Patent Publication Number: US-2021170932-A1

Title: Composite Mat for Vehicles

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Korean Patent Application No. 10-2019-0160988, filed on Dec. 5, 2019, which application is hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a composite mat for a vehicle. 
     BACKGROUND 
     A monocoque type vehicle body structure is applied to existing vehicles. 
     In such a monocoque type vehicle body structure, a lower structure of a vehicle body is completed by assembling a carpet, which is a combination of a non-woven fabric and a pad, to an upper surface of a lower frame in a vehicle body, in particular, at the lower portion of a center of the vehicle body, and assembling an undercover to a lower surface of the lower frame. 
     In order to complete such a lower vehicle body structure, elements such as a carpet and an undercover are separately manufactured, and are then assembled to a lower frame. For this reason, a large number of elements are required, and weight is increased and, as such, there may be a problem in that the number of assembly processes is excessively increased. 
     In particular, the lower structure of the vehicle body is completed by machining the elements through pressing using molds and welding the machined elements. For this reason, there is a drawback in that large-scale plant and equipment investment for a press factory, a vehicle body welding factory, a painting factory, etc. is required. 
     Furthermore, when various products should be manufactured in reduced numbers, increased design modification is required for production of elements of the products. For this reason, the number of molds is remarkably increased in this case and, as such, there is a problem of increased manufacturing costs. 
     Therefore, it is necessary to develop a new lower vehicle body structure capable of securing cost competitiveness through reduction of manufacturing costs and weight of the lower vehicle body structure while appropriately coping with a smart factory environment, thereby achieving an enhancement in ease of assembly of a vehicle body. 
     The above matters disclosed in this section are merely for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that the matters form the related art already known to a person skilled in the art. 
     SUMMARY 
     Embodiments of the present invention have been made in view of problems in the art, and embodiments of the present invention provide a composite mat for a vehicle capable of securing cost competitiveness while reducing the number of assembly processes through simplification of the lower structure of a vehicle body, thereby coping with a smart factory environment. 
     In accordance with an embodiment of the present invention, a composite mat for a vehicle is provided. The composite mat comprises a composite material assembled to an upper surface of a floor module at a lower portion of a vehicle body, the composite material being configured by stacking a glass fiber mat and a polyurethane resin layer on a surface of a honeycomb layer, and a woven fabric layer is stacked on the composite material such that the woven fabric layer is integrated with the composite material. 
     The composite material may be configured by sequentially stacking glass fiber mats and polyurethane resin layers on opposite surfaces of the honeycomb layer. The woven fabric layer may be stacked on one of the polyurethane resin layers, which forms an uppermost layer of the composite material. 
     An edge portion of the composite material may be formed to have a shape surrounded by the polyurethane resin layers. 
     One surface of the composite material may be seated on each fastening surface of frame members constituting floor modules of the lower portion of the vehicle body. A fastening reinforcing member may be inserted between a portion of the other surface of the composite material corresponding to the fastening surface and the woven fabric layer. A fastening member may extend through the woven fabric layer, the fastening reinforcing member and the composite material, and may be fastened to the fastening surface. 
     The composite material may be seated on each fastening surface of frame members constituting floor modules of the lower portion of the vehicle body. A cylindrical fastening reinforcing member may be inserted through the woven fabric layer and the composite material. A fastening member may extend through the fastening reinforcing member, thereby fastening the composite mat to the fastening surface. 
     Each of the frame members may be formed to have a tubular shape while having an opened cross-sectional structure with a side opening portion at one peripheral surface thereof. A mounting plate may be coupled between side closing sections respectively formed at opposite sides of the side opening portion. The composite material may be seated on and fastened to an upper surface of the mounting plate. 
     A flange may be formed at an end of each side closing section in accordance with folding of the end toward the side opening portion. A structural adhesive may be coated between the flange and the composite material. 
     An adhesive receiving groove, in which the structural adhesive is received, may be formed at the composite material to guide a path along which the structural adhesive is coated. 
     A step groove may be formed at an end of the composite material disposed adjacent to the adhesive receiving groove in the same plane as the adhesive receiving groove. 
