Abstract:
A permanent magnet motor, generator or the like that uses ceramic magnets in the rotor to concentrate the magnetic flux in the airgap. Magnet poles are formed by pole plates with tabs forming north and south poles with magnetic separators therebetween. Magnet sections are stacked axially. Connection to the shaft is made by means of a collet or other attachment method.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Rotary electric machines including electric motors, generators, and the like have employed permanent magnets for some time. These machines take on many different topologies, the two most common topologies that use internal rotors being “Surface Permanent Magnet—SPM” and “Interior Permanent Magnet—IPM.” Additionally there is a topology “Interior PM—flux squeeze” that is also shown in the prior art. These topologies can be seen in the following patents and applications incorporated herein by reference: 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
             
             
               
                 U.S. Pat. App. No. 
                 2007/0057589 
                 shows IPM 
               
               
                 U.S. Pat. No. 
                 7,362,025 
                 shows IPM 
               
               
                 U.S. Pat. No. 
                 6,703,746 
                 shows IPM 
               
               
                 U.S. Pat. App. No. 
                 2009/0134731 
                 shows SPM 
               
               
                 U.S. Pat. No. 
                 7,486,037 
                 shows SPM 
               
               
                 U.S. Pat. No. 
                 3,072,813 
                 shows Interior PM-flux squeeze 
               
               
                 U.S. Pat. No. 
                 7,148,598 
                 shows Interior PM-flux squeeze 
               
               
                   
               
             
          
         
       
     
         [0002]    Generally high efficiency motors and generators use rare earth magnets that contain Neodymium (Nd) and Dysprosium (Dy) which are both expensive and which may be limited in supply at times. The lowest cost magnets per energy density are generally ceramic-based magnets. These magnets have lower magnetic properties than their rare earth counterparts but are readily available and inexpensive. 
         [0003]    It is the general object of the present invention to provide a high efficiency rotary electric machine employing lower strength permanent magnets. 
         [0004]    A further object of the invention is to provide rotary electric machines of the aforesaid type with magnet sections arranged in axially extending series for substantial enhancement of machine performance. 
         [0005]    A further object of the invention is to provide a robust attachment means from the magnet sections to the shaft that does not short out the magnetic circuit. 
       SUMMARY OF THE INVENTION 
       [0006]    In fulfillment of the forgoing object and in accordance with the present invention a magnet configuration is used that concentrates the lower strength magnets into high flux density in the airgap. This is accomplished by separating the rotor into layers where each layer is a self-contained multi-pole rotor. In an internal rotor configuration, these layers each have a flat disc shaped magnet in the center with magnetically soft material that has alternating integral tabs that generate alternating north and south poles. These magnet sections are stacked mating north poles to north poles and south poles to south poles. 
         [0007]    An important feature of the invention resides in the provision of magnetic separators between alternating tabs to prevent flux from shorting between poles. 
         [0008]    Rotor sections can be held together axially and rotationally at their center sections at a common shaft by means of non-magnetic spacers or by using a non-magnetic shaft. Various attachment means may be employed including press fits, keyways, and the like. In addition, it is advantageous to provide a means of holding each magnet section to each other in low flux density regions because the magnetic forces urge the magnet sections apart and attachment at the center of rotation only may not be sufficient. 
         [0009]    Attachment means to the shaft is preferably done my means of a non-magnetic collet to accomplish mechanical attachment and magnet separation. Alternatively this could be accomplished by means of a press fit, keyway, or spline. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic view of three different types of prior art. These include Surface Permanent Magnet (SPM), Interior Permanent Magnet (IPM), and Interior PM—flux squeeze (Flux squeeze) 
           [0011]      FIG. 2  shows a stack of magnet sections in a 6-pole design, 
           [0012]      FIG. 3  shows a single magnet section of the type shown in  FIG. 2 , 
           [0013]      FIG. 4  shows a cross section of the magnet section of  FIG. 3 , 
           [0014]      FIG. 5  shows the ceramic magnet portion of the magnet section of  FIG. 3 , 
           [0015]      FIG. 6  shows a complete rotor assembly on a common shaft, 
           [0016]      FIG. 7  is an enlarged fragmentary illustration showing a detail view from the center of the cross section shown in  FIG. 6 , 
           [0017]      FIG. 8  shows a three dimensional view of the collet assembly, 
           [0018]      FIG. 9  shows a fastener similar to a U-drive screw that can connect two magnet sections together, 
           [0019]      FIG. 10  shows a configuration with the stator outside the rotor for a tab pole motor, 
           [0020]      FIG. 11  shows tab pole plates that surround the magnet, 
           [0021]      FIG. 12  shows a 3D sectional view of the magnet assembly with the flux path shown, 
           [0022]      FIG. 13  shows a segmental part of a multi-part magnet, and 
           [0023]      FIG. 14  shows a magnet section with openings for interconnecting sections. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
       [0024]    Referring particularly to  FIG. 2 , a stack of six (6) magnet assemblies or sections  11  is shown in a six pole configuration. Each section has three north poles  12   a - 12   f  and three south poles  13   a - 13   f  respectively located on tabs extending from opposite pole plates  12  and  13 ,  FIG. 4 . Ceramic magnet  14  is disposed between the pole plates  12  and  13  and through openings  15 , 15  are provided in areas of low flux density. Tabs of the same polarity are aligned axially with each other as shown in  FIG. 2  with tabs  12   a - 12   f  aligned axially and tabs  13   a - 13   f  similarly aligned. 
         [0025]    The ceramic magnet per se is best shown in  FIG. 5  and has a center region  17  that is magnetized similar to a speaker magnet with north and south poles on opposite generally planar faces. Circumaxially spaced pole separation regions or separators  16 , 16  may be integral with the magnet or may be separate parts. They are magnetized orthogonal to the center region  17  with the magnetizing direction extending arcuately between tabs  12  and  13  in  FIG. 3 . Tab separation regions are magnetized generally perpendicular to conical inner surfaces  18 , 18  of connectors extending to the center region  17 . An alternate configuration of the magnet is shown in  FIG. 13  where segments of a magnet are made separately and joined together at  46 . 
         [0026]    The flux path is shown in  FIG. 12  with flux supplied by magnet  38  traveling in the direction of arrow  39 . The flux then travels through pole plate at  37  in the direction of arrow  40 , exits through the pole tab and crosses the air gap to the stator. Arrows  41 , 42 , and  43  show flow through the stator and arrow  44  shows the return flow across the air gap to the pole plate at  36 . Finally the flux returns to the magnet as illustrated by the arrow  45 . 
         [0027]    Pole plates may be connected together to connect magnet sections by double-sided U-drive screws as shown in  FIG. 9  pressed into openings  15 , 15 ,  FIG. 3 . Lead in portions  28 , 28  on each end of the screws facilitate entry and splined portions  29 ,  29  grip the plates for interconnection. An alternate attachment means is shown in  FIGS. 13 and 14  where a small through opening  48  may be accommodated by providing a small recess in the magnet at  47 . 
         [0028]    The shaft may be press fit in a central opening in each magnet section and is preferably enlarged diametrically beyond the magnet sections as shown in  FIG. 6  as may be required for external attachment An elliptical transition region  20  is preferred as illustrated. 
         [0029]    The preferable attachment means of the magnets to the shaft is a collet as shown in  FIG. 8 . The collet is comprised of two split rings  21  and  24  that are compressed together with screws  22 . The tapered engagement faces  25   a,    25   b,  and  26  translate the axial forces of the screws to radial forces that lock the magnet section to the shaft. This is accomplished by using friction on the shaft outside diameter against the inside diameter of split ring  21  to hold the collet to the shaft. Further there is friction along  25   a  and  25   b  that lock the collet to the magnet section while the two collet sections are locked together with friction of surface  26 . 
         [0030]    An alternative means to connect the magnet sections to the shaft is a press fit. When this is done the shaft would be non-magnetic or a non-magnetic collar would be inserted between shaft and magnet section. Alternatively, the shaft could be connected to the magnet sections by means of a spline or keyway. 
         [0031]    Finally, individual restraining bands may be provided as at  21 ,  21  about the circumference of each magnet section or, alternatively, a single large common band or other restraining means may be employed for the several sections. The assembly process for each band may be a thermal shrink fit by heating the band or by cooling the rotor before assembly to insure a tight fit. Depending on geometry the band may be made of either magnetic or nonmagnetic material. For some geometries the best choice is an austenitic grade of stainless steel. In some cases it may be necessary to fill the gap between the magnet and the band with a gap filling material, which hardens when heated, or by other means. Preferably, the gap filing material should have a much lower modulus of elasticity than the magnets or the pole plates.