Patent Publication Number: US-2013251551-A1

Title: Compressor shell with multiple diameters

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to compressors for compressing refrigerant and more particularly to housing and component mounting features of a compressor with some embodiments directed toward scroll compressors. 
     BACKGROUND OF THE INVENTION 
     A scroll compressor is a certain type of compressor that is used to compress refrigerant for such applications as refrigeration, air conditioning, industrial cooling and freezer applications, and/or other applications where compressed fluid may be used. Such prior scroll compressors are known, for example, as exemplified in U.S. Pat. Nos. 6,398,530 to Hasemann; 6,814,551, to Kammhoff et al.; 6,960,070 to Kammhoff et al.; and 7,112,046 to Kammhoff et al., all of which are assigned to a Bitzer entity closely related to the present assignee. As the present disclosure pertains to improvements that can be implemented in these or other scroll compressor designs, the entire disclosures of U.S. Pat. Nos. 6,398,530; 7,112,046; 6,814,551; and 6,960,070 are hereby incorporated by reference in their entireties. 
     As is exemplified by these patents, scroll compressors assemblies conventionally include an outer housing having a scroll compressor contained therein. A scroll compressor includes first and second scroll compressor members. A first compressor member is typically arranged stationary and fixed in the outer housing. A second scroll compressor member is movable relative to the first scroll compressor member in order to compress refrigerant between respective scroll ribs which rise above the respective bases and engage in one another. Conventionally the movable scroll compressor member is driven about an orbital path about a central axis for the purposes of compressing refrigerant. An appropriate drive unit, typically an electric motor, is provided usually within the same housing to drive the movable scroll member. 
     In some scroll compressors, it is known to have axial restraint, whereby the fixed scroll member has a limited range of movement. This can be desirable due to thermal expansion when the temperature of the orbiting scroll and fixed scroll increases causing these components to expand. Examples of an apparatus to control such restraint are shown in U.S. Pat. No. 5,407,335, issued to Caillat et al., the entire disclosure of which is hereby incorporated by reference. 
     The present invention is directed towards improvements over the state of the art as it relates to the above-described features and other features of scroll compressors. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, embodiments of the invention provide a compressor assembly that includes a compressor mechanism adapted to compress a fluid. The compressor assembly may be preferably a scroll compressor but may also be a piston, screw, or other compressor, as certain aspects of the invention may be applicable thereto. A motor is operably connected to the compressor mechanism for driving the compression mechanism to compress fluid. A shell section housing the motor, with the shell section including a central portion with a reduced inner perimeter relative to at least one end of the shell section. The motor is press fit in the central portion of the shell. 
     In a particular embodiment, the compressor assembly further includes a first step and a second step formed into the shell section. Each of the first step and the second step transition to a different inner perimeter of the shell section relative to the central portion. 
     In a further embodiment, the compressor assembly further includes first and second outer portions that are generally cylindrical and sandwich the central portion therebetween. The central portion being generally cylindrical and joined to the first and second outer portions via the first and second steps, respectively. 
     In another aspect, embodiments of the invention provide a compressor assembly including a compressor mechanism adapted to compress a fluid. A motor operatively connected to the compressor mechanism for driving the compression mechanism to compress fluid is included as well. A shell section is included that surrounds at least in part the motor. The shell section includes a first step and a second step formed into the shell section with each of the first step and second step transitioning to a different inner perimeter of the shell section relative to the central portion. The first and second outer portions are generally cylindrical and sandwich the central portion therebetween. The central portion is generally cylindrical and joined to the first and second outer portions via the first and second steps, respectively. 
     In a further embodiment, the compressor assembly further includes a first bearing housing and a second bearing housing. The first bearing housing is press fit into the first outer portion and the second bearing housing is press fit into the second outer portion. The first and second bearing housings having journaled therein a drive shaft connected to a rotor of the motor, and a stator of the motor that is disposed between the first and second bearing housings. 
     In another aspect, embodiments of the invention provide a method of housing a motor in a compressor assembly by forming a shell section including a generally cylindrical wall from sheet steel material. Then forming a central portion into the shell section with a reduced inner perimeter relative to at least one end of the shell section. Further, press fitting the motor in the central portion with direct engagement between the generally cylindrical wall and an outer periphery of the motor and driving a compression mechanism with the motor. 
     In a further embodiment, the lengths of one or both ends of the shell sections are trimmed to an outer step length, or a corresponding sized starting blank is installed in a suspended position on the expander to result in the outer step length. 
     In a further embodiment, upper and lower bearing members are press fit into the shell section on opposite sides of the motor, and the bearings support a drive shaft driven by the motor. The drive shaft transfers the output of the motor to the compression mechanism. 
     Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a cross-sectional isometric view of a scroll compressor assembly, according to an embodiment of the invention; 
         FIG. 2  is a cross-sectional isometric view of an upper portion of the scroll compressor assembly of  FIG. 1 ; 
         FIG. 3  is an exploded isometric view of selected components of the scroll compressor assembly of  FIG. 1 ; 
         FIG. 4  is a perspective view of an exemplary key coupling and movable scroll compressor body, according to an embodiment of the invention; 
         FIG. 5  is a top isometric view of the pilot ring, constructed in accordance with an embodiment of the invention; 
         FIG. 6  is a bottom isometric view of the pilot ring of  FIG. 5 ; 
         FIG. 7  is an exploded isometric view of the pilot ring, crankcase, key coupler and scroll compressor bodies, according to an embodiment of the invention; 
         FIG. 8  is a isometric view of the components of  FIG. 7  shown assembled; 
         FIG. 9  is a cross-sectional isometric view of the components in the top end section of the outer housing, according to an embodiment of the invention; 
         FIG. 10  is an exploded isometric view of the components of  FIG. 9 ; 
         FIG. 11  is a top isometric view of the floating seal, according to an embodiment of the invention; 
         FIG. 12  is a bottom isometric view of the floating seal of  FIG. 11 ; 
         FIG. 13  is an exploded isometric view of selected components for an alternate embodiment of the scroll compressor assembly; 
         FIG. 14  is a cross-sectional isometric view of a portion of a scroll compressor assembly, constructed in accordance with an embodiment of the invention; 
         FIG. 15  is a cross-sectional view of a compressor shell including a motor and upper and lower bearing members, constructed in accordance with an embodiment of the invention; 
         FIG. 16  is a flow diagram illustrating steps for constructing the shell from  FIG. 15 ; 
         FIG. 17  is a close up of a cross-sectional view of the shell from  FIG. 15  in accordance with an embodiment of the present invention; 
         FIG. 18  is a cross-section view of a scroll compressor in accordance with an embodiment of the present invention; 
         FIG. 19  is a cross-sectional view of a scroll compressor in accordance with an embodiment of the present invention; 
         FIG. 20  is an isometric cross-section view of a scroll compressor that includes a motor spacer, in accordance with an embodiment of the present invention; 
         FIG. 21  is an exploded view of a motor including a motor spacer, in accordance with an embodiment of the present invention; and 
         FIG. 22  is a cross-section view of a scroll compressor that includes a motor spacer, in accordance with an embodiment of the present invention. 
