Flywheel

Abstract

The flywheel 100 includes a plurality of discs 102 arranged in a stack 104 and joining means for joining peripheral regions of adjacent discs together for flywheel rotation. The plurality of discs includes at least first and second end discs at opposite ends of the stack and one or more discs between the first and second end discs. Each disc includes first and second opposing faces, each of which includes a central region and a peripheral region surrounding the central region, the peripheral region adjacent a periphery P of the disc. One, some, or all of the discs include a first set of joining areas 112 in the peripheral region of the first face, one or more spacing areas 112a in the peripheral region separating the joining areas on the first face, a second set of joining areas 114 in the peripheral region of the second face, and one or more spacing areas 114a in the peripheral region separating the joining areas on the second face. At least one of the bonding areas 112 on the first side is positioned opposite the spacing area 114a on the second side of the disk, or is positioned opposite both a portion of the spacing area 114a and a portion of the bonding area 112 on the second side of the disk, and / or one or more of the bonding areas 114 on the second side is positioned opposite the spacing area 114a on the first side of the disk, or is positioned opposite both a portion of the spacing area 112a and a portion of the bonding area 112 on the first side of the disk.

Description

[Technical Field]

[0001] The present invention relates to flywheels, and particularly, but not exclusively, to flywheels used for energy storage and / or release. [Background technology]

[0002] A flywheel is a device that includes a rotor assembly and an inertial element that can be used as a means to store kinetic energy, with the majority of the stored energy being stored in the inertial element that has a high moment of inertia relative to other elements of the rotor assembly, such as mountings for electric machines and low-friction bearings.

[0003] Electric machines are commonly used to accelerate an inertial element to store energy or to decelerate an inertial element to release energy. An inertial element stores energy through its angular momentum; the faster it rotates, the more energy it stores, and energy storage is proportional to the square of the angular velocity.

[0004] To store high levels of energy (i.e., have a high capacity for energy storage), the inertial elements must operate at very high peripheral velocities, e.g., speeds above the speed of sound (when measured in air under standard atmospheric conditions as opposed to conditions within the flywheel casing). Therefore, the construction of inertial elements in energy storage flywheels differs significantly from the construction of inertial elements in flywheels designed for other applications.

[0005] For example, a significantly different application is providing a flywheel mounted on the crankshaft of an internal combustion engine to smooth intermittent torque and prevent the engine from stalling. Flywheels used for such smoothing typically have rotor peripheral speeds of only tens of meters per second (relatively low energy capacity), while energy storage flywheels have rotor peripheral speeds of only hundreds of meters per second (relatively high energy capacity). As a result, flywheels in such smoothing applications are not subjected to the extremely high stresses that energy storage flywheel types must withstand. A further difference is that energy storage flywheels can store energy for seconds, minutes, or even hours and then distribute that energy when needed. In the case of flywheels used for torque smoothing, small amounts of energy are passively transferred to and from the flywheel in synchronization with the pulsations of the internal combustion engine.

[0006] Therefore, the energy stored per unit mass of rotor material in an energy storage flywheel is 10 to 100 times greater than that of a flywheel used for engine torque smoothing, and energy storage flywheels need to be volumetrically compact and lightweight to offer performance competitive with other energy storage technologies such as batteries.

[0007] The main design challenge for inertial elements used in energy storage class flywheels is how to withstand the high centrifugal stresses caused by high peripheral speeds while at the same time maximizing safety during operation of the energy storage flywheel.

[0008] One approach is to make the risk of rotor structural failure negligible, i.e., to ensure that the flywheel inertia elements are not subject to material damage. This can be done by using ultra-high quality materials, by using non-destructive testing means to ensure material quality, and by closely monitoring the rotor's usage, especially the number of operating cycles it undergoes. These techniques have been developed by the aerospace industry, but the materials required and the monitoring performed are both costly and time consuming.

[0009] Another approach is to accept that the inertial element may fail during operation, and in the unlikely event that debris (which has high linear kinetic energy) escapes from the inertial element, it must be contained by a casing to avoid property damage and, more seriously, personal injury. This can be achieved at lower cost than the first approach, as lower-cost materials can be used for mass manufacturing, and monitoring can be more lenient, reducing maintenance costs. However, to ensure safety, the mass of the containment element must be significantly larger than the mass of the inertial element it contains; experts recommend a value on the order of 10 times the mass of the inertial element. The size and expense associated with implementing such safety containment means that the primary practical implementation involves placing energy storage flywheels (typically with monolithic steel inertial elements) in underground bunkers. As such, installation costs remain high and flexibility in how stored energy can be deployed is reduced.

[0010] A third approach is to fabricate inertial elements from fiber composites, which can result in materials that are substantially stronger than those used in the previous approach. Traditionally, composite materials have always been assumed to fail with relatively little impact, based on the assumption that the inertial elements would theoretically be dispersed into many fine particles that could be more easily contained using lighter, less expensive casings than those used in the second approach. However, some failure modes of inertial elements remain extremely severe due to their higher energy storage levels, generating high pressures inside the casing. Therefore, flywheel energy storage systems that use composite materials in inertial elements are also typically deployed in very thick and heavy containment vessels or underground bunkers for safety reasons.

[0011] A fourth approach is to use metallic materials for the inertial elements. The metallic material is typically steel, but rather than using a monolithic cylindrical design, the inertial elements can be assembled from a stack of thin disks or laminations. Because the highest stresses in rotating disks are tangential and radial, using a series of thin disks means that the rotor can operate at peripheral speeds as high as (or even higher than) a monolithic cylinder. In fact, because axial stresses are reduced, stresses can be substantially reduced using this approach. In the event of a structural failure in an inertial element of this configuration, only a fragmented portion of the entire inertial element will result. This approach therefore substantially reduces the level of containment required for safe operation of the flywheel and allows the use of a much lighter casing. That is, no thick, heavy casing or bunker installation is required, significantly reducing costs, facilitating installation of the flywheel on the ground, and providing a compact configuration.

[0012] An important consideration with this fourth approach is ensuring that failure of one disk does not propagate far through the stack, otherwise a cascading failure could occur, releasing fragments from multiple disks. Additionally, the disks / laminations must be securely fastened together in the stack, and the stack must be connected to the shaft so that the rotor can rest in the bearings.

[0013] From a commercial perspective, it is understandable that low-cost manufacturing techniques for flywheel rotors are important, as otherwise it would be more economical to continue using alternative energy storage means such as electrochemical batteries or ultracapacitors, even though they offer less practical solutions for energy storage applications where flywheel-based systems are the ideal energy storage solution.

[0014] US Patent No. 5,949,663 discloses a laminated flywheel and recognizes that a central hole in the disk results in high stress, reduced peripheral speed, and reduced performance. Additionally, it achieves favorable high strength properties with thin steel compared to thick monolithic cylinders.

[0015] The '1999 patent discloses two methods for connecting a disc and a connecting means to a shaft for a bearing. First, a description will be given with reference to FIG. 12 of the '1999 patent, which is substantially reproduced in FIG. 1 (prior art) of the present application. This first method employs joining the surfaces of the disc (1) by adhesive, soldering or brazing (2). The connecting means and the shaft (3) are also joined.

[0016] The problem with this approach is that the seam area is placed under very high stress, requiring very strong joining materials to prevent the joint from failing. However, if the joint is strong, a crack in one lamination can propagate to other laminations, resulting in undesirable cascading failures. As a result, minor events that cause only one lamination to fail are not realized.

[0017] The reason for the high stresses at the joints will now be explained with reference to FIG. 1 (PRIOR ART) of the present application, which for ease of explanation is annotated with reference to FIG. 12 of US Pat. No. 5,999,549.

[0018] When the disks rotate at high speeds, the maximum radial and tangential stresses occur in the region around the center of the disk. This reduces the axial thickness of the disk by an amount shown as Δt due to the Poisson's ratio effect. The cross-sectional shape of each disk during rotation is shown in dotted lines (the deformation is exaggerated for illustrative purposes). Because the bond is relatively thin, it is difficult to absorb the force of the disks trying to separate at the bore unless the bond is very strong.

[0019] There is an additional problem in that each of the smaller discs connects to a connecting means on a shaft having a smaller diameter than the main disc. The radial extension of the upper smaller disc, denoted Δr2, will be less than the extension Δr1 of the adjacent main disc. This will cause significant shear stresses in the joint, which must be strong enough to resist.

[0020] However, for the reasons mentioned above, a strong joint would inevitably result in cascading failures if one of the disks were to crack. The crack would most likely form around the center of one of the disks. As the crack propagated radially outward across the disk, it would transfer the load through the strong joint to two adjacent disks, increasing stresses in those disks. Because those adjacent disks were already operating under high stress, this increased local stress could potentially cause cracks in the adjacent disks as well. This process would continue until several, if not all, of the disks were cracked, resulting in a highly undesirable multiple-disk failure mode.

[0021] Finally, adding a stepped profile (see Figure 13 of D1) can strengthen the joint, but it places high stresses on the disc at the corners of the stepped profile on the female side of the mating part. Stepped profiles are also expensive to manufacture.

[0022] The '699 patent attempts to address some of the above problems by using spigots on each of the discs and collars between each joint. However, such joints require precision manufacturing. While this may be feasible for limited production of the heavy, large-scale flywheels described in the '699 patent, it would be prohibitively costly for mass production of flywheels. This design may also be somewhat unstable in use, given the narrow diameter of the joints and the lack of mechanical locking of the discs together.

[0023] Patent Document 3 discloses a laminated flywheel structure in which bolts can be inserted into the disks through specially shaped openings to reduce stress at the openings. Figure 2 (prior art) of this application shows Figure 14 of Patent Document 3, in which a disk stack (12) is clamped between two end plates (20) using an array of bolts (42, 44). The end plates (20) connect the disk stack to a shaft for rotation. The bolts are threaded through specially shaped openings in the disks (12) and are secured in place within the holes by inserts. The disks with openings disclosed in Patent Document 3 are intended to operate at the same speed as disks without openings. However, to ensure flywheel stability, the structure requires precise fit between its parts, which is expensive.

[0024] It is an object of the present invention to mitigate or substantially eliminate the above-mentioned problems, particularly (but not exclusively) by providing a flywheel which has reduced containment requirements and which preferably can be manufactured at relatively low cost. [Prior art documents] [Patent documents]

[0025] [Patent Document 1] US Patent: US7267028 (Gabrys) [Patent Document 2] US Patent: US10138980 (Sanders et al.) [Patent Document 3] European Patent: EP2759043(Pullen) Summary of the Invention

[0026] The flywheel provided by the present invention comprises: a plurality of discs (or stack / multiple stacks) arranged in a stack, the plurality of discs including at least first and second end discs at opposite ends of the stack and one or more discs between the first and second end discs, each of the discs including first and second opposite (opposite facing) sides, each of the first and second opposite sides including a central region and a peripheral region disposed around (or adjacent / near) the central region, the peripheral region adjacent a periphery of the disc; and (primary) joining means for joining adjacent peripheral regions of adjacent discs together for flywheel rotation; one, some, or all of said one or more disks: a first set of bonding areas (which may be considered pads) in the peripheral region of the first surface, and one or more spacing areas in the peripheral region to separate the bonding areas on the first surface; a second set of bonding areas (which may be considered pads) in the peripheral region of the second surface, and one or more spacing areas in the peripheral region to separate the bonding areas on the second surface; At least one of the disks one or more of the bonding areas on the first surface is located opposite the spacing area on the second surface of the disk, or opposite both a portion of the spacing area and a portion of the bonding area on the second surface of the disk; One or more of the bonding areas on the second surface are at least either positioned opposite the spacing area on the first surface of the disk, or positioned opposite both a portion of the spacing area and a portion of the bonding area on the first surface of the disk.

