Patent Publication Number: US-2015061320-A1

Title: Vehicle body frame structure of motor vehicle

Description:
TECHNICAL FIELD 
     The present invention relates to a vehicle body frame structure of a motor vehicle, the structure including a pair of left and right front side frames, a pair of left and right bumper beam extensions, a bumper beam, a pair of left and right upper members, and a pair of left and right lower members. 
     BACKGROUND ART 
     An arrangement in which a metal frame module is disposed in front of a dashboard, a crash rail, made of an FRP, is disposed in front of the metal frame module, and when a vehicle is involved in a frontal collision the resin is separated from the fiber of the crash rail by means of the collision load to thus absorb collision energy is known from Patent Document 1 below. 
     Furthermore, an arrangement in which a crash rail, made of an FRP, is formed into a pyramidal shape having a closed cross-section, the cross-sectional area gradually increasing from the front end toward the rear end, and when a collision load is inputted the crash rail crumples sequentially from the extremity side so as to absorb collision energy is known from Patent Document 2 below. 
     RELATED ART DOCUMENTS 
     Patent Document 
     
         
         Patent Document 1: GB Patent No. 2367270 
         Patent Document 2: U.S. Pat. No. 6,406,088 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     When a vehicle is involved in a frontal collision and the collision load is inputted into a bumper beam, it is possible to transmit the collision load from the bumper beam to a crash rail (bumper beam extension) and absorb it, but when a vehicle is involved in a narrow offset frontal collision and the collision load is inputted further outside in the vehicle width direction than the bumper beam extension, there is a possibility that the collision load will not be able to be efficiently transmitted to the bumper beam extension. In order to solve this problem, the bumper beam may be made to project toward the outside in the vehicle width direction from the front ends of a pair of left and right bumper beam extensions, but this causes the problem that the bumper beam protrudes forward and outward in the vehicle width direction to thus increase the dimensions of the vehicle body front part. 
     The present invention has been accomplished in light of the above circumstances, and it is an object thereof to absorb a collision load effectively either in the case of a frontal collision or in the case of a narrow offset frontal collision while avoiding any increase in the dimensions of a vehicle body front part. 
     Means for Solving the Problems 
     In order to attain the above object, according to a first aspect of the present invention, there is provided a vehicle body frame structure of a motor vehicle, the structure comprising a pair of left and right front side frames extending from a lower part of a front wall part of a cabin toward a front of a vehicle body, a pair of left and right bumper beam extensions, made of a fiber-reinforced resin, extending from a front end of the front side frame toward the front of the vehicle body, a bumper beam, made of a fiber-reinforced resin, extending in a vehicle width direction and connected to front ends of the pair of left and right bumper beam extensions, a pair of left and right upper members extending from an upper part at an outer end in the vehicle width direction of the front wall part of the cabin toward the front of the vehicle body, and a pair of left and right lower members, made of a fiber-reinforced resin, extending, while bending, from front ends of the pair of left and right upper members downwardly toward the front, forwardly and inwardly in the vehicle width direction and connected to the front ends of the pair of left and right bumper beam extensions, wherein front faces and outer faces in the vehicle width direction of the pair of left and right lower members and a front face of the bumper beam are curved into a U-shape pointing toward the front of the vehicle body when viewed from above. 
     Further, according to a second aspect of the present invention, in addition to the first aspect, the bumper beam is connected to inner walls in the vehicle width direction at the front ends of the pair of left and right bumper beam extensions, the pair of left and right lower members are connected to outer walls in the vehicle width direction at the front ends of the pair of left and right bumper beam extensions, and the front faces and the outer faces in the vehicle width direction of the pair of left and right lower members, front end faces of the pair of left and right bumper beam extensions, and the front face of the bumper beam are curved into a U-shape pointing toward the front of the vehicle body when viewed from above. 
     Furthermore, according to a third aspect of the present invention, in addition to the first or second aspect, a bumper beam support portion supporting the outer end in the vehicle width direction of the bumper beam is provided on an inner face in the vehicle width direction of the front end part of the bumper beam extension, and a lower member support portion supporting a front end, bent inwardly in the vehicle width direction, of the lower member is provided on an outer face in the vehicle width direction of the front end part of the bumper beam extension. 
     Moreover, according to a fourth aspect of the present invention, in addition to any one of the first to third aspects, a weak portion is provided in the front end part of the bumper beam extension. 
     Further, according to a fifth aspect of the present invention, in addition to any one of the first to fourth aspects, the bumper beam, the lower member and the bumper beam extension comprise a main body part having an open cross section and a rib connecting inner faces of the main body part, the main body part is formed by hardening continuous fibers with a resin, and the rib is formed by hardening discontinuous fibers with a resin. 
     Furthermore, according to a sixth aspect of the present invention, in addition to the fifth aspect, the bumper beam and the lower member comprise a plurality of vertical ribs in an interior of the main body part having a squared U-shaped cross section. 
     Moreover, according to a seventh aspect of the present invention, in addition to the fifth aspect, the bumper beam extension comprises a plurality of X-shaped ribs in an interior of the main body part having an S-shaped cross section. 
     Further, according to an eighth aspect of the present invention, in addition to any one of the first to seventh aspect, a width in a vertical direction of the bumper beam is larger in a middle part in the vehicle width direction than in an end part in the vehicle width direction. 
     Furthermore, according to a ninth aspect of the present invention, in addition to the first aspect, the main body part of the bumper beam extension is formed so as to have an S-shaped cross section while comprising a first side wall, a second side wall and a third side wall, which are disposed substantially parallel to each other, a first bottom wall connecting end parts on one side of the first side wall and the second side wall, and a second bottom wall connecting end parts on the other side of the third side wall and the second side wall, the first side wall, the first bottom wall and the second side wall being connected via a first rib forming an X-shape when viewed in the vehicle width direction, and the third side wall, the second bottom wall and the second side wall being connected via a second rib forming an X-shape when viewed in the vehicle width direction. 
     Moreover, according to a tenth aspect of the present invention, in addition to the ninth aspect, the main body part of the bumper beam extension is formed from a continuous fiber-reinforced resin in which continuous fibers are hardened with a resin, and the first and second ribs are formed from a discontinuous fiber-reinforced resin in which discontinuous fibers are hardened with a resin. 
