Abstract
The present disclosure relates to a magnetically geared apparatus. In an example the magnetically geared comprises: a first mover comprising a plurality of first permanent magnets; a stator; a second mover; and a flux shield aligned with the first plurality of permanent magnets for attenuating magnetic flux. One of the stator and the second mover comprises a plurality of pole pieces and is positioned between the first mover and the other of the stator and the second mover. The first mover, the stator and the second mover are aligned in a first direction, and wherein the flux shield is spaced from the plurality of first permanent magnets in a second direction perpendicular to the first direction by a nonmagnetic region, thereby attenuating magnetic flux in the second direction.
Claims
1. A magnetically geared apparatus comprising: a first mover comprising a plurality of first permanent magnets; a stator; a second mover; and a flux shield aligned with the plurality of first permanent magnets for attenuating magnetic flux, wherein one of the stator and the second mover comprises a plurality of pole pieces and is positioned between the first mover and another of the stator and the second mover, wherein the first mover, the stator and the second mover are aligned in a first direction, and wherein the flux shield is spaced from the plurality of first permanent magnets in a second direction perpendicular to the first direction by a non-magnetic region, thereby attenuating the magnetic flux in the second direction.
2. The magnetically geared apparatus of claim 1, wherein the first mover, the stator and the second mover are arranged around a shaft and are axially aligned with one another, and wherein one of the first mover and the second mover is mechanically coupled to the shaft; and optionally wherein the first mover, the stator and the second mover are housed within a metal casing; and wherein the flux shield is located between the plurality of first permanent magnets and the metal casing.
3. The magnetically geared apparatus of claim 1, wherein the first mover, the stator and the second mover are concentrically arranged around a shaft.
4. The magnetically geared apparatus of claim 3, wherein the second mover comprises an electrically conductive pole piece support structure mechanically coupled to the shaft; and the flux shield is located between the plurality of first permanent magnets and the electrically conductive pole piece support structure, and optionally wherein the plurality of pole pieces are coupled to the electrically conductive pole piece support structure via an electrically insulating pole piece spacer, such that the plurality of pole pieces are axially spaced from the electrically conductive pole piece support structure by the electrically insulating pole piece spacer.
5. The magnetically geared apparatus of claim 1, wherein the first mover, the stator and the second mover are housed within a metal casing, and wherein the flux shield is located between the plurality of first permanent magnets and the metal casing.
6. The magnetically geared apparatus of claim 1, wherein the first mover comprises a permanent magnet support structure, and wherein the flux shield is mechanically coupled to the permanent magnet support structure.
7. The magnetically geared apparatus of claim 4, wherein the flux shield is mechanically coupled to the electrically conductive pole piece support structure.
8. The magnetically geared apparatus of claim 1, wherein the non-magnetic region is a non-magnetic, electrically insulating spacer.
9. The magnetically geared apparatus of claim 1, wherein the non-magnetic region comprises an air gap.
10. The magnetically geared apparatus of claim 1, wherein the flux shield comprises a conductor.
11. The magnetically geared apparatus of claim 1, wherein the flux shield comprises an un-magnetised magnetisable material, and optionally wherein the flux shield comprises one of a laminate and a soft magnetic composite SMC.
12. The magnetically geared apparatus of claim 1, wherein the flux shield comprises an annular ring, and optionally wherein the flux shield comprises a plurality of circumferential segments arranged to form the annular ring, the plurality of circumferential segments being circumferentially spaced from one another.
13. The magnetically geared apparatus of claim 1, wherein the another of the stator and the second mover comprises a plurality of second permanent magnets.
14. The magnetically geared apparatus of claim 1, wherein the stator comprises a plurality of windings, and the second mover is located between the stator and the first mover and comprises the plurality of pole pieces.
15. The magnetically geared apparatus of claim 14, wherein the stator further comprises a plurality of second permanent magnets, and optionally wherein the plurality of second permanent magnets are arranged between the plurality of windings and the second mover.
16. The magnetically geared apparatus of claim 1, wherein the flux shield comprises a first flux shield axially spaced from a first axial end of the plurality of first permanent magnets, and a second flux shield axially spaced from a second axial end of a plurality of second permanent magnets.
17. The magnetically geared apparatus of claim 1, wherein the plurality of first permanent magnets are circumferentially arranged such that each of the plurality of first permanent magnets occupies a predefined arc length, and wherein the flux shield is axially spaced from the plurality of first permanent magnets by a distance that is between one tenth and one half of the predefined arc length.
18. A magnetically geared apparatus comprising: a first rotor comprising a plurality of first permanent magnets; a stator; and a second rotor positioned between the first rotor and the stator, the second rotor comprising a pole piece support structure, the pole piece support structure comprising wall regions and a pole piece region, and a plurality of pole pieces coupled to the pole piece region; wherein the first rotor, the stator and the second rotor are concentrically arranged around a shaft, and wherein at least one wall region of the pole piece support structure is axially spaced from the plurality of first permanent magnets so as to minimise axial flux leakage into the at least one wall region from the plurality of first permanent magnets.
