Abstract:
The apparatus of the present invention provides a stator for an electric motor. The apparatus includes a plurality of stator components assembled together to form a generally annular stator core. A wire is wrapped around at least a portion of the stator core to form a stator winding. A first generally annular end plate and a second generally annular end plate are mounted to axially opposite sides of the stator core such that the stator core is axially trapped and retained therebetween. A fastener applies a clamping load to the first and second end plates such that the stator core is compressed therebetween. The clamping load from the fastener is applied directly to the first and second end plates which distribute the clamping load to the stator core such that the plurality of components are held together without the fastener directly applying the clamping load to the stator core. A corresponding method for providing a stator is similarly provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of U.S. patent application Ser. No. 11/402,541, filed Apr. 12, 2006, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention pertains generally to a method and apparatus for assembling a stator of an electric motor.  
       BACKGROUND OF THE INVENTION  
       [0003]     It is known to construct an electric motor using three or more concentrated windings wherein one or more of the windings are provided for each of three electrical phases. These windings can distribute magnetic flux to multiple poles of the stator in the electric motor. Such a motor is three-dimensional, in that the magnetic flux passing through the concentrated winding is conducted both around the circumference and along the axis of the motor in the stator.  
         [0004]     Manufacturing and assembling a three-phase electric motor includes producing a plurality of motor components having relatively complex geometries, and performing additional processing steps such as, for example, winding the stator wire around the stator core teeth in a predefined pattern. In an effort to reduce manufacturing costs, a plurality of component segments may be pre-formed and assembled together to produce the motor.  
       SUMMARY OF THE INVENTION  
       [0005]     The apparatus of the present invention includes a plurality of stator components composed of generally insulated ferromagnetic particles. The stator components are assembled together to form a generally annular stator core. A wire is wrapped around at least a portion of the stator core to form a stator winding. A first generally annular end plate and a second generally annular end plate are mounted to axially opposite sides of the stator core such that the stator core is axially trapped and retained therebetween. A fastener applies a clamping load to the first and second end plates such that the stator core is compressed therebetween. The clamping load from the fastener is applied directly to the first and second end plates which distribute the clamping load to the stator core such that the plurality of components are held together without the fastener directly applying the clamping load to the stator core.  
         [0006]     The plurality of stator components include a plurality of protrusions and depressions adapted to facilitate the alignment of the stator components as they are assembled to form the stator core.  
         [0007]     The first and second end plates include a plurality of protrusions and/or depressions adapted to facilitate the alignment of the first and second end plates relative to the stator core.  
         [0008]     The apparatus of the present invention includes a first annular member disposed between the first end plate and the stator core, and a second annular member disposed between the second end plate and the stator core, wherein the first and second annular members are configured to more evenly distribute the clamping load from the fastener to the stator core.  
         [0009]     The apparatus of the present invention includes an adhesive disposed between the first end plate and the stator core, and between the second end plate and the stator core, wherein the adhesive is configured to hold the plurality of components together with a reduced fastener clamping load.  
         [0010]     The method of the present invention includes assembling the plurality of stator components such that at least some of the alignment protrusions and the alignment depressions engage to align the stator components and form a stator core. A wire is wrapped around at least a portion of the stator core to form a stator winding. The first and second end plates are mounted to axially opposite sides of the stator core such that the stator core is axially trapped and retained therebetween. A clamping load is applied to the first and second end plates with a fastener such that the stator core is compressed therebetween. The clamping load from the fastener is applied directly to the first and second end plates which distribute the clamping load to the stator core such that the plurality of components are held together without the fastener directly applying the clamping load to the stator core.  
         [0011]     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a perspective view of a stator assembly in accordance with the present invention;  
         [0013]      FIG. 2  is a perspective view of a center segment of the stator assembly of  FIG. 1 ;  
         [0014]      FIG. 3  is a perspective view of a sub-assembly of the stator assembly of  FIG. 1 ;  
         [0015]      FIG. 4  is a perspective view of an end segment of the stator assembly of  FIG. 1 ; and  
         [0016]      FIG. 5  is an exploded view of the stator assembly of  FIG. 1 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows a perspective view of a stator assembly  10  for an electric motor (not shown). In an effort to reduce manufacturing costs, the stator assembly  10  includes a plurality of component segments that are assembled together to produce the motor. More precisely, the stator assembly  10  includes a plurality of center segments  12  (i.e., six identical center segments which are attached together), at least one coil winding  14 , a plurality of end segments  16  (i.e., six identical end segments which are attached together), a plurality of end plates  18 , and at least one fastener such as the bolts or bars  80 . The center segments  12  and the end segments  16  are composed of pressure shaped ferromagnetic particles that are generally coated and insulated to provide low electrical conductivity. According to a preferred embodiment, the ferromagnetic particles are a powdered metal composition which is pressed to form the shapes of the center segments  12  and the end segments  16 .  
