JP4753682B2 - Fuel cell system and scavenging method in the system - Google Patents

Description

  The present invention relates to a fuel cell system capable of scavenging at least one of a fuel gas channel and an oxidant gas channel with a scavenging gas such as air when power generation is stopped or after power generation is stopped, and a scavenging treatment method in the system. .

  For example, in a polymer electrolyte fuel cell, an electrolyte membrane / electrode structure in which an anode electrode (fuel electrode) and a cathode electrode (oxidant electrode) are provided on both sides of an electrolyte membrane made of a polymer ion exchange membrane, While being held by the separator, a fuel gas flow path is formed between the anode electrode and the separator, and an oxidant gas flow path is formed between the cathode electrode and the separator. This fuel cell is usually used as a fuel cell stack by laminating a predetermined number of electrolyte membrane / electrode structures and separators.

  In a fuel cell, a fuel gas, for example, a hydrogen-containing gas, supplied to an anode electrode through a fuel gas channel is hydrogen ionized on an electrode catalyst and moves to a cathode electrode through an appropriately humidified electrolyte membrane. The electrons generated during the movement are taken out to an external circuit and used as direct current electric energy. Since the oxidant gas, for example, oxygen-containing gas such as air, is supplied to the cathode electrode through the oxidant gas flow path, the hydrogen ions, electrons, and oxygen gas react with each other at the cathode electrode. Is generated. Moisture is also stored in the anode electrode due to reverse diffusion from the cathode side or high humidity of the fuel gas.

  If water is excessive in any of the electrodes, a water clogging state may occur. Therefore, in such a fuel cell system, when the fuel cell system is shut down, the cathode electrode is secured in order to ensure the next startability. In addition to the anode electrode and the cathode scavenging treatment technology, which circulates the oxidant gas not only to the anode electrode but also removes the generated water adhering to the electrolyte membrane, electrode structure and separator in the fuel cell, has been proposed. (See Patent Document 1).

Japanese Patent Laying-Open No. 2003-331893 (FIG. 4)

  By the way, in this anode / cathode both-side scavenging treatment technique, the oxidant gas flow rate is set to a large flow rate in order to remove droplets. For this reason, during the scavenging process, the drive of the air compressor that discharges oxidant gas, for example, air, is increased.

  However, in the fuel cell system, when the power generation time from the start to the stop is short, the generation of generated water due to the power generation operation may be less on the anode electrode side and more on the cathode electrode side. Even in such a case, the above-described scavenging treatment on both the anode and cathode electrodes at a large flow rate requires a large capacity air compressor, and there is a problem that there is a lot of noise to operate the large flow rate air compressor. . In addition, a large capacity air compressor is large and heavy, and further has a disadvantage that energy consumption is larger than that of a normal capacity air compressor.

  The present invention has been made in consideration of the above-described problems, and enables the use of scavenging means with low energy consumption. As a result, energy consumption when power generation is stopped is reduced, and noise is reduced. An object of the present invention is to provide a fuel cell system and a scavenging treatment method in the system.

  The present invention also enables the use of scavenging means with low energy consumption, and as a result, reduces the energy consumption when power generation is stopped, and improves the next startability, and the fuel cell system An object of the present invention is to provide a scavenging method in a system.

  In this section, for ease of understanding, an example will be described with reference to the accompanying drawings. Therefore, the contents described in this section should not be construed as being limited to those having the reference numerals.

The fuel cell system according to the present invention includes a fuel cell that generates electric power using the fuel gas supplied to the fuel gas flow channel and the oxidant gas supplied to the oxidant gas flow channel, and the fuel gas when the power generation of the fuel cell is stopped. Scavenging means (70, 36, 54) for scavenging at least one of the fuel gas flow path through which the oxidant flows or the oxidant gas flow path through which the oxidant gas circulates, and when the fuel cell is stopped, Moisture amount detection means for detecting the amount of water generated by power generation of the fuel cell in the fuel gas flow path based on a moisture state at the time of starting the fuel cell and a moisture state at the time of stopping the fuel cell (70, S5, S12, S18), and when the amount of water present in the fuel gas flow path is equal to or less than a predetermined value, the scavenging means uses the scavenging gas to liquid in the oxidant gas flow path. Remove drops A first scavenging process (S8g, S8h) for scavenging at a possible large flow rate, and a second scavenging process (S8i, S8j) for scavenging at a large flow rate capable of removing droplets in the fuel gas flow path by the scavenging gas. After the first scavenging process, a third scavenging process (S8m, S8n) is performed in which the scavenging gas scavenges the oxidant gas flow path at a smaller flow rate than the large flow rate.

  The order of the scavenging process is as follows: first scavenging process → second scavenging process → third scavenging process, first scavenging process → third scavenging process → second scavenging process, or second scavenging process → first scavenging process → first scavenging process Any order of the three scavenging processes may be used.

  According to the present invention, when the amount of water present in the fuel gas channel is equal to or less than a predetermined value when power generation is stopped, the scavenging gas scavenges at a large flow rate that can remove droplets in the oxidant gas channel. A scavenging process, a second scavenging process for scavenging at a large flow rate capable of removing droplets in the fuel gas flow path, and a small flow rate less than the large flow rate in the oxidant gas flow path after the first scavenging process. Since the third scavenging process for scavenging is performed, a large amount of scavenging gas is not simultaneously supplied to the oxidant gas flow path and the fuel gas flow path as in the prior art, so that energy consumption is small. The scavenging means can be used. As a result, the energy consumption of the scavenging means can be reduced, and further, the noise of the scavenging means can be reduced.

  Since noise can be reduced, the merchantability of the fuel cell system and the vehicle equipped with the fuel cell system can be improved. Further, since the inside of the fuel cell can be properly dried, the next good startability can be ensured. In particular, in the polymer electrolyte fuel cell, when the operation is stopped, the water content (same as the water content) of the solid polymer electrolyte membrane can be in a state where the next good startability can be secured.

  In this case, the moisture amount detection means can estimate the moisture amount more accurately by detecting the moisture amount based on the moisture state when the fuel cell is started and the moisture state when the fuel cell is stopped. .