19. A rotor for a magnetically geared apparatus comprising concentrically arranged magnetically interacting components, the rotor comprising: a support structure; a plurality of permanent magnets coupled to the support structure; and one of: a flux shield coupled to the support structure, the flux shield being axially aligned with the plurality of permanent magnets and further being axially spaced from the plurality of permanent magnets by a non-magnetic region.
20. A rotor for a magnetically geared apparatus comprising axially aligned magnetically interacting components, the rotor comprising: a support structure; a plurality of permanent magnets coupled to the support structure; and a flux shield coupled to the support structure, the flux shield being radially aligned with the plurality of permanent magnets and further being radially spaced from the plurality of permanent magnets by a non-magnetic region.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0063] FIG. 1a schematically illustrates a first magnetically geared apparatus according to the prior art;
[0064] FIG. 1b shows the magnetically geared apparatus according to FIG. 1a, viewed along the axial direction A-A;
[0065] FIG. 2a schematically illustrates a second magnetically geared apparatus according to the prior art;
[0066] FIG. 2b shows the magnetically geared apparatus according to FIG. 2a, viewed along the axial direction A-A;
[0067] FIG. 3a shows a second magnetically geared apparatus according to the present disclosure;
[0068] FIG. 3b shows a variation of the second magnetically geared apparatus according to FIG. 3a;
[0069] FIG. 4 shows a third magnetically geared apparatus according to the present disclosure;
[0070] FIG. 5 shows a fourth magnetically geared apparatus according to the present disclosure;
[0071] FIG. 6 shows a fifth magnetically geared apparatus according to the present disclosure;
[0072] FIG. 7 shows a sixth magnetically geared apparatus according to the present disclosure;
[0073] FIG. 8a shows a seventh magnetically geared apparatus according to the present disclosure;
[0074] FIG. 8b shows a variation of the magnetically geared apparatus of FIG. 8a;
[0075] FIG. 9 shows an eighth magnetically geared apparatus according to the present disclosure;
[0076] FIG. 10 shows a ninth magnetically geared apparatus according to the present disclosure;
[0077] FIG. 11 shows a tenth magnetically geared apparatus according to the present disclosure;
[0078] FIG. 12 shows an eleventh magnetically geared apparatus according to the present disclosure;
[0079] FIG. 13 shows a rotor according to the present disclosure;
[0080] FIG. 14 shows an illustration of axial flux leakage within a magnetically geared apparatus according to the present disclosure;
[0081] FIG. 15a shows magnetic flux density in a support member within a magnetically geared apparatus according to the prior art;
[0082] FIG. 15b shows magnetic flux density in a support member within a magnetically geared apparatus according to the present disclosure;
[0083] FIGS. 16a-16d show various flux shield structures for use in any of the examples in the present disclosure;
[0084] FIG. 17 shows a first axially-arranged magnetically geared apparatus according to the present disclosure;
[0085] FIG. 18 shows a second axially-arranged magnetically geared apparatus according to the present disclosure;
[0086] FIG. 19 shows a third axially-arranged magnetically geared apparatus according to the present disclosure;
[0087] FIG. 20 shows a linear magnetically geared apparatus according to the present disclosure;
[0088] FIG. 21 shows a first magnetic gear according to the present disclosure;
[0089] FIG. 22 shows a second magnetic gear according to the present disclosure;
[0090] FIG. 23 shows a third magnetic gear according to the present disclosure; and
[0091] FIG. 24 shows a fourth magnetic gear according to the present disclosure.
[0092] Like reference numerals are used for like components in the drawings.
DETAILED DESCRIPTION
[0093] Herein, the axial direction refers to the direction A-A shown in FIGS. 1a and 2a. Where two components are said to be axially aligned, they are aligned with one another in a direction parallel to the axis A-A. Similarly, where two components are said to be axially spaced from one another, there exists a gap between them in a direction parallel to the axis A-A. The radial direction is defined as being perpendicular to the axis A-A. The circumferential direction is defined as being concentric to the axis A-A.
[0094] Referring to FIG. 1a, the second rotor 106 of the first magnetically geared apparatus 100 has an open cup configuration, in which the pole pieces 112 are supported by a pole piece support structure which includes a single steel support member 126 at a first axial end of the pole pieces 112. No support member is present at the second axial end of the pole pieces 112. Steel is used as the support member for its high stiffness, thereby preventing deformation of the second rotor 106.
[0095] By contrast, we see with reference to FIG. 2a that the second rotor 106 of the second magnetically geared apparatus 200 has a closed cup configuration, in which the pole pieces 112 are supported by a pole piece support structure that includes a first steel support member 126a (sometimes referred to herein as a wall region) at a first axial end of the pole pieces 112, and a second steel support member 126b (also sometimes referred to herein as a wall region) at a second axial end of the pole pieces 112. A pole piece region, comprising the pole pieces 112, is defined between the wall regions. Also shown in FIG. 2a is aluminium casing 122. The stator 102 is mounted to an inner surface of the casing 122. The casing 122 conceals the moving components of the apparatus 200. Aluminium is lightweight and durable, and thus a suitable casing material.
[0096] As the reader will understand, the first magnetically geared apparatus 100 could have a closed cup configuration as shown in FIG. 2a, and the second magnetically geared apparatus 200 could have an open cup configuration as shown in FIG. 1a. Furthermore, although not shown in FIG. 1a, the apparatus 100 may also include an aluminium casing 122.
