Fuel cell system

Abstract

To provide a fuel cell system advantageous for reducing a control load required for purging and suppressing power consumption required for control.SOLUTION: A fuel cell system includes: a flow path branching device 14 provided in a discharge flow path 39, of a fuel cell stack 12, on a cathode side; a first bypass flow path 16 discharging gas branched from the flow path branching device 14; and an absorbent 20 provided in the first bypass flow path 16 and absorbing water vapor. Purge treatment of the fuel cell stack 12 is performed by: estimating a water vapor absorption amount that can be absorbed by the absorbent 20 based on a humidity H of the fuel cell stack 12 and a temperature T of the absorbent 20; calculating a time required for purging according to the estimated water vapor absorption amount; and introducing purging gas into the fuel cell stack 12 based on the time required for purging to circulate the purging gas from the fuel cell stack 12 to the first bypass flow path 16.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system. [Background technology]

[0002] In recent years, fuel cell systems have been attracting attention as a power source for automobiles and homes. A fuel cell system is equipped with a fuel cell stack, which is made up of multiple power generating elements called unit cells, each of which includes an anode electrode (hydrogen electrode) to which hydrogen gas is supplied, a cathode electrode (oxygen electrode) to which oxygen gas is supplied, and an electrolyte membrane disposed between these electrodes. Electricity is extracted from the anode electrode and cathode electrode through a chemical reaction between hydrogen and oxygen. Furthermore, water produced at the cathode electrode as a result of the chemical reaction is discharged from the fuel cell stack, while the electrolyte membrane of the fuel cell stack is maintained in an appropriately wet state, thereby generating electricity. In a sub-zero atmosphere, if the water in the gas flow passages inside the fuel cell stack freezes after the operation of the fuel cell is stopped, the chemical reaction does not proceed properly, and the start-up performance of the fuel cell decreases. Therefore, in a sub-zero atmosphere, after the operation of the fuel cell is stopped, it is necessary to carry out a purge (scavenging) in which water in the gas flow passage is forcibly discharged with compressed air. When carrying out purging, it is necessary to estimate the time tp required for purging. In Patent Document 1 (Figures 25 to 27, etc.), when estimating the required purge time tp using a discharge rate map that correlates the required purge time tp with the water content in the fuel cell, the impedance measurement value of the fuel cell is measured in real time, and the drainage rate map is corrected in real time based on the measurement value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5482897 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned conventional technology, the drainage rate map is corrected in real time based on the impedance measurement value of the fuel cell measured in real time, which increases the control load required for purging and leaves room for improvement in terms of reducing power consumption. The present invention has been made in view of the above circumstances, and has as its object to provide a fuel cell system that is advantageous in reducing the control load required for purging and suppressing the power consumption required for control. [Means for solving the problem]

[0005] In order to achieve the above object, one embodiment of the present invention is characterized by comprising: a fuel cell stack; a flow path branching device provided in an exhaust flow path on a cathode side of the fuel cell stack and branching a liquid water flow and a gas flow; a first bypass flow path through which the gas branched from the flow path branching device is discharged; an adsorbent provided in the first bypass flow path and adsorbing water vapor contained in the gas; a first sensor for detecting humidity in the fuel cell stack; a second sensor for detecting a temperature of the adsorbent; a purge time calculation unit that estimates a water vapor adsorption amount adsorbable by the adsorbent based on the humidity in the fuel cell stack detected by the first sensor and the temperature of the adsorbent detected by the second sensor, and calculates a purge time required to purge water from the fuel cell stack in accordance with the estimated water vapor adsorption amount; and a purge control unit that performs a purge process of the fuel cell stack by introducing a purge gas into the fuel cell stack based on the purge time and circulating the purge gas from the fuel cell stack to the first bypass flow path. Furthermore, one embodiment of the present invention is characterized in that it includes a map generation unit that generates a humidity adsorption characteristic curve map that associates an adsorption characteristic curve, which defines the relationship between the purge elapsed time from the start of purging of the fuel cell stack and the amount of water vapor adsorbed by the adsorbent, with the humidity of the fuel cell stack, and a temperature adsorption characteristic curve map that associates the adsorption characteristic curve with the temperature of the adsorbent, and the estimation of the water vapor adsorption amount by the purge required time calculation unit is performed based on the adsorption characteristic curve identified from the humidity adsorption characteristic curve map based on the humidity detected by the first sensor after a predetermined time has elapsed from the start of purging, and the adsorption characteristic curve identified from the temperature adsorption characteristic curve map based on the temperature detected by the second sensor after a predetermined time has elapsed from the start of purging. In one embodiment of the present invention, the flow path branching device is configured as a gas-liquid separator. Furthermore, one embodiment of the present invention further includes a second bypass flow path that introduces high-temperature dry air into the first bypass flow path, bypassing the fuel cell stack, and a third sensor that detects humidity in the first bypass flow path downstream of the adsorbent, and the purge control unit performs a regeneration process for the adsorbent by introducing the dry air from the second bypass flow path into the first bypass flow path after the purge process is completed, and terminates the regeneration process when the humidity detected by the third sensor stabilizes at or below a predetermined threshold value. In one embodiment of the present invention, a back pressure valve is provided in the first bypass flow path downstream of the adsorbent, and the purge control unit reduces the pressure of the dry air by opening the back pressure valve in advance when performing regeneration treatment of the adsorbent. [Effects of the Invention]

