Patent Publication Number: US-2023158928-A1

Title: Impact absorbing member

Description:
FIELD 
     The present invention relates to an impact absorbing member. 
     BACKGROUND 
     In recent times, improvement of impact safety at the time of impact of an automobile has been proactively promoted along with lightening of weight for improving the fuel economy of vehicles. For example, the following PTL 1 describes an impact absorbing member continuously undergoing bending deformation due to an impact load and absorbing impact energy by a smaller load amplitude while reducing the maximum load at that time. 
     CITATIONS LIST 
     Patent Literature 
     
         
         [PTL 1] Japanese Unexamined Patent Publication No. 2011-85156 
       
    
     SUMMARY 
     Technical Problem 
     Impact absorbing members used for vehicles are designed to be provided at various locations of vehicles. The impact absorbing member described in PTL 1 is configured from a tubular member. Impact energy is absorbed by continuous bending deformation increasing the length of a folded back part where the outer wall is folded back due to an impact load. In such a constitution, there is the problem that the impact absorbing member is a closed cross-section 3D structure and the 3D space occupied becomes large, so if the space cannot be sufficiently secured, the impact absorbing member cannot be installed. 
     Therefore, the present invention has as its object the provision of an impact absorbing member able to absorb the energy at the time of an impact using a smaller space. 
     Solution to Problem 
     The gist of the present disclosure is as follows: 
     (1) An impact absorbing member comprising 
     a sheet member having bent parts and a plurality of sheet parts connected through the bent parts and 
     a restraining member restraining the plurality of sheet parts, 
     the plurality of sheet parts being superposed in a state folded back at the bent parts in a first direction, 
     the restraining member restraining the superposed plurality of sheet parts from both sides in a second direction, 
     the first direction being a direction connecting one end part among two end parts of the sheet member and the bent part adjoining the sheet part at which the end part is positioned, 
     the second direction being a direction perpendicular to the first direction. 
     (2) The impact absorbing member according to the above (1), wherein 
     the restraining member is a hollow member, and 
     the superposed plurality of sheet parts are arranged inside the hollow member. 
     (3) The impact absorbing member according to the above (1) or (2), wherein 
     the sheet member has two bent parts and three sheet parts connected through the two bent parts, and 
     the three sheet parts are superposed in a state alternately folded back at the two bent parts in the first direction. 
     (4) The impact absorbing member according to the above (3), wherein 
     the second direction is a thickness direction of the sheet member, 
     the restraining member has two restraining surfaces restraining the superposed plurality of sheet parts in the second direction, 
     in the second direction, a clearance “c” of an average value of a clearance of a portion where a sheet part and a restraining surface approach the most in the vicinity of one of the bent parts and a clearance of a portion where a sheet part and a restraining surface approach the most in the vicinity of the other of the bent parts satisfies the following formula (1): 
         c/c*≤ 0.3  (1)
 
     when a length in the first direction of a sheet part positioned at the middle in the second direction among the three sheet parts is l 0  and, at a bent part, a radius of curvature of a center line of thickness of a sheet part connected to the bent part is “r”, c*=l 0 /2−r. 
     (5) The impact absorbing member according to the above (3) or (4), wherein 
     the second direction is a thickness direction of the sheet member, and 
     at the superposed plurality of sheet parts, a clearance c′ of inside surfaces of sheet parts facing each other in the second direction satisfies the following formula (2) when an average of the thicknesses of the superposed plurality of sheet parts in the second direction is “t”: 
         c′/t≤ 0.2  (2)
 
     (6) The impact absorbing member according to any one of the above (1) to (5), wherein one of the two end parts of the sheet member is connected to a hinge part supporting a seatback of a vehicular use seat and the other is connected to a side frame of a seat cushion. 
     Advantageous Effects of Invention 
     According to the present invention, an impact absorbing member able to absorb the energy at the time of impact using a smaller space is provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic view showing the configuration of a vehicle seat to which an impact absorbing member according to one embodiment of the present invention is applied. 
         FIG.  2    is a perspective view showing a configuration of an impact absorbing member. 
         FIG.  3    is a side view of a vehicular seat seen from a left side and a view showing the state where a large load is applied to a seatback in an arrow A 1  direction by front impact of a vehicle and where the seatback deforms to the front of the vehicle. 
         FIG.  4    is a schematic view showing the state of a hinge part seen in an arrow A 3  direction in  FIG.  3   . 
         FIG.  5 A  is a schematic view showing in time series a state of deformation of an impact absorbing member upon receiving a tensile load. 
         FIG.  5 B  is a schematic view showing in time series a state of deformation of an impact absorbing member upon receiving a tensile load. 
         FIG.  5 C  is a schematic view showing in time series a state of deformation of an impact absorbing member upon receiving a tensile load. 
         FIG.  6 A  is a schematic view showing a state of deformation of a sheet member if a tensile load is applied in a first direction of an impact absorbing member if a restraining member is not provided. 
         FIG.  6 B  is a schematic view showing a state of deformation of a sheet member if a tensile load is applied in a first direction of an impact absorbing member if a restraining member is not provided. 
         FIG.  7    is a graph showing a relationship between a stroke and reaction force when applying a tensile load to an impact absorbing member. 
         FIG.  8    is a graph showing amounts of energy absorbed per volume for an invention example and comparative example explained in  FIG.  7   . 
         FIG.  9    is a schematic view showing the case where there is a single bent part. 
         FIG.  10    is a schematic view showing an example of giving a sheet member the function of a restraining member. 
         FIG.  11    is a schematic view showing an example of installing an impact absorbing member other than at a hinge part of a vehicular seat. 
         FIG.  12    is a perspective view showing a vehicle body frame of a vehicle and a view showing an example of application of impact absorbing members according to the present embodiment at a region R 1 , region R 2 , and region R 3  of a vehicle. 
         FIG.  13 A  is a schematic view showing in greater detail a state of deformation of a sheet member if a tensile load is applied in a first direction of an impact absorbing member if a restraining member is provided. 
         FIG.  13 B  is a schematic view showing in greater detail a state of deformation of a sheet member if a tensile load is applied in a first direction of an impact absorbing member if a restraining member is provided. 
         FIG.  14    is a cross-sectional view showing a constitution of an impact absorbing member. 
         FIG.  15    is a schematic view showing a limit if making a clearance “c” between a sheet member and restraining member larger and if the sheet member and restraining member abut. 
         FIG.  16    is a graph calculating by simulation a relationship between a ratio c/c* of a clearance “c” to a critical clearance c* and an absorbed energy of the impact absorbing member when applying a tensile load to an impact absorbing member. 
         FIG.  17    is a graph calculating and plotting, in addition to a characteristic C3 shown in  FIG.  16   , a characteristic C4 in the case of making l 0  a value of 20 cm and a characteristic C5 in the case of making a thickness of the steel sheet forming the sheet member a value of 2 mm. 
