Abstract:
A permanent magnet motor is provided with a housing, a rotating shaft supported within the housing, and magnetic coils arranged within the housing. A hydrostatic bearing is disposed on the rotating shaft, the hydrostatic bearing having a permanent magnet incorporated therewith that restricts movement of the rotating shaft in a radial direction.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/149,794, filed Feb. 4, 2009, which is incorporated by reference as if fully set forth. 
    
    
     FIELD OF INVENTION 
     This application is generally related to motors or generators having magnetic elements, and more particularly related to hydrostatic bearings constructed with a permanent magnet that can be used as the permanent magnetic element of motors or generators. 
     BACKGROUND 
     Some motors are designed to use coils in order to generate a magnetic field. These motors include two sets of coils, one located in the stator and one located in the rotor. One set of coils is energized using conductive contacts or brushes that may touch on the shaft or the moving body. The current fed to these coils creates an electromagnetic field. Other motors and generators employ permanent magnets to provide motion. Electricity is produced when coils of copper windings are moved relative to the flux fields generated by the magnets. Alternatively, electricity may be fed into the coils to produce motion. In both of these scenarios, separate bearings are used to define the relative motion between the coils and magnets, which may be linear or rotary in nature. In either case, the flux field creates an attractive force that must be resisted by the bearings. This force is mitigated in some degree when there is an opposing force applied at 180° from other magnets. Although the opposing force mitigates the flux field&#39;s attractive force, it is not a stabilizing force. For example, as the coils get closer to the magnets on one side, the attractive force from those magnets increase, which moves the coils further away from the magnets that are arranged at 180° and decreases the applied opposing force. In the absence of separate bearings, the coils and magnets would come into contact and disable the motor or generator&#39;s function. 
     Permanent magnet motors employ magnets made of, for example and without limitation, neodymium NdFeB or ferrite. There are multiple methods for manufacturing these magnets, such as through casting in a mold, pressing, injection molding, or bonding. In most cases, these magnets are porous, which is especially true for magnets that are sintered. These magnets may be magnetized after they have been formed into their desired shape. Motors and generators may employ a wide variety of magnetic circuit designs. Permanent magnets may be used on the outside diameter of a rotating body or on the interior of a housing. They may use switched reluctance or induction and may use AC or DC current. 
     Motors and generators&#39; efficiency and power can be increased by minimizing the distance between the coils in the magnets. As the distance between the coils decreases, the flux field force increases. However, due to the unstable relationship between the coils and magnets as described above, relatively large gaps between coils must be used in the manufacture of motors and generators. Such an arrangement is shown by U.S. Pat. No. 5,036,235 to Klecker. 
     Design engineers have been trying to achieve more functionality in less space. The paradigm today in the design of motors and generators is to have separate bearings and motor functions. This results in assemblies that are longer, larger in diameter, and heavier than if the motor and bearing elements can be one in the same. For example, see the assembly shown by U.S. Pat. No. 5,443,413 to Pflager et al. 
     In U.S. Pat. No. 5,098,203 to Henderson, magnets are inserted into the face of a hydrostatic bearing assembly in order to increase the stiffness of the hydrostatic film with the magnets&#39; preload force. However, there is no disclosure of using such magnets in a motor or generator. 
     One of ordinary skill in the art of hydrostatic bearings would appreciate that air and other gases are examples of a fluid used in hydrostatic bearings. This means that the broad term of hydrostatic bearings encompasses aerostatic bearings, as discussed in U.S. Pat. No. 5,488,771 to Devitt et al. The terms “hydrostatic bearings” and “hydrodynamic bearings” are both encompassed in the definition of “fluid film bearings.” Hydrostatic bearings are differentiated from hydrodynamic bearings by the use of an external pressure source, which allows hydrostatic bearings to operate even with zero velocity between the relative bearing faces. In contrast, hydrodynamic bearings require relative motion between bearing faces to create fluid film pressure. One of ordinarily skill in the art would also appreciate that hydrostatic bearings exhibit hydrodynamic effects when there is relative motion between the bearing faces. These hydrodynamic effects are an unavoidable result of the shear of the hydrostatic fluid caused by the relative motion of the bearing surfaces, and are included in the operation of hydrostatic bearings. 
     Accordingly, it is an object of the present application to combine the bearing and motor functionalities, provide economy of space, and improve efficiency by reducing the gap in the flux field to the thickness of the hydrostatic bearing fluid. 
     SUMMARY 
     A permanent magnet motor is disclosed, the permanent magnet motor having a housing, a rotating shaft supported within the housing, and magnetic coils arranged within the housing. A hydrostatic bearing is disposed on the rotating shaft, the hydrostatic bearing having a permanent magnet incorporated therewith that restricts movement of the rotating shaft in a radial direction. 
     A method for making a permanent magnet motor is also disclosed. The method includes the steps of providing a housing with a rotating shaft supported therein, arranging magnetic coils within the housing, and disposing a hydrostatic bearing on the rotating shaft. The hydrostatic bearing has a permanent magnet incorporated therewith that restricts movement of the rotating shaft in a radial direction. For sake of brevity, this summary does not list all aspects of the present device, which is described in further detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a prior art motor having separate bearing and motor components; 
         FIG. 2  is a cross-sectional view of an embodiment of the hydrostatic bearing of the current invention, which utilizes porous magnetic material as the restrictor for the hydrostatic bearing; and 
         FIG. 3  is a cross-sectional view of another hydrostatic bearing that serves as the permanent magnet in a motor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Certain terminology is used in the following description for convenience only and is not limiting. The words “inner,” “outer,” “top,” and “bottom” designate directions in the drawings to which reference is made. The terminology includes the words specifically noted above, derivatives thereof, and words of similar import. 
