Abstract:
Embodiments of the invention provide an electric machine module and a method for cooling an electric machine. The apparatus and method include providing the electric machine including a rotor and a stator with stator end turns and enclosing at least a portion of the electric machine within a housing. The method also includes introducing a coolant into a machine cavity, directing the coolant toward the stator end turns, and returning a portion of the coolant which flows past the stator end turns back toward the stator end turns using a rotating agitator member operatively coupled to the rotor.

Description:
BACKGROUND 
     Hybrid vehicles offer an opportunity for vehicle drivers to engage in environmentally-conscious behavior because of hybrids&#39; improved fuel economy and reduced emissions. Hybrid vehicles combine traditional internal combustion engines with an electro-mechanical transmission. Electric motors located within the electro-mechanical transmission provide energy to propel the vehicle, reducing the need for energy provided by the internal combustion engine, thereby increasing fuel economy and reducing emissions. 
     As with any electric machine, the hybrid transmission&#39;s electric motor rejects some energy in the form of heat. Efficient removal of heat from the electric motor can improve the lifespan of the electric machine as well as improve the electric machine&#39;s operating efficiency. 
     SUMMARY 
     Some embodiments of the invention provide an electric machine module capable of being cooled by a coolant. The electric machine module can include an electric machine including a rotor with generally opposing end faces and a stator with stator end turns. The electric machine module can also include an agitator member operatively coupled to the rotor adjacent the generally opposing end faces and extending substantially outward along at least a portion of an axial length of the stator end turns. 
     Some embodiments of the invention provide a method for cooling an electric machine. The method can include providing the electric machine including a rotor with generally opposing end faces and a stator substantially circumscribing the rotor and including stator end turns. The method can also include substantially enclosing at least a portion of the electric machine within a housing and defining at least a portion of a machine cavity with an inner wall of the housing. The method can further include introducing a coolant into the machine cavity, directing the coolant toward the stator end turns, and returning a portion of the coolant which flows past the stator end turns back toward the stator end turns for cooling using a rotating agitator member operatively coupled to the rotor near the generally opposing end faces. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an electric machine module according to one embodiment of the invention. 
         FIG. 2  is a partial cross-sectional view of an electric machine with an agitator member, according to one embodiment of the invention. 
         FIG. 3  is another cross-sectional view of the electric machine module according to one embodiment of the invention. 
         FIG. 4  is a perspective view of a portion of the electric machine of  FIG. 2 . 
         FIG. 5  is a partial perspective view of a portion of the electric machine of  FIG. 2 . 
         FIG. 6  is a cross-sectional view of the electric machine of  FIG. 2 . 
         FIG. 7A  is a cross-sectional view of an electric machine module according to another embodiment of the invention. 
         FIG. 7B  is a cross-sectional view of an electric machine module according to yet another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     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. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
     The following discussion is presented to enable a person skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other embodiments and applications without departing from embodiments of the invention. Thus, embodiments of the invention are not intended to be limited to embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of embodiments of the invention. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of embodiments of the invention. 
       FIG. 1  illustrates an electric machine module  10  according to one embodiment of the invention. The machine module  10  can include an electric machine  12  and a housing  14 . The electric machine  12  can be disposed within a machine cavity  16  defined at least partially by an inner wall  18  of the housing  14 . The electric machine  12  can include a rotor  20 , a stator  22  substantially circumscribing the rotor  20 , stator end turns  24 , and bearings  26 , and can be disposed about a main output shaft  28 . In some embodiments, the electric machine  12  can also include a rotor hub  30  or can have a “hub-less” design (not shown). 
     The electric machine  12  can be, without limitation, an electric motor, such as a hybrid electric motor, an electric generator, or a vehicle alternator. In one embodiment, the electric machine  12  can be an induction belt-alternator-starter (BAS). In another embodiment, the electric machine  12  can be a High Voltage Hairpin (HVH) electric motor for use in a hybrid vehicle. 
     Components of the electric machine  12  such as, but not limited to, the stator end turns  24 , the rotor  20 , and the rotor hub  30  can generate heat during operation of the electric machine  12 . These components can be cooled to enhance the performance of and increase the lifespan of the electric machine  12 . 
