Abstract:
Electrical devices such as motors and generators create heat as they operate. This can lead to lower performance and life. Therefore, it is important to provide cooling for such devices. This is particularly true in heavy duty applications such as earthmoving or other industries. Methods and apparatus are disclosed to provide cooling that involves the circulation of two fluids in defined pathways. Heat within a case or other enclosure for an electrical device is transferred to one fluid. Heat from the one fluid is subsequently transferred to the other fluid. In one example, this heat transfer may occur across fins for increased effectiveness. It is also preferred that the flow of fluid beclosed loop so that contaminants are not introduced into the electrical device. By providing the heat transfer out of the electrical device as described, cooling is enhanced that can lead to longer lived and better performing devices.

Description:
TECHNICAL FILED  
         [0001]    The invention relates to cooling electrical devices, and more particularly to cooling devices such as motors and generators through heat transfer between two fluids.  
         BACKGROUND  
         [0002]    Electrical devices can generate considerable heat as they operate.  
           [0003]    For example, the life and performance of motors and generators can be reduced because of such heat, limiting the severity applications to which they may be applied. In cases such as earthmoving or other heavy duty industrial applications, use of motors and generators can be beneficial for drive systems and other applications provided the heat is effectively managed. Of course, these severe applications typically result in more heat that must be managed. It is therefore important to provide systems to deal with the heat in a cost effective and efficient design manner.  
           [0004]    U.S. Pat. No. 5,519,269, issued May 21, 1996, to Lindberg is an example of a method of cooling an electrical induction motor. Coolant is provided into the motor housing, directed through slots in the stator and back out the motor. Coolant needs to be kept from the gap between the rotor and stator and directed across the windings. PCT Publication PCT/US00/06309, published Sep. 14, 2000 (Gregory C Jeppesen inventor) shows another cooling system for a motor. A fluid nozzle allows compressed fluid to expand rapidly into the motor housing. Exhaust ports maintain a positive pressure differential between chambers in the motor to enhance cooling fluid flow through the motor. Thus, the invention requires a source of compressed fluid such as air.  
           [0005]    The disclosed invention is directed to overcoming one or more of the problems set forth above.  
         SUMMARY OF THE INVENTION  
         [0006]    In one embodiment of the present invention, an electrical device has a rotor and a stator positioned about the rotor. An outer wall around the stator defines a cooling chamber between the stator and outer wall. First and second fluid sources are also provided. A first circulation pathway is defined adjacent a surface of the stator for the fluid from the first source. A second circulation pathway is defined through an air gap between the stator and rotor and through the cooling chamber for the fluid from the second source.  
           [0007]    In another embodiment of the present invention, a method of cooling an electrical device is provided. Steps include directing a first flow of fluid adjacent an outer surface of a stator and directing a second flow of fluid between the stator and a wall positioned about the stator. Another step includes transferring heat in fluid of the second flow of fluid to the fluid of the first flow of fluid. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a schematic diagram showing an exemplary system having motors and a generator according to principles of the present invention.  
         [0009]    [0009]FIG. 2 is a cross-sectional view taken lengthwise through the center of the generator in FIG. 1.  
         [0010]    [0010]FIG. 3 is a cross-sectional view along lines  3 - 3  of FIG. 2.  
         [0011]    [0011]FIG. 4 is a cross-sectional view taken lengthwise through the left side final drive and motor of FIG. 1.  
     
    
     DETAILED DESCRIPTION  
       [0012]    Referring to FIG. 1, a schematic of an exemplary system  10  using principles of the present invention will first be described. The system  10  includes electrical devices  12  useful for purposes to be described. One of the electrical devices  12  is a generator  14 , such as an AC generator, driven by an internal combustion engine  16  through a shaft  18  of the engine  16 . The generator  14  produces electricity that is directed through lines  20  to a controller  22  and then onto a drive system  24 . The drive system  24  further includes two additional electrical devices  12  which are first and second motors  26 ,  28 , such as AC induction motors. First and second final drives  30 ,  32  are each associated with and driven by a respective one of the motors  26 ,  28 . The system  10  is representative of a means for driving a vehicle or work machine (not shown). As will be appreciated, electrical energy produced by the generator  14  will power motors  26 ,  28  to rotate final drives  30 ,  32  and drive wheels (one shown in FIG. 4, reference numeral  33 ) connected to final drives  30 ,  32 . The present invention is not limited to systems or applications such as described. Such systems and applications are simply used for illustration purposes.  
