JP2019067708A - Fuel cell system - Google Patents

Abstract

To provide a fuel cell system capable of increasing circulation amount of fuel off-gas during low load, while restraining shortage of fuel gas in the fuel cell.SOLUTION: A fuel cell system has a fuel cell, a fuel injection system for injecting fuel gas flowing in from an accumulator part according to a duty ratio, a pressure regulator regulating the first pressure of the fuel gas flowing into the fuel injection system, an ejector for mixing the fuel off-gas with the fuel gas, a detector for detecting the second pressure of the fuel off-gas recirculated to the fuel cell, and a control section for controlling the duty ratio and the pressure regulator. The ratio of the diffuser diameter of the ejector and the nozzle diameter is lower than the value when the load is lower than a prescribed value, and the circulation flow rate becomes peak when the first pressure is a prescribed lower limit value, and when the load becomes lower than a prescribed value, the control section controls the pressure regulator so as to lower the first pressure, and controls the duty ratio so that the second pressure is maintained at the pressure before the load of the fuel cell lowers.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a fuel cell system.

  When the load of the fuel cell is low, for example, drainage and scavenging in the fuel gas circulation system, it is desirable to increase the circulation amount of the fuel off gas because the fuel consumption is deteriorated if the supply amount of the fuel gas is increased. With regard to the increase in the amount of circulation, for example, it is known to increase the circulation flow ratio of the ejector by reducing the pressure at the inlet of the circulation passage of the ejector in the circulation system of fuel gas to improve the fuel efficiency. ).

Unexamined-Japanese-Patent No. 2004-139877

  However, when the pressure at the inlet of the circulation path is reduced, the pressure of the entire circulation system is reduced, so that the partial pressure of the fuel gas in the fuel cell is reduced, which causes a problem of insufficient fuel gas.

  Therefore, the present invention has been made in view of the above problems, and provides a fuel cell system capable of increasing the circulation amount of fuel off gas at low load while suppressing the shortage of fuel gas in the fuel cell. The purpose is

  The fuel cell system described in the present specification includes a fuel cell that generates electric power using a fuel gas, an accumulator that accumulates the fuel gas, and an injector that injects the fuel gas flowing from the accumulator according to a duty ratio of a control signal. And a pressure regulating valve for adjusting a first pressure of the fuel gas flowing into the injector from the pressure accumulator, and a fuel off gas recirculated to the fuel cell to the fuel gas injected from the injector. An ejector introduced to the fuel cell, a detector for detecting a second pressure of the fuel off gas recirculated to the fuel cell, and a controller for controlling the duty ratio and the pressure regulating valve, The ejector accommodates the nozzle from which the fuel gas is jetted and the nozzle, and the fuel off gas is sucked by the negative pressure generated by the fuel gas jetted from the nozzle. And a diffuser through which the fuel gas and the fuel off gas flow from the suction chamber to the fuel cell, and a ratio of the diameter of the nozzle to the diameter of the diffuser is such that the load of the fuel cell is a predetermined value When the ratio of the flow rate of the fuel gas and the fuel off gas flowing through the diffuser to the flow rate of the fuel gas flowing through the nozzle is lower when the first pressure is lower than a predetermined lower limit value The control unit controls the pressure regulating valve to lower the first pressure when the load on the fuel cell becomes lower than the predetermined value, and the second pressure is smaller than the value of the fuel cell. The duty ratio is controlled to be maintained at the pressure before the drop in load.

  According to the fuel cell system of the present invention, it is possible to increase the circulation amount of fuel off gas at low load while suppressing the shortage of fuel gas in the fuel cell.

It is a block diagram which shows an example of a fuel cell system. It is a sectional view showing an example of an ejector. It is a figure which shows the example of the change of the circulating flow rate ratio with respect to the ratio of the nozzle diameter with respect to the diffuser diameter of an ejector. It is a flowchart which shows an example of control processing of the amount of circulation of fuel off gas. It is a time chart which shows an example of operation of a fuel cell system.

  FIG. 1 is a block diagram showing an example of a fuel cell system. The fuel cell system is mounted on, for example, a fuel cell vehicle, but is not limited thereto.

