Abstract:
A method and apparatus for assembling a fuel cell stack is disclosed, wherein the apparatus includes a plurality of dunnage cassettes adapted to cooperate with a plurality of containers, a fixture, and an assembly device to simultaneously assemble a plurality of membrane electrode assemblies together with a plurality of bipolar plates.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 12/189,231 filed Aug. 11, 2008, the entire disclosure of which is hereby incorporated herein by reference 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a method of assembling a fuel cell stack. More particularly, the invention is directed to a modular production method, scalable from a low volume to a high volume production, and an apparatus for assembling a plurality of bipolar plates together with a plurality of membrane electrode assemblies. 
       BACKGROUND SUMMARY 
       [0003]    Fuel cell systems are increasingly being used as a power source in a wide variety of applications. Fuel cell systems have been proposed for use in power consumers such as vehicles as a replacement for internal combustion engines, for example. Fuel cells may also be used as stationary electric power plants in buildings and residences, as portable power in video cameras, computers, and the like. Typically, the fuel cells generate electricity used to charge batteries or to provide power for an electric motor. 
         [0004]    Fuel cells are electrochemical devices which directly combine a fuel such as hydrogen and an oxidant such as oxygen to produce electricity. The oxygen is typically supplied by an air stream. The hydrogen and oxygen combine to result in the formation of water. Other fuels can be used such as natural gas, methanol, gasoline, and coal-derived synthetic fuels, for example. The term “fuel cell” is typically used to refer to either a single cell or a plurality of cells depending upon the context in which it is used. The plurality of cells is typically bundled together and arranged to form a stack with the plurality of cells commonly arranged in electrical series. Since single fuel cells can be assembled into stacks of varying sizes, systems can be designed to produce a desired energy output level providing flexibility of design for different applications. 
         [0005]    Different fuel cell types can be provided such as phosphoric acid, alkaline, molten carbonate, solid oxide, and proton exchange membrane (PEM), for example. The basic components of a PEM-type fuel cell are two electrodes separated by a polymer membrane electrolyte. Each electrode is coated on one side with a thin catalyst layer. The electrodes, catalyst, and membrane together form a membrane electrode assembly (MEA). 
         [0006]    In a typical PEM-type fuel cell, the MEA is sandwiched between “anode” and “cathode” diffusion mediums (hereinafter “DM&#39;s”) or diffusion layers that are formed from a resilient, conductive, and gas permeable material such as carbon fabric or paper. The DM&#39;s serve as the primary current collectors for the anode and cathode as well as provide mechanical support for the MEA. The DM&#39;s and MEA, collectively referred to as MEA hereinafter, are pressed between a pair of electronically conductive plates such as bipolar plates, for example, which serve as secondary current collectors for collecting the current from the primary current collectors. 
         [0007]    Both of the MEA and the bipolar plate are flexibly thin, approximately less than 1.0 mm, and extremely delicate with special coatings and/or fluid channels. As such, each MEA and bipolar plate is individually packaged with a protective separator to militate against damage thereto during shipping. Accordingly, conventional assembly requires that each MEA and bipolar plate be removed and de-stacked from the individual packages and then re-stacked with either a manual or an automated pick-and-place means. The de-stacking and re-stacking operations, in addition to the delicate nature and limited handling area of the MEA and the bipolar plates, result in a slow assembly process and/or expensive tooling. Furthermore, packing and disposing of the protective separators adds time and cost to the manufacturing cycle. 
         [0008]    It would be desirable to develop a modular production method, scalable from a low volume to a high volume production, and produce an apparatus for assembling the MEA and the bipolar plates for a fuel cell stack wherein a cost thereof is minimized and an efficiency thereof is maximized. 
       SUMMARY OF THE INVENTION 
       [0009]    According to the present invention, a modular production method, scalable from a low volume to a high volume production, and an apparatus for assembling the MEA and the bipolar plates for a fuel cell stack wherein a cost thereof is minimized and an efficiency thereof is maximized, has surprisingly been discovered. 