         [0013]    Further referring to FIG. 1, a first source of fluid  34  is shown in this embodiment as a pump  36  and reservoir  38 . The first source  34  further includes a heat exchanger  42 . The pump  36  and heat exchanger  42  are shown connected through input lines  44  and output lines  46  to the drive system  24 . Input line  48  and output line  50  connect the heat exchanger  42  and pump  36  to the generator  14 . In the illustration shown, the fluid of the first source of fluid  34  is a liquid suitable for cooling purposes. The type of liquid will depend upon the application, but can include water, oil or an anti-freeze solution.  
         [0014]    A second source of fluid  52  is also shown in connection with each of the electrical devices  12 . The second source of fluid  52  with respect to first and second motors  26 ,  28  includes, for example, a blower  54  and input  56  and output  58  lines. The input line  56  connects to a manifold  60 . As illustrated, the first and second motors  26 ,  28  and manifold  60  are positioned inside a case  62 . The output line  58  opens into case  62  between the first and second motors  26 ,  28 . With respect to the generator  14 , the second source of fluid  52  is contained within a housing  64  of the generator  14 . In part, the source  52  includes a fluid mover  66 . The fluid of the second source of fluid  52  for both the generator  14  and motors  26 , 28  is preferably, as illustrated, air.  
         [0015]    In addition, sensors  68  are schematically illustrated. These sensors  68 , such as speed and rotation sensors, as is well known in the art, facilitate operation of the motors  26 ,  28  and final drives  30 ,  32  for control of the drive system  24  in driving, turning and stopping an associated machine or vehicle.  
         [0016]    Further details of features described with respect to FIG. 1 will now be discussed with reference to the other drawings.  
         [0017]    Referring to FIGS. 2 and 3, the generator  14  is shown in greater detail. The generator  14  includes a rotor  70  and stator  72 . Rotor  70  has an axis  74  about which it is rotatable and first and second opposed ends  76 ,  78 . Rotor  70  is of known construction with a shaft  80  on bearings  82  at either of the ends  76 ,  78  (only the one at second end  78  shown). The rotor  70  is driven by connection with engine  16  to the shaft  80  at the first end  76  for rotation about the axis  74 . Stator  72  is similarly of known construction. Typically the rotor  70  and stator  72  will each have a plurality of laminations stacked on one another. Each also typically uses a copper conductor. In the case of the stator  72 , the ends  84  of the copper windings (representing the copper conductor) wound in slots of the stator  72  are shown in FIG. 2. The stator  72  has an outer or circumferential surface  86  and first and second opposed ends  88 ,  90 . The stator  72  is positioned about the rotor  70 . With the rotor  70 , the stator  72  defines an air gap  92  between the stator and rotor  70 . Construction and operation of the stator  72  and rotor  70  are not shown nor described in detail, as elements of such electrical devices are well known.  
         [0018]    An outer wall  94  is positioned about the stator  72 . The outer wall  94  is part of an enclosure  96  of the generator  14 . The enclosure  96  surrounds the operating parts of the generator  14 , including the stator  72  and rotor  70 . Preferably, the enclosure  96  provides a relatively air tight compartment. It will be appreciated that the shaft  80  is not fully enclosed in order to connect to engine  16 . Seals (not shown) may be used to provide sealing between the rotating shaft  80  and the enclosure  96 .  
         [0019]    Between the outer wall  94  and the stator  72  is a space or cooling chamber  98 . This space  98  extends circumferentially around the stator  72  and is open at the ends  88 ,  90  of the stator  72  into the enclosure  96 . Fins  100  extend outwardly and radially into the cooling chamber  98  and around the circumference of the stator  72 . The fins  100  are oriented along axis  74  and extend from the surface  86  of the stator  72 . Adjacent fins  100  define spaces  101  between one another. In the circumferential or outer surface  86  of the stator  72  are openings  102  that extend preferably along the axis  74 , and thus longitudinally along the outer surface  86 . The openings  102  are divided into channels  104  by dividers  106  that extend inwardly and radially into the openings  102 . The dividers  106  define adjacent channels (illustrated at  104 ′,  104 ″). As shown, dividers  106  preferably extend immediately adjacent bottom surfaces  108  of openings  102 . They may touch surfaces  108  but do not need to.  