     As shown in  FIG. 1 , the rotor  20  can include generally opposing end faces  32 ,  34 . A balance ring  36  can be coupled to the rotor  20  and/or the rotor hub  30  at a location proximal to the generally opposing end faces  32 ,  34 . In some embodiments, the balance ring  36  can be coupled to the rotor hub  30  using threads, a plurality of threaded fasteners, a friction fitting, welding, or another conventional coupling manner so that the balance ring  36  can rotate substantially synchronously with the rotor  20  and the rotor hub  30  during operation of the electric motor  12 . In addition, the balance ring  36  can be “staked” to a lip  35  on an inner diameter of the rotor hub  30  and a portion of the balance ring  36  can be heat pressed to a lamination stack of the rotor  20  (e.g., for axial support), as shown in  FIG. 3 . Additional components, such as steel insert pieces, can also be used to help clamp the balance ring  36  to the rotor hub  30  around the lip  35 . The balance ring  36  can extend axially from the rotor hub  30  into the machine cavity  16  and can provide stability for the rotor  20  and rotor hub  30  during operation of the electric machine  12 . In one embodiment, the balance ring  36  comprises cast aluminum. 
     In other embodiments, such as those including the hub-less design, the balance ring  36  can be coupled to the rotor  20  proximal to the generally opposing end faces  32 ,  34 , as shown in  FIG. 2 . The balance ring  36  can be coupled to the rotor  20  using threads, a plurality of threaded fasteners, a friction fitting, welding, or another conventional coupling manner so that the balance ring  36  can rotate substantially synchronously with the rotor  20  during operation of the electric motor  12 . The balance ring  36  can provide stability for the rotor  20  during operation of the electric machine  12 . In either the hub-less design or embodiments including the rotor hub  30 , the balance ring  36  can be operatively coupled to the rotor  20  (i.e., through direct coupling or coupling via the rotor hub  30 ) due to the fact that it can rotate with the rotor  20  during operation of the electric machine. 
     In some embodiments, an agitator member  38  can be a ring-shaped member coupled to the rotor  20 , the rotor hub  30 , and/or the balance ring  36  proximal to the generally opposing end faces  32 ,  34 . More specifically, at least a portion of the agitator member  38  can be coupled to the rotor  20 , the rotor hub  30  and/or the balance ring  36  such that the agitator member  38  synchronously rotates with the rotor  20  and the rotor hub  30  when the electric machine  12  is in operation. The agitator member  38  can be coupled to the rotor  20 , the rotor hub  30 , and/or the balance ring  36  using threads, one or more threaded fasteners, a friction fitting, welding, or another conventional coupling manner. In one embodiment, the agitator member  38  can be staked to a lip (not shown) on the inner diameter of the rotor hub  20  and further axial support can be provided by heat pressing a portion of the agitator member  34  in a lamination stack surrounding the rotor  20 . In another embodiment, the agitator member  38  can be cast as part of the rotor  20  during rotor fabrication so that the agitator member  38  and the rotor  20  are integral. In yet another embodiment, the agitator member  38  can be integral with the balance ring  36 . The agitator member  38  can extend axially away from the rotor  20  and/or the rotor hub  30  into the machine cavity  16 . 
     In some embodiments, the agitator member  38  can be coupled to the rotor  20  and/or the rotor hub  30  with or without the balance ring  36 . If the balance ring  36  is present, an axial length of the agitator member  38  can be substantially equal to or longer than an axial length of the balance ring  36 . For example, in one embodiment, at least a portion of the agitator member  38  can extend axially past the balance ring  36  (i.e., axially away from the rotor  20 ). In addition, the agitator member  38  can extend substantially parallel to the stator end turns  24  along at least a portion of an axial length of the stator end turns  24 . In some embodiments, the agitator member  38  can extend substantially axially outward about as far as the stator end turns  24 . In other embodiments, the axial length of the agitator member  38  can be shorter than or longer than the axial length of the stator end turns  24 . 
     In either the hub-less design or embodiments including the rotor hub  30 , the agitator member  38  can be operatively coupled to the rotor  20  (i.e., through direct coupling or coupling via the rotor hub  30  or the balance ring  36 ) due to the fact that it can rotate with the rotor  20  during operation of the electric machine. 
