Patent Publication Number: US-2023144195-A1

Title: Vehicle Center Frame Module

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2021-0153397, filed on Nov. 9, 2021, which application is hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a vehicle center frame module. 
     BACKGROUND 
     A vehicle frame, which is a structure designed to install chassis components or a vehicle body, should be sufficiently protected from local or overall damages due to deformation, torsion, tension, compression, and/or vibration caused by the vehicle&#39;s propulsion force, brake action, a centrifugal force during steering, an impact from a road surface, a vertical load due to the weight of the vehicle body, and various reaction forces. It should be of a structure that can sufficiently absorb impact energy applied to the vehicle in the event of a collision. 
     Due to diversification of the vehicle market, the vehicle frame is being changed in various ways from an existing monocoque structure to a novel structure such as a purpose built vehicle (PBV) frame and a space frame, to meet each vehicle&#39;s purpose. In particular, a low-cost electric vehicle (EV) requires a vehicle body structure which is created by breaking an existing method in order to maximize profitability. 
     Existing vehicles use pressed steel materials and aluminum materials for the frame, and thus the material cost and investment cost thereof may be relatively high. 
     In addition, since a joint portion between structural members constituting the existing vehicle frame is made by welding, the joint portion between the structural members may be easily damaged by an impact load during a side collision of the vehicle. In addition, it may be difficult to uniformly distribute a load transferred from the front of the vehicle body. Thus, it may be difficult to safely protect a passenger compartment and a battery. 
     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 center frame module. Particular embodiments relate to a vehicle center frame module that can significantly improve side crash performance (crashworthiness) of a vehicle. 
     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 center frame module using a relatively inexpensive material such as a mass-produced steel pipe, thereby significantly reducing the manufacturing cost thereof, compared to when using pressed steel materials and aluminum materials, and significantly improving side crash performance (crashworthiness) of a vehicle, thereby safely protecting a battery and a passenger compartment. 
     According to an embodiment of the present disclosure, a vehicle center frame module may include a pair of side sills and two or more crossmembers connecting the pair of side sills in a transverse direction of the vehicle. Each side sill may include a side sill inner having a closed cross section and a side sill outer having a closed cross section, and an inboard side surface of the side sill outer and an outboard side surface of the side sill inner may be joined. The crossmembers may include a first crossmember and a second crossmember located behind the first crossmember. 
     Each of the side sill inner and the side sill outer may have a closed cross section, and a cavity of the side sill outer may be separated from a cavity of the side sill inner. That is, the side sill may have a double closed cross section through the two separated cavities, thereby enhancing strength and stiffness thereof. Thus, side crashworthiness of the vehicle may be improved so that the battery and the passenger compartment may be safely protected. 
     The side sill inner may be made of a material having higher strength and stiffness than that of the side sill outer. 
     As the material of the side sill inner has higher strength and stiffness than the material of the side sill outer, side stiffness of the center frame module may be significantly improved. 
     Specifically, the side sill inner may be made of a high-tensile strength steel plate. 
     Accordingly, the side sills may have improved side crashworthiness, thereby safely protecting the battery and the passenger compartment. 
     A cross-sectional area of the side sill inner may be greater than a cross-sectional area of the side sill outer. 
     Accordingly, the strength and stiffness of the side sill inner may be greater than the strength and stiffness of the side sill outer. When a side impact load is applied to the side sill, the side sill inner may sufficiently withstand the impact load. 
     The side sill inner and the side sill outer may be joined to form a stepped structure. 
     Accordingly, a vertical height of the side sill may be relatively increased, thereby stably covering the side impact load applied to the side sill. 
     A bottom surface of the side sill outer may be located lower than a bottom surface of the side sill inner. 
     Accordingly, the side sill inner and the side sill outer may more safely protect a battery case located under the center frame module in the event of a side collision of the vehicle. 
     The side sill may further include a rivet nut for mounting a battery assembly, and the rivet nut may extend through the side sill inner. 
     The rivet nut may extend through the side sill inner, thereby stably securing mounting stiffness of the battery assembly. 
     The rivet nut may include a nut body extending through the side sill inner, a top head provided on a top end of the nut body, and a bottom head provided on a bottom end of the nut body. 
     Accordingly, the rivet nut having the top head and the bottom head may be firmly mounted in the side sill inner of the side sill, thereby improving assembly of the battery assembly and sufficiently securing the mounting stiffness of the battery assembly. 
     The nut body may have internal threads provided on an inner circumferential surface thereof, the top head may be supported and joined to a top surface of the side sill inner, and the bottom head may be supported and joined to a bottom surface of the side sill inner. 
     The top head may apply an external force to the top surface of the side sill inner in a vertical downward direction, and the bottom head may apply an external force to the bottom surface of the side sill inner in a vertical upward direction so that the rivet nut may be quite firmly mounted in the side sill inner. 
     Both end portions of each crossmember may be coupled to the pair of side sills through a pair of support brackets, respectively. 
     Accordingly, each end portion of each crossmember may be more firmly supported and joined to the corresponding side sill through the corresponding support bracket. 
     Each support bracket may include a first fixed surface which is fixed to the crossmember, and a second fixed surface which is fixed to the side sill inner. The first fixed surface may be perpendicular to the second fixed surface. 