     The structural adhesive may be coated between the composite material and the flange disposed inwardly of the vehicle body, as compared to a position where the fastening member is fastened. 
     A reinforcing member made of metal may be inserted between the composite material and the woven fabric layer. 
     Deformation guide members having a predetermined diameter may be inserted between the composite material and the woven fabric layer such that the deformation guide members form a lattice structure. 
     In accordance with embodiments of the present invention, the composite mat is simply assembled to a center floor module at the lower portion of the vehicle body, to configure a bottom surface of the lower portion of the vehicle body. Accordingly, the number of elements required to complete the lower structure of the vehicle body is reduced. Thus, it may be possible not only to secure cost competitiveness through reduction of the manufacturing costs and weight of the lower structure of the vehicle body, but also to enhance ease of assembly of the floor mat assembled to the lower portion of the vehicle body, and, as such, the composite mat may appropriately cope with a smart factory environment. 
     As the center floor mat and other mats disposed therebeneath are assembled to the frame members in a bolting manner in accordance with embodiments of the present invention, the lower portion of the vehicle body is completed. Accordingly, the lower portion of the vehicle body does not require large-scale pressing, vehicle body welding, and painting factories and, as such, may appropriately cope with a smart factory environment. In addition, the assembly process of the vehicle body may be simplified and, as such, ease of assembly may be enhanced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and other advantages of embodiments of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a view illustrating a composite mat according to a preferred embodiment of the present invention in a state in which layers of the composite mat are exploded; 
         FIG. 2  is a view illustrating an integrated structure of the composite mat according to the preferred embodiment of the present invention; 
         FIG. 3  is a view illustrating a center floor mat prepared using the composite mat according to the illustrated embodiment of the present invention; 
         FIG. 4  is a view illustrating a vehicle body shape applicable to the center floor mat of  FIG. 3 ; 
         FIG. 5  is a view illustrating an assembled state of the center floor mat of  FIG. 3  to a lower portion of a vehicle body; 
         FIG. 6  is a view showing a cross-section of a portion A of  FIG. 5  corresponding to an edge portion of the center floor mat; 
         FIG. 7  is a cross-sectional view taken along line B-B of  FIG. 5 ; 
         FIG. 8  is a cross-sectional view taken along line C-C of  FIG. 5 ; 
         FIG. 9  is a view illustrating a structure in which a dash mat and the center floor mat are assembled in the case of  FIG. 8 ; 
         FIG. 10  is a cross-sectional view taken along line D-D of  FIG. 5 ; 
         FIG. 11  is a view illustrating a position where a structural adhesive is bonded to the center floor mat in accordance with an embodiment of the present invention; 
         FIGS. 12 to 14  are views illustrating positions where a reinforcing member is applied to the center floor mat in accordance with embodiments of the present invention, respectively; 
         FIG. 15  is a view illustrating a state in which deformation guide members are applied to the center floor mat  100  in accordance with an embodiment of the present invention; 
         FIG. 16  is a view showing cross-sections respectively taken along lines E-E and E′-E′ of  FIG. 15 ; 
         FIG. 17  is a view explaining manufacture of a frame member according to an embodiment of the present invention; and 
         FIG. 18  is a view showing a state in which a cylindrical fastening reinforcing member is applied and fastened to the center floor mat in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     Referring to  FIG. 1 , a composite mat  100  for vehicles according to a preferred embodiment of the present invention, which is applicable to a lower portion of a vehicle body  10  in a miniature electric vehicle, is shown. A center floor mat may be manufactured using the composite mat  100 , which is configured by a plurality of stacked layers. The center floor mat may be assembled to the lower portion of the vehicle body  10 . 
       FIG. 1  is a view illustrating the composite mat  100  according to a preferred embodiment of the present invention in a state in which layers of the composite mat  100  are exploded.  FIG. 2  is a view illustrating an integrated structure of the composite mat  100  according to a preferred embodiment of the present invention. 
