Patent Publication Number: US-9406984-B2

Title: Air-cooled battery module for a vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. application Ser. No. 13/950,342 filed Jul. 25, 2013, now U.S. Pat. No. 9,287,596, issued Mar. 15, 2016, the disclosure of which is hereby incorporated in its entirety by reference herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an air-cooled high voltage traction battery module for a vehicle. 
     BACKGROUND 
     Hybrid electric vehicles (HEVs) include a high voltage traction battery for supplying power to an electric motor used to propel the vehicle. The traction battery may include several battery modules, each having an array of individual battery cells capable of delivering and storing electric energy to and from the electric motor. Use of the traction battery during travel may cause the temperature of individual battery cells within the battery modules to increase. Air-cooled and fluid-cooled systems have been developed to introduce relatively cool air or liquid into the traction battery while removing undesirable heat from within. This inhibits the battery from overheating, which would otherwise cause the battery to operate less efficiently. 
     SUMMARY 
     According to one embodiment, a high-voltage traction battery assembly for a hybrid electric vehicle is provided. An array of battery cells is stacked along a longitudinal axis. A first end plate and an opposing second end plate are spaced therefrom along the longitudinal axis. The end plates are secured to respective ends of the array. A first sidewall and an opposing second sidewall are spaced therefrom, and each sidewall is secured to both end plates extending generally perpendicular to the end plates. The battery module does not include an upper cover or a lower cover attached thereto. The first sidewall has a first ridge defining a first airflow passage between the array and the first ridge, and the second sidewall has a second ridge defining a second airflow passage between the array and the second ridge. The first end plate defines an inlet opening therethrough and aligned with the first airflow passage, and the second end plate defines an outlet opening therethrough and aligned with the second airflow passage. This enables air to flow through the inlet opening and the first airflow passage, across the array, and through the second airflow passage and outlet. 
     In another embodiment, a battery module is provided. A first and a second array of battery cells are arranged side-by-side. Each array has an upper surface and two longitudinal side surfaces defined by the collective surfaces of the battery cells within each array. A first pair of sidewalls covers the side surfaces of the first array. A second pair of sidewalls covers the side surfaces of the second array. Each sidewall has an interior channel extending along the length of the sidewall and spaced apart from the side surface that the sidewall covers. An airflow passage is therefore defined between the respective side surface and the interior channel. Two end plates are disposed at opposing ends of each array and secured to at least some of the sidewalls such that the battery module does not include an upper cover or a lower cover secured or otherwise attached thereto. Each end plate defines a pair of openings that align with at least some of the airflow passages. The airflow passages of the first and second side-by-side arrays define two exteriorly-disposed airflow passages and two interiorly-disposed airflow passages. The interiorly-disposed airflow passages define inflow passages and the exteriorly-disposed airflow passages define outflow passages. Caps cover openings in the end plates at one end of each of the airflow passages such that air flows into the inflow passages, across the battery cells, and out of the outflow passages during a battery cooling event. A double inlet plate has a pair of openings aligned with the interiorly-disposed openings and is mounted to both of the side-by-side arrays. 
     Another battery module is also provided according to the present disclosure. The battery module includes an array of battery cells, each cell having a top surface and opposing side surfaces. A pair of opposing sidewalls each has an interior channel spaced apart from respective side surfaces of the sidewall to define an airflow passage therebetween. The pair of opposing sidewalls each also has an exterior channel spaced from the interior channel. A pair of end plates are each mounted to the exterior channels of both of the sidewalls. A bracket mounts one of the end plates with one of the sidewalls. The bracket has a flange extending into the exterior channel of the one of the sidewalls. The attachment of the sidewalls and the end plates via the bracket enables the absence of covers attached to the battery module above and/or below the array of battery cells. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an exemplary powertrain of a hybrid electric vehicle; 
         FIG. 2  is a perspective view of a battery module according to one embodiment; 
         FIG. 3  is a partially-exploded perspective view of the battery module of  FIG. 2 ; 
         FIG. 4  is a perspective view of a sidewall of the battery module illustrating internal and external channels extending along the length of the sidewall; 
         FIG. 5  is a perspective view of an end plate of the battery module with a cap covering one opening of the end plate; 
         FIG. 6  is a cross-sectional perspective view of two side-by-side battery modules; and 
         FIG. 7  is a cross-sectional top schematic view of the two side-by-side battery modules of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the embodiments. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
     Referring to  FIG. 1 , a schematic diagram of a hybrid electric vehicle (HEV)  10  is illustrated according to an embodiment of the present disclosure.  FIG. 1  illustrates representative relationships among the components. Physical placement and orientation of the components within the vehicle may vary. The HEV  10  includes a powertrain  12 . The powertrain  12  includes an engine  14  that drives a transmission  16 , which may be referred to as a modular hybrid transmission (MHT). As will be described in further detail below, transmission  16  includes an electric machine such as an electric motor/generator (M/G)  18 , an associated traction battery  20 , a torque converter  22 , and a multiple step-ratio automatic transmission, or gearbox  24 . 
