Abstract:
A cooling system of an electric machine includes a rotor having a shaft, a hub mounted to the shaft, and a core mounted to the hub. A bearing assembly is secured to the shaft and has a rotating portion and a fixed portion including a fluid inlet. A plurality of nozzle features are fluidly connected to the fluid inlet via a manifold. A cooling system of an electric machine includes a rotor having a shaft and a hub mounted to the shaft, a fluid inlet having a rotating portion and having a fixed portion, a fluid manifold, and a plurality of nozzle features disposed in the hub and fluidly connected to the fluid inlet via the manifold. A method of cooling an electric machine includes spraying coolant from a plurality of hub nozzles onto end turns of a stator winding.

Description:
BACKGROUND 
       [0001]    The present invention is directed to improving the performance and efficiency of electric machines and, more particularly, to a spray cooling system. 
         [0002]    An electric machine is generally structured for operation as a motor and/or a generator, and may have electrical windings, for example in a rotor and/or in a stator. Such windings may include conductor wire formed as solid conductor segments or bars that are shaped to be securely held within a core, bobbin, or other structure. The conductors may be formed of copper, aluminum, or other electrically conductive material by various manufacturing operations, including casting, forging, welding, bending, heat treating, coating, jacketing, or other appropriate processes. Such conductors are typically formed as individual segments that are assembled into a stator and then welded together. 
         [0003]    The stator has a cylindrical core that secures the conductor segments of the stator windings in slots disposed around the circumference of the core. In many electric machines, the stator core is densely populated so that each angular position has several layers of conductor segments installed therein. In a densely packed stator operating at a high performance level, excessive heat may be generated in the stator windings. In some applications, heat must be actively removed to prevent it from reaching impermissible levels that may cause damage and/or reduction in performance or life of the motor. Various apparatus and methods are known for removing heat. One exemplary method includes providing the electric machine with a water jacket having fluid passages through which a cooling liquid, such as water, may be circulated to remove heat. Another exemplary method may include providing an air flow, which may be assisted with a fan, through or across the electric machine to promote cooling. A further exemplary method may include spraying or otherwise directing oil or other coolant directly onto end turns of a stator. 
         [0004]    Rotors of electric machines may include windings, axially extending induction bars, and/or permanent magnets that generate heat. Friction, eddy currents, hysteresis losses, and other aspects of machine operation also generate heat. Such heat may cause lowering of machine efficiency and output, and excessive heat may result in physical damage and mechanical problems. For example, in internal permanent magnet (IPM) rotors, the magnets are sensitive to heat and will de-magnetize when subjected to excessive heat generated from power losses in the motor. 
         [0005]    Conventional electric machines are not adequately cooled. Although various structures and methods have been employed for cooling an electric machine, improvement remains desirable. 
       SUMMARY 
       [0006]    It is therefore desirable to obviate the above-mentioned disadvantages by providing a structure and method for spraying coolant onto stator end turns. 
         [0007]    According to an exemplary embodiment, a cooling system of an electric machine includes a rotor having a shaft, a hub mounted to the shaft, and a core mounted to the hub. A bearing assembly is secured to the shaft and has a rotating portion and a fixed portion including a fluid inlet. A plurality of nozzle features are fluidly connected to the fluid inlet via a manifold. 
         [0008]    According to another exemplary embodiment, a cooling system of an electric machine includes a rotor having a shaft and a hub mounted to the shaft, a fluid inlet having a rotating portion and having a fixed portion, a fluid manifold, and a plurality of nozzle features disposed in the hub and fluidly connected to the fluid inlet via the manifold. 
         [0009]    According to a further exemplary embodiment, a method of cooling an electric machine includes spraying coolant from a plurality of hub nozzles onto end turns of a stator winding. 
