JP2010097739A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system detecting and controlling with high accuracy a volume of liquid component collected in a tank of a separating part. <P>SOLUTION: The fuel cell system is provided with a fuel cell stack, a first supply part supplying fuel, a second supply part supplying gas containing an oxidant, a separating part 10 retaining liquid 38 separated from gas-liquid mixture fluid consisting of either a reaction product generated at an anode electrode and a cathode electrode or gas, and equipped with a tank 30 with side faces processed in irregular shapes, a liquid volume detecting part 36 consisting of a pair of detection electrodes 36A, 36B for detecting a volume of the liquid 38, the detection electrodes 36A, 36B fitted along the irregular shapes. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell system, and more particularly, to a liquid level detection in a tank in which a liquid separated from a gas-liquid mixed fluid discharged from a fuel cell is stored.

  2. Description of the Related Art In recent years, electronic devices have become rapidly portable and cordless, and there is an increasing demand for secondary batteries that are small and lightweight and have high energy density as power sources for driving these devices. In addition, technological development for large-sized secondary batteries, which are required not only for small consumer applications but also for long-term durability and safety, such as for power storage and electric vehicles, has been accelerated. Furthermore, a fuel cell that can be used continuously for a long time by supplying fuel is attracting attention rather than a secondary battery that requires charging.

  The fuel cell includes at least a fuel cell stack including a cell stack, a fuel supply unit that supplies fuel to the cell stack, and an oxidant supply unit that supplies an oxidant. In general, a cell stack is formed by laminating a membrane electrode assembly including an anode electrode, a cathode electrode, and an electrolyte membrane interposed between these electrodes, and a separator, and arranging end plates at both ends in the laminating direction. Configured.

  As such a fuel cell stack, a direct methanol fuel cell (DMFC) has been developed. In DMFC, an aqueous methanol solution is used as a fuel, and oxygen in the air is used as an oxidant. As a result, carbon dioxide which is a reaction product and an aqueous solution such as unreacted methanol and water which are the remainder of the fuel are discharged from the anode electrode. Therefore, in a portable device, the discharged aqueous solution is generally returned to the fuel supply unit. On the other hand, nitrogen, unreacted oxygen and the like that have passed through the cathode electrode are discharged from the cathode electrode together with water and water vapor as reaction products. At this time, in the fuel cell system, since water is required for the reaction of the anode electrode, the water generated by the cathode electrode is returned to the fuel supply unit and reused. Accordingly, the liquid component discharged from the fuel cell stack is circulated and used, thereby improving the portability of the fuel cell system.

  However, when the liquid component is returned directly to the fuel supply unit, it becomes difficult to generate power in the fuel cell system with an optimal fuel concentration.

  Therefore, instead of returning the exhaust from the fuel cell stack directly to the fuel supply unit, after separating the gas component and the liquid component, the liquid component is stored in the tank and the required amount is supplied to the fuel supply unit. The method to do is generally done. Therefore, it is important to manage the amount of liquid component stored in the tank.

  On the other hand, in order to detect the amount of fuel stored in the fuel tank, a method is disclosed in which a pair of electrodes is provided in the fuel tank and the amount of fuel stored is detected from a change in capacitance between the electrodes (for example, , See Patent Document 1).

  In addition, a fuel cell system having a capacitance type liquid amount detection function for detecting the amount of liquid in a tank that collects a solution discharged from an anode electrode and a cathode electrode of a fuel cell is disclosed (for example, Patent Document 2). reference). Hereinafter, the liquid amount detection function for detecting the liquid amount in the tank of the fuel cell system shown in Patent Document 2 will be briefly described with reference to FIG.

  12 (a) is a schematic perspective view of a tank 110 for explaining the liquid level detection function of a conventional fuel cell system, FIG. 12 (b) is a sectional view taken along the line 12B-12B of FIG. 12 (a), and FIG. FIG. 12C is a sectional view taken along line 12C-12C in FIG.

As shown in FIGS. 12 (a) and 12 (b), the tank 110 was discharged from the introduction tube 132A for introducing the solution discharged from the anode electrode (not shown) and the cathode electrode (not shown). An introduction pipe 132B for introducing the solution and a discharge pipe 132C for discharging the solution are provided. Further, as shown in FIG. 12C, the tank 110 has a liquid amount detection unit 136 including a pair of detection electrodes 136A and 136B provided on the opposing flat side surfaces. Then, the amount of the solution existing between the pair of detection electrodes 136A and 136B is detected by a change in capacitance.
JP 2006-040836 A JP 2007-220453 A

  However, according to the fuel cell system of Patent Document 1, for example, the amount of fuel present in a fuel tank such as a fuel cartridge is detected, and the amount of liquid components such as water discharged from the cathode electrode and stored in the tank. It is not the structure which detects. However, it is possible to apply the technique of Patent Document 1 to detect the amount of the liquid component in the tank.

  However, even when the technology of Patent Document 1 is applied, when a fuel cell system having excellent portability is constructed, the amount of liquid components stored is limited due to the demand for miniaturization and thinning of the tank. Furthermore, it is required to detect the amount of the liquid component with high accuracy so that the liquid component does not overflow or deplete from the tank. This is because the detection error and the like are suppressed by improving the liquid volume detection function, so that the amount of liquid component stored can be increased even in a tank having the same capacity.

