Abstract:
A stator of an electric motor or generator comprises a core formed of ferromagnetic material having a plurality of teeth arranged circumferentially about an axis. In one aspect of the invention, at least one retaining member connects the end portions of at least two of the teeth to each other in a manner inhibiting relative movement between said tooth end portions. By inhibiting relative movement between said tooth end portions, vibration is reduced. Vibration can also be reduced by welding interior surfaces of a core to each other. Reducing the vibration reduces the noise emissions of the stator during operation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a divisional application of U.S. patent application Ser. No. 12/890,298, filed Sep. 24, 2010, which claims the benefit of U.S. Provisional Application No. 61/286,305, filed Dec. 14, 2009, each of which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention pertains generally to electric motors and generators. More specifically, this invention pertains to the reduction of noise generated by a stator or rotor, which is partially caused by relative movement between the teeth of the rotor or stator as teeth pass through non-constant magnetic flux fields. The invention increases the stiffness between the teeth in a manner inhibiting the relative movement. 
         [0004]    2. General Background 
         [0005]    Electric motors and generators are primarily comprised of a rotor and a stator. The stator may encircle the rotor or vice versa. Alternatively, the rotor and stator may lie axially side by side. In operation, at least one of these components creates fluctuating magnetic fields by passing fluctuating electrical currents through windings. Such a component typically comprises a generally circular ferromagnetic core that has a plurality of radially extending teeth. Each tooth is encircled by a winding that induces a magnetic field throughout the tooth. The magnetic forces acting on each tooth fluctuates during operation and, as a result, each adjacent pair of teeth experience forces that at some times force the pair of teeth toward each other and at other times away from each other. This causes vibration within the rotor or stator, which in turn generates undesirable audible noise. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is aimed at reducing or inhibiting relative movement and vibration of the teeth of stators and rotors. This is achieved by mechanically connecting the free ends of the teeth to each other and/or by stiffening the body portion of the core via one or more welds. 
         [0007]    In one aspect of the invention, a stator of an electric motor or generator comprises a core, a plurality of windings, and at least one retaining member. The core is formed of ferromagnetic material and has a circular body and a plurality of teeth. The circular body defines a central axis. The axis defines radial and circumferential directions. The teeth are arranged circumferentially about the axis. Each of the teeth extends radially from the circular body to a respective tooth end portion. Each of the windings extends around a respective one of the teeth in a manner such that the winding lies radially between the tooth end portion of the respective tooth and the circular body. The retaining member connects the tooth end portions of at least two of the teeth to each other in a manner inhibiting relative movement between said tooth end portions. 
         [0008]    In another aspect of the present invention, a method of assembling a stator of an electric motor or generator comprises a step of attaching at least one retaining member to a core of the stator or rotor. The core is formed of ferromagnetic material and has a circular body and a plurality of teeth. The circular body defines a central axis. The axis defines radial and circumferential directions. The teeth are arranged circumferentially about the axis and each of the teeth extends radially from the circular body to a respective tooth end portion. The stator or rotor also comprises a plurality of windings. Each of the windings extends around a respective one of the teeth in a manner such that the winding lies radially between the tooth end portion of the respective tooth and the circular body. The retaining member connects the tooth end portions of at least two of the teeth to each other in a manner inhibiting relative movement between said tooth end portions. 
         [0009]    Further features and advantages of the present invention, as well as the operation of the invention, are described in detail below with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective exploded view of a core of a stator or rotor and insulating shrouds that encase the core. 
           [0011]      FIG. 2  is a perspective view of an embodiment of the invention with a few of the windings removed and part of one of the insulating shrouds cut-away for purposes of describing the invention. 
           [0012]      FIG. 3  is detail view of the embodiment of the invention within circle  3 - 3  shown in  FIG. 2 . 
           [0013]      FIG. 4  is detail top plan view showing the tooth end portions of several teeth and a few retaining members of the embodiment of the invention. 
           [0014]      FIG. 5  is a perspective view of a retaining member of the embodiment of the invention. 
           [0015]      FIG. 6  is another perspective view of the retaining member shown in  FIG. 5 . 
           [0016]      FIG. 7  is a side view of the retaining member shown in  FIGS. 5 and 6 . 
