Abstract:
An electric motor including a motor portion, a cooling portion and a plurality of heat pipes. The motor portion includes a stator and a rotor that when energized with electric current causes the rotor to rotate. The motor portion comprises a motor frame that encloses the rotor and stator from exterior elements. The cooling portion is adjacent the motor portion and exterior of the motor portion. It defines a fluid chamber containing a quantity of fluid that is prevented from contacting interior of the motor portion. The plurality of heat pipes within the motor portion extend from the motor portion to the cooling portion such that the fluid contacts the heat pipe within the cooling portion in order to remove heat from the heat pipe.

Description:
[0001]     The present invention claims priority to U.S. Provisional Application Ser. No. 60/805,192, filed Jun. 19, 2006, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to electric motors. More specifically, the invention relates to an electric motor having at least one heat pipe installed therein to assist in cooling of the motor.  
       BACKGROUND OF THE INVENTION  
       [0003]     Electric motors are used for a multitude of tasks and frequently those motors are used in applications where cooling of the motor is difficult. Commonly, these hard-to-cool applications involve large motors. One example of a hard-to-cool application is a motor powering a dry-pit submersible or an explosion-proof submersible motor. Many other hard-to-cool applications exist and the present invention is not limited to submersible motors. In the past these hard-to-cool applications utilized motors that were oversized for the application or placed in an enclosure that did not offer as much protection as a totally enclosed motor. These oversized motors are more expensive to purchase.  
         [0004]     Heat pipes are also generally known. Heat pipes, generally, are a heat transfer mechanism that can transport large quantities of heat with a very small difference in temperature between hot and cold interfaces. A typical heat pipe consists of sealed hollow tube made of a thermoconductive metal such as copper or aluminum. The pipe contains a relatively small quantity of a “working fluid” or coolant (such as water, ethanol or mercury) with the remainder of the pipe being filled with vapor phase of the working fluid, all other gases being excluded. Internally, in order to overcome gravitational forces (or because of their absence in the case of space applications) most heat pipes contain a wick structure. This typically consists of metal powder sintered onto the inside walls of the tube, but may in principle be any material capable of soaking up the coolant.  
       SUMMARY OF THE INVENTION  
       [0005]     An electric motor including a motor portion, a cooling portion and a plurality of heat pipes. The motor portion includes a stator and a rotor that when energized with electric current causes the rotor to rotate. The motor portion comprises a motor frame that encloses the rotor and stator from exterior elements. The cooling portion is adjacent the motor portion and exterior of the motor portion. It defines a fluid chamber containing a quantity of fluid that is prevented from contacting interior of the motor portion. The plurality of heat pipes within the motor portion extend from the motor portion to the cooling portion such that the fluid contacts the heat pipe within the cooling portion in order to remove heat from the heat pipe. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a cross sectional view of a stator core and frame of a motor according to an embodiment of the present invention;  
         [0007]      FIG. 2  is a perspective, cross sectional view of a motor according to an embodiment of the present invention;  
         [0008]      FIG. 3  is an end view of a motor according to an embodiment of the present invention;  
         [0009]      FIG. 4  is a cross-sectional side view of a motor according to an embodiment of the present invention;  
         [0010]      FIG. 5  is a enlarged, perspective cross-sectional of a motor according to an embodiment of the present invention;  
         [0011]      FIG. 6  is a close up cross sectional view of wound stator with a heat pipe inserted in center of the winding according to an embodiment of the present invention;  
         [0012]      FIG. 7  is an end view of a stator core and frame of a motor according to another embodiment of the present invention;  
         [0013]      FIG. 8  is an end view of a stator core and frame of a motor according to another embodiment of the present invention;  
         [0014]      FIG. 9  is an enlarged view of a heat pipe installed in a rotor bar according to an embodiment of the present invention;  
         [0015]      FIG. 10  is a perspective cross sectional view of a motor according to an embodiment of the present invention;  
         [0016]      FIG. 11  is an enlarged partial view of a motor having heat pipes installed therein according to an embodiment of the present invention;  
         [0017]      FIG. 12  is a side cross sectional view of a motor having heat pipes cooled by ducted air according to an embodiment of the present invention;  
         [0018]      FIG. 13  is a cross sectional perspective view of a motor having heat pipes cooled by ducted air according to an embodiment of the present invention;  
         [0019]      FIG. 14  is a side cross sectional view of a motor having heat pipes cooled by a fan according to an embodiment of the present invention;  
         [0020]      FIG. 15  is a cross sectional perspective view of a motor having heat pipes cooled by a fan according to an embodiment of the present invention;  
         [0021]      FIG. 16  is a side cross sectional view of a motor having heat pipes cooled by liquid according to an embodiment of the present invention;  
         [0022]      FIG. 17  is a cross sectional perspective view of a motor having heat pipes cooled by liquid according to an embodiment of the present invention; 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]     While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated.  
