Patent Publication Number: US-2007120427-A1

Title: Electric machine having a liquid-cooled rotor

Description:
TECHNICAL FIELD  
      The present disclosure relates generally to an electric machine and, more particularly, to an electric machine having a liquid-cooled rotor.  
     BACKGROUND  
      Electric machines such as, for example, motors and generators may be used to generate mechanical power in response to an electrical input or to generate electrical power in response to a mechanical input. Magnetic, resistive, and mechanical losses within the motors and generators during mechanical and electrical power generation can cause a build up of heat, which may be dissipated to avoid malfunction and/or failure of the electric machine. One of the limitations on the power output of the electric machines may be the capacity of the electric machine to dissipate this heat.  
      One method of dissipating heat within an electric machine includes directing a cooling medium into the electric machine via a rotor. For example, U.S. Pat. No. 5,019,733 (the &#39;733 patent) to Kano et al. teaches an excitation-type AC generator having stator and field coils cooled by a fluid passing through passageways within a rotating shaft. Specifically, during circulation, the fluid is directed axially into one end of a rotor shaft and then outward via radially-bored passageways to spray the fluid onto the stator and field coils, thereby removing heat from the generator.  
      Although the radially-bored passageways of the rotor shaft may facilitate some heat removal from portions of the generator, they may remove too little heat, and the removal of heat may be disproportionate. In particular, because the cooling fluid enters the rotor shaft from only one end and then is immediately redirected away from the rotor, it may be ineffective for removing substantial amounts of heat from the rotor. In addition, because little or no heat is removed from the other end of the rotor, the distribution of heat along the rotor may be disproportionate, possibly resulting in damage to components of the generator.  
      The disclosed electric machine is directed to overcoming one or more of the problems set forth above.  
     SUMMARY OF THE INVENTION  
      In one aspect, the present disclosure is directed to an electric machine that includes a housing having at least one fluid passageway, a stator fixedly disposed within the housing, and a rotor rotatingly disposed radially inward from the stator. The rotor includes a first axial bore, a first radial passageway, a second axial bore, and a second radial passageway. The first axial bore is in fluid communication with the at least one fluid passageway of the housing. The first radial passageway is in fluid communication with the first axial bore and configured to communicate fluid from the first axial bore with the stator. The second axial bore is in fluid communication with the at least one fluid passageway of the housing. The second radial passageway is in fluid communication with the second axial bore and configured to communicate fluid from the second axial bore with the stator.  
      In another aspect, the present disclosure is directed to an electric machine including a housing having at least one fluid passageway, a stator fixedly disposed within the housing, and a rotor rotatingly disposed radially inward from the stator. The rotor includes an axial bore, a rotor end ring, and a first radial passageway. The axial bore is in fluid communication with the at least one passageway of the housing. The rotor end ring has an interior annular channel, and the first radial passageway is in fluid communication with the axial bore and the interior annular channel. The first radial passageway is configured to communicate fluid from the axial bore with the stator via the interior annular channel.  
      In yet another aspect, the present disclosure is directed to a method of operating an electric machine. The method includes rotating a rotor disposed radially inward of a stator. The method also includes directing fluid into the electric machine through a housing external to the stator, directing fluid from the housing axially into a first end of the rotor and a second end of the rotor, and directing fluid from the first and second ends of the rotor radially outward to the stator via axially spaced apart first and second passageways.  
      In yet another aspect, the present disclosure is directed to a method of operating an electric machine. The method includes rotating a rotor disposed radially inward of a stator. The method also includes directing fluid into the electric machine through a housing external to the stator, directing fluid from the housing axially into an end of the rotor, directing fluid from the end of the rotor radially outward to an interior annular channel of a rotor end ring via a first passageway, and directing fluid from the interior annular channel to the stator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagrammatic illustration of an exemplary disclosed work machine; and  
       FIG. 2  is a cutaway-view illustration of an electric machine for the work machine of  FIG. 1 . 