     Referring to the drawings, in accordance with a preferred embodiment of the present invention, the composite mat  100  is configured by bonding a woven fabric layer  120  to a composite material  110 . The composite material  110  is assembled to an upper surface of a floor module at the lower portion of the vehicle body  10 . The composite material  110  is configured by sequentially stacking a glass fiber mat  114  and a polyurethane resin layer  116  on each of opposite surfaces of a honeycomb layer  112 . 
     The woven fabric layer  120  is stacked on the composite material  110  such that the woven fabric layer  120  is integrated with the composite material  110  and, as such, the composite mat  100  is manufactured. 
     In this case, the honeycomb layer  112  has a honeycomb structure. The honeycomb layer  112  may be made of polypropylene (PP). The woven fabric layer  120  may be a carpet which is a kind of woolen fabric. 
     For reference, the composite material  110 , which constitutes the composite mat  100 , may be produced through foaming. The composite material  110  may be produced while having different thicknesses in accordance with different molding conditions. Preferably, the composite material  110  is formed to have a thickness of about 7 t, and the woven fabric layer  120  is formed to have a thickness of about 1 to 3 t. 
     That is, the composite mat  100  may be manufactured by stacking the woven layer  120  on the composite material  110  configured through stacking of the honeycomb layer  112 , the glass fiber mats  114  and the polyurethane resin layers  116 . Using the composite mat  100  manufactured as described above, a center floor mat for the lower portion of the vehicle body may be prepared, as shown in  FIGS. 3 and 5 . The center floor mat, which is designated by the same reference numeral as the composite mat  100 , that is, the center floor mat  100 , may be assembled to a center floor module  14  supporting the lower portion of the vehicle body  10 . 
     In accordance with a preferred embodiment of the present invention, a floor surface of the lower portion of the vehicle body  10  is configured through simple assembly of the composite mat  100  to the center floor module  14  at the lower portion of the vehicle body  10 , as described above. Accordingly, the number of elements needed to configure a lower structure of the vehicle body  10  may be reduced. Thus, it may be possible not only to secure cost competitiveness through reduction in manufacturing costs and weight, but also to enhance ease of assembly of the floor mat assembled to the lower portion of the vehicle body  10 , and, as such, the composite mat may appropriately cope with a smart factory environment. 
     For reference, a front floor module  12  is connected to a front portion of the center floor module  14 , and a rear floor module  16  is connected to a rear portion of the center floor module  14 . Spaces may be formed at connecting portions of the center floor module  14  to the front and rear floor modules  12  and  16 , in particular, corner portions of the center floor module  14 . Due to such spaces, the center floor module  14  may have portions which cannot support the center floor mat  100 . To this end, reinforcing plates  40  are additionally connected to respective corner portions in an attached manner, not only to enhance rigidity of the corner portions, but also to enable the center floor mat  100  to be assembled to the corner portions while being supported by the reinforcing plates  40 . 
     In addition, it may be possible to prepare a dash mat to be assembled to a dash module and a rear floor mat to be assembled to the rear floor module  16 , as well as the center floor mat  100 . These mats may be assembled to the associated modules in the same assembly manner as the center floor mat, respectively. 
     Hereinafter, the structure of the composite mat  100  according to a preferred embodiment of the present invention will be described with reference to  FIGS. 1 and 2 . The composite material  110  is configured by sequentially stacking the glass fiber mat  114  and the polyurethane resin layer  116  on each of opposite surfaces of the honeycomb layer  112 . 
     The woven fabric layer  120  is then stacked on the polyurethane resin layer  116  such that the woven fabric layer  120  is integrated with the polyurethane resin layer  116 . 
     In this case, as shown in the drawings, the woven fabric layer  120  may be stacked only on the polyurethane resin layer  116  at one side with reference to the honeycomb layer  112 . Alternatively, the woven fabric layer  120  may be stacked on each of the polyurethane resin layers  116  at both sides with reference to the honeycomb layer  112 . 
     Meanwhile,  FIG. 6  is a view showing an edge portion of the center floor mat  100  prepared using the composite mat  100  according to embodiments of the present invention. 
     Referring to  FIG. 6 , an edge portion of the composite material  110  may be formed to have a shape surrounded by the polyurethane resin layers  116 . 