[0006] According to one embodiment of the present invention, the required purge time tp can be calculated by a simple process in which the amount of water vapor adsorbed by the adsorbent is estimated based on the detection results of the humidity of the fuel cell stack and the temperature of the adsorbent. This eliminates the need for complex processes as in conventional technology, and is advantageous in reducing the control load required for purging on the control device and suppressing the power consumption required for control. Furthermore, if the estimation of the water vapor adsorption amount by the purge required time calculation unit is performed using the humidity adsorption characteristic curve map and the temperature adsorption characteristic curve map, the control load required for estimating the water vapor adsorption amount can be reduced, which is more advantageous in reducing the control load required for purging in the control device and suppressing the power consumption required for control. Furthermore, if the flow path branching device is configured as a gas-liquid separator, it is possible to prevent liquid water and foreign matter contained in the liquid water from being adsorbed by the adsorbent in the first bypass flow path, which is advantageous in preventing the adsorption of water vapor by the adsorbent from being hindered. Furthermore, if a second bypass flow path is provided that bypasses the fuel cell stack and introduces high-temperature dry air into the first bypass flow path, and the adsorbent is regenerated by introducing dry air from the second bypass flow path into the first bypass flow path, and the regeneration process is terminated when the humidity detected by the third sensor stabilizes at or below a predetermined threshold value, this simple configuration, which uses the first bypass flow path and the second bypass flow path in combination, makes it possible to efficiently perform the adsorbent purging process and regeneration process, and is also advantageous in reducing the control load on the control device. Furthermore, if a back pressure valve is provided downstream of the adsorbent in the first bypass flow path, and the pressure of the high-temperature dry air is reduced by opening the back pressure valve in advance when performing the adsorbent regeneration process, the water vapor from the adsorbent can be reduced in pressure and desorbed using high-temperature dry air with just the simple configuration of providing a back pressure valve, which is advantageous in reducing the cost of the fuel cell system while improving the efficiency of the adsorbent regeneration process. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is an overall configuration diagram of a fuel cell system according to an embodiment; [Figure 2] This is a diagram in which an adsorption characteristic curve, which defines the relationship between the purging time and the adsorption amount of the adsorbent, is correlated with the humidity of the adsorbent, and corresponds to the adsorption characteristic curve map for humidity. [Figure 3] 1 is a diagram in which an adsorption characteristic curve, which defines the relationship between the purging time and the adsorption amount of the adsorbent, is correlated with the temperature of the adsorbent, and corresponds to a temperature adsorption characteristic curve map. [Figure 4] 1 is a diagram showing an adsorption characteristic curve that defines the relationship between the purging time and the adsorption amount of the adsorbent, and that corresponds to the flow velocity of air flowing near the adsorbent. [Figure 5] FIG. 2 is a diagram showing the relationship between the temperature of an adsorbent and the adsorption capacity of the adsorbent. [Figure 6] 1 is a diagram showing the relationship between the relative humidity of air and the adsorption capacity of an adsorbent. [Figure 7] 4 is a flowchart showing a purge process of a fuel cell system. [Figure 8] 1 is a flowchart illustrating a regeneration process of an adsorbent. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the fuel cell system 10 according to the embodiment includes a fuel cell stack 12 (FC stack), a flow path branching device 14, a first bypass flow path 16, a second bypass flow path 18, an adsorbent 20, a first sensor 22, a second sensor 24, a third sensor 26, a back pressure valve 28, and a control device 30. In this embodiment, a case will be described in which the fuel cell system 10 is mounted on a vehicle (electric vehicle) and used as a battery that supplies power to a drive motor. Note that the vehicle referred to here is assumed to be a fuel cell vehicle (FCV) equipped with only the fuel cell system 10, but it may also be a plug-in hybrid fuel cell vehicle that is provided with a separate battery pack that supplies power to the motor and is capable of external charging or external power supply.