         [0010]    In one embodiment, the method for assembling a fuel cell stack comprises the steps of providing a plurality of dunnage cassettes adapted to receive one of a membrane electrode assembly and a bipolar plate therein; providing a plurality of containers adapted to receive the dunnage cassettes therein; providing a fixture adapted to receive the dunnage cassettes therein; providing an assembly device having a plurality of locating rods disposed thereon, the locating rods adapted to assemble at least one membrane electrode assembly together with at least one bipolar plate; disposing the at least one membrane electrode assembly into the dunnage cassettes; disposing the at least one bipolar plate into the dunnage cassettes; inserting the dunnage cassettes into the containers; disposing the containers adjacent opposing sides of the fixture; causing the dunnage cassettes to slide from the containers into the fixture; causing the locating rods of the assembly device to extend through the dunnage cassettes; and causing the dunnage cassettes and the containers to retract from the fixture having the at least one membrane electrode assembly and the at least one bipolar plate remain on the assembly device. 
         [0011]    In another embodiment, the method for assembling a fuel cell stack comprises the steps of providing at least one membrane electrode assembly; providing at least one bipolar plate; providing a plurality of dunnage cassettes including at least one tab and at least one of a raised portion, at least one holding clip, and a retaining lip formed thereon, wherein the dunnage cassettes are adapted to receive one of the at least one membrane electrode assembly and the at least one bipolar plate therein, the dunnage cassettes further including at least one slot formed therein; providing a plurality of containers having a plurality of channels formed therein, the channels adapted to receive the dunnage cassettes therein, wherein one end of each of the channels includes a stop formed therein; providing a fixture having a plurality of channels formed therein, the channels adapted to receive the dunnage cassettes therein; providing an assembly device having a plurality of locating rods disposed thereon, the locating rods adapted to assemble the at least one membrane electrode assembly together with the at least one bipolar plate; disposing the at least one membrane electrode assembly into the dunnage cassettes; disposing the at least one bipolar plate into the dunnage cassettes; inserting the dunnage cassettes into the channels of the containers; disposing the containers adjacent opposing sides of the fixture, wherein at least one of the containers is offset a predetermined distance from an edge of the fixture; causing the dunnage cassettes to slide from the containers into the channels of the fixture; causing the locating rods of the assembly device to extend through the dunnage cassettes; causing a nose portion of the locating rods to release the at least one holding clip of the dunnage cassettes; and causing the dunnage cassettes and the containers to retract from the fixture having the at least one membrane electrode assembly and the at least one bipolar plate remain on the assembly device. 
         [0012]    In one embodiment, the apparatus for assembling a fuel cell stack comprises a plurality of dunnage cassettes adapted to receive one of a membrane electrode assembly and a bipolar plate therein, the dunnage cassettes including at least one slot formed therein; a plurality of containers having a plurality of channels formed therein, the channels adapted to receive the dunnage cassettes therein; a fixture having a plurality of channels formed therein, the channels adapted to receive the dunnage cassettes therein, wherein the channels of the containers are substantially aligned with alternating channels of the fixture; and an assembly device having a plurality of locating rods disposed thereon, the locating rods adapted to assemble the at least one membrane electrode assembly together with the at least one bipolar plate, wherein the at least one slot of the dunnage cassettes permit the dunnage cassettes to be removed from the locating rods. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is an exploded perspective view of an apparatus for assembling a fuel cell stack according to an embodiment of the invention; 
           [0014]      FIG. 2  is an enlarged side perspective view of a dunnage cassette for the apparatus for assembling the fuel cell stack illustrated in  FIG. 1  having one of an MEA and a bipolar plate disposed therein; 
           [0015]      FIG. 3  is an enlarged fragmentary top cross-sectional view of the dunnage cassette illustrated in  FIG. 2 , wherein the dunnage cassette includes a raised portion and a retaining lip formed thereon; 
           [0016]      FIG. 4  is a side perspective view of a container for the apparatus for assembling the fuel cell stack illustrated in  FIG. 1  having a plurality of the dunnage cassettes disposed therein; 
           [0017]      FIG. 5  is a cross-sectional view of the container illustrated in  FIG. 4 ; 
           [0018]      FIG. 6  is a partially exploded perspective view of the apparatus illustrated in  FIG. 1 ; 
           [0019]      FIG. 7  is an enlarged fragmentary top cross-sectional view of the dunnage cassette illustrated in  FIG. 2 , wherein a locating rod of an assembly device is releasing a holding clip of the dunnage cassette from one of an MEA and a bipolar plate; and 
           [0020]      FIG. 8  is a partially exploded perspective view of the apparatus illustrated in  FIGS. 1 and 6 , wherein an actuator has caused the MEA and bipolar plates to be disposed into a fixture. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    The following detailed description and appended drawings describe and illustrate various exemplary embodiments of the invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner. In respect of the methods disclosed, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical. 
