Fuel cell system

Abstract

To suppress the drop in generated voltage due to a drop in fuel gas pressure.SOLUTION: A fuel cell system 100 includes a fuel cell stack 1 configured by stacking multiple power generation cells, injectors 5a1 to 5a3, 5b that inject fuel gas supplied to the fuel cell stack 1, a detection unit 6 that detects the pressure of the fuel gas supplied to the fuel cell stack 1, and a control unit 10 that sets the injection cycle of the injectors 5a1 to 5a3, 5b and controls the injectors 5a1 to 5a3, 5b to inject fuel gas at each injection cycle. When the pressure difference between the pressure detected by detection unit 6 and a target pressure reaches or exceeds a predetermined value, the control unit 10 controls the injectors 5a1 to 5a3, 5b to inject fuel gas earlier than the end of the injection cycle.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] By using a fuel cell for a vehicle drive source or the like, it is possible to contribute to an improvement in energy efficiency. As a technology related to such a fuel cell, conventionally, a device configured to control an injector that injects fuel gas of the fuel cell has been known (see, for example, Patent Document 1). In the device described in Patent Document 1, a target pressure of the fuel gas flowing into the fuel gas flow path is set every predetermined period, the pressure of the fuel gas flowing into the fuel gas flow path is detected, and the driving of a plurality of injectors is controlled so that the detected pressure approaches the target pressure. At the time of system startup, the driving cycle of the injector is set shorter than that during normal control.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, even if the driving cycle is adjusted as in the device described in Patent Document 1 above, in a predetermined operating state such as purging to discharge impurities from the fuel gas circulation flow path or when the vehicle accelerates and the required power generation amount suddenly increases, the pressure of the fuel gas temporarily decreases with respect to the target pressure, and there is a risk that the generated voltage decreases.

Means for Solving the Problems

[0005] A fuel cell system according to one aspect of the present invention includes a fuel cell stack formed by stacking a plurality of power generation cells, an injector that injects fuel gas supplied to the fuel cell stack, a detection unit that detects the pressure of the fuel gas supplied to the fuel cell stack, and a unit that sets the injection cycle of the injector and each injection cycle Perform spraying The system includes a control unit that controls the injector in the following way. The control unit, when the pressure difference between the pressure detected by the detection unit and the target pressure exceeds a predetermined value, This time Before the injection cycle has elapsed The system sets the next injection cycle, which will begin when the pressure difference exceeds a predetermined value, and performs the next injection when the pressure difference exceeds a predetermined value. Control the injector in this way. [Effects of the Invention]

[0006] According to the present invention, it is possible to suppress the decrease in power generation voltage caused by a decrease in fuel gas pressure. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram showing an example of the overall configuration of a fuel cell system according to an embodiment of the present invention. [Figure 2] A time chart illustrating the injection sequence of the large-diameter and small-diameter injectors shown in Figure 1. [Figure 3A] A time chart illustrating the pressure drop in fuel gas during purging. [Figure 3B] A time chart corresponding to Figure 3A, illustrating the suppression of pressure drop due to interrupt injection. [Figure 4A] A time chart illustrating the pressure drop in fuel gas during acceleration. [Figure 4B] A time chart corresponding to Figure 4A, illustrating the suppression of pressure drop due to interrupt injection. [Figure 5] A flowchart showing an example of the injection permission determination process performed by the ECU in Figure 1. [Figure 6A] A time chart illustrating the pressure rise of fuel gas when interrupt injection is permitted even when a large-diameter injector is open. [Figure 6B]A time chart illustrating the pressure rise of fuel gas when interrupt injection is permitted under the condition that the large-diameter injector valve is closed. [Figure 7] A flowchart showing an example of the valve opening time setting process performed by the ECU in Figure 1. [Figure 8] This diagram illustrates the valve opening times for each injector set by the ECU in Figure 1. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to Figures 1 to 8. Figure 1 is a schematic diagram showing an example of the overall configuration of a fuel cell system 100 according to an embodiment of the present invention. As shown in Figure 1, the fuel cell system 100 mainly comprises a fuel cell stack 1, which is composed of multiple power generation cells stacked on top of each other, and an ECU (Electronic Control Unit) 10, which controls each part of the fuel cell system 100. The fuel cell system 100 can be mounted on a vehicle, for example, and generate electricity for driving the vehicle. The fuel cell system 100 can also be mounted on mobile bodies other than vehicles, such as aircraft and ships, as well as robots and various industrial machines.

[0009] Each power cell in the fuel cell stack 1 has a membrane electrode assembly (MEA) in which electrodes (electrode catalyst layer and gas diffusion layer, etc.) are provided on both sides of a solid polymer electrolyte membrane. Fuel gas containing hydrogen is supplied to the anode electrode of each power cell in the fuel cell stack 1 via the anode channel 2, and oxidizing gas such as air containing oxygen is supplied to the cathode electrode via the cathode channel 3. As a result, electrochemical reactions proceed at the electrodes of each power cell, and power is generated in the fuel cell stack 1.

[0010] An oxidizing gas, such as compressed air, is supplied to the cathode channel 3 via a compressor (not shown). After a portion of the oxidizing gas supplied to the cathode channel 3 is used at the cathode electrode, it is discharged to the outside from the cathode channel 3 as oxidizing exhaust gas.

[0011] The anode flow path 2 is connected to a fuel gas tank in which high-pressure fuel gas is stored via ejectors 4a and 4b, an injector 5, and a pressure reducing valve (pressure regulating valve) not shown. The fuel gas in the fuel gas tank is reduced in pressure to a predetermined supply pressure by the pressure reducing valve, then injected by the injector 5, and supplied to the anode flow path 2 via the ejectors 4a and 4b.

[0012] The injector 5 has a valve body that opens and closes an injection hole and a coil that drives the valve body, and is controlled by the ECU 10. More specifically, a drive current is supplied to the coil of the injector 5 via a driver circuit not shown in accordance with an opening / closing command from the ECU 10, whereby the injector 5 is driven to open and close. That is, when the coil is energized in response to an on command from the ECU 10, the injector 5 opens, and when the energization of the coil is cut off in response to an off command from the ECU 10, the injector 5 closes. When the injector 5 opens, the fuel gas reduced in pressure to a predetermined supply pressure by the pressure reducing valve is injected and supplied to the anode flow path 2.

