Patent Publication Number: US-2023155225-A1

Title: Battery pack case including over-fusion prevention structure

Description:
TECHNICAL FIELD 
     This application claims the benefit of priority to Korean Patent Application No. 2020-0157624 filed on Nov. 23, 2020, the disclosure of which is incorporated herein by reference in its entirety. 
     The present invention relates to a battery pack case including an over-fusion prevention structure. More particularly, the present invention relates to a battery pack case including an over-fusion prevention structure capable of preventing external defects from occurring on a coupling portion of the battery pack case due to over-fusion when ultrasonic welding is performed for coupling of the battery pack case. 
     BACKGROUND ART 
     A battery pack constituted by secondary batteries connected to each other in series or in parallel is used as an energy source for medium- or large-sized devices, which require high output and high capacity. The battery pack may include a plurality of battery cells, a structure configured to perform electrical connection between the battery cells, a structure configured to control the operation of the battery cells, and a structure configured to adjusting heat generation/heat dissipation of the battery cells in a battery pack case, and coupling of the battery pack case is performed in the state in which the structures are received therein to manufacture the battery pack. 
     As a coupling method of a battery pack case manufactured using a polymer resin, there is used a method of pressurizing the polymer resin in a molten state using frictional heat by ultrasonic vibration in order to achieve fusion. If a joint of the battery pack case is over-fused or pressing force is inaccurately controlled, the molten resin flows outwards, whereby burrs are generated. 
       FIG.  1    is a vertical sectional view of a coupling portion of a conventional battery pack case, and  FIG.  2    is a front view of the coupling portion of the battery pack case of  FIG.  1   . 
     Referring to  FIGS.  1  and  2   , the battery pack case is constituted by a first case  10  located above and a second case  20  located below. A projecting portion  11  is formed on a coupling portion of the first case  10  at a middle part of the first case in a thickness direction D thereof so as to project downwards therefrom, and a grooved portion  22  is formed in a coupling portion of the second case  20  at a middle part of the second case in a thickness direction D thereof so as to be concave. The projecting portion  11  of the first case  10  is inserted into and fixed to the grooved portion  22  of the second case  20 , whereby the battery pack case is assembled. 
     The projecting portion  11  includes an energy director  15  formed at the end thereof such that the width of the energy director in the thickness direction D thereof is gradually decreased. When vibration is applied to the first case  10  and the second case  20 , the energy director  15  is melted in the grooved portion  22  of the second case  20  while being vibrated, whereby the grooved portion  22  is filled with the projecting portion  11 . 
     At this time, if the first case is excessively pressed toward the second case in the state in which the energy director  15  is melted, the energy director may be over-fused, whereby some of the melted energy director may flow out of the case. As a result, burrs  30  may be generated, as shown in  FIG.  2   . 
       FIG.  2    shows the state in which the burrs  30  are generated at the coupling portions of the first case  10  and the second case  20  due to over-fusion. In order to prevent generation of defects, such as burrs, it is important to maintain a uniform distance between the first case and the second case in a height direction thereof at the coupling portions of the first case and the second case. 
     In connection therewith, Patent Document 1 discloses a battery pack configured such that a battery pack case includes a front case and a rear case, a plurality of fusion protrusions made of a resin is formed along the edge of the rear case, i.e. the part of the rear case that contacts the front case, and outflow prevention recesses configured to prevent outflow of the fusion protrusions are formed along the edge of the front case at the region of the front case that contacts the fusion protrusions of the rear case. 
     However, the outflow prevention recesses of Patent Document 1 have difficulty completely preventing the fusion protrusions from flowing out of the outflow prevention recesses when the fusion protrusions are melted. That is, time and force control is necessary when the front case and the rear case are coupled to each other, and, if the fusion protrusions flow out of the outflow prevention recesses in the state in which the fusion protrusions are melted, it is difficult to prevent external defects, such as the burrs of  FIG.  2   , from occurring between the battery cases. 
