Fuel cell system

Abstract

To provide a fuel cell system capable of performing low voltage driving of a fuel cell under low stoichiometric control during idling or in the case of start under a low temperature environment while suppressing deterioration of a supercharger.SOLUTION: A fuel cell system includes: a gas supply passage which connects a compressor and a fuel cell and in which an oxidant gas is circulated; a gas exhaust passage which connects the fuel cell and a turbine and in which an exhaust gas is circulated; an exhaust gas recirculation passage which is branched from the gas exhaust passage and confluent to the gas supply passage; a blower for recirculation which is provided in the exhaust gas recirculation passage and blows the exhaust gas; a valve for recirculation which is provided in the exhaust gas recirculation passage and opens / closes the exhaust gas recirculation passage; and a control device which performs driving control of the blower for recirculation and opening / closing control of the valve for recirculation. The control device executes control for opening the valve for recirculation and supplying the exhaust gas to the fuel cell via the blower for recirculation during a period in which driving of the compressor is stopped.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a fuel cell system that is applied to, for example, a fuel cell vehicle. [Background technology]

[0002] In general, a fuel cell system supplies hydrogen gas to one electrode (fuel electrode) and oxygen gas to the other electrode (air electrode), and generates electrical energy through the reaction between these.

[0003] In recent years, air (oxygen gas) has also been supplied to fuel cells via a supercharger such as an electric turbocharger. As shown in Patent Document 1, a cathode gas intake system that supplies oxygen gas to the fuel cell is configured to include a known air filter that takes in air, a known electric turbocharger that compresses the air taken in by the air filter, and a known intercooler that cools the compressed air that has been compressed by the electric turbocharger and has increased in temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-140874 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the current technology, not limited to the above-mentioned patent documents, has the following problems. Specifically, fuel cells mounted on vehicles are sometimes operated intermittently to achieve control under conditions of reduced stoichiometry, such as when idling or starting in a low-temperature environment (hereinafter, fuel cell operation control under such low-oxygen conditions is also referred to as "low stoichiometric control"). When a turbocharger is operated intermittently to supply oxygen gas to the fuel cell, it is desirable to reduce the number of starts and stops as much as possible, since this can accelerate deterioration of the compressor, for example. In particular, when air bearings are used in the compressor for the purpose of weight reduction, the deterioration of the air bearings due to friction during the above-mentioned starts and stops can become significant.

[0006] The present disclosure has been made in consideration of the above-mentioned problems as an example, and aims to provide a fuel cell system in which oxygen gas is supplied to a fuel cell via a turbocharger, in which deterioration of the turbocharger is suppressed and the fuel cell can be driven at low voltage under low stoichiometric control during idling or startup in a low temperature environment. [Means for solving the problem]

[0007] In order to solve the above problems, a fuel cell system in one embodiment of the present disclosure is a fuel cell system that supplies oxidant gas supplied from a compressor of a turbocharger to a fuel cell and exhausts exhaust gas generated by operation of the fuel cell to a turbine of the turbocharger, and includes: a gas supply passage that connects the compressor and the fuel cell and through which the oxidant gas flows; a gas exhaust passage that connects the fuel cell and the turbine and through which the exhaust gas flows; an exhaust gas recirculation passage that branches from the gas exhaust passage and merges into the gas supply passage; a recirculation blower that is provided in the exhaust gas recirculation passage and blows the exhaust gas; a recirculation valve that is provided in the exhaust gas recirculation passage and opens and closes the exhaust gas recirculation passage; and a control device that controls the operation of the recirculation blower and the opening and closing of the recirculation valve, and the control device opens the recirculation valve during a period when operation of the compressor is stopped, and controls the supply of the exhaust gas to the fuel cell via the recirculation blower. [Effects of the Invention]