         [0020]    In a preferred construction, an outer cap  110  is provided. The outer cap  110  has a wall  112  with an inner circumferential surface  114  of substantially equal diameter to that of the outer surface  86  of stator  72 . Fins  100  and dividers  106  are connected to the wall  112 , preferably in an integral fashion such as might be accomplished through casting the outer cap  110 . The dividers  106  are radially aligned with the fins  100 . The dividers  106  are, practically speaking, a part of the fins  100  for purposes to be explained.  
         [0021]    For ease of construction, it is contemplated that the outer cap  110  is assembled from a plurality of sections  116  (three shown at  116 ′,  116 ″,  116 ′″). The sections  116  can be welded one to another to fit about and preferably be positioned in full contact with the surface  86  of the stator  72 . The sections  116  can be steel castings or other suitable material for use in the interior environment of the generator  14  (or motor  26 ,  28 ) and to facilitate heat transfer, as will be explained later. The stator  72  itself may, in one embodiment, have an outer portion  118  separate from the stator laminations that are built up and wound with copper wire. This outer portion  118  (shown only in FIG. 3) facilitates providing the openings  102  in the outer surface  86  of the stator  72 . This is accomplished by constructing the outer portion  118  separately, such as through a steel casting. The openings  102  can be cast into the outer portion  118 . The outer portion  118  is preferably constructed of thin annular pieces of similar thickness to the copper wound laminations of the stator  72  that are then press fit to each stator lamination. The thin annular pieces may also be welded to each of the copper wound laminations.  
         [0022]    Referring to FIG. 2, an in-flow manifold  120  and out-flow manifold  122  are provided in connection with the channels  104  (not shown in FIG. 2). Each of the manifolds  120 ,  122  is associated with a respective end  90 , 88  of stator  72  and extends continuously about that end  90 , 88 . The manifolds  120 ,  122  are so located as to be in fluid communication with the channels  104  in the stator  72 . The in-flow manifold  120  is in fluid connection with input line  48  via a line  123  that extends from the manifold  120  and opens out on housing  64 . The out-flow manifold  122  is in fluid connection with output line  50  via a line  124  that extends from the manifold  122  and also opens out on housing  64 . Each manifold  120 ,  122  is formed by a step  125  in the outer circumferential portion of the stator  72  and the outer cap  110 . The outer cap  110  has a circular tab  126  (as shown, an extension of thin wall  112 ) at each end  88 ,  90  that is fastened, typically by welding, to the outer circumferential portion of the stator  72 . This connection is fluid tight to prevent fluid flow from the manifold  120 ,  122  and channels  104  into the enclosure  96 .  
         [0023]    Fluid mover  66  includes an impeller  127 . The fluid mover  66  is located adjacent the first ends  88 ,  76  of stator  72  and rotor  70  inside the enclosure  96 . The impeller  127  is of typical, known construction and is rotationally coupled to the shaft  80 , such as by a press fit. Thus, the impeller  127  rotates with the rotor  70  and will move fluid (air) as it rotates. The impeller  127  is constructed so that it will direct or push air through openings  128  in an interior wall  129  (and into cooling chamber  98 ) and take air adjacent the gap  92  between the rotor  70  and stator  72 . The interior wall  129  and another interior wall  130  adjacent the other ends  90 ,  78  of the stator  72  and rotor  70  provide structural support for the stator  72 . Inner wall  130  also has openings  131  through which fluid may pass through cooling chamber  98  as will be described.  
         [0024]    Referring now to FIG. 4, an embodiment in which the electrical device  12  is a motor will be discussed. Shown is the first motor  26  coupled to first final drive  30 . The construction of motor  26 , as disclosed in FIG. 4, is similar to generator  14 . Further, motors  28 ,  30  are of the same construction. The second motor  28 , as will be appreciated from a reference to FIG. 1, is positioned to the right of manifold  60 . The sensor  68 ′ and bearing  132  associated with second motor  28  are shown in FIG. 4. The motors  28 ,  30  and manifold  60  are contained within case or enclosure  62 . A space or chamber  131  is defined between the case  62  and the motor  28 .  
         [0025]    The construction of motors  28 ,  30  will not be discussed in detail. However, a brief overview of the construction will be made of motor  26  for orientation purposes and to assist in describing some different aspects of motors  26 ,  28  from generator  14 .  
