Patent Publication Number: US-2022216567-A1

Title: Battery module, electric power unit, and working machine

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of International Patent Application No. PCT/JP2019/039154 filed on Oct. 3, 2019, the entire disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a battery module, an electric power unit, and a working machine. 
     Description of the Related Art 
     Japanese Patent No. 3742261 discloses an arrangement of a battery pack with a plurality of cells arranged therein, in which an outer case is provided with a suction port and an exhaust port, and a ventilation passage is formed where cooling air entering from the suction port passes around and/or between the plurality of cells and is exhausted from the exhaust port. 
     The battery pack may be placed on a floor, a shelf, or the like in a state in which it is detached from a charger or a power tool. In such a case, a foreign substance may enter from the suction port or the exhaust port. The arrangement described in PTL 1 takes no measure to prevent entry of the foreign substance. 
     Therefore, the present invention has as its object to provide a battery module advantageous in reducing entry of foreign substances to the inside with a simple arrangement. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a battery module comprising: a cell assembly formed by sandwiching a plurality of battery cells by a pair of holding members; and an accommodation case configured to accommodate the cell assembly, wherein the accommodation case includes a vent hole for gas, and wherein a flow path passing through the vent hole is formed in a labyrinth structure by covering the vent hole by a connecting portion between the pair of holding members. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing an arrangement example of a working machine; 
         FIG. 2  is an external view (top perspective view) of a battery module; 
         FIG. 3  is an external view (top view) of the battery module; 
         FIG. 4  is an external view (bottom perspective view) of the battery module; 
         FIG. 5  is an external view (bottom view) of the battery module; 
         FIG. 6  is an exploded view of the battery module; 
         FIG. 7  is a view of a lower member of an accommodation case when viewed from above (a state in which cell assemblies are not accommodated); 
         FIG. 8  is a view of the lower member of the accommodation case when viewed from above (a state in which the cell assemblies are accommodated); 
         FIG. 9  is an enlarged view of a region R 1  in  FIG. 8 ; 
         FIG. 10  is a view showing the flow of a gas in the accommodation case; 
         FIG. 11  is a view showing the cell assembly and the lower member of the accommodation case; 
         FIG. 12  is a sectional view of the battery module in an intermediate position between a first holding member and a second holding member; and 
         FIG. 13  is a view of an upper member of the accommodation case when viewed from inside. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments are not intended to limit the scope of the claimed invention, and limitation is not made an invention that requires all combinations of features described in the embodiments. Two or more of the multiple features described in the embodiments may be combined as appropriate. Furthermore, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted. 
     First Embodiment 
     A working machine  1  of the first embodiment according to the present invention will be described.  FIG. 1  is a schematic view showing an arrangement example of the working machine  1 . The working machine  1  of this embodiment is a working machine (electric working machine) including an electric power unit  10  that includes a battery module  100  and a motor device  11 . Examples of the working machine  1  include a plate compactor, a rammer, a lawn mower, a cultivator, and a snow remover, and  FIG. 1  illustrates a plate compactor. The working machine  1  includes, for example, the electric power unit  10 , a working unit  20  (working mechanism), a power transmission mechanism  30 , and a steering handle  40 . The working unit  20  is a unit for performing predetermined work, and in this embodiment, it is a unit that performs rolling compaction work to compact the ground. 
     The electric power unit  10  includes, for example, the battery module  100  and the motor device  11 . The battery module  100  is a storage battery including a plurality of battery cells, and can be configured to be attachable/detachable to/from the motor device  11 . The specific arrangement of the battery module  100  will be described later. The motor device  11  can include a motor  11   a  that is operated by electric power from the battery module  100 , and a control unit (not shown) that controls driving of the motor. The control unit can be a PDU (Power Drive Unit), but may be configured to include a processor represented by a CPU, a storage device such as a semiconductor memory, an interface with an external device, and the like. 
