Patent Publication Number: US-8967128-B2

Title: Multiple layer bypass hydrocarbon trap

Description:
TECHNICAL FIELD 
     The present disclosure relates to a multiple layer hydrocarbon trap, such as may be used in an air induction system of a vehicle to reduce or eliminate evaporative hydrocarbon emissions. 
     BACKGROUND 
     When an internal combustion engine is shut off, unburned hydrocarbon fuel vapors may be left in the air induction system, engine cylinders, engine crankcase, etc. These hydrocarbon fuel vapors may migrate out of the engine cylinders through an open intake valve into the intake manifold along with vapors that have migrated from a crankcase to the intake manifold through a PCV (Positive Crankcase Ventilation) system. After the engine is shut off, the vapors may travel through the fresh air intake system and into the surrounding atmosphere. Further, vapors may also migrate from a crankcase, through a crankcase fresh air hose, to the fresh air intake system and then out into the surrounding atmosphere. Changes in ambient air temperatures may further encourage hydrocarbon fuel vapors to migrate from the vehicle. 
     To reduce the escape of hydrocarbon vapors from the engine air induction system (AIS), some vehicles include a hydrocarbon trap in the AIS having one or more hydrocarbon adsorbing surfaces to adsorb vaporized hydrocarbons during engine off soaks. These AIS hydrocarbon traps may be periodically purged of the temporarily stored hydrocarbon vapors when the engine is restarted and the vapors are inducted into the cylinders along with fresh air and consumed during normal engine combustion. 
     A flow-through hydrocarbon trap is positioned such that substantially all the vapors emanating from inside the engine during engine off soaks must pass through it before reaching atmosphere. A bypass hydrocarbon trap is also positioned in the vapor flow path, but only a portion of the vapors pass by or through it prior to reaching atmosphere. Although the flow-through trap is generally more efficient at reducing the amount of hydrocarbon vapors emitted to the environment, a bypass trap may be used to further reduce the escape of any vapors that pass through the flow-through trap, or that may bypass the flow-through trap based on the design of the AIS for some applications. A bypass trap may be used alone or in combination with one or more flow-through traps and/or bypass traps. 
     Various types of AIS flow through and/or bypass hydrocarbon traps are described in commonly owned U.S. Pat. Nos. 8,191,539; 7,458,366; and 6,905,536, for example. While suitable for various applications, these approaches may require a unique design for each application. Unique designs require additional engineering and development resources and fail to leverage available economies of scale afforded by a design that is more easily adapted to multiple applications. For example, previous designs may require different dimensions for different applications. Similarly, considerations relative to the engine volume may require more or less absorber channel openings. Many prior AIS hydrocarbon traps are difficult to scale and/or package within a vehicle due to space limitations and size and material constraints. 
     SUMMARY 
     An air induction system for an engine includes an air filter box configured to receive an air filter that separates the air filter box into an atmosphere side and a filtered air side, a clean-air duct coupled downstream from the air filter box and upstream of the engine relative to a direction of air flow during engine operation, a flow-through hydrocarbon trap positioned within the clean-air duct, and a bypass hydrocarbon trap secured within the air filter box on the filtered air side and adjacent to airflow through the air filter box, the hydrocarbon trap having a plurality of generally flat layers of hydrocarbon adsorbing material sandwiched together and secured one to another. 
     In various embodiments, the bypass hydrocarbon trap comprises a plurality of grommets each extending through the plurality of generally flat layers of hydrocarbon adsorbing material to secure the layers one to another. The grommets may be secured to ribs extending along an interior upper surface of the air filter box and may be heat staked to the interior of the air filter box. In one embodiment, the plurality of generally flat layers of hydrocarbon adsorbing material are adhesively secured to each other. In another embodiment, a generally flat carbon adsorbing material is formed into a multiple-layer spiral secured by a grommet extending through at least two layers. The grommet is secured to an interior portion of the air induction system of the vehicle. 