  In general, when the dielectric constant of a substance sandwiched between electrodes is constant, the capacitance is proportional to the area of the opposing electrodes and inversely proportional to the distance between the electrodes. Therefore, in order to detect the storage amount of the liquid component with high accuracy, for example, when the height of the tank is increased, the tank becomes large and it is difficult to reduce the size and thickness of the fuel cell system. Moreover, when the distance between the opposing electrodes is narrowed, there is a problem that the amount of liquid storage required for the tank cannot be secured. In other words, in a fuel cell system mounted on a portable device or the like, it is important to secure a necessary amount of liquid components in the tank and to reduce the size and thickness.

  Further, the fuel cell system of Patent Document 2 also discloses a liquid amount detection function for directly detecting the liquid amount in the tank as shown in FIG. 12, but in the case of detecting the liquid amount with high accuracy, the patent There is the same problem as the fuel cell system of Document 1.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a fuel cell system that detects and controls the amount of liquid component stored in a tank of a separation unit with high accuracy.

  To achieve the above object, a fuel cell system according to the present invention includes a fuel cell stack including a membrane electrode assembly in which an anode electrode, a cathode electrode, and an electrolyte membrane interposed between the anode electrode and the cathode electrode are stacked. A first supply section for supplying fuel to the anode electrode, a second supply section for supplying a gas containing an oxidant to the cathode electrode, a reaction product generated at the anode electrode, a residue of fuel, and a reaction generated at the cathode electrode A gas-liquid separation membrane that separates the liquid from the gas-liquid mixed fluid composed of at least one of the product and the gas that has passed through the cathode electrode, and a tank that holds the separated liquid and has opposite side surfaces processed into irregular shapes A separation unit, and a liquid level detection unit comprising a pair of detection electrodes for detecting the amount of liquid in the tank provided on opposite sides of the tank. Having the structure provided along the Jo.

  With this configuration, it is possible to enlarge the facing area of the detection electrodes constituting the liquid amount detection unit provided in the tank, detect the amount of the liquid component with high accuracy, and control the amount.

  According to the present invention, the opposing area of the detection electrodes constituting the liquid amount detection unit provided in the tank is enlarged, and the amount of the liquid component is detected and controlled with high accuracy. A fuel cell system can be realized.

  According to a first aspect of the present invention, a fuel cell stack including a membrane electrode assembly in which an anode electrode, a cathode electrode, an electrolyte membrane interposed between the anode electrode and the cathode electrode are stacked, and fuel is supplied to the anode electrode The first supply part, the second supply part for supplying a gas containing an oxidant to the cathode electrode, the reaction product and fuel residue generated at the anode electrode, the reaction product generated at the cathode electrode and the cathode electrode A separation unit having a gas-liquid separation membrane that separates a liquid from a gas-liquid mixed fluid composed of at least one of gas, and a tank that holds the separated liquid and has opposite side surfaces processed into a concavo-convex shape; A liquid amount detection unit comprising a pair of detection electrodes for detecting the amount of liquid in the tank provided on the opposite side surface, and the liquid amount detection unit has a configuration provided along an uneven shape .

  With this configuration, it is possible to detect and control the amount of the liquid component with high accuracy by expanding the facing area of the detection electrodes provided in the tank.

  According to a second aspect of the present invention, in the first aspect, the spacing between the concave and convex shapes is equal. As a result, the liquid level and the capacitance can be detected with high linearity as well as high sensitivity, so that controllability can be improved.

  According to a third aspect of the present invention, in the first aspect of the present invention, the opposing intervals of the concavo-convex shape are different. Accordingly, since the liquid amount and the electrostatic capacity can be changed discontinuously by the distance between the electrodes facing each other with high sensitivity, the sensitivity in a region where particularly high detection accuracy is required can be further improved.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the concavo-convex shape is a corrugated shape. Thereby, the workability of the detection electrode can be improved.

  According to a fifth aspect of the present invention, in the first aspect, the computer further includes a calculation unit that is connected to the detection electrode and detects the amount of the liquid in the separation unit. Accordingly, the amount of liquid in the tank can be grasped by the calculation unit, and the amount of liquid in the tank can be controlled based on the grasped amount.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, taking a direct methanol fuel cell (DMFC) as an example. The present invention is not limited to the contents described below as long as it is based on the basic characteristics described in this specification.

(Embodiment 1)
FIG. 1 is a block diagram showing the configuration of the fuel cell system according to Embodiment 1 of the present invention. FIG. 2 is a schematic cross-sectional view illustrating the power generation operation of the fuel cell stack according to Embodiment 1 of the present invention.

  Hereinafter, the outline of the fuel cell system and the operation of the fuel cell stack will be described with reference to FIGS. 1 and 2.

  As shown in FIG. 1, the fuel cell system includes at least a fuel cell stack 1, a fuel tank 4, a first supply unit 5 including a fuel pump that supplies fuel, and a second supply unit 6 including an air pump that supplies air. A control unit 7 including a calculation unit 7A, a power storage unit 8, a DC / DC converter 9, and a separation unit 10 including a tank 12 including a liquid amount detection unit 11 including a pair of detection electrodes. At this time, if necessary, a cooling unit 13 such as a cooling fan is provided to cool the tank 12 of the separation unit 10.