    
    
     DETAILED DESCRIPTION  
       FIG. 1  illustrates an exemplary power system  10  having a power source  12 , a cooling system  14 , and an electric machine  16 . Power system  10  may form a portion of a mobile work machine  18  such as, for example, a dozer, an articulated truck, an excavator, or any other mobile work machine known in the art, with electric machine  16  functioning as the main propulsion unit of work machine  18 . It is contemplated that electric machine  16  may alternatively function as the main electrical power-generating unit of work machine  18 . It is also contemplated that power system  10  may alternatively form a portion of a stationary work machine such as a generator set, a pump, or any other suitable stationary work machine.  
      Power source  12  may be configured to produce a rotational mechanical power output and may include a combustion engine. For example, power source  12  may include a diesel engine, a gasoline engine, a gaseous fuel-powered engine, or any other type of combustion engine apparent to one skilled in the art. It is also contemplated that power source  12  may alternatively embody a non-combustion source of power such as a fuel cell, a battery, or any other source of power known in the art.  
      Cooling system  14  may embody a pressurized system configured to transfer heat to or from power source  12  and/or electric machine  16 . Cooling system  14  may include, among other things, a heat exchanger  20 , a fan  22 , and a source  24  configured to pressurize a heat-transferring medium.  
      Heat exchanger  20  may embody a liquid-to-air heat exchanger configured to facilitate the transfer of heat to or from the heat-transferring medium. For example, heat exchanger  20  may include a tube and fin-type heat exchanger, a tube and shell-type heat exchanger, a plate-type heat exchanger, or any other type of heat exchanger known in the art. Heat exchanger  20  may be connected to source  24  via a supply conduit  26 , and to a housing  27  of electric machine  16  via a return conduit  28 . It is contemplated that heat exchanger  20  may function as the main radiator of power source  12 , the engine oil cooler, the transmission oil cooler, the brake oil cooler, or any other cooling component of power source  12 . It is further contemplated that heat exchanger  20  may alternatively be dedicated to conditioning only the heat-transferring medium supplied to electric machine  16 .  
      Fan  22  may be disposed proximal to heat exchanger  20  and configured to produce a flow of air across heat exchanger  20  for liquid-to-air heat transfer. It is contemplated that fan  22  may be omitted or remotely located, if desired, and a secondary fluid circuit (not shown) may connect to heat exchanger  20  to transfer heat to or from the heat-transferring medium via liquid-to-liquid heat transfer.  
      Source  24  may embody any device for pressurizing the heat-transferring medium within cooling system  14 . For example, source  24  may include a fixed displacement pump, a variable displacement pump, a variable flow pump, or any other type of pump known in the art. Source  24  may be disposed between heat exchanger  20  and electric machine  16 , and driven hydraulically, mechanically, or electrically by power source  12 . It is contemplated that source  24  may alternatively be located remotely from power source  12  and driven by a means other than power source  12 . It is also contemplated that source  24  may be dedicated to pressurizing only the heat-transferring medium directed to electric machine  16 . Source  24  may be connected to housing  27  by way of a supply conduit  30 .  
      The heat-transferring medium may be a low-pressure fluid or a high-pressure fluid. Low-pressures fluids may include, for example, water, glycol, a water-glycol mixture, a blended air mixture, a power source oil such as transmission oil, engine oil, brake oil, diesel fuel, or any other low-pressure fluid known in the art for transferring heat. High-pressure fluids may include, for example, R-134, propane, nitrogen, helium, or any other high-pressure fluid known in the art.  
      Electric machine  16  may be electrically coupled to power source  12  by way of a generator  32  and power electronics  34 . In particular, generator  32  may be drivably connected to power source  12  via a flywheel (not shown), a spring or hydraulic coupling (not shown), a planetary gear arrangement (not shown), or in any other suitable manner. Generator  32  may be connected to power source  12  such that a mechanical output rotation of power source  12  results in a corresponding electrical output directed via power electronics  34  to electric machine  16 .  