[0008] According to the fuel cell system of the present disclosure, it is possible to suppress deterioration of the supercharger and drive the fuel cell at low voltage under low stoichiometric control during idling or startup in a low temperature environment. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram showing functional blocks of a fuel cell vehicle equipped with a fuel cell system according to a first embodiment. [Figure 2] 1 is a functional block diagram including a control device (FCCU) and its peripheral devices according to a first embodiment. [Figure 3] 4 is a flowchart showing a low voltage driving method in a low stoichiometric state of the fuel cell system according to the first embodiment. [Figure 4] FIG. 2 is a schematic diagram showing the state of gas circulation in the cathode system of the fuel cell system in a low stoichiometric state. [Figure 5] FIG. 6 is a schematic diagram showing the configuration of a cathode system of a fuel cell system according to a second embodiment. [Figure 6] FIG. 10 is a schematic diagram showing the configuration of a cathode system of a fuel cell system according to a third embodiment. [Figure 7] FIG. 10 is a schematic diagram showing the configuration of a cathode system of a fuel cell system according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] First Embodiment Next, preferred embodiments for carrying out the present disclosure will be described. Furthermore, configurations other than those detailed below can be implemented by appropriately supplementing elemental technologies and configurations related to known fuel cell systems, including those described in the above-mentioned patent documents.

[0011] <Fuel cell system 100> First, the configuration of a fuel cell system 100 according to a preferred embodiment of the present disclosure will be described with reference to Fig. 1. The fuel cell system 100 according to this embodiment is mounted on a known fuel cell vehicle (FCV) equipped with, for example, a hydrogen gas supply mechanism (anode gas system) (not shown) that supplies hydrogen gas to the fuel cell 1, and an oxidant gas supply mechanism (cathode gas system) that supplies oxidant gas (air containing oxygen) to the fuel cell 1. Note that the fuel cell 1 may be, for example, a known polymer electrolyte fuel cell (PEFC), although other known fuel cells may also be used.

[0012] The fuel cell vehicle FCV is a vehicle that is driven using power generated by a fuel cell 1, and is equipped with various well-known electrical modules such as a DC / DC converter, an inverter, a battery such as a lithium-ion secondary battery, and an electric motor. Although the following description will be centered on the cathode gas system, various known devices and recirculation mechanisms may be added to the anode gas system without departing from the spirit of this embodiment.

[0013] The fuel cell system 100 is configured to have the function of supplying oxidant gas supplied from the compressor 11 of the turbocharger 10 to the fuel cell 1 in the cathode gas system, and discharging the exhaust gas generated by the operation of this fuel cell 1 to the turbine 12 of the turbocharger 10. [Cathode gas system] Next, the configuration of the cathode gas system included in the fuel cell system 100 of this embodiment will be described in detail. 1, in a cathode gas system that supplies oxygen gas to a fuel cell 1, compressed air is supplied to the fuel cell 1 via a turbocharger 10 (electric turbocharger). More specifically, in the cathode gas system of this embodiment, oxidant gas that has passed through a known air compressor 62 and air filter 63 provided in a gas suction passage 24 is supplied to a compressor 11 of the turbocharger 10. In this way, the gas suction passage 24 is configured to have the function of supplying the oxidant gas that has been connected to the turbocharger 10 and passed through the air filter 63 to the compressor 11.

[0014] The turbocharger 10 has a structure in which the above-mentioned compressor 11 and turbine 12 are connected via a shaft 13. Furthermore, the turbocharger 10 as an electric turbocharger is provided with a known electric motor 14, and is capable of driving the compressor 11 via the electric motor 14 under the control of a control device 40 described later.

[0015] The air compressed by the compressor 11 is supplied to the fuel cell 1 via a gas supply flow path 21. The gas supply flow path 21 connects the cathode of the fuel cell 1 and the compressor 11 of the turbocharger 10. The air (oxidant gas) compressed by the compressor 11 flows through this gas supply flow path 21.

[0016] The intercooler 61 is installed in the gas supply passage 21. The intercooler 61 is configured to have the function of cooling the compressed air (oxidant gas) whose temperature has increased as a result of being compressed by the turbocharger 10. Note that a specific example of the intercooler 61 is not particularly limited as long as it can cool the compressed air, and for example, a known cooling device using a known coolant WT can be exemplified.

