Abstract:
A thermal control system includes a stator having conductor end turns at opposite axial ends thereof, and first and second cooling systems respectively disposed at the opposite axial stator ends, each cooling system having a cover, a coolant inlet, a coolant outlet, and at least one cooling channel. Thermally conductive potting compound thermally mates the cooling systems with the end turns. A method of cooling end turns includes providing a cooling system for each axial end of the stator, each cooling system having at least one cooling channel that includes a coolant inlet and a coolant outlet, and thermally mating each cooling system to the respective end turns. A method of cooling end turns includes providing separate cooling systems in each axial end plate of an electric machine, and filling space within the end turns, and between the end turns and the cooling systems, with thermally conductive potting compound.

Description:
BACKGROUND 
     The present invention is directed to improving the performance and thermal efficiency of electric machines and, more particularly, to methods and apparatus for removing heat from stator end turns. 
     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 may be formed as individual segments that are assembled into a stator and then welded together. 
     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. 
     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. The aggregate heat may cause lowering of machine efficiency and output, and excessive heat may result in physical damage and mechanical problems. 
     Conventional electric machines are not adequately cooled. Although various structures and methods have been employed for cooling an electric machine, improvement remains desirable. 
     SUMMARY 
     It is therefore desirable to obviate the above-mentioned disadvantages by providing methods and apparatus for minimizing thermal resistance and increasing thermal efficiency. 
     According to an exemplary embodiment, a thermal control system includes a stator having conductor end turns at opposite axial ends thereof, and first and second cooling systems respectively disposed at the opposite axial stator ends, each cooling system having a cover, a coolant inlet, a coolant outlet, and at least one cooling channel. Thermally conductive potting compound thermally mates the cooling systems with the end turns. 
     According to another exemplary embodiment, a method of cooling end turns includes providing a cooling system for each axial end of the stator, each cooling system having at least one cooling channel that includes a coolant inlet and a coolant outlet, and thermally mating each cooling system to the respective end turns. 
     According to a further exemplary embodiment, a method of cooling end turns includes providing separate cooling systems in each axial end plate of an electric machine, and filling space within the end turns, and between the end turns and the cooling systems, with thermally conductive potting compound. 
     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 
       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: 
         FIG. 1  is a schematic view of an electric machine; 
         FIG. 2  is a cross-sectional view of a stator coolant system, according to an exemplary embodiment; 
         FIG. 3  is a perspective view of the inner portion of an exemplary end cover/coolant channel assembly for the axial end of a housing having crown type end turns; 
         FIG. 4  is a perspective view of the outer portion of an exemplary end cover/coolant channel assembly for the axial end of a housing having crown type end turns; 
         FIG. 5  is a perspective view of the inner portion of an exemplary end cover/coolant channel assembly for the axial end of a housing having weld type end turns; 
         FIG. 6  is a perspective view of the outer portion of an exemplary end cover/coolant channel assembly for the axial end of a housing having weld type end turns; and 
         FIG. 7  is a schematic view of a cooling system  51  for electric machine  1 , according to an exemplary embodiment. 
     
    
    
     Corresponding reference characters indicate corresponding or similar parts throughout the several views. 
     DETAILED DESCRIPTION 
     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. 
       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 such as an internal permanent magnet (IPM) type machine. 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 . 
