Abstract:
Permanent magnet bearings are incorporated into rotating equipment, such as induction machines, in addition to active magnetic or lubricated primary shaft support bearings. The passive magnetic bearings incorporate permanent magnets that generate directionally oriented magnetic fields of selective intensity. The magnetic field directions are aligned with a desired shaft support bearing preload direction and intensity, for example to exert axial thrust or radial preloads on the support bearings. A plurality of magnetic bearings may be oriented in opposed relationship with neutral or offsetting resultant forces. The passive magnetic force preload may be utilized to offset rotor vertical weight during induction startup or stopping cycles. Passive magnetic force preload may be applied to lubricated bearings to assure their operational stability. The passive magnetic bearings can also absorb radial or axial thrust forces imparted on the rotor shaft during induction machine operation, that may reduce machine operational noise, and energy consumption.

Description:
BACKGROUND OF THE DISCLOSURE 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to induction machine and other rotating equipment bearings and more particularly methods and apparatus for exerting preload bias forces on induction machine lubricated or active magnetic bearings that support rotating shafts, through use of passive, permanent magnet bearings. 
         [0003]    2. Description of the Prior Art 
         [0004]    Known rotating equipment and induction machines, such as motors, often utilize lubricated mechanical bearings to support a rotating rotor. Exemplary lubricated bearing types include rolling element anti-friction bearings (e.g., ball- or roller-type) wherein the rolling elements are lubricated by a non-pressurized boundary film layer between the element and its associated bearing race, hydrodynamic journal or thrust bearings that generate self supporting pressurized lubricant films and hydrostatic bearings that employ externally pressurized lubricant. 
         [0005]    During motor or other rotating machine starting or stopping the rotor shaft may not be supported by a lubricating film within a lubricated bearing, possibly resulting in bearing rotational instability and/or premature bearing/shaft wear. One past solution has been application of auxiliary pressurized “oil jacking” systems to introduce pressurized lubricant to the bearings during induction machine starting or stopping cycles, analogous to a hydrostatic bearing. Such auxiliary systems add installation and maintenance expense to a machine installation, and may not be cost effective for smaller machines. In the past active magnetic bearings that require an electrical power supply to generate a levitation field have been used as replacements for or in conjunction with lubricated bearings in some high power output induction machines. 
         [0006]    During normal motor operation, changes in driven shaft load or operating speed or lack of sufficient damping at the rotor shaft and bearing interface may cause lubricating film instability in the lubricated bearings. For example, rolling elements in anti-friction bearings may skid rather than roll relative to the corresponding bearing race, resulting in flat spots on the rolling element or bearing race scoring. In another example, oil slingers used to supply lubricant to bearings may fail to transfer sufficient quantities of lubricant if they lose contact with its corresponding rotor shaft journal. In another example, damping may be reduced below a useable threshold due to insufficient loading and/or high circumferential speed. 
         [0007]    In the past active magnetic bearings have been used as the primary support bearings, in parallel with secondary support lubricated bearings in the event of magnetic bearing failure as in the case of a power loss. In these applications the active magnetic support bearings have exerted damping and or stiffening forces on spinning rotors that employ the secondary support lubricated bearings. However, the manufacture and operational costs and complexity of active bearings as compared to those of traditional lubricated bearings are not suitable for all induction machine applications. Additionally, systems which employ magnetic bearings must supply energy to the system to levitate the rotor against gravitational forces. 
         [0008]    Thus, a need exists in the art for a method and apparatus that selectively apply desired oriented preload force direction and magnitude on induction machine lubricated bearings, in order to reduce machine wear during starting and stopping cycles. 
         [0009]    Another need exists in the art for a method and apparatus that selectively apply desired oriented preload force direction and magnitude on induction machine lubricated bearings, in order to enhance bearing stability during machine operation, including transient machine operation, and in order to reduce bearing noise emission. 
         [0010]    Yet another need exists in the art for a method and apparatus that passively and selectively apply desired oriented preload force direction and magnitude on induction machine lubricated bearings, without the need for external power sources and energy consumption associated with active magnetic bearings. 
