Abstract:
A battery pack apparatus comprising a first cell bank and a laminated cooling plate. The first cell bank includes a first tray and at least one battery cell coupled to the tray. The laminated cooling plate being in contact with the first cell bank and including a plurality of face sheets and a plurality of internal sheets. The face sheets forming a fluid inlet and a fluid outlet. The plurality of internal sheets forming a plurality of fluid passages connecting the fluid inlet to the fluid outlet. The internal sheets further formed to include fluid pathways defining the fluid passages wherein none of the fluid pathways individually defining an uninterrupted flow path.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 61/482,908 filed May 5, 2011. The disclosure of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to battery packs for automotive vehicles. More particularly, the present disclosure relates to battery cooling apparatus using a fluid state medium to cool battery packs having at least one stacked array of rechargeable battery cells. 
         [0003]    Electric vehicles, including hybrid electric vehicles, have electric motors for propelling the vehicles along roadways, for example, and these electric motors typically rely upon onboard rechargeable batteries as their energy source. Battery packs having a fairly large number of individual rechargeable battery cells are frequently used with such vehicles. An example of a battery cell that is used in electric vehicles is a lithium ion battery cell. When recharging and when discharging to provide power to the electric motors of electric vehicles, the battery cells generate heat that needs to be removed in order to maintain the battery cells below their maximum allowable temperatures so that the battery cells are not damaged or destroyed by the heat. When removing heat from battery packs, it is desirable but not necessary to have the faces of each of the battery cells maintained at a fairly uniform temperature. 
         [0004]    It is known in the art that liquid-cooling provides significant convection coefficients and can be used to cool battery packs. However, some of these systems include dozens or hundreds of liquid-sealed connections. This proliferation of connections may add cost and risk of leakage to the liquid coolers for use with battery packs. Accordingly, there is a need for an improved liquid cooled battery pack apparatus. 
       SUMMARY 
       [0005]    A battery pack apparatus for an automotive vehicle is provided and comprises one or more of the features recited in the appended claims and/or the following features which, alone or in any combination, may comprise patentable subject matter: 
         [0006]    A laminate cooling plate having a top surface and a bottom surface may include a fluid inlet, a fluid outlet, and a plurality of internal sheets. The internal sheets may form a plurality of fluid passages between the top surface and the bottom surface. Each of the plurality of fluid passages may form an S-shaped circuit that connects the fluid inlet to the fluid outlet. The internal sheets may be formed to include fluid pathways cooperating to define the fluid passages. 
         [0007]    In some embodiments, some of the fluid pathways may individually define an uninterrupted flow path. Each of the plurality of fluid passages may independently connect the fluid inlet to the fluid outlet. 
         [0008]    In some embodiments, the plurality of fluid passages may interdigitally couple to the fluid inlet and the fluid outlet. The fluid inlet and the fluid outlet may be aligned so that the fluid outlet lies in a footprint of the fluid inlet when viewing the top surface of the laminate cooling plate. It is contemplated that the plurality of passages may be substantially the same length and each of the plurality of passages may have an equal number of turns. 
         [0009]    In some embodiments, each of the plurality of internal sheets may be formed to include a plurality of pathways. The plurality of pathways of each of the plurality of internal sheets may cooperate with the plurality of pathways of the other internal sheets to define the plurality of passageways. 
         [0010]    A battery pack apparatus may include a first cell bank and a laminated cooling plate. The first cell bank may include a first tray and at least one battery cell coupled to the tray. The laminated cooling plate may be in contact with the first cell bank and may include a plurality of face sheets forming a fluid inlet and a fluid outlet and a plurality of internal sheets forming a plurality of fluid passages connecting the fluid inlet to the fluid outlet. The internal sheets may be formed to include fluid pathways defining the fluid passages wherein none of the fluid pathways individually defining an uninterrupted flow path. 
         [0011]    In some embodiments, the fluid passages may provide an independent flow path between the fluid inlet and the fluid outlet. The plurality of face sheets may include a top face sheet formed to include an external inlet hole and a bottom face sheet formed to include an external outlet hole. It is contemplated that a substantially similar pressure drop may be produced along each of the plurality of fluid passages. 
