Patent Publication Number: US-2010112424-A1

Title: Battery pack structure

Description:
TECHNICAL FIELD 
     The present invention generally relates to a battery pack structure, and particularly to a battery pack structure that is mounted on a vehicle as a drive power source and is formed of a lithium-ion battery. 
     BACKGROUND ART 
     In connection with a conventional battery pack structure, for example, Japanese Patent Laying-Open No. 9-120808 has disclosed an alkaline storage battery of a stacked sealed type that aims to achieve a reduced weight and high productivity as well as a stable and enhanced fastening strength, to prevent deformation of each cell in use and to suppress lowering of performance (Patent Document 1). In the patent document 1, end plates are arranged on opposite ends of the stacked cells, respectively. The vertical walls of the end plates are fastened and fixed together by a plurality of binding bands each having a belt-like form. The binding band is made of a stainless steel plate. 
     Japanese Patent Laying-Open No. 2006-24445 has disclosed a battery assembly aiming at long life and increased safety (Patent Document 2). The battery assembly disclosed in the patent document 2 includes a plurality of battery boxes, restraint plates arranged on the opposite ends of the plurality of battery boxes, and a restraint rod restraining the plurality of battery boxes to prevent increase in distance between the restraint plates. The restraint plates are screwed to a lower casing accommodating the battery assembly. 
     Japanese Patent Laying-Open No. 2002-343324 has disclosed a battery restraint structure aiming to facilitate an operation for restraining the battery (Patent Document 3). In the patent document 3, a plurality of batteries are integrally restrained to form an onboard battery pack for a vehicle. The battery is, e.g., a nickel hydrogen battery. 
     In the battery pack structure disclosed in the above patent document 1, the binding bands that generate a fastening force in a stacking direction of the cells integrally hold the plurality of cells to form a module storage battery. When this module storage battery is accommodated in a casing body to form a battery pack, it is required to fix firmly the storage battery to the casing body. For this, it may be envisaged to couple the storage battery and the casing body together using independent parts such as brackets. However, this results in a problem that the parts of the battery pack increase in number. 
     DISCLOSURE OF THE INVENTION 
     An object of the invention is to overcome the above problem, and particularly to provide a battery pack structure in which a battery is fixed to a casing body while suppressing increase in number of parts. 
     A battery pack structure includes a battery including a plurality of stacked battery cells; a casing body accommodating the battery; and a restraint member generating a fastening force in a direction of stacking of the battery cells to hold integrally the plurality of battery cells. The restraint member is fixed to the casing body. 
     In the battery pack structure thus configured, the restraint member integrally holding the plurality of battery cells is used as a member fixing the battery to the casing body. Thereby, the battery can be fixed to the casing body while suppressing increase in number of parts. 
     Preferably, the restraint member is made of metal. In the battery pack structure thus configured, the battery can be fixed to the casing body more firmly. 
     Preferably, the casing body and the restraint member are made of an electrically conductive material. The casing body is electrically grounded. In the battery pack structure thus configured, an electrolyte may leak from the battery to short-circuit the restraint member to the battery. Even in this case, an electric shock can be prevented because the restraint member is fixed to the electrically grounded casing body. 
     Preferably, the casing body includes a lower casing carrying the battery, and an upper casing combined with the lower casing to cover the battery. The restraint member is fixed to the lower casing. In the battery pack structure thus configured, the restraint member can be fixed to the lower casing with the battery laid on the lower casing in a battery assembling step. Therefore, it is possible to improve workability in the battery assembling process. 
     Preferably, the battery is formed of a lithium-ion battery. In the battery pack structure thus configured, the foregoing effect(s) described above can be achieved in the battery pack internally having the lithium-ion battery. 
     As described above, the invention can provide the battery pack structure that fixes the battery to the casing body while suppressing increase in number of parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of an assembly of a battery pack employing a battery pack structure of an embodiment of the invention. 
         FIG. 2  is a cross section of the battery pack taken along line II-II in  FIG. 1 . 
