Abstract:
A torus motor system includes a hollow stator and a rotor which is driven along a rotor path formed within the hollow stator by a magnet system. The rotor operates as a piston within the rotor path to intake and discharge fluid therefrom. The forces on the rotor all tend to center the rotor within the rotor path. The rotor is accelerated away from the inlet port on the magnet system and decelerated as the rotor approaches the discharge port.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a motor system, and more particularly to an electromagnetically driven rotary machine in which a rotor is electromagnetically driven within a hollow elliptical stator.  
         [0002]     Reciprocating compressor/pumps are highly desirable for use in numerous applications, particularly in environments where liquid flow rate is relatively low and the required liquid pressure rise is relatively high. For applications requiring less pressure rise and greater flow rate, rotary centrifugal compressor/pumps may be favored because of their simplicity, inexpensive and low maintenance requirements.  
         [0003]     A typical air compressor load increases almost linearly as the piston moves to compress the air. In a pump application the load is generally constant along the length of travel.  
         [0004]     Although both are effective, the reciprocating and the rotary pump each provides tradeoffs which affect efficiency in a compressor/pump application.  
         [0005]     Accordingly, it is desirable to provide a machine for pump/compressor applications with the benefits of both a reciprocating and a rotary machine which generally matches the required load to provide efficient operation.  
       SUMMARY OF THE INVENTION  
       [0006]     A torus motor system according to the present disclosure includes a hollow stator and a rotor which is driven within the hollow stator by a magnet assembly. The hollow stator defines a rotor path which communicates a fluid from an inlet port to a discharge port. The rotor path is formed an ellipse within the stator. The rotor is at least partially arcuate in shape to match the internal elliptical geometry of the rotor path. The rotor operates as a piston within the rotor path to intake and discharge fluid therefrom. Although the geometry according to the present disclosure has wider use, the torus motor system is conceived primarily for pump/compressor applications.  
         [0007]     A multitude of magnet types are usable with the present invention such that various motor types (i.e. induction, Permanent Magnet, Switched Reluctance etc.) will benefit from the torus geometry. The magnet geometry provides magnets that are spaced the farthest apart to move the rotor the fastest, but provide the lowest load (i.e. the magnetic attractive forces diminish with distance). Conversely, magnets that are spaced the closest move the rotor the slowest but provide much more load. This is preferred because as the rotor passes the inlet, there is minimal load applied to the rotor. The load increases as the rotor approaches the discharge because gas is compressed in front of the rotor and a vacuum is pulled behind the rotor. The magnets are therefore spaced farthest apart where the load is smallest, and closest where the load is the largest which is an advantage over linear reciprocating pump/compressors.  
         [0008]     The torus motor and compressor (or pump) are one mechanism as opposed to a multiple of separate mechanisms as in a typical compressor or pump. The efficiency of the torus motor/compressor compares favorably with a rotary compressor because there are minimal air end and package losses because of less piping and the elimination of an oil separator. Because there are few components and no couplings or gears between the driving force and the work, efficiency is increased. Even if the torus motor has the same efficiency as a rotary compressor, a torus compressor will have a 15% to 20% power efficiency advantage.  
         [0009]     Generally, the benefits of the torus motor/compressor versus a typical compressor are: very few moving parts; high reliability; oil free operation; high efficiency; uncomplicated and relatively inexpensive; effective speed control with variable speed drives; few leak points; sealed stator; and various speed/load capabilities readily achieved.  
