Abstract:
A rechargeable battery pack for improving watertight performance for unit cells and a protection circuit module by draining water having permeated into a case while allowing inflow and outflow of cooling air into/out of the case. The rechargeable battery pack includes at least one unit cell including a rechargeable battery, and a case for supporting the unit cell and receiving the same, wherein the case includes a bottom, a reinforcing rib protruded in the bottom, and a drainage hole formed in the bottom beneath the reinforcing rib.

Description:
CLAIM OF PRIORITY 
       [0001]    This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application earlier filed in the Korean Intellectual Property Office on the 31 of Mar. 2011 and there duly assigned Serial No. 10-2011-0029517. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The described technology relates generally to a rechargeable battery pack with improved watertight performance and a unit cell protecting function. 
         [0004]    2. Description of the Related Art 
         [0005]    A rechargeable battery can be used as a unit cell, or unit cells can be used by electrically connecting them with each other depending on the types of devices. For example, a rechargeable battery pack includes a plurality of unit cells, a protection circuit module (PCM) for protecting the unit cells, and a case for electrically connecting the unit cells and the protection circuit module and embedding them in the case. 
         [0006]    For example, the case includes an air hole at a position that is higher than the lowest position of the bottom so as to control outer air to inflow into the unit cells and cool the unit cells. 
         [0007]    The rechargeable battery pack with the case is applicable to portable machine tools. In this case, rainwater may enter the case through the air hole when it rains. 
         [0008]    The air hole is formed at a high position from the bottom of the case, so water having permeated through the air hole does not come out of the air hole but remains in the case. The water collected inside the case enters the gaps between the unit cells and it also enters the protection circuit module depending on how the rechargeable battery pack is provided, and it generates an electrical short so that the rechargeable battery pack may be seriously damaged and may not be used any longer. 
         [0009]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY OF THE INVENTION 
       [0010]    The described technology has been made in an effort to provide a rechargeable battery pack for improving watertight performance for unit cells and a protection circuit module by discharging water having permeated into a case while allowing inflow and outflow of cooling air into/out of the case. 
         [0011]    The present invention has been made in another effort to provide a rechargeable battery pack for improving a protection function for the unit cells by preventing permeation of a foreign substance while discharging the permeated water. 
         [0012]    An exemplary embodiment provides a rechargeable battery pack that includes: at least one unit cell including a rechargeable battery; and a case for supporting the unit cell and receiving the same, wherein the case includes a bottom, a reinforcing rib protruded in the bottom, and a drainage hole formed in the bottom corresponding to the reinforcing rib. 
         [0013]    The case further includes a supporter formed in the bottom corresponding to a side part of the unit cell so as to support the side part of the unit cell. 
         [0014]    The rechargeable battery pack further includes a ventilating sheet provided between the supporter and the unit cell. 
         [0015]    The rechargeable battery pack further includes an insulating sheet provided between the supporter and the unit cell. 
         [0016]    The rechargeable battery pack further includes a buffering sheet provided between the supporter and the unit cell. 
         [0017]    The drainage hole is further extended in the bottom of the reinforcing rib. 
         [0018]    The reinforcing rib has a height and a width that are set in the bottom, and forms a groove connected to the drainage hole to be disposed in the drainage hole. 
         [0019]    The drainage hole is formed to have a circular cylinder shape extending from the inside of the bottom to the outside thereof. 
         [0020]    The drainage hole is formed to have a truncated circular cone shape extending from the inside of the bottom to the outside thereof. 
         [0021]    The bottom has a gradient so that a part where the drainage hole is formed is low. 
         [0022]    The drainage hole is formed in an outer portion of the bottom, and the bottom is formed to have a high center and a low outer portion. 
         [0023]    The drainage hole is formed in the outer portion of the bottom, and the bottom is formed to have a thick center and a thin outer portion. 
