US3698262A

US3698262A - Fixed element rotor structures

Info

Publication number: US3698262A
Application number: US167643A
Authority: US
Inventors: David W Rabenhorst
Original assignee: Johns Hopkins University
Current assignee: Johns Hopkins University
Priority date: 1971-07-30
Filing date: 1971-07-30
Publication date: 1972-10-17
Anticipated expiration: 1989-10-17

Abstract

The invention relates to inertial energy storage devices wherein a central hub holds a multiplicity of anisotropic filaments, the filaments extending from the hub in fixed relation thereto and in parallel planes perpendicular to an axis of rotation through said hub. Each filament extending from the central hub is so disposed within the structure that the stress component imposed on said filament acts uniaxially along its length.

Description

United States Patent Rabenhorst [54] FIXED ELEMENT ROTOR STRUCTURES [72] Inventor: David W. Rabenhorst, Silver Spring,

[73] Assignee: The Johns Hopkins University, Baltimore, Md.

221 Filed: July 30,1971 2'1 Appl. No.: 167,643

521 U.S.Cl... ..74/572, 74/5 511 Int.Cl ..Fl6h33/02 [58] Field of Search ..74/572,5; 15/l79, 181

[56] References Cited UNITED STATES PATENTS 1,514,530 2/1926 Adams "ls/181 [451 Oct. 17, 1972 Peterson 15/1 79 Primary Examiner-William F. *ODea Assistant Examiner-J. D. Shoemaker Attorney-John S. Lacey ABSTRACT The invention relates to inertial energy storage devices wherein a central hub holds a multiplicity of anisotropic filaments, the filaments extending from the hub in fixed relation thereto and in parallel planes perpendicular to an axis of rotation through said hub. Each filament extending from the central hub is so disposed within the structure that the stress component imposed on said filament acts uniaxially along its length.

21 Claims, 13 Drawing Figures Charvat ..15/179 PAIENTEDum 1 1 m2 v 3. 698. 262

sum

1 or 6 INVENTOR. DAVID w. RABENHORST F I 6. 3a

PATENTED CH m2 3.698262 SHEET 2 0F 6 INVENTO DAVID w. RABENHOR PATENT'EYDBET H 1912 3.698, 262

SHEET 3 [IF 6 INVENTOR. DAVID W. RAB ENHORST V PATENTEUH 11 1972 SHEET t [If 6 INVENTOR. F I 8 7 DAVID w. RABENHORST PATENTEDMHHQH 3.s9e,-2s2

' I SHEEI 5 OF 6 INVENTOR. DAVID W. RABENHORST FIXED ELEMENT ROTOR STRUCTURES STATEMENT OF GOVERNMENT INTEREST The invention herein described was made in the course of or under a contract or subcontract thereunder, with the Department of the Navy.

CROSS-REFERENCE TO RELATED APPLICATION The present invention comprises a novel modification of the invention described in co-pendingUS. Pat. application, Ser. No. 60,047, filed July 31, 1970, entitled Filament Rotor Structures, by the same inventor.

BACKGROUND OF THE INVENTION A. Field of the Invention v The invention relates to energy storage devices, such as flywheels, and particularly to performance-optimized high-speed rotary structures. Application of the invention ranges from use as the sole power source of a quiet, pollution-free urban vehicle to use as a home emergency power supply unit.

. B. Description of the Prior Art The flywheel has been used for centuries as an efficient energy storage device. Since the flywheel is an inertial device governed by the laws of kinetic energy, maximum performance is attained at maximum speed, the performance being generally quadrupled with a two-fold increase in speed. The speed of the rotating body, however, cannot be increased beyond its burstingof an isotropic steel structure is substantially less than that obtainable with modern anisotropic filamentary materials. High strength filaments typically exhibit substantially greater strength-to-density characteristics over the best isotropic materials, such as steel or titanium. Only a small portion of this strength advantage can be used in the prior art flywheels due to the inherent isotropic stresses in these structures. In the rim type flywheel, stresses normal to the wound filaments exist at all locations other than the outer edge. Additionally, the problem of attachment of the rim to the hub, requiring additional weight, has been a principal factor inhibiting further development of this flywheel structure.

