Patent Publication Number: US-2023137848-A1

Title: Battery-module protection structure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. 2021-178600 filed on Nov. 1, 2021, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The disclosure relates to battery-module protection structures that protect battery modules accommodated within vehicle frames of vehicles. 
     A known battery-module protection structure in the related art is described in, for example, Japanese Unexamined Patent Application Publication (JP-A) No. 2004-243882. 
     A battery pack is installed on the upper surface of the vehicle floor behind the rear seat. A battery protection cover is fastened to a right wheel house and a left wheel house by using bolts such that the battery protection cover accommodates battery modules. According to this structure, the battery protection cover is used as a housing for the battery pack as well as a rear cross member. 
     SUMMARY 
     An aspect of the disclosure provides a battery-module protection structure configured to protect a battery module accommodated within a vehicle frame of a vehicle from an external impact. The battery-module protection structure includes a rail disposed within the vehicle frame, a pedestal securing the battery module and secured to the rail by using a securing member, and the vehicle frame serving as a housing of the battery module. The pedestal is configured such that, in a case where the vehicle receives the external impact and the securing member breaks, the pedestal moves in an inner direction of the vehicle along the rail while securing the battery module. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate an example embodiment and, together with the specification, serve to describe the principles of the disclosure. 
         FIG.  1    schematically illustrates a vehicle equipped with a battery-module protection structure according to an embodiment of the disclosure; 
         FIG.  2    is an exploded perspective view illustrating the battery-module protection structure according to the embodiment of the disclosure; 
         FIG.  3 A  is a top view illustrating the battery-module protection structure according to the embodiment of the disclosure; 
         FIG.  3 B  is a cross-sectional view illustrating the battery-module protection structure according to the embodiment of the disclosure; 
         FIG.  4 A  is a cross-sectional view illustrating the battery-module protection structure according to the embodiment of the disclosure; 
         FIG.  4 B  is a cross-sectional view illustrating the battery-module protection structure according to the embodiment of the disclosure; 
         FIG.  5    is a cross-sectional view illustrating the battery-module protection structure according to the embodiment of the disclosure; 
         FIG.  6 A  is a cross-sectional view illustrating a first modification of the battery-module protection structure according to the embodiment of the disclosure; 
         FIG.  6 B  is a cross-sectional view illustrating the first modification of the battery-module protection structure according to the embodiment of the disclosure; 
         FIG.  7 A  is a cross-sectional view illustrating a second modification of the battery-module protection structure according to the embodiment of the disclosure; and 
         FIG.  7 B  is a cross-sectional view illustrating the second modification of the battery-module protection structure according to the embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the battery-module protection structure disclosed in JP-A No. 2004-243882, the battery protection cover has a predetermined bonding strength or higher, and is fastened to the right wheel house and the left wheel house by using bolts. 
     On the other hand, although JP-A No. 2004-243882 discloses that the battery pack is installed on the vehicle floor, JP-A No. 2004-243882 does not disclose a specific method for securing the battery pack to the vehicle floor. However, from referring to the drawings, it is assumable that the battery pack is secured to the vehicle floor. 
     For example, when the vehicle is involved in a lateral collision, the wheel houses and the battery protection cover may sometimes become deformed toward the interior of the vehicle. If the battery pack collides with the deformed wheel houses, since the battery pack is secured to the vehicle floor, it is difficult to relieve the impact occurring during the collision. As a result, it is problematic in that the battery pack may possibly become damaged, and adjacent battery cells in the battery pack may possibly become damaged as a result of the battery cells colliding with each other. 
     It is desirable to provide a battery-module protection structure that protects a battery module accommodated within a vehicle frame of a vehicle. 
     In the following, an embodiment of the disclosure is described in detail with reference to the accompanying drawings. Note that the following description is directed to an illustrative example of the disclosure and not to be construed as limiting to the disclosure. Factors including, without limitation, numerical values, shapes, materials, components, positions of the components, and how the components are coupled to each other are illustrative only and not to be construed as limiting to the disclosure. Further, elements in the following example embodiment which are not recited in a most-generic independent claim of the disclosure are optional and may be provided on an as-needed basis. The drawings are schematic and are not intended to be drawn to scale. Throughout the present specification and the drawings, elements having substantially the same function and configuration are denoted with the same numerals to avoid any redundant description. 