[0097] As the reader will understand, by replacing the stator with a further rotor comprising the second plurality of permanent magnets 120, and dispensing with the windings, a magnetic gear is formed, that does not include windings, with a fixed gear ratio. This applies also to FIGS. 4-7, for example.
[0098] The inventors have found that magnetic flux can stray axially from the axial ends of the first permanent magnets 110, and into the steel support member(s) 126 and the casing 122. When this happens, eddy currents are induced in these components, which in turn leads to Ohmic losses in the first magnetically geared apparatus 100 and in the second magnetically geared apparatus 200. The steel support member(s) could be milled, drilled or shaped to reduce eddy currents. However, doing so would negatively affect the structural rigidity and robustness of the support member(s). Although steel is mentioned as the metal of choice throughout, other metals may be used and the features disclosed herein are appropriate for use in any magnetically geared apparatus in which eddy currents may be induced unintentionally due to stray axial flux.
[0099] The present disclosure addresses this problem of stray axial flux. In each of FIGS. 3a to 12, a magnetically geared apparatus according to the present disclosure is shown, in which a flux shield is arranged to prevent or reduce stray axial flux from giving rise to eddy currents in the steel support member(s) 126 or aluminium casing 122. In FIG. 13, a rotor according to the present disclosure is disclosed, for use as the first rotor 104 in the first magnetically geared apparatus, or as the first rotor 104 in the second magnetically geared apparatus. As the reader will understand, the principles disclosed in this document can be applied to magnetic gears (see, for example, FIGS. 21-24 below), to magnetic motor/generators (see, for example, FIGS. 4-7 and 17-20 below), and to magnetic power split devices (see, for example, FIGS. 3a, 3b below).
[0100] In each of the examples below, the flux shield may be attached to the apparatus by adhesive, bolts, rivets or clips, or indeed using any other fixing means. As the reader will understand, the flux shield in each of the examples below could be used in combination with a first magnetically geared apparatus 100 according to FIGS. 1a-1b, or in combination with a second magnetically geared apparatus according to FIGS. 2a-2b, in order to improve performance and efficiency. As is described in more detail below, the (or each) flux shield is spaced from the first permanent magnets by a non-magnetic, electrically insulating region. The non-magnetic, electrically insulating region may be a spacer component (see, for example, the spacers 304a, 304b of FIG. 3a). Alternatively, it may be an airgap (see, for example, FIG. 6).
[0101] In the examples below, the flux shield is formed of an un-magnetised soft magnetic composite material. However, in some examples, it may be formed of laminated steel sheets. In other examples, it may be formed of copper.
[0102] FIG. 3a shows a third magnetically geared apparatus 300, according to the present disclosure. The magnetically geared apparatus 300 includes only a first plurality of permanent magnets 110. That is to say, it does not include a second plurality of permanent magnets coupled to the stator. Therefore, it is particularly suited for use as a power split device, similar to FIGS. 1a-1b. The third magnetically geared apparatus 300 includes a first annular magnetic flux shield 302a at a first axial end of the first rotor 104, and a second annular magnetic flux shield 302b at a second axial end of the first rotor 104. Each of the flux shields 302a, 302b is axially aligned with the first permanent magnets 110, and spaced apart from the first permanent magnets 110 by a respective annular spacer 304a, 304b. That is to say, each spacer 304a/304b is interposed between an axial end of the first permanent magnets 110 and a respective magnetic flux shield 302a/302b. In an alternative example, each flux shield 302a/302b may be spaced apart from a respective axial end of the first permanent magnets 110 by a respective air gap instead of or in addition to a spacer.
[0103] Due to the positioning and material of the flux shields 302a, 302b, the flux shields 302a, 302b reduce or substantially prevent stray axial flux lines from the first permanent magnets 110 from reaching the steel support member 126, and further reduce or substantially prevent stray axial flux lines from reaching the metal casing 122.
[0104] Labelled on FIG. 3a are the radial direction R, and the axial direction A. The radial direction R is perpendicular to the axial direction A. As can be seen, the stator 102, first rotor 104, and second rotor 106 are concentrically arranged. That is to say, they are aligned in the radial direction. The flux shield 302a, on the other hand, is aligned with the first permanent magnets 110 in the axial direction, and is spaced from the first permanent magnets 110 in the axial direction. Accordingly, the flux shield 302a attenuates flux straying in the axial direction, and encourages flux to propagate in the radial directioni.e. radially towards the pole pieces 112 and the stator 102.
[0105] Also shown in FIG. 3a are an input shaft 118a and an output shaft 118b. The input shaft 118a is mechanically coupled to the first rotor 104, such that the input shaft 118a drives the first rotor 104. The output shaft 118b is mechanically coupled to the second rotor 106, such that the second rotor drives the output shaft 118b. The input shaft 118a extends from a first axial end of the magnetically geared apparatus 300, while the output shaft 118b extends from a second axial end of the magnetically geared apparatus 300. The second rotor 106 has an open cup structure, and is open at its first axial end in order to accommodate the input shaft 118a. The first rotor 104 also has an open cup structure, and is open at its second axial end in order to accommodate the output shaft 118b. The input shaft 118a is coupled to the casing 122 via bearings 124. The output shaft 118b is coupled to the casing 122 and to the first rotor 104 via bearings 124. The first rotor 104 is the radially inner-most rotor. The second rotor 106 is arranged radially between the first rotor 104 and the stator 102.
