Abstract:
A battery assembly according to an exemplary aspect of the present disclosure includes, among other things, a cell stack and an array structure. At least one of the cell stack and the array structure includes a biased profile configured to bias the cell stack and a portion of the array structure together.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to a battery assembly for an electrified vehicle. The battery assembly includes one or more components having biased profiles configured to bias a cell stack into contact with a heat exchanger, such as a cold plate. 
       BACKGROUND 
       [0002]    The need to reduce automotive fuel consumption and emissions is well known. Therefore, vehicles are being developed that either reduce or completely eliminate reliance on internal combustion engines. Electrified vehicles are one type of vehicle being developed for this purpose. In general, electrified vehicles differ from conventional motor vehicles because they are selectively driven by one or more battery powered electric machines. Conventional motor vehicles, by contrast, rely exclusively on the internal combustion engine to propel the vehicle. 
         [0003]    High voltage battery assemblies are employed to power the electric machines of electrified vehicles. Battery assemblies include cell stacks constructed of a plurality of battery cells. An array structure binds and/or houses the battery cells. A heat exchanger, such as a cold plate, may be positioned relative to the battery cells for thermally managing the heat generated by the cells. 
       SUMMARY 
       [0004]    A battery assembly according to an exemplary aspect of the present disclosure includes, among other things, a cell stack and an array structure. At least one of the cell stack and the array structure includes a biased profile configured to bias the cell stack and a portion of the array structure together. 
         [0005]    In a further non-limiting embodiment of the foregoing battery assembly, the cell stack includes a plurality of battery cells disposed side-by-side between opposing end plates. 
         [0006]    In a further non-limiting embodiment of either of the foregoing battery assemblies, the portion of the array structure includes a heat exchanger configured as a cold plate. 
         [0007]    In a further non-limiting embodiment of any of the foregoing battery assemblies, the array structure includes at least one of a tensile member, a tray, a cover and a heat exchanger. 
         [0008]    In a further non-limiting embodiment of any of the foregoing battery assemblies, the cell stack includes the biased profile, the biased profile configured such that a first portion of a plurality of battery cells of the cell stack slide or bend relative to a second portion of the plurality of battery cells. 
         [0009]    In a further non-limiting embodiment of any of the foregoing battery assemblies, the portion of the array structure is a heat exchanger that includes the biased profile, the biased profile including an arched shape. 
         [0010]    In a further non-limiting embodiment of any of the foregoing battery assemblies, the arched shape is curved toward the cell stack in its unloaded position. 
         [0011]    In a further non-limiting embodiment of any of the foregoing battery assemblies, the array structure includes the biased profile, the biased profile including an arched shape. 
         [0012]    In a further non-limiting embodiment of any of the foregoing battery assemblies, the arched shape is curved toward the cell stack in its unloaded position. 
         [0013]    In a further non-limiting embodiment of any of the foregoing battery assemblies, a heat exchanger is positioned on a first side of the cell stack and a tensile member of the array structure is positioned on a second side of the cell stack. 
         [0014]    In a further non-limiting embodiment of any of the foregoing battery assemblies, a heat exchanger is positioned between a tray of the array structure and the cell stack. 
         [0015]    In a further non-limiting embodiment of any of the foregoing battery assemblies, the biased profile is configured to move one of the cell stack and the portion of the array structure toward the other of the cell stack and the portion of the array structure. 
         [0016]    In a further non-limiting embodiment of any of the foregoing battery assemblies, the biased profile biases at least two battery cells of the cell stack into contact with the portion. 
         [0017]    In a further non-limiting embodiment of any of the foregoing battery assemblies, the array structure includes a tray and a cover. 
         [0018]    In a further non-limiting embodiment of any of the foregoing battery assemblies, the tray includes the biased profile and the cover includes a second biased profile, the biased profile and the second biased profile cooperating to bias the cell stack and the portion together. 
         [0019]    A method according to another exemplary aspect of the present disclosure includes, among other things, configuring at least one component of a battery assembly to include a biased profile. The battery assembly includes at least a cell stack and a heat exchanger. The cell stack and the heat exchanger are biased into contact with one another. 
         [0020]    In a further non-limiting embodiment of the foregoing method, a tray of the battery assembly includes the biased profile. The biasing step includes positioning the heat exchanger and the cell stack on top of the tray such that initial contact with the tray is made near a mid-span of the cell stack and the heat exchanger. Contact between the heat exchanger and peripheral portions of the cell stack is progressively developed as the heat exchanger is moved further into contact with the tray. 
