Fuel cell system

Abstract

The present invention provides a fuel cell system. A fuel cell system mounted on a vehicle includes: a fuel cell stack; a refrigerant circulation passage connected to the fuel cell stack; a refrigerant circulation pump disposed in the refrigerant circulation passage and configured to circulate the refrigerant; and a controller configured to control the power generation amount of the fuel cell stack and control the refrigerant circulation pump according to a requested driving force of the vehicle. The controller is configured to set the rotational speed of the refrigerant circulation pump within a range equal to or lower than a rotational speed upper limit based on the temperature of the fuel cell stack, and when the vehicle speed is equal to or lower than a stop determination value, the controller sets the rotational speed upper limit to be lower than when the vehicle speed is higher than the stop determination value.

Description

Technical Field

[0001] The present invention relates to a fuel cell system mounted on a vehicle. Background Art

[0002] JP2017 - 84665A discloses a fuel cell system including a circulation passage connected to a fuel cell, a pump for circulating cooling water through the circulation passage, a radiator for releasing heat from the cooling water, and a storage tank connected to the circulation passage via a water flow rate regulating valve. In such a fuel cell system, when the discharge amount of the pump becomes larger than the circulation water amount (including the supply amount from the storage tank), the pressure at the pump inlet decreases. Therefore, cavitation may occur in the pump, and the circulation passage made of elastic materials such as rubber and resin may be deformed and narrowed. To solve these problems, the fuel cell system according to JP2017 - 84665A estimates the shortage of cooling water in the circulation passage and drives the pump at a specified forced inflow rotation speed when it is determined that there is a shortage of cooling water, so that the cooling water pressure at the pump inlet is equal to the inflow pressure of the water flow rate regulating valve.

[0003] However, when controlling the rotation speed of the pump based on the pressure of the cooling water at the pump inlet rather than the temperature of the fuel cell, the ability to cool the fuel cell may become excessive or insufficient. In addition, depending on the driving state of the vehicle, it is very likely to drive the pump at the forced inflow rotation speed, so the temperature of the fuel cell may become unstable. Summary of the Invention

[0004] In view of the above background, an object of the present invention is to provide a fuel cell system that can suppress the negative pressure generated at the pump inlet and stabilize the temperature of the fuel cell stack.

[0005] To achieve this object, an aspect of the present invention provides a fuel cell system 1 mounted on a vehicle 2, the fuel cell system including: a fuel cell stack 4; a refrigerant circulation passage 65 connected to the fuel cell stack, the refrigerant being configured to circulate through the refrigerant circulation passage; a refrigerant circulation pump 64 disposed in the refrigerant circulation passage and configured to circulate the refrigerant; a storage tank 72 connected to the refrigerant circulation passage via a regulating valve 71; a vehicle speed sensor 83 configured to acquire the vehicle speed of the vehicle; temperature acquisition units 75, 76 configured to acquire the temperature of the fuel cell stack; and a controller 8 configured to control the power generation amount of the fuel cell stack and control the refrigerant circulation pump according to the requested driving force of the vehicle, wherein the controller is configured to set the rotational speed of the refrigerant circulation pump within a range equal to or lower than the rotational speed upper limit based on the temperature of the fuel cell stack, and when the vehicle speed is equal to or lower than a stop determination value, the controller sets the rotational speed upper limit to be lower than when the vehicle speed is higher than the stop determination value.

[0006] According to this aspect, when the vehicle speed is equal to or lower than the stop determination value, the rotational speed of the refrigerant circulation pump is suppressed, and a pressure drop at the pump inlet (the inlet of the refrigerant circulation pump) is prevented. When the vehicle speed is equal to or lower than the stop determination value, it is estimated that the power generation amount of the fuel cell stack will decrease, and thus the temperature of the fuel cell stack will decrease. Therefore, even if the rotational speed of the refrigerant circulation pump is suppressed, the temperature of the fuel cell stack is prevented from rising. Accordingly, a fuel cell system can be provided that can suppress the negative pressure generated at the pump inlet and stabilize the temperature of the fuel cell stack.

[0007] In the above aspect, preferably, when the temperature of the fuel cell stack is equal to or higher than a specified temperature threshold, when the power generation amount of the fuel cell stack is equal to or lower than a specified power generation threshold, the controller sets the rotational speed upper limit to be lower than when the power generation amount of the fuel cell stack is higher than the power generation threshold.

[0008] According to this aspect, when the power generation amount of the fuel cell stack is equal to or less than the power generation threshold, the rotational speed of the refrigerant circulation pump is suppressed, and a pressure drop at the pump inlet is prevented. When the power generation amount of the fuel cell stack is equal to or less than the power generation threshold, it is estimated that the temperature of the fuel cell stack will decrease. Therefore, even if the rotational speed of the refrigerant circulation pump is suppressed, the temperature of the fuel cell stack is prevented from rising.

