Abstract:
A bus bar assembly according to an exemplary aspect of the present disclosure includes, among other things, a plurality of battery cells and a bus bar assembly that electrically connects the plurality of battery cells. The bus bar assembly includes a flexible cable, a voltage sense lead connected to the flexible cable, and a bus bar connected to the voltage sense lead.

Description:
TECHNICAL FIELD 
     This disclosure relates to a battery assembly for an electrified vehicle. Bus bar assemblies electrically connect a plurality of battery cells of the battery assembly. Each bus bar assembly includes a flexible cable, a voltage sense lead integrated with the flexible cable, and a bus bar connected to the voltage sense lead. 
     BACKGROUND 
     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. 
     Electrified vehicle powertrains are typically equipped with a battery assembly having a plurality of battery cells that store electric power for powering the electric machines and other electric loads of the electrified vehicle. The battery cells must be reliably connected to one another in order to achieve the voltage and power levels necessary for powering these electric loads. Separate bus bars, individual sense lead wires, plastic moldings, metal stampings, wire crimps, grommet moldings, and other parts are commonly used to sufficiently connect the battery cells. 
     SUMMARY 
     A bus bar assembly according to an exemplary aspect of the present disclosure includes, among other things, a plurality of battery cells and a bus bar assembly that electrically connects the plurality of battery cells. The bus bar assembly includes a flexible cable, a voltage sense lead connected to the flexible cable, and a bus bar connected to the voltage sense lead. 
     In a further non-limiting embodiment of the foregoing bus bar assembly, the bus bar is connected to a negative terminal of a first battery cell and a positive terminal of a second battery cell. 
     In a further non-limiting embodiment of either of the foregoing bus bar assemblies, the flexible cable includes an opening configured to expose the voltage sense lead for connection with the bus bar. 
     In a further non-limiting embodiment of any of the foregoing bus bar assemblies, the bus bar is welded to the voltage sense lead. 
     In a further non-limiting embodiment of any of the foregoing bus bar assemblies, a jumper wire connects between the voltage sense lead and the bus bar. 
     In a further non-limiting embodiment of any of the foregoing bus bar assemblies, the voltage sense lead is integrated with the flexible cable. 
     In a further non-limiting embodiment of any of the foregoing bus bar assemblies, the voltage sense lead is sandwiched between a first dielectric layer and a second dielectric layer of the flexible cable. 
     In a further non-limiting embodiment of any of the foregoing bus bar assemblies, the bus bar includes a body and a tab that protrudes from the body. 
     In a further non-limiting embodiment of any of the foregoing bus bar assemblies, the body is welded to terminals of two of the plurality of battery cells and the tab is welded to the voltage sense lead. 
     In a further non-limiting embodiment of any of the foregoing bus bar assemblies, the bus bar is integrated within the flexible cable. 
     A method according to an exemplary aspect of the present disclosure includes, among other things, providing a flexible cable, integrating a voltage sense lead to the flexible cable, and connecting a bus bar to the voltage sense lead to assembly a bus bar assembly. 
     In a further non-limiting embodiment of the foregoing method, the method includes electrically connecting a plurality of battery cells of a battery assembly using the bus bar assembly. 
     In a further non-limiting embodiment of either of the foregoing methods, the connecting step occurs before the integrating step. 
     In a further non-limiting embodiment of any of the foregoing methods, the connecting step occurs after the integrating step. 
     In a further non-limiting embodiment of any of the foregoing methods, the connecting step includes welding a jumper wire to the voltage sense lead and the bus bar. 
     In a further non-limiting embodiment of any of the foregoing methods, the connecting step includes laser welding the bus bar to the voltage sense lead. 
     In a further non-limiting embodiment of any of the foregoing methods, the integrating step includes imbedding the voltage sense lead within the flexible cable. 
     In a further non-limiting embodiment of any of the foregoing methods, the integrating step includes sandwiching the voltage sense lead between a first dielectric layer and a second dielectric layer of the flexible cable. 
     In a further non-limiting embodiment of any of the foregoing methods, the method includes feeding a strip of material into the flexible cable and forming notches in the strip of material to form the bus bar. 
     In a further non-limiting embodiment of any of the foregoing methods, the feeding step includes feeding the strip of material between a first layer and a second layer of the flexible cable. 
     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. 
     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 
         FIG. 1  schematically illustrates a powertrain of an electrified vehicle. 
         FIG. 2  illustrates a battery assembly of an electrified vehicle. 
         FIGS. 3A, 3B, 3C and 3D  schematically illustrate a method of assembling a bus bar assembly according to a first embodiment of this disclosure. 
         FIG. 4  illustrates a bus bar. 
         FIGS. 5A, 5B, 5C and 5D  schematically illustrate a method of assembling a bus bar assembly according to another embodiment of this disclosure. 
         FIG. 6  illustrates a bus bar assembly. 
