Fuel cell system

Abstract

A fuel cell system is provided with: a first supply unit that has a first injector and a first ejector and supplies fuel gas to a fuel cell via a first supply flow path connected to a gas inflow unit; a second supply unit that has a second injector and a second ejector and supplies the fuel gas to the fuel cell via a second supply flow path connected to the gas inflow unit; and a control unit that controls the first injector and the second injector. The circulation flow ratio of the second ejector is higher than the circulation flow ratio of the first ejector. The control unit controls the first injector and the second injector such that the other of the first injector and the second injector injects the fuel gas during a predetermined period when either the first injector or the second injector injects the fuel gas during the predetermined period.

Description

Technical Field

[0001] This invention relates to a fuel cell system having multiple ejectors. Background Technology

[0002] In recent years, efforts have been actively undertaken to achieve a low-carbon society and even a decarbonized society. Research and development related to fuel cells in the vehicle sector is also underway to reduce carbon dioxide emissions and improve energy efficiency. Regarding this, fuel cell systems with a pair of ejectors with different recirculation capacities in the flow path supplying fuel gas to the fuel cell are known (see, for example, Patent Document 1). In the system described in Patent Document 1, when the required power-to-weight ratio threshold is low, fuel gas is supplied to the fuel cell using a first ejector with a high recirculation capacity. Then, when there is an abnormality in the fuel gas injection from the first ejector, the supply from the first ejector is stopped, and fuel gas is supplied to the fuel cell using a second ejector with a low recirculation capacity.

[0003] Existing technical documents Patent documents Patent document 1: Japanese Patent Application Publication No. 2021-118047 (JP2021-118047). Summary of the Invention

[0004] The problem the invention aims to solve However, in a fuel cell system with a pair of ejectors having different cycle capacities, the system described in Patent Document 1 above has room for improvement from the viewpoint of optimizing the drainage performance of the fuel cell.

[0005] Solution for solving the problem A fuel cell system according to one embodiment of the present invention comprises: a fuel cell that generates electricity through an electrochemical reaction of fuel gas and oxidant gas, and having a gas inlet for fuel gas to flow into and a gas outlet for fuel gas to flow out; a first supply unit having a first injector for injecting fuel gas and supplying fuel gas to the fuel cell via a first supply channel connected to the gas inlet; a second supply unit having a second injector for injecting fuel gas and supplying fuel gas to the fuel cell via a second supply channel connected to the gas inlet; and a control unit that controls the first and second injectors to inject fuel gas in an injection mode corresponding to the required power. The first supply unit further comprises a first ejector disposed between the first injector and the gas inlet, which guides fuel gas flowing out of the gas outlet through a first circulation channel to the first supply channel; the second supply unit further comprises a second ejector disposed between the second injector and the gas inlet, which guides fuel gas flowing out of the gas outlet through a second circulation channel to the second supply channel. The first injector and the second injector are configured such that the fuel gas injection quantity per unit time of the first injector is greater than that of the second injector per unit time. The first ejector and the second ejector are configured such that the ratio of the circulation volume of the first ejector to the fuel gas injection quantity of the first injector (i.e., a first circulation flow rate ratio) is less than the ratio of the circulation volume of the second ejector to the fuel gas injection quantity of the second injector (i.e., a second circulation flow rate ratio). The control unit controls the first and second injectors in such a manner that when either the first or second injector injects fuel gas during a predetermined cycle, the other injects fuel gas during the predetermined cycle.

[0006] Invention Effects Using this invention, the drainage performance of fuel cell stacks can be improved. Attached Figure Description

[0007] Figure 1 This is a perspective view that schematically illustrates the overall structure of a fuel cell stack according to an embodiment of the present invention; Figure 2 It is shown Figure 1 A three-dimensional diagram showing the schematic structure of the integrated electrode assembly included in the fuel cell stack; Figure 3 This means that in Figure 1 A diagram of stagnant water generated within a fuel cell stack; Figure 4 This is a diagram that schematically illustrates the main structural components of a fuel cell system according to an embodiment of the present invention; Figure 5 It is shown Figure 4 A diagram showing the structure of the ejector included in a fuel cell system; Figure 6 It is a graph showing the relationship between the ejector's injection rate and the ejector's circulation rate; Figure 7A It is shown Figure 4 An example of a fuel gas injection pattern for a fuel cell system; Figure 7B It is shown Figure 7A A diagram of a variant example; Figure 8 This is a graph illustrating an example of how the pressure difference between the inlet and outlet of the fuel cell stack and the drainage rate of stagnant water change over time, as obtained by the fuel cell system according to an embodiment of the present invention. Figure 9 It is shown Figure 8 A comparative example diagram; Figure 10 This is a graph showing the relationship between the lag time from the end of ejection on the large ejector side to the start of ejection on the small ejector side and the drainage rate of the retained water. Figure 11 It is shown by Figure 4 A flowchart of an example of the processing performed by the ECU; Figure 12 It is shown Figure 4 A graph showing the relationship between the injection cycle and valve opening time of the injector; Figure 13 It is shown by Figure 1 A diagram showing the stable and unstable regions of power generation implemented by a fuel cell stack, corresponding to instantaneous gas flow rate and average gas flow rate; Figure 14A This is a timing diagram illustrating an example of the operation of a fuel cell system during transitional operation according to an embodiment of the present invention; Figure 14B This is a timing diagram illustrating another example of the operation of a fuel cell system during transitional operation according to an embodiment of the present invention; Figure 15A It is shown by Figure 4 A flowchart illustrating an example of the processing performed by the ECU is shown. Figure 14A The timing diagram corresponds to a flowchart of an example of the processing.

[0008] Figure 15B It is shown Figure 4 An example of the processing performed by the ECU is shown in the diagram. Figure 14B The timing diagram corresponds to a flowchart of an example of the processing. Figure 16 This is a diagram illustrating an example of how the injector's spray pattern changes when the required power is increased. Detailed Implementation

[0009] The following is for reference Figures 1 to 16 Embodiments of the present invention will be described. The fuel cell system of the embodiments of the present invention has a fuel cell stack as the main body of the fuel cell. The fuel cell is, for example, mounted on a vehicle to generate electricity for vehicle propulsion. First, the overall structure of the fuel cell stack will be briefly described. It should be noted that the fuel cell stack is sometimes simply referred to as a fuel cell, and sometimes as the fuel cell body.

[0010] Figure 1 This is a perspective view schematically illustrating the overall structure of a fuel cell stack 100 according to an embodiment of the present invention. Hereinafter, for convenience, as shown in the figures, the three mutually orthogonal axial directions are defined as the front-rear direction, the left-right direction, and the up-down direction, and the structure of each part will be described according to this definition. These directions are not necessarily the same as the front-rear, left-right, and up-down directions of a vehicle. For example, Figure 1 The front-back direction can be the front-back direction of the vehicle, the left-right direction, or the up-down direction.

[0011] like Figure 1 As shown, the fuel cell stack 100 is generally rectangular in shape and includes: a battery stack 101, which is formed by stacking multiple power generating cells 1 in the front-to-back direction; and end units 102, which are disposed at the front and rear ends of the battery stack 101. The length of the battery stack 101 in the left-to-right direction is longer than its length in the top-to-bottom direction. For convenience, Figure 1 A single power generation cell 1 is shown. The power generation cell 1 has: an integrated electrode assembly 2 (UEA) having a membrane electrode assembly including an electrolyte membrane and electrodes; and separators 3, 3, which are disposed on the front and rear sides of the integrated electrode assembly 2, clamping the integrated electrode assembly 2. The integrated electrode assembly 2 and the separators 3 are arranged alternately in the front-rear direction. The integrated electrode assembly 2 is sometimes referred to as a membrane electrode structure.