[0027] The present invention addresses the problem of catastrophic flywheel failure by substantially preventing crack propagation through the stack of disks. In particular, the method of bonding the disks together substantially prevents a crack that initiates in one disk from migrating or crossing over to the other disks. This is because the structural bond between the disks (i.e., bond sufficient to maintain the integrity of the flywheel at operating speeds) is limited to the bonded area; a crack would have to grow into one of the bonded areas to propagate to another disk. While a crack could potentially migrate or cross over to an adjacent disk, any crack is unlikely to actually propagate completely from one element to another due to the structure of the inertial elements within the flywheel.

[0028] Because cracks are substantially unable to propagate through the series of disks, the containment requirements of the flywheel (in the event of a catastrophic disk failure) are substantially reduced. Specifically, one need only consider the bursting of a maximum of two, three, or four disks rather than the entire flywheel, and the mass ejected as a result of the failure should have a relatively low mass or kinetic energy. The flywheel therefore operates more safely and can be operated for longer periods at the high rotational speeds (preferably supersonic relative to the speed of sound in air at atmospheric pressure) required for significant energy storage.

[0029] The flywheel of the present invention also has a simpler construction than the prior art devices cited above. In particular, because the joint is provided at a location where the disks are subjected to lower stresses, the circular lamination openings of the '666 patent are not required and the associated disk stresses are avoided. Additionally, the likelihood of crack propagation is substantially reduced when compared to the device disclosed in the '666 patent, addressing the shortcomings discussed with respect to the '666 patent.

[0030] The number and placement of the joining and spacing areas are selected to provide adequate structural integrity to the flywheel when rotating at flywheel speed.

[0031] During flywheel rotation, the discs thin somewhat and are able to move apart, minimizing the contact area between the opposing central regions of adjacent discs. By having joining means at the joining zones in the peripheral regions, disc separation during use has low or negligible effect on the interface between adjacent disc / rotor element pairs.

[0032] It will be appreciated that the nature of the disc-to-disc bonding in the present flywheel requires that only a portion of the adjacent peripheral regions be bonded, while other portions of the adjacent peripheral regions remain as spacing areas that are not bonded to adjacent discs or that are not bonded in a way that would facilitate crack propagation between the discs.

[0033] The spaced areas between the main (structural) bonded areas may be non-bonded areas.

[0034] The spacing areas between the primary (structural) bond areas may create a second type of disc-to-disc bond area that provides a non-structural bond - in other words, a bond that is designed to withstand the rotational forces of the flywheel during normal operation, but that will fail if a crack attempts to propagate or begins to propagate therethrough.

[0035] The spaced apart area may be partially or wholly occupied by a secondary bonding means / agent that is different from the primary bonding means / agent.

[0036] Thus, the spacing area does not necessarily have to consist of any "empty space." The term spacing area is intended to indicate that the main joining areas for the structural integrity of the flywheel are discrete or separated from one another, i.e., there is a discontinuity.

[0037] The flywheel structure relies solely on the bonding of the disks to each other and to the plate members by the primary bonding means to maintain structural integrity.

[0038] This flywheel has a speed of at least 350 meters per second (ms) -1 ) may be possible to achieve a peripheral speed of

[0039] The flywheel may have a kinetic energy storage capacity of at least 100 kilojoules (kJ) in use. Preferably, the flywheel may have a kinetic energy storage capacity of at least 200 kJ, at least 250 kJ, or at least 300 kJ.

[0040] The flywheel may be provided in or as part of an installation, such as a power plant or machinery. The flywheel may be large enough for use in a multi-megawatt power system or station. The dimensions of the stack of discs may be on the order of several meters. For example, the height of the stack of discs may be 1 to 8 meters long. The discs may each have a diameter of 1 to 5 meters.

[0041] A stack of disks may have a mass on the order of tens or hundreds of tons, for example, a stack may have a mass of about 100 tons or several hundred tons.

[0042] The flywheel (particularly its inertial element) may have a minimum stored energy of 25 kJ per kilogram when in use.

[0043] Each disc may be considered a stack or inertia element of the flywheel (or stacked inertia element), and each disc is configured or structured to store most of the kinetic energy in the flywheel as the stack rotates.

[0044] Any of the spacing areas may be located at substantially the same radial distance from the disc center (or may cover the same radial extent) as the bonding area located therebetween.

[0045] The spacing area on one face of a given disk may overlap with the spacing area on the opposite face of that disk in addition to overlapping with the bonding area on the opposite face.

[0046] The peripheral region may be envisaged to extend beyond a distance of at least half the radius of the disc. The peripheral region may be envisaged to extend beyond a distance of at least two-thirds the radius of the disc. The peripheral region may be envisaged to extend beyond a distance of at least three-quarters the radius of the disc. The peripheral region may be envisaged to extend beyond a distance of at least 80% of the radius of the disc. This radius may be considered as the straight line distance from the centre of the disc (located on the flywheel axis of rotation in use) radially outwards to the edge of the disc.

[0047] Battlement-like or crenellated (or pseudo-battlement-like or pseudo-crienated) joint arrangements may also be provided, i.e. the arrangement of joint areas may be viewed as a series of battlements (especially the horizontal portions thereof) when viewed from the side of a given disc or viewed radially relative to the axis of rotation of the stack of flywheel discs.

[0048] In other words, the bond areas may alternate (or be staggered) on opposite sides of the disk in the circumferential direction of the disk, which may be achieved by both having each bond area on a first side opposite a corresponding spaced area on a second side of the disk, and having each bond area on the second side opposite a corresponding spaced area on the first side of the disk.

[0049] The battlemented or staggered nature of the disk-to-disk joint or seam ensures that no more than two disks or rotor elements can fail catastrophically. This significantly reduces the requirements for any containment that may need to be provided around the flywheel. Both the cost and weight of the containment are correspondingly reduced.

[0050] Individual flywheels according to the present invention can be placed in close proximity (preferably nested) to one another as part of a flywheel plant, as a flywheel failure in a first flywheel is unlikely to materially affect or impede the continued operation of adjacent flywheels in the vicinity of the failed flywheel.

[0051] A surface located on a radial path from the flywheel rotation axis taken perpendicular to the stack of discs and passing through the centre of the spacing area does not pass through the joining area of ​​the main joining means, which may be the case for a single disc, a pair of adjacent discs, a part of a stack containing three or more discs, or preferably the entire stack of discs.

[0052] For a given disk, a first set of bonding areas on a first surface may be rotationally offset from (or staggered relative to) a second set of bonding areas on a second surface about the flywheel axis of rotation.

[0053] The first and second sets of bond areas may be out of phase about the flywheel axis of rotation, i.e., a given bond area may be located exactly opposite the spacing area and spaced equidistant (circumferentially around the disk) from the nearest opposing bond area on the other side of the same disk.

[0054] This reduces crack propagation between adjacent disks longitudinally along the stack (stacking direction).

[0055] Each spacing area may have a larger area or a larger angular extent than the opposing joining area to separate the joining areas on opposite faces of the disk.

[0056] This reduces the likelihood of crack propagation between adjacent disks by increasing the relative disk penetration distance between adjacent bond areas on opposite faces of the disks.

[0057] For a given disk, the first and second sets of bond areas may be rotationally offset from (or staggered relative to) the second set of bond areas on the second surface about the flywheel axis of rotation, where the bond areas on the first surface at least partially overlap with the bond areas and spacing areas on the second surface.

[0058] This means that a given joining area need not be located exactly opposite the spacing area or opposite the middle of the spacing area, and need not be equidistantly spaced (circumferentially around the disk) from the nearest opposite joining area on the other side of the disk.

[0059] When stacked, the bond area between each pair of disks may be rotationally offset from the bond area of ​​an adjacent pair of disks, and the rotational offset between the bond areas of adjacent pairs of disks may be envisioned to form a spiral arrangement throughout the stack of disks.

[0060] In other words, when viewed from the side of a given disk, each bonding area on a first surface is opposite a portion of a corresponding spacing area and a portion of a corresponding bonding area on a second surface of the disk, and each bonding area on the second surface is opposite a portion of a corresponding spacing area and a portion of a corresponding bonding area on the first surface of the disk, thereby providing a spiral bonding arrangement.

[0061] This arrangement has been found to increase the bending stiffness of the stack at the expense of the overlapping joint areas. If the bending stiffness is too low, elements of the flywheel structure may resonate at frequencies within or near the operating range of the flywheel.

[0062] The first set of bond areas of each disk may be rotationally offset from the corresponding second set of bond areas of that disk by substantially the same amount. That is, all disks in the stack may have substantially identical first and second bond areas. The disks may have different orientations when placed in the stack.

[0063] The rotational offset between each set of bond areas may be substantially the same between each adjacent pair.

[0064] The orientation of the disks in the stack may form a repeating pattern.

[0065] The repeating pattern can consist of multiple disks with each disk in one of three orientations: for example, the first disk in the stack can have the same orientation as the fourth disk in the stack, the second disk in the stack can have the same orientation as the fifth disk in the stack, and so on.

[0066] A repeating pattern can consist of multiple disks with each disk in one of four orientations, for example, the first disk in the stack can have the same orientation as the fifth disk in the stack, the second disk in the stack can have the same orientation as the sixth disk in the stack, and so on.

[0067] The bonded and spacing areas may be regularly or equidistantly spaced throughout the peripheral region.

[0068] Each bond area may be substantially identical to each other bond area on a given face of a given disk. Each spacing area may be substantially identical to each other spacing area on a given face of a given disk.

[0069] Each joining area on a given face of at least one disk may be the same. Each spacing area on a given face of at least one disk may be the same. The areas may be the same, for example, in terms of size and / or shape and / or angular extent, but may be located at different positions on the disk face / side. The joining and spacing areas on the disk face may follow the formula: 2N(p+g)=360°, where N is the number of joining areas on a given face, p is the angular extent (in degrees) of one given joining area, and g is the angular extent (in degrees) of one given spacing area.

[0070] The width of the bond area spanning the circumference of the disc may be greater than the width of the spacing area, i.e. the bond area may occupy a larger proportion of the periphery of the disc than the spacing area.

[0071] One of the discs in the stack may include a single continuous bond area extending around the periphery of at least one face, or in other words, the stack may include a mix of continuous and battlemented bonds.

[0072] The continuous joint may vary in thickness circumferentially and may be shaped to match a battlement joint pattern to maximize rotor bending stiffness.