     Patent Document 2 discloses a vibration fusion structure between a resin case and a resin cover capable of preventing burrs generated when the resin case and the resin cover are fused to each other using vibration from leaking out into an inner space surrounded by the resin case and the resin cover, wherein projection portions projecting from the resin case and the resin cover are fused to each other by vibration to form a joint at fused portions of the resin case and the resin cover and wherein an inner burr concealment wall, an outer burr concealment wall, and a middle burr concealment wall are formed in order to prevent melting and flowing of the projecting portions. 
     In Patent Document 2, when the fused portions are melted, it is possible to prevent the melted portions from flowing out of coupling portions of the resin case and the resin cover to a certain extent, since the plurality of concealment walls is formed. However, it is not possible to completely prevent burrs from flowing out of the coupling portions of the resin case and the resin cover, like Patent Document 1. 
     Therefore, there is a need for a battery pack case having a structure capable of fundamentally preventing generation of external defects as the result of an energy director of a battery case melted by vibration heat flowing out of the battery case. 
     Korean Patent Application Publication No. 2004-0085478 (2004 Oct. 8) 
     Japanese Registered Patent Publication No. 4948004 (2012 Mar. 16) 
     DISCLOSURE 
     Technical Problem 
     The present invention has been made in view of the above problems, and it is an object of the present invention to provide a battery pack case including an over-fusion prevention structure capable of preventing generation of burrs on a coupling portion of the battery pack case due to over-fusion of the battery pack case, thereby reducing external defects. 
     Technical Solution 
     In order to accomplish the above object, the present invention provides a battery pack case configured to receive a plurality of battery cells, the battery pack case including a first case and a second case coupled to each other through engagement therebetween, wherein a projecting portion is formed on a coupling portion of the first case at a middle part of the first case in a thickness direction thereof so as to project therefrom, a grooved portion is formed in a coupling portion of the second case at a middle part of the second case in a thickness direction thereof such that the projecting portion is inserted into the grooved portion, and a uniform gap is formed between the outside of the projecting portion of the first case and the outside of the grooved portion of the second case in the state in which the first case and the second case are coupled and thermally fused to each other. 
     A support structure configured to form the gap may be formed in the grooved portion of the second case. 
     A stopper rib may be formed in the grooved portion of the second case as the support structure. 
     A stopper recess may be formed at the position of the projecting portion of the first case corresponding to the stopper rib. 
     The depth of the stopper recess may be less than the height of the projecting portion. 
     The depth of the stopper recess may be greater than the height of the stopper rib based on the state before the projecting portion is melted. 
     The projecting portion may include an energy director configured to be melted by thermal fusion and a support portion excluding the energy director. 
     The sum of the height of the stopper rib and the length of the projecting portion at the part thereof at which the stopper recess is formed may be greater than the depth of the grooved portion of the second case in the state in which the first case and the second case are coupled and thermally fused to each other. 
     A gap may be present between the projecting portion and an inner surface of the grooved portion before the first case and the second case are thermally fused to each other, and the projecting portion and the grooved portion may be fused to each other in the state in which the first case and the second case are thermally fused to each other. 
     The support structure may be formed on at least one side of each of outer peripheries of the first case and the second case at which the first case and the second case are coupled to each other. 
     The support structure may be formed on the entireties of outer peripheries of the first case and the second case at which the first case and the second case are coupled to each other. 
     Advantageous Effects 
     As is apparent from the above description, in a battery pack case according to the present invention, a support structure is formed at coupling portions of a first case and a second case, whereby it is possible to maintain a uniform coupling distance between the first case and the second case even when coupling force is excessively applied to the first case and the second case in the state in which a projecting portion of the first case is melted. 
     Since the coupling distance between the first case and the second case is maintained uniform, as described above, it is possible to prevent generation of burrs due to over-fusion at the coupling portions of the first case and the second case, whereby it is possible to reduce an external defect rate. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG.  1    is a vertical sectional view of a coupling portion of a conventional battery pack case. 
