Patent Publication Number: US-2023145164-A1

Title: Vehicle Floor System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2021-0153395, filed on Nov. 9, 2021, which application is hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a vehicle floor system. 
     BACKGROUND 
     In recent years, as the perception of environmental crisis and depletion of oil resources has increased, research and development of eco-friendly electric vehicles have actively been conducted. Electric vehicles include plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), fuel cell electric vehicles (FCEVs), etc. 
     An electric vehicle is equipped with a battery assembly which is mounted to a vehicle body. The battery assembly includes one or more battery cells (or battery modules), electric/electronic components connected to the battery cells, and a battery case in which the battery cells and the electric/electronic components are mounted. The battery assembly may be mounted under a floor of the vehicle body. 
     In order to mount the battery assembly under the floor and increase an interior space, the electric vehicle needs to reduce structural members compared to an internal combustion engine vehicle. In addition, it is necessary to reduce the cross-sectional area of each structural member. 
     In order to increase all electric range (AER) of the electric vehicle, the capacity and size of the battery assembly are gradually increasing. Considering marketability, etc., however, the size of a vehicle bottom structure (including the floor) may not relatively increase to match the increased size of the battery assembly. Accordingly, since it is necessary to increase the capacity of the battery assembly while minimizing the cross-sectional areas of the structural members mounted on the floor and a space between the battery assembly and the vehicle body, an impact absorbing space required for the safety of the battery assembly is relatively decreasing. 
     As the impact absorbing space is decreasing, various methods for the safety of the battery assembly may be required. For example, in order to ensure the safety of the battery assembly, the structural members may be made of materials having relatively high stiffness or strength (ultra high-tensile strength steel) or various reinforcing members may be additionally provided between the structural members of the vehicle body. 
     However, even if the structural members are made of materials having high stiffness or strength or various reinforcing members are additionally provided between the structural members in a situation in which the impact absorbing space is decreasing due to an increase in the size of the battery assembly, there is a limit to improving side crash performance. Thus, it may be difficult to sufficiently secure the safety of a passenger compartment and the battery assembly. 
     The above information described in this background section is provided to assist in understanding the background of the inventive concept, and may include any technical concept which is not considered as the prior art that is already known to those skilled in the art. 
     SUMMARY 
     The present disclosure relates to a vehicle floor system. Particular embodiments relate to a vehicle floor system capable of significantly improving side crash performance. 
     Embodiments of the present disclosure can solve problems occurring in the prior art while advantages achieved by the prior art are maintained intact. 
     An embodiment of the present disclosure provides a vehicle floor system significantly improving side crash performance, thereby sufficiently securing the safety of a passenger compartment and a battery assembly. 
     According to an embodiment of the present disclosure, a vehicle floor system may include a floor, a pair of side longitudinal members disposed on both side edges of the floor, a structural transverse member disposed on the floor and extending in a width or transverse direction of a vehicle, and a battery assembly disposed under the floor. Each side longitudinal member may extend in a longitudinal direction of the vehicle, the side longitudinal member may include a horizontal rib provided therein, and the horizontal rib may be aligned with the structural transverse member in the width or transverse direction of the vehicle. 
     Accordingly, the horizontal rib of the side longitudinal member and the structural transverse member may sufficiently support impact energy (impact load) transferred in the width or transverse direction of the vehicle during a side collision of the vehicle, and thus side crash performance (crashworthiness) of the floor may be significantly improved. 
     A thickness of the side longitudinal member may increase from the interior side thereof toward the exterior side thereof. 
     Specifically, the side longitudinal member may include an exterior portion facing the exterior of the vehicle, and an interior portion facing the interior of the vehicle, and a thickness of the exterior portion may be greater than that of the interior portion. 
     Specifically, the side longitudinal member may include a plurality of vertical ribs extending vertically therein, the plurality of vertical ribs may include a first vertical rib adjacent to the exterior portion, and a second vertical rib adjacent to the interior portion, and a thickness of the first vertical rib may be greater than that of the second vertical rib. 
     The strength of the side longitudinal member may increase from the interior side thereof toward the exterior side thereof, and accordingly the amount of deformation of the side longitudinal member due to the impact energy during a side collision of the vehicle may increase from the exterior side thereof toward the interior side thereof. Thus, the impact energy may be stably absorbed. 
     The structural transverse member may include a central web, a first side web connected to the central web through a first interior side wall, a second side web connected to the central web through a second interior side wall, a first flange connected to the first side web through a first exterior side wall, and a second flange connected to the second side web through a second exterior side wall. 
     The central web, the first flange, and the second flange may be fixed to a top surface of the floor, and the first side web and the second side web may be offset upwardly with respect to the central web. 
