Abstract:
A drive hub is mounted to an element and has a surface which presents away from the element and produces a magnetic field which extends from and returns to the drive hub. If depicted graphically, concentrations of field lines would appear to extend from two or more North domains defined in the surface to two or more South domains defined in the surface, the North and South domains being arranged to encircle a rotation axis in spaced alternating relation. A driven hub is spaced and frontwardly adjacent to drive hub, coupled to the element and constrained against movement but for axial rotation. Driven hub includes non-magnetic, electrically-conductive material having low magnetic permeability and receptors, receptors having a high magnetically permeability, being spaced to the axis and arranged such that rotation of the drive hub relative to the driven hub creates a net rotational force that urges co-rotation of the hubs.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 61/623,649 filed Apr. 13, 2012, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of couplings. 
     BACKGROUND OF THE INVENTION 
     It is known to provide for a magnetic coupling between an impeller and a motor in the context of foot spa units. In known couplings, high performance permanent magnets are used in pairs. 
     SUMMARY OF THE INVENTION 
     Forming one aspect of the invention is apparatus for coupling a rotating element to a rotatable element, the rotating element rotating around a rotation axis. This apparatus comprises a drive hub and a driven hub. The drive hub: in use, is mounted to the rotating element for rotation therewith about the rotation axis; has a front surface which presents away from the rotating element in use; and has magnetic properties such that, in the absence of externalities, a magnetic field is produced which extends from and returns to the drive hub, the magnetic field being characterized in that, if depicted graphically, concentrations of field lines would appear to extend from two or more North pole domains defined in the front surface to two or more South pole domains defined in the front surface, the North and South pole domains being spaced apart from each other and arranged to encircle the rotation axis in alternating relation. The driven hub: in use, is disposed in spaced, frontwardly adjacent relation to the drive hub, is fixedly coupled to the rotatable element and is at least substantially constrained against movement but for rotation, with the rotatable element, about the rotation axis; and includes a rotor body of a non-magnetic, electrically-conductive material having relatively low magnetic permeability and a plurality of receptors, the receptors being made at least in part of material having a relatively high magnetically permeability and arranged in spaced relation to the rotation axis. The receptors are arranged such that rotation of the drive hub relative to the driven hub creates a net rotational force on the driven hub that urges the driven hub to rotate in the same direction as the drive hub. 
     According to another aspect of the invention, the receptors can provide for magnetic field lines that pass through the rotor body in a manner such that, in the aggregate, the through-passing field lines are dominated by field lines that extend through the rotor body in a direction that is substantially tangential to the direction of rotation. 
     According to another aspect of the invention, each of the North pole domains can be defined by a respective permanent magnet and each of the South pole domains can be defined by a respective permanent magnet. 
     According to another aspect of the invention, the number of North pole domains can equal the number of South pole domains. 
     According to another aspect of the invention, in use, the permanent magnets can be equally spaced about the rotation axis. 
     According to another aspect of the invention, the drive hub can have a backer plate defined by a material having relatively high magnetic permeability. 
     According to another aspect of the invention, the drive hub can have a backer plate defined by a ferromagnetic material. 
     According to another aspect of the invention, the drive hub can have a backer plate defined by an iron alloy. 
     According to another aspect of the invention, the rotor body can be made of a paramagnetic material. 
     According to another aspect of the invention, the rotor body can be made of an aluminum alloy. 
     According to another aspect of the invention, the receptors can be made from a ferromagnetic material. 
     According to another aspect of the invention, the receptors can be made of an iron alloy. 
     According to another aspect of the invention, the driven hub can have a face disk defined by a material having relatively high magnetic permeability, the face disk being coupled to the rotatable element in use. 
     According to another aspect of the invention, the face disc can be made of a ferromagnetic material. 
     According to another aspect of the invention, the face disc can be made of an iron alloy. 
     According to another aspect of the invention, R can equal N+S−1 or N+S+1 wherein 
     N=the number of North pole domains; 
     S=the number of South pole domains; and 
     R=the number of receptors. 
     According to another aspect of the invention, N can be 2, S can be 2 and R can be 3. 
     According to another aspect of the invention, the permanent magnets can be disc-shaped. 
     According to another aspect of the invention: each receptor can include a rod-shaped primary receiver; the primary receivers can be equally spaced from one another about the rotation axis; and the distance from the centre of each primary receiver to the rotational axis can be at least substantially equal to the distance between the centre of each permanent magnet and the rotation axis. 