  The fuel cell system includes a fuel cell 1, a fuel tank 2, a pressure control valve 3, an injector 4, an ejector 5, an ECU (Electronic Control Unit) 6, a main stop valve 70, and a gas-liquid separator 71. A purge valve 72, anode supply passages R20 to R22, R21a, anode discharge passages R23 to R25, and a recirculation passage R26 are provided. The fuel cell system further includes a compressor 80, a humidifier 81, pressure sensors 90 and 91, a temperature sensor 92, cathode supply paths R10 and R11, and cathode discharge paths R12 and R13.

  The fuel cell 1 is a solid polymer fuel cell, and is formed by stacking a plurality of single cells each provided with a membrane electrode assembly, and the cathode is supplied with air containing oxygen as an example of an oxidant gas. The anode is supplied with hydrogen gas as an example of fuel gas. The fuel cell 1 generates electric power by the chemical reaction between the oxidant gas and the fuel gas in each unit cell.

  The oxidant gas is supplied to the fuel cell 1 via the cathode supply passages R10 and R11. The oxidant off gas is discharged from the fuel cell 1 to the outside through the cathode discharge passages R12 and R13.

  The compressor 80 introduces oxidant gas from the outside air and compresses it. The compressor 80 delivers the oxidant gas to the humidifier 81 via the cathode supply passage R10.

  The humidifier 81 humidifies the oxidant gas and sends it to the fuel cell 1 via the cathode supply passage R11. The fuel off gas is introduced into the humidifier 81 from the fuel cell 1 via the cathode discharge passage R12. The humidifier 81 humidifies the fuel gas by the water contained in the fuel off gas. The humidifier 81 discharges the fuel off gas from the cathode discharge passage R13 to the outside.

  Further, the fuel gas is supplied to the fuel cell 1 via the anode supply paths R20 to R22. The fuel off gas is discharged from the fuel cell 1 to the outside through the anode discharge passages R23 to R25.

  The fuel tank 2 is an example of an accumulator and accumulates fuel gas. A main stop valve 70 is connected to the outlet of the fuel tank 2. The main stop valve 70 is normally maintained in the open state according to the control of the ECU 6. The fuel gas flows from the main stop valve 70 through the anode supply passage R 20 and enters the pressure regulating valve 3.

  The pressure regulating valve 3 adjusts the pressure of fuel gas flowing from the fuel tank 2 to the injector 4 (hereinafter referred to as “injector source pressure”) in accordance with the control of the ECU 6. The pressure sensor 90 is provided in the anode supply passage R21, detects the injector source pressure Po, and notifies the ECU 6 of it. The injector source pressure is an example of the first pressure.

  The injector 4 is an example of the injection device, and injects the fuel gas flowing from the fuel tank 2 in accordance with the duty ratio of the control signal S. The ECU 6 controls the duty ratio of the control signal S, and outputs the control signal S to the injector 4.

  For example, when the signal value (voltage level) of the control signal S is “1”, the injector 4 injects fuel gas by opening the solenoid valve, and the signal value of the control signal S is “0”. Stop the injection by closing the solenoid valve. Therefore, in the injector 4, the injection amount of the fuel gas per unit time is controlled by the duty ratio of the control signal S. The fuel gas injected from the injector 4 flows into the ejector 5 through the anode supply passage R21a.

  The ejector 5 mixes the fuel gas injected from the injector 4 with the fuel off gas recirculated to the fuel cell 1 and introduces it into the fuel cell 1. The fuel off gas is sucked into the ejector 5 from the recirculation passage R26. The fuel gas mixed with the fuel off gas is supplied to the fuel cell 1 from the anode supply passage R22.

  The fuel off gas flows from the fuel cell 1 through the anode discharge passage R23 and enters the gas-liquid separator 71. The gas-liquid separator 71 separates and stores liquid water from the fuel off gas, and delivers the fuel off gas to the recirculation passage R26. A pressure sensor 91 is provided in the recirculation passage R26. The pressure sensor 91 is an example of a detection unit, and detects the pressure (denoted as “circulation system pressure”) of the fuel off gas recirculated to the fuel cell 1. The circulatory pressure is an example of the second pressure. Further, the pressure sensor 91 may be provided in the anode supply passage R22, and it is also possible to calculate the pressure of the fuel off gas based on the ejector 5 and the injector primary pressure.

