JP5538014B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  In a fuel cell, a membrane electrode structure is formed by sandwiching a solid polymer electrolyte membrane between an anode electrode and a cathode electrode from both sides, and a pair of separators are arranged on both sides of the membrane electrode structure to form a flat unit fuel. A battery (hereinafter referred to as “unit cell”) is configured, and a plurality of unit cells are stacked to form a fuel cell stack. In this fuel cell, a hydrogen gas is supplied as a fuel gas to an anode gas passage formed between the anode electrode and the anode side separator, and a cathode gas passage formed between the cathode electrode and the cathode side separator. Is supplied with air as an oxidant gas. As a result, hydrogen ions generated by the catalytic reaction at the anode electrode permeate the solid polymer electrolyte membrane and move to the cathode electrode, and the cathode electrode causes an electrochemical reaction with oxygen in the air to generate power. Further, water is generated along with this power generation (hereinafter referred to as generated water).

In this type of fuel cell, the generated water (hereinafter referred to as residual water) remaining in the reaction gas channel (the anode gas channel and the cathode gas channel) is used to supply the fuel gas and the oxidizing gas to the membrane electrode structure. This hinders power generation performance. When the fuel cell is driven below freezing point, the power generation area in the membrane electrode structure is reduced due to the freezing of the residual water, thereby reducing the power generation performance.
Accordingly, a scavenging technique has been proposed in which a predetermined gas is supplied into the reaction gas flow path to discharge and remove residual water. It is necessary to perform scavenging before the temperature of the fuel cell falls below freezing point. Therefore, Patent Document 1 discloses a technique for determining the scavenging timing in the anode gas flow path with a temperature sensor (absolute value) in the cooling system. Patent Document 2 discloses a technique for performing a freeze prevention operation for a water circulation line in accordance with an outside air temperature detected by an outside air temperature sensor and a water temperature detected by a water temperature sensor.

US Pat. No. 7,270,904 JP 2007-294186 A

  However, when an offset failure occurs in the temperature sensor, the temperature of the fuel cell cannot be accurately detected. Therefore, there is a problem that it becomes difficult to perform scavenging before the fuel cell becomes below freezing point. In this case, since generated water freezes inside the fuel cell, the startability and power generation performance of the fuel cell system are deteriorated.

In view of this, a technique has been developed that eliminates the effect of offset failure by using the difference between the measured value of the temperature sensor immediately after the fuel cell is stopped and the measured value of the current temperature sensor. In this technique, scavenging is performed when the calculated difference exceeds the difference threshold. For example, the difference threshold is set to a difference between the surface temperature immediately after the fuel cell is stopped and the surface temperature (about 0 ° C.) at which scavenging is to be performed.
However, immediately after the fuel cell is stopped, the temperature change becomes large due to the influence of internal heat, so that the correlation between the surface temperature of the fuel cell and the measured value of the temperature sensor cannot be obtained. Therefore, even if the difference calculated from the measured value of the temperature sensor exceeds the difference threshold set from the surface temperature of the fuel cell, the surface temperature of the fuel cell may not be the scavenging temperature (about 0 ° C.). is there. As a result, it is difficult to perform scavenging at an appropriate timing.

  Therefore, an object of the present invention is to provide a fuel cell system capable of performing scavenging at an appropriate timing.

