JP2007294305A - Cooling system of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a start time of a fuel cell from low temperature, in relation to a cooling system of a fuel cell using a solid polymer electrolyte. <P>SOLUTION: In starting a fuel cell system from low temperature, a first electronic control valve 7 selects the side of a first bypass passage 5, and a second electronic control valve 9 runs most of a flow to the side of a second bypass passage 8 and a part of the flow to the side of a fuel cell stack 1. Next, a cooling fluid pump 4 and a heating device 6 are started, and power generation of the fuel cell stack 1 is started. When the temperature of the second bypass passage 8 detected by a first temperature sensor 10 or the temperature of the fuel cell stack 1 detected by a second temperature sensor 11 reaches an operation lower-limit value, the total flow of the second electronic control valve 9 is run to the fuel cell stack 1 side, and the heating operation of the heating device 6 is stopped. Thereafter, when the cooling fluid temperature reaches the upper limit of the operation temperature by reaction heat by the power generation of the fuel cell stack 1, the first electronic control valve 7 is gradually changed over to the side of a radiator 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell cooling system using a solid polymer electrolyte, and more particularly to a fuel cell cooling system with improved start-up characteristics at low temperatures.

In the conventional polymer electrolyte fuel cell system, when the fuel cell temperature starts from below freezing point, the cooling medium heated by the electric heater is supplied to the fuel cell to warm up the fuel cell. After reaching the temperature, heating by the electric heater was stopped, and the temperature was raised to the target operating temperature by reaction heat generated by power generation of the fuel cell (for example, Patent Document 1).
Japanese Patent Laying-Open No. 2005-44668 (page 7, FIG. 2)

  However, in the conventional fuel cell system, when the temperature is below the freezing point and below the reference temperature, the entire amount of the cooling medium is supplied to the fuel cell, which prevents the fuel cell from being heated by power generation and requires a long time to start the fuel cell. There was a problem. Even if power generation is started after the temperature of the fuel cell is increased, it takes time for the entire fuel cell system to start up.

  Accordingly, an object of the present invention is to provide a fuel cell system that can shorten the startup time.

  In order to achieve the above object, the present invention bypasses a radiator in a fuel cell cooling system in which a coolant is circulated by a coolant pump between a polymer electrolyte fuel cell stack and a radiator to cool the fuel cell. A first bypass flow path including a heating device, a second bypass flow path that bypasses the fuel cell stack, a first valve that switches between the first bypass flow path and the flow path that passes through the radiator, and a second bypass flow A second valve for controlling a flow rate ratio between the passage and the flow path through the fuel cell stack, and when starting the fuel cell stack from a low temperature, the first valve is opened to the first bypass flow path side, While the flow rate ratio controlled by the valve is decreased on the side of the second bypass flow path and decreased on the side of the fuel cell stack, power generation of the fuel cell stack, coolant pump, When the apparatus is started and when either the second bypass flow path or the fuel cell stack reaches a predetermined temperature, the total flow rate of the second valve is set to the fuel cell stack side. Cooling system.

  In the present invention having the above-described configuration, when starting the fuel cell stack from a low temperature, the first valve is switched to the first bypass flow path side so that the total flow rate of the coolant bypasses the radiator and the flow rate controlled by the second valve. Since the fuel cell stack power generation and the coolant pump and the heating device are started up with the ratio of the second bypass channel side increased and the fuel cell stack side decreased, a part of the coolant flows to the fuel cell stack. Thus, without providing a temperature sensor inside the fuel cell stack, when the temperature of the fuel cell stack or the temperature of the second bypass channel reaches a predetermined temperature, the total flow rate of the second valve is set to the fuel cell stack side. be able to.

  According to the present invention, when the fuel cell stack is started up, the radiator is bypassed and most of the low-temperature coolant is disconnected from the coolant circulation circuit during warm-up, and the heating device and the fuel cell provided in the first bypass channel Since the remaining portion of the coolant is heated by reaction heat generated by the power generation of the stack, there is an effect that the warm-up time of the fuel cell can be shortened.

  Also, the coolant flowing out from the fuel cell stack without installing a temperature sensor in the fuel cell stack can be obtained by flowing a small amount of coolant to the second bypass flow path that bypasses the fuel cell stack. There is an effect that the valve switching timing can be accurately determined by the temperature of the valve.

