Abstract:
An aspect of the present invention provides a fuel cell apparatus that includes at least one fuel cell stack including a plurality of unit fuel cells, each unit fuel cell including a membrane electrode assembly including an electrolyte membrane and electrodes arranged on each side the electrode membrane, and a pair of separators sandwiching the membrane electrode assembly, a casing arranged and configured to accommodate the fuel cell stack, and at least one elastic member arranged part or whole of the circumference of the fuel cell stack in contact with an inner wall of the casing.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a fuel cell apparatus having a casing for accommodating fuel cells each includes an electrolyte membrane, electrodes arranged on both surfaces of the electrolyte membrane, respectively, and a pair of separators sandwiching the electrolyte membrane and electrodes. 
     An anti-shock (or vibration proof) structure for a fuel cell is disclosed in Japanese Laid-Open Patent Publication No. 2003-203670. According to the disclosure, a plurality of unit fuel cells are stacked one upon another to form a fuel cell stack. Each side face of the stack in a cell stacking direction is covered with a plate. Between the plate and the stack, there is arranged an elastic member having low-friction, insulation, and shock absorption characteristics. 
     SUMMARY OF THE INVENTION 
     Fuel cells are often housed in a casing when used. In the casing, the fuel cells are set to be not in contact with inner walls of the casing. Once the fuel cells in the casing are installed in a mobile body such as a vehicle, the fuel cells and casing are subjected to vibration and shock during the driving of the vehicle. The casing and fuel cells may vibrate under a specific mode such as a torsional mode, bending mode, or rigid vibration mode that applies strong stress to the casing, fuel cells, and parts that support the fuel cells in the casing. Such stress may break the separators and supporting parts of the fuel cells, to deteriorate the performance and reliability of the fuel cells. An object of the present invention is to improve the antishock and vibration proof characteristics of fuel cells enclosed in a casing. 
     An aspect of the present invention provides a fuel cell apparatus that includes at least one fuel cell stack including a plurality of unit fuel cells, each unit fuel cell including a membrane electrode assembly including an electrolyte membrane and electrodes arranged on each side the electrode membrane, and a pair of separators sandwiching the membrane electrode assembly, a casing arranged and configured to accommodate the fuel cell stack, and at least one elastic member arranged part or whole of the circumference of the fuel cell stack in contact with an inner wall of the casing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view generally showing a fuel cell stack according to a first embodiment of the present invention. 
         FIG. 2  is an exploded perspective view showing the unit fuel cell  1 . 
         FIG. 3  is a sectional front view showing the fuel cell stack  3  of  FIG. 1 . 
         FIG. 4  is a view showing a casing  63  accommodating fuel cell stacks each corresponding to the fuel cell stack  3  of the first embodiment. 
         FIG. 5  is a sectional view taken along a line A-A of  FIG. 4 . 
         FIG. 6  is a plan view showing a separator used for the fuel cell stack shown in  FIG. 4 . 
         FIG. 7  is a plan view showing a modification of the separator  67  of the first embodiment shown in  FIG. 6 . 
         FIG. 8  is a plan view showing a separator  67  for a fuel cell according to a second embodiment of the present invention. 
         FIG. 9  is a plan view showing a separator  67  for a fuel cell according to a third embodiment of the present invention. 
         FIG. 10  is a plan view showing a separator  67  for a fuel cell according to a fourth embodiment of the present invention. 
         FIG. 11  is a view showing a modification of the second embodiment shown in  FIG. 8  and corresponds to a sectional view taken along a line B-B of  FIG. 4 . 
         FIG. 12  is a view showing a modification of the third embodiment shown in  FIG. 9  and corresponds to a sectional view taken along a line B-B of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Various embodiments of the present invention will be described with reference to the accompanying drawings. It is to be noted that same or similar reference numerals are applied to the same or similar parts and elements throughout the drawings, and the description of the same or similar parts and elements will be omitted or simplified. 
