Patent Publication Number: US-2013241326-A1

Title: Liquid cooled dynamoelectric machine

Description:
BACKGROUND OF THE INVENTION 
     The present invention is related to dynamoelectric machines and, in particular, to cooling of dynamoelectric machines. 
     A dynamoelectric machine is any type of machine that can generate motion from electricity or vice-versa and includes, for example, motors and generators. As such, the term “machine” as used herein shall refer to both motors and generators unless specifically limited to the contrary. These machines include both a rotor and a stator separated by a rotor-stator gap. The machine can be cooled by the flow of a liquid coolant flow through the rotor-stator gap. Such a machine is referred to as a liquid cooled machine. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one embodiment, an electric motor that includes an outer housing, a stator disposed within the outer housing and a rotor disposed within the stator that, in combination with the stator, defines a rotor-stator gap between them, is disclosed. The rotor of this embodiment includes a main rotor body and a rotor body extension extending axially from an end of the main rotor body. In this embodiment, the main rotor body includes an axial hole formed at least partially along a length thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is cut-away side view of prior art motor coupled to a pump; 
         FIG. 2  is cut-away side view of a permanent magnet motor according to one embodiment; 
         FIG. 3  is a cross-section of the rotor of the motor shown in  FIG. 2 ; 
         FIGS. 4   a - 4   c  show a process by which a stator channel may be formed in the rotor shown in  FIG. 3 ; 
         FIG. 5  is cut-away side view of an induction motor according to another embodiment; and 
         FIG. 6  is a cross-section of the rotor of the motor shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One environment where liquid cooled machines are utilized is on aircrafts. It has been discovered, however, that in such situations the liquid coolant flow the rotor-stator can result in windage losses. The windage losses results from the friction between the rotor and the coolant. In some cases, the losses can equal up to 70-80% of the machine&#39;s electromagnetic heat loss. As a result, and in the event that the machine is a motor, more motor input power is required from the aircraft electrical power system. In addition, increased windage loss results in lower motor efficiency such that motor efficiency is in the 83-85% range. Embodiments of the present invention are directed to liquid cooled machines having reduced windage losses. This can be accomplished, for example, by flowing the liquid coolant through one or more of: an internal portion of the rotor and an external portion of the stator. In one embodiment, no cooling liquid is allowed to pass into the rotor-stator gap. In one embodiment, fluid is only passed through the rotor and the stator is cooled by providing a high conductivity thermal gap pad between an end turn of the stator and the outer housing of the machine. 
     To provide context, a cross-section of a prior art permanent magnet motor  100  is illustrated in  FIG. 1 . The motor  100  is coupled to a pump component  102  to form a pump  104  used to circulate, for example, a cooling fluid such as a propylene glycol/water mixture through one or more systems of an aircraft. In the illustrated system, the fluid being pumped by the pump  104  is also used to cool the motor  100  as will be described further below. 
     The cooling fluid is initially drawn into an inlet plenum  108  (not shown) formed in the pump component  102 . The fluid is then drawn into a volute  111  formed between the pump component  102  and the motor  100  by the rotation of an impeller  106  and then expelled out of the pump  104  at an outlet (not shown) of the volute  111 . However, not all of the fluid is expelled out of the volute  111 . In particular, some of the fluid travels into and through the motor  100  and serves to cool it. The path of the fluid is shown by arrows A. 
     As illustrated, the impeller  106  is directly coupled to the rotor  114  of the motor  100 . A thrust bearing  150  is disposed between the impeller  106  and the inlet plenum  108 . Fluid that is not expelled from the volute  111  can enter the motor  100  by passing through journal bearing  152  as shown by arrow A′. Thereafter, the fluid enters the interior  109  of the motor  100  and then travels through the rotor-stator gap  110 , as described above. The fluid then passes through one or more bearings such as journal bearing  160  and bumper bearing  162  and is drawn back towards the volute  111  through an inner channel  112  of the rotor  114  and provided back into the pump component  102 . As described above, having the fluid pass through the rotor-stator gap  110  can result in windage losses. 