[0009] In the above aspect, preferably, when the vehicle speed is equal to or lower than the stop determination value, the controller sets the upper limit of the increase speed of the rotational speed of the refrigerant circulation pump to be lower than when the vehicle speed is higher than the stop determination value.

[0010] According to this aspect, when the vehicle speed is equal to or lower than the stop determination value, the increasing speed of the rotational speed of the refrigerant circulation pump is suppressed, and a pressure drop at the pump inlet is prevented. When the vehicle speed is equal to or lower than the stop determination value, it is estimated that the power generation amount of the fuel cell stack decreases, and thus the temperature of the fuel cell stack decreases. Therefore, even if the increasing speed of the rotational speed of the refrigerant circulation pump is suppressed, an increase in the temperature of the fuel cell stack is prevented.

[0011] In the above aspect, preferably, when the fuel cell stack stops generating power and the temperature of the fuel cell stack is equal to or lower than a prescribed low temperature threshold value, the controller executes low temperature period control to drive the refrigerant circulation pump at a prescribed low temperature period rotational speed, and in the low temperature period control, the controller sets the increasing speed of the rotational speed of the refrigerant circulation pump to be lower than the upper limit of the increasing speed of the rotational speed of the refrigerant circulation pump when the vehicle speed is higher than the stop determination value.

[0012] According to this aspect, when the fuel cell stack stops generating power, the increasing speed of the rotational speed of the refrigerant circulation pump is suppressed, and a pressure drop at the pump inlet is prevented. When the fuel cell stack stops generating power, it is estimated that the temperature of the fuel cell stack decreases. Therefore, even if the increasing speed of the rotational speed of the refrigerant circulation pump is suppressed, an increase in the temperature of the fuel cell stack is prevented.

[0013] Therefore, according to the above aspect, a fuel cell system can be provided that can suppress a negative pressure generated at the pump inlet and stabilize the temperature of the fuel cell stack. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a block diagram of a fuel cell system;

[0015] Figure 2 is a block diagram of a fuel cell system;

[0016] Figure 3 is an explanatory diagram showing an embodiment of a second map;

[0017] Figure 4 is a flowchart of a program for controlling a refrigerant circulation pump executed by a fuel cell controller;

[0018] Figure 5A is an explanatory diagram showing a target rotational speed of the refrigerant circulation pump when performing stop period power generation control; and

[0019] Figure 5B is an explanatory diagram showing a target rotational speed of the refrigerant circulation pump when performing low temperature period control. DETAILED DESCRIPTION

[0020] Hereinafter, a fuel cell system 1 according to an embodiment of the present invention will be described. The fuel cell system 1 is installed on a vehicle 2. As Figure 1 shown, the fuel cell system 1 includes: a fuel cell stack 4, a fuel gas supply device 5 configured to supply fuel gas to the fuel cell stack 4; an oxidant gas supply device 6 configured to supply oxidant gas to the fuel cell stack 4; a refrigerant supply device 7 configured to supply refrigerant to the fuel cell stack 4; and a fuel cell controller 8. In the present embodiment, the fuel gas is hydrogen, and the oxidant gas is air.

[0021] The fuel cell stack 4 includes a plurality of power generation cells 10 stacked one by one. Each power generation cell 10 includes: an electrolyte membrane and an electrode structure 11 (hereinafter simply referred to as "structure 11"); and a first separator 12 and a second separator 13 configured to hold the structure 11 therebetween. The first separator 12 and the second separator 13 may be made of metal or carbon.

[0022] The structure 11 includes: a solid polymer electrolyte membrane 15 (hereinafter simply referred to as "electrolyte membrane 15"); and an anode 16 (electrode) and a cathode 17 (electrode) configured to hold the electrolyte membrane 15 therebetween. The electrolyte membrane 15 may be composed of a thin film of a moisture-containing fluorine-based electrolyte (such as perfluorosulfonic acid). Alternatively, the electrolyte membrane 15 may be composed of a thin film of a hydrocarbon-based electrolyte.

[0023] A plurality of hydrogen channels 21 are formed between the first separator 12 and the structure 11 for supplying hydrogen to the anode 16. A plurality of air channels 22 are formed between the second separator 13 and the structure 11 for supplying air to the cathode 17. A plurality of refrigerant channels 23 through which refrigerant passes are formed between the adjacent first separator 12 and the second separator 13.

[0024] The fuel cell stack 4 is provided with a hydrogen inlet 24, a hydrogen outlet 25, an air inlet 26, an air outlet 27, a refrigerant inlet 28, and a refrigerant outlet 29. The hydrogen inlet 24 is connected to the supply side (hydrogen supply side) of each hydrogen channel 21. The hydrogen outlet 25 is connected to the discharge side (hydrogen discharge side) of each hydrogen channel 21. The air inlet 26 is connected to the supply side (air supply side) of each air channel 22. The air outlet 27 is connected to the discharge side (air discharge side) of each air channel 22. The refrigerant inlet 28 is connected to the supply side (refrigerant supply side) of each refrigerant channel 23. The refrigerant outlet 29 is connected to the discharge side (refrigerant discharge side) of each refrigerant channel 23.

