Fuel cell system

Abstract

The present invention provides a fuel cell system capable of suppressing the occurrence of local fuel gas shortage in a fuel cell. The fuel cell system is characterized in that a control unit performs duty cycle control on at least one injector selected from a group consisting of a first injector and a second injector according to an output current value to drive the injector so as to maintain the pressure of the fuel gas to the fuel cell within a specified range, determines whether the output current value is greater than a specified first threshold value, and when it is determined that the output current value is greater than the specified first threshold value, performs duty cycle control on the first injector to drive the injector, and performs duty cycle control on the second injector to drive the injector in a manner that the second injector is opened while at least the first injector is closed.

Description

Technical Field

[0001] The present disclosure relates to fuel cell systems. Background Art

[0002] A fuel cell (FC) is a power generation device that extracts electrical energy through an electrochemical reaction between a fuel gas such as hydrogen and an oxidant gas such as oxygen in a fuel cell stack (hereinafter referred to as a cell stack) composed of one single cell or a plurality of stacked single cells (hereinafter referred to as a unit). In many cases, the fuel gas and oxidant gas actually supplied to the fuel cell are a mixture of gases that do not contribute to oxidation or reduction. In particular, the oxidant gas is often air containing oxygen.

[0003] In the following, fuel gas and oxidant gas may not be particularly distinguished and may be simply referred to as "reactant gas" or "gas". In addition, a single cell and a fuel cell stack composed of stacked single cells may be referred to as a fuel cell.

[0004] The single cell of the fuel cell generally includes a membrane electrode assembly (MEA: Membrane Electrode Assembly).

[0005] The membrane electrode assembly has a structure in which a catalyst layer and a gas diffusion layer (GDL, hereinafter referred to as a diffusion layer) are sequentially formed on both sides of a solid polymer electrolyte membrane (hereinafter also referred to as an "electrolyte membrane"). Therefore, the membrane electrode assembly is sometimes referred to as a membrane electrode gas diffusion layer assembly (MEGA).

[0006] The single cell has two separators sandwiching the two sides of the membrane electrode gas diffusion layer assembly as needed. The separator usually has a structure in which a groove serving as a flow path for the reaction gas is formed on the surface in contact with the gas diffusion layer. The separator has electron conductivity and also functions as a collector of the generated electricity.

[0007] In the fuel electrode (anode) of the fuel cell, hydrogen (H) as fuel gas supplied from the gas flow path and the gas diffusion layer is 2 ) is protonated by the action of the catalyst in the catalyst layer and moves to the oxidant electrode (cathode) through the electrolyte membrane. The electrons generated at the same time perform work through the external circuit and move to the cathode. The oxygen (O 2 ) reacts with protons and electrons in the cathode catalyst layer to generate water. The generated water gives the electrolyte membrane an appropriate amount of humidity, and excess water is discharged to the outside of the system through the gas diffusion layer.

[0008] Various studies have been conducted on fuel cell systems that are mounted on a fuel cell vehicle (hereinafter, sometimes referred to as a vehicle) for use.

[0009] For example, Patent Document 1 discloses a fuel cell system that achieves an improvement in the circulation capacity of a fuel circulation device that circulates anode off-gas discharged from a fuel cell stack.

[0010] Patent Document 2 discloses a fuel cell system that suppresses a decrease in the power generation performance of a fuel cell.

[0011] Patent Document 3 discloses a fuel cell system that can stably circulate fuel off-gas to a fuel cell through simple control, improve the drainage efficiency of the fuel cell according to the situation, and suppress noise and vibration during operation of the injector.

[0012] Patent Document 4 discloses a fuel cell system capable of appropriately supplying fuel gas.

[0013] Patent Document 1: Japanese Patent Application Publication No. 2011-179333

[0014] Patent Document 2: Japanese Patent Application Publication No. 2020-123458

[0015] Patent Document 3: Japanese Patent Application Publication No. 2019-169264

[0016] Patent Document 4: Japanese Patent Application Publication No. 2014-123555

[0017] In a fuel gas system of a fuel cell system, it is important to improve the circulation capacity of a fuel circulation device that circulates fuel off-gas discharged from the fuel cell.

[0018] When the power generation of the fuel cell is large, the pressure in the circulation flow path in the injector closed valve drops sharply, and due to the deviation of the pressure detection value of the pressure sensor, the signal transmission delay, etc., it falls below the lower limit of the set pressure range. As a result, there is a concern that hydrogen deficiency will occur in the fuel cell and the fuel cell catalyst will deteriorate.

[0019] In the structure of the above-mentioned Patent Document 1, the first injector and the second injector inject alternately, and the injection amount of the fuel supplied by each is the same. When the fuel cell is performing high-load power generation, the problem of a sharp drop in pressure in the circulation flow path when the injector is stopped cannot be solved. Therefore, there is a concern that a local fuel gas shortage occurs in the fuel cell, and the catalyst of the fuel cell may be degraded. Summary of the invention

[0020] The present disclosure has been made in view of the above-mentioned actual situation, and a main object of the present disclosure is to provide a fuel cell system capable of suppressing the occurrence of local fuel gas deficiency in a fuel cell.

