Patent Publication Number: US-9419504-B2

Title: Hybrid induction motor with self aligning permanent magnet inner rotor

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to electric motors and in particular to an induction motor having an independently rotating permanent magnet rotor variably coupled to an inductive rotor to reconfigure the motor from asynchronous induction operation at startup to synchronous operation after startup 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 a 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 inside the rotor, and the rotating field inductively induces current in the bars. The current induced in the bars creates an induced magnetic field which cooperates with the stator magnetic field to produce torque and thus rotation of the rotor. 
     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 (called slipping) 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 induce current in the bars to produce torque, and the induction motors are therefore called asynchronous motors. 
     Unfortunately, low power induction motors are not highly efficient at designed operating speed, and are even less efficient under reduced loads because the amount of power consumed by the stator remains constant at such reduced 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 hybrid induction motor which includes an inductive rotor and an independently rotating permanent magnet rotor. The inductive rotor is a squirrel cage rotor permanently coupled to a motor load (for example, a motor shaft) for induction motor operation at startup. The permanent magnet rotor is variably coupled to the inductive rotor (or to the load) through a clutch and is allowed to rotate independently of the inductive rotor at startup. The independently rotating permanent magnet rotor quickly reaches synchronous RPM at startup. As the inductive rotor approaches or reaches synchronous RPM, the coupling between the inductive rotor and the inner permanent magnet rotor increases until the two rotors are coupled and rotate at the synchronous RPM and the motor transitions to efficient synchronous operation. 
     In one embodiment, the inner permanent magnet rotor is coupled to the inductive rotor through a discrete position slip clutch providing discrete angular positions of rotational alignment between the permanent magnet rotor and the inductive rotor 
     In accordance with one aspect of the invention, there is provided a hybrid induction motor including an outer inductive rotor and a freely rotating inner permanent magnet rotor free to rotate with rotating stator flux. When power is applied to the motor, the inner permanent magnet rotor immediately accelerates to keep up with the rotating stator field, while the outer inductive rotor and load comes up to speed. As the outer inductive rotor approaches synchronous RPM (the RPM of the stator magnetic field and of the inner permanent magnet rotor) a locking clutch engages, synchronizing the outer inductive rotor inner with the inner permanent magnet rotor. The locking clutch locks at just over the designed torque of the motor, any over load will unlock the clutch and begin to slip until the load is brought back to near synchronous speed. The clutch locks are designed to skip at a certain frequency just out of working slip and engage within operating frequency. 
     In accordance with another aspect of the invention, there is provided a hybrid induction motor including an inner permanent magnet rotor coupled with the rotating stator magnetic field. The inner permanent magnet rotor reaches synchronous RPM before outer inductive rotor only needing to overcome initial friction of the slip clutch (clutch torque is set to peak torque of motor rating) and inertia of inner permanent magnet rotor itself. 
     In accordance with still another aspect of the invention, there is provided an outer inductive rotor including amortisseur windings which accelerates as a normal induction motor rotor without any negative permanent magnet influence or transient breaking torque and benefitting from a positive applied torque provided by the inner permanent magnet rotor through the slip clutch which contributes to the starting torque. Such amortisseur windings provide torque without fluctuation or pulsation inherent in fixed Line Start Permanent Magnet (LSPM) motors during starting 
     In accordance with yet another aspect of the invention, there is provided a hybrid induction motor which is self regulating and avoids magnetic overload and stall if to much load is applied. As the motor approaches magnetic overload or stall, the permanent magnet rotor disengages from the inductive rotor and maintains synchronous RPM, The inductive and permanent magnet rotors re-couple when the transient event is past. 
     In accordance with still another aspect of the invention, there is provided a hybrid induction motor which can safely use ferrite magnets because the clutch mechanism does not expose the magnets to high coercive demagnetizing forces because the clutch allows the permanent magnet rotor to rotate at synchronous speed until excessive load is brought under control. 
    
    
     
       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. 1  shows an embodiment of an electric motor configuration having an independently rotating inner permanent magnet rotor, an inductive rotor fixedly coupled to a motor shaft and outside the permanent magnet rotor, and a stator outside the inductive rotor, according to the present invention. 
