Patent Publication Number: US-2006013708-A1

Title: Drive shaft for compressor

Description:
PRIORITY REFERENCE  
      This application claims the benefit of priority under 35 U.S.C. §119(e) to provisional application Ser. No. 60/589,051, filed in the name of Zer Kai Yap on Jul. 19, 2004. 
    
    
     BACKGROUND  
      The present invention relates generally to hermetic compressor assemblies having two compressor mechanisms driven by a single motor and, more particularly, to hermetic compressor assemblies having an improved drive shaft operably coupling the motor to the two compressor mechanisms.  
      Compressor assemblies having two compressor mechanisms operably coupled to a single motor by a drive shaft are known. In many such assemblies, the drive shaft includes two integral eccentric portions defined at one end of the shaft. These eccentric portions are often machined into, or integrally molded with, the shaft such that they are unitary with the shaft. The motor includes a rotating rotor which defines a central bore extending through the rotor along a rotational axis. The end of the drive shaft opposite the eccentric portions extends into the bore and is affixed to the rotor for rotation therewith. Each of the integral eccentric portions operably engages one of the two compressor mechanisms, thereby mounting both of the two compressor mechanisms at one end of the drive shaft and adjacent one end of the motor.  
      Still other dual mechanism compressor assemblies are known in which the unitary eccentric portions are defined at opposite ends of the drive shaft. In such assemblies, the two compressor mechanisms are operably mounted about the eccentric portions at opposite ends of the shaft and are thereby positioned adjacent opposite ends of the motor. Such an arrangement may be used to improve the balance of the compressor assembly, which may reduce the vibration and lower noise. However, oftentimes the eccentric portions define a larger cross-section than that of the drive shaft. These eccentric portions cannot fit through the bore of the rotor and, consequently, it is difficult to assemble such a compressor using a one-piece shaft. Instead, these compressor mechanisms require a two-piece drive shaft that is joined inside the rotor. The two-piece drive shaft design may be less rigid than the one-piece design, thereby causing the shaft to bend or deflect. Deflection of the shaft may cause the misalignment of the bearings, which ultimately may result in leaks and housing deformation.  
      Due to the problems associated with a drive shaft having unitary eccentric portions, a need remains for a hermetic compressor assembly having two compressor mechanisms operably engaged to opposite ends of a drive shaft without the use of eccentric portions unitarily defined in the drive shaft.  
     SUMMARY OF THE INVENTION  
      The present invention provides a compressor assembly that uses a shaft, which does not include unitarily defined eccentric portions at both ends and which extends through the motor to operably engage a compression mechanism at each end of the shaft on the opposite ends of the motor.  
      The compressor assembly comprises, in one form thereof, a motor including a stator and a rotor, and a drive shaft including an elongate central portion and first and second end portions located on opposite ends of the central portion. The drive shaft defines a rotational axis. First end portion, second end portion and central portions define respective first, second and third cross-sectional configurations oriented perpendicular to the rotational axis. Each of the first and second cross-sectional configurations has an outer perimeter disposed radially within the outer perimeter of the third cross-sectional configuration relative to the rotational axis. The drive shaft extends through the rotor with the central portion being rotationally secured to the rotor, the first end portion disposed proximate a first end of the motor and the second portion disposed proximate a second end of the motor. A first compressor mechanism is disposed proximate the first end of the motor and is operatively coupled to the first end portion of the drive shaft wherein the first end portion rotationally drives the first compressor mechanism. A second compressor mechanism is disposed proximate the second end of the motor and is operatively coupled to the second end portion of the drive shaft wherein the second end portion rotationally drives the second compressor mechanism.  
      In another form, the compressor assembly comprises a motor including a stator and a rotor, and a drive shaft comprising an elongate central portion and first and second end portions located on opposite ends of the central portion. The drive shaft defines a rotational axis. The first end portion, second end portion and central portion define first, second and third cross-sectional configurations, respectively, oriented perpendicular to the rotational axis. Each of the first and second cross-sectional configurations has an outer perimeter disposed radially within the outer perimeter of the third cross-sectional configuration relative to the rotational axis. The first and second end portions each define a substantially similar non-circular cross-sectional configuration. The first and second configurations are rotationally offset by 180 degrees relative to the rotational axis. The drive shaft extends through the rotor with the central portion being rotationally secured to the rotor, the first end portion disposed proximate a first end of the motor and the second end portion disposed proximate a second end of the motor. A first rotary compressor mechanism is disposed proximate the first end of the motor and operatively coupled to the first end portion of the drive shaft wherein the first end portion rotationally drives the first compressor mechanism. A second rotary compressor mechanism is disposed proximate the second end of the motor and is operatively coupled to the second end portion of the drive shaft wherein the second end portion rotationally drives the second compressor mechanism.  