     The engine  14  and the M/G  18  are both drive sources for the HEV  10 . The engine  14  generally represents a power source that may include an internal combustion engine such as a gasoline, diesel, or natural gas powered engine, or a fuel cell. The engine  14  generates an engine power and corresponding engine torque that is supplied to the M/G  18  when a disconnect clutch  26  between the engine  14  and the M/G  18  is at least partially engaged. The M/G  18  may be implemented by any one of a plurality of types of electric machines. For example, M/G  18  may be a permanent magnet synchronous motor. Power electronics  56  condition direct current (DC) power provided by the battery  20  to the requirements of the M/G  18 , as will be described below. For example, power electronics may provide three phase alternating current (AC) to the M/G  18 . 
     When the disconnect clutch  26  is at least partially engaged, power flow from the engine  14  to the M/G  18  or from the M/G  18  to the engine  14  is possible. For example, the disconnect clutch  26  may be engaged and M/G  18  may operate as a generator to convert rotational energy provided by a crankshaft  28  and M/G shaft  30  into electrical energy to be stored in the battery  20 . The disconnect clutch  26  can also be disengaged to isolate the engine  14  from the remainder of the powertrain  12  such that the M/G  18  can act as the sole drive source for the HEV  10 . Shaft  30  extends through the M/G  18 . The M/G  18  is continuously drivably connected to the shaft  30 , whereas the engine  14  is drivably connected to the shaft  30  only when the disconnect clutch  26  is at least partially engaged. 
     The M/G  18  is connected to the torque converter  22  via shaft  30 . The torque converter  22  is therefore connected to the engine  14  when the disconnect clutch  26  is at least partially engaged. The torque converter  22  includes an impeller fixed to M/G shaft  30  and a turbine fixed to a transmission input shaft  32 . The torque converter  22  thus provides a hydraulic coupling between shaft  30  and transmission input shaft  32 . The torque converter  22  transmits power from the impeller to the turbine when the impeller rotates faster than the turbine. The magnitude of the turbine torque and impeller torque generally depend upon the relative speeds. When the ratio of impeller speed to turbine speed is sufficiently high, the turbine torque is a multiple of the impeller torque. A torque converter bypass clutch  34  may also be provided that, when engaged, frictionally or mechanically couples the impeller and the turbine of the torque converter  22 , permitting more efficient power transfer. The torque converter bypass clutch  34  may be operated as a launch clutch to provide smooth vehicle launch. Alternatively, or in combination, a launch clutch similar to disconnect clutch  26  may be provided between the M/G  18  and gearbox  24  for applications that do not include a torque converter  22  or a torque converter bypass clutch  34 . In some applications, disconnect clutch  26  is generally referred to as an upstream clutch and launch clutch  34  (which may be a torque converter bypass clutch) is generally referred to as a downstream clutch. 
     The gearbox  24  may include gear sets (not shown) that are selectively placed in different gear ratios by selective engagement of friction elements such as clutches and brakes (not shown) to establish the desired multiple discrete or step drive ratios. The friction elements are controllable through a shift schedule that connects and disconnects certain elements of the gear sets to control the ratio between a transmission output shaft  36  and the transmission input shaft  32 . The gearbox  24  is automatically shifted from one ratio to another based on various vehicle and ambient operating conditions by an associated controller, such as a powertrain control unit (PCU)  50 . The gearbox  24  then provides powertrain output torque to output shaft  36 . 
