JP6927071B2 - Fuel cell system - Google Patents

Description

The present invention relates to a fuel cell system.

Regarding a fuel cell system, for example, in order to control the water content of a fuel cell, a technique for controlling drainage on the anode side based on the pressure loss of the anode of a single cell is known (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2009-259418

Since the amount of drainage from the fuel cell changes dynamically according to the operating state of the fuel cell, it is useful to appropriately grasp the amount of drainage when controlling the drainage as in the above technique, for example. However, Patent Document 1 does not have a description regarding grasping the amount of wastewater.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel cell system capable of appropriately grasping the amount of drainage of a fuel cell.

The fuel cell system described in the present specification includes a fuel cell that generates power from fuel gas, a pressure accumulator that accumulates the fuel gas, an injector that intermittently injects the fuel gas that flows from the accumulator, and the fuel cell. A recirculation path through which the fuel off gas recirculated to the fuel flows, an ejector in which the fuel off gas from the recirculation path is mixed with the fuel gas injected from the injector and introduced into the anode of the fuel cell, and the fuel. It has a detection device that detects the current value output from the battery and a control device that controls one injection time and injection amount of the injector, and the control device has a water content on the anode side of the fuel cell. Based on the correlation between the pressure loss in the recirculation path and the current value, the pressure loss is estimated from the water content and the current value, and the pressure loss in the recirculation path and the pressure loss in the recirculation path are estimated from the estimated pressure loss. The flow rate is estimated based on the correlation of the flow rates of the fuel off gas, and the fuel gas and the fuel off gas introduced from the ejector into the fuel cell based on the estimated flow rate, the injection amount, and the injection time. Is calculated, and the amount of drainage on the anode side of the fuel cell is calculated based on the force product and the water content.

According to the present invention, the displacement amount of the fuel cell can be appropriately grasped.

It is a block diagram which shows an example of a fuel cell system. It is a flowchart which shows an example of the temperature control processing. It is a figure which shows an example of the correlation of water content, current value, and pressure loss. It is a waveform diagram which shows an example of the control signal output to an injector. It is a figure which shows an example of the correlation of the pressure loss in the recirculation path and the flow rate of fuel off gas. It is a figure which shows an example of the correlation of the temperature, the current value, and the upper limit value or the lower limit value of a fuel cell. It is a figure which shows an example of the correlation of a control value and a target temperature. It is a figure which shows an example of the change characteristic of the overvoltage of an anode with respect to the partial pressure of a fuel gas for each humidity. It is a time chart which shows an example of temperature control. It is a time chart showing another example of temperature control.

FIG. 1 is a configuration diagram showing an example of a fuel cell system. The fuel cell system is installed in, for example, a fuel cell vehicle, but is not limited to this.

The fuel cell system includes a fuel cell 1, a fuel tank 2, a pressure regulating valve 3, an injector 4, an ejector 5, an ECU (Electronic Control Unit) 6, a main stop valve 70, a gas-liquid separator 71, and the like. It has a purge valve 72, an anode supply path R20 to R23, an anode discharge path R24 to R26, and a recirculation path R27. The fuel cell system includes a compressor 80, a humidifier 81, a bypass valve 82, a radiator 90, a three-way valve 91, a pump 92, a temperature sensor 93, a current sensor 94, a battery 95, and a cathode supply. It has passages R10 and R11, cathode discharge passages R12 and R13, cooling water supply passages R31 and R32, and cooling water discharge passages R33 and R34.

The fuel cell 1 is a solid polymer fuel cell, which is configured by stacking a plurality of single cells each having a membrane electrode assembly, and air containing oxygen as an example of an oxidizing agent gas is supplied to the cathode. Then, hydrogen gas is supplied to the anode as an example of the fuel gas. The fuel cell 1 generates electricity by chemically reacting the oxidant gas and the fuel gas in each single cell.

