Flywheel energy storage device

Abstract

An example flywheel energy storage device includes a continuously curved fiber-resin composite ovoid shell. A hub is concentrically arranged inside and outside the shell at the shaft. Multiple radially oriented fiber-resin composite spiral wraps of uniform width are used to construct the ovoid shell and couple the shell to the hub for common rotation and torque transfer. An integrated internal structure is connected to and provides compressive support for the outer ovoid shell. When rotating, the ovoid shell is slightly elongated to increase the effective moment of inertia of the flywheel at operating speed.

Description

[0001] Priority claim

[0002] This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 857,088, filed on June 4, 2019, for "Catenary Flywheel Kinetic Battery" to James B. Clegern, the entire contents of which are hereby incorporated by reference into this application as if fully set forth herein. Background Art

[0003] Flywheels have been used as a device for storing energy in the form of rotational kinetic energy for more than 2,000 years. In larger form factors (typically 10 kWh or more), they can provide the heart of energy storage systems (ESS) for renewable and conventional grids, from multi-module utility systems to single-unit residential / commercial systems. Vacuum-enclosed flywheels combined with ultra-low friction magnetic bearings are particularly well suited for ESS applications that require frequent charge / discharge cycles every day because they have essentially no parts that wear. Examples of these high-cycle ESS applications include supporting the intermittency of renewable energy, powering electric vehicle charging stations, and stabilizing grid frequency regulation. Typically, however, current-generation flywheels with potential use in these applications rotate at relatively low speeds and are made of large amounts of structural materials such as steel or composite fiber-resin laminate layers. These high-quality flywheels are typically costly, both in terms of initial cost and installation cost, for the energy they can store, limiting applications to locations where volume or mass are not limited.

[0004] When examining the energy storage capabilities of flywheels, they are largely limited by the structural design and choice of structural materials. The structural design dictates how the flywheel is connected to the rotating shaft to transfer torque, and where the structural mass is placed to maximize the rotational moment of inertia. The structural material properties (i.e., strength, density, elasticity, fatigue resistance, etc.) determine the operating speed and life of the flywheel based on the structural design. For example, with each evolution of structural materials, from the Stone Age, Bronze Age, Iron Age, to the current composite age, improvements in flywheel structural material properties have allowed for faster rotational speeds for a given structural design.

[0005] The kinetic energy storage (Ek) capacity of a flywheel is determined by the standard equation Ek = 1 / 2Iω^2, where the structural design mass position in the moment of inertia (I) and the flywheel speed (ω) are the two energy storage drivers. Of the two energy storage drivers, increasing the structural mass and moment of inertia (I) for a given structural material is the standard way to achieve greater energy storage. This involves adding thickness or height to a conventional disc, cylindrical rim, or annular rim structural flywheel design after the maximum speed is reached for the given structural material. The use of composite materials for conventional mass concentrated flywheels has been commercially demonstrated, with a 1250 kg unit capable of storing 25 kWh of energy. The use of steel materials for conventional mass concentrated flywheels has been commercially demonstrated, with a 2270 kg unit capable of storing 50 kWh of energy. Even the use of concrete materials for conventional mass concentrated flywheels has been commercially demonstrated, with a 3000 kg unit capable of storing 10 kWh of energy.

[0006] There are three challenges to increasing flywheel energy storage by adding mass. First, flywheel energy storage capacity increases linearly with the increase in flywheel mass, resulting in practical operational limitations on manufacturing, delivering, and placing large flywheels with high energy storage capacity. Second, as the mass of the flywheel increases, each subsystem supporting the flywheel (i.e., bearings, support structures, and vacuum housing) must also be "scaled up" to handle the added mass, thereby increasing the mass and complexity of the entire system. Third, the increase in overall mass and subsystem complexity make the increase in energy storage a significant cost driver, and many flywheel energy storage systems are priced well beyond a reasonable payback time frame.

