Fuel cell system

Abstract

Fuel cell system, comprising: a first fuel cell (4a) and a second fuel cell (4b); a first purging device (14a) and a second purging device (14b) that can purge the first fuel cell (4a) and the second fuel cell (4b) independently of each other, wherein the first purging device (14a) is a first air compressor that supplies oxygenated air as cathode gas to the first fuel cell (4a) and the second purging device (14b) is a second air compressor that supplies oxygenated air as cathode gas to the second fuel cell (4a); and a control device (2) configured to control the first and second flushing devices (14a, 14b; 29a, 29b; 26a, 26b), wherein the control device (2) is configured to to control the rotational speed of the first rinsing device (14a) and the rotational speed of the second rinsing device (14b) so that they are equal to each other, to control the purge time of the first fuel cell (4a) so that it is shorter than the purge time of the second fuel cell (4b), and to start and complete the purging of the first fuel cell (4a) within a period in which the purging of the second fuel cell (4b) is carried out, where the electrical power generation volume of the second fuel cell (4b) is smaller than the electrical power generation volume of the first fuel cell (4a), the first fuel cell (4a) and the second fuel cell (4b) are purged when an ignition state of the fuel cell system is changed to an OFF state, and the control device (2) is configured to purge the first fuel cell (4a) with an amount of consumed electrical power that is less than the amount of electrical power consumed by purging the second fuel cell (4b).

Description

BACKGROUND OF THE INVENTION 1. Scope of the invention

[0001] The invention relates to a fuel cell system. 2. Description of the state of the art

[0002] It is known in the prior art to flush a fuel cell in order to drain the liquid water remaining in the fuel cell. For example, in Japanese patent application JP 2005-276529A, one or more of a plurality of fuel cells in a system equipped with the plurality of fuel cells are flushed (see JP 2005-276529A). A fuel cell system comprising a secondary battery, first and second fuel cells, and first and second flushing devices configured to flush the first and second fuel cells respectively, is the subject of DE 10 2019 123049A1.A control device is configured to perform a first purging process in which the first fuel cell is purged by driving the first purging device using charged power from the secondary battery when the first and second fuel cells are in a state of suspended power generation, and to perform a second purging process in which the second fuel cell is purged by driving the second purging device using generated power from the first fuel cell when the first fuel cell is in a power generation state and the second fuel cell is in a state of suspended power generation, wherein the control device is configured to perform the first purging process and then perform the second purging process when ignition is switched on. SUMMARY OF THE INVENTION

[0003] The amount of electrical power consumed by such a flushing process should be small, but it is also necessary to remove sufficient water from the fuel cells through flushing.

[0004] The invention provides a fuel cell system that can adequately drain water from at least one of a plurality of fuel cells while suppressing an increase in the amount of electrical power consumed by the purging process.

[0005] One aspect of the invention relates to a fuel cell system. This fuel cell system is equipped with a first fuel cell, a second fuel cell, a first purging device, and a second purging device that can purge the first fuel cell and the second fuel cell independently of each other, wherein the first purging device is a first air compressor that supplies oxygen-containing air as cathode gas to the first fuel cell, and the second purging device is a second air compressor that supplies oxygen-containing air as cathode gas to the second fuel cell (4a), and a control device configured to control the first and second purging devices.The control device is configured to control the rotational speed of the first purging device and the rotational speed of the second purging device so that they are equal to each other, to control the purging time of the first fuel cell so that it is shorter than the purging time of the second fuel cell, and to start and complete the purging of the first fuel cell within a period in which the purging of the second fuel cell is carried out. The generating volume of electrical power or current generation volume of the second fuel cell is less than the generating volume of electrical power or current generation volume of the first fuel cell.The first fuel cell and the second fuel cell are purged when an ignition state of the fuel cell system is changed to an OFF state, and the control device is configured to purge the first fuel cell with an amount of consumed electrical power that is less than the amount of electrical power consumed by purging the second fuel cell.

[0006] The amount of liquid water remaining in the fuel cell decreases as the volume of electrical power generated decreases. Therefore, the amount of electrical power required to sufficiently remove water through purging is less in the second fuel cell, which has a small volume of electrical power generated, than in the first fuel cell, which has a large volume of electrical power generated. Consequently, sufficient water can be removed from the second fuel cell with a small amount of electrical power consumed by purging the second fuel cell.

[0007] The control device can be configured to purge the first fuel cell and the second fuel cell in such a way that the purge time of the first fuel cell and the purge time of the second fuel cell overlap at least partially.

[0008] The fuel cell system can be equipped with a third fuel cell that has a greater electrical power output than the second fuel cell. The first and second purging devices can be capable of purging the first, second, and third fuel cells independently. The control device does not need to be configured to purge the third fuel cell.

