JP2007317475A - Fuel cell system - Google Patents

Abstract

An object of the present invention is to provide a fuel cell system capable of suppressing freezing during system operation stop and improving the startability of system operation.
A supply device that pumps oxidizing gas to a fuel cell, a bypass passage that connects a supply passage and a discharge passage so that the oxidizing gas flows bypassing the fuel cell, and a bypass valve that opens and closes the bypass passage; And a control device that executes a scavenging process for driving at least the inside of the fuel cell by driving the supply device when the operation of the fuel cell system is stopped. When the ratio of the oxidizing gas flow rate flowing from the connection portion to the downstream of the bypass valve to the oxidizing gas flow rate flowing from the connection portion between the supply passage and the bypass passage to the fuel cell is defined as a diversion ratio, the control device Is controlled so that the diversion ratio increases during the scavenging process.
[Selection] Figure 4

Description

  The present invention relates to a fuel cell system capable of bypassing an oxidizing gas to a fuel cell.

  A fuel cell mounted on a fuel cell vehicle or the like generates electric power and generates water by a chemical reaction between hydrogen in a fuel gas supplied to an anode and oxygen in an oxidizing gas supplied to a cathode. The generated water is discharged from the inside of the fuel cell to the discharge path of both gases by the flow of the fuel gas and the oxidizing gas.

The fuel cell system described in Patent Document 1 includes a bypass path that connects an oxidizing gas supply path and an oxidizing off-gas exhaust path, and includes a three-way valve at a connection portion between the bypass path and the supply path. During normal operation of this fuel cell system, the three-way valve selects the fuel cell side. On the other hand, when it is determined that the back pressure regulating valve on the discharge path is frozen at the start of the fuel cell system, the three-way valve selects the bypass path side. By this selection, the oxidizing gas is caused to flow into the bypass passage, and the back pressure adjusting valve located in the vicinity thereof is heated.
JP 2005-158282 A

  However, since the processing is after the back pressure regulating valve is frozen, it takes time to thaw the back pressure regulating valve, resulting in a decrease in the startability of the system itself. In addition, the generated water may be frozen not only by the back pressure regulating valve but also in the fuel cell and in the discharge path, and also in the bypass path and the three-way valve.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel cell system capable of suppressing freezing during system operation stop and improving the startability of system operation. .

  In order to achieve the above object, a fuel cell system according to the present invention includes a supply path through which an oxidizing gas supplied to a fuel cell flows, a supply device provided in the supply path, for pumping the oxidizing gas to the fuel cell, and a fuel cell. A fuel provided with a discharge path through which discharged oxidation off-gas flows, a bypass path that connects the supply path and the discharge path so that the oxidizing gas flows through the fuel cell, and a bypass valve that opens and closes the bypass path The battery system includes a control device that executes a scavenging process for driving the supply device and scavenging at least the inside of the fuel cell when the operation of the fuel cell system is stopped, and the oxidation flowing to the fuel cell from the connection portion between the supply passage and the bypass passage When the ratio of the flow rate of the oxidizing gas flowing from the connection portion to the downstream of the bypass valve with respect to the gas flow rate is defined as a diversion ratio, the control device performs the scavenging process. In the middle run, controls such diversion ratio increases.

  According to such a configuration, since the scavenging process is performed when the system is stopped, the generated water remaining in the fuel cell can be discharged downstream of the discharge path, and water icing in the fuel cell and the discharge path can be suppressed. . Further, in order to increase the diversion ratio during the scavenging process, the oxidizing gas flows at least through the bypass passage to the downstream of the bypass valve. Thereby, moisture remaining in the bypass valve and the bypass passage can be discharged to the discharge passage, and the atmosphere in the bypass passage can be replaced with the oxidizing gas. Therefore, it is possible to suppress water icing in the bypass valve and the bypass path. And since such a scavenging process is performed when the system operation is stopped, the startability of the system operation can be improved.

  Preferably, after performing the scavenging process at the first diversion ratio, the control device changes to a second diversion ratio that is larger than the first diversion ratio during the execution of the scavenging process.