     The following description will assume that the motors disclosed hereafter include are disposed such that a cooling fluid can be provided to them. For instance, the motors could be coupled to a pump portion to form a volute in which an impeller is disposed. The motor turns the impeller to expel a fluid and some of the fluid is drawn into the motor and used to cool the motor. 
       FIG. 2  is a partial cross-section of a motor  200  according to one embodiment. In this embodiment, a cooling fluid is circulated in a manner such that it does not enter the rotor-stator gap  202 . As described above, the fluid is driven by an impeller  199  coupled to a rotor  201  of the motor  200 . In this embodiment, the motor  200  is a permanent magnet motor and includes a stator  205  surrounding the rotor  201 . 
     The rotor  201  includes one or more permanent magnets  204  disposed about a rotor body  206 . The permanent magnets  204  are disposed in a rotor sleeve that includes end plates  208 . In the illustrated embodiment, the rotor body  206  includes a rotor body extension  207  that has smaller outer diameter than other portions of the rotor body  206 . 
     Referring now to  FIG. 3 , cross-section of the rotor  201  is illustrated. The rotor  201  includes a rotor shaft  311  surrounded by a rotor body  206 . The rotor shaft  311  defines an inner channel  310  that, as described below, can provide a return fluid path. While not illustrated, it shall be understood that the rotor body extension  207  surrounds portions of the shaft  311 . 
     Arranged about the rotor body  206  are the permanent magnets  204  described above. The permanent magnets  204  are surrounded by a rotor sleeve  304 . In one embodiment, the magnets are arranged such that a channel  308  is created between adjacent magnets  204  and the rotor sleeve  304 . 
     As illustrated, the rotor  201  further includes a plurality of axial holes  340  formed in the rotor body  206 . These axial holes  340  extend axially along a portion of the rotor  201 . In an alternative embodiment, and as disclosed further below, the axial holes  340  could extend along the entire length of the rotor  206 . Referring now to both  FIGS. 2 and 3 , the number of axial holes  340  is variable and form part of a rotor body channel that allows the fluid to enter the channel  308  without entering the gap  202 . 
     In  FIG. 2 , the cross-section is taken such that the channel  308  is visible. In the illustrated embodiment, rather than being drawn through the rotor-stator gap  110  ( FIG. 1 ), cooling fluid is drawn through the channel  308  as indicated by arrow B and then provided through the inner channel  310  of the rotor  200  as indicated by arrow C. 
     In  FIG. 2  it can be seen that seals  220  are provided that prevent fluid from entering the gap  202 . In one embodiment, and referring now to both  FIGS. 2 and 3 , the seals  220  are provided such that the passes through the journal bearing  242  and is directed towards the rotor holes  340  by the seals  220 . In  FIG. 2  the rotor holes  340  are not visible indicating that they are not in the same axial plane is the channel  308  in one embodiment. Of course, in one embodiment, one or more of the channels  308  could be in the same axial plane as one of the rotor holes  340 . 
     Regardless of the orientation of the rotor holes  340  and the channels  308 , the rotor holes  340  form part of a rotor channel ( FIGS. 4   a - 4   c ) that fluidly couples the region immediately to right of the journal bearing  242  a region immediately to the left of the first end plate  208   a.  Fluid then traverses the channel  308  until it reaches the second end plate  208   b  and is directed though another rotor channel to journal bearing  244 . 
       FIGS. 4   a - 4   c  show how the rotor channels  350  can be formed in the rotor  201 . In particular, one or more axial holes  340  are axially formed (e.g., drilled) though the rotor body extension  207  and into another portion of the rotor body  206  that shall be referred to herein as the main rotor body  209  ( FIG. 4   a ). It shall be understood that the rotor body extension  207  and the main rotor body  209  could be formed of as a unitary piece or as two separate pieces. In one embodiment, the diameter of the main rotor body  209  is greater than the diameter of the rotor body extension  207 . This process is repeated on both ends of the rotor  206 . 
