step S106, the ECU 60 determines the operating pressure based on the operating temperature. That is, the operating pressure is determined from the operating temperature when the system is stopped based on the map shown in FIG. 7A (the water removal processing time map indicated by the solid line). When the water removal process is performed, the operating pressure is reduced from the map for the water storage process indicated by the broken line in FIG.

  In this way, at the time of water removal treatment, the evaporation of water can be promoted by reducing the operating pressure as a whole and performing water removal treatment, so the pressure is increased and the details (flow path etc.) are clogged. It is more effective in terms of drying than considering the point of sweeping out condensed water. Although not shown, the ECU 60 drives the compressor 34 by controlling the motor 35 so that the rotation speed corresponds to the determined operating pressure. Thereby, the pressure of the air flowing through the cathode channel 20 of the fuel cell 12 is adjusted.

  And it progresses to step S107 and ECU60 determines water removal processing time based on operation temperature. That is, based on the map shown in FIG. 7B, the water removal processing time is determined from the operating temperature when the system is stopped. As shown in FIG. 7 (b), when the operating temperature is high, the amount of water contained in the cathode offgas is large and the amount of condensed water generated is also large, so that the water removal processing time is set long. Further, when the operating temperature is low, the water contained in the cathode off gas is small and the amount of condensed water produced is also small, so the water removal treatment time is set short. The water removal processing time is preferably set in consideration of the current water level of the water storage section 42a.

  The operating temperature may include the FC refrigerant temperature, but is not limited to this, and may be one that directly measures the temperature of the fuel cell 12, and the outlet of the anode channel 18 It may be the temperature, the outlet temperature of the cathode channel 20 or the like. Further, the operating temperature such as the FC refrigerant temperature may be corrected based on the outside air temperature or the intake air temperature.

  In step S108, the ECU 60 opens the drain valve 47. Thereby, discharge of the condensed water stored in the water storage section 42a to the outside via the pipe b10 is started. While the drain valve 47 is open, the generated condensed water is discharged to the outside through the pipe b10, so that the condensed water does not accumulate in the water storage section 42a.

  In step S109, the ECU 60 starts the operation of the timer 66 and starts measuring the water removal processing time.

  And it progresses to step S110 and ECU60 judges whether the determined water removal processing time passed, and when it judges that the water removal processing time has not passed (No), processing of step S110 is performed. When it is determined that the water removal processing time has elapsed (Yes), the process proceeds to step S111, and the drain valve 47 is closed. Then, the process proceeds to step S112, and the ECU 60 stops the operation of the compressor 34.

  As described above, when water removal processing is performed, when the operating temperature is high, the cathode off gas contains a large amount of water. Therefore, by increasing the operating pressure (see FIG. 7A), condensation generated in the expander turbine 40 A lot of water is generated, and the water removal processing time is set longer (see FIG. 7B). Further, when the operating temperature is low, the cathode off gas contains less water. Therefore, by reducing the operating pressure, the condensed water generated in the expander turbine 40 is reduced, and the water removal processing time is set short. Further, when water removal treatment is performed, the decompression operation is performed more than at the time of water storage treatment, whereby the saturated water vapor pressure is increased and the evaporation of moisture is promoted, thereby drying the flow path through which the condensed water including the water storage portion 42a flows. It becomes possible to make it.

<Effect of fuel cell system>
As described above, according to the fuel cell system 10 according to the present embodiment, when it is determined that the condensed water stored in the water storage section 42a does not freeze at the next system startup when the system is stopped, By condensing condensed water in the portion 42a, it is possible to prevent water shortage (insufficient humidification) even when the fuel cell 12 is activated at a high temperature when the system is activated next time.

  In the present embodiment, the next startup temperature at the next system startup is predicted, and when the next startup temperature is higher than the predetermined value A, water storage processing is performed, and when the next startup temperature is equal to or lower than the predetermined value A, water is removed. Processing is performed. Thus, by predicting based on temperature, it can be determined appropriately whether condensed water freezes at the time of next system starting. As a result, it is possible to prevent the fuel cell 12 from being appropriately humidified.

  Further, according to the present embodiment, the cathode offgas (exhaust oxidation) is provided by providing the expander turbine 40 as the expansion means and the transmission shaft 40a that obtains regenerative energy of the expander turbine 40 and transmits the driving force to the compressor 34. The pressure of the agent) can be used effectively, and the power consumption of the compressor 34 can be reduced.

  Moreover, in this embodiment, when performing a water storage process, it operate | moves using the detected operating temperature based on the map (broken line) shown in FIG. 7 obtained from the relationship of FIG. 3 (a) and FIG.3 (b). The pressure is obtained, and the compressor 34 is controlled so as to reach the operation pressure until the water level value by the water level sensor 64 reaches a predetermined water level B. Thereby, since the condensed water can be immediately injected from the water storage section 42a at the next system startup, it is possible to avoid water shortage (humidification shortage) at the time of high temperature start. Furthermore, when the operating temperature is high, the operating pressure is increased, the differential pressure across the expander turbine 40 is increased, and the temperature of the cathode offgas is greatly reduced, so that the amount of condensed water is increased, and the stored water is stored. Condensed water can be stored in the part 42a in a short time. Further, when the operating temperature is low, the power consumption of the motor 35 can be reduced by reducing the operating pressure.