In order to solve the above-described problems, a fuel cell system according to the present invention (for example, the fuel cell system 100 in the embodiment) is supplied with a fuel and an oxidant to generate power (for example, the fuel cell 1 in the embodiment). ), Fuel supply means (for example, hydrogen tank 15 in the embodiment) for supplying the fuel to a fuel flow path (for example, the anode gas flow path 11 in the embodiment) of the fuel cell, and an oxidant flow of the fuel cell An oxidant supply means (for example, the air compressor 7 in the embodiment) for supplying the oxidant to a passage (for example, the cathode gas flow path 12 in the embodiment), and from the oxidant supply means when the fuel cell is stopped. Scavenging means for supplying scavenging by supplying an oxidant to at least one of the fuel flow path and the oxidant flow path (for example, in the embodiment) An air compressor 7, a scavenging gas introduction valve 23, a scavenging gas discharge valve 21a and a back pressure control valve 10), and fuel cell temperature adjusting means for supplying refrigerant to the fuel cell and adjusting the temperature of the fuel cell by heat exchange. In a fuel cell system comprising (for example, the cooling water pump 42 in the embodiment) and a control unit (for example, the controller 60 in the embodiment) that controls the respective means, at least one of the respective means. A temperature sensor that measures the temperature (for example, the cooling water temperature sensor T3 in the embodiment), and the control unit includes a measurement value of the temperature sensor and a surface temperature of the fuel cell after the fuel cell is stopped. predetermined time so correlation can be taken (for example, predetermined time t1 in the embodiment) based on the measured value of the temperature sensor at the time has elapsed An initial value (for example, temperature initial value A in the embodiment) is set, and a difference (for example, implementation) between the initial value and a measured value of the temperature sensor after the predetermined time (for example, current temperature B in the embodiment) When the difference C) in the form exceeds a difference threshold (for example, the difference threshold D in the embodiment), scavenging is performed by the scavenging means.

  According to this configuration, the measured value of the temperature sensor and the surface temperature of the fuel cell can be correlated by avoiding the time when the temperature change is large immediately after the fuel cell is stopped after a predetermined time has elapsed. It becomes like this. Thereby, when the difference calculated from the measured value of the temperature sensor exceeds the difference threshold, the surface temperature of the fuel cell becomes the scavenging temperature. Therefore, scavenging can be performed at an appropriate timing.

Further, the predetermined time is preset according to a rate of decrease in the surface temperature of the fuel cell.
According to this configuration, the time from when the fuel cell is stopped until the rate of decrease of the measured value of the temperature sensor becomes equal to the rate of decrease of the surface temperature of the fuel cell can be set as a predetermined time. As a result, when a predetermined time elapses after the fuel cell is stopped, the correlation between the surface temperature of the fuel cell and the measured value of the temperature sensor can be obtained.

The predetermined time is when the rate of change of the measured value of the temperature sensor reaches or falls below a predetermined rate of change set in advance.
When the measured value of the temperature sensor approaches the surface temperature of the fuel cell, the rate of change of the measured value of the temperature sensor decreases. Therefore, by setting the time when the rate of change of the measured value of the temperature sensor falls below the predetermined rate of change as the predetermined time, the time point at which the measured value of the temperature sensor can be correlated with the surface temperature of the fuel cell can be accurately grasped. be able to.

The difference threshold is set based on the initial value.
When a predetermined time elapses after the fuel cell is stopped, the measured value of the temperature sensor and the surface temperature of the fuel cell can be correlated. Therefore, the difference threshold value to be calculated from the surface temperature of the fuel cell can be set based on the initial value calculated from the measured value of the temperature sensor. As a result, it is not necessary to add a temperature sensor for measuring the surface temperature of the fuel cell, and an increase in manufacturing cost can be suppressed.

The temperature sensor measures the temperature of the refrigerant after heat exchange with the fuel cell in the fuel cell temperature adjusting means.
The measured value of the temperature sensor of the refrigerant has a faster temperature decrease rate than the measured value of the temperature sensor of the fuel or oxidant. Therefore, it is possible to reliably determine scavenging before the fuel cell becomes below freezing point.

  According to the present invention, the correlation between the measured value of the temperature sensor and the surface temperature of the fuel cell can be obtained by avoiding the time when the temperature change is large immediately after the fuel cell is stopped after a predetermined time has elapsed. It becomes like this. Thereby, when the difference calculated from the measured value of the temperature sensor exceeds the difference threshold, the surface temperature of the fuel cell becomes the scavenging temperature. Therefore, scavenging can be performed at an appropriate timing.

