Patent Publication Number: US-2009226793-A1

Title: Fuel cell stack assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2007-0129544 filed Dec. 13, 2007, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     (a) Technical Field 
     The present invention relates to a fuel cell stack assembly, in which a wire is used to assemble a fuel cell stack while maintaining a constant surface pressure on each fuel cell by utilizing a wide elasticity range of the wire, which can ensure a high fastening force even with a small amount of material, thus making the fuel cell lightweight and maximizing the package efficiency. 
     (b) Background Art 
     In general, a fuel cell stack refers to an electrical energy generating device, in which a plurality of unit cells are piled up. 
     Such a fuel cell stack has a structure in which one to two hundred separators, gas diffusion layers (GDLs), gaskets, and the like are stacked in orderly manner, and end plates are attached to both ends of the fuel cell stack. 
     In a prior art fuel cell stack, the end plates on both ends of the fuel cell stack are typically coupled by means of bands or full thread bolts. 
     The prior art fuel cell stack, however, has drawbacks. For instance, since the gasket is often made from a rubber material having visco-elastic property that varies depending on ambient temperature of the stack, initial tightening force may be weakened as time goes by and may eventually fail to maintain the tightening force uniformly. In order to complement the incomplete tightening force on the gasket, the end plates on both ends of the stack are required to be further secured by means of an additional bolts or bands. 
     Hereinafter, the drawbacks of the prior art fuel cell stack assembly will be described in detail with reference to FIGS. A 1  and  1 B. 
       FIG. 1A  is a schematic view of a conventional fuel cell stack in which end plates  20  are assembled by means of bolts  10 , and  FIG. 1B  is a schematic view of a conventional fuel cell stack in which end plates  20  are assembled by means of bands  30 . 
     The fuel cell stack as shown in  FIG. 1A  has drawbacks in that since the overall volume of a stack  50  is increased, it is difficult to package the stack  50 . Moreover, the weight of the stack  50  is increased due to the weight of the bolts  10 , and stress is concentrated on a thread portion of the bolt  10  when a load acts in the longitudinal direction of the bolt  10 , and thus the thread portion may be easily damaged. 
     The fuel cell stack as shown in  FIG. 1B  has drawbacks in that it is difficult to control the surface pressure with respect to a stack  60 , and it is also difficult to control the initial surface pressure since the size of the bands  30  is not uniform. 
     The information disclosed in the Background section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art. 
     SUMMARY OF THE DISCLOSURE 
     The present invention has been made in an effort to solve the above-described problems associated with prior art. The present invention is directed to a fuel cell stack assembly which can maintain a constant surface pressure on the fuel cell by utilizing a wide elasticity range of the wire, and ensure a high fastening force even with a small amount of material, thus making the fuel cell lightweight and maximizing the package efficiency. 
     In one aspect, the present invention provides a fuel cell stack assembly for a fuel cell, the fuel cell stack assembly comprising: at least one wire for fastening end plates mounted on both end portions of a fuel cell stack; at least one tensioner mounted on at least one portion of the top surface of an upper end plate; at least one tension guide each of which includes a central guide for guiding up and down movement of the tensioner and surrounds the tensioner; at least one upper guide mounted on both sides of the top surface of the upper end plate for guiding the wire; and at least one lower guide mounted on both sides of the bottom surface of a lower end plate for guiding the wire. 
     Preferably, the tensioner may be mounted on the top surface of the upper end plate by means of a tension bolt such that the height of the tensioner can be adjusted by the tension bolt, thereby the tension of the wire being able to be adjusted. 
     Suitably, each of the tensioner, the upper guide and the lower guide may include a plurality of guide grooves such that the wires received in the guide grooves do not interfere with each other. 
     Also suitably, the lower guide may include a locking groove formed therein in a direction perpendicular to the guide grooves of the lower guide. Both ends of the wire are connected to a locking member mounted thereon. The locking member can be inserted into the locking groove of the lower guide. 
     Preferably, the wire is formed of, e.g., a piano wire or a shape memory alloy. 
     It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like. 
     The above features and advantages of the present invention will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated in and form a part of this specification, and the following Detailed Description, which together serve to explain by way of example the principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments thereof illustrated the accompanying drawings which are given hereinafter by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1A  is a schematic view of a conventional fuel cell stack assembled by means of bolts; 
         FIG. 1B  is a schematic view of a conventional fuel cell stack assembled by means of bands; 
         FIG. 2  is a schematic top view of a fuel cell stack assembly in accordance with a preferred embodiment of the present invention; 
         FIG. 3  is a schematic bottom view of the fuel cell stack assembly of  FIG. 2 ; and 
         FIGS. 4 to 6  are detailed views of the fuel cell stack assembly of  FIG. 2 . 
     
    
    
     Reference numerals set forth in the Drawings includes reference to the following elements as further discussed below: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 100: upper end plate 
               
               
                   
                 110: tensioner 
               
               
                   
                 120: tension guide 
               
               
                   
                 130: upper guide 
               
               
                   
                 140: lower end plate 
               
               
                   
                 150: lower guide 
               
               
                   
                 160: locking member 
               
               
                   
                 200: wire 
               
               
                   
                   
               
            
           
         
       
