Abstract:
A heat sink element for an adjustable speed magnetic drive unit operable by relative rotation of a conductor rotor assembly and a magnet rotor assembly includes a base portion and a plurality of groupings of fins. The base portion includes a mounting face that is sized and dimensioned to be coupled to the conductor rotor assembly, and an opposing convective heat transfer face. The plurality of groupings of fins extend from the convective heat transfer face of the base portion. Adjacent fins in each grouping of fins are separated by a channel that extends along a longitudinal direction of the fins. The plurality of groupings of fins are separated by at least one slot that extends substantially transverse to the longitudinal direction.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to heat sink assemblies and associated retrofit methods for adjustable speed magnetic drive systems. 
         [0003]    2. Description of the Related Art 
         [0004]    Adjustable speed magnetic drive systems operate by transmitting torque from a motor to a load across an air gap. There is no mechanical connection between the driving and driven sides of the equipment. Torque is created by the interaction of powerful rare-earth magnets on one side of the drive with induced magnetic fields on the other side. By varying the air gap spacing, the amount of torque transmitted can be controlled, thus permitting speed control. 
         [0005]    Conventionally, adjustable speed drives of this type consist of three sets of components. A magnet rotor assembly, containing rare-earth magnets, is attached to the load. A conductor rotor assembly is attached to the motor. The conductor rotor assembly includes a rotor made of a conductive material, such as aluminum, copper, or brass. Actuation components control the air gap spacing between the magnet rotors and the conductor rotors. Relative rotation of the conductor and magnet rotor assemblies induces a powerful magnetic coupling across the air gap. Varying the air gap spacing between the magnet rotors and the conductor rotors results in controlled output speed. The output speed is adjustable, controllable, and repeatable. 
         [0006]    The principle of magnetic induction requires relative motion between the magnets and the conductors. This means that the output speed is always less than the input speed. The difference in speed is known as slip. Typically, slip during operation at a full rating motor speed is between 1% and 3%. 
         [0007]    The relative motion of the magnets in relation to the conductor rotor causes eddy currents to be induced in the conductor material. The eddy currents in turn create their own magnetic fields. It is the interaction of the permanent magnet fields with the induced eddy current magnetic fields that allow torque to be transferred from the magnet rotor to the conductor rotor. The electrical eddy currents in the conductor material create electrical heating in the conductor material. 
         [0008]    Conventionally, fins are arranged on an external surface of the conductor rotors to aid in the removal of heat during operation of the drive unit.  FIGS. 1 and 2  illustrate one such conventional configuration. An adjustable speed drive  10  includes conductor rotors  12  and  14  coupled together by spacers  16 . A plurality of heat transfer elements  20  are circumferentially arrayed on an external surface of the conductor rotors  12  and  14 . As shown in  FIGS. 2A-2C , each heat transfer element  20  includes a plurality of fins  26  that extend from a base  22  to define a plurality of channels  28  between the fins  26 . The heat transfer elements  20  can be secured to the conductor rotors  12  and  14  via openings  24  in the base  22 . The heat transfer elements  20  are coupled to the conductor rotors  12  and  14  such that the fins  26  and channels  28  extend in a substantially radial direction relative to an axis of rotation of the conductor rotors  12  and  14 . As the adjustable speed drive is operated, the rotation of the rotors  12  and  14  causes air to flow radially outward through the channels  28 , thereby cooling the conductor rotors  12  and  14 . 
       BRIEF SUMMARY 
       [0009]    It has been observed that the inclusion of heat sink assemblies on the conductor rotors of an adjustable speed drive generate an unacceptable amount of noise during operation. It has been further observed that by reducing the fin height on the heat sinks, sound levels can be reduced to acceptable ranges for lower speed operation of the adjustable speed drive. It has also been observed that including slots across the fins and heat sink elements also has a favorable effect on sound level reduction, including at high speeds of operation. 
         [0010]    A heat sink element for an adjustable speed magnetic drive unit operable by relative rotation of a conductor rotor assembly and a magnet rotor assembly may be summarized as including a base portion that includes a mounting face that is sized and dimensioned to be coupled to the conductor rotor assembly, and an opposing convective heat transfer face; a plurality of groupings of fins extending from the convective heat transfer face of the base portion, adjacent fins in each grouping of fins separated by a channel that extends along a longitudinal direction of the fins, the plurality of groupings of fins being separated by at least one slot that extends substantially transverse to the longitudinal direction. A height of the fins in each grouping may vary across the grouping. The height of the fins may increase linearly towards a centerline of the heat sink element to form a tented profile. A height of the fins in each grouping may vary across the grouping to form a non-linear, curved profile. The plurality of groupings of fins may be separated by more than two slots that extend substantially transverse to the longitudinal direction. 