I The present inertial energy storage device offers substantial improvement in useable energy density due not only to the advantageous utilization of the high uniaxial strength of filamentary materials, but also to the more efficient packaging density provided by the invention. The structure Y of the invention permits maximum utilization of the uniaxial strength of each filament while packaging a multiplicity of filaments within an extremely compact volume.

The significance of the present energy storage device is best understood by its application to the urban vehicle. Although flywheels have been used in short-range vehicles, such as in the Swiss Oerlikon bus and in the British Gyreacta transmission, those devices produced only about three watt-hours per pound. Thus, energy density of the devices was even lower than that of available lead-acid batteries at the same discharge rate. However, certain characteristics of flywheels caused their use in preference tostorage batteries, despite the problems then encountered in the use of flywheel structures. Firstly, the flywheel can be charged and discharged virtually an infinite number of times without degrading performance. Secondly, it can becharged at any reasonable rate. Thirdly, it can be discharged at any rate within the design limitations of ancillary equipment without degrading performance. These capabilities are largely responsible for the proposed use of flywheels in pollution-free urban vehicles. In most previous proposals, the rapid discharge capabilityof the flywheel has been primarily used to lend increased acceleration power to the vehicle in order to minimize the overall size of the main propulsion power plant. The present energy storage device provides a power plant of sufficient energy density to also enable its economic and practical use as the primary energy source in an urban vehicle.

SUMMARY OF THE INVENTION In a first embodiment, the invention provides a high performance inertial energy storage device wherein a central hub holds a multiplicity of uniaxial filamentary elements in radiating disposition to the hub. In particular, straight anisotropic rods or composite rods of filamentary or whisker materials are disposed around the periphery of the central hub in substantially parallel relation tothe major stress component acting on the rods during rotation thereof. As is the case with other flywheel devices, the performance ofthe present in vention is directly proportional to the specific strength of the material used in its construction. By utilizing the large specific strengths of filamentary materials, i.e., by

aligning the individual filaments substantially parallel to the major stress component which acts along the axis of each individual filament, a dramatic energy density increase in the total structure results, thus making a flywheel-type structure useful to a wide variety of applications beyond the capabilities of prior art rotary energy storage devices. Since the invention allows the filaments in the device to be in line with the respective force vectors generated by their own rotating masses, virtually all of the available strength of the filamentary materials is effectively used, thereby maximizing packaging density (watt-hrs/pound and watt-hrs lunit vol.) without performance degradation.

In a second embodiment of the invention, a central hub having arcuate internal support surfaces holds a multiplicity of anisotropic elements in fixed, pre-determined positions within the energy storage device, the- Accordingly, it is an object of the invention to provide a high power-density energy storage device which also has a high energy density capability.

It is a particular object of the invention to provide a rotary energy storage member comprised of anisotropic filaments or rods radiating from a central hub, each said filament being substantially parallel to the major local stress component acting thereon.

A further object of the invention is to provide a rotary energy storage member comprised of anisotropic filaments or rods held in fixed positions within a central hub, the filaments each being fanned out to a predetermined curvature.

Another object of the invention is to provide an energy storage device which can be readily and efficiently made from a large number of small discrete rod-like elements in order to minimize the likelihood of simultaneous failure of all such elements and thus maximize the safety of the device.

It is also an important object of the invention to provide a rotor structure having inherent gimballing capability about a stationary spin axis in order to minimize gyroscopic loads on the rotor and its spin bearings.

A still further object of the invention is tor provide a densely packaged", efficient, economical, high performance and pollution-free energy storage device useful in an urban vehicle for alleviating the increasing contribution of motorized vehicles to noise and air pollution problems.

Additional objects, advantages, and uses of the invention will become apparent from the following detailed description of the preferred embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged perspective view of a single, essentially uniaxial filament illustrating the major stress component acting on the filament during rotation thereof;

FIG. 2 is a plan view of a circular brush rotor fabricated according to the invention, the rotor being shown partly broken away to illustrate filaments aligned along local stress vectors;

FIG. 3a is a section of the circular brush rotor of FIG. 2 taken along line 3-3 thereof;

FIG. 3b is an enlarged detail elevation of a portion of the rotor of FIG. 30;

FIG. 4 is an idealized detail plan view of a greatly enlarged portion of the peripheral surface area of the hub;

FIG. 5 is a perspective of a modified rotor in which the hub and rods are laminated together in alternating fashion to build up a rotor structure;

