Abstract:
A drive for a sealed magnetically geared system comprising a housing defining a sealed chamber, a driving member including a first set of magnets, and a driven member comprising a second set of magnets, one of the members being located inside the chamber, wherein the first and second sets of magnets are arranged to produce different numbers of magnetic poles, and the housing includes a wall extending between the members and supporting a plurality of pole pieces which are arranged to modulate the magnetic field acting between the magnets.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to sealed systems such as pumps and turbines, and in particular to drive systems for such systems. 
       BACKGROUND TO THE INVENTION 
       [0002]    Pumps and turbines are used in a wide variety of applications and are connected to a source of rotational or linear power, such as motors, actuators or complementary pumps or turbines in a number of different ways. In some pumps the source of power operates at a different speed from the driven mechanism. Also, it is often required that the fluid in which the pump or other mechanism is immersed must be prevented from contaminating the rest of the drive system. Therefore, a pump or turbine may comprise a hermetic seal between the source of rotational or linear power and the pump, turbine or other mechanism and some form of gearing between the drive system and the driven mechanism. 
       SUMMARY OF INVENTION 
       [0003]    The present invention provides a magnetically geared system comprising a housing defining a sealed chamber, a driving member including a first set of magnets, and a driven member comprising a second set of magnets, one of the members being located inside the chamber, wherein the first and second sets of magnets are arranged to produce different numbers of magnetic poles, and the housing includes a wall extending between the members and supporting a plurality of pole pieces which are arranged to modulate the magnetic field acting between the magnets. 
         [0004]    The chamber is sealed, for example, the chamber is capable of sealing in a fluid, that is, liquid and gas. Depending on the application it may be hermetically sealed. 
         [0005]    The spacing of the magnetic poles in the first set of magnets may be greater than the spacing of the magnetic poles of the second set such that the driven member is driven at a slower speed than the driving member. Alternatively spacing of the magnetic poles of the first set of magnets may be greater than the spacing of the magnetic poles of the second set such that the driven member is driven at a higher speed than the driving member. 
         [0006]    The system may be rotary, in which case the members may be rotors. In this case the first set of magnets may include a lower number of magnets, or at least may define a smaller number of magnetic poles, than the second set such that the second rotor is driven at a slower speed than the first rotor. Alternatively the first set of magnets may include a higher number of magnets, or at least a higher number of magnetic poles, than the second set such that the second rotor is driven at a higher speed than the first rotor. 
         [0007]    The wall may be tubular in form and the coupling arranged to operate radially, with one of the rotors arranged radially inside the wall and the other of the rotors arranged radially outside the wall. Alternatively the coupling may be arranged to act axially, with the rotors arranged on opposite sides of a flat wall, spaced apart in the axial direction of their common axis of rotation. The coupling may also be arranged to act linearly, in which the wall may be a flat plate and the members in the form of translators which are positioned on either side of the wall. The coupling may also be arranged to act linearly, with the wall being tubular and with one translator arranged radially outside the wall and the other translator arranged radially inside the wall. 
         [0008]    The first rotor may be located radially outside the wall and the second rotor arranged radially inside the wall. 
         [0009]    The pole pieces may be completely embedded in the wall such that the pole pieces are hermetically sealed from the fluid chamber and the source of mechanical power. The pole pieces may be embedded in the wall such that the pole pieces are hermetically sealed from the fluid chamber but not sealed from the source of mechanical power. The pole pieces may be embedded in the wall such that the pole pieces are hermetically sealed from the source of mechanical power but not sealed from the fluid chamber. 
         [0010]    The present invention further provides a geared magnetic drive system comprising a high speed rotor including a first set of magnets, and a low speed rotor including a second set of magnets, wherein the first set of magnets includes a lower number of magnetic poles than the second set, and a plurality of pole pieces located between the rotors and arranged to modulate the magnetic field generated by at least some of the magnets such that rotation of one of the rotors causes rotation of the other, wherein the high speed rotor is located radially outside the low speed drive rotor. 
