Abstract:
An adjustable coupler has a group of magnet rotors with permanent magnets separated by air gaps from non-ferrous conductor rotors presented by a group of conductor rotors. One of the rotors is mounted to its shaft via a slidable hub. The hub and the rotor attached thereto rotate with the shaft, but are movable lengthwise along the shaft. The air gaps are adjusted by axial movement of the hub and one of the groups relative to the other to vary the slip of the coupler and control the load speed under varying load conditions.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to permanent magnet couplers of the type having a magnet rotor on one shaft adjustably spaced from a conductor rotor on another shaft. More particularly, the invention relates to mounting the adjustable rotor to its respective shaft.  
         BACKGROUND OF THE INVENTION  
         [0002]    Induction motors are used, for example, to drive fans, blowers, pumps and compressors. It has been recognized that when these motors are operated at full speed they normally have excess capacity as compared to the load requirements, and this excess capacity is compounded when the load is variable. It has also been recognized that if the output of the motors could be adjusted to provide only the needed power, a significant reduction of energy usage would result. Hence, variable speed drives (VSD&#39;s) have been developed in the form of electronic devices which match motor speed to that required for a given application. A typical VSD rectifies incoming AC voltage and current into DC, then inverts the DC back to AC at a different voltage and frequency. The output voltage and frequency is determined by the actual power needs and is set automatically by a control system or by an operator.  
           [0003]    Heretofore, VSD&#39;s have generally been so expensive that they have not been used extensively for energy savings. It has been reported that VSD&#39;s require the availability of highly trained maintenance personnel and shorten motor life.  
           [0004]    U.S. Pat. No. 5,477,094 (the &#39;094 patent) shows a magnetic coupler in which a magnet rotor unit is straddled by two conductor rotors which are connected together to rotate as a conductor rotor unit on one shaft while the magnet rotor unit is mounted to rotate on a second shaft. The magnet rotor unit has a set of permanent magnets arranged with their opposite poles spaced by air gaps from ferrous-backed electroconductive rings mounted on the respective conductor rotors. Rotation of one of the two shafts results in rotation of the other shaft by magnetic action without there being any direct mechanical connection between the shafts.  
           [0005]    The &#39;094 patent also discloses the concept of having two magnet rotors rather than a single magnet rotor unit, with each magnet rotor having a respective set of permanent magnets spaced by an air gap from one of the electroconductive elements presented by the conductor rotors. The two magnet rotors are axially moveable relative to one another and are spring biased apart.  
           [0006]    In U.S. Pat. No. 6,005,317 (the &#39;317 patent), the magnet rotors are positively positioned relative to each other such as to vary their axial positions automatically at will from a remote control location to provide by air gap adjustment a variable torque from a constant speed motor to a variable torque load operating at a lower constantly maintained speed.  
           [0007]    Instead of spring biasing the two magnet rotors as in the &#39;094 patent, the positions of the magnet rotors in the &#39;317 patent are controlled from a stationary control mechanism which communicates with an adjusting mechanism operating on the magnet rotors to selectively move them toward one another to widen the air gaps or to move them further apart to narrow the air gaps. Gap adjustment varies the rotational slip between the magnet rotor units and the conductor rotor units for a given torque load and hence affects the speed of the load. For a given torque load the air gaps can be adjusted to provide the torque at a preset rotational speed differential below the speed of the motor.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention is directed toward adjustable magnetic couplers in which a magnet rotor and a conductor rotor are positioned in proximity with each other such that rotation of one rotor results in rotation of the other. A hub is engaged with a first shaft, and is configured to slide with respect to the first shaft but not rotate with respect to the first shaft. Consequently, as the first shaft rotates, the hub rotates with it. The magnet rotor is coupled to the hub and the conductor rotor is coupled to a second shaft, or vice versa. The rotors are configured to rotate with the respective shaft. A push-pull mechanism is rotatably coupled to the hub such that the push-pull mechanism maintains stationary even when the first shaft and the hub rotate. The push-pull mechanism is operative to move the hub and the rotor attached thereto axially along the first rotary shaft. Axial movement of one rotor with respect to the other rotor changes the distance between the magnet rotor and the conductor rotor, altering the performance of the coupler.  