     Accordingly, each crossmember may be firmly supported to the side sill inner of the corresponding side sill through the support bracket. 
     The support bracket may further include an inclined surface extending obliquely between the first fixed surface and the second fixed surface. 
     Accordingly, each crossmember may be stably supported to the side sill through the inclined surface of the support bracket. 
     Each crossmember may be made of a high-tensile strength steel plate. 
     As the crossmember is made of a high-tensile strength steel plate, the side crashworthiness of the side sill may be improved, thereby safely protecting the battery and the passenger compartment in the event of a side collision of the vehicle. 
     The vehicle center frame module may further include two or more side longitudinal members connected perpendicularly to the two or more crossmembers. 
     The side longitudinal members may include a pair of first side longitudinal members extending from the first crossmember to the second crossmember, and a pair of second side longitudinal members extending from the second crossmember toward the rear of the vehicle. 
     Each second side longitudinal member may be aligned with a corresponding first side longitudinal member in a longitudinal direction of the vehicle. 
     The plurality of side longitudinal members may be connected perpendicularly to the plurality of crossmembers so that static stiffness and dynamic stiffness of the center frame module may be increased. In particular, during a side collision of the vehicle, an impact load may be transferred along the plurality of crossmembers through the side sill in the transverse direction of the vehicle, and the impact load may be transferred through the plurality of side longitudinal members connected perpendicularly to the plurality of crossmembers in the longitudinal direction of the vehicle so that the load may be uniformly distributed in the center frame module. 
    
    
     
       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 vehicle frame to which a vehicle center frame module according to an exemplary embodiment of the present disclosure is applied; 
         FIG.  2    illustrates a plan view of the vehicle frame illustrated in  FIG.  1   , from which a pair of roof rails are removed; 
         FIG.  3    illustrates an enlarged view of portion A of  FIG.  2   ; 
         FIG.  4    illustrates a cross-sectional view, taken along line B-B of  FIG.  3   ; 
         FIG.  5    illustrates a cross-sectional view, taken along line C-C of  FIG.  3   ; 
         FIG.  6    illustrates a cross-sectional view, taken along line D-D of  FIG.  3   ; 
         FIG.  7    illustrates a cross-sectional view, taken along line E-E of  FIG.  3   ; and 
         FIG.  8    illustrates a cross-sectional view, taken along line F-F of  FIG.  3   . 
     
    
    
     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. 
       FIG.  1    illustrates a vehicle frame  1  to which a vehicle center frame module according to an exemplary embodiment of the present disclosure is applied. 
     Referring to  FIG.  1   , the vehicle frame  1  may include a center frame module  10 , a front structure  6  connected to the front of the center frame module  10 , a rear frame module  9  connected to the rear of the center frame module  10 , and an intermediate structure  20  disposed between the center frame module  10  and the rear frame module  9 . 
     A pair of front pillars  5   a  may extend from the front of the center frame module  10  in a height direction of the vehicle, and the pair of front pillars  5   a  may be spaced apart from each other in a transverse direction of the vehicle. 
     A pair of center pillars  5   b  may extend from the center of the center frame module  10  in the height direction of the vehicle, and the pair of center pillars  5   b  may be spaced apart from each other in the transverse direction of the vehicle. 
     A pair of rear pillars  5   c  may extend from the rear of the center frame module  10  in the height direction of the vehicle, and the pair of rear pillars  5   c  may be spaced apart from each other in the transverse direction of the vehicle. 
     A pair of roof rails  3  may be disposed above the center frame module  10 , and each roof rail  3  may extend in a longitudinal direction of the vehicle. Each roof rail  3  may connect a top end of the corresponding front pillar  5   a , a top end of the corresponding center pillar  5   b , and a top end of the corresponding rear pillar  5   c . Each roof rail  3  may have a front extension portion  3   a  extending obliquely from a front end thereof, and a rear extension portion  3   b  extending obliquely from a rear end thereof. 
     Referring to  FIGS.  2  and  3   , the center frame module  10  may include a pair of side sills  30  disposed on both side edges thereof, a plurality of crossmembers  11  and  12  connecting the pair of side sills  30  in the transverse direction of the vehicle, and a plurality of side longitudinal members  13   a  and  13   b  connected perpendicularly to the plurality of crossmembers  11  and  12 . 
     The pair of side sills  30  may be spaced apart from each other in the transverse direction of the vehicle, and each side sill  30  may extend in the longitudinal direction of the vehicle. Referring to  FIGS.  2  and  3   , the side sill  30  may include a side sill inner  31  facing the interior of the vehicle, and a side sill outer  32  facing the exterior of the vehicle. 
     The side sill inner  31  may have an angular cross section or a circular cross section with a cavity defined therein, and accordingly the side sill inner  31  may have a closed cross section. 
     An inboard side surface of the side sill outer  32  may be fixed to an outboard side surface of the side sill inner  31  using fasteners, welding, and/or the like. The side sill outer  32  may be made of a mass-produced steel pipe having an angular cross section or a circular cross section with a cavity defined therein, and accordingly the side sill outer  32  may have a closed cross section. For example, the mass-produced steel pipe may be SGH400, SGH490, or the like. 
