Abstract:
A humidification system for a fuel cell includes a humidifier having a bundled plurality of tube type hollow thread members made of a water permeable membrane. The humidifier transfers a water content contained in a discharge gas, which is emitted from a fuel cell, to a supply gas, which is supplied to the fuel cell, when one of the discharge gas and the supply gas is passed through the inside of the tube type hollow thread members and the other one of the discharge gas and the supply gas is passed through between the tube type hollow thread members. Manometers P 1 , P 2 , P 3 , and P 4  detect a difference in pressure of the supply gas and the discharge gas, respectively, between an upper stream side and a down stream side of the humidifier. A determination unit determines a generation of clogging in the humidifier based on detection signals from the manometers.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a humidification system for a fuel cell. More specifically, the present invention relates to a humidification system provided with a fuel cell which has been adapted as an energy source for a vehicle, such as an electric vehicle.  
           [0003]    2. Description of Related Art  
           [0004]    Recently, a vehicle, such as an electric vehicle, which utilizes a “clean energy”, such as a solid polymer type fuel cell, has been developed. The Japanese Unexamined Patent Application, First Publication No. 6-132038, for instance, discloses a solid polymer electrolyte type fuel cell which may be used for such an energy source.  
           [0005]    In general, a solid polymer type fuel cell that is used for such vehicles has a laminate structure in which a power generating element is supported by gas separating members from both sides thereof. In the laminate structure, a plurality of gas passageways for supplying a reaction gas is formed on a power generating element which is formed by a hydrogen ion conductive solid polymer being sandwiched by a pair of carbon electrodes carrying platinum catalyst (i.e., a solid polymer electrolyte membrane-electrode joined unit) and each electrode surface.  
           [0006]    When the above-mentioned solid polymer type fuel cell is used, hydrogen gas is supplied to one of the electrodes as a fuel supply gas and oxygen or air is supplied to the other electrode as a supply gas for an oxidizing agent. In such a manner, electricity is extracted directly from chemical energy obtained by an oxidation reduction reaction of the fuel supply gas.  
           [0007]    That is, the electric energy is taken out of the series of electrochemical reactions in which the hydrogen gas is ionized at the anode side to move in the solid polymer electrolyte and the electrons are moved toward the cathode side via an external load to react with the oxygen to produce water.  
           [0008]    In the above-mentioned fuel cell, if the solid polymer electrolyte membrane is dried out, the efficiency in the ion conductivity thereof is decreased. Accordingly, the efficiency in the energy conversion is also decreased. Therefore, it is necessary to supply water to the solid polymer electrolyte membrane so that an excellent ion conductivity thereof may be maintained.  
           [0009]    For this reason, a humidification device is provided with a fuel cell of the above type, which is capable of humidifying supply gas, such as a fuel supply gas and a supply gas for an oxidizing agent, and supplying water to the solid polymer electrolyte membrane so that an excellent reaction of at the membrane may be maintained.  
           [0010]    The structure of an example of the humidification device will be explained with reference to FIG. 10. In FIG. 10, a humidification device is indicated by a numeral  1 . In the humidification device  1 , outside air which is pressurized by a super charger  2  is supplied to a supply gas line  5  as a supply gas for an oxidizing agent and the supply gas is humidified by the humidification device  1 . The humidified air is then supplied to a fuel cell (hereinafter referred to as a stack)  3  and the oxygen contained in the humidified air is used as an oxidizing agent. After that, the gas is emitted as a discharge gas.  
           [0011]    Also, the discharge gas containing water which is generated when reacted in the stack  3  is supplied to the humidification device  1 , via a discharge gas line  6 , from the stack  3 . The water vapor contained in the discharge gas is transferred to the supply gas in the humidification device  1  and then evacuated.  
           [0012]    As shown in FIG. 4, a pressure regulating valve  4  which regulates the inner pressure of the stack  3  is provided with the discharge gas line  6 .  
           [0013]    A humidifier  11  as shown in FIGS. 11 and 12 is disposed in the humidification device  1 .  