[0007] The second driver for energy storage places a focus on increasing flywheel speed, as it increases the flywheel’s energy storage capacity by a factor of two. Two areas of development in flywheels could lead to increased speeds: structural design and stronger structural materials. The use of lighter, stronger composite materials to replace heavier metals and fiberglass has become the mainstream in conventional structural mass flywheel designs of the traditional disc, cylindrical rim, or toroidal rim type. In the 1970s, research was conducted to explore new structural flywheel designs that would increase energy storage capacity, taking advantage of the flexibility of new manufacturing techniques for continuous filament winding of resin-impregnated composite fiber materials. These new structural designs were promising, but only added to the traditional toroidal rim mass flywheel design. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a perspective view of an example of a flywheel energy storage device;

[0009] Figure 2 is a side view of an example elliptical egg-shaped flywheel;

[0010] Figure 3 is a cross-sectional view of an example elliptical egg-shaped flywheel, including a bearing subsystem and a transmission subsystem;

[0011] Figure 4 is a detailed cross-sectional view of the right bearing subsystem and the gearbox subsystem;

[0012] Figure 5 is a detailed cross-sectional view of the left bearing subsystem;

[0013] Figure 6-7 is a cross-sectional view of another example elliptical egg-shaped flywheel. DETAILED DESCRIPTION

[0014] A high-speed, compact flywheel system is disclosed that is suitable for storing excess energy from renewable and conventional utility electric utilities and distributing the energy when the energy is needed. An example high-speed elliptical egg-shaped flywheel includes a composite shell composed of helically wound bands of resin-impregnated composite fiber material combined with an internal composite structure that provides compressive support. In one example, the fiber-wound composite shell is coupled to a rotating shaft via pairs of structural flange plates concentrically arranged on either side of the shaft, with multiple composite shell fiber bands connected for torque transfer. A large portion of the flywheel shell interior is hollow to maximize the flywheel moment of inertia mass at the maximum allowable shell radius.

[0015] The flywheel's oval and elliptical curvature is formed to support the centripetal forces that vary with the radius of each fiber wound outside the helix. This allows for two planes of structural support, which can significantly increase the allowable tip speed compared to conventional disc or cylindrical flywheels of equal diameter and the same structural materials. The all-composite nature of the elliptical flywheel structure improves operational safety and allows for maximum and consistent utilization of composite material strength in its optimal embodiment.

[0016] In one example, an elliptical egg-shaped flywheel includes multiple sets of spiral windings, each set of spiral windings having a uniform width. Each set of spiral windings has layers extending around the outer surface of the shell and the hub located on both sides of the rotation axis. In another example, each set of spiral windings has a nearly continuous single-ended filamentary material wound in a unidirectional relationship and encapsulated in a resin matrix. In another example, during rotation, each set of spiral windings is uniformly stressed over the width of each winding. In another example, each set of spiral windings has a radially oriented layered composite shell. In another example, the spiral windings are arranged in an overlapping relationship on a portion of the hub near the rotation axis.

[0017] In one example, each layer of radially oriented helical winding is initially angled at about 5 degrees and stepped to about 35 degrees to accumulate the mass of the winding layers away from the axis of rotation, thereby increasing the moment of inertia of the flywheel.

[0018] In one example, the radially oriented helical winding is configured to transfer tensile tip stresses under compressive stress to a thickened structure close to the axis of rotation, thereby maximizing the effective strength of the fiber-wound composite laminate.

[0019] The elliptical egg-shaped flywheel may have an integrated internal structure connected to and providing compressive support for the outer egg-shaped shell. In one example, the internal structure is formed of a metal or nearly continuous single-ended filamentary material that is wound in multiple layers in a unidirectional relationship and encapsulated in a resin matrix. In another example, the internal structure is formed of a metal composite laminate layer that is wound in multiple layers in a unidirectional relationship and bonded to the inner layer of the outer egg-shaped shell. The minimum inside-outside ratio of the internal structure compared to the outer diameter of the egg-shaped shell is about 0.1.

[0020] In one example, the inner and outer circumferences of the oval shell are in the shape of a rotating ellipse. In one example, the oval shell spirally wound layers are used twice to control the inertial mass of the flywheel.