     Each of the side sill inner  31  and the side sill outer  32  may have a closed cross section, and the cavity of the side sill outer  32  may be separated from the cavity of the side sill inner  31 . Since the cavity of the side sill inner  31  and the cavity of the side sill outer  32  are separated from each other, the side sill  30  may have a double closed cross section, thereby enhancing strength and stiffness thereof. 
     The side sill inner  31  may be made of a material having higher strength and stiffness than a material of the side sill outer  32 . As the material of the side sill inner  31  has higher strength and stiffness than the material of the side sill outer  32 , side stiffness of the center frame module  10  may be significantly improved. 
     According to an exemplary embodiment, the side sill inner  31  may be made of a high-tensile strength steel plate such as SPFC1180Y through hot stamping, hot forming, press hardening, and/or roll forming. Accordingly, side crash performance (crashworthiness) of the side sills  30  may be improved so that a battery and a passenger compartment may be safely protected in the event of a side collision. 
     The cross-sectional areas and thicknesses of the side sill inner  31  and the side sill outer  32  may be determined to have the same or similar moment of inertia compared to an existing side sill according to the related art. 
     According to an exemplary embodiment, as illustrated in  FIGS.  3  and  4   , the cross-sectional area of the side sill inner  31  may be greater than the cross-sectional area of the side sill outer  32 . In addition, the thickness of the side sill inner  31  may be greater than the thickness of the side sill outer  32 . 
     The side sill inner  31  and the side sill outer  32  may be joined to form a stepped structure. Referring to  FIGS.  3  and  4   , a bottom surface of the side sill outer  32  may be located lower than a bottom surface of the side sill inner  31 . Accordingly, the side sill inner  31  and the side sill outer  32  may more safely protect a battery case  100  located under the center frame module  10  in the event of a side collision of the vehicle. 
     Each side edge of an upper body may be directly mounted on the side sill outer  32  of the corresponding side sill  30 . Referring to  FIGS.  3  and  4   , a top surface of the side sill outer  32  may be located lower than a top surface of the side sill inner  31 , and accordingly a mounting space of the upper body may be sufficiently secured. 
     Referring to  FIGS.  2  and  3   , a battery assembly may be disposed under the vehicle frame  1 . The battery assembly may include the battery case  100 , and a plurality of battery mounts  101  extending from both side edges of the battery case  100  in a direction parallel to the transverse direction of the vehicle. 
     The side sill  30  may further include a rivet nut  50  for mounting the battery assembly. The rivet nut  50  may extend vertically through the side sill inner  31 . Specifically, the rivet nut  50  may include a nut body  51  extending through the cavity of the side sill inner  31 , a top head  53  provided on a top end of the nut body  51 , and a bottom head  54  provided on a bottom end of the nut body  51 . 
     The rivet nut  50  having the top head  53  and the bottom head  54  may be firmly mounted in the side sill inner  31  of the side sill  30 , thereby improving assembly of the battery assembly and sufficiently securing mounting stiffness of the battery assembly. 
     The nut body  51  may have internal threads provided on an inner circumferential surface thereof, and the nut body  51  may extend through the top surface and bottom surface of the side sill inner  31 . The top head  53  may be supported and joined to the top surface of the side sill inner  31 , and the bottom head  54  may be supported and joined to the bottom surface of the side sill inner  31 . The top head  53  may apply an external force to the top surface of the side sill inner  31  in a vertical downward direction, and the bottom head  54  may apply an external force to the bottom surface of the side sill inner  31  in a vertical upward direction so that the rivet nut  50  may be firmly mounted in the side sill inner  31 . For example, the rivet nut  50  may be riveted to the side sill inner  31  through a nut riveter or the like. 
     Each battery mount  101  may extend from each side edge of the battery case  100  toward the side sill inner  31 , each battery mount  101  may have a mounting pipe  55  provided on an end portion thereof, and the mounting pipe  55  may be aligned with the rivet nut  50  of the side sill inner  31 . Specifically, a central longitudinal axis of the mounting pipe  55  may be aligned with a central longitudinal axis of the rivet nut  50 . The mounting pipe  55  may not have any internal threads therein. 
     A mounting bolt  56  may be mounted into the mounting pipe  55  of the battery mount  101  and the rivet nut  50  of the side sill inner  31 . The mounting bolt  56  may have a head  56   a  and external threads  56   b , and the head  56   a  may be supported to a bottom surface of the battery mount  101 . The external threads  56   b  of the mounting bolt  56  may be screwed into the internal threads of the nut body  51  of the rivet nut  50  through the mounting pipe  55 . Accordingly, the mounting bolt  56  may be firmly mounted into the mounting pipe  55  and the rivet nut  50 , thereby sufficiently securing the mounting stiffness of the battery assembly. 
     The plurality of crossmembers  11  and  12  may include a first crossmember  11  and a second crossmember  12  located behind the first crossmember  11 . 
     The first crossmember  11  may extend in the transverse direction of the vehicle, and the second crossmember  12  may extend in the transverse direction of the vehicle. The first crossmember  11  may be parallel to the second crossmember  12 . The second crossmember  12  may be spaced apart from the first crossmember  11  toward the rear of the vehicle. The first crossmember  11  and the second crossmember  12  may be located in the middle of the center frame module  10 . 
