Abstract:
A single phase, three-speed Pole-changing electric motor has a stator and a rotor rotatably mounted within the stator. The stator includes a core having a plurality of slots, and a plurality of windings in the slots for operating at least three speeds. The windings are configured and arranged so that a substantial portion of the windings used in operating at one speed are used in operating at another speed. The reconnection of windings for different speeds is simple and easy to implement, for example with an external timer, switch, or relay.

Description:
FIELD OF THE INVENTION 
     This invention relates to a single phase three-speed induction motor, and in particular to such a motor in which a substantial portion of the windings are shared for operation at different speeds. 
     BACKGROUND OF THE INVENTION 
     Multispeed pole-changing single phase motors typically comprise separate windings for operation at each speed. For example, in the case of a three speed induction motor, the stator might include an eight-pole main winding for operation at low speed, a six-pole main winding for operation at medium speed, and a four-pole main winding for operation at high speed. A separate auxiliary winding is often provided for starting the motor. This auxiliary winding is typically a four-pole winding for so-called “hard” starting. In these motors, only a small portion of the windings, the coils under one pole are shared for operation at different speeds. The application of different approaches for winding sharing in the prior art is limited by complicated reconnection which substantially increases the motor cost. 
     To accommodate a large number of windings in the limited slot size the windings typically are made of copper, which is relatively expensive. 
     SUMMARY OF TIE INVENTION 
     The present invention relates to a three speed, pole changing single phase capacitor-start or split phase induction motor in which a substantial portion of the windings for the various speeds are shared through a simple winding reconnection. This leaves more room in the slots, and allows bulkier but less expensive materials (such as aluminum) to be used for the windings. More particularly, the motor of the present invention comprises a stator, and a rotor rotatably mounted within the stator. The stator comprises a core, which is conventionally made of a stack plurality of laminations of a magnetically permeable material. The core has a plurality of slots therein for receiving the windings. According to the present invention, these windings include a first winding, having four coil sections; a second winding having two coil sections; a third winding having two coil sections; a fourth winding having six coil sections; and an auxiliary starting winding having six coil sections. 
     Shared winding techniques have been proposed before. However, the feasibility of such techniques largely depends on the simplicity of the winding reconnection. The winding configuration of the present invention used the existing starting switch and requires only one additional single pole, single throw contact from a switch outside the motor, such as a timer, relay, electronic switch, etc. As compared with separate winding motors this is very easy and inexpensive to implement. 
     The windings are connectable to operate in a four pole high speed configuration, a six pole medium speed configuration, and an eight pole low speed configuration. More particularly the first winding, the second winding, and the third winding are arranged in the slots so that they can be connected to operate in a four pole conventional configuration. The second winding and the third winding are also arranged in the slots so that they can be connected to operate in an eight pole consequent configuration. The fourth winding is arranged in the slots so that it can be connected to operate in a six pole conventional configuration. Lastly, the auxiliary winding is arranged in the slots so that it can be operated in a six pole conventional configuration during start-up of the motor. 
     Because in this preferred embodiment the windings for eight pole operation are fully shared with the windings for four pole operation, there is extra room in the stator slots. This allows a bulkier but lighter material, such as aluminum, to be used for the windings instead of a more compact but heavier materials such as copper. Thus the resultant motor is significantly lighter, not just because of the elimination of a separate winding for operation in the eight pole-mode, but because the space freed up by the elimination of the separate eight pole winding allows a lighter material to be used for the remaining windings. Furthermore, aluminum is considerably less expensive than copper, so the motor is less expensive to manufacture. 
     These and other features and advantages will be in part apparent, and in part pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a three speed single phase electric motor constructed according to the principles of this invention; 
     FIG. 2 is a winding diagram of the motor; 
     FIG. 3 is a winding diagram of the motor, illustrating the first, second, and third windings connected to operate in a four pole (high speed) mode; 
     FIG. 4 is winding diagram of the motor, illustrating the second and third windings connected to operate in an eight pole (low speed) mode; 
     FIG. 5 is a winding diagram of the motor, illustrating the fourth winding connected to operate in a six pole (medium speed) mode; and 
     FIG. 6 is a winding diagram of the motor, illustrating the auxiliary winding connected to operate in an six pole starting mode. 
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A three speed, single phase electric motor constructed according to the principles of the present invention, indicated generally as  20 , is shown schematically in FIG.  1 . The motor  20  comprises a stator of conventional construction formed of a stack of laminations of a magnetically permeable material, with a plurality of slots for holding windings. 
     The motor  20  comprises a first winding  22  having four coil sections, a second winding  24  having two coil sections, a third winding  26  having two coil sections, and a fourth winding  28  having six coil sections. The motor also has an auxiliary winding  30  having six coil sections for start up. As shown in FIG. 1, the first coil  22 , the second coil  24 , and the third coil  26  are arranged to be connected to a power supply to operate in a conventional four pole (high speed) mode. The second coil  24  and the third coil  26  are also arranged to be connected to a power supply to operate in a consequent eight pole (low speed) mode. The fourth winding  28  is configured to be connected to a power supply to operate in a conventional six pole (medium speed) mode. Lastly, the auxiliary winding  30  is configured to be connected to a power supply during start-up with the fourth winding  28 , to start the motor. 