[0073] The joint area can be asymmetric, for example, it has been found that welding disks using an asymmetric joint area results in the best metallurgical properties of the weld and surrounding materials and minimizes the time it takes to create the joint.

[0074] The shape of the joining area can have rounded corners (rounding / chamfering), which avoids sharp corners in the joining geometry and reduces stress.

[0075] A space may be provided between one or more bonded areas and the periphery of the disc. This configuration has been found to reduce stress in the bonded areas by keeping the bond away from the edge. This configuration may be achieved by removing material after the bond is made.

[0076] Having a relatively uniform bond pattern contributes to a more even distribution of forces or stresses in the flywheel during operation, which can reduce the likelihood of disk failure in the flywheel.

[0077] Each disk of the flywheel may have a suitable number of bonding areas. The number of bonding areas may vary among disks within the flywheel. Preferably, at least eight bonding areas may be provided in the peripheral region. In some embodiments, there may be an integer number of bonding areas ranging from 8 to 32 on each side of the disk. This includes an even or odd number of bonding areas, such as 9, 10, 11, 12, 13, 14, 15, or 16 (or more) bonding areas in the peripheral region. More bonding areas may be provided if desired. A corresponding number of spacing areas should be provided in the peripheral region.

[0078] In some embodiments, it is preferred to provide a set of substantially U-shaped joining areas. Where U-shaped areas are provided, the straight sides of the U-shape may be parallel to one another or may be disposed substantially radially on the surface of the disc. It should be noted that the U-shape need not have precisely parallel sides. However, it will be understood that any suitable size and / or shape of joining area and / or spacing area may be provided per disc.

[0079] The bond area may be tangent to the periphery of the disc or may extend from / to the periphery of the disc, which maximizes the distance of the bond area from the center of the flywheel to a location that minimizes thinning of the disc as the flywheel rotates.

[0080] One, some, or all of the bonding areas may each include a recess formed in the peripheral region. One or more of these recesses may be formed by chemical etching or mechanical stamping of the disk. The depth of the recess is small relative to the thickness of the disk, typically on the order of a few tens of micrometers.

[0081] The recess(es) can provide an area where a bonding means or material can be accommodated between the disks. In some embodiments, the bonding material can flow or be drawn into the recess(es) in the process of bonding the disks together into a stack. This can alleviate the need for using shims or shim plates.

[0082] At least one shim may be provided in the stack. Multiple shims may be provided in the stack. A shim (each shim) may be positioned between a given pair of adjacent disks. The shim may not be substantially bonded to the disks, but may be held in place between the disks primarily by disk-to-disk bonding.

[0083] The shim may be made from a metal or metal alloy, or any other suitable material. If the shim is made from a metal or metal alloy, it may be or include steel, aluminum, or titanium, although other suitable metals / alloys are contemplated and this list should not be construed as exhaustive.

[0084] Any one or more of the shims may include a plurality of peripheral voids or notches in its periphery. The peripheral voids may correspond to or define the joining areas on each side of adjacent disks. One, some, or all of the peripheral voids may extend inward from the edge of the shim toward the center of the shim.

[0085] The use of one or more shims between each of one or more pairs of adjacent disks facilitates more precise control of the shape of the bond area compared to depositing a bonding agent on the disk faces and clamping the stack (the time required to bond the disks together). The peripheral gap of the shim can provide a precisely sized axial gap as small as tens of micrometers. The use of shims can be particularly advantageous for brazed or soldered joints between disks, since the bonding agent can flow into the gap (pocket) provided by placing the shim between the disk pair.

[0086] The shim may be provided with an appropriate size, shape, and / or arrangement of peripheral voids.

[0087] Any of the shims may include a central opening sized to correspond to the central region of the adjacent disk, and the central opening may have a diameter greater than half the diameter of the shim, which reduces the weight of the shim.

[0088] When shims are provided between each or every pair of adjacent disks, the peripheral gaps of adjacent shims (on opposite sides of the disks) are rotationally offset (or staggered) or out of phase with each other about the flywheel axis of rotation.

[0089] This reduces crack propagation between adjacent disks longitudinally along the stack.

[0090] At least one carrier sheet for carrying the bonding means may be provided. Multiple carrier sheets may be provided. A carrier sheet (each carrier sheet) may be provided between a pair of adjacent discs in the stack. The carrier sheet may be porous or fibrous. The carrier sheet may be envisaged as a mat, such as a porous or fibrous mat.

[0091] This provides another means for bonding adjacent pairs of disks together. A bonding agent or substance can be provided at predetermined locations on each side of the carrier sheet for bonding adjacent disks. This facilitates accurate placement of the bonding means and ensures that the required bonding pad pattern is provided during the process of bonding the disks in the stack together, including any necessary clamping of the stack during the time required to bond the disks together.

[0092] When recesses, shims, and / or carrier sheets in the disk faces, or any combination thereof, are used to facilitate disk-to-disk bonding in a stack, the relative orientation of the bonding areas provided or facilitated by those contours on the first pair of disks (Disks 1 and 2) and the second pair of disks (Disks 2 and 3) can be taken into consideration, preferably to rotationally offset or stagger the bonding areas, i.e., to provide out-of-phase bonding areas.

[0093] The shim and / or carrier sheet may be thin compared to the thickness of a given disk, for example, each may have a thickness that is substantially 10% or less of the thickness of the disk.

[0094] The joining means may join only a portion of each disk to its adjacent disk in the stack to inhibit crack propagation between adjacent disks longitudinally along the stack, and the joining means may join only a portion of the disk-facing surface of each disk in the stack to the opposing disk.

[0095] The bonding means may include a first bonding agent and a second bonding agent. The first bonding agent may be on the first side and / or the second side of a given disc. The second bonding agent may be on the first side and / or the second side of a given disc. The second bonding agent may be different from the first bonding agent.

[0096] The first and second bonding agents may be provided on the first and second sides of the disc in an alternating or "out-of-phase" arrangement, i.e., the first bonding agent on the first side may be out-of-phase with respect to the first bonding agent on the second side, and the second bonding agent on the first side may be out-of-phase with respect to the second bonding agent on the second side.

[0097] A secondary bonding means may be provided for conducting heat between at least one of the pairs of adjacent disks, the secondary bonding means being more thermally conductive than the primary bonding means.

[0098] This allows for heat flow from one disk (or rotor element) to another in the axial direction, i.e., longitudinally along the stack, by conduction. Because heat may be generated within the rotor assembly during use, for example by the electric machine used to drive the rotor assembly, it is important to effectively dissipate this heat. While the through-pad bonding means provides one path for heat conduction, heat conduction can be enhanced by having additional heat conducting means, which can be achieved by providing secondary bonding means at locations between the bonded areas.

[0099] The secondary bonding means may provide a weaker disk-to-disk bond than the primary bonding means to inhibit crack propagation through the secondary bonding means, and in this case, axial overlap of the two areas of the secondary bonding means on either side of a given disk may be provided to maximize thermal conduction between the disks.

[0100] The secondary attachment means should be strong enough (relative to the rotor) to withstand the high centrifugal fields so that it remains in place as the flywheel rotates, while also being weak enough so as not to promote crack propagation through the stack.

[0101] For example, a relatively weak type of solder can be used as the thermal conduction means, and this thermal conduction means will fail before a crack can transfer from one disk to another. That is, if a crack were to grow into the area joined by the secondary joining means, the secondary joining means will fail before the adjacent disk fails, i.e., before the crack can transfer or cross over to the adjacent disk. This is why overlap of the areas is acceptable, while it is important not to have overlap of the structurally joined areas (provided by the primary joining means).

[0102] The area of ​​one, some or all of the secondary joining means may be larger than the joining area of ​​the primary joining means, which may improve thermal conductivity between the disks.

[0103] The secondary joining means may be provided in one or more portions of the spacing area. The secondary joining means may be provided at a distance from the main joining means. This is preferred when the spacing area is wider than the corresponding joining area.

[0104] The secondary bonding means (e.g., a weaker solder or weaker bonding agent / means compared to the primary bonding pad) may entirely fill the spaced apart area, i.e., there may be no empty space or gap between the primary and secondary bonding means.

[0105] Sections of the spacing area may accommodate secondary bonding means that provide areas of thermally conductive (but non-structural) disk-to-disk bonding of suitable size for the purpose of better dissipating heat between the disks of the stack.

[0106] The joining means may be selected to consist of any of the following: welding, brazing, soldering, diffusion bonding, adhesives such as strong engineering or structural adhesives (e.g., epoxies).

[0107] It will be appreciated that any suitably strong joining means may be used that will withstand the flywheel rotation.

[0108] Brazing and soldering are given as examples of low melting point soft metals or alloys that can be used, it being understood that other soft metals or alloys (preferably having melting points below about 600°C) could be used instead, since temperatures above 600°C can adversely affect the structure / strength of the steel disc, i.e. its heat treatment.

[0109] If welding is used to join the abutting disk faces, local temperatures above 600° C. may occur. However, this may be limited by heat treating the disk or portions thereof, or modified disk material properties may be acceptable if the area of ​​the weld is at or near the periphery of the disk and therefore has lower bulk stresses than the center.

[0110] First and second plate members (or cheek plates) may be disposed at opposite ends of the stack, and the first and second plate members may be joined to opposite ends of the stack.

[0111] The stack of discs may not include clamping means for clamping the discs in the stack together, i.e. there may be no clamping element clamping the stack together.

[0112] The first and second plate members may lack openings for clamping the stack together.

[0113] The plate member(s) should ideally be structured so that they are subjected to stress levels equivalent to or similar to those experienced by the disks during use.

[0114] Each disc may be of similar or substantially the same thickness, and either or both of the first and second plate members may have a thickness that is substantially the same as the thickness of the disc.

[0115] The term end plate is intended to refer to an element located at the axial end of the disc stack adapted to facilitate rotation of the disc stack, i.e. may have one or more connections or bearing stands for connection to drive means for the flywheel.

[0116] The first and second end plates can be thicker than the disks. For example, the end plates can be approximately twice as thick as a given disk in the stack, or approximately three or four times as thick as a given disk, or anywhere from approximately one to four times as thick. The thickness of the end plates and disks can be measured in a direction parallel to the flywheel axis of rotation. This can improve the rigidity of the end plates for connecting the shaft to the rest of the stack.

[0117] At the periphery of either or both end plates, the end plates may be as thin as either or most of the rotor disks. One or both end plates may be shallow conical (as viewed from the side of the stack) to increase stiffness, i.e., provide a stiff element or plate to which the shaft can be connected.

[0118] By having a plate member that is much thinner axially (i.e., thinner in a direction parallel to the flywheel rotation axis) than conventional heavy clamping plate members, the containment means can also be thinner and lighter compared to flywheel devices that have clamping means for the inertial elements of the flywheel.

[0119] For similar reasons, the mass of the plate members may be selected so that catastrophic failure of the plate members does not result in failure of the containment means, and therefore the containment requirements of the device installed around the flywheel to safely contain outgoing plate debris need not significantly exceed the containment requirements for a scenario in which a portion of the disk stack fails catastrophically.