FIG. 6 is a plan view of another modification of the invention, the rotor employed being fitted with a gimballing device to provide attachment to a rotatable shaft;

FIG. 7 is a section of the rotor of FIG. 6 taken along line 77 thereof;

FIG. 8 is a perspective of still another embodiment of the invention-illustrating a rotor having diverging, or fanned out elements;

FIG. 9 is an enlarged detail plan view of aportion of v the hub and of the elements comprising the rotor of FIG. 8;

' have most often been used in the construction of FIG. 10 is a schematic illustrating the relationships for determining the position of each element within the rotor; and

FIGS. 11a and 11b are charts showing graphically the relationships shown in FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The performance, i.e., the stored kinetic energy of a rotating body, is directly proportional to theuseable specific strength of the material used in the fabrication of the body. Isotropic materials, such as solid steel,

kinetic energy structures, or flywheels. However, the best isotropic material exhibits only a small fraction of the strength-to-density of anisotropic materials, such as music wire, Fiberglas or boron filaments, for example. It will thus be understood that a flywheel rotor configured to maximize the anisotropic strength characteristics of uniaxial filamentary or whisker materials is capable of increased performance relative to flywheels composed of isotropic materials. In a first embodiment, the present invention not only provides a rotary structure comprised of straight anisotropic filamentary material which maximizes performance and also permits considerably increased rotor weight within a given volume, hence more energy per volume, relative to prior straight filament rotor structures. This increase is primarily due to the inclusion within the present rotor structure of a circular hub and anisotropic elements around the full periphery of said hub. Additional advantage is provided by the ability of the present structure to allow alignment of each radial element in the structure along the local stress vector acting on said element.

For illustration of the concept embodied in the invention, a single filament or thin rod 10 is shown in FIG. 1 to be spinning about an axis normal to its longitudinal axis. If the diameter of the filament 10 is infinitely small, the total stresses in it are directed along its length from its spinning axis towardits ends, i.e., the direction of the centrifugal forces acting on it, said centrifugal forces, for the situation described, being the only forces acting on it during rotation. If the filament 10 were the only element in a flywheel or rotating structure, all of its allowable strength at its center would contribute to the kinetic energy of such a flywheel. However, in order to obtain a rotary structure of sufficient mass to possess utility, a plurality of filaments have previously been bound together in mutually parallel or near parallel relation by suitable hub means. While producing substantially improved energy storage structures, such filament rotary structures are subject to minor loads which are not directed along the longitudinal axes of the filaments, such loads tending to reduce the energy storage capability of the structures. In the embodiments of the present invention, the filaments are disposed within the rotary structure so that the local stress vector acting on each filament is effectively directed along its longitudinal axis.

A circular brush rotor is seen at 5 in FIGS. 2 and 3a to comprise a plurality of filaments 10 radially extending from a central cylindrical hub 12. The hub 12 has two centrally mounted shaft members 14 extending from either end thereof, the longitudinal axis extending through'the shaft members 14 being coincident with the axis of rotation 6 of the rotor 5. The hub 12 may be formed of any essentially isotropic material having high specific strength or may be formed from layers of filament-wound composite materials 1 joined into a laminate in a manner to be described further hereinafter. The filaments 10 are chosen from a variety of anisotropic materials having essentially uniaxial load bearing capabilities, e.g., Fiberglas, graphite, quartz, or boron filamentary rods.

The filaments 10 extend radially from the cylindrical surface 16 of the hub 12 around the full periphery of said hub. As can be seen more readily in FIG. 3b, each filament 10 has its inner end portion secured in a hole 18 in the surface 16 of the hub 12. The inner ends of the filaments l are preferably secured in the holes 18 by a suitable adhesive,'such as epoxyJSince the inner ends of the filaments 10 extend into the holes 18 for a finite distance-and adhere to the walls of said holes over the full areas of mutual contact, a bond of sufficient strength to prevent pull-out of the filaments during high-speed rotation of the rotor 5 is planes The filaments areseen in FIG. 3a to extend radially from the hub 12 in successive planes perpendicular to the axis of rotation 6 of the rotor 5, co-planar filaments 10 extending inwardly toward a co-planar point lying on said axis of rotation.- Essentially, if each filament 10 were extended inwardly to the center of .the rotor 5, the filaments would meet at points along the axis of rotation 6. Thus, if a plane is taken through the rotor 5 perpendicular to the axis of rotation 6, each filament 10 lying in that plane is coincident with a radius extending from the geometrical center of the plane, said geometrical center lyingon the axis of rotation 6 of the rotor 5.

