Abstract:
A reconfigurable electric motor includes rotatable permanent magnets in a rotor, the magnets having a first position producing a weak magnetic field and a second position producing a strong magnetic field. The motor is reconfigurable from an asynchronous induction motor at startup into a synchronous motor for efficient operation. The motor includes a squirrel cage for induction motor operation at startup with the permanent magnets positioned to product the weak magnetic field to not interfere with the startup. When the motor reaches sufficient RPM, the permanent magnets rotate to produce a strong magnetic field for high efficiency synchronous operation. The permanent magnets are magnetically biased to come to rest in the weak magnetic field position and a centrifugal mechanism holds the magnets in the weak magnetic field position until sufficient RPM are reached for transition to synchronous operation.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to electric motors and in particular to rotatable permanent magnets in a rotor to reconfigure the motor from an asynchronous induction motor at startup into a synchronous motor for efficient operation. 
     A preferred form of electric motors are brushless AC induction motors. The rotors of induction motors include a cage (or squirrel cage resembling a “hamster wheel”) rotating inside the stator. The cage comprises axially running bars angularly spaced apart on the outer perimeter of the rotor. An AC current provided to the stator introduces a rotating stator magnetic field in the stator, and the rotating field inductively induces current in the bars. The current induced in the bars then cooperate with the same stator magnetic field to produce torque and thus rotation of the motor. 
     The introduction of current into the bars requires that the bars are not moving (or rotating) synchronously with the rotating stator magnetic field because electromagnetic induction requires relative motion between a magnetic field and a conductor in the field. As a result the rotor must slip with respect to the rotating stator magnetic field to produce torque and the induction motors are thus asynchronous motors. 
     Unfortunately, low power induction motors are not highly efficient, and lose efficiency under reduced loads because the amount of power consumed by the stator remains constant at low loads. 
     One approach to improving induction motor efficiency has been to add permanent magnets to the rotor. The motor initially starts in the same manner as a typical induction motor, but as the motor reached its operating speed, the stator magnetic field cooperates with the permanent magnets to enter synchronous operation. Unfortunately, the permanent magnets are limited in size because if the permanent magnets are too large, they prevent the motor from starting. Such size limitation limits the benefit obtained from the addition of the permanent magnets. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by providing a reconfigurable electric motor which includes rotatable permanent magnets in a rotor, the magnets having a first position producing a weak magnetic field and a second position producing a strong magnetic field. The motor is reconfigurable from an asynchronous induction motor at startup into a synchronous motor for efficient operation. The motor includes a squirrel cage for induction motor operation at startup with the permanent magnets positioned to product the weak magnetic field to not interfere with the startup. When the motor reaches sufficient RPM, the permanent magnets rotate to produce a strong magnetic field for high efficiency synchronous operation. The permanent magnets are magnetically biased to come to rest in the weak magnetic field position and a centrifugal mechanism holds the magnets in the weak magnetic field position until sufficient RPM are reached for transition to synchronous operation. 
     In accordance with one aspect of the invention, there is provided a reconfigurable brushless AC electric motor, starting in asynchronous mode and transitioning after startup to a more efficient synchronous mode. The motor includes a stator receiving an AC power signal and generating a rotating stator magnetic field and a rotor. The rotor includes bars forming a squirrel cage structure for inductively cooperation with the rotating stator magnetic field providing the asynchronous mode of operation for motor startup and at least one rotatable permanent magnet for efficient synchronous operation. The permanent magnet resides inside the rotor and cooperates with pole pieces. The permanent magnet has a first position resulting in a weak magnetic field to allow the inductive motor startup and is rotatable to a second position resulting in a strong magnetic field for cooperation with the rotating stator magnetic field for the efficient synchronous operation. A centrifugal latching mechanism retains the permanent magnet in the weak magnetic field position for startup and until sufficient RPM is reached to transition to synchronous operation. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1A  is a side view of a reconfigurable electric motor according to the present invention. 
         FIG. 1B  is an end view of the reconfigurable electric motor. 
