Patent Publication Number: US-2013252052-A1

Title: Integrated Busbar, Terminal Pin And Circuit Protection For Sensing Individual Battery Cell Voltage

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to voltage-sensing components used in conjunction with a battery-powered system, and more particularly to a method of integrating separate voltage-sensing components into a unified battery assembly as a way to increase assembly robustness and manufacturability of battery cell voltage-sensing components. 
     The increasing demand to improve vehicular fuel economy and reduce vehicular emissions has led to the development of both hybrid vehicles and pure electric vehicles. Pure electric vehicles may be powered by a battery pack (also called a battery), while hybrid vehicles include two or more energy sources, such as a gasoline (also referred to as an internal combustion) engine used as either a backup to or in cooperation with a battery pack. There are two broad versions of hybrid vehicles currently in use. In a first version (known as a charge-depleting hybrid architecture), the battery can be charged off a conventional electrical grid such as a 120 VAC or 240 VAC power line. In a second version (known as a charge-sustaining hybrid architecture), the battery receives all of its electrical charging from one or both of the internal combustion engine and regenerative braking. In either version, the battery pack is typically made from numerous modules, which in turn are made up of numerous individual cells. Numerous frames, trays, covers and related structure may be included to provide support for the various cells, modules and packs, and as such help to define a larger assembly of such cells, modules or packs. 
     In one form, the cells of the battery pack delivers direct current (DC) electricity; this current may in turn be used to provide power to various vehicle systems, such as motors, electric traction systems (ETS) or the like, as well as ancillary equipment. A power inverter is typically employed for components that need alternating current (AC) rather than DC power; these power inverters typically include capacitor modules and an integrated gate bipolar transistor (IGBT) for converting the DC input signal to an AC output signal. In a common form, these modules are connected via busbar or cabling assemblies. The busbars interact electrically with the various cells of the battery pack through thin metal tabs that project out of an edge of the generally planar cells of the pack. Both the bus bars and the tabs are typically made of copper, aluminum or alloys thereof. In some cases, the tabs or related conductors may be coated with a thin layer of other metal to enhance corrosion resistance or other desirable properties. 
     The busbar is generally seen to be advantageous over cabling assemblies because (among other things) it—in addition to providing electrical connectivity—makes it possible to integrate voltage-sensing and monitoring electronics with the power connection. Furthermore, its general structure allows all of the tabs used to provide electrical connection among the individual cells to be reliably and repeatably positioned relative to one another through a simple assembly operation. In one form, the monitoring (such as cell voltage-sensing through the circuit-protection fuses) is typically accomplished using a circuit protection device (i.e., a fuse) as an electrical interface between the busbar and a terminal pin that is formed as part of the aforementioned frame that is used to provide structural support of the battery cell or cells. 
     Despite these advantages, conventional busbars suffer from certain drawbacks. These shortcomings are particularly acute when trying to connect the circuit-protection fuses to the frame after the frame has already been molded or otherwise formed. First, in one common assembly approach, the busbar must be snap-fit or heat staked to the frame. The snap fit in particular is not a robust process and allows for too much variation. Second, resistance welding the small leads of the fuse to both the busbar and the terminal pin requires fine alignment and process windows, which are difficult to meet when incorporated into a larger part. Third, the fuse leads themselves may be exposed to mechanical loads; generally, the small leads of the fuse are not robust enough to function as both a mechanical and electrical link between the terminal and busbar. Thus, any errors or reduction in weld quality will influence throughput as the fuse leads eventually fatigue and fail. Likewise, these assembly difficulties result in a significant probability of failure and related production reject rate, thereby driving up production costs. 