      The present invention also provides a method of assembling a compressor assembly. The method, in one form thereof, includes providing a motor having a stator and a rotor, the rotor having an axially extending central bore, forming a drive shaft with an integral elongate member wherein the drive shaft includes an elongate central portion and first and second end portions located on opposite ends of the central portion, the drive shaft defining a rotational axis, the first end portion defining a first cross-sectional configuration oriented perpendicular to the rotational axis, the second end portion defining a second cross-sectional configuration oriented perpendicular to the rotational axis and the central portion defining a third cross-sectional configuration oriented perpendicular to the rotational axis wherein each of the first and second cross-sectional configurations has an outer perimeter disposed radially within the outer perimeter of the third cross-sectional configuration relative to the rotational axis, securing the drive shaft to the rotor by thermally expanding the rotor, inserting one of the first and second end portions of the drive shaft through the central bore of the rotor wherein the first end portion of the drive shaft accessible from a first end of the rotor and the second end portion of the drive shaft is accessible from a second end of the rotor, and allowing the rotor to cool and rotationally secure the drive shaft in the central bore of the rotor in a shrink-fit engagement, operably coupling a first compressor mechanism to the first end portion of the drive shaft wherein the drive shaft rotationally drives the first compressor mechanism, and operably coupling a second compressor mechanism to the second end portion of the drive shaft wherein the drive shaft rotationally drives the second compressor mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:  
       FIG. 1  is a sectional view of a dual mechanism hermetic compressor assembly according to the present invention;  
       FIG. 2  is a top sectional view of the compressor assembly of  FIG. 1  taken along lines  2 - 2 ;  
       FIG. 3  is an inner end perspective view of the crankcase/shaft assembly of the compressor assembly of  FIG. 1 ;  
       FIG. 4  is an outside end view of the compressor mechanism of the compressor assembly of  FIG. 1 ;  
       FIG. 5  is a perspective view of the shaft roller assembly of the compressor assembly of  FIG. 1 ;  
       FIG. 6  is a perspective view of the inner roller of the compressor assembly of  FIG. 1 ;  
       FIG. 7  is a perspective view of the shaft of the compressor assembly of  FIG. 1 ;.  
       FIG. 8  is a perspective view of a shaft according to another embodiment of the present invention;  
       FIG. 9  is a perspective view of a shaft/eccentric/piston assembly according to the embodiment of  FIG. 8 ; and  
       FIG. 10  is a sectional view of compressor assembly with the assembly in  FIG. 9 . 
    
    
      Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplification set out herein illustrates embodiments of the invention, in several forms, the embodiments disclosed below are not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise forms disclosed.  
     DESCRIPTION OF THE PRESENT INVENTION  
      Referring first to  FIG. 1 , compressor assembly  10  generally includes first compressor mechanism  14 , second compressor mechanism  16  and motor assembly  18 , all of which are disposed within interior volume  13  of housing  12 . Housing  12  includes first and second end members  12   a ,  12   b  and cylindrical main member  12   c . Housing members  12   a ,  12   b ,  12   c  are hermetically sealed to one another to define interior volume  13 .  
      Still referring to  FIG. 1 , motor assembly  18  defines first end  26  and opposite second end  28  and includes rotor  20 , stator  22  and stator windings  24 . Motor assembly  18  is connected to a power source (not shown) which drives the rotation of rotor  20  about rotational axis A-A. Elongate drive shaft  30  extends through motor assembly  18  and operably connects first and second compressor mechanisms  14 ,  16  to motor assembly  18 . Drive shaft  30  extends through a central bore in rotor  20  along rotational axis A-A and is rotatably secured to rotor  20  for rotation therewith about axis A-A. Shaft  30  may be secured to rotor  20  using conventional shrink-fit methods. One such method includes thermally expanding rotor  20 , inserting shaft  30  through the central bore of thermally expanded rotor  20 , and allowing rotor  20  to cool and, thus, shrink around shaft  30  to secure shaft  30  within rotor  20 .  
