Abstract:
A battery module including a plurality of unit batteries arranged in series, an end plate located at each end of the plurality of unit batteries, a plurality of connecting members connected to each end plate to fix the end plates to the unit batteries, and at least one reinforcing member on each end plate, the reinforcing member serving to enhance the resistance to bending of each end plate.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of Korean Patent Application Nos. 10-2005-0069442 and 10-2005-0069482 filed on Jul. 29, 2005, both applications filed in the Korean Intellectual Property Office, the entire content of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a battery module having end plates with increased resistance to bending. 
     2. Description of the Related Art 
     Recently, a high output rechargeable battery (“unit battery”) using nonaqueous electrolyte and having a high energy density has been developed. High capacity batteries are used as the power source for driving motors, such as those of hybrid electric vehicles. 
     A high capacity secondary battery (“battery module”) is composed of a plurality of unit batteries. The unit battery includes an electrode assembly having positive and negative electrodes and a separator interposed between the positive and negative electrodes, a case for receiving the electrode assembly, a cap assembly for sealing the case, and positive and negative terminals extending from the cap assembly and electrically connected to the positive and negative electrodes, respectively. 
     The unit batteries are arranged in series in a housing, spaced from each other by a predetermined distance, and have their terminals are connected. The unit batteries are securely fixed to each other to form a battery module. 
     In a conventional battery module, end plates are disposed adjacent end unit batteries of the battery module to allow a compressive force to be applied to the unit batteries, thereby fixing the unit batteries to each other. Connecting members such as restraint rods are screw-coupled to the end plates. 
     However, when the battery module is used for a long time, swelling occurs in the unit batteries causing the unit batteries to apply stress to the end plates. As a result, the end plates may be deformed and the connecting member may become unstably coupled from the end plates. Stress may become concentrated on the unstable coupling portion between the end plates and the connecting members, causing damage to the unstable coupling portion. 
     By increasing a thickness of the connecting member or the end plate, the above problem may be solved. However, a thicker connecting member results in an increase in the weight of the battery module, thus deteriorating the performance of the device powered by the battery module. 
     SUMMARY OF THE INVENTION 
     The present invention provides a battery module including end plates having an enhanced resistance to bending. 
     According to one exemplary embodiment of the present invention, a battery module is provided including a plurality of unit batteries arranged in series, an end plate located at each end of the plurality of unit batteries, a plurality of connecting members connected to each end plate to fix the end plates to the plurality of unit batteries, and at least one reinforcing member on each end plate, the at least one reinforcing member enhancing resistance to bending of each end plate. 
     The reinforcing member may be formed of an H-beam and arranged in parallel with an edge of the end plate. The reinforcing member may be fixed on the end plate by welding. The end plate may be provided at opposite side edges with holes through which the connecting members are inserted. A contacting portion contacts each end of the plurality of unit batteries and extending portions extend from the contacting portion and are connected to the connecting members. 
     The extending portions may correspond to sides of the unit battery and a height of the extending portion is substantially identical to the contacting portion. The extending portion may be ring-shaped. 
     The reinforcing member may be installed on only the contacting portion or on both the contacting and extending portions. The reinforcing member may be installed on and extend from a surface of the end plate. Alternatively, the reinforcing member may be formed of a wrinkled plate with a plurality of peaks and valleys. The peaks and valleys may be arc-shaped and alternately arranged in a direction such that the reinforcing member has a wave-shaped cross-section. The wave shaped cross section may be different shapes, such as rectangular or triangular. The peaks and valleys may be oriented in a direction perpendicular or parallel to a height of the battery module. 
     Two reinforcing members may be combined with one end plate and the reinforcing members may be disposed such that an orientation of the peaks and valleys of a first reinforcing member is perpendicular to the orientation of the peaks and valleys of a second reinforcing member. 