[0013] The fuel gas supplied to the anode flow path 2 is partially used at the anode electrode and then discharged from the anode flow path 2 as fuel exhaust gas. The fuel exhaust gas contains, in addition to the fuel gas (hydrogen), permeated nitrogen and permeated water vapor that permeate from the cathode side to the anode side through the membrane electrode assembly. The fuel exhaust gas discharged from the anode flow path 2 is separated from water via a gas-liquid separator not shown, and then sucked in as anode reflux gas via the ejectors 4a and 4b and supplied (refluxed) again to the anode flow path 2.

[0014] The injector 5 includes a large-diameter injector 5a and a small-diameter injector 5b provided in parallel with each other. The effective cross-sectional area of the injection hole of the large-diameter injector 5a is larger than the effective cross-sectional area of the injection hole of the small-diameter injector 5b, and the injection amount per unit time of the large-diameter injector 5a is larger than the injection amount per unit time of the small-diameter injector 5b.

[0015] The large-diameter injector 5a may be configured as a single injector having a larger hole diameter than the small-diameter injector 5b, or may be configured as a plurality of injectors having the same hole diameter as the small-diameter injector 5b. Hereinafter, an example in which the large-diameter injector 5a includes three large-diameter injectors 5a1 to 5a3 having a larger hole diameter than the small-diameter injector 5b will be described. The large-diameter injectors 5a1 to 5a3 are provided in parallel with each other. The fuel gas injected from the large-diameter injectors 5a1 to 5a3 is supplied to the anode flow path 2 via the ejector 4a, and the fuel gas injected from the small-diameter injector 5b is supplied to the anode flow path 2 via the ejector 4b.

[0016] The fuel gas injected from each injector 5 flows into the nozzle portions of the ejectors 4a and 4b and is accelerated, and by generating a low-pressure space inside the ejectors 4a and 4b, the fuel exhaust gas discharged from the anode flow path 2 is sucked into the inside of the ejectors 4a and 4b. The fuel gas and the fuel exhaust gas that have merged inside the ejectors 4a and 4b are discharged through the diffuser portions of the ejectors 4a and 4b while being entrained and mixed, and are supplied to the anode flow path 2. Hereinafter, the mixed gas discharged from the ejectors 4a and 4b and supplied to the anode flow path 2 is referred to as "anode supply gas". The anode supply gas contains fuel gas (hydrogen), permeated nitrogen, and permeated water vapor.

[0017] A pressure sensor 6 for detecting the pressure P of the fuel gas supplied to the fuel cell stack 1 is provided near the inlet of the anode flow path 2. Specifically, the pressure sensor 6 detects the pressure (total pressure) of the anode supply gas containing the fuel gas. By subtracting the nitrogen partial pressure and the water vapor partial pressure of the anode supply gas from the total pressure of the anode supply gas detected by the pressure sensor 6, the hydrogen partial pressure of the anode supply gas corresponding to the pressure P of the fuel gas (hydrogen) can be calculated. The nitrogen partial pressure and the water vapor partial pressure of the anode supply gas can be calculated based on the flow rates (permeation amounts) of the permeated nitrogen and the permeated water vapor and the discharge amount of the anode reflux gas described later. The permeation amount can be calculated based on the power generation state of the fuel cell stack 1, such as the power generation amount (current value) and the stack temperature.

[0018] Near the outlet of the anode flow path 2, an on-off valve 7 is provided to open and close the return flow path connecting the anode flow path 2 and the ejectors 4a and 4b. The on-off valve 7 is normally closed. The on-off valve 7 is temporarily opened when the hydrogen concentration (relative partial pressure of hydrogen) of the anode supply gas decreases due to an increase in the nitrogen concentration (relative partial pressure of nitrogen) of the anode supply gas. When the on-off valve 7 is temporarily opened, a portion of the anode return gas flowing through the return flow path is discharged (purged), thereby suppressing the decrease in the hydrogen concentration of the anode supply gas and maintaining the hydrogen concentration above a certain level. The on-off valve 7 is controlled by the ECU 10.

[0019] The ECU 10 is comprised of a computer including a CPU, RAM, ROM, I / O interface, and other peripheral circuits. Sensors such as a pressure sensor 6, a vehicle accelerator position sensor, and a stack temperature sensor are connected to the ECU 10, and detected values ​​from each sensor are input to the ECU 10. In addition, various parts of the fuel cell system 100, such as the injector 5 and the on / off valve 7, are connected to the ECU 10, and the ECU 10 controls each part of the fuel cell system 100, including the injector 5. The ECU 10 receives the required power generation amount of the fuel cell system 100, for example, via the vehicle accelerator position sensor.

[0020] <Calculation of required injection volume Q> The ECU 10 calculates the flow rate (required injection amount) Q of fuel gas to be supplied to the anode flow path 2 of the fuel cell stack 1 based on the required power generation amount of the fuel cell system 100. More specifically, it calculates the required power generation amount of the fuel cell system 100 based on the accelerator opening detected by the accelerator opening sensor, and calculates the flow rate (power generation consumption) of fuel gas (hydrogen) consumed per unit time by power generation in the fuel cell stack 1. It also calculates the flow rate (permeation amount) of permeated hydrogen that permeates from the anode side to the cathode side through the membrane electrode assembly, the amount of anode reflux gas discharged, the pressure fluctuation of the target fuel gas pressure P0, and the amount of pressure P feedback relative to the target pressure P0. Then, it calculates the required injection amount Q by adding the feedback amount to the calculated power generation consumption, permeation amount, discharge amount, and pressure fluctuation (feedforward amount).

