Abstract
A linear electromotive machine, for example a motor, generator and/or eddy-current brake is disclosed. The machine comprises a stator and a rotor, the rotor comprising a Halbach magnet array mounted on a fibre-reinforced polymer rotor frame. Also disclosed is a transportation system including such a machine and a method of manufacturing such a machine.
Claims
1. A linear electromotive machine comprising a stator and a rotor, the rotor comprising a Halbach magnet array mounted on a fibre-reinforced polymer rotor frame.
2. A machine as claimed in claim 1 wherein the rotor frame is a carbon-fibre-reinforced polymer frame.
3. A machine as claimed in claim 1 wherein the frame does not include magnetic material.
4. A machine as claimed in claim 1 wherein the Halbach magnet array is comprised of a first row of magnets and a second row of magnets spaced apart from the first row, each row of magnets itself being a Halbach array having a strong field side and a weak field side.
5. A machine as claimed in claim 4 wherein the surfaces of the first and second rows from which strong field sides emanate face toward one another.
6. A machine as claimed in claim 4 wherein the machine is configured such that, in use, the stator passes between the first and second row of magnets.
7. A machine as claimed in claim 4 wherein the rotor frame comprises two walls extending parallel to each other.
8. A machine as claimed in claim 7 wherein the first row of magnets is located adjacent the distal end of one wall and the second set of magnets is located adjacent the distal end of the other wall.
9. A machine as claimed in claim 7 wherein the machine is configured such that, in use, the stator passes between the two walls.
10. A machine as claimed in claim 1 wherein the linear electromotive machine is an alternating current synchronous motor.
11. A machine as claimed in claim 10 wherein the linear electromotive machine is a polyphase machine, for example a three phase machine.
12. A machine as claimed in claim 1 wherein the stator comprises a first set of coils and a second set of coils, and the coils of the first set are offset relative to the second set of coils so that corresponding coils of each group are not aligned and an n-pole harmonic of a magnetic field produced by the groups is substantially cancelled, where n is a positive, even integer.
13. A transportation system comprising a carriage configured to follow a predetermined path and an electromotive machine comprising a stator and a rotor, the rotor comprising a Halbach magnet array mounted on a fibre-reinforced polymer rotor frame, the rotor being mounted on the carriage.
14. A transportation system according to claim 13, wherein the carriage is configured to travel along a guide and the stator is mounted adjacent to and/or on the guide.
15. A transportation system according to claim 13, wherein the transportation system is an amusement ride, for example a roller coaster.
16. A method of manufacturing an electromotive machine comprising a rotor and a stator, the method comprising the following steps: forming a rotor using a fibre-reinforced polymer; and mounting a Halbach magnet array on the rotor.
17. A method according to claim 16, wherein the fibre-reinforced polymer is carbon fibre.
18. A method according to claim 16, wherein the step of forming a rotor using a fibre-reinforced polymer comprises laying up a plurality of fibres on a skeleton.
Description
DESCRIPTION OF THE DRAWINGS
[0045] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:
[0046] FIG. 1 shows a cross sectional end view of a linear electromotive machine rotor according to a first example embodiment of the invention;
[0047] FIG. 2 shows a perspective view of the rotor of the first embodiment;
[0048] FIG. 3 shows a Halbach magnet array for use in the rotor of the first embodiment;
[0049] FIG. 4a shows a cross sectional end view of a linear electromotive machine including a rotor according to the first embodiment;
[0050] FIG. 4b shows a cross sectional plan view of a linear electromotive machine including a rotor according to the first embodiment;
[0051] FIG. 4c shows a schematic of the coils of a stator of a linear electromotive machine suitable for use with a rotor according to the first embodiment;
[0052] FIGS. 5a and 5b show a linear electromotive machine according to additional embodiments of the invention;
[0053] FIG. 6 shows a linear electromotive machine according to a third embodiment of the invention;
[0054] FIGS. 7a and 7b show transportation systems suitable for use with a rotor in accordance with embodiments of the invention; and
[0055] FIG. 8 shows a flow chart for a method of manufacturing a rotor in accordance with embodiments of the invention.