         [0011]    Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic section through a rotary magnetic gearing system used in the present invention; 
           [0013]      FIG. 2  is a graph illustrating magnetic spatial harmonics associated with the assembly of  FIG. 1 ; 
           [0014]      FIG. 3  is a longitudinal section through a pump according to an embodiment of the invention; 
           [0015]      FIG. 4  is a longitudinal section through a pump according to a second embodiment of the invention; 
           [0016]      FIG. 5  is a longitudinal section through a pump according to a third embodiment of the invention 
           [0017]      FIG. 6  is a section through a linear drive system according to a further embodiment of the invention; 
           [0018]      FIG. 7  is a section through a flywheel according to a further embodiment of the invention; and 
           [0019]      FIG. 8  is a section through a flywheel according to a further embodiment of the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    Referring to  FIG. 1 , a rotary magnetic gear  100  comprises a first or inner rotor  102 , a second or outer rotor  104  having a common axis of rotation with the first rotor  102 , and a number of pole pieces  106  of ferromagnetic material. The first rotor  102  comprises a support  108  carrying a first set of permanent magnets  110 , arranged to produce a spatially varying magnetic field with a number of magnetic poles. In this embodiment, the first rotor  102  comprises eight permanent magnets, or four pole-pairs, arranged to produce a spatially varying magnetic field. The second rotor  104  comprises a support  112  carrying a second set of permanent magnets  114 , arranged to produce a spatially varying magnetic field with a different number of poles than is produced by the first set of magnets  110 . The second rotor  104  comprises 46 permanent magnets or 23 pole-pairs arranged to produce a spatially varying field. The first and second sets of permanent magnets include different numbers of magnets providing different numbers of magnetic poles. Accordingly, without any modulation of the magnetic fields they produce, there would be little or no useful magnetic coupling or interaction between the permanent magnets  112  and  114  such that rotation of one rotor would not cause rotation of the other rotor. 
         [0021]    The ferromagnetic pole pieces  106  are used to control the way in which the fields of the permanent magnets  110  and  114  interact. The pole pieces  106  modulate the magnetic fields of the permanent magnets  110  and  114  so that they interact to the extent that rotation of one rotor will induce rotation of the other rotor in a geared manner. The number of pole pieces is chosen to be equal to the sum of the number of pole-pairs of the two sets of permanent magnets. Rotation of the first rotor  102  at a speed ω 1  will induce rotation of the second rotor  104  at a speed ω 2 where  ω 1 &gt;ω 2 . The ratio between the speeds of rotation ω 1  and ω 2 , i.e. the gearing ratio of the coupling, is equal to the ratio between the angular spacing of the magnets on the first and second rotors, and therefore in this case also equal to the ratio between the numbers of magnets  110  and  114  on the first and second rotors  102 ,  104 . The gear can operate in reverse, so that rotation of the second rotor  104  causes rotation of the first rotor at a higher speed. 
         [0022]      FIG. 2  shows a harmonic spectrum  200  of the spatial distribution of the magnetic flux density of the first set of permanent magnets  110  mounted on the inner rotor  102  of the magnetic gear  100  of  FIG. 1 , in the airgap adjacent to the second set of permanent magnets  114  mounted on the outer rotor  104 . It can be appreciated that the spectrum  200  comprises a first or fundamental component  202  associated with the first set of permanent magnets  110  of the first rotor  102 . This is the component of the field of which the spatial frequency corresponds to the spatial frequency of the polarity of the magnets  110  and therefore corresponds to four pole-pairs. The pole pieces  106  modulate the magnetic field of the permanent magnets  110  to provide components of the magnetic field of different spatial frequencies corresponding to different numbers of pole pairs. For the permanent magnets  110 , for example, this results in a relatively large asynchronous harmonic  204  having a number of pole pairs which is equal to the difference between the number of pole pieces  106  and the number of pole pairs of the magnets  110  on the inner rotor. This is arranged, by appropriate selection of the number of pole pieces  106 , to be the same as the number of pole pairs of the permanent magnets  114  on the outer rotor  104 , which enables coupling between the first  102  and the second  104  rotors. Also, with the pole pieces  106  held stationary and the inner rotor  102  rotated, this component of the field rotates at a lower speed than the inner rotor such that movement of one induces movement of the other, in a geared manner. 