[0106] Because the second rotor 106 has an open structure and is open at its first axial end, it includes only a single (second) steel support member 126b. It is this arrangement which defines the open cup structure. Because of this open cup structure, the first flux shield 302a at the first axial end of the first permanent magnets 110 acts to prevent stray axial flux from reaching the casing 122. The second flux shield 302b acts to prevent stray axial flux from reaching the steel support member 126b. In some examples, where there is a sufficiently large gap between the first permanent magnets 110 and the casing 122 at the first axial end of the apparatus (i.e. the end that is distal from the steel support member 126b), the first flux shield 302a may be dispensed with.
[0107] FIG. 3b shows a variation 300 of the magnetically geared apparatus 300 shown in FIG. 3a. Similarly to FIG. 3a, the magnetically geared apparatus 300 of FIG. 3b comprises an input shaft 118a and an output shaft 118b. The input shaft 118a is mechanically coupled to the first rotor 104, such that the input shaft 118a drives the first rotor 104. The output shaft 118b is mechanically coupled to the second rotor 106, such that the second rotor 106 drives the output shaft 118b. In fact, the output shaft 118b comprises a hollow shaft 118b which is directly coupled to the first steel support member 126a. Both the input shaft 118a and the output shaft 118b extend from the same (first) axial end of the magnetically geared apparatus 300, and are concentric with one another. The input shaft 118a is arranged concentrically within the hollow output shaft 118b. The input shaft 118a is coupled to the casing 122 and to the second rotor 106 via bearings. The output shaft 118b is coupled to the casing 122 and to the first rotor 104 via bearings.
[0108] FIG. 4 shows a fourth magnetically geared apparatus 400, according to the present disclosure. The magnetically geared apparatus 400 includes both a first plurality of permanent magnets 110, and a second plurality of permanent magnets 120. Therefore, it is particularly suited for use as a high-torque motor/generator, similar to FIGS. 2a-2b. The fourth magnetically geared apparatus 400 includes the same flux shields 302a, 302b and spacers 304a, 304b as are included in the third magnetically geared apparatus 300. The flux shields 302a, 302b of FIG. 4 provide the same benefits as those of FIGS. 3a-3b.
[0109] FIG. 5 shows a fifth magnetically geared apparatus 500, according to the present disclosure. The fifth magnetically geared apparatus 500 is similar to the fourth magnetically geared apparatus 400 of FIG. 4, however the first plurality of permanent magnets 110 is split into two sub-pluralities of permanent magnets. Second rotor 106 is accordingly divided into two halves and comprises a first plurality of pole pieces 112a at a first half thereof, and a second plurality of pole pieces 112b at a second half thereof. Further, the second rotor 106 comprises a first steel support member 126a at the first axial end of the first half, a second steel support member 126b at the second axial end of the second half, and a third steel support member 126c axially between the first and second support members 126a, 126b. The third steel support member 126c is interposed between the first plurality of pole pieces 112a and the second plurality of pole pieces 112b. Furthermore, the plurality of first permanent magnets 110 comprises a first sub-plurality of the first permanent magnets 110a at a first half of the first rotor 104, and a second sub-plurality of the first permanent magnets 110b at a second half of the first rotor 104. The first plurality of pole pieces 112a of the second rotor 106 corresponds to (is radially aligned with) the first sub-plurality of permanent magnets 110a of the first rotor 104, and similarly the second plurality of pole pieces 112b of the second rotor 106 corresponds to (is radially aligned with) the second sub-plurality of permanent magnets 110b of the first rotor 104.
[0110] The first rotor 104 comprises a first annular flux shield 302a axially spaced from a first axial end of the first sub-plurality of permanent magnets 110a by a first spacer 304a; a second annular flux shield 302b axially spaced from a second axial end of the second sub-plurality of permanent magnets 110b by a second spacer 304b; a third annular flux shield 302c axially spaced from the second axial end of the first sub-plurality of first permanent magnets 110a by a third spacer 304c; and a fourth annular flux shield 302d axially spaced from the first axial end of the second sub-plurality of first permanent magnets 110b by a fourth spacer 304d. Accordingly, the third and fourth axial flux shields 302c, 302d reduce or substantially prevent axial flux from leaking into the third steel support member 126c, while the first axial flux shield 302a reduces or substantially prevents leakage into the first steel support member 126a, and the second axial flux shield 302b reduces or substantially prevents leakage into the second steel support member 126b.