         FIG.  2    is a front view of the coupling portion of the battery pack case of  FIG.  1   . 
         FIG.  3    is a vertical sectional view of coupling portions of a first case and a second case according to the present invention. 
         FIG.  4    is a perspective view of the first case according to the present invention. 
         FIG.  5    is a perspective view of the second case according to the present invention. 
         FIG.  6    is a vertical sectional view showing the state in which the first case and the second case are fused to each other. 
     
    
    
     BEST MODE 
     Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings such that the preferred embodiments of the present invention can be easily implemented by a person having ordinary skill in the art to which the present invention pertains. In describing the principle of operation of the preferred embodiments of the present invention in detail, however, a detailed description of known functions and configurations incorporated herein will be omitted when the same may obscure the subject matter of the present invention. 
     In addition, the same reference numbers will be used throughout the drawings to refer to parts that perform similar functions or operations. In the case in which one part is said to be connected to another part throughout the specification, not only may the one part be directly connected to the other part, but also, the one part may be indirectly connected to the other part via a further part. In addition, that a certain element is included does not mean that other elements are excluded, but means that such elements may be further included unless mentioned otherwise. 
     In addition, a description to embody elements through limitation or addition may be applied to all inventions, unless particularly restricted, and does not limit a specific invention. 
     Also, in the description of the invention and the claims of the present application, singular forms are intended to include plural forms unless mentioned otherwise. 
     Also, in the description of the invention and the claims of the present application, “or” includes “and” unless mentioned otherwise. Therefore, “including A or B” means three cases, namely, the case including A, the case including B, and the case including A and B. 
     In addition, all numeric ranges include the lowest value, the highest value, and all intermediate values therebetween unless the context clearly indicates otherwise. 
     An embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
     A battery pack case according to the present invention includes a first case and a second case, which are separated from each other. The first case and the second case have a structure in which the first case and the second case are coupled to each other through engagement therebetween. 
     Specifically, a projecting portion is formed on a coupling portion of the first case at a middle part of the first case in a thickness direction thereof so as to project therefrom, and a grooved portion is formed in a coupling portion of the second case at a middle part of the second case in a thickness direction thereof such that the projecting portion is inserted into the grooved portion. Consequently, the projecting portion may be inserted into the grooved portion, whereby engagement therebetween may be achieved. 
     In connection therewith,  FIG.  3    is a vertical sectional view of coupling portions of a first case and a second case according to the present invention. 
     Referring to  FIG.  3   ,  FIG.  3 ( a )  shows the state in which ultrasonic welding is being performed in the state in which the first case  100  and the second case  200  are coupled to each other, and  FIG.  3 ( b )  shows the state in which ultrasonic welding has been completed. 
     The battery pack case includes the first case  100  and the second case  200 . A projecting portion  110  is formed on a coupling portion of the first case  100  at a middle part of the first case  100  in a thickness direction D thereof so as to project downwards therefrom, and a grooved portion  220  is formed in a coupling portion of the second case  200  at a middle part of the second case  200  in a thickness direction D thereof such that the projecting portion  110  is inserted into the grooved portion. The projecting portion  110  is inserted into the grooved portion  220 , whereby the first case and the second case are primarily coupled to each other. 
     When ultrasonic vibration is applied to the first case  100  and the second case  200  in this state, frictional heat is generated at the interface between the projecting portion  110  of the first case  100  and the grooved portion  220  of the second case  200 , whereby the end of the projecting portion  110  is melted. That is, the projecting portion  110  includes an energy director  150  configured to be melted by heat and a support portion  160  excluding the energy director  150 . 