In the scavenging method in the fuel cell system according to the present invention, when the power generation of the fuel cell that generates power using the fuel gas supplied to the fuel gas passage and the oxidant gas supplied to the oxidant gas passage is stopped, In a scavenging method in a fuel cell system in which at least one of the flowing fuel gas channel or the oxidizing gas channel in which the oxidizing gas flows is scavenged with a scavenging gas, the fuel gas is stopped when the fuel cell is stopped. Moisture amount detection step (S5,) for detecting the amount of moisture generated by power generation of the fuel cell in the flow path based on the moisture state at the time of starting the fuel cell and the moisture state at the time of stopping the fuel cell . S12, S18), and when the amount of water present in the fuel gas channel is below a predetermined value, the scavenging gas can remove droplets in the oxidant gas channel. A first scavenging process step (S8g, S8h) for scavenging at a flow rate; a second scavenging process step (S8i, S8j) for scavenging at a large flow rate capable of removing droplets in the fuel gas flow path by the scavenging gas; After the first scavenging process step, scavenging is performed by a third scavenging process step (S8m, S8n) in which the scavenging gas scavenges the oxidant gas flow path at a smaller flow rate than the large flow rate. .

  The order of the scavenging process steps is as follows: first scavenging process step → second scavenging process step → third scavenging process step, first scavenging process step → third scavenging process step → second scavenging process step, or second scavenging process Any order of step → first scavenging processing step → third scavenging processing step may be used.

  According to the present invention, when the amount of water present in the fuel gas channel is equal to or less than a predetermined value when power generation is stopped, the scavenging gas scavenges at a large flow rate that can remove droplets in the oxidant gas channel. A scavenging process step, a second scavenging process step for scavenging at a large flow rate capable of removing droplets in the fuel gas flow path, and after the first scavenging process step, the oxidant gas flow path in the oxidant gas flow path from the large flow rate. Since the third scavenging process step of scavenging with a small small flow rate is performed, a large flow rate of scavenging gas is not simultaneously supplied to the oxidant gas flow channel and the fuel gas flow channel as in the prior art. It is possible to use the scavenging means with low consumption, and as a result, the energy consumption of the scavenging means can be reduced, and furthermore, the noise of the scavenging means can be reduced.

  Since noise can be reduced, the merchantability of the fuel cell system and the vehicle equipped with the fuel cell system can be improved. Further, since the inside of the fuel cell can be properly dried, the next good startability can be ensured. In particular, in the polymer electrolyte fuel cell, when the operation is stopped, the water content (same as the water content) of the solid polymer electrolyte membrane can be in a state where the next good startability can be secured.

  In this case, in the moisture amount detection step, the moisture amount can be estimated more accurately by detecting the moisture amount based on the moisture state when the fuel cell is started and the moisture state when the fuel cell is stopped. .

  According to the present invention, in the fuel cell system, when power generation is stopped, the amount of energy consumed by the scavenging process when power generation is stopped is reduced and the noise is reduced when the amount of water in the fuel gas flow path is equal to or less than a predetermined value. be able to. Moreover, the energy consumption amount at the time of power generation stop can be reduced, and the next startability can be improved.

  According to the present invention, it is possible to use scavenging means with low energy consumption in the fuel cell system. As a result, energy consumption when power generation is stopped is reduced, noise is reduced, and the next start-up performance is improved. Can be improved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a fuel cell vehicle 12 including a fuel cell system 10 to which an embodiment of the present invention is applied.

  The fuel cell vehicle 12 is basically a fuel cell 14 and a power storage device (energy storage) that assists the output of the fuel cell 14 and is charged by the generated current If of the fuel cell 14. It is composed of a capacitor 16 such as an electric double layer capacitor, a load 18 including a driving motor for traveling, and an auxiliary machine such as an air compressor 36. Here, the power storage device can be replaced by a battery other than the capacitor 16, or both can be used.

  The fuel cell 14 has a stack structure in which a plurality of fuel cell cells configured by holding a solid polymer electrolyte membrane between an anode electrode and a cathode electrode are stacked and integrated.

  Specifically, as shown in the exploded perspective view of the fuel cell 114 of FIG. 2, each fuel cell 114 includes an electrolyte membrane (solid polymer electrolyte membrane) / electrode structure 120 and the electrolyte membrane / electrode structure. And metal separators 122 and 124 that sandwich the body 120.

  One end edge of the fuel cell 114 in the direction of arrow B communicates with each other in the direction of arrow A, which is the stacking direction, and an oxidant for supplying an oxidant gas that is one reaction gas, for example, an oxygen-containing gas The gas supply communication hole 130a, the cooling medium supply communication hole 132a for supplying the cooling medium, and the fuel gas discharge communication hole 134b for discharging the other reactive gas, for example, the hydrogen-containing gas, are indicated by an arrow C. Arranged in the direction (vertical direction).

  The other end edge of fuel cell 114 in the direction of arrow B communicates with each other in the direction of arrow A, and a fuel gas supply communication hole 134a for supplying fuel gas, and a cooling medium discharge communication for discharging the cooling medium. The holes 132b and the oxidant gas discharge communication holes 130b for discharging the oxidant gas are arranged in the direction of arrow C.

  The electrolyte membrane / electrode structure 120 includes, for example, an electrolyte membrane (solid polymer electrolyte membrane) 120b in which a perfluorosulfonic acid thin film is impregnated with water, and an anode electrode 120a and a cathode electrode 120c held between the electrolyte membranes 120b. With.

  The anode electrode 120a and the cathode electrode 120c include a gas diffusion layer made of carbon paper or the like, and an electrode catalyst layer in which a porous carbon particle having a platinum alloy supported on the surface is uniformly applied to the surface of the gas diffusion layer. Have. The electrode catalyst layer is bonded to both surfaces of the electrolyte membrane 120b.

  On the surface 122a of the separator 122 facing the electrolyte membrane / electrode structure 120, an oxidant gas flow channel (also referred to as a reaction gas flow channel) communicating with the oxidant gas supply communication hole 130a and the oxidant gas discharge communication hole 130b. ) 146 is provided. The oxidant gas flow path 146 is formed between, for example, a plurality of grooves extending in the direction of arrow B and the cathode electrode 120c.