     As the structural transverse member has an M-shaped cross section, the structural transverse member may have enough strength and stiffness. 
     The first side web and the second side web may be aligned with the horizontal rib of the side longitudinal member in the width or transverse direction of the vehicle. 
     Accordingly, the pair of side longitudinal members and the structural transverse member may increase transverse stiffness and transverse strength of a vehicle body. 
     The vehicle floor system may further include an additional transverse member disposed above the structural transverse member, and a top wall of the side longitudinal member may be aligned with the additional transverse member in the width or transverse direction of the vehicle. 
     Accordingly, the pair of side longitudinal members and the additional transverse member may increase transverse stiffness and transverse strength of the vehicle body. 
     The additional transverse member may be attached to the structural transverse member so that the additional transverse member and the structural transverse member may form a closed cross section. 
     Accordingly, the additional transverse member and the structural transverse member may increase stiffness and strength of the vehicle body. 
     The battery assembly may include a battery case in which a plurality of battery cells are received, a battery cover with which the battery case is covered, at least one battery transverse member disposed in the battery case, and a side mount protruding from an exterior side surface of the battery case toward a side sill and the side longitudinal member. 
     The side mount may be joined to the corresponding side longitudinal member through a side mounting bolt, and the side mount may be aligned with the battery transverse member in the width or transverse direction of the vehicle. 
     At least a portion of the side longitudinal member may overlap the side mount of the battery assembly. 
     Specifically, a deformation section may be defined between an exterior side surface of the side longitudinal member and the exterior side surface of the battery case, and the deformation section may include a first section corresponding to a width of the exterior portion of the side longitudinal member, and a second section in which the interior portion of the side longitudinal member and the side mount overlap vertically. 
     Since the thickness of the interior portion of the side longitudinal member is less than the thickness of the exterior portion thereof, the strength of the second section may be lower than that of the first section. 
     The battery assembly may be mounted to the floor through a plurality of fasteners, and each fastener may be mounted in a predetermined position which is ⅓ of a distance between a pair of side sills. 
     The plurality of fasteners may be mounted at predetermined points (e.g., ⅓ of the distance between the pair of side sills), thereby preventing the floor, the structural transverse member, and the battery transverse member from being deformed (bent) in the event of a side collision of the vehicle. In particular, the battery assembly may be prevented from coming off or being separated from the floor, and thus safety of the battery assembly may be ensured. 
     The plurality of fasteners may directly connect the battery assembly and the structural transverse member. 
     The side longitudinal member may be directly mounted on the side edge of the floor, the structural transverse member may be disposed above the floor, and the additional transverse member may be disposed between the structural transverse member and the floor. 
     A plurality of fasteners may directly connect the battery assembly and the additional transverse member. 
     The structural transverse member may be disposed below the floor, and a plurality of fasteners may directly connect the battery assembly and the structural transverse member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of embodiments of the present disclosure will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    illustrates a plan view of a vehicle floor system according to an exemplary embodiment of the present disclosure; 
         FIG.  2    illustrates a bottom view of a vehicle floor system according to an exemplary embodiment of the present disclosure; 
         FIG.  3    illustrates a cross-sectional view, taken along line A-A of  FIG.  1   ; 
         FIG.  4    illustrates a cross-sectional view, taken along line B-B of  FIG.  3   ; 
         FIG.  5    illustrates an enlarged view of portion C of  FIG.  3   ; 
         FIG.  6    illustrates a cross-sectional view of a vehicle floor system according to another exemplary embodiment of the present disclosure; and 
         FIG.  7    illustrates a cross-sectional view of a vehicle floor system according to another exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals will be used throughout to designate the same or equivalent elements. In addition, a detailed description of well-known techniques associated with the present disclosure will be omitted in order not to unnecessarily obscure the gist of the present disclosure. 
     Terms such as first, second, A, B, (a), and (b) may be used to describe the elements in exemplary embodiments of the present disclosure. These terms are only used to distinguish one element from another element, and the intrinsic features, sequence or order, and the like of the corresponding elements are not limited by the terms. Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meanings as those generally understood by those with ordinary knowledge in the field of art to which the present disclosure belongs. Such terms as those defined in a generally used dictionary are to be interpreted as having meanings equal to the contextual meanings in the relevant field of art, and are not to be interpreted as having ideal or excessively formal meanings unless clearly defined as having such in the present application. 
     Referring to  FIGS.  1  to  3   , a vehicle floor system according to an exemplary embodiment of the present disclosure may include a floor  11  disposed on the bottom of a vehicle body. 