     According to another aspect of the invention: each receptor can include a pair of rod-shaped secondary receivers; in each receptor, the secondary receivers can be equally spaced from the centre of the primary receiver; and in each receptor, the pair of rod-shaped secondary receivers and the primary receiver can be all arranged in a line which does not intersect the rotation axis. 
     According to another aspect of the invention, each of the primary receivers can be intersected by two of the lines. 
     According to another aspect of the invention, with respect to each receptor, the shortest distance between a secondary receiver of said each receptor and the primary receiver that forms no part of said each receptor and is intersected by the line associated with said each receptor can at least substantially equal the distance between the secondary receivers of said each receptor. 
     The apparatus can be used as part of an improved spa, which forms another aspect of the invention. The spa includes; a basin for containing water; a motor mounted exteriorly of the basin and having a rotating shaft; and a centrifugal pump mounted interiorly of the basin and including an impeller which, in use, is rotated by the motor for circulating water contained in the basin. The improvement comprises the apparatus in use such that the rotating shaft defines the rotating element and the impeller defines the rotatable element. 
     Other advantages of the present invention will become evident upon review of the accompanying detailed description and drawings, the latter being briefly described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is cross-sectional, partially exploded view of a foot spa according to the prior art; 
         FIG. 2  is a front perspective view of encircled structure  2  of  FIG. 1 ; 
         FIG. 3  is a rear perspective view of encircled structure  2  of  FIG. 1 ; 
         FIG. 4  is an exploded perspective view of encircled structure  2  of  FIG. 1 ; 
         FIG. 5  is a view similar to  FIG. 1  showing a foot spa according to an exemplary embodiment of the invention; 
         FIG. 6  is a perspective view of encircled structure  6  of  FIG. 3 ; 
         FIG. 7  is a partially exploded view of the structure of  FIG. 6 ; 
         FIG. 8  is an exploded view of the structure of encircled area  8  of  FIG. 7 ; 
         FIG. 9  is a view along section  9 - 9  of  FIG. 7 ; 
         FIG. 10  is another partially exploded view of the structure of  FIG. 6 ; 
         FIG. 11  is a view showing the counterpart to encircled structure  11  of  FIG. 1  in the exemplary embodiment; 
         FIG. 12  is a view of the structure of  FIG. 11 , showing magnetic field lines; and 
         FIG. 13  is an end view showing the relationship between the structure of encircled area  13 A of  FIG. 10  to encircled structure  13 B of  FIG. 11 , in use; 
         FIG. 14  is a schematic view showing a postulated flux arrangement, viewed along L 1 -L 1  of  FIG. 13 , of the structure of  FIG. 5  in use; and 
         FIG. 15  is a view similar to  FIG. 14 , showing another geometry and the postulated flux arrangement thereof. 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment of the present invention is described in detail in the following paragraphs. 
     However, by way of background, reference is now made to  FIGS. 1-4 , which show a prior art spa product. 
     This spa will be seen to include: a basin; a motor, encompassed by encircled area  11 ; and a centrifugal pump, encompassed by encircled area  2 . 
     The basin is for containing water. 
     The motor is mounted exteriorly of the basin. 
     The pump is positioned interiorly of the basin and has an impeller, as seen in exploded view  FIG. 4 . 
     The prior art spa will also be understood to include a coupling constructed in accordance with the teachings of U.S. Pat. No. 7,393,188 and US 2011/0176943, incorporated herein by reference. This prior art coupling, not shown, is defined by a series of permanent magnets fixed to the motor for rotation, and a further series of permanent magnets fixed to the impeller. 
     The attraction between these magnets serves to releasably mount the impeller, and the balance of the pump within it is housed, to the basin and also to rotatably couple the impeller to the drive shaft. Pin and socket connections are shown in  FIG. 1 , but it will be appreciated that these connections serve only to hold the pump in position and against rotation; it is indeed magnetic attraction that holds the pump to the basin. 
     Notably, a 1:1 paired relationship exists between the magnets of the motor and the magnets of the impeller: for each magnet fixed to the motor there is provided a magnet fixed to the impeller. 
     This arrangement has been well-received in the marketplace. 
     Reference is now made to  FIGS. 5-12 , which show an improved spa  20  which represents an advance over that of  FIGS. 1-4 . 
     This spa  20  continues to include a basin  22 , a motor  23  and a pump  24  which are all generally similar to the corresponding structures of the prior art but for the coupling  26 , 28  between the impeller  27  and motor  23 . 
     The inventive coupling, shown by way of example in  FIGS. 6-10 , comprises a drive hub  26  fixedly coupled to the motor  23  for rotation and a driven hub  28  which, in use, is disposed in spaced, frontwardly adjacent relation to the drive hub  26 , is fixedly coupled to the rotatable element, i.e. the impeller  27  portion of the pump  24 , and is at least substantially constrained against movement but for rotation, with the rotatable element, about the rotation axis X-X. 