[0120] It will be appreciated that for joining the plate members to the stack, either or both of the plate members may have joining and spacing areas corresponding to adjacent disks, and therefore the above disclosure relating to disk-to-disk joining may also be applied to disk-to-plate joining.

[0121] Each disc may be made of metal or may be a metal laminate. Each disc in the stack may lack a through hole for receiving a clamping means.

[0122] One or more additional stack elements may be disposed on or joined to one or both ends of the stack. The additional stack elements may be provided in place of plate members. Each of the additional stack elements may include laminations having a circumference with a smaller diameter than the disks in the stack, a non-circular perimeter, or a central opening. It will be understood that any of the disks may also include any of these geometries.

[0123] The stack elements (or additional rotor elements) can be formed using relatively low-cost methods, such as stamping, water-jet cutting, or laser cutting. One or more rotor elements can be formed by joining or bonding together either circular laminations with reduced outer diameters, laminations with noncircular outlines, or laminations with central openings. The joining can be achieved by having battlemented or offset joining areas, as previously described, or by annular ring-shaped continuous joining. The latter is acceptable when the diameter of the rotor elements is smaller than the diameter of the disks that make up the main body of the stack. This is because if two or more rotor elements that make up an end plate fail, the energy released should not be substantially greater than the energy of the two failed disks or laminations.

[0124] Note that if the end plates are slightly thicker than the disc thickness (or the average disc thickness), the energy released in the event of a catastrophic flywheel failure can be relatively high.

[0125] At a maximum, the end plates can have around twice the mass of the majority of the discs. However, the energy involved (in terms of containment requirements) should not be doubled. This means that the majority of the mass must be close to the centre of the flywheel. This is where the additional elements can be thought of as forming a shallow cone (when viewed from the side of the stack). This cone-like shape can be created by joining shapes of a smaller size and shape, or it can be made from a machined disc made from a thicker material than the sheet used to form the majority (or any) of the discs.

[0126] A plurality of additional stack elements may be provided at one or both ends of the stack, with the width or diameter of successive additional stack elements decreasing in a direction toward the end of the stack. In other words, in a direction away from the end of the stack, the first adjacent stack element may have a width or diameter smaller than the width or diameter of the stack, and each subsequent stack element may have a width or diameter smaller than the width or diameter of the preceding stack element.

[0127] This aspect can help provide cheek plates that have a relatively low weight while remaining sufficiently stiff to withstand bending forces applied to the flywheel shaft. While such forces are typically small, if the end plates are too stiff, the entire shaft can resonate and lead to failure. One option is to use end plates with a relatively thick, solid, shallow conical shape (or contoured conical shape), or to stack flat disks of decreasing diameter for similar reasons.

[0128] A flywheel assembly may be provided that includes one or more flywheels according to the present invention.

[0129] The (or each) flywheel may be mounted to a drive assembly that facilitates rotation of the (or each) flywheel to store or release energy in at least one of the flywheels. The drive assembly may be mechanical, electrical, or any other suitable form of drive means.

[0130] According to another aspect of the present invention, there is provided a method of manufacturing or constructing a flywheel, the method comprising: Stacking a plurality of flywheel discs to form a stack of discs; enabling (or implementing) bonding between adjacent disks in the stack of disks, with the bonding area of ​​adjacent disks overlapping to an extent that increases or decreases depending on the stiffness of the stack of disks required to avoid bending resonance of the flywheel at a particular frequency during operation of the flywheel.

[0131] A flywheel requires sufficient stiffness, e.g., sufficient bending stiffness, to suppress bending resonance of the flywheel assembly or its components. Bending stiffness can be increased by providing overlapping bond areas as described above, thereby suppressing bending resonance of the flywheel during operation. This must be balanced against the risk of crack propagation through the stack due to the overlapping bond areas.

[0132] Certain configurations of the flywheel discs, end plates, shafts, drive means, and / or bonding patterns between the flywheel discs can create a bending resonance configuration or a configuration prone to bending resonance when the operating speed frequency coincides with the bending resonance frequency of the flywheel device. If such an event occurs within the operating speed range of the configuration, catastrophic failure can occur. Clearly, this is undesirable and should be avoided.

[0133] The term susceptible to bending resonance does not mean that the flywheel will necessarily resonate during operation, but rather refers to a configuration in which the likelihood of bending resonance occurring increases in relation to various other possible configurations of the disks and how they are joined together in the stack, i.e., the flywheel is more or less susceptible to bending resonance.

[0134] If the interface areas of adjacent disks are arranged in a configuration aimed at increasing rotor stiffness, an anti-bending resonance or bending resonance resistant configuration can be obtained, which may result in the bending resonance frequency of the configuration being above and therefore outside the operating speed range of the flywheel arrangement.

[0135] The first bending resonance frequency of the flywheel (or its disk stack) preferably exceeds the operating speed or speed range of the flywheel, and the flywheel disk stack may be constructed or bonded together to have a bending stiffness or rigidity that facilitates this, taking into account the intended operating speed of the flywheel (which may have values ​​of thousands or tens of thousands of revolutions per minute).

[0136] One way to achieve a bending resonance resistant configuration may be to have the bonded areas of the opposite far faces of adjacent disks overlap to a small extent (or overlap each other in a direction along the stack) to inhibit crack propagation, at the expense of reducing the stiffness of the stack. Thus, the first bending resonance frequency of the flywheel may be above the operating speed range of the flywheel. It will be understood that an anti-bending resonance or bending resonance resistant configuration does not necessarily require the bonded areas to overlap to all or a certain extent.

[0137] When flywheel disks are arranged in an anti-bending resonance or bending resonance resistant configuration, the bond areas on the opposite far faces of adjacent disks overlap to a large extent (or overlap each other in a direction along the stack) to increase stack stiffness despite the possibility of increased crack propagation through the adjacent disks. In this case, the intention is for the bending resonance frequency of the flywheel (or its disk stack) to exceed the operating speed range of the flywheel. However, it will be understood that an anti-bending resonance or bending resonance resistant configuration does not necessarily require the bond areas to overlap to all or any particular extent.

[0138] The terms anti-bending resonance configuration and bending resonance resistant configuration may refer to a configuration in which the disk-to-disk joints are provided in areas that result in a relatively low likelihood of the flywheel undergoing bending resonance when the flywheel is rotating at a given speed, compared to a random arrangement of the joint areas. That is, when the relative positions of the joint areas in the overall stack mean that the flywheel (or its disk stack) does not undergo bending resonance at one or more frequencies that fall within the operating speed range of the flywheel. In other words, bending resonance should be either below or above the operating speed range of the flywheel.

[0139] In the case of bending resonance resistant configurations, damping means may be provided and / or the arrangement or nature of the disk-to-disk joints may damp bending resonances.

[0140] The term flexural resonance resistant does not mean that the flywheel will not flexurally resonate during operation, but rather refers to a configuration in which the likelihood of flexural resonance is reduced compared to various other possible configurations of the disks and the manner in which they are joined together in the stack. That is, it will be understood that the flywheel is less susceptible to flexural resonance, although flexural resonance may still occur in a flexural resonance resistant configuration, but the number of resonant frequencies will be relatively reduced when compared to a flexural resonance prone configuration.

[0141] Software (such as ANSYS®) can be used to simulate flywheel operation and allow for the exploration of bending resonances at different frequencies during flywheel rotation, to model configurations that are prone to bending resonance and / or resistant to bending resonance, thereby establishing predicted model configurations that are prone to bending resonance and / or resistant to bending resonance, which can then be used when manufacturing or building a flywheel.

[0142] To determine whether a particular arrangement of flywheel discs will create a bending resonance susceptible and / or bending resonance resistant configuration, any one or more of the following factors may be considered: number of bond areas, size and / or shape of bond areas, arrangement or relative distribution of bond areas on various discs, extent of overlap of bond areas for a given pair of flywheel discs, flywheel disc material properties (e.g., weight, density, Young's modulus), flywheel disc dimensions / thickness, characteristics of bonding means / materials, location(s) and / or distribution of bonding means / materials, flywheel orientation during operation, flywheel operating speed and / or speed range (e.g., including normal design operating speed and abnormally high and / or low operating speeds that remain within design capabilities / tolerances), flywheel operating temperature, flywheel stiffness, and individually selected combinations thereof.

[0143] The flywheel may include any of the features or combination of features of the flywheel and / or flywheel disc described in any of the above embodiments.

[0144] According to another aspect of the present invention, there is provided a flywheel comprising: a plurality of disks arranged in a stack; the plurality of disks includes at least first and second end disks at opposite ends of the stack and one or more disks between the first and second end disks, each of the disks including first and second opposite faces, each of the first and second opposite faces including a central region and a peripheral region disposed about the central region, the peripheral region adjacent a periphery of the disk; and joining means for joining adjacent peripheral regions of adjacent discs to one another for flywheel rotation; one, some, or all of said plurality of discs a first set of bonded areas in the peripheral region of the first surface, and one or more spacing areas in the peripheral region to separate the bonded areas of the first surface; a second set of bonded areas in the peripheral region of the second surface and one or more spacing areas in the peripheral region to separate the bonded areas of the second surface; one or more of the bonding areas on the first surface are located opposite the spacing areas on the second surface of the disk; one or more of the bonding areas on the second surface are located opposite the spacing areas on the first surface of the disk.

[0145] The flywheel may include any of the features or combination of features of the flywheel and / or flywheel disc described in any of the above embodiments. [Brief explanation of the drawings]

