Abstract:
A battery thermal management system according to an exemplary aspect of the present disclosure includes, among other things, a bimetallic member moveable between a first position and a second position in response to a temperature change to selectively restrict flow of a coolant through a duct.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to an electrified vehicle, and more particularly, but not exclusively, to a battery thermal management system that employs a bimetallic member. The bimetallic member is adapted to alter the resistance to coolant flow through a battery pack as a function of cell temperature. 
       BACKGROUND 
       [0002]    Electrified vehicles, such as hybrid electric vehicles (HEV&#39;s), plug-in hybrid electric vehicles (PHEV&#39;s), battery electric vehicles (BEV&#39;s), or fuel cell vehicles differ from conventional engine vehicles in that they are powered by one or more electric machines (i.e., electric motors and/or generators) instead of or in addition to an internal combustion engine. High voltage current for powering the electric machines is typically supplied by a high voltage traction battery pack. 
         [0003]    Electrified vehicle battery packs are made up of multiple battery modules. The battery cells of each battery module may need to be thermally managed to remove excess heat out of the battery pack. Some battery packs are air cooled and typically push or pull pressurized air through a battery pack inlet and outlet. As air flows through the battery pack toward the outlet, a gradient of temperature and pressure may be created. This may cause the battery cells to age at varying rates. 
       SUMMARY 
       [0004]    A battery thermal management system according to an exemplary aspect of the present disclosure includes, among other things, a bimetallic member moveable between a first position and a second position in response to a temperature change to selectively restrict flow of a coolant through a duct. 
         [0005]    In a further non-limiting embodiment of the foregoing system, the bimetallic member is made of at least two dissimilar materials. 
         [0006]    In a further non-limiting embodiment of either of the foregoing systems, the bimetallic member is a bimetallic coil. 
         [0007]    In a further non-limiting embodiment of any of the foregoing systems, the bimetallic member is a bimetallic strip that includes a first strip of material and a second strip of material affixed to the first strip of material. 
         [0008]    In a further non-limiting embodiment of any of the foregoing systems, a surface is connected to the bimetallic member. 
         [0009]    In a further non-limiting embodiment of any of the foregoing systems, the surface is a plate or a vane. 
         [0010]    In a further non-limiting embodiment of any of the foregoing systems, a control arm extends between the bimetallic member and a surface. 
         [0011]    In a further non-limiting embodiment of any of the foregoing systems, a first side of the control arm is connected to the bimetallic member and a second side of the control arm is connected to the surface. 
         [0012]    In a further non-limiting embodiment of any of the foregoing systems, movement of the bimetallic member between the first position and the second position moves the surface to change a dimension of the duct. 
         [0013]    In a further non-limiting embodiment of any of the foregoing systems, the bimetallic member is comprised of a first material and the control arm and the surface are comprised of a second material that is different from the first material. 
         [0014]    A battery pack according to another exemplary aspect of the present disclosure includes, among other things, a first battery cell, a second battery cell, and a duct that extends between the first battery cell and the second battery cell. A surface is positioned relative to the duct and moveable between a first position and a second position to control flow of coolant through the duct. 
         [0015]    In a further non-limiting embodiment of the foregoing battery pack, the surface is part of a bimetallic member. 
         [0016]    In a further non-limiting embodiment of either of the foregoing battery packs, the surface is connected to a bimetallic member. 
         [0017]    In a further non-limiting embodiment of any of the foregoing battery packs, the surface is connected to a control arm that is connected to a bimetallic member. 
         [0018]    In a further non-limiting embodiment of any of the foregoing battery packs, a bimetallic member is in contact with the first battery cell and the surface is in contact with the second battery cell. 
         [0019]    A method according to another exemplary aspect of the present disclosure includes, among other things, controlling a flow of a coolant through a battery pack using a bimetallic member. 
         [0020]    In a further non-limiting embodiment of the foregoing method, the controlling step includes moving the bimetallic member between a first position and a second position to change a dimension of a duct that extends between adjacent battery cells of the battery pack. 
         [0021]    In a further non-limiting embodiment of either of the foregoing methods, the moving step includes positioning a surface relative to the adjacent battery cells in response to moving the bimetallic member. 
         [0022]    In a further non-limiting embodiment of any of the foregoing methods, the controlling step includes moving the bimetallic member in response to absorbing heat from a battery cell housed within the battery pack. 
         [0023]    In a further non-limiting embodiment of any of the foregoing methods, the controlling step includes redirecting the coolant from relatively cool portions of the battery pack to relatively warm portions of the battery pack with the bimetallic member. 
         [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 according to a first embodiment of this disclosure. 
           [0028]      FIG. 3  illustrates a battery pack according to a second embodiment of this disclosure. 
           [0029]      FIG. 4  illustrates a battery pack according to another embodiment of this disclosure. 
           [0030]      FIG. 5  illustrates a bimetallic strip that may be employed by a battery thermal management system. 