         [0024]     The preferred embodiment of the present invention comprises a totally enclosed motor having one or more heat pipes installed in order to increase cooling capability of the motor. The inventive motor is particularly adapted to applications where cooling is problematic. A motor made according to the present invention allows smaller, more efficient motors to be implemented where previously not possible. The invention allows for higher continuous power density. While the preferred embodiment is primarily shown and described with respect to a distributed winding induction motor, the invention may be implemented in other types of motors without departing from the scope of the present invention. By way of example and not limitation, various motor types (e.g. induction, synchronous, permanent magnet, and dc), various rotor types (fabricated copper bar, aluminum die cast, and permanent magnet, wound rotor), motor cooling methods (Totally Enclosed Fan Cooled (TEFC), submersible, hermetic, Totally Enclosed Pipe Ventilated (TEPV), Totally Enclosed Water Cooled (TEWC)) may be used although not shown in the preferred embodiment as one of ordinary skill in the art would recognize.  
         [0025]     As used throughout this application, the term fluid should be defined to include a liquid or a gas. Various different liquids and liquid combinations could be used, such as water or water mixed with an alcohol, for example, or oil, and various gases could be used, such as pure gases or gas combinations, such as air.  
         [0026]     What is described below is the use of heat pipes in an electric motor. In one embodiment heat pipes are incorporated into the stator slot to directly cool the windings. Most of the heat in an electric motor is generated in the motor winding. Thus, putting the heat pipe in close proximity to the copper winding will make the heat transfer most efficient there. The heat pipes may also be implemented in the core/laminations of the stator. While less so than the windings, heat is generated in the core. In addition, the heat conduction path from the windings thru the core is shorter and involves one less interface (as compared to heat pipes in the frame or back iron ring). Heat pipes may also be implemented in the frame. The heat pipes in the frame absorb heat that is generated in the winding and the core. The conduction path is longer, and an additional interface (the core to frame interface) is encountered. This reduces the efficiency of the heat transfer. However, it will still be superior to the heat transfer efficiency as compared to a traditional TEFC or TEWC motors commonly used in industry. Heat pipes may be implemented also in the back iron ring. Same arguments apply here as in the heat pipes in the Frame. A disadvantage here is that an additional part, the back iron ring (BIR), is required. An advantage is that a manufacturer&#39;s standard laminations &amp; frames can be used.  
         [0027]     Heat pipes may also be implemented in the rotor. Longer rotor bars are used and extend beyond the end connector. These extensions cool the bars as they circulate in the air. Rotor efficiency is related to rotor resistance. The resistance itself is a function of rotor bar temperature. If the bar operating temperature drops, then the resistance drops, with subsequent increase in efficiency. Moreover, across the line starting causes severe rotor heating. The number of permissible starts for a large induction motor is related to how much heat the rotor bars can absorb. With heat pipes in the rotor bars, the heat is moved so rapidly from the bars that the rotor bars have a higher effective heat capacity. This in turn increases the number of hot starts that the motor can be subjected to. The heat pipes may be implemented, such as for example fabricated or cast induction rotors, solid (bar-less) rotors, stacked lamination rotors, wound rotors, including induction, synchronous, DC rotors, and permanent magnet rotors.  