      As illustrated in  FIG. 1 , drive shaft  30  is integrally formed as a single unit and defines first end portion  32 , elongate central portion  34  and second end portion  36 . First and second end portions  32 ,  36  of shaft  30  protrude from respective first and second ends  26 ,  28  of motor assembly  18  and operably engage first and second compressor mechanisms  14 ,  16 , respectively, thereby positioning first and second compressor mechanisms  14 ,  16  proximate opposite ends of motor assembly  18 . The positioning of first and second compressor mechanisms  14 ,  16  proximate opposite ends of motor assembly  18  provides improved balance in comparison to an assembly wherein one or more compressors are positioned proximate a single end of the motor. This improved balance may result in lower vibration and, ultimately, lower noise. The configuration of first and second end portions  34 ,  36  and their engagement with first and second compressor mechanisms  14 ,  16  is described in further detail below.  
      Turning to  FIGS. 1 and 2 , first and second compressor mechanisms  14 ,  16  are identical rotary-type mechanisms and each generally includes crankcase  38 , annular cylinder block  40 , top member  42 , and roller assembly  43 . Cylinder block  40  is mounted between crankcase  38  and top member  42 . Top member  42 , cylinder block  40  and crankcase  38  are secured to one another by fasteners (not shown) which extend through fastener-receiving holes  42   a ,  40   a ,  38   a  of top member  42 , cylinder block  40 , and crankcase  38 , respectively. Cylinder block  40  defines an inside wall which cooperates with crankcase  38  and top member  42  to form compression chamber  52  in which a compressible fluid, such as a refrigerant, may be compressed.  
      As shown in  FIGS. 1 and 2 , roller assembly  43  is disposed within compression chamber  52  and includes eccentric inner roller  44  and main roller  48  rotatably mounted about eccentric inner roller  44 . Inner roller  44  is operably coupled to drive shaft  30 , the rotation of which causes roller assembly  43  to orbit within compression chamber  52 . The engagement between drive shaft  30  and inner roller  44  is described in further detail below. Needle roller bearings (not shown) may be mounted between inner roller  44  and main roller  48  to facilitate the rotation of main roller  48  about inner roller  44 . Main roller  48  defines a cylindrical outer surface which travels along and sealingly engages the inside wall of cylinder block  40  to give compression chamber  52  an evolving crescent shape. Sliding vane  50  reciprocates within slot  51  defined in cylinder block  40  and engages main roller  48 .  
      Referring to  FIG. 1 , crankcase  38  of each of first and second mechanisms  14 ,  16  is mounted on respective first and second ends  26 ,  28  of motor assembly  18 , thereby securing first and second compressor mechanisms  14 ,  16  to opposite ends of motor assembly  18 . Crankcase  38  may be mounted to motor assembly  18  in any conventional manner. One such manner involves inserting bolts (not shown) through holes  39  ( FIGS. 2-4 ), which extend through legs  41  of crankcase  38 , and engaging the bolts to threaded holes (not shown) in stator  22 .  
      As illustrated in  FIGS. 1 and 3 - 4 , crankcase  38  defines a substantially cylindrical perimetrical sidewall  45  that firmly and sealingly bears against main housing member  12   c . The firm engagement between the sidewall of crankcase  38  and main housing member may be achieved by conventional shrink-fit methods. As a result of the sealed engagement between crankcase  38  and housing  12 , the crankcases  38  of first and second compression mechanisms  14 ,  16  cooperate with one another to sealingly divide interior plenum  13  into first discharge plenum  66 , second discharge plenum  68  and suction plenum  69 . First discharge plenum  66  includes that portion of interior plenum  13  located between crankcase  38  of first compression mechanism  14  and first end member  12   a  of housing  12 . Second discharge plenum  68  includes the portion of interior plenum  13  located between crankcase  38  of second compression mechanism  16  and second end member  12   b  of housing  12 . Suction plenum  69  comprises the portion of interior plenum  13  located between the crankcases of first and second compression mechanisms  14 ,  16 . Suction inlet  15  extends through main housing member  12   c  and communicates with suction plenum  69 . First and second discharge tubes  70 ,  72  extend through first and second end housing members  12   a ,  12   c , respectively, and communicate with respective discharge plenums  66 ,  68 .  