1 is a block diagram showing a schematic configuration of a fuel cell system according to an embodiment. It is a flowchart of the scavenging execution judgment method of the fuel cell system concerning an embodiment. It is a flowchart of a temperature initial value setting subroutine. (A) is a graph which shows a time-dependent change of a cooling water temperature sensor measurement value, (b) is a graph which shows a time-dependent change of the change rate of a cooling water temperature sensor measurement value. (A) is a table which shows the relationship between a temperature initial value and a difference threshold value, (b) is a graph which shows the time-dependent change of a difference. It is a timing chart of a scavenging process.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Fuel cell system)
FIG. 1 is a block diagram showing a schematic configuration of a fuel cell system. The fuel cell system 100 includes a fuel cell stack (hereinafter simply referred to as a fuel cell) 1 that supplies a cathode gas and an anode gas to generate electric power. The fuel cell 1 is formed by stacking a number of unit fuel cells (hereinafter referred to as “unit cells”) and electrically connecting them in series. The unit cell has a sandwich structure in which separators are arranged on both sides of the membrane electrode structure. Specifically, the membrane electrode structure is configured by arranging an anode electrode and a cathode electrode on both sides of a solid polymer electrolyte membrane (electrolyte membrane) made of, for example, a fluorine-based electrolyte material. An anode-side separator is disposed facing the anode electrode of the membrane electrode structure, and an anode gas flow path 11 is formed therebetween. A cathode-side separator is disposed facing the cathode electrode of the membrane electrode structure, and a cathode gas flow path 12 is formed between them.

  In this fuel cell 1, a fuel gas such as hydrogen gas is supplied as an anode gas to the anode gas flow path 11, and an oxidant gas such as air containing oxygen is supplied as the cathode gas flow path 12 to the cathode gas flow path 12. Then, hydrogen ions generated by the catalytic reaction at the anode electrode pass through the solid polymer electrolyte membrane and move to the cathode electrode. The hydrogen ions cause an electrochemical reaction with oxygen at the cathode electrode to generate power, and water is generated on the cathode electrode side with the power generation.

  A fuel gas supply path 17 is connected to the inlet side of the anode gas flow path 11 of the fuel cell 1. The fuel gas supply path 17 includes a hydrogen tank 15, an electromagnetic shut-off valve (not shown) that shuts off the flow of the fuel gas, a pressure-reducing valve (not shown) that decompresses the fuel gas according to the pressure of the oxidant gas, A filter (not shown) that removes impurities in the fuel gas supply path 17, a heat exchanger (not shown) that adjusts the temperature of the fuel gas, and an ejector 19 that joins the anode off-gas to the fuel gas supply path 17, It is provided in order.

An anode circulation path 18 is provided from the outlet side of the anode gas flow path 11 of the fuel cell 1 to the ejector 19.
The fuel gas supplied from the hydrogen tank 15 is supplied to the anode gas passage 11 of the fuel cell 1 through the fuel gas supply passage 17. The anode off gas is sucked into the ejector 19 through the anode circulation path 18, merges with the fuel gas supplied from the hydrogen tank 15, is supplied to the fuel cell 1 again, and is circulated.

  An anode off-gas discharge pipe 22 is branched from the anode circulation path 18 via an electromagnetically driven purge valve 21. When the concentration of impurities (moisture, air, nitrogen, etc.) in the anode off-gas circulating through the fuel cell 1 becomes high, the purge valve 21 is periodically opened according to the operating state of the fuel cell 1, and the anode off-gas It is discharged through the anode off-gas discharge pipe 22. A scavenging gas discharge pipe 22a is branched from the anode circulation path 18 via an electromagnetically driven scavenging gas discharge valve 21a. The scavenging will be described later.