  A fuel gas flow path (also referred to as a reaction gas flow path) 148 communicating with the fuel gas supply communication hole 134a and the fuel gas discharge communication hole 134b is formed on the surface 124a of the separator 124 facing the electrolyte membrane / electrode structure 120. It is formed. The fuel gas channel 148 is formed, for example, between a plurality of grooves that extend in the direction of arrow B and the anode electrode 120a.

  A cooling medium flow path 150 is formed between the surface 122b of the separator 122 and the surface 124b of the separator 124 to guide the cooling medium supplied from the cooling medium supply communication hole 132a to the cooling medium discharge communication hole 132b. The cooling medium flow path 150 is integrally configured to extend in the direction of arrow B by overlapping a plurality of grooves provided in the separator 122 and a plurality of grooves provided in the separator 124.

Referring again to FIG. 1, the fuel cell 14 includes a hydrogen supply port 20 for supplying a fuel gas, for example, hydrogen (H ₂ ) gas, to the fuel cell 14, and an unused hydrogen gas discharged from the fuel cell 14. A hydrogen discharge port 22 for discharging exhaust gas containing oxygen, an air supply port 24 for supplying air (air) containing an oxidant gas, for example, oxygen (O ₂ ) to the fuel cell 14, and unused oxygen And an air discharge port 26 for discharging the air containing the fuel cell 14 from the fuel cell 14.

  In addition, in the vicinity of the hydrogen discharge port 22 and the air discharge port 26, as temperature detecting means for detecting (measuring) the temperature Th of the gas in the hydrogen discharge port 22 and the temperature To of the gas in the air discharge port 26. Temperature sensors 71 and 72 are attached. In addition, a temperature sensor (not shown) for detecting (measuring) the temperature of the cooling medium is also provided near the outlet side of the cooling medium discharge communication hole 132b (FIG. 2) in the fuel cell 14, although not shown.

  A hydrogen supply channel 28 communicates with the hydrogen supply port 20. The hydrogen supply flow path 28 is provided with an ejector 48, and the ejector 48 supplies hydrogen gas supplied from a hydrogen tank 42 storing high-pressure hydrogen through a hydrogen supply valve 44 to a hydrogen supply flow path 28 and a hydrogen supply port. The exhaust gas containing unused hydrogen gas that has not been used in the fuel cell 14 is sucked from the hydrogen circulation passage 46 communicating with the hydrogen discharge port 22 and supplied to the fuel cell 14 again. .

  In the hydrogen circulation channel 46, water accumulated in the anode electrode 120a and fuel gas containing nitrogen gas that has permeated the electrolyte membrane 120b from the cathode electrode 120c and mixed into the anode electrode 120a are supplied to the hydrogen purge channel 32 and a dilution box (not shown). A hydrogen purge valve 30 for a relatively large flow rate that is appropriately opened during normal power generation operation or the like is provided in order to ensure the stability of power generation by discharging to the outside through the air, and a catch (not shown) of the hydrogen circulation channel 46 A drain valve 50 having a relatively small flow rate is provided for discharging water or the like stored in the tank together with the exhaust gas containing hydrogen gas to the atmosphere through the exhaust passage 52 and the dilution box.

  On the other hand, an air supply passage 34 is communicated with the air supply port 24, and an air compressor 36 integrated with an air compressor motor that compresses and supplies air from the atmosphere is connected to the air supply passage 34. An intercooler (I / C) 55 that cools compressed air (high-temperature dry compressed air) discharged from the air compressor 36, and a humidifier 56 that supplies moisture to the cooled air and discharges it as humidified air. The intercooler bypass valve 57 and the humidifier bypass valve 58 that bypass the intercooler 55 and the humidifier 56 are connected.

  Further, the air discharge port 26 is provided with a back pressure control valve 38 for adjusting the pressure of the air supplied from the air compressor 36 to the fuel cell 14 through the air supply flow path 34 and the air supply port 24. The 14 air discharge ports 26 communicate with the atmosphere through the air discharge flow path 40 via the back pressure control valve 38.

  Furthermore, compressed air is supplied to the hydrogen supply port 20 via the air introduction flow path 53 between the hydrogen supply flow path 28 and the air supply flow path 35 (the communication path between the humidifier 56 and the intercooler 55) of the fuel cell 14. An air introduction valve 54 that is opened during the so-called anode scavenging process is provided.

  Except for the back pressure control valve 38, the hydrogen supply valve 44, the air introduction valve 54, the hydrogen purge valve 30, the drain valve 50, the intercooler bypass valve 57, and the humidifier bypass valve 58 are ON / OFF valves.

  Further, the fuel cell system 10 and the fuel cell vehicle 12 on which the fuel cell system 10 is mounted are provided with a control device 70, and the control device 70 opens and closes the various valves of the fuel cell system 10 and the fuel cell vehicle 12. All operations are controlled, including control of the load 18, control of auxiliary equipment such as the air compressor 36, charge / discharge control of the capacitor 16, on / off control of the contactor 82 of the discharge resistor 80, and the like.

  The control device 70 is configured by a computer (ECU), and also operates as functional means for realizing various functions by executing programs stored in a memory based on various inputs. In this embodiment, the control device 70 functions as scavenging means, moisture amount detection means, capacitor remaining capacity detection (calculation) means, timing means (counter / timer), and the like.

In FIG. 1, a thick solid line indicates a power line, and a thin solid line indicates a signal line. Moreover, the double line has shown piping.

  During normal power generation operation of the fuel cell system 10, the hydrogen supply valve 44 is basically opened and the back pressure control valve 38 is opened in an appropriate amount by the valve control by the control device 70, and the hydrogen purge valve 30. The drain valve 50 is appropriately opened but is normally closed, and the air introduction valve 54, the intercooler bypass valve 57, and the humidifier bypass valve 58 are closed.

  During this normal power generation operation, the fuel gas supplied from the hydrogen tank 42 is supplied to the hydrogen supply port 20 of the fuel cell 14 through the hydrogen supply channel 28 via the ejector 48.

  The fuel gas supplied to the hydrogen supply port 20 is supplied to the anode electrode 120a along the fuel gas flow path 148 through the fuel gas supply communication hole 134a constituting each fuel cell 114, and moves along the anode electrode 120a. Exhaust gas containing unused hydrogen gas containing moisture is discharged from the hydrogen discharge port 22 through the fuel gas discharge communication hole 134 b and sent to the hydrogen circulation passage 46.

