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 technology]

[0002] Using fuel cells as a driving source for a vehicle can contribute to improving energy efficiency. As a technology related to such fuel cells, a device that controls an injector that injects fuel gas for the fuel cell is known (see, for example, Patent Document 1). The device described in Patent Document 1 sets a target pressure of the fuel gas flowing into the fuel gas flow passage at predetermined intervals, detects the pressure of the fuel gas flowing into the fuel gas flow passage, and controls the drive of multiple injectors so that the detected pressure approaches the target pressure, and when the system starts up, sets the drive cycle of the injectors to be shorter than during normal control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-102948 Summary of the Invention [Problem to be solved by the invention]

[0004] However, even if the drive cycle is adjusted as in the device described in Patent Document 1, there is a risk that the fuel gas pressure may temporarily drop below the target pressure under certain operating conditions, such as purging to expel impurities from the fuel gas circulation flow path or when the vehicle accelerates and the required amount of power generation increases sharply, resulting in a drop in the power generation voltage. [Means for solving the problem]

[0005] A fuel cell system according to one aspect of the present invention includes a fuel cell stack configured by stacking a plurality of power generation cells, an injector that injects fuel gas supplied to the fuel cell stack, a detector that detects the pressure of the fuel gas supplied to the fuel cell stack, and a controller that sets an injection period for the injector and controls the injector to inject fuel gas at each injection period. When the pressure difference between the pressure detected by the detector and a target pressure reaches a predetermined value or more, the controller controls the injector to inject fuel gas earlier than the injection period has elapsed. [Effects of the Invention]

[0006] According to the present invention, it is possible to suppress a drop in generated voltage due to a drop in fuel gas pressure. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram schematically illustrating an example of the overall configuration of a fuel cell system according to an embodiment of the present invention. [Figure 2] 3 is a timing chart for explaining the injection order of the large-diameter injector and the small-diameter injector of FIG. 1; [Figure 3A] 5 is a time chart for explaining a pressure drop of fuel gas during purging. [Figure 3B] 3B is a time chart corresponding to FIG. 3A and illustrating suppression of pressure drop due to interrupt injection. [Figure 4A] 4 is a time chart for explaining a drop in fuel gas pressure during acceleration. [Figure 4B] 4B is a time chart corresponding to FIG. 4A and illustrating suppression of pressure drop due to interrupt injection. [Figure 5] 4 is a flowchart showing an example of an injection permission determination process executed by the ECU of FIG. [Figure 6A] 6 is a time chart for explaining the rise in fuel gas pressure when interrupt injection is permitted even when the valve of the large diameter injector is open. [Figure 6B]6 is a time chart for explaining the pressure rise of fuel gas when interrupt injection is permitted on the condition that the valve of the large diameter injector is closed. [Figure 7] 2 is a flowchart showing an example of a valve opening time setting process executed by the ECU of FIG. 1; [Figure 8] FIG. 2 is a diagram for explaining the valve opening time of each injector set by the ECU in FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to Figs. 1 to 8. Fig. 1 is a diagram schematically showing an example of the overall configuration of a fuel cell system 100 according to an embodiment of the present invention. As shown in Fig. 1, the fuel cell system 100 mainly comprises a fuel cell stack 1 formed by stacking a plurality of power-generating cells, and an ECU (Electronic Control Unit) 10 that controls each part of the fuel cell system 100. The fuel cell system 100 is mounted, for example, on a vehicle and can generate electric power for driving the vehicle. The fuel cell system 100 can also be mounted on moving bodies other than vehicles, such as aircraft and ships, robots, and various types of industrial machinery.

[0009] Each power generation cell of the fuel cell stack 1 has a membrane electrode assembly (MEA) in which electrodes (electrode catalyst layers, gas diffusion layers, etc.) are provided on both sides of a solid polymer electrolyte membrane. A fuel gas containing hydrogen is supplied to the anode electrode of each power generation cell of the fuel cell stack 1 via an anode flow path 2, and an oxidant gas such as air containing oxygen is supplied to the cathode electrode via a cathode flow path 3. This causes an electrochemical reaction to proceed at the electrodes of each power generation cell, and power is generated in the fuel cell stack 1.

