JP2007288850A - Fuel cell vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell vehicle that can execute deciding of inhibiting idle stop with high precision. <P>SOLUTION: A decision for inhibiting idle stop is made by estimating the amount of nitrogen and water produced as impurities in the fuel gas flow channel. The amount of nitrogen in the fuel gas flow channel is calculated from the amount of nitrogen, transmitted from a cathode 13 to an anode 12 via an electrolyte film 11. When purging or draining is to be performed, the amount of nitrogen discharged by purging or draining is excluded from the amount of nitrogen transmitted. The amount of water produced in the fuel gas flow channel is estimated, by extracting current from a fuel cell 10 by discharge at idle stop, and extracting the current generated from the fuel cell 10 in case of normal power generation. When purging or draining is to be performed during normal power generation and water is discharged, the amount of water discharged is excluded from the amount of water produced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell vehicle having an idle stop function.

In automobiles that use gasoline or light oil as fuel, the engine is stopped when the vehicle is stopped to reduce emissions of substances that cause global warming, such as carbon dioxide, and air pollutants, and to prevent waste of noise and energy. It is recommended to perform idling stop (idling stop) to stop. Therefore, various technologies having an idle stop function have been proposed for fuel cell vehicles, for example, a technology for performing an idle stop when a required power generation amount for a fuel cell becomes a predetermined value or less. . However, in consideration of return from idle stop, it may be preferable not to execute idle stop. For this reason, there has been proposed a technique for prohibiting idling stop even when the required power generation amount is a predetermined value or less (see, for example, Patent Document 1).
Japanese Patent Laying-Open No. 2004-173450 (FIG. 3)

  However, in the conventional fuel cell vehicle, there is a case in which the shift to the idle stop is performed immediately before the prohibition of the idle stop is executed. In such a case, there is a problem that the power generation stability at the time of the idle stop return is impaired. .

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a fuel cell vehicle capable of executing an idle stop prohibition determination with high accuracy.

  According to a first aspect of the present invention, there is provided a fuel cell in which fuel gas and oxidant gas are supplied across a membrane electrode assembly to generate power, a fuel gas flow passage through which the fuel gas flows, and the oxidant gas. An oxidant gas flow path that circulates, a low-load stop means that stops power generation of the fuel cell when the required power generation amount of the fuel cell is a predetermined value or less, and an impurity that estimates the amount of impurities in the fuel gas flow path The low load when the amount estimating means, the impurity discharging means for discharging impurities in the fuel gas flow passage, and the amount of impurities in the fuel gas flow passage are equal to or greater than a predetermined value for reducing the power generation performance of the fuel cell. Low-load stop prohibiting means for prohibiting a low-load stop by the stop means.

  According to the first aspect of the present invention, since prohibition of low load stop (idle stop) is determined according to the amount of impurities present in the fuel gas flow passage, impurities can be reliably discharged before low load stop. This makes it possible to improve power generation stability when returning from a low load stop.

  According to a second aspect of the present invention, the impurity amount estimating means includes a partial pressure difference between the nitrogen partial pressure in the oxidant gas flow passage and the nitrogen partial pressure in the fuel gas flow passage, and the inclusion of the membrane electrode assembly. The nitrogen amount in the fuel gas flow passage is estimated based on a nitrogen permeation coefficient obtained from the relationship between the amount of water and temperature.

  According to the invention of claim 2, the amount of nitrogen as an impurity in the fuel gas flow passage can be detected with high accuracy.

  According to a third aspect of the present invention, the impurity amount estimating means uses the impurity discharge means based on the nitrogen amount in the fuel gas flow passage when the nitrogen in the fuel gas flow passage is discharged by the impurity discharge means. It is characterized by excluding nitrogen emissions.

  According to the third aspect of the invention, the amount of nitrogen as an impurity in the fuel gas flow passage can be detected with higher accuracy by considering the amount of nitrogen discharged from the fuel gas flow passage.

  The invention according to claim 4 is characterized in that the impurity amount estimating means estimates a moisture amount in the fuel gas flow passage based on a current value taken out from the fuel cell.

  According to the fourth aspect of the present invention, water is generated by taking out current from the fuel cell. By taking this moisture amount into consideration, the moisture amount as an impurity in the fuel gas flow passage can be accurately determined. Can be detected.