[0017] The inlet valve 51 is disposed in the gas supply passage 21. As an example, the inlet valve 51 of this embodiment may be disposed downstream of the intercooler 61 (on the side closer to the fuel cell 1) in the gas supply passage 21. The inlet valve 51 is configured to have the function of controlling the flow rate of the oxidant gas flowing into the cathode of the fuel cell 1 via the gas supply passage 21.

[0018] The inlet valve 51 is controlled by a control device 40, which will be described later. The control device 40 controls the current supplied to the inlet valve 51 to open and close the gas supply passage 21. As the inlet valve 51, various known valve mechanisms, such as a solenoid valve, can be used, as long as the inlet valve 51 is provided in the gas supply passage 21 and functions to adjust the amount of oxidant gas supplied to the fuel cell 1. As an example, the inlet valve 51 may be a normally closed valve that opens when current is applied, or a normally open valve that closes when current is applied.

[0019] After the hydrogen gas and the oxidant gas undergo a chemical reaction in the fuel cell 1, exhaust gas containing moisture (cathode off-gas) is discharged from the cathode of the fuel cell 1 through a gas exhaust flow path 22. The gas exhaust flow path 22 connects the cathode of the fuel cell 1 with the turbine 12 of the turbocharger 10. The exhaust gas containing moisture produced at the cathode of the fuel cell 1 flows through this gas exhaust flow path 22.

[0020] The back pressure valve 52 is installed in the gas exhaust flow path 22. The back pressure valve 52 is configured to have the function of adjusting the supply pressure of air (oxidant gas) supplied to the fuel cell 1 by adjusting the amount of exhaust gas discharged from the fuel cell 1. The control device 40 controls the supply current to the back pressure valve 52 to open and close the gas exhaust flow path 22. The exhaust gas that flows into the turbine 12 of the turbocharger 10 via the gas exhaust passage 22 is then discharged outside the vehicle via the gas exhaust passage 25. As described above, the gas exhaust passage 25 of this embodiment is connected to the turbocharger 10 and has the function of discharging the exhaust gas from the turbine 12 to outside the vehicle.

[0021] As the back pressure valve 52, various known valve mechanisms such as a solenoid valve can be applied as long as they are provided in the gas exhaust flow path 22 and function to adjust the supply pressure of the oxidant gas to the fuel cell 1. As an example, the back pressure valve 52 may be a normally closed valve that opens when energized, or a normally open valve that closes when energized.

[0022] The bypass valve 53 is installed in the bypass flow path 23 that bypasses the gas supply flow path 21 and the gas exhaust flow path 22. The bypass valve 53 is configured to have the function of maintaining the flow rate of air supplied to the fuel cell 1 at a predetermined required air flow rate by adjusting the flow rate of air introduced into the gas exhaust flow path 22 via the bypass flow path 23. In this way, the bypass flow path 23 is provided with a known bypass valve 53 that is controlled by the control device 40 and can adjust the flow path area of ​​the bypass flow path 23. The bypass valve 53 may be equipped with a known bypass valve opening sensor (not shown) that detects the opening degree.

[0023] [Low stoichiometric drive mechanism] 1 and 4, the low stoichiometry drive mechanism 30 mounted on the fuel cell system 100 of this embodiment will be described. The low stoichiometry drive mechanism 30 is configured to drive the fuel cell 1 under low stoichiometry control while maintaining the voltage of the fuel cell 1 at a low voltage (for example, about 0.8 V for a fuel cell equipped with an OCV of about 1 V) when the accelerator of the fuel cell vehicle FCV is off, for example, during idling.

[0024] More specifically, the low stoichiometry drive mechanism 30 of this embodiment is configured to include an exhaust gas recirculation path 31, a recirculation blower 32, and a recirculation valve 33. That is, the low stoichiometry drive mechanism 30 of the present disclosure is characterized mainly in that it is equipped with not only a valve for low stoichiometry control but also a blower.

[0025] The exhaust gas return channel 31 has a starting end connected to the gas exhaust channel 22 and a terminal end connected to the gas supply channel 21. Specifically, the exhaust gas return channel 31 branches off from the gas exhaust channel 22 via a branch point JT2. Therefore, as shown in FIG. 4, the cathode offgas of the fuel cell 1 can flow into the exhaust gas return channel 31 via the branch point JT2. The exhaust gas return channel 31 also merges with the gas supply channel 21 via a junction JT1. Therefore, as shown in FIG. 4, the cathode offgas of the fuel cell 1 can flow from the exhaust gas return channel 31 to the gas supply channel 21 via the junction JT1.