  Furthermore, since the coolant flows through the fuel cell stack during warm-up, a large temperature distribution difference does not occur in the fuel cell stack, and heat distortion is less likely to occur, resulting in a decrease in the sealing performance and strength of the fuel cell stack. And the life of the fuel cell stack can be extended.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. Although not particularly limited, the fuel cell cooling system described in each of the following embodiments is a cooling system suitable for a fuel cell vehicle in which the startup time from below freezing point is shortened.

  FIG. 1 is a configuration diagram illustrating the configuration of a first embodiment of a fuel cell cooling system according to the present invention, in which electronic control valves are used as first and second valves.

  In FIG. 1, a fuel cell stack 1 is a fuel cell stack in which a plurality of fuel cells using a solid polymer electrolyte are stacked. The radiator 2 is a heat exchanger that radiates the coolant by heat exchange between the coolant and the outside air. The fuel cell stack 1 and the radiator 2 are annularly connected by a main flow path 3 for cooling liquid, and the cooling liquid is circulated by a cooling liquid pump 4 disposed on the main flow path 3 to cool the fuel cell stack 1. It is possible.

  The first bypass channel 5 is a channel that bypasses the radiator 2. The first electronic control valve 7 is a three-way valve that can be switched by a control signal, and can switch between the first bypass channel 5 and the channel that passes through the radiator 2. On the first bypass flow path 5, for example, a heating device 6 such as an electric heater or a hydrogen combustion device is provided so that the coolant passing through the first bypass flow path 5 can be heated.

  The second bypass channel 8 is a channel that bypasses the fuel cell stack 1. The second electronic control valve 9 is a three-way valve that can change the flow rate ratio by a control signal, and can set the ratio between the flow rate of the second bypass flow path 8 and the flow rate through the fuel cell stack 1 to a desired value. .

  The first temperature sensor 10 detects the temperature of the coolant flowing through the second bypass flow path 8. The second temperature sensor 11 detects the temperature of the coolant flowing out from the fuel cell stack 1. The first temperature sensor 10 and the second temperature sensor 11 are each connected to a controller (not shown), and the controller, based on the detected values of these temperature sensors, the first electronic control valve 7, the second electronic control valve 9, and the heating The apparatus 6 is controlled to perform warm-up control when starting up the fuel cell system.

  For example, an aqueous solution of a melting point depressant such as ethylene glycol is used as the coolant, and the concentration of the melting point depressant is adjusted so that the coolant does not freeze in the environment where the fuel cell system is used.

  In the case of starting the fuel cell system from a low temperature such as below freezing point, the first electronic control valve 7 and the second electronic control valve 9 switch the cooling flow path so as to bypass the radiator 2 and the fuel cell stack 1, respectively. Next, the cooling pump is started to circulate the cooling liquid, the cooling liquid is heated by the heating device 6 to raise the temperature, and the fuel gas and the oxidant gas are supplied to the fuel cell stack 1 to extract the warm-up output current. . The heating device 6 may be a combustor or an electric heater that burns hydrogen. In the case of an electric heater, electric power can be consumed as a load when the fuel cell is warmed up.

  The second electronic control valve 9 opens slightly to the fuel cell stack 1 side so that the minimum coolant flows to the fuel cell stack 1 side, and causes the fuel cell stack 1 to start power generation. At this time, it is desirable that the flow rate flowing through the fuel cell stack 1 is 1/10 or less of the outlet flow rate of the coolant pump 4, but it is particularly 1 [L / min] or more and 5 [L / min] or less. It is desirable to do so. If an antifreeze such as an ethylene glycol aqueous solution is used as the cooling liquid, the viscosity increases below freezing point, and if it is 1 [L / min] or less, it does not flow smoothly in the stack. If it is 5 [L / min] or more, the amount of water passing through the fuel cell stack 1 increases, and the amount of heat taken out from the fuel cell stack 1 increases. While reducing the amount of heat taken out from the fuel cell stack 1 as much as possible, the flow of the coolant to the fuel cell stack 1 reduces the rise in stack temperature due to the reaction heat of the fuel cell stack 1, and the first provided at the outlet of the fuel cell stack 1. The temperature of the fuel cell stack 1 can be detected by the two temperature sensor 11.

