Patent Publication Number: US-2005135943-A1

Title: Molded compressor base

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of U.S. Provisional Application No. 60/532,221, filed Dec. 23, 2003. 
    
    
     BACKGROUND OF THE INVENTION  
      The present invention relates generally to a mounting arrangement for a compressor. More specifically, the present invention relates to a molded base for mounting a compressor.  
      Compressors used in heating, ventilating, and air conditioning (HVAC) applications or refrigeration applications are usually mounted to a structure associated with the HVAC system or refrigeration system. For example, a compressor can be mounted to the housing or enclosure of an outdoor unit of an air conditioning system. Typically, a compressor is mounted to the corresponding structure, e.g., a base pan used with the housing or enclosure, through the use of a mounting foot, mounting brackets, mounting plate, or other similar mounting arrangement. These types of mounting arrangements require the compressor and its associated mounting hardware to be attached to the corresponding structure using mechanical means such as bolts, screws, etc. or by other means such as by welding or adhesives. One problem with this type of compressor mounting is that any vibrations or sound emitted from the compressor as a result of operation of the compressor is transmitted through the mounting arrangement to the corresponding structure. This situation can result in a system that is very noisy and can possibly damage other components of the system due to excessive vibrations. To address these vibration concerns, mounting arrangements for compressors have incorporated some vibration damping features or structures. For example, the use of rubber materials between the mounting arrangement and the corresponding mounting structure have been used to provide vibration damping. However, these additional vibration damping features or structures are still not effective in eliminating the transmission of vibrations from the compressor to the corresponding structure.  
      One example of this type of mounting arrangement for compressors can be found in U.S. Pat. No. 6,032,478, which is directed to the construction of the outdoor condensing section of an air conditioner. The structure for the mounting of the compressor is part of the lower wall of the lower part of the outdoor housing. The compressor has a triangular mounting plate attached thereto. The mounting plate has openings and elastomeric bushings at each of the three corners thereof to facilitate attachment to the lower wall through the mounting structure. Three substantially identical mounting structures are provided, one associated with each of the openings in the plate. The compressor is thus mounted through the mounting plate and elastomeric bushings to studs in a manner such that movement of the compressor in any direction can be absorbed by or reacted through the elastomeric bushings. As discussed above, this configuration still has the problem of transmission of sound and vibration from the compressor to the outdoor housing because not all of the vibrations can be removed or eliminated.  
      Another technique that has been utilized to limit the sound and vibration emanating from a compressor has been to enclose the compressor in a cover or enclosure. The cover typically includes sound damping materials that can absorb or limit some of the sound and vibration from the compressor. However, a problem with the covers is that the compressor is still mounted to the corresponding structure using the mounting hardware configurations discussed above. Thus, vibrations can still be transmitted from the compressor through the mounting arrangement to the corresponding structure.  
      One example of a cover for compressors can be found in U.S. Pat. No. 5,588,810, which is directed to a sound barrier cover for a compressor unit. The barrier or cover has a semi-rigid outer shell provided as two approximate halves or cover sections of strong material and a resilient sound absorbing cushion adhered to the inner surface of each half to provide the separate cover sections. One drawback of this technique of sound and vibration damping is that the sound and vibrations can still be transmitted to the structure through the mounting arrangement of the compressor.  
      Therefore, what is needed is a simple and economical mounting arrangement for a compressor that can assist in limiting the transmission of sound and vibrations from the compressor to the surrounding structure.  
     SUMMARY OF THE INVENTION  
      One embodiment of the present invention is directed to a mounting arrangement for a compressor. The mounting arrangement includes a base and a projection extending from the base. The projection has an outer surface and an inner surface disposed opposite the outer surface. The inner surface is configured to provide a cavity in the projection to receive and hold a compressor in a predetermined position for mounting of a compressor.  
      Another embodiment of the present invention is directed to a mounting arrangement for a compressor. The mounting arrangement includes a base having a substantially planar surface and a projection extending from the substantially planar surface of the base. The projection has an outer surface and an inner surface disposed opposite the outer surface. The inner surface is configured to provide a cavity in the projection to receive and hold a compressor in a predetermined position for mounting of a compressor.  