     (First Embodiment) 
       FIG. 1  is a perspective view generally showing a fuel cell stack according to a first embodiment of the present invention. Fuel cells in this embodiment are employed, but not limited the present invention, solid polymer electrolyte fuel cells and are simply referred to as “fuel cells.” The fuel cells are installed in, for example, a fuel-cell vehicle. The fuel cells may be installed in any other purpose. In  FIG. 1 , a plurality of unit fuel cells  1  each generating a voltage of about 1 V are stacked one upon another to form a fuel cell stack  3 . Each fuel cell  1  in the stack  3  is rectangular and thin. A tension rod  5  is passed through each of the four corners of the stack  3 , to fasten the fuel cells  1  together. The tension rods  5  apply contact pressure to the stack  3  and maintain the pressure. The tension rods  5  may be made of metal. The number of the tension rods  5  is not limited to four. An optional number of tension rods are usable if they can secure a required fastening force. 
     Ends of the fuel cell stack  3  in the stacking direction are provided with collecting plates  29  and  31 , insulating plates  33  and  35 , and end plates  37  and  39 . The end plate  37  at one end of the stack  3  has a fuel gas inlet  51 , a fuel gas outlet  53 , an oxidant gas inlet  55 , an oxidant gas outlet  57 , a cooling water inlet  59 , and a cooling water outlet  61 . According to the first embodiment, these inlets and outlets are circular. This, however, does not limit the present invention. They may have arbitrary shapes. 
       FIG. 2  is an exploded perspective view showing the unit fuel cell  1 . The fuel cell  1  has a membrane electrode assembly (MEA)  13  consisting of an electrolyte membrane  7 , an anode electrode  9 , and a cathode electrode  11 . On each side of the MEA  13 , there are seals  19  and  21 . On the seals  19  and  21 , there are separators  15  and  17 , respectively. The separator  15  has a passage for supplying a fuel (hydrogen) gas to the anode electrode  9 . The separator  17  has a passage  25  for supplying an oxidant (oxygen, usually air) gas to the cathode electrode  11 . In the MEA  13 , the electrolyte membrane  7  is a polymeric ion exchange membrane, the anode electrode (fuel electrode)  9  has a catalyst layer and a gas diffusion layer, and the cathode electrode (air electrode)  11  has a catalyst layer and a gas diffusion layer. The electrolyte membrane  7  is an ion exchange membrane made of solid polymer such as fluorine-based resin having proton conductivity and showing good electric conductivity under a wet state. The separators  15  and  17  are made by compressing and forming gas-impermeable carbon or a mixture of carbon and thermosetting resin. 
     The separator  15  has the fuel gas passage (not shown) on the anode electrode  9  side, and the separator  17  has the oxidant gas passage  25  on the cathode electrode  11  side. A coolant passage  27  is formed as required. The fuel gas passage, oxidant gas passage  25 , and coolant passage  27  are sealed with the seals  19  and  21  under the fastening force of the tension rods  5  applied to the fuel cells  1  in the stacking direction. The seals  19  and  21  are made of rubber-like elastic material such as silicon rubber, ethylene-propylene-diene rubber (EPDM), and fluorine rubber. 
       FIG. 3  is a sectional front view showing the fuel cell stack  3  of  FIG. 1 . At one end of the stack  3 , an inner end plate  47  is arranged between the end plate  39  and the insulating plate  35 . Between the end plate  39  and the inner end plate  47 , there is arranged an absorbing member  49  such as a disc spring to absorb pressure variation acting on the stack  3 . 
       FIG. 4  is a view showing a casing  63  accommodating fuel cell stacks each corresponding to the fuel cell stack  3  of the first embodiment. The casing  63  is installed in a mobile body such as a vehicle. The casing  63  encloses a plurality of fuel cell stacks  65 A,  65 B, and  65 C. The casing  63  may be composed of an upper cover and a lower cover that are joined together to define a closed inner space. The number of fuel cell stacks stored in the casing  63  is not limited to three. It may be one, two, four, or more. Each of the stacks  65 A,  65 B, and  65 C is fixed to a block  66  with a rod  68 . The block  66  is fixed to a side wall of the casing  63 . 