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

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

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

Further, the cathode supply paths R10 and R11 are branched and connected to the humidifier 81 and the bypass valve 82. The opening degree of the bypass valve 82 is adjusted by a control signal from the ECU 6. A part of the air in the cathode supply path R10 is introduced into the fuel cell 1 via the bypass valve 82 and the cathode supply path R11 according to the opening degree of the bypass valve 82.

The fuel tank 2 is an example of a pressure accumulator, and stores fuel gas by accumulating it. A main check valve 70 is connected to the outlet of the fuel tank 2. The main check valve 70 is maintained in an open state during power generation of the fuel cell 1 according to the control of the ECU 6. The fuel gas flows from the main check valve 70 through the anode supply path R20 and enters the pressure regulating valve 3.

The pressure regulating valve 3 adjusts the pressure of the fuel gas flowing from the fuel tank 2 into the injector 4 according to a control signal from the ECU 6. The fuel gas that has passed through the pressure regulating valve 3 flows into the injector 4 via the anode supply path R21. The injector 4 intermittently injects the fuel gas flowing from the fuel tank 2 according to the control signal from the ECU 6. The fuel gas injected from the injector 4 flows into the ejector 5 via the anode supply path R22.

The ejector 5 mixes the fuel gas injected from the injector 4 with the fuel off gas recirculated in the fuel cell 1 and introduces the fuel gas into the fuel cell 1. Fuel off gas is sucked into the ejector 5 from the recirculation path R27. The fuel gas mixed with the fuel off gas is supplied to the fuel cell 1 from the anode supply path R23. Therefore, assuming that the injection amount of the fuel gas from the injector 4 to the ejector 5 is Qin and the flow rate of the fuel off gas from the recirculation path R27 to the ejector 5 is Qre, the fuel gas and the fuel off gas from the ejector 5 to the fuel cell 1 are used. The flow rate of is Qin + Qre.

The fuel off gas flows from the fuel cell 1 through the anode discharge path R24 and enters the gas-liquid separator 71. The gas-liquid separator 71 separates and stores the liquid water from the fuel off gas, and sends the fuel off gas to the recirculation path R27.

The purge valve 72 is connected to the gas-liquid separator 71 via the anode discharge path R25. 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 the liquid water in the gas-liquid separator 71 are discharged to the outside from the anode discharge passages R25 and R26.

Further, the cooling water is introduced from the radiator 90 into the fuel cell 1 via the cooling water supply paths R31 and R32 to cool the fuel cell 1. The cooling water discharged from the fuel cell 1 returns to the radiator 90 via the cooling water discharge passages R33 and R34. The radiator 90 cools the cooling water from the cooling water discharge path R34 and sends it back to the cooling water supply path R31.

The three-way valve 91 is connected to the cooling water supply passages R31 and R32 and the cooling water discharge passage R34. The cooling water discharge path R34 is branched and connected to the radiator 90 and the three-way valve 91. The cooling water introduced into the three-way valve 91 from the cooling water supply path R31 and the cooling water discharge path R34 is sent out from the cooling water supply path R32 to the fuel cell 1.

The opening degree of the three-way valve 91 is controlled by a control signal from the ECU 6. Thereby, the ECU 6 can control the ratio of the cooling water from the radiator 90 to the cooling water from the cooling water discharge path R34 in the cooling water sent to the fuel cell 1.

A pump 92 is connected between the cooling water discharge passages R33 and R34. The pump 92 circulates the cooling water between the fuel cell 1 and the radiator 90. The driving force of the pump 92 is controlled by a control signal from the ECU 6. Thereby, the ECU 6 can control the circulation amount of the cooling water.

The temperature sensor 93 detects the temperature of the cooling water flowing through the cooling water discharge path R34. The ECU 6 acquires the temperature of the cooling water from the temperature sensor 93.

Further, the battery 95 stores a part of the electric power output from the fuel cell 1. The current sensor 94 is an example of a detection device, and detects a current value output from the fuel cell 1. The ECU 6 acquires a current value from the current sensor 94.

