FLYWHEEL

Abstract

A flywheel (1100) comprising a plurality of discs (1102) arranged in a stack (1104), including at least first and second end discs at either end of the stack (1104), each of the plurality of discs (1102) including a plurality of disc apertures therethrough, first and second plate members (1106) disposed at opposing ends of the stack (1104), one or both of the first and second plate members (1106) including a plurality of plate apertures (1106a) therethrough for alignment with a corresponding series of disc apertures through the stack (1104), in which one or both of the plate members (1106) includes one or more recesses (1106c) which are disposed on a disc-facing side thereof and positioned adjacent to one or more of the plurality of plate apertures (1106a), and connection means (1114) for clamping the first and second plate members (1106) together about the stack of discs, the connection means (1114) extending through each of the plurality of disc apertures, in which a spacer or space-filling means (1138) is provided between the or each connection means (1114) and the respective disc apertures for supporting the connection means (1114), the spacer or space-filling means (1138) extending from a position within the stack (1104) into the one or more recesses (1106c) of one or both of the plate members (1106).

Claims

1. A flywheel comprising a plurality of discs arranged in a stack, including at least first and second end discs at either end of the stack, each of the plurality of discs including a plurality of disc apertures therethrough, first and second plate members disposed at opposing ends of the stack, one or both of the first and second plate members including a plurality of plate apertures therethrough for alignment with a corresponding series of disc apertures through the stack, in which one or both of the plate members includes one or more recesses which are disposed on a disc-facing side thereof and positioned adjacent to one or more of the plurality of plate apertures, and connection means for clamping the first and second plate members together about the stack of discs, the connection means extending through each of the plurality of disc apertures, in which a spacer or space-filling means is provided between the or each connection means and the respective disc apertures for supporting the connection means, the spacer or space-filling means extending from a position within the stack into the one or more recesses of one of the plate members.

2. A flywheel as claimed in claim 1, in which the spacer or space-filling means is in the form of a sleeve fitted around the connection means.

3. A flywheel as claimed in claim 2, in which the sleeve has an external sidewall profile which substantially matches an internal sidewall profile of each disc aperture in a series of aligned disc apertures in the stack for snugly fitting therein, the sleeve extending into the one or more recesses of one or both of the plate members.

4. A flywheel as claimed in claim 2, in which the sleeve is rigid.

5. A flywheel as claimed in claim 2, in which the sleeve is flexible and includes one or more cavities or channels.

6. A flywheel as claimed in claim 1, in which the spacer or space-filling means comprises a set material, and the connection means includes a conduit for conveying a material flow, for forming the set material, into the one or more recesses and space between the connection means and the disc apertures.

7. A flywheel as claimed in claim 6, in which the set material includes at least one of: a thermoplastic material, with or without a strengthening filler; a thermoset plastic material, with or without a strengthening filler; and a low melting point metal.

8. A flywheel as claimed in claim 1, in which a minimum width of each plate aperture is substantially less than a width of each disc aperture.

9. A flywheel as claimed in claim 1, in which one or both of the first plate member and the second plate member include: one or more clamping areas in abutment with the respective end disc, and at least one recessed area which is substantially spaced apart from the respective end disc.

10. A flywheel as claimed in claim 9, in which the at least one recessed area is closer to the stack centre than the one or more clamping areas.

11. A flywheel as claimed in claim 9, in which the at least one recessed area is substantially concave and/or substantially annular in shape.

12. A flywheel as claimed in claim 1, in which the connection means includes one or more bolts or threaded studs including a sidewall with an outer surface.

13. A flywheel as claimed in claim 12, in which each bolt or threaded stud is hollow.

14. A flywheel as claimed in claim 12, in which a cross-section of each bolt or threaded stud may be substantially constant.

15. A flywheel as claimed in claim 1, in which one or both of the first and second plate members includes a circumferential lip or a plurality of lip members configured to fit around the periphery of one or both of the first and second end discs respectively.

16. A flywheel assembly comprising one or more flywheels as claimed claim 1, the or each flywheel being mounted on or to a drive assembly for facilitating rotation of the or each flywheel for storing energy in or deploying energy from at least one of the flywheels.

17. A flywheel as claimed in claim 1, in which the spacer or space-filling means extends from the position within the stack into the one or more recesses of both of the plate members.

18. A flywheel as claimed in claim 1, in which the connection means extends through each of the plurality of disc apertures without contacting the plurality of discs.