     Embodiments according to the present disclosure may also include an air induction system hydrocarbon trap for a vehicle having a housing adapted to be coupled to the air induction system and a plurality of layers of hydrocarbon adsorbing material sandwiched together and secured one to another to form a single adsorbing assembly, the single adsorbing assembly being secured within the housing such that airflow through the housing passes by the single adsorbing assembly. In one embodiment, a plurality of grommets each extending through the plurality of generally flat layers of hydrocarbon adsorbing material secure the layers one to another and form a single adsorbing assembly. The single adsorbing assembly may be secured to an upper interior surface of the housing. The housing may be configured to accept a flow-through air filter that separates the housing into an atmosphere side and a filtered air side, with the air induction system further including a clean-air duct coupled between the housing and an engine of the vehicle and a flow-through hydrocarbon trap positioned within the clean-air duct. 
     A hydrocarbon trap disposed within an air induction system of a vehicle according to various embodiments of the present disclosure includes a plurality of generally flat layers of hydrocarbon adsorbing material sandwiched together and mechanically secured one to another by a plurality of grommets passing through the plurality of generally flat layers to form a single adsorbing assembly for being secured to ribs extending from an upper interior surface of an air box of the air induction system. 
     Various embodiments according to the present disclosure may provide one or more advantages. For example, a multiple layer hydrocarbon trap according to embodiments of the present disclosure may include multiple layers of generally flat polygonal sheets secured together by a plurality of grommets or similar fasteners that may be secured to the clean side of an air box cover. This construction method allows the bundle to be manufactured separately and subsequently assembled to the cover allowing for a more flexible manufacturing process. Of course alternate methods of assembling the bundle may be provided. A multiple layer hydrocarbon trap according to various embodiments of the present disclosure provides a modular solution that can be easily adapted to multiple applications by selecting the number of layers of adsorbing material without changes to the packaging. Embodiments according to the present disclosure may reduce cost by providing a universal design that results in higher volumes. Similarly, a generally flat rectangular or polygonal shape reduces scrap in adsorbing material cutting. A hydrocarbon trap having a universal design according to embodiments of the present disclosure may also reduce engineering costs and time to market. In addition, a universal design according to embodiments of the present disclosure allows for usage of adsorbing material from various vendors and facilitates competitive bidding to further reduce costs. 
     The above advantages and other advantages and features will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a representative vehicle application for a multiple layer bypass hydrocarbon trap according to embodiments of the present disclosure; 
         FIG. 2  is a diagram illustrating a vehicle air induction system (AIS) having bypass and flow-through hydrocarbon traps according to one embodiment of the present disclosure and shows the flow of hydrocarbon vapors during engine off soaks; 
         FIG. 3  illustrates a representative air box having a multiple layer hydrocarbon trap according to one embodiment of the present disclosure; 
         FIG. 4  is a partial cross-sectional view of a multiple layer hydrocarbon trap according to one embodiment of the present disclosure; 
         FIG. 5  is a top view of the embodiment of  FIG. 4 ; and 
         FIGS. 6 and 7  illustrate alternative embodiments of a multiple layer hydrocarbon trap for use as a bypass or flow-through trap according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present disclosure are described herein; however, it is to be understood that the disclosed embodiments are merely exemplary and may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may 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 present invention. 
     A multiple layer AIS hydrocarbon trap and related methods and systems are described herein. The multiple layer AIS hydrocarbon trap may be integrated into an engine of an automotive vehicle, for example. A representative application of a bypass AIS hydrocarbon trap is described and illustrated with respect to  FIGS. 1 and 2 . 
       FIG. 1  is a schematic diagram showing one cylinder of multi-cylinder engine  10 , which may be included in a propulsion system of an automobile. While a conventional powertrain arrangement is illustrated, a multiple layer hydrocarbon trap according to embodiments of the present disclosure may also be used in a hybrid vehicle having an engine in combination with a traction battery and one or more electrical machines to propel the vehicle. Engine  10  may be controlled at least partially by a control system including controller  12  and by input from a vehicle operator  132  via an input device  130 . In this example, input device  130  includes an accelerator pedal and a pedal position sensor  134  for generating a corresponding pedal position signal PP. Combustion chamber (i.e. cylinder)  30  of engine  10  may include combustion chamber walls  32  with piston  36  positioned therein. Piston  36  may be coupled to crankshaft  40  so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft  40  may be coupled to at least one drive wheel of a vehicle via an intermediate transmission system. Further, a starter motor (or electrical machine in hybrid applications) may be coupled to crankshaft  40  via a flywheel to enable a starting operation of engine  10 . 