         [0021]    In a further non-limiting embodiment of either of the foregoing methods, the heat exchanger includes the biased profile. The biasing step includes positioning the cell stack on top of the heat exchanger such that initial contact with the heat exchanger is made near a mid-span of the cell stack. Contact between the heat exchanger and peripheral portions of the cell stack is progressively developed as the heat exchanger is moved into contact with a tray of the battery assembly. 
         [0022]    In a further non-limiting embodiment of any of the foregoing methods, a tensile member of the battery assembly includes the biased profile and the biasing step includes pushing the cell stack toward the heat exchanger using the biased profile. 
         [0023]    In a further non-limiting embodiment of any of the foregoing methods, the cell stack includes the biased profile. The biasing step includes displacing a first portion of the cell stack relative to a second portion of the cell stack such that initial contact with the heat exchanger is made near a mid-span of the cell stack. The method further includes progressively loading the second portion of the cell stack against the heat exchanger as the cell stack is forced against the heat exchanger. 
         [0024]    The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
         [0025]    The various features and advantages of this disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  schematically illustrates a powertrain of an electrified vehicle. 
           [0027]      FIG. 2  illustrates a battery assembly according to a first embodiment of this disclosure. 
           [0028]      FIG. 3  illustrates a battery assembly according to a second embodiment of this disclosure. 
           [0029]      FIG. 4  illustrates a battery assembly according to another embodiment of this disclosure. 
           [0030]      FIG. 5  illustrates a battery assembly according to yet another embodiment of this disclosure. 
           [0031]      FIG. 6  illustrates a battery assembly according to yet another embodiment of this disclosure. 
           [0032]      FIG. 7  illustrates an assembled battery assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    This disclosure details a battery assembly for an electrified vehicle. The battery assembly may include a cell stack, a heat exchanger and an array structure. At least one of the cell stack, the heat exchanger and the array structure includes a component having a biased profile configured to bias the cell stack into contact with the heat exchanger. In some embodiments, the biased profile includes an arched or crowned shape, although other shapes are also contemplated within the scope of this disclosure. The biased component profiles promote improved battery cell to heat exchanger contact across the entire length of the cell stack to achieve a desired level of thermal conductivity between the cells and the heat exchanger. These and other features are discussed in greater detail in the following paragraphs of this detailed description. 
         [0034]      FIG. 1  schematically illustrates a powertrain  10  for an electrified vehicle  12 . Although depicted as a hybrid electric vehicle (HEV), it should be understood that the concepts described herein are not limited to HEV&#39;s and could extend to other electrified vehicles, including, but not limited to, plug-in hybrid electric vehicles (PHEV&#39;s), battery electric vehicles (BEV&#39;s) and fuel cell vehicles. 
         [0035]    In one embodiment, the powertrain  10  is a power-split powertrain system that employs a first drive system and a second drive system. The first drive system includes a combination of an engine  14  and a generator  18  (i.e., a first electric machine). The second drive system includes at least a motor  22  (i.e., a second electric machine), the generator  18 , and a battery assembly  24 . In this example, the second drive system is considered an electric drive system of the powertrain  10 . The first and second drive systems generate torque to drive one or more sets of vehicle drive wheels  28  of the electrified vehicle  12 . Although a power-split configuration is shown, this disclosure extends to any hybrid or electric vehicle including full hybrids, parallel hybrids, series hybrids, mild hybrids or micro hybrids. 
         [0036]    The engine  14 , which in one embodiment is an internal combustion engine, and the generator  18  may be connected through a power transfer unit  30 , such as a planetary gear set. Of course, other types of power transfer units, including other gear sets and transmissions, may be used to connect the engine  14  to the generator  18 . In one non-limiting embodiment, the power transfer unit  30  is a planetary gear set that includes a ring gear  32 , a sun gear  34 , and a carrier assembly  36 . 
         [0037]    The generator  18  can be driven by the engine  14  through the power transfer unit  30  to convert kinetic energy to electrical energy. The generator  18  can alternatively function as a motor to convert electrical energy into kinetic energy, thereby outputting torque to a shaft  38  connected to the power transfer unit  30 . Because the generator  18  is operatively connected to the engine  14 , the speed of the engine  14  can be controlled by the generator  18 . 