         [0010]    The foregoing summary does not limit the invention, which is defined by the attached claims. Similarly, neither the Title nor the Abstract is to be taken as limiting in any way the scope of the claimed invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0011]    The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: 
           [0012]      FIG. 1  is a schematic view of an electric machine; 
           [0013]      FIG. 2  is a perspective view of an exemplary rotor assembly; 
           [0014]      FIG. 3  is a cross-sectional schematic view of a cooling system of an electric machine, according to an exemplary embodiment; 
           [0015]      FIG. 4  is a schematic elevation view of a portion of an exemplary hub after a series of machining processes; 
           [0016]      FIG. 5  is a schematic top view of a nozzle block, according to an exemplary embodiment; and 
           [0017]      FIG. 6  is a schematic top view of a rotor assembly, according to an exemplary embodiment. 
       
    
    
       [0018]    Corresponding reference characters indicate corresponding or similar parts throughout the several views. 
       DETAILED DESCRIPTION 
       [0019]    The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of these teachings. 
         [0020]      FIG. 1  is a schematic view of an exemplary electric machine  1  having a stator  2  that includes stator windings  3  such as one or more coils. An annular rotor body  4  may also contain windings and/or permanent magnets and/or conductor bars such as those formed by a die-casting process. Rotor body  4  is part of a rotor that includes an output shaft  5  supported by a front bearing assembly  6  and a rear bearing assembly  7 . Bearing assemblies  6 ,  7  are secured to a housing  8 . Typically, stator  2  and rotor body  4  are essentially cylindrical in shape and are concentric with a central longitudinal axis  9 . Although rotor body  4  is shown radially inward of stator  2 , rotor body  4  in various embodiments may alternatively be formed radially outward of stator  2 . Electric machine  1  may be an induction motor/generator or other device. In an exemplary embodiment, electric machine  1  may be a traction motor for a hybrid or electric type vehicle. Housing  8  may have a plurality of longitudinally extending fins (not shown) formed to be spaced from one another on a housing external surface for dissipating heat produced in the stator windings  3 . 
         [0021]      FIG. 2  is a perspective view of an exemplary rotor assembly  10 . A shaft  11  may have a center bore  12  that is either threaded or smooth. A hub  13  has a center bore  14  with a diameter slightly larger than the diameter of shaft  11 , whereby shaft  11  fits snugly therein and is secured thereto by a compression plate  15 . Hub  13  is integrally formed with an inner cylinder  16  and a number of spokes  18  extending radially outward to an outer cylinder  17 . The radially outer surface  19  of hub  13  is interference fit to the radially inner surface  20  of a rotor lamination stack  21 . A bearing assembly  22  has a rotating inner portion  23  connected to shaft  11 , an outer portion  24  connected to a support structure (not shown), and a bearing portion  25  therebetween. 
         [0022]      FIG. 3  is a cross-sectional schematic view of a cooling system  26  of an electric machine, according to an exemplary embodiment. A hub  27  has an annular, reinforced inner portion  28  secured to a shaft  29 , for example by an interference fit, a compression fit, or by other structure. Hub  27  may be cast, forged, machined, and/or molded of steel, aluminum, resin, or other high strength material. Shaft  29  extends through an annular inner opening  30  of a bearing assembly  31 , and is secured thereto by a compression fit, or by other structure such as an interference fit, set screw(s), or other. Shaft  29  further extends through another annular inner opening  32  of bearing assembly  31 , and is secured thereto by a compression fit, or by other structure. An axially inward bearing set  33  and an axially outward bearing set  34  allow shaft  29  to rotate. A rotor lamination stack  35  is formed of individual round steel laminations, each coated with an electrical insulation material. Lamination stack  35  is secured to hub  27  by an