     SUMMARY OF THE INVENTION 
     In accordance with the teachings of the present invention, a method of forming an integrated circuit for use in a battery-powered automobile propulsion system is disclosed. The circuit includes a fuse with leads for establishing electrical communication between a busbar and a terminal pin. In a preferred form, there is a circuit for each cell within a larger battery pack or related assembly. In the present context, the circuit may be formed as part of a connector housing (also referred to herein more simply as housing) that in turn is permanently secured to or otherwise formed as part of the frame; in either event, the integral nature of the connection between the frame and the voltage-sensing circuit is such that being rigidly secured to one another, they are integral in functional sense, even if some visible indicia of their original separate nature may remain. As such, by being integrated into the frame within the present context, the voltage-sensing circuit becomes a structural whole, thereby exhibiting the enhanced structural robustness vis-à-vis the approach of the prior art, where separately-formed voltage-sensing circuits that are more vulnerable to repeated handling and related breakage-prone events are likely to occur. In particular, the combination of the busbar, fuse and terminal pin that make up the integrated voltage-sensing circuit are—once coupled to the housing—configured as a modular whole with and within the housing such that together the housing and the circuit define an autonomous part that is a structurally-robust integrated structure within itself, as well as when it is secured to the larger frame (such as by overmolding, encapsulation or the like) to become an integral part thereof. 
     In accordance with another aspect of the present invention, an assembly for sensing voltage produced by a battery cell within a battery pack made up of a plurality of battery cells is disclosed. As mentioned above, the assembled circuit provides the means to measure the voltage of each individual cell in a battery pack. The voltage-sensing circuit is made up of at least three components, including a terminal pin, cladded busbar and fuse (i.e. circuit protection) that are assembled together to fit in a modular housing that in turn may be secured to a battery frame. By integrating these electrically-conductive pieces within a housing and further integrating this housing into a frame (for example, an injection-molded frame), a greater robustness of all components can be realized. This is especially valuable for the fuse that links the terminal pin and busbar, as being part of a compact, modular housing that can withstand far more harsh handling treatment than can the fuse and related components individually. 
     In accordance with yet another aspect of the present invention, a battery pack configured to provide propulsive power to a vehicle is disclosed. The battery pack includes numerous battery cells, a frame for each battery cell to allow the cell to be secured and a voltage-sensing circuit secured to the frame, where the voltage-sensing circuit includes the aforementioned fuse, busbar and terminal pin, as well as a housing configured to maintain the fuse, the busbar and the terminal pin in electrical communication with one another. In one particular form, the housing defines a molded structure such that once the connection between the various electrically-conductive components are made, the voltage-sensing circuit defines a modular unit. As mentioned above, the molded structure of the housing is preferably further molded into the molded structure of frame; such molding, encapsulation, overmolding or the like ensures an integral connection between the housing and frame. In a preferred form, the shapes defined by the molded housing include various formations for receiving the electrically-conductive parts of the voltage-sensing circuit. It will be appreciated by those skilled in the art that the battery pack may include additional features for mechanical or electrical support, including additional frames, containers, cooling circuits or the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of specific embodiments can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIG. 1  is a schematic diagram of an exemplary vehicle configured with a hybrid power source, showing the integration of a battery pack with and various other subcomponents of the vehicle; 
         FIGS. 2A and 2B  show respective top and elevation views of the connection between a busbar, terminal pin and fuse of a voltage-sensing circuit according to the prior art; 
         FIG. 3A  shows the molded housing with the terminal pin placed therein according to an aspect of the present invention; 
         FIG. 3B  shows the housing of  FIG. 3A  connected to the busbar and fuse to define a modular, integral voltage-sensing circuit according to an aspect of the present invention; 
         FIG. 4A  shows the busbar of  FIG. 3B  in isolation; 
         FIG. 4B  shows the terminal pin of  FIGS. 3A and 3B  in isolation; 
         FIG. 5A  shows a view from one side of the integration of the modular, integral voltage-sensing circuit of  FIG. 3B  into a portion of a battery cell frame; and 