     In the illustrated embodiment, this constraint is provided by capturing the driven hub  28  in a chamber defined by an intake disc  37 , a backer ring  39  and a bearing pan  41  from which a spindle  43  extends. The intake disc  37  is an injection molded plastic component which defines the jet outlets  45  of the pump and the water inlets  49 . The backer ring  39  is secured to the intake disc  37  by sonic welding or the like, carries a plurality of sockets  55  for engagement with the basin pins  57 , and defines an aperture  59 . The bearing pan  41  is a shallow disc adapted for press-fit engagement in the aperture  59 , and has the spindle  43  extending therefrom. The spindle  43  is adapted to receive the driven hub  28  for rotation thereabout, and to support the driven hub  28  in spaced relation from the bearing pan  41 , to avoid friction. 
     The exemplary drive hub  26  is shown mounted to the motor  23  in  FIG. 11  and will be seen to include a backer plate  30  and a drive body  32 . 
     The backer plate  30  is made of a ferromagnetic material, namely, an iron alloy, so as to have high magnetic permeability, and is coupled to the drive shaft (not shown) of the motor  23 . 
     The drive body  32  is a disc of aluminum alloy coupled to the side of the backer plate  30  opposite to that which is coupled to the drive shaft of the motor  23 . 
     As seen in  FIG. 12 , defined within the drive body  32  are four sockets  36 , spaced apart from each other and arranged to encircle the rotation axis X-X. 
     Mounted in each socket  36  is a disc-shaped permanent Neodyium magnet  38 , 38 , 40 , 40 , the poles being arranged in alternating relation such that, in the front face of the drive hub, i.e. the face opposite the backer plate  30 , there are defined two North pole domains  42  and two South pole domains  44 . 
     The magnetic properties of this arrangement in the absence of externalities are depicted in idealized fashion in  FIG. 12 ; herein, a magnetic field which extends from and returns to the hub  26  is shown, the magnetic field being characterized in that, field lines  99  extend from the two North pole domains  42  to the two South pole domains  44 . The magnetic field lines  99  emanating from the backside of the driven hub  28  are not shown, for reasons of clarity, but will understood to be concentrated within the backer plate  30 , by virtue of the ferromagnetic nature thereof. 
     The driven hub  28  is shown in exploded view in  FIG. 8  and will be seen to include a face disk  46 , a rotor body  48  and a plurality of receptors  50 . 
     The face disk  46  is constructed of a ferromagnetic material having high magnetic permeability, namely, an iron alloy, and is coupled to the impeller  27  in use. 
     The rotor body  48  is a constructed out of a non-magnetic, electrically conductive material having relatively low magnetic permeability, specifically, an aluminum alloy, and has a plurality of bores  52 , 54  defined therein. 
     Each receptor  50  includes a primary receiver  56  and a pair of secondary receivers  58 . The primary  56  and secondary  58  receivers are rod-shaped, mounted one within each bore  52 , 54  and are made of ferromagnetic material, namely, iron alloy, the bores being arranged such, as seen in  FIG. 13 , that: the primary receivers  56  are equally spaced from one another about the rotation axis X-X the distance D 1  from the centre of each primary receiver  56  to the rotational axis X-X is at least substantially equal to the distance D 2  between the centre of each permanent magnet  38 , 40  and the rotation axis X-X in each receptor, the pair of rod-shaped secondary receivers  58  and the primary receiver  56  are all arranged in an associated line L 1 ,L 2 ,L 3  which does not intersect the rotation axis each of the primary receivers  56  is intersected by two of the lines the secondary receivers  58  of each receptor  50  are equally spaced from the centre of the primary receiver  56  thereof with respect to each receptor  50 , the shortest distance D 4  between a secondary receiver  58  of said each receptor and the primary receiver  56  intersected by the line associated with said each receptor  50 , at least substantially equals the distance D 3  between the secondary receivers  58  of said each receptor  50   
     This arrangement of the receptors  50  is such that rotation of the drive hub  26  relative to driven hub  28  urges the driven hub  28  to rotate in the same direction as the drive hub  26 . Without intending to be bound by theory, it is believed that (i) this arrangement provides for magnetic field lines that pass through the rotor body in a manner such that, in the aggregate, the through-passing field lines are dominated by field lines that extend through the rotor body in a direction that is substantially tangential to the direction of rotation axis, as shown in  FIG. 14 , (ii) this phenomenon being well suited to produce a strong induced magnetic coupling. 
     An advantage of this arrangement is that, in contrast to the prior art coupling discussed hereinbefore, the coupling of the present invention can be removed and replaced without bringing the motor to rest. [In the prior art coupling, the inertia of the driven hub is too large to permit a dynamic magnet coupling at normal operating speeds: if the pump is, for example, dislodged in use, any attempt to replace the pump while the motor remains in motion will simply result in vibration of the impeller; no useful rotation will occur.] 
     Yet further, motors used with the present coupling are less susceptible to burn-out than motors used with the prior art coupling. In the prior art, if the impeller is restrained against rotation, such as occurs if the pump becomes plugged, the motor is also restrained against rotation by the magnetic force; this is not the case with the present coupling. 
     Notable about this arrangement is that the permanent magnets reside only on the motor, therefore tending to reduce the cost associated with the pump assembly. This is also advantageous, as pumps are susceptible to damage and clogging and are therefore more frequently replaced than motors. 
     Whereas, but a single exemplary embodiment of the invention is herein described, variations are possible. 
     For example, it is not essential that, as in the exemplary embodiment illustrated: 
     