       FIG. 2  is a cross-sectional view of a stator coolant system, according to an exemplary embodiment. A substantially annular stator body  10  is populated with a number of conductor segments  11 . Conductor segments  11  may be formed as hairpins and inserted so that the crown ends of segments  11  extend from one axial end of stator core  10  as end turns  12  and the weld ends of segments  11  extend from the opposite axial end of stator core  10  as end turns  13 . Housing  8  is structured for holding bearing assemblies  6 ,  7  that secure shaft  5 . Housing  8  is formed with a substantially annular cooling jacket  14  that is proximate an inner housing surface  15  having an interference fit with stator core  10 . Housing  8  includes coolant ports  16 ,  17  for inputting and outputting coolant to/from cooling jacket  14 . For example, hot coolant may be transferred from cooling jacket  14  into an external heat exchanger (not shown) which removes the heat energy received by the coolant. The heat exchanger may be a radiator, oil cooler, or a similar device. Cooling jacket  14  substantially circumscribes portions of stator assembly  2 . A thermally conductive potting material  18  is injected for encapsulating end turns  12 ,  13 . End covers  19 ,  20  enclose the axial ends of housing  8  and are sealed thereto with O-rings  25 ,  26 , gaskets, or other. End covers  19 ,  20  are typically cast and machined using aluminum or other metal. End cover  19  includes a coolant channel assembly having a chamber/channel  27  with coolant inlet  28  and outlet  29  ports, thereby forming an end plate in which a cooling system according to the present disclosure is disposed at one axial end of the stator. Channel  27  is enclosed by a thin metal shell or dome  30 . In an exemplary embodiment, dome  30  is sealed to end cover  19  with O-rings  21 ,  23 . Dome  30  is pressed into engagement with potting material  18  prior to curing, whereby potting material  18  conforms to dome  30  and air is removed between dome  30  and end turns  13  by pressurized injection of potting material  18 . Channel  27  may be pressurized and/or surfaces may be cooled/heated during assembly to assure that there is no air trapped within potting material  18 . Channel  27  may contain manifold(s), guides, or other internal structure  33  for assuring coolant flow uniformity. At the other axial end of housing  8 , end cover  20  is structured and installed in a like manner. End cover  20  includes a coolant channel assembly having a chamber/channel  34  with coolant inlet  35  and outlet  36  ports, thereby forming an end plate in which a cooling system according to the present disclosure is disposed at the opposite axial end of the stator. Channel  34  is enclosed by a thin metal shell or dome  37 . In an exemplary embodiment, dome  37  is sealed to end cover  20  by O-rings  22 ,  24 . Dome  37  is pressed into engagement with potting material  18  prior to curing, whereby potting material  18  conforms to dome  37  and air is removed between dome  37  and end turns  12  by pressurized injection of potting material  18 . Channel  34  may be pressurized and/or surfaces may be cooled/heated during assembly to assure that there is no air trapped within potting material  18 . Channel  34  may contain manifold(s), guides, or other internal structure  38  for assuring coolant flow uniformity. 
       FIG. 3  and  FIG. 4  are perspective views of the respective inner and outer portions of an exemplary end cover/coolant channel assembly  40  for the axial end of housing  8  having crown type end turns  12  ( FIG. 2 ). Dome or shell  37  has a radially inward surface  39  with multiple tiers for accommodating one or more coolant paths therewithin. Fasteners  31  secure dome  37  to end cover  20 . Coolant outlet  36  is formed in a sidewall of end cover  20 . A first end turn cooling tier  41  may be radially inward of a second end turn cooling tier  42  when the associated space within housing  8  is available. In order to provide uniform cooling when available internal space dictates the use of different tiers or levels in a circumferential direction, the enclosed coolant channels may have differing corresponding widths or conductance surface areas. For example, the width of channel  43  may be tapered. In another exemplary embodiment, the conductance surface area of a given coolant channel may be increased, such as by shaping the channel in a known serpentine form. The outer perimeter  44  of end cover  20  is substantially flat so that it may be flush with housing  8  when fastened thereto at fastening locations  45 . An outer annular sealing location  46  and an inner annular sealing location  47  may have a uniform radially inner surface for securing respective O-rings therein. In such a case, the radial space between outer and inner locations  46 ,  47  may be utilized as one or more coolant channels. 
     In an exemplary embodiment, the conductance surface area of a given coolant channel may be increased, such as by shaping the channel in a known serpentine form. The outer perimeter  44  of end cover  20  is substantially flat so that it may be flush with housing  8  when fastened thereto at fastening locations  45 . An outer annular sealing location  46  and an inner annular sealing location  47  may have a uniform radially inner surface for securing respective O-rings therein. In such a case, the radial space between outer and inner locations  46 ,  47  may be utilized as one or more coolant channels. 