[0025] The fuel gas supply device 5 includes a hydrogen tank 31 configured to store high-pressure hydrogen. The hydrogen tank 31 is connected to the hydrogen inlet 24 of the fuel cell stack 4 via a hydrogen supply passage 32. The hydrogen supply passage 32 is provided with an injector 33 and an ejector 34 arranged in series. When the pressure in the ejector 34 becomes negative, the ejector 34 sucks hydrogen from the hydrogen discharge passage 35.

[0026] The hydrogen discharge passage 35 is connected to the hydrogen outlet 25 of the fuel cell stack 4. The hydrogen discharge passage 35 is configured to discharge anode exhaust gas (discharged hydrogen) from the fuel cell stack 4, and the anode exhaust gas is hydrogen that has been at least partially used in the anode 16. The hydrogen discharge passage 35 is connected to the ejector 34.

[0027] The hydrogen discharge passage 35 is provided with a gas-liquid separation device 37. The gas-liquid separation device 37 is configured to separate liquid from the anode exhaust gas and discharge the separated liquid to a discharge passage 38. The discharge passage 38 is provided with a discharge valve 39. The gas separated by the gas-liquid separation device 37 is sucked into the ejector 34 via the hydrogen discharge passage 35.

[0028] The oxidant gas supply device 6 is provided with an air supply passage 41. One end of the air supply passage 41 is provided with an air suction port 42 for introducing air from the atmosphere (outside). The other end of the air supply passage 41 is connected to the air inlet 26 of the fuel cell stack 4. The air supply passage 41 is provided with an air pump 44, a temperature regulator 45, and a humidifier 46, and the air pump 44, the temperature regulator 45, and the humidifier 46 are arranged in series in order from the air suction port 42 side. The air pump 44 consists of a compressor driven by an electric motor. The temperature regulator 45 can consist of a heater including a heating wire.

[0029] An air discharge passage 48 is connected to the air outlet 27 of the fuel cell stack 4. The air discharge passage 48 is configured to discharge cathode exhaust gas from the fuel cell stack 4, and the cathode exhaust gas is compressed air that has been at least partially used in the cathode 17.

[0030] The air discharge passage 48 is provided with a humidifier 46. In the humidifier 46, the compressed air supplied from the air pump 44 exchanges moisture and heat with the cathode exhaust gas. The cathode exhaust gas discharged from the fuel cell stack 4 has a higher temperature and higher humidity than the compressed air passing through the air supply passage 41. Therefore, the temperature and humidity of the compressed air supplied from the air pump 44 increase in the humidifier 46. The humidifier 46 can be composed of a membrane filtration humidifier using a hollow fiber membrane. The humidifier 46 can be provided with one passage for the compressed air to pass through and another passage for the cathode exhaust gas to pass through, and these two passages can be separated by a hollow fiber membrane.

[0031] The portion of the air supply passage 41 between the temperature regulator 45 and the humidifier 46 is connected to the portion of the air discharge passage 48 on the downstream side of the humidifier 46 via an air bypass passage 51. The air bypass passage 51 is provided with an air flow rate regulating valve 52 configured to regulate the flow rate of the air flowing through the air bypass passage 51. The downstream portion of the air discharge passage 48 is connected to the discharge passage 38. The outlet of the air discharge passage 48 is configured to discharge the cathode exhaust gas and the liquid separated from the anode exhaust gas to the outside.

[0032] The portion of the hydrogen discharge passage 35 between the gas-liquid separation device 37 and the ejector 34 and the portion of the air supply passage 41 between the humidifier 46 and the air inlet 26 are connected via an anode exhaust gas suction passage 55. The anode exhaust gas suction passage 55 is provided with a switching valve 56. The anode exhaust gas suction passage 55 is configured to supply the anode exhaust gas to the air supply passage 41.

[0033] The refrigerant supply device 7 includes: a refrigerant supply passage 61 connected to the refrigerant inlet 28 of the fuel cell stack 4; a refrigerant discharge passage 62 connected to the refrigerant outlet 29 of the fuel cell stack 4; and a radiator 63 connected to the refrigerant supply passage 61 and the refrigerant discharge passage 62. The refrigerant supply passage 61 is provided with a refrigerant circulation pump 64 configured to circulate the refrigerant. The refrigerant supply passage 61, the refrigerant discharge passage 62, and the radiator 63 constitute a refrigerant circulation passage 65 for circulating the refrigerant. The refrigerant circulation passage 65 is connected to the fuel cell stack 4.