19. A flywheel comprising a plurality of discs arranged in a stack, including at least first and second end discs at either end of the stack, each of the plurality of discs including a plurality of disc apertures therethrough, first and second plate members disposed at opposing ends of the stack, one or both of the first and second plate members including a plurality of plate apertures therethrough for alignment with a corresponding series of disc apertures through the stack, in which both of the plate members includes one or more recesses which are disposed on a disc-facing side thereof and positioned adjacent to one or more of the plurality of plate apertures, and connection means for clamping the first and second plate members together about the stack of discs, the connection means extending through each of the plurality of disc apertures, in which a spacer or space-filling means for supporting the connection means is provided between the or each connection means and a plurality of the respective plurality of disc apertures around the connection means, the spacer or space-filling means extending from a position within the stack into the one or more recesses of one or both of the plate members.

20. A flywheel assembly comprising one or more flywheels as claimed in claim 19, the or each flywheel being mounted on or to a drive assembly for facilitating rotation of the or each flywheel for storing energy in or deploying energy from at least one of the flywheels.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0140] For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which:

[0141] FIG. 1 shows a side view of a first prior art flywheel device from U.S. Pat. No. 7,267,028;

[0142] FIG. 2 shows a cross-sectional side view of a second prior art flywheel device from EP2759043;

[0143] FIG. 3 shows a cross-sectional side view of a first embodiment of a flywheel;

[0144] FIG. 3A shows a top view of a disc of the flywheel of FIG. 3;

[0145] FIG. 4 shows an enlarged partial cross-sectional side view of the flywheel of FIG. 3, including a first version of a connection means for the flywheel;

[0146] FIG. 4A shows a cross-sectional side view of a second version of connection means for the flywheel of FIG. 3;

[0147] FIG. 4B shows a cross-sectional side view of a third version of connection means for the flywheel of FIG. 3;

[0148] FIG. 4C shows a cross-sectional side view of a fourth version of connection means for the flywheel of FIG. 3;

[0149] FIG. 5 shows a partial cross-sectional side view of a second embodiment of a flywheel, including a fifth version of connection means;

[0150] FIG. 6 shows a partial cross-sectional side view of a third embodiment of a flywheel, including a fifth version of connection means;

[0151] FIG. 7 shows a partial cross-sectional side view of a fourth embodiment of a flywheel, including an intermediate support member;

[0152] FIG. 8 shows a top view of a disc for any of the flywheels of FIGS. 3, 5, 6 and 7, including a first embodiment of a surface layer applied to the disc;

[0153] FIG. 9 shows a top view of a disc for any of the flywheels of FIGS. 3, 5, 6 and 7, including a second embodiment of a surface layer applied to the disc;

[0154] FIG. 10 shows a partial cross-sectional side view of a fifth embodiment of a flywheel;

[0155] FIG. 10A shows a perspective view of a first version of a locating means for the flywheel of FIG. 10;

[0156] FIG. 11 shows a partial cross-sectional side view of a sixth embodiment of a flywheel;

[0157] FIG. 11A shows a perspective view of a second version of a locating means for the flywheel of FIG. 11;

[0158] FIG. 12 shows a partial cross-sectional side view of a seventh embodiment of a flywheel;

[0159] FIG. 12A shows a perspective view of a third version of a locating means for the flywheel of FIG. 12;

[0160] FIG. 13 shows a partial cross-sectional side view of an eighth embodiment of a flywheel;

[0161] FIG. 13A shows a perspective view of the flywheel of FIG. 13;

[0162] FIG. 14 shows a partial cross-sectional side view of a ninth embodiment of a flywheel;

[0163] FIG. 14A shows a perspective view of the flywheel of FIG. 14;

[0164] FIG. 15A shows a cross-sectional side view of a tenth embodiment of a flywheel;

[0165] FIG. 15B shows an enlarged partial cross-sectional side view of the flywheel of FIG. 15A;

[0166] FIG. 15C shows an enlarged partial cross-sectional side view of a variant of the flywheel of FIG. 15A;

[0167] FIG. 16 shows a cross-sectional side view of an eleventh embodiment of a flywheel;

[0168] FIG. 16A shows a perspective view of a first embodiment of a spacer for connection means of the flywheel of FIG. 16;

[0169] FIG. 16B shows an end view of a second embodiment of a spacer for the connection means of the flywheel of FIG. 16;

[0170] FIG. 17 shows a cross-sectional side view of a twelfth embodiment of a flywheel; and

[0171] FIG. 17A shows an enlarged partial cross-sectional side view of the flywheel of FIG. 17.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0172] FIGS. 1 and 2 relate to prior art devices, which are described in the background section.

[0173] FIGS. 3 and 3A relate to a first embodiment of a flywheel, indicated generally at 100. The flywheel 100 is designed for use in kinetic energy storage which can be used, in conjunction with a suitable electrical motor-generator or mechanical drive (or any other suitable type of drive means) to provide a means of storing electrical energy.

