Abstract:
A battery pack according to an exemplary aspect of the present disclosure includes, among other things, a heat exchanger plate including a plate body including an interior wall and an exterior wall and an air gap enclosed inside the plate body and extending between the interior wall and the exterior wall.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to a battery pack for an electrified vehicle. The battery pack includes a heat exchanger plate having an integrated air gap. The air gap is configured to thermally isolate an internal cooling circuit of the heat exchanger plate from an exterior environment of the pack. 
       BACKGROUND 
       [0002]    The need to reduce automotive fuel consumption and emissions is well known. Therefore, vehicles are being developed that reduce or completely eliminate reliance on internal combustion engines. Electrified vehicles are one type of vehicle currently 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 drive the vehicle. 
         [0003]    A high voltage battery pack for powering electric machines and other electrical loads typically includes multiple battery cells. The battery cells release heat during charging and discharging operations. It is often desirable to dissipate this heat from the battery pack to improve capacity and life of the battery cells. 
       SUMMARY 
       [0004]    A battery pack according to an exemplary aspect of the present disclosure includes, among other things, a heat exchanger plate including a plate body including an interior wall and an exterior wall and an air gap enclosed inside the plate body and extending between the interior wall and the exterior wall. 
         [0005]    In a further non-limiting embodiment of the foregoing battery pack, the interior wall includes an exterior surface that faces toward an interior of the battery pack. 
         [0006]    In a further non-limiting embodiment of either of the foregoing battery packs, the exterior wall includes an exterior surface that is exposed to an exterior environment. 
         [0007]    In a further non-limiting embodiment of any of the foregoing battery packs, the air gap extends between the exterior wall and an internal wall of the plate body. 
         [0008]    In a further non-limiting embodiment of any of the foregoing battery packs, the internal wall establishes a floor of an internal cooling circuit disposed inside the plate body. 
         [0009]    In a further non-limiting embodiment of any of the foregoing battery packs, the internal cooling circuit establishes a serpentine passage inside the plate body. 
         [0010]    In a further non-limiting embodiment of any of the foregoing battery packs, the plate body includes a first plate piece, a second plate piece and a third plate piece that are connected together. 
         [0011]    In a further non-limiting embodiment of any of the foregoing battery packs, at least one standoff extends between the exterior wall and an internal wall of the plate body. 
         [0012]    In a further non-limiting embodiment of any of the foregoing battery packs, the air gap is a static pocket of air inside the plate body. 
         [0013]    In a further non-limiting embodiment of any of the foregoing battery packs, the air gap is configured to limit the thermal transfer of heat from an exterior environment into an internal cooling circuit disposed inside the plate body. 
         [0014]    A battery pack according to another exemplary aspect of the present disclosure includes, among other things, an enclosure defining an interior, a battery array housed within the interior, a heat exchanger plate including an interior wall proximate the battery array and an exterior wall exposed to an exterior environment outside of the enclosure, and an air gap disposed inside the heat exchanger plate. 
         [0015]    In a further non-limiting embodiment of the foregoing battery pack, the battery array includes a plurality of battery cells positioned relative to the interior wall of the heat exchanger plate. 
         [0016]    In a further non-limiting embodiment of either of the foregoing battery packs, the heat exchanger plate includes an internal cooling circuit including a plurality of fluid channels. 
         [0017]    In a further non-limiting embodiment of any of the foregoing battery packs, a plurality of walls divide the plurality of fluid channels. 
         [0018]    In a further non-limiting embodiment of any of the foregoing battery packs, the internal cooling circuit establishes a serpentine passage. 
         [0019]    In a further non-limiting embodiment of any of the foregoing battery packs, the heat exchanger plate forms a base of the enclosure. 
         [0020]    In a further non-limiting embodiment of any of the foregoing battery packs, the heat exchanger plate forms a sidewall of the enclosure. 
         [0021]    In a further non-limiting embodiment of any of the foregoing battery packs, the air gap extends between the exterior wall and an internal wall disposed inside the heat exchanger plate. 