         [0011]    Yet another need exists in the art for a method and apparatus capable of reducing active magnetic bearing noise emission, and/or eliminate or reduce the need of additional lubricated bearings as secondary, back up bearings in the event of an active magnetic bearing failure. 
       SUMMARY OF THE INVENTION 
       [0012]    Accordingly, an object of the invention is to realize a method and apparatus to passively apply preload force on induction machine lubricated bearings in desired direction and magnitude, in order to reduce machine wear during starting and stopping cycles, and in order to enhance lubricated bearing stability during machine operation, including transient machine operation, and to reduce bearing energy consumption or frictional losses as well as noise emission. 
         [0013]    These and other objects are achieved in accordance with the present invention by incorporation of permanent magnet bearings in rotating machines, including induction machines, in addition to lubricated or active magnetic shaft support bearings. The permanent magnet bearings incorporate permanent magnets that generate directionally oriented magnetic fields of selective intensity. The magnetic field directions are aligned with a desired support bearing (whether lubricated or active magnetic bearing) preload direction and intensity, for example to exert axial thrust or radial preloads on the support bearings. By application of a plurality of magnetic bearings their respective magnetic forces may be oriented in opposed relationship with canceled or offsetting resultant forces. The passive magnetic preload may be utilized to offset rotor vertical weight during induction startup or stopping cycles. Passive preload may be applied to rolling element bearings to assure proper element contact with its corresponding bearing race, or to assure that oil slingers maintain sufficient lubricant film stability for transport of lubricant to bearings (as opposed to undesired oil whip or oil whirl instabilities that can potentially lead to bearing failure. The passive magnetic bearings can also absorb radial or axial thrust forces imparted on the rotor shaft during induction machine operation, that can help reduce noise emissions generated at the support bearing/shaft interface. 
         [0014]    The present invention features an induction machine apparatus, including a machine housing and a bearing housing coupled to the machine housing. A stator is in the machine housing and a rotor is in turn oriented within the stator. The rotor has a rotor shaft rotatively captured in the bearing housing. A support bearing that is a lubricated bearing or an active magnetic bearing is in the bearing housing and rotatively captures the rotor shaft. A permanent magnet bearing is coupled to the machine housing, and exerts a directional magnetic force on the rotor shaft that generates a desired intensity and magnitude preload force on the support bearing. The magnetic force preload on the rotor and support bearing may be oriented axially, radially, sideways, up or down in any desired direction or intensity. Solid or laminated electrical steel may be positioned proximal the permanent magnet in order to orient and/or vary intensity of the generated magnetic force. 
         [0015]    The present invention also features an induction machine or other rotating machine apparatus, including a machine housing and a bearing housing coupled to the machine housing. A stator is in the machine housing, along with a rotor oriented within the stator. The rotor has a rotor shaft that is rotatively captured in the bearing housing by a support bearing that is a lubricated or active magnetic bearing. A permanent magnet bearing is located in the bearing housing in tandem with the support bearing. The magnetic bearing has a permanent magnet oriented in opposed spaced relationship with the rotor shaft and exerts a directional magnetic force thereon. Electrical steel laminations are oriented proximal the permanent magnet for orienting the magnetic force exerted on the shaft. The permanent magnet bearing directional magnetic force generates a desired intensity and magnitude preload force on the support bearing. 
         [0016]    The present invention also features a method for preloading bias force on a support bearing (whether an active magnetic or a lubricated bearing) in an induction or other rotating machine that has a machine housing; a bearing housing coupled to the machine housing; a stator in the machine housing; a rotor oriented within the stator, having a rotor shaft rotatively captured in the bearing housing by a support bearing that is an active magnetic or a lubricated bearing. In this method the preload bias force is performed by providing a permanent magnet bearing that generates a directional magnetic force; coupling the permanent magnet bearing to the induction machine proximal the rotor; and orienting the permanent magnet bearing so that its directional magnetic force is exerted on the rotor shaft and generates a desired preload force intensity and direction on the shaft support bearing. A plurality of permanent magnet bearings may be coupled to the induction machine and oriented to generate opposed preload forces on the active magnetic or lubricated support bearing, with neutral or offsetting combined resultant preload force. 