         [0012]    The plurality of internal sheets may include a first internal sheet formed to include an internal inlet hole and a first plurality of fluid pathways extending through the first internal sheet. The plurality of internal sheets may include a second internal sheet formed to include a second plurality of fluid pathways extending through the second internal sheet. The plurality of internal sheets may include a third internal sheet formed to include an internal outlet hole and a third plurality of fluid pathways extending through the third internal sheet. 
         [0013]    A pattern of the second plurality of fluid pathways may be substantially similar to a pattern of the first plurality of internal pathways. The second internal sheet may be indexed with respect to the first internal sheet so that the second plurality of fluid pathways is aligned with the first plurality of fluid pathways. 
         [0014]    The first internal sheet may include a first interruption blocking the first plurality of fluid pathways at a point. The second internal sheet may include a second interruption blocking the second plurality of fluid pathways at a point. The third internal sheet may include a third interruption blocking the third plurality of fluid pathways at a point. It is contemplated that the first interruption, the second interruption, and the third interruption may be spaced apart from one another. 
         [0015]    A battery pack apparatus may include a first cell bank and a laminated cooling plate. The first cell bank may include a first tray and at least one battery cell. The laminated cooling plate may be in contact with the first cell bank and may include a plurality of sheets. Each sheet may be formed to include cutouts forming a flow path through the laminated cooling plate. Each of the cutouts may extend through the thickness of a sheet. 
         [0016]    The laminated cooling plate may include a fluid inlet, a fluid outlet, and a plurality of fluid flow passages connecting the fluid inlet and the fluid outlet. Each of the plurality of fluid flow passages may provide an independent flow path between the fluid inlet and the fluid outlet. 
         [0017]    The plurality of internal sheets may include a first internal sheet formed to include an internal inlet hole and a first plurality of fluid pathways extending through the first internal sheet. The plurality of internal sheets may include a second internal sheet formed to include a second plurality of fluid pathways extending through the second internal sheet. The plurality of internal sheets may include a third internal sheet formed to include an internal outlet hole and a third plurality of fluid pathways extending through the third internal sheet. 
         [0018]    The first internal sheet, the second internal sheet, and the third internal sheet may be indexed relative to one another and brazed together so that the first plurality of pathways, the second plurality of pathways, and the third plurality of pathways cooperate to define the plurality of fluid flow passageways connecting the fluid flow inlet and the fluid flow outlet. 
         [0019]    Additional features, which alone or in combination with any other feature(s), such as those listed above and those listed in the appended claims, may comprise patentable subject matter and will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the embodiments as presently perceived. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The detailed description particularly refers to the accompanying figures, in which: 
           [0021]      FIG. 1  is a cross sectional diagrammatic view of a battery pack including a top cell bank, a bottom cell bank, and a cooling plate situated between the top cell bank and the bottom cell bank and showing that a top surface of the cooling plate contacts both a battery cell and a thermally conductive tray included in the top cell bank and a bottom surface of the cooling plate contacts both a battery cell and a thermally conductive tray included in the bottom cell bank to remove heat generated by the top and the bottom cell banks. 