[0012] The separator 3 has a pair of front and rear thin metal plates with a corrugated cross-section, and the outer peripheries of these plates are joined together to form a single unit. The separator 3 uses a conductive material with excellent corrosion resistance, such as titanium, titanium alloy, or stainless steel. A cooling channel for the flow of cooling medium is formed inside the separator 3 (between the pair of thin plates), and the power generation surface of the power generation cell 1 is cooled by the flow of the cooling medium. For example, water can be used as the cooling medium. A mixture of water and ethylene glycol can also be used. The surfaces (front and rear surfaces) of the separator 3 facing the integrated electrode assembly 2 are formed into an uneven shape by stamping or the like to form a gas flow channel between the separator 3 and the membrane electrode assembly 2. The cooling channel can also be formed by a mesh channel or by a cold medium contact surface welding type, in which components are welded to the cold medium contact surface to form the channel.

[0013] The septum 3 on the front side of the integrated electrode assembly 2 is, for example, an anode-side septum (anode septum), forming an anode flow channel for fuel gas flow between the anode septum 3 and the membrane electrode assembly 2. The septum 3 on the rear side of the integrated electrode assembly 2 is, for example, a cathode-side septum (cathode septum), forming a cathode flow channel for oxidant gas flow between the cathode septum 3 and the membrane electrode assembly 2. For example, hydrogen can be used as the fuel gas, and for example, air can be used as the oxidant gas.

[0014] Figure 2 This is a perspective view showing the schematic structure of the integrated electrode assembly 2. (See diagram below.) Figure 2 As shown, the integrated electrode assembly 2 has a generally rectangular membrane electrode assembly 20 (MEA) and a frame 21 supporting the membrane electrode assembly 20. The membrane electrode assembly 20 has an electrolyte membrane, an anode electrode disposed on the front surface of the electrolyte membrane, and a cathode electrode disposed on the rear surface of the electrolyte membrane.

[0015] Electrolyte membranes can be solid polymeric electrolyte membranes, such as films made of perfluorosulfonic acid polymers containing water. They are not limited to fluorinated electrolyte membranes; hydrocarbon electrolyte membranes can also be used.

[0016] The anode electrode has an electrode catalyst layer formed on the front surface of the electrolyte membrane, serving as the reaction field for the electrode reaction, and a gas diffusion layer disposed on the front surface of the electrode catalyst layer, which diffuses and supplies fuel gas. The cathode electrode has an electrode catalyst layer formed on the rear surface of the electrolyte membrane, serving as the reaction field for the electrode reaction, and a gas diffusion layer disposed on the rear surface of the electrode catalyst layer, which diffuses and supplies oxidant gas. The electrode catalyst layer includes a catalytic metal that promotes the electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas, a proton-conducting electrolyte (such as an ionomer), and electron-conducting carbon particles. The gas diffusion layer is composed of a permeable conductive component, such as a porous carbon body.

[0017] At the anode electrode, the fuel gas (hydrogen) supplied via the anode channel and gas diffusion layer is ionized by a catalyst and moves through the electrolyte membrane toward the cathode electrode. The generated electrons are extracted as electrical energy via an external circuit. At the cathode electrode, the oxidant gas (oxygen) supplied via the cathode channel and gas diffusion layer reacts with hydrogen ions introduced from the anode electrode and electrons moving from the anode electrode to produce water. The generated water provides appropriate humidity to the electrolyte membrane, and the remaining water is discharged to the outside of the integrated electrode assembly 2 along the gas flow.

[0018] The frame 21 is a thin, generally rectangular plate made of insulating resin, rubber, or the like. A generally rectangular opening 21a is provided in the center of the frame 21. The membrane electrode assembly 20 is positioned to cover the entire opening 21a and is supported by the periphery of the opening 21a. Three through holes 211-213 are arranged vertically on the left side of the opening 21a of the frame 21, penetrating the frame 21 in the front-back direction. Three through holes 214-216 are arranged vertically on the right side of the opening 21a, penetrating the frame 21 in the front-back direction.

[0019] like Figure 1 As shown, through holes 311 to 316 are formed in the front and rear partitions 3 of the integrated electrode assembly 2 at positions corresponding to the through holes 211 to 216 of the frame 21, respectively. These through holes 311 to 316 penetrate the partition 3 in the front-rear direction. The through holes 311 to 316 are connected to the through holes 211 to 216 of the frame 21. Through the collection of these interconnected through holes 211 to 216 and 311 to 316, flow channels PA1 to PA6 (shown with arrows for convenience) are formed, penetrating the battery stack 101 and extending in the front-rear direction. Flow channels PA1 to PA6 are sometimes also called manifolds. Flow channels PA1 to PA6 are connected to the external manifolds of the fuel cell stack 100.

[0020] The flow channel PA1 (solid arrow), extending forward through through holes 211 and 311, is the fuel gas supply channel. The flow channel PA6 (solid arrow), extending backward through through holes 216 and 316, is the fuel gas discharge channel. The fuel gas supply channel PA1 and the fuel gas discharge channel PA6 communicate with the anode channel, which is positioned facing the front surface of the membrane electrode assembly 20, as shown by the solid arrows. Fuel gas flows from left to right through the anode channel via the fuel gas supply channel PA1 and the fuel gas discharge channel PA6. The communication between the anode channel and other channels PA2 to PA5 is cut off by a seal (not shown). The fuel gas flowing in the fuel gas discharge channel PA6 is the fuel gas remaining after a portion of the anode electrode has been used; this is sometimes referred to as fuel exhaust.

[0021] The flow channel PA4 (dashed arrow), extending forward through through holes 214 and 314, is the oxidant gas supply channel. The flow channel PA3 (dashed arrow), extending backward through through holes 213 and 313, is the oxidant gas discharge channel. The oxidant gas supply channel PA4 and the oxidant gas discharge channel PA3 are connected to the cathode channel, which is positioned facing the rear surface of the membrane electrode assembly 20, as shown by the dashed arrow. Oxidant gas flows from right to left in the cathode channel via the oxidant gas supply channel PA4 and the oxidant gas discharge channel PA3. The connection between the cathode channel and other channels PA1, PA2, PA5, and PA6 is severed by a seal (not shown). The oxidant gas flowing in the oxidant gas discharge channel PA3 is the oxidant gas remaining after a portion of the cathode electrode has been used; this is sometimes referred to as oxidant exhaust. Sometimes, fuel exhaust and oxidant exhaust are not distinguished, and they are referred to as reaction exhaust.

[0022] The flow channel PA5 (dashed arrow) extending forward through through holes 215 and 315 is the cooling medium supply channel. The flow channel PA2 (dashed arrow) extending backward through through holes 212 and 312 is the cooling medium discharge channel. The cooling medium supply channel PA5 and the cooling medium discharge channel PA2 are connected to the cooling channels inside the partition 3, and the cooling medium flows through the cooling medium supply channel PA5 and the cooling medium discharge channel PA2. The connection between the cooling channels and other channels PA1, PA3, PA4, and PA6 is cut off by a seal (not shown).

[0023] The end units 102 disposed on the front and rear sides of the battery stack 101 respectively have a terminal plate 4, an insulating plate 5, and an end plate 6. Multiple through holes 102a to 102f are formed in the rear end unit 102, extending through the end unit 102 in the front-rear direction. Through hole 102a is formed on the extension line of the fuel gas supply channel PA1 and communicates with it. Through hole 102b is formed on the extension line of the cooling medium discharge channel PA2 and communicates with it. Through hole 102c is formed on the extension line of the oxidant gas discharge channel PA3 and communicates with it. Through hole 102d is formed on the extension line of the oxidant gas supply channel PA4 and communicates with it. Through hole 102e is formed on the extension line of the cooling medium supply channel PA5 and communicates with it. The through hole 102f is opened on the extension line of the fuel gas discharge channel PA6 and is connected to the fuel gas discharge channel PA6.