[0174] Many applications are possible for the flywheel 100, including but not limited to any one or more of: local grid boosting for fast charging electric vehicles; uninterruptible power supplies; trackside rail; demand side management; and electrical grid services as some examples. The flywheel 100 could be provided in a vehicle with an electric propulsion system, such as a car, truck, bus, train, plane or boat.

[0175] The flywheel 100 could also be used to provide kinetic energy storage where the stored energy can be transmitted mechanically to assist a vehicle accelerating and to retrieve otherwise lost kinetic energy. The structure of the flywheel 100 is primarily described with respect to the flywheel at rest, unless otherwise specified.

[0176] The flywheel 100 includes a plurality of discs 102 (also referred to as laminates). In this embodiment fourteen discs 102 are provided, but it will be appreciated that any suitable number of discs may be provided in other embodiments subject to there at least being first and second end discs.

[0177] The discs 102 are substantially circular in profile in this embodiment. Centres of the discs 102 are aligned along a common longitudinal axis A-A to provide a stack 104 of discs. The stack 104 is substantially cylindrical in this embodiment.

[0178] The stack 104 may be considered to provide an inertial element of the flywheel 100. The stack 104 may be considered as a laminate stack.

[0179] The discs 102 may each be made of steel in this embodiment, although another suitable metal, alloy or composite material may be used in other embodiments.

[0180] Each disc 102 has a plurality of disc apertures 102a in this embodiment. Each disc 102 in the stack is substantially the same in this embodiment, preferably to a tolerance on the order of microns or tens of microns.

[0181] One of the discs 102 is depicted in FIG. 3A and has four disc apertures 102a. The disc apertures 102a in each disc 102 are aligned on common axes with corresponding disc apertures in the other discs in the stack 104 in this embodiment. This provides a plurality of sets or series of aligned disc apertures through the stack (in this case four sets), which may be considered to be stack apertures.

[0182] It will be appreciated that any suitable number of disc apertures may be provided through the discs 102, in any suitable positions and sizes, for allowing the discs to be secured together by connection means.

[0183] The disc apertures 102a are disposed near the periphery of each disc 102. The disc apertures 102a are equidistantly spaced around the axis A-A. The disc apertures 102a may be considered to be arranged on a pitch circle, indicated by the imaginary circular dot-dash line in FIG. 3A. In this embodiment, the discs each have four-fold rotational symmetry when viewed end-on.

[0184] The shapes of the disc apertures 102 are selected to minimise stresses during disc rotation at flywheel speeds. Details of suitable shapes are discussed in EP2759043 which is incorporated herein by reference.

[0185] Each disc aperture 102a is approximately elliptical in profile in this embodiment. The pitch circle intercepts a centre of each disc aperture in FIG. 3A. It will be appreciated that other embodiments may include various other non-circular shapes of disc aperture, or in some cases circular disc apertures.

[0186] A pair of plate members 106 (also referred to as cheek plates) are disposed at either end of the stack 104. The plate members 106 are secured or clamped together about the stack 104. The plate members 106 in this embodiment each have a diameter which is less than a diameter of the disc stack 104.

[0187] The cheek plates 106 allow the laminate stack 104 to be connected to bearing landings 150. The cheek plates 106 also allow the stack 104 to be connected or fitted (or more generally provided in operative engagement) together with an electrical machine rotor part or mechanical drive part 160.

[0188] Each plate member 106 has a central stack-facing portion 108 which contacts a corresponding central region of one of the end discs 102.

[0189] Each plate member 106 has a substantially annular stack-facing portion 110 disposed around the central portion 108. The annular portion 110 is slightly recessed to space it apart from the respective end disc 102 of the stack 104. The annular portion 110 has a concave profile.

[0190] Each plate member 106 has a second substantially annular stack-facing portion 112, disposed around the first annular portion 110. The second annular portion 112 provides a clamping area or areas for securing together the plate members 106 about the stack 104.

[0191] Plate apertures 106a are provided through each plate member for receiving connection means. The plate apertures 106a are narrower than the disc apertures 102 where the plate apertures 106a open into the stack 104. The plate apertures 106a have a diameter which substantially corresponds to an external diameter of the connection means in this embodiment.

[0192] Each plate member 106 is thickest at the longitudinal axis A-A in this embodiment. Each plate member 106 gradually thins moving radially outwards from the axis A-A. The thinnest portion of each plate member 106 is approximately in the middle of the first annular portion 110. Each plate member 106 has an exterior concave region opposing the stack-facing concave portion 110. Moving further radially outwards, each plate member 106 is somewhat thicker at the second annular portion 112 than at the concave regions.