           [0009]    In another embodiment of the present invention, a pair of adjustable rotors are spaced from a fixed rotor assembly, and are adjustable through the use of a push-pull mechanism similar to that discussed above. A first adjustable rotor is linked to the second adjustable rotor such that movement of one rotor results in movement of the other. In one particular embodiment, movement of the hub and the first adjustable rotor in one direction results in a corresponding movement of the second adjustable rotor in an opposite direction. Accordingly, movement of the first adjustable rotor results in an adjustment of the spacing between both adjustable rotors and a third, fixed rotor. As the adjustable rotors are configured with magnets and the fixed rotor configured with an electroconductive ring, or vice versa, adjustment of the spacing between the three rotors results in an adjustment to the performance of the system.  
           [0010]    In yet another embodiment of the present invention, the adjustable magnetic coupler comprises two fixed rotors and two adjustable rotors. The fixed rotors are coupled to a shaft to rotate with the shaft, but are not permitted to move axially along the shaft. The adjustable rotors, on the other hand, are movable in an axial direction with respect to the shaft, but are not permitted to rotate with respect to the shaft. One of the adjustable rotors is mounted on a slidable hub. The adjustable rotors are linked together such that axial movement of one adjustable rotor results in a corresponding axial movement of the other adjustable rotor. Consequently, adjustment by a push-pull mechanism of the hub and one adjustable rotor results in a corresponding adjustment of the other adjustable rotor. Using the push-pull mechanism, the first and second adjustable rotors can be spaced by a desired distance from the respective first and second fixed rotors, modifying the performance of the magnetic coupler system. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a longitudinal sectional view of a magnetic coupler according to an embodiment of the invention, shown in a narrow gap position, viewed along Section  1 - 1  in FIG. 5.  
         [0012]    [0012]FIG. 2 is a perspective view of the magnetic coupler of FIG. 1 without the conductor rotors.  
         [0013]    [0013]FIG. 3 is a plan view corresponding to FIG. 2.  
         [0014]    [0014]FIG. 4 is a plan view like FIG. 3, but with the gap adjustment mechanism retracted so that the magnet rotors are in a wide gap position.  
         [0015]    [0015]FIG. 5 is a transverse sectional view of the portion of the magnetic coupler of FIG. 4, viewed along Section  5 - 5 .  
         [0016]    [0016]FIG. 6 is a left end view of the portion of the magnetic coupler of FIG. 2.  
         [0017]    [0017]FIG. 7 is a perspective view of the portion of the magnetic coupler of FIG. 2 wherein the magnet rotor in the forefront has been removed. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    The present invention is generally directed toward magnetic couplers in which a first rotating shaft transfers rotational energy to a separate, second rotating shaft. In particular, the present invention is directed toward a system which allows one rotor to be axially adjusted with respect to the other rotor to modify the performance of the magnetic coupler. Many specific details of certain embodiments of the invention are set forth in the following description and in FIGS.  1 - 7  to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments, or may be practiced without several of the details described in the following description.  
         [0019]    [0019]FIG. 1 illustrates a magnetic coupler  10  according to one embodiment of the present invention. An input shaft  20  and an output shaft  21  have mounted thereon a conductor rotor unit  22  and a pair of magnet rotors  24 / 25 , respectively. The conductor rotor unit  22  has two axially spaced conductor rotors  26 / 27  having respective conductor rings  28 / 29  facing toward one another and formed from a non-ferrous material with high electrical conductivity, such as copper. The conductor rotor unit  22  is mounted on a conductor hub  36 . Conductor rotor  27  is spaced apart from the output shaft  21  (and the assembly attached thereto, discussed below) by an annular clearance space  40 . The hub  36  is mounted on the input shaft  20 , such as by a wedge-type coupling or a key connection.  