         [0028]     In addition to where a heat pipe is placed in a motor to absorb heat, where the other end of the heat pipe is placed to reject heat (“the condensing end”) is important. In submersible motors the heat may be placed in an oil chamber associated with the motor to rejected heat to oil within the oil chamber. The oil is, in turn, cooled by the mounting plate. The mounting plate is an integral part of the submersible motor and serves two functions: it closes off the bottom of the oil chamber and provides for means of mounting the pump directly on the motor (which is commonly the practice on submersible motors). The mounting plate may be considered to be an ‘infinite cold plate’—it stays at constant temperature as a result of the pumping of a high volume of fluid at relatively cool temperatures.  
         [0029]     In water cooled motor with the preferred embodiment of the present invention, the condenser end of the heat pipe is cooled by a cooling head—a water cooler which surrounds the condenser end. In addition to more efficient heat extraction there are additional advantages. For instance, the cooing portion of the motor (i.e. the ‘wet head’) does not have to surround the frame itself, which is commonly done on totally enclosed water cooled (TEWC) machines. Likewise elaborate air circulation throughout internal motor components and then through a water-to-air heat exchanger is also not required. Also, leaks are contained to the cooling head. In addition, the cooling head to can be switched from a ‘wet head’ to an ‘air head’ if cooling water is no longer available.  
         [0030]     In air cooled motors, motor with the preferred embodiment of the present invention, the condenser end of the heat pipe is cooled by ‘air head’ cooling head—an air heat exchanger which extracts heat from the condenser end of the heat pipes to fins to the cooling air that blows over the fins. In addition to more efficient heat extraction (as a result of where the heat pipes pick up the heat from the winding and stator) there are additional advantages. For instance, the air can be easily routed thru the heat exchanger like in a pipe ventilated motor. This easy air routing is not possible with current TEFC motors. In addition, the cooling head to can be switched from an ‘air head’ to a ‘wet head’.  
         [0031]     In hermetically sealed motors, the condenser end of the heat pipe is cooled by evaporative cooling of the cooling media. This is much the same as the way that coil end turns and the core is directly cooled in current hermetic motors. However, with the advent of heat pipes, it is possible to extract heat from the winding within the core just more efficiently without directly exposing sensitive internal motor components to the harsh chemicals and environmental conditions which current technology hermetic motors do. In the present invention, the motor does not have to be hermetically sealed. The cooling end (which is separate from the motor enclosure portion) can be independently hermetically sealed and cooled In that regard and referring to  FIG. 1 , there is shown the stator core  12  of an electric motor  10 . The motor  10  is shown in partial view, and without its windings, for clarity of display. The stator core  12  comprises laminations of electrical steel that form a plurality of slots  14  and bores  16  that are radially spaced about the stator core  12 . As with conventional electric motors, the slots  14  are wound with a stator winding  18 . In the preferred embodiment of the present invention, heat pipes  20  are inserted in each slot  14  of the motor with the stator winding  18 . Moreover, heat pipes  22  are placed within each bore  16  of the stator core  12 .  
         [0032]     Referring to  FIGS. 2-4 , the heat pipes  20  and  22  extend through a drive end bearing housing  24  and a heat pipe clamp plate  26  of the motor  10  and into a chamber  28  that is preferably filled with oil. The oil acts a heat sink and transfers the heat to a mounting plate  29 . The pump, itself, is mounted directly to the mounting plate  29 . The pump is cooled by the fluid (pump medium) that it is pumping. In addition, some of the pumped fluid is directly in contact with the mounting plate. Therefore, the fluid cools the pump and the mounting plate, as well as the pump cools the mounting plate  29 . The mounting plate  29  itself in turn cools the oil, the oil cools the heat pipes, and the heat pipes cool the stator core and winding, as described herein. As a result, the heat pipes increase the capacity of heat dissipation. The heat pipes  20  and  22  in the stator core  12  and stator winding  18  move the heat generated in the stator core  12  and stator winding  18  to the oil in the chamber  28 . The oil is dielectric, so that submersible motor moisture probes, in submersible pump applications, can properly function.  