[0021] The fuel cell system of the present disclosure is a fuel cell system,

[0022] The above-mentioned fuel cell system has:

[0023] Fuel cells;

[0024] A current sensor, detecting an output current value of the fuel cell;

[0025] A fuel gas supply unit, which supplies fuel gas to the fuel cell;

[0026] a circulation flow path connecting the fuel gas outlet of the fuel cell with the fuel gas inlet of the fuel cell and capable of returning the fuel exhaust gas discharged from the fuel gas outlet of the fuel cell as a circulation gas to the fuel gas inlet of the fuel cell for circulation;

[0027] An ejector is arranged in the circulation flow path;

[0028] A fuel gas supply flow path connecting the fuel gas supply unit and the ejector;

[0029] An ejector assembly is arranged at a position upstream of the ejector in the fuel gas supply flow path;

[0030] A gas-liquid separator is arranged at a position upstream of the ejector in the circulation flow path;

[0031] A fuel off-gas discharge flow path, branching from the gas-liquid separator of the circulation flow path, and capable of discharging the fuel off-gas to the outside of the fuel cell system;

[0032] A pressure sensor is disposed in the circulation flow path; and

[0033] Control Department,

[0034] The injector assembly includes a first injector and a second injector in parallel.

[0035] an injection amount of the fuel gas per unit time of the second injector is smaller than an injection amount of the fuel gas per unit time of the first injector,

[0036] The control unit controls the duty ratio of at least one injector selected from the group consisting of the first injector and the second injector to drive the injector according to the output current value so that the pressure of the fuel gas supplied to the fuel cell is maintained within a predetermined range.

[0037] The control unit determines whether the output current value is greater than a predetermined first threshold value.

[0038] When it is determined that the output current value is greater than the specified first threshold value, the control unit drives the first injector by performing duty cycle control, and drives the second injector by performing duty cycle control in a manner that opens the second injector at least when the first injector is closed.

[0039] In the fuel cell system disclosed in the present invention, when it is determined that the output current value is greater than the specified first threshold value, the control unit can drive the first injector by performing duty cycle control, and drive the second injector by performing duty cycle control in a manner such that the second injector is opened after the first injector is closed and the second injector is closed after the first injector is opened.

[0040] In the fuel cell system of the present disclosure, when it is determined that the output current value is greater than the predetermined first threshold value, the control unit may perform a control to drive the first injector by duty-controlling and to always open the second injector.

[0041] In the fuel cell system of the present disclosure, when it is determined that the output current value is less than the predetermined first threshold value, the control unit may determine whether the output current value is less than the predetermined second threshold value which is smaller than the predetermined first threshold value.

[0042] When it is determined that the output current value is equal to or less than the predetermined second threshold value, the control unit always closes the valve of the first injector and drives the second injector by performing duty ratio control.

[0043] When it is determined that the output current value is greater than the predetermined second threshold value, the control unit causes the second injector to be always closed and drives the first injector by performing duty ratio control.

[0044] According to the fuel cell system of the present disclosure, it is possible to suppress the occurrence of local fuel gas deficiency in the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 1 is a schematic configuration diagram showing an example of a fuel cell system of the present disclosure.

[0046] Figure 2 This is a diagram showing an example of the relationship between the on-off valve state of the first injector and the pressure P in the circulation flow path when the fuel cell generates electricity at a constant medium load current.

[0047] Figure 3This is a diagram showing an example of the relationship between the on-off valve state of the first injector and the pressure P in the circulation flow path when the fuel cell in the conventional technology is generating electricity at a constant high load current.

[0048] Figure 4 This is a diagram showing an example of the relationship between the first injector on-off valve state, the second injector on-off valve state, and the pressure P in the circulation flow path when the fuel cell in the present disclosure is generating electricity at a constant high load current.

[0049] Figure 5 This is a diagram showing another example of the relationship between the first injector on-off valve state, the second injector on-off valve state, and the pressure P in the circulation flow path when the fuel cell in the present disclosure is generating electricity at a constant high load current.

[0050] Figure 6 This is a diagram showing another example of the relationship between the first injector on-off valve state, the second injector on-off valve state, and the pressure P in the circulation flow path when the fuel cell in the present disclosure is generating electricity at a constant high load current.

[0051] Figure 7 1 is a flow chart showing an example of control of the fuel cell system of the present disclosure.

[0052] 10…Fuel cell (battery pack); 11…Fuel gas supply flow path; 12…Circulation flow path; 13…Fuel exhaust gas discharge flow path; 21…Fuel gas supply unit (hydrogen tank); 22…Main check valve; 23…Pressure regulating valve; 24…1st injector (Injector); 25…2nd injector; 26…Ejector (Ejector); 27…Gas-liquid separator; 28…Exhaust and drain valve; 29…Pressure sensor; 30…Current sensor; 40…Control unit (ECU); 100…Fuel cell system. DETAILED DESCRIPTION

[0053] The fuel cell system of the present disclosure is a fuel cell system,

[0054] The above-mentioned fuel cell system has:

[0055] Fuel cells;

[0056] A current sensor, detecting an output current value of the fuel cell;

[0057] A fuel gas supply unit, which supplies fuel gas to the fuel cell;

[0058] a circulation flow path connecting the fuel gas outlet of the fuel cell with the fuel gas inlet of the fuel cell and capable of returning the fuel exhaust gas discharged from the fuel gas outlet of the fuel cell as a circulation gas to the fuel gas inlet of the fuel cell for circulation;

[0059] An ejector is arranged in the circulation flow path;

[0060] A fuel gas supply flow path connecting the fuel gas supply unit and the ejector;

[0061] An ejector assembly is arranged at a position upstream of the ejector in the fuel gas supply flow path;

[0062] A gas-liquid separator is arranged at a position upstream of the ejector in the circulation flow path;

[0063] A fuel off-gas discharge flow path, branching from the gas-liquid separator of the circulation flow path, and capable of discharging the fuel off-gas to the outside of the fuel cell system;

[0064] A pressure sensor is disposed in the circulation flow path; and

[0065] Control Department,

[0066] The injector assembly includes a first injector and a second injector in parallel.