  The fuel cell stack 1 has a power generation unit, and the generated power is output from the positive terminal 2 and the negative terminal 3. Then, the output power is input to the DC / DC converter 9. At this time, the first supply unit 5 supplies a fuel such as an aqueous methanol solution in the fuel tank 4 to the anode electrode 21 of the fuel cell stack 1, and the second supply unit 6 supplies a gas such as air as an oxidant to the fuel cell stack. 1 is supplied to one cathode electrode 22. The control unit 7 controls driving of the first supply unit 5 that supplies fuel and the second supply unit 6 that supplies gas such as air, and controls the DC / DC converter 9 to control external devices (not shown). ) And charging / discharging of the power storage unit 8 are controlled. The fuel tank 4, the first supply unit 5, and the control unit 7 constitute a fuel supply unit that supplies fuel to the anode electrode 21 in the fuel cell stack 1. On the other hand, the second supply unit 6 and the control unit 7 constitute an oxidant supply unit that supplies a gas such as an oxidant to the cathode electrode 22 in the fuel cell stack 1. The separation unit 10 separates a liquid component (mainly water) from the gas-liquid mixed fluid discharged from the anode electrode 21 and the cathode electrode 22 and stores the separated liquid component in the tank 12. The stored liquid component is stored in the fuel tank 4. The fuel is supplied to the first supply unit 5 together with the fuel supplied from.

  Hereinafter, the structure and operation of the fuel cell stack 1 will be briefly described.

  As shown in FIG. 2, the fuel cell stack 1 includes a membrane electrode assembly (MEA) 24 that is an electromotive portion, and an anode side end plate 25 and a cathode side end plate 26 that are disposed so as to sandwich the MEA 24. . When the fuel cell stack is configured by stacking a plurality of MEAs 24, separators are provided between the MEAs 24 and stacked via the separators. The anode side end plate 25 and the cathode side end plate 26 sandwich both ends of the MEA 24 in the stacking direction.

  The MEA 24 is configured by laminating an anode electrode 21, a cathode electrode 22, and an electrolyte membrane 23 interposed between the anode electrode 21 and the cathode electrode 22. The anode electrode 21 is configured by laminating a diffusion layer 21A, a microporous layer (MPL) 21B, and a catalyst layer 21C in this order from the anode side end plate 25 side. Similarly, the cathode electrode 22 is configured by laminating a diffusion layer 22A, a microporous layer (MPL) 22B, and a catalyst layer 22C in this order from the cathode side end plate 26 side. Further, the positive electrode terminal 2 is electrically connected to the cathode electrode 22, and the negative electrode terminal 3 is electrically connected to the anode electrode 21.

  Here, the diffusion layers 21A and 22A are made of, for example, carbon paper, carbon felt, carbon cloth, or the like. The MPLs 21B and 22B are made of, for example, polytetrafluoroethylene or a tetrafluoroethylene / hexafluoropropylene copolymer and carbon. The catalyst layers 21C and 22C are formed by highly dispersing a catalyst suitable for each electrode reaction such as platinum and ruthenium on the carbon surface and binding the catalyst body with a binder. The electrolyte membrane 23 is made of an ion exchange membrane that transmits hydrogen ions, such as a perfluorosulfonic acid / tetrafluoroethylene copolymer. The anode side end plate 25, the cathode side end plate 26 and the separator are made of, for example, a carbon material or stainless steel. The anode electrode 21 is supplied with a fuel flow path 25A through which fuel flows, and the cathode electrode 22 is supplied with a gas such as an oxidant. The circulating gas channel 26A is provided in a groove shape, for example.

  In the fuel cell stack 1 configured as described above, as shown in FIGS. 1 and 2, an aqueous solution containing methanol as a fuel is supplied to the anode electrode 21 by the first supply unit 5 including a fuel pump, and the cathode electrode A gas such as air that is an oxidant pressurized by the second supply unit 6 composed of an air pump or the like is supplied to 22. Then, the methanol aqueous solution supplied to the anode electrode 21, methanol and water vapor derived therefrom are diffused over the entire surface of the MPL 21B in the diffusion layer 21A, and further pass through the MPL 21B to reach the catalyst layer 21C. Similarly, oxygen contained in the air supplied to the cathode electrode 22 diffuses over the entire surface of the MPL 22B in the diffusion layer 22A, passes through the MPL 22B, and reaches the catalyst layer 22C. Further, the methanol that has reached the catalyst layer 21C reacts as shown in the formula (1), and the oxygen that reaches the catalyst layer 22C reacts as shown in the formula (2).

  As a result, electric power is generated, and a gas-liquid mixed fluid such as carbon dioxide is produced on the anode electrode 21 side and water is produced on the cathode electrode 22 side as reaction products, which are supplied to the separation unit 10 shown in FIG. Is done. In the following, as will be described in detail with reference to FIG. 3, the carbon dioxide in the anode electrode 21 is exhausted from the fuel cell system to the outside through the gas-liquid separation membrane of the separator 10, and the cathode electrode A gas such as nitrogen that does not react at 22 and unreacted oxygen are also exhausted to the outside of the fuel cell system. At this time, not all of the methanol in the methanol aqueous solution contributes to the reaction on the anode electrode 21 side, so the methanol aqueous solution discharged as shown in FIG. 1 is supplied through the tank 12 of the separation unit 10 to the first supply. Reflux to part 5. Similarly, in order to supply water consumed by the reaction of the anode electrode 21, the water generated at the cathode electrode 22 is also refluxed to the first supply unit 5 via the tank 12 of the separation unit 10 and moved to the anode electrode 21 side. Supplied.