     The floor  11  may define the bottom of a passenger compartment, and support interior components of the passenger compartment such as a plurality of vehicle seats and vehicle mats. 
     A pair of side longitudinal members  12  may be disposed on both side edges of the floor  11 , and each side longitudinal member  12  may extend in a longitudinal direction of the vehicle. 
     Referring to  FIGS.  1  to  3   , a pair of side sills may be disposed along both side edges of the floor  11 , and each side sill may extend in the longitudinal direction of the vehicle. Each side sill may include a side sill inner  13  facing the interior of the vehicle (that is, a central longitudinal axis of the floor  11 ) and a side sill outer (not shown) facing the exterior of the vehicle. The side sill outer (not shown) may be joined to the side sill inner  13  using fasteners, welding, and/or the like. Each side sill inner  13  may be connected to each side edge of the floor  11  through a mounting bracket  14 . 
     According to an exemplary embodiment, each side longitudinal member  12  may be a side sill reinforcement received in the side sill inner  13  of each side sill, and the side longitudinal member  12  may be an extruded product manufactured by an extrusion process. 
     Referring to  FIGS.  3  and  5   , each side longitudinal member  12  may include an exterior portion  21  facing the exterior of the vehicle, and an interior portion  22  facing the interior of the vehicle. 
     Referring to  FIG.  5   , the exterior portion  21  may include an exterior side wall  21   a  facing the exterior of the vehicle, an exterior top wall  21   b  facing the top of the vehicle, and an exterior bottom wall  21   c  facing the bottom of the vehicle. The interior portion  22  may include an interior side wall  22   a  facing the interior of the vehicle, an interior top wall  22   b  facing the top of the vehicle, and an interior bottom wall  22 C facing the bottom of the vehicle. 
     Referring to  FIG.  5   , each side longitudinal member  12  may include a horizontal rib  23  provided horizontally therein, and a plurality of vertical ribs  24  and  25  provided vertically therein. The side longitudinal member  12  may include a plurality of cavities defined by the horizontal rib  23  and the plurality of vertical ribs  24  and  25 . The horizontal rib  23  may extend horizontally between the exterior portion  21  and the interior portion  22 . That is, the horizontal rib  23  may extend in a width or transverse direction of the vehicle. Specifically, the horizontal rib  23  may extend horizontally to connect between the exterior side wall  21   a  and the interior side wall  22   a . The plurality of vertical ribs  24  and  25  may include a first vertical rib  24  adjacent to the exterior side wall  21   a  of the exterior portion  21 , and a second vertical rib  25  adjacent to the interior side wall  22   a  of the interior portion  22 . The second vertical rib  25  may be spaced apart from the first vertical rib  24  toward the interior of the vehicle. A top end of the second vertical rib  25  may be attached to a connection portion between the exterior top wall  21   b  and the interior top wall  22   b , and a bottom end of the second vertical rib  25  may be attached to a connection portion between the exterior bottom wall  21   c  and the interior bottom wall  22 C. 
     Referring to  FIG.  5   , the horizontal rib  23  may include a first horizontal rib  23   a  horizontally connecting the exterior side wall  21   a  and the first vertical rib  24 , a second horizontal rib  23   b  horizontally connecting the first vertical rib  24  and the second vertical rib  25 , and a third horizontal rib  23   c  horizontally connecting the second vertical rib  25  and the interior side wall  22   a.    
     The strength of the side longitudinal member  12  may increase from the interior side thereof toward the exterior side thereof, and accordingly the thickness of the side longitudinal member  12  may increase from the interior side thereof toward the exterior side thereof. Referring to  FIG.  5   , a thickness t 1  of the exterior portion  21  may be greater than a thickness t 2  of the interior portion  22 , and a thickness t 3  of the first vertical rib  24  may be greater than a thickness t 4  of the second vertical rib  25 . A thickness t 5  of the first horizontal rib  23   a  may be greater than a thickness t 6  of the second horizontal rib  23   b , and the thickness t 6  of the second horizontal rib  23   b  may be greater than a thickness t 7  of the third horizontal rib  23   c . For example, the thickness t 1  of the exterior portion  21  may be 5 mm, and the thickness t 2  of the interior portion  22  may be 3.5 mm. The thickness t 3  of the first vertical rib  24  may be 3 mm, and the thickness t 4  of the second vertical rib  25  may be 2.5 mm. The thickness t 5  of the first horizontal rib  23   a  may be 4 mm, the thickness t 6  of the second horizontal rib  23   b  may be 3.5 mm, and the thickness t 7  of the third horizontal rib  23   c  may be 3 mm. 