[0024] More specifically, a fuel gas tank storing high-pressure fuel gas is connected to through-hole 102a via an ejector, injector, etc., as described below. Fuel gas is supplied to the fuel cell stack 100 via through-hole 102a. Fuel gas (fuel exhaust) is discharged from through-hole 102f. A compressor for oxidant gas supply is connected to through-hole 102d, and oxidant gas compressed by the compressor is supplied to the fuel cell stack 100 via through-hole 102d. Oxidant gas (oxidant exhaust) is discharged from through-hole 102c. A pump for cooling medium supply is connected to through-hole 102e, and cooling medium is supplied to the fuel cell stack 100 via through-hole 102e. Cooling medium is discharged from through-hole 102b. The discharged cooling medium is cooled by heat exchange in a radiator and then supplied to the fuel cell stack 100 again via through-hole 102e.

[0025] The above is a general structure of the fuel cell stack 100. However, in the fuel cell stack 100, the generated water sometimes remains near the membrane electrode assembly 20 and becomes stagnant water. Figure 3 This is a schematic cross-sectional view of the main part of the membrane electrode assembly 20, illustrating the generation of such stagnant water. (See image.) Figure 3 As indicated by arrow A, the generated water at the cathode electrode flows through the electrolyte membrane 22 of the membrane electrode assembly 20 to the anode electrode and remains near the anode electrode, which includes the catalyst electrode layer 23 and the gas diffusion layer 24 (e.g., in the region where ionomers exist). For convenience, such water remaining in the membrane electrode assembly 20 is referred to as MEA stagnant water W1.

[0026] Furthermore, even when the generated water flowing to the anode electrode reaches the anode flow channel 33 of the separator 3, sometimes a portion of the generated water and a portion of the condensate water generated in the anode flow channel 33 remain and accumulate within the anode flow channel 33. For convenience, such water remaining in the flow channel is referred to as flow channel stagnant water W2. The generated water (MEA stagnant water W1, flow channel stagnant water W2) accumulated in the fuel cell stack becomes a major cause of unstable power generation and deterioration of electrode performance, and therefore needs to be drained quickly. Considering this, in this embodiment, the fuel cell system is configured as follows.

[0027] Figure 4 This is a diagram that schematically illustrates the main structural components of a fuel cell system 10 according to an embodiment of the present invention. Figure 4 The diagram primarily illustrates the structure related to the flow of fuel gas. For example... Figure 4As shown, the fuel cell system 10 includes a tank 11 for storing high-pressure fuel gas and a supply channel PA1 connecting the tank 11 to a through-hole 102a, which serves as the inlet for the fuel gas. The supply channel PA1 has a pair of supply channels PA11 and PA12 arranged side-by-side. A large flow rate of fuel gas can pass through the supply channel PA11. For convenience, the supply channel PA11 is referred to as the large channel, and the supply channel PA12 as the small channel. The fuel cell system 10 includes a gas supply section SP1 that supplies fuel gas to the fuel cell stack 100 via the large channel PA11 and a gas supply section SP2 that supplies fuel gas to the fuel cell stack 100 via the small channel PA12.

[0028] Gas supply unit SP1 has an ejector (INJ) 31 and an ejector (EJE) 41 sandwiched between a can 11 on the large flow channel PA11 and a through hole 102a. Gas supply unit SP2 has an ejector (INJ) 32 and an ejector (EJE) 42 sandwiched between a can 11 on the small flow channel PA12 and a through hole 102a. It should be noted that, although not shown in the figure, a pressure reducing mechanism is provided between the can 11 and the ejectors 31 and 32, and gas supply units SP1 and SP2 function as canister pressure supply mechanisms, respectively. The ejector 31 comprises multiple (three in the figure) ejectors (INJ) 31A, 31B, and 31C respectively sandwiched between flow channels PA111, PA112, and PA113 branching off from the large flow channel PA11 and arranged in parallel.

[0029] The injector 32 and each of the injectors 31A to 31C have the same structure (such as the diameter of the injection orifice). Injector 32 has a valve body for opening and closing the flow channel PA12 and a coil for driving the valve body. Injectors 31A, 31B, and 31C each have a valve body for opening and closing the flow channels PA111, PA112, and PA113 and a coil for driving the valve body. According to the command from ECU 50, current flows through the coils of these injectors 31A to 31C and 32, thereby driving the injectors 31A to 31C and 32 to open and close. That is, when the injectors 31A to 31C and 32 open according to the command from ECU 50, the coil is energized, and the injectors 31A to 31C and 32 open their valves. When the injectors 31A to 31C and 32 close according to the command from ECU 50, the energization to the coil is cut off, and the injectors 31A to 31C and 32 close their valves. The drive current is supplied to the coils of injectors 31A-31C and 32 via a drive circuit not shown.

[0030] Injectors 31 and 32 are opened and closed by PWM control implemented by ECU 50. ECU 50 controls the ratio of the valve opening time (pulse width) Ti to the period T0 of the pulse waveform, i.e., the duty cycle (Ti / T0), thereby adjusting the injection quantity of fuel gas injected by injectors 31A-31C and 32 in one valve opening. Injectors 31A-31C are arranged in parallel, therefore the maximum injection quantity of injector 31 in the large flow channel PA11 is greater than the maximum injection quantity of injector 32 in the small flow channel PA12. Hereinafter, injector 31 is sometimes referred to as the large injector, and injector 32 as the small injector. The large injector 31 refers to the injector on the injector 41 side, and the small injector 32 refers to the injector on the injector 42 side.

[0031] Through hole 102f, which serves as the outlet for fuel gas ( Figure 1 The gas-liquid separator 43 is connected to the gas-liquid separator 43. In the gas-liquid separator 43, water contained in the fuel exhaust is separated from and stored. A drain valve 44 is connected to the gas-liquid separator 43. When the drain valve 44 is opened, the water stored in the gas-liquid separator 43 is discharged to the outside. The drain valve 44 opens and closes according to instructions from the ECU 50. The gas-liquid separator 43 is connected to ejectors 41 and 42 via circulation channels PA21 and PA22, respectively. The fuel exhaust separated in the gas-liquid separator 43 flows back to ejectors 41 and 42 via circulation channels PA21 and PA22.

[0032] Figure 5 This is a diagram showing the schematic structure of the ejector 41 (for convenience, referred to as the large ejector) in the large flow channel PA11. Figure 5 As shown, the large ejector 41 has a nozzle section 411, an suction section 412, a confluence section 413, and a diffuser section 414. (As shown...) Figure 5 As shown by the solid arrow, the fuel gas ejected from the injector 31 flows into the diffuser 414 via the confluence section 413 after passing through the small-diameter nozzle section 411. At this time, as... Figure 5 As shown by the dashed arrow, fuel exhaust gas is drawn from the circulation channel PA21 into the large ejector 41 via the suction section 412. The drawn-in fuel exhaust gas merges with the fuel gas that has passed through the nozzle section 411 at the confluence section 413, and then becomes a uniform flow at the diffuser section 414 before passing through the through hole 102a ( Figure 4 ) is supplied to fuel cell stack 100.

[0033] Although the illustration is omitted, the ejector 42 (referred to as the small ejector for convenience) in the small flow channel PA12 is the same as the large ejector 41, having a nozzle section, an suction section, a confluence section, and a diffuser section. Furthermore, due to the flow of fuel gas through the nozzle section, fuel exhaust gas is drawn in from the circulation channel PA22 via the suction section and supplied to the fuel cell stack 100 via the through-hole 102a. The diameter of the nozzle section of the small ejector 42 is smaller than the diameter of the nozzle section 411 of the large ejector 41.

[0034] Figure 6 This is a graph showing the relationship between the valve opening times Ti1 and Ti2 of each injector 31 and 32 during one injection, and the injection quantity and circulation quantity. (See figure) Figure 6 As shown, when the instantaneous injection quantities q10 and q20 obtained by dividing the injection quantity Q0 of injectors 31 and 32 in one injection by the valve opening times Ti1 and Ti2 are defined as the injection quantity of injectors 31 and 32 per unit time, q10 > q20.

