Abstract:
A high torque axial gap electric motor includes rotor and stator disks containing magnets fixed to their respective faces, where the magnets contain triangular ridges arranged in concentric circles. The face of each rotor magnet ridge is parallel to the face of a stator magnet ridge, creating an air gap with a cross-section that has a zigzag appearance. The preferred embodiment uses a three-phase motor design with multiple rotors and stators and permanent magnets.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 62/015,452 filed Jun. 22, 2014, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to electric motors, in particular, to axial gap electric motors. 
       BACKGROUND OF THE INVENTION 
       [0003]    Over the years, many variations on the electric motor have been used to convert electrical energy into mechanical energy. Despite these many variations, there exists a need for an electric motor with an adjustable amount of torque to suit particular applications. In particular, there is a need for an electric motor that provides a larger amount of torque without increasing the size or weight of the motor. This type of high torque motor would be useful in a variety of applications, including electric vehicles. 
         [0004]    One type of electric motor in use today is the axial gap or pancake motor. An axial gap motor uses one or more disk shaped stators fixed to a frame and one or more disk shaped rotors angularly fixed to an output shaft. This design allows the motor to be more compact than radial gap electric motors. Axial gap motors are self-centering due to the magnetic field generated between the rotor disk and stator disk, making them suited for high speed rotation. However, there is a need for an electric motor that benefits from the compact size of axial gap motors, but produces more torque at a low RPM. 
         [0005]    Accordingly, it is an object of the present invention to provide an axial gap motor with an increased amount of torque at low RPMs without increasing the size or weight of the motor. It is also an object of the present invention to provide a means of adjusting the torque output of the motor to suit different applications. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention provides an electric motor comprising a support assembly fixed to two stator disks and three rotor disks angularly fixed to an output shaft. The stator disks comprise a flat non-magnetic disk, windings for three phases and permanent magnets mounted on the flat surfaces of the stator. The rotor disks comprise a flat non-magnetic disk with permanent magnets fixed to each flat surface that faces a stator disk. The permanent magnets mounted on the rotor are shaped with two peaks when a cross section of the magnet is viewed. The permanent magnets mounted to the stator are shaped with two valleys that correspond to the peaks on the rotor magnets in a cross sectional view. The resultant air gap between the rotor and stator magnets has a cross section with a zigzag appearance. 
         [0007]    The invention has application to electric motors in general and would be particularly beneficial when used in applications requiring a compact motor with high torque at low RPMs, such as in an electric or hybrid vehicle. Such vehicles require large amounts of torque to accelerate from a stop, but also benefit from the reduced power consumption of a low RPM electric motor. The invention is also applicable in low torque applications because it is capable of producing higher amounts of horsepower and torque than other electric motors of a similar size and weight. 
         [0008]    In the invention is an axial gap electric motor comprising a first, second and third disk shaped rotor angularly fixed to an output shaft and a first and second disk shaped stator fixed to a support assembly. The first stator is positioned between the first and second rotors and the second stator is positioned between the second and third rotors. Each rotor face that directly opposes a stator face contains a circular array of permanent magnets with two concentric ridges. Both faces of each stator contain three phases of windings with a permanent magnet affixed to both faces of the stator for each winding. The permanent magnets fixed to the stator faces contain three concentric ridges that correspond to the ridges in the rotor magnets. The preferred embodiment disclosed herein uses three rotors and two stators, however, it is to be understood that rotors and stators may be added or subtracted to optimize the invention for a particular application. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]      FIG. 1  is a side view of the invention with the dust cover removed. 
           [0010]      FIG. 2  is a sectioned side view of the invention with the dust cover installed. 
           [0011]      FIG. 3  is a perspective view of a rotor magnet. 
           [0012]      FIG. 4  is a side view of a rotor magnet. 
           [0013]      FIG. 5  is a front view of a rotor showing the magnet arrangement on the rotor face. 
           [0014]      FIG. 6  is a perspective view of a stator magnet. 
           [0015]      FIG. 7  is a side view of a stator magnet. 
           [0016]      FIG. 8  is a front view of a stator showing the magnet and windings arrangement on the stator face. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    In  FIG. 1 , is a side view of the invention comprising a first rotor  10 , a second rotor  11 , a third rotor  12 , a first stator  13 , a second stator  14 , a support structure  15 , a first bearing  16 , a second bearing  17  and an output shaft  18 . Each rotor and stator is disk shaped with two flat opposing faces and is constructed from a non-magnetic material. Permanent magnets with two ridges (rotor magnets)  19  are affixed to each rotor face opposite a stator face and arranged in a circle about the axis of rotation. The rotor magnets  19  are preferably Neodymium N50 magnets, a strong rare earth magnet. While N50 magnets represent the preferred embodiment, other types of magnets may be substituted depending on the torque output needed from the motor. The rotor magnets  19  can be mounted using fasteners or an adhesive. 