The holes 18 in which the inner ends of the filaments 10 are held may be formed by chemical milling, stamping, or in someother suitable manner. However, a particular manner of accomplishing attachment of the elements to the hub is indicated in FIG. 4. In this view, the hub 12 is composedof successive disc-like layers 20. Semi-cylindrical depressions 22 are pressed into upper 6 laminated disc hub 12 composed of high strength steel.

In the modification of FIG. 5, a high strength, lightweight hub 21 is formed by alternately bonding together layers of the filaments l0 and filament-wound sheets 23. The layers of filaments l0 and sheets 23 are laminated together with an epoxy adhesive 25 to give solid bi-axial laminar strength properties to the hub 21. The hub 21 therefore has greater strength-to-density and less weight than a hub fabricated from isotropic material. g The rotor of the present invention may be gimballed, as shown in FIGS. 6 and 7, to minimize gyroscopic precession loading on the rotor and on bearings used to support shafting holding the rotor. The internal gimbal device shown generally at 30 avoids the necessity-for otherwise having large external gimbal rings and associated bearings. More importantly, rotor shaft 32 does not have to be gimballed, enabling its outputto be used directly. The gimbal device 30 is seen to comprise a cruciform member 34 having shaft pins 36 extending therefrom along the minor axis of the member and gimbal pins 38 extending along the major axis of said member. The cruciform member 34 is disposed within a transverse opening 40 in the shaft 32, the shaft pins 36 having their outer ends rotatably received within aligned bearings. r

A circular brush rotor 44 is fitted with a hub 46 having an axial channel 48 disposed therein for receiving the shaft 32. The ends of the gimbal pins 38, which extend longitudinally from the transverse opening 40, are rotatably received within aligned bearings 50 disposed in the wall which defines the channel 48. The rotor 44 is thus fully gimballed in the axial channel 48. For any foreseeable vehicular application in which the rotor 44 and lower faces 24 and 26 of the layers 20, except the top and bottom surfaces of the uppermost and lowermost layers, respectively, so that the depressions 22 of one layer 20 confront those of adjacent layers, the longitudinal axes of said depressions 22 extending radially from the geometrical centers of the

faces

24 and 26. The inner ends of the filaments 10 are then placed into confronting semi-cylindrical depressions 22 of adjacent layers 20. The diameter of the filaments 10 may typically be 0.03 inch, the layers 20 having a thickness of 0.04 inch to provide maximum packaging with reasonable separation between successive layers of filaments. The lateral displacement from center-line to centerline of the filaments 10 may also reasonably be 0.04 inch. The disc-like layers 20 may be vacuum welded along adjoining .upper and lower faces 24 and 26 to assure high strength for the hub 12. I

The actual number of the filaments 10 per unit area of the cylindrical surface 16 is determined by the capacity of the hub 12 to withstand the combined loading on said filaments within said unit area and the loading due to the rotation of the hub itself. Typically, uniaxial Fiberglas rods of the dimensions noted above, i.e., 0.03 inch diameter, prove useful with the is to be used with a stationary vertical spin axis, reasonable gimbal limits, allowing tiltingof the hub, are provided by the internal gimbal device 30.

FIGS. 8 and 9 illustrate still another embodiment of the invention, i.e., a rotor, shown generally at 60, which has elements contoured into a fixed-fanned brush shape. The rotor 60 comprises a unitary central hub 62 having arcuate side walls 64 curved toward each other and spaced by flat, parallel upper and

lower walls

66 and 68, the walls 66 and68 terminating in arcuate edges 69. Shaft members 70 are attached to the

walls

66 and 68 and extend above and below said walls on the axis of rotation of the hub 62. An assembly of anisotropic filament-like elements 72 extends through a central longitudinal cavity 74 in the hub 62, the elements 72 being held in fixed, predetermined positions within said hub. As can be seen more clearly in FIG. 9, the elements 72, except elements 72a at the exact midpoint of the assembly which are straight, are held in fixed, precontoured, arcuate positions within the hub 62 by a matrix material 76, such as epoxy. The shape of each element 72 is determined by means to be described hereinafter. I