The ECU 6 controls the operation of the fuel cell system. The ECU 6 includes, for example, a CPU (Central Processing Unit) 60, a program memory 61, a database memory 62, and the like. The CPU 60 operates according to the program stored in the program memory 61. Further, various databases are held in the database memory 62.

The ECU 6 is an example of a control device, and controls one injection time and injection amount of the injector 4. One injection time of the injector 4 is controlled according to the duty ratio of the control signal from the ECU 6. Further, the injection amount of the injector 4 at one time is controlled by the control signal output from the ECU 6 to the pressure regulating valve 3.

The ECU 6 estimates the fuel gas discharge capacity of the fuel cell 1 based on the operating state of the fuel cell 1, and estimates the water content on the anode side of the fuel cell 1 from the estimated discharge capacity. The ECU 6 compares the estimated water content with a predetermined threshold value, and controls the amount of drainage of the fuel gas by controlling the temperature of the fuel cell 1 according to the comparison result.

Examples of the temperature control means for the fuel cell 1 include the following means.

The ECU 6 can increase the calorific value of the fuel cell 1 by increasing the electric power generated by the fuel cell 1. At this time, the surplus electric power is stored in, for example, the battery 95.

Further, the ECU 6 can control the flow rate of the fuel gas that bypasses the humidifier 81 among the fuel gases supplied to the fuel cell 1 by adjusting the opening degree of the bypass valve 82 with the control signal. When the flow rate of the fuel gas bypassing the humidifier 81 increases, the humidity of the fuel cell 1 decreases and the temperature rises, and when the flow rate of the fuel gas bypassing the humidifier 81 decreases, the humidity of the fuel cell 1 rises. The temperature rises.

Further, the ECU 6 can control the temperature of the fuel cell 1 more effectively by controlling the circulation amount of the cooling water. The ECU 6 can control the circulation amount of the cooling water by adjusting, for example, the opening degree of the three-way valve 91 and the driving force of the pump 92 with a control signal. When the circulation amount of the cooling water increases, the temperature of the fuel cell 1 decreases, and when the circulation amount of the cooling water decreases, the temperature of the fuel cell 1 rises. The ECU 6 may execute a combination of a plurality of temperature control means among the above temperature control means.

When the temperature is controlled, the ECU 6 estimates the amount of fuel off gas that can be discharged from the fuel cell 1 from the operating state of the fuel cell 1.

FIG. 2 is a flowchart showing an example of the temperature control process. This process is executed by the CPU 60 of the ECU 6 reading the program from the program memory 61.

The ECU 6 periodically repeats each of the following steps St1 to St15, for example. At this time, the ECU 6 repeats each process in the same cycle as the injection cycle of the injector 4, as an example. That is, each process of steps St1 to St15 is executed so as to be synchronized with the injection of the injector 4.

Further, the ECU 6 repeatedly calculates the water content W on the anode side of the fuel cell 1 by repeating each process of steps St1 to St15. At this time, the previously calculated water content W is used for calculating the new water content W. Therefore, the ECU 6 calculates the water content W at the current time (that is, the current cycle) from the water content W at the time before (that is, the previous cycle) by the injection cycle of the injector 4. The ECU 6 controls the temperature of the fuel cell 1 according to the calculated water content W.

First, the ECU 6 sets the water content W calculated in the previous cycle to the water content W'used for calculating the water content W in the current cycle (step St1). When the processing of step St1 is executed for the first time after the CPU 60 is started, the ECU 6 uses a predetermined initial value as the water content W. The initial value of the water content W is determined based on, for example, the initial water content on the anode side of the fuel cell 1.

Next, the ECU 6 acquires the temperature of the fuel cell 1 from the temperature sensor 93 (step St2). The ECU 6 acquires the temperature of the fuel cell 1 by correcting the temperature of the cooling water detected by the temperature sensor 93, for example.