     The motor device  11  is provided with a cooling fan  11   b  as an exhaust unit for exhausting the gas in an accommodation case  120  from exhaust holes formed in the accommodation case  120  of the battery module  100 . The cooling fan  11   b  may also be used for cooling the motor  11   a,  or may be provided separately from a component for cooling the motor  11   a.  In this embodiment, the cooling fan  11   b  is rotatably attached to the shaft member of the motor  11   a,  and configured to rotate together with the shaft member of the motor  11   a,  thereby drawing the gas in the accommodation case  120  of the battery module  100  and exhausting the gas in the accommodation case  120  from the exhaust holes. 
     Next, the arrangement of the battery module  100  of this embodiment will be described. Each of  FIGS. 2 to 5  is an external view of the battery module  100 .  FIG. 2  shows a top perspective view of the battery module  100 ,  FIG. 3  shows a top view of the battery module  100 ,  FIG. 4  shows a bottom perspective view of the battery module  100 , and  FIG. 5  shows a bottom view of the battery module  100 .  FIG. 6  is an exploded view of the battery module  100 . 
     As shown in  FIG. 6 , the battery module  100  can include, for example, cell assemblies  110  ( 110   a,    110   b ) each including a plurality of cylindrical battery cells  111 , the accommodation case  120  for accommodating the cell assemblies  110 , a circuit board  131  on which a control circuit for controlling charge/discharge of the plurality of battery cells  111  is formed, and a connector  132  as an external interface. The circuit board  131  is arranged on the cell assemblies  110 , and is electrically connected to the cell assemblies  110  (the plurality of battery cells  111 ) and the connector  132  via a cable  133 . The connector  132  is arranged in a connector housing  124  provided in the accommodation case  120 . 
     As shown in  FIG. 6 , each cell assembly  110  includes the plurality of battery cells  111  arrayed with the cell axes directed in one direction, and a holding portion  112  that holds the plurality of battery cells  111 .  FIG. 6  shows an arrangement example of the battery module  100  in which a plurality (two) of cell assemblies  110   a  and  110   b  having the same shape are symmetrically accommodated in the accommodation case  120 .  FIG. 6  shows the left cell assembly  110   a  in a state in which the plurality of battery cells  111  are held by the holding portion  112 , and the right cell assembly  110   b  in a state before the plurality of battery cells  111  are held by the holding portion  112 . 
     Each of the plurality of battery cells  111  has a columnar (cylindrical) shape, and the plurality of battery cells  111  are arrayed in a plurality of rows (ten rows) in the X direction and a plurality of stages (four stages) in the Z direction (second direction) while each cell axis (column axis) is directed in the Y direction (first direction). In this embodiment, the direction in which the cell axis of each battery cell  111  is directed is the Y direction (horizontal direction), but it is not limited to the Y direction (horizontal direction) as long as the cell axes of the respective battery cells  111  are directed in the same direction. Note that in the following description, the direction in which the cell axes of the plurality of battery cells  111  are directed may be referred to as the “first direction”. 
     The holding portion  112  includes a pair of members (a first holding member  112   a  and a second holding member  112   b ) formed with a plurality of insertion ports  113  into which the plurality of battery cells  111  are respectively inserted. The first holding member  112   a  is located on the outer side of the holding portion  112  in the first direction (Y direction) (on the side of a peripheral space  142  to be described later), and the second holding member  112   b  is located on the inner side of the holding portion  112  in the first direction (on the side of the other cell assembly  110 ). In the first direction (Y direction) in which the cell axis of each battery cell  111  is directed, the first holding member  112   a  and the second holding member  112   b  sandwich the plurality of battery cells  111  such that each battery cell  111  is inserted into each insertion port  113 , and in this state, the first holding member  112   a  and the second holding member  112   b  are fixed to each other using fixing members such as screws. Thus, the holding portion  112  can hold the plurality of battery cells  111 . 
     The accommodation case  120  is configured to include two surfaces (for example, an upper surface and a lower surface) that sandwich the cell assemblies  110  in a direction different from the first direction (Y direction) in which the cell axis of each battery cell  111  is directed, more specifically, in the second direction (Z direction) which is a direction perpendicular to the first direction. In this embodiment, as shown in  FIGS. 2 to 6 , the accommodation case  120  includes an upper member  121  including the upper surface and a lower member  122  including the lower surface. A handle member  123  is attached to an upper portion of the upper member  121  using fixing members such as screws. For example, as shown in  FIG. 6 , screw holes  121   g  for attaching the handle member  123  are provided in the upper member  121 . The plurality of cell assemblies  110  are inserted inside the lower member  122  and fixed thereto using fixing members such as screws. Then, the upper member  121  and the lower member  122  are stacked on each other and fixed to each other using fixing members such as screws. For example, as shown in  FIGS. 4 and 5 , screw holes  122   e  for fixing the plurality of cell assemblies  110  are provided in the lower member  122 . 
