Abstract:
The disclosure relates to a vehicle body structure safeguarding a fuel tank from damage resulting from collisions without greatly increasing the weight of the vehicle. The vehicle body structure includes a front floor under which a fuel cell stack case accommodating a fuel cell stack is disposed, and side sills and floor frames which extend along the sides of the vehicle, and on which a sub-frame for housing a fuel tank is installed. The front face of the sub-frame and the rear face of the fuel cell stack case are flat and oppose each other.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a vehicle body structure for a vehicle, such as a fuel cell vehicle, in which a fuel tank for storing a fuel gas, such as a hydrogen gas, is installed. 
   2. Description of the Related Art 
   Among automobiles, a fuel cell vehicle is known, in which electrical power is generated in a fuel cell by providing hydrogen as a fuel gas and oxygen as an oxidizing gas, and a motor is operated by the electrical power for driving the vehicle. 
   Among such fuel cell vehicles, a type of vehicle is known, in which a fuel tank for storing a hydrogen gas to be supplied to a fuel cell units is installed in the rear portion of the vehicle. 
   An example of a body structure, in which a fuel tank is supported in the rear portion of the vehicle as described above, is disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 09-300987. In this supporting structure, a fuel tank storing a fuel gas (hydrogen) is mounted in a chassis frame having a rectangular frame shape while the upside of the fuel tank is directed upward, and the chassis frame supporting the fuel tank is mounted on a body frame from beneath the body frame. 
   According to such a structure, because the fuel tank can be easily mounted on the body frame along with suspension parts for both sides and other elements, productivity may be increased, and production cost may be reduced. In addition, by installing the fuel tank, suspension parts for both sides, and other elements on the chassis frame, the size and weight of the vehicle may be reduced. 
   However, in the conventional body structure described above, in order to protect the fuel tank by the chassis frame, the strength and rigidity of the chassis frame must be increased by, for example, increasing thickness of material for forming the chassis frame, or by adding reinforcements to the chassis frame, and as a result, problems are encountered in that the vehicle weight is increased, and consequently, fuel efficiency is degraded. 
   Another proposal has been made in Japanese Unexamined Patent Application, First Publication No. Hei 11-348815, in which an upper frame is formed so as to include a curved portion, and lower frames are configured in parallel to each other so as to absorb the energy at a rear collision; however, the performance is not satisfactory. 
   SUMMARY OF THE INVENTION 
   In consideration of the above circumstances, an object of the present invention is to provide a vehicle body structure which greatly improves safety of a fuel tank against collision without greatly increasing vehicle weight. 
   In order to achieve the above object, the present invention provides a vehicle body structure comprising: a front floor under which a fuel cell stack case, accommodating a fuel cell stack, is disposed; and side sills and floor frames which extend along the sides of the vehicle, and on which a sub-frame having a fuel tank is installed, wherein the front face of the sub-frame and the rear face of the fuel cell stack case are formed to be flat and oppose each other. 
   According to the above structure of the present invention, when a load is applied to the sub-frame, the load is distributed to the side sills and floor frames from the sub-frame, and thus the load is received by the entirety of the body. In addition, even when the sub-frame is moved forward, the front face of the sub-frame abuts against the rear face of the fuel cell stack case which is disposed in front of the sub-frame while being disposed under the front floor, and as result, the load is distributed over the entirety of flat surfaces. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view showing an embodiment of the present invention. 
       FIG. 2  is a perspective view showing the embodiment shown in  FIG. 1  in an assembled state. 
       FIG. 3  is a plan view showing the embodiment in the assembled state. 
       FIG. 4  is a side view showing the embodiment in the assembled state. 
       FIG. 5  is a cross-sectional view taken along the line A—A in FIG.  3 . 
       FIG. 6  is a perspective view showing a front bracket in the embodiment shown in FIG.  1 . 
       FIG. 7  is a perspective view showing a rear bracket in the embodiment shown in FIG.  1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An embodiment of the present invention will be explained below with reference to  FIGS. 1  to  5 . 