           [0022]      FIG. 2  is a diagrammatic view of a fluid cooling system including the battery pack of  FIG. 1  showing the cooling plate fluidly coupled to a pump and a fluid reservoir and suggesting that a fluid medium can be pumped through the cooling plate to remove heat from the top and bottom cell banks; 
           [0023]      FIG. 3  is a detailed diagrammatic view of the battery pack of  FIG. 2  showing that the cooling plate is a laminate cooling plate including a plurality of sheets fused together to provide a substantially leak-proof plate; 
           [0024]      FIG. 4  is a top plan view of a top face sheet included in the laminate cooling plate shown diagrammatically in  FIG. 3  showing an external inlet hole and a plurality small fastener holes formed in the top face sheet; 
           [0025]      FIG. 5  is a top plan view of a first interior sheet included in the laminate cooling plate of  FIG. 3  showing that an interior inlet hole, a plurality small fastener holes, and a first plurality of pathways are formed through the first interior sheet and showing that each of the first plurality of pathways are blocked by a first series of interruptions; 
           [0026]      FIG. 6  is a top plan view of a second interior sheet included in the laminate cooling plate of  FIG. 3  showing a plurality small fastener holes and a second plurality of pathways formed through the second interior sheet with a pattern substantially similar to the first plurality of pathways formed in the first interior sheet of  FIG. 5  and showing that each of the second plurality of pathways are blocked by a second series of interruptions that do not align with the first series of interruptions included in the first interior sheet shown in  FIG. 5 ; 
           [0027]      FIG. 7  is a top plan view of a third interior sheet included in the laminate cooling plate of  FIG. 3  showing that an interior outlet hole, a plurality small fastener holes, and a third plurality of pathways are formed through the third interior sheet, the third plurality of pathways having a pattern substantially similar to the first and the second plurality of pathways formed in the first and the second interior sheets of  FIGS. 5 and 6 , and showing that each of the third plurality of pathways are blocked by a third series of interruptions that do not align with the first or the second series of interruptions included in the first and the second interior sheets shown in  FIGS. 5 and 6 ; 
           [0028]      FIG. 8  is a top plan view of a bottom face sheet included in the laminate cooling plate shown diagrammatically in  FIG. 3  showing an exterior outlet hole and a plurality small fastener holes formed in the bottom face sheet; 
           [0029]      FIG. 9  is a top plan view of a cell block showing a plurality of battery cells supported by a cell retention tray and a plurality of bus bars situated along the length of the cell retention tray so that the battery cells can be connected in series and electrically coupled as a group at an end of the cell block; 
           [0030]      FIG. 10  is a detail view of the bus bar of  FIG. 9  showing that the bus bar is electrically insulated from the cell retention tray and is accessible from above and below the cell retention tray such that welding equipment can touch top and bottom surfaces of the bus bars to form connections to the battery cells through a series of weld windows; and 
           [0031]      FIG. 11  is a partially exploded perspective view of a cell block and the cooling plate of  FIG. 1  showing that the cell bank includes a first cell block, a second cell block, and a third cell block, the first, second, and third cell blocks electrically coupled in series. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    An illustrative battery pack apparatus  10  includes laminate cooling plate  12 , a top cell bank  14 , and a bottom cell bank  16  as shown in  FIG. 1 . Cooling plate  12  has a top surface  18  and a bottom surface  20 . Top cell bank  14  is coupled to top surface  18  of cooling plate  12  so that heat generated by top cell bank  14  may be transferred to cooling plate  12 . Bottom cell bank  16  is coupled to bottom surface  20  of cooling plate  12  so that cooling plate  12  so that heat generated by bottom cell bank  16  may be transferred to cooling plate  12 . 
         [0033]    Cooling plate  12  is coupled to a fluid inlet coupling  22  and a fluid outlet coupling  24  so that a liquid cooling medium can be passed through cooling plate  12  to remove heat from cooling plate  12 . Cooling plate  12  is configured so that a cool fluid medium enters cooling plate  12  through fluid inlet coupling  22  and the fluid medium flows through cooling plate  12  and exits cooling plate  12  after absorbing heat from cooling plate  12  through fluid outlet coupling  24 . In the illustrative embodiment, a thin layer of thermal gel or another interface compound may be spread at the interface of the cooling plate  12  with the top cell bank  14  and the bottom cell bank  16  to reduce air gaps that could provide thermal barriers between the cooling plate and the cell banks  14 ,  16 . 
         [0034]    Top cell bank  14  illustratively includes a plurality of cell blocks  26  and at least one sensor  28  as shown in  FIGS. 1 and 2 . Cell blocks  26  produce heat when battery pack apparatus  10  is electrically charged or loaded. At least one sensor  28  is illustratively configured to measure the temperature of each cell block  26 . 
         [0035]    Bottom cell bank  16  illustratively includes a plurality of cell blocks  30  and at least one sensor  32  as shown in  FIGS. 1 and 2 . Cell blocks  30  produce heat when battery pack apparatus  10  is electrically charged or loaded. At least one sensor  32  is illustratively configured to measure the temperature of each cell block  26 . 