     Each end portion of the first crossmember  11  may be joined to the corresponding side sill  30  using fasteners, welding, and/or the like, and accordingly the first crossmember  11  may connect the pair of side sills  30  in the transverse direction of the vehicle. 
     Each end portion of the second crossmember  12  may be joined to the corresponding side sill  30  using fasteners, welding, and/or the like, and accordingly the second crossmember  12  may connect the pair of side sills  30  in the transverse direction of the vehicle. 
     Both end portions of each of the crossmembers  11  and  12  may be supported with respect to the pair of side sills  30  through a pair of support brackets  33 , respectively. That is, each end portion of each of the crossmembers  11  and  12  may be more firmly supported and joined to the corresponding side sill  30  through the corresponding support bracket  33 . 
     Referring to  FIG.  4   , each support bracket  33  may connect a bottom surface of each of the crossmembers  11  and  12  adjacent to an end face of each of the crossmembers  11  and  12  to the inboard side surface of the corresponding side sill inner  31 . Accordingly, the pair of support brackets  33  may stably support a vertical load acting on the crossmembers  11  and  12  and the side sills  30 . 
     Referring to  FIG.  4   , each support bracket  33  may include a first fixed surface  33   a  fixed to each of the crossmembers  11  and  12 , and a second fixed surface  33   b  fixed to the side sill inner  31 . The first fixed surface  33   a  may be perpendicular to the second fixed surface  33   b.    
     Specifically, the first fixed surface  33   a  may be horizontally flat to match the bottom surface of each of the crossmembers  11  and  12 , and the first fixed surface  33   a  may be fixed to the bottom surface of each of the crossmembers  11  and  12  adjacent to each end face thereof using fasteners, welding, and/or the like. The second fixed surface  33   b  may be vertically flat to match the inboard side surface of the side sill inner  31 , and the second fixed surface  33   b  may be fixed to the inboard side surface of the side sill inner  31  using fasteners, welding, and/or the like. Accordingly, the bottom surface of each of the crossmembers  11  and  12  adjacent to each end face thereof may be firmly supported with respect to the side sill inner  31  of the corresponding side sill  30  through the corresponding support bracket  33 . 
     In addition, each support bracket  33  may further include an inclined surface  33   c  extending obliquely between the first fixed surface  33   a  and the second fixed surface  33   b , and each of the crossmembers  11  and  12  may be stably supported with respect to the side sill  30  through the inclined surface  33   c  of the support bracket  33 . 
     According to an exemplary embodiment, the first crossmember  11  and the second crossmember  12  may be seat crossmembers on which vehicle seats are mounted using brackets, and the first crossmember  11  and the second crossmember  12  may support the vehicle seats. 
     The first crossmember  11  and the second crossmember  12  may connect the pair of side sills  30  in the transverse direction of the vehicle in the middle of the center frame module  10  so that the first crossmember  11  and the second crossmember  12  may have relatively high static stiffness and dynamic stiffness. Accordingly, the first crossmember  11  and the second crossmember  12  may serve as stiffness members for enhancing static stiffness and dynamic stiffness of the vehicle body. 
     The first crossmember  11  and the second crossmember  12  may have an angular cross section or a circular cross section with a cavity defined therein, and accordingly the first crossmember  11  and the second crossmember  12  may have a closed cross section. According to an exemplary embodiment, the first crossmember  11  and the second crossmember  12  may be made of a high-tensile strength steel plate such as SPFC1180Y through hot stamping, hot forming, press hardening, and/or roll forming. Accordingly, the high-strength crossmembers  11  and  12  may improve side crashworthiness of the side sills  30 , thereby safely protecting the battery and the passenger compartment in the event of a side collision of the vehicle. 
     The plurality of side longitudinal members  13   a  and  13   b , may be connected perpendicularly to the plurality of crossmembers  11  and  12  so that static stiffness and dynamic stiffness of the center frame module  10  may be increased. In particular, during a side collision of the vehicle, an impact load may be transferred along the plurality of crossmembers  11  and  12  through the side sill  30  in the transverse direction of the vehicle, and the impact load may be transferred through the plurality of side longitudinal members  13   a  and  13   b  connected perpendicularly to the plurality of crossmembers  11  and  12  in the longitudinal direction of the vehicle so that the load may be uniformly distributed in the center frame module  10 . 
     The plurality of side longitudinal members  13   a  and  13   b  may include a pair of first side longitudinal members  13   a  extending from the first crossmember  11  to the second crossmember  12 , and a pair of second side longitudinal members  13   b  extending from the second crossmember  12  toward the rear of the vehicle. 
     The pair of first side longitudinal members  13   a  may be spaced apart from each other in the transverse direction of the vehicle, and each first side longitudinal member  13   a  may extend in the longitudinal direction of the vehicle. Each first side longitudinal member  13   a  may be located between a central longitudinal axis of the vehicle and the side sill  30 . A front end of the first side longitudinal member  13   a  may be joined to the first crossmember  11  using fasteners, welding, and/or the like, and a rear end of the first side longitudinal member  13   a  may be joined to the second crossmember  12  using fasteners, welding, and/or the like. 