         [0011]    An adjustable speed magnetic drive unit may be summarized as including a magnet rotor assembly; a conductor rotor assembly positioned relative to the magnet rotor assembly such that there is an air gap between the magnet rotor assembly and the conductor rotor assembly, and such that relative rotation of the conductor and magnet rotor assemblies induces a magnetic coupling across the air gap; and a heat sink assembly coupled to the conductor assembly, the heat sink assembly including a plurality of groupings of fins arrayed in a substantially circumferential direction relative to an axis of rotation of the conductor assembly, the plurality of circumferential arrays of fins being separated by at least one slot that extends substantially transverse to a radial direction relative to the axis of rotation of the conductor rotor assembly. The heat sink assembly may include a plurality of heat sink elements that are arranged on an external surface of the conductor rotor assembly, each heat sink element including the plurality of groupings of fins. On at least one of the heat sink assemblies, a height of the fins within each of the plurality of groupings of fins may vary across the respective grouping of fins. On the at least one of the heat sink assemblies, the fins may define a tented profile. On the at least one of the heat sink assemblies, the fins may define a curved profile. Each heat sink element may include more than two slots that extends substantially transverse to the radial direction. 
         [0012]    A method of reducing noise generated by an adjustable speed magnetic drive unit that is operable by relative rotation of a conductor rotor assembly and a magnet rotor assembly may be summarized as including removing a first heat sink element from the conductor rotor assembly, the first heat sink element including a first plurality of fins that extend in a substantially radial direction relative to an axis of rotation of the conductor rotor assembly; and then coupling a second heat sink element to the conductor rotor assembly in place of the first heat sink element, the second heat sink element including a second plurality of fins that extend in a substantially radial direction relative to the axis of rotation of the conductor rotor assembly, a total exposed surface area of the second plurality of fins being less than a total exposed surface area of the first plurality of fins. An average fin height of the first plurality of fins may be greater than an average fin height of the second plurality of fins. The first plurality of fins may extend uninterrupted in the radial direction on the first heat sink element, and the second plurality of fins may include at least one slot that extends substantially transverse to the radial direction and separates the second plurality of fins into at least two radial groupings. An average fin height of the first plurality of fins may be substantially the same as an average fin height of the second plurality of fins. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0013]    In the drawings, identical reference numbers identify similar elements or acts. 
           [0014]      FIG. 1A  is an isometric view of a conventional heat sink arrangement on an adjustable speed drive. 
           [0015]      FIG. 1B  is a front view of the adjustable speed drive of  FIG. 1A . 
           [0016]      FIG. 1C  is a left side view of the adjustable speed drive of  FIG. 1A . 
           [0017]      FIG. 1D  is a right side view of the adjustable speed drive of  FIG. 1A . 
           [0018]      FIG. 2A  is a top view of a conventional heat sink of the adjustable speed drive of  FIGS. 1A-1D . 
           [0019]      FIG. 2B  is a front view of the heat sink of  FIG. 2A . 
           [0020]      FIG. 2C  is an isometric view of the heat sink of  FIG. 2B . 
           [0021]      FIG. 3  shows the sound levels generated by various heat sink arrangements at various rotational speeds for adjustable speed drives. 
           [0022]      FIG. 4A  is a top view of a heat sink element having a reduced fin height relative to the heat sink element shown in  FIGS. 2A-2C . 
           [0023]      FIG. 4B  is a front view of the heat sink element of  FIG. 4A . 
           [0024]      FIG. 4C  is an isometric view of the heat sink element of  FIG. 4A . 
           [0025]      FIG. 5A  is an isometric view of an adjustable speed drive according to one aspect of the present disclosure. 
           [0026]      FIG. 5B  is a front view of the adjustable speed drive of  FIG. 5A . 
           [0027]      FIG. 5C  is a left side view of the adjustable speed drive of  FIG. 5A . 
           [0028]      FIG. 5D  is a right side view of the adjustable speed drive of  FIG. 5A . 
           [0029]      FIG. 6A  is a top view of a heat sink element used with the adjustable speed drive of  FIG. 5A . 
           [0030]      FIG. 6B  is a front view of the heat sink element of  FIG. 6A . 
           [0031]      FIG. 6C  is an isometric view of the heat sink element of  FIG. 6A . 