[0021] In one example, adding or removing layers configures the flywheel energy storage capacity to increase or decrease through multiple winding layers.

[0022] The elliptical egg shaped flywheel may also have a dual boss plate connected to the innermost and outermost egg shaped shell layers to connect the egg shaped shell to the shaft for co-rotation and torque transfer. By keeping the boss plate radius below 15% of the elliptical egg radius, the structural strength of the boss plate is never exceeded, thereby eliminating the weakness of the conventional flywheel structure.

[0023] The systems and methods described herein have several energy storage advantages. These include, but are not limited to, providing a flywheel that utilizes its structural mass more efficiently; providing a method for increasing the speed of a flywheel without structural failure; providing a flexible flywheel structure that can adapt to its load distribution; providing an economical flywheel structure that can be customized to the customer's energy storage needs; and combining the advantages of a smaller, high energy density flywheel with a smaller, compact subsystem to form a low-cost energy storage system. Further advantages will become apparent by studying the following description and accompanying drawings.

[0024] Before continuing, it should be noted that as used herein, the terms “includes” and “including” mean, but are not limited to, “includes” or “including” and “includes atleast” or “including at least”. The term “based on” means “based on” and “based at least in part on”.

[0025] Figure 1is a perspective view of an example flywheel energy storage device 10. The example of the system 10 includes a sealed flywheel assembly 12 on a mounting structure 14. A vacuum port 16 is provided through the sealed flywheel assembly 12. The flywheel assembly 12 is operably associated with an electric motor or generator 18 mounted on a platform 20. For example, the flywheel assembly 12 can be operably associated with the generator 18 through a gearbox connecting rod 22. In one example, the generator 18 can include a cooling line 24 operably associated with a cooling subsystem 26.

[0026] In one example, the generator 18 is operably associated with a power control subsystem 28 having a power connection 30 and a control and monitoring connection 32. For example, the power control subsystem 28 may be operably associated with the generator 18 via an engagement control 34.

[0027] Control of the subsystems and / or the gearbox may be based at least in part on operating conditions in the flywheel assembly 12. For example, control may be based at least in part on one or more sensors via connection 36.

[0028] In one example, the flywheel assembly 12 includes a high speed three-dimensional (3D) elliptical oval flywheel 50 mounted on a shaft 52 associated with the gearbox 22 . Figure 2 A side view of an example elliptical egg shaped flywheel 50 is shown. The elliptical egg shaped flywheel 50 provides significant inertial mass and operating speed improvements over two-dimensional disk, ring or cylindrical shapes (even disk, ring or cylindrical shapes made of the same structural material and having the same or similar diameter). Table 1 provides a comparison of examples of flywheel performance under the same geometric and material constraints.

[0029] Table 1: Flywheel performance

[0030]

[0031] In an example, the elliptical oval flywheel 50 comprises layers of helically wound resin impregnated composite fiber material forming an oval shell shape. This configuration provides a means of moving significant inertial mass to the maximum flywheel diameter.

[0032] Adjusting the number of helically wound layers of the elliptical egg-shaped flywheel 50 allows for adjustment of the flywheel inertial mass. Each layer of the helically wound composite fiber material is in nearly pure tension, maximizing the performance of the structural material, while the curvature of the ovoid composite shell minimizes stress concentrations that are detrimental to structural integrity. The 3D nature of the ovoid composite shell also allows the composite fiber structural material at the maximum diameter of the flywheel to share stress in two planes, similar to the membrane stresses within a spherical pressure vessel, allowing the flywheel to exceed a significant fraction of the typical hoop stress limit of a hoop-wound disk, torus, or cylinder.

[0033] During operation, the vacuum sealed flywheel 50 transmits torque and energy through the sealed vacuum outer shell 12 via a two-part magnetic transmission connected to the flywheel shaft 52 and connected to the external motor / generator 18, and the gear transmission is used to match the flywheel rotational speed to the operating speed of the external motor / generator 18.

[0034] Although not shown, an outer housing may also be provided to house the motor / generator and connections (e.g., to the flywheel vacuum housing 12) and external magnetic transmission. In one example, one or more sensors 36 provide position, temperature, vibration, flywheel rpm, and pressure readings that are transmitted to a control display via wiring embedded in the vacuum housing 12.