DETAILED DESCRIPTION
[0056] FIG. 1 shows a cross sectional view of a rotor 1 of a linear electromotive machine according to a first embodiment of the invention. The rotor comprises a rotor frame 20 and two linear magnet arrays 10. The rotor frame 20 is U shaped with two parallel sides, a closed side joining the parallel sides, and an open side. A linear Halbach magnet array 10 (see FIG. 3 for more detail) is mounted on the inner surfaces of each of the parallel sides of the rotor frame 20 at the distal end of the parallel sides and adjacent to the open side such that a space is formed in between the magnet arrays 10. The magnetic field 30 emanating from the inside faces 10a of the magnet arrays 10 is represented by a dashed line in FIG. 1 and projects into the space between the magnets 10, the fields 30 from the two arrays combine with one another along the lengths of the arrays. The magnet arrays 10 connect to the rotor frame 20 via outside faces 10b. Rotor frame 20 is made from carbon fibre reinforced polymer. Enclosed within the carbon-fibre-reinforced polymer frame 20 is a U shaped foam skeleton 21 (the outline of which is denoted by a dashed line in FIG. 1). In other embodiments the skeleton 21 may be absent. In some embodiments a mounting bracket for fixing the rotor frame 20 to a carriage is mounted on the frame.
[0057] A perspective view of the rotor 1 of the first embodiment is shown in FIG. 2. The thickness of the sides of the rotor frame 20 is variable along the length of the rotor frame 20. Thinner portions 22 of the frame 20 alternate along the length of the frame 20 with thicker portions 23 to form a ribbed frame. The inner faces of the sides of the rotor frame 20 are flat such that the variations in thickness from the ribbed and non-ribbed sections are only present on the outside of the rotor frame.
[0058] In FIG. 2 the magnet arrays 10 are mounted along the edge of the parallel sides of the rotor frame adjacent to the open side and are the same length as the rotor frame. In other embodiments the magnets may be longer or shorter than the rotor frame, or mounted further from the open side. In FIG. 2 the magnet arrays 10 are show as a single continuous array but in further embodiments the magnet arrays 10 may be comprised of two or more connected or disconnected smaller magnets or magnet arrays.
[0059] FIG. 3 shows a plan view of magnet array 10 with inside face 10a (shown at the top side in FIG. 3) and outside face 10b (shown at the bottom side in FIG. 3). Each magnet array 10 is comprised of a series of individual magnets 12 arranged in a Halbach array configuration. In the embodiment shown in FIG. 3, the magnets 12 of the Halbach array are oriented such that the polarity of each magnet is aligned either with, or perpendicular to, the longitudinal axis of the array, and each magnet 12 is rotated 90 with respect to the adjacent magnet in a repeating pattern such that every fourth magnet is has its polarity oriented in the same direction (the polarity is indicated by an arrow in FIG. 3). In other embodiments, successive magnets in the array may be rotated by a smaller angle, for example 45, 30, or less, in a similar repeating pattern. In such configurations the magnetic field is asymmetric with a strong field 14 in which the magnetic flux is augmented (compared to the flux that would be present in an array with alternating (N-S-N-S) polarity) emanating from one side of the magnet array (the strong-field side) and a weak field 16 in which the magnetic flux is substantially cancelled emanating from the opposite side of the array (the weak-field side).
[0060] In the first embodiment the magnet arrays 10 are mounted on the body 20 such that the strong field 14 emanates from the inside faces of the magnet arrays, when mounted facing one another on the rotor frame 20. The strong fields 14 interact with one another such that they combine to form a single strong magnetic field between the magnet arrays. In this arrangement the outside faces 10b of the magnet arrays are adjacent to the parallel sides of the rotor frame 20.
[0061] The magnetic field emanating from the outside face 10b of the magnet array is a substantially cancelled weak field 16 and there is little or no flux. Consequently rotor bodies in accordance with the present invention need not include a conventional back iron comprised of a ferromagnetic material and/or may include a very much smaller back iron. Not only does the absence of a back iron (or reduction in its size) offer a potential weight saving over conventional rotor frames, it also facilitates the use of carbon-fibre rotor frame thereby further increasing the potential for weight saving.
[0062] A cross sectional view of a machine including a rotor in accordance with the first embodiment of the invention is shown in FIG. 4a. A linear stator 40 is positioned in the channel space between the sides of the rotor 1 such that the hollow of the channel of the U shaped rotor 1 straddles the stator 40 and the stator sits within the magnetic field 30 that exists between the two rows of magnet arrays 10.