         FIG. 2  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  2 - 2  of  FIG. 1A . 
         FIG. 3  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with a single permanent magnet in a radially aligned rotor configuration. 
         FIG. 4  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with a single four pole permanent magnet in a radially aligned rotor configuration. 
         FIG. 5  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with a single four pole hollow permanent magnet in a radially aligned rotor configuration. 
         FIG. 6  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with four permanent magnets in a radially aligned rotor configuration. 
         FIG. 7  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with four pairs of permanent magnets in a radially aligned rotor configuration. 
         FIG. 8  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with four permanent magnets in a flux squeeze rotor configuration. 
         FIG. 9A  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with a single permanent magnet rotated to provide a minimum magnetic field in a radially aligned rotor configuration. 
         FIG. 9B  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with a single permanent magnet rotated to provide a maximum magnetic field in a radially aligned rotor configuration. 
         FIG. 10A  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with a single four pole permanent magnet rotated to provide a minimum magnetic field in a radially aligned rotor configuration. 
         FIG. 10B  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with a single four pole permanent magnet rotated to provide a maximum magnetic field in a radially aligned rotor configuration. 
         FIG. 11A  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with a single hollow four pole permanent magnet rotated to provide a minimum magnetic field in a radially aligned rotor configuration. 
         FIG. 11B  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with a single hollow four pole permanent magnet rotated to provide a maximum magnetic field in a radially aligned rotor configuration. 
         FIG. 12A  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with four permanent magnets rotated to provide a minimum magnetic field in a radially aligned rotor configuration. 
         FIG. 12B  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with four permanent magnets rotated to provide a maximum magnetic field in a radially aligned rotor configuration. 
         FIG. 13A  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with four pairs of permanent magnets rotated to provide a minimum magnetic field in a radially aligned rotor configuration. 
         FIG. 13B  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with four pairs of permanent magnets rotated to provide a maximum magnetic field in a radially aligned rotor configuration. 
         FIG. 14A  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with four permanent magnets rotated to provide a minimum magnetic field in a flux squeeze rotor. 
         FIG. 14B  is a cross-sectional view of the reconfigurable electric motor according to the present invention taken along line  3 - 3  of  FIG. 2  showing an embodiment of the present invention with four permanent magnets rotated to provide a maximum magnetic field in a flux squeeze rotor. 
         FIG. 15A  is a side cross-sectional view of the reconfigurable electric motor according to the present invention with a centrifugal latching mechanism holding a single permanent magnet in a minimum magnetic field position. 
         FIG. 15B  is an end view of the reconfigurable electric motor according to the present invention with the centrifugal latching mechanism holding the single permanent magnet in a minimum magnetic field position. 
         FIG. 16A  is a side cross-sectional view of the reconfigurable electric motor according to the present invention with the centrifugal latching mechanism releasing the single permanent magnet in a maximum magnetic field position. 
         FIG. 16B  is an end view of the reconfigurable electric motor according to the present invention with the centrifugal latching mechanism releasing the single permanent magnet in a maximum magnetic field position. 
         FIG. 17A  is a side cross-sectional view of the reconfigurable electric motor according to the present invention with the centrifugal latching mechanism holding four permanent magnets in a minimum magnetic field position. 
         FIG. 17B  is an end view of the reconfigurable electric motor according to the present invention with the centrifugal latching mechanism holding the four permanent magnets in a minimum magnetic field position. 
         FIG. 18A  is a side cross-sectional view of the reconfigurable electric motor according to the present invention with the centrifugal latching mechanism releasing the four permanent magnets in a maximum magnetic field position. 