      Electric machine  16  may include multiple components that interact to produce mechanical power in response to an electrical input. Specifically, electric machine  16  may include a first motor  36 , a second motor  38 , and a third motor  40  disposed within housing  27  and operatively coupled to an output shaft  42 . As electrical power is supplied from generator  32  to electric machine  16 , first, second, and third motors  36 - 40  may apply a torque to output shaft  42  at a range of rotational speeds. Output shaft  42  may be connected to a traction device  44  of work machine  18 , thereby propelling work machine  18  in response to the applied torque. It is contemplated that rather than producing a mechanical output in response to an electrical input, electric machine  16  may alternatively produce electrical power in response to a mechanical input.  
      Output shaft  42  may embody a cylindrical coupling member for transferring power into and/or out of electric machine  16 . Output shaft  42  may extend from one end of housing  27  to an opposing end of housing  27 . It is also contemplated that output shaft  42  may protrude from both ends or only one end of housing  27  and/or that multiple shafts may be included within electric machine  16  and interconnected by means of a gear arrangement.  
      As illustrated in  FIG. 2 , first, second, and third motors  36 - 40  may be radially arranged about output shaft  42  and coupled to output shaft  42  by way of a gear arrangement  45 . In particular, each of motors  36 - 40  may include a rotor shaft  46  rotatably supported within housing  27  by one or more bearings  47 , and having external splines  48 . Together, the rotor shafts  46  of each of motors  36 - 40  may function to simultaneously rotate a driven gear member  50  by way of a plurality of spur gears  52 . That is, external splines  48  may engage internal splines of spur gears  52 , while external gear teeth of spur gears  52  may mesh with external gear teeth of driven gear member  50 . Driven gear member  50  may then, in turn be operatively connected to output shaft  42  such that output shaft  42  may rotate in correspondence with an input rotation of rotor shafts  46 .  
      Gear arrangement  45  may receive an input rotation via rotor shafts  46  and/or one or more other gear members (not shown) of gear arrangement  45 , and generate a corresponding output rotation of output shaft  42 . Alternatively, gear arrangement  45  may receive an input rotation via output shaft  42  and correspondingly rotate rotor shafts  46  to generate an electrical output. Multiple input and output combinations may be possible.  
      Each of motors  36 - 40  may include components that interact to rotate rotor shafts  46  in response to an electrical input. In particular, each machine may include a rotor assembly  60  and a stator assembly  62 . It is contemplated that motors  36 - 40  may contain additional or different components such as, for example, control systems, processors, power electronics, one or more sensors, power storage devices, and/or other components known in the art.  
      Rotor assembly  60  may include a stack of steel laminations  64  having multiple protruding portions, also known as rotor teeth. The rotor teeth may be interconnected by way of one or more end rings  66  and configured to interact with an electrically-induced magnetic field within electric machine  16  to cause a rotation of rotor shaft  46 . Laminations  64  may be fastened to rotor shaft  46  by, for example, interference fit, welding, threaded fastening, chemical bonding, or in any other appropriate manner. As each protruding portion interacts with the magnetic field, a torque may be produced that rotates rotor shaft  46 .  
      Stator assembly  62  may include components fixed to housing  27  that are configured to produce the electrically-induced magnetic field described above. Specifically, stator assembly  62  may include laminations of steel  68  having protruding portions, also known as stator teeth, that extend inward from an iron sleeve  70 , and windings  72  of copper wire wrapped around and epoxied to each protruding portion of laminations  68  to form a plurality of poles. As electrical current is sequentially applied to windings  72 , a rotating magnetic field may be generated through the plurality of poles.  
      As described above, motors  36 - 40  may be contained within a single common housing  27 . Housing  27  may be configured to house the rotor assemblies  60 , stator assemblies  62 , and bearings  47  associated with motors  36 - 40 . In particular, housing  27  may include an outer shell  74 , a first end cap  76 , and a second end cap  78 . Outer shell  74  may annularly enclose rotor and stator assemblies  60 ,  62 , and connect to first and second end caps  76 ,  78 . First and second end caps  76 ,  78  may support bearings  47  and may each include a centrally-located through-hole that allows the extension of rotor shaft  46  through housing  27 . It is contemplated that one or both of first and second end caps  76 ,  78  may be integral with outer shell  74 , if desired.  