  The purge valve 72 is connected to the gas-liquid separator 71 via the anode discharge passage R24. The purge valve 72 is opened and closed under the control of the ECU 6. When the purge valve 72 is opened, the fuel off gas and liquid water in the gas-liquid separator 71 are discharged to the outside from the anode discharge passages R24 and R25.

  The ECU 6 controls the operation of the fuel cell system. The ECU 6 includes, for example, a CPU (Central Processing Unit), a memory, and the like, and operates in accordance with a program for driving the CPU.

  The ECU 6 is a load required for the fuel cell 1 according to the required power by the degree of opening of the accelerator pedal (not shown), the state of charge of the battery, and the state of the external device such as the indoor air conditioner Decide. The ECU 6 performs various controls in accordance with the load. For example, when the load is low, the ECU 6 controls the duty ratio of the control signal S and the pressure regulating valve 3 as an example of the control unit. The control of the duty ratio and the pressure regulating valve 3 will be described later.

  The temperature sensor 92 detects the temperature Tm in the fuel cell 1 and notifies the ECU 6 of it. The ECU 6 determines whether the fuel cell system is warming up based on the temperature Tm. When the fuel cell 1 has a low load, the ECU 6 performs control to increase the circulation flow ratio of the fuel off gas in the ejector 5 in order to drain the anode supply passage R22 and the anode discharge passage R23 when it is in warm air as an example. Do.

  FIG. 2 is a cross-sectional view showing an example of the ejector 5. The ejector 5 has a nozzle 50, a suction chamber 51, and a diffuser 52. The fuel gas having flowed through the anode supply passage R21 is ejected from the nozzle 50. The nozzle 50 has a substantially cylindrical shape, and the diameter of its tip is indicated by d.

  Further, the suction chamber 51 accommodates the nozzle 50, and the fuel off gas is sucked by the negative pressure generated by the fuel gas ejected from the nozzle 50. The suction chamber 51 has a substantially rectangular parallelepiped shape, and a suction hole 51a for suctioning the fuel off gas is provided on one surface. The fuel off gas is sucked into the suction chamber 51 from the recirculation passage R26 through the suction hole 51a.

  Fuel gas and fuel off gas flowing from the suction chamber 51 to the fuel cell 1 flow through the diffuser 52. The diffuser 52 includes a tapered portion 52a, a parallel portion 52b, and a diverging portion 52c. The tapered portion 52a is a flow path whose width is narrowed from the suction chamber 51 toward the parallel portion 52b. The parallel part 52b is a flow path of a fixed width connecting the tapered part 52a and the divergent part 52c. The parallel portion 52 b has a substantially cylindrical shape, and its diameter is indicated by D. The diverging portion 52c is a flow passage whose width extends from the parallel portion 52b toward the anode supply passage R22.

  With the above structure, the fuel gas is introduced from the nozzle 50 into the suction chamber 51, and the fuel off gas is sucked into the suction chamber 51 from the suction hole 51a by the negative pressure by the injection of the fuel gas. The fuel gas and the fuel off gas are mixed and supplied from the diffuser 52 to the fuel cell 1 via the anode supply passage R22.

  The performance of the ejector 5 is defined by the circulation flow ratio Rcy. The circulating flow rate ratio is the ratio of the outflow amount Qout of the fuel gas and the fuel off gas flowing out of the ejector 5 to the inflow amount Qin of the fuel gas which is the driving gas, and when the loss of the nozzle 50 is taken into consideration, Calculated by (1). That is, the circulation flow ratio is an example of the ratio of the flow rates of the fuel gas and the fuel off gas flowing through the diffuser 52 to the flow rate of the fuel gas flowing through the nozzle 50.

  In equation (1), the variable P0 is the pressure of the fuel gas flowing into the nozzle 50, the variable P1 is the pressure of the fuel off gas sucked into the suction chamber 51, and the variable P2 is the fuel flowing out of the diffuser 52 Gas and fuel off gas pressure. Further, D / d is a ratio of the diameter of the nozzle 50 to the diameter of the diffuser 52. Here, α is a parameter according to the shape of the ejector 5. The relationship between D / d and the circulation flow ratio is described below.