[0034] In the portion of the refrigerant supply passage 61 between the radiator 63 and the refrigerant circulation pump 64, a thermostatic valve 67 is provided. When the refrigerant flowing through the refrigerant supply passage 61 is at a relatively high temperature, the thermostatic valve 67 opens, and when the refrigerant flowing through the refrigerant supply passage 61 is at a relatively low temperature, the thermostatic valve 67 closes. The refrigerant discharge passage 62 and the refrigerant supply passage 61 are connected via a refrigerant bypass passage 68 that bypasses the radiator 63 and the thermostatic valve 67. The refrigerant bypass passage 68 is connected to the portion of the refrigerant supply passage 61 between the thermostatic valve 67 and the refrigerant circulation pump 64. When the thermostatic valve 67 is closed, the refrigerant flows from the refrigerant discharge passage 62 to the refrigerant supply passage 61 via the refrigerant bypass passage 68.

[0035] The portion of the refrigerant supply passage 61 between the thermostatic valve 67 and the refrigerant circulation pump 64 is connected to the storage tank 72 via the regulating valve 71. More specifically, the storage tank 72 can be connected to the portion of the refrigerant supply passage 61 between the portion connected to the refrigerant bypass passage 68 and the refrigerant circulation pump 64 via the regulating valve 71. Hereinafter, the pressure of the refrigerant at the portion of the refrigerant supply passage 61 connected to the inlet of the refrigerant circulation pump 64 will be referred to as the "pump inlet pressure". When the pump inlet pressure becomes equal to or lower than a specified first pressure, the regulating valve 71 opens. Accordingly, the refrigerant is supplied from the storage tank 72 to the refrigerant supply passage 61. Further, when the pump inlet pressure becomes equal to or higher than a specified second pressure, which is higher than the first pressure, the regulating valve 71 opens. Accordingly, the refrigerant is discharged from the refrigerant supply passage 61 to the storage tank 72.

[0036] The refrigerant supply passage 61 and the refrigerant discharge passage 62 are made of resin or rubber to prevent metal ions from eluting into the cooling water and to maintain the insulating state of the refrigerant.

[0037] An inlet temperature sensor 75 configured to detect the temperature of the refrigerant is provided in the portion of the refrigerant supply passage 61 between the refrigerant inlet 28 and the refrigerant circulation pump 64. The inlet temperature sensor 75 is configured to detect the temperature of the refrigerant flowing into the refrigerant inlet 28. An outlet temperature sensor 76 configured to detect the temperature of the refrigerant is provided in the portion of the refrigerant discharge passage 62 between the refrigerant outlet 29 and the refrigerant bypass passage 68. The outlet temperature sensor 76 is configured to detect the temperature of the refrigerant flowing out of the refrigerant outlet 29. The inlet temperature sensor 75 and the outlet temperature sensor 76, as temperature acquisition units, are configured to acquire the temperature of the fuel cell stack 4.

[0038] The fuel cell controller 8 is composed of an electronic control unit (ECU) including a CPU, a non-volatile memory (read only memory: ROM), a volatile memory (random access memory: RAM), etc. As Figure 2 shown, the fuel cell controller 8 is configured to control the air pump 44, the injector 33, the refrigerant circulation pump 64, the switching valve 56, the discharge valve 39, the air flow rate regulating valve 52, and the temperature regulator 45.

[0039] The fuel cell controller 8 is connected to the vehicle controller 81, and the vehicle controller 81 is configured to control the running of the vehicle 2. Similar to the fuel cell controller 8, the vehicle controller 81 is composed of an electronic control unit (ECU) including a CPU, a non-volatile memory, a volatile memory, etc. The vehicle controller 81 is configured to control the electric motor 87, the braking device 88, and the steering device 89 as drive sources based on signals from the driving operation members 82 (such as an accelerator pedal, a brake pedal, and a steering wheel), the vehicle sensors 84 (such as a vehicle speed sensor 83 and a temperature sensor), and the switches 86 (such as a power switch 85 (ignition switch)). The fuel cell controller 8 and the vehicle controller 81 may be integrally formed. The fuel cell controller 8 and the vehicle controller 81 are connected to the battery 91.

[0040] The power switch 85 is turned on and off by the user. The vehicle controller 81 switches the power supply state of the vehicle 2 via a signal from the power switch 85. More specifically, when the power switch 85 is turned on, the vehicle controller 81 sets the power supply state to "on", so that the power from the fuel cell stack 4 and the battery 91 is supplied to the electric motor 87. On the other hand, when the power switch 85 is turned off, the vehicle controller 81 sets the power supply state to "off", thereby prohibiting the supply of power from the fuel cell stack 4 and the battery 91 to the electric motor 87.

[0041] The vehicle speed sensor 83 is a sensor configured to acquire the vehicle speed of the vehicle 2. The vehicle speed sensor 83 may be composed of, for example, a sensor configured to detect the rotational speed of the wheels or a sensor configured to detect the rotational speed of the electric motor 87.