  A catch tank 25 is provided in the anode circulation path 18 near the outlet of the anode gas flow path 11. The catch tank 25 captures the generated water discharged from the anode gas flow path 11. A drain pipe 22b extends from the catch tank 25 via an electromagnetically driven drain valve 21b. The drain valve 21b is periodically opened, and the generated water and the anode off gas are discharged from the catch tank 25 through the drain pipe 22b.

  The anode off gas and the scavenging gas contain unreacted fuel gas. Therefore, the anode off-gas discharge pipe 22, the scavenging gas discharge pipe 22 a and the drain pipe 22 b are connected to the diluter 30. The diluter 30 dilutes the anode off gas and the scavenging gas with the cathode off gas and the oxidant gas, and discharges them to the outside.

On the other hand, an oxidant gas supply path 8 is connected to the inlet side of the cathode gas flow path 12 of the fuel cell 1. The oxidant gas supply path 8 is provided with an air compressor 7 that supplies the oxidant gas and a humidifier (not shown) that humidifies the oxidant gas using the cathode off gas. A cathode offgas discharge pipe 9 is connected to the outlet side of the cathode gas passage 12. The cathode offgas discharge pipe 9 passes through the humidifier and is connected to the diluter 30 via the back pressure control valve 10.
The air pressurized by the air compressor 7 is supplied to the cathode gas flow path 12 of the fuel cell 1 through the oxidant gas supply path 8. After this oxygen in the air is used as an oxidant for power generation, it is discharged from the fuel cell 1 as a cathode off gas.

  A bypass flow path 32 is branched from the oxidant gas supply path 8 and connected to the diluter 30. The bypass passage 32 is provided with a dilution ventilation valve (not shown) that switches the communication state of the bypass passage 32. When the cathode off gas is insufficient in the diluter 30, the oxidant gas can be supplied to the diluter 30 through the bypass channel 32.

Inside the fuel cell 1, there is provided a cooling water passage 40 through which cooling water flows as a refrigerant. A cooling water circulation path 41 is provided outside the fuel cell 1, and the cooling water circulates through the cooling water flow path 40 and the cooling water circulation path 41. The cooling water circulation path 41 is provided with a cooling water pump 42 that supplies cooling water to the cooling water path 40. The cooling water circulation path 41 is provided with an FC radiator 44 that performs heat exchange of the cooling water discharged from the cooling water path 40.
The fuel cell 1 generates heat as power is generated, but is cooled by exchanging heat with the cooling water flowing through the cooling water passage 40. The cooling water discharged from the fuel cell 1 is supplied to the fuel cell 1 again by the cooling water pump 42 and circulates after heat exchange with the outside air is performed by the FC radiator 44.

(Temperature sensor)
An anode gas temperature sensor (TH2STKOUT) T1 for detecting the temperature of the anode gas (anode off gas) is provided in the anode circulation path 18 near the outlet of the anode gas path 11. A cathode gas temperature sensor (TASTKOUT) T2 for detecting the temperature of the cathode gas (cathode offgas) is provided in the cathode offgas discharge pipe 9 near the outlet of the cathode gas passage 12. A cooling water temperature sensor (TWSTKOUT) T3 for detecting the temperature of the cooling water is provided in the cooling water circulation path 41 near the outlet of the cooling water flow path 40.

(Scavenging gas supply means)
The fuel cell system 100 includes scavenging gas supply means for supplying a scavenging gas to the reaction gas channel (the anode gas channel 11 and the cathode gas channel 12). Specifically, air is supplied from the air compressor 7 as a scavenging gas. In order to supply air to the anode gas passage 11, a scavenging gas introduction passage 24 is provided branched from the oxidant gas supply passage 8. The scavenging gas introduction path 24 is connected to the fuel gas supply path 17 via the scavenging gas introduction valve 23. In addition to the air compressor 7 and the scavenging gas introduction valve 23, the scavenging gas discharge valve 21a and the back pressure control valve 10 function as scavenging gas supply means.