         [0017]    The objects and features of the present invention may be applied jointly or severally in any combination or sub-combination by those skilled in the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
           [0019]      FIG. 1  is a schematic cross-sectional elevation of an induction machine with a horizontally oriented rotor rotational axis, incorporating embodiments of the passive magnetic bearings of the present invention; 
           [0020]      FIG. 2  is an elevational view of a journal bearing embodiment of a passive magnetic bearing of the present invention within a bearing housing; 
           [0021]      FIG. 3  is a perspective view of the bearing embodiment of  FIG. 2  without a bearing housing; 
           [0022]      FIG. 4  is a schematic elevational view of an embodiment of the bearing of  FIG. 2 , applying an upwardly biasing preload on a horizontal rotational axis rotor; 
           [0023]      FIG. 5  is a schematic elevational view of an embodiment of the bearing of  FIG. 2  applying a upwardly biasing preload on a horizontal rotational axis rotor; 
           [0024]      FIG. 6  is a schematic elevational view of an embodiment of the bearing of  FIG. 2 , with a pair of opposed bearings applying opposing upwardly and downwardly oriented offsetting resultant biasing preload on a horizontal rotational axis rotor; 
           [0025]      FIG. 7  is a perspective view of an axial flux, radial force bearing embodiment of a passive magnetic bearing of the present invention, within a bearing housing that is shown in phantom; 
           [0026]      FIG. 8  is a side elevational view of the bearing embodiment of  FIG. 7 ; 
           [0027]      FIG. 9  is a schematic elevational view of an embodiment of the bearing of  FIG. 7 , with a pair of opposed bearings applying upward radially oriented offsetting resultant biasing preload on a horizontal rotational axis rotor; 
           [0028]      FIG. 10  is a schematic cross-sectional elevation of an induction machine with a vertically oriented rotor rotational axis, incorporating embodiments of the passive magnetic bearings of the present invention; 
           [0029]      FIG. 11  is a perspective view of an alternative embodiment of an axial thrust bearing embodiment of a passive magnetic bearing of the present invention as incorporated into the vertically oriented rotor shaft induction machine of  FIG. 10 ; and 
           [0030]      FIG. 12  is a schematic elevational view of an embodiment of the passive magnetic bearings of the present invention as incorporated into the vertically oriented rotor shaft induction machine of  FIG. 10 , with pairs of opposed bearings of  FIG. 2  applying opposing radially oriented (horizontal) offsetting resultant biasing preload and a bearing of  FIG. 11  applying an upwardly directed biasing preload on a vertical rotational axis rotor. 
       
    
    
       [0031]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
       DETAILED DESCRIPTION 
       [0032]    After considering the following description, those skilled in the art will clearly realize that the teachings of the present invention can be readily utilized in induction machines, such as motors, in order to apply biasing preloads of any desired magnitude and direction to their active magnetic or lubricated shaft support bearings without external energy sources. For example, the passive magnetic bearings of the present invention do not need external electrical power sources to generate magnetic fields as is required for known active magnetic bearings. Similarly, auxiliary pressurized lubrication systems are not needed to create lubricated bearing preload biasing forces, as is required in known “oil jacking” solutions for hydrodynamic and rolling element bearings or known hydrostatic bearings. The permanent magnetic bearings may be substituted for or supplement secondary support lubricated bearings that are used in tandem with primary active magnetic support bearings in case of failure of or loss of electrical power to the active magnetic primary support bearing. 
         [0033]      FIG. 1  schematically depicts an induction machine motor  20 , having a motor housing  22 , a stator  24  and a horizontally oriented rotor  26 . The rotor  26  is rotatively mounted in the motor housing by rotor shaft  28 , captured within a pair of bearing housings  30 . Each bearing housing  30  has a shaft support bearing assembly  32 , which may incorporate a known active magnetic bearing and/or a known lubricated bearing. Henceforth in this description reference will be made to lubricated support bearings, but it should be understood that active magnetic bearings may be substituted for them. The lubricated bearing may be a known radial journal bearing, an axial thrust bearing or both. The lubricated bearing  32  may be any known lubricated bearing, including by way of example rolling element anti-friction bearings, hydrodynamic bearings or hydrostatic bearings. A plurality of radially oriented permanent magnet bearings  40  are incorporated as part of the motor  20 . As shown, the permanent magnet bearings  40  are located within the bearing housings  30  in tandem with the lubricated bearings  32 , and exert magnetic force directly on the rotor shaft  28 . Permanent magnet bearings  40  are also incorporated within the stator  24  and exert magnetic force on the rotor  26  laminations. The rotor  26  laminations are affixed to and transfer magnetic force to the rotor shaft  28 . In either magnetic bearing  40  location, resultant magnetic forces generated by the permanent magnet bearings are imparted on the rotor shaft and in turn into the lubricated bearings  32 , whether those magnetic bearings are incorporated in the bearing housing  30  or stator  24  or both. 