         [0026]    Motor  26  has a rotor  133  and stator  134 , along with an outer cap  136  with fins  138  and dividers  140 . The rotor  133  and stator  134  have a gap  141  between them. A cooling chamber  142  is located between wall  144  and stator  134 . In-flow  146  and out-flow  148  manifolds connect with channels (not shown), in part defined by dividers  140 . The manifolds  146 ,  148  connect through the case  62  and wall  144  via internal lines  149 ,  150  to in-flow and out-flow lines  44 ,  46 , respectively. The construction of channels is the same as the embodiment described with respect to FIGS. 2 and 3. Shaft  151 , at a first end  152  of rotor  133 , drives final drive  30  as instructed by controller  22 . Shaft  151  rotates about axis  154 . Another shaft  156 , at a second end  158  of rotor  133  rotationally supports the rotor  133  on bearing  160 .  
         [0027]    Manifold  60  is located adjacent shaft  156 . The manifold  60  is connected by structure  162  associated with the second end  158  of motor  26  and a second end  164  of motor  28 . The structure  162  can be any sort of bracket or similar arrangement that connects to the ends  158 ,  164  and supports the manifold  60  to remain in position between the motors  26 ,  28 . Manifold  60  has an opening  166  that fluidly connects with input line  56 . Manifold  60  is of generally circular construction and is preferably made of sheet metal or the like. Manifold  60  fluidly communicates through the second ends  158 ,  164  of motors  26 ,  28  through one or more openings  168  (two shown) in each end plate  170 ′,  170 ″ associated with a respective end  158 ,  164  of the motors  26 ,  28 . If additional structure blocks fluid communication between the air manifold  60  and the interior of the motors  26 ,  28 , then similarly additional openings or other types of fluid pathways would be needed.  
         [0028]    An opening  172  in a cylindrical wall  174  of case  62  is connected to output line  58  so that the line  58  and the interior space  131  of the case  62  are in fluid communication with line  58 . Case  62  provides a generally air tight container in which the motors  26 ,  28  and manifold  60  reside. It will be appreciated from FIG. 4 that case  62  includes the cylindrical wall  174 , flanges  176  and an end wall  177 . Shaft  151  extends through end wall  177 . Seals (not shown) may be used to facilitate air tightness of case  62  as needed. Additionally, there is an annular interior wall  178  that has openings  179  and that supports the placement of stator  134  within the case  62 . At the other end  158  of motor  26  is another annular wall  180  with openings  181 .  
         [0029]    Industrial Applicability  
         [0030]    In operation of a motor or generator, such as illustrated by motors  26 ,  28  and generator  14 , considerable heat occurs in the rotors and stators. The heat must be dissipated or otherwise controlled to optimize operation and increase the life. Through the construction, methods and operation disclosed, cooling is provided to control heat.  
         [0031]    In an exemplary method, a step of directing a first flow of fluid adjacent the outer surface  86  of stator  72  occurs. The first flow of fluid occurs along a first circulation pathway  182  shown by arrows in FIG. 2. The fluid in the first flow of fluid is provided from the earlier discussed first source of fluid  34 . Thus, it will be seen that fluid (preferably liquid) moved by pump  36  is directed through input line  48  and heat exchanger  42  to generator  14 . The fluid passes through line  123  into manifold  120 . From manifold  120 , the flow is directed into and through the channels  104  that are in the outer surface  86 . The fluid flows through the channels  104  and then into manifold  122  and line  124 . From line  124 , the fluid will flow through output line  50  to return to pump  36 . The fluid thus is moved through the first circulation pathway  182  by action of pump  36 .  
         [0032]    A step of directing a second flow of fluid between the stator  72  and wall  94  also occurs. The second flow of fluid occurs along a second circulation pathway  184  also shown by arrows in FIG. 2. The fluid in the second flow of fluid is provided from the second source of fluid  52 . In this example, impeller  128  rotating with the rotor  70  moves the fluid (air in this example). Impeller  128  will typically always rotate when engine  16  is running, so the flow of cooling air will occur continuously. As the rotor  70  turns, impeller  128  directs air flow inside the enclosure  96  through pathway  184 . Air is drawn through and from the gap  92  between stator  72  and rotor  70  into a central portion  186  of impeller  128  and then pushed from a top portion  188  through openings  128  and between the spaces  101  between the fins  100 . The air continues past the fins  100  and back into an area  190  of enclosure  96 . The air further circulates past second end  90  of stator  72  and into the air gap  92  where it continues back to central portion  186  of impeller  128 .  