     Further, according to an eleventh aspect of the present invention, in addition to the ninth or tenth aspect, the first and second ribs are provided as pluralities along a vehicle body fore-and-aft direction. 
     Furthermore, according to a twelfth aspect of the present invention, in addition to any one of the ninth to eleventh aspects, the position in the vehicle body fore-and-aft direction of an X-shaped intersection point of the first rib coincides with the position in the vehicle body fore-and-aft direction of an X-shaped intersection point of the second rib. 
     Moreover, according to a thirteenth aspect of the present invention, in addition to any one of the ninth to twelfth aspects, front ends of the first and second ribs are positioned to the rear of the front end of the bumper beam extension by a predetermined distance. 
     Further, according to a fourteenth aspect of the present invention, in addition to any one of the ninth to thirteenth aspects, the second side wall has a draft angle in the vehicle width direction for removal from a mold. 
     Furthermore, according to a fifteenth aspect of the present invention, in addition to the first aspect, the lower member comprises a first portion extending downwardly toward the front from the front end of the upper member, a second portion bending via a first bent portion at a front end of the first portion and extending forwardly in a horizontal direction, and a third portion bending toward the inner side in the vehicle width direction via a second bent portion at a front end of the second portion and connected to the front end of the bumper beam extension, the lower member comprises a main body part having a squared U-shaped cross section opening outwardly in the vehicle width direction while comprising a bottom wall and a pair of side walls, and comprises a plurality of ribs connecting the bottom wall and the pair of side walls, the bottom wall is formed from a continuous fiber-reinforced resin in which continuous fibers are hardened with a resin, and the pair of side walls and the ribs are formed from a discontinuous fiber-reinforced resin in which discontinuous fibers are hardened with a resin. 
     Moreover, according to a sixteenth aspect of the present invention, in addition to the fifteenth aspect, the ribs are formed into a lattice shape with a horizontal rib extending along a longitudinal direction of the lower member and a plurality of vertical ribs intersecting the horizontal rib. 
     Further, according to a seventeenth aspect of the present invention, in addition to the sixteenth aspect, one of the vertical ribs is disposed in the first bent portion. 
     Furthermore, according to an eighteenth aspect of the present invention, in addition to the sixteenth aspect, the horizontal rib is connected to the bottom wall and extends rearwardly from the front end of the lower member. 
     Moreover, according to a nineteenth aspect of the present invention, in addition to any one of the fifteenth to eighteenth aspects, the lower member comprises a flange at the front end for connection to the front end of the bumper beam extension, and the flange is formed from a discontinuous fiber-reinforced resin in which discontinuous fibers are hardened with a resin. 
     A front side frame base part  23  and a front side frame extremity part  24  of an embodiment correspond to the front side frame of the present invention, a first bottom wall  31   d , a second reinforcing flange  31   g , and a first linking portion  31   j  of the embodiment correspond to the bumper beam support part of the present invention, a first reinforcing flange  31   f , a fourth linking portion  31   n , and a fifth linking portion  31   o  of the embodiment correspond to the lower member support part of the present invention, a first rib  32 , a second rib  33 , a horizontal rib  38 , a vertical rib  39 , a horizontal rib  41 , and a vertical rib  42  of the embodiment correspond to the rib of the present invention, a second mounting flange  34   g  of the embodiment corresponds to the flange of the present invention, and a first side wall  36  and a second side wall  37  of the embodiment correspond to the side wall of the present invention. 
     Effects of the Invention 
     In accordance with the first aspect of the present invention, since the bumper beam, which is made of a fiber-reinforced resin and extends in the vehicle width direction, and the pair of left and right lower members, which are made of a fiber-reinforced resin and extend downwardly toward the front, forwardly, and inwardly in the vehicle width direction while bending from the front ends of the pair of left and right upper members, are connected to the front ends of the pair of left and right bumper beam extensions, which are made of a fiber-reinforced resin and extend from the front ends of the pair of left and right front side frames toward the front of the vehicle body, and the front faces and the outer faces in the vehicle width direction of the pair of left and right lower members and the front face of the bumper beam are curved into a U-shape pointing toward the front of the vehicle body when viewed from above, not only is it possible to reduce the weight of the vehicle body frame in the front part of the motor vehicle, but it is also possible to transmit to the bumper beam extensions a collision load inputted even into the bumper beam or inputted even into the front parts of the lower members, thus absorbing the collision load and, moreover, since the bumper beam does not protrude from the lower members toward the front of the vehicle body, it is possible to reduce the dimensions of the vehicle body front part. 
     Furthermore, in accordance with the second aspect of the present invention, since the bumper beam is connected to inner walls in the vehicle width direction at the front ends of the pair of left and right bumper beam extensions, the pair of left and right lower members are connected to outer walls in the vehicle width direction at the front ends of the pair of left and right bumper beam extensions, and the front faces and the outer faces in the vehicle width direction of the pair of left and right lower members, the front end faces of the pair of left and right bumper beam extensions, and the front face of the bumper beam are curved into a U-shape pointing toward the front of the vehicle body when viewed from above, not only is it possible to reduce the weight of the vehicle body frame in the front part of the motor vehicle, it is also possible to transmit to the bumper beam extensions a collision load inputted even into the bumper beam or inputted even into the front parts of the lower members, thus absorbing the collision load and, moreover, since the bumper beam does not protrude from the lower members toward the front of the vehicle body, it is possible to reduce the dimensions of the vehicle body front part. 
     Moreover, in accordance with the third aspect of the present invention, since the bumper beam support part for supporting the inner end in the vehicle width direction of the bumper beam is provided on the inner face in the vehicle width direction of the front end part of the bumper beam extension, it is possible to transmit from the bumper beam support part to the bumper beam extension a collision load inputted into the bumper beam when there is a frontal collision to thus efficiently absorb it and, furthermore, since the lower member support part for supporting the front end, bending inwardly in the vehicle width direction, of the lower member is provided on the outer face in the vehicle width direction of the front end part of the bumper beam extension, it is possible to transmit from the lower member support part to the bumper beam extension a collision load inputted into the front part of the lower member when there is a narrow offset frontal collision to thus efficiently absorb it. 
     Moreover, in accordance with the fourth aspect of the present invention, since the front end part of the bumper beam extension includes the weak part, it is possible for the weak part to crumple at the initial stage of a collision, thus reducing the peak load. 