      One advantage of the present invention is that the process of mounting of the compressor is greatly simplified.  
      Another advantage of the present invention is that sound and vibration from the compressor can be damped to limit or prevent transmission of the sound and vibration to the structure.  
      Still another advantage of the present invention is that the cost for mounting the compressor is reduced.  
      Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  illustrates one embodiment of a molded compressor base of the present invention.  
       FIG. 2  illustrates an alternate embodiment of the molded compressor base of the present invention.  
       FIG. 3  illustrates still another alternate embodiment of the molded compressor base of the present invention.  
       FIG. 4  illustrates a cover to be used with the molded compressor base of  FIG. 1 .  
       FIG. 5  is an exploded view of a mounting arrangement for a compressor using the molded compressor base of  FIG. 1  and the cover of  FIG. 4 .  
       FIG. 6  is a view of an assembled mounting arrangement of  FIG. 5 .  
       FIG. 7  illustrates an alternate embodiment of the molded compressor base of  FIG. 1 . 
    
    
      Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  shows one embodiment of the molded compressor base of the present invention. A molded compressor base or mounting  100  preferably has a base with a substantially planar base surface  102 . The base surface  102  of the molded compressor base  100  is preferably sized to provide adequate mounting and support for a compressor (not shown) residing in the molded compressor base  100 . In addition, the base surface  102  is preferably sized for placement or mounting of the molded compressor base  100  in a corresponding structure or enclosure requiring the compressor. For example, the base surface  102  can be sized for placement of the molded compressor base  100  in the outdoor unit of a HVAC system, in the outdoor section of a window air conditioning unit or in a refrigerating unit or refrigerator. The base surface  102  can have any shape including geometric shapes, e.g., square, rectangular, circular, oval, elliptical, and triangular, and suitable non-geometric shapes, that can provide mounting and support for a compressor while still permitting placement of the molded compressor base  100  in the corresponding structure.  
      The base surface  102  may include one or more means, structures or areas for connecting the molded compressor base  100  to the corresponding structure or enclosure in or on which the molded compressor base  100  is to be placed. For example, the base surface  102  may include one or more apertures or holes  124  (see  FIG. 7 ) for receiving a bolt or screw or other type of fastener to connect the molded compressor base  100  to a base pan used in the corresponding structure or enclosure, or, alternatively, the molded compressor base  100  may include one or more extensions  126  (see  FIG. 7 ) from the base surface  104  that mate with apertures or recesses in a base pan used in the corresponding structure or enclosure for an interference or frictional connection. The extensions may be integrally formed from the same material as the base, but can also be formed from an elastomeric or other material capable of damping vibration that is inserted into the base to damp vibration between the base and the corresponding structure. Furthermore, it is to be understood that the base surface  102  does not have to include any means, structures or areas for connecting the molded compressor base  100  to the corresponding structure or enclosure and may reside in the corresponding structure or enclosure without being connected to the structure.  
      In another embodiment of the present invention, the base surface  102  of the molded compressor base  100  can be part of the corresponding structure or enclosure into which the molded compressor base  100  is to be placed. For example, the base surface  102  of the molded compressor base  100  can be used as a base pan in an outdoor unit. In this embodiment, the molded compressor base  100  does not have to be connected to any other structure for the mounting of the compressor, but may be connected to additional components of the corresponding structure or enclosure of which the molded compressor base  100  is a part. When the molded compressor base  100  is part of the corresponding structure or enclosure, the base surface  102  is sized and shaped to correspond to and interact with the remaining components of the corresponding structure or enclosure.  
      Furthermore, in this embodiment of the present invention, the molded compressor base  100  can include additional mounting structures or arrangements for mounting additional components of the corresponding structure or enclosure. For example, the molded compressor base  100  can include appropriate mounting structures for the mounting of a fan motor used in the corresponding structure or enclosure. Similarly, the molded compressor base  100  could include other corresponding mounting structures for other components, e.g., an accumulator, a muffler, or other similar device that is operationally associated with the compressor or the HVAC or refrigeration system. The additional mounting structures for other components can be integrally formed in the molded compressor base  100  or alternatively, the additional mounting structures can be connected to the molded compressor base  100 .  