     The handle member  123  (grip member) that is gripped by a user when carrying the battery module  100  is attached to the upper portion of the upper member  121 . In this embodiment, a partial region  121   a  in the upper portion of the upper member  121  is formed in a recess shape when viewed from the outside of the accommodation case  120 . The handle member  123  is configured to cover a part (a partial region  121   a - 1 ) of the recess region  121   a  in the upper member  121 , and is attached to the outer edge of the partial region  121   a - 1  by fixing members such as screws. Further, in order to drain water and the like having entered the inside of the accommodation case  120 , the recess region  121   a  covered by the handle member  123  is provided with communication holes  121   b  that allow fluid to communicate between the outside and the inside of the accommodation case  120 . The specific arrangement of the communication hole  121   b  will be described later in the second embodiment. 
     As shown in  FIGS. 4 and 5 , suction holes  125  for taking a gas (air) for cooling the plurality of battery cells  111  into the accommodation case  120  and exhaust holes  126  for exhausting the gas having passed between the plurality of battery cells  111  are provided, as vent holes for gas, in the lower member  122  (the lower surface of the accommodation case  120 ). Since such the suction holes  125  and exhaust holes  126  are provided in the lower member  122 , when the battery module  100  is attached to the motor device  11 , the cooling fan  11   b  of the motor device  11  can draw the gas in the accommodation case  120  from the exhaust holes  126  of the accommodation case  120  so that the gas can be circulated in the accommodation case  120 . Here, both the suction holes  125  and the exhaust holes  126  may be provided in the upper surface (upper member  121 ) of the accommodation case  120 , but it is preferable to provide them in the lower surface (lower member  122 ) of the accommodation case  120  in terms of preventing rain and the like from entering the inside of the accommodation case  120 . 
     Each of  FIGS. 7 and 8  is a view of the lower member  122  of the accommodation case  120  when viewed from above (+Z direction).  FIG. 7  is a view of the lower member  122  when viewed from above in a state in which the cell assemblies  110   a  and  110   b  are not accommodated.  FIG. 8  is a view of the lower member  122  when viewed from above in a state in which the cell assemblies  110   a  and  110   b  are accommodated.  FIG. 9  is an enlarged view of a region R 1  in  FIG. 8  when viewed from obliquely above as indicated by an arrow B. 
     The accommodation case  120  is configured to include an accommodation space  141  in which the cell assembly  110  is to be accommodated (arranged), and the peripheral space  142  located on the side of the cell assembly  110  in the first direction (Y direction). The suction holes  125  are provided in a surface included in the lower surface of the accommodation case  120  and defining the peripheral space  142 , and the exhaust holes  126  are provided in a surface included in the lower surface of the accommodation case  120  and defining the accommodation space  141 . More specifically, the lower surface of the accommodation case  120  (lower member  122 ) can include a mounting surface  122   a,  as the surface defining the accommodation space  141 , on which the cell assembly  110  is mounted, and an inclined surface  122   b,  as the surface defining the peripheral space  142 , which is inclined with respect to the mounting surface  122   a  on the side of the mounting surface  122   a  in the first direction. A plurality of the exhaust holes  126  arrayed along the X direction are provided in the mounting surface  122   a,  and a plurality of the suction holes  125  arrayed along the X direction are provided in the inclined surface  122   b.    