[0021] <Setting the injection period Tint> The ECU 10 calculates the current value based on the power generation requirement of the fuel cell system 100, and also calculates the hydrogen partial pressure of the anode supply gas (fuel gas pressure P) based on the total pressure of the anode supply gas detected by the pressure sensor 6. Then, by referring to a predetermined characteristic map, it calculates (sets) the injection period Tint according to the calculated current value and the hydrogen partial pressure of the anode supply gas. The injection period Tint is set to be shorter for high loads with large current values, and also shorter for low hydrogen partial pressure of the anode supply gas.

[0022] <Calculation of the maximum injection volume Qi for each injector> The ECU 10 calculates the maximum injection amount Qi that each injector 5 can inject per unit time. Each injector 5 is controlled by PWM control, and the amount of fuel gas injected by each injector 5 in one valve opening is adjusted by the duty cycle (Ti / Tint), which is the ratio of the valve opening time (pulse width) Ti to the pulse waveform period (injection period) Tint. The maximum injection amount Qi for each injector 5 is the injection amount at a duty cycle of 100%.

[0023] Figure 2 is a time chart illustrating the injection sequence of the large-diameter injector 5a and the small-diameter injector 5b. As shown in Figure 2, when the injection cycle Tint(t1) is set at time t1, the large-diameter injector 5a opens first during the set injection cycle Tint(t1), and fuel gas injection by the large-diameter injector 5a begins. Then, at time t2, when the opening time Tia of the large-diameter injector 5a, which corresponds to the duty cycle, has elapsed, the large-diameter injector 5a closes, stopping fuel gas injection by the large-diameter injector 5a, and the small-diameter injector 5b opens, starting fuel gas injection by the small-diameter injector 5b. Then, at time t3, when the opening time Tib of the small-diameter injector 5b, which corresponds to the duty cycle, has elapsed, the small-diameter injector 5b closes, stopping fuel gas injection by the small-diameter injector 5b.

[0024] As for the large-diameter injectors 5a, for example, there are cases where two large-diameter injectors 5a1 and 5a2 are used, and cases where three large-diameter injectors 5a1 to 5a3 are used, and the multiple large-diameter injectors 5a1 to 5a3 are controlled to open and close simultaneously. When two large-diameter injectors 5a1 and 5a2 are used, the effective cross-sectional area of ​​the injection holes of the large-diameter injectors 5a is twice that of a single large-diameter injector 5a1. Similarly, when three large-diameter injectors 5a1 to 5a3 are used, the effective cross-sectional area of ​​the injection holes of the large-diameter injectors 5a is three times that of a single large-diameter injector 5a1.

[0025] The ECU10 calculates the maximum injection volume Qia(2) for the two large-diameter injectors 5a1 and 5a2, the maximum injection volume Qia(3) for the three large-diameter injectors 5a1 to 5a3, and the maximum injection volume Qib for the small-diameter injector 5b. The maximum injection volume Qi can be calculated using the following formula, with respect to the effective cross-sectional area S, pressure Pinj, temperature Tinj, specific heat ratio of hydrogen γ, and gas constant R of each injector 5. Qi=S×Pinj / R / Tinj×γ×{2 / (γ+1)}^{(γ+1) / (γ-1)}

[0026] <Normal injection> Figures 3A to 4B are time charts showing an example of the time variation of the actual fuel gas pressure P, calculated based on the target fuel gas pressure P0 and the value detected by the pressure sensor 6. The ECU 10 controls each injector 5 to inject fuel gas (normal injection) at set injection cycles Tint.

[0027] In the example shown in Figure 3A, the injection period Tint(t10) is calculated at time t10, and after the injection period Tint(t10) has elapsed from time t10, the next injection period Tint(t12) is calculated at time t12. When the injection period Tint is calculated at times t10 and t12, the injector 5 is opened (turned on), the fuel gas pressure P rises and exceeds the target pressure P0, and then the injector 5 is closed (turned off), and the fuel gas pressure P gradually decreases.

[0028] At this time, before the injection cycle Tint(t10) has elapsed at time t12, the fuel gas pressure P may drop sharply if, for example, the on-off valve 7 (Figure 1) is opened at time t11, purging the anode reflux gas. When the pressure P drops and deviates from the target pressure P0, the hydrogen concentration at the anode electrode becomes insufficient, and concentration overvoltage is consumed to maintain the current value by increasing the probability of electron transfer between the anode electrode and hydrogen, causing the output voltage (generated voltage) to decrease.

[0029] In the example in Figure 4A, the injection period Tint(t20) is calculated at time t20, and after the injection period Tint(t20) has elapsed from time t20, the injection period Tint(t22) is calculated at time t22. Then, before the injection period Tint(t20) has elapsed at time t22, at time t21, for example, the accelerator pedal of the vehicle is pressed, increasing the accelerator opening, and the required power generation amount (current value) and the target pressure P0 of the fuel gas increase. In this case, if the fuel gas pressure P deviates from the target pressure P0, the generated voltage will decrease.

[0030] <Interrupted injection> Therefore, in this embodiment, in order to suppress the decrease in generated voltage due to a decrease in fuel gas pressure, interrupt injection is performed when the pressure difference ΔP between the actual fuel gas pressure P and the target pressure P0 becomes α or greater, and the fuel gas is injected earlier than the injection cycle Tint has elapsed. That is, the ECU 10 controls the injector 5 to perform normal injection when the injection cycle Tint has elapsed, and also controls the injector 5 to perform interrupt injection when the pressure difference ΔP becomes α or greater, even if the injection cycle Tint has not elapsed.

[0031] In the example shown in Figure 3B, if the pressure difference ΔP exceeds a predetermined value α at time t13 before the injection period Tint(t10) set at time t10 has elapsed, the injector 5 is controlled to set the next injection period Tint(t13) and perform an interrupt injection. This prevents the fuel gas pressure P from dropping and deviating from the target pressure P0, thereby suppressing a decrease in the generated voltage.

[0032] In the example shown in Figure 4B, if the pressure difference ΔP exceeds a predetermined value α at time t23 before the injection cycle Tint(t20) set at time t20 has elapsed, the injector 5 is controlled to set the next injection cycle Tint(t23) and perform an interrupt injection. This allows the fuel pressure P to be rapidly increased before the fuel gas pressure P deviates from the target pressure P0, thereby improving the vehicle's acceleration response.