     Referring to  FIG.  5   , the side longitudinal member  12  may be divided into a first closed cross section V 1 , a second closed cross section V 2 , and a third closed cross section V 3  in a width or transverse direction thereof. The first closed cross section V 1  may be defined between the exterior portion  21  and the first vertical rib  24 , the second closed cross section V 2  may be defined between the first vertical rib  24  and the second vertical rib  25 , and the third closed cross section V 3  may be defined between the second vertical rib  25  and the interior portion  22 . The strength of the first closed cross section V 1  may be higher than that of the second closed cross section V 2 , and the strength of the second closed cross section V 2  may be higher than that of the third closed cross section V 3 . The third closed cross section V 3  may have the lowest strength. Accordingly, during a side collision of the vehicle, when impact energy is transferred to the first closed cross section V 1 , the second closed cross section V 2 , and the third closed cross section V 3 , the first closed cross section V 1  may be less deformed, the second closed cross section V 2  may be more deformed than the first closed cross section V 1 , and the third closed cross section V 3  may be significantly deformed. That is, as the strength of the side longitudinal member  12  increases from the interior side thereof toward the exterior side thereof, the side longitudinal member  12  may be sequentially deformed by the impact energy, and thus it may stably absorb the impact energy. 
     Referring to  FIG.  3   , a structural transverse member  15  may be attached to the floor  11 , and the structural transverse member  15  may extend in the width or transverse direction of the vehicle. The structural transverse member  15  may be aligned with the horizontal rib  23  of the side longitudinal member  12  in the width or transverse direction of the vehicle. 
     Referring to  FIG.  4   , the structural transverse member  15  may have an M-shaped cross section, and accordingly the structural transverse member  15  may have enough strength and stiffness. The cross section of the structural transverse member  15  may have the same shape and size in the width or transverse direction of the vehicle. The structural transverse member  15  may include a central web  15   a , and first and second side webs  15   b  and  15   c  located symmetrically on both sides of the central web  15   a.    
     The central web  15   a  may be flat to match a top surface of the floor  11 , and the central web  15   a  may be attached to the floor  11  using fasteners, welding, and/or the like. 
     The first side web  15   b  and the second side web  15   c  may be offset upwardly with respect to the central web  15   a , and the central web  15   a  and the first and second side webs  15   b  and  15   c  may extend along a longitudinal direction of the structural transverse member  15 . The first side web  15   b  and the second side web  15   c  may be flat. 
     A first edge of the central web  15   a  may be connected to the first side web  15   b  through a first interior side wall  15   h , and a second edge of the central web  15   a  may be connected to the second side web  15   c  through a second interior side wall  15   i . The first interior side wall  15   h  may be inclined from the central web  15   a  toward the first side web  15   b , and the second interior side wall  15   i  may be inclined from the central web  15   a  toward the second side web  15   c.    
     The structural transverse member  15  may include a first flange  15   d  connected to the first side web  15   b  through a first exterior side wall  15   f , and a second flange  15   e  connected to the second side web  15   c  through a second exterior side wall  15   g . The first flange  15   d  and the second flange  15   e  of the structural transverse member  15  may be fixed to the top surface of the floor  11  using fasteners, welding, and/or the like. The first exterior side wall  15   f  may be inclined from the first side web  15   b  toward the first flange  15   d , and the second exterior side wall  15   g  may be inclined from the second side web  15   c  toward the second flange  15   e.    
     The horizontal rib  23  of each side longitudinal member  12  may be aligned with the first side web  15   b  and the second side web  15   c  of the structural transverse member  15  in the width or transverse direction of the vehicle. Accordingly, the pair of side longitudinal members  12  and the structural transverse member  15  may increase transverse stiffness and transverse strength of the vehicle body. 
     In particular, the horizontal rib  23  of the side longitudinal member  12  may be horizontally aligned with the structural transverse member  15  so that the horizontal rib  23  of the side longitudinal member  12  and the structural transverse member  15  may sufficiently support the impact energy (impact load) transferred in the width or transverse direction of the vehicle during a side collision of the vehicle, and thus side crash performance (crashworthiness) of the floor  11  may be improved. 
     Referring to  FIGS.  3  and  4   , the vehicle floor system according to an exemplary embodiment of the present disclosure may further include an additional transverse member  16  disposed above the structural transverse member  15 . The additional transverse member  16  may extend in the width or transverse direction of the vehicle, and a longitudinal axis of the additional transverse member  16  may be parallel to a longitudinal axis of the structural transverse member  15 . For example, the longitudinal axis of the additional transverse member  16  may coincide with the longitudinal axis of the structural transverse member  15 . A cross section of the additional transverse member  16  may have the same shape and size in the width or transverse direction of the vehicle. The additional transverse member  16  may have an M-shaped cross section similar to that of the structural transverse member  15 , and the size of the additional transverse member  16  may be greater than that of the structural transverse member  15 . 