     The reinforcing member is provided with holes through which the connecting members are inserted. Portions of the reinforcing member around the holes may be formed to have flat surfaces. The connecting members may be restraint rods inserted through the holes and fixed on the reinforcing members by nuts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a battery module according to an exemplary embodiment of the present invention. 
         FIG. 2  is a perspective view of an end plate of the battery module of  FIG. 1 . 
         FIG. 3  is a perspective view of an alternate end plate and a reinforcing member of the present invention. 
         FIG. 4  is a perspective view of another alternate end plate of the present invention. 
         FIG. 5  is an exploded perspective view of a battery module according to another exemplary embodiment of the present invention. 
         FIG. 6  is a perspective view of an assembled battery module of  FIG. 5 . 
         FIG. 7  is a perspective view of an alternate embodiment of a battery module of the present invention. 
         FIG. 8  is a partial side sectional view of an alternate embodiment of an end plate and a reinforcing member of the present invention. 
         FIG. 9  is a partial sectional view of an alternate embodiment of an end plate and a reinforcing plate of the present invention. 
         FIGS. 10 and 11  are sectional views of alternate embodiments of reinforcing members of the present invention. 
         FIG. 12  is a perspective view of a battery module according to another exemplary embodiment of the present invention. 
         FIG. 13  is a perspective view of a battery module according to yet another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , a battery module  100  of the present embodiment includes a plurality of unit batteries  10  and a plurality of barriers  25  disposed adjacent each planar surface of the unit batteries to provide coolant passages. 
     End plates  30  are installed adjacent each end unit battery to bookend the unit batteries  10  of the battery module  100 . Each end plate  30  includes a contact portion  31  contacting a corresponding adjacent barrier  25  and extending portions  32  extending from the contact portion  31 . 
     In one exemplary embodiment, a height of each extending portion  32  is identical to a height “h” of the contacting portion  31 . However, the present invention is not limited to this case. 
     The end plates  30  are connected to each other by connecting members  35 , such as restraint rods, to fix the unit batteries  10  and the barriers  25 . In one exemplary embodiment, two connecting members  35  are installed on each extending portion  32  of each end plate  30 . The extending portions  32  are provided with holes  37  ( FIG. 2 ) through which the connecting members  35  are inserted. In one exemplary embodiment, each extending portion  32  is provided with two holes  37 . 
     The end plates  30  are connected by the connecting members  35  inserted through the holes  37  and fixed by nuts  36  threaded to each end of each connecting member  36 . The nuts  36  provided a compressive force to the battery module allowing the unit batteries  10  and the barriers  25  to be fixed to each other. 
     A reinforcing member  34  is installed on each of the end plates  30 . In one exemplary embodiment, the reinforcing member  34  is formed on only the contact portion  31  of the end plate  30  so as not to interfere with coupling the connecting members  35  to the extending portions  32 . As shown in  FIG. 1 , the reinforcing member  34  is formed on an exterior planar surface of the end plate  30  which does not contact a barrier  25 . 
     The existence of the reinforcing member  34  on the exterior planar surface of the end plate  30  prevents stress concentration where the end plate  30  contacts the barrier  25  by preventing deformation of the end plate caused by expansion of the unit batteries  10 . The reinforcing member  34  also effectively dissipates heat generated from the unit batteries  10  by increasing the heat transmission area of the end plate  30 . 
     In this embodiment, the reinforcing member  34  includes a plurality of H-beams arranged on the outer surface of the end plate  30  at predetermined intervals. The reinforcing member  34  is fixed on the outer surface of the end plate  30  by, for example, welding. The number and size of H-beams of the reinforcing member  34  is not specifically limited and may be dictated by specifications for the battery module  100  to which the end plates  30  are applied. 
     Forming the reinforcing member  34  on the end plate  30  allows the thickness of the end plate  30  to be less than a conventional end plate. As a result, the end plate  30  is lighter than a conventional end plate, thus reducing a weight of the battery module as compared with a conventional battery module. 