         [0010]     The present invention therefore provides a machine for pump/compressor applications with the benefits of both a reciprocating and a rotary machine which generally matches the required load to provide efficient operation.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
         [0012]      FIG. 1A  is a general perspective view of an torus motor system;  
         [0013]      FIG. 1B  is a sectional view taken along line  1 B- 1 B of the torus motor system of  FIG. 1A ;  
         [0014]      FIG. 1C  is an exploded view of a stator assembly;  
         [0015]      FIG. 1D  is an expanded view of one side of a stator assembly;  
         [0016]      FIG. 2A  is a top view of a magnet assembly;  
         [0017]      FIG. 2B  is a face view of a magnet circuit board for the magnet assembly of  FIG. 2A ;  
         [0018]      FIG. 2C  is a top view of a magnet assembly in a disassembled condition;  
         [0019]      FIG. 2D  is a perspective view of the magnet assembly of  FIG. 2A ;  
         [0020]      FIG. 3A  is a sectional view of a switched reluctance torus motor system;  
         [0021]      FIG. 3B  is an exploded view of another magnet assembly;  
         [0022]      FIG. 4  is a side view of rotor for a torus motor system;  
         [0023]      FIG. 5  is a top view of an torus motor system illustrating a magnet system geometry;  
         [0024]      FIG. 6  is a sequential illustration of a torus motor system illustrating movement of a multiple of rotors within the stator;  
         [0025]      FIG. 7A  schematically illustrates a magnet firing order and rotor movement for a one-lobe rotor;  
         [0026]      FIG. 7B  schematically illustrates a magnet firing order and rotor movement for a two-lobe rotor;  
         [0027]      FIG. 8  schematically illustrates a magnet firing orders for rotors with one, two, three and four lobes on a twelve magnet stator; and  
         [0028]      FIG. 9  schematically illustrates a magnet firing orders for two magnets firing at the same time and acting on two and four lobe rotor on a 24 magnet stator. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]      FIG. 1A  illustrates a torus motor system  10  that generally includes a hollow stator  12  and a rotor  14  which is driven within the hollow stator  12  by a magnet system  16 . The motor and compressor (or pump) are one mechanism. As opposed to two (or more) separate mechanisms in a typical compressor or pump. Although the rotor of the torus motor system  10  does not actually rotate, but rather is driven in an elliptical path as defined by the hollow stator  12 , Applicant will refer to the moving member of the motor as a rotor.  
         [0030]     The hollow stator  12  defines an inlet port  18  and a discharge port  20  which communicates with the interior of the hollow stator  12 . It should be understood that although the motor system  10  will be described as a compressor for a gas, other uses such as that of a fluid pump or a mechanical motor drive will likewise benefit from the present invention. A rotor path R is preferably formed as a ring defined about a center point A, however other shapes such as ellipses or the like will also be usable with the present invention. The rotor path R is also preferably circular in cross-section ( FIG. 1B ), however, other shapes may also be used with the present invention.  
         [0031]     Referring to  FIG. 1C , the hollow stator  12  is preferably formed of a first and a second stator portions  22   a ,  22   b  which are mounted together to define the rotor path R. The stator material is a non-magnetic material such as stainless steel or plastic. Each stator portions  22   a ,  22   b  is preferably a mirror image of the other. The separation between the stator portions  22   a ,  22   b  is preferably a plane which includes the center point A and divides the rotor path R, however, other separation planes will also be usable with the present invention.  
         [0032]     Referring to  FIG. 1D , a seal  24   i ,  24   o , is located within a groove  25   i ,  25   o  defined about an inner circumference Ri and an outer circumference Ro of the rotor path R. The seals  24   i ,  24   o  seal the rotor path R when the stator portions  21   a ,  21   b  are assembled together.  
         [0033]     The hollow stator  12  defines a multitude of teeth  26  about the rotor path R. Each tooth  26  defines a stator inner diameter  12   i  and a stator outer diameter  12   o . Preferably, each tooth is frustro-triangular in shape. That is, the small end of the tooth  26  defines the stator inner diameter  12   i  while the large end of the tooth  26  defines the stator outer diameter  12   o.    
         [0034]     At least one alignment pin  28  is mounted within an aperture  30  formed in the tooth  26 . Each tooth  26  is formed by the stator portions  22   a ,  22   b  to retain the magnet system  16  ( FIG. 1B ) and provide fastener receipt apertures  31  for fasteners f such that the fasteners f and pins  28  will not penetrate into the rotor path R ( FIG. 1B ).  
         [0035]     It should be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit from the instant invention. Alternatively, for example, the stator cross-section does not have a closed shape. A slot around the side of the stator guides a pin extending through the slot to transfer motion to some other device.  
         [0036]     Referring to  FIG. 2A , the magnet system  16  includes a magnet assembly  32  which is mounted between each tooth  26  of the hollow stator  12  ( FIG. 1B ). Each magnet assembly  32  is preferably manufactured from a multiple of laminated magnet circuit boards  34  ( FIG. 2B ). Each magnet circuit board  34  is manufactured in board portions  34   a ,  34   b  to facilitate assembly around the hollow stator  12 . The laminations of one board portion  34   a  are interleaved with the laminations of the other board portion  34   b . The laminations have spacer washers  35  between layers to hold the board portions  34   a ,  34   b  to properly locate the mating board portions. The magnet circuit boards  34  are preferably located between cooling fins  36  and held together with fasteners  40  such as screws. The screws  40  are preferably threaded into the cooling fins  36  which are also manufactured in multiple portions to mount about the hollow stator  12 . Each portion  32   a ,  32  may be first separately assembled ( FIG. 2C ) and then joined together around the stator by an interface fastener  40 A.  