Although FIG. 9 shows for simplicity only a portion of one co-planar layer of elements 72 in the rotor 60, the actual structure of the rotor may be appreciated by reference to axes of

symmetry

78 and 80. The longitudinal axis of symmetry 78 is coincident with the longitudinal axis of the rotor 60, the pattern of the elements 72 shown to the right of the axis 78 in FIG. 9

being duplicated in mirror image to the left of said axis 78. Similarly, the pattern of the elements 72 above the transverse axis of symmetry 80 in FIG. 9 is duplicated in mirror image below the axis 80. The longitudinal and transverse axes of

symmetry

78 and 80 intersect at the geometrical midpoint of the axis of rotation of the rotor 60. The structure of the rotor 60 is completed by building up in stacked relation a plurality of layers of the pattern of elements 72 thus described.

The elements 72 and 72a may be of the same length or, alternately, one or more of the elements 72a may be made longer than the remaining elements 72 as a safety measure. The additional loading on an extra long element 72a would cause that element to fail first if the speed of the rotor 60 exceeded design limitations. By being disposed centrally in the structure, failure of the element 72a would not produce substantial imbalance while providing a warning of excessive speed or imminent rotor failure.

Straight elements 72a, contained in a plane perpendicular to the upper and

lower walls

66 and 68 and extending through the longitudinal axis of symmetry 78, remain straight during rotation of the rotor 60, thereby fully utilizing the inherent strength-to-density of said elements 72a to carry the tension loading, or stress, which is directed along the length of said elements. The elements 72 on either side of the straight elements 72a thus described are held in contiguous relation along the transverse axis of symmetry 80, each element 72 diverging from the axis 80 in progressively greater degrees of curvature, i.e., the inner elements 72 having a greater radius of curvature than the outer elements 72, the element 72b adjacent to the straight element 72a having the largest radius of curvature and the outermost element 72c having the smallest radius of curvature. The inner surfaces 82 of the side walls 64 of the hub 62 are formed with a radius of curvature equal to that of the outermost elements 720. Thus, midportions of the elements 72c are contiguous to and are supported by the surface 82 of the wall 64 along the full length of said wall. The remaining elements 72 are held in place and supported by the matrix material 76 which surrounds the midportions of said elements within the central cavity 74.

As can be seen with reference to FIGS. 9 nd 10, those portions of the elements 72 which extend externally of the hub 62 are aligned along extended radii of an imaginary circle 83 defined in part by the arcuate edges 69 of the hub 62. The elements 72 must be positioned within the hub 62 with the proper curvature in order for the portions of the elements 72 external of the hub to be directed as described. Although the straight elements 721: are the only elements within the rotor 60 which are positioned to permit maximum utilization of the strength-to-density of the elements, proper choice of the radii of curvature of the remaining elements 72 hub 62 may be determined from the relationships illustrated in FIG. 10. In FIG. 10, a single element 72 is schematically shown. in its predetermined location within the rotor 60, the displacement of the element 72 from the axis of rotation being taken as normal from the longitudinal axis of said element to the longitudinal axis of symmetry 78. That portion of the element 72 extending beyond the circle 83, which circle is defined in part by the arcuate edges 69 of the hub 62,1ies along an extended radius r of the circle 83 drawn to the point of intersection of the longitudinal axis of the element and said circle. The tangent to the circle 83 through the aforementioned point of intersection defines the radius of curvature R of that portion of the element 72 lying within the hub 62. In particular, theradius of curvature R is that portion of the tangent lying between the aforementioned point of intersection on the circle 83 and the intersection of the tangent with the extended transverse axis of symmetry 80. The angle 0 between the radius of curvature R and the extended transverse axis of symmetry is identical to the angle defined by the longitudinal axis of symmetry 78 and the extended radius r with which the element 72 aligns beyond the circle 83.

The relationships between the above described values define the position of the element 72, which relationships are shown graphically in FIGS. 11a and 11b. FIG. 11a shows the relation between the angle 0 and D/r, while FIG. 11b illustrates the relation between R/r and D/r. For a given displacement D and radius r, the radius of curvature R of each element 72 may be determined from either FIG. Ila or 11b. Alternatively, given the displacement D and the radius r, the radius of curvature R for the given element 72 may be directly determined from the relationship:

1 r f 2 D In practice, the stress loss encountered due to bending of the elements 72 should be limited to 20 percent or less to maintain performance capabilities of the rotor 60. The following relationship allows determination of the maximum desirable radius of curvature R for a given element 72:

S t Y/ 4R 2 where: Q I

S Bending stress loss;

t= thickness of an element;

Y= modulus of elasticity of the material;

R radius of curvature.