     Combustion chamber  30  may receive intake air from an air induction system having one or more hydrocarbon traps according to the present disclosure as illustrated in greater detail in  FIG. 2 . The air induction system generally includes an intake manifold  44  and intake passage  42 . Combustion chamber  30  may exhaust combustion gases via exhaust passage  48 . Intake manifold  44  and exhaust passage  48  can selectively communicate with combustion chamber  30  via respective intake valve  52  and exhaust valve  54 . In some embodiments, combustion chamber  30  may include two or more intake valves and/or two or more exhaust valves. In further examples, the intake manifold may selectively communicate with a PCV (Positive Crankcase Ventilation) system via a PCV valve. The PCV system may allow combusted gases that leak or migrate past the rings of piston  36  into the crankcase as blow-by to be vented into the intake manifold. 
     In this example, intake valve  52  and exhaust valves  54  may be controlled by cam actuation via respective cam actuation systems  51  and  53 . Cam actuation systems  51  and  53  may each include one or more cams and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT) and/or variable valve lift (VVL) systems that may be operated by controller  12  to vary valve operation. The position of intake valve  52  and exhaust valve  54  may be determined by position sensors  55  and  57 , respectively. In alternative embodiments, intake valve  52  and/or exhaust valve  54  may be controlled by electric valve actuation. For example, cylinder  30  may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and/or VCT systems. 
     Fuel injector  66  is shown arranged in intake passage  44  in a configuration that provides what is known as port injection of fuel into the intake port upstream of combustion chamber  30 . Fuel injector  66  may inject fuel in proportion to the pulse width of signal FPW received from controller  12  via electronic driver  68 . Fuel may be delivered to fuel injector  66  by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. In some embodiments, combustion chamber  30  may alternatively or additionally include a fuel injector coupled directly to combustion chamber  30  for injecting fuel directly therein, in a manner known as direct injection. 
     Intake passage  42  may include a throttle  62  having a throttle plate  64 . In this particular example, the position of throttle plate  64  may be varied by controller  12  via a signal provided to an electric motor or actuator included with throttle  62 , a configuration that is commonly referred to as electronic throttle control (ETC). In this manner, throttle  62  may be operated to vary the intake air provided to combustion chamber  30  among other engine cylinders. The position of throttle plate  64  may be provided to controller  12  by throttle position signal TP. Intake passage  42  may include a mass air flow sensor  120  and a manifold air pressure sensor  122  for providing respective signals MAF and MAP to controller  12 . In further examples, the intake passage  42  may be included as part of an air intake system which may feature an air filter and/or one or more AIS hydrocarbon traps as described herein. 
     Ignition system  88  can provide an ignition spark to combustion chamber  30  via spark plug  92  in response to spark advance signal SA from controller  12 , under select operating modes. Though spark ignition components are shown, in some embodiments, combustion chamber  30  or one or more other combustion chambers of engine  10  may be operated in a compression ignition mode, with or without an ignition spark. 
     Exhaust gas sensor  126  is shown coupled to exhaust passage  48  upstream of emission control device  70 . Sensor  126  may be any suitable sensor for providing an indication of exhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor. Emission control device  70  is shown arranged along exhaust passage  48  downstream of exhaust gas sensor  126 . Device  70  may be a three way catalyst (TWC) or other emission control device. 
