ELECTRIC MOTOR WITH HEAT PIPES

The present invention claims priority to U.S. Provisional Application Serial No. 60/805,192, filed June 19, 2006, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

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

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.

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

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

Fig. 1 is a cross sectional view of a stator core and frame of a motor according to an embodiment of the present invention;

Fig. 2 is a perspective, cross sectional view of a motor according to an embodiment of the present invention;

Fig. 3 is an end view of a motor according to an embodiment of the present invention; Fig. 4 is a cross-sectional side view of a motor according to an embodiment of the present invention;

Fig. 5 is a enlarged, perspective cross-sectional of a motor according to an embodiment of the present invention;

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;

Fig. 7 is an end view of a stator core and frame of a motor according to another embodiment of the present invention;

Fig. 8 is an end view of a stator core and frame of a motor according to another embodiment of the present invention;

Fig. 9 is an enlarged view of a heat pipe installed in a rotor bar according to an embodiment of the present invention; Fig. 10 is a perspective cross sectional view of a motor according to an embodiment of the present invention;

Fig. 11 is an enlarged partial view of a motor having heat pipes installed therein according to an embodiment of the present invention;

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;

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;

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;

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;

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; 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

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. 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.

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.

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's standard laminations & frames can be used. 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.

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. 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.

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'.

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. 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. 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.

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.

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.

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.

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. 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.

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.

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.

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.

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.

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. 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 & 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.

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.

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.

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.

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.

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.

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.

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.