Abstract:
A motor is provided including a stator core having a plurality of stator fins projecting outwardly from the stator core. A plurality of stator cooling channels is defined between adjacent stator fins. A flow mixer ring is axially aligned with the stator core and separated therefrom by an axial gap. The flow mixer ring includes a plurality of ring fins projecting inwardly from an interior surface and a plurality of ring cooling channels defined between the plurality of ring fins. The plurality of ring fins extends from a first surface over at least a portion of an axial length of the flow mixer ring.

Description:
BACKGROUND OF THE INVENTION 
     Exemplary embodiments of this invention generally relate to electrical machines and, more particularly, to a stator structure of an electrical machine for improved cooling. 
     A stator core generates a considerable amount of heat during operation. It is important to remove this heat because overheating of the stator will reduce the life and performance of motors and generators, thereby limiting the range of applications in which they may be used. Conventional stators include a plurality of fins disposed around the outside circumference of the stator. A cooling fluid, such as air, oil, or another coolant for example, will flow through the cooling channels created between adjacent fins to remove heat from the stator through convection. 
     In some applications, foreign material from the environment, such as dirt and debris, will enter the stator assembly. This foreign material may become lodged in the stator assembly so as to form a blockage in one or more cooling channels. The blockage impedes the flow of the cooling fluid to a portion of the stator, such that heat from that area of the stator is not efficiently removed. Occurrence of such blockages cause the temperature of the stator to rise and can ultimately lead to a winding failure. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one embodiment of the invention, a flow mixer ring for use in a motor is provided including a generally circular body constructed from a thermally conductive material. A plurality of fins projects inwardly from an outer surface of the body. A plurality of cooling channels is defined between the plurality of fins. The plurality of fins extends from a first surface over at least a portion of an axial length of the flow mixer ring. 
     According to an alternate embodiment of the invention, a motor is provided including a stator core having a plurality of stator fins projecting outwardly from the stator core. A plurality of stator cooling channels is defined between adjacent stator fins. A flow mixer ring is axially aligned with the stator core and separated therefrom by an axial gap. The flow mixer ring includes a plurality of ring fins projecting inwardly from an outer surface and a plurality of ring cooling channels defined between the plurality of ring fins. The plurality of ring fins extends from a first surface over at least a portion of an axial length of the flow mixer ring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a front view of a stator core according to an embodiment of the invention; 
         FIG. 2  is a perspective view of a stator core according to an embodiment of the invention; and 
         FIG. 3  is a front view of a flow mixer ring according to an embodiment of the invention; 
         FIG. 4  is a perspective view of a flow mixer ring according to an embodiment of the invention; 
         FIG. 5  is a perspective view of the flow mixer ring aligned with the stator core according to an embodiment of the invention; and 
         FIG. 6  is a top view of a flow mixer ring and stator core according to an embodiment of the invention. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIGS. 1 and 2 , a generally circular stator core  20  of an electrical machine or motor is illustrated. The stator core  20  may be made from iron or any other conventionally used material. The stator core  20  includes a plurality of substantially identical and outwardly projecting fins  35 , located around the outside diameter  25  thereof. The fins  35  define an outer periphery of the stator  20 . In one embodiment, the fins  35  are uniform in size. A plurality of cooling channels  40  are created between adjacent fins  35  such that a cooling fluid, such as air for example, may flow through the cooling channels  40  to remove heat from the stator core  20 . The stator core  20  also includes a plurality of inwardly projecting teeth  45  that define an inner periphery  30  of the stator core  20 . The teeth  45  also provide winding spaces  50  that receive the stator windings (not shown) of the stator core  20 . 