[0067] an injection amount of the fuel gas per unit time of the second injector is smaller than an injection amount of the fuel gas per unit time of the first injector,

[0068] The control unit controls the duty ratio of at least one injector selected from the group consisting of the first injector and the second injector to drive the injector according to the output current value so that the pressure of the fuel gas supplied to the fuel cell is maintained within a predetermined range.

[0069] The control unit determines whether the output current value is greater than a predetermined first threshold value.

[0070] When it is determined that the output current value is greater than the specified first threshold value, the control unit drives the first injector by performing duty cycle control, and drives the second injector by performing duty cycle control in a manner that opens the second injector at least when the first injector is closed.

[0071] In a fuel cell system having a first injector, a second injector having a smaller injection amount per unit time than the first injector, and a circulating flow path as a fuel gas system, there is a concern that the power generation of the fuel cell is large, and the pressure of the circulating flow path drops sharply when the first injector stops, resulting in a local fuel gas shortage. According to the present disclosure, in the case where the power generation of the fuel cell is large and the pressure drop in the circulating flow path is large when the first injector is closed, the second injector is used to slow down the pressure drop in the circulating flow path. That is, the fuel gas is injected from the second injector when the injection of the first injector stops, and the sharp pressure drop in the circulating flow path is suppressed. According to the present disclosure, even if the pressure in the circulating flow path drops sharply, the situation where it is lower than the lower limit of the set pressure range can be reduced. As a result, the occurrence of fuel gas shortage in the fuel cell can be suppressed, and the degradation of the catalyst of the fuel cell can be suppressed.

[0072] Figure 1 1 is a schematic configuration diagram showing an example of a fuel cell system of the present disclosure.

[0073] Figure 1 The fuel cell system 100 shown in the figure has a fuel cell 10, and has a fuel gas supply flow path 11, a circulation flow path 12, a fuel exhaust gas discharge flow path 13, a fuel gas supply unit 21, a main stop valve 22, a pressure regulating valve 23, a first injector 24, a second injector 25, an ejector 26, a gas-liquid separator 27, an exhaust and drain valve 28, a pressure sensor 29, a current sensor 30, and a control unit 40 as a fuel gas system. In addition, in Figure 1 Only the fuel gas system is shown in the figure, and the illustration of other oxidant gas systems, cooling systems, etc. is omitted.

[0074] The pressure sensor 29 detects the pressure of the fuel gas. The pressure sensor 29 is electrically connected to the control unit 40 and provides the detected pressure of the fuel gas to the control unit 40.

[0075] The current sensor 30 detects the output current value of the fuel cell. The current sensor 30 is electrically connected to the control unit 40 and provides the detected output current value of the fuel cell to the control unit 40.

[0076] The pressure regulating valve 23 is electrically connected to the control unit 40 , and reduces the pressure applied to the first injector 24 and the second injector 25 to, for example, about 1 MPa.

[0077] The gas-liquid separator 27 is disposed at a branch point between the circulation flow path 12 and the fuel off-gas discharge flow path 13 , separates fuel gas and water from the fuel off-gas discharged from the anode outlet, and returns the fuel gas to the circulation flow path 12 as a circulation gas.

[0078] The control unit 40 is electrically connected to the exhaust / drain valve 28 , and opens the exhaust / drain valve 28 as necessary to discharge unnecessary gas, water, and the like from the fuel off-gas discharge passage 13 to the outside.

[0079] The ejector 26 is disposed at a junction of the circulation flow path 12 and the fuel gas supply flow path 11 .

[0080] The first injector 24 and the second injector 25 are provided in the fuel gas supply flow path 11 at a position upstream of the ejector 26 .

[0081] The control unit 50 is electrically connected to the first injector 24 and the second injector 25, and switches the driving / stopping of the first injector 24 and the second injector 25 according to the output current value of the fuel cell 10. The fuel gas injection amount per unit time of the second injector 25 is smaller than the fuel gas injection amount per unit time of the first injector 24.

[0082] For the control unit 50, when the output current value of the fuel cell 10 is small, fuel gas is supplied only from the second injector 25; when the output current value is medium, fuel gas is supplied only from the first injector 24; when the output current value is large, fuel gas is supplied from both the first injector 24 and the second injector 25.

[0083] Figure 1 The fuel off-gas not used in the fuel cell 10 is recirculated by the ejector 26 , but a circulation pump may be provided in place of the ejector 26 . In addition, the fuel cell system 100 may include a circulation pump at a position upstream of the ejector 26 in the circulation flow path 12 .

[0084] In the present disclosure, fuel gas and oxidant gas are collectively referred to as reaction gas. The reaction gas supplied to the anode is fuel gas, and the reaction gas supplied to the cathode is oxidant gas. Fuel gas is a gas mainly containing hydrogen, and may also be hydrogen. Oxidant gas may be oxygen, air, dry air, etc.

[0085] The fuel cell system of the present disclosure is generally used by being mounted on a vehicle having an electric motor as a driving source.

[0086] Furthermore, the fuel cell system of the present disclosure may be mounted on a vehicle that can travel using the electric power of a secondary battery.

[0087] The electric motor is not particularly limited, and may be a conventionally known drive motor.

[0088] The vehicle may be a fuel cell vehicle.

[0089] A vehicle may be equipped with the fuel cell system of the present disclosure.

[0090] The fuel cell system of the present disclosure includes a fuel cell.