     Furthermore, in accordance with the fifth aspect of the present invention, since the bumper beam, the lower member, and the bumper beam extension include the main body part formed by hardening the continuous fibers with a resin so as to have an open cross section, and the ribs that are formed by hardening the discontinuous fibers with a resin and that provide a connection between the inner faces of the main body part, it is possible to achieve a balance between strength and moldability by reinforcing the main body part having a relatively simple shape with the continuous fibers having high strength and reinforcing the main body part having a relatively complicated shape with the discontinuous fibers having high moldability. As a result, opening of the jaws of the main body part having an open cross section can be prevented by means of the ribs, thereby giving high strength with a lightweight structure. 
     Moreover, in accordance with the sixth aspect of the present invention, since the bumper beam and the lower member have the plurality of vertical ribs in the interior of the main body part having a squared U-shaped cross section, the strength against twisting or bending of the main body part can be enhanced by means of the ribs and collision energy can be efficiently absorbed by the main body part and the ribs being sequentially crumpled from the end side by the collision load. 
     Furthermore, in accordance with the seventh aspect of the present invention, since the bumper beam extension has the plurality of X-shaped ribs in the interior of the main body part having an S-shaped cross section, the strength against twisting or bending of the main body part can be enhanced by means of the ribs, and collision energy can be efficiently absorbed by the main body part and the rib being sequentially crumpled from the end side by the collision load. 
     Moreover, in accordance with the eighth aspect of the present invention, since the width in the vertical direction of the bumper beam is larger for the middle part in the vehicle width direction than for the end parts in the vehicle width direction, even if the height of the bumper beam and the height of a member that is collided with are different, the probability of the collision load being able to be received by means of the bumper beam to thus absorb the impact increases. 
     Furthermore, in accordance with the ninth aspect of the present invention, since the main body part of the bumper beam extension includes the first side wall, the first bottom wall, the second side wall, the second bottom wall, and the third side wall and is formed so as to have an S-shaped cross section, the first side wall, the first bottom wall, and the second side wall are connected via the first rib forming an X-shape when viewed in the vehicle width direction, and the third side wall, the second bottom wall, and the second side wall are connected via the second rib forming an X-shape when viewed in the vehicle width direction, when a collision load is inputted into the bumper beam extension in its longitudinal direction, the first and second ribs can prevent the jaws of the opening part of the bumper beam extension, which has an open cross section, from opening, and the main body part and the first and second ribs of the bumper beam extension are compressed in the longitudinal direction and buckle to thus absorb collision energy effectively. Moreover, since the bumper beam extension has an open cross section, not only is it light in weight, but it is also easy to carry out molding using a mold. 
     Furthermore, in accordance with the tenth aspect of the present invention, since the main body part of the bumper beam extension is formed from a continuous fiber-reinforced resin in which continuous fibers are hardened with a resin, the strength of the main body part can be enhanced by means of the continuous fibers and, moreover, since the first and second ribs are formed from a discontinuous fiber-reinforced resin in which discontinuous fibers are hardened with a resin, the ribs having a complicated shape can be molded using a fiber-reinforced resin member, thereby enabling a balance between strength and moldability of the bumper beam extension to be achieved. 
     Furthermore, in accordance with the eleventh aspect of the present invention, since the pluralities of first and second ribs are provided along the vehicle body fore-and-aft direction, it is possible to absorb collision energy with a stable load over a long period from the initial time of collision to the final time of collision while holding down the peak load to a low level. 
     Moreover, in accordance with the twelfth aspect of the present invention, since the position in the vehicle body fore-and-aft direction of the X-shaped intersection point of the first rib is made to coincide with the position in the vehicle body fore-and-aft direction of the X-shaped intersection point of the second rib, it is possible to crumple the bumper beam extension stepwise from the extremity side while more reliably preventing open of the jaws of the main body part of the bumper beam extension by means of the first and second ribs. 
     Furthermore, in accordance with the thirteenth aspect of the present invention, since the front ends of the first and second ribs are positioned to the rear of the front end of the bumper beam extension by a predetermined distance, it is possible to easily crumple the front end part of the bumper beam extension, in which the first and second ribs are not formed, at the initial stage of a frontal collision, thus reducing the peak load at the initial stage of collision. 
     Moreover, in accordance with the fourteenth aspect of the present invention, since the second side wall of the main body part of the bumper beam extension has a draft angle in the vehicle width direction, the bumper beam extension can easily be removed from the mold. 
     Furthermore, in accordance with the fifteenth aspect of the present invention, since the lower member includes the first portion extending downwardly toward the front from the front end of the upper member, the second portion bending via the first bent portion at the front end of the first portion and extending forwardly in the horizontal direction, and the third portion bending inwardly in the vehicle width direction via the second bent portion at the front end of the second portion and connected to the front end of the bumper beam extension, when there is a narrow offset frontal collision, if a collision load in the fore-and-aft direction is inputted into the front end of the lower member, there is a possibility that the lower member would fold back via the first and second bent portions and the collision load would not be able to be absorbed effectively. However, since the lower member includes the main body part having a squared U-shaped draft section opening outwardly in the vehicle width direction while having the bottom wall and the pair of side walls, and the plurality of ribs providing a connection between the bottom wall and the pair of side walls, the bottom wall is formed from a continuous fiber-reinforced resin in which the continuous fibers are hardened with a resin, and the pair of side wall parts and the ribs are formed from a discontinuous fiber-reinforced resin in which the discontinuous fibers are hardened with a resin, even if the collision load acts so as to fold back the first bent portion, which is bent in the vertical direction, the continuous fiber-reinforced resin of the bottom wall provides resistance thereto, and the side wall parts also provide resistance thereto, thus preventing the first bent portion from breaking and, moreover, even if the collision load acts so as to fold back the second bent portion, which is bent in the left and right direction, the side wall parts and the rib provide resistance thereto, thus preventing the second bent portion from breaking. This enables the lower member to be sequentially crumpled from the front side toward the rear side by means of the load of a frontal collision, thus absorbing the collision load effectively. Moreover, since the bottom wall of the lower member curves only in the second bent portion, the lower member can be press formed using a mold. 
     Moreover, in accordance with the sixteenth aspect of the present invention, since the rib of the lower member is formed in a lattice shape so as to have the horizontal rib extending along the longitudinal direction of the lower member and the plurality of vertical ribs intersecting the horizontal rib, it is possible to reinforce effectively the main body part of the lower member while lightening the weight by reducing the thickness of the rib, thereby enabling the main body part and the rib to be crumpled by a collision load and thus absorb the collision energy. 