      Referring back to  FIG. 1 , extending from the base surface  102  is a substantially upright projection  104 . The upright projection or cradle  104  has an outer surface  106  and an inner surface  108 . The outer surface  106  can have any suitable geometric or non-geometric shape, but is preferably shaped similar to the shape of the compressor positioned inside the upright projection  104 . The inner surface or mounting area  108  of the upright projection  104  provides a cavity or opening in the upright projection  104  to receive and hold a compressor placed or positioned inside the upright projection  104 . The inner surface  108  of the upright projection  104  can hold any type of compressor including a reciprocating compressor, a scroll compressor, or a rotary compressor. The inner surface  108  is generally contoured to correspond to the housing of the compressor positioned in the upright projection  104 . In one embodiment of the present invention, the inner surface  108  may have one or more apertures or holes to permit the drainage of liquids accumulating in the inner surface  108  of the upright projection  104 .  
      In addition, the upright projection  104  extends to a top surface  110 , which connects, bridges or spans the outer surface  106  and the inner surface  108 . The top surface  110  can preferably be a curved surface to permit easy insertion and positioning of the compressor in the upright projection  104 . However, the top surface  110  can also be a flat or squared surface or an angled or pointed surface. The outer surface  106  is preferably substantially perpendicular to the base surface  102 . However, the outer surface  106  does not have to be substantially perpendicular and may deviate from the perpendicular, possibly to simplify the manufacturing process.  
      The upright projection  104  and its inner surface  108  can receive and hold a compressor in position for the mounting of the compressor. The upright projection  104  and inner surface  108  can be configured to receive and hold a compressor oriented in a variety of different positions.  FIG. 1  illustrates one embodiment of the upright projection  104  for mounting a compressor in a substantially horizontal position.  FIG. 2  illustrates one embodiment of the upright projection  104  for mounting the compressor in a substantially vertical position.  FIG. 3  illustrates one embodiment of the upright projection  104  for mounting the compressor at a substantially forty-five degree angle position. In other embodiments of the present invention, the upright projection  104  can hold and mount the compressor at any angled position between a substantially horizontal position and a substantially vertical position depending on the requirements of the user of the molded compressor base  100 .  
      It is appreciated by those having ordinary skill in the art that the molded compressor base of the present invention requires minimal height, which likewise lowers the position, and therefore the center of gravity of the mounted compressor. Lowering the center of gravity of the mounted compressor improves its transportability, providing a more inherently stable installation.  
      In another embodiment of the present invention, the upright projection  104  and the inner surface  108  can be configured for multiple compressor mounting arrangements that can mount the compressor in a variety of different positions or orientations in the upright projection  104 . In still another embodiment of the present invention, the upright projection  104  and the inner surface  108  can be configured for mounting compressors having two or more different sizes in the upright projection  104  in either same position or orientation or in different positions and orientations.  
      In a preferred embodiment of the present invention, the upright projection  104  mounts a compressor in a horizontal or substantially horizontal position as shown in  FIG. 1 . In this embodiment, the upright projection  104  preferably mounts the compressor at an angle of between 2 degrees and 12 degrees. More preferably, the compressor is mounted at an angle of 7 degrees. To obtain this angled mounting position for the compressor, the inner surface  108  of the upright projection  104  is angled at an end  114  to raise one end of the compressor when the compressor is positioned in the upright projection  104 . Similarly, as shown in  FIG. 1 , the outer surface  106  of the upright projection  104  has an end  116  corresponding to the raised or angled end  114  of the inner surface  108 , projecting higher or further away from the base surface  102  than the other portions of the outer surface  106 . In the embodiment shown in  FIG. 1 , the top surface  110  is not substantially parallel with the base surface  102  because of the disproportionate heights of the outer surface  106 . However, in another embodiment of the present invention, the top surface  110  can be substantially parallel to the base surface  102  because the outer surface  106  can have a substantially uniform height without a raised end  116 , while the inner surface  108  still has the raised end  114  to raise one end of the compressor. In a preferred embodiment of the present invention, the top of the compressor is preferably positioned at the raised end  114  of the inner surface  108  and the oil sump of the compressor is preferably positioned at the opposed non-angled end of the inner surface  108 .  