  FIG. 3 is a view showing an example of a change in circulation flow ratio to the ratio of the nozzle diameter d to the diffuser diameter D of the ejector 5. The code Ga indicates the characteristics when the load of the fuel cell 1 is lower than a predetermined threshold TH (for example, 20%), and the code Gb indicates the load when the load of the fuel cell 1 is higher than the predetermined threshold TH Show the characteristics.

  In the graphs of symbols Ga and Gb, the horizontal axis indicates D / d, and the vertical axis indicates the circulation flow ratio. The characteristics of the change of the circulation flow ratio to D / d differ depending on the injector base pressure Po. The characteristics L1 and H1 indicate changes in the circulation flow ratio when the injector base pressure Po is the predetermined upper limit Pmax, and the characteristics L3 and H3 indicate the circulation flow when the injector base pressure Po is the predetermined lower limit Pmin. It shows the change of ratio. Further, the characteristics L2 and H2 indicate changes in the circulation flow ratio when the injector base pressure Po is an intermediate value Pmid between the upper limit Pmax and the lower limit Pmin.

  When considering the design of the ejector 5, since the characteristics L1 to L3 and the characteristics H1 to H3 at the low load time are different from each other at the low load time, the D / d at which the circulation flow ratio is maximum is also between the low load and the high load time. It is different. Therefore, if the low load ejector 5 and the high load ejector 5 having different D / d are separately provided, the ejector 5 is switched depending on the load to be used regardless of the load. The flow rate ratio is maximized. However, providing a plurality of ejectors 5 is not preferable because the cost of the fuel cell system increases.

  For this reason, D / d of the ejector 5 is determined to a value Ra corresponding to the peak PH of the circulation flow ratio of the characteristic H1 so that the circulation flow ratio at high load is maximum, for example. Further, the specified value of the injector source pressure Po is set to the upper limit value Pmax corresponding to the characteristic H1.

  However, assuming that the injector source pressure Po is the upper limit Pmax, the circulation flow ratio at low load conforms to the characteristic L1, so the smallest value among the circulation flow ratios of the characteristics L1 to L3 according to D / d = Ra. It becomes. That is, in the case of D / d = Ra, the circulation flow ratio at high load increases as the injector base pressure Po increases, as indicated by the arrow AH, and the circulation flow ratio at low load is indicated by the arrow AL. As the injector base pressure Po is larger, it becomes smaller.

  Therefore, the ECU 6 controls the pressure regulating valve 3 so that the injector source pressure Po becomes lower than a specified value at low load. At this time, the ECU 6 lowers the injector base pressure Po to a value close to the lower limit value Pmin or the lower limit value Pmin, for example, so as to obtain a circulation flow rate ratio capable of securing a sufficient circulation amount of fuel gas. As a result, the ECU 6 can control the injector source pressure Po to a value at which the maximum value of the circulation flow ratio can be obtained at both high load and low load.

  Thus, if D / d is determined such that the circulation flow ratio at high load is maximum, the relationship between the injector source pressure Po at low load and the circulation flow ratio is opposite to that at high load. Relationship. That is, D / d may be determined from the range in which the circulation flow ratio decreases as the injector base pressure Po increases.

  Referring to the characteristics L1 to L3 at low load, the relationship between the injector base pressure Po and the circulation flow ratio changes at a boundary at D / d = Ro which is a peak PL of the circulation flow ratio of the characteristic L3. When D / d is equal to or higher than Ro, the circulation flow ratio increases as the injector base pressure Po increases, as indicated by the arrow AL ′, and when D / d is smaller than Ro, as indicated by the arrow AL. The smaller the injector base pressure Po, the smaller.

  For this reason, D / d is determined so that the circulation flow rate ratio of the fuel off gas in the ejector 5 becomes smaller than the value Ro when the low load and the injector base pressure Po is the lower limit value Pmin. Be done.

  As described above, when the load is low, the ECU 6 controls the pressure regulating valve 3 so that the injector source pressure Po falls below a specified value. However, when the injector primary pressure Po decreases, the circulating pressure Pc decreases, so that the partial pressure of the fuel gas in the fuel cell 1 may decrease and the fuel gas may run short. Therefore, the ECU 6 controls the duty ratio such that the circulating system pressure Pc is maintained at a pressure before the reduction of the load of the fuel cell 1 at the time of low load.