[0146] For a better understanding of the 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 drawings in which: [Figure 1] FIG. 1 is a side view of a first prior art flywheel device taken from Patent Document 1. [Figure 2] FIG. 1 is a cross-sectional side view of a second prior art flywheel device taken from Patent Document 3. [Figure 3]1 is a side view of a first embodiment of a flywheel of the present invention; [Figure 3A] FIG. 4 is a top view of a first embodiment of a disk in the flywheel of FIG. 3; [Figure 3B] Underside view of the disk in Figure 3A. [Figure 4] 3B shows a top view of the disk of FIG. 3A, depicting the bonding areas on the top and bottom surfaces of the disk. [Figure 5] A top view of the disk of FIG. 4 is shown, illustrating examples of possible crack paths in this disk. [Figure 6] 4 shows a perspective view of a second embodiment of a disk in the flywheel of FIG. 3, including a joining area that is a welded area. [Figure 7] FIG. 4 is an enlarged partial perspective view of a portion of the flywheel of FIG. 3; [Figure 8A] 4 shows a top perspective view of a third embodiment of a disk in the flywheel of FIG. 3, illustrating the bonding area of ​​bonding material deposited on the top surface of the disk. [Figure 8B] 8B shows a bottom perspective view of the disk of FIG. 8A, depicting the bonding area of ​​bonding material deposited on the underside of the disk. [Figure 9A] FIG. 1 is a top view of a first embodiment of a shim for a flywheel. [Figure 9B] FIG. 10 is a top view of a second embodiment of a shim for a flywheel. [Figure 9C] 9C is an enlarged partial perspective view of the shim of FIG. 9A or FIG. 9B in a disk for a flywheel. [Figure 10A] 9C shows an exploded partial side view of a second embodiment of a flywheel, including the shim of FIG. 9A or FIG. 9B. [Figure 10B] FIG. 10B is a partial side view of the flywheel of FIG. 10A. [Figure 11] FIG. 10 is a partial perspective view of a third embodiment of a disk for a flywheel. [Figure 12A] FIG. 1 is a top view of a first embodiment of a carrier sheet for a flywheel. [Figure 12B] FIG. 10 is a top view of a second embodiment of a carrier sheet for a flywheel. [Figure 13A]FIG. 10 is a top view of a fourth embodiment of a disk for a flywheel. [Figure 13B] 13B is a bottom view of the disk of FIG. 13A. [Figure 14] FIG. 10 is a side view of a third embodiment of a flywheel. [Figure 14A] FIG. 15 is a top view of the first disk for the flywheel end plate in FIG. 14 . [Figure 14B] 15 is a top view of the second disk for the flywheel end plate in FIG. 14. [Figure 14C] 15 is a top view of the third disk for the flywheel end plate in FIG. 14. [Figure 15] 10 shows a cross section of a fourth embodiment of the flywheel. [Figure 15A] 16 is a top view of a disk in a first orientation in the flywheel of FIG. 15; [Figure 15B] 16 is a top view of a disk in a second orientation in the flywheel of FIG. 15; [Figure 15C] 16 is a top view of a disk in a third orientation in the flywheel of FIG. 15; [Figure 16] 10 shows a cross section of a fifth embodiment of a flywheel. [Figure 16A] 17A and 17B are top views showing the stacking of four discs in different orientations in the flywheel of FIG. 16. [Figure 17] 10 shows a cross section of a sixth embodiment of the flywheel. [Figure 17A] 18 is a top view of a disk in a first orientation in the flywheel of FIG. 17; [Figure 17B] 18 is a top view of a disk in a second orientation in the flywheel of FIG. 17; [Figure 17C] 18 is a top view of a disk in a third orientation in the flywheel of FIG. 17; [Figure 18] 10 shows a cross section of a seventh embodiment of the flywheel. [Figure 18A] 19 is a top view of a disk in a first orientation in the flywheel of FIG. 18; [Figure 18B] 19 is a top view of a disk in a second orientation in the flywheel of FIG. 18; [Figure 18C] 19 is a top view of a disk in a third orientation in the flywheel of FIG. 18; [Figure 19] 10 shows a cross section of an eighth embodiment of the flywheel. [Figure 19A] 20 is a top view of a disk in a first orientation in the flywheel of FIG. 19; [Figure 19B] 20 is a top view of a disk in a second orientation in the flywheel of FIG. 19; [Figure 19C] 20 is a top view of a disk in a third orientation in the flywheel of FIG. 19; [Figure 19D] FIG. 20 is a top view of a disk in the flywheel of FIG. 19 in a fourth orientation. [Figure 20] 10 shows a cross section of a ninth embodiment of the flywheel. [Figure 20A] 21 is a top view of a disk in a first orientation in the flywheel of FIG. 20; [Figure 20B] 21 is a top view of a disk having a continuous bonded area in the flywheel of FIG. 20. FIG. [Figure 20C] 21 is a top view of a disk in a second orientation in the flywheel of FIG. 20; [Figure 21] 10 shows a cross section of a tenth embodiment of a flywheel. [Figure 21A] 22 is a top view of a disk in a first orientation in the flywheel of FIG. 21; [Figure 21B] 22 is a top view of a disk having a continuous bonded area in the flywheel of FIG. 21. FIG. [Figure 21C] 22 is a top view of a disk in a second orientation in the flywheel of FIG. 21; [Figure 22] FIG. 10 is a top view of a fifth embodiment of a disk for a flywheel. [Figure 23] FIG. 10 is a top view of a sixth embodiment of a disk for a flywheel. DETAILED DESCRIPTION OF THE INVENTION

[0147] 1 and 2 relate to prior art devices described in the Background section.

[0148] 3 relates to a first embodiment of a flywheel generally designated "100." Flywheel 100 is designed for use in a kinetic energy storage device that can be used in conjunction with a suitable motor-generator or mechanical drive (or other suitable type of drive means) to provide a means of storing electrical energy.

[0149] Many applications are possible for the flywheel 100, some examples of which include, but are not limited to, one or more of local grid boosting for fast charging electric vehicles, uninterruptible power supplies, trackside rail, demand side management, and electric grid services. The flywheel 100 may also be provided in vehicles with electric propulsion systems, such as cars, trucks, buses, trains, airplanes, or ships.

[0150] Flywheel 100 can also be used to provide a kinetic energy storage device capable of mechanically transferring stored energy to assist in vehicle acceleration and recover kinetic energy that would otherwise be lost. The structure of flywheel 100 will be primarily described with respect to the flywheel at rest (i.e., not moving / rotating) unless otherwise specified.

[0151] Flywheel 100 includes a plurality of discs (also called stacks or rotor elements), some of which are designated "102." Each disc 102 is substantially the same size and shape in this example. Each disc 102 is joined to an adjacent disc to form a stack 104. None of the discs 102 require any disc openings because there is no need to accommodate any connecting or clamping elements that pass through the stack 104.

[0152] In this embodiment, fifteen discs 102 are provided, but it will be appreciated that in other embodiments any suitable number of discs may be provided, provided there are at least first and second end discs and at least one disc therebetween.

[0153] The disks 102, in this example, are substantially circular in outline. The centers of each disk 102 are aligned along a common longitudinal axis AA to provide a stack of disks 104. The stack 104, in this example, is substantially cylindrical.

[0154] The stack 104 may be thought of as providing the inertia element for the flywheel 100. The stack 104 may be considered a lamination stack.

[0155] Each of the disks 102 may be bonded to the adjacent disk by a primary bonding means (or primary bonding agent) selected from welding, brazing, soldering, diffusion bonding, or a strong engineering adhesive, which bonding is provided in a battlement pattern (or battlement arrangement) as described in more detail below with respect to Figures 3A and 3B.

[0156] The disks 102 may each be made from metal laminate or steel in this example, although other suitable metals, alloys, or composite materials may be used in other examples.

[0157] Each disk 102 does not have any openings for receiving bolts or other clamping means, and each disk 102 in the stack is preferably substantially identical in this embodiment, optionally to a tolerance on the order of a few microns or tens of microns.

[0158] Plate members or cheek plates (which may also be referred to as rotor elements) 106 are provided at either end of the stack 104. The plate members 106 are joined to the disks at either end of the stack 104 by any of the means previously described for joining the disks to one another.

[0159] In this embodiment, the plate members 106 are approximately the same diameter as the disks 102. Each plate member 106 is approximately the same thickness as a given one of the disks 102. The outer surface area of ​​each plate member 106 is approximately parallel to the face of the adjacent disk from the radial edge of the plate member 106 toward the axis AA to approximately one-third of the plate member radius. The thickness of the plate members 106 then gradually increases as they move further toward the axis AA.

[0160] The plate members 106 facilitate connection of the lamination stack 104 to the bearing pedestal 108. The cheek plates 106 also enable the stack 104 to be connected or fixed together (or more broadly provided in movable engagement with) an electric machine rotor portion or electric motor-generator rotor portion 110.

[0161] It will be understood that the precise form of the plate member is not essential to the invention.

[0162] Figures 3A and 3B show one disc 102 in the stack from the top and bottom, respectively. The top view corresponds to plane XX of disc 102 in Figure 3. The bottom view corresponds to plane YY of the opposite face of the same disc in Figure 3. Each disc face shown in Figures 3A and 3B shows disc 102 as viewed from the opposite face at the same relative rotational position about the flywheel axis of rotation AA.

[0163] 3A shows a first set of twelve bonding areas or pads (one of which is designated "112") on a first surface of the disc 102. The pads 112 are regularly spaced along the periphery P of the disc. The location of each pad shown can be considered to correspond to the location of the numbers 1-12 on a watch face. Of course, this is not required, and it will be understood that in alternative embodiments, any suitable number of bonding areas and bonding area locations / sizes can be provided.

[0164] FIG. 3B shows a second set of twelve bonding areas or pads (one of which is designated "114") on the second side of disk 102. Pads 114 are again regularly spaced along the periphery of the disk. The location of each illustrated pad can be considered to correspond to an intermediate position between the numbers 1 and 12 on the clock face. In other words, the bonding pattern on this side is the same as that of FIG. 3A, except that the bonding pads are incremented circumferentially around the disk by half the pitch from one bonding pad to the next. Again, of course, such an arrangement is not required, and it will be understood that in other embodiments, any suitable number of bonding areas and bonding area locations / sizes can be provided without overlapping with pads 112 on the other side.

[0165] The resulting bonding arrangement may be considered to provide a battlement-like or crenellated bonding pattern, particularly in the peripheral region of the disk. That is, when viewed along the side of the disk and moving circumferentially around the disk, the upper bonding pads 112 are joined by the lower bonding pads 114, which in turn are joined by the upper bonding pads 112, which in turn are joined by the lower bonding pads 114, and so on. These pads may thus be considered the horizontal portions of the battlement / creel. The spaced apart areas 112a, 114a on either side of each bonding pad may be considered the "vertical" portions of the battlement / creel.

[0166] Pads 112, 114 are generally U-shaped in this embodiment. Each U-shape is substantially the same size and shape as the other U-shapes in this embodiment. The U-shape of each pad is positioned so that the U-shape is at the periphery of the disk, with the curved end of the U-shape closest to the center of the disk.

[0167] It should be emphasized that the pads 112, 114 in each peripheral region of the disk can be of any shape and size and can be positioned separately, provided that they do not overlap with the pads 114, 112 opposite the main bonding means on the other side of the disk.

[0168] Note that pads 112, 114 do not extend too far toward the center of the disk. This is to prevent the joint from being placed under high tensile stress during flywheel rotation as a result of the reduction in laminate thickness due to Poisson's ratio effects when operating at high speeds. In this particular embodiment, pads 112, 114 extend inward a distance that is approximately 15% of the disk radius.

[0169] A spacing area (or gap) 112a is disposed between each pair of adjacent pads 112. A spacing area (or gap) 114a is disposed between each pair of adjacent pads 114. The spacing areas 112a, 114a are areas of the surface that do not have a primary interface (or in some embodiments, a disk-to-disk interface) on each side of the disk. The spacing areas can be considered to complement the shape of the pads.

[0170] Each spacing area 112a, 114a is larger in area than two adjacent joining areas 112, 114 on the same side of the disk 102. In this embodiment, the angular extent of each spacing area along the periphery of the disk is approximately (or slightly more than) twice the angular extent of each joining area along the periphery of the disk.

[0171] Similar joint patterns can be used for both disk-to-disk and disk-to-endplate joints.

[0172] Figure 4 depicts the pads 112, 114 shown in both Figures 3A and 3B, treating the disk 102 as transparent for illustrative purposes only. The pads 114 in Figure 3B on the bottom surface are shown with a "light" fill to distinguish them from the pads on the top surface.