  Thereby, the liquid component such as water discharged from the fuel cell stack 1 is circulated through the separation unit 10, whereby the concentration of the methanol aqueous solution that is the fuel can be adjusted. As a result, it is not necessary to supply water from the outside, and it is not necessary to discharge (dispose) the water of the reaction product to the outside. Therefore, the portability and portability of the fuel cell system and the utilization efficiency of fuel and the like are improved.

  In order to efficiently circulate a liquid such as water through the separation unit 10, the liquid collected in the tank 12 of the separation unit 10 is within a predetermined range so that the liquid does not overflow or become drought. It is important to maintain the amount of liquid and supply it to the first supply unit 5. This is because when the amount of liquid, that is, the amount of liquid or the amount of storage becomes excessive, water leaks from the tank 12 of the separation unit 10. In addition, when the liquid storage amount becomes too small, the concentration of fuel supplied to the anode electrode cannot be adjusted.

  In other words, in order to maintain high reliability of the fuel cell system, it is particularly important to detect the amount of liquid stored in the tank 12 of the separation unit 10 with high sensitivity and control it with high accuracy.

  Therefore, the structure and detection sensitivity of the liquid amount detection unit of the separation unit 10 that detects the amount of liquid with high accuracy will be described in detail below with reference to FIGS. 3 and 4.

  FIG. 3A is a perspective view of the separation portion according to Embodiment 1 of the present invention, FIG. 3B is a cross-sectional view taken along line 3B-3B in FIG. 3A, and FIG. 3C is FIG. 3C-3C cross-sectional view of FIG.

  As shown in FIG. 3A, the separation unit 10 includes at least a tank 30, a liquid amount detection unit 36 including a pair of detection electrodes provided on opposite sides of the tank 30, a gas-liquid separation film 31, It consists of introduction pipes 32A and 32B and a discharge pipe 32C. At this time, the introduction pipes 32A and 32B are connected to the upper part of the tank 30, and the discharge pipe 32C is connected to the lower part of the tank 30, respectively. Then, water and water vapor, which are reaction products generated at the cathode electrode, and gas passing through the cathode electrode flow into the tank 30 of the separation unit 10 from the introduction pipe 32A. On the other hand, water containing carbon dioxide, which is a reaction product generated at the anode electrode, and unreacted methanol, which is a residue of fuel, flows into the tank 30 of the separation unit 10 from the introduction pipe 32B.

  The gas-liquid separation film 31 provided on the upper surface of the tank 30 separates a gas component such as carbon dioxide and water vapor, which is a gas-liquid mixed fluid, and a liquid component such as water, and gases an excess gas component to the outside. The liquid 38 is stored in the tank 30 while being discharged in a state. The liquid 38 stored in the tank 30 is supplied to the inlet side of the first supply unit 5 shown in FIG. 1 through a valve (not shown) provided in the discharge pipe 32C. The gas-liquid separation membrane 31 is a fluororesin such as polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), or tetrafluoroethylene / hexafluoropropylene copolymer (FEP). It can be comprised with the sheet | seat of the porous body made by. Alternatively, cloth, paper, or nonwoven fabric sheet made of carbon fiber coated with these fluororesins can be used. The tank 30 is made of an insulating material such as resin or ceramic.

  Further, as shown in FIGS. 3A and 3C, the pair of opposing side surfaces of the tank 30 are processed into a concavo-convex shape having an equal interval, for example, in a wavy shape, and a pair of side surfaces along the concavo-convex shape. The detection electrodes 36A and 36B are provided to configure the liquid amount detection unit 36. Then, it is detected whether or not the amount of the liquid 38 in the tank 30 is maintained within a predetermined range based on a change in capacitance (electric capacity) between the detection electrode 36A and the detection electrode 36B. That is, by detecting in parallel the capacitance of the gas portion and the liquid portion existing between the opposing detection electrodes 36A and 36B, the amount of the liquid 38 is calculated by the calculation unit 7A of the control unit 7 from the change. The amount of liquid 38 is detected. At this time, the wall surface (side surface) of the tank 30 is connected in series between the detection electrodes and constitutes a part of the capacitance. Therefore, in order to improve detection accuracy, the wall surface (side surface) of the tank 30 should be made of a material having a low dielectric constant. Is preferred.

  Then, the control unit 7 controls the flow rate of the second supply unit 6 based on the liquid amount of the liquid 38, and controls the liquid amount of the liquid 38 in the tank 30 within a predetermined range.

  Hereinafter, the relationship between the amount of liquid detected by the liquid amount detection unit provided along the concave-convex shape of the tank and the capacitance between the detection electrodes facing each other will be described with reference to FIG.