[0026] 4 and other figures, the exhaust gas recirculation path 31 of this embodiment is connected to the gas supply path 21 via a junction JT1 provided upstream of the inlet valve 51. The exhaust gas recirculation path 31 of this embodiment is branched off from the gas exhaust path 22 via a branch point JT2 provided downstream of the back pressure valve 52.

[0027] The recirculation blower 32 is provided in the exhaust gas recirculation path 31. The recirculation blower 32 is configured to have the function of blowing exhaust gas in the exhaust gas recirculation path 31 during the low stoichiometric control. There are no particular limitations on the recirculation blower 32 as long as it has water resistance that enables it to perform the above-mentioned function, and various known blowers that can be mounted on fuel cell vehicles can be used.

[0028] Furthermore, when the compressor 11 is equipped with a known air bearing, it is preferable that the air blowing capacity of the reflux blower 32 can cover a range below the minimum rotation speed of the air bearing. From this perspective, it is preferable that the air blowing capacity of the reflux blower 32 is lower than that of the compressor 11. More specifically, it is even more preferable that the air blowing capacity of the reflux blower 32 is about 10 to 15% of the air blowing capacity of the compressor 11. This makes it possible to supply air to the fuel cell required for low stoichiometry control without intermittently operating the turbocharger 10.

[0029] The reflux valve 33 is provided in the exhaust gas reflux path 31. In this embodiment, the reflux valve 33 is preferably provided downstream of the reflux blower 32 in the exhaust gas reflux path 31. However, the reflux valve 33 in this embodiment may also be provided upstream of the reflux blower 32. The reflux valve 33 is configured to have the function of opening and closing the flow path in the exhaust gas reflux path 31 under the control of a control device 40, which will be described later. Various known valve mechanisms, such as a solenoid valve, can be used as the reflux valve 33. For example, the reflux valve 33 may be a normally closed valve that opens when energized, or a normally open valve that closes when energized.

[0030] The low stoichiometry drive mechanism 30 having the above-described configuration is controlled by, for example, a control device 40. That is, the control device 40 of this embodiment is configured to have the function of controlling the drive of the reflux blower 32 and the opening and closing of the reflux valve 33. The control device 40 is included in the fuel cell system 100 of this embodiment. The control device 40 is also referred to as an FCCU (fuel cell control unit), and is configured to include one or more processors such as a CPU (Central Processing Unit), and one or more memories such as a RAM (Random Access Memory) or a ROM (Read Only Memory) communicably connected to the processor. The above-mentioned FCCU may be installed in a fuel cell vehicle (FCV) as an ECU (electronic control unit) that controls the driving of the vehicle.

[0031] In this way, the control device 40 can execute a computer program by one or more processors to open the reflux valve 33 during the period when the compressor 11 in the turbocharger 10 is not operating, and control the supply of exhaust gas (cathode off-gas) to the fuel cell 1 via the exhaust gas reflux path 31 and the reflux blower 32.

[0032] The computer program is a computer program for causing a processor to execute a low-voltage driving method (see FIG. 3) in a low stoichiometric state of a fuel cell system to be executed by the control device 40. The computer program executed by the processor may be recorded in a storage device MD electrically connected to the control device 40, or may be stored on an external cloud server or the like and made downloadable via a known in-vehicle communication device CD and a network NET.

[0033] <Control device> Next, functions of the control device 40 of this embodiment will be described with reference to FIG. The control device 40 is configured to have the function of driving the fuel cell 1 at low voltage under low stoichiometric control during idling or startup in a low temperature environment while suppressing deterioration of the turbocharger 10 in the fuel cell system 100 described above.

[0034] More specifically, the control device 40 of this embodiment includes a voltage measurement unit 41, a valve control unit 42, a reflux blower control unit 43, and a presentation control unit 44. The control device 40 is electrically connected to sensors SR mounted on the fuel cell vehicle FCV, and is configured to be able to acquire desired information from the sensors SR.