  The exhaust gas discharged into the hydrogen circulation channel 46 is returned to the hydrogen supply channel 28 under the suction action of the ejector 48 and then supplied again as fuel gas into the fuel cell 14. This fuel gas is a gas containing moisture, that is, a humidified gas.

  On the other hand, the air is supplied from the compressor 102 as compressed air in which the outside air is compressed. During normal operation, the humidified air is supplied to the air supply flow path 34 through the intercooler 55 and the humidifier 56. This air, that is, the oxidant gas, is supplied from the air supply port 24 to the cathode electrode 120c along the oxidant gas flow path 146 through the oxidant gas supply communication hole 130a constituting each fuel cell 114, and along the cathode electrode 120c. Then, the exhaust gas containing unused air is discharged from the air discharge port 26 to the air discharge passage 40 through the oxidant gas discharge communication hole 130b.

  Thereby, in each fuel cell 114, hydrogen, which is the fuel gas supplied to the anode electrode 120a, reacts with oxygen in the oxidant gas supplied to the cathode electrode 120c to generate power.

  This power generation process will be described. Hydrogen gas is hydrogen ionized at the anode electrode 120a to generate hydrogen ions and electrons. The hydrogen ions reach the cathode electrode 120c side with moisture in the electrolyte membrane 120b. The generated electrons are output as a generated current If from the anode electrode 120a through a negative terminal plate (not shown), and through an electric current / voltage sensor 60, an external load {load (electric load) 18, an auxiliary machine for the air compressor 36, etc.} And reaches the cathode electrode 120c. Then, on the cathode electrode 120c side of the electrolyte membrane 120b, oxygen combines with hydrogen ions and electrons to become water. The surplus water is stored in the oxidant gas channel 146 (droplet generation in the oxidant gas channel 146).

  Thus, in the fuel cell 114, when the hydrogen ions generated at the anode electrode 120a move through the electrolyte membrane 120b to the cathode electrode 120c, water molecules are accompanied. Therefore, in order to maintain the conductivity of hydrogen ions, the electrolyte membrane 120b is required to be in a predetermined wet state (predetermined water content) including moisture.

  When the power generation state continues for a certain time or longer, the generated water generated on the cathode electrode 120c side passes through the electrolyte membrane 120b and the anode electrode 120a and is transmitted to the fuel gas channel 148 side. (Droplet generation in the fuel gas flow path 148).

  That is, as shown in FIG. 3, when the ignition switch 76 is turned on and power generation is started in the fuel cell 14, the oxidant gas flow path 146 (cathode side) is first shown as shown in the moisture amount characteristic 311. ), And then, for example, after a predetermined power generation time at the time point ta, a droplet exceeding a predetermined value (predetermined water amount) wa becomes a fuel gas flow path 148 ( It will also occur on the anode side. During the soak (when the fuel cell system 10 in which the ignition switch 76 is off is stopped and left), the moisture gradually decreases.

  During a normal power generation operation in which the fuel cell 14 generates power using both supplied reaction gases, the generated current If extracted from the fuel cell 14 is supplied to the load 18 and the air compressor 36 via the current / voltage sensor 60 of the fuel cell 14. Is supplied to the capacitor 16 via the current / voltage sensor 62 of the capacitor 16 and the capacitor 16 is charged. The integrated power generation amount of the fuel cell 14 is calculated and managed by the control device 70 based on the output of the current / voltage sensor 60, and the remaining capacity of the capacitor 16 is stored in the memory based on the output of the current / voltage sensor 62. Is done.

  The capacitor 16 is charged with the generated current If of the fuel cell 14 under the control of the control device 70. The power stored in the capacitor 16 is mainly supplied to the load 18 and the air compressor 36 when the power generation of the fuel cell 14 is stopped. When the driving force is transmitted from the driving wheel to the driving motor as the load 18 when the fuel cell vehicle 12 is decelerated, the driving motor functions as a generator and generates a so-called regenerative braking force. Thereby, the kinetic energy of the vehicle body can be recovered as electric energy, and the electric energy is regenerated (accumulated) from the load 18 side to the capacitor 16.

  During the normal power generation operation, in the fuel cell vehicle 12 equipped with the fuel cell system 10, the control device 70 calculates the required power from the accelerator pedal depression amount Ap, the vehicle speed Vs, and the like, and the fuel is calculated based on the calculated required power. Various controls such as sending control signals to the battery 14, the load 18, the air compressor 36, the back pressure control valve 38, and the like are performed. Further, the control device 70 includes a current / voltage sensor 60, 62, an outside air temperature sensor 74, and a temperature sensor 71, 72, respectively, in order to reliably execute the low temperature start control such as the load 18 control and the below freezing point start control. , Generated current If, generated voltage (terminal voltage for each fuel cell 114) Vf, current flowing into the capacitor 16, voltage Vc of the capacitor 16, outside temperature Ta, gas temperature Th in the hydrogen discharge port 22, and in the air discharge port 26 Each signal of the gas temperature To is taken in. The generated voltage Vf is a terminal voltage for each fuel cell 114, but in the following description, an average voltage and a total voltage can be used as appropriate for the generated voltage Vf.

  Further, the control device 70 includes an on signal (a signal for turning the fuel cell system 10 from an off state) that is a start signal (start signal) of the fuel cell vehicle 12 and the fuel cell system 10 and an off signal that is a stop signal. An ignition switch (IG switch) 76 for outputting (a signal for turning the fuel cell system 10 from an on state to an off state) is connected.

  Basically, the operation related to the scavenging process of the fuel cell system 10 configured and operated as described above and the fuel cell vehicle 12 equipped with the fuel cell system 10 will be described based on the flowchart of FIG.

  In step S1, when the control device 70 detects an ON signal of the ignition switch 76, which is an activation signal of the fuel cell system 10 (fuel cell vehicle 12), power generation of the fuel cell 14 is started in step S2.

  During power generation, in step S3, it is detected whether or not the ignition switch 76 has output an off signal.