[0009] Each of the first and second fuel cells can be equipped with a plurality of individual cells, respectively. The electrical power output of each individual cell can be a value obtained by multiplying the power output area of ​​each individual cell by the electrode thickness of each individual cell. The electrical power output of the first fuel cell can be the sum of the electrical power outputs of the plurality of individual cells with which the first fuel cell is equipped. The electrical power output of the second fuel cell can be the sum of the electrical power outputs of the plurality of individual cells with which the second fuel cell is equipped. The control device can be configured to stop electrical power output when the generation of electrical power ceases.Power generation through the first fuel cell and the second fuel cell only to purge the second fuel cell.

[0010] A fuel cell system is created that can adequately remove water from at least one of a plurality of fuel cells, while suppressing an increase in the amount of electrical power consumed by flushing. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The features and advantages as well as the technical and economic significance of an exemplary embodiment of the invention are described below with reference to the accompanying drawings, in which reference numerals denote identical elements; here, the following are shown: Fig. 1 a configuration view of a fuel cell system installed in a vehicle; Fig. 2A and Fig. 2B Explanatory views of a fuel cell's electrical power generation volume; Fig. 3 a flowchart showing an example of a flushing control system; Fig. 4 a time diagram showing an example of the flushing control; Fig. 5 a flowchart showing a modified example of the flushing control; Fig. 6 a timeline showing the modified example of the flushing control; Fig. 7A a view showing three fuel cells used in the system; Fig. 7B a view showing three fuel cells used in the system; and Fig. 7C is a view showing three fuel cells used in the system. DETAILED DESCRIPTION OF EXECUTION FORM Fuel cell system configuration

[0012] Fig. Figure 1 is a configuration view of a fuel cell system (hereinafter referred to simply as the system) 1, installed in a vehicle. The system 1 includes an electronic control unit (an ECU) 2, fuel cells (hereinafter referred to as FCs) 4a, 4b, secondary batteries (hereinafter referred to as BATs) 8a, 8b, cathode gas supply systems 10a, 10b, anode gas supply systems 20a, 20b, electrical power control systems 30a, 30b, a motor 50, and the like. The system 1 includes a cooling system (not shown) that cools the FCs 4a, 4b by circulating coolant through them.

[0013] Each of the fuel cells 4a and 4b is a fuel cell that generates electrical power or current when supplied with cathode gas and anode gas. Each of the fuel cells 4a and 4b is obtained by stacking a plurality of individual cells of the polyelectrolyte type. In the present embodiment, the fuel cell 4b is smaller than the fuel cell 4a and also has a lower rated power. In particular, the fuel cells 4a and 4b are obtained by stacking the same individual cells, and the number of stacked individual cells in the fuel cell 4b is smaller than the number of stacked individual cells in the fuel cell 4a. The fuel cell 4b has a smaller electrical power-generating volume than the fuel cell 4a. The fuel cell 4a is an example of the first fuel cell, and the fuel cell 4b is an example of the second fuel cell (details are described later).

[0014] The cathode gas supply systems 10a, 10b supply air containing oxygen as cathode gas to the FCs 4a, 4b. In particular, the cathode gas supply systems 10a, 10b include supply lines 11a, 11b, exhaust lines 12a, 12b, bypass lines 13a, 13b, air compressors (hereinafter referred to as ACPs) 14a, 14b, bypass valves 15a, 15b, charge air coolers 16a, 16b and backpressure valves 17a, 17b.

[0015] Supply lines 11a and 11b are connected to the cathode inlet manifolds of FCs 4a and 4b. Exhaust lines 12a and 12b are connected to the cathode outlet manifolds of FCs 4a and 4b. Bypass line 13a connects supply line 11a to exhaust line 12a. Bypass line 13b also connects supply line 11b to exhaust line 12b. Bypass valve 15a and bypass line 13b are located at the points where supply line 11a and bypass line 13a are connected. Bypass valve 15a changes the connection state between supply line 11a and bypass line 13a. Likewise, the bypass valve 15b changes the connection state between the supply line 11b and the bypass line 13b.The ACP 14a, the bypass valve 15a, and the charge air cooler 16a are provided in this order on the upstream side of the supply line 11a. The backpressure valve 17a is provided on the exhaust line 12a on the upstream side of a section where the exhaust line 12a and the bypass line 13a are connected. Similarly, the ACP 14b, the bypass valve 15b, and the charge air cooler 16b are provided in this order on the upstream side of the supply line 11b. The backpressure valve 17b is provided on the exhaust line 12b on the upstream side of a section where the exhaust line 12b and the bypass line 13b are connected.