         FIG. 18B  is an end view of the reconfigurable electric motor according to the present invention with the centrifugal latching mechanism releasing the four permanent magnets in a maximum magnetic field position. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
     A side view of a reconfigurable electric motor  10  according to the present invention is shown in  FIG. 1A , an end view of the reconfigurable electric motor  10  is shown in  FIG. 1B , and a cross-sectional view of the reconfigurable electric motor  10  taken along line  2 - 2  of  FIG. 1A  is shown in  FIG. 2 . The motor  20  includes stator windings  14  and a rotor  12  residing inside the stator windings  14 . The motor  10  is a brushless AC inductive motor including at least one permanent magnet  16  (see  FIGS. 3-7 ) in the rotor  12 , which magnet  16  may be adjusted to provide a weak magnetic field at startup for initial asynchronous operation and a strong magnetic field after startup for efficient synchronous operation. 
     A cross-sectional view of the reconfigurable electric motor  10  taken along line  3 - 3  of  FIG. 2  showing a first embodiment of the motor  10  comprising a two motor  30   a  with a single two pole rotatable Interior Permanent Magnet (IPM)  16  in the rotor  12  is shown in  FIG. 3 . The magnet  16  is shown with air gaps  21  on each side of the magnet  16  splitting the North (N) and South (S) poles of the magnet  16  in a radially aligned configuration. Bars  32  of a squirrel cage element for inductive operation are angularly spaced apart around the outer radius of the rotor  12  reaching the length of the rotor  12 . The bar may be straight or may be twisted to reduce noise among other benefits. The magnet  16  and rods  32  are carried by rotor pole pieces  20  separated by the air gaps  21 . The pole pieces  20  are preferably constructed from laminated layers of insulated magnetically conducting material, for example, iron or steel. 
     A cross-sectional view of the reconfigurable electric motor  10  according to the present invention taken along line  3 - 3  of  FIG. 2  showing a second embodiment of the motor  10  comprising a four pole motor  30   b  with a single four pole permanent magnet  16   a  in a radially aligned rotor configuration is shown in  FIG. 4 . The pole piece  20  is divided into four quarter sections with air gaps  21  between adjacent sections. The motor  30   b  is otherwise like the motor  30   a.    
     A cross-sectional view of the reconfigurable electric motor  10  according to the present invention taken along line  3 - 3  of  FIG. 2  showing a third embodiment of the motor  10  comprising a four pole motor  30   c  with a single hollow four pole permanent magnet  16   b  in a radially aligned rotor configuration is shown in  FIG. 5 . A steel shaft  23  runs through the center of the hollow magnet  16   b . The motor  30   c  is otherwise like the motor  30   b.    
     A cross-sectional view of the reconfigurable four pole electric motor  10  according to the present invention taken along line  3 - 3  of  FIG. 2  showing a fourth embodiment of the motor  10  comprising a four pole motor  30   d  with four two pole permanent magnets  16  angularly spaced apart in a radially aligned rotor configuration is shown in  FIG. 6 . The pole piece comprises four outer pole pieces  20   a  and a single hollow center pole piece  20   b . The magnets  16  are sandwiched radially between the center pole piece  20   b  and the outer pole pieces  20   a  and air gaps  21  separate each outer pole piece  20   a  from an adjacent outer pole piece  20   a  and separate the center pole piece  20   b  from the outer pole pieces  20   a . Bars  32  of the squirrel cage element for inductive operation are angularly spaced apart around the outer radius of the rotor  12  reaching the length of the rotor  12 . The bar may be straight or may be twisted to reduce noise among other benefits. The pole pieces  20   a  and  20   b  are preferably constructed from laminated layers of insulated magnetically conducting material, for example, iron or steel. 
     A cross-sectional view of the reconfigurable four pole electric motor  10  according to the present invention taken along line  3 - 3  of  FIG. 2  showing a fifth embodiment of the motor  10  comprising a four pole motor  30   e  with four pairs of two pole permanent magnets  16  angularly spaced apart in a radially aligned rotor configuration is shown in  FIG. 7 . Other similar embodiments may include groups of magnets comprising four groups of three or more magnets. The motor  30   e  is otherwise like the motor  30   d.    