         [0034]      FIGS. 2 and 3  show an exemplary permanent magnetic bearing  40  mounted in a bearing block housing  30  that circumscribes the rotor shaft  28 . The bearing  40  includes a sector-shaped permanent magnet  40  that has a radial circumference of less than 180°, and preferably between approximately 40° and 60°. The magnet  42  is mounted within the stationary bearing block  30  a spaced distance from the spinning rotor shaft  28 . The permanent magnet  42  may be composed of known permanent magnet materials, including but not limited to neodynium iron boron, Samarium cobalt, Alnico, ferrite, ceramics, as well as other metal alloys or composite materials. Permanent magnet material  42  must be selected for the appropriate operating temperature and may be selected from any of the known grades of magnets. The permanent magnet  42  may be more compact where using stronger magnets, which would be indicated by a high maximum B-H product. A sector-shaped stationary ferromagnetic core of electrical steel  44  envelops the outer diameter of the permanent magnet  42 , also within the bearing block  30  a spaced distance from the spinning rotor shaft  28  and with a radially-spaced gap  43  flanking both sides of the permanent magnet  42 , in order to assist with directional orientation of the magnetic field flux lines generated by the permanent magnet. The ferromagnetic core  44  is preferably constructed of a lamination stack oriented parallel to the axial ends of the permanent magnet  42 . The ferromagnetic core  44  axial and radial dimensions may be altered at the discretion of one skilled in the art. For example, while the core  44  is shown as semi-circular, it can be constructed as a full annular shaped core of 360°. Similarly, the axial length of the core  44  can be less than or greater than the length of the permanent magnet  2 . 
         [0035]      FIGS. 4-6  show application of the permanent magnet bearing  40  to provide different preload orientations on rotor shaft  28  that in turn will cause the same preload orientations on the lubricated bearings (or alternatively active magnetic bearings) that are supporting the shaft. For simplicity of these figures, the lubricated bearings and other structural components of the induction machine are not shown. In  FIG. 4 , the magnetic field flux lines (and hence the magnetic force orientation) of the sector shaped permanent magnet  40  are radially outwardly directed by circumferential angle α, in an upwardly direction relative to the rotational axis of rotor shaft  28  (denoted by radius r). Due to the orientation of the flux lines, the flux density is greatest in the upper region. Hence as shown in  FIG. 4  the preload force (denoted by the arrows F mu ) is upwardly directed. In contrast the magnetic field flux of the permanent magnet  40  of  FIG. 5  is downwardly directed, (i.e., attracting the rotor shaft) the pre-load forces however remain unchanged (denoted by the arrows F mu ). In  FIG. 6  a pair of opposed permanent magnets  42 A,  42 B generate opposing preload forces denoted by F mu  and F md . The resultant force (F mu +F md ) can be tuned by selection of respective field intensities and directional orientation, though generally in a horizontally oriented rotor shaft induction machine the upward preload is greater than or equal to the downward preload. Additionally, since the forces generated are inversely related to their proximity between the rotor and stator, each magnet contributes a negative stiffness at this region to the rotordynamic operation of the system. The direction and magnitude of this negative stiffness can be tuned to counterbalance that of the primary bearing system, approaching a free-free condition. This effect can be positively applied to a system to attain higher rotor lateral critical speed. While two opposed magnetic bearings with permanent magnets  42 A and  42 B are shown in  FIG. 6 , a plurality of two or more such bearings can be combined at the discretion of one skilled in the art, depending on the desired preload force to be generated and the physical dimensional constraints of the induction machine. 