[0035] Therefore, when the gas circulation volume per unit time of the large ejector 41 is defined as q11 and the gas circulation volume per unit time of the small ejector 42 is defined as q21, the ratio of the circulation volume (suction volume) q11 of the large ejector 41 to the injection volume q10 of the large ejector 31 per unit time, i.e., the circulation flow rate ratio, is less than the ratio of the circulation volume (suction volume) q21 of the small ejector 42 to the injection volume q20 of the small ejector 32 per unit time, i.e., the circulation flow rate ratio. Therefore, the small ejector 42 has higher circulation capacity (circulation performance, suction performance). Furthermore, when the circulation volume of a single injection by the large ejector 41 and the small ejector 42 is defined as Q11 and Q21 respectively, the flow rate of the fuel gas downstream of the small ejector 42 (Q0+Q21) is greater than the flow rate of the fuel gas downstream of the large ejector 41 (Q0+Q11).

[0036] Figure 4 The ECU 50 is a computer comprising a CPU (Central Processing Unit), ROM (Read-Only Memory), RAM (Random Access Memory), and other peripheral circuits. A signal from the accelerator pedal opening sensor 51, used to detect the accelerator pedal opening (accelerator opening), is input to the ECU 50. Based on the signal from the accelerator pedal opening sensor 51, the ECU 50 calculates the required power that the fuel cell stack 100 needs to generate, i.e., the power required by the drive motor. It should be noted that the drive motor is one example of a load mounted on the vehicle. Considering the power requirements of other loads, the ECU 50 can also calculate all required power.

[0037] The larger the accelerator opening, the greater the power demand calculated by ECU 50. ECU 50 controls injectors 31 and 32 to inject fuel gas in the injection mode corresponding to the power demand. Injection modes include a dual-injection mode where fuel is injected from both injectors 31 and 32 in one cycle T0, and a single-injection mode where fuel is injected from only one injector 31 or injector 32. When the power demand (e.g., current density) is defined as below a specified value E1, a medium-load state is defined as a power demand greater than the specified value E1 but below a specified value E2 (greater than E1), and a high-load state is defined as a power demand greater than the specified value E2, ECU 50 drives injectors 31 and 32 to open and close, so that fuel gas is injected in dual-injection mode regardless of whether it is a low-load, medium-load, or high-load state. That is, the duty cycle of the large injector 31 and the duty cycle of the small injector 32 are controlled according to the power demand. It should be noted that fuel gas can also be injected in a single injection mode under specified load conditions (such as high load conditions).

[0038] The duty cycle control (PWM control) of the large injector 31 includes sequentially selecting two injectors 31A, 31B, or 31A, 31C, or 31B, 31C, and turning them on and off at the same time each cycle. For example, initially, injectors 31A and 31B are turned on and off at the same time each cycle; in the next cycle, injectors 31A and 31C are turned on and off at the same time each cycle; in the next cycle, injectors 31B and 31C are turned on and off at the same time each cycle, and this operation is repeated. It should be noted that, under low load conditions, any one of injectors 31A to 31C can be selected sequentially and turned on and off at predetermined times. Under high load conditions, all three injectors 31A to 31C can be turned on and off at the same time each cycle.

[0039] ECU 50 does not always control injectors 31 and 32 in dual-injection mode; it can also control injectors 31 and 32 in single-injection mode as needed based on power requirements. For example, it can activate or deactivate only the large injector 31 under low load conditions, and activate or deactivate only the small injector 32 under high load conditions. In other words, ECU 50 can change the injection mode according to power requirements.

[0040] Figure 7A This is a diagram showing an example of the injection pattern of fuel gas injected from injectors 31 and 32 in the fuel cell system 10 of this embodiment. Figure 7A The horizontal axis represents time, and the vertical axis represents the fuel gas flow rate q1 downstream of the large ejector 41. Figure 6 The fuel gas flow rate q2 downstream of the small ejector 42 (q10+q11) and q11) Figure 6 (q20+q21 in the original text). Figure 7A In the example shown, during period T0, the large injector 31 is opened for a predetermined valve opening time Ti1. Additionally, simultaneously with the opening of the large injector 31, the small injector 32 is opened for a predetermined valve opening time Ti2.

[0041] The jet volume per unit time of the large jet 31, i.e., the instantaneous jet volume, is greater than that of the small jet 32. Figure 6 Therefore, the instantaneous gas flow rate q1 downstream of the large ejector 41 when the large ejector 31 opens is greater than the instantaneous gas flow rate q2 downstream of the small ejector 42 when the small ejector 32 opens. On the other hand, the valve opening time (opening period) Ti2 of the small ejector 32 is longer than the valve opening time (opening period) Ti1 of the large ejector 31. Therefore, the gas flow rate downstream of the small ejector 42 when the small ejector 32 opens once is greater than the gas flow rate downstream of the large ejector 41 when the large ejector 31 opens once.

[0042] When the injector 31 is Figure 7A When ta is turned on, immediately afterwards, in the anode channel 33 ( Figure 3 The flow rate and velocity of the fuel gas reach their maximum. The side with the higher instantaneous gas flow rate has a better drainage effect on the MEA stagnant water W1, thereby guiding the MEA stagnant water W1 to the anode channel 33.

[0043] That is, the faster the flow rate of fuel gas in the anode channel 33, the better the drainage effect of MEA stagnant water W1. However, in this embodiment, although the valve opening time Ti1 is short, a large flow rate q1 of fuel gas is supplied via the large ejector 41 during a predetermined period T0. Therefore, the MEA stagnant water W1 can be easily guided to the anode channel 33, and the MEA stagnant water W1 can be discharged well. In particular, in Figure 7A In the example, when the large ejector 31 is open, the small ejector 32 is open. Therefore, the instantaneous flow rate of the fuel gas flowing in the anode channel 33 per unit time is greater than the instantaneous flow rate q1 per unit time of the large ejector 41 by (q1+q2), which can further improve the drainage effect of the MEA stagnant water W1.

[0044] On the other hand, in order to effectively discharge the stagnant water W2 from the flow channel to the outside of the fuel cell stack 100, the drainage rate needs to be within the specified value Va ( Figure 8 Therefore, it is necessary to ensure sufficient acceleration time for the stagnant water W2 in the flow channel. In this embodiment, the opening time Ti2 of the small ejector 32 is set to be longer than the opening time Ti1 of the large ejector 31, thus ensuring sufficient acceleration time through the jetting of the small ejector 32. This allows the stagnant water W2 in the anode flow channel to achieve sufficient acceleration time. Figure 3 It is discharged smoothly with the flow of fuel gas.

[0045] Figure 7B This is another example of the injection pattern of fuel gas injected from injectors 31 and 32 in the fuel cell system 10 of this embodiment. Figure 7B In the example, at point tb when the large jet 31 is closed, the small jet 32 ​​is activated. Figure 7B In this example, a relatively large instantaneous supply of fuel gas is also provided via the large ejector 41, thus effectively removing the MEA stagnant water W1. Furthermore, the time ratio from the opening of the large ejector 31 to the closing of the small ejector 32 is... Figure 7A Therefore, the fuel gas flows in the anode channel 33 for a longer period of time, which allows for better discharge of the channel stagnant water W2.

[0046] exist Figure 7A , Figure 7B In this example, the small injector 32 is activated simultaneously with or at the same time as the large injector 31 is closed, rather than activating the small injector 32 after a predetermined time has elapsed since the large injector 31 was closed. That is, the small injector 32 is activated during the period from the opening to the closing of the large injector 31. In other words, the small injector 32 activates immediately after the large injector 31 is activated. This further achieves the effects described below.

[0047] Figure 8 This is a graph showing the change in pressure difference between the fuel gas inlet (through-hole 102a) and outlet (through-hole 102f) over time, as well as the change in velocity (drainage velocity V) of the channel stagnant water W2 flowing in the anode channel 33. In the graph, the change in pressure difference is represented by a dashed line, and the change in drainage velocity V is represented by a solid line. Figure 8 Corresponding to the situation where the large jet 31 is closed while the small jet 32 ​​is open. Figure 7B The situation is as follows. It should be noted that... Figure 8 The valve opening time Ti1 of the large injector 31 is compared to Figure 7A short, Figure 8 The duty cycle of the large jet 31 is also higher than... Figure 7A Small.