     A protection structure  11  for a battery module  10  according to the embodiment of the disclosure will be described in detail below with reference to the drawings. In each drawing, the front-rear direction indicates the front-rear direction of a vehicle  12 , the left-right direction indicates the vehicle-width direction of the vehicle  12 , and the up-down direction indicates the height direction of the vehicle  12 . 
       FIG.  1    schematically illustrates the protection structure  11  for the battery module  10  according to this embodiment.  FIG.  2    is an exploded perspective view illustrating the protection structure  11  for the battery module  10  according to this embodiment.  FIG.  3 A  is a top view illustrating the protection structure  11  for the battery module  10  according to this embodiment.  FIG.  3 B  is a cross-sectional view illustrating the protection structure  11  for the battery module  10  according to this embodiment. In  FIG.  1   , a rail  31  and a pedestal  32  are omitted for illustrative purposes. In  FIG.  3 A , a cross member  13  is omitted for illustrative purposes. 
     As illustrated in  FIG.  1   , in the vehicle  12 , such as an automobile or an electric train, the battery module  10  is installed for supplying electric power to a motor and various electrical components. Examples of an automobile serving as the vehicle  12  include an electrical vehicle (EV), a hybrid electrical vehicle (HEV), and a plug-in hybrid electrical vehicle (PHEV), all of which are becoming popular in recent years. 
     In this embodiment, for example, the battery module  10  is accommodated within the cross member  13  serving as a vehicle frame below the rear seat of the vehicle  12 . As illustrated in  FIG.  1   , the cross member  13  is a hollow structure and is disposed on the upper surface of a floor panel  16 . The cross member  13  extends in the vehicle-width direction of the vehicle  12  and has opposite sides respectively joined to side sills  17  and  18 . 
     The floor panel  16  is disposed to cover the upper side of a propeller shaft  14 , an exhaust pipe  15 , and an under cover  20 . The center of the floor panel  16  in the vehicle-width direction is provided with a tunnel  19  extending in the front-rear direction of the vehicle  12 . The propeller shaft  14  and the exhaust pipe  15  are disposed in the tunnel  19 . The tunnel  19  in the floor panel  16  serves as a protrusion region protruding upward into the vehicle  12 . 
     With this structure, the center of the cross member  13  is provided with a protrusion region  21  that conforms to the shape of the floor panel  16 . The battery module  10  is accommodated within the cross member  13  at each of the opposite sides of the protrusion region  21  in the vehicle-width direction. Although details will be provided later, the cross member  13  also serves as a housing for the battery module  10 . Since a battery casing in the related art is not used for the battery module  10 , the manufacturing cost of the battery module  10  is reduced, and the total weight of the battery module  10  is reduced. 
     As illustrated in  FIG.  2   , the protection structure  11  for the battery module  10  mainly includes the cross member  13  used as a housing for the battery module  10 , the floor panel  16  that supports the cross member  13  from below, the rail  31  disposed within the cross member  13 , the pedestal (base)  32  engaged with and secured to the rail  31 , and the battery module  10  secured to the upper surface of the pedestal  32 . 
     The cross member  13  is disposed in the vehicle-width direction of the vehicle  12  and includes, for example, a lower cross member  33  and an upper cross member  34 . The lower cross member  33  includes, for example, a bottom plate  33 A and a rear plate  33 B, and is substantially L-shaped in cross section. The upper cross member  34  includes, for example, a top plate  34 A and a front plate  34 B, and is substantially L-shaped in cross section. 
     The bottom plate  33 A of the lower cross member  33  conforms to the shape of the floor panel  16 , and the lower cross member  33  is disposed on the upper surface of the floor panel  16 . The upper cross member  34  is fixed to the lower cross member  33  by welding. A cavity  35  (see  FIG.  1   ) that is substantially rectangular in cross section is provided within the cross member  13 . 