         [0022]      FIG. 1  shows an apparatus  10  for assembling a fuel cell stack  12  according to an embodiment of the invention. The apparatus  10  includes a plurality of dunnage cassettes  14 , a pair of containers  16 ,  18 , a fixture  20 , and an assembly device  22 . Each of the dunnage cassettes  14  shown is a tray  23  adapted to removably receive one of an MEA  25  and a bipolar plate  26  therein. It is understood that each of the dunnage cassettes  14  can also be a “clam shell” package including the tray  23  having a cover pivotally attached thereto. The dunnage cassettes  14  are generally rectangular in shape, although it is understood that the dunnage cassettes  14  can have any size and shape as desired. As illustrated in  FIG. 2 , a first tab  28  is formed on an upper edge  32  of the tray  23  adjacent an outer edge  36  thereof. A second tab  30  is formed on a lower edge  34  of the tray  23  adjacent the outer edge  36  thereof. While the edges  32 ,  34 , have been referred to as upper and lower, respectively, it is understood that the tray  23  may be oriented in a variety of locations, wherein the edges  32 ,  34  may be in different positions. 
         [0023]    The tray  23  may also include at least one of a pair of holding clips  38 ,  39 , a raised portion  40 , and a retaining lip  41  formed thereon. Additional or fewer clips may be disposed on the tray  23 , if desired. In the embodiment shown, the clips  38 ,  39  are disposed on opposing corners of the tray  23 , wherein the clips  38 ,  39  are in a substantially diagonal relation to each other. It is understood that the clips  38 ,  39  can be disposed elsewhere on the tray  23  as desired. It is further understood that the clips  38 ,  39  can have any shape as desired. The clips  38 ,  39  are adapted to extend though respective apertures  46 ,  48  formed in the MEA  25  and the bipolar plate  26  to retain the MEA  25  and the bipolar plate  26  in the dunnage cassettes  14 . The raised portion  40  is formed adjacent the edges  32 ,  34 ,  36  of the tray  23  creating a recessed area. The raised portion  40  is adapted to locate and retain the MEA  25  and the bipolar plate  26  in the dunnage cassettes  14 . In the embodiment shown in  FIG. 3 , the retaining lip  41  is formed adjacent the raised portion  40  of the tray  23  and extends laterally outwardly from the tray  23 . It is understood that the retaining lip  41  can be formed elsewhere on the tray  23  as desired such as adjacent the edges  32 ,  34 ,  36  of the tray  23 , for example. It is further understood that the retaining lip  41  can have any shape as desired. The retaining lip  41  includes a shoulder  42  formed therein. A gap B is formed between an inner surface of the tray  23  and the shoulder  42  of the retaining lip  41  to receive the MEA  25  and the bipolar plate  26  therein. The retaining lip  41  is adapted to locate and retain the MEA  25  and the bipolar plate  26  in the dunnage cassettes  14 . 
