Abstract:
One embodiment of the present invention is a unique gas turbine engine. Another embodiment is a unique gas turbine engine high speed rolling element bearing system. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for gas turbine engines and high speed rolling element bearing systems for gas turbine engines. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application 61/290,834, filed Dec. 29, 2009, and is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to gas turbine engines, and more particularly, to a high speed rolling element bearing system for a gas turbine engine. 
       BACKGROUND 
       [0003]    Gas turbine engines and high speed rolling element bearing systems for gas turbine engines remain an area of interest. Some existing systems have various shortcomings, drawbacks, and disadvantages relative to certain applications. Accordingly, there remains a need for further contributions in this area of technology. 
       SUMMARY 
       [0004]    One embodiment of the present invention is a unique gas turbine engine. Another embodiment is a unique gas turbine engine high speed rolling element bearing system. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for gas turbine engines and high speed rolling element bearing systems for gas turbine engines. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0006]      FIG. 1  schematically illustrates a gas turbine engine in accordance with an embodiment of the present invention. 
           [0007]      FIG. 2  schematically illustrates aspects of the gas turbine engine of  FIG. 1 . 
           [0008]      FIG. 3  schematically illustrates a gas turbine engine bearing system in a first operating state in accordance with an embodiment of the present invention. 
           [0009]      FIG. 4  schematically illustrates a gas turbine engine bearing system in a second operating state in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    For purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nonetheless be understood that no limitation of the scope of the invention is intended by the illustration and description of certain embodiments of the invention. In addition, any alterations and/or modifications of the illustrated and/or described embodiment(s) are contemplated as being within the scope of the present invention. Further, any other applications of the principles of the invention, as illustrated and/or described herein, as would normally occur to one skilled in the art to which the invention pertains, are contemplated as being within the scope of the present invention. 
         [0011]    Referring now to the drawings, an in particular  FIG. 1 , a non-limiting example of a gas turbine engine  10  in accordance with an embodiment of the present invention is depicted. In one form, gas turbine engine  10  is an aircraft propulsion power plant. In other embodiments, gas turbine engine  10  may be a land-based or marine engine. In one form, gas turbine engine  10  is a multi-spool turbofan engine. In other embodiments, gas turbine engine  10  may be a single or multi-spool turbofan, turboshaft, turbojet, turboprop gas turbine or combined cycle engine. 
         [0012]    Gas turbine engine  10  includes a fan system  12 , a compressor system  14 , a diffuser  16 , a combustion system  18  and a turbine system  20 . Combustion system  18  is fluidly disposed between compressor system  14  and turbine system  20 . Fan system  12  includes a fan rotor system  22 . Compressor system  14  includes a compressor rotor system  24 . Turbine system  20  includes a turbine rotor system  26 . Turbine rotor system  26  is drivingly coupled to compressor rotor system  24  and fan rotor system  22  via a shafting system  28 . Coupled to shafting system  28  is a high speed rolling element bearing system  30  that is operative to react varying and intermittent thrust loads. 
         [0013]    In various embodiments, fan rotor system  22 , compressor rotor system  24  and turbine rotor system  26  each include one or more rotors. In one form, each expansion rotor is drivingly coupled to a corresponding compression rotor via a separate main shaft of shafting system  28 , forming a spool of engine  10 . 
         [0014]    Referring now to  FIG. 2 , in one form, engine  10  includes a spool  34  and a spool  36 . Spool  34  is formed of a compressor rotor  24 A coupled to a turbine rotor  26 A via a shaft  28 A. Spool  36  is formed of a compressor rotor  24 B coupled to a turbine rotor  26 B via a shaft  28 B. In one form, spool  34  and spool  36  may be selectively coupled to each other by clutch system  32 , which is controlled by means not shown. In other embodiments, clutch system  32  may selectively couple other gas turbine engine rotors, e.g., including one or more fan  12  rotors. In various embodiments, clutch system  32  may be any rotating clutch in a gas turbine engine. In one form, bearing system  30  reacts thrust loads from clutch system  32 . In other embodiments, bearing system  30  may react other intermittent and/or varying thrust loads. 