[0035] Examples of the sensors SR include a known voltage sensor SR1 capable of measuring the voltage value of the fuel cell 1 and a known current sensor SR2 capable of measuring the current value of the fuel cell 1. The sensors SR of this embodiment may also include various known sensors mounted on a vehicle, such as an acceleration sensor, a GPS sensor, an angular velocity sensor, a steering angle sensor, an accelerator pedal sensor, and a brake pedal sensor.

[0036] (Voltage measurement section) The voltage measurement unit 41 executes a process of measuring the voltage value of the fuel cell 1 via the voltage sensor SR1. When a fuel cell stack in which fuel cells 1 are stacked is used in a fuel cell vehicle FCV, the voltage measurement unit 41 may measure the voltage value of the fuel cell stack, or may measure the voltage values ​​of the fuel cells 1 that make up the fuel cell stack individually.

[0037] (Valve control unit) The valve control unit 42 executes a process to adjust the opening of the recirculation valve 33 to a fully open state when the fuel cell 1 is under the above-mentioned low stoichiometry control (when the recirculation blower 32 is driven). In addition, the valve control unit 42 executes a process to adjust the opening of the recirculation valve 33 to a fully closed state when the above-mentioned low stoichiometry control is not being performed (when the recirculation blower 32 is stopped).

[0038] (Reflux blower control unit) The reflux blower control unit 43 executes a process for adjusting the airflow rate of the reflux blower 32 when the fuel cell 1 is under the above-described low stoichiometry control. As an example, the reflux blower control unit 43 may cooperate with the above-described valve control unit 42 to adjust the airflow rate of the reflux blower 32 in accordance with the voltage value of the fuel cell 1 when the fuel cell 1 is under the above-described low stoichiometry control. For example, if the voltage value of the fuel cell 1 under the low stoichiometry control drops, the reflux blower control unit 43 may increase the airflow rate of the reflux blower 32 by the amount of the above-described drop in voltage value. This makes it possible to maintain a constant voltage value of the fuel cell 1 under low stoichiometry control.

[0039] (Presentation control unit) The presentation control unit 44 executes a process of displaying various information such as the fuel cell system 100 and the vehicle status on the presentation device PD. Here, examples of the presentation device PD in this embodiment include a well-known in-vehicle display DP and in-vehicle speaker SP, as shown in Fig. 2. The presentation control unit 44 may also execute control to display the above-mentioned various information on an external terminal such as a smartphone carried by a passenger of the fuel cell vehicle FCV.

[0040] <Low voltage driving method for fuel cell system in a sub-stoichiometric state> Next, a low-voltage driving method in a low stoichiometric state of the fuel cell system 100 in this embodiment will be described with reference to Figure 3. The low-voltage driving method may be used as a program algorithm that can be executed by the control device 40. A program having such an algorithm may be distributed so as to be downloadable from outside the vehicle via a known in-vehicle communication device CD and network NET, or may be stored in the above-mentioned storage device MD.

[0041] First, in step 11, the control device 40 proceeds to step 12 if the vehicle system is ON, and ends the process if the system is not ON. Next, in step 12, the control device 40 determines whether or not the fuel cell 1 requires low stoichiometry control. As an example, the control device 40 may execute low stoichiometry control of the fuel cell 1 based on detection values ​​from the sensors SR. Examples of detection values ​​from the sensors SR that contribute to determining whether or not low stoichiometry control is possible include accelerator opening information from an accelerator pedal sensor, current value information from a current sensor of the fuel cell 1, brake pedal force information from a brake pedal sensor, the remaining charge of the high-voltage battery (SOC value), the state of the shift lever (whether the shift lever is positioned in "P" for parking, "R" for reverse, "N" for neutral, or "D" for normal driving), and traffic congestion information around the vehicle.

