Abstract:
An electric motor assembly. A stator includes a set of windings and has a first end, a second end, and an outer radial surface. A rotor includes a shaft having an axis. A first frame supports the shaft at a first axial position. A canopy substantially surrounds the first frame. The canopy includes a fluid inlet and a fluid discharge. A second frame supports the shaft at a second axial position and includes at least one fluid outlet. A chute is positioned downstream of the canopy fluid discharge. The chute directs fluid flow along the outer radial surface of the stator towards the fluid outlet. A fan is coupled to the shaft downstream of the fluid outlet for rotation with the shaft.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/246,875, filed Sep. 29, 2009, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The invention relates to air-cooled electric motors. More specifically, the invention relates to improved cooling and corrosion resistance in air-cooled electric pump motors. 
         [0003]    Generally, motors used in pumps and similar applications include steel, or other metal, covers and mainframes that tend to rust or deteriorate. The significance of the problem increases in humid environments where moisture causes rust build-up. Rust can develop or corrosion can occur in bearings, mainframes, stators, windings and shafts; all of which can lead to premature motor failure. Bearing failure, also caused by pump seal failures, causes grease removal and dirt intrusion. Chlorine can cause damage to critical components of motors by promoting corrosion. 
         [0004]    Furthermore, temperature control in motors is commonly a problem due to the fact that discharge air that has already increased in temperature across the motor re-circulates. The air removes heat from the motor and is typically controlled to keep it flowing across the hottest components. If the air has already been heated, it cannot effectively continue to perform the task. 
       SUMMARY 
       [0005]    In one embodiment, the invention provides an electric motor assembly. A stator includes a set of windings and has a first end, a second end, and an outer radial surface. A rotor includes a shaft having an axis. A first frame supports the shaft at a first axial position. A canopy substantially surrounds the first frame. The canopy includes a fluid inlet and a fluid discharge. A second frame supports the shaft at a second axial position and includes at least one fluid outlet. A chute is positioned downstream of the canopy fluid discharge. The chute directs fluid flow along the outer radial surface of the stator towards the fluid outlet. A fan is coupled to the shaft for rotation with the shaft. 
         [0006]    In another embodiment, the invention provides a method of air-cooling an electric motor assembly that substantially reduces recirculation of the air. The method includes drawing air into an air inlet disposed about a first frame. The air inlet includes an inner wall and an outer wall. A flange disposed downstream of the air inlet directs the air radially inward and across an external surface of a stator cup disposed between the first frame and a stator. A chute confines the air radially outward of an external surface of the stator. The air is drawn into a fan compartment of a second frame through a fan compartment inlet and discharged through an air outlet of the fan compartment. 
         [0007]    In still another embodiment, the invention provides an electric motor. The motor has a stator including a plurality of stator windings. A potting cup is disposed at a first axial end of the stator. A frame includes a potting portion disposed at a second axial end of the stator. The stator, potting cup, and frame are adhesively coupled together as one by a potting compound. 
         [0008]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of an airflow path through a motor according to one embodiment of the invention. 
           [0010]      FIG. 2  is a bottom perspective view of a canopy of the motor of  FIG. 1 . 
           [0011]      FIG. 3  illustrates a flow path for water entering the canopy of the motor of  FIG. 1 . 
           [0012]      FIG. 4  is a perspective view of a flange of the motor of  FIG. 1 . 
           [0013]      FIG. 5  is a perspective view illustrating the relationship of a lead end stator cup and a stator of the motor of  FIG. 1 . 
           [0014]      FIG. 6  is a perspective view of the opposite lead end frame of the motor of  FIG. 1 . 
           [0015]      FIG. 7  is a cutaway perspective view of a motor according to another embodiment of the invention. 
           [0016]      FIG. 8  is a partial perspective view of a potting compound structure formed around windings of the motor of  FIG. 7 . 
           [0017]      FIG. 9  is a cutaway perspective view of winding end turns encapsulated by the potting compound structure of the motor of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0019]    With reference to  FIGS. 1-6 , in one embodiment of the invention, an electric motor assembly  10  has been designed to provide a path for a fluid, such as air, that brings the fluid into effective heat-exchange contact with the hottest components of the motor, and substantially limits re-circulation of the fluid.  FIGS. 1-6  illustrate various aspects of this embodiment of the invention. 