         [0023]    One skilled in the art understands how to select and design the pole pieces  106 , given the first  110  and second  114  permanent magnets, to achieve the necessary magnetic circuit or coupling such that gearing between the first  102  and second  104  rotors results, as can be appreciated from, for example, K. Atallah, D. Howe, “ A novel high - performance magnetic gear”, IEEE Transactions on Magnetics , Vol. 37, No. 4, pp. 2844-2846, 2001 and K. Atallah, S. D. Calverley, D. Howe, “ Design, analysis and realisation of a high performance magnetic gear”, IEE Proceedings - Electric Power Applications , Vol. 151, pp. 135-143, 2004. 
         [0024]    Referring to  FIG. 3 , a pump  300  comprises a housing  350  defining a fluid chamber  352  having an inlet  354  and an outlet  356 . The physical design of the pump is not relevant for the present invention, but in this embodiment the pump has an impellor  358 , rotation of which causes fluid to flow from the inlet  354  to the outlet  356 . The impellor  358  is driven by a drive system  360  through a magnetic gear which corresponds to that of  FIG. 1 , with corresponding parts indicated by the same reference numerals increased by 200. The magnetic gear includes an input rotor  302 , which is driven by the drive system  360  via a drive shaft  362 , and an output rotor  304  which is directly mechanically coupled to the impellor  358 . 
         [0025]    One wall  370  of the housing  350 , which forms one wall of the fluid chamber  352 , includes an inwardly projecting portion  372  including a cylindrical portion  374  and an inner end wall  376 . The cylindrical portion  374  therefore surrounds an outward facing recess  378 , in which the input rotor  302  is located. The output rotor  304  extends around the cylindrical portion, being radially outside it, but within the fluid chamber  352 . The pole pieces  306  of the drive system are embedded within the cylindrical wall portion  374 , which extends between the input and output rotors  302 ,  304 . Therefore the pole pieces  306  are below both the inner and outer surfaces  380 ,  382  of the cylindrical wall portion  374 , being completely enclosed within the material of the cylindrical wall portion  374 . This part of the housing is moulded, with the pole pieces being moulded into the wall. This means that the outer surface  382  of the cylindrical wall portion  374  is smooth. As the permanent magnets  314 , which are on the radially inner side of the output rotor  304 , are only spaced from the cylindrical wall portion  374  by a small distance, it is advantageous to have the surface of the cylindrical wall portion  374  smooth as this reduces losses due to turbulence in the fluid in the gap between the output rotor  304  and the cylindrical wall portion  374 . The same is true for the radially inner surface  380  which needs to be smooth to reduce losses from air turbulence around the high speed rotor  302 . In other embodiments the pole pieces are attached to the cylindrical wall in other ways. For example they may be mounted on the surface of the cylindrical wall or may be flush with either or both of the inner and outer surfaces  380 ,  382 . 
         [0026]    It will be appreciated that in operation the magnetic gear provides a geared drive between the drive system  360  and the pump without the need for any mechanical coupling between the inside and the outside of the fluid chamber  352 . The drive to the pump is provided purely via the coupling of the magnetic fields of the rotors through the wall  370  of the fluid chamber. The embedding of the pole pieces  306  within the wall  370  allows the close proximity of the permanent magnets  310 ,  314  of the rotors to the pole pieces  306  to be maintained, thereby maintaining an efficient coupling. 
         [0027]    Referring to  FIG. 4 , a second embodiment operates in a similar manner to the first embodiment with corresponding parts being indicated by corresponding reference numerals increased by 100. In this embodiment, the end wall  470  includes an outwardly projecting portion  472  including a cylindrical portion  474  and an outer end wall  476 . The input rotor  402  of the geared drive coupling is therefore arranged radially outside the cylindrical wall portion  474  and the output rotor  404  is arranged radially inside the cylindrical wall portion, and therefore also radially inside the input rotor  402 . The input rotor  402  again has fewer permanent magnets  410  than the output rotor  404 , and its magnets are at a greater spacing, in this case the input rotor has four pole pairs, the output rotor permanent magnets  414  include 23 pole pairs, and there are 27 pole pieces  406  embedded in the cylindrical wall section  474 . It will be appreciated that in this arrangement, operation is similar to the first embodiment, and the output rotor  404  will rotate more slowly than the input rotor  402 , the gear ratio being determined by the ratio of the numbers of permanent magnets on the rotors  402 ,  404  in the same way as in the first embodiment. 