  According to the fuel cell system of the present invention, the idling stop prohibition determination can be executed with high accuracy.

  FIG. 1 is an overall configuration diagram showing a fuel cell system mounted on a fuel cell vehicle according to the present embodiment, FIG. 2 is a main flowchart for determining whether to stop idling, FIG. 3 is a sub-flowchart for calculating a nitrogen permeation amount, and FIG. 4 is a graph showing the relationship between the nitrogen partial pressure of the anode and the elapsed time, FIG. 5 is a sub-flowchart for calculating the nitrogen discharge amount, and FIG. 6A is a map showing the relationship between the temperature of the MEA and the nitrogen permeability coefficient. , (B) is a map showing the relationship between the gas temperature and the water content of the MEA, (c) is a map showing the relationship between the anode pressure and the nitrogen discharge amount, and FIG. 7 is a sub-flowchart for calculating the water content. 8 (a) is a map showing the relationship between the discharge current and the water generation amount, (b) is a map showing the relationship between the generated current and the water discharge amount, and FIG. 9 is a sub-flowchart showing the idling stop prohibition determination. Yes, (a) shows the case which is based on nitrogen emissions, a case based on (b) the water content.

  As shown in FIG. 1, the fuel cell vehicle V of the present embodiment includes a fuel cell 10, an anode system 20, a cathode system 30, a cooling system 40, a high voltage system 50, a control unit 60, and the like. System 1 is provided.

  The fuel cell 10 is provided with an anode (hydrogen electrode) 12 containing a catalyst on one side of a solid polymer electrolyte membrane (hereinafter abbreviated as electrolyte membrane) 11 and a cathode (air electrode) 13 containing a catalyst on the other side. And a single cell composed of a pair of conductive separators 14 and 15 provided on both sides of the MEA and the membrane electrode assembly (hereinafter abbreviated as MEA (Membrane Electrode Assembly)). . A plurality of the single cells are laminated in the thickness direction to constitute a fuel cell (also referred to as a fuel cell stack) 10. In addition, an anode flow path 14a through which hydrogen as a fuel gas flows is formed in the separator 14 facing the anode 12, and air (oxygen) as an oxidant gas flows through the separator 15 facing the cathode 13. A cathode channel 15a is formed. Further, the fuel cell 10 is formed with a cooling channel 16a through which a coolant for cooling the fuel cell 10 flows so as not to mix with the hydrogen and air.

  The anode system 20 supplies and discharges hydrogen to and from the anode 12 of the fuel cell 10, and includes a hydrogen supply pipe 21a, a hydrogen discharge pipe 21b, a hydrogen circulation pipe 21c, a drain pipe 21d, a high-pressure hydrogen tank 22, and a shutoff. A valve 23, an ejector 24, a purge valve 25, a steam separator 26, a drain valve 27, a pressure sensor 28, a temperature sensor 29, and the like are provided.

  One end of the hydrogen supply pipe 21 a is connected to the high-pressure hydrogen tank 22, and the other end is connected to the inlet of the anode flow path 14 a of the fuel cell 10 via the shut-off valve 23 and the ejector 24. One end of the hydrogen discharge pipe 21 b is connected to the outlet of the anode flow path 14 a of the fuel cell 10, and the other end is connected to the purge valve 25. One end of the hydrogen circulation pipe 21 c is connected to a steam / water separator 26 described later, and the other end is connected to the ejector 24. One end of the drain pipe 21 d is connected to the steam separator 26, and the other end is connected to the drain valve 27.

  The high-pressure hydrogen tank 22 is a container filled with high-purity hydrogen at a very high pressure.

  The shut-off valve 23 is provided in the vicinity of the high-pressure hydrogen tank 22, and hydrogen is supplied to the anode 12 of the fuel cell 10 by opening the valve.

  The ejector 24 uses the flow of hydrogen supplied from the high-pressure hydrogen tank 22 to the fuel cell 10 to suck and circulate unreacted hydrogen discharged from the fuel cell 10 through the hydrogen circulation pipe 21c. It is something that can be done.

  The purge valve 25 is a shut-off valve. When the purge valve 25 is closed, the hydrogen supplied from the high-pressure hydrogen tank 22 circulates, and when opened, impurities (nitrogen and water) can be discharged.