The rotor 60 may be gimballed according to the principles described in the previously mentioned co-pending patent application Ser. No. 60,047, by the present inventor.

It is to be understood that the foregoing description of the invention is illustrative, and that various modifications to the structure and manner of fabrication of the rotors disclosed herein may be made without departing from the scope of the invention.

Iclaim:

1. An energy storage device having an axis of rotation extending transversely therethrough, comprising a plurality of anisotropic, filament-like members having maximum strength-to-density along their longitudinal axes, the longitudinal axes of portions of said members extending radially from the axis of rotation of the device,

hub means for holding the members in planes perpendicular to the axis of rotation of the device, the axis of rotation of the device being coincident with the longitudinal axis of said hub means, I the hub means being comprised of disc-like layers of material, adjacent layers having confronting semicylindrical depressions in the upper and lower faces thereof, the confronting semi-cylindrical depressions cooperating to receive portions of each of the members within the hub means and said layers clamping said portions of said members i in said depressions. 2. The energy storage device of claim 1 wherein the adjacent layers are joined along respective upper and lower faces.

3. An energy storage device having an axis of rotation extending transversely therethrough, comprising a plurality of anisotropic, filament-like members having maximum strength-to-density along their lon gitudinal axes, hub means for holding the members in planes perpendicular to the axis of rotation of the device, the

axis of rotation of the device being coincident with thelongitudinal axis of said hub means and the longitudinal axes of the members being aligned along radii emanating from points along the axis of rotation, the members being disposed around the 7 full periphery of the hub means,

the hub means being comprised of disc-like layers of material, adjacent layers having confronting semicylindrical depressions in the upper and lower faces thereof, the confronting semi-cylindrical depressions cooperating to receive portions of each of the members within the hub means and said layers clamping said portions of said members in said depressions. i

4. An energy storage device having an axis of rotation extending transversely therethrough, comprising a plurality of anisotropic, filament-like members having maximum strength-to-density along their longitudinal axes, the longitudinal axes of portions of said members extending radially from the axis of rotation of the device, and

hub means comprising layers of parallel planar spiral wound filaments disposed in alternation with respect to parallel layers of radially extending filament-like members.

5. The energy storage device of claim 4 wherein the members are disposed around the full periphery of the hub means.

6. The energy storage device of claim 4 and further comprising matrix means disposed between the sheets and the members to bond said sheets and members into a unitary structure.

7. An energy storage device having an axis of rotation extending transversely therethrough, comprising;

a plurality of anisotropic, filament-like members having maximum strength-to-density along their longitudinal axes, the longitudinal axes of portions of said members extending radially from the axis of rotation of the device;

hub means having an axial channel extending therethrough, the longitudinal axis of said channel being coincident with the axis of rotation of the device, the hub means further having aligned bearings in the walls of the axial channel,

.0 a shaft extending through the axial channel, the longitudinal axis of the shaft being. disposed coincident with the axis-of rotation of the device, the

shaft having a transverse opening formed therein and further having aligned bearings formed in the walls of said transverse opening, and

a cruciform member disposed within the transverse opening and having pairs of gimbal pins, one pair of said pins being rotatably received within the bearings in the shaft and the other pair of said pins, the axes of which are disposed at right angles to the axes of the first-mentioned pair of pins, being rotatably received within the aligned hearings in the hub means, thereby allowing said hub means to tilt relative to the shaft. g

8. An energy storage device having an axis of rotation extending transversely therethrough, comprising,

a plurality of anisotropic, filament-like members having maximum strength-to-density along their longitudinal axes, the longitudinal axes of portions of said members extending radially from the axes of rotation of the device, and

hub means comprising arcuate side walls, the side walls being curved toward each other and toward the axis of rotation of the device.

9. The energy storage device of claim 8 wherein the filament-like members are held by the hub means in fixed, predetermined positions, portions of the members within said hub means being arcuate.

10. The energy storage device of claim 9 wherein the portions of the members extending externally of the hub means are straight and aligned along radii emanating from the axis of rotation of the device.