           [0032]      FIG. 7A  is an adjustable speed drive according to another aspect of the present disclosure. 
           [0033]      FIG. 7B  is a front view of the adjustable speed drive of  FIG. 7A . 
           [0034]      FIG. 7C  is a left side view of the adjustable speed drive of  FIG. 7A . 
           [0035]      FIG. 7D  is a right side view of the adjustable speed drive of  FIG. 7A . 
           [0036]      FIG. 8A  is a top view of a heat sink element used with the adjustable speed drive illustrated in  FIGS. 7A-7D . 
           [0037]      FIG. 8B  is a front view of the heat sink element shown in  FIG. 8A . 
           [0038]      FIG. 8C  is an isometric view of the heat sink element shown in  FIG. 8A . 
           [0039]      FIG. 9A  is a top view of a heat sink element according to another aspect of the present disclosure. 
           [0040]      FIG. 9B  is a front view of the heat sink element of  FIG. 9A . 
           [0041]      FIG. 9C  is an isometric view of the heat sink element of  FIG. 9A . 
           [0042]      FIG. 10A  is a top view of a heat sink element according to another aspect of the present disclosure. 
           [0043]      FIG. 10B  is a front view of the heat sink element of  FIG. 10A . 
           [0044]      FIG. 10C  is an isometric view of the heat sink element of  FIG. 10A . 
           [0045]      FIG. 11A  is top view of a heat sink element according to another aspect of the present disclosure. 
           [0046]      FIG. 11B  is a front view of the heat sink element of  FIG. 11A . 
           [0047]      FIG. 11C  is an isometric view of the heat sink element of  FIG. 11A . 
       
    
    
     DETAILED DESCRIPTION 
       [0048]    In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the invention. However, one skilled in the art will understand that the invention may be practiced without these details. 
         [0049]    Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.” 
         [0050]    Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
         [0051]    As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its broadest sense, that is as meaning “and/or” unless the content clearly dictates otherwise. 
         [0052]    The Abstract of the Disclosure provided herein is for convenience only and does not interpret the scope or meaning of the embodiments. 
         [0053]    As noted above, it has been recognized that heat sinks on adjustable speed drives can create an undesirably loud whistling noise above a threshold rotational speed of the adjustable speed drive. An evaluation of several heat sink profiles revealed that the whistle noise is a function of heat sink fin height, length, and rotational speed of the adjustable speed drive.  FIG. 3  shows the sound level generated from one side of an adjustable speed drive when operated with no heat sinks as well as different heat sink configurations at 900 rotations per minute (rpm), 1200 rpm, 1500 rpm, and 1800 rpm. 
         [0054]    Various heat sink heights were tested, including full height heat sinks, half height heat sinks, and third height heat sinks.  FIGS. 2 and 4  respectively illustrate examples of full and half height heat sinks. Each of the fins  26  of the heat sink  20  in  FIGS. 2A-2C  has a height H of about 0.80 inches above the base  22 . The heat sink  30 , shown in  FIGS. 4A-4C , includes a base  32  from which includes a plurality of fins  36 . The fins  36  have a height h that is about 0.40 inches, or half the height of the height H of the heat sink  20  shown in  FIGS. 2A-2C . The fins  36  define channels  38  in the heat sink element  30 . The heat sink element  30  can be secured to a conductor rotor via the holes  34  in the base  32 . 
         [0055]    As shown in  FIG. 3 , reducing the height of the fins of the heat sink resulted in a significant reduction in noise generation for operations at low speeds. For example, the amount of noise generated by the half height heat sink configuration on the adjustable speed drive operated at 900 and 1200 rpm was comparable to that generated by the adjustable speed drive that did not have any heat sinks. However, as the speed was increased to 1500 rpm, the noise generated by the half heat sink configuration increased to greater than 90 decibels, compared to the less than 80 decibels for no heat sinks, and greater than 100 decibels for full height heat sinks. As the speed was increased to 1800 rpm, the noise generated by the half heat sink configuration was within five decibels of the noise generated by the full height heat sinks, and was about 15 decibels greater than the noise generated by the drive unit with no heat sinks. Notably, the noise benefits persisted across each speed of operation that was tested for heat sinks that were one third the height of the full height heat sinks. 
         [0056]    Heat sinks having a tented profile were also tested. These heat sinks have a variable fin height across the heat sink. Fin heights increase linearly from one side of the heat sink to a maximum fin height at the center, and then decrease linearly to the other side of the heat sink. The resulting profile resembles a tent. As shown in  FIG. 3 , the tented profile heat sinks did not achieve as significant a noise reduction as the half height heat sinks for 900, 1200, and 1500 rpm, and was comparable to the noise reduction of the half height heat sink at 1800 rpm. 