     It should be understood that the hydraulically controlled gearbox  24  used with a torque converter  22  is but one example of a gearbox or transmission arrangement; any multiple ratio gearbox that accepts input torque(s) from an engine and/or a motor and then provides torque to an output shaft at the different ratios is acceptable for use with embodiments of the present disclosure. For example, gearbox  24  may be implemented by an automated mechanical (or manual) transmission (AMT) that includes one or more servo motors to translate/rotate shift forks along a shift rail to select a desired gear ratio. As generally understood by those of ordinary skill in the art, an AMT may be used in applications with higher torque requirements, for example. 
     As shown in the representative embodiment of  FIG. 1 , the output shaft  36  is connected to a differential  40 . The differential  40  drives a pair of wheels  42  via respective axles  44  connected to the differential  40 . The differential transmits approximately equal torque to each wheel  42  while permitting slight speed differences such as when the vehicle turns a corner. Different types of differentials or similar devices may be used to distribute torque from the powertrain to one or more wheels. In some applications, torque distribution may vary depending on the particular operating mode or condition, for example. 
     The powertrain  12  further includes an associated powertrain control unit (PCU)  50 . While illustrated as one controller, the PCU  50  may be part of a larger control system and may be controlled by various other controllers throughout the vehicle  10 , such as a vehicle system controller (VSC). It should therefore be understood that the powertrain control unit  50  and one or more other controllers can collectively be referred to as a “controller” that controls various actuators in response to signals from various sensors to control functions such as starting/stopping engine  14 , operating M/G  18  to provide wheel torque or charge battery  20 , select or schedule transmission shifts, etc. Controller  50  may include a microprocessor or central processing unit (CPU) in communication with various types of computer readable storage devices or media. Computer readable storage devices or media may include volatile and nonvolatile storage in read-only memory (ROM), random-access memory (RAM), and keep-alive memory (KAM), for example. KAM is a persistent or non-volatile memory that may be used to store various operating variables while the CPU is powered down. Computer-readable storage devices or media may be implemented using any of a number of known memory devices such as PROMs (programmable read-only memory), EPROMs (electrically PROM), EEPROMs (electrically erasable PROM), flash memory, or any other electric, magnetic, optical, or combination memory devices capable of storing data, some of which represent executable instructions, used by the controller in controlling the engine or vehicle. 
     The controller communicates with various engine/vehicle sensors and actuators via an input/output (I/O) interface that may be implemented as a single integrated interface that provides various raw data or signal conditioning, processing, and/or conversion, short-circuit protection, and the like. Alternatively, one or more dedicated hardware or firmware chips may be used to condition and process particular signals before being supplied to the CPU. As generally illustrated in the representative embodiment of  FIG. 1 , PCU  50  may communicate signals to and/or from engine  14 , disconnect clutch  26 , M/G  18 , launch clutch  34 , transmission gearbox  24 , and power electronics  56 . Although not explicitly illustrated, those of ordinary skill in the art will recognize various functions or components that may be controlled by PCU  50  within each of the subsystems identified above. Representative examples of parameters, systems, and/or components that may be directly or indirectly actuated using control logic executed by the controller include fuel injection timing, rate, and duration, throttle valve position, spark plug ignition timing (for spark-ignition engines), intake/exhaust valve timing and duration, front-end accessory drive (FEAD) components such as an alternator, air conditioning compressor, battery charging, regenerative braking, M/G operation, clutch pressures for disconnect clutch  26 , launch clutch  34 , and transmission gearbox  24 , and the like. Sensors communicating input through the I/O interface may be used to indicate turbocharger boost pressure, crankshaft position (PIP), engine rotational speed (RPM), wheel speeds (WS 1 , WS 2 ), vehicle speed (VSS), coolant temperature (ECT), intake manifold pressure (MAP), accelerator pedal position (PPS), ignition switch position (IGN), throttle valve position (TP), air temperature (TMP), exhaust gas oxygen (EGO) or other exhaust gas component concentration or presence, intake air flow (MAF), transmission gear, ratio, or mode, transmission oil temperature (TOT), transmission turbine speed (TS), torque converter bypass clutch  34  status (TCC), deceleration or shift mode (MDE), for example. 