[0042] If it is determined in step 12 that low stoichiometric control is not required for the fuel cell 1, the control device 40 completes the low voltage drive process of this embodiment. If it is determined in step 12 that low stoichiometric control is required for the fuel cell 1, the control device 40 proceeds to step 13 and performs preparations for low voltage drive. That is, in step 13, the control device 40 opens the inlet valve 51 and the back pressure valve 52, while controlling the bypass valve 53 to be closed.

[0043] This stops the flow of gas through the bypass passage 23. At this time, the control device 40 may also stop driving the electric motor 14 of the turbocharger 10. This also stops driving the air bearing, if the compressor 11 is equipped with one.

[0044] In step 14 following step 13, the valve control unit 42 of the control device 40 controls the recirculation valve 33 from a fully closed state to a fully open state. As a result, a gas flow path is established that is made up of the exhaust gas recirculation path 31, the gas supply path 21, the fuel cell 1, and the gas exhaust path 22, as shown in FIG.

[0045] In step 15 following step 14, the recirculation blower control section 43 of the control device 40 drives the recirculation blower 32. As a result, as shown in Fig. 4, the blowing action of the recirculation blower 32 generates a flow of exhaust gas in the gas flow path including the exhaust gas recirculation path 31, making it possible to drive the fuel cell 1 at a low voltage without drawing current. Note that while the recirculation blower 32 is being driven, the control device 40 in principle stops driving the turbocharger 10 except during a voltage recovery process, which will be described later.

[0046] As described above, in the low stoichiometry control of this embodiment, the driving of the turbocharger 10 is stopped, which eliminates the need for, for example, intermittent driving of the turbocharger 10, thereby contributing to a longer life of the turbocharger 10. Since the compressor 11 of the turbocharger 10 does not require intermittent driving, it is also possible to mount an air bearing on the compressor 11, which contributes to weight reduction.

[0047] In step 16 following step 15, the control device 40 determines whether or not to continue the low stoichiometric control described above. As an example, the control device 40 may determine whether or not to continue the low stoichiometric control of the fuel cell 1 based on the detection values ​​from the sensors SR, in the same manner as in step 12.

[0048] If it is determined in step 16 that low stoichiometric control should be continued (Yes in step 16), the control device 40 determines in the following step 17A whether the voltage value of the fuel cell 1 under low stoichiometric control is within a normal range. More specifically, the voltage measurement unit 41 of the control device 40 determines whether the voltage value of the fuel cell 1 acquired via the voltage sensor SR1 is within a predetermined normal range (for example, 0.7 to 0.9 V for a fuel cell with an electromotive force of about 1 V). Such a range can be determined in advance through experiments, simulations, etc., depending on the specifications of the fuel cell 1, etc.

[0049] If it is determined in step 17A that the voltage value of the fuel cell 1 under low stoichiometric control is within the normal range, the control device 40 returns to step 16 to determine whether or not to continue the low stoichiometric control. In this way, if low stoichiometric control is necessary and the voltage value of the fuel cell 1 under low stoichiometric control is within the normal range, the processing of step 16 and step 17A described above will be repeated.

[0050] If it is determined in step 17A that the voltage value of the fuel cell 1 under low stoichiometric control is not within the normal range, the control device 40 proceeds to step 18A and executes a process to restore the voltage value of the fuel cell 1. As an example, the control device 40 may execute at least one of (a) temporarily driving the turbocharger 10, (b) adjusting the air flow rate of the return blower 32, and (c) opening the preliminary return flow path so that the voltage value of the fuel cell 1 under low stoichiometric control falls within the normal range.

[0051] Here, the preliminary return flow path used in step 18A can be, for example, the above-mentioned bypass flow path 23. Specifically, as a process for restoring the voltage value of the fuel cell 1 in step 18A, the control device 40 temporarily opens the bypass valve 53 to allow the gas (oxygen) remaining in the bypass flow path 23 to flow into the above-mentioned gas flow path. In other words, by opening the bypass valve 53, the control device 40 can execute a process for adding the bypass flow path 23 to the gas flow path as a preliminary return flow path.

