Abstract:
A rotary compressor comprising a rotor having a plurality of permanent magnets mounted thereon and a stator, where the rotor is aligned with respect to the stator via a magnetic attraction between the permanent magnets and the stator. The compressor includes a housing and is configured such that the rotor does not entirely bear against a top or bottom portion of the compressor housing. The permanent magnets of the rotor are sized and configured such that the magnetic attraction between the magnets and the stator, regardless of whether the stator is energized, positions, or suspends, the rotor substantially intermediate the top and bottom portions of the housing. As a result, less or, possibly, even no friction is experienced between the rotor and the compressor housing which reduces the potential for the rotor to seize or stall and allows the compressor to be operated with little or no oil.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 60/675,623, entitled ROTARY COMPRESSOR WITH PERMANENT MAGNET MOTOR, filed on Apr. 28, 2005, the entire disclosure of which is hereby expressly incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to rotary compressors. More specifically, the present invention relates to rotary compressors including a rotor and a stator where the rotor includes permanent magnets which align the rotor with respect to the stator.  
         [0004]     2. Description of the Related Art  
         [0005]     Electronic components, such as microprocessors and other integrated circuits, for example, typically generate a lot of heat during operation. Dissipating this heat has become increasingly important to improve the working life and efficiency of these components. In the past, air based cooling systems were typically used to dissipate the heat produced by electronic components. However, with advancements in electronic component technology, an improved cooling system was needed. In response to this need, refrigerant based cooling systems were developed.  
         [0006]     Previous refrigerant-based cooling systems were typically very large and heavy and often required more power to operate than the entire electronic system that they were cooling. Owing to their size, the major components of the cooling system were typically located remote from the electronic devices to be cooled. As a result, a complex system of tubing or plumbing was necessary to bring the cooling refrigerant into thermal exchange with the electronic components. Consequently, these refrigerant-based cooling systems were not modular and self-contained and often required special expertise and tools for their operation and maintenance.  
         [0007]     In addition, previous refrigerant-based cooling systems were not directly attached to the components that needed to be cooled and a dedicated cooling unit was typically not provided for each heat source. Further, previous refrigerant-based cooling systems typically employed compressors that were orientation dependent and could not be operated when positioned at angles of more than 30 or 40 degrees with respect to the horizon, for example. As a result, these previous refrigerant-based cooling systems were particularly unsuited for the electronics industry that often required orientation-independent operation.  
         [0008]     Moreover, previous refrigerant-based cooling systems used large amounts of oil to lubricate the moving components of the system. However, the oil added weight to the refrigeration system and it sometimes leaked therefrom. Lubrication of all of the moving components of the system typically required multiple oil sumps, pumps and complex lubricant inventory control systems for priming the compressor at startup, for example. However, most compressors, especially miniature compressors for cooling electronic equipment, for example, did not have room for these oil circulation systems. What is need is an improvement over the forgoing.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention includes a rotary compressor comprising a rotor having permanent magnets and a stator where the rotor is aligned with respect to the stator via a magnetic attraction between the permanent magnets and the stator. In one embodiment, the compressor includes a housing which is configured such that the rotor does not entirely bear against a top or bottom portion of the compressor housing. In this embodiment, the permanent magnets of the rotor are sized and configured such that the magnetic attraction between the rotor magnets and the stator, regardless of whether the stator is energized, positions, or suspends, the rotor substantially intermediate the top and bottom portions of the housing. As a result, less or, possibly, even no friction is experienced between the rotor and the compressor housing thereby reducing the potential for the rotor to seize or stall, especially during the start-up of the compressor. Aligning the rotor in this way, in one embodiment, allows the compressor to be operated with little or no oil in the compressor housing. Also, in one embodiment, the interaction of the permanent magnets and the stator can align the axis of the rotor with the axis of the stator such that the rotor rotates substantially concentrically within the stator. In a further embodiment, the compressor is configured such that the compression chamber of the compressor is located in the interior of the rotor and the permanent magnets are secured within recesses located around the outside perimeter of the rotor.  