The fuel cell system 100 includes a controller 60 that controls the operation of each unit.
The controller 60 includes an offset failure determination unit (not shown) that determines whether the cooling water temperature sensor T3 has an offset failure. The controller 60 also includes an initial value setting unit (not shown) that sets an initial temperature value based on the measured value of the coolant temperature sensor T3 when a predetermined time has elapsed since the fuel cell system was stopped. Yes. Further, the controller 60 includes a threshold setting unit (not shown) that sets a difference threshold for determining whether or not scavenging is performed based on the set initial value. The controller 60 includes a difference calculation unit (not shown) that calculates a difference between the initial temperature value and the measured value of the coolant temperature sensor T3 after the predetermined time. In addition, the controller 60 includes a scavenging execution determination unit (not shown) that determines the scavenging execution by comparing the calculated difference with the difference threshold value. Details of these will be described later.

In addition, the controller 60 includes a scavenging control unit that scavenges the reaction gas passage in a state where the power generation of the fuel cell 1 is stopped. The scavenging of the reaction gas channel is a process of discharging and removing residual water by supplying a scavenging gas (air in this embodiment) into the reaction gas channel.
FIG. 6 is a timing chart of the scavenging process. As a scavenging process, an example will be described in which scavenging of the cathode gas flow path is first performed and then scavenging of the anode gas flow path is performed. Only one of the cathode gas channel and the anode gas channel may be scavenged.

  When scavenging the cathode gas flow path 12, the controller 60 closes the scavenging gas discharge valve 21a and opens the back pressure control valve 10. The controller 60 operates the air compressor 7 to supply air as a scavenging gas. The air supplied from the air compressor 7 does not flow through the anode gas flow path 11 because the scavenging gas discharge valve 21a is closed, and flows through the cathode gas flow path 12 because the back pressure control valve 10 is opened. . This scavenging gas is discharged from the cathode offgas discharge pipe 9 together with residual water in the cathode gas flow path 12 and droplets attached to the cathode electrode.

  When scavenging the anode gas flow path 11, the controller 60 closes the back pressure control valve 10 and opens the scavenging gas introduction valve 23 and the scavenging gas discharge valve 21 a. The controller 60 operates the air compressor 7 to supply air as a scavenging gas. The air supplied from the air compressor 7 does not flow through the cathode gas flow path 12 because the back pressure control valve 10 is closed, and the anode gas because the scavenging gas introduction valve 23 and the scavenging gas discharge valve 21a are open. Flows through the flow path 11. This scavenging gas is discharged from the scavenging gas discharge pipe 22a along with residual water in the anode gas flow path 11 and droplets attached to the anode electrode.

  Note that the scavenging gas introduction valve 23 is also opened during the scavenging of the cathode gas flow path, and the pressure of the scavenging gas is applied to the anode gas flow path 11 to ensure the pressure balance on both sides of the membrane electrode structure. Thereby, deterioration of the membrane electrode structure is prevented. Further, since the anode gas passage 11 has a larger pressure loss than the cathode gas passage 12, the scavenging of the anode gas passage 11 increases the output of the air compressor 7. Along with this, the pressure in the fuel cell also increases.

(Method for determining scavenging performance)
Next, a scavenging execution determination method in the fuel cell system will be described.
FIG. 2 is a flowchart of the scavenging execution determination method for the fuel cell system according to the embodiment. The scavenging execution determination method of the present embodiment starts when the ignition switch is turned off (S8) and the fuel cell is stopped.