     A cross-sectional view of the reconfigurable four pole electric motor  10  according to the present invention taken along line  3 - 3  of  FIG. 2  showing a sixth embodiment of the motor  10  comprising a four pole motor  30   f  with four two pole permanent magnets  16  angularly spaced apart in a flux squeeze rotor configuration is shown in  FIG. 8 . The four magnets  16  reside angularly between four angularly spaced apart pole pieces  20   c . The motor  30   f  is otherwise like the motor  30   d.    
     A cross-sectional view of the motor  30   a  (see  FIG. 3 ) taken along line  3 - 3  of  FIG. 2  with the single two pole permanent magnet  16  rotated to provide a minimum (or weak) magnetic field  24   a  is shown in  FIG. 9A . The weakened magnetic field  24   a  does not interfere with starting the motor  30   a  in an inductive mode for initial asynchronous operation. 
     A cross-sectional view of the motor  30   a  taken along line  3 - 3  of  FIG. 2  with the single two pole permanent magnet  16  rotated to provide a maximum (or strong) magnetic field is shown in  FIG. 9B . The strong magnetic field would interfere with starting the motor  30   a , but provides more efficient operation in a synchronous more after startup of the motor  30   a.    
     A cross-sectional view of the motor  30   b  (see  FIG. 4 ) taken along line  3 - 3  of  FIG. 2  with the single four pole permanent magnet  16   a  rotated to provide a minimum (or weak) magnetic field  24   a  is shown in  FIG. 10A . The weakened magnetic field  24   a  does not interfere with starting the motor in an inductive mode for initial asynchronous operation. 
     A cross-sectional view of the motor  30   b  taken along line  3 - 3  of  FIG. 2  with the single four pole permanent magnet  16   a  rotated to provide a maximum (or strong) magnetic field is shown in  FIG. 10B . The strong magnetic field would interfere with starting the motor  30   b , but provides more efficient operation in a synchronous more after startup of the motor  30   b.    
     A cross-sectional view of the motor  30   c  (see  FIG. 5 ) taken along line  3 - 3  of  FIG. 2  with the single hollow four pole permanent magnet  16   b  rotated to provide a minimum (or weak) magnetic field  24   a  is shown in  FIG. 11A . The weakened magnetic field  24   a  does not interfere with starting the motor in an inductive mode for initial asynchronous operation. 
     A cross-sectional view of the motor  30   c  taken along line  3 - 3  of  FIG. 2  with the single hollow four pole permanent magnet  16   b  rotated to provide a maximum (or strong) magnetic field is shown in  FIG. 11B . The strong magnetic field would interfere with starting the motor  30   c , but provides more efficient operation in a synchronous more after startup of the motor  30   c.    
     A cross-sectional view of the motor  30   d  (see  FIG. 6 ) taken along line  3 - 3  of  FIG. 2  with the four two pole permanent magnets  16  rotated to provide a minimum (or weak) magnetic field  24   a  is shown in  FIG. 12A . The weakened magnetic field  24   a  does not interfere with starting the motor  30   d  in an inductive mode for initial asynchronous operation. 
     A cross-sectional view of the motor  30   d  taken along line  3 - 3  of  FIG. 2  with the four two pole permanent magnets  16  rotated to provide a maximum (or strong) magnetic field is shown in  FIG. 12B . The strong magnetic field would interfere with starting the motor  30   d , but provides more efficient operation in a synchronous more after startup of the motor  30   d.    
     A cross-sectional view of the motor  30   e  (see  FIG. 7 ) taken along line  3 - 3  of  FIG. 2  with the four pairs of two pole permanent magnets  16  rotated to provide a minimum (or weak) magnetic field  24   a  is shown in  FIG. 13A . The weakened magnetic field  24   a  does not interfere with starting the motor  30   e  in an inductive mode for initial asynchronous operation. 
     A cross-sectional view of the motor  30   e  taken along line  3 - 3  of  FIG. 2  with the four pairs of two pole permanent magnets  16  rotated to provide a maximum (or strong) magnetic field is shown in  FIG. 13B . The strong magnetic field would interfere with starting the motor  30   e , but provides more efficient operation in a synchronous more after startup of the motor  30   e.    