         [0015]    During the operation of gas turbine engine  10 , air is drawn into the inlet of fan  12  and pressurized by fan  12 . Some of the air pressurized by fan  12  is directed into compressor system  14 , and the balance is directed into a bypass duct (not shown). Compressor system  14  further pressurizes the air received from fan  12 , which is then discharged into diffuser  16 . Diffuser  16  reduces the velocity of the pressurized air, and directs the diffused airflow is into combustion system  18 . Fuel is mixed with the air in combustion system  18 , which is then combusted in a combustion system  18  combustion liner (not shown). The hot gases exiting combustor  18  are directed into turbine system  20 , which extracts energy in the form of mechanical shaft power to drive fan system  12  and compressor system  14  via shafting system  28 . The hot gases exiting turbine system  20  are directed into a nozzle (not shown), and provide a component of the thrust output by gas turbine engine  10 . 
         [0016]    At some engine  10  operating points, it is desirable to couple spool  34  with spool  36 , whereas at other engine  10  operating points, it is desirable that spool  34  and spool  36  are decoupled. Coupling is performed using clutch system  32 , with the primary thrust loads from the clutching operation being reacted by bearing system  30 . Upon completion of the clutching operation, the primary thrust load is removed from bearing system  30 . 
         [0017]    When the thrust load carrying capacity of a single ball bearing is inadequate, it becomes necessary to use two or more bearings in tandem to share the load. Also, in some applications, tandem mounted bearings may be desirable for use in place of a single ball bearing at lower thrust loads where size is a concern—tandem mounted bearings are often able to carry the same load with a more compact physical size of the bearings, e.g., a smaller diameter. Tandem mounted thrust bearings are thrust bearings modified in a manner that allows for load-sharing between each of the tandem mounted bearings, e.g., equal load sharing. However, tandem mounted bearings can only carry thrust in one direction, and do not do well when the axial load is removed. Although it may be possible to employ one or more additional bearings that are adjusted against the tandem mounted bearings to carry the axial loads acting contrary to the tandem design thrust direction, such a solution results in an otherwise unnecessary bearing, which adds weight, cost and potential reliability concerns to the bearing system and the engine. 
         [0018]    In order to overcome problems associated with loss of the thrust load, embodiments of the present invention include a preload generating device that applies an axial preload thrust load to tandem mounted thrust bearings in a manner that allows for continued operation during thrust load reversal and/or when the thrust load is no longer acting on the pair of bearings. The thrust preload is applied between the bearings, and does not require the use of additional bearings to address thrust loads acting contrary to the tandem bearing set&#39;s design direction. Embodiments of the present invention are similarly applicable to two-thrust-bearing systems as well as bearing systems having more than two thrust bearings. 
         [0019]    Referring now to  FIGS. 3 and 4 , aspects of a non-limiting example of high speed rolling element bearing system  30  in accordance with an embodiment of the present invention are depicted. High speed rolling element bearing system  30  includes a tandem mounted high speed rolling element thrust bearing  38  and high speed rolling element thrust bearing  40 , and also includes a preload generator  42 . In one form, the thrust bearings are ball thrust bearings. In other embodiments, other high speed rolling element thrust bearings may be employed. Bearings  38  and  40  may be made from materials known in the art that are typical for gas turbine engine applications. 
         [0020]    Bearing  38  includes an outer ring  44 , a plurality of balls  46 , a separator  48  and an inner ring  50 . Outer ring  44  includes an outer ring ball groove  52 . In one form, outer ring  44 , which may be referred to as an outer race, is a single-piece ring. In other embodiments, outer ring  44  may be a multi-piece ring, such as a split outer ring. Inner ring  50  includes an inner ring ball groove  54 . In one form, inner ring  50 , which may be referred to as an inner race, is a split inner ring. In other embodiments, inner ring  50  may be a single-piece ring. Balls  46  are disposed in grooves  52  and  54  between outer ring  44  and inner ring  50 . Separator  48  is disposed between outer ring  44  and inner ring  50 . In one form, separator  50  is an outer ring piloted separator. Other embodiments may employ other separator piloting schemes, e.g., may employ an inner ring piloted separator. Separator  48  is operative to separate each ball  46  from adjacent balls  46 . In one form, bearing  38  is operative to react and transfer radial and thrust loads between inner ring  50  and outer ring  44 . In other embodiments, bearing  40  may be structured to transmit only or predominantly only thrust loads. 