     A separation space is present between the projecting portion  110  and the inner surface of the grooved portion  220  before the first case  100  and the second case  200  are thermally fused to each other.  FIG.  3 ( a )  shows the state in which ultrasonic welding is being performed, wherein half or more of the energy director  150  is melted. When the first case  100  and the second case  200  are pressed so as to be closer to each other while the energy director  150  is melted, the separation space between the projecting portion  110  and the inner surface of the grooved portion  220  is fully filled with the melted energy director. 
     The grooved portion  220  of the second case  200  is configured to have a structure in which opposite sides of a concave groove project. When ultrasonic welding is performed in the state in which the projecting portion  110  is inserted into the grooved portion  220 , therefore, it is possible to prevent bending of the projecting portion and to maintain the projecting shape of the projecting portion in the grooved portion  220 . 
     Also, even in the state in which the energy director  150  is melted by ultrasonic welding, a uniform gap H is formed between the outside  111  of the projecting portion  110  of the first case and the outside  222  of the grooved portion  220  of the second case, since a support structure is formed at the first case  100  and the second case  200  according to the present invention, as shown in  FIGS.  4  and  5   . 
     As described above, the gap H is formed between the outside  111  of the projecting portion of the first case and the outside  222  of the grooved portion of the second case, as the coupling portions of the first case and the second case, along the entire outer peripheries thereof, whereby it is possible to solve a conventional problem in that burrs are generated on the coupling portions due to over-fusion of the battery case. Consequently, it is possible to remarkably reduce external defects. 
       FIG.  4    is a perspective view of the first case according to the present invention, and  FIG.  5    is a perspective view of the second case according to the present invention. 
     Referring to  FIGS.  4  and  5   , a support structure is formed at the outer periphery of one open surface of the first case  100  and the outer periphery of one open surface of the second case  200  in order to form the gap H of  FIG.  3   . 
     Specifically, the projecting portion  110  of the first case  100  includes an energy director  150  and a support portion  160 , and a stopper recess  170  is formed in the projecting portion  110 . 
     A stopper rib  270 , which is a support structure configured to maintain the gap H between the first case  100  and the second case  200 , is formed in the grooved portion  220  of the second case  200 . The stopper rib  270  is formed in the grooved portion  220  so as to project upwards, and performs a function of preventing the projecting portion of the first case  100  from being deeply coupled to the grooved portion even when the projecting portion is excessively melted. 
     In consideration of the fact that ultrasonic welding must be performed in the state in which the projecting portion  110  is deeply inserted into the grooved portion  220  to a certain extent in order to achieve stable fusion, however, it is preferable for the stopper recess  170  to be formed at the position of the projecting portion  110  corresponding to the stopper rib  270  such that the stopper rib  270  is mounted in the stopper recess  170 . 
     Also, in consideration of the fact that the energy director  150  is melted and the grooved portion  220  is filled with the melted energy director  150  in the state in which the stopper rib  270  is mounted in the stopper recess  170  in order to achieve sealing of the battery pack, the support portion  160  must be provided at the part at which the stopper recess  170  is formed in order to completely seal the battery pack. Consequently, it is preferable for the depth a 1  of the stopper recess to be less than the height a 2  of the projecting portion. 
     Meanwhile, the energy director is melted such that the height of the energy director is reduced or removed in the state in which the stopper rib  270 , which is formed so as to project, is disposed in the stopper recess  170 . At this time, the stopper rib must be deeply inserted into the innermost side of the stopper recess in order to stably fix the first case and the second case to each other. Consequently, the depth of the stopper recess  170  may be greater than the height of the stopper rib  270  based on the state before the energy director is melted. 
       FIG.  6    is a vertical sectional view showing the state in which the first case and the second case are fused to each other. 
     Referring to  FIG.  6   , the sum b 1  of the height of the stopper rib  270  and the length of the projecting portion  110  at the part thereof at which the stopper recess is formed is greater than the depth b 2  of the grooved portion of the second case  200  in the state in which the first case  100  and the second case  200  are coupled and thermally fused to each other. That is, in the state in which the first case and the second case are coupled and thermally fused to each other, the lower end of the support portion may be coupled to the stopper rib in contact therewith, and the sum of the height of the support portion and the height of the stopper rib may be greater than the depth b 2  of the grooved portion of the second case. 