  The steam separator 26 is a tank having a function of separating hydrogen discharged from the fuel cell 10 and produced water.

  The drain valve 27 is a shut-off valve, and is provided downstream of the steam / water separator 26. By opening the drain valve 27, generated water accumulated in the steam / water separator 26 is discharged to the outside of the vehicle.

  The anode gas flow path 14a, the hydrogen supply pipe 21a, the hydrogen discharge pipe 21b, the hydrogen circulation pipe 21c and the drain pipe 21d constitute the fuel gas flow passage of the present invention.

  The pressure sensor 28 is provided in the vicinity of the inlet of the fuel cell 10 in the hydrogen supply pipe 21a, detects the pressure on the anode 12 (An) side, and obtains the nitrogen partial pressure based on this pressure.

  The temperature sensor 29 is provided in the vicinity of the outlet of the fuel cell 10 in the hydrogen discharge pipe 21b, and detects the temperature of the anode off gas. This temperature is used as the MEA temperature and gas temperature described later.

  Although not shown, the hydrogen supply pipe 21a is provided with a regulator (pressure reducing valve) for reducing the pressure of the high-pressure hydrogen discharged from the high-pressure hydrogen tank 22.

  The cathode system 30 supplies and discharges air to and from the cathode 13 of the fuel cell 10, and includes an air supply pipe 31a, an air discharge pipe 31b, an air compressor 32, a back pressure valve 33, a pressure sensor 34, and a temperature sensor 35. Etc.

  The air supply pipe 31 a is a flow path through which air flows, one end of which is connected to the air compressor 32, and the other end is connected to the inlet of the cathode flow path 15 a of the fuel cell 10. One end of the air discharge pipe 31 b is connected to the outlet of the cathode flow path 15 a of the fuel cell 10, and the other end is connected to the back pressure valve 33. Note that a pipe provided downstream of the back pressure valve 33 communicates with the outside of the vehicle (in the atmosphere).

  The air compressor 32 is composed of a supercharger or the like driven by a motor, takes in air in the atmosphere outside the vehicle, compresses it, and supplies the compressed air to the cathode 13 of the fuel cell 10.

  The back pressure valve 33 is a valve whose opening degree can be adjusted, such as a butterfly valve, and can adjust the pressure of the cathode 13 of the fuel cell 10.

  The cathode flow path 15a, the air supply pipe 31a and the air discharge pipe 31b constitute the oxidant gas flow passage of the present invention.

  The pressure sensor 34 is provided in the vicinity of the inlet of the fuel cell 10 in the air supply pipe 31a, and detects the pressure of air.

  The temperature sensor 35 is provided in the vicinity of the outlet of the fuel cell 10 in the air discharge pipe 31b, and detects the temperature of the cathode offgas. This temperature is used as the MEA temperature and gas temperature described later.

  Although not shown, the air supply pipe 31 a is provided with a humidifier (not shown) for humidifying the air to a humidity suitable for the reaction in the fuel cell 10.

  The cooling system 40 includes cooling pipes 41 and 42, a radiator 43, a bypass pipe 44, a circulation pump 45, a temperature sensor 46, and the like.

  The cooling pipe 41 is a flow path through which a cooling medium (radiator liquid) mainly composed of ethylene glycol, for example, has one end connected to the outlet of the cooling flow path 16a of the fuel cell 10 and the other end connected to the radiator 43. Connected to the entrance. The cooling pipe 42 is a similar flow path, one end of which is connected to the outlet of the radiator 43 and the other end is connected to the inlet of the cooling flow path 16 a of the fuel cell 10.

  The radiator 43 is composed of a pipe provided with fins and the like, and has a function of radiating heat from the cooling medium warmed by the fuel cell 10.

  The bypass pipe 44 is a flow path for allowing the coolant discharged from the fuel cell 10 to flow through the radiator 43.

  The circulation pump 45 is provided in the cooling pipe 42 and circulates the cooling medium between the fuel cell 10 and the radiator 43 by the power of the motor.

  The temperature sensor 46 is provided in the vicinity of the fuel cell 10 in the cooling pipe 41 and detects the temperature of the cooling medium discharged from the fuel cell 10. This temperature is used as the temperature of MEA described later.