         [0036]    Battery pack apparatus  10  is configured for use in a cooling system  40  as shown diagrammatically in  FIG. 2 . Cooling system  40  includes a fluid medium reservoir  42 , a pump  44 , and a controller  46 . Reservoir  42  holds a fluid medium to be pumped through cooling plate  12 . In some embodiments, reservoir  42  is also a cooler that actively or passively cools the fluid medium stored therein. Pump  44  is configured to pump fluid medium from reservoir  42  through cooling plate  12  and back into reservoir  42  as suggested by arrows  48 ,  49  shown in  FIG. 2 . 
         [0037]    Controller  46  is coupled to temperature sensors  28 ,  32  included in cell banks  14 ,  16  to receive information about the temperature of cell banks  14 ,  16  over time as shown in  FIG. 2 . Controller  46  is also coupled to pump  44  so that controller  46  directs pump  44 . Controller  46  directs pump  44  to increase or decrease the flow rate of fluid medium through cooling plate  12  in response to information received from sensors  28 ,  32  so that the rate of heat transfer through cooling plate  12  maintains cell banks  14 ,  16  in a predetermined range. 
         [0038]    Cooling plate  12  is a laminate plate including a plurality of sheets  51 ,  52 ,  53 ,  54 ,  55  stacked together and fused to produce a single substantially leak-proof plate as shown diagrammatically in  FIG. 3 . In the illustrative embodiment, sheets  51 ,  52 ,  53 ,  54 ,  55  each have a thickness of about 4 mm so that cooling plate  12  has a combined thickness of about 20 mm. Additionally, each sheet  51 ,  52 ,  53 ,  54 ,  55  includes a platform  50  and a connection ear  56  as shown in  FIGS. 4-8 . Platform  50  has a width  50 W, illustratively about 360 mm, and a length  50 L, illustratively 510 mm, as shown, for example, in  FIG. 4 . 
         [0039]    Cooling plate  12  illustratively includes top face sheet  51 , first internal sheet  52 , second internal sheet  53 , third internal sheet  54 , and bottom face sheet  55  as shown in  FIGS. 4-8 . Top face sheet  51  is formed to include an external inlet hole  60  extending through connection ear  56  of top face sheet  51  and configured to couple to fluid inlet coupling  22 . Additionally, platform  50  of top face sheet  51  is substantially smooth and flat so that a continuous thermal connection can be maintained between top cell bank  14  and top face sheet  51  of cooling plate  12  as suggested in  FIGS. 1-3 . 
         [0040]    First internal sheet  52  is formed to include an internal inlet hole  76 , a plurality of feeder slots  78 , and a plurality of pathways  80  that each extend through the entire thickness of first internal sheet  52  as shown in  FIG. 5 . Feeder slots  78  are illustratively about 6 mm wide. Internal inlet hole  76  and feeder slots  78  extend through connection ear  56  of first internal sheet  52 . Internal inlet hole  76  is aligned with external inlet hole  60  as suggested by  FIGS. 4 and 5 . 
         [0041]    Plurality of pathways  80  are formed through platform  50  of first internal sheet  52  and each of the plurality of pathways form an S-shape that doubles back on itself as shown in  FIG. 5  so that a substantially uniform temperature can be maintained throughout cooling plate  12 . Plurality of pathways  80  of first internal sheet  52  illustratively includes eight individual pathways each coupled at a first end to internal inlet hole  76  by one of the plurality of feeder slots  78  as shown in  FIG. 5 . 
         [0042]    Plurality of pathways  80  of first internal sheet  52  are interrupted by a series of interruptions  82  included in first internal sheet  52  as shown in  FIG. 5 . Series of interruptions  82  provide structural support for first internal sheet  52  prior to fusing of sheets  51 ,  52 ,  53 ,  54 ,  55  to form cooling plate  12 . 
