Abstract:
A dynamoelectric machine, having a stator and rotor, is enclosed in a sealed housing. An impeller fixed to the rotor shaft creates air circulation through the housing and machine components for contact with one or more sealed containers of a coolant medium. The sealed container provides heat transfer from the circulated air through evaporation of the coolant medium. The sealed container has one closed end located within the housing and another closed end external to the housing. Heat from the evaporated coolant medium is transferred to the environment external to the housing through condensation of the vapor at the external end of the container. The sealed container may be stationary or rotatable with the rotor shaft. A plurality of heat transfer containers may be provided.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a cooling system for a dynamoelectric machine and, more particularly, to a machine having an enclosed structure with an embedded heat exchanger. 
   BACKGROUND ART 
   Vertical solid shaft pumps are primarily used for industrial and utility water and sewage deep well applications. Typically, vertical solid shaft pump motors are either of the open drip-proof fan-cooled configuration or canned submersible solid shaft motor drives. Open drip-proof motors are suited for dry pit locations only and do not meet the requirements for submersible and explosion proof applications. 
   Submersible motors, which are cooled to some degree solely by exposure to the submersible environment, tend to overheat when operated continuously in open air. If the submersible environment is not sufficient to adequately cool the submersible motor, or if the motor is to be used in open air, additional cooling means are typically provided. A conventional liquid cooling system is illustrated in  FIG. 1 . The motor  10  is encased in a liquid cooling jacket  12  having an inlet port  14  and an outlet port  16 . This system is an open loop system from the perspective of the motor, in that it requires external provisions, such as a pump or other prime mover, for maintaining flow of the liquid coolant. 
   Solid shaft pump motors present particular challenges in order to accommodate motor cooling requirements that vary with their specific usage. A need exists for a solid shaft pump motor having a self-contained cooling system that is operable in a variety of environments, including dry pit, dry pit submersible and explosion proof conditions. Such a pump motor should meet minimum regulatory requirements, such as U/L, Factory Mutual, CE and CSA requirements, without the need for external cooling, and be capable of handling high reverse load that occurs during backflow. 
   DISCLOSURE OF THE INVENTION 
   The present invention fulfills the above described needs, at least in part, by provision of a submersible embedded-cooling solid shaft pump motor construction. A dynamoelectric machine, having a stator and rotor, is enclosed in a sealed housing. Air can be circulated through the housing and machine components for contact with a sealed container of a coolant medium. The coolant medium may comprise, for example, water. The sealed container provides heat transfer from the circulated air through evaporation of the coolant medium. The sealed container may be a cylindrical hollow pipe having one closed end within the housing and another closed end external to the housing. Heat from the evaporated coolant medium can be transferred to the environment external to the housing through condensation of the vapor at the external end of the container. While this arrangement is suitable for submersible pump motor applications, the machine cooling system is beneficial in a variety of motor and generator applications. 
   Preferably, the sealed housing comprises a central portion in which the machine stator is mounted to the housing and the rotor is mounted to a shaft journaled to the housing for rotation about a longitudinal axis. A cavity in the housing longitudinally adjacent to each end of the central portion provides a sizable volume for air flow circulation, created by an impeller mounted on the shaft at one end portion cavity. The coolant medium container may be mounted to a partition dividing the central portion from the opposite end portion and extend through an end cap of the housing. Heat transfer is facilitated by provision of one or more cooling fins at the external end of the container. A plurality of such coolant medium containers can be situated in the end portion cavity to increase heat transfer capacity. 
   As a further aspect of the invention, an additional sealed cooling pipe configured as an annular ring may be provided that surrounds the shaft and is in fixed contact with the shaft for rotation therewith. The pipe, which contains a coolant medium, preferably extends through the opposite housing end cap with a closed end located external to the housing. An impeller of a pump driven by the motor may be mounted on the external end of the cooling pipe as an additional means for transferring heat from the pipe to the external environment. Internal screw threads may be provided within the heat pipe to aid the flow of coolant medium in the vertical direction. With the addition of the screw threads and external heat transfer provision, the annular ring cooling pipe may, in itself, provide sufficient motor cooling. 
   Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawing and in which like reference numerals refer to similar elements and in which: 
       FIG. 1  is a view of a motor liquid cooling system of the prior art. 
       FIG. 2  is a perspective view of a sealed motor having an embedded self-contained cooling system in accordance with the present invention. 
       FIG. 3  is a partial perspective view of the system of  FIG. 2 . 
       FIG. 4  is an exploded view of elements within system of  FIG. 2 . 
       FIG. 5  is a cross-sectional view of a sealed motor with embedded self-contained cooling system in accordance with a second embodiment of the invention. 
       FIG. 6  is an enlarged partial cross-sectional view of the shaft and rotational heat pipe of the invention shown in  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIG. 2 , a sealed housing  20  comprises three longitudinal portions that terminate in end caps  22  and  24 . As can be seen more clearly in the partial view of  FIG. 3  and the exploded view of  FIG. 4 , a centrally located stator core housing  26  is affixed to end caps  22  and  24  via respective partitions  28  and  30 . The partitions divide the central portion, which houses the machine elements, from end portions defined by the end caps. Each end cap is of one-piece construction of cast iron, forged steel or other material that meets explosion proof requirements. Holes for through bolts  36  are provided in the end caps, partitions and central housing section, with minimum edge distance to meet explosion proof requirements. With the end caps bolted to the central section via the partitions, explosion proof and submersion proof joints are formed. Shaft  32 , which may be formed of one-piece stainless steel, is mounted for rotation through bearings  34  and seals, not shown, at end cap  22  and partition  30 . 0-rings, labyrinth connections and tight fitting tolerances may be used individually or in combination to provide adequate sealing to prevent fluid transfer due to pressure changes within the motor. The motor in use is intended to be vertically oriented with end cap  24  upwards of end cap  22 . 
   Stator core  26  is slotted to accommodate stator windings  27 . The machine rotor comprises a plurality of permanent magnets  36  mounted to the outer periphery of cylindrical supporting structure  38 . Ribs of the supporting structure, at radially spaced intervals, are joined to the outer periphery and to an inner annular ring. The inner periphery of the annular ring is affixed to shaft  32 . The supporting structure  38  may be formed, for example, of solid low carbon steel or a stack of low carbon steel lamination sheets, to provide a back iron magnetic flux path between adjacent permanent magnets. The permanent magnets, which are successively of alternating magnetic polarity, provide a high amplitude alternating magnetic field when rotating relative to the stator. 
   The internal portions of end caps  22  and  24  form transitioning flow channels for an internal forced air cooling system and are shaped to smooth the flow of internal air. Impeller  40 , mounted on shaft  32  within the end portion defined by end cap  22 , creates air flow during machine operation. Air circulates between end portions through openings in the rotor support structure, through the radial air gap between the rotor and stator elements, and through passages in the slotted stator core. Closed heat transfer pipes  42  extend in longitudinal direction from partition  30  through end cap  24  to the external environment. The tubes contain a fluid coolant medium such as water. External cooling fins  44  are mounted to the ends of the heat transfer pipes that are external to the housing. 
   During machine operation, heat is removed from the motor by the forced air flow. The heat transfer pipes are heated convectively by the air that has been forced through the motor. The working fluid in the pipes absorbs the heat, evaporates to a gas and rises up the heat transfer pipes toward end cap  24  and external fins  44 . Heat is transferred from the gas in the heat transfer pipes to end cap  24  and fins  44 , which are convectively cooled by outside air. The cooling causes the gas to condense back to liquid that then flows downwardly in the heat transfer pipes toward partition  30  to continue the heat transfer cycle. 
   The minimum mass flow rate of the working fluid is determined by the latent heat of vaporization of the fluid. Capillary action is based on the surface tension of the fluid and the wicking material structure. Cooling system materials may be copper or aluminum and structurally configured so that fluid undergoes phase change from liquid to gas at specific temperatures, based on the operating temperature range of the motor. With the heat transfer pipes provided in the present invention, the heat generated by a machine, such as a pump motor, is quickly dissipated. The pump thus can be operated over long duration with a relatively uniform internal temperature distribution without the need for external cooling systems. As a further consequence, the external size of the motor can be reduced for a given power rating. 