[0052] In this embodiment, the control device 40 executes the recovery process for the voltage value of the fuel cell 1 based on the transition of the voltage value in the fuel cell 1, but the above-mentioned voltage value recovery process may also be executed based on, for example, an increase in the rotation speed of the reflux blower 32 or the passage of a predetermined time. As an example, the control device 40 may prioritize the above-mentioned recovery process (b), and execute the above-mentioned recovery process (a) when the rotation speed of the reflux blower 32 exceeds a threshold value.

[0053] After executing the recovery process for the voltage value of the fuel cell 1 in step 18A, the control device 40 proceeds to step 16 and executes the process of step 16 again after the recovery process.

[0054] On the other hand, if it is determined in step 16 that continuation of low stoichiometry control is not necessary, the control device 40 executes processing to return the driving state of the fuel cell 1 to normal operation in step 17B and thereafter. More specifically, the control device 40 first executes control to stop driving the above-mentioned return blower 32 in step 17B. Next, the control device 40 executes control to change the return valve 33 from a fully open state to a fully closed state in step 18B.

[0055] The control device 40 then executes a process to return the inlet valve 51 and the back pressure valve 52 to their normal states in step 19, thereby completing the low voltage drive process of this embodiment. As an example, the control device 40 may adjust the opening of the bypass valve 53 so as to achieve a predetermined required air flow rate while keeping the inlet valve 51 and the back pressure valve 52 open in step 19.

[0056] As described above, according to the fuel cell system 100 and the low-voltage drive method in a low-stoichiometry state in the first embodiment, the fuel cell can be driven at low voltage via the low-stoichiometry drive mechanism 30 without the need to drive the turbocharger 10, and therefore it is possible to control the fuel cell at low stoichiometry while suppressing deterioration of the turbocharger.

[0057] Second Embodiment <Fuel cell system 110> 5 shows a fuel cell system 110 according to a second embodiment of the present disclosure. In the second embodiment described below, differences from the first embodiment will be mainly described, and components having the same functions as those in the first embodiment will be given the same reference numerals and descriptions thereof will be omitted as appropriate.

[0058] In the gas exhaust flow path 22 in the first embodiment described above, a confluence of the bypass flow path 23 is provided between the branch point JT2 and the back pressure valve 52 (see FIG. 4). In contrast, the gas exhaust flow path 22 in the second embodiment is characterized in that a gas-liquid separator 34 is further provided between the branch point JT2 of the exhaust gas recirculation flow path 31 and the back pressure valve 52.

[0059] That is, in the fuel cell system 110 of the second embodiment, the above-described low stoichiometry drive mechanism 30 is configured to further include a gas-liquid separator 34 that is provided in the gas exhaust flow path 22 and performs gas-liquid separation on the exhaust gas (cathode off-gas). The gas-liquid separator 34 may be installed between the branch point JT2 of the exhaust gas recirculation flow path 31 and the junction of the bypass flow path 23. This allows the exhaust gas to be circulated to the recirculation blower 32 with excess moisture removed, thereby preventing breakdown of the recirculation blower 32 and the addition of excess moisture to the fuel cell 1.

[0060] Third Embodiment <Fuel cell system 120> FIG. 6 shows a fuel cell system 120 according to a third embodiment of the present disclosure. In the gas supply passage 21 of the first embodiment described above, the confluence JT1 of the exhaust gas recirculation passage 31 is provided downstream of the intercooler 61 (see FIG. 4). In contrast, the gas supply passage 21 of the third embodiment is characterized in that the confluence JT1 is provided upstream of the intercooler 61.

[0061] That is, in the fuel cell system 110 of the second embodiment, the confluence JT1 of the low stoichiometry drive mechanism 30 is installed between the compressor 11 of the turbocharger 10 and the intercooler 61. This allows air upstream of the intercooler 61 and air remaining on the turbocharger 10 side of the gas exhaust passage 22 to flow into the gas flow path, making it possible to more easily secure oxygen required for low stoichiometry control.

[0062] Fourth Embodiment <Fuel cell system 130> FIG. 7 shows a fuel cell system 130 according to a fourth embodiment of the present disclosure. The low stoichiometry drive mechanism 30 in the fourth embodiment is characterized mainly in that, in addition to the above-described reflux valve 33, a check valve is provided on the upstream side or downstream side of the turbocharger 10.