  According to this configuration, since the diversion ratio is changed stepwise, the diversion ratio can be easily changed.

  More preferably, the control device changes the first diversion ratio to the second diversion ratio by increasing the opening of the bypass valve.

  By doing so, the diversion ratio can be changed with a simple structure.

  Here, in one embodiment of the present invention, the first diversion ratio may be greater than 0, that is, part of the oxidizing gas may flow downstream of the bypass valve, for example, at the beginning of the scavenging process. However, in order to efficiently perform scavenging in the fuel cell, in a preferred embodiment of the present invention, the control device controls the closing of the bypass valve so that the first diversion ratio becomes zero, while the first When changing from the current diversion ratio to the second diversion ratio, the bypass valve may be controlled to open.

  Preferably, the bypass valve at the second diversion ratio is set to a predetermined opening degree so that the oxidizing gas flowing downstream of the bypass valve does not flow backward to the upstream side of the discharge path.

  According to this configuration, at the second diversion ratio, water that can remain in the bypass valve or the bypass path can be prevented from flowing back to the upstream side of the discharge path, and this moisture is transferred to the downstream side of the discharge path. Can be discharged.

  Preferably, the fuel cell system of the present invention further includes a pressure regulating valve provided in the discharge path.

  Preferably, the fuel cell system of the present invention further includes a humidifier that is provided in the supply path downstream of the connection portion and humidifies the oxidizing gas.

  According to this configuration, the relatively high-humidity oxidizing gas humidified by the humidifier can be supplied to the fuel cell. Further, during the scavenging process, a relatively low-humidity oxidizing gas that has not been humidified by the humidifier can be caused to flow downstream of the bypass valve, and scavenging of the bypass valve and the bypass passage can be suitably performed.

  As described above, according to the fuel cell system of the present invention, freezing while the system operation is stopped can be suppressed, and the startability of the system operation can be improved.

  Hereinafter, a fuel cell system according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings. First, a scavenging process when the operation of the fuel cell system of the present invention is stopped will be described as a first embodiment. Next, as a modification, a configuration in consideration of freezing of the bypass valve will be described.

<First Embodiment>
FIG. 1 is a configuration diagram of a fuel cell system 1.
The fuel cell system 1 of the present embodiment can be mounted on a vehicle such as a fuel cell vehicle (FCHV), an electric vehicle, and a hybrid vehicle. Of course, not only the vehicle but also various moving bodies (for example, ships, airplanes, robots, etc.) ) And stationary power sources.

  The fuel cell system 1 includes a fuel cell 2, an oxidizing gas piping system 3 that supplies air (oxygen) as an oxidizing gas to the fuel cell 2, and a fuel gas piping system that supplies hydrogen gas as a fuel gas to the fuel cell 2. 4, a refrigerant piping system 5 that supplies the refrigerant to the fuel cell 2 to cool the fuel cell 2, a power system 6 that charges and discharges the power of the system 1, and a control device 7 that performs overall control of the entire system. ing.

  The fuel cell 2 is formed of, for example, a solid polymer electrolyte type and has a stack structure in which a large number of single cells are stacked. The single cell has an air electrode (cathode) on one surface of an electrolyte made of an ion exchange membrane, a fuel electrode (anode) on the other surface, and a pair of the air electrode and the fuel electrode sandwiched from both sides. Of separators. An oxidizing gas is supplied to the oxidizing gas channel 2a of one separator, and a fuel gas is supplied to the fuel gas channel 2b of the other separator. The fuel cell 2 generates electric power by the electrochemical reaction of the supplied fuel gas and oxidizing gas. The electrochemical reaction in the fuel cell 2 is an exothermic reaction, and the temperature of the solid polymer electrolyte fuel cell 2 is approximately 60 to 80 ° C.

