Abstract:
The invention relates to an electric synchronous machine. There is a need for a dual rotor electric synchronous machine which has a mechanism for adjusting the rotor relative angular displacement while the machine is running in order to reduce back emf. There is a need for such an adjusting mechanism which can carry high torque loads. an electric synchronous machine is provided with a housing, first and second shafts rotatably supported in the housing, each with a corresponding rotor fixed thereon, both having permanent magnet field poles. Each rotor is surrounded by a corresponding annular stator, and stator coils are wound through both stators. A planetary transmission is coupled between the first and second shafts and operable during rotation of the first and second shafts to adjust an angular orientation of the second shaft with respect to the first shaft.

Description:
BACKGROUND 
       [0001]    The present invention relates to brushless permanent magnet motors and generators, especially those which must operate over a wide speed range, such as those used in hybrid vehicles or machine tools. 
         [0002]    Brushless permanent magnet motors have a back-emf that is proportional to their speed. At high speeds, the back-emf of the motor can be much higher than the power supply can deliver. Above this speed, additional current out of phase with the back-emf must be added in order to weaken the magnetic field of the motor. This is known as “field weakening”, and is described in U.S. Pat. No. 5,677,605 assigned to Unique Mobility, Inc. This current creates electrical power losses and heat, and requires the electronics to have an increased current capacity. 
         [0003]    One attempt to solve this problem is described in U.S. Pat. No. 6,998,757 wherein a multi-rotor synchronous machine includes first and second rotors are disposed on the outer and inner periphery of a stator core. A mechanism installed inside the second rotor controls relative rotation of the first and second rotors. An electromagnetic machine with two rotors is described in U.S. Pat. No. 4,739,201. The rotors are angularly displaced relative to each other in order to reduce torque ripple, but no mechanism is described for controlling or varying the relative angular displacement between the rotors. Another electromagnetic machine with two rotors is described in U.S. Pat. No. 6,975,055, where the two rotors with field magnets are screwed onto a threaded rod. 
         [0004]    However, none of these machines appears to have a mechanism for adjusting the rotor relative angular displacement which is simple, inexpensive, capable of operating while the machine is running and which can carry high torque loads. 
       SUMMARY 
       [0005]    Accordingly, an object of this invention is to provide a dual rotor electromagnetic machine with a mechanism for adjusting the rotor relative angular displacement which is simple and inexpensive. 
         [0006]    Another object of this invention is to provide a dual rotor electromagnetic machine with such a mechanism which is capable of operating while the machine is running. 
         [0007]    Another object of this invention is to provide a dual rotor electromagnetic machine with such a mechanism which can carry high torque loads. 
         [0008]    These and other objects are achieved by the present invention, wherein an electric synchronous machine includes a housing and a pair of shafts rotatably supported in the housing. A first rotor is fixed for rotation with the first shaft and a second rotor is fixed for rotation with the second shaft. Both rotors carry permanent magnet field poles. A first annular stator is mounted in the housing and surrounds the first rotor. A second annular stator is mounted in the housing and surrounds the second rotor. Both stators have stator coils wound thereon. A gap separates the first and second stators. A coupling mechanism is coupled to the first and second shafts and is operable during rotation of the first and second shafts to adjust an angular orientation of the second shaft with respect to the first shaft. 
         [0009]    The coupling mechanism is a planetary transmission with a first sun gear coupled to the first shaft, a second sun gear coupled to the second shaft, a first planet gear set coupled to the first sun gear, a second planet gear set coupled to the second sun gear, a planet carrier rotatably supporting the first and second planet gear sets, a fixed ring gear fixed to the housing and meshingly engaging the first planetary gear set, and a movable ring gear rotatably supported by the housing and meshingly engaging the second planetary gear set. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective view of a electromagnetic machine embodying the present invention with an end plate removed; 
           [0011]      FIG. 2  is a sectional view of the electromagnetic machine of  FIG. 1 ; 
           [0012]      FIG. 3  is a view taken along lines  3 - 3  of  FIG. 2 ; 
           [0013]      FIG. 4  is a view taken along lines  4 - 4  of  FIG. 2 ; and 
           [0014]      FIG. 5  is an end view of the electromagnetic machine of  FIG. 1 ; and 
           [0015]      FIG. 6  is a perspective view of the rotor assembly of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring to  FIG. 1 , a multi-rotor synchronous electromagnetic machine  10  has a housing  11  which includes a first end housing  12 , a center housing  14  and a second end housing  16 . A cylindrical housing ring  18  projects from an end of the housing  16  and surrounds a planetary gear mechanism  20 . An actuator  22  with a worm gear  24  is attached to the housing ring  18 . 