[0042] The vehicle controller 81 is configured to determine the requested driving force of the vehicle 2 (more specifically, the electric motor 87) and control the electric motor 87 based on the requested driving force. For example, the vehicle controller 81 may determine the requested driving force based on the depression amount of the accelerator pedal. In addition, the vehicle controller 81 may determine the requested driving force based on the depression amount of the accelerator pedal and the vehicle speed. Alternatively, the vehicle controller 81 may be configured to perform autonomous driving control and determine the requested driving force based on the action plan created therefor.

[0043] The fuel cell controller 8 receives information about the requested driving force, the power supply state, and the vehicle speed from the vehicle controller 81. In addition, the fuel cell controller 8 is connected to the inlet temperature sensor 75 and the outlet temperature sensor 76, and is configured to receive signals related to the refrigerant temperature from the inlet temperature sensor 75 and the outlet temperature sensor 76.

[0044] The fuel cell controller 8 is configured to perform power generation control during travel to supply power (electricity) required for the vehicle 2 to travel. In the power generation control during travel, the fuel cell controller 8 determines the target power generation amount of the fuel cell stack 4 based on the requested driving force. The relationship between the requested driving force and the target power generation amount of the fuel cell stack 4 can be defined by a map. In addition, the fuel cell controller 8 determines the opening degree of the injector 33 and the driving amount of the air pump 44 based on the target power generation amount. The relationship between the target power generation amount and the opening degree of the injector 33 and the relationship between the target power generation amount and the driving amount of the air pump 44 can be defined by a map. The fuel cell controller 8 controls the injector 33 and the air pump 44 based on the opening degree of the injector 33 and the driving amount of the air pump 44, and thus supplies hydrogen and air to the fuel cell stack 4. Therefore, an oxidation-reduction reaction occurs in the fuel cell stack 4, and thus electricity is generated by the fuel cell stack 4. Through the power generation control during travel performed by the fuel cell controller 8, the power generation amount of the fuel cell stack 4 changes according to the requested driving force of the vehicle 2.

[0045] When the vehicle 2 stops and the remaining amount of the battery 91 is equal to or less than a specified value, the fuel cell controller 8 performs power generation control during stop to charge the battery 91. More specifically, when the vehicle speed is equal to or lower than a stop determination value and the SOC of the battery 91 is equal to or lower than a specified SOC determination value, the fuel cell controller 8 performs power generation control during stop. The stop determination value is set to a vehicle speed at which the vehicle 2 can be regarded as stopped. The SOC determination value is a value set to determine that the battery 91 needs to be charged. In the power generation control during stop, the fuel cell controller 8 sets a specified target power generation amount, and determines the opening degree of the injector 33 and the driving amount of the air pump 44 based on the target power generation amount. The fuel cell controller 8 controls the injector 33 and the air pump 44 based on the opening degree of the injector 33 and the driving amount of the air pump 44, thereby supplying hydrogen and air to the fuel cell stack 4. Therefore, an oxidation-reduction reaction occurs in the fuel cell stack 4, and thus electricity is generated by the fuel cell stack 4.

[0046] The fuel cell controller 8 controls the refrigerant circulation pump 64 based on the temperature of the fuel cell stack 4 and the target power generation amount. The fuel cell controller 8 can estimate the temperature of the fuel cell stack 4 based on at least one of the refrigerant temperature at the refrigerant inlet 28 (hereinafter referred to as "refrigerant inlet temperature") detected by the inlet temperature sensor 75 and the refrigerant temperature at the refrigerant outlet 29 (hereinafter referred to as "refrigerant outlet temperature") detected by the outlet temperature sensor 76. For example, the fuel cell controller 8 can estimate the temperature of the fuel cell stack 4 by using a map that defines the relationship between the refrigerant outlet temperature and the fuel cell stack 4. Alternatively, the fuel cell controller 8 can estimate the temperature of the fuel cell stack 4 by using a map that defines the relationship between the fuel cell stack 4 and the difference between the refrigerant inlet temperature and the refrigerant outlet temperature. In another embodiment, the fuel cell stack 4 may be provided with a temperature sensor configured to directly obtain the temperature of the fuel cell stack 4.

[0047] The fuel cell controller 8 sets an upper limit (rpm) of the rotational speed of the refrigerant circulation pump 64 based on the temperature of the fuel cell stack 4 and the target power generation amount. The relationship among the temperature of the fuel cell stack 4, the target power generation amount, and the upper limit of the rotational speed of the refrigerant circulation pump 64 is defined by one or more rotational speed upper limit maps. Preferably, a plurality of rotational speed upper limit maps are preset according to various conditions.

[0048] In the present embodiment, when the vehicle speed is higher than the stop determination value, the fuel cell controller 8 uses the first map (an example of the rotational speed upper limit map), and when the vehicle speed is equal to or lower than the stop determination value, it uses the second map (an example of the rotational speed upper limit map). The first map and the second map are set such that the upper limit of the rotational speed of the refrigerant circulation pump 64 increases as the target power generation amount increases, and the upper limit of the rotational speed of the refrigerant circulation pump 64 increases as the temperature of the fuel cell stack 4 increases.