  The oxidizing gas piping system 3 includes a supply path 11 through which the oxidizing gas supplied to the fuel cell 2 flows, a discharge path 12 through which the oxidizing off gas discharged from the fuel cell 2 flows, and the oxidizing gas flows bypassing the fuel cell 2. And a bypass 17. The downstream end of the supply path 11 communicates with the upstream end of the oxidizing gas flow path 2a, and the upstream end of the discharge path 12 communicates with the downstream end of the oxidizing gas flow path 2a. The oxidizing off gas includes pumping hydrogen generated on the air electrode side of the fuel cell 2 (details will be described later). Further, the oxidizing off gas is in a highly moist state because it contains moisture generated by the cell reaction of the fuel cell 2.

  The supply path 11 is provided with a compressor 14 (feeder) that takes in the oxidizing gas (outside air) via the air cleaner 13 and a humidifier 15 that humidifies the oxidizing gas pumped to the fuel cell 2 by the compressor 14. Yes. The humidifier 15 exchanges moisture between the low-humidity oxidizing gas flowing in the supply passage 11 and the high-humidity oxidizing off-gas flowing in the discharge passage 12, and appropriately supplies the oxidizing gas supplied to the fuel cell 2. Humidify.

  The back pressure of the oxidizing gas supplied to the fuel cell 2 is regulated by a back pressure adjusting valve 16 disposed in the discharge path 12 near the cathode outlet. In the vicinity of the back pressure adjustment valve 16, a pressure sensor P1 for detecting the pressure in the discharge passage 12 is provided. The oxidizing off gas passes through the back pressure regulating valve 16 and the humidifier 15 and is finally exhausted into the atmosphere outside the system as exhaust gas.

  The bypass path 17 connects the supply path 11 and the discharge path 12. A supply side connection B between the bypass path 17 and the supply path 11 is located between the compressor 14 and the humidifier 15. Further, the discharge side connection portion C between the bypass path 17 and the discharge path 12 is located on the downstream side of the humidifier 15. The bypass passage 17 is provided with a bypass valve 18 that is an on-off valve (shut valve) driven by a motor or a solenoid. The bypass valve 18 is connected to the control device 7 and opens and closes the bypass path 17. In the following description, the oxidizing gas that is bypassed downstream of the bypass passage 17 by opening the bypass valve 18 is referred to as “bypass air”.

  The fuel gas piping system 4 includes a hydrogen supply source 21, a supply path 22 through which hydrogen gas supplied from the hydrogen supply source 21 to the fuel cell 2 flows, and a supply path for supplying hydrogen offgas (fuel offgas) discharged from the fuel cell 2. 22, a circulation path 23 for returning to the junction point A of 22, a pump 24 that pumps the hydrogen off-gas in the circulation path 23 to the supply path 22, and a purge path 25 that is branched and connected to the circulation path 23. . The hydrogen gas flowing out from the hydrogen supply source 21 to the supply path 22 by opening the main valve 26 is supplied to the fuel cell 2 through the pressure regulating valve 27 and other pressure reducing valves and the shutoff valve 28. The purge passage 25 is provided with a purge valve 33 for discharging the hydrogen off gas to a hydrogen diluter (not shown).

  The refrigerant piping system 5 includes a refrigerant channel 41 communicating with the cooling channel 2 c in the fuel cell 2, a cooling pump 42 provided in the refrigerant channel 41, and a radiator 43 that cools the refrigerant discharged from the fuel cell 2. And a bypass passage 44 that bypasses the radiator 43, and a switching valve 45 that sets the flow of cooling water to the radiator 43 and the bypass passage 44. The refrigerant flow path 41 includes a temperature sensor 46 provided near the refrigerant inlet of the fuel cell 2 and a temperature sensor 47 provided near the refrigerant outlet of the fuel cell 2. The refrigerant temperature detected by the temperature sensor 47 reflects the internal temperature of the fuel cell 2 (hereinafter referred to as the temperature of the fuel cell 2). The cooling pump 42 circulates and supplies the refrigerant in the refrigerant channel 41 to the fuel cell 2 by driving the motor.