Next, the ECU 6 acquires the current value output from the fuel cell 1 from the current sensor 94 (step St3). Next, the ECU 6 estimates the pressure loss in the recirculation path R27 from the water content W'on the anode side of the fuel cell 1 and the current value output from the fuel cell 1 based on the pressure loss database (step St4).

The pressure loss database shows the correlation between the water content W'on the anode side of the fuel cell 1, the pressure loss in the recirculation path R27, and the current value output from the fuel cell 1. The pressure loss database is stored in the database memory 62 in advance. The correlation between the water content W', the current value, and the pressure loss will be described below.

FIG. 3 is a diagram showing an example of the correlation between the water content W', the current value, and the pressure loss. Reference numeral G1 indicates an example of a graph of the change characteristic of the pressure loss with respect to the water content W'for each of the current values I1, I2, ..., In (n: positive integer) in the fuel cell 1. In the graph of reference numeral G1, the horizontal axis represents the water content W'and the vertical axis represents the pressure loss. The relationship of I1> I2> ...> In is established between the current values I1, I2, ..., In, as indicated by the arrows.

The pressure loss gradually increases as the water content W'increases. Further, the pressure loss is larger as the current values I1 to In are larger, regardless of the water content W'.

Reference numeral G2 indicates an example of a pressure drop database. The pressure drop database is constructed based on the correlation shown by the graph of reference numeral G1.

In the pressure loss database, as an example, the pressure loss corresponding to the water content W'and the current value is registered. The ECU 6 searches the pressure loss database for the pressure loss corresponding to the water content W'and the current value. For example, when the water content W'is Wa and the current value is I1, the pressure loss is Paa.

With reference to FIG. 2 again, after estimating the pressure loss, the ECU 6 acquires the injection time and the injection amount Qin of the injector 4 (step St5). The ECU 6 acquires the injection amount Qin from, for example, a control signal for controlling the opening degree of the pressure regulating valve 3.

Further, the ECU 6 acquires the injection time of the injector 4 from, for example, a control signal output to the injector 4.

FIG. 4 is a waveform diagram showing an example of a control signal output to the injector 4. The control signal is generated, for example, as a pulse having a constant period. The potential of the control signal repeats high potential Von and low potential Voff (<Von) in a period Tc. Here, the period Tc corresponds to the period in which each process of steps St1 to St15 is executed, as described above.

When the potential of the control signal is the high potential Von, the injector 4 injects the fuel gas, and when the potential of the control signal is the low potential Voff, the injector 4 stops the injection of the fuel gas. The ECU 6 acquires the injection time Ton at which the control signal becomes the high potential Von in the period Tc as the injection time.

With reference to FIG. 2 again, after acquiring the injection time and the injection amount of the injector 4, the ECU 6 estimates the flow rate Qre of the fuel off gas in the recirculation path R27 from the pressure loss estimated in the process of step St4 based on the flow rate database. (Step St6). The flow rate database shows the correlation between the pressure loss in the recirculation path R27 and the flow rate Qre of the fuel off gas. The flow rate database is stored in the database memory 62 in advance. The correlation between the pressure loss and the fuel off-gas flow rate Qre will be described below.

FIG. 5 is a diagram showing an example of the correlation between the pressure loss in the recirculation path R27 and the flow rate of the fuel off gas. Reference numeral G11 indicates an example of a graph of the change characteristic of the flow rate Qre with respect to the pressure loss. In the graph of reference numeral G11, the horizontal axis represents the pressure loss and the vertical axis represents the flow rate Qre. The flow rate Qre decreases at a constant rate with respect to the increase in pressure loss.

Reference numeral G12 indicates an example of a flow rate database. The flow rate database is constructed based on the correlation shown by the graph of reference numeral G11.

For example, the pressure loss and the flow rate Qre are registered in the flow rate database in association with each other. The ECU 6 searches the flow rate database for the flow rate Qre corresponding to the pressure loss estimated by the pressure loss database. For example, when the pressure loss is P1, the flow rate Qre is Q1.