     Furthermore, in accordance with the seventeenth aspect of the present invention, since one of the plurality of vertical ribs is disposed in the first bent portion for reinforcement, when a large bending moment is applied to the first bent portion due to the load of an offset frontal collision, it is possible to prevent the lower member from breaking via the first bent portion, thus ensuring the impact absorption performance. 
     Moreover, in accordance with the eighteenth aspect of the present invention, since the horizontal rib is connected to the bottom wall and extends rearwardly from the front end of the lower member, due to the high strength bottom wall, which is reinforced with the continuous fibers, being further reinforced with the horizontal rib, when the load of an offset frontal collision is inputted into the front end of the lower member, it is possible to prevent the lower member from breaking via the first bent portion or the second bent portion, thus ensuring the impact absorption performance. 
     Furthermore, in accordance with the nineteenth aspect of the present invention, since the flange is provided at the front end of the lower member, the front end of the lower member can easily be connected to the front end of the bumper beam extension. Moreover, since the flange is formed from a discontinuous fiber-reinforced resin in which the discontinuous fibers are hardened with a resin, the main body part and the flange of the lower member can be molded all at once, thus enabling the number of processing steps to be cut. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of the framework of a motor vehicle containing a fiber-reinforced resin as a main body. (first embodiment) 
         FIG. 2  is an enlarged view of part  2  in  FIG. 1 . (first embodiment) 
         FIG. 3  is a view in the direction of arrow  3  in  FIG. 2 . (first embodiment) 
         FIG. 4  shows perspective views of a bumper beam extension. (first embodiment) 
         FIG. 5  shows perspective views of a lower member. (first embodiment) 
         FIG. 6  is a perspective view of a bumper beam. (first embodiment) 
         FIG. 7  shows sectional views along lines  7 (A)- 7 (A),  7 (B)- 7 (B), and  7 (C)- 7 (C) in  FIG. 2 . (first embodiment) 
         FIG. 8  shows enlarged views from the direction of arrow  8 (A) and the direction of arrow  8 (B) in  FIG. 7 . (first embodiment) 
         FIG. 9  shows diagrams for explaining the structure and operation of a mold. (first embodiment) 
         FIG. 10  is a diagram for explaining the operation when the motor vehicle is involved in a frontal collision. (first embodiment) 
         FIG. 11  shows diagrams for explaining the operation of absorbing an impact by means of the bumper beam extension. (first embodiment) 
     
    
    
     EXPLANATION OF REFERENCE NUMERALS AND SYMBOLS 
     
         
           11  Cabin 
           16  Front wall part 
           16   a  Wheel house 
           22  Upper member 
           23  Front side frame base part (front side frame) 
           24  Front side frame extremity part (front side frame) 
           25  Bumper beam extension 
           27  Lower member 
           29  Bumper beam 
           31  Main body part 
           31   a  First side wall 
           31   b  Second side wall 
           31   c  Third side wall 
           31   d  First bottom wall (bumper beam support portion) 
           31   e  Second bottom wall 
           31   f  First reinforcing flange (lower member support portion) 
           31   g  Second reinforcing flange (bumper beam support portion) 
           31   j  First linking portion (bumper beam support portion) 
           31   n  Fourth linking portion (lower member support portion) 
           31   o  Fifth linking portion (lower member support portion) 
           31   p  Weak portion 
           32  First rib (rib) 
           33  Second rib (rib) 
           34  Main body part 
           34   a  First portion 
           34   b  Second portion 
           34   c  Third portion 
           34   d  First bent portion 
           34   e  Second bent portion 
           34   g  Second mounting flange (flange) 
           35  Bottom wall 
           36  First side wall (side wall) 
           37  Second side wall (side wall) 
           38  Horizontal rib (rib) 
           39  Vertical rib (rib) 
           40  Main body part 
           41  Horizontal rib (rib) 
           42  Vertical rib (rib) 
           44 A Continuous fiber 
           44 B Continuous fiber 
           45  Discontinuous fiber 
           46  Mold 
       
    
     MODE FOR CARRYING OUT THE INVENTION 
     A mode for carrying out the present invention is explained below by reference to  FIG. 1  to  FIG. 11 . 
     First Embodiment 
     As shown in  FIG. 1  to  FIG. 3 , a cabin  11  made of carbon fiber-reinforced resin (CFRP) is formed into a bathtub shape while including a front floor panel  12 , a rear floor panel  14  connected to the rear end of the front floor panel  12  via a kick-up part  13 , left and right side sill parts  15  and  15  extending in the fore-and-aft direction along opposite edges in the vehicle width direction of the front floor panel  12  and the rear floor panel  14 , a front wall part  16  rising from front ends of the front floor panel  12  and the left and right side sill parts  15  and  15 , and a rear wall part  17  rising from rear ends of the rear floor panel  14  and the left and right side sill parts  15  and  15 . Fixed to upper faces of the left and right side sill parts  15  and  15  are an inverted U-shaped roll bar  18  and left and right stays  19  and  19  reinforcing the roll bar  18 . 
     Metal linking modules  20  and  20  are secured to opposite end parts in the vehicle width direction on a front face of the front wall part  16  of the cabin  11  by means of bolts, which are not illustrated. In each linking module  20 , a damper housing  21 , an upper member  22 , and a front side frame base part  23  are formed as a unit, and the rear end of a metal front side frame extremity part  24 , which is a separate member, is linked in series to the front end of the front side frame base part  23 . The upper member  22  is a member disposed above a wheel house  16   a  (see  FIG. 1 ) formed in the front wall part  16  of the cabin  11 . 
     Rear ends of left and right bumper beam extensions  25  and  25  made of a CFRP are secured to front ends of the left and right front side frame extremity parts  24  and  24  by means of bolts  26 , and rear ends of left and right lower members  27  and  27  made of a CFRP by means of bolts  28  are secured to front ends of the upper members  22  and  22  of the left and right linking modules  20  and  20 . Opposite end parts in the vehicle width direction of a bumper beam  29  made of a CFRP are connected to inner faces in the vehicle width direction of front ends of the left and right bumper beam extensions  25  and  25 , and inner faces in the vehicle width direction of front ends of the left and right lower members  27  and  27  are connected to outer faces in the vehicle width direction of the front ends of the left and right bumper beam extensions  25  and  25 . A front bulkhead  30  is connected to inner faces in the vehicle width direction of the left and right bumper beam extensions  25  and  25 , the front bulkhead  30  being formed into a rectangular frame shape by joining an upper member  30   a , a lower member  30   b , and left and right side members  30   c  and  30   c  made of a CFRP. 