       FIG. 5  is a sectional view taken along a line A-A of  FIG. 4 . One end in the cell stacking direction of each of the fuel cell stacks  65 A,  65 B, and  65 C is fixed to the block  66  with the rod  68 . The block  66  is fixed to an inner wall of the casing  63 . One end of the rod  68  is fixed to one of the end plates  37  and  39 , for example, the end plate  37  of the fuel cell stack, and the other end of the rod  68  is slidably inserted into a slide hole  66   a  formed in the block  66 . 
       FIG. 6  is a plan view showing a separator used for the fuel cell stack shown in  FIG. 4 . Instead of the separators  15  and  17  shown in  FIG. 2 , the fuel cell stacks  65 A,  65 B, and  65 C in the casing  63  may employ separators  67  one of which is shown in  FIG. 6 . The separator  67  has a seal  69  that corresponds to the seal  19  or  21  shown in  FIG. 2 . The seal  69  is made by, for example, integral molding on the separator  67 . 
     The seal  69  surrounds a reactive gas (fuel gas or oxidant gas) passage  71  and manifold holes  73 ,  75 ,  77 ,  79 ,  81 , and  83 . These manifold holes  73 ,  75 ,  77 ,  79 ,  81 , and  83  correspond to the fuel gas inlet  51 , fuel gas outlet  53 , oxidant gas inlet  55 , oxidant gas outlet  57 , cooling water inlet  59 , and cooling water outlet  61  of  FIG. 1 , respectively. At the four corners of the separator  67 , there are holes  85  to pass the tension rods  5  of  FIG. 1 . The seal  69  is integral with an elastic member  87  that extends along the periphery of the separator  67 . The seal  69  and elastic member  87  are made of the same material. The elastic member  87  may be integral with a seal that is on the back of the separator  67  of  FIG. 6  and is between the adjacent unit fuel cells. 
     Each unit fuel cell  1  may have the separator  67  of  FIG. 6 , and a plurality of such unit fuel cells  1  are stacked one upon another to form the fuel cell stack  3  shown in  FIG. 1 . In  FIG. 4 , the elastic members  87  cover the circumference of the fuel cell stack  3 . In this case, the elastic members  87  of the separators  67  may be tightly arranged without a gap in the cell stacking direction. Alternatively, the elastic members  87  of the adjacent unit fuel cells  1  may have a gap between them. 
     The elastic members  87  of each of the end stacks  65 A and  65 C in the casing  63  are in contact with an inner wall  63   a  of the casing  63  at three sides thereof except the side that faces the center stack  65 B. The elastic members  87  of the center stack  65 B are in contact with the inner wall  63   a  of the casing  63  at two sides thereof except the two sides that face the end stacks  65 A and  65 C, respectively. The elastic members  87  of the adjacent stacks  65 A and  65 B are in contact with each other through a contact area  10 . The elastic members  87  of the adjacent stacks  65 B and  65 C are in contact with each other through a contact area  20 . Namely, each of the four side end faces of each elastic member  87  is in contact with the inner wall  63   a  of the casing  63  or a side end face of the adjacent elastic member  87 . This configuration immovably positions the stacks  65 A,  65 B, and  65 C in the casing  63 . 
     If vibration or shock is applied to the casing  63  accommodating the fuel cell stacks  65 A,  65 B, and  65 C during the running of the vehicle in which the casing  63  is installed, the elastic members  87  around the separators  67  absorb the vibration or shock, to prevent the torsional and bending deformation of the casing  63  and stacks  65 A,  65 B, and  65 C. This prevents the breakage of the parts of the casing  63  and stacks  65 A,  65 B, and  65 C and secures the performance and reliability of the fuel cells. This configuration also reduces load on the fuel cell supporting parts such as the blocks  66  and rods  68  and prevents the playing of the fuel cell supporting parts. Also reduced is the vibration of the outer faces of the casing  63 . This results in improving the rigidity of the casing  63 . Each elastic member  87  may be made of insulating material, and the elastic members  87  in the fuel cell stack  3  may be tightly attached to each other in the cell stacking direction. This eliminates an insulating sheet covering the circumferential face of the stack  65 A ( 65 B,  65 C), to reduce the total number of parts and weight of the fuel cell apparatus. 