         FIG. 2  shows an embodiment of an electric motor configuration having the inductive rotor coupled to a motor shaft, the independently rotating permanent magnet rotor outside the inductive rotor, and the stator outside the permanent magnet rotor, according to the present invention. 
         FIG. 3  shows an embodiment of an electric motor configuration having the stator inside the rotors, the independently rotating permanent magnet rotor outside the stator, and the inductive rotor coupled to a load and outside the permanent magnet rotor and the stator, according to the present invention. 
         FIG. 4  shows an embodiment of an electric motor configuration having the stator inside the rotors, the inductive rotor coupled to a load and outside the stator, and independently rotating permanent magnet rotor outside the inductive rotor, according to the present invention. 
         FIG. 5  shows the relative RPM and torque of the inductive and permanent magnet rotors. 
         FIG. 6  shows a side view of a continuous slip clutch according to the present invention. 
         FIG. 7  shows an end view of the continuous slip clutch according to the present invention. 
         FIG. 8  shows a side view of a discrete slip clutch according to the present invention. 
         FIG. 9  shows an end view of the discrete slip clutch according to the present invention. 
         FIG. 10  shows a side view of a centrifugal clutch coupling the permanent magnet rotor and the inductive rotor according to the present invention. 
         FIG. 11  shows a cross-sectional view of the centrifugal clutch coupling the permanent magnet rotor and the inductive rotor taken along line  11 - 11  of  FIG. 10  according to the present invention. 
         FIG. 12  shows a side view of an electro-magnetic clutch coupling the permanent magnet rotor and the inductive rotor according to the present invention. 
         FIG. 13  shows a cross-sectional view of the electro-magnetic clutch coupling the permanent magnet rotor and the inductive rotor taken along line  13 - 13  of  FIG. 12  according to the present invention. 
         FIG. 14  shows a side view of a first embodiment of a motor according to the present invention. 
         FIG. 15  shows a cross-sectional view of the first embodiment of the motor according to the present invention. 
         FIG. 16  shows a more detailed side view of a first rotor of the first embodiment of the motor according to the present invention. 
         FIG. 17  shows a side view of a first inductive rotor of the first embodiment of the motor according to the present invention. 
         FIG. 18  shows a cross-sectional view of the first inductive rotor of the first embodiment of the motor according to the present invention. 
         FIG. 19A  shows a side view of a first permanent magnet rotor of the first embodiment of the motor according to the present invention. 
         FIG. 19B  shows an end view of the first permanent magnet rotor of the first embodiment of the motor according to the present invention. 
         FIG. 20  shows a cross-sectional view of the first permanent magnet rotor of the first embodiment of the motor according to the present invention taken along line  20 - 20  of  FIG. 19A . 
         FIG. 21  shows first stator magnetic field lines of the first embodiment of the motor according to the present invention. 
         FIG. 22  shows a side view of a second embodiment of the motor according to the present invention. 
         FIG. 23  shows a cross-sectional view of the second embodiment of the motor according to the present invention. 
         FIG. 24  shows a detailed side view of a second rotor of the second embodiment of the motor according to the present invention. 
         FIG. 25  shows a side view of a second inductive rotor of the second embodiment of the motor according to the present invention. 
         FIG. 26  shows a cross-sectional view of the second inductive rotor of the second embodiment of the motor according to the present invention. 
         FIG. 27A  shows a side view of a second permanent magnet rotor of the second embodiment of the motor according to the present invention. 
         FIG. 27B  shows an end view of the second permanent magnet rotor of the second embodiment of the motor according to the present invention. 
         FIG. 28  shows a cross-sectional view of the second permanent magnet rotor of the second embodiment of the motor according to the present invention taken along line  28 - 28  of  FIG. 27A . 
         FIG. 29  shows stator magnetic field lines of the permanent magnet rotor of the second embodiment of the motor according to the present invention. 
         FIG. 30  shows a side view of a third embodiment of the motor according to the present invention. 
         FIG. 31  shows a cross-sectional view of the third embodiment of the motor according to the present invention. 
         FIG. 32  shows a detailed side view of a third rotor of the third embodiment of the motor according to the present invention. 
         FIG. 33  shows a side view of a third inductive rotor of the third embodiment of the motor according to the present invention. 
         FIG. 34  shows a cross-sectional view of the third inductive rotor of the third embodiment of the motor according to the present invention. 