[0016] The ACPs 14a and 14b supply oxygenated air as cathode gas to the FCs 4a and 4b via the supply lines 11a and 11b. The cathode gas supplied to the FCs 4a and 4b is discharged via the exhaust lines 12a and 12b. The charge air coolers 16a and 16b cool the cathode gas supplied to the FCs 4a and 4b. The backpressure valves 17a and 17b regulate the backpressure on the cathode sides of the FCs 4a and 4b.

[0017] The anode gas supply systems 20a, 20b supply hydrogen gas as anode gas to the FCs 4a, 4b. In particular, the anode gas supply systems 20a, 20b include tanks 20Ta, 20Tb, supply lines 21a, 21b, exhaust lines 22a, 22b, circulation lines 23a, 23b, tank valves 24a, 24b, pressure control valves 25a, 25b, injectors (hereinafter referred to as INJs) 26a, 26b, gas-liquid separators 27a, 27b, drain valves 28a, 28b and hydrogen circulation pumps (hereinafter referred to as HPs) 29a, 29b.

[0018] Tank 20Ta and the anode inlet manifold of FC 4a are connected via supply line 21a. Similarly, tank 20Tb and the anode inlet manifold of FC 4b are connected via supply line 21b. Hydrogen gas, used as the anode gas, is stored in tanks 20Ta and 20Tb. Exhaust lines 22a and 22b are connected to the anode outlet manifolds of FCs 4a and 4b, respectively. Circulation line 23a connects the gas-liquid separator 27a to supply line 21a. Circulation line 23b connects the gas-liquid separator 27b to supply line 21b. The tank valve 24a, the pressure regulating valve 25a, and the INJ 26a are located on the supply line 21a from an upstream side, in that order. When the tank valve 24a is open, the opening degree of the pressure regulating valve 25a is adjusted, and the INJ 26a injects anode gas.Thus, anode gas is supplied to FC 4a. The ECU 2 controls the actuation of the tank valve 24a, the pressure regulating valve 25a, and the INJ 26a. The same applies to the tank valve 24b, the pressure regulating valve 25b, and the INJ 26b.

[0019] The gas-liquid separator 27a and the drain valve 28a are arranged in this order on the upstream side of the exhaust pipe 22a. The gas-liquid separator 27a separates water from the anode gas discharged from the FC 4a and stores the water. The water stored in the gas-liquid separator 27a is discharged from system 1 to the outside via the exhaust pipe 22a by opening the drain valve 28a. The actuator of the drain valve 28a is controlled by the ECU 2. The same applies to the gas-liquid separator 27b and the drain valve 28b.

[0020] Circulation line 23a is a pipeline for recirculating or recirculating anode gas to the FC 4a and is connected to the gas-liquid separator 27a at an upstream end section. The HP 29a is located in circulation line 23a. The anode gas exiting the FC 4a is pressurized by the HP 29a and fed into supply line 21a. The drive of the HP 29a is controlled by the ECU 2. The same applies to circulation line 23b and the HP 29b.

[0021] The electrical power control systems 30a, 30b include fuel cell DC / DC converters or fuel cell DC-DC converters (hereinafter referred to as FDCs) 32a, 32b, battery DC / DC converters or battery DC-DC converters (hereinafter referred to as BDCs) 34a, 34b, and auxiliary inverters or auxiliary inverters (hereinafter referred to as AINVs) 39a, 39b. The electrical power control systems 30a, 30b share a motor inverter (hereinafter referred to as MINV) 38, which is connected to the motor 50. Each of the FDCs 32a, 32b adjusts the DC power from each of the FCs 4a, 4b and outputs the set DC power to the MINV 38. Each of the BDCs 34a, 34b adjusts the DC power output of each of the BATs 8a, 8b and outputs the set DC power to the MINV 38. The electrical power generated by each of the FCs 4a, 4b can be stored in each of the BATs 8a, 8b.The MINV 38 converts the input DC power into three-phase AC power and supplies the motor 50 with this three-phase AC power. The motor 50 causes the vehicle to move via the drive wheels 5.

[0022] The electrical power of the FC 4a and the BAT 8a can be supplied to load devices other than the motor 50 via the AINV 39a. Likewise, the electrical power of the FC 4b and the BAT 8b can be supplied to the load devices via the AINV 39b. It should be noted that the load devices include auxiliary devices for the FCs 4a and 4b, as well as auxiliary devices for the vehicle. The auxiliary devices for FCs 4a, 4b include the aforementioned ACPs 14a, 14b, the aforementioned bypass valves 15a, 15b, the aforementioned backpressure valves 17a, 17b, the aforementioned tank valves 24a, 24b, the aforementioned pressure regulating valves 25a, 25b, the aforementioned INJs 26a, 26b, 26b, the aforementioned drain valves 28a, 28b and the aforementioned HPs 29a, 29b. Auxiliary devices for the vehicle include, for example, an air conditioning system, a lighting system, a hazard light and the like.