     Referring to  FIG.  4   , the additional transverse member  16  may include a central web  16   a , and first and second side webs  16   b  and  16   c  located symmetrically on both sides of the central web  16   a . The first side web  16   b  and the second side web  16   c  may be offset upwardly with respect to the central web  16   a , and the central web  16   a  and the first and second side webs  16   b  and  16   c  may extend along a longitudinal direction of the additional transverse member  16 . The central web  16   a  of the additional transverse member  16  may be flat to match a top surface of the central web  15   a  of the structural transverse member  15 , and the central web  16   a  of the additional transverse member  16  may be fixed to the central web  15   a  of the structural transverse member  15  using fasteners, welding, and/or the like. 
     A first edge of the central web  16   a  may be connected to the first side web  16   b  through a first interior side wall  16   h , and a second edge of the central web  16   a  may be connected to the second side web  16   c  through a second interior side wall  16   i . The first interior side wall  16   h  may be inclined from the central web  16   a  toward the first side web  16   b , and the second interior side wall  16   i  may be inclined from the central web  16   a  toward the second side web  16   c.    
     The first side web  16   b  of the additional transverse member  16  may be spaced apart upwardly from the first side web  15   b  of the structural transverse member  15 , and the second side web  16   c  of the additional transverse member  16  may be spaced apart upwardly from the second side web  15   c  of the structural transverse member  15 . 
     The additional transverse member  16  may include a first flange  16   d  connected to the first side web  16   b  through a first exterior side wall  16   f , and a second flange  16   e  connected to the second side web  16   c  through a second exterior side wall  16   g . The first exterior side wall  16   f  may be inclined from the first side web  16   b  toward the first flange  16   d , and the second exterior side wall  16   g  may be inclined from the second side web  16   c  toward the second flange  16   e.    
     The first flange  16   d  of the additional transverse member  16  may be flat to match the first flange  15   d  of the structural transverse member  15 , and the first flange  16   d  of the additional transverse member  16  may be fixed to the first flange  15   d  of the structural transverse member  15  using fasteners, welding, and/or the like. The second flange  16   e  of the additional transverse member  16  may be flat to match the second flange  15   e  of the structural transverse member  15 , and the second flange  16   e  of the additional transverse member  16  may be fixed to the second flange  15   e  of the structural transverse member  15  using fasteners, welding, and/or the like. 
     The first side web  16   b  and the second side web  16   c  of the additional transverse member  16  may be aligned with the top wall of the side longitudinal member  12  in the width or transverse direction of the vehicle. Accordingly, the pair of side longitudinal members  12  and the additional transverse member  16  may increase transverse stiffness and transverse strength of the vehicle body. 
     In particular, the top wall of the side longitudinal member  12  may be horizontally aligned with the additional transverse member  16  so that the top wall of the side longitudinal member  12  and the additional transverse member  16  may sufficiently support the impact energy (impact load) transferred in the width or transverse direction of the vehicle during a side collision of the vehicle. 
     A cavity may be formed between the additional transverse member  16  and the structural transverse member  15 , and the additional transverse member  16  may be attached to the structural transverse member  15  so that the additional transverse member  16  and the structural transverse member  15  may form a closed cross section. Thus, the additional transverse member  16  and the structural transverse member  15  may increase strength and stiffness of the vehicle body. 
     According to an exemplary embodiment, the additional transverse member  16  and the structural transverse member  15  may be made of the same or similar material, and the additional transverse member  16  and the structural transverse member  15  may be manufactured by the same manufacturing process. The additional transverse member  16  may be fixed to the structural transverse member  15  using fasteners, welding, and/or the like so that the additional transverse member  16  and the structural transverse member  15  may be integrally joined. 
     According to another exemplary embodiment, the additional transverse member  16  may be manufactured together with the structural transverse member  15  by casting, extruding, and/or the like so that the additional transverse member  16  and the structural transverse member  15  may form a unitary one-piece structure. Accordingly, a material of the additional transverse member  16  may be the same as that of the structural transverse member  15 . 
     For example, since the structural transverse member  15  is located below the additional transverse member  16 , it may be referred to as a lower transverse member, and since the additional transverse member  16  is located above the structural transverse member  15 , it may be referred to as an upper transverse member. 