         [0038]    The ring gear  32  of the power transfer unit  30  may be connected to a shaft  40 , which is connected to vehicle drive wheels  28  through a second power transfer unit  44 . The second power transfer unit  44  may include a gear set having a plurality of gears  46 . Other power transfer units may also be suitable. The gears  46  transfer torque from the engine  14  to a differential  48  to ultimately provide traction to the vehicle drive wheels  28 . The differential  48  may include a plurality of gears that enable the transfer of torque to the vehicle drive wheels  28 . In one embodiment, the second power transfer unit  44  is mechanically coupled to an axle  50  through the differential  48  to distribute torque to the vehicle drive wheels  28 . 
         [0039]    The motor  22  can also be employed to drive the vehicle drive wheels  28  by outputting torque to a shaft  52  that is also connected to the second power transfer unit  44 . In one embodiment, the motor  22  and the generator  18  cooperate as part of a regenerative braking system in which both the motor  22  and the generator  18  can be employed as motors to output torque. For example, the motor  22  and the generator  18  can each output electrical power to the battery assembly  24 . 
         [0040]    The battery assembly  24  is an exemplary electrified vehicle battery. The battery assembly  24  may include a high voltage traction battery pack that includes a plurality of battery cells capable of outputting electrical power to operate the motor  22  and the generator  18 . Other types of energy storage devices and/or output devices can also be used to electrically power the electrified vehicle  12 . 
         [0041]    In one non-limiting embodiment, the electrified vehicle  12  has two basic operating modes. The electrified vehicle  12  may operate in an Electric Vehicle (EV) mode where the motor  22  is used (generally without assistance from the engine  14 ) for vehicle propulsion, thereby depleting the battery assembly  24  state of charge up to its maximum allowable discharging rate under certain driving patterns/cycles. The EV mode is an example of a charge depleting mode of operation for the electrified vehicle  12 . During EV mode, the state of charge of the battery assembly  24  may increase in some circumstances, for example due to a period of regenerative braking. The engine  14  is generally OFF under a default EV mode but could be operated as necessary based on a vehicle system state or as permitted by the operator. 
         [0042]    The electrified vehicle  12  may additionally operate in a Hybrid (HEV) mode in which the engine  14  and the motor  22  are both used for vehicle propulsion. The HEV mode is an example of a charge sustaining mode of operation for the electrified vehicle  12 . During the HEV mode, the electrified vehicle  12  may reduce the motor  22  propulsion usage in order to maintain the state of charge of the battery assembly  24  at a constant or approximately constant level by increasing the engine  14  propulsion. The electrified vehicle  12  may be operated in other operating modes in addition to the EV and HEV modes within the scope of this disclosure. 
         [0043]      FIG. 2  is an exploded view of a battery assembly  24  that could be employed within an electrified vehicle. For example, the battery assembly  24  could be employed within the electrified vehicle  12  of  FIG. 1 . The battery assembly  24  includes a plurality of battery cells  58  for supplying electrical power to various components of the electrified vehicle  12 . Although a specific number of battery cells  58  are illustrated in  FIG. 2 , the battery assembly  24  could include a greater or fewer number of cells within the scope of this disclosure. In other words, this disclosure is not limited to the specific configuration shown in  FIG. 1 . 
         [0044]    The battery cells  58  may be stacked side-by-side between opposing end plates  60  to construct a cell stack  62  (i.e., a grouping of battery cells). The end plates  60  cooperate to apply an axial compressive force to the battery cells  58  of the cell stack  62 . In one embodiment, the battery cells  58  are prismatic, lithium-ion cells. However, battery cells having other geometries (cylindrical, pouch, etc.) and/or chemistries (nickel-metal hydride, lead-acid, etc.) could alternatively be utilized within the scope of this disclosure. 
         [0045]    The battery assembly  24  may additionally include an array structure  64  for bounding, housing and/or surrounding the cell stack  62 . The array structure  64  may include various components including tensile members, binding members, enclosure members (e.g., cover and tray), heat exchangers (e.g., cold plates) etc. In the non-limiting embodiment of  FIG. 2 , the array structure  64  includes a cover  66  and a tray  68 . Although not shown, other components may make up the array structure  64 . 