[0091] The fuel cell may include only one unit cell, or may be a stacked body including a plurality of unit cells stacked together, that is, a fuel cell stack.

[0092] The number of stacked cells is not particularly limited, and may be, for example, 2 to several hundred, or 2 to 300.

[0093] The fuel cell stack may include end plates at both ends in the stacking direction of the single cells.

[0094] A single cell of a fuel cell includes at least a membrane electrode gas diffusion layer assembly.

[0095] The membrane electrode gas diffusion layer assembly includes an anode side gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode side gas diffusion layer in this order.

[0096] The cathode (oxidant electrode) includes a cathode catalyst layer and a cathode-side gas diffusion layer.

[0097] The anode (fuel electrode) includes an anode catalyst layer and an anode-side gas diffusion layer.

[0098] The cathode catalyst layer and the anode catalyst layer are collectively referred to as catalyst layers. In addition, as the anode catalyst and the cathode catalyst, for example, Pt (platinum), Ru (ruthenium) and the like can be cited, as the matrix material and the conductive material supporting the catalyst, for example, carbon materials such as carbon and the like can be cited.

[0099] The cathode-side gas diffusion layer and the anode-side gas diffusion layer are collectively referred to as a gas diffusion layer.

[0100] The gas diffusion layer may be a gas-permeable conductive member or the like.

[0101] Examples of the conductive member include carbon porous bodies such as carbon cloth and carbon paper, and metal porous bodies such as metal mesh and foamed metal.

[0102] The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include fluorine-based electrolyte membranes such as a film of perfluorosulfonic acid containing water and hydrocarbon-based electrolyte membranes. Examples of the electrolyte membrane include Nafion membranes (manufactured by DuPont).

[0103] The single cell may include two separators sandwiching both sides of the membrane electrode gas diffusion layer assembly as needed. One of the two separators is an anode side separator, and the other is a cathode side separator. In the present disclosure, the anode side separator and the cathode side separator are collectively referred to as separators.

[0104] The separator may have supply holes and discharge holes for allowing the reaction gas and the coolant to flow in the stacking direction of the single cells. As the coolant, for example, a mixed solution of ethylene glycol and water may be used to prevent freezing at low temperatures.

[0105] Examples of the supply holes include fuel gas supply holes, oxidant gas supply holes, and refrigerant supply holes.

[0106] Examples of the discharge hole include a fuel gas discharge hole, an oxidant gas discharge hole, and a refrigerant discharge hole.

[0107] The partition may have more than one fuel gas supply hole, may have more than one oxidant gas supply hole, may have more than one refrigerant supply hole, may have more than one fuel gas discharge hole, may have more than one oxidant gas discharge hole, and may have more than one refrigerant discharge hole.

[0108] The separator may have a reaction gas flow path on a surface in contact with the gas diffusion layer. Also, the separator may have a coolant flow path for maintaining a constant temperature of the fuel cell on a surface opposite to the surface in contact with the gas diffusion layer.

[0109] When the separator is an anode side separator, it may have one or more fuel gas supply holes, one or more oxidant gas supply holes, one or more refrigerant supply holes, one or more fuel gas discharge holes, one or more oxidant gas discharge holes, and one or more refrigerant discharge holes. The anode side separator may have a fuel gas flow path for the fuel gas to flow from the fuel gas supply hole to the fuel gas discharge hole on the surface in contact with the anode side gas diffusion layer, and may have a refrigerant flow path for the refrigerant to flow from the refrigerant supply hole to the refrigerant discharge hole on the surface opposite to the surface in contact with the anode side gas diffusion layer.

[0110] When the partition is a cathode side partition, it may have one or more fuel gas supply holes, one or more oxidant gas supply holes, one or more refrigerant supply holes, one or more fuel gas discharge holes, one or more oxidant gas discharge holes, and one or more refrigerant discharge holes. The cathode side partition may have an oxidant gas flow path for the oxidant gas to flow from the oxidant gas supply holes to the oxidant gas discharge holes on the surface in contact with the cathode side gas diffusion layer, and may have a refrigerant flow path for the refrigerant to flow from the refrigerant supply holes to the refrigerant discharge holes on the surface opposite to the surface in contact with the cathode side gas diffusion layer.

[0111] The separator may also be an airtight conductive member, etc. As the conductive member, for example, it may be dense carbon that becomes airtight by compressing carbon, or a metal (such as iron, aluminum, and stainless steel, etc.) plate formed by stamping, etc. In addition, the separator may have a current collecting function.

[0112] The fuel cell stack may have a manifold such as an inlet manifold through which the supply holes communicate, and an outlet manifold through which the exhaust holes communicate.

[0113] Examples of the inlet manifold include an anode inlet manifold, a cathode inlet manifold, and a refrigerant inlet manifold.

[0114] Examples of the outlet manifold include an anode outlet manifold, a cathode outlet manifold, and a refrigerant outlet manifold.

[0115] The fuel cell system includes a fuel gas supply unit, a fuel gas supply flow path, a circulation flow path, an ejector, an ejector assembly unit, a gas-liquid separator, a fuel exhaust gas discharge flow path, a control unit, a current sensor, and a pressure sensor as a fuel gas system of the fuel cell.

[0116] The fuel gas supply unit supplies the fuel gas to the fuel cell. Specifically, the fuel gas supply unit supplies the fuel gas to the anode of the fuel cell.

[0117] Examples of the fuel gas supply unit include a fuel tank and the like, and more specifically, a liquid hydrogen tank, a compressed hydrogen tank and the like.

