Abstract:
An electromagnetic transmission assembly. The electromagnetic transmission assembly includes a stator having a central axis and a plurality of selectively-energized electromagnetic poles. A first rotor assembly is rotatably supported for rotation about the central axis. The first rotor assembly including a first rotor shaft and a castellated rotor including a plurality of radially arranged ferromagnetic pole portions disposed in a housing. A second rotor assembly is rotatably supported for rotation about the central axis. The second rotor assembly includes a second rotor shaft and a permanent-magnet rotor. The first rotor assembly is at least partially magnetically coupled to the second rotor assembly when the plurality of electromagnetic poles are energized.

Description:
BACKGROUND 
       [0001]    The present invention relates to the transmission of power and torque. 
         [0002]    More specifically, the invention relates to transmissions that change speed and torque between an input shaft and an output shaft. The variety of mechanical gear and transmission designs is extensive. However, mechanical gears and transmissions have a number of disadvantages including frictional wear, lubrication requirements, maintenance, and noise. 
         [0003]    The use of magnetic or electromagnetic coupling can overcome several disadvantages of mechanical transmissions. For example, the frictional wear of mechanical gear teeth that mechanical transmissions may experience is substantially eliminated by magnetic coupling. The use of non-contact magnetic power transfer enables input and output shafts to be isolated and reduces maintenance schedule requirements. Furthermore, unlike mechanical transmissions with mechanical gear teeth, magnetic gears and transmissions have inherent, non-destructive overload protection. 
       SUMMARY 
       [0004]    In one embodiment, the invention provides an electromagnetic transmission assembly. The electromagnetic transmission assembly includes a stator having a central axis and a plurality of selectively-energized electromagnetic poles. A first rotor assembly is rotatably supported for rotation about the central axis. The first rotor assembly including a first rotor shaft and a castellated rotor including a plurality of radially arranged ferromagnetic pole portions disposed in a housing. A second rotor assembly is rotatably supported for rotation about the central axis. The second rotor assembly includes a second rotor shaft and permanent-magnets mounted on or in the rotor. The first rotor assembly is at least partially magnetically coupled to the second rotor assembly when the plurality of electromagnetic poles are energized. 
         [0005]    In another embodiment the invention provides a method of a selectively coupling a prime mover to a load. An electromagnetic transmission is provided. The transmission includes a stator having a central axis and a plurality of selectively-energized electromagnetic poles, a first rotor assembly rotatably supported for rotation about the central axis, the first rotor assembly and a second rotor assembly. A prime mover is coupled to one of the inner rotor and the outer rotor. A load is coupled to the other of the inner rotor and the outer rotor. The electromagnetic poles are selectively energized to create a magnetic field at least partially coupling the first rotor assembly and the second rotor assembly. The prime mover and load are operated in asynchronous driving relation. The electromagnetic poles are selectively deenergized, thereby substantially decoupling the first rotor assembly and the second rotor assembly such that prime mover operates substantially independent of the load. 
         [0006]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a cross-sectional view of an electromagnetic transmission according to a first aspect of the invention. 
           [0008]      FIG. 2  is a cross-sectional perspective view of an electromagnetic transmission according to a second aspect of the invention. 
           [0009]      FIG. 3  is a perspective view of a portion of a shaft and outer rotor of an electromagnetic transmission. 
           [0010]      FIG. 4  is a perspective view of a portion of a shaft and inner rotor of an electromagnetic transmission. 
           [0011]      FIG. 5  is a cross-sectional view of an electromagnetic transmission according to a third aspect of the invention. 
           [0012]      FIG. 6  is top view of a distributed winding stator. 
           [0013]      FIG. 7  is a perspective view of a concentrated winding stator. 
           [0014]      FIG. 8  is a schematic illustration of stator windings connected to a DC power supply. 
           [0015]      FIG. 9  is a cross-sectional view of a motor, electromagnetic transmission, and compressor combination. 
           [0016]      FIG. 10  is a perspective view of a castellated rotor construction according to yet another aspect of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0018]      FIG. 1  is a cross-section of an electromagnetic transmission  10  according to a first aspect of the invention. The electromagnetic transmission  10  includes a stator  12 , a first shaft  14 , and a second shaft  16 . The first shaft  14  is rotatably supported by a first bearing assembly  18 , and the second shaft  16  is rotatably supported by a second bearing assembly  20 . 
         [0019]    The stator  12  includes a plurality of stator windings  22 . A DC power supply  24  is selectively coupled to the stator windings  22  via a switch  26 . The DC power supply  24  may be, for example, a battery, a capacitor, a rectifier, or other source of DC current. The switch  26  may be a mechanical, electric, or electronic device, as is known in the art. 