[0193] It will be appreciated that the form of the plate members is not considered to be essential to the present invention. Plate members like those of the prior art, such as those depicted in FIG. 2, may be used instead in related embodiments.

[0194] Whilst the flywheel is described above as having two plate members, it will be appreciated that embodiments are envisaged where only one plate member is provided at one stack end, if the other stack end is configured for securing the plate member in place to clamp the stack of discs together.

[0195] Connection means is provided to secure the plate members together. In this embodiment, a plurality of connection means are provided. The connection means in this embodiment is clamping means in the form of a plurality of bolts, rivets or threaded studs, referred to generally as clamping elements 114.

[0196] Each of the four clamping elements 114 in this embodiment is disposed centrally through a series of the disc apertures 102. The clamping elements 114 are provided on the pitch circle. Ends of the clamping elements 114 are secured by fixing means 116 (e.g. nuts or similar) which bear against the plate members 106 to provide a clamping force about the stack 104.

[0197] Recessed or countersunk external regions 118 are provided on the plates 106 for the fixing means to fit within. In this embodiment, external threaded portions of the ends of each clamping element 114 are disposed in the countersunk regions.

[0198] The clamping elements 114 do not touch the discs 102 or disc apertures 102a. The clamping elements 114 are only supported at the plate members 106 in this embodiment. This reduces stresses in the laminates 102 at the disc apertures 102a during high-speed flywheel rotation because the apertures 102a do not provide support to the clamping elements 114.

[0199] A gap is provided between the exterior of each clamping element 114 and the surrounding interior walls of the disc apertures 102a around it. Parts of the curved disc aperture walls immediately to either side of the clamping element 114 are seen most clearly in the cross-section of FIG. 4.

[0200] The flywheel 100 can provided as part of an assembly with a suitable drive mechanism. The assembly may be considered to be part of an energy harvesting and deployment system. The assembly is provided in containment suitable for safe operation of the flywheel, taking account of the mass and energy storage capacity of the flywheel.

[0201] During use, the flywheel 100 is rotated by the drive mechanism about the axis A-A to store kinetic energy in the flywheel 100. The flywheel 100 can deform radially outwards at speeds on the order of hundreds of metres per second, when used to store substantial amounts of kinetic energy.

[0202] The drive mechanism can be used to deploy a portion of the stored kinetic energy in a rotating flywheel by reducing the rotational rate of the flywheel, harvesting the stored kinetic energy and converting it into another useful form, e.g. electrical energy. Further instances of energy gathering and harvesting may be carried out as needed, which may include thousands or millions of cycles of energy deployment on the order of hundreds of kilojoules, several megajoules, or greater e.g. if multiple flywheels are provided in an assembly and work together in parallel.

[0203] Variations of the above flywheel embodiment and component parts are contemplated within the scope of the present invention. Features of the following embodiments are the same as above except where described otherwise.

[0204] Like reference numerals are used to refer to like features in the following embodiments, incrementing each numeral by a multiple of 100, e.g. feature 102 corresponds to features 202, 302 and so on in later embodiments.

[0205] FIG. 4 depicts a first type of the clamping element 114 for the flywheel 100. The clamping element 114 is solid and has a substantially constant cross-sectional width.

[0206] A second type of clamping element 114a (FIG. 4A) is contemplated where the element is hollow instead of solid. The hollow bore extends through the entire length of the element 114a as shown, but it will be appreciated that a number of hollow sections or pockets could be provided inside the element instead.

[0207] A third type of clamping element 114b (FIG. 4B) is further contemplated where the element is hollow and has a tapered external cross-section. The external wall of the element 114b tapers inwards towards a middle of the element 114b from both ends as shown.

[0208] A fourth type of clamping element 114c (FIG. 4C) is yet further contemplated where the element is hollow and has a concave external cross-section. The curvature of the external cross-section provides an elongate mid-section which is substantially thinned along a majority of the length of the element 114c. Each of the first to fourth types of clamping element 114-114c is a linear clamping element.

[0209] FIG. 5 depicts a fifth type of clamping element 214 (FIGS. 5 and 6) in a second embodiment of a flywheel, indicated generally at 200. The flywheel 200 is similar to the first flywheel 100 save for the different clamping elements and plate members.

[0210] The element 214 is a curved clamping element. Note that the sizes of the disc apertures 202a need to be correspondingly larger than for the linear elements to provide the gap between the clamping element 214 and the disc apertures 202a.

[0211] The element 214 is solid in this embodiment but could be hollow in other embodiments. The clamping element 214 follows a curved longitudinal axis. The curvature of the element 214 substantially approximates to a catenary (or part of a catenary). The element 214 can be pre-shaped accordingly prior to insertion into the stack.