     In some embodiments, the agitator member  38  and the balance ring  36  can be an integral structure, as described above. In other embodiments, the balance ring  36  and the agitator member  38  can comprise two or more independent components. The balance ring  36  and the agitator member  38  can be fabricated from aluminum, steel, stainless steel, or other similar materials. In some embodiments, the agitator member  38  can be oriented so that it extends substantially parallel to an axis of rotation  40  of the rotor  20 . In other embodiments, the agitator member  38  can be oriented in either a positive or negative direction relative to the rotor&#39;s axis of rotation  40 . 
     In addition, the agitator member  38  can include a radially distal surface  42  and a radially proximal surface  44 . The radial location of a both the radially distal surface  42  and the radially proximal surface  44  can vary. For example, the radially distal surface  42  can have a shorter radius than the rotor  20  (e.g., by a length “x”, as shown in  FIG. 4 ) or can have a radius equal to a radius of the rotor  20  (as shown in  FIG. 2 ). In some embodiments, the radially distal surface  42  can have a shorter radius than the radius of the rotor  20  to provide substantial radial separation between an underside of the stator end turns  24  and the agitator member  38 . 
     In some embodiments, as shown in to  FIG. 4 , a plurality of struts  46  can provide support for the agitator member  38 . The plurality of struts  46  can be cast or otherwise formed in the agitator member  38  so that the struts  46  and the agitator member  38  are a unitary body. 
     In some embodiments, at least a portion of the housing  14  can include a plurality of coolant apertures  48 . The coolant apertures  48  can be in fluid communication with, for example, a coolant jacket  50  located substantially around the electric machine  12  (e.g., within an inner wall of the housing  14  or along the outside or inside of the housing  14  substantially surrounding an outer diameter of the stator  22 ) and the machine cavity  16 . A coolant, such as transmission fluid, ethylene glycol, an ethylene glycol/water mixture, water, oil, or a similar substance, can originate from a fluid source (not shown), flow throughout the coolant jacket  50 , and can be dispersed through the coolant apertures  48  into the machine cavity  16 . 
     In one embodiment, the coolant apertures  48  can be positioned so that the coolant can be dispersed onto the stator end turns  24 , as shown in  FIG. 2 . After reaching the stator end turns  24 , the coolant can receive heat energy from the stator end turns  24 , which can result in cooling of the electric machine  12 . Some of the coolant can be dispersed past the stator end turns  24  or, for example, splash or drip from the stator end turns  24  onto the radially distal surface  42  of the agitator member  38 . In addition, some of the coolant that comes in contact with the stator end turns  24  can continue to flow toward the radially distal surface  42 . As the coolant reaches the radially distal surface  42 , the coolant can be substantially radially slung back outward on to the stator end turns  24  due to the rotation of the agitator member  38  in synchronicity with the rotor  20 . The process of radially slinging the coolant toward the stator end turns  24  can serve to recycle the coolant, and thus, maximize cooling potential of the coolant. 
     In some embodiments, the process of radially slinging the coolant back toward the stator end turns  24  using the agitator member  38  can be considered a “multiple-pass” method of cooling, as the coolant can reach the stator end turns  24  multiple times to provide additional cooling. Conventional electric machines use a “single-pass” method of cooling where the coolant only reaches the stator end turns  24  once and then is discharged away from the electric machine  12  without further cooling benefits. In addition, the single-pass method only permits the coolant to reach radially outer surfaces of the stator ends turns  24 , whereas the multiple-pass method allows coolant to be slung back towards radially inner surfaces of the stator end turns  24 . As a result, the multiple-pass cooling method allows the coolant to reach both the radially outer surface as well as the radially inner surface of the stator end turns  24 , and thus, provides enhanced cooling. 
     In one embodiment, as shown in  FIGS. 4 ,  5 , and  6 , the radially distal surface  42  can include a textured surface  52 . The textured surface  52  can have different textures such as scalloping, ribbing, ridging, etc. In some embodiments, the textured surface  52  can be asymmetric in shape to increase the force with which the coolant is slung. In another embodiment, the radially distal surface  42  can lack texture and can include a substantially planar or smooth surface. 