  When the off signal is detected, in the next step S4, the temperature is detected by the temperature detecting means for detecting the temperature of the fuel cell 14, in this embodiment, the temperature sensor 71 attached to the hydrogen discharge port 22. ) Detect Th. This temperature Th is a temperature when the fuel cell 14 is stopped, and is assumed to be Te (Th = Te). As a sensor for detecting the temperature of the fuel cell 14, a temperature sensor (not shown) attached to the hydrogen supply port 20 is used instead of the temperature sensor 71 provided at the hydrogen discharge port 22, and the temperature of the cooling medium is detected. A temperature sensor (not shown) or a temperature sensor 72 provided at the air outlet 26 can be used.

  Next, in step S5, a moisture content (water content) determination process in the fuel gas channel at the time of stop is performed.

  The determination of the moisture amount can be performed using, for example, a change in the weight of the fuel cell 14 or a power generation characteristic (power generation map) that is a relationship between the power generation current If and the power generation voltage Vf in FIG. Here, the determination is made from the power generation characteristics (current / voltage characteristics) 300 when the temperature Th of the fuel cell 14 shown in FIG. 5 is Th = 25 [° C.]. Note that power generation characteristics at each temperature are stored in advance in the memory.

  As can be seen from the power generation characteristic 300 of FIG. 5, when the generated current If increases, the voltage drop of the generated voltage Vf increases. However, when the moisture content of the electrolyte membrane 120b decreases, the generated voltage Vf increases with respect to the increased amount of the generated current If. The amount of decrease increases. A characteristic 301 is a power generation characteristic when the amount of moisture is optimal, and the amount of decrease in the generated voltage Vf with respect to the increase in the generated current If is the smallest. A characteristic 304 is a power generation characteristic when the moisture amount is the lowest. A characteristic 305 indicates a power generation characteristic of a predetermined value (threshold value) with respect to the moisture content. That is, there is relatively much moisture on the upper side than the characteristic 305, and relatively little moisture on the lower side.

  Thus, in the fuel gas flow passage water content determination process in step S5, in other words, from the detected temperature Th (Th = Te) of the fuel cell 14 immediately before the system is stopped when the ignition switch 76 is turned off. A power generation characteristic 300 at a temperature Th = Te (here, Te = 25 [° C.]) is selected, and a normal scavenging process region (described later) in which the current water content is determined to be relatively large. The amount of water in the three-stage scavenging treatment region (region where the three-stage scavenging processing described later) 303 is determined as to whether or not the amount of water in the normal region (region requiring the scavenging treatment) 302 is relatively small. In order to determine whether or not the current value is, the current generated current If and the generated voltage Vf (when the ignition switch 76 is off) are plotted.

  Next, in step S6, if the plotted point is in the three-stage scavenging treatment region 303, which is a region below the predetermined value represented by the characteristic 305 (a region where the absolute water content is determined to be small), step S8 is performed. In the normal scavenging process area 302 that is an area exceeding the predetermined value represented by the characteristic 305 (area where the absolute water content is determined to be normal), the normal scavenging process in step S7 is performed. I do.

  Next, the significance and processing contents of the normal scavenging process in step S7 and the three-stage scavenging process in step S8 will be described.

  First, the operation of the normal scavenging process in step S7 will be described with reference to the flowchart of FIG.

  In this case, in step S7a, the hydrogen supply valve 44 is closed (shut off) by the control device 70, and the supply of fuel gas to the fuel cell 14 is stopped.

  Next, in step S7b, the intercooler bypass valve 57 and the humidifier bypass valve 58 are opened, and the amount of air discharged from the air compressor 36 is further increased so that a large amount of dry air flows into the fuel cell 14 from the air supply port 24. To be introduced.

  The generated water (droplets) in the oxidant gas flow path 146 in the fuel cell 14 is caused to flow through the air discharge port 26, the back pressure control valve 38, and the air discharge flow path 40 by the introduced large amount of dry air. By discharging the air together with scavenging air, the scavenging process on the cathode side is started.

  Next, discharge control is started in step S7c. The discharge control is a process performed for the purpose of, for example, consuming fuel gas remaining in the fuel gas flow path 148 of the fuel cell 14 in a short time. In this case, the contactor 82 is closed and the generated current If is reduced. Part is consumed by the discharge resistor 80. In the discharge control, the generated current If is also used to drive the air compressor 36.

  Next, when the cathode-side scavenging process is completed after the elapse of a predetermined time in step S7d, the operation of the air compressor 36 is stopped in step S7e, whereby the supply of air to the fuel cell 14 is stopped. At this time, the back pressure control valve 38 is fully opened, and the oxidant gas flow path 146 is opened to the outside air.

  Next, in step S7f, it is determined whether or not the generated voltage Vf of the fuel cell 14 has become a value equal to or lower than a predetermined voltage. When the generated voltage Vf becomes equal to or lower than the predetermined voltage, the contactor 82 is opened in step S7g, and discharge control is performed. Is terminated.

  Next, in step S7h, the control device 70 itself, that is, the ECU enters the sleep state, and the fuel cell system 10 enters the system stop state.

  As described above, in the normal scavenging process, the fuel cell system 10 is brought into the system stop state in a short time after the OFF state of the ignition switch 76 is detected in step S3. There is no sense of incongruity.

  Next, during the soaking of the fuel cell system 10, the controller 70 wakes up at predetermined time intervals determined in advance according to the system temperature (the temperature Th of the fuel cell 14) in steps S7i, S7j, and S7k. Thus, the temperature Th of the fuel cell 14 is detected, and it is determined whether the detected temperature Th is equal to or lower than a predetermined temperature Td, for example, Td = 5 [° C.] (Th ≦ Td). As a result, the outside temperature Ta is low. It is determined whether or not it has become.

  If the determination in step S7k is affirmative, it is determined that the outside air temperature Ta may become a low temperature such as below freezing point, and in order to avoid freezing of the droplets in the fuel gas flow path 148 in the fuel cell 14. In step S 7 l, the air compressor 36 is driven by the electric power of the capacitor 16, the air introduction valve 54 is opened, and the high-temperature compressed air discharged from the air compressor 36 is passed through the intercooler bypass valve 57, the air introduction passage 53, and the air introduction valve 54. Then, scavenging by the air on the anode side is started by introducing the fuel gas channel 148 and the oxidant gas channel 146 of the fuel cell 14 from both the hydrogen supply port 20 and the air supply port 24.

