Abstract:
A rotor mounting assembly includes a first resilient ring, a second resilient ring and a spacer. The resilient rings and the spacer are fabricated from center punch laminates produced from a stator bore punch process. The second resilient ring includes at least one aperture in addition to a central bore. A method of fabricating the rotor mounting assembly includes positioning a press pin through the aperture to contact the first resilient ring which allows a press to simultaneously presses both resilient rings onto a knurled rotor shaft, reducing manufacturing cost.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to electric motors and, more particularly, to methods and apparatus for reducing vibration in a rotor core assembly for electric motors.  
           [0002]    Electric motors are used in many applications worldwide. Typically, the rotational force and torque generated within the motor is delivered by a rotor shaft. The torque generated is the product of current applied to the motor and an electromagnetic field maintained about stator. When a rotor-generated magnetic field enters a stator-generated magnetic field the rotor tends to speed up and when the rotor magnetic field leaves the stator magnetic field the rotor tends to slow down. The torque produced is therefore non-uniform and known to those in the art as torque ripple or cogging. Torque ripple, and various machine imperfections, may generate objectionable noise and vibration at the motor shaft in some applications.  
           [0003]    One example of such an application occurs when a motor drives a fan. Imbalances in the fan, combined with torque ripple, generate vibrations which are transmitted to the motor and fan mounting. These vibrations generate undesirable noise. Continued exposure over time to such vibrations loosens motor and fan assemblies, and ultimately could cause failure of the motor. Damping systems are typically employed to minimize the effects of the vibrational energy induced into the motor and fan system.  
         SUMMARY OF INVENTION  
         [0004]    In an exemplary embodiment, a resilient rotor mounting assembly facilitating a simplified assembly with fewer press operations includes a first resilient ring, a second resilient ring and a substantially tubular spacer. The resilient rings and the spacer are fabricated from center punch laminates generated from a stator laminate bore punch process. The resilient rings attach to opposite ends of the spacer. The resilient rings each include a central bore with a diameter to receive the rotor shaft. The diameter of the first resilient ring central bore is larger than the diameter of the second resilient ring central bore. The rotor shaft includes a first knurled portion and a second knurled portion, each sized to fit the bore diameter of one of the resilient rings. The first knurled portion has a larger diameter and is distal from a press used in the press operations. In the exemplary embodiment the second resilient ring includes two apertures in addition to the central bore.  
           [0005]    A method of constructing the resilient mounting assembly includes fabricating the resilient rings and the spacer from center blank laminates produced from a stator laminate bore punch process. The resilient rings include a resilient insert. An operator attaches the resilient rings to the spacer and inserts the rotor shaft in the resilient mounting assembly. The first resilient ring passes over the second knurled portion. The operator inserts a press pin through the aperture in the second resilient ring and into contact with the first resilient ring. A press pin shoulder is also positioned against the second resilient ring. The press simultaneously presses both resilient rings onto the rotor shaft knurled portions in one operation, reducing manufacturing cost.  
           [0006]    During operation, non-uniform magnetic fields of the motor generate torque ripple in the rotor core. The resilient inserts of the rotor mounting assembly damp vibrations generated as a result of such torque ripple. Reductions in torque ripple reduce vibrations and noise of the motor. As a result, more complex and expensive damping systems may be eliminated. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0007]    [0007]FIG. 1 is an exploded perspective view of a motor.  
         [0008]    [0008]FIG. 2 is an enlarged top view of a punched laminate element.  
         [0009]    [0009]FIG. 3 is side view of an exemplary embodiment of a rotor shaft.  
         [0010]    [0010]FIG. 4 is cross-sectional view of an exemplary embodiment of a laminated rotor mounting assembly.  
         [0011]    [0011]FIG. 5 is a side view of a first resilient ring of the laminated rotor mounting assembly of FIG. 4.  
         [0012]    [0012]FIG. 6 is a side view of a second resilient ring of the laminated rotor mounting assembly of FIG. 4.  
         [0013]    [0013]FIG. 7 is a cross-sectional view of an inner metal insert of the rotor mounting assembly of FIG. 6.  
         [0014]    [0014]FIG. 8 is an enlarged cross-sectional view of an alternative inner metal insert. 
     
    
     DETAILED DESCRIPTION  
       [0015]    [0015]FIG. 1 is an exploded perspective view of a motor  10  including a housing  12 , a stator assembly  14  and a rotor assembly  16 . Housing  12  includes a pair of end shields  18 ,  20  and a shell  22 . Stator assembly  14  mounts in housing  12  and includes a stator core  24  with a stator bore  26  extending therethrough. Stator core  24  provides support for a plurality of stator windings  28 . In one embodiment, stator bore  26  is substantially cylindrical about a central axis  30 . In one embodiment, motor  10  is an electronically commutated motor for use in heating, ventilation, and air conditioning (HVAC) systems such as a GE 39 Frame motor commercially available from General Electric Company, Schenectady, N.Y., and manufactured in Springfield, Mo.  