     The pair of second side longitudinal members  13   b  may be spaced apart from each other in the transverse direction of the vehicle, and each second side longitudinal member  13   b  may extend in the longitudinal direction of the vehicle. Each second side longitudinal member  13   b  may be located between the central longitudinal axis of the vehicle and the side sill  30 . A front end of the second side longitudinal member  13   b  may be joined to the second crossmember  12  using fasteners, welding, and/or the like, and a rear end of the second side longitudinal member  13   b  may be joined to the intermediate structure  20  using fasteners, welding, and/or the like. 
     Each second side longitudinal member  13   b  may be aligned with the corresponding first side longitudinal member  13   a  in the longitudinal direction of the vehicle. In particular, the front end of the second side longitudinal member  13   b  and the rear end of the corresponding first side longitudinal member  13   a  may face each other with the second crossmember  12  interposed therebetween. A longitudinal axis of the second side longitudinal member  13   b  may be aligned with a longitudinal axis of the corresponding first side longitudinal member  13   a.    
     Referring to  FIGS.  1  and  2   , the front structure  6  may be connected to the center frame module  10 , the pair of front pillars  5   a , and the pair of front extension portions  3   a . The front structure  6  may include a pair of front side members  61 , a pair of fender upper members  62  located above the pair of front side members  61 , respectively, a bumper back beam  63  connecting front ends of the pair of front side members  61 , a front end module  64  connected to the pair of front side members  61  and the pair of fender upper members  62 , and an upper crossmember  65  connecting the pair of front pillars  5   a.    
     The pair of front side members  61  may be spaced apart from each other in the transverse direction of the vehicle on the front of the vehicle, and each front side member  61  may extend in the longitudinal direction of the vehicle. According to an exemplary embodiment, the front side member  61  may be made of a mass-produced steel pipe having an angular cross section or a circular cross section with a cavity defined therein, and accordingly the front side member  61  may have a closed cross section. For example, the mass-produced steel pipe may be SGH400, SGH490, or the like. 
     The pair of fender upper members  62  may be spaced apart from each other in the transverse direction of the vehicle, and each fender upper member  62  may extend in the longitudinal direction of the vehicle. Each fender upper member  62  may be upwardly spaced apart from the corresponding front side member  61 . 
     The bumper back beam  63  may extend in the transverse direction of the vehicle, and the bumper back beam  63  may connect the front ends of the pair of front side members  61 . Each end portion of the bumper back beam  63  may be joined to the front end of the corresponding front side member  61 . According to an exemplary embodiment, the bumper back beam  63  may be made of a high-tensile strength steel plate through hot stamping, hot forming, press hardening, and/or roll forming. 
     The front end module  64  may be a frame supporting a heat exchanger such as a radiator, a condenser, and an intercooler. 
     The upper crossmember  65  may extend in the transverse direction of the vehicle, and each end portion of the upper crossmember  65  may be joined to the corresponding front pillar  5   a . Referring to  FIGS.  1  and  2   , a pair of strut bars  66  may extend from the upper crossmember  65  to the pair of fender upper members  62 , respectively, and the pair of strut bars  66  may be spaced apart from each other in a longitudinal direction of the upper crossmember  65 . A top end of each strut bar  66  may be joined to a portion of the upper crossmember  65  adjacent to the end portion of the upper crossmember  65 , and a bottom end of each strut bar  66  may be joined to the corresponding fender upper member  62 . That is, the pair of fender upper members  62  may be connected to the upper crossmember  65  through the pair of strut bars  66 . 
     Referring to  FIG.  2   , the rear frame module  9  may include a pair of rear side members  91 , a rear crossmember  92  connecting the pair of rear side members  91 , and a rear back beam  93  connecting rear ends of the rear side members  91 . 
     The pair of rear side members  91  may be spaced apart from each other in the transverse direction of the vehicle on the rear of the vehicle, and each rear side member  91  may extend in the longitudinal direction of the vehicle. Each rear side member  91  may extend from a rear portion of the corresponding side sill  30  to the rear of the vehicle, and a front portion of the rear side member  91  may be joined to the inboard side surface of the rear portion of the corresponding side sill  30  using fasteners, welding, and/or the like. That is, the pair of rear side members  91  may be connected to the inboard side surfaces of the pair of side sills  30 , respectively. The rear crossmember  92  and the rear back beam  93  may extend in the transverse direction of the vehicle. 
     According to an exemplary embodiment, the rear side member  91  may be made of a mass-produced steel pipe having an angular cross section or a circular cross section with a cavity defined therein, and accordingly the rear side member  91  may have a closed cross section. For example, the mass-produced steel pipe may be SGH400, SGH490, or the like. 
     Referring to  FIG.  1   , the rear frame module  9  may be located higher than the center frame module  10 , and the intermediate structure  20  may connect the center frame module  10  and the rear frame module  9 . 
     Referring to  FIG.  2   , the vehicle frame  1  according to an exemplary embodiment of the present disclosure may further include a rear subframe  80  mounted on the rear frame module  9 . The rear subframe  80  may include a pair of front mounting portions  81  mounted on the front portions of the pair of rear side members  91 , respectively, and a pair of rear mounting portions  82  mounted on the rear portions of the pair of rear side members  91 , respectively. 