  FIG. 2 is a diagram illustrating the relationship between the time during which the temperature of the fuel cell stack rises to a temperature at which the fuel cell stack can be operated and the flow rate of the coolant flowing through the stack. As shown in FIG. 2, it can be seen that the temperature rise time is shorter when the amount of the coolant is smaller.

  The temperature of the coolant flowing through the second bypass channel 8 is detected by the first temperature sensor 10, and the temperature of the fuel cell stack due to the reaction heat of power generation is detected by the second temperature sensor 11.

  When the detected value of the first temperature sensor 10 or the second temperature sensor 11 reaches a predetermined operating temperature of the fuel cell (preferably about 50 ° C. or higher), the second electronic control valve 9 is gradually moved to the fuel cell stack side. The coolant flowing through the second bypass channel 8 is introduced into the fuel cell stack 1. The second electronic control valve 9 is gradually moved to the fuel cell stack 1 side while adjusting the opening of the second electronic control valve 9 so that the detected value of the second temperature sensor 11 does not fall below the lower limit of the operating temperature of the fuel cell. Switch to the full flow. Moreover, the heating by the heating device 6 is stopped when the detected value of the first temperature sensor 10 is raised to a predetermined operating temperature. When the detected value of the second temperature sensor 11 reaches the upper limit of the fuel cell operating temperature (temperature that requires cooling), the first electronic control valve 7 is maintained at a predetermined temperature while being opened or closed to the radiator 2 side. Control the temperature of the coolant to

  When the coolant is introduced into the fuel cell stack in a state where the coolant is not sufficiently heated by the heating device and the coolant is not sufficiently warm as in the prior art, the temperature rise due to power generation of the fuel cell stack is delayed. End up. In addition, if the coolant is sufficiently warmed before being introduced into the fuel cell stack, there will be a large difference between the temperature of the warmed coolant and the temperature of the fuel cell stack, resulting in a large temperature difference in the fuel cell stack resulting in thermal distortion, etc. Affects stack strength. In addition, if a temperature sensor is incorporated in the fuel cell stack, the structure of the fuel cell stack becomes complicated and a control circuit for the coolant is required, resulting in a high cost configuration.

  In the present embodiment, power generation of the fuel cell stack is started in parallel with the heating of the coolant by the heating device, and most of the coolant is bypassed through the fuel cell stack and a part of the coolant flows to the fuel cell stack. The temperature of the fuel cell stack at the time of startup can be detected without hindering the temperature rise due to power generation of the fuel cell stack.

  According to this embodiment, it is possible to maximize the temperature rise due to power generation of the fuel cell stack. In addition, by flowing the minimum amount of coolant that can be passed through the fuel cell stack, the temperature of the coolant in the fuel cell stack can be accurately detected without installing a temperature sensor in the stack having a complicated structure. The switching timing of the valve can be accurately determined based on the coolant temperature. In addition, since the coolant flows in the fuel cell stack, there is no large temperature distribution difference in the stack, and it becomes difficult to generate strain due to heat in the stack, and it suppresses the deterioration of the stack sealing performance and strength due to strain. Can do.

  In addition, according to the present embodiment, an electronic control valve is provided for the valve for switching the bypass flow path, and a temperature sensor is provided for the temperature detection device, so that the valve opening degree for accurately detecting the temperature of the coolant and switching the bypass flow path is set. It can be finely controlled, and a rapid change in temperature such as a heat shock can be suppressed with respect to the fuel cell stack.

  FIG. 3 is a configuration diagram for explaining the configuration of the second embodiment of the cooling system for a fuel cell according to the present invention, in which a thermostat valve is used for the first and second valves.

  In FIG. 3, a fuel cell stack 1 is a fuel cell stack in which a plurality of fuel cells using a solid polymer electrolyte are stacked. The radiator 2 is a heat exchanger that radiates the coolant by heat exchange between the coolant and the outside air. The fuel cell stack 1 and the radiator 2 are annularly connected by a main flow path 3 for cooling liquid, and the cooling liquid is circulated by a cooling liquid pump 4 disposed on the main flow path 3 to cool the fuel cell stack 1. It is possible. For example, an aqueous solution of a melting point depressant such as ethylene glycol is used as the coolant, and the concentration of the melting point depressant is adjusted so that the coolant does not freeze in the environment where the fuel cell system is used.