     In comparison to conventional balance rings, the agitator member  38 , including the textured surface  52  or the substantially planar surface, can enhance radial slinging of the coolant because it provides more surface area to receive the coolant. Also, because the agitator member  34  can synchronously rotate with the rotor  20  and/or the rotor hub  30 , centrifugal force can force the coolant away from the agitator member  38  so that the coolant can be dispersed onto the stator end turns  24 . In one embodiment, the amount and shape of texturing on the textured surface  52  can be selected to provide a desired amount of cooling without slinging the coolant at velocities which can possibly erode the stator end turns  24 . In addition, compared to conventional balance rings, the agitator member  38  can further increase air circulation within the machine cavity  16 , and thus, enhance electric machine cooling, because its larger mass, relative to a balance ring alone, can displace more air when the agitator member  38  is in motion. In one embodiment, the textured surface  52  can be shaped similar to pump or fan vanes to help increase air circulation and/or increase radial slinging of the coolant. 
     In some embodiments, the agitator member  38  can include a plurality of agitator channels  54 . As shown in  FIGS. 2 and 5 , the agitator channels  54  can extend radially through the agitator member  38 . The plurality of agitator channels  54  can extend through any desired radial length of the agitator member  38 , such as a full length of the agitator member  34  or a portion of the full length of the agitator member  38 . The agitator channels  54  can be positioned at nearly any distance along the axial length of the agitator member  38  (e.g., more proximal to the rotor  20 , centrally along the axial length, or more distal from the rotor  20 ). For example, as shown in  FIG. 5 , the plurality of agitator channels  54  can be positioned axially distal from the rotor  20 . The location of each of the plurality of agitator channels  54  can be symmetric or asymmetric along the agitator member  38  (i.e., not each agitator channel may be positioned at the same distance along the axial length of the agitator member  38 ). 
     Additionally, any number of agitator channels  54  can be included in the agitator member  38 , or in attachments to the agitator member  38 . In some embodiments, as shown in  FIG. 5 , each of the plurality of agitator channels  54  can be circular in shape. In other embodiments, the agitator channels  54  can have similar or different shapes, including circular, square, rectangle, oval, and/or other shapes. Also, the plurality of agitator channels  54  can include similar or varying radii or diameters. The agitator channels  54  can be of sufficient size to allow passage of a portion of the coolant through the agitator channels  54 , as described below. The agitator channels  54  can be sized and positioned so that another portion of the coolant that reaches the agitator member  38  can continue to be substantially radially slung toward the stator end turns  24 . 
     In some embodiments, an additional volume of the coolant also can be expelled near the rotor hub  30 , for example, from a base of the rotor hub  30  or from the main input shaft  28 . The coolant expelled near the rotor hub  30  can flow radially outward toward the housing  12  (e.g., due to centrifugal force). A portion of the coolant can reach the radially proximal surface  44  of the agitator member  38 , and the agitator channels  54  can provide a pathway for the coolant to flow between the radially proximal surface and the radially distal surface. More specifically, the coolant  50  flowing radially outward onto the agitator member  38  can flow through the agitator channels  54  so that it reaches the radially distal surface  42  and is substantially radially slung toward the stator end turns  24 , or at least concentrated near the stator end turns  24 . The additional volume of coolant can further aid in cooling the electric machine  12 , including the stator end turns  24 . 
       FIGS. 7A and 7B  illustrate the electric machine module  10  according to another embodiment of the invention. As shown in  FIG. 7A , a cover  56  can be coupled to the inner wall  18  and at least partially surround the stator end turns  24  so that the cover  56  and each of the stator end turns  24  define a stator cavity  58  around the stator end turns  24 . The stator cavity  58  can be in fluid communication with the machine cavity  16 . The cover  56  can also substantially surround the stator  22 . For example,  FIG. 7A  illustrates the cover entirely surrounding the stator  22  as well as partially surrounding the stator end turns  24  (e.g., as an integral stator housing ring and cover assembly). In some embodiments, additional caps (not shown) can enclose the cover  56  within the housing  14 . In other embodiments, the cover  56  can be a part of the housing  14  (e.g., extending from the inner wall  18  on either end of the stator  22  to partially surround the stator end turns  24 ). 
     The cover  56  can extend a desired radial distance from the inner wall  18  and, in some embodiments, can turn back inward axially, as shown in  FIGS. 7A and 7B . The cover  56  can also be positioned a desired axial distance from the housing  14 . The desired distances can be uniform or vary along radial portions of, or along the circumference of, the electric machine  12  and, as a result, the stator cavity  58  can be uniform or vary in size along the radial portions. In addition, in some embodiments, the stator cavity  58  may not extend around the entire 360 degrees of the stator end turns  24  (i.e., some radial portions of the stator end turns  24  are not surrounded by the cover  56 ). 