     The rail  31  extends in the vehicle-width direction of the vehicle  12  and is secured on the bottom plate  33 A of the lower cross member  33 . During the normal traveling mode of the vehicle  12 , the rail  31  supports the pedestal  32  in a secured state. When the vehicle  12  is involved in a lateral collision and the pedestal  32  detaches from the rail  31  due to a large external impact applied to the pedestal  32 , the rail  31  guides the traveling of the pedestal  32 . 
     In a state where the lower surface of the pedestal  32  is partially engaged with the rail  31 , the pedestal  32  is secured to the upper surface of the rail  31 . The pedestal  32  is also used as a placement plate for the battery module  10  by having the battery module  10  secured on the upper surface on the pedestal  32 . 
     Protection walls  22  located away from the ends of the battery module  10  are provided near the ends of the pedestal  32  at the outer sides of the vehicle cabin. Although details will be provided later, when the vehicle  12  is involved in a lateral collision, the protection walls  22  deform and receive the side sills  17  and  18  entering the vehicle  12 , so as to prevent the side sills  17  and  18  from colliding with the battery module  10 . 
     The battery module  10  is disposed on the upper surface of the pedestal  32  and has battery cells (not illustrated) coupled to each other in series via a bus bar (not illustrated). Each battery cell is, for example, a secondary cell, such as a nickel-hydrogen cell or a lithium-ion cell. For example, the battery cells each have a shape of a rectangular flat plate and are disposed in the extending direction (i.e., the left-right direction of the drawing) of the rail  31  while being evenly spaced apart from each other with a small cooling gap therebetween. The battery module  10  is electrically coupled to a BCU (not illustrated) serving as an electronic device and to a junction box (not illustrated). 
     As illustrated in  FIG.  3 A , the pedestal  32  is substantially rectangular in top view. The pedestal  32  is also used as a placement plate for the battery module  10  and has a tabular body larger than the battery module  10 . The four corners of the pedestal  32  individually have securing regions  42 . The securing regions  42  are used as regions for securing the pedestal  32  to the rail  31  by using bolts. 
     The rail  31  has four threaded holes (not illustrated) at the securing locations of the four securing regions  42 . The securing regions  42  have holes (not illustrated) for receiving and supporting bolts  43 . The pedestal  32  is disposed on the upper surface of the rail  31  in a state where the threaded holes and the holes are positioned with respect to each other, and is secured to the rail  31  by using the bolts  43  serving as securing members. 
     Although details will be provided later, for example, when a large external impact is applied to the pedestal  32  due to the vehicle  12  being involved in a lateral collision, the pedestal  32  moves toward the interior (in an inner direction) of the vehicle  12  together with the battery module  10 . In this case, the four bolts  43  break near the boundary regions between the rail  31  and the securing regions  42 , so that the pedestal  32  detaches from the rail  31 . 
       FIG.  3 B  is a cross-sectional view of the protection structure  11  for the battery module  10 , taken along line IIIB-IIIB in  FIG.  3 A . As illustrated in  FIG.  3 B , the rail  31  extends in the vehicle-width direction and has a predetermined width W 1 . The rail  31  has, for example, a substantially protruding shape in cross section. The rail  31  has a receiver recess  31 B to be engaged with an engagement protrusion  32 A of the pedestal  32 . 
     With this structure, the engagement protrusion  32 A of the pedestal  32  engages with the receiver recess  31 B of the rail  31 , and the lower surface of the pedestal  32  abuts on the upper surface of the rail  31 . As mentioned above, the pedestal  32  is secured to the rail  31  by using the bolts  43 , and the engagement protrusion  32 A is engaged with the receiver recess  31 B, so that the pedestal  32  is stably secured to the upper surface of the rail  31 . 
     As mentioned above, the cavity  35  that is substantially rectangular in cross section is provided within the cross member  13 . The battery module  10  utilizes the cavity  35  in the cross member  13  so as to be accommodated in the cavity  35 . The battery module  10  is disposed at a position located away from the bottom plate  33 A and the rear plate  33 B of the lower cross member  33  and from the top plate  34 A and the front plate  34 B of the upper cross member  34 . 