[0033] Figure 5 is a flowchart showing an example of the injection permission determination process performed by the ECU 10. The process in Figure 5 starts when the ECU 10 is activated and is executed repeatedly at predetermined intervals. As shown in Figure 5, first, in step S1, it is determined whether or not the injection period Tint has elapsed. If the result in step S1 is positive, the process proceeds to step S2, where normal injection is permitted and the process ends. On the other hand, if the result in step S1 is negative, the process proceeds to step S3, where it is determined whether or not the pressure difference ΔP is greater than or equal to a predetermined value α. If the result in step S3 is positive, the process proceeds to step S4, and if the result in step S3 is negative, the process ends. In step S4, it is determined whether or not at least the large-diameter injector 5a is closed. If the result in step S4 is positive, the process proceeds to step S2, where interrupt injection is permitted and the process ends. On the other hand, if the result in step S4 is negative, the process ends without permitting interrupt injection.

[0034] Figure 6A is a time chart illustrating the pressure rise of the fuel gas when interrupt injection is permitted even when the large-diameter injector 5a is open. Figure 6B is a time chart illustrating the pressure rise of the fuel gas when interrupt injection is permitted under the condition that the large-diameter injector 5a is closed.

[0035] In the example shown in Figure 6A, after normal injection is performed at time t40, the required power generation amount (current value) and the target fuel gas pressure P0 increase at time t41, and when the pressure difference ΔP exceeds a predetermined value α at time t42, interrupt injection is permitted, and the injector 5 is commanded to open until time t44. Subsequently, before the injector 5 is commanded to close at time t44, if the pressure difference ΔP is still above the predetermined value α at time t43, further interrupt injection is permitted, and the injector 5 is commanded to open until time t45. In this case, from time t42 to time t45, the injector 5 opens beyond the normal opening time Ti, and the pressure P rises. If the pressure P becomes excessive relative to the target pressure P0, and the hydrogen concentration at the anode electrode becomes excessive, the power generation efficiency may deteriorate, or the membrane electrode assembly may be damaged.

[0036] The ECU 10 permits interrupt injection provided that at least the large-diameter injector 5a is closed (step S4 in Figure 5). In this case, as shown in Figure 6B, it is possible to prevent the pressure P from becoming excessive relative to the target pressure P0 and to prevent excessive fuel gas from being supplied to the fuel cell stack 1.

[0037] <Calculation of valve opening time Ti for each injector> Figure 7 is a flowchart showing an example of the valve opening time setting process performed by the ECU 10. The process in Figure 7 is executed when injection (normal injection, interrupt injection) is permitted in the injection permission determination process in Figure 5.

[0038] <Valve opening time Ti when using two large-diameter injectors and one small-diameter injector (assuming the large-diameter injector's opening time is the minimum opening time)> As shown in Figure 7, in step S10, the temporary valve opening time Ti_tmp for each injector 5 is calculated assuming the use of two large-diameter injectors 5a1 and 5a2 and a small-diameter injector 5b. In step S10, the temporary valve opening time Tia_tmp for the large-diameter injector 5a is set to a predetermined minimum valve opening time Tia_min (for example, about 12 ms), and the temporary valve opening time Tib_tmp for the small-diameter injector 5b is calculated.

[0039] More specifically, using the injection period Tint, the maximum injection volume Qia(2) of the two large-diameter injectors 5a1 and 5a2, and the minimum valve opening time Tia_min of the large-diameter injector 5a, the minimum injection volume Qia_min of the two large-diameter injectors 5a1 and 5a2 is calculated using the following formula. Qia_min = Tia_min / Tint × Qia(2)

[0040] Then, using the calculated minimum injection volume Qia_min, required injection volume Q, injection period Tint, and maximum injection volume Qib of the two large-diameter injectors 5a1 and 5a2, the temporary valve opening time Tib_tmp of the small-diameter injector 5b is calculated using the following formula. Tib_tmp / Tint×Qib=Q-Qia_min

[0041] Next, in step S11, it is determined whether the temporary valve opening time Tib_tmp of the small-diameter injector 5b calculated in step S10 is less than or equal to the maximum valve opening time Tib_max of the small-diameter injector 5b. The maximum valve opening time Ti_max of each injector 5 is determined as the shorter of the time obtained by subtracting the minimum valve opening time Ti_min from the injection period Tint (for example, about 95%) and the injection period Tint.

[0042] If affirmed in step S11, the process proceeds to step S19, where the valve opening time Tia of the large-diameter injector 5a is set to the minimum valve opening time Tia_min, and the valve opening time Tib of the small-diameter injector 5b is set to the temporary valve opening time Tib_tmp calculated in step S10. Once the valve opening time Ti of each injector 5 is set in step S19, each injector 5 is controlled to inject fuel gas based on the set valve opening time Ti.

[0043] <Valve opening time Ti when using two large-diameter injectors and one small-diameter injector (when the valve opening time of the large-diameter injector is greater than the minimum valve opening time)> On the other hand, if step S11 is rejected, the process proceeds to step S12, where the redistributed injection amount Qia_red to be injected by the two large-diameter injectors 5a1 and 5a2 in addition to the injection at the minimum valve opening time Tia_min is calculated. More specifically, the redistributed injection amount Qia_red is calculated using the following formula, with the maximum injection amount Qib of the small-diameter injector 5b, the temporary valve opening time Tib_tmp of the small-diameter injector 5b, and the maximum valve opening time Tib_max of the small-diameter injector 5b. Qia_red=Qib×(Tib_tmp-Tib_max)

[0044] Next, in step S13, the redistribution valve opening time Tia_red is calculated, which is the time at which the two large-diameter injectors 5a1 and 5a2 should continue to open (inject) beyond the minimum valve opening time Tia_min. More specifically, the redistribution valve opening time Tia_red is calculated using the following formula, with the redistribution injection amount Qia_red calculated in step S12, the maximum injection amount Qia(2) of the two large-diameter injectors 5a1 and 5a2, and the maximum injection amount Qib of the small-diameter injector 5b. Tia_red = Qia_red / (Qia(2) - Qib)