      In a preferred embodiment of the present invention, the upright projection  104  holds and supports a compressor having a substantially cylindrical shape with curved end caps at each end. To hold a compressor having a substantially cylindrical shape in the substantially horizontal position, the inner surface  108  of the upright projection  104  is preferably a seamless, continuous surface extending from the top surface  110  to the base surface  102  and is shaped as a curved or arced channel  118  with rounded or curved ends  120  as shown in  FIG. 1 . The curved channel  118  with rounded ends  120  of the inner surface  108  cradles and holds the compressor in position because the compressor conformably resides in the channel and is held in position by the walls and ends of the channel. Preferably, between about one-quarter and about three-quarters of the compressor housing can project or be disposed above the top surface  110  when the compressor is positioned in the inner surface  108  of the upright projection  104 .  
      In another embodiment of the present invention, the molded compressor base  100  may include one or more mounting structures  122  (see  FIG. 7 ) disposed on or in the inner surface  108  to further hold the compressor in position in the upright projection  104 . The mounting structures  122  are preferably made or formed from an elastomeric material, rubber material or other similar material that can frictionally hold a compressor in position that is placed on the mounting structures  122 , and that can provide some damping of any sound and/or vibration emitted by the compressor. The mounting structures  122  are preferably located on the curved ends  120  of the inner surface  108 , but can be located anywhere on the inner surface  108 .  
      The upright projection  104  can also include one or more supporting ribs  112  (see  FIG. 2 ) that are molded into the outer surface  106  of the upright projection  104 . The supporting ribs  112  are preferably used for providing additional strength, stiffness and stability to the upright projection  104  to aid in the retaining of the compressor in the upright projection  104 . The supporting ribs  112  are also used to prevent any folding or warping of the base surface  102 . The supporting ribs  112  are generally wedge shaped, however, the supporting ribs  112  could also be rectangular in shape. In addition, the angled surface of the supporting rib  112  could also have a slight curve.  
      The bottom of the molded compressor base  100  has a shape that directly corresponds to the surfaces and projections located on the top of the molded compressor base  100 . In other words, the material that is used for manufacturing the molded compressor base  100  preferably has a substantially uniform thickness over the entire surface of the molded compressor base  100 . The upright projections  104  when viewed from the bottom define indented regions or recesses that have substantially the same shape as the upright projections  104 . In a preferred embodiment of the present invention, the thickness of the material of the molded compressor base  100  is between about 0.05 and about 0.5 inches. More preferably, the thickness of the material of the molded compressor base  100  can be up to about 0.25 inches. The indented regions in the bottom of the molded compressor base  100  having a uniform thickness can permit several molded compressor bases  100  to be stacked or nested together in a manner that does not require a lot of space. In other words, the spacing between corresponding portions of stacked molded compressor bases  20  can approach zero, since the corresponding portions of the adjacent molded compressor bases  20  can be conformally fitted together.  
      In another embodiment, however, the molded compressor base  100  could have a flat bottom with any spaces between the surfaces and projections on the top of the molded compressor base  100  being filled with the same material as the molded compressor base  100 . In other embodiments, the bottom of the molded compressor base  100  could be filled with sound and/or vibration damping materials or other similar materials that would provide the molded compressor base  100  with greater sound and vibration damping capabilities.  
      The molded compressor base  100  is preferably formed from a plastic or composite material as a single or unitary, integral piece. Any suitable material, such as plastic or a composite material, can be used that is inert, and has adequate strength and durability to hold a compressor in position during extended operation of the compressor in any operating environment. In one embodiment of the present invention, the molded compressor base  100  is formed from a thermoplastic material.  
      In a preferred embodiment of the present invention, the plastic or composite material used to form the molded compressor base  100  can inherently have sound and/or vibration damping properties to damp sound and vibration from the compressor. The sound and/or vibration damping properties of the plastic or composite material can be obtained from the incorporation of the appropriate types and amounts of constituent materials to form the plastic or composite material of the molded compressor base  100 . These sound and/or vibration damping properties inherent in the plastic or composite material of the molded compressor base  100  can be used with other sound and/or vibration damping techniques.  