  The power system 6 includes a high-voltage DC / DC converter 61, a battery 62, a traction inverter 63, a traction motor 64, and various auxiliary inverters 65, 66, and 67. The high-voltage DC / DC converter 61 is a direct-current voltage converter that adjusts the direct-current voltage input from the battery 62 and outputs it to the traction inverter 63 side, and the direct-current input from the fuel cell 2 or the traction motor 64. And a function of adjusting the voltage and outputting it to the battery 62. The charge / discharge of the battery 62 is realized by these functions of the high-voltage DC / DC converter 61. Further, the output voltage of the fuel cell 2 is controlled by the high voltage DC / DC converter 61.

  The traction inverter 63 converts a direct current into a three-phase alternating current and supplies it to the traction motor 64. The traction motor 64 (power generation device) is, for example, a three-phase AC motor. The traction motor 64 constitutes, for example, a main power source of the vehicle 100 on which the fuel cell system 1 is mounted, and is connected to the wheels 101L and 101R of the vehicle 100. The auxiliary machine inverters 65, 66, and 67 control the driving of the motors of the compressor 14, the pump 24, and the cooling pump 42, respectively.

  The control device 7 is configured as a microcomputer having a CPU, ROM, and RAM therein. The CPU performs desired processing according to the control program, and performs various processes and controls such as control of low-efficiency operation described later. The ROM stores control programs and control data processed by the CPU. The RAM is mainly used as various work areas for control processing.

  The control device 7 includes a pressure sensor (P1) and temperature sensors (46, 47) used in the gas system (3, 4) and the refrigerant system 5, and an outside air temperature sensor that detects the outside air temperature in the environment where the fuel cell system 1 is placed. 51, and detection signals from various sensors such as an accelerator opening sensor that detects the accelerator opening of the vehicle 100 are input, and control is performed on each component (such as the feeder 14, the back pressure adjusting valve 16, and the bypass valve 18). Output a signal. In addition, when it is necessary to warm up the fuel cell 2 such as when starting at a low temperature, the control device 7 performs an operation with low power generation efficiency using various maps stored in the ROM.

  FIG. 2 is a diagram showing the relationship between the output current (hereinafter referred to as “FC current”) of the fuel cell 2 and the output voltage (hereinafter referred to as “FC voltage”). FIG. 2 shows the case where the fuel cell system 1 is operated with relatively high power generation efficiency (hereinafter referred to as “normal operation”) as a solid line, and the fuel cell system 1 is operated with relatively low power generation efficiency (hereinafter referred to as “normal operation”). The case of “low efficiency operation”) is indicated by a dotted line.

  When the fuel cell system 1 is normally operated, the fuel cell 2 is operated in a state where the air stoichiometric ratio is set to 1.0 or more (theoretical value) so that high power generation efficiency can be obtained while suppressing power loss (see FIG. (See solid line part 2). Here, the air stoichiometric ratio means an oxygen surplus ratio, and indicates how much oxygen is supplied to oxygen necessary for reacting with hydrogen without excess or deficiency.

  On the other hand, when the fuel cell 2 is warmed up, the fuel cell 2 is set with the air stoichiometric ratio set to less than 1.0 (theoretical value) in order to increase the power loss and raise the temperature of the fuel cell 2. (See the dotted line portion in FIG. 2). When the air stoichiometric ratio is set to a low value and the low efficiency operation is performed, the power loss (that is, the heat loss) of the energy that can be extracted by the reaction between hydrogen and oxygen is positively increased. While it is possible to warm up, pumping hydrogen is generated at the air electrode of the fuel cell 2.

3A and 3B are diagrams for explaining the generation mechanism of pumping hydrogen, in which FIG. 3A shows a battery reaction during normal operation, and FIG. 3B shows a battery reaction during low-efficiency operation.
Each single cell 80 of the fuel cell 2 includes an electrolyte membrane 81 and an anode and a cathode that sandwich the electrolyte membrane 81. A fuel gas containing hydrogen (H ₂ ) is supplied to the anode, and an oxidizing gas containing oxygen (O ₂ ) is supplied to the cathode. When fuel gas is supplied to the anode, the reaction of the following formula (1) proceeds, and hydrogen is separated from hydrogen ions and electrons. Hydrogen ions generated at the anode pass through the electrolyte membrane 81 and move to the cathode, while electrons move from the anode through the external circuit to the cathode.
Anode: H ₂ → 2H ⁺ + 2e ⁻ (1)