         [0024]    According to the embodiment, a drainage hole is formed at a part where a reinforcing rib is positioned on the bottom of the case so the inflow and outflow of the cooling air is allowed and the water having permeated into the case is discharged. Therefore, watertight performance for the unit cells and the protection circuit module is improved. In addition, according to the exemplary embodiment, the reinforcing rib is provided in the drainage hole so the permeated water is discharged to the drainage hole and permeation of alien substance is prevented. Accordingly, the unit cell protecting function is improved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which like reference symbols indicate the same or similar components, wherein: 
           [0026]      FIG. 1  shows a perspective view of a rechargeable battery pack according to a first exemplary embodiment; 
           [0027]      FIG. 2  shows a top plan view of a lower case shown in  FIG. 1 ; 
           [0028]      FIG. 3  shows a cross-sectional view with respect to a line shown in  FIG. 2 ; 
           [0029]      FIG. 4  shows a cross-sectional view with respect to a line IV-IV shown in  FIG. 2 ; 
           [0030]      FIG. 5  shows a partial cutaway perspective view of a drainage hole shown in  FIG. 4 ; 
           [0031]      FIG. 6  shows a partial cross-sectional view of a rechargeable battery pack according to a second exemplary embodiment; 
           [0032]      FIG. 7  shows a cross-sectional view of a rechargeable battery pack according to a third exemplary embodiment; and 
           [0033]      FIG. 8  shows a cross-sectional view of a rechargeable battery pack according to a fourth exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. The drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
         [0035]      FIG. 1  shows a perspective view of a rechargeable battery pack  100  according to a first exemplary embodiment. Referring to  FIG. 1 , the rechargeable battery pack  100  includes unit cells  10  configured as a rechargeable battery, and a case  20  for receiving the unit cells  10  and supporting the same. 
         [0036]    For example, the unit cells  10  can be formed to be a cylindrical rechargeable battery for repeatedly performing charging and discharging operations. That is, the unit cell includes an electrode assembly formed by providing a separator and stacking/spirally winding a positive electrode and a negative electrode, a can containing an electrolyte solution and an electrode assembly, and a cap assembly (not shown) provided to the can in an airtight structure. 
         [0037]    The case  20  sets the number of unit cells  10  to be received, and it is formed to receive the unit cells  10  in a limited space in an optimized manner. For example, the case  20  includes a lower case  21  for receiving the unit cells  10  and supporting the same, and an upper to case  22  for receiving the protection circuit module (not shown) electrically connected to the unit cells  10  to be combined with the lower case  21 . 
         [0038]    The rechargeable battery pack  100  according to the first exemplary embodiment can be used for a power tool that is frequently used in the field. Therefore, the case  20  requires excellent watertight characteristic, and it also needs an excellent cooling characteristic for the built-in unit cells  10 . 
         [0039]      FIG. 2  shows a top plan view of a lower case  21  shown in  FIG. 1 , and  FIG. 3  shows a cross-sectional view with respect to a line III-III shown in  FIG. 2 . Referring to  FIG. 2  and  FIG. 3 , the lower case  21  includes a bottom  23  for forming a space for receiving the unit cells  10 , a side wall  24  formed to surround an outer portion of the bottom  23 , and a supporter  25  formed on the bottom  23  corresponding to a side part of the unit cell  10  to support the side part of the unit cell  10 . 
         [0040]    For example, in the case of receiving five unit cells  10 , the bottom  23  includes five pairs of supporters  25  for supporting the five unit cells  10 . Also, the side wall  24  includes a spacer  26  and is formed to surround the side of the unit cells  10  that are stacked in two layers. The number of the unit cells  10  supported by the bottom  23  and the number of layers of the unit cells  10  stacked on the bottom  23  are set in various ways according to the required outputs. 
         [0041]    The unit cells  10  are electrically connected to a protection circuit module  11  in series or in parallel by a connecting member (not shown). The protective circuit module  11  forms a protective circuit on a printed circuit board to protect the unit cells  10  from an overcharge, overdischarge, overcurrent, and short circuit. 
         [0042]    The supporter  25  include curved concave grooves so as to stably support unit cells  10  that are formed as cylindrical rechargeable batteries. Further, the supporter  25  is formed on both sides (in the y-axis direction shown in  FIG. 2 ) of the bottom  23  so as to support both ends of each unit cell  10 . 