         [0020]    Each of the magnet rotors  24 / 25  has a non-ferrous mounting disc  42  backed by a ferrous backing disc  43 , preferably of mild steel. The mounting discs  42  may be aluminum or a suitable non-magnetic composite, and each is formed with a set of spaced cutouts  44  arranged in a circle and receiving a respective set of permanent magnets  46  seated against the respective backing disc  43 . Adjacent magnets may have their polarities reversed. The magnets  46  are spaced by air gaps  32 / 33  from the conductor rings  28 / 29  of the conductor rotor unit  22 .  
         [0021]    The conductor rotors  26 / 27  can be formed with ventilation holes or similar features to assist in the circulation of air through the air gaps  32 / 33  for cooling the conductor rings  28 / 29 . Cooling air for the conductor rings  28 / 29  is free to enter the air gaps  32 / 33  from the clearance space  40 .  
         [0022]    In accordance with the illustrated embodiment of the present invention, the magnet rotors  24 / 25  are mounted so as to rotate in unison with the output shaft  21 , and also to be axially moveable relative to one another in opposite axial directions for adjustment of the air gaps  32 / 33 . To this end, magnet rotor  24  is fixedly coupled to a hub  50  that is engaged with the output shaft  21  to slide along the length of the output shaft, but not to rotate with respect to the output shaft. The hub  50 , and with it the magnet rotor  24 , are thus movable axially to adjust air gap  33 . Magnet rotor  25  is slidably engaged with a bushing  47  at a distal end of the output shaft  21  to move axially with respect to the output shaft, but not to rotate with respect to the output shaft. Axial movement of magnetic rotor  25  with respect to output shaft  21  changes the air gap  32 .  
         [0023]    A push-pull means  61  is provided to move the magnet rotors  24 / 25  axially along a rotary axis of the output shaft  21  in opposite directions to vary the width of the air gaps  32 / 33 . The push-pull means  61  comprises a barrel element  63 , an inner barrel  62 , and the hub  50  for axially moving the magnet rotor  24 , and a mechanism linked between the magnet rotors for moving the magnet rotor  25  in response to movement of the magnet rotor  24 . In the illustrated embodiment, the second mechanism includes a fifth rotor  52  and pins  51  (FIG. 7).  
         [0024]    As best illustrated in FIGS. 5 and 7, the fifth rotor  52  in the illustrated embodiment is generally triangle-shaped in elevation providing three outer edge faces  52   a , each of which has a central ear  53  projecting radially therefrom. The ears  53  are formed with radial bores extending toward the shaft  21  to receive fasteners  54  on which bushings or bearings  55  are sleeved (FIG. 5). The bearings  55  receive center hub portions of swing units  56 , each pivotally attached to a link  57 , which is in turn pivotally attached to a flange  58  (FIG. 7). The flanges  58  may be mounted on the discs  42  by cap screws  60   a  (FIG. 7). For each assembly, one flange  58  is attached to one of the magnet rotors  24 / 25  and an opposing flange is attached to the other magnet rotor. Consequently, when the first magnet rotor  24  moves axially, the magnet rotor and the flange  58  move the adjacent link  57 , which in turn rotates the swing unit  56 , which in turn urges the opposing link  57  to move the other magnet rotor  25 . Consequently, axial movement in a first direction by magnet rotor  24  results in axial movement in an opposing second direction by magnet rotor  25 . In the illustrated embodiment, the bearing  55  is located in the center of the swing unit  56 . Consequently, the amount of movement by the second magnet rotor  25  is the same as the amount of movement by the first magnet rotor  24 .  
         [0025]    When the magnet rotor  24  is pushed away from the conductor rotor  27  to increase the width of the air gap  33 , the other magnet rotor  25  is pulled toward the fifth rotor  52 , increasing the width of the air gap  32 . Likewise, when the magnet rotor  24  is pulled toward the conductor rotor  27  to narrow the width of the air gap  33 , the other magnet rotor  25  will be pushed toward the conductor rotor  26  and narrow the air gap  32 .  