         [0028]    This embodiment has the advantage that the smaller diameter rotor  404  is the output rotor, which is the rotor inside the fluid chamber. This results in a simpler construction of the housing  450 , but more significantly, much less drag on the output rotor, which reduces the losses within the drive coupling and makes it more efficient. It will be appreciated that this arrangement, with the inner rotor being the low speed rotor and the outer rotor being the high speed rotor, which is not achievable with a mechanical drive coupling, can be used in other applications apart from pumps. 
         [0029]    Referring to  FIG. 5  in the third embodiment of the invention, the drive coupling is axially orientated. The input rotor  502  has a circular array of magnets  510  with their poles at their axial ends, again with alternating polarity around the array. The end wall  570  of the fluid chamber  552  between the rotors is flat, and has a circular array of pole pieces  506  embedded within it. The low speed, output rotor  504  has a circular array of magnets  514 , arranged on the opposite side of the end wall  570  to the magnets  510  on the input rotor  502 , again with their poles at their axial ends and with alternating polarity around the rotor  504 . It will be appreciated that this embodiment will operate in substantially the same way as the first and second embodiments, with the gearing ratio determined by the ratio of the numbers of magnets  510 ,  514  on the input and output rotors  502 ,  504 , and the number of pole pieces being selected as required. 
         [0030]    Referring to  FIG. 6 , in a further embodiment of the invention, the drive system is linear, and the magnetic gear comprises an input member  602  or translator arranged to move linearly in either direction along an axis X, an output member  604  or translator also arranged to move linearly in either direction along the same axis, and a wall  674  which encloses a fluid chamber  652  in which the output member  604  is located. In this embodiment the input member  602 , output member  604  and wall  674  are annular, with  FIG. 6  showing a section through one side of the gear system. In other embodiments the input and output members and the wall between them are flat and planar. 
         [0031]    The gear system of  FIG. 6  is the linear equivalent of the gear system of  FIG. 3 , with movement of the input member  602  producing movement of the output member  604  at a lower speed, the ratio of the speeds depending on the linear spacing of the two sets of magnets  610 ,  614  and the pole pieces  606 . 
         [0032]    The linear gear system of  FIG. 6  can be used in a number of applications, for example for controlling robots inside hermetically sealed enclosures. 
         [0033]    Referring to  FIG. 7 , in a further embodiment of the invention the magnetic gearing system is used to drive a flywheel which forms one of the rotary members  704 . The other of the rotary members  702  is used to input energy to the flywheel and also to extract energy from it. The flywheel is supported on a very low friction bearing system, and the fluid chamber is annular so that the flywheel  704  is entirely enclosed within it. The fluid chamber  752  is in this case a vacuum chamber, being evacuated to a very low pressure so as to minimise the energy loss from the flywheel. The chamber  752  is therefore sealed so as to be airtight. The gearing is arranged such that the input member  702  is the low speed rotor and the flywheel  704  is the high speed rotor. Suitable gearing ratios would be of the order of 10 to 1 up to 30 to 1. 
         [0034]    Referring to  FIG. 8 , where like parts to that described in  FIG. 7  are provided with identical reference numerals, the rotary member  702  is an outer rotor and arranged as the low speed, high pole piece number rotor. In this way the magnetic gearing system is inverted compared to that described in relation to  FIG. 7 . 
         [0035]    While in each of the embodiments described above, each of the permanent magnets is a simple dipole with one north and one south pole, it will be appreciated that, while the positioning of the magnetic poles is critical to the operation of each embodiment, any arrangement of pole pairs can be provided by a number of different arrangements of magnets, i.e. blocks of magnetized material. For example more than one pole pair can be provided by a single magnetized block.