[0023] The ECU 2 includes a central processing unit (CPU), a read-only memory (ROM), and a random access memory (RAM). An accelerator pedal depressor sensor 6, an ignition switch 7, the ACPs 14a, 14b, the bypass valves 15a, 15b, the backpressure valves 17a, 17b, the tank valves 24a, 24b, the pressure control valves 25a, 25b, the INJs 26a, 26b, the drain valves 28a, 28b, the FDCs 32a, 32b, and the BDCs 34a, 34b are electrically connected to the ECU 2. The ECU 2 calculates one of the total power outputs required by the FCs 4a, 4b based on a reading from the accelerator pedal depressor sensor 6. The ECU 2 controls the auxiliary devices for the FCs 4a, 4b and the like so that the total electrical power generated by the FCs 4a, 4b converges with the required power and controls the amounts of anode gas and cathode gas supplied to each of the FCs 4a, 4b. Flush control

[0024] The ECU 2 executes a purge control to perform the purge by driving the ACP 14b and supplying cathode gas to a cathode gas flow channel in the FC 4b to remove the remaining liquid water in the FC 4b, during which time the generation of electrical power by the FC 4b is stopped. This is because if the system 1 stops while the liquid water remains in the cathode gas flow channel of the FC 4b, the remaining liquid water will freeze, depending on the ambient air temperature or similar factors. If the system 1 is subsequently activated, the output power of the FC 4b may deteriorate due to an increased pressure drop in the cathode gas. In the present embodiment, the purge can be performed by supplying cathode gas to the FC 4a by driving the ACP 14a. Accordingly, ACPs 14a, 14b are examples of the flushing device that can flush FCs 4a, 4b independently of each other.The ECU 2 is an example of the control device that controls the ACPs 14a and 14b as examples of the purging device. In the present embodiment, however, the ECU 2 only purges the FC 4b, since the generating volume differs from electrical power or current generating volume, as described below. Electricity generation volume

[0025] Fig. 2A is an explanatory view of the generation volume of electrical power or electricity generation volume of FC 4a, and Fig. Figure 2B is an illustrative view of the electrical power generation volume of FC 4b. Each FC 4a, 4b is obtained by stacking a plurality of identical individual cells 41. The electrical power generation volume of FC 4a is the sum of the electrical power generation volumes of the respective individual cells 41 with which FC 4a is equipped. Likewise, the electrical power generation volume of FC 4b is the sum of the electrical power generation volumes of the respective individual cells 41 with which FC 4b is equipped. The electrical power generation volume of each individual cell 41 is a value obtained by multiplying the electrode area S of each individual cell 41 and the electrode thickness T of each individual cell 41.The electrode area S is the area of ​​a region where an electrolyte membrane overlaps with an anode catalyst layer and a cathode catalyst layer, respectively, located on one surface and the other surface of the electrolyte membrane. The electrode thickness T is the average thickness of the region where the electrolyte membrane overlaps with the anode catalyst layer and the cathode catalyst layer. As shown in the... Fig. 2A and Fig. As shown in Figure 2B, the current-generating volume of each individual cell 41 is a value obtained by multiplying the electrode area S and the electrode thickness T. It should be noted that the number of stacked individual cells 41 in FC 4a is Na, and that the number of stacked individual cells 41 in FC 4b is Nb, which is less than Na. Accordingly, the electrical power-generating volume, or current-generating volume, of FC 4a is a value obtained by multiplying the electrode area S, the electrode thickness T, and the number Na of individual cells 41. The electrical power-generating volume, or current-generating volume, of FC 4b is a value obtained by multiplying the electrode area S, the electrode thickness T, and the number Nb of individual cells 41.

[0026] As the volume of electrical power generated increases, so does the rated power output, the amount of liquid water produced in each fuel cell during power generation, and the amount of liquid water remaining in each fuel cell when the system shuts down. The volume of the reaction gas flow channel in each fuel cell also increases with the power generation volume. Consequently, the amount of energy required to adequately flush the system with water also increases with the power generation volume, as does the amount of electrical power required.In the present embodiment, the ECU 2 can discharge sufficient water from the FC 4b with low power consumption by flushing the FC 4b, which has a small power-generating volume, without flushing the FC 4a, which has a large power-generating volume, as described above. The flushing control is described in detail below. Details on the flushing control

[0027] Fig. Figure 3 is a flowchart showing an example of a flushing control system. Fig. Figure 4 is a timeline showing the example of a flushing control system. Fig. Figure 4 shows the change between the ON and OFF states of an ignition, the respective rotational speeds of ACPs 14a, 14b, and the current generation states of FCs 4a, 4b. The present control is carried out repeatedly at intervals with a predetermined time period.