         [0018]     Referring to  FIG. 2 , a center segment  12  is shown in more detail. The center segment  12  defines a front surface  24 , a back surface  26  opposite the front surface  24 , and opposing end portions  28 . The center segment  12  also defines a radially outer shell portion  20  and a plurality of teeth  22  extending therefrom. The teeth  22  each extend radially inward from the shell portion  20  and terminate in a flanged end portion  32 . The center segment  12  includes a plurality alignment features such as, for example, the alignment protrusions  34 , the alignment depressions  35  and/or the alignment depressions  36 . To facilitate alignment, the protrusions  34  and the depressions  36  are preferably generally conical so as to allow for a margin of error during initial engagement and thereafter self-center to precisely align components during assembly; however, alternate alignment feature configurations may be envisioned. According to a preferred embodiment, the back surface  26  includes one alignment protrusion  34  and one alignment depression  36  and the front surface  24  includes three alignment depressions  35 .  
         [0019]     As shown in  FIG. 3 , two center segments  12  placed back-to-back (i.e.,  26  to  26 ), and a coil winding  14  are assembled together to form a sub-assembly such as the sub-assembly  38 , and thereafter three sub-assemblies  38 ,  38 ′ and  38 ″ are assembled together to form a generally annular sub-assembly  42  as will be described in detail hereinafter.  
         [0020]     The sub-assemblies  38 ,  38 ′ and  38 ″ each include two center segments  12  such as the center segments  12 ′ and  12 ″ that are assembled together and have multiple layers of wire  40  (shown schematically in  FIG. 3 ) wound therearound. The wire  40  wound about the respective center segments  12 ′ and  12 ″ in the manner described hereinafter defines a coil winding  14  for each respective sub assembly  38 ,  38 ′ and  38 ″. The two center segments  12 ′ and  12 ″ are assembled by placing them back-to-back such that their respective back surfaces  26  (shown in  FIG. 2 ) engage each other. As the back surfaces  26  of the respective center segments  12  and  12 ″ are brought together, the alignment protrusion  34  (shown in  FIG. 2 ) of the center segment  12 ′ is insertable into an alignment depression  36  (shown in  FIG. 2 ) on the back of the center segment  12 ″, and the alignment protrusion  34  of the center segment  12 ″ is insertable into the alignment depression  36  on the back of the center segment  12 ′ such that the center segments  12 ′ and  12 ″ are aligned with each other. Thereafter, the wire  40  is wrapped around the teeth  22  of the center segments  12 ′ and  12 ″ radially outwardly of the respective flanged end portions  32  thereby forming a coil winding  14  and completing each respective sub-assembly  38 ,  38 ′ and  38 ″. Each coil winding  14  is schematically shown as being generally rectangular; however, it should be appreciated that each winding  14  is actually composed of individual strands of wire  40  wrapped around the teeth  22  multiple times. Three sub-assemblies  38 ,  38 ′ and  38 ″ are positioned such that their respective end portions  28  (shown in  FIG. 2 ) engage or abut each other to form the generally annular sub-assembly  42 .  
         [0021]     Referring to  FIG. 4 , one of the end segments  16  is shown in more detail. The end segment  16  defines an inner surface  50 , an outer surface  52  opposite the inner surface  50 , and opposing end portions  54 . The end segment  16  also defines a radially outer housing portion  56  and a plurality of teeth  58  extending therefrom. The teeth  58  each extend radially inward from the housing portion  56  and terminate in a flanged end portion  60 . The end segment  16  includes a plurality of alignment features such as the alignment protrusions  64 . According to a preferred embodiment the inner surface  50  of each end segment  16  includes two alignment protrusions  64  adapted to engage complimentary alignment depressions  35  of the sub-assembly  42  such that the end segment  16  is aligned relative thereto. Additionally, the outer surface  52  of each end segment  16  includes two alignment protrusions  64  for alignment with an end plate  18 . Three end segments  16  are positioned, preferably within a fixture, such that their respective end portions  54  engage or abut as at  55  (shown in  FIG. 1 ) to form generally annular end rings  66  and  66 ′ (shown in  FIG. 5 ).  
         [0022]     Referring to  FIG. 5 , the annular end plates  18  and  18 ′ are generally O-shaped and each include a plurality of bolt holes  70 . The end plates  18 ,  18 ′ also include a plurality of alignment features such as the alignment depressions  72 . The alignment depressions  72  each receive an alignment protrusion  64  from one of the end rings  66  and  66 ″ such that the end plates  18 ,  18 ′ are respectively aligned relative thereto. The end plates  18 ,  18 ′ are preferably composed of non-magnetic stainless steel; however, alternate compositions such as fiberglass reinforced plastic may be envisioned.  