         [0043]    Therefore, an air flow path (P) is formed in the x-axis direction between each supporter  25  on both sides and between the unit cells  10  and the bottom  23 . The cooling air is supplied to the bottom part of the unit cell  10  and between the unit cells  10  through the air flow path (P) to prevent overheating of the unit cells  10 . 
         [0044]    For this purpose, the lower case  21  includes an air hole  27  on a radial part  30  where the bottom  23  is connected to the side wall  24 . The air hole  27  is formed (in the z-axis direction shown in  FIG. 2 ) in radial part  30  at a position that is higher than the lowest surface of the bottom  23  by a predetermined height (H) to control permeation of moisture into the lower case  21  and allow flow of the cooling air. 
         [0045]    For example, the side wall  24  is formed in a dual-layer configuration of an outer wall  241  and an inner wall  242  that are distanced from each other. The air hole  27  is formed in radial part  30  and between the outer wall  241  and inner wall  242 . The inner wall  242  has a height protruded from the bottom  23 , and the height (H) of the air hole  27  is set by the height of the inner wall  242 . 
         [0046]    In the first exemplary embodiment, two air holes  27  are formed at the radial part  30  where the bottom  23  is connected to the side wall  24 . An appropriate number of air holes can be formed depending on the flow amount of the cooling air (not shown). 
         [0047]    As shown in  FIG. 3 , the rechargeable battery pack  100  according to the first exemplary embodiment includes a sheet  31  with at least one of ventilation, insulation, and buffering functions between the supporter  25  and the unit cells  10 . For example, the sheet  31  is formed with an insulating tape or an adhesive sponge to flexibly respond to the curved concave groove of the supporter  25 . 
         [0048]    When the sheet  31  has the buffering characteristic, it can stably support each unit cell  10  on the supporter  25 . When the sheet  31  has ventilation, it forms a cooling air path between the supporter  25  and the unit cell  10  to prevent deterioration of cooling performance of the unit cell  10  on the supporter  25 . Also, when the sheet  31  has insulation, it can prevent the short circuit of the unit cells  10  and the protection circuit module  11  by moisture having permeated between the supporter  25  and the unit cell  10 . 
         [0049]    The lower case  21  includes a reinforcing rib  28  protruded inside from the bottom  23 , and a drainage hole  29  corresponding to the reinforcing rib  28 . The reinforcing rib  28  is formed between the supporter  25  and the side wall  24  so that it may relate to the drainage hole  29  (refer to  FIG. 2 ). The reinforcing rib  28  can be formed on various positions in the bottom (not shown). 
         [0050]    The drainage hole  29  is formed to ease the discharge of moisture having permeated into the case  20  and simultaneously the reinforcing rib  28  prevents entry of foreign substances. Further, the drainage hole  29  allows the cooling air to flow, together with the air hole  27 . Since the permeated moisture is discharged, watertight performance for the unit cells  10  and the protection circuit module  11  is improved. The protection function for the unit cells  10  is improved by preventing the permeation of an external foreign substance. 
         [0051]      FIG. 4  shows a cross-sectional view with respect to a line IV-IV shown in  FIG. 2 , and  FIG. 5  shows a partial cutaway perspective view of a drainage hole  29  shown in  FIG. 4 . Referring to  FIG. 4  and  FIG. 5 , the drainage hole  29  discharges the internal moisture, and the reinforcing rib  28  provided in the drainage hole  29  prevents entry of a foreign object through the drainage hole  29 . The reinforcing rib  28  provided in the drainage hole  29  prevents permeation of the foreign substance that may occur when the drainage hole  29  is formed in the bottom  23 . 
         [0052]    Also, the drainage hole  29  is further extended in the side direction of the reinforcing rib  28  and is formed in the bottom  23 . For example, the reinforcing rib  28  has a height H 1  and a width W 1  that are set in the bottom  23  and is provided over the drainage hole  29 . The drainage hole  29  is formed to have a diameter larger than the width W 1  of the reinforcing rib  28  so a part of the drainage hole  29  is exposed outside the width W 1  of the reinforcing rib  28  to drain water. 