         [0037]     Referring to  FIG. 2B  the magnet circuit board portions  34   a ,  34   b  have a circuit foil pattern on the back side. When assembled to be interleaved together, the magnet circuit boards  34  produce a coil of circuit foils. Circuit board portion  34   a  (“bar” because of its shape) has a power lead pad LP for connection of power leads P to power the magnet assembly  32 .  
         [0038]     Electrical current is communicated through the power lead P to the lead pad LP and passes through a plated through hole connected to a circuit foil on the other side of the board (cannot be seen on the drawing). That foil mates with the lowest foil on the top side of the U-bar circuit board portion  34   b  (“U-bar” because of its shape). The foil runs to the top of the U-bar circuit board  34   b  portion where it is mated with a foil on the back side of the next bar circuit board portion  34   a  and so on. The inner most foil on the U-bar board has a plated through hole that connects to the pattern on the back side. That is, when the boards are interleaved together ( FIG. 2A ) they form an electromagnetic circuit coil.  
         [0039]     Generally, for the same size board, the larger the foil coils the less turns can be made, but higher currents can be carried and the impedance is lowered. Carried to the extreme, the boards could be entirely covered and provide two turns per lamination (one per side). This construction follows that of a type of magnet known as a Bitter disk which is a round copper foil with a hole in the middle. The disk also has a cut along a radius. These disks can be interleaved with thin insulation between them to form a helix. The disks overlap for a small distance at the cut where there is no insulation. The insulation is the same shape as the disks. Such round magnets are more efficient than other shapes (like the long thin windings of a typical rotary motor) and Bitter disk magnets are more efficient than round wire wound magnets.  
         [0040]     It should be understood that a multitude of magnet types are usable with the present invention such as that various motor types (i.e. induction, Permanent Magnet, Switched Reluctance etc.) will benefit from the torus geometry.  
         [0041]     Referring to  FIG. 3A , a Switched Reluctance Torus motor is similar to the Induction Torus motor except magnet coils Ct, Cb are mounted in pairs to magnet lamination L, one on the top of the hollow stator  12  and one on the bottom, with laminations that go through the magnet cores and encircle the hollow stator  12 . The magnet laminations ( FIG. 3B ) provide a path between the magnets for the magnetic flux. The iron in the rotor is attracted to the gap between the two magnets when they are energized as in a rotary reluctance motor.  
         [0042]     Referring to  FIG. 4 , the rotor  14  is at least partially arcuate in shape to match the internal geometry of the rotor path R. The rotor  14  includes a lamination  42  manufactured of magnetic material such as iron and/or steel. The lamination  42  fit within the rotor path R to match the interior geometry of the hollow stator  12 . For example, with a rotor path R that is circular in cross section ( FIG. 1B ), the rotor  14  includes a multitude of washer-shaped laminations  42  which are retained together on a non-metallic arcuate rotor rod  44 . The non-metallic arcuate rotor rod  44  is preferably a brass, stainless steel, plastic or other such like material. The laminations  42  are sandwiched together with a head retainer  46  and a tail retainer  48  which are mounted to the arcuate rotor rod  44  through threading or the like. The retainers  46 ,  48  are preferably manufactured of non-metallic materials such as stainless steel, Teflon or other such like material and may at least partially operate as a seal within the rotor path R of the hollow stator  12 . The preferred thickness of the lamination is generally between half and one times the thickness of the magnet assemblies  32  within the magnet system  16 . Each rotor  14  preferably contains more than one set of laminations (a set of laminations will hereafter be called a rotor lobe). The spacing and size of these lobes depends on the spacing and thickness of the magnets.  
         [0043]     The forces on the rotor all tend to center the rotor in the rotor path R of the hollow stator  12 . Both magnetic forces and the force of fluid trying to blow by the rotor  14  tend to center it in the rotor path R. The forces tend to impact the face of the rotor laminations  42  and if the tolerances between the rotor and stator are minimized, there may not be a need for a seal at all. That is, the rotor  14  will ride on a fluid bearing (similar to a hydrostatic bearing), or a gas bearing if compressing a gas.  