         FIG. 35A  shows a side view of a third permanent magnet rotor of the third embodiment of the motor according to the present invention. 
         FIG. 35B  shows an end view of the third permanent magnet rotor of the third embodiment of the motor according to the present invention. 
         FIG. 36  shows stator magnetic field lines of the permanent magnet rotor of the third embodiment of the motor according to the present invention. 
         FIG. 37  shows a side view of a fourth embodiment of the motor according to the present invention. 
         FIG. 38  shows an exploded view of a fourth rotor of the fourth embodiment of the motor according to the present invention. 
         FIG. 39  shows a side view of a fourth inductive rotor of the fourth embodiment of the motor according to the present invention. 
         FIG. 40  shows a cross-sectional view of the fourth inductive rotor of the fourth embodiment of the motor according to the present invention. 
         FIG. 41  shows a side view of a fourth permanent magnet rotor of the fourth embodiment of the motor according to the present invention. 
         FIG. 42  shows a cross-sectional view of the fourth permanent magnet rotor of the fourth embodiment of the motor according to the present invention taken along line  42 - 42  of  FIG. 41 . 
         FIG. 43  shows a side view of the fourth rotor at low RPM with the centrifugal clutch slipping; 
         FIG. 44  shows a cross-sectional view of the fourth rotor taken along line  44 - 44  of  FIG. 43 . 
         FIG. 45  shows a side view of the fourth rotor at high RPM with the centrifugal clutch engaged; 
         FIG. 46  shows a cross-sectional view of the fourth rotor taken along line  46 - 46  of  FIG. 45 . 
         FIG. 47  shows a side view of a fifth embodiment of the motor according to the present invention. 
         FIG. 48  shows an exploded view of a fifth rotor of the fifth embodiment of the motor according to the present invention. 
         FIG. 49  shows a side view of a fifth inductive rotor of the fifth embodiment of the motor according to the present invention. 
         FIG. 50  shows a cross-sectional view of the fifth inductive rotor of the fifth embodiment of the motor according to the present invention. 
         FIG. 51  shows a side view of a fifth permanent magnet rotor of the fifth embodiment of the motor according to the present invention. 
         FIG. 52  shows a cross-sectional view of the fifth permanent magnet rotor of the fifth embodiment of the motor according to the present invention taken along line  52 - 52  of  FIG. 51 . 
         FIG. 53  shows a side view of a sixth embodiment of the motor according to the present invention. 
         FIG. 54  shows an exploded view of a sixth rotor of the sixth embodiment of the motor according to the present invention. 
         FIG. 55  shows a side view of a sixth inductive rotor of the sixth embodiment of the motor according to the present invention. 
         FIG. 56  shows a cross-sectional view of the sixth inductive rotor of the sixth embodiment of the motor according to the present invention taken along line  56 - 56  of  FIG. 55 . 
         FIG. 57  shows a side view of a core laminate of the sixth embodiment of the motor according to the present invention. 
         FIG. 58  shows a cross-sectional view of the core laminate of the sixth embodiment of the motor according to the present invention taken along line  58 - 58  of  FIG. 57 . 
         FIG. 59A  shows a side view of a sixth permanent magnet rotor of the sixth embodiment of the motor according to the present invention. 
         FIG. 59B  shows an end view of the sixth permanent magnet rotor of the sixth embodiment of the motor according to the present invention. 
         FIG. 60  shows a perspective view of an inductive strip for wrapping around the sixth permanent magnet rotor of the sixth embodiment of the motor according to the present invention. 
         FIG. 61  shows the inductive strip unwrapped according to the present invention. 
         FIG. 62  shows a side view of a seventh embodiment of the motor according to the present invention. 
         FIG. 63  shows a side view of a eighth embodiment of the motor according to the present invention. 
         FIG. 64  shows a side view of a ninth embodiment of the motor according to the present invention. 
     
    
    
     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. 