[0028] The ECU 2 determines, based on an output signal from ignition switch 7, whether the ignition OFF state has been detected (step S1). If the result of step S1 is "No," the current control process is terminated. If the ignition OFF state is detected (Yes in step S1), the ECU 2 stops the power generation by FCs 4a and 4b (step S3, at time t1). Specifically, FCs 4a and 4b are electrically disconnected from the load devices by switches in FDs 32a and 32b. Simultaneously, the ECU 2 stops the supply of anode and cathode gas to FC 4a and the supply of anode gas to FC 4b by closing the tank valves 24a and 24b and the pressure control valves 25a and 25b, and by stopping the actuation of INJs 26a and 26b and ACP 14a.

[0029] Furthermore, ECU 2 continues to drive ACP 14b based on the electrical power charged to BAT 8b and begins purging FC 4b (step S5, at time t1). As a condition for purging FC 4b, the rotational speed of ACP 14b is set to a speed α suitable for purging FC 4b, and the purge time is set to a time interval β. The rotational speed α is higher than the rotational speed of ACP 14b when the electrical power generated by FC 4b is regulated according to the required power output. For example, the rotational speed α is 2000 rpm. The time interval is, for example, 20 seconds. This allows liquid water to be drained from a cathode flow channel in FC 4b. ECU 2 completes the purging of FC 4b at time t2, after the time elapsed since the start of the purge.By executing the purge control when the ignition is OFF, the output power of FC 4b can be ensured since the activation of system 1 as described above. FC 4b is purged by ACP 14b, whereby the connection between supply line 11b and bypass line 13b is broken by the bypass valve 15b and the backpressure valve 17b remains open.

[0030] As described above, the ECU 2 purges FC 4b, but not FC 4a, whose current-generating volume is larger than that of FC 4b. Accordingly, in the present embodiment, the amount of electrical power consumed by purging is less than in the case where FC 4a, whose current-generating volume is large, is sufficiently purged, and FC 4b, whose current-generating volume is small, is not. Thus, the total electrical power with which BATs 8a, 8b are charged can be ensured in the present embodiment. Accordingly, it is also possible, if the power required immediately after switching on system 1 is large, to drive motor 50 primarily based on the electrical power with which BATs 8a, 8b are charged, rather than on the electrical power generated by FCs 4a, 4b.Thus, the acceleration response when starting the vehicle is ensured immediately after activation of system 1. ECU 2 can issue a command to purge only FC 4a or a command to purge both FC 4a and FC 4b, unless the generation of electrical power by both FC 4a and FC 4b is stopped.

[0031] Additionally, as described above, the FC 4b is flushed. Therefore, when system 1 is activated, power generation can be started early, without taking into account the fact that liquid water is still present in the FC 4b. As described in the Fig. 2A and Fig. As shown in Figure 2B, the volume of FC 4b is smaller than the volume of FC 4a, and the quantities of cathode and anode gas required to ensure power generation by FC 4b are also smaller than those required by FC 4a. Therefore, when system 1 is activated, the cathode and anode gas can be supplied within a short time to meet the power generation requirements of FC 4b, allowing power generation by FC 4b to start early. Thus, the responsive power output of FC 4b upon activation of system 1 is guaranteed.

[0032] Furthermore, as the volume of electrical power generated increases, so does the amount of purge gas required to ensure sufficient water drainage through purging. Therefore, the required amount of purge gas in FC 4a is greater than in FC 4b. Assuming that the flow rate of purge gas supplied to FC 4a and the flow rate of purge gas supplied to FC 4b are equal, the time until completion of the purge process is shorter when, as in the present embodiment, FC 4b is purged and FC 4a is not, than when FC 4a is purged and FC 4b is not. Thus, in the present embodiment, the purging of FC 4b is completed, and the drive of ACP 14b is stopped shortly after the ignition is switched off.Therefore, it prevents the time that the ACP 14b continues to run after the ignition is switched off from being prolonged, and the strange feeling developed by the driver can be mitigated.