[0063] A plan view of the electromotive machine of FIG. 4a is shown in FIG. 4b. The rotor 1 is denoted by a dashed-line box in FIG. 4b. The stator 40 comprises a first set of windings on a first side 40a of the machine and a second set of windings on a second side 40b of the machine, the rotor 1 extending over both sides of the stator 40. Each set of windings comprises current conducting coils wound in windings 41a, 41b, 41c as shown in FIG. 4b. Each winding is wound with a separate phase of a three-phase AC supply, where each phase is separated by 120 electrical degrees in time and the three phases are arranged in a repeating pattern such that every third winding is supplied by the same phase (different coils being indicated by different shading patterns in FIG. 4). The windings 41a, 41b, 41c may be concentrated windings, distributed windings, or any other type of windings. The windings shown in FIG. 4 are offset with respect to one another by a pitch of one and a half windings. In this arrangement the coils of each winding 41a, 41b, 41c are half way between two coils of the corresponding phase on the opposite side of the rotor.
[0064] The coils of windings 41a, 41b, 41c of the first side 40a and second side 40b are wound in opposite directions, as can be seen in FIG. 4c, where O and X indicate coils conductors wound out of and into the plane of the figure, respectively and the dashed lines indicate separations in the halves of the coils. Taking, for example, winding 41b, it can be seen that the coils on the first side 40a are wound with the left half coming out of the plane of the figure, and the right half going into the plane of the figure, and that the equivalent coil on the second side 40b is wound in the opposite direction. When the windings are wound in this manner and offset by one and a half coil pitches, unwanted harmonics of the travelling magnetic field from both sides of the stator destructively interfere such that they are substantially cancelled, leaving only desired components of the travelling magnetic fields.
[0065] With particular reference to FIG. 4b, when energised in sequence the windings 41a, 41b, 41c of the stator produce a travelling magnetic field 60 around the windings that travels along the length of the stator in a manner that is well known in the art. The travelling magnetic field interacts with the magnetic field between the rows of magnet arrays 10 to produce a thrusting force on the rotor (shown by the arrows on the rotor) that urges the rotor along the stator.
[0066] A second embodiment of the invention with a single sided stator 140 and single sided rotor 101 is shown in FIG. 5a. In this embodiment the single sided stator 140 comprises windings 41 wound in the same manner as one of the sides of the two sided stator described in relation to FIG. 4b. The rotor 101 is also constructed in the same manner as previously described, with a carbon fibre rotor frame 120 and Halbach magnet array 110 mounted thereon. The Halbach array 110 is arranged such that the strong field side is on the same side as the stator 140. FIG. 5a shows the windings of the second embodiment wound without a solid core, but in other embodiments, as in FIG. 5b windings 41 may be wound in slots on a core 42.
[0067] A cross sectional view of a third embodiment of the invention is shown in FIG. 6. The rotor of this embodiment comprises a rotor frame 620 with two outer linear magnet arrays 610 and two inner linear magnet arrays 611. The rotor frame 620 is a W shape with two parallel outer sides 621, an inner wall 622 located between and extending parallel to the two outer sides 621, a closed side joining the parallel outer sides 621 and inner wall 622, and an open side. An outer linear magnet array 610 is mounted on the distal end of the inner surface of each of the parallel outer sides 621 and adjacent to the open side, in a similar manner to the first embodiment. Two inner linear magnet arrays 611 are mounted on the distal end of the inner wall 622, with one array 611 on either side of the wall 622. Each outer magnet array 610 faces an inner magnet array 611. In this embodiment, a space is formed between both outer magnet array/inner magnet array pairings in a similar manner to the magnet array pair of the first embodiment.
[0068] Each outer side 621 is subject to a unidirectional net magnetic attraction force toward the inner wall 622 due to the magnetic attraction between the outer linear magnet arrays 610 and inner linear magnet arrays 611. The outer sides 621 are of sufficient thickness and strength to prevent the movement of the sides and outer linear magnet arrays toward the inner linear magnet arrays 611. The two inner linear magnet arrays 610 of the inner wall 622 are subject to two substantially equal magnetic attractive forces toward the outer linear magnet arrays 610, but in opposite directions. There is very little net directional force on the inner wall 622, and as such, the inner limb 622 of the example shown in FIG. 6 is thinner and has a lower strength than the outer sides 621. This reduction in thickness results helps to keep the weight of the rotor frame 620 down.