           [0014]    The humidifier  11  is formed by a plurality of tube type porous hollow thread members  12  which are made of a vapor permeable membrane (i.e., a water permeable membrane). The plurality of tube type porous hollow thread members  12  are contained in a cylidrically shaped casing  14  which has a plurality of opening portions  13  formed around its peripheral surface in the proximity to both ends thereof. The outer surfaces of the hollow thread members  12  as well as the outer surface of the hollow thread member  12  and the inner surface of the casing  14  are sealed at both ends of the casing  14 .  
           [0015]    In the humidifier  11 , the supply gas is supplied from the opening portions  13  located in the proximity to one of the two ends of the casing  14 . The supply gas is passed through the gap present between each of the hollow thread members  12  and exited from the opening portions  13  located in the proximity to the other end of the casing  14 . Also, the discharge gas supplied from the stack  3  is supplied to the hollow thread members  12  from one end of the casing and exited from the other end.  
           [0016]    As shown in FIG. 13, the hollow thread member  12  has numerous capillary portions  15  and the vapor contained in the discharge gas, which is introduced to the hollow thread members  12 , is condensed in the capillary portions  15  and moved toward an outer periphery side thereof. The condensed vapor is then evaporated into the supply gas.  
           [0017]    That is, the water content of the discharge gas is transferred to the supply gas in the humidifier  11  so that the humidification of the supplied gas is performed.  
           [0018]    However, since extremely thin threads having an inner diameter of, for instance, about 0.3 mm (cf. the capillary portion size is about 4 nm) are used as the hollow thread members  12  in the humidifier  11 , there is a danger that the capillaries of the hollow thread members  12  may be blocked by dust contained in the discharge gas which is supplied from the stack  3 . Also, since the hollow thread members  12  used in the humidifier  11  are bundled and the supply gas is passed through between each of the hollow thread members  12 , there is a danger that the gap between each of the hollow thread members  12  may also be blocked by dust which may be contained in the supply gas.  
           [0019]    If the capillaries of the hollow thread members  12  or the gap between each of the hollow thread members  12  is blocked, a transfer of the vapor contained in the discharge gas to the supply gas cannot be satisfactorily carried out and, hence, a sufficient amount of water cannot be supplied to the stack  3 . Thus, the efficiency in power generation of the stack  3  is decreased and this may lead to a cause of the failure of the stack  3 .  
         SUMMARY OF THE INVENTION  
         [0020]    Accordingly, one of the objectives of the present invention is to provide a humidification system for a fuel cell which does not have the above-mentioned problems.  
           [0021]    Another objective of the present invention is to provide a humidification system for a fuel cell which is capable of quickly detecting a clogging in a humidifier so that the affect to a stack caused by the decrease in humidification of a supply gas due to the clogging in the humidifier may be suppressed to a minimal level.  
           [0022]    The above objectives may be achieved by a humidification system for a fuel cell according to the present invention, including: a humidifier having a bundled plurality of tube type hollow thread members made of a water-permeable membrane, the humidifier transferring a water content contained in a discharge gas, which is emitted from a fuel cell, to a supply gas, which is supplied to the fuel cell, when one of the discharge gas and the supply gas is passed through the inside of the tube type hollow thread members and the other one of the discharge gas and the supply gas is passed through between the tube type hollow thread members; and a detection device which detects a generation of clogging in or between the tube type hollow thread members.  
           [0023]    According to the above humidification system, since the detection device which is capable of detecting clogging is provided with the humidifier which humidifies the supply gas by transferring water vapor contained in the discharge gas to the supply gas by means of the water-permeable membrane that forms the bundled plurality of hollow thread members, it becomes possible to minimize the occurrence of problems, such as a decrease in the power generation efficiency of the fuel cell due to an insufficient degree of humidification of supply gas caused by the clogging in the humidifier, and avoid a failure of the fuel cell.  
           [0024]    The above objectives may also be achieved by a humidification system for a fuel cell, wherein the detection device includes: a manometer which detects a difference in pressure of at least one of the supply gas and the discharge gas between an upper stream side and a down stream side of the humidifier; and a determination unit which determines a generation of clogging in the humidifier based on a detection signal from the manometer.  