         [0033]    A step of transferring heat in the fluid of the second flow of fluid (second circulation pathway  184 ) to the fluid of the first flow of fluid (first circulation pathway  182 ) further occurs. It will be appreciated that heat in the rotor  70  and stator  72  will transfer into the air in the enclosure  96  as the air circulates. Further, as the air circulates past fins  100  in cooling chamber  98 , a step occurs of transferring heat from the air to the fins  100 . Transfer of heat from the fins  100  will then occur to the liquid in the channels  104  (first circulation pathway  184 ). Heat transfer is enhanced by direct contact of dividers  106  with the liquid. For this reason in the embodiment shown, dividers  106  are shown extending fully into openings  102  to enhance the heat transfer effect. Some heat may also transfer directly from the stator  72  into the liquid. The heat is ultimately dissipated outside the generator  14  by directing it through heat exchanger  42 . Thus, a step of blowing air within enclosure  96  occurs in a closed loop, so that air within the enclosure  96  is recirculated.  
         [0034]    Cooling motors  26 ,  28  is similar to that above described. The air circulation pathways do differ, however, and will be described. Referring to FIG. 4, a first circulation pathway  192  is illustrated by arrows. The first circulation pathway  192 , for liquid flow in the embodiment shown, includes manifolds  146 ,  148  and channels (not shown) in stator  134 . Liquid enters manifold  146  through line  44  and internal line  149  and then into channels (not shown) associated with stator  134 . The liquid will be circulated through the channels toward the opposite manifold  148  and then be drawn out of the motor  26  through line  150  into line  46  and back to pump  36 .  
         [0035]    A second circulation pathway  194 , shown by arrows, is also illustrated in FIG. 4. The pathway  194  includes the manifold  60  that takes air pushed by blower  54  through line  56 . The air is directed through openings  168  into gap  141  and then across first end  152  of stator  134 . The air passes through openings  179  into cooling chamber  142  and along fins  138  in spaces between fins  138 . Air then exits the cooling chamber  142  through openings  181  and into the larger space in case  62 . From the case  62 , the air is drawn through opening  172  and line  58  back to blower  54  for redistribution. Thus, air distribution for motor  26  (and motor  28 ) is also closed loop.  
         [0036]    Cooling of motor  26  thus occurs by transfer of heat from the rotor  133  and stator  134  to air as flow occurs in the second circulation pathway  194  by manifold  60 . The air then flows into cooling chamber  142  where the heat it contains is transferred to fins  138  and hence into the liquid in the first circulation pathway  192 . Air manifold  60  similarly distributes air into a circulation pathway (not shown) in the second motor  28 . Thus it will be seen that pump  36  and heat exchanger  42  serve both motors  26 ,  28  for purposes of liquid coolant flow. And the use of the single manifold  60  located between the two motors  26 ,  28  provides for a compact and efficient packaging arrangement, plus lowers cost by reducing parts.  
         [0037]    The heat exchanger  42  and pump  36  further serve to supply generator  14  with liquid coolant flow. This arrangement conserves needed space in the illustrated application, which can be limited on vehicles or work machines. Further, generator  14  and motors  26 ,  28 , may have different heat loads or experience unequal or sub optimum coolant flow in the lines to each. In such an event, it may be desirable to regulate flow from the pump  36  to each by using one or more flow regulators (not shown). In such case, the appropriate amount of flow can be directed to each electrical device  12  as needed or required.  
         [0038]    Further, the motor  26  (and motor  28 ) does not always operate. This means rotor  133  does not always rotate, providing flow of air for cooling purposes, as is typical with generator  14 . Even so, motor  26  will benefit from constant air flow for cooling purposes, because of the high loads on the motor  26 . The blower  54  can provide a continuous flow of air, because it can be operated by electrical power independently of the rotor  133 .  
         [0039]    The use of closed loops with “air tight” cases or housings for cooling eliminates (or at least significantly eliminates) use of outside air in cooling. Outside air, in the environments in which some generators or motors operate, can contain contaminants that will reduce the effectiveness of the electrical device. For example, for an off-highway truck or other earthmover, the air may carry dust or dirt that might clog the circulation pathways  184 ,  194  and cause the electrical devices  12  to fail. The liquid cooling in the first circulation pathways  182 ,  192  facilitates the closed loop operation by providing a heat transfer mechanism to remove heat from the interiors of generator  14  and motor  26 ,  28 .  
         [0040]    The embodiments illustrated above and in the drawings have been shown by way of example. There is no intent to limit the invention to the exemplary forms disclosed. All modifications, equivalents and alternatives falling within scope of the appended claims are intended to be covered.