  FIG. 4 is a schematic diagram for explaining the relationship between the amount of liquid detected by the liquid amount detection unit of the fuel cell system according to Embodiment 1 of the present invention and the capacitance. In FIG. 4, for comparison, a characteristic B indicating the relationship between the amount of liquid detected by the liquid amount detection unit having the conventional configuration described in FIG. 12 and the capacitance is also shown. 4 shows the amount of liquid in the tank 30 of the separation unit 10 on the horizontal axis and the capacitance detected by the liquid amount detection unit 36 with respect to the amount of liquid on the vertical axis. .

  As shown in FIG. 4, the characteristic A indicating the relationship between the amount of liquid obtained by the liquid quantity detection unit and the capacitance of the present embodiment is higher than the characteristic B obtained by the conventional liquid quantity detection part. It can be seen that the change in the capacitance with respect to the change in the amount is large and the sensitivity is high. This is because, when the amount of liquid in the tank is equal, the area of the opposing electrode can be increased by configuring the detection electrode in a waveform shape, so that a large capacitance can be detected according to the electrode area. In addition, since the interval between the detection electrodes is constant in spite of the waveform-shaped detection electrodes, the relationship between the liquid amount and the capacitance has a high linearity like the conventional liquid amount detection unit. Yes. Thereby, while being able to simplify the control structure of a control part, highly accurate control is realizable.

  According to the present embodiment, highly accurate control can be realized by enlarging the electrode area and improving the detection sensitivity of the liquid amount detection unit by the pair of detection electrodes 36A and 36B facing each other in a waveform shape.

  In addition, according to the present embodiment, by increasing the area of the detection electrode, the temperature of the liquid stored in the tank of the separation unit is efficiently dissipated, and the amount of liquid due to the transpiration amount (evaporation amount) of the liquid is reduced. Excessive decrease can be suppressed. As a result, it is possible to realize a fuel cell system with excellent fuel efficiency by suppressing the shortage of the liquid that is supplied to the first supply unit and adjusts the concentration of the fuel. Therefore, the detection electrodes 36A and 36B are preferably formed of copper or an alloy thereof, aluminum or an alloy thereof from the viewpoint of thermal conductivity. These metal plates and foils can be combined with the tank 30 for use. Or you may form as a thin film by methods, such as vapor deposition. Further, as shown in FIG. 3A, the detection electrodes 36 </ b> A and 36 </ b> B are preferably provided on the entire side surface of the tank 30. Thereby, heat dissipation can be promoted, and detection sensitivity can be increased by increasing the electrode area.

  In addition, according to the present embodiment, since the side surface of the tank is processed into a corrugated shape, there are no inflection points or shielded regions in the uneven shape, so the detection electrode can be attached by attaching metal or by vapor deposition. Can be easily formed.

  In the present embodiment, an example in which the wave pitch of the waveform shape is formed constant has been described. However, the present invention is not limited to this, and the waveform shape is arbitrary as long as the intervals between the opposing detection electrodes are equal.

  Hereinafter, another example of the liquid amount detection unit of the fuel cell system according to Embodiment 1 of the present invention will be described with reference to FIG.

  FIG. 5A is a perspective view of another example of the separation portion in Embodiment 1 of the present invention, FIG. 5B is a cross-sectional view taken along line 5B-5B in FIG. 5A, and FIG. It is the 5C-5C sectional view taken on the line of Fig.5 (a).

  As shown in FIGS. 5 (a) and 5 (c), for example, a trapezoidal shape is provided on the opposite side surface of the tank 52 of the separation unit 50, and the interval between the opposing trapezoidal shapes is equal. It differs from the said liquid quantity detection part 36 by the point which provided the pair of detection electrodes 56A and 56B of the liquid quantity detection part 56 along. Other configurations and materials are the same, and the description is omitted.

  That is, as shown in FIG. 5C, the pair of opposing side surfaces of the tank 52 is processed into a concavo-convex shape so that the opposing intervals are equal, for example, in a trapezoidal shape, and a pair of detection electrodes along the concavo-convex shape. 56A and 56B are provided to configure the liquid amount detection unit 56. In the same manner as described above, whether or not the amount of the liquid 38 in the tank 52 is maintained within a predetermined range is detected by a change in capacitance (electric capacity) between the detection electrode 56A and the detection electrode 56B. The

  The relationship between the amount of liquid detected by the liquid amount detection unit 56 provided in the separation unit 50 of the above embodiment and the capacitance is the same as in FIG.

  According to the above-described embodiment, highly accurate control can be realized by increasing the detection sensitivity of the liquid amount detection unit by enlarging the electrode area with the pair of detection electrodes 56A and 56B facing each other in a trapezoidal uneven shape. .

  In the above embodiment, the concavo-convex shape has been described by taking the trapezoidal shape as an example. Is optional. Moreover, when expanding an electrode area and improving heat dissipation, rectangular uneven | corrugated shape may be sufficient.

  Hereinafter, an example of a method for measuring the amount (reserved amount) of the liquid 38 from the change in capacitance between the pair of detection electrodes of the liquid amount detection unit will be briefly described with reference to FIGS. 6 and 7.

  6 is a block circuit diagram showing a configuration of a calculation unit of the control unit of the fuel cell system according to Embodiment 1 of the present invention, and FIG. 7 is a waveform diagram at main positions of the block circuit diagram shown in FIG.