     Arrangements of Inductive and Permanent Magnet Rotors 
     A first electric motor configuration  10 ′ having an independently rotating inner permanent magnet rotor  26 , an inductive rotor  20  coupled to a motor shaft  32  (or other load) and outside the permanent magnet rotor  26 , and a stator  12  outside the inductive rotor  20 , according to the present invention is shown in  FIG. 1 . The independently rotating inner permanent magnet rotor  26  is variably coupled to the inductive rotor  20 . The variably coupling allows the independently rotating inner permanent magnet rotor  26  to rotationally accelerate to synchronous speed very quickly at motor  10 ′ startup, independently of the inductive rotor  20  which is connected to a load and rotationally accelerates slower than the inner permanent magnet rotor  26 . The variably coupling may be in the form of a slip clutch, a centrifugal clutch, or an electrically controlled clutch as described in the following paragraphs. Once the inductive rotor  20  approached synchronous speed, the inductive rotor  20  and the permanent magnet rotor  26  lock into synchronous operation and a squirrel cage in the inductive rotor  20  ceases to generate current due to the lack of slippage between the rotating stator magnetic field and the bars of the squirrel cage, and the motor  10 ′ operates as an efficient permanent magnet motor. 
     A second electric motor configuration  10 ″ having the inductive rotor  20  coupled to a motor shaft  32 , the independently rotating permanent magnet rotor  26  outside the inductive rotor, and the stator  12  outside the independently rotating permanent magnet rotor  26 , according to the present invention, is shown in  FIG. 2 . The electric motor configuration  10 ″ is similar in principle to the electric motor configuration  10 ′, with the exception that the permanent magnet rotor  26  resides outside the inductive rotor  20  (i.e., is between the inductive rotor  20  and the stator  12 . The permanent magnet rotor  26  preferably comprises a ring magnet. 
     A third electric motor configuration  10 ′″ having the stator  12  inside the rotors  20  and  26 , the independently rotating permanent magnet rotor  26  outside the stator  12 , and the inductive rotor  20  coupled to a load and outside the permanent magnet rotor  26  and stator  12 , according to the present invention, is shown in  FIG. 3 . The electric motor configuration  10 ′″ is similar in principle to the electric motor configuration  10 ′, with the exception that the stator  12  is inside both rotors  20  and  26 , and the permanent magnet rotor  26  is preferably a ring magnet residing between the stator  12  and inductive rotor  20 . 
     A fourth electric motor configuration  10 ″″ having the stator  12  inside the rotors  20  and  26 , the inductive rotor  20  coupled to a load and outside the stator  12 , and independently rotating permanent magnet rotor  26  outside the inductive rotor  20 , according to the present invention is shown in  FIG. 4 . The electric motor configuration  10 ″″ is similar in principle to the electric motor configuration  10 ′, with the exception that the stator  12  is inside both rotors  20  and  26 , and the permanent magnet rotor  26  resides outside the inductive rotor  20 . The permanent magnet rotor  26  preferably comprises a ring magnet. 
     The relative RPM and torque of the inductive rotor  20  and permanent magnet rotor  26  at motor startup is shown in  FIG. 5 . The permanent magnet rotor torque  48  rises very quickly when power  40  is applied allowing the permanent magnet rotor  26  overcome any connection and to break loose from the inductive rotor  20  and the permanent magnet rotor RPM  42  quickly reach synchronous RPM. As the RPM  44  of the inductive rotor approached synchronous RPM and the torque  48  drops, the permanent magnet rotor  26  and inductive rotor  20  lock into synchronous RPM and the motor converts to highly efficient permanent magnet operation. 
     Embodiments of Clutches which Variably Couple the Inductive and Permanent Magnet Rotors 
     A side view of a continuous slip clutch  34 ′ according to the present invention is shown in  FIG. 6  and an end view of the continuous slip clutch  34 ′ is shown in  FIG. 7 . The continuous slip clutch  34 ′ includes an annular plate  52  carried by the permanent magnet rotor  26  and pushed against an annular friction surface  54  of the induction rotor  20  by springs  50 . The continuous slip clutch  34 ′ provides a constant kinetic friction with the springs  50  selected to allow the permanent magnet rotor  26  to break loose from the induction rotor at startup when the permanent magnet rotor torque  48  (see  FIG. 5 ) peaks, and allows the two rotors  20  and  26  to lock into synchronous RPM when the permanent magnet rotor torque  48  drops. 