         [0021]    Bearing  40  includes an outer ring  56 , a plurality of balls  58 , a separator  60  and an inner ring  62 . Outer ring  56  includes an outer ring ball groove  64 . In one form, outer ring  56 , which may be referred to as an outer race, is a single-piece ring. In other embodiments, outer ring  56  may be a multi-piece ring, such as a split outer ring. Inner ring  62  includes a inner ring ball groove  66 . In one form, inner ring  62 , which may be referred to as an inner race, is a split inner ring. In other embodiments, inner ring  62  may be a single-piece ring. Balls  58  are disposed in grooves  66  and  66  between outer ring  56  and inner ring  62 . Separator  60  is disposed between outer ring  56  and inner ring  62 . In one form, separator  60  is an outer ring piloted separator. Other embodiments may employ other separator piloting schemes, e.g., may employ an inner ring piloted separator. Separator  60  is operative to separate each ball  58  from adjacent balls  58 . In one form, bearing  40  is operative to react and transfer radial and thrust loads between inner ring  62  and outer ring  56 . In other embodiments, bearing  40  may be structured to transmit only or predominantly only thrust loads. 
         [0022]    In one form, outer rings  44  and  56  are mounted in a static bearing housing  68 , and inner rings  50  and  62  are mounted on a rotating shaft  70 . Other rotating and/or static structures (not shown) may be positioned adjacent to outer rings  44  and  56  and inner rings  50  and  62 , e.g., to transmit loads through one or both of bearings  38  and  40  and/or to position one or both of bearings  38  and  40  in radial, circumferential and/or axial directions. In the depicted embodiment, the primary thrust load is applied against inner ring  50  and against inner ring  62 ; and the primary thrust load reaction is applied against outer ring  56  and against outer ring  44 , that is, the primary thrust load is reacted through outer ring  56  and outer ring  44 . In other embodiments, high speed rolling element bearing system  30  may be configured for other loading schemes. Also, in other embodiments, inner rings  50  and  62  may mounted in a static bearing housing  68 , and outer rings  44  and  56  may be mounted on a shaft  70 . In still other embodiments, outer rings  44  and  56  may be mounted on a rotating structure, e.g., a first shaft, and inner rings  50  and  62  may be mounted on another rotating structure, e.g., a second shaft that rotates in the same or opposite direction as the first shaft. 
         [0023]    Preload generator  42  is operative to generate a preload in the form of a thrust load between the bearing  38  and bearing  40  upon removal of the primary thrust load that is externally generated and applied to bearings  38  and  40  (that is, generated externally of bearings  38  and  40 , which in the present non-limiting example is a clutch system  32  thrust load). In particular, preload generator  42  is configured to generate a thrust load that loads bearing  38  against bearing  40  upon the removal of the primary thrust load or the reduction of the primary thrust load to a level less than the thrust exerted by preload generator  42 . By loading bearing  38  against bearing  40 , both bearings  38  and  40  are loaded in thrust, which promotes operational stability and increased life of the bearings, as compared to tandem mounted high speed ball thrust bearings that that are operated in the absence of a thrust load or operated at a thrust load that is substantially lower than the design thrust load or design thrust load range. 