         FIG. 5B  shows a view from the opposing side of the integrated voltage-sensing circuit of  FIG. 5A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to  FIG. 1 , a schematic diagram of a hybrid-powered vehicle  10  in accordance with the present invention is shown. Within the present context, it will be appreciated that the term “vehicle” may apply to car, truck, van sport utility vehicle (SUV) or the like. Vehicle  10  includes an ICE  20 , battery  30  and an electronic control system  40 , where one or both of ICE  20  and battery  30  may be coupled to an electric motor/generator  25 . Vehicle  10  further includes a powertrain  50  (which could be in the form of a driveshaft or the like) to deliver propulsive power from the ICE  20 , motor/generator  25  or battery  30  to one or more of the wheels  60 . Battery  30  includes a state of charge (SOC) system  32  and power inverter assembly  34 , the latter of which includes various modules, including those for the IGBT and capacitors (not shown) as well as other conductive elements configured to provide a pathway for current flow between these and other associated battery-related electronic components. Busbar assemblies (portions of which are shown and discussed in more detail below) provide compact, reliable electrical connection between these various modules. Additional support equipment, such as radiator  60 , is also shown. Although the battery  30  (which as discussed above may be placed in a frame as part of a larger assembly) is shown in the rear of vehicle  10 , it may be located in any suitable location to facilitate its electrical coupling (via busbars discussed in more detail below) to the various electrical components. In one embodiment, battery  30  is an assembly or pack made up of numerous lithium ion (Li-ion) cells (not individually shown). The electronic control system  40  may include a variable motor drive module  42  to control electric motor torque and speed, as well as other vehicular functions. It will be appreciated by those skilled in the art that while vehicle  10  is presently shown as a hybrid-powered vehicle, that one with purely electric power (i.e., one with no need for ICE  20 ) is also deemed to be within the scope of the present invention. 
     Referring next to  FIGS. 2A and 2B , details depicting a portion of a notional prior art busbar subassembly  100  ( FIG. 2A ) and voltage-sensing circuit  105  made up of the connection between a busbar  110  and terminal pin  120  through a fuse  130  is shown. In particular, the various components making up the voltage-sensing circuit  105  are directly attached to a portion of frame  140  that is used to provide mechanical or structural support for these and other components. Furthermore, additional components, such as battery cell-supporting tray  36 , are preferably sized to structurally cooperate with frame  140 . In one form, the frame  140  is about ten inches (i.e., about 250 millimeters) in length along its longest edge and further includes apertures  150  formed therein to promote connection through a bolt or related fastener (not shown). It will be appreciated by those skilled in the art that only a small part of frame  140  is shown, where numerous such frames  140  (with mounted cells  36  and voltage-sensing circuits  105 ) are stacked or otherwise arranged to provide a mechanically rigid pathway to facilitate the flow of current from the individual battery cells  36  to the various power-consuming components in vehicle  10 . Depending on the configuration, other components (not shown) of each individual busbar subassembly  100  may include a positive DC terminal, a negative DC terminal and an AC terminal, as well as numerous other components to establish electrical connectivity between the positive and negative terminals of the individual battery cells, as well as to other components of battery  30 . Each busbar subassembly  100  transfers current received from the positive and negative terminals of the DC source (i.e., battery cell  36 ) to (among other components) IGBT devices, power diodes or other components that can either convert the DC signal to a single-phase AC signal. As mentioned above, in one form, at least the electrically-conductive portions of busbar subassembly  100  may be made from copper or a copper alloy, and may additionally be plated. 
     Upon stacking and connecting the various individual frames  140 , a structural assembly resembling a substantially complete battery pack (such as battery  30 ) is formed. As mentioned above, each battery cell within battery  30  is mounted to a corresponding frame  140  that includes a mounting location where fuse  130  may be secured to the busbar  110  and terminal pin  120 . In one particular form, a chassis or related larger container (not shown) may also be used to provide enclosure and related environmental protection for not only the battery  30 , but also the internal electronic components, such as those that make up the power inverter assembly  34 ; such an additional container may be made from a suitable material with conductive features that can be grounded to the chassis of vehicle  10  to provide a ground source for housed electrical components. 