Here, in the case of the normal operation shown in FIG. 3A, that is, when the supply of the oxidizing gas to the cathode is sufficient (air stoichiometric ratio ≧ 1.0), the following equation (2) proceeds and oxygen, hydrogen Water is produced from ions and electrons.
Cathode: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)

On the other hand, in the case of the low-efficiency operation shown in FIG. 3B, that is, when the supply of the oxidizing gas to the cathode is insufficient (air stoichiometric ratio <1.0), the following formula is set according to the insufficient oxidizing gas amount. (3) proceeds and hydrogen ions and electrons recombine to generate hydrogen. The produced hydrogen is discharged from the cathode together with the oxidizing off gas. Note that hydrogen generated at the cathode by recombination of dissociated hydrogen ions and electrons, that is, the anode gas generated at the cathode is called pumping hydrogen.
Cathode: 2H ⁺ + 2e ⁻ → H ₂ (3)

  Thus, in a state where the supply of the oxidizing gas to the cathode is insufficient, pumping hydrogen is included in the oxidizing off gas. Therefore, when the fuel cell system 1 performs low-efficiency operation, the control device 7 controls the opening of the bypass valve 18 so that a part of the oxidizing gas supplied by the compressor 13 is diverted to the bypass path 17. Yes. The dilute bypass air dilutes the hydrogen concentration in the oxidation off gas, and the oxidation off gas having the hydrogen concentration reduced to a safe range is exhausted from the discharge path 12 to the outside.

  The low-efficiency operation is performed at the time of starting the fuel cell system 1 mainly for the purpose of warming up the fuel cell 2, and is performed only at the time of starting at a low temperature. For example, when the outside air temperature detected by the outside air temperature sensor 51 at the start of the fuel cell system 1 is a predetermined low temperature (for example, 0 ° C. or less), the fuel cell system 1 is operated at a low efficiency. When the warm-up of the fuel cell 2 is completed, the fuel cell system 1 shifts from the low efficiency operation to the normal operation. The bypass valve 18 is opened when the fuel cell system 1 that performs low-efficiency operation is started, and is closed during normal operation after the low-efficiency operation.

FIG. 4 is a flowchart showing a processing flow at the end of operation of the fuel cell system 1 of the present embodiment.
First, when the operation stop of the fuel cell system 1 is instructed by, for example, an operation of turning off an ignition switch by the driver of the vehicle 100 (step S1), the control device 7 ends the normal operation of the fuel cell system 2, A scavenging process is executed (step S2).

  Here, the scavenging process means scavenging the inside of the fuel cell 2 by discharging at least water in the fuel cell 2 to the outside at the end of the operation of the fuel cell system 2. In the scavenging process of the cathode system (oxidizing gas piping system 3), the supply of hydrogen gas to the fuel cell 2 is stopped, and the oxidizing gas is supplied to the oxidizing gas passage 2a by driving the compressor 14, and the supplied oxidation is performed. This is performed by discharging moisture containing the generated water remaining in the oxidizing gas flow path 2a to the discharge path 12 by the gas. A scavenging process of the anode system (fuel gas piping system 4) is also performed, but detailed description thereof is omitted here.

  In the scavenging process, the control device 7 mainly controls the compressor 14, the back pressure adjustment valve 16, and the bypass valve 18. Specifically, the control device 7 controls the motor rotation speed of the compressor 14 so that the oxidizing gas suitable for the scavenging process is supplied to the fuel cell 2. In addition, the control device 7 controls the back pressure adjustment valve 16 to be fully opened, intermittently opened or closed, or half open, for example. Furthermore, the control device 7 controls the opening degree of the bypass valve 18 so that a predetermined diversion ratio is obtained.

Here, the “diversion ratio” is the flow rate of the oxidizing gas flowing from the supply side connection B to the downstream side of the bypass valve 18 with respect to the flow rate of the oxidation gas flowing from the supply side connection B to the fuel cell 2 ( That is, the ratio of the bypass air flow rate) is defined by the following equation (10).
γ = M _BY / M _SUP (10)
Here, γ is a diversion ratio, M _BY is a flow rate of bypass air, and M _SUP is a flow rate of the oxidizing gas flowing from the supply side connection B to the fuel cell 2.