interference fit, and a keying structure (not shown) is typically also utilized for circumferentially aligning the laminations with one another and with hub  27 . The radially outward portions of bearing sets  33 ,  34  are fixedly secured to a support structure  36  mounted to a frame  37  using bolts  38 . Support structure  36  of bearing assembly  31  encloses an annular chamber  39  in the axial space between bearing sets  33 ,  34 . A coolant inlet tube  40  extends through support structure  36  and has a coolant outlet  41  within chamber  39 . The other end of coolant inlet tube  40  terminates in a fluid connector  42  secured to support structure  36 . A coolant supply line  43  includes one or more valve(s)  44  and flow meter(s)  45 , and connects to fluid connector  42 . A coolant tube  46  extends longitudinally between an inlet  47 , within chamber  39 , and a manifold  48 . A number of coolant tube sections  49 ,  50  extend radially along corresponding spokes  18  between manifold  48  and manifolds  51 ,  52 , respectively. Coolant tube  53  extends axially between manifold  51  and nozzle block  57 . Coolant tube  54  extends axially between manifold  51  and nozzle block  58 . Coolant tube  55  extends axially between manifold  52  and nozzle block  59 . Coolant tube  56  extends axially between manifold  52  and nozzle block  60 . The coolant tubing may be a light gauge non-magnetic metal, high temperature nylon reinforced plastic, or other material, and typically has an inside diameter of 0.8 to 2 mm. Portions of shaft  29  may include grooves or channels for securing tubing sections  46 ,  49 ,  50 . For example, a groove may have a circular cross-section. Any imbalance in shaft  29  and the rotor assembly may be easily corrected by manufacturing methods known in the art. An air gap  61  separates the outer circumference of lamination stack  35  from the inner diameter of stator  2 . Nozzle blocks  57 ,  59  are axially aligned with end turns  62 , and nozzle blocks  58 ,  60  are axially aligned with end turns  63 . A sump portion  64  is provided for collecting coolant by gravity flow. 
         [0023]    In operation, a pump (not shown) provides coolant from a heat exchanger (not shown) to supply line  43 . For example, the pump may also supply the coolant to a cooling jacket (not shown) in the body of stator  2 . The coolant fills chamber  39  and then fills tubing  46 ,  49 ,  50 ,  53 - 56 . The continued pumping causes the coolant to be discharged from nozzle blocks  57 - 60 . The coolant pressure and the centrifugal force of rotor rotation cause the discharged coolant to spray onto end turns  62 ,  63  and lamination stack  35 . Since the total space of the enclosed coolant paths is small, a pressure of 3-10 psi will typically cause coolant to exit the nozzles with a high force. 
         [0024]    Placement of axial coolant channels in hub  27  may be performed by post-casting machining. For example, tubes  53 - 56  may be formed as longitudinal channels by drilling channels having a diameter of approximately 1.5 mm. Similarly, radially oriented tubes  49 ,  50  may also be formed as channels by drilling. The use of hub  27  for implementing rotor coolant channels provides advantages compared with conventional channels formed in a rotor lamination core. For example, machining coolant channels into a lamination stack causes electrical shorting therein. 
         [0025]      FIG. 4  is a schematic elevation view of a portion of an exemplary hub  67  after a series of machining processes. A cavity  66  is formed at an axial end of hub  67 , leaving a radially inner annular wall  68 , a radially outer annular wall  69 , and an axially facing surface  65 . A bore  70  is drilled to a limited depth below surface  65 . For example, bore  70  may be drilled and tapped to receive a 6 mm thread. An O-ring  71  or other sealing structure may be placed at a location within bore  70 . An exemplary hub adapter  72  has a threaded insert portion  73  that screws into the threaded portion of bore  70 . When adapter  72  is screwed in and properly seated, fluid channel  75  of adapter  72  is aligned with fluid channel  74  of hub  67 , and the fluid connection is sealed by O-ring  71 . Fluid channel  75  has a radially extending portion  76  with a fluid connector  77  that faces radially outward. 