         FIG.  18    is a graph calculating by simulation a relationship between a ratio c′/t of a clearance c′ of a superposed portion of a sheet member with respect to an average thickness “t” of a plurality of sheet parts and an absorbed energy when applying a tensile load to an impact absorbing member. 
         FIG.  19    is a graph calculating by simulation a relationship between a ratio c′/t of a clearance c′ of a superposed portion of a sheet member with respect to an average thickness “t” of a plurality of sheet parts and an absorbed energy when applying a tensile load to an impact absorbing member. 
         FIG.  20    is a graph calculating by simulation a relationship between a ratio c′/t of a clearance c′ of a superposed portion of a sheet member with respect to an average thickness “t” of a plurality of sheet parts and an absorbed energy when applying a tensile load to an impact absorbing member. 
         FIG.  21 A  is a schematic view for explaining the reason why a rate of decrease of absorbed energy with respect to an increase of the ratio c′/t becomes greater if the value of c′/t exceeds 0.2. 
         FIG.  21 B  is a schematic view for explaining the reason why a rate of decrease of the absorbed energy with respect to an increase of the ratio c′/t becomes greater if the value of c′/t is morning than 0.2. 
         FIG.  22    is a view showing in detail the definitions (methods of measurement) of thickness “t”, clearance “c”, clearance c′, radius of curvature “r”, and length l 0 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Below, an impact absorbing member according to an embodiment of the present invention will be explained with reference to the drawings. First, referring to  FIG.  1   , the configuration of a vehicular seat  100  to which this impact absorbing member is applied will be explained.  FIG.  1    is a schematic view showing the configuration of the vehicular seat  100 . The vehicular seat  100  is, for example, used as a driver&#39;s seat or navigator&#39;s seat. 
     The vehicular seat  100  has a seat cushion  50  forming a sitting part and a seatback  60  forming a back rest. The seat cushion  50  is supported on a vehicle floor through a pair of left and right side rails (not shown) etc. installed on the floor. 
     Note that,  FIG.  1    schematically shows a frame part of the vehicular seat  100  having the seat cushion  50  and the seatback  60 . The vehicular seat  100  is configured by these members plus foam rubber or other inside packing and leather or fabric or other outside covering. 
     The seat cushion  50  has a side frame  102  and a side frame  104  provided at the left and right. The side frame  102  and the side frame  104  are connected and form an integral unit by a connecting member  110 , connecting member  112 , and connecting member  114  extending in a vehicle width direction. 
     The seatback  60  has a side frame  106  and a side frame  108  provided at the left and right. The side frame  106  and the side frame  108  are connected and form an integral unit by a connecting member  116  and connecting member  118  extending in the vehicle width direction. 
     The seat cushion  50  and the seatback  60  are connected by a left and right hinge part  70  and hinge part  80 . Due to the seat cushion  50  and the seatback  60  being connected by the hinge parts  70 ,  80 , an angle of the seatback  60  with respect to the seat cushion  50  can be changed about the hinge parts  70 ,  80 . Due to this, a reclining function of the vehicular seat  100  is realized. 
     The hinge part  70  and the hinge part  80  differ in structure. Giving as an example the case where the vehicular seat  100  is a seat at a driver&#39;s seat side of a right hand steering wheel vehicle, the hinge part  70  at the right side when facing the front of the vehicle is configured so that the side frame  108  of the seatback  60  can pivot with respect to the side frame  104  of the seat cushion  50  about a shaft  72  extending in the vehicle width direction as a center of rotation. 
     On the other hand, at the hinge part  80  at the left side when facing the front of the vehicle, the side frame  106  of the seatback  60  is connected with the side frame  102  of the seat cushion  50  through the impact absorbing member  10 . In more detail, the hinge part  80  is configured so that the impact absorbing member  10  can pivot with respect to the side frame  102  of the seat cushion  50  about the center of rotation of the shaft  82  extending in the vehicle width direction. Further, it is configured so that the side frame  106  of the seatback  60  can pivot with respect to the impact absorbing member  10  about the center of rotation of the shaft  84  extending in the vehicle width direction. In this way, the impact absorbing member  10  has one of the two end parts of the sheet member  12  connected to the hinge part supporting the seatback  60  of the vehicular seat  100  and has the other connected to the side frame  102  of the seat cushion  50 . 
     A reclining device (not shown) for adjusting the angle of the seatback  60  is provided at only the hinge part  70  at the right side when facing the front of the vehicle. The reclining device is, for example, provided with a latch mechanism and fixes the angle of the side frame  108  of the seatback  60  with respect to the side frame  104  of the seat cushion  50  to the angle adjusted to by the user. The side frame  106  and the side frame  108  are integrally connected by the connecting member  116  and the connecting member  118 , so if the angle of the side frame  108  with respect to the side frame  104  is fixed by the one hinge part  70 , the angle of the side frame  106  with respect to the side frame  102  is also fixed. Due to this, the angle of the seatback  60  with respect to the seat cushion  50  is fixed. By the reclining device being provided at only the one hinge part  70 , the number of parts is cut and the production costs are reduced. 
       FIG.  2    is a perspective view showing the configuration of the impact absorbing member  10 . Further,  FIG.  14    is a cross-sectional view showing the configuration of the impact absorbing member  10 . The impact absorbing member  10  is provided with the sheet member  12  having bent parts  12   a  and a plurality of sheet parts  12   b  connected through the bent parts  12   a . The plurality of sheet parts  12   b  are superposed in a state folded back in the first direction at the bent parts  12   a . Further, the impact absorbing member  10  is provided with a restraining member  14  restraining the superposed plurality of sheet parts  12   b  from the two sides in the second direction. The first direction is a direction connecting one end part  12   c  among two end parts  12   c  of the sheet member  12  and the bent part  12   a  adjoining the sheet part  12   b  at which the end part  12   c  is positioned. Note that, the direction connecting the other end part  12   c  of the sheet member  12  and the bent part  12   a  adjoining the sheet part  12   b  at which that end part  12   c  is positioned preferably matches the first direction. The first direction is designed to match the direction in which it is anticipated that the later explained impact load will be applied. The second direction is a direction perpendicular to the first direction. The second direction preferably includes the thickness direction and width direction of the sheet member  12  (sheet parts  12   b ). Here, the thickness direction of the sheet member  12  (sheet parts  12   b ) shows the normal direction with respect to the surface of the sheet parts  12   b  (also referred to as the direction perpendicular to the surface). The width direction of the sheet member  12  (sheet parts  12   b ) corresponds to the width direction of the sheet parts  12   b  and shows the direction perpendicular to the first direction and thickness direction. The restraining member  14  restrains (limits) movement of the sheet parts  12   b  in the second direction to thereby efficiently transmit the impact load applied to an end part  12   c  of the sheet member  12  in the first direction. In particular, the sheet parts  12   b  are planar shapes, so restraint of the sheet parts  12   b  with respect to the thickness direction where deformation is easy is effective for absorbing the impact load. Here, “restraint of the sheet parts  12   b  from the two sides in the second direction” indicates limiting the amount of movement of the sheet parts  12   b  in the second direction. For this reason, the restraining member  14  and the sheet parts  12   b  may closely contact each other in the second direction or may be in a state in close proximity. However, the distance between the restraining member  14  and the sheet parts  12   b  in the second direction is preferably made within the later explained distance so as to efficiently absorb the impact load. Note that,  FIG.  14    shows a cross-section along the first direction of the impact absorbing member  10 . 