At the start of the scavenging process in step S2, the diversion ratio γ is set to the _first diversion ratio γ ₁ . Here, the first diversion ratio γ ₁ = 0 (where M _SUP > 0) was set. In other words, the bypass valve 18 is closed, and the oxidizing gas is flown into the fuel cell 2 exclusively without being divided at the supply side connection portion B. In this way, by setting the first diversion ratio γ ₁ = 0, scavenging in the fuel cell 2 can be performed more efficiently than when the oxidizing gas is diverted as bypass air. In other embodiments, the following expression (11) may be satisfied.
γ ₁ > 0 (11)

The control device 7 executes the scavenging process at the _first diversion ratio γ ₁ until a predetermined time t ₁ has elapsed from the start of the scavenging process (step S3; NO). For example, the predetermined time t ₁ is set to a time when the drainage of the water in the fuel cell 2 is completed. After the elapse of the predetermined time t ₁ (step S3; YES), the control device 7 changes the diversion ratio so as to increase the diversion ratio (step S4). That is, the control device 7 changes the _second diversion ratio γ ₂ larger than the first diversion ratio γ ₁ during the execution of the scavenging process.

The change to the _second diversion ratio γ ₂ is performed by increasing the opening degree of the bypass valve 18, that is, by opening the bypass valve 18 in this embodiment. As a result of the change to the _second diversion ratio γ ₂ , a part of the oxidizing gas pumped by the compressor 14 is supplied to the fuel cell 2, while the rest flows as downstream air downstream of the bypass valve 18. By doing so, even if water discharged from the fuel cell 2 or the like flows into the bypass passage 17 or the bypass valve 18, for example, water that can exist in these can be discharged again to the discharge passage 12 by the bypass air.

Here, the moisture taken away by the bypass air is preferably discharged downstream of the discharge path 12 instead of upstream of the discharge path 12. Therefore, in the present embodiment, the bypass valve 18 at the second diversion ratio γ ₂ is set to a predetermined opening degree so that the bypass air does not flow backward to the upstream side of the discharge path 12. More specifically, the predetermined opening degree of the bypass valve 18 is an opening degree that directs the flow of the bypass air to the downstream side of the discharge path 12 by the flow of the oxidizing gas discharged from the fuel cell 2, for example, Full open or half open. By configuring in this way, it is possible to prevent water from flowing back into the upstream portion of the discharge passage 12 (the portion where the back pressure adjusting valve 16 is present) and the fuel cell 2.

  In addition, you may make it the water | moisture content carried away by bypass air flow to the downstream of the discharge path 12 by adjusting the piping structure of the discharge path 12. FIG. For example, what is necessary is just to comprise the connection form of the bypass path 18 and the discharge path 12 so that bypass air may flow out toward the downstream of the discharge path 12 in the discharge side connection part C. For example, the downstream end of the bypass path 18 may be open toward the downstream side of the discharge path 12 instead of the upstream side of the discharge path 12.

The control device 7 executes the scavenging process with the _second diversion ratio γ ₂ until a predetermined time t ₂ (t ₂ > t ₁ is satisfied) from the start of the scavenging process (step S5; NO). The predetermined time t _2, for example, the discharge of the water of the bypass valve 18 and the bypass passage 17 on the downstream side is set to a time to complete. Note that when the scavenging process is being executed at the second diversion ratio γ ₂ , the control device 7 can appropriately adjust the rotation speed of the compressor 14 and the opening degree of the back pressure adjustment valve 16.

After the elapse of the predetermined time t ₂ (step S5; YES), the control device 7 stops driving the compressor 14 and ends the scavenging process (step S6). The bypass valve 18 may be closed at the end of the scavenging process. After the exhaust process is completed, the operation stop of the fuel cell system 1 is completed, and the fuel cell system 1 waits for the next activation.