           [0025]    According to the above humidification system, the determination unit measures the difference in pressure of at least one of the supply gas and the discharge gas between an upper stream side and a down stream side of the humidifier based on the detection signal from the manometers and, based on the result, the generation of clogging in or between the hollow thread members in the humidifier may be easily detected. Accordingly, problems in the humidification system, such as a failure of the fuel cell, may be prevented.  
           [0026]    The above objectives may also be achieved by a humidification system for a fuel cell, wherein the detection device includes: a dew point recorder which detects a dew point of at least one of the supply gas, which is supplied to the fuel cell, and the discharge gas, which is emitted from the fuel cell and introduced to the humidifier; and a determination unit which determines a generation of clogging in the humidifier based on a detection signal from the dew point recorder.  
           [0027]    According to the above humidification system, the determination unit measures the dew point of at least one of the supply gas, which is introduced to the fuel cell from the humidifier, and the discharge gas, which is emitted to the humidifier from the fuel cell, based on the detection signal from the dew point recorder and, based on the result, the generation of clogging in or between the hollow thread members in the humidifier may be easily detected. Accordingly, problems in the humidification system, such as a failure of the fuel cell, may be prevented.  
           [0028]    The above objectives may also be achieved by a humidification system for a fuel cell, wherein the detection device includes: a voltmeter which detects a voltage of the fuel cell; and a determination unit which determines a generation of clogging in the humidifier based on a detection signal from the voltmeter.  
           [0029]    According to the above humidification system, the determination unit easily measures the output state of the fuel cell based on the detection signal from the voltmeter and, based on the result, the generation of clogging in or between the hollow thread members in the humidifier may be detected. Accordingly, problems in the humidification system, such as a failure of the fuel cell, may be prevented.  
           [0030]    The above objectives may also be achieved by a humidification system for a fuel cell, wherein the determination unit determines if clogging is generated in or between the tube type hollow thread members by comparing the detection signal with a predetermined threshold value.  
           [0031]    According to the above humidification system, the determination unit easily determines if clogging is generated in or between the hollow thread members by comparing the detection signal with the predetermined threshold value. Accordingly, an adverse effect to the fuel cell due to the clogging may be prevented.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    Some of the features and advantages of the invention have been described, and others will become apparent from the detailed description which follows and from the accompanying drawings, in which:  
         [0033]    [0033]FIG. 1 is a schematic diagram showing a simplified arrangement of a fuel cell for explaining a configuration and a structure of a humidification system for a fuel cell according to a first embodiment of the present invention;  
         [0034]    [0034]FIG. 2 is a block diagram for explaining a function of the humidification system for a fuel cell according to the first embodiment of the present invention;  
         [0035]    [0035]FIG. 3 is a flow chart for explaining a determination control of clogging carried out by the humidification system for a fuel cell according to the first embodiment of the present invention;  
         [0036]    [0036]FIG. 4 is a schematic diagram showing a simplified arrangement of a fuel cell for explaining a configuration and a structure of a humidification system for a fuel cell according to a second embodiment of the present invention;  
         [0037]    [0037]FIG. 5 is a block diagram for explaining a function of the humidification system for a fuel cell according to the second embodiment of the present invention;  
         [0038]    [0038]FIG. 6 is a flow chart for explaining a determination control of clogging carried out by the humidification system for a fuel cell according to the second embodiment of the present invention;  
         [0039]    [0039]FIG. 7 is a schematic diagram showing a simplified arrangement of a fuel cell for explaining a configuration and a structure of a humidification system for a fuel cell according to a third embodiment of the present invention;  
         [0040]    [0040]FIG. 8 is a block diagram for explaining a function of the humidification system for a fuel cell according to the third embodiment of the present invention;  
         [0041]    [0041]FIG. 9 is a flow chart for explaining a determination control of clogging carried out by the humidification system for a fuel cell according to the third embodiment of the present invention;  
         [0042]    [0042]FIG. 10 is a schematic diagram for explaining an arrangement of a fuel cell provided with a humidification device;  
         [0043]    [0043]FIG. 11 is a perspective view of a humidifier for explaining a configuration and a structure of the humidifier which forms a part of a humidification device;  
         [0044]    [0044]FIG. 12 is a cross-sectional view of a humidifier for explaining a configuration and a structure of the humidifier which forms a part of a humidification device; and  
         [0045]    [0045]FIG. 13 is a cross-sectional view of a water permeable membrane for explaining the structure of the water permeable membrane which forms a part of the humidifier.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0046]    The invention summarized above and defined by the enumerated claims may be better understood by referring to the following detailed description, which should be read with reference to the accompanying drawings. This detailed description of a particular preferred embodiment, set out below to enable one to build and use one particular implementation of the invention, is not intended to limit the enumerated claims, but to serve as a particular example thereof. Note that in the following drawings, the same numerals are used for explaining the same structure shown in the above-described prior art and the explanation thereof will be omitted.  