[0048] like Figure 8As shown, when the large injector 31 opens at time ta, the pressure difference (dashed line) increases instantaneously, and the drainage velocity V (solid line) also increases. Afterwards, as the large injector 31 closes, the pressure difference decreases, but the small injector 32 opens at time tb, so the pressure difference does not drop to 0. Throughout the entire opening time Ti2 of the small injector 32, the pressure difference remains at a specified value. Therefore, although the drainage velocity V decreases beyond time tb, the decrease is small, and it remains at least higher than the specified value Va until time tc, when the opening time Ti2 ends. That is, from time ta when the large injector 31 opens to time tc when the small injector 32 closes, a pressure difference above the specified value is continuously generated in the fuel cell stack 100, thus maintaining the kinetic energy of the water flowing in the anode channel 33 above the specified value Va. Therefore, without accelerating the stagnant water from 0 to above the specified value Va, the stagnant water W2 in the channel can be effectively discharged. The specified value Va is the minimum drainage rate required for the smooth discharge of stagnant water W2 from the flow channel.

[0049] Figure 9 yes Figure 8 Comparative examples. In Figure 9 In the diagram, after the large ejector 31 closes, the small ejector 32 opens at time point tb after time Tc. Therefore, before the small ejector 32 opens, the pressure difference (dashed line) is 0, and the drainage velocity V (solid line) is also 0. Thus, during the period from the opening of the large ejector 31 to the closing of the small ejector 32, continuous drainage is interrupted. Furthermore, at time point tb, after the pressure difference begins to rise again, the drainage velocity V increases steadily. Thus, when the time Tc (conveniently referred to as the lag time) from the closing of the large ejector 31 to the opening of the small ejector 32 is long, the drainage velocity V decreases significantly (e.g., becomes 0). Therefore, in order to increase the drainage velocity V to a specified value Va (… Figure 8 The above methods require time and significant energy, making them difficult to drain effectively.

[0050] This point, in Figure 8 In this example, since the large ejector 31 is closed while the small ejector 32 is open, the lag time Tc is 0, which allows the drainage velocity V to be maintained above the specified value Va. Therefore, there is no need to accelerate the stagnant water to above the specified value Va, and no energy is required to increase the drainage velocity V, thus enabling efficient drainage.

[0051] Figure 10 This is a graph showing the relationship between the lag time Tc and the drainage velocity V of the anode channel 33. (See figure) Figure 10As shown, the drainage velocity V gradually decreases with the increase of the lag time Tc. The lag time Tc for the drainage velocity V to reach a specified value Va is called the specified lag time Tc1. The specified lag time Tc1 is pre-stored in the memory of ECU 50. ECU 50 determines the injection timing of the small injector 32, ensuring that the small injector 32 is activated before the specified lag time Tc1 has elapsed after the large injector 31 has closed. It should be noted that the situations in which the small injector 32 is activated before the specified lag time Tc1 has elapsed include, for example... Figure 7A The case shown is where the small injector 32 and the large injector 31 are activated simultaneously, and as shown in the example. Figure 7B The diagram shows the case where the small injector 32 is open when the large injector 31 is closed. That is, it includes the case where there is no lag time Tc.

[0052] It should be noted that the fuel cell system 10 is equipped with multiple drive circuits (not shown) to supply drive current to the injectors 31 and 32. However, due to the constraints of these drive circuits during operation, a specified lag time Tc is sometimes required. In this case, a lower limit time of the lag time Tc is preset, and the ECU 50 sets the lag time Tc in a manner that is above the lower limit time and below the specified lag time Tc1.

[0053] Figure 11 This is a flowchart illustrating an example of the processing performed by ECU 50 according to a program pre-stored in memory. The processing shown in the flowchart is the process of injecting fuel gas from injectors 31 and 32 in a dual-injection mode, which is repeated at predetermined times. Figure 11 The processing.

[0054] like Figure 11 As shown, firstly, in step S1, the required power is calculated based on the signal from the accelerator opening sensor 51. Next, in step S2, the target injection quantity of fuel gas per unit time for the injectors 31 and 32 as a whole is calculated based on the calculated required power. Then, in step S3, the target duty cycle of the large injector 31 and the target duty cycle of the small injector 32 are calculated in a manner that injects the target injection quantity calculated in step S2. For example, the target period and target duty cycle are calculated simultaneously with reference to pre-stored characteristics.

[0055] Figure 12This is a graph showing the relationship between the cycle and valve opening time in a pre-stored dual-injection mode. Characteristic f1 in the graph represents the large injector 31, and characteristic f2 represents the small injector 32. Both characteristics f1 and f2 increase to the right; as the cycle T0 increases, the valve opening time Ti increases. The range from the lower limit cycle T0a to the upper limit cycle T0b in the graph represents the control range, within which the ECU 50 calculates the target cycle and target duty cycle. It should be noted that the ECU 50 can also calculate the target cycle and target duty cycle using a predefined formula.

[0056] Next, in step S4, the ECU 50 outputs a control signal to the large injector 31 (more specifically, the drive circuit) in a manner that the large injector 31 opens and closes according to the target duty cycle. As a result, the large injector 31 opens its valve, supplying a momentarily large flow rate q1 to the fuel cell stack 100 via the large ejector 41. Figure 7A , Figure 7B The fuel gas is used to effectively guide the MEA stagnant water W1 accumulated near the anode electrode to the anode channel 33.

[0057] Next, in step S5, the ECU 50 outputs a control signal to the small injector 32 (more specifically, the drive circuit) in a manner that the small injector 32 opens and closes according to the target duty cycle and the target duty cycle. In this case, the control signal is output so that the small injector 32 opens after a predetermined lag time Tc1 following the closing of the large injector 31. For example, the ECU 50 outputs the control signal in a manner that the small injector 32 opens simultaneously with the large injector 31 or simultaneously with the closing of the large injector 31. In this case, the predetermined lag time Tc1 is 0. Therefore, since the small injector 32 opens immediately after the large injector 31 opens, the drainage velocity V of the stagnant water W2 in the flow channel can be ensured to be above the predetermined value Va during the period from the opening of the large injector 31 to the closing of the small injector 32. Figure 8 It can effectively discharge the stagnant water W2 in the anode channel.

[0058] Figure 13 This is a graph showing the range of power generation conditions required to achieve stable power generation. In the graph, the horizontal axis is parallel to... Figure 7A The vertical axis represents the instantaneous flow velocity of the fuel gas corresponding to gas flow rates q1 and q2. The vertical axis represents the total flow rate of fuel gas supplied to the fuel cell stack 100 during a specified time (e.g., period T0). Figure 6 The average gas flow rate is obtained by dividing the sum of the injection quantity Q0 and the circulation quantities Q11 and Q21 by a specified time (e.g., T0). With characteristic f3 as the boundary, the right side is the stable region AR1 for power generation, and the left side is the unstable region AR2 for power generation.

[0059] According to characteristic f3, the average gas flow rate decreases as the instantaneous gas velocity increases. Therefore, assuming that stable power generation is desired solely from the injection of the large ejector 31, the average gas flow rate is small, thus in, for example... Figure 13 The control target value is determined within region AR11. In this case, the range of the control target is narrow, thus imposing more constraints on the fuel cell system and leading to increased costs. In contrast, in this embodiment, not only the large injector 31, but also the small injector 32 with a high circulation flow ratio is used to inject fuel gas, thus increasing the average gas flow rate. Therefore, it is possible to, for example... Figure 13 The target control value is determined within the AR12 region. Therefore, stable power generation can be easily achieved while suppressing cost increases without significantly increasing the instantaneous gas flow channel.

