Abstract:
A motor is provided with a set of end cap guides on the ends of a stator winding assembly to plot the placement of end caps into the correct placement relative to the stator winding assembly so that the rotor assembly is maintained concentric with the stator. The end cap guides may be rings fitting within the winding insulators on the ends of the stator stack or may be integrated as guide segments with the winding insulators to outline an interrupted cylindrical inner surface coinciding with the inner diameter of the stator winding assembly. The guides allow proper positioning of the rotor assembly without increasing the stator stack length.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to manufacture and assembly of rotary dynamoelectric machines (electric motors or generators), and in particular relates to housings, covers, bearing shields, end plates, or other structural mounting arrangements that are specially adapted to facilitate the proper centering and balancing, including axial alignment, of a rotor within a stator. 
       BACKGROUND ART 
       [0002]    Assembling a motor so that its rotor and stator maintain a concentric relationship is essential to smooth and efficient operation of the motor. End caps of the motor casing, also referred to sometimes as end plates or bearing shields, seat the rotor assembly (rotor, drive shaft and bearings), so the mounting of the end caps is important for establishing the proper centering and alignment of the rotor within the stator. 
         [0003]    Piloting the end cap to the stator&#39;s inner diameter is commonly used in the industry today to establish and maintain concentricity of the rotor relative to the stator. This typical motor construction is illustrated in  FIGS. 1 and 2 . A stator winding assembly  11  comprises conductive windings  13 , which define a set of coils for some predefined number of electromagnetic poles, all wound around an annular core or frame. The stator winding assembly  11  has a stator stack length L s  and is also characterized by an inner diameter ID s  of a central region into which a rotor assembly fits. An insulator  15  is used on each end of the stator core to support the windings  13  and to prevent the stator&#39;s windings from shorting to the core. A rotor assembly includes a rotor stack  17  of permanent magnets with a rotor stack length L rp , an axial drive shaft  19 , and bearings  21  and  22 . The rotor assembly has an outer diameter that is slightly less than the inner diameter of the stator assembly so that the rotor fits within the stator with a small air gap  23  therebetween that allows the rotor to freely rotate on its bearings  21  about its drive axis A. Two end caps  25  and  26  are provided (end cap  25  is seen in  FIGS. 2A-C ) that fit over the ends of the stator winding assembly  11 . There is a central opening  27  in at least one of the end caps  25  (or openings  27  and  28  in both end caps  25  and  26  as shown here) through which the drive shaft  19  projects. A space  29  is also provided in the end caps  25  and  26  to seat the rotor assembly at its bearings  21  and  22 . The stator stack length L s  is slightly larger on both ends than the corresponding rotor stack length L rp  so that a surface  31  of the end caps  25  and  26  can pilot into the resulting space and fit snuggly against the inner diameter of the stator winding assembly. This guarantees that the rotor assembly will be in a concentric position relative to the stator. Once a position, the end caps  25  and  26  are often secured tightly to the stator core using screws. 
         [0004]    However, because the stator stack must be slightly longer than the rotor to provide the stator surfaces needed to guide the end caps into position, a disadvantage is that the motor length is necessarily increased for a given torque, or seen another way, that torque is reduced for a given motor length. It would be desirable if the end caps could be positioned precisely without increasing the stator stack length. 
       SUMMARY DISCLOSURE 
       [0005]    A set of guides is provided that have dimensions coinciding with the inner diameter of the stator winding assembly. These guides are attached at both ends of the stator and serve to pilot the placement of the end caps without lengthening the stator relative to the rotor. In one embodiment, the guides are a pair of rings with the same inner diameter as and attached concentrically to the stator winding assembly. In another embodiment, the guides are integrated with the winding insulator for the stator assembly. The guides outline a cylindrical inner surface with an inner diameter equal to that of the stator winding assembly, but are interrupted circumferentially by a series of lengthwise slots between the stator pole locations of the insulator to allow for winding needle passage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a side sectional view of a motor according to the prior art. 
           [0007]      FIGS. 2A-2C  are perspective, side and plan views, respectively, of an end cap for the motor of  FIG. 1 . 
           [0008]      FIG. 3  is a side sectional view of a motor according to a first embodiment of the invention. 
           [0009]      FIGS. 4A and 4B  are perspective and plan views, respectively, of a guide ring for the motor embodiment of  FIG. 3 . 
           [0010]      FIGS. 5A and 5B  are perspective and end views, respectively, of a stator winding assembly for the motor embodiment of  FIG. 3 . 
           [0011]      FIG. 6  is a side sectional view of a motor according to a second embodiment of the invention. 
           [0012]      FIGS. 7A-7C  are perspective, side and plan views, respectively, of an end cap for the motors in  FIGS. 3 and 6 . 
           [0013]      FIGS. 8A and 8B  are perspective and end views, respectively, of a winding insulator with integrated end cap guides for the motor embodiment of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    With reference to  FIG. 3 , a first embodiment of a motor  40  in accord with the present invention includes a stator winding assembly  41  with conductive windings  43 , which define a set of coils for some predefined number of electromagnetic poles, all wound around a generally annular core or frame. Although eight winding coils  43  are seen in  FIG. 5B , the number of windings  43  can vary from one model of motor to another, with there being a minimum number of coils. The stator winding assembly  41  is characterized by a stator stack length L s  defined by its ion core, and is also characterized by an inner diameter ID s  of a central region into which a rotor assembly fits. A winding insulator  45  is used at the ends of the stator core to support the windings  43  where they make a turn and to prevent the stator&#39;s windings from shorting to the stator&#39;s iron core. Being nonmagnetic, the winding insulator serves only as a support frame and is not counted as part of the stator&#39;s stack length L s . 