     
    
    
     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the present invention is illustrated in the figures as a scroll compressor assembly  10  generally including an outer housing  12  in which a scroll compressor  14  can be driven by a drive unit  16 . The scroll compressor assembly  10  may be arranged in a refrigerant circuit for refrigeration, industrial cooling, freezing, air conditioning or other appropriate applications where compressed fluid is desired. Appropriate connection ports provide for connection to a refrigeration circuit and include a refrigerant inlet port  18  and a refrigerant outlet port  20  extending through the outer housing  12 . The scroll compressor assembly  10  is operable through operation of the drive unit  16  to operate the scroll compressor  14  and thereby compress an appropriate refrigerant or other fluid that enters the refrigerant inlet port  18  and exits the refrigerant outlet port  20  in a compressed high-pressure state. 
     The outer housing for the scroll compressor assembly  10  may take many forms. In particular embodiments of the invention, the outer housing  12  includes multiple shell sections. In the embodiment of  FIG. 1 , the outer housing  12  includes a central cylindrical housing section  24 , and a top end housing section  26 , and a single-piece bottom shell  28  that serves as a mounting base. In certain embodiments, the housing sections  24 ,  26 ,  28  are formed of appropriate sheet steel and welded together to make a permanent outer housing  12  enclosure. However, if disassembly of the housing is desired, other housing assembly provisions can be made that can include metal castings or machined components, wherein the housing sections  24 ,  26 ,  28  are attached using fasteners. 
     As can be seen in the embodiment of  FIG. 1 , the central housing section  24  is cylindrical, joined with the top end housing section  26 . In this embodiment, a separator plate  30  is disposed in the top end housing section  26 . During assembly, these components can be assembled such that when the top end housing section  26  is joined to the central cylindrical housing section  24 , a single weld around the circumference of the outer housing  12  joins the top end housing section  26 , the separator plate  30 , and the central cylindrical housing section  24 . In particular embodiments, the central cylindrical housing section  24  is welded to the single-piece bottom shell  28 , though, as stated above, alternate embodiments would include other methods of joining (e.g., fasteners) these sections of the outer housing  12 . Assembly of the outer housing  12  results in the formation of an enclosed chamber  31  that surrounds the drive unit  16 , and partially surrounds the scroll compressor  14 . In particular embodiments, the top end housing section  26  is generally dome-shaped and includes a respective cylindrical side wall region  32  that abuts the top of the central cylindrical housing section  24 , and provides for closing off the top end of the outer housing  12 . As can also be seen from  FIG. 1 , the bottom of the central cylindrical housing section  24  abuts a flat portion just to the outside of a raised annular rib  34  of the bottom end housing section  28 . In at least one embodiment of the invention, the central cylindrical housing section  24  and bottom end housing section  28  are joined by an exterior weld around the circumference of a bottom end of the outer housing  12 . 
     In a particular embodiment, the drive unit  16  in is the form of an electrical motor assembly  40 . The electrical motor assembly  40  operably rotates and drives a shaft  46 . Further, the electrical motor assembly  40  generally includes a stator  50  comprising electrical coils and a rotor  52  that is coupled to the drive shaft  46  for rotation together. The stator  50  is supported by the outer housing  12 , either directly or via an adaptor. For purposes of the present disclosure the term motor may or may not include a motor spacer according to different embodiments. Both possibilities are covered by the independent claims appended hereto. The stator  50  may be press-fit directly into outer housing  12 , or may be fitted with an adapter  602  (See  FIGS. 21 ,  22 ) and press-fit into the outer housing  12 . In a particular embodiment, the rotor  52  is mounted on the drive shaft  46 , which is supported by upper and lower bearings  42 ,  44 . Energizing the stator  50  is operative to rotatably drive the rotor  52  and thereby rotate the drive shaft  46  about a central axis  54 . Applicant notes that when the terms “axial” and “radial” are used herein to describe features of components or assemblies, they are defined with respect to the central axis  54 . Specifically, the term “axial” or “axially-extending” refers to a feature that projects or extends in a direction parallel to the central axis  54 , while the terms “radial’ or “radially-extending” indicates a feature that projects or extends in a direction perpendicular to the central axis  54 . 
     With reference to  FIG. 1 , the lower bearing member  44  includes a central, generally cylindrical hub  58  that includes a central bushing and opening to provide a cylindrical bearing  60  to which the drive shaft  46  is journaled for rotational support. A plate-like ledge region  68  of the lower bearing member  44  projects radially outward from the central hub  58 , and serves to separate a lower portion of the stator  50  from an oil lubricant sump  76 . An axially-extending perimeter surface  70  of the lower bearing member  44  may engage with the inner diameter surface of the central housing section  24  to centrally locate the lower bearing member  44  and thereby maintain its position relative to the central axis  54 . This can be by way of an interference and press-fit support arrangement between the lower bearing member  44  and the outer housing  12 . 
     In the embodiment of  FIG. 1 , the drive shaft  46  has an impeller tube  47  attached at the bottom end of the drive shaft  46 . In a particular embodiment, the impeller tube  47  is of a smaller diameter than the drive shaft  46 , and is aligned concentrically with the central axis  54 . As can be seen from  FIG. 1 , the drive shaft  46  and impeller tube  47  pass through an opening in the cylindrical hub  58  of the lower bearing member  44 . At its upper end, the drive shaft  46  is journaled for rotation within the upper bearing member  42 . Upper bearing member  42  may also be referred to as a “crankcase”. 