         [0016]    Rotor assembly  16  is positioned within stator bore  26  and includes a rotor core  32 , a rotor mounting assembly  34 , and a rotor shaft  36 . Rotor shaft  36  is substantially cylindrical and concentric about axis  30 . Rotor mounting assembly  34  extends axially through rotor core  32  and rotor shaft  36  extends axially through rotor mounting assembly  34 .  
         [0017]    [0017]FIG. 2 is an enlarged top view of a punched laminate element  42 . Stator core  24  is fabricated from multiple laminate elements  42 . Specifically, stator bore  26  is formed by punching a center blank lamination  44  from each laminate element  42  and the subsequent interlocking of the laminate elements  42 . As described below, an insert lamination  46 , an outer ring lamination  48 , and a spacer lamination  50  are formed by punching a center blank lamination  44 .  
         [0018]    [0018]FIG. 3 is a side view of an exemplary embodiment of rotor shaft  36 . As illustrated, rotor shaft  36  includes a first knurled portion  52  and a second knurled portion  54 . First knurled portion  52  is knurled to facilitate a secure press fit relationship and has a first outside diameter  56 . Second knurled portion  54  is also knurled and has a second outside diameter  58 . In an exemplary embodiment first outside diameter  56  is larger than second outside diameter  58 . In an exemplary embodiment a first knurled set  60  is formed on first knurled portion  52  and includes a spaced arrangement of a plurality of first knurls  62 . A second knurled set  64  is formed on second knurled portion  54  and also includes a spaced arrangement of second knurls  66 . In an exemplary embodiment shaft  36  includes a third outside diameter  68 .  
         [0019]    [0019]FIG. 4 is a cross-sectional view of an exemplary embodiment of laminated rotor mounting assembly  34 . Rotor mounting assembly  34  includes a first resilient ring  80 , a second resilient ring  82  and a laminated spacer  84 . First resilient ring  80  includes a first inner metal insert  86  and a first resilient insert  88 . Second resilient ring  82  includes a second inner metal insert  90  and a second resilient insert  92 .  
         [0020]    [0020]FIG. 5 is a side view of first resilient ring  80  of laminated rotor mounting assembly  34  of FIG. 4. FIG. 6 is a side view of second resilient ring  82 . As shown in FIGS. 4, 5 and  6 , resilient inserts  88 ,  92  circumferentially abut inner metal inserts  86 ,  90 . First inner metal insert  86  includes a first central bore  94  with a first inner diameter  96 . As illustrated in FIG. 6, second inner metal insert  90  includes a second central bore  98  with a second inner diameter  100 . In an exemplary embodiment first inner diameter  96  is larger than second inner diameter  100 . Each central bore  94 ,  98  receives rotor shaft  36 . First central bore  94  is sized to pass over second knurled portion  54  and facilitate a secure press fit relationship between first inner metal insert  86  and first knurled portion  52 . Second central bore  98  is sized to facilitate a secure press fit relationship between second inner metal insert  90  and second knurled portion  54 .  
         [0021]    In an alternative embodiment shown in FIG. 5, first central bore  94  includes a third knurled set  102  of spaced apart third knurls  104  complementary to second knurled set  64 , arranged to pass axially between second knurls  66  of second knurled portion  54 , while facilitating a secure press fit relationship between first inner metal insert  86  and first knurled portion  52 . In an alternative embodiment (not shown), second central bore  98  also included a fourth knurled set (not shown) to facilitate a secure press fit between second inner metal insert  90  and second knurled portion  54 .  
         [0022]    As shown in FIGS. 4 and 5 first inner metal insert  86  includes an external side  112  and an internal side  114 . As shown in FIGS. 4 and 7 second inner metal insert  90  includes an external side  116  and an internal side  118 . In an exemplary embodiment, shown in FIGS. 4 and 7, second inner metal insert  90  includes two apertures  120 ,  122  extending axially through the second inner metal insert  90  from the external side  116  to the internal side  118 .  
         [0023]    In an alternative embodiment, illustrated in FIG. 8, apertures  120 ,  122  each include an open boundary with central bore  98 , forming a non-circular central bore having lobes  124 ,  126 .  
         [0024]    Inner metal insert  86 ,  90  each include an outer cylindrical edge  134 ,  136 . In one embodiment, outer cylindrical edges  134 ,  136  are scalloped, as illustrated in FIGS. 5 and 6 to facilitate coupling between inner metal inserts  86 ,  90  and resilient inserts  88 ,  92 . In one embodiment, as shown in FIGS. 2 and 7 for inner metal insert  90 , each inner metal insert  86 ,  90  is fabricated from a plurality of insert laminations  46  punched from center blank laminations  44 . Insert laminations  46  are interlocked to provide cost-effective and reliable inner metal inserts  86 ,  90 .  
         [0025]    In the exemplary embodiment each resilient ring  80 ,  82  further includes a laminated outer annular ring  144 ,  146  which circumferentially abut resilient inserts  88 ,  92 . Each laminated outer annular ring  144 ,  146  is fabricated from a plurality of punched outer ring laminations  48 , as shown in FIG. 2. In one embodiment, center blank laminations  44  are punched to fabricate outer ring laminations  48 . Outer ring laminations  48  are interlocked to form specifically sized, laminated outer annular rings  144 ,  146 .  