[0045] Next, in step S14, the temporary valve opening time Ti_tmp for each injector 5 is calculated assuming the use of two large-diameter injectors 5a1 and 5a2 and a small-diameter injector 5b. More specifically, using the minimum valve opening time Tia_min for the large-diameter injector 5a, the maximum valve opening time Tib_max for the small-diameter injector 5b, and the redistribution valve opening time Tia_red calculated in step S13, the temporary valve opening time Tia_tmp for the large-diameter injector 5a and the temporary valve opening time Tib_tmp for the small-diameter injector 5b are calculated using the following formula. Tia_tmp = Tia_min + Tia_red Tib_tmp=Tib_max-Tia_red

[0046] Next, in step S15, it is determined whether the temporary valve opening time Tia_tmp of the large-diameter injector 5a calculated in step S14 is equal to a predetermined valve opening time (for example, less than or equal to the maximum valve opening time Tia_max of the large-diameter injector 5a), and whether the temporary valve opening time Tib_tmp of the small-diameter injector 5b is less than or equal to the maximum valve opening time Tib_max of the small-diameter injector 5b. The predetermined valve opening time is not limited to the maximum valve opening time Tia_max of the large-diameter injector 5a, but may be a fixed value set separately by testing or the like. If affirmed in step S15, the process proceeds to step S19, where the valve opening times Tia and Tib of each injector 5a and 5b are set to the temporary valve opening times Tia_tmp and Tib_tmp calculated in step S14. Alternatively, instead of the process in step S15, it may be determined whether the current value (generated current value) of the fuel cell stack 1 is equal to or greater than a predetermined current value, and if affirmed, the process proceeds to step S16, and if denied, the process proceeds to step S19. In other words, under operating conditions where the power generation state is stable when the generated current value is above a predetermined current value, whether the small-diameter injector 5b is used or only the large-diameter injector 5a is used without the small-diameter injector 5b, the number of operations of the small-diameter injector 5b is reduced, thereby minimizing deterioration due to wear of the small-diameter injector 5b while improving the power generation stability of the fuel cell stack 1.

[0047] <Valve opening time Ti when using only two large-diameter injectors> On the other hand, if step S15 is rejected, the process proceeds to step S16 to calculate the temporary valve opening time Tia_tmp assuming that only the two large-diameter injectors 5a1 and 5a2 are used. More specifically, using the required injection amount Q, injection period Tint, and the maximum injection amounts Qia(2) of the two large-diameter injectors 5a1 and 5a2, the temporary valve opening time Tia_tmp of the large-diameter injector 5a is calculated using the following formula. Tia_tmp / Tint × Qia(2) = Q

[0048] Next, in step S17, it is determined whether the temporary valve opening time Tia_tmp of the large-diameter injector 5a calculated in step S16 is less than or equal to a predetermined valve opening time (for example, the maximum valve opening time Tia_max of the large-diameter injector 5a). If this is confirmed in step S17, the process proceeds to step S19, where the valve opening time Tia of the large-diameter injector 5a is set to the temporary valve opening time Tia_tmp calculated in step S16, and the valve opening time Tib of the small-diameter injector 5b is set to "0". Alternatively, instead of the process in step S17, it may be determined whether the power generation current value of the fuel cell stack 1 is greater than or equal to a predetermined current value, and if this is confirmed, the process proceeds to step S18, and if not, the process proceeds to step S19.

[0049] <Valve opening time Ti when using only 3 large-diameter injectors> On the other hand, if the condition is rejected in step S17, the process proceeds to step S18 to calculate the temporary valve opening time Tia_tmp assuming that only the three large-diameter injectors 5a1 to 5a3 are used. More specifically, the temporary valve opening time Tia_tmp for the large-diameter injector 5a is calculated using the following formula, with respect to the required injection amount Q, the injection period Tint, and the maximum injection amount Qia(3) of the three large-diameter injectors 5a1 to 5a3. Next, in step S19, the valve opening time Tia for the large-diameter injector 5a is set to the temporary valve opening time Tia_tmp calculated in step S18, and the valve opening time Tib for the small-diameter injector 5b is set to "0". Tia_tmp / Tint × Qia(3) = Q

[0050] <Combination of load and injector> FIG. 8 is a diagram for explaining the valve opening time Ti of each injector 5 set by the ECU 10. As shown in FIG. 8, in the first load region (Q≦Q1) where the required power generation amount (load) of the fuel cell stack 1 is small and the required injection amount Q is less than or equal to the first threshold value Q1, the temporary valve opening time Tib_tmp of the small-diameter injector 5b calculated in step S10 of FIG. 7 is less than or equal to the maximum valve opening time Tib_max (affirmative in S11). In such a first load region, injection (normal injection, interrupt injection) is performed using the two large-diameter injectors 5a1, 5a2 and the small-diameter injector 5b, and the valve opening time Tia of the large-diameter injector 5a is set to the minimum valve opening time Tia_min.

[0051] In the second load region (Q1<Q≦Q2) where the required power generation amount of the fuel cell stack 1 is slightly small and the required injection amount Q is greater than the first threshold value Q1 and less than or equal to the second threshold value Q2, the temporary valve opening time Tib_tmp of the small-diameter injector 5b calculated in step S10 of FIG. 7 is greater than the maximum valve opening time Tib_max (negative in S11). Also, the temporary valve opening time Tia_tmp of the large-diameter injector 5a calculated in step S14 is less than or equal to the maximum valve opening time Tia_max (affirmative in S15). In such a second load region, injection (normal injection, interrupt injection) is performed using the two large-diameter injectors 5a1, 5a2 and the small-diameter injector 5b, and the valve opening time Tia of the large-diameter injector 5a is set longer than the minimum valve opening time Tia_min.