         [0010]     In one form of the invention, a rotary compressor comprises a housing having a top plate and a bottom plate, a stator, a rotor having a plurality of permanent magnets positioned around an outer periphery of the rotor, the rotor including a central cavity, a post having an outer perimeter, the post being positioned within the central cavity and intermediate the top plate and the bottom plate, the post further including a vane slot, a vane slidably disposed within the vane slot, a roller having an inner perimeter, the roller positioned within the central cavity of the rotor such that the inner perimeter of the roller is eccentric with respect to the outer perimeter of the post, a spring positioned within the vane slot and compressed between the vane and the post, the spring biasing the vane against the roller, and a compression chamber defined between the vane, the roller and the post, wherein the rotor is aligned with the stator by a magnetic attraction between the stator and the permanent magnets. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The above-mentioned and other features and objects of this invention 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:  
         [0012]      FIG. 1  is a perspective cross-sectional view of a rotary compressor in accordance with an embodiment of the present invention;  
         [0013]      FIG. 2  is a perspective view of the post, vane and roller arrangement of the compressor of  FIG. 1  with components of the compressor removed;  
         [0014]      FIG. 3  is a schematic of the stator, roller and rotor of the compressor of  FIG. 1  illustrating the relative relationship of these components; and  
         [0015]      FIG. 4  is a schematic of the rotor and stator of the compressor of  FIG. 1  illustrating the relative relationship thereof. 
     
    
       [0016]     Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplifications set out herein illustrate an embodiment of the invention, the embodiment disclosed below is not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise form disclosed.  
       DETAILED DESCRIPTION  
       [0017]     Refrigeration circuits typically comprise, in serial order, a compressor, a condenser, a throttling valve, and an evaporator. Referring to the exemplary rotary compressor illustrated in  FIG. 1 , refrigerant, such as R245fa, for example, enters the rotary compressor through suction inlet  17 . The refrigerant then flows through distributor  16 , and passage  14  in top plate  11  where it is drawn into a chamber defined between post  4 , vane  5  and roller  6  of a compression, or pump, mechanism. As described in further detail below, roller  6  is positioned eccentric with respect to post  4  such that, when roller  6  is orbited with respect to post  4  by rotor  7 , the refrigerant in the chamber is compressed to a discharge pressure. The refrigerant is then discharged from the pump mechanism through a discharge valve (not illustrated) into passage  2  in bottom plate  3  and exits the compressor through manifold  12  and outlet  1 . In some embodiments, either the low pressure flow passage  14  or the high pressure flow passage  2  can be in fluid communication with the internal volume region of the compressor defined between top plate  11  and bottom plate  3 .  
         [0018]     In the present embodiment, rotor  7  of the pump mechanism includes a substantially circular outer perimeter and a substantially circular interior cavity where the interior cavity of rotor  7  is offset, or eccentric, with respect to the outer perimeter of rotor  7 . The interior cavity of rotor  7  is sized and configured to closely receive roller  6 . Roller  6  includes a substantially circular interior cavity which envelops post  4 . As a result of the interior cavity of rotor  7  being eccentric with respect to the outside perimeter of rotor  7 , the center of roller  6  is also eccentric with respect to the outer perimeter of rotor  7 . When positioned over post  4 , the circular outside perimeter of rotor  7  is substantially concentric with the center of post  4  while the center of roller  6  is eccentric with the center of post  4 . Owing to the eccentric alignment of post  4  and roller  6 , two crescent shaped pockets are defined between post  4 , roller  6  and vane  5  which comprise suction and compression pockets during the operation of the compressor. As illustrated in  FIG. 1 , bottom plate  3  and top plate  11  also define the boundaries of the suction and compression pockets. Post  4 , referring to  FIG. 1 , can be captured by, squeezed between, or fastened to top plate  11  and bottom plate  3 . As a result, in the present embodiment, the height of the post  4  determines the distance between top plate  11  and bottom plate  3 .  
         [0019]     Referring to  FIG. 2 , vane  5  is positioned within vane slot  15  of post  4  and is biased against roller  6  by a spring (not illustrated). In an alternative embodiment, vane  5  is biased against roller  6  by refrigerant within vane slot  15  at the discharge pressure, for example. When rotor  7  is rotated about post  4 , as described in further detail below, rotor  7  drives roller  6  such that it orbits with respect to post  4 . As roller  6  orbits, the surface of the interior cavity of roller  6  contacts vane  5  to force vane  5  to reciprocate within vane slot  15 . As roller  6  is orbited, vane  5  separates the expanding and contracting suction and compression chambers. Compression of refrigerant within the contracting compression chamber forces the discharge valve in bottom plate  3  to open so that the refrigerant may escape form the compression chamber.  