     With this structure, although the entire vehicle  12  including the cross member  13  shakes due to vibrations occurring when the vehicle  12  is traveling, the battery module  10  is prevented from colliding with the cross member  13 . Moreover, the battery module  10  is surrounded and covered by the cross member  13 , so as to be prevented from colliding with other components of the vehicle  12 . 
     In other words, in this embodiment, the cross member  13  is used as a housing for the battery module  10 . Since a housing serving as a battery casing in the related art is not used for the battery module  10 , the manufacturing cost of the battery module  10  is reduced, and the total weight of the battery module  10  is reduced. 
     The protection structure  11  for the battery module  10  when the vehicle  12  receives an external impact will now be described in detail with reference to  FIG.  4 A  to  FIG.  5   .  FIG.  4 A  is a cross-sectional view illustrating the protection structure  11  for the battery module  10  before the vehicle  12  according to this embodiment receives an external impact.  FIG.  4 B  is a cross-sectional view illustrating the protection structure  11  for the battery module  10  after the vehicle  12  according to this embodiment receives an external impact.  FIG.  5    is a cross-sectional view illustrating the protection structure  11  for the battery module  10  according to this embodiment. Although the following description relates to a case where an external impact is applied due to a lateral collision from the right side of the vehicle  12 , the same applies to a case where an external impact is applied due to a lateral collision from the left side of the vehicle  12 , and a description of such a case will thus be omitted. 
     An external impact in this embodiment is, for example, an external input force applied to the vehicle  12  when the vehicle  12  is involved in a lateral collision. An external impact is not limited to such an external input force occurring due to a lateral collision. An example of an external impact includes an external input force applied when the vehicle  12  rolls over due to a collision accident and the side sills  17  and  18  become deformed toward the interior (in an inner direction) of the vehicle  12 . 
     As illustrated in  FIG.  4 A , with regard to the cross member  13 , the lower cross member  33  and the upper cross member  34  are joined to each other by welding. The cross member  13  is a hollow structure having the cavity  35 . The rail  31  extends in the vehicle-width direction of the vehicle  12  and is secured on the bottom plate  33 A of the lower cross member  33 . The pedestal  32  is secured to the rail  31  and supports the battery module  10  in a secured state on the upper surface thereof. 
     As illustrated in  FIG.  4 A , the top plate  34 A of the upper cross member  34  extends in a substantially horizontal state from the side sill  18  (see  FIG.  1   ) to a securing region R 1  of the pedestal  32 . The top plate  34 A is then inclined diagonally upward from the securing region R 1  of the pedestal  32  toward the center of the vehicle  12 . In this embodiment, the top plate  34 A is inclined diagonally upward at least to a location above a bent segment  13 A of the cross member  13  such that a sufficient space can be ensured above the bent segment  13 A. 
     According to this structure, with regard to the width of the cavity  35  in the height direction of the vehicle  12 , a width W 3  at the bent segment  13 A of the cross member  13  is larger than a width W 2  at the securing region R 1  of the pedestal  32 . In the securing region R 1  of the pedestal  32 , a sufficient space is also ensured above the battery module  10 . 
       FIG.  4 A  illustrates a state where a large external impact is not applied to the pedestal  32  during the normal traveling mode of the vehicle  12 . In this state, even if vibrations occurring during the traveling of the vehicle  12  are applied to the pedestal  32 , the pedestal  32  is maintained in the secured state on the upper surface of the rail  31  by using the bolts  43  (see  FIG.  3 A ). With the sufficient space ensured between the battery module  10  and the cross member  13 , the battery module  10  is prevented from colliding with the cross member  13 , so that the battery cells are prevented from being damaged. Furthermore, the battery module  10  is maintained in the secured state on the upper surface of the pedestal  32 , so that the battery cells are prevented from being deformed and damaged as a result of colliding with each other due to vibrations occurring during the traveling of the vehicle  12 . 