     The drive shaft  46  further includes an offset eccentric drive section  74  that has a cylindrical drive surface  75  (shown in  FIG. 2 ) about an offset axis that is offset relative to the central axis  54 . This offset drive section  74  is journaled within a cavity of a movable scroll compressor body  112  of the scroll compressor  14  to drive the movable scroll compressor body  112  about an orbital path when the drive shaft  46  rotates about the central axis  54 . To provide for lubrication of all of the various bearing surfaces, the outer housing  12  provides the oil lubricant sump  76  at the bottom end of the outer housing  12  in which suitable oil lubricant is provided. The impeller tube  47  has an oil lubricant passage and inlet port  78  formed at the end of the impeller tube  47 . Together, the impeller tube  47  and inlet port  78  act as an oil pump when the drive shaft  46  is rotated, and thereby pumps oil out of the lubricant sump  76  into an internal lubricant passageway  80  defined within the drive shaft  46 . During rotation of the drive shaft  46 , centrifugal force acts to drive lubricant oil up through the lubricant passageway  80  against the action of gravity. The lubricant passageway  80  has various radial passages projecting therefrom to feed oil through centrifugal force to appropriate bearing surfaces and thereby lubricate sliding surfaces as may be desired. 
     As shown in  FIGS. 2 and 3 , the upper bearing member, or crankcase,  42  includes a central bearing hub  87  into which the drive shaft  46  is journaled for rotation, and a thrust bearing  84  that supports the movable scroll compressor body  112 . (See also  FIG. 9 ). Extending outward from the central bearing hub  87  is a disk-like portion  86  that terminates in an intermittent perimeter support surface  88  defined by discretely spaced posts  89 . In the embodiment of  FIG. 3 , the central bearing hub  87  extends below the disk-like portion  86 , while the thrust bearing  84  extends above the disk-like portion  86 . In certain embodiments, the intermittent perimeter support surface  88  is adapted to have an interference and press-fit with the outer housing  12 . In the embodiment of  FIG. 3 , the crankcase  42  includes four posts  89 , each post having an opening  91  configured to receive a threaded fastener. It is understood that alternate embodiments of the invention may include a crankcase with more or less than four posts, or the posts may be separate components altogether. Alternate embodiments of the invention also include those in which the posts are integral with the pilot ring instead of the crankcase. 
     In certain embodiments such as the one shown in  FIG. 3 , each post  89  has an arcuate outer surface  93  spaced radially inward from the inner surface of the outer housing  12 , angled interior surfaces  95 , and a generally flat top surface  97  which can support a pilot ring  160 . In this embodiment, intermittent perimeter support surface  88  abuts the inner surface of the outer housing  12 . Further, each post  89  has a chamfered edge  94  on a top, outer portion of the post  89 . In particular embodiments, the crankcase  42  includes a plurality of spaces  244  between adjacent posts  89 . In the embodiment shown, these spaces  244  are generally concave and the portion of the crankcase  42  bounded by these spaces  244  will not contact the inner surface of the outer housing  12 . 
     The upper bearing member or crankcase  42  also provides axial thrust support to the movable scroll compressor body  112  through a bearing support via an axial thrust surface  96 . While, as shown  FIGS. 1-3 , the crankcase  42  may be integrally provided by a single unitary component,  FIGS. 13 and 14  show an alternate embodiment in which the axial thrust support is provided by a separate collar member  198  that is assembled and concentrically located within the upper portion of the upper bearing member  199  along stepped annular interface  100 . The collar member  198  defines a central opening  102  that is a size large enough to clear a cylindrical bushing drive hub  128  of the movable scroll compressor body  112  in addition to the eccentric offset drive section  74 , and allow for orbital eccentric movement thereof. 
     Turning in greater detail to the scroll compressor  14 , the scroll compressor includes first and second scroll compressor bodies which preferably include a stationary fixed scroll compressor body  110  and a movable scroll compressor body  112 . While the term “fixed” generally means stationary or immovable in the context of this application, more specifically “fixed” refers to the non-orbiting, non-driven scroll member, as it is acknowledged that some limited range of axial, radial, and rotational movement is possible due to thermal expansion and/or design tolerances. 
     The movable scroll compressor body  112  is arranged for orbital movement relative to the fixed scroll compressor body  110  for the purpose of compressing refrigerant. The fixed scroll compressor body includes a first rib  114  projecting axially from a plate-like base  116  and is designed in the form of a spiral. Similarly, the movable scroll compressor body  112  includes a second scroll rib  118  projecting axially from a plate-like base  120  and is in the shape of a similar spiral. The scroll ribs  114 ,  118  engage in one another and abut sealingly on the respective surfaces of bases  120 ,  116  of the respectively other compressor body  112 ,  110 . As a result, multiple compression chambers  122  are formed between the scroll ribs  114 ,  118  and the bases  120 ,  116  of the compressor bodies  112 ,  110 . Within the chambers  122 , progressive compression of refrigerant takes place. Refrigerant flows with an initial low pressure via an intake area  124  surrounding the scroll ribs  114 ,  118  in the outer radial region (see e.g.  FIGS. 1-2 ). Following the progressive compression in the chambers  122  (as the chambers progressively are defined radially inward), the refrigerant exits via a compression outlet  126  which is defined centrally within the base  116  of the fixed scroll compressor body  110 . Refrigerant that has been compressed to a high pressure can exit the chambers  122  via the compression outlet  126  during operation of the scroll compressor  14 . 