     A vehicle is provided with various impact absorbing structures for absorbing impact at the time of impact. For example, in a front side member or other member forming a vehicle body floor, the space for provision of an impact absorbing structure is relatively easy to secure. On the other hand, in a vehicular seat  100  installed in a vehicle compartment, the space for provision of an impact absorbing structure is extremely limited. Therefore, the size of an impact absorbing member  10  to be provided at the vehicular seat  100  is preferably as small as possible. 
     In the present embodiment, the impact absorbing member  10  is comprised of a sheet member  12  superposed on itself by being folded back. The thickness of the bent parts  12   a  or sheet parts  12   b  of the sheet member  12  is several mm or so. Therefore, the space occupied by the impact absorbing member  10  is kept down. In particular, the space occupied in the thickness direction is kept down. Therefore, the impact absorbing member  10  can be installed even in a narrow clearance etc. and can be reliably housed even in a vehicular seat  100  in which only restricted space can be secured. 
     In the example shown in  FIG.  2   , the sheet member  12  is formed by a strip-shaped steel sheet being folded back at two bent parts  12   a  so that the steel sheet is superposed in three layers. The superposed parts of the strip steel sheet (sheet parts  12   b ) of the sheet member  12  may closely contact each other or predetermined clearances may be provided between the superposed sheet parts  12   b  as explained later. Note that, it is sufficient that there be at least one bent part  12   a . If there is one bent part  12   a , the sheet member  12  is configured by two superposed sheet parts  12   b . Further, if there are three bent parts  12   a , the sheet member  12  is comprised of four superposed sheet parts  12   b . Note that, the sheet member  12  may be comprised of a metal sheet other than a steel sheet. 
     The restraining member  14  is comprised of a steel tube or other hollow member, for example, is comprised of a square pipe cut short in the longitudinal direction. The restraining member  14  may also be formed in a hollow shape by bending a sheet member. In this case, the bent end parts may be joined by welding etc. or the end parts need not be joined and a clearance may be provided between the end parts. Three superposed sheet parts  12   b  are placed in the restraining member  14 . As shown in  FIG.  2    and  FIG.  14   , the restraining member  14  has two restraining surfaces  14   a  restraining the three superposed sheet parts  12   b  in the second direction (thickness direction of sheet parts  12   b ). The distance D between the two restraining surfaces  14   a  facing each other at the inside of the restraining member  14  in the thickness direction of the sheet parts  12   b  is made about three times the average thickness “t” of the three sheet parts  12   b . The end parts  12   c  of the sheet member  12  are preferably provided with a hole  18  in which a shaft  82  is to be inserted and a hole  16  in which a shaft  84  is to be inserted. Note that, if there is a single bent part  12   a , the sheet member  12  is comprised of two superposed sheet parts  12   b , so the distance D between the two restraining surfaces  14   a  facing each other at the inside of the restraining member  14  is made about 2 times the average thickness “t” of the two sheet parts  12   b . Similarly, if there are three bent parts  12   a , the sheet member  12  is comprised of four superposed sheet parts  12   b , so the distance D between restraining surfaces  14   a  facing each other at the inside of the restraining member  14  is made about 4 times the average thickness “t” of the four sheet parts  12   b . The restraining surfaces  14   a  of the restraining member  14  and the outer surface of the sheet member  12  may closely contact each other or as explained later a predetermined clearance may be provided. 
     Note that, the restraining member  14  restrains the superposed plurality of sheet parts  12   b  from the two sides in the second direction perpendicular to the first direction. It may also restrain the sheet parts  12   b  from the two sides in the thickness direction of the sheet member  12  and additionally restrain the sheet parts  12   b  from the two sides in the width direction of the sheet member  12 . 
     To keep the restraining member  14  from moving with respect to the sheet member  12  in the state where three superposed sheet parts  12   b  are placed in the restraining member  14 , the restraining member  14  and the sheet member  12  may be fixed together by spot welding etc. However, if ending up completely fastening together the restraining member  14  and the sheet member  12 , if an impact load is applied, sometimes deformation of the sheet member  12  will be obstructed, so it is preferable to fasten together the restraining member  14  and sheet member  12  by a low strength of an extent where the part breaks in the case where an impact load is applied to the impact absorbing member  10 . 
     Inside the seatback  60 , a three-point type of seatbelt device (not shown) is housed. At the time of use of the seatbelt, the body of the seated party is strapped against the seatback  60  by the seatbelt. For this reason, if the vehicle is involved in an impact (front impact) at the time of use of the seatbelt, a large impact load (inertia force) is applied to the seatback  60  in the direction shown by the arrow A 1  in  FIG.  1   . Note that, as a configuration where a three-point type of seatbelt device in housed in the seatback  60 , for example, the configuration described in Japanese Unexamined Patent Publication No. 2012-76494 etc. can be applied. 
       FIG.  3    is a side view of the vehicular seat  100  seen from the left side and a view showing the state where a large load is applied to the seatback  60  in the arrow A 1  direction by front impact of a vehicle and where the seatback  60  deforms to the front of the vehicle. In the state shown in  FIG.  3   , at the hinge part  70  at the right side when facing the front of the vehicle, the angle of the side frame  108  of the seatback  60  with respect to the side frame  104  of the seat cushion  50  is fixed by the reclining device. For this reason, while depending on the magnitude of the load applied, the angle of the side frame  108  to the side frame  104  basically does not greatly change. For this reason, a large acceleration is caused at the side frame  108  at the time of front impact. Note that, in the hinge part  70  as well, a change may occur in the angle of the side frame  108  with respect to the side frame  104  due to a stopper being over ridden in the latch mechanism etc. 