     As illustrated in  FIG.  4 B , when the vehicle  12  is involved in a lateral collision and the side sill  18  (see  FIG.  1   ) becomes deformed toward the interior (in the inner direction) of the vehicle  12 , the side sill  18  collides with the corresponding protection wall  22  of the pedestal  32 , so that an external impact indicated by an arrow  51  (see  FIG.  4 A ) is applied to the pedestal  32 . Then, the external impact is applied to the four bolts  43  (see  FIG.  3 A ) via the pedestal  32 . If the external impact is greater than the design strength of the bolts  43 , the four bolts  43  break, as mentioned above. As a result, the pedestal  32  detaches from the rail  31 , and the pedestal  32  moves toward the interior (in an inner direction) of the vehicle  12  via the rail  31 . 
     As mentioned above, the width W 3  of the cavity  35  at the bent segment  13 A of the lower cross member  33  is larger than the width W 2  of the cavity  35  at the securing region R 1  of the pedestal  32 . After the pedestal  32  that has moved toward the center of the vehicle  12  collides with the rail  31  located at the bent segment  13 A of the cross member  13 , the leading end of the pedestal  32  is lifted upward along the rail  31  disposed in an inclined fashion. 
     As illustrated in  FIG.  4 B , the cavity  35  at the bent segment  13 A has the larger width W 3  so that the upper surface of the battery module  10  moving together with the pedestal  32  is prevented from colliding with the top plate  34 A of the upper cross member  34 . In this case, the engagement protrusion  32 A at the leading end of the pedestal  32  disengages from the receiver recess  31 B (see  FIG.  3 B ) of the rail  31 , whereas the engagement protrusion  32 A at the trailing end of the pedestal  32  is maintained in the engaged state with the receiver recess  31 B. 
     With this structure, the pedestal  32  moves in an inner direction of the vehicle  12  while being guided by the rail  31 . As a result, the battery module  10  on the upper surface of the pedestal  32  is prevented from colliding with the top plate  34 A, the front plate  34 B, and the rear plate  33 B of the cross member  13 , and the battery cells are prevented from being damaged. Furthermore, the battery module  10  is maintained in the secured state on the upper surface of the pedestal  32 , so that the battery cells are prevented from being deformed and damaged as a result of colliding with each other. 
     Furthermore, the protection walls  22  located away from end plates (not illustrated) of the battery module  10  are provided near the ends of the pedestal  32  at the outer sides of the vehicle cabin. The protection walls  22  are larger than the end plates of the battery module  10 . Each protection wall  22  is located between the corresponding end plate of the battery module  10  and the side sill  18 . 
     With this structure, when the vehicle  12  is involved in a lateral collision and the side sill  18  becomes deformed toward the interior (in an inner direction) of the vehicle  12 , the side sill  18  collides with the protection wall  22  so that the side sill  18  is less likely to collide with the battery module  10 . On the other hand, the protection wall  22  receives the aforementioned external impact, and the pedestal  32  transmits the external impact to the bolts  43 . If the external impact exceeds the design strength of the bolts  43 , the pedestal  32  detaches from the rail  31  by breaking the bolts  43 . As a result, as mentioned above, the pedestal  32  moves toward the center of the vehicle  12 , so that the battery module  10  is prevented from colliding with the deformed side sill  18  and the protection wall  22 , whereby the battery module  10  is prevented from being damaged. 
     The pedestal  32  is not limited to the case where the pedestal  32  is provided with the protection walls  22 . As mentioned above, the battery module  10  is secured to the position located inwardly away from each end of the pedestal  32 . Therefore, even in a structure where the pedestal  32  is not provided with the protection walls  22 , the deformed side sill  18  collides with the corresponding end of the pedestal  32 , so that effects similar to the structure having the protection walls  22  are achieved. However, with the pedestal  32  having the protection walls  22 , the battery module  10  is less likely to be damaged, as compared with the structure not having the protection walls  22 . 