     The structures of the bumper beam extensions  25  and  25  are now explained by reference to  FIG. 2  to  FIG. 4 . Since the left and right bumper beam extensions  25  and  25  are mirror symmetric members, the structure of the left bumper beam extension  25  is explained as being representative thereof. 
     The bumper beam extension  25 , which is made of a CFRP, is a member comprising a main body part  31  extending linearly in the fore-and-aft direction, the main body part  31  being formed so as to have an S-shaped cross section while comprising an upper first side wall  31   a , a middle second side wall  31   b , and a lower third side wall  31   c , which are disposed substantially parallel to each other, a first bottom wall  31   d  providing a connection between inner ends in the vehicle width direction of the first side wall  31   a  and the second side wall  31   b , and a second bottom wall  31   e  providing a connection between outer ends in the vehicle width direction of the third side wall  31   c  and the second side wall  31   b . A first reinforcing flange  31   f  protrudes upwardly from the outer end in the vehicle width direction of the first side wall  31   a , and a second reinforcing flange  31   g  protrudes downwardly from the inner end in the vehicle width direction of the third side wall  31   c . A first mounting flange  31   h , which is fixed to the front end of the front side frame extremity part  24  by means of the bolts  26  and  26 , protrudes upwardly from the rear end of the first side wall  31   a , and a second mounting flange  31   i , which is fixed to the front end of the front side frame extremity part  24  by means of the bolts  26  and  26 , protrudes downwardly from the rear end of the third side wall  31   c.    
     Furthermore, a first linking portion  31   j  and a second linking portion  31   k , which are triangular, are projectingly provided on an inner face in the vehicle width direction of the first bottom wall  31   d , a triangular third linking portion  31   m  is projectingly provided on an inner face in the vehicle width direction of the second reinforcing flange  31   g , a triangular fourth linking portion  31   n  is projectingly provided on an outer face in the vehicle width direction of the second bottom wall  31   e , and a plate-shaped fifth linking portion  31   o  is provided so as to project outwardly in the vehicle width direction from the lower end of the second bottom wall  31   e . The first side wall  31   a  and the third side wall  31   c  extend horizontally when viewed from the front, and the second side wall  31   b  has a draft angle that is inclined relative to the horizontal direction in order to facilitate removal from a mold (see  FIG. 4 ). 
     Three first ribs  32  formed into an X-shape are formed in succession in the fore-and-aft direction in a space that is surrounded by the first side wall  31   a , the first bottom wall  31   d , and the second side wall  31   b  and that opens outwardly in the vehicle width direction. Similarly, three second ribs  33  formed into an X-shape are formed in succession in the fore-and-aft direction in a space that is surrounded by the third side wall  31   c , the second bottom wall  31   e , and the second side wall  31   b  and that opens inwardly in the vehicle width direction. The positions of three intersection points of the X-shaped first ribs  32  and the positions of three intersection points of the X-shaped second ribs  33  are aligned in the vehicle body fore-and-aft direction. In other words, the three intersection points of the second ribs  33  on the lower side are positioned beneath the three intersection points of the first ribs  32  on the upper side (see  FIG. 4 ). Furthermore, front ends of the first ribs  32  and the second ribs  33  are positioned to the rear of the front end of the main body part  31  with a weak portion  31   p  having a length a interposed between the front end of the main body part  31  and the front ends of the first and second ribs  32  and  33  (see  FIG. 4 ). 
     The structures of the lower members  27  and  27  are now explained by reference to  FIG. 2 ,  FIG. 3 , and  FIG. 5 . Since the left and right lower members  27  and  27  are mirror symmetric members, the structure of the left lower member  27  is explained as being representative thereof. 
     A main body part  34  of the lower member  27 , which is made of a CFRP, includes a first portion  34   a  extending downwardly toward the front from the front end of the upper member  22 , a second portion  34   b  bending upwardly from the front end of the first portion  34   a  via a first bent portion  34   d  and extending substantially horizontally and forwardly, and a third portion  34   c  bending inwardly in the vehicle width direction from the front end of the second portion  34   b  via a second bent portion  34   e  and extending substantially horizontally and inwardly in the vehicle width direction. The main body part  34  is formed so as to have a squared U-shaped cross section while including a bottom wall  35  forming an inner face in the vehicle width direction and a rear face, a first side wall  36  extending from the upper edge of the bottom wall  35  outwardly in the vehicle width direction and forwardly, and a second side wall  37  extending from the lower edge of the bottom wall  35  outwardly in the vehicle width direction and forwardly. 
     First mounting flanges  34   f  joined to the front end of the upper member  22  by means of the bolts  28  are provided at the rear end of the first portion  34   a , and a second mounting flange  34   g  connected to the bumper beam extension  25  is provided at the inner end in the vehicle width direction of the third portion  34   c.    
     Formed in a lattice shape in the interior of the main body part  34  are one horizontal rib  38  that protrudes from the bottom wall  35  in parallel with the first and second side walls  36  and  37  so as to extend outwardly in the vehicle width direction and forwardly and a plurality of vertical ribs  39  intersecting the horizontal rib  38  and connected to the bottom wall  35  and the first and second side walls  36  and  37 . Among the plurality of vertical ribs  39 , one  39  ( 1 ) is disposed at the position of the first bent portion  34   d  of the lower member  27  (see  FIG. 5  (A)). 
     The structure of the bumper beam  29  is now explained by reference to  FIG. 2 ,  FIG. 3 , and  FIG. 6 . 
     A main body part  40  of the bumper beam  29  is a member having a squared U-shaped cross section with an open front face and including a bottom wall  40   a  and upper and lower side walls  40   b  and  40   c , and flanges  40   d  and  40   e  protrude in the vertical direction from the front edges of the upper and lower side walls  40   b  and  40   c . Formed in a lattice shape on an inner face of the main body part  40  are one horizontal rib  41  extending in the vehicle width direction and a plurality of vertical ribs  42  extending in the vertical direction so as to be perpendicular to the horizontal rib  41 , the rear edge of the horizontal rib  41  being connected to the bottom wall  40   a , and the rear edges and the upper and lower edges of the vertical ribs  42  being connected to the bottom wall  40   a  and the side walls  40   b  and  40   c . A pair of left and right plate-shaped end brackets  43  and  43  made of a fiber-reinforced resin are provided at opposite ends in the vehicle width direction of the main body part  40 . 