     Control logic or functions performed by PCU  50  may be represented by flow charts or similar diagrams in one or more figures. These figures provide representative control strategies and/or logic that may be implemented using one or more processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Although not always explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending upon the particular processing strategy being used. Similarly, the order of processing is not necessarily required to achieve the features and advantages described herein, but is provided for ease of illustration and description. The control logic may be implemented primarily in software executed by a microprocessor-based vehicle, engine, and/or powertrain controller, such as PCU  50 . Of course, the control logic may be implemented in software, hardware, or a combination of software and hardware in one or more controllers depending upon the particular application. When implemented in software, the control logic may be provided in one or more computer-readable storage devices or media having stored data representing code or instructions executed by a computer to control the vehicle or its subsystems. The computer-readable storage devices or media may include one or more of a number of known physical devices which utilize electric, magnetic, and/or optical storage to keep executable instructions and associated calibration information, operating variables, and the like. 
     An accelerator pedal  52  is used by the driver of the vehicle to provide a demanded torque, power, or drive command to propel the vehicle. In general, depressing and releasing the pedal  52  generates an accelerator pedal position signal that may be interpreted by the controller  50  as a demand for increased power or decreased power, respectively. Based at least upon input from the pedal, the controller  50  commands torque from the engine  14  and/or the M/G  18 . The controller  50  also controls the timing of gear shifts within the gearbox  24 , as well as engagement or disengagement of the disconnect clutch  26  and the torque converter bypass clutch  34 . Like the disconnect clutch  26 , the torque converter bypass clutch  34  can be modulated across a range between the engaged and disengaged positions. This produces a variable slip in the torque converter  22  in addition to the variable slip produced by the hydrodynamic coupling between the impeller and the turbine. Alternatively, the torque converter bypass clutch  34  may be operated as locked or open without using a modulated operating mode depending on the particular application. 
     To drive the vehicle with the engine  14 , the disconnect clutch  26  is at least partially engaged to transfer at least a portion of the engine torque through the disconnect clutch  26  to the M/G  18 , and then from the M/G  18  through the torque converter  22  and gearbox  24 . The M/G  18  may assist the engine  14  by providing additional power to turn the shaft  30 . This operation mode may be referred to as a “hybrid mode” or an “electric assist mode.” 
     To drive the vehicle with the M/G  18  as the sole power source, the power flow remains the same except the disconnect clutch  26  isolates the engine  14  from the remainder of the powertrain  12 . Combustion in the engine  14  may be disabled or otherwise OFF during this time to conserve fuel. The traction battery  20  transmits stored electrical energy through wiring  54  to power electronics  56  that may include an inverter, for example. The power electronics  56  convert DC voltage from the battery  20  into AC voltage to be used by the M/G  18 . The PCU  50  commands the power electronics  56  to convert voltage from the battery  20  to an AC voltage provided to the M/G  18  to provide positive or negative torque to the shaft  30 . This operation mode may be referred to as an “electric only” operation mode. 
     In any mode of operation, the M/G  18  may act as a motor and provide a driving force for the powertrain  12 . Alternatively, the M/G  18  may act as a generator and convert kinetic energy from the powertrain  12  into electric energy to be stored in the battery  20 . The M/G  18  may act as a generator while the engine  14  is providing propulsion power for the vehicle  10 , for example. The M/G  18  may additionally act as a generator during times of regenerative braking in which rotational energy from spinning wheels  42  is transferred back through the gearbox  24  and is converted into electrical energy for storage in the battery  20 . 
     It should be understood that the schematic illustrated in  FIG. 1  is merely exemplary and is not intended to be limited. Other configurations are contemplated that utilize selective engagement of both an engine and a motor to transmit through the transmission. For example, the M/G  18  may be offset from the crankshaft  28 , an additional motor may be provided to start the engine  14 , and/or the M/G  18  may be provided between the torque converter  22  and the gearbox  24 . Other configurations are contemplated without deviating from the scope of the present disclosure. 
     Referring to  FIGS. 2 and 3 , a battery module  100  is illustrated. The battery module  100  may be one of many battery modules that collectively make up the battery  20 . Each battery module  100  includes a stacked array of battery cells  102 . The cells  102  are each capable of storing electric energy from and delivering electric energy to the power electronics  56  in the manner described above. As each cell  102  is capable of holding its own electric charge, a battery electronic control module (BECM) or other controller is responsible for the distribution of charge into, out of, and amongst the individual battery cells  102 . 
     The cells  102  are stacked face-to-face along the length of the battery module  100 . A small spacing or gap may exist between the faces of the cells  102  to allow for airflow across the faces of the cells  102 . 
     First and second end plates  104 ,  106  are disposed at respective ends of the array of battery cells  102  to define the ends of the battery module  100 . Each end plate  104 ,  106  can be identically manufactured and designed such that the same end plate can be assembled to the battery module  100  as either a first end plate  104  or a second end plate  106 . 