         [0044]     Referring to  FIG. 5 , a controller  50  drives the magnet system  16 . The controller  50  may be a variable speed controller, a switched reluctance speed controller which controls a poly-phase power source  52 . Induction and Switched Reluctance Torus motors need special control considerations. Although the induction motor could be connected directly to the power source, the benefits of an electronic drive are preferred. For further understanding of other aspects of the unique control needs with the Torus motor which and associated components thereof, attention is directed to U.S. patent application Ser. No. ______, entitled “TRANSISTOR MATRIX SWITCHED RELUCTANCE VARIABLE SPEED MOTOR DRIVE,” which is assigned to the assignee of the instant invention and which is hereby incorporated herein in its entirety.  
         [0045]     The arrangement of the magnet system  16  for the poly-phase power source  52  such as arrangement for a three phase motor includes the phases ( 1 ,  2 , and  3 ) as illustrated in  FIG. 5 . The magnets are preferably spaced such that at one end they are farther apart then at the other. This arrangement has several advantages. The controller only has to maintain one frequency. The rotor  14  will speed up and slow in response to the magnet spacing ( FIG. 6 ). The pole spacing is actually a gradient, as opposed to fixed spacing in the case of common squirrel cage induction motors.  
         [0046]     The magnet geometry provides for magnets that are spaced the farthest apart to move the rotor the fastest, but provide the lowest load (i.e. the magnetic attractive forces diminish with distance). Conversely, magnets that are spaced the closest move the rotor the slowest but provide much more load. This is preferred because as the rotor passes the inlet, there is little load on it. The load increases as the rotor approaches the discharge (because it is compressing gas in front of the rotor and pulling a vacuum behind the rotor). The magnets should therefore be spaced farthest apart where the load is smallest, and closest where the load is the largest.  
         [0047]     Although this geometry may have wider use, it is conceived primarily for pump and compressor applications. The four views ( 1 - 4 ) show various points in a cycle with two rotors  14   a ,  14   b . The two rotors  14   a ,  14   b  move in a circular path within the hollow stator  12 . The rotors do not move at constant speed around the hollow stator  12 . As they pass the inlet port  18  they accelerate, as they approach the discharge port  20  they decelerate. View  1  shows rotor  14   a  approaching the discharge port  20  (it is slowing down) while rotor  14   b  is passing the inlet port  18  (it is speeding up). View  2  shows both rotors at about the same speed. View  3  shows that because of the difference in speed, air is being drawn into the stator through the inlet port  18 , and at the same time the air between the rotors (top left) is being compressed. View  4  shows rotor  14   a  passing the discharge port  20  and the air being pushed out by rotor  14   b . If a cycle is defined as one rotor going completely around the stator, the four views depict one half of a cycle. There are two compression cycles (one for each rotor) for each revolution of the rotors.  
         [0048]     Pump applications are similar, except that liquid pumps would have larger inlet and discharge ports so that the discharge port is open when the trailing rotor closes the inlet port. This is because liquids do not compress much, so the discharge port needs to be open so that the trailing rotor can push the liquid out the discharge.  
         [0049]     To maintain a multitude of rotors  14  in a desired relative orientation, at least one magnet is selectively switched on or off in response to a sensor S which communicates with the controller  50 . The position of the rotors are sensed by the sensor and the particular magnet is shut down for a time to cause the rotor passing the particular magnet to slow more than normal. This allows the rotors to be controlled and maintained in sync. The magnet directly across from the inlet and discharge is preferred ( FIG. 5 ). The switch for the magnet may be a transistor, and the sensor may be a Hall effect device located on the inlet side of the magnet such that the rotor is sensed as it approached the magnet.  
         [0050]     Referring to  FIGS. 7A and 7B  the magnet firing order and rotor movement for a one lobe rotor and a two lobe rotor ( FIG. 7B ) are illustrated. The magnets are spaced 30° apart. The firing sequence for the one-lobe rotor energizes the magnet in a counter clockwise order, the rotor will rotate counter clockwise 30° each time the next magnet ahead of the rotor is fired.  