[0060] The following effects can be achieved by adopting this implementation method.

[0061] (1) The fuel cell system 10 includes: a fuel cell stack 100 that generates electricity through an electrochemical reaction between fuel gas and oxidant gas, and is provided with a through-hole 102a as a gas inlet for fuel gas inflow and a through-hole 102f as a gas outlet for fuel gas outflow; a gas supply unit SP1 that has a large injector 31 for injecting fuel gas and supplies fuel gas to the fuel cell stack 100 via a large flow channel PA11 connected to the through-hole 102a; a gas supply unit SP2 that has a small injector 32 for injecting fuel gas and supplies fuel gas to the fuel cell stack 100 via a small flow channel PA12 connected to the through-hole 102a; and an ECU 50 that controls the large injector 31 and the small injector 32 to inject fuel gas in an injection mode corresponding to the required power. Figure 4 The gas supply unit SP1 also has a large ejector 41, which... The injector 41 is positioned between the large injector 31 and the through-hole 102a, guiding the fuel gas discharged from the through-hole 102f through the circulation channel PA21 to the large channel PA11. Figure 4 The gas supply unit SP2 also has a small ejector 42, which is disposed between the small ejector 32 and the through hole 102a. The fuel gas discharged from the through hole 102f is guided to the small flow channel PA12 via the circulation channel PA22. Figure 4 The large injector 31 and the small injector 32 are configured such that the fuel gas injection quantity q10 per unit time of the large injector 31 is greater than the fuel gas injection quantity q20 per unit time of the small injector 32. Figure 6The large ejector 41 and the small ejector 42 are configured such that the ratio of the circulation volume q11 of the large ejector 41 to the fuel gas injection volume q10 of the large ejector 31, i.e., the circulation flow ratio (first circulation flow ratio), is smaller than the ratio of the circulation volume q21 of the small ejector 42 to the fuel gas injection volume q20 of the small ejector 32, i.e., the circulation flow ratio (second circulation flow ratio). Figure 6 ). The ECU 50 controls the large injector 31 and the small injector 32 to inject fuel gas for a longer duration than that of the large injector 31 during the specified cycle T0 when the large injector 31 injects fuel gas. Figure 7A , Figure 7B ).

[0062] This structure not only eliminates the stagnant water W2 accumulated in the anode channel 33, but also allows the MEA stagnant water W1 accumulated inside the membrane electrode assembly 20 to be discharged from the fuel cell stack 100 within a specified period T0, thus optimizing drainage performance. This improves the drainage performance of the fuel cell stack 100 and suppresses power generation instability and electrode performance degradation. Specifically, when the instantaneous gas flow rate increases due to the opening of the large injector 31, the MEA stagnant water W1 can be discharged effectively. However, conversely, because the fuel gas injection time is short, sufficient acceleration time for the stagnant water W2 in the channel cannot be ensured, resulting in poor drainage of the stagnant water W2. On the other hand, the opening time Ti2 of the small injector 32 is longer than the opening time Ti1 of the large injector 31 (…). Figure 12 Therefore, the drainage performance of the channel stagnant water W2 is improved due to the opening of the small injector 32, but conversely, because the instantaneous gas flow rate is small, the MEA stagnant water W1 cannot be fully discharged. In this embodiment, by using a dual-injection mode that combines the injection of the large injector 31 and the injection of the small injector 32 to inject fuel gas, the MEA stagnant water W1 and the channel stagnant water W2 can be discharged well.

[0063] (2) The ECU 50 controls the large injector 31 and the small injector 32 to inject fuel gas simultaneously with or within a specified time (e.g., valve opening time Ti1) after the large injector 31 injects fuel gas. Figure 7A , Figure 7B In order to smoothly discharge stagnant water from the fuel cell stack 100, the drainage rate V needs to be set to a predetermined value Va or higher. However, in this embodiment, the drainage rate V can be maintained at a predetermined value Va or higher from the start of the injection of the large injector 31 to the end of the injection of the small injector 32, thus achieving effective drainage.

[0064] (3) The ECU50 controls the large injector 31 and the small injector 32 to inject fuel gas by the small injector 32 before the fuel gas injection quantity of the large injector 31 becomes 0. Figure 8 For example, the small ejector 32 is opened after a predetermined lag time Tc1 following the closing of the large ejector 31. This suppresses the decrease in drainage velocity V and enables effective drainage.

[0065] (4) The large ejector 31 is composed of multiple ejectors 31A to 31C with the same structure as the small ejector 32. Figure 4 Therefore, it is possible to reduce the variety of components and construct a fuel cell system at a low cost.

[0066] However, in the fuel cell system 10 of this embodiment, the supply of fuel gas changes according to the increase or decrease in power demand, and consequently the amount of water generated also changes. Therefore, during transitional operation with increasing or decreasing power demand, it is preferable to perform different controls than during non-transitional operation to improve drainage performance. With this in mind, in this embodiment, the fuel cell system 10 is further configured as follows.

[0067] Figure 14A , Figure 14B These are timing diagrams showing an example of the operation during transitional operation of the fuel cell system 10 of this embodiment, and graphs showing the changes in the flow rate of fuel gas per unit time (large EJE flow rate) Q1 after passing through the large ejector 41, the flow rate of fuel gas per unit time (small EJE flow rate) Q2 after passing through the small ejector 42, the amount of generated water Q3 generated in the membrane electrode assembly 20, and the current A flowing to the load (driving motor) over time. Figure 14A For example, the action required when an increase in the amount of pressure applied to the accelerator pedal necessitates an increase in electrical charge. Figure 14B This action occurs when the amount of pressure applied to the accelerator pedal decreases, thus requiring a reduction in electrical power.

[0068] Figure 14A , Figure 14B The large EJE flow rate Q1 is the value obtained by dividing the flow rate of fuel gas flowing through the large ejector 41 when the large ejector 31 injects fuel gas once by the period T0, which is equivalent to the average flow rate of fuel gas flowing through the large ejector 41. Figure 14A , Figure 14BThe small EJE flow rate Q2 is the value obtained by dividing the flow rate of fuel gas flowing through the small ejector 42 when the small injector 32 injects fuel gas once by the period T0, and it is equivalent to the average flow rate of fuel gas flowing through the small ejector 42. The same characteristics are also observed when replacing the large EJE flow rate Q1 and the small EJE flow rate Q2 with the average injection quantity of the large injector 31 obtained by dividing the injection quantity of the large injector 31 once by the period T0, and the average injection quantity of the small injector 32 obtained by dividing the injection quantity of the small injector 32 once by the period T0.

[0069] Figure 14A , Figure 14B It is a timing diagram of the specified processing performed by ECU50. Figure 15A , Figure 15B This is a flowchart illustrating an example of the processing executed by ECU 50 according to a predetermined program, corresponding to... Figure 14A and Figure 14B The timing diagram. It should be noted that during execution... Figure 15A , Figure 15B During the process, it is necessary to detect the pressure P of the fuel gas at the inlet of the fuel cell stack 100. This pressure P is determined by, for example, as... Figure 4 Pressure sensor 52, which is connected to the flow channel downstream of ejectors 41 and 42, is used for detection.

[0070] When the specified control initiation conditions are met Figure 15A , Figure 15B The flowchart begins. Specifically, ECU 50 determines, based on the signal from accelerator opening sensor 51, whether the required increase in power is above a predetermined value. More specifically, it determines whether the required power has increased above a predetermined value or whether the percentage increase in required power is above a predetermined value. Then, when ECU 50 determines that the required increase in power is above a predetermined value, it determines that the control start condition is met and begins... Figure 15A The processing.

[0071] like Figure 15A As shown, in step S11, ECU50 first calculates the target pressure Pa of the fuel gas at the inlet of the fuel cell stack 100. In this case, in order to increase the inlet pressure P in advance, ECU50 calculates a target pressure Pa that is higher than a specified value or a specified proportion higher than the control pressure Pb corresponding to the required power determined according to the accelerator pedal opening. The greater the increase in required power, the greater the target pressure Pa.