     A cross-sectional view of the motor  30   f  (see  FIG. 8 ) taken along line  3 - 3  of  FIG. 2  with the four two pole permanent magnets  16  rotated to provide a minimum (or weak) magnetic field  24   a  in the flux squeeze rotor configuration is shown in  FIG. 14A . The weakened magnetic field  24   a  does not interfere with starting the motor  30   f  in an inductive mode for initial asynchronous operation. 
     A cross-sectional view of the motor  30   f  taken along line  3 - 3  of  FIG. 2  with the four two pole permanent magnets  16  rotated to provide a maximum (or strong) magnetic field in the flux squeeze rotor configuration is shown in  FIG. 14B . The strong magnetic field would interfere with starting the motor  30   f , but provides more efficient operation in a synchronous more after startup of the motor  30   f.    
     A side cross-sectional view of the motor  30   a  (see  FIG. 3 ) with a centrifugal latching mechanism  40  holding the single permanent magnet  16  in a minimum magnetic field position (see  FIG. 9A ) is shown in  FIG. 15A  and a corresponding end view of the motor  30   a  with the centrifugal latching mechanism holding the single permanent magnet in the minimum magnetic field position (see  FIG. 9A ) is shown in  FIG. 15B . A second side cross-sectional view of the motor  30   a  with the centrifugal latching mechanism  40  having released the single permanent magnet  16  to the maximum magnetic field position is shown in  FIG. 16A  and a corresponding end view of the motor  30   a  with the centrifugal latching mechanism having released the single permanent magnet to the maximum magnetic field position is shown in  FIG. 16B . The centrifugal latching mechanism  40  includes weights  44 , rotating plate  50 , spring disk  48 , sliding plate  46 , pins  42 , and pin seats  52 . The weights  44  and spring disk  48  are selected so that at an appropriate RPM the weights  44  move outward causing the spring disk  48  to snap from a first extended position as in  FIG. 15A  to a retraced position as in  FIG. 16A  thereby retracting the pins  42  from seats  52  releasing the magnet  16 . 
     The magnet  16  is magnetically urged to the weak magnetic field position when the motor  30   a  is stationary, and the centrifugal latching mechanism  40  also urges the pins  42  into the pin seats  52  when the motor  30   a  is stationary. As a result, the motor  30   a  returns to the weak magnet mode whenever the motor  30   a  stops allowing the motor to startup as an asynchronous induction motor. When the motor  30   a  reaches sufficient RPM, the centrifugal latching mechanism  40  pulls the pins  42  from the pin seats  52  releasing the magnet  16 . At sufficient RPM, the magnetic fields in the motor  30   a  urge the permanent magnet  16  to rotate 90 degrees to the strong magnet position, thus providing efficient synchronous operation. 
     An example of a suitable centrifugal latching mechanism is the Synchrosnap® Centrifugal mechanism made by TORQ Corp. In Bedford, Ohio. For use in the present invention, the Synchrosnap® Centrifugal mechanism is only slightly modified to actuate the pins  42  instead of providing an electrical switch function. 
     A second example of the apparatus for switching between a weak magnetic field and a strong magnetic field applied to the motor  30   f  (see  FIG. 8 ) is shown in  FIGS. 17A  (side view weak field),  17 B (end view weak field),  18 A (side view strong field), and  18 B (end view strong field). The four magnets  16  of the motor  30   f  each are attached to a small gear  60 , and the small gears all engage a larger gear  62 , whereby all of the magnets  16  remain rotationally aligned. The pins  42  engage the pin seats  52  in the large gear  62  when the motor  30   f  is at rest, and when the motor  30   f  reaches sufficient RPM, the centrifugal latching mechanism  40  pulls the pins  42  from the pin seats  52  releasing the magnet  16 . As with the motor  30   a , the permanent magnets  16  of the motor  30   f  are magnetically urged to the weak field position (see  FIG. 14A ) when the motor  30   f  is stopped, and are magnetically urged to the strong field position (see  FIG. 14B ) at RPM sufficient for synchronous operation. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.