  The first bypass channel 5 is a channel that bypasses the radiator 2. The first thermostat valve 17 is a three-way valve that automatically switches the flow path depending on the temperature, and can switch between the first bypass flow path 5 and the flow path that passes through the radiator 2. On the first bypass flow path 5, for example, a heating device 6 such as an electric heater or a hydrogen combustion device is provided so that the coolant passing through the first bypass flow path 5 can be heated. The first thermostat valve 17 has a temperature characteristic of switching the flow path from the first bypass flow path 5 to the flow path passing through the radiator 2 at, for example, 50 to 60 ° C. or higher.

  FIG. 4 is a schematic cross-sectional view showing an example of the structure of a thermostat valve used in the first thermostat valve 17, and shows (a) high temperature, (b) switching, and (c) low temperature. This thermostat valve is not different from a general-purpose wax-type thermostat valve. Inside the wax container 103, a wax having a melting point at the switching temperature, a synthetic rubber sleeve, and a piston are incorporated in the center of the sleeve. A spring (not shown) that biases the wax container 103 downward is provided.

  In the high temperature state of FIG. 4A, the wax melts and the volume expands, and the wax container 103 moves relatively upward by pushing the piston out of the wax container 103 against the force of the spring, and the radiator and the cooling are performed. The valve 101 flow path to the liquid pump is opened, and the valve 102 on the first bypass flow path side is closed.

  At the low temperature in FIG. 4 (c), the volume of the wax is reduced because the wax is solidified, and the piston is pushed into the wax container 103 by the force of the spring, so that the wax container 103 relatively moves downward, and the first bypass flow path The valve 102 to the coolant pump is opened, and the radiator-side valve 101 is closed.

  The second bypass channel 8 is a channel that bypasses the fuel cell stack 1. The second thermostat valve 19 is a three-way valve that automatically switches the flow path depending on the temperature, and switches between the second bypass flow path 8 and the flow path that passes through the fuel cell stack 1. The second thermostat valve 19 has a temperature characteristic of switching the flow path from the first bypass flow path 5 to the flow path via the radiator 2 at, for example, 10 to 20 ° C. or higher.

  FIG. 5 is a schematic cross-sectional view showing a structural example of a thermostat valve used in the second thermostat valve 19, and shows (a) at a high temperature, (b) at the time of switching, and (c) at a low temperature. This thermostat valve has a structure in which an orifice hole 105 is added to the valve 101 of the thermostat valve shown in FIG. The other structure is the same as that of FIG. 4, but the melting point temperature of the wax is set to, for example, 10 to 20 ° C. lower than that of the first thermostat valve. Even when the wax container 103 closes the valve 101 at a low temperature lower than the wax melting point temperature, the second thermostat valve is connected to the first bypass flow path and the radiator side flow path from the fuel cell stack 1 through the orifice hole 105. It has the characteristic of leaking a small amount of flow in the direction.

  At start-up when the coolant temperature is lower than the operating temperature of the fuel cell stack, such as below the freezing point, the first thermostat valve 17 is switched to the first bypass flow path 5 side, and the second thermostat valve 19 is switched to the second bypass flow path. It has switched to the 8 side.

  Therefore, the coolant circulates among the first bypass channel 5, the coolant pump 4, and the second bypass channel 8. After starting, the heating device 6 is supplied with power from the fuel cell stack 1 and gradually heats the coolant. The coolant in the fuel cell stack 1 starts power generation at the same time as the start-up, so that the temperature rises by power generation of the fuel cell itself.

  The orifice hole 105 of the second thermostat valve 19 has a minimum flow rate of coolant even when the valve 101 is closed (for example, when the coolant is below the freezing point and the coolant is ethylene glycol or the like, the viscosity increases, but in that state 1 [L / min] It is set to such a size that 5 [L / min] or less is desirable. The second thermostat valve 19 starts switching to the fuel cell stack side when the temperature of the coolant in the second bypass passage 8 rises and the wax warms and reaches the lower limit temperature for operating the fuel cell.