         FIG. 3  is a cross section of the battery pack taken along line III-III in  FIG. 1 . 
         FIG. 4  is a cross section showing a modification of the battery pack structure in  FIG. 1 . 
     
    
    
     BEST MODES FOR CARRYING OUT THE INVENTION 
     Embodiments of the invention will now be described with reference to the drawings. In the following description, the same or corresponding portions bear the same reference numbers. 
       FIG. 1  is an exploded view of an assembly of a battery pack employing a battery pack structure of an embodiment of the invention.  FIG. 2  is a cross section of the battery pack taken along line II-II in  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , a battery pack  10  is mounted on a hybrid vehicle that employs, as drive power sources, an internal combustion engine such as a gasoline or Diesel engine and a chargeable battery (secondary battery). Battery pack  10  is mounted in an appropriate position on the vehicle and, for example, is mounted in a vehicle compartment such as a space under a seat or in a console box, or in a luggage room. 
     Battery pack  10  includes a battery  20 , which is a lithium-ion battery. Battery  20  may be any chargeable secondary battery and, for example, may be a nickel hydrogen battery. 
     Battery  20  includes a plurality of battery cells  21 , which are stacked in a direction that is indicated by an arrow  101  in  FIG. 1  and will be referred to as a “stacking direction” of battery cells  21  hereinafter. In this embodiment, battery sets each formed of battery cells  21   m  and  21   n  that are arranged in parallel are stacked in the direction indicated by arrow  101 . Battery  20  is a square-shaped battery. Battery  20  has a weight of 10 kg or more. Battery  20  has substantially a rectangular parallelepiped form. In a plan view, battery  20  has long and short sides. The direction of the long side matches the stacking direction of battery cells  21 . 
     Battery cells  21  include positive and negative terminals  26  and  27 . The plurality of battery cells  21  are stacked such that positive terminal  26  of each battery cell  21  is aligned to a negative terminal  27  of neighboring battery cell  21 . Positive terminal  26  of each battery cell  21  is connected to negative terminal  27  of neighboring battery cell  21  by a bus bar. The plurality of battery cells  21  are electrically connected together in series. 
     Each battery cell  21  is pinched by a battery holder  34 , which is made of a resin material such as polypropylene or polymer of polypropylene. Battery holder  34  forms a cooling air passage  23  between battery cells  21  neighboring together in the stacking direction. Battery  20  heated by the charging/discharging is cooled by cooling air passing through cooling air passage  23 . Battery holder  34  forms a discharge gas passage  39  that externally discharges a gas generated in battery cell  21 . 
       FIG. 3  is a cross section of the battery pack taken along line III-III in  FIG. 1 . Referring to  FIGS. 1 to 3 , end plates  40  and  41  are arranged on the opposite sides of the stacked battery cells  21 , respectively. The plurality of battery cells  21  are held between end plates  40  and  41 , which are made of a resin material such as polypropylene or polymer of polypropylene. 
     Battery pack  10  includes restraint bands  50  as restraint members. The plurality of restraint bands  50  are employed. Each restraint band  50  is made of metal. Restraint band  50  is made of an electrically conductive material. Restraint band  50  is made of, e.g., a steel plate. Restraint bands  50  have a strength larger than battery holder  34  and end plates  40  and  41 . Restraint band  50  has a belt-like form. Restraint band  50  has a substantially rectangular section. Restraint band  50  may have another section, e.g., of a circular form or a polygonal form other than the rectangular form. 
     Restraint band  50  generates a fastening force in the stacking direction of battery cells  21 . Restraint band  50  extends in the stacking direction of battery cells  21 , and goes around battery  20 . Restraint band  50  pushes end plates  40  and  41  to reduce a distance between them. According to this structure, restraint band  50  integrally holds the plurality of stacked battery cells  21  together. 
