Abstract:
A system for cooling an electrical machine is disclosed. The electrical machine includes a rotor, a stator, and at least one cooling tube extending through the stator. During operation of the electrical machine, fluid flows through the tube and carries away heat generated by the electrical machine.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Provisional Patent Application No. 61/108,300, entitled “Hydroformed Cooling Channels in Stator Laminations,” filed on Oct. 24, 2008 by the same inventors hereof, the disclosure of which is expressly incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present disclosure relates to a system for cooling an electrical machine. More particularly, the present disclosure relates to a system for cooling stator laminations of the electrical machine. 
         [0004]    2. Description of the Related Art 
         [0005]    Electrical machines, including motors and generators, operate by rotating a rotor relative to a stator that surrounds the rotor. Electrical machines generate heat during operation that flows radially outward from the rotor to the stator to an exterior housing. To cool the electrical machine, air or a liquid coolant may be directed through channels located in the exterior housing, through apertures located in sealed laminations of the stator, or through channels located between coils of the stator, for example. 
       SUMMARY 
       [0006]    The present disclosure provides a system for cooling an electrical machine. The electrical machine includes a rotor, a stator, and at least one cooling tube extending through the stator. During operation of the electrical machine, fluid flows through the tube and carries away heat generated by the machine. 
         [0007]    According to an embodiment of the present disclosure, an electrical machine is provided including a rotor and a stator. The stator includes a lamination stack that includes a plurality of laminations aligned coaxially, the lamination stack defining a central bore sized to receive the rotor and at least one cooling bore, at least one tube extending through the at least one cooling bore of the lamination stack, and a cooling fluid positioned in the at least one tube. 
         [0008]    According to another embodiment of the present disclosure, an electrical machine is provided including a rotor and a stator. The stator includes a lamination stack that includes a plurality of laminations aligned coaxially. Each of the plurality of laminations includes an outer periphery, an inner periphery defining a central aperture, the central apertures of the plurality of laminations being aligned to define a central bore sized to receive the rotor, and at least one surface defining a radial aperture, the radial apertures of the plurality of laminations aligned to define at least one cooling bore. The stator also includes at least one tube extending through the at least one cooling bore of the lamination stack and a cooling fluid positioned in the at least one tube. 
         [0009]    According to yet another embodiment of the present disclosure, a method of manufacturing an electrical machine is providing including the steps of providing an electrical machine that includes a rotor and a stator, the stator defining a central bore that is sized to receive the rotor and at least one cooling bore, and inserting at least one tube into the at least one cooling bore of the stator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The above-mentioned and other features of the present disclosure will become more apparent and the present disclosure itself will be better understood by reference to the following description of embodiments of the present disclosure taken in conjunction with the accompanying drawings, wherein: 
           [0011]      FIG. 1  is a perspective view of an embodiment of a motor including a rotor and a stator with cooling tubes extending therethrough; 
           [0012]      FIG. 2  is a perspective view of the motor of  FIG. 1  showing the motor also including a housing; 
           [0013]      FIG. 3  is a top plan view of the stator of  FIG. 1  shown without the cooling tubes extending therethrough; 
           [0014]      FIG. 4  is a view similar to  FIG. 3  showing cooling tubes extending between coils of the stator; 
           [0015]      FIGS. 5 and 6  are schematic illustrations of an exemplary method of assembling cooling tubes in a stator; 
           [0016]      FIGS. 7 and 8  are schematic illustrations of another exemplary method of assembling cooling tubes in a stator; and 
           [0017]      FIG. 9  is a schematic illustration of an exemplary method of operating a stator having cooling tubes extending therethrough. 
       
    
    
       [0018]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate exemplary embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION 
       [0019]      FIG. 1  provides an illustrative electrical machine in the form of motor  10 . Although the electrical machine is illustrated and described herein as motor  10 , machines of the present disclosure may also include generators, for example. Motor  10  includes rotor  12 , stator  14 , and, optionally, housing  16  ( FIG. 2 ) surrounding stator  14 . In operation, power is supplied to motor  10  to rotate rotor  12  relative to the surrounding stator  14 . 