  As shown in FIG. 6, the calculation unit 7 </ b> A includes a pulse generation unit 41, resistors 43 and 44, an exclusive OR gate 45, and a pulse time measurement unit 42. At this time, the pulse generator 41 is connected to one terminal of the resistors 43 and 44, and the other terminal is connected to the input terminal of the exclusive OR gate 45. The detection electrode 36A is connected to the ground, and the detection electrode 36B is connected between the resistor 44 and the input terminal of the exclusive OR gate 45. The output terminal of the exclusive OR gate 45 is connected to the pulse time measuring unit 42.

  Hereinafter, a method for measuring the amount of liquid from a change in capacitance will be described with reference to FIG.

  First, the pulse signal shown in FIG. 7A is input from the pulse generator 41 to one terminal of the resistors 43 and 44.

  Next, as shown in FIG. 7B, the pulse signal input to one terminal of the resistor 43 has substantially the same timing as the input pulse signal at the point X which is the other terminal of the resistor 43. Is output. At this time, the pulse signal is input to the exclusive OR gate 45 in a state where the waveform is slightly dull due to the resistance value of the resistor 43 and the stray capacitance caused by the wiring or the like at the rise and fall of the pulse signal.

  On the other hand, as shown in FIG. 7C, the other terminal of the resistor 44, the point Y, has a pulse signal input to the resistor 44 due to the capacitance C between the detection electrode 36A and the detection electrode 36B. At the rise and fall, the signal is input to the exclusive OR gate 45 in a state of being largely dull due to the time constant of the resistance value R and the capacitance C of the resistor.

  Next, as shown in FIG. 7 (d), the output of the point Z which is the output of the exclusive OR gate 45 is between the detection electrodes at both rising and falling timings with respect to one input pulse. A pulse signal having a width proportional to the capacitance is output. The pulse signal width is measured by the pulse time measurement unit 42 to estimate the capacitance between the detection electrodes. Further, the calculation unit 7A that stores in advance a relational expression between the estimated capacitance and the amount of liquid in the tank calculates the amount of liquid in the tank from the relational expression.

  Similarly to the output at the point X, the output at the point Y is similarly dull due to the time constant between the input capacitance (floating capacitance) and the resistance value of the resistor 43 if the detection electrode is not connected. Therefore, in order to accurately estimate the capacitance, it is preferable to align the resistance values of the resistors 43 and 44 as much as possible to suppress errors caused by the input capacitance.

(Embodiment 2)
The fuel cell system according to Embodiment 2 of the present invention will be described below with reference to the drawings. Except for the separation unit, the fuel cell system is the same as that of the first embodiment described with reference to FIG.

  FIG. 8A is a perspective view of the separation portion according to Embodiment 2 of the present invention, FIG. 8B is a cross-sectional view taken along line 8B-8B in FIG. 8A, and FIG. 8C is FIG. Is a cross-sectional view taken along line 8C-8C.

  As shown in FIGS. 8A and 8C, the pair of detection electrodes 76A and 76B of the liquid amount detection unit 76 provided on the opposite side surfaces of the tank 72 of the separation unit 70 are provided so as to have different intervals. This is different from the liquid amount detection unit of the first embodiment. Other configurations and materials are the same, and the description is omitted.

  That is, as shown in FIG. 8C, the pair of opposing side surfaces of the tank 72 is processed into a concavo-convex shape so that the opposing interval differs, for example, in a waveform shape, and the pair of detection electrodes 76A along the concavo-convex shape. , 76B are provided to constitute the liquid amount detection unit 56. Similarly to the first embodiment, whether or not the amount of the liquid 38 in the tank 72 is maintained within a predetermined range due to a change in capacitance (electric capacitance) between the detection electrode 76A and the detection electrode 76B. Is detected.

  Hereinafter, the relationship between the amount of liquid detected by the liquid amount detection unit provided along the concavo-convex shape of the tank and the capacitance between the opposing detection electrodes will be described with reference to FIG.

  FIG. 9 is a schematic diagram for explaining the relationship between the amount of liquid detected by the liquid amount detection unit of the fuel cell system according to Embodiment 2 of the present invention and the capacitance. In FIG. 9, for comparison, a characteristic B indicating the relationship between the amount of liquid detected by the liquid amount detection unit having the conventional configuration described in FIG. 12 and the capacitance is also shown. In FIG. 9, the horizontal axis indicates the amount of liquid in the tank 52 of the separation unit 10, and the vertical axis indicates the capacitance detected by the liquid amount detection unit with respect to the liquid amount.

  As shown in FIG. 9, the characteristic C indicating the relationship between the amount of liquid obtained by the liquid quantity detection unit 76 of the present embodiment and the capacitance is similar to the characteristic A in FIG. It can be seen that the change in the capacitance with respect to the change in the liquid amount is larger and the sensitivity is higher than the characteristic B obtained in the part.

  Further, since the interval between the waveform-shaped detection electrodes varies depending on the position, the detected capacitance changes with respect to the amount of liquid in synchronization with the change in the interval between the opposing waveforms. That is, as the interval between the detection electrodes is reduced, a larger capacitance is obtained, and as the interval between the detection electrodes is increased, a smaller capacitance is obtained. As a result, the gradient of the change in capacitance with respect to the amount of liquid is detected differently. Therefore, by narrowing the interval between the waveform-shaped detection electrodes facing each other at the upper limit and lower limit positions of the liquid amount in the tank 72, the amount of liquid is detected with high sensitivity, particularly at the upper limit position and the lower limit position. It can be controlled with accuracy.