[0049] The upper limit of the rotational speed set based on the second map is equal to or lower than the upper limit of the rotational speed set based on the first map. That is, when setting the upper limit of the rotational speed by using the second map, the upper limit of the rotational speed is suppressed (set lower) compared with the case of setting the upper limit of the rotational speed by using the first map.

[0050] In addition, the second map is set such that when the temperature of the fuel cell stack 4 is equal to or higher than the specified temperature threshold, the upper limit of the rotational speed is set lower when the power generation amount of the fuel cell stack 4 is equal to or less than the specified power generation threshold than when the power generation amount of the fuel cell stack 4 is greater than the power generation threshold. Therefore, compared with the case where the power generation amount is relatively large, in the case where the power generation amount is relatively small, even if the temperature of the fuel cell stack 4 is the same in the above two cases, the upper limit of the rotational speed is set lower.

[0051] Figure 3 An embodiment of the second mapping is shown. In Figure 3 , the upper limit of the third rotational speed is set higher than the upper limit of the first rotational speed, and the upper limit of the fourth rotational speed is set higher than the upper limit of the third rotational speed. From the relationship between the upper limit of the fourth rotational speed and the upper limit of the third rotational speed, it can be understood that compared with the case where the power generation amount of the fuel cell stack 4 is relatively large, in the case where the power generation amount of the fuel cell stack 4 is relatively small, even if the temperature of the fuel cell stack 4 is the same in the above two cases, the upper limit of the rotational speed is set lower. For example, the upper limit of the second rotational speed can be set to be higher than the upper limit of the third rotational speed and lower than the upper limit of the fourth rotational speed.

[0052] Based on the temperature of the fuel cell stack 4, the fuel cell controller 8 sets the rotational speed of the refrigerant circulation pump 64 within a range equal to or lower than the upper limit of the rotational speed. For example, the fuel cell controller 8 obtains the rotational speed of the refrigerant circulation pump 64 as a provisional rotational speed based on the temperature of the fuel cell stack 4 by using a mapping that defines the relationship between the temperature of the fuel cell stack 4 and the rotational speed of the refrigerant circulation pump 64. Then, the fuel cell controller 8 can set the provisional rotational speed as the target rotational speed when the provisional rotational speed is equal to or lower than the upper limit of the rotational speed, and set the upper limit of the rotational speed as the target rotational speed when the provisional rotational speed is higher than the upper limit of the rotational speed.

[0053] The fuel cell controller 8 controls the power supplied to the refrigerant circulation pump 64 based on the set target rotational speed, so as to drive the refrigerant circulation pump 64 at the target rotational speed.

[0054] When the vehicle 2 stops and the temperature of the fuel cell stack 4 is equal to or lower than a prescribed low-temperature threshold, the fuel cell controller 8 executes low-temperature period control, so as to drive the refrigerant circulation pump 64 at a prescribed low-temperature period rotational speed. According to the low-temperature period control executed by the fuel cell controller 8, the refrigerant is supplied to the fuel cell stack 4, so the refrigerant causes the temperature of the fuel cell stack 4 to rise. Therefore, the fuel cell stack 4 is prevented from freezing.

[0055] Next, a program for controlling the refrigerant circulation pump executed by the fuel cell controller 8 will be described with reference to Figure 4 The fuel cell controller 8 executes the refrigerant circulation pump control at a prescribed time interval. First, the fuel cell controller 8 obtains the target power generation amount (S1). As described above, the target power generation amount is calculated (determined) when the fuel cell controller 8 executes the power generation control during the driving period or the power generation control during the stop period.

[0056] Next, the fuel cell controller 8 determines whether the power supply state is "ON" based on the information about the power supply state obtained from the vehicle controller 81 (S2).

[0057] When the power supply state is "ON" (when the determination result in S2 is "YES"), the fuel cell controller 8 determines whether the vehicle 2 has stopped (S3). When the vehicle speed is equal to or lower than the stop determination value, the fuel cell controller 8 can determine that the vehicle 2 has stopped.

[0058] When the vehicle 2 has stopped (when the determination result in S3 is "YES"), the fuel cell controller 8 sets the upper limit of the rotational speed of the refrigerant circulation pump 64 based on the temperature of the fuel cell stack 4 and the target power generation amount by using a second map (S4).

[0059] When the vehicle 2 has not stopped (when the determination result in S3 is "NO"), the fuel cell controller 8 sets the upper limit of the rotational speed of the refrigerant circulation pump 64 based on the temperature of the fuel cell stack 4 and the target power generation amount by using a first map (S5).

[0060] After setting the upper limit of the rotational speed of the refrigerant circulation pump 64 in step S4 or S5, the fuel cell controller 8 sets the target rotational speed of the refrigerant circulation pump 64 based on the temperature of the fuel cell stack 4 and the upper limit of the rotational speed of the refrigerant circulation pump 64 (S6). Then, the fuel cell controller 8 drives (controls) the refrigerant circulation pump 64 based on the target rotational speed of the refrigerant circulation pump 64 (S7).