     Referring to  FIG.  1   , a dash crossmember  67  may connect lower portions of the pair of front pillars  5   a . The dash crossmember  67  may be mounted under a dash panel, and the dash panel may serve as a partition between a front compartment and the passenger compartment. In addition, both end portions of the dash crossmember  67  may be joined to the pair of side sills  30  using fasteners, welding, and/or the like, respectively. 
     Each front side member  61  may extend from the bumper back beam  63  toward the rear of the vehicle, and the front side member  61  may be connected to the dash crossmember  67 . Accordingly, the dash crossmember  67  may support the pair of front side members  61 . Specifically, a rear end of each front side member  61  may be joined to the dash crossmember  67  using fasteners, welding, and/or the like, and the front end of each front side member  61  may be joined to the corresponding end portion of the bumper back beam  63  using fasteners, welding, and/or the like. 
     Referring to  FIGS.  2  and  3   , the center frame module  10  may further include a front crossmember  14  located behind the dash crossmember  67 , a pair of rear lower members  15  extending from the dash crossmember  67  to the front crossmember  14 , and a center longitudinal member  16  extending from the dash crossmember  67  to the first crossmember  11 . 
     The front crossmember  14  may extend in the transverse direction of the vehicle. The front crossmember  14  may be parallel to the first crossmember  11  and the second crossmember  12 . The front crossmember  14  may be spaced apart from the dash crossmember  67  toward the rear of the vehicle, and be adjacent to the front end of the center frame module  10 . Both end portions of the front crossmember  14  may be joined to the pair of side sills  30 , respectively, and accordingly the front crossmember  14  may connect the pair of side sills  30  in the transverse direction of the vehicle. 
     The front crossmember  14  may have an angular cross section or a circular cross section with a cavity defined therein, and accordingly the front crossmember  14  may have a closed cross section. According to an exemplary embodiment, the front crossmember  14  may be made of a high-tensile strength steel plate such as SPFC1180Y through hot stamping, hot forming, press hardening, and/or roll forming. Accordingly, the high-strength front crossmember  14  may improve crashworthiness and stiffness of the center frame module  10 , thereby safely protecting the battery and the passenger compartment in the event of a collision of the vehicle. 
     The pair of rear lower members  15  may be spaced apart from each other in the transverse direction of the vehicle, and each rear lower member  15  may extend in the longitudinal direction of the vehicle. According to an exemplary embodiment, the rear lower member  15  may be made of a high-tensile strength steel plate such as SPFC1470 through hot stamping, hot forming, press hardening, and/or roll forming, whereby front crash performance (crashworthiness) of the vehicle may be improved, and thus the battery and the passenger compartment may be safely protected in the event of a front collision. 
     The center longitudinal member  16  may extend in the central longitudinal axis of the vehicle. 
     According to an exemplary embodiment of the present disclosure, except for the strength members or stiffness members such as the bumper back beam  63 , the first and second crossmembers  11  and  12 , the rear lower member  15 , and the side sill inner  31 , most of the members constituting the center frame module  10 , the front structure  6 , and the rear frame module  9  may be made of mass-produced steel pipes. In particular, the mass-produced steel pipe may have an angular cross section or a circular cross section with a cavity defined therein, and the shape and size thereof may be standardized. Each member made of the mass-produced steel pipe may have a closed cross section. Thus, the vehicle frame  1  according to an exemplary embodiment of the present disclosure may form a relatively inexpensive and stable space frame. 
     Meanwhile, during the assembly of the vehicle frame  1 , the pair of side sills  30  may not be preassembled to the center frame module  10 , but may be loaded onto both sides of the center frame module  10  when the upper body is loaded onto the center frame module  10 . Then, the pair of side sills  30  together with the upper body may be assembled to both side edges of the center frame module  10 . 
     As illustrated in  FIG.  2   , each rear end of the front side member  61  may be joined to the dash crossmember  67 , and the rear lower member  15  corresponding to the front side member  61  may be joined to the dash crossmember  67  so as to be aligned with the front side member  61 . A front end of each rear lower member  15  may be joined to the dash crossmember  67  using fasteners, welding, and/or the like, and a rear end of each rear lower member  15  may be joined to the front crossmember  14  using fasteners, welding, and/or the like. The front end of the rear lower member  15  may face the rear end of the front side member  61  with the dash crossmember  67  interposed therebetween. That is, the front end of the rear lower member  15  may be aligned with the rear end of the front side member  61 . 
     Referring to  FIG.  2   , the rear portion of the front side member  61  may extend obliquely toward the dash crossmember  67 , and the rear lower member  15  may extend obliquely from the front side member  61  toward the dash crossmember  67 . As the rear lower member  15  is inclined at the same angle as the rear portion of the front side member  61 , the front end of the rear lower member  15  may be aligned with the rear end of the front side member  61 . 
     Referring to  FIG.  6   , the front side member  61  may have an opening  41  provided in the rear end thereof, and the dash crossmember  67  may be fitted into the opening  41  of the front side member  61 . 
