Abstract:
A rotor mount assembly, located between a rotor shaft and a plurality of magnetic elements, resiliently damps vibrations induced from the plurality of magnetic elements. The rotor mount assembly includes a first resilient ring, a second resilient ring, and a laminated spacer. The laminated spacer includes laminates from a stator core center punch. Both resilient rings include an inner metal insert which, in one embodiment, comprises laminates.

Description:
BACKGROUND OF INVENTION 
     This invention relates generally to electric motors and, more particularly, to methods and apparatus for reducing vibration in a rotor assembly for electric motors. 
     Electric motors are used in countless varieties and 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 in a 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 produces objectionable noise and vibration at the motor shaft in some applications. 
     One example of such an application occurs when a motor drives a fan. Imbalances in the fan, combined with torque ripple, produce vibrations which are transmitted to the motor and fan mounting. These vibrations produce undesirable noise. Continued exposure over time to such vibrations loosens motor and fan assemblies, and ultimately 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 
     A motor that includes a laminated rotor mounting assembly facilitates reducing or eliminating torque ripple and vibrations produced in a rotor core is described. The motor includes a stator assembly and a rotor assembly within a housing. The rotor assembly includes a rotor shaft, a plurality of magnetic elements and a rotor mounting assembly therebetween. The rotor mounting assembly includes a pair of resilient rings and a laminated spacer. Each resilient ring includes an inner metal insert and a resilient insert. In the exemplary embodiment the resilient ring includes a laminated outer annular ring which attaches to the laminated spacer. In another embodiment the laminated spacer circumferentially encloses the resilient ring. The inner metal insert attaches to the rotor shaft and the magnetic elements attach to the outer cylindrical surface of the spacer. 
     During operation, the rotor assembly rotates to align with a magnetic field generated within the stator assembly. The non-uniform magnetic fields generate torque ripple in the rotor core. The resilient inserts of the rotor mounting assembly damp vibrations and noise that may be 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. The laminated outer annular ring and laminated spacer provide a reliable and cost-effective interface between the resilient inserts and the plurality of magnetic elements. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is an exploded perspective view of a motor. 
     FIG. 2 is an enlarged top view of a laminate element. 
     FIG. 3 is cross-sectional view of an exemplary embodiment of a laminated rotor core assembly. 
     FIG. 4 is a side view of a resilient ring of the laminated rotor mounting assembly of FIG.  3 . 
     FIG. 5 is a cross-sectional view of an inner metal insert of the rotor mounting assembly of FIG.  3 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is an exploded perspective view of a motor  10  including a motor housing assembly  14 . Motor housing assembly  14  includes end shields  16 ,  18  and a shell  20 . End shields  16 ,  18  connect to shell  20  with a plurality of fasteners (not shown) such that a cavity is defined by end shields  16 ,  18  and shell  20 . In one embodiment, end shields  16 ,  18  are cast aluminum and shell  20  is rolled and welded steel. 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, Plainville, Conn., and manufactured in Springfield, Miss. 
     A stator assembly  24  and a rotor assembly  26  are positioned within the cavity created by end shields  16 ,  18  and shell  20 . Stator assembly  24  includes a stator core  28  with a stator bore  30  extending therethrough. Stator core  28  provides support for a plurality of stator windings  32 . FIG. 2 is an enlarged top view of a laminate element  34 . Stator core  28  is fabricated from a plurality of laminate elements  34 . Specifically, stator bore  30  is formed by punching a center blank lamination  36  from each laminate element  34  and the subsequent interlocking of the laminate elements  34 . In an exemplar embodiment, stator bore  30  is substantially cylindrical about a central axis  38 . 
     Rotor assembly  26  is positioned within stator bore  30  and includes a rotor core  40 , a plurality of magnetic elements  41 , a rotor mounting assembly  42 , a rotor shaft  44 , and an outer rotor surface  45 . Rotor shaft  44  is substantially concentric about axis  38  and rotor shaft  44  axially extends through rotor mounting assembly  42 . Rotor mounting assembly  42  supports magnetic elements  41 . 
     Rotor mounting assembly  42  includes a first resilient ring  46 , a second resilient ring  48  and a laminated spacer  50 . Each resilient ring  46 ,  48  includes an inner metal insert  52  and a resilient insert  54 . As shown in FIGS. 3 and 4, resilient insert  54  circumferentially encloses and abuts inner metal insert  52 . Since resilient rings  46 ,  48  are substantially identical, only resilient ring  46  is described. Resilient ring  46  includes an external end  58  and an interior end  60 . 