     As illustrated in  FIG.  5   , a reinforcement member  52  may be disposed for the tunnel  19  in the floor panel  16  such that the reinforcement member  52  reinforces the floor panel  16  at least in the region where the rail  31  is disposed. The reinforcement member  52  is composed of the same material as the floor panel  16  and is secured to the floor panel  16  by using, for example, bolts. In the tunnel  19 , the propeller shaft  14  and the exhaust pipe  15  are disposed between the reinforcement member  52  and the floor panel  16 . 
     As mentioned above with reference to  FIG.  4 B , when the aforementioned external impact is applied to the vehicle  12  and the pedestal  32  detaches from the rail  31 , the leading end of the pedestal  32  collides with the rail  31  at the bent segment  13 A of the lower cross member  33 . In this case, although a large impact force is also applied to the floor panel  16 , the reinforcement member  52  prevents the tunnel  19  from collapsing as a result of the floor panel  16  deforming in the opening direction. As a result, the propeller shaft  14  and the exhaust pipe  15  are prevented from being damaged as a result of the floor panel  16  colliding with the propeller shaft  14  and the exhaust pipe  15 . 
     Next, first and second modifications of the protection structure  11  for the battery module  10  according to this embodiment will be described in detail with reference to  FIG.  6 A  to  FIG.  7 B .  FIG.  6 A  is a cross-sectional view illustrating the protection structure  11  for the battery module  10  before the vehicle  12  according to this embodiment receives an external impact.  FIG.  6 B  is a cross-sectional view illustrating the protection structure  11  for the battery module  10  after the vehicle  12  according to this embodiment receives an external impact.  FIG.  7 A  is a cross-sectional view illustrating the protection structure  11  for the battery module  10  according to this embodiment.  FIG.  7 B  is a cross-sectional view illustrating the protection structure  11  for the battery module  10  after the vehicle  12  according to this embodiment receives an external impact. 
     In the following description, same reference signs will be used for components identical to those in the protection structure  11  for the battery module  10  described with reference to  FIG.  1    to  FIG.  5   , and redundant descriptions will be omitted. Although the following description relates to a case where an external impact is applied due to a lateral collision from the right side of the vehicle  12 , the same applies to a case where an external impact is applied due to a lateral collision from the left side of the vehicle  12 , and a description of such a case will thus be omitted. 
     First, the first modification of the protection structure  11  for the battery module  10  will be described with reference to  FIG.  6 A  and  FIG.  6 B . 
     As illustrated in  FIG.  6 A , with regard to a cross member  61 , the lower cross member  33  and an upper cross member  62  are joined to each other by welding. The cross member  61  is a hollow structure having a cavity  63 . The rail  31  extends in the vehicle-width direction of the vehicle  12  and is secured on the bottom plate  33 A of the lower cross member  33 . The pedestal  32  is secured to the rail  31  and supports the battery module  10  in a secured state on the upper surface thereof. 
     As illustrated in  FIG.  6 A , a top plate  62 A of the upper cross member  62  extends in a substantially horizontal state. With regard to the width of the cavity  63  in the height direction of the vehicle  12 , a width W 5  at the bent segment  13 A of the lower cross member  33  is smaller than a width W 4  at the securing region R 1  of the pedestal  32 . In the securing region R 1  of the pedestal  32 , a sufficient space is ensured above the battery module  10 . 
     As illustrated in  FIG.  6 A , a guide wall  64  located away from the corresponding end plate of the battery module  10  is provided near an end of the pedestal  32  toward the center of the vehicle  12 . The guide wall  64  extends diagonally upward toward the center of the vehicle  12  and has a width substantially equal to that of the pedestal  32  in the breadth direction thereof (i.e., the front-rear direction in the drawing). The distal end of the guide wall  64  extends to a position higher than the battery module  10  secured to the upper surface of the pedestal  32 . Although not illustrated, the protection walls  22  may be provided near the ends of the pedestal  32  at the outer sides of the vehicle cabin. 