[0111] FIG. 6 shows a sixth magnetically geared apparatus 600, according to the present disclosure. The sixth magnetically geared apparatus 600 is similar to the fourth magnetically geared apparatus 400, with the spacers 304a, 304b absent. The sixth magnetically geared apparatus 600 therefore includes a first annular magnetic flux shield 302a aligned with and axially spaced from a first axial end of the plurality of first permanent magnets 110, and a second annular magnetic flux shield 302b aligned with and axially spaced from a second axial end of the plurality of first permanent magnets 110. However, in contrast with earlier examples, the spacing between the plurality of first permanent magnets 110 and each of the flux shields 302a, 302b instead comprises an air gap. In particular, instead of being attached to the first rotor 104, each of the flux shields 302a, 302b is attached to an inner surface of respective one of the first and second support members 126a, 126b, and is axially spaced from the plurality of first permanent magnets 110 by an air gap. Therefore, it can be seen that spacers are not necessarily required, as long as a non-magnetic and electrically insulating region is provided between the axial ends of the plurality of permanent magnets and the respective flux shields. This region may be provided by a spacer, as previously described, by an air gap, or by a combination of the two.
[0112] FIG. 7 shows a seventh magnetically geared apparatus, according to the present disclosure. The seventh magnetically geared apparatus 700 represents a slight variation of the magnetically geared apparatus 600 of FIG. 6. In particular, the first magnetic flux shield 302a in the seventh magnetically geared apparatus 700 is attached to the first support member 126a with a first spacer 304a therebetween; and the second magnetic flux spacer 302b in the seventh magnetically geared apparatus 700 is attached to the second support member 126b with a second spacer 304b therebetween. Accordingly, the first magnetic flux shield 302a is axially spaced from the plurality of first permanent magnets 110 by an electrically insulating region comprising an air gap, and from the first support member 126a by the first spacer 304a. Similarly, the second magnetic flux shield 302b is axially spaced from the plurality of first permanent magnets 110 by electrically insulating region comprising an air gap, and from the second support member 126b by the second spacer 304b.
[0113] As shown in FIGS. 3a to 7, the flux shields 302 may have a rectangular cross-sectional profile. However, as shown in FIGS. 8a, 8b and 9, the flux shields 302 could have a non-rectangular cross-sectional profile. Two such non-rectangular cross-sectional profiles are shown in FIGS. 8a, 8b and 9.
[0114] The first magnetic flux shield 302a in the magnetically geared apparatus 800 of FIG. 8a has substantially triangular cross-section, specifically a chamfered radially inner edge and a chamfered radially outer edge, such that the first flux shield 302a is thickest at a radial centre of its cross-section. In other examples, the first magnetic flux shield 302a may have a rounded cross-sectional profile. For example, in the magnetically geared apparatus 801 of FIG. 8b, the first magnetic flux shield 302a may be shaped as a curved segment, such that the flux shield 302a is thickest at a radial centre of its cross-section. The specific cross-sectional profile may be selected according to the path of the flux leakage in the magnetically geared apparatus in question. A chamfered cross-sectional profile as shown in FIG. 8a, or a rounded cross-sectional profile as shown in FIG. 8b, may be particularly useful for a magnetically geared apparatus in which a majority of the axial stray flux extends from a radial midpoint of each of the first permanent magnets 110. In such examples, the chamfered or rounded profile further helps to reduce or substantially prevent eddy currents, and hence Ohmic losses, in the pole piece support members.
[0115] In yet other examples, the flux shield may include slits, holes, pockets, and/or grooves formed therein. The slits may be formed in the radial and/or circumferential direction. Such features may help to reduce eddy currents, and hence Ohmic losses, in the flux shield itself. More on this in FIGS. 16d-16d below.
[0116] FIG. 9 shows a partial view of a ninth magnetically geared apparatus 900, according to the present disclosure. In the magnetically geared apparatus 900 of FIG. 9, the first magnetic flux shield 302a extends partially along a radially outer edge of the first spacer 304a. Accordingly, at least some stray flux lines extending from the radially outer edge of the plurality of first permanent magnets 110 are caught by the flux shield.
[0117] While FIGS. 8a, 8b and 9 do not show the second axial end of the magnetically geared apparatus 800, 900, the reader will understand that the magnetically geared apparatus in each of these examples may include a second magnetic flux shield 302b and second spacer 304b, as in previous examples. The second magnetic flux shield 302b and second spacer 304b in each example may have the same cross-sectional profile as the first magnetic flux shield 302a and first spacer 304a, or may have a different cross-sectional profile.
[0118] As shown in the tenth magnetically geared apparatus 1000 of FIG. 10, a first non-magnetic, electrically insulating pole piece spacer 1002a (as distinct from the first spacer 304a) may be provided between the first support member 126a and the pole pieces 112. Although not shown in FIG. 10, a second non-magnetic, electrically insulating pole piece spacer 1002b may be provided between the second support member 126b and the pole pieces 112. This helps to break the flux path from the pole pieces to the first support member, thereby enhancing the flux shield effect.
[0119] As shown in the eleventh magnetically geared apparatus 1100 of FIG. 11, the plurality of first permanent magnets 110 may be chamfered at a first axial end thereof, such that a radially outer edge of each of the first permanent magnets is shorter than a radially inner edge of each of the first permanent magnets. This advantageously increases the reluctance of the path closest to the pole pieces 112. The spacer 304a is wedge-shaped and similarly chamfered to account for and correspond to the chamfer of the first permanent magnets 110. In particular, a radially inner edge of the spacer 304a is shorter than a radially outer edge of the spacer 304a. Although not shown in FIG. 11, the second spacer 304b may also be wedge-shaped, with a radially outer edge of the second spacer 304b having a greater axial length than a radially inner edge.