         [0043]    Second internal sheet  53  is formed to include a plurality of pathways  84  that each extend through the entire thickness of second internal sheet  54  as shown in  FIG. 6 . Plurality of pathways  84  of second internal sheet  53  are formed through platform  50  of second internal sheet  53  and each of the plurality of pathways form an S-shape that doubles back on itself as shown in  FIG. 6  so that a substantially uniform temperature can be maintained throughout cooling plate  12 . Plurality of pathways  84  of second internal sheet  53  illustratively includes eight individual pathways aligned with the plurality of pathways  80  of first internal sheet  52  as suggested by  FIGS. 5 and 6 . 
         [0044]    Plurality of pathways  84  of second internal sheet  53  are interrupted by a series of interruptions  86  included in second internal sheet  53  as shown in  FIG. 6 . Series of interruptions  86  provide structural support for second internal sheet  53  prior to fusing of sheets  51 ,  52 ,  53 ,  54 ,  55  to form cooling plate  12 . Further, series of interruptions  86  of second internal sheet  53  are spaced apart from and form a pattern different than series of interruptions  82  of first internal sheet  52  so that they do not align when sheets  51 ,  52 ,  53 ,  54 ,  55  are fused to form cooling plate  12 . 
         [0045]    Third internal sheet  54  is formed to include an internal outlet hole  88 , a plurality of feeder slots  89 , and a plurality of pathways  90  that each extend through the entire thickness of third internal sheet  54  as shown in  FIG. 7 . Feeder slots  89  are illustratively about 6 mm wide. Internal outlet hole  88  and feeder slots  89  extend through connection ear  56  of third internal sheet  54 . 
         [0046]    Plurality of pathways  90  are formed through platform  50  of third internal sheet  54  and each of the plurality of pathways form an S-shape that doubles back on itself as shown in  FIG. 7  so that a substantially uniform temperature can be maintained throughout cooling plate  12 . Plurality of pathways  90  of third internal sheet  54  illustratively includes eight individual pathways aligned with the plurality of pathways  80  of first internal sheet  52  and plurality of pathways  84  of second internal sheet  53  as suggested by  FIGS. 5-7 . Each of the plurality of pathways  90  included in third internal sheet  54  are coupled at a second end to internal outlet hole  88  by one of the plurality of feeder slots  89  as shown in  FIG. 7 . 
         [0047]    Plurality of pathways  90  of third internal sheet  54  are interrupted by a series of interruptions  92  included in third internal sheet  54  as shown in  FIG. 7 . Series of interruptions  92  provide structural support for third internal sheet  54  prior to fusing of sheets  51 ,  52 ,  53 ,  54 ,  55  to form cooling plate  12 . Further, series of interruptions  92  of third internal sheet  54  are spaced apart from and form a pattern different than series of interruptions  82  of first internal sheet  52  and series of interruptions  86  of second internal sheet  53  so that they do not align when sheets  51 ,  52 ,  53 ,  54 ,  55  are fused to form cooling plate  12 . 
         [0048]    Bottom face sheet  55  is formed to include an external outlet hole  94  extending through connection ear  56  of bottom face sheet  55  and configured to couple to fluid outlet coupling  24 . External outlet hole  94  is aligned with internal outlet hole  88  of third internal sheet  54  as suggested by  FIGS. 7 and 8 . Additionally, platform  50  of bottom face sheet  55  is substantially smooth and flat so that a continuous thermal connection can be maintained between bottom cell bank  16  and bottom face sheet  55  of cooling plate  12  as suggested in  FIGS. 1-3 . 
         [0049]    Each pathway included in the plurality of pathways  80 ,  84 ,  90  of sheets  52 ,  53 ,  54 ,  55  are illustratively about 2 mm wide and are formed by one of a water jet or a laser. The center of each cut forming the pathways of the illustrative embodiment is about 10 mm from the centerline of an adjacent cut leaving about 8 mm of sheet material between each cut forming a pathway. Additionally, in the illustrative embodiment, each of the pathways  80 ,  84 ,  90  are the same length. Turns in the pathways are each illustratively about ninety-degrees with about a 5 mm radius. In other embodiments, other tools or methods, such as extrusion, may be used to form pathways of alternate dimensions. 