[0118] The fuel gas supply unit is electrically connected to the control unit, and can control the opening and closing of a main check valve of the fuel gas supply unit according to a control signal from the control unit, thereby controlling the on / off of the supply of fuel gas to the fuel cell.

[0119] The circulation flow path connects the fuel gas outlet of the fuel cell and the fuel gas inlet of the fuel cell.

[0120] The circulation flow path can return the fuel gas discharged from the fuel gas outlet of the fuel cell, that is, the fuel off-gas, as the circulation gas to the fuel gas inlet of the fuel cell to circulate it. The fuel gas inlet may be a fuel gas supply hole, an anode inlet manifold, or the like.

[0121] An ejector is arranged in the circulation flow path.

[0122] The ejector may be disposed, for example, at a confluence portion of the circulation flow path with the fuel gas supply flow path. The ejector supplies a mixed gas including the fuel gas and the circulation gas to the anode of the fuel cell. As the ejector, a conventionally known ejector may be used.

[0123] The circulation pump may be arranged at a position upstream of the ejector in the circulation flow path. The circulation pump may be arranged at a confluence portion of the circulation flow path with the fuel gas supply flow path instead of the ejector. The circulation pump may serve as a propulsion force for circulating the fuel exhaust gas as the circulation gas. The circulation pump is electrically connected to the control unit, and the flow rate of the circulation gas can be adjusted by controlling the on / off of the drive of the circulation pump and the rotation speed, etc., by the control unit.

[0124] The fuel gas supply flow path connects the fuel gas supply unit and the ejector. The fuel gas supply flow path enables the supply of fuel gas to the ejector.

[0125] The ejector aggregate portion is disposed in the fuel gas supply flow path at a position upstream of the ejector.

[0126] The injector assembly unit includes a first injector and a second injector arranged in parallel.

[0127] The injection amount of the fuel gas per unit time of the second injector is smaller than the injection amount of the fuel gas per unit time of the first injector. Conventionally known injectors can be appropriately used as the first injector and the second injector.

[0128] The pressure regulating valve may be disposed in the fuel gas supply flow path at a position upstream of the injector assembly portion. The pressure regulating valve is electrically connected to the control unit and reduces the pressure applied to the first injector and the second injector.

[0129] The gas-liquid separator (anode gas-liquid separator) is arranged upstream of the ejector in the circulation flow path.

[0130] The gas-liquid separator may be disposed at a branch point between the fuel off-gas discharge flow path and the circulation flow path.

[0131] The gas-liquid separator may be arranged in the fuel off-gas discharge flow path at a position upstream of the exhaust and drain valve.

[0132] The gas-liquid separator separates the water contained in the fuel gas discharged from the fuel gas outlet, that is, the fuel exhaust gas, from the fuel gas. As a result, the fuel gas can be returned to the circulation flow path as circulating gas, and the exhaust and drain valve of the fuel exhaust gas discharge flow path can be opened to discharge unnecessary gas and water to the outside. In addition, since the gas-liquid separator can suppress the flow of excess water into the circulation flow path, the freezing of the circulation pump and the like caused by the water can be suppressed.

[0133] The fuel off-gas discharge flow path branches off from the circulation flow path via the gas-liquid separator.

[0134] The fuel off-gas discharge flow path can discharge the fuel off-gas discharged from the fuel gas outlet of the fuel cell to the outside of the fuel cell system. The fuel gas outlet may be a fuel gas discharge hole, an anode outlet manifold, or the like.

[0135] An exhaust / drain valve (fuel off-gas discharge valve) may be disposed in the fuel off-gas discharge flow path. The exhaust / drain valve is disposed in the fuel off-gas discharge flow path at a position downstream of the gas-liquid separator.

[0136] The exhaust and drain valve can discharge fuel exhaust gas and water to the outside (outside the system), where the outside can be the outside of the fuel cell system or the outside of the vehicle.

[0137] The exhaust and drain valve is electrically connected to the control unit, and the exhaust and drain valve can be opened and closed by the control unit to adjust the discharge flow of the fuel exhaust gas to the outside. In addition, the fuel gas pressure (anode pressure) supplied to the anode of the fuel cell can be adjusted by adjusting the opening of the exhaust and drain valve.

[0138] The fuel exhaust gas may include fuel gas that passes through the anode without reacting, water generated at the cathode and reaches the anode, etc. The fuel exhaust gas may include corrosive substances generated at the catalyst layer and electrolyte membrane, etc., and oxidant gas that may be supplied to the anode during scavenging.

[0139] The current sensor detects the output current value of the fuel cell. The current sensor is electrically connected to the control unit and provides the detected output current value of the fuel cell to the control unit.

[0140] As the current sensor, a conventionally known ammeter or the like can be used.

[0141] The pressure sensor is disposed in the circulation flow path. From the viewpoint of improving detection accuracy, the pressure sensor may be disposed in a region of the circulation flow path downstream of the ejector and between the ejector and the fuel cell.

[0142] The pressure sensor detects the pressure of the fuel gas. The pressure sensor is electrically connected to the control unit and provides the detected pressure of the fuel gas to the control unit.

[0143] As the pressure sensor, a conventionally known pressure gauge or the like can be used.

[0144] As the oxidant gas system of the fuel cell, the fuel cell system may include an oxidant gas supply unit, an oxidant gas supply flow path, and an oxidant off-gas discharge flow path.

[0145] The oxidant gas supply unit supplies the oxidant gas to the fuel cell. Specifically, the oxidant gas supply unit supplies the oxidant gas to the cathode of the fuel cell.