[0212] The curved clamping element 214 is arranged with such that, in profile, its convex side is radially outside its concave side with respect to the flywheel axis A-A (refer to FIG. 3 for the position of the same axis in the flywheel 200).

[0213] Due to the curvature of the clamping element 214, the plate members in this embodiment include angled recesses 218a, 218b for the fixing means 216. The recesses are angled such that are each on an axis which is not perpendicular to a plane of each plate member 206. In this embodiment, the angle is around 15 degrees to an axis which is perpendicular to the plane of the plate member 206. The angle will vary depending on the height of the stack, the diameter of the clamping element 114 and size of the disc aperture openings, 202a but will typically be within 10-30 degrees.

[0214] The first recess 218a is angled in opposition to the second recess 218b. It will be appreciated that corresponding angled recesses are provided for each curved clamping element through the stack 204.

[0215] FIG. 6 depicts the same clamping element as FIG. 5, but provided in a third embodiment of a flywheel, indicated generally at 300. The flywheel 300 is similar to the second flywheel 200 save for differences in the discs.

[0216] In this embodiment, the stack of discs includes at least two different types or variations of discs 302. The first two discs 302x and the last two discs 302x in the stack are a first type of disc, and have a first set of disc apertures 302b co-aligned along a first axis. The discs 302y in the stack between the pairs of end discs 302x are a second type of disc, and have a second set of disc apertures 302c co-aligned along a second axis.

[0217] The second axis is disposed radially outwards of the first axis, relative to the flywheel axis A-A. The disc apertures 302b, 302c can thus be smaller in size than the disc apertures 202a in the FIG. 5 embodiment whilst still maintaining a gap between the element 214 and the disc apertures 302b, 302c.

[0218] It will be appreciated that the size and position of the disc apertures may be provided in any arrangement which accommodates the size and shape of the clamping element through the stack. Thus, three or more disc types may be provided, and in some embodiments it is envisaged that each disc could have its disc apertures slightly offset from those of its immediate neighbours to overall provide a stack aperture which most closely approximates the shape of the non-linear clamping element.

[0219] FIG. 7 relates to a fourth embodiment of flywheel, indicated generally at 400. The flywheel 400 is similar to the first flywheel 100 save for the different stack arrangement.

[0220] In some embodiments, the number of discs 402 provides a stack which is sufficiently long that the corresponding connection element(s) 414 could become too highly stressed during flywheel rotation. To mitigate this, an intermediate plate 420 is provided partway through the stack 404 to support the connection element 414 within the body of the stack. In this embodiment, there are eighteen discs 402 which are split into first and second groups of nine discs on either side of the intermediate plate. The intermediate plate has plate apertures 420a which substantially correspond to the size and shape of the connection element 414 for supporting that element.

[0221] It will be appreciated that the intermediate plate 420 may be sized and/or shaped differently to the discs 402 and/or the plate members 406. For example, in some embodiments, the intermediate plate may include recessed regions on its surfaces for minimising contact area with and stresses on the adjacent discs 402. The intermediate plate recessed regions may be concave and/or annular, similarly to the end plate recessed regions.

[0222] It will also be appreciated that the intermediate plate may be used in conjunction with any of the types of connecting element discussed herein, where the intermediate plate apertures and connecting elements are suitably configured.

[0223] FIGS. 8 and 9 relate to a material which is provided as a layer or layers between given pairs of adjacent discs. For brevity, the reference numerals used will refer to the first embodiment of the flywheel 100, but the material layer(s) may be provided in any embodiments of the invention, between some or all of the adjacent pairs of discs in the stack.

[0224] In FIG. 8, a partial surface layer 122 is provided on a peripheral annular surface region of the disc 102, passing around the apertures 102a. In FIG. 9, a plurality of partial surface layers 124 are provided, each layer 124 being arranged around one of the apertures 102a in an approximately elliptical or oval shape (although layers with circular perimeters or other shapes of perimeter may be provided in other embodiments).

[0225] The or each layer helps to minimise or substantially prevent rotation of one disc relative to its neighbouring discs by increasing friction and reducing the likelihood of slippage. This is in addition to the clamping force provided by the plate members 106 which also mitigates slippage.

[0226] The or each layer can be made of thermoplastic, or a thermosetting plastic, or a soft metal or alloy such as solder. The plastic/metal is applied as a thin layer or film on one or both sides of the disc in the shaded region indicated in FIG. 8 or the regions indicated in FIG. 9.

[0227] FIGS. 10 and 10A relate to a fifth embodiment of a flywheel, indicated generally at 500. The main difference to the first flywheel 100 is the provision of a pocket or recess at each plate aperture 506a. Each pocket is provided on the stack-facing side of the plate member 506.