     First and second sidewalls  108 ,  110  are mounted to both end plates  104 ,  106 . The sidewalls  108 ,  110  have a length extending along a longitudinal axis of the module  100  to cover the side surfaces of the battery cells  102 . Just as the end plates  104 ,  106  cover the ends of the battery module  100 , the sidewalls encase the sides of the cells  102  within the module  100 . When mounted together, the sidewalls  108 ,  110  and the end plates  104 ,  106  collectively define the boundaries of the battery module  100  and at least partially encapsulate the array of battery cells  102 . 
     During extensive operation of the vehicle, the temperature in the battery  20  may rise. Temperature management is essential to insure optimum, safe, and efficient use of the battery  20 . In order to maintain a desirable temperature in the battery  20 , ambient fluid (such as air) should be introduced into the battery module  100 . The description provided below relates to the packaging and structure of battery modules to facilitate optimum fluid flow within the battery module to maintain and control the battery temperature. 
     The first end plate  104  includes a pair of openings cut out of the plates for directing air through the battery module  100  to cool the battery cells  102 . Of those two openings, one opening is an inlet opening  114  while the other opening may be capped or otherwise covered, as subsequently explained in further detail. The inlet opening  114  is aligned with a first airflow passage, or inflow passage  116 . The inflow passage  116  is an open region within the battery module  100  between the side surfaces of the battery cells  102  and the interior surface of the first sidewall  108 . The first sidewall  108  includes a longitudinal ledge or ridge  118  that forms an interior channel  120  within the first sidewall  108 . The ridge  118  extends along the entire length of the interior surface of the first sidewall  108 . The ridge  118  provides an air gap between the sides of the battery cells  102  and the first sidewall  108  to facilitate air circulation across the sides of the cells  102 . During a cooling cycle, air flows from an external device (such as a fan) and into the inlet opening  114 , whereupon the air is directed through the inflow passage  116  and interior channel  120 , and toward the outlet opening discussed below. 
     The second end plate  106  includes a pair of openings similar to and aligned with the openings in the first end plate  104 . Of these two openings, one opening is an outlet opening  124  while the other opening may be capped or otherwise covered, as subsequently explained in further detail. The outlet opening  124  is aligned with a second airflow passage, or outflow passage  126 , that is located on the opposite side of the battery calls  102  from the inflow passage  116 . Similar to the first sidewall  108 , the second sidewall  110  includes a longitudinal ledge or ridge  128  that forms an interior channel  130  within the second sidewall. The ridge  128  extends along the entire length of the second sidewall  110  and provides an air gap between the sides of the battery cells  102  and the second sidewall  110 . During a cooling cycle, after air is directed into the inflow passage  116  from the inlet opening, the air is able to pass between the battery cells  102  and into the interior channel  130  of the second sidewall  110 . The air then exits through the outflow passage  126  and the outlet opening  124  of the second end plate  106 . Additional detail regarding the airflow through the battery module  100  is provided with reference to  FIG. 7  below. 
     The end plates  104 ,  106  and the sidewalls  108 ,  110  are secured together via brackets  134 . The brackets  134  include a generally planar face  136  configured to rest on the backside of the corners of the end plates  104 ,  106 . The brackets  134  also include a flange  138  extending transversely from the face  136  of the bracket  134 . The flange  138  extends into an exterior channel  140  of the corresponding sidewall  108 ,  110  with which the bracket  134  mounts with. 
     As more clearly shown in  FIG. 4 , the exterior channel  140  is provided at an upper region of each of the sidewalls, such as first sidewall  108  shown. The exterior channel  140  is vertically spaced from the interior channel  120  and extends along the length of the sidewall  108 . An upper shelf or flange  142  defines the top of the exterior channel  140 . The exterior channel  140  serves as an attachment point for the flange  138  of the brackets  134  to secure the end plates  104 ,  106  to the sidewalls  108 . For example, the  138  of the bracket mates with the top surface  142  of the exterior channel  140  for attachment. 