     The movable scroll compressor body  112  engages the eccentric offset drive section  74  of the drive shaft  46 . More specifically, the receiving portion of the movable scroll compressor body  112  includes the cylindrical bushing drive hub  128  which slideably receives the eccentric offset drive section  74  with a slideable bearing surface provided therein. In detail, the eccentric offset drive section  74  engages the cylindrical bushing drive hub  128  in order to move the movable scroll compressor body  112  about an orbital path about the central axis  54  during rotation of the drive shaft  46  about the central axis  54 . Considering that this offset relationship causes a weight imbalance relative to the central axis  54 , the assembly typically includes a counterweight  130  that is mounted at a fixed angular orientation to the drive shaft  46 . The counterweight  130  acts to offset the weight imbalance caused by the eccentric offset drive section  74  and the movable scroll compressor body  112  that is driven about an orbital path. The counterweight  130  includes an attachment collar  132  and an offset weight region  134  (see counterweight  130  shown best in  FIGS. 2 and 3 ) that provides for the counterweight effect and thereby balancing of the overall weight of the components rotating about the central axis  54 . This provides for reduced vibration and noise of the overall assembly by internally balancing or cancelling out inertial forces. 
     With reference to  FIGS. 4 and 7 , the guiding movement of the scroll compressor  14  can be seen. To guide the orbital movement of the movable scroll compressor body  112  relative to the fixed scroll compressor body  110 , an appropriate key coupling  140  may be provided. Keyed couplings  140  are often referred to in the scroll compressor art as an “Oldham Coupling.” In this embodiment, the key coupling  140  includes an outer ring body  142  and includes two axially-projecting first keys  144  that are linearly spaced along a first lateral axis  146  and that slide closely and linearly within two respective keyway tracks or slots  115  (shown in  FIGS. 1 and 2 ) of the fixed scroll compressor body  110  that are linearly spaced and aligned along the first axis  146  as well. The slots  115  are defined by the stationary fixed scroll compressor body  110  such that the linear movement of the key coupling  140  along the first lateral axis  146  is a linear movement relative to the outer housing  12  and perpendicular to the central axis  54 . The keys can comprise slots, grooves or, as shown, projections which project axially (i.e., parallel to central axis  54 ) from the ring body  142  of the key coupling  140 . This control of movement along the first lateral axis  146  guides part of the overall orbital path of the movable scroll compressor body  112 . 
     Referring specifically to  FIG. 4 , the key coupling  140  includes four axially-projecting second keys  152  in which opposed pairs of the second keys  152  are linearly aligned substantially parallel relative to a second transverse lateral axis  154  that is perpendicular to the first lateral axis  146 . There are two sets of the second keys  152  that act cooperatively to receive projecting sliding guide portions  254  that project from the base  120  on opposite sides of the movable scroll compressor body  112 . The guide portions  254  linearly engage and are guided for linear movement along the second transverse lateral axis by virtue of sliding linear guiding movement of the guide portions  254  along sets of the second keys  152 . 
     It can be seen in  FIG. 4  that four sliding contact surfaces  258  are provided on the four axially-projecting second keys  152  of the key coupling  140 . As shown, each of the sliding contact surfaces  258  is contained in its own separate quadrant  252  (the quadrants  252  being defined by the mutually perpendicular lateral axes  146 ,  154 ). As shown, cooperating pairs of the sliding contact surfaces  258  are provided on each side of the first lateral axis  146 . 
     By virtue of the key coupling  140 , the movable scroll compressor body  112  has movement restrained relative to the fixed scroll compressor body  110  along the first lateral axis  146  and second transverse lateral axis  154 . This results in the prevention of relative rotation of the movable scroll body as it allows only translational motion. More particularly, the fixed scroll compressor body  110  limits motion of the key coupling  140  to linear movement along the first lateral axis  146 ; and in turn, the key coupling  140  when moving along the first lateral axis  146  carries the movable scroll  112  along the first lateral axis  146  therewith. Additionally, the movable scroll compressor body can independently move relative to the key coupling  140  along the second transverse lateral axis  154  by virtue of relative sliding movement afforded by the guide portions  254  which are received and slide between the second keys  152 . By allowing for simultaneous movement in two mutually perpendicular axes  146 ,  154 , the eccentric motion that is afforded by the eccentric offset drive section  74  of the drive shaft  46  upon the cylindrical bushing drive hub  128  of the movable scroll compressor body  112  is translated into an orbital path movement of the movable scroll compressor body  112  relative to the fixed scroll compressor body  110 . 
     The movable scroll compressor body  112  also includes flange portions  268  projecting in a direction perpendicular relative to the guiding flange portions  262  (e.g. along the first lateral axis  146 ). These additional flange portions  268  are preferably contained within the diametrical boundary created by the guide flange portions  262  so as to best realize the size reduction benefits. Yet a further advantage of this design is that the sliding faces  254  of the movable scroll compressor body  112  are open and not contained within a slot. This is advantageous during manufacture in that it affords subsequent machining operations such as finishing milling for creating the desirable tolerances and running clearances as may be desired. 
     Generally, scroll compressors with movable and fixed scroll compressor bodies require some type of restraint for the fixed scroll compressor body  110  which restricts the radial movement and rotational movement but which allows some degree of axial movement so that the fixed and movable scroll compressor bodies  110 ,  112  are not damaged during operation of the scroll compressor  14 . In embodiments of the invention, that restraint is provided by a pilot ring  160 , as shown in  FIGS. 5-9 .  FIG. 5  shows the top side of pilot ring  160 , constructed in accordance with an embodiment of the invention. The pilot ring  160  has a top surface  167 , a cylindrical outer perimeter surface  178 , and a cylindrical first inner wall  169 . The pilot ring  160  of  FIG. 5  includes four holes  161  through which fasteners, such as threaded bolts, may be inserted to allow for attachment of the pilot ring  160  to the crankcase  42 . In a particular embodiment, the pilot ring  160  has axially-raised portions  171  (also referred to as mounting bosses) where the holes  161  are located. One of skill in the art will recognize that alternate embodiments of the pilot ring may have greater or fewer than four holes for fasteners. The pilot ring  160  may be a machined metal casting, or, in alternate embodiments, a machined component of iron, steel, aluminum, or some other similarly suitable material. 
       FIG. 6  shows a bottom view of the pilot ring  160  showing the four holes  161  along with two slots  162  formed into the pilot ring  160 . In the embodiment of  FIG. 6 , the slots  162  are spaced approximately 180 degrees apart on the pilot ring  160 . Each slot  162  is bounded on two sides by axially-extending side walls  193 . As shown in  FIG. 6 , the bottom side of the pilot ring  160  includes a base portion  163  which is continuous around the entire circumference of the pilot ring  160  forming a complete cylinder. But on each side of the two slots  162 , there is a semi-circular stepped portion  164  which covers some of the base portion  163  such that a ledge  165  is formed on the part of the pilot ring  160  radially inward of each semi-circular stepped portion  164 . The inner-most diameter or the ledge  165  is bounded by the first inner wall  169 . 