[0033] As described above, the volume of FC 4b is smaller than the volume of FC 4a, so the heat capacity of FC 4b is smaller than the heat capacity of FC 4a. It should be noted that, for example, the warm-up operation for generating electrical power can be carried out by increasing the heat loss of each of the fuel cells by reducing the stoichiometric ratio of cathode gas compared to the point of normal operation, in order to raise the temperature of each of the fuel cells to a temperature suitable for power generation at an early stage if the system 1 is in a low-temperature environment at activation.It should be noted that if fuel cells 4a and 4b are caused to generate the same electrical power under identical conditions, such as the stoichiometric ratio of reactant gas, the heat loss in fuel cell 4b, which has a smaller power-generating volume than fuel cell 4a, is greater due to the characteristics of fuel cells. Therefore, the amount of electrical power generated by fuel cell 4b is likely to be greater than that generated by fuel cell 4a. Furthermore, the heat capacity of fuel cell 4b is also lower than that of fuel cell 4a. Even if fuel cells 4a and 4b are caused to generate the same electrical power, the temperature of fuel cell 4b is likely to rise before that of fuel cell 4a, reaching a temperature suitable for power generation.Therefore, if system 1 is activated at a low temperature, it is also possible to increase the temperature of the FC 4b early through warm-up operation, and the response behavior of the power output of the FC 4b can be ensured.

[0034] As described above, the temperature of FC 4b can be increased by having FC 4b generate electrical power early in the activation of system 1. Therefore, increasing the temperature of FC 4a can be aided by utilizing the heat from FC 4b. For example, a coolant channel can be configured so that the coolant, having absorbed heat from FC 4b, flows through FC 4a before passing through a cooler. Furthermore, FC 4b can be in direct or indirect contact with FC 4a via an element with high thermal conductivity, such as copper, so that the heat generated by FC 4b is transferred to FC 4a. For example, FC 4b can be in contact with a point near an area of ​​FC 4a where liquid water is likely to freeze. Simultaneously, the heat from the auxiliary equipment for FC 4b, which has already generated electrical power, can be used to transfer heat to FC 4a.the ACP 14b and the like, to which the FC 4a is transferred by keeping these auxiliary devices in contact with the FC 4a directly or indirectly.

[0035] Furthermore, power generation by FC 4a can be initiated as soon as a certain amount of heat is transferred from FC 4b to FC 4a after power generation by FC 4b has commenced upon activation of system 1. Therefore, if ice remains in FC 4a upon activation of system 1, problems such as hydrogen shortage in FC 4a can be prevented by melting the ice in FC 4a using the heat from FC 4b and then initiating power generation in FC 4a. Variation example for the flushing control

[0036] Next, a modified example of the flushing control is described. Fig. Figure 5 is a flowchart showing the modified example of the flushing control. Fig. Figure 6 is a time diagram showing the modified example of the rinsing control. Process steps identical to those of the embodiment described above are each identified by the same reference numerals, thus avoiding redundant descriptions.

[0037] If the result of step S1 is "Yes" and after the process of step S3 has been carried out, ECU 2 purges both FCs 4a and 4b (step S5a). Specifically, the purging of each FC 4a and 4b is performed based on the electrical power with which each BAT is charged. The condition for purging FC 4b is the same as described above. The condition for purging FC 4a is that the rotational speed of ACP 14a is equal to the rotational speed α, and the purge time is set to a shorter time interval γ than the time interval β. For example, the time interval γ is 10 seconds. Accordingly, the purging of FC 4a is completed at time t2a, and then the purging of FC 4b is completed at time t2. ECU 2 can issue a command to purge FC 4a, but an ECU (not shown) that is different from ECU 2 can issue a command to purge FC 4a.

[0038] Thus, both FCs 4a and 4b are flushed, but the amount of electrical power consumed by ACP 14a while flushing FC 4a is less than the amount of electrical power consumed by ACP 14b while flushing FC 4b. Therefore, sufficient water can be drained from FC 4b while preventing an increase in the amount of electrical power consumed by flushing both FCs 4a and 4b. Furthermore, FC 4a is also partially flushed, allowing the amount of water removed from FC 4a to remain within acceptable limits. This improves the responsiveness of the power output of FC 4a when System 1 is activated.

[0039] Furthermore, the timing for the start of the FC 4a purge and the timing for the start of the FC 4b purge are essentially the same. Therefore, the time interval from when the ignition is switched off to when the two ACPs 14a and 14b are stopped after the purge of both FCs 4a and 4b is complete is not extended. This mitigates the strange sensation experienced by the driver due to the continued operation of ACPs 14a and 14b after the ignition is switched off.

[0040] In the present modified example, the rinsing of FC 4a and the rinsing of FC 4b are started essentially simultaneously, although the invention is not limited to this. From the perspective of completing the rinsing of FCs 4a and 4b within a short time, it is desirable that the rinsing of FC 4a is started and completed while FC 4b is being rinsed.