[0009] The fuel cell stack 12 is constructed by stacking multiple power generating elements called single cells, each of which includes an anode electrode (hydrogen electrode) to which hydrogen gas is supplied, a cathode electrode (oxygen electrode) to which oxygen gas (air) is supplied, and an electrolyte membrane disposed between the electrodes, although neither is shown. An anode gas flow passage through which hydrogen gas flows is formed on the anode electrode side, and a cathode gas flow passage through which oxygen gas flows is formed on the cathode electrode side. Electrons are removed from the hydrogen gas by the anode electrode, and the hydrogen ions generated by the removal of the electrons pass through the electrolyte membrane and reach the cathode electrode. On the other hand, oxygen gas is given electrons from the cathode electrode, and becomes oxygen ions, which combine with hydrogen ions that have passed through the electrolyte membrane to produce water. By connecting an external circuit (load) between the cathode electrode and the anode electrode, power is supplied to the external circuit. In this way, electricity is extracted from the anode and cathode electrodes of the fuel cell stack 12 through the chemical reaction between hydrogen and oxygen.

[0010] The inlet of the anode gas flow channel is connected to a hydrogen tank via a hydrogen gas supply channel 32, and the outlet of the anode gas flow channel is connected to a first liquid water discharge channel 38A via an anode gas-liquid separator . The anode gas-liquid separator 36 separates a liquid (liquid water) from the hydrogen gas supplied from the outlet of the anode gas flow path and supplies the liquid to a first liquid water discharge path 38A, while supplying the hydrogen gas to a hydrogen gas circulation path 42 in which a hydrogen gas recirculation pump 40 is installed. The liquid supplied to the first liquid water discharge path 38A is discharged to the outside of the fuel cell stack 12 via a second liquid water discharge path 38B, which will be described later. The inlet of the anode gas flow path and the anode gas-liquid separator 36 are connected via a hydrogen gas circulation path 42 . The hydrogen gas supply passage 32 is also provided with a first hydrogen gas regulation valve 44A that regulates the amount of hydrogen gas supplied from the hydrogen tank 34 to the anode gas passage. In addition, a second hydrogen gas adjustment valve 44B is provided in the hydrogen gas circulation path 42 upstream of the hydrogen gas recirculation pump 40 in the direction in which the hydrogen gas flows, to adjust the amount of hydrogen gas separated from the anode gas-liquid separator 36 that is supplied to the anode gas flow path.

[0011] The inlet of the cathode gas flow channel is connected to an air compressor 48 via an oxygen gas supply channel 46, and the outlet of the cathode gas flow channel is connected to a second liquid water discharge channel 38B. The air compressor 48 compresses atmospheric air to generate and supply high-temperature dry air. The temperature of the dry air is, for example, about 60°C to 80°C, and the temperature of the dry air supplied from the air compressor 48 does not change during operation of the fuel cell system 10, even during the purging process and the regeneration process of the adsorbent 20, which will be described later. The second liquid water discharge channel 38B is connected to the channel branching device 14 via a branch channel 3802 provided midway in the extension direction thereof.

[0012] The second bypass flow path 18 bypasses the fuel cell stack 12 and connects the oxygen gas supply flow path 46 to the flow path branching device 14, and as described below, introduces high-temperature dry air supplied from the air compressor 48 into the first bypass flow path 16 via the flow path branching device 14.

[0013] The flow path branching device 14 is provided in the discharge flow path 39 on the cathode side of the fuel cell stack 12, which is constituted by the second liquid water discharge path 38B including the branch flow path 3802, and branches the flow of liquid water and the flow of gas. In this embodiment, the flow path branching device 14 is composed of a cathode gas-liquid separator 50, which separates a liquid (liquid water) from a gas (air) supplied from an outlet of the cathode gas flow path, and supplies the liquid to a second liquid water discharge path 38B via a third liquid water discharge path 38C, while supplying the air to a first bypass flow path 16, which will be described later. The liquid supplied to the third liquid water discharge path 38C is discharged to the outside of the fuel cell stack 12 via the second liquid water discharge path 38B.

[0014] In the drawing, reference numeral 52A denotes a first air on-off valve interposed in the oxygen gas supply flow path 46. The first air on-off valve 52A supplies air from the air compressor 48 to the cathode gas flow path when it is opened, and stops the supply of air from the air compressor 48 to the cathode gas flow path when it is closed.

[0015] Also, reference numeral 52B denotes a second air on-off valve disposed in the second bypass flow path 18. The second air on-off valve 52B supplies air from the air compressor 48 to the second bypass flow path 18 when opened, and stops the supply of air from the air compressor 48 to the second bypass flow path 18 when closed.

[0016] Furthermore, reference numeral 52C denotes a third air on-off valve interposed in the branch flow path 3802, in other words, interposed between the cathode gas-liquid separator 50 and the second bypass flow path 18 and the second liquid water discharge path 38B. The third air on-off valve 52C supplies air to the cathode gas-liquid separator 50 when it is opened, and stops the supply of air to the cathode gas-liquid separator 50 when it is closed.

[0017] Furthermore, reference numeral 52D denotes a fourth air on-off valve 52D that is interposed in the second liquid water discharge passage 38B at a location downstream of the cathode gas-liquid separator 50 in the air flow direction. The fourth air on-off valve 52D supplies air to the second liquid water discharge channel 38B when it is open, and stops the supply of air to the second liquid water discharge channel 38B when it is closed.