         [0053]    In addition to this, the reinforcing rib  28  includes a groove  28   a  connected to the drainage hole  29 . That is, the groove  28   a  is formed to face the drainage hole  29  on the reinforcing rib  28 . Accordingly, the drainage hole  29  passes through the bottom  23  to be connected to the side of the reinforcing rib  28  through the groove  28   a . That is, the moisture having permeated into the case  20  flows on the bottom  23  to be discharged outside the lower case  21  after having passed through the groove  28   a  of the reinforcing rib  28  and the drainage hole  29 . 
         [0054]    The drainage hole  29  can be formed to have a circular cylinder shape extending from the inside of the bottom  23  to the outside thereof. The drainage hole  29  is formed corresponding to the reinforcing rib  28  of the bottom  23  so the reinforcing rib  28  and the drainage hole  29  can be formed in the lower case  21  by changing a part of a pattern for manufacturing the existing lower case. Therefore, the additional cost for forming the drainage hole  29  is minimized. 
         [0055]    Various others exemplary embodiments will now be described, and the same configurations as in the first exemplary embodiment will not be described and different configurations from the first exemplary embodiment will be described. 
         [0056]      FIG. 6  shows a partial cross-sectional view of the lower case of a rechargeable battery pack according to a second exemplary embodiment. Referring to  FIG. 6 , a drainage hole  229  is formed to have a truncated circular cone shape extending from the inside of the bottom  223  to the outside thereof. A groove  228   a  of the reinforcing rib  228  corresponding to the drainage hole  229  is formed to have a truncated circular cone shape (or wedge shape) extending to a drainage hole  229  from the side that faces the drainage hole  229 . 
         [0057]    The truncated circular cone shape of the drainage hole  229  can further easily discharge the moisture having entered the lower case  221  compared to the circular cylinder shape of the drainage hole  29  described in the first exemplary embodiment. The drainage hole  229  can prevent intrusion of foreign substances by the side part of the truncated circular cone, and groove  228   a  also helps prevent intrusion of foreign substances. 
         [0058]    The drainage hole  229  in the truncated circular cone shape and the groove  228   a  ease the separation process of the pattern when manufacturing the lower case  221  more than the drainage hole  29  in the circular cylinder shape and the groove  28   a.    
         [0059]      FIG. 7  shows a cross-sectional view of the lower case of a rechargeable battery pack according to a third exemplary embodiment. Referring to  FIG. 7 , a supporter  325  is formed on the bottom  323  corresponding to a side part of the unit cell  10  to support the side part of the unit cell  10 . The bottom  323  may have a gradient so that the part where a drainage hole  329  corresponding to a reinforcing rib  328  may be lower than a central part of bottom  323 . 
         [0060]    The gradient of the bottom  323  can be formed in various manners. For example, the bottom  323  is formed to have a high center and a low outer portion. That is, the drainage hole  329  is formed on the low part of the bottom  323 , that is, the outer portion of the bottom  323 . 
         [0061]    The bottom  323  of the rechargeable battery pack  300  according to the third exemplary embodiment increases the drainage through the drainage hole  329  by controlling the moisture having permeated into the lower case  321  to move to the outer portion by the gradient. 
         [0062]      FIG. 8  shows a cross-sectional view of the lower case of a rechargeable battery pack according to a fourth exemplary embodiment. Referring to  FIG. 8 , a supporter  425  is formed on the bottom  423  corresponding to a side part of the unit cell  10  to support the side part of the unit cell  10 . The bottom  423  is formed to have a thick center portion and a thin outer portion. A drainage hole  429  is formed on a low part of the bottom  423 , that is, the outer portion of the bottom  423 . 
         [0063]    While the bottom  323  according to the third exemplary embodiment is formed with the same thickness to have a concave outer part, the bottom  423  according to the fourth exemplary embodiment is formed to have a flat outer portion and a convex inner center. The bottom  423  increases drainage by controlling the moisture having permeated into the lower case  421  to move to the outside drainage hole  429 . 
         [0064]    While this disclosure has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.