         [0026]      FIG. 5  is a schematic top view of an exemplary nozzle block  78 , according to an exemplary embodiment. A body  79  may be formed by casting or by other processing appropriate for the chosen body material, such as metal. Nozzle block  78  is formed to fit within cavity  66  and rest atop axial end surface  65  ( FIG. 4 ). Individual nozzles  80  are positioned to have a rear opening  81  in communication with a manifold portion  82  common to rear openings  81  of all nozzles  80  of block  78 . Nozzles  80  may be formed in any of several different ways. For example, a bore  83  may be machined from either a side of manifold  82  or from an external surface  84 , and then a pre-formed nozzle may be installed and secured such as by threads, epoxy, or other structure. In an alternative embodiment, nozzle  80  may be formed by a fine machining process after a wide diameter portion  85  has been cast; a tapered throat portion  86  and a small diameter tip  87  may be formed by precision machining. Alternatively, small diameter needle tips (not shown) may be installed after the casting process and secured by press fitting, threads, or by other structure. A fluid connector  88  extends from manifold  82  for mating with fluid connector  77  of  FIG. 4 . When connectors  77 ,  88  are properly mated and nozzle block  78  is seated on surface  65  of hub  67 , the radially outward surface  89  of hub adapter  72  is contiguous with surface  90  of nozzle block  78  and adapter  72  fits within nozzle block slot  91 . 
         [0027]    Surface  84  of nozzle block  78  may be formed as any number of individual surfaces. For example, a first set of nozzles  80  may be referenced from a first surface and a second set of nozzles  80  may be referenced from a second surface. In a case where three nozzles  80  form a set and a center nozzle  80  is referenced, each other nozzle  80  may be angled away from center by 0-45 degrees. The amount of angling may depend on the force, volume, width, elevation, coverage and other parameters of the spray  92  from each nozzle  80  or from sets thereof. Horizontal and vertical spacing and elevation of individual nozzles  80  may be varied as required for providing optimum cooling of stator end turns  62 ,  63 . 
         [0028]      FIG. 6  is a schematic top view of a rotor assembly  93 , according to an exemplary embodiment. Lamination stack  35  is secured to hub  94 . Hub  94  has an annular inner shaft attachment portion  95 , spokes  96 , and an outer rim portion  97 . Radially extending fluid channels  98  are in fluid communication with an axial fluid channel  99  at the center of shaft  29 . Radial channels  98  pass through radially extending bores  100  formed in shaft  29 . Each bore  100  is mated to a respective inner channel portion  101  and a spoke channel  102 . Each spoke channel  102  feeds an axially extending bore/tube  74  in fluid communication with a passageway  75  formed in adapter  72  ( FIG. 4 ). Each adapter  72  is mated with a respective nozzle block  78 . Sizes of channels and bores, for example, may be 0.5 to 1.5 mm or any other appropriate diameter. 
         [0029]    In operation, the relatively small sizes of fluid paths within rotor assembly  93  assures that coolant being ejected through nozzles  80  of nozzle blocks  78  has acceptable velocity to produce spray  92  ( FIG. 5 ) that travels past lamination stack  35  and impacts stator end turns  62 ,  63  ( FIG. 3 ). Nozzle angle and elevation are typically set to maximize and focus sprays  92  on stator end turns  62 ,  63 . Overspray and other coolant being ejected from nozzles  80  typically also impacts the body of stator  2 , lamination stack  35 , and portions of hub  27  ( FIG. 3 ), thereby providing ancillary cooling of other portions of electric machine  1 . Depending upon the particular application, the high spray velocity created by use of small diameter channels/tubing may be balanced with a need to maximize coolant flow volume. For example, any nozzle channels may have an increased size without compromising structural integrity. Axial channel/tube  46  and manifold  48  of shaft  29 , and radial channels  100 ,  101  may have an increased size when material strength and rigidity are not thereby rendered insufficient. 
         [0030]    Various types of nozzles  80  may be used, such as cone pattern spray nozzles, fan pattern spray nozzles or needle jet nozzles. A jet is a substantially continuous column of moving liquid, in contrast to a spray which is formed from discrete droplets. Nozzles  80  may differ according to their relative positions respecting one another. For example, nozzles  80  may be declined, inclined, leading, trailing, or central. The location of nozzles  80  may also be varied to the extent that the sprays or jets from the nozzles do not excessively interfere with each other. Nozzles  80  may produce spray  92  as a coherent stream having a high peak impact force on end turns  62 ,  63 , or nozzles  80  may be structured to provide spray  92  that expands and disperses into any degree of fine droplets. 
         [0031]    While various embodiments incorporating the present invention have been described in detail, further modifications and adaptations of the invention may occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention.