Abstract:
First and second stator circuitry for respective use with first and second stators in a multi-stator motor are configured so that the first stator circuitry is substantially unaffected by a failure of the second stator circuitry to energize a second winding in the second stator. To that end, the motor includes a rotor that rotates through a plurality of rotational positions, the first stator having the first stator circuitry and a first winding, and the second stator having the second stator circuitry and a second winding. The first stator circuitry energizes the first winding in response to the rotational position of the rotor. In a similar manner, the second stator circuitry energizes the second winding in response to the rotational position of the rotor.

Description:
FIELD OF THE INVENTION 
     The invention generally relates to electric motors and, more particularly, the invention relates to electric motors with multiple stators. 
     BACKGROUND OF THE INVENTION 
     Rotational torque in an electric motor typically is improved when multiple stators are utilized to rotate a common rotor. Such motors generally are referred to as “multi-stator” motors. Each stator in a multi-stator motor typically includes poles and windings that are selectively energized by shared energizing circuitry. Energizing circuitry typically includes magnetic sensors (e.g., Hall effect sensors) to detect the rotational position of the rotor, switching circuitry to alternatively energize the windings and poles of selected stators, voltage regulation circuitry for regulating input voltage, and current limiting circuitry (e.g., a fuse) for limiting input current into the motor. 
     Problems arise, however, when the energizing circuitry malfunctions. For example, the voltage regulation circuitry may malfunction, consequently not providing enough energizing voltage to the windings. Accordingly, the motor undesirably may not operate since the windings cannot be energized. Other similar energizing circuitry malfunctions also can cause the motor to stop functioning. It therefore would be desirable to have energizing circuitry on an electric motor that enables the motor to continue operating even if such circuitry does malfunction. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, first and second stator circuitry for respective use with first and second stators in a multi-stator motor are configured so that, when operating, the first stator circuitry will continue to energize a first winding in the first stator even when the second stator circuitry fails to energize a second winding in the second stator. To that end, the motor includes a rotor that rotates through a plurality of rotational positions, the first stator having the first stator circuitry and the first winding, and the second stator having the second stator circuitry and the second winding. The first stator circuitry energizes the first winding in response to the rotational position of the rotor. In a similar manner, the second stator circuitry energizes the second winding in response to the rotational position of the rotor. 
     In other embodiments of the invention, the operation of the second stator circuitry is substantially unaffected by a failure of the first stator circuitry to energize the first winding. The first stator circuitry may include means for receiving power from a first power source, while the second stator circuitry may include means for receiving power from a second power source. Failure of one power source therefore does not affect the performance of the stator utilizing the other power source. 
     In yet other aspects of the invention, the first stator circuitry includes a first voltage regulator for regulating input voltage into the first stator circuitry, and a first current limiter for limiting input current into the first stator circuitry. In a similar manner, the second stator may include a second voltage regulator for regulating input voltage into the second stator circuitry, and a second current limiter for limiting input current into the second stator circuitry. In preferred embodiments, the first stator and the second stator are substantially concentric. In other embodiments, the first stator is angularly offset from the second stator. The first stator also may include a first pole that contacts the second winding, thus reducing the profile of the motor. In yet other embodiments, the rotor may include an impeller. 
     In another aspect of the invention, the first stator circuitry is substantially independently operable from the second stator circuitry. Specifically, the first stator circuitry may be considered to be electrically independent from the second stator circuitry. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects and advantages of the invention will be appreciated more fully from the following further description thereof with reference to the accompanying drawings wherein: 
     FIG. 1 schematically shows a cross-sectional view of a fan having a multi-stator electric motor configured in accordance with preferred embodiments of the invention. 
     FIGS. 2A and 2B schematically show first and second stators that are angularly offset by about forty-five degrees. 
     FIG. 3 schematically shows a cross-sectional view of the assembled first and second stators. 
     FIG. 4 schematically shows a preferred magnet utilized by the preferred motor shown in FIG.  1 . 
     FIG. 5 schematically shows preferred first and second stator circuits for controlling the energization of the first and second stators. 