         [0047]    A humidification system  21  according to an embodiment of the present invention is shown in FIG. 1. In the humidification system  21  shown in FIG. 1, a supply gas line  5   a  is located at an upper stream side for supplying a supply gas to a humidifier  11  of a humidification device  1  and a supply gas line  5   b  is located at a down stream side for introducing the supply gas, which is emitted from the humidifier  11 , to a stack  3 . Manometers P 1  and P 2  are provided with the supply gas lines  5   a  and  5   b , respectively, so that the pressure inside each of the supply gas lines  5   a  and  5   b  is measured by the manometers P 1  and P 2 , respectively.  
         [0048]    Also, a discharge gas line  6   a  is located at an upper stream side for supplying a discharge gas from the stack  3  to the humidifier  11  of the humidification device  1  and a discharge gas line  6   b  is located at a down stream side for emitting the discharge gas which is emitted from the humidifier  11 . Manometers P 3  and P 4  are provided with the discharge gas lines  6   a  and  6   b , respectively, so that the pressure inside each of the discharge gas lines  6   a  and  6   b  is measured by the manometers P 3  and P 4 , respectively.  
         [0049]    Next, the control system of the humidification system  21  will be explained with reference to FIG. 2.  
         [0050]    As shown in FIG. 2, the manometers P 1 , P 2 , P 3 , and P 4  provided with the supply gas lines  5   a  and  5   b , and the discharge gas lines  6   a  and  6   b , respectively, are connected to a determination unit  22  and detection signals of the manometers P 1 , P 2 , P 3 , and P 4  are output to the determination unit  22 . The determination unit  22  may be, for instance, a computer program that can be run by a computer hardware.  
         [0051]    Also, as shown in FIG. 2, an alarm unit  23  which generates an alarm, a driving device  24  which drives the stack  3 , and a drive switching device  25  which switches the driving source from the stack  3  to another driving source, such as batteries, are connected to the determination unit  22 .  
         [0052]    Next, a process for determining a generation of clogging which is carried out by the determination unit  22  of the humidifier  11  in the humidification device  1  will be explained with reference to a flow chart shown in FIG. 3.  
         [0053]    When the stack  3  is actuated and a supply of the supply gas is started, the supply gas is first humidified, in the humidification device  1 , by water components contained in the discharge gas emitted from the stack  3 . The humidified supply gas is then supplied to the stack  3 .  
         [0054]    At this time, detection signals from the manometers P 1 , P 2 , P 3 , and P 4  provided with the supply gas lines  5   a  and  5   b  and the discharge gas lines  6   a  and  6   b , respectively, which are connected to the humidification device  1 , are sent to the determination unit  22  (in step S 1 ).  
         [0055]    When the detection signals of the manometers P 1 , P 2 , P 3 , and P 4  are sent to the determination unit  22 , the determination unit  22  measures the difference in pressure between the supply gas lines  5   a  and  5   b  based on the detection signals from the manometers P 1  and P 2 , and the difference between the discharge gas lines  6   a  and  6   b  based on the manometers P 3  and P 4 . The determination unit  22  then determines if these differences are larger than the respective predetermined threshold value (in step S 2 ).  
         [0056]    If the difference in pressure between the supply gas lines  5   a  and  5   b  or between the discharge gas lines  6   a  and  6   b  is larger than the predetermined threshold value, the determination unit  22  determines if clogging is caused in the humidification device  1  (in step S 3 ).  