  For example, the ECU 6 performs feedback control of the duty ratio of the control signal S based on the amount of change per unit time of the circulating pressure Pc notified from the pressure sensor 91. As a result, the decrease in the partial pressure of the fuel gas in the fuel cell 1 is prevented, so the shortage of the fuel gas is suppressed.

  FIG. 4 is a flowchart showing an example of control processing of the circulation amount of the fuel off gas. In this process, as one example, the ECU 6 increases the circulation amount of the fuel off gas in order to efficiently drain the liquid water generated in the anode supply passage R22 and the anode discharge passage R23 during the low load warm air, but is limited to this It is possible to increase the amount of circulation under other circumstances where it is not necessary to increase the amount of circulation.

  The ECU 6 calculates the load of the fuel cell 1 according to the required power according to the state of the external device such as the degree of opening of the accelerator pedal (step St1). Next, the ECU 6 compares the load with a predetermined threshold value TH (for example, 20%) (step St2). When the load is equal to or higher than the threshold TH (Yes in step St2), the ECU 6 maintains the injector base pressure Po at a prescribed value (for example, the upper limit Pmax) (step St3).

  When the load is lower than the threshold TH (No in step St2), the ECU 6 compares the temperature Tm of the cooling water notified from the temperature sensor 92 with a predetermined value Tw (for example, 30 ° C.) (step St4). When the temperature Tm of the cooling water is equal to or higher than the predetermined value Tw (No in step St4), the ECU 6 determines that the fuel cell system is not in the warm state, and executes the processing in step St3.

  Further, when the temperature Tm of the cooling water is lower than the predetermined value Tw (Yes in step St4), the ECU 6 determines that the fuel cell system is warming up, and the necessary circulation amount of the fuel off gas based on various conditions. Are determined (step St5). Next, the ECU 6 controls the pressure regulating valve 3 to reduce the injector source pressure Po in accordance with the required circulation amount (step St6). Thereby, the circulation flow rate ratio of the ejector 5 is increased.

  At this time, the ECU 6 prestores, for example, a table in which the correspondence relationship between the load and circulation flow ratio and the injector base pressure Po is mapped in the memory, and the circulation flow ratio and load calculated according to the above equation (1) The control target value of the injector primary pressure Po may be determined by searching the table from the above. The ECU 6 performs feedback control so that the injector base pressure Po notified from the pressure sensor 90 becomes the control target value. For this reason, the decrease in the circulation flow rate ratio is suppressed by the injector source pressure Po being excessively reduced. The specified value of the injector base pressure Po and the control target value at the time of reduction are larger than the pressure at which the necessary amount of circulation can be obtained when the duty ratio of the control signal S is the maximum value.

  Next, the ECU 6 detects the amount of change in the circulating pressure Pc (step St7). At this time, for example, the ECU 6 periodically obtains the circulating pressure Pc from the pressure sensor 91, and detects the amount of change by calculating the difference between the previous circulating pressure Pc and the latest circulating pressure Pc. It is also good.

  Next, the ECU 6 controls the duty ratio of the control signal S so that the amount of change in the circulatory system pressure Pc is compensated (step St8). Thereby, the circulating system pressure Pc is maintained at the pressure before the decrease of the load of the fuel cell 1. Therefore, the decrease in the partial pressure of the fuel gas in the fuel cell 1 is prevented, and the shortage of the fuel gas is suppressed. The processes of steps St7 and St8 may be performed before the process of step St6.

  Thus, the control process of the circulation amount of the fuel off gas is performed.

  FIG. 5 is a time chart showing an example of the operation of the fuel cell system. The time chart shows temporal changes in load, injector base pressure Po, control signal S, its duty ratio, fuel gas supply amount, fuel off gas circulation amount, circulation flow rate ratio, and circulation system pressure Pc. Note that FIG. 5 shows an operation in the case where the decrease in the injector source pressure Po or the maintenance of the circulating pressure Pc at the low load time as described above is not performed as a comparative example (see dotted line).

