Abstract:
A method of adjusting speed and torque of a dynamoelectric machine is disclosed. The machine includes a main winding, and a divided winding each configured to generate a plurality of poles. The method includes the steps of energizing the main winding and controlling the amount of electromagnetic flux at each pole.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to electric motors and more particularly, to methods for controlling the torque produced in electric motors. 
     Electric motors typically include a stationary outer portion, or housing, with a bore therethrough, a stator mounted in the housing, a rotor rotatably mounted in the housing, and a rotor core having a bore therethrough and a substantially straight shaft extending through the rotor core bore. The shaft is rotatably supported by a set of bearings and rotates utilizing magnetic fields. The stator includes a bore therethrough, stator coils and stator windings, with each stator coil wound around a respective stator winding. The rotor extends through the stator bore and includes a set of windings. Electrical current flows through the stator coil in the respective stator winding in a time sequential manner, which generates a stator magnetic field that repels/attracts a rotor magnetic field. The electrical current flowing through the stator constantly changes in time and direction, resulting in a constantly changing stator magnetic field. Due to the changing current direction and a resulting rotating stator magnetic field of constant magnitude, the rotor is caused to rotate and generate mechanical energy. 
     Many electric motors are fabricated to operate at multiple speeds. One way in which multiple speeds are obtained is by providing additional windings, connected a variety of ways in the circuit. Sometimes windings with a diminished number of turns of wire at a pole are created by “tapping” the existing windings. The tapping of existing windings disconnects part of a winding from the rest of the circuit. However, depending on the location of the tap, the number of turns of wire tapped, and the remaining turns of wire active in the machine, an electromagnetic imbalance in the normal near-sinusoidal flux distribution can be created because a number of adjacent poles are not energized. Even harmonics and sub-harmonics are added to the decomposition of flux distribution when poles are tapped adding a new forcing function which drives vibration and adds losses, reduces the effect of the electromagnetic flux, and results in less torque per ampere of stator current. 
     One method for overcoming an electromagnetic imbalance is to provide a tap only between full complements of poles. This method is similar to electrically providing additional, distinct windings, and has the manufacturing benefit, of depending on fewer pieces of machinery to create the final set of windings, although unenergized poles are still present. 
     It would therefore be desirable to provide another method of controlling the speed of an electric motor that does not suffer from electrical imbalance and is distinct electro-magnetically from conventional methods such as the tapping between full complements of poles and therefore eliminating even subharmonics of the decomposition of the flux distribution. 
     BRIEF SUMMARY OF THE INVENTION 
     In an exemplary embodiment, a method of adjusting speed and torque of a dynamoelectric machine is disclosed. The machine includes a main winding, and a divided winding each configured to generate a plurality of poles. The main winding includes winding at each pole which are alternately wound, the divided winding includes winding which are consecutively wound. The method includes the steps of energizing the main winding and controlling the amount of electromagnetic flux at each pole. The amount of electromagnetic flux at each pole is controlled by energizing the divided winding. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of one embodiment of a divided winding motor. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a schematic diagram illustrating one embodiment of a divided winding motor  10 . In motor  10 , synchronous speed and fundamental pole structure are held constant. 
     Divided winding motor  10  is a six-pole motor. Main winding  12 , includes six windings  14 ,  16 ,  18 ,  20 ,  22 , and  24 . Each winding  14 ,  16 ,  18 ,  20 ,  22 , and  24  has a polarity, commonly referred to as a “north” or “south” pole depending on the direction a wire (not shown) of each winding  14 ,  16 ,  18 ,  20 ,  22 , and  24  is wound with respect to a voltage source  26 . For purposes of illustration, windings  14 ,  16 ,  18 ,  20 ,  22 , and  24  are wound such that windings  14 ,  18 , and  22  located at poles one  28 , three  30 , and five  32  respectively, are “south” poles or “odd” poles. Windings  16 ,  20 , and  24  located at poles two  34 , four  36 , and six  38  respectively, are “north” poles or “even” poles. 