         [0017]    Referring now to  FIG. 2 , the center housing  14  has an inner sleeve  30  and an outer sleeve  32 . An end plate  19  covers the housing ring  18 . A plurality of water cooling channels  34  are formed in the outer peripheral surface of inner sleeve  30 , and these channels  34  are covered and sealed by the outer sleeve  32 . Sleeve  30  preferably has a T-shaped cross sectional shape and is formed of a heat conducting material, such as aluminum. Sleeve  30  has an annular central leg  31  which projects radially inwardly from an inner surface of cylindrical rim  33 . End housing  12  has a central opening  36 . End plate  19  forms a central blind bore  38 . Bearing  40  is mounted in the opening  36  and a bearing  42  is mounted in the bore  38  and thereby rotatably support a two-part shaft assembly  44 . 
         [0018]    Shaft assembly  44  includes a first hollow outer shaft  46  and a second solid inner shaft  48 . Second shaft  48  includes a larger diameter portion  50  and a smaller diameter portion  52  which rotatably receives first shaft  46 . The larger diameter portion  50  of shaft  48  is rotatably supported by bearing  40 , and an end  53  of portion  52  is rotatably supported by bearing  42 . Larger diameter portion  50  extends through first shaft  46  to end  53  which projects outwardly of an axial end of first shaft  46 . A bearing sleeve  49  rotatably supports an inner end of hollow shaft  46  adjacent to a shoulder which joins the larger and smaller diameter portions of shaft  48 . 
         [0019]    Hollow annular stators  54  and  56  are non-rotatably mounted inside the housing  11  concentric with the shaft assembly  44  and are preferably made of steel. A conventional hollow annular coil assembly  58  is non-rotatably mounted inside the stators  54  and  56 , and is also concentric with the shaft assembly  44 . 
         [0020]    A first rotor  60  is integral to or mounted on and fixed for rotation with the first shaft  46 . A second rotor  62  is integral with or mounted on and fixed for rotation with the larger diameter portion  50  of second shaft  48 , and is spaced axially apart from first rotor  60 . An air gap separates stator assemblies  54  and  56  from the rotors  60  and  62 . 
         [0021]    An annular magnetic sensing ring  61  is mounted on shaft  46  next to an outer end surface of rotor  60 . An annular magnetic sensing ring  63  is mounted on shaft  50  next to an outer end surface of rotor  62 . The magnetic sensing rings  61  and  63  are conventional sensing rings and may be used to provide signals indicating the position of the shafts they are mounted on. The motor preferably has 3-phase windings. A controller (not shown) delivers current to the windings based upon the sensed position of the shafts. 
         [0022]    Referring now to  FIGS. 2 and 5 , a planetary transmission  20  is surrounded by housing ring  18 . The planetary transmission  20  includes a first sun gear  72  formed on the outer end of first shaft  46 , and a second sun gear  74  mounted on and fixed for rotation by splines (not shown) with the end  53  of the inner shaft  48 . Sun gears  72  and  74  preferably have the same outer diameter. A rotatable planet carrier  75  includes a plurality of planet carrier posts  76 . A first set of planet gears  78  are rotatably mounted on the posts  76  for meshing engagement with the teeth of first sun gear  72 . A second set of planet gears  82  are rotatably mounted adjacent to planet gears  78  on the posts  76  for meshing engagement with sun gear  74 . A fixed ring gear  84  is fixed to an inner surface of ring housing  18  and meshingly engages the first planetary gears  78 . A movable ring gear  86  is rotatably mounted in the ring housing  18  adjacent to fixed ring gear  84 . Ring gear  86  meshingly engages the second planetary gears  82 . The worm gear  24  of actuator  22  meshingly engages teeth formed on the outer surface of ring gear  86 . 