         [0020]    An inner rotor  28  is coupled to the first shaft  14  such that the inner rotor  28  rotates synchronously with the first shaft  14 . The inner rotor  28  includes a plurality of permanent magnets  30  arranged radially about a longitudinal axis  32  of the first shaft  14 . An arrangement of this type is illustrated in  FIG. 4  in a permanent magnet rotor  428  with radially arranged permanent magnets  430 . 
         [0021]    Referring back to  FIG. 1 , an outer rotor  34  is coupled to the second shaft  16  such that the outer rotor  34  rotates synchronously with the second shaft  16 . A first air gap  36  separates the outer rotor  34  from the inner rotor  28 . A second air gap  38  separates the outer rotor  34  from the surrounding stator  12 . 
         [0022]    The outer rotor  34  includes a base portion  40  coupled to a distal end  42  of the second shaft  16 . An annular rotor body  44  extends axially from the base portion  40 .  FIG. 3  illustrates an outer rotor  334  with many of the features of the rotor  34 . As shown in the rotor  334 , a rotor body  344  includes radially arranged ferromagnetic pole portions  346 . The ferromagnetic pole portions  346  form teeth, or castellations  348 , captured between non-magnetic portions  350 . This castellated ferromagnetic structure modulates a magnetic flux from the permanent magnets  30  or  430  ( FIG. 4 ) of the inner rotor  28  or  428 . Each of the ferromagnetic pole portions  346  may be formed as a stack of ferromagnetic laminations or may be formed unitarily. 
         [0023]    Referring back to  FIG. 1 , the electromagnetic transmission  10  has at least a first operating mode and a second operating mode. In a first operating mode, the DC power supply switch is open. If an external torque is applied to either the first shaft  14  or the second shaft  16 , that shaft will rotate substantially freely of the other shaft, with only minimal magnetic braking effects due to the permanent magnets  30  of the inner rotor  28 . In this first operating mode, substantial transmission of power from the first shaft  14  to the second shaft  16 , or from the second shaft  16  to the first shaft  14  will not occur. 
         [0024]    In the second operating mode, the DC power supply switch  26  is closed such that current from the DC power supply  24  is supplied to the stator windings  22 . A current flowing into the stator windings  22  creates a number of fixed electromagnetic poles, where the number of poles depends upon the particular winding structure.  FIGS. 6 and 7  illustrate two examples of stator winding structures. The stator winding  22  in the embodiment of  FIG. 1  or any of the embodiments discussed below may use a distributed or concentrated layout.  FIG. 6  illustrates an example of a six-pole stator  612  with distributed winding  622 .  FIG. 7  illustrates an example of a twelve-pole stator  712  with concentrated windings  722 . 
         [0025]    Due to magnetic coupling between the inner rotor  28  and the outer rotor  34 , rotating the first shaft  14  by the application of an external torque results in rotation on the second shaft  16 . Alternatively, rotating the second shaft  16  results in rotation of the first shaft  14 . A torque relationship between rotational speed of the first shaft  14  and the second shaft  16  is determined by the number of permanent magnets  30  on the inner rotor  28 , the number of ferromagnetic pole portions  346  ( FIG. 3 ) on the outer rotor  34 , and the pattern of the stator windings  22 . A gearing ratio G r  is determined by the number n s  of ferromagnetic pole portions  346  on the outer rotor  34  divided by the number of pole pairs p of the permanent magnet the inner rotor  28 : 
         [0000]    
       
      
       G 
       r 
       =n 
       s 
       /p 
      
     
         [0000]    A preferred number of stator pole pairs is equal to the absolute value of the difference of the number of castellations and the number of inner rotor magnetic pole pairs. 
         [0026]      FIG. 2  illustrates a second embodiment of an electromagnetic transmission  210 . The electromagnetic transmission  210  has a number of similarities to the electromagnetic transmission of  FIG. 1 , and similar components and features have been given similar reference numerals with a “2”-prefix. The electromagnetic transmission  210  includes the addition of a unidirectional mechanical transmission coupling device  252  for mechanically coupling an inner rotor  228  and an outer rotor  234 . The unidirectional mechanical coupling device  252  may be, for example, a drawn cup roller bearing  352 , as illustrated with the outer rotor  334  of  FIG. 3 . The unidirectional mechanical coupling device  252  allows free rotation in one direction (a disengaged operating mode) and transmits torque in the opposite direction (an engaged operating mode). 
         [0027]    The electromagnetic transmission  210  of  FIG. 2  has four modes of operation. In a first mode of operation, a DC power supply switch  226  is open and the unidirectional mechanical coupling device  252  is disengaged. The inner rotor  228  and the outer rotor  234  may rotate independently of each other and there is substantially no power transfer between the first shaft  214  and the second shaft  216  except for minor magnetic braking torque. 
         [0028]    In a second mode of operation, the DC power supply switch  226  is open and the unidirectional mechanical coupling device  252  is engaged. In the second mode, the first shaft  214  and the second shaft  216  rotate synchronously in a first direction of rotation with a minimal power loss due to magnetic braking effects. However, because the coupling device  252  is unidirectional, in a second direction of rotation of the second shaft  216  there is substantially no power transmission to the first shaft  214 . 