   As shown in  FIG. 1 , a rear floor  2 , which is formed so as to be bent backward and upward, and so as to include steps, is connected to the rear edge of a front floor  1 . A cross member  4 , which is a part of a main skeletal structure of the vehicle body, is connected to the underside of a stepped portion  3  of the rear floor  2 . Under the front floor  1 , there are provided floor frames  5  and  6  which are parts of the main skeletal structure, and which extend along the sides of the vehicle body. 
   Inside sills  7  and  8  are connected to the side edges of the front floor, respectively, and inside sill extensions  9  and  10  are connected to the rear ends of the inside sills  7  and  8 , respectively. The inside sills  7  and  8  are connected to outside sills (not shown), respectively, to form a part of the main skeletal structure of the vehicle body. 
   As shown in  FIG. 6 , front brackets  11  and  12  are connected to the inside surface of the inside sill extensions  9  and  10 , respectively ( FIG. 6  shows only left elements). 
   The front brackets  11  and  12  respectively comprise inner walls  11   a  and  12   a , front walls  11   b  and  12   b , rear walls  11   c  and  12   c , bottom walls  11   d  and  12   d , flanges  11   e  and  12   e  which are disposed on the outer edges of the front brackets  11  and  12  to be connected to the inside sill extensions  9  and  10 , flanges  11   f  and  12   f  which are disposed on the upper edges of the rear walls  11   c  and  12   c  to be connected to the bottom walls  13   a  and  14   a  of rear frames  13  and  14 , which will be explained below, and flanges  11   g  and  12   g  which are disposed on the upper edges of the front walls  11   b  and  12   b  to be connected to the underside of the cross member  4 . In addition, the front walls  11   b  and  12   b  extend forwardly along with the inner walls  11   a  and  12   a  to respectively form connection portions  11   h  and  12   h  which are to be connected to the floor frames  5  and  6 . The inner walls  11   a  and  12   a  are formed to be connected to the side walls of the rear frames  13  and  14 , respectively. In the bottom walls lid and  12   d , there are provided vertically extending collar nuts  15  and  16 , respectively. 
   The rear frames  13  and  14  are connected to the underside of the rear floor  2  to form a part of the main skeletal structure of the vehicle body. 
   The bottom walls  13   a  and  14   a  of the rear frames  13  and  14  are connected to the rear walls  11   c  and  12   c  of the front brackets  11  and  12 , which are configured as explained above, and the side walls of the rear frames  13  and  14  are connected to the inner walls  11   a  and  12   a , respectively. The inner walls of the inside sill extensions  9  and  10  are respectively connected to the flanges  11   e  and  12   e , which are disposed on the outer edges of the front brackets  11  and  12 . The rear ends of the floor frames  5  and  6  are connected to the connection portions  11   h  and  12   h . As a result, the front ends of the rear frames  13  and  14  are connected to the inside sills  7  and  8 , as well as to the floor frames  5  and  6  via the front brackets  11  and  12 , respectively. 
   Rear brackets  17  and  18 , which have substantially U-shaped cross sections as shown in  FIG. 7  (only left rear bracket  17  is shown), are connected to the undersides of the rear ends of the rear frames  13  and  14 , respectively. Each of the rear brackets  17  and  18  comprises two side walls  17   a  (or  18   a ), which act to absorb collisional energy, and two flanges  17   b  (or  18   b ) connected to the rear ends of the side walls  17   a  (or  18   a ). The inner surfaces of the side walls  17   a  (or  18   b ) are connected to the outer surfaces of the side walls of the rear frame  13  (or  14 ). In a bottom wall  17   c  (or  18   c ) of the rear bracket  17  (or  18 ), specifically in the front portion thereof, there is provided a vertically extending collar nut  19  (or  20 ). 
   As shown in  FIGS. 1 and 2 , two cross members  4 A and  4 B, which are disposed in the longitudinal direction with respect to each other while extending laterally, are connected to the rear frames  13  and  14  while being disposed there between. A bumper beam  21  is disposed at the rear ends of the rear frames  13  and  14 , and more specifically, the bumper beam  21  is connected to the flanges  17   b  and  18   b  of the rear brackets  17  and  18 . 
   The sub-frame  22  is fixed, from underneath the vehicle body, to the collar nuts  15  and  16  of the front brackets  11  and  12 , and to the collar nuts  19  and  20  of the rear brackets  17  and  18  using four bolts  23 . 
   As shown in  FIG. 1 , the sub-frame  22  is formed by lateral frame members  24  and  25 , and by longitudinal members  26  and  27  in a rectangular frame shape. The sub-frame  22  further comprises a cross beam  28  extending laterally. In two spaces partitioned by the cross beam  28 , two hydrogen tanks  29  and  30  as fuel tanks are disposed and fixed by tightening bands  31  and  32 , respectively. In addition, suspension units  33  are mounted on the sub-frame  22 . 
   At the comers of the sub-frame  22 , where the front ends of the lateral frame members  24  and  25  and the two ends of the front frame member  26  meet, there are provided through holes  34  and  35 , respectively, into which the bolts  23  to be engaged with the collar nuts  15  and  16  are inserted. At the comers of the sub-frame  22 , where the rear ends of the lateral frame members  24  and  25  and the two ends of the rear frame member  27  meet, there are provided through holes  36  and  37 , respectively, into which the bolts  23  to be engaged with the collar nuts  19  and  20  are inserted. 
   The sub-frame  22  configured as explained above is fixed to the rear frames  13  and  14  in such a manner that the bolts  23  are inserted into the through holes  34 ,  35 ,  36 , and  37 , and the bolts  23  are further inserted into the collar nuts  15  and  16  of the front brackets  11  and  12 , and into the collar nuts  19  and  20  of the rear brackets  17  and  18 , and then the bolts  23  are tightened. The front frame member  26  of the sub-frame  22  includes a flat surface  26   a.    
   As shown in  FIGS. 3  to  5 , a fuel cell stack case  39  accommodating a fuel cell  38  is disposed under the front floor  1  so as to extend from the floor frame  5  to the floor frame  6 . A hydrogen gas supplied from the hydrogen tanks  29  and  30 , and oxygen contained in air supplied from a compressor (not shown) react in the fuel cell  38  to 
   As shown in  FIG. 5 , the fuel cell stack case  39  comprises a case body  39   a  for receiving the fuel cell  38 , and a cover  39   b  disposed on the case body  39   a . The case body  39   a  is formed so as to have a convex portion in the upper portion thereof, and the cover  39   b  includes a concove portion to accommodate the convex portion of the case body  39   a . The case body  39   a  and the cover  39   b  are fixed to the bottom walls  5   a  and  6   a  of the floor frames  5  and  6  in such a manner that bolt  40  are engaged with nuts  41  from beneath the vehicle body, and the bolts  40  are tightened. The rear face of the fuel cell stack case  39 , i.e., the rear face of the case body  39   a , is formed as a flat surface  39   c  as shown in  FIG. 3. A  treatment device, which must be provided with the fuel cell  38  for treating residual gases and condensed water after reaction, may be preferably disposed in the vicinity of the rear portion of the fuel cell stack case  39 . 
   The flat surface  39   c  of the fuel cell stack case  39  configured as explained above is disposed so as to oppose the front flat surface  26   a  of the sub-frame (i.e., of the front member  26 ). 
   As shown in  FIGS. 3 and 4 , between the floor frame  5  and the inside sill  7 , and between the floor frame  6  and the inside sill  8 , there are provided three brackets  42  in one side, i.e., six brackets  42  in both sides, so as to connect the floor frames  5  and  6  and the inside sills  7  and  8 , respectively. Each of the brackets  42  comprises flanges  42   a  to be connected to the floor frame  5  (or  6 ), to the inside sill  7  (or  8 ), and to the underside of the front floor  1 . 