       FIG. 3  is a perspective view of an alternate end plate  40 . As shown in  FIG. 3 , the end plate  40  is substantially similar to the end plate  30  of  FIG. 1 . However, each extending portion  42  to which the connecting member is coupled is ring-shaped with a hole  47  through which the connecting member is insertable. Two ring-shaped extending portions  42  are formed on each end of a contact portion  41  of the end plate  40 . Since the overall area of the extending portion  42  is less than the extending portion  32  of  FIG. 1 , the end plate  40  is lighter, thus reducing the weight of the battery module. 
       FIG. 4  is a perspective view of an alternate end plate  50  of the present invention. As shown in  FIG. 4 , a reinforcing member  54  is formed on both contacting and extending portions  51 ,  52  of the end plate  50 . Holes  57  for coupling a connecting member are formed on the extending portions  52 . 
     The end plate  50  effectively distributes stress applied to the extending portions  52  as well as stress applied to the contacting portion  51 , preventing deformation of the end plate  50  by external force. 
     Referring to  FIGS. 5 and 6 , a battery module  200  includes a plurality of unit batteries  60  and end plates  62  disposed adjacent each end unit battery to bookend the unit batteries  60 . Connecting members  64  are inserted through holes  62   a ,  66   a  in each end plate  62  and in the reinforcing member  66  is secured to the end plates  62  by nuts  65 , thereby fixing the unit batteries  60  and the end plates  62 . 
     A reinforcing member  66  formed as a wrinkled plate is installed on the end plate  62 . The reinforcing member  66  may be coupled to the connecting members  62  such that it extends from the end plate  62 . Alternatively, the reinforcing member  66  may be coupled to the connecting members  62  such that it is welded to the end plate  62 . 
     The reinforcing member  66  is provided with a plurality of peaks and valleys  66   b , giving the reinforcing member  66  a wave-shaped cross-section. The peaks and valleys  66   b  may be oriented in a horizontal direction (along an X-axis in  FIG. 5 ) in parallel with each other. That is, the peaks and valleys  66   b  are oriented perpendicular to a height h of the battery module. In one exemplary embodiment as shown in  FIG. 8 , the peak or valley  66   b  where the nut is threaded to the connecting member  62  is flat. More specifically, at a portion of the reinforcing member  66  around each hole  66   a , a first surface  66   c  contacting the nut  65  and a second surface  66   d  contacting the reinforcing member  66  are formed to be flat. Alternatively, as shown in  FIG. 9 , both side end portions of a reinforcing member  70 , where holes  70   a  are formed to receive a connecting member  71  may be formed to be flat without having a peak or a valley. 
     In another exemplary embodiment as shown in  FIG. 7 , the peaks and valleys  66   b  may be arranged in a vertical direction (along a Y-axis in  FIG. 7 ). That is, the peaks and valleys  66   b  extend in a direction parallel to a height “h” of the battery module. 
       FIGS. 10 and 11  are sectional views of alternate configurations of reinforced members of the present invention. Referring to  FIG. 10 , peaks and valleys  76  of a reinforcing member  72  are formed to have a generally rectangular cross-section. That is, the elements making up the peaks and valleys  76  are perpendicular with respect to each other. Referring to  FIG. 11 , peaks and valleys  87  of a reinforcing member  74  are formed to have a generally triangular cross-section. 
       FIGS. 12 and 13  are perspective views of battery modules according to alternate embodiments of the present invention. In battery modules  300 ,  400  of these exemplary embodiments, two or more reinforcing members  82 ,  84  are combined with one end plate  80 . The reinforcing members  82 ,  84  are disposed such that the direction of the peaks and valleys of a first reinforcing member is perpendicular to the direction of the peaks and valleys of a second reinforcing member. 
     The battery modules according to the foregoing embodiments can be used as the power source to drive motors, such as those for hybrid electric vehicles, electric vehicles, electric scooters, electric bicycles, wireless vacuum cleaners, or the like. 
     Although exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.