         [0022]    In a further non-limiting embodiment of any of the foregoing battery packs, the internal wall establishes a floor of an internal cooling circuit disposed inside the heat exchanger plate. 
         [0023]    In a further non-limiting embodiment of any of the foregoing battery packs, the air gap is configured to limit the thermal transfer of heat from the exterior environment into an internal cooling circuit of the heat exchanger plate. 
         [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 pack of an electrified vehicle. 
           [0028]      FIG. 3  illustrates another exemplary battery pack. 
           [0029]      FIG. 4  illustrates a heat exchanger plate of a battery pack. 
           [0030]      FIG. 5  is a cross-sectional view through section A-A of  FIG. 4 . 
           [0031]      FIG. 6  is a cross-sectional view of another exemplary heat exchanger plate. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    This disclosure details exemplary battery pack designs for use in electrified vehicles. A heat exchanger plate is utilized to thermally manage heat generated by battery cells of a battery pack. In some embodiments, the heat exchanger plate includes an integrated air gap configured to limit the thermal transfer of heat from an outside environment to an internal cooling circuit of the plate. These and other features are discussed in greater detail in the following paragraphs of this detailed description. 
         [0033]      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. 
         [0034]    In one non-limiting 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 pack  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. 
         [0035]    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 . 
         [0036]    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 . 
         [0037]    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 . 
         [0038]    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 pack  24 . 
         [0039]    The battery pack  24  is an exemplary electrified vehicle battery. The battery pack  24  may be a high voltage traction battery pack that includes a plurality of battery assemblies  25  (i.e., battery arrays or groupings of battery cells) capable of outputting electrical power to operate the motor  22 , the generator  18  and/or other electrical loads of the electrified vehicle  12 . Other types of energy storage devices and/or output devices can also be used to electrically power the electrified vehicle  12 . 
         [0040]    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 pack  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 pack  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. 
         [0041]    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 pack  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. 
         [0042]      FIG. 2  illustrates portions of a battery pack  24  that can be employed within an electrified vehicle. For example, the battery pack  24  could be part of the electrified vehicle  12  of  FIG. 1 . The battery pack  24  includes a plurality of battery cells  56  that store electrical power for powering various electrical loads of the electrified vehicle  12 . Although a specific number of battery cells  56  are depicted in  FIG. 2 , the battery pack  24  could employ a fewer or greater number of battery cells within the scope of this disclosure. In other words, this disclosure is not limited to the specific configuration shown in  FIG. 2 . 
         [0043]    The battery cells  56  may be stacked side-by-side along a longitudinal axis A to construct a grouping of battery cells  56 , sometimes referred to as a “cell stack.” The battery pack  24  can include one or more separate groupings of battery cells  56 . In other words, the battery pack  24  could include multiple cell stacks. 
         [0044]    In another non-limiting embodiment, the battery cells  56  are prismatic, lithium-ion cells. However, battery cells having other geometries (cylindrical, pouch, etc.), other chemistries (nickel-metal hydride, lead-acid, etc.), or both, could alternatively be utilized within the scope of this disclosure. 
         [0045]    In yet another non-limiting embodiment, spacers  58 , which can alternatively be referred to as separators or dividers, are positioned between adjacent battery cells  56  of each grouping of battery cells  56 . The spacers  58  can include thermally resistant and electrically isolating plastics and/or foams. The battery cells  56  and the spacers  58 , along with any other support structures (e.g., rails, walls, plates, etc.), may collectively be referred to as a battery array  60 . One battery array  60  is shown in  FIG. 2 ; however, the battery pack  24  could include multiple battery arrays. 
         [0046]    An enclosure  65  may generally surround each battery array  60  of the battery pack  24 . The enclosure  65  includes a plurality of walls  67  that define an interior for housing the battery arrays  60 . 