           [0017]      FIG. 8  is a top view of the retaining member shown in  FIGS. 5-7 . 
           [0018]      FIG. 9  is a perspective view of the core of a stator or rotor showing another aspect of the invention. 
           [0019]      FIG. 10  is a detail view of the core shown in  FIG. 9 . 
       
    
    
       [0020]    Reference numerals in the written specification and in the drawing figures indicate corresponding items. 
       DETAILED DESCRIPTION 
       [0021]    An exemplary embodiment of a core of a stator or rotor in accordance with the invention is shown in  FIG. 1  along with insulating shrouds that encase the core. The core  10  is formed of ferromagnetic material and is preferably in the form of a stack of laminations or spirally overlaid laminations. The core  10  has a generally circular body  12  (in this case a ring shaped body) and a plurality of teeth  14  that extend radially from the circular body (in this case radially outward). Each tooth  14  has an end portion  16  opposite the circular body  12  and an intermediate portion  18  that extends from the circular body to the end portion. The intermediate portion  18  of each tooth  14  perpendicularly bisects the tooth&#39;s end portion  16  in a manner giving the tooth a T-shaped configuration. Together the insulating shrouds  20  encase the core  10  and electrically shield the core from the windings  22 . Each winding  22  (represented by a generally toroidal element in the figures) encircles the intermediate portion  18  of a respective tooth  14 . 
         [0022]    It should be appreciated that generally circular as used above and in the claims simply means the circular body of the core encircles a central axis. The circular body  12  needs not be perfectly round and could, for example, be polygonal. 
         [0023]    The preferred method of reducing relative movement between the teeth  14  of the core  10  utilizes a plurality of plastic retaining members  24 . Each retaining member  24  is preferably wedged between the end portions  16  of a respective pair of adjacent teeth  14  and snapped in place. This is explained in greater detail below. 
         [0024]    One of the retaining members  24  is shown by itself in  FIG. 5-8 . The retaining member  24  comprises a plurality of compression protrusions  26  that have load bearing surfaces  28 . A wedging surface  30  preferably intersects each load bearing surface  28  and is oriented at an angle relative to the respective load bearing surface. The retaining member  24  also preferably comprises a plurality of generally resilient tabs  32 . Each tab  32  comprises a locking protrusion  34 . Still further, the retaining member  24  comprises a plurality of blocking protrusions  36  configured to ensure proper positing of the retaining member  24  relative to the core  10 . 
         [0025]    Each retaining member  24  is configured to be wedged between a respective pair of adjacent teeth  14  of the core  10  as shown in  FIG. 2-4 . This is done by radially forcing the retaining member  24  against the respective pair of adjacent teeth  14 . The wedging surfaces  30  are configured to engage the opposing sides of the end portions  16  of the teeth  14  and to thereby exert an increasing compression force against such opposing sides as the retaining member is pushed into position. Ultimately, the load bearing surfaces  28  of the retaining member engage the opposing sides of the end portions  16  of the teeth  14  and maintain a compressional force against the opposing sides. While the retaining member  24  is being attached to the core  10  as described above, the tabs also engage the opposing sides of the end portions  16  of the teeth  14 . As a result, the tabs  32  resiliently defect toward the center of the gap that lies between the pair of teeth  14  as the retaining member  24  is being attached to the core  10 . Eventually, the blocking protrusions  36  of the retaining member  24  engage the exterior surfaces of the teeth  14  and thereby prevent any further insertion of the retaining member into the gap that lies between the teeth. When this point is reached, the locking protrusions  36  of the tabs  32  of the retaining member  24  are beyond the sides of the end portions  16  of the teeth  14 , which causes the tabs to at least partially resiliently return to their undeflected configuration. This causes the locking protrusions  36  to engage the surfaces of the end portions  16  of the teeth  14  that face the intermediate portions  18  of the teeth, thereby locking the retaining member in place relative to the core  10 . 
         [0026]    When attached to the core  10  as described above, each retaining member  24  inhibits the respective pair of teeth  14  from moving toward each other. With each adjacent pair of teeth  14  having a retaining member  24  positioned therebetween, the teeth and the retaining members all become locked together and thereby form a structural ring. This greatly reduces the relative movement between any of teeth  14  and, as a result, greatly reduces the amount of noise generated by the rotor or stator during operation. 