         [0029]    In a third mode of operation, the DC power supply switch  226  is shut and the unidirectional mechanical coupling device  252  is disengaged. Rotation on one of the first shaft  214  and the outer shaft  216  results in rotation of the other of the first shaft  214  and the outer shaft  216  by magnetic coupling between the inner rotor  228  and the outer rotor  234 . A ratio of the speed between the first shaft  214  and the second shaft  216  is determined by the number of inner rotor permanent magnets  230 , the number of ferromagnetic pole portions  246 , and the number of stator winding poles. 
         [0030]    In a fourth mode of operation, the DC power supply switch  226  is shut and the unidirectional mechanical transmission  252  device is engaged. In this fourth mode of operation, the first shaft and the second shaft rotate substantially synchronously, though additional braking torque may be present compared to the second mode of operation. 
         [0031]      FIG. 5  illustrates an electromagnetic transmission  510  according to yet another aspect of the invention. The electromagnetic transmission  510  has a number of similarities to the electromagnetic transmission of  FIG. 1 , and similar components and features have been given similar reference numerals with a “5”-prefix. The electromagnetic transmission of  FIG. 5  includes an electromagnetic coupler  554  for coupling an inner rotor  528  and an outer rotor  534  for synchronous rotation. The electromagnetic coupler  554  includes a coupler power supply  556  for selectively supplying current to electromagnetic portions  558  of the outer rotor  534 . Although the coupler power supply  556  is illustrated as separate from a DC power supply  524  for the stator windings  522 , the stator windings  522  and electromagnetic coupler  554  may be powered from a common power supply, with independent switching. 
         [0032]    In a first mode of operation, a DC power supply switch  526  is open, and the electromagnetic coupler  554  is disengaged (i.e., deenergized). The first shaft  514  and the second shaft  516  rotate substantially freely and independently of each other, with the exception of magnetic braking forces caused by permanent magnets  530  of the inner rotor  528 . 
         [0033]    In a second mode of operation, the DC power supply switch  526  is also open, but the electromagnetic coupler  554  is engaged via the coupler power supply  556 . In this second mode, the first shaft  514  and the second shaft  516  rotate substantially synchronously. Power and torque are transmitted from the first shaft  514  to the second shaft  516  or vice versa. 
         [0034]    In a third mode of operation, the DC power supply switch  526  is shut and the electromagnetic coupler  554  is disengaged (i.e., deenergized). The first shaft  514  and the second shaft  516  rotate with a speed ratio determined by the number of inner rotor permanent magnets  530 , the number of ferromagnetic pole portions ( 346 , see  FIG. 3 ) on the outer rotor  534  , and the number of stator winding  522  poles. 
         [0035]    In a fourth mode of operation, the DC power supply switch  526  is shut and the electromagnetic coupler  554  is engaged via the power supply  556 . In this fourth mode of operation, the first shaft  514  and the second shaft  516  rotate substantially synchronously, though additional braking torque may be present compared to the second mode of operation. 
         [0036]    Each of the previously described aspects of the invention may use a variety of stator core laminations and windings. In one arrangement, the number of stator magnetic poles equals the absolute value of the difference of the number of castellations and inner rotor magnetic poles. 
         [0037]      FIG. 8  illustrates an example of phase winding connections  858  between the stator windings  822  and a DC power supply  824  for an electromagnetic transmission. As illustrated in  FIG. 8 , parallel windings B and Y are in series with winding R. 
         [0038]      FIG. 9  illustrates an exemplary prime mover/transmission/load system  960  using an electromagnetic transmission  910 . In the illustrated system the prime mover is an electric motor  962 , and may be any known type of AC or DC motor, including switch reluctance types. Alternatively, a diesel, gasoline, LPG, or CNG internal combustion engine, gas turbine, or other non-electrical prime mover may be used. An output shaft  964  of the prime mover is coupled to an outer rotor  934  of the electromagnetic transmission  910 . A load, in this case a screw compressor  966 , is coupled to an inner rotor  928 . The electromagnetic transmission  910  allows for a desired speed ratio (i.e., a reduction) between the prime mover and the load, but has the aforementioned advantages of overload protection and reduced mechanical friction losses. 
         [0039]      FIG. 10  illustrates an alternative configuration of a castellated outer rotor  1034 . In the castellated outer rotor  1034 , ferromagnetic portions  1046  extend distally from a non-magnetic base portion  1040 . Unlike the outer rotor illustrated in  FIG. 3 , the outer rotor does not have non-magnetic material surrounding the ferromagnetic portions  1046 . Instead, the ferromagnetic portions  1046  form teeth that are separated by air. 
         [0040]    Thus, the invention provides, among other things, an electromagnetic transmission. Various features and advantages of the invention are set forth in the following claims.