[0010] An oxidant gas such as air compressed by a compressor (not shown) is supplied to the cathode flow channel 3. A portion of the oxidant gas supplied to the cathode flow channel 3 is used at the cathode electrode, and then discharged to the outside from the cathode flow channel 3 as oxidant exhaust gas.

[0011] A fuel gas tank storing high-pressure fuel gas is connected to the anode flow path 2 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 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 element that opens and closes an injection hole and a coil that drives the valve element, 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 response to an opening / closing command from the ECU 10, thereby driving the injector 5 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 coil is de-energized in response to an OFF command from the ECU 10, the injector 5 closes. When the injector 5 opens, fuel gas whose pressure has been reduced to a predetermined supply pressure by a pressure reducing valve is injected and supplied to the anode flow path 2.

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

[0014] The injectors 5 include a large-diameter injector 5a and a small-diameter injector 5b arranged in parallel. The effective cross-sectional area of ​​the injection hole of the large-diameter injector 5a is larger than that of the small-diameter injector 5b, and the injection amount per unit time of the large-diameter injector 5a is larger than that of the small-diameter injector 5b.

[0015] The large-diameter injector 5a may be configured as a single injector with a larger hole diameter than the small-diameter injector 5b, or as multiple injectors with the same hole diameter as the small-diameter injector 5b. The following describes an example in which the large-diameter injector 5a includes three large-diameter injectors 5a1-5a3 with larger hole diameters than the small-diameter injector 5b. The large-diameter injectors 5a1-5a3 are arranged in parallel with one another. The fuel gas injected from the large-diameter injectors 5a1-5a3 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 of the ejector 4a, 4b and is accelerated, creating a low-pressure space inside the ejector 4a, 4b, which draws the fuel exhaust gas discharged from the anode flow path 2 into the ejector 4a, 4b. The fuel gas and fuel exhaust gas that join inside the ejector 4a, 4b are discharged through the diffuser of the ejector 4a, 4b while being entrained and mixed, and are supplied to the anode flow path 2. Hereinafter, the mixed gas discharged from the ejector 4a, 4b and supplied to the anode flow path 2 will be referred to as the "anode supply gas." The anode supply gas contains fuel gas (hydrogen), permeated nitrogen, and permeated water vapor.

[0017] A pressure sensor 6 is provided near the inlet of the anode flow path 2 to detect the pressure P of the fuel gas supplied to the fuel cell stack 1. Specifically, the pressure sensor 6 detects the pressure (total pressure) of the anode supply gas, which includes the fuel gas. The hydrogen partial pressure of the anode supply gas, which corresponds to the pressure P of the fuel gas (hydrogen), can be calculated by subtracting the nitrogen partial pressure and 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 nitrogen partial pressure and water vapor partial pressure of the anode supply gas can be calculated based on the flow rates (permeation amounts) of the permeated nitrogen and permeated water vapor and the discharge amount of the anode reflux gas, which will be 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 stack temperature.

[0018] An on-off valve 7 is provided near the outlet of the anode flow path 2 to open and close the reflux path connecting the anode flow path 2 to 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 hydrogen partial pressure) of the anode supply gas decreases due to an increase in the nitrogen concentration (relative nitrogen partial pressure) of the anode supply gas. When the on-off valve 7 is temporarily opened, a portion of the anode reflux gas flowing through the reflux path is discharged (purged), thereby suppressing a decrease in the hydrogen concentration of the anode supply gas and maintaining the hydrogen concentration at a certain level or higher. The on-off valve 7 is controlled by the ECU 10.

[0019] The ECU 10 includes a computer having a CPU, RAM, ROM, an 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. The ECU 10 is also connected to each part of the fuel cell system 100, such as the injector 5 and the on-off valve 7, and controls each part of the fuel cell system 100, including the injector 5. The required power generation amount of the fuel cell system 100 is input to the ECU 10, for example, via the vehicle accelerator position sensor.

[0020] <Calculation of required injection amount Q> The ECU 10 calculates the flow rate (required injection amount) Q of the 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, the ECU 10 calculates the required power generation amount of the fuel cell system 100 based on the accelerator opening degree detected by the accelerator opening degree sensor, and calculates the flow rate (power generation consumption amount) of the fuel gas (hydrogen) consumed per unit time by power generation in the fuel cell stack 1. The ECU 10 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 discharge amount of anode reflux gas, pressure fluctuation of the fuel gas target pressure P0, and the feedback amount of pressure P relative to the target pressure P0. The required injection amount Q is then calculated by adding the feedback amount to the calculated power generation consumption amount, permeation amount, discharge amount, and pressure fluctuation (feedforward amount).