[0146] As the oxidizing gas supply unit, for example, an air compressor or the like can be used.

[0147] The oxidant gas supply unit is electrically connected to the control unit. The oxidant gas supply unit is driven according to a control signal from the control unit. The oxidant gas supply unit can be controlled by the control unit to select at least one of the group consisting of a flow rate and a pressure of the oxidant gas supplied from the oxidant gas supply unit to the cathode.

[0148] The oxidant gas supply flow path connects the oxidant gas supply unit to the oxidant gas inlet of the fuel cell. The oxidant gas supply flow path enables the supply of oxidant gas from the oxidant gas supply unit to the cathode of the fuel cell. The oxidant gas inlet can be an oxidant gas supply hole, a cathode inlet manifold, etc.

[0149] The oxidant exhaust gas discharge passage is connected to the oxidant gas outlet of the fuel cell. The oxidant exhaust gas discharge passage enables the oxidant gas discharged from the cathode of the fuel cell, that is, the oxidant exhaust gas, to be discharged to the outside. The oxidant gas outlet can be an oxidant gas discharge hole, a cathode outlet manifold, etc.

[0150] The oxidant off-gas discharge flow path may be provided with an oxidant gas pressure regulating valve.

[0151] The oxidant gas pressure regulating valve is electrically connected to the control unit, and the control unit opens the oxidant gas pressure regulating valve to discharge the oxidant gas after the reaction, that is, the oxidant waste gas, from the oxidant waste gas discharge flow path to the outside. In addition, the oxidant gas pressure (cathode pressure) supplied to the cathode can be adjusted by adjusting the opening of the oxidant gas pressure regulating valve.

[0152] The fuel cell system may include a coolant supply unit and a coolant circulation flow path as a cooling system for the fuel cell.

[0153] The coolant circulation flow path communicates with the coolant supply hole and the coolant discharge hole provided in the fuel cell, and can circulate the coolant supplied from the coolant supply unit inside and outside the fuel cell.

[0154] The refrigerant supply unit is electrically connected to the control unit. The refrigerant supply unit is driven according to a control signal from the control unit. The refrigerant supply unit controls the flow rate of the refrigerant supplied from the refrigerant supply unit to the fuel cell by the control unit. Thus, the temperature of the fuel cell can be controlled.

[0155] The refrigerant supply unit may be, for example, a cooling water pump or the like.

[0156] The refrigerant circulation flow path may be provided with a radiator for radiating heat of the cooling water.

[0157] A storage tank storing the refrigerant may be provided in the refrigerant circulation flow path.

[0158] The fuel cell system may include a secondary battery.

[0159] As long as the secondary battery (storage battery) can realize charging and discharging, for example, a nickel-metal hydride secondary battery and a lithium-ion secondary battery and other previously known secondary batteries can be cited. In addition, the secondary battery can include a storage element such as a double-layer capacitor. The secondary battery can also be a structure in which a plurality of batteries are connected in series. The secondary battery supplies power to a motor and an oxidant gas supply unit, etc. The secondary battery can be configured to be charged from a power source external to the vehicle, such as a household power source. The secondary battery can be charged by the output of a fuel cell. The charging and discharging of the secondary battery can be controlled by a control unit.

[0160] The control unit physically includes, for example, a CPU (central processing unit) or other processing unit, a ROM (read-only memory) for storing control programs and control data processed by the CPU, a RAM (random access memory) or other storage devices mainly used as various work areas for control processing, and an input / output interface. In addition, the control unit may be, for example, a control unit such as an electronic control unit (ECU: Electronic Control Unit).

[0161] The control unit may be electrically connected to an ignition switch that can be mounted on a vehicle. The control unit may be configured to be operable by an external power supply even when the ignition switch is turned off.

[0162] The control unit controls the duty ratio of at least one injector selected from the group consisting of the first injector and the second injector according to the output current value so that the pressure of the fuel gas to the fuel cell is maintained within a predetermined range.

[0163] The control unit determines whether the output current value is larger than a predetermined first threshold value.

[0164] When it is determined that the output current value is greater than a predetermined first threshold value, the control unit performs duty cycle control on the first injector to drive the first injector, and performs duty cycle control on the second injector to drive the second injector so that the second injector is opened when at least the first injector is closed.

[0165] The duty ratio of the injector is the ratio of the valve opening time to the time of one cycle, with one cycle starting from the time when the injector valve is opened and ending when the valve is opened again after closing.

[0166] In the present disclosure, duty cycle control refers to control in a manner that the duty cycle becomes an arbitrary value greater than 0% and less than 100%. Since the state where the duty cycle is 0% is a state where there is no drive instruction from the control unit and the injector is stopped with the valve closed, it is not a state where the duty cycle is controlled. Since the state where the duty cycle is 100% is a state where the injector is always driven with the valve open, it is not a state where the duty cycle is controlled. The controlled duty cycle is not particularly limited as long as it maintains the pressure of the fuel gas to the fuel cell within a specified range and is greater than 0% and less than 100%, and can be appropriately set according to the output current value. The control unit monitors the value of the pressure of the fuel gas detected by the pressure sensor, so that the control unit can control the duty cycle in a manner that maintains the pressure of the fuel gas within a specified range.

[0167] The predetermined first threshold value of the output current value may be, for example, the output current value of the fuel cell when the fuel cell is generating electricity at a high load current. The specific output current value may be appropriately set according to the performance of the fuel cell.