       FIG.  6 A  illustrates a state where a large external impact is not applied to the pedestal  32  during the normal traveling mode of the vehicle  12 . In this state, even if vibrations occurring during the traveling of the vehicle  12  are applied to the pedestal  32 , the pedestal  32  is maintained in the secured state on the upper surface of the rail  31  by using the bolts  43  (see  FIG.  3 A ). In the cavity  63 , a sufficient space is ensured between the battery module  10  and the cross member  61 . With this structure, the battery module  10  is prevented from colliding with the cross member  61  due to the aforementioned vibrations, so that the battery cells are prevented from being damaged. Furthermore, the battery module  10  is maintained in the secured state on the upper surface of the pedestal  32 , so that the battery cells are prevented from being deformed and damaged as a result of colliding with each other due to the aforementioned vibrations. 
     As illustrated in  FIG.  6 B , when the vehicle  12  is involved in a lateral collision and the side sill  18  (see  FIG.  1   ) becomes deformed toward the interior (in an inner direction) of the vehicle  12 , the side sill  18  collides with the corresponding end of the pedestal  32  or the corresponding protection wall  22 , so that an external impact indicated by an arrow  65  (see  FIG.  6 A ) is applied to the pedestal  32 . Then, the external impact is applied to the four bolts  43  (see  FIG.  3 A ) via the pedestal  32 . If the external impact is greater than the design strength of the bolts  43 , the four bolts  43  break, as mentioned above. As a result, the pedestal  32  detaches from the rail  31 , and the pedestal  32  moves toward the interior (in an inner direction) of the vehicle  12  via the rail  31 . 
     As illustrated in  FIG.  6 B , the pedestal  32  moves toward the center of the vehicle  12  and collides with the rail  31  at the bent segment  13 A of the lower cross member  33 . Then, the pedestal  32  and the guide wall  64  are lifted upward via a slope of the rail  31 . As a result, the distal end of the guide wall  64  collides with the top plate  62 A of the cross member  61  before the battery module  10  collides therewith. 
     In this case, the cross member  61  also receives an external force in the compressing direction (i.e., the left-right direction in the drawing) due to the external impact, and the top plate  62 A undergoes a collision with the guide wall  64  from the direction of the cavity  63 . Then, the cross member  61  becomes deformed into an inverted V-shape centered on the collision region between the guide wall  64  and the top plate  62 A. As a result of the cross member  61  undergoing the inverted-V-shaped deformation, the width W 5  of the cavity  63  above the bent segment  13 A of the lower cross member  33  increases, so that the battery module  10  is less likely to collide with the cross member  61 . 
     With this structure, when the pedestal  32  moves toward the interior (in an inner direction) of the vehicle  12  while being guided by the rail  31 , the battery module  10  is prevented from colliding with the top plate  62 A, the front plate (not illustrated), and the rear plate  33 B of the cross member  61 . Moreover, the battery cells in the battery module  10  are prevented from being deformed and damaged. 
     Next, the second modification of the protection structure  11  for the battery module  10  will be described with reference to  FIG.  7 A  and  FIG.  7 B . 
     As illustrated in  FIG.  7 A , with regard to a cross member  71 , the lower cross member  33  and an upper cross member  72  are joined to each other by welding. The cross member  71  is a hollow structure having a cavity  73 . The rail  31  extends in the vehicle-width direction of the vehicle  12  and is secured on the bottom plate  33 A of the lower cross member  33 . The pedestal  32  is secured to the rail  31  and supports the battery module  10  in a secured state on the upper surface thereof. 
     As illustrated in  FIG.  7 A , a top plate  72 A of the upper cross member  72  extends in a substantially horizontal state. With regard to the width of the cavity  73  in the height direction of the vehicle  12 , a width W 7  at the bent segment  13 A of the lower cross member  33  is smaller than a width W 6  at the securing region R 1  of the pedestal  32 . In the securing region R 1  of the pedestal  32 , a sufficient space is ensured above the battery module  10 . 
     In the securing region R 1  of the pedestal  32 , the top plate  72 A is provided with a protrusion  74  by utilizing the cavity  73  above the battery module  10 . The protrusion  74  is provided without being in contact with the upper surface of the battery module  10  and extends in the front-rear direction of the vehicle  12 . The region where the top plate  72 A is provided with the protrusion  74  has a recessed bead  76  extending in the front-rear direction of the vehicle  12 . 