     Inner metal insert  52  circumferentially attaches to rotor shaft  44 . In one embodiment, rotor shaft  44  includes a pair of knurled portions  62  that facilitate a secure press fit relationship between rotor shaft  44  and inner metal insert  52 . Inner metal insert  52  includes an outer cylindrical edge  64 . In one embodiment, outer cylindrical edge  64  is scalloped, as illustrated in FIG. 4, to facilitate coupling between inner metal insert  52  and resilient insert  54 . In one embodiment, inner metal insert  52  is fabricated from a plurality of insert laminations  56  punched from a plurality of center blank laminations  36 . Insert laminations  56 , punched to specific dimensions are interlocked to provide a cost-effective and reliable inner metal insert  52 . 
     Laminated spacer  50  includes an outer cylindrical surface  66 , an inner cylindrical surface  68 , a first radial side  70  and a second radial side  72 , and has a thickness  74  between outer cylindrical surface  66  and inner cylindrical surface  68 . Laminated spacer  50  is fabricated from a plurality of spacer laminations  79  punched from a plurality of center blank laminations  36  as shown in FIG.  2 . In one embodiment, spacer laminations  79  are punched and interlocked to form laminated spacer  50 . Outer cylindrical surface  66  is sized to accommodate magnetic elements  41 . Magnetic elements  41  attach to outer cylindrical surface  66  of laminated spacer  50  and define outer rotor surface  45 . In one embodiment, magnetic elements  41  include arc magnets as used in a brushless DC motor, wherein outer cylindrical surface  66  is sized to facilitate attachment of arc magnets. In an exemplary embodiment, magnetic elements  41  are secured to outer cylindrical surface  66  by adhesive (not shown). Inner cylindrical surface  68  does not contact rotor shaft  44 . Thickness  74  may be varied to optimize laminated spacer mass for noise reduction. 
     In the exemplary embodiment resilient ring  46  further includes a laminated outer annular ring  76 , which circumferentially encloses and abuts resilient insert  54 . Laminated outer annular ring  76  is fabricated from a plurality of outer annular ring laminations  77  formed from a plurality of center blank laminations  36 . In one embodiment, as illustrated in FIG. 2, outer annular ring laminations  77  are punched and interlocked to form laminated outer annular ring  76 . As illustrated in FIGS. 3 and 4, laminated outer annular ring  76  includes an outer cylindrical portion  78 , an interior radial face  80 , and an external radial face  82 . Interior radial face  80  attaches to first radial side  70  of laminated spacer  50 . In one embodiment, shown in FIG. 3, interior radial face  80  interlocks with laminated spacer  50  to extend outer cylindrical surface  66 . In the exemplary embodiment interior radial face  80  is substantially coplanar with interior end  60 . 
     In an alternative embodiment, laminated spacer  50  circumferentially encloses resilient ring  46 , which does not include a laminated outer annular ring. Rather, laminated spacer  50  extends to external end  58  of resilient ring  46 . 
     Laminated spacer  50  is fabricated using methods known in the art. In one embodiment, laminate elements  34  are punched and laminated to form stator bore  30  in stator core  28 . The punched out center blank laminations  36  are further punched to form spacer laminations  79  which are interlocking to form laminated spacer  50 . In an alternative embodiment, center blank laminations  36  may be specifically sized and spacer laminations  79  punched during the stator bore punching. Spacer laminations  79  are interlocked by methods known in the art, such as adhesive bonding, interlocking features, mechanical pinning, or welding. 
     Resilient insert  54  is fabricated from a suitable rubber material or elastomer. As is known in the art, an insert molding or transfer molding press process is used to attach resilient insert  54  to inner metal insert  52 . 
     During operation, as motor  10  is energized, magnetic elements  41  (shown in FIG. 1) rotate to align. with a magnetic field. generated within stator assembly  24  (shown in FIG.  1 ). As torque ripple occurs in magnetic elements  41 , resilient insert  54  of rotor mount assembly  42  damps vibrations and non-uniform torque transmitted to rotor shaft  44 . As a result, motor operation is quiet and smooth. More complex and expensive damping systems may be eliminated. Laminated outer annular ring  76  and laminated spacer  50  contribute to a reliable and cost-effective assembly between rotor shaft  44  and magnetic elements  41 . 
     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.