[0018] Furthermore, reference numeral 54A denotes a first check valve interposed in the second bypass flow path 18, and reference numeral 54B denotes a second check valve provided in the second liquid water discharge path 38B. The above-mentioned first hydrogen gas regulating valve 44A, second hydrogen gas regulating valve 44B, first air on-off valve 52A, second air on-off valve 52B, third air on-off valve 52C, and fourth air on-off valve 52D are controlled by a control device 30 described later.

[0019] The first bypass flow path 16 discharges the gas (air) separated by the cathode gas-liquid separator 50 to the outside of the fuel cell stack 12.

[0020] The adsorbent 20 is provided in the first bypass flow path 16 and adsorbs water vapor contained in the gas flowing through the first bypass flow path 16. As the adsorbent 20, a water vapor adsorbing porous body capable of adsorbing water vapor can be used. As such a water vapor adsorbing porous body, various conventionally known desiccants that can absorb moisture, such as silica gel, and can be regenerated by desorbing (drying) the absorbed moisture, can be used.

[0021] The first sensor 22 is provided in the fuel cell stack 12, detects the temperature and humidity H of the fuel cell stack 12, and supplies the detection results to a control device 30, which will be described later. In this embodiment, the detection results of the temperature of the fuel cell stack 12 are used, for example, when the fuel cell stack 12 is in operation, but are not used during the purging process or the regeneration process of the adsorbent 20, which will be described later, and therefore, the temperature detection results of the first sensor 22 will not be described below. The second sensor 24 is provided in the adsorbent 20, detects the temperature T of the adsorbent 20, and supplies the detection result to the control device 30, which will be described later. The third sensor 26 is provided at a location downstream of the adsorbent 20 in the first bypass flow path 16, detects the humidity at a location downstream of the adsorbent 20 in the first bypass flow path 16, and supplies the detection result to the control device 30 described later.

[0022] The back pressure valve 28 is provided in the first bypass flow path 16 at a location downstream of the adsorbent 20, and its opening degree is adjusted by the control device 30 described later, thereby adjusting the back pressure of the first bypass flow path 16. In this embodiment, the pressure of the air flowing from the air compressor 48 to the first bypass flow path 16, in other words, the back pressure of the first bypass flow path 16, is adjusted by the back pressure valve 28 to between atmospheric pressure and, for example, 2 atmospheres.

[0023] The control device 30 is responsible for controlling the fuel cell system 10, and is composed of a CPU, a ROM for storing and memorizing control programs, etc., a RAM as the operating area for the control programs, a memory unit such as an EEPROM for storing various data in a rewritable manner, and an interface unit for interfacing with peripheral circuits, etc., all of which are not shown. The control device 30 functions as a purge required time calculation unit 30A, a map generation unit 30B, and a purge control unit 30C by the CPU executing a control program.

[0024] The purge time calculation unit 30A estimates the amount of water vapor adsorption that can be adsorbed by the adsorbent 20 based on the humidity H of the fuel cell stack 12 detected by the first sensor 22 and the temperature T of the adsorbent 20 detected by the second sensor 24, and calculates the purge time tp required to purge the water in the fuel cell stack 12 based on the estimated amount of water vapor adsorption.

[0025] The map generating section 30B generates a humidity adsorption characteristic curve map and a temperature adsorption characteristic curve map. The humidity adsorption characteristic curve map is a map in which an adsorption characteristic curve that defines the relationship between the purge elapsed time t from the start of purging of the fuel cell stack 12 and the amount A of water vapor adsorbed by the adsorbent 20 is associated with the humidity H of the fuel cell stack 12. The temperature adsorption characteristic curve map is a map in which an adsorption characteristic curve that defines the relationship between the purge elapsed time t and the amount A of water vapor adsorbed by the adsorbent 20 is associated with the temperature T of the adsorbent 20 . The humidity adsorption characteristic curve map and the temperature adsorption characteristic curve map may be generated by the map generation unit 30B, for example, by reading out data of each humidity adsorption characteristic curve stored in a recording medium, or by calculating based on a correlation equation for calculating each humidity adsorption characteristic curve.

[0026] Here, the adsorption characteristic curve, the humidity adsorption characteristic curve map, and the temperature adsorption characteristic curve map will be described in detail. FIG. 2 corresponds to the adsorption characteristic curve map for humidity generated by the map generation unit 30B, and is a diagram in which the adsorption characteristic curve defining the relationship between the purge elapsed time t and the adsorption amount A of the adsorbent 20 is associated with the humidity H = H1, H2, H3, H4 (where H1 > H2 > H3 > H4) of the fuel cell stack 12 detected by the first sensor 22. The temperature T is assumed to be constant. It can be seen that as the purge elapsed time t elapses, the adsorption amount A increases, and the higher the humidity H, the greater the increase in the adsorption amount A. Also, for each adsorption characteristic curve, when a certain amount of purge elapsed time t has passed, the adsorption amount A reaches its respective upper limit value, and after that, even as time passes, the adsorption amount A hardly increases.