     FIG. 6 schematically shows an alternative embodiment of first and second stator circuits for controlling the energization of the first and second stators. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows a cross-sectional view of a fan  10  having a multi-stator electric motor  12  that is configured in accordance with preferred embodiments of the invention. To that end, the fan  10  includes an impeller  14  mechanically coupled to the motor  12 , and an exterior fan housing  16 . The fan housing  16  may be manufactured from metal, plastic, or other suitable material. It should be noted, however, that use of preferred embodiments of the motor  12  within the fan  10  is for exemplary purposes only. Accordingly, preferred embodiments of the motor  12  may be used in both related and unrelated applications. 
     The motor  12  includes a rotor  18  for rotating the impeller  14 , a first stator  20  having four poles  22  (FIG. 2A) and four windings  24 , and a second stator  26  also having four poles  28  (FIG. 2B) and four windings  30 . In preferred embodiments, the first stator  20  is substantially concentric with the second stator  26 . In other embodiments, the first stator  20  is angularly offset from the second stator  26  by about forty-five degrees, thus improving the output motor torque (see FIGS. 2A and 2B, which show the two stators offset by about forty-five degrees). Output motor torque is improved because each stator provides maximum torque at the null point  32  (FIG. 4) of the other stator. As shown in FIG. 3, the windings  24  of the first stator  20  contact the poles  28  of the second stator  26 , while the windings  30  of the second stator  26  contact the poles  22  of the first stator  20 . This arrangement reduces the overall profile of the motor  12 , consequently reducing the overall profile of the fan  10 . 
     The rotor  18  preferably includes an annular permanent magnet  34  in a steel cup  36  (FIG.  1 ). A central shaft  38 , which is secured to a top, interior face of the cup  36 , preferably is received in a plurality of bearings  40  within the first and second stators  20  and  26 . The magnet  34  preferably is a one-piece magnet and has the magnetic pattern shown in FIG.  4 . As shown in FIG. 4, the magnet  34  preferably includes a commutation section  42  and two north-south pairs  44  that each have the aforementioned null point  32 . 
     In accordance with preferred embodiments of the invention, the windings  24  and  30  in each of the stators each are energized by independent first and second stator circuits  46  and  48 . More particularly, as shown in FIG. 5, the windings  24  of the first stator  20  are energized by the first stator circuit  46 , while the windings  30  of the second stator  26  are energized by the second stator circuit  48 . The two stator circuits preferably share no common elements and thus, operate independently of each other. In the event that one of the two stator circuits  46  or  48  fails, then the other stator circuit should continue energizing its corresponding windings. Accordingly, although at a reduced capacity, the fan  10  should continue to operate even if one such stator circuit fails. 
     As noted above, FIG. 5 shows a preferred embodiment of the first and second stator circuits  46  and  48 . The first stator circuit  46  includes a first Hall effect sensor  50  for determining the rotational position of the rotor  18 , a first current limiting element  52  for significantly limiting current if the temperature of the first stator circuit  46  increases above a predetermined temperature, and a first Zener diode regulator Z 1  across the input of the first Hall sensor  50  for limiting the maximum input voltage to the first Hall sensor  50 . The first current limiting element  52  preferably includes two accompanying resistors (“first circuit resistors R 1 ”) and a diode (“first circuit diode D 1 ”) for limiting voltage and current into the first circuit. Additionally, the first Hall sensor  50  preferably has a transistor pair (“first circuit transistor pair Q 1 ”) coupled to its two output ports to control switching to the four windings  24  of the first stator  20 . A direct current (“DC”) input voltage preferably is applied across first and second terminals  62  and  64 , which may include a reverse polarity diode  66  to ensure against potential reverse polarity conditions. The reverse polarity diode  66  is optionally included in preferred embodiments and thus, need not be included on the first terminal  62 . The DC input voltage (e.g., twelve volts) may be produced from any known source such as, for example, a battery or a conventionally rectified alternating current (“AC”) voltage source. 
     As shown in FIG. 5, the second stator circuit  48  includes elements that are substantially identical to, but operatively independent from, the elements in the first stator circuit  46 . More specifically, the second stator circuit  48  includes a second Hall effect sensor  68  for determining the rotational position of the rotor  18 , a second current limiting element  70  for significantly limiting current if the temperature of the second stator circuit  48  increases above a predetermined temperature, and a second Zener diode regulator Z 2  across the input of the second Hall sensor  68  for limiting the maximum input voltage to the second Hall sensor  68 . The second current limiting element  70  preferably includes two accompanying resistors (“second circuit resistors R 2 ”) and a diode (“second circuit diode D 2 ”) for limiting voltage and current into the second stator circuit  48 . Additionally, the second Hall sensor  68  preferably has a transistor pair (“second circuit transistor pair Q 2 ”) coupled to its two output ports to control switching to the four windings  30  on the second stator  26 . In a manner similar to the first stator circuit  46 , power to the second stator circuit  48  is derived from a DC input voltage applied across the first and second terminals  62  and  64 . In an alternative embodiment, the current limiting elements  52  and  70  may include other known current limiting devices. Those devices may include, but are not limited to, power MOSFETS or power transistors with appropriate sensing circuitry, or positive temperature coefficient (“PTC”) thermistors, which are sensitive to incremental current conditions. 
     As shown in FIG. 1, the first and second stator circuits  46  and  48  may be formed on a printed circuit board  80  within the housing  16 . The first Hall sensor  50  and second Hall sensor  68  preferably extend upwardly from the circuit board  80  and into the rotor  18  for sensing the rotational position of the magnet  34 . In preferred embodiments, the first Hall sensor  50  and second Hall sensor  68  are circumferentially positioned on the circuit board  80  in any one of several forty-five degree multiples. For example, the Hall sensors  50  and  68  may be circumferentially positioned apart by either one of about forty-five degrees, ninety degrees, one hundred thirty-five degrees, one hundred eighty degrees, two hundred twenty-five degrees, two hundred-seventy degrees, or three-hundred fifteen degrees. If more than two stators are used, then those skilled in the art should be able to position each Hall effect sensor in the resulting circuits appropriately. 
     FIG. 6 shows another embodiment of the first and second stator circuits  46  and  48  in which independent power sources are utilized for each of the two stator circuits  46  and  48 . More particularly, the first stator circuit  46  receives input voltage across the first and second terminals  62  and  64 , while the second stator circuit  48  receives input voltage across the third and second terminals  82  and  64 . Accordingly, failure of one of the two power sources does not affect operation of the other stator circuit. For example, if a first voltage source (powering the first stator circuit  46 ) fails, the second stator circuit  48  will operate in an unimpeded manner since such stator circuit does not rely upon such first power source. 
     In preferred embodiments, the following elements and/or element values may be used: 
     first and second Hall sensors  50  and  68 : Model Number SS42R Microswitches, available from Honeywell Microswitch Incorporated of Freeport, Ill.; 
     first and second current limiting elements  52  and  70 : Model Number LM317T devices, available from SGS Thompson Microelectronics of Phoenix, Ariz.; 
     first and second circuit resistors RI and R 2 : about one Ohm; 
     first and second circuit diodes D 1  and D 2 : conventionally known model number  1 N4003 diodes; 
     transistors in the first and second transistor pairs Q 1  and Q 2 : conventionally known model number TIP102 transistors; 
     Zener diodes Z 1  and Z 2 : Conventionally known model number 1N759 Zener diodes; 
     reverse polarity diode  66 : conventionally known model number 1N4003 diode; 
     As suggested above, alternative embodiments of the invention include three or more stators that each have independent stator circuits. Accordingly, failure of all but one stator circuit should not cause the rotor  18  to stop rotating. In a manner similar to the first and second stator circuits  46  and  48  described above, each additional stator circuit preferably includes independently operating Hall sensors, voltage regulator Zener diodes, and current limiting elements. Of course, additional elements may be added as necessary to further control the windings of each stator. Conversely, certain of the elements of the stator circuits may be omitted such as, for example, the current limiting elements. Omission of such element, however, may reduce circuit reliability and performance. 
     Although various exemplary embodiments of the invention have been disclosed, it should be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the true scope of the invention. These and other obvious modifications are intended to be covered by the appended claims.