         [0026]    As best illustrated in FIGS. 1 and 3, pushing and pulling of the magnet rotor  24  to vary the width of the air gaps  32 / 33  can be accomplished by using a barrel cam  61  which has an inner barrel element  62  partially overlapped by the barrel element  63 . The inner barrel element  62  is mounted by a first bearing unit  64  on the output shaft  21  and the outer element  63  is mounted by a second bearing unit  66  to the hub  50 . The output shaft  21  and hub  50  can thus rotate with respect to the barrel cam  61 . The barrel element  63  has a groove  70  which engages a sliding block  71  (FIG. 3) coupled to the inner barrel element  62 . A first arm  72  is attached to the inner barrel  62  and a second arm  73  (FIG. 1) is attached to the outer barrel  63 . Relative movement of the first and second arms  72 / 73  results in barrel cam  61  moving the hub  50  axially with respect to the output shaft  21 .  
         [0027]    Axial movement of the outer barrel  63  acts through the second bearing  66  to correspondingly push or pull the magnet rotor  24 . As before described, this results in equal endwise motion of the other magnet rotor  25  in the opposite direction by responsive operation of the swing arms  56 . Thus, selective relative movement of the first and second arms  72 / 73  results in varying the air gaps  32 / 33 , and thereby varies the output speed of the magnetic coupler  10 . The first and second arms  72 / 73  may, for example, be connected to a stationary electric rotary positioner which is controlled by a process controller. If, for example, the load is a pump whose flow output is to be controlled, a measuring device in the output stream feeds the output data to the process controller which then signals the rotary positioner for the required rotary movement of the first or second arm  72 / 73  to properly adjust the output speed of the magnetic coupler.  
         [0028]    The output shaft  21 , rather than being the actual input shaft of the load, can be an add-on shaft section as shown in FIG. 1. This add-on section of output shaft  21  is connected at a distal end portion  21   a  to the fifth rotor  52  via an end plate  80  which covers the inner end face of the add-on section of output shaft  21 , and bushing  47  which extends between the end plate and the fifth rotor. A bolt  82  connects the end plate  80  to the shaft  21 .  
         [0029]    The shaft  21  expands from the necked portion  21   a  to an intermediate cylindrical portion receiving the hub  50 , and then is formed with an annular shoulder  21   c  against which the inner race of the first bearing  64  is seated. The coupler  86  has a complementary adapter hub component  86   b  with a neck  86   c  sized to receive the actual input shaft  21  of the load. A wedge-type squeeze unit  87  is sleeved on the coupler neck  86   c  to force fit the coupler  86  to the shaft  21  responsive to tightening of screws  89 . The hub components  86   a  and  86   b  of the coupler  86  are secured together by bolts  88 . A squeeze unit similar to unit  87  can also be used to secure hub  36  to the shaft  20 .  
         [0030]    The described arrangement incorporating the shaft section  21  and coupler  86  makes it possible to easily install or remove the magnetic coupling  10  of the present invention without moving the load and its related input shaft  21  or the prime motor and its shaft  20 . The structure also allows the magnetic coupler  10  to be used with loads or motors having varying shaft sizes. By replacing flange  86  with a reducing flange or an oversized flange, the same magnetic coupler  10  can be used in more situations.  
         [0031]    The present invention has numerous advantages over magnetic couplers of the prior art. For example, because the first magnet rotor  24  is attached to the hub  50  and the hub is attached to the output shaft  21 , the magnet rotor is more stable than in prior versions where a bearing was situated between the magnet rotor and the output shaft. The close relationship between the magnet rotor  24 , the hub  50 , and the output shaft  21  results in improved concentricity and reduced angular deflection of the magnet rotor out of its operating alignment. Also, because the hub  50  rotates with the output shaft  21 , the relative rotation between the parts is transferred to one of the bearings  64 / 66 . It is thus less likely that adjacent parts will make contact during operation, contact which would result in either seizing or extreme wear.  
         [0032]    Still further, the pivotal couplings between the first and second magnet rotors  24 / 25  remove all torsional forces from the coupling and, as a result, from the magnet rotors. Also, pivoting couplings, as opposed to sliding couplings, will result in less wear and are less likely to be impeded or blocked in their travel. For each of these reasons, the relative motion between the magnet rotors  24 / 25  may experience less resistance.  
         [0033]    From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.