[0173] The inner ring is indicated on the disk face by "113." The inner ring 113 is an imaginary line representing the inscribed circle located at the innermost extent of the pad 114. The diameter of the inner ring 113 in this example is approximately 85% of the diameter of the disk 102.

[0174] By having identical, regularly spaced pairs of pads on the same face of the disk and identical, regularly spaced spacing areas between these pairs of pads, i.e., by alternating arrangement, the relationship between the number of pads N, the angular extent p of a given pad in the peripheral region, and the angular extent g of a given spacing area next to that pad can be described using the formula: 2N(p+g)=360°, which assumes that the entire circumference of the disk is occupied by a combination of bonding areas and spacing areas.

[0175] When the discs all have the same number of bonding pads and spacing areas on each side of them, the bonding pattern is now considered part of stack 104. For the alternating sets of 12 pads and 12 spacing areas on the first disc, the pitch is equal to 30 degrees (i.e., 1 / 12 of 360°). The sets of bonding pads on the second disc adjacent to the first disc are incremented by 15 degrees. The sets of bonding pads on the third disc adjacent to the second disc on the face away from the first disc are incremented by another 15 degrees, thus resulting in substantially the same bonding pattern (including orientation about the flywheel axis AA) as the first disc.

[0176] It will be appreciated that this results in a bonding pattern that alternates between Pattern 1 (for odd-numbered disks in the stack) and Pattern 2 (for even-numbered disks in the stack). Of course, other patterns may appear in other embodiments of stacks having identical disks and bonding pads, but this is not required, and in some cases there may not be a discernible repeating pattern. It does not matter whether the stack has an even or odd number of disks, nor does it matter whether the two disks at the ends of the stack share the same bonding pattern(s) in the same relative orientation around the stack.

[0177] It will also be understood that this arrangement means that each bonding area 112 on the first surface is positioned opposite a spacing area 114a on the second surface of the same disk, and each bonding area 114 on the second surface is positioned opposite a spacing area 112a on the first surface of the same disk.

[0178] Figure 5 shows variations of hypothetical crack propagation paths through a given disk having a battlement-like joint arrangement (in this case the disk of Figure 4). Cracks are most likely to initiate in the most highly stressed region of the rotor element, at the center of the rotor element, although the invention is equally applicable to cracks initiating from other locations.

[0179] Analysis and testing of flywheels has shown that such cracks tend to grow primarily radially outward, perpendicular to the plane of maximum principal stress, which is either hoop or tangential. Although the crack can branch into two, these two cracks still tend to grow primarily radially. Because the rotor elements are thin, the crack also remains primarily in the radial-axial plane, i.e., the crack surface is perpendicular to the disk surface of the rotor element.

[0180] The mechanism for crack growth is metal fatigue. Before the crack reaches the outer radius, it typically reaches a critical size and then grows extremely rapidly as a "fast fracture." At this point, the forces within the rotor element become so great that the cracked rotor element splits open, causing the entire rotor to become unbalanced and the machine to shut down. Alternatively, the pad joint may shear, causing the cracked rotor element to rub against the containment casing, shutting down the rotor.

[0181] If the crack follows the path illustrated as path X in FIG. 5, passing between pad 112 and pad 114, the crack cannot transfer to the second rotor element.

[0182] If the crack were to follow the path illustrated as path Y in Figure 5, it could pass through one of the pads 112. The crack could also move to a second rotor element 102 connected to the same pad 112 as the cracked first rotor element 102. Even in this case, the crack in the second rotor element is unlikely to cause rapid failure because the crack in this second element would not be long enough to cause rapid failure. Meanwhile, the battlemented nature of the seam ensures that no more than one rotor element fails catastrophically. This significantly reduces the requirements for containment measures.

[0183] An example of a branching crack is shown in Figure 5 as path Z, where both branches pass through the same pad 112. Such a crack also does not result in a major or total failure of the rotor for the reasons explained above for a single crack.

[0184] It is statistically unlikely that two or more cracks will initiate separately in different locations and simultaneously grow to a critical size causing rapid failure. It is possible for two cracks to grow in the same rotor element at different locations and then merge to form a single crack that may then grow to a critical size causing failure. However, this too will not result in a major or total failure of the rotor for the reasons explained above for a single crack.

[0185] Disk-to-disk and disk-to-plate bonding should be accomplished using a bonding material or adhesive (or other means) strong enough to maintain the structural integrity of the flywheel 100 at high speeds. As previously mentioned, bonding may in some cases be accomplished by welding, soldering, brazing, or other fabrication techniques to provide a bonded interface between adjacent disks. Specific examples are described below.

[0186] 6 shows an example of a disk 102' having welded (or diffusion bonded) sections, one of which is designated "116." One way to accomplish this is to first clamp the rotor elements (disks 102 and / or plate members 106) together, either individually or all together in a complete stack 104'. Then, the battlement pads 116 are created by welding means.

[0187] Electron beam welding is the preferred method because it avoids significantly changing the material properties of the rotor element. However, other welding means may be selected, for example for cost-effectiveness, provided that the rotor element material properties are not substantially adversely affected. Even in this case, some reduction or weakening of the material properties in the area of ​​the pads may be acceptable when compared to the material around the center of the rotor element, given that stresses in the rotor element are generally lower at the location of the pads, i.e., in the peripheral area of ​​the disk.

[0188] 7 shows the details of the welds and how they result in a cast pattern for the stack 104' of disks 102'. The weld areas 116 are offset from one seam to the other in the pattern in the manner previously described. The shape and depth of each weld 116 can be selected to provide the appropriate shape and depth for the disk-to-disk joint to allow proper and safe operation of the flywheel 100.

[0189] 8A and 8B show an example of a disk 102" having bonding areas where a bonding agent is applied directly to the surface of the disk. One of the bonding areas is designated "118." It will be understood that using a bonding agent is an alternative to welding, but these options are not considered mutually exclusive.

[0190] The shape of the pad 118 means may vary from pad to pad when the bonding means is deposited and drawn in the stack assembly process. More preferably, the shape of each pad should be controlled to ensure a strong and uniform structure. The pad pattern depicted on the disk 102" is substantially similar to that of Figures 3A and 3B, except in this example there are 16 pads 118 on each side, each with a random or irregularly shaped profile. Of course, other shapes are possible.

[0191] The joining means for the pads 118 may be brazing, soldering, or adhesive. In some embodiments, it may be advantageous to deposit two different types of joining agents on adjacent rotor elements. One example of this includes having a braze on one side of the rotor element 102" and a flux on the other side. In another example, two different portions of an engineering adhesive system may be placed on adjacent faces of adjacent rotor elements.

[0192] Once the rotor elements are assembled into the inertia element or stack, they are heated to form the joint or to set the joining material, with the exception of engineering adhesives which do not require heat to cure the joint.

[0193] It should be noted that localized heating (targeted heating) can be achieved using an electron beam similar to that produced by machines used for electron beam welding. This is particularly suitable for brazed seams, where the braze is locally melted by the electron beam.

[0194] The amount of adhesive deposited must be carefully controlled to ensure that adhesive pads on the same disk face remain spaced or separated from one another when the rotor elements are pressed together, and to avoid adhesive pads 118 on opposite faces of the rotor elements overlapping one another as the material spreads in compression between the disks.

[0195] FIG. 9A shows a first embodiment of a shim 120 that fits between two disks 102. The shim 120 is thin compared to the disks 102. The shim 120 is substantially circular and has a series of peripheral indentations or notches 120a, which in this example are substantially U-shaped, providing gaps 120a that extend inward toward the center of the shim 120. The U-shaped gaps may, in some instances, correspond to the U-shaped pads 112, 114 described above with respect to FIGS. 3A and 3B. However, the flywheel of FIG. 3 does not necessarily require shims to provide these pads. Of course, other shapes of pads are possible in other embodiments.

[0196] 9B shows a second embodiment of a shim 122 that is similar to the first shim 120. The shim 122 also has a U-shaped gap 122a around its periphery. However, in this example, the shim 122 is substantially annular and has a central opening or hole 122b extending through the center. The central opening 122b corresponds to the central region of the disk.

[0197] FIG. 9C shows either shim 120, 122 in position relative to the disk 102, providing a pocket, approximately designated "124," to receive the bonding material. To form the brazed or soldered joint, it is typically advantageous to create a small, precisely sized axial gap h, which may be on the order of 10 to 100 micrometers deep. This can be accomplished inexpensively in this example using shims 120, 122. This allows for easier control of the pad shape than the method described with reference to FIGS. 8A and 8B, which involves depositing a bonding medium and clamping the rotor elements. The notches 120a, 122a facilitate the flow of solder or brazing material into the stack, forming the pads 112, 114 precisely as needed. The solder or brazing material does not substantially flow into areas other than the pockets provided by the shims 120, 122 between the pair of disks 102.

[0198] Variations of the above flywheel embodiments and components are contemplated within the scope of the present invention. Features of the following embodiments are similar to those described above unless otherwise noted.

[0199] Like reference numerals are used to refer to like parts in the following examples, with each number increasing by a multiple of 100, for example part 102 corresponds to parts 202, 302, etc. in subsequent examples.

[0200] Figures 10A and 10B show a second embodiment of a flywheel 200. The flywheel 200 includes a series of shims 120 (and / or 122) as described with respect to Figures 9A-9C. An alternating arrangement of disks 202 and shims 120 is provided. It will be understood that similar bearings 208 and motor-generator rotor portions 210 are provided, although not all are shown.

[0201] The shims 120 are arranged in an alternating pattern relative to one another in the manner previously described for the pad in Figures 3A and 3B, i.e., to obtain the chest-like pad pattern, a given pair of adjacent shims 120 are rotationally offset to avoid the notch 120a of one shim 120 overlapping the notch 120a of the immediately adjacent shim 120.

[0202] To create the bond pads, one of the methods described above can be used, or alternatively, the entire rotor can be assembled with the shim 120 (or 122) in place and a dip brazing or dip soldering method can be used. This method involves dipping the rotor elements (i.e., the stack of disks) either partially or fully into a liquid braze or solder, which draws the braze or solder into the pockets 124, where it can form the bond areas or pads 212, 214 once the flywheel is removed and the braze / solder has solidified.

[0203] 11 shows a portion of a disk that may be provided in either embodiment of the flywheel 100, 200, without the need for shims 120, 122. In this example, a small recess of depth h is provided in one or more areas of the disk. This physical depression or recess 224 in the surface of the disk 202 is on the order of tens of micrometers deep.

[0204] A suitable number of recesses 224 may be provided on both sides of the disk 202 to facilitate bonding in areas similar to those described in the previous embodiments, i.e., recesses 224 on one side of the disk 202 do not overlap with recesses on the other side of the disk.

[0205] The braze or solder can be flowed into the recesses by any of the methods previously described during flywheel assembly. The recesses 224 in the disk 202 are formed directly into the surface of the disk by chemical etching or mechanical stamping.

[0206] 12A relates to another means of providing a bonding agent between pairs of discs 202 in a stack 204. Instead of shims (or some of the shims), an appropriate number of thin flexible sheets 226 may be provided for each positioning between adjacent pairs of discs 202 in a flywheel 200.