     Further, as shown in  FIGS. 6 to 9 , the accommodation case  120  includes, in the peripheral space  142 , a plurality of ribs  127  each extending in the second direction (Z direction) which is the array direction (stacking direction) of the plurality of battery cells  111 . The plurality of ribs  127  can be provided to reinforce the accommodation case  120 , but in this embodiment, they are arranged as baffle plates for guiding the gas taken into the peripheral space  142  from the suction holes  125  to the second direction (Z direction). For example, each of the plurality of ribs  127  is connected to a side surface  122   c,  that connects the upper surface and the lower surface of the accommodation case  120 , and the lower surface (inclined surface  122   b ) of the accommodation case  120 , and has a plate shape parallel to the first direction (Y direction) and the second direction (Z direction). Further, the plurality of ribs  127  are provided so as to be spaced apart from each other along the X direction such that at least one suction hole  125  is arranged therebetween. 
     By arranging the plurality of ribs  127  as baffle plates as described above, the gas taken into the peripheral space  142  from the plurality of suction holes  125  can be efficiently guided to the second direction, so that the plurality of battery cells  111  in the cell assembly  110  can be efficiently cooled. In addition, since the number of parts of the battery module  100  is reduced by making the plurality of ribs  127  function as the baffle plates, the device arrangement can be simplified and the device cost can be decreased. 
     Next, the flow of the gas in the accommodation case  120  will be described.  FIG. 10  is a perspective view of the Y-Z section (the section taken along A-A in  FIGS. 3 and 5 ) of the battery module  100 . In  FIG. 10 , the flow of the gas is indicated by arrows, and the size of the arrow represents the flow rate of the gas. Note that in the actual battery module  100 , the circuit board  131  is arranged on the cell assemblies  110   a  and  110   b  as described above, but the circuit board  131  is not shown in  FIG. 10  for clarity.  FIG. 11  is a view showing a state in which the cell assembly  110  ( 110   a ) is separated from the lower member  122  of the accommodation case  120  when viewed from obliquely below on the peripheral space  142  side. 
     The gas taken into the peripheral space  142  from the plurality of suction holes  125  is guided to the second direction (+Z direction) toward the upper surface by the plurality of ribs  127  serving as the baffle plates. The gas guided by the plurality of ribs  127  in the peripheral space  142  is guided to gaps between the plurality of battery cells  111  (into the accommodation space  141 ) via a plurality of openings  114  formed in the first holding member  112   a  of the cell assembly  110 , and exhausted from the plurality of exhaust holes  126 . In this manner, in the battery module  100  of this embodiment, the suction holes  125  and the exhaust holes  126  are provided in the lower surface of the accommodation case  120  and airflows in opposite directions are generated in the accommodation space  141  and the peripheral space  142 . Thus, the plurality of battery cells  111  arrayed in the accommodation space  141  can be efficiently cooled. 
     In this embodiment, as shown in  FIGS. 6 and 11 , the plurality of openings  114  formed in the first holding member  112   a  include a plurality of first openings  114   a  and a plurality of second openings  114   b.  The plurality of first openings  114   a  can be provided on the downstream side of the gas in the peripheral space  142 , specifically, above the plurality of battery cells  111  (the plurality of insertion holes  113 ), more specifically, above the top battery cells  111 . Further, the plurality of second openings  114   b  can be provided on the upstream side of the gas in the peripheral space  142 , specifically, between the plurality of battery cells  111 . Note that each of the plurality of second openings  114   b  is formed smaller than each of the plurality of first openings  114   a.  By providing the plurality of first openings  114   a  and the plurality of second openings  114   b  in the first holding member  112   a  as described above, the plurality of battery cells  111  can be efficiently cooled. Here, in each of the cell assemblies  110   a  and  110   b,  the plurality of openings  114  (the first openings  114   a  and the second openings  114   b ) may be formed in the second holding member  112   b  arranged on the inner side in the battery module  100 , as in the first holding member  112   a.  In this case, as shown in  FIG. 10 , it is also possible to guide the gas to a gap between the plurality of cell assemblies  110   a  and  110   b  (between a plurality of the accommodation spaces  141 ) via the first openings  114   a  of the second holding member  112   b,  and further guide the gas from the second openings  114   b  of the second holding member  112   b  to gaps between the plurality of battery cells  111 . This can further improve the cooling efficiency of the battery cells  111  of the plurality of cell assemblies  110   a  and  110   b.    