     When the sidewall  108  is mounted, a ledge  142  in the upper region of the sidewall  108  rests on a portion of the top surfaces of the battery cells  102 . This ledge  142  enables the sidewall  108  to provide a secure upper perimeter about the battery cells  102  without the need for a separate upper plate to fully cover the upper sides of the battery cells  102 . A similar ledge can be provided on the bottom of the sidewall  108  to at least partially cover a portion of the bottom surfaces of the battery cells. Additional brackets  146  can be placed throughout the exterior channel  140  to secure the sidewalls  108 ,  110  either directly or indirectly to the battery cells  102 . 
     With the disclosure above, a unitary battery module  100  having a single array of battery cells  102  is therefore provided. The end plates  104 ,  106  contain the array of battery cells  102  from both longitudinal ends, while the sidewalls  108 ,  110  contain the array of battery cells  102  from the sides. The sidewalls  108 ,  110  also partially cover and secure the top surfaces of the battery cells  102  via ledge  144  without the need for a full cover above or below the top and bottom surfaces of the battery cells  102 . The absence of a top or bottom cover reduces the amount of parts and the weight of the battery module  100  while maintaining a secure battery module shell formed by the secured end plates  104 ,  106  and the sidewalls  108 ,  110 . The single-array, unitary battery module  100  can be easily transported, positioned, and assembled into vehicles along with other similar battery modules to make up the entire battery  20 . 
     In order to cool the battery modules, a cooling cycle may include an activation of a fan by a controller. The controller may command the activation of the fan (and thus the cooling cycle) based on several factors such as battery cell temperature, discharge rate, and/or state of charge (SOC). During a cooling cycle, air is directed from the inflow passage  116 , across the faces of the battery cells  102 , and out through the outflow passage  126 . The cooling cycle introduces ambient air into the battery module  100  and removes hot air from within to regulate and maintain the battery temperature. In order to force the air in this flow pattern, caps  150  are attached to the end plates  104 ,  106 . 
       FIG. 5  shows an isolated view of an end plate such as first end plate  104  with such a cap  150 . The cap  150  is sized to cover the opening  152  in the end plate  104  that is not the inlet opening  114 . Once secured (via screws, etc.) to the end plate  104  and over the opening  152 , the cap  150  inhibits air from flowing out of the first end plate  104 . 
     A similar cap is provided on the second end plate  106  to cover the opening in the end plate  106  that is not the outlet opening  124 . This forces the air to exit through the outlet opening  124  of the second end plate  106  rather than the capped opening of the second end plate  106 . 
       FIGS. 6 and 7  both illustrate two separate battery modules connected together to form a high-voltage traction battery assembly. Each battery module includes the features as described with reference to  FIGS. 1-5 . For explanation purposes, the connected battery modules will be referred to as first battery module  200  and second battery module  300 , each having parts and features similar to the battery module  100  described above with reference numbers increasing by  100  for each battery module  200 ,  300 . 
     The first battery module  200  has an inflow passage  216  adjacent to an inflow channel  316  of the second battery module  300 . The adjacent inflow passages  216 ,  316  begin at the respective inlet openings  214 ,  314  of the side-by-side end plates  204 ,  304 . An inlet bracket or double-inlet plate  260  is mounted to both end plates  204 ,  304  and secures the two battery modules  200 ,  300  together. The bracket  260  may include protrusions or fins for connecting to an external machine (e.g., a fan, now shown). This allows one connection point for the two interior-most openings of the four openings formed in the side-by-side end plates  204 ,  304  of the separate battery modules  200 ,  300 . 
     Caps  250 ,  350  are secured to the respective end plates  204 ,  304 . The caps cover the exterior-most openings in the end plates  204 ,  304  that are not the inlet openings  214 ,  314 . Additional caps are provided at the opposite ends of the battery modules  200 ,  300  to cover the interior-most openings formed in the end plates  206 ,  306 . A first sidewall  208  of the first battery module  200  and a second sidewall  310  of the second battery module  300  are exteriorly-disposed relative to the pair of battery modules  200 ,  300 . Similarly, a second sidewall  210  of the first battery module  200  and a first sidewall  308  of the second battery module  300  are interiorly-disposed within the pair of battery modules and define the boundaries of the respective inflow passages  216 ,  316 . 
     During a cooling cycle, the caps force air to flow into the two adjacent inflow passages  216 ,  316 , across the battery cells  202 ,  302  of each respective module  200 ,  300 , and out of the exterior outflow passages  226 ,  326  on opposite sides of the side-by-side battery modules  200 ,  300 . Arrows  400  indicate the airflow path throughout the battery modules  200 ,  300 . 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.