     Controller  12  is shown in  FIG. 1  as a microcomputer, including microprocessor unit  102 , input/output ports  104 , an electronic storage medium for executable programs and calibration values shown as read only memory chip  106  in this particular example, random access memory  108 , keep alive memory  110 , and a data bus. Controller  12  may receive various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including measurement of inducted mass air flow (MAF) from mass air flow sensor  120 ; engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; a profile ignition pickup signal (PIP) from Hall effect sensor  118  (or other type) coupled to crankshaft  40 ; throttle position (TP) from a throttle position sensor; and absolute manifold pressure signal, MAP, from sensor  122 . Engine speed signal, RPM, may be generated by controller  12  from signal PIP. Manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum, or pressure, in the intake manifold. Note that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. Storage medium read-only memory  106  can be programmed with computer readable data representing instructions executable by processor  102  for performing various engine and/or vehicle control methods. 
       FIG. 2  provides a schematic illustration of an example air intake system  150  including at least one hydrocarbon trap. As described in more detail below, in one embodiment, a bypass hydrocarbon trap  160  includes a plurality of generally flat layers of hydrocarbon adsorbing material sandwiched together and secured one to another by a plurality of grommets passing through the plurality of generally flat layers to form a single adsorbing assembly for being secured to ribs extending from an upper interior surface of an air box  154  of the air induction system. Further, as described in more detail below, the trap  160  may be permanently secured within air box  154  using tamper evident fasteners, such as by heat staking, for example, to operate as a passive emissions control device that does not require monitoring by the on-board diagnostics (OBD) system. 
     As generally shown in  FIG. 2 , air intake system  150  may include an atmosphere or dirty air duct  152 , an air box  154 , and a filtered or clean air duct  156  coupled to the engine. Air box  154  may be configured to accept an air filter  158  that separates air box  154  into an atmosphere or dirty side downstream of air filter  158 , and a filtered or clean side upstream of filter  158  between atmosphere and the engine. Air filter  158  may be positioned between an air box cover  153  and an air box tray  155 . Air filter  158  may be disposed in air box  154  along with one or more hydrocarbon traps, such as multiple layer bypass hydrocarbon trap  160  and/or a flow-through hydrocarbon trap  162 . One or more sensors, such as mass air flow (MAF) sensor  120  may also be disposed in the air intake system as previously described. A PCV fresh air port  166  and throttle  62  may further be disposed in the air intake system. It should be appreciated that in addition to the above ports, the clean air duct may include additional ports, such as a brake aspiration port, a fuel vapor purging port, etc. Note that the flow indicated by the arrows in  FIG. 2  represents the vapor flow during engine off periods, which is generally opposite that of the air flow into the engine during engine on/running periods. 
     As used herein, a flow-through trap is a trap where substantially all the vapors emanating from inside the engine during engine off soaks must pass before reaching the surrounding environment. A bypass trap is a trap positioned in the airflow such that vapors emanating from inside the engine during engine off soaks pass by the trap before reaching the surrounding environment. Although the flow-through trap is generally more efficient at reducing the amount of hydrocarbon vapors emitted to the environment, the bypass trap also does reduce the release of such vapors and may be used alone or in combination with one or more flow-through traps and/or bypass traps. Although generally described herein as a bypass trap, it should be appreciated that the multiple layer hydrocarbon trap as disclosed may also be used as a flow-through hydrocarbon trap. 
     During engine off, evaporative emissions may migrate or diffuse through the air intake system. The escape of the hydrocarbons from the air induction system may result in hydrocarbons being released into the surrounding environment. For example, the unburned hydrocarbon fuel vapors may migrate from the engine as indicated at  170  or from the PCV fresh air port  166 , (flow indicated at  172 ) back through the flow through hydrocarbon trap  162  and/or the bypass hydrocarbon trap  160 . Non-adsorbed emissions may flow through air box  154 , dirty air duct  152 , and/or water drain  174 . By using a multiple layer hydrocarbon trap as described herein, the amount of hydrocarbons released to the surrounding environment or atmosphere can be substantially reduced or eliminated. 
     As described in more detail below, the hydrocarbon trap is described as an adsorbing trap, such that the trap is adapted to collect and adhere hydrocarbon gases, such as the “light ends” of gasoline, on the surface of the adsorbing material in the trap. These “light ends” of gasoline have been found to be one of the primary constituents of the vapors emanating from a typical air induction system during engine off soaks. As generally understood by those of ordinary skill in the art, a hydrocarbon trap according to the present disclosure should include material that facilitates adsorption rather than absorption so that the trapped hydrocarbons are more easily released from the material for combustion within the engine during subsequent trap purging cycles. 