         [0020]    Stator  14  includes lamination stack  20  and coils  22 . Lamination stack  20  includes a plurality of individual laminations  24  layered and secured together axially. Adjacent laminations  24  may be secured together by welding, with a bonding agent, with a fastening device, or by another suitable technique. 
         [0021]    As shown in  FIG. 3 , each lamination  24  is a disk-shaped body constructed of electrical steel or another suitable ferromagnetic material. Lamination  24  includes an outer periphery  26  and an inner periphery  28  that defines a central aperture  30 . When laminations  24  are layered together, adjacent central apertures  30  align to form a central bore  32  that extends axially through lamination stack  20 . Central bore  32  is sized to receive rotor  12  ( FIG. 1 ). Inner periphery  28  of lamination  24  also includes a plurality of radially-spaced winding teeth  40 . Adjacent winding teeth  40  define winding slots  42  therebetween. When laminations  24  are layered together, wires, such as insulated copper wires, extend through winding slots  42  and wrap around winding teeth  40  to form coils  22 . Outer periphery  26  of lamination  24  may include any number of alignment features (not shown), such as indentations, protrusions, and/or markings, to indicate when adjacent laminations  24  are properly aligned. 
         [0022]    Referring still to  FIG. 3 , each lamination  24  also includes a plurality of radial apertures  50 . Radial apertures  50  are spaced radially across the disk-shaped body of lamination  24 . Radial apertures  50  may be formed in lamination  24  by any suitable method. For example, after lamination  24  is stamped from a metal sheet, radial apertures  50  may be formed by cutting or punching holes into the metal sheet. As another example, radial apertures  50  may be formed during a molding process. Radial apertures  50  may be circular, oval, triangular, or another suitable shape. When laminations  24  are layered together, adjacent apertures  50  cooperate to form a plurality of cooling bores  52  that extend through lamination stack  20 . In an embodiment, cooling bores  52  extend through lamination stack  20  in a direction essentially parallel to central bore  32 . This parallel arrangement may be achieved by aligning adjacent radial apertures  50  directly on top of one another. In another embodiment, cooling bores  52  extend through lamination stack  20  in a helical path around central bore  32 . This helical arrangement may be achieved by slightly offsetting adjacent radial apertures  50 . In addition to any alignment features (not shown) on outer periphery  26  of lamination  24 , apertures  50  themselves may indicate when adjacent laminations  24  are properly aligned. Cooling bores  52  are defined by wall  54  of lamination stack  20 . Due to imperfections in the manufacturing of laminations  24  and apertures  50 , wall  54  of lamination stack  20  may not be perfectly straight or even. For example, some apertures  50  may be slightly larger than others, so wall  54  may be jagged or uneven. Such an imperfection  56  on wall  54  is shown in  FIG. 5 . The scale of imperfection  56  may be exaggerated for purposes of illustration. 
         [0023]    The number, spacing, shape, and diameter of apertures  50 , and thus the number, spacing, shape, and diameter of cooling bores  52 , may vary to accomplish adequate cooling of motor  10 . For example, a large motor may include more cooling bores  52  than a small motor. As another example, a motor that is run at high speeds and generates a significant amount of heat may include more cooling bores  52  than a motor that is run at lower speeds. 
         [0024]    Referring again to  FIG. 1 , stator  14  of motor  10  includes cooling tubes  60 . Cooling tubes  60  extend through lamination stack  20  of stator  14 , and specifically through cooling bores  52  in lamination stack  20  of stator  14 . Cooling tubes  60  may be constructed of a thermally conductive material, such as copper, a copper alloy, aluminum, or an aluminum alloy, or another suitable material, such as steel or a steel alloy. Each cooling tube  60  includes input end  62  and output end  64 , as shown in  FIG. 5 . 