     The distance between the upper and lower side walls  40   b  and  40   c  of the bumper beam  29  is H1 for a middle part in the vehicle width direction of the bumper beam  29  and H2 for opposite end parts in the vehicle width direction, H2 being smaller than H1. That is, the width in the vertical direction of the bumper beam  29  is larger for an intermediate part in the vehicle width direction than in the opposite end parts in the vehicle width direction (see  FIG. 6 ). Therefore, even when the height of the bumper beam  29  is different from the height of a member that is collided with, the collision load can be received by the bumper beam  29 , thus increasing the probability of the impact being able to be absorbed. 
     As shown in  FIG. 7  (A), the first side wall  31   a , the second side wall  31   b , the third side wall  31   c , the first bottom wall  31   d , and the second bottom wall  31   e  of the main body part  31  of the bumper beam extension  25  are formed from a material formed by hardening, with a resin, a woven cloth formed by plain weaving continuous fibers  44 A,  44 B made of carbon fiber (see  FIG. 8  (A)), and other parts including the first ribs  32  and the second ribs  33  are formed from a material formed by hardening, with a resin, randomly tangled discontinuous fibers  45  made of carbon fiber (see  FIG. 8  (B)). Furthermore, inner faces of the first side wall  31   a , the second side wall  31   b , and the first bottom wall  31   d  and inner faces of the third side wall  31   c , the second side wall  31   b , and the second bottom wall  31   e  are covered with a thin film formed by hardening, with a resin, discontinuous fibers  45  made of carbon fiber. 
     As shown in  FIG. 7  (B), the bottom wall  35  of the main body part  34  of the lower member  27  is formed from a material formed by hardening, with a resin, a woven cloth formed by plain weaving continuous fibers  44 A,  44 B made of carbon fiber, but other parts such as the first side wall  36 , the second side wall  37 , the horizontal rib  38 , and the vertical ribs  39  are formed from a material formed by hardening, with a resin, randomly tangled discontinuous fibers  45  made of carbon fiber. Furthermore, an inner face of the bottom wall  35  is covered with a thin film formed by hardening, with a resin, discontinuous fibers  45  made of carbon fiber. 
     As shown in  FIG. 7  (C), the bottom wall  40   a , the upper and lower side walls  40   b  and  40   c , and the upper and lower flanges  40   d  and  40   e  of the main body part  40  of the bumper beam  29  are formed from a material formed by hardening, with a resin, a woven cloth formed by plain weaving continuous fibers  44 A,  44 B made of carbon fiber, but other parts such as the horizontal rib  41 , the vertical ribs  42 , and the end brackets  43  and  43  are formed from a material formed by hardening, with a resin, randomly tangled discontinuous fibers  45  made of carbon fiber. Furthermore, an inner face of the main body part  40  is covered with a thin film formed by hardening, with a resin, discontinuous fibers  45  made of carbon fiber. 
     The structure of a mold  46  for press forming the bumper beam  29  is now explained by reference to  FIG. 9 . 
     As shown in  FIG. 9  (A), a mold  46  for press forming the bumper beam  29  includes a female die  47  having a recessed cavity  47   a  for molding an outer surface of the main body part  40  and a male die  48  having a projecting core  48   a  for molding an inner surface of the main body part  40 , and a horizontal groove  48   b  for molding the horizontal rib  41  and vertical grooves  48   c  for molding the vertical ribs  42  are formed in the core  48   a . In a state in which the mold  46  is opened, a first prepreg  49  of continuous fibers and a second prepreg  50  of discontinuous fibers are disposed in an upper part of the cavity  47   a  of the female die  47  in a preheated state. In the present embodiment, the length of the discontinuous fibers of the second prepreg  50  is set at 0.9 mm to 4.4 mm. 
     The prepreg is formed by impregnating a woven cloth or UD (sheet in which continuous fibers are aligned in one direction) formed from a continuous fiber such as carbon fiber, glass fiber, or aramid fiber or a mat of discontinuous fibers as a reinforcing material with a semi-cured thermosetting resin (epoxy resin, polyester resin, etc.) or a thermoplastic resin (nylon 6, polypropylene, etc.), and it has the flexibility to conform to the shape of the mold. In the case of a thermosetting resin, a plurality of sheets of prepreg are layered, inserted into the mold, and heated to for example on the order of 130° C. while applying pressure, and the thermosetting resin cures to thus give a fiber-reinforced resin product. In the case of a thermoplastic resin, a plurality of sheets of pre-heated prepreg are layered, inserted into the mold, molded under pressure, and then cooled, thus giving a fiber-reinforced resin product. 
     Subsequently, as shown in  FIG. 9  (B), the male die  48  is lowered relative to the female die  47 , and the first prepreg  49  is pressed by means of the cavity  47   a  of the female die  47  and the core  48   a  of the male die  48 , thus molding the main body part  40  of the bumper beam  29  having a squared U-shaped cross section. In this process, since the second prepreg  50  containing discontinuous fibers as a reinforcing material is easily deformable, the second prepreg  50  sandwiched between the first prepreg  49  and the core  48   a  of the male die  48  flows into the horizontal groove  48   b  and vertical grooves  48   c  of the core  48   a , thus molding the horizontal rib  41 , the vertical ribs  42 , and the end brackets  43  and  43  of the bumper beam  29  at the same time. Furthermore, part of the second prepreg  50  is layered as a thin film along the inner surface of the main body part  40 . 
     Subsequently, as shown in  FIG. 9  (C), the bumper beam  29  is completed by cutting off an excess part of the flanges  40   d  and  40   e  of the main body part  40  of the bumper beam  29  that has been taken out of the mold  46 . 