[0052] In the low load region (Q≦Q2) where the required power generation amount of the fuel cell stack 1 is relatively small and the required injection amount Q is relatively small, the valve opening time Ti per injection cycle Tint is shorter than that in the high load region (Q>Q2), and the time (Tint - Ti) when injection is not performed tends to be long. Therefore, drainage in the anode flow path 2 may be stagnant. In such a low load region, the small-diameter injector 5b, for which the required valve opening time Ti for the same injection amount is longer than that of the large-diameter injector 5a, is preferentially used, and the valve opening time Tib of the small-diameter injector 5b is set longer than the valve opening time Tia of the large-diameter injector 5a (Tia<Tib).

[0053] As a result, the valve opening time Ti (= Tia + Tib) per injection cycle Tint can be lengthened, and the water (liquid) staying in the anode flow path 2 can be smoothly discharged to the outside of the fuel cell stack. Further, by preferentially using the small-diameter injector 5b, even when the number of injections of the injector 5 increases due to the interrupt injection, deterioration due to wear of the large-diameter injector 5a that is essential for ensuring the required injection amount Q can be minimized.

[0054] In the third load region (Q2 < Q ≤ Q3) where the required power generation amount of the fuel cell stack 1 is slightly large and the required injection amount Q is larger than the second threshold value Q2 and not more than the third threshold value Q3, the temporary valve opening time Tib_tmp of the small-diameter injector 5b calculated in step S10 of FIG. 7 is larger than the maximum valve opening time Tib_max, and the temporary valve opening time Tia_tmp of the large-diameter injector 5a calculated in step S14 is larger than the maximum valve opening time Tia_max (negated in S11 and S15). Further, the temporary valve opening time Tia_tmp of the large-diameter injector 5a calculated in step S16 becomes not more than the maximum valve opening time Tia_max (affirmed in S17). In such a third load region, injection (normal injection, interrupt injection) is performed using only the two large-diameter injectors 5a1 and 5a2.

[0055] In the fourth load region (Q3 < Q) where the required power generation amount of the fuel cell stack 1 is large and the required injection amount Q is larger than the third threshold value Q3, the temporary valve opening time Tib_tmp of the small-diameter injector 5b calculated in step S10 of FIG. 7 is larger than the maximum valve opening time Tib_max, the temporary valve opening time Tia_tmp of the large-diameter injector 5a calculated in step S14 is larger than the maximum valve opening time Tia_max, and the temporary valve opening time Tia_tmp of the large-diameter injector 5a calculated in step S16 is larger than the maximum valve opening time Tia_max (negated in S11, S15, and S17). In such a fourth load region, injection (normal injection, interrupt injection) is performed using only the three large-diameter injectors 5a1 to 5a3.

[0056] In the high-load region (Q>Q2) where the power generation requirement of fuel cell stack 1 is relatively large and the required injection amount Q is relatively large, the valve opening time Ti per injection period Tint tends to be longer than in the low-load region (Q≦Q2). In such high-load regions, only the large-diameter injector 5a is used, which requires a shorter valve opening time Ti for the same injection amount than the small-diameter injector 5b, thereby shortening the valve opening time Ti (=Tia) per injection period Tint. This allows for the preferential use of the small-diameter injector 5b while reliably injecting the required injection amount Q within the injection period Tint even in the high-load region (Q>Q2), thereby satisfying the required power generation.

[0057] This embodiment can provide the following effects and advantages. (1) The fuel cell system 100 comprises a fuel cell stack 1 made up of multiple power generation cells stacked on top of each other, an injector 5 that injects fuel gas supplied to the fuel cell stack 1, a pressure sensor 6 that detects the pressure P of the fuel gas supplied to the fuel cell stack 1, and an ECU 10 that sets the injection period Tint of the injector 5 and controls the injector 5 to inject fuel gas at each injection period Tint (Figure 1).

[0058] The ECU 10 controls the injector 5 to inject fuel gas earlier than the injection cycle Tint has elapsed when the pressure difference ΔP between the pressure P detected by the pressure sensor 6 and the target pressure P0 exceeds a predetermined value α (Figure 5). In this way, the pressure P of the fuel gas supplied to the fuel cell stack 1 is constantly monitored, and when the pressure difference ΔP with respect to the target pressure P0 exceeds a predetermined value α, an interrupt injection is performed without waiting for the injection cycle Tint to elapse, thereby suppressing a decrease in the generated voltage due to a drop in fuel gas pressure (Figures 3B and 4B).

[0059] (2) The ECU 10 calculates the required injection quantity Q of the fuel gas based on the required power generation quantity of the fuel cell stack 1, sets the injection cycle Tint based on the pressure P detected by the pressure sensor 6 and the required power generation quantity, sets the valve opening time Ti of the injector 5 based on the required injection quantity Q and the injection cycle Tint, and controls the injector 5 to inject the fuel gas based on the valve opening time Ti.

[0060] Even if the injection cycle Tint is set in consideration of the required injection quantity Q and the pressure P in this way, the pressure difference ΔP may become excessive before the set injection cycle Tint elapses, and the power generation voltage may decrease (FIGS. 3A and 4A). By monitoring the pressure difference ΔP and performing interrupt injection without waiting for the elapse of the injection cycle Tint as necessary, it is possible to suppress the decrease in the power generation voltage due to the decrease in the pressure of the fuel gas (FIGS. 3B and 4B).

[0061] (3) The injector 5 includes a large-diameter injector 5a and a small-diameter injector 5b having a smaller diameter than the large-diameter injector 5a, and the valve opening time Ti includes the valve opening time Tia of the large-diameter injector 5a and the valve opening time Tib of the small-diameter injector 5b (FIG. 1). When the required injection quantity Q is less than or equal to the second threshold value Q2 (Q ≦ Q2), the ECU 10 sets the valve opening time Tib of the small-diameter injector 5b to be longer than the valve opening time Tia of the large-diameter injector 5a (Tia < Tib). When the required injection quantity is greater than the second threshold value Q2 (Q > Q2), the ECU 10 sets the valve opening time Tia of the large-diameter injector 5a to be longer than the valve opening time Tib of the small-diameter injector 5b (Tia > Tib = 0) (FIG. 8).