Referring to FIG. 2 again, the ECU 6 estimates the flow rate Qre of the fuel off gas, and then the fuel gas introduced from the ejector 3 into the fuel cell 1 based on the estimated flow rate Qre, the injection amount Qin of the injector 4, and the injection time Ton. And the impulse A of the fuel off gas is calculated (step St7). Here, the flow rates of the fuel gas and the fuel off gas introduced into the fuel cell 1 are the sum of the injection amount Qin of the fuel gas and the flow rate Qre of the fuel off gas.

A = (Qin + Qre) ^4/7 x Ton ... (1)

The ECU 6 calculates the impulse A from the above equation (1), for example. As a result, the amount of change in the unit time of the momentum of the fuel gas and the fuel off gas sent from the ejector 5 to the flow path on the anode side in the fuel cell 1 is calculated.

ΔW = k × W ′ × A ・ ・ ・ (2)

Next, the ECU 6 calculates the displacement ΔW based on the impulse A and the water content W'(step St8). The ECU 6 calculates, for example, the displacement ΔW from the above equation (2). Here, the constant k is a constant determined according to the configuration of the flow path on the anode side in the fuel cell 1 and various conditions.

In this way, the ECU 6 calculates the impulse A from the water content W'on the anode side of the fuel cell 1, the injection time Ton and the injection amount Qin of the injector 4, and the flow rate Qre of the fuel off gas in the recirculation path R27, and the impulse A. The drainage amount ΔW is calculated from A and the water content W'. Here, since the impulse A and the water content W'are parameters related to the operating state on the anode side of the fuel cell 1, the ECU 6 can appropriately grasp the drainage amount ΔW from the operating state on the anode side of the fuel cell 1. can.

Further, the ECU 6 estimates the pressure loss based on the pressure loss database, and estimates the flow rate Qre from the flow rate database. Therefore, it is not necessary to provide each sensor for detecting the pressure loss and the flow rate Qre in the fuel cell system, and the scale of the fuel cell system is reduced as compared with the case where such a sensor is provided.

W = W'-ΔW × Tc ・ ・ ・ (3)

Next, the ECU 6 calculates the water content W of this cycle from the water content W'and the drainage amount ΔW (step St9). The ECU 6 calculates the water content W from the above formula (3), for example. At this time, the water content W is a value obtained by subtracting the amount of drainage (ΔW × Tc) discharged into the period Tc from the water content W'before Tc seconds.

Next, the ECU 6 determines the upper limit value Wu of the water content W (step St10), and determines the lower limit value Wd of the water content W (step St11). The lower limit value Wd may be determined before the upper limit value Wu. The ECU 6 determines, for example, the upper limit value Wu from the correlation between the temperature of the fuel cell 1 acquired from the temperature sensor 93, the current value acquired from the current sensor 94, and the upper limit value Wu. The lower limit value Wd is determined from the correlation between the temperature, the current value, and the lower limit value Wd. For example, the upper limit value Wu and the lower limit value Wd are determined from the upper limit value database and the lower limit value database showing the above correlation, respectively.

FIG. 6 is a diagram showing an example of the correlation between the temperature, the current value, and the upper limit value Wu or the lower limit value Wd of the fuel cell 1. Reference numeral G21 indicates an example of a graph of change characteristics of the upper limit value Wu (or lower limit value Wd) with respect to the temperature for each of the current values I1, I2, ..., In in the fuel cell 1. In the graph of reference numeral G21, the horizontal axis indicates the temperature, and the vertical axis indicates the upper limit value Wu (or the lower limit value Wd). The relationship of I1> I2> ...> In is established between the current values I1, I2, ..., In, as indicated by the arrows.

The upper limit value Wu (or lower limit value Wd) decreases at a constant rate with increasing temperature. Further, the upper limit value Wu (or the lower limit value Wd) is larger as the current values I1 to In are larger, regardless of the temperature.