         FIG. 7  illustrates a battery assembly exhibiting cell height variations between adjacent battery cells. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure details a battery assembly for an electrified vehicle. The battery assembly may employ a bus bar assembly for electrically connecting a plurality of battery cells of the battery assembly. The bus bar assembly may include a flexible cable, a voltage sense lead embedded within the flexible cable, and a bus bar connected to the voltage sense lead. The bus bar assemblies of this disclosure accommodate variations between cell terminal heights of adjacent battery cells and enable a simplified assembly process for constructing the battery assembly. These and other features are discussed in greater detail in the following paragraphs of this detailed description. 
       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. 
     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. 
     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 . 
     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 . 
     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 . 
     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 . 
     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 . 
     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. 
     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. 
       FIG. 2  illustrates a battery assembly  24  that can be incorporated into 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 battery cells within the scope of this disclosure. In other words, this disclosure is not limited to the specific configuration shown in  FIG. 2 . 
     The battery cells  58  may be stacked side-by-side to construct a grouping of battery cells, sometimes referred to as a battery array. 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. 
     Each battery cell  58  includes a positive terminal (designated by the symbol (+)) and a negative terminal (designed by the symbol (−)). However, only one terminal of each battery cell  58  is shown in  FIG. 2 . The battery cells  58  are arranged such that each battery cell  58  terminal is disposed adjacent to a terminal of an adjacent battery cell  58  having an opposite polarity. For example, in one non-limiting embodiment, the negative terminal (−) of a first battery cell  58 - 1  is positioned adjacent to a positive terminal (+) of a second battery cell  58 - 2 . This alternating pattern continues across the entire span of the grouping of battery cells  58 . 
     The battery assembly  24  may include one or more bus bar assemblies  60 . The bus bar assemblies  60  electrically connect the battery cells  58  relative to one another. In one non-limiting embodiment, the bus bar assembly  60  extends across a top surface  65  of each battery cell  58  along an axis A that is generally perpendicular to an axis B of each battery cell  58 . 
     The exemplary bus bar assembly  60  may include a flexible cable  62 , one or more voltage sense leads  64 , and one or more bus bars  66 . In the illustrated embodiment, the bus bar assembly  60  includes a plurality of voltage sense leads  64  and a plurality of bus bars  66 . However, this disclose is not limited to the exact configuration shown. It should be understood that the bus bar assembly  60  could include any configuration having one or more voltage sense leads and one or more bus bars. 
     In use, the bus bar assembly  60  provides an integrated circuit for electrically connecting the battery cells  58  such that electrical power may be distributed throughout the electrified vehicle. High voltage current from each battery cell  58  is conducted through the bus bars  66 . The voltage of each battery cell  58  may be measured by the voltage sense leads  64 , which communicate voltage signals to another component, such as a control module (not shown) of the battery assembly  24 . 
     In one embodiment, the flexible cable  62  is made of a pliable (i.e., bendable) material. Various plastic materials may be suitable for constructing the flexible cable  62 . Non-limiting examples of suitable plastic materials include polyester (PET), polyimide (PI), polyethylene napthalate (PEN), polyethermide (PEI), and various fluropolymers (FEP) and/or copolymers. In another embodiment, the flexible cable  62  is made of Kapton®, which is available from DuPont. 
     Because of the pliable nature of the flexible cable  62 , the bus bar assembly  60  is configured to accommodate any cell height variations between the battery cells  58  of the battery assembly  24  (see, for example,  FIG. 7 ). Cell height variations can occur during assembly of the battery assembly  24 . 
     Each voltage sense lead  64  may be integrated with the flexible cable  62 . In this disclosure, the term “integrated” means the voltage sense leads  64  are fabricated directly on or imbedded within the flexible cable  62 . In one embodiment, the voltage sense leads  64  include copper traces or wires that are printed onto the flexible cable  62 . The voltage sense leads  64  may be applied onto or into the flexible cable  62  using a variety of additive or subtractive techniques. Non-limiting examples of such techniques include printing, plating, etching, laminating, engraving, milling, ablation, etc. 
     In another embodiment, the voltage sense leads  64  are sandwiched between a first dielectric layer  68 A and a second dielectric layer  68 B of the flexible cable  62  (see  FIG. 3B ). The first dielectric layer  68 A and a second dielectric layer  68 B may be sealed together to prevent moisture from wicking into the voltage sense leads  64 . The flexible cable  62  could also include additional layers. 
     In one embodiment, the bus bars  66  are stamped, relatively thin strips of metal that are configured to conduct power generated by the battery cells  58 . In one non-limiting embodiment, the bus bars  66  are made of aluminum. In another embodiment, the bus bars  66  are bimetallic members that can be made of multiple materials, such as copper and aluminum. Other materials having conductive properties may also be suitable. 
     As discussed in greater detail below, each bus bar  66  may be welded to one of the voltage sense leads  64  and may be welded to the terminals of two adjacent battery cells  58  to connect the bus bar assembly  60  to the plurality of battery cells  58 . For example, as depicted in  FIG. 2 , a first weld bead  90  may be used to attach the bus bars  66  to the voltage sense leads  64  and a second weld bead  92  may be used to attach the bus bars  66  to the battery cell  58  terminals. 