[0063] That is, the check valve in the fourth embodiment is configured to include at least one of an upstream valve 35 provided in the gas suction passage 24 on the upstream side of the turbocharger 10, and a downstream valve 36 provided in the gas discharge passage 25 on the downstream side of the turbocharger 10. Note that the upstream valve 35 is preferably installed downstream of the air filter 63 in the gas suction passage 24.

[0064] The control device 40 may perform control to close the check valve described above, for example, during a period when the compressor 11 of the turbocharger 10 is stopped and the recirculation blower 32 is operating. This blocks the path from the downstream side of the turbocharger 10 to the upstream side of the turbocharger 10 via the exhaust gas recirculation path, preventing the intrusion of air that may contain foreign matter (contamination) from the exhaust side, and allowing the work of the recirculation blower to be used efficiently for gas circulation within the fuel cell. Note that a known check valve that does not have a power mechanism and that automatically closes due to the force of a backflowing fluid may be used as the check valve suitable for this embodiment.

[0065] Although the preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, the present disclosure is not limited to such examples. It is clear that a person skilled in the art of the present disclosure may attempt further modifications to these embodiments and variations within the scope of the technical ideas set forth in the claims, and it is understood that these modifications also fall within the technical scope of the present disclosure.

[0066] For example, although a humidifier or the like is omitted in the fuel cell systems of the above-described embodiments, a known humidifier or the like may be added as appropriate to humidify the cathode gas supplied to the fuel cell 1. As a method for humidifying the air supplied to the fuel cell 1, various known devices may be used, such as a method using a water vapor exchange membrane that reuses moisture in the air exhausted from the fuel cell 1, or a membrane humidifier or sprayer that supplies moisture such as pure water to the air. [Explanation of symbols]

[0067] 100~130 Fuel cell system 10. Turbocharger 30 Low stoichiometric drive mechanism 40 Control device

Claims

1. A fuel cell system in which an oxidant gas supplied from a compressor of a turbocharger is supplied to a fuel cell, and exhaust gas generated by driving the fuel cell is discharged to a turbine of the turbocharger, a gas supply flow path connecting the compressor and the fuel cell and through which the oxidant gas flows; a gas exhaust flow path connecting the fuel cell and the turbine and through which the exhaust gas flows; an exhaust gas return passage branching from the gas exhaust passage and merging into the gas supply passage; a recirculation blower provided in the exhaust gas recirculation path for blowing the exhaust gas; a recirculation valve provided in the exhaust gas recirculation path for opening and closing the exhaust gas recirculation path; a control device that controls the drive of the reflux blower and the opening and closing of the reflux valve, The control device opens the reflux valve while the compressor is not operating, and controls the exhaust gas to be supplied to the fuel cell via the reflux blower.

2. an inlet valve provided in the gas supply passage to adjust the amount of oxidant gas supplied to the fuel cell; a back pressure valve provided in the gas exhaust flow path to adjust the amount of exhaust gas discharged from the fuel cell; the exhaust gas recirculation path is connected to the gas supply path via a junction provided upstream of the inlet valve, and the exhaust gas recirculation path branches off from the gas exhaust path via a branching portion provided downstream of the back pressure valve. The fuel cell system according to claim 1 .

3. The gas-liquid separator is provided in the gas exhaust passage and performs gas-liquid separation on the exhaust gas. The gas-liquid separator is installed in the gas exhaust flow path between the branching portion and the back pressure valve. The fuel cell system according to claim 2 .

4. an intercooler provided in the gas supply passage for cooling the oxidant gas; The junction is disposed in the gas supply passage upstream of the intercooler.

4. The fuel cell system according to claim 2 or 3.

5. a gas suction passage connected to the turbocharger and supplying the oxidant gas that has passed through an air filter to the compressor; a gas discharge flow path connected to the turbocharger and discharging the exhaust gas from the turbine to the outside of the vehicle; a backflow prevention valve provided in at least one of the gas suction flow path and the gas discharge flow path, the control device controls the backflow prevention valve to close during a period when the compressor is stopped and the reflux blower is operating. The fuel cell system according to claim 4 .

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