     A side view of a discrete slip clutch  34 ″ according to the present invention is shown in  FIG. 8  and an end view of the discrete slip clutch  34 ″ is shown in  FIG. 9 . The discrete slip clutch  34 ″ includes uniformly spaced apart teeth  59  on an annular plate  56  and cooperating grooves  58  to cause the discrete slip clutch  34 ″ to lock into a selected relationship between the permanent magnet rotor  26  and induction rotor  20  to align poles of the rotor with the stator magnetic field. Such discrete alignment is preferred when the rotor has small number of poles, for example, four poles. 
     A side view of a centrifugal clutch  34 ′″ coupling the permanent magnet rotor  26  and the inductive rotor  20  according to the present invention is shown in  FIG. 10  and a cross-sectional view of the centrifugal clutch  34 ′″ coupling the permanent magnet rotor  26  and the inductive rotor  20  taken along line  11 - 11  of  FIG. 10  is shown in  FIG. 11 . Vanes  60  attached to the inductive rotor  20  reach into a concave cylindrical mouth  64  on one end of the permanent magnet rotor  26 . Centrifugal masses  62  reside between the vanes  60  and are held to rotate with the inductive rotor  20 . As the rotational speed of the inductive rotor  20  approaches synchronous speed, the masses  62  are pushed against a cylindrical inner face of the mouth  64  locking the rotation of the permanent magnet rotor  26  to the rotation of the inductive rotor  20 . 
     A side view of an electro-magnetic clutch  34 ″″ coupling the permanent magnet rotor  26  and the inductive rotor  20  according to the present invention is shown in  FIG. 12  and a cross-sectional view of the electro-magnetic clutch  34 ″″ coupling the permanent magnet rotor  26  and the inductive rotor  20  taken along line  13 - 13  of  FIG. 11  is shown in  FIG. 13 . The electro-magnetic clutch  34 ″″ includes coils (or solenoids)  74  receiving current through inductive windings  76  in the inductive rotor  20 . The coil  74  pulls clutch shoes  70  away from the cylindrical inner face of the mouth  64  and spring  72  push the shoes towards the cylindrical inner face of the mouth  64 . The shoes  70  may further include masses similar to the masses  62  in  FIG. 11  to add to the engagement against the cylindrical inner face of the mouth  64  as the inductive rotor RPM increases. The current produced by the windings  76  is proportional to the difference between the inductive rotor RPM and the synchronous RPM, thus disengaging the electro-magnetic clutch  34 ′″ at startup and engaging the electro-magnetic clutch  34 ′″ as the inductive rotor RPM approaches synchronous RPM. 
     Motor Designs Embodying the Present Invention 
     A side view of a first motor  10   a  according to the present invention is shown in  FIG. 14 , a cross-sectional view of the first motor  10   a  is shown in  FIG. 15 , a more detailed side view of the rotor of the first motor  10   a  is shown in  FIG. 16 , a side view of the inductive rotor  20   a  of the first motor  10   a  is shown in  FIG. 17 , a cross-sectional view of the inductive rotor  20   a  of the first motor  10   a  is shown in  FIG. 18 , a side view of the permanent magnet rotor  26   a  of the first motor  10   a  is shown in  FIG. 19A , an end view of the permanent magnet rotor  26   a  of the first motor  10   a  is shown in  FIG. 19B , a cross-sectional view of the permanent magnet rotor  26   a  of the first motor  10   a  is shown in  FIG. 20 , and the stator magnetic field  50   a  of the first motor  10   a  is shown in  FIG. 21 . The Motor  10   a  includes a housing  11 , stator windings  14 , and stator back iron  18 . The inductive rotor  20   a  includes bars  22   a  reaching nearly the entire depth of the inductive rotor  20   a  to avoid flux leakage and extend the stator magnetic field  32  into the permanent magnet rotor  26   a . The motor  10   a  includes a clutch  34   a  which may be a clutch  34 ′,  34 ″,  34 ′″, or  34 ″″. 