     An engagement bracket  75  extends in the front-rear direction of the vehicle  12  at the end of the battery module  10  at the outer side of the vehicle cabin. The engagement bracket  75  is located at the outer side of the vehicle cabin relative to the protrusion  74 , and protrudes upward to a position higher than the upper surface of the battery module  10 . Although not illustrated, the protection walls  22  may be provided near the ends of the pedestal  32  at the outer sides of the vehicle cabin. 
       FIG.  7 A  illustrates a state where a large external impact is not applied to the pedestal  32  during the normal traveling mode of the vehicle  12 . In this state, even if vibrations occurring during the traveling of the vehicle  12  are applied to the pedestal  32 , the pedestal  32  is maintained in the secured state on the upper surface of the rail  31  by using the bolts  43  (see  FIG.  3 A ). In the cavity  73 , a sufficient space is ensured between the battery module  10  and the cross member  71  without the battery module  10  being in contact with the protrusion  74 . 
     With this structure, the battery module  10  is prevented from colliding with the cross member  71  due to the aforementioned vibrations, so that the battery cells are prevented from being damaged. Furthermore, the battery module  10  is maintained in the secured state on the upper surface of the pedestal  32 , so that the battery cells are prevented from being deformed and damaged as a result of colliding with each other due to the aforementioned vibrations. 
     As illustrated in  FIG.  7 B , when the vehicle  12  is involved in a lateral collision and the side sill  18  (see  FIG.  1   ) becomes deformed toward the interior (in an inner direction) of the vehicle  12 , the side sill  18  collides with the corresponding end of the pedestal  32  or the corresponding protection wall  22 , so that an external impact indicated by an arrow  77  (see  FIG.  7 A ) is applied to the pedestal  32 . Then, the external impact is applied to the four bolts  43  (see  FIG.  3 A ) via the pedestal  32 . If the external impact is greater than the design strength of the bolts  43 , the four bolts  43  break, as mentioned above. As a result, the pedestal  32  detaches from the rail  31 , and the pedestal  32  moves toward the interior (in an inner direction) of the vehicle  12  via the rail  31 . 
     In this case, the cross member  71  also receives an external force in the compressing direction (i.e., the left-right direction in the drawing) due to the external impact. As mentioned above, the top plate  72 A has the bead  76 , so that the cross member  71  becomes deformed into a V-shape centered on the bead  76 . As a result of the cross member  71  undergoing the V-shaped deformation, the protrusion  74  approaches the upper surface of the battery module  10 . 
     As a result, when the pedestal  32  moves toward the interior (in an inner direction) of the vehicle  12  via the rail  31 , the engagement bracket  75  engages with the protrusion  74 . The engagement between the engagement bracket  75  and the protrusion  74  inhibits movement of the pedestal  32  toward the interior (in an inner direction) of the vehicle  12 . As a result of a sudden stoppage of the pedestal  32 , the leading end of the pedestal  32  in the traveling direction thereof is lifted upward. 
     As illustrated in  FIG.  7 B , the cross member  71  undergoes the V-shaped deformation centered on the bead  76 , so that the width of the cavity  73  increases toward the bent segment  13 A of the lower cross member  33 . The battery module  10  is then lifted upward toward the widened space via the pedestal  32 , so that the battery module  10  is less likely to collide with the cross member  71 . 
     With this structure, when the pedestal  32  moves toward the interior (in an inner direction) of the vehicle  12  while being guided by the rail  31 , the battery module  10  is prevented from colliding with the top plate  72 A, the front plate (not illustrated), and the rear plate  33 B of the cross member  71 . Moreover, the battery cells in the battery module  10  are prevented from being deformed and damaged. 
     The battery-module protection structure according to the embodiment of the disclosure has the battery module accommodated within the vehicle frame, and the pedestal on which the battery module is secured is secured to the rail disposed within the vehicle frame. With this structure, when the vehicle is involved in a lateral collision and receives a large external impact, the pedestal detaches from the rail together with the battery module and moves toward the interior (in an inner direction) of the vehicle, so that the battery module is less likely to be damaged.