      In another embodiment of the present invention, the molded compressor base  100  can be at least partially coated with one or more coating materials that can provide sound and/or vibration damping for the compressor. The sound and/or vibration damping coating materials may be used in conjunction with a molded compressor base  100  made from a material, such as a plastic or composite material, inherently having sound and/or vibration damping properties. Alternatively, the sound and/or vibration damping coating materials may be used in conjunction with a molded compressor base  100  made from a plastic or composite material that does not inherently have sound and/or vibration damping properties. The sound and/or vibration damping coating materials can be applied to the entire molded compressor base  100  or to predetermined areas of the molded compressor base  100 . For example, the sound and/or vibration damping coating materials can be applied to the inner surface  108  or to preselected portions of the inner surface  108  to provide sound and/or vibration damping for the compressor. The sound and/or vibration damping material can include a fiberglass material or a foam material, including open-cell foam or closed-cell foam.  
      While the upright projection  104  and the inner surface  108  of the molded compressor base  100  can adequately hold the compressor in position, it may be desired to employ or use additional techniques and/or devices for further holding the compressor in the upright projection  104 . An example of a technique to further hold the compressor in position in the upright projection  104  involves the attaching of the compressor to the inner surface  108  of the upright projection with an adhesive. An example of a device for further holding a compressor in position can include a variety of mechanical attaching devices such as straps extending over the compressor to hold the compressor in position. The straps can extend across or span opposed sides of the upright projection  104  to hold the compressor in position. A further example involves the inner surface  108  having a frictional contact with the compressor sufficient to hold the compressor in position.  
      In a preferred embodiment of the present invention, the compressor is further held in the upright projection  104  by a cover extending over at least some, and preferably all, of the compressor and top surface  110  of the upright projection  104 .  FIG. 4  illustrates one embodiment of a cover  400  that can be used with the molded compressor base  100  and upright projection  104  of  FIG. 1 . The cover  400  preferably has a shape that is substantially similar to the shape of the compressor to be placed in the upright projection  104 . The cover  400  can be attached to any of the surfaces of the upright projection  104  by any suitable means, techniques or devices that can hold the compressor in position in the upright projection  104 , but the cover  400  can also extend over or cover the entire upright projection  104  and be attached to the base surface  102 . For example, the cover  400  can form an interference or frictional connection with the upright projection  104  to hold the compressor in place, such as mounting structure  122  as previously discussed which may be secured either to the upright projection  104  or the cover  400  or both. In another example, the cover  400  and upright projection  104  can have mating components that connect the cover  400  to the upright projection  104  to hold the compressor in position. In still another example, the cover  400  can be connected to the upright projection  104  using mechanical fasteners such as snaps or clasps.  
      The cover  400  is preferably formed from a material, such as a plastic or composite material, as a single or unitary, integral piece, which plastic or composite material may or may not be the same as the plastic or composite material used for the molded compressor base  100 . Any suitable plastic or composite material can be used that is inert, and has adequate strength and durability to hold a compressor in position during extended operation of the compressor in any operating environment. In one embodiment of the present invention, the cover  400  is formed from a thermoplastic material.  
      In a preferred embodiment of the present invention, the plastic or composite material used to form the cover  400  can inherently have sound and/or vibration damping properties to damp sound and vibration from the compressor. The sound and/or vibration damping properties of the plastic or composite material can be obtained from the incorporation of the appropriate types and amounts of constituent materials in forming the plastic or composite material of the cover  400 . These sound and/or vibration damping properties inherent in the plastic or composite material of the cover  400  can be used with other sound and/or vibration damping capabilities.  
      In another embodiment of the present invention, the cover  400  can be coated with one or more coating materials that can provide sound and/or vibration damping for the compressor. The sound and/or vibration damping coating materials may be used in conjunction with a cover  400  made from a plastic or composite material inherently having sound and/or vibration damping properties. Alternatively, the sound and/or vibration damping coating materials may be used in conjunction with a cover  400  made from a plastic or composite material that does not inherently have sound and/or vibration damping properties. The sound and/or vibration damping coating materials can be applied to the entire cover  400  or to predetermined areas of the cover  400 . The sound and/or vibration damping material can include a fiberglass material or a foam material, including open-cell foam or closed-cell foam.  