         [0026]    As illustrated in FIGS. 4 and 5, first laminated outer annular ring  144  in first resilient ring  80  includes an interior radial face  152  and an external radial face  154 . As illustrated in FIGS. 4 and 6, second laminated outer annular ring  146  in second resilient ring  82  includes an interior radial face  158  and an external radial face  160 .  
         [0027]    Laminated spacer  84  includes an outer cylindrical surface  162 , an inner surface  164 , a first radial side  166  and a second radial side  168 , and has a thickness  170  between outer cylindrical surface  162  and inner surface  164 . In one embodiment, outer cylindrical surface  162  receives magnets, as used in a brushless DC motor, wherein outer cylindrical surface  162  is sized to facilitate attachment of arc magnets. Inner surface  164  does not contact rotor shaft  36 . Thickness  170  may be varied to optimize laminated spacer mass for noise reduction. In one embodiment, laminated spacer  84  includes a pair of axial openings  172 ,  174 , positioned to align with apertures  120 ,  122 . First radial side  166  of laminated spacer  84  attaches to interior radial face  152  of outer annular ring  144 , and second radial side  168  attaches to interior radial face  158  of outer annular ring  146 .  
         [0028]    Laminated spacer  84  is fabricated using center blank laminations  44 . In one embodiment, laminate element  42  is punched and laminated to produce stator bore  26  in stator core  24 . Punched center blank laminations  44  are punched to form spacer laminations  50 . Spacer laminations  50  are interlocking to form laminated spacer  84 . In an alternative embodiment, center blank laminations  44  are sized and punched during the stator bore  26  punching. Spacer laminations  50  are interlocked by methods known in the art, such as adhesive bonding, mechanical pinning, interlocking features or welding.  
         [0029]    Resilient inserts  88 ,  92  are fabricated from a suitable rubber material or elastomer. As is known in the art, an insert molding, transfer molding or press process is used to install resilient inserts  88 ,  92  between inner metal inserts  86 ,  90  and outer annular rings  144 ,  146 .  
         [0030]    In constructing resilient mounting assembly  34 , resilient rings  80 ,  82  and spacer  84  are fabricated from resilient inserts  88 ,  92  and center blank laminations  44  produced from a stator laminate bore punch process. Inner metal inserts  86 ,  90 , outer annular rings  144 ,  146 , and laminated spacer  84  are assembled from insert laminations  46 , outer ring laminations  48 , and spacer laminations  50  punched from center blank laminations  44 . In one embodiment, shown in FIG. 2, dimensions of insert laminations  46 , outer ring laminations  48 , and spacer laminations  50  are formed during the initial stator laminate bore punch process. In an alternate embodiment, center blank laminations  44  are punched separately to the desired dimensions. Insert laminations  46 , outer ring laminations  48 , and spacer laminations  50  are then interlocked by methods known in the art such as adhesive bonding, mechanical pinning, interlocking features or welding to fabricate inner metal inserts  86 ,  90 , outer annular rings  144 ,  146 , and laminated spacer  84 . The interlocked laminates may be machined prior to assembly of resilient mounting assembly  34 .  
         [0031]    The operator attaches resilient rings  80 ,  82  to spacer  84 . In one embodiment the operator secures arc magnets to resilient rings  80 ,  82  and spacer  84 , completing rotor assembly  16  with the exception of installation of rotor shaft  36 . This allows for reduced handling of rotor shaft  36  and more flexible assembly procedures. The operator inserts rotor shaft  36  in the resilient mounting assembly  34 . First resilient ring  80  passes over second knurled portion  54  and shaft  36  until it abuts first knurled portion  52 . Second resilient ring  82  will abut second knurled portion  54 . The operator inserts a pair of press pins  190 , shown in FIG. 4, each including a stepped portion  192 , through apertures  120 ,  122  in the second resilient ring  82  and into contact with internal side  114  of first resilient ring  80 . Stepped portions  192  are in contact with external side  11   6  of second resilient ring  82 . In another embodiment, multiple pairs of press pins (not shown) are used to press both resilient rings  80 ,  82 . The operator operates the press (not shown) to simultaneously press both resilient rings  80 ,  82  into a press fit relationship with the rotor shaft knurled portions  52 ,  54  from one axial direction, in one operation, reducing manufacturing cost.  
         [0032]    During operation, as motor  10  is energized, rotor core  32  (shown in FIG. 1) rotates to align with a magnetic field generated within stator assembly  14  (shown in FIG. 1). As torque ripple occurs in rotor core  32 , resilient inserts  88 ,  92  of rotor mounting assembly  34  damp vibrations and non-uniform torque transmitted to rotor shaft  36 . As a result, motor  10  operation is quiet and smooth. More complex and expensive damping systems may be eliminated. Laminated outer annular rings  144 ,  146  and laminated spacer  84  contribute to a reliable and cost-effective assembly between rotor shaft  36  and rotor core  32 .  
         [0033]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.