[0061] When the power supply state is not "ON" (when the determination result in S2 is "NO"), the fuel cell controller 8 determines whether the stop period power generation control is being executed (S8). When the stop period power generation control is being executed (when the determination result in S8 is "YES"), the fuel cell controller 8 sets a first rate limit to suppress the change amount per unit time of the target rotational speed of the refrigerant circulation pump 64 (S9). The first rate limit is set to the acceptable change amount per unit time of the target rotational speed of the refrigerant circulation pump 64. Subsequently, the fuel cell controller 8 sets the target rotational speed of the refrigerant circulation pump 64 based on the base rotational speed of the refrigerant circulation pump 64 in the stop period power generation control and the first rate limit (S10). The base rotational speed of the refrigerant circulation pump 64 in the stop period power generation control can be set based on a prescribed map. In this map, the base rotational speed can be set according to the time elapsed since the start of the stop period power generation control. The target rotational speed can be set based on the base rotational speed such that the change amount per unit time becomes equal to or less than the first rate limit. Therefore, as Figure 5A shown, a rapid increase in the target rotational speed is suppressed. After setting the target rotational speed of the refrigerant circulation pump 64 in step S10, the fuel cell controller 8 drives (controls) the refrigerant circulation pump 64 based on the target rotational speed of the refrigerant circulation pump 64 (S7).

[0062] When power generation control during a stop period is not being executed (when the determination result in S8 is "No"), the fuel cell controller 8 determines whether low-temperature period control is being executed (S11). When low-temperature period control is being executed (when the determination result in S11 is "Yes"), the fuel cell controller 8 sets a second rate limit to suppress the change amount per unit time of the target rotational speed of the refrigerant circulation pump 64 (S12). The second rate limit is set to the acceptable change amount per unit time of the target rotational speed of the refrigerant circulation pump 64. The second rate may be equal to or different from the first rate. Subsequently, the fuel cell controller 8 sets the target rotational speed of the refrigerant circulation pump 64 based on the base rotational speed of the refrigerant circulation pump 64 and the second rate limit during low-temperature period control (S13). The base rotational speed of the refrigerant circulation pump 64 during low-temperature period control may be set based on a prescribed map. In this map, the base rotational speed may be set according to the time elapsed since the start of low-temperature period control. The target rotational speed may be set based on the base rotational speed so that the change amount per unit time becomes equal to or less than the second rate limit. Therefore, as Figure 5B shown, a rapid increase in the target rotational speed is suppressed. After setting the target rotational speed of the refrigerant circulation pump 64 in step S13, the fuel cell controller 8 drives (controls) the refrigerant circulation pump 64 based on the target rotational speed of the refrigerant circulation pump 64 (S7).

[0063] When low-temperature period control is not being executed (when the determination result in S11 is "No"), the fuel cell controller 8 stops the refrigerant circulation pump 64 (S14).

[0064] According to the above configuration, when the power supply state is "ON" and the vehicle 2 is traveling, the upper limit of the rotational speed of the refrigerant circulation pump 64 is set based on the first map. On the other hand, when the power supply state is "ON" and the vehicle 2 is stopped, the upper limit of the rotational speed of the refrigerant circulation pump 64 is set based on the second map. In the second map, the upper limit of the rotational speed of the refrigerant circulation pump 64 is set lower than in the first map. Therefore, when the vehicle 2 is stopped, the target rotational speed of the refrigerant circulation pump 64 is set lower than when the vehicle 2 is traveling. When the vehicle 2 stops (when the vehicle speed is equal to or lower than the stop determination value), it is estimated that the power generation amount of the fuel cell stack 4 decreases, and thus the temperature of the fuel cell stack 4 decreases. Therefore, even if the rotational speed of the refrigerant circulation pump 64 is suppressed, the temperature of the fuel cell stack 4 is prevented from rising. Therefore, it is possible to provide such a fuel cell system 1 that can suppress the negative pressure generated at the inlet of the refrigerant circulation pump 64 and stabilize the temperature of the fuel cell stack 4. Since the negative pressure generated at the inlet of the refrigerant circulation pump 64 is suppressed, deformation of the refrigerant supply passage 61 and cavitation of the refrigerant circulation pump 64 can be suppressed.

[0065] In addition, the second mapping is set such that when the temperature of the fuel cell stack 4 is equal to or higher than a specified temperature threshold, the upper limit of the rotational speed is set lower when the power generation amount of the fuel cell stack 4 is equal to or less than a specified power generation threshold than when the power generation amount of the fuel cell stack 4 is greater than the power generation threshold. Therefore, in a case where the power generation amount is relatively small, compared with a case where the power generation amount is relatively large, even if the temperature of the fuel cell stack 4 is the same in the above two cases, the upper limit of the rotational speed is set lower. When the power generation amount of the fuel cell stack 4 is equal to or less than the power generation threshold, it is estimated that the temperature of the fuel cell stack 4 decreases. Therefore, even if the rotational speed of the refrigerant circulation pump 64 is suppressed, an increase in the temperature of the fuel cell stack 4 is also prevented.