First, the temperature initial value A is set (S10).
FIG. 3 is a flowchart of the temperature initial value setting subroutine. In the temperature initial value setting subroutine (S10), it is first determined whether an offset failure has occurred in the coolant temperature sensor T3 (S32). The temperature sensor offset failure is a failure in which the temperature sensor always outputs a measured value deviated from a correct temperature value by a predetermined temperature. A method of determining whether or not an offset failure has occurred in the temperature sensor can be performed using a correlation map of each temperature sensor T1, T2, and T3 prepared in advance. The correlation map records the measured values of the temperature sensors T1, T2, and T3 at a plurality of time points, and grasps the correlation between the measured values. The measured values of the coolant temperature sensor T3 are predicted by applying the measured values of the anode gas temperature sensor T1 and the cathode gas temperature sensor T2 to the correlation map, and the predicted measured value and the output measured value always deviate by a predetermined temperature. If it is, it can be determined that an offset failure has occurred in the coolant temperature sensor T3.

  If the determination in S32 is No (no offset failure), the process proceeds to S34 and RTC monitoring is started. RTC (Real Time Clock) monitoring is to start a part of the system periodically (for example, every 5 minutes) and monitor the system state while the fuel cell system is stopped. In the present embodiment, after a predetermined time has elapsed since the fuel cell was stopped, the measured value of the coolant temperature sensor T3 is monitored to determine the scavenging.

Next, it is determined whether a predetermined time has elapsed since the fuel cell was stopped (S36). A method for setting the predetermined time will be described with reference to FIG.
FIG. 4A is a graph showing changes over time in measured values of the cooling water temperature sensor and the surface temperature of the fuel cell. The horizontal axis represents the time since the fuel cell stopped, and the vertical axis represents the temperature. Have taken. Since the stopped fuel cell is cooled from the surface toward the inside, immediately after the fuel cell is stopped, the temperature change becomes large due to the influence of internal heat. Since the cooling water flows out from the inside of the fuel cell, the temperature of the cooling water reflects the internal temperature of the fuel cell. Therefore, immediately after the stop of the fuel cell, the temperature change rate does not match between the measured value of the coolant temperature sensor T3 and the surface temperature of the fuel cell, and the correlation between the two cannot be obtained. However, since the temperature distribution of the fuel cell becomes smaller with the passage of time, the temperature change rate becomes equal between the measured value of the cooling water temperature sensor T3 and the surface temperature of the fuel cell, and both can be correlated. . Therefore, in the present embodiment, the time t1 from when the fuel cell is stopped until the temperature change rate becomes equal between the measured value of the coolant temperature sensor T3 and the surface temperature of the fuel cell is set to a predetermined time. . The predetermined time t1 is obtained in advance by experiments or the like.

  FIG. 4B is a graph showing the change with time of the temperature change rate of the measured value of the cooling water temperature sensor. Immediately after the stop of the fuel cell, the rate of change of the measured value of the coolant temperature sensor T3 increases, but the temperature distribution of the fuel cell decreases with time, so the change of the measured value of the coolant temperature sensor T3 decreases. The rate is small. Therefore, the time when the change rate of the measured value of the cooling water temperature sensor T3 reaches or falls below a predetermined change rate set in advance may be set as the predetermined time. Specifically, the rate of change of the measured value of the cooling water temperature sensor T3 is calculated as needed, and the time when the rate of change becomes equal to or lower than the predetermined temperature change rate Q is defined as the time when the predetermined time t1 has elapsed.

  When the determination in S36 is Yes (the predetermined time t1 has elapsed), the process proceeds to S38, and the measured value of the cooling water temperature sensor T3 is set to the temperature initial value A. Since no offset failure has occurred in the cooling water temperature sensor T3, the measured value of the cooling water temperature sensor T3 indicates the true cooling water temperature.

  On the other hand, if the determination in S32 is Yes (there is an offset failure), the process proceeds to S40, and it is determined whether the warm-up is complete when the fuel cell is stopped. If the warm-up is completed, the temperature distribution of the fuel cell is sufficiently small, and is a complete warm-up equivalent temperature (for example, 70 ° C.). Therefore, if the determination in S40 is Yes (warm-up complete state), the complete warm-up equivalent temperature is immediately set to the temperature initial value A.