      As also illustrated in  FIG. 2 , electric machine  16  may include an internal cooling circuit to direct the heat-transferring medium throughout or near the heat-generating components of electric machine  16 . Specifically, the heat-transferring medium may enter housing  27  via a distribution block  80 , proceed via a first passageway  82  to first end cap  76 , and via a second passageway  84  to second end cap  78 . First and second passageways  82 ,  84  may be internal passageways within outer shell  74  or may alternatively embody external tubing. After entering first and second end caps  76 ,  78 , the heat-transferring medium may be directed annularly to rotor shaft  46  of each of motors  36 - 40  via an annular channel  86  located within each of first and second end caps  76 ,  78 .  
      From annular channels  86 , the heat-transferring medium may be simultaneously directed into each rotor shaft  46  by way of axial passageways, and then redirected radially outward. Specifically, rotor shaft  46  may include a first axial bore  88  recessed within a first end surface  90  a blind depth, and a second axial bore  92  recessed within a second opposing end surface  94  a blind depth. The bore diameters and blind depths of first and second axial bores  88 ,  92  may or may not be equal. The heat-transferring medium may flow into rotor shaft  46  via first and second axial bores  88 ,  92 , and then radially outward via first and second sets of radial passageways  96 ,  98 . Radial passageways  96 ,  98  may extend outward from first and second axial bores, respectively, to an outer surface of rotor shaft  46 .  
      Upon exiting rotor shaft  46  via first and second sets of radial passageways  96 ,  98 , the heat-transferring medium may flow toward stator assembly  62  by way of end rings  66 . In particular, because of the rotating forces associated with rotor shaft  46  and the pressure induced by source  24  (referring to  FIG. 1 ), the heat-transferring medium may be sprayed radially outward from rotor shaft  46  into an interior annular channel  100  located within each end ring  66 . Interior annular channels  100  may help to retain the heat-transferring medium against rotor assembly  60  for maximum heat transfer. Once end rings  66  are filled with the heat-transferring medium, the medium may spill out of interior annular channels  100 , across the face of end rings  66 , and toward stator assembly  62 . After spraying on the components of stator assembly  62  for additional heat transfer, the heat-transferring medium may be pulled by gravity toward a sump (not shown) connected to housing  27 , where the heat-transferring medium may collect for return to heat exchanger  20 .  
      In addition to transferring heat with electric machine  16 , the heat-transferring medium may also lubricate portions of electric machine  16 . In particular, an additional radial passageway  106  within rotor shaft  46  may direct the heat-transferring medium from first axial bore  88  to bearing  47  located toward first end surface  90 . After forcing the heat-transferring medium from one side of bearing  47  through bearing  47  to an opposing side, thereby lubricating bearing  47 , the heat-transferring medium may combine with the fluid exiting interior annular channels  86  to transfer heat with stator assembly  62 . Bearing  47  located toward second end surface  92  may be lubricated by the heat-transferring medium before the medium enters second axial bore  92  by way of a lubrication chamber  104  located in second end cap  78 . Another radial passageway  102  within rotor shaft  46  may direct the heat-transferring medium from first axial bore  88  to the splined connection between rotor shaft  46  and spur gear  52  and to the external teeth of spur gear  52  for lubrication purposes.  
      In addition to directing the heat-transferring medium through electric machine  16 , external annular heat transfer from stator assembly  62  may be provided by way of iron sleeve  70 . In particular, iron sleeve  70  may include one or more annular grooves  110  located in an outer surface of iron sleeve  70  that, together with an inner annular surface of outer shell  74 , may form annular fluid passageways. The heat-transferring medium may enter annular grooves  110  by way of distribution block  80  and, after transferring heat with the external annular surface of stator assembly  62 , may drain to the sump. It is also contemplated that iron sleeve  70  may be omitted, if desired, or retained and annular grooves  110  omitted.  