     On the other hand, in the state shown in  FIG.  3   , at the hinge part  80  at the left side when facing the front of the vehicle, the angle of the side frame  106  of the seatback  60  with respect to the side frame  102  of the seat cushion  50  is not fixed. Therefore, if a load is applied in the direction of the arrow A 1 , the angle of the side frame  106  with respect to the side frame  102  will greatly change. Further, if an impact load is applied in the direction of the arrow A 1 , an impact load in a direction in which the shaft  82  and the shaft  84  move apart (arrow A 2  direction shown in  FIG.  3   ) is applied in the first direction and a tensile load is applied to the first direction of the impact absorbing member  10 . Note that, in the present embodiment, the example was shown where the shaft  82  and the shaft  84  were inserted into the hole  16  and the hole  18  of the end parts  12   c  of the sheet member  12  so that the impact absorbing member  10  was connected with other members, but the method of connecting the end parts of the impact absorbing member  10  and other members is not limited to this. For example, they may be connected by welding. 
       FIG.  4    is a schematic view showing the state of the hinge part  80  viewed in the arrow A 3  direction in  FIG.  3   . As shown in  FIG.  4   , if force in the arrow A 2  direction is applied to the side frame  106 , since the shaft  84  is inserted in the one hole  16  of the impact absorbing member  10 , the force in the arrow A 2  direction is transmitted from the shaft  84  to the sheet member  12 . The shaft  82  is inserted in the other hole  18  of the impact absorbing member  10 , so the shaft  82  is fixed to the side frame  102 . Therefore, force acts in a direction where the shaft  82  and the shaft  84  move apart and a tensile load is applied to the impact absorbing member  10 . 
     Due to this, the impact absorbing member  10  deforms so that the sheet member  12  is extended in the first direction.  FIG.  5 A  to  FIG.  5 C  are schematic views showing in time series the state of deformation of the impact absorbing member  10  upon receiving a tensile load in the case where there are two bent parts  12   a . Note that, in  FIG.  5 A  to  FIG.  5 C , the bent parts  12   a  and sheet parts  12   b  of the sheet member  12  are illustrated from the width direction of the sheet member  12 . The length L in the first direction of the sheet part  12   b  positioned in the middle among the three sheet parts  12   b  is shown.  FIG.  5 A  shows the state in which a tensile load is applied in the first direction of the impact absorbing member  10 . From this state, impact energy starts to be absorbed by the impact absorbing member  10 . In the state shown in  FIG.  5 A , the outer surfaces of the two bent parts  12   a  of the sheet member  12  are positioned at the outside of the restraining member  14 . In the state shown in  FIG.  5 A , the length L of the sheet part  12   b  positioned in the middle among the three sheet parts  12   b  is the same extent as the length of the restraining member  14 . 
       FIG.  5 B  shows the state of deformation of the sheet member  12  due to a tensile load being applied in the first direction of the impact absorbing member  10 . In this state, the two bent parts  12   a  of the sheet member  12  shown in  FIG.  5 A  are extended and the outer surfaces of the newly formed bent parts  12   a ′ enter the inside of the restraining member  14 . In the state shown in  FIG.  5 B , the length L of the sheet part  12   b  positioned in the middle among the three sheet parts  12   b  becomes shorter than the length of the restraining member  14 . 
       FIG.  5 C  shows the state of further deformation of the sheet member  12  from the state shown in  FIG.  5 B  due to a tensile load being applied in the first direction of the impact absorbing member  10 . In this state, the two bent parts  12   a ′ of the sheet member  12  shown in  FIG.  5 B  are extended and the positions of the newly formed bent parts  12   a ″ enter the inside of the restraining member  14  further than the bent parts  12   a ′ of  FIG.  5 B . In the state shown in  FIG.  5 C , the length L of the sheet part  12   b  positioned in the middle among the three sheet parts  12   b  becomes further shorter than  FIG.  5 B . 
     As explained above, in the process shown in  FIG.  5 A ,  FIG.  5 B , and  FIG.  5 C , the sheet member  12  of the impact absorbing member  10  is extended whereby the length L of a portion where the sheet member  12  is superposed by being folded back (sheet part  12   b  positioned in the middle among the three sheet parts  12   b ) decreases. At this time, the two bent parts are extended and new bent parts are formed adjoining the original bent parts. By repetition of this, the locations forming the two bent parts move in the first direction of the sheet member  12  toward the inside of the restraining member  14 . That is, the deformation of the sheet member  12  is propagated in the first direction and the deformation spreads to the entire region of the sheet member  12 , so deformation in a direction outside the planes of the bent parts (thickness direction of sheet member  12 ) is suppressed. Note that, in the state before application of an impact load, the lower limit L of the sheet part  12   b  positioned in the middle of the three sheet parts  12   b  is preferably made about the thickness of the steel sheet forming the sheet member  12  for securing the ability of the locations of the bent parts to move in the first direction. 
     Here, as explained above, the distance D between the two restraining surfaces  14   a  facing each other at the inside of the restraining member  14  is made about 3 times the average thickness “t” of the plurality of sheet parts  12   b . In the thickness direction of the sheet member  12 , the sheet member  12  and the restraining member  14  are engaged. Due to this engaged state, in the process of application of an impact load and movement of the locations forming the bent parts in the first direction toward the inside of the restraining member  14 , deformation of the superposed sheet member  12  in the thickness direction (arrow A 4  direction shown in  FIGS.  5 A to  5 C ) is suppressed by the restraining member  14 . Therefore, the sheet member  12  will not deform so as to spread in the thickness direction. The locations forming the two bent parts deform so as to move in the first direction toward the inside of the restraining member  14 . Due to this, the tensile load applied to the first direction of the impact absorbing member  10  is reliably absorbed. 
       FIG.  6 A  and  FIG.  6 B  are schematic views for explaining the state of deformation of the sheet member  12  in the case where a tensile load is applied in the first direction of the impact absorbing member  10  when a restraining member  14  is not provided.  FIG.  6 A  shows the moment generated when a tensile load is applied in the first direction, while  FIG.  6 B  shows the state of deformation of the sheet member  12  upon application of a tensile load F to the sheet member  12 . 
     As shown in  FIG.  6 A , if a tensile load F is applied in the first direction, a moment M 1  is generated making the superposed sheet parts  12   b  rotate to the right in the figure about the point O. For this reason, as shown in  FIG.  6 B , the sheet parts  12   b  deform while rotating to the right. 
     As shown in  FIG.  6 B , if no restraining member  14  is provided, the sheet member  12  ends up deforming while spreading in the thickness direction. For this reason, the sheet member  12  deforms in a direction where the bends are extended at the bent parts  12   a . At this time, the region R 1  of the sheet member  12  shown in  FIG.  6 B  does not deform much at all but deforms in a direction where only the bent parts  12   a  are extended, so due to the region R 1  not deforming, the reaction force in the case where a tensile load is applied to the sheet member  12  becomes smaller. Due to this, the reaction force at the time when the bends at the bent parts  12   a  are extended is sufficiently smaller than the reaction force at the time when, in the process shown in  FIG.  5 A ,  FIG.  5 B , and  FIG.  5 C , the locations becoming the two bent parts deform while each moving in the first direction toward the inside of the restraining member  14 . For this reason, if no restraining member  14  is provided, the reaction force with respect to the tensile load ends up falling and the impact energy becomes insufficiently absorbed. Note that, the restraining member  14  has a strength of an extent enabling occurrence of deformation shown in  FIG.  6 B  to be suppressed. 