[0069] In one example of the third embodiment, the inner linear magnet arrays 611 are Halbach arrays, and substantially no magnetic flux is present in the inner limb. In another example, the inner linear magnet arrays 611 are conventional magnetic arrays, with the sides of the inner linear magnet arrays 611 that are in contact with the inner limb being of opposite magnetic polarity such that a substantial magnetic flux is present in the inner limb.
[0070] In one example, the third embodiment may be considered as two rotors of the first embodiment joined together.
[0071] A transportation system 70 comprising a linear electromotive machine according to the first embodiment is shown in FIG. 7a. The transportation system comprises moveable carriage 80 and stationary guiding track 90. The movable carriage 80 comprises rollers 85, and a rotor 1 in accordance with the first embodiment. A stator 40 is mounted on the track 90. The rotor 1 and the stator 40 combine to form an electromotive machine as described above. The rotor 1 is affixed to the carriage body 80. In use, the rollers 85 of the carriage 80 travel along the track 90. When the stator 40 is energised the interaction of the moving magnetic field of the stator 40 and moving magnetic field of the rotor 1 combine to produce a thrusting force denoted by arrow 101 in FIG. 7a that moves the carriage 80 along the stationary guiding track 90 from left to right as shown in FIG. 7a.
[0072] In a further example of a transportation system 70, shown in FIG. 7b, a stator 40 comprising conductor 41 is mounted on the stationary guiding track 90. In this example, as the carriage 80 moves forward the rotor 1 passes in close proximity to the conductor 41. Eddy currents are induced in the conductor 41 which produce a decelerating force indicated by arrow 103 in FIG. 7b that acts to reduce the speed of a carriage 80 travelling from left to right in FIG. 7b. In this example the rotor acts as an eddy current brake.
[0073] In the transportation system of FIGS. 7a and 7b the rollers 85 are mounted to the movable carriage body 80, however they may equally be attached to the stationary guiding track such that the carriage body rolls over the rollers.
[0074] In some embodiments the transportation system 70 is a roller coaster. In other embodiments the transportation system is a freight or baggage handling system. In further embodiments the transportation system is a public transport system. In further embodiments the transportation system is a vehicle launching system. In some embodiments (not shown) rollers 85 are replaced with wheels.
[0075] An example process for manufacturing a rotor according to the invention is shown in FIG. 8. In step 801 a mould suitable for forming the rotor frame is produced. In step 802 a releasing agent or material is optionally applied to the mould to facilitate removal of the rotor frame from the mould. In step 803 carbon fibres are laid over or in the mould in the approximate shape of the rotor frame. In step 804 the polymer resin is applied to the carbon fibres. The resin may be painted on, sprayed on, or applied in any other suitable method. Alternatively, the carbon fibres may be impregnated with resin prior to use in step 803. In step 805 the fibres and resin are forced into approximately to the final shape of the rotor frame. This step may be done with a compression process, vacuum process, or any other suitable process. It is to be understood that the application of resin to the fibres in step 804 could alternatively occur at the same time as the compression as in, for example, a vacuum infusion method. In step 806 the compressed fibres and resin are cured. Step 806 may or may not include heating the resin and fibres to facilitate curing. In step 807 the cured rotor frame is removed from the mould. In step 808 the frame may undergo finishing processes including trimming, hole drilling, sanding and polishing, or any other finishing process typically applied to carbon fibre manufactured components. In step 809 Halbach arrays are mounted to the frame. It is to be understood, however, that the mounting of Halbach arrays could occur as part of an earlier step, for example, prior to the application of resin, or alternatively, for example, prior to the application of carbon fibres. Optionally, a skeleton or former may be used in addition to or instead of the mould in order to allow the fibres to be formed into the desired shape during the laying up process. The fibres may be shaped around the skeleton prior to curing. The skeleton may remain within the frame after curing. The skeleton may be made of a low density material, for example a foam and/or wood. Accordingly, methods in accordance with the present embodiment using a skeleton may allow for the production of a wider range of shapes of frame and/or a lighter frame as it may be possible to achieve the same frame shape with less fibre-reinforced polymer material.
[0076] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.
[0077] In the embodiments described above the Halbach arrays are mounted on the inside of the rotor frame. It will be appreciated that magnet arrays could additionally or alternatively be mounted on the outside of the rotor frame.
[0078] In the embodiments described above the rotor body is IF or W shaped. It will be appreciated that a differently shaped rotor body may be used.
[0079] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.
