Abstract:
A rotor position sensor mounting system includes a sensor assembly fixedly engaged with a stator assembly. The stator assembly includes a plurality of stator laminations including a plurality of sections separated by a plurality of first gaps. Each first gap is defined by a first pair of edges. The stator assembly also includes first and second stator end caps attached to the stator laminations and including a plurality of sections separated by a plurality of second gaps. Each second gap is defined by a pair of stator end cap section edges. At least one pair of stator end cap section edges includes a first notch and a second notch separated by a bridge. The sensor assembly engages the second notch and is maintained in position with the bridge and the stator laminations.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates generally to electric motors, and more particularly to positioning rotor position sensing devices within electric motors.  
           [0002]    Some electric motors require a rotor position-sensing device for proper operation. Rotor position sensing devices provide information to a motor controller. In order to provide reliable information, the sensors need to be positioned very accurately, otherwise the motor may fail to run or may run inefficiently.  
           [0003]    Hall effect devices are ubiquitous in automotive, aircraft, appliance and tool applications where non-contact sensing is required. Hall effect devices are sensors that detect motion, position or change in field strength of an electromagnet, a permanent magnet, or a ferromagnetic material with an applied magnetic bias. Electric motors typically use electromagnetic fields to create torque or force. It is known to use hall effect devices in electric motors to sense a position of a rotor magnet. The hall effect device must be accurately positioned relative to the midpoint of the rotor magnet. Displaced hall effect devices can produce hysteresis and motor current discontinuities that disturb torque.  
           [0004]    It would be desirable to provide a method and system for mounting a rotor position sensor that reliably and accurately mounts a sensor within an electric motor rotor at a low cost.  
         SUMMARY OF INVENTION  
         [0005]    In an exemplary embodiment of the invention, a rotor position sensor mounting system includes a stator assembly and a sensor assembly. A sensor attaches to the stator assembly and is maintained in a fixed relation with respect to a plurality of stator laminations and a stator end cap.  
           [0006]    More particularly, the stator laminations include a plurality of sections separated by a plurality of gaps. Each gap is defined by a pair of edges. The stator end cap attaches to the stator laminations and includes a plurality of sections separated by a plurality of gaps. Each stator end cap gap is defined by a pair of edges. At least one pair of stator end cap section edges includes a first notch and a second notch separated by a bridge. The sensor assembly engages the second notch and is maintained in position with the bridge and the stator laminations. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0007]    [0007]FIG. 1 is an exploded partial cut-away view of a motor assembly including a hall effect assembly and a stator assembly.  
         [0008]    [0008]FIG. 2 is a perspective view of a hall effect housing shown in FIG. 1.  
         [0009]    [0009]FIG. 3 is a top view of the hall effect housing shown in FIG. 1.  
         [0010]    [0010]FIG. 4 is an end view of the hall effect housing shown in FIG. 1 illustrating a second end.  
         [0011]    [0011]FIG. 5 is an end view of the hall effect housing shown in FIG. 1 illustrating a first end.  
         [0012]    [0012]FIG. 6 is a perspective view of the stator assembly shown in FIG. 1.  
         [0013]    [0013]FIG. 7 is an enlarged side view of the motor assembly shown in FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0014]    [0014]FIG. 1 is an exploded partial cut-away view of a motor assembly  10  including a hall effect assembly  12  and a stator assembly  14 . In one embodiment, the motor is an 84 MM electronically commutated motor (ECM) commercially available from the General Electric Company, Schenectady, N.Y. Hall effect assembly  12  includes a hall effect housing  16 , a hall effect device  18 , a printed circuit board (PCB)  20 , a plurality of sensing leads  22 , and a cable tie  24 . Stator assembly  14  includes a plurality of stator laminations  28 , a first stator end cap  30 , a second stator end cap (not shown), and a plurality of stator windings  32 . Motor assembly  10  also includes a rotor magnet  33 , attached to a rotor assembly (not shown). In one embodiment, stator laminations  28  are fabricated from steel and first stator end cap  30  and the second stator end cap are fabricated from molded plastic.  