     That is, the glass fiber mats  114  are disposed inside the composite material  110  and, as such, an overlap structure is applied to the edge portion of the composite material  110  such that the edge portion of the composite material  110  is surrounded by the polyurethane resin layer  116 . Accordingly, formation and dispersion of glass fiber dust may be prevented. 
     Meanwhile,  FIG. 4  is a view showing a shape of the vehicle body  10  to which the center floor mat  100  according to an embodiment of the present invention is applicable.  FIG. 5  is a view showing an assembled state of the center floor mat  100  to the lower portion of the vehicle body  10 . 
     Referring to  FIGS. 4, 5 and 7 , one surface of the composite material  110  is seated on each fastening surface of frame members  20  constituting the floor modules of the lower portion of the vehicle body  10 . A fastening reinforcing member  130  is inserted between a portion of the other surface of the composite material  110  corresponding to each fastening surface and the woven fabric layer  120 . 
     A fastening member b extends through the woven fabric layer  120 , the fastening reinforcing member  130  and the composite material  110 , and is fastened to the fastening surface. 
     The frame members  20  constitute, for example, the center floor module  14  at the lower portion of the vehicle body  10  through assembly thereof. In this case, the center floor module  14  is formed to have a substantially quadrangular shape and, as such, the center floor mat  100  is prepared to have a shape covering the center floor mat  100 , that is, a quadrangular shape. 
     In this case, opposite lateral ends and a rear end of the center floor mat  100  are assembled in a fastened manner to upper surfaces of the opposite side frame members  20  and the rear frame member  20 , which constitute the center floor module  14 . A front end of the center floor mat  100  is assembled in a fastened manner to a lower surface of the frame member  20  disposed at a front side of the center floor module  14 . 
     In particular, the fastening reinforcing member  130  may be manufactured to have a shape of a washer made of stainless steel. The fastening reinforcing member  130  is inserted between the woven fabric layer  120  and the composite material  110  in foaming of the center floor mat  100  and, as such, may be fixed. 
     That is, in the case in which the center floor mat  100  is directly fastened to each frame member  20 , degradation of durability may occur when a crack is formed due to a fastening torque caused by the fastening member b or a load at an associated fastening area. 
     To this end, in accordance with an embodiment of the present invention, the washer-shaped fastening reinforcing member  130  inserted into the inside of the center floor mat  100  is configured to support a fastening load of the fastening member b. Accordingly, the load applied to each fastening area is distributed by the associated fastening reinforcing member  130  and, as such, a stable fastening structure may be realized. 
     In addition, the fastening reinforcing member  130  is fastened in a pressed state by the fastening member b and, as such, the associated fastening area is reduced in thickness, thereby achieving enhancement in fastening rigidity and dimensional stability. 
     Meanwhile,  FIG. 18  is a view showing a structure of the center floor mat  100  assembled to the lower portion of the vehicle body  10  in accordance with another embodiment of the present invention. 
     Referring to  FIG. 18 , the composite material  110  is seated on each fastening surface of the frame members  20  constituting the floor modules of the lower portion of the vehicle body  10 . A cylindrical fastening reinforcing member  130  is inserted into through holes formed through the woven fabric layer  120  and the composite material  110 . 
     A fastening member b extends through the fastening reinforcing member  130  and, as such, the composite mat  100  is fastened to the fastening surface. 
     For example, the fastening reinforcing member  130  may be a cylindrical insert nut. The fastening reinforcing member  130  extends in a cross-sectional direction of the center floor mat  100 , and is bonded to the center floor mat  100 , and as such, a structure in which an outer circumferential surface of the fastening reinforcing member  130  is surrounded by the center floor mat  100  is formed. 
     That is, when the fastening reinforcing member  130  is a cylindrical insert nut, threads of a bolt used as the fastening member b contact an inner circumferential surface of the insert nut, and the outer circumferential surface of the insert nut is completely surrounded by an inner surface of the through hole of the center floor mat  100  while contacting the inner surface of the through hole. Accordingly, dispersion of glass fibers constituting the composite material  110  may be prevented. 