     A second inner wall  189  runs along the inner diameter of each semi-circular stepped portion  164 . Each semi-circular stepped portion  164  further includes a bottom surface  191 , a notched section  166 , and a chamfered lip  190 . In the embodiment of  FIG. 6 , each chamfered lip  190  runs the entire length of the semi-circular stepped portion  164  making the chamfered lip  190  semi-circular as well. Each chamfered lip  190  is located on the radially-outermost edge of the bottom surface  191 , and extends axially from the bottom surface  191 . Further, each chamfered lip  190  includes a chamfered edge surface  192  on an inner radius of the chamfered lip  190 . When assembled, the chamfered edge surface  192  is configured to mate with the chamfered edge  94  on each post  89  of the crankcase. The mating of these chamfered surfaces allows for an easier, better-fitting assembly, and reduces the likelihood of assembly problems due to manufacturing tolerances. 
     In the embodiment of  FIG. 6 , the notched sections  166  are approximately 180 degrees apart on the pilot ring  160 , and each is about midway between the two ends of the semi-circular stepped portion  164 . The notched sections  166  are bounded on the sides by sidewall sections  197 . Notched sections  166  thus extend radially and axially into the semi-circular stepped portion  164  of the pilot ring  160 . 
       FIG. 7  shows an exploded view of the scroll compressor  14  assembly, according to an embodiment of the invention. The top-most component shown is the pilot ring  160  which is adapted to fit over the top of the fixed scroll compressor body  110 . The fixed scroll compressor body  110  has a pair of first radially-outward projecting limit tabs  111 . In the embodiment of  FIG. 7 , one of the pair of first radially-outward projecting limit tabs  111  is attached to an outermost perimeter surface  117  of the first scroll rib  114 , while the other of the pair of first radially-outward projecting limit tabs  111  is attached to a perimeter portion of the fixed scroll compressor body  110  below a perimeter surface  119 . In further embodiments, the pair of first radially-outward projecting limit tabs  111  are spaced approximately 180 degrees apart. Additionally, in particular embodiments, each of the pair of first radially-outward-projecting limit tabs  111  has a slot  115  therein. In particular embodiments, the slot  115  may be a U-shaped opening, a rectangular-shaped opening, or have some other suitable shape. 
     The fixed scroll compressor body  110  also has a pair of second radially-outward projecting limit tabs  113 , which, in this embodiment, are spaced approximately 180 degrees apart. In certain embodiments, the second radially-outward projecting limit tabs  113  share a common plane with the first radially-outward-projecting limit tabs  111 . Additionally, in the embodiment of  FIG. 7 , one of the pair of second radially-outward projecting limit tabs  113  is attached to an outermost perimeter surface  117  of the first scroll rib  114 , while the other of the pair of second radially-outward projecting limit tabs  113  is attached to a perimeter portion of the fixed scroll compressor body  110  below the perimeter surface  119 . The movable scroll compressor body  112  is configured to be held within the keys of the key coupling  140  and mates with the fixed scroll compressor body  110 . As explained above, the key coupling  140  has two axially-projecting first keys  144 , which are configured to be received within the slots  115  in the first radially-outward-projecting limit tabs  111 . When assembled, the key coupling  140 , fixed and movable scroll compressor bodies  110 ,  112  are all configured to be disposed within crankcase  42 , which can be attached the to the pilot ring  160  by the threaded bolts  168  shown above the pilot ring  160 . 
     Referring still to  FIG. 7 , the fixed scroll compressor body  110  includes plate-like base  116  (see  FIG. 14 ) and a perimeter surface  119  spaced axially from the plate-like base  116 . In a particular embodiment, the entirety of the perimeter surface  119  surrounds the first scroll rib  114  of the fixed scroll compressor body  110 , and is configured to abut the first inner wall  169  of the pilot ring  160 , though embodiments are contemplated in which the engagement of the pilot ring and fixed scroll compressor body involve less than the entire circumference. In particular embodiments of the invention, the first inner wall  169  is precisely toleranced to fit snugly around the perimeter surface  119  to thereby limit radial movement of the first scroll compressor body  110 . The plate-like base  116  further includes a radially-extending top surface  121  that extends radially inward from the perimeter surface  119 . The radially-extending top surface  121  extends radially inward towards a step-shaped portion  123  (see  FIG. 8 ). From this step-shaped portion  123 , a cylindrical inner hub region  172  and peripheral rim  174  extend axially (i.e., parallel to central axis  54 , when assembled into scroll compressor assembly  10 ). 
       FIG. 8  shows the components of  FIG. 7  fully assembled. The pilot ring  160  securely holds the fixed scroll compressor body  110  in place with respect to the movable scroll compressor body  112  and key coupling  140 . The threaded bolts  168  attach the pilot ring  160  and crankcase  42 . As can be seen from  FIG. 8 , each of the pair of first radially-outward projecting limit tabs  111  is positioned in its respective slot  162  of the pilot ring  160 . As stated above, the slots  115  in the pair of first radially-outward projecting limit tabs  111  are configured to receive the two axially-projecting first keys  144 . In this manner, the pair of first radially-outward projecting limit tabs  111  engage the side portion  193  of the pilot ring slots  162  to prevent rotation of the fixed scroll compressor body  110 , while the key coupling first keys  144  engage a side portion of the slot  115  to prevent rotations of the key coupling  140 . Limit tabs  111  also provide additional (to limit tabs  113 ) axial limit stops. 
     Though not visible in the view of  FIG. 8 , each of the pair of second radially-outward projecting limit tabs  113  (see  FIG. 7 ) is nested in its respective notched section  166  of the pilot ring  160  to constrain axial movement of the fixed scroll compressor body  110  thereby defining a limit to the available range of axial movement of the fixed scroll compressor body  110 . The pilot ring notched sections  166  are configured to provide some clearance between the pilot ring  160  and the pair of second radially-outward projecting limit tabs  113  to provide for axial restraint between the fixed and movable scroll compressor bodies  110 ,  112  during scroll compressor operation. However, the radially-outward projecting limit tabs  113  and notched sections  166  also keep the extent of axial movement of the fixed scroll compressor body  110  to within an acceptable range. 