     The battery module  100  configured as described above may be placed on a floor, a shelf, or the like in a state in which it is detached from the working machine  1  (motor device  11 ), that is, stand alone. In this case, if a foreign substance (for example, a wire or a screw) on the floor or shelf enters from the vent hole (suction hole  125  or exhaust hole  126 ) of the accommodation case  120 , the battery cell  111  in the accommodation case  120  can be damaged. Therefore, the battery module  100  of this embodiment takes measures to reduce entry of foreign substances from the suction holes  125  and the exhaust holes  126  formed in the accommodation case  120 . 
     As a specific arrangement, guard members  128  for reducing entry of foreign substances from the suction holes  125  are provided in the accommodation case  120 . As shown in  FIG. 9 , each guard member  128  extends in the longitudinal direction of the suction hole  125  and is provided inside the accommodation case  120  with respect to the suction hole  125 . That is, the guard member  128  is a member that covers the suction hole  125  so as not to block the suction hole  125  in the inside of the accommodation case  120 . By providing the guard member  128  to the suction hole  125  in this manner, the flow path that passes through the suction hole  125  can be formed in a labyrinth structure, so that it is possible to reduce entry of foreign substances such as wires into the accommodation case  120  from the suction hole  125 . 
     Similar to the suction hole  125 , a guard member  129  for the exhaust hole  126  is provided in the accommodation case  120  so that a labyrinth structure can be formed. However, some exhaust holes  126   a  are not provided with the guide members  129 , and a connecting portion  112   c  between the first holding member  112   a  and the second holding member  112   b  in the cell assembly  110  has the role (function) of the guard member  129 . With this arrangement, the battery module  100  (accommodation case  120 ) can be simplified and miniaturized. That is, as shown in  FIGS. 11 and 12 , the plurality of exhaust holes  126  include the exhaust holes  126   a  each of which is covered by the connecting portion  112   c  between the first holding member  112   a  and the second holding member  112   b  so as not to block the exhaust holes  126   a  in the inside of the accommodation case  120  so that the flow path is formed in the labyrinth structure. 
     Here, the connecting portion  112   c  is a member provided in at least one of the first holding member  112   a  and the second holding member  112   b  and used to connect them. The connecting portion  112   c  can be configured to include, for example, a screw hole or the like so that a fixing member (such as a screw) for fixing the first holding member  112   a  and the second holding member  112   b  to each other can be inserted. Further, the connecting portions  112   c  can be provided at several positions in the upper portion and the lower portion of the holding portion  112  so that, for example, the gas having passed between the plurality of battery cells  111  can be efficiently exhausted from the exhaust holes  126  of the accommodation case  120 . In this embodiment, the connecting portions  112   c  are provided at three positions in each of the upper end and the lower end of the holding portion  112 . 
       FIG. 12  is a Z-X sectional view (a sectional view taken along a line C-C in  FIGS. 3 and 5 ) of the battery module  100 , that is, a Z-X sectional view of the cell assembly  110   a  at an intermediate position between the first holding member  112   a  and the second holding member  112   b.    FIG. 12  also shows an enlarged view of the lower portion (a region R 2 ) of the battery module  100 . 
     As shown in  FIG. 12 , the exhaust hole  126  above which no connecting portion  112   c  of the holding portion  112  is arranged is provided with the guard member  129  inside the accommodation case  120 , so that the flow path passing through the exhaust hole  126  is formed in the labyrinth structure. On the other hand, the exhaust hole  126   a  above which the connecting portion  112   c  is arranged is provided with no guard member  129  but covered by the connecting portion  112   c,  so that the flow path passing through the exhaust hole  126   a  is formed in the labyrinth structure. With this arrangement, it can be avoided that the guard member  129  and the connecting portion  112   c  are overlapped with each other above the exhaust hole  126   a,  so that the battery module  100  (accommodation case  120 ) can be simplified and miniaturized. Consequently, this leads to a decrease in device cost such as a reduction in material cost. 