         [0047]    The battery array  60  of the battery pack  24  is positioned relative to a heat exchanger plate  62  such that the battery cells  56  are either in contact with or in close proximity to the heat exchanger plate  62 . Although not shown, a thermal insulation material could be positioned between the heat exchanger plate  62  and the battery array  60 . In one non-limiting embodiment, the heat exchanger plate  62  acts as a base of the enclosure  65  (see  FIG. 2 ). In another non-limiting embodiment, the heat exchanger plate  62  acts as a wall (here, a sidewall) of the enclosure  65  (see  FIG. 3 ). In either of these embodiments, the heat exchanger plate  62  includes at least one exterior surface  64  exposed to an exterior environment  66  (i.e., the environment that surrounds the outside of the battery pack  24 ). 
         [0048]    The heat exchanger plate  62  is equipped with features for thermally managing the battery cells  56  of each battery array  60 . For example, heat may be generated and released by the battery cells  56  during charging operations, discharging operations, extreme ambient conditions, or other conditions. It is often desirable to remove the heat from the battery pack  24  to improve capacity and life of the battery cells  56 . The heat exchanger plate  62  is configured to conduct the heat out of the battery cells  56 . In other words, the heat exchanger plate  62  acts as a heat sync to remove heat from the heat sources (i.e., the battery cells  56 ). The heat exchanger plate  62  can alternatively be employed to heat the battery cells  56 , such as during extremely cold ambient conditions. Exemplary heat exchanger plate designs for thermally managing the battery cells  56  of the battery pack  24  are further detailed below. 
         [0049]    A heat exchanger plate  62  according to a first non-limiting embodiment of this disclosure is illustrated in  FIGS. 4 and 5  (with continued reference to  FIG. 2 ). The heat exchanger plate  62  includes a plate body  68  and an internal cooling circuit  70  formed inside the plate body  68 . The heat exchanger plate  62  may be an extruded part or a machined part. Other manufacturing techniques are also contemplated within the scope of this disclosure. In another non-limiting embodiment, the heat exchanger plate  62  is made of aluminum. Other materials are also suitable for constructing the heat exchanger plate  62 . 
         [0050]    A coolant C is selectively circulated through the internal cooling circuit  70  to thermally condition the battery cells  56  of the battery pack  24 . In one non-limiting embodiment, the coolant C is a conventional type of coolant mixture such as water mixed with ethylene glycol. However, other coolants, including gases, are also contemplated within the scope of this disclosure. 
         [0051]    In one non-limiting embodiment, the internal cooling circuit  70  includes a plurality of fluid channels  72  that extend inside the heat exchanger plate  62 . In one non-limiting embodiment, the fluid channels  72  connect to one another for communicating the coolant C through the heat exchanger plate  62 . The fluid channels  72  can be configured in different sizes and shapes to help meter and balance the flow of the coolant C through the internal cooling circuit  70 . The size and shape of each fluid channel  72  and the total number of fluid channels  72  are not intended to limit this disclosure and can be specifically tuned to the cooling requirements of the battery pack  24 . 
         [0052]    In one non-limiting embodiment, the fluid channels  72  establish a serpentine passage  75  inside the plate body  68 . The serpentine passage  75  extends between an inlet  76  and an outlet  78 . Walls  74  are disposed inside the plate body  68  to separate adjacent fluid channels  72  of the internal cooling circuit  70  from one another. The walls  74  extend between opposing end walls  80 A,  80 B of the heat exchanger plate  62 . In one non-limiting embodiment, each wall  74  extends from one of the opposing end walls  80 A,  80 B toward the other opposing end wall  80 A,  80 B but terminates prior to reaching the opposing end wall  80 A,  80 B. For example, the walls  74  may terminate by a distance D inwardly from the opposing end wall  80 A,  80 B. In this way, the flow of the coolant C is not blocked by the walls  74  and can turn from one fluid channel  72  to another as it travels along the serpentine passage  75 . 