  In addition, since the coolant from the fuel cell stack 1 flows through the second thermostat valve 19 to a minimum, a small amount of coolant passes through the fuel cell stack 1 and is merged in the second thermostat valve 19. Therefore, even when the temperature of the fuel cell stack 1 rises before the second bypass flow path 8, the second thermostat valve 19 can be switched, and the fuel cell stack 1 can be prevented from overheating. When the coolant temperature exceeds the lower limit of the stack operating temperature, the second thermostat valve 19 is completely switched to the fuel cell stack 1 side, and a lot of coolant circulates in the fuel cell stack 1. When the upper limit of the stack operating temperature is exceeded, the first thermostat valve 17 starts to open to the radiator 2 side, so that the coolant can be cooled by the radiator 2.

  According to the second embodiment, the thermostat valve is installed at the junction of the bypass flow path, so that the stack is activated at a low temperature without using complicated and expensive components such as an electronic control valve, a temperature sensor, and a control arithmetic device. Can be performed efficiently. In particular, the second thermostat valve is installed on the downstream side of the fuel cell stack, so that the temperature of the coolant raised by the heating device circulating through the first and second bypass passages is detected and the fuel cell stack is operated. When the temperature reaches the lower limit of the temperature, the valve begins to open gradually, but if the coolant temperature on the fuel cell stack side has not yet risen sufficiently, cold coolant will mix as soon as it begins to open and the valve will suddenly It doesn't happen to open. Therefore, a rapid temperature change is not caused to the fuel cell stack, and the strength of the fuel cell stack is not affected.

  FIG. 6 is a system configuration diagram illustrating the configuration of a third embodiment of the cooling system for a fuel cell according to the present invention. As the first thermostat valve 17 and the second thermostat valve 29, the general thermostat valve shown in FIG. 4 can be used.

  In the third embodiment, compared to the second embodiment, the second thermostat valve 29 is not provided with an orifice hole, and the connection portion of the fuel cell stack 1 of the second thermostat valve 29 and the connection portion of the first bypass flow path 5 are provided. In between, a third thermostat valve 31 is provided in parallel, and an orifice hole is provided in the third thermostat valve.

  FIG. 7 is a schematic cross-sectional view showing an example of a thermostat valve used for the third thermostat valve 31, and shows (a) high temperature, (b) switching, and (c) low temperature. When the temperature shown in FIG. 7A is high, the third thermostat valve is fully opened. When the temperature shown in FIG. 7C is low, the wax container 103 closes the valve 101. It can pass through three thermostat valves. The flow rate passing through the orifice hole 105 is, for example, below the freezing point and, when the coolant is ethylene glycol or the like, the viscosity increases, but in that state, it is preferably 1 [L / min] or more and 5 [L / min] or less.

  When the coolant is below freezing point, the first thermostat valve 17 and the second thermostat valve 29 are switched to the first bypass flow path 5 side and the second bypass flow path 8 side, respectively. In this state, starting the coolant pump 4 and heating the heating device 6 and starting the power generation of the fuel cell stack 1 will cool the coolant pump 4, the second bypass channel 8, and the first bypass channel 5. The liquid circulates, the coolant is warmed by the heating device 6, and heat exchange between the fuel cell stack 1 and the coolant starts. Further, a minimum amount of coolant flows through the fuel cell stack 1 through the orifice hole of the third thermostat valve 31. When the temperature of the fuel cell stack 1 rises before the second bypass flow path 8, when there is no heating device 6, when the capacity of the heating device 6 is small, when the heating device 6 fails and does not work Even when the amount of coolant flowing through the third thermostat valve 31 is very small, the third thermostat valve 31 opens when the temperature rises, and the fuel cell stack regardless of the opening degree of the second thermostat valve 29. 1 starts to circulate more coolant.

  In the case of the second thermostat valve 19 (FIG. 5) of the second embodiment, the coolant temperature from the second bypass passage 8 becomes dominant with respect to the wax, and the fuel is ahead of the second bypass passage 8. Even when the cooling temperature from the battery stack 1 is raised, the second thermostat valve 19 is not switched to the fuel cell stack side.

  According to the third embodiment, when the power generation of the fuel cell stack is increased immediately after startup, such as when the power generation of the fuel cell stack is increased, or when a large-capacity heating device cannot be mounted, the heating of the fuel cell stack is fast, In the case where the temperature of the circulating bypass passage is slow, the configuration of the second embodiment has a minimum flow rate of the coolant flow from the fuel cell stack depending on the fuel cell system. Even if the temperature rises to a temperature that requires cooling, the coolant temperature in the second bypass passage may not rise sufficiently, and the time for the second thermostat valve to switch to the fuel cell stack side may be delayed.