         [0024]    In one form, preload generator  42  is disposed between outer ring  44  and outer ring  56 , and is operative to axially translate one or both of outer rings  44  and  56  to increase the distance between them upon the removal or reduction of the primary thrust load as set forth above. In other embodiments, preload generator  42  may be positioned in other locations, and may be operative to increase or decrease the axial distance between outer rings  44  and  56  upon the removal of the primary thrust load. In still other embodiments, preload generator  42  may be configured to increase or decrease the axial distance between inner rings  50  and  62  upon the removal or reduction of the primary thrust load as set forth above, and to provide a thrust load between inner rings  50  and  62  to load bearing  38  against bearing  40 . In still other embodiments, preload generator  42  may be configured to increase and/or decrease the axial distance between outer rings  44  and  56  and between inner rings  50  and  62  upon the removal or reduction of the primary thrust load as set forth above, and to provide a thrust load between inner rings  50  and  62  and between outer rings  44  and  56  to load bearing  38  against bearing  40 . 
         [0025]    In one form, preload generator  42  operates in a collapsed state when the primary thrust load is present, and operates in an expanded state when the primary thrust load is removed or reduced to being less than the thrust load exerted by preload generator  42 . In the collapsed state, preload generator  42  controls the spacing between both of the outer rings or both of the inner rings so that bearings  38  and  40  react the primary thrust load in parallel. That is, so that bearings  38  and  40  share the primary thrust load, in which case the cross-corner loading direction in bearings  38  and  40  have an axial component in the same direction, which is left-to-right in the depicted example of  FIG. 3 , and indicated as cross-corner loading direction D 1 . The actual cross-corner loading direction varies with the degree of load sharing as between bearings  38  and  40  when reacting the primary thrust load. The use of the term, “parallel” refers to both bearings  38  and  40  being used to react the load, but does not refer to the degree of load sharing as between bearings  38  and  40 . 
         [0026]    In the expanded state, preload generator  42  generates a thrust preload that loads bearing  38  against bearing  40 , which results in a cross-corner loading direction in bearing  38  being opposite that of bearing  40 , i.e., having axial components with opposite directions. In the example of  FIG. 4 , preload generator  42  loads bearing  38  against bearing  40 , which results in bearing  40  having a cross-corner loading direction axial component in the right-to-left direction, which is opposite the left-to-right direction of the axial component of the cross-corner loading of bearing  38 . The cross-corner loading direction D 4  of bearing  40  is seen in  FIG. 4  as being opposite the cross-corner loading direction D 3  of bearing  38  as a result of loading bearing  38  against bearing  40 . 
         [0027]    In the illustrated embodiment, preload generator  42  controls the spacing between outer rings  44  and  56  when in the collapsed state. The load sharing percentage in one form is approximately equal loading on bearing  38  and bearing  40 , i.e., 50% of the primary thrust load is reacted by each of bearing  38  and bearing  40 . In other embodiments, other load sharing distributions may be employed. Also, in other embodiments, preload generator  42  may be configured to control the spacing between bearing  38  and bearing  40  in an expanded state, and may load bearing  38  against bearing  40  in the collapsed state. 
         [0028]    In one form, preload generator  42  includes a plurality of compression devices in the form of springs  72  disposed between outer ring  44  and outer ring  56  in a spacer  74 . In other embodiments, only a single compression device may be employed, e.g., a wave spring, a bellows or a coil spring. In one form, spacer  74  is a split spacer. In other embodiments, spacer  74  may not be a split spacer. In one form, spacer  74  is formed separately from bearings  38  and  40 . In other embodiments, spacer  74  may be integral with one or both of bearings  38  and  40 , e.g., integral with one or both of outer rings  44  and  56  or integral with one or both of inner rings  50  and  62 . Spacer  74  axial positions outer rings  44  and  56  with respect to each other by a desired amount. A spacer  76  between inner rings  50  and  62  is employed to space inner ring  50  apart from inner ring  62  by a desired amount. 
         [0029]    In one form, the axial spacing between outer rings  44  and  56 , and the axial spacing between inner rings  50  and  62  are selected to cause bearing  38  and bearing  40  to share the primary thrust load when preload generator  42  is in the collapsed state, and to determine the percentage load sharing of the primary thrust load. More particularly, the geometries of grooves  52  and  64  and their locations relative to each other, and the geometries of grooves  54  and  66  and their locations relative to each other are selected to cause bearing  38  and bearing  40  to share the primary thrust load when preload generator  42  is in the collapsed state, and to determine the percentage load sharing of the primary thrust load. 