           [0031]      FIGS. 6A and 6B  illustrate a battery thermal management system according to one embodiment of this disclosure. 
           [0032]      FIG. 7  illustrates a bimetallic coil that may be employed by a battery thermal management system. 
           [0033]      FIGS. 8A and 8B  illustrate a battery thermal management system according to another embodiment of this disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    This disclosure relates to a battery thermal management system for thermally managing one or more battery cells of a battery pack. The battery thermal management system employs a bimetallic member that is moveable to alter an amount of coolant that can be directed through ducts that extend between adjacent battery cells. Movement of the bimetallic member is driven by material properties and may be triggered by a temperature change of one or more battery cells. These and other features are discussed in greater detail below within this detailed description. 
         [0035]      FIG. 1  schematically illustrates a powertrain  10  of an electrified vehicle  12 . The electrified vehicle  12  may be a HEV, PHEV, BEV, or any other vehicle. In other words, this disclosure is not limited to any particular type of electrified vehicle, and could also extend to non-automotive electrified vehicles (e.g., locomotives, airplanes, ships, submarines, etc.). 
         [0036]    The powertrain  10  includes a drive system having at least a motor  36  (i.e., an electric machine) and a battery pack  50 . The battery pack  50  may include a high voltage battery that is capable of outputting electrical power to operate the motor  36 . Although not shown by  FIG. 1 , the battery pack  50  may include multiple battery modules that are electrically connected to one another. 
         [0037]    In one embodiment, the drive system generates torque to drive one or more sets of vehicle drive wheels  30  of the electrified vehicle  12 . For example, the motor  36  can be powered by the battery pack  50  to electrically drive the vehicle drive wheels  30  by outputting torque to a shaft  46 . 
         [0038]    Of course, this view is highly schematic. It should be appreciated that the powertrain  10  of the electrified vehicle  12  could employ additional components, including but not limited to, an internal combustion engine, a generator, a power transfer unit, and one or more control systems, within the scope of this disclosure. 
         [0039]      FIG. 2  illustrates a battery pack  50  for an electrified vehicle, such as the electrified vehicle  12  of  FIG. 1  or any other electrified vehicle. The battery pack  50  includes a housing  60  that generally surrounds one or more battery modules  62 A,  62 B, etc. Two battery modules  62 A,  62 B are illustrated in  FIG. 2 ; however, it should be understood that the battery pack  50  could include any number of battery modules. 
         [0040]    Each battery module  62  includes a plurality of battery cells  64  (i.e., two or more cells). In one embodiment, the battery cells  64  may be lithium ion cells. In another embodiment, the battery cells  64  are nickel metal hydride cells. Other types of cells are additionally contemplated. 
         [0041]    The battery cells  64  of each battery module  62  may be spaced from one another to establish ducts  74  between adjacent battery cells  64 . Although not shown, spacers may be positioned within the ducts  74  to retain and position the battery cells  64  relative to one another. The ducts  74  define conduits for communicating coolant C, such as airflow, through the battery pack  50 . 
         [0042]    Heat may be generated by each battery cell  64  during charging and discharging operations. Heat may also be transferred into the battery cells  62  during key-off conditions of the electrified vehicle  12  as a result of relatively extreme (i.e., hot) ambient conditions. The battery pack  50  may therefore include a battery thermal management system  66  for thermally managing the heat generated by the battery cells  64 . 
         [0043]    The battery thermal management system  66  may include an inlet  70  and an outlet  72 . Coolant C may enter the battery pack  50  through the inlet  70  and be circulated inside of the housing  60  prior to exiting through the outlet  72 . For example, the coolant C may be communicated through the ducts  74  as well as over and around the battery cells  64  to remove heat from the battery cells  64 . Therefore, the coolant C that exits the outlet  72  will be warmer than the coolant C that enters the inlet  70 . 
         [0044]    In one embodiment, the battery thermal management system  66  includes one or more surfaces  68  that are positioned relative to the ducts  74 . The surfaces  68  are moveable to control the flow of coolant C through the battery pack  50 , including through the ducts  74 . In a first non-limiting embodiment, the surfaces  68  are positioned to extend at least partially into the ducts  74  (i.e., between adjacent battery cells  64 ) of the first battery module  62 A to control the flow of coolant C between the battery cells  64 . In another embodiment, the surfaces  68  may be mounted to the housing  60  and moveable to control the flow of the coolant C into the ducts  74  (see  FIG. 3 ). In yet another embodiment, the surfaces  68  are positioned between the battery cells  64  of both the battery module  62 A and the battery module  62 B (see  FIG. 4 ). Multiple embodiments for moving the surfaces  68  to control the flow of the coolant C through the battery pack  50  are detailed below. 