  The air flowing through the fuel gas flow path 148 in the fuel cell 14 is discharged from the hydrogen discharge port 22, and at the beginning of the anode-side air scavenging process, the air is diluted through the small flow rate drain valve 50 and the discharge flow path 52. It is discharged together with the fuel gas and the generated water (droplets), and after a predetermined time, it is discharged together with the generated water (droplets) through the hydrogen purge valve 30 and the hydrogen purge flow path 32 with a large flow rate. In this way, the anode-side scavenging process is performed.

  In step S7m, after the anode side scavenging process is performed for a predetermined time, the air compressor 36 is stopped in step S7n, and all the remaining valves are closed to stop the anode side scavenging process (anode scavenging process). Thus, the normal scavenging process ends, and the system of the fuel cell system 10 is stopped in step S9 (FIG.).

  As described above, when the outside air temperature Ta decreases, the inside of the fuel gas passage 148 is automatically scavenged to ensure stable and reliable start-up at a low temperature such as the next freezing point.

  Next, the operation of the three-stage scavenging process in step S8 will be described with reference to the flowchart in FIG. 7 and the time chart in FIG.

  In this case, when the OFF state of the ignition switch 76 is detected at time t10 in order to ensure the current system stop control and the reliable start-up at a low temperature such as the next freezing point, first, in step S8a, first, the generated current If Thus, the capacitor 16 is charged to a predetermined capacity (time t10 to t11).

  After the charging is completed, in step S8b, the hydrogen supply valve 44 is closed and the supply of fuel gas to the fuel cell 14 is stopped. Even if the hydrogen supply valve 44 is closed, the fuel gas remains in the fuel gas flow path 148. In order to consume this residual gas, the supply of air is continued in step S8c.

  Therefore, in step S8d, the generated current If is supplied to an auxiliary machine such as the air compressor 36 to generate power and consume the fuel gas (time points t11 to t12). As the fuel gas is consumed, the gas pressure in the fuel gas flow path 148 gradually decreases (time points t11 to t12).

  Next, in step S8e, in order to satisfy the dilution requirement for the fuel gas discharged from the fuel cell system 10 to the outside, the drain valve 50 having a relatively small flow rate is opened and the air introduction valve 54 is opened (time t12). .

  Next, in steps S8f, 8g, and 8h, a process for discharging the droplets in the oxidant gas flow path 146 is performed (time points t12 to t13). At this time, in step S8f, the contactor 82 is closed, and discharge control is started to cause the discharge resistor 80 to consume the generated current If (time t12). At this time t12, the fuel gas flow rate in the fuel gas flow path 148 becomes almost zero.

  Next, in step S18g, the amount of air discharged from the air compressor 36 is set to a large flow rate (time point t12), and the large amount of air is supplied for a predetermined time in step S18h (time point t12 to t13). The liquid droplets remaining in the oxidant gas flow path 146 are discharged (removed) by flowing through 146. Note that the time required for removing the droplets in the oxidant gas flow path 146 from time t11 to t13 is about 20 [sec].

  In addition, since the air introduction valve 54 is opened at time t12, air is also introduced into the fuel gas flow path 148 after this time t12, but the high-volume hydrogen purge valve 30 is closed and the low-flow-rate hydrogen flow valve 148 is closed. Since the drain valve 50 is opened, only a small flow rate of air is introduced into the fuel gas flow path 148. At this time t12 to t13, the fuel gas discharged from the drain valve 50 through the discharge flow path 52 is diluted with the large amount of oxidant gas discharged from the air discharge flow path 40 to the outside air through the dilution box. Fuel gas is discharged.

  In this way, the droplet is discharged (removed) from the fuel gas channel 148 from the time t13 when the droplet is discharged from the oxidant gas channel 146 and the fuel gas is diluted and discharged.

  In this case, by opening the hydrogen purge valve 30 with a large flow rate in step S8i (time point t13), a predetermined time (time points t13 to t14) is set in step S8i in the fuel gas flow path 148 where the diluted fuel gas remains. A large flow of air is circulated, and droplets in the fuel gas flow path 148 are discharged (removed). In step S8k, the air introduction valve 54 is closed.

  Here, as shown at time t12-14, the oxidant gas flow path 146 and the fuel gas flow path are divided in time so that the flow rate in the oxidant gas flow path 146 and the flow rate in the fuel gas flow path 148 do not increase simultaneously. Since the droplets in 148 are removed, the driving of the air compressor 36 can be suppressed and noise can be reduced. As a result, it is possible to use an air compressor 36 that is smaller, lighter and has a smaller capacity than the conventional technology. In addition, the small, light and small capacity air compressor 36 can reduce the energy consumption because the motor and fan can be made smaller and lighter than a large air compressor. Further, the small, light, and small capacity air compressor 36 can reduce noise, so that the commerciality of the fuel cell system 10 and the fuel cell vehicle 12 can be improved.

  Next, in steps S81 to S8o, drying on the cathode electrode 120c side of the fuel cell 14 is promoted, and processing for ensuring start-up at a low temperature such as the next freezing point is performed (time t14 to t15).

  At this time, in step S81, the humidifier bypass valve 58 and the intercooler bypass valve 57 are opened (time t13), and in step S18m, the drive of the air compressor 36 is reduced to set a small flow rate air amount. Is supplied into the oxidant gas flow path 146 (time t14). The process of opening the bypass valves 57 and 58 in step S81 may be performed at the start of the large flow scavenging process in step S8g (time point t12).

  In step S8n, the low temperature dry air is circulated in the oxidant gas flow path 146 for a predetermined time, thereby ensuring the next low temperature start (time t14 to t15). This predetermined time is a predetermined time until the water content of the electrolyte membrane 120b becomes the optimum amount determined from the next start-up property.

  Specifically, as shown in FIG. 9, between the next startability (maximum possible output after power generation becomes possible) and the water content of the electrolyte membrane 120b, the water content is not high but low. Since it is known that there is a relationship (characteristic 84) in which the startability becomes high (maximum possible output becomes high) in the intermediate state, a small flow rate until the next startability becomes a predetermined value or more on the characteristic 84 The supply time of the dry air is set to the predetermined time in step S8n.