     Referring to  FIG.  1   , both end portions of the additional transverse member  16  may be fixed to the pair of side sill inners  13  through a pair of end brackets  17 , respectively. Referring to  FIG.  3   , each end portion of the additional transverse member  16  may be fixed to the corresponding side sill inner  13  through the corresponding end bracket  17 . Each end bracket  17  may include a first flange  17   a  fixed to the side sill inner  13  using fasteners, welding, and/or the like, and a second flange  17   b  fixed to the end portion of the additional transverse member  16  using fasteners, welding, and/or the like. 
     According to an exemplary embodiment, each end portion of the structural transverse member  15  and each end portion of the additional transverse member  16  may be directly attached to the corresponding side sill inner  13 . 
     According to another exemplary embodiment, when it is difficult to form the structural transverse member  15  and the additional transverse member  16 , each end portion of the structural transverse member  15  and each end portion of the additional transverse member  16  may be spaced apart from the adjacent side sill inner  13  by a predetermined minimum gap g as illustrated in  FIGS.  3  and  5   . In particular, the gap g between the end portion of each of the transverse members  15  and  16  and the side sill inner  13  needs to be minimized to 10 mm or less. 
     Referring to  FIG.  3   , a battery assembly  50  may be disposed under the floor  11 , and the battery assembly  50  may include a battery case  51  in which a plurality of battery cells are received, and a battery cover  52  with which a top opening of the battery case  51  is covered. 
     The battery assembly  50  may include one or more battery transverse members  53  disposed in the battery case  51 , and the battery transverse member  53  may extend in a width or transverse direction of the battery case  51 . 
     The battery assembly  50  may include a pair of side mounts  55  each protruding from an exterior side surface of the battery case  51  toward the corresponding side sill inner  13  and the corresponding side longitudinal member  12 . Each side mount  55  may be made of an aluminum material, and the side mount  55  may be joined to the corresponding side longitudinal member  12  through a side mounting bolt  56 . The side mount  55  may be aligned with the battery transverse member  53  in the width or transverse direction of the vehicle. 
     Referring to  FIG.  2   , the battery assembly  50  may be mounted to the floor  11  of the vehicle body through a plurality of fasteners  6   o . According to an exemplary embodiment, each fastener  60  may directly connect the battery assembly  50  and the structural transverse member  15 . Referring to  FIGS.  3  and  4   , each fastener  60  may include a nut  61  and a bolt  62 . The battery assembly  50  may be mounted on the floor  11  of the vehicle body through the plurality of nuts  61  and the plurality of bolts  62 . Each nut  61  may extend through the battery assembly  50 , and a top end of the nut  61  may be supported to a bottom surface of the floor  11 . Each bolt  62  may be screwed into the corresponding nut  61  to join the floor  11  and the battery assembly  50 . Threads of the bolt  62  may extend through the structural transverse member  15  and the floor  11 , and a head of the bolt  62  may be seated on the structural transverse member  15 . Referring to  FIG.  4   , the head of the bolt  62  may be mounted on the top surface of the central web  15   a  of the structural transverse member  15 . Accordingly, the plurality of fasteners  60  may firmly connect the battery assembly  50  and the structural transverse member  15 . 
     Referring to  FIG.  2   , the pair of side sill inners  13  may be spaced apart from each other by a predetermined distance L, and the plurality of fasteners  60  may be mounted in a predetermined position which is offset from each side sill inner  13 . In particular, the mounting position of each of the fasteners  60  may be ⅓ of the distance L between the pair of side sill inners  13 . That is, the plurality of fasteners  60  may substantially connect the battery assembly  50  and the structural transverse member  15  at predetermined points (e.g., ⅓ of the distance L between the pair of side sill inners  13 ), thereby preventing the floor  11 , the structural transverse member  15 , and the battery transverse member  53  from being deformed (bent) in the event of a side collision of the vehicle, and preventing the battery assembly  50  from coming off or being separated from the floor  11 , thus ensuring safety of the battery assembly  50 . 