     A side view of a second motor  10   b  according to the present invention is shown in  FIG. 22 , a cross-sectional view of the second motor  10   b  is shown in  FIG. 23 , a more detailed side view of the rotor  16   b  of the second motor  10   b  is shown in  FIG. 24 , a side view of the inductive rotor  20   b  of the second motor  10   b  is shown in  FIG. 25 , a cross-sectional view of the inductive rotor  20   b  of the second motor  10   b  taken along line  26 - 26  of  FIG. 25  is shown in  FIG. 26 , a side view of the permanent magnet rotor  26   b  of the second motor  10   b  is shown in  FIG. 27A , an end view of the permanent magnet rotor  26   b  of the second motor  10   b  is shown in  FIG. 27B , a cross-sectional view of the permanent magnet rotor  26   b  of the second motor  10   b  taken along line  28 - 28  of  FIG. 27A  is shown in  FIG. 28 , and the stator magnetic field of the second motor  10   b  is shown in  FIG. 29 . The motor  10   b  includes a housing  11 , stator windings  14 , and stator back iron  16 . The inductive rotor  20   b  includes four air gaps  25  creating four poles and reaching nearly the entire depth of the inductive rotor  20   a  to avoid flux leakage and extend the stator magnetic field  32  into the permanent magnet rotor  26   a . The motor  10   a  includes a clutch  34   a  which may be a clutch  34 ′,  34 ″,  34 ′″, or  34 ″″ but is preferably a clutch  34 ″. 
     A side view of a third motor  10   c  according to the present invention is shown in  FIG. 30 , a cross-sectional view of the third motor  10   c  is shown in  FIG. 31 , a more detailed side view of the rotor  16   c  of the third motor  10   c  is shown in  FIG. 32 , a side view of the inductive rotor  20   c  of the third motor  10   c  is shown in  FIG. 33 , a cross-sectional view of the inductive rotor  20   c  of the third motor  10   c  taken along line  34 - 34  of  FIG. 33  is shown in  FIG. 34 , a side view of the permanent magnet rotor  26   c  of the third motor  10   c  is shown in  FIG. 35A , an end view of the permanent magnet rotor  26   c  of the third motor  10   c  is shown in  FIG. 35B , and the stator magnetic field  50   c  of the third motor  10   c  is shown in  FIG. 36 . The motor  10   c  includes a clutch  34   c  which may be a clutch  34 ′,  34 ″,  34 ′″, or  34 ″″ but is preferably a clutch  34 ″. 
     A side view of a fourth motor  10   d  according to the present invention is shown in  FIG. 37 , an exploded side view of the rotor  16   d  of the fourth motor  10   d  is shown in  FIG. 38 , a side view of the inductive rotor  20   d  of the fourth motor  10   d  is shown in  FIG. 39 , a cross-sectional view of the inductive rotor  20   d  of the fourth motor  10   d  taken along line  40 - 40  of  FIG. 38  is shown in  FIG. 40 , a side view of the permanent magnet rotor  26   d  of the fourth motor  10   d  is shown in  FIG. 41 , and a cross-sectional view of the permanent magnet rotor  26   d  of the fourth motor  10   d  taken along line  42 - 42  of  FIG. 41  is shown in  FIG. 35B . The motor  10   d  includes a clutch  34   d  which may be a clutch  34 ′,  34 ″,  34 ′″, or  34 ″″ but is preferably a centrifugal clutch  34 ′″. 
     A side view of the fourth rotor  16   d  at low RPM with the centrifugal clutch  34 ′″ slipping is shown in  FIG. 43  and a cross-sectional view of the fourth rotor  34 ′″ taken along line  44 - 44  of  FIG. 43  is shown in  FIG. 44 . The rotational speed  66   a  is low and only small centrifugal force  68   a  is created in the weights  62 , therefore only lightly coupling the rotation of the permanent magnet rotor  26   d  with the inductive rotor  20   d.    
     A side view of the fourth rotor  16   d  at high RPM with the centrifugal clutch  34 ″″ locking is shown in  FIG. 45  and a cross-sectional view of the fourth rotor  34 ″″ taken along line  46 - 46  of  FIG. 45  is shown in  FIG. 46 . The rotational speed  66   b  is high and large centrifugal force  68   b  is created in the weights  62 , therefore strongly coupling the rotation of the permanent magnet rotor  26   d  with the inductive rotor  20   d.    