     According to an exemplary embodiment, the opening  41  may include a top engaging portion  41   a  joined to a top surface of the dash crossmember  67 , and a front engaging portion  41   b  joined to a front surface of the dash crossmember  67 . The top engaging portion  41   a  may be horizontally flat to match the top surface of the dash crossmember  67 , and the top engaging portion  41   a  may be joined to the top surface of the dash crossmember  67  by welding (CO 2  welding or the like), using fasteners, and/or the like. The front engaging portion  41   b  may be vertically flat to match the front surface of the dash crossmember  67 , and the front engaging portion  41   b  may be joined to the front surface of the dash crossmember  67  by welding (CO 2  welding or the like), using fasteners, and/or the like. Accordingly, the opening  41  of the front side member  61  may have an L-shaped cross section, and thus the rear end of the front side member  61  may be mechanically joined to the dash crossmember  67 . That is, the rear end of the front side member  61  may be quite firmly joined to the dash crossmember  67  through a mechanical joint system. According to another exemplary embodiment of the present disclosure, the opening  41  of the front side member  61  may have a U-shaped cross section, and thus the rear end of the front side member  61  may be more firmly joined to the dash crossmember  67 . 
     Referring to  FIG.  6   , each rear lower member  15  may have a front engaging portion  42  provided on the front end thereof. The front engaging portion  42  may be vertically flat to match a rear surface of the dash crossmember  67 , and the front engaging portion  42  may be joined to the rear surface of the dash crossmember  67  by welding (CO 2  welding or the like), using fasteners, and/or the like. A bracket  43  may be integrally connected to the front end of the rear lower member  15  using fasteners, welding, and/or the like, and the bracket  43  may have a bottom engaging portion  43   a  horizontally flat to match a bottom surface of the dash crossmember  67 . Accordingly, the front engaging portion  42  of the rear lower member  15  and the bottom engaging portion  43   a  of the bracket  43  may form an L-shaped cross section, and thus the front end of the rear lower member  15  may be mechanically joined to the dash crossmember  67 . That is, the front end of the rear lower member  15  may be quite firmly joined to the dash crossmember  67  through a mechanical joint system. 
     As described above, the rear end of the front side member  61  and the front end of the rear lower member  15  may be joined and supported to the dash crossmember  67  through the mechanical joint system, and thus a load transferred to the front side member  61  may be uniformly distributed and transferred to the dash crossmember  67  and the rear lower member  15 . 
     Referring to  FIG.  6   , each rear lower member  15  may have an opening  44  provided in the rear end thereof, and the front crossmember  14  may be fitted into the opening  44  of the rear lower member  15 . 
     According to an exemplary embodiment, the opening  44  may include a top engaging portion  44   a  joined to a top surface of the front crossmember  14 , a front engaging portion  44   b  joined to a front surface of the front crossmember  14 , and a bottom engaging portion  44   c  joined to a bottom surface of the front crossmember  14 . The top engaging portion  44   a  may be horizontally flat to match the top surface of the front crossmember  14 , and the top engaging portion  44   a  may be joined to the top surface of the front crossmember  14  by welding (CO 2  welding or the like), using fasteners, and/or the like. The front engaging portion  44   b  may be vertically flat to match the front surface of the front crossmember  14 , and the front engaging portion  44   b  may be joined to the front surface of the front crossmember  14  by welding (CO 2  welding or the like), using fasteners, and/or the like. The bottom engaging portion  44   c  may be horizontally flat to match the bottom surface of the front crossmember  14 , and the bottom engaging portion  44   c  may be joined to the bottom surface of the front crossmember  14  by welding (CO 2  welding or the like), using fasteners, and/or the like. The opening  44  of the rear lower member  15  may have a U-shaped cross section, and thus the rear end of the rear lower member  15  may be mechanically joined to the front crossmember  14 . That is, the rear end of the rear lower member  15  may be quite firmly joined to the front crossmember  14  through a mechanical joint system. 
     Referring to  FIGS.  2  and  3   , a front end of the center longitudinal member  16  may be joined to a central portion of the dash crossmember  67  using fasteners, welding, and/or the like, and a rear end of the center longitudinal member  16  may be joined to a central portion of the first crossmember  11  using fasteners, welding, and/or the like. The pair of rear lower members  15  may be symmetrical to each other with respect to the center longitudinal member  16 . 
     Referring to  FIG.  7   , the center longitudinal member  16  may have a front opening  45  provided in the front end thereof, and a rear opening  46  provided in the rear end thereof. 
     The dash crossmember  67  may be fitted into the front opening  45  of the center longitudinal member  16 . According to an exemplary embodiment, the front opening  45  may include a front engaging portion  45   a  joined to the rear surface of the dash crossmember  67 , and a bottom engaging portion  45   b  joined to the bottom surface of the dash crossmember  67 . The front engaging portion  45   a  may be vertically flat to match the rear surface of the dash crossmember  67 , and the front engaging portion  45   a  may be joined to the rear surface of the dash crossmember  67  by welding (CO 2  welding or the like), using fasteners, and/or the like. The bottom engaging portion  45   b  may be horizontally flat to match the bottom surface of the dash crossmember  67 , and the bottom engaging portion  45   b  may be joined to the bottom surface of the dash crossmember  67  by welding (CO 2  welding or the like), using fasteners, and/or the like. Accordingly, the front opening  45  of the center longitudinal member  16  may have an L-shaped cross section, and thus the front end of the center longitudinal member  16  may be mechanically joined to the dash crossmember  67 . That is, the front end of the center longitudinal member  16  may be quite firmly joined to the dash crossmember  67  through a mechanical joint system. 