  The high voltage system 50 includes a voltage controller (VCU) 51, a power storage device 52, a travel motor 53, a discharge resistor 54, an ammeter 55, a voltmeter 56, and the like.

  The voltage controller 51 includes a DC / DC converter and the like, and a voltage (current) output from the fuel cell 10 based on a voltage (current) command value output from the control unit 60, that is, a power generation command for the fuel cell 10. To control.

  The power storage device 52 includes a battery or a capacitor, and stores electricity generated by the fuel cell 10. For example, the battery is a lead storage battery, a lithium ion secondary battery, a lithium polymer secondary battery, a nickel hydride storage battery, or the like, and the capacitor is an electric double layer capacitor or an electrolytic capacitor.

  The travel motor 53 is, for example, a permanent magnet type three-phase AC synchronous motor, and rotationally drives drive wheels provided in the fuel cell vehicle V with electric power supplied from the fuel cell 10 and / or the power storage device 52.

  The discharge resistor 54 is for preventing the fuel cell 10 from being deteriorated when the fuel cell 10 is exposed to a high potential state, and is appropriately connected to the fuel cell 10 for discharging. . Incidentally, the fuel cell 10 is in a high potential state because the hydrogen of the anode 12 and the oxygen in the air of the cathode 13 are on the catalyst without drawing a load (air compressor 32, travel motor 53, etc.) from the fuel cell 10. Because it reacts with.

  The ammeter 55 detects a current value taken from the fuel cell 10 during power generation or discharge.

  The voltmeter 56 detects a voltage value (for example, an open circuit voltage) of the fuel cell 10. The open circuit voltage is a voltage when no load is pulled from the fuel cell 10.

  The control unit 60 includes a CPU (Central Processing Unit), a memory, an input / output interface, and the like, and includes a low load stopping unit, an impurity amount estimating unit, and a low load stop prohibiting unit. The control unit 60 is electrically connected to the shut-off valve 23, the purge valve 25, the drain valve 27, the air compressor 32, and the back pressure valve 33, and opens and closes the shut-off valve 23, the purge valve 25, and the drain valve 27, and the air compressor. The rotational speed of the motor 32 and the opening degree of the back pressure valve 33 can be controlled. The control unit 60 is connected to the pressure sensors 28 and 34 and the temperature sensors 29, 35, and 46, and acquires pressure information and temperature information. The controller 60 is connected to the voltage controller 51 and transmits a current command value to be taken out from the fuel cell 10 to the voltage controller 51.

  Note that the low load stop is a so-called idle stop, which is to stop power generation when the power generation request amount of the fuel cell 10 becomes a predetermined value or less. As a condition for the required power generation amount to be a predetermined value or less, for example, the brake pedal is depressed, the fuel cell vehicle V is stopped (vehicle speed is 0 km / h), the accelerator is turned off, and the air compressor 32 is turned on. This is when power supply is stopped or when power supply to the air compressor 32 is stopped and the shut-off valve 23 is closed. Note that power to other necessary auxiliary machines is supplied from the power storage device 52.

  Next, the operation of the fuel cell vehicle V of the present embodiment will be described with reference to FIGS. 2 to 9 (refer to FIG. 1 as appropriate). When the fuel cell vehicle V is stopped with the ignition switch (IGSW) turned off (OFF), the shutoff valve 23, the purge valve 25 and the drain valve 27 are closed, the air compressor 32 is turned off, The back pressure valve 33 is opened and the circulation pump 45 is turned off.

  First, in step S1 of FIG. 2, when the ignition switch (IGSW) of the fuel cell vehicle V is turned on, the control unit 60 opens the shut-off valve 23 and starts the fuel cell from the high pressure hydrogen tank 22. Hydrogen is supplied to the anode 12 of 10, the air compressor 32 is driven to take in outside air, and air is supplied to the cathode 13 of the fuel cell 10. Thereby, in the anode 12 of the fuel cell 10, hydrogen is decomposed into hydrogen ions (protons) and electrons by the action of the catalyst, and the hydrogen ions permeate the electrolyte membrane 11 and move to the cathode 13, and the electrons are loaded. It moves to the cathode 13, and at the cathode 13, hydrogen ions and electrons react with oxygen contained in the air by the action of the catalyst to generate water.