[0027] FIG. 3 corresponds to the adsorption characteristic curve map for temperature generated by the map generation unit 30B, and is a diagram in which the relationship between the purge elapsed time t and the adsorption amount A of the adsorbent 20 is associated with the temperature T = T1, T2, T3, T4 (where T1 < T2 < T3 < T4) of the adsorbent 20. The humidity H is assumed to be constant. It can be seen that as the purge elapsed time t elapses, the adsorption amount A increases, and the lower the temperature T, the greater the increase in the adsorption amount A. Also, for each adsorption characteristic curve, when a certain amount of purge elapsed time t has passed, the adsorption amount A reaches its respective upper limit value, and after that, even as time passes, the adsorption amount A hardly increases.

[0028] FIG. 4 is a diagram in which the adsorption characteristic curve defining the relationship between the purge elapsed time t and the adsorption amount A of the adsorbent 20 is associated with the air flow velocity U = U1, U2, U3, U4 (where U1 > U2 > U3 > U4) flowing near the adsorbent 20. The humidity H and the temperature T are assumed to be constant. It can be seen that as the purge elapsed time t elapses, the adsorption amount A increases, and the higher the flow velocity U, the greater the increase in the adsorption amount A. Also, each adsorption characteristic curve converges to a substantially the same upper limit value of the adsorption amount A when a certain amount of purge elapsed time t has passed, and after that, even as time passes, the adsorption amount A hardly increases.

[0029] As shown in FIGS. 2, 3, and 4, it can be seen that the amount of adsorption A that the adsorbent 20 can adsorb is dependent on the humidity H, temperature T, and flow rate U as environmental conditions. The dependency of the adsorbent 20 will be further explained below. FIG. 5 is a diagram showing the adsorption capacity of the adsorbent 20 versus the temperature T (° C.) when the pressure (ambient pressure) of the environment in which the adsorbent 20 is placed is a predetermined atmospheric environmental condition (for example, 1.3 kPa). Looking at the example of silica gel in Figure 5, we can see that the adsorption capacity decreases as the temperature increases. FIG. 6 is a graph showing the adsorption capacity of the adsorbent 20 versus the relative humidity (% RH) when the temperature (ambient temperature) of the environment in which the adsorbent 20 is placed is a predetermined temperature condition (for example, 25° C.). Looking at the example of silica gel in Figure 6, we can see that the adsorption capacity increases as the relative humidity increases. The activated alumina and molecular sieve shown in FIGS. 5 and 6 are recyclable desiccants like silica gel, and can be used in the present embodiment in the same way as silica gel.

[0030] Therefore, as explained with reference to FIG. 2, if the humidity H is known, the adsorption characteristic curve can be specified or estimated. Therefore, for example, if 90% of the upper limit value of the adsorption amount A is set as the threshold value, the required purge time tp required to reach the threshold value can be instantly calculated by the required purge time calculation unit 30A from the humidity adsorption characteristic curve map of FIG. 2. As will be explained with reference to FIG. 3, if the temperature T is known, the adsorption characteristic curve can be identified or estimated. Therefore, for example, if 90% of the upper limit of the adsorption amount A is set as the threshold value, the required purge time tp required to reach the threshold value can be instantly calculated by the required purge time calculation unit 30A from the temperature adsorption characteristic curve map of FIG. 3. Note that, because the actual adsorption amount A is affected by both humidity H and temperature T, the final required purge time tp may be obtained by calculating the average value of two required purge times tp, namely, the required purge time tp calculated from Fig. 2 and the required purge time tp calculated from Fig. 3. Alternatively, the final required purge time tp may be obtained by calculating the average value after appropriately weighting the two required purge times tp. Furthermore, the method of obtaining the final required purge time tp from the two required purge times tp, taking into account the effects of both humidity H and temperature T, is not limited to the above example. Alternatively, the map generating unit 30B may generate a three-dimensional adsorption characteristic curve map that defines three values: the purge elapsed time t, the adsorption amount A associated with the humidity H, and the adsorption amount A associated with the temperature T; in other words, a three-dimensional adsorption characteristic curve map that includes the adsorption characteristic curve map for humidity and the adsorption characteristic curve map for temperature, rather than generating the humidity adsorption characteristic curve map and the temperature adsorption characteristic curve map separately. In this case, the required purge time tp can be immediately calculated by the required purge time calculation unit 30A from the three-dimensional adsorption characteristic curve map.