[0120] FIG. 12 shows a twelfth example of a magnetically geared apparatus 1200, according to the present disclosure. The pole pieces 112 of the twelfth example are chamfered 1202, such that the radially inner edge of the plurality of pole pieces 112 has a greater axial length than a radially outer edge thereof. In addition, the radially outer edge length is similar or the same as the radially outer edge length of the plurality of permanent magnets 110. This advantageously increases the reluctance of the path closest to the first permanent magnets 110. The first support member 126a may be similarly tapered to conform to the taper of the pole pieces 112. Although not shown in FIG. 12, the other axial end of the pole pieces 112 may be similarly chamfered.
[0121] FIG. 13 shows a rotor 104 according to the present disclosure, for use as the first rotor 104 in the first magnetically geared apparatus 100, or as the first rotor 104 in the second magnetically geared apparatus 200. The rotor 104 includes a plurality of circumferentially arranged first permanent magnets 110, mounted to a first permanent magnet support structure 1300. Each of the first permanent magnets 110 is laminated in the axial direction, and is segmented in the circumferential direction. In the illustrated example, each of the first permanent magnets 110 includes six axially laminated circumferential segments 110a-110f, each segment being an axial row of axially laminated permanent magnets 110. By configuring the permanent magnets in this way, losses due to eddy currents are minimised. The first permanent magnets 110 are spaced from one another in the circumferential direction.
[0122] The rotor 104 of FIG. 13 makes use of the flux shield and electrically insulating region concepts previously described. A first annular flux shield 302a is bolted or otherwise attached to a first axial end of the first rotor 104; and a second annular flux shield 302b is bolted or otherwise attached to a second axial end of the first rotor 104. Where the bolts are steel, they may be electrically insulated from the flux shields 302a, 302b by an insulating material, for example by an insulating coating or spacer. The steel bolts are non-magnetised. Each of the flux shields 302a, 302b comprises an annular ring having, for example, the same diameter as the first rotor 104, and being axially aligned with the plurality of circumferentially arranged first permanent magnets 110. Each flux shield 302a, 302b has an outer diameter that generally matches or exceeds an outer diameter of the plurality of first permanent magnets 110, and an inner diameter that generally matches an inner diameter of the plurality of first permanent magnets 110. In some examples, the flux shield may extend radially outwards of the outer diameter of the plurality of first permanent magnets, and/or protrude radially inwards of the inner diameter of the plurality of first permanent magnets.
[0123] Each of the flux shields 302a, 302b is segmented in the circumferential direction. In the example shown, the number of first permanent magnets 110 is equal to the number of flux shield segments 1302, with each flux shield segment 1302 being axially aligned with a respective axial end of one of the first permanent magnets 110. The flux shield segments 1302 are affixed to the first rotor 104 by bolts 1304. The flux shield segments are separated from one another by a (small) air gap, for simplicity of construction. Additionally, where the flux shield comprises an electrical conductor, the air gap may help to reduce eddy currents in the flux shield.
[0124] Positioned between the first permanent magnets 110 and the first flux shield 302a is an electrically insulating region, in this case the first spacer 304a. Positioned between the first permanent magnets 110 and the second flux shield 302b is another electrically insulating region, in this case the second spacer 304b. Similarly to the flux shields 302a, 302b, the first and second spacers 304a, 304b are segmented in the circumferential direction. That is to say, between each flux shield segment 1302 and its respective first permanent magnet 110 is a respective spacer segment 1306. In other words, each circumferential spacer segment 1306 is interposed between a respective first permanent magnet 110 and flux shield segment 1302 pair. Spacer segments 1306 are also affixed to the first rotor by the bolts 1304.
[0125] FIG. 14 illustrates how the flux shield 302 intercepts axial flux lines extending from an axial end of the plurality of first permanent magnets 110, and redirects those flux lines back towards the first permanent magnets 110 and pole pieces 112, thereby substantially reducing the amount of axial flux that reaches the support member 126. In effect, the flux shield 302 provides a magnetic path for the axial magnetic leakage field to return to the permanent magnet rotor, reducing the magnitude of field propagating in the surrounding structure. This in turn reduces eddy currents in the surrounding structure.
[0126] FIG. 15a shows magnetic flux density in a support member 126 within a magnetically geared apparatus according to FIGS. 1a-1b or 2a-2b. FIG. 15b shows magnetic flux density in a support member 126 within a magnetically geared apparatus according to the present disclosure, with a flux shield 302 present. As can be seen, the magnetic flux density in the support member 126 is substantially reduced where the flux shield 302 is used. Eddy currents are thereby also reduced.
[0127] As has been discussed above, the flux shield may include slits, holes and/or pockets to further prevent losses within the magnetically geared apparatus. This may be particularly important where the flux shield comprises a conductor, such as copper. In such examples, eddy currents may be supported in the flux shield, which may lead to Ohmic losses. By including slits, holes and/or pockets, any such currents must follow a tortuous path through the flux shield. Because the length of the path that the eddy currents must travel is increased, Ohmic losses are reduced.