  On the other hand, when the determination in S40 is No (not the warm-up completion state), the temperature distribution immediately after the fuel cell is stopped is large. Therefore, a value obtained by adding a maximum offset amount (for example, 5 ° C.) to the measured value of the coolant temperature sensor T3 (offset failure) at the time when the predetermined time t1 has elapsed since the fuel cell stopped is calculated as the temperature. Set to initial value A. The maximum offset amount is obtained in advance by experiments or the like.

Returning to FIG. 2, the difference threshold value D for determining the execution of scavenging is set (S12).
The scavenging needs to be performed before the surface temperature of the fuel cell becomes below freezing point. Therefore, it is conceivable to set the difference threshold D as the difference between the surface temperature immediately after the fuel cell is stopped and the surface temperature (about 0 ° C.) at the time of scavenging. However, in this case, it is necessary to add a temperature sensor for measuring the surface temperature of the fuel cell. By the way, as described above, after a predetermined time t1 has elapsed since the fuel cell stopped, the temperature change rate becomes equal between the measured value of the coolant temperature sensor T3 and the surface temperature of the fuel cell. There is a correlation. Therefore, the difference threshold D is set based on the measured value of the coolant temperature sensor T3. Specifically, as shown in FIG. 4, the initial temperature A of the coolant temperature sensor T3 corresponding to the surface temperature immediately after the stop of the fuel cell and the coolant temperature sensor T3 corresponding to the surface temperature at the time of scavenging are shown. A difference from a reference value P (for example, 5 ° C.) is set to a difference threshold D (D = A−P).

  FIG. 5A is a table showing the relationship between the temperature initial value and the difference threshold value. Since the reference value P of the cooling water temperature sensor T3 is constant, the temperature initial value A and the difference threshold value D have a proportional relationship. If the initial temperature value A is applied to this table, the difference threshold value D can be obtained.

  Returning to FIG. 2, RTC monitoring is started (S14). Specifically, first, the current temperature B of the cooling water is read from the measured value of the cooling water temperature sensor T3 (S16). Next, a difference C (C = AB) between the initial temperature value A and the current temperature B is calculated (S18). If the cooling water temperature sensor T3 has an offset failure, the difference C may be calculated using the measured value of the cooling water temperature sensor T3 at the time when the predetermined time t1 has elapsed as the temperature initial value A. Then, it is determined whether the difference C exceeds the difference threshold D (C> D) (S20).

FIG. 5B is a graph showing the change of the difference C with time. The difference C increases with time, and the difference C exceeds the difference threshold D at time t2.
As shown in FIG. 4A, the current temperature B, which is the measured value of the cooling water temperature sensor T3, becomes B = P at time t2. After time t2, B <P, so that difference C (C = A−B)> difference threshold D (D = A−P).

In FIG. 2, when the determination in S20 is Yes (C> D), the process proceeds to S22 and scavenging is performed. The specific scavenging method is as described above.
When scavenging is completed, the residual water in the reaction gas channel is discharged and removed, so that it is not necessary to perform scavenging again. Therefore, RTC monitoring is stopped after the scavenging of S22 is completed (S24).

As described above in detail, the controller 60 of the fuel cell system according to the present embodiment performs the initial temperature based on the measured value of the coolant temperature sensor T3 when the predetermined time t1 has elapsed since the fuel cell was stopped. A value A is set, and when the difference C between the temperature initial value A and the measured value B of the coolant temperature sensor T3 after the predetermined time t1 exceeds the difference threshold D, scavenging is performed by the scavenging means; did.
According to this configuration, the measured value of the cooling water temperature sensor T3 and the surface temperature of the fuel cell can be obtained by avoiding the time when the predetermined time t1 has elapsed after the fuel cell has stopped and the temperature change immediately after the stop is large. The correlation becomes possible. Thereby, when the difference calculated from the measured value of the coolant temperature sensor T3 exceeds the difference threshold, the surface temperature of the fuel cell becomes the scavenging temperature. Therefore, scavenging can be performed at an appropriate timing.