[0062] Thereby, the valve opening time Ti per injection cycle Tint = (Tia + Tib) can be lengthened, and the water (liquid) staying in the anode flow path 2 can be smoothly discharged to the outside of the fuel cell stack. Further, by preferentially using the small-diameter injector 5b, even when the number of injections of the injector 5 increases due to interrupt injection, deterioration due to wear of the large-diameter injector 5a, which is essential for ensuring the required injection quantity Q, can be minimized.

[0063] (4) The ECU 10 sets the valve opening time Tia for the large-diameter injector 5a and the valve opening time Tib for the small-diameter injector 5b based on the minimum valve opening time Tia_min for the large-diameter injector 5a (Figure 7). This allows the small-diameter injector 5b to be used preferentially.

[0064] (5) The ECU 10 sets the valve opening time Tia of the large-diameter injector 5a to the minimum valve opening time Tia_min, calculates the minimum injection amount Qia_min of the large-diameter injectors 5a (5a1, 5a2) based on the minimum valve opening time Tia_min, and sets the valve opening time Tib of the small-diameter injector 5b based on the difference between the required injection amount Q and the minimum injection amount Qia_min (Q-Qa_min) (S10, S19 in Figure 7). This allows the small-diameter injector 5b to be used preferentially in the first load region (Q≦Q1) (Figure 8).

[0065] (6) The ECU 10 calculates the minimum injection amount Qia_min for the large-diameter injector 5a (5a1, 5a2) based on the minimum valve opening time Tia_min, and sets the temporary valve opening time Tib_tmp for the small-diameter injector 5b based on the difference between the required injection amount Q and the minimum injection amount Qia_min (S10 in Figure 7). Then, when the temporary valve opening time Tib_tmp is less than or equal to the maximum valve opening time Tib_max for the small-diameter injector 5b, the valve opening time Tia for the large-diameter injector 5a (5a1, 5a2) is set to the minimum valve opening time Tia_min, and the valve opening time Tib for the small-diameter injector 5b is set to the temporary valve opening time Tib_tmp (affirmed in S11 → S19).

[0066] Also, when the temporary valve opening time Tib_tmp is greater than the maximum valve opening time Tib_max, the valve opening time Tia of the large-diameter injector 5a (5a1, 5a2) is set based on the difference between the temporary valve opening time Tib_tmp and the maximum valve opening time Tib_max (Tib_tmp - Tib_max) and the minimum valve opening time Tia_min, and the valve opening time Tib of the small-diameter injector 5b is set based on the difference between the temporary valve opening time Tib_tmp and the maximum valve opening time Tib_max (Tib_tmp - Tib_max) and the maximum valve opening time Tib_max (S11 is negative → S12~S14, S19). Thereby, the small-diameter injector 5b can be preferentially used in the first load region (Q ≦ Q1) and the second load region (Q1 < Q ≦ Q2) (Fig. 8).

[0067] (7) The ECU 10 calculates the minimum injection amount Qia_min of the large-diameter injector 5a (5a1, 5a2) based on the minimum valve opening time Tia_min, sets the temporary valve opening time Tib_tmp of the small-diameter injector 5b based on the difference between the required injection amount Q and the minimum injection amount Qia_min (Q - Qa_min), and when the temporary valve opening time Tib_tmp of the small-diameter injector 5b is greater than the maximum valve opening time Tib_max of the small-diameter injector 5b, the temporary valve opening time Tia_tmp of the large-diameter injector 5a (5a1, 5a2) is set based on the difference between the temporary valve opening time Tib_tmp and the maximum valve opening time Tib_max of the small-diameter injector 5b (Tib_tmp - Tib_max) and the minimum valve opening time Tia_min (negative at S11 in Fig. 7 → S12~S14).

[0068] Furthermore, when the temporary opening time Tia_tmp of the large-diameter injectors 5a (5a1, 5a2) is less than or equal to a predetermined opening time (for example, the maximum opening time Tia_max of the large-diameter injectors 5a), the injectors 5 are controlled to inject fuel gas using both the large-diameter injectors 5a (5a1, 5a2) and the small-diameter injectors 5b (affirmed in S15 → S19). Also, when the temporary opening time Tia_tmp of the large-diameter injectors 5a (5a1, 5a2) is greater than the predetermined opening time, the injectors 5 are controlled to inject fuel gas using only the large-diameter injectors 5a (5a1 and 5a2, or 5a1, 5a2 and 5a3) (negated in S15 → S16~S19). This allows the small-diameter injectors 5b to be used preferentially, while reliably injecting the required injection amount Q within the injection cycle Tint even in the high-load region (Q>Q2), thereby satisfying the required power generation amount.

[0069] (8) The ECU 10 controls the injector 5 to inject fuel gas only when the large-diameter injector 5a is in a closed state. This prevents an excess of fuel gas from being supplied to the fuel cell stack 1.

[0070] (9) The ECU 10 calculates the minimum injection amount Qia_min for the large-diameter injector 5a (5a1, 5a2) based on the minimum valve opening time Tia_min, sets the temporary valve opening time Tib_tmp for the small-diameter injector 5b based on the difference between the required injection amount Q and the minimum injection amount Qia_min (Q-Qa_min), and when the temporary valve opening time Tib_tmp for the small-diameter injector 5b is greater than the maximum valve opening time Tib_max for the small-diameter injector 5b, it sets the temporary valve opening time Tia_tmp for the large-diameter injector 5a (5a1, 5a2) based on the difference between the temporary valve opening time Tib_tmp and the maximum valve opening time Tib_max for the small-diameter injector 5b (Tib_tmp-Tib_max) and the minimum valve opening time Tia_min (negated in S11 in Figure 7 → S12~S14). Then, when the power generation current value of the fuel cell stack 1 is less than a predetermined current value, the injector 5 is controlled to inject fuel gas using the large-diameter injector 5a (5a1, 5a2) and the small-diameter injector 5b (S19). Also, when the power generation current value is equal to or greater than the predetermined current value, the injector 5 is controlled to inject fuel gas using only the large-diameter injector 5a (5a1 and 5a2, or 5a1, 5a2 and 5a3) (S16~S19). In this case, under operating conditions where the power generation state is stable whether the small-diameter injector 5b is used or only the large-diameter injector 5a is used without the small-diameter injector 5b, the number of operations of the small-diameter injector 5b can be reduced, minimizing deterioration due to wear of the small-diameter injector 5b while improving the power generation stability of the fuel cell stack 1.