         [0050]    Each sheet of plurality of sheets  51 ,  52 ,  53 ,  54 ,  55  are formed to include a plurality of fastener holes  95 ,  96 ,  97 ,  98  as shown in  FIGS. 4-8 . Fastener holes  95 ,  96  extend through connection ears  56  of sheets  51 ,  52 ,  53 ,  54 ,  55 . Fastener holes  97 ,  98  extend through platform  50  of sheets  51 ,  52 ,  53 ,  54 ,  55  and are configured to receive fasteners (not shown) for coupling cell banks  14 ,  16  to cooling plate  12 . Fastener holes  97 ,  98  are located about midway along the width  50 W of platform  50  as indicated by distance  99 , illustratively about 180 mm, in  FIGS. 4 and 8 . Fastener hole  97  and fastener hole  98  are each spaced approximately one-third of length  50 L from opposing ends of platform  50  along the length  50 L of platform  50  as indicated by distances  97 D and  98 D in  FIGS. 4 and 8 . 
         [0051]    To fuse the plurality of sheets  51 ,  52 ,  53 ,  54 ,  55 , the sheets are stacked as indicated diagrammatically in  FIG. 3  and indexed so that the plurality of pathways  80 ,  84 ,  90  of internal sheets  52 ,  53 ,  54  are aligned. Then the stacked sheets  51 ,  52 ,  53 ,  54 ,  55  are brazed so that the contacting portions of the sheet melt together forming cooling plate  12  with an inlet  100 , an outlet  102 , and a plurality of fluid passageways  106  defined by the plurality of pathways  80 ,  84 ,  90  of internal sheets  52 ,  53 ,  54 . Sheets  51 ,  52 ,  53 ,  54 ,  55  are illustratively constructed of braze alloy aluminum sheet material. In other embodiments, other thermally conductive metals or other materials are used. The aluminum sheets  51 ,  52 ,  53 ,  54 ,  55  are anodized with a thin coating after brazing to provide electrical isolation while maintaining overall heat transfer. 
         [0052]    Inlet  100  is formed from external inlet hole  60  and internal inlet hole  76  as suggested in  FIGS. 2 and 3 . Inlet  100  is coupled to a first end of each of the internal passageways  106  by feeder slots  78 . Outlet  102  is formed from external outlet hole  94  and internal outlet hole  88  as suggested in  FIGS. 2 and 3 . Outlet  102  is coupled to a second end of each of the internal passageways by feeder slots  89  so that the plurality of passageways  106  is interdigitally coupled to the inlet  100  and the outlet  102 . Each of the plurality of fluid passageways provides an independent flow path from the inlet  100  to the outlet  102  as suggested by  FIGS. 5 and 7 . 
         [0053]    Top cell bank  14  includes plurality of cell blocks  26  as shown in  FIG. 1 . Bottom cell bank  16  includes plurality of cell blocks  30  as shown in  FIG. 1 . Each cell block included in top cell bank  14  and bottom cell bank  16  are substantially similar and thus an exemplary cell block  110  is shown in  FIG. 9  and described illustratively herein. 
         [0054]    Cell block  110  includes a retention tray  112 , a plurality of battery cells  114 , and a plurality of bus bars  116  as shown, for example in  FIG. 9 . Retention tray  112  is illustratively constructed from anodized aluminum for high thermal and low electrical conductivity and is configured to support plurality of battery cells  114  and bus bars  116  as shown in  FIG. 9 . Battery cells  114  are illustratively rechargeable electrochemical lithium cells. Bus bars  116  are coupled to each of the battery cells  114  so that plurality of battery cells  114  are connected in series. 
         [0055]    Retention tray  112  includes a base  120  and a raised divider  122  forming pockets  124  as shown in FIGS.  2  and  9 - 11 . Base  120  contacts battery cells  114  and transmits heat from battery cells  114  to retention tray  112 . Raised divider  122  contacts either cooling plate  12  or a base  120  of another retention tray  112  thereby passing heat to the cooling plate  12  as suggested in  FIG. 1 . 