      Referring now to  FIGS. 1 and 4 , top member  42  of each of first and second compression mechanisms  14 ,  16  includes discharge port  56 , which provides fluid communication between compression chambers  52  of first and second compression mechanisms  14 ,  16  and respective discharge plenums  66 ,  68 . As illustrated in  FIG. 4 , the outer surface of top member  42  defines recess  58  which surrounds and extends from discharge port  56 . Discharge valve assembly  60  fits within recess  58  and includes flexible discharge valve member  62 , rigid valve retainer  64 , and valve fastener  65 . Valve assembly  60  is mounted within recess  58  by valve fastener  65 , which engages valve fastener opening  67 .  
      Referring to  FIGS. 1 and 3 , crankcase  38  of each of first and second compression mechanisms  14 ,  16  defines inlet opening  74  by which the refrigerant flows into compression chamber  52 . Compressor assembly  10  can be configured as either a single-stage compressor, in which the refrigerant enters both first and second compressor mechanisms  14 ,  16  at suction pressure and is compressed therein and discharged at a final pressure, or a two-stage compressor, in which the refrigerant enters first compressor mechanism  14  at suction pressure, is compressed to an intermediate pressure, and is discharged to second compressor mechanism  16  wherein the refrigerant is further compressed to and discharged at a final pressure. In first compressor mechanism  14 , inlet opening  74  communicates the refrigerant from suction plenum  69  to compression chamber  52 . In second compressor mechanism  16 , inlet opening  74  is in fluid communication with compression chamber  52  and either suction plenum  69 , if compressor assembly  10  is a single-stage compressor, or first discharge tube  70 , if compressor assembly is a two-stage compressor. If compressor assembly is a two-stage compressor, first discharge tube  70  may extend from first end housing member  12   a , through main housing member  12   c , and join inlet opening  74  of second compressor mechanism  16 .  
      Referring now to  FIGS. 5-7 , the configuration of drive shaft  30  and its engagement with first and second compressor mechanisms  14 ,  16  will now be described. As noted above, drive shaft  30  is a unitary elongate member including elongate central portion  34  and first and second end portions  32 ,  36  located on opposite ends of central portion  34 . Drive shaft  30  may be made of steel or any other rigid material sufficient to withstand the pressures and forces generated during operation without deformation or deflection. Drive shaft  30  extends along and rotates about rotational axis A-A. Each of first end portion  32 , central portion  34  and second end portion  36  defines a cross-sectional configuration oriented perpendicular to rotational axis A-A. As shown in  FIGS. 5 and 7 , the cross-sectional configuration of central portion  34  is substantially circular, while the cross-sectional configurations of first and second end portions  32 ,  36  are substantially non-circular. The cross-sectional configurations of first and second end portions  32 ,  36  define a pair of opposing planar flats  33  which give the cross-sectional configurations of first and second end portions  32 ,  36  an outer perimeter that is disposed radially within the outer perimeter of the cross-sectional configuration of central portion  34  relative to the rotational axis A-A. The cross-sectional configuration of first and second end portions  32 ,  36  may be machined into shaft  30  or, alternatively, shaft  30  may be molded to form by any conventional method, such as by investment casting.  
      Turning to  FIG. 6 , inner roller  44  of each of the roller assemblies  43  of the first and second compressor mechanisms  14 ,  16  includes an outer cylindrical surface which defines roller axis A 1 -A 1 . A shaft mounting opening  46  extends through inner roller  44  along a line parallel to but spaced apart from the corresponding roller axis. Opening  46  has a substantially non-circular configuration, which includes a pair of opposing flats  47 . The overall configuration of opening  46  is complementary to the cross-sectional configurations of first and second end portions  32 ,  36  of shaft  30 , such that first and second end portions  32 ,  36  of shaft  30  may be slip-fit into opening  46  of roller  44  of first and second compressor mechanisms  14 ,  16 , respectively. This slip-fit engagement prevents relative rotation of shaft  30  with respect to inner roller  44 . Because opening  46  is offset from the corresponding roller axis, the rotation of shaft  30  imparts an orbiting motion to inner roller  44 .  