         [0020]      FIG. 1  illustrates a complete airflow path through the motor assembly  10 . The motor assembly  10  includes a rotor  15  including a rotating shaft  20 , and a stator  25  including a number of windings  30 . The rotor  15  is operable to rotate with respect to the stator  25  as a result of applying a current through the windings  30 . For ease of description, it is assumed that the stator is manufactured with a number of stacked laminations. However, it is to be understood that other manufacturing processes to form the stator  25  fall within the scope of the invention. 
         [0021]    Air enters a canopy  35  through an air inlet  40  at a first end  45  of the motor assembly  10 . The canopy  35  provides an enclosure for electrical components of the motor, and also provides a conduit  50  for an airflow  55  from the first end  45  of the motor assembly  10 . The airflow  55  reaches a discharge end  60  of the canopy  35  and is redirected radially inwards via a flange  70  towards a lead end stator cup  65 . The airflow  55  flows around the lead end stator cup  65  towards the stator  25 . Next, the airflow  55  travels along an outer stator wall  75 . An air chute  80 , disposed between the flange  70  and an opposite lead end frame  85 , confines the airflow  55  along the outer stator wall  75  from an inlet end  90  to a discharge end  95 . Upon exiting the air chute  80 , the airflow  55  travels across a winding portion  100  of the opposite lead end frame  85 . Finally, a fan  105  draws the airflow  55  in through the opposite lead end frame  85  and expels the air between structural ribs  110 . 
         [0022]    Within the canopy  35 , the conduit  50  is defined between an inner canopy wall  115  and an outer canopy wall  120 .  FIG. 2  illustrates this double-wall structure of the canopy  35  in greater detail. By utilizing a double-wall structure, the canopy  35  provides both the air inlet  40  from the first end  45  of the motor, and an enclosure for electrical components of the motor. Referring back to  FIG. 1 , an inner canopy void  125  is encapsulated by the inner canopy wall  115  and a lead end frame  130  of the motor. The inner canopy void  125  encloses electrical components (controller, wire leads, etc.) mounted to the lead end frame  130 . The configuration of the canopy  35 , including the location and geometry of the air inlet  40 , substantially reduces air re-circulation from the fan  105 . Having the air inlet  40  around the entire circumference of the canopy reduces the “pull” (or differential pressure) at the inlet and thereby reduces the recirculation of exhausted air back into the motor. Reducing recirculation enables the motor to cool more efficiently. 
         [0023]    As illustrated in  FIG. 3 , the outer canopy wall  120  abuts the flange  70  at a junction  135  downstream (with respect to the airflow) of a junction  140  of the inner canopy wall  115  with the lead end frame  130 . This construction enables water to enter the motor assembly at the outer canopy wall/flange junction  135  and travel down the airflow  55  path without being able to reach the juncture  140  between the inner canopy wall and the lead end frame. Thus, the electrical components encapsulated between the inner canopy void  125  and the lead end frame  130  are better protected from water or accumulating moisture that may enter the motor externally. 
         [0024]      FIG. 3  also illustrates the airflow  55  transitioning from the confines of the canopy  35  to the lead end stator cup  65 . The airflow  55  reaches the discharge end  60  of the canopy and is directed radially inward towards the lead end stator cup  65  by the flange  70 . The flange  70  is mounted directly to the underside of the lead end frame  130 . The flange  70  also mounts tightly to the canopy  35  and redirects the airflow  55  to flow directly against the lead end stator cup  65 . As illustrated in  FIG. 4 , the flange  70  is radiused around its roughly rectangular shape for minimal restriction of the airflow. 