[0035] The external motor / generator 18 is supported by the translation platform 14 and the controller 28 to allow the coupling and decoupling of the external magnetic transmission device with the vacuum outer shell. This allows the vacuum-sealed elliptical egg-shaped flywheel 50 to be disconnected from the external motor / generator 18, eliminating a significant source of standby power loss. A small backup chemical battery is typically charged by the motor / generator 18 during operation, or by other external power sources to maintain the power required for the sensor assembly and active axial thrust bearing when the motor / generator 18 is disconnected. With the motor / generator 18 disconnected, the standby time of the elliptical egg-shaped flywheel ESS before 50% of the power remaining can exceed 250 hours. Using an external plug-in power source or solar array to charge the backup chemical battery, the standby time of the elliptical egg-shaped flywheel ESS can exceed 350 hours until 50% of the power remaining.

[0036] Figure 3 is a cross-sectional view of an example elliptical egg-shaped flywheel 50 , including bearing subsystems 54 a , 54 b and transmission subsystem 56 . Figure 4 is the right bearing subsystem 54a (from Figure 3 Detailed area 4) in and a detailed cross-sectional view of the gearbox subsystem 56. Figure 5 is a detailed cross-sectional view of the left bearing subsystem 54b (from Figure 3 Detailed area in 5).

[0037] The example elliptical egg-shaped flywheel 50 may include an ovoid composite shell 58 with radial composite fibers wrapped on an integrated composite compression support structure 60. The example elliptical egg-shaped flywheel 50 may be mounted on the shaft 52 by an internal boss plate support 64 and an external balancing boss plate 66, as well as an outer shell guide plate 68 and a boss plate attachment 62 on an internal boss plate 70. The elliptical egg-shaped flywheel 50 is supported at both ends of the shaft 52 by an axial ground bearing, an electromagnet axial stabilizer 72, and a radial ground bearing 74. The rotating PM bearing 76, the fixed PM bearing 78, and the axial electromotive bearing 80 are also visible and carry most of the load and stabilize the system. The internal PM gearbox 82, the reducer plate 84, the rear bearing housing plate 86, and the bearing housing 88 are also visible.

[0038] The elliptical egg-shaped flywheel 50 can be constructed on an internal compression support 90. In one example, the internal compression support 90 is a circumferentially wound hollow cylinder of resin-impregnated composite fiber material of radius r1, and its thickness provides compression support when the flywheel is in operation. The internal compression support is bonded in place to the inner elliptical egg-shaped winding of the outer oval shell.

[0039] In one example, the composite fiber material for the elliptical oval flywheel structure is selected to have minimal elongation when subjected to stress (e.g., similar to carbon / graphite fibers) so as not to compromise the structural integrity of the flywheel relative to the vacuum housing. Certain composite materials (such as reinforced plastics, fiberglass, ultra-high density polyethylene, basalt, and aramid fibers) continue to elongate or "creep" under load and may not be suitable for this flywheel application due to its high continuous load requirements when actively operating.

[0040] In one example, the outer shell of the elliptical egg-shaped flywheel 50 is composed of a plurality of helically wound resin-impregnated composite fiber laminate layers, the laminate layers including a thickness t0 with each layer completely covering the circumference of the flywheel radius r0. The inner laminate layers follow the inner elliptical egg shape that is removed after winding is completed, forming an internal void. The inner laminate layers follow a low-angle helical winding path, around the flywheel shaft and shaft support, and bonded to the outer surface of the inner boss flange plate. Each additional laminate layer gradually increases its helical winding path angle, so that its maximum angle is equal to the inner support cylinder outer radius r1.

[0041] After adding the required number of laminate layers to provide stress support and inertial mass, the outer laminate layers are completed with an optimal helix angle elliptical path. In each laminate layer between two layers, the elliptical path transitions to a perpendicular path through an elliptical section through the thickness of the internal hollow cylindrical support to allow compressive stresses to be concentrated in the area of ​​maximum internal structural support.

