Abstract:
A brushless permanent magnet (BPM) electric machine including a segmented stator having interconnected stator segment assemblies defining M stator teeth. Each of said M stator teeth having substantially the same axially facing size and shape. N coil windings are individually wound about the stator teeth. N&lt;M.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to electric machines, and more particularly to a reduced coil segmented stator for an electric machine.  
       BACKGROUND OF THE INVENTION  
       [0002]     Electric machines, such as motors and generators, typically include a stator that is mounted inside a housing and a rotor that is supported for rotation relative to the stator. Electric machines are often integrated into devices such as appliances. The size, capacity and/or cost of the device incorporating the electric machine may be an important factor in the purchasing decision. These factors also have a significant impact on the overall size, capacity and cost, respectively, of the device.  
       SUMMARY OF THE INVENTION  
       [0003]     Accordingly, the present invention provides a brushless permanent magnet (BPM) electric machine including a segmented stator having interconnected stator segment assemblies defining M stator teeth. Each of said M stator teeth have substantially the same axially facing shape and size. N coil windings are individually wound about the stator teeth, where N&lt;M.  
         [0004]     In other features, the first plurality includes M stator teeth and the second plurality includes N=M/2 coil windings. M can be equal to 12.  
         [0005]     In still another feature, the second plurality of coil windings are electrically interconnected to define three phases.  
         [0006]     In yet another feature, the BPM electric machine further includes a rotor having a plurality of permanent magnets disposed thereabout.  
         [0007]     In yet another feature, the N coil windings are wound about every other one of the M stator teeth.  
         [0008]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0010]      FIG. 1  is a schematic illustration of an exemplary brushless permanent magnet (BPM) electric machine according to the present invention;  
         [0011]      FIG. 2  is a more detailed view of a portion of  FIG. 1  illustrating a coil winding cross-section;  
         [0012]      FIG. 3  is a more detailed view of a portion of  FIG. 1  illustrating an alternative coil winding cross-section; and  
         [0013]      FIG. 4  is a more detail view of a portion of  FIG. 1  illustrating an alternative stator segment core.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     The following detailed description provides preferred exemplary embodiments only and is not intended to limit the scope, applicability or configuration of the present invention. Rather, the detailed description of the preferred exemplary embodiments will provide those skilled in the art with an enabling description for implementing the preferred exemplary embodiments of the present invention. It will be understood that various changes may be made in the function and arrangement of the elements without departing from the spirit and scope of the invention as set forth in the appended claims.  
         [0015]     Referring now to  FIG. 1 , an electric machine  10  is shown and includes a housing  12 , a segmented stator  14  mounted in the housing  12 , and a rotor assembly  16  supported for rotation relative to the segmented stator  14 . The electric machine  10  is a brushless permanent magnet (BPM) electric machine. While the present invention is being described in conjunction with BPM electric machines, skilled artisans will appreciate that other types of electric machines may be employed.  
         [0016]     The segmented stator  14  includes a plurality of stator segment assemblies  18  that can be individually assembled and subsequently combined to define the segmented stator  14 . As will be detailed, each stator segment assembly  18  includes a stator segment core  20  that forms a stator tooth  22 , a key  21  and a slot  23 . The stator teeth  22  of all of the stator segment assemblies  18  have substantially identical size and profiles. As a result, a single type of stator segment assembly  18  is used, which reduces cost.  
         [0017]     The keys  21  and slots  23  of the individual stator segment cores  20  interconnect. As can be appreciated, the keys  21  and slots  23  may include mating profiles having other shapes. Alternatively, the keys  21  and slots  23  may be omitted. Selective stator segment assemblies include coil windings  24  that are wound around the stator tooth  22 , in accordance with the present invention. More particularly, every other segmented stator assembly  18  includes a coil winding  24 . The number of coil windings N is defined according to the following relationship:
 
 N=M/ 2, wherein  M =# of stator teeth
 
         [0018]     The coil windings  24  are wound about the selective stator teeth  22  to define three phases A, B and C as single-layer or double-layer concentrated windings. That is to say, a single phase is wound about a single stator tooth  22  and is not distributed across multiple stator teeth, as would occur in a distributed winding scheme. The exemplary segmented stator  14  includes twelve (12) stator segment assemblies  18  and six (6) coil windings  24 . The assembled segmented stator  14  defines twelve ( 12 ) slots between the stator teeth  22 .  