     With continuing reference to  FIG. 2 , the hydrocarbon trap may be disposed in any suitable location in the air intake or air induction system. For example, as shown, the hydrocarbon trap  160  may be disposed within the air box  154 . In the representative embodiment illustrated in  FIG. 2 , hydrocarbon trap  160  is secured to an upper interior surface of air box  154 . The hydrocarbon trap  160  may be secured to interior ribs extending along the upper surface of air box cover  153  as illustrated and described with reference to  FIG. 3 . Positioning of the hydrocarbon trap  160  in air box cover  153  may depend on whether there is enough space  159  beyond the MAF sensor to accommodate the trap. In other examples, the hydrocarbon trap may be positioned before the MAF sensor  120 . In even other examples, where the PCV fresh air port is separate from the main inlet air filtration system, i.e. uses a separate air filtration system, the hydrocarbon trap may be disposed anywhere between MAF sensor  120  and throttle plate  64 . In even further examples, a multiple layer hydrocarbon trap  160  may be disposed within the engine intake manifold, a resonator, etc. 
     As shown in  FIG. 2 , a representative embodiment of an air induction system for an engine/vehicle includes an air filter box or housing  154  configured to receive an air filter  158  that separates the air filter box into an atmosphere side  180  and a filtered air side  182 . A clean-air duct  156  coupled downstream from air filter box  155  and upstream of the engine relative to a direction of air flow during engine operation. A flow-through hydrocarbon trap  162  is positioned within the clean-air duct  158 . A bypass hydrocarbon trap  160  is secured within the air filter box  154  on the filtered air side  182  and adjacent to airflow  172  through air filter box  154 . Hydrocarbon trap  160  includes a plurality of generally flat layers (best illustrated in  FIG. 4 ) of hydrocarbon adsorbing material sandwiched together and secured one to another. 
       FIG. 3  illustrates a representative air box cover having a multiple layer hydrocarbon trap secured to ribs extending along an upper interior surface of the air box cover according to one embodiment of the present disclosure.  FIG. 4  is a partial cross-sectional view of a multiple layer hydrocarbon trap according to one embodiment of the present disclosure, and  FIG. 5  is a top view of the embodiment of  FIG. 4 . 
     As illustrated in  FIGS. 3-5 , multiple layer hydrocarbon trap  226  includes a plurality of mechanical fasteners  212 . In the representative embodiment illustrated, mechanical fasteners  212  are implemented by grommets generally represented by grommets  220  and  222  each having a through hole  250 , an upper flange  252 , and a lower flange  254 . Grommets or other mechanical fasteners extend through a plurality of layers  240 ,  242 ,  244  of generally flat sheets of hydrocarbon adsorbing material that are sandwiched together. Grommets  220 ,  222  or other mechanical fasteners extending through the multiple layers  240 ,  242 ,  244  may be positioned based on the particular application to secure the layers one to another to form a single adsorbing assembly or sub-assembly to facilitate ease of assembly into air box cover  153 . Grommets or other mechanical fasteners  212  may also be used to secure the single adsorbing sub-assembly within air box cover  153 . 
     In one embodiment, air box cover  153  includes a plurality of ribs  210  extending along an upper surface (as installed in a vehicle) and along sides of the air box to provide structural support for the air box, which may be made of plastic, for example. One or more grommets  222  may be aligned with and/or secured to an associated rib  210 . In one embodiment, air box cover  153  includes a plurality of alignment pins  230  that extend through associated grommets  220  to position the hydrocarbon adsorbing sub-assembly within air box cover  153 . The sub-assembly may be secured to cover  153  by heat staked alignment pins  230  to grommets  222 . In other embodiments, multiple layers  240 ,  242 ,  244  of generally flat sheets of hydrocarbon adsorbing material are secured one to another by adhesive. Similarly, the hydrocarbon trap material, which may be an adsorbing material such as carbon paper or other material, is secured within cover  153  by adhesive, by ultrasonic welding, a mechanical fastener, such as a screw, or a combination thereof. 