[0207] The adhesive is applied to the carrier sheet 226 in the pattern of the pads 212, aimed near or at the sheet edges located in the peripheral region of the sheet 226. While any suitable sheet can be used, preferably the sheet 226 is made from a porous material. The carrier sheet 226 can be a fiber mat. The bonding agent is thus provided at predetermined locations to achieve the desired bonding pattern in the stack of discs 202 when the stack is clamped and the bonding process is performed.

[0208] As with the previous embodiment, care must be taken to ensure that the adhesive areas 212 do not overlap on adjacent carrier sheets 226 in the stack 204. That is, for two carrier sheets to be placed on either side of a given disc, the adhesive areas on one carrier sheet should not overlap with the adhesive areas on the other carrier sheet.

[0209] FIG. 12B shows a modified carrier sheet 228, which differs from carrier sheet 226 in that it has a central opening 228a to minimize the weight of the sheet.

[0210] Figures 13A and 13B show another embodiment of disk 302 viewed from above and below, respectively. The disk surfaces shown in Figures 13A and 13B show opposite faces of disk 102 in the same relative rotational position about flywheel axis of rotation AA.

[0211] A plurality of discs 302, whether including shims, carrier sheets, disc surface recesses, or any combination thereof, can be provided in a stack suitable for use in the flywheel described above.

[0212] 13A shows a first set of twelve bonding areas or pads 312 (dark fill pattern) on a first side of disk 302 and a second set of twelve pads 330 (light fill pattern) on the same side of disk 302. The first set of pads 312 are intended to receive a primary bonding means that provides a structural bond for the stack of disks. The second set of pads 330 are intended to receive another bonding agent that provides a weaker disk-to-disk bond while providing good thermal conduction between the disks.

[0213] The first and second sets of pads 312, 330 are regularly spaced around the periphery of the disc. The positions of the illustrated pads 312 can be considered to correspond to the positions of the numbers 1-12 on a watch face, while the other set of pads 330 are located between adjacent pairs of pads 312 in the first set.

[0214] In this particular example, the pads 312, 330 are all U-shaped in plan view, however, as previously mentioned, any suitable number, location and size of pads / areas may be provided.

[0215] 13B shows a third set of twelve bonding areas or pads 314 (dark fill pattern) on the second side of disk 302 and a fourth set of twelve pads 332 (light fill pattern) on the same side of disk 302. The third set of pads 314 are intended to receive a primary bonding means that provides a structural bond for the stack of disks. The fourth set of pads 332 are intended to receive another bonding agent that provides a weaker disk-to-disk bond while still providing good thermal conduction between the disks.

[0216] The third and fourth sets of pads 314, 332 are also regularly spaced around the periphery of the disc. The position of the illustrated pad 314 can be considered to correspond to a midpoint between the positions of the numbers 1-12 on a watch face, with the fourth set of pads 332 being located between adjacent pairs of pads in the third set 112. In other words, the bonding pattern on this surface is the same as that of Figure 13A, except that the bonding pads are incremented circumferentially around the disc by half the pitch from one bonding pad to the next.

[0217] In this particular example, the pads 314, 332 are all U-shaped in plan view. However, as previously mentioned, any suitable number, position, and size of pads / areas may be provided, provided that no pad 314 overlaps a pad 312 on the other side. It is permissible for any of the pads 330 in the second set to overlap any of the pads 332 in the fourth set.

[0218] It will be appreciated that spacing areas 312a, 314a are provided between pads 312, 314 on either side of disk 302 for reasons previously discussed. Secondary bonding agent pads 330, 332 may be considered to be located within the spacing areas.

[0219] It is also contemplated that in another embodiment, the highly thermally conductive pads 330, 332 may be larger than the other pads 312, 314. In this case, the thermal conduction between the disks may be further improved.

[0220] It will also be appreciated that various embodiments of the present invention may include electron beam welding the entire disk assembly according to any suitable variation of the battlement pattern described above, in which case the entire rotor / stack of disks may be immersed in a solder bath, with no gap or spacing area between the (primary) structural bond and the (secondary) thermal bond.

[0221] The reason for providing the second and fourth sets of pads 330, 332 is to dissipate heat within the flywheel during use. Heat is generated within the rotor assembly, for example, by the electrical machine. Therefore, in addition to ensuring the structural integrity of the flywheel through the primary joining means, it is important that heat be readily transferred axially from one rotor element to another via thermal conduction.

[0222] This can be accomplished by providing additional areas where the disks 302 may be bonded together in a manner that does not promote crack propagation, so that the selected secondary bonding means will fail before a crack can propagate through it to an adjacent disk. This example improves thermal conductivity compared to an embodiment in which only the primary bonding means of the pads 312, 314 provide a path for heat conduction.

[0223] The secondary joining means in this example may be a weaker type of solder (e.g., weaker than the solder / braze used as the primary joining agent), but may be used in examples where, for example, welding or an engineering adhesive is provided as the primary joining means.

[0224] FIG. 14 shows another embodiment of a flywheel 300. Instead of the plate members of the previous embodiment, this involves providing end plates 306 composed of laminates 334 of various shapes, as a way to minimize costs. Examples of possible laminate shapes 334a, 334b, and 334c are shown in FIGS. 14A, 14B, and 14C, although other suitable shapes may optionally be provided. These shapes can be produced by stamping, water jet cutting, or laser cutting.

[0225] In the illustrated example, the end plates 306 at each end of the stack are provided by assembly of any of the rotor elements 334 shown in Figures 14A-14C. That is, circular laminations with reduced outer diameters, and / or laminations with non-circular outer shapes, and / or laminations with central openings may be sequentially assembled together to provide the end plates 306.

[0226] These shapes are joined together using battlement joints as described above, or by continuous annular ring joints, the latter being permitted because the diameter of these rotor elements 334 is smaller than the main disk 302. This ensures that if more than two of the rotor elements 334 making up the end plate 306 fail, the energy released will not be greater than the failure of two laminations 302.

[0227] Referring to Figure 15, another embodiment of a flywheel is generally designated "400." Flywheel 400 is generally similar to the flywheels described above. In this embodiment, each disk 402 has a bond area 412 on a first face that is rotationally offset about the flywheel axis relative to a bond area 412 on a second face such that each bond area 412 on the first face at least partially overlaps a bond area 414 and a clearance area 414a on the second face.

[0228] When the disks 402 are stacked, each disk 402 is positioned in one of three orientations, rather than two orientations as described in the previous embodiment. That is, the second disk in the stack is angularly displaced or offset by an angle relative to the first disk in the stack. The third disk in the stack is angularly displaced by a larger angle relative to the first disk in the stack. In other words, each disk is at a different angular position relative to each other. Figure 15A shows the flywheel disk 402 in Orientation A. Figure 15B shows the flywheel disk 402 in Orientation C. Figure 15C shows the flywheel disk 402 in Orientation D.

[0229] As can be seen most clearly in Figure 15, the bond pattern after stacking alternates between orientations A, C, and D. The bond pattern in the stack forms a repeating sequence of ACD. The bond pattern between each pair of bonded disks 402 can be considered to form a spiral arrangement throughout the stack.

[0230] A flywheel stack with the arrangement shown in FIG. 15 has a higher bending stiffness at the expense of having overlapping joint areas 412, 414. If the bending stiffness is too low, elements of the flywheel assembly, such as the inertia rotor, the electric machine, and the shaft comprising the bearing support, may resonate at frequencies within or near the operating range of the flywheel 400. While the overlapping joint areas 412 increase the risk of crack propagation, because the axial thickness of the individual disks 402 is still substantially less than the thickness of the stack, even in this unlikely event, a lighter casing can still safely contain the rupture. For example, the assembly can tolerate failure of up to three or four disks that can be safely contained.

[0231] Sufficient bending stiffness is required in the flywheel for the intended application to mitigate resonance, but this must be balanced against the risk of crack propagation through the stack due to the degree of overlap of the bond area.

[0232] Referring to Figure 16, another embodiment of a flywheel is generally designated "500." The flywheel is generally similar to flywheel 400 shown in Figure 15, except that in this embodiment there is a greater degree of overlap between first bond area 512 and second bond area 514. To achieve the repeating pattern of bond areas, each disk 502 is provided in one of four orientations. The four orientations A, E, B, and F are shown in Figure 16A.

[0233] The degree of rotational offset of the bonding pattern between adjacent pairs of disks 502 is substantially the same throughout the stack.

[0234] As seen most clearly in Figure 16, the bond pattern after stacking alternates between Orientation A, Orientation E, Orientation B, and Orientation F. The bond pattern in the stack forms a repeating sequence of AEBF. As noted above, the bond pattern between each pair of disks 502 can be considered to form a spiral arrangement throughout the stack.

[0235] The bending stiffness of the flywheel 500 is further increased compared to the flywheel 400 described in FIG. 15, at the expense of increased overlap of the joint areas.

[0236] Referring to Figure 17, another embodiment of a flywheel is generally designated "600." Three disks 602 are shown for simplicity. In this embodiment, the bond area 612 on a first face of each disk 602 is rotationally offset by an angle β relative to the bond area 614 on the opposite face. The bond pattern between each adjacent pair of disks 602 is rotationally offset by the angle β.

[0237] For example, the bond pattern between the second and third disks 602 is rotationally offset by an angle β relative to the bond pattern between the first and second disks 602. The bond pattern between the third and fourth disks 602 is rotationally offset by an angle 2β relative to the bond pattern between the first and second disks 602.

[0238] No orientation of any disk 602 matches the orientation of the immediately preceding disk 602. In other words, there is no repeating pattern. However, a helical arrangement of the bonding surfaces throughout the stack is still achieved.

[0239] Referring to Figure 18, another embodiment of a flywheel is generally designated "700." Flywheel 700 is generally similar to flywheel 600 shown in Figure 17, except that in this embodiment, the spacing areas 712a, 714a between adjacent bond areas are reduced in size. Crack propagation can be suppressed by carefully selecting angle β.

[0240] 18A, 18B, and 18C, the bond areas 712, 714 of the disk 702 in this embodiment are asymmetrical. When the bond involves welding, the asymmetrical bond areas have been found to improve the metallurgical properties of the weld and surrounding materials and minimize the speed of the bonding operation.

[0241] Referring to FIG. 19, another embodiment of a flywheel is generally designated "800." In this embodiment, each flywheel disc 802 is arranged in one of four orientations. FIG. 19A shows a flywheel disc 802 in orientation A. FIG. 19B shows a flywheel disc 802 in orientation B. FIG. 15C shows a flywheel disc 802 in orientation C. FIG. 15D shows a flywheel disc 802 in orientation D. In this embodiment, there is no repeating pattern of bond areas 812, 814 throughout the stack.