     In this embodiment, the connecting portion  112   c  is preferably configured to have a planar shape  112   e  in which the surface on the exhaust hole  126   a  side has a larger area than the exhaust hole  126   a.  This can improve the function of preventing a foreign substance from entering through the exhaust hole  126   a  by the connecting portion  112   c.  In addition, the connecting portion  112   c  is preferably configured to cover a plurality of the exhaust holes  126   a,  that is, to be arranged above the plurality of the exhaust holes  126   a.  In the example shown in  FIG. 12 , one connecting portion  112   c  is configured to cover two exhaust holes  126   a  adjacent to each other. This can further simplify the battery module  100 . Further, as shown in the enlarged view in  FIG. 12 , the connecting portion  112   c  is preferably configured to include, at a position facing a portion between the plurality of the exhaust holes  126   a  in the accommodation case  120 , a convex portion  112   d  protruding toward the portion. With this arrangement, it is possible to bring the connecting portion  112   c  closer to the exhaust hole  126   a,  and restrict the entry path of foreign substances from the exhaust hole  126   a.  For example, in the example shown in the enlarged view in  FIG. 12 , the entry path of foreign substances from the exhaust hole  126   a  is restricted to one of the +X direction and the −X direction, so that the effect of reducing entry of foreign substances can be improved. 
     As has been described above, in the battery module  100  of this embodiment, the flow path passing through the vent hole (exhaust hole  126   a ) of the accommodation case  120  is formed in the labyrinth structure by covering the vent hole by the connecting portion  112   c  of the holding portion  112 . With this arrangement, the battery module  100  (accommodation case  120 ) can be simplified, and a decrease in device cost such as a reduction in material cost can be implemented. 
     Second Embodiment 
     The battery module  100  described above may be placed on a floor, a shelf, or the like by a user in an arbitrary posture or orientation in a state in which it is detached from the working machine  1  (motor device  11 ) (that is, stand alone). For example, the battery module  100  may be placed such that the lower surface formed with the vent holes (suction holes  125  and exhaust holes  126 ) faces upward. In this case, if water enters from the vent hole, it is accumulated inside the accommodation case  120 . Therefore, in a battery module  100  of this embodiment, communication holes  121   b  for draining water having entered the inside of an accommodation case  120  are formed in an upper member  121  (a surface opposite to the surface formed with the vent holes) of the accommodation case  120 . Note that this embodiment basically takes over the arrangement of the battery module  100  of the first embodiment, unless otherwise specified. 
     The communication hole  121   b  is a hole that allows fluid to communicate between the inside and the outside of the accommodation case  120  and, as shown in  FIG. 6 , is provided in a recess partial region  121   a - 1  covered by a handle member  123  in the upper member  121  of the accommodation case  120 . More specifically, the communication hole  121   b  is provided in a side surface (inclined surface) of the recess partial region  121   a - 1 . By providing the communication hole  121   b  as described above, even when the battery module  100  is placed upside down (that is, such that the lower surface formed with the vent holes faces upward), water having entered the accommodation case  120  can be drained through the communication hole  121   b.  In addition, since the communication hole  121   b  is provided in the side surface (inclined surface  121   a - 2 ) of the recess partial region  121   a - 1 , when the battery module  100  is placed upside down (that is, such that the lower surface formed with the vent holes faces upward), the communication hole  121   b  is located lower as compared with a case in which the communication hole  121   b  is provided in the bottom surface of the recess partial region  121   a - 1 . Accordingly, it is possible to further suppress accumulation of water in the accommodation case  120 . Since the communication hole  121   b  is covered by the handle member  123 , it is possible to prevent rain and the like from entering the inside of the accommodation case  120  through the communication hole  121   b  in a normal posture. Note that the normal posture is the posture of the battery module  100  in which the lower surface provided with the vent holes is directed downward, such as a case in which it is attached to a motor device  11  or the like. 
     Further, in order to further prevent rain and the like from entering the inside of the accommodation case  120  from the communication hole  121   b  in the normal posture, the flow path passing through the communication hole  121   b  may be formed in a labyrinth structure. For example, as shown in  FIG. 10 , a protruding portion  121   c  protruding upward (+Z direction) is provided in a recess region  121   a  (more specifically, the partial region  121   a - 1 ) in the upper member  121 , and the communication hole  121   b  is formed in the center of the protruding portion  121   c.  Then, the handle member  123  is configured so as to cover the protruding portion  121   c  and such that a gap G between the handle member  123  and the upper member  121  is formed lower than the distal end of the protruding portion  121   c.  That is, the flow path direction different from the flow path direction of the communication hole  121   b  is formed by the gap G, so that the flow path communicating from the communication hole  121   b  to the outside can be formed in the labyrinth structure. 