       FIGS. 3A, 3B, 3C and 3D  schematically illustrate a method of assembling the bus bar assembly  60 . Referring first to  FIG. 3A , a flexible cable  62  of a desired size and shape is provided and includes a plurality of integrated voltage sense leads  64 . The voltage sense leads  64  may be integrated within the flexible cable  62 , such as by printing the voltage sense leads  64  onto the flexible cable  62  or by sandwiching the voltage sense leads  64  between a first dielectric layer  68 A and a second dielectric layer  68 B of the flexible cable  62  (see  FIG. 3B ). 
     As shown in  FIG. 3C , openings  70  may next be formed in the flexible cable  62 . In one non-limiting embodiment, the openings  70  are cut-outs formed in the flexible cable  62 , such as through a top layer of the flexible cable  62 , a bottom layer, or both. The openings  70  expose portions of each voltage sense lead  64 . 
       FIG. 3D  illustrates connection of the bus bars  66  to the voltage sense leads  64 . In one embodiment, one bus bar  66  may be welded to one voltage sense lead  64  at the portions of the voltage sense leads  64  that are exposed at the openings  70 . In another non-limiting embodiment, the bus bars  66  are laser welded to the voltage sense leads  64 . Once the bus bars  66  are welded to the voltage sense leads  64  via one or more weld beads  90 , the bus bar assembly  60  is fully assembled and ready for attachment to a plurality of battery cells  58  of a battery assembly  24  (see, for example,  FIG. 2 ). 
       FIG. 4  illustrates an exemplary bus bar  66  that may be utilized within the bus bar assembly  60  described above. The bus bar  66  includes a body  72  and a tab  74  that protrudes from the body  72 . The tab  74  may extend over top of the flexible cable  62 , underneath the flexible cable  62 , or between layers of the flexible cable  62  and is configured for attachment to one of the voltage sense leads  64  (see  FIG. 3D ). In one embodiment, the body  72  of the bus bar  66  is contiguous with an edge  99  of the flexible cable  62  but does not overlap with the edge  99  (see  FIG. 3D ). 
       FIGS. 5A, 5B and 5C  schematically illustrate a method of constructing a bus bar assembly  160 . 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. 
     In this exemplary embodiment, a flexible cable  162  is provided having a plurality of voltage sense leads  164  embedded within the flexible cable  162 . As illustrated in  FIG. 5A , a strip of material  176  may be fed into the flexible cable  162  by moving the strip of material  176  in a direction D that is substantially parallel to the longitudinal axis of the flexible cable  162 . For example, the strip of material  176  may be fed onto an outer surface  169  of the flexible cable  162  (see  FIG. 5A ) or could be fed between layers  165 ,  175  of the flexible cable  162  (see  FIG. 5D ). The strip of material  176  may be electrically connected to the voltage sense leads  164  either before or after the strip of material  176  has been fed into the flexible cable  162 . In other words, the voltage sense leads  164  and the strip of material  176  may be integrated with the flexible cable  162  either together or separately. 
     Referring to  FIG. 5B , the strip of material  176  may then be notched to form a plurality of bus bars  166 . The strip of material  176  may be cut in any known manner to create notches  198  that extend between the bus bars  166 . The notches  198  electrically isolate the bus bars  166  from one another. 
     Finally, as shown in  FIG. 5C , the bus bars  166  may be welded to attach the bus bar assembly  160  to the terminals of the battery cells  158 . In one non-limiting embodiment, the bus bars  166  are laser welded to the terminal of the battery cells  158 . The welding process creates a weld bead  192  to fixedly secure the bus bars  166  to the terminals of the battery cell  158 . 
       FIG. 6  illustrates another bus bar assembly  260 . The bus bar assembly  260  includes a flexible cable  262 , a plurality of voltage sense leads  264  and a plurality of bus bars  266 . Each voltage sense lead  264  may be integrated with the flexible cable  262 . Each bus bar  266  may be electrically connected to one of the voltage sense leads  264  and may be welded to the terminals of two adjacent battery cells (not shown in  FIG. 6 ) to connect the bus bar assembly  260  to the plurality of battery cells. In one embodiment, jumper wires  278  may extend between the voltage sense leads  264  and the bus bars  266  to electrically connect these components. The jumper wires  278  may be welded to both the voltage sense leads  264  and the bus bars  266 . 
     The bus bars  266  may be electrically connected to the voltage sense leads  264  either before or after integration with the flexible cable  262 . If before, the bus bars  266  and voltage sense leads  264  may be fed together into the flexible cable  262 . If after, the bus bars  266  and the voltage sense leads  264  may be integrated into the flexible cable separately. Openings  270  may optionally be formed in the flexible cable  262  to expose the voltage sense leads  264  for enabling connection of the jumper wires  278  to the voltage sense leads  264 . 
     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. 
     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. 
     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.