  And it progresses to step S2 and the control part 60 calculates the nitrogen permeation amount to a fuel gas flow path. This nitrogen permeation amount is obtained by the sub-flow chart of FIG. That is, in step S21, the control unit 60 obtains pressure information (air inlet pressure) from the pressure sensor 34, and multiplies the air inlet pressure by a nitrogen composition ratio (about 80%) contained in the air to obtain the cathode. The 13 side nitrogen partial pressure is obtained.

  In step S22, the controller 60 obtains a partial pressure difference S by subtracting the nitrogen partial pressure on the anode 12 side from the nitrogen partial pressure on the cathode 13 side obtained in step S21. Note that the nitrogen partial pressure on the anode 12 side is such that nitrogen contained in the air supplied to the cathode 13 permeates through the electrolyte membrane 11, so that as time passes (when no nitrogen is discharged), as shown in FIG. The nitrogen partial pressure on the anode 12 side rises so as to gradually approach the nitrogen partial pressure on the cathode 13 side, and finally becomes the same pressure as each other.

  And it progresses to step S23 and the control part 60 calculates a nitrogen permeability coefficient based on the map shown to Fig.6 (a) calculated | required beforehand by experiment etc. FIG. As shown in FIG. 6A, when the MEA temperature is low, the nitrogen permeability coefficient is low, and when the MEA temperature is high, the nitrogen permeability coefficient is high. The temperature of the MEA is, for example, the temperature TH obtained from the temperature sensor 29 on the anode 12 side, the temperature TA obtained from the temperature sensor 35 on the cathode 13 side, or the temperature TC obtained from the temperature sensor 46 on the cooling side. A high temperature, that is, a temperature on the side where the nitrogen permeability coefficient becomes larger is selected. In the map of FIG. 6A, the relationship between the temperature of the MEA and the nitrogen permeation coefficient varies depending on the water content of the MEA. The water content of the MEA is as shown in the map of FIG. 6B. As the gas temperature increases, it increases. As the gas temperature at this time, the higher one of the temperature TH obtained from the temperature sensor 29 and the temperature TA obtained from the temperature sensor 35, that is, the temperature at which the nitrogen permeation coefficient is increased is selected.

  Then, the process proceeds to step S24, and the partial pressure difference S calculated in step S22 is multiplied by the nitrogen permeation coefficient of MEA (in the first case), thereby obtaining the nitrogen permeation amount into the fuel gas flow passage. If this sub-flow is passed for the second time or later, a new value is obtained by adding the nitrogen permeation amount obtained by multiplying the nitrogen permeation amount calculated this time (current) by the nitrogen permeation coefficient to the previously calculated nitrogen permeation amount. Nitrogen permeation amount.

  After calculating the nitrogen permeation amount, the process returns to step S2 of the main flowchart in FIG. 2, and the control unit 60 calculates the nitrogen discharge amount (step S3). This nitrogen discharge amount is obtained by the sub-flow chart of FIG. That is, in step S31, the control unit 60 determines whether a purge process has been executed. In the purge process, by opening the purge valve 25, nitrogen contained in the air of the cathode 13 by the power generation of the fuel cell 10 and water generated at the cathode 13 permeate the anode 12 through the electrolyte membrane 11, This is a process for preventing a decrease in the power generation performance due to a decrease in the hydrogen concentration of the anode 12. This purge process is executed, for example, by opening the purge valve 25 every elapse of a predetermined time.

  In step S31, when the purge process is executed (Yes), the process proceeds to step S32, and the nitrogen discharge amount is calculated based on the map of FIG. As shown in FIG. 6 (c), when the anode pressure obtained from the pressure sensor 28 is low, the nitrogen discharge amount decreases, and when the anode pressure is high, the nitrogen discharge amount increases. In this map, the relationship between the anode pressure and the nitrogen discharge amount varies according to the nitrogen partial pressure of the anode 12. Since the anode pressure in step S32 is a gauge pressure, that is, a relative pressure with respect to the atmospheric pressure, regardless of the difference in altitude at which the fuel cell vehicle V travels (runs at a high altitude or travels at a low altitude). Therefore, it is possible to always calculate an appropriate nitrogen emission amount.

  Then, the process proceeds to step S36, where the nitrogen discharge amount calculated this time (current) is added to the previously calculated nitrogen discharge amount to obtain a new nitrogen discharge amount.