     The cover  56  can comprise plastic, aluminum, steel, a polymeric material, or a similar material. In some embodiments, the size of the stator cavity  58  can vary depending on the dielectric properties of the coolant and the materials from which the cover  56  are fabricated or depending on its radial position within the electric machine module  10 . In one embodiment, the size of the stator cavity  58  can be reduced by coating an area of the cover  56  closest to the stator end turns  24  with a material of high dielectric strength, such as an epoxy material  60 , as shown in  FIG. 3 . In another embodiment, an upper portion of the electric machine module  10  can include a substantially larger stator cavity  58  than a lower portion of the electric machine module  10 . 
     In some embodiments, the cover  56  can be coupled to the inner wall  18  by press fitting, friction fitting, threaded fasteners, or a similar coupling manner. In addition, the cover  56  can comprise one or more parts, where some parts of the cover  56  are integral with the inner wall  18  and other parts of the cover are coupled to the inner wall  18 . The stator cavity  58  can receive the coolant from the cooling jacket  50  and the coolant apertures  48  (similar to that shown in  FIG. 2 ), or from a cooling jacket  59  formed between the cover  56  and the inner wall  18  through coolant apertures  61  of the cover  56 . The cooling jacket  59  can receive the coolant from a feed port  62 , as shown in  FIGS. 6-7B , in fluid communication with the fluid source. After the coolant flows into the stator cavity  58 , the cover  56  can help concentrate the flowing coolant within the stator cavity  52  so that the coolant can remain in contact with or near the stator end turns  24  for a prolonged time period in order to help transfer more heat energy. The coolant can eventually disperse out of the stator cavity  58  toward the machine cavity  16 . Compared to conventional cooling systems, the cover  56  can greatly enhance cooling of the stator end turns  24  because the cover  56  can prevent at least some of the coolant from quickly dispersing away from the stator end turns  24  and can help concentrate the coolant near the heat energy-radiating stator end turns  24 . 
     In one embodiment, as shown in  FIG. 7B , the stator cavity  58  can be defined by the cover  56  and the stator end turns  24  as well as the agitator member  38 . The stator cavity  58  can be in fluid communication with the machine cavity  16 , as described above. When the coolant enters the stator cavity  58 , the coolant can flow onto the stator end turns  24  and can be concentrated within the stator cavity  58  by the presence of the cover  56 . In addition, when the coolant flows toward the agitator member  38 , it can be radially slung back toward the stator end turns  24  and the cover  56  where it can once again become concentrated around the stator end turns  24 . The combination of the cover  56  and the agitator member  38  can synergistically improve cooling efficiency by applying and recycling the coolant near and around the stator end turns  24 . 
     Because the stator cavity  58  can be in fluid communication with the machine cavity  16  in some embodiments, some of the coolant can flow into the machine cavity  16  while a significant portion of the coolant can remain within the stator cavity  58 . In some embodiments, further cooling can be achieved using an additional volume of coolant expelled from near the rotor hub  30 . The additional volume of coolant can flow radially outward, through some of the plurality of agitator channels  52 , and toward the stator cavity  58  so that it can be applied and reapplied to the stator end turns  24 . The additional flow of coolant can lead to more efficient heat energy transfer because of exchange of the coolant and repeated recycling of the coolant near the stator end turns  24 . 
     After flowing over the electric machine components, the coolant can pool at or near a bottom portion of the housing  12  (e.g., by flowing in the machine cavity  16  outside of the cover  56  or through drain ports  64  of the cover  56 ). A drain (not shown) can be located at or near the bottom portion in order permit removal of pooling coolant from the housing  12 . The drain can be coupled to an element which can remove the heat energy from the drained coolant, such as a radiator or other suitable heat exchanger, so that it can be circulated back to the fluid source. 
     It will be appreciated by those skilled in the art that while the invention has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto. The entire disclosure of each patent and publication cited herein is incorporated by reference, as if each such patent or publication were individually incorporated by reference herein. Various features and advantages of the invention are set forth in the following claims.