       FIG. 1  shows a prior art permanent magnet motor having a rotatable shaft  100  supported relative to a housing or stator  105  by a set of bearings  103  at each end of the rotatable shaft  100 . The bearings  103  may be formed as plain, rolling, fluid film, or magnetic bearings, or any other form well known to those of ordinarily skill in the art of bearings. In this case, the bearings  103  provide both radial and axial constraint. The bearings  103  provide radial constraint by having an outer diameter that corresponds to the inner diameter of the housing or stator  105 , and provide axial constraint by being disposed between a shoulder  100 a of the rotatable shaft  100  and a stationary retaining cap  106  of the housing or stator  105 . Accordingly, the bearings  103  substantially constrains five degrees of freedom of the rotatable shaft  100 , leaving only rotation unrestrained. 
     The prior art motor&#39;s motor elements are completely separate from the permanent magnets. Coils  101  are wrapped by 360° around the inner diameter of the housing or stator  105 . Magnets  102  are disposed around the outer diameter of the rotatable shaft  100 , leaving an air gap  104  between the magnets  102  and coils  101 . The air gap  104  must be large enough to accommodate error motions in the bearings  103 , out of balance centrifugal forces, and centrifugal force growth of the magnets  102  and rotor. 
       FIG. 2  shows an embodiment of a hydrostatic bearing according to the present invention. A magnetic material  200  that can be acted upon by an attractive magnetic field from a porous magnet  201  is separated from the porous magnet  201  by a pressurized hydrostatic film  206 . The hydrostatic film pressure is maintained by a continuous flow of fluid, which is pumped through the porous magnet  201  by a pressure higher than ambient pressure. This pressurized fluid is introduced through input ports  202  and distributed across a back surface of the porous magnet  201  by a labyrinth  204 . As shown in  FIG. 2 , the labyrinth  204  may be formed in a non-porous housing  203 . In an alternative embodiment, which is not illustrated by the drawings, the labyrinth  204  may be formed in the porous magnet  201  itself. In a further alternative embodiment, also not illustrated by the drawings, the labyrinth may be formed in a separate modular bearing component that is mounted inside of the non-porous housing  203  or to a separate structure using a mounting stud  205 , which may be attached through a flexure, gimbal mount, bolted joint, or bonded in place as disclosed in U.S. Pat. No. 5,488,771 to Devitt et al. In the above embodiments, the non-porous housing  203  and the porous magnet  201  are laminated together by any suitable means, such as through gluing, glazing, or grazing operations. These methods are well known in the art of manufacturing porous media hydrostatic bearings and have been described in U.S. Pat. No. 6,515,288 to Ryding et al. The pressurized fluid is also useful for removing heat from the bearing surfaces of the hydrostatic bearing and from the hydrostatic gap. 
       FIG. 3  shows a preferred embodiment of a hydrostatic bearing according to the present invention utilized in a permanent magnet motor. A rotating shaft  300  is provided with porous permanent magnet components  302  laminated onto the outer diameter of the rotating shaft  300 . A labyrinth  312  is provided behind the porous magnet components  302  in a similar manner as described above with respect to  FIG. 2 . In order to supply the labyrinth  312  with a pressurized hydrostatic fluid, the fluid can be ported through a hole  309  in each retaining cap  306  on either side of the housing  305  and distributed through a groove  310  in the retaining caps&#39; inner diameter that functions as a rotary union due to the small clearance  307  between the retaining caps  306  and rotating shaft  300 , and finally into a hole  311  in the rotating shaft  300 . This pressurized hydrostatic fluid then issues from the face of the porous magnet components  302 , creating a pressurized film  304  that separates the porous magnet components  302  from the magnetic coils  301  despite the attraction between them. The attractive force between the porous magnet components  302  and magnetic coils  301  is used for the purposes of the motor or generator functionality, which is enhanced over the current art because the gap can be made smaller due to the safety afforded by the separation force of the pressurized fluid film  304  from the hydrostatic bearing functionality. This is because the flux field strength is very sensitive to the gap thickness. At very high pressures, this fluid film force may be used to counter the centrifugal force attempting to separate the porous magnet components  302  from the rotating shaft  300 . While  FIG. 3  shows the use of the porous magnet components  302  as the restrictive element in the hydrostatic bearing, other well known forms of restrictive compensation such as orifice or step compensation may be employed. 
     The embodiment of the hydrostatic bearing shown in  FIG. 3  only provides radial restraint, so conventional rolling, plain, fluid film, or magnetic bearings may be used for axial restraint. Preferably, additional hydrostatic bearings  303  are used to provide axial restraint, and pressurized fluid from the same labyrinth  312  and fluid source is employed to create a hydrostatic bearing gap  308  on both ends of the rotating shaft  300 , creating opposing forces and providing two-directional axial restraint. Although not shown in the drawings, the same bearing and motor/generator arrangement may be employed in both the axial and radial directions. 
     While various methods, configurations, and features of the present invention have been described above and shown in the drawings, one of ordinary skill in the art will appreciate from this disclosure that any combination of the above features can be used without departing from the scope of the present invention. It is also recognized by those skilled in the art that changes may be made to the above described methods and embodiments without departing from the broad inventive concept thereof. For example, the coils  301  shown in  FIG. 3  may be located on the rotating shaft  300  while the porous magnet components  302  are located on the inner diameter of the housing  305 , with electricity fed to the coils  301  via a conductive contact brush. Additionally, the embodiments of the invention are capable of being scaled up with coils and magnet diameters potentially reaching tens of meters.