[0031] As for the flow velocity U, as shown in FIG. 4, the upper limit values ​​of the respective adsorption characteristic curves converge to a single value. Therefore, when, for example, 90% of the upper limit value is set as the threshold value, the threshold value becomes a single value, and the purge time tp required to reach the threshold value of the adsorption amount A differs for each flow velocity U. However, the flow rate U is a fixed value determined by the specifications of the fuel cell system 10 (fuel cell stack 12) regardless of the environment surrounding the fuel cell system 10 (fuel cell stack 12). Therefore, there is no need to consider the influence of changes in the flow rate U when calculating the required purge time tp. In the above explanation, the threshold values ​​for humidity H, temperature T, and flow rate U are set to 90% of the upper limit of the adsorption amount A, but these threshold values ​​do not need to be the same, and the threshold values ​​can be set to any value other than 90% of the upper limit.

[0032] As described above, in this embodiment, the estimation of the water vapor adsorption amount by the purge duration calculation unit 30A is performed based on the adsorption characteristic curve identified from the humidity adsorption characteristic curve map based on the humidity H detected by the first sensor 22 after a predetermined time has elapsed since the start of purge, and the adsorption characteristic curve identified from the temperature adsorption characteristic curve map based on the temperature T detected by the second sensor 24 after a predetermined time has elapsed since the start of purge.

[0033] The purge control unit 30C performs a purge process on the fuel cell stack 12 by introducing purge gas (dry air supplied from the air compressor 48) from the air compressor 48 to the fuel cell stack 12 based on the calculated purge time tp and circulating the purge gas from the fuel cell stack 12 to the first bypass flow path 16. After the purge process is completed, the purge control unit 30C introduces dry air from the air compressor 48 from the second bypass flow path 18 to the first bypass flow path 16 to regenerate the adsorbent 20, which will be described later, and terminates the regeneration process when the humidity detected by the third sensor 26 stabilizes at or below a predetermined threshold value. Furthermore, when performing the regeneration treatment of the adsorbent 20, the purge control unit 30C opens the back pressure valve 28 in advance to reduce the pressure of the dry air. The specific operation of the purge control unit 30C will be described with reference to the flowcharts of FIGS.

[0034] First, the purge process in the fuel cell system 10 will be described with reference to the flowchart of FIG. The control device 30 determines whether the operation of the fuel cell system 10 has stopped (step S10). If the result in step S10 is negative, the purging process is not necessary, and the process thereafter is skipped and the process is terminated. If step S10 is positive, the control device 30 determines whether or not the purge condition is met (step S12). The purge condition is that there is a risk of water freezing inside the fuel cell stack 12, and more specifically, whether the temperature detection result of the first sensor 22 or the temperature detection result of the second detection sensor is zero degrees or close to zero degrees. Note that it is optional to use the temperature detection result of an outside air temperature sensor mounted on the vehicle to determine the purge condition.

[0035] If the result in step S12 is negative, the purging process is not necessary, and the process thereafter is skipped and the process is terminated. If step S12 is positive, the control device 30 (purge control unit 30C) closes the second air on-off valve 52B and the fourth air on-off valve 52D, opens the first air on-off valve 52A and the third air on-off valve 52C (step S14), and throttles the backpressure valve 28 to increase the backpressure of the first bypass flow path 16 to, for example, 2 atmospheres (step S16). As a result, the high-temperature dry air supplied from the air compressor 48 passes through the fuel cell stack 12 and is guided via the cathode gas-liquid separator 50 to the first bypass flow path 16, thereby starting the purging process (step S18). That is, the high-temperature dry air efficiently removes moisture (water vapor) from inside the fuel cell stack 12, and then the moisture is discharged toward the first bypass flow path 16. In the first bypass flow path 16, the dry air with a back pressure increased to 2 atmospheres flows, and the water vapor is efficiently adsorbed by the adsorbent 20 in a short time.

[0036] Next, the control device 30 (purging time calculation unit 30A) acquires the detection result of the humidity H from the first sensor 22 and the detection result of the temperature T from the second sensor 24 (step S20). Then, based on the detection results of the acquired humidity H and temperature T, the purge required time tp is calculated from the humidity adsorption characteristic curve map (FIG. 2) and the temperature adsorption characteristic curve map (FIG. 3) generated by the map generating unit 30B (step S22).

[0037] Next, the control device 30 (purge control section 30C) determines whether or not the required purge time tp has elapsed since the start of the purge process (step S24). If the result of step S24 is negative, the process returns to step S24 and the purge process continues. If step S24 is positive, the first air on-off valve 52A is closed, the supply of air from the air compressor 48 to the fuel cell stack 12 is stopped, and the purging process is ended (step S26). This purging process purges the moisture inside the fuel cell stack 12, preventing a decrease in the start-up performance of the fuel cell system 10 (fuel cell stack 12) due to frozen moisture in cold conditions such as below freezing.