         [0057]    If it is determined that the clogging is caused in the humidification device  1  by the determination unit  22 , the determination unit  22  carries out an alarm check (in step S 4 ) and, if the number of alarm exceeds a predetermined threshold value, the determination unit  22  outputs a signal to the alarm unit  23  so that an alarm lamp is lit by the alarm unit  23  to notify the generation of clogging in the humidification device  1  (in step S 5 ). In stead of lighting the alarm lamp, the alarm unit  23  may produce an alarm sound.  
         [0058]    Also, the determination unit  22  decreases the output of the stack  3  which is driven by the stack driving device  24  (in step S 6 ).  
         [0059]    After that, the determination unit  22  determines if the decreased output of the stack  3  is less than a predetermined threshold value (in step S 7 ). If the output is equal to or less than the predetermined threshold value, the determination unit  22  stops the operation of the stack  3  by the stack driving device  24  to terminate the generation of the output by the stack  3  (in step S 8 ) and outputs a control signal to the drive switching device  25  to switch the driving output from the stack  3  to batteries so that the vehicle may be driven by the electric power generated by the batteries (in step S 9 ).  
         [0060]    As mentioned above, according to the humidification system  21 , the determination unit  22  determines the difference in pressure of the supply gas and that of the discharge gas, respectively, between the upper stream side and the down stream side of the humidifier  11  of the humidification system  1  based on the detection signal from the manometers P 1 , P 2 , P 3  and P 4 . Then, based on the results in the above procedure, the generation of clogging in the hollow thread members  12  or between the hollow thread members  12  may be determined very easily.  
         [0061]    In this manner, problems such as the decrease in power generation efficiency of the stack  3  due to insufficient humidification caused by clogging in or between the hollow thread members  12  may be detected at an early stage thereof to minimize the damage which may be given to the system. Also, the failure of the stack  3  which can be caused by such a damage may be prevented.  
         [0062]    In the embodiment explained above, although the pressure of both the supply gas and the discharge gas at the upper stream side and the down stream side is detected, it is possible to measure the pressure of only one of the gasses and carry out a determination process for generation of clogging based on the difference in pressure of that gas.  
         [0063]    Next, a second embodiment according to the present invention will be explained.  
         [0064]    As shown in FIG. 4, dew point recorders Td 1  and Td 2  are provided with the supply gas line  5   a  and the discharge gas line  6   a , respectively, of the humidification system  21 . These dew point recorders Td 1  and Td 2  detect the dew point of the gas in the supply gas line  5   b  and discharge gas line  6   a , respectively. As shown in FIG. 5, detection signals from the dew point recorders Td 1  and Td 2  are output to the determination unit  22 .  
         [0065]    In the humidification device  1 , if the clogging in or between the hollow thread members  12  is caused in the humidifier  11 , the dew point of the supply gas and that of the discharge gas is decreased because the humidification capacity thereof for the supply gas is decreased.  
         [0066]    That is, in the humidification system  21 , the decrease in the dew point of the gas in association with the decrease in the humidification performance of the humidifier  1  is detected.  
         [0067]    In the humidification system  21 , as shown in FIG. 6, when the detection signals from the dew point recorders Td 1  and Td 2  are output to the determination unit  22  (in step S 11 ), the determination unit  22  measures, based on the detection signals from the dew point recorders Td 1  and Td 2 , the dew point of the supply gas introduced to the stack  3  from the humidification device  1  and that of the discharge gas emitted to the humidification device  1  from the stack  3 , and determines if the dew point of the gas is less than a predetermined threshold value (in step S 12 ). If it is less than or equal to the threshold value, the determination unit  22  carries out a clogging determination to determine if clogging is caused in the humidification device  1  (in step S 13 ).  
         [0068]    The determination unit  22 , if it is determined that clogging is caused in the humidification device  1 , carries out an alarm checking (in step S 14 ) and, if the number of alarms exceeds a predetermined threshold value, outputs a signal to the alarm unit  23  so that an alarm is lit by the alarm unit  23  to notify the occurrence of the clogging in the humidification device  1  (in step S 15 ). At that time, the determination unit  22  decreases the output of the stack  3  which is driven by the stack driving device  24  (in step S 16 ).  