[0042] The elliptical egg-shaped flywheel 50 is supported and stabilized along its axis of rotation and axis 52 by active electromagnetic thrust bearings, attached radial magnetic bearings and outer housing fixed radial magnetic bearings, axial electrodynamic bearings and backup ground bearings. A portion of the outer boss flange plate on either side of the flywheel provides a balancing mass to fine tune the inertia axis along the axis of rotation.

[0043] Elliptical egg-shaped flywheel structure Figure 3 , showing an inner compression support of radius r1 and thickness t1, an outer boss flange plate, an inner boss flange plate, a shaft support, and an inner shaft support. Also included in this view is a helically wound guide plate connected to the end of the inner compression support.

[0044] Figure 3 Also shown is a fully elliptical outer spiral winding layer of radius r0, provided with a compression support of width W which doubles as an axial compression support. Figure 3 Also shown is a partially elliptical outer spiral winding layer of radius r0, provided with a plurality of inner compression supports of width W. The side view shows the location of the inner compression supports, for example, relative to the system of the flywheel diameter.

[0045] An example of an elliptical oval flywheel outer shell showing a stepped composite fiber resin winding starting at a low angle extending to an optimum helix angle elliptical path that intersects the outer radius of a hollow inner compression support cylinder. A plurality of helically wound resin impregnated composite fiber laminate layers are wound to comprise each layer of the oval composite outer shell.

[0046] Finite element analysis results for an example elliptical egg-shaped flywheel 50 with example inner and outer elliptical spiral wound laminate layers and inner hollow cylindrical compression support. A predicted safety factor (SF) is included to account for the flywheel stress analysis at an operating speed of 36,000 rpm.

[0047] Before continuing, it should be noted that the above examples are provided for the purpose of illustration and are not intended to be limiting. Other devices and / or device configurations may be used to perform the operations described herein.

[0048] In one example, the components and connections shown in the figure can be used for the following operations. The operations shown and described herein are used to illustrate example implementations. Note that the operations are not limited to the order shown. Other operations can also be implemented.

[0049] In one exemplary operation, the elliptical egg-shaped flywheel 50 rotates about a horizontal or vertical axis on an axis 52 within a vacuum housing 12 supported by magnetic bearings ( Figure 3-5). Magnetic bearings provide support in radial and axial directions. The speed of the elliptical egg-shaped flywheel 50 can be increased or decreased by transmitting torque through the vacuum shell 12 (for example, through a magnetic transmission device connected to the flywheel shaft 52 and the external motor / generator 18), so its energy storage level can be increased or decreased. The magnetic transmission acts as an intermediary between the elliptical egg-shaped flywheel 50 and the external motor / generator 18, allowing rotational energy to be transferred through the wall of the vacuum shell 12 through magnetic coupling. Power input and output are provided by the external motor / generator 18, which draws power from a user source to accelerate the elliptical egg-shaped flywheel 50, converting electrical power into rotational kinetic energy, and then pushing power to the user when the user decelerates the elliptical egg-shaped flywheel 50, converting the rotational kinetic energy back into electrical energy.

[0050] When the elliptical egg-shaped flywheel is in operation, various design aspects increase the available energy storage. In one example, the inner and outer elliptical arches of the egg-shaped shell are slightly extended (e.g., about 1-2% compared to the static state) due to the centripetal force pulling the structure radially. This slightly extends the outer radius of the flywheel, increasing the moment of inertia of the flywheel when in operation, thereby increasing the energy storage capacity by 3-5%. This flexibility allows the 3D structural design to be adapted to its load distribution while providing positive benefits to the flywheel's energy storage capacity.

[0051] In one example, the elliptical egg-shaped flywheel 50 may also utilize carbon / graphite fiber composite fibers that have a total elongation of about 1-2% under load. When these fibers are wound in a radial spiral, the expected elongation under load will slightly extend the outer radius of the flywheel. This will increase the flywheel moment of inertia when the flywheel is in operation, thereby increasing the energy storage capacity by about 3-5%. This flexibility allows the 3D structural design to adapt its load distribution while providing positive benefits to the flywheel energy storage capacity.