         [0019]     The rotor assembly  16  includes a rotor core  26  having a plurality of permanent magnets  28  distributed therearound. The exemplary rotor assembly  16  includes eight (8) permanent magnets defining eight (8) poles. Although the exemplary electric machine  10  is a 3-phase, 12-slot, 8-pole BPM electric machine having 6-coils, it is anticipated that the reduced coil windings of the present invention can be implemented in other segmented stator electric machines including, but not limited to, a 3-phase, 18-slot, 12-pole BPM electric machine having 9 coils.  
         [0020]     When assembling the electric motor  10 , the individual stator segment assemblies  18  are initially assembled. As discussed above, only select stator segment assemblies  18  are wound with the coil windings  24 . The non-wound and pre-wound stator segment assemblies  18  are assembled together to form the segmented stator  14 . The coil windings  24  of the pre-wound stator segment assemblies are connected to define a circuit in a manner known in the art. More particularly, leads (not shown) of the individual coil windings  24  are electrically connected such that the phases A, B and C induce alternating eddy currents when an electrical current is applied. The eddy currents induce rotation of the rotor.  
         [0021]     Segmented stator assemblies provide specific advantages over other stator assemblies known in the art, such as single-piece stator assemblies. Segmented stator assemblies provide an improved power density over a single-piece stator assembly having an equivalent number of coil windings. More particularly, because the coil windings are pre-wound prior to assembling the stator segment assemblies, the slot fill between the stator teeth  22  can be increased. This is because the winding mechanism is not obstructed by adjacent stator teeth  22 . As a result, a segmented stator assembly includes a higher power density, which enables a higher torque output than a similarly sized, single-piece stator electric motor having an equivalent number of windings. Accordingly, the reduced coil segmented stator assembly  14  of the present invention provides a higher power density than a reduced coil single-piece stator assembly.  
         [0022]     The reduced coil winding construction achieves significant gains in the manufacturing process. More particularly, less material (e.g., coil wire) is required to manufacture the electric machine  10 . In this manner, material cost is reduced. Further, because there are fewer coils than a conventional electric machine  10 , there are fewer coil leads to connect during the manufacturing process. In this manner, the manufacturing process is simplified and manufacturing costs are reduced. Additionally, because the coil windings are completely separated, the potential for shorting is reduced and phase insulation is generally not required. Because the segmented stator assembly  14  provides a higher power density per coil than an equivalently sized single-piece stator electric machine, the reduction in power density that results from the reduced number of winding coils  24  is not as severe as would be in a reduced coil single-piece stator electric machine.  
         [0023]     Referring now to  FIGS. 2 and 3 , because N=M/2, there is more slot space  29  available between the stator teeth  22 . As a result, each coil winding  24  can include more turns than would be possible in an equivalently sized single-piece stator electric machine having a full-winding construction (i.e., N=M). More specifically, the dashed lines indicate the mid-point of the slot spaces  29 . Traditionally, coil windings were limited to a cross-section that extended at or near the mid-point of the slot spaces  29  due to adjacent coil windings (see  FIG. 2 ). The reduced coil winding construction of the present invention enables the coil windings  24  to extend past the mid-point of the slot spaces  29  because there is no adjacent coil winding.  
         [0024]     As an example, in a full-winding construction (i.e., N=M) electric machine, each coil winding may be limited to 100 turns because of the limited slot space between adjacent coil windings. In the electric machine  10 , the coil windings  24  could achieve greater than 100 turns each (e.g., 200 turns). In this manner, the power density of the reduced coil winding electric machine  10  can be improved. It is also anticipated that the cross-section of coil windings  24  can vary to achieve the desired number of turns. Square, rectangular and trapezoidal-shaped cross-sections are exemplary cross-sections that can be implemented. Because the coil windings  24  can be pre-wound on the stator segment assemblies  18 , the cross-section can be easily shaped to accommodate the desired number of windings.  
         [0025]     Referring now to  FIG. 4 , an alternative stator segment core  20 ′ is illustrated and includes a straight back surface  40  that extends perpendicular to the adjacent stator tooth  22 . The coil windings  24  run adjacent to the back surface  40 . In this manner, the slot space  29  is more effectively used.  
         [0026]     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.