         [0024]    A pair of slots  43 ,  44  may also be formed in the tray  23 . Additional or fewer slots may be formed in the tray  23 , if desired. The slots  43 ,  44  are formed adjacent opposing edges  32 ,  34  of the tray  23 . The slot  43  is formed in an upper portion of the tray  23 , extending inwardly from an outer edge  50  thereof to the clip  38 . The slot  44  is formed in a lower portion of the tray  23 , extending inwardly from the outer edge  50  thereof to the clip  39 . It is understood that the slots  43 ,  44  can be formed elsewhere in the tray  23  as desired. 
         [0025]    As illustrated in  FIG. 4 , the dunnage cassettes  14  are adapted to be slideably received in the containers  16 ,  18 . The containers  16 ,  18  are box-like having an upper section  51 , a lower section  52 , and opposing side sections  54 ,  56 . It is understood that the containers  16 ,  18  can have any size and shape as desired. A front and a rear of each of the containers  16 ,  18  are open to receive the dunnage cassettes  14  therein and to permit the dunnage cassettes  14  to be received into the fixture  20 . It is understood that the containers  16 ,  18  can be produced from any conventional material such as a polymer and a metal, for example. The dunnage cassettes  14  are disposed in a plurality of spaced-apart channels  58  formed in each of the containers  16 ,  18 . The channels  58  are formed in the upper section  51  and the lower section  52  of the containers  16 ,  18  and spaced at a predetermined distance D. In the embodiment shown, the predetermined distance D is at least a width of one of the dunnage cassettes  14 . It is understood that the predetermined distance D can be any distance as desired. As shown in  FIG. 5 , each of the channels  58  includes a stepped portion  60  adapted to receive the tabs  28 ,  30  therein. A stop  62  is formed in the stepped portion  60  at an end  64  of each of the channels  58 . The stop  62  cooperates with the tabs  28 ,  30  to retain the dunnage cassettes  14  within the containers  16 ,  18  and cause the dunnage cassettes  14  to be extracted from the fixture  20  by the containers  16 ,  18  during operation of the apparatus  10 . 
         [0026]    Referring to  FIG. 6 , the fixture  20  includes a first plate  66  and a second plate  68 . Each of the first plate  66  and the second plate  68  includes a plurality of spaced-apart channels  70  formed therein. The channels  70  are formed in the plates  66 ,  68  in a substantially parallel relation to an edge  72  of the fixture  20 . The channels  70  are adapted to receive the dunnage cassettes  14  from the containers  16 ,  18  therein. 
         [0027]    The assembly device  22  is disposed adjacent the fixture  20 . In the embodiment shown, the assembly device  22  includes an end plate  74  having a first locating rod  76  and a second locating rod  78  laterally extending therefrom. Additional locating rods may be disposed on the end plate  74  if desired. The end plate  74  is generally rectangular in shape and adapted to abut the fixture  20  during operation of the apparatus  10 . It is understood that the end plate  74  can have other shapes as desired. The locating rods  76 ,  78  are disposed adjacent opposing corners of the end plate  74 , wherein the locating rods  76 ,  78  are in a substantially diagonal relation to each other. It is understood that the locating rods  76 ,  78  can be disposed elsewhere on the end plate  74  as desired. As illustrated in  FIG. 7 , the locating rods  76 ,  78  are adapted to extend though the respective apertures  46 ,  48  formed in the MEA  25  and the bipolar plate  26 . A nose portion  79  of the locating rods  76 ,  78  contacts and releases the clips  38 ,  39  of the dunnage cassettes  14  from each of the MEA  25  and the bipolar plate  26 , as indicated in  FIG. 7  by the dashed lines. 