[0052] In one example, the inner structural composite cylinder also allows for radial bending (from the oval shell compressive stresses) and radial expansion of the hoop composite fibers. The resulting slight increase in the radius of the composite cylinder bends into the upper void space without placing additional stress on the outer oval shell as would be the case with conventional rim wrapping.

[0053] In one example, by moving the helical winding angle of each subsequent winding layer of the ovoid shell upward, the fibers (which would otherwise be concentrated around the shaft) are moved to a larger radius, thereby increasing the effective moment of inertia of the flywheel while still expanding the tensile stresses of the fiber layers through the increasing cross-sectional thickness of the shell radiating outward from the shaft.

[0054] In one example, overlapping layers of a spiral outer winding placed in an elliptical arch create the 3D nature of an ovoid composite shell. This allows the structural composite in the flywheel ovoid shell to share stresses in two planes, similar to membrane stresses in a spherical pressure vessel. This allows the ovoid flywheel to exceed the classical hoop stress limit of a hoop-wound disk, ring or cylinder of the same radius by approximately 40%, thereby significantly increasing the operating speed of the ovoid flywheel and thus its energy storage level. As the aspect ratio of the ovoid flywheel approaches 1.0 and the flywheel is spherical (rather than ovoid), the stress improvement in two planes over classical hoop stress approaches 100%. The increased compressive stresses from the increased aspect ratio must be handled by adding internal flywheel structure.

[0055] When these five aspects are combined into an elliptical egg-shaped flywheel structure, the energy storage capacity is increased fivefold compared to a conventional flywheel of the same structural material, mass, and diameter.

[0056] Example. Designed and evaluated by finite element analysis (FEA) Figure 1 Example of an elliptical oval flywheel shown. The example flywheel design is an oval housing and internal support windings with a medium strength 3000mPa carbon composite fiber laminate with epoxy resin impregnation. The boss flange is simulated in stainless steel AISI A514. Figure 3 As shown, the simulated flywheel is modeled in a closed vacuum environment and uses magnetic bearings to run almost frictionlessly. The maximum diameter of the simulated flywheel is about 1.0 meter, and the width on the connecting shaft is about 0.45 meter.

[0057] After analysis, it was determined that the energy stored in the simulated flywheel was approximately 50.9 kWh and the flywheel inertia was approximately 24.1 kg-m 2 , running speed is about 36000 rpm.

[0058] System stresses maintained a safety factor of approximately 1.4 to 2.2. The simulated flywheel operation was not only within the expected safety factor for commercial applications, but also achieved a gravimetric energy density of approximately 205 Wh / kg based on the total mass of the flywheel and approximately 490 Wh / L based on the volume of the flywheel. This compares to approximately 20 Wh / kg and 45 Wh / L for a conventional 2D cylindrical flywheel. Fatigue analysis indicates that the elliptical egg-shaped flywheel will provide more than 200,000 charge and discharge cycles during its service life.

[0059] Using a high-strength carbon composite fiber laminate with a strength of 4100mPa, an operating speed of over 49,000rpm was achieved with the same simulated flywheel geometry and the same safety factor, and an energy storage capacity of approximately 97kWh was achieved.

[0060] Figure 6-7is a cross-sectional view of another example elliptical egg-shaped flywheel. Figure 6 The elliptical egg-shaped flywheel 150 in FIG. 1 is more conical than the elliptical egg-shaped flywheel 50. The elliptical egg-shaped flywheel 150 has the same width (the width W1 is substantially the same as the width W of the flywheel 50) and has an internal support structure 153 near the shaft 152. Figure 7 The elliptical egg-shaped flywheel 250 in FIG. 2 is wider (width W2 ), having a central internal support structure 253 and another support structure 254 near the shaft 252 .

[0061] The systems and methods disclosed herein provide an elliptical egg-shaped flywheel having a greater energy storage capacity per unit mass than previously known rotating energy storage devices. It will be appreciated that the elliptical egg-shaped flywheel described herein is particularly suitable for providing energy storage with a small operating footprint and mass for use in deployed utility and renewable energy locations, residential and commercial locations, and potentially transportation, for example, to power electric vehicle charging stations.