         [0030]    Springs  72  are configured to be overcome by the primary thrust load so that spacer  74  collapses (closes) upon the application of the primary thrust load, and controls the axial spacing between outer rings  44  and  56 . Springs  72  are configured with a spring force that is overcome by the primary thrust load, so that upon the application of the primary thrust load, springs  72  compress, allowing spacer  74  to collapse under the primary thrust load. Springs  72  are also operative to generate a preload thrust between bearings  38  and  40  upon the removal or reduction of the primary thrust load as set forth above. When the primary thrust load is removed or reduced below the spring force of springs  72 , springs  72  drive outer rings  44  and  56  apart, expanding spacer  74 , and loading bearing  38  against bearing  40 . 
         [0031]    When the primary thrust load is removed, or is reduced to a level below the force exerted by springs  72 , springs  72  displace outer rings  44  and  56  relative to each other, providing a preload thrust that loads bearing  38  against bearing  40 .  FIG. 3  illustrates an example of a collapsed state of preload generator  42 , wherein both sides of spacer  74  are in contact with each other.  FIG. 4  illustrates an example of an expanded state of preload generator  42 , wherein there is a gap G between side  74 A of spacer  74  and side  74 B of spacer  74 . 
         [0032]    In one form, springs  72  are preload-generating devices in the form of coil springs. In other embodiments, other types of springs may be employed. In still other embodiments, other types of preload-generating devices may be employed, e.g., hydraulic pistons or diaphragms, etc., e.g., that are operated by engine lubrication oil pressure or fuel pressure; electromagnetic solenoids or electromagnets, etc. Although springs  72  are compressive devices, in other embodiments, tensile devices may be employed, e.g., extension springs, hydraulic pistons or diaphragms, etc., which may be positioned appropriately to generate preload. 
         [0033]    During the operation of engine  10 , the application of the primary thrust load collapses preload generator  42 , and bearings  38  and  40  react the primary thrust load. Upon removal of the primary thrust load, or reduction of the primary thrust load to less than the thrust preload generated by preload generator  42 , preload generator  42  expands, loading bearing  38  against bearing  40 . 
         [0034]    Embodiments of the present invention include a high speed rolling element bearing system for reacting a primary thrust load, comprising: a first high speed rolling element thrust bearing; a second high speed rolling element thrust bearing, wherein the first thrust bearing and the second thrust bearing are dimensionally configured to react the primary thrust load in parallel; and a preload generator operative to generate a thrust preload between the first bearing and the second bearing upon removal of the primary thrust load. 
         [0035]    In a refinement, the first thrust bearing includes a first outer ring and a first inner ring; the second thrust bearing includes a second outer ring and a second inner ring; and the preload generator displaces one of the first outer ring and the first inner ring relative to a respective one of the second outer and the second inner ring. 
         [0036]    In another refinement, the preload generator includes a spring operative to displace the one of the first outer ring and the first inner ring. 
         [0037]    In yet another refinement, the spring is a coil spring. 
         [0038]    In still another refinement, the high speed rolling element bearing system further comprises a spacer that axially positions the one of the first outer ring and the first inner ring relative to the respective one of the second outer and the second inner ring, wherein the coil spring is disposed within the spacer. 
         [0039]    In yet still another refinement, the spacer is a split spacer having a first half and a second half, and wherein the action of the spring separates the first half from the second half. 
         [0040]    In a further refinement, the first thrust bearing and the second thrust bearing have a cross-corner loading direction axial components that are in the same direction when the first thrust bearing and the second thrust bearing are reacting the primary thrust load and the primary thrust load is greater than the thrust preload; and wherein the cross-corner loading direction axial components are in opposite directions when the primary thrust load is less than the thrust preload. 