         [0023]     Having identified the components of the stator assembly  10  hereinabove, the assembly steps will now be described with reference to  FIG. 5  showing an exploded view of the stator assembly  10 . It should be appreciated that, unless otherwise specified, the assembly steps do not necessarily have to be performed in the order described.  
         [0024]     A first end plate  18  is located and retained, preferably in a fixture (not shown). A first end ring  66  composed of three end segments  16  is then mounted to the first end plate  18 . As the first end ring  66  is mounted to the first end plate  18 , alignment protrusions  64  of the end ring  66  are inserted into complementary alignment depressions  72  of the end plate  18  such that the first end ring  66  is aligned relative to the first end plate  18 . The sub-assembly  42  which is assembled in the manner described hereinabove is then mounted to the first end ring  66 . As the sub-assembly  42  is mounted to the first end ring  66 , alignment protrusions  64  of the end ring  66  are inserted into complementary alignment depressions  35  of the sub-assembly  42  such that the sub-assembly  42  is aligned relative to the first end ring  66 . A second end ring  66 ′ composed of three end segments  16  is then mounted to the sub-assembly  42 . As the second end ring  66 ′ is mounted to the sub-assembly  42 , alignment protrusions  64  of the end ring  66 ′ are inserted into complementary alignment depressions  35  of the sub-assembly  42  such that the second end ring  66 ′ is aligned relative to the sub-assembly  42 . A second end plate  18 ′ is then mounted to the second end ring  66 ′. As the second end plate  18 ′ is mounted to the second end ring  66 ′, alignment protrusions  64  of the second end ring  66 ′ are inserted into complementary alignment depressions  72  of the second end plate  18 ′ such that the second end ring  66 ′ is aligned relative to the second end plate  18 ′.  
         [0025]     After the previously described components of the stator assembly have been aligned and assembled, preferably in a fixture (not shown), the first and second end plates  18  and  18 ′ are held together by a plurality of fasteners such as the bolts or bars  80 . The bolts  80  are configured to pass axially through gaps formed between the teeth  22  and the teeth  58  to retain the end plates  18  and  18 ′. The bolts  80  are preferably composed of a non-magnetic material such as non-magnetic stainless steel or titanium having low electrical conductivity to minimize eddy currents in the bolts  80  caused by leakage flux.  
         [0026]     The bolts  80  transmit a substantial clamping force through the end plates  18  and  18 ′ to retain the remaining components of the stator assembly  10 . The clamping loads from the bolts  80  are initially transferred to the end plates  18  and  18 ′ which are configured to more uniformly distribute such loads to the end rings  66 ,  66 ′ and the sub-assembly  42 . The end plates  18  and  18 ′ are therefore composed of a stronger material than that of the end rings  66 ,  66 ′ and the sub-assembly  42  which are preferably composed of powdered metal. Accordingly, the stronger end plates  18  and  18 ′ are adapted to adsorb and distribute the relatively large clamping loads that hold the stator assembly  10  together, and to thereby protect the powdered metal components from such loads.  
         [0027]     For purposes of the present invention, the center segments  12  and the end segments  16  which are assembled together in the manner previously described define a generally annular stator core  84 . In other words, the stator core  84  includes all the components of the stator assembly  10  except the stator wire  40  and the coil windings  14 , the end plates  18 , and the bolts  80 .  
         [0028]     According to a preferred embodiment, a first annular member  90  is disposed between the first end plate  18  and the first end ring  66 , and a second annular member  90 ′ is disposed between the second end plate  18 ′ and the second end ring  66 ′. The annular members  90 ,  90 ′ are preferably composed of a pliable material such as that typically used for gaskets. The annular members  90 ,  90 ′ are adapted to prevent load spikes caused by irregularities in the end plates  18 ,  18 ′ or in the end rings  66 ,  66 ′, and to more uniformly distribute the loads applied by the bolts  80 .  
         [0029]     According to another preferred embodiment, adhesive  92  is disposed between the first end plate  18  and the first annular member  90 , between the annular member  90  and the first end ring  66 , and/or between the first end ring  66  and the sub-assembly  42 . Similarly, adhesive  92 ′ is disposed between the sub-assembly  42  and the second end ring  66 ′, between the second end ring  66 ′ and the annular member  90 ′, and/or between the annular member  90 ′ and the end plate  18 ′. The adhesive  92 ,  92 ′ acts to hold the stator assembly  10  together and thereby reduces the requisite bolt  80  clamping loads such that the powdered metal components do not become damaged.  
         [0030]     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.