         [0045]    In a first non-limiting embodiment, best shown in  FIG. 2 , the surfaces  68  themselves are made of bimetallic members  76  that are moveable to change a dimension D of the ducts  74 . For example, the bimetallic members  76  may absorb heat from the battery cells  64 . As heat is absorbed, the bimetallic members  76  may move or straighten to permit a greater amount of coolant C to pass through the ducts  74 . In one embodiment, the bimetallic members  76  are positioned or otherwise biased to close-off the ducts  74  (see top left portion of  FIG. 2 ). Therefore, in cooler sections of the battery pack  50  (e.g., near battery cells  64  that are closer to the inlet  70 ), the bimetallic members  76  do not move, bend or otherwise alter their shape such that the surfaces  68  block the communication of coolant C through the ducts  74 . In this way, the coolant C may be directed to relatively warmer areas of the battery pack  50  (e.g., near battery cells  64  that are closer to the outlet  72 ) without first becoming over-heated prior to reaching these locations. 
         [0046]      FIG. 5  illustrates a first exemplary bimetallic member  76  that can be used to convert a temperature change into mechanical displacement. In this embodiment, the bimetallic member  76  is configured as a bimetallic strip that includes a first strip of material  80  and a second strip of material  82  affixed to the first strip of material  80 . The first strip of material  80  may be affixed to the second strip of material  82  in any known manner. The first strip of material  80  and the second strip of material  82  are made of different materials. In one embodiment, the first strip of material  80  is steel and the second strip of material  82  is copper. In another embodiment, the first strip of material  80  is steel and the second strip of material  82  is brass. Other materials may also be suitable for constructing the bimetallic member  76 . 
         [0047]    Because the first strip of material  80  and the second strip of material  82  are different materials, they tend to expand at different rates as they are heated. Accordingly, the different expansions of these materials cause the bimetallic member  76  to bend toward position X′ (shown in phantom lines) if heated and bend toward position X if cooled (or vice versa). The displacement of the bimetallic member  76  can be controlled by positioning the strip of material having the highest coefficient of thermal expansion at a desired position relative to the heat source. 
         [0048]      FIGS. 6A and 6B  illustrate another exemplary battery thermal management system  166 . 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. 
         [0049]    In this embodiment, the battery thermal management system  166  includes a bimetallic member  176  and a surface  168  connected to the bimetallic member  176 . In other words, unlike the embodiment of  FIG. 2 , the surface  168  is a separate component from the bimetallic member  176 . The surface  168  may be a plate, a vane or any other surface. In one embodiment, the bimetallic member  176  is attached or at least in contact with a battery cell  64 A on a first side of a duct  174  and the surface  168  is attached or at least in contact with a battery cell  64 B that is positioned on a second side of the duct  174 . 
         [0050]    The bimetallic member  176  is adapted to move the surface  168  to change a dimension associated with the duct  174  that extends between the adjacent battery cells  64 A,  64 B. For example, in a first position X in which the battery cells  64 A,  64 B are relatively cold (see  FIG. 6A ), the bimetallic member  176  is in a retracted state such that a portion of the surface  168  is moved away from the battery cell  64 B to restrict the duct  174  to a dimension D-1. In a second position X′ in which the battery cells  64 A,  64 B are relatively warm (see  FIG. 6B ), the bimetallic member  176  absorbs heat from the battery cell  64 A and expands to move the surface  168  back toward the battery cell  64 B, thereby opening the duct  174  to a dimension D-2. In one embodiment, the dimension D-2 is larger than the dimension D-1 such that additional coolant C is fed through the duct  174  to cool the battery cells  64 A,  64 B. 
         [0051]      FIG. 7  illustrates an exemplary bimetallic member  176  that may be utilized with the thermal management system  166  of  FIGS. 6A and 6B . In this embodiment, the bimetallic member  176  is a bimetallic coil. The bimetallic coil may uncoil when heated (see  FIG. 6B ) and coil back to its original position when not being heated (see  FIG. 6A ). Of course, an opposite configuration is also contemplated in which the bimetallic member  176  coils when heated and uncoils when cooled. 
         [0052]      FIGS. 8A and 8B  illustrate another exemplary battery thermal management system  266 . The battery thermal management system  266  is similar to the battery thermal management system  166  of  FIGS. 6A and 6B  but includes a control arm  278 . For example, in one non-limiting embodiment, the battery thermal management system  266  includes a bimetallic member  276 , a surface  268  and the control arm  278 . The control arm  278  extends between the bimetallic member  276  and the surface  268 . In one embodiment, a first side of the control arm  278  is connected to the bimetallic member  276  and a second side of the control arm  278  is connected to the surface  268 . Accordingly, movement of the bimetallic member  276  is transferred to the surface  268  through the control arm  278  in order to expand or restrict the duct  274 . 
         [0053]    In one embodiment, the surface  268  and the control arm  278  are made from the same material. Suitable materials include polymers and metals, including but not limited to, polypropylene, polybutylene, terephthalate, aluminum, steel and other materials. 
         [0054]    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. 
         [0055]    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. 
         [0056]    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.