     
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the drawings attached hereinafter, wherein like reference numerals refer to like elements throughout. The embodiments are described below so as to explain the present invention by referring to the figures. 
       FIG. 2  is a schematic top view of a fuel cell stack assembly in accordance with a preferred embodiment of the present invention,  FIG. 3  is a schematic bottom view thereof, and  FIGS. 4 to 6  are detailed views thereof. 
     In a preferred embodiment of the present invention, as shown in  FIGS. 2 and 3 , a fuel cell stack is assembled by winding a plurality of wire  200  on a tensioner  110  and an upper guide  130 , which are mounted on a portion of the top surface of an upper end plate  100 , and inserting a locking member  160  into a lower guide  150  mounted on a portion of the bottom surface of a lower end plate  140 , thus maintaining a constant surface pressure on a fuel cell. 
     More particularly, each of the two end portions of the wire  200  is connected to the locking member  160 . A middle portion of the wire  200  is wound on the tensioner  110  and the upper guide  130 . The locking member  160  is inserted into a locking groove  151  of the lower guide  150   
     Preferably, the wire  200  may be formed of a piano wire. The piano wire is generally formed of a spring steel material having a diameter of 0.1 to 5 mm. Also preferably, the piano wires may be twisted into a rope, if necessary. 
     Normally, the piano wire formed of a spring steel material and having a diameter of about 1 mm has a break load of about 1230 N and a tensile strength of about 151 MPa. 
     Moreover, if the wire  200  is made of a piano wire through a drawing process and the like, it can prevent defects such as impurities, pores and the like, which are associated with a fuel cell stack in which end plates are assembled by a bolt or band and have a strength close to the theoretical value, thus enabling the fuel cell stack to be lightweight and efficiently packaged. 
     In addition, when the wire  200  is formed of a super elastic alloy, the elasticity range may be increased 8 to 10 times compared with that formed of a spring steel. When it is formed of a shape memory alloy, it is possible to facilitate the wire compensation for a change in the surface pressure due to a thermal expansion at an operational temperature (about 80° C.) of the fuel cell. 
     In order to adjust the tension of the wire  200 , as shown in  FIG. 4 , a plurality of tensioners  110  are mounted on a plurality of portions of the top surface of the upper end plate  100  by means of tension bolts  111 . In this case, the vertical position of each of the tensioners  110  can be adjusted by the tension bolt  111  and thus the tension of the wire  200  can be adjusted according to the height of the tension bolt  111 . 
     In particular, when the tensioner  110  is moved upward by rotating the tension bolt  111  in one direction, the tension of the wire  200  is increased, whereas, when the tensioner  110  is moved downward by rotating the tension bolt  111  in the opposite direction, the tension of the wire  200  is decreased, such that it is possible to maintain a constant surface pressure on the fuel cell by adjusting the height of the tensioner  110  according to the tensile state of the wire  200 . 
     In this case, a plurality of guide grooves  112  are formed on a plurality of portions of the top surface of the tensioner  110  at regular intervals so that the wires  200  can be wound on the tensioner  110  without interfering with each other. 
     Preferably, it is possible to provide a ratchet wheel for winding the wire  200  instead of the tensioner  110  at the position where the tensioner  110  is mounted. In this case, the adjustment range for the wire length may be increased, and thus it is possible to fasten the wire  200  without a press during an initial connection of the wire  200 . 
     Furthermore, a tension guide  120  having a central groove in shape of “π” is mounted on a portion of the top surface of the upper end plate  100  so as to surround the tensioner  110  at both ends of the tensioner  110 , thus being able to guide the vertical (up and down) movement of the tensioner  110 . 
     Each end of the tension guide  120  has a projection surface  121 . The projection surface  121  is in contact with a portion of the top surface of the upper end plate  100 . A bolt  122  is inserted into the projection surface  121  so as to fix the tension guide  120  to the upper end plate  100 . 
     As shown in  FIG. 5 , a plurality of the upper guides  130  are mounted on a plurality of portions of the top surface of the upper end plate  100 . Preferably, the upper guides  130  are positioned along side portions of the top surface at both sides of the tensioner  110  by means of bolt  132  so as to guide the wire  200  coming from both sides of the tensioner  110 . 
     In this case, each of the upper guides  130  includes a plurality of guide grooves  131  formed thereon to prevent the wires  200  from interfering with each other. Suitably, the guide grooves  131  of the upper guide  130  may be formed with a curved surface to prevent stress from being concentrated on the wires  200 . 
     In addition, as shown in  FIGS. 5 and 6 , a plurality of the lower guides  150  are mounted on a plurality of portions of the bottom surface of the lower end plate  140  by means of bolts  153  so as to guide the wire  200  introduced to the lower end plate  140 . 
     In this case, each of the lower guide  150  includes a plurality of guide grooves  152  formed at regular intervals the same as the guide grooves  131  of the upper guide  130 . A locking groove  151  is formed on one side of the guide groove  152  of the lower guide  150  in the longitudinal direction thereof (i.e., perpendicular to the guide groove) so that the locking member  160  mounted on the end of the wire  200  is inserted therein. 
     That is, the locking members  160  mounted on both ends of the wires  200  are inserted into the locking grooves  151  provided on both sides of the lower end plate  140  such that the wire  200  maintains the tightness at a constant tension and the tension is adjusted according to the height of the tensioner  110  on which the wire  200  is wound. 
     Preferably, the locking member  160  may be formed of a cylindrical metal material so that the plurality of wires  200  are connected at regular intervals. 
     As described above, the fuel cell stack assemblies in accordance with the preferred embodiments of the present invention provide advantages including the following: 1) since the fuel cell stack is assembled by means of the wire, it is possible to maintain a constant surface pressure on the fuel cell by utilizing a wide elasticity range of the wire; 2) even with a small amount of material, it is possible to ensure a high fastening force, thus making the fuel cell lightweight and maximizing the package efficiency; and 3) with the up and down movement of the tensioner, it is possible to adjust the tension of the wires to control the surface pressure on the fuel cell and easily measure the tension associated directly with the surface pressure on the fuel cell. 
     The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.