  As described above, according to the fuel cell system 1 of the present embodiment, since the scavenging process is executed when the operation is stopped, moisture that can exist in the fuel cell 2 can be discharged downstream of the discharge path 12, and Since the diversion ratio γ is changed in the middle of the scavenging process, the water that may exist in the bypass passage 17 and the bypass valve 18 can be discharged downstream of the discharge passage 12 by the bypass air.

  As a result, not only the inside of the fuel cell 2 but also the inside of the discharge path 12, the back pressure adjusting valve 16, the bypass path 17, and the bypass valve 18 on the discharge path 12 can be scavenged. Therefore, even if the fuel cell system 1 after operation is placed in a low temperature environment (for example, below freezing point), freezing in various components (2, 12, 16, 17 and 18) can be suppressed, and various components Freezing of (2, 12, 16, 17 and 18) can be suppressed, and as a result, the startability at the next start-up can be improved.

  In the fuel cell system 1 of the present embodiment, relatively low-humidity bypass air that has not been humidified by the humidifier 15 flows downstream of the bypass valve 18 during the scavenging process. Thereby, since bypass air with a low moisture content can be supplied to the downstream of the bypass valve 18 and the bypass path 17, scavenging of the bypass valve 18 and the bypass path 17 can be performed suitably.

  In the above example, the diversion ratio γ is changed in two stages, but it is of course possible to change it in multiple stages or steplessly (continuously). Further, although the oxidizing gas has been described as an example of the gas used for the scavenging process, the essence of the present embodiment can be applied to the scavenging process that does not use the oxidizing gas. For example, an inert gas such as nitrogen gas may be used as the gas for the scavenging process, and another supply device or the above-described compressor 14 may be driven to change the diversion ratio γ during the scavenging process.

<Modification>
Next, a configuration in consideration of freezing of the bypass valve 18 in the fuel cell system 1 will be described with reference to FIGS. This configuration in consideration of freezing can be applied to the configuration of the fuel cell system 1 as described above regardless of whether or not the scavenging process of the first embodiment is executed.

<Modification 1>
As shown in FIG. 5, the bypass valve 18 is provided with a heater 200. The heater 200 is connected to the control device 7 and configured to be able to control its temperature. With such a configuration, even when the bypass valve 18 is frozen, the heater 200 can be driven to quickly defrost the bypass valve 18. The heater 200 may be driven when the outside air temperature of the outside air temperature sensor 51 is below freezing point, for example. The heater 200 may be incorporated in the valve body of the bypass valve 18 or may be attached to the valve body.

<Modification 2>
As shown in FIG. 6, a filter 210 is provided on the downstream side (secondary side) of the bypass valve 18. The filter 210 is made of a porous filter, and is provided on the bypass path 17 instead of on the discharge path 12. By setting it as such a structure, it can suppress with the filter 210 that moisture, such as produced water, flows into the bypass valve 18 by the driving | operation etc. of the fuel cell system 1. FIG. Thereby, the freezing of the water | moisture content by the bypass valve 18 at the time of low temperature can be suppressed.

<Modification 3>
As indicated by a one-dot chain line 220 in FIG. 7, the compressor 14 and the bypass valve 18 have an integral structure. For example, by incorporating the bypass valve 18 in a part of the casing of the compressor 14, the two can be configured as an integral structure. The compressor 14 radiates heat to the outside due to exhaust heat of the motor or the like during driving, and the heat radiation or heat can keep the bypass valve 18 warm. As a result, freezing of the bypass valve 18 can be suppressed, and it can be thawed even if it is temporarily frozen.

<Modification 4>
As shown in FIG. 8, the refrigerant piping system 5 includes a refrigerant circuit that circulates the refrigerant to the bypass valve 18. The refrigerant circuit includes a supply circuit 230 that supplies refrigerant to, for example, the valve body of the bypass valve 18, and a discharge circuit 231 that discharges refrigerant that has flowed through the valve body of the bypass valve 18, for example. One end of the supply circuit 230 communicates with a portion of the refrigerant flow path 41 near the refrigerant outlet of the fuel cell 2. One end of the discharge circuit 231 communicates with a portion of the refrigerant flow path 41 downstream of the radiator 43.