         [0015]    Hall effect device  18  is mounted to a first end  34  of PCB  20  and is electrically connected thereto. Sensing leads  22  are mounted to a second end  36  of PCB  20  which includes a plurality of openings  38 . The number of openings equals the number of sensing leads  22  and one sensing lead  22  is positioned within a respective opening. In one embodiment, sensing leads  22  are positioned through openings  38  and are soldered to PCB  20 . Cable tie  24  is connected to sensing leads  22 . In one embodiment, cable tie  24  attaches sensing leads  22  to hall effect housing  16  and maintains sensing leads  22  in a fixed relationship thereto.  
         [0016]    PCB  20  is positioned at least partially within hall effect housing  16  such that hall effect device  18  is within a cavity  40  of hall effect housing  16 . Stator laminations  28  include a plurality of gaps  42  (only one gap is shown in FIG. 1) extending a length of stator laminations  28  and first stator end cap  30  includes a plurality of gaps  44  (only one gap is shown in FIG. 1). Gaps  42  are aligned with gaps  44 . Hall effect housing  16  fits within gap  44  and engages first stator end cap  30  and fits within gap  42  and engages stator laminations  28  to securely and accurately position hall effect device  18  with respect to rotor magnet  26 . In one embodiment, hall effect housing  16  engages first stator end cap  30  with a snap-fit relationship to tangentially and radially position hall effect device  18 .  
         [0017]    Hall effect assembly  12  includes an insulating encapsulating compound that is well known in the art and which is poured into cavity  40  to encapsulate the electrical connection of sensing leads  22  to PCB  20  at openings  38  and protect the connections from moisture. In addition, the electrical connections are insulated to provide adequate creepage and clearance distances to stator laminations  28 , stator windings  32 , and a metal center post (not shown in FIG. 1) that supports stator assembly  14 .  
         [0018]    [0018]FIG. 2 is a perspective view of hall effect housing  16  including a first portion  60  and a second portion  62 . First portion  60  and second portion  62  each include a bottom wall  64 , a pair of first side walls  66  extending perpendicularly from bottom wall  64 , a pair of second, angled side walls  68  extending at an angle from side walls  66 , and a top wall  70  connecting angled side walls  68  and extending parallel to bottom wall  64 . In one embodiment, housing  16  is fabricated from molded plastic.  
         [0019]    Housing first portion  60  includes a pair of arms  72  extending from side walls  66  at a first end section  74  thereof. Arms  72  include an angled extension portion  76  that extends at an angle from side walls  66  and a middle portion  78  that extends parallel to side walls  66  and to a longitudinal axis  80  of housing  16 . Arms  72  also include a raised portion  82  that extends from a first end  84  of middle portion  78  perpendicularly to longitudinal axis  80 . Middle portion  78  and raised portion  82  form an L shape for arms  72 .  
         [0020]    Housing first portion  60  also includes a ledge  86  extending from bottom wall  64  at first end section  74 . Ledge  86  extends beyond middle portion first end  84  and includes a curved lip  88  at a first end  90  thereof to provide for a flexible strain relief for sensing leads  22  (shown in FIG. 1) when PCB  20  (shown in FIG. 1) is inserted within housing cavity  40 . Ledge  86  also includes a plurality of support ribs  92  (only one support rib is shown in FIG. 2) that provide support for ledge  86 .  
         [0021]    Housing first portion  60  includes a second end section  94  at which side walls  66  and angled side walls  68  transition to walls  66  and  68  having a reduced height in housing second portion  62  with respect to a height of walls  66  and  68  in housing first portion  60 . Walls  66  include a stepped transition portion  96  at second end section  94  and walls  68  include a stepped transition portion  98  at second end section  94 . Bottom wall  64  includes a step  99  that corresponds to stepped transition portion  96  of side walls  66 .  