[0168] The lower limit of the pressure within the predetermined range of the fuel gas can be appropriately set based on empirical rules to a pressure at which local fuel gas shortage is unlikely to occur. The upper limit of the pressure within the predetermined range of the fuel gas can be appropriately set based on empirical rules to a pressure at which electrolyte membrane degradation is unlikely to occur.

[0169] When it is determined that the output current value is greater than a specified first threshold value, as a first embodiment, the control unit can perform duty cycle control on the first injector to drive the first injector, and perform duty cycle control on the second injector to drive the second injector in a manner that the second injector opens the valve simultaneously with the closing of the valve of the first injector, and closes the valve of the second injector simultaneously with the opening of the valve of the first injector.

[0170] When it is determined that the output current value is greater than a specified first threshold value, as a second embodiment, the control unit can perform duty cycle control on the first injector to drive the first injector, and perform duty cycle control on the second injector to drive the second injector in a manner such that the second injector opens the valve after the first injector closes the valve, and closes the valve after the first injector opens the valve.

[0171] When it is determined that the output current value is greater than the predetermined first threshold value, as a third embodiment, the control unit may perform a control to drive the first injector by performing duty control on the first injector and to always open the second injector (duty ratio 100%).

[0172] When it is determined that the output current value is equal to or less than a predetermined first threshold value, the control unit determines whether the output current value is equal to or less than a predetermined second threshold value that is smaller than the predetermined first threshold value.

[0173] When it is determined that the output current value is equal to or less than the predetermined second threshold value, the control unit may always close the valve of the first injector and perform duty ratio control on the second injector to drive the second injector. This can improve the fuel efficiency.

[0174] On the other hand, when it is determined that the output current value is greater than the predetermined second threshold value, the control unit can always close the valve of the second injector and perform duty cycle control on the first injector to drive the first injector. Thus, for example, during normal operation of the fuel cell, fuel gas can be supplied to the fuel cell using only the first injector.

[0175] The second threshold value of the output current value may be, for example, the output current value of the fuel cell when the fuel cell is generating electricity at a medium load current. The specific output current value may be appropriately set according to the performance of the fuel cell. That is, when the fuel cell is generating electricity at a medium load current, the second injector is stopped (the valve is always closed, and the duty cycle is 0%), and the fuel gas is periodically injected from the first injector (duty cycle control). When the fuel cell is generating electricity at a load current less than the medium load current, the first injector is stopped (the valve is always closed, and the duty cycle is 0%), and the fuel gas is periodically injected from the second injector (duty cycle control).

[0176] Figure 2 This is a diagram showing an example of the relationship between the on-off valve state of the first injector and the pressure P in the circulation flow path when the fuel cell is generating electricity at a constant medium load current.

[0177] Since the fuel cell is generating electricity at a constant load current, a constant amount of fuel gas is consumed in the fuel cell per unit time. If the pressure P in the circulation path reaches the lower limit PL, the control unit (ECU) causes the first injector to open the valve. The amount of fuel gas injected when the first injector opens the valve is greater than the amount of fuel gas consumed by the fuel cell. Therefore, when the first injector is open, the pressure P in the circulation path rises. If the pressure P in the circulation path reaches the upper limit PU, the ECU causes the first injector to close the valve. When the first injector is closed, the pressure P in the circulation path decreases because the fuel cell consumes fuel gas by generating electricity. By repeating the above process, the pressure P in the circulation path is maintained within the range of above the lower limit PL and below the upper limit PU.

[0178] Figure 3 This is a diagram showing an example of the relationship between the on-off valve state of the first injector and the pressure P in the circulation flow path when the fuel cell in the conventional technology is generating electricity at a constant high load current.

[0179] Since the fuel cell is generating electricity at a constant high load current, the amount of fuel gas consumed per unit time in the fuel cell is greater than that at a medium load. On the other hand, the first injector controls the amount of fuel gas injection by the valve opening time, and the amount of fuel gas injected per unit time during the valve opening is constant. Therefore, the slope of the pressure increase during the valve opening of the first injector becomes smaller, and the slope of the pressure decrease during the valve closing of the first injector becomes larger.

[0180] When the pressure P in the circulation flow path reaches the lower limit PL, the first injector opens again. However, if the slope of the pressure drop is large, the pressure may easily fall below the lower limit PL due to a delay in the response of the first injector, a delay in the signal of the pressure sensor, a deviation in the detected value, and the like.

[0181] <First embodiment>

[0182] Figure 4 This is a diagram showing an example of the relationship between the first injector on-off valve state, the second injector on-off valve state, and the pressure P in the circulation flow path when the fuel cell in the present disclosure is generating electricity at a constant high load current.

[0183] In the first embodiment of the present disclosure, the second injector is opened while the first injector is closed to supply fuel gas to the fuel cell, thereby reducing the slope of the pressure drop while the first injector is closed.

[0184] The amount of fuel gas injected per unit time by the second injector is less than the amount of fuel consumed by the fuel cell at high load. Therefore, during the period when the second injector opens the valve and injects fuel gas, the pressure P in the circulation flow path also gradually decreases. That is, the pressure drop rate during the closing of the first injector is faster than Figure 3 The comparative example shown is slow.

[0185] Therefore, the pressure in the circulation flow path is unlikely to fall below the lower limit value PL, and the occurrence of local fuel gas deficiency and catalyst degradation can be suppressed in the fuel cell.

[0186] <Second embodiment>

[0187] Figure 5 This is a diagram showing another example of the relationship between the first injector on-off valve state, the second injector on-off valve state, and the pressure P in the circulation flow path when the fuel cell in the present disclosure is generating electricity at a constant high load current.

