Abstract:
A rotor drive motor includes permanently magnetized blades with the opposite poles spaced apart along a radial direction. Two or more stators have a U-shaped core and coil winding, the legs extending radially inwardly and against a housing shroud. Each of the stators are energized in alternately reversed polarities to cause the blades to be rotated continuously. The housing may include a conduit sealed thereto isolating the stators and power circuit components from hazardous materials.

Description:
CROSS REFERENCE OF RELATED APPLICATION 
     This application is a continuation-in-part of Ser. No. 09/172,524, filed on Oct. 14, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention concerns an improvement to the rotor drive motor described in the parent application referenced above. 
     That application describes a rotor drive motor featuring permanently magnetized fan blades on the rotor which interact with the magnetic fields generated by stator coils arranged at each corner of an enclosing housing. 
     This greatly reduces the bulk of the fan hub by eliminating the conventional fan motor located at the fan hub, increasing the space available for air flow to substantially improve the performance and efficiency of the fan, particularly useful for installations in constrained spaces. 
     The fan blades are permanently magnetized in a radial orientation, with each successive blade having magnetic poles oppositely oriented relative to the poles of the adjacent magnetized fan blades. The polarity of the magnetic fields generated by the stator coils are successively reversed by reversing the current applied thereto as each fan blade passes each stator. 
     By this arrangement, the rotor drive motor stators are thereby located outside the air flow space. 
     The efficiency of this arrangement depends on the interaction between the stator magnetic field and the magnetic field of the permanently magnetized fan blades. 
     It is an object of the present invention to improve the output of this rotor drive motor by increasing the torque generated by the interaction of the stator coil and blade magnetic fields. 
     Another advantage of the improved rotor drive motor using exterior stator coils and magnetized fan blades is that the air flow does not pass through, past, or over the electrical components of the motor and controls. 
     It is another object of the present invention to provide a fan motor housing arrangement which isolates the air flow from any contact with the electrical components to render the fan suitable for use in an explosive or contaminated atmosphere. 
     SUMMARY OF THE INVENTION 
     These and other objects of the present invention which will be understood upon a reading of the following specification and claims are achieved by configuring the core of each stator in a U-shape, with the legs of the core each directed radially inwardly and abutting against the housing shroud. This core configuration has been found to increase the stator coil magnetic field flux density in the radial direction, and to thereby maximize the drive torque generated by the interaction of the stator coil and blade magnetic field. This, in turn increases the power output of the rotor drive motor and the fluid flow volume generated by rotation of the blades for a given electrical voltage applied to the stator coil windings. 
     The rotor drive preferably consists of only two stator coils, which are alternatively energized periodically in synchronism with the rotation of the magnetized rotor blades, which are permanently magnetized so as to be of successively opposite polarity. 
     A pair of sensors are positioned so as to be triggered as each blade sweeps past a detection location associated with each sensor, and power control circuitry causes each stator coil to be briefly energized by an electrical current of the proper polarity to cause a magnetic field to be generated interacting with each fan blade to drive the fan rotor in a given direction. 
     In a second aspect of the present invention, the blade shroud is sealed to fluid flow passage conduits thereby isolating the electrical components which are disposed externally of the shroud from the air flow. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an end view of a fan incorporating a rotor drive motor according to the present invention. 
     FIG. 2 is a partially sectional view of the rotor drive motor shown in FIG.  1 . 
     FIG. 3 is an end view of a second embodiment of the invention. 
     FIGS. 4A-4D are end views of the embodiment shown in FIG. 1 in different rotated condition of the fan blades, with a diagrammatic depiction of the energizing conditions of the two stator coils. 
     FIG. 5 is a schematic diagram of one of two identical electrical circuits for operating the rotor drive motor according to the invention. 
     FIG. 6 is an enlarged fragmentary view of a portion of the embodiment shown in FIG. 1 with the stator and rotor blade. 
     FIG. 7 is a partially sectional view of a centrifugal fan having an impeller driven by the rotor drive according to the present invention. 
     FIG. 8 is a view of the section  8 — 8  in FIG.  7 . 
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 U.S.C. 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims. 