[0072] Next, in step S12, ECU 50 determines whether the pressure P detected by pressure sensor 52 is less than the target pressure Pa. If step S12 is affirmative (S12: Yes), the process proceeds to step S13, where ECU 50, while keeping the duty cycle of the small injector 32 constant, instantaneously increases the duty cycle of the large injector 31 to the target value corresponding to the target pressure Pa. Thus... Figure 14A As shown, with the small EJE flow rate Q2 constant, the large EJE flow rate Q1 increases instantaneously (at time t1). The increase in duty cycle continues until the pressure P detected by pressure sensor 52 reaches the target pressure Pa. As a result, the amount of generated water produced in the membrane electrode assembly 20 increases, and the current A flowing to the load increases.

[0073] When step S12 is negative (S12: No), proceed to step S14. The ECU 50, while maintaining a constant duty cycle for the small injector 32, controls the duty cycle of the large injector 31 to the target value corresponding to the control pressure Pb. Thus, as... Figure 14A As shown, the large EJE flow rate Q1 is reduced to a value corresponding to the control pressure Pb and maintained at that value. As a result, the increase in generated water stops, and the increase in current A stops (at time t2). It should be noted that in step S14, the duty cycle of the small ejector 32 can also be changed (e.g., reduced).

[0074] When the power demand increases, the duty cycle of the large injector 31 is instantaneously increased while keeping the duty cycle of the small injector 32 constant (step S13), thus increasing the instantaneous gas flow rate through the anode channel 33. This allows for the effective removal of the MEA stagnant water W1 that increases due to the increased power generation. Specifically, immediately after the increase in fuel gas supply, water accumulates near the membrane electrode assembly 20 instead of in the anode channel 33. Therefore, by instantaneously increasing the injection rate of the large injector 31, which is suitable for draining the MEA stagnant water W1, the stagnant water within the fuel cell stack can be effectively removed.

[0075] When a power reduction is requested, the ECU 50 determines, based on the signal from the accelerator opening sensor 51, whether the requested power reduction is greater than or equal to a predetermined value. More specifically, it determines whether the requested power has decreased by a predetermined value or whether the percentage reduction is greater than or equal to a predetermined value. Then, when it is determined that the requested power reduction is greater than or equal to the predetermined value, the control start condition is deemed met, and the control begins. Figure 15B The processing.

[0076] like Figure 15BAs shown, in step S21, ECU50 first calculates the target pressure Pa of the fuel gas at the inlet of the fuel cell stack 100. In this case, in order to reduce the inlet pressure P in advance, ECU50 calculates a target pressure Pa that is lower than a specified value or a specified percentage lower than the control pressure Pb corresponding to the required power determined according to the accelerator pedal opening. The greater the reduction in required power, the smaller the target pressure Pa.

[0077] Next, in step S22, ECU 50 determines whether the pressure P detected by pressure sensor 52 is greater than the target pressure Pa. If step S22 is affirmative (S22: Yes), the process proceeds to step S23, where ECU 50, while keeping the duty cycle of the small injector 32 constant, instantaneously reduces the duty cycle of the large injector 31 to the target value corresponding to the target pressure Pa. Thus... Figure 14B As shown, with the small EJE flow rate Q2 constant, the large EJE flow rate Q1 decreases instantaneously (at time t3). The decrease in duty cycle continues until the pressure P detected by pressure sensor 52 reaches the target pressure Pa. Consequently, the amount of generated water produced in the membrane electrode assembly 20 decreases, and the current A flowing to the load decreases.

[0078] When step S22 is negative (S22: No), proceed to step S24. The ECU 50, while maintaining a constant duty cycle for the small injector 32, controls the duty cycle of the large injector 31 to the target value corresponding to the control pressure Pb. Thus, as... Figure 14B As shown, the large EJE flow rate Q1 is increased to a value corresponding to the control pressure Pb and maintained at that value. As a result, the decrease in water generation stops, and the decrease in current A stops (at time t4). It should be noted that in step S24, the duty cycle of the small ejector 32 can also be changed (e.g., increased).

[0079] When the required power is reduced, the duty cycle of the large injector 31 is instantaneously reduced while keeping the duty cycle of the small injector 32 constant (step S23), thus reducing the instantaneous gas flow rate through the anode channel 33. At this time, the amount of MEA stagnant water W1 generated decreases due to the reduced power generation, but the instantaneous gas injection rate is correspondingly reduced, thus effectively draining the stagnant water. That is, the MEA stagnant water W1 decreases shortly after the fuel gas supply, but the channel stagnant water W2 decreases later than the MEA stagnant water W1. Taking this into account, the duty cycle of the small injector 32 is maintained to facilitate the drainage of the channel stagnant water W2, thus effectively draining the stagnant water from the fuel cell stack.

[0080] exist Figure 15A In step S13, while keeping the duty cycle of the small injector 32 constant, the duty cycle of the large injector 31 is increased. A specific example of this will be explained. Figure 16 These are diagrams showing examples of the pulse waveforms of injectors 31 and 32 before changing the duty cycle of the large injector 31, and examples of the pulse waveforms after changing the duty cycle (first example and second example). It should be noted that in... Figure 16 In the middle, it is the spray mode where the large jet 31 and the small jet 32 ​​are activated simultaneously, but it can also be that the small jet 32 ​​is activated after the large jet 31 is activated. The spray mode is not limited to this. Figure 16 Examples.

[0081] like Figure 16 As shown, before the duty cycle of the large jet 31 is changed ( Figure 14A Before time t1, the large injector 31 and the small injector 32 are opened in period T0 respectively. The pulse width (valve opening time) of the large injector 31 is Ti1, and the pulse width (valve opening time) of the small injector 32 is Ti2.

[0082] After the change ( Figure 14A In the first example (after time point t1), the large injector 31 and the small injector 32 are activated at the same period T10 as period T0. The pulse width of the large injector 31 is Ti11, and the pulse width of the small injector 32 is Ti21. The pulse width Ti21 of the small injector 32 is equal to the pulse width Ti2 before the change. On the other hand, the pulse width Till of the large injector 31 is longer than the pulse width Til before the change. Thus, with the duty cycle of the small injector 32 remaining constant, the duty cycle of the large injector 31 increases.

[0083] In the second modified example, the large injector 31 and the small injector 32 are activated during a period T20 shorter than the period T0. The pulse width of the large injector 31 is Ti12, and the pulse width of the small injector 32 is Ti22. The pulse width Ti12 of the large injector 31 is equal to the pulse width Ti1 before the modification. On the other hand, the pulse width Ti22 of the small injector 32 decreases accordingly with the shortening of the period and becomes shorter than the pulse width Ti2. Thus, with the duty cycle of the small injector 32 remaining constant, the duty cycle of the large injector 31 increases.

[0084] exist Figure 15B In step S23, while keeping the duty cycle of the small injector 32 constant, the duty cycle of the large injector 31 is reduced, but the pulse waveform in this case is also different from... Figure 16 The changes are similar. In this case, in the first example after the change, within the same cycle as before the change, the pulse width Ti11 of the large injector 31 is shorter than the pulse width Ti1 before the change. Furthermore, in the second example after the change, the changed cycle T20 is longer than the previous cycle T0, and correspondingly, the pulse width Ti22 of the small injector 32 is longer than before the change. Figure 15A , 5In configuration B, the duty cycle of the small injector 32 is kept constant, while the duty cycle of the large injector 31 is increased or decreased. However, the duty cycle of the small injector 32 does not have to be constant. That is, when the power demand increases, the increase in the duty cycle of the large injector 31 is greater than the increase in the duty cycle of the small injector 32. On the other hand, as long as the ECU 50 controls the large injector 31 and the small injector 32 in a manner that the decrease in the duty cycle of the large injector 31 is greater than the decrease in the duty cycle of the small injector 32 when the power demand decreases, the duty cycle of the small injector 32 does not have to be constant.