     A side view of a fifth motor  10   e  according to the present invention is shown in  FIG. 47 , an exploded side view of the fifth rotor  16   e  of the fifth motor  10   e  is shown in  FIG. 48 , a side view of the fifth inductive rotor  20   e  of the fifth motor  10   e  is shown in  FIG. 49 , a cross-sectional view of the fifth inductive rotor  20   e  of the fifth motor  10   e  taken along line  50 - 50  of  FIG. 49  is shown in  FIG. 50 , a side view of the fifth permanent magnet rotor  26   e  of the fifth motor  10   e  is shown in  FIG. 51 , and a cross-sectional view of the permanent magnet rotor  26   e  of the fifth motor  10   e  taken along line  52 - 52  of  FIG. 51  is shown in  FIG. 52 . The motor  10   e  includes a clutch  34   e  which may be a clutch  34 ′,  34 ″,  34 ′″, or  34 ″″ but is preferably a centrifugal clutch  34 ″″. 
     A side view of a sixth motor  10   f  according to the present invention is shown in  FIG. 53 , an exploded side view of the sixth rotor  16   f  of the sixth motor  10   f  is shown in  FIG. 54 , a side view of the sixth inductive rotor  20   f  of the sixth motor  10   f  is shown in  FIG. 55 , a cross-sectional view of the sixth inductive rotor  20   f  of the sixth motor  10   f  taken along line  56 - 56  of  FIG. 55  is shown in  FIG. 56 , a side view of a core laminate  31  is shown in  FIG. 57  and a cross-sectional view of the core laminate  31  is shown in  FIG. 58 , a side view of the sixth permanent magnet rotor  26   f  of the sixth motor  10   f  is shown in  FIG. 59A , an end view of the permanent magnet rotor  26   f  of the sixth motor  10   f  is shown in  FIG. 59B , a perspective view of an inductive strip  23  for wrapping around the sixth permanent magnet rotor of the sixth embodiment of the motor according to the present invention is shown in  FIG. 60 , and the inductive strip  23  unwrapped is shown in  FIG. 61 . The core laminate  31  is fixed to the motor shaft  32  and the permanent magnet  26   f  rotates around the core laminate  31 . The inductive strip  23  includes spaced apart conducting stripes  23   a  all electrically connected to conducting rings  23   b  at each end of the inductive strip  23 . An embodiment of the inductive strip  23  is a copper strip adhered to the ring magnet. The thickness of copper strip is preferably between 0.015 and 0.020 inches, keeping the air gap to a minimum but allowing a good eddy current affect to quickly draw the permanent magnet rotor to synchronism RPM leaving the outer inductive rotor to accelerate under load allowing the clutch to pull the inductive rotor to final synchronous RPM. The permanent magnet rotor  26   f  is a simple ring magnet variably coupled to the inductive rotor as described above. The motor  10   f  includes a clutch  34   e  which may be a clutch  34 ′,  34 ″,  34 ′″, or  34 ″″ but is preferably a centrifugal clutch  34 ″″. 
     A side view of a seventh embodiment of the motor  10   g  according to the present invention is shown in  FIG. 62 . The motor  10   g  includes a stator  12   g , a permanent magnet rotor  26   g , an inductive rotor  20   g , cage rotor end rings  17   g , and a clutch  34   g . The permanent magnet rotor  26   g  is a ring magnet having a copper outer wrap. 
     A side view of an eighth embodiment of the motor  10   h  according to the present invention is shown in  FIG. 63 . The motor  10   h  includes a stator  12   h , a permanent magnet rotor  26   h , an inductive rotor  20   h , cage rotor end rings  17   h , and a clutch  34   h . The permanent magnet rotor  26   h  is a ring magnet having a copper inner wrap. The motor  10   h  has an internal stator  12   h  and the inductive rotor  20   h  and permanent magnet rotor  26   h  are outside the stator  12   h . The clutch  34   h  is inside the cage rotor end rings  17   h.    
     A side view of a ninth embodiment of the motor  10   i  according to the present invention is shown in  FIG. 64 . The motor  10   i  includes a stator  12   i , a permanent magnet rotor  26   i , an inductive rotor  20   i , cage rotor end rings  17   i , and a clutch  34   i . The permanent magnet rotor  26   i  is a ring magnet having a copper inner wrap. The motor  10   h  has an internal stator  12   i  and the inductive rotor  20   i  and permanent magnet rotor  26   i  are outside the stator  12   i . The clutch  34   i  is outside the cage rotor end rings  17   i.    
     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.