     FIG. 5  is a cross-sectional view of a modified embodiment of the above-described motor cooling system. Central core  26 , upon which stator windings  27  are formed, is contained within an outer housing  21 . The outer housing  21  is configured with a cylindrical longitudinal side surface  23  that culminates in top surface  25 . Housing  21  is joined at its bottom to end cap  22  and at its top to end cap  24 . Partitions  30 , secured to the end cap  24 , define an upper cooling area that contains closed heat transfer pipes  42 . The heat transfer pipes extend through surface  25  of outer housing surface  21 . Cooling fins  44  are mounted on the external portions of the heat transfer pipes. End cap  24  defines an area for placement of wiring and control devices for the machine. 
   Affixed to motor shaft  32  for rotation therewith is a sealed pipe  50 , which is depicted in greater detail in  FIG. 6 . Rotor supporting structure  38  is directly mounted to the sealed pipe  50 . Shaft  32  is coupled to stationary partition  30  and end cap  22  via the sealed pipe  50  and bearings  34 . Impeller  40  is mounted on the pipe  50  for rotation therewith to provide air circulation through the internal structure of the machine. Shaft  32  and pipe  50  are attached to impeller blades  46  of an external pump which is to be driven by the motor. As shown in  FIG. 6 , pipe  50  comprises an annular portion  52 , shown in cross section, and an integrated helical threaded screw portion  54 . The screw threads join the annular portion  52  to the shaft  32  to form a separation channel  56  therebetween in which a coolant, such as water, is maintained. 
   Pump impeller  46  provides an external heat sink for motor cooling. Rotary motion is used to return condensate, formed in the pipe during external heat transfer to the impeller, to the hot evaporator side within the motor. The screw threads  54  work against gravity to provide upward fluid flow without need of wicking. A slight taper in the direction of the condenser, as shown in  FIG. 5  provides an axial component of the centrifugal force that aids the condensate to return to the evaporator. As the shaft rotates, the condensate material is pushed back into the evaporator side by upward thrust force. Tapering increases the heat transfer coefficient in comparison with a non-tapered rotating heat pipe as production of a condensate film in the pipe is minimized. Provision of a screw insert in the pipe increases the performance of the rotating heat pipe, in comparison with a heat pipe lacking the screw, at low speeds. The centrifugal force of the rotating heat pipe depends upon the rotational speed of the shaft. When the speed is low, centrifugal force alone is insufficient to return the condensate to the evaporator side, absent the internal screw. With the provision of the integrated screw portion, a continuous heat transfer loop is thus maintained without the use of valves, pumps or compressors. 
   In this disclosure there are shown and described only preferred embodiments of the invention and but a few examples of its versatility. It is to be understood that the invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein. For example, the stator core  26  may be fabricated of soft magnetic composites assembled into a steel shell that provides improved environmental sealing for special cases when high pressure sealing of the motor in required. The external surface of the upper end cap may have a series of fins to increase convective heat transfer to the outside air. 
   The illustrated arrangement of four sets of three heat transfer pipes, each set coupled to respective external cooling fins, is merely exemplary. The number of heat transfer pipes and external fins and their relative configurations can be changed as appropriate to comply with physical dimensions of the machine and expected loads. In addition, although an embodiment is exemplified that incorporates both stationary and rotating heat transfer pipes, provision of a rotating heat transfer pipe with integrated helical screw without additional stationary cooling pipes may be sufficient for particular machine applications. 
   Rotor structure can be modified to further enhance the forced air circulation, such as providing holes or spaces in the back iron. Spacers may be placed between the rotor magnets to control the pulsation of air as the rotor spins, thereby increasing the heat transfer rate from the rotor to the air contained within the motor and also to minimize the air drag resistance acting on the rotor. The magnets may also be contoured to produce specific cogging and active torque profiles. 
   The present invention is not limited to pump applications and may be used in other applications such as turbines, down hole well, flood control, agriculture and irrigation, mine slurry, aeration and mixing, below deck ships and dry pit environments. All materials can be selected for their ability to withstand extreme environmental conditions while immersed in salt water, oil and untreated sewage water.