[0228] A plurality of spacers 526 are provided for fitting into some or all of the pockets at either end of the stack. The spacers 526 are locating means for locating the ends of the stack of discs 502 to the plate members 506 to prevent relative movement of those parts. A hole 528 is provided through the middle of each spacer for receiving a given connection element.

[0229] The size and shape of each spacer 526 is configured to snugly fit each pocket and also snugly fit into each end disc aperture. The spacer 526 of FIG. 10A has a substantially elliptical sidewall in this embodiment.

[0230] FIGS. 11 and 11A relate to a sixth embodiment of a flywheel, indicated generally at 600. This embodiment is similar to the fifth flywheel 500 and its apertured spacer 526. However, each spacer 626 in this embodiment is provided with an elliptical sidewall 626a in a first half for fitting an end disc aperture 602a, and with a circular sidewall 626b in a second half for fitting a corresponding round pocket at the plate aperture 606a.

[0231] FIGS. 12 and 12A relate to a seventh embodiment of a flywheel, indicated generally at 700. This embodiment is similar to the fifth flywheel 500 and its apertured spacer 526. However, each spacer 726 in this embodiment is provided with a circular sidewall 726a (akin to a washer) in a first half for fitting a corresponding pocket at the plate aperture 706a, and with an elliptical sidewall 726b in a second half.

[0232] The elliptical sidewall 726b is larger in diameter than the corresponding end disc aperture. However, the spacer is formed of (or machined from) a malleable material and the action of clamping the plate members 706 together about the stack causes the spacer 726 to change shape to conform to the end disc aperture 702a and/or plate aperture 706a.

[0233] Note that the spacers 526, 626 of FIGS. 10A and 11A may also be formed or machined from any suitable material, which may include a malleable material.

[0234] FIGS. 13 and 13A relate to an eighth embodiment of a flywheel, indicated generally at 800. The main difference to the first flywheel 100 is in the shape of the plate members 806. Each plate member 806 includes a peripheral lip 828. The lip 828 may be considered to be an alternative or additional locating means to the spacers discussed above, for locating the stack to the plate members.

[0235] The lip 828 is circular and sized to correspond to the exterior sidewall of the end disc 802. In this case, the lip 828 has a substantially U-shaped cross-section at the disc-engaging portion. In some embodiments, each lip 828 can be a precision fit to its corresponding end disc 802.

[0236] FIGS. 14 and 14A relate to a ninth embodiment of a flywheel, indicated generally at 900. This embodiment is similar to the eighth flywheel 800. However, instead of having a continuous circular lip, each plate member 906 includes another engagement means for the end disc edge. In this case, a plurality of arms or lip members 928 is provided.

[0237] The four lip members 928 in this embodiment (three of which are visible) are equally spaced around the plate member 906. The lip members 928 may be integrally formed with the plate 906. In some embodiments, the lip members 928 are sized to provide a precision fit about the corresponding end disc 902.

[0238] Note that the shape of the plate members illustrated in FIGS. 13 to 14A as a simple disc is for illustration purposes only and is not to be construed as limiting or indicative of the shape or structure of the plate members in any flywheel embodiment.

[0239] It will be appreciated that the various versions of clamping elements, discs, plate members, spacers and material layers/films discussed for FIGS. 4 to 14A may be provided in any possible combination with the flywheel 100 of FIGS. 3 and 3A.

[0240] FIGS. 15A and 15B relate to a tenth embodiment of a flywheel, indicated generally at 1000. The flywheel 1000 in this embodiment has some similarities to the flywheel 100 described earlier, but is substantially different in that the connection means involves disc-to-disc bonding instead of clamping.

[0241] The flywheel 1000 includes a plurality of discs 1002 in a stack 1004. Each disc 1002 is substantially the same size and shape, and aligned along a common axis B-B of the flywheel 1000. Each disc 1002 is bonded to each of its neighbouring discs. None of the discs 1002 necessarily requires any disc apertures because the stack does not need to accommodate any connecting elements extending between the plate members.

[0242] Plate members or cheek plates 1006 are provided at either end of the stack 1004. The plate members 1006 are bonded to the ends of the stack 1004. The plate members 1006 may not include a recessed stack-facing portion, unlike the plate members in FIG. 3, for example.

[0243] In this embodiment, the plate members 1006 are substantially the same diameter as the discs 1002. Each plate member 1006 is thicker than one of the discs 1002. An outer surface of each plate member 1006 lies approximately parallel to the plane of the neighbouring disc, moving from a radial edge of the plate member 1006 towards the axis B-B to a position approximately at a quarter of the plate member radius. The plate member 1006 thickness then gradually increases moving further towards the axis B-B.