     Referring to  FIG.  3   , a deformation section S may be defined between an exterior side surface of each side longitudinal member  12  and the exterior side surface of the battery case  51  of the battery assembly  50 , and a support section T may be defined in an interior space of the battery case  51  of the battery assembly  50 . The deformation section S may be divided into a first section S 1  and a second section S 2 , and the first section S 1  may correspond to a width of the exterior portion  21  of each side longitudinal member  12 . Since the exterior portion  21  of the side longitudinal member  12  has the greatest thickness, the first section S 1  may have relatively high strength. The second section S 2  may be an overlapping section of the interior portion  22  of each side longitudinal member  12  and each side mount  55  of the battery assembly  50 . In particular, a portion of the second closed cross section V 2  and the third closed cross section V 3  of the side longitudinal member  12  may overlap the side mount  55  of the battery assembly  50 . Since the thickness of the interior portion  22  of the side longitudinal member  12  is less than the thickness of the exterior portion  21  thereof, the strength of the second section S 2  may be lower than that of the first section S 1 . The structural transverse member  15  and the battery transverse member  53  may overlap each other in the support section T so that the structural transverse member  15  and the battery transverse member  53  may effectively support the impact energy generated during a side collision of the vehicle. When the impact energy is sequentially transferred to the deformation section S and the support section T during the side collision of the vehicle, the first section S 1  may primarily support the impact energy to absorb approximately 30% of the impact energy. Since the strength of the first section S 1  is higher than that of the second section S 2 , the second section S 2  may be more deformed than the first section S 1 . In particular, the side mount  55  of the battery assembly  50  may be horizontally aligned with the battery transverse member  53  so that during the side collision of the vehicle, the side mount  55  of the battery assembly  50  may be bent to a V-shape while the portion of the second closed cross section V 2  and the third closed cross section V 3  of the side longitudinal member  12  are deformed, and accordingly the second section S 2  may be much more deformed than the first section S 1 , thereby absorbing most of the remaining impact energy. That is, during the side collision of the vehicle, the deformation section S may be sufficiently deformed to appropriately absorb the impact energy, and the support section T may absorb and support the remaining impact energy. 
     As described above, the side longitudinal member  12  may have different strength for each section, and the battery transverse member  53  and the structural transverse member  15  may overlap vertically, thereby absorbing and supporting the impact energy during the side collision, thus sufficiently securing the safety of the battery assembly  50 . In particular, the horizontal rib  23  of the side longitudinal member  12  may be aligned with the first and second side webs  15   b  and  15   c  of the structural transverse member  15  in the width or transverse direction of the vehicle so that the structural transverse member  15  may increase an absorption rate of impact energy at the initial stage of the side collision. 
       FIG.  6    illustrates a vehicle floor system according to another exemplary embodiment of the present disclosure. Referring to  FIG.  6   , each side longitudinal member  42  may have a structure in which a side sill including a side sill inner and a side sill outer and a side sill reinforcement are joined. Each side longitudinal member  42  may be mounted on each side edge of the floor  11 , and the side longitudinal member  42  may extend in the longitudinal direction of the vehicle. A structural transverse member  45  may be disposed above the floor  11 , and the structural transverse member  45  may extend in the width or transverse direction of the vehicle. Each end portion of the structural transverse member  45  may be mounted to the corresponding side longitudinal member  42  through an end bracket  47 . The vehicle floor system may further include an additional transverse member  46  located below the structural transverse member  45 , and the additional transverse member  46  may be fixed to the top surface of the floor  11  using fasteners, welding, and/or the like. The additional transverse member  46  may be disposed between the structural transverse member  45  and the floor  11 . The structural transverse member  45  may be attached to the additional transverse member  46  using fasteners, welding, and/or the like, and a cavity may be formed between the structural transverse member  45  and the additional transverse member  46  so that the structural transverse member  45  and the additional transverse member  46  may form a closed cross section. Thus, the additional transverse member  46  and the structural transverse member  45  may increase strength and stiffness of the vehicle body. Each fastener  60  may connect the battery assembly  50  and the additional transverse member  46 . 
     In the exemplary embodiment illustrated in  FIG.  6   , since the structural transverse member  45  is located above the additional transverse member  46 , it may be referred to as an upper transverse member, and since the additional transverse member  46  is located below the structural transverse member  45 , it may be referred to as a lower transverse member. 
     Referring to  FIG.  6   , each side longitudinal member  42  may include an exterior portion  121  facing the exterior of the vehicle, and an interior portion  122  facing the interior of the vehicle. The exterior portion  121  may include an exterior side wall  121   a  facing the exterior of the vehicle, an exterior top wall  121   b  facing the top of the vehicle, and an exterior bottom wall  121 C facing the bottom of the vehicle. The interior portion  122  may include an interior side wall  122   a  facing the interior of the vehicle, an interior top wall  122   b  facing the top of the vehicle, and an interior bottom wall  122 C facing the bottom of the vehicle. The side longitudinal member  42  may include a horizontal rib  123  provided horizontally therein, and a plurality of vertical ribs  124  and  125  provided vertically therein. The side longitudinal member  42  may include a plurality of cavities defined by the horizontal rib  123  and the plurality of vertical ribs  124  and  125 . The horizontal rib  123  may extend horizontally to connect between the exterior side wall  121   a  and the interior side wall  122   a . The plurality of vertical ribs  124  and  125  may include a first vertical rib  124  adjacent to the exterior side wall  121   a , and a second vertical rib  125  adjacent to the interior side wall  122   a . The second vertical rib  125  may be spaced apart from the first vertical rib  124  toward the interior of the vehicle. The horizontal rib  123  may include a first horizontal rib  123   a  horizontally connecting the exterior side wall  121   a  and the first vertical rib  124 , a second horizontal rib  123   b , horizontally connecting the first vertical rib  124  and the second vertical rib  125 , and a third horizontal rib  123   c  horizontally connecting the second vertical rib  125  and the interior side wall  122   a . The horizontal rib  123  of the side longitudinal member  42  may be aligned with the structural transverse member  45  in the width or transverse direction of the vehicle. 