  The process of step S8n can be determined as a substitute based on whether or not the remaining capacity of the capacitor 16 has decreased to a capacity required for starting at a low temperature such as the next freezing point.

  In addition, although the discharge control started in step S8f is not shown in the flowchart, the time t14 when the gas pressure in the fuel gas flow path 148 falls below a predetermined value or the generated voltage Vf of the fuel cell 14 falls below the predetermined value. When lowered, the contactor 82 is opened and the discharge control process is terminated.

  Next, in step S8o, the driving of the air compressor 36 is stopped, the bypass valves 57 and 58 are closed, and the three-stage scavenging process is completed.

  In this way, during the current operation of the ignition switch 76 in step S3, both the oxidizing gas channel 146 on the cathode electrode 120c side and the fuel gas channel 148 on the anode electrode 120a side are provided. By performing the three-stage scavenging process when it is determined that water has been generated, stable startability can be ensured at the next low temperature such as below the freezing point.

  In the above-described three-stage scavenging process, the cathode side large flow rate first scavenging process (time points t12 to t13: steps S8g and S8h), the anode side large flow rate second scavenging process (time points t13 to t14: steps S8i and S8j), The cathode side small flow rate third scavenging process (time points t14 to t15: S8m, S8n) is performed in this order. Instead, as shown in the time chart of FIG. 10, the cathode side large flow rate first scavenging process is performed. (Time t12 to t13), cathode side small flow rate third scavenging process (time point t13 to t14a), anode side large flow rate second scavenging process (time point t13a to t15) may be performed in this order.

  Alternatively, as shown in the time chart of FIG. 11, the anode side high flow rate second scavenging process (time t12 to t13), the cathode side high flow rate second scavenging process (time point t13 to t14), and the cathode side small flow rate third scavenging process. You may make it carry out in order of (time t14-t15).

  The first scavenging process and the second scavenging process have substantially the same time, and the third scavenging process time is longer than the first scavenging process and the second scavenging process time.

  FIG. 12 shows a configuration of a fuel cell vehicle 12A equipped with a fuel cell system 10A according to another embodiment.

  In this fuel cell system 10A, a flow rate sensor (flow rate detection means) 90 for measuring a volume flow rate in order to measure the amount of hydrogen consumption provided in the hydrogen supply channel with respect to the fuel cell system 10 shown in FIG. , A flow rate sensor (flow rate detection means) 91 for measuring a volume flow rate provided in the air discharge flow path 40 for measuring the integrated air flow rate, and a humidity sensor (humidity) for measuring the relative humidity RH of the air discharge flow path 40 This is different in that a detection means) 92 and a wind speed sensor (wind speed detection means) 93 for measuring the wind speed are additionally provided. The flow sensors 90 and 91 and the humidity sensor 92 are connected to the control device 70, respectively.

  In this case, the control device 70 integrates the amount of power generation from the time when the ignition switch 76 is turned on to the time when the ignition switch 76 is turned off, more specifically, from the time when the power generation is started until the time when the power generation ends (based on the time measured by the current / voltage sensor 60 and the timer). And each of the oxidant gas flow passage integrated flow rate (based on the flow rate sensor 91 and timer) and the hydrogen consumption (based on the flow rate sensor 90 and timer) are calculated (detected), and functions as each means. .

  Next, operations related to the scavenging process of the fuel cell system 10A of FIG. 12 and the fuel cell vehicle 12A equipped with the fuel cell system 10A will be described based on the flowchart of FIG.

  In step S11, when the control device 70 detects an ON signal of the ignition switch 76, in steps S12 and S13, prior to the start of power generation, a moisture state determination process for determining whether the moisture content on the anode side before startup is relatively large or small. Is done.

  Here, it is determined that the moisture content is low. (1) When the soak period from when the previous ignition switch 76 is turned off to when the ignition switch 76 is turned on is long and dry, (2) the ignition switch When the anti-freezing start countermeasure process such as a three-stage scavenging process for preventing freezing is performed the previous time before turning on 76, (3) the humidity of the outside air in the soak is low and the wind speed detected by the wind speed sensor 93 is large. This is a case where drying is promoted even in a short soak period. In these cases, it is determined that the amount of moisture on the anode side is small, and in other cases, it is determined that the amount of moisture on the anode side is large.

  If it is determined that the amount of moisture on the anode side is large, then power generation is started in step S14, and it is detected whether the ignition switch 76 has output an off signal in step S15 during power generation. .

  When the off signal is detected, the normal scavenging process in step S7 described above is performed.

  On the other hand, if it is determined in step S13 that the amount of moisture is small, then power generation is started in step S16, and whether or not the ignition switch 76 outputs an off signal in step S17 during power generation. Detected.

  When the off signal is detected, in steps S18 and S19, further determination processing of the moisture state on the anode side by the current power generation is performed.

  Here, the determination that the water content is low is determined when (a) the integrated power generation amount is equal to or less than a predetermined value from the start of power generation to the end of power generation, and (b) oxidant gas oxidant gas flow When the road passage integrated flow rate is equal to or less than a predetermined value, (c) the case where the hydrogen consumption is equal to or less than the predetermined value is applicable.

  Also, the determination that the moisture is low is (d) when the difference in the temperature Th between the ON state (S11) and the OFF state (S17) of the ignition switch 76 is equal to or less than a predetermined value. (E) The ignition switch When the temperature Th (Th = Te) when 76 is off (S17) is equal to or lower than a predetermined value, (f) the temperature Th when the ignition switch 76 is on (S11) is equal to the predetermined temperature Ta (Ta is 0 [° C.], for example) ) And the case where the temperature Th when the ignition switch 76 is off (S17) is equal to or lower than a predetermined temperature Tb (Ta <Tb, Tb is, for example, 10 [° C.]).

  Furthermore, the determination that the moisture content is low corresponds to the case where (g) the integrated power generation amount from the start of power generation to the end of power generation is equal to or less than a predetermined value.

  In step S19, when it is determined that the amount of moisture on the anode side from the start of power generation to the end of power generation is less than a predetermined value, the three-stage scavenging process of step S8 described above is performed, and the above (a) to ( When the requirement of g) is not met, it is determined that the amount of water exceeds a predetermined value, and the normal scavenging process in step S7 is performed.