Reference numeral G22 indicates an example of an upper limit value database or a lower limit value database. The upper limit database and the lower limit database are configured based on the correlation shown by the graph of reference numeral G21.

In the upper limit value database, as an example, the upper limit value Wu corresponding to the temperature and current values is registered. Further, in the lower limit value database, as an example, the lower limit value Wd corresponding to the temperature and current values is registered. The ECU 6 searches the upper limit value database for the upper limit value Wu corresponding to the temperature and current values, and searches the lower limit value Wd corresponding to the temperature and current values from the lower limit value database. In the case of the upper limit value database, for example, when the temperature is Ka and the current value is I1, the upper limit value Wu is Waa.

With reference to FIG. 2 again, the ECU 6 determines the upper limit value Wu and the lower limit value Wd, and then compares the water content W with the upper limit value Wu (step St12). When the water content W exceeds the upper limit value Wu (Yes in step St12), the ECU 6 raises the temperature of the fuel cell 1 so that the drainage amount ΔW on the anode side of the fuel cell 1 increases (step St14). After that, each process after step St1 is executed in the next cycle.

Further, when the water content W is equal to or less than the upper limit value Wu (No in step St12), the ECU 6 compares the water content W with the lower limit value Wd (step St13). When the water content W is lower than the lower limit value Wd (Yes in step St13), the ECU 6 lowers the temperature of the fuel cell 1 so that the drainage amount ΔW on the anode side of the fuel cell 1 decreases (step St15). After that, each process after step St1 is executed in the next cycle.

Further, even when the water content W is equal to or higher than the lower limit value Wd (No in step St13), each process after step St1 is executed in the next cycle. In this way, the temperature control process is executed. The temperature control means is as described above.

In steps St14 and St15, the ECU 6 calculates the temperature control control value Δk and determines the target temperature To from the control value Δk.

Δk = (W-Wu) / (W'× A) ・ ・ ・ (4)
Δk = (Wd−W) / (W'× A) ・ ・ ・ (5)

For example, the ECU 6 calculates the control value Δk from the above equation (4) in step St14, and calculates the control value Δk from the above equation (5) in step St15. The control value Δk is a correction value of the constant k of the above equation (2) with respect to the difference between the water content W and the upper limit value Wu or the lower limit value Wd. The ECU 6 determines the target temperature To based on the target temperature database showing the correlation between the control value Δk and the target temperature To. The target temperature database is stored in the database memory 62 in advance. The correlation between the control value Δk and the target temperature To will be described below.

FIG. 7 is a diagram showing an example of the correlation between the control value Δk and the target temperature To. Reference numeral G31 indicates an example of a graph of the change characteristic of the control value Δk with respect to the target temperature To. In the graph of reference numeral G31, the horizontal axis represents the target temperature To and the vertical axis represents the control value Δk. The control value Δk increases at a constant rate with respect to the increase in the target temperature To.

Reference numeral G32 indicates an example of the target temperature database. The target temperature database is constructed based on the correlation shown by the graph of reference numeral G31.

For example, the control value Δk and the target temperature To are registered in the target temperature database in association with each other. The ECU 6 searches the target temperature database for the target temperature To corresponding to the control value Δk calculated from the equation (4) or the equation (5). For example, when the control value Δk is k1, the target temperature To is x1.

The ECU 6 controls the temperature so that the temperature of the fuel cell 1 becomes the target temperature To. At this time, as described below, the ECU 6 can control the humidity of the fuel cell 1 while suppressing the deterioration of fuel consumption by controlling the temperature without increasing the supply amount of the fuel gas.

FIG. 8 is a diagram showing an example of the change characteristic of the overvoltage of the anode with respect to the partial pressure of the fuel gas for each humidity. In FIG. 8, the horizontal axis represents the partial pressure [Pa] of the fuel gas, and the vertical axis represents the overvoltage [v] of the anode.