     The reason for this is that the support structure is formed at the first case and the second case such that a uniform gap H is formed between the outside  111  of the projecting portion of the first case and the outside  222  of the grooved portion of the second case in the state in which the first case and the second case are coupled and thermally fused to each other. 
     In a concrete example, the support structure may be constituted by a pair of a stopper recess and a stopper rib, and the support structure may be formed on at least one side of each of the outer peripheries of the first case and the second case at which the first case and the second case are coupled to each other. That is, one or more pairs of stopper recesses and stopper ribs may be formed on the one side of each of the outer peripheries. 
     Alternatively, the support structure may be formed on the entire outer peripheries of the first case and the second case at which the first case and the second case are coupled to each other. That is, one or more support structures, each of which is constituted by a pair of a stopper recess and a stopper rib, may be formed on one side of each of the outer peripheries, and a plurality of support structures may be disposed at the entire outer peripheries. The support structures may be disposed so as to be spaced apart from each other by a predetermined distance, or may be disposed only on the straight outer periphery portions excluding corners of the outer peripheries. 
     As described above, the battery pack case according to the present invention includes a support structure configured to prevent over-fusion between the first case and the second case as the result of excessively close coupling therebetween when the first case and the second case are thermally fused to each other in a state of being coupled to each other. The stopper recess of the first case is caught by the stopper rib of the second case by the provision of the support structure, whereby the first case is prevented from being further inserted into the grooved portion of the second case. Consequently, it is possible to prevent a melted battery case resin from flowing out over the side walls of the grooved portion, and therefore it is possible to prevent external defects at the coupling portion of the battery pack case. 
     Additionally, the battery pack case according to the present invention may be a case for battery packs that are used as energy sources for various kinds of devices, wherein a through-hole, through which electrode terminals of battery cells received in the battery pack case are withdrawn outwards, may be formed in the battery pack case. 
     Alternatively, a structure configured to stably mount the battery pack case in various kinds of devices, such as a hook structure, may be added to the battery pack case according to the present invention. 
     Those skilled in the art to which the present invention pertains will appreciate that various applications and modifications are possible within the category of the present invention based on the above description. 
     DESCRIPTION OF REFERENCE SYMBOLS 
       10 ,  100 : First cases 
       11 ,  110 : Projecting portions 
       15 ,  150 : Energy directors 
       20 ,  200 : Second cases 
       22 ,  220 : Grooved portions 
       30 : Burrs 
       111 : Outside of projecting portion 
       160 : Support portion 
       170 : Stopper recess 
       222 : Outside of grooved portion 
       270 : Stopper rib 
     a 1 : Depth of stopper recess 
     a 2 : Height of projecting portion 
     b 1 : Sum of height of stopper rib and length of projecting portion at part at which stopper recess is formed 
     b 2 : Depth of grooved portion 
     D: Thickness direction 
     H: Gap 
     INDUSTRIAL APPLICABILITY 
     The present invention relates to a battery pack case configured to receive a plurality of battery cells, the battery pack case including a first case and a second case coupled to each other through engagement therebetween, wherein a projecting portion is formed on a coupling portion of the first case at a middle part of the first case in a thickness direction thereof so as to project therefrom, a grooved portion is formed in a coupling portion of the second case at a middle part of the second case in a thickness direction thereof such that the projecting portion is inserted into the grooved portion, and a uniform gap is formed between the outside of the projecting portion of the first case and the outside of the grooved portion of the second case in the state in which the first case and the second case are coupled and thermally fused to each other, whereby the melted projecting portion is prevented from flowing out over the outside of the projecting portion of the first case and the outside of the grooved portion of the second case during ultrasonic welding, and therefore the present invention has industrial applicability.