      As shown in  FIG. 1 , first and second end portions  32 ,  36  of drive shaft  30  extend through and are journaled in crankcase  38  of first and second compression mechanisms  14 ,  16 , respectively. Roller  44  of first and second compressor mechanisms  14 ,  16  is mounted, as described above, on first and second end portions  32 ,  36  of shaft  30 . As shown in  FIG. 5 , roller  44  of first and second compressor mechanisms  14 ,  16  may be oriented on shaft  30  such that roller axis A 1 -A 1  of each of first and second compressor mechanisms  14 ,  16  are positioned diametrically opposite one another relative to rotational axis A-A. Such an orientation may aid in rotationally balancing shaft  30 . In addition or in the alternative, the cross-sectional configurations of first and second end portions  32 ,  36  may be oriented so as to be rotationally offset from one another relative to rotational axis A-A. More specifically, the cross-sectional configurations of each of first and second end portions  32 ,  36  defines a line of symmetry which divides the cross-sectional configuration into two symmetrical halves. As shown in  FIG. 7 , the cross-sectional configurations of first and second end portions  32 ,  36  may be oriented such that the line of symmetry of first end portion  32  is rotationally offset from the line of symmetry of second end portion  36  by 180° relative to rotational axis A-A.  
      In alternative embodiments, the cross-sectional configurations of first and second end portions and their corresponding shaft receiving openings may take different shapes. For instance, first and second end portions and their corresponding shaft receiving openings may be square, semi-circular, or pentagonal in cross-section.  
      As illustrated in  FIGS. 1 and 2  and described above, both first and second compressor mechanisms  14 ,  16  may be rotary-type compression mechanisms. Alternatively, first and second compressor mechanisms may be any type of compression mechanism, including reciprocating-piston mechanisms, orbiting-scroll mechanisms, and rotary-screw mechanisms. For instance, first and/or second compressor mechanisms could be an orbiting-scroll mechanism such as that disclosed in U.S. Pat. No. 5,013,225 to Richardson, Jr. which is assigned to Tecumseh Products Company, the assignee of the present invention and which is hereby incorporated by reference. In this case, the shaft receiving opening may be defined in the hub of the orbiting plate and the shaft may be slip-fit into the opening. It should also be understood that first and second compressor mechanisms need not necessarily be identical to one another. In other words, first compressor mechanism may be of a different type than that of second compressor mechanism.  
      In operation, rotor  20  rotates about rotational axis A-A which in turn causes the rotation of shaft  30  about axis A-A. The rotation of shaft  30  imparts a rotational force on roller  44  of both first and second compressor mechanisms  14 ,  16 . This rotational force is translated into an orbiting motion of rollers  44  simultaneously within chambers  52  of both first and second compressor mechanisms  14 ,  16 . As roller  44  orbits within chamber  52 , it engages sliding vane  50  and the inside wall of cylinder block  40  to cause the crescent-shaped chamber  52  to expand and contract in size and, thereby, draw in and compress the refrigerant within the chambers  52  of first and second compressor mechanisms  14 ,  16 . The refrigerant is drawn into suction plenum  69  at suction pressure via suction inlet  15 .  
      Assuming compressor assembly  10  is a two-stage compressor, the refrigerant flows from suction plenum  69  to compression chamber  52  of first compressor mechanism  15  via inlet opening  74 . The refrigerant is compressed within compression chamber  52  of first compressor mechanism  14 . When the pressure of the refrigerant within chamber  52  of first compressor mechanism  14  reaches a pressure sufficient to bias valve member  62  away from port  56 , the refrigerant is discharged through discharge port  56  into first discharge plenum  66 . From discharge plenum  66  the refrigerant enters discharge tube  70  and flows to second compressor mechanism  16  where it enters compression chamber  52  of second compressor mechanism  16  through inlet opening  74  of second compressor mechanism  16 . The refrigerant is then compressed to a higher pressure and is discharged through discharge port  56  of second compressor mechanism  16  when the pressure within compression chamber  52  of second compressor mechanism  16  is sufficient to bias valve member  62  away from port  56 . From second discharge plenum  68  the refrigerant enters second discharge tube  72  and exits compressor assembly  10 .  