     In accordance with the above-described structure, a fastening torque is generated between a head portion of the bolt and the insert nut in accordance with thread fastening of the threads of the bolt during bolting of the bolt. Accordingly, a stable fastening structure may be formed by the fastening reinforcing member  130  at the associated fastening area. 
     For reference, the fastening member b may be a bolt/nut. In this case, each fastening area may be fastened in a bolting manner. 
     In this case, the center floor mat  100  and other mats disposed therebeneath are assembled to the frame members  20  in a bolting manner and as such, the lower portion of the vehicle body  10  is completed. In this regard, the lower portion of the vehicle body  10  does not require large-scale pressing, vehicle body welding, and painting factories and, as such, may appropriately cope with a smart factory environment. In addition, the assembly process of the vehicle body  10  may be simplified and, as such, ease of assembly may be enhanced. 
       FIG. 7  is a view showing a cross-section of an area where the center floor mat  100  is assembled to one frame member  20 . 
     Referring to  FIG. 7 , the frame member  20  is formed to have a tubular shape while having an opened cross-sectional structure with a side opening portion  24  at one peripheral surface thereof. A mounting plate  30  is coupled between side closing sections  22  respectively formed at opposite sides of the side opening portion  24 . 
     Accordingly, the composite material  110  may be seated on and fastened to an upper surface of the mounting plate  30 . 
     For example, as illustrated in  FIG. 17 , the frame member  20 , to which the center floor mat  100  is fastened, is a tube having an opened cross-sectional structure having one opened surface. That is, the frame member  20  is formed to have a “U”-shaped cross-section perpendicular to a longitudinal direction thereof and, as such, has a structure in which three of the peripheral surfaces of the frame member  20  are closed, and the remaining one peripheral surface is opened. 
     In addition, a fastening portion  25  having a longitudinal extension shape is formed at an end of a side connecting section  21 . The fastening portion  25  is folded toward a corresponding end of the frame member  20  and, as such, is fixed to the end of the frame member  20  while closing an opening OP at the end of the frame member  20 . 
     That is, the side closing sections  22 , which are respectively connected to opposite side edges of the side connecting section  21  facing the side opening portion  24  among the three closed peripheral surfaces of the frame member  20 , are folded in a direction perpendicular to the side connecting section  21  and, as such, the frame member  20  has a “U”-shaped structure. 
     Since the center floor mat  100  should be assembled to the side opening portion  24  of the “U”-shaped frame member  20 , a separate mounting plate  30  is assembled between the opposite side closing sections  22 . 
     Accordingly, an upper surface of the mounting plate  30  serves as a fastening surface and, as such, the center floor mat  100  is coupled to the upper surface of the mounting plate  30 . Thus, the mounting plate  30  not only provides a mounting seat surface of the center floor mat  100 , but also prevents divergence or convergence of the opposite side closing sections  22 , thereby securing torsional rigidity of the opposite side closing sections  22 . 
     For reference, as shown in  FIG. 4 , the fastening portion  25  is fastened to another frame member  20  by fastening members b under the condition that the fastening portion  25  is in surface contact with the other frame member  20 . In accordance with such an assembly method, a frame of the vehicle  10  is completed. 
       FIG. 8  is a cross-sectional view taken along line C-C of  FIG. 5 . Referring to  FIG. 8 , the center floor mat  100  is assembled to the frame member  20  under the condition that a matching surface angle of the frame member  20  is adjusted to be matched with a shaping angle of the center floor mat  100 . 
     In addition,  FIG. 9  is a view illustrating a structure in which a dash mat is assembled to the frame member  20 , together with the center floor mat  100 , in the case of  FIG. 8 . The dash mat may be coupled to the frame member  20  through bolting under the condition that the dash mat overlaps with the center floor mat  100 . Although not shown, a rear floor mat may be coupled to a rear end of the center floor mat  100  through bolting under the condition that the rear floor mat overlaps with the center floor mat  100 . 
     Meanwhile,  FIG. 10  is a cross-sectional view taken along line D-D of  FIG. 5 . 
     Referring to  FIG. 10  together with  FIG. 7 , an end of each side closing section  22  is folded toward the side opening portion  24 , thereby forming a flange  23 . A structural adhesive  200  is coated between the flange  23  of one side closing section  22  and the composite material  110 . 