     Referring to FIGS. 1 and 2, the rotor drive motor  10  according to the present invention includes a housing comprised of mounting flanges  12  integral with a cylindrical shroud housing  14 . 
     Disposed at two corners of the flanges  12  are two stators  16 A- 16 B, comprised of a U-shaped core  18  with windings  20  around the section  22  connecting the two legs  24 . 
     Each leg  24  extends in an approximately radial direction with respect to the rotor  26 . 
     The rotor  26  is comprised of an array of radially extending fan blades  28 , which are magnetized to have the respective poles spaced apart in a radial direction, with successive blades  28 A,  28 B in the array of alternately opposite polarity as indicated. As seen in FIGS. 1 and 3, the magnetized blade portion includes the radially outer portion which is bounded by the leading edge of each blade, and each core leg has a circumferential width that is less than the circumferential width of the magnetized blade portion. 
     The fan blades  28  are fixed to (or integrally formed with) a central hub  30  included in the rotor  26  which is rotatable on bearings  36 , a support axle  32  held by a series of struts  34  extending across a circular opening defined within the flange  12  to a central web  38 . 
     The fan blades  28  are preferably constructed of permanently magnetized plastic of a known material or have pieces of ferromagnetic material applied thereto which may be magnetized. Magnetized plastic material avoids the build up of static electricity which could otherwise occur, to prevent any resultant sparking due to a discharge of such static. 
     The housing portions are of a non-ferromagnetic material such as a suitable plastic, which is nonetheless freely permeable by magnetic flux. 
     A stainless steel shroud also produces very good performance of the rotor drive. 
     For a particular fan of 5 inches diameter, the thickness of the shroud  14  has been found to preferably be between ⅛-¼ inch. This thickness substantially defines the gap between the ends of the stator core legs  24  and the outer tips of the blades  28 , when adding a slight clearance between the blade tips and the inside surface of the shroud  14  to allow for thermal expansion. The size of the gap has been found to significantly affect the driving power developed. Accordingly, a fan having a varied diameter would have a proportionately varied shroud thickness. 
     The details concerning the fan blades  28  and bearing axis support are similar to those disclosed in the above referenced parent application. 
     The rotor drive includes two identical power and control circuits. The circuit diagram of one of the circuits is shown in FIGS.  5 . The components of both circuits are preferably mounted on a single circuit board  40  attached to one of the flanges  12 , and both preferably share the same power source. 
     As can be determined by a reviewing the circuit diagram in FIG. 5, the components in each circuit include a pair of uni-polar Hall effect sensors U 1  and U 2  of a commercially available type. In the preferred embodiment, U 1  and U 2  are enclosed in an IC package and can be purchased from Micronas, part number HAL508UA. The sensors U 1 , U 2  are mounted on the circuit board  40  in close proximity to one another, and together comprise a sensor assembly  41 . Each assembly  41  is oriented so as to be triggered upon the movement of a blade leading edge to a precise trigger point  42 A,  42 B, respectively. In the preferred embodiment, assembly  41  in one circuit is oriented so as to be triggered upon the movement of a blade leading edge to a precise trigger point  42 A, and the assembly  41  in the other circuit is oriented to be triggered upon the movement of a blade leading edge to a precise trigger point  42 B. 
     Each sensor U 1 , U 2  acts as a switch and is triggered by the presence of a particular blade polarity, each sensor sensing the opposite polarity with respect to one another. In the preferred embodiment, U 1  is triggered by the presence of the north pole, and U 2  is triggered by the presence of the south pole. Together, uni-polar sensors U 1 , U 2  serve to function as a dual output bipolar sensor. 
     The blades  28  are equally spaced apart a particular distance so that when a leading edge of a blade  28 A or  28 B reaches trigger point  42 A, a next trailing blade  28 B or  28 A is centered between the legs  24  of the stator coil  16 A. When a leading edge of a blade  28 A or  28 B reaches the trigger point  42 B, a leading blade  28 A or  28 B is centered on the stator coil  16 B (see FIGS.  4 A- 4 D). Thus, only one blade  28 A,  28 B at a time can trigger sensors U 1 , U 2  in each sensor assembly  41 . 
     The respective trigger points  42 A, B are oriented with blades  28  so that the respective stator coil  16 A, B having a blade positioned between its legs  24  will energize upon startup. 
     When the leading edge of a blade  28 A registers with trigger point  42 A, the coil of stator  16 A is energized so as to produce the polarity indicated in FIG.  4 A. When the sensor U 2  in the first circuit detects the leading edge of blade  28 A, this causes an optical coupler IC package U 3  to establish high and low states on its terminals such as to turn on two of the P-channel and N-channel MOS-FETS Q 1 , Q 2 , Q 3  and Q 4  to apply positive voltage from a battery  46  (other power source) of the stator  16 A and to ground the other side, setting up the magnetic polarity in FIG.  4 A. 
     This causes the trailing blade  28 B to be rotated counterclockwise by the repulsion-attraction set up. This rotation causes the sensor U 2  to turn off (at a point determined by the blade width and pitch angle), but the rotor  26  will continue to coast to the position shown in FIG.  4 B. 
     At this point, a blade  28 B moves into registry with the second trigger point  42 B. This causes sensor U 1 in  the second circuit to be activated, which in turn causes the windings  20  of stator coil  16 B to be energized with an associated circuit so as to establish the magnetic polarity shown in FIG.  4 B. This sets up a repulsion attraction with the blade  28 B centered between the legs of stator  16 B, to urge the rotor  26  to continue its counterclockwise rotation. 
     After stator  16 B is de-energized by movement of the blade  28 B past trigger point  42 B, the rotor  26  coasts into the position shown in FIG. 4C, where a trailing blade  28 B moves into registry with the trigger point  42 A of sensor U 1  in the first circuit causing the stator  16 A to be re-energized but with an opposite polarity as shown. The rotor  26  is again initially urged to rotate counterclockwise and coasts into the position shown in FIG. 4D after the stator  16 A is de-energized. 
     This brings trigger point  42 B of sensor U 2  in the second circuit into registry with a blade  28 A, causing U 2  to be activated and the power circuit to re-energize stator  16 B. The entire described four stage cycle repeats over and over to cause continuous counterclockwise rotation of the rotor  26 . 
     In the preferred embodiment, the quad optical coupler IC package U 3 can be purchased from NEC under the part number PS2505-4NEC, the P-channel and N-channel MOS-FETS Q 1 , Q 2  can be purchased by International Rectifier under the part number IRF4905, and the P-channel and N-channel MOS-FETS Q 3 , Q 4  can be purchased by International Rectifier under the part number IRL3705N. The diodes D 1 -D 4  in the circuit of FIG. 5 can be purchased by Liteon Power Semiconductor under the part number 1N4936CT. And finally, the remaining items are commercially available and preferably have values as follows: C 1 —2200 microfarad, 35 Volt; R 1 —4.7K Ohms, ½ Watt; R 2 , R 4 , R 6 , and R 8 —2.2K Ohms, ¼ Watt; and R 3 , R 5 , R 7 , and R 9 —10K Ohms, ¼ Watt. 
     It is to be understood that the above circuit could be modified by one skilled in the art to achieve acceptable results. For example, one of the sensors U 1 , U 2  in each circuit could be removed. As such, each assembly  41  would act as a single uni-polar sensor rather than a bipolar sensor, and coils  16 A, B would be energized with the same polarity during each cycle rather than being successively reversed in polarity. Consequently, the efficiency and performance would be reduced, but the intent of the invention would be realized. 
     Rotation can be reversed by reversing the polarity of the power source and resulting stator coil  16 . 
     This arrangement locates the electrical components out of the path of the fluid flow. Accordingly, conduits  48 ,  50  may be sealed to the shroud as shown in FIG. 2 to allow use of the fan in hazardous environments. 
     FIG. 3 shows a four stator arrangement, utilizing two additional stators  16 C,  16 D (with additional sensors and power circuits, not shown). 
     FIG. 7 and 8 illustrate an application of the rotor drive to the impeller  56  of a centrifugal pump  52 , in which the blades  54  of the impeller  56  are radially magnetized as described and stators  58 ,  60  provided with U-shaped cores  62 .