      In still another embodiment of the present invention, the cover  400  can be sized and shaped to permit sound and/or vibration damping materials to be inserted or placed between the compressor and the cover  400 . The sound and/or vibration damping materials placed between the compressor and the cover  400  can be used in conjunction with or independent of other sound and/or vibration damping techniques. One example of a sound and/or vibration damping material that can be used is a sound damping foam material. In addition, the sound and/or vibration damping material can be used to further secure or hold the compressor in the upright projection  104  once the cover  400  is fastened to the upright projection  104 .  
      In a preferred embodiment of the present invention, the cover  400  holds a compressor having a substantially cylindrical shape with curved end caps at each end in the corresponding upright projection  104  of the molded compressor base  100 . To hold a compressor having a substantially cylindrical shape in the substantially horizontal position, the cover  400  preferably has a corresponding semi-cylindrical shape with rounded or curved ends as shown in  FIG. 4 . The cover  400  preferably has a shape and height that can cover the portions of the compressor that are not covered or held by the upright projection  104 , while still retaining or holding the compressor in place in the upright projection  104  with substantially no movement of the compressor in the upright projection  104 .  
      The cover  400  preferably permits the passage of suction and discharge pipes that connect to the compressor. The passage of the pipes can be between the top surface  110  of the upright projection and the cover  400  through cutouts or slots formed in the cover  400  at the corresponding location of the pipes. The suction and discharge pipes can be brazed to corresponding connections on the compressor and then the cover  400  can be put into position over the compressor by aligning the slots in the cover  400  with the corresponding pipes. Alternatively, the pipes can pass through apertures formed in the cover  400 . In still another alternative, the passage of the pipes can again be between the top surface  110  and the cover  400 , but pass through cutouts or slots formed in the upright projection  104  at the corresponding location of the pipes.  
      In a preferred embodiment of the present invention, the cover  400  has at least one protruding portion  402  extending from the basic semi-cylindrical shape of the cover  400 . The protruding portion  402  extends over and beyond the top surface  110  of the upright projection  104 . The extension of the protruding portion  402  over the upright projection permits electrical connections to be routed between the protruding portion  402  and the upright projection  104  for subsequent connection to corresponding terminals on the compressor. The protruding portion  402  can be used as a substitute to the mounting of a terminal box on the compressor because the protruding portion  402  and cover  400  provide adequate protection of the electrical connections to the compressor. The protruding portion  402  preferably has a curved or arced shape and is sized to permit passage of the electrical connections between the upright projection  104  and the protruding portion  402  for connection to the terminals on the compressor located substantially adjacent to the protruding portion. While the protruding portion  402  preferably has a curved shape, it is to be understood that the protruding portion can have any suitable size or shape. In another embodiment of the present invention, the cover  400  can have a second, or further multiple, protruding portions for the piping connections to the compressor.  
      In yet another embodiment of the present invention, indicia can be molded into the cover  400 , such as the name of the manufacturer. Additionally, indicia relating to safety or other operational warnings can also be molded into the cover  400 , instead of warning tags or signs applied by adhesive. Therefore, the indicia is more prominent, and less likely to be lost, since the cover  400  is preferably of unitary construction.  
       FIG. 5  illustrates the assembly process of the molded compressor base  100  and the cover  400  for a compressor in one embodiment of the present invention. The compressor is positioned in the molded compressor base  100  and then the cover  400  is placed over the compressor in the molded compressor base  100  to secure the compressor in the molded compressor base  100 . If the compressor is to be finally installed in the molded compressor base  100 , the electrical and piping connections to the compressor have to preferably be completed before the cover  400  is placed over the compressor, otherwise, the cover  400  has to be removed to complete the electrical and piping connections to the compressor. In another embodiment, the cover  400  and/or the compressor can be designed to permit electrical and piping connections to be completed after the cover  400  has been placed over the compressor in the molded compressor base  100 .  
       FIG. 6  illustrates the molded compressor base  100  and the cover  400  of  FIG. 5  in the assembled position. As can be seen in  FIG. 6 , the use of the cover  400  and the molded compressor can provide substantial environmental protection to a compressor positioned between the cover  400  and molded compressor base  100 . In addition, the cover  400  and molded compressor base  100  can operate to provide substantial sound and/or vibration damping of sound and vibrations from the compressor.  
      While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.