     On the other hand,  FIG.  13 A  and  FIG.  13 B  are schematic views showing in greater detail the state of deformation of a sheet member  12  if a tensile load is applied in the first direction of the impact absorbing member  10  in the case where a restraining member  14  is provided.  FIG.  13 A  shows the moment which occurs when a tensile load F is applied in the first direction of the impact absorbing member  10 , while  FIG.  13 B  shows the state of deformation of the sheet member  12  upon application of the tensile load F to the sheet member  12 . 
     As shown in  FIG.  13 A , if the tensile load F is applied in the first direction of the impact absorbing member  10 , a moment M 1  is generated which would make the superposed sheet parts  12   b  rotate to the right in the figure about the point O. If the sheet parts  12   b  try to rotate to the right in the figure due to this, the sheet parts  12   b  abut against the restraining member  14  whereby the sheet parts  12   b  receive the force “f” shown in  FIG.  15    from the restraining member  14 . Due to this, a moment M 2  is generated making the superposed sheet parts  12   b  rotate to the left in the figure about the point O. Therefore, unlike  FIG.  6 B , there is no deformation of the sheet member  12  in the thickness direction and the sheet parts  12   b  will not deform while being rotated to the right. 
     If the clearance between the sheet member  12  and the restraining member  14  is large, when the tensile force F is applied in the first direction of the impact absorbing member  10 , the sheet parts  12   b  rotate to the right in the figure within the range of the clearance until the sheet member  12  abuts against the restraining member  14 . Until the sheet member  12  abuts against the restraining member  14 , the state is the same as  FIG.  6 B . If the sheet member  12  abuts against the restraining member  14 , the sheet member  12  receives the force “f” shown in  FIG.  13 A  from the restraining member  14  and a large reaction force starts up. Therefore, if like in the present embodiment a moment is generated if an impact load is applied, a drop in the absorbed energy can be suppressed by suitably managing the clearance between the sheet member  12  and the restraining member  14 . 
     As shown in  FIG.  13 B , in the process of deformation of the sheet member  12  of the impact absorbing member  10 , in the regions R 2 , the bent parts  12   a  shown in  FIG.  15 A  are extended and in the regions R 3 , new bent parts  12   a ′ are formed adjoining the original bent parts  12   a . In this way, if the original bent parts are extended, new bent parts are formed adjoining the original bent parts. By repetition of this, the deformation is propagated so that the bent parts move. Therefore, the region R 1  as shown in  FIG.  6 B  where the sheet member  12  does not deform is not formed and the reaction force when an impact load is applied increases and the absorbed energy becomes larger. Note that, in the present embodiment, the sheet member  12  is used to obtain a sufficient absorbed energy when an impact load is applied, but if hypothetically using a rod member, a sufficient absorbed energy is difficult to obtain. 
       FIG.  7    is a graph showing a relationship between a stroke and reaction force when applying a tensile load to the impact absorbing member  10 . Note that, the “stroke” is the amount of extension of the impact absorbing member  10  when applying a tensile load. The stroke when not applying a tensile load is defined as 0. In  FIG.  7   , the characteristic C1 showing the relationship between the stroke and reaction force of the impact absorbing member  10  according to the present embodiment (invention example) and the characteristic C2 showing the relationship between the stroke and reaction force of an impact absorbing member according to a comparative example are shown. 
     Note that, the invention example uses a cold rolled steel sheet comprised of steel sheet having a tensile strength of 1180 MPa as a material and bends the steel sheet to obtain a sheet member  12  having an average thickness “t” of the sheet parts  12   b  of 1 mm and a width 60 mm of the sheet parts  12   b . Further, the comparative example uses a cold rolled steel sheet comprised of steel sheet having a tensile strength of 1180 MPa as a material to obtain a thickness “t” of 1 mm and a width of 60 mm. Further, the length of the restraining member  14  of the invention example in the first direction was made 40 mm. The shape of the invention example, like the impact absorbing member  10  shown in  FIG.  2   , was made an N-shape having bent parts at two locations. Further, the shape of the comparative example was made a simple sheet shape without folds (without bent parts). In the comparative example, no restraining member  14  was provided. 
     As shown in  FIG.  7   , in the characteristic C1 of the invention example, until the stroke became more than 60 mm, the locations forming the two bent parts deformed while moving in the first direction toward the inside of the restraining member  14 , whereby a reaction force continuously is generated. On the other hand, in the characteristic C2 of the comparative example, with a stroke of 5 mm or less, the reaction force rapidly rose, then the sheet member broke and the desired reaction force could not be obtained. Note that, in the invention example, a stroke of about two times the length of the restraining member  14  in the first direction can be secured, but if the stroke becomes more than 60 mm, the sheet member  12  becomes on the verge of breakage and calculation is stopped. 
       FIG.  8    is a graph showing amounts of energy absorbed per volume for the invention example and comparative example explained in  FIG.  7   . Note that, the amount of absorbed energy is obtained from the integrated value of the reaction forces with respect to the stroke. As shown in  FIG.  8   , in the invention example, the impact energy was sufficiently absorbed in the process of propagation of deformation of the locations forming the bent parts moving in the first direction toward the inside of the restraining member  14 . In other words, in the invention example, deformation of the sheet member  12  is propagated so that the locations forming the bent parts move in the first direction, so the entire region of the sheet member  12  deforms and the amount of energy absorbed per unit volume becomes greater. On the other hand, in the comparative example, at the time of a small stroke, the reaction force rapidly rose, then the sheet member broke early and the desired impact absorbing capability could not be obtained. From the above, it is learned that, according to the invention example, it is possible to absorb greater impact energy by a small occupied space. 
     As explained above, the restraining surfaces  14   a  of the restraining member  14  and the outer surface of the sheet member  12  may closely contact each other or a predetermined clearance may be provided. Further, the sheet parts  12   b  may closely contact each other or, as explained later, a predetermined clearance may be provided between the sheet parts  12   b . The greater the clearance between the sheet member  12  and the restraining member  14 , the greater the amount of rotating of the sheet parts  12   b  inside of the restraining member  14  due to the moment M 1  explained in  FIG.  13 A  and the larger the region R 1  shown in  FIG.  6 B  at which the sheet member  12  does not deform, so the more the reaction force at the time of application of the tensile load falls. Further, the greater the clearance between the sheet parts  12   b , the larger the region R 1  shown in  FIG.  6 B  at which the sheet member  12  does not deform, so the more the reaction force at the time of application of the tensile load falls. Below, the results of simulation of the preferable numerical ranges for the clearance between the sheet member  12  and the restraining member  14  and the clearance between the inside surfaces of the sheet parts  12   b  will be explained. 
     First, as shown in  FIG.  14   , the thickness “t” of the sheet member  12 , clearance “c”, clearance c′, radius of curvature “r” of the bent parts  12   a , and length l 0  will be defined.  FIG.  22    is a view showing in detail the definitions (methods of measurement) of the thickness “t”, clearance “c”, clearance c′, radius of curvature “r”, and length  1   p  shown in  FIG.  14   . In  FIG.  22   , “mp” shows the thickness measurement parts, while the thickness “t” of the sheet member  12  is made the average value of the thicknesses measured at the thickness measurement parts at these six locations. 
     The clearance “c” is the average value of the clearance c 1  of the portion where the sheet part  12   b  and the restraining surface  14   a  of the restraining member  14  approach each other the most in the vicinity of one bent part  12   a  and the clearance c 2  of the portion where the sheet part  12   b  and the restraining surface  14   a  of the restraining member  14  approach each other the most in the vicinity of the other bent part  12   a  and corresponds to the clearance between the sheet member  12  and the restraining member  14 . The clearance c′ is the average value of the clearances c′ 1 , c′ 2  between the sheet part  12   b  positioned in the middle among the three sheet parts  12   b  and each of the two sheet parts  12   b  positioned at the two sides of the sheet part  12   b  and corresponds to the clearance between the sheet parts  12   b . Further, the radius of curvature “r” is r=(r 1 +r 2 +t)/2 when the radii of the inscribed circles at the insides of the bends of the two bent parts  12   a  (shown by the broken lines in the figure) are respectively r 1  and r 2 . The radius of curvature “r” corresponds to the radius of curvature of the centerline of thickness. Further, the length l 0  is the distance in the first direction between the centers of the inscribed circles at the insides of the bends of the two bent parts  12   a  and corresponds to the length of the sheet part  12   b  positioned in the middle in the three sheet parts  12   b . The measurement position of the clearance c′ 1  is preferably separated from the bent part  12   a  at the left side in the figure and is made the portion where the sheet part  12   b  and the restraining surface  14   a  approach the most at the right side from the line l c  showing the position of ½ of the length l 0 . Similarly, the measurement position of the clearance c′ 2  is preferably separated from the bent part  12   a  at the right side in the figure and is made the portion where the sheet part  12   b  and the restraining surface  14   a  approach the most at the left side from the line l c  showing the position of ½ of the length l 0 . The thickness measurement parts mp are the same locations as the locations for measurement of the clearance “c” and clearance c′. In the case of the present example, the thicknesses are measured at the same measurement locations mp as the clearances c1, c2, c′1, and c′2 and the average is made the thickness “t” (also referred to as the “thickness average”). Note that, the length l 0  is the length in the state where no impact load is applied (initial state), for example, becomes the length L shown in  FIG.  5 A  (L=1 0 ). Note that, the thickness “t” of the sheet member  12 , clearance “c”, clearance c′, radius of curvature “r” of bent parts  12   a , and length l 0  are respectively measured at cross section when cutting the impact absorbing member  10  at the position of ½ in the width direction in the first direction. At this time, if the restraining member  14  and the sheet member  12  are not joined, the impact absorbing member  10  as a whole is fixed in place by a resin. 
     First, the preferable numerical range of the clearance “c” of the sheet member  12  and the restraining member  14  will be explained. As explained in  FIG.  13 A , if a tensile load F is applied in the first direction of the impact absorbing member  10 , a moment M 1  is generated centered about the point O. Due to this, the sheet parts  12   b  try to rotate to the right in the figure, but the sheet member  12  abuts against the restraining member  14 , whereby the sheet member  12  receives the force “f” shown in  FIG.  13 A  from the restraining member  14 . If the clearance “c” between the sheet member  12  and the restraining member  14  is 0, the sheet parts  12   b  will not rotate to the right in the restraining member  14 . 
     On the other hand, if the clearance “c” between the sheet member  12  and the restraining member  14  is large, when the tensile load F is applied in the first direction of the impact absorbing member  10 , the sheet parts  12   b  rotate to the right in the figure in the range of the clearance “c”. Further, if the sheet member  12  abuts against the restraining member  14 , the sheet member  12  receives the force “f” shown in  FIG.  13 A  from the restraining member  14 . In this case, until the sheet member  12  abuts against the restraining member  14 , deformation similar to  FIG.  6 B  occurs and the reaction force falls. 
     If the clearance “c” between the sheet member  12  and the restraining member  14  becomes further larger, when the tensile load F is applied in the first direction of the impact absorbing member  10 , the sheet parts  12   b  further rotate to the right in the figure and sometimes the sheet member  12  no longer abuts against the restraining member  14 . In this case, the sheet member  12  does not receive the force “f” shown in  FIG.  13 A .  FIG.  15    is a schematic view showing the limit when making the clearance “c” between the sheet member  12  and the restraining member  14  larger and the sheet member  12  and restraining member  14  abut. The clearance “c” when making the clearance “c” between the sheet member  12  and restraining member  14  larger and the state shown in  FIG.  15    occurs, that is, when reaching the limit when the sheet member  12  abuts against the restraining member  14 , is defined as the critical clearance c*. From the geometric relationship shown in  FIG.  15   , the following formula (1) stands. 
       Distance  D  between restraining surfaces 14 a  of restraining member 14= l   0 +2( r+t/ 2)  (1)
 
     On the other hand, from  FIG.  14   , the following formula (2) stands. 
         D =2 c*+ 3 t +2(2 r−t )  (2)
 
     If removing D from formula (1) and formula (2) and solving them for c*, the following formula (3) is obtained. Note that, in formula (2) and formula (3), 2r−t=c′. 
         c*=l   0 /2− r =( l   0   −c′−t )/2  (3)
 
     For the sheet member  12  to receive the force “f” shown in  FIG.  13 A , preferably the clearance “c” between the sheet member  12  and the restraining member  14  is made smaller than the critical clearance c*, that is, the ratio c/c* of the clearance “c” with respect to the critical clearance c* is made less than 1. The inventors engaged in intensive studies and as a result found that in a region where the ratio c/c* is less than 1, the absorbed energy of the impact absorbing member  10  when a tensile load is input changes in accordance with the ratio c/c* and that the larger the ratio c/c*, the more reduced the absorbed energy. Furthermore, they learned that if making the ratio c/c* larger, there is a critical point where the absorbed energy rapidly decreases. 
       FIG.  16    is a graph calculating by simulation the relationship between the ratio c/c* of the clearance “c” to the critical clearance c* and an absorbed energy of the impact absorbing member  10  when applying a tensile load to an impact absorbing member  10 . In  FIG.  16   , the abscissa indicates the ratio c/c* and the ordinate indicates the absorbed energy. The characteristic C3 shown in  FIG.  16    was found by simulation of the change of absorbed energy in the case of using as the steel sheet forming the sheet member  12  a cold rolled steel sheet of 1 mm thickness having a tensile strength of 1180 MPa, making the l 0  shown in  FIG.  14    a value of 10 cm, and changing the ratio c/c*. Note that, the restraining member  14  was simulated as a rigid fixed object. 
     As shown in  FIG.  16   , it is learned that in the region where the ratio c/c* is less than 1, the more the clearance “c” increases, that is, the more the ratio c/c* increases, the more the absorbed energy falls, but if c/c* becomes more than 0.3, the rate of decrease of the absorbed energy with respect to an increase of the ratio c/c* becomes greater. In other words, it is learned that the smaller the clearance “c”, the more the absorbed energy increases, but if the ratio c/c* is near 0.3, the absorbed energy becomes saturated. Further, if c/c* becomes more than 0.6, the rate of decrease of the absorbed energy with respect to an increase of the ratio c/c* becomes further greater. 
       FIG.  17    is a graph calculating the plotting, in addition to the characteristic C3 shown in  FIG.  16   , the characteristic C4 in the case of making l 0  a value of 20 cm and the characteristic C5 in the case of making the thickness of the steel sheet forming the sheet member  12  a value of 2 mm. Note that, the characteristic C4 is the same as the characteristic C3 in the conditions other than l 0 , and the characteristic C5 is the same as the characteristic C3 in the conditions other than the thickness. 
     As shown in  FIG.  17   , even in the characteristic C4 in the case of making l 0  a value of 20 cm and the characteristic C5 in the case of making the thickness of the steel sheet forming the sheet member  12  a value of 2 mm, it is learned that if c/c* is more than 0.3, the rate of decrease of the absorbed energy with respect to the increase of the ratio c/c* becomes larger. Further, in the characteristic C4 and the characteristic C5 as well, it is learned that if c/c* becomes more than 0.6, the rate of decrease of the absorbed energy with respect to the increase of the ratio c/c* becomes further larger. Therefore, to increase the absorbed energy to raise the impact absorption ability of the impact absorbing member  10 , it is suitable to make the value of the ratio c/c* a value of 0.6 or less, more preferably make the value of the ratio c/c* a value of 0.3 or less. Further, to increase the absorbed energy to the maximum extent, it is suitable to make the clearance “c” zero and make the sheet member  12  and the restraining member  14  closely contact each other. 
     Next, the suitable numerical range of the clearance c′ of the inside surfaces of the sheet parts  12   b  will be explained.  FIG.  18    to  FIG.  20    are graphs calculating by simulation the relationship between the ratio c′/t of the clearance c′ of sheet parts  12   b  with respect to an average thickness “t” of a plurality of sheet parts  12   b  and an absorbed energy when applying a tensile load to an impact absorbing member  10 . In  FIG.  18    to  FIG.  20   , the abscissas show the ratio c′/t and the ordinates show the absorbed energy. The characteristic C6 shown in  FIG.  18    was found by simulation of the change of absorbed energy in the case of using as the steel sheet forming the sheet member  12  cold rolled steel sheet of 1 mm thickness having a tensile strength of 1180 MPa and changing the clearance c′ between sheet parts  12   b . Further, the characteristic C7 shown in  FIG.  19    shows the results of simulation in the case of making the thickness of the steel sheet forming the sheet member  12  a value of 2 mm, while the characteristic C8 shown in  FIG.  20    shows the results of simulation in the case of making the thickness of the steel sheet forming the sheet member  12  a value of 3 mm. In the simulations of the characteristic C7 shown in  FIG.  19    and the characteristic C8 shown in  FIG.  20   , the conditions other than thicknesses were made the same as the simulation of the characteristic C6 shown in  FIG.  18   . 
     As shown in  FIG.  18    to  FIG.  20   , it will be understood that at all thicknesses, the more the clearance c′ between the sheet parts  12   b  increases, that is, the more the ratio c′/t increases, the more the absorbed energy falls, but if c′/t becomes more than 0.2, the rate of decrease of the absorbed energy with respect to the increase of the ratio c′/t becomes larger. In other words, it will be understood that the smaller the clearance c′, the more the absorbed energy increases, but more saturated the absorbed energy becomes near the ratio c′/t of 0.2. Therefore, to increase the absorbed energy to raise the impact absorbing capability of the impact absorbing member  10 , it is suitable to make the value of the ratio c′/t a value of 0.2 or less. Further, to enlarge the absorbed energy to the maximum extent, it is suitable to make the clearance c′ zero and make the sheet parts  12   b  closely contact each other. 
     Note that, when the sheet member  12  deforms, bending plastic deformation occurs. The sheet member  12  is required to have a bending ability able to withstand this. The preferable clearance c′ of the sheet parts  12   b  with each other is 20% or less of the thickness “t”, so in terms of the radius of curvature “r” of the center line of thickness of the bent part, it is preferable that there be bendability of about r/t=0.6 and in terms of the radius of curvature “r” of the inside of the bend of the bent part, it is preferable that there be bendability of r/t=0.1. 
       FIG.  21 A  and  FIG.  21 B  are schematic views for explaining the reason why the rate of decrease of the absorbed energy with respect to the increase of the ratio c′/t becomes larger if the value of c′/t is more than 0.2.  FIG.  21 A  shows the state before a tensile load is applied to the sheet member  12 , while  FIG.  21 B  shows the state where the tensile load F is applied to the sheet member  12  and the sheet member  12  deforms. Note that, for convenience in explanation, in  FIG.  21 A  and  FIG.  21 B , the case is illustrated where c′/t is larger than 1. 
     As shown in  FIG.  21 B , in the process of deformation of the sheet member  12  of the impact absorbing member  10 , at the regions R 2 , the bent parts  12   a  shown in  FIG.  21 A  are extended and new bent parts  12   a ′ are formed at the region R 3 . At this time, if the ratio c′/t of the clearance c′ with respect to the thickness “t” exceeds 0.2, new bent parts  12   a ′ are formed at the regions R 3  away from the regions R 2  where the bent parts  12   a  are extended and regions R 4  where no bent parts are formed appear between the regions R 2  and the regions R 3 . That is, if the ratio c′/t is 0.2 or less, as explained in  FIG.  13 B , if the original bent parts  12   a  are extended, new bent parts  12   a ′ are formed adjoining the original bent parts  12   a . By repetition of this, deformation is propagated while the bent parts move, but if the ratio c′/t is more than 0.2, it is believed that new bent parts  12   a ′ are formed at positions away from the original bent parts  12   a . Due to this, in the regions R 4  between the original bent parts  12   a  and the new bent parts  12   a ′, the sheet member  12  does not deform, so the absorbed energy falls. 
     Therefore, to keep new bent parts  12   a ′ from ending up being formed at positions away from the original bent parts  12   a , it is preferable to make the ratio c′/t a value of 0.2 or less. Due to this, if an impact load is input, it is possible to keep the absorbed energy from ending up falling. 
     Modification 
     As explained above, there need only be one or more bent parts  12   a  of the impact absorbing member  10 .  FIG.  9    is a schematic view showing the case where there is one bent part  12   a . In the example shown in  FIG.  9   , if a load is applied in the first direction in the arrow direction, the bent part  12   a  deforms while moving to the right. More specifically, in the constitution shown in  FIG.  9   , if the sheet member  12  receives a tensile load in the arrow A 5  direction from the member  20  connected to the end part  12   d , force in the arrow A 6  direction will be received from the member  22  connected to the end part  12   e  and the location becoming the bent part will deform in the first direction like moving to the right in the figure and deformation of the sheet member  12  will be propagated. 
     Note that, in  FIG.  9   , at the end part  12   e , a compressive force is applied in the first direction, so if deformation etc. occurs at the sheet member  12  at the end part  12   e , there is a possibility that the energy absorbed in the case of application of an impact load will not be stable. In particular, if the steel sheet forming the sheet member  12  is thin or if the cross-sectional area of the end part  12   e  is small etc., there is a possibility that deformation etc. will occur at the sheet member  12  at the end part  12   e . Further, if there are three or more bent parts  12   a , when receiving an impact load and the sheet member  12  deforms, there is a possibility that the superposed portion of the sheet member  12  will easily separate from the restraining member  14  Therefore, it is preferable to make the number of bent parts  12   a  two parts. 
       FIG.  10    is a schematic view showing an example of giving a sheet member  12  the function of a restraining member  14 . In the example shown in  FIG.  10   , as another example of the restraining member, a restraining piece  12   f  having a U-shape in the width direction of the sheet member  12  viewed from the first direction is provided. The restraining piece  12   f  is formed by making the sheet member  12  stick out in the width direction and bending it into a U-shape viewed from the first direction. As shown in  FIG.  10   , by the restraining piece  12   f  being provided integrally with the sheet member  12 , the number of parts forming the impact absorbing member  10  is cut. 
       FIG.  11    is a schematic view showing an example of installing an impact absorbing member  10  other than at a hinge part of a vehicular seat  100 . The vehicular seat  100  shown in  FIG.  11    has the side frame  102  of the seat cushion  50  divided into an upper side frame  102   a  and a lower side frame  102   b . The upper side frame  102   a  and the lower side frame  102   b  are connected by the impact absorbing member  10  according to the present embodiment. The side frame  104  (not shown in  FIG.  11   ) of the seat cushion  50  is also configured in the same way as the side frame  102 . According to such a configuration, by dividing the side frames  102 ,  104  of the seat cushion  50 , the side frames  102 ,  104  are made smaller and further reduction of the weight of the vehicular seat  100  is achieved. 
     In the configuration shown in  FIG.  11   , at the time of front impact, the impact energy is absorbed by the seatback  60  deforming to the front of the vehicle and the sheet member  12  of the impact absorbing member  10  at the rear side of the vehicle extending in the first direction. Further, at the time of rear impact, the impact energy is absorbed by the seatback  60  deforming to the rear of the vehicle and the sheet member  12  of the impact absorbing member  10  at the front side of the vehicle extending in the first direction. Further, at the time of side impact, the impact energy is absorbed by the sheet members  12  of the impact absorbing members  10  at the front side of the vehicle and the rear side of the vehicle extending in the first direction. 
     In the above-mentioned embodiment, the case where a tensile load was applied to the impact absorbing member  10  was explained, but even if a compressive load is applied to the impact absorbing member  10 , the impact load is absorbed by a locations forming the bent parts deforming while moving in the first direction and the sheet member  12  of the impact absorbing member  10  contracting in the first direction. 
     Examples of Application to Other Than Vehicular Seat 
     In the above-mentioned embodiment, an example where the impact absorbing member  10  was applied to a vehicular seat  100  was shown. On the other hand, the impact absorbing member  10  can be applied to various parts of a vehicle.  FIG.  12    is a perspective view showing a vehicle body frame  200  of a vehicle and a view showing an example of application of impact absorbing members according to the present embodiment at a region R 11 , region R 12 , and region R 13  of a vehicle. 
     At the region R 11 , an impact absorbing member  10  is provided at the connecting part of the center pillar  210  and the side sill  220 . In this case, one hole  16  of the impact absorbing member  10  is fixed to the center pillar  210 , and the other hole  18  of the impact absorbing member  10  is fixed to the side sill  220  side. Due to this configuration, if the center pillar  210  deforms in a direction away from the side sill  220  at the time of a side impact etc., the sheet member  12  of the impact absorbing member  10  extends in the first direction whereby the impact energy is absorbed. 
     In the region R 12 , an impact absorbing member  10  is applied to an engine mount of a vehicle. In this case, one of the holes  16  of the impact absorbing member  10  is affixed to the engine (not shown) and the other hole  18  is affixed to the vehicle body frame  200 . If the vehicle is in an impact, a large force due to inertial force is applied to the engine, but the sheet member  12  of the impact absorbing member  10  extends in the first direction whereby the impact energy is absorbed. 
     In the region R 13 , an impact absorbing member  10  is applied to an opening/closing part of the hood. In this case, one of the holes  16  of the impact absorbing member  10  is affixed to the vehicle body frame  200  while the other hole  18  is affixed to a latch part mechanically engaging with the hood when the hood is closed. For example, if a vehicle strikes a pedestrian, sometimes the head or body of the pedestrian will hit the hood and a force will be applied to a direction pushing down the hood. In such a case, a tensile load is applied to the impact absorbing member  10 , and the sheet member  12  of the impact absorbing member  10  extends in the first direction whereby the impact energy is absorbed. Therefore, the safety of the pedestrian is secured. 
     As explained above, according to the present embodiment, even in the case where space is limited, the impact absorbing member  10  can be installed, so it becomes possible to efficiently absorb impact energy. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10 . impact absorbing member 
               12 . sheet member 
               12   a ,  12   a ′,  12   a ″. bent parts 
               12   b . sheet parts 
               12   c ,  12   d ,  12   e . end parts 
               12   f  restraining pieces 
               14 . restraining member 
               16 ,  18 . holes 
               20 ,  22 . members 
               50 . seat cushion 
               60 . seatback 
               70 ,  80 . hinge parts 
               72 ,  82 ,  84 . shafts 
               100 . vehicular seats 
               102 ,  104 ,  106 ,  108 . side frames 
               102   a . upper side frame 
               102   b . lower side frame 
               110 ,  112 ,  114 ,  116 ,  118 . connecting members 
               200 . vehicle body frame 
               210 . center pillar 
               220 . side sill