     It should be noted that “limit tab” is used generically to refer to either or both of the radially-outward projecting limit tabs  111 ,  113 . Embodiments of the invention may include just one of the pairs of the radially-outward projecting limit tabs, or possibly just one radially-outward projecting limit tab, and particular claims herein may encompass these various alternative embodiments 
     As illustrated in  FIG. 8 , the crankcase  42  and pilot ring  160  design allow for the key coupling  140 , and the fixed and movable scroll compressor bodies  110 ,  112  to be of a diameter that is approximately equal to that of the crankcase  42  and pilot ring  160 . As shown in  FIG. 1 , the diameters of these components may abut or nearly abut the inner surface of the outer housing  12 , and, as such, the diameters of these components is approximately equal to the inner diameter of the outer housing  12 . It is also evident that when the key coupling  140  is as large as the surrounding compressor outer housing  12  allows, this in turn provides more room inside the key coupling  140  for a larger thrust bearing which in turn allows a larger scroll set. This maximizes the scroll compressor  14  displacement available within a given diameter outer housing  12 , and thus uses less material at less cost than in conventional scroll compressor designs. 
     It is contemplated that the embodiments of  FIGS. 7 and 8  in which the first scroll compressor body  110  includes four radially-outward projecting limit tabs  111 ,  113 , these limit tabs  111 ,  113  could provide radial restraint of the first scroll compressor body  110 , as well as axial and rotation restraint. For example, radially-outward projecting limit tabs  113  could be configured to fit snugly with notched sections  166  such that these limit tabs  113  sufficiently limit radial movement of the first scroll compressor body  110  along first lateral axis  146 . Additionally, each of the radially-outward-projecting limit tabs  111  could have a notched portion configured to abut the portion of the first inner wall  169  adjacent the slots  162  of the pilot ring  160  to provide radial restraint along second lateral axis  154 . While this approach could potentially require maintaining a certain tolerance for the limit tabs  111 ,  113  or the notched section  166  and slots  162 , in these instances, there would be no need to precisely tolerance the entire first inner wall  169  of the pilot ring  160 , as this particular feature would not be needed to provide radial restraint of the first scroll compressor body  110 . 
     With reference to  FIGS. 9-12 , the upper side (e.g. the side opposite the scroll rib) of the fixed scroll  110  supports a floating seal  170  above which is disposed the separator plate  30 . In the embodiment shown, to accommodate the floating seal  170 , the upper side of the fixed scroll compressor body  110  includes an annular and, more specifically, the cylindrical inner hub region  172 , and the peripheral rim  174  spaced radially outward from the inner hub region  172 . The inner hub region  172  and the peripheral rim  174  are connected by a radially-extending disc region  176  of the base  116 . As shown in  FIG. 12 , the underside of the floating seal  170  has circular cutout adapted to accommodate the inner hub region  172  of the fixed scroll compressor body  110 . Further, as can be seen from  FIGS. 9 and 10 , the perimeter wall  173  of the floating seal is adapted to fit somewhat snugly inside the peripheral rim  174 . In this manner, the fixed scroll compressor body  110  centers and holds the floating seal  170  with respect to the central axis  54 . 
     In a particular embodiment of the invention, a central region of the floating seal  170  includes a plurality of openings  175 . In the embodiment shown, one of the plurality of openings  175  is centered on the central axis  54 . That central opening  177  is adapted to receive a rod  181  which is affixed to the floating seal  170 . As shown in  FIGS. 9 through 12 , a ring valve  179  is assembled to the floating seal  170  such that the ring valve  179  covers the plurality of openings  175  in the floating seal  170 , except for the central opening  177  through which the rod  181  is inserted. The rod  181  includes an upper flange  183  with a plurality of openings  185  therethrough, and a stem  187 . As can be seen in  FIG. 9 , the separator plate  30  has a center hole  33 . The upper flange  183  of rod  181  is adapted to pass through the center hole  33 , while the stem  187  is inserted through central opening  177 . The ring valve  179  slides up and down the rod  181  as needed to prevent back flow from a high-pressure chamber  180 . With this arrangement, the combination of the separator plate  30 , the fixed scroll compressor body  110 , and floating seal  170  serve to separate the high pressure chamber  180  from a lower pressure region  188  within the outer housing  12 . Rod  181  guides and limits the motion of the ring valve  179 . While the separator plate  30  is shown as engaging and constrained radially within the cylindrical side wall region  32  of the top end housing section  26 , the separator plate  30  could alternatively be cylindrically located and axially supported by some portion or component of the scroll compressor  14 . 
     In certain embodiments, when the floating seal  170  is installed in the space between the inner hub region  172  and the peripheral rim  174 , the space beneath the floating seal  170  is pressurized by a vent hole (not shown) drilled through the fixed scroll compressor body  110  to chamber  122  (shown in  FIG. 2 ). This pushes the floating seal  170  up against the separator plate  30  (shown in  FIG. 9 ). A circular rib  182  presses against the underside of the separator plate  30  forming a seal between high-pressure discharge gas and low-pressure suction gas. 
     While the separator plate  30  could be a stamped steel component, it could also be constructed as a cast and/or machined member (and may be made from steel or aluminum) to provide the ability and structural features necessary to operate in proximity to the high-pressure refrigerant gases output by the scroll compressor  14 . By casting or machining the separator plate  30  in this manner, heavy stamping of such components can be avoided. 
     During operation, the scroll compressor assembly  10  is operable to receive low-pressure refrigerant at the housing inlet port  18  and compress the refrigerant for delivery to the high-pressure chamber  180  where it can be output through the housing outlet port  20 . This allows the low-pressure refrigerant to flow across the electrical motor assembly  40  and thereby cool and carry away from the electrical motor assembly  40  heat which can be generated by operation of the motor. Low-pressure refrigerant can then pass longitudinally through the electrical motor assembly  40 , around and through void spaces therein toward the scroll compressor  14 . The low-pressure refrigerant fills the chamber  31  formed between the electrical motor assembly  40  and the outer housing  12 . From the chamber  31 , the low-pressure refrigerant can pass through the upper bearing member or crankcase  42  through the plurality of spaces  244  that are defined by recesses around the circumference of the crankcase  42  in order to create gaps between the crankcase  42  and the outer housing  12 . The plurality of spaces  244  may be angularly spaced relative to the circumference of the crankcase  42 . 