  If the purge process is not executed in step S31 (No), the process proceeds to step S33, and it is determined whether the drain process is executed. The drain process is a process of opening the drain valve 27 and discharging the generated water accumulated in the steam / water separator 26. In addition, the drain process is performed by opening the drain valve 27 based on, for example, the elapse of a predetermined time or the detection value of a water level sensor (not shown).

  In step S33, when the drain process is executed (Yes), that is, when only the drain process is executed without executing the purge process, the nitrogen discharge is performed based on the map of FIG. Calculate the amount. In step S33, when the drain process is not executed (No), that is, when neither the purge process nor the drain process is executed, nitrogen is not discharged from the fuel gas flow path, so the nitrogen discharge amount is 0. In step S36, the nitrogen discharge amount calculated this time (current) is added to the nitrogen discharge amount calculated last time to obtain a new nitrogen discharge amount.

  After calculating the nitrogen discharge amount, the process returns to step S3 in the main flowchart of FIG. 2, and the control unit 60 calculates the moisture amount (step S4). This moisture amount is obtained by the sub-flowchart of FIG. First, in step S41, the control unit 60 determines whether or not idling is stopped.

  In step S41, when it is determined that the idling is stopped (Yes), the control unit 60 proceeds to step S42 and obtains the water generation amount. When idling is stopped, power generation is stopped (no load is applied) in a state where hydrogen is present in the anode 12 and air is present in the cathode 13, so that hydrogen and oxygen are respectively catalyst in the fuel cell 10. And the fuel cell 10 becomes a high potential state. If such a high potential state continues for a long time, the catalyst or the like may be deteriorated, so that a process of drawing current from the fuel cell 10 is necessary. Therefore, when the control unit 60 of the present embodiment detects an open circuit voltage value from the voltmeter 56 and determines that the open circuit voltage is too high, the fuel cell 10 and the discharge resistor 54 are connected, A process of taking out a current (discharge current) from the fuel cell 10 is performed. As a result, discharging is performed by the discharge resistor 54, and the fuel cell 10 can be prevented from being exposed to a high potential state.

  In this way, by connecting the fuel cell 10 and the discharge resistor 54 and extracting the current from the fuel cell 10, hydrogen and oxygen in the air react at the cathode 13 to generate water, and this generated water (impurity ) Permeate to the fuel gas flow path side through the electrolyte membrane 11. The amount of generated water that has permeated into the fuel gas flow passage corresponds to the amount of water in the present invention. The amount of water generated by the discharge current is calculated based on the map of FIG. 8A obtained in advance through experiments or the like, and the amount of water generated increases as the discharge current increases.

  The means for preventing the fuel cell 10 from entering a high potential state is not limited to the use of the discharge resistor 54, and any means capable of extracting current from the fuel cell 10 may be used. The current taken out from the battery may be stored in the power storage device 52.

  Then, after the water generation amount is calculated, the process proceeds to step S48, and the water generation amount calculated in step S42 is obtained as the water amount in the fuel gas flow passage (first time). In the process passing through step S42, the purge process and the drain process are not executed, so the water discharge amount becomes zero. In addition, if the subflow of FIG. 7 is passed for the second time or later, the water generation amount calculated this time is added to the water amount calculated last time to obtain a new water amount.

  Further, in step S41, when the control unit 60 determines that the idling is not stopped (No), that is, when normal power generation is performed and the generated current is taken out from the fuel cell 10 under the control of the voltage controller 51. In step S43, the amount of water generated in the fuel gas flow passage is calculated based on the map shown in FIG. That is, as shown in FIG. 8B, the amount of water generated increases as the generated current increases. Note that the water generated at the cathode 13 when the generated current is taken out from the fuel cell FC permeates the anode 12 through the electrolyte membrane 11. The amount of water that has passed through the anode 12 corresponds to the amount of water in the present invention.

  In step S44, the control unit 60 determines whether the purge process has been executed. When the purge process is executed in step S44 (Yes), the generated water is discharged through the purge valve 25, and thus the generated water discharge amount (water discharge amount) is calculated (step S45). Note that the water discharge amount at this time is greatly influenced by the flow velocity in the fuel gas flow passage. Therefore, when the purge process is executed, the water discharge amount is corrected according to the flow velocity. If the purge process is not executed in step S44 (No), the process proceeds to step S46 without obtaining the water discharge amount.