  As described above, the temperature of the solid polymer electrolyte fuel cell 2 is approximately 60 to 80 ° C., so the temperature of the refrigerant in the vicinity of the refrigerant outlet is approximately 60 to 80 ° C. With the above configuration, the refrigerant at this temperature can be circulated through the bypass valve 18 and can be used for heat exchange in the bypass valve 18. Thereby, since the bypass valve 18 can be kept warm or heated, it is possible to suppress freezing of the bypass valve 18 and to defrost even if it is temporarily frozen. Note that an on-off valve may be provided in the supply circuit 230 or the discharge circuit 231 so that the circulation and stop of the refrigerant to the bypass valve 18 may be controlled by the on-off valve.

1 is a configuration diagram of a fuel cell system according to a first embodiment. FIG. It is a graph which shows the relationship between FC electric current and FC voltage which concern on 1st Embodiment. It is a figure for demonstrating the generation | occurrence | production mechanism of the pumping hydrogen which concerns on 1st Embodiment, (A) shows the battery reaction at the time of normal operation, (B) shows the battery reaction at the time of low efficiency operation. 3 is a flowchart showing a processing flow at the end of operation of the fuel cell system 1 according to the first embodiment. It is a block diagram which expands and shows the oxidizing gas piping system which concerns on the modification 1. FIG. It is a block diagram which expands and shows the oxidizing gas piping system which concerns on the modification 2. As shown in FIG. It is a block diagram which expands and shows the oxidizing gas piping system which concerns on the modification 3. It is a block diagram which expands and shows the oxidizing gas piping system and refrigerant piping system which concern on the modification 4.

Explanation of symbols

  1: fuel cell system, 2: fuel cell, 7: control device, 11: supply path, 12: discharge path, 14: compressor (supply machine), 15: humidifier, 16: back pressure regulating valve (pressure regulating valve), 17: Bypass path, 18: Bypass valve, B: Supply side connection, C: Discharge side connection

Claims (7)

A supply path through which oxidizing gas supplied to the fuel cell flows;
A feeder that is provided in the supply path and pumps the oxidizing gas to the fuel cell;
An exhaust path through which the oxidizing off-gas exhausted from the fuel cell flows;
A bypass path connecting the supply path and the discharge path so that the oxidizing gas flows bypassing the fuel cell;
In a fuel cell system comprising a bypass valve for opening and closing the bypass path,
When the operation of the fuel cell system is stopped, a control device is provided that executes a scavenging process for driving the supply device and scavenging at least the inside of the fuel cell.
The ratio of the flow rate of the oxidizing gas flowing from the connection portion to the downstream of the bypass valve with respect to the flow rate of the oxidizing gas flowing from the connection portion between the supply passage and the bypass passage to the fuel cell is defined as a flow dividing ratio. When defined
The said control apparatus is a fuel cell system controlled so that the said diversion ratio becomes large in the middle of execution of the said scavenging process.   2. The control device according to claim 1, wherein after performing the scavenging process at a first diversion ratio, the control device changes to a second diversion ratio that is larger than the first diversion ratio during execution of the scavenging process. Fuel cell system.   The fuel cell system according to claim 2, wherein the control device changes the first diversion ratio to the second diversion ratio by increasing an opening of the bypass valve.   The control device closes the bypass valve so that the first diversion ratio becomes zero, and opens the bypass valve when changing from the first diversion ratio to the second diversion ratio. The fuel cell system according to claim 2 or 3, which is controlled.   The bypass valve at the second diversion ratio is set to a predetermined opening degree so that the oxidizing gas flowing downstream of the bypass valve does not flow backward to the upstream side of the discharge path. Item 5. The fuel cell system according to Item 3 or 4.   The fuel cell system according to any one of claims 1 to 5, further comprising a pressure regulating valve provided in the discharge path. The fuel cell system according to any one of claims 1 to 6, further comprising a humidifier that is provided in the supply path downstream of the connection portion and humidifies the oxidizing gas.

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