[0128] FIG. 16a shows a pole piece segment 1600 having no slits, holes or pockets. An oval eddy current path 1602 is formed in response to the axial flux F.
[0129] FIG. 16b shows a pole piece segment 1604 having pockets 1606 formed therein. The pockets do not extend all of the way through the flux shield segment 1604. As shown, an eddy current path 1608 is formed around the pockets 1606.
[0130] FIG. 16c shows a pole piece segment 1610 having slits 1612a, 1612b formed therein. Slits 1612a extend radially into the pole piece segment 1610. Slits 1612b extend circumferentially into the pole piece segment 1610. An eddy current path 1614 is formed around the slits 1612a, 1612b.
[0131] FIG. 16d shows a pole piece segment 1620 having holes 1622 formed therethrough. The holes 1622 extend axially through the segment 1620. Eddy current paths 1624, 1626 are formed around the slits holes 1622.
[0132] In the above examples, a radial arrangement of the magnetic apparatus has been focused on. However, as the reader will appreciate, an axial arrangement could alternatively be used. FIG. 17 shows a first axial arrangement; FIG. 18 shows a second axial arrangement; FIG. 19 shows a third axial arrangement. FIG. 20 shows a radial-arrangement, but in which the apparatus is configured for linear axial movement rather than rotational movement.
[0133] In FIG. 17, the stator 102, first rotor 104, and second rotor 106 are each arranged around the rotatable output shaft 118. However, rather than being arranged concentrically relative to one another as in previous examples, the stator 102 is located towards a first axial end of the apparatus, the first rotor 104 is located towards a second axial end of the apparatus, and the second rotor 106 is located axially between the stator 102 and the first rotor 104. Thus, the first rotor 104, the second rotor 106 and the stator 102 are axially separated. In this arrangement, axial flux is desired while radial flux is not wanted. Accordingly, the flux shield 302 is radially aligned with the first plurality of permanent magnets 110 so as to be located between the first plurality of permanent magnets 110 and the casing 122. The flux shield 302 is radially spaced from the first plurality of permanent magnets 110 by the spacer 304. However, as the reader will appreciate, the flux shield 302 could alternatively be spaced from the first plurality of permanent magnets 110 by an air gap.
[0134] Also labelled on FIG. 17 are the radial direction R, and the axial direction A. The radial direction R is perpendicular to the axial direction A. As can be seen, the stator 102, first rotor 104, and second rotor 106 are spaced from one another in the axial direction A. In other words, the stator 102, first rotor 104 and the second rotor 106 are aligned with each other in the axial direction A. The flux shield 302, on the other hand, is aligned with the first permanent magnets 110 in the radial direction, and is spaced from the first permanent magnets 110 in the radial direction. Accordingly, the flux shield 302 attenuates flux straying in the radial direction, and encourages flux to propagate in the axial directioni.e. axially towards the pole pieces 112 and the stator 102.
[0135] The second axial arrangement of FIG. 18 is a modification of the axial arrangement in FIG. 17. The apparatus includes a stator 102 which includes a first stator portion 102a at a first axial end, and a second stator portion 102b at a second axial end. First rotor 104 is located at an axial centre of the apparatus. A second rotor 106 is arranged such that a first plurality of pole pieces 112a are arranged axially between the first stator portion 102a and the first rotor 104; and such that a second plurality of pole pieces 112b are arranged axially between the second stator portion 102b and the first rotor 104. Pole piece support member 126 mechanically couples the first plurality of pole pieces 112a with the second plurality of pole pieces 112b. Again, axial flux is desired while radial flux is not wanted. Accordingly, the flux shield 302 is radially aligned with the first plurality of permanent magnets 110 so as to be located between the first plurality of permanent magnets 110 and pole piece support member 126. The flux shield 302 is radially spaced from the first plurality of permanent magnets 110 by the spacer 304. However, as the reader will appreciate, the flux shield 302 could alternatively be spaced from the first plurality of permanent magnets 110 by an air gap.
[0136] As the reader will understand, the second stator portion 102b and the second plurality of pole pieces 112b could be dispensed with, and as such are not essential.
[0137] The third axial arrangement of FIG. 19 is an alternative modification of the axial arrangement in FIG. 17. The apparatus includes a first permanent magnet rotor 104a at a first axial end, and a second permanent magnet rotor 104b at a second axial end. Stator 102 is located at an axial centre of the apparatus. A first pole piece rotor 106a is arranged such that a first plurality of pole pieces 112a are arranged axially between the first permanent magnet rotor 104a and the stator 102; and a second pole piece rotor 106b is arranged such that a second plurality of pole pieces 112b are arranged axially between the second permanent magnet rotor 104b and the stator 102. Again, axial flux is desired while radial flux is not wanted. Accordingly, a first flux shield 302a is radially aligned with the permanent magnets 110 of the first rotor 104a, and a second flux shield 302b is radially aligned with the permanent magnets 110 of the second rotor 104b. Each flux shield 302a, 302b is radially spaced from the first plurality of permanent magnets 110 by a respective spacer 304a, 304b. However, as the reader will appreciate, each flux shield 302a, 302b could alternatively be spaced from the first plurality of permanent magnets 110 by a respective air gap.