         [0051]     Referring to  FIG. 7B , the length of the two lobe rotor is one and one half the distance between the magnets. The two-lobe rotor has a different firing order. View  1  shows the rotor positioned after the first magnet has been energized. This brings the leading end of the rotor in range of the third magnet. The third magnet is then energized, which brings the trailing end in range of the second magnet. This firing sequence moves the rotor clockwise 15° each firing of a magnet.  
         [0052]     The two-lobe rotor moves at half speed as the one-lobe rotor ( FIG. 7A ), but the load is higher. This is analogous to rotor motors with different numbers of poles. The two-lobe rotor develops much more than twice the load of the one lobe rotor, because the magnetic force acting on the rotor is proportional to the inverse square of the distance from the rotor lobe to the center of the magnet. More lobes provide slower but more powerful motors, however, the rotors must be lengthened to add more lobes which may require increasing the stator diameter and using more magnets.  
         [0053]      FIG. 8  illustrates a magnet firing orders for rotors with one, two, three and four lobes on a twelve-magnet stator. The magnets are evenly spaced, 30° apart. The lines across the chart illustrate rotary travel in degrees. The vertical lines represent the magnet placement on the stator. The rotors are shown at positions where they line up with an energized magnet. The shaded rotor lobe is the lobe that is under the influence of an energized magnet.  
         [0054]     The first firing order is for a one-lobe rotor. The sequence is 0, 30, 60, 90 and 120 degrees. The rotor moves 30° each time a magnet is fired.  
         [0055]     The second sequence is for a two-lobe rotor. The sequence is 0, 60, 30, 90, 60, 120 and 90 degrees. The rotor moves 15° each time a magnet is fired.  
         [0056]     The third sequence is for a three-lobe rotor. The sequence is 0, 90, 60, 30, 120, 90 and 60 degrees. The rotor moves 10° each time a magnet is fired.  
         [0057]     There is a problem for motors with more than two lobes. Depending on the length, number of lobes and lobe spacing there may be cases in the firing sequence where a magnet will be acting on two lobes, pulling one forward and one backward such that the rotor will freeze. The bottommost sequence for a four-lobe rotor shows this problem (marked with arrows).  
         [0058]      FIG. 9  illustrated two magnets firing at the same time and acting on two rotor lobes. This doubles the load capability. A two-lobe rotor firing sequence is shown on top and a four-lobe sequence is shown on the bottom which corrects the deficiency pointed out in  FIG. 8 . Note that this chart is for a 24-magnet stator with magnets spaced at 15° intervals.  
         [0059]     Any combination of rotor lengths, number of rotor lobes, lobe spacing, diameter of stator, number of magnets and magnet spacing may be utilized with the present invention. These options make the torus motor adaptable to different speed/load applications. The same stator for example may be combined with different rotors to provide different speed/load capabilities.  
         [0060]     The major components of the efficiency of a rotary screw compressor are the air end, the motor and the package losses. The air end and motor efficiencies go up as the size of the machine increases. The following table shows the efficiency ranges of these components from 10 Hp to 100 Hp machines. Cooler losses are not considered.  
                                                   Rotary Screw Air compressors 10-100 HP   Efficiency                           Air End Efficiency   75%-85%           Motor Efficiency (Premium Efficiency)   85%-95%           Package Losses   4%-5%           Total Efficiency   60%-75%                      
 
         [0061]     A Torus motor/compressor efficiency compares favorably because there are almost no air end losses and the package losses are less because of minimal piping and no oil separator. The efficiency of the compressor will be slightly less than the motor efficiency. Because there are fewer constraints on magnet design, there is reason to believe that because of better magnet designs, torus motors can be more efficient than rotary motors.  
         [0062]     The torus motor in the example could be high speed without the problems normally associated with high rpm motors. The rotor has little inertia and there are no bearings to limit speed. High volumes could be moved with a relatively small package. The above example would operate as an effective low speed pump but high speed would probably require four rotors and two sets of inlet and discharge ports. Because there are few components and no couplings or gears between the driving force and the work, better efficiency is improved. The geometry of the motor windings is also less constrained than in typical rotary motors, so greater system efficiency could be realized with more efficient electric magnet designs. Even if the torus motor has the same efficiency as above, the torus compressor may have a power efficiency of 80%-90% compared to 60%-75% (a 15% to 20% advantage).  
         [0063]     Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention.  
         [0064]     The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.