         [0046]    Heat may be generated by the battery cells  58  during charging and discharging operations. Heat may also be transferred into or out of the battery cells  58  due to relative temperature differences between the battery cells  58  and ambient conditions. A heat exchanger  70  may therefore be utilized to thermally condition (i.e., heat or cool) the battery cells  58  via thermal conduction. In one embodiment, the heat exchanger  70  is configured as a cold plate that is positioned between the cell stack  62  and the tray  68 . In another embodiment, the functions of the heat exchanger  70  and the tray  68  may be achieved by a single component. Other configurations are also contemplated. 
         [0047]    One or more components of the battery assembly  24  may include a biased profile that promotes contact between the battery cells  58  and the heat exchanger  70  along a portion of a length L or the entire length L of the cell stack  62 . In one non-limiting embodiment, the tray  68  includes a biased profile  72  configured to bias the cell stack  62  and the heat exchanger  70  into contact with one another. The biased profile  72  may include an arched shape in its unloaded position. For example, the tray  68  may be curved in a direction toward the heat exchanger  70  such that a middle portion  71  of the tray  68  extends in a plane P 1 . The Plane P 1  is above a plane P 2  that extends through peripheral portions  73  of the tray  68 . 
         [0048]    During assembly of the battery assembly  24 , the heat exchanger  70  and the cell stack  62  are placed on top of the tray  68  such that initial contact with the tray  68  is made near a mid-span M of the cell stack  62 . Battery cell  58  to heat exchanger  70  contact is progressively developed extending outwardly toward the end plates  60  of the cell stack  62  until the end plates  60  contact the heat exchanger  70  (or contact the tray  68 ). Alternatively, initial contact between the cell stack  62  and the tray  68  may be made near one of the end plates  60  and then progressively developed from the end plate  60  toward the opposite end plate  60 . 
         [0049]    Once fully loaded as shown in phantom lines  68 ′, the tray  68  may no longer exhibit the biased profile  72 . The battery assembly  24  may then be fastened together using any known manner. In this embodiment, the tray  68  acts as a leaf spring that is biased into the heat exchanger  70  to move the heat exchanger  70  into contact with the battery cells  58  of the cell stack  62  along two or more cells in the length L of the cell stack  62 . A view of the battery assembly  24  after loading the tray  68  is shown in  FIG. 7 . 
         [0050]    In another non-limiting embodiment, it may be desirable to have a non-uniform load across the span of the cell stack  62  (i.e., high spring load near the mid-span M and moderate spring load near the end plates  60 ). Non-uniform loading can be developed by thickening the loading element (in this example, the tray  68 ), by adding tailored patches/blanks (additional layers of bonded material), by adding ribs, by stamping beads/darts or otherwise increasing the cross section area moment of inertia, or by varying the material properties of either the loading element or the response element (i.e., the components that are loaded by the loading element and exert a responsive force back onto the loading element). These are non-limiting examples of how non-uniform loading could be achieved. 
         [0051]      FIG. 3  is an exploded view of another battery assembly  124 . In this disclosure, like reference numbers designate like elements where appropriate and reference numerals with the addition of 100 or multiples thereof designate modified elements that are understood to incorporate the same features and benefits of the corresponding original elements. The battery assembly  124  may include a cell stack  162 , a heat exchanger  170  and an array structure  164  including a cover  166  and a tray  168 . 
         [0052]    The battery assembly  124  of  FIG. 3  is similar to the battery assembly  24  of  FIG. 2  except that, in this embodiment, the heat exchanger  170  provides the biased profile  172  instead of the tray  168 . The biased profile  172  of the heat exchanger  170  includes an arched shape that is curved in a direction toward the cell stack  162 . For example, the heat exchanger  170  may be curved in a direction toward the cell stack  162  such that a middle portion  175  of the heat exchanger  170  extends outwardly of peripheral portions  177  of the heat exchanger  170 . 
         [0053]    During assembly of the battery assembly  124 , the cell stack  162  is placed on top of the heat exchanger  170  such that initial contact with the heat exchanger  170  is made near a mid-span M of the cell stack  162 . Battery cell  158  to heat exchanger  170  contact is progressively developed outwardly toward the ends of the cell stack  162  as the heat exchanger  170  is moved into contact with the tray  168 , thereby causing the peripheral portions  177  to flex outwardly in a direction of arrows D 1  toward the cell stack  162 . The battery assembly  124  may then be fastened together in any known manner. In this embodiment, the heat exchanger  170  acts as a leaf spring for biasing the heat exchanger  170  into contact with the cell stack  162 . 