     As described above, since the fiber-reinforced resin for the main body part  40  of the bumper beam  29  having a simple squared U-shaped cross section is reinforced with plain-woven continuous fibers  44 A,  44 B having a high strength, and the fiber-reinforced resin for the horizontal rib  41 , the vertical ribs  42 , and the end brackets  43  and  43 , which have complicated shapes and are difficult to reinforce with plain-woven continuous fibers, is reinforced with the discontinuous fibers  45  having a high degree of freedom of molding, it is possible to achieve a balance between strength and moldability of the bumper beam  29 . Moreover, since the first prepreg  49  containing continuous fibers and the second prepreg  50  containing discontinuous fibers are placed within one and the same mold  46  to thus mold the bumper beam  29  in one step, compared with a case in which they are molded separately and integrated by adhesion or melt bonding, it is possible to cut the production cost. 
     The mold  46  for press forming the bumper beam  29  is explained above, but the bumper beam extensions  25  and  25  and the lower members  27  and  27  may also be press formed using a mold having a similar structure. In this way, since the bumper beam  16 , the bumper beam extensions  25  and  25 , and the lower members  27  and  27  all have an open cross section, not only are they light in weight, but it is also easy to carry out molding using the mold. 
     The structure via which the bumper beam  29  and the lower member  27  are joined to the bumper beam extension  25  is now explained. 
     As shown in  FIG. 2  to  FIG. 5 , the outer end in the vehicle width direction of the bumper beam  29  extending in the vehicle width direction is joined to an inner face in the vehicle width direction at the front end of the bumper beam extension  25  extending in the fore-and-aft direction. In this arrangement, the front part of the first bottom wall  31   d  of the main body part  31  and the front part of the second reinforcing flange  31   g  of the bumper beam extension  25  are melt bonded to the end bracket  43  of the bumper beam  29 , and the first linking portion  31   j  provided on the first bottom wall  31   d  of the bumper beam extension  25  is melt bonded to the bottom wall  40   a  of the main body part  40  of the bumper beam  29 . The first bottom wall  31   d , the second reinforcing flange  31   g , and the first linking portion  31   j  of the bumper beam extension  25  form a bumper beam support part. 
     Furthermore, the second mounting flange  34   g  at the extremity of the lower member  27  is melt bonded to the first reinforcing flange  31   f  of the bumper beam extension  25 , a lower face of an extremity part of the second side wall  37  of the lower member  27  is melt bonded to an upper face of the fifth linking portion  31   o  protruding from the second bottom wall  31   e  of the bumper beam extension  25 , and an extremity part of the bottom wall  35  of the lower member  27  is melt bonded to the fourth linking portion  31   n  provided on the second bottom wall  31   e  of the bumper beam extension  25 . The first reinforcing flange  31   f , the fifth linking portion  31   o , and the fourth linking portion  31   n  of the bumper beam extension  25  form a lower member support part. 
     The side member  30   c  of the front bulkhead  30  is melt bonded to the second linking portion  31   k  and the third linking portion  31   m  of the main body part  31  of the lower member  27 . 
     The operation of the embodiment of the present invention having the above arrangement is now explained. 
     As shown in  FIG. 10 , since the bumper beam  29 , which is made of a CFRP and extends in the vehicle width direction, and the pair of left and right lower members  27  and  27 , which are made of a CFRP and extend from the front ends of the pair of left and right upper members  22  and  22  downwardly toward the front, forwardly, and inwardly in the vehicle width direction while bending, are connected to the inner faces in the vehicle width direction and the outer faces in the vehicle width direction of the front ends of the pair of left and right bumper beam extensions  25  and  25 , which are made of a CFRP and extend from the pair of left and right front side frame extremity parts  24  and  24  toward the front of the vehicle body, in this state the outer faces in the vehicle width direction and the front faces of the pair of left and right lower members  27  and  27 , the front end faces of the pair of left and right bumper beam extensions  25  and  25 , and the front face of the bumper beam  29  form a shape that is curved into a U-shape pointing toward the front of the vehicle body when viewed from above. 
     In this way, due to the use of a CFRP as much as possible, not only is it possible to reduce the weight of the vehicle body frame in the front part of the motor vehicle, but it is also possible to transmit to the bumper beam extensions  25  and  25  the load of a frontal collision, inputted even into the bumper beam  29  or inputted even into the front parts of the lower members  27  and  27 , thus absorbing the collision load and, moreover, since the bumper beam  29  does not protrude from the lower members  27  and  27  toward the front of the vehicle body, it is possible to reduce the dimensions of the vehicle body front part. 
     That is, in  FIG. 10 , if a collision load F1 when there is a frontal collision is inputted into the bumper beam  29 , the collision load F1 is transmitted from the bumper beam  29  to the left and right bumper beam extensions  25  and  25  and efficiently absorbed by crumpling of the bumper beam extensions  25  and  25 , which are impact absorbing members. Furthermore, if a collision load F2 when there is a narrow offset frontal collision is inputted into the front part of the left or right lower member  27 , the collision load F2 is transmitted from the lower member  27  to the left or right bumper beam extension  25  and efficiently absorbed by crumpling of the bumper beam extension  25 , which is an impact absorbing member. Moreover, if a collision load F3 when there is an offset frontal collision is directly inputted into the front end of the left or right lower member  27 , the collision load F3 is efficiently absorbed by crumpling of the bumper beam extension  25 , which is an impact absorbing member. 
     As shown in  FIG. 11 , when the bumper beam extension  25  crumples due to a collision load from the front, since the first and second ribs  32 ,  33  are not provided on the weak portion  31   p , which spans the length a of the extremity of the main body part  31 , the weak portion  31   p  readily buckles, thus reducing the initial peak load of the collision. 
     Furthermore, since the bumper beam  29 , the lower member  27 , and the bumper beam extension  25  include the main body parts  40 ,  34 , and  31  formed by hardening the continuous fibers  44 A,  44 B with a resin so as to have an open cross section, and the ribs  41 ,  42 ,  38 ,  39 ,  32 , and  33  that are formed by hardening the discontinuous fibers  45  with a resin and that provide a connection between the inner faces of the main body parts  40 ,  34 , and  31 , it is possible to achieve a balance between strength and moldability by reinforcing the main body parts  40 ,  34 , and  31  having a relatively simple shape with the continuous fibers  44 A,  44 B having high strength and reinforcing the ribs  41 ,  42 ,  38 ,  39 ,  32 , and  33  having a relatively complicated shape with the discontinuous fibers  45  having high moldability. As a result, opening of the jaws of the main body parts  40 ,  34 , and  31  having an open cross section can be prevented by means of the ribs  41 ,  42 ,  38 ,  39 ,  32 , and  33 , thereby giving high strength with a lightweight structure. 