     According to this embodiment, the elastic member  87  and seal  69  are made of the same material and are integrally formed on the separator  67 . Namely, there is no need of adding a new process for forming the elastic member  87 , i.e., the configuration of the first embodiment is manufacturable through existing processes. Forming a conventional seal for the separator  67  needs an opening for pouring seal material to be prepared in the plane of the separator  67  in the vicinity of the location where the seal  69  is formed. According to the first embodiment of the present invention, the seal  69  is simultaneously formed with the peripheral elastic member  87 , and therefore, an opening for pouring material of the separator  67  and elastic member  87  can be formed at the periphery of the separator  67 . Accordingly, the embodiment can effectively use the area of the separator  67  and expand an electricity generating active area. 
       FIG. 7  is a plan view showing a modification of the separator  67  of the first embodiment shown in  FIG. 6 . According to the modification, the elastic member  89  integral with the seal  69  has an undulated circumferential face. Due to the undulation, the circumferential face of the elastic member  89  partly gets in contact with the inner wall of the casing  63  and the elastic member  89  of the adjacent fuel cell stack. The circumferential face of the elastic member  89  may have any other shape. For example, it may have angular irregularities. 
     (Second Embodiment) 
       FIG. 8  is a plan view showing a separator  67  for a fuel cell according to a second embodiment of the present invention. The separator  67  has a rectangular shape. From a central part of each edge of the rectangular separator  67 , a rectangular elastic member  91  protrudes. The elastic member  91  is integral with a seal  69 . The elastic member  91  has an inner part  91   a  that is on a plane of the separator  67  and an outer part  91   b  that partly covers a peripheral edge of the separator  67 . The parts  91   a  and  91   b  provide the elastic member  91  with an L-shaped cross section. 
     The second embodiment provides the same effect as the first embodiment. The quantity of material necessary for forming the elastic members  91  of the second embodiment is smaller than that for forming the elastic members  89  of the first embodiment As a result, the second embodiment can reduce material cost and weight compared with the first embodiment. When installing the fuel cell stacks  65 A,  65 B, and  65 C in the casing  63 , the second embodiment can reduce friction against the inner wall  63   a  of the casing  63  shown in  FIG. 4 , to thereby improve installation workability. 
     (Third Embodiment) 
       FIG. 9  is a plan view showing a separator  67  for a fuel cell according to a third embodiment of the present invention. The third embodiment arranges two elastic members  93  on each of the top and bottom sides of the separator  67 . The elastic members  93  are integral with a seal  69 . Like the elastic member  91  of  FIG. 8 , the elastic member  93  of  FIG. 9  has an inner part  93   a  that is on a plane of the separator  67  and an outer part  93   b  that partly covers a peripheral edge of the separator  67 . The parts  93   a  and  93   b  provide the elastic member  93  with an L-shaped cross section. 
     (Fourth Embodiment) 
       FIG. 10  is a plan view showing a separator  67  for a fuel cell according to a fourth embodiment of the present invention. The fourth embodiment arranges two elastic members  95  on each of the left and right sides of the separator  67 . Like the elastic member  91  of  FIG. 8 , the elastic member  95  of  FIG. 10  has an inner part  95   a  that is on a plane of the separator  67  and an outer part  95   b  that partly covers a peripheral edge of the separator  67 . The parts  95   a  and  95   b  provide the elastic member  95  with an L-shaped cross section. 
     The elastic members  91 ,  93 , and  95  shown in  FIGS. 8 ,  9 , and  10  have a rectangular shape in a plan view. Instead, they may have an optional shape such as a semicircle, trapezoid, and ellipse. 