[0071] In the above embodiment, an example was described in Figure 1, etc., in which three large-diameter injectors 5a1 to 5a3 and one small-diameter injector 5b are provided. However, the injectors that inject fuel gas are not limited to this configuration. For example, only a single injector may be provided. In this case as well, if the pressure difference between the detected pressure and the target pressure exceeds a predetermined value, interrupt injection can be performed, injecting fuel gas earlier than the injection cycle has elapsed.

[0072] In the above embodiment, an example using at least two large-diameter injectors 5a1 and 5a2 was described in Figures 7 and 8, but the combination of injectors is not limited to the examples given. The combination of injectors can be appropriately determined according to the hole diameter of each injector. For example, a combination using one large-diameter injector 5a and one small-diameter injector 5b, with the valve opening time Tia of the large-diameter injector 5a set to the minimum valve opening time Tia_min, may be used as the combination for low load conditions.

[0073] The above description is merely an example, and the present invention is not limited by the embodiments and modifications described above, as long as the features of the present invention are not impaired. It is also possible to arbitrarily combine one or more of the above embodiments and modifications, and to combine modifications with each other. [Explanation of Symbols]

[0074] 1 Fuel cell stack, 2 Anode channel, 3 Cathode channel, 4a, 4b Ejectors, 5 Injectors, 5a1-5a3 Large diameter injectors, 5b Small diameter injectors, 6 Pressure sensor, 7 On / off valve, 10 ECU, 100 Fuel cell system

Claims

1. A fuel cell stack composed of multiple power generation cells stacked on top of each other, An injector that injects fuel gas supplied to the fuel cell stack, A detection unit for detecting the pressure of the fuel gas supplied to the fuel cell stack, The system includes a control unit that sets the injection cycle of the injector and controls the injector to perform injections at each injection cycle, The fuel cell system is characterized in that, when the pressure difference between the pressure detected by the detection unit and the target pressure exceeds a predetermined value, the control unit sets the next injection cycle to start earlier than the current injection cycle has elapsed, starting from the point when the pressure difference exceeds the predetermined value, and controls the injector to perform the next injection from the point when the pressure difference exceeds the predetermined value.

2. In the fuel cell system according to claim 1, The fuel cell system is characterized in that the control unit calculates the required amount of fuel gas to be injected based on the required amount of power generated by the fuel cell stack, sets the injection cycle based on the pressure detected by the detection unit and the required amount of power generated, sets the valve opening time of the injector based on the required amount of injection and the injection cycle, and controls the injector to perform the injection based on the valve opening time.

3. In the fuel cell system according to claim 2, The injector includes a first injector and a second injector having a smaller diameter than the first injector. The valve opening time includes the first valve opening time of the first injector and the second valve opening time of the second injector. The fuel cell system is characterized in that the control unit sets the second valve opening time to be longer than the first valve opening time when the requested injection amount is less than or equal to a predetermined threshold, and sets the first valve opening time to be longer than the second valve opening time when the requested injection amount is greater than the threshold.

4. In the fuel cell system according to claim 3, The fuel cell system is characterized in that the control unit sets the first valve opening time and the second valve opening time based on the minimum valve opening time of the first injector.

5. In the fuel cell system according to claim 4, The fuel cell system is characterized in that the control unit sets the first valve opening time to the minimum valve opening time, calculates the minimum injection amount of the first injector based on the minimum valve opening time, and sets the second valve opening time based on the difference between the required injection amount and the minimum injection amount.

6. In the fuel cell system according to claim 4, The control unit, Based on the minimum valve opening time, the minimum injection amount of the first injector is calculated. The temporary opening time of the second injector is set based on the difference between the requested injection amount and the minimum injection amount. When the temporary valve opening time is less than or equal to the maximum valve opening time of the second injector, the first valve opening time is set to the minimum valve opening time, and the second valve opening time is set to the temporary valve opening time. A fuel cell system characterized in that, when the temporary valve opening time is greater than the maximum valve opening time, the first valve opening time is set based on the difference between the temporary valve opening time and the maximum valve opening time and the minimum valve opening time, and the second valve opening time is set based on the difference between the temporary valve opening time and the maximum valve opening time and the maximum valve opening time.

7. In the fuel cell system according to claim 4, The control unit, Based on the minimum valve opening time, the minimum injection amount of the first injector is calculated. The temporary opening time of the second injector is set based on the difference between the requested injection amount and the minimum injection amount. When the temporary opening time of the second injector is greater than the maximum opening time of the second injector, the temporary opening time of the first injector is set based on the difference between the temporary opening time of the second injector and the maximum opening time of the second injector, and the minimum opening time. When the pre-opening time of the first injector is less than or equal to a predetermined opening time, the injector is controlled to perform the injection using the first injector and the second injector. A fuel cell system characterized in that, when the temporary opening time of the first injector is greater than the predetermined opening time, the injector is controlled to perform the injection using only the first injector.

8. In the fuel cell system according to any one of claims 3 to 7, The fuel cell system is characterized in that the control unit controls the injector to perform the injection on the condition that the first injector is in a closed valve state.

9. In the fuel cell system according to claim 4, The control unit, Based on the minimum valve opening time, the minimum injection amount of the first injector is calculated. The temporary opening time of the second injector is set based on the difference between the requested injection amount and the minimum injection amount. When the temporary opening time of the second injector is greater than the maximum opening time of the second injector, the temporary opening time of the first injector is set based on the difference between the temporary opening time of the second injector and the maximum opening time of the second injector, and the minimum opening time. When the power generation current value of the fuel cell stack is less than a predetermined current value, the injectors are controlled to perform the injection using the first injector and the second injector. A fuel cell system characterized in that when the generated current value is equal to or greater than the predetermined current value, the injector is controlled to perform the injection using only the first injector.

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