     After passing through the plurality of spaces  244  in the crankcase  42 , the low-pressure refrigerant then enters the intake area  124  between the fixed and movable scroll compressor bodies  110 ,  112 . From the intake area  124 , the low-pressure refrigerant enters between the scroll ribs  114 ,  118  on opposite sides (one intake on each side of the fixed scroll compressor body  110 ) and is progressively compressed through chambers  122  until the refrigerant reaches its maximum compressed state at the compression outlet  126  from which it subsequently passes through the floating seal  170  via the plurality of openings  175  and into the high-pressure chamber  180 . From this high-pressure chamber  180 , high-pressure compressed refrigerant then flows from the scroll compressor assembly  10  through the housing outlet port  20 . 
       FIGS. 13 and 14  illustrate an alternate embodiment of the invention. Instead of a crankcase  42  formed as a single piece,  FIGS. 13 and 14  show an upper bearing member or crankcase  199  combined with a separate collar member  198 , which provides axial thrust support for the scroll compressor  14 . In a particular embodiment, the collar member  198  is assembled into the upper portion of the upper bearing member or crankcase  199  along stepped annular interface  100 . Having a separate collar member  198  allows for a counterweight  230  to be assembled within the crankcase  199 , which is attached to the pilot ring  160 . This allows for a more compact assembly than described in the previous embodiment where the counterweight  130  was located outside of the crankcase  42 . 
     As is evident from the exploded view of  FIG. 13  and as stated above, the pilot ring  160  can be attached to the upper bearing member or crankcase  199  via a plurality of threaded fasteners to the upper bearing member  199  in the same manner that it was attached to crankcase  42  in the previous embodiment. The flattened profile of the counterweight  230  allows for it to be nested within an interior portion  201  of the upper bearing member  199  without interfering with the collar member  198 , the key coupling  140 , or the movable scroll compressor body  112 . 
     Turning to additional features employed in the first embodiment and that can be employed in other scroll compressor configurations or compressors generally, a compressor housing and motor sub-assembly  300  includes a housing or shell  302  with multiple diameters, as shown in  FIG. 15 . It is understood that this embodiment of sub-assembly  300  is employed in the embodiments of  FIGS. 1-14  and as such only the housing features and press fitting options of this embodiment are described below. The descriptions of the other components of this compressor assembly  300  and operation thereof can be had from earlier embodiments that include the same structures. The shell  302  includes a center portion  304 , a first outer portion  306 , and a second outer portion  308 . Inside shell  302  is a motor  314 , which includes stator  316 . The motor  314  is press fit inside of shell  302  such that the stator  316  makes contact with the center portion  304  of the shell  302 . Also, the motor  314  includes annularly spaced vertical lubricant flow passages or channels  340  that span an entire vertical length of the motor  314 . (See also  FIG. 20 ). 
     In the embodiment of the invention shown in  FIG. 15 , the first and second portions  306  and  308  have larger inner diameters and inner perimeters, compared with the center portion  304 , which has a smaller inner diameter and inner perimeter. Several advantages are realized by varying the inner diameter or inner perimeter of shell  302 . Primarily, by having a narrower inner diameter or inner perimeter of the center portion  304 , a shorter interference length is achieved while press fitting the motor  314  into the shell  302 . During the press fitting process, the stator  316  will scrape the inside surface of the shell  302 . This can cause some surface interruption or damage to both the shell  302  and the stator  316 . The portion of the surface of the shell  302  that scrapes the motor  314  during the press fitting process is called the interference surface. Because the center portion  304  diameter is narrower than the diameter of either the first or the second outer portions  306  and  308 , the interference surface is minimized. This in turn minimizes the damage done to both the shell  302  and the motor  314 . 
     Furthermore, by minimizing the interference surface minimal damage is done to the shell  302 , which preserves the interior surface integrity of the first and second outer portions  306  and  308 . By preserving the interior surface integrity of the first and second outer portions  306  and  308 , other press-fit components can be inserted into shell  302  and press fit along uninterrupted and previously non-interfered with surfaces, such as first and second bearing housings  318  and  320  that can be press fit into opposite ends of the shell. The first and second bearing housings  318  and  320  are used to support, guide and/or retain a drive shaft that powers a compression mechanism and is driven by the motor  314 . 
     A secondary benefit to varying the diameter of shell  302  is achieving a shorter press stroke while press fitting the motor  314  into the center portion  304  of shell  302 . The press stroke is the motion that is undertaken while press fitting an object inside a shell. By minimizing the press stroke, time and energy is saved while manufacturing the compressor assembly  300 . 
     A method  500  of making the shell  302  (from  FIG. 15 ) is illustrated in  FIG. 16 . To achieve a shell with a varying diameter a sheet of metal material  502 , which is typically steel, is rolled into an approximate thickness and shape, then welded along an axial weld seam  504  to form a cylinder  506 . Once formed into a cylinder  506 , the material that encompasses the first and second outer portions  306  and  308  and center portion  304  is expanded by using an expander containing an expander tool (not illustrated). The expander tool can be used to form a family of shells that vary in length of the first and second outer portions  306  and  308  only. As an aside, typically, all portions of the cylinder  506  are expanded using the expander tool in order to maintain diameter, straightness, and concentricity requirements of the compressor shell. Although, other embodiments of the method  500  are contemplated, such as only expanding the outer portions  306  and  308  because the center portion  304  already has the desired diameter. 
     After expansion, the length of the outer portions  306  and  308  can be adjusted by cutting away material such as an end ring portion  510  from the first or second outer portions  306  and  308 . Or an appropriately sized starting sheet of material is used to form a non expanded cylinder or starting blank  506 , which is suspended in position on the expander resulting in the proper outer step length. Further, the diameter of the first and second outer portions  306  and  308  is typically between about 1% and about 5% larger than the diameter of the center portion  304  in order to facilitate press fitting the motor  314  into the center portion  304 , while providing clearance relative to the insertion outer portions. However, other relative diameter sizes are contemplated such that the first and second outer portions  306  and  308  are more than 5% larger than the diameter of the center portion  304 . 