[0038] Next, the regeneration process of the adsorbent 20 in the fuel cell system 10 will be described with reference to the flowchart of FIG. The regeneration treatment of the adsorbent 20 means desorbing the water vapor adsorbed by the adsorbent 20 to regenerate the water vapor adsorption function of the adsorbent 20. First, the control device 30 determines whether or not the regeneration process condition is met (step S50). The regeneration processing condition is, for example, that the purge processing in FIG. 7 has been completed, in other words, that the required purge time tp has elapsed. If step S50 is negative, the process returns to step S50. If step S50 is positive, the control device 30 (purge control section 30C) opens the second air on-off valve 52B (step S52), thereby enabling high-temperature dry air supplied from the air compressor 48 to be supplied from the second bypass flow path 18 to the first bypass flow path 16.

[0039] Then, the control device 30 (purge control unit 30C) opens the back pressure valve 28 to reduce the back pressure of the first bypass flow path 16 to atmospheric pressure, and supplies high-temperature dry air supplied from the air compressor 48 to the first bypass flow path 16, thereby starting the regeneration process (step S54). At this time, by reducing the back pressure of the first bypass flow path 16 to atmospheric pressure, the high-temperature dry air supplied from the air compressor 48 flows in a reduced-pressure state through the first bypass flow path 16. As a result, the water vapor adsorbed to the adsorbent 20 is desorbed under reduced pressure, and the regeneration process of the adsorbent 20 is performed efficiently in a short time.

[0040] Next, the control device 30 (purge control unit 30C) starts the operation of the third sensor 26 and acquires from the third sensor 26 the humidity detection result at a location downstream of the adsorbent 20 in the first bypass flow path 16 (step S56).

[0041] Next, the control device 30 (purge control unit 30C) determines whether the humidity detection result acquired from the third sensor 26 has stabilized at a predetermined threshold value (e.g., 1% RH) or less (step S58). Whether the humidity detection result has stabilized may be determined, for example, by whether multiple consecutively acquired humidity detection results are all below the predetermined threshold value. If step S58 is negative, the process returns to step S58. If step S58 is positive, the control device 30 (purge control unit 30C) determines that water vapor has been desorbed from the adsorbent 20 and regeneration of the adsorbent 20 has been completed, and therefore closes the second air on-off valve 52B and the third air on-off valve 52C to stop the flow of air from the second bypass flow path 18 to the first bypass flow path 16, and terminates the operation of the third sensor 26 (step S60), thereby completing the regeneration process of the adsorbent 20. If the fuel cell system 10 is not operated after the regeneration process, the operation of the air compressor 48 is stopped after the regeneration process.

[0042] According to this embodiment, the system includes a flow path branching device 14 provided in the discharge flow path 39 on the cathode side of the fuel cell stack 12, a first bypass flow path 16 that discharges gas branched from the flow path branching device 14, and an adsorbent 20 provided in the first bypass flow path 16 that adsorbs water vapor contained in the gas.The amount of water vapor adsorption that can be achieved by the adsorbent 20 is estimated based on the humidity H of the fuel cell stack 12 and the temperature T of the adsorbent 20, and a purge time tp required to purge the water in the fuel cell stack 12 is calculated in accordance with the estimated water vapor adsorption amount.Purge gas is introduced into the fuel cell stack 12 based on the purge time tp, and the purge gas is circulated from the fuel cell stack 12 to the first bypass flow path 16, thereby performing a purge process on the fuel cell stack 12. Therefore, the purge time tp can be calculated by a simple process such as calculating it from the amount of water vapor adsorption of the adsorbent 20 estimated based on the humidity H of the fuel cell stack 12 and the detection results of the temperature T of the adsorbent 20 detected by the second sensor 24. Therefore, there is no need for complex processing such as measuring the impedance value of the fuel cell in real time and correcting the drainage speed map in real time based on that measurement value, as in conventional technology, which is advantageous in reducing the control load required for purging in the control device 30 and suppressing the power consumption required for control.

[0043] Furthermore, in this embodiment, the estimation of the water vapor adsorption amount by the purge required time calculation unit 30A is performed using the humidity adsorption characteristic curve map and the temperature adsorption characteristic curve map, which reduces the control load required for estimating the water vapor adsorption amount, and is more advantageous in reducing the control load required for purging in the control device 30 and suppressing the power consumption required for control.

[0044] Note that, as the flow path branching device 14, for example, a three-way valve that branches the flow of liquid water and the flow of gas may be used. However, if the flow path branching device 14 is configured as a gas-liquid separator as in the present embodiment, it is possible to prevent the liquid water and foreign matter contained in the liquid water from being adsorbed by the adsorbent 20 in the first bypass flow path 16, which is advantageous in preventing the adsorption of water vapor by the adsorbent 20 from being hindered.