     Restraint band  50  includes an upper restraint band  51  as a first restraint band and a lower restraint band  56  as a second restraint band. Upper restraint band  51  extends from a top end of battery  20  to side surfaces thereof. Lower restraint band  56  extends from the bottom surface of battery  20  to side surfaces thereof. Upper and lower restraint bands  51  and  56  partially overlap together on the side surfaces of battery  20 . Upper and lower restraint bands  51  and  56  are coupled together by pin members  58  on the side surfaces of battery  20 . 
     Restraint band  50  may take another form and, for example, may be formed of only upper restraint band  51 . In this case, upper restraint band  51  is coupled to end plates  40  and  41  so that the fastening force can be generated in the stacking direction of battery cells  21 . 
     Battery pack  10  includes a battery casing  31 . Battery  20  is accommodated in battery casing  31 . Battery casing  31  forms an outer shell of battery pack  10 . Battery casing  31  is made of metal. Battery casing  31  is made of an electrically conductive material. For ensuring a strength, battery casing  31  is made of, e.g., a galvanized steel plate. Battery casing  31  is fixed to a vehicle body. Battery casing  31  is electrically grounded. 
     Battery casing  31  includes upper and lower casings  32  and  33 . Lower casing  33  includes a carrying surface  33   c . Battery  20  is laid on carrying surface  33   c . In other words, lower casing  33  bears a weight of battery  20 . Carrying surface  33   c  is provided with stud bolts  35  and  36 . Upper casing  32  is combined with lower casing  33  to cover battery  20 . Lower casing  33  is arranged vertically under battery  20 , and upper casing  32  is arranged vertically above battery  20 . 
     Restraint band  50  is fixed to battery casing  31 . More specifically, upper restraint band  51  is fixed to lower casing  33 . Upper restraint band  51  includes flanges  52 . Flange  52  is opposed to carrying surface  33   c  and is parallel to it. Flange  52  is formed by bending the end of upper restraint band  51  into an L-shaped form. Flange  52  is provided with a hole  51   h . Stud bolt  36  is inserted into hole  51   h . A nut  54  is engaged with stud bolt  36  to fix battery  20  to battery casing  31 . The ends of upper restraint band  51  is fixed to battery casing  31 . 
     In this embodiment, battery holder  34  is fixed to battery casing  31 . More specifically, battery holder  34  is fixed to lower casing  33 . Battery holder  34  includes flanges  37 . Flange  37  is opposed to carrying surface  33   c  and is parallel to it. Flange  37  is provided with a hole  37   h . Stud bolt  35  is fitted into hole  37   h . A nut  53  is engaged with stud bolt  35  to fix battery  20  to battery casing  31 . 
     Restraint bands  50  and battery holder  34  fix the four sides, in a plan view, of battery  20  to battery casing  31 . Restraint band  50  fixes the short sides, in the plan view, of battery  20  to battery casing  31 . Battery holder  34  fixes the long sides, in the plan view, of battery  20  to battery casing  31 . Restraint band  50  fixes the opposite ends, in the stacking direction of battery cells  21 , of battery  20  to battery casing  31 . Battery holder  34  fixes the opposite ends, in the direction perpendicular to the stacking direction of battery cells  21 , of battery  20  to battery casing  31 . 
     Restraint band  50  is present as an electric conductor arranged near a high-pressure portion. In this case, an electrolyte may leak from battery  20  to restraint band  50  so that battery  20  may be short-circuited to restraint band  50 . In the embodiment, however, restraint band  50  is fixed to electrically grounded battery casing  31 . Also, battery casing  31  accommodates a battery monitor unit  71  together with battery  20 . Battery monitor unit  71  has a function of detecting electric leak of battery casing  31 . Accordingly, battery pack  10  of the embodiment can prevent an electric shock that may occur through restraint band  50 , and further can detects the short circuit between battery  20  and restraint band  50  in an early stage. 
     A battery pack structure according to the embodiment of the invention includes battery  20  including the plurality of stacked battery cells  21 , battery casing  31  serving as the casing body accommodating battery  20 , and restraint bands  50  that generate the fastening force in the stacking direction of battery cells  21  and serves as the restraint member integrally holding the plurality of battery cells  21 . Restraint band  50  is fixed to battery casing  31 . 