  In step S46, it is determined whether drain processing has been executed. When the drain process is executed in step S46 (Yes), the generated water is discharged through the drain valve 27, and thus the generated water discharge amount (water discharge amount) is calculated. In this case as well, the water discharge amount is corrected according to the flow velocity in the fuel gas flow passage, as in the purge process. If the drain process is not executed in step S46 (No), the process proceeds to step S48 without obtaining the water discharge amount.

  In step S48, the water discharge amount calculated when the purge process or the drain process is performed is subtracted from the water generation amount obtained from step S43, and this is used as the water amount permeated to the fuel gas flow passage. . In this way, the water amount calculated last time is added to the current water amount calculated from the water generation amount and the water discharge amount to obtain a new water amount.

  After calculating the water content, the process returns to the main flowchart of FIG. 2 and proceeds to step S5, where it is determined whether or not to stop idling. This idle stop prohibition determination is made based on the sub-flow charts of FIGS. 9 (a) and 9 (b). FIG. 9A shows an idle stop prohibition determination based on the amount of nitrogen in the fuel gas flow passage, and FIG. 9B shows an idle stop prohibition determination based on the amount of water in the fuel gas flow passage. Is to do. Note that the subflows shown in FIGS. 9A and 9B correspond to the low load stop prohibiting means in the present invention, respectively.

  As shown in FIG. 9A, in step S51, the nitrogen determined in the subflow of FIG. 4 from the nitrogen permeation amount (integrated value) from the oxidant gas flow path to the fuel gas flow path determined in the subflow of FIG. The amount of nitrogen in the fuel gas flow passage is obtained by subtracting the discharge amount (integrated value). In step S52, it is determined whether or not the nitrogen amount is equal to or greater than the predetermined value Hn. If the nitrogen amount is equal to or greater than the predetermined value Hn (Yes), that is, excessive nitrogen remains in the fuel gas flow passage. If YES in step S53, the flow advances to step S53 to prohibit idle stop. The predetermined value Hn corresponds to a predetermined value for reducing the power generation performance of the fuel cell 10 of the present invention.

  In step S52, if the nitrogen amount is less than the predetermined value Hn (No), the process proceeds to step S54 to determine whether the nitrogen amount is less than the predetermined value Ln. The predetermined value Ln is a value smaller than the predetermined value Hn. In step S54, if the nitrogen amount is less than the predetermined value Ln (Yes), the process proceeds to step S55, and if the idle stop is prohibited, the idle stop prohibited state is canceled. In step S54, when the nitrogen amount is equal to or greater than the predetermined value Ln (No), that is, when the nitrogen amount is between the predetermined value Hn and the predetermined value Ln, the state is maintained as it is. That is, when the idle stop is prohibited, the idle stop prohibition is maintained, and when the idle stop prohibition is released, the idle stop prohibition is released.

  As described above, by performing the idling stop prohibition determination in consideration of the amount of nitrogen as an impurity in the fuel gas flow passage, idling stop is executed in a state where a large amount of nitrogen exists in the fuel gas flow passage. There is nothing to do. Therefore, since nitrogen can be discharged before the idle stop is executed, the power generation stability when returning from the idle stop can be improved.

  Further, as shown in FIG. 9B, in step S61, it is determined whether or not the amount of water in the fuel gas flow passage obtained in the subflow of FIG. 7 is equal to or greater than a predetermined value Hw. In step S61, if the amount of water is equal to or greater than the predetermined value Hw (Yes), it means that excessive moisture remains in the fuel gas flow passage, and thus the process proceeds to step S62, and idle stop is prohibited. The predetermined value Hw corresponds to a predetermined value for reducing the power generation performance of the fuel cell 10 of the present invention.

  In step S61, when the water content is equal to or less than the predetermined value Hw (No), the process proceeds to step S63, and it is determined whether or not the water content is less than the predetermined value Lw (<predetermined value Hw). In step S63, if the amount of water is less than the predetermined value Lw (Yes), it is determined that the amount of water is an amount that does not impair the power generation stability at the time of return to idling stop, and the process proceeds to step S64 to stop idling. If it is in the prohibited state, the idle stop prohibited state is canceled. If idle stop is not prohibited, the prohibition of idle stop is canceled as it is.