[0045] In addition, in this embodiment, a second bypass flow path 18 is provided to introduce high-temperature dry air into the first bypass flow path 16, bypassing the fuel cell stack 12. After the purge process is completed, dry air is introduced from the second bypass flow path 18 into the first bypass flow path 16 to regenerate the adsorbent 20. The regeneration process is terminated when the humidity detected by the third sensor 26 stabilizes at or below a predetermined threshold value. Therefore, by using a simple configuration in which the first bypass flow path 16 and the second bypass flow path 18 are combined, purging and regeneration processes using the adsorbent 20 can be performed efficiently, and this is also advantageous in reducing the control load on the control device 30.

[0046] In addition, in this embodiment, a back pressure valve 28 is provided in the first bypass flow path 16 at a location downstream of the adsorbent 20, and when performing regeneration treatment of the adsorbent 20, the back pressure valve 28 is opened in advance to reduce the pressure of the high-temperature dry air. Therefore, with a simple configuration such as providing the back pressure valve 28, the water vapor in the adsorbent 20 can be decompressed and desorbed using high-temperature dry air, which is advantageous in terms of reducing the cost of the fuel cell system 10 and improving the efficiency of the regeneration process of the adsorbent 20. [Explanation of symbols]

[0047] 10. Fuel Cell System 12 Fuel cell stack (FC stack) 14 Flow path branching device 16 First bypass flow path 18 Second bypass flow path 20 Adsorbents 22 First sensor 24 Second sensor 26 Third Sensor 28 Back pressure valve 30 Control device 30A Purge time calculation section 30B Map generation unit 30C Purge control unit 32 Hydrogen gas supply line 34 Hydrogen Tank 36 Anode gas-liquid separator 38A 1st liquid water discharge channel 38B 2nd liquid water discharge channel 38C 3rd liquid water discharge channel 3802 Branch channel 39 Discharge flow path 40 Hydrogen gas recirculation pump 42 Hydrogen gas circulation path 44A Hydrogen gas first adjusting valve 44B Hydrogen gas second adjusting valve 46 Oxygen gas supply channel 48 Air Compressor 50 Cathode gas-liquid separator 52A First Air On-Off Valve 52B Second air shut-off valve 52C Air third shut-off valve 52D No. 4 air shutoff valve 54A First check valve 54B Second check valve

Claims

1. a fuel cell stack; a flow path branching device that is provided in an exhaust flow path on the cathode side of the fuel cell stack and that branches a liquid water flow and a gas flow; a first bypass flow path that discharges the gas branched from the flow path branching device; an adsorbent provided in the first bypass flow path and configured to adsorb water vapor contained in the gas; a first sensor for detecting humidity in the fuel cell stack; a second sensor for detecting the temperature of the adsorbent; a required purge time calculation unit that estimates a water vapor adsorption amount that can be adsorbed by the adsorbent based on the humidity of the fuel cell stack detected by the first sensor and the temperature of the adsorbent detected by the second sensor, and calculates a required purge time required to purge water from within the fuel cell stack in accordance with the estimated water vapor adsorption amount; a purge control unit that performs a purge process on the fuel cell stack by introducing a purge gas into the fuel cell stack based on the required purge time and circulating the purge gas from the fuel cell stack to the first bypass flow path; A fuel cell system comprising:

2. a map generating unit that generates a humidity adsorption characteristic curve map that associates an adsorption characteristic curve, which defines the relationship between the amount of water vapor adsorbed by the adsorbent and the purging time elapsed since the start of purging of the fuel cell stack, with the humidity of the fuel cell stack, and a temperature adsorption characteristic curve map that associates the adsorption characteristic curve with the temperature of the adsorbent, the estimation of the water vapor adsorption amount by the purge required time calculation unit is performed based on the adsorption characteristic curve identified from the humidity adsorption characteristic curve map based on the humidity detected by the first sensor after a predetermined time has elapsed since the start of the purge, and the adsorption characteristic curve identified from the temperature adsorption characteristic curve map based on the temperature detected by the second sensor after a predetermined time has elapsed since the start of the purge.

2. The fuel cell system according to claim 1.

3. The flow path branching device is composed of a gas-liquid separator.

2. The fuel cell system according to claim 1.

4. a second bypass flow path that bypasses the fuel cell stack and introduces high-temperature dry air into the first bypass flow path; a third sensor that detects humidity in the first bypass flow path downstream of the adsorbent, the purge control unit, after the purge process is completed, performs a regeneration process of the adsorbent by introducing the dry air from the second bypass flow path to the first bypass flow path, and terminates the regeneration process when the humidity detected by the third sensor becomes stable at or below a predetermined threshold value.

4. The fuel cell system according to claim 1, wherein the fuel cell system comprises: a first electrode;

5. a back pressure valve is provided in the first bypass flow path downstream of the adsorbent; the purge control unit reduces the pressure of the dry air by opening the back pressure valve in advance when performing the regeneration treatment of the adsorbent.

5. The fuel cell system according to claim 4.

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