         [0053]    In use, the coolant C is communicated into the inlet  76  of the serpentine passage  75  and is then communicated through the fluid channels  72  that define the serpentine passage  75  before exiting through the outlet  78 . The coolant C picks up the heat conducted through heat exchanger plate  62  from the battery cells  56  as it meanders along its path. Although not shown, the coolant C exiting the outlet  78  may be delivered to a radiator or some other heat exchanging device, be cooled, and then returned to the inlet  76  in a closed loop. 
         [0054]    Referring now primarily to  FIG. 5 , the plate body  68  of the heat exchanger plate  62  includes an interior wall  84 , which faces toward an interior of the battery pack  24 , and an exterior wall  86 , which faces toward the exterior environment  66  (see also  FIG. 2 ). The interior wall  84  includes an exterior surface  88  that interfaces with the battery cells  56  of the battery pack  24 , and the exterior surface  64  of the exterior wall  86  is exposed to the exterior environment  66 . The plate body  68  may additionally include an internal wall  90 . In one non-limiting embodiment, the internal wall  90  is a floor of the internal cooling circuit  70 . The internal wall  90  therefore aids in guiding the coolant C as it passes through the internal cooling circuit  70 . In another non-limiting embodiment, the internal wall  90  is completely inside the heat exchanger plate  62  and therefore is not directly exposed to either the interior of the battery pack  24  or the exterior environment  66 . 
         [0055]    An air gap  82  is disposed inside the heat exchanger plate  62 . In one non-limiting embodiment, the air gap  82  is disposed between the interior wall  84  and the exterior wall  86  of the plate body  68 . In yet another non-limiting embodiment, the air gap  82  is positioned between the exterior wall  86  of the plate body  68  and the internal wall  90  of the plate body  68 . The air gap  82  may be positioned at any location inside the plate body  68  that is between the internal cooling circuit  70  and the portion of the plate body  68  that is exposed to the exterior environment  66 . 
         [0056]    The air gap  82  is configured to limit the thermal transfer of heat from the exterior environment  66  into the internal cooling circuit  70  of the heat exchanger plate  62 . For example, the air gap  82 , which is a static pocket of air, acts as an insulator so that less heat from the exterior environment  66  is introduced into the internal cooling circuit  70 . In other words, the air gap  82  reduces the thermal path between the exterior surface  64  and the internal cooling circuit  70 , thereby improving the efficiency of the heat exchanger plate  62 . 
         [0057]    One or more standoffs  92  can optionally be positioned inside the plate body  68 . In one non-limiting embodiment, standoffs  92  extend across the air gap  82  between the exterior wall  86  and the internal wall  90 . The standoffs  92  can be used for reinforcing portions of the heat exchanger plate  62 . 
         [0058]      FIG. 6  illustrates a heat exchanger plate  162  according to another embodiment of this disclosure. In this non-limiting embodiment, the heat exchanger plate  162  includes a plate body  168  constructed from multiple pieces of stamped metal that are either brazed or welded together. A first plate piece  94  establishes the interior wall of the heat exchanger plate  162 , a second plate piece  96  establishes the exterior wall of the heat exchanger plate  162 , and a third plate piece  98  establishes the internal wall of the heat exchanger plate  162 . In one non-limiting embodiment, the third plate piece  98  is a wavy piece of material that includes a plurality of ridges  99 . 
         [0059]    The third plate piece  98  is first attached to the first plate piece  94  to establish an internal cooling circuit  170  of the heat exchanger plate  162 . The second plate piece  96  is then attached to the first plate piece  94  to construct the heat exchanger plate  162 . In one non-limiting embodiment, the second plate piece  96  is attached to the first plate piece  94  (with connected third plate piece  98 ) such that an air gap  182  extends between the second plate piece  96  and the third plate piece  98 . The ridges  99  of the third plate piece  98  do not contact the second plate piece  96  to avoid interrupting the air gap  182 . 
         [0060]    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. 
         [0061]    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. 
         [0062]    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.