  By adopting the configuration of Example 3, even when the temperature of the fuel cell stack is raised before the second bypass flow path, the third thermostat valve is opened first before the second thermostat valve is switched. Cooling of the fuel cell stack can be started quickly, and efficient power generation can be performed.

It is a figure explaining the structure of Example 1 of the cooling system of the fuel cell which concerns on this invention. FIG. 6 is a relationship diagram between a temperature raising time and a stack coolant flow rate. It is a figure explaining the structure of Example 2 of the cooling system of the fuel cell which concerns on this invention. 6 is a schematic cross-sectional view showing an example of a first thermostat valve used in Example 2. FIG. 6 is a schematic cross-sectional view showing an example of a second thermostat valve used in Example 2. FIG. It is a figure explaining the structure of Example 3 of the cooling system of the fuel cell which concerns on this invention. 6 is a schematic cross-sectional view showing an example of a third thermostat valve used in Example 3. FIG.

Explanation of symbols

1: Fuel cell stack 2: Radiator 3: Main flow path 4: Coolant pump 5: First bypass flow path 6: Heating device 7: First electronic control valve 8: Second bypass flow path 9: Second electronic control valve 10: first temperature sensor 11: second temperature sensor 17: first thermostat valve 19: second thermostat valve

Claims (4)

In a fuel cell cooling system for cooling a fuel cell by circulating a coolant between a polymer electrolyte fuel cell stack and a radiator by a coolant pump,
A first bypass flow path that bypasses the radiator and includes a heating device;
A second bypass flow path for bypassing the fuel cell stack;
A first valve for switching between the first bypass flow path and the flow path via the radiator;
A second valve for controlling a flow rate ratio between the second bypass flow path and the flow path passing through the fuel cell stack,
When starting the fuel cell stack from a low temperature, the first valve is opened to the first bypass channel side, and the flow rate ratio controlled by the second valve is increased in the second bypass channel side and reduced to the fuel cell stack side. Power generation of the battery stack and startup of the coolant pump and heating device,
A fuel cell cooling system, characterized in that when either one of the second bypass channel and the fuel cell stack reaches a predetermined temperature, the total flow rate of the second valve is set to the fuel cell stack side. The first valve is a first electronic control valve;
The second valve is a second electronic control valve;
Install the first temperature sensor in the second bypass flow path,
2. The fuel cell cooling system according to claim 1, wherein the second temperature sensor is installed between the outlet of the fuel cell stack and the second bypass flow path. The first valve is a first thermostat valve whose opening degree is switched to the radiator side when the upper limit of the operating temperature is exceeded,
The second valve is a second thermostat valve whose opening is switched to the fuel cell stack side when the lower limit of the operating temperature is exceeded,
The second thermostat valve has a small amount of leakage flow to the fuel cell stack side,
When the fuel cell stack is started from a low temperature, when the power generation of the fuel cell stack and the coolant pump and the heating device are started, the coolant is circulated mostly through the first bypass channel and the second bypass channel. , Some of which pass through the fuel cell stack,
When either one of the second bypass flow path and the flow path passing through the fuel cell stack exceeds a lower limit of the operating temperature, the total flow rate of the second thermostat valve automatically becomes the fuel cell stack side. Item 4. The fuel cell cooling system according to Item 1. The first valve is a first thermostat valve whose opening degree is switched to the radiator side when the upper limit of the operating temperature is exceeded,
The second valve is a second thermostat valve whose opening is switched to the fuel cell stack side when the lower limit of the operating temperature is exceeded,
A third bypass passage that bypasses between the fuel cell stack side and the radiator side of the second thermostat valve, and when the lower limit of the operating temperature is exceeded, the third bypass passage is fully opened and a small amount when fully closed. A third thermostat valve having a leakage flow rate,
When the fuel cell stack is started from a low temperature, when the power generation of the fuel cell stack and the coolant pump and the heating device are started, the coolant is circulated mostly through the first bypass channel and the second bypass channel. , Some of which pass through the fuel cell stack,
If either the second bypass flow path or the flow path passing through the fuel cell stack exceeds the lower limit of the operating temperature, the total flow rate of the second thermostat valve becomes the fuel cell stack side or the third thermostat valve is fully opened. The fuel cell cooling system according to claim 1, wherein

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