     INDUSTRIAL APPLICABILITY  
      The disclosed electric machine finds potential application in any power system where it is desirable to dissipate substantial amounts of heat from an electric machine in a controlled and uniform manner. The disclosed electric machine finds particular applicability in vehicle drive systems. However, one skilled in the art will recognize that the disclosed electric machine could be utilized in relation to other drive systems that may or may not be associated with a vehicle. The heat-transferring operation of electric machine  16  will now be described.  
      Referring to  FIG. 1 , when power system  10  is in operation, the heat-transferring medium, conditioned (heated or cooled) by heat exchanger  20 , may be pumped by source  24  through power source  12  and/or electric machine  16 . As the heat-transferring medium courses through power source  12  and/or electric machine  16 , heat may be continuously transferred to or from power source  12  and/or electric machine  16 . Upon exiting electric machine  16 , the flow of the heat-transferring medium from electric machine  16  may be directed to rejoin the flow of the heat-transferring medium exiting power source  12  where both flows may then be routed through heat exchanger  20  to either expel heat or absorb heat during a conditioning process.  
      As the flow of the heat-transferring medium enters electric machine  16  by way of distribution block  80  (referring to  FIG. 2 ), it may first be directed via first and second passageways  82 ,  84  to first and second end caps  76 ,  78  where the flow may then be directed radially inward to first and second axial bores  88 ,  92  of rotor shaft  46 . Upon entering first and second axial bores  88 ,  92 , the flow may be sprayed radially outward via the radial passageways  96 ,  98 ,  102 ,  106 .  
      After exiting radial passageways  96 ,  98 ,  102 ,  106 , the heat-transferring medium may fill interior annular channels  100  and spill over end rings  66  toward stator assembly  62 , lubricate bearing  47  located toward first end surface  90 , and lubricate the splined engagement between rotor shaft  46  and spur gear  52  and the external gear teeth of spur gear  52 . The heat-transferring medium may then drain to the sump for recirculation through heat exchanger  20  (referring to  FIG. 1 ) via return conduit  28 .  
      In addition to directing the heat-transferring medium through rotor shaft  46  to transfer heat with rotor assembly  60  and internal surfaces of stator assembly  62 , the heat-transferring medium may be directed to transfer heat with the external annular surface of stator assembly  62 . In particular, the heat-transferring medium may be simultaneously directed through annular grooves  110  of iron sleeve  70  to transfer heat with the outer surfaces of windings  72  and the protruding portions of stator assembly  62 .  
      Greater cooling efficiency of electric machine  16  may be realized because the heat-transferring medium is directed evenly to components within electric machine  16  that tend to generate the greatest amount of heat. Specifically, because the heat-transferring medium is directed to both ends of rotor shaft  46  and to stator assembly  62 , a greater amount of heat may be transferred than if the fluid only contacted a single end of rotor shaft  46  and/or never removed heat from stator assembly  62 . Further, because the heat-transferring medium transfers heat evenly with electric machine  16  (e.g., with opposing ends of rotor shaft  46 , rather than only a single end), the heat-induced stresses experienced by the components of electric machine  16  may be reduced, as compared to disproportionate heat transfer.  
      Additional advantages may be realized because the fluid passageways of electric machine  16  direct the heat-transferring medium both within and around stator assembly  62 . In particular, transferring heat with both inner and outer surfaces of stator assembly  62  may increase the heat-transferring capacity of electric machine  16  as compared to only transferring heat with one of the inner or outer surfaces of stator assembly  62 .  
      It will be apparent to those skilled in the art that various modifications and variations can be made to the electric machine of the present disclosure. Other embodiments of the electric machine will be apparent to those skilled in the art from consideration of the specification and practice of the electric machine disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.