         [0028]    It is understood that the apparatus  10  can further include at least one actuator  80 , as shown in  FIGS. 1 ,  6 , and  8 , and a compression device (not shown). The at least one actuator  80  is adapted to cause the dunnage cassettes  14  to be received into the fixture  20  and the assembly device  22  to abut the fixture  20 . The compression device is adapted to properly bundle the MEAs  25  and the bipolar plates  26  into the fuel cell stack  12  and complete the assembly process. 
         [0029]    In operation, the tray  23  of each of the dunnage cassettes  14  receives one of the MEA  25  and the bipolar plate  26  therein. As shown in  FIGS. 2 and 3 , at least one of the holding clips  38 ,  39 , the raised portion  40 , and the retaining lip  41  of each tray  23  retain the MEA  25  and the bipolar plate  26  therein to militate against damage thereto. Thereafter, as illustrated in  FIG. 4 , the dunnage cassettes  14  having the MEAs  25  disposed therein are then slideably received into the container  16 , and the dunnage cassettes  14  having the bipolar plates  26  disposed therein are slideably received into the container  18 . It is understood that the dunnage cassettes  14  having the MEAs  25  disposed therein can be disposed into the container  18  and the dunnage cassettes  14  having the bipolar plates  26  disposed therein can be disposed into the container  16 , if desired. Accordingly, the tabs  28 ,  30  of each of the dunnage cassettes  14  are disposed in the stepped portion  60  of each of the channels  58 . 
         [0030]    The containers  16 ,  18  are then disposed adjacent opposing sides of the fixture  20 . As shown in  FIG. 6 , the container  16  is offset a predetermined distance G from the edge  72  of the fixture  20 , and the container  18  is offset the predetermined distance G from the rear of the fixture  20 . The predetermined distance G illustrated is approximately the width of one of the dunnage cassettes  14  to cause the channels  58  of the containers  16 ,  18  to substantially align with alternate channels  70  of the fixture  20 , although it is understood that the predetermined distance G can be any distance as desired. As shown in  FIG. 8 , the dunnage cassettes  14  of the containers  16 ,  18  are then caused by the at least one actuator  80  to slide into the fixture  20 , until the tabs  28 ,  30  formed thereon abut the stop  62  formed in each end  64  of the channels  58 . Accordingly, the MEAs  25  and the bipolar plates  26  are disposed in the fixture  20  in an interleaved pattern having the apertures  46 ,  48  substantially aligned. 
         [0031]    Thereafter, as shown in  FIG. 1 , the assembly device  22  is caused by the at least one actuator  80  to abut the edge  72  of the fixture  20 . Accordingly, the locating rods  76 ,  78  of the assembly device  22  are caused to extend through the respective apertures  46 ,  48  of the MEAs  25  and the bipolar plates  26 . In the embodiment shown, the nose portion  79  of each of the locating rods  76 ,  78  substantially contacts the clips  38 ,  39  to release the MEAs  25  and the bipolar plates  26  from the dunnage cassettes  14 . Once the locating rods  76 ,  78  have released the MEAs  25  and the bipolar plates  26  from the dunnage cassettes  14 , the at least one actuator  80  and the containers  16 ,  18  are caused to retract from the fixture  20 . When the containers  16 ,  18  retract, the stop  62  formed in the end  64  of each of the channels  58  engages the tabs  28 ,  30  to also cause the dunnage cassettes  14  to retract from the fixture  20 . As the dunnage cassettes  14  retract, the locating rods  76 ,  78  slide along the respective slots  43 ,  44  formed therein and the MEAs  25  and the bipolar plates  26  are removed from the recessed area of the tray  23  and released from the retaining lip  41  thereof. Once the dunnage cassettes  14  are fully retracted from the fixture  20 , the compression device assembles the MEAs  25  and the bipolar plates  26  disposed on the locating rods  76 ,  78  of the assembly device  22  into the fuel cell stack  12  and completes the assembly operation. 
         [0032]    From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, make various changes and modifications to the invention to adapt it to various usages and conditions.