         [0033]     With the heat pipes  20  and  22  thus inserted, top ends  21  of the heat pipes  20  and  22  that are in the stator core  12  and stator winding  18  serve as an evaporator portion of the heat pipes  20  and  22 . Bottom ends  23  of the heat pipes  20  and  22  serve as the condenser end of the heat pipe  20  or  22 . The oil is kept cooled by conduction, convection and radiation of heat from the exterior surface of the chamber  28 . Moreover, when the motor is used to operate a fluid pump, the fluid moving through the pump acts as a coolant for the motor and is essentially a constant temperature heat sink.  
         [0034]      FIG. 5  shows the sealing arrangement between the drive end bearing housing  24  and the clamping plate  26 . The drive end bearing housing  24  includes a plurality of bores  32  through which the heat pipes  20  and  22  extend into the chamber  28 . Counterbores  34  are formed on the chamber  28  side of the drive end bearing housing  24  which contain o-rings (not shown). The o-rings within the counterbore  34  are compressed slightly by the clamping plate  26  after the clamping plate is installed over the heat pipes  20  and  22  in order to sealing the heat pipes  20  and  22  and prevent oil from escaping the chamber  28 .  
         [0035]     Shown in  FIG. 6 , the wire  36  of the stator core winding  18  is in close proximity to the heat pipe  20  in order to dissipate heat from the stator core winding  18 . In the manufacturing process the heat pipe will be located in a position chosen for manufacturing ease and thermal efficiency. This can be at the top of the slot, center of the slot or end of the slot. The heat pipe  20  is shown centrally located within the slot  14  by first winding the stator slot  14  to a depth of roughly half the depth of the slot  14  minus half of the diameter of the heat pipe  20 . The heat pipe  20  is then inserted into the slot  14  and the remaining wire  36  of the stator winding  18  is wound within the slot  14 . While noting that the heat pipe  20  is shown as having a diameter of less than the width of the slot  14 , it is within the scope of the present invention to comprise a heat pipe  20  that fits snugly or with a small interference fit within the slot  14  of the stator  12 . While the present invention is illustrated with respect to a random wound stator, it should be apparent to one of ordinary skill in the art that the other winding techniques such as form wound coils may be used without departing from the scope of the present invention. The heat pipe  20  may also be located within the top or bottom of the slot  14  without departing from the scope of the present invention.  
         [0036]     The heat pipes  22  of the stator core  12  also extend in to the oil of the chamber  28  and dissipate heat from the outer diameter of the stator core  12 .  
         [0037]     The above-described stator core of  FIG. 6  and windings  12  and  18  of the present invention comprise an integral piece and represent a first option for forming the stator core  12 . The first option consists of using a stator core  12  with the particular standard frame size but having slot geometry and a stator outside diameter of one size smaller standard frame size. In this manner, minimal tooling change is required from presenting existing tooling. However, this method will use significantly more electrical steel due to the increased size of the stator core  12  and thus is more expensive. Finally, the heat pipe bores  16  must be punched or machined into the stator core  12 .  
         [0038]     The second option, shown in  FIG. 7 , is to use a particular standard frame size outer frame  100  or “mechanical package,” one larger standard frame size inner stator ring  102  or “electrical package” and a back iron ring  104 . The back iron ring is designed to make up the difference in the outer diameter of the stator ring  102  and the inner diameter of the outer frame  100 . For example, if the outer frame  100  was for a 440 standard frame size and the inner ring was for a 400 standard frame size stator, the back iron ring would be approximately 1.25 inches thick for this example. It would thereby bridge the gap between a 17.5-inch stator outside diameter of a 400 standard frame size motor and the 20-inch outside diameter of a 440 standard frame size motor. The heat pipe holes  16  would be bored or gun drilled in the back iron ring  104 .  