     Radial orifices  344  are formed in both the main rotor body  209  and the rotor body extension  207  such they contact the axial holes  340  ( FIG. 4   b ). It shall be understood that the order of forming the radial orifices  344  and the axial holes  340  can be reversed without departing from the teachings herein. In one embodiment, the radial orifice  344  formed in the main rotor body  209  is located such that it will be between the end plates  208  shown in  FIG. 2  when they are disposed on the rotor. 
     An end portion of the axial holes  340  is then filled with a plug  346  such that a rotor channel  350  is formed whereby fluid flows into the radial orifice  344  on the rotor body extension  307  through a portion of the main rotor body  209  and exits the main rotor body  209  at an outer diameter thereof. Of course, fluid could also flow in the opposite direction. 
     Referring again to  FIG. 2 , the stator  205  includes end turns  211 . In one embodiment, the end turns  211 . In one embodiment, a highly conductive thermal gap pad  213  is disposed between the end turns  211  and the outer housing  215  of the motor  200  to improve transfer of heat from the end turns  211  to the outer housing  215 . In this and other embodiments, the thermal gap pad  213  can be formed, for example, of a high heat conductive silicone rubber. 
       FIG. 5  shows a partial cross-section of a motor  400  according to another embodiment. In this embodiment, a cooling fluid is circulated in a manner such that it does not enter the rotor-stator gap and is driven, as described above, by an impeller (not shown). The motor shown in  FIG. 5  is an induction motor. Such a motor includes a rotor  401  having a rotor shaft  402  with rotor laminations  404  disposed thereon. One of ordinary skill will realize that the laminations  404  provide a structural support for one or more rotor windings (not shown). In this embodiment, the rotor shaft  402  includes one or more channels  470  formed therein and the cooling flow (shown by the arrows in  FIG. 4 ) is directed through these channels  470 . It shall be understood that the fluid could also flow through in the inner channel  410  of the rotor but that is not required. In contrast to the prior embodiment, the channels traverse through the entire length of the main rotor body  500  and do not extend through rotor body extensions  502 . 
     The motor  400  further includes an outer housing  420  that surrounds the stator  430 . In this embodiment, a housing channel  422  or a plurality of axially or circumferentially disposed channels are provided within the outer housing  420  through which cooling fluid may flow. The cooling fluid enters the housing channel  422  through an opening  421  in the outer housing  420 . 
     The stator  430  can include end turns  432 . In one embodiment, a highly conductive thermal gap pad  434  is disposed between the end turns  432  and the outer housing  420  to improve transfer of heat from the end turns  432  to the outer housing  420 . The heat is then carried at least partially away by the fluid traveling through the housing channels.  422 . 
     As illustrated, the fluid leaves the housing channel  422  and passes through at least journal bearing  460 . Seals  462  are provided around the rotor  402  to keep the fluid from entering the rotor-stator gap  450 . The fluid is then forced to travel through rotor channels  470  formed in the rotor  401 . As can best be seen in  FIG. 6 , the rotor channels  470  are formed in the main rotor body  500  of the rotor  401  radially inward from the laminations  404 . 
     Referring again to  FIG. 4 , the fluid then exits the rotor  402  and re-enters the volute (not shown) by passing through journal bearing  472 . 
     In summary, in this embodiment, liquid from pump outlet enters the motor housing channels  422  and then flows axially through these channels to the distal end of the motor  400 . After passing through the journal bearing  460  at the distal end of the motor  400 , the fluid is denied entry into the rotor-stator gap  450  by seals  462  and, as such, passes through rotor channels  470  and then, ultimately, back to the pump outlet. In this manner, heat from or both of stator and rotor can be carried away by the liquid. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.