     The other elements in this exemplary embodiment may be similar to or the same as those in the exemplary embodiment illustrated in  FIGS.  1  to  5   . 
       FIG.  7    illustrates a vehicle floor system according to another exemplary embodiment of the present disclosure. Referring to  FIG.  7   , each side longitudinal member  72  may be received in the side sill inner  13  of the side sill, and the side longitudinal member  72  may extend in the longitudinal direction of the vehicle. A structural transverse member  75  may be disposed below the floor  11 , and the structural transverse member  75  may extend n the width or transverse direction of the vehicle. A seat cross member  18  may be attached to the top surface of the floor  11 , and the seat crossmember  18  may extend in the width or transverse direction of the vehicle. A vehicle seat may be mounted on the seat crossmember  18  through a plurality of brackets. Each end portion of the structural transverse member  75  may be directly mounted on an inboard side surface of the side sill inner  13  using fasteners, welding, and/or the like. Each fastener  60  may directly connect the battery assembly  50  and the structural transverse member  75 . 
     Referring to  FIG.  7   , each side longitudinal member  72  may include an exterior portion  221  facing the exterior of the vehicle, and an interior portion  222  facing the interior of the vehicle. The exterior portion  221  may include an exterior side wall  221   a  facing the exterior of the vehicle, an exterior top wall  221   b  facing the top of the vehicle, and an exterior bottom wall  221 C facing the bottom of the vehicle. The interior portion  222  may include an interior side wall  222   a  facing the interior of the vehicle, an interior top wall  222   b  facing the top of the vehicle, and an interior bottom wall  222 C facing the bottom of the vehicle. The side longitudinal member  72  may include a horizontal rib  223  provided horizontally therein, and a plurality of vertical ribs  224  and  225  provided vertically therein. The side longitudinal member  72  may include a plurality of cavities defined by the horizontal rib  223  and the plurality of vertical ribs  224  and  225 . The horizontal rib  223  may extend horizontally to connect between the exterior side wall  221   a  and the interior side wall  222   a . The plurality of vertical ribs  224  and  225  may include a first vertical rib  224  adjacent to the exterior side wall  221   a , and a second vertical rib  225  adjacent to the interior side wall  222   a . The second vertical rib  225  may be spaced apart from the first vertical rib  224  toward the interior of the vehicle. The horizontal rib  223  may include a first horizontal rib  223   a  horizontally connecting the exterior side wall  221   a  and the first vertical rib  224 , a second horizontal rib  223   b  horizontally connecting the first vertical rib  224  and the second vertical rib  225 , and a third horizontal rib  223   c  horizontally connecting the second vertical rib  225  and the interior side wall  222   a . The horizontal rib  223  of the side longitudinal member  72  may be aligned with the structural transverse member  75  in the width or transverse direction of the vehicle. 
     The other elements in this exemplary embodiment may be similar to or the same as those in the exemplary embodiment illustrated in  FIGS.  1  to  5   . 
     As set forth above, according to exemplary embodiments of the present disclosure, the side longitudinal member may have a different strength for each section, and the battery transverse member and the structural transverse member may overlap vertically, thereby absorbing and supporting the impact energy during a side collision of the vehicle, thus sufficiently securing the safety of the battery assembly. In particular, the horizontal rib of the side longitudinal member may be aligned with the structural transverse member in the width or transverse direction of the vehicle so that the structural transverse member may increase the absorption rate of impact energy at the initial stage of the side collision. 
     According to exemplary embodiments of the present disclosure, the structural members of the vehicle such as the floor, the side longitudinal members, the structural transverse member, and the additional transverse member may be manufactured by a process that can improve stiffness and/or strength such as hot stamping, hot forming, press hardening, and/or roll forming. Thus, each structural member may have a cross section with increased bending stiffness against a lateral load acting on the side of the vehicle. 
     Hereinabove, although the present disclosure has been described with reference to exemplary embodiments and the accompanying drawings, the present disclosure is not limited thereto, but may be variously modified and altered by those skilled in the art to which the present disclosure pertains without departing from the spirit and scope of the present disclosure claimed in the following claims.