         [0015]    A rotor assembly includes a rotor stack  47  of permanent magnets with a rotor stack length L r , an axial drive shaft  49 , and bearings  51  and  52 . The rotor assembly has an outer diameter that is slightly less than the inner diameter of the stator assembly so that the rotor fits within the stator with a small air gap  53  therebetween that allows the rotor to freely rotate on its bearings  51  and  52  about its drive axis A. 
         [0016]    A pair of end caps  55  and  56  are provided that fit over the ends of the stator winding assembly  41 . There is a central opening  57  in at least one of the end caps  55  (or both end caps as shown here) through which the drive shaft  49  projects. A space is also provided in the end caps  55  and  56  to seat the rotor assembly at its bearings  51  and  52 . Outside of that space for the bearings is an annular elevated region  65  that is used to seat the end caps  55  and  56  in the correct position relative to the stator winding assembly  41  by means of rings  61  and  62 . 
         [0017]    The stator stack length L s  is equal to the corresponding rotor stack length L r . In order that the end caps  55  and  56  can pilot into the correct position relative to the inner diameter ID s  of the stator winding assembly, a pair of end cap positioning rings  61  and  62  is provided (a ring  61  is seen also in  FIGS. 4A and 4B  in isolation; ring  62  is identical). The rings  61  and  62  have an inner diameter D substantially equal to the inner diameter ID s  of the stator winding assembly  41  within a specified tolerance. The ring inner diameter must at least be large enough that the rotor assembly can fit through one of the rings into the central region within the stator assembly. The rings can be made of any material (metal or plastic) and fit within the winding insulator  45  at the respective ends of the stator winding assembly  41  (as seen in  FIGS. 5A and 5B  with the end caps and rotor assembly removed), so that the inner surfaces  63  of the rings  61  and  62  substantially coincide with the inner diameter of the stator winding assembly  41  within a specified tolerance. These rings  61  and  62  are installed on the stator assembly  41  after winding process for the stator coils has been completed. 
         [0018]    Each end cap  55  or  56  has an annular elevated region  65  that fits snuggly into one of the rings  61  and  62 , thereby properly centering each end caps  55  or  56  and the rotor assembly seated by the end caps  55  and  56 . The end caps  55  and  56  pilot on the rings  61  and  62  instead of the stator winding assembly. This guarantees that the rotor assembly will be in a concentric position relative to the stator. The end cap  85  seen in  FIGS. 7A-7C  is structurally same as the end cap  55  and  56  in  FIG. 3 . When seated the end caps  55  and  56  are adhesively bonded to the stator assembly  41 . 
         [0019]    With reference to  FIG. 6 , a second embodiment of a motor  70  in accord with the present invention includes a stator winding assembly  71  with conductive windings  73 , which define a set of coils for some predefined number of electromagnetic poles, all wound around a generally annular core or frame. The stator winding assembly  71  is characterized by a stator stack length L s  and also by an inner diameter ID s  of a central region into which a rotor assembly fits. An insulator  75  is used to prevent the stator&#39;s windings from shorting. A rotor assembly includes a rotor stack  77  of permanent magnets with a rotor stack length L r , an axial drive shaft  79 , and bearings  81  and  82 . The rotor assembly has an outer diameter that is slightly less than the inner diameter of the stator assembly so that the rotor fits within the stator with a small air gap  83  therebetween that allows the rotor to freely rotate on its bearings  81  and  82  about its drive axis A. A pair of end caps  85  and  86  are provided that fit over the ends of the stator winding assembly  71 . There is a central opening  87  in at least one of the end caps  85  (or both end caps as shown here) through which the drive shaft  79  projects. A space is also provided in the end caps  85  and  86  to seat the rotor assembly at its respective bearings  81  and  82 . Outside of that space for the bearings is an annular elevated region  95  that is used to seat the end caps  85  and  86  in the correct position relative to the stator winding assembly  71 . 
         [0020]    The stator stack length L s  is equal to the corresponding rotor stack length L r . In order that each end cap  85  or  86  can pilot into the correct position relative to the inner diameter ID s  of the stator winding assembly, the winding insulator  75  (seen in  FIGS. 8A and 8B  in isolation) has a set of guide segments  91  integrated therein. The number of guide segments  91  may vary, but a minimum of three are required, preferably distributed around the winding insulator  75 . The guide segments  91  outline a cylindrical inner diameter D substantially equal to the inner diameter ID s  of the stator winding assembly  71  within a specified tolerance, replacing the rings  61  and  62  of the first embodiment. The outlined cylindrical inner diameter defined by the guide segments  91  must at least be large enough that the rotor assembly can fit past the guide segments  91  into the central region within the stator assembly  71 . The guide segments  91  form parts of the ends of the winding insulator  75 , so that the inner surfaces  93  of the guide segments  91  substantially coincide with the inner diameter of the stator winding assembly  71  within a specified tolerance. The guide segments  91  cannot form a complete ring on the winding insulator  75 , since spaces are needed between the stator poles for the winding needle to pass through during the winding process, but not all winding poles need have an associated winding segment. 
         [0021]    As seen in  FIGS. 7A-7C , each end cap  85  and  86  has an annular elevated region  95  that fits snuggly with its outer surface  97  in contact with the inner surfaces  93  of the guide segments  91 , thereby properly centering the end caps  85  and  86 , and the rotor assembly seated by end cap  85 . This guarantees that the rotor assembly will be in a concentric position relative to the stator. The end caps  85  and  86  are adhered to the stator assembly  71 . 
         [0022]    The present invention takes advantage of the presence of the winding insulator  45  or  75  attached to the ends of the stator winding assembly  41  or  71 , by providing a ring  61  or integrated guide segments  91  for positioning the end caps  55  or  85  without lengthening the stator stack length L s . The stator can be the same length as the rotor, thus reducing overall motor length while maintaining motor torque.