11. The energy storage device of claim 9, wherein the radius of curvature of the fixed arcuate portion of each of the members is dependent upon the distance of said member from a plane taken through the longitudinal axis of the device and perpendicular tothe transverse axis thereof, theradius of curvature of each said member being determined according to the relationship:

where:

R radius of curvature of a given member,

r== radius of the hub means; and.

D distance from the given member to the said plane. g

12. The energy storage device of claim 9 and further comprising matrix means for maintaining the members in fixed positions within the hub means.

13. An energy storage device having an axis of rotation extending transversely therethrough, comprising,

a plurality of anisotropic, filament-like members having maximum strength-to-density along their longitudinal axes, the longitudinal axes of portions of said members extending radially from the'axis of rotation of the device, and

hub means for holding portions of the filament-like members, i

the members disposed in a plane through the longitudinal axis of the device and perpendicular to the transverse axis thereof being straight and the members on either side of said plane having portions within the hub fixed in predetermined arcuate configurations.

14. The energy storage device of claim 13 and further comprising matrix means for maintaining the members in fixed positions within the hub means.

15. The energy storage device of claim 13 wherein the portions of the members extending externally of the hub means are. straight and are aligned along radii of the hub means.

16. The energy storage device of claim 13, wherein the radius of curvature of the fixed arcuate portion of each of themembers is dependenton the distance of said member from the said plane, the radius of curvature of each said member being determined according to the relationship:

where:

R radius of curvature of a given member; r= radius of the hub means; and D distance from the given member to the plane. 17. In an energy storage system, a rotatable shaft, and

an energy storage structure having its midpoint mounted for tilting movement on the shaft and having an axis of rotation coincident with the axis of rotation of the shaft when the longitudinal axes of a cross-section taken through the structure is perpendicular to the shaft, said structure comprising a plurality of anisotropic, filament-like members having maximum strengthto-density along their longitudinal axes, the longitudinal axes of major portions of said members extending radially from the axis of rotation of the 12 device.

18. The energy storage system of claim 17, and further comprising hub means having an axial channel extending 'therethrough, the hub means further having aligned bearings in the walls of the axial channel, the shaft extending through theaxial channel and having a transverse opening formed therein and further having alined bearings formed in the walls of said transverse openings, and

a cruciform member disposed within the transverse opening and having pairs of gimbal pins, one pair of said pins being rotatably received within the bearings in the shaft and the other pair of said pins, the axes of which are disposed at right angles to the axes of the first-mentioned pair of pins, being rotatably received within the aligned bearings in the hub means, thereby allowing said hub means to tilt relative to the shaft.

19. The energy storage system of claim 17, and further comprising hub means for holding the members in planes perpendicular to the axis of rotation of the device.

20. The energy storage system of claim 19 wherein the members are disposed around the full periphery of the hub means.

21. The energy storage system of claim 20 wherein the hub means is formed with a plurality of radially directedholes extending from the surface of said hub means inwardly toward the axis of rotation of the structure, each hole receiving therein a portion of one of said members.

Claims

1. An energy storage device having an axis of rotation extending transversely therethrough, comprising a plurality of anisotropic, filament-like members having maximum strength-to-density along their longitudinal axes, the longitudinal axes of portions of said members extending radially from the axis of rotation of the device, hub means for holding the members in planes perpendicular to the axis of rotation of the device, the axis of rotation of the device being coincident with the longitudinal axis of said hub means, the hub means being comprised of disc-like layers of material, adjacent layers having confronting semi-cylindrical depressions in the upper and lower faces thereof, the confronting semicylindrical depressions cooperating to receive portions of each of the members within the hub means and said layers clamping said portions of said members in said depressions.

2. The energy storage device of claim 1 wherein the adjacent lAyers are joined along respective upper and lower faces.

3. An energy storage device having an axis of rotation extending transversely therethrough, comprising a plurality of anisotropic, filament-like members having maximum strength-to-density along their longitudinal axes, hub means for holding the members in planes perpendicular to the axis of rotation of the device, the axis of rotation of the device being coincident with the longitudinal axis of said hub means and the longitudinal axes of the members being aligned along radii emanating from points along the axis of rotation, the members being disposed around the full periphery of the hub means, the hub means being comprised of disc-like layers of material, adjacent layers having confronting semi-cylindrical depressions in the upper and lower faces thereof, the confronting semi-cylindrical depressions cooperating to receive portions of each of the members within the hub means and said layers clamping said portions of said members in said depressions.