         [0039]     Referring to  FIG. 8 , a third option is to integrally cast or fabricate a special frame  200 . This frame  200  integrates the back iron ring  104  of the second option into an outer frame  202 , and does not require an additional part of the back iron ring  104 . This frame  200  has the outer sizings of a particular size frame (440, for example), but is cast to accommodate a stator of one smaller standard motor size (400, for example). The option requires a new casting pattern for the frame (if the frame is cast), but has the advantage of using standard electrical components and takes advantage of casting cheaper cast iron to take up the gap between the outer frame and the stator core  204  instead of using more expensive electrical steel or an additional back iron ring. The heat pipe holes  16  would be bored or drilled in the frame when the frame is machined.  
         [0040]     Referring to  FIG. 6 , the stator winding  18  is wrapped in a slot  14  of the stator core  12  and about the heat pipe  20 . In that regard, the winding  18  is first wrapped to half of the depth of the slot  14  in the stator core  12  minus half the diameter of the heat pipe  20 . The heat pipe  20  is then inserted, and the stator winding  18  is continued over the heat pipe  20 . By reducing the operating temperature of the stator winding  18 , the amount of current the stator winding  18  can carry is effectively increased and the resistance of the stator winding  18  is similarly reduced.  
         [0041]     Heat pipes may similarly be inserted into the rotor to assist in dissipating heat. Specifically, referring back to  FIGS. 2-4 , heat pipes  28  can be inserted into rotor bars  40  of a rotor  42  of the motor  10 . The rotor  42 , of course, is mounted on the shaft  45  which rotates within the stator  12  on bearings  44 . As shown in  FIG. 10 , the rotor  42  is punched with a cavity  46  therein for accepting a rotor bar  40 . The rotor bar  40  comprises two halves  50  and  52  which envelope the heat pipe  38  within the rotor  42 . While splitting the rotor bar in two halves is desirable for ease of installation of a heat pipe  22 , the rotor bar  40  can comprise a single, integral rotor bar  40  and the heat pipe  38  inserted on top or below the rotor bar  40  without departing from the scope of the present invention. Moreover, while the heat pipe may be installed in the rotor bar, it may also be either be installed additionally or exclusively within the rotor core, as shown in  FIG. 4A .  
         [0042]     Referring to  FIGS. 10 and 11 , the rotor bars  40  extend beyond the rotor  42  into an air pocket formed between the rotor  42  and the end plate (not shown in  FIG. 10 ) to essentially form a fan. The rotor bar  40  may also extend The fan cools the exposed ends of the rotor bars  40  and heat pipes  38  as the rotor  42  rotates. An end connector ring  54  is further disposed on the extended portion of the rotor bars  40  and the heat pipes  38 . A benefit of the end connector ring  54  is that it serves as a heat sink for the rotor bars. Cooling the rotor bars and end connector ring results in a more efficient rotor. Allowing the end connector to serve as an additional heat sink for the rotor bars increases how much heat the bars themselves can absorb, which in turn increases the number of starts, or amount of time in a stalled condition that the rotor can be subjected to.  
         [0043]     As discussed, the heat pipes  38  in the rotor bars  40  move the heat generated in the rotor bars  40 . The heat pipes each comprise a first end  39 , which forms an evaporator end, and second end  41 , which comprises a condenser end.  