  The load of the fuel cell 1 is constant in the period from time t0 to time t1, but starts to decrease from time t1 and falls below the threshold TH at time t2. Thereafter, the load on the fuel cell 1 stops decreasing at time t3 and becomes constant.

  When the load of the fuel cell 1 becomes lower than the threshold TH, the ECU 6 controls the pressure regulating valve 3 so that the injector base pressure Po decreases from the specified value (Pmax) to the control target value (Px). The injector base pressure Po starts to decrease from time t2 and reaches the control target value at time t3. On the other hand, in the comparative example, the injector base pressure Po is maintained constant.

  Therefore, in the embodiment, the circulation flow ratio increases with the decrease of the injector base pressure Po in the period from time t2 to t3, but in the case of the comparative example, the circulation flow ratio becomes constant regardless of the decrease of the load.

  The circulation amount of the fuel off gas decreases during the period from time t1 to t3 in which the load of the fuel cell 1 is reduced, and becomes constant after time t3. The circulation amount in the example is increased because the circulation flow ratio is higher than in the comparative example. Therefore, for example, the drainage capacity at low load is improved.

  Further, the ECU 6 controls the duty ratio such that the amount of fuel gas supplied corresponds to the load of the fuel cell 1 and the circulating pressure Pc is maintained at a pressure before the decrease of the load of the fuel cell 1. . Also, the pulse width of the control signal S changes based on the duty ratio.

  Therefore, the amount of fuel gas supplied decreases with a decrease in load in the period from time t2 to t3, and the circulating system pressure Pc is in spite of the fact that the injector primary pressure Po is reduced in the period from time t2 to t3. , Has been kept constant. Therefore, the decrease in the partial pressure of the fuel gas in the fuel cell 1 is prevented, and the shortage of the fuel gas is suppressed.

  On the other hand, in the case of the comparative example, the duty ratio is only controlled so that the amount of fuel gas supplied corresponds to the load of the fuel cell 1, so the injector base pressure Po is temporarily set to time t2 to t3. In the period, the circulating system pressure Pc decreases with the decrease of the injector base pressure Po. Therefore, the partial pressure of the fuel gas in the fuel cell 1 may be reduced, and the fuel gas may be insufficient.

  As described above, according to the fuel cell system of the present embodiment, it is possible to increase the circulation amount of the fuel gas at low load while suppressing the shortage of the fuel gas in the fuel cell 1.

  The embodiments described above are examples of preferred implementations of the invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

1 fuel cell 2 fuel tank (accumulator)
3 Pressure regulator 4 injector (injector)
5 Ejector 6 ECU (Control Unit)
50 Nozzle 52 Diffuser 90, 91 Pressure Sensor (Detection Unit)

Claims (1)

A fuel cell that generates electricity from fuel gas;
An accumulator for accumulating the fuel gas;
An injection device for injecting the fuel gas flowing from the pressure accumulation unit according to a duty ratio of a control signal;
A pressure regulating valve that regulates a first pressure of the fuel gas flowing into the injection device from the pressure accumulation unit;
An ejector for mixing the fuel gas injected from the injector with the fuel off gas recirculated to the fuel cell and introducing it to the fuel cell;
A detection unit that detects a second pressure of the fuel off gas recirculated to the fuel cell;
A control unit that controls the duty ratio and the pressure regulating valve;
The ejector is
A nozzle from which the fuel gas is ejected;
A suction chamber which accommodates the nozzle and in which the fuel off gas is sucked by a negative pressure generated by the fuel gas jetted from the nozzle;
And a diffuser through which the fuel gas and the fuel off gas flow from the suction chamber toward the fuel cell.
The ratio of the nozzle diameter to the diffuser diameter is relative to the flow rate of the fuel gas flowing through the nozzle when the load of the fuel cell is lower than a predetermined value and the first pressure is a predetermined lower limit value. A ratio of flow rates of the fuel gas and the fuel off gas flowing through the diffuser is smaller than a peak value;
The control unit controls the pressure regulating valve so that the first pressure is lowered when the load of the fuel cell is lower than the predetermined value, and the second pressure is before the load of the fuel cell is reduced. A fuel cell system comprising controlling the duty ratio to be maintained at a pressure.

Images