[0021] <Setting the injection cycle Tint> The ECU 10 calculates the current value based on the required power generation amount of the fuel cell system 100, and 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 referencing a predetermined characteristics map, the ECU 10 calculates (sets) the injection period Tint according to the calculated current value and hydrogen partial pressure of the anode supply gas. The injection period Tint is set so that it becomes shorter as the current value becomes higher and the load becomes larger, and becomes shorter as the hydrogen partial pressure of the anode supply gas becomes lower.

[0022] <Calculating the maximum injection amount 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 injection amount of fuel gas that each injector 5 injects per valve opening is adjusted by the duty ratio (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 of each injector 5 is the injection amount at a duty ratio of 100%.

[0023] FIG. 2 is a time chart illustrating the injection order of the large-diameter injector 5a and the small-diameter injector 5b. As shown in FIG. 2, when an injection cycle Tint(t1) is set at time t1, the large-diameter injector 5a is first opened during the set injection cycle Tint(t1), and the large-diameter injector 5a starts injecting fuel gas. After that, at time t2, when the valve-open time Tia of the large-diameter injector 5a corresponding to the duty ratio has elapsed, the large-diameter injector 5a closes and stops injecting fuel gas, and the small-diameter injector 5b opens and starts injecting fuel gas. After that, at time t3, when the valve-open time Tib of the small-diameter injector 5b corresponding to the duty ratio has elapsed, the small-diameter injector 5b closes and stops injecting fuel gas.

[0024] The large-diameter injectors 5a may be, for example, two large-diameter injectors 5a1 and 5a2, or three large-diameter injectors 5a1 to 5a3, which 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 the 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 the single large-diameter injector 5a1.

[0025] ECU 10 calculates the maximum injection quantity Qia(2) of the two large-diameter injectors 5a1 and 5a2, the maximum injection quantity Qia(3) of the three large-diameter injectors 5a1 to 5a3, and the maximum injection quantity Qib of small-diameter injector 5b. The maximum injection quantity Qi can be calculated using the effective cross-sectional area S of each injector 5, the pressure Pinj, the temperature Tinj, the specific heat ratio γ of hydrogen, and the gas constant R according to the following equation: Qi=S×Pinj / R / Tinj×γ×{2 / (γ+1)}^{(γ+1) / (γ-1)}

[0026] <Normal injection> 3A to 4B are time charts showing an example of the change over time of the target fuel gas pressure P0 and the actual fuel gas pressure P calculated based on the detection value of the pressure sensor 6. The ECU 10 controls each injector 5 so as to inject fuel gas (normal injection) at every set injection period Tint.

[0027] 3A, the injection period Tint(t10) is calculated at time t10, and when the injection period Tint(t10) has elapsed since 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 (ON), the fuel gas pressure P increases and exceeds the target pressure P0, and then the injector 5 is closed (OFF), and the fuel gas pressure P gradually decreases.

[0028] At this time, before the injection cycle Tint (t10) elapses at time t12, for example, the on-off valve 7 (FIG. 1) may be opened at time t11 to purge the anode return gas, causing a sudden drop in fuel gas pressure P. If 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 increase the probability of electron exchange between the anode electrode and hydrogen and maintain the current value, resulting in a drop in output voltage (generated voltage).

[0029] 4A, the injection period Tint(t20) is calculated at time t20, and when the injection period Tint(t20) has elapsed since time t20, the injection period Tint(t22) is calculated at time t22. Then, before the injection period Tint(t20) elapses at time t22, at time t21, for example, the accelerator pedal of the vehicle is depressed, 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, when the fuel gas pressure P deviates from the target pressure P0, the generated voltage decreases.

[0030] <Interruption Spray> Therefore, in this embodiment, in order to suppress a drop in power generation voltage due to a drop in fuel gas pressure, when the pressure difference ΔP between the actual fuel gas pressure P and the target pressure P0 becomes equal to or greater than a predetermined value α, an interrupt injection is performed to inject fuel gas earlier than the injection period Tint has elapsed. That is, the ECU 10 controls the injector 5 to perform normal injection when the injection period Tint has elapsed, and also controls the injector 5 to perform interrupt injection when the pressure difference ΔP becomes equal to or greater than the predetermined value α even if the injection period Tint has not elapsed.