     For example, ends of the opposite side closing sections  22  may be folded in facing directions, thereby forming flanges  23 , respectively. 
     That is, each flange  23  is formed to have a shape bent from the corresponding side closing section  22  toward the side opening portion  24  and, as such, secures rigidity at the end of the side closing section  22  while serving to provide a seat surface on which the mounting plate  30  is mounted. 
     In particular, the structural adhesive  200  is coated on a planar surface of the flange  23  extending in a width direction and, as such, the flange  23  serves as a sealing surface for the structural adhesive  200 . 
       FIG. 11  is a view illustrating a position where the structural adhesive  200  is bonded to the center floor mat  100  in accordance with an embodiment of the present invention. 
     Referring to  FIG. 11  together with  FIG. 10 , an adhesive receiving groove  118 , in which the structural adhesive  200  is received, may be formed at the composite material  110  to guide a path along which the structural adhesive  200  is coated. 
     That is, in accordance with embodiments of the present invention, the center floor mat  100  is fastened alone to the frame members  20  constituting a floor module through bolting, or is fastened in common to the frame members  20 , together with another floor mat, through bolting. 
     However, in matching areas except for the fastening area, sealing is required. Accordingly, a sealing task for the matching areas is carried out using the structural adhesive  200 . 
     In connection with this, in accordance with an embodiment of the present invention, the structural adhesive  200 , which is of a foam type, may be used. As the adhesive receiving groove  118 , which has an engraved shape, is formed in an area where the structural adhesive  200  will be applied, it may be possible to correctly coat the structural adhesive  200  over the application area. 
     In addition, in accordance with an embodiment of the present invention, a step groove  119  may be formed at an end of the composite material  110  disposed adjacent to the adhesive receiving groove  118  in the same plane as the adhesive receiving groove  118 . 
     That is, the step groove  119  is formed at the end of the composite material  110  disposed adjacent to the area where the structural adhesive  200  is applied such that the step groove  119  has a height corresponding to a depth of the adhesive receiving groove  118 . Accordingly, it may be possible to prevent loosening of the composite material  110  due to the weight thereof during curing of the structural adhesive  200 , thereby securing dimensional stability. 
     In addition, the structural adhesive  200  may be coated between the composite material  110  and the flange  23  disposed inwardly of the vehicle body  10 , as compared to a position where the fastening member b is fastened. 
     That is, as the structural adhesive  200  is coated over the flange disposed inwardly of the area where the composite mat  100  and the frame member  20  are fastened through bolting, moisture sealing is maintained by the structural adhesive  200  even when moisture penetrates into bolting portions of the composite mat  100  and the frame member  20 . As a result, penetration of moisture into the interior of the vehicle body  10  may be prevented by the structural adhesive  200 . 
     Meanwhile,  FIGS. 12 to 14  are views illustrating positions where a reinforcing member  140  is applied to the center floor mat  100  in accordance with embodiments of the present invention. 
     Referring to  FIGS. 12 to 14 , the reinforcing member  140 , which is made of metal, may be inserted between the composite material  110  and the woven fabric layer  120 . 
     For example, in the case of  FIG. 12 , the reinforcing member  140 , which is made of stainless steel, is inserted into an area where the center floor mat  100  is fastened through bolting to the frame members  20  joined in a lateral direction at a middle portion of the center floor module  14 . In this case, rigidity and strength at the reinforcing area are enhanced and, as such, collision performance may be enhanced. 
     In the case of  FIG. 13 , an aluminum sheet is inserted into each planar floor portion of the center floor mat  100 . In this case, thermal insulation performance at the corresponding reinforcing area may be enhanced. 
     In the case of  FIG. 14 , the thickness of the carpet at each planar floor portion of the center floor mat  100  is increased. In this case, vibration and noise is reduced by the corresponding reinforcing area and, as such, noise, vibration and harshness (NVH) performance may be enhanced. 
     Thus, in accordance with embodiments of the present invention, the reinforcing member  140 , which may be made of different materials in accordance with target performance of the composite mat  100 , is inserted and molded during foaming of the composite mat  100  and, as such, collision performance and sound absorption and insulation/thermal insulation performance may be separately provided at desired areas. 