         [0022]    Housing second portion  62  includes a first section  100  and a second section  102 . First section  100  includes a first housing guide  104  extending from each side wall  66 . First housing guide  104  includes a first section  106  and a second section  108 . First section  106  extends from housing first portion  60  and is substantially planar therewith. First housing guide second section  108  extends longitudinally from first section  106  and beyond first section  106  away from longitudinal axis  80 . First housing guide second section  108  includes a first end  110  adjacent first section  106  and having a first height and a second end  112  having a second height. In one embodiment, the height of second end  112  is less than the height of first end  110 . In an alternative embodiment, the height of second end  112  is the same as the height of first end  110 . A step  114  extends between a side surface  116  of second section  108  and a side surface  118  of first section  106 .  
         [0023]    Housing second portion first section  100  also includes a second housing guide  120  extending from each angled side wall  68  and having a top surface  122  coplanar with a top surface  124  of top wall  70  at housing first portion  60  and housing second portion  62 . In an alternative embodiment, top surface  122  is coplanar with top surface  124  of top wall  70  at housing first portion  60  and is not coplanar with top surface  124  of top wall  70  at housing second portion  62 . Second housing guides  120  have a first portion  126  and a second portion  128 . Second housing guide first portion  126  extends a greater distance from angled side wall  68  than second housing guides second portion  128 .  
         [0024]    Second housing guides second portion  128  has a substantially uniform thickness and second housing guide first portion  126  has a first thickness adjacent angled side wall  68  and a second greater thickness at an outer edge  130 . The second housing guide first portion thickness is the same as the second housing guide second portion first thickness. In one embodiment, the first portion thickness at outer edge  130  is greater at a first end  132  of second housing guide  120  than at a second end  134  of second housing guide  120 . In an alternative embodiment, the first portion thickness at outer edge  130  is substantially uniform from first end  132  to second end  134 . A gap  136  extends between first housing guide  104  and second housing guide  120  on each side of housing  16 .  
         [0025]    Housing second portion second section  102  includes a pair of internal guides  138  (only one is shown in FIG. 2) that extend from a first end  140  of housing  16  towards housing first portion  60 . The guides extend within housing cavity  40  from an inner wall (not shown) of housing second angled side walls  68 .  
         [0026]    [0026]FIG. 3 is a top view of housing  16  including guides  138  extending from end  140 . End  140  is beveled at top wall  70 , second angled side walls  68 , first side walls  66 , and bottom wall  64  (shown in FIG. 2) such that an angled connector portion  142  extends between end  140  and top wall  70 , second angled side walls  68 , first side walls  66 , and bottom wall  64 . Guides  138  taper towards second angled side wall  68  at an end  144 . Second housing guides second portion  128  extends from a top portion of second angled side walls  68  a distance approximately equal to a distance that first side walls  66  extend from top wall  70 .  
         [0027]    [0027]FIG. 4 is an end view of housing  16  including a second end  146 . Cavity  40  extends into housing  16  at end  146  and step  99  extends from bottom wall  64  into cavity  40 . Internal guides  138  extend into a top portion of cavity  40 . Second housing guides  120  have a wedge shape to facilitate attaching housing  16  to stator assembly  14  (shown in FIG. 1) as will be described below in greater detail.  
         [0028]    [0028]FIG. 5 is an end view of housing  16  including first end  140 . Internal guides  138  extend into cavity  40  and form cavity  40  into a substantially inverted T shape at end  140 . Housing step  99  extends between a first portion  148  of bottom wall  64  and a second portion  150  of bottom wall  64  and is angled therebetween such that step  99  forms a ramp between first portion  148  and second portion  150 . Housing support ribs  92  extend from bottom wall  64  and connect to lip  88 .  