         [0036]      FIGS. 7 and 8  show a permanent magnet bearing  50  embodiment that generates axially oriented magnetic flux and attractive (upwardly directed) preload forces on a rotor shaft  26 . For simplicity of  FIG. 7  the bearing mounting block  30  is shown in phantom lines. The permanent magnet bearing  50  has a stationary permanent magnet  52  that has a generally rectangular block shape, and generates magnetic force in an axial direction relative to the shaft  26 . However, the permanent magnet  52  may also be constructed of any other desired shape, including the sector shape of that shown in  FIG. 2 . The magnet  52  is spaced a distance away from the spinning rotor shaft  28 . A pair of electrical steel cores  54  flank the axial ends of the permanent magnet  52  and are affixed in a stationary position within the bearing block, spaced from the spinning rotor shaft  28 . The cores  54  shape the magnetic field generated by the permanent magnet  52 , and are preferably constructed of a lamination stack oriented parallel to the axial ends of the permanent magnet. Additional magnetic field shaping may be accomplished by placement of an electrical steel core  56  in a fixed position directly on the rotor shaft  28 , and thereby rotating with the shaft. If the axial preload permanent magnetic bearing is located in the induction machine stator  24 , the rotor  26  laminations may serve as the rotating steel core  56 . 
         [0037]    In  FIG. 9  a pair of permanent magnet axially oriented magnetic field preload bearings  50  are incorporated in an induction machine to impart tandem upwardly directed preloads F mu  on the rotor  26  through use of a pair of opposed permanent magnets  52 A and  52 B. As in the case of radially oriented preload permanent magnetic bearings  40  of  FIG. 2 , the number and location of bearings and resultant preload force (here in  FIG. 9  the resultant of F mu  on each side of the shaft) may be selected by one skilled in the art. 
         [0038]    In  FIG. 10  the vertical shaft induction machine  120  has a machine housing  122  including stator  124  and vertically oriented rotor  126  having a rotor shaft  128  that is rotatively captured in bearing housings  130  and  130 A. Each of the bearing housings  130 ,  130 A have lubricated journal bearings  32 , as well as radially oriented permanent magnet bearings  40 , such as those shown in  FIG. 2 . The bearing housing  130 A also includes axial thrust bearings to support the weight of the spinning rotor  126  that are shown as lubricated thrust bearing  132 A of known construction, and permanent magnet thrust bearing  150 . As shown in  FIG. 10  the rotor shaft  126  includes a thrust flange  127  that abuts against and provides a journal surface for the lubricated thrust bearings  132  and the lubricated journal bearings  32 . The rotor thrust flange  127  as shown also includes an optional electrical steel flange-like insert  156 . 
         [0039]    The permanent magnet axial thrust bearing embodiment  150  is shown in  FIG. 11 , and includes a mounting bracket formed in the bearing housing  130 A. An annular shaped permanent magnet  152  circumscribes the rotor shaft  128  and generates an upwardly directed magnetic field that is shaped by electrical steel core  152  and the electrical steel core  156  that is affixed to the rotating shaft  128 . The electrical steel core  156  is formed with a hub portion  155 A that is concentric with and spaced away from the inner diameter of the permanent magnet  152  and a flange portion  155 B radially projecting from the hub portion and in abutting contact with an axial face of the permanent magnet. 
         [0040]    The permanent magnet axial thrust bearing  150  can be used in applications other than to support weight of a vertically oriented rotor shaft. For example, they may be applied to horizontally oriented shaft rotors directly on the shaft as a substitute for the embodiment  50  shown in  FIGS. 7 and 8 . Alternatively they may be applied to the rotor laminations as is shown in the induction machine embodiment of  FIG. 1  by orienting the mounting bracket proximal and parallel to one or both ends of the rotor  26  lamination stack. In such an application the rotor laminations substitute for the electrical steel core  156 . 
         [0041]      FIG. 12  schematically depicts the magnetic fields and resultant magnetic forces F r , F u  that are imparted on the vertically oriented rotor  126 . As with other embodiments described herein, the resultant preload forces magnitudes and directions imparted on the vertical rotor shaft  128  can be selectively chosen for any given application. 
         [0042]    Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.