       FIG. 15  is a view illustrating a state in which deformation guide members  150  are applied to the center floor mat  100  in accordance with an embodiment of the present invention.  FIG. 16  is a view showing cross-sections respectively taken along lines E-E and E′-E′ of  FIG. 15 . For reference, the cross-section taken along line E-E and the cross-section taken along line E′-E′ may be shown to have the same cross-sectional shape. 
     Referring to  FIGS. 15 and 16 , the deformation guide members  150 , which have a predetermined diameter, may be inserted between the composite material  110  and the woven fabric layer  120  such that the deformation guide members  150  form a lattice structure. 
     That is, the center floor mat  100  prepared by the composite mat  100  may exhibit non-uniform deformation directions upon collision of the vehicle due to application of the composite material  110  which has a multilayer structure. 
     To this end, the deformation guide members  150 , which have a constant diameter, are inserted while being uniformly spaced apart from one another in longitudinal and lateral directions and, as such, may uniformly guide collision deformation upon front/side collision of the vehicle. 
     Meanwhile, in accordance with embodiments of the present invention, the fastening reinforcing member  130  is inserted between the multilayer composite material  110  and the woven fabric layer  120  in the composite mat  100  such that the fastening reinforcing member  130  is integrated with the composite material  110  and the woven fabric layer  120 . 
     Accordingly, the composite mat  100  may be seated on each fastening surface of the frame members  20  constituting the floor module of the lower portion of the vehicle body  10 , and the composite mat  100  may be fastened to the fastening surface in accordance with extension of the fastening member b through the woven fabric layer  120 , the fastening reinforcing member  130  and the composite material  110 . 
     As the washer-shaped reinforcing fastening member  130 , which is inserted into the composite mat  100 , is configured to support a fastening load of the fastening member b, a stable fastening structure may be realized by the fastening reinforcing member  130 . In addition, when the fastening reinforcing member is formed to have a cylindrical shape, it may be possible to prevent the possibility of dispersion of glass fibers occurring at the composite material  110  in the area where the fastening reinforcing member  130  is fastened. 
     Hereinafter, a method for coupling the composite mat  100  to each frame member  20  through bolting will be described with reference to  FIG. 7 . First, a portion of the composite mat  100 , which should be fastened to the upper surface of the mounting plate  30  joined to the frame member  20 , is seated on the upper surface of the mounting plate  30 . 
     In this case, bolting holes may be formed at the mounting plate  30  and the composite mat  100 , respectively. In connection with this, the composite mat  100  is seated on the mounting plate  30  in a state in which the bolting holes are aligned with each other. 
     Thereafter, a bolt is coupled to the bolting holes. Since the frame member  20  is opened at one peripheral surface thereof, a nut is inserted through the opened side opening portion  24 , and the bolt is then fastened using a tool. Thus, an assembly task of the composite mat  100  and the frame member  20  may be conveniently and simply carried out. 
     As the center floor mat  100  and other mats disposed therebeneath are assembled to the frame members  20  in a bolting manner in accordance with embodiments of the present invention, the lower portion of the vehicle body lo is completed. Accordingly, the lower portion of the vehicle body  10  does not require large-scale pressing, vehicle body welding, and painting factories and, as such, may appropriately cope with a smart factory environment. In addition, the assembly process of the vehicle body  10  may be simplified and, as such, ease of assembly may be enhanced. 
     In particular, the composite mat  100  is simply assembled to the center floor module  14  at the lower portion of the vehicle body lo in accordance with embodiments of the present invention, to configure a bottom surface of the lower portion of the vehicle body  10 . Accordingly, the number of elements required to complete the lower structure of the vehicle body  10  is reduced. Thus, it may be possible not only to secure cost competitiveness through reduction of the manufacturing costs and weight of the lower structure of the vehicle body  10 , but also to enhance ease of assembly of the floor mat assembled to the lower portion of the vehicle body  10 , and, as such, the composite mat may appropriately cope with a smart factory environment. 
     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.