     The above approach to battery  30  construction necessitates that each voltage-sensing circuit  105  in general—and each fuse  130  in particular—be picked and placed onto the frame  140 ; furthermore the electrical leads (which are typically very small—for example—0.6 millimeter in diameter) of fuse  130  need to be aligned with the terminal pin  120  and busbar  110  for proper resistance welding. The manipulation of objects with disparate scales (specifically, the large scale of frame  140  and the much smaller scale of fuse  130 ) increases complexity of the assembling process, as movements deemed fine-motor within the larger scale may be far too coarse for the particular needs of the fuse  130  and its fragile leads. This in turn leads to potential handling or process-related damage to the voltage-sensing circuit  105 . 
     Referring next to  FIGS. 3A ,  3 B,  4 A and  4 B, the various components making up a voltage-sensing circuit subassembly  200  (also referred to herein as assembly) according to an aspect of the present invention are shown. Referring first to  FIGS. 3A and 3B , the subassembly  200  includes a housing  202  for containing the voltage-sensing circuit  205  as a way to reduce complexity, process variability and cost by having at least the busbar  210  and terminal pin  220  be integrally-formed within the housing  202  that will in turn be integrally formed (such as by overmolding or encapsulation) with a frame (such as frame  240 ) such that placement and alignment of fuse  230  is achieved with a significant reduction in the risk of damage. Various formations are defined in housing  202 , including apertures  202 A that permit liquid forms of molded frame material (for example, polypropylene) to pass through such that upon solidification, form a permanent, integral connection between the frame and housing  202 . Other formations, such as  202 B,  202 C and  202 D are used to define spaces where the busbar  210 , terminal pin  220  and fuse  230 , respectively may be mounted or otherwise placed. Likewise, connector  202 E may be used to define a mounting location for other equipment that makes up, or is otherwise connected to, the frame. Formation  202 G defines a bent path (shown notionally as being roughly serpentine) to allow the leads from fuse  210  to be attached to complementary surfaces on the busbar  210  and terminal pin  220 .  FIG. 3B  shows with particularity how the housing  202  and the entirety of the busbar  210  form the voltage-sensing circuit subassembly  200 . In one form of construction, the terminal pin  220  is placed in a mold—which may be a pre-defined slot or related shape formed in the housing  202 , while the busbar  210  may be joined to the housing through appropriate connection. In any event, once the busbar subassembly  200  is formed, the fuse  230  may be inserted into the cavity or related indentation corresponding to formation  202 D. As mentioned above, the electrically-conductive nature of the busbar  210  and terminal pin  220  is such that when secured to corresponding electrically-conductive leads  234 ,  232  of fuse  230 , they form an electrically-continuous circuit  205 . In particular, shaped portions  201 D and  230 A formed in the busbar  210  and terminal pin  220  respectively are sized to promote secure connection between the small-diameter leads  234 ,  232  of fuse  230 . In one form, the connection may be through appropriate mechanical means, such as snap-fit, heat staking or the like, while electrical connection may be accomplished through resistance welding or another joining method to establish the fuse joints discussed below. 
     Referring with particularity to  FIGS. 4A and 4B , as with the busbar subassembly  100  of the prior art, busbar subassembly  200  includes (in addition to fuse  230  that functions as a circuit-protection mechanism) a busbar  210  and terminal pin  220 . Referring with particularity to  FIG. 4A , the busbar  210  includes a generally conductive face  210 A made from a copper alloy secured to a backing  210 B made from an aluminum alloy. Aperture  210 C is sized to cooperate with the detent-shaped formation  202 B of the housing  202  of  FIG. 3A . 
     Referring next to  FIGS. 5A and 5B , the integration of the frame  240  and the housing  202  is shown, where surface details are added to the latter to better emphasize initial lines of demarcation between the two structures. Unlike the prior art, the voltage-sensing circuit  205 , by virtue of its integrated construction within housing  202 , voltage-sensing circuit subassembly  200  and frame  240 , has an increased resistance to environmental and mechanical loading, thus reducing the probability of a failure. The construction of the voltage-sensing circuit  205  is such that at least the locations within housing  202  where the fuse  230  and its leads  232 ,  234  are placed forms an integral structure that may subsequently be secured to frame  240 . Thus in one form, the modular housing  202  and voltage-sensing circuit  205  may be secured to the frame  240  during a molding process of the frame  240  such that upon completion of the molding, the housing  202  and at least a portion of the voltage-sensing circuit  205  are encapsulated within the frame  240 . 