         [0025]      FIG. 5  illustrates several aspects of the lead end stator cup  65 . The lead end stator cup has an upstream end  145 , a downstream end  150 , and an outer radial surface  155 . The outer radial surface  155  has longitudinal ribs  160  that penetrate the airflow path around the outer radial surface  155  to improve heat transfer from the stator windings  30 . The cross-sectional profile of the outer radial surface  155  smoothly transitions from round at the upstream end  145 , to the profile of the stator  25  at the downstream end  150  end in order to provide a smooth flow path that minimizes restrictions and to bring the airflow across the outer stator surface  75 . Referring back to  FIG. 3 , an inside radius  165  brings the lead end stator cup  65  casting close to the windings  30  for improved heat transfer. The lead end stator cup  65  may also encapsulate, surround, or support a potting compound surrounding the stator windings  30  in some embodiments, and may therefore be referred to as a “potting cup.” 
         [0026]    Referring to  FIG. 1 , air flows from the stator inlet end  90  to the discharge end  95 , with the airflow  55  captured between the outer stator surface  75  and the air chute  80 . The air chute  80  is positively captured, without the use of fasteners, by the flange  70  at the inlet end  90  and by the opposite lead end frame  85  at the discharge end  95 . The airflow  55  is directed across the winding portion  100  of the opposite lead end frame  85 . The fan  105  draws air into a fan compartment  185  through a fan inlet  205  of the opposite lead end frame  85  and expels the air between structural ribs  110 . The fan compartment  185  is offset from the outer radius of the fan  105 , but is tight to a top shelf  190  and bottom shelf  195  of the fan to lessen noise production and reduce recirculation. 
         [0027]      FIG. 6  illustrates several additional features of the opposite lead end frame  85 . The winding portion  100  is profiled to bring the casting near the windings  30  for effective heat transfer. The winding portion  100  may encapsulate, surround, or support a potting compound surrounding the windings  30  in some embodiments, and therefore may be referred to as a “potting portion.” Like the lead end stator cup  65 , the winding portion  100  has longitudinal ribs  170  in the air path to improve heat transfer as the airflow approaches the fan inlet  205 . A shelf  175  matches the outer profile of the air chute  80  and provides separation that prevents air recirculation between the air outlet at the structural ribs  110  and the air inlet  40  ( FIG. 1 ). Neither the air chute  80  nor the shelf  175  overhang the mounting flange  180  where bolts are used to mount or otherwise couple the motor to a pump or other load. A top surface of the winding portion  100  has four reinforcement ribs  200  that prevent oscillation of the wall that separates the winding portion  100  and a fan compartment  185  to stabilize and improve the life of the bearing. 
         [0028]    Materials: Most external components, including the canopy and air chute, are made out of a plastic. Making these components out of plastic, in combination with thermal barrier provided by the airflow path, maintains the outer surfaces of the motor assembly cool to the touch. 
         [0029]      FIG. 7  illustrates a motor assembly  210  similar to that of  FIGS. 1-8 , but without a canopy, flange, or air chute. Similar features of the two constructions have been given the same reference numbers. In this construction of the invention, a potting compound  215  surrounding the windings  30  is integral to the motor assembly  210 . 
         [0030]    The potting compound  215  is an insulating resin capable of being poured or injected. Various resins may be used, including epoxies, silicones, urethanes and hybrids. The potting compound solidifies to become a fixed component.  FIG. 7  illustrates an assembly consisting of an opposite lead end frame  85 , a stator  25 , and a lead end stator cup  65  (i.e., a “potting cup”), all of which are permanently held together by the potting compound  215 . The potting compound is injected into the assembly as a liquid. After injection, the potting compound solidifies to become a fixed component of the assembly. With reference to  FIG. 8 , the potting compound  215  fills any voids or channels that would normally run through walls of the stator  25 . Furthermore, and with reference to  FIG. 9 , the potting compound fills end turns of the stator windings  30  up to the edge of the lead end stator cup  65 . 
         [0031]    The potting compound serves to protect the motor components from shock and vibration and provides electrical insulation and weatherproofing benefits to the components. In addition, by filling the air gaps between the stator and surrounding components, the potting compound increases the rate of heat transfer from the stator to the lead end stator cup and opposite lead end frame. 
         [0032]    Thus, the invention provides, among other things, a new and useful air-cooled electric motor. Various features and advantages of the invention are set forth in the following claims.