     As previously described, the number of layers  240 - 242  may be increased or decreased to provide a desired area or volume of hydrocarbon adsorbing material for a particular application. Various representative embodiments of a bypass hydrocarbon trap according to the present disclosure include five layers or six layers of hydrocarbon adsorbing material with each sheet having a nominal thickness of 0.02850 inches (0.7239 mm) with a combined thickness of about 0.150-0.180 inches (3.81-4.57 mm). 
       FIGS. 6 and 7  illustrate alternative embodiments of a multiple layer hydrocarbon trap according to the present disclosure. While illustrated as a generally circular coiled arrangement, those of ordinary skill in the art will recognize that the hydrocarbon adsorbing material may be formed into various geometries to fit within an air box, duct, etc. and used as a flow-through or bypass trap depending on the particular application. Similarly, the coiled or otherwise formed embodiments may include a single layer that is formed in a spiral, undulating, or wrapped fashion to create multiple layers as depicted in the embodiment of  FIG. 6 . Alternatively, multiple layers of the hydrocarbon adsorbing material may first be stacked and then coiled or otherwise formed as generally represented in the embodiment of  FIG. 7 . 
     Multiple layer hydrocarbon trap  626  may include a plurality of mechanical fasteners generally represented by fastener  612 . In the representative embodiments illustrated in  FIGS. 6 and 7 , mechanical fasteners  612 ,  712  are implemented by grommets each having a through hole  650 ,  750 , an upper or outer flange  652 ,  752 , and a lower or inner flange  654 ,  754 . Grommets or other mechanical fasteners extend through at least two layers  640 ,  642 ,  644  (or  740 ,  742 ,  744 ) of generally flat sheets of hydrocarbon adsorbing material that are sandwiched together and formed into a desired geometry for an air duct, air box, etc. Grommets  620 ,  720  or other mechanical fasteners extending through the multiple layers may be positioned based on the particular application to secure the layers one to another to form a single adsorbing assembly or sub-assembly to facilitate ease of assembly into an air box, air duct, or the like. Grommets or other mechanical fasteners may also be used to secure the single adsorbing sub-assembly within the air box, air duct, etc. 
     As described with respect to the embodiments of  FIGS. 2-5 , the embodiments of  FIGS. 6 and 7  may include one or more grommets aligned with and/or secured to an associated rib, flange, or other structure on an interior of an air box, air duct, etc. The sub-assembly hydrocarbon adsorbing subassembly may be secured to associated structure with in the air induction system by heat staked alignment pins. Multiple layers  640 ,  642 ,  644  (or  740 ,  742 ,  744 ) of sheets of hydrocarbon adsorbing material may be secured one to another by adhesive. As previously described, the number of layers may be increased or decreased to provide a desired area or volume of hydrocarbon adsorbing material for a particular application. 
     As those of ordinary skill in the art will appreciate based on the representative embodiments described above, various embodiments according to the present disclosure may provide advantages such as securing multiple layers of sheets of hydrocarbon adsorbing material together for ease of assembly within an air box cover. This construction method allows the bundle to be manufactured separately and subsequently assembled to the cover allowing for a more flexible manufacturing process. Use of multiple layers of generally flat sheets sandwiched together provides a modular solution that can be easily adapted to multiple applications by selecting the number of layers of adsorbing material without changes to the packaging. Embodiments according to the present disclosure may reduce cost by providing a universal design that results in higher volumes of component pieces, such as the layers of adsorbing material. Similarly, a generally flat rectangular or polygonal shape reduces scrap in adsorbing material cutting. A hydrocarbon trap having a universal design according to embodiments of the present disclosure may also reduce engineering costs and time to market. In addition, a universal design according to embodiments of the present disclosure allows for usage of adsorbing material from various vendors and facilitates competitive bidding to further reduce costs. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments discussed herein that are 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 may be desirable for particular applications.