     Referring with particularity to  FIG. 5B , the fuse  230  (in general) and the fuse joints  236 ,  238  formed between the leads  232 ,  234  and their corresponding connection points on the respective terminal pin  220  and busbar  210  (in particular) are especially vulnerable to damage that can occur during normal fabrication and handling. Leads  232  and  234  extending from opposing ends of fuse  230  provide electrical connectivity to the terminal pin  220  and busbar  210 , respectively, preferably through a resistance welding process. By having both properly-sized resilient connections and precision alignment between the leads  232  and  234 , the fuse  230  may be secured to the housing  202  and the remainder of the busbar subassembly  200  with a higher degree of confidence that subsequent frame-handling (i.e., large-scale) operations will not exploit minute differences in small-scale misalignments within the fuse  230 , busbar  210  and terminal pin  220  to jeopardize reliable fabrication of the voltage-sensing circuit  205 . In a particular form, at least a significant portion of the busbar  210  and terminal pin  220  are encapsulated by the plastic of the frame  240  during the overmold process, while fuse  230  is preferably left substantially uncovered by the material of the frame  240 . As can be seen in both of the present figures, there is significant coverage of the connection between the busbar  210  and the housing  202 , as well as between the terminal pin  220  and the housing  202 , while the fuse  230  and its leads  232 ,  234  remain substantially uncovered. The cavity or related indentation  202 D (as best shown in  FIG. 3A ) in housing  202  has integrally-formed tabs or detents  202 F to allow the fuse  230  to be securely snap-fit into place, while the serpentine walls  202 G promote secure alignment of the leads  232 ,  234  to the respective contact surfaces of terminal pin  220  and busbar  210 . 
     In one form, the fuse joints  236 ,  238  formed between the leads  232 ,  234  and their corresponding connection points on the respective terminal pin  220  and busbar  210  may be done through resistance welding. The tolerances that a smaller assembly (such as that which fits within or otherwise cooperates with housing  202 ) makes possible are a good fit with the dimensions of the fuse  230  and the demands of resistance welding. Furthermore, the compact, modular nature of housing  202  allows a fuse  230  secured thereto to be handled in a manner more consistent with the larger-scale structure of frame  240 . Likewise, the present design of housing  202  is easily integrated within the host frame  240  by overmolding, thereby increasing structural continuity and related overall robustness and manufacturability. 
     By the present construction, the order of assembly of the present invention is the opposite of that of the prior art where the three electrically-connected components  110 ,  120  and  130  of the voltage-sensing circuit  105  are assembled after the molding or forming of the battery cell frame  140 , whereas in the present invention, the components  210 ,  220  and  230  are combined in a single standalone unit before molding the battery cell frame  240 . This enhances circuit  205  integrity by providing a built-in carrier in the form of housing  202  (at a first, more modular level) and the larger assembly  200  (at a second, slightly larger level). Furthermore, by using an overmolding process to secure the housing  202  or assembly  200  to the frame  240 , at least the busbar  210 , transfer pin  220  and their respective interconnects to the housing  202  are secured in place with a barrier to the ambient environment. 
     It is noted that terms like “preferably,” “commonly,” and “typically” are not utilized herein to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the present invention. Likewise, for the purposes of describing and defining the present invention it is noted that the term “substantially” is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     For the purposes of describing and defining the present invention it is noted that the terms “battery”, “battery pack” or the like are utilized herein to represent a combination of individual battery cells used to provide electric current, preferably for vehicular, propulsive or related purposes. Furthermore, variations on the terms “automobile”, “automotive”, “vehicular” or the like are meant to be construed generically unless the context dictates otherwise. As such, reference to an automobile will be understood to cover cars, trucks, buses, motorcycles and other similar modes of transportation unless more particularly recited in context. 
     Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.