     Divided winding motor  10  includes a switch  40  that, when set in a high position  42 , energizes a “start” or auxiliary winding  44  which supplies an increased amount of torque at poles  28 ,  30 ,  32 ,  34 ,  36 , and  38  required to get a rotor (not shown) rotating under a start condition. Auxiliary winding  44  includes six windings  46 ,  48 ,  50 ,  52 ,  54 , and  56 . Each winding  46 ,  48 ,  50 ,  52 ,  54 , and  56  has a polarity, commonly referred to as a “north” or “south” pole depending on the direction the wire which constitutes windings  46 ,  48 ,  50 ,  52 ,  54 , and  56  is wound with respect to voltage source  26 . For purposes of illustration, auxiliary windings  46 ,  48 ,  50 ,  52 ,  54 , and  56  are wound such that windings  46 ,  50 , and  54  located at poles one  28 , three  32 , and five  36  respectively, are “south” poles or “odd” poles. Windings  48 ,  52 , and  56  located at poles two  34 , four  38 , and six  42  respectively, are “north” poles or “even” poles. 
     Motor  10  further includes a divided winding  58  in series with auxiliary winding  44 . Divided winding  58  differs from main winding  12  and auxiliary winding  44  since individual windings of divided winding  58  are not wound at alternating poles. Also individual windings of divided winding  58  are wound in a direction opposite the windings of main winding  12  or auxiliary winding  44 . Divided winding  58  includes three consecutive windings  60 ,  62 , and  64  located at “south” poles of motor  10 , or “odd” poles one  28 , three  30 , and five  32 . Three more consecutive windings  66 ,  68 , and  70  are located at “north” poles of motor  10 , or “even” poles two  34 , four  36 , and six  38 . 
     The consecutive windings allow divided winding  58  to be energized in different ways to control an amount of electromagnetic flux at poles  28 ,  30 ,  32 ,  34 ,  36 , and  38 . In one embodiment, the full winding is energized as illustrated by switch position  72 . In an alternative embodiment, only the “north” poles of divided winding  58  are energized, as illustrated by switch position  74 . By switching in any or all of divided winding  58 , current is reduced in auxiliary winding  44 , thereby changing the amount of electromagnetic flux at each pole  28 ,  30 ,  32 ,  34 ,  36 , and  38 . In a further alternative embodiment, divided winding  58  is in series with main winding  12 . In such an embodiment, switching into the circuit windings of divided winding  58  reduces current of main winding  12 . 
     Other embodiments can be constructed and those described above are illustrative, not limiting. For example, the wire that constitutes divided winding  58  can be wound in a same direction as the wire that constitutes the windings of main winding  12  or auxiliary winding  44 . In such an embodiment, “north” poles are located at poles one  28 , three  30 , and five  32  and “south” poles are located at poles two  34 , four  36 , and six  38  to add to the electromagnetic flux generated by main winding  12 . In another embodiment, polarity of voltage source  26 , as connected to divided winding  58 , and with respect to the polarity of main winding  12  or auxiliary winding  44 , can be connected such that the windings of divided winding  58  become either “north” or “south” poles regardless of the direction the wire which constitutes the windings of divided winding  58  are wound. 
     Divided winding motor  10  is different than other consequent pole winding designs (not shown) in that only the strength, or torque, of the motor, and subsequently the operating point, is changed. The divided winding motor  10  does not suffer from the electrical imbalance of “tapped” winding motors, which are well known in the art, and therefore is distinct electro-magnetically from conventional methods of tapping full complements of poles. When “north” poles and “south” poles of divided winding  58  are mirror images of one another, and energized together, electromagnetic imbalance is limited. However, by winding main winding  12  and divided winding  58 , or if included, auxiliary winding  44 , with different wire diameters and/or a different number of turns of wire in the windings, different performances and a material cost savings can be achieved. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit scope of the claims.