     Additionally, after forming the shell  302  from the process described above, the first and second outer portions  306  and  308  have respective first and second open ends  326  and  328 . At this point the components that are required for a compressor mechanism of the compressor assembly  300  are press fit into the shell  302 . Once the compressor mechanism is inside the shell  302 , end housing sections  330  and  332  are attached to shell  302 . Various methods are used to attach the end housing sections  330  and  332 , such as press fitting, and preferably welding the end housing sections to the shell  302 . 
     The process described above results in a first step  322  that connects the first outer portion  306  to the center portion  304 , and a second step  324  that connects the center portion  304  to the second outer portion  308 . An enlarged view of the first step  322  and the second step  324  are shown in  FIG. 17 . The embodiment of the shell  302  shown in  FIG. 17  is similar to the shell  302  of  FIG. 15  in that both the first and second steps  322  and  324  expand the diameter of the first and second outer portions  306  and  308  to be larger than the diameter of the center portion  304 . Further, in the embodiment illustrated in  FIG. 17  the first and second steps  322  and  324  are tapered and may form a conical surface. The tapered surface assists in centering the motor  314  during press fitting as it will automatically correct any misalignment upon contact to guide down to a smaller diameter. 
       FIG. 18  illustrates a cross sectional view of the scroll compressor assembly  10  of  FIG. 1  with the shell  302  from  FIGS. 15-17 . The motor  40  is press fit into the shell  302 , similar to embodiment described in  FIG. 15 . An outer diameter of the stator  50  is pressed into (i.e. interferes with) the inner diameter of the center portion  304  of the shell  302 . Further, the stator  50  is longer than the center portion  304  of the shell  302  by at least 5 millimeters. This creates an annular lubrication region or an annular gap  334  in a ring-shaped region where stator  50  meets a funnel surface  336  of the shell  302 . The annular gap  334  comprises a wedge shaped channel that has a vertical height and a width. The height (H) is measured from where the shell  302  meets the stator  50  to the top of the stator  50 , and the width (W) is measured from the inner surface of the first outer portion  306  to the edge of the stator  50 . The height is typically at least 5 millimeters and the width is typically at least 2.5 millimeters. In other embodiments of the compressor, the width may be as much as 27 millimeters. 
     Lubricating fluid (e.g. oil) is carried from sump  76  to the upper bearing or crankcase  42  to lubricate the surfaces between the crankcase  42  and the scroll compressor bodies. The lubricant is drawn upward by a centrifugal force created by the motor  40  rotating an impeller  47  of the drive shaft to draw lubricant from the sump  76  up through an internal lubrication path  80 . During operation of the scroll compressor  14 , lubricating fluid will flow outward toward the shell  302  because the rotation of the shaft  46  pushes the lubricant fluid away from a center axis  54 , and gravity causes the lubricating fluid to drain down toward the sump  76  for reuse. Therefore, the lubricating fluid will flow down the inner wall of shell  302  where it meets the funnel surface  336  to pool into the annular gap  334 . Because the stator  50  is longer than the center portion  304  of shell  302  the spent lubricant will collect in the annular gap  334  and continue to drain toward sump  76  rather than spread uniformly across a flat upper surface of the stator  50  and potentially flowing inward toward the center axis  54  to become entrained with the refrigerant gas. 
       FIG. 19  illustrates a horizontal cross section of the scroll compressor assembly  10  from  FIG. 18 . The cross section is through the stator  50  and illustrates flats or recesses  338  formed vertically and spanning the entire length of the stator  50 . The recesses  338  create lubrication flow passages  340  between the recesses  338  and an inner surface of the shell  302  that allow the spent lubricant that is captured in the annular gap  334  to drain through the motor  50  toward the sump  76 . The recesses  338  are arranged in relative spaced angular orientation around the stator  50  such that one lubrication flow passage  340  is formed by each recess  338 . 
       FIG. 20  illustrates another embodiment of the scroll compressor assembly  10  from  FIG. 18 . In this particular embodiment, a motor  614  includes an adaptor ring that provides a motor spacer  602  that provides a larger outer diameter and periphery for the motor  614  for press fitting. Ideally, the shell  302  will have a center portion  304  diameter such that the motor  40  (see  FIG. 18 ) with a standard diameter stator  50  can be press fit into the shell  302  without the adaptor  602 . However, in the event that a motor  614  with a nonstandard size stator  616 , or a smaller sized motor that has sufficient output power is used, the shell  302  is still capable of housing the motor  614  because it includes the motor spacer  602 . 
       FIG. 21  illustrates the motor  614  including the motor spacer  602 . The motor spacer  602  includes a generally circular inner surface  644  with a diameter large enough that it wraps around the stator  616  of the motor  614 . The inner surface  644  of the motor spacer  602  should have a tight grip around the stator  616  such that the motor spacer  602  does not slide off the stator  616  during the press fitting process. 
     Furthermore, an external surface of the motor spacer  602  includes raised portions  642 . The raised portions  642  are spaced periodically around the circumference of the motor spacer  602 . The raised portions  642  are the portions of the motor spacer  602  that make contact with the inner surface of the shell  302  (see  FIG. 17 ). While the embodiment of the motor spacer  602  illustrated in  FIG. 21  shows six raised portions  642 , more or less than six raised portions  642  are contemplated. In between each raised portions  642  is a thin portion that forms a valley  646  that allows lubricant oil flowing downward toward the sump  76  (see  FIG. 20 ) to flow around the motor spacer  602 . 
       FIG. 22  illustrates a cross section through the stator  616  and motor spacer  602  from  FIGS. 20-21 . The motor stator  616  has flats or recesses  638 . The recesses  638  and valleys  646  work together to form lubricant flow passages  640  between the stator  616  and the inner surface of the shell section  304  (see  FIG. 20 ) and around the motor spacer  602 . Lubricant flow passages  640  operate such that lubricant oil will flow downward through the lubricant flow passages  640  to a sump  76  (see  FIG. 20 ). 
     All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.