[0031] 3B, if the pressure difference ΔP becomes equal to or greater than the predetermined value α at time t13 before the injection cycle Tint(t10) set at time t10 elapses, the next injection cycle Tint(t13) is set and the injector 5 is controlled to perform an interrupt injection. This prevents the fuel gas pressure P from decreasing and deviating from the target pressure P0, thereby suppressing a decrease in the power generation voltage.

[0032] 4B, if the pressure difference ΔP becomes equal to or greater than the predetermined value α at time t23 before the injection cycle Tint(t20) set at time t20 elapses, the next injection cycle Tint(t23) is set and the injector 5 is controlled to perform interrupt injection. This allows the fuel pressure P to be quickly increased before the fuel gas pressure P deviates from the target pressure P0, thereby improving the acceleration response of the vehicle.

[0033] FIG. 5 is a flowchart showing an example of an injection permission determination process executed by the ECU 10. The process in FIG. 5 starts when the ECU 10 is started and is repeatedly executed at a predetermined cycle. As shown in FIG. 5, first, in step S1, it is determined whether or not the injection cycle Tint has elapsed. If the result in step S1 is affirmative, 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 equal to or greater than a predetermined value α. If the result in step S3 is affirmative, 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 affirmative, 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] Fig. 6A is a time chart for explaining the fuel gas pressure rise when interrupt injection is permitted even when the large-diameter injector 5a is open, and Fig. 6B is a time chart for explaining the fuel gas pressure rise when interrupt injection is permitted on the condition that the large-diameter injector 5a is closed.

[0035] In the example of FIG. 6A , after normal injection is performed at time t40, the required power generation amount (current value) and the target pressure P0 of the fuel gas increase at time t41. When the pressure difference ΔP becomes equal to or greater than the predetermined value α at time t42, interrupt injection is permitted, and the injector 5 is commanded to open until time t44. If the pressure difference ΔP remains equal to or greater than the predetermined value α at time t43 before the injector 5 is commanded to close at time t44, interrupt injection is permitted again, and the injector 5 is commanded to open until time t45. In this case, from time t42 to time t45, the injector 5 is opened beyond the normal valve opening time Ti, and the pressure P increases. If the pressure P becomes higher than the target pressure P0 and the hydrogen concentration at the anode electrode becomes excessive, this may result in a deterioration in power generation efficiency or damage to the membrane electrode assembly.

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

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

[0038] <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 the minimum valve opening time)> 7, first, in step S10, assuming that two large-diameter injectors 5a1, 5a2 and a small-diameter injector 5b are used, the temporary valve-opening time Ti_tmp of each injector 5 is calculated. In step S10, the temporary valve-opening time Tia_tmp of 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 of the small-diameter injector 5b is calculated.

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

[0040] Then, using the calculated minimum injection quantity Qia_min, required injection quantity Q, injection period Tint, and maximum injection quantity Qib of the small-diameter injector 5b, the temporary valve opening time Tib_tmp of the small-diameter injector 5b is calculated using the following equation: 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 equal to or less than the maximum valve opening time Tib_max of the small-diameter injector 5b. The maximum valve opening time Tib_max of each injector 5b is determined as the shorter of a predetermined percentage (e.g., about 95%) of the injection cycle Tint or the injection cycle Tint minus the minimum valve opening time Ti_min.

[0042] If the result in step S11 is YES, 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 made longer than the minimum valve opening time)> On the other hand, if the result in step S11 is negative, the routine proceeds to step S12, where the reallocated injection amount Qia_red to be injected from the two large-diameter injectors 5a1, 5a2 in addition to the injection during the minimum valve opening time Tia_min is calculated. More specifically, the reallocated injection amount Qia_red is calculated using 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 according to the following formula: Qia_red=Qib×(Tib_tmp-Tib_max)

[0044] Next, in step S13, the reallocated valve opening time Tia_red, during which the two large-diameter injectors 5a1 and 5a2 should continue to open (inject) beyond the minimum valve opening time Tia_min, is calculated. More specifically, the reallocated valve opening time Tia_red is calculated using the reallocated 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, according to the following formula: Tia_red = Qia_red / (Qia(2)-Qib)

