Abstract:
A permanent magnet motor having a stator back iron in the form of a “slinky” and a plurality of winding sections in circumaxially spaced relationship about the back rion. Each winding section comprises a conductor wound helically about the back iron with each coil adjacent the next and ending in a radial plane. A permanent magnet motor surrounds the stator.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Permanent magnet electric motors have been available for some time and have been found generally satisfactory for certain tasks. Needed improvements have been noted however in certain design features.  
       SUMMARY OF THE INVENTION  
       [0002]     Initially, a slotless stator design is preferred. With the elimination of the need for teeth on the steel back iron, more easily manufactured tolerances can be employed. In addition, cogging of the motor is eliminated.  
         [0003]     Secondly, a substantially improved back iron is provided. The back iron is formed of steel but in a highly unconventional manner. A continuous coil much in the nature of a “slinky” is formed. This reduces iron losses, noise generation, and power draw as compared with sectional back irons of the conventional type. Moreover, the use of the “slinky” design accommodates a most desirable feature whereby the grain of the steel, preferably grain oriented silicon steel, can be aligned with the direction of rotation. This also enhances motor efficiency.  
         [0004]     By encapsulating the back iron in a pair of mating molded plastic members in face-to-face relationship a number of requirements are met. The molded plastic provides circumaxially spaced separators accommodating a convenient and efficient method of winding stator wire about the back iron. Use of the molded plastic members also provides insulation between back iron and the wire, which eliminates the need for additional coating. Finally, the molded members accommodate a press fit between one of the members and a main housing of the motor. This provides a positive structural link and the necessary precise alignment between the stator and the rotor, which is also supported by bearings mounted in a bearing tower supported in the housing.  
         [0005]     Winding of the stator wire about the back iron is accomplished with sections  25 , 25  of wire wound between the separators on the molded plastic members. Each section of wire  25 , 25  is would helically with each coil in closely spaced relationship with each adjacent coil. With a number of sections of wire  25 , 25 , for example twelve [12], there are of course a large number of lead wires or wire ends, twenty-four [24] in the present example. Preferably, each lead or wire end is attached to a conductive pin, which is mounted in one of the plastic members. The pins, in turn, are connected to a P.C. board, which connects all of sections of wire in appropriate relationship. Preferably, the board is of copper construction and has a second conventional board associated with it. The circuit boards also carry additional circuitry, thermistors, hall sensors and connectors.  
         [0006]     Further in winding the wire sections, and particularly when wire of relatively large diameter is required, Litz wire is preferred. This avoids excessive eddy current losses otherwise encountered.  
         [0007]     While the helically wound wire sections may create more heat than other types of windings, they also provide a unique opportunity for cooling the motor. Portions of the windings inside the back iron are essentially unused electrically but provide a convenient heat sink for the remainder of the windings. By designing the motor with air moving blades on the rotor and openings directing airflow through the center of the back iron and over these portions of the windings substantial cooling of the motor is achieved. Contamination problems are avoided since the air is not directed to flow through the air gap externally of the back iron and windings. Additionally, the inner portions of the windings provide a convenient location for thermistors which engage the wire and can be directly attached to the P.C. board. A second level of protection is thus provided with the thermistors set to turn off when temperature exceeds a preset limit.  
         [0008]     The use of a copper P.C. board provides a substantial reduction in electrical resistance as well as a convenient motor cooling system. The copper of the board which connects the winding sections has a resistance much lower than the wire itself or a trace on a standard P.C. board. This of course substantially enhances motor efficiency.  
         [0009]     With regard to cooling, the copper board serves as a heat sink for the winding sections and mounts or the FETS (Field Effect Transistors). By inducing a cooling airflow over the copper board, the winding sections and FETS are indirectly cooled. Finally, the stator may be encased in molded plastic. This allows the motor to be in airflow as in a blower installation. The smooth plastic rather than the relatively rough surfaces of the winding sections are disposed in the airflow and this avoids depositing debris on the windings. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0010]      FIG. 1  is perspective view of the improved stator back iron of the invention.  
         [0011]      FIG. 2  is an exploded perspective showing the back iron and a pair of associated molded plastic annular members each having a U-shaped configuration to receive one half of the back iron.  
         [0012]      FIG. 2A  is a perspective view of the stator with winding sections in place.  
         [0013]      FIG. 3  is a perspective view showing a base portion of a motor housing with the back iron, plastic members, and a plurality of winding sections thereon mounted in the housing.  
         [0014]      FIG. 3A  is a top view of a stator disposed within a permanent magnet rotor.  
         [0015]      FIG. 4  is a fragmentary enlarged perspective showing end wires of a winding section attached to connecting pins and a pin holder.  
         [0016]      FIG. 5  is a top view of a copper P.C. board with FETS mounted thereon and pin receiving openings therein.  
         [0017]      FIG. 6  is a cross sectional view through the motor embodying several features of the present invention.  
         [0018]      FIG. 7  is another cross sectional view through a second motor embodying other features of the invention, and  
         [0019]      FIG. 8  shows an assembled stator encased in plastic.  
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0020]     Referring initially to  FIG. 1 , it will be observed that a back iron  10  of the invention is shown with the first few coils at the top separated. This is for purposes of illustration only and it will be understood that the coils are in fact in close engagement with each other in a “slinky” like configuration. As mentioned above, silicone steel is preferred with its grain oriented in the direction of rotation. A single long strip of steel is preferred in forming a one-piece coil although a limited number of coil sections may be employed. As mentioned, the back iron is encapsulated by a pair of similar molded plastic members  12  and  14 . Each of the members has an annular shape with a generally U-shaped cross section open toward the back iron. Thus, annular slots, visible in the member  14  but not in the member  12 , receive the back iron when the members are in face-to-face engagement. Axially aligned separators  16 ,  16  on the members provide for efficient winding of sections of stator wire and spaced connectors  17 ,  17  project inwardly for attachment of the stator to a base portion  18  of the motor housing,  FIG. 3 . A central mounting boss  20  integral with the housing base portion  18  is provided with three slots  22 ,  22  which receive the three connectors  17 ,  17  in a light press fit. A central opening  24  in the boss  20  receives a bearing tower and the stator and rotor are thus precisely located relative to each other.  
         [0021]     Each winding section  25  of the stator comprises a length of wire wound helically about the back iron between adjacent separator  16 ,  16 . Twelve (12) winding sections  25 ,  25  are shown in  FIGS. 2A and 3A  but the number of sections is of course subject to wide variation. When heavy wire is required, LITZ wire is preferred to avoid excessive eddy current losses.  
         [0022]     Reverting to  FIG. 2 , it will be observed that twenty-four (24) connector pins  26 ,  26  are shown with twelve (12) pin holders  28 ,  28  formed integrally on the lower plastic member  14 . A single pin holder  28  is illustrated more clearly in  FIG. 4  with two (2) pins  26 ,  26  mounted therein. Leads or end wires  30 ,  30  from section of stator winding are also shown attached to the pins  26 ,  26  respectively by soldering or other means.  
         [0023]     A copper P.C. board  27  is illustrated in  FIG. 5  and may be mounted as best shown in  FIG. 6  at one end of the stator. Twenty-four (24) small openings  32 ,  32  are provided respectively for the pins  26 ,  26 . Soldering or other attachment means may be employed. FETS  34 ,  34  may also be mounted on the board in a conventional manner. The copper board has much lower electrical resistance than traces on a conventional board and this of course improved motor efficiency. Further, as mentioned above, the copper board serves as a heat sink for the winding sections as better illustrated in  FIG. 6 . An inlet opening  18  allows cooling air to enter the motor housing and pass over the board at the urging of a small fan  38  mounted on the rotor of the motor. Air flow is depicted by the small arrows  40 ,  40 . With exhaust occurs radially outwardly form the blades of the fan as shown.  
         [0024]     In  FIG. 7 , a further embodiment of the invention is shown. A motor  42  has an annular opening  44  radially inward of its P.C. board  46  which received cooling air and a fan  48  draws the air through the motor as indicated by the arrows  50 ,  50 . As will be observed, the air flows through the inner portion of the stator adjacent the end turns of the winding sections. As mentioned above, this provides an efficient means of cooling the winding sections without risk of contamination of the air gap. It will also be observed that the cooling air passes over the P.C. board  46  in the motor shown, the board is conventional but of course a copper board would be cooled as above if substituted for the conventional board.  
         [0025]     Finally, in  FIG. 8 a  stator is shown completely enclosed in molded plastic. As mentioned above, this minimizes motor contamination.  
         [0026]     As will be apparent from the foregoing, a number of improvements in permanent magnet motors have been achieved with the result substantial improvement in both motor performance and sound attenuation.