         [0069]    After that, the determination unit  22  determines if the decreased output of the stack  3  is less than a predetermined threshold value (in step S 17 ). If the output is less than or equal to the predetermined threshold value, the determination unit  22  stops the operation of the stack  3  by the stack driving device  24  to terminate the generation of the output of the stack  3  (in step S 18 ) and outputs a control signal to the drive switching device  25  to switch the driving output to batteries from the stack  3  so that the vehicle may be driven by the electric power generated by the batteries (in step S 19 ).  
         [0070]    As explained above, in the humidification system  21 , the determination unit  22  measures the dew point of the supply gas introduced to the stack  3  from the humidifier  11  of the humidification system  21  and that of the discharge gas emitted to the humidifier  11  of the humidification device  1  from the stack  3  and, based on the results, the occurrence of clogging in or between the hollow thread members  12  in the humidifier  11  is easily detected. Accordingly, the failure of the stack  3  which can be caused by such clogging may be prevented.  
         [0071]    Also, in this embodiment, only one of the dew point recorders Td 1  and Td 2  may be used and the occurrence of the clogging may be determined based on that detection.  
         [0072]    [0072]FIG. 7 is a diagram showing a third embodiment according to the present invention. In FIG. 7, the humidification system  21  includes a voltmeter V which detects a voltage of each cell of the stack  3 . The detection signal from the voltmeter V is output to the determination unit  22  as shown in FIG. 8.  
         [0073]    In the humidification device  1 , if the clogging is caused in or between the hollow thread members  12  in the humidifier  11 , the voltage in cells of the stack  3  is decreased due to the lowering in the humidification capacity thereof for the supply gas.  
         [0074]    That is, in the humidification system  21 , the decrease in cell voltage in association with the decrease in the humidification capacity of the humifidication device  1  is detected.  
         [0075]    In the humidification system  21 , as shown in FIG. 9, when the detection signal of the voltmeter V is output to the determination unit  22  (in step S 21 ), the determination unit  22  measures, based on the detection signal from the voltmeter V, the cell voltage of the stack  3  and determines if the cell voltage is less than a predetermined threshold value (in step S 22 ). If the cell voltage is less than or equal to the threshold value, the determination unit  22  carries out a determination process to determine if clogging is generated in the humidification device  1  (in step S 23 ).  
         [0076]    The determination unit  22 , if it is determined that clogging is caused in the humidification device  1 , carries out an alarm checking (in step S 24 ) and, if the number of alarms exceeds a predetermined threshold value, outputs a signal to the alarm unit  23  so that an alarm is lit by the alarm unit  23  to notify the occurrence of the clogging in the humidification device  1  (in step S 25 ). At that time, the determination unit  22  decreases the output of the stack  3  which is driven by the stack driving device  24  (in step S 26 ).  
         [0077]    After that, the determination unit  22  determines if the decreased output of the stack  3  is less than a predetermined threshold value (in step S 27 ). If the output of the stack  3  is equal to or less than the predetermined threshold value, the determination unit  22  stops the operation of the stack  3  by the stack driving device  24  to terminate the generation of the output (in step S 28 ) and outputs a control signal to the drive switching device  25  to switch the driving output to batteries from the stack  3  so that the vehicle may be driven by the electric power generated by the batteries (in step S 29 ).  
         [0078]    That is, in the humidification system  21 , the determination unit  22  measures the output state of the stack  3  based on the detection signal from the voltmeter V and, based on the results, the occurrence of clogging in or between the hollow thread members  12  in the humidifier  11  of the humidification device  1  is easily detected. Accordingly, the failure of the stack  3  which can be caused by such clogging may be prevented.  
         [0079]    Having thus described an exemplary embodiment of the invention, it will be apparent that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements, though not expressly described above, are nonetheless intended and implied to be within the spirit and scope of the invention. Accordingly, the foregoing discussion is intended to be illustrative only; the invention is limited and defined only by the following claims and equivalents thereto.