         [0025]    An exemplary method of positioning cooling tubes  60  in lamination stack  20  is illustrated schematically in  FIGS. 5 and 6 . First, cooling tube  60  is inserted into cooling bore  52  of lamination stack  20 . Cooling tube  60  may be a straight, round tube, or cooling tube  60  may have another suitable shape. Next, output end  64  of cooling tube  60  is sealed. After output end  64  is sealed, cooling tube  60  is hydroformed. Specifically, fluid is directed into input end  62  of cooling tube  60  until cooling tube  60  conforms to the shape of cooling bore  52 . Initially, pressurized fluid inside cooling tube  60  forces cooling tube  60  to expand outwardly within cooling bore  52 , as illustrated schematically in  FIG. 5 . The pressure applied to cooling tube  60  is indicated by arrows P. The internal pressure should be sufficient to cause the tube material to yield. For example, the internal pressure applied to cooling tube  60  may be slightly greater than atmospheric pressure or as high as approximately 100 psi, 500 psi, 1,000 psi, 5,000 psi, 10,000 psi, or more. The internal pressure may vary depending on, for example, the type of material chosen for cooling tube  60 , the thickness of cooling tube  60 , and the degree of deformation required of cooling tube  60 . As an example, a higher internal pressure would be required to hydroform a tube constructed of steel than would be required to hydroform a tube constructed of a softer material, such as copper or aluminum. As another example, a higher internal pressure would be required to hydroform a thick-walled, rigid tube than would be required to hydroform a thin-walled, pliable tube, such as a tube having a thickness similar to an aluminum soda can. Eventually, the cooling tube  60  contacts wall  54  of lamination stack  20 , as illustrated schematically in  FIG. 6 . Hydroforming cooling tube  60  while it is positioned within cooling bore  52  causes cooling tube  60  to mimic the shape of wall  54 , even if wall  54  includes imperfection  56 , for example. According to an exemplary embodiment of the present method, a friction fit is achieved between cooling tube  60  and wall  54  of lamination stack  20  surrounding cooling bore  52 . An exemplary cooling tube  60  requires a low internal pressure to yield to the shape of cooling bore  52  and also maintains sufficient strength after the hydroforming process. 
         [0026]    Cooling tubes  60  may shrink slightly after hydroforming. To ensure that adequate contact is maintained between cooling tubes  60  and walls  54  of lamination stack  20  after hydroforming, lamination stack  20  may be preheated. Heating lamination stack  20  causes cooling bores  52  to expand in diameter. As cooling tubes  60  shrink and begin to pull away from walls  54  of lamination stack  20  after hydroforming, cooling bores  52  also shrink and walls  54  may remain substantially in contact with cooling tubes  60 . 
         [0027]    Another exemplary method of positioning cooling tubes  60  in lamination stack  20  is illustrated schematically in  FIGS. 7 and 8 . First, lamination stack  20  is preheated. Lamination stack  20  need only be heated to a temperature that causes cooling bore  52  to expand to a size that is capable of receiving cooling tube  60  therein. For example, lamination stack may be heated to a temperature of approximately 100° C., 200° C., 300° C., or more. The temperature may vary depending on, for example, the type of material chosen for lamination stack  20 , the size of lamination stack  20 , the size of cooling bore  52 , and the size of cooling tubes  60 . According to an exemplary embodiment of the present invention, lamination stack  20  may be heated during an annealing process, and cooling tubes  60  may be inserted following the annealing process to avoid having to reheat lamination stack  20 . Next, cooling tube  60  is inserted into cooling bore  52  of the pre-heated lamination stack  20 , as shown in  FIG. 7 . As lamination stack  20  cools, cooling bores  52  shrink and walls  54  contact cooling tubes  60 , as shown in  FIG. 8 . According to an exemplary embodiment of the present method, a friction fit may be achieved between cooling tube  60  and wall  54  of lamination stack  20  surrounding cooling bore  52 , with or without hydroforming cooling tube  60 . 