       FIG. 11  is a view showing a modification of the second embodiment shown in  FIG. 8  and corresponds to a sectional view taken along a line B-B of  FIG. 4 . Like the embodiment of  FIG. 8 , a separator  67  according to the modification has a rectangular shape. Each side of the separator  67  is provided with a rectangular elastic member  97  or  99 . The elastic member  99  is arranged between the adjacent fuel cell stacks  65 A and  65 B, or between  65 B and  65 C. Confronting faces of the adjacent elastic members  99  are provided with concaves and convexes that engage with each other. This configuration promotes easy assembling of the fuel cell stacks  65 A,  65 B, and  65 C into the casing  63  and prevents displacements between the adjacent fuel cell stacks. 
       FIG. 12  is a view showing a modification of the third embodiment shown in  FIG. 9  and corresponds to a sectional view taken along a line B-B of  FIG. 4 . Like the embodiment of  FIG. 9 , the modification arranges two elastic members  101  on each of the top and bottom sides of a separator  67 . According to the modification, an outer end  101   a  of each elastic member  101  protrudes from the separator  67  so that the protruding end  101   a  may be in contact with the inner wall  63   a  of the casing  63  and/or the protruding end  101   a  of the elastic member  101  of the separator  67  of the adjacent fuel cell stack. 
     Any one of the elastic members  87 ,  89 ,  91 ,  93 ,  95 ,  97 ,  99 , and  101  of the above-mentioned embodiments and modifications may be made of a different material from the seal  69 . In this case, each elastic member is fixed to the periphery of the separator  67  with adhesive or is integrally formed with the separator  67  in a process that is different from a process of forming the seal  69 . According to the above-mentioned embodiments and modifications, the tension rods  5  are passed through the fuel cell stack  3  ( 65 A,  65 B,  65 C). Instead, each side face of the fuel cell stack  3  may be covered with a tension plate that extends in a fuel cell stacking direction. For such an arrangement, the elastic members  87  and  89  of the present invention are also applicable. 
     The separator  67  may be made of metal. The shape of the separator  67  is not limited to a rectangle. It may be circular, triangular, or polygonal such as pentagonal. The separator  67  may have an optional shape if the periphery of the shape is exposed to the outside. The shape of the casing  63  must conform to the shape of the separator  67 . 
     According to the present invention, the elastic member is arranged at the periphery of the separator so that the elastic member may absorb vibration or shock externally applied to the casing. By doing so, the elastic member prevents the breakage of parts of the casing and fuel cells and secures the performance and reliability of the fuel cells. 
     At least one face of the separator is provided with the seal that is made of the same material as that of the elastic member. Employing the same material for the seal and elastic member enables the seal and elastic member to be simultaneously formed on the separator and eliminates a new process to be added for forming the elastic member. Namely, the elastic member is manufacturable through existing processes. 
     Forming a conventional seal for a separator needs a seal-material-pouring opening to be prepared in a plane of the separator in the vicinity of a location where the seal is formed. According to the present invention, the seal is simultaneously formed with the peripheral elastic member, and therefore, an opening for pouring material of the separator and elastic member can be formed at the periphery of the separator. Accordingly, the present invention can effectively use the area of the separator and expand an electricity generating active area. 
     At least one face of the separator is provided with the seal that is integral with the elastic member. Accordingly, there is no need of newly adding a process for forming the elastic member. Namely, the elastic member is manufacturable through existing processes. 
     The elastic member is entirely formed along the periphery of the separator, to efficiently absorb vibration and shock applied to the casing and fuel cells. This results in minimizing the twisting, bending, and deformation of the casing and fuel cells. 
     The separator may have a polygonal shape and each side of the polygonal separator may partly have the elastic member. The separator may have a rectangular shape with two opposite sides thereof each provided with the elastic member. This configuration can reduce material cost and weight compared with arranging the elastic member entirely along the periphery of the separator. The partial arrangement of the elastic member improves assembling workability because the partial arrangement of the elastic member reduces friction against the inner wall of the casing when fuel cell stacks are installed in the casing. 
     The entire contents of Japanese patent application P2004-219107 filed Jul. 27 th , 2004 are hereby incorporated by reference. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.