     The first crossmember  11  may be fitted into the rear opening  46  of the center longitudinal member  16 . According to an exemplary embodiment, the rear opening  46  may include a top engaging portion  46   a  joined to a top surface of the first crossmember  11 , a rear engaging portion  46   b  joined to a front surface of the first crossmember  11 , and a bottom engaging portion  46   c  joined to a bottom surface of the first crossmember  11 . The top engaging portion  46   a  may be horizontally flat to match the top surface of the first crossmember  11 , and the top engaging portion  46   a  may be joined to the top surface of the first crossmember  11  by welding (CO 2  welding or the like), using fasteners, and/or the like. The rear engaging portion  46   b  may be vertically flat to match the front surface of the first crossmember  11 , and the rear engaging portion  46   b  may be joined to the front surface of the first crossmember  11  by welding (CO 2  welding or the like), using fasteners, and/or the like. The bottom engaging portion  46   c  may be horizontally flat to match the bottom surface of the first crossmember  11 , and the bottom engaging portion  46   c  may be joined to the bottom surface of the first crossmember  11  by welding (CO 2  welding or the like), using fasteners, and/or the like. Accordingly, the rear opening  46  of the center longitudinal member  16  may have a U-shaped cross section, and thus the rear end of the center longitudinal member  16  may be mechanically joined to the first crossmember  11 . That is, the rear end of the center longitudinal member  16  may be quite firmly joined to the first crossmember  11  through a mechanical joint system. 
     Referring to  FIGS.  2  and  3   , both end portions of the front crossmember  14  may be joined to the pair of side sills  30  using fasteners, welding, and/or the like, respectively. 
     Referring to  FIG.  8   , the front crossmember  14  may have a pair of side openings  48  provided in both end portions thereof, respectively. The side sill inner  31  of each side sill  30  may be fitted into the corresponding side opening  48  of the front crossmember  14 . According to an exemplary embodiment, each side opening  48  may include a side engaging portion  48   a  joined to the inboard side surface of the side sill inner  31  of the side sill  30 , and a bottom engaging portion  48   b  joined to the bottom surface of the side sill inner  31  of the side sill  30 . The side engaging portion  48   a  may be vertically flat to match the inboard side surface of the side sill inner  31  of the side sill  30 , and the side engaging portion  48   a  may be joined to the inboard side surface of the side sill inner  31  of the side sill  30  by welding (CO 2  welding or the like), using fasteners, and/or the like. The bottom engaging portion  48   b  may be horizontally flat to match the bottom surface of the side sill inner  31  of the side sill  30 , and the bottom engaging portion  48   b  may be joined to the bottom surface of the side sill inner  31  of the side sill  30  by welding (CO 2  welding or the like), using fasteners, and/or the like. Accordingly, the side opening  48  of the front crossmember  14  may have an L-shaped cross section, and thus each end portion of the front crossmember  14  may be mechanically joined to the side sill  30 . That is, both end portions of the front crossmember  14  may be quite firmly joined to the pair of side sills  30  through a mechanical joint system. 
     Referring to  FIG.  8   , the front crossmember  14  may include a center opening  47  provided in a central portion thereof. The center longitudinal member  16  may be fitted into the center opening  47  of the front crossmember  14 . According to an exemplary embodiment, the center opening  47  may include a bottom engaging portion  47   a  joined to a bottom surface of the center longitudinal member  16 , a first side engaging portion  47   b  joined to a first side surface of the center longitudinal member  16 , and a second side engaging portion  47   c  joined to a second side surface of the center longitudinal member  16 . The bottom engaging portion  47   a  may be horizontally flat to match the bottom surface of the center longitudinal member  16 , and the bottom engaging portion  47   a  may be joined to the bottom surface of the center longitudinal member  16  by welding (CO 2  welding or the like), using fasteners, and/or the like. The first side engaging portion  47   b  may be vertically flat to match the first side surface of the center longitudinal member  16 , and the first side engaging portion  47   b  may be joined to the first side surface of the center longitudinal member  16  by welding (CO 2  welding or the like), using fasteners, and/or the like. The second side engaging portion  47   c  may be vertically flat to match the second side surface of the center longitudinal member  16 , and the second side engaging portion  47   c  may be joined to the second side surface of the center longitudinal member  16  by welding (CO 2  welding or the like), using fasteners, and/or the like. Accordingly, the center opening  47  of the front crossmember  14  may have a U-shaped cross section, and thus the center longitudinal member  16  may be mechanically joined to the central portion of the front crossmember  14 . That is, the center longitudinal member  16  may be quite firmly joined to the central portion of the front crossmember  14  through a mechanical joint system. 
     As set forth above, the vehicle center frame module according to exemplary embodiments of the present disclosure may use a relatively inexpensive material such as a mass-produced steel pipe, thereby significantly reducing the manufacturing cost thereof, compared to when using pressed steel materials and aluminum materials, and may significantly improve side crashworthiness of a vehicle, thereby safely protecting the battery and the passenger compartment. 
     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.