         [0023]    As best seen in  FIG. 3 , the first rotor  60  includes an annular rotor member  90  and a plurality of permanent magnets  91 - 96  mounted on the periphery thereof. Magnets  91 ,  93  and  95  have their north magnetic poles oriented radially outwardly. Magnets  92 ,  94  and  96  are positioned between respective pairs of the magnets  91 ,  93  and  95 , and have their south magnetic poles oriented radially outwardly. As a result, as one progresses around the periphery of rotor  60 , each magnet has a magnetic pole orientation which is opposite to or shifted 180 degrees with respect to that of the adjacent magnet. 
         [0024]    As best seen in  FIG. 4 , the second rotor  62  includes an annular rotor member  100  and a plurality of permanent magnets  101 - 106  mounted on the periphery thereof. Magnets  101 ,  103  and  105  have their north magnetic poles oriented radially outwardly. Magnets  102 ,  104  and  106  are positioned between respective pairs of the magnets  101 ,  103  and  105 , and have their south magnetic poles oriented radially outwardly. As a result, as one progresses around the periphery of second rotor  62 , each magnet has a magnetic pole orientation which is opposite to or shifted 180 degrees with respect to that of the adjacent magnet. The magnets  91 - 96  and  101 - 106  preferably have the same angular width. They may also have the same axial length. 
         [0025]    As best seen in  FIG. 2 , stators  54  and  56  are axially spaced apart, and the gap or space between them is filled by leg  31  of sleeve  30 , and a coolant channel  35  is formed in leg  31  to conduct heat away therefrom. As best seen in  FIGS. 3 and 4 , the leg  31  of the sleeve  30  extends radially inwardly and includes a plurality of slots  37 , each of which receives a corresponding one of the coils  58 . As a result, the leg  31  surrounds all but the inner end of each coil  58 , so as to effectively conduct heat away from the coils  58 . 
         [0026]    The rotors  60  and  62  rotate at the motor speed. As shown in  FIG. 6 , below a base speed, rotors  60  and  62  are oriented with respect to each other so that the north and south poles of their respective magnets  91 - 96  and  101 - 106  have the same alignment in the radial direction. This causes the voltages in each coil section  58  to create maximum back-emf. Above a base motor speed, the rotors  60  and  62  are intentionally misaligned with respect to each other, by rotating ring gear  86 . For example, rotating ring gear  86  counter-clockwise viewing  FIG. 1  will rotate sun gear  74 , shaft  48  and second rotor  62  clockwise with respect to first rotor  60 . With the planetary transmission  20  the alignment of the rotors  60  and  62  can be varied and controlled while the motor  10  is operating, and the planetary transmission  20  will withstand operation at high power and torque levels. 
         [0027]    Preferably, one of the rotors  60  and  62 , and the magnets mounted thereon will be longer in the axial direction than the other rotor and its magnets. For example, in  FIG. 2  rotor  62  is axially longer than rotor  60  in a ratio of 55% to 45%. As a result, at a base speed with the rotors  60  and  62  aligned as shown in  FIG. 6 , the combined emf will be a maximum (100%). The misalignment of rotors  60  and  62  reduces the sum of the back-emfs. Thus, at this same speed, if the rotors are fully misaligned, the combined back-emf will be 10% of the maximum (55%-45%). At ten times the base speed, if the rotors are fully misaligned, the combined back-emf will be 100% of the maximum at the base speed (10×(55−45)). 
         [0028]    Alternatively, if the magnets on each rotor have the same size and shape, and have the same magnetic properties, the rotors can be fully misaligned (by 60 degrees for rotors carrying 6 magnets), or so that a north pole on rotor  60  is aligned with a south pole on rotor  62 , and no back-emf will be generated. Thus, the motor  10  can be configured to produce no back emf voltage during overspeed operation, and thereby protect against voltage overloads and shorting of the coils  58 . 
         [0029]    While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. For example, the rotors and magnets can have different sizes, shapes and materials, or the rotors can carry fewer or more magnets. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.