     As is known in the art, electrical machines typically include a rotor disposed within a stator. The stator is cooled by airflow through the electrical machine. According to one embodiment, an electrical machine includes a flow mixer ring, such as flow mixer ring  60 , as illustrated in  FIGS. 3-5 . The flow mixer ring  60  has a generally circular body and includes a plurality of similar fins  70  that protrude toward the interior of the ring  60  from an interior surface  62  of the flow mixer ring  60 , and cooling channels  72  are defined between pairs of adjacent fins  70 . In one embodiment, the fins  70  and cooling channels  72  of the flow mixer ring  60  are substantially similar in shape and size to the fins  35  and cooling channels  40  of the stator core  20 . Alternatively, the fins  70  and cooling channels  72  may be a different size and/or shape than the fins  35  and cooling channels  40  of the stator core  20 . As illustrated in  FIGS. 3 and 4 , the fins  70  may protrude inwardly from the interior surface  62  of the flow mixer ring  60 . In such embodiments, the interior surface  62  has a diameter substantially equal to the outer periphery defined by the fins  35  of the stator core  20 . The inwardly projecting fins  70  define an inner periphery  64  of the flow mixer ring  60 . In one embodiment, the inner periphery  64  of the flow mixer ring  60  has a diameter about equal to the outer diameter  25  of the stator core  20 . 
     The flow mixer ring  60  has a limited axial length L relative to the length of the stator core  20  and is made from a thermally conductive material, for example a metal. In one embodiment, the axial length L of the flow mixer ring  60  is in the range of about 0.06 inches (0.1524 centimeters) to about 0.1 inches (0.254 centimeters). The flow mixer ring  60  may be manufactured from a piece of sheet metal, such as with a stamping or punching process. Alternatively, the flow mixer ring  60  may be formed from a washer by removing material from the inner periphery  64  of the washer to create the plurality of fins  70  and cooling channels  72 . 
     Referring now to  FIGS. 5 and 6 , in operation, the flow mixer ring  60  is positioned upstream from the stator core  20  in a housing (not shown) such that the cooling fluid, flowing in the direction indicated by arrow C, first passes through the cooling channels  72  of the flow mixer ring  60  before entering the cooling channels  40  of the stator core  20 . The flow mixer ring  60  is arranged adjacent the stator core  20  such that an axial gap  74  separates the flow mixer ring  60  and a first end  22  of the stator core  20 . The flow mixer ring  60  may be retained in a desired position, adjacent the stator core  20 , using a snap ring or retainer ring for example. The axial gap  74  has, in one embodiment, a distance in the range of about 0.2 inches (0.508 centimeters) to about 0.5 inches (1.27 centimeters). In another embodiment, the axial gap  74  is integrally formed into the flow mixer ring  60  (see  FIG. 4 ). In such alternative embodiments, the axial length L of the flow mixer ring  60  is increased, and the fins  70  extend from adjacent a front surface  66  of the flow mixer ring  60  over only a portion of the axial length L. In such instances, the axial gap  74  is positioned between a back surface  68  of the flow mixer ring  60  and the plurality of fins  70 . 
     In operation, the flow mixer ring  60  is positioned adjacent the stator core  20  such that the plurality of fins  70  and cooling channels  72  of the flow mixer ring  60  are offset from the fins  35  and cooling channels  40  of the stator core  20 . In one embodiment, the flow mixer ring  60  is rotated about half the width of a fin  70  such that a portion of each fin  70  overlaps with a fin  35  of the stator core  20  and a portion of each fin  70  overlaps with an adjacent cooling channel  40  of the stator core  20 . This rotation of the flow mixer ring  60  relative to the stator core  20  ensures that the cooling fluid entering the cooling channels  40  of the stator core  20  have a turbulent flow. 
     By positioning the flow mixer ring  60  upstream from the stator core  20 , the flow mixer ring  60  acts as a screen to prevent foreign material from entering the cooling channels  40  of the stator core  20  and forming a blockage  80  (see  FIG. 5 ). After circumventing a blockage, the cooling fluid will disperse from the axial gap between the flow mixer ring and the stator core  20  to all cooling channels  40  of the state core  20 . The axial gap  74  allows the cooling fluid to flow to neighboring channels, thereby preventing the stator core  20  from overheating, even in the event of a blocked channel  80 . In addition, the flow mixer ring  60  may be warmed by the operation of the motor. As a result, the flow mixer ring  60  may be considered self-cleaning with respect to some blockages, such as those formed by ice and fog for example. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while the various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.