  After the normal scavenging process in step S7 or the three-stage scavenging process in step S8, the system termination process in step S9 is performed.

  The determination process of the anode-side moisture state after power generation in steps S18 and S19 described above, in other words, the determination process for determining the three-stage scavenging process or the normal scavenging process may be determined by searching a map (lookup table). it can.

  FIG. 14 shows a scavenging process determination map 200 to be searched. In the scavenging process determination map 200, the scavenging process is determined using the power generation start temperature Ts and the power generation stop temperature Te as coordinate points.

  Basically, the normal scavenging process region 201 is determined in the region where the power generation start temperature Ts and the power generation end temperature Te are relatively high, and the power generation end temperature Te is low in the three-stage scavenging process region 203. It is determined.

  As described above, according to the above-described embodiment, at least the fuel gas flow path 148 through which the fuel gas flows or the oxidant gas flow path 146 through which the oxidant gas circulates when the power generation of the fuel cell 14 is stopped or after the power generation is stopped. The fuel cell system 10 including scavenging means (70, 36, 54) for scavenging one side with scavenging gas, in this embodiment with air, is the target.

  Then, when the fuel cell system 10 in which the ignition switch 76 is switched from the on state to the off state is stopped, the amount of water present in the fuel gas flow path 148 detected by the water amount detecting means (70, S5, S12, S18) is When the value is equal to or less than a predetermined value, the scavenging means scavenges the droplets in the oxidant gas channel 146 with a large flow rate of air and the droplets in the fuel gas channel 148 at a high flow rate. The second scavenging process step of scavenging with air and the third scavenging process step of scavenging the oxidant gas flow path 146 with a small flow rate of air are performed in the predetermined order (cathode side large flow rate first scavenging process → anode side large amount). Flow order second scavenging process → cathode side small flow rate third scavenging process, cathode side high flow rate first scavenging process → cathode side small flow rate third scavenging process → anode side large flow rate second scavenging process, So that the anode side carried out at a high flow rate the second scavenging process → cathode high flow second scavenging process → cathode side small flow third scavenging process → order), the so-called three-stage scavenging process.

  Here, the first and second scavenging treatment steps are for a relatively short time because they are for removing droplets, and the third scavenging treatment step is for a relatively long time because they are for drying the electrolyte membrane 120b. Is done.

  As described above, when the power generation of the fuel cell system 10 is stopped, the first scavenging process step and the second scavenging process step for scavenging with a large flow of air are not performed at the same time, so the air compressor 36 with low power consumption and low noise is used. be able to.

  In addition, since the moisture content of the electrolyte membrane 120b when power generation is stopped can be set to an optimum value or a value close to the optimum value, the next startability can be improved.

1 is a schematic configuration diagram of a fuel cell vehicle equipped with a fuel cell system according to an embodiment of the present invention. It is a disassembled perspective view of the fuel battery cell laminated | stacked on a fuel cell as a stack. It is a characteristic view of the water content example of the fuel cell during soak and during power generation. It is a flowchart with which operation | movement description of a scavenging process is provided. It is a power generation characteristic figure used for moisture content determination. It is a flowchart which concerns on normal scavenging processing. It is a flowchart which concerns on a three-stage scavenging process. It is a time chart which concerns on a three-stage scavenging process. It is a characteristic view which shows the relationship between moisture content and next startability. 6 is a time chart according to another example of the three-stage scavenging process. 12 is a time chart according to still another example of the three-stage scavenging process. It is a schematic block diagram of the fuel cell vehicle carrying the fuel cell system which concerns on other embodiment. It is a flowchart with which operation | movement description of the scavenging process which concerns on other embodiment is provided. It is explanatory drawing of a scavenging process determination map.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 10A ... Fuel cell system 12, 12A ... Fuel cell vehicle 14 ... Fuel cell 16 ... Capacitor 18 ... Load 36 ... Air compressor 54 ... Air introduction valve 70 ... Control device 71 ... Temperature sensor 76 ... Ignition switch

Claims (2)

A fuel cell that generates power using a fuel gas supplied to the fuel gas flow path and an oxidant gas supplied to the oxidant gas flow path;
Scavenging means for scavenging at least one of the fuel gas flow path through which the fuel gas flows or the oxidant gas flow path through which the oxidant gas flows when the fuel cell stops power generation;
When the fuel cell is stopped, the amount of water generated by power generation of the fuel cell in the fuel gas flow path is based on the moisture state when the fuel cell is started and the moisture state when the fuel cell is stopped. and a water amount detecting means for detecting Te,
The scavenging means is configured such that when the amount of water present in the fuel gas flow path is a predetermined value or less,
A first scavenging process for scavenging at a large flow rate capable of removing droplets in the oxidant gas flow path by the scavenging gas;
A second scavenging process for scavenging at a large flow rate capable of removing droplets in the fuel gas flow path by the scavenging gas;
After the first scavenging process, a third scavenging process for scavenging the oxidant gas flow path with the scavenging gas at a smaller flow rate than the large flow rate;
The fuel cell system characterized by performing. The fuel gas channel through which the fuel gas flows or the oxidant gas when the power generation of the fuel cell that generates power by the fuel gas supplied to the fuel gas channel and the oxidant gas supplied to the oxidant gas channel is stopped In a scavenging treatment method in a fuel cell system for scavenging at least one of the oxidant gas flow channels through which the gas flows with scavenging gas
When the fuel cell is stopped, the amount of water generated by power generation of the fuel cell in the fuel gas flow path is based on the moisture state when the fuel cell is started and the moisture state when the fuel cell is stopped. and water amount detection step of detecting Te,
A first scavenging process step of scavenging at a large flow rate capable of removing droplets in the oxidant gas flow path by the scavenging gas when the amount of water present in the fuel gas flow path is a predetermined value or less;
A second scavenging treatment step of scavenging at a large flow rate capable of removing droplets in the fuel gas flow path with the scavenging gas;
After the first scavenging process step, scavenging is performed in a third scavenging process step in which the scavenging gas scavenges the oxidant gas flow path at a smaller flow rate than the large flow rate. Processing method.

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