Reference numerals G41 and G42 are graphs of change characteristics when the humidity of the fuel cell 1 is 20% RH, and reference numerals G51 and G52 are graphs of change characteristics when the humidity of the fuel cell 1 is 100% RH. Further, the graphs of reference numerals G41 and G51 are referred to as “lower Pt” when the amount of platinum (Pt), which is a catalyst of the anode electrode of the fuel cell 1, is lower than that of the graphs of reference numerals G42 and G52. ) Shows the changing characteristics.

The overvoltage of the anode decreases as the partial pressure of the fuel gas increases and converges to a nearly constant value. At low Pt, the overvoltage rises over the entire range of partial pressure, regardless of whether the humidity is 20% RH or 100% RH.

For example, when the fuel gas is supplied so that the partial pressure is within the range Ra, the change characteristic at the time of low Pt in the environment where the humidity is 20% RH, that is, the dry environment (see reference numeral G41) is low Pt. Compared with the change characteristic when it is not converted (see reference numeral G42), the amount of change in the overvoltage with respect to the partial pressure becomes larger. When the sensitivity of the overvoltage is high as described above, the power generation efficiency of the fuel cell 1 changes greatly every time the supply amount of the fuel gas changes.

On the other hand, for example, if the amount of fuel gas supplied is increased so that the partial pressure falls within the range Rb (> Ra), the amount of change in the overvoltage with respect to the partial pressure becomes small, so that the change in power generation efficiency is suppressed. .. However, if the amount of fuel gas supplied increases, fuel efficiency may deteriorate.

Therefore, the ECU 6 can suppress a change in power generation efficiency by maintaining the humidity at 100% RH as an example by controlling the temperature. When the fuel gas is supplied so that the partial pressure is within the range Ra, the Pt is lowered in the environment where the humidity is 100% RH, that is, the change characteristic at the time of lowering the Pt in the wet environment (see reference numeral G51). Similar to the change characteristic when not (see reference numeral G52), the amount of change in overvoltage with respect to partial pressure is small.

In this way, the ECU 6 can control the humidity of the fuel cell 1 while suppressing the deterioration of fuel consumption by controlling the temperature without increasing the supply amount of the fuel gas. However, for example, when deterioration of fuel efficiency does not matter, the ECU 6 may control the humidity by increasing the amount of drainage by increasing the amount of fuel gas supplied.

Next, an example of temperature control by the ECU 6 will be described. In the following example, the ECU 6 controls the temperature without increasing the supply amount of the fuel gas.

FIG. 9 is a time chart showing an example of temperature control. FIG. 9 shows the load required for the fuel cell 1 (required load), the amount of fuel gas supplied to the fuel cell 1, the temperature, humidity, and power generation efficiency of the fuel cell 1, and the anode side of the fuel cell 1. Changes in the amount of wastewater and water content of the fuel cell system with respect to time are shown. The solid line shows the change due to the temperature control of the ECU 6 of the embodiment, and the dotted line shows the change due to the temperature control of the comparative example.

It is assumed that the required load is constant at times t1 to t7. Further, it is assumed that the fuel gas supply amount, temperature, drainage amount, humidity, power generation efficiency, and fuel consumption are constant at times t1 to t2.

In this example, the temperature control when the water content W exceeds the upper limit value Wu will be mentioned. The water content W increases at time t1 to t3 due to insufficient drainage (drainage capacity).

The ECU 6 of the comparative example increases the displacement amount by increasing the fuel gas supply amount at the time t2 when the water content W exceeds the upper limit value Wu. Therefore, the water content W gradually decreases from time t3 to t6, but the fuel consumption gradually decreases from time t2 to t7 because the fuel gas supply amount increases excessively with respect to the required load. Further, since the water content is below the lower limit value Wd at time t5, the humidity and power generation efficiency gradually decrease at time t5 to t7.