[0244] The plate members 1006 allow the laminate stack 1004 to be connected to bearing landings 1050. The cheek plates 1006 also allow the stack 1004 to be connected to be fitted together with an electrical machine rotor part 1060.

[0245] The disc-to-disc and disc-to-plate bonds should be made using a bonding material or means which is strong enough to maintain structural integrity of the flywheel 1000 during high-speed rotation. Epoxy resin, with or without toughening additives, is one such example, but should in no way be construed as the only possible bonding means. It is contemplated that other suitable resins, glues or adhesives may be used. Bonding may be achieved in some cases by soldering, brazing or other processing techniques to provide bonded interfaces between adjacent discs, for example.

[0246] The disc-to-disc bonding is provided by a bonding area 1030 near or at the outer portion of each disc 1002. That is, at a peripheral region 1032 of each disc 1002. Central regions 1034 (or regions within each peripheral region 1032) of each disc are not bonded together. This means that only part of the surface of each disc 1002 is bonded to its neighbouring discs 1002 (or neighbouring disc and neighbouring plate member) in the stack 1004.

[0247] Considering disc thickness in a direction parallel to the flywheel axis B-B, the peripheral region 1032 of each disc 1002 is marginally thicker than the central region 1034 of that disc 1002. The difference in thickness is exaggerated in FIGS. 15B and 15C solely for the purpose of illustration. It will be appreciated that the difference in thickness may be on the order of microns or tens of microns, as long as a sufficient space is provided between adjacent central regions 1034 to provide them substantially out of direct contact with each other.

[0248] The peripheral region 1032 of each disc 1002 includes a raised landing (or landing feature) 1032a on each end face, which provides the annular bonding area 1030. It will be appreciated that, in some embodiments, the landings may only be provided on one end face of each disc.

[0249] Each landing 1032a is substantially annular in shape when considering the stack from an end-on view, along the flywheel axis B-B.

[0250] Each landing 1032a is bonded to a corresponding substantially planar surface or landing 1032a in the peripheral region of a neighbouring disc 1002. The thickness of the bonding is exaggerated in FIGS. 15B and 15C solely for the purpose of illustration.

[0251] A peripheral region of a disc-facing side of each plate member 1006 includes a substantially planar surface or landing 1006b. Each landing 1006b is bonded to the corresponding outer landing 1032a of the respective end disc of the stack 1004. A central region of the plate member 1006 is spaced from the central region 1034 of the end disc 1002.

[0252] The landings 1032a, 1006b on the discs and plate members can be formed by stamping or forging the discs 1002 and plate members 1006.

[0253] FIG. 15C relates to a variant of the flywheel 1000 in FIGS. 15A and 15B. In this case, the discs 1002 have substantially the same thickness across their full diameter. That is, they do not have raised peripheral landings. The plate members 1006 also do not have raised landings.

[0254] In this case, a shim or plurality of shims 1036 are provided between adjacent discs 1002, and between each end disc 1002 and the adjacent plate member 1006. The shim 1036 is annular in shape, or if multiple shim pieces 1036 are provided between each pair of adjacent discs then shims are arranged annularly between the discs.

[0255] The shim(s) can be made of metal or any other suitable material, such as a material impregnated with an adhesive, for example. The shim may in some embodiments be made from a bonding agent, such as solder, which is applied over a substantially annular area on the disc(s) 1002 and/or plate member 1006 being bonded.

[0256] The shim(s) are thin enough to provide a small gap or space between opposing central regions of neighbouring discs 1002, to keep the central regions substantially out of contact. The shims at the ends of the stack 1004 similarly provide a small gap or space between the outward-facing central region of each end disc 1002 and the stack-facing central region of the plate member 1006, to keep the central regions substantially out of contact. The thickness of the shims is exaggerated in FIG. 15C solely for the purpose of illustration.

[0257] It will be appreciated that some contact may be provided between neighbouring central regions, but the present invention aims to minimise the extent of disc-to-disc contact, such that contact is mainly at the periphery of each disc.

[0258] Each shim or set of shim(s) 1036 is bonded to opposing peripheral regions of an adjacent pair of discs 1002. That is, bonding areas 1030 are provided on either side of the shim(s) to provide shim-to-disc bonds. A first face of the shim is bonded to a first peripheral region of a first disc. A second opposing face of the shim is bonded to a second peripheral region of a second disc. The bonding means/material is similar to that of FIG. 15B, but may be tailored according to the shim material to maximise bond strength.

[0259] Similarly, a shim or shims 1036 are bonded to opposing peripheral regions of each end disc 1002 and its adjacent plate member 1006. A first face of the or each shim is bonded to an outer peripheral region at the end of the stack 1004. A second opposing face of the shim is bonded to the stack-facing peripheral region of the plate member 1006.