         [0028]    It is also within the scope of the present disclosure that cooling tubes  60  may be positioned between adjacent coils  22  of stator  14 , as shown in  FIG. 4 . In  FIG. 4 , cooling tubes  60  are shown on a single side of lamination stack  20  for purposes of illustration. However, it is within the scope of the present disclosure that cooling tubes  60  may be placed between all adjacent coils  22  or in an alternating arrangement to surround lamination stack  20 , for example. Advantageously, placing cooling tubes  60  between adjacent coils  22  cools the coils  22  directly, rather than indirectly through lamination stack  20 . Cooling tubes  60  may be inserted between adjacent coils  22  and hydroformed against coils  22  as described above with respect to cooling bores  52  of lamination stack  20 . 
         [0029]    During operation of motor  10 , a cooling fluid is directed through cooling tubes  60  to cool motor  10 . The cooling fluid may include, for example, oil, water, a mixture of water and ethylene glycol, a mixture of water and propylene glycol, or another suitable heat transfer fluid. Exemplary cooling fluids are capable of removing more heat from motor  10  than air, for example. As illustrated schematically in  FIG. 9 , the cooling fluid travels from source tank S, into input end  62  of cooling tube  60 , through lamination stack  20 , out of output end  64  of cooling tube  60 , and to destination tank D. The direction of fluid flow is indicated by arrow F. Heat generated by motor  10  is transferred from lamination stack  20 , through the walls of cooling tubes  60 , and into the cooling fluid flowing therein. The direction of heat flow is indicated by arrow H. According to an exemplary embodiment of the present disclosure, the direct, friction-fit contact between cooling tube  60  and wall  54  of lamination stack  20  that is achieved through hydroforming allows heat to transfer directly from lamination stack  20  to cooling tube  60 . The heated fluid that is delivered to destination tank D may be cooled and recycled back to source tank S. 
         [0030]    Referring still to  FIG. 9 , cooling tubes  60  may be coupled to fluid lines  70 . Fluid lines  70  may be constructed of flexible rubber tubing, for example. As illustrated schematically in  FIG. 4 , fluid lines  70  direct the cooling fluid from source tank S to input end  62  of cooling tube  60 , and from output end  64  of cooling tube  60  to destination tank D. According to an exemplary embodiment of the present disclosure, fluid lines  70  are coupled to input end  62  and output end  64  of cooling tube  60  in a manner that prevents fluid leakage between the components. 
         [0031]    To promote even cooling of lamination stack  20 , the cooling fluid may flow in alternating directions through lamination stack  20 . For example, the cooling fluid may flow in a first direction through some cooling tubes  60 , such as the direction indicated by arrow F in  FIG. 9 , and in a second direction through other cooling tubes  60 , such as a direction opposite arrow F in  FIG. 9 . This alternating pattern of fluid flow ensures that one side of lamination stack  20  is not cooled to a greater degree than the opposite side of lamination stack  20 . 
         [0032]    Cooling tubes  60  of the present disclosure may eliminate the need for a sealant that surrounds cooling bores  52 . Without cooling tubes  60 , lamination stack  20  must be adequately sealed to prevent cooling fluid from leaking between adjacent laminations  24  and toward rotor  12  and coils  22 . The sealant may be an ineffective heat conductor, which reduces the heat transfer efficiency of motor  10 . Also, the sealant must be allowed to cure or dry, which increases the time required to manufacture motor  10 . 
         [0033]    Cooling tubes  60  of the present disclosure may also eliminate the need for housing  16  ( FIG. 2 ) of motor  10 . Rather than cooling stator  14  indirectly by directing cooling fluid through housing  16 , stator  14  may now be cooled directly. Eliminating housing  16  reduces the cost of manufacturing motor  10  and the weight of motor  10 . 
         [0034]    While this invention has been described as having preferred designs, the present invention can 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 and which fall within the limits of the appended claims.