  In step S63, when the water content is not less than the predetermined value Lw (No), that is, when the water content is between the predetermined value Hw and the predetermined value Lw, the state is maintained as it is. That is, when the idle stop is prohibited, the idle stop prohibition is maintained, and when the idle stop prohibition is released, the idle stop prohibition is released.

  As described above, the idling stop prohibition determination is executed by estimating the amount of generated water as an impurity in the fuel gas flow passage, so that the idling stop is executed in a state where a large amount of generated water exists in the fuel gas flow passage. It will not be done. Therefore, the generated water can be discharged before the idle stop is executed, so that the power generation stability when returning from the idle stop can be improved.

  In the present embodiment, the idle stop prohibition determination is made by estimating the nitrogen amount and the generated water amount in the fuel gas flow passage, but the idle stop prohibition determination may be made based on only the nitrogen amount or only the generated water amount. . As in this embodiment, by considering both nitrogen and generated water, the amount of impurities in the fuel gas flow passage can be detected with high accuracy, and power generation stability at the time of return from idle stop can be improved. Become.

It is a whole lineblock diagram showing the fuel cell system carried in the fuel cell vehicle of this embodiment. It is a main flowchart which judges idling stop prohibition. 3 is a sub-flowchart for calculating a nitrogen permeation amount. It is a graph which shows the relationship between the nitrogen partial pressure of an anode, and elapsed time. 3 is a sub-flowchart for calculating a nitrogen discharge amount. (A) is a map showing the relationship between the temperature of the MEA and the nitrogen permeation coefficient, (b) is a map showing the relationship between the gas temperature and the water content of the MEA, and (c) is a relationship between the anode pressure and the nitrogen discharge amount. It is a map to show. It is a sub-flowchart for calculating moisture content. (A) is a map showing the relationship between the discharge current and the amount of water generated, and (b) is a map showing the relationship between the generated current and the amount of water discharged. It is a sub-flowchart which shows idle stop prohibition judgment, (a) is based on the amount of nitrogen discharge, (b) is based on the amount of moisture.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fuel cell 14a Anode flow path 21a Hydrogen supply piping 21b Hydrogen discharge piping 21c Hydrogen circulation piping 21d Drain piping 25 Purge valve (impurity discharge means)
27 Drain valve (impurity discharge means)
28, 34 Pressure sensor 29, 35, 46 Temperature sensor 31a Air supply pipe 31b Air discharge pipe 54 Discharge resistance 55 Ammeter 60 Control unit V Fuel cell vehicle

Claims (4)

A fuel cell in which fuel gas and oxidant gas are supplied across the membrane electrode assembly to generate power; and
A fuel gas flow passage through which the fuel gas flows;
An oxidant gas flow passage through which the oxidant gas flows;
A low-load stop means for stopping power generation of the fuel cell when the required power generation amount of the fuel cell is a predetermined value or less;
An impurity amount estimating means for estimating an impurity amount in the fuel gas flow passage;
Impurity discharging means for discharging impurities in the fuel gas flow passage;
Low-load stop prohibiting means for prohibiting a low-load stop by the low-load stop means when the amount of impurities in the fuel gas flow passage is equal to or greater than a predetermined value that reduces the power generation performance of the fuel cell. A fuel cell vehicle.   The impurity amount estimation means is obtained from the relationship between the partial pressure difference between the nitrogen partial pressure in the oxidant gas flow passage and the nitrogen partial pressure in the fuel gas flow passage, and the water content and temperature of the membrane electrode assembly. 2. The fuel cell vehicle according to claim 1, wherein an amount of nitrogen in the fuel gas flow passage is estimated based on a nitrogen permeation coefficient that is generated.   The impurity amount estimating means removes the nitrogen discharge amount by the impurity discharge means from the nitrogen amount in the fuel gas flow passage when nitrogen in the fuel gas flow passage is discharged by the impurity discharge means. The fuel cell vehicle according to claim 2.   2. The fuel cell vehicle according to claim 1, wherein the impurity amount estimating means estimates a moisture amount in the fuel gas flow passage based on a current value taken out from the fuel cell.

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