     In this preferred embodiment, all of the windings for operating in the eight pole mode (windings  24  and  26 ) are windings that are also used to operate in the four pole mode, no separate winding is provided to operate in the eight pole mode. This means that there is additional room in the slots in the stator as compared to other three speed motors. This additional room facilitates manufacture of the motor, and it allows bulkier but less expensive materials such as aluminum to be used for the windings instead of the more expensive copper to reduce the material cost and the motor weight. 
     The configuration of the winding to operate in the four pole (high speed); six pole (medium speed), and eight pole (low speed) modes, is achieved by switches  32 ,  34  and  36 , which are preferably external to the motor. 
     Switch  32  operates between a first 6 pole position, and a second 4 pole/8 pole position. Switch  34  operates between a first 4 pole position and second 8 pole position. Switch  36  operates between a first 4 pole position and a second 6 pole/8 pole position. A starting switch  38  is also provided to temporarily connect the six pole main winding  28  and the auxiliary winding  30  to power to start the motor. 
     The physical arrangement of the windings in the slots in the stator is best shown in FIGS. 2-6. As shown in FIGS. 2-6, the stator core  40  has a plurality of slots (a total of 34 as shown). The first winding  22  comprises four coil sections  22   a ,  22   b ,  22   c , and  22   d , connected in series such that in 4-pole operational mode when the coil sections  22   a  and  22   c  form north poles, the coil sections  22   b  and  22   d  form south poles. The second winding  24  comprises two coil sections  24   a  and  24   b , connected in series. The third winding  26  comprises two coil sections  26   a  and  26   b , connected in series. In 4-pole operational mode, the winding  24  and  26  are in parallel and both of them together are in series with the winding  22 . The winding  24  is positioned in the slots, such that coil section  24   a  is aligned with coil section  22   d  and coil section  24   b  is aligned with coil section  22   b . The coil sections  24   a  and  24   b  are configured, so that when they are powered in 4-pole operational mode, they will have the same polarity as the coil sections  22   d  and  22   b  with which they are aligned. Likewise, the coil sections  26   a  and  26   b  are aligned with coil sections  22   c  and  22   a , respectively. The coil sections  26   a  and  26   b  are configured, so that when they are powered in 4-pole operational mode, they will have the same polarity as the coil sections  22   c  and  22   a  with which they are aligned. In this configuration, the first, second, and third windings cooperate to operate in a conventional four pole mode, with the coil sections  22   a  and  26   b  forming a north pole, the coil sections  22   d  and  24   a  forming a south pole, coil sections  22   c  and  26   a  forming a north pole, and coil sections  22   b  and  24   b  forming a south pole. 
     The first, second, and third windings are connected for operation the four pole (high speed) mode, when switch  32  is in the 4 pole/8 pole position, switch  34  is in the 4 pole position, and switch  36  is in the 4 pole position. This configuration is shown in FIG. 3, in which the coil sections forming a north pole are hatched and the coil sections forming a south pole are cross-hatched. 
     The second and third windings  24  and  26  are also connected in series, and when powered in series, the coil sections  24   a  and  24   b  of the second winding, and coil sections  26   a  and  26   b  of the third winding all form poles in the same direction, in this case north, which forms an eight pole consequent winding. 
     When the second and third windings  24  and  26  are connected and powered in series, the coil sections  24   a  and  24   b  of the second winding and the coil sections  26   a  and  26   b  of the third winding all form poles with the same polarity, (for example all north), which forms an eight pole consequent winding. 
     The fourth winding  28  comprises winding sections  28   a ,  28   b ,  28   c ,  28   d ,  28   e , and  28   f . The coil sections are configured and connected so that coil sections  28   a ,  28   c , and  28   e  form south poles, and so that winding sections  28   b ,  28   d , and  28   f  form north poles. When the winding  28  is connected to power, the winding operates in a six pole conventional mode. 
     The fourth winding is connected for operation in the six pole (medium speed) mode when switch  32  is in the 6 pole mode, switch  36  is in the 6/8 pole mode, and switch  34  is in either the 4 pole or 8 pole position. The coil sections are arranged around the circumference of the stator to form alternating poles. This configuration is shown in FIG. 5, in which coil sections forming a north pole are hatched and coil section forming a south pole are cross-hatched. 
     Lastly the auxiliary winding  30  comprises coil sections  30   a ,  30   b ,  30   c ,  30   d ,  30   e , and  30   f . The coil sections are configured and connected so that winding sections  30   a ,  30   c , and  30   e  form south poles, and so that winding sections  30   b ,  30   d , and  30   f  form north poles. When the auxiliary winding  30  and the fourth winding  28  are connected to power, (caused by the operation of the starting switch  38 ) the winding operates in a six pole conventional mode to start the motor. The coil sections are arranged around the circumference of the stator to form alternating poles. This configuration is shown in FIGS. 5 and 6 in which coil sections forming a north pole are hatched, and the coil sections forming a south pole are cross-hatched. During starting the 6 pole main winding  28  and the 6 pole auxiliary winding  30  are both energized. They are shifted in space by 90 electrical degrees or 30 mechanical degrees.