Abstract:
An electric motor includes a rotor cup housing having an annular flange extending circumferentially from a sidewall. The motor further includes a stator including a stator core having a winding thereon and a rotor positioned at least partially around the stator. A rotor shaft is positioned at least partially within the stator.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates generally to electric motors and more particularly to rotor cups used with electric motors.  
           [0002]    Electric motors that include external rotors are also known as inside out motors, and include magnetic elements mounted on an inner surface of a cup-shaped rotor bell. A stator is located inside a plurality of permanent magnets on the rotor bell. The stator and its supporting structure are shaped to receive a bearing for rotatably mounting a rotor shaft through the stator so that the shaft and rotor bell may rotate relative to the stator. The rotor bell rotates as a result of the magnetic interaction of the permanent magnets and magnetic fields created by energizing windings of the stator.  
           [0003]    During motor operation the rotor spins, and if the weight distribution of the rotor is not balanced, unwanted vibration is induced within the motor. Vibration generates vibratory stresses within various motor components. These stresses degrade operating performance of the motor and reduce its useful life. Therefore, a balanced rotor reduces operational vibration and improves motor life. If a part is press-fit onto the rotor cup, the cup must be supported without allowing forces to be transmitted to the motor bearings. If the cup is not properly supported, the bearings may be damaged, thus reducing product lifetime or increasing audible noise. To facilitate balancing the rotor, various types of balancing rings are added to the rotor cups, and these rings provide a place to add or remove material to achieve the desired rotor balance. The rings constitute additional parts which increase the process cost of the product.  
           [0004]    Many times magnets are not press-fit into the rotor cup, but rather are fitted to include a gap between the cup and the magnet. The gap is filled with an adhesive. This gap requires additional fixtures to hold the magnet in a desired position concentric to the rotor cup to maintain proper balance. If concentricity is not tightly maintained, balance is sacrificed. At times, the magnet is press-fit into the rotor cup and pushing the magnet into the rotor cup results in the magnet breaking, resulting in higher manufacturing costs.  
           [0005]    When press-fitting components onto a rotor cup, the roundness of a rotor cup is difficult to maintain to a tight tolerance and is often accomplished by making multiple strikes on the part during the forming operation or by increasing the thickness of the material. Increasing material thickness and making multiple strikes increase the product cost.  
           [0006]    It would be desirable to reduce operational vibration and improve the roundness of stamped rotor cups. It would be further desirable for the rotor cup to have a surface for supporting the rotor cup while a load is attached. It would be still further desirable to provide a smooth surface for lead-in when pressing an item, such as a molded permanent magnet, into the rotor cup.  
         SUMMARY OF INVENTION  
         [0007]    In an exemplary embodiment of the invention, an electric motor includes a rotor cup assembly including a rotor cup housing having a unitary annular flange. The rotor cup housing further includes a top, a bottom, a circumferential sidewall and a cavity defined by the sidewall and the top. The annular flange is a ring which extends circumferentially from the rotor cup sidewall. The annular flange increases stiffness of the rotor cup. In addition, the annular flange provides a large surface area that allows the removal or addition of material to dynamically or statically balance the rotor. Furthermore, the annular flange provides a smooth-surface for lead-in when pressing an item, such as a molded permanent magnet, into the rotor cup. The integrated annular flange assists in maintaining the shape of the rotor cup and results in improving rotor cup balance. As a result, a cost-effective and reliable external rotor cup is provided. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]    [0008]FIG. 1 is a perspective view of a known rotor cup.  
         [0009]    [0009]FIG. 2 is a perspective view of a rotor cup with an annular flange in accordance with one embodiment of the present invention.  
         [0010]    [0010]FIG. 3 is a perspective view of an inside-out motor including the flanged rotor cup shown in FIG. 2.  
         [0011]    [0011]FIG. 4 is a side view of the motor shown in FIG. 3 in a position to be attached to a load.  
         [0012]    [0012]FIG. 5 is a perspective view of the rotor cup flange shown in FIG. 2 in a position to receive a magnet. 
     
    
     DETAILED DESCRIPTION  
       [0013]    [0013]FIG. 1 is a perspective view of a known rotor cup  10  including a closed end  12 , an open end  14 , and a sidewall  16  extending between open end  14  and closed end  12 . Open end  14  is defined by a lower edge  18  of sidewall  16  and includes a substantially uniform circumferential thickness  20 .  
         [0014]    [0014]FIG. 2 is a perspective view of a rotor cup  22  including an annular flange  24 . In one embodiment, flange  24  is unitary with rotor cup  22 . Rotor cup  22  further includes a circumferential sidewall  26  having a first diameter  28 , a top surface  30 , and an open bottom  32 . Sidewall  26  has a height  34  measured between top surface  30  and a top edge  36  of annular flange  24 . Annular flange  24  is fabricated from the same material as rotor cup  22 . In one embodiment, annular flange  24  is fabricated from stamped steel. Annular flange  24  is substantially circular in shape and has an inside diameter  28  and an outside diameter  40 . Inside diameter  38  is smaller than outside diameter  40 . Annular flange  24  has a height  42  measured between a bottom edge  44  and top edge  36 . In addition, annular flange  24  is outwardly flared from sidewall  26  by an angle φ measured between sidewall  26  and bottom edge  44 . Angle φ permits annular flange  24  to have an outwardly flared curved edge  46  which allows rotor cup  22  to lay flat on a surface (not shown in FIG. 2).  
         [0015]    Annular flange  24  increases rotor cup  22  stiffness. In addition, because curved edge  46  is outwardly flared by an angle φ, edge  46  provides additional surface area and strength to support rotor cup  22 .  
         [0016]    [0016]FIG. 3 is a perspective view of an inside-out motor  50  including flanged rotor cup  22  shown in FIG. 2. Rotor cup  22  includes annular flange  24  and top surface  30 . Sidewall  26  extends to top surface  30  so that a top edge  52  is rounded. Inside-out motor  50  further includes a rotor shaft  54 , a rotor  56 , a stator (not shown), and a frame  58 . Rotor shaft  54  is mounted on frame  58  which is attached to the stator such that rotor  56  rotates freely relative to the stator without contacting the stator. In one embodiment, rotor cup  22  is balanced to rotate without vibration. Annular flange  24  permits weights to be attached to flange  24  to achieve a desired level of rotor balance. In another embodiment, material is machined away from flange  24  to achieve a desired level of rotor balance.  
         [0017]    [0017]FIG. 4 is a side view of inside-out motor  50  shown in FIG. 3 positioned to be attached to a load  60 . In one embodiment, load  60  is a fan. Inside-out motor annular flange  24  rests on a surface  62  of a tooling apparatus  64  while supporting rotor cup  22 . Load  60  is pressed onto rotor cup  22  in a vertical direction  66 . Annular flange  24  provides a smooth surface when load  60  is pressed onto rotor cup  22 . Annular flange  24  has an increased surface area because of outwardly flared edge  37  (shown in FIG. 2).  
         [0018]    [0018]FIG. 5 is a perspective view of rotor cup  22  including annular flange  24  positioned to receive a magnet  68 . Annular flange  24  is configured in a lead-in position to receive circumferential magnet  68 . Annular flange  24  is outwardly flared by an angle φ and is tapered which assists to guide magnet  68  into rotor cup  22 .  
         [0019]    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.