     As has been described above, the accommodation case  120  of this embodiment includes the communication holes  121   b  in the recess partial region  121   a - 1  covered by the handle member  123 . Thus, even if the battery module  100  is placed upside down and water enters the accommodation case  120 , the water can be drained through the communication holes  121   b.    
     Third Embodiment 
     In the third embodiment, an example will be described in which a communication hole  121   d  (second communication hole) for draining water from the inside of the accommodation case  120  is provided in a connector housing  124 .  FIG. 13  is a view of an upper member  121  of the accommodation case  120  when viewed from the inside (−Z direction side).  FIG. 13  also shows an enlarged perspective view of the connector housing  124  (a region R 3 ) in the upper member  121 . As shown in  FIG. 13 , the upper member  121  is provided with screw holes  121   h  for fixing it to a lower member  122  by fixing members (such as screws). Note that this embodiment basically takes over the arrangement of the battery module  100  of each of the first and second embodiments, unless otherwise specified. 
     The accommodation case  120  is configured to define (divide) a cell accommodation space (an accommodation space  141  and a peripheral space  142 ) in which a cell assembly  110  is to be accommodated and a terminal accommodation space (the internal space of the connector housing  124 ) in which a connector  132  (terminal) as an external interface that performs charge and discharge of the plurality of battery cells  111  is to be accommodated. The communication hole  121   d  for draining water from the inside of the accommodation case is formed in a partition wall  120   a  for partitioning the cell accommodation space and the terminal accommodation space, that is, a side wall between the cell accommodation space and the terminal accommodation space. In this embodiment, an opening  122   d  for allowing a cable  133  connected to the connector  132  to pass therethrough is formed in the lower member  122  of the accommodation case  120  as shown in  FIGS. 7 and 8 , and the communication hole  121   d  is formed in the upper member  121  of the accommodation case  120  as shown in  FIG. 13 . That is, the opening  122   d  for allowing the cable  133  to pass therethrough and the communication hole  121   d  are formed at positions spaced apart from each other in the partition wall  120   a.  With this arrangement, even when the battery module  100  is placed upside down (in a state in which the upper member  121  of the accommodation case  120  faces downward), water having entered the accommodation case  120  (for example, water that is easily accumulated outside a recess partial region  121   a - 1 ) can be efficiently drained from the accommodation case  120  via the communication hole  121   d.  In addition, by providing the communication hole  121   d  in the partition wall  120   a  so as to be narrower than the opening  122   d,  it is possible to achieve both rigidity and drainage of the accommodation case  120 . 
     Further, as shown in  FIG. 13 , the upper member  121  in the connector housing  124  is provided with ribs  121   e  for fixing the position of the connector  132  in the connector housing  124 . Each rib  121   e  is formed with a notch  121   f  for allowing water coming out of the cell accommodation space via the communication hole  121   d  to pass therethrough. With this arrangement, even when the battery module  100  is placed with the connector housing  124  facing downward, water having entered the accommodation case  120  can be drained from the accommodation case  120  via the flow path including the communication hole  121   d  and the notches  121   f.    
     SUMMARY OF EMBODIMENTS 
     1. The battery module according to the above-described embodiment comprises
         a cell assembly (for example,  110 ) formed by sandwiching a plurality of battery cells (for example,  111 ) by a pair of holding members (for example,  112   a,    112   b ), and   an accommodation case (for example,  120 ) configured to accommodate the cell assembly,   wherein the accommodation case includes a vent hole (for example,  126   a ) for gas, and   a flow path passing through the vent hole is formed in a labyrinth structure by covering the vent hole by a connecting portion (for example,  112   c ) between the pair of holding members.       

     According to this arrangement, it is possible to reduce entry of foreign substances (wires) from the vent hole of the battery module with a simple structure. 