  According to the present embodiment, the detection sensitivity of the amount of liquid can be improved by increasing the electrode area of the detection electrodes 76A and 76B. Furthermore, by narrowing the interval between the detection electrodes at least at a predetermined position, the detection sensitivity of the amount of liquid at the predetermined position is further increased, and high-precision control is realized.

  In the present embodiment, the concave-convex detection electrode having a corrugated shape has been described as an example in which the positions of the bottoms (or the tops of the convex parts) of the concave parts facing each other are completely matched in the height direction of the tank. Not limited to this. For example, the position of the bottom part (or the top part of the convex part) of the opposing concave part is shifted from the concave / convex shape of the liquid amount detection part 36 of the first embodiment to the concave / convex shape of the liquid quantity detection part 76 of the present embodiment. You may provide by arrangement. Similarly, the amount of liquid can be detected with high sensitivity.

  Hereinafter, another example of the liquid amount detection unit of the fuel cell system according to Embodiment 2 of the present invention will be described with reference to FIG.

  FIG. 10A is a perspective view of another example of the separation portion according to Embodiment 2 of the present invention, FIG. 10B is a cross-sectional view taken along the line 10B-10B of FIG. 10A, and FIG. It is the 10C-10C sectional view taken on the line of Fig.10 (a).

  As shown in FIG. 10A and FIG. 10C, the opposing side surfaces of the tank 82 of the separation unit 80 are processed into an uneven shape, for example, in a trapezoidal shape so that the interval between the opposing trapezoidal shapes is different. It differs from the said liquid quantity detection part 76 by the point which provided the pair of detection electrodes 86A and 86B of the liquid quantity detection part 86 along the shape.

  That is, as shown in FIG. 10C, the pair of opposing side surfaces of the tank 82 are processed into a concavo-convex shape, for example, in a trapezoidal shape so that the opposing interval is different, and the pair of detection electrodes 86A along the concavo-convex shape. , 86B are provided, and the liquid amount detection unit 86 is configured. In the same manner as described above, whether or not the amount of the liquid 38 in the tank 82 is maintained within a predetermined range is detected based on a change in capacitance (electric capacity) between the detection electrode 86A and the detection electrode 86B. The

  The relationship between the amount of liquid detected by the liquid amount detection unit 86 provided in the separation unit 80 of the above embodiment and the capacitance is the same as in FIG.

  According to the embodiment described above, highly accurate control can be realized by enlarging the electrode area by the pair of detection electrodes 86A and 86B facing each other in a trapezoidal uneven shape and improving the detection sensitivity of the liquid amount detection unit. .

  In the above-described embodiment, the description has been given of the example in which the concave and convex detection electrodes having a trapezoidal shape are arranged by shifting the positions of the bottom portions of the concave portions facing each other (or the top portions of the convex portions) in the height direction of the tank. It is not limited to this. For example, the position of the bottom part of the concave part (or the top part of the convex part) may be completely matched, and the amount of liquid can be detected with high sensitivity.

  In the case where the uneven shape is shifted, the uneven shape may be provided in a rectangular shape. Hereinafter, the reason will be described with reference to FIG. FIG. 11A is a perspective view of still another example of the separating portion according to Embodiment 2 of the present invention, FIG. 11B is a cross-sectional view taken along line 11B-11B of FIG. 11A, and FIG. FIG. 11 is a sectional view taken along line 11C-11C in FIG.

  As shown in FIGS. 11 (a) and 11 (c), the effective electrode areas of the substantially opposing detection electrodes 96A and 96B constituting the liquid amount detection unit 96 of the tank 92 of the separation unit 90 are the same as those in the related art. It is about the same as the electrode area of the liquid amount detection unit. This is because the horizontal detection electrodes do not face each other. However, as indicated by arrows in FIG. 11 (c), the detection electrodes 96A and 96B facing each other are formed with different intervals at three locations, and the detected capacitance is reduced by reducing the effective interval. growing.

  In each of the above embodiments, the case has been described in which the amount of liquid in the tank is detected and controlled basically when the fuel cell system is installed on a flat place, but the present invention is not limited to this. For example, a tilt sensor or the like may be incorporated in the fuel cell system, the tilt amount of the tank may be detected by the tilt sensor, and the liquid amount may be corrected using the tilt amount, and the same processing may be performed. Thereby, restrictions, such as a use place, such as a portable apparatus, can be relieved greatly, for example, while a use range is expanded, control accuracy can further be improved.

  Further, in each of the above-described embodiments, the liquid amount detection unit has been described as an example in which the detection electrode is provided on the entire surface of the opposing side surface of the tank. For example, a detection electrode divided into a plurality of parts, such as two, is formed and used as a sensor for detecting the amount of inclination along with the detection of the liquid amount from the measured capacitance value between a plurality of opposing detection electrodes. May be. Specifically, for example, in FIG. 3A, if the detection electrode of the liquid amount detection unit 36 is divided into left and right, the capacitance of the left and right liquid amount detection units when the tank is tilted in the left and right direction in the drawing. There will be a difference. From this difference, the left and right tilt amounts can be detected. In addition, if the detection electrode is divided into upper and lower parts, the amount of tilt before and after can be detected. Furthermore, if the detection electrode is divided into left and right and up and down, the left and right and front and back tilt amounts can be detected. Similarly, another plurality of divided detection electrodes may be formed on different side surfaces of the tank.