[0041] In the aforementioned modified example, the conditions for purging FCs 4a and 4b are that the rotational speed of ACP 14a and the rotational speed of ACP 14b are equal, and the purging time of FC 4a is shorter than the purging time of FC 4b. Thus, the amount of electrical power consumed by purging FC 4a is reduced compared to the amount of electrical power consumed by purging FC 4b, but the invention is not limited to this. For example, the purging time of FC 4a and the purging time of FC 4b are equal, but the amount of electrical power consumed by purging FC 4a can be reduced compared to the amount of electrical power consumed by purging FC 4b by making the rotational speed of ACP 14a lower than the rotational speed of ACP 14b.This ensures that the amount of electrical power consumed by flushing FC 4a, 4b can be prevented from increasing, while at the same time sufficient water can be drained from FC 4b.

[0042] In the aforementioned embodiment and the aforementioned modified example, the FC 4b, with a smaller number of stacked individual cells than the FC 4a, is shown by way of example as the second fuel cell, which has a smaller electrical power generation volume than the first fuel cell, but the invention is not limited thereto. For example, the second fuel cell can have a smaller electrical power generation volume than the first fuel cell, wherein the number of stacked individual cells in the first fuel cell and the number of stacked individual cells in the second fuel cell are the same, and wherein the electrode area of ​​each of the individual cells in the second fuel cell is smaller than the electrode area of ​​each of the individual cells in the first fuel cell.Alternatively, the second fuel cell can have a smaller electrical power generation volume than the first fuel cell, wherein the number of stacked individual cells in the first fuel cell and the number of stacked individual cells in the second fuel cell are the same, and wherein the electrode area of ​​each of the individual cells in the first fuel cell and the electrode area of ​​each of the individual cells in the second fuel cell are also the same, but the electrode thickness of each of the individual cells in the second fuel cell is smaller than the electrode thickness of each of the individual cells in the first fuel cell. Variation example of the system

[0043] Next, the purge control system in a system equipped with three fuel cells is described. Each of the Fig. Figures 7A to 7C show a view depicting three fuel cells used in a system. The other configuration details are in the Fig. 7A to 7C omitted.

[0044] A in Fig. In Figure 7A, system 1a is equipped with an additional FC 4c, which has a larger power generation volume than FC 4b but the same power generation volume as FC 4a. In system 1a, FC 4b is purged, while FCs 4a and 4c are not. The amount of electricity consumed can be kept low by refraining from purging FCs 4a and 4c, whose power generation volume is greater than that of FC 4b. The same applies if FC 4c has a larger power generation volume than FC 4b but a smaller power generation volume than FC 4a.

[0045] A in Fig. System 1b, as shown in Figure 7B, is equipped with an additional FC 4d besides FCs 4a and 4b. The FC 4d's power generation volume is equal to that of FC 4b. In this case, FCs 4b and 4d are purged. The amount of power consumption can be kept low by refraining from purging FC 4a, whose power generation volume is greater than that of FCs 4b and 4d.

[0046] A in Fig. System 1c, as shown in Figure 7C, is equipped with an additional FC 4e besides FCs 4a and 4b. FC 4e has a smaller power generation volume than FC 4b. In this case, FC 4b is purged. Power consumption can be kept low by not purging FCs 4a and 4e.

[0047] Even in the Fig.In the modified examples shown in 7A to 7C, FC 4a and FC 4c can be flushed in such a way that the amount of electrical power consumed during the flushing of each FC 4a, 4c is less than the amount of electrical power consumed by FC 4b. In this case as well, the flushing time of FC 4b and the flushing time of each of the FCs 4a, 4c are preferably such that they overlap at least partially. Further examples of variations

[0048] In the embodiment and variations described above, only the cathode side is purged. However, only the anode side can be purged, or both the cathode and anode sides can be purged. If the anode side is purged, the FC 4b can be purged by driving the HP 29b, using the anode gas remaining in the circulation line 23b as a purge gas, and circulating this anode gas to the FC 4b, for example, after the FC 4b stops generating current upon detection of the ignition's OFF state. In this case, the amount of electrical power consumed by driving the HP 29b after the FC 4b stops generating current can be considered the amount of electrical power consumed by purging the FC 4b. Each of the HPs 29a, 29b can be considered an example of the flushing device that can flush each of the FCs 4a, 4b.