         [0057]    It was further observed that, unexpectedly, the sound level generated by an adjustable speed drive could be greatly reduced without reducing the height of the heat sinks merely by including transverse slots across the fins of the heat sinks. As shown in  FIG. 3 , the noise benefits of slotted heat sinks persisted even as the speed of the adjustable speed drive was increased from 900 rpm to 1800 rpm for full height heat sinks with slots, tented heat sinks that include slots, and half height heat sinks that include slots. 
         [0058]      FIGS. 5A-5D  illustrate an adjustable speed drive  50  that includes slotted, full-height heat sinks  60 . The adjustable speed drive  50  includes two conductor rotors  52  and  54  that are coupled via spacers  56 . The conductor rotors  52  and  54  include a rotor made of a conductive material, such as aluminum, copper, or brass.  FIGS. 6A-6C  illustrate the slotted heat sink elements  60  in greater detail. Each heat sink element  60  includes a base  62  from which extend a plurality of fins  66 . The fins  66  define channels  68  therebetween and extend a full-height H above the base  62 . The heat transfer element  60  further includes a plurality of slots  67  that extend substantially transverse to the direction of extension of the fins  66 , thereby dividing the fins into a plurality of groups in the radial direction with respect to an axis of rotation of the conductor rotors. The heat transfer elements  60  can be affixed to the conductor rotors  52  and  54  via mounting holes  64 . 
         [0059]    It was further observed that noise savings could also be obtained by changing the shape of the spacer elements  56  that couple the conductor rotors  52  and  54 . Specifically, as shown in  FIG. 5A , each spacer  56  includes a radius  56   a  and  56   b  on leading and trailing edges thereof. By contrast, as shown in  FIG. 1A , the spacers  16  include abrupt edges  16   a  and  16   b  on leading and trailing edges thereof. 
         [0060]    It was further observed that the number of slots used in the heat sink transfer element can vary depending upon the size of the adjustable speed drive.  FIGS. 7A-7D  illustrate an adjustable speed drive according to another aspect of the present disclosure. The adjustable speed drive  70  includes conductor rotor elements  72  and  74  coupled by spacers  76  having leading and trailing edges  70   a  and  70   b.  Heat transfer elements  80  are affixed to the opposing faces of the conductor rotor elements  72  and  74 .  FIGS. 8A-8C  illustrate the heat transfer elements  80  in greater detail. Each heat transfer element  80  includes a base  82  from which extend fins  86  to a height H. The fins  86  define a plurality of channels  88 . Two slots  87  transect the fins  86 . The heat transfer element  80  can be secured to the conductor rotor  72  or  74  via the mounting poles  84  in the base  82 . 
         [0061]      FIGS. 9A-9C  illustrate a heat transfer element that includes three transverse slots. The heat transfer element  90  includes a base  92  from which extend fins  96  to a height h. The fins  96  define channels  98 . Transverse slots  97  divide the plurality of fins into four groups. The heat transfer elements  90  can be secured to conductor rotor elements via mounting holes  94  in the base  92 . 
         [0062]      FIGS. 10A-10C  illustrate a heat transfer element  100  that includes four transverse slots  107 . The transverse slots  107  divide and separate a plurality of groups of fins  106  that extend from a base  102 . The fins reach a height H. The heat transfer element  100  can be affixed to a rotary conductive element via mounting holes  104  in the base  102 . 
         [0063]      FIGS. 11A-11C  illustrate a heat transfer element  110  according to another aspect of the present disclosure. Fins  116  extend from a base  112 . The fins  116  define channels  118  therebetween. Slots  117  divide and separate the fins  116  into a plurality of groups. The base  112  includes mounting holes  114  to secure the heat transfer element to a conductor rotor. Unlike previous examples, the height of the fins  116  varies to create a curved profile. In particular, as shown in  FIG. 11B , the fins vary in a nonlinear fashion from a minimal height h′ to a maximum height H′. 
         [0064]    In addition to new installations, noise improvements can be achieved by replacing existing heat transfer elements with any of the improved heat transfer elements described herein. For example, full height heat transfer elements can be replaced with half-height heat transfer elements for low-speed applications. For higher speed applications, full height heat transfer elements can be replaced with slotted heat transfer elements, having the appropriate height necessary for the desired heat transfer. 
         [0065]    The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.