[0085] In addition to the effects described above, this implementation method can also achieve the following effects.

[0086] (1) The ECU 50 controls the large injector 31 and the small injector 32 in the following manner: when the injection mode is a dual injection mode in which the large injector 31 and the small injector 32 inject fuel gas respectively, when the power demand increases, the average injection quantity of the large injector 31 per unit time increases compared to the small injector 32; on the other hand, when the power demand decreases, the average injection quantity of the large injector 31 per unit time decreases compared to the small injector 32. Figure 15A , Figure 15B ).

[0087] Therefore, when power demand increases, the injection volume of the large injector 31 is preferentially increased compared to the small injector 32. When power demand increases, the MEA stagnant water W1 increases, followed by the channel stagnant water W2. However, by preferentially increasing the injection volume of the large injector 31, the drainage performance of the MEA stagnant water W1 can be improved, effectively removing stagnant water from the fuel cell stack. Conversely, when power demand decreases, the injection volume of the large injector 31 is preferentially decreased compared to the small injector 32. When power demand decreases, the MEA stagnant water W1 decreases, followed by the channel stagnant water W2. However, by preferentially decreasing the injection volume of the large injector 31, the drainage performance of the channel stagnant water W2 can be maintained, effectively removing stagnant water from the fuel cell stack.

[0088] (2) The ECU 50 controls the injectors 31 and 32 in the following manner: when the injection mode is dual injection mode, the large injector 31 injects fuel gas at a duty cycle (Ti1 / T0) (first target duty cycle) corresponding to the required power, and the small injector 32 injects fuel gas at a duty cycle (Ti2 / T0) (second target duty cycle) corresponding to the required power. Figure 16Furthermore, in dual-injection mode, when power demand increases, ECU 50 increases the duty cycle of the large injector 31 by a greater extent than that of the small injector 32. Conversely, when power demand decreases, ECU 50 decreases the duty cycle of the large injector 31 by a greater extent than that of the small injector 32. Thus, by changing the duty cycle, good drainage performance of the fuel cell stack corresponding to transitional operation can be obtained.

[0089] (3) When the injection mode is dual injection mode, when the power demand increases, ECU 50 increases the duty cycle of the large injector while keeping the duty cycle of the small injector 32 constant. On the other hand, when the power demand decreases, ECU 50 decreases the duty cycle of the large injector 31 while keeping the duty cycle of the small injector 32 constant. Figure 15A , 15B Therefore, by simply changing the duty cycle of the large injector, good drainage performance of the fuel cell stack corresponding to transitional operation can be obtained, and it is easy to configure.

[0090] It should be noted that in the above embodiments, fuel gas flows into the fuel cell stack 100 through the through-hole 102a opened in the end unit 102, but the configuration of the gas inflow section is not limited to the above description. In the above embodiments, fuel gas flows out of the fuel cell stack 100 through the through-hole 102f opened in the end unit 102, but the configuration of the gas outflow section is not limited to this. In the above embodiments, the injector 31 includes three injectors 31A to 31C with the same structure as the injector 32, but the configuration of the injector 31 is not limited to this. For example, the injector 31 may also be composed of a single injector with a large injection volume, instead of multiple injectors 31A to 31C.

[0091] In the above embodiment, fuel gas is supplied to the fuel cell stack 100 as a gas supply section SP1, which is a first supply section, using a large injector 31 (first injector) and a large ejector 41 (first ejector) disposed in a large flow channel PA11 (first supply flow channel). Additionally, fuel gas is supplied to the fuel cell stack 100 as a gas supply section SP2, which is a second supply section, using a small injector 32 (second injector) and a small ejector 42 (second ejector) disposed in a small flow channel PA12 (second supply flow channel). However, the configuration of the first and second supply sections is not limited to those described above. Reed valves may also be installed in the circulation channels PA21 (first circulation channel) and PA22 (second circulation channel).

[0092] In the above embodiment, the ECU 50, as the control unit, causes the small injector 32 to inject fuel gas simultaneously with the large injector 31 injecting fuel gas or simultaneously with the large injector 31 ceasing to inject fuel gas. Figure 7A , Figure 7B However, the configuration of the control unit can be any form, as long as the first and second injectors are controlled in such a way that when either the first or second injector injects fuel gas during a predetermined cycle, the other injector injects fuel gas during that predetermined cycle. However, from the viewpoint of improving drainage performance, it is preferable to control the first and second injectors in such a way that the second injector injects fuel gas simultaneously with or within a predetermined time after the first injector injects fuel gas. That is, it is preferable to control the injectors so that the second injector injects fuel gas immediately after the first injector injects fuel gas. Alternatively, it is preferable to control the first and second injectors so that the second injector opens within a predetermined lag time Tc1 after the first injector finishes injecting fuel gas. In other words, it is preferable to control the first and second injectors so that the second injector injects fuel gas at least until the amount of fuel gas injected by the first injector becomes zero.

[0093] In the above embodiments, an example of applying the fuel cell system 10 to a vehicle was described, but the fuel cell system of the present invention can also be applied to mobile bodies other than vehicles such as aircraft and ships, robots, and various industrial machinery.

[0094] The above description is merely an example, and the above embodiments and modifications do not limit the invention as long as they do not destroy its features. One or more of the above embodiments and modifications can be combined in any way, and modifications can also be combined with each other.

[0095] Explanation of reference numerals in the attached figures 31, 32: Injectors; 31A, 31B, 31C: Injectors; 41, 42: Ejectors; 50: ECU; 100: Fuel cell stack; 102a, 102f: Through-hole; PA11: Large flow channel; PA12: Small flow channel; PA21, PA22: Circulation channels; SP1, SP2: Gas supply sections.

Claims

1. A fuel cell system, characterized in that, have: A fuel cell generates electricity through an electrochemical reaction between fuel gas and oxidant gas, and has a gas inlet for fuel gas to flow in and a gas outlet for fuel gas to flow out. A first supply section has a first injector for injecting fuel gas and supplies fuel gas to the fuel cell via a first supply channel connected to the gas inlet section; A second supply section having a second injector for injecting fuel gas, supplying fuel gas to the fuel cell via a second supply channel connected to the gas inlet section; and The control unit controls the first and second injectors to inject fuel gas in an injection mode corresponding to the required power. The first supply section also includes a first ejector, which is disposed between the first injector and the gas inlet section, guiding the fuel gas flowing out of the gas outlet section through a first circulation channel to the first supply channel. The second supply section also includes a second ejector, which is disposed between the second injector and the gas inlet section, guiding the fuel gas flowing out of the gas outlet section through a second circulation channel to the second supply channel. The first injector and the second injector are configured such that the fuel gas injection rate of the first injector per unit time is greater than the fuel gas injection rate of the second injector per unit time. The first ejector and the second ejector are configured such that the ratio of the circulation volume of the first ejector to the fuel gas injection volume of the first injector, i.e., the first circulation flow rate ratio, is less than the ratio of the circulation volume of the second ejector to the fuel gas injection volume of the second injector, i.e., the second circulation flow rate ratio. The control unit controls the first injector and the second injector in such a manner that when either the first injector or the second injector injects fuel gas during a predetermined period, the other injector injects fuel gas during the predetermined period.

2. The fuel cell system according to claim 1, characterized in that, The control unit controls the first injector and the second injector to inject fuel gas simultaneously with the first injector or within a predetermined time after the first injector injects fuel gas.

3. The fuel cell system according to claim 2, characterized in that, The control unit controls the first injector and the second injector to inject fuel gas by the second injector before the fuel gas injection quantity of the first injector becomes 0.

4. The fuel cell system according to any one of claims 1 to 3, characterized in that, The first injector includes a plurality of injectors with the same structure as the second injector.

5. The fuel cell system according to any one of claims 1 to 3, characterized in that, The injection time of the fuel gas from the second injector is longer than that of the first injector during the specified period.

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