         [0020]     As discussed above, roller  6  is closely received within the interior cavity of rotor  7 . Roller  6  includes small chamfers around its upper and lower surfaces which may facilitate the insertion of roller  6  into the interior cavity of rotor  7 , for example. During operation, in the present embodiment, roller  6  can rotate within the interior cavity of rotor  7 . In this embodiment, the rotational speeds of roller  6  and rotor  7  can be substantially independent, i.e., although the rotation of rotor  7  can cause roller  6  to rotate about its own axis, roller  6  does not necessarily rotate at the same speed as rotor  7  about its axis. As a result, roller  6  can rotate about its axis at a slower rate than rotor  7  which can minimize the wear on vane  5 . In an alternative arrangement, roller  6  may be permanently secured, or press fit, for example, into the interior cavity of rotor  7 . In this embodiment, roller  6  rotates about post  4  at the same speed as rotor  7 . However, this concurrent rotation may lead to excessive wear of the vane  5  as roller  6  may make more revolutions with respect to vane  5  than when roller  6  is permitted to independently rotate.  
         [0021]     In the present embodiment, the outer perimeter of rotor  7  includes recesses  8  which are sized and configured for receiving permanent magnets  9 . Recesses  8  and permanent magnets  9  can have co-operating features which interlock to keep magnets  9  securely in position. In alternative embodiments, magnets  9  can be press-fit into recesses  8 , fastened or glued into place, for example. In further alternative embodiments, the compressor may include a single multi-poled annular magnet that surrounds the perimeter of rotor  7 . As illustrated in  FIG. 1 , the compressor further includes stator  10  positioned about the outer perimeter of rotor  7 . Stator  10 , in this embodiment, includes an iron or ferrous-material core  25  and conductive windings  26 , such as copper wire, wrapped around, or at least partially surrounding, core  25 . In the present embodiment, stator  10  is positioned within the compressor housing, In other embodiments, stator  10  can be positioned outside of the compressor housing where the housing is permeable to magnetic fields.  
         [0022]     In operation, stator  10  creates a magnetic field that interacts with permanent magnets  9 . More particularly, windings  26  of stator  10  are energized by an electric current passing therethrough to generate a rotating or commutated magnetic field. Owing to the poles created by the magnetic field, the permanent magnets embedded within rotor  7  and positioned within the magnetic field are motivated to rotate rotor  7 . As illustrated in  FIG. 1 , rotor  7 , in the present embodiment, has a plurality of evenly spaced permanent magnets  9  positioned around the outer perimeter thereof. In other embodiments, permanent magnets  9  may be unevenly spaced to achieve a desired velocity or acceleration of rotor  7 . In further embodiments, permanent magnets  9  may have different sizes or they may be the same size.  
         [0023]     As discussed above, permanent magnets  9  may be magnetically attracted to electromagnetic poles created by stator  10  when the windings of the stator are energized. In the present embodiment, permanent magnets  9  are also magnetically attracted to stator  10  regardless of whether the windings of stator  10  are energized. More particularly, in the present embodiment, permanent magnets  9  are attracted to iron core  25  of stator  10 . In one embodiment, the attraction between permanent magnets  9  and iron core  25  is sufficient to hold rotor  7  in a levitated position intermediate top plate  11  and bottom plate  3 . Stated another way, when the compressor is not operating, rotor  7  can be held in position such that a gap is present between rotor  7  and top plate  11  and also between rotor  7  and bottom plate  3 . During operation of the compressor, the stator windings are energized to generate a magnetic field which causes rotor  7  to rotate with respect to stator  10  while the attraction between permanent magnets  9  and stator  10  can maintain rotor  7  in position. In fact, in one embodiment, the magnetic attraction between permanent magnets  9  and iron core  25  is so strong that it is very difficult to move rotor  7  axially with respect to stator  10  or to separate rotor  7  from stator  10 . As a result, during the assembly and/or disassembly of the compressor, a handle can be attached to rotor  7  and grasped by the installer to place rotor  7  within stator  10  to prevent potential injury to the installer&#39;s fingers.  
         [0024]     Referring to  FIG. 3 , rotor  7 , in the present embodiment, has an axial height such that the gaps, L A , between rotor  7  and plates  3  and  11  are between approximately 0.004″ and 0.125″. In another embodiment, these gaps are between approximately 0.02″ and 0.10″. As discussed above, roller  6  and plates  3  and  11  define boundaries of the suction and discharge chambers of the compressor. As a result, in the present embodiment, the clearance between roller  6  and plates  3  and  11  is very small. For example, in the present embodiment, the top and bottom surfaces of roller  6  are disposed closely adjacent to top plate  11  and bottom plate  3  with a small gap, L B , of only between approximately 0.0004″ and 0.0015″. In the present embodiment, both top plate  11  and bottom plate  3  include a raised portion extending therefrom, i.e., raised portions  22  and  20 , respectively. Raised portions  20  and  22  have very smooth, mirror-like surfaces  26  and  24 , respectively, having a surface roughness (Ra) of approximately 15 microinches, for example. Smooth surfaces  24  and  26  may facilitate the relative movement between roller  6 , for example, and plates  3  and  11  in the event that they contact each other.  