       FIG. 5  and  FIG. 6  are perspective views of the respective inner and outer portions of an exemplary end cover/coolant channel assembly  50  for the axial end of housing  8  having weld type end turns  13  ( FIG. 2 ). Dome or shell  30  has a radially inward surface  32  with multiple tiers for accommodating one or more coolant paths therewithin. Coolant inlet  28  is formed in a sidewall of end cover  19 . A perimeter mounting surface  67  is flat and may be provided with a gasket or O-ring (not shown) for flush mounting to a corresponding perimeter attachment surface of housing  8 . A number of perimeter mounting holes  48  are provided for fasteners (not shown) such as bolts or the like. An end turn cooling tier  66  is typically about 5 mm away from associated weld end turns  13  when assembly  50  is secured to housing  8 . 
       FIG. 7  is a schematic view of a cooling system  51  for electric machine  1 , according to an exemplary embodiment. Crown end cooling assembly  40  includes cooling channels  52 ,  53  that are connected to coolant inlet  35  via a manifold  54  that may be a partition within chamber  34 . Channels  52 ,  53  combine to feed heated coolant to outlet port  36 . Similarly, weld end cooling assembly  50  has one or more internal cooling channels  55 ,  56  fluidly connected to inlet port  28  and outlet port  29 . A pump  57  supplies coolant to inlet ports  28 ,  35  via respective valves  58 ,  59 . Stator cooling jacket  14  may also be fed by pump  57 , where coolant flow thereto may optionally be controlled by a valve  49 . The heated coolant being output by cooling assemblies  40 ,  50  and by cooling jacket  14  may be combined, such as at a sump area (not shown) of electric machine  1 , whereby the combined heated coolant is fed to a heat exchanger  60  for removal of heat from the coolant. The cooled coolant is then returned to pump  57 . A controller  61  receives control and sensor signals for controlling the operation of pump  57  and valves  49 ,  58 ,  59 . For example, one or more thermocouples  62  measure the temperature(s) at different locations and provide corresponding analog or digital signals to controller  61 . Stator  2  may include a circuit  63  containing a clock for time stamping signals from thermocouples  62 , whereby data may be analyzed, aggregated, or otherwise utilized for providing information, control signals, history, and for implementing other functions. Coolant temperature, pressure, and flow may thereby be monitored and controlled. Controller  61  may be may be in communication with or integrated into a vehicle engine control module (ECM) (not shown). For example, a cold-starting operation of a vehicle may cause the ECM to limit electrical and/or mechanical power availability to pump  57 , or a recurring sequence of starting operations for a hybrid vehicle may delay or modulate such power. Controls for the operation of pump  57  and valves  49 ,  58 ,  59  may alternatively be distributed, or independently based on a self-contained logic, for example including temperature, motor speed, voltage, or current sensor signals sent directly to controller  61 . 
     In various embodiments, electric machine  1  may include more than one cooling jacket  14 , and cooling assemblies  40 ,  50  may contain any number of common or independent coolant channels. Associated control may include any number of valves for regulating and controlling coolant flow to the various jackets, assemblies, and channels. For example, multiple channels within a cooling assembly  40 ,  50  may be independently controlled, such as by use of additional valves and control signals. A suitable coolant may include transmission fluid, ethylene glycol, an ethylene glycol/water mixture, water, oil, motor oil, a gas, a mist, any combination thereof, or another substance. The channels may be formed of thermally conductive and substantially non-magnetic material. For example, domes  30 ,  37  may be formed of metal, high temperature thermoplastic, or other thermally conductive materials having suitable rigidity and strength, whereby the channel shape does not become deformed or leak during assembly or when exposed to high temperature and internal pressure. Internal passages, manifolds, and the like may be formed to direct coolant flow and also to provide the necessary strength by serving as a structural support framework. The thickness of domes  30 ,  37  is typically less in areas nearest end turns  12 ,  13 . Providing greater thickness in other areas of domes  30 ,  37  may improve structural integrity. For example, channels may be required to maintain an internal pressure of 8-10 psi or greater. By completely filling end turns  12 ,  13  and space between the end turns and the thinner portions of domes  30 ,  37  with potting material  18 , the heat of end turns  12 ,  13  is conducted to the coolant flow through a short distance and through thermally conductive materials. 
     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.