         [0018]    In  FIG. 2  is a sectioned side view of the invention shown with a dust cover  30  installed. As seen in this view, the stator contains windings  21  comprising wire wrapped through the stator disk. There are three phases of windings in the preferred embodiment. Each winding  21  is recessed into a groove on the face of each stator and a stator magnet  20  is affixed to each winding. The stator magnets can be made of the same classes of magnetic material as the rotor magnets. The stator magnets can be mounted to the face of the stators using fasteners or adhesives as well, however the stator magnets must have a low resistance electrical connection to its corresponding winding  21 . 
         [0019]    The dust cover  30  is attached to studs  31  that are attached to the outer ring of bearing  17  using nuts  32 . Extending from the inside of the dust cover  30  are eight fully threaded rods  33 . The rods  33  pass through smooth circular openings  34  in the stators  13  and  14 , the cover  30  and the support structure  15 . Each rod  33  is fixed to the dust cover  30  on one end with a nut  36  and fixed to the support structure  15  at its opposite end using a nut  36 . The stators  13  and  14  are fixed to the rod  33  using nuts  36  tightened on either side of the respective stator. 
         [0020]    The sectioned side view of  FIG. 2  shows the cross section of the rotor magnets  19 , the stator magnets  20  and the air gap between them. The peaks  37  on the rotor magnets correspond to the valleys  38  in the stator magnets. The distance in the axial direction between the peaks  37  and the valleys  38  is between 1.2 and 3.0 mm in the preferred embodiment. Increasing the axial distance within these parameters increases the torque output of the motor and reducing the axial distance within these parameters decreases the torque output of the motor. It is understood that this particular range of distances is applicable only to the preferred embodiment, which uses a rotor of approximately 354 mm in diameter. The range in axial distances that are appropriate for a particular motor depend on the size of the motor, the strength of the magnet used and the angle of the peaks and valleys in the rotor and stator magnets respectively. 
         [0021]      FIGS. 3, 4 and 5  show the rotor magnets  19  and their arrangement on stator  10  in detail. While only one rotor is shown in this  FIG. 5 , it is understood that rotors  11  and  12  use an identical arrangement of magnets. 
         [0022]      FIG. 3  shows a perspective view of a single rotor magnet  19 . The top edge of the rotor magnet  50  and bottom edge of the rotor magnet  51  are curved about the axis of the rotor. The peaks  37  are likewise curved about the axis of the rotor. The sides of the rotor magnets  52  are flat and perpendicular to the rotor surface and taper together towards the bottom edge of the rotor magnet  51 . Therefore the top edge of the rotor magnet  50  is longer than the bottom edge of the rotor magnet  51 . 
         [0023]      FIG. 4  shows a side view of a single rotor magnet. The peaks  37  have an angle  53 . Changing the angle of the peaks adjusts the magnetic flux. The angle of the peaks  53  can be in the range of 20° to 36°. Within this range, increasing the angle increases the torque output of the motor. In the preferred embodiment, the angle  53  is 30°.  FIG. 5  shows the rotor magnets  19  mounted on rotor  10 . 
         [0024]      FIGS. 6, 7, and 8  show the stator magnets  20  and their arrangement on stator  13 . While only one side of stator  13  is shown, it is understood that the opposite side of stator  13  and both sides of stator  14  use an identical arrangement of magnets. 
         [0025]    In  FIG. 6 , the top edge of the stator magnet  60  and bottom edge of the stator magnet  61  are curved about the axis of the stator. The valleys  38  are likewise curved about the axis of the stator. The curvature of the top edge of the stator magnet  60 , the bottom edge of the stator magnet  61  and the valleys  38  are identical to the curvature of the top edge of the rotor magnet  50 , bottom edge of the rotor magnet  51  and peaks  37  respectively. The sides of the stator magnets  62  are flat and perpendicular to the stator surface and taper together towards the bottom edge of the stator magnet  61 . Therefore, the top edge of the stator magnet  60  is longer than the bottom edge of the stator magnet  61 . 
         [0026]    In  FIG. 7 , the angle  63  of the valleys  38  is equal to the angle  53  of the peaks  37  in the rotor magnets  19  in  FIG. 4 . In the preferred embodiment, the angle  63  is 30°. 
         [0027]      FIG. 8  shows the stator magnets  20  arranged on the stator  13 . The windings  21  pass through an inner opening  70  and an outer opening  71  on the stator. Each winding  21  has a stator magnet  20  mounted above so that the winding  21  is pressed between the back of the stator magnet  20  and the face of stator  13 . The preferred embodiment uses a three phase design so that there are three stator magnets for each rotor magnet. 
         [0028]    What has been described is an electric motor for the conversion of electrical energy to mechanical energy. It is well known in the art that electric motors can alternatively be used as generators, converting mechanical energy into electrical energy. While this disclosure shows the invention as an electric motor, it is also capable of being used as a generator. In this disclosure, there are shown and described only the preferred embodiments of the invention, but, as aforementioned, it is to be understood that the invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.