The difference threshold D is set based on the temperature initial value A.
When the predetermined time t1 has elapsed since the fuel cell stopped, the measured value of the coolant temperature sensor T3 and the surface temperature of the fuel cell can be correlated. Therefore, the difference threshold D to be calculated from the surface temperature of the fuel cell can be set based on the temperature initial value A calculated from the measured value of the coolant temperature sensor T3. As a result, it is not necessary to add a temperature sensor for measuring the surface temperature of the fuel cell, and an increase in manufacturing cost can be suppressed.

  The technical scope of the present invention is not limited to the above-described embodiment, and includes various modifications made to the above-described embodiment without departing from the spirit of the present invention. That is, the specific structure and shape described in the embodiment are merely examples, and can be changed as appropriate. For example, the configuration of the fuel cell system is not limited to that described above.

  In the embodiment, the temperature initial value A, the current temperature B, the difference C, and the difference threshold D are calculated based on the measured value of the cooling water temperature sensor T3. However, the measured value of the anode gas temperature sensor T1 or the cathode gas temperature sensor T2 is calculated. The initial temperature value A, the current temperature B, the difference C, and the difference threshold value D may be calculated based on the above. However, the measured value of the cooling water temperature sensor T3 is faster in temperature decrease than the measured values of the anode gas temperature sensor T1 and the cathode gas temperature sensor T2. Therefore, scavenging can be more reliably determined before the fuel cell is below freezing point.

  A ... Initial temperature value (initial value) B ... Current temperature (measured value of temperature sensor) C ... Difference D ... Difference threshold t1 ... Predetermined time T3 ... Cooling water temperature sensor (temperature sensor) 1 ... Fuel cell 7 ... Air compressor ( 10 ... Back pressure control valve (scavenging means) 11 ... Anode gas flow path (fuel flow path) 12 ... Cathode gas flow path (oxidant flow path) 15 ... Hydrogen tank (fuel supply means) 21a ... Scavenging gas discharge valve (scavenging means) 23 ... Scavenging gas introduction valve (scavenging means) 42 ... Cooling water pump (fuel cell temperature adjusting means) 60 ... Controller (control unit) 100 ... Fuel cell system

Claims (5)

A fuel cell that is supplied with fuel and an oxidant to generate electricity;
Fuel supply means for supplying the fuel to a fuel flow path of the fuel cell;
Oxidant supply means for supplying the oxidant to the oxidant flow path of the fuel cell;
Scavenging means for performing scavenging by supplying an oxidant from the oxidant supply means to at least one of the fuel flow path and the oxidant flow path when the fuel cell is stopped;
A fuel cell temperature adjusting means for supplying a refrigerant to the fuel cell and adjusting the temperature of the fuel cell by heat exchange;
In a fuel cell system comprising a control unit that controls each of the means,
A temperature sensor for measuring the temperature of at least one of the means;
The control unit sets the measured value of the temperature sensor at a time when a predetermined time has passed since the measured value of the temperature sensor and the surface temperature of the fuel cell can be correlated after the fuel cell is stopped. An initial value is set based on the scavenging means when the difference between the initial value and the measured value of the temperature sensor after the predetermined time exceeds a difference threshold value.
A fuel cell system.   The fuel cell system according to claim 1, wherein the predetermined time is set in advance according to a rate of decrease in the surface temperature of the fuel cell.   2. The fuel cell system according to claim 1, wherein the predetermined time is a time when a change rate of a measurement value of the temperature sensor reaches a preset predetermined change rate or less.   The fuel cell system according to any one of claims 1 to 3, wherein the difference threshold is set based on the initial value.   5. The fuel cell according to claim 1, wherein the temperature sensor measures the temperature of the refrigerant after heat exchange with the fuel cell in the fuel cell temperature adjusting means. system.

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