[0045] Next, in step S14, assuming that two large-diameter injectors 5a1, 5a2 and a small-diameter injector 5b are used, the temporary valve-opening time Ti_tmp of each injector 5 is calculated. More specifically, using the minimum valve-opening time Tia_min of the large-diameter injector 5a, the maximum valve-opening time Tib_max of the small-diameter injector 5b, and the reallocated valve-opening time Tia_red calculated in step S13, the temporary valve-opening time Tia_tmp of the large-diameter injector 5a and the temporary valve-opening time Tib_tmp of the small-diameter injector 5b are calculated according to the following equations. 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 a predetermined valve opening time (for example, equal to or less than 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 equal to or less than 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, and may be a fixed value separately set through testing or the like. If the result in step S15 is affirmative, the process proceeds to step S19, where the valve opening times Tia and Tib of the injectors 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 (power generation current value) of the fuel cell stack 1 is equal to or greater than a predetermined current value. If the result is affirmative, the process proceeds to step S16, and if the result is negative, the process proceeds to step S19. In other words, under operating conditions where the power generation current value is equal to or greater than a predetermined current value and the power generation state is stable whether the small-diameter injector 5b is used or whether only the large-diameter injector 5a is used without the small-diameter injector 5b, the number of times the small-diameter injector 5b is operated is reduced, thereby minimizing deterioration due to wear of the small-diameter injector 5b and 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 the result in step S15 is negative, the process proceeds to step S16, where the temporary valve-opening time Tia_tmp is calculated assuming that only the two large-diameter injectors 5a1 and 5a2 are used. More specifically, the temporary valve-opening time Tia_tmp of the large-diameter injector 5a is calculated using the required injection amount Q, the injection period Tint, and the maximum injection amount Qia(2) of the two large-diameter injectors 5a1 and 5a2 according to the following equation: 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 equal to or shorter than a predetermined valve opening time (for example, the maximum valve opening time Tia_max of the large-diameter injector 5a). If the result in step S17 is affirmative, 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." Note that instead of the process in step S17, it may be determined whether the power generation current value of the fuel cell stack 1 is equal to or greater than a predetermined current value, and if the result is affirmative, the process proceeds to step S18, and if the result is negative, the process proceeds to step S19.

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

[0050] <Load and injector combination> 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 not more than 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 not more than 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 and 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 larger than the first threshold value Q1 and not more than 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 becomes larger 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 not more than 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 and 5a2 and the small-diameter injector 5b, and the valve opening time Tia of the large-diameter injector 5a is set to be 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, so the drainage of 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 to be 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. Also, 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, which 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). Also, 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 a high load region (Q>Q2) where the required power generation amount of the fuel cell stack 1 is relatively large and the required injection amount Q is also relatively large, the valve open time Ti per injection cycle Tint tends to be longer than in a low load region (Q≦Q2). In such a high load region, only the large-diameter injector 5a, which requires a shorter valve open time Ti than the small-diameter injector 5b for the same injection amount, is used, thereby shortening the valve open time Ti (=Tia) per injection cycle Tint. This allows the small-diameter injector 5b to be used preferentially, ensuring that the required injection amount Q is injected within the injection cycle Tint even in the high load region (Q>Q2), thereby satisfying the required power generation amount.

[0057] According to this embodiment, the following effects can be achieved. (1) The fuel cell system 100 includes a fuel cell stack 1 configured by stacking a plurality of power generation cells, 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 an injection period Tint of the injector 5 and controls the injector 5 to inject fuel gas at each injection period Tint (FIG. 1).

[0058] When the pressure difference ΔP between the pressure P detected by the pressure sensor 6 and the target pressure P0 becomes equal to or greater than a predetermined value α, the ECU 10 controls the injector 5 to inject fuel gas earlier than the injection period Tint has elapsed (FIG. 5). In this way, by constantly monitoring the pressure P of the fuel gas supplied to the fuel cell stack 1 and performing an interrupt injection before the injection period Tint has elapsed when the pressure difference ΔP from the target pressure P0 becomes equal to or greater than the predetermined value α, it is possible to suppress a drop in the generated voltage due to a drop in the fuel gas pressure (FIGS. 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 period 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 period Tint, and controls the injector 5 to inject the fuel gas based on the valve opening time Ti.