[0138] FIG. 20 shows the linear arrangement. In FIG. 20, the stator 102, first translator 104 and second translator 106 are concentrically arranged around the translatable output shaft 118, such that the stator 102 is located radially outside of the first translator 104, and such that the second translator 106 is located radially between the stator 102 and the first translator 104. As shown, the second translator 106 is coupled to the output shaft 118. Each of the output shaft 118, the first translator 104, and the second translator 106 are configured to translate axially relative to the stator 102. The windings 108 are wound toroidally around the stator 102. As with previous examples, the first translator 104 comprises a first plurality of permanent magnets 110; the stator 102 comprises a second plurality of permanent magnets 120 and a plurality of windings 108; and the second translator 106 comprises a plurality of pole pieces 112 and support members 126a, 126b. In this example, radial flux is desired and axial flux is not wanted. Accordingly, a first flux shield 302a is axially aligned with the first plurality of permanent magnets 110 so as to be located between the first plurality of permanent magnets 110 and the first support member 126a; and a second flux shield 302b is axially aligned with the first plurality of permanent magnets 110 so as to be located between the first plurality of permanent magnets 110 and the second support member 126b. Each flux shield 302a, 302b is spaced from the first plurality of permanent magnets 110 by a respective spacer 304a, 304b. However, as the reader will appreciate, each flux shield 302a, 302b could alternatively be spaced from the first plurality of permanent magnets 110 by a respective air gap.
[0139] FIG. 21 shows a magnetic gear 2100 according to the present disclosure. The magnetic gear 2100 is in most respects the same as the magnetic gear 300 from FIG. 3a, save for one key difference. In particular, whereas the magnetically geared apparatus 300 comprises only windings 108 on the stator 102, the magnetic gear 2100 comprises only second permanent magnets 120 on the stator 102. The presence of the second permanent magnets 120 (rather than windings) on the stator 102 in FIG. 21 may make the apparatus 2100 suitable for use as a magnetic gear, rather than as a power split device.
[0140] Similarly, FIG. 22 shows a magnetic gear 2200 which is in all respects the same as the magnetic gear 300 from FIG. 3b, save for one key difference. In particular, whereas the magnetically geared apparatus 300 comprises only windings 108 on the stator 102, the magnetic gear 2200 comprises only second permanent magnets 120 on the stator 102. It is the presence of the second permanent magnets 120 (rather than windings) on the stator 102 in FIG. 22 which makes the apparatus 2200 suitable for use as a magnetic gear, rather than as a power split device.
[0141] FIG. 23 shows further magnetic gear 2300 according to the present disclosure. In the magnetic gear 2300, the pole pieces 112 are mounted on a stator 2302 (which in turn is coupled to the casing 122), and the plurality of second permanent magnets 120 are mounted on a second rotor 2304. The stator 2302 carrying the pole pieces 106 is located between the first rotor 104 and the second rotor 2304. The second rotor 2304 is open at a first axial end, and comprises a steel support member 2306 at a second axial end (i.e. has an open cup structure). The first rotor 104 similarly has an open cup structure, and is open at its second axial end. The first rotor 104 is coupled to an input shaft 118a, so as to be driven by the input shaft 118a. The second rotor 2304 is coupled to an output shaft 118b so as to drive the output shaft 118b. The input shaft 118a extends from a first axial end of the magnetic gear 2300. The first flux shield 302a at the first axial end of the first permanent magnets 110 acts to prevent stray axial flux from reaching the casing 122. The second flux shield 302b acts to prevent stray axial flux from reaching the steel support member 2306.
[0142] Finally, FIG. 24 shows a variation 2400 of the magnetic gear 2300 shown in FIG. 23. Rather than having the input shaft 118a extending from the first axial end and the output shaft 118b extending from the second axial end as in FIG. 23, the magnetic gear 2400 of FIG. 24 has both the input and output shafts 118a, 118b extending from the first axial end of the magnetic gear 2400. Moreover, the input shaft 118a, which is mechanically coupled to the first rotor 104, is concentrically arranged with the hollow output shaft 118b. The hollow output shaft 118b is mechanically coupled to the steel support member 2306.
[0143] The term comprising should be interpreted as meaning including but not limited to, such that it does not exclude the presence of features not listed. The examples described and shown in the accompanying drawings are provided as examples of ways in which the invention may be put into effect and are not intended to be limiting on the scope of the invention. Modifications may be made, and elements may be replaced with functionally and structurally equivalent parts, and features of different embodiments may be combined without departing from the disclosure. In particular, the features described in the above examples may be combined with one another insofar as such a combination is technically possible. For example, any one of the examples described above may use flux shields that are shaped as shown in FIG. 8a, 8b or 9, or may surround an exterior edge of the spacer as shown in FIG. 9. In any of the examples above, a spacer 1002a as shown in FIG. 10 may be included. In any of the examples above, axial ends of the plurality of first permanent magnets 110 may be chamfered as shown in FIG. 11, and/or axial ends of the pole pieces 112 may be chamfered as shown in FIG. 12.