       
         
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 N = the number of North pole domains in the front face = 2 
               
               
                   
                 S = the number of South pole domains in the front face = 2 
               
               
                   
                 R = the number of receptors = N + S − 1 = 3 
               
               
                   
                   
               
             
          
         
       
     
     N and S could, for example, each equal 3. As well, for example, R could equal N+S+1. All that is required is that the receptors be arranged so as to avoid resonance and provide the (suspected inductive) coupling provided by the present invention. 
     As well, whereas the illustrated receptors include a primary and a pair of secondary receivers, arranged in intersecting lines, this is not critical: it is known, for example, that the secondary receivers can be omitted entirely, albeit with a modest decrease in coupling efficacy. Primary receivers can be omitted entirely, with a significant decrease in coupling efficacy. [Omission of both primary and secondary receivers results in a coupling that lacks practical utility; while it is believed that inductive couplings can be made without receptors as found in the present invention, such couplings would require permanent magnets of vastly greater strength, and commensurately, much higher cost and weight.] 
     As well, whereas various specific materials, such as aluminum alloy, iron alloy and Neodyium are herein specified, it is understood that other materials, having similar magnetic properties, can be readily substituted therefore. 
     Without limitation, whereas the exemplary rotor body is described to be an aluminum alloy, i.e. a paramagnetic material, this is not believed to be essential, and other non-magnetic, electrically conductive materials can be substituted therefor. 
     As well, whereas the size and placement of the receivers in the illustrated embodiment is known to be useful, this is not critical. Variations can be made, and other arrangement may be as good as, or better than, that described. Notably, adding more ferromagnetic material to the driven hub can reduce coupling efficacy. 
     Without intending to be bound by theory, it is believed that additional iron can cause the magnetic flux lines to substantially bypass the rotor body altogether, as shown in  FIG. 15 , thereby reducing, rather than increasing, the postulated induced currents. 
     Further, whereas the illustrated embodiment shows the use of iron alloys, i.e. ferromagnetic materials, in all components wherein relatively high magnetic permeability is required, ferromagnetic properties may not be necessary and iron alloys is certainly not necessary. 
     Accordingly, the invention should be understood as limited only by the accompanying claims, purposively construed.