         [0041]    In a yet further refinement, the first thrust bearing includes a first outer ring with a first outer ring groove, a first inner ring having a first inner ring groove, and a first plurality of rolling elements constrained within the first outer ring groove and the first inner ring groove and operative to transmit rotating loads between the first outer ring and the first inner ring; the second thrust bearing includes a second outer ring with a second outer ring groove, a second inner ring having a second inner ring groove, and a second plurality of rolling elements constrained within the second outer ring groove and the second inner ring groove and operative to transmit rotating loads between the second outer ring and the second inner ring; the first inner ring groove and the second inner ring groove are positioned in a fixed relationship to each other; and the preload generator displaces the first outer ring groove relative to the second outer ring groove upon the removal of the primary thrust load. 
         [0042]    In a still further refinement, the first thrust bearing and the second thrust bearing are loaded against each other without the use of a third thrust bearing. 
         [0043]    Embodiments of the present invention include a gas turbine engine, comprising: a compressor rotor system; a combustion system in fluid communication with the compressor rotor system; a turbine rotor system in fluid communication with the combustion system; and a high speed rolling element bearing system for reacting a primary thrust load, wherein the high speed rolling element bearing system is coupled to one or more components of one or both of the compressor rotor system and the turbine rotor system, and wherein the high speed rolling element bearing system includes: a first high speed rolling element thrust bearing; a second high speed rolling element thrust bearing, wherein the first thrust bearing and the second thrust bearing are dimensionally configured to react the primary thrust load in parallel; and wherein the bearing system further includes a preload generator operative to load the first bearing and the second bearing against each other upon removal of the primary thrust load. 
         [0044]    In a refinement, the first thrust bearing includes a first outer ring and a first inner ring; the second thrust bearing includes a second outer ring and a second inner ring; and the preload generator displaces one of the first outer ring and the first inner ring relative to a respective one of the second outer and the second inner ring. 
         [0045]    In another refinement, the preload generator includes a spring operative to displace the one of the first outer ring and the first inner ring. 
         [0046]    In yet another refinement, the spring is a coil spring. 
         [0047]    In yet still another refinement, the high speed rolling element bearing system further comprises a spacer that axially positions the one of the first outer ring and the first inner ring relative to the respective one of the second outer and the second inner ring, wherein the coil spring is disposed within the spacer. 
         [0048]    In a further refinement, the spacer is a split spacer having a first half and a second half, and wherein the action of the spring separates the first half from the second half. 
         [0049]    In a yet further refinement, the first thrust bearing and the second thrust bearing have cross-corner loading direction axial components that are in the same direction when the first thrust bearing and the second thrust bearing are reacting the primary thrust load; and wherein the cross-corner loading direction axial components are in opposite directions upon removal of the primary thrust load. 
         [0050]    In a still further refinement, the first thrust bearing includes a first outer ring with a first outer ring groove, a first inner ring having a first inner ring groove, and a first plurality of rolling elements constrained within the first outer ring groove and the first inner ring groove and operative to transmit rotating loads between the first outer ring and the first inner ring; the second thrust bearing includes a second outer ring with a second outer ring groove, a second inner ring having a second inner ring groove, and a second plurality of rolling elements constrained within the second outer ring groove and the second inner ring groove and operative to transmit rotating loads between the second outer ring and the second inner ring; the first inner ring groove and the second inner ring groove are positioned in a fixed relationship to each other; and the preload generator displaces the first outer ring groove relative to the second outer ring groove upon the removal of the primary thrust load. 
         [0051]    In a yet still further refinement, the first thrust bearing and the second thrust bearing are loaded against each other without the use of a third thrust bearing. 
         [0052]    Embodiments of the present invention include a gas turbine engine, comprising: a compressor rotor system; a combustion system in fluid communication with the compressor rotor system; a turbine rotor system in fluid communication with the combustion system; means for reacting a primary thrust load, wherein the means for reacting is coupled to one or more components of one or both of the compressor rotor system and the turbine rotor system; and means for providing a thrust preload to the means for reacting upon removal of the primary thrust load. 
         [0053]    In a refinement, the means for providing a thrust preload employs a spring to provide the thrust preload. 
         [0054]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one” and “at least a portion” are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.