     2. In the battery module according to the above-described embodiment,
         a surface of the connecting portion on a side of the vent hole has a planar shape having a larger area than the vent hole.       

     According to this arrangement, the connecting portion between the two holding members can cover the entire vent hole, so that it is possible to further reduce entry of foreign substances from the vent hole. 
     3. In the battery module according to the above-described embodiment,
         the connecting portion is configured to cover a plurality of the vent holes, and includes, at a position facing a portion between the plurality of the vent holes in the accommodation case, a convex portion (for example,  112   d ) protruding toward the portion.       

     According to this arrangement, the entry path of foreign substances from the vent hole is restricted, so that the effect of reducing entry of foreign substances can be improved. 
     4. The battery module according to the above-described embodiment comprises
         a cell assembly (for example,  110 ) formed by sandwiching a plurality of battery cells (for example,  111 ) by a pair of holding members (for example,  112   a,    112   b ),   an accommodation case (for example,  120 ) configured to accommodate the cell assembly, and   a grip member (for example,  123 ) provided so as to cover a partial region (for example,  121   a - 1 ) of the accommodation case from the outside,   wherein the accommodation case includes a communication hole (for example,  121   b ) for fluid in the partial region covered by the grip member.       

     According to this arrangement, even if the battery module is placed upside down and water enters the accommodation case, the water can be drained through the communication hole. In addition, since the communication hole is covered by the grip member, it is possible to reduce entry of rain and the like from the communication hole during normal use. 
     5. In the battery module according to the above-described embodiment,
         the partial region covered by the grip member is formed in a recess shape when viewed from the outside of the accommodation case, and   the communication hole is provided in a side surface of the partial region formed in the recess shape.       

     According to this arrangement, when the battery module is placed upside down, it is possible to efficiently drain water that is easily accumulated outside the recess partial region in the accommodation case. 
     6. In the battery module according to the above-described embodiment,
         the side surface of the partial region in which the communication hole is provided is an inclined surface inclined with respect to a bottom surface of the partial region.       

     According to this arrangement, when the battery module is placed upside down, the communication hole is located lower as compared with a case in which the communication hole is provided in the bottom surface of the recess partial region. Accordingly, it is possible to further suppress accumulation of water in the accommodation case. 
     7. In the battery module according to the above-described embodiment,
         a flow path passing through the communication hole is formed in a labyrinth structure by the grip member.       

     According to this arrangement, it is possible to further reduce entry of rain and the like from the communication hole. 
     8. In the battery module according to the above-described embodiment,
         the accommodation case is configured to include a cell accommodation space in which the cell assembly is accommodated and a terminal accommodation space in which a terminal (for example,  132 ) configured to perform charge and discharge of the plurality of battery cells is accommodated, and   in the accommodation case, a second communication hole (for example,  121   d ) that communicates between the cell accommodation space and the terminal accommodation space is provided in a partition wall (for example,  120   a ) configured to partition the cell accommodation space and the terminal accommodation space.       

     According to this arrangement, water having entered the accommodation case can be drained through the second communication hole. In addition, since the second communication hole is provided in the partition wall between the cell accommodation space and the terminal accommodation space, it is possible to reduce entry of rain and the like from the second communication hole during normal use. 
     9. In the battery module according to the above-described embodiment,
         the terminal is electrically connected to the plurality of battery cells via a cable (for example,  133 ), and   the second communication hole is provided, in the partition wall, at a position spaced apart from an opening (for example,  122   d ) through which the cable passes.       

     According to this arrangement, water having entered the accommodation case can be efficiently drained through the second communication hole. 
     10. In the battery module according to the above-described embodiment,
         the accommodation case is formed by a pair of members (for example,  121 ,  122 ) separable in a direction different from an array direction of the cell accommodation space and the terminal accommodation space,   the second communication hole is formed in one of the pair of members, and   the opening through which the cable passes is formed in the other one of the pair of members.       

     According to this arrangement, the opening through which the cable passes and the second communication hole are formed in different members, so that it is possible to reduce the influence, on the terminal and the cable, of water drained from the cell accommodation space to the terminal accommodation space via the second communication hole, and the accommodation case can be manufactured more easily. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.