         [0027]    Although  FIG. 3  depicts the stator or rotor with a few windings  22  removed and with the upper insulating shroud partially cut-away, it should be appreciated that the retaining members  24  can be, and preferably are, attached to the stator or rotor after all the windings are in place. As such, it should also be appreciated that the present invention could be added to existing stators or rotors to reduce their noise emissions. 
         [0028]    Still further, although the preferred embodiment of the invention utilizes the compression-type retaining members described above, it should be appreciated that the inventors contemplate other ways to inhibit the teeth from moving relative to each other. For example, providing a tension-type retaining member or retaining members can yield generally the same benefits. More specifically, tying the end portions of the teeth of a stator or rotor together via a generally non-stretchable adhesive tape, or via stiff fiber, can inhibit each pair of adjacent teeth from moving away from each other and thereby inhibit the teeth from moving relative to each other. It should also be appreciate that all of the teeth need not necessarily be restrained given that restraining some of the teeth still reduces the noise generated, albeit to a lesser degree. 
         [0029]      FIGS. 9 and 10  depict another embodiment of a method of stiffening the core of a rotor or stator. The core  50  shown in  FIG. 9  is similar to the core described above and comprises a circular body portion  52  and a plurality of teeth  54 . The teeth  54  extend radially outward from the circular body portion  52 . As shown in  FIGS. 9 and 10 , the manner in which the core is formed creates a plurality of slits  56  that extend radially outward partially through the circular body portion  52  of the core  50 . This occurs because the core  50  is preferably formed by bending the laminations that make up the core (which are originally straight) partially around the axis. It should be appreciated that forming the laminations in an initially straight manner results in less scrap material waste during the formation of the laminations. It should also be appreciated that prior to bending the laminations, the slits  56  are formed open, but later close as the laminations are bent. As seen most clearly in  FIG. 10 , to facilitate the bending, the slits  56  extend radially almost completely through the circular body portion  52 . This initially leaves the circular body portion  52  with little stiffness perpendicular to the axis. 
         [0030]    As a result of the slits  56 , the core  50  comprises a plurality of interior surfaces  58  that form a ring. Each slit  56  extends between a respective pair of adjacent interior surfaces  58 . In accordance with one aspect of the invention, the interior surfaces  58  adjacent one of slits  56  are welded to each other. Preferably, an annular bead weld  60  is formed that welds each of the interior surfaces  58  to its adjacent interior surfaces. The bead weld is preferably centrally positioned on the core  50  with respect to the axial direction. By welding an adjacent pair of interior surfaces  58  to each other, the stiffness of the core  50  at the location of the slit  56  that separates such interior surfaces is increased substantially since the interior surfaces are no longer able to move relative to each other. Even though the weld maybe relatively axially thin, it effectively negates the impact that the slits  56  would otherwise have on the stiffness of the core  50 . This reduces vibration, which reduces the noise emitted by the stator or rotor. 
         [0031]    It should be appreciated that the welding aspect of the invention can be used independently or in combination with the retaining member aspect discussed above. Moreover, to further enhance the stiffness of a rotor or stator, the inventors have discovered that a hermitic water-based epoxy varnish applied to the windings of the rotor or stator can reduce vibration of the teeth of the core and thereby further reduce the noise emitted by the rotor or stator. 
         [0032]    In view of the foregoing, it should be appreciated that the invention achieves the several advantages over exiting rotor and stator designs. 
         [0033]    As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by the above-described exemplary embodiment, but should be defined only in accordance with the following claims appended hereto and their equivalents. 
         [0034]    It should also be understood that when introducing elements of the present invention in the claims or in the above description of exemplary embodiments of the invention, the terms “comprising,” “including,” and “having” are intended to be open-ended and mean that there may be additional elements other than the listed elements. Additionally, the term “portion” should be construed as meaning some or all of the item or element that it qualifies. Moreover, use of identifiers such as first, second, and third should not be construed in a manner imposing any relative position or time sequence between limitations. Still further, the order in which the steps of any method claim that follows are presented should not be construed in a manner limiting the order in which such steps must be performed. It should be appreciated that generally circular simply means the circular body of the core encircles a central axis. The circular body needs not be perfectly round and could, for example, be polygonal.