[0060] Even if the injection period 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 period 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 period 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 Ti of the large-diameter injector 5a to be longer than the valve opening time Ti of the small-diameter injector 5b (Tia>Tib = 0) (FIG. 8).

[0062] Thereby, the valve opening time Ti per injection period 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. Also, 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 of the large-diameter injector 5a and the valve opening time Tib of the small-diameter injector 5b based on the minimum valve opening time Tia_min of the large-diameter injector 5a (FIG. 7), thereby allowing 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 injector 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 (Q-Qa_min) between the required injection amount Q and the minimum injection amount Qia_min (S10, S19 in FIG. 7). This allows the small-diameter injector 5b to be used preferentially in the first load range (Q≦Q1) (FIG. 8).

[0065] (6) The ECU 10 calculates the minimum injection quantity Qia_min of 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 of the small-diameter injector 5b based on the difference between the required injection quantity Q and the minimum injection quantity Qia_min (S10 in FIG. 7). If the temporary valve-opening time Tib_tmp is equal to or shorter than the maximum valve-opening time Tib_max of the small-diameter injector 5b, the ECU 10 sets the valve-opening time Tia of the large-diameter injector 5a (5a1, 5a2) to the minimum valve-opening time Tia_min, and sets the valve-opening time Tib of the small-diameter injector 5b to the temporary valve-opening time Tib_tmp (Yes 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 (Tib_tmp - Tib_max) between the temporary valve opening time Tib_tmp and the maximum valve opening time 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 (Tib_tmp - Tib_max) between the temporary valve opening time Tib_tmp and the maximum valve opening time Tib_max and the maximum valve opening time Tib_max (negated in S11 → 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 (Q - Qa_min) between the required injection amount Q and the minimum injection amount Qia_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, sets the temporary valve opening time Tia_tmp of the large-diameter injector 5a (5a1, 5a2) based on the difference (Tib_tmp - Tib_max) between the temporary valve opening time Tib_tmp and the maximum valve opening time Tib_max of the small-diameter injector 5b and the minimum valve opening time Tia_min (negated in S11 of Fig. 7 → S12~S14).

[0068] When the temporary valve-opening time Tia_tmp of the large-diameter injector 5a (5a1, 5a2) is equal to or shorter than a predetermined valve-opening time (e.g., the maximum valve-opening time Tia_max of the large-diameter injector 5a), the injectors 5 are controlled to inject fuel gas using both the large-diameter injector 5a (5a1, 5a2) and the small-diameter injector 5b (Yes in S15 → S19). When the temporary valve-opening time Tia_tmp of the large-diameter injector 5a (5a1, 5a2) is greater than the predetermined valve-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) (No in S15 → S16 to S19). This allows the small-diameter injector 5b to be used preferentially, ensuring that the required injection amount Q is injected within the injection period Tint even in the high load range (Q>Q2), thereby satisfying the required power generation amount.

[0069] (8) The ECU 10 controls the injectors 5 so that fuel gas is injected only when the large-diameter injectors 5a are in a closed valve state. This prevents excessive fuel gas from being supplied to the fuel cell stack 1.

[0070] (9) The ECU 10 calculates the minimum injection quantity Qia_min of 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 of the small-diameter injector 5b based on the difference (Q-Qa_min) between the required injection quantity Q and the minimum injection quantity Qia_min. If the temporary valve opening time Tib_tmp of the small-diameter injector 5b is longer than the maximum valve opening time Tib_max of the small-diameter injector 5b, the ECU 10 sets the temporary valve opening time Tia_tmp of the large-diameter injector 5a (5a1, 5a2) based on the difference (Tib_tmp-Tib_max) between the temporary valve opening time Tib_tmp and the maximum valve opening time Tib_max of the small-diameter injector 5b and the minimum valve opening time Tia_min (No in S11 of FIG. 7 → S12 to S14). When the power generation current value of the fuel cell stack 1 is less than a predetermined current value, the injectors 5 are controlled to inject fuel gas using the large-diameter injectors 5a (5a1, 5a2) and the small-diameter injectors 5b (S19). When the power generation current value is equal to or greater than the predetermined current value, the injectors 5 are controlled to inject fuel gas using only the large-diameter injectors 5a (5a1 and 5a2, or 5a1, 5a2, and 5a3) (S16 to S19). In this case, under operating conditions where the power generation current value is equal to or greater than the predetermined current value and the power generation state is stable whether the small-diameter injector 5b is used or whether only the large-diameter injector 5a is used without the small-diameter injector 5b, the number of times the small-diameter injector 5b is operated can be reduced, minimizing deterioration due to wear of the small-diameter injector 5b and improving the power generation stability of the fuel cell stack 1.