         [0025]     As discussed above, rotor  7 , in the present embodiment, does not touch top plate  11  and bottom plate  3  regardless of whether the compressor is on or off. Thus, no lubrication is necessary between rotor  7  and top plate  11  and bottom plate  3  thereby allowing for the reduction in the overall amount of lubrication used in the compressor. In the alternative embodiment described above where roller  6  is secured to rotor  7 , the weight of rotor  7  may be transmitted into plates  3  and  11  through roller  6 . In order to lubricate the interface between roller  6  and vane  5 , and the interfaces between roller  6  and plates  11  and  3 , oil may be injected from an oil sump in the compressor into vane slot  15  behind vane  5  such that the oil moves into the compression chamber during suction. In one embodiment, the oil sump in the compressor surrounds raised portion  24  of bottom plate  3 . The oil may be injected from the oil sump into the suction refrigerant stream at a location near the suction inlet of the compressor.  
         [0026]     In the present embodiment, the gaps between the moving parts of the compressor and top plate  11  and bottom plate  3  are large enough to account for manufacturing and assembly tolerances, while small enough to perform the above-described functions. This is particularly advantageous during the start-up of the compressor. More particularly, as rotor  7 , in the present embodiment, does not touch plates  3  and  7  while the compressor is off, rotor  7  does not need to overcome the static and/or dynamic friction between rotor  7  and plates  3  and  11  when the compressor is turned on. Accordingly, less energy and torque from stator  10  is required to start the compressor. Further, as there is no friction between rotor  7  and plates  3  and  11 , the possibility of the rotor stalling or seizing is substantially reduced, especially when rotor  7  has little to no momentum during the start-up of the compressor.  
         [0027]     Although the above-discussed embodiments include a rotor  7  that is levitated intermediate plates  3  and  11 , rotor  7  may inevitably contact one or both of top plate  11  and bottom plate  3 . For example, the magnetic attraction between permanent magnets  9  and iron core  25  may be insufficient to suspend the entire weight of, i.e., levitate, rotor  7 . Accordingly, rotor  7  will only be partially supported by the magnetic attraction between magnets  9  and iron core  25 , and rotor  7  will nonetheless bear against one of plates  3  and  11 . In this event, however, at least some of the weight of rotor  7  will be gravitationally supported by the magnetic attraction between magnets  9  and iron core  25 , thereby resulting in a lower contact force between rotor  7  and plates  3  and  11 . As a result, some friction may be present between rotor  7  and plates  3  and  11  and, thus, it may be advantageous to provide a lubricant between rotor  7  and plates  3  and  11  to facilitate the movement of rotor  7 .  
         [0028]     In the present embodiment, the compressor further includes a journal bearing or rolling element for aligning the center of rotor  7  with the axis of stator  10 . In this embodiment, referring to  FIG. 1 , top plate  11  includes shoulder  13  having a race, or perimeter, of rolling elements  18  which are in bearing contact with rotor  7  in circumferential groove  19 . Shoulder  13  and rolling elements  18  substantially center rotor  7  within stator  10 . As a result, rotor  7  can remain substantially centered within stator  10  regardless of the orientation of the compressor. For example, even if the compressor is positioned such that axis  21  of stator  10  is at angle more than 30 or 40 degrees with respect to the horizon, rotor  7  will remain substantially centered with respect to axis  21  owing to shoulder  13  and positioned intermediate plates  3  and  11  owing to the magnetic attraction between magnets  9  and iron core  25 . As discussed above, the weight of the rotor in some previous compressors, when positioned in such an orientation, caused the rotor to bear against the compressor housing and/or stator, thereby rendering the compressor inefficient or even inoperable. As a result, aligning rotor  7  according to the present invention is particularly suitable in electronics cooling applications which often require the compressor to be orientation independent.  
         [0029]     As discussed above, unlike previous rotary compressors for cooling systems with compressors that used large amounts of oil for the compressor operation, the present invention provides a rotary compressor that requires little or no oil in operation. This is a significant advantage since, as discussed above, in the electronics industry, the use of oil can be problematic in terms of system operation, maintenance, potential leaks and weight. Further, owing to the arrangement of the rotor and roller within the stator, as described above, the compressor can be very compact and positioned adjacent to or secured against a heat source such as a microprocessor, for example. As a result, a compressor in accordance with the present invention can meet the cooling needs of sophisticated electronic components and systems, as well as other high heat producing systems, for example.  
         [0030]     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. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.