         [0056]    Battery cells  114  are positioned in pockets  124  of retention tray  112  formed between raised divider  122  of retention tray  112  so that very little space if any is left between the face of the cell and the retention tray as shown, for example, in FIGS.  1  and  9 - 11 . A small amount of thermal interface gel may be applied to the battery cells  114  to reduce or eliminate any air gap that might create thermal barriers between the battery cells  114  and the retention trays  112 . In the illustrative embodiment, two by six series of battery cells  114  is utilized to achieve a desired system voltage. In other embodiments, other configurations may be used to provide different voltage outputs. 
         [0057]    Bus bars  116  are coupled to the retention tray  112  as shown, for example in  FIGS. 9 and 10 . Bus bars  116  are electrically couples to battery cells  114  so that battery cells  114  form a series along retention tray  112 . In some embodiments, bus bars  116  are made from aluminum that is anodized except at the point of connection with the battery cells  114 . Bus bars  116  are accessible for welded connection to battery cells  114  on both the top and bottom surfaces of the bus bars  116  via weld windows  126  provided in retention tray  112  as shown in  FIG. 10 . Bus bars  116  include insulated areas  128  between connections to battery cells  114  as shown in  FIG. 10 . The insulated areas are illustratively heat shrunk electrical insulation. 
         [0058]    After cell block  110  is constructed, plurality of cell blocks  30  can be assembled into bottom cell bank  16  as suggested in  FIG. 11 . Each cell block  110  is coupled to another cell block  110  to form a series circuit of battery cells  114  as suggested by arrows  130 ,  132  shown in  FIG. 11 . 
         [0059]    The assembly process for this system begins by mounting bus bars  116  within retention tray  112  of a first cell block  110 A. Then battery cells  114  are mounted into retention tray  112  using spray adhesive. Cell terminals are electrically connected, in some embodiments ultrasonically welded, to the bus bars  116 . At least one sensor  28  is installed with sensing leads which are fastened permanently in place. Cell terminals are covered with Kapton™ tape to ensure electrical isolation from contact. Cell block  110 A is then treated with thermal interface gel compound (a thin layer) on battery cell  114  faces and thermal grease on the interface tray contact areas. Cell block  110  is then mounted to the cooling plate  12 . 
         [0060]    The next step in the process is to assemble another cell block  110 B including battery cells  114  as before. After thermal compounds are applied, this cell block  110 B is mounted to the back of the cell block  110 A previously attached. A bus bar  116  of the second cell block is connected using a threaded fastener to the bus bar  116  of the first cell block  110 A at one end only as suggested in  FIG. 11 . Next, a third cell block  110 C is built up in the same way and mounted to the back of the second cell block  110 B. The electrical bus of cell block  110 C is connected to the bus bar  116  of the second cell block  110 B at the opposite end from the previous layer in order to continue the series electrical connection as suggested in  FIG. 11 . 
         [0061]    At this point, the unit is half complete and threaded fasteners (not shown) are installed to hold the cell blocks  110 A,  110 B,  110 C to the cooling plate  12  before turning the battery pack apparatus  10  over. The process of attaching a plurality of cell blocks  30  to this second side of the cold plate is a repeat of the process of the first side. With each added cell block  110 , the bus structure is connected to the previous cell block  110  in such a way as to continue a serial electrical connection of battery cell pairs. 
         [0062]    Once all three cell blocks  110  included in cell bank  16  are attached in piggyback fashion to the second side of the cooling plate  12 , then threaded fasteners (not shown) are installed to hold them in place. Next, in some embodiments (not shown), layers of top and bottom insulation/structure are placed on the large outer surfaces and multiple straps are attached, encircling the assembly, to hold the layers tightly together. 
         [0063]    An alternative assembly method exists which is to start with the outermost (bottom) cell block  110  and build the entire assembly from the bottom upwards. This technique includes the benefit of eliminating the step of turning the assembly over halfway through the assembly process. 
         [0064]    Although certain illustrative embodiments have been described in detail above, many embodiments, variations and modifications are possible that are still within the scope and spirit of this disclosure as described herein and as defined in the following claims.