  Moreover, in this embodiment, when performing a water removal process, based on the map (solid line) shown in FIG. 7 obtained from the relationship of FIG. 3 (a) and FIG.3 (b), it uses the detected operating temperature. The operation pressure is obtained, and the compressor 35 is driven by controlling the motor 35 at a rotational speed corresponding to the operation pressure, and the drain valve 47 is opened to discharge water until the water removal processing time elapses. is there. This prevents the fuel cell 12 from being properly humidified by preventing the freezing at the next system start-up by performing a water removal process when there is a possibility that the temperature will reach below freezing point while the system is stopped. Can be prevented.

  Further, according to the present embodiment, the next startup temperature can be appropriately predicted by using at least one of the outside air temperature, calendar information, and GPS information as the next startup temperature.

<Modification>
Note that the present invention is not limited to the above-described embodiment, and as shown in the modified example of FIG. 8, another air supply device 39 is provided in the pipe b <b> 2 between the compressor 34 and the humidifier 38. Alternatively, the fuel cell system 10A may be used. The air supply unit 39 includes, for example, an air compressor, a fan, and the like, and is driven by an electric motor (not shown) without depending on the regenerative energy of the expander turbine 40. When the air supply unit 39 is operated based on a control signal from the ECU 60, air containing oxygen is taken in from the pipe b1 and supplied to the fuel cell 12. In the modification shown in FIG. 8, the compressor 34 is disposed on the upstream side of the fuel cell 12, and the air supply device 39 is disposed in series on the downstream side. However, the present invention is not limited to this. Instead, the air supply unit 39 may be disposed upstream of the fuel cell 12 and the compressor 34 may be disposed downstream thereof.

  Further, in the present embodiment, the adiabatic mechanical expansion type expander turbine 40 is described as an example of the expansion means, but the expansion unit is not limited to the adiabatic mechanical expansion type, and is configured using an adiabatic free expansion type. You may make it do. As an adiabatic free-expansion type, a configuration in which a back pressure valve is provided on the pipe b5 in place of the expander turbine 40 can be cited. By reducing the opening of the back pressure valve, the pressure on the upstream side of the back pressure valve is high. The pressure on the downstream side is lowered, the differential pressure across the back pressure valve is increased, and the generation of condensed water can be promoted.

  In the present embodiment, the fuel cell system 10 including the humidifier 38 has been described as an example. However, the fuel cell 12 is appropriately humidified only by the configuration in which the condensed water is injected upstream of the compressor 34. Any fuel cell system that does not include the humidifier 38 may be used.

10, 10A Fuel cell system 12 Fuel cell 34 Compressor 40 Expander turbine 40a Transmission shaft 42 Second gas-liquid separator (water recovery means)
42a Water reservoir (water recovery means)
44a, 44b Water injection mechanism (water injection means)
47 Drain valve 60 ECU (control unit)
61 Refrigerant temperature sensor (temperature sensor)
62 Intake air temperature sensor (temperature sensor)
63 Outside temperature sensor (temperature sensor)
64 Water level sensor

Claims (6)

A fuel cell that is supplied with fuel and oxidant to generate electricity;
An oxidant supply channel through which an oxidant supplied to the fuel cell flows;
An oxidant discharge passage through which an exhaust oxidant discharged from the fuel cell flows;
An expansion means disposed in the oxidant discharge flow path to expand the discharged oxidant;
A compressor disposed in the oxidant supply flow path;
A water recovery means disposed downstream of the expansion means for recovering condensed water;
Water injection means for injecting the condensed water recovered by the water recovery means to the oxidant supply flow path,
When it is determined that the condensed water will not freeze at the next system start-up when the system is stopped, the condensate is stored in the water recovery means. A fuel cell system comprising a control unit that performs a water removal process for discharging water from the water recovery means.   The controller predicts a next startup temperature at the next system startup, performs the water storage process when the next startup temperature is higher than a predetermined value, and removes the water when the next startup temperature is lower than a predetermined value. The fuel cell system according to claim 1, wherein processing is performed.   The fuel cell according to claim 1, wherein the expansion unit includes an expander turbine and a transmission shaft that obtains regenerative energy of the expander turbine and transmits a driving force to the compressor. system. The water recovery means includes a water storage part for storing condensed water,
A water level sensor for detecting the water level of the water reservoir and a temperature sensor for detecting a fuel cell related temperature related to the temperature of the fuel cell;
When the water storage process is performed when the system is stopped, the control unit, the relationship between the fuel cell related temperature and the amount of water vapor necessary for the fuel cell, and the pressure of the fuel cell and the amount of water vapor necessary for the fuel cell Based on the relationship, the operating pressure necessary for the fuel cell is obtained using the detected temperature related to the fuel cell, and the compressor is set so that the operating pressure becomes the operating pressure until the water level value by the water level sensor reaches a predetermined value. The fuel cell system according to any one of claims 1 to 3, wherein the fuel cell system is controlled. The water recovery means includes a drain valve for discharging the recovered condensed water to the outside,
The control unit obtains the water removal processing time based on the detected fuel cell related temperature using the relationship between the fuel cell related temperature and the water removal processing time when performing the water removal processing when the system is stopped. ,
Based on the relationship between the fuel cell related temperature and the amount of water vapor required for the fuel cell, and the relationship between the pressure of the fuel cell and the amount of water vapor required for the fuel cell, the detected temperature related to the fuel cell is used. The operation pressure required for the fuel cell is obtained, and the control of the compressor according to the operation pressure and the water discharge by the drain valve are performed until the water removal processing time elapses. Item 5. The fuel cell system according to Item 4.   The said control part estimates the said next starting temperature using at least any one among outside temperature, calendar information, and GPS information, The any one of Claims 2-4 characterized by the above-mentioned. Fuel cell system.

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