         [0044]     Moreover, the heat pipes  20 ,  22  and  38  are heated initially as part of the manufacturing process such that the pressure within the heat pipe  20 ,  22  and  38  causes it to expand. The heating is sufficient such that it causes the heat pipe to yield &amp; expand. This does two things. It mechanically secures the heat pipe  20 ,  22  and  38  to the stator core  12  or rotor  42 , as the case may be, and increases the degree of thermal contact between the stator core  12  or rotor  42  and the heat pipe  20 ,  22  and  28 . The heat pipe may alternatively be pressed into position in a vertical or horizontal motor frame with the heat pipes now extending out and through the opposite drive end bracket or held in position by a fastening method such as epoxy, solder or braze. Each heat pipe would still be individually “O” ring sealed through the opposite drive end bracket using the same counter bore process as described above.  
         [0045]     Referring to  FIGS. 12 and 13 , heat pipes may be implemented in an air cooled motor. In  FIGS. 12 and 13 , like numerals represent like features of the prior described embodiments. The motor  10  further includes an air chamber  300  into which heat pipes from the motor  10  (except the heat pipes of the rotor) extend. The air chamber  300  includes an air inlet  302  from which air is ducted to cool the heat pipes and an air outlet  304  through which heated air that has passed over the heat pipes exits. Cooling fins  306  are attached to the heat pipes and provide greater surface through which to extract heat from the heat pipes.  
         [0046]     Referring to  FIGS. 14 and 15 , heat pipes may be implemented in a fan cooled motor. In  FIGS. 14 and 15 , like numerals represent like features of the prior described embodiments. The motor  10  further includes an air chamber  400  into which heat pipes from the motor  10  (except the heat pipes of the rotor) extend. The air chamber  400  includes an air inlet  402  from which air is ducted to cool the heat pipes and an air outlet  404  through which heated air that has passed over the heat pipes exits. A fan  406  attached to the shaft  45  forces air from the air inlet  402  to the air outlet  404  over the heat pipes. Cooling fins  408  are attached to the heat pipes and provide greater surface through which to extract heat from the heat pipes.  
         [0047]     The heat pipes of the motor  10  may also be cooled by a liquid-based coolant, for example water or ethylene-glycol/water combinations. In  FIGS. 16 and 17 , like numerals represent like features of the prior described embodiments. The motor  10  further includes a coolant chamber  500 . The heat pipes of the motor, except the heat pipes of the rotor, extend into the coolant chamber  500 . The coolant chamber  500  includes a coolant inlet  502  into which coolant is piped and a coolant outlet  504  through which coolant is routed after it has passed over the heat pipes. Cooling fins are not shown in the present embodiment, but one of ordinary skill in the art would recognize based upon the teachings of the prior embodiments that cooling fins may be implemented in this embodiment as well.  
         [0048]     While not specifically discussed herein, it is further contemplated that heat pipes may also be installed into the rotor itself to further assist in heat dissipation and also in the center of the motor shaft to assist in shaft cooling, which would be particularly useful in reducing bearing heat. As discussed above, this would be beneficial to all rotor types and not only to copper bar induction motor rotors.  
         [0049]     Also while not specifically discussed herein, it is contemplated that the outer motor housing may implement cooling fins, particularly on the exterior of the chamber, as a particular implementation may require.  
         [0050]     While not specifically discussed herein, the present invention may be implemented in all types of electric motors. It is therefore not narrowly limited to induction motors or synchronous motors, but may be used in motors of all types (alternating current (synchronous, induction, permanent magnet, etc.) and direct current motors) all motor voltages (low voltage (less than 600 volt), medium voltage (2300/4160/6600 volt) or high voltage (13.8 KV)) can be used with single-phase and three phase motors, all motor enclosures (e.g. totally enclosed fan cooled, totally enclosed submersible, open motors (WPI/WPII), hermetic motors, etc.) all rotor types (fabricated copper bar, fabricated aluminum, die cast aluminum, permanent magnet, wound rotor, etc.), super conductor motors, and motors of constant or variable speed.  
         [0051]     The above examples show that the invention has far ranging application and should not be limited merely to the embodiments shown and described in detail. The specification is provided merely as an example and the scope of the invention is not so limited.