[0062] It should be noted that the examples shown and described are provided for purposes of illustration and are not intended to be limiting. Other examples are also contemplated, including but not limited to vertically oriented elliptical egg-shaped flywheels.

Claims

1. A flywheel energy storage device, comprising: A fiber-resin composite elliptical oval shell having an axial axis; a hub boss plate on each side of the elliptical oval shell, the hub boss plates being concentrically disposed inside and outside the elliptical oval shell and connected to the axial shaft; and a plurality of radially oriented fiber-resin composite spiral windings connecting the housing to the hub boss plate for common rotation and transmitting torque to the axial shaft; an axially oriented internal compression support between the axial walls of the elliptical oval shell, the internal compression support being a circumferentially wound hollow cylinder of resin impregnated composite fiber material; In which, during rotation, the elliptical shell is slightly stretched to increase the moment of inertia around the elliptical shell, Each layer of the radially oriented helical winding is initially angled 5 degrees and gradually increased to 35 degrees to allow the mass accumulation of the helical wound layers to be away from the axis of rotation, thereby increasing the moment of inertia of the flywheel.

2. The flywheel energy storage device according to claim 1 further comprises a plurality of groups of spiral windings, each group of spiral windings having a uniform width.

3. A flywheel energy storage device according to claim 2, wherein each set of spiral windings has layers extending around the outer surfaces of the housing and the hub on both sides of the rotating axis.

4. A flywheel energy storage device according to claim 2, wherein each set of spiral windings has a nearly continuous single-ended filamentary material wound in a unidirectional relationship and encapsulated in a resin matrix.

5. The flywheel energy storage device of claim 2, wherein each set of spiral windings is uniformly stressed over the width of each winding during rotation.

6. A flywheel energy storage device according to claim 2, wherein each set of spiral windings has a radially oriented layered composite shell.

7. A flywheel energy storage device according to claim 2, wherein the spiral windings are arranged in overlapping relationship at a portion of the hub close to the rotation axis.

8. The flywheel energy storage device of claim 1, wherein the radially oriented spiral winding is configured to transfer tensile tip stresses to the thickened structure near the rotation axis under compressive stress, thereby maximizing the effective strength of the fiber wound composite laminate layer.

9. The flywheel energy storage device of claim 1 further comprising an integrated internal structure connected to and providing compressive support for the external elliptical oval housing.

10. A flywheel energy storage device according to claim 9, wherein the internal structure is formed of metal or a nearly continuous single-ended filamentary material wound in a plurality of layers in a unidirectional relationship and encapsulated in a resin matrix.

11. The flywheel energy storage device according to claim 10, wherein: The minimum ratio of the diameter of the inner structure to the diameter of the outer elliptical oval shell is 0.

1.

12. A flywheel energy storage device as claimed in claim 9 wherein said inner structure is formed of metal, composite laminate layers wound in a plurality of layers in a unidirectional relationship and bonded to the inner layer of said outer elliptical oval shell.

13. The flywheel energy storage device according to claim 12, wherein: The minimum ratio of the diameter of the inner structure to the diameter of the outer elliptical oval shell is 0.

1.

14. The flywheel energy storage device of claim 1, wherein the outer elliptical oval housing has a usable aspect ratio of 0.1 to 1.

0.

15. The flywheel energy storage device according to claim 1, wherein the inner and outer peripheral surfaces of the elliptical shell are rotational ellipses.

16. The flywheel energy storage device of claim 1, wherein the oval shell spirally wound layers are used twice to control the inertial mass of the flywheel.

17. The flywheel energy storage device of claim 16, wherein adding or removing layers configures the flywheel energy storage capacity to increase or decrease through a plurality of wound layers.

18. The flywheel energy storage device of claim 1, further comprising a double boss plate connected to both sides of the innermost and outermost oval shell layers to connect the elliptical oval shell to the shaft to achieve co-rotation and torque transmission.

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