Abstract:
A method of assembling a battery assembly includes forming battery packs, each pack including battery cells and cooling passages extending along a length of the pack, connecting terminals of each pack to a dc source and charging each pack to a desired state of charge, installing battery packs on a tray located on an automatically guided cart, using the cart to carry the battery assembly to locations where method steps are performed including performing testing for fluid leaks in a cooling circuit comprising interconnected passages of each pack on the tray and installing electric circuits in the assembly.

Description:
BACKGROUND OF INVENTION 
       [0001]    The present invention relates generally to the module of a complete battery pack in a vehicle whose propulsion system is at least partly electric powered. 
         [0002]    A rechargeable electric storage battery is mounted on a tray located at the underside of a vehicle with its lower surface exposed to the road. It has been conventional practice to form such battery trays in multiple pieces of high strength material such as multiple stampings that are welded together. The lower surface of the tray is covered with a panel. 
         [0003]    A battery tray casting in one-piece would reduce overall complexity of a battery tray formed of multiple welded stampings. 
         [0004]    A need exists in the industry for a method for assembling battery packs for automotive and other applications using a tray formed in a single piece and multiple battery packs supported on the tray. Preferably the battery tray would minimize the number of required fasteners and eliminate or avoid tooling required during vehicle and component assembly to accommodate a multi-piece battery tray. 
       SUMMARY OF INVENTION 
       [0005]    A method of assembling a battery assembly includes forming battery packs, each pack including battery cells and cooling passages extending along a length of the pack, connecting terminals of each pack to a dc source and charging each pack to a desired state of charge, installing battery packs on a tray located on an automatically guided cart, using the cart to carry the battery assembly to locations where method steps are performed including performing testing for fluid leaks in a cooling circuit comprising interconnected passages of each pack on the tray and installing electric circuits in the assembly. 
         [0006]    The tray insulates the batteries against harm due to the ambient air temperature in the operating environment. 
         [0007]    The tray, preferably formed in one-piece of sheet metal with multiple reinforcement bars, minimizes aerodynamic drag by using a cover. 
         [0008]    The one piece design minimizes mass and the number of fasteners. Because tooling normally used to accommodate a multi-piece design is not required during vehicle module and component module assembly, the tray design minimizes piece cost and requires low investment cost and reduces tooling lead time. 
         [0009]    The ribs enable the structural, impact, and durability requirements of the tray to be realized. 
         [0010]    The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  is a perspective view of a battery tray; 
           [0012]      FIG. 2  is perspective view showing two aligned battery packs as they are assembled on the vertical leg of the tray; 
           [0013]      FIG. 3  is a perspective view of a bulkhead; 
           [0014]      FIG. 4  is a perspective view of the completed module showing a cover secured to the tray; 
           [0015]      FIG. 5  is a perspective view showing bus bars and a mid-pack fuse of the battery pack assembly; 
           [0016]      FIG. 6  is a perspective view showing VTSM plug connectors of the battery pack assembly; and 
           [0017]      FIG. 7  is a diagram showing the assembly steps in substantially chronological order. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Referring now to the drawings of the components of an electric storage battery assembly  10 ,  FIG. 1  illustrates a battery support tray  12 , which is preferably of sheet metal. When viewed from above, the tray  12  is tee-shaped having a cross leg  14  and a longitudinal leg  16 . 
         [0019]    A battery unit comprises three packs. In addition to the 72-section pack  18  and a 90-section pack  20  shown in  FIG. 2 , the battery includes a 126-section pack. Each battery pack is formed with integral fluid cooling passages  19 ,  21 , each passage extending along the length of the battery pack and located on opposite lateral sides of the battery cells  25 . The fluid cooling passages  19 ,  21  of each battery section are connected to the corresponding passages of an adjacent battery section or to another portion of a cooling circuit by hoses and tubes  22 ,  24 . 
         [0020]    Each battery pack includes multiple voltage temperature sub-modules (VTSM) stacked along a length of the battery pack, each module comprising a battery cell  25 , replacement frame, jacket and foam. Each VTSM has a positive tab and a negative tab. The tabs of adjacent VTSMs are welded together such that the modules of a fully charged battery pack produce an output voltage of about 40 to 50 volts. Preferably, the cells contain the battery electrolyte, lithium ions, in the form of a gel. 
         [0021]    Referring to  FIGS. 1 and 2 , the longitudinal leg  16  of tray  12  supports the battery sections  18 ,  20 , which comprise 72 cells and 90 cells, respectively. The third battery pack (not shown) having 126 cells is supported on the cross leg  14  of tray  12 . 
         [0022]    The bulkhead  26 , shown in  FIG. 3  is secured by about 7 screws or bolts to a cover  28 , which encloses the battery assembly  10 , as shown in  FIG. 4 . The ends of the cooling tubes  22 ,  24  extend through the thickness of bulkhead  26  so that the coolant, a 50 percent mixture of de-ionized water and glycol, can circulate through the battery packs. Fastening strips (not shown) secure a lateral edge of each battery pack to the tray  12 . Screws or bolts secure the fastening strips to the tray  12 . The cover  28  is secured by about forty-nine screws  30  to the tray  12 . 
         [0023]    The overall length of the tray is about 1638 mm. The width of the cross leg  14  is about 937 mm. The width of the longitudinal leg  14  is about 395 mm. The thickness of the tray  12  is about 2 mm. 