     Battery  20  is mounted on the hybrid vehicle that is the vehicle. Battery  20  is mounted on the hybrid vehicle as a drive power source. 
     The above battery pack structure according to the embodiment of the invention uses restraint band  50  as the means for fixing battery  20  to battery casing  31  so that it is not necessary to employ an additional member such as a bracket, and increase in number of the parts can be avoided. 
     For accommodating battery  20  in battery casing  31 , battery  20  must be fixed firmly to battery casing  31 . Particularly, when battery  20  is a lithium-ion battery, it is necessary to satisfy requirements that are determined in predetermined vibration test and impact test according to the laws and regulations about transportation. Since battery  20  to be mounted on the vehicle as the drive power source has a large weight, it is difficult to satisfy the above requirements. 
     According to the embodiment, however, restraint band  50  made of metal is fixed to battery casing  31 . Therefore, battery  20  can be fixed more firmly to battery casing  31 , as compared with the case where only battery holder  34  made of a resin material is fixed to battery casing  31 . 
     Then, a method of assembling battery pack  10  in  FIG. 1  will be described. First, the plurality of battery cells  21  are stacked, and end plates  40  and  41  are arranged on the opposite sides thereof, respectively. A pressure is applied in the stacking direction to the plurality of stacked battery cells  21 . Restraint bands  50  are arranged on battery  20  that is kept in the pressure-receiving state so that the plurality of battery cells  21  are integrated. The applied pressure is released to complete a stack assembly of battery  20 . Battery  20  is laid on carrying surface  33   c  of lower casing  33 . Restraint band  50  is fastened to lower casing  33  with nuts  53  and  54 . Upper casing  32  is fixed to lower casing  33 . Through the above steps, battery pack  10  in  FIG. 1  is completed. 
     In battery pack  10  of the embodiment, since restraint band  50  is fixed to lower casing  33 , the fastening operation can be performed with battery  20  laid on lower casing  33 . Therefore, it is possible to improve workability in the process of fixing battery  20  to battery casing  31 . 
       FIG. 4  is a cross section showing a modification of the battery pack structure in  FIG. 1 .  FIG. 1  shows, on an enlarged scale, a portion where restraint band  50  is fixed to battery casing  31 . 
     Referring to  FIG. 4 , lower restraint band  56  in this modification includes a flange  57 . Flange  57  overlaps with flange  52 . Flange  57  has a hole  56   h  communicating with hole  51   h . A pin member  58  couples flanges  52  and  57  together. Stud bold  36  is fitted into holes  51   h  and  56   h . By engaging nut  54  with stud bold  36 , battery  20  is fixed to battery casing  31 . 
     According to the above structure, the portions of flanges  52  and  57  overlapping together are fixed to battery casing  31  so that battery  20  can be fixed to battery casing  31  more firmly. 
     Although this embodiment employs the structure that uses both restraint band  50  and battery holder  34  for fixing battery  20  to battery casing  31 , a structure that uses only restraint band  50  may be employed. The form in which battery cells  21  are stacked is not restricted to that shown in  FIG. 1 , and battery  20  may be formed of battery cells  21  stacked, e.g., in one row. 
     The invention may be applied to a Fuel Cell Hybrid Vehicle (FCHB) using a fuel cell and a battery as drive power sources as well as an Electric Vehicle (EV). In the hybrid vehicle of the embodiment, the internal combustion engine operates in an operation point of optimum fuel consumption. In the fuel cell hybrid vehicle, the fuel cell operates in an operation point of optimum power generation efficiency. Both the types of hybrid vehicles use the batteries basically in the same manner. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by the terms of the appended claims. 
     INDUSTRIAL APPLICABILITY 
     The invention is used in the hybrid vehicle that uses the internal combustion engine and the battery as drive power sources, the fuel cell hybrid vehicle using the fuel cell and the battery as the drive power sources, and the electric vehicle.