[0066] When the vehicle speed is equal to or lower than a stop determination value, the fuel cell controller 8 sets a lower upper limit of the increasing speed of the rotational speed of the refrigerant circulation pump 64 than when the vehicle speed is higher than the stop determination value. When the vehicle 2 stops, the power generation amount of the fuel cell stack 4 set based on the target driving force decreases. Therefore, even if the rotational speed of the refrigerant circulation pump 64 is suppressed, an increase in the temperature of the fuel cell stack 4 is also prevented.

[0067] In a case where the power supply state is "disconnected" and stop period power generation control or low temperature period control is being executed, a rate limit (the first rate limit or the second rate limit) is set to suppress the target rotational speed. In a case where the power supply state is "disconnected", compared with a case where the power supply state is "connected", it is estimated that the power generation amount of the fuel cell stack 4 decreases, and thus the temperature of the fuel cell stack 4 decreases. Therefore, even if the increasing speed of the rotational speed of the refrigerant circulation pump 64 is suppressed, an increase in the temperature of the fuel cell stack 4 is also prevented. Therefore, it is possible to provide such a fuel cell system 1 that can suppress a negative pressure generated at the inlet of the refrigerant circulation pump 64 and stabilize the temperature of the fuel cell stack 4.

[0068] Specific embodiments of the present invention have been described above, but the present invention should not be limited by the above embodiments, and various modifications and changes can be made within the scope of the present invention.

Claims

1. A fuel cell system installed on a vehicle, the fuel cell system comprising: Fuel cell stack; A refrigerant circulation passage connected to the fuel cell stack, and the refrigerant is configured to circulate through the refrigerant circulation passage; A refrigerant circulation pump arranged in the refrigerant circulation passage and configured to circulate the refrigerant; A storage tank connected to the refrigerant circulation passage via a regulating valve; A vehicle speed sensor configured to obtain the vehicle speed of the vehicle; A temperature acquisition unit configured to acquire the temperature of the fuel cell stack; And A controller configured to control the power generation amount of the fuel cell stack and control the refrigerant circulation pump according to the requested driving force of the vehicle, wherein the controller is configured to set the rotational speed of the refrigerant circulation pump within a range equal to or lower than the rotational speed upper limit based on the temperature of the fuel cell stack, when the vehicle speed is equal to or lower than the stop determination value, compared with when the vehicle speed is higher than the stop determination value, the controller sets the rotational speed upper limit to be lower, and the stop determination value is set to a vehicle speed at which the vehicle can be regarded as stopped, when the vehicle speed is equal to or lower than the stop determination value, and the temperature of the fuel cell stack is equal to or higher than the first temperature threshold and lower than the second temperature threshold higher than the first temperature threshold, when the power generation amount of the fuel cell stack is equal to or lower than the specified power generation threshold, compared with when the power generation amount of the fuel cell stack is higher than the power generation threshold, the controller sets the rotational speed upper limit to be lower, when the vehicle speed is equal to or lower than the stop determination value, the temperature of the fuel cell stack is equal to or higher than the second temperature threshold, and the power generation amount of the fuel cell stack is equal to or lower than the power generation threshold, compared with when the vehicle speed is equal to or lower than the stop determination value, the temperature of the fuel cell stack is equal to or higher than the first temperature threshold and lower than the second temperature threshold, and the power generation amount of the fuel cell stack is equal to or lower than the power generation threshold, the controller sets the rotational speed upper limit to be higher, and when the vehicle speed is equal to or lower than the stop determination value, the temperature of the fuel cell stack is equal to or higher than the second temperature threshold, and the power generation amount of the fuel cell stack is equal to or lower than the power generation threshold, the controller sets the rotational speed upper limit to the same value as the rotational speed upper limit when the vehicle speed is equal to or lower than the stop determination value, the temperature of the fuel cell stack is equal to or higher than the second temperature threshold, and the power generation amount of the fuel cell stack is higher than the power generation threshold.

2. The fuel cell system according to claim 1, wherein, when the vehicle speed is equal to or lower than the stop determination value, compared with when the vehicle speed is higher than the stop determination value, the controller sets the upper limit of the increase speed of the rotational speed of the refrigerant circulation pump to be lower.

3. The fuel cell system according to claim 1, wherein, when the fuel cell stack stops generating power and the temperature of the fuel cell stack is equal to or lower than the specified low temperature threshold, the controller performs low temperature period control to drive the refrigerant circulation pump at a specified low temperature period rotational speed, and In the low-temperature period control, the controller sets the increasing speed of the rotational speed of the refrigerant circulation pump to be lower than the upper limit of the increasing speed of the rotational speed of the refrigerant circulation pump when the vehicle speed is higher than the stop determination value.

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