  In each of the above embodiments, the DMFC has been described as an example. However, the present invention is not limited to this, and the configuration of the present invention can be applied to any fuel cell that uses a power generation element similar to a cell stack. For example, the present invention can be applied to a so-called solid polymer electrolyte fuel cell using hydrogen as a fuel or a methanol reforming fuel cell.

  According to the fuel cell system of the present invention, it is useful as a power source for electronic devices that are particularly required to have high reliability, small size, and portability.

1 is a block diagram showing a configuration of a fuel cell system according to Embodiment 1 of the present invention. Sectional schematic diagram explaining the power generation operation of the fuel cell stack according to Embodiment 1 of the present invention. (A) The perspective view of the isolation | separation part in Embodiment 1 of this invention, (b) The 3B-3B sectional view taken on the line of Fig.3 (a), (c) The 3C-3C sectional view taken on the line of Fig.3 (a) Schematic diagram illustrating the relationship between the amount of liquid detected by the liquid amount detection unit of the fuel cell system according to Embodiment 1 of the present invention and the capacitance. (A) Perspective view of another example of separation part in Embodiment 1 of this invention, (b) 5B-5B sectional drawing of Fig.5 (a), (c) 5C-5C line of Fig.5 (a) Cross section 1 is a block circuit diagram showing a configuration of a calculation unit of a control unit of a fuel cell system according to Embodiment 1 of the present invention. Waveform diagram at main positions in the block circuit diagram shown in FIG. (A) Perspective view of separation part in embodiment 2 of the present invention, (b) 8B-8B sectional view of FIG. 8 (a), (c) 8C-8C sectional view of FIG. 8 (a) Schematic diagram illustrating the relationship between the amount of liquid detected by the liquid amount detection unit of the fuel cell system and the capacitance in Embodiment 2 of the present invention. (A) The perspective view of another example of the separation part in Embodiment 2 of this invention, (b) 10B-10B sectional view taken on the line of FIG. 10 (a), (c) The 10C-10C line of FIG. 10 (a) Cross section (A) Perspective view of still another example of separation part in Embodiment 2 of the present invention, (b) 11B-11B cross-sectional view of FIG. 11 (a), (c) 11C-11C of FIG. 11 (a) Line cross section (A) The schematic perspective view of the tank explaining the liquid amount detection function of the conventional fuel cell system, (b) 12B-12B sectional view taken on the line of FIG. 12 (a), (c) 12C-12C of FIG. 12 (a) Line cross section

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 Positive electrode terminal 3 Negative electrode terminal 4 Fuel tank 5 1st supply part 6 2nd supply part 7 Control part 7A Calculation part 8 Power storage part 9 DC / DC converter 10, 50, 70, 80, 90 Separation part 11, 36, 56, 76, 86, 96, 136 Liquid quantity detection unit 12, 30, 52, 72, 82, 92, 110 Tank 13 Cooling unit 21 Anode electrode 21A, 22A Diffusion layer 21B, 22B Microporous layer (MPL)
21C, 22C catalyst layer 22 cathode electrode 23 electrolyte membrane 24 membrane electrode assembly (MEA)
25 Anode side end plate 25A Fuel flow path 26 Cathode side end plate 26A Gas flow path 31 Gas-liquid separation membrane 32A, 32B, 132A, 132B Inlet pipe 32C, 132C Discharge pipe 36A, 36B, 56A, 56B, 76A, 76B, 86A , 86B, 96A, 96B, 136A, 136B Detection electrode 38 Liquid 41 Pulse generation unit 42 Pulse time measurement unit 43, 44 Resistor 45 Exclusive OR gate

Claims (5)

A fuel cell stack including a membrane electrode assembly in which an anode electrode, a cathode electrode, and an electrolyte membrane interposed between the anode electrode and the cathode electrode are stacked;
A first supply unit for supplying fuel to the anode electrode;
A second supply part for supplying a gas containing an oxidant to the cathode electrode;
A gas for separating a liquid from a gas-liquid mixed fluid composed of at least one of a reaction product generated at the anode electrode and a residue of the fuel, a reaction product generated at the cathode electrode, and the gas passed through the cathode electrode. A separation unit having a liquid separation membrane and a tank that holds the separated liquid and has opposite side surfaces processed into a concavo-convex shape;
A liquid amount detection unit comprising a pair of detection electrodes for detecting the amount of the liquid in the tank provided on the opposite side surfaces of the tank;
The fuel cell system, wherein the liquid amount detection unit is provided along the uneven shape. 2. The fuel cell system according to claim 1, wherein the opposing intervals of the concave and convex shapes are equal. The fuel cell system according to claim 1, wherein an interval between the concave and convex shapes is different. The fuel cell system according to any one of claims 1 to 3, wherein the uneven shape is a corrugated shape. The fuel cell system according to claim 1, further comprising a calculation unit connected to the detection electrode and detecting an amount of the liquid in the separation unit.

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