4. An energy storage device having an axis of rotation extending transversely therethrough, comprising a plurality of anisotropic, filament-like members having maximum strength-to-density along their longitudinal axes, the longitudinal axes of portions of said members extending radially from the axis of rotation of the device, and hub means comprising layers of parallel planar spiral wound filaments disposed in alternation with respect to parallel layers of radially extending filament-like members.

7. An energy storage device having an axis of rotation extending transversely therethrough, comprising; a plurality of anisotropic, filament-like members having maximum strength-to-density along their longitudinal axes, the longitudinal axes of portions of said members extending radially from the axis of rotation of the device; hub means having an axial channel extending therethrough, the longitudinal axis of said channel being coincident with the axis of rotation of the device, the hub means further having aligned bearings in the walls of the axial channel, a shaft extending through the axial channel, the longitudinal axis of the shaft being disposed coincident with the axis of rotation of the device, the shaft having a transverse opening formed therein and further having aligned bearings formed in the walls of said transverse opening, and a cruciform member disposed within the transverse opening and having pairs of gimbal pins, one pair of said pins being rotatably received within the bearings in the shaft and the other pair of said pins, the axes of which are disposed at right angles to the axes of the first-mentioned pair of pins, being rotatably received within the aligned bearings in the hub means, thereby allowing said hub means to tilt relative to the shaft.

8. An energy storage device having an axis of rotation extending transversely therethrough, comprising, a plurality of anisotropic, filament-like members having maximum strength-to-density along their longitudinal axes, the longitudinal axes of portions of said members extending radially from the axes of rotation of the device, and hub means comprising arcuate side walls, the side walls being curved toward each other and toward the axis of rotation of the device.

11. The energy storage device of claim 9, wherein the radius of curvature of the fixed arcuate portion of each of the members is dependent upon the distance of said member from a plane taken through the longitudinal axis of the device and perpendicular to the transverse axis thereof, the radius of curvature of each said member being determined according to the relationship: where: R radius of curvature of a given member; r radius of the hub means; and D distance from the given member to the said plane.

13. An energy storage device having an axis of rotation extending transversely therethrough, comprising, a plurality of anisotropic, filament-like members having maximum strength-to-density along their longitudinal axes, the longitudinal axes of portions of said members extending radially from the axis of rotation of the device, and hub means for holding portions of the filament-like members, the members disposed in a plane through the longitudinal axis of the device and perpendicular to the transverse axis thereof being straight and the members on either side of said plane having portions within the hub fixed in predetermined arcuate configurations.

15. The energy storage device of claim 13 wherein the portions of the members extending externally of the hub means are straight and are aligned along radii of the hub means.

16. The energy storage device of claim 13, wherein the radius of curvature of the fixed arcuate portion of each of the members is dependent on the distance of said member from the said plane, the radius of curvature of each said member being determined according to the relationship: where: R radius of curvature of a given member; r radius of the hub means; and D distance from the given member to the plane.

17. In an energy storage system, a rotatable shaft, and an energy storage structure having its midpoint mounted for tilting movement on the shaft and having an axis of rotation coincident with the axis of rotation of the shaft when the longitudinal axes of a cross-section taken through the structure is perpendicular to the shaft, said structure comprising a plurality of anisotropic, filament-like members having maximum strength-to-density along their longitudinal axes, the longitudinal axes of major portions of said members extending radially from the axis of rotation of the device.

18. The energy storage system of claim 17, and further comprising hub means having an axial channel extending therethrough, the hub means further having aligned bearings in the walls of the axial channel, the shaft extending through the axial channel and having a transverse opening formed therein and further having alined bearings formed in the walls of said transverse openings, and a cruciform member disposed within the transverse opening and having pairs of gimbal pins, one pair of said pins being rotatably received within the bearings in the shaft and the other pair of said pins, the axes of which are disposed at right angles to the axes of the first-mentioned pair of pins, being rotatably received within the aligned bearings in the hub means, thereby allowing said hub means to tilt relative to the shaft.

21. The energy storage system of claim 20 wherein the hub means is formed with a plurality of radially dirEcted holes extending from the surface of said hub means inwardly toward the axis of rotation of the structure, each hole receiving therein a portion of one of said members.