[0242] The bond pattern of the end plate 806 and adjacent disk 802 is out of phase with the bond pattern of the disk 802 and the adjacent disk 802 on the other side. The angular offset between the bond pattern of each end plate 806 and its adjacent disk 802 is greater than the angular offset between the bond pattern of each disk 802 and its adjacent disk 802. This means that, in the worst case, a crack that initiates within an end plate 806 can only migrate into the adjacent disk 802 and no further. A crack that initiates in a disk 802 adjacent to an end plate 806 can only migrate into either the end plate 806 or the adjacent disk 802 on the other side, but not both. In other words, the event of failure of an end plate 806 and more than one disk 802 is avoided.

[0243] Referring to FIG. 20, another embodiment of a flywheel is generally designated "900." In this embodiment, disks 902' having continuous bond areas 912' are used. FIG. 20A shows a flywheel disk 902 in orientation A. FIG. 20B shows a flywheel disk 902' having continuous bond areas 912'. FIG. 20C shows a flywheel disk 902 in orientation B. The continuous bond areas 912' extend around the periphery of several pairs of bonded disks 902'. In other words, the stack includes a mix of battlement-like and continuous bond patterns. This configuration also achieves high bending stiffness. In other embodiments, the thickness of the continuous bond areas 912' can be adjusted to correspond to the bond areas 912, 914 of adjacent disks 902 having battlement-like bond patterns.

[0244] This embodiment has the drawback that up to four disks can fail, but if the disks 902, 902' in the main stack are thinner than the end plates, then failure of four disks 902, 902' is no worse than failure of an end plate and one disk 902.

[0245] Referring to FIG. 21, another embodiment of a flywheel is generally designated "1000." This embodiment is generally similar to the embodiment described above with respect to FIG. 20. A disk 902" having a continuous bond area 912" as described above is used. FIG. 21A shows a flywheel disk 902 in Orientation A. FIG. 21B shows a flywheel disk 902" having a continuous bond area 912". FIG. 21C shows a flywheel disk 902 in Orientation B. In this embodiment, the continuous bond area 912" is shaped to correspond to the bond areas 912, 914 of an adjacent disk 902 having a battlement-like bond pattern. In other words, the continuous bond area 912" has alternating regions of thicker (or wider) areas 912a" and thinner (or narrower) areas 912b.

[0246] The continuous bond area 912" can be considered to have wavy inner and outer edges relative to the radial extent of the disk 902".

[0247] 22, there is shown another embodiment of a flywheel disc 1002. This embodiment is generally similar to the flywheel disc described above, except that the bond area 1012 in this embodiment includes rounded edges. The rounded edges have been found to reduce stress on the disc 1002.

[0248] 23, there is shown another embodiment of a flywheel disc 1102. This embodiment is generally similar to the flywheel disc described above, except that the bond area 1112 in this embodiment is located away from the periphery. It has been found that moving the bond area 1112 away from the periphery reduces stress on the disc 1102.

[0249] It is emphasized that any of the disks 102, 202, 302, 402, 502, 602, 702, 802, 902, 902', 902", 1002, 1102 may be used in any of the flywheel embodiments, and any combination of shims, carrier sheets, and disk recesses may be used with any suitable primary joining means.

[0250] The flywheel 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000 may be provided as part of an assembly with a suitable drive mechanism, which assembly may be considered part of an energy recovery and release system, and which is provided in a containment vessel suitable for safe operation of the flywheel, taking into account the mass and energy storage capacity of the flywheel.

[0251] In use, the flywheel 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000 is rotated about axis AA by a drive mechanism, storing kinetic energy in the flywheel. The flywheel 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000 may deform radially outward at speeds on the order of several hundred meters per second when used to store a significant amount of kinetic energy.

[0252] The drive mechanism can be used to release some of the stored kinetic energy of the rotating flywheel by slowing the rotational speed of the flywheel, thereby extracting the stored kinetic energy and converting it into another useful form, such as electrical energy. Other examples of energy collection and extraction are performed as needed, which can involve thousands or millions of cycles of energy release on the order of hundreds of kilojoules, megajoules, or more, for example, when multiple flywheels are provided in an assembly and operated together in parallel.

[0253] While various examples and embodiments of flywheels and flywheel components (such as discs and mating means) have been presented above, it will be understood that other embodiments of flywheels may be provided, in which any combination of features from any two or more of the embodiments may be provided as a new embodiment within the scope of the present disclosure.

[0254] The above embodiments are provided by way of example only, and various changes and modifications will be apparent to those skilled in the art without departing from the scope of the invention as defined by the claims.

Claims

1. 1. A flywheel comprising a plurality of discs arranged in a stack and a joining means, the plurality of disks includes at least first and second end disks at opposite ends of the stack and one or more disks between the first and second end disks; each of the disks includes opposite first and second surfaces, each of the first and second surfaces including a central region and a peripheral region disposed about the central region, the peripheral region adjacent a periphery of the disk; the joining means joins the adjacent peripheral regions of the adjacent discs together for flywheel rotation; one, some, or all of said one or more disks: a first set of bonded areas in the peripheral region of the first surface, and one or more spacing areas in the peripheral region to separate the bonded areas of the first surface; a second set of bonded areas in the peripheral region of the second surface and one or more spacing areas in the peripheral region to separate the bonded areas on the second surface; At least one of the disks one or more of the bonding areas on the first surface are located opposite the spacing area on the second surface of the disk, or opposite both a portion of the spacing area and a portion of the bonding area on the second surface of the disk; one or more of the joining areas on the second surface are located opposite the clearance area on the first surface of the disk, or are located opposite both a portion of the clearance area and a portion of the joining area on the first surface of the disk.

2. 2. The flywheel of claim 1, wherein each of the bond areas on the first surface is located opposite a corresponding spacing area on the second surface of the disk, and each of the bond areas on the second surface is located opposite a corresponding spacing area on the first surface of the disk, thereby providing a battlement-like or pseudo-battlement-like bond arrangement when viewed from a side of the disk.

3. 2. The flywheel of claim 1, wherein a spiral joint arrangement is provided when viewed from a side of the disk by both: each of the joint areas on the first surface being positioned opposite a portion of the corresponding spacing area and a portion of the corresponding joint area on the second surface of the disk; and each of the joint areas on the second surface being positioned opposite a portion of the corresponding spacing area and a portion of the corresponding joint area on the first surface of the disk.

4. 4. A flywheel according to claim 1, wherein, in any of the disks, the first set of bond areas on the first surface are rotationally offset from the second set of bond areas on the second surface about the flywheel axis of rotation.

5. 5. The flywheel of claim 4, wherein the first and second sets of interface areas are in antiphase about the flywheel axis of rotation.

6. 6. A flywheel according to claim 1, wherein each of the spacing areas has a larger area or a larger angular extent than an opposite joining area to space the joining areas on opposite faces of the disk.

7. A flywheel according to any preceding claim, wherein the joining areas and the spacing areas are regularly or equidistantly spaced throughout the peripheral region.

8. 8. A flywheel according to claim 1, wherein on the first surface and / or the second surface of any of the disks, each of the joining areas is substantially identical to each of the other joining areas on the first and / or second surface, and each of the spacing areas is substantially identical to each of the other spacing areas on the first and / or second surface.

9. 9. A flywheel according to claim 8, which is dependent on claim 7, wherein each of the joining areas of the first and / or second faces of at least one of the disks is identical and each of the spacing areas of said faces is identical, and the joining and spacing areas of said faces obey the equation 2N(p+g)=360°, where N is the number of the joining areas of said faces, p is the angular extent (in degrees) of one of the joining areas, and g is the angular extent (in degrees) of one of the spacing areas.

10. A flywheel according to any one of claims 1 to 9, wherein at least eight of said bonding areas are provided in said peripheral region.

11. A flywheel according to any preceding claim, wherein some of the joining areas each include a recess formed in the peripheral region.

12. A flywheel according to any preceding claim, wherein at least one of the bonding regions is asymmetric.

13. A flywheel according to any preceding claim, wherein at least one of the bonding regions is spaced from the peripheral edge.

14. At least one shim is provided in the stack; the shim is disposed between adjacent pairs of the disks; 14. A flywheel according to any one of claims 1 to 13, wherein the shim includes a plurality of peripheral voids at its periphery, the peripheral voids corresponding to or defining the joining areas on the faces of each of the adjacent disks.

15. 15. The flywheel of claim 14, wherein the shim includes a central opening sized to correspond to the central region of the adjacent disk, the central opening having a diameter greater than half the diameter of the shim.

16. 16. A flywheel according to claim 14 or 15, when dependent on claim 4, wherein a shim is provided between each pair of adjacent disks in the stack, the shims in adjacent shim pairs being rotationally offset or out of phase with each other about the flywheel axis of rotation.

17. 17. A flywheel as claimed in any one of the preceding claims, wherein at least one porous or fibrous carrier sheet is provided between at least one pair of adjacent discs in the stack for carrying the joining means.

18. A flywheel as claimed in any preceding claim, wherein the coupling means joins only a portion of each of the discs to each adjacent disc in the stack.

19. 19. A flywheel according to any one of the preceding claims, wherein in at least one of the discs, the bonding means includes a first bonding agent on the first and second faces of the disc, and a second bonding agent on the first and second faces of the disc.

20. secondary joining means are provided for conducting heat between at least one pair of adjacent said disks; the secondary bonding means has a higher thermal conductivity than the bonding means; A flywheel as claimed in any preceding claim, wherein the secondary join means provides a disc to disc bond that is weaker than the join means so as to inhibit crack propagation through the secondary join means.

21. 21. A flywheel as claimed in claim 20, wherein said secondary joining means is provided in one or more portions of said spacing area and is selectively spaced from said joining means.

22. A flywheel according to any one of claims 1 to 21, wherein the joining means comprises welding, brazing, soldering, diffusion bonding or a strong engineering adhesive.

23. first and second plate members disposed at opposite ends of the stack; the first and second plate members do not have openings for clamping the stack together; A flywheel according to any preceding claim, wherein the first and second plate members are joined to the opposite ends of the stack.

24. each of said disks having a similar thickness; 24. The flywheel of claim 23, wherein either or both of the first and second plate members have a thickness substantially the same as a thickness of the disc.

25. A flywheel as claimed in any preceding claim, wherein each of the discs in the stack is free of through holes.

26. one or more additional stack elements are disposed on or joined to one or both ends of the stack; Each of the additional stack elements comprises: a circumference of a smaller diameter than the discs in the stack; Non-circular perimeter, A flywheel according to any one of claims 1 to 25, including laminations having one or more of: a central opening;

27. a plurality of said additional stack elements are provided at one or both ends of said stack; 27. A flywheel as claimed in claim 26, wherein the width or diameter of successive additional stack elements decreases in a direction towards the ends of the stack.

28. A flywheel assembly including one or more flywheels according to any one of claims 1 to 27, A flywheel assembly, wherein the flywheel is mounted to at least one drive assembly that facilitates rotation of the flywheel to store energy in or release energy from the flywheel.

29. 1. A method of constructing a flywheel, comprising: stacking a plurality of discs to form a stack of discs; enabling or achieving bonding between adjacent disks with bonding areas of adjacent disks overlapping to an extent that increases or decreases depending on the stiffness of the disk stack required to avoid resonances, in particular bending resonances, of the flywheel at specific frequencies during operation of the flywheel.

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