         [0029]    [0029]FIG. 6 is a perspective view of stator assembly  14  illustrating stator lamination gaps  42 , first stator end cap gaps  44  and a plurality of second stator end cap gaps  152 . Stator lamination gaps  42  are narrower than end cap gaps  44  and  152  which are substantially the same size. Stator lamination gaps  42  are defined by a stator lamination first edge  154  and a stator lamination second edge  156 . First edge  154  includes a step  158  that extends a length of stator lamination first edge  154 . First edge  154  is at substantially the same radial height as second edge  156 . First stator end cap gaps  44  are defined by a first stator end cap first edge  160  and a first stator end cap second edge  162 .  
         [0030]    First stator end cap  30  includes a first end  164  from which a first notch  166  extends along each of edges  160  and  162  of at least one gap  44 . Notches  166  extend from an inner portion  168  of first stator end cap  30  to an outer surface  170  of first stator end cap  30  at a bridge  172 . Inner portion  168  is adjacent an inner surface  169  of first stator end cap  30 . Notches  166  form a ramp between first end  164  and bridge  172  and flare away from edges  160  and  162  from bridge  172  to first end  164 . In one embodiment, notches  166  extend from one edge  160  and one edge  162 . In an alternative embodiment, notches  166  extend from more than one edge  160  and more than one edge  162 . In a further alternative embodiment, notches  166  are not flared.  
         [0031]    Notched edges  160  and  162  also include a step  174  that extends from bridge  172  to a second notch  176 . Second notch  176  extends from bridge  172  to stator laminations  28  and flares away from edges  160  and  162  from bridge  172  to stator laminations  28 . In addition, notches  176  increase in depth from bridge  172  to stator laminations  28 . In an alternative embodiment, notches  176  are not flared and have a substantially uniform depth.  
         [0032]    [0032]FIG. 7 is an enlarged side view of motor assembly  10  including hall effect housing  16  connected to stator assembly  14  at stator laminations  28  and first stator end cap  30 . Second housing guides first portion  126  fits, i.e. nests, within second notches  176  and extends from a first end  178  of stator laminations  28  to bridge  172 . Second housing guides second portion  128  fits over stator lamination second edge  156  and stator lamination first edge  154  and abuts first edge step  158 . Stator laminations  28  are circumferentially ramped from first edge step  158  to second edge  156 . Second housing guides second portion  128  is substantially flush with an upper portion  180  of stator laminations  28  adjacent step  158 .  
         [0033]    Motor assembly  10  is assembled by positioning first stator end cap  30  adjacent stator laminations  28  and press fitting first stator end cap  30  into stator laminations  28 . Second stator end cap  182  (shown in FIG. 6) is positioned adjacent stator laminations  28  and is press fit onto stator laminations  28 . Printed circuit board  20  is positioned within housing  16  such that hall effect device  18  is maintained in a fixed relation with respect to housing  16 . Step  99  guides hall effect device  18  to a proper height and internal guides  138  guide hall effect device  18  to, and maintain hall effect device  18  in, the proper position with respect to housing first side walls  66 . Housing first end  140  is then positioned within first stator end cap gap  44 . Housing  16  is slid along a length of gaps  44  and  42  such that first housing guides  104  contact inner surface  169  and second housing guides  120  contact notches  166 . Housing  16  is slid further into gaps  44  and  42  such that second housing guides  120  contact bridge  172  and slide over bridge  172 . Housing  16  is inserted further within gaps  44  and  42  such that second housing guides first portion  126  nests within second notches  176  and second housing guides second portion  128  lies adjacent an outer surface of stator laminations  28 .  
         [0034]    Housing  16  is fabricated from a flexible material such that second housing guides  120  spring back into a relaxed position once guides enter notches  176 . Due to the wedge shape of guides  120  and  104 , housing  16  easily attaches to first stator end cap  30  and stator laminations  28  in a frictional snap-fit relationship that maintain housing  16  and hall effect device  18  accurately positioned with respect to stator assembly  14 . In one embodiment, housing  16  is fabricated from injection molded plastic.  
         [0035]    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.