[0260] It will be appreciated that both bonding means described in relation to FIGS. 15B and 15C may be provided in a given flywheel, if required.

[0261] FIG. 16 relates to an eleventh embodiment of a flywheel, indicated generally at 1100. The flywheel 1100 in this embodiment has similar features to the flywheel 100 described earlier for the first embodiment, but is substantially different in that the connection means is provided in contact (particularly indirect contact) with some or all of the disc apertures 1102.

[0262] It will be appreciated that the various versions of clamping elements, discs, plate members, spacers and material layers/films discussed for FIGS. 4 to 14A may be provided in the flywheel 1100 to the extent that the selected features do not conflict with the following.

[0263] A number of supports or space-filling elements 1138 are provided for each supporting one of the clamping elements 1114 within the stack 1104. The support 1138 may be considered to be a sheath or sleeve for snugly fitting around the clamping element 1114 and for snugly fitting to the interior of a series of the disc apertures 1102.

[0264] Each plate member 1106 has a recess 1106c around each of its plate apertures 1106a. Each recess 1106c is configured to engage an end of one of the supports 1138.

[0265] FIG. 16A shows the elongate sleeve 1138. End walls 1138b of the sleeve 1138 extend through the stack and into the respective recesses 1106c in the plate members 1106 in FIG. 16. The sleeve 1138 has an external sidewall profile 1138a which is substantially elliptical to match the substantially elliptical internal sidewall profile of each disc aperture in the stack 1104. The sleeve 1138 is rigid in this embodiment. A bore 1140 is provided through the middle of the support 1138 for receiving and supporting the clamping element.

[0266] It will be appreciated that the support 1138 may be considered to be an elongate, double-ended version of the spacer of FIG. 11A, but designed to fit to all of the disc apertures and along the length of the clamping element.

[0267] FIG. 16B depicts an end-on view of a variant of the support 1138. In this case, a series of elongate channels 1142 are provided along some or all of length of the support 1138. The channels allow the support 1138 to be substantially flexible along some or all of its length, and minimise its mass.

[0268] The channels 1142 are provided around the periphery of the sleeve 1138. The channels do not intersect the bore 1140 which receives the clamping element. The channels 1142 can be formed by extruding the sleeve 1138, for example.

[0269] The channels 1142 are of different sizes. Each channel 1142 has an approximately cylindrical bore. The diameter of that bore is selected such that the circumference of the bore does not quite extend into the region behind the end wall 1138b, as viewed in FIG. 16B. The size of the bores may be altered in other embodiments to selectively control the rigidity or flexibility of the support sleeve 1138.

[0270] It will be appreciated that a plurality of cavities may be provided within the body of the support 1138, 1138 to achieve a similar effect in other embodiments. The arrangement of the channels/cavities is not limited to the arrangement depicted in FIG. 16B, and any suitable arrangement may be provided.

[0271] FIGS. 17 and 17A relate to a twelfth embodiment of a flywheel, indicated generally at 1200. The flywheel 1200 in this embodiment is similar to the flywheel 100, but is substantially different in that the connection means is provided in contact (particularly indirect contact) with some or all of the disc apertures 1202.

[0272] However, unlike the eleventh flywheel 1100, this flywheel 1200 does not include a sleeve in the space between the connection elements and the disc apertures. A different support means is provided for the connection elements.

[0273] Each clamping element 1214 includes a conduit 1244. Each conduit includes an axial inlet 1246a through an end of the clamping element 1214, and a radial outlet 1246b (or in some embodiments multiple radial outlets) at the sidewall of the clamping element 1214. The outlet 1246b is inset from the inner end (i.e. the pointed end in FIG. 17A) of the conduit 1244.

[0274] The conduit(s) 1244 permit a fluid material 1248 to be introduced, e.g. injected under pressure, through each clamping element to flow into the space around the clamping element 1214. The fluid material can flow into recesses 1206c at the plate apertures 1206a as well as between the disc apertures 1002a and the clamping element 1214. In this respect, the fluid material may be introduced after the flywheel 1200 has been assembled.

[0275] In some embodiments, the fluid material may be molten and cool to form a solid support or spacer around part or all of the clamping element. In other embodiments, the fluid material may set/cure to form a similar form of solid support. The material solidifies to provide support extending along the stack, extending into the plate members.

[0276] The material may be a thermoplastic or thermosetting plastic (optionally including a strengthening filler in the flow). The material may be a low melting point metal or alloy, such as solder. Ideally, the melting point of the material should be below 600 C.

[0277] The embodiments described above are provided by way of example only, and various changes and modifications will be apparent to persons skilled in the art without departing from the scope of the present invention as defined by the appended claims.