[0049] In the aforementioned embodiment and the aforementioned modified example, the anode gas supply systems 20a, 20b are each equipped with the HPs 29a, 29b, but the invention is not limited thereto. The anode gas supply systems 20a, 20b can be equipped with ejectors instead of the HPs 29a, 29b. In the event that the anode side is purged in this configuration, the FC 4b can be purged using the anode gas injected by the INJ 26b as purge gas, e.g., after the power generation by the FC 4b has stopped upon detection of the OFF state of the ignition. In this case, the amount of electrical power consumed by driving the INJ 26b after the power generation by the FC 4b has stopped can be considered the amount of electrical power consumed by purging the FC 4b.Each of the INJs 26a, 26b can be considered an example of the flushing device capable of flushing each of the FCs 4a, 4b.

[0050] In the aforementioned embodiment and the aforementioned modified example, purging is performed with the ignition switched off. However, purging can be performed before the ignition's switch-on state is detected and current generation by FCs 4a and 4b is started.

[0051] In the aforementioned embodiment, the BVTs 8a, 8b are provided corresponding to the FCs 4a, 4b, but the invention is not limited thereto. A secondary battery connected to the two FCs 4a, 4b can be provided. In the aforementioned embodiment, the tanks 20Ta, 20Tb are provided corresponding to the FCs 4a, 4b, but the invention is not limited thereto. One tank used for the two FCs 4a, 4b can be provided instead of the tanks 20Ta, 20Tb. Alternatively, three or more tanks can be provided.

[0052] The vehicle on which the fuel cell system is mounted does not necessarily have to be a car, but can be a two-wheeled vehicle, a rail vehicle, a ship, an aircraft, or the like. This vehicle can also be a hybrid vehicle that can be powered by both a conventional engine and a combustion engine.

[0053] Although the preferred embodiment of the invention has been described in detail above, the invention is not limited to this specific embodiment. The invention can be subjected to various changes and modifications within the scope of the invention as set out in the claims.

Claims

[1] Fuel cell system comprising: a first fuel cell (4a) and a second fuel cell (4b); a first purging device (14a) and a second purging device (14b) that can purge the first fuel cell (4a) and the second fuel cell (4b) independently of each other, wherein the first purging device (14a) is a first air compressor that supplies oxygenated air as cathode gas to the first fuel cell (4a) and the second purging device (14b) is a second air compressor that supplies oxygenated air as cathode gas to the second fuel cell (4a); and a control device (2) configured to control the first and second flushing devices (14a, 14b; 29a, 29b; 26a, 26b), wherein the control device (2) is configured to to control the rotational speed of the first rinsing device (14a) and the rotational speed of the second rinsing device (14b) so that they are equal to each other, to control the purge time of the first fuel cell (4a) so that it is shorter than the purge time of the second fuel cell (4b), and to start and complete the purging of the first fuel cell (4a) within a period in which the purging of the second fuel cell (4b) is carried out, where the electrical power generation volume of the second fuel cell (4b) is smaller than the electrical power generation volume of the first fuel cell (4a), the first fuel cell (4a) and the second fuel cell (4b) are purged when an ignition state of the fuel cell system is changed to an OFF state, and the control device (2) is configured to purge the first fuel cell (4a) with an amount of consumed electrical power that is less than the amount of electrical power consumed by purging the second fuel cell (4b). [2] Fuel cell system according to claim 1, wherein the control device (2) is configured to purge the first fuel cell (4a) and the second fuel cell (4b) such that a purge time of the first fuel cell (4a) and a purge time of the second fuel cell (4b) overlap at least partially. [3] Fuel cell system according to claim 1 or 2, further comprising: a third fuel cell (4c) with an electrical power generation volume greater than the electrical power generation volume of the second fuel cell (4b), wherein the first and second purging devices (14a, 14b) can purge the first fuel cell (4a), the second fuel cell (4b) and the third fuel cell (4c) independently of each other, and the control device (2) is not configured to purge the third fuel cell (4c). [4] Fuel cell system according to any one of claims 1 to 3, wherein each of the first fuel cell (4a) and the second fuel cell (4b) is equipped with a plurality of individual cells, The generating volume of electrical power of each of the individual cells is a value obtained by multiplying the current generating area of ​​each individual cell and the electrode thickness of each individual cell together. the electrical power generation volume of the first fuel cell (4a) is a sum of the electrical power generation volumes of the majority of the individual cells with which the first fuel cell (4a) is equipped, and the electrical power generation volume of the second fuel cell (4b) is a sum of the electrical power generation volumes of the majority of the individual cells with which the second fuel cell (4b) is equipped. [5] Fuel cell system according to any one of claims 1 to 4, wherein the purging time of the second fuel cell (4b) is a period of time in which the draining of water from a cathode flow channel of the second fuel cell (4b) is completed.

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