         [0024]      FIG. 5  shows high voltage positive polarity bus bars  34  and negative polarity bus bars  35 , which carry electric current between the battery packs and terminals  36 ,  37  located on bulkhead  26  (shown in  FIG. 3 ); a removable mid-pack fuse  38  of a manual service disconnect module (MSM); low voltage cables  40 ; and connector clips  42 , which engage the battery cells. The MDM is located in the vehicle console such that the fuse  38  can be removed from the power supply circuit, thereby disconnecting the electric power source from the vehicle&#39;s electrical circuit. 
         [0025]    The battery assembly includes three electrically interconnected circuit boards: a voltage, temperature, sensing module (VTSM) located on the top of the battery; a voltage, current, temperature module (VITM) located on the BDU; and a voltage, current, control module (VICM) located in the vehicle.  FIG. 6  shows an arrangement of plugs  44  and wiring  45  that connect to PCBs of a battery controller, which continually monitors the battery&#39;s output, charging rate, draw rate, state of charge and other variables. 
         [0026]      FIG. 7  illustrates the steps for assembling and testing the components of the battery assembly  10  in substantially chronological order. At step  50 , the assembly process begins with the delivery of the three battery packs  18 ,  20  (the first two shown in  FIG. 2 ), each battery pack assembled with the cells  25  and cooling passages  19 ,  21  in place. 
         [0027]    At step  52 , section stack, barcodes representing the serial numbers of battery pack components are applied to the battery packs  18 ,  20 . 
         [0028]    At step  54 , section leak test, the fluid cooling circuit of each battery pack is leak tested. Rejected parts that fail (F) the test are banked (B) at  56  for subsequent repair and potential return to the process at step  50 . 
         [0029]    At step  58 , interconnect board install, electrically interconnected VTSM boards are installed in the battery assembly. 
         [0030]    At step  60 , welding/verify, quality of the welds that join the tabs of the battery cells is verified and a buffer zone is provided. Any that fail (F) are banked (B) for subsequent repair. 
         [0031]    At step  62 , the terminals of each battery pack  18 ,  20  are connected through a charger to a source of dc electric power, whereby the storage cells of each battery pack are charged with electric current to a predetermined state of charge. 
         [0032]    At step  64 , pack module test, an electrical load test of each battery pack is performed to verify the state of charge. Data may be collected, step  63 , at this point in the assembly process. Such data may include added charge, date/time stamp, and the charger number. 
         [0033]    At step  66 , the tray  12  is loaded onto an automated guiding cart (ACG), an unmanned cart having a control system that guides the steering of the ACG such that the cart follows a predefined path on the factory floor between work stations where assembly steps are performed. The path is defined by magnets placed on the floor, and the battery assembly is carried on the ACG between the work stations instead of on a conveyor belt. 
         [0034]    At step  68 , the three battery packs  18 ,  20  are loaded on and secured to the tray  12 , which is now supported on and carried by the ACG. 
         [0035]    At step  70 , an ACG loop starts by installing and securing the bulkhead  26  to the tray at the lower end of the battery packs  18 ,  20  on the tray&#39;s longitudinal leg  16 . 
         [0036]    At step  72 , all cooling fluid hoses and tubes  22 ,  24  are installed and interconnected to the fluid passages  19 ,  21  of the battery packs. 
         [0037]    At step  74 , the fluid cooling circuit is leak tested. Rejected circuits that fail (F) the test are removed for subsequent repair and are replaced. 
         [0038]    At step  76 , the cover  28  is secured to the tray  12 , either using bolts or screws or a snap-on technique that requires no removable fasteners. 
         [0039]    At step  78 , the VTSM is installed and scanned after its installation. 
         [0040]    At step  80 , the low voltage cable  40  is routed through the battery assembly  10 . 
         [0041]    At step  82 , the mid-pack fuse  38  is installed. 
         [0042]    At step  84 , a service disconnect (MSD) housing and bracket are installed. The MSD housing comprises two plastic housing parts, which contain a large fuse, from which positive and negative polarity wires extend through the housing to the vehicle&#39;s electric circuit. 
         [0043]    At step  86 , an electrical connection of the VTSM interconnect board to the battery assembly  10  is completed manually. 
         [0044]    At step  88 , small bus bars are installed, and at step  90 , the bus bars  34 ,  35  are installed. 
         [0045]    At step  92 , electrical tests of each of the three battery packs are conducted after an operator makes connections at the front of bulkhead  26 . Rejected parts that fail (F) the test are removed for subsequent repair and are replaced. Data may be collected, step  91 , at this point in the assembly process. Such data may include VITM and VTSM&#39;s number, electronic part numbers, and a part number may be assigned to create a bar code. 
         [0046]    Preferably no fluid leak testing is performed at the battery plant. Instead at step  94 , the cooling system of the battery pack is tested for leaks using a technique called air mass flow differential leak testing, with fluid fill if required. 
         [0047]    At step  96 , a closeout cover install/service disconnect housing is attached manually to cover  28 , and leak detection of the cover-tray-BDU interface is performed using a helium spectrometer. 
         [0048]    At step  98 , a pressure decay test is performed on the cooling circuit. Rejected parts that fail the test are removed for subsequent repair and are replaced. 
         [0049]    At step  100 , a crossbar (not shown), which is installed manually to the top battery assembly  10 , facilitates installing and securing the assembly  10  to a bracket on the vehicle chassis. 
         [0050]    At step  102 , barcodes and labels are applied to the exterior of the cover  28  of the battery assembly  10 . 
         [0051]    At step  104 , a final quality inspection is performed. Parts that fail (F) are removed for subsequent repair. 
         [0052]    At step  106 , the battery assembly  10  is removed from the ACG and transferred to a shipping rack, from which it is taken to a vehicle assembly plant where the battery assembly is installed in a vehicle. 
         [0053]    While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.