         [0054]      FIG. 4  illustrates another battery assembly  224 . The battery assembly  224  may include a cell stack  262 , a heat exchanger  270  and an array structure  264  including a tensile member  266  and a tray  268 . In some non-limiting embodiments, the tensile member  266  may be configured as either a binding member or a wall positioned at least partly over the cell stack  262 . 
         [0055]    The tensile member  266  may include a biased profile  272 . The biased profile  272  includes an arched shape that is curved in a direction toward the cell stack  262 . The arched shape of the tensile member  266  pushes the cells stack  262  toward the heat exchanger  270  during assembly to promote improved contact across at least two cells within the length L of the cell stack  262 . 
         [0056]      FIG. 5  is an exploded view of yet another battery assembly  324 . In this embodiment, a tensile member  366  of the battery assembly  324  includes a first biased profile  372 A and a tray  368  of the battery assembly  324  includes a second biased profile  372 B. The first and second biased profiles  372 A,  372 B may be the same or different biased profiles. The first and second biased profiles  372 A,  372 B promote contact between the cell stack  362  and the heat exchanger  370  across at least two cells within the length L of the cell stack  362 . 
         [0057]      FIG. 6  illustrates yet another exemplary battery assembly  424 . The battery assembly  424  may include a cell stack  462 , a heat exchanger  470  and an array structure  464 . The array structure  464  may include a cover  466  and a tray  468 . 
         [0058]    In this non-limiting embodiment, the cell stack  462  is adapted to include a biased profile  472 . The biased profile  472  may be achieved by displacing the battery cells  458  of the cell stack  462  relative to one another to form a depression  499  on the side of the cell stack  462  closest to the cover  466 . For example, a first portion P 1  of the battery cells  458  near a mid-span M of the cell stack  462  may be displaced or moved relative to a second portion P 2  of the battery cells  458  near end plates  460  of the cell stack  462 . Displacement of the battery cells  458  in this manner configures the cell stack  462  in a chevron shape. Other shapes such as a curve or parabola may alternatively be employed which would result in variations in the initial cell to cell displacement. Furthermore, some battery cells  458  may intentionally not be displaced with respect to their neighboring battery cells  458  in order to influence the degree of contact developed between various battery cells  458  and the tray  468  or heat exchanger  470 . In another non-limiting embodiment, one or more battery cells  458  may be displaced relative to other battery cells  458  of the cell stack  462  after pushing the battery cells  458  into good contact with the tray  468  or heat exchanger  470 . 
         [0059]    The first portion P 1  of the battery cells  458  may be displaced in a direction toward the tray  468  (and the heat exchanger  470 ). This causes the battery cells  458  near the mid-span M to contact the heat exchanger  470  first and progressively load the rest of the battery cells  458  against the heat exchanger  470  as the entire cell stack  462  is forced to be seated against the heat exchanger  470  and/or the tray  468 . The contact between the cell stack  462  and the heat exchanger  470  may be the result of the heat exchanger  470  and the tray  468  bending to conform about the arch of the battery cells  458 , or alternatively or additionally may be the result of the battery cells  458  slipping with respect to one another such that the battery cells  458  near the mid-span M slide upwardly with respect to neighboring battery cells  458  until the neighboring battery cells  458  also make contact with the heat exchanger  470 , and so on. Alternatively, the cell stack  462  may bend rather than slip to approach a flat geometry in contact with the heat exchanger  470 . 
         [0060]    The exploded views of  FIGS. 2-6  are not necessarily drawn to scale and may be somewhat exaggerated to better illustrate the salient features of this disclosure. Multiple “biased profiles” such as shown in these figures may be combined with one another to achieve a desired amount of contact between the battery cells and the heat exchanger of a battery assembly. The shapes of the biased profiles may be curved, chevron, or other shapes as needed depending on the differences in stiffness between the various components of the battery assembly. For example, biased profiles may not be uniformly curved such as shown in  FIGS. 2-6  and could be constructed to provide different degrees of curves and flatness at different portions along the length of the component having the biased profile. 
         [0061]    Although the different non-limiting embodiments are illustrated as having specific components or steps, the embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments. 
         [0062]    It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should be understood that although a particular component arrangement is disclosed and illustrated in these exemplary embodiments, other arrangements could also benefit from the teachings of this disclosure. 
         [0063]    The foregoing description shall be interpreted as illustrative and not in any limiting sense. A worker of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. For these reasons, the following claims should be studied to determine the true scope and content of this disclosure.