   According to the above embodiment, when, for example, a load is applied to the bumper beam  21  disposed at the rear ends of the rear frames  13  and  14 , the load is distributed to the inside sills  7  and  8 , and to the floor frames  5  and  6  via the front brackets  11  and  12 . As a result, because a heavy load is not applied to the sub-frame  22 , the hydrogen tanks  29  and  30  can be reliably protected. 
   Moreover, because the front portion of the sub-frame  22  is connected to the front brackets  11  and  12  via the collar nuts  15  and  16 , and the inside sills  7  and  8  disposed the inner side of the vehicle and the floor frames  5  and  6  disposed outer side of the vehicle are connected to the front brackets  11  and  12 , respectively, and when, for example, an impact load is forwardly applied to the rear portion of the sub-frame  22  as shown by the arrow in  FIG. 3 , the impact load is divided into two through the front brackets  11  and  12 , and the divided loads are distributed to the inside sills  7  and  8 , and to the floor frames  5  and  6 . 
   Accordingly, the supportable load of the vehicle body may be increased by the amount distributed to both inside sills  7  and  8 , and the floor frames  5  and  6  if compared with the case in which a load is supported merely by either of the inside sills  7  and  8 , or the floor frames  5  and  6  in a concentrated manner. Moreover, the impact load is applied to the inside sills  7  and  8 , and the floor frames  5  and  6  in compressive directions, which is preferable in terms of strength. 
   As a result, the hydrogen tanks  29  and  30  installed on the sub-frame  22  can be reliably protected. 
   Furthermore, when an impact load is forwardly applied to the sub-frame  22  as described above, and even when the sub-frame  22  is moved forward, because the flat surface  26   a  of the front frame member  26  of the sub-frame  22  is disposed so as to oppose the flat surface  39   c  of the rear face of the fuel cell stack case  39 , and because the flat surface  26   a  of the sub-frame  22  transmits the impact load uniformly to the entirety of the flat surface  39   c  of the fuel cell stack case  39 , the impact load is distributed over the entirety of the flat surface  39   c  of the fuel cell stack case  39 ; therefore, the fuel cell stack case  39  can be reliably prevented from being broken in contrast to the case in which the impact load is applied to a portion of the rear face of the fuel cell stack case  39  in a concentrated manner. 
   Moreover, because the movement of the flat surface  26   a  of the sub-frame  22  is restrained by the flat surface  39   c  of the fuel cell stack case  39 , the deformation of the rear floor  2  at the stepped portion  3  is also restrained; therefore, the deformation of the rear floor  2  at the stepped portion  3  can be minimized. 
   If the treatment device for treating residual gases or the like after reaction is disposed in the vicinity of the rear portion of the fuel cell stack case  39  as mentioned above, the treatment device may function to restrain the forward movement of the sub-frame  22 ; therefore, safety performance may further be improved. 
   As explained above, when an impact load is forwardly applied to the sub-frame  22 , the impact load is distributed to the inside sills  7  and  8 , and in the floor frames  5  and  6  through the front brackets  11  and  12 . Even when the sub-frame  22  is moved forward, the flat surface  26   a  of the sub-frame  22  is supported by the flat surface  39   c  of the fuel cell stack case  39 ; therefore, the deformation of the entire vehicle body including the sub-frame  22  may be minimized. 
   As a result, safety of the hydrogen tanks  29  and  30  against collision can be greatly improved without adding reinforcements to the frame or body, and thus without a great increase in vehicle weight. 
   Advantageous Effects Obtainable by the Invention 
   As described above, according to the present invention, a load applied to the sub-frame is received by the side sills and the floor frames in a dissipated manner, and when the sub-frame is moved forward, the front flat surface of the sub-frame is uniformly supported by the rear flat surface of the fuel cell stack case; therefore, the strength and rigidity of the vehicle body against an aft-to-fore impact load may be increased.