[0071] In the above embodiment, an example in which three large-diameter injectors 5a1-5a3 and one small-diameter injector 5b are provided is described with reference to Figure 1 etc., but the injectors that inject fuel gas are not limited to this. For example, only a single injector may be provided. Even in this case, similarly, when the pressure difference between the detected pressure and the target pressure becomes equal to or exceeds a predetermined value, an interrupt injection can be performed in which fuel gas is injected earlier than the end of the injection cycle.

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

[0073] The above description is merely an example, and the present invention is not limited to the above-described embodiment and modifications as long as the features of the present invention are not impaired. One or more of the above-described embodiment and modifications can be arbitrarily combined, and modifications can also be combined with each other. [Explanation of symbols]

[0074] 1 fuel cell stack, 2 anode flow path, 3 cathode flow path, 4a, 4b ejector, 5 injector, 5a1 to 5a3 large diameter injector, 5b small diameter injector, 6 pressure sensor, 7 on-off valve, 10 ECU, 100 fuel cell system

Claims

1. a fuel cell stack formed by stacking a plurality of power generation cells; an injector that injects fuel gas to be supplied to the fuel cell stack; a detection unit that detects the pressure of the fuel gas supplied to the fuel cell stack; a control unit that sets an injection cycle of the injector and controls the injector to inject the fuel gas at each injection cycle, The control unit controls the injector to inject the fuel gas earlier than the injection period has elapsed when the pressure difference between the pressure detected by the detection unit and the target pressure becomes equal to or greater than a predetermined value.

2. 2. The fuel cell system according to claim 1, The control unit calculates the required injection amount of the fuel gas based on the required power generation amount of the fuel cell stack, sets the injection period based on the pressure detected by the detection unit and the required power generation amount, sets a valve opening time of the injector based on the required injection amount and the injection period, and controls the injector to inject the fuel gas based on the valve opening time.

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

4. 4. 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 a minimum valve opening time of the first injector.

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

6. 5. The fuel cell system according to claim 4, The control unit calculating a minimum injection amount of the first injector based on the minimum valve opening time; setting a temporary valve opening time of the second injector based on the difference between the required injection amount and the minimum injection amount; when the temporary valve opening time is equal to or less than 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 first valve opening time set based on the difference between the temporary valve opening time and the maximum valve opening time and the minimum valve opening time when the temporary valve opening time is longer than the maximum valve opening time, and a second valve opening time set based on the difference between the temporary valve opening time and the maximum valve opening time and the maximum valve opening time.

7. 5. The fuel cell system according to claim 4, The control unit calculating a minimum injection amount of the first injector based on the minimum valve opening time; setting a temporary valve opening time of the second injector based on the difference between the required injection amount and the minimum injection amount; when the temporary valve opening time of the second injector is longer than the maximum valve opening time of the second injector, the temporary valve opening time of the first injector is set based on the difference between the temporary valve opening time of the second injector and the maximum valve opening time of the second injector and the minimum valve opening time; When a temporary valve-opening time of the first injector is equal to or shorter than a predetermined valve-opening time, the injectors are controlled so as to inject the fuel gas using the first injector and the second injector; A fuel cell system comprising: a control unit that controls the first injector so that the fuel gas is injected using only the first injector when the temporary valve-open time of the first injector is longer than the predetermined valve-open time.

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

9. 5. The fuel cell system according to claim 4, The control unit calculating a minimum injection amount of the first injector based on the minimum valve opening time; setting a temporary valve opening time of the second injector based on the difference between the required injection amount and the minimum injection amount; when the temporary valve opening time of the second injector is longer than the maximum valve opening time of the second injector, the temporary valve opening time of the first injector is set based on the difference between the temporary valve opening time of the second injector and the maximum valve opening time of the second injector and the minimum valve opening time; When a generated current value of the fuel cell stack is less than a predetermined current value, the injectors are controlled so as to inject the fuel gas using the first injector and the second injector; a first injector that is controlled so as to inject the fuel gas only when the generated current value is equal to or greater than the predetermined current value;

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