On the other hand, the ECU 6 of the embodiment increases the amount of drainage by gradually raising the temperature at time t2 to t4 without increasing the fuel gas supply amount. As the temperature rises, the amount of water that can be contained in the fuel gas in the fuel gas flow path of the fuel cell 1 increases. Therefore, as the viscosity of the fuel gas increases, the force acting on the liquid water in the fuel gas flow path increases. This increases the amount of drainage.

The ECU 6 stops the temperature control because the temperature reaches the target temperature To at the time t4. The water content W decreases from time t3 to t6 due to the increase in the amount of drainage, but since the temperature starts to decrease at time t6, the decrease in the water content W is suppressed. Therefore, the humidity, the power generation efficiency, and the fuel consumption are kept substantially constant unlike the comparative example.

FIG. 10 is a time chart showing another example of temperature control. In FIG. 10, description of items common to FIG. 9 will be omitted.

It is assumed that the required load is constant at times t11 to t16. Further, it is assumed that the fuel gas supply amount, temperature, drainage amount, humidity, power generation efficiency, and fuel consumption are constant at times t11 to t12.

In this example, the temperature control when the water content W falls below the lower limit value Wd is given. The water content W gradually decreases at time t11 to t12 due to the excessive drainage amount (drainage capacity), and falls below the lower limit value Wd at time t12.

Since the ECU 6 of the comparative example sets the fuel gas supply amount according to the required load, the fuel gas supply amount cannot be reduced even if the water content W is reduced. Therefore, the amount of drainage is kept constant even after the time t12. Therefore, the water content W continues to decrease at times t12 to t15 and is maintained at a minimum at times t15 to t16.

Therefore, the humidity gradually decreases from time t13 to t16. As a result, the power generation efficiency and fuel consumption also gradually decrease from time t13 to t16.

On the other hand, in the ECU 6 of the embodiment, since the water content W was below the lower limit value Wd at time t12, the temperature was lowered from time t12 to t14, and at time t14, the temperature reached the target temperature To, so that the temperature control was stopped. .. Therefore, the temperature and the amount of drainage decrease at time t12 to t14, and are maintained substantially constant at time t14 to t15. Further, the water content W is maintained constant by the decrease in the amount of drainage from time t12 to t14.

The water content W starts to increase at time t14 due to the stop of temperature control, but the increase is suppressed because the temperature and the amount of drainage gradually increase from time t15 to t16. Therefore, the humidity, the power generation efficiency, and the fuel consumption are kept substantially constant unlike the comparative example.

As described above, the ECU 6 of the embodiment can control the humidity of the fuel cell 1 while suppressing the deterioration of the fuel consumption by controlling the temperature without increasing the supply amount of the fuel gas.

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

1 Fuel cell 2 Fuel gas tank 4 Injector 5 Ejector 6 ECU
94 Current sensor R27 Recirculation path

Claims (1)

Fuel cells that generate electricity from fuel gas and
An accumulator that accumulates the fuel gas and
An injector that intermittently injects the fuel gas flowing from the accumulator,
The recirculation path through which the fuel off gas recirculated to the fuel cell flows,
An ejector that mixes the fuel gas injected from the injector with the fuel off gas from the recirculation path and introduces the fuel gas into the anode of the fuel cell.
A detection device that detects the current value output from the fuel cell, and
It has a control device for controlling one injection time and injection amount of the injector.
The control device is
Based on the correlation between the water content on the anode side of the fuel cell, the pressure loss in the recirculation path, and the current value, the pressure loss is estimated from the water content and the current value.
From the estimated pressure loss, the flow rate is estimated based on the correlation between the pressure loss in the recirculation path and the flow rate of the fuel off gas.
Based on the estimated flow rate, the injection amount, and the injection time, the impulses of the fuel gas and the fuel off gas introduced from the ejector into the fuel cell are calculated.
A fuel cell system characterized in that the amount of drainage on the anode side of the fuel cell is calculated based on the impulse and the water content.

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