     In particular, since the bumper beam  29  and the lower member  27  have the plurality of vertical ribs  42 ,  39  in the interior of the main body parts  40  and  34  having a squared U-shaped cross section, the strength against twisting or bending of the main body parts  40  and  34  can be enhanced by means of the vertical ribs  42 ,  39 , and collision energy can be efficiently absorbed by the main body parts  40  and  34  and the vertical ribs  42 ,  39  being sequentially crumpled from the end side by the collision load. 
     Furthermore, with regard to the bumper beam extension  25 , since the pluralities of first and second ribs  32 ,  33  are provided along the vehicle body fore-and-aft direction in the interior of the main body part  31  having an S-shaped cross section, it is possible to absorb collision energy with a stable load over a long period from the initial time of collision to the final time of collision while holding down the peak load to a low level and, moreover, since the position in the vehicle body fore-and-aft direction of the X-shaped intersection point of the first ribs  32  is made to coincide with the position in the vehicle body fore-and-aft direction of the X-shaped intersection point of the second ribs  33 , it is possible to crumple the impact absorbing member stepwise from the extremity side while more reliably preventing opening of the jaws of the main body part  31  of the impact absorbing member by means of the first and second ribs  32 ,  33 . 
     Furthermore, since the second side wall  31   b  of the main body part  31  of the bumper beam extension  25  has a draft angle in the vehicle width direction, the bumper beam extension  25  can easily be removed from the mold. 
     Since each lower member  27  includes the first portion  34   a  extending downwardly toward the front from the front end of the upper member  22 , the second portion  34   b  bending via the first bent portion  34   d  at the front end of the first portion  34   a  and extending forwardly in the horizontal direction, and the third portion  34   c  bending inwardly in the vehicle width direction via the second bent portion  34   e  at the front end of the second portion  34   b  and connected to the front end of the bumper beam extension  25 , when there is a narrow offset frontal collision, if a collision load in the fore-and-aft direction is inputted into the front end of the lower member  27 , there is a possibility that the lower member  27  would fold back via the first and second bent portions  34   d  and  34   e  and the collision load would not be able to be absorbed effectively. 
     However, since each lower member  27  includes the main body part  34  having a squared U-shaped cross section opening outwardly in the vehicle width direction while having the bottom wall  35  and the first and second side walls  36  and  37 , and the horizontal rib  38  and the vertical ribs  39  providing a connection between the bottom wall  35  and the first and second side walls  36  and  37 , the bottom wall  35  is formed from a continuous fiber-reinforced resin in which the continuous fibers  44 A,  44 B are hardened with a resin, and the first and second side walls  36  and  37 , the horizontal rib  38 , and the vertical ribs  39  are formed from a discontinuous fiber-reinforced resin in which the discontinuous fibers  45  are hardened with a resin, even if the collision load acts so as to fold back the first bent portion  34   d , which is bent in the vertical direction, the continuous fiber-reinforced resin of the bottom wall  35  provides resistance thereto, and the first and second side walls  36  and  37 , the horizontal rib  38 , and the vertical ribs  39  also provide resistance thereto, thus preventing the first bent portion  34   d  from breaking. Furthermore, even if the collision load acts so as to fold back the second bent portion  34   e , which is bent in the left and right direction, the first and second side walls  36  and  37 , the horizontal rib  38 , and the vertical ribs  39  provide resistance thereto, thus preventing the second bent portion  34   e  from breaking. 
     This enables the lower member  27  to be sequentially crumpled from the front side toward the rear side by means of the load of a frontal collision, thus absorbing the collision load effectively. Moreover, since the bottom wall  35  of the lower member  27  curves only in the second bent portion  34   e , the lower member  27  can be press formed using a mold. 
     Since the ribs of each lower member  27  are formed in a lattice shape with the horizontal rib  38  extending along the longitudinal direction of the lower member  27  and the plurality of vertical ribs  39  intersecting the horizontal rib  38 , it is possible to reinforce effectively the main body part  34  of the lower member  27  while lightening the weight by reducing the thickness of the horizontal rib  38  and the vertical ribs  39 , thereby enabling the main body part  34 , the horizontal rib  38 , and the vertical ribs  39  to be crumpled by a collision load to thus absorb the collision energy. 
     Furthermore, since one of the plurality of vertical ribs  39  is disposed in the first bent portion  34   d  for reinforcement, when a large bending moment is applied to the first bent portion  34   d  due to the load of an offset frontal collision, it is possible to prevent the lower member  27  from breaking via the first bent portion  34   d , thus ensuring the impact absorption performance. Moreover, since the horizontal rib  38  is connected to the bottom wall  35  and extends rearwardly from the front end of the lower member  27 , due to the high strength bottom wall  35 , which is reinforced with the continuous fibers  44 A,  44 B, being further reinforced with the horizontal rib  38 , when the load of an offset frontal collision is inputted into the front end of the lower member  27 , it is possible to prevent the lower member  27  from breaking via the first bent portion  34   d  or the second bent portion  34   e , thus ensuring the impact absorption performance. 
     Furthermore, since the second mounting flange  34   g  is provided at the front end of the lower member  27 , the front end of the lower member  27  can easily be connected to the front end of the bumper beam extension  25 . Moreover, since the second mounting flange  34   g  is formed from a discontinuous fiber-reinforced resin in which the discontinuous fibers  45  are hardened with a resin, the main body part  34  and the second mounting flange  34   g  of the lower member  27  can be molded all at once, thus enabling the number of processing steps to be cut. 
     An embodiment of the present invention is explained above, but the present invention may be modified in a variety of ways as long as the modifications do not depart from the spirit and scope thereof. 
     For example, the fiber-reinforced resin of the present invention is not limited to a CFRP, and an FRP reinforced with any fiber may be used. 
     Furthermore, in the embodiment the bumper beam  29  and the lower member  27  are connected to the front end of the bumper beam extension  25 , but it is not always necessary for the lower member  27  to be connected to the bumper beam extension  25 . 
     Moreover, the outer end in the vehicle width direction of the bumper beam  29  and the inner end in the vehicle width direction of the lower member  27  may be directly connected, and a rear face of the bumper beam  29  or a rear face of the lower member  27  may be supported by a front end face of the bumper beam extension  25 .