[0188] In the first embodiment, the valve opening timing of the second injector coincides with the valve closing timing of the first injector, but they may not coincide with each other.

[0189] exist Figure 5In the timing chart shown, in the second embodiment, the second injector opens while the first injector is closed until the first injector opens. However, the second injector opens after the first injector closes, and the second injector closes after the first injector opens.

[0190] When the valve opening and closing control is performed in such a manner that the opening and closing periods of the first injector and the closing and closing periods of the second injector are the same as in the first embodiment, if the response delay of the first injector is greater than the response delay of the second injector, a period of time in which both valves are closed occurs when the pressure P in the circulation flow path is near the lower limit value, and there is a concern that the slope of the pressure drop will increase. If the second injector is closed after the ECU confirms that the first injector is open, as in the second embodiment, the slope of the pressure drop can be suppressed from increasing.

[0191] In addition, there is a time when the second injector closes its valve just after the first injector closes its valve, and the slope of the pressure P in the circulation flow path becomes larger, but since it is sufficiently separated from the lower limit PL, the pressure P is lower than the lower limit PL, and the possibility of fuel gas shortage in the fuel cell is low. In addition, if the state of excessive pressure becomes longer, the electrolyte membrane is prone to deterioration, but in the second embodiment, since the pressure is first reduced all at once and then gradually reduced, the state of excessive pressure can be quickly eliminated, and the degradation of the electrolyte membrane can be suppressed.

[0192] <Third embodiment>

[0193] Figure 6 This is a diagram showing another example of the relationship between the first injector on-off valve state, the second injector on-off valve state, and the pressure P in the circulation flow path when the fuel cell in the present disclosure is generating electricity at a constant high load current.

[0194] In the third embodiment, when the fuel cell is generating electricity at a high load current, the second injector is always open regardless of the valve opening state of the first injector. In the third embodiment, although the fuel utilization rate is worse than in the first and second embodiments, in the third embodiment, the second injector is opened while the valve of the first injector is closed to supply fuel gas, thereby suppressing a sharp drop in the pressure P in the circulation flow path while the valve of the first injector is closed.

[0195] Figure 7 1 is a flowchart showing an example of control of the fuel cell system of the present disclosure.

[0196] The control unit detects an output current value of the fuel cell detected by the current sensor.

[0197] The control unit determines whether the detected output current value is larger than a predetermined first threshold value.

[0198] When it is determined that the output current value is greater than a specified first threshold value, the control unit performs duty cycle control on the first injector to drive the first injector, and performs duty cycle control on the second injector to drive the second injector in a manner that opens the valve of at least the first injector when the valve is closed, and then ends the control.

[0199] On the other hand, when it is determined that the output current value is equal to or less than the predetermined first threshold value, the control unit determines whether the output current value is equal to or less than a predetermined second threshold value that is smaller than the predetermined first threshold value.

[0200] When it is determined that the output current value is equal to or less than the predetermined second threshold value, the control unit causes the first injector to be always closed, performs duty ratio control on the second injector to drive the second injector, and then ends the control.

[0201] On the other hand, when it is determined that the output current value is larger than the predetermined second threshold value, the control unit causes the second injector to be always closed, performs duty ratio control on the first injector to drive the first injector, and then ends the control.

Claims

1. A fuel cell system, It is characterized in that The fuel cell system comprises: Fuel cells; A current sensor, detecting an output current value of the fuel cell; a fuel gas supply unit for supplying fuel gas to the fuel cell, a circulation flow path connecting the fuel gas outlet of the fuel cell with the fuel gas inlet of the fuel cell and capable of returning the fuel exhaust gas discharged from the fuel gas outlet of the fuel cell to the fuel gas inlet of the fuel cell as a circulation gas; An ejector, arranged in the circulation flow path; A fuel gas supply flow path connecting the fuel gas supply unit and the ejector; an ejector assembly portion, arranged at a position upstream of the ejector in the fuel gas supply flow path; a gas-liquid separator disposed at a position upstream of the ejector in the circulation flow path; a fuel off-gas discharge flow path branching from the gas-liquid separator of the circulation flow path and capable of discharging the fuel off-gas to the outside of the fuel cell system; A pressure sensor is arranged in the circulation flow path; as well as Control Department, The injector assembly includes a first injector and a second injector arranged in parallel. an injection amount of the fuel gas per unit time of the second injector is smaller than an injection amount of the fuel gas per unit time of the first injector, The control unit drives at least one injector selected from the group consisting of the first injector and the second injector by performing duty control according to the output current value so as to maintain the pressure of the fuel gas supplied to the fuel cell within a predetermined range. The control unit determines whether the output current value is greater than a predetermined first threshold value. When it is determined that the output current value is greater than the predetermined first threshold value, the control unit drives the first injector by performing duty cycle control, and drives the second injector by performing duty cycle control in a manner that the second injector opens a valve after the first injector closes a valve, and the second injector closes a valve after the first injector opens a valve. When it is determined that the output current value is equal to or less than the first threshold value, the control unit determines whether the output current value is equal to or less than a second threshold value that is smaller than the first threshold value. When it is determined that the output current value is equal to or less than the predetermined second threshold value, the control unit causes the first injector to be always closed and drives the second injector by performing duty ratio control. When it is determined that the output current value is larger than the predetermined second threshold value, the control unit causes the second injector to be always closed and drives the first injector by performing duty ratio control.

2. The fuel cell system according to claim 1, It is characterized in that When it is determined that the output current value is larger than the predetermined first threshold value, the control unit performs a control to drive the first injector by performing duty control and to always open the second injector.

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