      If compressor assembly  10  is configured as a single-stage compressor, the refrigerant flows from suction plenum  69  into the compression chambers  52  of both first and second compressor mechanisms  14 ,  16 . The refrigerant is then compressed within compression chambers  52  of first and second compressor mechanisms  14 ,  16  and is discharged through discharge ports  56  and into first and second discharge plenums  66  and  68 , respectively. From discharge plenums  66 ,  68  the refrigerant enters discharge tubes  70 ,  72 , respectively, and exits the compressor assembly  10 .  
      In an alternative embodiment shown in  FIGS. 8-10 , compressor  110  generally includes motor assembly,  18 , first and second compressor mechanisms  114 ,  116  and shaft  130 , which also does not include unitarily defined eccentric portions. As shown in  FIG. 8 , shaft  130  includes a one-piece elongate member defining first end portion  132  and opposite second end portion  136 . Shaft  130  extends through a central bore in rotor  20  of motor assembly  18  along rotational axis A-A and is rotatably secured to rotor  20  for rotation therewith. First and second end portions  132 ,  136  of shaft  130  are positioned adjacent opposite ends of motor assembly  18 . Each of first and second end portions  132 ,  136  define a central opening  138  extending axially into first and second end portions  132 ,  136  along rotational axis A-A. Groove  140  extends around the circumference of each of first and second end portions  132 ,  136  (not shown at end portion  132 ) and extends inward toward central opening  138 .  
      First and second compressor mechanisms  114 ,  116  each include eccentric member  144 . Eccentric member  144  of first and second compressor mechanisms  114 ,  116  each includes substantially cylindrical eccentric portion  144   a  which defines member axis A 1 -A 1 , and a linking rod  144   b  extending from eccentric portion  144   a  along a rod axis parallel to but spaced apart from member axis A 1 -A 1 . Linking rod  144   b  is sized and shaped to fit within central opening  138  and defines groove  146 , which extends around the circumference of linking rod  144   b . Grooves  140  and  146  cooperate to define a lubrication passage. Opening  162  is formed in groove  146  and acts as a lubrication passage for delivering lubricant to grooves  140  and  146 . Eccentric member defines a lubrication passage  160  extending through linking rod  144   b  and eccentric portion  144   a  along the rod axis.  
      An eccentric member  144  may be mounted to each of first and second end portions  132 ,  136  of shaft  130  by press fitting linking rod  144   b  into central opening  138 . Alternative means may be provided for securing rod  144   b  in central opening  138 . To achieve optimum balance eccentric members  144  may be oriented on shaft  130  such that member axis A 1 -A 1  of each of first and second compressor mechanisms  114 ,  116  are positioned diametrically opposite one another relative to rotational axis A-A.  
      As illustrated in  FIGS. 9-10 , first and second compressor mechanisms  114 ,  116  may be reciprocating piston-type compressor mechanisms. First and second compressor mechanisms  114 ,  116  each includes piston  149  which operably engages eccentric member  144  through linkage key  150 . Linkage key  150  includes a ring portion  150   a  which is rotatably mounted about cylindrical eccentric portion  144   a  of eccentric member  144 . Ring portion  150   a  includes a lubrication passage  164  for communicating lubrication fluid to the mating surfaces of ring portion  150   a  and eccentric portion  144   a . Linkage key also includes a linkage arm  150   b  which extends from linkage ring and engages piston  149  in a conventional manner. The rotation of shaft  130  about rotational axis A-A imparts a rotational force on eccentric member  144  causing eccentric member  144  to orbit about rotational axis A-A. The orbiting motion of eccentric member  144  imparts a reciprocating motion to piston  149  within cylindrical chamber  148  through linkage key  150 .  
      While  FIGS. 9-10  illustrate compressor mechanisms  114  and  116  as reciprocating piston-type mechanisms, it is contemplated that other compressor mechanisms may be used. For instance, member  144  could serve as the inner roller of a rotary-type compressor mechanism and, therefore, a rotary-type compressor mechanism could be mounted to the opposite ends of drive shaft  130 .  
      While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles.